Gitiles
Code Review Sign In
gerrit-public.fairphone.software / platform / external / llvm / 0ce12d5a078a00f56d9470cfb951857b2a89ac06 / . / docs / ProgrammersManual.html
blob: 1a7f215ae0ae439fb980860085920f62c3ef9c55 [file] [log] [blame]
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN"
2 "http://www.w3.org/TR/html4/strict.dtd">
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3<html>
4<head>
Owen Anderson5e8c50e2009-06-16 17:40:28 +0000[diff] [blame]5 <meta http-equiv="Content-type" content="text/html;charset=UTF-8">
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>
Chris Lattner9d69d4a2011-07-18 01:40:02 +0000[diff] [blame]62 <li><a href="#dss_tinyptrvector">"llvm/ADT/TinyPtrVector.h"</a></li>
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]63 <li><a href="#dss_smallvector">"llvm/ADT/SmallVector.h"</a></li>
64 <li><a href="#dss_vector">&lt;vector&gt;</a></li>
65 <li><a href="#dss_deque">&lt;deque&gt;</a></li>
66 <li><a href="#dss_list">&lt;list&gt;</a></li>
Gabor Greif3899e492009-02-27 11:37:41 +0000[diff] [blame]67 <li><a href="#dss_ilist">llvm/ADT/ilist.h</a></li>
Argyrios Kyrtzidis81df0892011-06-15 19:56:01 +0000[diff] [blame]68 <li><a href="#dss_packedvector">llvm/ADT/PackedVector.h</a></li>
Chris Lattnerc5722432007-02-03 19:49:31 +0000[diff] [blame]69 <li><a href="#dss_other">Other Sequential Container Options</a></li>
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]70 </ul></li>
Chris Lattner7314a202011-07-22 20:46:49 +0000[diff] [blame]71 <li><a href="#ds_string">String-like containers</a>
Chris Lattner66827462011-07-22 21:36:29 +0000[diff] [blame]72 <ul>
73 <li><a href="#dss_stringref">llvm/ADT/StringRef.h</a></li>
74 <li><a href="#dss_twine">llvm/ADT/Twine.h</a></li>
75 <li><a href="#dss_smallstring">llvm/ADT/SmallString.h</a></li>
76 <li><a href="#dss_stdstring">std::string</a></li>
77 </ul></li>
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]78 <li><a href="#ds_set">Set-Like Containers (std::set, SmallSet, SetVector, etc)</a>
79 <ul>
80 <li><a href="#dss_sortedvectorset">A sorted 'vector'</a></li>
81 <li><a href="#dss_smallset">"llvm/ADT/SmallSet.h"</a></li>
82 <li><a href="#dss_smallptrset">"llvm/ADT/SmallPtrSet.h"</a></li>
Chris Lattnerc28476f2007-09-30 00:58:59 +0000[diff] [blame]83 <li><a href="#dss_denseset">"llvm/ADT/DenseSet.h"</a></li>
Jakob Stoklund Olesen62588622012-02-22 00:56:08 +0000[diff] [blame]84 <li><a href="#dss_sparseset">"llvm/ADT/SparseSet.h"</a></li>
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]85 <li><a href="#dss_FoldingSet">"llvm/ADT/FoldingSet.h"</a></li>
86 <li><a href="#dss_set">&lt;set&gt;</a></li>
87 <li><a href="#dss_setvector">"llvm/ADT/SetVector.h"</a></li>
Chris Lattnerc5722432007-02-03 19:49:31 +0000[diff] [blame]88 <li><a href="#dss_uniquevector">"llvm/ADT/UniqueVector.h"</a></li>
Chris Lattner2fdd0052011-11-15 22:40:14 +0000[diff] [blame]89 <li><a href="#dss_immutableset">"llvm/ADT/ImmutableSet.h"</a></li>
90 <li><a href="#dss_otherset">Other Set-Like Container Options</a></li>
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]91 </ul></li>
Chris Lattnerf3692522007-02-03 19:51:56 +0000[diff] [blame]92 <li><a href="#ds_map">Map-Like Containers (std::map, DenseMap, etc)</a>
93 <ul>
94 <li><a href="#dss_sortedvectormap">A sorted 'vector'</a></li>
Chris Lattner796f9fa2007-02-08 19:14:21 +0000[diff] [blame]95 <li><a href="#dss_stringmap">"llvm/ADT/StringMap.h"</a></li>
Chris Lattnerf3692522007-02-03 19:51:56 +0000[diff] [blame]96 <li><a href="#dss_indexedmap">"llvm/ADT/IndexedMap.h"</a></li>
97 <li><a href="#dss_densemap">"llvm/ADT/DenseMap.h"</a></li>
Jeffrey Yasskin71a5c222009-10-22 22:11:22 +0000[diff] [blame]98 <li><a href="#dss_valuemap">"llvm/ADT/ValueMap.h"</a></li>
Jakob Stoklund Olesenaca0da62010-12-14 00:55:51 +0000[diff] [blame]99 <li><a href="#dss_intervalmap">"llvm/ADT/IntervalMap.h"</a></li>
Chris Lattnerf3692522007-02-03 19:51:56 +0000[diff] [blame]100 <li><a href="#dss_map">&lt;map&gt;</a></li>
Jakob Stoklund Olesen4359e5e2011-04-05 20:56:08 +0000[diff] [blame]101 <li><a href="#dss_inteqclasses">"llvm/ADT/IntEqClasses.h"</a></li>
Chris Lattner2fdd0052011-11-15 22:40:14 +0000[diff] [blame]102 <li><a href="#dss_immutablemap">"llvm/ADT/ImmutableMap.h"</a></li>
Chris Lattnerf3692522007-02-03 19:51:56 +0000[diff] [blame]103 <li><a href="#dss_othermap">Other Map-Like Container Options</a></li>
104 </ul></li>
Daniel Berlin1939ace2007-09-24 17:52:25 +0000[diff] [blame]105 <li><a href="#ds_bit">BitVector-like containers</a>
106 <ul>
107 <li><a href="#dss_bitvector">A dense bitvector</a></li>
Dan Gohman5f7775c2010-01-05 18:24:00 +0000[diff] [blame]108 <li><a href="#dss_smallbitvector">A "small" dense bitvector</a></li>
Daniel Berlin1939ace2007-09-24 17:52:25 +0000[diff] [blame]109 <li><a href="#dss_sparsebitvector">A sparse bitvector</a></li>
110 </ul></li>
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]111 </ul>
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]112 </li>
Chris Lattnerae7f7592002-09-06 18:31:18 +0000[diff] [blame]113 <li><a href="#common">Helpful Hints for Common Operations</a>
Chris Lattnerae7f7592002-09-06 18:31:18 +0000[diff] [blame]114 <ul>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]115 <li><a href="#inspection">Basic Inspection and Traversal Routines</a>
116 <ul>
117 <li><a href="#iterate_function">Iterating over the <tt>BasicBlock</tt>s
118in a <tt>Function</tt></a> </li>
119 <li><a href="#iterate_basicblock">Iterating over the <tt>Instruction</tt>s
120in a <tt>BasicBlock</tt></a> </li>
121 <li><a href="#iterate_institer">Iterating over the <tt>Instruction</tt>s
122in a <tt>Function</tt></a> </li>
123 <li><a href="#iterate_convert">Turning an iterator into a
124class pointer</a> </li>
125 <li><a href="#iterate_complex">Finding call sites: a more
126complex example</a> </li>
127 <li><a href="#calls_and_invokes">Treating calls and invokes
128the same way</a> </li>
129 <li><a href="#iterate_chains">Iterating over def-use &amp;
130use-def chains</a> </li>
Chris Lattner2e438ca2008-01-03 16:56:04 +0000[diff] [blame]131 <li><a href="#iterate_preds">Iterating over predecessors &amp;
132successors of blocks</a></li>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]133 </ul>
134 </li>
135 <li><a href="#simplechanges">Making simple changes</a>
136 <ul>
137 <li><a href="#schanges_creating">Creating and inserting new
138 <tt>Instruction</tt>s</a> </li>
139 <li><a href="#schanges_deleting">Deleting <tt>Instruction</tt>s</a> </li>
140 <li><a href="#schanges_replacing">Replacing an <tt>Instruction</tt>
141with another <tt>Value</tt></a> </li>
Tanya Lattnerb011c662007-06-20 18:33:15 +0000[diff] [blame]142 <li><a href="#schanges_deletingGV">Deleting <tt>GlobalVariable</tt>s</a> </li>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]143 </ul>
Reid Spencerfe8f4ff2004-11-01 09:02:53 +0000[diff] [blame]144 </li>
Jeffrey Yasskin714257f2009-04-30 22:33:41 +0000[diff] [blame]145 <li><a href="#create_types">How to Create Types</a></li>
Chris Lattnerae7f7592002-09-06 18:31:18 +0000[diff] [blame]146<!--
147 <li>Working with the Control Flow Graph
148 <ul>
149 <li>Accessing predecessors and successors of a <tt>BasicBlock</tt>
150 <li>
151 <li>
152 </ul>
Reid Spencerfe8f4ff2004-11-01 09:02:53 +0000[diff] [blame]153-->
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]154 </ul>
155 </li>
Chris Lattnerd9d6e102005-04-23 16:10:52 +0000[diff] [blame]156
Owen Anderson8bc1b3b2009-06-16 01:17:16 +0000[diff] [blame]157 <li><a href="#threading">Threads and LLVM</a>
158 <ul>
Owen Anderson1ad70e32009-06-16 18:04:19 +0000[diff] [blame]159 <li><a href="#startmultithreaded">Entering and Exiting Multithreaded Mode
160 </a></li>
Owen Anderson8bc1b3b2009-06-16 01:17:16 +0000[diff] [blame]161 <li><a href="#shutdown">Ending execution with <tt>llvm_shutdown()</tt></a></li>
162 <li><a href="#managedstatic">Lazy initialization with <tt>ManagedStatic</tt></a></li>
Owen Andersone0c951a2009-08-19 17:58:52 +0000[diff] [blame]163 <li><a href="#llvmcontext">Achieving Isolation with <tt>LLVMContext</tt></a></li>
Jeffrey Yasskin01eba392010-01-29 19:10:38 +0000[diff] [blame]164 <li><a href="#jitthreading">Threads and the JIT</a></li>
Owen Anderson8bc1b3b2009-06-16 01:17:16 +0000[diff] [blame]165 </ul>
166 </li>
167
Chris Lattnerd9d6e102005-04-23 16:10:52 +0000[diff] [blame]168 <li><a href="#advanced">Advanced Topics</a>
169 <ul>
Chris Lattnerf1b200b2005-04-23 17:27:36 +0000[diff] [blame]170
Chris Lattner1afcace2011-07-09 17:41:24 +0000[diff] [blame]171 <li><a href="#SymbolTable">The <tt>ValueSymbolTable</tt> class</a></li>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]172 <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]173 </ul></li>
174
Joel Stanley9b96c442002-09-06 21:55:13 +0000[diff] [blame]175 <li><a href="#coreclasses">The Core LLVM Class Hierarchy Reference</a>
Chris Lattner9355b472002-09-06 02:50:58 +0000[diff] [blame]176 <ul>
Reid Spencer303c4b42007-01-12 17:26:25 +0000[diff] [blame]177 <li><a href="#Type">The <tt>Type</tt> class</a> </li>
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]178 <li><a href="#Module">The <tt>Module</tt> class</a></li>
Reid Spencerfe8f4ff2004-11-01 09:02:53 +0000[diff] [blame]179 <li><a href="#Value">The <tt>Value</tt> class</a>
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]180 <ul>
181 <li><a href="#User">The <tt>User</tt> class</a>
Chris Lattner9355b472002-09-06 02:50:58 +0000[diff] [blame]182 <ul>
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]183 <li><a href="#Instruction">The <tt>Instruction</tt> class</a></li>
184 <li><a href="#Constant">The <tt>Constant</tt> class</a>
185 <ul>
186 <li><a href="#GlobalValue">The <tt>GlobalValue</tt> class</a>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]187 <ul>
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]188 <li><a href="#Function">The <tt>Function</tt> class</a></li>
189 <li><a href="#GlobalVariable">The <tt>GlobalVariable</tt> class</a></li>
190 </ul>
191 </li>
192 </ul>
193 </li>
Reid Spencerfe8f4ff2004-11-01 09:02:53 +0000[diff] [blame]194 </ul>
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]195 </li>
196 <li><a href="#BasicBlock">The <tt>BasicBlock</tt> class</a></li>
197 <li><a href="#Argument">The <tt>Argument</tt> class</a></li>
198 </ul>
Reid Spencerfe8f4ff2004-11-01 09:02:53 +0000[diff] [blame]199 </li>
200 </ul>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]201 </li>
Chris Lattner9355b472002-09-06 02:50:58 +0000[diff] [blame]202</ol>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]203
Chris Lattner69bf8a92004-05-23 21:06:58 +0000[diff] [blame]204<div class="doc_author">
205 <p>Written by <a href="mailto:sabre@nondot.org">Chris Lattner</a>,
Chris Lattner94c43592004-05-26 16:52:55 +0000[diff] [blame]206 <a href="mailto:dhurjati@cs.uiuc.edu">Dinakar Dhurjati</a>,
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]207 <a href="mailto:ggreif@gmail.com">Gabor Greif</a>,
Owen Anderson8bc1b3b2009-06-16 01:17:16 +0000[diff] [blame]208 <a href="mailto:jstanley@cs.uiuc.edu">Joel Stanley</a>,
209 <a href="mailto:rspencer@x10sys.com">Reid Spencer</a> and
210 <a href="mailto:owen@apple.com">Owen Anderson</a></p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]211</div>
212
Chris Lattner9355b472002-09-06 02:50:58 +0000[diff] [blame]213<!-- *********************************************************************** -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]214<h2>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]215 <a name="introduction">Introduction </a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]216</h2>
Chris Lattner9355b472002-09-06 02:50:58 +0000[diff] [blame]217<!-- *********************************************************************** -->
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]218
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]219<div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]220
221<p>This document is meant to highlight some of the important classes and
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]222interfaces available in the LLVM source-base. This manual is not
223intended to explain what LLVM is, how it works, and what LLVM code looks
224like. It assumes that you know the basics of LLVM and are interested
225in writing transformations or otherwise analyzing or manipulating the
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]226code.</p>
227
228<p>This document should get you oriented so that you can find your
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]229way in the continuously growing source code that makes up the LLVM
230infrastructure. Note that this manual is not intended to serve as a
231replacement for reading the source code, so if you think there should be
232a method in one of these classes to do something, but it's not listed,
233check the source. Links to the <a href="/doxygen/">doxygen</a> sources
234are provided to make this as easy as possible.</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]235
236<p>The first section of this document describes general information that is
237useful to know when working in the LLVM infrastructure, and the second describes
238the Core LLVM classes. In the future this manual will be extended with
239information describing how to use extension libraries, such as dominator
240information, CFG traversal routines, and useful utilities like the <tt><a
241href="/doxygen/InstVisitor_8h-source.html">InstVisitor</a></tt> template.</p>
242
243</div>
244
Chris Lattner9355b472002-09-06 02:50:58 +0000[diff] [blame]245<!-- *********************************************************************** -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]246<h2>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]247 <a name="general">General Information</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]248</h2>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]249<!-- *********************************************************************** -->
250
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]251<div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]252
253<p>This section contains general information that is useful if you are working
254in the LLVM source-base, but that isn't specific to any particular API.</p>
255
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]256<!-- ======================================================================= -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]257<h3>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]258 <a name="stl">The C++ Standard Template Library</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]259</h3>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]260
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]261<div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]262
263<p>LLVM makes heavy use of the C++ Standard Template Library (STL),
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]264perhaps much more than you are used to, or have seen before. Because of
265this, you might want to do a little background reading in the
266techniques used and capabilities of the library. There are many good
267pages that discuss the STL, and several books on the subject that you
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]268can get, so it will not be discussed in this document.</p>
269
270<p>Here are some useful links:</p>
271
272<ol>
273
Nick Lewyckyea1fe2c2010-10-09 21:12:29 +0000[diff] [blame]274<li><a href="http://www.dinkumware.com/manuals/#Standard C++ Library">Dinkumware
275C++ Library reference</a> - an excellent reference for the STL and other parts
276of the standard C++ library.</li>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]277
278<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]279O'Reilly book in the making. It has a decent Standard Library
280Reference that rivals Dinkumware's, and is unfortunately no longer free since the
281book has been published.</li>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]282
283<li><a href="http://www.parashift.com/c++-faq-lite/">C++ Frequently Asked
284Questions</a></li>
285
286<li><a href="http://www.sgi.com/tech/stl/">SGI's STL Programmer's Guide</a> -
287Contains a useful <a
288href="http://www.sgi.com/tech/stl/stl_introduction.html">Introduction to the
289STL</a>.</li>
290
291<li><a href="http://www.research.att.com/%7Ebs/C++.html">Bjarne Stroustrup's C++
292Page</a></li>
293
Tanya Lattner79445ba2004-12-08 18:34:56 +0000[diff] [blame]294<li><a href="http://64.78.49.204/">
Reid Spencer096603a2004-05-26 08:41:35 +0000[diff] [blame]295Bruce Eckel's Thinking in C++, 2nd ed. Volume 2 Revision 4.0 (even better, get
296the book).</a></li>
297
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]298</ol>
299
300<p>You are also encouraged to take a look at the <a
301href="CodingStandards.html">LLVM Coding Standards</a> guide which focuses on how
302to write maintainable code more than where to put your curly braces.</p>
303
304</div>
305
306<!-- ======================================================================= -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]307<h3>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]308 <a name="stl">Other useful references</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]309</h3>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]310
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]311<div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]312
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]313<ol>
Misha Brukmana0f71e42004-06-18 18:39:00 +0000[diff] [blame]314<li><a href="http://www.fortran-2000.com/ArnaudRecipes/sharedlib.html">Using
315static and shared libraries across platforms</a></li>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]316</ol>
317
318</div>
319
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]320</div>
321
Chris Lattner9355b472002-09-06 02:50:58 +0000[diff] [blame]322<!-- *********************************************************************** -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]323<h2>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]324 <a name="apis">Important and useful LLVM APIs</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]325</h2>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]326<!-- *********************************************************************** -->
327
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]328<div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]329
330<p>Here we highlight some LLVM APIs that are generally useful and good to
331know about when writing transformations.</p>
332
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]333<!-- ======================================================================= -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]334<h3>
Misha Brukman2c122ce2005-11-01 21:12:49 +0000[diff] [blame]335 <a name="isa">The <tt>isa&lt;&gt;</tt>, <tt>cast&lt;&gt;</tt> and
336 <tt>dyn_cast&lt;&gt;</tt> templates</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]337</h3>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]338
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]339<div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]340
341<p>The LLVM source-base makes extensive use of a custom form of RTTI.
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]342These templates have many similarities to the C++ <tt>dynamic_cast&lt;&gt;</tt>
343operator, but they don't have some drawbacks (primarily stemming from
344the fact that <tt>dynamic_cast&lt;&gt;</tt> only works on classes that
345have a v-table). Because they are used so often, you must know what they
346do and how they work. All of these templates are defined in the <a
Chris Lattner695b78b2005-04-26 22:56:16 +0000[diff] [blame]347 href="/doxygen/Casting_8h-source.html"><tt>llvm/Support/Casting.h</tt></a>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]348file (note that you very rarely have to include this file directly).</p>
349
350<dl>
351 <dt><tt>isa&lt;&gt;</tt>: </dt>
352
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]353 <dd><p>The <tt>isa&lt;&gt;</tt> operator works exactly like the Java
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]354 "<tt>instanceof</tt>" operator. It returns true or false depending on whether
355 a reference or pointer points to an instance of the specified class. This can
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]356 be very useful for constraint checking of various sorts (example below).</p>
357 </dd>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]358
359 <dt><tt>cast&lt;&gt;</tt>: </dt>
360
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]361 <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]362 converts a pointer or reference from a base class to a derived class, causing
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]363 an assertion failure if it is not really an instance of the right type. This
364 should be used in cases where you have some information that makes you believe
365 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]366 and <tt>cast&lt;&gt;</tt> template is:</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]367
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]368<div class="doc_code">
369<pre>
370static bool isLoopInvariant(const <a href="#Value">Value</a> *V, const Loop *L) {
371 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))
372 return true;
Chris Lattner69bf8a92004-05-23 21:06:58 +0000[diff] [blame]373
Bill Wendling82e2eea2006-10-11 18:00:22 +0000[diff] [blame]374 // <i>Otherwise, it must be an instruction...</i>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]375 return !L-&gt;contains(cast&lt;<a href="#Instruction">Instruction</a>&gt;(V)-&gt;getParent());
376}
377</pre>
378</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]379
380 <p>Note that you should <b>not</b> use an <tt>isa&lt;&gt;</tt> test followed
381 by a <tt>cast&lt;&gt;</tt>, for that use the <tt>dyn_cast&lt;&gt;</tt>
382 operator.</p>
383
384 </dd>
385
386 <dt><tt>dyn_cast&lt;&gt;</tt>:</dt>
387
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]388 <dd><p>The <tt>dyn_cast&lt;&gt;</tt> operator is a "checking cast" operation.
389 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]390 pointer to it (this operator does not work with references). If the operand is
391 not of the correct type, a null pointer is returned. Thus, this works very
Misha Brukman2c122ce2005-11-01 21:12:49 +0000[diff] [blame]392 much like the <tt>dynamic_cast&lt;&gt;</tt> operator in C++, and should be
393 used in the same circumstances. Typically, the <tt>dyn_cast&lt;&gt;</tt>
394 operator is used in an <tt>if</tt> statement or some other flow control
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]395 statement like this:</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]396
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]397<div class="doc_code">
398<pre>
399if (<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]400 // <i>...</i>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]401}
402</pre>
403</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]404
Misha Brukman2c122ce2005-11-01 21:12:49 +0000[diff] [blame]405 <p>This form of the <tt>if</tt> statement effectively combines together a call
406 to <tt>isa&lt;&gt;</tt> and a call to <tt>cast&lt;&gt;</tt> into one
407 statement, which is very convenient.</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]408
Misha Brukman2c122ce2005-11-01 21:12:49 +0000[diff] [blame]409 <p>Note that the <tt>dyn_cast&lt;&gt;</tt> operator, like C++'s
410 <tt>dynamic_cast&lt;&gt;</tt> or Java's <tt>instanceof</tt> operator, can be
411 abused. In particular, you should not use big chained <tt>if/then/else</tt>
412 blocks to check for lots of different variants of classes. If you find
413 yourself wanting to do this, it is much cleaner and more efficient to use the
414 <tt>InstVisitor</tt> class to dispatch over the instruction type directly.</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]415
Misha Brukman2c122ce2005-11-01 21:12:49 +0000[diff] [blame]416 </dd>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]417
Misha Brukman2c122ce2005-11-01 21:12:49 +0000[diff] [blame]418 <dt><tt>cast_or_null&lt;&gt;</tt>: </dt>
419
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]420 <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]421 <tt>cast&lt;&gt;</tt> operator, except that it allows for a null pointer as an
422 argument (which it then propagates). This can sometimes be useful, allowing
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]423 you to combine several null checks into one.</p></dd>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]424
Misha Brukman2c122ce2005-11-01 21:12:49 +0000[diff] [blame]425 <dt><tt>dyn_cast_or_null&lt;&gt;</tt>: </dt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]426
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]427 <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]428 <tt>dyn_cast&lt;&gt;</tt> operator, except that it allows for a null pointer
429 as an argument (which it then propagates). This can sometimes be useful,
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]430 allowing you to combine several null checks into one.</p></dd>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]431
Misha Brukman2c122ce2005-11-01 21:12:49 +0000[diff] [blame]432</dl>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]433
434<p>These five templates can be used with any classes, whether they have a
435v-table or not. To add support for these templates, you simply need to add
436<tt>classof</tt> static methods to the class you are interested casting
437to. Describing this is currently outside the scope of this document, but there
438are lots of examples in the LLVM source base.</p>
439
440</div>
441
Daniel Dunbar6e0d1cb2009-07-25 04:41:11 +0000[diff] [blame]442
443<!-- ======================================================================= -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]444<h3>
Daniel Dunbar6e0d1cb2009-07-25 04:41:11 +0000[diff] [blame]445 <a name="string_apis">Passing strings (the <tt>StringRef</tt>
446and <tt>Twine</tt> classes)</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]447</h3>
Daniel Dunbar6e0d1cb2009-07-25 04:41:11 +0000[diff] [blame]448
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]449<div>
Daniel Dunbar6e0d1cb2009-07-25 04:41:11 +0000[diff] [blame]450
451<p>Although LLVM generally does not do much string manipulation, we do have
Chris Lattner81187ae2009-07-25 07:16:59 +0000[diff] [blame]452several important APIs which take strings. Two important examples are the
Daniel Dunbar6e0d1cb2009-07-25 04:41:11 +0000[diff] [blame]453Value class -- which has names for instructions, functions, etc. -- and the
454StringMap class which is used extensively in LLVM and Clang.</p>
455
456<p>These are generic classes, and they need to be able to accept strings which
457may have embedded null characters. Therefore, they cannot simply take
Chris Lattner81187ae2009-07-25 07:16:59 +0000[diff] [blame]458a <tt>const char *</tt>, and taking a <tt>const std::string&amp;</tt> requires
Daniel Dunbar6e0d1cb2009-07-25 04:41:11 +0000[diff] [blame]459clients to perform a heap allocation which is usually unnecessary. Instead,
Benjamin Kramer38e59892010-07-14 22:38:02 +0000[diff] [blame]460many LLVM APIs use a <tt>StringRef</tt> or a <tt>const Twine&amp;</tt> for
461passing strings efficiently.</p>
Daniel Dunbar6e0d1cb2009-07-25 04:41:11 +0000[diff] [blame]462
Daniel Dunbar6e0d1cb2009-07-25 04:41:11 +0000[diff] [blame]463<!-- _______________________________________________________________________ -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]464<h4>
Daniel Dunbar6e0d1cb2009-07-25 04:41:11 +0000[diff] [blame]465 <a name="StringRef">The <tt>StringRef</tt> class</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]466</h4>
Daniel Dunbar6e0d1cb2009-07-25 04:41:11 +0000[diff] [blame]467
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]468<div>
Daniel Dunbar6e0d1cb2009-07-25 04:41:11 +0000[diff] [blame]469
470<p>The <tt>StringRef</tt> data type represents a reference to a constant string
471(a character array and a length) and supports the common operations available
472on <tt>std:string</tt>, but does not require heap allocation.</p>
473
Chris Lattner81187ae2009-07-25 07:16:59 +0000[diff] [blame]474<p>It can be implicitly constructed using a C style null-terminated string,
475an <tt>std::string</tt>, or explicitly with a character pointer and length.
Daniel Dunbar6e0d1cb2009-07-25 04:41:11 +0000[diff] [blame]476For example, the <tt>StringRef</tt> find function is declared as:</p>
Chris Lattner81187ae2009-07-25 07:16:59 +0000[diff] [blame]477
Benjamin Kramer38e59892010-07-14 22:38:02 +0000[diff] [blame]478<pre class="doc_code">
479 iterator find(StringRef Key);
480</pre>
Daniel Dunbar6e0d1cb2009-07-25 04:41:11 +0000[diff] [blame]481
482<p>and clients can call it using any one of:</p>
483
Benjamin Kramer38e59892010-07-14 22:38:02 +0000[diff] [blame]484<pre class="doc_code">
Daniel Dunbar6e0d1cb2009-07-25 04:41:11 +0000[diff] [blame]485 Map.find("foo"); <i>// Lookup "foo"</i>
486 Map.find(std::string("bar")); <i>// Lookup "bar"</i>
487 Map.find(StringRef("\0baz", 4)); <i>// Lookup "\0baz"</i>
488</pre>
Daniel Dunbar6e0d1cb2009-07-25 04:41:11 +0000[diff] [blame]489
490<p>Similarly, APIs which need to return a string may return a <tt>StringRef</tt>
491instance, which can be used directly or converted to an <tt>std::string</tt>
492using the <tt>str</tt> member function. See
493"<tt><a href="/doxygen/classllvm_1_1StringRef_8h-source.html">llvm/ADT/StringRef.h</a></tt>"
494for more information.</p>
495
496<p>You should rarely use the <tt>StringRef</tt> class directly, because it contains
497pointers to external memory it is not generally safe to store an instance of the
Benjamin Kramer38e59892010-07-14 22:38:02 +0000[diff] [blame]498class (unless you know that the external storage will not be freed). StringRef is
499small and pervasive enough in LLVM that it should always be passed by value.</p>
Daniel Dunbar6e0d1cb2009-07-25 04:41:11 +0000[diff] [blame]500
501</div>
502
503<!-- _______________________________________________________________________ -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]504<h4>
Daniel Dunbar6e0d1cb2009-07-25 04:41:11 +0000[diff] [blame]505 <a name="Twine">The <tt>Twine</tt> class</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]506</h4>
Daniel Dunbar6e0d1cb2009-07-25 04:41:11 +0000[diff] [blame]507
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]508<div>
Daniel Dunbar6e0d1cb2009-07-25 04:41:11 +0000[diff] [blame]509
510<p>The <tt>Twine</tt> class is an efficient way for APIs to accept concatenated
511strings. For example, a common LLVM paradigm is to name one instruction based on
512the name of another instruction with a suffix, for example:</p>
513
514<div class="doc_code">
515<pre>
516 New = CmpInst::Create(<i>...</i>, SO->getName() + ".cmp");
517</pre>
518</div>
519
520<p>The <tt>Twine</tt> class is effectively a
521lightweight <a href="http://en.wikipedia.org/wiki/Rope_(computer_science)">rope</a>
522which points to temporary (stack allocated) objects. Twines can be implicitly
523constructed as the result of the plus operator applied to strings (i.e., a C
524strings, an <tt>std::string</tt>, or a <tt>StringRef</tt>). The twine delays the
Dan Gohmancf0c9bc2010-02-25 23:51:27 +0000[diff] [blame]525actual concatenation of strings until it is actually required, at which point
Daniel Dunbar6e0d1cb2009-07-25 04:41:11 +0000[diff] [blame]526it can be efficiently rendered directly into a character array. This avoids
527unnecessary heap allocation involved in constructing the temporary results of
528string concatenation. See
529"<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]530for more information.</p>
Daniel Dunbar6e0d1cb2009-07-25 04:41:11 +0000[diff] [blame]531
532<p>As with a <tt>StringRef</tt>, <tt>Twine</tt> objects point to external memory
533and should almost never be stored or mentioned directly. They are intended
534solely for use when defining a function which should be able to efficiently
535accept concatenated strings.</p>
536
537</div>
538
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]539</div>
Daniel Dunbar6e0d1cb2009-07-25 04:41:11 +0000[diff] [blame]540
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]541<!-- ======================================================================= -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]542<h3>
Misha Brukman2c122ce2005-11-01 21:12:49 +0000[diff] [blame]543 <a name="DEBUG">The <tt>DEBUG()</tt> macro and <tt>-debug</tt> option</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]544</h3>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]545
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]546<div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]547
548<p>Often when working on your pass you will put a bunch of debugging printouts
549and other code into your pass. After you get it working, you want to remove
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]550it, 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]551across).</p>
552
553<p> Naturally, because of this, you don't want to delete the debug printouts,
554but you don't want them to always be noisy. A standard compromise is to comment
555them out, allowing you to enable them if you need them in the future.</p>
556
Chris Lattner695b78b2005-04-26 22:56:16 +0000[diff] [blame]557<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]558file provides a macro named <tt>DEBUG()</tt> that is a much nicer solution to
559this problem. Basically, you can put arbitrary code into the argument of the
560<tt>DEBUG</tt> macro, and it is only executed if '<tt>opt</tt>' (or any other
561tool) is run with the '<tt>-debug</tt>' command line argument:</p>
562
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]563<div class="doc_code">
564<pre>
Daniel Dunbar06388ae2009-07-25 01:55:32 +0000[diff] [blame]565DEBUG(errs() &lt;&lt; "I am here!\n");
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]566</pre>
567</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]568
569<p>Then you can run your pass like this:</p>
570
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]571<div class="doc_code">
572<pre>
573$ opt &lt; a.bc &gt; /dev/null -mypass
Bill Wendling82e2eea2006-10-11 18:00:22 +0000[diff] [blame]574<i>&lt;no output&gt;</i>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]575$ opt &lt; a.bc &gt; /dev/null -mypass -debug
576I am here!
577</pre>
578</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]579
580<p>Using the <tt>DEBUG()</tt> macro instead of a home-brewed solution allows you
581to not have to create "yet another" command line option for the debug output for
582your pass. Note that <tt>DEBUG()</tt> macros are disabled for optimized builds,
583so they do not cause a performance impact at all (for the same reason, they
584should also not contain side-effects!).</p>
585
586<p>One additional nice thing about the <tt>DEBUG()</tt> macro is that you can
587enable or disable it directly in gdb. Just use "<tt>set DebugFlag=0</tt>" or
588"<tt>set DebugFlag=1</tt>" from the gdb if the program is running. If the
589program hasn't been started yet, you can always just run it with
590<tt>-debug</tt>.</p>
591
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]592<!-- _______________________________________________________________________ -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]593<h4>
Chris Lattnerc9151082005-04-26 22:57:07 +0000[diff] [blame]594 <a name="DEBUG_TYPE">Fine grained debug info with <tt>DEBUG_TYPE</tt> and
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]595 the <tt>-debug-only</tt> option</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]596</h4>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]597
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]598<div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]599
600<p>Sometimes you may find yourself in a situation where enabling <tt>-debug</tt>
601just turns on <b>too much</b> information (such as when working on the code
602generator). If you want to enable debug information with more fine-grained
603control, you define the <tt>DEBUG_TYPE</tt> macro and the <tt>-debug</tt> only
604option as follows:</p>
605
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]606<div class="doc_code">
607<pre>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]608#undef DEBUG_TYPE
Daniel Dunbar06388ae2009-07-25 01:55:32 +0000[diff] [blame]609DEBUG(errs() &lt;&lt; "No debug type\n");
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]610#define DEBUG_TYPE "foo"
Daniel Dunbar06388ae2009-07-25 01:55:32 +0000[diff] [blame]611DEBUG(errs() &lt;&lt; "'foo' debug type\n");
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]612#undef DEBUG_TYPE
613#define DEBUG_TYPE "bar"
Daniel Dunbar06388ae2009-07-25 01:55:32 +0000[diff] [blame]614DEBUG(errs() &lt;&lt; "'bar' debug type\n"));
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]615#undef DEBUG_TYPE
616#define DEBUG_TYPE ""
Daniel Dunbar06388ae2009-07-25 01:55:32 +0000[diff] [blame]617DEBUG(errs() &lt;&lt; "No debug type (2)\n");
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]618</pre>
619</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]620
621<p>Then you can run your pass like this:</p>
622
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]623<div class="doc_code">
624<pre>
625$ opt &lt; a.bc &gt; /dev/null -mypass
Bill Wendling82e2eea2006-10-11 18:00:22 +0000[diff] [blame]626<i>&lt;no output&gt;</i>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]627$ opt &lt; a.bc &gt; /dev/null -mypass -debug
628No debug type
629'foo' debug type
630'bar' debug type
631No debug type (2)
632$ opt &lt; a.bc &gt; /dev/null -mypass -debug-only=foo
633'foo' debug type
634$ opt &lt; a.bc &gt; /dev/null -mypass -debug-only=bar
635'bar' debug type
636</pre>
637</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]638
639<p>Of course, in practice, you should only set <tt>DEBUG_TYPE</tt> at the top of
640a 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]641you <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]642<tt>#undef</tt>'s). Also, you should use names more meaningful than "foo" and
643"bar", because there is no system in place to ensure that names do not
644conflict. If two different modules use the same string, they will all be turned
645on when the name is specified. This allows, for example, all debug information
646for instruction scheduling to be enabled with <tt>-debug-type=InstrSched</tt>,
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]647even if the source lives in multiple files.</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]648
Daniel Dunbarc3c92392009-08-07 23:48:59 +0000[diff] [blame]649<p>The <tt>DEBUG_WITH_TYPE</tt> macro is also available for situations where you
650would like to set <tt>DEBUG_TYPE</tt>, but only for one specific <tt>DEBUG</tt>
651statement. It takes an additional first parameter, which is the type to use. For
Benjamin Kramer8040cd32009-10-12 14:46:08 +0000[diff] [blame]652example, the preceding example could be written as:</p>
Daniel Dunbarc3c92392009-08-07 23:48:59 +0000[diff] [blame]653
654
655<div class="doc_code">
656<pre>
657DEBUG_WITH_TYPE("", errs() &lt;&lt; "No debug type\n");
658DEBUG_WITH_TYPE("foo", errs() &lt;&lt; "'foo' debug type\n");
659DEBUG_WITH_TYPE("bar", errs() &lt;&lt; "'bar' debug type\n"));
660DEBUG_WITH_TYPE("", errs() &lt;&lt; "No debug type (2)\n");
661</pre>
662</div>
663
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]664</div>
665
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]666</div>
667
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]668<!-- ======================================================================= -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]669<h3>
Chris Lattner0be6fdf2006-12-19 21:46:21 +0000[diff] [blame]670 <a name="Statistic">The <tt>Statistic</tt> class &amp; <tt>-stats</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]671 option</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]672</h3>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]673
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]674<div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]675
676<p>The "<tt><a
Chris Lattner695b78b2005-04-26 22:56:16 +0000[diff] [blame]677href="/doxygen/Statistic_8h-source.html">llvm/ADT/Statistic.h</a></tt>" file
Chris Lattner0be6fdf2006-12-19 21:46:21 +0000[diff] [blame]678provides a class named <tt>Statistic</tt> that is used as a unified way to
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]679keep track of what the LLVM compiler is doing and how effective various
680optimizations are. It is useful to see what optimizations are contributing to
681making a particular program run faster.</p>
682
683<p>Often you may run your pass on some big program, and you're interested to see
684how many times it makes a certain transformation. Although you can do this with
685hand 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]686for big programs. Using the <tt>Statistic</tt> class makes it very easy to
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]687keep track of this information, and the calculated information is presented in a
688uniform manner with the rest of the passes being executed.</p>
689
690<p>There are many examples of <tt>Statistic</tt> uses, but the basics of using
691it are as follows:</p>
692
693<ol>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]694 <li><p>Define your statistic like this:</p>
695
696<div class="doc_code">
697<pre>
Chris Lattner0be6fdf2006-12-19 21:46:21 +0000[diff] [blame]698#define <a href="#DEBUG_TYPE">DEBUG_TYPE</a> "mypassname" <i>// This goes before any #includes.</i>
699STATISTIC(NumXForms, "The # of times I did stuff");
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]700</pre>
701</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]702
Chris Lattner0be6fdf2006-12-19 21:46:21 +0000[diff] [blame]703 <p>The <tt>STATISTIC</tt> macro defines a static variable, whose name is
704 specified by the first argument. The pass name is taken from the DEBUG_TYPE
705 macro, and the description is taken from the second argument. The variable
Reid Spencer06565dc2007-01-12 17:11:23 +0000[diff] [blame]706 defined ("NumXForms" in this case) acts like an unsigned integer.</p></li>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]707
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]708 <li><p>Whenever you make a transformation, bump the counter:</p>
709
710<div class="doc_code">
711<pre>
Bill Wendling82e2eea2006-10-11 18:00:22 +0000[diff] [blame]712++NumXForms; // <i>I did stuff!</i>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]713</pre>
714</div>
715
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]716 </li>
717 </ol>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]718
719 <p>That's all you have to do. To get '<tt>opt</tt>' to print out the
720 statistics gathered, use the '<tt>-stats</tt>' option:</p>
721
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]722<div class="doc_code">
723<pre>
724$ opt -stats -mypassname &lt; program.bc &gt; /dev/null
Bill Wendling82e2eea2006-10-11 18:00:22 +0000[diff] [blame]725<i>... statistics output ...</i>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]726</pre>
727</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]728
Reid Spencer6b6c73e2007-02-09 16:00:28 +0000[diff] [blame]729 <p> When running <tt>opt</tt> on a C file from the SPEC benchmark
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]730suite, it gives a report that looks like this:</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]731
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]732<div class="doc_code">
733<pre>
Gabor Greif04367bf2007-07-06 22:07:22 +0000[diff] [blame]734 7646 bitcodewriter - Number of normal instructions
735 725 bitcodewriter - Number of oversized instructions
736 129996 bitcodewriter - Number of bitcode bytes written
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]737 2817 raise - Number of insts DCEd or constprop'd
738 3213 raise - Number of cast-of-self removed
739 5046 raise - Number of expression trees converted
740 75 raise - Number of other getelementptr's formed
741 138 raise - Number of load/store peepholes
742 42 deadtypeelim - Number of unused typenames removed from symtab
743 392 funcresolve - Number of varargs functions resolved
744 27 globaldce - Number of global variables removed
745 2 adce - Number of basic blocks removed
746 134 cee - Number of branches revectored
747 49 cee - Number of setcc instruction eliminated
748 532 gcse - Number of loads removed
749 2919 gcse - Number of instructions removed
750 86 indvars - Number of canonical indvars added
751 87 indvars - Number of aux indvars removed
752 25 instcombine - Number of dead inst eliminate
753 434 instcombine - Number of insts combined
754 248 licm - Number of load insts hoisted
755 1298 licm - Number of insts hoisted to a loop pre-header
756 3 licm - Number of insts hoisted to multiple loop preds (bad, no loop pre-header)
757 75 mem2reg - Number of alloca's promoted
758 1444 cfgsimplify - Number of blocks simplified
759</pre>
760</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]761
762<p>Obviously, with so many optimizations, having a unified framework for this
763stuff is very nice. Making your pass fit well into the framework makes it more
764maintainable and useful.</p>
765
766</div>
767
Chris Lattnerf623a082005-10-17 01:36:23 +0000[diff] [blame]768<!-- ======================================================================= -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]769<h3>
Chris Lattnerf623a082005-10-17 01:36:23 +0000[diff] [blame]770 <a name="ViewGraph">Viewing graphs while debugging code</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]771</h3>
Chris Lattnerf623a082005-10-17 01:36:23 +0000[diff] [blame]772
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]773<div>
Chris Lattnerf623a082005-10-17 01:36:23 +0000[diff] [blame]774
775<p>Several of the important data structures in LLVM are graphs: for example
776CFGs made out of LLVM <a href="#BasicBlock">BasicBlock</a>s, CFGs made out of
777LLVM <a href="CodeGenerator.html#machinebasicblock">MachineBasicBlock</a>s, and
778<a href="CodeGenerator.html#selectiondag_intro">Instruction Selection
779DAGs</a>. In many cases, while debugging various parts of the compiler, it is
780nice to instantly visualize these graphs.</p>
781
782<p>LLVM provides several callbacks that are available in a debug build to do
783exactly that. If you call the <tt>Function::viewCFG()</tt> method, for example,
784the current LLVM tool will pop up a window containing the CFG for the function
785where each basic block is a node in the graph, and each node contains the
786instructions in the block. Similarly, there also exists
787<tt>Function::viewCFGOnly()</tt> (does not include the instructions), the
788<tt>MachineFunction::viewCFG()</tt> and <tt>MachineFunction::viewCFGOnly()</tt>,
789and the <tt>SelectionDAG::viewGraph()</tt> methods. Within GDB, for example,
Jim Laskey543a0ee2006-10-02 12:28:07 +0000[diff] [blame]790you can usually use something like <tt>call DAG.viewGraph()</tt> to pop
Chris Lattnerf623a082005-10-17 01:36:23 +0000[diff] [blame]791up a window. Alternatively, you can sprinkle calls to these functions in your
792code in places you want to debug.</p>
793
794<p>Getting this to work requires a small amount of configuration. On Unix
795systems with X11, install the <a href="http://www.graphviz.org">graphviz</a>
796toolkit, and make sure 'dot' and 'gv' are in your path. If you are running on
797Mac OS/X, download and install the Mac OS/X <a
798href="http://www.pixelglow.com/graphviz/">Graphviz program</a>, and add
Reid Spencer128a7a72007-02-03 21:06:43 +0000[diff] [blame]799<tt>/Applications/Graphviz.app/Contents/MacOS/</tt> (or wherever you install
Chris Lattnerf623a082005-10-17 01:36:23 +0000[diff] [blame]800it) to your path. Once in your system and path are set up, rerun the LLVM
801configure script and rebuild LLVM to enable this functionality.</p>
802
Jim Laskey543a0ee2006-10-02 12:28:07 +0000[diff] [blame]803<p><tt>SelectionDAG</tt> has been extended to make it easier to locate
804<i>interesting</i> nodes in large complex graphs. From gdb, if you
805<tt>call DAG.setGraphColor(<i>node</i>, "<i>color</i>")</tt>, then the
Reid Spencer128a7a72007-02-03 21:06:43 +0000[diff] [blame]806next <tt>call DAG.viewGraph()</tt> would highlight the node in the
Jim Laskey543a0ee2006-10-02 12:28:07 +0000[diff] [blame]807specified color (choices of colors can be found at <a
Chris Lattner302da1e2007-02-03 03:05:57 +0000[diff] [blame]808href="http://www.graphviz.org/doc/info/colors.html">colors</a>.) More
Jim Laskey543a0ee2006-10-02 12:28:07 +0000[diff] [blame]809complex node attributes can be provided with <tt>call
810DAG.setGraphAttrs(<i>node</i>, "<i>attributes</i>")</tt> (choices can be
811found at <a href="http://www.graphviz.org/doc/info/attrs.html">Graph
812Attributes</a>.) If you want to restart and clear all the current graph
813attributes, then you can <tt>call DAG.clearGraphAttrs()</tt>. </p>
814
Chris Lattner83f94672011-06-13 15:59:35 +0000[diff] [blame]815<p>Note that graph visualization features are compiled out of Release builds
816to reduce file size. This means that you need a Debug+Asserts or
817Release+Asserts build to use these features.</p>
818
Chris Lattnerf623a082005-10-17 01:36:23 +0000[diff] [blame]819</div>
820
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]821</div>
822
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]823<!-- *********************************************************************** -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]824<h2>
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]825 <a name="datastructure">Picking the Right Data Structure for a Task</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]826</h2>
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]827<!-- *********************************************************************** -->
828
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]829<div>
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]830
Reid Spencer128a7a72007-02-03 21:06:43 +0000[diff] [blame]831<p>LLVM has a plethora of data structures in the <tt>llvm/ADT/</tt> directory,
832 and we commonly use STL data structures. This section describes the trade-offs
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]833 you should consider when you pick one.</p>
834
835<p>
836The first step is a choose your own adventure: do you want a sequential
837container, a set-like container, or a map-like container? The most important
838thing when choosing a container is the algorithmic properties of how you plan to
839access the container. Based on that, you should use:</p>
840
841<ul>
Reid Spencer128a7a72007-02-03 21:06:43 +0000[diff] [blame]842<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]843 of an value based on another value. Map-like containers also support
844 efficient queries for containment (whether a key is in the map). Map-like
845 containers generally do not support efficient reverse mapping (values to
846 keys). If you need that, use two maps. Some map-like containers also
847 support efficient iteration through the keys in sorted order. Map-like
848 containers are the most expensive sort, only use them if you need one of
849 these capabilities.</li>
850
851<li>a <a href="#ds_set">set-like</a> container if you need to put a bunch of
852 stuff into a container that automatically eliminates duplicates. Some
853 set-like containers support efficient iteration through the elements in
854 sorted order. Set-like containers are more expensive than sequential
855 containers.
856</li>
857
858<li>a <a href="#ds_sequential">sequential</a> container provides
859 the most efficient way to add elements and keeps track of the order they are
860 added to the collection. They permit duplicates and support efficient
Reid Spencer128a7a72007-02-03 21:06:43 +0000[diff] [blame]861 iteration, but do not support efficient look-up based on a key.
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]862</li>
863
Chris Lattnerdced9fb2009-07-25 07:22:20 +0000[diff] [blame]864<li>a <a href="#ds_string">string</a> container is a specialized sequential
865 container or reference structure that is used for character or byte
866 arrays.</li>
867
Daniel Berlin1939ace2007-09-24 17:52:25 +0000[diff] [blame]868<li>a <a href="#ds_bit">bit</a> container provides an efficient way to store and
869 perform set operations on sets of numeric id's, while automatically
870 eliminating duplicates. Bit containers require a maximum of 1 bit for each
871 identifier you want to store.
872</li>
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]873</ul>
874
875<p>
Reid Spencer128a7a72007-02-03 21:06:43 +0000[diff] [blame]876Once the proper category of container is determined, you can fine tune the
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]877memory use, constant factors, and cache behaviors of access by intelligently
Reid Spencer128a7a72007-02-03 21:06:43 +0000[diff] [blame]878picking a member of the category. Note that constant factors and cache behavior
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]879can be a big deal. If you have a vector that usually only contains a few
880elements (but could contain many), for example, it's much better to use
881<a href="#dss_smallvector">SmallVector</a> than <a href="#dss_vector">vector</a>
882. Doing so avoids (relatively) expensive malloc/free calls, which dwarf the
883cost of adding the elements to the container. </p>
884
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]885<!-- ======================================================================= -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]886<h3>
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]887 <a name="ds_sequential">Sequential Containers (std::vector, std::list, etc)</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]888</h3>
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]889
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]890<div>
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]891There are a variety of sequential containers available for you, based on your
892needs. Pick the first in this section that will do what you want.
Chris Lattner3b4f4172011-07-22 21:34:12 +0000[diff] [blame]893
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]894<!-- _______________________________________________________________________ -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]895<h4>
Chris Lattner8ae42612011-04-05 23:18:20 +0000[diff] [blame]896 <a name="dss_arrayref">llvm/ADT/ArrayRef.h</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]897</h4>
Chris Lattner8ae42612011-04-05 23:18:20 +0000[diff] [blame]898
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]899<div>
Chris Lattner8ae42612011-04-05 23:18:20 +0000[diff] [blame]900<p>The llvm::ArrayRef class is the preferred class to use in an interface that
901 accepts a sequential list of elements in memory and just reads from them. By
902 taking an ArrayRef, the API can be passed a fixed size array, an std::vector,
903 an llvm::SmallVector and anything else that is contiguous in memory.
904</p>
905</div>
906
907
908
909<!-- _______________________________________________________________________ -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]910<h4>
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]911 <a name="dss_fixedarrays">Fixed Size Arrays</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]912</h4>
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]913
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]914<div>
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]915<p>Fixed size arrays are very simple and very fast. They are good if you know
916exactly how many elements you have, or you have a (low) upper bound on how many
917you have.</p>
918</div>
919
920<!-- _______________________________________________________________________ -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]921<h4>
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]922 <a name="dss_heaparrays">Heap Allocated Arrays</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]923</h4>
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]924
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]925<div>
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]926<p>Heap allocated arrays (new[] + delete[]) are also simple. They are good if
927the number of elements is variable, if you know how many elements you will need
928before the array is allocated, and if the array is usually large (if not,
929consider a <a href="#dss_smallvector">SmallVector</a>). The cost of a heap
930allocated array is the cost of the new/delete (aka malloc/free). Also note that
931if you are allocating an array of a type with a constructor, the constructor and
Reid Spencer128a7a72007-02-03 21:06:43 +0000[diff] [blame]932destructors will be run for every element in the array (re-sizable vectors only
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]933construct those elements actually used).</p>
934</div>
935
936<!-- _______________________________________________________________________ -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]937<h4>
Chris Lattner9d69d4a2011-07-18 01:40:02 +0000[diff] [blame]938 <a name="dss_tinyptrvector">"llvm/ADT/TinyPtrVector.h"</a>
939</h4>
940
941
942<div>
943<p><tt>TinyPtrVector&lt;Type&gt;</tt> is a highly specialized collection class
944that is optimized to avoid allocation in the case when a vector has zero or one
945elements. It has two major restrictions: 1) it can only hold values of pointer
946type, and 2) it cannot hold a null pointer.</p>
947
948<p>Since this container is highly specialized, it is rarely used.</p>
949
950</div>
951
Chris Lattner9d69d4a2011-07-18 01:40:02 +0000[diff] [blame]952<!-- _______________________________________________________________________ -->
953<h4>
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]954 <a name="dss_smallvector">"llvm/ADT/SmallVector.h"</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]955</h4>
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]956
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]957<div>
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]958<p><tt>SmallVector&lt;Type, N&gt;</tt> is a simple class that looks and smells
959just like <tt>vector&lt;Type&gt;</tt>:
960it supports efficient iteration, lays out elements in memory order (so you can
961do pointer arithmetic between elements), supports efficient push_back/pop_back
962operations, supports efficient random access to its elements, etc.</p>
963
964<p>The advantage of SmallVector is that it allocates space for
965some number of elements (N) <b>in the object itself</b>. Because of this, if
966the SmallVector is dynamically smaller than N, no malloc is performed. This can
967be a big win in cases where the malloc/free call is far more expensive than the
968code that fiddles around with the elements.</p>
969
970<p>This is good for vectors that are "usually small" (e.g. the number of
971predecessors/successors of a block is usually less than 8). On the other hand,
972this makes the size of the SmallVector itself large, so you don't want to
973allocate lots of them (doing so will waste a lot of space). As such,
974SmallVectors are most useful when on the stack.</p>
975
976<p>SmallVector also provides a nice portable and efficient replacement for
977<tt>alloca</tt>.</p>
978
979</div>
980
981<!-- _______________________________________________________________________ -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]982<h4>
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]983 <a name="dss_vector">&lt;vector&gt;</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]984</h4>
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]985
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]986<div>
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]987<p>
988std::vector is well loved and respected. It is useful when SmallVector isn't:
989when the size of the vector is often large (thus the small optimization will
990rarely be a benefit) or if you will be allocating many instances of the vector
991itself (which would waste space for elements that aren't in the container).
992vector is also useful when interfacing with code that expects vectors :).
993</p>
Chris Lattner32d84762007-02-05 06:30:51 +0000[diff] [blame]994
995<p>One worthwhile note about std::vector: avoid code like this:</p>
996
997<div class="doc_code">
998<pre>
999for ( ... ) {
Chris Lattner9bb3dbb2007-03-28 18:27:57 +0000[diff] [blame]1000 std::vector&lt;foo&gt; V;
Jim Grosbach087f0502011-10-28 20:52:20 +0000[diff] [blame]1001 // make use of V.
Chris Lattner32d84762007-02-05 06:30:51 +0000[diff] [blame]1002}
1003</pre>
1004</div>
1005
1006<p>Instead, write this as:</p>
1007
1008<div class="doc_code">
1009<pre>
Chris Lattner9bb3dbb2007-03-28 18:27:57 +0000[diff] [blame]1010std::vector&lt;foo&gt; V;
Chris Lattner32d84762007-02-05 06:30:51 +0000[diff] [blame]1011for ( ... ) {
Jim Grosbach087f0502011-10-28 20:52:20 +0000[diff] [blame]1012 // make use of V.
Chris Lattner32d84762007-02-05 06:30:51 +0000[diff] [blame]1013 V.clear();
1014}
1015</pre>
1016</div>
1017
1018<p>Doing so will save (at least) one heap allocation and free per iteration of
1019the loop.</p>
1020
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]1021</div>
1022
1023<!-- _______________________________________________________________________ -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]1024<h4>
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1025 <a name="dss_deque">&lt;deque&gt;</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]1026</h4>
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1027
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]1028<div>
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1029<p>std::deque is, in some senses, a generalized version of std::vector. Like
1030std::vector, it provides constant time random access and other similar
1031properties, but it also provides efficient access to the front of the list. It
1032does not guarantee continuity of elements within memory.</p>
1033
1034<p>In exchange for this extra flexibility, std::deque has significantly higher
1035constant factor costs than std::vector. If possible, use std::vector or
1036something cheaper.</p>
1037</div>
1038
1039<!-- _______________________________________________________________________ -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]1040<h4>
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]1041 <a name="dss_list">&lt;list&gt;</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]1042</h4>
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]1043
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]1044<div>
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]1045<p>std::list is an extremely inefficient class that is rarely useful.
1046It performs a heap allocation for every element inserted into it, thus having an
1047extremely high constant factor, particularly for small data types. std::list
1048also only supports bidirectional iteration, not random access iteration.</p>
1049
1050<p>In exchange for this high cost, std::list supports efficient access to both
1051ends of the list (like std::deque, but unlike std::vector or SmallVector). In
1052addition, the iterator invalidation characteristics of std::list are stronger
1053than that of a vector class: inserting or removing an element into the list does
1054not invalidate iterator or pointers to other elements in the list.</p>
1055</div>
1056
1057<!-- _______________________________________________________________________ -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]1058<h4>
Gabor Greif3899e492009-02-27 11:37:41 +0000[diff] [blame]1059 <a name="dss_ilist">llvm/ADT/ilist.h</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]1060</h4>
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]1061
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]1062<div>
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]1063<p><tt>ilist&lt;T&gt;</tt> implements an 'intrusive' doubly-linked list. It is
1064intrusive, because it requires the element to store and provide access to the
1065prev/next pointers for the list.</p>
1066
Gabor Greif2946d1c2009-02-27 12:02:19 +0000[diff] [blame]1067<p><tt>ilist</tt> has the same drawbacks as <tt>std::list</tt>, and additionally
1068requires an <tt>ilist_traits</tt> implementation for the element type, but it
1069provides some novel characteristics. In particular, it can efficiently store
1070polymorphic objects, the traits class is informed when an element is inserted or
Gabor Greif0cbcabe2009-03-12 09:47:03 +0000[diff] [blame]1071removed from the list, and <tt>ilist</tt>s are guaranteed to support a
1072constant-time splice operation.</p>
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]1073
Gabor Greif0cbcabe2009-03-12 09:47:03 +0000[diff] [blame]1074<p>These properties are exactly what we want for things like
1075<tt>Instruction</tt>s and basic blocks, which is why these are implemented with
1076<tt>ilist</tt>s.</p>
Gabor Greif3899e492009-02-27 11:37:41 +0000[diff] [blame]1077
1078Related classes of interest are explained in the following subsections:
1079 <ul>
Gabor Greif01862502009-02-27 13:28:07 +0000[diff] [blame]1080 <li><a href="#dss_ilist_traits">ilist_traits</a></li>
Gabor Greif2946d1c2009-02-27 12:02:19 +0000[diff] [blame]1081 <li><a href="#dss_iplist">iplist</a></li>
Gabor Greif3899e492009-02-27 11:37:41 +0000[diff] [blame]1082 <li><a href="#dss_ilist_node">llvm/ADT/ilist_node.h</a></li>
Gabor Greif6a65f422009-03-12 10:30:31 +0000[diff] [blame]1083 <li><a href="#dss_ilist_sentinel">Sentinels</a></li>
Gabor Greif3899e492009-02-27 11:37:41 +0000[diff] [blame]1084 </ul>
1085</div>
1086
1087<!-- _______________________________________________________________________ -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]1088<h4>
Argyrios Kyrtzidis81df0892011-06-15 19:56:01 +0000[diff] [blame]1089 <a name="dss_packedvector">llvm/ADT/PackedVector.h</a>
1090</h4>
1091
1092<div>
1093<p>
1094Useful for storing a vector of values using only a few number of bits for each
1095value. Apart from the standard operations of a vector-like container, it can
1096also perform an 'or' set operation.
1097</p>
1098
1099<p>For example:</p>
1100
1101<div class="doc_code">
1102<pre>
1103enum State {
1104 None = 0x0,
1105 FirstCondition = 0x1,
1106 SecondCondition = 0x2,
1107 Both = 0x3
1108};
1109
1110State get() {
1111 PackedVector&lt;State, 2&gt; Vec1;
1112 Vec1.push_back(FirstCondition);
1113
1114 PackedVector&lt;State, 2&gt; Vec2;
1115 Vec2.push_back(SecondCondition);
1116
1117 Vec1 |= Vec2;
1118 return Vec1[0]; // returns 'Both'.
1119}
1120</pre>
1121</div>
1122
1123</div>
1124
1125<!-- _______________________________________________________________________ -->
1126<h4>
Gabor Greif01862502009-02-27 13:28:07 +0000[diff] [blame]1127 <a name="dss_ilist_traits">ilist_traits</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]1128</h4>
Gabor Greif01862502009-02-27 13:28:07 +0000[diff] [blame]1129
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]1130<div>
Gabor Greif01862502009-02-27 13:28:07 +0000[diff] [blame]1131<p><tt>ilist_traits&lt;T&gt;</tt> is <tt>ilist&lt;T&gt;</tt>'s customization
1132mechanism. <tt>iplist&lt;T&gt;</tt> (and consequently <tt>ilist&lt;T&gt;</tt>)
1133publicly derive from this traits class.</p>
1134</div>
1135
1136<!-- _______________________________________________________________________ -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]1137<h4>
Gabor Greif2946d1c2009-02-27 12:02:19 +0000[diff] [blame]1138 <a name="dss_iplist">iplist</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]1139</h4>
Gabor Greif2946d1c2009-02-27 12:02:19 +0000[diff] [blame]1140
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]1141<div>
Gabor Greif2946d1c2009-02-27 12:02:19 +0000[diff] [blame]1142<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]1143supports a slightly narrower interface. Notably, inserters from
1144<tt>T&amp;</tt> are absent.</p>
Gabor Greif01862502009-02-27 13:28:07 +0000[diff] [blame]1145
1146<p><tt>ilist_traits&lt;T&gt;</tt> is a public base of this class and can be
1147used for a wide variety of customizations.</p>
Gabor Greif2946d1c2009-02-27 12:02:19 +0000[diff] [blame]1148</div>
1149
1150<!-- _______________________________________________________________________ -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]1151<h4>
Gabor Greif3899e492009-02-27 11:37:41 +0000[diff] [blame]1152 <a name="dss_ilist_node">llvm/ADT/ilist_node.h</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]1153</h4>
Gabor Greif3899e492009-02-27 11:37:41 +0000[diff] [blame]1154
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]1155<div>
Gabor Greif3899e492009-02-27 11:37:41 +0000[diff] [blame]1156<p><tt>ilist_node&lt;T&gt;</tt> implements a the forward and backward links
1157that are expected by the <tt>ilist&lt;T&gt;</tt> (and analogous containers)
1158in the default manner.</p>
1159
1160<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]1161<tt>T</tt>, usually <tt>T</tt> publicly derives from
1162<tt>ilist_node&lt;T&gt;</tt>.</p>
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]1163</div>
1164
1165<!-- _______________________________________________________________________ -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]1166<h4>
Gabor Greif6a65f422009-03-12 10:30:31 +0000[diff] [blame]1167 <a name="dss_ilist_sentinel">Sentinels</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]1168</h4>
Gabor Greif6a65f422009-03-12 10:30:31 +0000[diff] [blame]1169
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]1170<div>
Dan Gohmancf0c9bc2010-02-25 23:51:27 +0000[diff] [blame]1171<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]1172citizen in the C++ ecosystem, it needs to support the standard container
1173operations, such as <tt>begin</tt> and <tt>end</tt> iterators, etc. Also, the
1174<tt>operator--</tt> must work correctly on the <tt>end</tt> iterator in the
1175case of non-empty <tt>ilist</tt>s.</p>
1176
1177<p>The only sensible solution to this problem is to allocate a so-called
1178<i>sentinel</i> along with the intrusive list, which serves as the <tt>end</tt>
1179iterator, providing the back-link to the last element. However conforming to the
1180C++ convention it is illegal to <tt>operator++</tt> beyond the sentinel and it
1181also must not be dereferenced.</p>
1182
1183<p>These constraints allow for some implementation freedom to the <tt>ilist</tt>
1184how to allocate and store the sentinel. The corresponding policy is dictated
1185by <tt>ilist_traits&lt;T&gt;</tt>. By default a <tt>T</tt> gets heap-allocated
1186whenever the need for a sentinel arises.</p>
1187
1188<p>While the default policy is sufficient in most cases, it may break down when
1189<tt>T</tt> does not provide a default constructor. Also, in the case of many
1190instances of <tt>ilist</tt>s, the memory overhead of the associated sentinels
1191is wasted. To alleviate the situation with numerous and voluminous
1192<tt>T</tt>-sentinels, sometimes a trick is employed, leading to <i>ghostly
1193sentinels</i>.</p>
1194
1195<p>Ghostly sentinels are obtained by specially-crafted <tt>ilist_traits&lt;T&gt;</tt>
1196which superpose the sentinel with the <tt>ilist</tt> instance in memory. Pointer
1197arithmetic is used to obtain the sentinel, which is relative to the
1198<tt>ilist</tt>'s <tt>this</tt> pointer. The <tt>ilist</tt> is augmented by an
1199extra pointer, which serves as the back-link of the sentinel. This is the only
1200field in the ghostly sentinel which can be legally accessed.</p>
1201</div>
1202
1203<!-- _______________________________________________________________________ -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]1204<h4>
Chris Lattnerc5722432007-02-03 19:49:31 +0000[diff] [blame]1205 <a name="dss_other">Other Sequential Container options</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]1206</h4>
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]1207
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]1208<div>
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1209<p>Other STL containers are available, such as std::string.</p>
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]1210
1211<p>There are also various STL adapter classes such as std::queue,
1212std::priority_queue, std::stack, etc. These provide simplified access to an
1213underlying container but don't affect the cost of the container itself.</p>
1214
1215</div>
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]1216</div>
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]1217
1218<!-- ======================================================================= -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]1219<h3>
Chris Lattner7314a202011-07-22 20:46:49 +0000[diff] [blame]1220 <a name="ds_string">String-like containers</a>
1221</h3>
1222
1223<div>
1224
1225<p>
Chris Lattner3b4f4172011-07-22 21:34:12 +0000[diff] [blame]1226There are a variety of ways to pass around and use strings in C and C++, and
1227LLVM adds a few new options to choose from. Pick the first option on this list
1228that will do what you need, they are ordered according to their relative cost.
1229</p>
1230<p>
1231Note that is is generally preferred to <em>not</em> pass strings around as
1232"<tt>const char*</tt>"'s. These have a number of problems, including the fact
1233that they cannot represent embedded nul ("\0") characters, and do not have a
1234length available efficiently. The general replacement for '<tt>const
1235char*</tt>' is StringRef.
1236</p>
1237
1238<p>For more information on choosing string containers for APIs, please see
1239<a href="#string_apis">Passing strings</a>.</p>
1240
1241
1242<!-- _______________________________________________________________________ -->
1243<h4>
1244 <a name="dss_stringref">llvm/ADT/StringRef.h</a>
1245</h4>
1246
1247<div>
1248<p>
1249The StringRef class is a simple value class that contains a pointer to a
1250character and a length, and is quite related to the <a
1251href="#dss_arrayref">ArrayRef</a> class (but specialized for arrays of
1252characters). Because StringRef carries a length with it, it safely handles
1253strings with embedded nul characters in it, getting the length does not require
1254a strlen call, and it even has very convenient APIs for slicing and dicing the
1255character range that it represents.
1256</p>
1257
1258<p>
1259StringRef is ideal for passing simple strings around that are known to be live,
1260either because they are C string literals, std::string, a C array, or a
1261SmallVector. Each of these cases has an efficient implicit conversion to
1262StringRef, which doesn't result in a dynamic strlen being executed.
1263</p>
1264
1265<p>StringRef has a few major limitations which make more powerful string
1266containers useful:</p>
1267
1268<ol>
1269<li>You cannot directly convert a StringRef to a 'const char*' because there is
1270no way to add a trailing nul (unlike the .c_str() method on various stronger
1271classes).</li>
1272
1273
1274<li>StringRef doesn't own or keep alive the underlying string bytes.
1275As such it can easily lead to dangling pointers, and is not suitable for
1276embedding in datastructures in most cases (instead, use an std::string or
1277something like that).</li>
1278
1279<li>For the same reason, StringRef cannot be used as the return value of a
1280method if the method "computes" the result string. Instead, use
1281std::string.</li>
1282
Chris Lattnerec8f1ea2011-07-23 17:18:57 +0000[diff] [blame]1283<li>StringRef's do not allow you to mutate the pointed-to string bytes and it
1284doesn't allow you to insert or remove bytes from the range. For editing
1285operations like this, it interoperates with the <a
1286href="#dss_twine">Twine</a> class.</li>
Chris Lattner3b4f4172011-07-22 21:34:12 +0000[diff] [blame]1287</ol>
1288
1289<p>Because of its strengths and limitations, it is very common for a function to
1290take a StringRef and for a method on an object to return a StringRef that
1291points into some string that it owns.</p>
1292
1293</div>
1294
1295<!-- _______________________________________________________________________ -->
1296<h4>
1297 <a name="dss_twine">llvm/ADT/Twine.h</a>
1298</h4>
1299
1300<div>
1301 <p>
1302 The Twine class is used as an intermediary datatype for APIs that want to take
1303 a string that can be constructed inline with a series of concatenations.
1304 Twine works by forming recursive instances of the Twine datatype (a simple
1305 value object) on the stack as temporary objects, linking them together into a
1306 tree which is then linearized when the Twine is consumed. Twine is only safe
1307 to use as the argument to a function, and should always be a const reference,
1308 e.g.:
1309 </p>
1310
1311 <pre>
1312 void foo(const Twine &amp;T);
1313 ...
1314 StringRef X = ...
1315 unsigned i = ...
1316 foo(X + "." + Twine(i));
1317 </pre>
1318
1319 <p>This example forms a string like "blarg.42" by concatenating the values
1320 together, and does not form intermediate strings containing "blarg" or
1321 "blarg.".
1322 </p>
1323
1324 <p>Because Twine is constructed with temporary objects on the stack, and
1325 because these instances are destroyed at the end of the current statement,
1326 it is an inherently dangerous API. For example, this simple variant contains
1327 undefined behavior and will probably crash:</p>
1328
1329 <pre>
1330 void foo(const Twine &amp;T);
1331 ...
1332 StringRef X = ...
1333 unsigned i = ...
1334 const Twine &amp;Tmp = X + "." + Twine(i);
1335 foo(Tmp);
1336 </pre>
1337
1338 <p>... because the temporaries are destroyed before the call. That said,
1339 Twine's are much more efficient than intermediate std::string temporaries, and
1340 they work really well with StringRef. Just be aware of their limitations.</p>
1341
1342</div>
1343
1344
1345<!-- _______________________________________________________________________ -->
1346<h4>
1347 <a name="dss_smallstring">llvm/ADT/SmallString.h</a>
1348</h4>
1349
1350<div>
1351
1352<p>SmallString is a subclass of <a href="#dss_smallvector">SmallVector</a> that
1353adds some convenience APIs like += that takes StringRef's. SmallString avoids
1354allocating memory in the case when the preallocated space is enough to hold its
1355data, and it calls back to general heap allocation when required. Since it owns
1356its data, it is very safe to use and supports full mutation of the string.</p>
1357
1358<p>Like SmallVector's, the big downside to SmallString is their sizeof. While
1359they are optimized for small strings, they themselves are not particularly
1360small. This means that they work great for temporary scratch buffers on the
1361stack, but should not generally be put into the heap: it is very rare to
1362see a SmallString as the member of a frequently-allocated heap data structure
1363or returned by-value.
Chris Lattner7314a202011-07-22 20:46:49 +0000[diff] [blame]1364</p>
1365
1366</div>
Chris Lattner3b4f4172011-07-22 21:34:12 +0000[diff] [blame]1367
1368<!-- _______________________________________________________________________ -->
1369<h4>
1370 <a name="dss_stdstring">std::string</a>
1371</h4>
1372
1373<div>
1374
1375 <p>The standard C++ std::string class is a very general class that (like
1376 SmallString) owns its underlying data. sizeof(std::string) is very reasonable
1377 so it can be embedded into heap data structures and returned by-value.
1378 On the other hand, std::string is highly inefficient for inline editing (e.g.
1379 concatenating a bunch of stuff together) and because it is provided by the
1380 standard library, its performance characteristics depend a lot of the host
1381 standard library (e.g. libc++ and MSVC provide a highly optimized string
1382 class, GCC contains a really slow implementation).
1383 </p>
1384
1385 <p>The major disadvantage of std::string is that almost every operation that
1386 makes them larger can allocate memory, which is slow. As such, it is better
1387 to use SmallVector or Twine as a scratch buffer, but then use std::string to
1388 persist the result.</p>
1389
1390
1391</div>
1392
1393<!-- end of strings -->
1394</div>
1395
Chris Lattner7314a202011-07-22 20:46:49 +0000[diff] [blame]1396
1397<!-- ======================================================================= -->
1398<h3>
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]1399 <a name="ds_set">Set-Like Containers (std::set, SmallSet, SetVector, etc)</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]1400</h3>
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]1401
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]1402<div>
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]1403
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1404<p>Set-like containers are useful when you need to canonicalize multiple values
1405into a single representation. There are several different choices for how to do
1406this, providing various trade-offs.</p>
1407
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1408<!-- _______________________________________________________________________ -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]1409<h4>
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1410 <a name="dss_sortedvectorset">A sorted 'vector'</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]1411</h4>
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1412
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]1413<div>
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1414
Chris Lattner3b23a8c2007-02-03 08:10:45 +0000[diff] [blame]1415<p>If you intend to insert a lot of elements, then do a lot of queries, a
1416great approach is to use a vector (or other sequential container) with
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1417std::sort+std::unique to remove duplicates. This approach works really well if
Chris Lattner3b23a8c2007-02-03 08:10:45 +0000[diff] [blame]1418your usage pattern has these two distinct phases (insert then query), and can be
1419coupled with a good choice of <a href="#ds_sequential">sequential container</a>.
1420</p>
1421
1422<p>
1423This combination provides the several nice properties: the result data is
1424contiguous in memory (good for cache locality), has few allocations, is easy to
1425address (iterators in the final vector are just indices or pointers), and can be
1426efficiently queried with a standard binary or radix search.</p>
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1427
1428</div>
1429
1430<!-- _______________________________________________________________________ -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]1431<h4>
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1432 <a name="dss_smallset">"llvm/ADT/SmallSet.h"</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]1433</h4>
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1434
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]1435<div>
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1436
Reid Spencer128a7a72007-02-03 21:06:43 +0000[diff] [blame]1437<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]1438are 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]1439has space for N elements in place (thus, if the set is dynamically smaller than
Chris Lattner14868db2007-02-03 08:20:15 +0000[diff] [blame]1440N, no malloc traffic is required) and accesses them with a simple linear search.
1441When the set grows beyond 'N' elements, it allocates a more expensive representation that
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1442guarantees efficient access (for most types, it falls back to std::set, but for
Chris Lattner14868db2007-02-03 08:20:15 +0000[diff] [blame]1443pointers it uses something far better, <a
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1444href="#dss_smallptrset">SmallPtrSet</a>).</p>
1445
1446<p>The magic of this class is that it handles small sets extremely efficiently,
1447but gracefully handles extremely large sets without loss of efficiency. The
1448drawback is that the interface is quite small: it supports insertion, queries
1449and erasing, but does not support iteration.</p>
1450
1451</div>
1452
1453<!-- _______________________________________________________________________ -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]1454<h4>
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1455 <a name="dss_smallptrset">"llvm/ADT/SmallPtrSet.h"</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]1456</h4>
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1457
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]1458<div>
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1459
Gabor Greif4de73682010-03-26 19:30:47 +0000[diff] [blame]1460<p>SmallPtrSet has all the advantages of <tt>SmallSet</tt> (and a <tt>SmallSet</tt> of pointers is
1461transparently implemented with a <tt>SmallPtrSet</tt>), but also supports iterators. If
Chris Lattner14868db2007-02-03 08:20:15 +0000[diff] [blame]1462more than 'N' insertions are performed, a single quadratically
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1463probed hash table is allocated and grows as needed, providing extremely
1464efficient access (constant time insertion/deleting/queries with low constant
1465factors) and is very stingy with malloc traffic.</p>
1466
Gabor Greif4de73682010-03-26 19:30:47 +0000[diff] [blame]1467<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]1468whenever an insertion occurs. Also, the values visited by the iterators are not
1469visited in sorted order.</p>
1470
1471</div>
1472
1473<!-- _______________________________________________________________________ -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]1474<h4>
Chris Lattnerc28476f2007-09-30 00:58:59 +0000[diff] [blame]1475 <a name="dss_denseset">"llvm/ADT/DenseSet.h"</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]1476</h4>
Chris Lattnerc28476f2007-09-30 00:58:59 +0000[diff] [blame]1477
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]1478<div>
Chris Lattnerc28476f2007-09-30 00:58:59 +0000[diff] [blame]1479
1480<p>
1481DenseSet is a simple quadratically probed hash table. It excels at supporting
1482small values: it uses a single allocation to hold all of the pairs that
1483are currently inserted in the set. DenseSet is a great way to unique small
1484values that are not simple pointers (use <a
1485href="#dss_smallptrset">SmallPtrSet</a> for pointers). Note that DenseSet has
1486the same requirements for the value type that <a
1487href="#dss_densemap">DenseMap</a> has.
1488</p>
1489
1490</div>
1491
1492<!-- _______________________________________________________________________ -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]1493<h4>
Jakob Stoklund Olesen62588622012-02-22 00:56:08 +0000[diff] [blame]1494 <a name="dss_sparseset">"llvm/ADT/SparseSet.h"</a>
1495</h4>
1496
1497<div>
1498
1499<p>SparseSet holds a small number of objects identified by unsigned keys of
1500moderate size. It uses a lot of memory, but provides operations that are
1501almost as fast as a vector. Typical keys are physical registers, virtual
1502registers, or numbered basic blocks.</p>
1503
1504<p>SparseSet is useful for algorithms that need very fast clear/find/insert/erase
1505and fast iteration over small sets. It is not intended for building composite
1506data structures.</p>
1507
1508</div>
1509
1510<!-- _______________________________________________________________________ -->
1511<h4>
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1512 <a name="dss_FoldingSet">"llvm/ADT/FoldingSet.h"</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]1513</h4>
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1514
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]1515<div>
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1516
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]1517<p>
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1518FoldingSet is an aggregate class that is really good at uniquing
1519expensive-to-create or polymorphic objects. It is a combination of a chained
1520hash table with intrusive links (uniqued objects are required to inherit from
Chris Lattner14868db2007-02-03 08:20:15 +0000[diff] [blame]1521FoldingSetNode) that uses <a href="#dss_smallvector">SmallVector</a> as part of
1522its ID process.</p>
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1523
Chris Lattner14868db2007-02-03 08:20:15 +0000[diff] [blame]1524<p>Consider a case where you want to implement a "getOrCreateFoo" method for
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1525a complex object (for example, a node in the code generator). The client has a
1526description of *what* it wants to generate (it knows the opcode and all the
1527operands), 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]1528only to find out it already exists, at which point we would have to delete it
1529and return the node that already exists.
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]1530</p>
1531
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1532<p>To support this style of client, FoldingSet perform a query with a
1533FoldingSetNodeID (which wraps SmallVector) that can be used to describe the
1534element that we want to query for. The query either returns the element
1535matching the ID or it returns an opaque ID that indicates where insertion should
Chris Lattner14868db2007-02-03 08:20:15 +0000[diff] [blame]1536take place. Construction of the ID usually does not require heap traffic.</p>
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1537
1538<p>Because FoldingSet uses intrusive links, it can support polymorphic objects
1539in the set (for example, you can have SDNode instances mixed with LoadSDNodes).
1540Because the elements are individually allocated, pointers to the elements are
1541stable: inserting or removing elements does not invalidate any pointers to other
1542elements.
1543</p>
1544
1545</div>
1546
1547<!-- _______________________________________________________________________ -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]1548<h4>
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1549 <a name="dss_set">&lt;set&gt;</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]1550</h4>
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1551
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]1552<div>
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1553
Chris Lattnerc5722432007-02-03 19:49:31 +0000[diff] [blame]1554<p><tt>std::set</tt> is a reasonable all-around set class, which is decent at
1555many things but great at nothing. std::set allocates memory for each element
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1556inserted (thus it is very malloc intensive) and typically stores three pointers
Chris Lattner14868db2007-02-03 08:20:15 +0000[diff] [blame]1557per element in the set (thus adding a large amount of per-element space
1558overhead). It offers guaranteed log(n) performance, which is not particularly
Chris Lattnerc5722432007-02-03 19:49:31 +0000[diff] [blame]1559fast from a complexity standpoint (particularly if the elements of the set are
1560expensive to compare, like strings), and has extremely high constant factors for
1561lookup, insertion and removal.</p>
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1562
Chris Lattner14868db2007-02-03 08:20:15 +0000[diff] [blame]1563<p>The advantages of std::set are that its iterators are stable (deleting or
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1564inserting an element from the set does not affect iterators or pointers to other
1565elements) and that iteration over the set is guaranteed to be in sorted order.
1566If the elements in the set are large, then the relative overhead of the pointers
1567and malloc traffic is not a big deal, but if the elements of the set are small,
1568std::set is almost never a good choice.</p>
1569
1570</div>
1571
1572<!-- _______________________________________________________________________ -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]1573<h4>
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1574 <a name="dss_setvector">"llvm/ADT/SetVector.h"</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]1575</h4>
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1576
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]1577<div>
Chris Lattneredca3c52007-02-04 00:00:26 +0000[diff] [blame]1578<p>LLVM's SetVector&lt;Type&gt; is an adapter class that combines your choice of
1579a set-like container along with a <a href="#ds_sequential">Sequential
1580Container</a>. The important property
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1581that this provides is efficient insertion with uniquing (duplicate elements are
1582ignored) with iteration support. It implements this by inserting elements into
1583both a set-like container and the sequential container, using the set-like
1584container for uniquing and the sequential container for iteration.
1585</p>
1586
1587<p>The difference between SetVector and other sets is that the order of
1588iteration is guaranteed to match the order of insertion into the SetVector.
1589This property is really important for things like sets of pointers. Because
1590pointer values are non-deterministic (e.g. vary across runs of the program on
Chris Lattneredca3c52007-02-04 00:00:26 +0000[diff] [blame]1591different machines), iterating over the pointers in the set will
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1592not be in a well-defined order.</p>
1593
1594<p>
1595The drawback of SetVector is that it requires twice as much space as a normal
1596set and has the sum of constant factors from the set-like container and the
1597sequential container that it uses. Use it *only* if you need to iterate over
1598the elements in a deterministic order. SetVector is also expensive to delete
Chris Lattneredca3c52007-02-04 00:00:26 +0000[diff] [blame]1599elements out of (linear time), unless you use it's "pop_back" method, which is
1600faster.
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1601</p>
1602
Bill Wendling34781732011-10-11 06:33:56 +0000[diff] [blame]1603<p><tt>SetVector</tt> is an adapter class that defaults to
1604 using <tt>std::vector</tt> and a size 16 <tt>SmallSet</tt> for the underlying
1605 containers, so it is quite expensive. However,
1606 <tt>"llvm/ADT/SetVector.h"</tt> also provides a <tt>SmallSetVector</tt>
1607 class, which defaults to using a <tt>SmallVector</tt> and <tt>SmallSet</tt>
1608 of a specified size. If you use this, and if your sets are dynamically
1609 smaller than <tt>N</tt>, you will save a lot of heap traffic.</p>
Chris Lattneredca3c52007-02-04 00:00:26 +0000[diff] [blame]1610
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1611</div>
1612
1613<!-- _______________________________________________________________________ -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]1614<h4>
Chris Lattnerc5722432007-02-03 19:49:31 +0000[diff] [blame]1615 <a name="dss_uniquevector">"llvm/ADT/UniqueVector.h"</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]1616</h4>
Chris Lattnerc5722432007-02-03 19:49:31 +0000[diff] [blame]1617
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]1618<div>
Chris Lattnerc5722432007-02-03 19:49:31 +0000[diff] [blame]1619
1620<p>
1621UniqueVector is similar to <a href="#dss_setvector">SetVector</a>, but it
1622retains a unique ID for each element inserted into the set. It internally
1623contains a map and a vector, and it assigns a unique ID for each value inserted
1624into the set.</p>
1625
1626<p>UniqueVector is very expensive: its cost is the sum of the cost of
1627maintaining both the map and vector, it has high complexity, high constant
1628factors, and produces a lot of malloc traffic. It should be avoided.</p>
1629
1630</div>
1631
Chris Lattner2fdd0052011-11-15 22:40:14 +0000[diff] [blame]1632<!-- _______________________________________________________________________ -->
1633<h4>
1634 <a name="dss_immutableset">"llvm/ADT/ImmutableSet.h"</a>
1635</h4>
1636
1637<div>
1638
1639<p>
1640ImmutableSet is an immutable (functional) set implementation based on an AVL
1641tree.
1642Adding or removing elements is done through a Factory object and results in the
1643creation of a new ImmutableSet object.
1644If an ImmutableSet already exists with the given contents, then the existing one
1645is returned; equality is compared with a FoldingSetNodeID.
1646The time and space complexity of add or remove operations is logarithmic in the
1647size of the original set.
1648
1649<p>
1650There is no method for returning an element of the set, you can only check for
1651membership.
1652
1653</div>
1654
Chris Lattnerc5722432007-02-03 19:49:31 +0000[diff] [blame]1655
1656<!-- _______________________________________________________________________ -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]1657<h4>
Chris Lattnerc5722432007-02-03 19:49:31 +0000[diff] [blame]1658 <a name="dss_otherset">Other Set-Like Container Options</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]1659</h4>
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1660
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]1661<div>
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1662
1663<p>
1664The STL provides several other options, such as std::multiset and the various
Chris Lattnerf1a30822009-03-09 05:20:45 +0000[diff] [blame]1665"hash_set" like containers (whether from C++ TR1 or from the SGI library). We
1666never use hash_set and unordered_set because they are generally very expensive
1667(each insertion requires a malloc) and very non-portable.
1668</p>
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1669
1670<p>std::multiset is useful if you're not interested in elimination of
Chris Lattner14868db2007-02-03 08:20:15 +0000[diff] [blame]1671duplicates, but has all the drawbacks of std::set. A sorted vector (where you
1672don't delete duplicate entries) or some other approach is almost always
1673better.</p>
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1674
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]1675</div>
1676
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]1677</div>
1678
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]1679<!-- ======================================================================= -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]1680<h3>
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]1681 <a name="ds_map">Map-Like Containers (std::map, DenseMap, etc)</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]1682</h3>
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]1683
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]1684<div>
Chris Lattnerc5722432007-02-03 19:49:31 +0000[diff] [blame]1685Map-like containers are useful when you want to associate data to a key. As
1686usual, there are a lot of different ways to do this. :)
Chris Lattnerc5722432007-02-03 19:49:31 +0000[diff] [blame]1687
1688<!-- _______________________________________________________________________ -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]1689<h4>
Chris Lattnerc5722432007-02-03 19:49:31 +0000[diff] [blame]1690 <a name="dss_sortedvectormap">A sorted 'vector'</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]1691</h4>
Chris Lattnerc5722432007-02-03 19:49:31 +0000[diff] [blame]1692
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]1693<div>
Chris Lattnerc5722432007-02-03 19:49:31 +0000[diff] [blame]1694
1695<p>
1696If your usage pattern follows a strict insert-then-query approach, you can
1697trivially use the same approach as <a href="#dss_sortedvectorset">sorted vectors
1698for set-like containers</a>. The only difference is that your query function
1699(which uses std::lower_bound to get efficient log(n) lookup) should only compare
1700the key, not both the key and value. This yields the same advantages as sorted
1701vectors for sets.
1702</p>
1703</div>
1704
1705<!-- _______________________________________________________________________ -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]1706<h4>
Chris Lattner796f9fa2007-02-08 19:14:21 +0000[diff] [blame]1707 <a name="dss_stringmap">"llvm/ADT/StringMap.h"</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]1708</h4>
Chris Lattnerc5722432007-02-03 19:49:31 +0000[diff] [blame]1709
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]1710<div>
Chris Lattnerc5722432007-02-03 19:49:31 +0000[diff] [blame]1711
1712<p>
1713Strings are commonly used as keys in maps, and they are difficult to support
1714efficiently: they are variable length, inefficient to hash and compare when
Chris Lattner796f9fa2007-02-08 19:14:21 +0000[diff] [blame]1715long, expensive to copy, etc. StringMap is a specialized container designed to
1716cope with these issues. It supports mapping an arbitrary range of bytes to an
1717arbitrary other object.</p>
Chris Lattnerc5722432007-02-03 19:49:31 +0000[diff] [blame]1718
Chris Lattner796f9fa2007-02-08 19:14:21 +0000[diff] [blame]1719<p>The StringMap implementation uses a quadratically-probed hash table, where
Chris Lattnerc5722432007-02-03 19:49:31 +0000[diff] [blame]1720the buckets store a pointer to the heap allocated entries (and some other
1721stuff). The entries in the map must be heap allocated because the strings are
1722variable length. The string data (key) and the element object (value) are
1723stored in the same allocation with the string data immediately after the element
1724object. This container guarantees the "<tt>(char*)(&amp;Value+1)</tt>" points
1725to the key string for a value.</p>
1726
Chris Lattner796f9fa2007-02-08 19:14:21 +0000[diff] [blame]1727<p>The StringMap is very fast for several reasons: quadratic probing is very
Chris Lattnerc5722432007-02-03 19:49:31 +0000[diff] [blame]1728cache efficient for lookups, the hash value of strings in buckets is not
Nick Lewycky2a80aca2010-08-01 23:18:45 +0000[diff] [blame]1729recomputed when looking up an element, StringMap rarely has to touch the
Chris Lattnerc5722432007-02-03 19:49:31 +0000[diff] [blame]1730memory for unrelated objects when looking up a value (even when hash collisions
1731happen), hash table growth does not recompute the hash values for strings
1732already in the table, and each pair in the map is store in a single allocation
1733(the string data is stored in the same allocation as the Value of a pair).</p>
1734
Chris Lattner796f9fa2007-02-08 19:14:21 +0000[diff] [blame]1735<p>StringMap also provides query methods that take byte ranges, so it only ever
Chris Lattnerc5722432007-02-03 19:49:31 +0000[diff] [blame]1736copies a string if a value is inserted into the table.</p>
1737</div>
1738
1739<!-- _______________________________________________________________________ -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]1740<h4>
Chris Lattnerc5722432007-02-03 19:49:31 +0000[diff] [blame]1741 <a name="dss_indexedmap">"llvm/ADT/IndexedMap.h"</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]1742</h4>
Chris Lattnerc5722432007-02-03 19:49:31 +0000[diff] [blame]1743
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]1744<div>
Chris Lattnerc5722432007-02-03 19:49:31 +0000[diff] [blame]1745<p>
1746IndexedMap is a specialized container for mapping small dense integers (or
1747values that can be mapped to small dense integers) to some other type. It is
1748internally implemented as a vector with a mapping function that maps the keys to
1749the dense integer range.
1750</p>
1751
1752<p>
1753This is useful for cases like virtual registers in the LLVM code generator: they
1754have a dense mapping that is offset by a compile-time constant (the first
1755virtual register ID).</p>
1756
1757</div>
1758
1759<!-- _______________________________________________________________________ -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]1760<h4>
Chris Lattnerc5722432007-02-03 19:49:31 +0000[diff] [blame]1761 <a name="dss_densemap">"llvm/ADT/DenseMap.h"</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]1762</h4>
Chris Lattnerc5722432007-02-03 19:49:31 +0000[diff] [blame]1763
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]1764<div>
Chris Lattnerc5722432007-02-03 19:49:31 +0000[diff] [blame]1765
1766<p>
1767DenseMap is a simple quadratically probed hash table. It excels at supporting
1768small keys and values: it uses a single allocation to hold all of the pairs that
1769are currently inserted in the map. DenseMap is a great way to map pointers to
1770pointers, or map other small types to each other.
1771</p>
1772
1773<p>
1774There are several aspects of DenseMap that you should be aware of, however. The
Talinbabd5982012-01-30 06:55:43 +0000[diff] [blame]1775iterators in a DenseMap are invalidated whenever an insertion occurs, unlike
Chris Lattnerc5722432007-02-03 19:49:31 +0000[diff] [blame]1776map. Also, because DenseMap allocates space for a large number of key/value
Chris Lattnera4a264d2007-02-03 20:17:53 +0000[diff] [blame]1777pairs (it starts with 64 by default), it will waste a lot of space if your keys
1778or values are large. Finally, you must implement a partial specialization of
Chris Lattner76c1b972007-09-17 18:34:04 +0000[diff] [blame]1779DenseMapInfo for the key that you want, if it isn't already supported. This
Chris Lattnerc5722432007-02-03 19:49:31 +0000[diff] [blame]1780is required to tell DenseMap about two special marker values (which can never be
Chris Lattnera4a264d2007-02-03 20:17:53 +0000[diff] [blame]1781inserted into the map) that it needs internally.</p>
Chris Lattnerc5722432007-02-03 19:49:31 +0000[diff] [blame]1782
Talinbabd5982012-01-30 06:55:43 +0000[diff] [blame]1783<p>
1784DenseMap's find_as() method supports lookup operations using an alternate key
1785type. This is useful in cases where the normal key type is expensive to
1786construct, but cheap to compare against. The DenseMapInfo is responsible for
1787defining the appropriate comparison and hashing methods for each alternate
1788key type used.
1789</p>
1790
Chris Lattnerc5722432007-02-03 19:49:31 +0000[diff] [blame]1791</div>
1792
1793<!-- _______________________________________________________________________ -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]1794<h4>
Jeffrey Yasskin71a5c222009-10-22 22:11:22 +0000[diff] [blame]1795 <a name="dss_valuemap">"llvm/ADT/ValueMap.h"</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]1796</h4>
Jeffrey Yasskin71a5c222009-10-22 22:11:22 +0000[diff] [blame]1797
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]1798<div>
Jeffrey Yasskin71a5c222009-10-22 22:11:22 +0000[diff] [blame]1799
1800<p>
1801ValueMap is a wrapper around a <a href="#dss_densemap">DenseMap</a> mapping
1802Value*s (or subclasses) to another type. When a Value is deleted or RAUW'ed,
1803ValueMap will update itself so the new version of the key is mapped to the same
1804value, just as if the key were a WeakVH. You can configure exactly how this
1805happens, and what else happens on these two events, by passing
1806a <code>Config</code> parameter to the ValueMap template.</p>
1807
1808</div>
1809
1810<!-- _______________________________________________________________________ -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]1811<h4>
Jakob Stoklund Olesenaca0da62010-12-14 00:55:51 +0000[diff] [blame]1812 <a name="dss_intervalmap">"llvm/ADT/IntervalMap.h"</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]1813</h4>
Jakob Stoklund Olesenaca0da62010-12-14 00:55:51 +0000[diff] [blame]1814
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]1815<div>
Jakob Stoklund Olesenaca0da62010-12-14 00:55:51 +0000[diff] [blame]1816
1817<p> IntervalMap is a compact map for small keys and values. It maps key
1818intervals instead of single keys, and it will automatically coalesce adjacent
1819intervals. When then map only contains a few intervals, they are stored in the
1820map object itself to avoid allocations.</p>
1821
1822<p> The IntervalMap iterators are quite big, so they should not be passed around
1823as STL iterators. The heavyweight iterators allow a smaller data structure.</p>
1824
1825</div>
1826
1827<!-- _______________________________________________________________________ -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]1828<h4>
Chris Lattnerc5722432007-02-03 19:49:31 +0000[diff] [blame]1829 <a name="dss_map">&lt;map&gt;</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]1830</h4>
Chris Lattnerc5722432007-02-03 19:49:31 +0000[diff] [blame]1831
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]1832<div>
Chris Lattnerc5722432007-02-03 19:49:31 +0000[diff] [blame]1833
1834<p>
1835std::map has similar characteristics to <a href="#dss_set">std::set</a>: it uses
1836a single allocation per pair inserted into the map, it offers log(n) lookup with
1837an extremely large constant factor, imposes a space penalty of 3 pointers per
1838pair in the map, etc.</p>
1839
1840<p>std::map is most useful when your keys or values are very large, if you need
1841to iterate over the collection in sorted order, or if you need stable iterators
1842into the map (i.e. they don't get invalidated if an insertion or deletion of
1843another element takes place).</p>
1844
1845</div>
1846
1847<!-- _______________________________________________________________________ -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]1848<h4>
Jakob Stoklund Olesen4359e5e2011-04-05 20:56:08 +0000[diff] [blame]1849 <a name="dss_inteqclasses">"llvm/ADT/IntEqClasses.h"</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]1850</h4>
Jakob Stoklund Olesen4359e5e2011-04-05 20:56:08 +0000[diff] [blame]1851
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]1852<div>
Jakob Stoklund Olesen4359e5e2011-04-05 20:56:08 +0000[diff] [blame]1853
1854<p>IntEqClasses provides a compact representation of equivalence classes of
1855small integers. Initially, each integer in the range 0..n-1 has its own
1856equivalence class. Classes can be joined by passing two class representatives to
1857the join(a, b) method. Two integers are in the same class when findLeader()
1858returns the same representative.</p>
1859
1860<p>Once all equivalence classes are formed, the map can be compressed so each
1861integer 0..n-1 maps to an equivalence class number in the range 0..m-1, where m
1862is the total number of equivalence classes. The map must be uncompressed before
1863it can be edited again.</p>
1864
1865</div>
1866
1867<!-- _______________________________________________________________________ -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]1868<h4>
Chris Lattner2fdd0052011-11-15 22:40:14 +0000[diff] [blame]1869 <a name="dss_immutablemap">"llvm/ADT/ImmutableMap.h"</a>
1870</h4>
1871
1872<div>
1873
1874<p>
1875ImmutableMap is an immutable (functional) map implementation based on an AVL
1876tree.
1877Adding or removing elements is done through a Factory object and results in the
1878creation of a new ImmutableMap object.
1879If an ImmutableMap already exists with the given key set, then the existing one
1880is returned; equality is compared with a FoldingSetNodeID.
1881The time and space complexity of add or remove operations is logarithmic in the
1882size of the original map.
1883
1884</div>
1885
1886<!-- _______________________________________________________________________ -->
1887<h4>
Chris Lattnerc5722432007-02-03 19:49:31 +0000[diff] [blame]1888 <a name="dss_othermap">Other Map-Like Container Options</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]1889</h4>
Chris Lattnerc5722432007-02-03 19:49:31 +0000[diff] [blame]1890
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]1891<div>
Chris Lattnerc5722432007-02-03 19:49:31 +0000[diff] [blame]1892
1893<p>
1894The STL provides several other options, such as std::multimap and the various
Chris Lattnerf1a30822009-03-09 05:20:45 +0000[diff] [blame]1895"hash_map" like containers (whether from C++ TR1 or from the SGI library). We
1896never use hash_set and unordered_set because they are generally very expensive
1897(each insertion requires a malloc) and very non-portable.</p>
Chris Lattnerc5722432007-02-03 19:49:31 +0000[diff] [blame]1898
1899<p>std::multimap is useful if you want to map a key to multiple values, but has
1900all the drawbacks of std::map. A sorted vector or some other approach is almost
1901always better.</p>
1902
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]1903</div>
1904
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]1905</div>
1906
Daniel Berlin1939ace2007-09-24 17:52:25 +0000[diff] [blame]1907<!-- ======================================================================= -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]1908<h3>
Daniel Berlin1939ace2007-09-24 17:52:25 +0000[diff] [blame]1909 <a name="ds_bit">Bit storage containers (BitVector, SparseBitVector)</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]1910</h3>
Daniel Berlin1939ace2007-09-24 17:52:25 +0000[diff] [blame]1911
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]1912<div>
Chris Lattner7086ce72007-09-25 22:37:50 +0000[diff] [blame]1913<p>Unlike the other containers, there are only two bit storage containers, and
1914choosing when to use each is relatively straightforward.</p>
1915
1916<p>One additional option is
1917<tt>std::vector&lt;bool&gt;</tt>: we discourage its use for two reasons 1) the
1918implementation in many common compilers (e.g. commonly available versions of
1919GCC) is extremely inefficient and 2) the C++ standards committee is likely to
1920deprecate this container and/or change it significantly somehow. In any case,
1921please don't use it.</p>
Daniel Berlin1939ace2007-09-24 17:52:25 +0000[diff] [blame]1922
1923<!-- _______________________________________________________________________ -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]1924<h4>
Daniel Berlin1939ace2007-09-24 17:52:25 +0000[diff] [blame]1925 <a name="dss_bitvector">BitVector</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]1926</h4>
Daniel Berlin1939ace2007-09-24 17:52:25 +0000[diff] [blame]1927
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]1928<div>
Dan Gohman5f7775c2010-01-05 18:24:00 +0000[diff] [blame]1929<p> The BitVector container provides a dynamic size set of bits for manipulation.
Daniel Berlin1939ace2007-09-24 17:52:25 +0000[diff] [blame]1930It supports individual bit setting/testing, as well as set operations. The set
1931operations take time O(size of bitvector), but operations are performed one word
1932at a time, instead of one bit at a time. This makes the BitVector very fast for
1933set operations compared to other containers. Use the BitVector when you expect
1934the number of set bits to be high (IE a dense set).
1935</p>
1936</div>
1937
1938<!-- _______________________________________________________________________ -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]1939<h4>
Dan Gohman5f7775c2010-01-05 18:24:00 +0000[diff] [blame]1940 <a name="dss_smallbitvector">SmallBitVector</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]1941</h4>
Dan Gohman5f7775c2010-01-05 18:24:00 +0000[diff] [blame]1942
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]1943<div>
Dan Gohman5f7775c2010-01-05 18:24:00 +0000[diff] [blame]1944<p> The SmallBitVector container provides the same interface as BitVector, but
1945it is optimized for the case where only a small number of bits, less than
194625 or so, are needed. It also transparently supports larger bit counts, but
1947slightly less efficiently than a plain BitVector, so SmallBitVector should
1948only be used when larger counts are rare.
1949</p>
1950
1951<p>
1952At this time, SmallBitVector does not support set operations (and, or, xor),
1953and its operator[] does not provide an assignable lvalue.
1954</p>
1955</div>
1956
1957<!-- _______________________________________________________________________ -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]1958<h4>
Daniel Berlin1939ace2007-09-24 17:52:25 +0000[diff] [blame]1959 <a name="dss_sparsebitvector">SparseBitVector</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]1960</h4>
Daniel Berlin1939ace2007-09-24 17:52:25 +0000[diff] [blame]1961
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]1962<div>
Daniel Berlin1939ace2007-09-24 17:52:25 +0000[diff] [blame]1963<p> The SparseBitVector container is much like BitVector, with one major
1964difference: Only the bits that are set, are stored. This makes the
1965SparseBitVector much more space efficient than BitVector when the set is sparse,
1966as well as making set operations O(number of set bits) instead of O(size of
1967universe). 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
1968(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).
1969</p>
1970</div>
Chris Lattnerf623a082005-10-17 01:36:23 +0000[diff] [blame]1971
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]1972</div>
1973
1974</div>
1975
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1976<!-- *********************************************************************** -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]1977<h2>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1978 <a name="common">Helpful Hints for Common Operations</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]1979</h2>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1980<!-- *********************************************************************** -->
1981
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]1982<div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1983
1984<p>This section describes how to perform some very simple transformations of
1985LLVM code. This is meant to give examples of common idioms used, showing the
1986practical side of LLVM transformations. <p> Because this is a "how-to" section,
1987you should also read about the main classes that you will be working with. The
1988<a href="#coreclasses">Core LLVM Class Hierarchy Reference</a> contains details
1989and descriptions of the main classes that you should know about.</p>
1990
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1991<!-- NOTE: this section should be heavy on example code -->
1992<!-- ======================================================================= -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]1993<h3>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1994 <a name="inspection">Basic Inspection and Traversal Routines</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]1995</h3>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1996
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]1997<div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1998
1999<p>The LLVM compiler infrastructure have many different data structures that may
2000be traversed. Following the example of the C++ standard template library, the
2001techniques used to traverse these various data structures are all basically the
2002same. For a enumerable sequence of values, the <tt>XXXbegin()</tt> function (or
2003method) returns an iterator to the start of the sequence, the <tt>XXXend()</tt>
2004function returns an iterator pointing to one past the last valid element of the
2005sequence, and there is some <tt>XXXiterator</tt> data type that is common
2006between the two operations.</p>
2007
2008<p>Because the pattern for iteration is common across many different aspects of
2009the program representation, the standard template library algorithms may be used
2010on them, and it is easier to remember how to iterate. First we show a few common
2011examples of the data structures that need to be traversed. Other data
2012structures are traversed in very similar ways.</p>
2013
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2014<!-- _______________________________________________________________________ -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]2015<h4>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2016 <a name="iterate_function">Iterating over the </a><a
2017 href="#BasicBlock"><tt>BasicBlock</tt></a>s in a <a
2018 href="#Function"><tt>Function</tt></a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]2019</h4>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2020
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]2021<div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2022
2023<p>It's quite common to have a <tt>Function</tt> instance that you'd like to
2024transform in some way; in particular, you'd like to manipulate its
2025<tt>BasicBlock</tt>s. To facilitate this, you'll need to iterate over all of
2026the <tt>BasicBlock</tt>s that constitute the <tt>Function</tt>. The following is
2027an example that prints the name of a <tt>BasicBlock</tt> and the number of
2028<tt>Instruction</tt>s it contains:</p>
2029
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2030<div class="doc_code">
2031<pre>
Bill Wendling82e2eea2006-10-11 18:00:22 +0000[diff] [blame]2032// <i>func is a pointer to a Function instance</i>
2033for (Function::iterator i = func-&gt;begin(), e = func-&gt;end(); i != e; ++i)
2034 // <i>Print out the name of the basic block if it has one, and then the</i>
2035 // <i>number of instructions that it contains</i>
Chris Lattner3fee6ed2009-09-08 05:15:50 +0000[diff] [blame]2036 errs() &lt;&lt; "Basic block (name=" &lt;&lt; i-&gt;getName() &lt;&lt; ") has "
Bill Wendling832171c2006-12-07 20:04:42 +0000[diff] [blame]2037 &lt;&lt; i-&gt;size() &lt;&lt; " instructions.\n";
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2038</pre>
2039</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2040
2041<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]2042invoking member functions of the <tt>Instruction</tt> class. This is
2043because the indirection operator is overloaded for the iterator
Chris Lattner7496ec52003-08-05 22:54:23 +0000[diff] [blame]2044classes. In the above code, the expression <tt>i-&gt;size()</tt> is
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2045exactly equivalent to <tt>(*i).size()</tt> just like you'd expect.</p>
2046
2047</div>
2048
2049<!-- _______________________________________________________________________ -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]2050<h4>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2051 <a name="iterate_basicblock">Iterating over the </a><a
2052 href="#Instruction"><tt>Instruction</tt></a>s in a <a
2053 href="#BasicBlock"><tt>BasicBlock</tt></a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]2054</h4>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2055
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]2056<div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2057
2058<p>Just like when dealing with <tt>BasicBlock</tt>s in <tt>Function</tt>s, it's
2059easy to iterate over the individual instructions that make up
2060<tt>BasicBlock</tt>s. Here's a code snippet that prints out each instruction in
2061a <tt>BasicBlock</tt>:</p>
2062
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2063<div class="doc_code">
Chris Lattner55c04612005-03-06 06:00:13 +0000[diff] [blame]2064<pre>
Bill Wendling82e2eea2006-10-11 18:00:22 +0000[diff] [blame]2065// <i>blk is a pointer to a BasicBlock instance</i>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2066for (BasicBlock::iterator i = blk-&gt;begin(), e = blk-&gt;end(); i != e; ++i)
Bill Wendling82e2eea2006-10-11 18:00:22 +0000[diff] [blame]2067 // <i>The next statement works since operator&lt;&lt;(ostream&amp;,...)</i>
2068 // <i>is overloaded for Instruction&amp;</i>
Chris Lattner3fee6ed2009-09-08 05:15:50 +0000[diff] [blame]2069 errs() &lt;&lt; *i &lt;&lt; "\n";
Chris Lattner55c04612005-03-06 06:00:13 +0000[diff] [blame]2070</pre>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2071</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2072
2073<p>However, this isn't really the best way to print out the contents of a
2074<tt>BasicBlock</tt>! Since the ostream operators are overloaded for virtually
2075anything you'll care about, you could have just invoked the print routine on the
Chris Lattner3fee6ed2009-09-08 05:15:50 +0000[diff] [blame]2076basic block itself: <tt>errs() &lt;&lt; *blk &lt;&lt; "\n";</tt>.</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2077
2078</div>
2079
2080<!-- _______________________________________________________________________ -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]2081<h4>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2082 <a name="iterate_institer">Iterating over the </a><a
2083 href="#Instruction"><tt>Instruction</tt></a>s in a <a
2084 href="#Function"><tt>Function</tt></a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]2085</h4>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2086
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]2087<div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2088
2089<p>If you're finding that you commonly iterate over a <tt>Function</tt>'s
2090<tt>BasicBlock</tt>s and then that <tt>BasicBlock</tt>'s <tt>Instruction</tt>s,
2091<tt>InstIterator</tt> should be used instead. You'll need to include <a
2092href="/doxygen/InstIterator_8h-source.html"><tt>llvm/Support/InstIterator.h</tt></a>,
2093and then instantiate <tt>InstIterator</tt>s explicitly in your code. Here's a
Chris Lattner69bf8a92004-05-23 21:06:58 +0000[diff] [blame]2094small 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]2095
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2096<div class="doc_code">
2097<pre>
2098#include "<a href="/doxygen/InstIterator_8h-source.html">llvm/Support/InstIterator.h</a>"
2099
Reid Spencer128a7a72007-02-03 21:06:43 +0000[diff] [blame]2100// <i>F is a pointer to a Function instance</i>
Chris Lattnerda021aa2008-06-04 18:20:42 +0000[diff] [blame]2101for (inst_iterator I = inst_begin(F), E = inst_end(F); I != E; ++I)
Chris Lattner3fee6ed2009-09-08 05:15:50 +0000[diff] [blame]2102 errs() &lt;&lt; *I &lt;&lt; "\n";
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2103</pre>
2104</div>
2105
2106<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]2107work list with its initial contents. For example, if you wanted to
2108initialize a work list to contain all instructions in a <tt>Function</tt>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2109F, all you would need to do is something like:</p>
2110
2111<div class="doc_code">
2112<pre>
2113std::set&lt;Instruction*&gt; worklist;
Chris Lattnerda021aa2008-06-04 18:20:42 +0000[diff] [blame]2114// or better yet, SmallPtrSet&lt;Instruction*, 64&gt; worklist;
2115
2116for (inst_iterator I = inst_begin(F), E = inst_end(F); I != E; ++I)
2117 worklist.insert(&amp;*I);
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2118</pre>
2119</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2120
2121<p>The STL set <tt>worklist</tt> would now contain all instructions in the
2122<tt>Function</tt> pointed to by F.</p>
2123
2124</div>
2125
2126<!-- _______________________________________________________________________ -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]2127<h4>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2128 <a name="iterate_convert">Turning an iterator into a class pointer (and
2129 vice-versa)</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]2130</h4>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2131
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]2132<div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2133
2134<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]2135instance when all you've got at hand is an iterator. Well, extracting
Chris Lattner69bf8a92004-05-23 21:06:58 +0000[diff] [blame]2136a reference or a pointer from an iterator is very straight-forward.
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]2137Assuming that <tt>i</tt> is a <tt>BasicBlock::iterator</tt> and <tt>j</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2138is a <tt>BasicBlock::const_iterator</tt>:</p>
2139
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2140<div class="doc_code">
2141<pre>
Bill Wendling82e2eea2006-10-11 18:00:22 +0000[diff] [blame]2142Instruction&amp; inst = *i; // <i>Grab reference to instruction reference</i>
2143Instruction* pinst = &amp;*i; // <i>Grab pointer to instruction reference</i>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2144const Instruction&amp; inst = *j;
2145</pre>
2146</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2147
2148<p>However, the iterators you'll be working with in the LLVM framework are
2149special: they will automatically convert to a ptr-to-instance type whenever they
2150need to. Instead of dereferencing the iterator and then taking the address of
2151the result, you can simply assign the iterator to the proper pointer type and
2152you get the dereference and address-of operation as a result of the assignment
2153(behind the scenes, this is a result of overloading casting mechanisms). Thus
2154the last line of the last example,</p>
2155
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2156<div class="doc_code">
2157<pre>
Chris Lattner2e438ca2008-01-03 16:56:04 +0000[diff] [blame]2158Instruction *pinst = &amp;*i;
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2159</pre>
2160</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2161
2162<p>is semantically equivalent to</p>
2163
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2164<div class="doc_code">
2165<pre>
Chris Lattner2e438ca2008-01-03 16:56:04 +0000[diff] [blame]2166Instruction *pinst = i;
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2167</pre>
2168</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2169
Chris Lattner69bf8a92004-05-23 21:06:58 +0000[diff] [blame]2170<p>It's also possible to turn a class pointer into the corresponding iterator,
2171and this is a constant time operation (very efficient). The following code
2172snippet illustrates use of the conversion constructors provided by LLVM
2173iterators. By using these, you can explicitly grab the iterator of something
2174without actually obtaining it via iteration over some structure:</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2175
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2176<div class="doc_code">
2177<pre>
2178void printNextInstruction(Instruction* inst) {
2179 BasicBlock::iterator it(inst);
Bill Wendling82e2eea2006-10-11 18:00:22 +0000[diff] [blame]2180 ++it; // <i>After this line, it refers to the instruction after *inst</i>
Chris Lattner3fee6ed2009-09-08 05:15:50 +0000[diff] [blame]2181 if (it != inst-&gt;getParent()-&gt;end()) errs() &lt;&lt; *it &lt;&lt; "\n";
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2182}
2183</pre>
2184</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2185
Dan Gohman525bf8e2010-03-26 19:39:05 +0000[diff] [blame]2186<p>Unfortunately, these implicit conversions come at a cost; they prevent
2187these iterators from conforming to standard iterator conventions, and thus
Dan Gohman0d91c112010-03-26 19:51:14 +0000[diff] [blame]2188from being usable with standard algorithms and containers. For example, they
2189prevent the following code, where <tt>B</tt> is a <tt>BasicBlock</tt>,
Dan Gohman525bf8e2010-03-26 19:39:05 +0000[diff] [blame]2190from compiling:</p>
2191
2192<div class="doc_code">
2193<pre>
2194 llvm::SmallVector&lt;llvm::Instruction *, 16&gt;(B-&gt;begin(), B-&gt;end());
2195</pre>
2196</div>
2197
2198<p>Because of this, these implicit conversions may be removed some day,
Dan Gohman0d91c112010-03-26 19:51:14 +0000[diff] [blame]2199and <tt>operator*</tt> changed to return a pointer instead of a reference.</p>
Dan Gohman525bf8e2010-03-26 19:39:05 +0000[diff] [blame]2200
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2201</div>
2202
2203<!--_______________________________________________________________________-->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]2204<h4>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2205 <a name="iterate_complex">Finding call sites: a slightly more complex
2206 example</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]2207</h4>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2208
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]2209<div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2210
2211<p>Say that you're writing a FunctionPass and would like to count all the
2212locations in the entire module (that is, across every <tt>Function</tt>) where a
2213certain function (i.e., some <tt>Function</tt>*) is already in scope. As you'll
2214learn 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]2215much more straight-forward manner, but this example will allow us to explore how
Reid Spencer128a7a72007-02-03 21:06:43 +0000[diff] [blame]2216you'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]2217is what we want to do:</p>
2218
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2219<div class="doc_code">
2220<pre>
2221initialize callCounter to zero
2222for each Function f in the Module
2223 for each BasicBlock b in f
2224 for each Instruction i in b
2225 if (i is a CallInst and calls the given function)
2226 increment callCounter
2227</pre>
2228</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2229
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2230<p>And the actual code is (remember, because we're writing a
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2231<tt>FunctionPass</tt>, our <tt>FunctionPass</tt>-derived class simply has to
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2232override the <tt>runOnFunction</tt> method):</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2233
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2234<div class="doc_code">
2235<pre>
2236Function* targetFunc = ...;
2237
2238class OurFunctionPass : public FunctionPass {
2239 public:
2240 OurFunctionPass(): callCounter(0) { }
2241
2242 virtual runOnFunction(Function&amp; F) {
2243 for (Function::iterator b = F.begin(), be = F.end(); b != be; ++b) {
Eric Christopher203e71d2008-11-08 08:20:49 +0000[diff] [blame]2244 for (BasicBlock::iterator i = b-&gt;begin(), ie = b-&gt;end(); i != ie; ++i) {
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2245 if (<a href="#CallInst">CallInst</a>* callInst = <a href="#isa">dyn_cast</a>&lt;<a
2246 href="#CallInst">CallInst</a>&gt;(&amp;*i)) {
Bill Wendling82e2eea2006-10-11 18:00:22 +0000[diff] [blame]2247 // <i>We know we've encountered a call instruction, so we</i>
2248 // <i>need to determine if it's a call to the</i>
Chris Lattner2e438ca2008-01-03 16:56:04 +0000[diff] [blame]2249 // <i>function pointed to by m_func or not.</i>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2250 if (callInst-&gt;getCalledFunction() == targetFunc)
2251 ++callCounter;
2252 }
2253 }
2254 }
Bill Wendling82e2eea2006-10-11 18:00:22 +0000[diff] [blame]2255 }
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2256
2257 private:
Chris Lattner2e438ca2008-01-03 16:56:04 +0000[diff] [blame]2258 unsigned callCounter;
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2259};
2260</pre>
2261</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2262
2263</div>
2264
Brian Gaekef1972c62003-11-07 19:25:45 +0000[diff] [blame]2265<!--_______________________________________________________________________-->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]2266<h4>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2267 <a name="calls_and_invokes">Treating calls and invokes the same way</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]2268</h4>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2269
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]2270<div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2271
2272<p>You may have noticed that the previous example was a bit oversimplified in
2273that it did not deal with call sites generated by 'invoke' instructions. In
2274this, and in other situations, you may find that you want to treat
2275<tt>CallInst</tt>s and <tt>InvokeInst</tt>s the same way, even though their
2276most-specific common base class is <tt>Instruction</tt>, which includes lots of
2277less closely-related things. For these cases, LLVM provides a handy wrapper
2278class called <a
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]2279href="http://llvm.org/doxygen/classllvm_1_1CallSite.html"><tt>CallSite</tt></a>.
Chris Lattner69bf8a92004-05-23 21:06:58 +0000[diff] [blame]2280It is essentially a wrapper around an <tt>Instruction</tt> pointer, with some
2281methods that provide functionality common to <tt>CallInst</tt>s and
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2282<tt>InvokeInst</tt>s.</p>
2283
Chris Lattner69bf8a92004-05-23 21:06:58 +0000[diff] [blame]2284<p>This class has "value semantics": it should be passed by value, not by
2285reference and it should not be dynamically allocated or deallocated using
2286<tt>operator new</tt> or <tt>operator delete</tt>. It is efficiently copyable,
2287assignable and constructable, with costs equivalents to that of a bare pointer.
2288If you look at its definition, it has only a single pointer member.</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2289
2290</div>
2291
Chris Lattner1a3105b2002-09-09 05:49:39 +0000[diff] [blame]2292<!--_______________________________________________________________________-->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]2293<h4>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2294 <a name="iterate_chains">Iterating over def-use &amp; use-def chains</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]2295</h4>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2296
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]2297<div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2298
2299<p>Frequently, we might have an instance of the <a
Chris Lattner00815172007-01-04 22:01:45 +0000[diff] [blame]2300href="/doxygen/classllvm_1_1Value.html">Value Class</a> and we want to
Misha Brukman384047f2004-06-03 23:29:12 +0000[diff] [blame]2301determine which <tt>User</tt>s use the <tt>Value</tt>. The list of all
2302<tt>User</tt>s of a particular <tt>Value</tt> is called a <i>def-use</i> chain.
2303For example, let's say we have a <tt>Function*</tt> named <tt>F</tt> to a
2304particular function <tt>foo</tt>. Finding all of the instructions that
2305<i>use</i> <tt>foo</tt> is as simple as iterating over the <i>def-use</i> chain
2306of <tt>F</tt>:</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2307
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2308<div class="doc_code">
2309<pre>
Chris Lattner2e438ca2008-01-03 16:56:04 +0000[diff] [blame]2310Function *F = ...;
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2311
Bill Wendling82e2eea2006-10-11 18:00:22 +0000[diff] [blame]2312for (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]2313 if (Instruction *Inst = dyn_cast&lt;Instruction&gt;(*i)) {
Chris Lattner3fee6ed2009-09-08 05:15:50 +0000[diff] [blame]2314 errs() &lt;&lt; "F is used in instruction:\n";
2315 errs() &lt;&lt; *Inst &lt;&lt; "\n";
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2316 }
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2317</pre>
Gabor Greif394fdfb2010-03-26 19:35:48 +0000[diff] [blame]2318</div>
2319
Gabor Greifce94319532010-03-26 19:40:38 +0000[diff] [blame]2320<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]2321operation. Instead of performing <tt>*i</tt> above several times, consider
Gabor Greifce94319532010-03-26 19:40:38 +0000[diff] [blame]2322doing it only once in the loop body and reusing its result.</p>
Gabor Greif4de73682010-03-26 19:30:47 +0000[diff] [blame]2323
Gabor Greif6091ff32010-03-26 19:04:42 +0000[diff] [blame]2324<p>Alternatively, it's common to have an instance of the <a
Misha Brukman384047f2004-06-03 23:29:12 +0000[diff] [blame]2325href="/doxygen/classllvm_1_1User.html">User Class</a> and need to know what
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2326<tt>Value</tt>s are used by it. The list of all <tt>Value</tt>s used by a
2327<tt>User</tt> is known as a <i>use-def</i> chain. Instances of class
2328<tt>Instruction</tt> are common <tt>User</tt>s, so we might want to iterate over
2329all of the values that a particular instruction uses (that is, the operands of
2330the particular <tt>Instruction</tt>):</p>
2331
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2332<div class="doc_code">
2333<pre>
Chris Lattner2e438ca2008-01-03 16:56:04 +0000[diff] [blame]2334Instruction *pi = ...;
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2335
2336for (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]2337 Value *v = *i;
Bill Wendling82e2eea2006-10-11 18:00:22 +0000[diff] [blame]2338 // <i>...</i>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2339}
2340</pre>
2341</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2342
Gabor Greif4de73682010-03-26 19:30:47 +0000[diff] [blame]2343<p>Declaring objects as <tt>const</tt> is an important tool of enforcing
Gabor Greifce94319532010-03-26 19:40:38 +0000[diff] [blame]2344mutation free algorithms (such as analyses, etc.). For this purpose above
Gabor Greif4de73682010-03-26 19:30:47 +0000[diff] [blame]2345iterators come in constant flavors as <tt>Value::const_use_iterator</tt>
2346and <tt>Value::const_op_iterator</tt>. They automatically arise when
2347calling <tt>use/op_begin()</tt> on <tt>const Value*</tt>s or
2348<tt>const User*</tt>s respectively. Upon dereferencing, they return
Gabor Greifce94319532010-03-26 19:40:38 +0000[diff] [blame]2349<tt>const Use*</tt>s. Otherwise the above patterns remain unchanged.</p>
2350
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2351</div>
2352
Chris Lattner2e438ca2008-01-03 16:56:04 +0000[diff] [blame]2353<!--_______________________________________________________________________-->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]2354<h4>
Chris Lattner2e438ca2008-01-03 16:56:04 +0000[diff] [blame]2355 <a name="iterate_preds">Iterating over predecessors &amp;
2356successors of blocks</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]2357</h4>
Chris Lattner2e438ca2008-01-03 16:56:04 +0000[diff] [blame]2358
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]2359<div>
Chris Lattner2e438ca2008-01-03 16:56:04 +0000[diff] [blame]2360
2361<p>Iterating over the predecessors and successors of a block is quite easy
2362with the routines defined in <tt>"llvm/Support/CFG.h"</tt>. Just use code like
2363this to iterate over all predecessors of BB:</p>
2364
2365<div class="doc_code">
2366<pre>
2367#include "llvm/Support/CFG.h"
2368BasicBlock *BB = ...;
2369
2370for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI) {
2371 BasicBlock *Pred = *PI;
2372 // <i>...</i>
2373}
2374</pre>
2375</div>
2376
2377<p>Similarly, to iterate over successors use
2378succ_iterator/succ_begin/succ_end.</p>
2379
2380</div>
2381
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]2382</div>
Chris Lattner2e438ca2008-01-03 16:56:04 +0000[diff] [blame]2383
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2384<!-- ======================================================================= -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]2385<h3>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2386 <a name="simplechanges">Making simple changes</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]2387</h3>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2388
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]2389<div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2390
2391<p>There are some primitive transformation operations present in the LLVM
Joel Stanley753eb712002-09-11 22:32:24 +0000[diff] [blame]2392infrastructure that are worth knowing about. When performing
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]2393transformations, it's fairly common to manipulate the contents of basic
2394blocks. This section describes some of the common methods for doing so
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2395and gives example code.</p>
2396
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]2397<!--_______________________________________________________________________-->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]2398<h4>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2399 <a name="schanges_creating">Creating and inserting new
2400 <tt>Instruction</tt>s</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]2401</h4>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2402
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]2403<div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2404
2405<p><i>Instantiating Instructions</i></p>
2406
Chris Lattner69bf8a92004-05-23 21:06:58 +0000[diff] [blame]2407<p>Creation of <tt>Instruction</tt>s is straight-forward: simply call the
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2408constructor for the kind of instruction to instantiate and provide the necessary
2409parameters. For example, an <tt>AllocaInst</tt> only <i>requires</i> a
2410(const-ptr-to) <tt>Type</tt>. Thus:</p>
2411
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2412<div class="doc_code">
2413<pre>
Nick Lewycky10d64b92007-12-03 01:52:52 +0000[diff] [blame]2414AllocaInst* ai = new AllocaInst(Type::Int32Ty);
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2415</pre>
2416</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2417
2418<p>will create an <tt>AllocaInst</tt> instance that represents the allocation of
Reid Spencer128a7a72007-02-03 21:06:43 +0000[diff] [blame]2419one integer in the current stack frame, at run time. Each <tt>Instruction</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2420subclass is likely to have varying default parameters which change the semantics
2421of the instruction, so refer to the <a
Misha Brukman31ca1de2004-06-03 23:35:54 +0000[diff] [blame]2422href="/doxygen/classllvm_1_1Instruction.html">doxygen documentation for the subclass of
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2423Instruction</a> that you're interested in instantiating.</p>
2424
2425<p><i>Naming values</i></p>
2426
2427<p>It is very useful to name the values of instructions when you're able to, as
2428this facilitates the debugging of your transformations. If you end up looking
2429at generated LLVM machine code, you definitely want to have logical names
2430associated with the results of instructions! By supplying a value for the
2431<tt>Name</tt> (default) parameter of the <tt>Instruction</tt> constructor, you
2432associate a logical name with the result of the instruction's execution at
Reid Spencer128a7a72007-02-03 21:06:43 +0000[diff] [blame]2433run time. For example, say that I'm writing a transformation that dynamically
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2434allocates space for an integer on the stack, and that integer is going to be
2435used as some kind of index by some other code. To accomplish this, I place an
2436<tt>AllocaInst</tt> at the first point in the first <tt>BasicBlock</tt> of some
2437<tt>Function</tt>, and I'm intending to use it within the same
2438<tt>Function</tt>. I might do:</p>
2439
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2440<div class="doc_code">
2441<pre>
Nick Lewycky10d64b92007-12-03 01:52:52 +0000[diff] [blame]2442AllocaInst* pa = new AllocaInst(Type::Int32Ty, 0, "indexLoc");
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2443</pre>
2444</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2445
2446<p>where <tt>indexLoc</tt> is now the logical name of the instruction's
Reid Spencer128a7a72007-02-03 21:06:43 +0000[diff] [blame]2447execution value, which is a pointer to an integer on the run time stack.</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2448
2449<p><i>Inserting instructions</i></p>
2450
2451<p>There are essentially two ways to insert an <tt>Instruction</tt>
2452into an existing sequence of instructions that form a <tt>BasicBlock</tt>:</p>
2453
Joel Stanley9dd1ad62002-09-18 03:17:23 +0000[diff] [blame]2454<ul>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2455 <li>Insertion into an explicit instruction list
2456
2457 <p>Given a <tt>BasicBlock* pb</tt>, an <tt>Instruction* pi</tt> within that
2458 <tt>BasicBlock</tt>, and a newly-created instruction we wish to insert
2459 before <tt>*pi</tt>, we do the following: </p>
2460
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2461<div class="doc_code">
2462<pre>
2463BasicBlock *pb = ...;
2464Instruction *pi = ...;
2465Instruction *newInst = new Instruction(...);
2466
Bill Wendling82e2eea2006-10-11 18:00:22 +0000[diff] [blame]2467pb-&gt;getInstList().insert(pi, newInst); // <i>Inserts newInst before pi in pb</i>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2468</pre>
2469</div>
Alkis Evlogimenos9a5dc4f2004-05-27 00:57:51 +0000[diff] [blame]2470
2471 <p>Appending to the end of a <tt>BasicBlock</tt> is so common that
2472 the <tt>Instruction</tt> class and <tt>Instruction</tt>-derived
2473 classes provide constructors which take a pointer to a
2474 <tt>BasicBlock</tt> to be appended to. For example code that
2475 looked like: </p>
2476
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2477<div class="doc_code">
2478<pre>
2479BasicBlock *pb = ...;
2480Instruction *newInst = new Instruction(...);
2481
Bill Wendling82e2eea2006-10-11 18:00:22 +0000[diff] [blame]2482pb-&gt;getInstList().push_back(newInst); // <i>Appends newInst to pb</i>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2483</pre>
2484</div>
Alkis Evlogimenos9a5dc4f2004-05-27 00:57:51 +0000[diff] [blame]2485
2486 <p>becomes: </p>
2487
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2488<div class="doc_code">
2489<pre>
2490BasicBlock *pb = ...;
2491Instruction *newInst = new Instruction(..., pb);
2492</pre>
2493</div>
Alkis Evlogimenos9a5dc4f2004-05-27 00:57:51 +0000[diff] [blame]2494
2495 <p>which is much cleaner, especially if you are creating
2496 long instruction streams.</p></li>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2497
2498 <li>Insertion into an implicit instruction list
2499
2500 <p><tt>Instruction</tt> instances that are already in <tt>BasicBlock</tt>s
2501 are implicitly associated with an existing instruction list: the instruction
2502 list of the enclosing basic block. Thus, we could have accomplished the same
2503 thing as the above code without being given a <tt>BasicBlock</tt> by doing:
2504 </p>
2505
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2506<div class="doc_code">
2507<pre>
2508Instruction *pi = ...;
2509Instruction *newInst = new Instruction(...);
2510
2511pi-&gt;getParent()-&gt;getInstList().insert(pi, newInst);
2512</pre>
2513</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2514
2515 <p>In fact, this sequence of steps occurs so frequently that the
2516 <tt>Instruction</tt> class and <tt>Instruction</tt>-derived classes provide
2517 constructors which take (as a default parameter) a pointer to an
2518 <tt>Instruction</tt> which the newly-created <tt>Instruction</tt> should
2519 precede. That is, <tt>Instruction</tt> constructors are capable of
2520 inserting the newly-created instance into the <tt>BasicBlock</tt> of a
2521 provided instruction, immediately before that instruction. Using an
2522 <tt>Instruction</tt> constructor with a <tt>insertBefore</tt> (default)
2523 parameter, the above code becomes:</p>
2524
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2525<div class="doc_code">
2526<pre>
2527Instruction* pi = ...;
2528Instruction* newInst = new Instruction(..., pi);
2529</pre>
2530</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2531
2532 <p>which is much cleaner, especially if you're creating a lot of
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2533 instructions and adding them to <tt>BasicBlock</tt>s.</p></li>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2534</ul>
2535
2536</div>
2537
2538<!--_______________________________________________________________________-->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]2539<h4>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2540 <a name="schanges_deleting">Deleting <tt>Instruction</tt>s</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]2541</h4>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2542
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]2543<div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2544
2545<p>Deleting an instruction from an existing sequence of instructions that form a
Chris Lattner49e0ccf2011-03-24 16:13:31 +0000[diff] [blame]2546<a href="#BasicBlock"><tt>BasicBlock</tt></a> is very straight-forward: just
2547call the instruction's eraseFromParent() method. For example:</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2548
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2549<div class="doc_code">
2550<pre>
2551<a href="#Instruction">Instruction</a> *I = .. ;
Chris Lattner9f8ec252008-02-15 22:57:17 +0000[diff] [blame]2552I-&gt;eraseFromParent();
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2553</pre>
2554</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2555
Chris Lattner49e0ccf2011-03-24 16:13:31 +0000[diff] [blame]2556<p>This unlinks the instruction from its containing basic block and deletes
2557it. If you'd just like to unlink the instruction from its containing basic
2558block but not delete it, you can use the <tt>removeFromParent()</tt> method.</p>
2559
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2560</div>
2561
2562<!--_______________________________________________________________________-->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]2563<h4>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2564 <a name="schanges_replacing">Replacing an <tt>Instruction</tt> with another
2565 <tt>Value</tt></a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]2566</h4>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2567
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]2568<div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2569
NAKAMURA Takumi9c55f592012-03-27 11:25:16 +0000[diff] [blame]2570<h5><i>Replacing individual instructions</i></h5>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2571
2572<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]2573permits use of two very useful replace functions: <tt>ReplaceInstWithValue</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2574and <tt>ReplaceInstWithInst</tt>.</p>
2575
NAKAMURA Takumi06c6d9a2011-04-18 01:17:51 +0000[diff] [blame]2576<h5><a name="schanges_deleting">Deleting <tt>Instruction</tt>s</a></h5>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2577
NAKAMURA Takumi9c55f592012-03-27 11:25:16 +0000[diff] [blame]2578<div>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]2579<ul>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2580 <li><tt>ReplaceInstWithValue</tt>
2581
Nick Lewyckyb6d1f392008-09-15 06:31:52 +0000[diff] [blame]2582 <p>This function replaces all uses of a given instruction with a value,
2583 and then removes the original instruction. The following example
2584 illustrates the replacement of the result of a particular
Chris Lattner58360822005-01-17 00:12:04 +0000[diff] [blame]2585 <tt>AllocaInst</tt> that allocates memory for a single integer with a null
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2586 pointer to an integer.</p>
2587
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2588<div class="doc_code">
2589<pre>
2590AllocaInst* instToReplace = ...;
2591BasicBlock::iterator ii(instToReplace);
2592
2593ReplaceInstWithValue(instToReplace-&gt;getParent()-&gt;getInstList(), ii,
Daniel Dunbar58c2ac02008-10-03 22:17:25 +0000[diff] [blame]2594 Constant::getNullValue(PointerType::getUnqual(Type::Int32Ty)));
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2595</pre></div></li>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2596
2597 <li><tt>ReplaceInstWithInst</tt>
2598
2599 <p>This function replaces a particular instruction with another
Nick Lewyckyb6d1f392008-09-15 06:31:52 +0000[diff] [blame]2600 instruction, inserting the new instruction into the basic block at the
2601 location where the old instruction was, and replacing any uses of the old
2602 instruction with the new instruction. The following example illustrates
2603 the replacement of one <tt>AllocaInst</tt> with another.</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2604
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2605<div class="doc_code">
2606<pre>
2607AllocaInst* instToReplace = ...;
2608BasicBlock::iterator ii(instToReplace);
2609
2610ReplaceInstWithInst(instToReplace-&gt;getParent()-&gt;getInstList(), ii,
Nick Lewycky10d64b92007-12-03 01:52:52 +0000[diff] [blame]2611 new AllocaInst(Type::Int32Ty, 0, "ptrToReplacedInt"));
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2612</pre></div></li>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]2613</ul>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2614
NAKAMURA Takumi9c55f592012-03-27 11:25:16 +0000[diff] [blame]2615</div>
2616
2617<h5><i>Replacing multiple uses of <tt>User</tt>s and <tt>Value</tt>s</i></h5>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2618
2619<p>You can use <tt>Value::replaceAllUsesWith</tt> and
2620<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]2621doxygen documentation for the <a href="/doxygen/classllvm_1_1Value.html">Value Class</a>
Misha Brukman384047f2004-06-03 23:29:12 +0000[diff] [blame]2622and <a href="/doxygen/classllvm_1_1User.html">User Class</a>, respectively, for more
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2623information.</p>
2624
2625<!-- Value::replaceAllUsesWith User::replaceUsesOfWith Point out:
2626include/llvm/Transforms/Utils/ especially BasicBlockUtils.h with:
2627ReplaceInstWithValue, ReplaceInstWithInst -->
2628
2629</div>
2630
Tanya Lattnerb011c662007-06-20 18:33:15 +0000[diff] [blame]2631<!--_______________________________________________________________________-->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]2632<h4>
Tanya Lattnerb011c662007-06-20 18:33:15 +0000[diff] [blame]2633 <a name="schanges_deletingGV">Deleting <tt>GlobalVariable</tt>s</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]2634</h4>
Tanya Lattnerb011c662007-06-20 18:33:15 +0000[diff] [blame]2635
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]2636<div>
Tanya Lattnerb011c662007-06-20 18:33:15 +0000[diff] [blame]2637
Tanya Lattnerc5dfcdb2007-06-20 20:46:37 +0000[diff] [blame]2638<p>Deleting a global variable from a module is just as easy as deleting an
2639Instruction. First, you must have a pointer to the global variable that you wish
2640 to delete. You use this pointer to erase it from its parent, the module.
Tanya Lattnerb011c662007-06-20 18:33:15 +0000[diff] [blame]2641 For example:</p>
2642
2643<div class="doc_code">
2644<pre>
2645<a href="#GlobalVariable">GlobalVariable</a> *GV = .. ;
Tanya Lattnerb011c662007-06-20 18:33:15 +0000[diff] [blame]2646
Tanya Lattnerc5dfcdb2007-06-20 20:46:37 +0000[diff] [blame]2647GV-&gt;eraseFromParent();
Tanya Lattnerb011c662007-06-20 18:33:15 +0000[diff] [blame]2648</pre>
2649</div>
2650
2651</div>
2652
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]2653</div>
2654
Jeffrey Yasskin714257f2009-04-30 22:33:41 +0000[diff] [blame]2655<!-- ======================================================================= -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]2656<h3>
Jeffrey Yasskin714257f2009-04-30 22:33:41 +0000[diff] [blame]2657 <a name="create_types">How to Create Types</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]2658</h3>
Jeffrey Yasskin714257f2009-04-30 22:33:41 +0000[diff] [blame]2659
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]2660<div>
Jeffrey Yasskin714257f2009-04-30 22:33:41 +0000[diff] [blame]2661
2662<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]2663statically, you can use <tt>TypeBuilder&lt;...&gt;::get()</tt>, defined
Jeffrey Yasskin714257f2009-04-30 22:33:41 +0000[diff] [blame]2664in <tt>llvm/Support/TypeBuilder.h</tt>, to retrieve them. <tt>TypeBuilder</tt>
2665has two forms depending on whether you're building types for cross-compilation
Misha Brukman1af789f2009-05-01 20:40:51 +0000[diff] [blame]2666or native library use. <tt>TypeBuilder&lt;T, true&gt;</tt> requires
Jeffrey Yasskin714257f2009-04-30 22:33:41 +0000[diff] [blame]2667that <tt>T</tt> be independent of the host environment, meaning that it's built
2668out of types from
2669the <a href="/doxygen/namespacellvm_1_1types.html"><tt>llvm::types</tt></a>
2670namespace and pointers, functions, arrays, etc. built of
Misha Brukman1af789f2009-05-01 20:40:51 +0000[diff] [blame]2671those. <tt>TypeBuilder&lt;T, false&gt;</tt> additionally allows native C types
Jeffrey Yasskin714257f2009-04-30 22:33:41 +0000[diff] [blame]2672whose size may depend on the host compiler. For example,</p>
2673
2674<div class="doc_code">
2675<pre>
Misha Brukman1af789f2009-05-01 20:40:51 +0000[diff] [blame]2676FunctionType *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]2677</pre>
2678</div>
2679
2680<p>is easier to read and write than the equivalent</p>
2681
2682<div class="doc_code">
2683<pre>
Owen Anderson5e8c50e2009-06-16 17:40:28 +0000[diff] [blame]2684std::vector&lt;const Type*&gt; params;
Jeffrey Yasskin714257f2009-04-30 22:33:41 +0000[diff] [blame]2685params.push_back(PointerType::getUnqual(Type::Int32Ty));
2686FunctionType *ft = FunctionType::get(Type::Int8Ty, params, false);
2687</pre>
2688</div>
2689
2690<p>See the <a href="/doxygen/TypeBuilder_8h-source.html#l00001">class
2691comment</a> for more details.</p>
2692
2693</div>
2694
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]2695</div>
2696
Chris Lattner9355b472002-09-06 02:50:58 +0000[diff] [blame]2697<!-- *********************************************************************** -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]2698<h2>
Owen Anderson8bc1b3b2009-06-16 01:17:16 +0000[diff] [blame]2699 <a name="threading">Threads and LLVM</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]2700</h2>
Owen Anderson8bc1b3b2009-06-16 01:17:16 +0000[diff] [blame]2701<!-- *********************************************************************** -->
2702
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]2703<div>
Owen Anderson8bc1b3b2009-06-16 01:17:16 +0000[diff] [blame]2704<p>
2705This section describes the interaction of the LLVM APIs with multithreading,
2706both on the part of client applications, and in the JIT, in the hosted
2707application.
2708</p>
2709
2710<p>
2711Note that LLVM's support for multithreading is still relatively young. Up
2712through version 2.5, the execution of threaded hosted applications was
2713supported, but not threaded client access to the APIs. While this use case is
2714now supported, clients <em>must</em> adhere to the guidelines specified below to
2715ensure proper operation in multithreaded mode.
2716</p>
2717
2718<p>
2719Note that, on Unix-like platforms, LLVM requires the presence of GCC's atomic
2720intrinsics in order to support threaded operation. If you need a
2721multhreading-capable LLVM on a platform without a suitably modern system
2722compiler, consider compiling LLVM and LLVM-GCC in single-threaded mode, and
2723using the resultant compiler to build a copy of LLVM with multithreading
2724support.
2725</p>
Owen Anderson8bc1b3b2009-06-16 01:17:16 +0000[diff] [blame]2726
2727<!-- ======================================================================= -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]2728<h3>
Owen Anderson1ad70e32009-06-16 18:04:19 +0000[diff] [blame]2729 <a name="startmultithreaded">Entering and Exiting Multithreaded Mode</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]2730</h3>
Owen Anderson8bc1b3b2009-06-16 01:17:16 +0000[diff] [blame]2731
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]2732<div>
Owen Anderson8bc1b3b2009-06-16 01:17:16 +0000[diff] [blame]2733
2734<p>
2735In order to properly protect its internal data structures while avoiding
Owen Anderson1ad70e32009-06-16 18:04:19 +0000[diff] [blame]2736excessive locking overhead in the single-threaded case, the LLVM must intialize
2737certain data structures necessary to provide guards around its internals. To do
2738so, the client program must invoke <tt>llvm_start_multithreaded()</tt> before
2739making any concurrent LLVM API calls. To subsequently tear down these
2740structures, use the <tt>llvm_stop_multithreaded()</tt> call. You can also use
2741the <tt>llvm_is_multithreaded()</tt> call to check the status of multithreaded
2742mode.
Owen Anderson8bc1b3b2009-06-16 01:17:16 +0000[diff] [blame]2743</p>
2744
2745<p>
Owen Anderson1ad70e32009-06-16 18:04:19 +0000[diff] [blame]2746Note that both of these calls must be made <em>in isolation</em>. That is to
2747say that no other LLVM API calls may be executing at any time during the
2748execution of <tt>llvm_start_multithreaded()</tt> or <tt>llvm_stop_multithreaded
2749</tt>. It's is the client's responsibility to enforce this isolation.
2750</p>
2751
2752<p>
2753The return value of <tt>llvm_start_multithreaded()</tt> indicates the success or
2754failure of the initialization. Failure typically indicates that your copy of
2755LLVM was built without multithreading support, typically because GCC atomic
2756intrinsics were not found in your system compiler. In this case, the LLVM API
2757will not be safe for concurrent calls. However, it <em>will</em> be safe for
Jeffrey Yasskin01eba392010-01-29 19:10:38 +0000[diff] [blame]2758hosting threaded applications in the JIT, though <a href="#jitthreading">care
2759must be taken</a> to ensure that side exits and the like do not accidentally
2760result in concurrent LLVM API calls.
Owen Anderson8bc1b3b2009-06-16 01:17:16 +0000[diff] [blame]2761</p>
2762</div>
2763
2764<!-- ======================================================================= -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]2765<h3>
Owen Anderson8bc1b3b2009-06-16 01:17:16 +0000[diff] [blame]2766 <a name="shutdown">Ending Execution with <tt>llvm_shutdown()</tt></a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]2767</h3>
Owen Anderson8bc1b3b2009-06-16 01:17:16 +0000[diff] [blame]2768
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]2769<div>
Owen Anderson8bc1b3b2009-06-16 01:17:16 +0000[diff] [blame]2770<p>
2771When you are done using the LLVM APIs, you should call <tt>llvm_shutdown()</tt>
Owen Anderson1ad70e32009-06-16 18:04:19 +0000[diff] [blame]2772to deallocate memory used for internal structures. This will also invoke
2773<tt>llvm_stop_multithreaded()</tt> if LLVM is operating in multithreaded mode.
2774As such, <tt>llvm_shutdown()</tt> requires the same isolation guarantees as
2775<tt>llvm_stop_multithreaded()</tt>.
Owen Anderson8bc1b3b2009-06-16 01:17:16 +0000[diff] [blame]2776</p>
2777
2778<p>
2779Note that, if you use scope-based shutdown, you can use the
2780<tt>llvm_shutdown_obj</tt> class, which calls <tt>llvm_shutdown()</tt> in its
2781destructor.
2782</div>
2783
2784<!-- ======================================================================= -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]2785<h3>
Owen Anderson8bc1b3b2009-06-16 01:17:16 +0000[diff] [blame]2786 <a name="managedstatic">Lazy Initialization with <tt>ManagedStatic</tt></a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]2787</h3>
Owen Anderson8bc1b3b2009-06-16 01:17:16 +0000[diff] [blame]2788
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]2789<div>
Owen Anderson8bc1b3b2009-06-16 01:17:16 +0000[diff] [blame]2790<p>
2791<tt>ManagedStatic</tt> is a utility class in LLVM used to implement static
2792initialization of static resources, such as the global type tables. Before the
2793invocation of <tt>llvm_shutdown()</tt>, it implements a simple lazy
2794initialization scheme. Once <tt>llvm_start_multithreaded()</tt> returns,
2795however, it uses double-checked locking to implement thread-safe lazy
2796initialization.
2797</p>
2798
2799<p>
2800Note that, because no other threads are allowed to issue LLVM API calls before
2801<tt>llvm_start_multithreaded()</tt> returns, it is possible to have
2802<tt>ManagedStatic</tt>s of <tt>llvm::sys::Mutex</tt>s.
2803</p>
Owen Anderson1ad70e32009-06-16 18:04:19 +0000[diff] [blame]2804
2805<p>
2806The <tt>llvm_acquire_global_lock()</tt> and <tt>llvm_release_global_lock</tt>
2807APIs provide access to the global lock used to implement the double-checked
2808locking for lazy initialization. These should only be used internally to LLVM,
2809and only if you know what you're doing!
2810</p>
Owen Anderson8bc1b3b2009-06-16 01:17:16 +0000[diff] [blame]2811</div>
2812
Owen Andersone0c951a2009-08-19 17:58:52 +0000[diff] [blame]2813<!-- ======================================================================= -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]2814<h3>
Owen Andersone0c951a2009-08-19 17:58:52 +0000[diff] [blame]2815 <a name="llvmcontext">Achieving Isolation with <tt>LLVMContext</tt></a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]2816</h3>
Owen Andersone0c951a2009-08-19 17:58:52 +0000[diff] [blame]2817
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]2818<div>
Owen Andersone0c951a2009-08-19 17:58:52 +0000[diff] [blame]2819<p>
2820<tt>LLVMContext</tt> is an opaque class in the LLVM API which clients can use
2821to operate multiple, isolated instances of LLVM concurrently within the same
2822address space. For instance, in a hypothetical compile-server, the compilation
2823of an individual translation unit is conceptually independent from all the
2824others, and it would be desirable to be able to compile incoming translation
2825units concurrently on independent server threads. Fortunately,
2826<tt>LLVMContext</tt> exists to enable just this kind of scenario!
2827</p>
2828
2829<p>
2830Conceptually, <tt>LLVMContext</tt> provides isolation. Every LLVM entity
2831(<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]2832in LLVM's in-memory IR belongs to an <tt>LLVMContext</tt>. Entities in
Owen Andersone0c951a2009-08-19 17:58:52 +0000[diff] [blame]2833different contexts <em>cannot</em> interact with each other: <tt>Module</tt>s in
2834different contexts cannot be linked together, <tt>Function</tt>s cannot be added
2835to <tt>Module</tt>s in different contexts, etc. What this means is that is is
2836safe to compile on multiple threads simultaneously, as long as no two threads
2837operate on entities within the same context.
2838</p>
2839
2840<p>
2841In practice, very few places in the API require the explicit specification of a
2842<tt>LLVMContext</tt>, other than the <tt>Type</tt> creation/lookup APIs.
2843Because every <tt>Type</tt> carries a reference to its owning context, most
2844other entities can determine what context they belong to by looking at their
2845own <tt>Type</tt>. If you are adding new entities to LLVM IR, please try to
2846maintain this interface design.
2847</p>
2848
2849<p>
2850For clients that do <em>not</em> require the benefits of isolation, LLVM
2851provides a convenience API <tt>getGlobalContext()</tt>. This returns a global,
2852lazily initialized <tt>LLVMContext</tt> that may be used in situations where
2853isolation is not a concern.
2854</p>
2855</div>
2856
Jeffrey Yasskin01eba392010-01-29 19:10:38 +0000[diff] [blame]2857<!-- ======================================================================= -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]2858<h3>
Jeffrey Yasskin01eba392010-01-29 19:10:38 +0000[diff] [blame]2859 <a name="jitthreading">Threads and the JIT</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]2860</h3>
Jeffrey Yasskin01eba392010-01-29 19:10:38 +0000[diff] [blame]2861
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]2862<div>
Jeffrey Yasskin01eba392010-01-29 19:10:38 +0000[diff] [blame]2863<p>
2864LLVM's "eager" JIT compiler is safe to use in threaded programs. Multiple
2865threads can call <tt>ExecutionEngine::getPointerToFunction()</tt> or
2866<tt>ExecutionEngine::runFunction()</tt> concurrently, and multiple threads can
2867run code output by the JIT concurrently. The user must still ensure that only
2868one thread accesses IR in a given <tt>LLVMContext</tt> while another thread
2869might be modifying it. One way to do that is to always hold the JIT lock while
2870accessing IR outside the JIT (the JIT <em>modifies</em> the IR by adding
2871<tt>CallbackVH</tt>s). Another way is to only
2872call <tt>getPointerToFunction()</tt> from the <tt>LLVMContext</tt>'s thread.
2873</p>
2874
2875<p>When the JIT is configured to compile lazily (using
2876<tt>ExecutionEngine::DisableLazyCompilation(false)</tt>), there is currently a
2877<a href="http://llvm.org/bugs/show_bug.cgi?id=5184">race condition</a> in
2878updating call sites after a function is lazily-jitted. It's still possible to
2879use the lazy JIT in a threaded program if you ensure that only one thread at a
2880time can call any particular lazy stub and that the JIT lock guards any IR
2881access, but we suggest using only the eager JIT in threaded programs.
2882</p>
2883</div>
2884
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]2885</div>
2886
Owen Anderson8bc1b3b2009-06-16 01:17:16 +0000[diff] [blame]2887<!-- *********************************************************************** -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]2888<h2>
Chris Lattnerd9d6e102005-04-23 16:10:52 +0000[diff] [blame]2889 <a name="advanced">Advanced Topics</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]2890</h2>
Chris Lattnerd9d6e102005-04-23 16:10:52 +0000[diff] [blame]2891<!-- *********************************************************************** -->
2892
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]2893<div>
Chris Lattnerf1b200b2005-04-23 17:27:36 +0000[diff] [blame]2894<p>
2895This section describes some of the advanced or obscure API's that most clients
2896do not need to be aware of. These API's tend manage the inner workings of the
2897LLVM system, and only need to be accessed in unusual circumstances.
2898</p>
Chris Lattnerd9d6e102005-04-23 16:10:52 +0000[diff] [blame]2899
Chris Lattner1afcace2011-07-09 17:41:24 +0000[diff] [blame]2900
Chris Lattnerf1b200b2005-04-23 17:27:36 +0000[diff] [blame]2901<!-- ======================================================================= -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]2902<h3>
Chris Lattner1afcace2011-07-09 17:41:24 +0000[diff] [blame]2903 <a name="SymbolTable">The <tt>ValueSymbolTable</tt> class</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]2904</h3>
Chris Lattnerf1b200b2005-04-23 17:27:36 +0000[diff] [blame]2905
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]2906<div>
Chris Lattner263a98e2007-02-16 04:37:31 +0000[diff] [blame]2907<p>The <tt><a href="http://llvm.org/doxygen/classllvm_1_1ValueSymbolTable.html">
2908ValueSymbolTable</a></tt> class provides a symbol table that the <a
Chris Lattnerd9d6e102005-04-23 16:10:52 +0000[diff] [blame]2909href="#Function"><tt>Function</tt></a> and <a href="#Module">
Chris Lattner263a98e2007-02-16 04:37:31 +0000[diff] [blame]2910<tt>Module</tt></a> classes use for naming value definitions. The symbol table
2911can provide a name for any <a href="#Value"><tt>Value</tt></a>.
Chris Lattner1afcace2011-07-09 17:41:24 +0000[diff] [blame]2912</p>
Chris Lattnerd9d6e102005-04-23 16:10:52 +0000[diff] [blame]2913
Reid Spencera6362242007-01-07 00:41:39 +0000[diff] [blame]2914<p>Note that the <tt>SymbolTable</tt> class should not be directly accessed
2915by most clients. It should only be used when iteration over the symbol table
2916names themselves are required, which is very special purpose. Note that not
2917all LLVM
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2918<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]2919an empty name) do not exist in the symbol table.
2920</p>
2921
Chris Lattner1afcace2011-07-09 17:41:24 +0000[diff] [blame]2922<p>Symbol tables support iteration over the values in the symbol
Chris Lattner263a98e2007-02-16 04:37:31 +0000[diff] [blame]2923table with <tt>begin/end/iterator</tt> and supports querying to see if a
2924specific name is in the symbol table (with <tt>lookup</tt>). The
2925<tt>ValueSymbolTable</tt> class exposes no public mutator methods, instead,
2926simply call <tt>setName</tt> on a value, which will autoinsert it into the
Chris Lattner1afcace2011-07-09 17:41:24 +0000[diff] [blame]2927appropriate symbol table.</p>
Chris Lattnerd9d6e102005-04-23 16:10:52 +0000[diff] [blame]2928
Chris Lattnerd9d6e102005-04-23 16:10:52 +0000[diff] [blame]2929</div>
2930
2931
2932
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2933<!-- ======================================================================= -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]2934<h3>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2935 <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]2936</h3>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2937
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]2938<div>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2939<p>The <tt><a href="http://llvm.org/doxygen/classllvm_1_1User.html">
Gabor Greiffd095b62009-01-05 16:05:32 +0000[diff] [blame]2940User</a></tt> class provides a basis for expressing the ownership of <tt>User</tt>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2941towards other <tt><a href="http://llvm.org/doxygen/classllvm_1_1Value.html">
2942Value</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]2943Use</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]2944addition and removal.</p>
2945
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2946<!-- ______________________________________________________________________ -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]2947<h4>
2948 <a name="Use2User">
2949 Interaction and relationship between <tt>User</tt> and <tt>Use</tt> objects
2950 </a>
2951</h4>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2952
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]2953<div>
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2954<p>
2955A subclass of <tt>User</tt> can choose between incorporating its <tt>Use</tt> objects
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2956or refer to them out-of-line by means of a pointer. A mixed variant
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2957(some <tt>Use</tt>s inline others hung off) is impractical and breaks the invariant
2958that the <tt>Use</tt> objects belonging to the same <tt>User</tt> form a contiguous array.
2959</p>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2960
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2961<p>
2962We have 2 different layouts in the <tt>User</tt> (sub)classes:
2963<ul>
2964<li><p>Layout a)
2965The <tt>Use</tt> object(s) are inside (resp. at fixed offset) of the <tt>User</tt>
2966object and there are a fixed number of them.</p>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2967
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2968<li><p>Layout b)
2969The <tt>Use</tt> object(s) are referenced by a pointer to an
2970array from the <tt>User</tt> object and there may be a variable
2971number of them.</p>
2972</ul>
2973<p>
Gabor Greifd41720a2008-06-25 00:10:22 +0000[diff] [blame]2974As of v2.4 each layout still possesses a direct pointer to the
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2975start of the array of <tt>Use</tt>s. Though not mandatory for layout a),
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2976we stick to this redundancy for the sake of simplicity.
Gabor Greifd41720a2008-06-25 00:10:22 +0000[diff] [blame]2977The <tt>User</tt> object also stores the number of <tt>Use</tt> objects it
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2978has. (Theoretically this information can also be calculated
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2979given the scheme presented below.)</p>
2980<p>
2981Special forms of allocation operators (<tt>operator new</tt>)
Gabor Greifd41720a2008-06-25 00:10:22 +0000[diff] [blame]2982enforce the following memory layouts:</p>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2983
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2984<ul>
Gabor Greifd41720a2008-06-25 00:10:22 +0000[diff] [blame]2985<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]2986
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2987<pre>
2988...---.---.---.---.-------...
2989 | P | P | P | P | User
2990'''---'---'---'---'-------'''
2991</pre>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2992
Gabor Greifd41720a2008-06-25 00:10:22 +0000[diff] [blame]2993<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]2994<pre>
2995.-------...
2996| User
2997'-------'''
2998 |
2999 v
3000 .---.---.---.---...
3001 | P | P | P | P |
3002 '---'---'---'---'''
3003</pre>
3004</ul>
3005<i>(In the above figures '<tt>P</tt>' stands for the <tt>Use**</tt> that
3006 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]3007
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]3008</div>
3009
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]3010<!-- ______________________________________________________________________ -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]3011<h4>
Gabor Greiffd095b62009-01-05 16:05:32 +0000[diff] [blame]3012 <a name="Waymarking">The waymarking algorithm</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]3013</h4>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]3014
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]3015<div>
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]3016<p>
Gabor Greifd41720a2008-06-25 00:10:22 +0000[diff] [blame]3017Since the <tt>Use</tt> objects are deprived of the direct (back)pointer to
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]3018their <tt>User</tt> objects, there must be a fast and exact method to
3019recover it. This is accomplished by the following scheme:</p>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]3020
Gabor Greifd41720a2008-06-25 00:10:22 +0000[diff] [blame]3021A 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]3022start of the <tt>User</tt> object:
3023<ul>
3024<li><tt>00</tt> &mdash;&gt; binary digit 0</li>
3025<li><tt>01</tt> &mdash;&gt; binary digit 1</li>
3026<li><tt>10</tt> &mdash;&gt; stop and calculate (<tt>s</tt>)</li>
3027<li><tt>11</tt> &mdash;&gt; full stop (<tt>S</tt>)</li>
3028</ul>
3029<p>
3030Given a <tt>Use*</tt>, all we have to do is to walk till we get
3031a stop and we either have a <tt>User</tt> immediately behind or
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]3032we have to walk to the next stop picking up digits
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]3033and calculating the offset:</p>
3034<pre>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]3035.---.---.---.---.---.---.---.---.---.---.---.---.---.---.---.---.----------------
3036| 1 | s | 1 | 0 | 1 | 0 | s | 1 | 1 | 0 | s | 1 | 1 | s | 1 | S | User (or User*)
3037'---'---'---'---'---'---'---'---'---'---'---'---'---'---'---'---'----------------
3038 |+15 |+10 |+6 |+3 |+1
3039 | | | | |__>
3040 | | | |__________>
3041 | | |______________________>
3042 | |______________________________________>
3043 |__________________________________________________________>
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]3044</pre>
3045<p>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]3046Only the significant number of bits need to be stored between the
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]3047stops, so that the <i>worst case is 20 memory accesses</i> when there are
30481000 <tt>Use</tt> objects associated with a <tt>User</tt>.</p>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]3049
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]3050</div>
3051
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]3052<!-- ______________________________________________________________________ -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]3053<h4>
Gabor Greiffd095b62009-01-05 16:05:32 +0000[diff] [blame]3054 <a name="ReferenceImpl">Reference implementation</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]3055</h4>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]3056
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]3057<div>
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]3058<p>
3059The following literate Haskell fragment demonstrates the concept:</p>
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]3060
3061<div class="doc_code">
3062<pre>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]3063> import Test.QuickCheck
3064>
3065> digits :: Int -> [Char] -> [Char]
3066> digits 0 acc = '0' : acc
3067> digits 1 acc = '1' : acc
3068> digits n acc = digits (n `div` 2) $ digits (n `mod` 2) acc
3069>
3070> dist :: Int -> [Char] -> [Char]
3071> dist 0 [] = ['S']
3072> dist 0 acc = acc
3073> dist 1 acc = let r = dist 0 acc in 's' : digits (length r) r
3074> dist n acc = dist (n - 1) $ dist 1 acc
3075>
3076> takeLast n ss = reverse $ take n $ reverse ss
3077>
3078> test = takeLast 40 $ dist 20 []
3079>
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]3080</pre>
3081</div>
3082<p>
3083Printing &lt;test&gt; gives: <tt>"1s100000s11010s10100s1111s1010s110s11s1S"</tt></p>
3084<p>
3085The reverse algorithm computes the length of the string just by examining
3086a certain prefix:</p>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]3087
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]3088<div class="doc_code">
3089<pre>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]3090> pref :: [Char] -> Int
3091> pref "S" = 1
3092> pref ('s':'1':rest) = decode 2 1 rest
3093> pref (_:rest) = 1 + pref rest
3094>
3095> decode walk acc ('0':rest) = decode (walk + 1) (acc * 2) rest
3096> decode walk acc ('1':rest) = decode (walk + 1) (acc * 2 + 1) rest
3097> decode walk acc _ = walk + acc
3098>
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]3099</pre>
3100</div>
3101<p>
3102Now, as expected, printing &lt;pref test&gt; gives <tt>40</tt>.</p>
3103<p>
3104We can <i>quickCheck</i> this with following property:</p>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]3105
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]3106<div class="doc_code">
3107<pre>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]3108> testcase = dist 2000 []
3109> testcaseLength = length testcase
3110>
3111> identityProp n = n > 0 && n <= testcaseLength ==> length arr == pref arr
3112> where arr = takeLast n testcase
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]3113>
3114</pre>
3115</div>
3116<p>
3117As expected &lt;quickCheck identityProp&gt; gives:</p>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]3118
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]3119<pre>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]3120*Main> quickCheck identityProp
3121OK, passed 100 tests.
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]3122</pre>
3123<p>
3124Let's be a bit more exhaustive:</p>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]3125
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]3126<div class="doc_code">
3127<pre>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]3128>
3129> deepCheck p = check (defaultConfig { configMaxTest = 500 }) p
3130>
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]3131</pre>
3132</div>
3133<p>
3134And here is the result of &lt;deepCheck identityProp&gt;:</p>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]3135
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]3136<pre>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]3137*Main> deepCheck identityProp
3138OK, passed 500 tests.
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]3139</pre>
3140
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]3141</div>
3142
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]3143<!-- ______________________________________________________________________ -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]3144<h4>
Gabor Greiffd095b62009-01-05 16:05:32 +0000[diff] [blame]3145 <a name="Tagging">Tagging considerations</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]3146</h4>
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]3147
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]3148<div>
3149
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]3150<p>
3151To maintain the invariant that the 2 LSBits of each <tt>Use**</tt> in <tt>Use</tt>
3152never change after being set up, setters of <tt>Use::Prev</tt> must re-tag the
3153new <tt>Use**</tt> on every modification. Accordingly getters must strip the
3154tag bits.</p>
3155<p>
Gabor Greifd41720a2008-06-25 00:10:22 +0000[diff] [blame]3156For layout b) instead of the <tt>User</tt> we find a pointer (<tt>User*</tt> with LSBit set).
3157Following this pointer brings us to the <tt>User</tt>. A portable trick ensures
3158that the first bytes of <tt>User</tt> (if interpreted as a pointer) never has
Gabor Greiffd095b62009-01-05 16:05:32 +0000[diff] [blame]3159the LSBit set. (Portability is relying on the fact that all known compilers place the
3160<tt>vptr</tt> in the first word of the instances.)</p>
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]3161
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]3162</div>
3163
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]3164</div>
3165
3166</div>
3167
3168<!-- *********************************************************************** -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]3169<h2>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3170 <a name="coreclasses">The Core LLVM Class Hierarchy Reference </a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]3171</h2>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3172<!-- *********************************************************************** -->
3173
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]3174<div>
Reid Spencer303c4b42007-01-12 17:26:25 +0000[diff] [blame]3175<p><tt>#include "<a href="/doxygen/Type_8h-source.html">llvm/Type.h</a>"</tt>
3176<br>doxygen info: <a href="/doxygen/classllvm_1_1Type.html">Type Class</a></p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3177
3178<p>The Core LLVM classes are the primary means of representing the program
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3179being inspected or transformed. The core LLVM classes are defined in
3180header files in the <tt>include/llvm/</tt> directory, and implemented in
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3181the <tt>lib/VMCore</tt> directory.</p>
3182
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3183<!-- ======================================================================= -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]3184<h3>
Reid Spencer303c4b42007-01-12 17:26:25 +0000[diff] [blame]3185 <a name="Type">The <tt>Type</tt> class and Derived Types</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]3186</h3>
Reid Spencer303c4b42007-01-12 17:26:25 +0000[diff] [blame]3187
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]3188<div>
Reid Spencer303c4b42007-01-12 17:26:25 +0000[diff] [blame]3189
3190 <p><tt>Type</tt> is a superclass of all type classes. Every <tt>Value</tt> has
3191 a <tt>Type</tt>. <tt>Type</tt> cannot be instantiated directly but only
3192 through its subclasses. Certain primitive types (<tt>VoidType</tt>,
3193 <tt>LabelType</tt>, <tt>FloatType</tt> and <tt>DoubleType</tt>) have hidden
3194 subclasses. They are hidden because they offer no useful functionality beyond
3195 what the <tt>Type</tt> class offers except to distinguish themselves from
3196 other subclasses of <tt>Type</tt>.</p>
3197 <p>All other types are subclasses of <tt>DerivedType</tt>. Types can be
3198 named, but this is not a requirement. There exists exactly
3199 one instance of a given shape at any one time. This allows type equality to
3200 be performed with address equality of the Type Instance. That is, given two
3201 <tt>Type*</tt> values, the types are identical if the pointers are identical.
3202 </p>
Reid Spencer303c4b42007-01-12 17:26:25 +0000[diff] [blame]3203
3204<!-- _______________________________________________________________________ -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]3205<h4>
Gabor Greiffd095b62009-01-05 16:05:32 +0000[diff] [blame]3206 <a name="m_Type">Important Public Methods</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]3207</h4>
Reid Spencer303c4b42007-01-12 17:26:25 +0000[diff] [blame]3208
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]3209<div>
Reid Spencer303c4b42007-01-12 17:26:25 +0000[diff] [blame]3210
3211<ul>
Duncan Sandsb0bc6c32010-02-15 16:12:20 +0000[diff] [blame]3212 <li><tt>bool isIntegerTy() const</tt>: Returns true for any integer type.</li>
Reid Spencer303c4b42007-01-12 17:26:25 +0000[diff] [blame]3213
Duncan Sandsb0bc6c32010-02-15 16:12:20 +0000[diff] [blame]3214 <li><tt>bool isFloatingPointTy()</tt>: Return true if this is one of the five
Reid Spencer303c4b42007-01-12 17:26:25 +0000[diff] [blame]3215 floating point types.</li>
3216
Reid Spencer303c4b42007-01-12 17:26:25 +0000[diff] [blame]3217 <li><tt>bool isSized()</tt>: Return true if the type has known size. Things
3218 that don't have a size are abstract types, labels and void.</li>
3219
3220</ul>
3221</div>
3222
3223<!-- _______________________________________________________________________ -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]3224<h4>
Gabor Greiffd095b62009-01-05 16:05:32 +0000[diff] [blame]3225 <a name="derivedtypes">Important Derived Types</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]3226</h4>
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]3227<div>
Reid Spencer303c4b42007-01-12 17:26:25 +0000[diff] [blame]3228<dl>
3229 <dt><tt>IntegerType</tt></dt>
3230 <dd>Subclass of DerivedType that represents integer types of any bit width.
3231 Any bit width between <tt>IntegerType::MIN_INT_BITS</tt> (1) and
3232 <tt>IntegerType::MAX_INT_BITS</tt> (~8 million) can be represented.
3233 <ul>
3234 <li><tt>static const IntegerType* get(unsigned NumBits)</tt>: get an integer
3235 type of a specific bit width.</li>
3236 <li><tt>unsigned getBitWidth() const</tt>: Get the bit width of an integer
3237 type.</li>
3238 </ul>
3239 </dd>
3240 <dt><tt>SequentialType</tt></dt>
Tobias Grosserd475c102011-07-12 11:37:02 +0000[diff] [blame]3241 <dd>This is subclassed by ArrayType, PointerType and VectorType.
Reid Spencer303c4b42007-01-12 17:26:25 +0000[diff] [blame]3242 <ul>
3243 <li><tt>const Type * getElementType() const</tt>: Returns the type of each
3244 of the elements in the sequential type. </li>
3245 </ul>
3246 </dd>
3247 <dt><tt>ArrayType</tt></dt>
3248 <dd>This is a subclass of SequentialType and defines the interface for array
3249 types.
3250 <ul>
3251 <li><tt>unsigned getNumElements() const</tt>: Returns the number of
3252 elements in the array. </li>
3253 </ul>
3254 </dd>
3255 <dt><tt>PointerType</tt></dt>
Chris Lattner302da1e2007-02-03 03:05:57 +0000[diff] [blame]3256 <dd>Subclass of SequentialType for pointer types.</dd>
Reid Spencer9d6565a2007-02-15 02:26:10 +0000[diff] [blame]3257 <dt><tt>VectorType</tt></dt>
Reid Spencer485bad12007-02-15 03:07:05 +0000[diff] [blame]3258 <dd>Subclass of SequentialType for vector types. A
3259 vector type is similar to an ArrayType but is distinguished because it is
Benjamin Kramer8040cd32009-10-12 14:46:08 +0000[diff] [blame]3260 a first class type whereas ArrayType is not. Vector types are used for
Reid Spencer303c4b42007-01-12 17:26:25 +0000[diff] [blame]3261 vector operations and are usually small vectors of of an integer or floating
3262 point type.</dd>
3263 <dt><tt>StructType</tt></dt>
3264 <dd>Subclass of DerivedTypes for struct types.</dd>
Duncan Sands8036ca42007-03-30 12:22:09 +0000[diff] [blame]3265 <dt><tt><a name="FunctionType">FunctionType</a></tt></dt>
Reid Spencer303c4b42007-01-12 17:26:25 +0000[diff] [blame]3266 <dd>Subclass of DerivedTypes for function types.
3267 <ul>
Dan Gohman4bb31bf2010-03-30 20:04:57 +0000[diff] [blame]3268 <li><tt>bool isVarArg() const</tt>: Returns true if it's a vararg
Reid Spencer303c4b42007-01-12 17:26:25 +0000[diff] [blame]3269 function</li>
3270 <li><tt> const Type * getReturnType() const</tt>: Returns the
3271 return type of the function.</li>
3272 <li><tt>const Type * getParamType (unsigned i)</tt>: Returns
3273 the type of the ith parameter.</li>
3274 <li><tt> const unsigned getNumParams() const</tt>: Returns the
3275 number of formal parameters.</li>
3276 </ul>
3277 </dd>
Reid Spencer303c4b42007-01-12 17:26:25 +0000[diff] [blame]3278</dl>
3279</div>
3280
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]3281</div>
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]3282
3283<!-- ======================================================================= -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]3284<h3>
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]3285 <a name="Module">The <tt>Module</tt> class</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]3286</h3>
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]3287
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]3288<div>
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]3289
3290<p><tt>#include "<a
3291href="/doxygen/Module_8h-source.html">llvm/Module.h</a>"</tt><br> doxygen info:
3292<a href="/doxygen/classllvm_1_1Module.html">Module Class</a></p>
3293
3294<p>The <tt>Module</tt> class represents the top level structure present in LLVM
3295programs. An LLVM module is effectively either a translation unit of the
3296original program or a combination of several translation units merged by the
3297linker. The <tt>Module</tt> class keeps track of a list of <a
3298href="#Function"><tt>Function</tt></a>s, a list of <a
3299href="#GlobalVariable"><tt>GlobalVariable</tt></a>s, and a <a
3300href="#SymbolTable"><tt>SymbolTable</tt></a>. Additionally, it contains a few
3301helpful member functions that try to make common operations easy.</p>
3302
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]3303<!-- _______________________________________________________________________ -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]3304<h4>
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]3305 <a name="m_Module">Important Public Members of the <tt>Module</tt> class</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]3306</h4>
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]3307
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]3308<div>
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]3309
3310<ul>
NAKAMURA Takumi9c55f592012-03-27 11:25:16 +0000[diff] [blame]3311 <li><tt>Module::Module(std::string name = "")</tt>
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]3312
NAKAMURA Takumi9c55f592012-03-27 11:25:16 +0000[diff] [blame]3313 <p>Constructing a <a href="#Module">Module</a> is easy. You can optionally
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]3314provide a name for it (probably based on the name of the translation unit).</p>
NAKAMURA Takumi9c55f592012-03-27 11:25:16 +0000[diff] [blame]3315 </li>
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]3316
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]3317 <li><tt>Module::iterator</tt> - Typedef for function list iterator<br>
3318 <tt>Module::const_iterator</tt> - Typedef for const_iterator.<br>
3319
3320 <tt>begin()</tt>, <tt>end()</tt>
3321 <tt>size()</tt>, <tt>empty()</tt>
3322
3323 <p>These are forwarding methods that make it easy to access the contents of
3324 a <tt>Module</tt> object's <a href="#Function"><tt>Function</tt></a>
3325 list.</p></li>
3326
3327 <li><tt>Module::FunctionListType &amp;getFunctionList()</tt>
3328
3329 <p> Returns the list of <a href="#Function"><tt>Function</tt></a>s. This is
3330 necessary to use when you need to update the list or perform a complex
3331 action that doesn't have a forwarding method.</p>
3332
3333 <p><!-- Global Variable --></p></li>
3334</ul>
3335
3336<hr>
3337
3338<ul>
3339 <li><tt>Module::global_iterator</tt> - Typedef for global variable list iterator<br>
3340
3341 <tt>Module::const_global_iterator</tt> - Typedef for const_iterator.<br>
3342
3343 <tt>global_begin()</tt>, <tt>global_end()</tt>
3344 <tt>global_size()</tt>, <tt>global_empty()</tt>
3345
3346 <p> These are forwarding methods that make it easy to access the contents of
3347 a <tt>Module</tt> object's <a
3348 href="#GlobalVariable"><tt>GlobalVariable</tt></a> list.</p></li>
3349
3350 <li><tt>Module::GlobalListType &amp;getGlobalList()</tt>
3351
3352 <p>Returns the list of <a
3353 href="#GlobalVariable"><tt>GlobalVariable</tt></a>s. This is necessary to
3354 use when you need to update the list or perform a complex action that
3355 doesn't have a forwarding method.</p>
3356
3357 <p><!-- Symbol table stuff --> </p></li>
3358</ul>
3359
3360<hr>
3361
3362<ul>
3363 <li><tt><a href="#SymbolTable">SymbolTable</a> *getSymbolTable()</tt>
3364
3365 <p>Return a reference to the <a href="#SymbolTable"><tt>SymbolTable</tt></a>
3366 for this <tt>Module</tt>.</p>
3367
3368 <p><!-- Convenience methods --></p></li>
3369</ul>
3370
3371<hr>
3372
3373<ul>
3374 <li><tt><a href="#Function">Function</a> *getFunction(const std::string
3375 &amp;Name, const <a href="#FunctionType">FunctionType</a> *Ty)</tt>
3376
3377 <p>Look up the specified function in the <tt>Module</tt> <a
3378 href="#SymbolTable"><tt>SymbolTable</tt></a>. If it does not exist, return
3379 <tt>null</tt>.</p></li>
3380
3381 <li><tt><a href="#Function">Function</a> *getOrInsertFunction(const
3382 std::string &amp;Name, const <a href="#FunctionType">FunctionType</a> *T)</tt>
3383
3384 <p>Look up the specified function in the <tt>Module</tt> <a
3385 href="#SymbolTable"><tt>SymbolTable</tt></a>. If it does not exist, add an
3386 external declaration for the function and return it.</p></li>
3387
3388 <li><tt>std::string getTypeName(const <a href="#Type">Type</a> *Ty)</tt>
3389
3390 <p>If there is at least one entry in the <a
3391 href="#SymbolTable"><tt>SymbolTable</tt></a> for the specified <a
3392 href="#Type"><tt>Type</tt></a>, return it. Otherwise return the empty
3393 string.</p></li>
3394
3395 <li><tt>bool addTypeName(const std::string &amp;Name, const <a
3396 href="#Type">Type</a> *Ty)</tt>
3397
3398 <p>Insert an entry in the <a href="#SymbolTable"><tt>SymbolTable</tt></a>
3399 mapping <tt>Name</tt> to <tt>Ty</tt>. If there is already an entry for this
3400 name, true is returned and the <a
3401 href="#SymbolTable"><tt>SymbolTable</tt></a> is not modified.</p></li>
3402</ul>
3403
3404</div>
3405
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]3406</div>
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]3407
Reid Spencer303c4b42007-01-12 17:26:25 +0000[diff] [blame]3408<!-- ======================================================================= -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]3409<h3>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3410 <a name="Value">The <tt>Value</tt> class</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]3411</h3>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3412
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]3413<div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3414
3415<p><tt>#include "<a href="/doxygen/Value_8h-source.html">llvm/Value.h</a>"</tt>
3416<br>
Chris Lattner00815172007-01-04 22:01:45 +0000[diff] [blame]3417doxygen info: <a href="/doxygen/classllvm_1_1Value.html">Value Class</a></p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3418
3419<p>The <tt>Value</tt> class is the most important class in the LLVM Source
3420base. It represents a typed value that may be used (among other things) as an
3421operand to an instruction. There are many different types of <tt>Value</tt>s,
3422such as <a href="#Constant"><tt>Constant</tt></a>s,<a
3423href="#Argument"><tt>Argument</tt></a>s. Even <a
3424href="#Instruction"><tt>Instruction</tt></a>s and <a
3425href="#Function"><tt>Function</tt></a>s are <tt>Value</tt>s.</p>
3426
3427<p>A particular <tt>Value</tt> may be used many times in the LLVM representation
3428for a program. For example, an incoming argument to a function (represented
3429with an instance of the <a href="#Argument">Argument</a> class) is "used" by
3430every instruction in the function that references the argument. To keep track
3431of this relationship, the <tt>Value</tt> class keeps a list of all of the <a
3432href="#User"><tt>User</tt></a>s that is using it (the <a
3433href="#User"><tt>User</tt></a> class is a base class for all nodes in the LLVM
3434graph that can refer to <tt>Value</tt>s). This use list is how LLVM represents
3435def-use information in the program, and is accessible through the <tt>use_</tt>*
3436methods, shown below.</p>
3437
3438<p>Because LLVM is a typed representation, every LLVM <tt>Value</tt> is typed,
3439and this <a href="#Type">Type</a> is available through the <tt>getType()</tt>
3440method. In addition, all LLVM values can be named. The "name" of the
3441<tt>Value</tt> is a symbolic string printed in the LLVM code:</p>
3442
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]3443<div class="doc_code">
3444<pre>
Reid Spencer06565dc2007-01-12 17:11:23 +0000[diff] [blame]3445%<b>foo</b> = add i32 1, 2
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]3446</pre>
3447</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3448
Duncan Sands8036ca42007-03-30 12:22:09 +0000[diff] [blame]3449<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]3450that the name of any value may be missing (an empty string), so names should
3451<b>ONLY</b> be used for debugging (making the source code easier to read,
3452debugging printouts), they should not be used to keep track of values or map
3453between them. For this purpose, use a <tt>std::map</tt> of pointers to the
3454<tt>Value</tt> itself instead.</p>
3455
3456<p>One important aspect of LLVM is that there is no distinction between an SSA
3457variable and the operation that produces it. Because of this, any reference to
3458the value produced by an instruction (or the value available as an incoming
Chris Lattnerd5fc4fc2004-03-18 14:58:55 +0000[diff] [blame]3459argument, for example) is represented as a direct pointer to the instance of
3460the class that
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3461represents this value. Although this may take some getting used to, it
3462simplifies the representation and makes it easier to manipulate.</p>
3463
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3464<!-- _______________________________________________________________________ -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]3465<h4>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3466 <a name="m_Value">Important Public Members of the <tt>Value</tt> class</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]3467</h4>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3468
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]3469<div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3470
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3471<ul>
3472 <li><tt>Value::use_iterator</tt> - Typedef for iterator over the
3473use-list<br>
Gabor Greifbbbf9a22010-03-26 19:59:25 +0000[diff] [blame]3474 <tt>Value::const_use_iterator</tt> - Typedef for const_iterator over
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3475the use-list<br>
3476 <tt>unsigned use_size()</tt> - Returns the number of users of the
3477value.<br>
Chris Lattner9355b472002-09-06 02:50:58 +0000[diff] [blame]3478 <tt>bool use_empty()</tt> - Returns true if there are no users.<br>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3479 <tt>use_iterator use_begin()</tt> - Get an iterator to the start of
3480the use-list.<br>
3481 <tt>use_iterator use_end()</tt> - Get an iterator to the end of the
3482use-list.<br>
3483 <tt><a href="#User">User</a> *use_back()</tt> - Returns the last
3484element in the list.
3485 <p> These methods are the interface to access the def-use
3486information in LLVM. As with all other iterators in LLVM, the naming
3487conventions follow the conventions defined by the <a href="#stl">STL</a>.</p>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3488 </li>
3489 <li><tt><a href="#Type">Type</a> *getType() const</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3490 <p>This method returns the Type of the Value.</p>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3491 </li>
3492 <li><tt>bool hasName() const</tt><br>
Chris Lattner9355b472002-09-06 02:50:58 +0000[diff] [blame]3493 <tt>std::string getName() const</tt><br>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3494 <tt>void setName(const std::string &amp;Name)</tt>
3495 <p> This family of methods is used to access and assign a name to a <tt>Value</tt>,
3496be aware of the <a href="#nameWarning">precaution above</a>.</p>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3497 </li>
3498 <li><tt>void replaceAllUsesWith(Value *V)</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3499
3500 <p>This method traverses the use list of a <tt>Value</tt> changing all <a
3501 href="#User"><tt>User</tt>s</a> of the current value to refer to
3502 "<tt>V</tt>" instead. For example, if you detect that an instruction always
3503 produces a constant value (for example through constant folding), you can
3504 replace all uses of the instruction with the constant like this:</p>
3505
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]3506<div class="doc_code">
3507<pre>
3508Inst-&gt;replaceAllUsesWith(ConstVal);
3509</pre>
3510</div>
3511
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3512</ul>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3513
3514</div>
3515
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]3516</div>
3517
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3518<!-- ======================================================================= -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]3519<h3>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3520 <a name="User">The <tt>User</tt> class</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]3521</h3>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3522
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]3523<div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3524
3525<p>
3526<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]3527doxygen info: <a href="/doxygen/classllvm_1_1User.html">User Class</a><br>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3528Superclass: <a href="#Value"><tt>Value</tt></a></p>
3529
3530<p>The <tt>User</tt> class is the common base class of all LLVM nodes that may
3531refer to <a href="#Value"><tt>Value</tt></a>s. It exposes a list of "Operands"
3532that are all of the <a href="#Value"><tt>Value</tt></a>s that the User is
3533referring to. The <tt>User</tt> class itself is a subclass of
3534<tt>Value</tt>.</p>
3535
3536<p>The operands of a <tt>User</tt> point directly to the LLVM <a
3537href="#Value"><tt>Value</tt></a> that it refers to. Because LLVM uses Static
3538Single Assignment (SSA) form, there can only be one definition referred to,
3539allowing this direct connection. This connection provides the use-def
3540information in LLVM.</p>
3541
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3542<!-- _______________________________________________________________________ -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]3543<h4>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3544 <a name="m_User">Important Public Members of the <tt>User</tt> class</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]3545</h4>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3546
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]3547<div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3548
3549<p>The <tt>User</tt> class exposes the operand list in two ways: through
3550an index access interface and through an iterator based interface.</p>
3551
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3552<ul>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3553 <li><tt>Value *getOperand(unsigned i)</tt><br>
3554 <tt>unsigned getNumOperands()</tt>
3555 <p> These two methods expose the operands of the <tt>User</tt> in a
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3556convenient form for direct access.</p></li>
3557
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3558 <li><tt>User::op_iterator</tt> - Typedef for iterator over the operand
3559list<br>
Chris Lattner58360822005-01-17 00:12:04 +0000[diff] [blame]3560 <tt>op_iterator op_begin()</tt> - Get an iterator to the start of
3561the operand list.<br>
3562 <tt>op_iterator op_end()</tt> - Get an iterator to the end of the
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3563operand list.
3564 <p> Together, these methods make up the iterator based interface to
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3565the operands of a <tt>User</tt>.</p></li>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3566</ul>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3567
3568</div>
3569
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]3570</div>
3571
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3572<!-- ======================================================================= -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]3573<h3>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3574 <a name="Instruction">The <tt>Instruction</tt> class</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]3575</h3>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3576
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]3577<div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3578
3579<p><tt>#include "</tt><tt><a
3580href="/doxygen/Instruction_8h-source.html">llvm/Instruction.h</a>"</tt><br>
Misha Brukman31ca1de2004-06-03 23:35:54 +0000[diff] [blame]3581doxygen info: <a href="/doxygen/classllvm_1_1Instruction.html">Instruction Class</a><br>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3582Superclasses: <a href="#User"><tt>User</tt></a>, <a
3583href="#Value"><tt>Value</tt></a></p>
3584
3585<p>The <tt>Instruction</tt> class is the common base class for all LLVM
3586instructions. It provides only a few methods, but is a very commonly used
3587class. The primary data tracked by the <tt>Instruction</tt> class itself is the
3588opcode (instruction type) and the parent <a
3589href="#BasicBlock"><tt>BasicBlock</tt></a> the <tt>Instruction</tt> is embedded
3590into. To represent a specific type of instruction, one of many subclasses of
3591<tt>Instruction</tt> are used.</p>
3592
3593<p> Because the <tt>Instruction</tt> class subclasses the <a
3594href="#User"><tt>User</tt></a> class, its operands can be accessed in the same
3595way as for other <a href="#User"><tt>User</tt></a>s (with the
3596<tt>getOperand()</tt>/<tt>getNumOperands()</tt> and
3597<tt>op_begin()</tt>/<tt>op_end()</tt> methods).</p> <p> An important file for
3598the <tt>Instruction</tt> class is the <tt>llvm/Instruction.def</tt> file. This
3599file contains some meta-data about the various different types of instructions
3600in LLVM. It describes the enum values that are used as opcodes (for example
Reid Spencerc92d25d2006-12-19 19:47:19 +0000[diff] [blame]3601<tt>Instruction::Add</tt> and <tt>Instruction::ICmp</tt>), as well as the
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3602concrete sub-classes of <tt>Instruction</tt> that implement the instruction (for
3603example <tt><a href="#BinaryOperator">BinaryOperator</a></tt> and <tt><a
Reid Spencerc92d25d2006-12-19 19:47:19 +0000[diff] [blame]3604href="#CmpInst">CmpInst</a></tt>). Unfortunately, the use of macros in
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3605this file confuses doxygen, so these enum values don't show up correctly in the
Misha Brukman31ca1de2004-06-03 23:35:54 +0000[diff] [blame]3606<a href="/doxygen/classllvm_1_1Instruction.html">doxygen output</a>.</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3607
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3608<!-- _______________________________________________________________________ -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]3609<h4>
3610 <a name="s_Instruction">
3611 Important Subclasses of the <tt>Instruction</tt> class
3612 </a>
3613</h4>
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]3614<div>
Reid Spencerc92d25d2006-12-19 19:47:19 +0000[diff] [blame]3615 <ul>
3616 <li><tt><a name="BinaryOperator">BinaryOperator</a></tt>
3617 <p>This subclasses represents all two operand instructions whose operands
3618 must be the same type, except for the comparison instructions.</p></li>
3619 <li><tt><a name="CastInst">CastInst</a></tt>
3620 <p>This subclass is the parent of the 12 casting instructions. It provides
3621 common operations on cast instructions.</p>
3622 <li><tt><a name="CmpInst">CmpInst</a></tt>
3623 <p>This subclass respresents the two comparison instructions,
3624 <a href="LangRef.html#i_icmp">ICmpInst</a> (integer opreands), and
3625 <a href="LangRef.html#i_fcmp">FCmpInst</a> (floating point operands).</p>
3626 <li><tt><a name="TerminatorInst">TerminatorInst</a></tt>
3627 <p>This subclass is the parent of all terminator instructions (those which
3628 can terminate a block).</p>
3629 </ul>
3630 </div>
3631
3632<!-- _______________________________________________________________________ -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]3633<h4>
3634 <a name="m_Instruction">
3635 Important Public Members of the <tt>Instruction</tt> class
3636 </a>
3637</h4>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3638
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]3639<div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3640
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3641<ul>
3642 <li><tt><a href="#BasicBlock">BasicBlock</a> *getParent()</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3643 <p>Returns the <a href="#BasicBlock"><tt>BasicBlock</tt></a> that
3644this <tt>Instruction</tt> is embedded into.</p></li>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3645 <li><tt>bool mayWriteToMemory()</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3646 <p>Returns true if the instruction writes to memory, i.e. it is a
3647 <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]3648 <li><tt>unsigned getOpcode()</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3649 <p>Returns the opcode for the <tt>Instruction</tt>.</p></li>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3650 <li><tt><a href="#Instruction">Instruction</a> *clone() const</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3651 <p>Returns another instance of the specified instruction, identical
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3652in all ways to the original except that the instruction has no parent
3653(ie it's not embedded into a <a href="#BasicBlock"><tt>BasicBlock</tt></a>),
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3654and it has no name</p></li>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3655</ul>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3656
3657</div>
3658
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]3659</div>
3660
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3661<!-- ======================================================================= -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]3662<h3>
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]3663 <a name="Constant">The <tt>Constant</tt> class and subclasses</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]3664</h3>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3665
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]3666<div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3667
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]3668<p>Constant represents a base class for different types of constants. It
3669is subclassed by ConstantInt, ConstantArray, etc. for representing
3670the various types of Constants. <a href="#GlobalValue">GlobalValue</a> is also
3671a subclass, which represents the address of a global variable or function.
3672</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3673
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3674<!-- _______________________________________________________________________ -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]3675<h4>Important Subclasses of Constant</h4>
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]3676<div>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3677<ul>
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]3678 <li>ConstantInt : This subclass of Constant represents an integer constant of
3679 any width.
3680 <ul>
Reid Spencer97b4ee32007-03-01 21:05:33 +0000[diff] [blame]3681 <li><tt>const APInt&amp; getValue() const</tt>: Returns the underlying
3682 value of this constant, an APInt value.</li>
3683 <li><tt>int64_t getSExtValue() const</tt>: Converts the underlying APInt
3684 value to an int64_t via sign extension. If the value (not the bit width)
3685 of the APInt is too large to fit in an int64_t, an assertion will result.
3686 For this reason, use of this method is discouraged.</li>
3687 <li><tt>uint64_t getZExtValue() const</tt>: Converts the underlying APInt
3688 value to a uint64_t via zero extension. IF the value (not the bit width)
3689 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]3690 For this reason, use of this method is discouraged.</li>
Reid Spencer97b4ee32007-03-01 21:05:33 +0000[diff] [blame]3691 <li><tt>static ConstantInt* get(const APInt&amp; Val)</tt>: Returns the
3692 ConstantInt object that represents the value provided by <tt>Val</tt>.
3693 The type is implied as the IntegerType that corresponds to the bit width
3694 of <tt>Val</tt>.</li>
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]3695 <li><tt>static ConstantInt* get(const Type *Ty, uint64_t Val)</tt>:
3696 Returns the ConstantInt object that represents the value provided by
3697 <tt>Val</tt> for integer type <tt>Ty</tt>.</li>
3698 </ul>
3699 </li>
3700 <li>ConstantFP : This class represents a floating point constant.
3701 <ul>
3702 <li><tt>double getValue() const</tt>: Returns the underlying value of
3703 this constant. </li>
3704 </ul>
3705 </li>
3706 <li>ConstantArray : This represents a constant array.
3707 <ul>
3708 <li><tt>const std::vector&lt;Use&gt; &amp;getValues() const</tt>: Returns
3709 a vector of component constants that makeup this array. </li>
3710 </ul>
3711 </li>
3712 <li>ConstantStruct : This represents a constant struct.
3713 <ul>
3714 <li><tt>const std::vector&lt;Use&gt; &amp;getValues() const</tt>: Returns
3715 a vector of component constants that makeup this array. </li>
3716 </ul>
3717 </li>
3718 <li>GlobalValue : This represents either a global variable or a function. In
3719 either case, the value is a constant fixed address (after linking).
3720 </li>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3721</ul>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3722</div>
3723
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]3724</div>
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]3725
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3726<!-- ======================================================================= -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]3727<h3>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3728 <a name="GlobalValue">The <tt>GlobalValue</tt> class</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]3729</h3>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3730
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]3731<div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3732
3733<p><tt>#include "<a
3734href="/doxygen/GlobalValue_8h-source.html">llvm/GlobalValue.h</a>"</tt><br>
Misha Brukman384047f2004-06-03 23:29:12 +0000[diff] [blame]3735doxygen info: <a href="/doxygen/classllvm_1_1GlobalValue.html">GlobalValue
3736Class</a><br>
Reid Spencerbe5e85e2006-04-14 14:11:48 +0000[diff] [blame]3737Superclasses: <a href="#Constant"><tt>Constant</tt></a>,
3738<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]3739
3740<p>Global values (<a href="#GlobalVariable"><tt>GlobalVariable</tt></a>s or <a
3741href="#Function"><tt>Function</tt></a>s) are the only LLVM values that are
3742visible in the bodies of all <a href="#Function"><tt>Function</tt></a>s.
3743Because they are visible at global scope, they are also subject to linking with
3744other globals defined in different translation units. To control the linking
3745process, <tt>GlobalValue</tt>s know their linkage rules. Specifically,
3746<tt>GlobalValue</tt>s know whether they have internal or external linkage, as
Reid Spencer8b2da7a2004-07-18 13:10:31 +0000[diff] [blame]3747defined by the <tt>LinkageTypes</tt> enumeration.</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3748
3749<p>If a <tt>GlobalValue</tt> has internal linkage (equivalent to being
3750<tt>static</tt> in C), it is not visible to code outside the current translation
3751unit, and does not participate in linking. If it has external linkage, it is
3752visible to external code, and does participate in linking. In addition to
3753linkage information, <tt>GlobalValue</tt>s keep track of which <a
3754href="#Module"><tt>Module</tt></a> they are currently part of.</p>
3755
3756<p>Because <tt>GlobalValue</tt>s are memory objects, they are always referred to
3757by their <b>address</b>. As such, the <a href="#Type"><tt>Type</tt></a> of a
3758global is always a pointer to its contents. It is important to remember this
3759when using the <tt>GetElementPtrInst</tt> instruction because this pointer must
3760be dereferenced first. For example, if you have a <tt>GlobalVariable</tt> (a
3761subclass 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]3762i32]</tt>, then the <tt>GlobalVariable</tt> is a pointer to that array. Although
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3763the address of the first element of this array and the value of the
3764<tt>GlobalVariable</tt> are the same, they have different types. The
Reid Spencer06565dc2007-01-12 17:11:23 +0000[diff] [blame]3765<tt>GlobalVariable</tt>'s type is <tt>[24 x i32]</tt>. The first element's type
3766is <tt>i32.</tt> Because of this, accessing a global value requires you to
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3767dereference the pointer with <tt>GetElementPtrInst</tt> first, then its elements
3768can be accessed. This is explained in the <a href="LangRef.html#globalvars">LLVM
3769Language Reference Manual</a>.</p>
3770
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3771<!-- _______________________________________________________________________ -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]3772<h4>
3773 <a name="m_GlobalValue">
3774 Important Public Members of the <tt>GlobalValue</tt> class
3775 </a>
3776</h4>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3777
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]3778<div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3779
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3780<ul>
3781 <li><tt>bool hasInternalLinkage() const</tt><br>
Chris Lattner9355b472002-09-06 02:50:58 +0000[diff] [blame]3782 <tt>bool hasExternalLinkage() const</tt><br>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3783 <tt>void setInternalLinkage(bool HasInternalLinkage)</tt>
3784 <p> These methods manipulate the linkage characteristics of the <tt>GlobalValue</tt>.</p>
3785 <p> </p>
3786 </li>
3787 <li><tt><a href="#Module">Module</a> *getParent()</tt>
3788 <p> This returns the <a href="#Module"><tt>Module</tt></a> that the
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3789GlobalValue is currently embedded into.</p></li>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3790</ul>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3791
3792</div>
3793
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]3794</div>
3795
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3796<!-- ======================================================================= -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]3797<h3>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3798 <a name="Function">The <tt>Function</tt> class</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]3799</h3>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3800
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]3801<div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3802
3803<p><tt>#include "<a
3804href="/doxygen/Function_8h-source.html">llvm/Function.h</a>"</tt><br> doxygen
Misha Brukman31ca1de2004-06-03 23:35:54 +0000[diff] [blame]3805info: <a href="/doxygen/classllvm_1_1Function.html">Function Class</a><br>
Reid Spencerbe5e85e2006-04-14 14:11:48 +0000[diff] [blame]3806Superclasses: <a href="#GlobalValue"><tt>GlobalValue</tt></a>,
3807<a href="#Constant"><tt>Constant</tt></a>,
3808<a href="#User"><tt>User</tt></a>,
3809<a href="#Value"><tt>Value</tt></a></p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3810
3811<p>The <tt>Function</tt> class represents a single procedure in LLVM. It is
Torok Edwin87469292009-10-12 13:37:29 +0000[diff] [blame]3812actually one of the more complex classes in the LLVM hierarchy because it must
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3813keep track of a large amount of data. The <tt>Function</tt> class keeps track
Reid Spencerbe5e85e2006-04-14 14:11:48 +0000[diff] [blame]3814of a list of <a href="#BasicBlock"><tt>BasicBlock</tt></a>s, a list of formal
3815<a href="#Argument"><tt>Argument</tt></a>s, and a
3816<a href="#SymbolTable"><tt>SymbolTable</tt></a>.</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3817
3818<p>The list of <a href="#BasicBlock"><tt>BasicBlock</tt></a>s is the most
3819commonly used part of <tt>Function</tt> objects. The list imposes an implicit
3820ordering of the blocks in the function, which indicate how the code will be
Benjamin Kramer8040cd32009-10-12 14:46:08 +0000[diff] [blame]3821laid out by the backend. Additionally, the first <a
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3822href="#BasicBlock"><tt>BasicBlock</tt></a> is the implicit entry node for the
3823<tt>Function</tt>. It is not legal in LLVM to explicitly branch to this initial
3824block. There are no implicit exit nodes, and in fact there may be multiple exit
3825nodes from a single <tt>Function</tt>. If the <a
3826href="#BasicBlock"><tt>BasicBlock</tt></a> list is empty, this indicates that
3827the <tt>Function</tt> is actually a function declaration: the actual body of the
3828function hasn't been linked in yet.</p>
3829
3830<p>In addition to a list of <a href="#BasicBlock"><tt>BasicBlock</tt></a>s, the
3831<tt>Function</tt> class also keeps track of the list of formal <a
3832href="#Argument"><tt>Argument</tt></a>s that the function receives. This
3833container manages the lifetime of the <a href="#Argument"><tt>Argument</tt></a>
3834nodes, just like the <a href="#BasicBlock"><tt>BasicBlock</tt></a> list does for
3835the <a href="#BasicBlock"><tt>BasicBlock</tt></a>s.</p>
3836
3837<p>The <a href="#SymbolTable"><tt>SymbolTable</tt></a> is a very rarely used
3838LLVM feature that is only used when you have to look up a value by name. Aside
3839from that, the <a href="#SymbolTable"><tt>SymbolTable</tt></a> is used
3840internally to make sure that there are not conflicts between the names of <a
3841href="#Instruction"><tt>Instruction</tt></a>s, <a
3842href="#BasicBlock"><tt>BasicBlock</tt></a>s, or <a
3843href="#Argument"><tt>Argument</tt></a>s in the function body.</p>
3844
Reid Spencer8b2da7a2004-07-18 13:10:31 +0000[diff] [blame]3845<p>Note that <tt>Function</tt> is a <a href="#GlobalValue">GlobalValue</a>
3846and therefore also a <a href="#Constant">Constant</a>. The value of the function
3847is its address (after linking) which is guaranteed to be constant.</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3848
3849<!-- _______________________________________________________________________ -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]3850<h4>
3851 <a name="m_Function">
3852 Important Public Members of the <tt>Function</tt> class
3853 </a>
3854</h4>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3855
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]3856<div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3857
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3858<ul>
3859 <li><tt>Function(const </tt><tt><a href="#FunctionType">FunctionType</a>
Chris Lattnerac479e52004-08-04 05:10:48 +0000[diff] [blame]3860 *Ty, LinkageTypes Linkage, const std::string &amp;N = "", Module* Parent = 0)</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3861
3862 <p>Constructor used when you need to create new <tt>Function</tt>s to add
3863 the the program. The constructor must specify the type of the function to
Chris Lattnerac479e52004-08-04 05:10:48 +0000[diff] [blame]3864 create and what type of linkage the function should have. The <a
3865 href="#FunctionType"><tt>FunctionType</tt></a> argument
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3866 specifies the formal arguments and return value for the function. The same
Duncan Sands8036ca42007-03-30 12:22:09 +0000[diff] [blame]3867 <a href="#FunctionType"><tt>FunctionType</tt></a> value can be used to
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3868 create multiple functions. The <tt>Parent</tt> argument specifies the Module
3869 in which the function is defined. If this argument is provided, the function
3870 will automatically be inserted into that module's list of
3871 functions.</p></li>
3872
Chris Lattner62810e32008-11-25 18:34:50 +0000[diff] [blame]3873 <li><tt>bool isDeclaration()</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3874
3875 <p>Return whether or not the <tt>Function</tt> has a body defined. If the
3876 function is "external", it does not have a body, and thus must be resolved
3877 by linking with a function defined in a different translation unit.</p></li>
3878
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3879 <li><tt>Function::iterator</tt> - Typedef for basic block list iterator<br>
Chris Lattner9355b472002-09-06 02:50:58 +0000[diff] [blame]3880 <tt>Function::const_iterator</tt> - Typedef for const_iterator.<br>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3881
Chris Lattner77d69242005-03-15 05:19:20 +0000[diff] [blame]3882 <tt>begin()</tt>, <tt>end()</tt>
3883 <tt>size()</tt>, <tt>empty()</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3884
3885 <p>These are forwarding methods that make it easy to access the contents of
3886 a <tt>Function</tt> object's <a href="#BasicBlock"><tt>BasicBlock</tt></a>
3887 list.</p></li>
3888
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3889 <li><tt>Function::BasicBlockListType &amp;getBasicBlockList()</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3890
3891 <p>Returns the list of <a href="#BasicBlock"><tt>BasicBlock</tt></a>s. This
3892 is necessary to use when you need to update the list or perform a complex
3893 action that doesn't have a forwarding method.</p></li>
3894
Chris Lattner89cc2652005-03-15 04:48:32 +0000[diff] [blame]3895 <li><tt>Function::arg_iterator</tt> - Typedef for the argument list
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3896iterator<br>
Chris Lattner89cc2652005-03-15 04:48:32 +0000[diff] [blame]3897 <tt>Function::const_arg_iterator</tt> - Typedef for const_iterator.<br>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3898
Chris Lattner77d69242005-03-15 05:19:20 +0000[diff] [blame]3899 <tt>arg_begin()</tt>, <tt>arg_end()</tt>
Chris Lattner89cc2652005-03-15 04:48:32 +0000[diff] [blame]3900 <tt>arg_size()</tt>, <tt>arg_empty()</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3901
3902 <p>These are forwarding methods that make it easy to access the contents of
3903 a <tt>Function</tt> object's <a href="#Argument"><tt>Argument</tt></a>
3904 list.</p></li>
3905
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3906 <li><tt>Function::ArgumentListType &amp;getArgumentList()</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3907
3908 <p>Returns the list of <a href="#Argument"><tt>Argument</tt></a>s. This is
3909 necessary to use when you need to update the list or perform a complex
3910 action that doesn't have a forwarding method.</p></li>
3911
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3912 <li><tt><a href="#BasicBlock">BasicBlock</a> &amp;getEntryBlock()</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3913
3914 <p>Returns the entry <a href="#BasicBlock"><tt>BasicBlock</tt></a> for the
3915 function. Because the entry block for the function is always the first
3916 block, this returns the first block of the <tt>Function</tt>.</p></li>
3917
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3918 <li><tt><a href="#Type">Type</a> *getReturnType()</tt><br>
3919 <tt><a href="#FunctionType">FunctionType</a> *getFunctionType()</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3920
3921 <p>This traverses the <a href="#Type"><tt>Type</tt></a> of the
3922 <tt>Function</tt> and returns the return type of the function, or the <a
3923 href="#FunctionType"><tt>FunctionType</tt></a> of the actual
3924 function.</p></li>
3925
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3926 <li><tt><a href="#SymbolTable">SymbolTable</a> *getSymbolTable()</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3927
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3928 <p> Return a pointer to the <a href="#SymbolTable"><tt>SymbolTable</tt></a>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3929 for this <tt>Function</tt>.</p></li>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3930</ul>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3931
3932</div>
3933
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]3934</div>
3935
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3936<!-- ======================================================================= -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]3937<h3>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3938 <a name="GlobalVariable">The <tt>GlobalVariable</tt> class</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]3939</h3>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3940
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]3941<div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3942
3943<p><tt>#include "<a
3944href="/doxygen/GlobalVariable_8h-source.html">llvm/GlobalVariable.h</a>"</tt>
3945<br>
Tanya Lattnera3da7772004-06-22 08:02:25 +0000[diff] [blame]3946doxygen info: <a href="/doxygen/classllvm_1_1GlobalVariable.html">GlobalVariable
Reid Spencerbe5e85e2006-04-14 14:11:48 +0000[diff] [blame]3947 Class</a><br>
3948Superclasses: <a href="#GlobalValue"><tt>GlobalValue</tt></a>,
3949<a href="#Constant"><tt>Constant</tt></a>,
3950<a href="#User"><tt>User</tt></a>,
3951<a href="#Value"><tt>Value</tt></a></p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3952
Benjamin Kramer8040cd32009-10-12 14:46:08 +0000[diff] [blame]3953<p>Global variables are represented with the (surprise surprise)
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3954<tt>GlobalVariable</tt> class. Like functions, <tt>GlobalVariable</tt>s are also
3955subclasses of <a href="#GlobalValue"><tt>GlobalValue</tt></a>, and as such are
3956always referenced by their address (global values must live in memory, so their
Reid Spencerbe5e85e2006-04-14 14:11:48 +0000[diff] [blame]3957"name" refers to their constant address). See
3958<a href="#GlobalValue"><tt>GlobalValue</tt></a> for more on this. Global
3959variables may have an initial value (which must be a
3960<a href="#Constant"><tt>Constant</tt></a>), and if they have an initializer,
3961they may be marked as "constant" themselves (indicating that their contents
3962never change at runtime).</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3963
3964<!-- _______________________________________________________________________ -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]3965<h4>
3966 <a name="m_GlobalVariable">
3967 Important Public Members of the <tt>GlobalVariable</tt> class
3968 </a>
3969</h4>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3970
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]3971<div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3972
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3973<ul>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3974 <li><tt>GlobalVariable(const </tt><tt><a href="#Type">Type</a> *Ty, bool
3975 isConstant, LinkageTypes&amp; Linkage, <a href="#Constant">Constant</a>
3976 *Initializer = 0, const std::string &amp;Name = "", Module* Parent = 0)</tt>
3977
3978 <p>Create a new global variable of the specified type. If
3979 <tt>isConstant</tt> is true then the global variable will be marked as
3980 unchanging for the program. The Linkage parameter specifies the type of
Duncan Sands667d4b82009-03-07 15:45:40 +0000[diff] [blame]3981 linkage (internal, external, weak, linkonce, appending) for the variable.
3982 If the linkage is InternalLinkage, WeakAnyLinkage, WeakODRLinkage,
3983 LinkOnceAnyLinkage or LinkOnceODRLinkage,&nbsp; then the resultant
3984 global variable will have internal linkage. AppendingLinkage concatenates
3985 together all instances (in different translation units) of the variable
3986 into a single variable but is only applicable to arrays. &nbsp;See
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3987 the <a href="LangRef.html#modulestructure">LLVM Language Reference</a> for
3988 further details on linkage types. Optionally an initializer, a name, and the
3989 module to put the variable into may be specified for the global variable as
3990 well.</p></li>
3991
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3992 <li><tt>bool isConstant() const</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3993
3994 <p>Returns true if this is a global variable that is known not to
3995 be modified at runtime.</p></li>
3996
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3997 <li><tt>bool hasInitializer()</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3998
3999 <p>Returns true if this <tt>GlobalVariable</tt> has an intializer.</p></li>
4000
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]4001 <li><tt><a href="#Constant">Constant</a> *getInitializer()</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]4002
Benjamin Kramer8040cd32009-10-12 14:46:08 +0000[diff] [blame]4003 <p>Returns the initial value for a <tt>GlobalVariable</tt>. It is not legal
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]4004 to call this method if there is no initializer.</p></li>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]4005</ul>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]4006
4007</div>
4008
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]4009</div>
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]4010
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]4011<!-- ======================================================================= -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]4012<h3>
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]4013 <a name="BasicBlock">The <tt>BasicBlock</tt> class</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]4014</h3>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]4015
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]4016<div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]4017
4018<p><tt>#include "<a
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]4019href="/doxygen/BasicBlock_8h-source.html">llvm/BasicBlock.h</a>"</tt><br>
Stefanus Du Toit24e04112009-06-17 21:12:26 +0000[diff] [blame]4020doxygen info: <a href="/doxygen/classllvm_1_1BasicBlock.html">BasicBlock
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]4021Class</a><br>
4022Superclass: <a href="#Value"><tt>Value</tt></a></p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]4023
Nick Lewyckyccd279d2011-02-17 02:19:22 +0000[diff] [blame]4024<p>This class represents a single entry single exit section of the code,
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]4025commonly known as a basic block by the compiler community. The
4026<tt>BasicBlock</tt> class maintains a list of <a
4027href="#Instruction"><tt>Instruction</tt></a>s, which form the body of the block.
4028Matching the language definition, the last element of this list of instructions
4029is always a terminator instruction (a subclass of the <a
4030href="#TerminatorInst"><tt>TerminatorInst</tt></a> class).</p>
4031
4032<p>In addition to tracking the list of instructions that make up the block, the
4033<tt>BasicBlock</tt> class also keeps track of the <a
4034href="#Function"><tt>Function</tt></a> that it is embedded into.</p>
4035
4036<p>Note that <tt>BasicBlock</tt>s themselves are <a
4037href="#Value"><tt>Value</tt></a>s, because they are referenced by instructions
4038like branches and can go in the switch tables. <tt>BasicBlock</tt>s have type
4039<tt>label</tt>.</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]4040
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]4041<!-- _______________________________________________________________________ -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]4042<h4>
4043 <a name="m_BasicBlock">
4044 Important Public Members of the <tt>BasicBlock</tt> class
4045 </a>
4046</h4>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]4047
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]4048<div>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]4049<ul>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]4050
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]4051<li><tt>BasicBlock(const std::string &amp;Name = "", </tt><tt><a
4052 href="#Function">Function</a> *Parent = 0)</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]4053
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]4054<p>The <tt>BasicBlock</tt> constructor is used to create new basic blocks for
4055insertion into a function. The constructor optionally takes a name for the new
4056block, and a <a href="#Function"><tt>Function</tt></a> to insert it into. If
4057the <tt>Parent</tt> parameter is specified, the new <tt>BasicBlock</tt> is
4058automatically inserted at the end of the specified <a
4059href="#Function"><tt>Function</tt></a>, if not specified, the BasicBlock must be
4060manually inserted into the <a href="#Function"><tt>Function</tt></a>.</p></li>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]4061
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]4062<li><tt>BasicBlock::iterator</tt> - Typedef for instruction list iterator<br>
4063<tt>BasicBlock::const_iterator</tt> - Typedef for const_iterator.<br>
4064<tt>begin()</tt>, <tt>end()</tt>, <tt>front()</tt>, <tt>back()</tt>,
4065<tt>size()</tt>, <tt>empty()</tt>
4066STL-style functions for accessing the instruction list.
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]4067
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]4068<p>These methods and typedefs are forwarding functions that have the same
4069semantics as the standard library methods of the same names. These methods
4070expose the underlying instruction list of a basic block in a way that is easy to
4071manipulate. To get the full complement of container operations (including
4072operations to update the list), you must use the <tt>getInstList()</tt>
4073method.</p></li>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]4074
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]4075<li><tt>BasicBlock::InstListType &amp;getInstList()</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]4076
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]4077<p>This method is used to get access to the underlying container that actually
4078holds the Instructions. This method must be used when there isn't a forwarding
4079function in the <tt>BasicBlock</tt> class for the operation that you would like
4080to perform. Because there are no forwarding functions for "updating"
4081operations, you need to use this if you want to update the contents of a
4082<tt>BasicBlock</tt>.</p></li>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]4083
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]4084<li><tt><a href="#Function">Function</a> *getParent()</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]4085
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]4086<p> Returns a pointer to <a href="#Function"><tt>Function</tt></a> the block is
4087embedded into, or a null pointer if it is homeless.</p></li>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]4088
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]4089<li><tt><a href="#TerminatorInst">TerminatorInst</a> *getTerminator()</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]4090
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]4091<p> Returns a pointer to the terminator instruction that appears at the end of
4092the <tt>BasicBlock</tt>. If there is no terminator instruction, or if the last
4093instruction in the block is not a terminator, then a null pointer is
4094returned.</p></li>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]4095
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]4096</ul>
4097
4098</div>
4099
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]4100</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]4101
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]4102<!-- ======================================================================= -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]4103<h3>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]4104 <a name="Argument">The <tt>Argument</tt> class</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]4105</h3>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]4106
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]4107<div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]4108
4109<p>This subclass of Value defines the interface for incoming formal
Chris Lattner58360822005-01-17 00:12:04 +0000[diff] [blame]4110arguments to a function. A Function maintains a list of its formal
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]4111arguments. An argument has a pointer to the parent Function.</p>
4112
4113</div>
4114
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]4115</div>
4116
Chris Lattner9355b472002-09-06 02:50:58 +0000[diff] [blame]4117<!-- *********************************************************************** -->
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]4118<hr>
4119<address>
4120 <a href="http://jigsaw.w3.org/css-validator/check/referer"><img
Misha Brukman44408702008-12-11 17:34:48 +0000[diff] [blame]4121 src="http://jigsaw.w3.org/css-validator/images/vcss-blue" alt="Valid CSS"></a>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]4122 <a href="http://validator.w3.org/check/referer"><img
Gabor Greifa9c0f2b2008-06-18 14:05:31 +0000[diff] [blame]4123 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]4124
4125 <a href="mailto:dhurjati@cs.uiuc.edu">Dinakar Dhurjati</a> and
4126 <a href="mailto:sabre@nondot.org">Chris Lattner</a><br>
NAKAMURA Takumib9a33632011-04-09 02:13:37 +0000[diff] [blame]4127 <a href="http://llvm.org/">The LLVM Compiler Infrastructure</a><br>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]4128 Last modified: $Date$
4129</address>
4130
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]4131</body>
4132</html>