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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,
Chris Lattner81187ae2009-07-25 07:16:59 +0000[diff] [blame]460many LLVM APIs use a <tt>const StringRef&amp;</tt> or a <tt>const
461Twine&amp;</tt> for passing 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
Daniel Dunbar6e0d1cb2009-07-25 04:41:11 +0000[diff] [blame]480<div class="doc_code">
Chris Lattner81187ae2009-07-25 07:16:59 +0000[diff] [blame]481 iterator find(const StringRef &amp;Key);
Daniel Dunbar6e0d1cb2009-07-25 04:41:11 +0000[diff] [blame]482</div>
483
484<p>and clients can call it using any one of:</p>
485
486<div class="doc_code">
487<pre>
488 Map.find("foo"); <i>// Lookup "foo"</i>
489 Map.find(std::string("bar")); <i>// Lookup "bar"</i>
490 Map.find(StringRef("\0baz", 4)); <i>// Lookup "\0baz"</i>
491</pre>
492</div>
493
494<p>Similarly, APIs which need to return a string may return a <tt>StringRef</tt>
495instance, which can be used directly or converted to an <tt>std::string</tt>
496using the <tt>str</tt> member function. See
497"<tt><a href="/doxygen/classllvm_1_1StringRef_8h-source.html">llvm/ADT/StringRef.h</a></tt>"
498for more information.</p>
499
500<p>You should rarely use the <tt>StringRef</tt> class directly, because it contains
501pointers to external memory it is not generally safe to store an instance of the
Chris Lattner81187ae2009-07-25 07:16:59 +0000[diff] [blame]502class (unless you know that the external storage will not be freed).</p>
Daniel Dunbar6e0d1cb2009-07-25 04:41:11 +0000[diff] [blame]503
504</div>
505
506<!-- _______________________________________________________________________ -->
507<div class="doc_subsubsection">
508 <a name="Twine">The <tt>Twine</tt> class</a>
509</div>
510
511<div class="doc_text">
512
513<p>The <tt>Twine</tt> class is an efficient way for APIs to accept concatenated
514strings. For example, a common LLVM paradigm is to name one instruction based on
515the name of another instruction with a suffix, for example:</p>
516
517<div class="doc_code">
518<pre>
519 New = CmpInst::Create(<i>...</i>, SO->getName() + ".cmp");
520</pre>
521</div>
522
523<p>The <tt>Twine</tt> class is effectively a
524lightweight <a href="http://en.wikipedia.org/wiki/Rope_(computer_science)">rope</a>
525which points to temporary (stack allocated) objects. Twines can be implicitly
526constructed as the result of the plus operator applied to strings (i.e., a C
527strings, an <tt>std::string</tt>, or a <tt>StringRef</tt>). The twine delays the
Dan Gohmancf0c9bc2010-02-25 23:51:27 +0000[diff] [blame]528actual concatenation of strings until it is actually required, at which point
Daniel Dunbar6e0d1cb2009-07-25 04:41:11 +0000[diff] [blame]529it can be efficiently rendered directly into a character array. This avoids
530unnecessary heap allocation involved in constructing the temporary results of
531string concatenation. See
532"<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]533for more information.</p>
Daniel Dunbar6e0d1cb2009-07-25 04:41:11 +0000[diff] [blame]534
535<p>As with a <tt>StringRef</tt>, <tt>Twine</tt> objects point to external memory
536and should almost never be stored or mentioned directly. They are intended
537solely for use when defining a function which should be able to efficiently
538accept concatenated strings.</p>
539
540</div>
541
542
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]543<!-- ======================================================================= -->
544<div class="doc_subsection">
Misha Brukman2c122ce2005-11-01 21:12:49 +0000[diff] [blame]545 <a name="DEBUG">The <tt>DEBUG()</tt> macro and <tt>-debug</tt> option</a>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]546</div>
547
548<div class="doc_text">
549
550<p>Often when working on your pass you will put a bunch of debugging printouts
551and other code into your pass. After you get it working, you want to remove
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]552it, 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]553across).</p>
554
555<p> Naturally, because of this, you don't want to delete the debug printouts,
556but you don't want them to always be noisy. A standard compromise is to comment
557them out, allowing you to enable them if you need them in the future.</p>
558
Chris Lattner695b78b2005-04-26 22:56:16 +0000[diff] [blame]559<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]560file provides a macro named <tt>DEBUG()</tt> that is a much nicer solution to
561this problem. Basically, you can put arbitrary code into the argument of the
562<tt>DEBUG</tt> macro, and it is only executed if '<tt>opt</tt>' (or any other
563tool) is run with the '<tt>-debug</tt>' command line argument:</p>
564
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]565<div class="doc_code">
566<pre>
Daniel Dunbar06388ae2009-07-25 01:55:32 +0000[diff] [blame]567DEBUG(errs() &lt;&lt; "I am here!\n");
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]568</pre>
569</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]570
571<p>Then you can run your pass like this:</p>
572
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]573<div class="doc_code">
574<pre>
575$ opt &lt; a.bc &gt; /dev/null -mypass
Bill Wendling82e2eea2006-10-11 18:00:22 +0000[diff] [blame]576<i>&lt;no output&gt;</i>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]577$ opt &lt; a.bc &gt; /dev/null -mypass -debug
578I am here!
579</pre>
580</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]581
582<p>Using the <tt>DEBUG()</tt> macro instead of a home-brewed solution allows you
583to not have to create "yet another" command line option for the debug output for
584your pass. Note that <tt>DEBUG()</tt> macros are disabled for optimized builds,
585so they do not cause a performance impact at all (for the same reason, they
586should also not contain side-effects!).</p>
587
588<p>One additional nice thing about the <tt>DEBUG()</tt> macro is that you can
589enable or disable it directly in gdb. Just use "<tt>set DebugFlag=0</tt>" or
590"<tt>set DebugFlag=1</tt>" from the gdb if the program is running. If the
591program hasn't been started yet, you can always just run it with
592<tt>-debug</tt>.</p>
593
594</div>
595
596<!-- _______________________________________________________________________ -->
597<div class="doc_subsubsection">
Chris Lattnerc9151082005-04-26 22:57:07 +0000[diff] [blame]598 <a name="DEBUG_TYPE">Fine grained debug info with <tt>DEBUG_TYPE</tt> and
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]599 the <tt>-debug-only</tt> option</a>
600</div>
601
602<div class="doc_text">
603
604<p>Sometimes you may find yourself in a situation where enabling <tt>-debug</tt>
605just turns on <b>too much</b> information (such as when working on the code
606generator). If you want to enable debug information with more fine-grained
607control, you define the <tt>DEBUG_TYPE</tt> macro and the <tt>-debug</tt> only
608option as follows:</p>
609
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]610<div class="doc_code">
611<pre>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]612#undef DEBUG_TYPE
Daniel Dunbar06388ae2009-07-25 01:55:32 +0000[diff] [blame]613DEBUG(errs() &lt;&lt; "No debug type\n");
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]614#define DEBUG_TYPE "foo"
Daniel Dunbar06388ae2009-07-25 01:55:32 +0000[diff] [blame]615DEBUG(errs() &lt;&lt; "'foo' debug type\n");
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]616#undef DEBUG_TYPE
617#define DEBUG_TYPE "bar"
Daniel Dunbar06388ae2009-07-25 01:55:32 +0000[diff] [blame]618DEBUG(errs() &lt;&lt; "'bar' debug type\n"));
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]619#undef DEBUG_TYPE
620#define DEBUG_TYPE ""
Daniel Dunbar06388ae2009-07-25 01:55:32 +0000[diff] [blame]621DEBUG(errs() &lt;&lt; "No debug type (2)\n");
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]622</pre>
623</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]624
625<p>Then you can run your pass like this:</p>
626
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]627<div class="doc_code">
628<pre>
629$ opt &lt; a.bc &gt; /dev/null -mypass
Bill Wendling82e2eea2006-10-11 18:00:22 +0000[diff] [blame]630<i>&lt;no output&gt;</i>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]631$ opt &lt; a.bc &gt; /dev/null -mypass -debug
632No debug type
633'foo' debug type
634'bar' debug type
635No debug type (2)
636$ opt &lt; a.bc &gt; /dev/null -mypass -debug-only=foo
637'foo' debug type
638$ opt &lt; a.bc &gt; /dev/null -mypass -debug-only=bar
639'bar' debug type
640</pre>
641</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]642
643<p>Of course, in practice, you should only set <tt>DEBUG_TYPE</tt> at the top of
644a 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]645you <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]646<tt>#undef</tt>'s). Also, you should use names more meaningful than "foo" and
647"bar", because there is no system in place to ensure that names do not
648conflict. If two different modules use the same string, they will all be turned
649on when the name is specified. This allows, for example, all debug information
650for instruction scheduling to be enabled with <tt>-debug-type=InstrSched</tt>,
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]651even if the source lives in multiple files.</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]652
Daniel Dunbarc3c92392009-08-07 23:48:59 +0000[diff] [blame]653<p>The <tt>DEBUG_WITH_TYPE</tt> macro is also available for situations where you
654would like to set <tt>DEBUG_TYPE</tt>, but only for one specific <tt>DEBUG</tt>
655statement. It takes an additional first parameter, which is the type to use. For
Benjamin Kramer8040cd32009-10-12 14:46:08 +0000[diff] [blame]656example, the preceding example could be written as:</p>
Daniel Dunbarc3c92392009-08-07 23:48:59 +0000[diff] [blame]657
658
659<div class="doc_code">
660<pre>
661DEBUG_WITH_TYPE("", errs() &lt;&lt; "No debug type\n");
662DEBUG_WITH_TYPE("foo", errs() &lt;&lt; "'foo' debug type\n");
663DEBUG_WITH_TYPE("bar", errs() &lt;&lt; "'bar' debug type\n"));
664DEBUG_WITH_TYPE("", errs() &lt;&lt; "No debug type (2)\n");
665</pre>
666</div>
667
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]668</div>
669
670<!-- ======================================================================= -->
671<div class="doc_subsection">
Chris Lattner0be6fdf2006-12-19 21:46:21 +0000[diff] [blame]672 <a name="Statistic">The <tt>Statistic</tt> class &amp; <tt>-stats</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]673 option</a>
674</div>
675
676<div class="doc_text">
677
678<p>The "<tt><a
Chris Lattner695b78b2005-04-26 22:56:16 +0000[diff] [blame]679href="/doxygen/Statistic_8h-source.html">llvm/ADT/Statistic.h</a></tt>" file
Chris Lattner0be6fdf2006-12-19 21:46:21 +0000[diff] [blame]680provides a class named <tt>Statistic</tt> that is used as a unified way to
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]681keep track of what the LLVM compiler is doing and how effective various
682optimizations are. It is useful to see what optimizations are contributing to
683making a particular program run faster.</p>
684
685<p>Often you may run your pass on some big program, and you're interested to see
686how many times it makes a certain transformation. Although you can do this with
687hand 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]688for big programs. Using the <tt>Statistic</tt> class makes it very easy to
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]689keep track of this information, and the calculated information is presented in a
690uniform manner with the rest of the passes being executed.</p>
691
692<p>There are many examples of <tt>Statistic</tt> uses, but the basics of using
693it are as follows:</p>
694
695<ol>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]696 <li><p>Define your statistic like this:</p>
697
698<div class="doc_code">
699<pre>
Chris Lattner0be6fdf2006-12-19 21:46:21 +0000[diff] [blame]700#define <a href="#DEBUG_TYPE">DEBUG_TYPE</a> "mypassname" <i>// This goes before any #includes.</i>
701STATISTIC(NumXForms, "The # of times I did stuff");
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]702</pre>
703</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]704
Chris Lattner0be6fdf2006-12-19 21:46:21 +0000[diff] [blame]705 <p>The <tt>STATISTIC</tt> macro defines a static variable, whose name is
706 specified by the first argument. The pass name is taken from the DEBUG_TYPE
707 macro, and the description is taken from the second argument. The variable
Reid Spencer06565dc2007-01-12 17:11:23 +0000[diff] [blame]708 defined ("NumXForms" in this case) acts like an unsigned integer.</p></li>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]709
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]710 <li><p>Whenever you make a transformation, bump the counter:</p>
711
712<div class="doc_code">
713<pre>
Bill Wendling82e2eea2006-10-11 18:00:22 +0000[diff] [blame]714++NumXForms; // <i>I did stuff!</i>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]715</pre>
716</div>
717
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]718 </li>
719 </ol>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]720
721 <p>That's all you have to do. To get '<tt>opt</tt>' to print out the
722 statistics gathered, use the '<tt>-stats</tt>' option:</p>
723
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]724<div class="doc_code">
725<pre>
726$ opt -stats -mypassname &lt; program.bc &gt; /dev/null
Bill Wendling82e2eea2006-10-11 18:00:22 +0000[diff] [blame]727<i>... statistics output ...</i>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]728</pre>
729</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]730
Reid Spencer6b6c73e2007-02-09 16:00:28 +0000[diff] [blame]731 <p> When running <tt>opt</tt> on a C file from the SPEC benchmark
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]732suite, it gives a report that looks like this:</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]733
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]734<div class="doc_code">
735<pre>
Gabor Greif04367bf2007-07-06 22:07:22 +0000[diff] [blame]736 7646 bitcodewriter - Number of normal instructions
737 725 bitcodewriter - Number of oversized instructions
738 129996 bitcodewriter - Number of bitcode bytes written
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]739 2817 raise - Number of insts DCEd or constprop'd
740 3213 raise - Number of cast-of-self removed
741 5046 raise - Number of expression trees converted
742 75 raise - Number of other getelementptr's formed
743 138 raise - Number of load/store peepholes
744 42 deadtypeelim - Number of unused typenames removed from symtab
745 392 funcresolve - Number of varargs functions resolved
746 27 globaldce - Number of global variables removed
747 2 adce - Number of basic blocks removed
748 134 cee - Number of branches revectored
749 49 cee - Number of setcc instruction eliminated
750 532 gcse - Number of loads removed
751 2919 gcse - Number of instructions removed
752 86 indvars - Number of canonical indvars added
753 87 indvars - Number of aux indvars removed
754 25 instcombine - Number of dead inst eliminate
755 434 instcombine - Number of insts combined
756 248 licm - Number of load insts hoisted
757 1298 licm - Number of insts hoisted to a loop pre-header
758 3 licm - Number of insts hoisted to multiple loop preds (bad, no loop pre-header)
759 75 mem2reg - Number of alloca's promoted
760 1444 cfgsimplify - Number of blocks simplified
761</pre>
762</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]763
764<p>Obviously, with so many optimizations, having a unified framework for this
765stuff is very nice. Making your pass fit well into the framework makes it more
766maintainable and useful.</p>
767
768</div>
769
Chris Lattnerf623a082005-10-17 01:36:23 +0000[diff] [blame]770<!-- ======================================================================= -->
771<div class="doc_subsection">
772 <a name="ViewGraph">Viewing graphs while debugging code</a>
773</div>
774
775<div class="doc_text">
776
777<p>Several of the important data structures in LLVM are graphs: for example
778CFGs made out of LLVM <a href="#BasicBlock">BasicBlock</a>s, CFGs made out of
779LLVM <a href="CodeGenerator.html#machinebasicblock">MachineBasicBlock</a>s, and
780<a href="CodeGenerator.html#selectiondag_intro">Instruction Selection
781DAGs</a>. In many cases, while debugging various parts of the compiler, it is
782nice to instantly visualize these graphs.</p>
783
784<p>LLVM provides several callbacks that are available in a debug build to do
785exactly that. If you call the <tt>Function::viewCFG()</tt> method, for example,
786the current LLVM tool will pop up a window containing the CFG for the function
787where each basic block is a node in the graph, and each node contains the
788instructions in the block. Similarly, there also exists
789<tt>Function::viewCFGOnly()</tt> (does not include the instructions), the
790<tt>MachineFunction::viewCFG()</tt> and <tt>MachineFunction::viewCFGOnly()</tt>,
791and the <tt>SelectionDAG::viewGraph()</tt> methods. Within GDB, for example,
Jim Laskey543a0ee2006-10-02 12:28:07 +0000[diff] [blame]792you can usually use something like <tt>call DAG.viewGraph()</tt> to pop
Chris Lattnerf623a082005-10-17 01:36:23 +0000[diff] [blame]793up a window. Alternatively, you can sprinkle calls to these functions in your
794code in places you want to debug.</p>
795
796<p>Getting this to work requires a small amount of configuration. On Unix
797systems with X11, install the <a href="http://www.graphviz.org">graphviz</a>
798toolkit, and make sure 'dot' and 'gv' are in your path. If you are running on
799Mac OS/X, download and install the Mac OS/X <a
800href="http://www.pixelglow.com/graphviz/">Graphviz program</a>, and add
Reid Spencer128a7a72007-02-03 21:06:43 +0000[diff] [blame]801<tt>/Applications/Graphviz.app/Contents/MacOS/</tt> (or wherever you install
Chris Lattnerf623a082005-10-17 01:36:23 +0000[diff] [blame]802it) to your path. Once in your system and path are set up, rerun the LLVM
803configure script and rebuild LLVM to enable this functionality.</p>
804
Jim Laskey543a0ee2006-10-02 12:28:07 +0000[diff] [blame]805<p><tt>SelectionDAG</tt> has been extended to make it easier to locate
806<i>interesting</i> nodes in large complex graphs. From gdb, if you
807<tt>call DAG.setGraphColor(<i>node</i>, "<i>color</i>")</tt>, then the
Reid Spencer128a7a72007-02-03 21:06:43 +0000[diff] [blame]808next <tt>call DAG.viewGraph()</tt> would highlight the node in the
Jim Laskey543a0ee2006-10-02 12:28:07 +0000[diff] [blame]809specified color (choices of colors can be found at <a
Chris Lattner302da1e2007-02-03 03:05:57 +0000[diff] [blame]810href="http://www.graphviz.org/doc/info/colors.html">colors</a>.) More
Jim Laskey543a0ee2006-10-02 12:28:07 +0000[diff] [blame]811complex node attributes can be provided with <tt>call
812DAG.setGraphAttrs(<i>node</i>, "<i>attributes</i>")</tt> (choices can be
813found at <a href="http://www.graphviz.org/doc/info/attrs.html">Graph
814Attributes</a>.) If you want to restart and clear all the current graph
815attributes, then you can <tt>call DAG.clearGraphAttrs()</tt>. </p>
816
Chris Lattnerf623a082005-10-17 01:36:23 +0000[diff] [blame]817</div>
818
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]819<!-- *********************************************************************** -->
820<div class="doc_section">
821 <a name="datastructure">Picking the Right Data Structure for a Task</a>
822</div>
823<!-- *********************************************************************** -->
824
825<div class="doc_text">
826
Reid Spencer128a7a72007-02-03 21:06:43 +0000[diff] [blame]827<p>LLVM has a plethora of data structures in the <tt>llvm/ADT/</tt> directory,
828 and we commonly use STL data structures. This section describes the trade-offs
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]829 you should consider when you pick one.</p>
830
831<p>
832The first step is a choose your own adventure: do you want a sequential
833container, a set-like container, or a map-like container? The most important
834thing when choosing a container is the algorithmic properties of how you plan to
835access the container. Based on that, you should use:</p>
836
837<ul>
Reid Spencer128a7a72007-02-03 21:06:43 +0000[diff] [blame]838<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]839 of an value based on another value. Map-like containers also support
840 efficient queries for containment (whether a key is in the map). Map-like
841 containers generally do not support efficient reverse mapping (values to
842 keys). If you need that, use two maps. Some map-like containers also
843 support efficient iteration through the keys in sorted order. Map-like
844 containers are the most expensive sort, only use them if you need one of
845 these capabilities.</li>
846
847<li>a <a href="#ds_set">set-like</a> container if you need to put a bunch of
848 stuff into a container that automatically eliminates duplicates. Some
849 set-like containers support efficient iteration through the elements in
850 sorted order. Set-like containers are more expensive than sequential
851 containers.
852</li>
853
854<li>a <a href="#ds_sequential">sequential</a> container provides
855 the most efficient way to add elements and keeps track of the order they are
856 added to the collection. They permit duplicates and support efficient
Reid Spencer128a7a72007-02-03 21:06:43 +0000[diff] [blame]857 iteration, but do not support efficient look-up based on a key.
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]858</li>
859
Chris Lattnerdced9fb2009-07-25 07:22:20 +0000[diff] [blame]860<li>a <a href="#ds_string">string</a> container is a specialized sequential
861 container or reference structure that is used for character or byte
862 arrays.</li>
863
Daniel Berlin1939ace2007-09-24 17:52:25 +0000[diff] [blame]864<li>a <a href="#ds_bit">bit</a> container provides an efficient way to store and
865 perform set operations on sets of numeric id's, while automatically
866 eliminating duplicates. Bit containers require a maximum of 1 bit for each
867 identifier you want to store.
868</li>
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]869</ul>
870
871<p>
Reid Spencer128a7a72007-02-03 21:06:43 +0000[diff] [blame]872Once the proper category of container is determined, you can fine tune the
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]873memory use, constant factors, and cache behaviors of access by intelligently
Reid Spencer128a7a72007-02-03 21:06:43 +0000[diff] [blame]874picking a member of the category. Note that constant factors and cache behavior
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]875can be a big deal. If you have a vector that usually only contains a few
876elements (but could contain many), for example, it's much better to use
877<a href="#dss_smallvector">SmallVector</a> than <a href="#dss_vector">vector</a>
878. Doing so avoids (relatively) expensive malloc/free calls, which dwarf the
879cost of adding the elements to the container. </p>
880
881</div>
882
883<!-- ======================================================================= -->
884<div class="doc_subsection">
885 <a name="ds_sequential">Sequential Containers (std::vector, std::list, etc)</a>
886</div>
887
888<div class="doc_text">
889There are a variety of sequential containers available for you, based on your
890needs. Pick the first in this section that will do what you want.
891</div>
892
893<!-- _______________________________________________________________________ -->
894<div class="doc_subsubsection">
895 <a name="dss_fixedarrays">Fixed Size Arrays</a>
896</div>
897
898<div class="doc_text">
899<p>Fixed size arrays are very simple and very fast. They are good if you know
900exactly how many elements you have, or you have a (low) upper bound on how many
901you have.</p>
902</div>
903
904<!-- _______________________________________________________________________ -->
905<div class="doc_subsubsection">
906 <a name="dss_heaparrays">Heap Allocated Arrays</a>
907</div>
908
909<div class="doc_text">
910<p>Heap allocated arrays (new[] + delete[]) are also simple. They are good if
911the number of elements is variable, if you know how many elements you will need
912before the array is allocated, and if the array is usually large (if not,
913consider a <a href="#dss_smallvector">SmallVector</a>). The cost of a heap
914allocated array is the cost of the new/delete (aka malloc/free). Also note that
915if you are allocating an array of a type with a constructor, the constructor and
Reid Spencer128a7a72007-02-03 21:06:43 +0000[diff] [blame]916destructors will be run for every element in the array (re-sizable vectors only
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]917construct those elements actually used).</p>
918</div>
919
920<!-- _______________________________________________________________________ -->
921<div class="doc_subsubsection">
922 <a name="dss_smallvector">"llvm/ADT/SmallVector.h"</a>
923</div>
924
925<div class="doc_text">
926<p><tt>SmallVector&lt;Type, N&gt;</tt> is a simple class that looks and smells
927just like <tt>vector&lt;Type&gt;</tt>:
928it supports efficient iteration, lays out elements in memory order (so you can
929do pointer arithmetic between elements), supports efficient push_back/pop_back
930operations, supports efficient random access to its elements, etc.</p>
931
932<p>The advantage of SmallVector is that it allocates space for
933some number of elements (N) <b>in the object itself</b>. Because of this, if
934the SmallVector is dynamically smaller than N, no malloc is performed. This can
935be a big win in cases where the malloc/free call is far more expensive than the
936code that fiddles around with the elements.</p>
937
938<p>This is good for vectors that are "usually small" (e.g. the number of
939predecessors/successors of a block is usually less than 8). On the other hand,
940this makes the size of the SmallVector itself large, so you don't want to
941allocate lots of them (doing so will waste a lot of space). As such,
942SmallVectors are most useful when on the stack.</p>
943
944<p>SmallVector also provides a nice portable and efficient replacement for
945<tt>alloca</tt>.</p>
946
947</div>
948
949<!-- _______________________________________________________________________ -->
950<div class="doc_subsubsection">
951 <a name="dss_vector">&lt;vector&gt;</a>
952</div>
953
954<div class="doc_text">
955<p>
956std::vector is well loved and respected. It is useful when SmallVector isn't:
957when the size of the vector is often large (thus the small optimization will
958rarely be a benefit) or if you will be allocating many instances of the vector
959itself (which would waste space for elements that aren't in the container).
960vector is also useful when interfacing with code that expects vectors :).
961</p>
Chris Lattner32d84762007-02-05 06:30:51 +0000[diff] [blame]962
963<p>One worthwhile note about std::vector: avoid code like this:</p>
964
965<div class="doc_code">
966<pre>
967for ( ... ) {
Chris Lattner9bb3dbb2007-03-28 18:27:57 +0000[diff] [blame]968 std::vector&lt;foo&gt; V;
Chris Lattner32d84762007-02-05 06:30:51 +0000[diff] [blame]969 use V;
970}
971</pre>
972</div>
973
974<p>Instead, write this as:</p>
975
976<div class="doc_code">
977<pre>
Chris Lattner9bb3dbb2007-03-28 18:27:57 +0000[diff] [blame]978std::vector&lt;foo&gt; V;
Chris Lattner32d84762007-02-05 06:30:51 +0000[diff] [blame]979for ( ... ) {
980 use V;
981 V.clear();
982}
983</pre>
984</div>
985
986<p>Doing so will save (at least) one heap allocation and free per iteration of
987the loop.</p>
988
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]989</div>
990
991<!-- _______________________________________________________________________ -->
992<div class="doc_subsubsection">
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]993 <a name="dss_deque">&lt;deque&gt;</a>
994</div>
995
996<div class="doc_text">
997<p>std::deque is, in some senses, a generalized version of std::vector. Like
998std::vector, it provides constant time random access and other similar
999properties, but it also provides efficient access to the front of the list. It
1000does not guarantee continuity of elements within memory.</p>
1001
1002<p>In exchange for this extra flexibility, std::deque has significantly higher
1003constant factor costs than std::vector. If possible, use std::vector or
1004something cheaper.</p>
1005</div>
1006
1007<!-- _______________________________________________________________________ -->
1008<div class="doc_subsubsection">
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]1009 <a name="dss_list">&lt;list&gt;</a>
1010</div>
1011
1012<div class="doc_text">
1013<p>std::list is an extremely inefficient class that is rarely useful.
1014It performs a heap allocation for every element inserted into it, thus having an
1015extremely high constant factor, particularly for small data types. std::list
1016also only supports bidirectional iteration, not random access iteration.</p>
1017
1018<p>In exchange for this high cost, std::list supports efficient access to both
1019ends of the list (like std::deque, but unlike std::vector or SmallVector). In
1020addition, the iterator invalidation characteristics of std::list are stronger
1021than that of a vector class: inserting or removing an element into the list does
1022not invalidate iterator or pointers to other elements in the list.</p>
1023</div>
1024
1025<!-- _______________________________________________________________________ -->
1026<div class="doc_subsubsection">
Gabor Greif3899e492009-02-27 11:37:41 +0000[diff] [blame]1027 <a name="dss_ilist">llvm/ADT/ilist.h</a>
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]1028</div>
1029
1030<div class="doc_text">
1031<p><tt>ilist&lt;T&gt;</tt> implements an 'intrusive' doubly-linked list. It is
1032intrusive, because it requires the element to store and provide access to the
1033prev/next pointers for the list.</p>
1034
Gabor Greif2946d1c2009-02-27 12:02:19 +0000[diff] [blame]1035<p><tt>ilist</tt> has the same drawbacks as <tt>std::list</tt>, and additionally
1036requires an <tt>ilist_traits</tt> implementation for the element type, but it
1037provides some novel characteristics. In particular, it can efficiently store
1038polymorphic objects, the traits class is informed when an element is inserted or
Gabor Greif0cbcabe2009-03-12 09:47:03 +0000[diff] [blame]1039removed from the list, and <tt>ilist</tt>s are guaranteed to support a
1040constant-time splice operation.</p>
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]1041
Gabor Greif0cbcabe2009-03-12 09:47:03 +0000[diff] [blame]1042<p>These properties are exactly what we want for things like
1043<tt>Instruction</tt>s and basic blocks, which is why these are implemented with
1044<tt>ilist</tt>s.</p>
Gabor Greif3899e492009-02-27 11:37:41 +0000[diff] [blame]1045
1046Related classes of interest are explained in the following subsections:
1047 <ul>
Gabor Greif01862502009-02-27 13:28:07 +0000[diff] [blame]1048 <li><a href="#dss_ilist_traits">ilist_traits</a></li>
Gabor Greif2946d1c2009-02-27 12:02:19 +0000[diff] [blame]1049 <li><a href="#dss_iplist">iplist</a></li>
Gabor Greif3899e492009-02-27 11:37:41 +0000[diff] [blame]1050 <li><a href="#dss_ilist_node">llvm/ADT/ilist_node.h</a></li>
Gabor Greif6a65f422009-03-12 10:30:31 +0000[diff] [blame]1051 <li><a href="#dss_ilist_sentinel">Sentinels</a></li>
Gabor Greif3899e492009-02-27 11:37:41 +0000[diff] [blame]1052 </ul>
1053</div>
1054
1055<!-- _______________________________________________________________________ -->
1056<div class="doc_subsubsection">
Gabor Greif01862502009-02-27 13:28:07 +0000[diff] [blame]1057 <a name="dss_ilist_traits">ilist_traits</a>
1058</div>
1059
1060<div class="doc_text">
1061<p><tt>ilist_traits&lt;T&gt;</tt> is <tt>ilist&lt;T&gt;</tt>'s customization
1062mechanism. <tt>iplist&lt;T&gt;</tt> (and consequently <tt>ilist&lt;T&gt;</tt>)
1063publicly derive from this traits class.</p>
1064</div>
1065
1066<!-- _______________________________________________________________________ -->
1067<div class="doc_subsubsection">
Gabor Greif2946d1c2009-02-27 12:02:19 +0000[diff] [blame]1068 <a name="dss_iplist">iplist</a>
1069</div>
1070
1071<div class="doc_text">
1072<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]1073supports a slightly narrower interface. Notably, inserters from
1074<tt>T&amp;</tt> are absent.</p>
Gabor Greif01862502009-02-27 13:28:07 +0000[diff] [blame]1075
1076<p><tt>ilist_traits&lt;T&gt;</tt> is a public base of this class and can be
1077used for a wide variety of customizations.</p>
Gabor Greif2946d1c2009-02-27 12:02:19 +0000[diff] [blame]1078</div>
1079
1080<!-- _______________________________________________________________________ -->
1081<div class="doc_subsubsection">
Gabor Greif3899e492009-02-27 11:37:41 +0000[diff] [blame]1082 <a name="dss_ilist_node">llvm/ADT/ilist_node.h</a>
1083</div>
1084
1085<div class="doc_text">
1086<p><tt>ilist_node&lt;T&gt;</tt> implements a the forward and backward links
1087that are expected by the <tt>ilist&lt;T&gt;</tt> (and analogous containers)
1088in the default manner.</p>
1089
1090<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]1091<tt>T</tt>, usually <tt>T</tt> publicly derives from
1092<tt>ilist_node&lt;T&gt;</tt>.</p>
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]1093</div>
1094
1095<!-- _______________________________________________________________________ -->
1096<div class="doc_subsubsection">
Gabor Greif6a65f422009-03-12 10:30:31 +0000[diff] [blame]1097 <a name="dss_ilist_sentinel">Sentinels</a>
1098</div>
1099
1100<div class="doc_text">
Dan Gohmancf0c9bc2010-02-25 23:51:27 +0000[diff] [blame]1101<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]1102citizen in the C++ ecosystem, it needs to support the standard container
1103operations, such as <tt>begin</tt> and <tt>end</tt> iterators, etc. Also, the
1104<tt>operator--</tt> must work correctly on the <tt>end</tt> iterator in the
1105case of non-empty <tt>ilist</tt>s.</p>
1106
1107<p>The only sensible solution to this problem is to allocate a so-called
1108<i>sentinel</i> along with the intrusive list, which serves as the <tt>end</tt>
1109iterator, providing the back-link to the last element. However conforming to the
1110C++ convention it is illegal to <tt>operator++</tt> beyond the sentinel and it
1111also must not be dereferenced.</p>
1112
1113<p>These constraints allow for some implementation freedom to the <tt>ilist</tt>
1114how to allocate and store the sentinel. The corresponding policy is dictated
1115by <tt>ilist_traits&lt;T&gt;</tt>. By default a <tt>T</tt> gets heap-allocated
1116whenever the need for a sentinel arises.</p>
1117
1118<p>While the default policy is sufficient in most cases, it may break down when
1119<tt>T</tt> does not provide a default constructor. Also, in the case of many
1120instances of <tt>ilist</tt>s, the memory overhead of the associated sentinels
1121is wasted. To alleviate the situation with numerous and voluminous
1122<tt>T</tt>-sentinels, sometimes a trick is employed, leading to <i>ghostly
1123sentinels</i>.</p>
1124
1125<p>Ghostly sentinels are obtained by specially-crafted <tt>ilist_traits&lt;T&gt;</tt>
1126which superpose the sentinel with the <tt>ilist</tt> instance in memory. Pointer
1127arithmetic is used to obtain the sentinel, which is relative to the
1128<tt>ilist</tt>'s <tt>this</tt> pointer. The <tt>ilist</tt> is augmented by an
1129extra pointer, which serves as the back-link of the sentinel. This is the only
1130field in the ghostly sentinel which can be legally accessed.</p>
1131</div>
1132
1133<!-- _______________________________________________________________________ -->
1134<div class="doc_subsubsection">
Chris Lattnerc5722432007-02-03 19:49:31 +0000[diff] [blame]1135 <a name="dss_other">Other Sequential Container options</a>
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]1136</div>
1137
1138<div class="doc_text">
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1139<p>Other STL containers are available, such as std::string.</p>
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]1140
1141<p>There are also various STL adapter classes such as std::queue,
1142std::priority_queue, std::stack, etc. These provide simplified access to an
1143underlying container but don't affect the cost of the container itself.</p>
1144
1145</div>
1146
1147
1148<!-- ======================================================================= -->
1149<div class="doc_subsection">
1150 <a name="ds_set">Set-Like Containers (std::set, SmallSet, SetVector, etc)</a>
1151</div>
1152
1153<div class="doc_text">
1154
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1155<p>Set-like containers are useful when you need to canonicalize multiple values
1156into a single representation. There are several different choices for how to do
1157this, providing various trade-offs.</p>
1158
1159</div>
1160
1161
1162<!-- _______________________________________________________________________ -->
1163<div class="doc_subsubsection">
1164 <a name="dss_sortedvectorset">A sorted 'vector'</a>
1165</div>
1166
1167<div class="doc_text">
1168
Chris Lattner3b23a8c2007-02-03 08:10:45 +0000[diff] [blame]1169<p>If you intend to insert a lot of elements, then do a lot of queries, a
1170great approach is to use a vector (or other sequential container) with
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1171std::sort+std::unique to remove duplicates. This approach works really well if
Chris Lattner3b23a8c2007-02-03 08:10:45 +0000[diff] [blame]1172your usage pattern has these two distinct phases (insert then query), and can be
1173coupled with a good choice of <a href="#ds_sequential">sequential container</a>.
1174</p>
1175
1176<p>
1177This combination provides the several nice properties: the result data is
1178contiguous in memory (good for cache locality), has few allocations, is easy to
1179address (iterators in the final vector are just indices or pointers), and can be
1180efficiently queried with a standard binary or radix search.</p>
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1181
1182</div>
1183
1184<!-- _______________________________________________________________________ -->
1185<div class="doc_subsubsection">
1186 <a name="dss_smallset">"llvm/ADT/SmallSet.h"</a>
1187</div>
1188
1189<div class="doc_text">
1190
Reid Spencer128a7a72007-02-03 21:06:43 +0000[diff] [blame]1191<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]1192are 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]1193has space for N elements in place (thus, if the set is dynamically smaller than
Chris Lattner14868db2007-02-03 08:20:15 +0000[diff] [blame]1194N, no malloc traffic is required) and accesses them with a simple linear search.
1195When the set grows beyond 'N' elements, it allocates a more expensive representation that
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1196guarantees efficient access (for most types, it falls back to std::set, but for
Chris Lattner14868db2007-02-03 08:20:15 +0000[diff] [blame]1197pointers it uses something far better, <a
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1198href="#dss_smallptrset">SmallPtrSet</a>).</p>
1199
1200<p>The magic of this class is that it handles small sets extremely efficiently,
1201but gracefully handles extremely large sets without loss of efficiency. The
1202drawback is that the interface is quite small: it supports insertion, queries
1203and erasing, but does not support iteration.</p>
1204
1205</div>
1206
1207<!-- _______________________________________________________________________ -->
1208<div class="doc_subsubsection">
1209 <a name="dss_smallptrset">"llvm/ADT/SmallPtrSet.h"</a>
1210</div>
1211
1212<div class="doc_text">
1213
Gabor Greif4de73682010-03-26 19:30:47 +0000[diff] [blame]1214<p>SmallPtrSet has all the advantages of <tt>SmallSet</tt> (and a <tt>SmallSet</tt> of pointers is
1215transparently implemented with a <tt>SmallPtrSet</tt>), but also supports iterators. If
Chris Lattner14868db2007-02-03 08:20:15 +0000[diff] [blame]1216more than 'N' insertions are performed, a single quadratically
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1217probed hash table is allocated and grows as needed, providing extremely
1218efficient access (constant time insertion/deleting/queries with low constant
1219factors) and is very stingy with malloc traffic.</p>
1220
Gabor Greif4de73682010-03-26 19:30:47 +0000[diff] [blame]1221<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]1222whenever an insertion occurs. Also, the values visited by the iterators are not
1223visited in sorted order.</p>
1224
1225</div>
1226
1227<!-- _______________________________________________________________________ -->
1228<div class="doc_subsubsection">
Chris Lattnerc28476f2007-09-30 00:58:59 +0000[diff] [blame]1229 <a name="dss_denseset">"llvm/ADT/DenseSet.h"</a>
1230</div>
1231
1232<div class="doc_text">
1233
1234<p>
1235DenseSet is a simple quadratically probed hash table. It excels at supporting
1236small values: it uses a single allocation to hold all of the pairs that
1237are currently inserted in the set. DenseSet is a great way to unique small
1238values that are not simple pointers (use <a
1239href="#dss_smallptrset">SmallPtrSet</a> for pointers). Note that DenseSet has
1240the same requirements for the value type that <a
1241href="#dss_densemap">DenseMap</a> has.
1242</p>
1243
1244</div>
1245
1246<!-- _______________________________________________________________________ -->
1247<div class="doc_subsubsection">
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1248 <a name="dss_FoldingSet">"llvm/ADT/FoldingSet.h"</a>
1249</div>
1250
1251<div class="doc_text">
1252
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]1253<p>
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1254FoldingSet is an aggregate class that is really good at uniquing
1255expensive-to-create or polymorphic objects. It is a combination of a chained
1256hash table with intrusive links (uniqued objects are required to inherit from
Chris Lattner14868db2007-02-03 08:20:15 +0000[diff] [blame]1257FoldingSetNode) that uses <a href="#dss_smallvector">SmallVector</a> as part of
1258its ID process.</p>
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1259
Chris Lattner14868db2007-02-03 08:20:15 +0000[diff] [blame]1260<p>Consider a case where you want to implement a "getOrCreateFoo" method for
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1261a complex object (for example, a node in the code generator). The client has a
1262description of *what* it wants to generate (it knows the opcode and all the
1263operands), 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]1264only to find out it already exists, at which point we would have to delete it
1265and return the node that already exists.
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]1266</p>
1267
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1268<p>To support this style of client, FoldingSet perform a query with a
1269FoldingSetNodeID (which wraps SmallVector) that can be used to describe the
1270element that we want to query for. The query either returns the element
1271matching the ID or it returns an opaque ID that indicates where insertion should
Chris Lattner14868db2007-02-03 08:20:15 +0000[diff] [blame]1272take place. Construction of the ID usually does not require heap traffic.</p>
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1273
1274<p>Because FoldingSet uses intrusive links, it can support polymorphic objects
1275in the set (for example, you can have SDNode instances mixed with LoadSDNodes).
1276Because the elements are individually allocated, pointers to the elements are
1277stable: inserting or removing elements does not invalidate any pointers to other
1278elements.
1279</p>
1280
1281</div>
1282
1283<!-- _______________________________________________________________________ -->
1284<div class="doc_subsubsection">
1285 <a name="dss_set">&lt;set&gt;</a>
1286</div>
1287
1288<div class="doc_text">
1289
Chris Lattnerc5722432007-02-03 19:49:31 +0000[diff] [blame]1290<p><tt>std::set</tt> is a reasonable all-around set class, which is decent at
1291many things but great at nothing. std::set allocates memory for each element
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1292inserted (thus it is very malloc intensive) and typically stores three pointers
Chris Lattner14868db2007-02-03 08:20:15 +0000[diff] [blame]1293per element in the set (thus adding a large amount of per-element space
1294overhead). It offers guaranteed log(n) performance, which is not particularly
Chris Lattnerc5722432007-02-03 19:49:31 +0000[diff] [blame]1295fast from a complexity standpoint (particularly if the elements of the set are
1296expensive to compare, like strings), and has extremely high constant factors for
1297lookup, insertion and removal.</p>
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1298
Chris Lattner14868db2007-02-03 08:20:15 +0000[diff] [blame]1299<p>The advantages of std::set are that its iterators are stable (deleting or
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1300inserting an element from the set does not affect iterators or pointers to other
1301elements) and that iteration over the set is guaranteed to be in sorted order.
1302If the elements in the set are large, then the relative overhead of the pointers
1303and malloc traffic is not a big deal, but if the elements of the set are small,
1304std::set is almost never a good choice.</p>
1305
1306</div>
1307
1308<!-- _______________________________________________________________________ -->
1309<div class="doc_subsubsection">
1310 <a name="dss_setvector">"llvm/ADT/SetVector.h"</a>
1311</div>
1312
1313<div class="doc_text">
Chris Lattneredca3c52007-02-04 00:00:26 +0000[diff] [blame]1314<p>LLVM's SetVector&lt;Type&gt; is an adapter class that combines your choice of
1315a set-like container along with a <a href="#ds_sequential">Sequential
1316Container</a>. The important property
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1317that this provides is efficient insertion with uniquing (duplicate elements are
1318ignored) with iteration support. It implements this by inserting elements into
1319both a set-like container and the sequential container, using the set-like
1320container for uniquing and the sequential container for iteration.
1321</p>
1322
1323<p>The difference between SetVector and other sets is that the order of
1324iteration is guaranteed to match the order of insertion into the SetVector.
1325This property is really important for things like sets of pointers. Because
1326pointer values are non-deterministic (e.g. vary across runs of the program on
Chris Lattneredca3c52007-02-04 00:00:26 +0000[diff] [blame]1327different machines), iterating over the pointers in the set will
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1328not be in a well-defined order.</p>
1329
1330<p>
1331The drawback of SetVector is that it requires twice as much space as a normal
1332set and has the sum of constant factors from the set-like container and the
1333sequential container that it uses. Use it *only* if you need to iterate over
1334the elements in a deterministic order. SetVector is also expensive to delete
Chris Lattneredca3c52007-02-04 00:00:26 +0000[diff] [blame]1335elements out of (linear time), unless you use it's "pop_back" method, which is
1336faster.
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1337</p>
1338
Chris Lattneredca3c52007-02-04 00:00:26 +0000[diff] [blame]1339<p>SetVector is an adapter class that defaults to using std::vector and std::set
1340for the underlying containers, so it is quite expensive. However,
1341<tt>"llvm/ADT/SetVector.h"</tt> also provides a SmallSetVector class, which
1342defaults to using a SmallVector and SmallSet of a specified size. If you use
1343this, and if your sets are dynamically smaller than N, you will save a lot of
1344heap traffic.</p>
1345
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1346</div>
1347
1348<!-- _______________________________________________________________________ -->
1349<div class="doc_subsubsection">
Chris Lattnerc5722432007-02-03 19:49:31 +0000[diff] [blame]1350 <a name="dss_uniquevector">"llvm/ADT/UniqueVector.h"</a>
1351</div>
1352
1353<div class="doc_text">
1354
1355<p>
1356UniqueVector is similar to <a href="#dss_setvector">SetVector</a>, but it
1357retains a unique ID for each element inserted into the set. It internally
1358contains a map and a vector, and it assigns a unique ID for each value inserted
1359into the set.</p>
1360
1361<p>UniqueVector is very expensive: its cost is the sum of the cost of
1362maintaining both the map and vector, it has high complexity, high constant
1363factors, and produces a lot of malloc traffic. It should be avoided.</p>
1364
1365</div>
1366
1367
1368<!-- _______________________________________________________________________ -->
1369<div class="doc_subsubsection">
1370 <a name="dss_otherset">Other Set-Like Container Options</a>
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1371</div>
1372
1373<div class="doc_text">
1374
1375<p>
1376The STL provides several other options, such as std::multiset and the various
Chris Lattnerf1a30822009-03-09 05:20:45 +0000[diff] [blame]1377"hash_set" like containers (whether from C++ TR1 or from the SGI library). We
1378never use hash_set and unordered_set because they are generally very expensive
1379(each insertion requires a malloc) and very non-portable.
1380</p>
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1381
1382<p>std::multiset is useful if you're not interested in elimination of
Chris Lattner14868db2007-02-03 08:20:15 +0000[diff] [blame]1383duplicates, but has all the drawbacks of std::set. A sorted vector (where you
1384don't delete duplicate entries) or some other approach is almost always
1385better.</p>
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1386
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]1387</div>
1388
1389<!-- ======================================================================= -->
1390<div class="doc_subsection">
1391 <a name="ds_map">Map-Like Containers (std::map, DenseMap, etc)</a>
1392</div>
1393
1394<div class="doc_text">
Chris Lattnerc5722432007-02-03 19:49:31 +0000[diff] [blame]1395Map-like containers are useful when you want to associate data to a key. As
1396usual, there are a lot of different ways to do this. :)
1397</div>
1398
1399<!-- _______________________________________________________________________ -->
1400<div class="doc_subsubsection">
1401 <a name="dss_sortedvectormap">A sorted 'vector'</a>
1402</div>
1403
1404<div class="doc_text">
1405
1406<p>
1407If your usage pattern follows a strict insert-then-query approach, you can
1408trivially use the same approach as <a href="#dss_sortedvectorset">sorted vectors
1409for set-like containers</a>. The only difference is that your query function
1410(which uses std::lower_bound to get efficient log(n) lookup) should only compare
1411the key, not both the key and value. This yields the same advantages as sorted
1412vectors for sets.
1413</p>
1414</div>
1415
1416<!-- _______________________________________________________________________ -->
1417<div class="doc_subsubsection">
Chris Lattner796f9fa2007-02-08 19:14:21 +0000[diff] [blame]1418 <a name="dss_stringmap">"llvm/ADT/StringMap.h"</a>
Chris Lattnerc5722432007-02-03 19:49:31 +0000[diff] [blame]1419</div>
1420
1421<div class="doc_text">
1422
1423<p>
1424Strings are commonly used as keys in maps, and they are difficult to support
1425efficiently: they are variable length, inefficient to hash and compare when
Chris Lattner796f9fa2007-02-08 19:14:21 +0000[diff] [blame]1426long, expensive to copy, etc. StringMap is a specialized container designed to
1427cope with these issues. It supports mapping an arbitrary range of bytes to an
1428arbitrary other object.</p>
Chris Lattnerc5722432007-02-03 19:49:31 +0000[diff] [blame]1429
Chris Lattner796f9fa2007-02-08 19:14:21 +0000[diff] [blame]1430<p>The StringMap implementation uses a quadratically-probed hash table, where
Chris Lattnerc5722432007-02-03 19:49:31 +0000[diff] [blame]1431the buckets store a pointer to the heap allocated entries (and some other
1432stuff). The entries in the map must be heap allocated because the strings are
1433variable length. The string data (key) and the element object (value) are
1434stored in the same allocation with the string data immediately after the element
1435object. This container guarantees the "<tt>(char*)(&amp;Value+1)</tt>" points
1436to the key string for a value.</p>
1437
Chris Lattner796f9fa2007-02-08 19:14:21 +0000[diff] [blame]1438<p>The StringMap is very fast for several reasons: quadratic probing is very
Chris Lattnerc5722432007-02-03 19:49:31 +0000[diff] [blame]1439cache efficient for lookups, the hash value of strings in buckets is not
Chris Lattner796f9fa2007-02-08 19:14:21 +0000[diff] [blame]1440recomputed when lookup up an element, StringMap rarely has to touch the
Chris Lattnerc5722432007-02-03 19:49:31 +0000[diff] [blame]1441memory for unrelated objects when looking up a value (even when hash collisions
1442happen), hash table growth does not recompute the hash values for strings
1443already in the table, and each pair in the map is store in a single allocation
1444(the string data is stored in the same allocation as the Value of a pair).</p>
1445
Chris Lattner796f9fa2007-02-08 19:14:21 +0000[diff] [blame]1446<p>StringMap also provides query methods that take byte ranges, so it only ever
Chris Lattnerc5722432007-02-03 19:49:31 +0000[diff] [blame]1447copies a string if a value is inserted into the table.</p>
1448</div>
1449
1450<!-- _______________________________________________________________________ -->
1451<div class="doc_subsubsection">
1452 <a name="dss_indexedmap">"llvm/ADT/IndexedMap.h"</a>
1453</div>
1454
1455<div class="doc_text">
1456<p>
1457IndexedMap is a specialized container for mapping small dense integers (or
1458values that can be mapped to small dense integers) to some other type. It is
1459internally implemented as a vector with a mapping function that maps the keys to
1460the dense integer range.
1461</p>
1462
1463<p>
1464This is useful for cases like virtual registers in the LLVM code generator: they
1465have a dense mapping that is offset by a compile-time constant (the first
1466virtual register ID).</p>
1467
1468</div>
1469
1470<!-- _______________________________________________________________________ -->
1471<div class="doc_subsubsection">
1472 <a name="dss_densemap">"llvm/ADT/DenseMap.h"</a>
1473</div>
1474
1475<div class="doc_text">
1476
1477<p>
1478DenseMap is a simple quadratically probed hash table. It excels at supporting
1479small keys and values: it uses a single allocation to hold all of the pairs that
1480are currently inserted in the map. DenseMap is a great way to map pointers to
1481pointers, or map other small types to each other.
1482</p>
1483
1484<p>
1485There are several aspects of DenseMap that you should be aware of, however. The
1486iterators in a densemap are invalidated whenever an insertion occurs, unlike
1487map. Also, because DenseMap allocates space for a large number of key/value
Chris Lattnera4a264d2007-02-03 20:17:53 +0000[diff] [blame]1488pairs (it starts with 64 by default), it will waste a lot of space if your keys
1489or values are large. Finally, you must implement a partial specialization of
Chris Lattner76c1b972007-09-17 18:34:04 +0000[diff] [blame]1490DenseMapInfo for the key that you want, if it isn't already supported. This
Chris Lattnerc5722432007-02-03 19:49:31 +0000[diff] [blame]1491is required to tell DenseMap about two special marker values (which can never be
Chris Lattnera4a264d2007-02-03 20:17:53 +0000[diff] [blame]1492inserted into the map) that it needs internally.</p>
Chris Lattnerc5722432007-02-03 19:49:31 +0000[diff] [blame]1493
1494</div>
1495
1496<!-- _______________________________________________________________________ -->
1497<div class="doc_subsubsection">
Jeffrey Yasskin71a5c222009-10-22 22:11:22 +0000[diff] [blame]1498 <a name="dss_valuemap">"llvm/ADT/ValueMap.h"</a>
1499</div>
1500
1501<div class="doc_text">
1502
1503<p>
1504ValueMap is a wrapper around a <a href="#dss_densemap">DenseMap</a> mapping
1505Value*s (or subclasses) to another type. When a Value is deleted or RAUW'ed,
1506ValueMap will update itself so the new version of the key is mapped to the same
1507value, just as if the key were a WeakVH. You can configure exactly how this
1508happens, and what else happens on these two events, by passing
1509a <code>Config</code> parameter to the ValueMap template.</p>
1510
1511</div>
1512
1513<!-- _______________________________________________________________________ -->
1514<div class="doc_subsubsection">
Chris Lattnerc5722432007-02-03 19:49:31 +0000[diff] [blame]1515 <a name="dss_map">&lt;map&gt;</a>
1516</div>
1517
1518<div class="doc_text">
1519
1520<p>
1521std::map has similar characteristics to <a href="#dss_set">std::set</a>: it uses
1522a single allocation per pair inserted into the map, it offers log(n) lookup with
1523an extremely large constant factor, imposes a space penalty of 3 pointers per
1524pair in the map, etc.</p>
1525
1526<p>std::map is most useful when your keys or values are very large, if you need
1527to iterate over the collection in sorted order, or if you need stable iterators
1528into the map (i.e. they don't get invalidated if an insertion or deletion of
1529another element takes place).</p>
1530
1531</div>
1532
1533<!-- _______________________________________________________________________ -->
1534<div class="doc_subsubsection">
1535 <a name="dss_othermap">Other Map-Like Container Options</a>
1536</div>
1537
1538<div class="doc_text">
1539
1540<p>
1541The STL provides several other options, such as std::multimap and the various
Chris Lattnerf1a30822009-03-09 05:20:45 +0000[diff] [blame]1542"hash_map" like containers (whether from C++ TR1 or from the SGI library). We
1543never use hash_set and unordered_set because they are generally very expensive
1544(each insertion requires a malloc) and very non-portable.</p>
Chris Lattnerc5722432007-02-03 19:49:31 +0000[diff] [blame]1545
1546<p>std::multimap is useful if you want to map a key to multiple values, but has
1547all the drawbacks of std::map. A sorted vector or some other approach is almost
1548always better.</p>
1549
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]1550</div>
1551
Daniel Berlin1939ace2007-09-24 17:52:25 +0000[diff] [blame]1552<!-- ======================================================================= -->
1553<div class="doc_subsection">
Chris Lattnerdced9fb2009-07-25 07:22:20 +0000[diff] [blame]1554 <a name="ds_string">String-like containers</a>
1555</div>
1556
1557<div class="doc_text">
1558
1559<p>
1560TODO: const char* vs stringref vs smallstring vs std::string. Describe twine,
1561xref to #string_apis.
1562</p>
1563
1564</div>
1565
1566<!-- ======================================================================= -->
1567<div class="doc_subsection">
Daniel Berlin1939ace2007-09-24 17:52:25 +0000[diff] [blame]1568 <a name="ds_bit">Bit storage containers (BitVector, SparseBitVector)</a>
1569</div>
1570
1571<div class="doc_text">
Chris Lattner7086ce72007-09-25 22:37:50 +0000[diff] [blame]1572<p>Unlike the other containers, there are only two bit storage containers, and
1573choosing when to use each is relatively straightforward.</p>
1574
1575<p>One additional option is
1576<tt>std::vector&lt;bool&gt;</tt>: we discourage its use for two reasons 1) the
1577implementation in many common compilers (e.g. commonly available versions of
1578GCC) is extremely inefficient and 2) the C++ standards committee is likely to
1579deprecate this container and/or change it significantly somehow. In any case,
1580please don't use it.</p>
Daniel Berlin1939ace2007-09-24 17:52:25 +0000[diff] [blame]1581</div>
1582
1583<!-- _______________________________________________________________________ -->
1584<div class="doc_subsubsection">
1585 <a name="dss_bitvector">BitVector</a>
1586</div>
1587
1588<div class="doc_text">
Dan Gohman5f7775c2010-01-05 18:24:00 +0000[diff] [blame]1589<p> The BitVector container provides a dynamic size set of bits for manipulation.
Daniel Berlin1939ace2007-09-24 17:52:25 +0000[diff] [blame]1590It supports individual bit setting/testing, as well as set operations. The set
1591operations take time O(size of bitvector), but operations are performed one word
1592at a time, instead of one bit at a time. This makes the BitVector very fast for
1593set operations compared to other containers. Use the BitVector when you expect
1594the number of set bits to be high (IE a dense set).
1595</p>
1596</div>
1597
1598<!-- _______________________________________________________________________ -->
1599<div class="doc_subsubsection">
Dan Gohman5f7775c2010-01-05 18:24:00 +0000[diff] [blame]1600 <a name="dss_smallbitvector">SmallBitVector</a>
1601</div>
1602
1603<div class="doc_text">
1604<p> The SmallBitVector container provides the same interface as BitVector, but
1605it is optimized for the case where only a small number of bits, less than
160625 or so, are needed. It also transparently supports larger bit counts, but
1607slightly less efficiently than a plain BitVector, so SmallBitVector should
1608only be used when larger counts are rare.
1609</p>
1610
1611<p>
1612At this time, SmallBitVector does not support set operations (and, or, xor),
1613and its operator[] does not provide an assignable lvalue.
1614</p>
1615</div>
1616
1617<!-- _______________________________________________________________________ -->
1618<div class="doc_subsubsection">
Daniel Berlin1939ace2007-09-24 17:52:25 +0000[diff] [blame]1619 <a name="dss_sparsebitvector">SparseBitVector</a>
1620</div>
1621
1622<div class="doc_text">
1623<p> The SparseBitVector container is much like BitVector, with one major
1624difference: Only the bits that are set, are stored. This makes the
1625SparseBitVector much more space efficient than BitVector when the set is sparse,
1626as well as making set operations O(number of set bits) instead of O(size of
1627universe). 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
1628(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).
1629</p>
1630</div>
Chris Lattnerf623a082005-10-17 01:36:23 +0000[diff] [blame]1631
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1632<!-- *********************************************************************** -->
1633<div class="doc_section">
1634 <a name="common">Helpful Hints for Common Operations</a>
1635</div>
1636<!-- *********************************************************************** -->
1637
1638<div class="doc_text">
1639
1640<p>This section describes how to perform some very simple transformations of
1641LLVM code. This is meant to give examples of common idioms used, showing the
1642practical side of LLVM transformations. <p> Because this is a "how-to" section,
1643you should also read about the main classes that you will be working with. The
1644<a href="#coreclasses">Core LLVM Class Hierarchy Reference</a> contains details
1645and descriptions of the main classes that you should know about.</p>
1646
1647</div>
1648
1649<!-- NOTE: this section should be heavy on example code -->
1650<!-- ======================================================================= -->
1651<div class="doc_subsection">
1652 <a name="inspection">Basic Inspection and Traversal Routines</a>
1653</div>
1654
1655<div class="doc_text">
1656
1657<p>The LLVM compiler infrastructure have many different data structures that may
1658be traversed. Following the example of the C++ standard template library, the
1659techniques used to traverse these various data structures are all basically the
1660same. For a enumerable sequence of values, the <tt>XXXbegin()</tt> function (or
1661method) returns an iterator to the start of the sequence, the <tt>XXXend()</tt>
1662function returns an iterator pointing to one past the last valid element of the
1663sequence, and there is some <tt>XXXiterator</tt> data type that is common
1664between the two operations.</p>
1665
1666<p>Because the pattern for iteration is common across many different aspects of
1667the program representation, the standard template library algorithms may be used
1668on them, and it is easier to remember how to iterate. First we show a few common
1669examples of the data structures that need to be traversed. Other data
1670structures are traversed in very similar ways.</p>
1671
1672</div>
1673
1674<!-- _______________________________________________________________________ -->
Chris Lattner69bf8a92004-05-23 21:06:58 +0000[diff] [blame]1675<div class="doc_subsubsection">
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1676 <a name="iterate_function">Iterating over the </a><a
1677 href="#BasicBlock"><tt>BasicBlock</tt></a>s in a <a
1678 href="#Function"><tt>Function</tt></a>
1679</div>
1680
1681<div class="doc_text">
1682
1683<p>It's quite common to have a <tt>Function</tt> instance that you'd like to
1684transform in some way; in particular, you'd like to manipulate its
1685<tt>BasicBlock</tt>s. To facilitate this, you'll need to iterate over all of
1686the <tt>BasicBlock</tt>s that constitute the <tt>Function</tt>. The following is
1687an example that prints the name of a <tt>BasicBlock</tt> and the number of
1688<tt>Instruction</tt>s it contains:</p>
1689
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1690<div class="doc_code">
1691<pre>
Bill Wendling82e2eea2006-10-11 18:00:22 +0000[diff] [blame]1692// <i>func is a pointer to a Function instance</i>
1693for (Function::iterator i = func-&gt;begin(), e = func-&gt;end(); i != e; ++i)
1694 // <i>Print out the name of the basic block if it has one, and then the</i>
1695 // <i>number of instructions that it contains</i>
Chris Lattner3fee6ed2009-09-08 05:15:50 +0000[diff] [blame]1696 errs() &lt;&lt; "Basic block (name=" &lt;&lt; i-&gt;getName() &lt;&lt; ") has "
Bill Wendling832171c2006-12-07 20:04:42 +0000[diff] [blame]1697 &lt;&lt; i-&gt;size() &lt;&lt; " instructions.\n";
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1698</pre>
1699</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1700
1701<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]1702invoking member functions of the <tt>Instruction</tt> class. This is
1703because the indirection operator is overloaded for the iterator
Chris Lattner7496ec52003-08-05 22:54:23 +0000[diff] [blame]1704classes. In the above code, the expression <tt>i-&gt;size()</tt> is
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1705exactly equivalent to <tt>(*i).size()</tt> just like you'd expect.</p>
1706
1707</div>
1708
1709<!-- _______________________________________________________________________ -->
Chris Lattner69bf8a92004-05-23 21:06:58 +0000[diff] [blame]1710<div class="doc_subsubsection">
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1711 <a name="iterate_basicblock">Iterating over the </a><a
1712 href="#Instruction"><tt>Instruction</tt></a>s in a <a
1713 href="#BasicBlock"><tt>BasicBlock</tt></a>
1714</div>
1715
1716<div class="doc_text">
1717
1718<p>Just like when dealing with <tt>BasicBlock</tt>s in <tt>Function</tt>s, it's
1719easy to iterate over the individual instructions that make up
1720<tt>BasicBlock</tt>s. Here's a code snippet that prints out each instruction in
1721a <tt>BasicBlock</tt>:</p>
1722
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1723<div class="doc_code">
Chris Lattner55c04612005-03-06 06:00:13 +0000[diff] [blame]1724<pre>
Bill Wendling82e2eea2006-10-11 18:00:22 +0000[diff] [blame]1725// <i>blk is a pointer to a BasicBlock instance</i>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1726for (BasicBlock::iterator i = blk-&gt;begin(), e = blk-&gt;end(); i != e; ++i)
Bill Wendling82e2eea2006-10-11 18:00:22 +0000[diff] [blame]1727 // <i>The next statement works since operator&lt;&lt;(ostream&amp;,...)</i>
1728 // <i>is overloaded for Instruction&amp;</i>
Chris Lattner3fee6ed2009-09-08 05:15:50 +0000[diff] [blame]1729 errs() &lt;&lt; *i &lt;&lt; "\n";
Chris Lattner55c04612005-03-06 06:00:13 +0000[diff] [blame]1730</pre>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1731</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1732
1733<p>However, this isn't really the best way to print out the contents of a
1734<tt>BasicBlock</tt>! Since the ostream operators are overloaded for virtually
1735anything you'll care about, you could have just invoked the print routine on the
Chris Lattner3fee6ed2009-09-08 05:15:50 +0000[diff] [blame]1736basic block itself: <tt>errs() &lt;&lt; *blk &lt;&lt; "\n";</tt>.</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1737
1738</div>
1739
1740<!-- _______________________________________________________________________ -->
Chris Lattner69bf8a92004-05-23 21:06:58 +0000[diff] [blame]1741<div class="doc_subsubsection">
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1742 <a name="iterate_institer">Iterating over the </a><a
1743 href="#Instruction"><tt>Instruction</tt></a>s in a <a
1744 href="#Function"><tt>Function</tt></a>
1745</div>
1746
1747<div class="doc_text">
1748
1749<p>If you're finding that you commonly iterate over a <tt>Function</tt>'s
1750<tt>BasicBlock</tt>s and then that <tt>BasicBlock</tt>'s <tt>Instruction</tt>s,
1751<tt>InstIterator</tt> should be used instead. You'll need to include <a
1752href="/doxygen/InstIterator_8h-source.html"><tt>llvm/Support/InstIterator.h</tt></a>,
1753and then instantiate <tt>InstIterator</tt>s explicitly in your code. Here's a
Chris Lattner69bf8a92004-05-23 21:06:58 +0000[diff] [blame]1754small 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]1755
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1756<div class="doc_code">
1757<pre>
1758#include "<a href="/doxygen/InstIterator_8h-source.html">llvm/Support/InstIterator.h</a>"
1759
Reid Spencer128a7a72007-02-03 21:06:43 +0000[diff] [blame]1760// <i>F is a pointer to a Function instance</i>
Chris Lattnerda021aa2008-06-04 18:20:42 +0000[diff] [blame]1761for (inst_iterator I = inst_begin(F), E = inst_end(F); I != E; ++I)
Chris Lattner3fee6ed2009-09-08 05:15:50 +0000[diff] [blame]1762 errs() &lt;&lt; *I &lt;&lt; "\n";
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1763</pre>
1764</div>
1765
1766<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]1767work list with its initial contents. For example, if you wanted to
1768initialize a work list to contain all instructions in a <tt>Function</tt>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1769F, all you would need to do is something like:</p>
1770
1771<div class="doc_code">
1772<pre>
1773std::set&lt;Instruction*&gt; worklist;
Chris Lattnerda021aa2008-06-04 18:20:42 +0000[diff] [blame]1774// or better yet, SmallPtrSet&lt;Instruction*, 64&gt; worklist;
1775
1776for (inst_iterator I = inst_begin(F), E = inst_end(F); I != E; ++I)
1777 worklist.insert(&amp;*I);
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1778</pre>
1779</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1780
1781<p>The STL set <tt>worklist</tt> would now contain all instructions in the
1782<tt>Function</tt> pointed to by F.</p>
1783
1784</div>
1785
1786<!-- _______________________________________________________________________ -->
1787<div class="doc_subsubsection">
1788 <a name="iterate_convert">Turning an iterator into a class pointer (and
1789 vice-versa)</a>
1790</div>
1791
1792<div class="doc_text">
1793
1794<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]1795instance when all you've got at hand is an iterator. Well, extracting
Chris Lattner69bf8a92004-05-23 21:06:58 +0000[diff] [blame]1796a reference or a pointer from an iterator is very straight-forward.
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]1797Assuming that <tt>i</tt> is a <tt>BasicBlock::iterator</tt> and <tt>j</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1798is a <tt>BasicBlock::const_iterator</tt>:</p>
1799
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1800<div class="doc_code">
1801<pre>
Bill Wendling82e2eea2006-10-11 18:00:22 +0000[diff] [blame]1802Instruction&amp; inst = *i; // <i>Grab reference to instruction reference</i>
1803Instruction* pinst = &amp;*i; // <i>Grab pointer to instruction reference</i>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1804const Instruction&amp; inst = *j;
1805</pre>
1806</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1807
1808<p>However, the iterators you'll be working with in the LLVM framework are
1809special: they will automatically convert to a ptr-to-instance type whenever they
1810need to. Instead of dereferencing the iterator and then taking the address of
1811the result, you can simply assign the iterator to the proper pointer type and
1812you get the dereference and address-of operation as a result of the assignment
1813(behind the scenes, this is a result of overloading casting mechanisms). Thus
1814the last line of the last example,</p>
1815
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1816<div class="doc_code">
1817<pre>
Chris Lattner2e438ca2008-01-03 16:56:04 +0000[diff] [blame]1818Instruction *pinst = &amp;*i;
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1819</pre>
1820</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1821
1822<p>is semantically equivalent to</p>
1823
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1824<div class="doc_code">
1825<pre>
Chris Lattner2e438ca2008-01-03 16:56:04 +0000[diff] [blame]1826Instruction *pinst = i;
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1827</pre>
1828</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1829
Chris Lattner69bf8a92004-05-23 21:06:58 +0000[diff] [blame]1830<p>It's also possible to turn a class pointer into the corresponding iterator,
1831and this is a constant time operation (very efficient). The following code
1832snippet illustrates use of the conversion constructors provided by LLVM
1833iterators. By using these, you can explicitly grab the iterator of something
1834without actually obtaining it via iteration over some structure:</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1835
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1836<div class="doc_code">
1837<pre>
1838void printNextInstruction(Instruction* inst) {
1839 BasicBlock::iterator it(inst);
Bill Wendling82e2eea2006-10-11 18:00:22 +0000[diff] [blame]1840 ++it; // <i>After this line, it refers to the instruction after *inst</i>
Chris Lattner3fee6ed2009-09-08 05:15:50 +0000[diff] [blame]1841 if (it != inst-&gt;getParent()-&gt;end()) errs() &lt;&lt; *it &lt;&lt; "\n";
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1842}
1843</pre>
1844</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1845
Dan Gohman525bf8e2010-03-26 19:39:05 +0000[diff] [blame]1846<p>Unfortunately, these implicit conversions come at a cost; they prevent
1847these iterators from conforming to standard iterator conventions, and thus
Dan Gohman0d91c112010-03-26 19:51:14 +0000[diff] [blame]1848from being usable with standard algorithms and containers. For example, they
1849prevent the following code, where <tt>B</tt> is a <tt>BasicBlock</tt>,
Dan Gohman525bf8e2010-03-26 19:39:05 +0000[diff] [blame]1850from compiling:</p>
1851
1852<div class="doc_code">
1853<pre>
1854 llvm::SmallVector&lt;llvm::Instruction *, 16&gt;(B-&gt;begin(), B-&gt;end());
1855</pre>
1856</div>
1857
1858<p>Because of this, these implicit conversions may be removed some day,
Dan Gohman0d91c112010-03-26 19:51:14 +0000[diff] [blame]1859and <tt>operator*</tt> changed to return a pointer instead of a reference.</p>
Dan Gohman525bf8e2010-03-26 19:39:05 +0000[diff] [blame]1860
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1861</div>
1862
1863<!--_______________________________________________________________________-->
1864<div class="doc_subsubsection">
1865 <a name="iterate_complex">Finding call sites: a slightly more complex
1866 example</a>
1867</div>
1868
1869<div class="doc_text">
1870
1871<p>Say that you're writing a FunctionPass and would like to count all the
1872locations in the entire module (that is, across every <tt>Function</tt>) where a
1873certain function (i.e., some <tt>Function</tt>*) is already in scope. As you'll
1874learn 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]1875much more straight-forward manner, but this example will allow us to explore how
Reid Spencer128a7a72007-02-03 21:06:43 +0000[diff] [blame]1876you'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]1877is what we want to do:</p>
1878
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1879<div class="doc_code">
1880<pre>
1881initialize callCounter to zero
1882for each Function f in the Module
1883 for each BasicBlock b in f
1884 for each Instruction i in b
1885 if (i is a CallInst and calls the given function)
1886 increment callCounter
1887</pre>
1888</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1889
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1890<p>And the actual code is (remember, because we're writing a
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1891<tt>FunctionPass</tt>, our <tt>FunctionPass</tt>-derived class simply has to
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1892override the <tt>runOnFunction</tt> method):</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1893
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1894<div class="doc_code">
1895<pre>
1896Function* targetFunc = ...;
1897
1898class OurFunctionPass : public FunctionPass {
1899 public:
1900 OurFunctionPass(): callCounter(0) { }
1901
1902 virtual runOnFunction(Function&amp; F) {
1903 for (Function::iterator b = F.begin(), be = F.end(); b != be; ++b) {
Eric Christopher203e71d2008-11-08 08:20:49 +0000[diff] [blame]1904 for (BasicBlock::iterator i = b-&gt;begin(), ie = b-&gt;end(); i != ie; ++i) {
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1905 if (<a href="#CallInst">CallInst</a>* callInst = <a href="#isa">dyn_cast</a>&lt;<a
1906 href="#CallInst">CallInst</a>&gt;(&amp;*i)) {
Bill Wendling82e2eea2006-10-11 18:00:22 +0000[diff] [blame]1907 // <i>We know we've encountered a call instruction, so we</i>
1908 // <i>need to determine if it's a call to the</i>
Chris Lattner2e438ca2008-01-03 16:56:04 +0000[diff] [blame]1909 // <i>function pointed to by m_func or not.</i>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1910 if (callInst-&gt;getCalledFunction() == targetFunc)
1911 ++callCounter;
1912 }
1913 }
1914 }
Bill Wendling82e2eea2006-10-11 18:00:22 +0000[diff] [blame]1915 }
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1916
1917 private:
Chris Lattner2e438ca2008-01-03 16:56:04 +0000[diff] [blame]1918 unsigned callCounter;
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1919};
1920</pre>
1921</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1922
1923</div>
1924
Brian Gaekef1972c62003-11-07 19:25:45 +0000[diff] [blame]1925<!--_______________________________________________________________________-->
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1926<div class="doc_subsubsection">
1927 <a name="calls_and_invokes">Treating calls and invokes the same way</a>
1928</div>
1929
1930<div class="doc_text">
1931
1932<p>You may have noticed that the previous example was a bit oversimplified in
1933that it did not deal with call sites generated by 'invoke' instructions. In
1934this, and in other situations, you may find that you want to treat
1935<tt>CallInst</tt>s and <tt>InvokeInst</tt>s the same way, even though their
1936most-specific common base class is <tt>Instruction</tt>, which includes lots of
1937less closely-related things. For these cases, LLVM provides a handy wrapper
1938class called <a
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]1939href="http://llvm.org/doxygen/classllvm_1_1CallSite.html"><tt>CallSite</tt></a>.
Chris Lattner69bf8a92004-05-23 21:06:58 +0000[diff] [blame]1940It is essentially a wrapper around an <tt>Instruction</tt> pointer, with some
1941methods that provide functionality common to <tt>CallInst</tt>s and
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1942<tt>InvokeInst</tt>s.</p>
1943
Chris Lattner69bf8a92004-05-23 21:06:58 +0000[diff] [blame]1944<p>This class has "value semantics": it should be passed by value, not by
1945reference and it should not be dynamically allocated or deallocated using
1946<tt>operator new</tt> or <tt>operator delete</tt>. It is efficiently copyable,
1947assignable and constructable, with costs equivalents to that of a bare pointer.
1948If you look at its definition, it has only a single pointer member.</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1949
1950</div>
1951
Chris Lattner1a3105b2002-09-09 05:49:39 +0000[diff] [blame]1952<!--_______________________________________________________________________-->
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1953<div class="doc_subsubsection">
1954 <a name="iterate_chains">Iterating over def-use &amp; use-def chains</a>
1955</div>
1956
1957<div class="doc_text">
1958
1959<p>Frequently, we might have an instance of the <a
Chris Lattner00815172007-01-04 22:01:45 +0000[diff] [blame]1960href="/doxygen/classllvm_1_1Value.html">Value Class</a> and we want to
Misha Brukman384047f2004-06-03 23:29:12 +0000[diff] [blame]1961determine which <tt>User</tt>s use the <tt>Value</tt>. The list of all
1962<tt>User</tt>s of a particular <tt>Value</tt> is called a <i>def-use</i> chain.
1963For example, let's say we have a <tt>Function*</tt> named <tt>F</tt> to a
1964particular function <tt>foo</tt>. Finding all of the instructions that
1965<i>use</i> <tt>foo</tt> is as simple as iterating over the <i>def-use</i> chain
1966of <tt>F</tt>:</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1967
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1968<div class="doc_code">
1969<pre>
Chris Lattner2e438ca2008-01-03 16:56:04 +0000[diff] [blame]1970Function *F = ...;
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1971
Bill Wendling82e2eea2006-10-11 18:00:22 +0000[diff] [blame]1972for (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]1973 if (Instruction *Inst = dyn_cast&lt;Instruction&gt;(*i)) {
Chris Lattner3fee6ed2009-09-08 05:15:50 +0000[diff] [blame]1974 errs() &lt;&lt; "F is used in instruction:\n";
1975 errs() &lt;&lt; *Inst &lt;&lt; "\n";
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1976 }
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1977</pre>
Gabor Greif394fdfb2010-03-26 19:35:48 +0000[diff] [blame]1978</div>
1979
Gabor Greifce94319532010-03-26 19:40:38 +0000[diff] [blame]1980<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]1981operation. Instead of performing <tt>*i</tt> above several times, consider
Gabor Greifce94319532010-03-26 19:40:38 +0000[diff] [blame]1982doing it only once in the loop body and reusing its result.</p>
Gabor Greif4de73682010-03-26 19:30:47 +0000[diff] [blame]1983
Gabor Greif6091ff32010-03-26 19:04:42 +0000[diff] [blame]1984<p>Alternatively, it's common to have an instance of the <a
Misha Brukman384047f2004-06-03 23:29:12 +0000[diff] [blame]1985href="/doxygen/classllvm_1_1User.html">User Class</a> and need to know what
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1986<tt>Value</tt>s are used by it. The list of all <tt>Value</tt>s used by a
1987<tt>User</tt> is known as a <i>use-def</i> chain. Instances of class
1988<tt>Instruction</tt> are common <tt>User</tt>s, so we might want to iterate over
1989all of the values that a particular instruction uses (that is, the operands of
1990the particular <tt>Instruction</tt>):</p>
1991
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1992<div class="doc_code">
1993<pre>
Chris Lattner2e438ca2008-01-03 16:56:04 +0000[diff] [blame]1994Instruction *pi = ...;
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1995
1996for (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]1997 Value *v = *i;
Bill Wendling82e2eea2006-10-11 18:00:22 +0000[diff] [blame]1998 // <i>...</i>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1999}
2000</pre>
2001</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2002
Gabor Greif4de73682010-03-26 19:30:47 +0000[diff] [blame]2003<p>Declaring objects as <tt>const</tt> is an important tool of enforcing
Gabor Greifce94319532010-03-26 19:40:38 +0000[diff] [blame]2004mutation free algorithms (such as analyses, etc.). For this purpose above
Gabor Greif4de73682010-03-26 19:30:47 +0000[diff] [blame]2005iterators come in constant flavors as <tt>Value::const_use_iterator</tt>
2006and <tt>Value::const_op_iterator</tt>. They automatically arise when
2007calling <tt>use/op_begin()</tt> on <tt>const Value*</tt>s or
2008<tt>const User*</tt>s respectively. Upon dereferencing, they return
Gabor Greifce94319532010-03-26 19:40:38 +0000[diff] [blame]2009<tt>const Use*</tt>s. Otherwise the above patterns remain unchanged.</p>
2010
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2011</div>
2012
Chris Lattner2e438ca2008-01-03 16:56:04 +0000[diff] [blame]2013<!--_______________________________________________________________________-->
2014<div class="doc_subsubsection">
2015 <a name="iterate_preds">Iterating over predecessors &amp;
2016successors of blocks</a>
2017</div>
2018
2019<div class="doc_text">
2020
2021<p>Iterating over the predecessors and successors of a block is quite easy
2022with the routines defined in <tt>"llvm/Support/CFG.h"</tt>. Just use code like
2023this to iterate over all predecessors of BB:</p>
2024
2025<div class="doc_code">
2026<pre>
2027#include "llvm/Support/CFG.h"
2028BasicBlock *BB = ...;
2029
2030for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI) {
2031 BasicBlock *Pred = *PI;
2032 // <i>...</i>
2033}
2034</pre>
2035</div>
2036
2037<p>Similarly, to iterate over successors use
2038succ_iterator/succ_begin/succ_end.</p>
2039
2040</div>
2041
2042
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2043<!-- ======================================================================= -->
2044<div class="doc_subsection">
2045 <a name="simplechanges">Making simple changes</a>
2046</div>
2047
2048<div class="doc_text">
2049
2050<p>There are some primitive transformation operations present in the LLVM
Joel Stanley753eb712002-09-11 22:32:24 +0000[diff] [blame]2051infrastructure that are worth knowing about. When performing
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]2052transformations, it's fairly common to manipulate the contents of basic
2053blocks. This section describes some of the common methods for doing so
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2054and gives example code.</p>
2055
2056</div>
2057
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]2058<!--_______________________________________________________________________-->
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2059<div class="doc_subsubsection">
2060 <a name="schanges_creating">Creating and inserting new
2061 <tt>Instruction</tt>s</a>
2062</div>
2063
2064<div class="doc_text">
2065
2066<p><i>Instantiating Instructions</i></p>
2067
Chris Lattner69bf8a92004-05-23 21:06:58 +0000[diff] [blame]2068<p>Creation of <tt>Instruction</tt>s is straight-forward: simply call the
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2069constructor for the kind of instruction to instantiate and provide the necessary
2070parameters. For example, an <tt>AllocaInst</tt> only <i>requires</i> a
2071(const-ptr-to) <tt>Type</tt>. Thus:</p>
2072
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2073<div class="doc_code">
2074<pre>
Nick Lewycky10d64b92007-12-03 01:52:52 +0000[diff] [blame]2075AllocaInst* ai = new AllocaInst(Type::Int32Ty);
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2076</pre>
2077</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2078
2079<p>will create an <tt>AllocaInst</tt> instance that represents the allocation of
Reid Spencer128a7a72007-02-03 21:06:43 +0000[diff] [blame]2080one integer in the current stack frame, at run time. Each <tt>Instruction</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2081subclass is likely to have varying default parameters which change the semantics
2082of the instruction, so refer to the <a
Misha Brukman31ca1de2004-06-03 23:35:54 +0000[diff] [blame]2083href="/doxygen/classllvm_1_1Instruction.html">doxygen documentation for the subclass of
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2084Instruction</a> that you're interested in instantiating.</p>
2085
2086<p><i>Naming values</i></p>
2087
2088<p>It is very useful to name the values of instructions when you're able to, as
2089this facilitates the debugging of your transformations. If you end up looking
2090at generated LLVM machine code, you definitely want to have logical names
2091associated with the results of instructions! By supplying a value for the
2092<tt>Name</tt> (default) parameter of the <tt>Instruction</tt> constructor, you
2093associate a logical name with the result of the instruction's execution at
Reid Spencer128a7a72007-02-03 21:06:43 +0000[diff] [blame]2094run time. For example, say that I'm writing a transformation that dynamically
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2095allocates space for an integer on the stack, and that integer is going to be
2096used as some kind of index by some other code. To accomplish this, I place an
2097<tt>AllocaInst</tt> at the first point in the first <tt>BasicBlock</tt> of some
2098<tt>Function</tt>, and I'm intending to use it within the same
2099<tt>Function</tt>. I might do:</p>
2100
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2101<div class="doc_code">
2102<pre>
Nick Lewycky10d64b92007-12-03 01:52:52 +0000[diff] [blame]2103AllocaInst* pa = new AllocaInst(Type::Int32Ty, 0, "indexLoc");
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2104</pre>
2105</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2106
2107<p>where <tt>indexLoc</tt> is now the logical name of the instruction's
Reid Spencer128a7a72007-02-03 21:06:43 +0000[diff] [blame]2108execution value, which is a pointer to an integer on the run time stack.</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2109
2110<p><i>Inserting instructions</i></p>
2111
2112<p>There are essentially two ways to insert an <tt>Instruction</tt>
2113into an existing sequence of instructions that form a <tt>BasicBlock</tt>:</p>
2114
Joel Stanley9dd1ad62002-09-18 03:17:23 +0000[diff] [blame]2115<ul>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2116 <li>Insertion into an explicit instruction list
2117
2118 <p>Given a <tt>BasicBlock* pb</tt>, an <tt>Instruction* pi</tt> within that
2119 <tt>BasicBlock</tt>, and a newly-created instruction we wish to insert
2120 before <tt>*pi</tt>, we do the following: </p>
2121
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2122<div class="doc_code">
2123<pre>
2124BasicBlock *pb = ...;
2125Instruction *pi = ...;
2126Instruction *newInst = new Instruction(...);
2127
Bill Wendling82e2eea2006-10-11 18:00:22 +0000[diff] [blame]2128pb-&gt;getInstList().insert(pi, newInst); // <i>Inserts newInst before pi in pb</i>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2129</pre>
2130</div>
Alkis Evlogimenos9a5dc4f2004-05-27 00:57:51 +0000[diff] [blame]2131
2132 <p>Appending to the end of a <tt>BasicBlock</tt> is so common that
2133 the <tt>Instruction</tt> class and <tt>Instruction</tt>-derived
2134 classes provide constructors which take a pointer to a
2135 <tt>BasicBlock</tt> to be appended to. For example code that
2136 looked like: </p>
2137
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2138<div class="doc_code">
2139<pre>
2140BasicBlock *pb = ...;
2141Instruction *newInst = new Instruction(...);
2142
Bill Wendling82e2eea2006-10-11 18:00:22 +0000[diff] [blame]2143pb-&gt;getInstList().push_back(newInst); // <i>Appends newInst to pb</i>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2144</pre>
2145</div>
Alkis Evlogimenos9a5dc4f2004-05-27 00:57:51 +0000[diff] [blame]2146
2147 <p>becomes: </p>
2148
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2149<div class="doc_code">
2150<pre>
2151BasicBlock *pb = ...;
2152Instruction *newInst = new Instruction(..., pb);
2153</pre>
2154</div>
Alkis Evlogimenos9a5dc4f2004-05-27 00:57:51 +0000[diff] [blame]2155
2156 <p>which is much cleaner, especially if you are creating
2157 long instruction streams.</p></li>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2158
2159 <li>Insertion into an implicit instruction list
2160
2161 <p><tt>Instruction</tt> instances that are already in <tt>BasicBlock</tt>s
2162 are implicitly associated with an existing instruction list: the instruction
2163 list of the enclosing basic block. Thus, we could have accomplished the same
2164 thing as the above code without being given a <tt>BasicBlock</tt> by doing:
2165 </p>
2166
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2167<div class="doc_code">
2168<pre>
2169Instruction *pi = ...;
2170Instruction *newInst = new Instruction(...);
2171
2172pi-&gt;getParent()-&gt;getInstList().insert(pi, newInst);
2173</pre>
2174</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2175
2176 <p>In fact, this sequence of steps occurs so frequently that the
2177 <tt>Instruction</tt> class and <tt>Instruction</tt>-derived classes provide
2178 constructors which take (as a default parameter) a pointer to an
2179 <tt>Instruction</tt> which the newly-created <tt>Instruction</tt> should
2180 precede. That is, <tt>Instruction</tt> constructors are capable of
2181 inserting the newly-created instance into the <tt>BasicBlock</tt> of a
2182 provided instruction, immediately before that instruction. Using an
2183 <tt>Instruction</tt> constructor with a <tt>insertBefore</tt> (default)
2184 parameter, the above code becomes:</p>
2185
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2186<div class="doc_code">
2187<pre>
2188Instruction* pi = ...;
2189Instruction* newInst = new Instruction(..., pi);
2190</pre>
2191</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2192
2193 <p>which is much cleaner, especially if you're creating a lot of
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2194 instructions and adding them to <tt>BasicBlock</tt>s.</p></li>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2195</ul>
2196
2197</div>
2198
2199<!--_______________________________________________________________________-->
2200<div class="doc_subsubsection">
2201 <a name="schanges_deleting">Deleting <tt>Instruction</tt>s</a>
2202</div>
2203
2204<div class="doc_text">
2205
2206<p>Deleting an instruction from an existing sequence of instructions that form a
Chris Lattner69bf8a92004-05-23 21:06:58 +0000[diff] [blame]2207<a href="#BasicBlock"><tt>BasicBlock</tt></a> is very straight-forward. First,
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2208you must have a pointer to the instruction that you wish to delete. Second, you
2209need to obtain the pointer to that instruction's basic block. You use the
2210pointer to the basic block to get its list of instructions and then use the
2211erase function to remove your instruction. For example:</p>
2212
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2213<div class="doc_code">
2214<pre>
2215<a href="#Instruction">Instruction</a> *I = .. ;
Chris Lattner9f8ec252008-02-15 22:57:17 +0000[diff] [blame]2216I-&gt;eraseFromParent();
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2217</pre>
2218</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2219
2220</div>
2221
2222<!--_______________________________________________________________________-->
2223<div class="doc_subsubsection">
2224 <a name="schanges_replacing">Replacing an <tt>Instruction</tt> with another
2225 <tt>Value</tt></a>
2226</div>
2227
2228<div class="doc_text">
2229
2230<p><i>Replacing individual instructions</i></p>
2231
2232<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]2233permits use of two very useful replace functions: <tt>ReplaceInstWithValue</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2234and <tt>ReplaceInstWithInst</tt>.</p>
2235
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]2236<h4><a name="schanges_deleting">Deleting <tt>Instruction</tt>s</a></h4>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2237
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]2238<ul>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2239 <li><tt>ReplaceInstWithValue</tt>
2240
Nick Lewyckyb6d1f392008-09-15 06:31:52 +0000[diff] [blame]2241 <p>This function replaces all uses of a given instruction with a value,
2242 and then removes the original instruction. The following example
2243 illustrates the replacement of the result of a particular
Chris Lattner58360822005-01-17 00:12:04 +0000[diff] [blame]2244 <tt>AllocaInst</tt> that allocates memory for a single integer with a null
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2245 pointer to an integer.</p>
2246
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2247<div class="doc_code">
2248<pre>
2249AllocaInst* instToReplace = ...;
2250BasicBlock::iterator ii(instToReplace);
2251
2252ReplaceInstWithValue(instToReplace-&gt;getParent()-&gt;getInstList(), ii,
Daniel Dunbar58c2ac02008-10-03 22:17:25 +0000[diff] [blame]2253 Constant::getNullValue(PointerType::getUnqual(Type::Int32Ty)));
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2254</pre></div></li>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2255
2256 <li><tt>ReplaceInstWithInst</tt>
2257
2258 <p>This function replaces a particular instruction with another
Nick Lewyckyb6d1f392008-09-15 06:31:52 +0000[diff] [blame]2259 instruction, inserting the new instruction into the basic block at the
2260 location where the old instruction was, and replacing any uses of the old
2261 instruction with the new instruction. The following example illustrates
2262 the replacement of one <tt>AllocaInst</tt> with another.</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2263
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2264<div class="doc_code">
2265<pre>
2266AllocaInst* instToReplace = ...;
2267BasicBlock::iterator ii(instToReplace);
2268
2269ReplaceInstWithInst(instToReplace-&gt;getParent()-&gt;getInstList(), ii,
Nick Lewycky10d64b92007-12-03 01:52:52 +0000[diff] [blame]2270 new AllocaInst(Type::Int32Ty, 0, "ptrToReplacedInt"));
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2271</pre></div></li>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]2272</ul>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2273
2274<p><i>Replacing multiple uses of <tt>User</tt>s and <tt>Value</tt>s</i></p>
2275
2276<p>You can use <tt>Value::replaceAllUsesWith</tt> and
2277<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]2278doxygen documentation for the <a href="/doxygen/classllvm_1_1Value.html">Value Class</a>
Misha Brukman384047f2004-06-03 23:29:12 +0000[diff] [blame]2279and <a href="/doxygen/classllvm_1_1User.html">User Class</a>, respectively, for more
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2280information.</p>
2281
2282<!-- Value::replaceAllUsesWith User::replaceUsesOfWith Point out:
2283include/llvm/Transforms/Utils/ especially BasicBlockUtils.h with:
2284ReplaceInstWithValue, ReplaceInstWithInst -->
2285
2286</div>
2287
Tanya Lattnerb011c662007-06-20 18:33:15 +0000[diff] [blame]2288<!--_______________________________________________________________________-->
2289<div class="doc_subsubsection">
2290 <a name="schanges_deletingGV">Deleting <tt>GlobalVariable</tt>s</a>
2291</div>
2292
2293<div class="doc_text">
2294
Tanya Lattnerc5dfcdb2007-06-20 20:46:37 +0000[diff] [blame]2295<p>Deleting a global variable from a module is just as easy as deleting an
2296Instruction. First, you must have a pointer to the global variable that you wish
2297 to delete. You use this pointer to erase it from its parent, the module.
Tanya Lattnerb011c662007-06-20 18:33:15 +0000[diff] [blame]2298 For example:</p>
2299
2300<div class="doc_code">
2301<pre>
2302<a href="#GlobalVariable">GlobalVariable</a> *GV = .. ;
Tanya Lattnerb011c662007-06-20 18:33:15 +0000[diff] [blame]2303
Tanya Lattnerc5dfcdb2007-06-20 20:46:37 +0000[diff] [blame]2304GV-&gt;eraseFromParent();
Tanya Lattnerb011c662007-06-20 18:33:15 +0000[diff] [blame]2305</pre>
2306</div>
2307
2308</div>
2309
Jeffrey Yasskin714257f2009-04-30 22:33:41 +0000[diff] [blame]2310<!-- ======================================================================= -->
2311<div class="doc_subsection">
2312 <a name="create_types">How to Create Types</a>
2313</div>
2314
2315<div class="doc_text">
2316
2317<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]2318statically, you can use <tt>TypeBuilder&lt;...&gt;::get()</tt>, defined
Jeffrey Yasskin714257f2009-04-30 22:33:41 +0000[diff] [blame]2319in <tt>llvm/Support/TypeBuilder.h</tt>, to retrieve them. <tt>TypeBuilder</tt>
2320has two forms depending on whether you're building types for cross-compilation
Misha Brukman1af789f2009-05-01 20:40:51 +0000[diff] [blame]2321or native library use. <tt>TypeBuilder&lt;T, true&gt;</tt> requires
Jeffrey Yasskin714257f2009-04-30 22:33:41 +0000[diff] [blame]2322that <tt>T</tt> be independent of the host environment, meaning that it's built
2323out of types from
2324the <a href="/doxygen/namespacellvm_1_1types.html"><tt>llvm::types</tt></a>
2325namespace and pointers, functions, arrays, etc. built of
Misha Brukman1af789f2009-05-01 20:40:51 +0000[diff] [blame]2326those. <tt>TypeBuilder&lt;T, false&gt;</tt> additionally allows native C types
Jeffrey Yasskin714257f2009-04-30 22:33:41 +0000[diff] [blame]2327whose size may depend on the host compiler. For example,</p>
2328
2329<div class="doc_code">
2330<pre>
Misha Brukman1af789f2009-05-01 20:40:51 +0000[diff] [blame]2331FunctionType *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]2332</pre>
2333</div>
2334
2335<p>is easier to read and write than the equivalent</p>
2336
2337<div class="doc_code">
2338<pre>
Owen Anderson5e8c50e2009-06-16 17:40:28 +0000[diff] [blame]2339std::vector&lt;const Type*&gt; params;
Jeffrey Yasskin714257f2009-04-30 22:33:41 +0000[diff] [blame]2340params.push_back(PointerType::getUnqual(Type::Int32Ty));
2341FunctionType *ft = FunctionType::get(Type::Int8Ty, params, false);
2342</pre>
2343</div>
2344
2345<p>See the <a href="/doxygen/TypeBuilder_8h-source.html#l00001">class
2346comment</a> for more details.</p>
2347
2348</div>
2349
Chris Lattner9355b472002-09-06 02:50:58 +0000[diff] [blame]2350<!-- *********************************************************************** -->
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2351<div class="doc_section">
Owen Anderson8bc1b3b2009-06-16 01:17:16 +0000[diff] [blame]2352 <a name="threading">Threads and LLVM</a>
2353</div>
2354<!-- *********************************************************************** -->
2355
2356<div class="doc_text">
2357<p>
2358This section describes the interaction of the LLVM APIs with multithreading,
2359both on the part of client applications, and in the JIT, in the hosted
2360application.
2361</p>
2362
2363<p>
2364Note that LLVM's support for multithreading is still relatively young. Up
2365through version 2.5, the execution of threaded hosted applications was
2366supported, but not threaded client access to the APIs. While this use case is
2367now supported, clients <em>must</em> adhere to the guidelines specified below to
2368ensure proper operation in multithreaded mode.
2369</p>
2370
2371<p>
2372Note that, on Unix-like platforms, LLVM requires the presence of GCC's atomic
2373intrinsics in order to support threaded operation. If you need a
2374multhreading-capable LLVM on a platform without a suitably modern system
2375compiler, consider compiling LLVM and LLVM-GCC in single-threaded mode, and
2376using the resultant compiler to build a copy of LLVM with multithreading
2377support.
2378</p>
2379</div>
2380
2381<!-- ======================================================================= -->
2382<div class="doc_subsection">
Owen Anderson1ad70e32009-06-16 18:04:19 +0000[diff] [blame]2383 <a name="startmultithreaded">Entering and Exiting Multithreaded Mode</a>
Owen Anderson8bc1b3b2009-06-16 01:17:16 +0000[diff] [blame]2384</div>
2385
2386<div class="doc_text">
2387
2388<p>
2389In order to properly protect its internal data structures while avoiding
Owen Anderson1ad70e32009-06-16 18:04:19 +0000[diff] [blame]2390excessive locking overhead in the single-threaded case, the LLVM must intialize
2391certain data structures necessary to provide guards around its internals. To do
2392so, the client program must invoke <tt>llvm_start_multithreaded()</tt> before
2393making any concurrent LLVM API calls. To subsequently tear down these
2394structures, use the <tt>llvm_stop_multithreaded()</tt> call. You can also use
2395the <tt>llvm_is_multithreaded()</tt> call to check the status of multithreaded
2396mode.
Owen Anderson8bc1b3b2009-06-16 01:17:16 +0000[diff] [blame]2397</p>
2398
2399<p>
Owen Anderson1ad70e32009-06-16 18:04:19 +0000[diff] [blame]2400Note that both of these calls must be made <em>in isolation</em>. That is to
2401say that no other LLVM API calls may be executing at any time during the
2402execution of <tt>llvm_start_multithreaded()</tt> or <tt>llvm_stop_multithreaded
2403</tt>. It's is the client's responsibility to enforce this isolation.
2404</p>
2405
2406<p>
2407The return value of <tt>llvm_start_multithreaded()</tt> indicates the success or
2408failure of the initialization. Failure typically indicates that your copy of
2409LLVM was built without multithreading support, typically because GCC atomic
2410intrinsics were not found in your system compiler. In this case, the LLVM API
2411will not be safe for concurrent calls. However, it <em>will</em> be safe for
Jeffrey Yasskin01eba392010-01-29 19:10:38 +0000[diff] [blame]2412hosting threaded applications in the JIT, though <a href="#jitthreading">care
2413must be taken</a> to ensure that side exits and the like do not accidentally
2414result in concurrent LLVM API calls.
Owen Anderson8bc1b3b2009-06-16 01:17:16 +0000[diff] [blame]2415</p>
2416</div>
2417
2418<!-- ======================================================================= -->
2419<div class="doc_subsection">
2420 <a name="shutdown">Ending Execution with <tt>llvm_shutdown()</tt></a>
2421</div>
2422
2423<div class="doc_text">
2424<p>
2425When you are done using the LLVM APIs, you should call <tt>llvm_shutdown()</tt>
Owen Anderson1ad70e32009-06-16 18:04:19 +0000[diff] [blame]2426to deallocate memory used for internal structures. This will also invoke
2427<tt>llvm_stop_multithreaded()</tt> if LLVM is operating in multithreaded mode.
2428As such, <tt>llvm_shutdown()</tt> requires the same isolation guarantees as
2429<tt>llvm_stop_multithreaded()</tt>.
Owen Anderson8bc1b3b2009-06-16 01:17:16 +0000[diff] [blame]2430</p>
2431
2432<p>
2433Note that, if you use scope-based shutdown, you can use the
2434<tt>llvm_shutdown_obj</tt> class, which calls <tt>llvm_shutdown()</tt> in its
2435destructor.
2436</div>
2437
2438<!-- ======================================================================= -->
2439<div class="doc_subsection">
2440 <a name="managedstatic">Lazy Initialization with <tt>ManagedStatic</tt></a>
2441</div>
2442
2443<div class="doc_text">
2444<p>
2445<tt>ManagedStatic</tt> is a utility class in LLVM used to implement static
2446initialization of static resources, such as the global type tables. Before the
2447invocation of <tt>llvm_shutdown()</tt>, it implements a simple lazy
2448initialization scheme. Once <tt>llvm_start_multithreaded()</tt> returns,
2449however, it uses double-checked locking to implement thread-safe lazy
2450initialization.
2451</p>
2452
2453<p>
2454Note that, because no other threads are allowed to issue LLVM API calls before
2455<tt>llvm_start_multithreaded()</tt> returns, it is possible to have
2456<tt>ManagedStatic</tt>s of <tt>llvm::sys::Mutex</tt>s.
2457</p>
Owen Anderson1ad70e32009-06-16 18:04:19 +0000[diff] [blame]2458
2459<p>
2460The <tt>llvm_acquire_global_lock()</tt> and <tt>llvm_release_global_lock</tt>
2461APIs provide access to the global lock used to implement the double-checked
2462locking for lazy initialization. These should only be used internally to LLVM,
2463and only if you know what you're doing!
2464</p>
Owen Anderson8bc1b3b2009-06-16 01:17:16 +0000[diff] [blame]2465</div>
2466
Owen Andersone0c951a2009-08-19 17:58:52 +0000[diff] [blame]2467<!-- ======================================================================= -->
2468<div class="doc_subsection">
2469 <a name="llvmcontext">Achieving Isolation with <tt>LLVMContext</tt></a>
2470</div>
2471
2472<div class="doc_text">
2473<p>
2474<tt>LLVMContext</tt> is an opaque class in the LLVM API which clients can use
2475to operate multiple, isolated instances of LLVM concurrently within the same
2476address space. For instance, in a hypothetical compile-server, the compilation
2477of an individual translation unit is conceptually independent from all the
2478others, and it would be desirable to be able to compile incoming translation
2479units concurrently on independent server threads. Fortunately,
2480<tt>LLVMContext</tt> exists to enable just this kind of scenario!
2481</p>
2482
2483<p>
2484Conceptually, <tt>LLVMContext</tt> provides isolation. Every LLVM entity
2485(<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]2486in LLVM's in-memory IR belongs to an <tt>LLVMContext</tt>. Entities in
Owen Andersone0c951a2009-08-19 17:58:52 +0000[diff] [blame]2487different contexts <em>cannot</em> interact with each other: <tt>Module</tt>s in
2488different contexts cannot be linked together, <tt>Function</tt>s cannot be added
2489to <tt>Module</tt>s in different contexts, etc. What this means is that is is
2490safe to compile on multiple threads simultaneously, as long as no two threads
2491operate on entities within the same context.
2492</p>
2493
2494<p>
2495In practice, very few places in the API require the explicit specification of a
2496<tt>LLVMContext</tt>, other than the <tt>Type</tt> creation/lookup APIs.
2497Because every <tt>Type</tt> carries a reference to its owning context, most
2498other entities can determine what context they belong to by looking at their
2499own <tt>Type</tt>. If you are adding new entities to LLVM IR, please try to
2500maintain this interface design.
2501</p>
2502
2503<p>
2504For clients that do <em>not</em> require the benefits of isolation, LLVM
2505provides a convenience API <tt>getGlobalContext()</tt>. This returns a global,
2506lazily initialized <tt>LLVMContext</tt> that may be used in situations where
2507isolation is not a concern.
2508</p>
2509</div>
2510
Jeffrey Yasskin01eba392010-01-29 19:10:38 +0000[diff] [blame]2511<!-- ======================================================================= -->
2512<div class="doc_subsection">
2513 <a name="jitthreading">Threads and the JIT</a>
2514</div>
2515
2516<div class="doc_text">
2517<p>
2518LLVM's "eager" JIT compiler is safe to use in threaded programs. Multiple
2519threads can call <tt>ExecutionEngine::getPointerToFunction()</tt> or
2520<tt>ExecutionEngine::runFunction()</tt> concurrently, and multiple threads can
2521run code output by the JIT concurrently. The user must still ensure that only
2522one thread accesses IR in a given <tt>LLVMContext</tt> while another thread
2523might be modifying it. One way to do that is to always hold the JIT lock while
2524accessing IR outside the JIT (the JIT <em>modifies</em> the IR by adding
2525<tt>CallbackVH</tt>s). Another way is to only
2526call <tt>getPointerToFunction()</tt> from the <tt>LLVMContext</tt>'s thread.
2527</p>
2528
2529<p>When the JIT is configured to compile lazily (using
2530<tt>ExecutionEngine::DisableLazyCompilation(false)</tt>), there is currently a
2531<a href="http://llvm.org/bugs/show_bug.cgi?id=5184">race condition</a> in
2532updating call sites after a function is lazily-jitted. It's still possible to
2533use the lazy JIT in a threaded program if you ensure that only one thread at a
2534time can call any particular lazy stub and that the JIT lock guards any IR
2535access, but we suggest using only the eager JIT in threaded programs.
2536</p>
2537</div>
2538
Owen Anderson8bc1b3b2009-06-16 01:17:16 +0000[diff] [blame]2539<!-- *********************************************************************** -->
2540<div class="doc_section">
Chris Lattnerd9d6e102005-04-23 16:10:52 +0000[diff] [blame]2541 <a name="advanced">Advanced Topics</a>
2542</div>
2543<!-- *********************************************************************** -->
2544
2545<div class="doc_text">
Chris Lattnerf1b200b2005-04-23 17:27:36 +0000[diff] [blame]2546<p>
2547This section describes some of the advanced or obscure API's that most clients
2548do not need to be aware of. These API's tend manage the inner workings of the
2549LLVM system, and only need to be accessed in unusual circumstances.
2550</p>
2551</div>
Chris Lattnerd9d6e102005-04-23 16:10:52 +0000[diff] [blame]2552
Chris Lattnerf1b200b2005-04-23 17:27:36 +0000[diff] [blame]2553<!-- ======================================================================= -->
2554<div class="doc_subsection">
2555 <a name="TypeResolve">LLVM Type Resolution</a>
2556</div>
Chris Lattnerd9d6e102005-04-23 16:10:52 +0000[diff] [blame]2557
Chris Lattnerf1b200b2005-04-23 17:27:36 +0000[diff] [blame]2558<div class="doc_text">
2559
2560<p>
2561The LLVM type system has a very simple goal: allow clients to compare types for
2562structural equality with a simple pointer comparison (aka a shallow compare).
2563This goal makes clients much simpler and faster, and is used throughout the LLVM
2564system.
2565</p>
2566
2567<p>
2568Unfortunately achieving this goal is not a simple matter. In particular,
2569recursive types and late resolution of opaque types makes the situation very
2570difficult to handle. Fortunately, for the most part, our implementation makes
2571most clients able to be completely unaware of the nasty internal details. The
2572primary case where clients are exposed to the inner workings of it are when
Gabor Greif04367bf2007-07-06 22:07:22 +0000[diff] [blame]2573building a recursive type. In addition to this case, the LLVM bitcode reader,
Chris Lattnerf1b200b2005-04-23 17:27:36 +0000[diff] [blame]2574assembly parser, and linker also have to be aware of the inner workings of this
2575system.
2576</p>
2577
Chris Lattner0f876db2005-04-25 15:47:57 +0000[diff] [blame]2578<p>
2579For our purposes below, we need three concepts. First, an "Opaque Type" is
2580exactly as defined in the <a href="LangRef.html#t_opaque">language
2581reference</a>. Second an "Abstract Type" is any type which includes an
Reid Spencer06565dc2007-01-12 17:11:23 +0000[diff] [blame]2582opaque type as part of its type graph (for example "<tt>{ opaque, i32 }</tt>").
2583Third, 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]2584float }</tt>").
2585</p>
2586
Chris Lattnerf1b200b2005-04-23 17:27:36 +0000[diff] [blame]2587</div>
2588
2589<!-- ______________________________________________________________________ -->
2590<div class="doc_subsubsection">
2591 <a name="BuildRecType">Basic Recursive Type Construction</a>
2592</div>
2593
2594<div class="doc_text">
2595
2596<p>
2597Because the most common question is "how do I build a recursive type with LLVM",
2598we answer it now and explain it as we go. Here we include enough to cause this
2599to be emitted to an output .ll file:
2600</p>
2601
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2602<div class="doc_code">
Chris Lattnerf1b200b2005-04-23 17:27:36 +0000[diff] [blame]2603<pre>
Reid Spencer06565dc2007-01-12 17:11:23 +0000[diff] [blame]2604%mylist = type { %mylist*, i32 }
Chris Lattnerf1b200b2005-04-23 17:27:36 +0000[diff] [blame]2605</pre>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2606</div>
Chris Lattnerf1b200b2005-04-23 17:27:36 +0000[diff] [blame]2607
2608<p>
2609To build this, use the following LLVM APIs:
2610</p>
2611
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2612<div class="doc_code">
Chris Lattnerf1b200b2005-04-23 17:27:36 +0000[diff] [blame]2613<pre>
Bill Wendling82e2eea2006-10-11 18:00:22 +0000[diff] [blame]2614// <i>Create the initial outer struct</i>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2615<a href="#PATypeHolder">PATypeHolder</a> StructTy = OpaqueType::get();
2616std::vector&lt;const Type*&gt; Elts;
Daniel Dunbar58c2ac02008-10-03 22:17:25 +0000[diff] [blame]2617Elts.push_back(PointerType::getUnqual(StructTy));
Nick Lewycky10d64b92007-12-03 01:52:52 +0000[diff] [blame]2618Elts.push_back(Type::Int32Ty);
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2619StructType *NewSTy = StructType::get(Elts);
Chris Lattnerf1b200b2005-04-23 17:27:36 +0000[diff] [blame]2620
Reid Spencer06565dc2007-01-12 17:11:23 +0000[diff] [blame]2621// <i>At this point, NewSTy = "{ opaque*, i32 }". Tell VMCore that</i>
Bill Wendling82e2eea2006-10-11 18:00:22 +0000[diff] [blame]2622// <i>the struct and the opaque type are actually the same.</i>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2623cast&lt;OpaqueType&gt;(StructTy.get())-&gt;<a href="#refineAbstractTypeTo">refineAbstractTypeTo</a>(NewSTy);
Chris Lattnerf1b200b2005-04-23 17:27:36 +0000[diff] [blame]2624
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2625// <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]2626// <i>kept up-to-date</i>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2627NewSTy = cast&lt;StructType&gt;(StructTy.get());
Chris Lattnerf1b200b2005-04-23 17:27:36 +0000[diff] [blame]2628
Bill Wendling82e2eea2006-10-11 18:00:22 +0000[diff] [blame]2629// <i>Add a name for the type to the module symbol table (optional)</i>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2630MyModule-&gt;addTypeName("mylist", NewSTy);
Chris Lattnerf1b200b2005-04-23 17:27:36 +0000[diff] [blame]2631</pre>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2632</div>
Chris Lattnerf1b200b2005-04-23 17:27:36 +0000[diff] [blame]2633
2634<p>
2635This code shows the basic approach used to build recursive types: build a
2636non-recursive type using 'opaque', then use type unification to close the cycle.
2637The type unification step is performed by the <tt><a
Chris Lattneraff26d12007-02-03 03:06:52 +0000[diff] [blame]2638href="#refineAbstractTypeTo">refineAbstractTypeTo</a></tt> method, which is
Chris Lattnerf1b200b2005-04-23 17:27:36 +0000[diff] [blame]2639described next. After that, we describe the <a
2640href="#PATypeHolder">PATypeHolder class</a>.
2641</p>
2642
2643</div>
2644
2645<!-- ______________________________________________________________________ -->
2646<div class="doc_subsubsection">
2647 <a name="refineAbstractTypeTo">The <tt>refineAbstractTypeTo</tt> method</a>
2648</div>
2649
2650<div class="doc_text">
2651<p>
2652The <tt>refineAbstractTypeTo</tt> method starts the type unification process.
2653While this method is actually a member of the DerivedType class, it is most
2654often used on OpaqueType instances. Type unification is actually a recursive
2655process. After unification, types can become structurally isomorphic to
2656existing types, and all duplicates are deleted (to preserve pointer equality).
2657</p>
2658
2659<p>
2660In the example above, the OpaqueType object is definitely deleted.
Reid Spencer06565dc2007-01-12 17:11:23 +0000[diff] [blame]2661Additionally, if there is an "{ \2*, i32}" type already created in the system,
Chris Lattnerf1b200b2005-04-23 17:27:36 +0000[diff] [blame]2662the pointer and struct type created are <b>also</b> deleted. Obviously whenever
2663a type is deleted, any "Type*" pointers in the program are invalidated. As
2664such, it is safest to avoid having <i>any</i> "Type*" pointers to abstract types
2665live across a call to <tt>refineAbstractTypeTo</tt> (note that non-abstract
2666types can never move or be deleted). To deal with this, the <a
2667href="#PATypeHolder">PATypeHolder</a> class is used to maintain a stable
2668reference to a possibly refined type, and the <a
2669href="#AbstractTypeUser">AbstractTypeUser</a> class is used to update more
2670complex datastructures.
2671</p>
2672
2673</div>
2674
2675<!-- ______________________________________________________________________ -->
2676<div class="doc_subsubsection">
2677 <a name="PATypeHolder">The PATypeHolder Class</a>
2678</div>
2679
2680<div class="doc_text">
2681<p>
2682PATypeHolder is a form of a "smart pointer" for Type objects. When VMCore
2683happily goes about nuking types that become isomorphic to existing types, it
2684automatically updates all PATypeHolder objects to point to the new type. In the
2685example above, this allows the code to maintain a pointer to the resultant
2686resolved recursive type, even though the Type*'s are potentially invalidated.
2687</p>
2688
2689<p>
2690PATypeHolder is an extremely light-weight object that uses a lazy union-find
2691implementation to update pointers. For example the pointer from a Value to its
2692Type is maintained by PATypeHolder objects.
2693</p>
2694
2695</div>
2696
2697<!-- ______________________________________________________________________ -->
2698<div class="doc_subsubsection">
2699 <a name="AbstractTypeUser">The AbstractTypeUser Class</a>
2700</div>
2701
2702<div class="doc_text">
2703
2704<p>
2705Some data structures need more to perform more complex updates when types get
Chris Lattner263a98e2007-02-16 04:37:31 +0000[diff] [blame]2706resolved. To support this, a class can derive from the AbstractTypeUser class.
2707This class
Chris Lattnerf1b200b2005-04-23 17:27:36 +0000[diff] [blame]2708allows it to get callbacks when certain types are resolved. To register to get
2709callbacks for a particular type, the DerivedType::{add/remove}AbstractTypeUser
Chris Lattner0f876db2005-04-25 15:47:57 +0000[diff] [blame]2710methods can be called on a type. Note that these methods only work for <i>
Reid Spencer06565dc2007-01-12 17:11:23 +0000[diff] [blame]2711 abstract</i> types. Concrete types (those that do not include any opaque
2712objects) can never be refined.
Chris Lattnerf1b200b2005-04-23 17:27:36 +0000[diff] [blame]2713</p>
Chris Lattnerd9d6e102005-04-23 16:10:52 +0000[diff] [blame]2714</div>
2715
2716
2717<!-- ======================================================================= -->
2718<div class="doc_subsection">
Chris Lattner263a98e2007-02-16 04:37:31 +0000[diff] [blame]2719 <a name="SymbolTable">The <tt>ValueSymbolTable</tt> and
2720 <tt>TypeSymbolTable</tt> classes</a>
Chris Lattnerd9d6e102005-04-23 16:10:52 +0000[diff] [blame]2721</div>
Chris Lattnerf1b200b2005-04-23 17:27:36 +0000[diff] [blame]2722
Chris Lattnerd9d6e102005-04-23 16:10:52 +0000[diff] [blame]2723<div class="doc_text">
Chris Lattner263a98e2007-02-16 04:37:31 +0000[diff] [blame]2724<p>The <tt><a href="http://llvm.org/doxygen/classllvm_1_1ValueSymbolTable.html">
2725ValueSymbolTable</a></tt> class provides a symbol table that the <a
Chris Lattnerd9d6e102005-04-23 16:10:52 +0000[diff] [blame]2726href="#Function"><tt>Function</tt></a> and <a href="#Module">
Chris Lattner263a98e2007-02-16 04:37:31 +0000[diff] [blame]2727<tt>Module</tt></a> classes use for naming value definitions. The symbol table
2728can provide a name for any <a href="#Value"><tt>Value</tt></a>.
2729The <tt><a href="http://llvm.org/doxygen/classllvm_1_1TypeSymbolTable.html">
2730TypeSymbolTable</a></tt> class is used by the <tt>Module</tt> class to store
2731names for types.</p>
Chris Lattnerd9d6e102005-04-23 16:10:52 +0000[diff] [blame]2732
Reid Spencera6362242007-01-07 00:41:39 +0000[diff] [blame]2733<p>Note that the <tt>SymbolTable</tt> class should not be directly accessed
2734by most clients. It should only be used when iteration over the symbol table
2735names themselves are required, which is very special purpose. Note that not
2736all LLVM
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2737<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]2738an empty name) do not exist in the symbol table.
2739</p>
2740
Chris Lattner263a98e2007-02-16 04:37:31 +0000[diff] [blame]2741<p>These symbol tables support iteration over the values/types in the symbol
2742table with <tt>begin/end/iterator</tt> and supports querying to see if a
2743specific name is in the symbol table (with <tt>lookup</tt>). The
2744<tt>ValueSymbolTable</tt> class exposes no public mutator methods, instead,
2745simply call <tt>setName</tt> on a value, which will autoinsert it into the
2746appropriate symbol table. For types, use the Module::addTypeName method to
2747insert entries into the symbol table.</p>
Chris Lattnerd9d6e102005-04-23 16:10:52 +0000[diff] [blame]2748
Chris Lattnerd9d6e102005-04-23 16:10:52 +0000[diff] [blame]2749</div>
2750
2751
2752
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2753<!-- ======================================================================= -->
2754<div class="doc_subsection">
2755 <a name="UserLayout">The <tt>User</tt> and owned <tt>Use</tt> classes' memory layout</a>
2756</div>
2757
2758<div class="doc_text">
2759<p>The <tt><a href="http://llvm.org/doxygen/classllvm_1_1User.html">
Gabor Greiffd095b62009-01-05 16:05:32 +0000[diff] [blame]2760User</a></tt> class provides a basis for expressing the ownership of <tt>User</tt>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2761towards other <tt><a href="http://llvm.org/doxygen/classllvm_1_1Value.html">
2762Value</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]2763Use</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]2764addition and removal.</p>
2765
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2766<!-- ______________________________________________________________________ -->
2767<div class="doc_subsubsection">
Gabor Greiffd095b62009-01-05 16:05:32 +0000[diff] [blame]2768 <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]2769</div>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2770
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2771<div class="doc_text">
2772<p>
2773A subclass of <tt>User</tt> can choose between incorporating its <tt>Use</tt> objects
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2774or refer to them out-of-line by means of a pointer. A mixed variant
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2775(some <tt>Use</tt>s inline others hung off) is impractical and breaks the invariant
2776that the <tt>Use</tt> objects belonging to the same <tt>User</tt> form a contiguous array.
2777</p>
2778</div>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2779
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2780<p>
2781We have 2 different layouts in the <tt>User</tt> (sub)classes:
2782<ul>
2783<li><p>Layout a)
2784The <tt>Use</tt> object(s) are inside (resp. at fixed offset) of the <tt>User</tt>
2785object and there are a fixed number of them.</p>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2786
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2787<li><p>Layout b)
2788The <tt>Use</tt> object(s) are referenced by a pointer to an
2789array from the <tt>User</tt> object and there may be a variable
2790number of them.</p>
2791</ul>
2792<p>
Gabor Greifd41720a2008-06-25 00:10:22 +0000[diff] [blame]2793As of v2.4 each layout still possesses a direct pointer to the
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2794start of the array of <tt>Use</tt>s. Though not mandatory for layout a),
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2795we stick to this redundancy for the sake of simplicity.
Gabor Greifd41720a2008-06-25 00:10:22 +0000[diff] [blame]2796The <tt>User</tt> object also stores the number of <tt>Use</tt> objects it
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2797has. (Theoretically this information can also be calculated
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2798given the scheme presented below.)</p>
2799<p>
2800Special forms of allocation operators (<tt>operator new</tt>)
Gabor Greifd41720a2008-06-25 00:10:22 +0000[diff] [blame]2801enforce the following memory layouts:</p>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2802
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2803<ul>
Gabor Greifd41720a2008-06-25 00:10:22 +0000[diff] [blame]2804<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]2805
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2806<pre>
2807...---.---.---.---.-------...
2808 | P | P | P | P | User
2809'''---'---'---'---'-------'''
2810</pre>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2811
Gabor Greifd41720a2008-06-25 00:10:22 +0000[diff] [blame]2812<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]2813<pre>
2814.-------...
2815| User
2816'-------'''
2817 |
2818 v
2819 .---.---.---.---...
2820 | P | P | P | P |
2821 '---'---'---'---'''
2822</pre>
2823</ul>
2824<i>(In the above figures '<tt>P</tt>' stands for the <tt>Use**</tt> that
2825 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]2826
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2827<!-- ______________________________________________________________________ -->
2828<div class="doc_subsubsection">
Gabor Greiffd095b62009-01-05 16:05:32 +0000[diff] [blame]2829 <a name="Waymarking">The waymarking algorithm</a>
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2830</div>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2831
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2832<div class="doc_text">
2833<p>
Gabor Greifd41720a2008-06-25 00:10:22 +0000[diff] [blame]2834Since the <tt>Use</tt> objects are deprived of the direct (back)pointer to
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2835their <tt>User</tt> objects, there must be a fast and exact method to
2836recover it. This is accomplished by the following scheme:</p>
2837</div>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2838
Gabor Greifd41720a2008-06-25 00:10:22 +0000[diff] [blame]2839A 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]2840start of the <tt>User</tt> object:
2841<ul>
2842<li><tt>00</tt> &mdash;&gt; binary digit 0</li>
2843<li><tt>01</tt> &mdash;&gt; binary digit 1</li>
2844<li><tt>10</tt> &mdash;&gt; stop and calculate (<tt>s</tt>)</li>
2845<li><tt>11</tt> &mdash;&gt; full stop (<tt>S</tt>)</li>
2846</ul>
2847<p>
2848Given a <tt>Use*</tt>, all we have to do is to walk till we get
2849a stop and we either have a <tt>User</tt> immediately behind or
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2850we have to walk to the next stop picking up digits
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2851and calculating the offset:</p>
2852<pre>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2853.---.---.---.---.---.---.---.---.---.---.---.---.---.---.---.---.----------------
2854| 1 | s | 1 | 0 | 1 | 0 | s | 1 | 1 | 0 | s | 1 | 1 | s | 1 | S | User (or User*)
2855'---'---'---'---'---'---'---'---'---'---'---'---'---'---'---'---'----------------
2856 |+15 |+10 |+6 |+3 |+1
2857 | | | | |__>
2858 | | | |__________>
2859 | | |______________________>
2860 | |______________________________________>
2861 |__________________________________________________________>
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2862</pre>
2863<p>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2864Only the significant number of bits need to be stored between the
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2865stops, so that the <i>worst case is 20 memory accesses</i> when there are
28661000 <tt>Use</tt> objects associated with a <tt>User</tt>.</p>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2867
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2868<!-- ______________________________________________________________________ -->
2869<div class="doc_subsubsection">
Gabor Greiffd095b62009-01-05 16:05:32 +0000[diff] [blame]2870 <a name="ReferenceImpl">Reference implementation</a>
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2871</div>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2872
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2873<div class="doc_text">
2874<p>
2875The following literate Haskell fragment demonstrates the concept:</p>
2876</div>
2877
2878<div class="doc_code">
2879<pre>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2880> import Test.QuickCheck
2881>
2882> digits :: Int -> [Char] -> [Char]
2883> digits 0 acc = '0' : acc
2884> digits 1 acc = '1' : acc
2885> digits n acc = digits (n `div` 2) $ digits (n `mod` 2) acc
2886>
2887> dist :: Int -> [Char] -> [Char]
2888> dist 0 [] = ['S']
2889> dist 0 acc = acc
2890> dist 1 acc = let r = dist 0 acc in 's' : digits (length r) r
2891> dist n acc = dist (n - 1) $ dist 1 acc
2892>
2893> takeLast n ss = reverse $ take n $ reverse ss
2894>
2895> test = takeLast 40 $ dist 20 []
2896>
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2897</pre>
2898</div>
2899<p>
2900Printing &lt;test&gt; gives: <tt>"1s100000s11010s10100s1111s1010s110s11s1S"</tt></p>
2901<p>
2902The reverse algorithm computes the length of the string just by examining
2903a certain prefix:</p>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2904
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2905<div class="doc_code">
2906<pre>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2907> pref :: [Char] -> Int
2908> pref "S" = 1
2909> pref ('s':'1':rest) = decode 2 1 rest
2910> pref (_:rest) = 1 + pref rest
2911>
2912> decode walk acc ('0':rest) = decode (walk + 1) (acc * 2) rest
2913> decode walk acc ('1':rest) = decode (walk + 1) (acc * 2 + 1) rest
2914> decode walk acc _ = walk + acc
2915>
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2916</pre>
2917</div>
2918<p>
2919Now, as expected, printing &lt;pref test&gt; gives <tt>40</tt>.</p>
2920<p>
2921We can <i>quickCheck</i> this with following property:</p>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2922
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2923<div class="doc_code">
2924<pre>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2925> testcase = dist 2000 []
2926> testcaseLength = length testcase
2927>
2928> identityProp n = n > 0 && n <= testcaseLength ==> length arr == pref arr
2929> where arr = takeLast n testcase
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2930>
2931</pre>
2932</div>
2933<p>
2934As expected &lt;quickCheck identityProp&gt; gives:</p>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2935
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2936<pre>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2937*Main> quickCheck identityProp
2938OK, passed 100 tests.
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2939</pre>
2940<p>
2941Let's be a bit more exhaustive:</p>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2942
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2943<div class="doc_code">
2944<pre>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2945>
2946> deepCheck p = check (defaultConfig { configMaxTest = 500 }) p
2947>
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2948</pre>
2949</div>
2950<p>
2951And here is the result of &lt;deepCheck identityProp&gt;:</p>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2952
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2953<pre>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2954*Main> deepCheck identityProp
2955OK, passed 500 tests.
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2956</pre>
2957
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2958<!-- ______________________________________________________________________ -->
2959<div class="doc_subsubsection">
Gabor Greiffd095b62009-01-05 16:05:32 +0000[diff] [blame]2960 <a name="Tagging">Tagging considerations</a>
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2961</div>
2962
2963<p>
2964To maintain the invariant that the 2 LSBits of each <tt>Use**</tt> in <tt>Use</tt>
2965never change after being set up, setters of <tt>Use::Prev</tt> must re-tag the
2966new <tt>Use**</tt> on every modification. Accordingly getters must strip the
2967tag bits.</p>
2968<p>
Gabor Greifd41720a2008-06-25 00:10:22 +0000[diff] [blame]2969For layout b) instead of the <tt>User</tt> we find a pointer (<tt>User*</tt> with LSBit set).
2970Following this pointer brings us to the <tt>User</tt>. A portable trick ensures
2971that the first bytes of <tt>User</tt> (if interpreted as a pointer) never has
Gabor Greiffd095b62009-01-05 16:05:32 +0000[diff] [blame]2972the LSBit set. (Portability is relying on the fact that all known compilers place the
2973<tt>vptr</tt> in the first word of the instances.)</p>
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2974
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2975</div>
2976
2977 <!-- *********************************************************************** -->
Chris Lattnerd9d6e102005-04-23 16:10:52 +0000[diff] [blame]2978<div class="doc_section">
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2979 <a name="coreclasses">The Core LLVM Class Hierarchy Reference </a>
2980</div>
2981<!-- *********************************************************************** -->
2982
2983<div class="doc_text">
Reid Spencer303c4b42007-01-12 17:26:25 +0000[diff] [blame]2984<p><tt>#include "<a href="/doxygen/Type_8h-source.html">llvm/Type.h</a>"</tt>
2985<br>doxygen info: <a href="/doxygen/classllvm_1_1Type.html">Type Class</a></p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2986
2987<p>The Core LLVM classes are the primary means of representing the program
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]2988being inspected or transformed. The core LLVM classes are defined in
2989header files in the <tt>include/llvm/</tt> directory, and implemented in
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2990the <tt>lib/VMCore</tt> directory.</p>
2991
2992</div>
2993
2994<!-- ======================================================================= -->
2995<div class="doc_subsection">
Reid Spencer303c4b42007-01-12 17:26:25 +0000[diff] [blame]2996 <a name="Type">The <tt>Type</tt> class and Derived Types</a>
2997</div>
2998
2999<div class="doc_text">
3000
3001 <p><tt>Type</tt> is a superclass of all type classes. Every <tt>Value</tt> has
3002 a <tt>Type</tt>. <tt>Type</tt> cannot be instantiated directly but only
3003 through its subclasses. Certain primitive types (<tt>VoidType</tt>,
3004 <tt>LabelType</tt>, <tt>FloatType</tt> and <tt>DoubleType</tt>) have hidden
3005 subclasses. They are hidden because they offer no useful functionality beyond
3006 what the <tt>Type</tt> class offers except to distinguish themselves from
3007 other subclasses of <tt>Type</tt>.</p>
3008 <p>All other types are subclasses of <tt>DerivedType</tt>. Types can be
3009 named, but this is not a requirement. There exists exactly
3010 one instance of a given shape at any one time. This allows type equality to
3011 be performed with address equality of the Type Instance. That is, given two
3012 <tt>Type*</tt> values, the types are identical if the pointers are identical.
3013 </p>
3014</div>
3015
3016<!-- _______________________________________________________________________ -->
3017<div class="doc_subsubsection">
Gabor Greiffd095b62009-01-05 16:05:32 +0000[diff] [blame]3018 <a name="m_Type">Important Public Methods</a>
Reid Spencer303c4b42007-01-12 17:26:25 +0000[diff] [blame]3019</div>
3020
3021<div class="doc_text">
3022
3023<ul>
Duncan Sandsb0bc6c32010-02-15 16:12:20 +0000[diff] [blame]3024 <li><tt>bool isIntegerTy() const</tt>: Returns true for any integer type.</li>
Reid Spencer303c4b42007-01-12 17:26:25 +0000[diff] [blame]3025
Duncan Sandsb0bc6c32010-02-15 16:12:20 +0000[diff] [blame]3026 <li><tt>bool isFloatingPointTy()</tt>: Return true if this is one of the five
Reid Spencer303c4b42007-01-12 17:26:25 +0000[diff] [blame]3027 floating point types.</li>
3028
3029 <li><tt>bool isAbstract()</tt>: Return true if the type is abstract (contains
3030 an OpaqueType anywhere in its definition).</li>
3031
3032 <li><tt>bool isSized()</tt>: Return true if the type has known size. Things
3033 that don't have a size are abstract types, labels and void.</li>
3034
3035</ul>
3036</div>
3037
3038<!-- _______________________________________________________________________ -->
3039<div class="doc_subsubsection">
Gabor Greiffd095b62009-01-05 16:05:32 +0000[diff] [blame]3040 <a name="derivedtypes">Important Derived Types</a>
Reid Spencer303c4b42007-01-12 17:26:25 +0000[diff] [blame]3041</div>
3042<div class="doc_text">
3043<dl>
3044 <dt><tt>IntegerType</tt></dt>
3045 <dd>Subclass of DerivedType that represents integer types of any bit width.
3046 Any bit width between <tt>IntegerType::MIN_INT_BITS</tt> (1) and
3047 <tt>IntegerType::MAX_INT_BITS</tt> (~8 million) can be represented.
3048 <ul>
3049 <li><tt>static const IntegerType* get(unsigned NumBits)</tt>: get an integer
3050 type of a specific bit width.</li>
3051 <li><tt>unsigned getBitWidth() const</tt>: Get the bit width of an integer
3052 type.</li>
3053 </ul>
3054 </dd>
3055 <dt><tt>SequentialType</tt></dt>
3056 <dd>This is subclassed by ArrayType and PointerType
3057 <ul>
3058 <li><tt>const Type * getElementType() const</tt>: Returns the type of each
3059 of the elements in the sequential type. </li>
3060 </ul>
3061 </dd>
3062 <dt><tt>ArrayType</tt></dt>
3063 <dd>This is a subclass of SequentialType and defines the interface for array
3064 types.
3065 <ul>
3066 <li><tt>unsigned getNumElements() const</tt>: Returns the number of
3067 elements in the array. </li>
3068 </ul>
3069 </dd>
3070 <dt><tt>PointerType</tt></dt>
Chris Lattner302da1e2007-02-03 03:05:57 +0000[diff] [blame]3071 <dd>Subclass of SequentialType for pointer types.</dd>
Reid Spencer9d6565a2007-02-15 02:26:10 +0000[diff] [blame]3072 <dt><tt>VectorType</tt></dt>
Reid Spencer485bad12007-02-15 03:07:05 +0000[diff] [blame]3073 <dd>Subclass of SequentialType for vector types. A
3074 vector type is similar to an ArrayType but is distinguished because it is
Benjamin Kramer8040cd32009-10-12 14:46:08 +0000[diff] [blame]3075 a first class type whereas ArrayType is not. Vector types are used for
Reid Spencer303c4b42007-01-12 17:26:25 +0000[diff] [blame]3076 vector operations and are usually small vectors of of an integer or floating
3077 point type.</dd>
3078 <dt><tt>StructType</tt></dt>
3079 <dd>Subclass of DerivedTypes for struct types.</dd>
Duncan Sands8036ca42007-03-30 12:22:09 +0000[diff] [blame]3080 <dt><tt><a name="FunctionType">FunctionType</a></tt></dt>
Reid Spencer303c4b42007-01-12 17:26:25 +0000[diff] [blame]3081 <dd>Subclass of DerivedTypes for function types.
3082 <ul>
3083 <li><tt>bool isVarArg() const</tt>: Returns true if its a vararg
3084 function</li>
3085 <li><tt> const Type * getReturnType() const</tt>: Returns the
3086 return type of the function.</li>
3087 <li><tt>const Type * getParamType (unsigned i)</tt>: Returns
3088 the type of the ith parameter.</li>
3089 <li><tt> const unsigned getNumParams() const</tt>: Returns the
3090 number of formal parameters.</li>
3091 </ul>
3092 </dd>
3093 <dt><tt>OpaqueType</tt></dt>
3094 <dd>Sublcass of DerivedType for abstract types. This class
3095 defines no content and is used as a placeholder for some other type. Note
3096 that OpaqueType is used (temporarily) during type resolution for forward
3097 references of types. Once the referenced type is resolved, the OpaqueType
3098 is replaced with the actual type. OpaqueType can also be used for data
3099 abstraction. At link time opaque types can be resolved to actual types
3100 of the same name.</dd>
3101</dl>
3102</div>
3103
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]3104
3105
3106<!-- ======================================================================= -->
3107<div class="doc_subsection">
3108 <a name="Module">The <tt>Module</tt> class</a>
3109</div>
3110
3111<div class="doc_text">
3112
3113<p><tt>#include "<a
3114href="/doxygen/Module_8h-source.html">llvm/Module.h</a>"</tt><br> doxygen info:
3115<a href="/doxygen/classllvm_1_1Module.html">Module Class</a></p>
3116
3117<p>The <tt>Module</tt> class represents the top level structure present in LLVM
3118programs. An LLVM module is effectively either a translation unit of the
3119original program or a combination of several translation units merged by the
3120linker. The <tt>Module</tt> class keeps track of a list of <a
3121href="#Function"><tt>Function</tt></a>s, a list of <a
3122href="#GlobalVariable"><tt>GlobalVariable</tt></a>s, and a <a
3123href="#SymbolTable"><tt>SymbolTable</tt></a>. Additionally, it contains a few
3124helpful member functions that try to make common operations easy.</p>
3125
3126</div>
3127
3128<!-- _______________________________________________________________________ -->
3129<div class="doc_subsubsection">
3130 <a name="m_Module">Important Public Members of the <tt>Module</tt> class</a>
3131</div>
3132
3133<div class="doc_text">
3134
3135<ul>
3136 <li><tt>Module::Module(std::string name = "")</tt></li>
3137</ul>
3138
3139<p>Constructing a <a href="#Module">Module</a> is easy. You can optionally
3140provide a name for it (probably based on the name of the translation unit).</p>
3141
3142<ul>
3143 <li><tt>Module::iterator</tt> - Typedef for function list iterator<br>
3144 <tt>Module::const_iterator</tt> - Typedef for const_iterator.<br>
3145
3146 <tt>begin()</tt>, <tt>end()</tt>
3147 <tt>size()</tt>, <tt>empty()</tt>
3148
3149 <p>These are forwarding methods that make it easy to access the contents of
3150 a <tt>Module</tt> object's <a href="#Function"><tt>Function</tt></a>
3151 list.</p></li>
3152
3153 <li><tt>Module::FunctionListType &amp;getFunctionList()</tt>
3154
3155 <p> Returns the list of <a href="#Function"><tt>Function</tt></a>s. This is
3156 necessary to use when you need to update the list or perform a complex
3157 action that doesn't have a forwarding method.</p>
3158
3159 <p><!-- Global Variable --></p></li>
3160</ul>
3161
3162<hr>
3163
3164<ul>
3165 <li><tt>Module::global_iterator</tt> - Typedef for global variable list iterator<br>
3166
3167 <tt>Module::const_global_iterator</tt> - Typedef for const_iterator.<br>
3168
3169 <tt>global_begin()</tt>, <tt>global_end()</tt>
3170 <tt>global_size()</tt>, <tt>global_empty()</tt>
3171
3172 <p> These are forwarding methods that make it easy to access the contents of
3173 a <tt>Module</tt> object's <a
3174 href="#GlobalVariable"><tt>GlobalVariable</tt></a> list.</p></li>
3175
3176 <li><tt>Module::GlobalListType &amp;getGlobalList()</tt>
3177
3178 <p>Returns the list of <a
3179 href="#GlobalVariable"><tt>GlobalVariable</tt></a>s. This is necessary to
3180 use when you need to update the list or perform a complex action that
3181 doesn't have a forwarding method.</p>
3182
3183 <p><!-- Symbol table stuff --> </p></li>
3184</ul>
3185
3186<hr>
3187
3188<ul>
3189 <li><tt><a href="#SymbolTable">SymbolTable</a> *getSymbolTable()</tt>
3190
3191 <p>Return a reference to the <a href="#SymbolTable"><tt>SymbolTable</tt></a>
3192 for this <tt>Module</tt>.</p>
3193
3194 <p><!-- Convenience methods --></p></li>
3195</ul>
3196
3197<hr>
3198
3199<ul>
3200 <li><tt><a href="#Function">Function</a> *getFunction(const std::string
3201 &amp;Name, const <a href="#FunctionType">FunctionType</a> *Ty)</tt>
3202
3203 <p>Look up the specified function in the <tt>Module</tt> <a
3204 href="#SymbolTable"><tt>SymbolTable</tt></a>. If it does not exist, return
3205 <tt>null</tt>.</p></li>
3206
3207 <li><tt><a href="#Function">Function</a> *getOrInsertFunction(const
3208 std::string &amp;Name, const <a href="#FunctionType">FunctionType</a> *T)</tt>
3209
3210 <p>Look up the specified function in the <tt>Module</tt> <a
3211 href="#SymbolTable"><tt>SymbolTable</tt></a>. If it does not exist, add an
3212 external declaration for the function and return it.</p></li>
3213
3214 <li><tt>std::string getTypeName(const <a href="#Type">Type</a> *Ty)</tt>
3215
3216 <p>If there is at least one entry in the <a
3217 href="#SymbolTable"><tt>SymbolTable</tt></a> for the specified <a
3218 href="#Type"><tt>Type</tt></a>, return it. Otherwise return the empty
3219 string.</p></li>
3220
3221 <li><tt>bool addTypeName(const std::string &amp;Name, const <a
3222 href="#Type">Type</a> *Ty)</tt>
3223
3224 <p>Insert an entry in the <a href="#SymbolTable"><tt>SymbolTable</tt></a>
3225 mapping <tt>Name</tt> to <tt>Ty</tt>. If there is already an entry for this
3226 name, true is returned and the <a
3227 href="#SymbolTable"><tt>SymbolTable</tt></a> is not modified.</p></li>
3228</ul>
3229
3230</div>
3231
3232
Reid Spencer303c4b42007-01-12 17:26:25 +0000[diff] [blame]3233<!-- ======================================================================= -->
3234<div class="doc_subsection">
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3235 <a name="Value">The <tt>Value</tt> class</a>
3236</div>
3237
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]3238<div class="doc_text">
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3239
3240<p><tt>#include "<a href="/doxygen/Value_8h-source.html">llvm/Value.h</a>"</tt>
3241<br>
Chris Lattner00815172007-01-04 22:01:45 +0000[diff] [blame]3242doxygen info: <a href="/doxygen/classllvm_1_1Value.html">Value Class</a></p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3243
3244<p>The <tt>Value</tt> class is the most important class in the LLVM Source
3245base. It represents a typed value that may be used (among other things) as an
3246operand to an instruction. There are many different types of <tt>Value</tt>s,
3247such as <a href="#Constant"><tt>Constant</tt></a>s,<a
3248href="#Argument"><tt>Argument</tt></a>s. Even <a
3249href="#Instruction"><tt>Instruction</tt></a>s and <a
3250href="#Function"><tt>Function</tt></a>s are <tt>Value</tt>s.</p>
3251
3252<p>A particular <tt>Value</tt> may be used many times in the LLVM representation
3253for a program. For example, an incoming argument to a function (represented
3254with an instance of the <a href="#Argument">Argument</a> class) is "used" by
3255every instruction in the function that references the argument. To keep track
3256of this relationship, the <tt>Value</tt> class keeps a list of all of the <a
3257href="#User"><tt>User</tt></a>s that is using it (the <a
3258href="#User"><tt>User</tt></a> class is a base class for all nodes in the LLVM
3259graph that can refer to <tt>Value</tt>s). This use list is how LLVM represents
3260def-use information in the program, and is accessible through the <tt>use_</tt>*
3261methods, shown below.</p>
3262
3263<p>Because LLVM is a typed representation, every LLVM <tt>Value</tt> is typed,
3264and this <a href="#Type">Type</a> is available through the <tt>getType()</tt>
3265method. In addition, all LLVM values can be named. The "name" of the
3266<tt>Value</tt> is a symbolic string printed in the LLVM code:</p>
3267
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]3268<div class="doc_code">
3269<pre>
Reid Spencer06565dc2007-01-12 17:11:23 +0000[diff] [blame]3270%<b>foo</b> = add i32 1, 2
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]3271</pre>
3272</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3273
Duncan Sands8036ca42007-03-30 12:22:09 +0000[diff] [blame]3274<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]3275that the name of any value may be missing (an empty string), so names should
3276<b>ONLY</b> be used for debugging (making the source code easier to read,
3277debugging printouts), they should not be used to keep track of values or map
3278between them. For this purpose, use a <tt>std::map</tt> of pointers to the
3279<tt>Value</tt> itself instead.</p>
3280
3281<p>One important aspect of LLVM is that there is no distinction between an SSA
3282variable and the operation that produces it. Because of this, any reference to
3283the value produced by an instruction (or the value available as an incoming
Chris Lattnerd5fc4fc2004-03-18 14:58:55 +0000[diff] [blame]3284argument, for example) is represented as a direct pointer to the instance of
3285the class that
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3286represents this value. Although this may take some getting used to, it
3287simplifies the representation and makes it easier to manipulate.</p>
3288
3289</div>
3290
3291<!-- _______________________________________________________________________ -->
3292<div class="doc_subsubsection">
3293 <a name="m_Value">Important Public Members of the <tt>Value</tt> class</a>
3294</div>
3295
3296<div class="doc_text">
3297
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3298<ul>
3299 <li><tt>Value::use_iterator</tt> - Typedef for iterator over the
3300use-list<br>
Gabor Greifbbbf9a22010-03-26 19:59:25 +0000[diff] [blame^]3301 <tt>Value::const_use_iterator</tt> - Typedef for const_iterator over
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3302the use-list<br>
3303 <tt>unsigned use_size()</tt> - Returns the number of users of the
3304value.<br>
Chris Lattner9355b472002-09-06 02:50:58 +0000[diff] [blame]3305 <tt>bool use_empty()</tt> - Returns true if there are no users.<br>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3306 <tt>use_iterator use_begin()</tt> - Get an iterator to the start of
3307the use-list.<br>
3308 <tt>use_iterator use_end()</tt> - Get an iterator to the end of the
3309use-list.<br>
3310 <tt><a href="#User">User</a> *use_back()</tt> - Returns the last
3311element in the list.
3312 <p> These methods are the interface to access the def-use
3313information in LLVM. As with all other iterators in LLVM, the naming
3314conventions follow the conventions defined by the <a href="#stl">STL</a>.</p>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3315 </li>
3316 <li><tt><a href="#Type">Type</a> *getType() const</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3317 <p>This method returns the Type of the Value.</p>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3318 </li>
3319 <li><tt>bool hasName() const</tt><br>
Chris Lattner9355b472002-09-06 02:50:58 +0000[diff] [blame]3320 <tt>std::string getName() const</tt><br>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3321 <tt>void setName(const std::string &amp;Name)</tt>
3322 <p> This family of methods is used to access and assign a name to a <tt>Value</tt>,
3323be aware of the <a href="#nameWarning">precaution above</a>.</p>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3324 </li>
3325 <li><tt>void replaceAllUsesWith(Value *V)</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3326
3327 <p>This method traverses the use list of a <tt>Value</tt> changing all <a
3328 href="#User"><tt>User</tt>s</a> of the current value to refer to
3329 "<tt>V</tt>" instead. For example, if you detect that an instruction always
3330 produces a constant value (for example through constant folding), you can
3331 replace all uses of the instruction with the constant like this:</p>
3332
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]3333<div class="doc_code">
3334<pre>
3335Inst-&gt;replaceAllUsesWith(ConstVal);
3336</pre>
3337</div>
3338
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3339</ul>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3340
3341</div>
3342
3343<!-- ======================================================================= -->
3344<div class="doc_subsection">
3345 <a name="User">The <tt>User</tt> class</a>
3346</div>
3347
3348<div class="doc_text">
3349
3350<p>
3351<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]3352doxygen info: <a href="/doxygen/classllvm_1_1User.html">User Class</a><br>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3353Superclass: <a href="#Value"><tt>Value</tt></a></p>
3354
3355<p>The <tt>User</tt> class is the common base class of all LLVM nodes that may
3356refer to <a href="#Value"><tt>Value</tt></a>s. It exposes a list of "Operands"
3357that are all of the <a href="#Value"><tt>Value</tt></a>s that the User is
3358referring to. The <tt>User</tt> class itself is a subclass of
3359<tt>Value</tt>.</p>
3360
3361<p>The operands of a <tt>User</tt> point directly to the LLVM <a
3362href="#Value"><tt>Value</tt></a> that it refers to. Because LLVM uses Static
3363Single Assignment (SSA) form, there can only be one definition referred to,
3364allowing this direct connection. This connection provides the use-def
3365information in LLVM.</p>
3366
3367</div>
3368
3369<!-- _______________________________________________________________________ -->
3370<div class="doc_subsubsection">
3371 <a name="m_User">Important Public Members of the <tt>User</tt> class</a>
3372</div>
3373
3374<div class="doc_text">
3375
3376<p>The <tt>User</tt> class exposes the operand list in two ways: through
3377an index access interface and through an iterator based interface.</p>
3378
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3379<ul>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3380 <li><tt>Value *getOperand(unsigned i)</tt><br>
3381 <tt>unsigned getNumOperands()</tt>
3382 <p> These two methods expose the operands of the <tt>User</tt> in a
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3383convenient form for direct access.</p></li>
3384
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3385 <li><tt>User::op_iterator</tt> - Typedef for iterator over the operand
3386list<br>
Chris Lattner58360822005-01-17 00:12:04 +0000[diff] [blame]3387 <tt>op_iterator op_begin()</tt> - Get an iterator to the start of
3388the operand list.<br>
3389 <tt>op_iterator op_end()</tt> - Get an iterator to the end of the
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3390operand list.
3391 <p> Together, these methods make up the iterator based interface to
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3392the operands of a <tt>User</tt>.</p></li>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3393</ul>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3394
3395</div>
3396
3397<!-- ======================================================================= -->
3398<div class="doc_subsection">
3399 <a name="Instruction">The <tt>Instruction</tt> class</a>
3400</div>
3401
3402<div class="doc_text">
3403
3404<p><tt>#include "</tt><tt><a
3405href="/doxygen/Instruction_8h-source.html">llvm/Instruction.h</a>"</tt><br>
Misha Brukman31ca1de2004-06-03 23:35:54 +0000[diff] [blame]3406doxygen info: <a href="/doxygen/classllvm_1_1Instruction.html">Instruction Class</a><br>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3407Superclasses: <a href="#User"><tt>User</tt></a>, <a
3408href="#Value"><tt>Value</tt></a></p>
3409
3410<p>The <tt>Instruction</tt> class is the common base class for all LLVM
3411instructions. It provides only a few methods, but is a very commonly used
3412class. The primary data tracked by the <tt>Instruction</tt> class itself is the
3413opcode (instruction type) and the parent <a
3414href="#BasicBlock"><tt>BasicBlock</tt></a> the <tt>Instruction</tt> is embedded
3415into. To represent a specific type of instruction, one of many subclasses of
3416<tt>Instruction</tt> are used.</p>
3417
3418<p> Because the <tt>Instruction</tt> class subclasses the <a
3419href="#User"><tt>User</tt></a> class, its operands can be accessed in the same
3420way as for other <a href="#User"><tt>User</tt></a>s (with the
3421<tt>getOperand()</tt>/<tt>getNumOperands()</tt> and
3422<tt>op_begin()</tt>/<tt>op_end()</tt> methods).</p> <p> An important file for
3423the <tt>Instruction</tt> class is the <tt>llvm/Instruction.def</tt> file. This
3424file contains some meta-data about the various different types of instructions
3425in LLVM. It describes the enum values that are used as opcodes (for example
Reid Spencerc92d25d2006-12-19 19:47:19 +0000[diff] [blame]3426<tt>Instruction::Add</tt> and <tt>Instruction::ICmp</tt>), as well as the
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3427concrete sub-classes of <tt>Instruction</tt> that implement the instruction (for
3428example <tt><a href="#BinaryOperator">BinaryOperator</a></tt> and <tt><a
Reid Spencerc92d25d2006-12-19 19:47:19 +0000[diff] [blame]3429href="#CmpInst">CmpInst</a></tt>). Unfortunately, the use of macros in
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3430this file confuses doxygen, so these enum values don't show up correctly in the
Misha Brukman31ca1de2004-06-03 23:35:54 +0000[diff] [blame]3431<a href="/doxygen/classllvm_1_1Instruction.html">doxygen output</a>.</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3432
3433</div>
3434
3435<!-- _______________________________________________________________________ -->
3436<div class="doc_subsubsection">
Reid Spencerc92d25d2006-12-19 19:47:19 +0000[diff] [blame]3437 <a name="s_Instruction">Important Subclasses of the <tt>Instruction</tt>
3438 class</a>
3439</div>
3440<div class="doc_text">
3441 <ul>
3442 <li><tt><a name="BinaryOperator">BinaryOperator</a></tt>
3443 <p>This subclasses represents all two operand instructions whose operands
3444 must be the same type, except for the comparison instructions.</p></li>
3445 <li><tt><a name="CastInst">CastInst</a></tt>
3446 <p>This subclass is the parent of the 12 casting instructions. It provides
3447 common operations on cast instructions.</p>
3448 <li><tt><a name="CmpInst">CmpInst</a></tt>
3449 <p>This subclass respresents the two comparison instructions,
3450 <a href="LangRef.html#i_icmp">ICmpInst</a> (integer opreands), and
3451 <a href="LangRef.html#i_fcmp">FCmpInst</a> (floating point operands).</p>
3452 <li><tt><a name="TerminatorInst">TerminatorInst</a></tt>
3453 <p>This subclass is the parent of all terminator instructions (those which
3454 can terminate a block).</p>
3455 </ul>
3456 </div>
3457
3458<!-- _______________________________________________________________________ -->
3459<div class="doc_subsubsection">
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3460 <a name="m_Instruction">Important Public Members of the <tt>Instruction</tt>
3461 class</a>
3462</div>
3463
3464<div class="doc_text">
3465
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3466<ul>
3467 <li><tt><a href="#BasicBlock">BasicBlock</a> *getParent()</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3468 <p>Returns the <a href="#BasicBlock"><tt>BasicBlock</tt></a> that
3469this <tt>Instruction</tt> is embedded into.</p></li>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3470 <li><tt>bool mayWriteToMemory()</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3471 <p>Returns true if the instruction writes to memory, i.e. it is a
3472 <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]3473 <li><tt>unsigned getOpcode()</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3474 <p>Returns the opcode for the <tt>Instruction</tt>.</p></li>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3475 <li><tt><a href="#Instruction">Instruction</a> *clone() const</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3476 <p>Returns another instance of the specified instruction, identical
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3477in all ways to the original except that the instruction has no parent
3478(ie it's not embedded into a <a href="#BasicBlock"><tt>BasicBlock</tt></a>),
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3479and it has no name</p></li>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3480</ul>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3481
3482</div>
3483
3484<!-- ======================================================================= -->
3485<div class="doc_subsection">
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]3486 <a name="Constant">The <tt>Constant</tt> class and subclasses</a>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3487</div>
3488
3489<div class="doc_text">
3490
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]3491<p>Constant represents a base class for different types of constants. It
3492is subclassed by ConstantInt, ConstantArray, etc. for representing
3493the various types of Constants. <a href="#GlobalValue">GlobalValue</a> is also
3494a subclass, which represents the address of a global variable or function.
3495</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3496
3497</div>
3498
3499<!-- _______________________________________________________________________ -->
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]3500<div class="doc_subsubsection">Important Subclasses of Constant </div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3501<div class="doc_text">
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3502<ul>
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]3503 <li>ConstantInt : This subclass of Constant represents an integer constant of
3504 any width.
3505 <ul>
Reid Spencer97b4ee32007-03-01 21:05:33 +0000[diff] [blame]3506 <li><tt>const APInt&amp; getValue() const</tt>: Returns the underlying
3507 value of this constant, an APInt value.</li>
3508 <li><tt>int64_t getSExtValue() const</tt>: Converts the underlying APInt
3509 value to an int64_t via sign extension. If the value (not the bit width)
3510 of the APInt is too large to fit in an int64_t, an assertion will result.
3511 For this reason, use of this method is discouraged.</li>
3512 <li><tt>uint64_t getZExtValue() const</tt>: Converts the underlying APInt
3513 value to a uint64_t via zero extension. IF the value (not the bit width)
3514 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]3515 For this reason, use of this method is discouraged.</li>
Reid Spencer97b4ee32007-03-01 21:05:33 +0000[diff] [blame]3516 <li><tt>static ConstantInt* get(const APInt&amp; Val)</tt>: Returns the
3517 ConstantInt object that represents the value provided by <tt>Val</tt>.
3518 The type is implied as the IntegerType that corresponds to the bit width
3519 of <tt>Val</tt>.</li>
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]3520 <li><tt>static ConstantInt* get(const Type *Ty, uint64_t Val)</tt>:
3521 Returns the ConstantInt object that represents the value provided by
3522 <tt>Val</tt> for integer type <tt>Ty</tt>.</li>
3523 </ul>
3524 </li>
3525 <li>ConstantFP : This class represents a floating point constant.
3526 <ul>
3527 <li><tt>double getValue() const</tt>: Returns the underlying value of
3528 this constant. </li>
3529 </ul>
3530 </li>
3531 <li>ConstantArray : This represents a constant array.
3532 <ul>
3533 <li><tt>const std::vector&lt;Use&gt; &amp;getValues() const</tt>: Returns
3534 a vector of component constants that makeup this array. </li>
3535 </ul>
3536 </li>
3537 <li>ConstantStruct : This represents a constant struct.
3538 <ul>
3539 <li><tt>const std::vector&lt;Use&gt; &amp;getValues() const</tt>: Returns
3540 a vector of component constants that makeup this array. </li>
3541 </ul>
3542 </li>
3543 <li>GlobalValue : This represents either a global variable or a function. In
3544 either case, the value is a constant fixed address (after linking).
3545 </li>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3546</ul>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3547</div>
3548
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]3549
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3550<!-- ======================================================================= -->
3551<div class="doc_subsection">
3552 <a name="GlobalValue">The <tt>GlobalValue</tt> class</a>
3553</div>
3554
3555<div class="doc_text">
3556
3557<p><tt>#include "<a
3558href="/doxygen/GlobalValue_8h-source.html">llvm/GlobalValue.h</a>"</tt><br>
Misha Brukman384047f2004-06-03 23:29:12 +0000[diff] [blame]3559doxygen info: <a href="/doxygen/classllvm_1_1GlobalValue.html">GlobalValue
3560Class</a><br>
Reid Spencerbe5e85e2006-04-14 14:11:48 +0000[diff] [blame]3561Superclasses: <a href="#Constant"><tt>Constant</tt></a>,
3562<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]3563
3564<p>Global values (<a href="#GlobalVariable"><tt>GlobalVariable</tt></a>s or <a
3565href="#Function"><tt>Function</tt></a>s) are the only LLVM values that are
3566visible in the bodies of all <a href="#Function"><tt>Function</tt></a>s.
3567Because they are visible at global scope, they are also subject to linking with
3568other globals defined in different translation units. To control the linking
3569process, <tt>GlobalValue</tt>s know their linkage rules. Specifically,
3570<tt>GlobalValue</tt>s know whether they have internal or external linkage, as
Reid Spencer8b2da7a2004-07-18 13:10:31 +0000[diff] [blame]3571defined by the <tt>LinkageTypes</tt> enumeration.</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3572
3573<p>If a <tt>GlobalValue</tt> has internal linkage (equivalent to being
3574<tt>static</tt> in C), it is not visible to code outside the current translation
3575unit, and does not participate in linking. If it has external linkage, it is
3576visible to external code, and does participate in linking. In addition to
3577linkage information, <tt>GlobalValue</tt>s keep track of which <a
3578href="#Module"><tt>Module</tt></a> they are currently part of.</p>
3579
3580<p>Because <tt>GlobalValue</tt>s are memory objects, they are always referred to
3581by their <b>address</b>. As such, the <a href="#Type"><tt>Type</tt></a> of a
3582global is always a pointer to its contents. It is important to remember this
3583when using the <tt>GetElementPtrInst</tt> instruction because this pointer must
3584be dereferenced first. For example, if you have a <tt>GlobalVariable</tt> (a
3585subclass 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]3586i32]</tt>, then the <tt>GlobalVariable</tt> is a pointer to that array. Although
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3587the address of the first element of this array and the value of the
3588<tt>GlobalVariable</tt> are the same, they have different types. The
Reid Spencer06565dc2007-01-12 17:11:23 +0000[diff] [blame]3589<tt>GlobalVariable</tt>'s type is <tt>[24 x i32]</tt>. The first element's type
3590is <tt>i32.</tt> Because of this, accessing a global value requires you to
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3591dereference the pointer with <tt>GetElementPtrInst</tt> first, then its elements
3592can be accessed. This is explained in the <a href="LangRef.html#globalvars">LLVM
3593Language Reference Manual</a>.</p>
3594
3595</div>
3596
3597<!-- _______________________________________________________________________ -->
3598<div class="doc_subsubsection">
3599 <a name="m_GlobalValue">Important Public Members of the <tt>GlobalValue</tt>
3600 class</a>
3601</div>
3602
3603<div class="doc_text">
3604
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3605<ul>
3606 <li><tt>bool hasInternalLinkage() const</tt><br>
Chris Lattner9355b472002-09-06 02:50:58 +0000[diff] [blame]3607 <tt>bool hasExternalLinkage() const</tt><br>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3608 <tt>void setInternalLinkage(bool HasInternalLinkage)</tt>
3609 <p> These methods manipulate the linkage characteristics of the <tt>GlobalValue</tt>.</p>
3610 <p> </p>
3611 </li>
3612 <li><tt><a href="#Module">Module</a> *getParent()</tt>
3613 <p> This returns the <a href="#Module"><tt>Module</tt></a> that the
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3614GlobalValue is currently embedded into.</p></li>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3615</ul>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3616
3617</div>
3618
3619<!-- ======================================================================= -->
3620<div class="doc_subsection">
3621 <a name="Function">The <tt>Function</tt> class</a>
3622</div>
3623
3624<div class="doc_text">
3625
3626<p><tt>#include "<a
3627href="/doxygen/Function_8h-source.html">llvm/Function.h</a>"</tt><br> doxygen
Misha Brukman31ca1de2004-06-03 23:35:54 +0000[diff] [blame]3628info: <a href="/doxygen/classllvm_1_1Function.html">Function Class</a><br>
Reid Spencerbe5e85e2006-04-14 14:11:48 +0000[diff] [blame]3629Superclasses: <a href="#GlobalValue"><tt>GlobalValue</tt></a>,
3630<a href="#Constant"><tt>Constant</tt></a>,
3631<a href="#User"><tt>User</tt></a>,
3632<a href="#Value"><tt>Value</tt></a></p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3633
3634<p>The <tt>Function</tt> class represents a single procedure in LLVM. It is
Torok Edwin87469292009-10-12 13:37:29 +0000[diff] [blame]3635actually one of the more complex classes in the LLVM hierarchy because it must
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3636keep track of a large amount of data. The <tt>Function</tt> class keeps track
Reid Spencerbe5e85e2006-04-14 14:11:48 +0000[diff] [blame]3637of a list of <a href="#BasicBlock"><tt>BasicBlock</tt></a>s, a list of formal
3638<a href="#Argument"><tt>Argument</tt></a>s, and a
3639<a href="#SymbolTable"><tt>SymbolTable</tt></a>.</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3640
3641<p>The list of <a href="#BasicBlock"><tt>BasicBlock</tt></a>s is the most
3642commonly used part of <tt>Function</tt> objects. The list imposes an implicit
3643ordering of the blocks in the function, which indicate how the code will be
Benjamin Kramer8040cd32009-10-12 14:46:08 +0000[diff] [blame]3644laid out by the backend. Additionally, the first <a
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3645href="#BasicBlock"><tt>BasicBlock</tt></a> is the implicit entry node for the
3646<tt>Function</tt>. It is not legal in LLVM to explicitly branch to this initial
3647block. There are no implicit exit nodes, and in fact there may be multiple exit
3648nodes from a single <tt>Function</tt>. If the <a
3649href="#BasicBlock"><tt>BasicBlock</tt></a> list is empty, this indicates that
3650the <tt>Function</tt> is actually a function declaration: the actual body of the
3651function hasn't been linked in yet.</p>
3652
3653<p>In addition to a list of <a href="#BasicBlock"><tt>BasicBlock</tt></a>s, the
3654<tt>Function</tt> class also keeps track of the list of formal <a
3655href="#Argument"><tt>Argument</tt></a>s that the function receives. This
3656container manages the lifetime of the <a href="#Argument"><tt>Argument</tt></a>
3657nodes, just like the <a href="#BasicBlock"><tt>BasicBlock</tt></a> list does for
3658the <a href="#BasicBlock"><tt>BasicBlock</tt></a>s.</p>
3659
3660<p>The <a href="#SymbolTable"><tt>SymbolTable</tt></a> is a very rarely used
3661LLVM feature that is only used when you have to look up a value by name. Aside
3662from that, the <a href="#SymbolTable"><tt>SymbolTable</tt></a> is used
3663internally to make sure that there are not conflicts between the names of <a
3664href="#Instruction"><tt>Instruction</tt></a>s, <a
3665href="#BasicBlock"><tt>BasicBlock</tt></a>s, or <a
3666href="#Argument"><tt>Argument</tt></a>s in the function body.</p>
3667
Reid Spencer8b2da7a2004-07-18 13:10:31 +0000[diff] [blame]3668<p>Note that <tt>Function</tt> is a <a href="#GlobalValue">GlobalValue</a>
3669and therefore also a <a href="#Constant">Constant</a>. The value of the function
3670is its address (after linking) which is guaranteed to be constant.</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3671</div>
3672
3673<!-- _______________________________________________________________________ -->
3674<div class="doc_subsubsection">
3675 <a name="m_Function">Important Public Members of the <tt>Function</tt>
3676 class</a>
3677</div>
3678
3679<div class="doc_text">
3680
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3681<ul>
3682 <li><tt>Function(const </tt><tt><a href="#FunctionType">FunctionType</a>
Chris Lattnerac479e52004-08-04 05:10:48 +0000[diff] [blame]3683 *Ty, LinkageTypes Linkage, const std::string &amp;N = "", Module* Parent = 0)</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3684
3685 <p>Constructor used when you need to create new <tt>Function</tt>s to add
3686 the the program. The constructor must specify the type of the function to
Chris Lattnerac479e52004-08-04 05:10:48 +0000[diff] [blame]3687 create and what type of linkage the function should have. The <a
3688 href="#FunctionType"><tt>FunctionType</tt></a> argument
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3689 specifies the formal arguments and return value for the function. The same
Duncan Sands8036ca42007-03-30 12:22:09 +0000[diff] [blame]3690 <a href="#FunctionType"><tt>FunctionType</tt></a> value can be used to
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3691 create multiple functions. The <tt>Parent</tt> argument specifies the Module
3692 in which the function is defined. If this argument is provided, the function
3693 will automatically be inserted into that module's list of
3694 functions.</p></li>
3695
Chris Lattner62810e32008-11-25 18:34:50 +0000[diff] [blame]3696 <li><tt>bool isDeclaration()</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3697
3698 <p>Return whether or not the <tt>Function</tt> has a body defined. If the
3699 function is "external", it does not have a body, and thus must be resolved
3700 by linking with a function defined in a different translation unit.</p></li>
3701
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3702 <li><tt>Function::iterator</tt> - Typedef for basic block list iterator<br>
Chris Lattner9355b472002-09-06 02:50:58 +0000[diff] [blame]3703 <tt>Function::const_iterator</tt> - Typedef for const_iterator.<br>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3704
Chris Lattner77d69242005-03-15 05:19:20 +0000[diff] [blame]3705 <tt>begin()</tt>, <tt>end()</tt>
3706 <tt>size()</tt>, <tt>empty()</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3707
3708 <p>These are forwarding methods that make it easy to access the contents of
3709 a <tt>Function</tt> object's <a href="#BasicBlock"><tt>BasicBlock</tt></a>
3710 list.</p></li>
3711
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3712 <li><tt>Function::BasicBlockListType &amp;getBasicBlockList()</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3713
3714 <p>Returns the list of <a href="#BasicBlock"><tt>BasicBlock</tt></a>s. This
3715 is necessary to use when you need to update the list or perform a complex
3716 action that doesn't have a forwarding method.</p></li>
3717
Chris Lattner89cc2652005-03-15 04:48:32 +0000[diff] [blame]3718 <li><tt>Function::arg_iterator</tt> - Typedef for the argument list
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3719iterator<br>
Chris Lattner89cc2652005-03-15 04:48:32 +0000[diff] [blame]3720 <tt>Function::const_arg_iterator</tt> - Typedef for const_iterator.<br>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3721
Chris Lattner77d69242005-03-15 05:19:20 +0000[diff] [blame]3722 <tt>arg_begin()</tt>, <tt>arg_end()</tt>
Chris Lattner89cc2652005-03-15 04:48:32 +0000[diff] [blame]3723 <tt>arg_size()</tt>, <tt>arg_empty()</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3724
3725 <p>These are forwarding methods that make it easy to access the contents of
3726 a <tt>Function</tt> object's <a href="#Argument"><tt>Argument</tt></a>
3727 list.</p></li>
3728
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3729 <li><tt>Function::ArgumentListType &amp;getArgumentList()</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3730
3731 <p>Returns the list of <a href="#Argument"><tt>Argument</tt></a>s. This is
3732 necessary to use when you need to update the list or perform a complex
3733 action that doesn't have a forwarding method.</p></li>
3734
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3735 <li><tt><a href="#BasicBlock">BasicBlock</a> &amp;getEntryBlock()</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3736
3737 <p>Returns the entry <a href="#BasicBlock"><tt>BasicBlock</tt></a> for the
3738 function. Because the entry block for the function is always the first
3739 block, this returns the first block of the <tt>Function</tt>.</p></li>
3740
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3741 <li><tt><a href="#Type">Type</a> *getReturnType()</tt><br>
3742 <tt><a href="#FunctionType">FunctionType</a> *getFunctionType()</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3743
3744 <p>This traverses the <a href="#Type"><tt>Type</tt></a> of the
3745 <tt>Function</tt> and returns the return type of the function, or the <a
3746 href="#FunctionType"><tt>FunctionType</tt></a> of the actual
3747 function.</p></li>
3748
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3749 <li><tt><a href="#SymbolTable">SymbolTable</a> *getSymbolTable()</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3750
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3751 <p> Return a pointer to the <a href="#SymbolTable"><tt>SymbolTable</tt></a>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3752 for this <tt>Function</tt>.</p></li>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3753</ul>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3754
3755</div>
3756
3757<!-- ======================================================================= -->
3758<div class="doc_subsection">
3759 <a name="GlobalVariable">The <tt>GlobalVariable</tt> class</a>
3760</div>
3761
3762<div class="doc_text">
3763
3764<p><tt>#include "<a
3765href="/doxygen/GlobalVariable_8h-source.html">llvm/GlobalVariable.h</a>"</tt>
3766<br>
Tanya Lattnera3da7772004-06-22 08:02:25 +0000[diff] [blame]3767doxygen info: <a href="/doxygen/classllvm_1_1GlobalVariable.html">GlobalVariable
Reid Spencerbe5e85e2006-04-14 14:11:48 +0000[diff] [blame]3768 Class</a><br>
3769Superclasses: <a href="#GlobalValue"><tt>GlobalValue</tt></a>,
3770<a href="#Constant"><tt>Constant</tt></a>,
3771<a href="#User"><tt>User</tt></a>,
3772<a href="#Value"><tt>Value</tt></a></p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3773
Benjamin Kramer8040cd32009-10-12 14:46:08 +0000[diff] [blame]3774<p>Global variables are represented with the (surprise surprise)
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3775<tt>GlobalVariable</tt> class. Like functions, <tt>GlobalVariable</tt>s are also
3776subclasses of <a href="#GlobalValue"><tt>GlobalValue</tt></a>, and as such are
3777always referenced by their address (global values must live in memory, so their
Reid Spencerbe5e85e2006-04-14 14:11:48 +0000[diff] [blame]3778"name" refers to their constant address). See
3779<a href="#GlobalValue"><tt>GlobalValue</tt></a> for more on this. Global
3780variables may have an initial value (which must be a
3781<a href="#Constant"><tt>Constant</tt></a>), and if they have an initializer,
3782they may be marked as "constant" themselves (indicating that their contents
3783never change at runtime).</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3784</div>
3785
3786<!-- _______________________________________________________________________ -->
3787<div class="doc_subsubsection">
3788 <a name="m_GlobalVariable">Important Public Members of the
3789 <tt>GlobalVariable</tt> class</a>
3790</div>
3791
3792<div class="doc_text">
3793
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3794<ul>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3795 <li><tt>GlobalVariable(const </tt><tt><a href="#Type">Type</a> *Ty, bool
3796 isConstant, LinkageTypes&amp; Linkage, <a href="#Constant">Constant</a>
3797 *Initializer = 0, const std::string &amp;Name = "", Module* Parent = 0)</tt>
3798
3799 <p>Create a new global variable of the specified type. If
3800 <tt>isConstant</tt> is true then the global variable will be marked as
3801 unchanging for the program. The Linkage parameter specifies the type of
Duncan Sands667d4b82009-03-07 15:45:40 +0000[diff] [blame]3802 linkage (internal, external, weak, linkonce, appending) for the variable.
3803 If the linkage is InternalLinkage, WeakAnyLinkage, WeakODRLinkage,
3804 LinkOnceAnyLinkage or LinkOnceODRLinkage,&nbsp; then the resultant
3805 global variable will have internal linkage. AppendingLinkage concatenates
3806 together all instances (in different translation units) of the variable
3807 into a single variable but is only applicable to arrays. &nbsp;See
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3808 the <a href="LangRef.html#modulestructure">LLVM Language Reference</a> for
3809 further details on linkage types. Optionally an initializer, a name, and the
3810 module to put the variable into may be specified for the global variable as
3811 well.</p></li>
3812
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3813 <li><tt>bool isConstant() const</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3814
3815 <p>Returns true if this is a global variable that is known not to
3816 be modified at runtime.</p></li>
3817
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3818 <li><tt>bool hasInitializer()</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3819
3820 <p>Returns true if this <tt>GlobalVariable</tt> has an intializer.</p></li>
3821
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3822 <li><tt><a href="#Constant">Constant</a> *getInitializer()</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3823
Benjamin Kramer8040cd32009-10-12 14:46:08 +0000[diff] [blame]3824 <p>Returns the initial value for a <tt>GlobalVariable</tt>. It is not legal
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3825 to call this method if there is no initializer.</p></li>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3826</ul>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3827
3828</div>
3829
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]3830
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3831<!-- ======================================================================= -->
3832<div class="doc_subsection">
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]3833 <a name="BasicBlock">The <tt>BasicBlock</tt> class</a>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3834</div>
3835
3836<div class="doc_text">
3837
3838<p><tt>#include "<a
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]3839href="/doxygen/BasicBlock_8h-source.html">llvm/BasicBlock.h</a>"</tt><br>
Stefanus Du Toit24e04112009-06-17 21:12:26 +0000[diff] [blame]3840doxygen info: <a href="/doxygen/classllvm_1_1BasicBlock.html">BasicBlock
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]3841Class</a><br>
3842Superclass: <a href="#Value"><tt>Value</tt></a></p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3843
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]3844<p>This class represents a single entry multiple exit section of the code,
3845commonly known as a basic block by the compiler community. The
3846<tt>BasicBlock</tt> class maintains a list of <a
3847href="#Instruction"><tt>Instruction</tt></a>s, which form the body of the block.
3848Matching the language definition, the last element of this list of instructions
3849is always a terminator instruction (a subclass of the <a
3850href="#TerminatorInst"><tt>TerminatorInst</tt></a> class).</p>
3851
3852<p>In addition to tracking the list of instructions that make up the block, the
3853<tt>BasicBlock</tt> class also keeps track of the <a
3854href="#Function"><tt>Function</tt></a> that it is embedded into.</p>
3855
3856<p>Note that <tt>BasicBlock</tt>s themselves are <a
3857href="#Value"><tt>Value</tt></a>s, because they are referenced by instructions
3858like branches and can go in the switch tables. <tt>BasicBlock</tt>s have type
3859<tt>label</tt>.</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3860
3861</div>
3862
3863<!-- _______________________________________________________________________ -->
3864<div class="doc_subsubsection">
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]3865 <a name="m_BasicBlock">Important Public Members of the <tt>BasicBlock</tt>
3866 class</a>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3867</div>
3868
3869<div class="doc_text">
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3870<ul>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3871
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]3872<li><tt>BasicBlock(const std::string &amp;Name = "", </tt><tt><a
3873 href="#Function">Function</a> *Parent = 0)</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3874
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]3875<p>The <tt>BasicBlock</tt> constructor is used to create new basic blocks for
3876insertion into a function. The constructor optionally takes a name for the new
3877block, and a <a href="#Function"><tt>Function</tt></a> to insert it into. If
3878the <tt>Parent</tt> parameter is specified, the new <tt>BasicBlock</tt> is
3879automatically inserted at the end of the specified <a
3880href="#Function"><tt>Function</tt></a>, if not specified, the BasicBlock must be
3881manually inserted into the <a href="#Function"><tt>Function</tt></a>.</p></li>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3882
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]3883<li><tt>BasicBlock::iterator</tt> - Typedef for instruction list iterator<br>
3884<tt>BasicBlock::const_iterator</tt> - Typedef for const_iterator.<br>
3885<tt>begin()</tt>, <tt>end()</tt>, <tt>front()</tt>, <tt>back()</tt>,
3886<tt>size()</tt>, <tt>empty()</tt>
3887STL-style functions for accessing the instruction list.
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3888
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]3889<p>These methods and typedefs are forwarding functions that have the same
3890semantics as the standard library methods of the same names. These methods
3891expose the underlying instruction list of a basic block in a way that is easy to
3892manipulate. To get the full complement of container operations (including
3893operations to update the list), you must use the <tt>getInstList()</tt>
3894method.</p></li>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3895
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]3896<li><tt>BasicBlock::InstListType &amp;getInstList()</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3897
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]3898<p>This method is used to get access to the underlying container that actually
3899holds the Instructions. This method must be used when there isn't a forwarding
3900function in the <tt>BasicBlock</tt> class for the operation that you would like
3901to perform. Because there are no forwarding functions for "updating"
3902operations, you need to use this if you want to update the contents of a
3903<tt>BasicBlock</tt>.</p></li>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3904
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]3905<li><tt><a href="#Function">Function</a> *getParent()</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3906
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]3907<p> Returns a pointer to <a href="#Function"><tt>Function</tt></a> the block is
3908embedded into, or a null pointer if it is homeless.</p></li>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3909
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]3910<li><tt><a href="#TerminatorInst">TerminatorInst</a> *getTerminator()</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3911
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]3912<p> Returns a pointer to the terminator instruction that appears at the end of
3913the <tt>BasicBlock</tt>. If there is no terminator instruction, or if the last
3914instruction in the block is not a terminator, then a null pointer is
3915returned.</p></li>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3916
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3917</ul>
3918
3919</div>
3920
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3921
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3922<!-- ======================================================================= -->
3923<div class="doc_subsection">
3924 <a name="Argument">The <tt>Argument</tt> class</a>
3925</div>
3926
3927<div class="doc_text">
3928
3929<p>This subclass of Value defines the interface for incoming formal
Chris Lattner58360822005-01-17 00:12:04 +0000[diff] [blame]3930arguments to a function. A Function maintains a list of its formal
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3931arguments. An argument has a pointer to the parent Function.</p>
3932
3933</div>
3934
Chris Lattner9355b472002-09-06 02:50:58 +0000[diff] [blame]3935<!-- *********************************************************************** -->
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3936<hr>
3937<address>
3938 <a href="http://jigsaw.w3.org/css-validator/check/referer"><img
Misha Brukman44408702008-12-11 17:34:48 +0000[diff] [blame]3939 src="http://jigsaw.w3.org/css-validator/images/vcss-blue" alt="Valid CSS"></a>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3940 <a href="http://validator.w3.org/check/referer"><img
Gabor Greifa9c0f2b2008-06-18 14:05:31 +0000[diff] [blame]3941 src="http://www.w3.org/Icons/valid-html401" alt="Valid HTML 4.01 Strict"></a>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3942
3943 <a href="mailto:dhurjati@cs.uiuc.edu">Dinakar Dhurjati</a> and
3944 <a href="mailto:sabre@nondot.org">Chris Lattner</a><br>
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]3945 <a href="http://llvm.org">The LLVM Compiler Infrastructure</a><br>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3946 Last modified: $Date$
3947</address>
3948
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3949</body>
3950</html>