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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
11<div class="doc_title">
12 LLVM Programmer's Manual
13</div>
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>
59 <li><a href="#dss_fixedarrays">Fixed Size Arrays</a></li>
60 <li><a href="#dss_heaparrays">Heap Allocated Arrays</a></li>
61 <li><a href="#dss_smallvector">"llvm/ADT/SmallVector.h"</a></li>
62 <li><a href="#dss_vector">&lt;vector&gt;</a></li>
63 <li><a href="#dss_deque">&lt;deque&gt;</a></li>
64 <li><a href="#dss_list">&lt;list&gt;</a></li>
Gabor Greif3899e492009-02-27 11:37:41 +0000[diff] [blame]65 <li><a href="#dss_ilist">llvm/ADT/ilist.h</a></li>
Chris Lattnerc5722432007-02-03 19:49:31 +0000[diff] [blame]66 <li><a href="#dss_other">Other Sequential Container Options</a></li>
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]67 </ul></li>
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]68 <li><a href="#ds_set">Set-Like Containers (std::set, SmallSet, SetVector, etc)</a>
69 <ul>
70 <li><a href="#dss_sortedvectorset">A sorted 'vector'</a></li>
71 <li><a href="#dss_smallset">"llvm/ADT/SmallSet.h"</a></li>
72 <li><a href="#dss_smallptrset">"llvm/ADT/SmallPtrSet.h"</a></li>
Chris Lattnerc28476f2007-09-30 00:58:59 +0000[diff] [blame]73 <li><a href="#dss_denseset">"llvm/ADT/DenseSet.h"</a></li>
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]74 <li><a href="#dss_FoldingSet">"llvm/ADT/FoldingSet.h"</a></li>
75 <li><a href="#dss_set">&lt;set&gt;</a></li>
76 <li><a href="#dss_setvector">"llvm/ADT/SetVector.h"</a></li>
Chris Lattnerc5722432007-02-03 19:49:31 +0000[diff] [blame]77 <li><a href="#dss_uniquevector">"llvm/ADT/UniqueVector.h"</a></li>
78 <li><a href="#dss_otherset">Other Set-Like ContainerOptions</a></li>
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]79 </ul></li>
Chris Lattnerf3692522007-02-03 19:51:56 +0000[diff] [blame]80 <li><a href="#ds_map">Map-Like Containers (std::map, DenseMap, etc)</a>
81 <ul>
82 <li><a href="#dss_sortedvectormap">A sorted 'vector'</a></li>
Chris Lattner796f9fa2007-02-08 19:14:21 +0000[diff] [blame]83 <li><a href="#dss_stringmap">"llvm/ADT/StringMap.h"</a></li>
Chris Lattnerf3692522007-02-03 19:51:56 +0000[diff] [blame]84 <li><a href="#dss_indexedmap">"llvm/ADT/IndexedMap.h"</a></li>
85 <li><a href="#dss_densemap">"llvm/ADT/DenseMap.h"</a></li>
Jeffrey Yasskin71a5c222009-10-22 22:11:22 +0000[diff] [blame]86 <li><a href="#dss_valuemap">"llvm/ADT/ValueMap.h"</a></li>
Chris Lattnerf3692522007-02-03 19:51:56 +0000[diff] [blame]87 <li><a href="#dss_map">&lt;map&gt;</a></li>
88 <li><a href="#dss_othermap">Other Map-Like Container Options</a></li>
89 </ul></li>
Chris Lattnerdced9fb2009-07-25 07:22:20 +0000[diff] [blame]90 <li><a href="#ds_string">String-like containers</a>
Benjamin Kramere15192b2009-08-05 15:42:44 +0000[diff] [blame]91 <!--<ul>
92 todo
93 </ul>--></li>
Daniel Berlin1939ace2007-09-24 17:52:25 +0000[diff] [blame]94 <li><a href="#ds_bit">BitVector-like containers</a>
95 <ul>
96 <li><a href="#dss_bitvector">A dense bitvector</a></li>
Dan Gohman5f7775c2010-01-05 18:24:00 +0000[diff] [blame]97 <li><a href="#dss_smallbitvector">A "small" dense bitvector</a></li>
Daniel Berlin1939ace2007-09-24 17:52:25 +0000[diff] [blame]98 <li><a href="#dss_sparsebitvector">A sparse bitvector</a></li>
99 </ul></li>
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]100 </ul>
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]101 </li>
Chris Lattnerae7f7592002-09-06 18:31:18 +0000[diff] [blame]102 <li><a href="#common">Helpful Hints for Common Operations</a>
Chris Lattnerae7f7592002-09-06 18:31:18 +0000[diff] [blame]103 <ul>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]104 <li><a href="#inspection">Basic Inspection and Traversal Routines</a>
105 <ul>
106 <li><a href="#iterate_function">Iterating over the <tt>BasicBlock</tt>s
107in a <tt>Function</tt></a> </li>
108 <li><a href="#iterate_basicblock">Iterating over the <tt>Instruction</tt>s
109in a <tt>BasicBlock</tt></a> </li>
110 <li><a href="#iterate_institer">Iterating over the <tt>Instruction</tt>s
111in a <tt>Function</tt></a> </li>
112 <li><a href="#iterate_convert">Turning an iterator into a
113class pointer</a> </li>
114 <li><a href="#iterate_complex">Finding call sites: a more
115complex example</a> </li>
116 <li><a href="#calls_and_invokes">Treating calls and invokes
117the same way</a> </li>
118 <li><a href="#iterate_chains">Iterating over def-use &amp;
119use-def chains</a> </li>
Chris Lattner2e438ca2008-01-03 16:56:04 +0000[diff] [blame]120 <li><a href="#iterate_preds">Iterating over predecessors &amp;
121successors of blocks</a></li>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]122 </ul>
123 </li>
124 <li><a href="#simplechanges">Making simple changes</a>
125 <ul>
126 <li><a href="#schanges_creating">Creating and inserting new
127 <tt>Instruction</tt>s</a> </li>
128 <li><a href="#schanges_deleting">Deleting <tt>Instruction</tt>s</a> </li>
129 <li><a href="#schanges_replacing">Replacing an <tt>Instruction</tt>
130with another <tt>Value</tt></a> </li>
Tanya Lattnerb011c662007-06-20 18:33:15 +0000[diff] [blame]131 <li><a href="#schanges_deletingGV">Deleting <tt>GlobalVariable</tt>s</a> </li>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]132 </ul>
Reid Spencerfe8f4ff2004-11-01 09:02:53 +0000[diff] [blame]133 </li>
Jeffrey Yasskin714257f2009-04-30 22:33:41 +0000[diff] [blame]134 <li><a href="#create_types">How to Create Types</a></li>
Chris Lattnerae7f7592002-09-06 18:31:18 +0000[diff] [blame]135<!--
136 <li>Working with the Control Flow Graph
137 <ul>
138 <li>Accessing predecessors and successors of a <tt>BasicBlock</tt>
139 <li>
140 <li>
141 </ul>
Reid Spencerfe8f4ff2004-11-01 09:02:53 +0000[diff] [blame]142-->
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]143 </ul>
144 </li>
Chris Lattnerd9d6e102005-04-23 16:10:52 +0000[diff] [blame]145
Owen Anderson8bc1b3b2009-06-16 01:17:16 +0000[diff] [blame]146 <li><a href="#threading">Threads and LLVM</a>
147 <ul>
Owen Anderson1ad70e32009-06-16 18:04:19 +0000[diff] [blame]148 <li><a href="#startmultithreaded">Entering and Exiting Multithreaded Mode
149 </a></li>
Owen Anderson8bc1b3b2009-06-16 01:17:16 +0000[diff] [blame]150 <li><a href="#shutdown">Ending execution with <tt>llvm_shutdown()</tt></a></li>
151 <li><a href="#managedstatic">Lazy initialization with <tt>ManagedStatic</tt></a></li>
Owen Andersone0c951a2009-08-19 17:58:52 +0000[diff] [blame]152 <li><a href="#llvmcontext">Achieving Isolation with <tt>LLVMContext</tt></a></li>
Jeffrey Yasskin01eba392010-01-29 19:10:38 +0000[diff] [blame]153 <li><a href="#jitthreading">Threads and the JIT</a></li>
Owen Anderson8bc1b3b2009-06-16 01:17:16 +0000[diff] [blame]154 </ul>
155 </li>
156
Chris Lattnerd9d6e102005-04-23 16:10:52 +0000[diff] [blame]157 <li><a href="#advanced">Advanced Topics</a>
158 <ul>
Chris Lattnerf1b200b2005-04-23 17:27:36 +0000[diff] [blame]159 <li><a href="#TypeResolve">LLVM Type Resolution</a>
160 <ul>
161 <li><a href="#BuildRecType">Basic Recursive Type Construction</a></li>
162 <li><a href="#refineAbstractTypeTo">The <tt>refineAbstractTypeTo</tt> method</a></li>
163 <li><a href="#PATypeHolder">The PATypeHolder Class</a></li>
164 <li><a href="#AbstractTypeUser">The AbstractTypeUser Class</a></li>
165 </ul></li>
166
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]167 <li><a href="#SymbolTable">The <tt>ValueSymbolTable</tt> and <tt>TypeSymbolTable</tt> classes</a></li>
168 <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]169 </ul></li>
170
Joel Stanley9b96c442002-09-06 21:55:13 +0000[diff] [blame]171 <li><a href="#coreclasses">The Core LLVM Class Hierarchy Reference</a>
Chris Lattner9355b472002-09-06 02:50:58 +0000[diff] [blame]172 <ul>
Reid Spencer303c4b42007-01-12 17:26:25 +0000[diff] [blame]173 <li><a href="#Type">The <tt>Type</tt> class</a> </li>
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]174 <li><a href="#Module">The <tt>Module</tt> class</a></li>
Reid Spencerfe8f4ff2004-11-01 09:02:53 +0000[diff] [blame]175 <li><a href="#Value">The <tt>Value</tt> class</a>
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]176 <ul>
177 <li><a href="#User">The <tt>User</tt> class</a>
Chris Lattner9355b472002-09-06 02:50:58 +0000[diff] [blame]178 <ul>
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]179 <li><a href="#Instruction">The <tt>Instruction</tt> class</a></li>
180 <li><a href="#Constant">The <tt>Constant</tt> class</a>
181 <ul>
182 <li><a href="#GlobalValue">The <tt>GlobalValue</tt> class</a>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]183 <ul>
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]184 <li><a href="#Function">The <tt>Function</tt> class</a></li>
185 <li><a href="#GlobalVariable">The <tt>GlobalVariable</tt> class</a></li>
186 </ul>
187 </li>
188 </ul>
189 </li>
Reid Spencerfe8f4ff2004-11-01 09:02:53 +0000[diff] [blame]190 </ul>
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]191 </li>
192 <li><a href="#BasicBlock">The <tt>BasicBlock</tt> class</a></li>
193 <li><a href="#Argument">The <tt>Argument</tt> class</a></li>
194 </ul>
Reid Spencerfe8f4ff2004-11-01 09:02:53 +0000[diff] [blame]195 </li>
196 </ul>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]197 </li>
Chris Lattner9355b472002-09-06 02:50:58 +0000[diff] [blame]198</ol>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]199
Chris Lattner69bf8a92004-05-23 21:06:58 +0000[diff] [blame]200<div class="doc_author">
201 <p>Written by <a href="mailto:sabre@nondot.org">Chris Lattner</a>,
Chris Lattner94c43592004-05-26 16:52:55 +0000[diff] [blame]202 <a href="mailto:dhurjati@cs.uiuc.edu">Dinakar Dhurjati</a>,
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]203 <a href="mailto:ggreif@gmail.com">Gabor Greif</a>,
Owen Anderson8bc1b3b2009-06-16 01:17:16 +0000[diff] [blame]204 <a href="mailto:jstanley@cs.uiuc.edu">Joel Stanley</a>,
205 <a href="mailto:rspencer@x10sys.com">Reid Spencer</a> and
206 <a href="mailto:owen@apple.com">Owen Anderson</a></p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]207</div>
208
Chris Lattner9355b472002-09-06 02:50:58 +0000[diff] [blame]209<!-- *********************************************************************** -->
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]210<div class="doc_section">
211 <a name="introduction">Introduction </a>
212</div>
Chris Lattner9355b472002-09-06 02:50:58 +0000[diff] [blame]213<!-- *********************************************************************** -->
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]214
215<div class="doc_text">
216
217<p>This document is meant to highlight some of the important classes and
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]218interfaces available in the LLVM source-base. This manual is not
219intended to explain what LLVM is, how it works, and what LLVM code looks
220like. It assumes that you know the basics of LLVM and are interested
221in writing transformations or otherwise analyzing or manipulating the
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]222code.</p>
223
224<p>This document should get you oriented so that you can find your
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]225way in the continuously growing source code that makes up the LLVM
226infrastructure. Note that this manual is not intended to serve as a
227replacement for reading the source code, so if you think there should be
228a method in one of these classes to do something, but it's not listed,
229check the source. Links to the <a href="/doxygen/">doxygen</a> sources
230are provided to make this as easy as possible.</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]231
232<p>The first section of this document describes general information that is
233useful to know when working in the LLVM infrastructure, and the second describes
234the Core LLVM classes. In the future this manual will be extended with
235information describing how to use extension libraries, such as dominator
236information, CFG traversal routines, and useful utilities like the <tt><a
237href="/doxygen/InstVisitor_8h-source.html">InstVisitor</a></tt> template.</p>
238
239</div>
240
Chris Lattner9355b472002-09-06 02:50:58 +0000[diff] [blame]241<!-- *********************************************************************** -->
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]242<div class="doc_section">
243 <a name="general">General Information</a>
244</div>
245<!-- *********************************************************************** -->
246
247<div class="doc_text">
248
249<p>This section contains general information that is useful if you are working
250in the LLVM source-base, but that isn't specific to any particular API.</p>
251
252</div>
253
254<!-- ======================================================================= -->
255<div class="doc_subsection">
256 <a name="stl">The C++ Standard Template Library</a>
257</div>
258
259<div class="doc_text">
260
261<p>LLVM makes heavy use of the C++ Standard Template Library (STL),
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]262perhaps much more than you are used to, or have seen before. Because of
263this, you might want to do a little background reading in the
264techniques used and capabilities of the library. There are many good
265pages that discuss the STL, and several books on the subject that you
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]266can get, so it will not be discussed in this document.</p>
267
268<p>Here are some useful links:</p>
269
270<ol>
271
272<li><a href="http://www.dinkumware.com/refxcpp.html">Dinkumware C++ Library
273reference</a> - an excellent reference for the STL and other parts of the
274standard C++ library.</li>
275
276<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]277O'Reilly book in the making. It has a decent Standard Library
278Reference that rivals Dinkumware's, and is unfortunately no longer free since the
279book has been published.</li>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]280
281<li><a href="http://www.parashift.com/c++-faq-lite/">C++ Frequently Asked
282Questions</a></li>
283
284<li><a href="http://www.sgi.com/tech/stl/">SGI's STL Programmer's Guide</a> -
285Contains a useful <a
286href="http://www.sgi.com/tech/stl/stl_introduction.html">Introduction to the
287STL</a>.</li>
288
289<li><a href="http://www.research.att.com/%7Ebs/C++.html">Bjarne Stroustrup's C++
290Page</a></li>
291
Tanya Lattner79445ba2004-12-08 18:34:56 +0000[diff] [blame]292<li><a href="http://64.78.49.204/">
Reid Spencer096603a2004-05-26 08:41:35 +0000[diff] [blame]293Bruce Eckel's Thinking in C++, 2nd ed. Volume 2 Revision 4.0 (even better, get
294the book).</a></li>
295
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]296</ol>
297
298<p>You are also encouraged to take a look at the <a
299href="CodingStandards.html">LLVM Coding Standards</a> guide which focuses on how
300to write maintainable code more than where to put your curly braces.</p>
301
302</div>
303
304<!-- ======================================================================= -->
305<div class="doc_subsection">
306 <a name="stl">Other useful references</a>
307</div>
308
309<div class="doc_text">
310
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]311<ol>
312<li><a href="http://www.psc.edu/%7Esemke/cvs_branches.html">CVS
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]313Branch and Tag Primer</a></li>
Misha Brukmana0f71e42004-06-18 18:39:00 +0000[diff] [blame]314<li><a href="http://www.fortran-2000.com/ArnaudRecipes/sharedlib.html">Using
315static and shared libraries across platforms</a></li>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]316</ol>
317
318</div>
319
Chris Lattner9355b472002-09-06 02:50:58 +0000[diff] [blame]320<!-- *********************************************************************** -->
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]321<div class="doc_section">
322 <a name="apis">Important and useful LLVM APIs</a>
323</div>
324<!-- *********************************************************************** -->
325
326<div class="doc_text">
327
328<p>Here we highlight some LLVM APIs that are generally useful and good to
329know about when writing transformations.</p>
330
331</div>
332
333<!-- ======================================================================= -->
334<div class="doc_subsection">
Misha Brukman2c122ce2005-11-01 21:12:49 +0000[diff] [blame]335 <a name="isa">The <tt>isa&lt;&gt;</tt>, <tt>cast&lt;&gt;</tt> and
336 <tt>dyn_cast&lt;&gt;</tt> templates</a>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]337</div>
338
339<div class="doc_text">
340
341<p>The LLVM source-base makes extensive use of a custom form of RTTI.
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]342These templates have many similarities to the C++ <tt>dynamic_cast&lt;&gt;</tt>
343operator, but they don't have some drawbacks (primarily stemming from
344the fact that <tt>dynamic_cast&lt;&gt;</tt> only works on classes that
345have a v-table). Because they are used so often, you must know what they
346do and how they work. All of these templates are defined in the <a
Chris Lattner695b78b2005-04-26 22:56:16 +0000[diff] [blame]347 href="/doxygen/Casting_8h-source.html"><tt>llvm/Support/Casting.h</tt></a>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]348file (note that you very rarely have to include this file directly).</p>
349
350<dl>
351 <dt><tt>isa&lt;&gt;</tt>: </dt>
352
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]353 <dd><p>The <tt>isa&lt;&gt;</tt> operator works exactly like the Java
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]354 "<tt>instanceof</tt>" operator. It returns true or false depending on whether
355 a reference or pointer points to an instance of the specified class. This can
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]356 be very useful for constraint checking of various sorts (example below).</p>
357 </dd>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]358
359 <dt><tt>cast&lt;&gt;</tt>: </dt>
360
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]361 <dd><p>The <tt>cast&lt;&gt;</tt> operator is a "checked cast" operation. It
Chris Lattner28e6ff52008-06-20 05:03:17 +0000[diff] [blame]362 converts a pointer or reference from a base class to a derived class, causing
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]363 an assertion failure if it is not really an instance of the right type. This
364 should be used in cases where you have some information that makes you believe
365 that something is of the right type. An example of the <tt>isa&lt;&gt;</tt>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]366 and <tt>cast&lt;&gt;</tt> template is:</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]367
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]368<div class="doc_code">
369<pre>
370static bool isLoopInvariant(const <a href="#Value">Value</a> *V, const Loop *L) {
371 if (isa&lt;<a href="#Constant">Constant</a>&gt;(V) || isa&lt;<a href="#Argument">Argument</a>&gt;(V) || isa&lt;<a href="#GlobalValue">GlobalValue</a>&gt;(V))
372 return true;
Chris Lattner69bf8a92004-05-23 21:06:58 +0000[diff] [blame]373
Bill Wendling82e2eea2006-10-11 18:00:22 +0000[diff] [blame]374 // <i>Otherwise, it must be an instruction...</i>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]375 return !L-&gt;contains(cast&lt;<a href="#Instruction">Instruction</a>&gt;(V)-&gt;getParent());
376}
377</pre>
378</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]379
380 <p>Note that you should <b>not</b> use an <tt>isa&lt;&gt;</tt> test followed
381 by a <tt>cast&lt;&gt;</tt>, for that use the <tt>dyn_cast&lt;&gt;</tt>
382 operator.</p>
383
384 </dd>
385
386 <dt><tt>dyn_cast&lt;&gt;</tt>:</dt>
387
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]388 <dd><p>The <tt>dyn_cast&lt;&gt;</tt> operator is a "checking cast" operation.
389 It checks to see if the operand is of the specified type, and if so, returns a
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]390 pointer to it (this operator does not work with references). If the operand is
391 not of the correct type, a null pointer is returned. Thus, this works very
Misha Brukman2c122ce2005-11-01 21:12:49 +0000[diff] [blame]392 much like the <tt>dynamic_cast&lt;&gt;</tt> operator in C++, and should be
393 used in the same circumstances. Typically, the <tt>dyn_cast&lt;&gt;</tt>
394 operator is used in an <tt>if</tt> statement or some other flow control
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]395 statement like this:</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]396
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]397<div class="doc_code">
398<pre>
399if (<a href="#AllocationInst">AllocationInst</a> *AI = dyn_cast&lt;<a href="#AllocationInst">AllocationInst</a>&gt;(Val)) {
Bill Wendling82e2eea2006-10-11 18:00:22 +0000[diff] [blame]400 // <i>...</i>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]401}
402</pre>
403</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]404
Misha Brukman2c122ce2005-11-01 21:12:49 +0000[diff] [blame]405 <p>This form of the <tt>if</tt> statement effectively combines together a call
406 to <tt>isa&lt;&gt;</tt> and a call to <tt>cast&lt;&gt;</tt> into one
407 statement, which is very convenient.</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]408
Misha Brukman2c122ce2005-11-01 21:12:49 +0000[diff] [blame]409 <p>Note that the <tt>dyn_cast&lt;&gt;</tt> operator, like C++'s
410 <tt>dynamic_cast&lt;&gt;</tt> or Java's <tt>instanceof</tt> operator, can be
411 abused. In particular, you should not use big chained <tt>if/then/else</tt>
412 blocks to check for lots of different variants of classes. If you find
413 yourself wanting to do this, it is much cleaner and more efficient to use the
414 <tt>InstVisitor</tt> class to dispatch over the instruction type directly.</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]415
Misha Brukman2c122ce2005-11-01 21:12:49 +0000[diff] [blame]416 </dd>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]417
Misha Brukman2c122ce2005-11-01 21:12:49 +0000[diff] [blame]418 <dt><tt>cast_or_null&lt;&gt;</tt>: </dt>
419
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]420 <dd><p>The <tt>cast_or_null&lt;&gt;</tt> operator works just like the
Misha Brukman2c122ce2005-11-01 21:12:49 +0000[diff] [blame]421 <tt>cast&lt;&gt;</tt> operator, except that it allows for a null pointer as an
422 argument (which it then propagates). This can sometimes be useful, allowing
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]423 you to combine several null checks into one.</p></dd>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]424
Misha Brukman2c122ce2005-11-01 21:12:49 +0000[diff] [blame]425 <dt><tt>dyn_cast_or_null&lt;&gt;</tt>: </dt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]426
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]427 <dd><p>The <tt>dyn_cast_or_null&lt;&gt;</tt> operator works just like the
Misha Brukman2c122ce2005-11-01 21:12:49 +0000[diff] [blame]428 <tt>dyn_cast&lt;&gt;</tt> operator, except that it allows for a null pointer
429 as an argument (which it then propagates). This can sometimes be useful,
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]430 allowing you to combine several null checks into one.</p></dd>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]431
Misha Brukman2c122ce2005-11-01 21:12:49 +0000[diff] [blame]432</dl>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]433
434<p>These five templates can be used with any classes, whether they have a
435v-table or not. To add support for these templates, you simply need to add
436<tt>classof</tt> static methods to the class you are interested casting
437to. Describing this is currently outside the scope of this document, but there
438are lots of examples in the LLVM source base.</p>
439
440</div>
441
Daniel Dunbar6e0d1cb2009-07-25 04:41:11 +0000[diff] [blame]442
443<!-- ======================================================================= -->
444<div class="doc_subsection">
445 <a name="string_apis">Passing strings (the <tt>StringRef</tt>
446and <tt>Twine</tt> classes)</a>
447</div>
448
449<div class="doc_text">
450
451<p>Although LLVM generally does not do much string manipulation, we do have
Chris Lattner81187ae2009-07-25 07:16:59 +0000[diff] [blame]452several important APIs which take strings. Two important examples are the
Daniel Dunbar6e0d1cb2009-07-25 04:41:11 +0000[diff] [blame]453Value class -- which has names for instructions, functions, etc. -- and the
454StringMap class which is used extensively in LLVM and Clang.</p>
455
456<p>These are generic classes, and they need to be able to accept strings which
457may have embedded null characters. Therefore, they cannot simply take
Chris Lattner81187ae2009-07-25 07:16:59 +0000[diff] [blame]458a <tt>const char *</tt>, and taking a <tt>const std::string&amp;</tt> requires
Daniel Dunbar6e0d1cb2009-07-25 04:41:11 +0000[diff] [blame]459clients to perform a heap allocation which is usually unnecessary. Instead,
Benjamin Kramer38e59892010-07-14 22:38:02 +0000[diff] [blame]460many LLVM APIs use a <tt>StringRef</tt> or a <tt>const Twine&amp;</tt> for
461passing strings efficiently.</p>
Daniel Dunbar6e0d1cb2009-07-25 04:41:11 +0000[diff] [blame]462
463</div>
464
465<!-- _______________________________________________________________________ -->
466<div class="doc_subsubsection">
467 <a name="StringRef">The <tt>StringRef</tt> class</a>
468</div>
469
470<div class="doc_text">
471
472<p>The <tt>StringRef</tt> data type represents a reference to a constant string
473(a character array and a length) and supports the common operations available
474on <tt>std:string</tt>, but does not require heap allocation.</p>
475
Chris Lattner81187ae2009-07-25 07:16:59 +0000[diff] [blame]476<p>It can be implicitly constructed using a C style null-terminated string,
477an <tt>std::string</tt>, or explicitly with a character pointer and length.
Daniel Dunbar6e0d1cb2009-07-25 04:41:11 +0000[diff] [blame]478For example, the <tt>StringRef</tt> find function is declared as:</p>
Chris Lattner81187ae2009-07-25 07:16:59 +0000[diff] [blame]479
Benjamin Kramer38e59892010-07-14 22:38:02 +0000[diff] [blame]480<pre class="doc_code">
481 iterator find(StringRef Key);
482</pre>
Daniel Dunbar6e0d1cb2009-07-25 04:41:11 +0000[diff] [blame]483
484<p>and clients can call it using any one of:</p>
485
Benjamin Kramer38e59892010-07-14 22:38:02 +0000[diff] [blame]486<pre class="doc_code">
Daniel Dunbar6e0d1cb2009-07-25 04:41:11 +0000[diff] [blame]487 Map.find("foo"); <i>// Lookup "foo"</i>
488 Map.find(std::string("bar")); <i>// Lookup "bar"</i>
489 Map.find(StringRef("\0baz", 4)); <i>// Lookup "\0baz"</i>
490</pre>
Daniel Dunbar6e0d1cb2009-07-25 04:41:11 +0000[diff] [blame]491
492<p>Similarly, APIs which need to return a string may return a <tt>StringRef</tt>
493instance, which can be used directly or converted to an <tt>std::string</tt>
494using the <tt>str</tt> member function. See
495"<tt><a href="/doxygen/classllvm_1_1StringRef_8h-source.html">llvm/ADT/StringRef.h</a></tt>"
496for more information.</p>
497
498<p>You should rarely use the <tt>StringRef</tt> class directly, because it contains
499pointers to external memory it is not generally safe to store an instance of the
Benjamin Kramer38e59892010-07-14 22:38:02 +0000[diff] [blame]500class (unless you know that the external storage will not be freed). StringRef is
501small and pervasive enough in LLVM that it should always be passed by value.</p>
Daniel Dunbar6e0d1cb2009-07-25 04:41:11 +0000[diff] [blame]502
503</div>
504
505<!-- _______________________________________________________________________ -->
506<div class="doc_subsubsection">
507 <a name="Twine">The <tt>Twine</tt> class</a>
508</div>
509
510<div class="doc_text">
511
512<p>The <tt>Twine</tt> class is an efficient way for APIs to accept concatenated
513strings. For example, a common LLVM paradigm is to name one instruction based on
514the name of another instruction with a suffix, for example:</p>
515
516<div class="doc_code">
517<pre>
518 New = CmpInst::Create(<i>...</i>, SO->getName() + ".cmp");
519</pre>
520</div>
521
522<p>The <tt>Twine</tt> class is effectively a
523lightweight <a href="http://en.wikipedia.org/wiki/Rope_(computer_science)">rope</a>
524which points to temporary (stack allocated) objects. Twines can be implicitly
525constructed as the result of the plus operator applied to strings (i.e., a C
526strings, an <tt>std::string</tt>, or a <tt>StringRef</tt>). The twine delays the
Dan Gohmancf0c9bc2010-02-25 23:51:27 +0000[diff] [blame]527actual concatenation of strings until it is actually required, at which point
Daniel Dunbar6e0d1cb2009-07-25 04:41:11 +0000[diff] [blame]528it can be efficiently rendered directly into a character array. This avoids
529unnecessary heap allocation involved in constructing the temporary results of
530string concatenation. See
531"<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]532for more information.</p>
Daniel Dunbar6e0d1cb2009-07-25 04:41:11 +0000[diff] [blame]533
534<p>As with a <tt>StringRef</tt>, <tt>Twine</tt> objects point to external memory
535and should almost never be stored or mentioned directly. They are intended
536solely for use when defining a function which should be able to efficiently
537accept concatenated strings.</p>
538
539</div>
540
541
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]542<!-- ======================================================================= -->
543<div class="doc_subsection">
Misha Brukman2c122ce2005-11-01 21:12:49 +0000[diff] [blame]544 <a name="DEBUG">The <tt>DEBUG()</tt> macro and <tt>-debug</tt> option</a>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]545</div>
546
547<div class="doc_text">
548
549<p>Often when working on your pass you will put a bunch of debugging printouts
550and other code into your pass. After you get it working, you want to remove
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]551it, 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]552across).</p>
553
554<p> Naturally, because of this, you don't want to delete the debug printouts,
555but you don't want them to always be noisy. A standard compromise is to comment
556them out, allowing you to enable them if you need them in the future.</p>
557
Chris Lattner695b78b2005-04-26 22:56:16 +0000[diff] [blame]558<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]559file provides a macro named <tt>DEBUG()</tt> that is a much nicer solution to
560this problem. Basically, you can put arbitrary code into the argument of the
561<tt>DEBUG</tt> macro, and it is only executed if '<tt>opt</tt>' (or any other
562tool) is run with the '<tt>-debug</tt>' command line argument:</p>
563
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]564<div class="doc_code">
565<pre>
Daniel Dunbar06388ae2009-07-25 01:55:32 +0000[diff] [blame]566DEBUG(errs() &lt;&lt; "I am here!\n");
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]567</pre>
568</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]569
570<p>Then you can run your pass like this:</p>
571
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]572<div class="doc_code">
573<pre>
574$ opt &lt; a.bc &gt; /dev/null -mypass
Bill Wendling82e2eea2006-10-11 18:00:22 +0000[diff] [blame]575<i>&lt;no output&gt;</i>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]576$ opt &lt; a.bc &gt; /dev/null -mypass -debug
577I am here!
578</pre>
579</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]580
581<p>Using the <tt>DEBUG()</tt> macro instead of a home-brewed solution allows you
582to not have to create "yet another" command line option for the debug output for
583your pass. Note that <tt>DEBUG()</tt> macros are disabled for optimized builds,
584so they do not cause a performance impact at all (for the same reason, they
585should also not contain side-effects!).</p>
586
587<p>One additional nice thing about the <tt>DEBUG()</tt> macro is that you can
588enable or disable it directly in gdb. Just use "<tt>set DebugFlag=0</tt>" or
589"<tt>set DebugFlag=1</tt>" from the gdb if the program is running. If the
590program hasn't been started yet, you can always just run it with
591<tt>-debug</tt>.</p>
592
593</div>
594
595<!-- _______________________________________________________________________ -->
596<div class="doc_subsubsection">
Chris Lattnerc9151082005-04-26 22:57:07 +0000[diff] [blame]597 <a name="DEBUG_TYPE">Fine grained debug info with <tt>DEBUG_TYPE</tt> and
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]598 the <tt>-debug-only</tt> option</a>
599</div>
600
601<div class="doc_text">
602
603<p>Sometimes you may find yourself in a situation where enabling <tt>-debug</tt>
604just turns on <b>too much</b> information (such as when working on the code
605generator). If you want to enable debug information with more fine-grained
606control, you define the <tt>DEBUG_TYPE</tt> macro and the <tt>-debug</tt> only
607option as follows:</p>
608
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]609<div class="doc_code">
610<pre>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]611#undef DEBUG_TYPE
Daniel Dunbar06388ae2009-07-25 01:55:32 +0000[diff] [blame]612DEBUG(errs() &lt;&lt; "No debug type\n");
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]613#define DEBUG_TYPE "foo"
Daniel Dunbar06388ae2009-07-25 01:55:32 +0000[diff] [blame]614DEBUG(errs() &lt;&lt; "'foo' debug type\n");
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]615#undef DEBUG_TYPE
616#define DEBUG_TYPE "bar"
Daniel Dunbar06388ae2009-07-25 01:55:32 +0000[diff] [blame]617DEBUG(errs() &lt;&lt; "'bar' debug type\n"));
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]618#undef DEBUG_TYPE
619#define DEBUG_TYPE ""
Daniel Dunbar06388ae2009-07-25 01:55:32 +0000[diff] [blame]620DEBUG(errs() &lt;&lt; "No debug type (2)\n");
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]621</pre>
622</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]623
624<p>Then you can run your pass like this:</p>
625
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]626<div class="doc_code">
627<pre>
628$ opt &lt; a.bc &gt; /dev/null -mypass
Bill Wendling82e2eea2006-10-11 18:00:22 +0000[diff] [blame]629<i>&lt;no output&gt;</i>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]630$ opt &lt; a.bc &gt; /dev/null -mypass -debug
631No debug type
632'foo' debug type
633'bar' debug type
634No debug type (2)
635$ opt &lt; a.bc &gt; /dev/null -mypass -debug-only=foo
636'foo' debug type
637$ opt &lt; a.bc &gt; /dev/null -mypass -debug-only=bar
638'bar' debug type
639</pre>
640</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]641
642<p>Of course, in practice, you should only set <tt>DEBUG_TYPE</tt> at the top of
643a 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]644you <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]645<tt>#undef</tt>'s). Also, you should use names more meaningful than "foo" and
646"bar", because there is no system in place to ensure that names do not
647conflict. If two different modules use the same string, they will all be turned
648on when the name is specified. This allows, for example, all debug information
649for instruction scheduling to be enabled with <tt>-debug-type=InstrSched</tt>,
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]650even if the source lives in multiple files.</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]651
Daniel Dunbarc3c92392009-08-07 23:48:59 +0000[diff] [blame]652<p>The <tt>DEBUG_WITH_TYPE</tt> macro is also available for situations where you
653would like to set <tt>DEBUG_TYPE</tt>, but only for one specific <tt>DEBUG</tt>
654statement. It takes an additional first parameter, which is the type to use. For
Benjamin Kramer8040cd32009-10-12 14:46:08 +0000[diff] [blame]655example, the preceding example could be written as:</p>
Daniel Dunbarc3c92392009-08-07 23:48:59 +0000[diff] [blame]656
657
658<div class="doc_code">
659<pre>
660DEBUG_WITH_TYPE("", errs() &lt;&lt; "No debug type\n");
661DEBUG_WITH_TYPE("foo", errs() &lt;&lt; "'foo' debug type\n");
662DEBUG_WITH_TYPE("bar", errs() &lt;&lt; "'bar' debug type\n"));
663DEBUG_WITH_TYPE("", errs() &lt;&lt; "No debug type (2)\n");
664</pre>
665</div>
666
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]667</div>
668
669<!-- ======================================================================= -->
670<div class="doc_subsection">
Chris Lattner0be6fdf2006-12-19 21:46:21 +0000[diff] [blame]671 <a name="Statistic">The <tt>Statistic</tt> class &amp; <tt>-stats</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]672 option</a>
673</div>
674
675<div class="doc_text">
676
677<p>The "<tt><a
Chris Lattner695b78b2005-04-26 22:56:16 +0000[diff] [blame]678href="/doxygen/Statistic_8h-source.html">llvm/ADT/Statistic.h</a></tt>" file
Chris Lattner0be6fdf2006-12-19 21:46:21 +0000[diff] [blame]679provides a class named <tt>Statistic</tt> that is used as a unified way to
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]680keep track of what the LLVM compiler is doing and how effective various
681optimizations are. It is useful to see what optimizations are contributing to
682making a particular program run faster.</p>
683
684<p>Often you may run your pass on some big program, and you're interested to see
685how many times it makes a certain transformation. Although you can do this with
686hand 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]687for big programs. Using the <tt>Statistic</tt> class makes it very easy to
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]688keep track of this information, and the calculated information is presented in a
689uniform manner with the rest of the passes being executed.</p>
690
691<p>There are many examples of <tt>Statistic</tt> uses, but the basics of using
692it are as follows:</p>
693
694<ol>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]695 <li><p>Define your statistic like this:</p>
696
697<div class="doc_code">
698<pre>
Chris Lattner0be6fdf2006-12-19 21:46:21 +0000[diff] [blame]699#define <a href="#DEBUG_TYPE">DEBUG_TYPE</a> "mypassname" <i>// This goes before any #includes.</i>
700STATISTIC(NumXForms, "The # of times I did stuff");
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]701</pre>
702</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]703
Chris Lattner0be6fdf2006-12-19 21:46:21 +0000[diff] [blame]704 <p>The <tt>STATISTIC</tt> macro defines a static variable, whose name is
705 specified by the first argument. The pass name is taken from the DEBUG_TYPE
706 macro, and the description is taken from the second argument. The variable
Reid Spencer06565dc2007-01-12 17:11:23 +0000[diff] [blame]707 defined ("NumXForms" in this case) acts like an unsigned integer.</p></li>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]708
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]709 <li><p>Whenever you make a transformation, bump the counter:</p>
710
711<div class="doc_code">
712<pre>
Bill Wendling82e2eea2006-10-11 18:00:22 +0000[diff] [blame]713++NumXForms; // <i>I did stuff!</i>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]714</pre>
715</div>
716
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]717 </li>
718 </ol>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]719
720 <p>That's all you have to do. To get '<tt>opt</tt>' to print out the
721 statistics gathered, use the '<tt>-stats</tt>' option:</p>
722
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]723<div class="doc_code">
724<pre>
725$ opt -stats -mypassname &lt; program.bc &gt; /dev/null
Bill Wendling82e2eea2006-10-11 18:00:22 +0000[diff] [blame]726<i>... statistics output ...</i>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]727</pre>
728</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]729
Reid Spencer6b6c73e2007-02-09 16:00:28 +0000[diff] [blame]730 <p> When running <tt>opt</tt> on a C file from the SPEC benchmark
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]731suite, it gives a report that looks like this:</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]732
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]733<div class="doc_code">
734<pre>
Gabor Greif04367bf2007-07-06 22:07:22 +0000[diff] [blame]735 7646 bitcodewriter - Number of normal instructions
736 725 bitcodewriter - Number of oversized instructions
737 129996 bitcodewriter - Number of bitcode bytes written
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]738 2817 raise - Number of insts DCEd or constprop'd
739 3213 raise - Number of cast-of-self removed
740 5046 raise - Number of expression trees converted
741 75 raise - Number of other getelementptr's formed
742 138 raise - Number of load/store peepholes
743 42 deadtypeelim - Number of unused typenames removed from symtab
744 392 funcresolve - Number of varargs functions resolved
745 27 globaldce - Number of global variables removed
746 2 adce - Number of basic blocks removed
747 134 cee - Number of branches revectored
748 49 cee - Number of setcc instruction eliminated
749 532 gcse - Number of loads removed
750 2919 gcse - Number of instructions removed
751 86 indvars - Number of canonical indvars added
752 87 indvars - Number of aux indvars removed
753 25 instcombine - Number of dead inst eliminate
754 434 instcombine - Number of insts combined
755 248 licm - Number of load insts hoisted
756 1298 licm - Number of insts hoisted to a loop pre-header
757 3 licm - Number of insts hoisted to multiple loop preds (bad, no loop pre-header)
758 75 mem2reg - Number of alloca's promoted
759 1444 cfgsimplify - Number of blocks simplified
760</pre>
761</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]762
763<p>Obviously, with so many optimizations, having a unified framework for this
764stuff is very nice. Making your pass fit well into the framework makes it more
765maintainable and useful.</p>
766
767</div>
768
Chris Lattnerf623a082005-10-17 01:36:23 +0000[diff] [blame]769<!-- ======================================================================= -->
770<div class="doc_subsection">
771 <a name="ViewGraph">Viewing graphs while debugging code</a>
772</div>
773
774<div class="doc_text">
775
776<p>Several of the important data structures in LLVM are graphs: for example
777CFGs made out of LLVM <a href="#BasicBlock">BasicBlock</a>s, CFGs made out of
778LLVM <a href="CodeGenerator.html#machinebasicblock">MachineBasicBlock</a>s, and
779<a href="CodeGenerator.html#selectiondag_intro">Instruction Selection
780DAGs</a>. In many cases, while debugging various parts of the compiler, it is
781nice to instantly visualize these graphs.</p>
782
783<p>LLVM provides several callbacks that are available in a debug build to do
784exactly that. If you call the <tt>Function::viewCFG()</tt> method, for example,
785the current LLVM tool will pop up a window containing the CFG for the function
786where each basic block is a node in the graph, and each node contains the
787instructions in the block. Similarly, there also exists
788<tt>Function::viewCFGOnly()</tt> (does not include the instructions), the
789<tt>MachineFunction::viewCFG()</tt> and <tt>MachineFunction::viewCFGOnly()</tt>,
790and the <tt>SelectionDAG::viewGraph()</tt> methods. Within GDB, for example,
Jim Laskey543a0ee2006-10-02 12:28:07 +0000[diff] [blame]791you can usually use something like <tt>call DAG.viewGraph()</tt> to pop
Chris Lattnerf623a082005-10-17 01:36:23 +0000[diff] [blame]792up a window. Alternatively, you can sprinkle calls to these functions in your
793code in places you want to debug.</p>
794
795<p>Getting this to work requires a small amount of configuration. On Unix
796systems with X11, install the <a href="http://www.graphviz.org">graphviz</a>
797toolkit, and make sure 'dot' and 'gv' are in your path. If you are running on
798Mac OS/X, download and install the Mac OS/X <a
799href="http://www.pixelglow.com/graphviz/">Graphviz program</a>, and add
Reid Spencer128a7a72007-02-03 21:06:43 +0000[diff] [blame]800<tt>/Applications/Graphviz.app/Contents/MacOS/</tt> (or wherever you install
Chris Lattnerf623a082005-10-17 01:36:23 +0000[diff] [blame]801it) to your path. Once in your system and path are set up, rerun the LLVM
802configure script and rebuild LLVM to enable this functionality.</p>
803
Jim Laskey543a0ee2006-10-02 12:28:07 +0000[diff] [blame]804<p><tt>SelectionDAG</tt> has been extended to make it easier to locate
805<i>interesting</i> nodes in large complex graphs. From gdb, if you
806<tt>call DAG.setGraphColor(<i>node</i>, "<i>color</i>")</tt>, then the
Reid Spencer128a7a72007-02-03 21:06:43 +0000[diff] [blame]807next <tt>call DAG.viewGraph()</tt> would highlight the node in the
Jim Laskey543a0ee2006-10-02 12:28:07 +0000[diff] [blame]808specified color (choices of colors can be found at <a
Chris Lattner302da1e2007-02-03 03:05:57 +0000[diff] [blame]809href="http://www.graphviz.org/doc/info/colors.html">colors</a>.) More
Jim Laskey543a0ee2006-10-02 12:28:07 +0000[diff] [blame]810complex node attributes can be provided with <tt>call
811DAG.setGraphAttrs(<i>node</i>, "<i>attributes</i>")</tt> (choices can be
812found at <a href="http://www.graphviz.org/doc/info/attrs.html">Graph
813Attributes</a>.) If you want to restart and clear all the current graph
814attributes, then you can <tt>call DAG.clearGraphAttrs()</tt>. </p>
815
Chris Lattnerf623a082005-10-17 01:36:23 +0000[diff] [blame]816</div>
817
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]818<!-- *********************************************************************** -->
819<div class="doc_section">
820 <a name="datastructure">Picking the Right Data Structure for a Task</a>
821</div>
822<!-- *********************************************************************** -->
823
824<div class="doc_text">
825
Reid Spencer128a7a72007-02-03 21:06:43 +0000[diff] [blame]826<p>LLVM has a plethora of data structures in the <tt>llvm/ADT/</tt> directory,
827 and we commonly use STL data structures. This section describes the trade-offs
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]828 you should consider when you pick one.</p>
829
830<p>
831The first step is a choose your own adventure: do you want a sequential
832container, a set-like container, or a map-like container? The most important
833thing when choosing a container is the algorithmic properties of how you plan to
834access the container. Based on that, you should use:</p>
835
836<ul>
Reid Spencer128a7a72007-02-03 21:06:43 +0000[diff] [blame]837<li>a <a href="#ds_map">map-like</a> container if you need efficient look-up
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]838 of an value based on another value. Map-like containers also support
839 efficient queries for containment (whether a key is in the map). Map-like
840 containers generally do not support efficient reverse mapping (values to
841 keys). If you need that, use two maps. Some map-like containers also
842 support efficient iteration through the keys in sorted order. Map-like
843 containers are the most expensive sort, only use them if you need one of
844 these capabilities.</li>
845
846<li>a <a href="#ds_set">set-like</a> container if you need to put a bunch of
847 stuff into a container that automatically eliminates duplicates. Some
848 set-like containers support efficient iteration through the elements in
849 sorted order. Set-like containers are more expensive than sequential
850 containers.
851</li>
852
853<li>a <a href="#ds_sequential">sequential</a> container provides
854 the most efficient way to add elements and keeps track of the order they are
855 added to the collection. They permit duplicates and support efficient
Reid Spencer128a7a72007-02-03 21:06:43 +0000[diff] [blame]856 iteration, but do not support efficient look-up based on a key.
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]857</li>
858
Chris Lattnerdced9fb2009-07-25 07:22:20 +0000[diff] [blame]859<li>a <a href="#ds_string">string</a> container is a specialized sequential
860 container or reference structure that is used for character or byte
861 arrays.</li>
862
Daniel Berlin1939ace2007-09-24 17:52:25 +0000[diff] [blame]863<li>a <a href="#ds_bit">bit</a> container provides an efficient way to store and
864 perform set operations on sets of numeric id's, while automatically
865 eliminating duplicates. Bit containers require a maximum of 1 bit for each
866 identifier you want to store.
867</li>
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]868</ul>
869
870<p>
Reid Spencer128a7a72007-02-03 21:06:43 +0000[diff] [blame]871Once the proper category of container is determined, you can fine tune the
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]872memory use, constant factors, and cache behaviors of access by intelligently
Reid Spencer128a7a72007-02-03 21:06:43 +0000[diff] [blame]873picking a member of the category. Note that constant factors and cache behavior
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]874can be a big deal. If you have a vector that usually only contains a few
875elements (but could contain many), for example, it's much better to use
876<a href="#dss_smallvector">SmallVector</a> than <a href="#dss_vector">vector</a>
877. Doing so avoids (relatively) expensive malloc/free calls, which dwarf the
878cost of adding the elements to the container. </p>
879
880</div>
881
882<!-- ======================================================================= -->
883<div class="doc_subsection">
884 <a name="ds_sequential">Sequential Containers (std::vector, std::list, etc)</a>
885</div>
886
887<div class="doc_text">
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.
890</div>
891
892<!-- _______________________________________________________________________ -->
893<div class="doc_subsubsection">
894 <a name="dss_fixedarrays">Fixed Size Arrays</a>
895</div>
896
897<div class="doc_text">
898<p>Fixed size arrays are very simple and very fast. They are good if you know
899exactly how many elements you have, or you have a (low) upper bound on how many
900you have.</p>
901</div>
902
903<!-- _______________________________________________________________________ -->
904<div class="doc_subsubsection">
905 <a name="dss_heaparrays">Heap Allocated Arrays</a>
906</div>
907
908<div class="doc_text">
909<p>Heap allocated arrays (new[] + delete[]) are also simple. They are good if
910the number of elements is variable, if you know how many elements you will need
911before the array is allocated, and if the array is usually large (if not,
912consider a <a href="#dss_smallvector">SmallVector</a>). The cost of a heap
913allocated array is the cost of the new/delete (aka malloc/free). Also note that
914if you are allocating an array of a type with a constructor, the constructor and
Reid Spencer128a7a72007-02-03 21:06:43 +0000[diff] [blame]915destructors will be run for every element in the array (re-sizable vectors only
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]916construct those elements actually used).</p>
917</div>
918
919<!-- _______________________________________________________________________ -->
920<div class="doc_subsubsection">
921 <a name="dss_smallvector">"llvm/ADT/SmallVector.h"</a>
922</div>
923
924<div class="doc_text">
925<p><tt>SmallVector&lt;Type, N&gt;</tt> is a simple class that looks and smells
926just like <tt>vector&lt;Type&gt;</tt>:
927it supports efficient iteration, lays out elements in memory order (so you can
928do pointer arithmetic between elements), supports efficient push_back/pop_back
929operations, supports efficient random access to its elements, etc.</p>
930
931<p>The advantage of SmallVector is that it allocates space for
932some number of elements (N) <b>in the object itself</b>. Because of this, if
933the SmallVector is dynamically smaller than N, no malloc is performed. This can
934be a big win in cases where the malloc/free call is far more expensive than the
935code that fiddles around with the elements.</p>
936
937<p>This is good for vectors that are "usually small" (e.g. the number of
938predecessors/successors of a block is usually less than 8). On the other hand,
939this makes the size of the SmallVector itself large, so you don't want to
940allocate lots of them (doing so will waste a lot of space). As such,
941SmallVectors are most useful when on the stack.</p>
942
943<p>SmallVector also provides a nice portable and efficient replacement for
944<tt>alloca</tt>.</p>
945
946</div>
947
948<!-- _______________________________________________________________________ -->
949<div class="doc_subsubsection">
950 <a name="dss_vector">&lt;vector&gt;</a>
951</div>
952
953<div class="doc_text">
954<p>
955std::vector is well loved and respected. It is useful when SmallVector isn't:
956when the size of the vector is often large (thus the small optimization will
957rarely be a benefit) or if you will be allocating many instances of the vector
958itself (which would waste space for elements that aren't in the container).
959vector is also useful when interfacing with code that expects vectors :).
960</p>
Chris Lattner32d84762007-02-05 06:30:51 +0000[diff] [blame]961
962<p>One worthwhile note about std::vector: avoid code like this:</p>
963
964<div class="doc_code">
965<pre>
966for ( ... ) {
Chris Lattner9bb3dbb2007-03-28 18:27:57 +0000[diff] [blame]967 std::vector&lt;foo&gt; V;
Chris Lattner32d84762007-02-05 06:30:51 +0000[diff] [blame]968 use V;
969}
970</pre>
971</div>
972
973<p>Instead, write this as:</p>
974
975<div class="doc_code">
976<pre>
Chris Lattner9bb3dbb2007-03-28 18:27:57 +0000[diff] [blame]977std::vector&lt;foo&gt; V;
Chris Lattner32d84762007-02-05 06:30:51 +0000[diff] [blame]978for ( ... ) {
979 use V;
980 V.clear();
981}
982</pre>
983</div>
984
985<p>Doing so will save (at least) one heap allocation and free per iteration of
986the loop.</p>
987
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]988</div>
989
990<!-- _______________________________________________________________________ -->
991<div class="doc_subsubsection">
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]992 <a name="dss_deque">&lt;deque&gt;</a>
993</div>
994
995<div class="doc_text">
996<p>std::deque is, in some senses, a generalized version of std::vector. Like
997std::vector, it provides constant time random access and other similar
998properties, but it also provides efficient access to the front of the list. It
999does not guarantee continuity of elements within memory.</p>
1000
1001<p>In exchange for this extra flexibility, std::deque has significantly higher
1002constant factor costs than std::vector. If possible, use std::vector or
1003something cheaper.</p>
1004</div>
1005
1006<!-- _______________________________________________________________________ -->
1007<div class="doc_subsubsection">
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]1008 <a name="dss_list">&lt;list&gt;</a>
1009</div>
1010
1011<div class="doc_text">
1012<p>std::list is an extremely inefficient class that is rarely useful.
1013It performs a heap allocation for every element inserted into it, thus having an
1014extremely high constant factor, particularly for small data types. std::list
1015also only supports bidirectional iteration, not random access iteration.</p>
1016
1017<p>In exchange for this high cost, std::list supports efficient access to both
1018ends of the list (like std::deque, but unlike std::vector or SmallVector). In
1019addition, the iterator invalidation characteristics of std::list are stronger
1020than that of a vector class: inserting or removing an element into the list does
1021not invalidate iterator or pointers to other elements in the list.</p>
1022</div>
1023
1024<!-- _______________________________________________________________________ -->
1025<div class="doc_subsubsection">
Gabor Greif3899e492009-02-27 11:37:41 +0000[diff] [blame]1026 <a name="dss_ilist">llvm/ADT/ilist.h</a>
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]1027</div>
1028
1029<div class="doc_text">
1030<p><tt>ilist&lt;T&gt;</tt> implements an 'intrusive' doubly-linked list. It is
1031intrusive, because it requires the element to store and provide access to the
1032prev/next pointers for the list.</p>
1033
Gabor Greif2946d1c2009-02-27 12:02:19 +0000[diff] [blame]1034<p><tt>ilist</tt> has the same drawbacks as <tt>std::list</tt>, and additionally
1035requires an <tt>ilist_traits</tt> implementation for the element type, but it
1036provides some novel characteristics. In particular, it can efficiently store
1037polymorphic objects, the traits class is informed when an element is inserted or
Gabor Greif0cbcabe2009-03-12 09:47:03 +0000[diff] [blame]1038removed from the list, and <tt>ilist</tt>s are guaranteed to support a
1039constant-time splice operation.</p>
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]1040
Gabor Greif0cbcabe2009-03-12 09:47:03 +0000[diff] [blame]1041<p>These properties are exactly what we want for things like
1042<tt>Instruction</tt>s and basic blocks, which is why these are implemented with
1043<tt>ilist</tt>s.</p>
Gabor Greif3899e492009-02-27 11:37:41 +0000[diff] [blame]1044
1045Related classes of interest are explained in the following subsections:
1046 <ul>
Gabor Greif01862502009-02-27 13:28:07 +0000[diff] [blame]1047 <li><a href="#dss_ilist_traits">ilist_traits</a></li>
Gabor Greif2946d1c2009-02-27 12:02:19 +0000[diff] [blame]1048 <li><a href="#dss_iplist">iplist</a></li>
Gabor Greif3899e492009-02-27 11:37:41 +0000[diff] [blame]1049 <li><a href="#dss_ilist_node">llvm/ADT/ilist_node.h</a></li>
Gabor Greif6a65f422009-03-12 10:30:31 +0000[diff] [blame]1050 <li><a href="#dss_ilist_sentinel">Sentinels</a></li>
Gabor Greif3899e492009-02-27 11:37:41 +0000[diff] [blame]1051 </ul>
1052</div>
1053
1054<!-- _______________________________________________________________________ -->
1055<div class="doc_subsubsection">
Gabor Greif01862502009-02-27 13:28:07 +0000[diff] [blame]1056 <a name="dss_ilist_traits">ilist_traits</a>
1057</div>
1058
1059<div class="doc_text">
1060<p><tt>ilist_traits&lt;T&gt;</tt> is <tt>ilist&lt;T&gt;</tt>'s customization
1061mechanism. <tt>iplist&lt;T&gt;</tt> (and consequently <tt>ilist&lt;T&gt;</tt>)
1062publicly derive from this traits class.</p>
1063</div>
1064
1065<!-- _______________________________________________________________________ -->
1066<div class="doc_subsubsection">
Gabor Greif2946d1c2009-02-27 12:02:19 +0000[diff] [blame]1067 <a name="dss_iplist">iplist</a>
1068</div>
1069
1070<div class="doc_text">
1071<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]1072supports a slightly narrower interface. Notably, inserters from
1073<tt>T&amp;</tt> are absent.</p>
Gabor Greif01862502009-02-27 13:28:07 +0000[diff] [blame]1074
1075<p><tt>ilist_traits&lt;T&gt;</tt> is a public base of this class and can be
1076used for a wide variety of customizations.</p>
Gabor Greif2946d1c2009-02-27 12:02:19 +0000[diff] [blame]1077</div>
1078
1079<!-- _______________________________________________________________________ -->
1080<div class="doc_subsubsection">
Gabor Greif3899e492009-02-27 11:37:41 +0000[diff] [blame]1081 <a name="dss_ilist_node">llvm/ADT/ilist_node.h</a>
1082</div>
1083
1084<div class="doc_text">
1085<p><tt>ilist_node&lt;T&gt;</tt> implements a the forward and backward links
1086that are expected by the <tt>ilist&lt;T&gt;</tt> (and analogous containers)
1087in the default manner.</p>
1088
1089<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]1090<tt>T</tt>, usually <tt>T</tt> publicly derives from
1091<tt>ilist_node&lt;T&gt;</tt>.</p>
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]1092</div>
1093
1094<!-- _______________________________________________________________________ -->
1095<div class="doc_subsubsection">
Gabor Greif6a65f422009-03-12 10:30:31 +0000[diff] [blame]1096 <a name="dss_ilist_sentinel">Sentinels</a>
1097</div>
1098
1099<div class="doc_text">
Dan Gohmancf0c9bc2010-02-25 23:51:27 +0000[diff] [blame]1100<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]1101citizen in the C++ ecosystem, it needs to support the standard container
1102operations, such as <tt>begin</tt> and <tt>end</tt> iterators, etc. Also, the
1103<tt>operator--</tt> must work correctly on the <tt>end</tt> iterator in the
1104case of non-empty <tt>ilist</tt>s.</p>
1105
1106<p>The only sensible solution to this problem is to allocate a so-called
1107<i>sentinel</i> along with the intrusive list, which serves as the <tt>end</tt>
1108iterator, providing the back-link to the last element. However conforming to the
1109C++ convention it is illegal to <tt>operator++</tt> beyond the sentinel and it
1110also must not be dereferenced.</p>
1111
1112<p>These constraints allow for some implementation freedom to the <tt>ilist</tt>
1113how to allocate and store the sentinel. The corresponding policy is dictated
1114by <tt>ilist_traits&lt;T&gt;</tt>. By default a <tt>T</tt> gets heap-allocated
1115whenever the need for a sentinel arises.</p>
1116
1117<p>While the default policy is sufficient in most cases, it may break down when
1118<tt>T</tt> does not provide a default constructor. Also, in the case of many
1119instances of <tt>ilist</tt>s, the memory overhead of the associated sentinels
1120is wasted. To alleviate the situation with numerous and voluminous
1121<tt>T</tt>-sentinels, sometimes a trick is employed, leading to <i>ghostly
1122sentinels</i>.</p>
1123
1124<p>Ghostly sentinels are obtained by specially-crafted <tt>ilist_traits&lt;T&gt;</tt>
1125which superpose the sentinel with the <tt>ilist</tt> instance in memory. Pointer
1126arithmetic is used to obtain the sentinel, which is relative to the
1127<tt>ilist</tt>'s <tt>this</tt> pointer. The <tt>ilist</tt> is augmented by an
1128extra pointer, which serves as the back-link of the sentinel. This is the only
1129field in the ghostly sentinel which can be legally accessed.</p>
1130</div>
1131
1132<!-- _______________________________________________________________________ -->
1133<div class="doc_subsubsection">
Chris Lattnerc5722432007-02-03 19:49:31 +0000[diff] [blame]1134 <a name="dss_other">Other Sequential Container options</a>
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]1135</div>
1136
1137<div class="doc_text">
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1138<p>Other STL containers are available, such as std::string.</p>
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]1139
1140<p>There are also various STL adapter classes such as std::queue,
1141std::priority_queue, std::stack, etc. These provide simplified access to an
1142underlying container but don't affect the cost of the container itself.</p>
1143
1144</div>
1145
1146
1147<!-- ======================================================================= -->
1148<div class="doc_subsection">
1149 <a name="ds_set">Set-Like Containers (std::set, SmallSet, SetVector, etc)</a>
1150</div>
1151
1152<div class="doc_text">
1153
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1154<p>Set-like containers are useful when you need to canonicalize multiple values
1155into a single representation. There are several different choices for how to do
1156this, providing various trade-offs.</p>
1157
1158</div>
1159
1160
1161<!-- _______________________________________________________________________ -->
1162<div class="doc_subsubsection">
1163 <a name="dss_sortedvectorset">A sorted 'vector'</a>
1164</div>
1165
1166<div class="doc_text">
1167
Chris Lattner3b23a8c2007-02-03 08:10:45 +0000[diff] [blame]1168<p>If you intend to insert a lot of elements, then do a lot of queries, a
1169great approach is to use a vector (or other sequential container) with
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1170std::sort+std::unique to remove duplicates. This approach works really well if
Chris Lattner3b23a8c2007-02-03 08:10:45 +0000[diff] [blame]1171your usage pattern has these two distinct phases (insert then query), and can be
1172coupled with a good choice of <a href="#ds_sequential">sequential container</a>.
1173</p>
1174
1175<p>
1176This combination provides the several nice properties: the result data is
1177contiguous in memory (good for cache locality), has few allocations, is easy to
1178address (iterators in the final vector are just indices or pointers), and can be
1179efficiently queried with a standard binary or radix search.</p>
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1180
1181</div>
1182
1183<!-- _______________________________________________________________________ -->
1184<div class="doc_subsubsection">
1185 <a name="dss_smallset">"llvm/ADT/SmallSet.h"</a>
1186</div>
1187
1188<div class="doc_text">
1189
Reid Spencer128a7a72007-02-03 21:06:43 +0000[diff] [blame]1190<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]1191are 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]1192has space for N elements in place (thus, if the set is dynamically smaller than
Chris Lattner14868db2007-02-03 08:20:15 +0000[diff] [blame]1193N, no malloc traffic is required) and accesses them with a simple linear search.
1194When the set grows beyond 'N' elements, it allocates a more expensive representation that
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1195guarantees efficient access (for most types, it falls back to std::set, but for
Chris Lattner14868db2007-02-03 08:20:15 +0000[diff] [blame]1196pointers it uses something far better, <a
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1197href="#dss_smallptrset">SmallPtrSet</a>).</p>
1198
1199<p>The magic of this class is that it handles small sets extremely efficiently,
1200but gracefully handles extremely large sets without loss of efficiency. The
1201drawback is that the interface is quite small: it supports insertion, queries
1202and erasing, but does not support iteration.</p>
1203
1204</div>
1205
1206<!-- _______________________________________________________________________ -->
1207<div class="doc_subsubsection">
1208 <a name="dss_smallptrset">"llvm/ADT/SmallPtrSet.h"</a>
1209</div>
1210
1211<div class="doc_text">
1212
Gabor Greif4de73682010-03-26 19:30:47 +0000[diff] [blame]1213<p>SmallPtrSet has all the advantages of <tt>SmallSet</tt> (and a <tt>SmallSet</tt> of pointers is
1214transparently implemented with a <tt>SmallPtrSet</tt>), but also supports iterators. If
Chris Lattner14868db2007-02-03 08:20:15 +0000[diff] [blame]1215more than 'N' insertions are performed, a single quadratically
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1216probed hash table is allocated and grows as needed, providing extremely
1217efficient access (constant time insertion/deleting/queries with low constant
1218factors) and is very stingy with malloc traffic.</p>
1219
Gabor Greif4de73682010-03-26 19:30:47 +0000[diff] [blame]1220<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]1221whenever an insertion occurs. Also, the values visited by the iterators are not
1222visited in sorted order.</p>
1223
1224</div>
1225
1226<!-- _______________________________________________________________________ -->
1227<div class="doc_subsubsection">
Chris Lattnerc28476f2007-09-30 00:58:59 +0000[diff] [blame]1228 <a name="dss_denseset">"llvm/ADT/DenseSet.h"</a>
1229</div>
1230
1231<div class="doc_text">
1232
1233<p>
1234DenseSet is a simple quadratically probed hash table. It excels at supporting
1235small values: it uses a single allocation to hold all of the pairs that
1236are currently inserted in the set. DenseSet is a great way to unique small
1237values that are not simple pointers (use <a
1238href="#dss_smallptrset">SmallPtrSet</a> for pointers). Note that DenseSet has
1239the same requirements for the value type that <a
1240href="#dss_densemap">DenseMap</a> has.
1241</p>
1242
1243</div>
1244
1245<!-- _______________________________________________________________________ -->
1246<div class="doc_subsubsection">
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1247 <a name="dss_FoldingSet">"llvm/ADT/FoldingSet.h"</a>
1248</div>
1249
1250<div class="doc_text">
1251
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]1252<p>
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1253FoldingSet is an aggregate class that is really good at uniquing
1254expensive-to-create or polymorphic objects. It is a combination of a chained
1255hash table with intrusive links (uniqued objects are required to inherit from
Chris Lattner14868db2007-02-03 08:20:15 +0000[diff] [blame]1256FoldingSetNode) that uses <a href="#dss_smallvector">SmallVector</a> as part of
1257its ID process.</p>
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1258
Chris Lattner14868db2007-02-03 08:20:15 +0000[diff] [blame]1259<p>Consider a case where you want to implement a "getOrCreateFoo" method for
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1260a complex object (for example, a node in the code generator). The client has a
1261description of *what* it wants to generate (it knows the opcode and all the
1262operands), 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]1263only to find out it already exists, at which point we would have to delete it
1264and return the node that already exists.
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]1265</p>
1266
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1267<p>To support this style of client, FoldingSet perform a query with a
1268FoldingSetNodeID (which wraps SmallVector) that can be used to describe the
1269element that we want to query for. The query either returns the element
1270matching the ID or it returns an opaque ID that indicates where insertion should
Chris Lattner14868db2007-02-03 08:20:15 +0000[diff] [blame]1271take place. Construction of the ID usually does not require heap traffic.</p>
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1272
1273<p>Because FoldingSet uses intrusive links, it can support polymorphic objects
1274in the set (for example, you can have SDNode instances mixed with LoadSDNodes).
1275Because the elements are individually allocated, pointers to the elements are
1276stable: inserting or removing elements does not invalidate any pointers to other
1277elements.
1278</p>
1279
1280</div>
1281
1282<!-- _______________________________________________________________________ -->
1283<div class="doc_subsubsection">
1284 <a name="dss_set">&lt;set&gt;</a>
1285</div>
1286
1287<div class="doc_text">
1288
Chris Lattnerc5722432007-02-03 19:49:31 +0000[diff] [blame]1289<p><tt>std::set</tt> is a reasonable all-around set class, which is decent at
1290many things but great at nothing. std::set allocates memory for each element
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1291inserted (thus it is very malloc intensive) and typically stores three pointers
Chris Lattner14868db2007-02-03 08:20:15 +0000[diff] [blame]1292per element in the set (thus adding a large amount of per-element space
1293overhead). It offers guaranteed log(n) performance, which is not particularly
Chris Lattnerc5722432007-02-03 19:49:31 +0000[diff] [blame]1294fast from a complexity standpoint (particularly if the elements of the set are
1295expensive to compare, like strings), and has extremely high constant factors for
1296lookup, insertion and removal.</p>
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1297
Chris Lattner14868db2007-02-03 08:20:15 +0000[diff] [blame]1298<p>The advantages of std::set are that its iterators are stable (deleting or
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1299inserting an element from the set does not affect iterators or pointers to other
1300elements) and that iteration over the set is guaranteed to be in sorted order.
1301If the elements in the set are large, then the relative overhead of the pointers
1302and malloc traffic is not a big deal, but if the elements of the set are small,
1303std::set is almost never a good choice.</p>
1304
1305</div>
1306
1307<!-- _______________________________________________________________________ -->
1308<div class="doc_subsubsection">
1309 <a name="dss_setvector">"llvm/ADT/SetVector.h"</a>
1310</div>
1311
1312<div class="doc_text">
Chris Lattneredca3c52007-02-04 00:00:26 +0000[diff] [blame]1313<p>LLVM's SetVector&lt;Type&gt; is an adapter class that combines your choice of
1314a set-like container along with a <a href="#ds_sequential">Sequential
1315Container</a>. The important property
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1316that this provides is efficient insertion with uniquing (duplicate elements are
1317ignored) with iteration support. It implements this by inserting elements into
1318both a set-like container and the sequential container, using the set-like
1319container for uniquing and the sequential container for iteration.
1320</p>
1321
1322<p>The difference between SetVector and other sets is that the order of
1323iteration is guaranteed to match the order of insertion into the SetVector.
1324This property is really important for things like sets of pointers. Because
1325pointer values are non-deterministic (e.g. vary across runs of the program on
Chris Lattneredca3c52007-02-04 00:00:26 +0000[diff] [blame]1326different machines), iterating over the pointers in the set will
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1327not be in a well-defined order.</p>
1328
1329<p>
1330The drawback of SetVector is that it requires twice as much space as a normal
1331set and has the sum of constant factors from the set-like container and the
1332sequential container that it uses. Use it *only* if you need to iterate over
1333the elements in a deterministic order. SetVector is also expensive to delete
Chris Lattneredca3c52007-02-04 00:00:26 +0000[diff] [blame]1334elements out of (linear time), unless you use it's "pop_back" method, which is
1335faster.
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1336</p>
1337
Chris Lattneredca3c52007-02-04 00:00:26 +0000[diff] [blame]1338<p>SetVector is an adapter class that defaults to using std::vector and std::set
1339for the underlying containers, so it is quite expensive. However,
1340<tt>"llvm/ADT/SetVector.h"</tt> also provides a SmallSetVector class, which
1341defaults to using a SmallVector and SmallSet of a specified size. If you use
1342this, and if your sets are dynamically smaller than N, you will save a lot of
1343heap traffic.</p>
1344
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1345</div>
1346
1347<!-- _______________________________________________________________________ -->
1348<div class="doc_subsubsection">
Chris Lattnerc5722432007-02-03 19:49:31 +0000[diff] [blame]1349 <a name="dss_uniquevector">"llvm/ADT/UniqueVector.h"</a>
1350</div>
1351
1352<div class="doc_text">
1353
1354<p>
1355UniqueVector is similar to <a href="#dss_setvector">SetVector</a>, but it
1356retains a unique ID for each element inserted into the set. It internally
1357contains a map and a vector, and it assigns a unique ID for each value inserted
1358into the set.</p>
1359
1360<p>UniqueVector is very expensive: its cost is the sum of the cost of
1361maintaining both the map and vector, it has high complexity, high constant
1362factors, and produces a lot of malloc traffic. It should be avoided.</p>
1363
1364</div>
1365
1366
1367<!-- _______________________________________________________________________ -->
1368<div class="doc_subsubsection">
1369 <a name="dss_otherset">Other Set-Like Container Options</a>
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1370</div>
1371
1372<div class="doc_text">
1373
1374<p>
1375The STL provides several other options, such as std::multiset and the various
Chris Lattnerf1a30822009-03-09 05:20:45 +0000[diff] [blame]1376"hash_set" like containers (whether from C++ TR1 or from the SGI library). We
1377never use hash_set and unordered_set because they are generally very expensive
1378(each insertion requires a malloc) and very non-portable.
1379</p>
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1380
1381<p>std::multiset is useful if you're not interested in elimination of
Chris Lattner14868db2007-02-03 08:20:15 +0000[diff] [blame]1382duplicates, but has all the drawbacks of std::set. A sorted vector (where you
1383don't delete duplicate entries) or some other approach is almost always
1384better.</p>
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1385
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]1386</div>
1387
1388<!-- ======================================================================= -->
1389<div class="doc_subsection">
1390 <a name="ds_map">Map-Like Containers (std::map, DenseMap, etc)</a>
1391</div>
1392
1393<div class="doc_text">
Chris Lattnerc5722432007-02-03 19:49:31 +0000[diff] [blame]1394Map-like containers are useful when you want to associate data to a key. As
1395usual, there are a lot of different ways to do this. :)
1396</div>
1397
1398<!-- _______________________________________________________________________ -->
1399<div class="doc_subsubsection">
1400 <a name="dss_sortedvectormap">A sorted 'vector'</a>
1401</div>
1402
1403<div class="doc_text">
1404
1405<p>
1406If your usage pattern follows a strict insert-then-query approach, you can
1407trivially use the same approach as <a href="#dss_sortedvectorset">sorted vectors
1408for set-like containers</a>. The only difference is that your query function
1409(which uses std::lower_bound to get efficient log(n) lookup) should only compare
1410the key, not both the key and value. This yields the same advantages as sorted
1411vectors for sets.
1412</p>
1413</div>
1414
1415<!-- _______________________________________________________________________ -->
1416<div class="doc_subsubsection">
Chris Lattner796f9fa2007-02-08 19:14:21 +0000[diff] [blame]1417 <a name="dss_stringmap">"llvm/ADT/StringMap.h"</a>
Chris Lattnerc5722432007-02-03 19:49:31 +0000[diff] [blame]1418</div>
1419
1420<div class="doc_text">
1421
1422<p>
1423Strings are commonly used as keys in maps, and they are difficult to support
1424efficiently: they are variable length, inefficient to hash and compare when
Chris Lattner796f9fa2007-02-08 19:14:21 +0000[diff] [blame]1425long, expensive to copy, etc. StringMap is a specialized container designed to
1426cope with these issues. It supports mapping an arbitrary range of bytes to an
1427arbitrary other object.</p>
Chris Lattnerc5722432007-02-03 19:49:31 +0000[diff] [blame]1428
Chris Lattner796f9fa2007-02-08 19:14:21 +0000[diff] [blame]1429<p>The StringMap implementation uses a quadratically-probed hash table, where
Chris Lattnerc5722432007-02-03 19:49:31 +0000[diff] [blame]1430the buckets store a pointer to the heap allocated entries (and some other
1431stuff). The entries in the map must be heap allocated because the strings are
1432variable length. The string data (key) and the element object (value) are
1433stored in the same allocation with the string data immediately after the element
1434object. This container guarantees the "<tt>(char*)(&amp;Value+1)</tt>" points
1435to the key string for a value.</p>
1436
Chris Lattner796f9fa2007-02-08 19:14:21 +0000[diff] [blame]1437<p>The StringMap is very fast for several reasons: quadratic probing is very
Chris Lattnerc5722432007-02-03 19:49:31 +0000[diff] [blame]1438cache efficient for lookups, the hash value of strings in buckets is not
Nick Lewycky2a80aca2010-08-01 23:18:45 +0000[diff] [blame^]1439recomputed when looking up an element, StringMap rarely has to touch the
Chris Lattnerc5722432007-02-03 19:49:31 +0000[diff] [blame]1440memory for unrelated objects when looking up a value (even when hash collisions
1441happen), hash table growth does not recompute the hash values for strings
1442already in the table, and each pair in the map is store in a single allocation
1443(the string data is stored in the same allocation as the Value of a pair).</p>
1444
Chris Lattner796f9fa2007-02-08 19:14:21 +0000[diff] [blame]1445<p>StringMap also provides query methods that take byte ranges, so it only ever
Chris Lattnerc5722432007-02-03 19:49:31 +0000[diff] [blame]1446copies a string if a value is inserted into the table.</p>
1447</div>
1448
1449<!-- _______________________________________________________________________ -->
1450<div class="doc_subsubsection">
1451 <a name="dss_indexedmap">"llvm/ADT/IndexedMap.h"</a>
1452</div>
1453
1454<div class="doc_text">
1455<p>
1456IndexedMap is a specialized container for mapping small dense integers (or
1457values that can be mapped to small dense integers) to some other type. It is
1458internally implemented as a vector with a mapping function that maps the keys to
1459the dense integer range.
1460</p>
1461
1462<p>
1463This is useful for cases like virtual registers in the LLVM code generator: they
1464have a dense mapping that is offset by a compile-time constant (the first
1465virtual register ID).</p>
1466
1467</div>
1468
1469<!-- _______________________________________________________________________ -->
1470<div class="doc_subsubsection">
1471 <a name="dss_densemap">"llvm/ADT/DenseMap.h"</a>
1472</div>
1473
1474<div class="doc_text">
1475
1476<p>
1477DenseMap is a simple quadratically probed hash table. It excels at supporting
1478small keys and values: it uses a single allocation to hold all of the pairs that
1479are currently inserted in the map. DenseMap is a great way to map pointers to
1480pointers, or map other small types to each other.
1481</p>
1482
1483<p>
1484There are several aspects of DenseMap that you should be aware of, however. The
1485iterators in a densemap are invalidated whenever an insertion occurs, unlike
1486map. Also, because DenseMap allocates space for a large number of key/value
Chris Lattnera4a264d2007-02-03 20:17:53 +0000[diff] [blame]1487pairs (it starts with 64 by default), it will waste a lot of space if your keys
1488or values are large. Finally, you must implement a partial specialization of
Chris Lattner76c1b972007-09-17 18:34:04 +0000[diff] [blame]1489DenseMapInfo for the key that you want, if it isn't already supported. This
Chris Lattnerc5722432007-02-03 19:49:31 +0000[diff] [blame]1490is required to tell DenseMap about two special marker values (which can never be
Chris Lattnera4a264d2007-02-03 20:17:53 +0000[diff] [blame]1491inserted into the map) that it needs internally.</p>
Chris Lattnerc5722432007-02-03 19:49:31 +0000[diff] [blame]1492
1493</div>
1494
1495<!-- _______________________________________________________________________ -->
1496<div class="doc_subsubsection">
Jeffrey Yasskin71a5c222009-10-22 22:11:22 +0000[diff] [blame]1497 <a name="dss_valuemap">"llvm/ADT/ValueMap.h"</a>
1498</div>
1499
1500<div class="doc_text">
1501
1502<p>
1503ValueMap is a wrapper around a <a href="#dss_densemap">DenseMap</a> mapping
1504Value*s (or subclasses) to another type. When a Value is deleted or RAUW'ed,
1505ValueMap will update itself so the new version of the key is mapped to the same
1506value, just as if the key were a WeakVH. You can configure exactly how this
1507happens, and what else happens on these two events, by passing
1508a <code>Config</code> parameter to the ValueMap template.</p>
1509
1510</div>
1511
1512<!-- _______________________________________________________________________ -->
1513<div class="doc_subsubsection">
Chris Lattnerc5722432007-02-03 19:49:31 +0000[diff] [blame]1514 <a name="dss_map">&lt;map&gt;</a>
1515</div>
1516
1517<div class="doc_text">
1518
1519<p>
1520std::map has similar characteristics to <a href="#dss_set">std::set</a>: it uses
1521a single allocation per pair inserted into the map, it offers log(n) lookup with
1522an extremely large constant factor, imposes a space penalty of 3 pointers per
1523pair in the map, etc.</p>
1524
1525<p>std::map is most useful when your keys or values are very large, if you need
1526to iterate over the collection in sorted order, or if you need stable iterators
1527into the map (i.e. they don't get invalidated if an insertion or deletion of
1528another element takes place).</p>
1529
1530</div>
1531
1532<!-- _______________________________________________________________________ -->
1533<div class="doc_subsubsection">
1534 <a name="dss_othermap">Other Map-Like Container Options</a>
1535</div>
1536
1537<div class="doc_text">
1538
1539<p>
1540The STL provides several other options, such as std::multimap and the various
Chris Lattnerf1a30822009-03-09 05:20:45 +0000[diff] [blame]1541"hash_map" like containers (whether from C++ TR1 or from the SGI library). We
1542never use hash_set and unordered_set because they are generally very expensive
1543(each insertion requires a malloc) and very non-portable.</p>
Chris Lattnerc5722432007-02-03 19:49:31 +0000[diff] [blame]1544
1545<p>std::multimap is useful if you want to map a key to multiple values, but has
1546all the drawbacks of std::map. A sorted vector or some other approach is almost
1547always better.</p>
1548
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]1549</div>
1550
Daniel Berlin1939ace2007-09-24 17:52:25 +0000[diff] [blame]1551<!-- ======================================================================= -->
1552<div class="doc_subsection">
Chris Lattnerdced9fb2009-07-25 07:22:20 +0000[diff] [blame]1553 <a name="ds_string">String-like containers</a>
1554</div>
1555
1556<div class="doc_text">
1557
1558<p>
1559TODO: const char* vs stringref vs smallstring vs std::string. Describe twine,
1560xref to #string_apis.
1561</p>
1562
1563</div>
1564
1565<!-- ======================================================================= -->
1566<div class="doc_subsection">
Daniel Berlin1939ace2007-09-24 17:52:25 +0000[diff] [blame]1567 <a name="ds_bit">Bit storage containers (BitVector, SparseBitVector)</a>
1568</div>
1569
1570<div class="doc_text">
Chris Lattner7086ce72007-09-25 22:37:50 +0000[diff] [blame]1571<p>Unlike the other containers, there are only two bit storage containers, and
1572choosing when to use each is relatively straightforward.</p>
1573
1574<p>One additional option is
1575<tt>std::vector&lt;bool&gt;</tt>: we discourage its use for two reasons 1) the
1576implementation in many common compilers (e.g. commonly available versions of
1577GCC) is extremely inefficient and 2) the C++ standards committee is likely to
1578deprecate this container and/or change it significantly somehow. In any case,
1579please don't use it.</p>
Daniel Berlin1939ace2007-09-24 17:52:25 +0000[diff] [blame]1580</div>
1581
1582<!-- _______________________________________________________________________ -->
1583<div class="doc_subsubsection">
1584 <a name="dss_bitvector">BitVector</a>
1585</div>
1586
1587<div class="doc_text">
Dan Gohman5f7775c2010-01-05 18:24:00 +0000[diff] [blame]1588<p> The BitVector container provides a dynamic size set of bits for manipulation.
Daniel Berlin1939ace2007-09-24 17:52:25 +0000[diff] [blame]1589It supports individual bit setting/testing, as well as set operations. The set
1590operations take time O(size of bitvector), but operations are performed one word
1591at a time, instead of one bit at a time. This makes the BitVector very fast for
1592set operations compared to other containers. Use the BitVector when you expect
1593the number of set bits to be high (IE a dense set).
1594</p>
1595</div>
1596
1597<!-- _______________________________________________________________________ -->
1598<div class="doc_subsubsection">
Dan Gohman5f7775c2010-01-05 18:24:00 +0000[diff] [blame]1599 <a name="dss_smallbitvector">SmallBitVector</a>
1600</div>
1601
1602<div class="doc_text">
1603<p> The SmallBitVector container provides the same interface as BitVector, but
1604it is optimized for the case where only a small number of bits, less than
160525 or so, are needed. It also transparently supports larger bit counts, but
1606slightly less efficiently than a plain BitVector, so SmallBitVector should
1607only be used when larger counts are rare.
1608</p>
1609
1610<p>
1611At this time, SmallBitVector does not support set operations (and, or, xor),
1612and its operator[] does not provide an assignable lvalue.
1613</p>
1614</div>
1615
1616<!-- _______________________________________________________________________ -->
1617<div class="doc_subsubsection">
Daniel Berlin1939ace2007-09-24 17:52:25 +0000[diff] [blame]1618 <a name="dss_sparsebitvector">SparseBitVector</a>
1619</div>
1620
1621<div class="doc_text">
1622<p> The SparseBitVector container is much like BitVector, with one major
1623difference: Only the bits that are set, are stored. This makes the
1624SparseBitVector much more space efficient than BitVector when the set is sparse,
1625as well as making set operations O(number of set bits) instead of O(size of
1626universe). 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
1627(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).
1628</p>
1629</div>
Chris Lattnerf623a082005-10-17 01:36:23 +0000[diff] [blame]1630
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1631<!-- *********************************************************************** -->
1632<div class="doc_section">
1633 <a name="common">Helpful Hints for Common Operations</a>
1634</div>
1635<!-- *********************************************************************** -->
1636
1637<div class="doc_text">
1638
1639<p>This section describes how to perform some very simple transformations of
1640LLVM code. This is meant to give examples of common idioms used, showing the
1641practical side of LLVM transformations. <p> Because this is a "how-to" section,
1642you should also read about the main classes that you will be working with. The
1643<a href="#coreclasses">Core LLVM Class Hierarchy Reference</a> contains details
1644and descriptions of the main classes that you should know about.</p>
1645
1646</div>
1647
1648<!-- NOTE: this section should be heavy on example code -->
1649<!-- ======================================================================= -->
1650<div class="doc_subsection">
1651 <a name="inspection">Basic Inspection and Traversal Routines</a>
1652</div>
1653
1654<div class="doc_text">
1655
1656<p>The LLVM compiler infrastructure have many different data structures that may
1657be traversed. Following the example of the C++ standard template library, the
1658techniques used to traverse these various data structures are all basically the
1659same. For a enumerable sequence of values, the <tt>XXXbegin()</tt> function (or
1660method) returns an iterator to the start of the sequence, the <tt>XXXend()</tt>
1661function returns an iterator pointing to one past the last valid element of the
1662sequence, and there is some <tt>XXXiterator</tt> data type that is common
1663between the two operations.</p>
1664
1665<p>Because the pattern for iteration is common across many different aspects of
1666the program representation, the standard template library algorithms may be used
1667on them, and it is easier to remember how to iterate. First we show a few common
1668examples of the data structures that need to be traversed. Other data
1669structures are traversed in very similar ways.</p>
1670
1671</div>
1672
1673<!-- _______________________________________________________________________ -->
Chris Lattner69bf8a92004-05-23 21:06:58 +0000[diff] [blame]1674<div class="doc_subsubsection">
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1675 <a name="iterate_function">Iterating over the </a><a
1676 href="#BasicBlock"><tt>BasicBlock</tt></a>s in a <a
1677 href="#Function"><tt>Function</tt></a>
1678</div>
1679
1680<div class="doc_text">
1681
1682<p>It's quite common to have a <tt>Function</tt> instance that you'd like to
1683transform in some way; in particular, you'd like to manipulate its
1684<tt>BasicBlock</tt>s. To facilitate this, you'll need to iterate over all of
1685the <tt>BasicBlock</tt>s that constitute the <tt>Function</tt>. The following is
1686an example that prints the name of a <tt>BasicBlock</tt> and the number of
1687<tt>Instruction</tt>s it contains:</p>
1688
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1689<div class="doc_code">
1690<pre>
Bill Wendling82e2eea2006-10-11 18:00:22 +0000[diff] [blame]1691// <i>func is a pointer to a Function instance</i>
1692for (Function::iterator i = func-&gt;begin(), e = func-&gt;end(); i != e; ++i)
1693 // <i>Print out the name of the basic block if it has one, and then the</i>
1694 // <i>number of instructions that it contains</i>
Chris Lattner3fee6ed2009-09-08 05:15:50 +0000[diff] [blame]1695 errs() &lt;&lt; "Basic block (name=" &lt;&lt; i-&gt;getName() &lt;&lt; ") has "
Bill Wendling832171c2006-12-07 20:04:42 +0000[diff] [blame]1696 &lt;&lt; i-&gt;size() &lt;&lt; " instructions.\n";
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1697</pre>
1698</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1699
1700<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]1701invoking member functions of the <tt>Instruction</tt> class. This is
1702because the indirection operator is overloaded for the iterator
Chris Lattner7496ec52003-08-05 22:54:23 +0000[diff] [blame]1703classes. In the above code, the expression <tt>i-&gt;size()</tt> is
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1704exactly equivalent to <tt>(*i).size()</tt> just like you'd expect.</p>
1705
1706</div>
1707
1708<!-- _______________________________________________________________________ -->
Chris Lattner69bf8a92004-05-23 21:06:58 +0000[diff] [blame]1709<div class="doc_subsubsection">
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1710 <a name="iterate_basicblock">Iterating over the </a><a
1711 href="#Instruction"><tt>Instruction</tt></a>s in a <a
1712 href="#BasicBlock"><tt>BasicBlock</tt></a>
1713</div>
1714
1715<div class="doc_text">
1716
1717<p>Just like when dealing with <tt>BasicBlock</tt>s in <tt>Function</tt>s, it's
1718easy to iterate over the individual instructions that make up
1719<tt>BasicBlock</tt>s. Here's a code snippet that prints out each instruction in
1720a <tt>BasicBlock</tt>:</p>
1721
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1722<div class="doc_code">
Chris Lattner55c04612005-03-06 06:00:13 +0000[diff] [blame]1723<pre>
Bill Wendling82e2eea2006-10-11 18:00:22 +0000[diff] [blame]1724// <i>blk is a pointer to a BasicBlock instance</i>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1725for (BasicBlock::iterator i = blk-&gt;begin(), e = blk-&gt;end(); i != e; ++i)
Bill Wendling82e2eea2006-10-11 18:00:22 +0000[diff] [blame]1726 // <i>The next statement works since operator&lt;&lt;(ostream&amp;,...)</i>
1727 // <i>is overloaded for Instruction&amp;</i>
Chris Lattner3fee6ed2009-09-08 05:15:50 +0000[diff] [blame]1728 errs() &lt;&lt; *i &lt;&lt; "\n";
Chris Lattner55c04612005-03-06 06:00:13 +0000[diff] [blame]1729</pre>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1730</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1731
1732<p>However, this isn't really the best way to print out the contents of a
1733<tt>BasicBlock</tt>! Since the ostream operators are overloaded for virtually
1734anything you'll care about, you could have just invoked the print routine on the
Chris Lattner3fee6ed2009-09-08 05:15:50 +0000[diff] [blame]1735basic block itself: <tt>errs() &lt;&lt; *blk &lt;&lt; "\n";</tt>.</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1736
1737</div>
1738
1739<!-- _______________________________________________________________________ -->
Chris Lattner69bf8a92004-05-23 21:06:58 +0000[diff] [blame]1740<div class="doc_subsubsection">
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1741 <a name="iterate_institer">Iterating over the </a><a
1742 href="#Instruction"><tt>Instruction</tt></a>s in a <a
1743 href="#Function"><tt>Function</tt></a>
1744</div>
1745
1746<div class="doc_text">
1747
1748<p>If you're finding that you commonly iterate over a <tt>Function</tt>'s
1749<tt>BasicBlock</tt>s and then that <tt>BasicBlock</tt>'s <tt>Instruction</tt>s,
1750<tt>InstIterator</tt> should be used instead. You'll need to include <a
1751href="/doxygen/InstIterator_8h-source.html"><tt>llvm/Support/InstIterator.h</tt></a>,
1752and then instantiate <tt>InstIterator</tt>s explicitly in your code. Here's a
Chris Lattner69bf8a92004-05-23 21:06:58 +0000[diff] [blame]1753small 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]1754
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1755<div class="doc_code">
1756<pre>
1757#include "<a href="/doxygen/InstIterator_8h-source.html">llvm/Support/InstIterator.h</a>"
1758
Reid Spencer128a7a72007-02-03 21:06:43 +0000[diff] [blame]1759// <i>F is a pointer to a Function instance</i>
Chris Lattnerda021aa2008-06-04 18:20:42 +0000[diff] [blame]1760for (inst_iterator I = inst_begin(F), E = inst_end(F); I != E; ++I)
Chris Lattner3fee6ed2009-09-08 05:15:50 +0000[diff] [blame]1761 errs() &lt;&lt; *I &lt;&lt; "\n";
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1762</pre>
1763</div>
1764
1765<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]1766work list with its initial contents. For example, if you wanted to
1767initialize a work list to contain all instructions in a <tt>Function</tt>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1768F, all you would need to do is something like:</p>
1769
1770<div class="doc_code">
1771<pre>
1772std::set&lt;Instruction*&gt; worklist;
Chris Lattnerda021aa2008-06-04 18:20:42 +0000[diff] [blame]1773// or better yet, SmallPtrSet&lt;Instruction*, 64&gt; worklist;
1774
1775for (inst_iterator I = inst_begin(F), E = inst_end(F); I != E; ++I)
1776 worklist.insert(&amp;*I);
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1777</pre>
1778</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1779
1780<p>The STL set <tt>worklist</tt> would now contain all instructions in the
1781<tt>Function</tt> pointed to by F.</p>
1782
1783</div>
1784
1785<!-- _______________________________________________________________________ -->
1786<div class="doc_subsubsection">
1787 <a name="iterate_convert">Turning an iterator into a class pointer (and
1788 vice-versa)</a>
1789</div>
1790
1791<div class="doc_text">
1792
1793<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]1794instance when all you've got at hand is an iterator. Well, extracting
Chris Lattner69bf8a92004-05-23 21:06:58 +0000[diff] [blame]1795a reference or a pointer from an iterator is very straight-forward.
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]1796Assuming that <tt>i</tt> is a <tt>BasicBlock::iterator</tt> and <tt>j</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1797is a <tt>BasicBlock::const_iterator</tt>:</p>
1798
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1799<div class="doc_code">
1800<pre>
Bill Wendling82e2eea2006-10-11 18:00:22 +0000[diff] [blame]1801Instruction&amp; inst = *i; // <i>Grab reference to instruction reference</i>
1802Instruction* pinst = &amp;*i; // <i>Grab pointer to instruction reference</i>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1803const Instruction&amp; inst = *j;
1804</pre>
1805</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1806
1807<p>However, the iterators you'll be working with in the LLVM framework are
1808special: they will automatically convert to a ptr-to-instance type whenever they
1809need to. Instead of dereferencing the iterator and then taking the address of
1810the result, you can simply assign the iterator to the proper pointer type and
1811you get the dereference and address-of operation as a result of the assignment
1812(behind the scenes, this is a result of overloading casting mechanisms). Thus
1813the last line of the last example,</p>
1814
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1815<div class="doc_code">
1816<pre>
Chris Lattner2e438ca2008-01-03 16:56:04 +0000[diff] [blame]1817Instruction *pinst = &amp;*i;
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1818</pre>
1819</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1820
1821<p>is semantically equivalent to</p>
1822
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1823<div class="doc_code">
1824<pre>
Chris Lattner2e438ca2008-01-03 16:56:04 +0000[diff] [blame]1825Instruction *pinst = i;
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1826</pre>
1827</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1828
Chris Lattner69bf8a92004-05-23 21:06:58 +0000[diff] [blame]1829<p>It's also possible to turn a class pointer into the corresponding iterator,
1830and this is a constant time operation (very efficient). The following code
1831snippet illustrates use of the conversion constructors provided by LLVM
1832iterators. By using these, you can explicitly grab the iterator of something
1833without actually obtaining it via iteration over some structure:</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1834
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1835<div class="doc_code">
1836<pre>
1837void printNextInstruction(Instruction* inst) {
1838 BasicBlock::iterator it(inst);
Bill Wendling82e2eea2006-10-11 18:00:22 +0000[diff] [blame]1839 ++it; // <i>After this line, it refers to the instruction after *inst</i>
Chris Lattner3fee6ed2009-09-08 05:15:50 +0000[diff] [blame]1840 if (it != inst-&gt;getParent()-&gt;end()) errs() &lt;&lt; *it &lt;&lt; "\n";
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1841}
1842</pre>
1843</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1844
Dan Gohman525bf8e2010-03-26 19:39:05 +0000[diff] [blame]1845<p>Unfortunately, these implicit conversions come at a cost; they prevent
1846these iterators from conforming to standard iterator conventions, and thus
Dan Gohman0d91c112010-03-26 19:51:14 +0000[diff] [blame]1847from being usable with standard algorithms and containers. For example, they
1848prevent the following code, where <tt>B</tt> is a <tt>BasicBlock</tt>,
Dan Gohman525bf8e2010-03-26 19:39:05 +0000[diff] [blame]1849from compiling:</p>
1850
1851<div class="doc_code">
1852<pre>
1853 llvm::SmallVector&lt;llvm::Instruction *, 16&gt;(B-&gt;begin(), B-&gt;end());
1854</pre>
1855</div>
1856
1857<p>Because of this, these implicit conversions may be removed some day,
Dan Gohman0d91c112010-03-26 19:51:14 +0000[diff] [blame]1858and <tt>operator*</tt> changed to return a pointer instead of a reference.</p>
Dan Gohman525bf8e2010-03-26 19:39:05 +0000[diff] [blame]1859
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1860</div>
1861
1862<!--_______________________________________________________________________-->
1863<div class="doc_subsubsection">
1864 <a name="iterate_complex">Finding call sites: a slightly more complex
1865 example</a>
1866</div>
1867
1868<div class="doc_text">
1869
1870<p>Say that you're writing a FunctionPass and would like to count all the
1871locations in the entire module (that is, across every <tt>Function</tt>) where a
1872certain function (i.e., some <tt>Function</tt>*) is already in scope. As you'll
1873learn 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]1874much more straight-forward manner, but this example will allow us to explore how
Reid Spencer128a7a72007-02-03 21:06:43 +0000[diff] [blame]1875you'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]1876is what we want to do:</p>
1877
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1878<div class="doc_code">
1879<pre>
1880initialize callCounter to zero
1881for each Function f in the Module
1882 for each BasicBlock b in f
1883 for each Instruction i in b
1884 if (i is a CallInst and calls the given function)
1885 increment callCounter
1886</pre>
1887</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1888
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1889<p>And the actual code is (remember, because we're writing a
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1890<tt>FunctionPass</tt>, our <tt>FunctionPass</tt>-derived class simply has to
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1891override the <tt>runOnFunction</tt> method):</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1892
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1893<div class="doc_code">
1894<pre>
1895Function* targetFunc = ...;
1896
1897class OurFunctionPass : public FunctionPass {
1898 public:
1899 OurFunctionPass(): callCounter(0) { }
1900
1901 virtual runOnFunction(Function&amp; F) {
1902 for (Function::iterator b = F.begin(), be = F.end(); b != be; ++b) {
Eric Christopher203e71d2008-11-08 08:20:49 +0000[diff] [blame]1903 for (BasicBlock::iterator i = b-&gt;begin(), ie = b-&gt;end(); i != ie; ++i) {
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1904 if (<a href="#CallInst">CallInst</a>* callInst = <a href="#isa">dyn_cast</a>&lt;<a
1905 href="#CallInst">CallInst</a>&gt;(&amp;*i)) {
Bill Wendling82e2eea2006-10-11 18:00:22 +0000[diff] [blame]1906 // <i>We know we've encountered a call instruction, so we</i>
1907 // <i>need to determine if it's a call to the</i>
Chris Lattner2e438ca2008-01-03 16:56:04 +0000[diff] [blame]1908 // <i>function pointed to by m_func or not.</i>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1909 if (callInst-&gt;getCalledFunction() == targetFunc)
1910 ++callCounter;
1911 }
1912 }
1913 }
Bill Wendling82e2eea2006-10-11 18:00:22 +0000[diff] [blame]1914 }
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1915
1916 private:
Chris Lattner2e438ca2008-01-03 16:56:04 +0000[diff] [blame]1917 unsigned callCounter;
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1918};
1919</pre>
1920</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1921
1922</div>
1923
Brian Gaekef1972c62003-11-07 19:25:45 +0000[diff] [blame]1924<!--_______________________________________________________________________-->
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1925<div class="doc_subsubsection">
1926 <a name="calls_and_invokes">Treating calls and invokes the same way</a>
1927</div>
1928
1929<div class="doc_text">
1930
1931<p>You may have noticed that the previous example was a bit oversimplified in
1932that it did not deal with call sites generated by 'invoke' instructions. In
1933this, and in other situations, you may find that you want to treat
1934<tt>CallInst</tt>s and <tt>InvokeInst</tt>s the same way, even though their
1935most-specific common base class is <tt>Instruction</tt>, which includes lots of
1936less closely-related things. For these cases, LLVM provides a handy wrapper
1937class called <a
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]1938href="http://llvm.org/doxygen/classllvm_1_1CallSite.html"><tt>CallSite</tt></a>.
Chris Lattner69bf8a92004-05-23 21:06:58 +0000[diff] [blame]1939It is essentially a wrapper around an <tt>Instruction</tt> pointer, with some
1940methods that provide functionality common to <tt>CallInst</tt>s and
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1941<tt>InvokeInst</tt>s.</p>
1942
Chris Lattner69bf8a92004-05-23 21:06:58 +0000[diff] [blame]1943<p>This class has "value semantics": it should be passed by value, not by
1944reference and it should not be dynamically allocated or deallocated using
1945<tt>operator new</tt> or <tt>operator delete</tt>. It is efficiently copyable,
1946assignable and constructable, with costs equivalents to that of a bare pointer.
1947If you look at its definition, it has only a single pointer member.</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1948
1949</div>
1950
Chris Lattner1a3105b2002-09-09 05:49:39 +0000[diff] [blame]1951<!--_______________________________________________________________________-->
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1952<div class="doc_subsubsection">
1953 <a name="iterate_chains">Iterating over def-use &amp; use-def chains</a>
1954</div>
1955
1956<div class="doc_text">
1957
1958<p>Frequently, we might have an instance of the <a
Chris Lattner00815172007-01-04 22:01:45 +0000[diff] [blame]1959href="/doxygen/classllvm_1_1Value.html">Value Class</a> and we want to
Misha Brukman384047f2004-06-03 23:29:12 +0000[diff] [blame]1960determine which <tt>User</tt>s use the <tt>Value</tt>. The list of all
1961<tt>User</tt>s of a particular <tt>Value</tt> is called a <i>def-use</i> chain.
1962For example, let's say we have a <tt>Function*</tt> named <tt>F</tt> to a
1963particular function <tt>foo</tt>. Finding all of the instructions that
1964<i>use</i> <tt>foo</tt> is as simple as iterating over the <i>def-use</i> chain
1965of <tt>F</tt>:</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1966
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1967<div class="doc_code">
1968<pre>
Chris Lattner2e438ca2008-01-03 16:56:04 +0000[diff] [blame]1969Function *F = ...;
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1970
Bill Wendling82e2eea2006-10-11 18:00:22 +0000[diff] [blame]1971for (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]1972 if (Instruction *Inst = dyn_cast&lt;Instruction&gt;(*i)) {
Chris Lattner3fee6ed2009-09-08 05:15:50 +0000[diff] [blame]1973 errs() &lt;&lt; "F is used in instruction:\n";
1974 errs() &lt;&lt; *Inst &lt;&lt; "\n";
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1975 }
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1976</pre>
Gabor Greif394fdfb2010-03-26 19:35:48 +0000[diff] [blame]1977</div>
1978
Gabor Greifce94319532010-03-26 19:40:38 +0000[diff] [blame]1979<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]1980operation. Instead of performing <tt>*i</tt> above several times, consider
Gabor Greifce94319532010-03-26 19:40:38 +0000[diff] [blame]1981doing it only once in the loop body and reusing its result.</p>
Gabor Greif4de73682010-03-26 19:30:47 +0000[diff] [blame]1982
Gabor Greif6091ff32010-03-26 19:04:42 +0000[diff] [blame]1983<p>Alternatively, it's common to have an instance of the <a
Misha Brukman384047f2004-06-03 23:29:12 +0000[diff] [blame]1984href="/doxygen/classllvm_1_1User.html">User Class</a> and need to know what
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1985<tt>Value</tt>s are used by it. The list of all <tt>Value</tt>s used by a
1986<tt>User</tt> is known as a <i>use-def</i> chain. Instances of class
1987<tt>Instruction</tt> are common <tt>User</tt>s, so we might want to iterate over
1988all of the values that a particular instruction uses (that is, the operands of
1989the particular <tt>Instruction</tt>):</p>
1990
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1991<div class="doc_code">
1992<pre>
Chris Lattner2e438ca2008-01-03 16:56:04 +0000[diff] [blame]1993Instruction *pi = ...;
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1994
1995for (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]1996 Value *v = *i;
Bill Wendling82e2eea2006-10-11 18:00:22 +0000[diff] [blame]1997 // <i>...</i>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1998}
1999</pre>
2000</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2001
Gabor Greif4de73682010-03-26 19:30:47 +0000[diff] [blame]2002<p>Declaring objects as <tt>const</tt> is an important tool of enforcing
Gabor Greifce94319532010-03-26 19:40:38 +0000[diff] [blame]2003mutation free algorithms (such as analyses, etc.). For this purpose above
Gabor Greif4de73682010-03-26 19:30:47 +0000[diff] [blame]2004iterators come in constant flavors as <tt>Value::const_use_iterator</tt>
2005and <tt>Value::const_op_iterator</tt>. They automatically arise when
2006calling <tt>use/op_begin()</tt> on <tt>const Value*</tt>s or
2007<tt>const User*</tt>s respectively. Upon dereferencing, they return
Gabor Greifce94319532010-03-26 19:40:38 +0000[diff] [blame]2008<tt>const Use*</tt>s. Otherwise the above patterns remain unchanged.</p>
2009
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2010</div>
2011
Chris Lattner2e438ca2008-01-03 16:56:04 +0000[diff] [blame]2012<!--_______________________________________________________________________-->
2013<div class="doc_subsubsection">
2014 <a name="iterate_preds">Iterating over predecessors &amp;
2015successors of blocks</a>
2016</div>
2017
2018<div class="doc_text">
2019
2020<p>Iterating over the predecessors and successors of a block is quite easy
2021with the routines defined in <tt>"llvm/Support/CFG.h"</tt>. Just use code like
2022this to iterate over all predecessors of BB:</p>
2023
2024<div class="doc_code">
2025<pre>
2026#include "llvm/Support/CFG.h"
2027BasicBlock *BB = ...;
2028
2029for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI) {
2030 BasicBlock *Pred = *PI;
2031 // <i>...</i>
2032}
2033</pre>
2034</div>
2035
2036<p>Similarly, to iterate over successors use
2037succ_iterator/succ_begin/succ_end.</p>
2038
2039</div>
2040
2041
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2042<!-- ======================================================================= -->
2043<div class="doc_subsection">
2044 <a name="simplechanges">Making simple changes</a>
2045</div>
2046
2047<div class="doc_text">
2048
2049<p>There are some primitive transformation operations present in the LLVM
Joel Stanley753eb712002-09-11 22:32:24 +0000[diff] [blame]2050infrastructure that are worth knowing about. When performing
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]2051transformations, it's fairly common to manipulate the contents of basic
2052blocks. This section describes some of the common methods for doing so
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2053and gives example code.</p>
2054
2055</div>
2056
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]2057<!--_______________________________________________________________________-->
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2058<div class="doc_subsubsection">
2059 <a name="schanges_creating">Creating and inserting new
2060 <tt>Instruction</tt>s</a>
2061</div>
2062
2063<div class="doc_text">
2064
2065<p><i>Instantiating Instructions</i></p>
2066
Chris Lattner69bf8a92004-05-23 21:06:58 +0000[diff] [blame]2067<p>Creation of <tt>Instruction</tt>s is straight-forward: simply call the
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2068constructor for the kind of instruction to instantiate and provide the necessary
2069parameters. For example, an <tt>AllocaInst</tt> only <i>requires</i> a
2070(const-ptr-to) <tt>Type</tt>. Thus:</p>
2071
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2072<div class="doc_code">
2073<pre>
Nick Lewycky10d64b92007-12-03 01:52:52 +0000[diff] [blame]2074AllocaInst* ai = new AllocaInst(Type::Int32Ty);
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2075</pre>
2076</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2077
2078<p>will create an <tt>AllocaInst</tt> instance that represents the allocation of
Reid Spencer128a7a72007-02-03 21:06:43 +0000[diff] [blame]2079one integer in the current stack frame, at run time. Each <tt>Instruction</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2080subclass is likely to have varying default parameters which change the semantics
2081of the instruction, so refer to the <a
Misha Brukman31ca1de2004-06-03 23:35:54 +0000[diff] [blame]2082href="/doxygen/classllvm_1_1Instruction.html">doxygen documentation for the subclass of
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2083Instruction</a> that you're interested in instantiating.</p>
2084
2085<p><i>Naming values</i></p>
2086
2087<p>It is very useful to name the values of instructions when you're able to, as
2088this facilitates the debugging of your transformations. If you end up looking
2089at generated LLVM machine code, you definitely want to have logical names
2090associated with the results of instructions! By supplying a value for the
2091<tt>Name</tt> (default) parameter of the <tt>Instruction</tt> constructor, you
2092associate a logical name with the result of the instruction's execution at
Reid Spencer128a7a72007-02-03 21:06:43 +0000[diff] [blame]2093run time. For example, say that I'm writing a transformation that dynamically
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2094allocates space for an integer on the stack, and that integer is going to be
2095used as some kind of index by some other code. To accomplish this, I place an
2096<tt>AllocaInst</tt> at the first point in the first <tt>BasicBlock</tt> of some
2097<tt>Function</tt>, and I'm intending to use it within the same
2098<tt>Function</tt>. I might do:</p>
2099
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2100<div class="doc_code">
2101<pre>
Nick Lewycky10d64b92007-12-03 01:52:52 +0000[diff] [blame]2102AllocaInst* pa = new AllocaInst(Type::Int32Ty, 0, "indexLoc");
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2103</pre>
2104</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2105
2106<p>where <tt>indexLoc</tt> is now the logical name of the instruction's
Reid Spencer128a7a72007-02-03 21:06:43 +0000[diff] [blame]2107execution value, which is a pointer to an integer on the run time stack.</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2108
2109<p><i>Inserting instructions</i></p>
2110
2111<p>There are essentially two ways to insert an <tt>Instruction</tt>
2112into an existing sequence of instructions that form a <tt>BasicBlock</tt>:</p>
2113
Joel Stanley9dd1ad62002-09-18 03:17:23 +0000[diff] [blame]2114<ul>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2115 <li>Insertion into an explicit instruction list
2116
2117 <p>Given a <tt>BasicBlock* pb</tt>, an <tt>Instruction* pi</tt> within that
2118 <tt>BasicBlock</tt>, and a newly-created instruction we wish to insert
2119 before <tt>*pi</tt>, we do the following: </p>
2120
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2121<div class="doc_code">
2122<pre>
2123BasicBlock *pb = ...;
2124Instruction *pi = ...;
2125Instruction *newInst = new Instruction(...);
2126
Bill Wendling82e2eea2006-10-11 18:00:22 +0000[diff] [blame]2127pb-&gt;getInstList().insert(pi, newInst); // <i>Inserts newInst before pi in pb</i>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2128</pre>
2129</div>
Alkis Evlogimenos9a5dc4f2004-05-27 00:57:51 +0000[diff] [blame]2130
2131 <p>Appending to the end of a <tt>BasicBlock</tt> is so common that
2132 the <tt>Instruction</tt> class and <tt>Instruction</tt>-derived
2133 classes provide constructors which take a pointer to a
2134 <tt>BasicBlock</tt> to be appended to. For example code that
2135 looked like: </p>
2136
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2137<div class="doc_code">
2138<pre>
2139BasicBlock *pb = ...;
2140Instruction *newInst = new Instruction(...);
2141
Bill Wendling82e2eea2006-10-11 18:00:22 +0000[diff] [blame]2142pb-&gt;getInstList().push_back(newInst); // <i>Appends newInst to pb</i>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2143</pre>
2144</div>
Alkis Evlogimenos9a5dc4f2004-05-27 00:57:51 +0000[diff] [blame]2145
2146 <p>becomes: </p>
2147
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2148<div class="doc_code">
2149<pre>
2150BasicBlock *pb = ...;
2151Instruction *newInst = new Instruction(..., pb);
2152</pre>
2153</div>
Alkis Evlogimenos9a5dc4f2004-05-27 00:57:51 +0000[diff] [blame]2154
2155 <p>which is much cleaner, especially if you are creating
2156 long instruction streams.</p></li>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2157
2158 <li>Insertion into an implicit instruction list
2159
2160 <p><tt>Instruction</tt> instances that are already in <tt>BasicBlock</tt>s
2161 are implicitly associated with an existing instruction list: the instruction
2162 list of the enclosing basic block. Thus, we could have accomplished the same
2163 thing as the above code without being given a <tt>BasicBlock</tt> by doing:
2164 </p>
2165
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2166<div class="doc_code">
2167<pre>
2168Instruction *pi = ...;
2169Instruction *newInst = new Instruction(...);
2170
2171pi-&gt;getParent()-&gt;getInstList().insert(pi, newInst);
2172</pre>
2173</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2174
2175 <p>In fact, this sequence of steps occurs so frequently that the
2176 <tt>Instruction</tt> class and <tt>Instruction</tt>-derived classes provide
2177 constructors which take (as a default parameter) a pointer to an
2178 <tt>Instruction</tt> which the newly-created <tt>Instruction</tt> should
2179 precede. That is, <tt>Instruction</tt> constructors are capable of
2180 inserting the newly-created instance into the <tt>BasicBlock</tt> of a
2181 provided instruction, immediately before that instruction. Using an
2182 <tt>Instruction</tt> constructor with a <tt>insertBefore</tt> (default)
2183 parameter, the above code becomes:</p>
2184
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2185<div class="doc_code">
2186<pre>
2187Instruction* pi = ...;
2188Instruction* newInst = new Instruction(..., pi);
2189</pre>
2190</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2191
2192 <p>which is much cleaner, especially if you're creating a lot of
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2193 instructions and adding them to <tt>BasicBlock</tt>s.</p></li>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2194</ul>
2195
2196</div>
2197
2198<!--_______________________________________________________________________-->
2199<div class="doc_subsubsection">
2200 <a name="schanges_deleting">Deleting <tt>Instruction</tt>s</a>
2201</div>
2202
2203<div class="doc_text">
2204
2205<p>Deleting an instruction from an existing sequence of instructions that form a
Chris Lattner69bf8a92004-05-23 21:06:58 +0000[diff] [blame]2206<a href="#BasicBlock"><tt>BasicBlock</tt></a> is very straight-forward. First,
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2207you must have a pointer to the instruction that you wish to delete. Second, you
2208need to obtain the pointer to that instruction's basic block. You use the
2209pointer to the basic block to get its list of instructions and then use the
2210erase function to remove your instruction. For example:</p>
2211
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2212<div class="doc_code">
2213<pre>
2214<a href="#Instruction">Instruction</a> *I = .. ;
Chris Lattner9f8ec252008-02-15 22:57:17 +0000[diff] [blame]2215I-&gt;eraseFromParent();
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2216</pre>
2217</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2218
2219</div>
2220
2221<!--_______________________________________________________________________-->
2222<div class="doc_subsubsection">
2223 <a name="schanges_replacing">Replacing an <tt>Instruction</tt> with another
2224 <tt>Value</tt></a>
2225</div>
2226
2227<div class="doc_text">
2228
2229<p><i>Replacing individual instructions</i></p>
2230
2231<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]2232permits use of two very useful replace functions: <tt>ReplaceInstWithValue</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2233and <tt>ReplaceInstWithInst</tt>.</p>
2234
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]2235<h4><a name="schanges_deleting">Deleting <tt>Instruction</tt>s</a></h4>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2236
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]2237<ul>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2238 <li><tt>ReplaceInstWithValue</tt>
2239
Nick Lewyckyb6d1f392008-09-15 06:31:52 +0000[diff] [blame]2240 <p>This function replaces all uses of a given instruction with a value,
2241 and then removes the original instruction. The following example
2242 illustrates the replacement of the result of a particular
Chris Lattner58360822005-01-17 00:12:04 +0000[diff] [blame]2243 <tt>AllocaInst</tt> that allocates memory for a single integer with a null
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2244 pointer to an integer.</p>
2245
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2246<div class="doc_code">
2247<pre>
2248AllocaInst* instToReplace = ...;
2249BasicBlock::iterator ii(instToReplace);
2250
2251ReplaceInstWithValue(instToReplace-&gt;getParent()-&gt;getInstList(), ii,
Daniel Dunbar58c2ac02008-10-03 22:17:25 +0000[diff] [blame]2252 Constant::getNullValue(PointerType::getUnqual(Type::Int32Ty)));
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2253</pre></div></li>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2254
2255 <li><tt>ReplaceInstWithInst</tt>
2256
2257 <p>This function replaces a particular instruction with another
Nick Lewyckyb6d1f392008-09-15 06:31:52 +0000[diff] [blame]2258 instruction, inserting the new instruction into the basic block at the
2259 location where the old instruction was, and replacing any uses of the old
2260 instruction with the new instruction. The following example illustrates
2261 the replacement of one <tt>AllocaInst</tt> with another.</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2262
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2263<div class="doc_code">
2264<pre>
2265AllocaInst* instToReplace = ...;
2266BasicBlock::iterator ii(instToReplace);
2267
2268ReplaceInstWithInst(instToReplace-&gt;getParent()-&gt;getInstList(), ii,
Nick Lewycky10d64b92007-12-03 01:52:52 +0000[diff] [blame]2269 new AllocaInst(Type::Int32Ty, 0, "ptrToReplacedInt"));
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2270</pre></div></li>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]2271</ul>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2272
2273<p><i>Replacing multiple uses of <tt>User</tt>s and <tt>Value</tt>s</i></p>
2274
2275<p>You can use <tt>Value::replaceAllUsesWith</tt> and
2276<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]2277doxygen documentation for the <a href="/doxygen/classllvm_1_1Value.html">Value Class</a>
Misha Brukman384047f2004-06-03 23:29:12 +0000[diff] [blame]2278and <a href="/doxygen/classllvm_1_1User.html">User Class</a>, respectively, for more
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2279information.</p>
2280
2281<!-- Value::replaceAllUsesWith User::replaceUsesOfWith Point out:
2282include/llvm/Transforms/Utils/ especially BasicBlockUtils.h with:
2283ReplaceInstWithValue, ReplaceInstWithInst -->
2284
2285</div>
2286
Tanya Lattnerb011c662007-06-20 18:33:15 +0000[diff] [blame]2287<!--_______________________________________________________________________-->
2288<div class="doc_subsubsection">
2289 <a name="schanges_deletingGV">Deleting <tt>GlobalVariable</tt>s</a>
2290</div>
2291
2292<div class="doc_text">
2293
Tanya Lattnerc5dfcdb2007-06-20 20:46:37 +0000[diff] [blame]2294<p>Deleting a global variable from a module is just as easy as deleting an
2295Instruction. First, you must have a pointer to the global variable that you wish
2296 to delete. You use this pointer to erase it from its parent, the module.
Tanya Lattnerb011c662007-06-20 18:33:15 +0000[diff] [blame]2297 For example:</p>
2298
2299<div class="doc_code">
2300<pre>
2301<a href="#GlobalVariable">GlobalVariable</a> *GV = .. ;
Tanya Lattnerb011c662007-06-20 18:33:15 +0000[diff] [blame]2302
Tanya Lattnerc5dfcdb2007-06-20 20:46:37 +0000[diff] [blame]2303GV-&gt;eraseFromParent();
Tanya Lattnerb011c662007-06-20 18:33:15 +0000[diff] [blame]2304</pre>
2305</div>
2306
2307</div>
2308
Jeffrey Yasskin714257f2009-04-30 22:33:41 +0000[diff] [blame]2309<!-- ======================================================================= -->
2310<div class="doc_subsection">
2311 <a name="create_types">How to Create Types</a>
2312</div>
2313
2314<div class="doc_text">
2315
2316<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]2317statically, you can use <tt>TypeBuilder&lt;...&gt;::get()</tt>, defined
Jeffrey Yasskin714257f2009-04-30 22:33:41 +0000[diff] [blame]2318in <tt>llvm/Support/TypeBuilder.h</tt>, to retrieve them. <tt>TypeBuilder</tt>
2319has two forms depending on whether you're building types for cross-compilation
Misha Brukman1af789f2009-05-01 20:40:51 +0000[diff] [blame]2320or native library use. <tt>TypeBuilder&lt;T, true&gt;</tt> requires
Jeffrey Yasskin714257f2009-04-30 22:33:41 +0000[diff] [blame]2321that <tt>T</tt> be independent of the host environment, meaning that it's built
2322out of types from
2323the <a href="/doxygen/namespacellvm_1_1types.html"><tt>llvm::types</tt></a>
2324namespace and pointers, functions, arrays, etc. built of
Misha Brukman1af789f2009-05-01 20:40:51 +0000[diff] [blame]2325those. <tt>TypeBuilder&lt;T, false&gt;</tt> additionally allows native C types
Jeffrey Yasskin714257f2009-04-30 22:33:41 +0000[diff] [blame]2326whose size may depend on the host compiler. For example,</p>
2327
2328<div class="doc_code">
2329<pre>
Misha Brukman1af789f2009-05-01 20:40:51 +0000[diff] [blame]2330FunctionType *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]2331</pre>
2332</div>
2333
2334<p>is easier to read and write than the equivalent</p>
2335
2336<div class="doc_code">
2337<pre>
Owen Anderson5e8c50e2009-06-16 17:40:28 +0000[diff] [blame]2338std::vector&lt;const Type*&gt; params;
Jeffrey Yasskin714257f2009-04-30 22:33:41 +0000[diff] [blame]2339params.push_back(PointerType::getUnqual(Type::Int32Ty));
2340FunctionType *ft = FunctionType::get(Type::Int8Ty, params, false);
2341</pre>
2342</div>
2343
2344<p>See the <a href="/doxygen/TypeBuilder_8h-source.html#l00001">class
2345comment</a> for more details.</p>
2346
2347</div>
2348
Chris Lattner9355b472002-09-06 02:50:58 +0000[diff] [blame]2349<!-- *********************************************************************** -->
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2350<div class="doc_section">
Owen Anderson8bc1b3b2009-06-16 01:17:16 +0000[diff] [blame]2351 <a name="threading">Threads and LLVM</a>
2352</div>
2353<!-- *********************************************************************** -->
2354
2355<div class="doc_text">
2356<p>
2357This section describes the interaction of the LLVM APIs with multithreading,
2358both on the part of client applications, and in the JIT, in the hosted
2359application.
2360</p>
2361
2362<p>
2363Note that LLVM's support for multithreading is still relatively young. Up
2364through version 2.5, the execution of threaded hosted applications was
2365supported, but not threaded client access to the APIs. While this use case is
2366now supported, clients <em>must</em> adhere to the guidelines specified below to
2367ensure proper operation in multithreaded mode.
2368</p>
2369
2370<p>
2371Note that, on Unix-like platforms, LLVM requires the presence of GCC's atomic
2372intrinsics in order to support threaded operation. If you need a
2373multhreading-capable LLVM on a platform without a suitably modern system
2374compiler, consider compiling LLVM and LLVM-GCC in single-threaded mode, and
2375using the resultant compiler to build a copy of LLVM with multithreading
2376support.
2377</p>
2378</div>
2379
2380<!-- ======================================================================= -->
2381<div class="doc_subsection">
Owen Anderson1ad70e32009-06-16 18:04:19 +0000[diff] [blame]2382 <a name="startmultithreaded">Entering and Exiting Multithreaded Mode</a>
Owen Anderson8bc1b3b2009-06-16 01:17:16 +0000[diff] [blame]2383</div>
2384
2385<div class="doc_text">
2386
2387<p>
2388In order to properly protect its internal data structures while avoiding
Owen Anderson1ad70e32009-06-16 18:04:19 +0000[diff] [blame]2389excessive locking overhead in the single-threaded case, the LLVM must intialize
2390certain data structures necessary to provide guards around its internals. To do
2391so, the client program must invoke <tt>llvm_start_multithreaded()</tt> before
2392making any concurrent LLVM API calls. To subsequently tear down these
2393structures, use the <tt>llvm_stop_multithreaded()</tt> call. You can also use
2394the <tt>llvm_is_multithreaded()</tt> call to check the status of multithreaded
2395mode.
Owen Anderson8bc1b3b2009-06-16 01:17:16 +0000[diff] [blame]2396</p>
2397
2398<p>
Owen Anderson1ad70e32009-06-16 18:04:19 +0000[diff] [blame]2399Note that both of these calls must be made <em>in isolation</em>. That is to
2400say that no other LLVM API calls may be executing at any time during the
2401execution of <tt>llvm_start_multithreaded()</tt> or <tt>llvm_stop_multithreaded
2402</tt>. It's is the client's responsibility to enforce this isolation.
2403</p>
2404
2405<p>
2406The return value of <tt>llvm_start_multithreaded()</tt> indicates the success or
2407failure of the initialization. Failure typically indicates that your copy of
2408LLVM was built without multithreading support, typically because GCC atomic
2409intrinsics were not found in your system compiler. In this case, the LLVM API
2410will not be safe for concurrent calls. However, it <em>will</em> be safe for
Jeffrey Yasskin01eba392010-01-29 19:10:38 +0000[diff] [blame]2411hosting threaded applications in the JIT, though <a href="#jitthreading">care
2412must be taken</a> to ensure that side exits and the like do not accidentally
2413result in concurrent LLVM API calls.
Owen Anderson8bc1b3b2009-06-16 01:17:16 +0000[diff] [blame]2414</p>
2415</div>
2416
2417<!-- ======================================================================= -->
2418<div class="doc_subsection">
2419 <a name="shutdown">Ending Execution with <tt>llvm_shutdown()</tt></a>
2420</div>
2421
2422<div class="doc_text">
2423<p>
2424When you are done using the LLVM APIs, you should call <tt>llvm_shutdown()</tt>
Owen Anderson1ad70e32009-06-16 18:04:19 +0000[diff] [blame]2425to deallocate memory used for internal structures. This will also invoke
2426<tt>llvm_stop_multithreaded()</tt> if LLVM is operating in multithreaded mode.
2427As such, <tt>llvm_shutdown()</tt> requires the same isolation guarantees as
2428<tt>llvm_stop_multithreaded()</tt>.
Owen Anderson8bc1b3b2009-06-16 01:17:16 +0000[diff] [blame]2429</p>
2430
2431<p>
2432Note that, if you use scope-based shutdown, you can use the
2433<tt>llvm_shutdown_obj</tt> class, which calls <tt>llvm_shutdown()</tt> in its
2434destructor.
2435</div>
2436
2437<!-- ======================================================================= -->
2438<div class="doc_subsection">
2439 <a name="managedstatic">Lazy Initialization with <tt>ManagedStatic</tt></a>
2440</div>
2441
2442<div class="doc_text">
2443<p>
2444<tt>ManagedStatic</tt> is a utility class in LLVM used to implement static
2445initialization of static resources, such as the global type tables. Before the
2446invocation of <tt>llvm_shutdown()</tt>, it implements a simple lazy
2447initialization scheme. Once <tt>llvm_start_multithreaded()</tt> returns,
2448however, it uses double-checked locking to implement thread-safe lazy
2449initialization.
2450</p>
2451
2452<p>
2453Note that, because no other threads are allowed to issue LLVM API calls before
2454<tt>llvm_start_multithreaded()</tt> returns, it is possible to have
2455<tt>ManagedStatic</tt>s of <tt>llvm::sys::Mutex</tt>s.
2456</p>
Owen Anderson1ad70e32009-06-16 18:04:19 +0000[diff] [blame]2457
2458<p>
2459The <tt>llvm_acquire_global_lock()</tt> and <tt>llvm_release_global_lock</tt>
2460APIs provide access to the global lock used to implement the double-checked
2461locking for lazy initialization. These should only be used internally to LLVM,
2462and only if you know what you're doing!
2463</p>
Owen Anderson8bc1b3b2009-06-16 01:17:16 +0000[diff] [blame]2464</div>
2465
Owen Andersone0c951a2009-08-19 17:58:52 +0000[diff] [blame]2466<!-- ======================================================================= -->
2467<div class="doc_subsection">
2468 <a name="llvmcontext">Achieving Isolation with <tt>LLVMContext</tt></a>
2469</div>
2470
2471<div class="doc_text">
2472<p>
2473<tt>LLVMContext</tt> is an opaque class in the LLVM API which clients can use
2474to operate multiple, isolated instances of LLVM concurrently within the same
2475address space. For instance, in a hypothetical compile-server, the compilation
2476of an individual translation unit is conceptually independent from all the
2477others, and it would be desirable to be able to compile incoming translation
2478units concurrently on independent server threads. Fortunately,
2479<tt>LLVMContext</tt> exists to enable just this kind of scenario!
2480</p>
2481
2482<p>
2483Conceptually, <tt>LLVMContext</tt> provides isolation. Every LLVM entity
2484(<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]2485in LLVM's in-memory IR belongs to an <tt>LLVMContext</tt>. Entities in
Owen Andersone0c951a2009-08-19 17:58:52 +0000[diff] [blame]2486different contexts <em>cannot</em> interact with each other: <tt>Module</tt>s in
2487different contexts cannot be linked together, <tt>Function</tt>s cannot be added
2488to <tt>Module</tt>s in different contexts, etc. What this means is that is is
2489safe to compile on multiple threads simultaneously, as long as no two threads
2490operate on entities within the same context.
2491</p>
2492
2493<p>
2494In practice, very few places in the API require the explicit specification of a
2495<tt>LLVMContext</tt>, other than the <tt>Type</tt> creation/lookup APIs.
2496Because every <tt>Type</tt> carries a reference to its owning context, most
2497other entities can determine what context they belong to by looking at their
2498own <tt>Type</tt>. If you are adding new entities to LLVM IR, please try to
2499maintain this interface design.
2500</p>
2501
2502<p>
2503For clients that do <em>not</em> require the benefits of isolation, LLVM
2504provides a convenience API <tt>getGlobalContext()</tt>. This returns a global,
2505lazily initialized <tt>LLVMContext</tt> that may be used in situations where
2506isolation is not a concern.
2507</p>
2508</div>
2509
Jeffrey Yasskin01eba392010-01-29 19:10:38 +0000[diff] [blame]2510<!-- ======================================================================= -->
2511<div class="doc_subsection">
2512 <a name="jitthreading">Threads and the JIT</a>
2513</div>
2514
2515<div class="doc_text">
2516<p>
2517LLVM's "eager" JIT compiler is safe to use in threaded programs. Multiple
2518threads can call <tt>ExecutionEngine::getPointerToFunction()</tt> or
2519<tt>ExecutionEngine::runFunction()</tt> concurrently, and multiple threads can
2520run code output by the JIT concurrently. The user must still ensure that only
2521one thread accesses IR in a given <tt>LLVMContext</tt> while another thread
2522might be modifying it. One way to do that is to always hold the JIT lock while
2523accessing IR outside the JIT (the JIT <em>modifies</em> the IR by adding
2524<tt>CallbackVH</tt>s). Another way is to only
2525call <tt>getPointerToFunction()</tt> from the <tt>LLVMContext</tt>'s thread.
2526</p>
2527
2528<p>When the JIT is configured to compile lazily (using
2529<tt>ExecutionEngine::DisableLazyCompilation(false)</tt>), there is currently a
2530<a href="http://llvm.org/bugs/show_bug.cgi?id=5184">race condition</a> in
2531updating call sites after a function is lazily-jitted. It's still possible to
2532use the lazy JIT in a threaded program if you ensure that only one thread at a
2533time can call any particular lazy stub and that the JIT lock guards any IR
2534access, but we suggest using only the eager JIT in threaded programs.
2535</p>
2536</div>
2537
Owen Anderson8bc1b3b2009-06-16 01:17:16 +0000[diff] [blame]2538<!-- *********************************************************************** -->
2539<div class="doc_section">
Chris Lattnerd9d6e102005-04-23 16:10:52 +0000[diff] [blame]2540 <a name="advanced">Advanced Topics</a>
2541</div>
2542<!-- *********************************************************************** -->
2543
2544<div class="doc_text">
Chris Lattnerf1b200b2005-04-23 17:27:36 +0000[diff] [blame]2545<p>
2546This section describes some of the advanced or obscure API's that most clients
2547do not need to be aware of. These API's tend manage the inner workings of the
2548LLVM system, and only need to be accessed in unusual circumstances.
2549</p>
2550</div>
Chris Lattnerd9d6e102005-04-23 16:10:52 +0000[diff] [blame]2551
Chris Lattnerf1b200b2005-04-23 17:27:36 +0000[diff] [blame]2552<!-- ======================================================================= -->
2553<div class="doc_subsection">
2554 <a name="TypeResolve">LLVM Type Resolution</a>
2555</div>
Chris Lattnerd9d6e102005-04-23 16:10:52 +0000[diff] [blame]2556
Chris Lattnerf1b200b2005-04-23 17:27:36 +0000[diff] [blame]2557<div class="doc_text">
2558
2559<p>
2560The LLVM type system has a very simple goal: allow clients to compare types for
2561structural equality with a simple pointer comparison (aka a shallow compare).
2562This goal makes clients much simpler and faster, and is used throughout the LLVM
2563system.
2564</p>
2565
2566<p>
2567Unfortunately achieving this goal is not a simple matter. In particular,
2568recursive types and late resolution of opaque types makes the situation very
2569difficult to handle. Fortunately, for the most part, our implementation makes
2570most clients able to be completely unaware of the nasty internal details. The
2571primary case where clients are exposed to the inner workings of it are when
Gabor Greif04367bf2007-07-06 22:07:22 +0000[diff] [blame]2572building a recursive type. In addition to this case, the LLVM bitcode reader,
Chris Lattnerf1b200b2005-04-23 17:27:36 +0000[diff] [blame]2573assembly parser, and linker also have to be aware of the inner workings of this
2574system.
2575</p>
2576
Chris Lattner0f876db2005-04-25 15:47:57 +0000[diff] [blame]2577<p>
2578For our purposes below, we need three concepts. First, an "Opaque Type" is
2579exactly as defined in the <a href="LangRef.html#t_opaque">language
2580reference</a>. Second an "Abstract Type" is any type which includes an
Reid Spencer06565dc2007-01-12 17:11:23 +0000[diff] [blame]2581opaque type as part of its type graph (for example "<tt>{ opaque, i32 }</tt>").
2582Third, a concrete type is a type that is not an abstract type (e.g. "<tt>{ i32,
Chris Lattner0f876db2005-04-25 15:47:57 +0000[diff] [blame]2583float }</tt>").
2584</p>
2585
Chris Lattnerf1b200b2005-04-23 17:27:36 +0000[diff] [blame]2586</div>
2587
2588<!-- ______________________________________________________________________ -->
2589<div class="doc_subsubsection">
2590 <a name="BuildRecType">Basic Recursive Type Construction</a>
2591</div>
2592
2593<div class="doc_text">
2594
2595<p>
2596Because the most common question is "how do I build a recursive type with LLVM",
2597we answer it now and explain it as we go. Here we include enough to cause this
2598to be emitted to an output .ll file:
2599</p>
2600
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2601<div class="doc_code">
Chris Lattnerf1b200b2005-04-23 17:27:36 +0000[diff] [blame]2602<pre>
Reid Spencer06565dc2007-01-12 17:11:23 +0000[diff] [blame]2603%mylist = type { %mylist*, i32 }
Chris Lattnerf1b200b2005-04-23 17:27:36 +0000[diff] [blame]2604</pre>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2605</div>
Chris Lattnerf1b200b2005-04-23 17:27:36 +0000[diff] [blame]2606
2607<p>
2608To build this, use the following LLVM APIs:
2609</p>
2610
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2611<div class="doc_code">
Chris Lattnerf1b200b2005-04-23 17:27:36 +0000[diff] [blame]2612<pre>
Bill Wendling82e2eea2006-10-11 18:00:22 +0000[diff] [blame]2613// <i>Create the initial outer struct</i>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2614<a href="#PATypeHolder">PATypeHolder</a> StructTy = OpaqueType::get();
2615std::vector&lt;const Type*&gt; Elts;
Daniel Dunbar58c2ac02008-10-03 22:17:25 +0000[diff] [blame]2616Elts.push_back(PointerType::getUnqual(StructTy));
Nick Lewycky10d64b92007-12-03 01:52:52 +0000[diff] [blame]2617Elts.push_back(Type::Int32Ty);
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2618StructType *NewSTy = StructType::get(Elts);
Chris Lattnerf1b200b2005-04-23 17:27:36 +0000[diff] [blame]2619
Reid Spencer06565dc2007-01-12 17:11:23 +0000[diff] [blame]2620// <i>At this point, NewSTy = "{ opaque*, i32 }". Tell VMCore that</i>
Bill Wendling82e2eea2006-10-11 18:00:22 +0000[diff] [blame]2621// <i>the struct and the opaque type are actually the same.</i>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2622cast&lt;OpaqueType&gt;(StructTy.get())-&gt;<a href="#refineAbstractTypeTo">refineAbstractTypeTo</a>(NewSTy);
Chris Lattnerf1b200b2005-04-23 17:27:36 +0000[diff] [blame]2623
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2624// <i>NewSTy is potentially invalidated, but StructTy (a <a href="#PATypeHolder">PATypeHolder</a>) is</i>
Bill Wendling82e2eea2006-10-11 18:00:22 +0000[diff] [blame]2625// <i>kept up-to-date</i>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2626NewSTy = cast&lt;StructType&gt;(StructTy.get());
Chris Lattnerf1b200b2005-04-23 17:27:36 +0000[diff] [blame]2627
Bill Wendling82e2eea2006-10-11 18:00:22 +0000[diff] [blame]2628// <i>Add a name for the type to the module symbol table (optional)</i>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2629MyModule-&gt;addTypeName("mylist", NewSTy);
Chris Lattnerf1b200b2005-04-23 17:27:36 +0000[diff] [blame]2630</pre>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2631</div>
Chris Lattnerf1b200b2005-04-23 17:27:36 +0000[diff] [blame]2632
2633<p>
2634This code shows the basic approach used to build recursive types: build a
2635non-recursive type using 'opaque', then use type unification to close the cycle.
2636The type unification step is performed by the <tt><a
Chris Lattneraff26d12007-02-03 03:06:52 +0000[diff] [blame]2637href="#refineAbstractTypeTo">refineAbstractTypeTo</a></tt> method, which is
Chris Lattnerf1b200b2005-04-23 17:27:36 +0000[diff] [blame]2638described next. After that, we describe the <a
2639href="#PATypeHolder">PATypeHolder class</a>.
2640</p>
2641
2642</div>
2643
2644<!-- ______________________________________________________________________ -->
2645<div class="doc_subsubsection">
2646 <a name="refineAbstractTypeTo">The <tt>refineAbstractTypeTo</tt> method</a>
2647</div>
2648
2649<div class="doc_text">
2650<p>
2651The <tt>refineAbstractTypeTo</tt> method starts the type unification process.
2652While this method is actually a member of the DerivedType class, it is most
2653often used on OpaqueType instances. Type unification is actually a recursive
2654process. After unification, types can become structurally isomorphic to
2655existing types, and all duplicates are deleted (to preserve pointer equality).
2656</p>
2657
2658<p>
2659In the example above, the OpaqueType object is definitely deleted.
Reid Spencer06565dc2007-01-12 17:11:23 +0000[diff] [blame]2660Additionally, if there is an "{ \2*, i32}" type already created in the system,
Chris Lattnerf1b200b2005-04-23 17:27:36 +0000[diff] [blame]2661the pointer and struct type created are <b>also</b> deleted. Obviously whenever
2662a type is deleted, any "Type*" pointers in the program are invalidated. As
2663such, it is safest to avoid having <i>any</i> "Type*" pointers to abstract types
2664live across a call to <tt>refineAbstractTypeTo</tt> (note that non-abstract
2665types can never move or be deleted). To deal with this, the <a
2666href="#PATypeHolder">PATypeHolder</a> class is used to maintain a stable
2667reference to a possibly refined type, and the <a
2668href="#AbstractTypeUser">AbstractTypeUser</a> class is used to update more
2669complex datastructures.
2670</p>
2671
2672</div>
2673
2674<!-- ______________________________________________________________________ -->
2675<div class="doc_subsubsection">
2676 <a name="PATypeHolder">The PATypeHolder Class</a>
2677</div>
2678
2679<div class="doc_text">
2680<p>
2681PATypeHolder is a form of a "smart pointer" for Type objects. When VMCore
2682happily goes about nuking types that become isomorphic to existing types, it
2683automatically updates all PATypeHolder objects to point to the new type. In the
2684example above, this allows the code to maintain a pointer to the resultant
2685resolved recursive type, even though the Type*'s are potentially invalidated.
2686</p>
2687
2688<p>
2689PATypeHolder is an extremely light-weight object that uses a lazy union-find
2690implementation to update pointers. For example the pointer from a Value to its
2691Type is maintained by PATypeHolder objects.
2692</p>
2693
2694</div>
2695
2696<!-- ______________________________________________________________________ -->
2697<div class="doc_subsubsection">
2698 <a name="AbstractTypeUser">The AbstractTypeUser Class</a>
2699</div>
2700
2701<div class="doc_text">
2702
2703<p>
2704Some data structures need more to perform more complex updates when types get
Chris Lattner263a98e2007-02-16 04:37:31 +0000[diff] [blame]2705resolved. To support this, a class can derive from the AbstractTypeUser class.
2706This class
Chris Lattnerf1b200b2005-04-23 17:27:36 +0000[diff] [blame]2707allows it to get callbacks when certain types are resolved. To register to get
2708callbacks for a particular type, the DerivedType::{add/remove}AbstractTypeUser
Chris Lattner0f876db2005-04-25 15:47:57 +0000[diff] [blame]2709methods can be called on a type. Note that these methods only work for <i>
Reid Spencer06565dc2007-01-12 17:11:23 +0000[diff] [blame]2710 abstract</i> types. Concrete types (those that do not include any opaque
2711objects) can never be refined.
Chris Lattnerf1b200b2005-04-23 17:27:36 +0000[diff] [blame]2712</p>
Chris Lattnerd9d6e102005-04-23 16:10:52 +0000[diff] [blame]2713</div>
2714
2715
2716<!-- ======================================================================= -->
2717<div class="doc_subsection">
Chris Lattner263a98e2007-02-16 04:37:31 +0000[diff] [blame]2718 <a name="SymbolTable">The <tt>ValueSymbolTable</tt> and
2719 <tt>TypeSymbolTable</tt> classes</a>
Chris Lattnerd9d6e102005-04-23 16:10:52 +0000[diff] [blame]2720</div>
Chris Lattnerf1b200b2005-04-23 17:27:36 +0000[diff] [blame]2721
Chris Lattnerd9d6e102005-04-23 16:10:52 +0000[diff] [blame]2722<div class="doc_text">
Chris Lattner263a98e2007-02-16 04:37:31 +0000[diff] [blame]2723<p>The <tt><a href="http://llvm.org/doxygen/classllvm_1_1ValueSymbolTable.html">
2724ValueSymbolTable</a></tt> class provides a symbol table that the <a
Chris Lattnerd9d6e102005-04-23 16:10:52 +0000[diff] [blame]2725href="#Function"><tt>Function</tt></a> and <a href="#Module">
Chris Lattner263a98e2007-02-16 04:37:31 +0000[diff] [blame]2726<tt>Module</tt></a> classes use for naming value definitions. The symbol table
2727can provide a name for any <a href="#Value"><tt>Value</tt></a>.
2728The <tt><a href="http://llvm.org/doxygen/classllvm_1_1TypeSymbolTable.html">
2729TypeSymbolTable</a></tt> class is used by the <tt>Module</tt> class to store
2730names for types.</p>
Chris Lattnerd9d6e102005-04-23 16:10:52 +0000[diff] [blame]2731
Reid Spencera6362242007-01-07 00:41:39 +0000[diff] [blame]2732<p>Note that the <tt>SymbolTable</tt> class should not be directly accessed
2733by most clients. It should only be used when iteration over the symbol table
2734names themselves are required, which is very special purpose. Note that not
2735all LLVM
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2736<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]2737an empty name) do not exist in the symbol table.
2738</p>
2739
Chris Lattner263a98e2007-02-16 04:37:31 +0000[diff] [blame]2740<p>These symbol tables support iteration over the values/types in the symbol
2741table with <tt>begin/end/iterator</tt> and supports querying to see if a
2742specific name is in the symbol table (with <tt>lookup</tt>). The
2743<tt>ValueSymbolTable</tt> class exposes no public mutator methods, instead,
2744simply call <tt>setName</tt> on a value, which will autoinsert it into the
2745appropriate symbol table. For types, use the Module::addTypeName method to
2746insert entries into the symbol table.</p>
Chris Lattnerd9d6e102005-04-23 16:10:52 +0000[diff] [blame]2747
Chris Lattnerd9d6e102005-04-23 16:10:52 +0000[diff] [blame]2748</div>
2749
2750
2751
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2752<!-- ======================================================================= -->
2753<div class="doc_subsection">
2754 <a name="UserLayout">The <tt>User</tt> and owned <tt>Use</tt> classes' memory layout</a>
2755</div>
2756
2757<div class="doc_text">
2758<p>The <tt><a href="http://llvm.org/doxygen/classllvm_1_1User.html">
Gabor Greiffd095b62009-01-05 16:05:32 +0000[diff] [blame]2759User</a></tt> class provides a basis for expressing the ownership of <tt>User</tt>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2760towards other <tt><a href="http://llvm.org/doxygen/classllvm_1_1Value.html">
2761Value</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]2762Use</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]2763addition and removal.</p>
2764
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2765<!-- ______________________________________________________________________ -->
2766<div class="doc_subsubsection">
Gabor Greiffd095b62009-01-05 16:05:32 +0000[diff] [blame]2767 <a name="Use2User">Interaction and relationship between <tt>User</tt> and <tt>Use</tt> objects</a>
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2768</div>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2769
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2770<div class="doc_text">
2771<p>
2772A subclass of <tt>User</tt> can choose between incorporating its <tt>Use</tt> objects
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2773or refer to them out-of-line by means of a pointer. A mixed variant
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2774(some <tt>Use</tt>s inline others hung off) is impractical and breaks the invariant
2775that the <tt>Use</tt> objects belonging to the same <tt>User</tt> form a contiguous array.
2776</p>
2777</div>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2778
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2779<p>
2780We have 2 different layouts in the <tt>User</tt> (sub)classes:
2781<ul>
2782<li><p>Layout a)
2783The <tt>Use</tt> object(s) are inside (resp. at fixed offset) of the <tt>User</tt>
2784object and there are a fixed number of them.</p>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2785
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2786<li><p>Layout b)
2787The <tt>Use</tt> object(s) are referenced by a pointer to an
2788array from the <tt>User</tt> object and there may be a variable
2789number of them.</p>
2790</ul>
2791<p>
Gabor Greifd41720a2008-06-25 00:10:22 +0000[diff] [blame]2792As of v2.4 each layout still possesses a direct pointer to the
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2793start of the array of <tt>Use</tt>s. Though not mandatory for layout a),
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2794we stick to this redundancy for the sake of simplicity.
Gabor Greifd41720a2008-06-25 00:10:22 +0000[diff] [blame]2795The <tt>User</tt> object also stores the number of <tt>Use</tt> objects it
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2796has. (Theoretically this information can also be calculated
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2797given the scheme presented below.)</p>
2798<p>
2799Special forms of allocation operators (<tt>operator new</tt>)
Gabor Greifd41720a2008-06-25 00:10:22 +0000[diff] [blame]2800enforce the following memory layouts:</p>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2801
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2802<ul>
Gabor Greifd41720a2008-06-25 00:10:22 +0000[diff] [blame]2803<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]2804
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2805<pre>
2806...---.---.---.---.-------...
2807 | P | P | P | P | User
2808'''---'---'---'---'-------'''
2809</pre>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2810
Gabor Greifd41720a2008-06-25 00:10:22 +0000[diff] [blame]2811<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]2812<pre>
2813.-------...
2814| User
2815'-------'''
2816 |
2817 v
2818 .---.---.---.---...
2819 | P | P | P | P |
2820 '---'---'---'---'''
2821</pre>
2822</ul>
2823<i>(In the above figures '<tt>P</tt>' stands for the <tt>Use**</tt> that
2824 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]2825
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2826<!-- ______________________________________________________________________ -->
2827<div class="doc_subsubsection">
Gabor Greiffd095b62009-01-05 16:05:32 +0000[diff] [blame]2828 <a name="Waymarking">The waymarking algorithm</a>
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2829</div>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2830
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2831<div class="doc_text">
2832<p>
Gabor Greifd41720a2008-06-25 00:10:22 +0000[diff] [blame]2833Since the <tt>Use</tt> objects are deprived of the direct (back)pointer to
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2834their <tt>User</tt> objects, there must be a fast and exact method to
2835recover it. This is accomplished by the following scheme:</p>
2836</div>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2837
Gabor Greifd41720a2008-06-25 00:10:22 +0000[diff] [blame]2838A 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]2839start of the <tt>User</tt> object:
2840<ul>
2841<li><tt>00</tt> &mdash;&gt; binary digit 0</li>
2842<li><tt>01</tt> &mdash;&gt; binary digit 1</li>
2843<li><tt>10</tt> &mdash;&gt; stop and calculate (<tt>s</tt>)</li>
2844<li><tt>11</tt> &mdash;&gt; full stop (<tt>S</tt>)</li>
2845</ul>
2846<p>
2847Given a <tt>Use*</tt>, all we have to do is to walk till we get
2848a stop and we either have a <tt>User</tt> immediately behind or
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2849we have to walk to the next stop picking up digits
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2850and calculating the offset:</p>
2851<pre>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2852.---.---.---.---.---.---.---.---.---.---.---.---.---.---.---.---.----------------
2853| 1 | s | 1 | 0 | 1 | 0 | s | 1 | 1 | 0 | s | 1 | 1 | s | 1 | S | User (or User*)
2854'---'---'---'---'---'---'---'---'---'---'---'---'---'---'---'---'----------------
2855 |+15 |+10 |+6 |+3 |+1
2856 | | | | |__>
2857 | | | |__________>
2858 | | |______________________>
2859 | |______________________________________>
2860 |__________________________________________________________>
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2861</pre>
2862<p>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2863Only the significant number of bits need to be stored between the
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2864stops, so that the <i>worst case is 20 memory accesses</i> when there are
28651000 <tt>Use</tt> objects associated with a <tt>User</tt>.</p>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2866
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2867<!-- ______________________________________________________________________ -->
2868<div class="doc_subsubsection">
Gabor Greiffd095b62009-01-05 16:05:32 +0000[diff] [blame]2869 <a name="ReferenceImpl">Reference implementation</a>
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2870</div>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2871
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2872<div class="doc_text">
2873<p>
2874The following literate Haskell fragment demonstrates the concept:</p>
2875</div>
2876
2877<div class="doc_code">
2878<pre>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2879> import Test.QuickCheck
2880>
2881> digits :: Int -> [Char] -> [Char]
2882> digits 0 acc = '0' : acc
2883> digits 1 acc = '1' : acc
2884> digits n acc = digits (n `div` 2) $ digits (n `mod` 2) acc
2885>
2886> dist :: Int -> [Char] -> [Char]
2887> dist 0 [] = ['S']
2888> dist 0 acc = acc
2889> dist 1 acc = let r = dist 0 acc in 's' : digits (length r) r
2890> dist n acc = dist (n - 1) $ dist 1 acc
2891>
2892> takeLast n ss = reverse $ take n $ reverse ss
2893>
2894> test = takeLast 40 $ dist 20 []
2895>
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2896</pre>
2897</div>
2898<p>
2899Printing &lt;test&gt; gives: <tt>"1s100000s11010s10100s1111s1010s110s11s1S"</tt></p>
2900<p>
2901The reverse algorithm computes the length of the string just by examining
2902a certain prefix:</p>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2903
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2904<div class="doc_code">
2905<pre>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2906> pref :: [Char] -> Int
2907> pref "S" = 1
2908> pref ('s':'1':rest) = decode 2 1 rest
2909> pref (_:rest) = 1 + pref rest
2910>
2911> decode walk acc ('0':rest) = decode (walk + 1) (acc * 2) rest
2912> decode walk acc ('1':rest) = decode (walk + 1) (acc * 2 + 1) rest
2913> decode walk acc _ = walk + acc
2914>
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2915</pre>
2916</div>
2917<p>
2918Now, as expected, printing &lt;pref test&gt; gives <tt>40</tt>.</p>
2919<p>
2920We can <i>quickCheck</i> this with following property:</p>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2921
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2922<div class="doc_code">
2923<pre>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2924> testcase = dist 2000 []
2925> testcaseLength = length testcase
2926>
2927> identityProp n = n > 0 && n <= testcaseLength ==> length arr == pref arr
2928> where arr = takeLast n testcase
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2929>
2930</pre>
2931</div>
2932<p>
2933As expected &lt;quickCheck identityProp&gt; gives:</p>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2934
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2935<pre>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2936*Main> quickCheck identityProp
2937OK, passed 100 tests.
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2938</pre>
2939<p>
2940Let's be a bit more exhaustive:</p>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2941
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2942<div class="doc_code">
2943<pre>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2944>
2945> deepCheck p = check (defaultConfig { configMaxTest = 500 }) p
2946>
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2947</pre>
2948</div>
2949<p>
2950And here is the result of &lt;deepCheck identityProp&gt;:</p>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2951
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2952<pre>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2953*Main> deepCheck identityProp
2954OK, passed 500 tests.
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2955</pre>
2956
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2957<!-- ______________________________________________________________________ -->
2958<div class="doc_subsubsection">
Gabor Greiffd095b62009-01-05 16:05:32 +0000[diff] [blame]2959 <a name="Tagging">Tagging considerations</a>
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2960</div>
2961
2962<p>
2963To maintain the invariant that the 2 LSBits of each <tt>Use**</tt> in <tt>Use</tt>
2964never change after being set up, setters of <tt>Use::Prev</tt> must re-tag the
2965new <tt>Use**</tt> on every modification. Accordingly getters must strip the
2966tag bits.</p>
2967<p>
Gabor Greifd41720a2008-06-25 00:10:22 +0000[diff] [blame]2968For layout b) instead of the <tt>User</tt> we find a pointer (<tt>User*</tt> with LSBit set).
2969Following this pointer brings us to the <tt>User</tt>. A portable trick ensures
2970that the first bytes of <tt>User</tt> (if interpreted as a pointer) never has
Gabor Greiffd095b62009-01-05 16:05:32 +0000[diff] [blame]2971the LSBit set. (Portability is relying on the fact that all known compilers place the
2972<tt>vptr</tt> in the first word of the instances.)</p>
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2973
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2974</div>
2975
2976 <!-- *********************************************************************** -->
Chris Lattnerd9d6e102005-04-23 16:10:52 +0000[diff] [blame]2977<div class="doc_section">
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2978 <a name="coreclasses">The Core LLVM Class Hierarchy Reference </a>
2979</div>
2980<!-- *********************************************************************** -->
2981
2982<div class="doc_text">
Reid Spencer303c4b42007-01-12 17:26:25 +0000[diff] [blame]2983<p><tt>#include "<a href="/doxygen/Type_8h-source.html">llvm/Type.h</a>"</tt>
2984<br>doxygen info: <a href="/doxygen/classllvm_1_1Type.html">Type Class</a></p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2985
2986<p>The Core LLVM classes are the primary means of representing the program
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]2987being inspected or transformed. The core LLVM classes are defined in
2988header files in the <tt>include/llvm/</tt> directory, and implemented in
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2989the <tt>lib/VMCore</tt> directory.</p>
2990
2991</div>
2992
2993<!-- ======================================================================= -->
2994<div class="doc_subsection">
Reid Spencer303c4b42007-01-12 17:26:25 +0000[diff] [blame]2995 <a name="Type">The <tt>Type</tt> class and Derived Types</a>
2996</div>
2997
2998<div class="doc_text">
2999
3000 <p><tt>Type</tt> is a superclass of all type classes. Every <tt>Value</tt> has
3001 a <tt>Type</tt>. <tt>Type</tt> cannot be instantiated directly but only
3002 through its subclasses. Certain primitive types (<tt>VoidType</tt>,
3003 <tt>LabelType</tt>, <tt>FloatType</tt> and <tt>DoubleType</tt>) have hidden
3004 subclasses. They are hidden because they offer no useful functionality beyond
3005 what the <tt>Type</tt> class offers except to distinguish themselves from
3006 other subclasses of <tt>Type</tt>.</p>
3007 <p>All other types are subclasses of <tt>DerivedType</tt>. Types can be
3008 named, but this is not a requirement. There exists exactly
3009 one instance of a given shape at any one time. This allows type equality to
3010 be performed with address equality of the Type Instance. That is, given two
3011 <tt>Type*</tt> values, the types are identical if the pointers are identical.
3012 </p>
3013</div>
3014
3015<!-- _______________________________________________________________________ -->
3016<div class="doc_subsubsection">
Gabor Greiffd095b62009-01-05 16:05:32 +0000[diff] [blame]3017 <a name="m_Type">Important Public Methods</a>
Reid Spencer303c4b42007-01-12 17:26:25 +0000[diff] [blame]3018</div>
3019
3020<div class="doc_text">
3021
3022<ul>
Duncan Sandsb0bc6c32010-02-15 16:12:20 +0000[diff] [blame]3023 <li><tt>bool isIntegerTy() const</tt>: Returns true for any integer type.</li>
Reid Spencer303c4b42007-01-12 17:26:25 +0000[diff] [blame]3024
Duncan Sandsb0bc6c32010-02-15 16:12:20 +0000[diff] [blame]3025 <li><tt>bool isFloatingPointTy()</tt>: Return true if this is one of the five
Reid Spencer303c4b42007-01-12 17:26:25 +0000[diff] [blame]3026 floating point types.</li>
3027
3028 <li><tt>bool isAbstract()</tt>: Return true if the type is abstract (contains
3029 an OpaqueType anywhere in its definition).</li>
3030
3031 <li><tt>bool isSized()</tt>: Return true if the type has known size. Things
3032 that don't have a size are abstract types, labels and void.</li>
3033
3034</ul>
3035</div>
3036
3037<!-- _______________________________________________________________________ -->
3038<div class="doc_subsubsection">
Gabor Greiffd095b62009-01-05 16:05:32 +0000[diff] [blame]3039 <a name="derivedtypes">Important Derived Types</a>
Reid Spencer303c4b42007-01-12 17:26:25 +0000[diff] [blame]3040</div>
3041<div class="doc_text">
3042<dl>
3043 <dt><tt>IntegerType</tt></dt>
3044 <dd>Subclass of DerivedType that represents integer types of any bit width.
3045 Any bit width between <tt>IntegerType::MIN_INT_BITS</tt> (1) and
3046 <tt>IntegerType::MAX_INT_BITS</tt> (~8 million) can be represented.
3047 <ul>
3048 <li><tt>static const IntegerType* get(unsigned NumBits)</tt>: get an integer
3049 type of a specific bit width.</li>
3050 <li><tt>unsigned getBitWidth() const</tt>: Get the bit width of an integer
3051 type.</li>
3052 </ul>
3053 </dd>
3054 <dt><tt>SequentialType</tt></dt>
3055 <dd>This is subclassed by ArrayType and PointerType
3056 <ul>
3057 <li><tt>const Type * getElementType() const</tt>: Returns the type of each
3058 of the elements in the sequential type. </li>
3059 </ul>
3060 </dd>
3061 <dt><tt>ArrayType</tt></dt>
3062 <dd>This is a subclass of SequentialType and defines the interface for array
3063 types.
3064 <ul>
3065 <li><tt>unsigned getNumElements() const</tt>: Returns the number of
3066 elements in the array. </li>
3067 </ul>
3068 </dd>
3069 <dt><tt>PointerType</tt></dt>
Chris Lattner302da1e2007-02-03 03:05:57 +0000[diff] [blame]3070 <dd>Subclass of SequentialType for pointer types.</dd>
Reid Spencer9d6565a2007-02-15 02:26:10 +0000[diff] [blame]3071 <dt><tt>VectorType</tt></dt>
Reid Spencer485bad12007-02-15 03:07:05 +0000[diff] [blame]3072 <dd>Subclass of SequentialType for vector types. A
3073 vector type is similar to an ArrayType but is distinguished because it is
Benjamin Kramer8040cd32009-10-12 14:46:08 +0000[diff] [blame]3074 a first class type whereas ArrayType is not. Vector types are used for
Reid Spencer303c4b42007-01-12 17:26:25 +0000[diff] [blame]3075 vector operations and are usually small vectors of of an integer or floating
3076 point type.</dd>
3077 <dt><tt>StructType</tt></dt>
3078 <dd>Subclass of DerivedTypes for struct types.</dd>
Duncan Sands8036ca42007-03-30 12:22:09 +0000[diff] [blame]3079 <dt><tt><a name="FunctionType">FunctionType</a></tt></dt>
Reid Spencer303c4b42007-01-12 17:26:25 +0000[diff] [blame]3080 <dd>Subclass of DerivedTypes for function types.
3081 <ul>
Dan Gohman4bb31bf2010-03-30 20:04:57 +0000[diff] [blame]3082 <li><tt>bool isVarArg() const</tt>: Returns true if it's a vararg
Reid Spencer303c4b42007-01-12 17:26:25 +0000[diff] [blame]3083 function</li>
3084 <li><tt> const Type * getReturnType() const</tt>: Returns the
3085 return type of the function.</li>
3086 <li><tt>const Type * getParamType (unsigned i)</tt>: Returns
3087 the type of the ith parameter.</li>
3088 <li><tt> const unsigned getNumParams() const</tt>: Returns the
3089 number of formal parameters.</li>
3090 </ul>
3091 </dd>
3092 <dt><tt>OpaqueType</tt></dt>
3093 <dd>Sublcass of DerivedType for abstract types. This class
3094 defines no content and is used as a placeholder for some other type. Note
3095 that OpaqueType is used (temporarily) during type resolution for forward
3096 references of types. Once the referenced type is resolved, the OpaqueType
3097 is replaced with the actual type. OpaqueType can also be used for data
3098 abstraction. At link time opaque types can be resolved to actual types
3099 of the same name.</dd>
3100</dl>
3101</div>
3102
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]3103
3104
3105<!-- ======================================================================= -->
3106<div class="doc_subsection">
3107 <a name="Module">The <tt>Module</tt> class</a>
3108</div>
3109
3110<div class="doc_text">
3111
3112<p><tt>#include "<a
3113href="/doxygen/Module_8h-source.html">llvm/Module.h</a>"</tt><br> doxygen info:
3114<a href="/doxygen/classllvm_1_1Module.html">Module Class</a></p>
3115
3116<p>The <tt>Module</tt> class represents the top level structure present in LLVM
3117programs. An LLVM module is effectively either a translation unit of the
3118original program or a combination of several translation units merged by the
3119linker. The <tt>Module</tt> class keeps track of a list of <a
3120href="#Function"><tt>Function</tt></a>s, a list of <a
3121href="#GlobalVariable"><tt>GlobalVariable</tt></a>s, and a <a
3122href="#SymbolTable"><tt>SymbolTable</tt></a>. Additionally, it contains a few
3123helpful member functions that try to make common operations easy.</p>
3124
3125</div>
3126
3127<!-- _______________________________________________________________________ -->
3128<div class="doc_subsubsection">
3129 <a name="m_Module">Important Public Members of the <tt>Module</tt> class</a>
3130</div>
3131
3132<div class="doc_text">
3133
3134<ul>
3135 <li><tt>Module::Module(std::string name = "")</tt></li>
3136</ul>
3137
3138<p>Constructing a <a href="#Module">Module</a> is easy. You can optionally
3139provide a name for it (probably based on the name of the translation unit).</p>
3140
3141<ul>
3142 <li><tt>Module::iterator</tt> - Typedef for function list iterator<br>
3143 <tt>Module::const_iterator</tt> - Typedef for const_iterator.<br>
3144
3145 <tt>begin()</tt>, <tt>end()</tt>
3146 <tt>size()</tt>, <tt>empty()</tt>
3147
3148 <p>These are forwarding methods that make it easy to access the contents of
3149 a <tt>Module</tt> object's <a href="#Function"><tt>Function</tt></a>
3150 list.</p></li>
3151
3152 <li><tt>Module::FunctionListType &amp;getFunctionList()</tt>
3153
3154 <p> Returns the list of <a href="#Function"><tt>Function</tt></a>s. This is
3155 necessary to use when you need to update the list or perform a complex
3156 action that doesn't have a forwarding method.</p>
3157
3158 <p><!-- Global Variable --></p></li>
3159</ul>
3160
3161<hr>
3162
3163<ul>
3164 <li><tt>Module::global_iterator</tt> - Typedef for global variable list iterator<br>
3165
3166 <tt>Module::const_global_iterator</tt> - Typedef for const_iterator.<br>
3167
3168 <tt>global_begin()</tt>, <tt>global_end()</tt>
3169 <tt>global_size()</tt>, <tt>global_empty()</tt>
3170
3171 <p> These are forwarding methods that make it easy to access the contents of
3172 a <tt>Module</tt> object's <a
3173 href="#GlobalVariable"><tt>GlobalVariable</tt></a> list.</p></li>
3174
3175 <li><tt>Module::GlobalListType &amp;getGlobalList()</tt>
3176
3177 <p>Returns the list of <a
3178 href="#GlobalVariable"><tt>GlobalVariable</tt></a>s. This is necessary to
3179 use when you need to update the list or perform a complex action that
3180 doesn't have a forwarding method.</p>
3181
3182 <p><!-- Symbol table stuff --> </p></li>
3183</ul>
3184
3185<hr>
3186
3187<ul>
3188 <li><tt><a href="#SymbolTable">SymbolTable</a> *getSymbolTable()</tt>
3189
3190 <p>Return a reference to the <a href="#SymbolTable"><tt>SymbolTable</tt></a>
3191 for this <tt>Module</tt>.</p>
3192
3193 <p><!-- Convenience methods --></p></li>
3194</ul>
3195
3196<hr>
3197
3198<ul>
3199 <li><tt><a href="#Function">Function</a> *getFunction(const std::string
3200 &amp;Name, const <a href="#FunctionType">FunctionType</a> *Ty)</tt>
3201
3202 <p>Look up the specified function in the <tt>Module</tt> <a
3203 href="#SymbolTable"><tt>SymbolTable</tt></a>. If it does not exist, return
3204 <tt>null</tt>.</p></li>
3205
3206 <li><tt><a href="#Function">Function</a> *getOrInsertFunction(const
3207 std::string &amp;Name, const <a href="#FunctionType">FunctionType</a> *T)</tt>
3208
3209 <p>Look up the specified function in the <tt>Module</tt> <a
3210 href="#SymbolTable"><tt>SymbolTable</tt></a>. If it does not exist, add an
3211 external declaration for the function and return it.</p></li>
3212
3213 <li><tt>std::string getTypeName(const <a href="#Type">Type</a> *Ty)</tt>
3214
3215 <p>If there is at least one entry in the <a
3216 href="#SymbolTable"><tt>SymbolTable</tt></a> for the specified <a
3217 href="#Type"><tt>Type</tt></a>, return it. Otherwise return the empty
3218 string.</p></li>
3219
3220 <li><tt>bool addTypeName(const std::string &amp;Name, const <a
3221 href="#Type">Type</a> *Ty)</tt>
3222
3223 <p>Insert an entry in the <a href="#SymbolTable"><tt>SymbolTable</tt></a>
3224 mapping <tt>Name</tt> to <tt>Ty</tt>. If there is already an entry for this
3225 name, true is returned and the <a
3226 href="#SymbolTable"><tt>SymbolTable</tt></a> is not modified.</p></li>
3227</ul>
3228
3229</div>
3230
3231
Reid Spencer303c4b42007-01-12 17:26:25 +0000[diff] [blame]3232<!-- ======================================================================= -->
3233<div class="doc_subsection">
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3234 <a name="Value">The <tt>Value</tt> class</a>
3235</div>
3236
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]3237<div class="doc_text">
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3238
3239<p><tt>#include "<a href="/doxygen/Value_8h-source.html">llvm/Value.h</a>"</tt>
3240<br>
Chris Lattner00815172007-01-04 22:01:45 +0000[diff] [blame]3241doxygen info: <a href="/doxygen/classllvm_1_1Value.html">Value Class</a></p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3242
3243<p>The <tt>Value</tt> class is the most important class in the LLVM Source
3244base. It represents a typed value that may be used (among other things) as an
3245operand to an instruction. There are many different types of <tt>Value</tt>s,
3246such as <a href="#Constant"><tt>Constant</tt></a>s,<a
3247href="#Argument"><tt>Argument</tt></a>s. Even <a
3248href="#Instruction"><tt>Instruction</tt></a>s and <a
3249href="#Function"><tt>Function</tt></a>s are <tt>Value</tt>s.</p>
3250
3251<p>A particular <tt>Value</tt> may be used many times in the LLVM representation
3252for a program. For example, an incoming argument to a function (represented
3253with an instance of the <a href="#Argument">Argument</a> class) is "used" by
3254every instruction in the function that references the argument. To keep track
3255of this relationship, the <tt>Value</tt> class keeps a list of all of the <a
3256href="#User"><tt>User</tt></a>s that is using it (the <a
3257href="#User"><tt>User</tt></a> class is a base class for all nodes in the LLVM
3258graph that can refer to <tt>Value</tt>s). This use list is how LLVM represents
3259def-use information in the program, and is accessible through the <tt>use_</tt>*
3260methods, shown below.</p>
3261
3262<p>Because LLVM is a typed representation, every LLVM <tt>Value</tt> is typed,
3263and this <a href="#Type">Type</a> is available through the <tt>getType()</tt>
3264method. In addition, all LLVM values can be named. The "name" of the
3265<tt>Value</tt> is a symbolic string printed in the LLVM code:</p>
3266
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]3267<div class="doc_code">
3268<pre>
Reid Spencer06565dc2007-01-12 17:11:23 +0000[diff] [blame]3269%<b>foo</b> = add i32 1, 2
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]3270</pre>
3271</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3272
Duncan Sands8036ca42007-03-30 12:22:09 +0000[diff] [blame]3273<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]3274that the name of any value may be missing (an empty string), so names should
3275<b>ONLY</b> be used for debugging (making the source code easier to read,
3276debugging printouts), they should not be used to keep track of values or map
3277between them. For this purpose, use a <tt>std::map</tt> of pointers to the
3278<tt>Value</tt> itself instead.</p>
3279
3280<p>One important aspect of LLVM is that there is no distinction between an SSA
3281variable and the operation that produces it. Because of this, any reference to
3282the value produced by an instruction (or the value available as an incoming
Chris Lattnerd5fc4fc2004-03-18 14:58:55 +0000[diff] [blame]3283argument, for example) is represented as a direct pointer to the instance of
3284the class that
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3285represents this value. Although this may take some getting used to, it
3286simplifies the representation and makes it easier to manipulate.</p>
3287
3288</div>
3289
3290<!-- _______________________________________________________________________ -->
3291<div class="doc_subsubsection">
3292 <a name="m_Value">Important Public Members of the <tt>Value</tt> class</a>
3293</div>
3294
3295<div class="doc_text">
3296
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3297<ul>
3298 <li><tt>Value::use_iterator</tt> - Typedef for iterator over the
3299use-list<br>
Gabor Greifbbbf9a22010-03-26 19:59:25 +0000[diff] [blame]3300 <tt>Value::const_use_iterator</tt> - Typedef for const_iterator over
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3301the use-list<br>
3302 <tt>unsigned use_size()</tt> - Returns the number of users of the
3303value.<br>
Chris Lattner9355b472002-09-06 02:50:58 +0000[diff] [blame]3304 <tt>bool use_empty()</tt> - Returns true if there are no users.<br>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3305 <tt>use_iterator use_begin()</tt> - Get an iterator to the start of
3306the use-list.<br>
3307 <tt>use_iterator use_end()</tt> - Get an iterator to the end of the
3308use-list.<br>
3309 <tt><a href="#User">User</a> *use_back()</tt> - Returns the last
3310element in the list.
3311 <p> These methods are the interface to access the def-use
3312information in LLVM. As with all other iterators in LLVM, the naming
3313conventions follow the conventions defined by the <a href="#stl">STL</a>.</p>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3314 </li>
3315 <li><tt><a href="#Type">Type</a> *getType() const</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3316 <p>This method returns the Type of the Value.</p>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3317 </li>
3318 <li><tt>bool hasName() const</tt><br>
Chris Lattner9355b472002-09-06 02:50:58 +0000[diff] [blame]3319 <tt>std::string getName() const</tt><br>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3320 <tt>void setName(const std::string &amp;Name)</tt>
3321 <p> This family of methods is used to access and assign a name to a <tt>Value</tt>,
3322be aware of the <a href="#nameWarning">precaution above</a>.</p>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3323 </li>
3324 <li><tt>void replaceAllUsesWith(Value *V)</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3325
3326 <p>This method traverses the use list of a <tt>Value</tt> changing all <a
3327 href="#User"><tt>User</tt>s</a> of the current value to refer to
3328 "<tt>V</tt>" instead. For example, if you detect that an instruction always
3329 produces a constant value (for example through constant folding), you can
3330 replace all uses of the instruction with the constant like this:</p>
3331
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]3332<div class="doc_code">
3333<pre>
3334Inst-&gt;replaceAllUsesWith(ConstVal);
3335</pre>
3336</div>
3337
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3338</ul>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3339
3340</div>
3341
3342<!-- ======================================================================= -->
3343<div class="doc_subsection">
3344 <a name="User">The <tt>User</tt> class</a>
3345</div>
3346
3347<div class="doc_text">
3348
3349<p>
3350<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]3351doxygen info: <a href="/doxygen/classllvm_1_1User.html">User Class</a><br>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3352Superclass: <a href="#Value"><tt>Value</tt></a></p>
3353
3354<p>The <tt>User</tt> class is the common base class of all LLVM nodes that may
3355refer to <a href="#Value"><tt>Value</tt></a>s. It exposes a list of "Operands"
3356that are all of the <a href="#Value"><tt>Value</tt></a>s that the User is
3357referring to. The <tt>User</tt> class itself is a subclass of
3358<tt>Value</tt>.</p>
3359
3360<p>The operands of a <tt>User</tt> point directly to the LLVM <a
3361href="#Value"><tt>Value</tt></a> that it refers to. Because LLVM uses Static
3362Single Assignment (SSA) form, there can only be one definition referred to,
3363allowing this direct connection. This connection provides the use-def
3364information in LLVM.</p>
3365
3366</div>
3367
3368<!-- _______________________________________________________________________ -->
3369<div class="doc_subsubsection">
3370 <a name="m_User">Important Public Members of the <tt>User</tt> class</a>
3371</div>
3372
3373<div class="doc_text">
3374
3375<p>The <tt>User</tt> class exposes the operand list in two ways: through
3376an index access interface and through an iterator based interface.</p>
3377
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3378<ul>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3379 <li><tt>Value *getOperand(unsigned i)</tt><br>
3380 <tt>unsigned getNumOperands()</tt>
3381 <p> These two methods expose the operands of the <tt>User</tt> in a
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3382convenient form for direct access.</p></li>
3383
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3384 <li><tt>User::op_iterator</tt> - Typedef for iterator over the operand
3385list<br>
Chris Lattner58360822005-01-17 00:12:04 +0000[diff] [blame]3386 <tt>op_iterator op_begin()</tt> - Get an iterator to the start of
3387the operand list.<br>
3388 <tt>op_iterator op_end()</tt> - Get an iterator to the end of the
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3389operand list.
3390 <p> Together, these methods make up the iterator based interface to
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3391the operands of a <tt>User</tt>.</p></li>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3392</ul>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3393
3394</div>
3395
3396<!-- ======================================================================= -->
3397<div class="doc_subsection">
3398 <a name="Instruction">The <tt>Instruction</tt> class</a>
3399</div>
3400
3401<div class="doc_text">
3402
3403<p><tt>#include "</tt><tt><a
3404href="/doxygen/Instruction_8h-source.html">llvm/Instruction.h</a>"</tt><br>
Misha Brukman31ca1de2004-06-03 23:35:54 +0000[diff] [blame]3405doxygen info: <a href="/doxygen/classllvm_1_1Instruction.html">Instruction Class</a><br>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3406Superclasses: <a href="#User"><tt>User</tt></a>, <a
3407href="#Value"><tt>Value</tt></a></p>
3408
3409<p>The <tt>Instruction</tt> class is the common base class for all LLVM
3410instructions. It provides only a few methods, but is a very commonly used
3411class. The primary data tracked by the <tt>Instruction</tt> class itself is the
3412opcode (instruction type) and the parent <a
3413href="#BasicBlock"><tt>BasicBlock</tt></a> the <tt>Instruction</tt> is embedded
3414into. To represent a specific type of instruction, one of many subclasses of
3415<tt>Instruction</tt> are used.</p>
3416
3417<p> Because the <tt>Instruction</tt> class subclasses the <a
3418href="#User"><tt>User</tt></a> class, its operands can be accessed in the same
3419way as for other <a href="#User"><tt>User</tt></a>s (with the
3420<tt>getOperand()</tt>/<tt>getNumOperands()</tt> and
3421<tt>op_begin()</tt>/<tt>op_end()</tt> methods).</p> <p> An important file for
3422the <tt>Instruction</tt> class is the <tt>llvm/Instruction.def</tt> file. This
3423file contains some meta-data about the various different types of instructions
3424in LLVM. It describes the enum values that are used as opcodes (for example
Reid Spencerc92d25d2006-12-19 19:47:19 +0000[diff] [blame]3425<tt>Instruction::Add</tt> and <tt>Instruction::ICmp</tt>), as well as the
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3426concrete sub-classes of <tt>Instruction</tt> that implement the instruction (for
3427example <tt><a href="#BinaryOperator">BinaryOperator</a></tt> and <tt><a
Reid Spencerc92d25d2006-12-19 19:47:19 +0000[diff] [blame]3428href="#CmpInst">CmpInst</a></tt>). Unfortunately, the use of macros in
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3429this file confuses doxygen, so these enum values don't show up correctly in the
Misha Brukman31ca1de2004-06-03 23:35:54 +0000[diff] [blame]3430<a href="/doxygen/classllvm_1_1Instruction.html">doxygen output</a>.</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3431
3432</div>
3433
3434<!-- _______________________________________________________________________ -->
3435<div class="doc_subsubsection">
Reid Spencerc92d25d2006-12-19 19:47:19 +0000[diff] [blame]3436 <a name="s_Instruction">Important Subclasses of the <tt>Instruction</tt>
3437 class</a>
3438</div>
3439<div class="doc_text">
3440 <ul>
3441 <li><tt><a name="BinaryOperator">BinaryOperator</a></tt>
3442 <p>This subclasses represents all two operand instructions whose operands
3443 must be the same type, except for the comparison instructions.</p></li>
3444 <li><tt><a name="CastInst">CastInst</a></tt>
3445 <p>This subclass is the parent of the 12 casting instructions. It provides
3446 common operations on cast instructions.</p>
3447 <li><tt><a name="CmpInst">CmpInst</a></tt>
3448 <p>This subclass respresents the two comparison instructions,
3449 <a href="LangRef.html#i_icmp">ICmpInst</a> (integer opreands), and
3450 <a href="LangRef.html#i_fcmp">FCmpInst</a> (floating point operands).</p>
3451 <li><tt><a name="TerminatorInst">TerminatorInst</a></tt>
3452 <p>This subclass is the parent of all terminator instructions (those which
3453 can terminate a block).</p>
3454 </ul>
3455 </div>
3456
3457<!-- _______________________________________________________________________ -->
3458<div class="doc_subsubsection">
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3459 <a name="m_Instruction">Important Public Members of the <tt>Instruction</tt>
3460 class</a>
3461</div>
3462
3463<div class="doc_text">
3464
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3465<ul>
3466 <li><tt><a href="#BasicBlock">BasicBlock</a> *getParent()</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3467 <p>Returns the <a href="#BasicBlock"><tt>BasicBlock</tt></a> that
3468this <tt>Instruction</tt> is embedded into.</p></li>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3469 <li><tt>bool mayWriteToMemory()</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3470 <p>Returns true if the instruction writes to memory, i.e. it is a
3471 <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]3472 <li><tt>unsigned getOpcode()</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3473 <p>Returns the opcode for the <tt>Instruction</tt>.</p></li>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3474 <li><tt><a href="#Instruction">Instruction</a> *clone() const</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3475 <p>Returns another instance of the specified instruction, identical
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3476in all ways to the original except that the instruction has no parent
3477(ie it's not embedded into a <a href="#BasicBlock"><tt>BasicBlock</tt></a>),
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3478and it has no name</p></li>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3479</ul>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3480
3481</div>
3482
3483<!-- ======================================================================= -->
3484<div class="doc_subsection">
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]3485 <a name="Constant">The <tt>Constant</tt> class and subclasses</a>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3486</div>
3487
3488<div class="doc_text">
3489
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]3490<p>Constant represents a base class for different types of constants. It
3491is subclassed by ConstantInt, ConstantArray, etc. for representing
3492the various types of Constants. <a href="#GlobalValue">GlobalValue</a> is also
3493a subclass, which represents the address of a global variable or function.
3494</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3495
3496</div>
3497
3498<!-- _______________________________________________________________________ -->
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]3499<div class="doc_subsubsection">Important Subclasses of Constant </div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3500<div class="doc_text">
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3501<ul>
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]3502 <li>ConstantInt : This subclass of Constant represents an integer constant of
3503 any width.
3504 <ul>
Reid Spencer97b4ee32007-03-01 21:05:33 +0000[diff] [blame]3505 <li><tt>const APInt&amp; getValue() const</tt>: Returns the underlying
3506 value of this constant, an APInt value.</li>
3507 <li><tt>int64_t getSExtValue() const</tt>: Converts the underlying APInt
3508 value to an int64_t via sign extension. If the value (not the bit width)
3509 of the APInt is too large to fit in an int64_t, an assertion will result.
3510 For this reason, use of this method is discouraged.</li>
3511 <li><tt>uint64_t getZExtValue() const</tt>: Converts the underlying APInt
3512 value to a uint64_t via zero extension. IF the value (not the bit width)
3513 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]3514 For this reason, use of this method is discouraged.</li>
Reid Spencer97b4ee32007-03-01 21:05:33 +0000[diff] [blame]3515 <li><tt>static ConstantInt* get(const APInt&amp; Val)</tt>: Returns the
3516 ConstantInt object that represents the value provided by <tt>Val</tt>.
3517 The type is implied as the IntegerType that corresponds to the bit width
3518 of <tt>Val</tt>.</li>
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]3519 <li><tt>static ConstantInt* get(const Type *Ty, uint64_t Val)</tt>:
3520 Returns the ConstantInt object that represents the value provided by
3521 <tt>Val</tt> for integer type <tt>Ty</tt>.</li>
3522 </ul>
3523 </li>
3524 <li>ConstantFP : This class represents a floating point constant.
3525 <ul>
3526 <li><tt>double getValue() const</tt>: Returns the underlying value of
3527 this constant. </li>
3528 </ul>
3529 </li>
3530 <li>ConstantArray : This represents a constant array.
3531 <ul>
3532 <li><tt>const std::vector&lt;Use&gt; &amp;getValues() const</tt>: Returns
3533 a vector of component constants that makeup this array. </li>
3534 </ul>
3535 </li>
3536 <li>ConstantStruct : This represents a constant struct.
3537 <ul>
3538 <li><tt>const std::vector&lt;Use&gt; &amp;getValues() const</tt>: Returns
3539 a vector of component constants that makeup this array. </li>
3540 </ul>
3541 </li>
3542 <li>GlobalValue : This represents either a global variable or a function. In
3543 either case, the value is a constant fixed address (after linking).
3544 </li>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3545</ul>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3546</div>
3547
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]3548
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3549<!-- ======================================================================= -->
3550<div class="doc_subsection">
3551 <a name="GlobalValue">The <tt>GlobalValue</tt> class</a>
3552</div>
3553
3554<div class="doc_text">
3555
3556<p><tt>#include "<a
3557href="/doxygen/GlobalValue_8h-source.html">llvm/GlobalValue.h</a>"</tt><br>
Misha Brukman384047f2004-06-03 23:29:12 +0000[diff] [blame]3558doxygen info: <a href="/doxygen/classllvm_1_1GlobalValue.html">GlobalValue
3559Class</a><br>
Reid Spencerbe5e85e2006-04-14 14:11:48 +0000[diff] [blame]3560Superclasses: <a href="#Constant"><tt>Constant</tt></a>,
3561<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]3562
3563<p>Global values (<a href="#GlobalVariable"><tt>GlobalVariable</tt></a>s or <a
3564href="#Function"><tt>Function</tt></a>s) are the only LLVM values that are
3565visible in the bodies of all <a href="#Function"><tt>Function</tt></a>s.
3566Because they are visible at global scope, they are also subject to linking with
3567other globals defined in different translation units. To control the linking
3568process, <tt>GlobalValue</tt>s know their linkage rules. Specifically,
3569<tt>GlobalValue</tt>s know whether they have internal or external linkage, as
Reid Spencer8b2da7a2004-07-18 13:10:31 +0000[diff] [blame]3570defined by the <tt>LinkageTypes</tt> enumeration.</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3571
3572<p>If a <tt>GlobalValue</tt> has internal linkage (equivalent to being
3573<tt>static</tt> in C), it is not visible to code outside the current translation
3574unit, and does not participate in linking. If it has external linkage, it is
3575visible to external code, and does participate in linking. In addition to
3576linkage information, <tt>GlobalValue</tt>s keep track of which <a
3577href="#Module"><tt>Module</tt></a> they are currently part of.</p>
3578
3579<p>Because <tt>GlobalValue</tt>s are memory objects, they are always referred to
3580by their <b>address</b>. As such, the <a href="#Type"><tt>Type</tt></a> of a
3581global is always a pointer to its contents. It is important to remember this
3582when using the <tt>GetElementPtrInst</tt> instruction because this pointer must
3583be dereferenced first. For example, if you have a <tt>GlobalVariable</tt> (a
3584subclass 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]3585i32]</tt>, then the <tt>GlobalVariable</tt> is a pointer to that array. Although
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3586the address of the first element of this array and the value of the
3587<tt>GlobalVariable</tt> are the same, they have different types. The
Reid Spencer06565dc2007-01-12 17:11:23 +0000[diff] [blame]3588<tt>GlobalVariable</tt>'s type is <tt>[24 x i32]</tt>. The first element's type
3589is <tt>i32.</tt> Because of this, accessing a global value requires you to
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3590dereference the pointer with <tt>GetElementPtrInst</tt> first, then its elements
3591can be accessed. This is explained in the <a href="LangRef.html#globalvars">LLVM
3592Language Reference Manual</a>.</p>
3593
3594</div>
3595
3596<!-- _______________________________________________________________________ -->
3597<div class="doc_subsubsection">
3598 <a name="m_GlobalValue">Important Public Members of the <tt>GlobalValue</tt>
3599 class</a>
3600</div>
3601
3602<div class="doc_text">
3603
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3604<ul>
3605 <li><tt>bool hasInternalLinkage() const</tt><br>
Chris Lattner9355b472002-09-06 02:50:58 +0000[diff] [blame]3606 <tt>bool hasExternalLinkage() const</tt><br>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3607 <tt>void setInternalLinkage(bool HasInternalLinkage)</tt>
3608 <p> These methods manipulate the linkage characteristics of the <tt>GlobalValue</tt>.</p>
3609 <p> </p>
3610 </li>
3611 <li><tt><a href="#Module">Module</a> *getParent()</tt>
3612 <p> This returns the <a href="#Module"><tt>Module</tt></a> that the
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3613GlobalValue is currently embedded into.</p></li>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3614</ul>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3615
3616</div>
3617
3618<!-- ======================================================================= -->
3619<div class="doc_subsection">
3620 <a name="Function">The <tt>Function</tt> class</a>
3621</div>
3622
3623<div class="doc_text">
3624
3625<p><tt>#include "<a
3626href="/doxygen/Function_8h-source.html">llvm/Function.h</a>"</tt><br> doxygen
Misha Brukman31ca1de2004-06-03 23:35:54 +0000[diff] [blame]3627info: <a href="/doxygen/classllvm_1_1Function.html">Function Class</a><br>
Reid Spencerbe5e85e2006-04-14 14:11:48 +0000[diff] [blame]3628Superclasses: <a href="#GlobalValue"><tt>GlobalValue</tt></a>,
3629<a href="#Constant"><tt>Constant</tt></a>,
3630<a href="#User"><tt>User</tt></a>,
3631<a href="#Value"><tt>Value</tt></a></p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3632
3633<p>The <tt>Function</tt> class represents a single procedure in LLVM. It is
Torok Edwin87469292009-10-12 13:37:29 +0000[diff] [blame]3634actually one of the more complex classes in the LLVM hierarchy because it must
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3635keep track of a large amount of data. The <tt>Function</tt> class keeps track
Reid Spencerbe5e85e2006-04-14 14:11:48 +0000[diff] [blame]3636of a list of <a href="#BasicBlock"><tt>BasicBlock</tt></a>s, a list of formal
3637<a href="#Argument"><tt>Argument</tt></a>s, and a
3638<a href="#SymbolTable"><tt>SymbolTable</tt></a>.</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3639
3640<p>The list of <a href="#BasicBlock"><tt>BasicBlock</tt></a>s is the most
3641commonly used part of <tt>Function</tt> objects. The list imposes an implicit
3642ordering of the blocks in the function, which indicate how the code will be
Benjamin Kramer8040cd32009-10-12 14:46:08 +0000[diff] [blame]3643laid out by the backend. Additionally, the first <a
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3644href="#BasicBlock"><tt>BasicBlock</tt></a> is the implicit entry node for the
3645<tt>Function</tt>. It is not legal in LLVM to explicitly branch to this initial
3646block. There are no implicit exit nodes, and in fact there may be multiple exit
3647nodes from a single <tt>Function</tt>. If the <a
3648href="#BasicBlock"><tt>BasicBlock</tt></a> list is empty, this indicates that
3649the <tt>Function</tt> is actually a function declaration: the actual body of the
3650function hasn't been linked in yet.</p>
3651
3652<p>In addition to a list of <a href="#BasicBlock"><tt>BasicBlock</tt></a>s, the
3653<tt>Function</tt> class also keeps track of the list of formal <a
3654href="#Argument"><tt>Argument</tt></a>s that the function receives. This
3655container manages the lifetime of the <a href="#Argument"><tt>Argument</tt></a>
3656nodes, just like the <a href="#BasicBlock"><tt>BasicBlock</tt></a> list does for
3657the <a href="#BasicBlock"><tt>BasicBlock</tt></a>s.</p>
3658
3659<p>The <a href="#SymbolTable"><tt>SymbolTable</tt></a> is a very rarely used
3660LLVM feature that is only used when you have to look up a value by name. Aside
3661from that, the <a href="#SymbolTable"><tt>SymbolTable</tt></a> is used
3662internally to make sure that there are not conflicts between the names of <a
3663href="#Instruction"><tt>Instruction</tt></a>s, <a
3664href="#BasicBlock"><tt>BasicBlock</tt></a>s, or <a
3665href="#Argument"><tt>Argument</tt></a>s in the function body.</p>
3666
Reid Spencer8b2da7a2004-07-18 13:10:31 +0000[diff] [blame]3667<p>Note that <tt>Function</tt> is a <a href="#GlobalValue">GlobalValue</a>
3668and therefore also a <a href="#Constant">Constant</a>. The value of the function
3669is its address (after linking) which is guaranteed to be constant.</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3670</div>
3671
3672<!-- _______________________________________________________________________ -->
3673<div class="doc_subsubsection">
3674 <a name="m_Function">Important Public Members of the <tt>Function</tt>
3675 class</a>
3676</div>
3677
3678<div class="doc_text">
3679
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3680<ul>
3681 <li><tt>Function(const </tt><tt><a href="#FunctionType">FunctionType</a>
Chris Lattnerac479e52004-08-04 05:10:48 +0000[diff] [blame]3682 *Ty, LinkageTypes Linkage, const std::string &amp;N = "", Module* Parent = 0)</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3683
3684 <p>Constructor used when you need to create new <tt>Function</tt>s to add
3685 the the program. The constructor must specify the type of the function to
Chris Lattnerac479e52004-08-04 05:10:48 +0000[diff] [blame]3686 create and what type of linkage the function should have. The <a
3687 href="#FunctionType"><tt>FunctionType</tt></a> argument
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3688 specifies the formal arguments and return value for the function. The same
Duncan Sands8036ca42007-03-30 12:22:09 +0000[diff] [blame]3689 <a href="#FunctionType"><tt>FunctionType</tt></a> value can be used to
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3690 create multiple functions. The <tt>Parent</tt> argument specifies the Module
3691 in which the function is defined. If this argument is provided, the function
3692 will automatically be inserted into that module's list of
3693 functions.</p></li>
3694
Chris Lattner62810e32008-11-25 18:34:50 +0000[diff] [blame]3695 <li><tt>bool isDeclaration()</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3696
3697 <p>Return whether or not the <tt>Function</tt> has a body defined. If the
3698 function is "external", it does not have a body, and thus must be resolved
3699 by linking with a function defined in a different translation unit.</p></li>
3700
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3701 <li><tt>Function::iterator</tt> - Typedef for basic block list iterator<br>
Chris Lattner9355b472002-09-06 02:50:58 +0000[diff] [blame]3702 <tt>Function::const_iterator</tt> - Typedef for const_iterator.<br>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3703
Chris Lattner77d69242005-03-15 05:19:20 +0000[diff] [blame]3704 <tt>begin()</tt>, <tt>end()</tt>
3705 <tt>size()</tt>, <tt>empty()</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3706
3707 <p>These are forwarding methods that make it easy to access the contents of
3708 a <tt>Function</tt> object's <a href="#BasicBlock"><tt>BasicBlock</tt></a>
3709 list.</p></li>
3710
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3711 <li><tt>Function::BasicBlockListType &amp;getBasicBlockList()</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3712
3713 <p>Returns the list of <a href="#BasicBlock"><tt>BasicBlock</tt></a>s. This
3714 is necessary to use when you need to update the list or perform a complex
3715 action that doesn't have a forwarding method.</p></li>
3716
Chris Lattner89cc2652005-03-15 04:48:32 +0000[diff] [blame]3717 <li><tt>Function::arg_iterator</tt> - Typedef for the argument list
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3718iterator<br>
Chris Lattner89cc2652005-03-15 04:48:32 +0000[diff] [blame]3719 <tt>Function::const_arg_iterator</tt> - Typedef for const_iterator.<br>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3720
Chris Lattner77d69242005-03-15 05:19:20 +0000[diff] [blame]3721 <tt>arg_begin()</tt>, <tt>arg_end()</tt>
Chris Lattner89cc2652005-03-15 04:48:32 +0000[diff] [blame]3722 <tt>arg_size()</tt>, <tt>arg_empty()</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3723
3724 <p>These are forwarding methods that make it easy to access the contents of
3725 a <tt>Function</tt> object's <a href="#Argument"><tt>Argument</tt></a>
3726 list.</p></li>
3727
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3728 <li><tt>Function::ArgumentListType &amp;getArgumentList()</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3729
3730 <p>Returns the list of <a href="#Argument"><tt>Argument</tt></a>s. This is
3731 necessary to use when you need to update the list or perform a complex
3732 action that doesn't have a forwarding method.</p></li>
3733
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3734 <li><tt><a href="#BasicBlock">BasicBlock</a> &amp;getEntryBlock()</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3735
3736 <p>Returns the entry <a href="#BasicBlock"><tt>BasicBlock</tt></a> for the
3737 function. Because the entry block for the function is always the first
3738 block, this returns the first block of the <tt>Function</tt>.</p></li>
3739
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3740 <li><tt><a href="#Type">Type</a> *getReturnType()</tt><br>
3741 <tt><a href="#FunctionType">FunctionType</a> *getFunctionType()</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3742
3743 <p>This traverses the <a href="#Type"><tt>Type</tt></a> of the
3744 <tt>Function</tt> and returns the return type of the function, or the <a
3745 href="#FunctionType"><tt>FunctionType</tt></a> of the actual
3746 function.</p></li>
3747
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3748 <li><tt><a href="#SymbolTable">SymbolTable</a> *getSymbolTable()</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3749
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3750 <p> Return a pointer to the <a href="#SymbolTable"><tt>SymbolTable</tt></a>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3751 for this <tt>Function</tt>.</p></li>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3752</ul>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3753
3754</div>
3755
3756<!-- ======================================================================= -->
3757<div class="doc_subsection">
3758 <a name="GlobalVariable">The <tt>GlobalVariable</tt> class</a>
3759</div>
3760
3761<div class="doc_text">
3762
3763<p><tt>#include "<a
3764href="/doxygen/GlobalVariable_8h-source.html">llvm/GlobalVariable.h</a>"</tt>
3765<br>
Tanya Lattnera3da7772004-06-22 08:02:25 +0000[diff] [blame]3766doxygen info: <a href="/doxygen/classllvm_1_1GlobalVariable.html">GlobalVariable
Reid Spencerbe5e85e2006-04-14 14:11:48 +0000[diff] [blame]3767 Class</a><br>
3768Superclasses: <a href="#GlobalValue"><tt>GlobalValue</tt></a>,
3769<a href="#Constant"><tt>Constant</tt></a>,
3770<a href="#User"><tt>User</tt></a>,
3771<a href="#Value"><tt>Value</tt></a></p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3772
Benjamin Kramer8040cd32009-10-12 14:46:08 +0000[diff] [blame]3773<p>Global variables are represented with the (surprise surprise)
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3774<tt>GlobalVariable</tt> class. Like functions, <tt>GlobalVariable</tt>s are also
3775subclasses of <a href="#GlobalValue"><tt>GlobalValue</tt></a>, and as such are
3776always referenced by their address (global values must live in memory, so their
Reid Spencerbe5e85e2006-04-14 14:11:48 +0000[diff] [blame]3777"name" refers to their constant address). See
3778<a href="#GlobalValue"><tt>GlobalValue</tt></a> for more on this. Global
3779variables may have an initial value (which must be a
3780<a href="#Constant"><tt>Constant</tt></a>), and if they have an initializer,
3781they may be marked as "constant" themselves (indicating that their contents
3782never change at runtime).</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3783</div>
3784
3785<!-- _______________________________________________________________________ -->
3786<div class="doc_subsubsection">
3787 <a name="m_GlobalVariable">Important Public Members of the
3788 <tt>GlobalVariable</tt> class</a>
3789</div>
3790
3791<div class="doc_text">
3792
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3793<ul>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3794 <li><tt>GlobalVariable(const </tt><tt><a href="#Type">Type</a> *Ty, bool
3795 isConstant, LinkageTypes&amp; Linkage, <a href="#Constant">Constant</a>
3796 *Initializer = 0, const std::string &amp;Name = "", Module* Parent = 0)</tt>
3797
3798 <p>Create a new global variable of the specified type. If
3799 <tt>isConstant</tt> is true then the global variable will be marked as
3800 unchanging for the program. The Linkage parameter specifies the type of
Duncan Sands667d4b82009-03-07 15:45:40 +0000[diff] [blame]3801 linkage (internal, external, weak, linkonce, appending) for the variable.
3802 If the linkage is InternalLinkage, WeakAnyLinkage, WeakODRLinkage,
3803 LinkOnceAnyLinkage or LinkOnceODRLinkage,&nbsp; then the resultant
3804 global variable will have internal linkage. AppendingLinkage concatenates
3805 together all instances (in different translation units) of the variable
3806 into a single variable but is only applicable to arrays. &nbsp;See
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3807 the <a href="LangRef.html#modulestructure">LLVM Language Reference</a> for
3808 further details on linkage types. Optionally an initializer, a name, and the
3809 module to put the variable into may be specified for the global variable as
3810 well.</p></li>
3811
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3812 <li><tt>bool isConstant() const</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3813
3814 <p>Returns true if this is a global variable that is known not to
3815 be modified at runtime.</p></li>
3816
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3817 <li><tt>bool hasInitializer()</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3818
3819 <p>Returns true if this <tt>GlobalVariable</tt> has an intializer.</p></li>
3820
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3821 <li><tt><a href="#Constant">Constant</a> *getInitializer()</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3822
Benjamin Kramer8040cd32009-10-12 14:46:08 +0000[diff] [blame]3823 <p>Returns the initial value for a <tt>GlobalVariable</tt>. It is not legal
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3824 to call this method if there is no initializer.</p></li>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3825</ul>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3826
3827</div>
3828
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]3829
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3830<!-- ======================================================================= -->
3831<div class="doc_subsection">
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]3832 <a name="BasicBlock">The <tt>BasicBlock</tt> class</a>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3833</div>
3834
3835<div class="doc_text">
3836
3837<p><tt>#include "<a
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]3838href="/doxygen/BasicBlock_8h-source.html">llvm/BasicBlock.h</a>"</tt><br>
Stefanus Du Toit24e04112009-06-17 21:12:26 +0000[diff] [blame]3839doxygen info: <a href="/doxygen/classllvm_1_1BasicBlock.html">BasicBlock
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]3840Class</a><br>
3841Superclass: <a href="#Value"><tt>Value</tt></a></p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3842
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]3843<p>This class represents a single entry multiple exit section of the code,
3844commonly known as a basic block by the compiler community. The
3845<tt>BasicBlock</tt> class maintains a list of <a
3846href="#Instruction"><tt>Instruction</tt></a>s, which form the body of the block.
3847Matching the language definition, the last element of this list of instructions
3848is always a terminator instruction (a subclass of the <a
3849href="#TerminatorInst"><tt>TerminatorInst</tt></a> class).</p>
3850
3851<p>In addition to tracking the list of instructions that make up the block, the
3852<tt>BasicBlock</tt> class also keeps track of the <a
3853href="#Function"><tt>Function</tt></a> that it is embedded into.</p>
3854
3855<p>Note that <tt>BasicBlock</tt>s themselves are <a
3856href="#Value"><tt>Value</tt></a>s, because they are referenced by instructions
3857like branches and can go in the switch tables. <tt>BasicBlock</tt>s have type
3858<tt>label</tt>.</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3859
3860</div>
3861
3862<!-- _______________________________________________________________________ -->
3863<div class="doc_subsubsection">
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]3864 <a name="m_BasicBlock">Important Public Members of the <tt>BasicBlock</tt>
3865 class</a>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3866</div>
3867
3868<div class="doc_text">
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3869<ul>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3870
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]3871<li><tt>BasicBlock(const std::string &amp;Name = "", </tt><tt><a
3872 href="#Function">Function</a> *Parent = 0)</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3873
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]3874<p>The <tt>BasicBlock</tt> constructor is used to create new basic blocks for
3875insertion into a function. The constructor optionally takes a name for the new
3876block, and a <a href="#Function"><tt>Function</tt></a> to insert it into. If
3877the <tt>Parent</tt> parameter is specified, the new <tt>BasicBlock</tt> is
3878automatically inserted at the end of the specified <a
3879href="#Function"><tt>Function</tt></a>, if not specified, the BasicBlock must be
3880manually inserted into the <a href="#Function"><tt>Function</tt></a>.</p></li>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3881
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]3882<li><tt>BasicBlock::iterator</tt> - Typedef for instruction list iterator<br>
3883<tt>BasicBlock::const_iterator</tt> - Typedef for const_iterator.<br>
3884<tt>begin()</tt>, <tt>end()</tt>, <tt>front()</tt>, <tt>back()</tt>,
3885<tt>size()</tt>, <tt>empty()</tt>
3886STL-style functions for accessing the instruction list.
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3887
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]3888<p>These methods and typedefs are forwarding functions that have the same
3889semantics as the standard library methods of the same names. These methods
3890expose the underlying instruction list of a basic block in a way that is easy to
3891manipulate. To get the full complement of container operations (including
3892operations to update the list), you must use the <tt>getInstList()</tt>
3893method.</p></li>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3894
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]3895<li><tt>BasicBlock::InstListType &amp;getInstList()</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3896
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]3897<p>This method is used to get access to the underlying container that actually
3898holds the Instructions. This method must be used when there isn't a forwarding
3899function in the <tt>BasicBlock</tt> class for the operation that you would like
3900to perform. Because there are no forwarding functions for "updating"
3901operations, you need to use this if you want to update the contents of a
3902<tt>BasicBlock</tt>.</p></li>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3903
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]3904<li><tt><a href="#Function">Function</a> *getParent()</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3905
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]3906<p> Returns a pointer to <a href="#Function"><tt>Function</tt></a> the block is
3907embedded into, or a null pointer if it is homeless.</p></li>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3908
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]3909<li><tt><a href="#TerminatorInst">TerminatorInst</a> *getTerminator()</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3910
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]3911<p> Returns a pointer to the terminator instruction that appears at the end of
3912the <tt>BasicBlock</tt>. If there is no terminator instruction, or if the last
3913instruction in the block is not a terminator, then a null pointer is
3914returned.</p></li>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3915
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3916</ul>
3917
3918</div>
3919
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3920
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3921<!-- ======================================================================= -->
3922<div class="doc_subsection">
3923 <a name="Argument">The <tt>Argument</tt> class</a>
3924</div>
3925
3926<div class="doc_text">
3927
3928<p>This subclass of Value defines the interface for incoming formal
Chris Lattner58360822005-01-17 00:12:04 +0000[diff] [blame]3929arguments to a function. A Function maintains a list of its formal
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3930arguments. An argument has a pointer to the parent Function.</p>
3931
3932</div>
3933
Chris Lattner9355b472002-09-06 02:50:58 +0000[diff] [blame]3934<!-- *********************************************************************** -->
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3935<hr>
3936<address>
3937 <a href="http://jigsaw.w3.org/css-validator/check/referer"><img
Misha Brukman44408702008-12-11 17:34:48 +0000[diff] [blame]3938 src="http://jigsaw.w3.org/css-validator/images/vcss-blue" alt="Valid CSS"></a>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3939 <a href="http://validator.w3.org/check/referer"><img
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Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3941
3942 <a href="mailto:dhurjati@cs.uiuc.edu">Dinakar Dhurjati</a> and
3943 <a href="mailto:sabre@nondot.org">Chris Lattner</a><br>
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]3944 <a href="http://llvm.org">The LLVM Compiler Infrastructure</a><br>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3945 Last modified: $Date$
3946</address>
3947
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3948</body>
3949</html>