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4<head>
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Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]6 <title>LLVM Programmer's Manual</title>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]7 <link rel="stylesheet" href="llvm.css" type="text/css">
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]8</head>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]9<body>
10
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]11<h1>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]12 LLVM Programmer's Manual
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]13</h1>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]14
Chris Lattner9355b472002-09-06 02:50:58 +0000[diff] [blame]15<ol>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]16 <li><a href="#introduction">Introduction</a></li>
Chris Lattner9355b472002-09-06 02:50:58 +0000[diff] [blame]17 <li><a href="#general">General Information</a>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]18 <ul>
Reid Spencerfe8f4ff2004-11-01 09:02:53 +0000[diff] [blame]19 <li><a href="#stl">The C++ Standard Template Library</a></li>
20<!--
21 <li>The <tt>-time-passes</tt> option</li>
22 <li>How to use the LLVM Makefile system</li>
23 <li>How to write a regression test</li>
Chris Lattner61db4652004-12-08 19:05:44 +0000[diff] [blame]24
Reid Spencerfe8f4ff2004-11-01 09:02:53 +0000[diff] [blame]25-->
Chris Lattner84b7f8d2003-08-01 22:20:59 +0000[diff] [blame]26 </ul>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]27 </li>
28 <li><a href="#apis">Important and useful LLVM APIs</a>
29 <ul>
30 <li><a href="#isa">The <tt>isa&lt;&gt;</tt>, <tt>cast&lt;&gt;</tt>
31and <tt>dyn_cast&lt;&gt;</tt> templates</a> </li>
Daniel Dunbar6e0d1cb2009-07-25 04:41:11 +0000[diff] [blame]32 <li><a href="#string_apis">Passing strings (the <tt>StringRef</tt>
Benjamin Kramere15192b2009-08-05 15:42:44 +0000[diff] [blame]33and <tt>Twine</tt> classes)</a>
Daniel Dunbar6e0d1cb2009-07-25 04:41:11 +0000[diff] [blame]34 <ul>
35 <li><a href="#StringRef">The <tt>StringRef</tt> class</a> </li>
36 <li><a href="#Twine">The <tt>Twine</tt> class</a> </li>
37 </ul>
Benjamin Kramere15192b2009-08-05 15:42:44 +0000[diff] [blame]38 </li>
Misha Brukman2c122ce2005-11-01 21:12:49 +0000[diff] [blame]39 <li><a href="#DEBUG">The <tt>DEBUG()</tt> macro and <tt>-debug</tt>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]40option</a>
41 <ul>
42 <li><a href="#DEBUG_TYPE">Fine grained debug info with <tt>DEBUG_TYPE</tt>
43and the <tt>-debug-only</tt> option</a> </li>
44 </ul>
45 </li>
Chris Lattner0be6fdf2006-12-19 21:46:21 +0000[diff] [blame]46 <li><a href="#Statistic">The <tt>Statistic</tt> class &amp; <tt>-stats</tt>
Reid Spencerfe8f4ff2004-11-01 09:02:53 +0000[diff] [blame]47option</a></li>
48<!--
49 <li>The <tt>InstVisitor</tt> template
50 <li>The general graph API
51-->
Chris Lattnerf623a082005-10-17 01:36:23 +0000[diff] [blame]52 <li><a href="#ViewGraph">Viewing graphs while debugging code</a></li>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]53 </ul>
54 </li>
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]55 <li><a href="#datastructure">Picking the Right Data Structure for a Task</a>
56 <ul>
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]57 <li><a href="#ds_sequential">Sequential Containers (std::vector, std::list, etc)</a>
58 <ul>
Chris Lattner8ae42612011-04-05 23:18:20 +0000[diff] [blame]59 <li><a href="#dss_arrayref">llvm/ADT/ArrayRef.h</a></li>
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]60 <li><a href="#dss_fixedarrays">Fixed Size Arrays</a></li>
61 <li><a href="#dss_heaparrays">Heap Allocated Arrays</a></li>
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>
72 <!--<ul>
73 todo
74 </ul>--></li>
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]75 <li><a href="#ds_set">Set-Like Containers (std::set, SmallSet, SetVector, etc)</a>
76 <ul>
77 <li><a href="#dss_sortedvectorset">A sorted 'vector'</a></li>
78 <li><a href="#dss_smallset">"llvm/ADT/SmallSet.h"</a></li>
79 <li><a href="#dss_smallptrset">"llvm/ADT/SmallPtrSet.h"</a></li>
Chris Lattnerc28476f2007-09-30 00:58:59 +0000[diff] [blame]80 <li><a href="#dss_denseset">"llvm/ADT/DenseSet.h"</a></li>
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]81 <li><a href="#dss_FoldingSet">"llvm/ADT/FoldingSet.h"</a></li>
82 <li><a href="#dss_set">&lt;set&gt;</a></li>
83 <li><a href="#dss_setvector">"llvm/ADT/SetVector.h"</a></li>
Chris Lattnerc5722432007-02-03 19:49:31 +0000[diff] [blame]84 <li><a href="#dss_uniquevector">"llvm/ADT/UniqueVector.h"</a></li>
85 <li><a href="#dss_otherset">Other Set-Like ContainerOptions</a></li>
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]86 </ul></li>
Chris Lattnerf3692522007-02-03 19:51:56 +0000[diff] [blame]87 <li><a href="#ds_map">Map-Like Containers (std::map, DenseMap, etc)</a>
88 <ul>
89 <li><a href="#dss_sortedvectormap">A sorted 'vector'</a></li>
Chris Lattner796f9fa2007-02-08 19:14:21 +0000[diff] [blame]90 <li><a href="#dss_stringmap">"llvm/ADT/StringMap.h"</a></li>
Chris Lattnerf3692522007-02-03 19:51:56 +0000[diff] [blame]91 <li><a href="#dss_indexedmap">"llvm/ADT/IndexedMap.h"</a></li>
92 <li><a href="#dss_densemap">"llvm/ADT/DenseMap.h"</a></li>
Jeffrey Yasskin71a5c222009-10-22 22:11:22 +0000[diff] [blame]93 <li><a href="#dss_valuemap">"llvm/ADT/ValueMap.h"</a></li>
Jakob Stoklund Olesenaca0da62010-12-14 00:55:51 +0000[diff] [blame]94 <li><a href="#dss_intervalmap">"llvm/ADT/IntervalMap.h"</a></li>
Chris Lattnerf3692522007-02-03 19:51:56 +0000[diff] [blame]95 <li><a href="#dss_map">&lt;map&gt;</a></li>
Jakob Stoklund Olesen4359e5e2011-04-05 20:56:08 +0000[diff] [blame]96 <li><a href="#dss_inteqclasses">"llvm/ADT/IntEqClasses.h"</a></li>
Chris Lattnerf3692522007-02-03 19:51:56 +0000[diff] [blame]97 <li><a href="#dss_othermap">Other Map-Like Container Options</a></li>
98 </ul></li>
Daniel Berlin1939ace2007-09-24 17:52:25 +0000[diff] [blame]99 <li><a href="#ds_bit">BitVector-like containers</a>
100 <ul>
101 <li><a href="#dss_bitvector">A dense bitvector</a></li>
Dan Gohman5f7775c2010-01-05 18:24:00 +0000[diff] [blame]102 <li><a href="#dss_smallbitvector">A "small" dense bitvector</a></li>
Daniel Berlin1939ace2007-09-24 17:52:25 +0000[diff] [blame]103 <li><a href="#dss_sparsebitvector">A sparse bitvector</a></li>
104 </ul></li>
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]105 </ul>
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]106 </li>
Chris Lattnerae7f7592002-09-06 18:31:18 +0000[diff] [blame]107 <li><a href="#common">Helpful Hints for Common Operations</a>
Chris Lattnerae7f7592002-09-06 18:31:18 +0000[diff] [blame]108 <ul>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]109 <li><a href="#inspection">Basic Inspection and Traversal Routines</a>
110 <ul>
111 <li><a href="#iterate_function">Iterating over the <tt>BasicBlock</tt>s
112in a <tt>Function</tt></a> </li>
113 <li><a href="#iterate_basicblock">Iterating over the <tt>Instruction</tt>s
114in a <tt>BasicBlock</tt></a> </li>
115 <li><a href="#iterate_institer">Iterating over the <tt>Instruction</tt>s
116in a <tt>Function</tt></a> </li>
117 <li><a href="#iterate_convert">Turning an iterator into a
118class pointer</a> </li>
119 <li><a href="#iterate_complex">Finding call sites: a more
120complex example</a> </li>
121 <li><a href="#calls_and_invokes">Treating calls and invokes
122the same way</a> </li>
123 <li><a href="#iterate_chains">Iterating over def-use &amp;
124use-def chains</a> </li>
Chris Lattner2e438ca2008-01-03 16:56:04 +0000[diff] [blame]125 <li><a href="#iterate_preds">Iterating over predecessors &amp;
126successors of blocks</a></li>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]127 </ul>
128 </li>
129 <li><a href="#simplechanges">Making simple changes</a>
130 <ul>
131 <li><a href="#schanges_creating">Creating and inserting new
132 <tt>Instruction</tt>s</a> </li>
133 <li><a href="#schanges_deleting">Deleting <tt>Instruction</tt>s</a> </li>
134 <li><a href="#schanges_replacing">Replacing an <tt>Instruction</tt>
135with another <tt>Value</tt></a> </li>
Tanya Lattnerb011c662007-06-20 18:33:15 +0000[diff] [blame]136 <li><a href="#schanges_deletingGV">Deleting <tt>GlobalVariable</tt>s</a> </li>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]137 </ul>
Reid Spencerfe8f4ff2004-11-01 09:02:53 +0000[diff] [blame]138 </li>
Jeffrey Yasskin714257f2009-04-30 22:33:41 +0000[diff] [blame]139 <li><a href="#create_types">How to Create Types</a></li>
Chris Lattnerae7f7592002-09-06 18:31:18 +0000[diff] [blame]140<!--
141 <li>Working with the Control Flow Graph
142 <ul>
143 <li>Accessing predecessors and successors of a <tt>BasicBlock</tt>
144 <li>
145 <li>
146 </ul>
Reid Spencerfe8f4ff2004-11-01 09:02:53 +0000[diff] [blame]147-->
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]148 </ul>
149 </li>
Chris Lattnerd9d6e102005-04-23 16:10:52 +0000[diff] [blame]150
Owen Anderson8bc1b3b2009-06-16 01:17:16 +0000[diff] [blame]151 <li><a href="#threading">Threads and LLVM</a>
152 <ul>
Owen Anderson1ad70e32009-06-16 18:04:19 +0000[diff] [blame]153 <li><a href="#startmultithreaded">Entering and Exiting Multithreaded Mode
154 </a></li>
Owen Anderson8bc1b3b2009-06-16 01:17:16 +0000[diff] [blame]155 <li><a href="#shutdown">Ending execution with <tt>llvm_shutdown()</tt></a></li>
156 <li><a href="#managedstatic">Lazy initialization with <tt>ManagedStatic</tt></a></li>
Owen Andersone0c951a2009-08-19 17:58:52 +0000[diff] [blame]157 <li><a href="#llvmcontext">Achieving Isolation with <tt>LLVMContext</tt></a></li>
Jeffrey Yasskin01eba392010-01-29 19:10:38 +0000[diff] [blame]158 <li><a href="#jitthreading">Threads and the JIT</a></li>
Owen Anderson8bc1b3b2009-06-16 01:17:16 +0000[diff] [blame]159 </ul>
160 </li>
161
Chris Lattnerd9d6e102005-04-23 16:10:52 +0000[diff] [blame]162 <li><a href="#advanced">Advanced Topics</a>
163 <ul>
Chris Lattnerf1b200b2005-04-23 17:27:36 +0000[diff] [blame]164
Chris Lattner1afcace2011-07-09 17:41:24 +0000[diff] [blame]165 <li><a href="#SymbolTable">The <tt>ValueSymbolTable</tt> class</a></li>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]166 <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]167 </ul></li>
168
Joel Stanley9b96c442002-09-06 21:55:13 +0000[diff] [blame]169 <li><a href="#coreclasses">The Core LLVM Class Hierarchy Reference</a>
Chris Lattner9355b472002-09-06 02:50:58 +0000[diff] [blame]170 <ul>
Reid Spencer303c4b42007-01-12 17:26:25 +0000[diff] [blame]171 <li><a href="#Type">The <tt>Type</tt> class</a> </li>
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]172 <li><a href="#Module">The <tt>Module</tt> class</a></li>
Reid Spencerfe8f4ff2004-11-01 09:02:53 +0000[diff] [blame]173 <li><a href="#Value">The <tt>Value</tt> class</a>
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]174 <ul>
175 <li><a href="#User">The <tt>User</tt> class</a>
Chris Lattner9355b472002-09-06 02:50:58 +0000[diff] [blame]176 <ul>
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]177 <li><a href="#Instruction">The <tt>Instruction</tt> class</a></li>
178 <li><a href="#Constant">The <tt>Constant</tt> class</a>
179 <ul>
180 <li><a href="#GlobalValue">The <tt>GlobalValue</tt> class</a>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]181 <ul>
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]182 <li><a href="#Function">The <tt>Function</tt> class</a></li>
183 <li><a href="#GlobalVariable">The <tt>GlobalVariable</tt> class</a></li>
184 </ul>
185 </li>
186 </ul>
187 </li>
Reid Spencerfe8f4ff2004-11-01 09:02:53 +0000[diff] [blame]188 </ul>
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]189 </li>
190 <li><a href="#BasicBlock">The <tt>BasicBlock</tt> class</a></li>
191 <li><a href="#Argument">The <tt>Argument</tt> class</a></li>
192 </ul>
Reid Spencerfe8f4ff2004-11-01 09:02:53 +0000[diff] [blame]193 </li>
194 </ul>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]195 </li>
Chris Lattner9355b472002-09-06 02:50:58 +0000[diff] [blame]196</ol>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]197
Chris Lattner69bf8a92004-05-23 21:06:58 +0000[diff] [blame]198<div class="doc_author">
199 <p>Written by <a href="mailto:sabre@nondot.org">Chris Lattner</a>,
Chris Lattner94c43592004-05-26 16:52:55 +0000[diff] [blame]200 <a href="mailto:dhurjati@cs.uiuc.edu">Dinakar Dhurjati</a>,
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]201 <a href="mailto:ggreif@gmail.com">Gabor Greif</a>,
Owen Anderson8bc1b3b2009-06-16 01:17:16 +0000[diff] [blame]202 <a href="mailto:jstanley@cs.uiuc.edu">Joel Stanley</a>,
203 <a href="mailto:rspencer@x10sys.com">Reid Spencer</a> and
204 <a href="mailto:owen@apple.com">Owen Anderson</a></p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]205</div>
206
Chris Lattner9355b472002-09-06 02:50:58 +0000[diff] [blame]207<!-- *********************************************************************** -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]208<h2>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]209 <a name="introduction">Introduction </a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]210</h2>
Chris Lattner9355b472002-09-06 02:50:58 +0000[diff] [blame]211<!-- *********************************************************************** -->
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]212
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]213<div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]214
215<p>This document is meant to highlight some of the important classes and
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]216interfaces available in the LLVM source-base. This manual is not
217intended to explain what LLVM is, how it works, and what LLVM code looks
218like. It assumes that you know the basics of LLVM and are interested
219in writing transformations or otherwise analyzing or manipulating the
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]220code.</p>
221
222<p>This document should get you oriented so that you can find your
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]223way in the continuously growing source code that makes up the LLVM
224infrastructure. Note that this manual is not intended to serve as a
225replacement for reading the source code, so if you think there should be
226a method in one of these classes to do something, but it's not listed,
227check the source. Links to the <a href="/doxygen/">doxygen</a> sources
228are provided to make this as easy as possible.</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]229
230<p>The first section of this document describes general information that is
231useful to know when working in the LLVM infrastructure, and the second describes
232the Core LLVM classes. In the future this manual will be extended with
233information describing how to use extension libraries, such as dominator
234information, CFG traversal routines, and useful utilities like the <tt><a
235href="/doxygen/InstVisitor_8h-source.html">InstVisitor</a></tt> template.</p>
236
237</div>
238
Chris Lattner9355b472002-09-06 02:50:58 +0000[diff] [blame]239<!-- *********************************************************************** -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]240<h2>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]241 <a name="general">General Information</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]242</h2>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]243<!-- *********************************************************************** -->
244
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]245<div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]246
247<p>This section contains general information that is useful if you are working
248in the LLVM source-base, but that isn't specific to any particular API.</p>
249
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]250<!-- ======================================================================= -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]251<h3>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]252 <a name="stl">The C++ Standard Template Library</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]253</h3>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]254
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]255<div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]256
257<p>LLVM makes heavy use of the C++ Standard Template Library (STL),
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]258perhaps much more than you are used to, or have seen before. Because of
259this, you might want to do a little background reading in the
260techniques used and capabilities of the library. There are many good
261pages that discuss the STL, and several books on the subject that you
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]262can get, so it will not be discussed in this document.</p>
263
264<p>Here are some useful links:</p>
265
266<ol>
267
Nick Lewyckyea1fe2c2010-10-09 21:12:29 +0000[diff] [blame]268<li><a href="http://www.dinkumware.com/manuals/#Standard C++ Library">Dinkumware
269C++ Library reference</a> - an excellent reference for the STL and other parts
270of the standard C++ library.</li>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]271
272<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]273O'Reilly book in the making. It has a decent Standard Library
274Reference that rivals Dinkumware's, and is unfortunately no longer free since the
275book has been published.</li>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]276
277<li><a href="http://www.parashift.com/c++-faq-lite/">C++ Frequently Asked
278Questions</a></li>
279
280<li><a href="http://www.sgi.com/tech/stl/">SGI's STL Programmer's Guide</a> -
281Contains a useful <a
282href="http://www.sgi.com/tech/stl/stl_introduction.html">Introduction to the
283STL</a>.</li>
284
285<li><a href="http://www.research.att.com/%7Ebs/C++.html">Bjarne Stroustrup's C++
286Page</a></li>
287
Tanya Lattner79445ba2004-12-08 18:34:56 +0000[diff] [blame]288<li><a href="http://64.78.49.204/">
Reid Spencer096603a2004-05-26 08:41:35 +0000[diff] [blame]289Bruce Eckel's Thinking in C++, 2nd ed. Volume 2 Revision 4.0 (even better, get
290the book).</a></li>
291
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]292</ol>
293
294<p>You are also encouraged to take a look at the <a
295href="CodingStandards.html">LLVM Coding Standards</a> guide which focuses on how
296to write maintainable code more than where to put your curly braces.</p>
297
298</div>
299
300<!-- ======================================================================= -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]301<h3>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]302 <a name="stl">Other useful references</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]303</h3>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]304
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]305<div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]306
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]307<ol>
Misha Brukmana0f71e42004-06-18 18:39:00 +0000[diff] [blame]308<li><a href="http://www.fortran-2000.com/ArnaudRecipes/sharedlib.html">Using
309static and shared libraries across platforms</a></li>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]310</ol>
311
312</div>
313
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]314</div>
315
Chris Lattner9355b472002-09-06 02:50:58 +0000[diff] [blame]316<!-- *********************************************************************** -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]317<h2>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]318 <a name="apis">Important and useful LLVM APIs</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]319</h2>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]320<!-- *********************************************************************** -->
321
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]322<div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]323
324<p>Here we highlight some LLVM APIs that are generally useful and good to
325know about when writing transformations.</p>
326
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]327<!-- ======================================================================= -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]328<h3>
Misha Brukman2c122ce2005-11-01 21:12:49 +0000[diff] [blame]329 <a name="isa">The <tt>isa&lt;&gt;</tt>, <tt>cast&lt;&gt;</tt> and
330 <tt>dyn_cast&lt;&gt;</tt> templates</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]331</h3>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]332
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]333<div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]334
335<p>The LLVM source-base makes extensive use of a custom form of RTTI.
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]336These templates have many similarities to the C++ <tt>dynamic_cast&lt;&gt;</tt>
337operator, but they don't have some drawbacks (primarily stemming from
338the fact that <tt>dynamic_cast&lt;&gt;</tt> only works on classes that
339have a v-table). Because they are used so often, you must know what they
340do and how they work. All of these templates are defined in the <a
Chris Lattner695b78b2005-04-26 22:56:16 +0000[diff] [blame]341 href="/doxygen/Casting_8h-source.html"><tt>llvm/Support/Casting.h</tt></a>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]342file (note that you very rarely have to include this file directly).</p>
343
344<dl>
345 <dt><tt>isa&lt;&gt;</tt>: </dt>
346
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]347 <dd><p>The <tt>isa&lt;&gt;</tt> operator works exactly like the Java
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]348 "<tt>instanceof</tt>" operator. It returns true or false depending on whether
349 a reference or pointer points to an instance of the specified class. This can
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]350 be very useful for constraint checking of various sorts (example below).</p>
351 </dd>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]352
353 <dt><tt>cast&lt;&gt;</tt>: </dt>
354
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]355 <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]356 converts a pointer or reference from a base class to a derived class, causing
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]357 an assertion failure if it is not really an instance of the right type. This
358 should be used in cases where you have some information that makes you believe
359 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]360 and <tt>cast&lt;&gt;</tt> template is:</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]361
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]362<div class="doc_code">
363<pre>
364static bool isLoopInvariant(const <a href="#Value">Value</a> *V, const Loop *L) {
365 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))
366 return true;
Chris Lattner69bf8a92004-05-23 21:06:58 +0000[diff] [blame]367
Bill Wendling82e2eea2006-10-11 18:00:22 +0000[diff] [blame]368 // <i>Otherwise, it must be an instruction...</i>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]369 return !L-&gt;contains(cast&lt;<a href="#Instruction">Instruction</a>&gt;(V)-&gt;getParent());
370}
371</pre>
372</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]373
374 <p>Note that you should <b>not</b> use an <tt>isa&lt;&gt;</tt> test followed
375 by a <tt>cast&lt;&gt;</tt>, for that use the <tt>dyn_cast&lt;&gt;</tt>
376 operator.</p>
377
378 </dd>
379
380 <dt><tt>dyn_cast&lt;&gt;</tt>:</dt>
381
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]382 <dd><p>The <tt>dyn_cast&lt;&gt;</tt> operator is a "checking cast" operation.
383 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]384 pointer to it (this operator does not work with references). If the operand is
385 not of the correct type, a null pointer is returned. Thus, this works very
Misha Brukman2c122ce2005-11-01 21:12:49 +0000[diff] [blame]386 much like the <tt>dynamic_cast&lt;&gt;</tt> operator in C++, and should be
387 used in the same circumstances. Typically, the <tt>dyn_cast&lt;&gt;</tt>
388 operator is used in an <tt>if</tt> statement or some other flow control
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]389 statement like this:</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]390
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]391<div class="doc_code">
392<pre>
393if (<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]394 // <i>...</i>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]395}
396</pre>
397</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]398
Misha Brukman2c122ce2005-11-01 21:12:49 +0000[diff] [blame]399 <p>This form of the <tt>if</tt> statement effectively combines together a call
400 to <tt>isa&lt;&gt;</tt> and a call to <tt>cast&lt;&gt;</tt> into one
401 statement, which is very convenient.</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]402
Misha Brukman2c122ce2005-11-01 21:12:49 +0000[diff] [blame]403 <p>Note that the <tt>dyn_cast&lt;&gt;</tt> operator, like C++'s
404 <tt>dynamic_cast&lt;&gt;</tt> or Java's <tt>instanceof</tt> operator, can be
405 abused. In particular, you should not use big chained <tt>if/then/else</tt>
406 blocks to check for lots of different variants of classes. If you find
407 yourself wanting to do this, it is much cleaner and more efficient to use the
408 <tt>InstVisitor</tt> class to dispatch over the instruction type directly.</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]409
Misha Brukman2c122ce2005-11-01 21:12:49 +0000[diff] [blame]410 </dd>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]411
Misha Brukman2c122ce2005-11-01 21:12:49 +0000[diff] [blame]412 <dt><tt>cast_or_null&lt;&gt;</tt>: </dt>
413
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]414 <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]415 <tt>cast&lt;&gt;</tt> operator, except that it allows for a null pointer as an
416 argument (which it then propagates). This can sometimes be useful, allowing
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]417 you to combine several null checks into one.</p></dd>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]418
Misha Brukman2c122ce2005-11-01 21:12:49 +0000[diff] [blame]419 <dt><tt>dyn_cast_or_null&lt;&gt;</tt>: </dt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]420
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]421 <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]422 <tt>dyn_cast&lt;&gt;</tt> operator, except that it allows for a null pointer
423 as an argument (which it then propagates). This can sometimes be useful,
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]424 allowing you to combine several null checks into one.</p></dd>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]425
Misha Brukman2c122ce2005-11-01 21:12:49 +0000[diff] [blame]426</dl>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]427
428<p>These five templates can be used with any classes, whether they have a
429v-table or not. To add support for these templates, you simply need to add
430<tt>classof</tt> static methods to the class you are interested casting
431to. Describing this is currently outside the scope of this document, but there
432are lots of examples in the LLVM source base.</p>
433
434</div>
435
Daniel Dunbar6e0d1cb2009-07-25 04:41:11 +0000[diff] [blame]436
437<!-- ======================================================================= -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]438<h3>
Daniel Dunbar6e0d1cb2009-07-25 04:41:11 +0000[diff] [blame]439 <a name="string_apis">Passing strings (the <tt>StringRef</tt>
440and <tt>Twine</tt> classes)</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]441</h3>
Daniel Dunbar6e0d1cb2009-07-25 04:41:11 +0000[diff] [blame]442
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]443<div>
Daniel Dunbar6e0d1cb2009-07-25 04:41:11 +0000[diff] [blame]444
445<p>Although LLVM generally does not do much string manipulation, we do have
Chris Lattner81187ae2009-07-25 07:16:59 +0000[diff] [blame]446several important APIs which take strings. Two important examples are the
Daniel Dunbar6e0d1cb2009-07-25 04:41:11 +0000[diff] [blame]447Value class -- which has names for instructions, functions, etc. -- and the
448StringMap class which is used extensively in LLVM and Clang.</p>
449
450<p>These are generic classes, and they need to be able to accept strings which
451may have embedded null characters. Therefore, they cannot simply take
Chris Lattner81187ae2009-07-25 07:16:59 +0000[diff] [blame]452a <tt>const char *</tt>, and taking a <tt>const std::string&amp;</tt> requires
Daniel Dunbar6e0d1cb2009-07-25 04:41:11 +0000[diff] [blame]453clients to perform a heap allocation which is usually unnecessary. Instead,
Benjamin Kramer38e59892010-07-14 22:38:02 +0000[diff] [blame]454many LLVM APIs use a <tt>StringRef</tt> or a <tt>const Twine&amp;</tt> for
455passing strings efficiently.</p>
Daniel Dunbar6e0d1cb2009-07-25 04:41:11 +0000[diff] [blame]456
Daniel Dunbar6e0d1cb2009-07-25 04:41:11 +0000[diff] [blame]457<!-- _______________________________________________________________________ -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]458<h4>
Daniel Dunbar6e0d1cb2009-07-25 04:41:11 +0000[diff] [blame]459 <a name="StringRef">The <tt>StringRef</tt> class</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]460</h4>
Daniel Dunbar6e0d1cb2009-07-25 04:41:11 +0000[diff] [blame]461
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]462<div>
Daniel Dunbar6e0d1cb2009-07-25 04:41:11 +0000[diff] [blame]463
464<p>The <tt>StringRef</tt> data type represents a reference to a constant string
465(a character array and a length) and supports the common operations available
466on <tt>std:string</tt>, but does not require heap allocation.</p>
467
Chris Lattner81187ae2009-07-25 07:16:59 +0000[diff] [blame]468<p>It can be implicitly constructed using a C style null-terminated string,
469an <tt>std::string</tt>, or explicitly with a character pointer and length.
Daniel Dunbar6e0d1cb2009-07-25 04:41:11 +0000[diff] [blame]470For example, the <tt>StringRef</tt> find function is declared as:</p>
Chris Lattner81187ae2009-07-25 07:16:59 +0000[diff] [blame]471
Benjamin Kramer38e59892010-07-14 22:38:02 +0000[diff] [blame]472<pre class="doc_code">
473 iterator find(StringRef Key);
474</pre>
Daniel Dunbar6e0d1cb2009-07-25 04:41:11 +0000[diff] [blame]475
476<p>and clients can call it using any one of:</p>
477
Benjamin Kramer38e59892010-07-14 22:38:02 +0000[diff] [blame]478<pre class="doc_code">
Daniel Dunbar6e0d1cb2009-07-25 04:41:11 +0000[diff] [blame]479 Map.find("foo"); <i>// Lookup "foo"</i>
480 Map.find(std::string("bar")); <i>// Lookup "bar"</i>
481 Map.find(StringRef("\0baz", 4)); <i>// Lookup "\0baz"</i>
482</pre>
Daniel Dunbar6e0d1cb2009-07-25 04:41:11 +0000[diff] [blame]483
484<p>Similarly, APIs which need to return a string may return a <tt>StringRef</tt>
485instance, which can be used directly or converted to an <tt>std::string</tt>
486using the <tt>str</tt> member function. See
487"<tt><a href="/doxygen/classllvm_1_1StringRef_8h-source.html">llvm/ADT/StringRef.h</a></tt>"
488for more information.</p>
489
490<p>You should rarely use the <tt>StringRef</tt> class directly, because it contains
491pointers to external memory it is not generally safe to store an instance of the
Benjamin Kramer38e59892010-07-14 22:38:02 +0000[diff] [blame]492class (unless you know that the external storage will not be freed). StringRef is
493small and pervasive enough in LLVM that it should always be passed by value.</p>
Daniel Dunbar6e0d1cb2009-07-25 04:41:11 +0000[diff] [blame]494
495</div>
496
497<!-- _______________________________________________________________________ -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]498<h4>
Daniel Dunbar6e0d1cb2009-07-25 04:41:11 +0000[diff] [blame]499 <a name="Twine">The <tt>Twine</tt> class</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]500</h4>
Daniel Dunbar6e0d1cb2009-07-25 04:41:11 +0000[diff] [blame]501
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]502<div>
Daniel Dunbar6e0d1cb2009-07-25 04:41:11 +0000[diff] [blame]503
504<p>The <tt>Twine</tt> class is an efficient way for APIs to accept concatenated
505strings. For example, a common LLVM paradigm is to name one instruction based on
506the name of another instruction with a suffix, for example:</p>
507
508<div class="doc_code">
509<pre>
510 New = CmpInst::Create(<i>...</i>, SO->getName() + ".cmp");
511</pre>
512</div>
513
514<p>The <tt>Twine</tt> class is effectively a
515lightweight <a href="http://en.wikipedia.org/wiki/Rope_(computer_science)">rope</a>
516which points to temporary (stack allocated) objects. Twines can be implicitly
517constructed as the result of the plus operator applied to strings (i.e., a C
518strings, an <tt>std::string</tt>, or a <tt>StringRef</tt>). The twine delays the
Dan Gohmancf0c9bc2010-02-25 23:51:27 +0000[diff] [blame]519actual concatenation of strings until it is actually required, at which point
Daniel Dunbar6e0d1cb2009-07-25 04:41:11 +0000[diff] [blame]520it can be efficiently rendered directly into a character array. This avoids
521unnecessary heap allocation involved in constructing the temporary results of
522string concatenation. See
523"<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]524for more information.</p>
Daniel Dunbar6e0d1cb2009-07-25 04:41:11 +0000[diff] [blame]525
526<p>As with a <tt>StringRef</tt>, <tt>Twine</tt> objects point to external memory
527and should almost never be stored or mentioned directly. They are intended
528solely for use when defining a function which should be able to efficiently
529accept concatenated strings.</p>
530
531</div>
532
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]533</div>
Daniel Dunbar6e0d1cb2009-07-25 04:41:11 +0000[diff] [blame]534
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]535<!-- ======================================================================= -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]536<h3>
Misha Brukman2c122ce2005-11-01 21:12:49 +0000[diff] [blame]537 <a name="DEBUG">The <tt>DEBUG()</tt> macro and <tt>-debug</tt> option</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]538</h3>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]539
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]540<div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]541
542<p>Often when working on your pass you will put a bunch of debugging printouts
543and other code into your pass. After you get it working, you want to remove
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]544it, 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]545across).</p>
546
547<p> Naturally, because of this, you don't want to delete the debug printouts,
548but you don't want them to always be noisy. A standard compromise is to comment
549them out, allowing you to enable them if you need them in the future.</p>
550
Chris Lattner695b78b2005-04-26 22:56:16 +0000[diff] [blame]551<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]552file provides a macro named <tt>DEBUG()</tt> that is a much nicer solution to
553this problem. Basically, you can put arbitrary code into the argument of the
554<tt>DEBUG</tt> macro, and it is only executed if '<tt>opt</tt>' (or any other
555tool) is run with the '<tt>-debug</tt>' command line argument:</p>
556
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]557<div class="doc_code">
558<pre>
Daniel Dunbar06388ae2009-07-25 01:55:32 +0000[diff] [blame]559DEBUG(errs() &lt;&lt; "I am here!\n");
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]560</pre>
561</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]562
563<p>Then you can run your pass like this:</p>
564
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]565<div class="doc_code">
566<pre>
567$ opt &lt; a.bc &gt; /dev/null -mypass
Bill Wendling82e2eea2006-10-11 18:00:22 +0000[diff] [blame]568<i>&lt;no output&gt;</i>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]569$ opt &lt; a.bc &gt; /dev/null -mypass -debug
570I am here!
571</pre>
572</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]573
574<p>Using the <tt>DEBUG()</tt> macro instead of a home-brewed solution allows you
575to not have to create "yet another" command line option for the debug output for
576your pass. Note that <tt>DEBUG()</tt> macros are disabled for optimized builds,
577so they do not cause a performance impact at all (for the same reason, they
578should also not contain side-effects!).</p>
579
580<p>One additional nice thing about the <tt>DEBUG()</tt> macro is that you can
581enable or disable it directly in gdb. Just use "<tt>set DebugFlag=0</tt>" or
582"<tt>set DebugFlag=1</tt>" from the gdb if the program is running. If the
583program hasn't been started yet, you can always just run it with
584<tt>-debug</tt>.</p>
585
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]586<!-- _______________________________________________________________________ -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]587<h4>
Chris Lattnerc9151082005-04-26 22:57:07 +0000[diff] [blame]588 <a name="DEBUG_TYPE">Fine grained debug info with <tt>DEBUG_TYPE</tt> and
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]589 the <tt>-debug-only</tt> option</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]590</h4>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]591
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]592<div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]593
594<p>Sometimes you may find yourself in a situation where enabling <tt>-debug</tt>
595just turns on <b>too much</b> information (such as when working on the code
596generator). If you want to enable debug information with more fine-grained
597control, you define the <tt>DEBUG_TYPE</tt> macro and the <tt>-debug</tt> only
598option as follows:</p>
599
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]600<div class="doc_code">
601<pre>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]602#undef DEBUG_TYPE
Daniel Dunbar06388ae2009-07-25 01:55:32 +0000[diff] [blame]603DEBUG(errs() &lt;&lt; "No debug type\n");
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]604#define DEBUG_TYPE "foo"
Daniel Dunbar06388ae2009-07-25 01:55:32 +0000[diff] [blame]605DEBUG(errs() &lt;&lt; "'foo' debug type\n");
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]606#undef DEBUG_TYPE
607#define DEBUG_TYPE "bar"
Daniel Dunbar06388ae2009-07-25 01:55:32 +0000[diff] [blame]608DEBUG(errs() &lt;&lt; "'bar' debug type\n"));
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]609#undef DEBUG_TYPE
610#define DEBUG_TYPE ""
Daniel Dunbar06388ae2009-07-25 01:55:32 +0000[diff] [blame]611DEBUG(errs() &lt;&lt; "No debug type (2)\n");
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]612</pre>
613</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]614
615<p>Then you can run your pass like this:</p>
616
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]617<div class="doc_code">
618<pre>
619$ opt &lt; a.bc &gt; /dev/null -mypass
Bill Wendling82e2eea2006-10-11 18:00:22 +0000[diff] [blame]620<i>&lt;no output&gt;</i>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]621$ opt &lt; a.bc &gt; /dev/null -mypass -debug
622No debug type
623'foo' debug type
624'bar' debug type
625No debug type (2)
626$ opt &lt; a.bc &gt; /dev/null -mypass -debug-only=foo
627'foo' debug type
628$ opt &lt; a.bc &gt; /dev/null -mypass -debug-only=bar
629'bar' debug type
630</pre>
631</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]632
633<p>Of course, in practice, you should only set <tt>DEBUG_TYPE</tt> at the top of
634a 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]635you <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]636<tt>#undef</tt>'s). Also, you should use names more meaningful than "foo" and
637"bar", because there is no system in place to ensure that names do not
638conflict. If two different modules use the same string, they will all be turned
639on when the name is specified. This allows, for example, all debug information
640for instruction scheduling to be enabled with <tt>-debug-type=InstrSched</tt>,
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]641even if the source lives in multiple files.</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]642
Daniel Dunbarc3c92392009-08-07 23:48:59 +0000[diff] [blame]643<p>The <tt>DEBUG_WITH_TYPE</tt> macro is also available for situations where you
644would like to set <tt>DEBUG_TYPE</tt>, but only for one specific <tt>DEBUG</tt>
645statement. It takes an additional first parameter, which is the type to use. For
Benjamin Kramer8040cd32009-10-12 14:46:08 +0000[diff] [blame]646example, the preceding example could be written as:</p>
Daniel Dunbarc3c92392009-08-07 23:48:59 +0000[diff] [blame]647
648
649<div class="doc_code">
650<pre>
651DEBUG_WITH_TYPE("", errs() &lt;&lt; "No debug type\n");
652DEBUG_WITH_TYPE("foo", errs() &lt;&lt; "'foo' debug type\n");
653DEBUG_WITH_TYPE("bar", errs() &lt;&lt; "'bar' debug type\n"));
654DEBUG_WITH_TYPE("", errs() &lt;&lt; "No debug type (2)\n");
655</pre>
656</div>
657
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]658</div>
659
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]660</div>
661
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]662<!-- ======================================================================= -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]663<h3>
Chris Lattner0be6fdf2006-12-19 21:46:21 +0000[diff] [blame]664 <a name="Statistic">The <tt>Statistic</tt> class &amp; <tt>-stats</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]665 option</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]666</h3>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]667
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]668<div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]669
670<p>The "<tt><a
Chris Lattner695b78b2005-04-26 22:56:16 +0000[diff] [blame]671href="/doxygen/Statistic_8h-source.html">llvm/ADT/Statistic.h</a></tt>" file
Chris Lattner0be6fdf2006-12-19 21:46:21 +0000[diff] [blame]672provides a class named <tt>Statistic</tt> that is used as a unified way to
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]673keep track of what the LLVM compiler is doing and how effective various
674optimizations are. It is useful to see what optimizations are contributing to
675making a particular program run faster.</p>
676
677<p>Often you may run your pass on some big program, and you're interested to see
678how many times it makes a certain transformation. Although you can do this with
679hand 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]680for big programs. Using the <tt>Statistic</tt> class makes it very easy to
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]681keep track of this information, and the calculated information is presented in a
682uniform manner with the rest of the passes being executed.</p>
683
684<p>There are many examples of <tt>Statistic</tt> uses, but the basics of using
685it are as follows:</p>
686
687<ol>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]688 <li><p>Define your statistic like this:</p>
689
690<div class="doc_code">
691<pre>
Chris Lattner0be6fdf2006-12-19 21:46:21 +0000[diff] [blame]692#define <a href="#DEBUG_TYPE">DEBUG_TYPE</a> "mypassname" <i>// This goes before any #includes.</i>
693STATISTIC(NumXForms, "The # of times I did stuff");
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]694</pre>
695</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]696
Chris Lattner0be6fdf2006-12-19 21:46:21 +0000[diff] [blame]697 <p>The <tt>STATISTIC</tt> macro defines a static variable, whose name is
698 specified by the first argument. The pass name is taken from the DEBUG_TYPE
699 macro, and the description is taken from the second argument. The variable
Reid Spencer06565dc2007-01-12 17:11:23 +0000[diff] [blame]700 defined ("NumXForms" in this case) acts like an unsigned integer.</p></li>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]701
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]702 <li><p>Whenever you make a transformation, bump the counter:</p>
703
704<div class="doc_code">
705<pre>
Bill Wendling82e2eea2006-10-11 18:00:22 +0000[diff] [blame]706++NumXForms; // <i>I did stuff!</i>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]707</pre>
708</div>
709
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]710 </li>
711 </ol>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]712
713 <p>That's all you have to do. To get '<tt>opt</tt>' to print out the
714 statistics gathered, use the '<tt>-stats</tt>' option:</p>
715
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]716<div class="doc_code">
717<pre>
718$ opt -stats -mypassname &lt; program.bc &gt; /dev/null
Bill Wendling82e2eea2006-10-11 18:00:22 +0000[diff] [blame]719<i>... statistics output ...</i>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]720</pre>
721</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]722
Reid Spencer6b6c73e2007-02-09 16:00:28 +0000[diff] [blame]723 <p> When running <tt>opt</tt> on a C file from the SPEC benchmark
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]724suite, it gives a report that looks like this:</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]725
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]726<div class="doc_code">
727<pre>
Gabor Greif04367bf2007-07-06 22:07:22 +0000[diff] [blame]728 7646 bitcodewriter - Number of normal instructions
729 725 bitcodewriter - Number of oversized instructions
730 129996 bitcodewriter - Number of bitcode bytes written
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]731 2817 raise - Number of insts DCEd or constprop'd
732 3213 raise - Number of cast-of-self removed
733 5046 raise - Number of expression trees converted
734 75 raise - Number of other getelementptr's formed
735 138 raise - Number of load/store peepholes
736 42 deadtypeelim - Number of unused typenames removed from symtab
737 392 funcresolve - Number of varargs functions resolved
738 27 globaldce - Number of global variables removed
739 2 adce - Number of basic blocks removed
740 134 cee - Number of branches revectored
741 49 cee - Number of setcc instruction eliminated
742 532 gcse - Number of loads removed
743 2919 gcse - Number of instructions removed
744 86 indvars - Number of canonical indvars added
745 87 indvars - Number of aux indvars removed
746 25 instcombine - Number of dead inst eliminate
747 434 instcombine - Number of insts combined
748 248 licm - Number of load insts hoisted
749 1298 licm - Number of insts hoisted to a loop pre-header
750 3 licm - Number of insts hoisted to multiple loop preds (bad, no loop pre-header)
751 75 mem2reg - Number of alloca's promoted
752 1444 cfgsimplify - Number of blocks simplified
753</pre>
754</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]755
756<p>Obviously, with so many optimizations, having a unified framework for this
757stuff is very nice. Making your pass fit well into the framework makes it more
758maintainable and useful.</p>
759
760</div>
761
Chris Lattnerf623a082005-10-17 01:36:23 +0000[diff] [blame]762<!-- ======================================================================= -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]763<h3>
Chris Lattnerf623a082005-10-17 01:36:23 +0000[diff] [blame]764 <a name="ViewGraph">Viewing graphs while debugging code</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]765</h3>
Chris Lattnerf623a082005-10-17 01:36:23 +0000[diff] [blame]766
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]767<div>
Chris Lattnerf623a082005-10-17 01:36:23 +0000[diff] [blame]768
769<p>Several of the important data structures in LLVM are graphs: for example
770CFGs made out of LLVM <a href="#BasicBlock">BasicBlock</a>s, CFGs made out of
771LLVM <a href="CodeGenerator.html#machinebasicblock">MachineBasicBlock</a>s, and
772<a href="CodeGenerator.html#selectiondag_intro">Instruction Selection
773DAGs</a>. In many cases, while debugging various parts of the compiler, it is
774nice to instantly visualize these graphs.</p>
775
776<p>LLVM provides several callbacks that are available in a debug build to do
777exactly that. If you call the <tt>Function::viewCFG()</tt> method, for example,
778the current LLVM tool will pop up a window containing the CFG for the function
779where each basic block is a node in the graph, and each node contains the
780instructions in the block. Similarly, there also exists
781<tt>Function::viewCFGOnly()</tt> (does not include the instructions), the
782<tt>MachineFunction::viewCFG()</tt> and <tt>MachineFunction::viewCFGOnly()</tt>,
783and the <tt>SelectionDAG::viewGraph()</tt> methods. Within GDB, for example,
Jim Laskey543a0ee2006-10-02 12:28:07 +0000[diff] [blame]784you can usually use something like <tt>call DAG.viewGraph()</tt> to pop
Chris Lattnerf623a082005-10-17 01:36:23 +0000[diff] [blame]785up a window. Alternatively, you can sprinkle calls to these functions in your
786code in places you want to debug.</p>
787
788<p>Getting this to work requires a small amount of configuration. On Unix
789systems with X11, install the <a href="http://www.graphviz.org">graphviz</a>
790toolkit, and make sure 'dot' and 'gv' are in your path. If you are running on
791Mac OS/X, download and install the Mac OS/X <a
792href="http://www.pixelglow.com/graphviz/">Graphviz program</a>, and add
Reid Spencer128a7a72007-02-03 21:06:43 +0000[diff] [blame]793<tt>/Applications/Graphviz.app/Contents/MacOS/</tt> (or wherever you install
Chris Lattnerf623a082005-10-17 01:36:23 +0000[diff] [blame]794it) to your path. Once in your system and path are set up, rerun the LLVM
795configure script and rebuild LLVM to enable this functionality.</p>
796
Jim Laskey543a0ee2006-10-02 12:28:07 +0000[diff] [blame]797<p><tt>SelectionDAG</tt> has been extended to make it easier to locate
798<i>interesting</i> nodes in large complex graphs. From gdb, if you
799<tt>call DAG.setGraphColor(<i>node</i>, "<i>color</i>")</tt>, then the
Reid Spencer128a7a72007-02-03 21:06:43 +0000[diff] [blame]800next <tt>call DAG.viewGraph()</tt> would highlight the node in the
Jim Laskey543a0ee2006-10-02 12:28:07 +0000[diff] [blame]801specified color (choices of colors can be found at <a
Chris Lattner302da1e2007-02-03 03:05:57 +0000[diff] [blame]802href="http://www.graphviz.org/doc/info/colors.html">colors</a>.) More
Jim Laskey543a0ee2006-10-02 12:28:07 +0000[diff] [blame]803complex node attributes can be provided with <tt>call
804DAG.setGraphAttrs(<i>node</i>, "<i>attributes</i>")</tt> (choices can be
805found at <a href="http://www.graphviz.org/doc/info/attrs.html">Graph
806Attributes</a>.) If you want to restart and clear all the current graph
807attributes, then you can <tt>call DAG.clearGraphAttrs()</tt>. </p>
808
Chris Lattner83f94672011-06-13 15:59:35 +0000[diff] [blame]809<p>Note that graph visualization features are compiled out of Release builds
810to reduce file size. This means that you need a Debug+Asserts or
811Release+Asserts build to use these features.</p>
812
Chris Lattnerf623a082005-10-17 01:36:23 +0000[diff] [blame]813</div>
814
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]815</div>
816
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]817<!-- *********************************************************************** -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]818<h2>
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]819 <a name="datastructure">Picking the Right Data Structure for a Task</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]820</h2>
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]821<!-- *********************************************************************** -->
822
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]823<div>
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]824
Reid Spencer128a7a72007-02-03 21:06:43 +0000[diff] [blame]825<p>LLVM has a plethora of data structures in the <tt>llvm/ADT/</tt> directory,
826 and we commonly use STL data structures. This section describes the trade-offs
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]827 you should consider when you pick one.</p>
828
829<p>
830The first step is a choose your own adventure: do you want a sequential
831container, a set-like container, or a map-like container? The most important
832thing when choosing a container is the algorithmic properties of how you plan to
833access the container. Based on that, you should use:</p>
834
835<ul>
Reid Spencer128a7a72007-02-03 21:06:43 +0000[diff] [blame]836<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]837 of an value based on another value. Map-like containers also support
838 efficient queries for containment (whether a key is in the map). Map-like
839 containers generally do not support efficient reverse mapping (values to
840 keys). If you need that, use two maps. Some map-like containers also
841 support efficient iteration through the keys in sorted order. Map-like
842 containers are the most expensive sort, only use them if you need one of
843 these capabilities.</li>
844
845<li>a <a href="#ds_set">set-like</a> container if you need to put a bunch of
846 stuff into a container that automatically eliminates duplicates. Some
847 set-like containers support efficient iteration through the elements in
848 sorted order. Set-like containers are more expensive than sequential
849 containers.
850</li>
851
852<li>a <a href="#ds_sequential">sequential</a> container provides
853 the most efficient way to add elements and keeps track of the order they are
854 added to the collection. They permit duplicates and support efficient
Reid Spencer128a7a72007-02-03 21:06:43 +0000[diff] [blame]855 iteration, but do not support efficient look-up based on a key.
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]856</li>
857
Chris Lattnerdced9fb2009-07-25 07:22:20 +0000[diff] [blame]858<li>a <a href="#ds_string">string</a> container is a specialized sequential
859 container or reference structure that is used for character or byte
860 arrays.</li>
861
Daniel Berlin1939ace2007-09-24 17:52:25 +0000[diff] [blame]862<li>a <a href="#ds_bit">bit</a> container provides an efficient way to store and
863 perform set operations on sets of numeric id's, while automatically
864 eliminating duplicates. Bit containers require a maximum of 1 bit for each
865 identifier you want to store.
866</li>
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]867</ul>
868
869<p>
Reid Spencer128a7a72007-02-03 21:06:43 +0000[diff] [blame]870Once the proper category of container is determined, you can fine tune the
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]871memory use, constant factors, and cache behaviors of access by intelligently
Reid Spencer128a7a72007-02-03 21:06:43 +0000[diff] [blame]872picking a member of the category. Note that constant factors and cache behavior
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]873can be a big deal. If you have a vector that usually only contains a few
874elements (but could contain many), for example, it's much better to use
875<a href="#dss_smallvector">SmallVector</a> than <a href="#dss_vector">vector</a>
876. Doing so avoids (relatively) expensive malloc/free calls, which dwarf the
877cost of adding the elements to the container. </p>
878
Chris Lattner3b4f4172011-07-22 21:34:12 +0000[diff] [blame]879</div>
880
881
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]882<!-- ======================================================================= -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]883<h3>
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]884 <a name="ds_sequential">Sequential Containers (std::vector, std::list, etc)</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]885</h3>
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]886
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]887<div>
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]888There are a variety of sequential containers available for you, based on your
889needs. Pick the first in this section that will do what you want.
Chris Lattner3b4f4172011-07-22 21:34:12 +0000[diff] [blame]890
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]891<!-- _______________________________________________________________________ -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]892<h4>
Chris Lattner8ae42612011-04-05 23:18:20 +0000[diff] [blame]893 <a name="dss_arrayref">llvm/ADT/ArrayRef.h</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]894</h4>
Chris Lattner8ae42612011-04-05 23:18:20 +0000[diff] [blame]895
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]896<div>
Chris Lattner8ae42612011-04-05 23:18:20 +0000[diff] [blame]897<p>The llvm::ArrayRef class is the preferred class to use in an interface that
898 accepts a sequential list of elements in memory and just reads from them. By
899 taking an ArrayRef, the API can be passed a fixed size array, an std::vector,
900 an llvm::SmallVector and anything else that is contiguous in memory.
901</p>
902</div>
903
904
905
906<!-- _______________________________________________________________________ -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]907<h4>
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]908 <a name="dss_fixedarrays">Fixed Size Arrays</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]909</h4>
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]910
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]911<div>
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]912<p>Fixed size arrays are very simple and very fast. They are good if you know
913exactly how many elements you have, or you have a (low) upper bound on how many
914you have.</p>
915</div>
916
917<!-- _______________________________________________________________________ -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]918<h4>
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]919 <a name="dss_heaparrays">Heap Allocated Arrays</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]920</h4>
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]921
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]922<div>
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]923<p>Heap allocated arrays (new[] + delete[]) are also simple. They are good if
924the number of elements is variable, if you know how many elements you will need
925before the array is allocated, and if the array is usually large (if not,
926consider a <a href="#dss_smallvector">SmallVector</a>). The cost of a heap
927allocated array is the cost of the new/delete (aka malloc/free). Also note that
928if you are allocating an array of a type with a constructor, the constructor and
Reid Spencer128a7a72007-02-03 21:06:43 +0000[diff] [blame]929destructors will be run for every element in the array (re-sizable vectors only
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]930construct those elements actually used).</p>
931</div>
932
933<!-- _______________________________________________________________________ -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]934<h4>
Chris Lattner9d69d4a2011-07-18 01:40:02 +0000[diff] [blame]935 <a name="dss_tinyptrvector">"llvm/ADT/TinyPtrVector.h"</a>
936</h4>
937
938
939<div>
940<p><tt>TinyPtrVector&lt;Type&gt;</tt> is a highly specialized collection class
941that is optimized to avoid allocation in the case when a vector has zero or one
942elements. It has two major restrictions: 1) it can only hold values of pointer
943type, and 2) it cannot hold a null pointer.</p>
944
945<p>Since this container is highly specialized, it is rarely used.</p>
946
947</div>
948
Chris Lattner9d69d4a2011-07-18 01:40:02 +0000[diff] [blame]949<!-- _______________________________________________________________________ -->
950<h4>
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]951 <a name="dss_smallvector">"llvm/ADT/SmallVector.h"</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]952</h4>
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]953
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]954<div>
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]955<p><tt>SmallVector&lt;Type, N&gt;</tt> is a simple class that looks and smells
956just like <tt>vector&lt;Type&gt;</tt>:
957it supports efficient iteration, lays out elements in memory order (so you can
958do pointer arithmetic between elements), supports efficient push_back/pop_back
959operations, supports efficient random access to its elements, etc.</p>
960
961<p>The advantage of SmallVector is that it allocates space for
962some number of elements (N) <b>in the object itself</b>. Because of this, if
963the SmallVector is dynamically smaller than N, no malloc is performed. This can
964be a big win in cases where the malloc/free call is far more expensive than the
965code that fiddles around with the elements.</p>
966
967<p>This is good for vectors that are "usually small" (e.g. the number of
968predecessors/successors of a block is usually less than 8). On the other hand,
969this makes the size of the SmallVector itself large, so you don't want to
970allocate lots of them (doing so will waste a lot of space). As such,
971SmallVectors are most useful when on the stack.</p>
972
973<p>SmallVector also provides a nice portable and efficient replacement for
974<tt>alloca</tt>.</p>
975
976</div>
977
978<!-- _______________________________________________________________________ -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]979<h4>
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]980 <a name="dss_vector">&lt;vector&gt;</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]981</h4>
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]982
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]983<div>
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]984<p>
985std::vector is well loved and respected. It is useful when SmallVector isn't:
986when the size of the vector is often large (thus the small optimization will
987rarely be a benefit) or if you will be allocating many instances of the vector
988itself (which would waste space for elements that aren't in the container).
989vector is also useful when interfacing with code that expects vectors :).
990</p>
Chris Lattner32d84762007-02-05 06:30:51 +0000[diff] [blame]991
992<p>One worthwhile note about std::vector: avoid code like this:</p>
993
994<div class="doc_code">
995<pre>
996for ( ... ) {
Chris Lattner9bb3dbb2007-03-28 18:27:57 +0000[diff] [blame]997 std::vector&lt;foo&gt; V;
Chris Lattner32d84762007-02-05 06:30:51 +0000[diff] [blame]998 use V;
999}
1000</pre>
1001</div>
1002
1003<p>Instead, write this as:</p>
1004
1005<div class="doc_code">
1006<pre>
Chris Lattner9bb3dbb2007-03-28 18:27:57 +0000[diff] [blame]1007std::vector&lt;foo&gt; V;
Chris Lattner32d84762007-02-05 06:30:51 +0000[diff] [blame]1008for ( ... ) {
1009 use V;
1010 V.clear();
1011}
1012</pre>
1013</div>
1014
1015<p>Doing so will save (at least) one heap allocation and free per iteration of
1016the loop.</p>
1017
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]1018</div>
1019
1020<!-- _______________________________________________________________________ -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]1021<h4>
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1022 <a name="dss_deque">&lt;deque&gt;</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]1023</h4>
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1024
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]1025<div>
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1026<p>std::deque is, in some senses, a generalized version of std::vector. Like
1027std::vector, it provides constant time random access and other similar
1028properties, but it also provides efficient access to the front of the list. It
1029does not guarantee continuity of elements within memory.</p>
1030
1031<p>In exchange for this extra flexibility, std::deque has significantly higher
1032constant factor costs than std::vector. If possible, use std::vector or
1033something cheaper.</p>
1034</div>
1035
1036<!-- _______________________________________________________________________ -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]1037<h4>
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]1038 <a name="dss_list">&lt;list&gt;</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]1039</h4>
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]1040
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]1041<div>
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]1042<p>std::list is an extremely inefficient class that is rarely useful.
1043It performs a heap allocation for every element inserted into it, thus having an
1044extremely high constant factor, particularly for small data types. std::list
1045also only supports bidirectional iteration, not random access iteration.</p>
1046
1047<p>In exchange for this high cost, std::list supports efficient access to both
1048ends of the list (like std::deque, but unlike std::vector or SmallVector). In
1049addition, the iterator invalidation characteristics of std::list are stronger
1050than that of a vector class: inserting or removing an element into the list does
1051not invalidate iterator or pointers to other elements in the list.</p>
1052</div>
1053
1054<!-- _______________________________________________________________________ -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]1055<h4>
Gabor Greif3899e492009-02-27 11:37:41 +0000[diff] [blame]1056 <a name="dss_ilist">llvm/ADT/ilist.h</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]1057</h4>
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]1058
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]1059<div>
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]1060<p><tt>ilist&lt;T&gt;</tt> implements an 'intrusive' doubly-linked list. It is
1061intrusive, because it requires the element to store and provide access to the
1062prev/next pointers for the list.</p>
1063
Gabor Greif2946d1c2009-02-27 12:02:19 +0000[diff] [blame]1064<p><tt>ilist</tt> has the same drawbacks as <tt>std::list</tt>, and additionally
1065requires an <tt>ilist_traits</tt> implementation for the element type, but it
1066provides some novel characteristics. In particular, it can efficiently store
1067polymorphic objects, the traits class is informed when an element is inserted or
Gabor Greif0cbcabe2009-03-12 09:47:03 +0000[diff] [blame]1068removed from the list, and <tt>ilist</tt>s are guaranteed to support a
1069constant-time splice operation.</p>
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]1070
Gabor Greif0cbcabe2009-03-12 09:47:03 +0000[diff] [blame]1071<p>These properties are exactly what we want for things like
1072<tt>Instruction</tt>s and basic blocks, which is why these are implemented with
1073<tt>ilist</tt>s.</p>
Gabor Greif3899e492009-02-27 11:37:41 +0000[diff] [blame]1074
1075Related classes of interest are explained in the following subsections:
1076 <ul>
Gabor Greif01862502009-02-27 13:28:07 +0000[diff] [blame]1077 <li><a href="#dss_ilist_traits">ilist_traits</a></li>
Gabor Greif2946d1c2009-02-27 12:02:19 +0000[diff] [blame]1078 <li><a href="#dss_iplist">iplist</a></li>
Gabor Greif3899e492009-02-27 11:37:41 +0000[diff] [blame]1079 <li><a href="#dss_ilist_node">llvm/ADT/ilist_node.h</a></li>
Gabor Greif6a65f422009-03-12 10:30:31 +0000[diff] [blame]1080 <li><a href="#dss_ilist_sentinel">Sentinels</a></li>
Gabor Greif3899e492009-02-27 11:37:41 +0000[diff] [blame]1081 </ul>
1082</div>
1083
1084<!-- _______________________________________________________________________ -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]1085<h4>
Argyrios Kyrtzidis81df0892011-06-15 19:56:01 +0000[diff] [blame]1086 <a name="dss_packedvector">llvm/ADT/PackedVector.h</a>
1087</h4>
1088
1089<div>
1090<p>
1091Useful for storing a vector of values using only a few number of bits for each
1092value. Apart from the standard operations of a vector-like container, it can
1093also perform an 'or' set operation.
1094</p>
1095
1096<p>For example:</p>
1097
1098<div class="doc_code">
1099<pre>
1100enum State {
1101 None = 0x0,
1102 FirstCondition = 0x1,
1103 SecondCondition = 0x2,
1104 Both = 0x3
1105};
1106
1107State get() {
1108 PackedVector&lt;State, 2&gt; Vec1;
1109 Vec1.push_back(FirstCondition);
1110
1111 PackedVector&lt;State, 2&gt; Vec2;
1112 Vec2.push_back(SecondCondition);
1113
1114 Vec1 |= Vec2;
1115 return Vec1[0]; // returns 'Both'.
1116}
1117</pre>
1118</div>
1119
1120</div>
1121
1122<!-- _______________________________________________________________________ -->
1123<h4>
Gabor Greif01862502009-02-27 13:28:07 +0000[diff] [blame]1124 <a name="dss_ilist_traits">ilist_traits</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]1125</h4>
Gabor Greif01862502009-02-27 13:28:07 +0000[diff] [blame]1126
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]1127<div>
Gabor Greif01862502009-02-27 13:28:07 +0000[diff] [blame]1128<p><tt>ilist_traits&lt;T&gt;</tt> is <tt>ilist&lt;T&gt;</tt>'s customization
1129mechanism. <tt>iplist&lt;T&gt;</tt> (and consequently <tt>ilist&lt;T&gt;</tt>)
1130publicly derive from this traits class.</p>
1131</div>
1132
1133<!-- _______________________________________________________________________ -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]1134<h4>
Gabor Greif2946d1c2009-02-27 12:02:19 +0000[diff] [blame]1135 <a name="dss_iplist">iplist</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]1136</h4>
Gabor Greif2946d1c2009-02-27 12:02:19 +0000[diff] [blame]1137
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]1138<div>
Gabor Greif2946d1c2009-02-27 12:02:19 +0000[diff] [blame]1139<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]1140supports a slightly narrower interface. Notably, inserters from
1141<tt>T&amp;</tt> are absent.</p>
Gabor Greif01862502009-02-27 13:28:07 +0000[diff] [blame]1142
1143<p><tt>ilist_traits&lt;T&gt;</tt> is a public base of this class and can be
1144used for a wide variety of customizations.</p>
Gabor Greif2946d1c2009-02-27 12:02:19 +0000[diff] [blame]1145</div>
1146
1147<!-- _______________________________________________________________________ -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]1148<h4>
Gabor Greif3899e492009-02-27 11:37:41 +0000[diff] [blame]1149 <a name="dss_ilist_node">llvm/ADT/ilist_node.h</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]1150</h4>
Gabor Greif3899e492009-02-27 11:37:41 +0000[diff] [blame]1151
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]1152<div>
Gabor Greif3899e492009-02-27 11:37:41 +0000[diff] [blame]1153<p><tt>ilist_node&lt;T&gt;</tt> implements a the forward and backward links
1154that are expected by the <tt>ilist&lt;T&gt;</tt> (and analogous containers)
1155in the default manner.</p>
1156
1157<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]1158<tt>T</tt>, usually <tt>T</tt> publicly derives from
1159<tt>ilist_node&lt;T&gt;</tt>.</p>
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]1160</div>
1161
1162<!-- _______________________________________________________________________ -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]1163<h4>
Gabor Greif6a65f422009-03-12 10:30:31 +0000[diff] [blame]1164 <a name="dss_ilist_sentinel">Sentinels</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]1165</h4>
Gabor Greif6a65f422009-03-12 10:30:31 +0000[diff] [blame]1166
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]1167<div>
Dan Gohmancf0c9bc2010-02-25 23:51:27 +0000[diff] [blame]1168<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]1169citizen in the C++ ecosystem, it needs to support the standard container
1170operations, such as <tt>begin</tt> and <tt>end</tt> iterators, etc. Also, the
1171<tt>operator--</tt> must work correctly on the <tt>end</tt> iterator in the
1172case of non-empty <tt>ilist</tt>s.</p>
1173
1174<p>The only sensible solution to this problem is to allocate a so-called
1175<i>sentinel</i> along with the intrusive list, which serves as the <tt>end</tt>
1176iterator, providing the back-link to the last element. However conforming to the
1177C++ convention it is illegal to <tt>operator++</tt> beyond the sentinel and it
1178also must not be dereferenced.</p>
1179
1180<p>These constraints allow for some implementation freedom to the <tt>ilist</tt>
1181how to allocate and store the sentinel. The corresponding policy is dictated
1182by <tt>ilist_traits&lt;T&gt;</tt>. By default a <tt>T</tt> gets heap-allocated
1183whenever the need for a sentinel arises.</p>
1184
1185<p>While the default policy is sufficient in most cases, it may break down when
1186<tt>T</tt> does not provide a default constructor. Also, in the case of many
1187instances of <tt>ilist</tt>s, the memory overhead of the associated sentinels
1188is wasted. To alleviate the situation with numerous and voluminous
1189<tt>T</tt>-sentinels, sometimes a trick is employed, leading to <i>ghostly
1190sentinels</i>.</p>
1191
1192<p>Ghostly sentinels are obtained by specially-crafted <tt>ilist_traits&lt;T&gt;</tt>
1193which superpose the sentinel with the <tt>ilist</tt> instance in memory. Pointer
1194arithmetic is used to obtain the sentinel, which is relative to the
1195<tt>ilist</tt>'s <tt>this</tt> pointer. The <tt>ilist</tt> is augmented by an
1196extra pointer, which serves as the back-link of the sentinel. This is the only
1197field in the ghostly sentinel which can be legally accessed.</p>
1198</div>
1199
1200<!-- _______________________________________________________________________ -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]1201<h4>
Chris Lattnerc5722432007-02-03 19:49:31 +0000[diff] [blame]1202 <a name="dss_other">Other Sequential Container options</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]1203</h4>
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]1204
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]1205<div>
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1206<p>Other STL containers are available, such as std::string.</p>
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]1207
1208<p>There are also various STL adapter classes such as std::queue,
1209std::priority_queue, std::stack, etc. These provide simplified access to an
1210underlying container but don't affect the cost of the container itself.</p>
1211
1212</div>
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]1213</div>
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]1214
1215<!-- ======================================================================= -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]1216<h3>
Chris Lattner7314a202011-07-22 20:46:49 +0000[diff] [blame]1217 <a name="ds_string">String-like containers</a>
1218</h3>
1219
1220<div>
1221
1222<p>
Chris Lattner3b4f4172011-07-22 21:34:12 +0000[diff] [blame]1223There are a variety of ways to pass around and use strings in C and C++, and
1224LLVM adds a few new options to choose from. Pick the first option on this list
1225that will do what you need, they are ordered according to their relative cost.
1226</p>
1227<p>
1228Note that is is generally preferred to <em>not</em> pass strings around as
1229"<tt>const char*</tt>"'s. These have a number of problems, including the fact
1230that they cannot represent embedded nul ("\0") characters, and do not have a
1231length available efficiently. The general replacement for '<tt>const
1232char*</tt>' is StringRef.
1233</p>
1234
1235<p>For more information on choosing string containers for APIs, please see
1236<a href="#string_apis">Passing strings</a>.</p>
1237
1238
1239<!-- _______________________________________________________________________ -->
1240<h4>
1241 <a name="dss_stringref">llvm/ADT/StringRef.h</a>
1242</h4>
1243
1244<div>
1245<p>
1246The StringRef class is a simple value class that contains a pointer to a
1247character and a length, and is quite related to the <a
1248href="#dss_arrayref">ArrayRef</a> class (but specialized for arrays of
1249characters). Because StringRef carries a length with it, it safely handles
1250strings with embedded nul characters in it, getting the length does not require
1251a strlen call, and it even has very convenient APIs for slicing and dicing the
1252character range that it represents.
1253</p>
1254
1255<p>
1256StringRef is ideal for passing simple strings around that are known to be live,
1257either because they are C string literals, std::string, a C array, or a
1258SmallVector. Each of these cases has an efficient implicit conversion to
1259StringRef, which doesn't result in a dynamic strlen being executed.
1260</p>
1261
1262<p>StringRef has a few major limitations which make more powerful string
1263containers useful:</p>
1264
1265<ol>
1266<li>You cannot directly convert a StringRef to a 'const char*' because there is
1267no way to add a trailing nul (unlike the .c_str() method on various stronger
1268classes).</li>
1269
1270
1271<li>StringRef doesn't own or keep alive the underlying string bytes.
1272As such it can easily lead to dangling pointers, and is not suitable for
1273embedding in datastructures in most cases (instead, use an std::string or
1274something like that).</li>
1275
1276<li>For the same reason, StringRef cannot be used as the return value of a
1277method if the method "computes" the result string. Instead, use
1278std::string.</li>
1279
1280<li>StringRef's allow you to mutate the pointed-to string bytes, but because it
1281doesn't own the string, it doesn't allow you to insert or remove bytes from
1282the range. For editing operations like this, it interoperates with the
1283<a href="#dss_twine">Twine</a> class.</li>
1284</ol>
1285
1286<p>Because of its strengths and limitations, it is very common for a function to
1287take a StringRef and for a method on an object to return a StringRef that
1288points into some string that it owns.</p>
1289
1290</div>
1291
1292<!-- _______________________________________________________________________ -->
1293<h4>
1294 <a name="dss_twine">llvm/ADT/Twine.h</a>
1295</h4>
1296
1297<div>
1298 <p>
1299 The Twine class is used as an intermediary datatype for APIs that want to take
1300 a string that can be constructed inline with a series of concatenations.
1301 Twine works by forming recursive instances of the Twine datatype (a simple
1302 value object) on the stack as temporary objects, linking them together into a
1303 tree which is then linearized when the Twine is consumed. Twine is only safe
1304 to use as the argument to a function, and should always be a const reference,
1305 e.g.:
1306 </p>
1307
1308 <pre>
1309 void foo(const Twine &amp;T);
1310 ...
1311 StringRef X = ...
1312 unsigned i = ...
1313 foo(X + "." + Twine(i));
1314 </pre>
1315
1316 <p>This example forms a string like "blarg.42" by concatenating the values
1317 together, and does not form intermediate strings containing "blarg" or
1318 "blarg.".
1319 </p>
1320
1321 <p>Because Twine is constructed with temporary objects on the stack, and
1322 because these instances are destroyed at the end of the current statement,
1323 it is an inherently dangerous API. For example, this simple variant contains
1324 undefined behavior and will probably crash:</p>
1325
1326 <pre>
1327 void foo(const Twine &amp;T);
1328 ...
1329 StringRef X = ...
1330 unsigned i = ...
1331 const Twine &amp;Tmp = X + "." + Twine(i);
1332 foo(Tmp);
1333 </pre>
1334
1335 <p>... because the temporaries are destroyed before the call. That said,
1336 Twine's are much more efficient than intermediate std::string temporaries, and
1337 they work really well with StringRef. Just be aware of their limitations.</p>
1338
1339</div>
1340
1341
1342<!-- _______________________________________________________________________ -->
1343<h4>
1344 <a name="dss_smallstring">llvm/ADT/SmallString.h</a>
1345</h4>
1346
1347<div>
1348
1349<p>SmallString is a subclass of <a href="#dss_smallvector">SmallVector</a> that
1350adds some convenience APIs like += that takes StringRef's. SmallString avoids
1351allocating memory in the case when the preallocated space is enough to hold its
1352data, and it calls back to general heap allocation when required. Since it owns
1353its data, it is very safe to use and supports full mutation of the string.</p>
1354
1355<p>Like SmallVector's, the big downside to SmallString is their sizeof. While
1356they are optimized for small strings, they themselves are not particularly
1357small. This means that they work great for temporary scratch buffers on the
1358stack, but should not generally be put into the heap: it is very rare to
1359see a SmallString as the member of a frequently-allocated heap data structure
1360or returned by-value.
Chris Lattner7314a202011-07-22 20:46:49 +0000[diff] [blame]1361</p>
1362
1363</div>
Chris Lattner3b4f4172011-07-22 21:34:12 +0000[diff] [blame]1364
1365<!-- _______________________________________________________________________ -->
1366<h4>
1367 <a name="dss_stdstring">std::string</a>
1368</h4>
1369
1370<div>
1371
1372 <p>The standard C++ std::string class is a very general class that (like
1373 SmallString) owns its underlying data. sizeof(std::string) is very reasonable
1374 so it can be embedded into heap data structures and returned by-value.
1375 On the other hand, std::string is highly inefficient for inline editing (e.g.
1376 concatenating a bunch of stuff together) and because it is provided by the
1377 standard library, its performance characteristics depend a lot of the host
1378 standard library (e.g. libc++ and MSVC provide a highly optimized string
1379 class, GCC contains a really slow implementation).
1380 </p>
1381
1382 <p>The major disadvantage of std::string is that almost every operation that
1383 makes them larger can allocate memory, which is slow. As such, it is better
1384 to use SmallVector or Twine as a scratch buffer, but then use std::string to
1385 persist the result.</p>
1386
1387
1388</div>
1389
1390<!-- end of strings -->
1391</div>
1392
Chris Lattner7314a202011-07-22 20:46:49 +0000[diff] [blame]1393
1394<!-- ======================================================================= -->
1395<h3>
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]1396 <a name="ds_set">Set-Like Containers (std::set, SmallSet, SetVector, etc)</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]1397</h3>
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]1398
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]1399<div>
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]1400
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1401<p>Set-like containers are useful when you need to canonicalize multiple values
1402into a single representation. There are several different choices for how to do
1403this, providing various trade-offs.</p>
1404
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1405<!-- _______________________________________________________________________ -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]1406<h4>
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1407 <a name="dss_sortedvectorset">A sorted 'vector'</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]1408</h4>
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1409
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]1410<div>
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1411
Chris Lattner3b23a8c2007-02-03 08:10:45 +0000[diff] [blame]1412<p>If you intend to insert a lot of elements, then do a lot of queries, a
1413great approach is to use a vector (or other sequential container) with
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1414std::sort+std::unique to remove duplicates. This approach works really well if
Chris Lattner3b23a8c2007-02-03 08:10:45 +0000[diff] [blame]1415your usage pattern has these two distinct phases (insert then query), and can be
1416coupled with a good choice of <a href="#ds_sequential">sequential container</a>.
1417</p>
1418
1419<p>
1420This combination provides the several nice properties: the result data is
1421contiguous in memory (good for cache locality), has few allocations, is easy to
1422address (iterators in the final vector are just indices or pointers), and can be
1423efficiently queried with a standard binary or radix search.</p>
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1424
1425</div>
1426
1427<!-- _______________________________________________________________________ -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]1428<h4>
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1429 <a name="dss_smallset">"llvm/ADT/SmallSet.h"</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]1430</h4>
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1431
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]1432<div>
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1433
Reid Spencer128a7a72007-02-03 21:06:43 +0000[diff] [blame]1434<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]1435are 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]1436has space for N elements in place (thus, if the set is dynamically smaller than
Chris Lattner14868db2007-02-03 08:20:15 +0000[diff] [blame]1437N, no malloc traffic is required) and accesses them with a simple linear search.
1438When the set grows beyond 'N' elements, it allocates a more expensive representation that
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1439guarantees efficient access (for most types, it falls back to std::set, but for
Chris Lattner14868db2007-02-03 08:20:15 +0000[diff] [blame]1440pointers it uses something far better, <a
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1441href="#dss_smallptrset">SmallPtrSet</a>).</p>
1442
1443<p>The magic of this class is that it handles small sets extremely efficiently,
1444but gracefully handles extremely large sets without loss of efficiency. The
1445drawback is that the interface is quite small: it supports insertion, queries
1446and erasing, but does not support iteration.</p>
1447
1448</div>
1449
1450<!-- _______________________________________________________________________ -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]1451<h4>
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1452 <a name="dss_smallptrset">"llvm/ADT/SmallPtrSet.h"</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]1453</h4>
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1454
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]1455<div>
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1456
Gabor Greif4de73682010-03-26 19:30:47 +0000[diff] [blame]1457<p>SmallPtrSet has all the advantages of <tt>SmallSet</tt> (and a <tt>SmallSet</tt> of pointers is
1458transparently implemented with a <tt>SmallPtrSet</tt>), but also supports iterators. If
Chris Lattner14868db2007-02-03 08:20:15 +0000[diff] [blame]1459more than 'N' insertions are performed, a single quadratically
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1460probed hash table is allocated and grows as needed, providing extremely
1461efficient access (constant time insertion/deleting/queries with low constant
1462factors) and is very stingy with malloc traffic.</p>
1463
Gabor Greif4de73682010-03-26 19:30:47 +0000[diff] [blame]1464<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]1465whenever an insertion occurs. Also, the values visited by the iterators are not
1466visited in sorted order.</p>
1467
1468</div>
1469
1470<!-- _______________________________________________________________________ -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]1471<h4>
Chris Lattnerc28476f2007-09-30 00:58:59 +0000[diff] [blame]1472 <a name="dss_denseset">"llvm/ADT/DenseSet.h"</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]1473</h4>
Chris Lattnerc28476f2007-09-30 00:58:59 +0000[diff] [blame]1474
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]1475<div>
Chris Lattnerc28476f2007-09-30 00:58:59 +0000[diff] [blame]1476
1477<p>
1478DenseSet is a simple quadratically probed hash table. It excels at supporting
1479small values: it uses a single allocation to hold all of the pairs that
1480are currently inserted in the set. DenseSet is a great way to unique small
1481values that are not simple pointers (use <a
1482href="#dss_smallptrset">SmallPtrSet</a> for pointers). Note that DenseSet has
1483the same requirements for the value type that <a
1484href="#dss_densemap">DenseMap</a> has.
1485</p>
1486
1487</div>
1488
1489<!-- _______________________________________________________________________ -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]1490<h4>
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1491 <a name="dss_FoldingSet">"llvm/ADT/FoldingSet.h"</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]1492</h4>
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1493
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]1494<div>
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1495
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]1496<p>
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1497FoldingSet is an aggregate class that is really good at uniquing
1498expensive-to-create or polymorphic objects. It is a combination of a chained
1499hash table with intrusive links (uniqued objects are required to inherit from
Chris Lattner14868db2007-02-03 08:20:15 +0000[diff] [blame]1500FoldingSetNode) that uses <a href="#dss_smallvector">SmallVector</a> as part of
1501its ID process.</p>
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1502
Chris Lattner14868db2007-02-03 08:20:15 +0000[diff] [blame]1503<p>Consider a case where you want to implement a "getOrCreateFoo" method for
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1504a complex object (for example, a node in the code generator). The client has a
1505description of *what* it wants to generate (it knows the opcode and all the
1506operands), 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]1507only to find out it already exists, at which point we would have to delete it
1508and return the node that already exists.
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]1509</p>
1510
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1511<p>To support this style of client, FoldingSet perform a query with a
1512FoldingSetNodeID (which wraps SmallVector) that can be used to describe the
1513element that we want to query for. The query either returns the element
1514matching the ID or it returns an opaque ID that indicates where insertion should
Chris Lattner14868db2007-02-03 08:20:15 +0000[diff] [blame]1515take place. Construction of the ID usually does not require heap traffic.</p>
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1516
1517<p>Because FoldingSet uses intrusive links, it can support polymorphic objects
1518in the set (for example, you can have SDNode instances mixed with LoadSDNodes).
1519Because the elements are individually allocated, pointers to the elements are
1520stable: inserting or removing elements does not invalidate any pointers to other
1521elements.
1522</p>
1523
1524</div>
1525
1526<!-- _______________________________________________________________________ -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]1527<h4>
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1528 <a name="dss_set">&lt;set&gt;</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]1529</h4>
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1530
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]1531<div>
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1532
Chris Lattnerc5722432007-02-03 19:49:31 +0000[diff] [blame]1533<p><tt>std::set</tt> is a reasonable all-around set class, which is decent at
1534many things but great at nothing. std::set allocates memory for each element
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1535inserted (thus it is very malloc intensive) and typically stores three pointers
Chris Lattner14868db2007-02-03 08:20:15 +0000[diff] [blame]1536per element in the set (thus adding a large amount of per-element space
1537overhead). It offers guaranteed log(n) performance, which is not particularly
Chris Lattnerc5722432007-02-03 19:49:31 +0000[diff] [blame]1538fast from a complexity standpoint (particularly if the elements of the set are
1539expensive to compare, like strings), and has extremely high constant factors for
1540lookup, insertion and removal.</p>
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1541
Chris Lattner14868db2007-02-03 08:20:15 +0000[diff] [blame]1542<p>The advantages of std::set are that its iterators are stable (deleting or
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1543inserting an element from the set does not affect iterators or pointers to other
1544elements) and that iteration over the set is guaranteed to be in sorted order.
1545If the elements in the set are large, then the relative overhead of the pointers
1546and malloc traffic is not a big deal, but if the elements of the set are small,
1547std::set is almost never a good choice.</p>
1548
1549</div>
1550
1551<!-- _______________________________________________________________________ -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]1552<h4>
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1553 <a name="dss_setvector">"llvm/ADT/SetVector.h"</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]1554</h4>
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1555
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]1556<div>
Chris Lattneredca3c52007-02-04 00:00:26 +0000[diff] [blame]1557<p>LLVM's SetVector&lt;Type&gt; is an adapter class that combines your choice of
1558a set-like container along with a <a href="#ds_sequential">Sequential
1559Container</a>. The important property
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1560that this provides is efficient insertion with uniquing (duplicate elements are
1561ignored) with iteration support. It implements this by inserting elements into
1562both a set-like container and the sequential container, using the set-like
1563container for uniquing and the sequential container for iteration.
1564</p>
1565
1566<p>The difference between SetVector and other sets is that the order of
1567iteration is guaranteed to match the order of insertion into the SetVector.
1568This property is really important for things like sets of pointers. Because
1569pointer values are non-deterministic (e.g. vary across runs of the program on
Chris Lattneredca3c52007-02-04 00:00:26 +0000[diff] [blame]1570different machines), iterating over the pointers in the set will
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1571not be in a well-defined order.</p>
1572
1573<p>
1574The drawback of SetVector is that it requires twice as much space as a normal
1575set and has the sum of constant factors from the set-like container and the
1576sequential container that it uses. Use it *only* if you need to iterate over
1577the elements in a deterministic order. SetVector is also expensive to delete
Chris Lattneredca3c52007-02-04 00:00:26 +0000[diff] [blame]1578elements out of (linear time), unless you use it's "pop_back" method, which is
1579faster.
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1580</p>
1581
Chris Lattneredca3c52007-02-04 00:00:26 +0000[diff] [blame]1582<p>SetVector is an adapter class that defaults to using std::vector and std::set
1583for the underlying containers, so it is quite expensive. However,
1584<tt>"llvm/ADT/SetVector.h"</tt> also provides a SmallSetVector class, which
1585defaults to using a SmallVector and SmallSet of a specified size. If you use
1586this, and if your sets are dynamically smaller than N, you will save a lot of
1587heap traffic.</p>
1588
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1589</div>
1590
1591<!-- _______________________________________________________________________ -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]1592<h4>
Chris Lattnerc5722432007-02-03 19:49:31 +0000[diff] [blame]1593 <a name="dss_uniquevector">"llvm/ADT/UniqueVector.h"</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]1594</h4>
Chris Lattnerc5722432007-02-03 19:49:31 +0000[diff] [blame]1595
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]1596<div>
Chris Lattnerc5722432007-02-03 19:49:31 +0000[diff] [blame]1597
1598<p>
1599UniqueVector is similar to <a href="#dss_setvector">SetVector</a>, but it
1600retains a unique ID for each element inserted into the set. It internally
1601contains a map and a vector, and it assigns a unique ID for each value inserted
1602into the set.</p>
1603
1604<p>UniqueVector is very expensive: its cost is the sum of the cost of
1605maintaining both the map and vector, it has high complexity, high constant
1606factors, and produces a lot of malloc traffic. It should be avoided.</p>
1607
1608</div>
1609
1610
1611<!-- _______________________________________________________________________ -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]1612<h4>
Chris Lattnerc5722432007-02-03 19:49:31 +0000[diff] [blame]1613 <a name="dss_otherset">Other Set-Like Container Options</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]1614</h4>
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1615
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]1616<div>
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1617
1618<p>
1619The STL provides several other options, such as std::multiset and the various
Chris Lattnerf1a30822009-03-09 05:20:45 +0000[diff] [blame]1620"hash_set" like containers (whether from C++ TR1 or from the SGI library). We
1621never use hash_set and unordered_set because they are generally very expensive
1622(each insertion requires a malloc) and very non-portable.
1623</p>
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1624
1625<p>std::multiset is useful if you're not interested in elimination of
Chris Lattner14868db2007-02-03 08:20:15 +0000[diff] [blame]1626duplicates, but has all the drawbacks of std::set. A sorted vector (where you
1627don't delete duplicate entries) or some other approach is almost always
1628better.</p>
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1629
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]1630</div>
1631
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]1632</div>
1633
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]1634<!-- ======================================================================= -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]1635<h3>
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]1636 <a name="ds_map">Map-Like Containers (std::map, DenseMap, etc)</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]1637</h3>
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]1638
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]1639<div>
Chris Lattnerc5722432007-02-03 19:49:31 +0000[diff] [blame]1640Map-like containers are useful when you want to associate data to a key. As
1641usual, there are a lot of different ways to do this. :)
Chris Lattnerc5722432007-02-03 19:49:31 +0000[diff] [blame]1642
1643<!-- _______________________________________________________________________ -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]1644<h4>
Chris Lattnerc5722432007-02-03 19:49:31 +0000[diff] [blame]1645 <a name="dss_sortedvectormap">A sorted 'vector'</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]1646</h4>
Chris Lattnerc5722432007-02-03 19:49:31 +0000[diff] [blame]1647
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]1648<div>
Chris Lattnerc5722432007-02-03 19:49:31 +0000[diff] [blame]1649
1650<p>
1651If your usage pattern follows a strict insert-then-query approach, you can
1652trivially use the same approach as <a href="#dss_sortedvectorset">sorted vectors
1653for set-like containers</a>. The only difference is that your query function
1654(which uses std::lower_bound to get efficient log(n) lookup) should only compare
1655the key, not both the key and value. This yields the same advantages as sorted
1656vectors for sets.
1657</p>
1658</div>
1659
1660<!-- _______________________________________________________________________ -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]1661<h4>
Chris Lattner796f9fa2007-02-08 19:14:21 +0000[diff] [blame]1662 <a name="dss_stringmap">"llvm/ADT/StringMap.h"</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]1663</h4>
Chris Lattnerc5722432007-02-03 19:49:31 +0000[diff] [blame]1664
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]1665<div>
Chris Lattnerc5722432007-02-03 19:49:31 +0000[diff] [blame]1666
1667<p>
1668Strings are commonly used as keys in maps, and they are difficult to support
1669efficiently: they are variable length, inefficient to hash and compare when
Chris Lattner796f9fa2007-02-08 19:14:21 +0000[diff] [blame]1670long, expensive to copy, etc. StringMap is a specialized container designed to
1671cope with these issues. It supports mapping an arbitrary range of bytes to an
1672arbitrary other object.</p>
Chris Lattnerc5722432007-02-03 19:49:31 +0000[diff] [blame]1673
Chris Lattner796f9fa2007-02-08 19:14:21 +0000[diff] [blame]1674<p>The StringMap implementation uses a quadratically-probed hash table, where
Chris Lattnerc5722432007-02-03 19:49:31 +0000[diff] [blame]1675the buckets store a pointer to the heap allocated entries (and some other
1676stuff). The entries in the map must be heap allocated because the strings are
1677variable length. The string data (key) and the element object (value) are
1678stored in the same allocation with the string data immediately after the element
1679object. This container guarantees the "<tt>(char*)(&amp;Value+1)</tt>" points
1680to the key string for a value.</p>
1681
Chris Lattner796f9fa2007-02-08 19:14:21 +0000[diff] [blame]1682<p>The StringMap is very fast for several reasons: quadratic probing is very
Chris Lattnerc5722432007-02-03 19:49:31 +0000[diff] [blame]1683cache efficient for lookups, the hash value of strings in buckets is not
Nick Lewycky2a80aca2010-08-01 23:18:45 +0000[diff] [blame]1684recomputed when looking up an element, StringMap rarely has to touch the
Chris Lattnerc5722432007-02-03 19:49:31 +0000[diff] [blame]1685memory for unrelated objects when looking up a value (even when hash collisions
1686happen), hash table growth does not recompute the hash values for strings
1687already in the table, and each pair in the map is store in a single allocation
1688(the string data is stored in the same allocation as the Value of a pair).</p>
1689
Chris Lattner796f9fa2007-02-08 19:14:21 +0000[diff] [blame]1690<p>StringMap also provides query methods that take byte ranges, so it only ever
Chris Lattnerc5722432007-02-03 19:49:31 +0000[diff] [blame]1691copies a string if a value is inserted into the table.</p>
1692</div>
1693
1694<!-- _______________________________________________________________________ -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]1695<h4>
Chris Lattnerc5722432007-02-03 19:49:31 +0000[diff] [blame]1696 <a name="dss_indexedmap">"llvm/ADT/IndexedMap.h"</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]1697</h4>
Chris Lattnerc5722432007-02-03 19:49:31 +0000[diff] [blame]1698
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]1699<div>
Chris Lattnerc5722432007-02-03 19:49:31 +0000[diff] [blame]1700<p>
1701IndexedMap is a specialized container for mapping small dense integers (or
1702values that can be mapped to small dense integers) to some other type. It is
1703internally implemented as a vector with a mapping function that maps the keys to
1704the dense integer range.
1705</p>
1706
1707<p>
1708This is useful for cases like virtual registers in the LLVM code generator: they
1709have a dense mapping that is offset by a compile-time constant (the first
1710virtual register ID).</p>
1711
1712</div>
1713
1714<!-- _______________________________________________________________________ -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]1715<h4>
Chris Lattnerc5722432007-02-03 19:49:31 +0000[diff] [blame]1716 <a name="dss_densemap">"llvm/ADT/DenseMap.h"</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]1717</h4>
Chris Lattnerc5722432007-02-03 19:49:31 +0000[diff] [blame]1718
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]1719<div>
Chris Lattnerc5722432007-02-03 19:49:31 +0000[diff] [blame]1720
1721<p>
1722DenseMap is a simple quadratically probed hash table. It excels at supporting
1723small keys and values: it uses a single allocation to hold all of the pairs that
1724are currently inserted in the map. DenseMap is a great way to map pointers to
1725pointers, or map other small types to each other.
1726</p>
1727
1728<p>
1729There are several aspects of DenseMap that you should be aware of, however. The
1730iterators in a densemap are invalidated whenever an insertion occurs, unlike
1731map. Also, because DenseMap allocates space for a large number of key/value
Chris Lattnera4a264d2007-02-03 20:17:53 +0000[diff] [blame]1732pairs (it starts with 64 by default), it will waste a lot of space if your keys
1733or values are large. Finally, you must implement a partial specialization of
Chris Lattner76c1b972007-09-17 18:34:04 +0000[diff] [blame]1734DenseMapInfo for the key that you want, if it isn't already supported. This
Chris Lattnerc5722432007-02-03 19:49:31 +0000[diff] [blame]1735is required to tell DenseMap about two special marker values (which can never be
Chris Lattnera4a264d2007-02-03 20:17:53 +0000[diff] [blame]1736inserted into the map) that it needs internally.</p>
Chris Lattnerc5722432007-02-03 19:49:31 +0000[diff] [blame]1737
1738</div>
1739
1740<!-- _______________________________________________________________________ -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]1741<h4>
Jeffrey Yasskin71a5c222009-10-22 22:11:22 +0000[diff] [blame]1742 <a name="dss_valuemap">"llvm/ADT/ValueMap.h"</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]1743</h4>
Jeffrey Yasskin71a5c222009-10-22 22:11:22 +0000[diff] [blame]1744
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]1745<div>
Jeffrey Yasskin71a5c222009-10-22 22:11:22 +0000[diff] [blame]1746
1747<p>
1748ValueMap is a wrapper around a <a href="#dss_densemap">DenseMap</a> mapping
1749Value*s (or subclasses) to another type. When a Value is deleted or RAUW'ed,
1750ValueMap will update itself so the new version of the key is mapped to the same
1751value, just as if the key were a WeakVH. You can configure exactly how this
1752happens, and what else happens on these two events, by passing
1753a <code>Config</code> parameter to the ValueMap template.</p>
1754
1755</div>
1756
1757<!-- _______________________________________________________________________ -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]1758<h4>
Jakob Stoklund Olesenaca0da62010-12-14 00:55:51 +0000[diff] [blame]1759 <a name="dss_intervalmap">"llvm/ADT/IntervalMap.h"</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]1760</h4>
Jakob Stoklund Olesenaca0da62010-12-14 00:55:51 +0000[diff] [blame]1761
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]1762<div>
Jakob Stoklund Olesenaca0da62010-12-14 00:55:51 +0000[diff] [blame]1763
1764<p> IntervalMap is a compact map for small keys and values. It maps key
1765intervals instead of single keys, and it will automatically coalesce adjacent
1766intervals. When then map only contains a few intervals, they are stored in the
1767map object itself to avoid allocations.</p>
1768
1769<p> The IntervalMap iterators are quite big, so they should not be passed around
1770as STL iterators. The heavyweight iterators allow a smaller data structure.</p>
1771
1772</div>
1773
1774<!-- _______________________________________________________________________ -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]1775<h4>
Chris Lattnerc5722432007-02-03 19:49:31 +0000[diff] [blame]1776 <a name="dss_map">&lt;map&gt;</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]1777</h4>
Chris Lattnerc5722432007-02-03 19:49:31 +0000[diff] [blame]1778
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]1779<div>
Chris Lattnerc5722432007-02-03 19:49:31 +0000[diff] [blame]1780
1781<p>
1782std::map has similar characteristics to <a href="#dss_set">std::set</a>: it uses
1783a single allocation per pair inserted into the map, it offers log(n) lookup with
1784an extremely large constant factor, imposes a space penalty of 3 pointers per
1785pair in the map, etc.</p>
1786
1787<p>std::map is most useful when your keys or values are very large, if you need
1788to iterate over the collection in sorted order, or if you need stable iterators
1789into the map (i.e. they don't get invalidated if an insertion or deletion of
1790another element takes place).</p>
1791
1792</div>
1793
1794<!-- _______________________________________________________________________ -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]1795<h4>
Jakob Stoklund Olesen4359e5e2011-04-05 20:56:08 +0000[diff] [blame]1796 <a name="dss_inteqclasses">"llvm/ADT/IntEqClasses.h"</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]1797</h4>
Jakob Stoklund Olesen4359e5e2011-04-05 20:56:08 +0000[diff] [blame]1798
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]1799<div>
Jakob Stoklund Olesen4359e5e2011-04-05 20:56:08 +0000[diff] [blame]1800
1801<p>IntEqClasses provides a compact representation of equivalence classes of
1802small integers. Initially, each integer in the range 0..n-1 has its own
1803equivalence class. Classes can be joined by passing two class representatives to
1804the join(a, b) method. Two integers are in the same class when findLeader()
1805returns the same representative.</p>
1806
1807<p>Once all equivalence classes are formed, the map can be compressed so each
1808integer 0..n-1 maps to an equivalence class number in the range 0..m-1, where m
1809is the total number of equivalence classes. The map must be uncompressed before
1810it can be edited again.</p>
1811
1812</div>
1813
1814<!-- _______________________________________________________________________ -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]1815<h4>
Chris Lattnerc5722432007-02-03 19:49:31 +0000[diff] [blame]1816 <a name="dss_othermap">Other Map-Like Container Options</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]1817</h4>
Chris Lattnerc5722432007-02-03 19:49:31 +0000[diff] [blame]1818
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]1819<div>
Chris Lattnerc5722432007-02-03 19:49:31 +0000[diff] [blame]1820
1821<p>
1822The STL provides several other options, such as std::multimap and the various
Chris Lattnerf1a30822009-03-09 05:20:45 +0000[diff] [blame]1823"hash_map" like containers (whether from C++ TR1 or from the SGI library). We
1824never use hash_set and unordered_set because they are generally very expensive
1825(each insertion requires a malloc) and very non-portable.</p>
Chris Lattnerc5722432007-02-03 19:49:31 +0000[diff] [blame]1826
1827<p>std::multimap is useful if you want to map a key to multiple values, but has
1828all the drawbacks of std::map. A sorted vector or some other approach is almost
1829always better.</p>
1830
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]1831</div>
1832
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]1833</div>
1834
Daniel Berlin1939ace2007-09-24 17:52:25 +0000[diff] [blame]1835<!-- ======================================================================= -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]1836<h3>
Daniel Berlin1939ace2007-09-24 17:52:25 +0000[diff] [blame]1837 <a name="ds_bit">Bit storage containers (BitVector, SparseBitVector)</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]1838</h3>
Daniel Berlin1939ace2007-09-24 17:52:25 +0000[diff] [blame]1839
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]1840<div>
Chris Lattner7086ce72007-09-25 22:37:50 +0000[diff] [blame]1841<p>Unlike the other containers, there are only two bit storage containers, and
1842choosing when to use each is relatively straightforward.</p>
1843
1844<p>One additional option is
1845<tt>std::vector&lt;bool&gt;</tt>: we discourage its use for two reasons 1) the
1846implementation in many common compilers (e.g. commonly available versions of
1847GCC) is extremely inefficient and 2) the C++ standards committee is likely to
1848deprecate this container and/or change it significantly somehow. In any case,
1849please don't use it.</p>
Daniel Berlin1939ace2007-09-24 17:52:25 +0000[diff] [blame]1850
1851<!-- _______________________________________________________________________ -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]1852<h4>
Daniel Berlin1939ace2007-09-24 17:52:25 +0000[diff] [blame]1853 <a name="dss_bitvector">BitVector</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]1854</h4>
Daniel Berlin1939ace2007-09-24 17:52:25 +0000[diff] [blame]1855
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]1856<div>
Dan Gohman5f7775c2010-01-05 18:24:00 +0000[diff] [blame]1857<p> The BitVector container provides a dynamic size set of bits for manipulation.
Daniel Berlin1939ace2007-09-24 17:52:25 +0000[diff] [blame]1858It supports individual bit setting/testing, as well as set operations. The set
1859operations take time O(size of bitvector), but operations are performed one word
1860at a time, instead of one bit at a time. This makes the BitVector very fast for
1861set operations compared to other containers. Use the BitVector when you expect
1862the number of set bits to be high (IE a dense set).
1863</p>
1864</div>
1865
1866<!-- _______________________________________________________________________ -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]1867<h4>
Dan Gohman5f7775c2010-01-05 18:24:00 +0000[diff] [blame]1868 <a name="dss_smallbitvector">SmallBitVector</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]1869</h4>
Dan Gohman5f7775c2010-01-05 18:24:00 +0000[diff] [blame]1870
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]1871<div>
Dan Gohman5f7775c2010-01-05 18:24:00 +0000[diff] [blame]1872<p> The SmallBitVector container provides the same interface as BitVector, but
1873it is optimized for the case where only a small number of bits, less than
187425 or so, are needed. It also transparently supports larger bit counts, but
1875slightly less efficiently than a plain BitVector, so SmallBitVector should
1876only be used when larger counts are rare.
1877</p>
1878
1879<p>
1880At this time, SmallBitVector does not support set operations (and, or, xor),
1881and its operator[] does not provide an assignable lvalue.
1882</p>
1883</div>
1884
1885<!-- _______________________________________________________________________ -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]1886<h4>
Daniel Berlin1939ace2007-09-24 17:52:25 +0000[diff] [blame]1887 <a name="dss_sparsebitvector">SparseBitVector</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]1888</h4>
Daniel Berlin1939ace2007-09-24 17:52:25 +0000[diff] [blame]1889
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]1890<div>
Daniel Berlin1939ace2007-09-24 17:52:25 +0000[diff] [blame]1891<p> The SparseBitVector container is much like BitVector, with one major
1892difference: Only the bits that are set, are stored. This makes the
1893SparseBitVector much more space efficient than BitVector when the set is sparse,
1894as well as making set operations O(number of set bits) instead of O(size of
1895universe). 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
1896(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).
1897</p>
1898</div>
Chris Lattnerf623a082005-10-17 01:36:23 +0000[diff] [blame]1899
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]1900</div>
1901
1902</div>
1903
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1904<!-- *********************************************************************** -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]1905<h2>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1906 <a name="common">Helpful Hints for Common Operations</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]1907</h2>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1908<!-- *********************************************************************** -->
1909
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]1910<div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1911
1912<p>This section describes how to perform some very simple transformations of
1913LLVM code. This is meant to give examples of common idioms used, showing the
1914practical side of LLVM transformations. <p> Because this is a "how-to" section,
1915you should also read about the main classes that you will be working with. The
1916<a href="#coreclasses">Core LLVM Class Hierarchy Reference</a> contains details
1917and descriptions of the main classes that you should know about.</p>
1918
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1919<!-- NOTE: this section should be heavy on example code -->
1920<!-- ======================================================================= -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]1921<h3>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1922 <a name="inspection">Basic Inspection and Traversal Routines</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]1923</h3>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1924
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]1925<div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1926
1927<p>The LLVM compiler infrastructure have many different data structures that may
1928be traversed. Following the example of the C++ standard template library, the
1929techniques used to traverse these various data structures are all basically the
1930same. For a enumerable sequence of values, the <tt>XXXbegin()</tt> function (or
1931method) returns an iterator to the start of the sequence, the <tt>XXXend()</tt>
1932function returns an iterator pointing to one past the last valid element of the
1933sequence, and there is some <tt>XXXiterator</tt> data type that is common
1934between the two operations.</p>
1935
1936<p>Because the pattern for iteration is common across many different aspects of
1937the program representation, the standard template library algorithms may be used
1938on them, and it is easier to remember how to iterate. First we show a few common
1939examples of the data structures that need to be traversed. Other data
1940structures are traversed in very similar ways.</p>
1941
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1942<!-- _______________________________________________________________________ -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]1943<h4>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1944 <a name="iterate_function">Iterating over the </a><a
1945 href="#BasicBlock"><tt>BasicBlock</tt></a>s in a <a
1946 href="#Function"><tt>Function</tt></a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]1947</h4>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1948
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]1949<div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1950
1951<p>It's quite common to have a <tt>Function</tt> instance that you'd like to
1952transform in some way; in particular, you'd like to manipulate its
1953<tt>BasicBlock</tt>s. To facilitate this, you'll need to iterate over all of
1954the <tt>BasicBlock</tt>s that constitute the <tt>Function</tt>. The following is
1955an example that prints the name of a <tt>BasicBlock</tt> and the number of
1956<tt>Instruction</tt>s it contains:</p>
1957
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1958<div class="doc_code">
1959<pre>
Bill Wendling82e2eea2006-10-11 18:00:22 +0000[diff] [blame]1960// <i>func is a pointer to a Function instance</i>
1961for (Function::iterator i = func-&gt;begin(), e = func-&gt;end(); i != e; ++i)
1962 // <i>Print out the name of the basic block if it has one, and then the</i>
1963 // <i>number of instructions that it contains</i>
Chris Lattner3fee6ed2009-09-08 05:15:50 +0000[diff] [blame]1964 errs() &lt;&lt; "Basic block (name=" &lt;&lt; i-&gt;getName() &lt;&lt; ") has "
Bill Wendling832171c2006-12-07 20:04:42 +0000[diff] [blame]1965 &lt;&lt; i-&gt;size() &lt;&lt; " instructions.\n";
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1966</pre>
1967</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1968
1969<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]1970invoking member functions of the <tt>Instruction</tt> class. This is
1971because the indirection operator is overloaded for the iterator
Chris Lattner7496ec52003-08-05 22:54:23 +0000[diff] [blame]1972classes. In the above code, the expression <tt>i-&gt;size()</tt> is
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1973exactly equivalent to <tt>(*i).size()</tt> just like you'd expect.</p>
1974
1975</div>
1976
1977<!-- _______________________________________________________________________ -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]1978<h4>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1979 <a name="iterate_basicblock">Iterating over the </a><a
1980 href="#Instruction"><tt>Instruction</tt></a>s in a <a
1981 href="#BasicBlock"><tt>BasicBlock</tt></a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]1982</h4>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1983
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]1984<div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1985
1986<p>Just like when dealing with <tt>BasicBlock</tt>s in <tt>Function</tt>s, it's
1987easy to iterate over the individual instructions that make up
1988<tt>BasicBlock</tt>s. Here's a code snippet that prints out each instruction in
1989a <tt>BasicBlock</tt>:</p>
1990
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1991<div class="doc_code">
Chris Lattner55c04612005-03-06 06:00:13 +0000[diff] [blame]1992<pre>
Bill Wendling82e2eea2006-10-11 18:00:22 +0000[diff] [blame]1993// <i>blk is a pointer to a BasicBlock instance</i>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1994for (BasicBlock::iterator i = blk-&gt;begin(), e = blk-&gt;end(); i != e; ++i)
Bill Wendling82e2eea2006-10-11 18:00:22 +0000[diff] [blame]1995 // <i>The next statement works since operator&lt;&lt;(ostream&amp;,...)</i>
1996 // <i>is overloaded for Instruction&amp;</i>
Chris Lattner3fee6ed2009-09-08 05:15:50 +0000[diff] [blame]1997 errs() &lt;&lt; *i &lt;&lt; "\n";
Chris Lattner55c04612005-03-06 06:00:13 +0000[diff] [blame]1998</pre>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1999</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2000
2001<p>However, this isn't really the best way to print out the contents of a
2002<tt>BasicBlock</tt>! Since the ostream operators are overloaded for virtually
2003anything you'll care about, you could have just invoked the print routine on the
Chris Lattner3fee6ed2009-09-08 05:15:50 +0000[diff] [blame]2004basic block itself: <tt>errs() &lt;&lt; *blk &lt;&lt; "\n";</tt>.</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2005
2006</div>
2007
2008<!-- _______________________________________________________________________ -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]2009<h4>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2010 <a name="iterate_institer">Iterating over the </a><a
2011 href="#Instruction"><tt>Instruction</tt></a>s in a <a
2012 href="#Function"><tt>Function</tt></a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]2013</h4>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2014
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]2015<div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2016
2017<p>If you're finding that you commonly iterate over a <tt>Function</tt>'s
2018<tt>BasicBlock</tt>s and then that <tt>BasicBlock</tt>'s <tt>Instruction</tt>s,
2019<tt>InstIterator</tt> should be used instead. You'll need to include <a
2020href="/doxygen/InstIterator_8h-source.html"><tt>llvm/Support/InstIterator.h</tt></a>,
2021and then instantiate <tt>InstIterator</tt>s explicitly in your code. Here's a
Chris Lattner69bf8a92004-05-23 21:06:58 +0000[diff] [blame]2022small 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]2023
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2024<div class="doc_code">
2025<pre>
2026#include "<a href="/doxygen/InstIterator_8h-source.html">llvm/Support/InstIterator.h</a>"
2027
Reid Spencer128a7a72007-02-03 21:06:43 +0000[diff] [blame]2028// <i>F is a pointer to a Function instance</i>
Chris Lattnerda021aa2008-06-04 18:20:42 +0000[diff] [blame]2029for (inst_iterator I = inst_begin(F), E = inst_end(F); I != E; ++I)
Chris Lattner3fee6ed2009-09-08 05:15:50 +0000[diff] [blame]2030 errs() &lt;&lt; *I &lt;&lt; "\n";
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2031</pre>
2032</div>
2033
2034<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]2035work list with its initial contents. For example, if you wanted to
2036initialize a work list to contain all instructions in a <tt>Function</tt>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2037F, all you would need to do is something like:</p>
2038
2039<div class="doc_code">
2040<pre>
2041std::set&lt;Instruction*&gt; worklist;
Chris Lattnerda021aa2008-06-04 18:20:42 +0000[diff] [blame]2042// or better yet, SmallPtrSet&lt;Instruction*, 64&gt; worklist;
2043
2044for (inst_iterator I = inst_begin(F), E = inst_end(F); I != E; ++I)
2045 worklist.insert(&amp;*I);
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2046</pre>
2047</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2048
2049<p>The STL set <tt>worklist</tt> would now contain all instructions in the
2050<tt>Function</tt> pointed to by F.</p>
2051
2052</div>
2053
2054<!-- _______________________________________________________________________ -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]2055<h4>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2056 <a name="iterate_convert">Turning an iterator into a class pointer (and
2057 vice-versa)</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]2058</h4>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2059
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]2060<div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2061
2062<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]2063instance when all you've got at hand is an iterator. Well, extracting
Chris Lattner69bf8a92004-05-23 21:06:58 +0000[diff] [blame]2064a reference or a pointer from an iterator is very straight-forward.
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]2065Assuming that <tt>i</tt> is a <tt>BasicBlock::iterator</tt> and <tt>j</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2066is a <tt>BasicBlock::const_iterator</tt>:</p>
2067
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2068<div class="doc_code">
2069<pre>
Bill Wendling82e2eea2006-10-11 18:00:22 +0000[diff] [blame]2070Instruction&amp; inst = *i; // <i>Grab reference to instruction reference</i>
2071Instruction* pinst = &amp;*i; // <i>Grab pointer to instruction reference</i>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2072const Instruction&amp; inst = *j;
2073</pre>
2074</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2075
2076<p>However, the iterators you'll be working with in the LLVM framework are
2077special: they will automatically convert to a ptr-to-instance type whenever they
2078need to. Instead of dereferencing the iterator and then taking the address of
2079the result, you can simply assign the iterator to the proper pointer type and
2080you get the dereference and address-of operation as a result of the assignment
2081(behind the scenes, this is a result of overloading casting mechanisms). Thus
2082the last line of the last example,</p>
2083
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2084<div class="doc_code">
2085<pre>
Chris Lattner2e438ca2008-01-03 16:56:04 +0000[diff] [blame]2086Instruction *pinst = &amp;*i;
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2087</pre>
2088</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2089
2090<p>is semantically equivalent to</p>
2091
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2092<div class="doc_code">
2093<pre>
Chris Lattner2e438ca2008-01-03 16:56:04 +0000[diff] [blame]2094Instruction *pinst = i;
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2095</pre>
2096</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2097
Chris Lattner69bf8a92004-05-23 21:06:58 +0000[diff] [blame]2098<p>It's also possible to turn a class pointer into the corresponding iterator,
2099and this is a constant time operation (very efficient). The following code
2100snippet illustrates use of the conversion constructors provided by LLVM
2101iterators. By using these, you can explicitly grab the iterator of something
2102without actually obtaining it via iteration over some structure:</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2103
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2104<div class="doc_code">
2105<pre>
2106void printNextInstruction(Instruction* inst) {
2107 BasicBlock::iterator it(inst);
Bill Wendling82e2eea2006-10-11 18:00:22 +0000[diff] [blame]2108 ++it; // <i>After this line, it refers to the instruction after *inst</i>
Chris Lattner3fee6ed2009-09-08 05:15:50 +0000[diff] [blame]2109 if (it != inst-&gt;getParent()-&gt;end()) errs() &lt;&lt; *it &lt;&lt; "\n";
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2110}
2111</pre>
2112</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2113
Dan Gohman525bf8e2010-03-26 19:39:05 +0000[diff] [blame]2114<p>Unfortunately, these implicit conversions come at a cost; they prevent
2115these iterators from conforming to standard iterator conventions, and thus
Dan Gohman0d91c112010-03-26 19:51:14 +0000[diff] [blame]2116from being usable with standard algorithms and containers. For example, they
2117prevent the following code, where <tt>B</tt> is a <tt>BasicBlock</tt>,
Dan Gohman525bf8e2010-03-26 19:39:05 +0000[diff] [blame]2118from compiling:</p>
2119
2120<div class="doc_code">
2121<pre>
2122 llvm::SmallVector&lt;llvm::Instruction *, 16&gt;(B-&gt;begin(), B-&gt;end());
2123</pre>
2124</div>
2125
2126<p>Because of this, these implicit conversions may be removed some day,
Dan Gohman0d91c112010-03-26 19:51:14 +0000[diff] [blame]2127and <tt>operator*</tt> changed to return a pointer instead of a reference.</p>
Dan Gohman525bf8e2010-03-26 19:39:05 +0000[diff] [blame]2128
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2129</div>
2130
2131<!--_______________________________________________________________________-->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]2132<h4>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2133 <a name="iterate_complex">Finding call sites: a slightly more complex
2134 example</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]2135</h4>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2136
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]2137<div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2138
2139<p>Say that you're writing a FunctionPass and would like to count all the
2140locations in the entire module (that is, across every <tt>Function</tt>) where a
2141certain function (i.e., some <tt>Function</tt>*) is already in scope. As you'll
2142learn 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]2143much more straight-forward manner, but this example will allow us to explore how
Reid Spencer128a7a72007-02-03 21:06:43 +0000[diff] [blame]2144you'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]2145is what we want to do:</p>
2146
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2147<div class="doc_code">
2148<pre>
2149initialize callCounter to zero
2150for each Function f in the Module
2151 for each BasicBlock b in f
2152 for each Instruction i in b
2153 if (i is a CallInst and calls the given function)
2154 increment callCounter
2155</pre>
2156</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2157
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2158<p>And the actual code is (remember, because we're writing a
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2159<tt>FunctionPass</tt>, our <tt>FunctionPass</tt>-derived class simply has to
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2160override the <tt>runOnFunction</tt> method):</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2161
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2162<div class="doc_code">
2163<pre>
2164Function* targetFunc = ...;
2165
2166class OurFunctionPass : public FunctionPass {
2167 public:
2168 OurFunctionPass(): callCounter(0) { }
2169
2170 virtual runOnFunction(Function&amp; F) {
2171 for (Function::iterator b = F.begin(), be = F.end(); b != be; ++b) {
Eric Christopher203e71d2008-11-08 08:20:49 +0000[diff] [blame]2172 for (BasicBlock::iterator i = b-&gt;begin(), ie = b-&gt;end(); i != ie; ++i) {
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2173 if (<a href="#CallInst">CallInst</a>* callInst = <a href="#isa">dyn_cast</a>&lt;<a
2174 href="#CallInst">CallInst</a>&gt;(&amp;*i)) {
Bill Wendling82e2eea2006-10-11 18:00:22 +0000[diff] [blame]2175 // <i>We know we've encountered a call instruction, so we</i>
2176 // <i>need to determine if it's a call to the</i>
Chris Lattner2e438ca2008-01-03 16:56:04 +0000[diff] [blame]2177 // <i>function pointed to by m_func or not.</i>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2178 if (callInst-&gt;getCalledFunction() == targetFunc)
2179 ++callCounter;
2180 }
2181 }
2182 }
Bill Wendling82e2eea2006-10-11 18:00:22 +0000[diff] [blame]2183 }
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2184
2185 private:
Chris Lattner2e438ca2008-01-03 16:56:04 +0000[diff] [blame]2186 unsigned callCounter;
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2187};
2188</pre>
2189</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2190
2191</div>
2192
Brian Gaekef1972c62003-11-07 19:25:45 +0000[diff] [blame]2193<!--_______________________________________________________________________-->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]2194<h4>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2195 <a name="calls_and_invokes">Treating calls and invokes the same way</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]2196</h4>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2197
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]2198<div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2199
2200<p>You may have noticed that the previous example was a bit oversimplified in
2201that it did not deal with call sites generated by 'invoke' instructions. In
2202this, and in other situations, you may find that you want to treat
2203<tt>CallInst</tt>s and <tt>InvokeInst</tt>s the same way, even though their
2204most-specific common base class is <tt>Instruction</tt>, which includes lots of
2205less closely-related things. For these cases, LLVM provides a handy wrapper
2206class called <a
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]2207href="http://llvm.org/doxygen/classllvm_1_1CallSite.html"><tt>CallSite</tt></a>.
Chris Lattner69bf8a92004-05-23 21:06:58 +0000[diff] [blame]2208It is essentially a wrapper around an <tt>Instruction</tt> pointer, with some
2209methods that provide functionality common to <tt>CallInst</tt>s and
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2210<tt>InvokeInst</tt>s.</p>
2211
Chris Lattner69bf8a92004-05-23 21:06:58 +0000[diff] [blame]2212<p>This class has "value semantics": it should be passed by value, not by
2213reference and it should not be dynamically allocated or deallocated using
2214<tt>operator new</tt> or <tt>operator delete</tt>. It is efficiently copyable,
2215assignable and constructable, with costs equivalents to that of a bare pointer.
2216If you look at its definition, it has only a single pointer member.</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2217
2218</div>
2219
Chris Lattner1a3105b2002-09-09 05:49:39 +0000[diff] [blame]2220<!--_______________________________________________________________________-->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]2221<h4>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2222 <a name="iterate_chains">Iterating over def-use &amp; use-def chains</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]2223</h4>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2224
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]2225<div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2226
2227<p>Frequently, we might have an instance of the <a
Chris Lattner00815172007-01-04 22:01:45 +0000[diff] [blame]2228href="/doxygen/classllvm_1_1Value.html">Value Class</a> and we want to
Misha Brukman384047f2004-06-03 23:29:12 +0000[diff] [blame]2229determine which <tt>User</tt>s use the <tt>Value</tt>. The list of all
2230<tt>User</tt>s of a particular <tt>Value</tt> is called a <i>def-use</i> chain.
2231For example, let's say we have a <tt>Function*</tt> named <tt>F</tt> to a
2232particular function <tt>foo</tt>. Finding all of the instructions that
2233<i>use</i> <tt>foo</tt> is as simple as iterating over the <i>def-use</i> chain
2234of <tt>F</tt>:</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2235
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2236<div class="doc_code">
2237<pre>
Chris Lattner2e438ca2008-01-03 16:56:04 +0000[diff] [blame]2238Function *F = ...;
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2239
Bill Wendling82e2eea2006-10-11 18:00:22 +0000[diff] [blame]2240for (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]2241 if (Instruction *Inst = dyn_cast&lt;Instruction&gt;(*i)) {
Chris Lattner3fee6ed2009-09-08 05:15:50 +0000[diff] [blame]2242 errs() &lt;&lt; "F is used in instruction:\n";
2243 errs() &lt;&lt; *Inst &lt;&lt; "\n";
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2244 }
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2245</pre>
Gabor Greif394fdfb2010-03-26 19:35:48 +0000[diff] [blame]2246</div>
2247
Gabor Greifce94319532010-03-26 19:40:38 +0000[diff] [blame]2248<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]2249operation. Instead of performing <tt>*i</tt> above several times, consider
Gabor Greifce94319532010-03-26 19:40:38 +0000[diff] [blame]2250doing it only once in the loop body and reusing its result.</p>
Gabor Greif4de73682010-03-26 19:30:47 +0000[diff] [blame]2251
Gabor Greif6091ff32010-03-26 19:04:42 +0000[diff] [blame]2252<p>Alternatively, it's common to have an instance of the <a
Misha Brukman384047f2004-06-03 23:29:12 +0000[diff] [blame]2253href="/doxygen/classllvm_1_1User.html">User Class</a> and need to know what
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2254<tt>Value</tt>s are used by it. The list of all <tt>Value</tt>s used by a
2255<tt>User</tt> is known as a <i>use-def</i> chain. Instances of class
2256<tt>Instruction</tt> are common <tt>User</tt>s, so we might want to iterate over
2257all of the values that a particular instruction uses (that is, the operands of
2258the particular <tt>Instruction</tt>):</p>
2259
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2260<div class="doc_code">
2261<pre>
Chris Lattner2e438ca2008-01-03 16:56:04 +0000[diff] [blame]2262Instruction *pi = ...;
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2263
2264for (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]2265 Value *v = *i;
Bill Wendling82e2eea2006-10-11 18:00:22 +0000[diff] [blame]2266 // <i>...</i>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2267}
2268</pre>
2269</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2270
Gabor Greif4de73682010-03-26 19:30:47 +0000[diff] [blame]2271<p>Declaring objects as <tt>const</tt> is an important tool of enforcing
Gabor Greifce94319532010-03-26 19:40:38 +0000[diff] [blame]2272mutation free algorithms (such as analyses, etc.). For this purpose above
Gabor Greif4de73682010-03-26 19:30:47 +0000[diff] [blame]2273iterators come in constant flavors as <tt>Value::const_use_iterator</tt>
2274and <tt>Value::const_op_iterator</tt>. They automatically arise when
2275calling <tt>use/op_begin()</tt> on <tt>const Value*</tt>s or
2276<tt>const User*</tt>s respectively. Upon dereferencing, they return
Gabor Greifce94319532010-03-26 19:40:38 +0000[diff] [blame]2277<tt>const Use*</tt>s. Otherwise the above patterns remain unchanged.</p>
2278
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2279</div>
2280
Chris Lattner2e438ca2008-01-03 16:56:04 +0000[diff] [blame]2281<!--_______________________________________________________________________-->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]2282<h4>
Chris Lattner2e438ca2008-01-03 16:56:04 +0000[diff] [blame]2283 <a name="iterate_preds">Iterating over predecessors &amp;
2284successors of blocks</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]2285</h4>
Chris Lattner2e438ca2008-01-03 16:56:04 +0000[diff] [blame]2286
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]2287<div>
Chris Lattner2e438ca2008-01-03 16:56:04 +0000[diff] [blame]2288
2289<p>Iterating over the predecessors and successors of a block is quite easy
2290with the routines defined in <tt>"llvm/Support/CFG.h"</tt>. Just use code like
2291this to iterate over all predecessors of BB:</p>
2292
2293<div class="doc_code">
2294<pre>
2295#include "llvm/Support/CFG.h"
2296BasicBlock *BB = ...;
2297
2298for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI) {
2299 BasicBlock *Pred = *PI;
2300 // <i>...</i>
2301}
2302</pre>
2303</div>
2304
2305<p>Similarly, to iterate over successors use
2306succ_iterator/succ_begin/succ_end.</p>
2307
2308</div>
2309
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]2310</div>
Chris Lattner2e438ca2008-01-03 16:56:04 +0000[diff] [blame]2311
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2312<!-- ======================================================================= -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]2313<h3>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2314 <a name="simplechanges">Making simple changes</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]2315</h3>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2316
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]2317<div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2318
2319<p>There are some primitive transformation operations present in the LLVM
Joel Stanley753eb712002-09-11 22:32:24 +0000[diff] [blame]2320infrastructure that are worth knowing about. When performing
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]2321transformations, it's fairly common to manipulate the contents of basic
2322blocks. This section describes some of the common methods for doing so
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2323and gives example code.</p>
2324
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]2325<!--_______________________________________________________________________-->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]2326<h4>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2327 <a name="schanges_creating">Creating and inserting new
2328 <tt>Instruction</tt>s</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]2329</h4>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2330
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]2331<div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2332
2333<p><i>Instantiating Instructions</i></p>
2334
Chris Lattner69bf8a92004-05-23 21:06:58 +0000[diff] [blame]2335<p>Creation of <tt>Instruction</tt>s is straight-forward: simply call the
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2336constructor for the kind of instruction to instantiate and provide the necessary
2337parameters. For example, an <tt>AllocaInst</tt> only <i>requires</i> a
2338(const-ptr-to) <tt>Type</tt>. Thus:</p>
2339
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2340<div class="doc_code">
2341<pre>
Nick Lewycky10d64b92007-12-03 01:52:52 +0000[diff] [blame]2342AllocaInst* ai = new AllocaInst(Type::Int32Ty);
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2343</pre>
2344</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2345
2346<p>will create an <tt>AllocaInst</tt> instance that represents the allocation of
Reid Spencer128a7a72007-02-03 21:06:43 +0000[diff] [blame]2347one integer in the current stack frame, at run time. Each <tt>Instruction</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2348subclass is likely to have varying default parameters which change the semantics
2349of the instruction, so refer to the <a
Misha Brukman31ca1de2004-06-03 23:35:54 +0000[diff] [blame]2350href="/doxygen/classllvm_1_1Instruction.html">doxygen documentation for the subclass of
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2351Instruction</a> that you're interested in instantiating.</p>
2352
2353<p><i>Naming values</i></p>
2354
2355<p>It is very useful to name the values of instructions when you're able to, as
2356this facilitates the debugging of your transformations. If you end up looking
2357at generated LLVM machine code, you definitely want to have logical names
2358associated with the results of instructions! By supplying a value for the
2359<tt>Name</tt> (default) parameter of the <tt>Instruction</tt> constructor, you
2360associate a logical name with the result of the instruction's execution at
Reid Spencer128a7a72007-02-03 21:06:43 +0000[diff] [blame]2361run time. For example, say that I'm writing a transformation that dynamically
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2362allocates space for an integer on the stack, and that integer is going to be
2363used as some kind of index by some other code. To accomplish this, I place an
2364<tt>AllocaInst</tt> at the first point in the first <tt>BasicBlock</tt> of some
2365<tt>Function</tt>, and I'm intending to use it within the same
2366<tt>Function</tt>. I might do:</p>
2367
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2368<div class="doc_code">
2369<pre>
Nick Lewycky10d64b92007-12-03 01:52:52 +0000[diff] [blame]2370AllocaInst* pa = new AllocaInst(Type::Int32Ty, 0, "indexLoc");
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2371</pre>
2372</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2373
2374<p>where <tt>indexLoc</tt> is now the logical name of the instruction's
Reid Spencer128a7a72007-02-03 21:06:43 +0000[diff] [blame]2375execution value, which is a pointer to an integer on the run time stack.</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2376
2377<p><i>Inserting instructions</i></p>
2378
2379<p>There are essentially two ways to insert an <tt>Instruction</tt>
2380into an existing sequence of instructions that form a <tt>BasicBlock</tt>:</p>
2381
Joel Stanley9dd1ad62002-09-18 03:17:23 +0000[diff] [blame]2382<ul>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2383 <li>Insertion into an explicit instruction list
2384
2385 <p>Given a <tt>BasicBlock* pb</tt>, an <tt>Instruction* pi</tt> within that
2386 <tt>BasicBlock</tt>, and a newly-created instruction we wish to insert
2387 before <tt>*pi</tt>, we do the following: </p>
2388
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2389<div class="doc_code">
2390<pre>
2391BasicBlock *pb = ...;
2392Instruction *pi = ...;
2393Instruction *newInst = new Instruction(...);
2394
Bill Wendling82e2eea2006-10-11 18:00:22 +0000[diff] [blame]2395pb-&gt;getInstList().insert(pi, newInst); // <i>Inserts newInst before pi in pb</i>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2396</pre>
2397</div>
Alkis Evlogimenos9a5dc4f2004-05-27 00:57:51 +0000[diff] [blame]2398
2399 <p>Appending to the end of a <tt>BasicBlock</tt> is so common that
2400 the <tt>Instruction</tt> class and <tt>Instruction</tt>-derived
2401 classes provide constructors which take a pointer to a
2402 <tt>BasicBlock</tt> to be appended to. For example code that
2403 looked like: </p>
2404
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2405<div class="doc_code">
2406<pre>
2407BasicBlock *pb = ...;
2408Instruction *newInst = new Instruction(...);
2409
Bill Wendling82e2eea2006-10-11 18:00:22 +0000[diff] [blame]2410pb-&gt;getInstList().push_back(newInst); // <i>Appends newInst to pb</i>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2411</pre>
2412</div>
Alkis Evlogimenos9a5dc4f2004-05-27 00:57:51 +0000[diff] [blame]2413
2414 <p>becomes: </p>
2415
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2416<div class="doc_code">
2417<pre>
2418BasicBlock *pb = ...;
2419Instruction *newInst = new Instruction(..., pb);
2420</pre>
2421</div>
Alkis Evlogimenos9a5dc4f2004-05-27 00:57:51 +0000[diff] [blame]2422
2423 <p>which is much cleaner, especially if you are creating
2424 long instruction streams.</p></li>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2425
2426 <li>Insertion into an implicit instruction list
2427
2428 <p><tt>Instruction</tt> instances that are already in <tt>BasicBlock</tt>s
2429 are implicitly associated with an existing instruction list: the instruction
2430 list of the enclosing basic block. Thus, we could have accomplished the same
2431 thing as the above code without being given a <tt>BasicBlock</tt> by doing:
2432 </p>
2433
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2434<div class="doc_code">
2435<pre>
2436Instruction *pi = ...;
2437Instruction *newInst = new Instruction(...);
2438
2439pi-&gt;getParent()-&gt;getInstList().insert(pi, newInst);
2440</pre>
2441</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2442
2443 <p>In fact, this sequence of steps occurs so frequently that the
2444 <tt>Instruction</tt> class and <tt>Instruction</tt>-derived classes provide
2445 constructors which take (as a default parameter) a pointer to an
2446 <tt>Instruction</tt> which the newly-created <tt>Instruction</tt> should
2447 precede. That is, <tt>Instruction</tt> constructors are capable of
2448 inserting the newly-created instance into the <tt>BasicBlock</tt> of a
2449 provided instruction, immediately before that instruction. Using an
2450 <tt>Instruction</tt> constructor with a <tt>insertBefore</tt> (default)
2451 parameter, the above code becomes:</p>
2452
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2453<div class="doc_code">
2454<pre>
2455Instruction* pi = ...;
2456Instruction* newInst = new Instruction(..., pi);
2457</pre>
2458</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2459
2460 <p>which is much cleaner, especially if you're creating a lot of
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2461 instructions and adding them to <tt>BasicBlock</tt>s.</p></li>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2462</ul>
2463
2464</div>
2465
2466<!--_______________________________________________________________________-->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]2467<h4>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2468 <a name="schanges_deleting">Deleting <tt>Instruction</tt>s</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]2469</h4>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2470
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]2471<div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2472
2473<p>Deleting an instruction from an existing sequence of instructions that form a
Chris Lattner49e0ccf2011-03-24 16:13:31 +0000[diff] [blame]2474<a href="#BasicBlock"><tt>BasicBlock</tt></a> is very straight-forward: just
2475call the instruction's eraseFromParent() method. For example:</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2476
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2477<div class="doc_code">
2478<pre>
2479<a href="#Instruction">Instruction</a> *I = .. ;
Chris Lattner9f8ec252008-02-15 22:57:17 +0000[diff] [blame]2480I-&gt;eraseFromParent();
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2481</pre>
2482</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2483
Chris Lattner49e0ccf2011-03-24 16:13:31 +0000[diff] [blame]2484<p>This unlinks the instruction from its containing basic block and deletes
2485it. If you'd just like to unlink the instruction from its containing basic
2486block but not delete it, you can use the <tt>removeFromParent()</tt> method.</p>
2487
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2488</div>
2489
2490<!--_______________________________________________________________________-->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]2491<h4>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2492 <a name="schanges_replacing">Replacing an <tt>Instruction</tt> with another
2493 <tt>Value</tt></a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]2494</h4>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2495
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]2496<div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2497
2498<p><i>Replacing individual instructions</i></p>
2499
2500<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]2501permits use of two very useful replace functions: <tt>ReplaceInstWithValue</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2502and <tt>ReplaceInstWithInst</tt>.</p>
2503
NAKAMURA Takumi06c6d9a2011-04-18 01:17:51 +0000[diff] [blame]2504<h5><a name="schanges_deleting">Deleting <tt>Instruction</tt>s</a></h5>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2505
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]2506<ul>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2507 <li><tt>ReplaceInstWithValue</tt>
2508
Nick Lewyckyb6d1f392008-09-15 06:31:52 +0000[diff] [blame]2509 <p>This function replaces all uses of a given instruction with a value,
2510 and then removes the original instruction. The following example
2511 illustrates the replacement of the result of a particular
Chris Lattner58360822005-01-17 00:12:04 +0000[diff] [blame]2512 <tt>AllocaInst</tt> that allocates memory for a single integer with a null
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2513 pointer to an integer.</p>
2514
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2515<div class="doc_code">
2516<pre>
2517AllocaInst* instToReplace = ...;
2518BasicBlock::iterator ii(instToReplace);
2519
2520ReplaceInstWithValue(instToReplace-&gt;getParent()-&gt;getInstList(), ii,
Daniel Dunbar58c2ac02008-10-03 22:17:25 +0000[diff] [blame]2521 Constant::getNullValue(PointerType::getUnqual(Type::Int32Ty)));
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2522</pre></div></li>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2523
2524 <li><tt>ReplaceInstWithInst</tt>
2525
2526 <p>This function replaces a particular instruction with another
Nick Lewyckyb6d1f392008-09-15 06:31:52 +0000[diff] [blame]2527 instruction, inserting the new instruction into the basic block at the
2528 location where the old instruction was, and replacing any uses of the old
2529 instruction with the new instruction. The following example illustrates
2530 the replacement of one <tt>AllocaInst</tt> with another.</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2531
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2532<div class="doc_code">
2533<pre>
2534AllocaInst* instToReplace = ...;
2535BasicBlock::iterator ii(instToReplace);
2536
2537ReplaceInstWithInst(instToReplace-&gt;getParent()-&gt;getInstList(), ii,
Nick Lewycky10d64b92007-12-03 01:52:52 +0000[diff] [blame]2538 new AllocaInst(Type::Int32Ty, 0, "ptrToReplacedInt"));
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2539</pre></div></li>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]2540</ul>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2541
2542<p><i>Replacing multiple uses of <tt>User</tt>s and <tt>Value</tt>s</i></p>
2543
2544<p>You can use <tt>Value::replaceAllUsesWith</tt> and
2545<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]2546doxygen documentation for the <a href="/doxygen/classllvm_1_1Value.html">Value Class</a>
Misha Brukman384047f2004-06-03 23:29:12 +0000[diff] [blame]2547and <a href="/doxygen/classllvm_1_1User.html">User Class</a>, respectively, for more
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2548information.</p>
2549
2550<!-- Value::replaceAllUsesWith User::replaceUsesOfWith Point out:
2551include/llvm/Transforms/Utils/ especially BasicBlockUtils.h with:
2552ReplaceInstWithValue, ReplaceInstWithInst -->
2553
2554</div>
2555
Tanya Lattnerb011c662007-06-20 18:33:15 +0000[diff] [blame]2556<!--_______________________________________________________________________-->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]2557<h4>
Tanya Lattnerb011c662007-06-20 18:33:15 +0000[diff] [blame]2558 <a name="schanges_deletingGV">Deleting <tt>GlobalVariable</tt>s</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]2559</h4>
Tanya Lattnerb011c662007-06-20 18:33:15 +0000[diff] [blame]2560
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]2561<div>
Tanya Lattnerb011c662007-06-20 18:33:15 +0000[diff] [blame]2562
Tanya Lattnerc5dfcdb2007-06-20 20:46:37 +0000[diff] [blame]2563<p>Deleting a global variable from a module is just as easy as deleting an
2564Instruction. First, you must have a pointer to the global variable that you wish
2565 to delete. You use this pointer to erase it from its parent, the module.
Tanya Lattnerb011c662007-06-20 18:33:15 +0000[diff] [blame]2566 For example:</p>
2567
2568<div class="doc_code">
2569<pre>
2570<a href="#GlobalVariable">GlobalVariable</a> *GV = .. ;
Tanya Lattnerb011c662007-06-20 18:33:15 +0000[diff] [blame]2571
Tanya Lattnerc5dfcdb2007-06-20 20:46:37 +0000[diff] [blame]2572GV-&gt;eraseFromParent();
Tanya Lattnerb011c662007-06-20 18:33:15 +0000[diff] [blame]2573</pre>
2574</div>
2575
2576</div>
2577
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]2578</div>
2579
Jeffrey Yasskin714257f2009-04-30 22:33:41 +0000[diff] [blame]2580<!-- ======================================================================= -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]2581<h3>
Jeffrey Yasskin714257f2009-04-30 22:33:41 +0000[diff] [blame]2582 <a name="create_types">How to Create Types</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]2583</h3>
Jeffrey Yasskin714257f2009-04-30 22:33:41 +0000[diff] [blame]2584
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]2585<div>
Jeffrey Yasskin714257f2009-04-30 22:33:41 +0000[diff] [blame]2586
2587<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]2588statically, you can use <tt>TypeBuilder&lt;...&gt;::get()</tt>, defined
Jeffrey Yasskin714257f2009-04-30 22:33:41 +0000[diff] [blame]2589in <tt>llvm/Support/TypeBuilder.h</tt>, to retrieve them. <tt>TypeBuilder</tt>
2590has two forms depending on whether you're building types for cross-compilation
Misha Brukman1af789f2009-05-01 20:40:51 +0000[diff] [blame]2591or native library use. <tt>TypeBuilder&lt;T, true&gt;</tt> requires
Jeffrey Yasskin714257f2009-04-30 22:33:41 +0000[diff] [blame]2592that <tt>T</tt> be independent of the host environment, meaning that it's built
2593out of types from
2594the <a href="/doxygen/namespacellvm_1_1types.html"><tt>llvm::types</tt></a>
2595namespace and pointers, functions, arrays, etc. built of
Misha Brukman1af789f2009-05-01 20:40:51 +0000[diff] [blame]2596those. <tt>TypeBuilder&lt;T, false&gt;</tt> additionally allows native C types
Jeffrey Yasskin714257f2009-04-30 22:33:41 +0000[diff] [blame]2597whose size may depend on the host compiler. For example,</p>
2598
2599<div class="doc_code">
2600<pre>
Misha Brukman1af789f2009-05-01 20:40:51 +0000[diff] [blame]2601FunctionType *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]2602</pre>
2603</div>
2604
2605<p>is easier to read and write than the equivalent</p>
2606
2607<div class="doc_code">
2608<pre>
Owen Anderson5e8c50e2009-06-16 17:40:28 +0000[diff] [blame]2609std::vector&lt;const Type*&gt; params;
Jeffrey Yasskin714257f2009-04-30 22:33:41 +0000[diff] [blame]2610params.push_back(PointerType::getUnqual(Type::Int32Ty));
2611FunctionType *ft = FunctionType::get(Type::Int8Ty, params, false);
2612</pre>
2613</div>
2614
2615<p>See the <a href="/doxygen/TypeBuilder_8h-source.html#l00001">class
2616comment</a> for more details.</p>
2617
2618</div>
2619
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]2620</div>
2621
Chris Lattner9355b472002-09-06 02:50:58 +0000[diff] [blame]2622<!-- *********************************************************************** -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]2623<h2>
Owen Anderson8bc1b3b2009-06-16 01:17:16 +0000[diff] [blame]2624 <a name="threading">Threads and LLVM</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]2625</h2>
Owen Anderson8bc1b3b2009-06-16 01:17:16 +0000[diff] [blame]2626<!-- *********************************************************************** -->
2627
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]2628<div>
Owen Anderson8bc1b3b2009-06-16 01:17:16 +0000[diff] [blame]2629<p>
2630This section describes the interaction of the LLVM APIs with multithreading,
2631both on the part of client applications, and in the JIT, in the hosted
2632application.
2633</p>
2634
2635<p>
2636Note that LLVM's support for multithreading is still relatively young. Up
2637through version 2.5, the execution of threaded hosted applications was
2638supported, but not threaded client access to the APIs. While this use case is
2639now supported, clients <em>must</em> adhere to the guidelines specified below to
2640ensure proper operation in multithreaded mode.
2641</p>
2642
2643<p>
2644Note that, on Unix-like platforms, LLVM requires the presence of GCC's atomic
2645intrinsics in order to support threaded operation. If you need a
2646multhreading-capable LLVM on a platform without a suitably modern system
2647compiler, consider compiling LLVM and LLVM-GCC in single-threaded mode, and
2648using the resultant compiler to build a copy of LLVM with multithreading
2649support.
2650</p>
Owen Anderson8bc1b3b2009-06-16 01:17:16 +0000[diff] [blame]2651
2652<!-- ======================================================================= -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]2653<h3>
Owen Anderson1ad70e32009-06-16 18:04:19 +0000[diff] [blame]2654 <a name="startmultithreaded">Entering and Exiting Multithreaded Mode</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]2655</h3>
Owen Anderson8bc1b3b2009-06-16 01:17:16 +0000[diff] [blame]2656
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]2657<div>
Owen Anderson8bc1b3b2009-06-16 01:17:16 +0000[diff] [blame]2658
2659<p>
2660In order to properly protect its internal data structures while avoiding
Owen Anderson1ad70e32009-06-16 18:04:19 +0000[diff] [blame]2661excessive locking overhead in the single-threaded case, the LLVM must intialize
2662certain data structures necessary to provide guards around its internals. To do
2663so, the client program must invoke <tt>llvm_start_multithreaded()</tt> before
2664making any concurrent LLVM API calls. To subsequently tear down these
2665structures, use the <tt>llvm_stop_multithreaded()</tt> call. You can also use
2666the <tt>llvm_is_multithreaded()</tt> call to check the status of multithreaded
2667mode.
Owen Anderson8bc1b3b2009-06-16 01:17:16 +0000[diff] [blame]2668</p>
2669
2670<p>
Owen Anderson1ad70e32009-06-16 18:04:19 +0000[diff] [blame]2671Note that both of these calls must be made <em>in isolation</em>. That is to
2672say that no other LLVM API calls may be executing at any time during the
2673execution of <tt>llvm_start_multithreaded()</tt> or <tt>llvm_stop_multithreaded
2674</tt>. It's is the client's responsibility to enforce this isolation.
2675</p>
2676
2677<p>
2678The return value of <tt>llvm_start_multithreaded()</tt> indicates the success or
2679failure of the initialization. Failure typically indicates that your copy of
2680LLVM was built without multithreading support, typically because GCC atomic
2681intrinsics were not found in your system compiler. In this case, the LLVM API
2682will not be safe for concurrent calls. However, it <em>will</em> be safe for
Jeffrey Yasskin01eba392010-01-29 19:10:38 +0000[diff] [blame]2683hosting threaded applications in the JIT, though <a href="#jitthreading">care
2684must be taken</a> to ensure that side exits and the like do not accidentally
2685result in concurrent LLVM API calls.
Owen Anderson8bc1b3b2009-06-16 01:17:16 +0000[diff] [blame]2686</p>
2687</div>
2688
2689<!-- ======================================================================= -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]2690<h3>
Owen Anderson8bc1b3b2009-06-16 01:17:16 +0000[diff] [blame]2691 <a name="shutdown">Ending Execution with <tt>llvm_shutdown()</tt></a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]2692</h3>
Owen Anderson8bc1b3b2009-06-16 01:17:16 +0000[diff] [blame]2693
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]2694<div>
Owen Anderson8bc1b3b2009-06-16 01:17:16 +0000[diff] [blame]2695<p>
2696When you are done using the LLVM APIs, you should call <tt>llvm_shutdown()</tt>
Owen Anderson1ad70e32009-06-16 18:04:19 +0000[diff] [blame]2697to deallocate memory used for internal structures. This will also invoke
2698<tt>llvm_stop_multithreaded()</tt> if LLVM is operating in multithreaded mode.
2699As such, <tt>llvm_shutdown()</tt> requires the same isolation guarantees as
2700<tt>llvm_stop_multithreaded()</tt>.
Owen Anderson8bc1b3b2009-06-16 01:17:16 +0000[diff] [blame]2701</p>
2702
2703<p>
2704Note that, if you use scope-based shutdown, you can use the
2705<tt>llvm_shutdown_obj</tt> class, which calls <tt>llvm_shutdown()</tt> in its
2706destructor.
2707</div>
2708
2709<!-- ======================================================================= -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]2710<h3>
Owen Anderson8bc1b3b2009-06-16 01:17:16 +0000[diff] [blame]2711 <a name="managedstatic">Lazy Initialization with <tt>ManagedStatic</tt></a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]2712</h3>
Owen Anderson8bc1b3b2009-06-16 01:17:16 +0000[diff] [blame]2713
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]2714<div>
Owen Anderson8bc1b3b2009-06-16 01:17:16 +0000[diff] [blame]2715<p>
2716<tt>ManagedStatic</tt> is a utility class in LLVM used to implement static
2717initialization of static resources, such as the global type tables. Before the
2718invocation of <tt>llvm_shutdown()</tt>, it implements a simple lazy
2719initialization scheme. Once <tt>llvm_start_multithreaded()</tt> returns,
2720however, it uses double-checked locking to implement thread-safe lazy
2721initialization.
2722</p>
2723
2724<p>
2725Note that, because no other threads are allowed to issue LLVM API calls before
2726<tt>llvm_start_multithreaded()</tt> returns, it is possible to have
2727<tt>ManagedStatic</tt>s of <tt>llvm::sys::Mutex</tt>s.
2728</p>
Owen Anderson1ad70e32009-06-16 18:04:19 +0000[diff] [blame]2729
2730<p>
2731The <tt>llvm_acquire_global_lock()</tt> and <tt>llvm_release_global_lock</tt>
2732APIs provide access to the global lock used to implement the double-checked
2733locking for lazy initialization. These should only be used internally to LLVM,
2734and only if you know what you're doing!
2735</p>
Owen Anderson8bc1b3b2009-06-16 01:17:16 +0000[diff] [blame]2736</div>
2737
Owen Andersone0c951a2009-08-19 17:58:52 +0000[diff] [blame]2738<!-- ======================================================================= -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]2739<h3>
Owen Andersone0c951a2009-08-19 17:58:52 +0000[diff] [blame]2740 <a name="llvmcontext">Achieving Isolation with <tt>LLVMContext</tt></a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]2741</h3>
Owen Andersone0c951a2009-08-19 17:58:52 +0000[diff] [blame]2742
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]2743<div>
Owen Andersone0c951a2009-08-19 17:58:52 +0000[diff] [blame]2744<p>
2745<tt>LLVMContext</tt> is an opaque class in the LLVM API which clients can use
2746to operate multiple, isolated instances of LLVM concurrently within the same
2747address space. For instance, in a hypothetical compile-server, the compilation
2748of an individual translation unit is conceptually independent from all the
2749others, and it would be desirable to be able to compile incoming translation
2750units concurrently on independent server threads. Fortunately,
2751<tt>LLVMContext</tt> exists to enable just this kind of scenario!
2752</p>
2753
2754<p>
2755Conceptually, <tt>LLVMContext</tt> provides isolation. Every LLVM entity
2756(<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]2757in LLVM's in-memory IR belongs to an <tt>LLVMContext</tt>. Entities in
Owen Andersone0c951a2009-08-19 17:58:52 +0000[diff] [blame]2758different contexts <em>cannot</em> interact with each other: <tt>Module</tt>s in
2759different contexts cannot be linked together, <tt>Function</tt>s cannot be added
2760to <tt>Module</tt>s in different contexts, etc. What this means is that is is
2761safe to compile on multiple threads simultaneously, as long as no two threads
2762operate on entities within the same context.
2763</p>
2764
2765<p>
2766In practice, very few places in the API require the explicit specification of a
2767<tt>LLVMContext</tt>, other than the <tt>Type</tt> creation/lookup APIs.
2768Because every <tt>Type</tt> carries a reference to its owning context, most
2769other entities can determine what context they belong to by looking at their
2770own <tt>Type</tt>. If you are adding new entities to LLVM IR, please try to
2771maintain this interface design.
2772</p>
2773
2774<p>
2775For clients that do <em>not</em> require the benefits of isolation, LLVM
2776provides a convenience API <tt>getGlobalContext()</tt>. This returns a global,
2777lazily initialized <tt>LLVMContext</tt> that may be used in situations where
2778isolation is not a concern.
2779</p>
2780</div>
2781
Jeffrey Yasskin01eba392010-01-29 19:10:38 +0000[diff] [blame]2782<!-- ======================================================================= -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]2783<h3>
Jeffrey Yasskin01eba392010-01-29 19:10:38 +0000[diff] [blame]2784 <a name="jitthreading">Threads and the JIT</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]2785</h3>
Jeffrey Yasskin01eba392010-01-29 19:10:38 +0000[diff] [blame]2786
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]2787<div>
Jeffrey Yasskin01eba392010-01-29 19:10:38 +0000[diff] [blame]2788<p>
2789LLVM's "eager" JIT compiler is safe to use in threaded programs. Multiple
2790threads can call <tt>ExecutionEngine::getPointerToFunction()</tt> or
2791<tt>ExecutionEngine::runFunction()</tt> concurrently, and multiple threads can
2792run code output by the JIT concurrently. The user must still ensure that only
2793one thread accesses IR in a given <tt>LLVMContext</tt> while another thread
2794might be modifying it. One way to do that is to always hold the JIT lock while
2795accessing IR outside the JIT (the JIT <em>modifies</em> the IR by adding
2796<tt>CallbackVH</tt>s). Another way is to only
2797call <tt>getPointerToFunction()</tt> from the <tt>LLVMContext</tt>'s thread.
2798</p>
2799
2800<p>When the JIT is configured to compile lazily (using
2801<tt>ExecutionEngine::DisableLazyCompilation(false)</tt>), there is currently a
2802<a href="http://llvm.org/bugs/show_bug.cgi?id=5184">race condition</a> in
2803updating call sites after a function is lazily-jitted. It's still possible to
2804use the lazy JIT in a threaded program if you ensure that only one thread at a
2805time can call any particular lazy stub and that the JIT lock guards any IR
2806access, but we suggest using only the eager JIT in threaded programs.
2807</p>
2808</div>
2809
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]2810</div>
2811
Owen Anderson8bc1b3b2009-06-16 01:17:16 +0000[diff] [blame]2812<!-- *********************************************************************** -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]2813<h2>
Chris Lattnerd9d6e102005-04-23 16:10:52 +0000[diff] [blame]2814 <a name="advanced">Advanced Topics</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]2815</h2>
Chris Lattnerd9d6e102005-04-23 16:10:52 +0000[diff] [blame]2816<!-- *********************************************************************** -->
2817
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]2818<div>
Chris Lattnerf1b200b2005-04-23 17:27:36 +0000[diff] [blame]2819<p>
2820This section describes some of the advanced or obscure API's that most clients
2821do not need to be aware of. These API's tend manage the inner workings of the
2822LLVM system, and only need to be accessed in unusual circumstances.
2823</p>
Chris Lattnerd9d6e102005-04-23 16:10:52 +0000[diff] [blame]2824
Chris Lattner1afcace2011-07-09 17:41:24 +0000[diff] [blame]2825
Chris Lattnerf1b200b2005-04-23 17:27:36 +0000[diff] [blame]2826<!-- ======================================================================= -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]2827<h3>
Chris Lattner1afcace2011-07-09 17:41:24 +0000[diff] [blame]2828 <a name="SymbolTable">The <tt>ValueSymbolTable</tt> class</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]2829</h3>
Chris Lattnerf1b200b2005-04-23 17:27:36 +0000[diff] [blame]2830
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]2831<div>
Chris Lattner263a98e2007-02-16 04:37:31 +0000[diff] [blame]2832<p>The <tt><a href="http://llvm.org/doxygen/classllvm_1_1ValueSymbolTable.html">
2833ValueSymbolTable</a></tt> class provides a symbol table that the <a
Chris Lattnerd9d6e102005-04-23 16:10:52 +0000[diff] [blame]2834href="#Function"><tt>Function</tt></a> and <a href="#Module">
Chris Lattner263a98e2007-02-16 04:37:31 +0000[diff] [blame]2835<tt>Module</tt></a> classes use for naming value definitions. The symbol table
2836can provide a name for any <a href="#Value"><tt>Value</tt></a>.
Chris Lattner1afcace2011-07-09 17:41:24 +0000[diff] [blame]2837</p>
Chris Lattnerd9d6e102005-04-23 16:10:52 +0000[diff] [blame]2838
Reid Spencera6362242007-01-07 00:41:39 +0000[diff] [blame]2839<p>Note that the <tt>SymbolTable</tt> class should not be directly accessed
2840by most clients. It should only be used when iteration over the symbol table
2841names themselves are required, which is very special purpose. Note that not
2842all LLVM
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2843<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]2844an empty name) do not exist in the symbol table.
2845</p>
2846
Chris Lattner1afcace2011-07-09 17:41:24 +0000[diff] [blame]2847<p>Symbol tables support iteration over the values in the symbol
Chris Lattner263a98e2007-02-16 04:37:31 +0000[diff] [blame]2848table with <tt>begin/end/iterator</tt> and supports querying to see if a
2849specific name is in the symbol table (with <tt>lookup</tt>). The
2850<tt>ValueSymbolTable</tt> class exposes no public mutator methods, instead,
2851simply call <tt>setName</tt> on a value, which will autoinsert it into the
Chris Lattner1afcace2011-07-09 17:41:24 +0000[diff] [blame]2852appropriate symbol table.</p>
Chris Lattnerd9d6e102005-04-23 16:10:52 +0000[diff] [blame]2853
Chris Lattnerd9d6e102005-04-23 16:10:52 +0000[diff] [blame]2854</div>
2855
2856
2857
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2858<!-- ======================================================================= -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]2859<h3>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2860 <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]2861</h3>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2862
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]2863<div>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2864<p>The <tt><a href="http://llvm.org/doxygen/classllvm_1_1User.html">
Gabor Greiffd095b62009-01-05 16:05:32 +0000[diff] [blame]2865User</a></tt> class provides a basis for expressing the ownership of <tt>User</tt>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2866towards other <tt><a href="http://llvm.org/doxygen/classllvm_1_1Value.html">
2867Value</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]2868Use</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]2869addition and removal.</p>
2870
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2871<!-- ______________________________________________________________________ -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]2872<h4>
2873 <a name="Use2User">
2874 Interaction and relationship between <tt>User</tt> and <tt>Use</tt> objects
2875 </a>
2876</h4>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2877
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]2878<div>
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2879<p>
2880A subclass of <tt>User</tt> can choose between incorporating its <tt>Use</tt> objects
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2881or refer to them out-of-line by means of a pointer. A mixed variant
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2882(some <tt>Use</tt>s inline others hung off) is impractical and breaks the invariant
2883that the <tt>Use</tt> objects belonging to the same <tt>User</tt> form a contiguous array.
2884</p>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2885
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2886<p>
2887We have 2 different layouts in the <tt>User</tt> (sub)classes:
2888<ul>
2889<li><p>Layout a)
2890The <tt>Use</tt> object(s) are inside (resp. at fixed offset) of the <tt>User</tt>
2891object and there are a fixed number of them.</p>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2892
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2893<li><p>Layout b)
2894The <tt>Use</tt> object(s) are referenced by a pointer to an
2895array from the <tt>User</tt> object and there may be a variable
2896number of them.</p>
2897</ul>
2898<p>
Gabor Greifd41720a2008-06-25 00:10:22 +0000[diff] [blame]2899As of v2.4 each layout still possesses a direct pointer to the
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2900start of the array of <tt>Use</tt>s. Though not mandatory for layout a),
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2901we stick to this redundancy for the sake of simplicity.
Gabor Greifd41720a2008-06-25 00:10:22 +0000[diff] [blame]2902The <tt>User</tt> object also stores the number of <tt>Use</tt> objects it
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2903has. (Theoretically this information can also be calculated
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2904given the scheme presented below.)</p>
2905<p>
2906Special forms of allocation operators (<tt>operator new</tt>)
Gabor Greifd41720a2008-06-25 00:10:22 +0000[diff] [blame]2907enforce the following memory layouts:</p>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2908
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2909<ul>
Gabor Greifd41720a2008-06-25 00:10:22 +0000[diff] [blame]2910<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]2911
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2912<pre>
2913...---.---.---.---.-------...
2914 | P | P | P | P | User
2915'''---'---'---'---'-------'''
2916</pre>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2917
Gabor Greifd41720a2008-06-25 00:10:22 +0000[diff] [blame]2918<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]2919<pre>
2920.-------...
2921| User
2922'-------'''
2923 |
2924 v
2925 .---.---.---.---...
2926 | P | P | P | P |
2927 '---'---'---'---'''
2928</pre>
2929</ul>
2930<i>(In the above figures '<tt>P</tt>' stands for the <tt>Use**</tt> that
2931 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]2932
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]2933</div>
2934
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2935<!-- ______________________________________________________________________ -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]2936<h4>
Gabor Greiffd095b62009-01-05 16:05:32 +0000[diff] [blame]2937 <a name="Waymarking">The waymarking algorithm</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]2938</h4>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2939
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]2940<div>
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2941<p>
Gabor Greifd41720a2008-06-25 00:10:22 +0000[diff] [blame]2942Since the <tt>Use</tt> objects are deprived of the direct (back)pointer to
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2943their <tt>User</tt> objects, there must be a fast and exact method to
2944recover it. This is accomplished by the following scheme:</p>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2945
Gabor Greifd41720a2008-06-25 00:10:22 +0000[diff] [blame]2946A 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]2947start of the <tt>User</tt> object:
2948<ul>
2949<li><tt>00</tt> &mdash;&gt; binary digit 0</li>
2950<li><tt>01</tt> &mdash;&gt; binary digit 1</li>
2951<li><tt>10</tt> &mdash;&gt; stop and calculate (<tt>s</tt>)</li>
2952<li><tt>11</tt> &mdash;&gt; full stop (<tt>S</tt>)</li>
2953</ul>
2954<p>
2955Given a <tt>Use*</tt>, all we have to do is to walk till we get
2956a stop and we either have a <tt>User</tt> immediately behind or
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2957we have to walk to the next stop picking up digits
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2958and calculating the offset:</p>
2959<pre>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2960.---.---.---.---.---.---.---.---.---.---.---.---.---.---.---.---.----------------
2961| 1 | s | 1 | 0 | 1 | 0 | s | 1 | 1 | 0 | s | 1 | 1 | s | 1 | S | User (or User*)
2962'---'---'---'---'---'---'---'---'---'---'---'---'---'---'---'---'----------------
2963 |+15 |+10 |+6 |+3 |+1
2964 | | | | |__>
2965 | | | |__________>
2966 | | |______________________>
2967 | |______________________________________>
2968 |__________________________________________________________>
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2969</pre>
2970<p>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2971Only the significant number of bits need to be stored between the
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2972stops, so that the <i>worst case is 20 memory accesses</i> when there are
29731000 <tt>Use</tt> objects associated with a <tt>User</tt>.</p>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2974
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]2975</div>
2976
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2977<!-- ______________________________________________________________________ -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]2978<h4>
Gabor Greiffd095b62009-01-05 16:05:32 +0000[diff] [blame]2979 <a name="ReferenceImpl">Reference implementation</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]2980</h4>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2981
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]2982<div>
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2983<p>
2984The following literate Haskell fragment demonstrates the concept:</p>
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2985
2986<div class="doc_code">
2987<pre>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2988> import Test.QuickCheck
2989>
2990> digits :: Int -> [Char] -> [Char]
2991> digits 0 acc = '0' : acc
2992> digits 1 acc = '1' : acc
2993> digits n acc = digits (n `div` 2) $ digits (n `mod` 2) acc
2994>
2995> dist :: Int -> [Char] -> [Char]
2996> dist 0 [] = ['S']
2997> dist 0 acc = acc
2998> dist 1 acc = let r = dist 0 acc in 's' : digits (length r) r
2999> dist n acc = dist (n - 1) $ dist 1 acc
3000>
3001> takeLast n ss = reverse $ take n $ reverse ss
3002>
3003> test = takeLast 40 $ dist 20 []
3004>
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]3005</pre>
3006</div>
3007<p>
3008Printing &lt;test&gt; gives: <tt>"1s100000s11010s10100s1111s1010s110s11s1S"</tt></p>
3009<p>
3010The reverse algorithm computes the length of the string just by examining
3011a certain prefix:</p>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]3012
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]3013<div class="doc_code">
3014<pre>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]3015> pref :: [Char] -> Int
3016> pref "S" = 1
3017> pref ('s':'1':rest) = decode 2 1 rest
3018> pref (_:rest) = 1 + pref rest
3019>
3020> decode walk acc ('0':rest) = decode (walk + 1) (acc * 2) rest
3021> decode walk acc ('1':rest) = decode (walk + 1) (acc * 2 + 1) rest
3022> decode walk acc _ = walk + acc
3023>
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]3024</pre>
3025</div>
3026<p>
3027Now, as expected, printing &lt;pref test&gt; gives <tt>40</tt>.</p>
3028<p>
3029We can <i>quickCheck</i> this with following property:</p>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]3030
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]3031<div class="doc_code">
3032<pre>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]3033> testcase = dist 2000 []
3034> testcaseLength = length testcase
3035>
3036> identityProp n = n > 0 && n <= testcaseLength ==> length arr == pref arr
3037> where arr = takeLast n testcase
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]3038>
3039</pre>
3040</div>
3041<p>
3042As expected &lt;quickCheck identityProp&gt; gives:</p>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]3043
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]3044<pre>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]3045*Main> quickCheck identityProp
3046OK, passed 100 tests.
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]3047</pre>
3048<p>
3049Let's be a bit more exhaustive:</p>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]3050
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]3051<div class="doc_code">
3052<pre>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]3053>
3054> deepCheck p = check (defaultConfig { configMaxTest = 500 }) p
3055>
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]3056</pre>
3057</div>
3058<p>
3059And here is the result of &lt;deepCheck identityProp&gt;:</p>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]3060
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]3061<pre>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]3062*Main> deepCheck identityProp
3063OK, passed 500 tests.
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]3064</pre>
3065
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]3066</div>
3067
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]3068<!-- ______________________________________________________________________ -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]3069<h4>
Gabor Greiffd095b62009-01-05 16:05:32 +0000[diff] [blame]3070 <a name="Tagging">Tagging considerations</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]3071</h4>
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]3072
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]3073<div>
3074
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]3075<p>
3076To maintain the invariant that the 2 LSBits of each <tt>Use**</tt> in <tt>Use</tt>
3077never change after being set up, setters of <tt>Use::Prev</tt> must re-tag the
3078new <tt>Use**</tt> on every modification. Accordingly getters must strip the
3079tag bits.</p>
3080<p>
Gabor Greifd41720a2008-06-25 00:10:22 +0000[diff] [blame]3081For layout b) instead of the <tt>User</tt> we find a pointer (<tt>User*</tt> with LSBit set).
3082Following this pointer brings us to the <tt>User</tt>. A portable trick ensures
3083that the first bytes of <tt>User</tt> (if interpreted as a pointer) never has
Gabor Greiffd095b62009-01-05 16:05:32 +0000[diff] [blame]3084the LSBit set. (Portability is relying on the fact that all known compilers place the
3085<tt>vptr</tt> in the first word of the instances.)</p>
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]3086
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]3087</div>
3088
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]3089</div>
3090
3091</div>
3092
3093<!-- *********************************************************************** -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]3094<h2>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3095 <a name="coreclasses">The Core LLVM Class Hierarchy Reference </a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]3096</h2>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3097<!-- *********************************************************************** -->
3098
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]3099<div>
Reid Spencer303c4b42007-01-12 17:26:25 +0000[diff] [blame]3100<p><tt>#include "<a href="/doxygen/Type_8h-source.html">llvm/Type.h</a>"</tt>
3101<br>doxygen info: <a href="/doxygen/classllvm_1_1Type.html">Type Class</a></p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3102
3103<p>The Core LLVM classes are the primary means of representing the program
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3104being inspected or transformed. The core LLVM classes are defined in
3105header files in the <tt>include/llvm/</tt> directory, and implemented in
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3106the <tt>lib/VMCore</tt> directory.</p>
3107
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3108<!-- ======================================================================= -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]3109<h3>
Reid Spencer303c4b42007-01-12 17:26:25 +0000[diff] [blame]3110 <a name="Type">The <tt>Type</tt> class and Derived Types</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]3111</h3>
Reid Spencer303c4b42007-01-12 17:26:25 +0000[diff] [blame]3112
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]3113<div>
Reid Spencer303c4b42007-01-12 17:26:25 +0000[diff] [blame]3114
3115 <p><tt>Type</tt> is a superclass of all type classes. Every <tt>Value</tt> has
3116 a <tt>Type</tt>. <tt>Type</tt> cannot be instantiated directly but only
3117 through its subclasses. Certain primitive types (<tt>VoidType</tt>,
3118 <tt>LabelType</tt>, <tt>FloatType</tt> and <tt>DoubleType</tt>) have hidden
3119 subclasses. They are hidden because they offer no useful functionality beyond
3120 what the <tt>Type</tt> class offers except to distinguish themselves from
3121 other subclasses of <tt>Type</tt>.</p>
3122 <p>All other types are subclasses of <tt>DerivedType</tt>. Types can be
3123 named, but this is not a requirement. There exists exactly
3124 one instance of a given shape at any one time. This allows type equality to
3125 be performed with address equality of the Type Instance. That is, given two
3126 <tt>Type*</tt> values, the types are identical if the pointers are identical.
3127 </p>
Reid Spencer303c4b42007-01-12 17:26:25 +0000[diff] [blame]3128
3129<!-- _______________________________________________________________________ -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]3130<h4>
Gabor Greiffd095b62009-01-05 16:05:32 +0000[diff] [blame]3131 <a name="m_Type">Important Public Methods</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]3132</h4>
Reid Spencer303c4b42007-01-12 17:26:25 +0000[diff] [blame]3133
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]3134<div>
Reid Spencer303c4b42007-01-12 17:26:25 +0000[diff] [blame]3135
3136<ul>
Duncan Sandsb0bc6c32010-02-15 16:12:20 +0000[diff] [blame]3137 <li><tt>bool isIntegerTy() const</tt>: Returns true for any integer type.</li>
Reid Spencer303c4b42007-01-12 17:26:25 +0000[diff] [blame]3138
Duncan Sandsb0bc6c32010-02-15 16:12:20 +0000[diff] [blame]3139 <li><tt>bool isFloatingPointTy()</tt>: Return true if this is one of the five
Reid Spencer303c4b42007-01-12 17:26:25 +0000[diff] [blame]3140 floating point types.</li>
3141
Reid Spencer303c4b42007-01-12 17:26:25 +0000[diff] [blame]3142 <li><tt>bool isSized()</tt>: Return true if the type has known size. Things
3143 that don't have a size are abstract types, labels and void.</li>
3144
3145</ul>
3146</div>
3147
3148<!-- _______________________________________________________________________ -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]3149<h4>
Gabor Greiffd095b62009-01-05 16:05:32 +0000[diff] [blame]3150 <a name="derivedtypes">Important Derived Types</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]3151</h4>
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]3152<div>
Reid Spencer303c4b42007-01-12 17:26:25 +0000[diff] [blame]3153<dl>
3154 <dt><tt>IntegerType</tt></dt>
3155 <dd>Subclass of DerivedType that represents integer types of any bit width.
3156 Any bit width between <tt>IntegerType::MIN_INT_BITS</tt> (1) and
3157 <tt>IntegerType::MAX_INT_BITS</tt> (~8 million) can be represented.
3158 <ul>
3159 <li><tt>static const IntegerType* get(unsigned NumBits)</tt>: get an integer
3160 type of a specific bit width.</li>
3161 <li><tt>unsigned getBitWidth() const</tt>: Get the bit width of an integer
3162 type.</li>
3163 </ul>
3164 </dd>
3165 <dt><tt>SequentialType</tt></dt>
Tobias Grosserd475c102011-07-12 11:37:02 +0000[diff] [blame]3166 <dd>This is subclassed by ArrayType, PointerType and VectorType.
Reid Spencer303c4b42007-01-12 17:26:25 +0000[diff] [blame]3167 <ul>
3168 <li><tt>const Type * getElementType() const</tt>: Returns the type of each
3169 of the elements in the sequential type. </li>
3170 </ul>
3171 </dd>
3172 <dt><tt>ArrayType</tt></dt>
3173 <dd>This is a subclass of SequentialType and defines the interface for array
3174 types.
3175 <ul>
3176 <li><tt>unsigned getNumElements() const</tt>: Returns the number of
3177 elements in the array. </li>
3178 </ul>
3179 </dd>
3180 <dt><tt>PointerType</tt></dt>
Chris Lattner302da1e2007-02-03 03:05:57 +0000[diff] [blame]3181 <dd>Subclass of SequentialType for pointer types.</dd>
Reid Spencer9d6565a2007-02-15 02:26:10 +0000[diff] [blame]3182 <dt><tt>VectorType</tt></dt>
Reid Spencer485bad12007-02-15 03:07:05 +0000[diff] [blame]3183 <dd>Subclass of SequentialType for vector types. A
3184 vector type is similar to an ArrayType but is distinguished because it is
Benjamin Kramer8040cd32009-10-12 14:46:08 +0000[diff] [blame]3185 a first class type whereas ArrayType is not. Vector types are used for
Reid Spencer303c4b42007-01-12 17:26:25 +0000[diff] [blame]3186 vector operations and are usually small vectors of of an integer or floating
3187 point type.</dd>
3188 <dt><tt>StructType</tt></dt>
3189 <dd>Subclass of DerivedTypes for struct types.</dd>
Duncan Sands8036ca42007-03-30 12:22:09 +0000[diff] [blame]3190 <dt><tt><a name="FunctionType">FunctionType</a></tt></dt>
Reid Spencer303c4b42007-01-12 17:26:25 +0000[diff] [blame]3191 <dd>Subclass of DerivedTypes for function types.
3192 <ul>
Dan Gohman4bb31bf2010-03-30 20:04:57 +0000[diff] [blame]3193 <li><tt>bool isVarArg() const</tt>: Returns true if it's a vararg
Reid Spencer303c4b42007-01-12 17:26:25 +0000[diff] [blame]3194 function</li>
3195 <li><tt> const Type * getReturnType() const</tt>: Returns the
3196 return type of the function.</li>
3197 <li><tt>const Type * getParamType (unsigned i)</tt>: Returns
3198 the type of the ith parameter.</li>
3199 <li><tt> const unsigned getNumParams() const</tt>: Returns the
3200 number of formal parameters.</li>
3201 </ul>
3202 </dd>
Reid Spencer303c4b42007-01-12 17:26:25 +0000[diff] [blame]3203</dl>
3204</div>
3205
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]3206</div>
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]3207
3208<!-- ======================================================================= -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]3209<h3>
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]3210 <a name="Module">The <tt>Module</tt> class</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]3211</h3>
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]3212
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]3213<div>
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]3214
3215<p><tt>#include "<a
3216href="/doxygen/Module_8h-source.html">llvm/Module.h</a>"</tt><br> doxygen info:
3217<a href="/doxygen/classllvm_1_1Module.html">Module Class</a></p>
3218
3219<p>The <tt>Module</tt> class represents the top level structure present in LLVM
3220programs. An LLVM module is effectively either a translation unit of the
3221original program or a combination of several translation units merged by the
3222linker. The <tt>Module</tt> class keeps track of a list of <a
3223href="#Function"><tt>Function</tt></a>s, a list of <a
3224href="#GlobalVariable"><tt>GlobalVariable</tt></a>s, and a <a
3225href="#SymbolTable"><tt>SymbolTable</tt></a>. Additionally, it contains a few
3226helpful member functions that try to make common operations easy.</p>
3227
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]3228<!-- _______________________________________________________________________ -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]3229<h4>
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]3230 <a name="m_Module">Important Public Members of the <tt>Module</tt> class</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]3231</h4>
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]3232
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]3233<div>
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]3234
3235<ul>
3236 <li><tt>Module::Module(std::string name = "")</tt></li>
3237</ul>
3238
3239<p>Constructing a <a href="#Module">Module</a> is easy. You can optionally
3240provide a name for it (probably based on the name of the translation unit).</p>
3241
3242<ul>
3243 <li><tt>Module::iterator</tt> - Typedef for function list iterator<br>
3244 <tt>Module::const_iterator</tt> - Typedef for const_iterator.<br>
3245
3246 <tt>begin()</tt>, <tt>end()</tt>
3247 <tt>size()</tt>, <tt>empty()</tt>
3248
3249 <p>These are forwarding methods that make it easy to access the contents of
3250 a <tt>Module</tt> object's <a href="#Function"><tt>Function</tt></a>
3251 list.</p></li>
3252
3253 <li><tt>Module::FunctionListType &amp;getFunctionList()</tt>
3254
3255 <p> Returns the list of <a href="#Function"><tt>Function</tt></a>s. This is
3256 necessary to use when you need to update the list or perform a complex
3257 action that doesn't have a forwarding method.</p>
3258
3259 <p><!-- Global Variable --></p></li>
3260</ul>
3261
3262<hr>
3263
3264<ul>
3265 <li><tt>Module::global_iterator</tt> - Typedef for global variable list iterator<br>
3266
3267 <tt>Module::const_global_iterator</tt> - Typedef for const_iterator.<br>
3268
3269 <tt>global_begin()</tt>, <tt>global_end()</tt>
3270 <tt>global_size()</tt>, <tt>global_empty()</tt>
3271
3272 <p> These are forwarding methods that make it easy to access the contents of
3273 a <tt>Module</tt> object's <a
3274 href="#GlobalVariable"><tt>GlobalVariable</tt></a> list.</p></li>
3275
3276 <li><tt>Module::GlobalListType &amp;getGlobalList()</tt>
3277
3278 <p>Returns the list of <a
3279 href="#GlobalVariable"><tt>GlobalVariable</tt></a>s. This is necessary to
3280 use when you need to update the list or perform a complex action that
3281 doesn't have a forwarding method.</p>
3282
3283 <p><!-- Symbol table stuff --> </p></li>
3284</ul>
3285
3286<hr>
3287
3288<ul>
3289 <li><tt><a href="#SymbolTable">SymbolTable</a> *getSymbolTable()</tt>
3290
3291 <p>Return a reference to the <a href="#SymbolTable"><tt>SymbolTable</tt></a>
3292 for this <tt>Module</tt>.</p>
3293
3294 <p><!-- Convenience methods --></p></li>
3295</ul>
3296
3297<hr>
3298
3299<ul>
3300 <li><tt><a href="#Function">Function</a> *getFunction(const std::string
3301 &amp;Name, const <a href="#FunctionType">FunctionType</a> *Ty)</tt>
3302
3303 <p>Look up the specified function in the <tt>Module</tt> <a
3304 href="#SymbolTable"><tt>SymbolTable</tt></a>. If it does not exist, return
3305 <tt>null</tt>.</p></li>
3306
3307 <li><tt><a href="#Function">Function</a> *getOrInsertFunction(const
3308 std::string &amp;Name, const <a href="#FunctionType">FunctionType</a> *T)</tt>
3309
3310 <p>Look up the specified function in the <tt>Module</tt> <a
3311 href="#SymbolTable"><tt>SymbolTable</tt></a>. If it does not exist, add an
3312 external declaration for the function and return it.</p></li>
3313
3314 <li><tt>std::string getTypeName(const <a href="#Type">Type</a> *Ty)</tt>
3315
3316 <p>If there is at least one entry in the <a
3317 href="#SymbolTable"><tt>SymbolTable</tt></a> for the specified <a
3318 href="#Type"><tt>Type</tt></a>, return it. Otherwise return the empty
3319 string.</p></li>
3320
3321 <li><tt>bool addTypeName(const std::string &amp;Name, const <a
3322 href="#Type">Type</a> *Ty)</tt>
3323
3324 <p>Insert an entry in the <a href="#SymbolTable"><tt>SymbolTable</tt></a>
3325 mapping <tt>Name</tt> to <tt>Ty</tt>. If there is already an entry for this
3326 name, true is returned and the <a
3327 href="#SymbolTable"><tt>SymbolTable</tt></a> is not modified.</p></li>
3328</ul>
3329
3330</div>
3331
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]3332</div>
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]3333
Reid Spencer303c4b42007-01-12 17:26:25 +0000[diff] [blame]3334<!-- ======================================================================= -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]3335<h3>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3336 <a name="Value">The <tt>Value</tt> class</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]3337</h3>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3338
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]3339<div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3340
3341<p><tt>#include "<a href="/doxygen/Value_8h-source.html">llvm/Value.h</a>"</tt>
3342<br>
Chris Lattner00815172007-01-04 22:01:45 +0000[diff] [blame]3343doxygen info: <a href="/doxygen/classllvm_1_1Value.html">Value Class</a></p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3344
3345<p>The <tt>Value</tt> class is the most important class in the LLVM Source
3346base. It represents a typed value that may be used (among other things) as an
3347operand to an instruction. There are many different types of <tt>Value</tt>s,
3348such as <a href="#Constant"><tt>Constant</tt></a>s,<a
3349href="#Argument"><tt>Argument</tt></a>s. Even <a
3350href="#Instruction"><tt>Instruction</tt></a>s and <a
3351href="#Function"><tt>Function</tt></a>s are <tt>Value</tt>s.</p>
3352
3353<p>A particular <tt>Value</tt> may be used many times in the LLVM representation
3354for a program. For example, an incoming argument to a function (represented
3355with an instance of the <a href="#Argument">Argument</a> class) is "used" by
3356every instruction in the function that references the argument. To keep track
3357of this relationship, the <tt>Value</tt> class keeps a list of all of the <a
3358href="#User"><tt>User</tt></a>s that is using it (the <a
3359href="#User"><tt>User</tt></a> class is a base class for all nodes in the LLVM
3360graph that can refer to <tt>Value</tt>s). This use list is how LLVM represents
3361def-use information in the program, and is accessible through the <tt>use_</tt>*
3362methods, shown below.</p>
3363
3364<p>Because LLVM is a typed representation, every LLVM <tt>Value</tt> is typed,
3365and this <a href="#Type">Type</a> is available through the <tt>getType()</tt>
3366method. In addition, all LLVM values can be named. The "name" of the
3367<tt>Value</tt> is a symbolic string printed in the LLVM code:</p>
3368
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]3369<div class="doc_code">
3370<pre>
Reid Spencer06565dc2007-01-12 17:11:23 +0000[diff] [blame]3371%<b>foo</b> = add i32 1, 2
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]3372</pre>
3373</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3374
Duncan Sands8036ca42007-03-30 12:22:09 +0000[diff] [blame]3375<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]3376that the name of any value may be missing (an empty string), so names should
3377<b>ONLY</b> be used for debugging (making the source code easier to read,
3378debugging printouts), they should not be used to keep track of values or map
3379between them. For this purpose, use a <tt>std::map</tt> of pointers to the
3380<tt>Value</tt> itself instead.</p>
3381
3382<p>One important aspect of LLVM is that there is no distinction between an SSA
3383variable and the operation that produces it. Because of this, any reference to
3384the value produced by an instruction (or the value available as an incoming
Chris Lattnerd5fc4fc2004-03-18 14:58:55 +0000[diff] [blame]3385argument, for example) is represented as a direct pointer to the instance of
3386the class that
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3387represents this value. Although this may take some getting used to, it
3388simplifies the representation and makes it easier to manipulate.</p>
3389
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3390<!-- _______________________________________________________________________ -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]3391<h4>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3392 <a name="m_Value">Important Public Members of the <tt>Value</tt> class</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]3393</h4>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3394
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]3395<div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3396
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3397<ul>
3398 <li><tt>Value::use_iterator</tt> - Typedef for iterator over the
3399use-list<br>
Gabor Greifbbbf9a22010-03-26 19:59:25 +0000[diff] [blame]3400 <tt>Value::const_use_iterator</tt> - Typedef for const_iterator over
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3401the use-list<br>
3402 <tt>unsigned use_size()</tt> - Returns the number of users of the
3403value.<br>
Chris Lattner9355b472002-09-06 02:50:58 +0000[diff] [blame]3404 <tt>bool use_empty()</tt> - Returns true if there are no users.<br>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3405 <tt>use_iterator use_begin()</tt> - Get an iterator to the start of
3406the use-list.<br>
3407 <tt>use_iterator use_end()</tt> - Get an iterator to the end of the
3408use-list.<br>
3409 <tt><a href="#User">User</a> *use_back()</tt> - Returns the last
3410element in the list.
3411 <p> These methods are the interface to access the def-use
3412information in LLVM. As with all other iterators in LLVM, the naming
3413conventions follow the conventions defined by the <a href="#stl">STL</a>.</p>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3414 </li>
3415 <li><tt><a href="#Type">Type</a> *getType() const</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3416 <p>This method returns the Type of the Value.</p>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3417 </li>
3418 <li><tt>bool hasName() const</tt><br>
Chris Lattner9355b472002-09-06 02:50:58 +0000[diff] [blame]3419 <tt>std::string getName() const</tt><br>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3420 <tt>void setName(const std::string &amp;Name)</tt>
3421 <p> This family of methods is used to access and assign a name to a <tt>Value</tt>,
3422be aware of the <a href="#nameWarning">precaution above</a>.</p>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3423 </li>
3424 <li><tt>void replaceAllUsesWith(Value *V)</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3425
3426 <p>This method traverses the use list of a <tt>Value</tt> changing all <a
3427 href="#User"><tt>User</tt>s</a> of the current value to refer to
3428 "<tt>V</tt>" instead. For example, if you detect that an instruction always
3429 produces a constant value (for example through constant folding), you can
3430 replace all uses of the instruction with the constant like this:</p>
3431
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]3432<div class="doc_code">
3433<pre>
3434Inst-&gt;replaceAllUsesWith(ConstVal);
3435</pre>
3436</div>
3437
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3438</ul>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3439
3440</div>
3441
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]3442</div>
3443
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3444<!-- ======================================================================= -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]3445<h3>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3446 <a name="User">The <tt>User</tt> class</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]3447</h3>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3448
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]3449<div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3450
3451<p>
3452<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]3453doxygen info: <a href="/doxygen/classllvm_1_1User.html">User Class</a><br>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3454Superclass: <a href="#Value"><tt>Value</tt></a></p>
3455
3456<p>The <tt>User</tt> class is the common base class of all LLVM nodes that may
3457refer to <a href="#Value"><tt>Value</tt></a>s. It exposes a list of "Operands"
3458that are all of the <a href="#Value"><tt>Value</tt></a>s that the User is
3459referring to. The <tt>User</tt> class itself is a subclass of
3460<tt>Value</tt>.</p>
3461
3462<p>The operands of a <tt>User</tt> point directly to the LLVM <a
3463href="#Value"><tt>Value</tt></a> that it refers to. Because LLVM uses Static
3464Single Assignment (SSA) form, there can only be one definition referred to,
3465allowing this direct connection. This connection provides the use-def
3466information in LLVM.</p>
3467
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3468<!-- _______________________________________________________________________ -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]3469<h4>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3470 <a name="m_User">Important Public Members of the <tt>User</tt> class</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]3471</h4>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3472
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]3473<div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3474
3475<p>The <tt>User</tt> class exposes the operand list in two ways: through
3476an index access interface and through an iterator based interface.</p>
3477
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3478<ul>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3479 <li><tt>Value *getOperand(unsigned i)</tt><br>
3480 <tt>unsigned getNumOperands()</tt>
3481 <p> These two methods expose the operands of the <tt>User</tt> in a
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3482convenient form for direct access.</p></li>
3483
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3484 <li><tt>User::op_iterator</tt> - Typedef for iterator over the operand
3485list<br>
Chris Lattner58360822005-01-17 00:12:04 +0000[diff] [blame]3486 <tt>op_iterator op_begin()</tt> - Get an iterator to the start of
3487the operand list.<br>
3488 <tt>op_iterator op_end()</tt> - Get an iterator to the end of the
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3489operand list.
3490 <p> Together, these methods make up the iterator based interface to
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3491the operands of a <tt>User</tt>.</p></li>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3492</ul>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3493
3494</div>
3495
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]3496</div>
3497
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3498<!-- ======================================================================= -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]3499<h3>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3500 <a name="Instruction">The <tt>Instruction</tt> class</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]3501</h3>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3502
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]3503<div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3504
3505<p><tt>#include "</tt><tt><a
3506href="/doxygen/Instruction_8h-source.html">llvm/Instruction.h</a>"</tt><br>
Misha Brukman31ca1de2004-06-03 23:35:54 +0000[diff] [blame]3507doxygen info: <a href="/doxygen/classllvm_1_1Instruction.html">Instruction Class</a><br>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3508Superclasses: <a href="#User"><tt>User</tt></a>, <a
3509href="#Value"><tt>Value</tt></a></p>
3510
3511<p>The <tt>Instruction</tt> class is the common base class for all LLVM
3512instructions. It provides only a few methods, but is a very commonly used
3513class. The primary data tracked by the <tt>Instruction</tt> class itself is the
3514opcode (instruction type) and the parent <a
3515href="#BasicBlock"><tt>BasicBlock</tt></a> the <tt>Instruction</tt> is embedded
3516into. To represent a specific type of instruction, one of many subclasses of
3517<tt>Instruction</tt> are used.</p>
3518
3519<p> Because the <tt>Instruction</tt> class subclasses the <a
3520href="#User"><tt>User</tt></a> class, its operands can be accessed in the same
3521way as for other <a href="#User"><tt>User</tt></a>s (with the
3522<tt>getOperand()</tt>/<tt>getNumOperands()</tt> and
3523<tt>op_begin()</tt>/<tt>op_end()</tt> methods).</p> <p> An important file for
3524the <tt>Instruction</tt> class is the <tt>llvm/Instruction.def</tt> file. This
3525file contains some meta-data about the various different types of instructions
3526in LLVM. It describes the enum values that are used as opcodes (for example
Reid Spencerc92d25d2006-12-19 19:47:19 +0000[diff] [blame]3527<tt>Instruction::Add</tt> and <tt>Instruction::ICmp</tt>), as well as the
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3528concrete sub-classes of <tt>Instruction</tt> that implement the instruction (for
3529example <tt><a href="#BinaryOperator">BinaryOperator</a></tt> and <tt><a
Reid Spencerc92d25d2006-12-19 19:47:19 +0000[diff] [blame]3530href="#CmpInst">CmpInst</a></tt>). Unfortunately, the use of macros in
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3531this file confuses doxygen, so these enum values don't show up correctly in the
Misha Brukman31ca1de2004-06-03 23:35:54 +0000[diff] [blame]3532<a href="/doxygen/classllvm_1_1Instruction.html">doxygen output</a>.</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3533
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3534<!-- _______________________________________________________________________ -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]3535<h4>
3536 <a name="s_Instruction">
3537 Important Subclasses of the <tt>Instruction</tt> class
3538 </a>
3539</h4>
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]3540<div>
Reid Spencerc92d25d2006-12-19 19:47:19 +0000[diff] [blame]3541 <ul>
3542 <li><tt><a name="BinaryOperator">BinaryOperator</a></tt>
3543 <p>This subclasses represents all two operand instructions whose operands
3544 must be the same type, except for the comparison instructions.</p></li>
3545 <li><tt><a name="CastInst">CastInst</a></tt>
3546 <p>This subclass is the parent of the 12 casting instructions. It provides
3547 common operations on cast instructions.</p>
3548 <li><tt><a name="CmpInst">CmpInst</a></tt>
3549 <p>This subclass respresents the two comparison instructions,
3550 <a href="LangRef.html#i_icmp">ICmpInst</a> (integer opreands), and
3551 <a href="LangRef.html#i_fcmp">FCmpInst</a> (floating point operands).</p>
3552 <li><tt><a name="TerminatorInst">TerminatorInst</a></tt>
3553 <p>This subclass is the parent of all terminator instructions (those which
3554 can terminate a block).</p>
3555 </ul>
3556 </div>
3557
3558<!-- _______________________________________________________________________ -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]3559<h4>
3560 <a name="m_Instruction">
3561 Important Public Members of the <tt>Instruction</tt> class
3562 </a>
3563</h4>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3564
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]3565<div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3566
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3567<ul>
3568 <li><tt><a href="#BasicBlock">BasicBlock</a> *getParent()</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3569 <p>Returns the <a href="#BasicBlock"><tt>BasicBlock</tt></a> that
3570this <tt>Instruction</tt> is embedded into.</p></li>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3571 <li><tt>bool mayWriteToMemory()</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3572 <p>Returns true if the instruction writes to memory, i.e. it is a
3573 <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]3574 <li><tt>unsigned getOpcode()</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3575 <p>Returns the opcode for the <tt>Instruction</tt>.</p></li>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3576 <li><tt><a href="#Instruction">Instruction</a> *clone() const</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3577 <p>Returns another instance of the specified instruction, identical
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3578in all ways to the original except that the instruction has no parent
3579(ie it's not embedded into a <a href="#BasicBlock"><tt>BasicBlock</tt></a>),
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3580and it has no name</p></li>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3581</ul>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3582
3583</div>
3584
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]3585</div>
3586
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3587<!-- ======================================================================= -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]3588<h3>
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]3589 <a name="Constant">The <tt>Constant</tt> class and subclasses</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]3590</h3>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3591
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]3592<div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3593
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]3594<p>Constant represents a base class for different types of constants. It
3595is subclassed by ConstantInt, ConstantArray, etc. for representing
3596the various types of Constants. <a href="#GlobalValue">GlobalValue</a> is also
3597a subclass, which represents the address of a global variable or function.
3598</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3599
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3600<!-- _______________________________________________________________________ -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]3601<h4>Important Subclasses of Constant</h4>
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]3602<div>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3603<ul>
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]3604 <li>ConstantInt : This subclass of Constant represents an integer constant of
3605 any width.
3606 <ul>
Reid Spencer97b4ee32007-03-01 21:05:33 +0000[diff] [blame]3607 <li><tt>const APInt&amp; getValue() const</tt>: Returns the underlying
3608 value of this constant, an APInt value.</li>
3609 <li><tt>int64_t getSExtValue() const</tt>: Converts the underlying APInt
3610 value to an int64_t via sign extension. If the value (not the bit width)
3611 of the APInt is too large to fit in an int64_t, an assertion will result.
3612 For this reason, use of this method is discouraged.</li>
3613 <li><tt>uint64_t getZExtValue() const</tt>: Converts the underlying APInt
3614 value to a uint64_t via zero extension. IF the value (not the bit width)
3615 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]3616 For this reason, use of this method is discouraged.</li>
Reid Spencer97b4ee32007-03-01 21:05:33 +0000[diff] [blame]3617 <li><tt>static ConstantInt* get(const APInt&amp; Val)</tt>: Returns the
3618 ConstantInt object that represents the value provided by <tt>Val</tt>.
3619 The type is implied as the IntegerType that corresponds to the bit width
3620 of <tt>Val</tt>.</li>
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]3621 <li><tt>static ConstantInt* get(const Type *Ty, uint64_t Val)</tt>:
3622 Returns the ConstantInt object that represents the value provided by
3623 <tt>Val</tt> for integer type <tt>Ty</tt>.</li>
3624 </ul>
3625 </li>
3626 <li>ConstantFP : This class represents a floating point constant.
3627 <ul>
3628 <li><tt>double getValue() const</tt>: Returns the underlying value of
3629 this constant. </li>
3630 </ul>
3631 </li>
3632 <li>ConstantArray : This represents a constant array.
3633 <ul>
3634 <li><tt>const std::vector&lt;Use&gt; &amp;getValues() const</tt>: Returns
3635 a vector of component constants that makeup this array. </li>
3636 </ul>
3637 </li>
3638 <li>ConstantStruct : This represents a constant struct.
3639 <ul>
3640 <li><tt>const std::vector&lt;Use&gt; &amp;getValues() const</tt>: Returns
3641 a vector of component constants that makeup this array. </li>
3642 </ul>
3643 </li>
3644 <li>GlobalValue : This represents either a global variable or a function. In
3645 either case, the value is a constant fixed address (after linking).
3646 </li>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3647</ul>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3648</div>
3649
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]3650</div>
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]3651
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3652<!-- ======================================================================= -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]3653<h3>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3654 <a name="GlobalValue">The <tt>GlobalValue</tt> class</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]3655</h3>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3656
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]3657<div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3658
3659<p><tt>#include "<a
3660href="/doxygen/GlobalValue_8h-source.html">llvm/GlobalValue.h</a>"</tt><br>
Misha Brukman384047f2004-06-03 23:29:12 +0000[diff] [blame]3661doxygen info: <a href="/doxygen/classllvm_1_1GlobalValue.html">GlobalValue
3662Class</a><br>
Reid Spencerbe5e85e2006-04-14 14:11:48 +0000[diff] [blame]3663Superclasses: <a href="#Constant"><tt>Constant</tt></a>,
3664<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]3665
3666<p>Global values (<a href="#GlobalVariable"><tt>GlobalVariable</tt></a>s or <a
3667href="#Function"><tt>Function</tt></a>s) are the only LLVM values that are
3668visible in the bodies of all <a href="#Function"><tt>Function</tt></a>s.
3669Because they are visible at global scope, they are also subject to linking with
3670other globals defined in different translation units. To control the linking
3671process, <tt>GlobalValue</tt>s know their linkage rules. Specifically,
3672<tt>GlobalValue</tt>s know whether they have internal or external linkage, as
Reid Spencer8b2da7a2004-07-18 13:10:31 +0000[diff] [blame]3673defined by the <tt>LinkageTypes</tt> enumeration.</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3674
3675<p>If a <tt>GlobalValue</tt> has internal linkage (equivalent to being
3676<tt>static</tt> in C), it is not visible to code outside the current translation
3677unit, and does not participate in linking. If it has external linkage, it is
3678visible to external code, and does participate in linking. In addition to
3679linkage information, <tt>GlobalValue</tt>s keep track of which <a
3680href="#Module"><tt>Module</tt></a> they are currently part of.</p>
3681
3682<p>Because <tt>GlobalValue</tt>s are memory objects, they are always referred to
3683by their <b>address</b>. As such, the <a href="#Type"><tt>Type</tt></a> of a
3684global is always a pointer to its contents. It is important to remember this
3685when using the <tt>GetElementPtrInst</tt> instruction because this pointer must
3686be dereferenced first. For example, if you have a <tt>GlobalVariable</tt> (a
3687subclass 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]3688i32]</tt>, then the <tt>GlobalVariable</tt> is a pointer to that array. Although
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3689the address of the first element of this array and the value of the
3690<tt>GlobalVariable</tt> are the same, they have different types. The
Reid Spencer06565dc2007-01-12 17:11:23 +0000[diff] [blame]3691<tt>GlobalVariable</tt>'s type is <tt>[24 x i32]</tt>. The first element's type
3692is <tt>i32.</tt> Because of this, accessing a global value requires you to
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3693dereference the pointer with <tt>GetElementPtrInst</tt> first, then its elements
3694can be accessed. This is explained in the <a href="LangRef.html#globalvars">LLVM
3695Language Reference Manual</a>.</p>
3696
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3697<!-- _______________________________________________________________________ -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]3698<h4>
3699 <a name="m_GlobalValue">
3700 Important Public Members of the <tt>GlobalValue</tt> class
3701 </a>
3702</h4>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3703
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]3704<div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3705
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3706<ul>
3707 <li><tt>bool hasInternalLinkage() const</tt><br>
Chris Lattner9355b472002-09-06 02:50:58 +0000[diff] [blame]3708 <tt>bool hasExternalLinkage() const</tt><br>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3709 <tt>void setInternalLinkage(bool HasInternalLinkage)</tt>
3710 <p> These methods manipulate the linkage characteristics of the <tt>GlobalValue</tt>.</p>
3711 <p> </p>
3712 </li>
3713 <li><tt><a href="#Module">Module</a> *getParent()</tt>
3714 <p> This returns the <a href="#Module"><tt>Module</tt></a> that the
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3715GlobalValue is currently embedded into.</p></li>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3716</ul>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3717
3718</div>
3719
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]3720</div>
3721
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3722<!-- ======================================================================= -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]3723<h3>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3724 <a name="Function">The <tt>Function</tt> class</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]3725</h3>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3726
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]3727<div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3728
3729<p><tt>#include "<a
3730href="/doxygen/Function_8h-source.html">llvm/Function.h</a>"</tt><br> doxygen
Misha Brukman31ca1de2004-06-03 23:35:54 +0000[diff] [blame]3731info: <a href="/doxygen/classllvm_1_1Function.html">Function Class</a><br>
Reid Spencerbe5e85e2006-04-14 14:11:48 +0000[diff] [blame]3732Superclasses: <a href="#GlobalValue"><tt>GlobalValue</tt></a>,
3733<a href="#Constant"><tt>Constant</tt></a>,
3734<a href="#User"><tt>User</tt></a>,
3735<a href="#Value"><tt>Value</tt></a></p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3736
3737<p>The <tt>Function</tt> class represents a single procedure in LLVM. It is
Torok Edwin87469292009-10-12 13:37:29 +0000[diff] [blame]3738actually one of the more complex classes in the LLVM hierarchy because it must
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3739keep track of a large amount of data. The <tt>Function</tt> class keeps track
Reid Spencerbe5e85e2006-04-14 14:11:48 +0000[diff] [blame]3740of a list of <a href="#BasicBlock"><tt>BasicBlock</tt></a>s, a list of formal
3741<a href="#Argument"><tt>Argument</tt></a>s, and a
3742<a href="#SymbolTable"><tt>SymbolTable</tt></a>.</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3743
3744<p>The list of <a href="#BasicBlock"><tt>BasicBlock</tt></a>s is the most
3745commonly used part of <tt>Function</tt> objects. The list imposes an implicit
3746ordering of the blocks in the function, which indicate how the code will be
Benjamin Kramer8040cd32009-10-12 14:46:08 +0000[diff] [blame]3747laid out by the backend. Additionally, the first <a
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3748href="#BasicBlock"><tt>BasicBlock</tt></a> is the implicit entry node for the
3749<tt>Function</tt>. It is not legal in LLVM to explicitly branch to this initial
3750block. There are no implicit exit nodes, and in fact there may be multiple exit
3751nodes from a single <tt>Function</tt>. If the <a
3752href="#BasicBlock"><tt>BasicBlock</tt></a> list is empty, this indicates that
3753the <tt>Function</tt> is actually a function declaration: the actual body of the
3754function hasn't been linked in yet.</p>
3755
3756<p>In addition to a list of <a href="#BasicBlock"><tt>BasicBlock</tt></a>s, the
3757<tt>Function</tt> class also keeps track of the list of formal <a
3758href="#Argument"><tt>Argument</tt></a>s that the function receives. This
3759container manages the lifetime of the <a href="#Argument"><tt>Argument</tt></a>
3760nodes, just like the <a href="#BasicBlock"><tt>BasicBlock</tt></a> list does for
3761the <a href="#BasicBlock"><tt>BasicBlock</tt></a>s.</p>
3762
3763<p>The <a href="#SymbolTable"><tt>SymbolTable</tt></a> is a very rarely used
3764LLVM feature that is only used when you have to look up a value by name. Aside
3765from that, the <a href="#SymbolTable"><tt>SymbolTable</tt></a> is used
3766internally to make sure that there are not conflicts between the names of <a
3767href="#Instruction"><tt>Instruction</tt></a>s, <a
3768href="#BasicBlock"><tt>BasicBlock</tt></a>s, or <a
3769href="#Argument"><tt>Argument</tt></a>s in the function body.</p>
3770
Reid Spencer8b2da7a2004-07-18 13:10:31 +0000[diff] [blame]3771<p>Note that <tt>Function</tt> is a <a href="#GlobalValue">GlobalValue</a>
3772and therefore also a <a href="#Constant">Constant</a>. The value of the function
3773is its address (after linking) which is guaranteed to be constant.</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3774
3775<!-- _______________________________________________________________________ -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]3776<h4>
3777 <a name="m_Function">
3778 Important Public Members of the <tt>Function</tt> class
3779 </a>
3780</h4>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3781
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]3782<div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3783
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3784<ul>
3785 <li><tt>Function(const </tt><tt><a href="#FunctionType">FunctionType</a>
Chris Lattnerac479e52004-08-04 05:10:48 +0000[diff] [blame]3786 *Ty, LinkageTypes Linkage, const std::string &amp;N = "", Module* Parent = 0)</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3787
3788 <p>Constructor used when you need to create new <tt>Function</tt>s to add
3789 the the program. The constructor must specify the type of the function to
Chris Lattnerac479e52004-08-04 05:10:48 +0000[diff] [blame]3790 create and what type of linkage the function should have. The <a
3791 href="#FunctionType"><tt>FunctionType</tt></a> argument
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3792 specifies the formal arguments and return value for the function. The same
Duncan Sands8036ca42007-03-30 12:22:09 +0000[diff] [blame]3793 <a href="#FunctionType"><tt>FunctionType</tt></a> value can be used to
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3794 create multiple functions. The <tt>Parent</tt> argument specifies the Module
3795 in which the function is defined. If this argument is provided, the function
3796 will automatically be inserted into that module's list of
3797 functions.</p></li>
3798
Chris Lattner62810e32008-11-25 18:34:50 +0000[diff] [blame]3799 <li><tt>bool isDeclaration()</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3800
3801 <p>Return whether or not the <tt>Function</tt> has a body defined. If the
3802 function is "external", it does not have a body, and thus must be resolved
3803 by linking with a function defined in a different translation unit.</p></li>
3804
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3805 <li><tt>Function::iterator</tt> - Typedef for basic block list iterator<br>
Chris Lattner9355b472002-09-06 02:50:58 +0000[diff] [blame]3806 <tt>Function::const_iterator</tt> - Typedef for const_iterator.<br>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3807
Chris Lattner77d69242005-03-15 05:19:20 +0000[diff] [blame]3808 <tt>begin()</tt>, <tt>end()</tt>
3809 <tt>size()</tt>, <tt>empty()</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3810
3811 <p>These are forwarding methods that make it easy to access the contents of
3812 a <tt>Function</tt> object's <a href="#BasicBlock"><tt>BasicBlock</tt></a>
3813 list.</p></li>
3814
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3815 <li><tt>Function::BasicBlockListType &amp;getBasicBlockList()</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3816
3817 <p>Returns the list of <a href="#BasicBlock"><tt>BasicBlock</tt></a>s. This
3818 is necessary to use when you need to update the list or perform a complex
3819 action that doesn't have a forwarding method.</p></li>
3820
Chris Lattner89cc2652005-03-15 04:48:32 +0000[diff] [blame]3821 <li><tt>Function::arg_iterator</tt> - Typedef for the argument list
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3822iterator<br>
Chris Lattner89cc2652005-03-15 04:48:32 +0000[diff] [blame]3823 <tt>Function::const_arg_iterator</tt> - Typedef for const_iterator.<br>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3824
Chris Lattner77d69242005-03-15 05:19:20 +0000[diff] [blame]3825 <tt>arg_begin()</tt>, <tt>arg_end()</tt>
Chris Lattner89cc2652005-03-15 04:48:32 +0000[diff] [blame]3826 <tt>arg_size()</tt>, <tt>arg_empty()</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3827
3828 <p>These are forwarding methods that make it easy to access the contents of
3829 a <tt>Function</tt> object's <a href="#Argument"><tt>Argument</tt></a>
3830 list.</p></li>
3831
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3832 <li><tt>Function::ArgumentListType &amp;getArgumentList()</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3833
3834 <p>Returns the list of <a href="#Argument"><tt>Argument</tt></a>s. This is
3835 necessary to use when you need to update the list or perform a complex
3836 action that doesn't have a forwarding method.</p></li>
3837
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3838 <li><tt><a href="#BasicBlock">BasicBlock</a> &amp;getEntryBlock()</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3839
3840 <p>Returns the entry <a href="#BasicBlock"><tt>BasicBlock</tt></a> for the
3841 function. Because the entry block for the function is always the first
3842 block, this returns the first block of the <tt>Function</tt>.</p></li>
3843
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3844 <li><tt><a href="#Type">Type</a> *getReturnType()</tt><br>
3845 <tt><a href="#FunctionType">FunctionType</a> *getFunctionType()</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3846
3847 <p>This traverses the <a href="#Type"><tt>Type</tt></a> of the
3848 <tt>Function</tt> and returns the return type of the function, or the <a
3849 href="#FunctionType"><tt>FunctionType</tt></a> of the actual
3850 function.</p></li>
3851
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3852 <li><tt><a href="#SymbolTable">SymbolTable</a> *getSymbolTable()</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3853
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3854 <p> Return a pointer to the <a href="#SymbolTable"><tt>SymbolTable</tt></a>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3855 for this <tt>Function</tt>.</p></li>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3856</ul>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3857
3858</div>
3859
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]3860</div>
3861
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3862<!-- ======================================================================= -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]3863<h3>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3864 <a name="GlobalVariable">The <tt>GlobalVariable</tt> class</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]3865</h3>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3866
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]3867<div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3868
3869<p><tt>#include "<a
3870href="/doxygen/GlobalVariable_8h-source.html">llvm/GlobalVariable.h</a>"</tt>
3871<br>
Tanya Lattnera3da7772004-06-22 08:02:25 +0000[diff] [blame]3872doxygen info: <a href="/doxygen/classllvm_1_1GlobalVariable.html">GlobalVariable
Reid Spencerbe5e85e2006-04-14 14:11:48 +0000[diff] [blame]3873 Class</a><br>
3874Superclasses: <a href="#GlobalValue"><tt>GlobalValue</tt></a>,
3875<a href="#Constant"><tt>Constant</tt></a>,
3876<a href="#User"><tt>User</tt></a>,
3877<a href="#Value"><tt>Value</tt></a></p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3878
Benjamin Kramer8040cd32009-10-12 14:46:08 +0000[diff] [blame]3879<p>Global variables are represented with the (surprise surprise)
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3880<tt>GlobalVariable</tt> class. Like functions, <tt>GlobalVariable</tt>s are also
3881subclasses of <a href="#GlobalValue"><tt>GlobalValue</tt></a>, and as such are
3882always referenced by their address (global values must live in memory, so their
Reid Spencerbe5e85e2006-04-14 14:11:48 +0000[diff] [blame]3883"name" refers to their constant address). See
3884<a href="#GlobalValue"><tt>GlobalValue</tt></a> for more on this. Global
3885variables may have an initial value (which must be a
3886<a href="#Constant"><tt>Constant</tt></a>), and if they have an initializer,
3887they may be marked as "constant" themselves (indicating that their contents
3888never change at runtime).</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3889
3890<!-- _______________________________________________________________________ -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]3891<h4>
3892 <a name="m_GlobalVariable">
3893 Important Public Members of the <tt>GlobalVariable</tt> class
3894 </a>
3895</h4>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3896
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]3897<div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3898
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3899<ul>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3900 <li><tt>GlobalVariable(const </tt><tt><a href="#Type">Type</a> *Ty, bool
3901 isConstant, LinkageTypes&amp; Linkage, <a href="#Constant">Constant</a>
3902 *Initializer = 0, const std::string &amp;Name = "", Module* Parent = 0)</tt>
3903
3904 <p>Create a new global variable of the specified type. If
3905 <tt>isConstant</tt> is true then the global variable will be marked as
3906 unchanging for the program. The Linkage parameter specifies the type of
Duncan Sands667d4b82009-03-07 15:45:40 +0000[diff] [blame]3907 linkage (internal, external, weak, linkonce, appending) for the variable.
3908 If the linkage is InternalLinkage, WeakAnyLinkage, WeakODRLinkage,
3909 LinkOnceAnyLinkage or LinkOnceODRLinkage,&nbsp; then the resultant
3910 global variable will have internal linkage. AppendingLinkage concatenates
3911 together all instances (in different translation units) of the variable
3912 into a single variable but is only applicable to arrays. &nbsp;See
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3913 the <a href="LangRef.html#modulestructure">LLVM Language Reference</a> for
3914 further details on linkage types. Optionally an initializer, a name, and the
3915 module to put the variable into may be specified for the global variable as
3916 well.</p></li>
3917
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3918 <li><tt>bool isConstant() const</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3919
3920 <p>Returns true if this is a global variable that is known not to
3921 be modified at runtime.</p></li>
3922
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3923 <li><tt>bool hasInitializer()</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3924
3925 <p>Returns true if this <tt>GlobalVariable</tt> has an intializer.</p></li>
3926
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3927 <li><tt><a href="#Constant">Constant</a> *getInitializer()</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3928
Benjamin Kramer8040cd32009-10-12 14:46:08 +0000[diff] [blame]3929 <p>Returns the initial value for a <tt>GlobalVariable</tt>. It is not legal
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3930 to call this method if there is no initializer.</p></li>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3931</ul>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3932
3933</div>
3934
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]3935</div>
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]3936
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3937<!-- ======================================================================= -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]3938<h3>
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]3939 <a name="BasicBlock">The <tt>BasicBlock</tt> class</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]3940</h3>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3941
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]3942<div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3943
3944<p><tt>#include "<a
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]3945href="/doxygen/BasicBlock_8h-source.html">llvm/BasicBlock.h</a>"</tt><br>
Stefanus Du Toit24e04112009-06-17 21:12:26 +0000[diff] [blame]3946doxygen info: <a href="/doxygen/classllvm_1_1BasicBlock.html">BasicBlock
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]3947Class</a><br>
3948Superclass: <a href="#Value"><tt>Value</tt></a></p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3949
Nick Lewyckyccd279d2011-02-17 02:19:22 +0000[diff] [blame]3950<p>This class represents a single entry single exit section of the code,
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]3951commonly known as a basic block by the compiler community. The
3952<tt>BasicBlock</tt> class maintains a list of <a
3953href="#Instruction"><tt>Instruction</tt></a>s, which form the body of the block.
3954Matching the language definition, the last element of this list of instructions
3955is always a terminator instruction (a subclass of the <a
3956href="#TerminatorInst"><tt>TerminatorInst</tt></a> class).</p>
3957
3958<p>In addition to tracking the list of instructions that make up the block, the
3959<tt>BasicBlock</tt> class also keeps track of the <a
3960href="#Function"><tt>Function</tt></a> that it is embedded into.</p>
3961
3962<p>Note that <tt>BasicBlock</tt>s themselves are <a
3963href="#Value"><tt>Value</tt></a>s, because they are referenced by instructions
3964like branches and can go in the switch tables. <tt>BasicBlock</tt>s have type
3965<tt>label</tt>.</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3966
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3967<!-- _______________________________________________________________________ -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]3968<h4>
3969 <a name="m_BasicBlock">
3970 Important Public Members of the <tt>BasicBlock</tt> class
3971 </a>
3972</h4>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3973
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]3974<div>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3975<ul>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3976
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]3977<li><tt>BasicBlock(const std::string &amp;Name = "", </tt><tt><a
3978 href="#Function">Function</a> *Parent = 0)</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3979
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]3980<p>The <tt>BasicBlock</tt> constructor is used to create new basic blocks for
3981insertion into a function. The constructor optionally takes a name for the new
3982block, and a <a href="#Function"><tt>Function</tt></a> to insert it into. If
3983the <tt>Parent</tt> parameter is specified, the new <tt>BasicBlock</tt> is
3984automatically inserted at the end of the specified <a
3985href="#Function"><tt>Function</tt></a>, if not specified, the BasicBlock must be
3986manually inserted into the <a href="#Function"><tt>Function</tt></a>.</p></li>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3987
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]3988<li><tt>BasicBlock::iterator</tt> - Typedef for instruction list iterator<br>
3989<tt>BasicBlock::const_iterator</tt> - Typedef for const_iterator.<br>
3990<tt>begin()</tt>, <tt>end()</tt>, <tt>front()</tt>, <tt>back()</tt>,
3991<tt>size()</tt>, <tt>empty()</tt>
3992STL-style functions for accessing the instruction list.
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3993
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]3994<p>These methods and typedefs are forwarding functions that have the same
3995semantics as the standard library methods of the same names. These methods
3996expose the underlying instruction list of a basic block in a way that is easy to
3997manipulate. To get the full complement of container operations (including
3998operations to update the list), you must use the <tt>getInstList()</tt>
3999method.</p></li>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]4000
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]4001<li><tt>BasicBlock::InstListType &amp;getInstList()</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]4002
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]4003<p>This method is used to get access to the underlying container that actually
4004holds the Instructions. This method must be used when there isn't a forwarding
4005function in the <tt>BasicBlock</tt> class for the operation that you would like
4006to perform. Because there are no forwarding functions for "updating"
4007operations, you need to use this if you want to update the contents of a
4008<tt>BasicBlock</tt>.</p></li>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]4009
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]4010<li><tt><a href="#Function">Function</a> *getParent()</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]4011
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]4012<p> Returns a pointer to <a href="#Function"><tt>Function</tt></a> the block is
4013embedded into, or a null pointer if it is homeless.</p></li>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]4014
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]4015<li><tt><a href="#TerminatorInst">TerminatorInst</a> *getTerminator()</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]4016
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]4017<p> Returns a pointer to the terminator instruction that appears at the end of
4018the <tt>BasicBlock</tt>. If there is no terminator instruction, or if the last
4019instruction in the block is not a terminator, then a null pointer is
4020returned.</p></li>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]4021
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]4022</ul>
4023
4024</div>
4025
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]4026</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]4027
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]4028<!-- ======================================================================= -->
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]4029<h3>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]4030 <a name="Argument">The <tt>Argument</tt> class</a>
NAKAMURA Takumi05d02652011-04-18 23:59:50 +0000[diff] [blame]4031</h3>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]4032
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]4033<div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]4034
4035<p>This subclass of Value defines the interface for incoming formal
Chris Lattner58360822005-01-17 00:12:04 +0000[diff] [blame]4036arguments to a function. A Function maintains a list of its formal
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]4037arguments. An argument has a pointer to the parent Function.</p>
4038
4039</div>
4040
NAKAMURA Takumif5af6ad2011-04-23 00:30:22 +0000[diff] [blame]4041</div>
4042
Chris Lattner9355b472002-09-06 02:50:58 +0000[diff] [blame]4043<!-- *********************************************************************** -->
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]4044<hr>
4045<address>
4046 <a href="http://jigsaw.w3.org/css-validator/check/referer"><img
Misha Brukman44408702008-12-11 17:34:48 +0000[diff] [blame]4047 src="http://jigsaw.w3.org/css-validator/images/vcss-blue" alt="Valid CSS"></a>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]4048 <a href="http://validator.w3.org/check/referer"><img
Gabor Greifa9c0f2b2008-06-18 14:05:31 +0000[diff] [blame]4049 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]4050
4051 <a href="mailto:dhurjati@cs.uiuc.edu">Dinakar Dhurjati</a> and
4052 <a href="mailto:sabre@nondot.org">Chris Lattner</a><br>
NAKAMURA Takumib9a33632011-04-09 02:13:37 +0000[diff] [blame]4053 <a href="http://llvm.org/">The LLVM Compiler Infrastructure</a><br>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]4054 Last modified: $Date$
4055</address>
4056
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]4057</body>
4058</html>