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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>
Misha Brukmana0f71e42004-06-18 18:39:00 +0000[diff] [blame]312<li><a href="http://www.fortran-2000.com/ArnaudRecipes/sharedlib.html">Using
313static and shared libraries across platforms</a></li>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]314</ol>
315
316</div>
317
Chris Lattner9355b472002-09-06 02:50:58 +0000[diff] [blame]318<!-- *********************************************************************** -->
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]319<div class="doc_section">
320 <a name="apis">Important and useful LLVM APIs</a>
321</div>
322<!-- *********************************************************************** -->
323
324<div class="doc_text">
325
326<p>Here we highlight some LLVM APIs that are generally useful and good to
327know about when writing transformations.</p>
328
329</div>
330
331<!-- ======================================================================= -->
332<div class="doc_subsection">
Misha Brukman2c122ce2005-11-01 21:12:49 +0000[diff] [blame]333 <a name="isa">The <tt>isa&lt;&gt;</tt>, <tt>cast&lt;&gt;</tt> and
334 <tt>dyn_cast&lt;&gt;</tt> templates</a>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]335</div>
336
337<div class="doc_text">
338
339<p>The LLVM source-base makes extensive use of a custom form of RTTI.
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]340These templates have many similarities to the C++ <tt>dynamic_cast&lt;&gt;</tt>
341operator, but they don't have some drawbacks (primarily stemming from
342the fact that <tt>dynamic_cast&lt;&gt;</tt> only works on classes that
343have a v-table). Because they are used so often, you must know what they
344do and how they work. All of these templates are defined in the <a
Chris Lattner695b78b2005-04-26 22:56:16 +0000[diff] [blame]345 href="/doxygen/Casting_8h-source.html"><tt>llvm/Support/Casting.h</tt></a>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]346file (note that you very rarely have to include this file directly).</p>
347
348<dl>
349 <dt><tt>isa&lt;&gt;</tt>: </dt>
350
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]351 <dd><p>The <tt>isa&lt;&gt;</tt> operator works exactly like the Java
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]352 "<tt>instanceof</tt>" operator. It returns true or false depending on whether
353 a reference or pointer points to an instance of the specified class. This can
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]354 be very useful for constraint checking of various sorts (example below).</p>
355 </dd>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]356
357 <dt><tt>cast&lt;&gt;</tt>: </dt>
358
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]359 <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]360 converts a pointer or reference from a base class to a derived class, causing
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]361 an assertion failure if it is not really an instance of the right type. This
362 should be used in cases where you have some information that makes you believe
363 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]364 and <tt>cast&lt;&gt;</tt> template is:</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]365
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]366<div class="doc_code">
367<pre>
368static bool isLoopInvariant(const <a href="#Value">Value</a> *V, const Loop *L) {
369 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))
370 return true;
Chris Lattner69bf8a92004-05-23 21:06:58 +0000[diff] [blame]371
Bill Wendling82e2eea2006-10-11 18:00:22 +0000[diff] [blame]372 // <i>Otherwise, it must be an instruction...</i>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]373 return !L-&gt;contains(cast&lt;<a href="#Instruction">Instruction</a>&gt;(V)-&gt;getParent());
374}
375</pre>
376</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]377
378 <p>Note that you should <b>not</b> use an <tt>isa&lt;&gt;</tt> test followed
379 by a <tt>cast&lt;&gt;</tt>, for that use the <tt>dyn_cast&lt;&gt;</tt>
380 operator.</p>
381
382 </dd>
383
384 <dt><tt>dyn_cast&lt;&gt;</tt>:</dt>
385
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]386 <dd><p>The <tt>dyn_cast&lt;&gt;</tt> operator is a "checking cast" operation.
387 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]388 pointer to it (this operator does not work with references). If the operand is
389 not of the correct type, a null pointer is returned. Thus, this works very
Misha Brukman2c122ce2005-11-01 21:12:49 +0000[diff] [blame]390 much like the <tt>dynamic_cast&lt;&gt;</tt> operator in C++, and should be
391 used in the same circumstances. Typically, the <tt>dyn_cast&lt;&gt;</tt>
392 operator is used in an <tt>if</tt> statement or some other flow control
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]393 statement like this:</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]394
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]395<div class="doc_code">
396<pre>
397if (<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]398 // <i>...</i>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]399}
400</pre>
401</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]402
Misha Brukman2c122ce2005-11-01 21:12:49 +0000[diff] [blame]403 <p>This form of the <tt>if</tt> statement effectively combines together a call
404 to <tt>isa&lt;&gt;</tt> and a call to <tt>cast&lt;&gt;</tt> into one
405 statement, which is very convenient.</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]406
Misha Brukman2c122ce2005-11-01 21:12:49 +0000[diff] [blame]407 <p>Note that the <tt>dyn_cast&lt;&gt;</tt> operator, like C++'s
408 <tt>dynamic_cast&lt;&gt;</tt> or Java's <tt>instanceof</tt> operator, can be
409 abused. In particular, you should not use big chained <tt>if/then/else</tt>
410 blocks to check for lots of different variants of classes. If you find
411 yourself wanting to do this, it is much cleaner and more efficient to use the
412 <tt>InstVisitor</tt> class to dispatch over the instruction type directly.</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]413
Misha Brukman2c122ce2005-11-01 21:12:49 +0000[diff] [blame]414 </dd>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]415
Misha Brukman2c122ce2005-11-01 21:12:49 +0000[diff] [blame]416 <dt><tt>cast_or_null&lt;&gt;</tt>: </dt>
417
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]418 <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]419 <tt>cast&lt;&gt;</tt> operator, except that it allows for a null pointer as an
420 argument (which it then propagates). This can sometimes be useful, allowing
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]421 you to combine several null checks into one.</p></dd>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]422
Misha Brukman2c122ce2005-11-01 21:12:49 +0000[diff] [blame]423 <dt><tt>dyn_cast_or_null&lt;&gt;</tt>: </dt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]424
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]425 <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]426 <tt>dyn_cast&lt;&gt;</tt> operator, except that it allows for a null pointer
427 as an argument (which it then propagates). This can sometimes be useful,
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]428 allowing you to combine several null checks into one.</p></dd>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]429
Misha Brukman2c122ce2005-11-01 21:12:49 +0000[diff] [blame]430</dl>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]431
432<p>These five templates can be used with any classes, whether they have a
433v-table or not. To add support for these templates, you simply need to add
434<tt>classof</tt> static methods to the class you are interested casting
435to. Describing this is currently outside the scope of this document, but there
436are lots of examples in the LLVM source base.</p>
437
438</div>
439
Daniel Dunbar6e0d1cb2009-07-25 04:41:11 +0000[diff] [blame]440
441<!-- ======================================================================= -->
442<div class="doc_subsection">
443 <a name="string_apis">Passing strings (the <tt>StringRef</tt>
444and <tt>Twine</tt> classes)</a>
445</div>
446
447<div class="doc_text">
448
449<p>Although LLVM generally does not do much string manipulation, we do have
Chris Lattner81187ae2009-07-25 07:16:59 +0000[diff] [blame]450several important APIs which take strings. Two important examples are the
Daniel Dunbar6e0d1cb2009-07-25 04:41:11 +0000[diff] [blame]451Value class -- which has names for instructions, functions, etc. -- and the
452StringMap class which is used extensively in LLVM and Clang.</p>
453
454<p>These are generic classes, and they need to be able to accept strings which
455may have embedded null characters. Therefore, they cannot simply take
Chris Lattner81187ae2009-07-25 07:16:59 +0000[diff] [blame]456a <tt>const char *</tt>, and taking a <tt>const std::string&amp;</tt> requires
Daniel Dunbar6e0d1cb2009-07-25 04:41:11 +0000[diff] [blame]457clients to perform a heap allocation which is usually unnecessary. Instead,
Benjamin Kramer38e59892010-07-14 22:38:02 +0000[diff] [blame]458many LLVM APIs use a <tt>StringRef</tt> or a <tt>const Twine&amp;</tt> for
459passing strings efficiently.</p>
Daniel Dunbar6e0d1cb2009-07-25 04:41:11 +0000[diff] [blame]460
461</div>
462
463<!-- _______________________________________________________________________ -->
464<div class="doc_subsubsection">
465 <a name="StringRef">The <tt>StringRef</tt> class</a>
466</div>
467
468<div class="doc_text">
469
470<p>The <tt>StringRef</tt> data type represents a reference to a constant string
471(a character array and a length) and supports the common operations available
472on <tt>std:string</tt>, but does not require heap allocation.</p>
473
Chris Lattner81187ae2009-07-25 07:16:59 +0000[diff] [blame]474<p>It can be implicitly constructed using a C style null-terminated string,
475an <tt>std::string</tt>, or explicitly with a character pointer and length.
Daniel Dunbar6e0d1cb2009-07-25 04:41:11 +0000[diff] [blame]476For example, the <tt>StringRef</tt> find function is declared as:</p>
Chris Lattner81187ae2009-07-25 07:16:59 +0000[diff] [blame]477
Benjamin Kramer38e59892010-07-14 22:38:02 +0000[diff] [blame]478<pre class="doc_code">
479 iterator find(StringRef Key);
480</pre>
Daniel Dunbar6e0d1cb2009-07-25 04:41:11 +0000[diff] [blame]481
482<p>and clients can call it using any one of:</p>
483
Benjamin Kramer38e59892010-07-14 22:38:02 +0000[diff] [blame]484<pre class="doc_code">
Daniel Dunbar6e0d1cb2009-07-25 04:41:11 +0000[diff] [blame]485 Map.find("foo"); <i>// Lookup "foo"</i>
486 Map.find(std::string("bar")); <i>// Lookup "bar"</i>
487 Map.find(StringRef("\0baz", 4)); <i>// Lookup "\0baz"</i>
488</pre>
Daniel Dunbar6e0d1cb2009-07-25 04:41:11 +0000[diff] [blame]489
490<p>Similarly, APIs which need to return a string may return a <tt>StringRef</tt>
491instance, which can be used directly or converted to an <tt>std::string</tt>
492using the <tt>str</tt> member function. See
493"<tt><a href="/doxygen/classllvm_1_1StringRef_8h-source.html">llvm/ADT/StringRef.h</a></tt>"
494for more information.</p>
495
496<p>You should rarely use the <tt>StringRef</tt> class directly, because it contains
497pointers to external memory it is not generally safe to store an instance of the
Benjamin Kramer38e59892010-07-14 22:38:02 +0000[diff] [blame]498class (unless you know that the external storage will not be freed). StringRef is
499small and pervasive enough in LLVM that it should always be passed by value.</p>
Daniel Dunbar6e0d1cb2009-07-25 04:41:11 +0000[diff] [blame]500
501</div>
502
503<!-- _______________________________________________________________________ -->
504<div class="doc_subsubsection">
505 <a name="Twine">The <tt>Twine</tt> class</a>
506</div>
507
508<div class="doc_text">
509
510<p>The <tt>Twine</tt> class is an efficient way for APIs to accept concatenated
511strings. For example, a common LLVM paradigm is to name one instruction based on
512the name of another instruction with a suffix, for example:</p>
513
514<div class="doc_code">
515<pre>
516 New = CmpInst::Create(<i>...</i>, SO->getName() + ".cmp");
517</pre>
518</div>
519
520<p>The <tt>Twine</tt> class is effectively a
521lightweight <a href="http://en.wikipedia.org/wiki/Rope_(computer_science)">rope</a>
522which points to temporary (stack allocated) objects. Twines can be implicitly
523constructed as the result of the plus operator applied to strings (i.e., a C
524strings, an <tt>std::string</tt>, or a <tt>StringRef</tt>). The twine delays the
Dan Gohmancf0c9bc2010-02-25 23:51:27 +0000[diff] [blame]525actual concatenation of strings until it is actually required, at which point
Daniel Dunbar6e0d1cb2009-07-25 04:41:11 +0000[diff] [blame]526it can be efficiently rendered directly into a character array. This avoids
527unnecessary heap allocation involved in constructing the temporary results of
528string concatenation. See
529"<tt><a href="/doxygen/classllvm_1_1Twine_8h-source.html">llvm/ADT/Twine.h</a></tt>"
Benjamin Kramere15192b2009-08-05 15:42:44 +0000[diff] [blame]530for more information.</p>
Daniel Dunbar6e0d1cb2009-07-25 04:41:11 +0000[diff] [blame]531
532<p>As with a <tt>StringRef</tt>, <tt>Twine</tt> objects point to external memory
533and should almost never be stored or mentioned directly. They are intended
534solely for use when defining a function which should be able to efficiently
535accept concatenated strings.</p>
536
537</div>
538
539
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]540<!-- ======================================================================= -->
541<div class="doc_subsection">
Misha Brukman2c122ce2005-11-01 21:12:49 +0000[diff] [blame]542 <a name="DEBUG">The <tt>DEBUG()</tt> macro and <tt>-debug</tt> option</a>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]543</div>
544
545<div class="doc_text">
546
547<p>Often when working on your pass you will put a bunch of debugging printouts
548and other code into your pass. After you get it working, you want to remove
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]549it, but you may need it again in the future (to work out new bugs that you run
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]550across).</p>
551
552<p> Naturally, because of this, you don't want to delete the debug printouts,
553but you don't want them to always be noisy. A standard compromise is to comment
554them out, allowing you to enable them if you need them in the future.</p>
555
Chris Lattner695b78b2005-04-26 22:56:16 +0000[diff] [blame]556<p>The "<tt><a href="/doxygen/Debug_8h-source.html">llvm/Support/Debug.h</a></tt>"
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]557file provides a macro named <tt>DEBUG()</tt> that is a much nicer solution to
558this problem. Basically, you can put arbitrary code into the argument of the
559<tt>DEBUG</tt> macro, and it is only executed if '<tt>opt</tt>' (or any other
560tool) is run with the '<tt>-debug</tt>' command line argument:</p>
561
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]562<div class="doc_code">
563<pre>
Daniel Dunbar06388ae2009-07-25 01:55:32 +0000[diff] [blame]564DEBUG(errs() &lt;&lt; "I am here!\n");
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]565</pre>
566</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]567
568<p>Then you can run your pass like this:</p>
569
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]570<div class="doc_code">
571<pre>
572$ opt &lt; a.bc &gt; /dev/null -mypass
Bill Wendling82e2eea2006-10-11 18:00:22 +0000[diff] [blame]573<i>&lt;no output&gt;</i>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]574$ opt &lt; a.bc &gt; /dev/null -mypass -debug
575I am here!
576</pre>
577</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]578
579<p>Using the <tt>DEBUG()</tt> macro instead of a home-brewed solution allows you
580to not have to create "yet another" command line option for the debug output for
581your pass. Note that <tt>DEBUG()</tt> macros are disabled for optimized builds,
582so they do not cause a performance impact at all (for the same reason, they
583should also not contain side-effects!).</p>
584
585<p>One additional nice thing about the <tt>DEBUG()</tt> macro is that you can
586enable or disable it directly in gdb. Just use "<tt>set DebugFlag=0</tt>" or
587"<tt>set DebugFlag=1</tt>" from the gdb if the program is running. If the
588program hasn't been started yet, you can always just run it with
589<tt>-debug</tt>.</p>
590
591</div>
592
593<!-- _______________________________________________________________________ -->
594<div class="doc_subsubsection">
Chris Lattnerc9151082005-04-26 22:57:07 +0000[diff] [blame]595 <a name="DEBUG_TYPE">Fine grained debug info with <tt>DEBUG_TYPE</tt> and
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]596 the <tt>-debug-only</tt> option</a>
597</div>
598
599<div class="doc_text">
600
601<p>Sometimes you may find yourself in a situation where enabling <tt>-debug</tt>
602just turns on <b>too much</b> information (such as when working on the code
603generator). If you want to enable debug information with more fine-grained
604control, you define the <tt>DEBUG_TYPE</tt> macro and the <tt>-debug</tt> only
605option as follows:</p>
606
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]607<div class="doc_code">
608<pre>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]609#undef DEBUG_TYPE
Daniel Dunbar06388ae2009-07-25 01:55:32 +0000[diff] [blame]610DEBUG(errs() &lt;&lt; "No debug type\n");
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]611#define DEBUG_TYPE "foo"
Daniel Dunbar06388ae2009-07-25 01:55:32 +0000[diff] [blame]612DEBUG(errs() &lt;&lt; "'foo' debug type\n");
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]613#undef DEBUG_TYPE
614#define DEBUG_TYPE "bar"
Daniel Dunbar06388ae2009-07-25 01:55:32 +0000[diff] [blame]615DEBUG(errs() &lt;&lt; "'bar' debug type\n"));
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]616#undef DEBUG_TYPE
617#define DEBUG_TYPE ""
Daniel Dunbar06388ae2009-07-25 01:55:32 +0000[diff] [blame]618DEBUG(errs() &lt;&lt; "No debug type (2)\n");
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]619</pre>
620</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]621
622<p>Then you can run your pass like this:</p>
623
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]624<div class="doc_code">
625<pre>
626$ opt &lt; a.bc &gt; /dev/null -mypass
Bill Wendling82e2eea2006-10-11 18:00:22 +0000[diff] [blame]627<i>&lt;no output&gt;</i>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]628$ opt &lt; a.bc &gt; /dev/null -mypass -debug
629No debug type
630'foo' debug type
631'bar' debug type
632No debug type (2)
633$ opt &lt; a.bc &gt; /dev/null -mypass -debug-only=foo
634'foo' debug type
635$ opt &lt; a.bc &gt; /dev/null -mypass -debug-only=bar
636'bar' debug type
637</pre>
638</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]639
640<p>Of course, in practice, you should only set <tt>DEBUG_TYPE</tt> at the top of
641a 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]642you <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]643<tt>#undef</tt>'s). Also, you should use names more meaningful than "foo" and
644"bar", because there is no system in place to ensure that names do not
645conflict. If two different modules use the same string, they will all be turned
646on when the name is specified. This allows, for example, all debug information
647for instruction scheduling to be enabled with <tt>-debug-type=InstrSched</tt>,
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]648even if the source lives in multiple files.</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]649
Daniel Dunbarc3c92392009-08-07 23:48:59 +0000[diff] [blame]650<p>The <tt>DEBUG_WITH_TYPE</tt> macro is also available for situations where you
651would like to set <tt>DEBUG_TYPE</tt>, but only for one specific <tt>DEBUG</tt>
652statement. It takes an additional first parameter, which is the type to use. For
Benjamin Kramer8040cd32009-10-12 14:46:08 +0000[diff] [blame]653example, the preceding example could be written as:</p>
Daniel Dunbarc3c92392009-08-07 23:48:59 +0000[diff] [blame]654
655
656<div class="doc_code">
657<pre>
658DEBUG_WITH_TYPE("", errs() &lt;&lt; "No debug type\n");
659DEBUG_WITH_TYPE("foo", errs() &lt;&lt; "'foo' debug type\n");
660DEBUG_WITH_TYPE("bar", errs() &lt;&lt; "'bar' debug type\n"));
661DEBUG_WITH_TYPE("", errs() &lt;&lt; "No debug type (2)\n");
662</pre>
663</div>
664
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]665</div>
666
667<!-- ======================================================================= -->
668<div class="doc_subsection">
Chris Lattner0be6fdf2006-12-19 21:46:21 +0000[diff] [blame]669 <a name="Statistic">The <tt>Statistic</tt> class &amp; <tt>-stats</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]670 option</a>
671</div>
672
673<div class="doc_text">
674
675<p>The "<tt><a
Chris Lattner695b78b2005-04-26 22:56:16 +0000[diff] [blame]676href="/doxygen/Statistic_8h-source.html">llvm/ADT/Statistic.h</a></tt>" file
Chris Lattner0be6fdf2006-12-19 21:46:21 +0000[diff] [blame]677provides a class named <tt>Statistic</tt> that is used as a unified way to
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]678keep track of what the LLVM compiler is doing and how effective various
679optimizations are. It is useful to see what optimizations are contributing to
680making a particular program run faster.</p>
681
682<p>Often you may run your pass on some big program, and you're interested to see
683how many times it makes a certain transformation. Although you can do this with
684hand inspection, or some ad-hoc method, this is a real pain and not very useful
Chris Lattner0be6fdf2006-12-19 21:46:21 +0000[diff] [blame]685for big programs. Using the <tt>Statistic</tt> class makes it very easy to
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]686keep track of this information, and the calculated information is presented in a
687uniform manner with the rest of the passes being executed.</p>
688
689<p>There are many examples of <tt>Statistic</tt> uses, but the basics of using
690it are as follows:</p>
691
692<ol>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]693 <li><p>Define your statistic like this:</p>
694
695<div class="doc_code">
696<pre>
Chris Lattner0be6fdf2006-12-19 21:46:21 +0000[diff] [blame]697#define <a href="#DEBUG_TYPE">DEBUG_TYPE</a> "mypassname" <i>// This goes before any #includes.</i>
698STATISTIC(NumXForms, "The # of times I did stuff");
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]699</pre>
700</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]701
Chris Lattner0be6fdf2006-12-19 21:46:21 +0000[diff] [blame]702 <p>The <tt>STATISTIC</tt> macro defines a static variable, whose name is
703 specified by the first argument. The pass name is taken from the DEBUG_TYPE
704 macro, and the description is taken from the second argument. The variable
Reid Spencer06565dc2007-01-12 17:11:23 +0000[diff] [blame]705 defined ("NumXForms" in this case) acts like an unsigned integer.</p></li>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]706
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]707 <li><p>Whenever you make a transformation, bump the counter:</p>
708
709<div class="doc_code">
710<pre>
Bill Wendling82e2eea2006-10-11 18:00:22 +0000[diff] [blame]711++NumXForms; // <i>I did stuff!</i>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]712</pre>
713</div>
714
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]715 </li>
716 </ol>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]717
718 <p>That's all you have to do. To get '<tt>opt</tt>' to print out the
719 statistics gathered, use the '<tt>-stats</tt>' option:</p>
720
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]721<div class="doc_code">
722<pre>
723$ opt -stats -mypassname &lt; program.bc &gt; /dev/null
Bill Wendling82e2eea2006-10-11 18:00:22 +0000[diff] [blame]724<i>... statistics output ...</i>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]725</pre>
726</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]727
Reid Spencer6b6c73e2007-02-09 16:00:28 +0000[diff] [blame]728 <p> When running <tt>opt</tt> on a C file from the SPEC benchmark
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]729suite, it gives a report that looks like this:</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]730
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]731<div class="doc_code">
732<pre>
Gabor Greif04367bf2007-07-06 22:07:22 +0000[diff] [blame]733 7646 bitcodewriter - Number of normal instructions
734 725 bitcodewriter - Number of oversized instructions
735 129996 bitcodewriter - Number of bitcode bytes written
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]736 2817 raise - Number of insts DCEd or constprop'd
737 3213 raise - Number of cast-of-self removed
738 5046 raise - Number of expression trees converted
739 75 raise - Number of other getelementptr's formed
740 138 raise - Number of load/store peepholes
741 42 deadtypeelim - Number of unused typenames removed from symtab
742 392 funcresolve - Number of varargs functions resolved
743 27 globaldce - Number of global variables removed
744 2 adce - Number of basic blocks removed
745 134 cee - Number of branches revectored
746 49 cee - Number of setcc instruction eliminated
747 532 gcse - Number of loads removed
748 2919 gcse - Number of instructions removed
749 86 indvars - Number of canonical indvars added
750 87 indvars - Number of aux indvars removed
751 25 instcombine - Number of dead inst eliminate
752 434 instcombine - Number of insts combined
753 248 licm - Number of load insts hoisted
754 1298 licm - Number of insts hoisted to a loop pre-header
755 3 licm - Number of insts hoisted to multiple loop preds (bad, no loop pre-header)
756 75 mem2reg - Number of alloca's promoted
757 1444 cfgsimplify - Number of blocks simplified
758</pre>
759</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]760
761<p>Obviously, with so many optimizations, having a unified framework for this
762stuff is very nice. Making your pass fit well into the framework makes it more
763maintainable and useful.</p>
764
765</div>
766
Chris Lattnerf623a082005-10-17 01:36:23 +0000[diff] [blame]767<!-- ======================================================================= -->
768<div class="doc_subsection">
769 <a name="ViewGraph">Viewing graphs while debugging code</a>
770</div>
771
772<div class="doc_text">
773
774<p>Several of the important data structures in LLVM are graphs: for example
775CFGs made out of LLVM <a href="#BasicBlock">BasicBlock</a>s, CFGs made out of
776LLVM <a href="CodeGenerator.html#machinebasicblock">MachineBasicBlock</a>s, and
777<a href="CodeGenerator.html#selectiondag_intro">Instruction Selection
778DAGs</a>. In many cases, while debugging various parts of the compiler, it is
779nice to instantly visualize these graphs.</p>
780
781<p>LLVM provides several callbacks that are available in a debug build to do
782exactly that. If you call the <tt>Function::viewCFG()</tt> method, for example,
783the current LLVM tool will pop up a window containing the CFG for the function
784where each basic block is a node in the graph, and each node contains the
785instructions in the block. Similarly, there also exists
786<tt>Function::viewCFGOnly()</tt> (does not include the instructions), the
787<tt>MachineFunction::viewCFG()</tt> and <tt>MachineFunction::viewCFGOnly()</tt>,
788and the <tt>SelectionDAG::viewGraph()</tt> methods. Within GDB, for example,
Jim Laskey543a0ee2006-10-02 12:28:07 +0000[diff] [blame]789you can usually use something like <tt>call DAG.viewGraph()</tt> to pop
Chris Lattnerf623a082005-10-17 01:36:23 +0000[diff] [blame]790up a window. Alternatively, you can sprinkle calls to these functions in your
791code in places you want to debug.</p>
792
793<p>Getting this to work requires a small amount of configuration. On Unix
794systems with X11, install the <a href="http://www.graphviz.org">graphviz</a>
795toolkit, and make sure 'dot' and 'gv' are in your path. If you are running on
796Mac OS/X, download and install the Mac OS/X <a
797href="http://www.pixelglow.com/graphviz/">Graphviz program</a>, and add
Reid Spencer128a7a72007-02-03 21:06:43 +0000[diff] [blame]798<tt>/Applications/Graphviz.app/Contents/MacOS/</tt> (or wherever you install
Chris Lattnerf623a082005-10-17 01:36:23 +0000[diff] [blame]799it) to your path. Once in your system and path are set up, rerun the LLVM
800configure script and rebuild LLVM to enable this functionality.</p>
801
Jim Laskey543a0ee2006-10-02 12:28:07 +0000[diff] [blame]802<p><tt>SelectionDAG</tt> has been extended to make it easier to locate
803<i>interesting</i> nodes in large complex graphs. From gdb, if you
804<tt>call DAG.setGraphColor(<i>node</i>, "<i>color</i>")</tt>, then the
Reid Spencer128a7a72007-02-03 21:06:43 +0000[diff] [blame]805next <tt>call DAG.viewGraph()</tt> would highlight the node in the
Jim Laskey543a0ee2006-10-02 12:28:07 +0000[diff] [blame]806specified color (choices of colors can be found at <a
Chris Lattner302da1e2007-02-03 03:05:57 +0000[diff] [blame]807href="http://www.graphviz.org/doc/info/colors.html">colors</a>.) More
Jim Laskey543a0ee2006-10-02 12:28:07 +0000[diff] [blame]808complex node attributes can be provided with <tt>call
809DAG.setGraphAttrs(<i>node</i>, "<i>attributes</i>")</tt> (choices can be
810found at <a href="http://www.graphviz.org/doc/info/attrs.html">Graph
811Attributes</a>.) If you want to restart and clear all the current graph
812attributes, then you can <tt>call DAG.clearGraphAttrs()</tt>. </p>
813
Chris Lattnerf623a082005-10-17 01:36:23 +0000[diff] [blame]814</div>
815
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]816<!-- *********************************************************************** -->
817<div class="doc_section">
818 <a name="datastructure">Picking the Right Data Structure for a Task</a>
819</div>
820<!-- *********************************************************************** -->
821
822<div class="doc_text">
823
Reid Spencer128a7a72007-02-03 21:06:43 +0000[diff] [blame]824<p>LLVM has a plethora of data structures in the <tt>llvm/ADT/</tt> directory,
825 and we commonly use STL data structures. This section describes the trade-offs
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]826 you should consider when you pick one.</p>
827
828<p>
829The first step is a choose your own adventure: do you want a sequential
830container, a set-like container, or a map-like container? The most important
831thing when choosing a container is the algorithmic properties of how you plan to
832access the container. Based on that, you should use:</p>
833
834<ul>
Reid Spencer128a7a72007-02-03 21:06:43 +0000[diff] [blame]835<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]836 of an value based on another value. Map-like containers also support
837 efficient queries for containment (whether a key is in the map). Map-like
838 containers generally do not support efficient reverse mapping (values to
839 keys). If you need that, use two maps. Some map-like containers also
840 support efficient iteration through the keys in sorted order. Map-like
841 containers are the most expensive sort, only use them if you need one of
842 these capabilities.</li>
843
844<li>a <a href="#ds_set">set-like</a> container if you need to put a bunch of
845 stuff into a container that automatically eliminates duplicates. Some
846 set-like containers support efficient iteration through the elements in
847 sorted order. Set-like containers are more expensive than sequential
848 containers.
849</li>
850
851<li>a <a href="#ds_sequential">sequential</a> container provides
852 the most efficient way to add elements and keeps track of the order they are
853 added to the collection. They permit duplicates and support efficient
Reid Spencer128a7a72007-02-03 21:06:43 +0000[diff] [blame]854 iteration, but do not support efficient look-up based on a key.
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]855</li>
856
Chris Lattnerdced9fb2009-07-25 07:22:20 +0000[diff] [blame]857<li>a <a href="#ds_string">string</a> container is a specialized sequential
858 container or reference structure that is used for character or byte
859 arrays.</li>
860
Daniel Berlin1939ace2007-09-24 17:52:25 +0000[diff] [blame]861<li>a <a href="#ds_bit">bit</a> container provides an efficient way to store and
862 perform set operations on sets of numeric id's, while automatically
863 eliminating duplicates. Bit containers require a maximum of 1 bit for each
864 identifier you want to store.
865</li>
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]866</ul>
867
868<p>
Reid Spencer128a7a72007-02-03 21:06:43 +0000[diff] [blame]869Once the proper category of container is determined, you can fine tune the
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]870memory use, constant factors, and cache behaviors of access by intelligently
Reid Spencer128a7a72007-02-03 21:06:43 +0000[diff] [blame]871picking a member of the category. Note that constant factors and cache behavior
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]872can be a big deal. If you have a vector that usually only contains a few
873elements (but could contain many), for example, it's much better to use
874<a href="#dss_smallvector">SmallVector</a> than <a href="#dss_vector">vector</a>
875. Doing so avoids (relatively) expensive malloc/free calls, which dwarf the
876cost of adding the elements to the container. </p>
877
878</div>
879
880<!-- ======================================================================= -->
881<div class="doc_subsection">
882 <a name="ds_sequential">Sequential Containers (std::vector, std::list, etc)</a>
883</div>
884
885<div class="doc_text">
886There are a variety of sequential containers available for you, based on your
887needs. Pick the first in this section that will do what you want.
888</div>
889
890<!-- _______________________________________________________________________ -->
891<div class="doc_subsubsection">
892 <a name="dss_fixedarrays">Fixed Size Arrays</a>
893</div>
894
895<div class="doc_text">
896<p>Fixed size arrays are very simple and very fast. They are good if you know
897exactly how many elements you have, or you have a (low) upper bound on how many
898you have.</p>
899</div>
900
901<!-- _______________________________________________________________________ -->
902<div class="doc_subsubsection">
903 <a name="dss_heaparrays">Heap Allocated Arrays</a>
904</div>
905
906<div class="doc_text">
907<p>Heap allocated arrays (new[] + delete[]) are also simple. They are good if
908the number of elements is variable, if you know how many elements you will need
909before the array is allocated, and if the array is usually large (if not,
910consider a <a href="#dss_smallvector">SmallVector</a>). The cost of a heap
911allocated array is the cost of the new/delete (aka malloc/free). Also note that
912if you are allocating an array of a type with a constructor, the constructor and
Reid Spencer128a7a72007-02-03 21:06:43 +0000[diff] [blame]913destructors will be run for every element in the array (re-sizable vectors only
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]914construct those elements actually used).</p>
915</div>
916
917<!-- _______________________________________________________________________ -->
918<div class="doc_subsubsection">
919 <a name="dss_smallvector">"llvm/ADT/SmallVector.h"</a>
920</div>
921
922<div class="doc_text">
923<p><tt>SmallVector&lt;Type, N&gt;</tt> is a simple class that looks and smells
924just like <tt>vector&lt;Type&gt;</tt>:
925it supports efficient iteration, lays out elements in memory order (so you can
926do pointer arithmetic between elements), supports efficient push_back/pop_back
927operations, supports efficient random access to its elements, etc.</p>
928
929<p>The advantage of SmallVector is that it allocates space for
930some number of elements (N) <b>in the object itself</b>. Because of this, if
931the SmallVector is dynamically smaller than N, no malloc is performed. This can
932be a big win in cases where the malloc/free call is far more expensive than the
933code that fiddles around with the elements.</p>
934
935<p>This is good for vectors that are "usually small" (e.g. the number of
936predecessors/successors of a block is usually less than 8). On the other hand,
937this makes the size of the SmallVector itself large, so you don't want to
938allocate lots of them (doing so will waste a lot of space). As such,
939SmallVectors are most useful when on the stack.</p>
940
941<p>SmallVector also provides a nice portable and efficient replacement for
942<tt>alloca</tt>.</p>
943
944</div>
945
946<!-- _______________________________________________________________________ -->
947<div class="doc_subsubsection">
948 <a name="dss_vector">&lt;vector&gt;</a>
949</div>
950
951<div class="doc_text">
952<p>
953std::vector is well loved and respected. It is useful when SmallVector isn't:
954when the size of the vector is often large (thus the small optimization will
955rarely be a benefit) or if you will be allocating many instances of the vector
956itself (which would waste space for elements that aren't in the container).
957vector is also useful when interfacing with code that expects vectors :).
958</p>
Chris Lattner32d84762007-02-05 06:30:51 +0000[diff] [blame]959
960<p>One worthwhile note about std::vector: avoid code like this:</p>
961
962<div class="doc_code">
963<pre>
964for ( ... ) {
Chris Lattner9bb3dbb2007-03-28 18:27:57 +0000[diff] [blame]965 std::vector&lt;foo&gt; V;
Chris Lattner32d84762007-02-05 06:30:51 +0000[diff] [blame]966 use V;
967}
968</pre>
969</div>
970
971<p>Instead, write this as:</p>
972
973<div class="doc_code">
974<pre>
Chris Lattner9bb3dbb2007-03-28 18:27:57 +0000[diff] [blame]975std::vector&lt;foo&gt; V;
Chris Lattner32d84762007-02-05 06:30:51 +0000[diff] [blame]976for ( ... ) {
977 use V;
978 V.clear();
979}
980</pre>
981</div>
982
983<p>Doing so will save (at least) one heap allocation and free per iteration of
984the loop.</p>
985
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]986</div>
987
988<!-- _______________________________________________________________________ -->
989<div class="doc_subsubsection">
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]990 <a name="dss_deque">&lt;deque&gt;</a>
991</div>
992
993<div class="doc_text">
994<p>std::deque is, in some senses, a generalized version of std::vector. Like
995std::vector, it provides constant time random access and other similar
996properties, but it also provides efficient access to the front of the list. It
997does not guarantee continuity of elements within memory.</p>
998
999<p>In exchange for this extra flexibility, std::deque has significantly higher
1000constant factor costs than std::vector. If possible, use std::vector or
1001something cheaper.</p>
1002</div>
1003
1004<!-- _______________________________________________________________________ -->
1005<div class="doc_subsubsection">
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]1006 <a name="dss_list">&lt;list&gt;</a>
1007</div>
1008
1009<div class="doc_text">
1010<p>std::list is an extremely inefficient class that is rarely useful.
1011It performs a heap allocation for every element inserted into it, thus having an
1012extremely high constant factor, particularly for small data types. std::list
1013also only supports bidirectional iteration, not random access iteration.</p>
1014
1015<p>In exchange for this high cost, std::list supports efficient access to both
1016ends of the list (like std::deque, but unlike std::vector or SmallVector). In
1017addition, the iterator invalidation characteristics of std::list are stronger
1018than that of a vector class: inserting or removing an element into the list does
1019not invalidate iterator or pointers to other elements in the list.</p>
1020</div>
1021
1022<!-- _______________________________________________________________________ -->
1023<div class="doc_subsubsection">
Gabor Greif3899e492009-02-27 11:37:41 +0000[diff] [blame]1024 <a name="dss_ilist">llvm/ADT/ilist.h</a>
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]1025</div>
1026
1027<div class="doc_text">
1028<p><tt>ilist&lt;T&gt;</tt> implements an 'intrusive' doubly-linked list. It is
1029intrusive, because it requires the element to store and provide access to the
1030prev/next pointers for the list.</p>
1031
Gabor Greif2946d1c2009-02-27 12:02:19 +0000[diff] [blame]1032<p><tt>ilist</tt> has the same drawbacks as <tt>std::list</tt>, and additionally
1033requires an <tt>ilist_traits</tt> implementation for the element type, but it
1034provides some novel characteristics. In particular, it can efficiently store
1035polymorphic objects, the traits class is informed when an element is inserted or
Gabor Greif0cbcabe2009-03-12 09:47:03 +0000[diff] [blame]1036removed from the list, and <tt>ilist</tt>s are guaranteed to support a
1037constant-time splice operation.</p>
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]1038
Gabor Greif0cbcabe2009-03-12 09:47:03 +0000[diff] [blame]1039<p>These properties are exactly what we want for things like
1040<tt>Instruction</tt>s and basic blocks, which is why these are implemented with
1041<tt>ilist</tt>s.</p>
Gabor Greif3899e492009-02-27 11:37:41 +0000[diff] [blame]1042
1043Related classes of interest are explained in the following subsections:
1044 <ul>
Gabor Greif01862502009-02-27 13:28:07 +0000[diff] [blame]1045 <li><a href="#dss_ilist_traits">ilist_traits</a></li>
Gabor Greif2946d1c2009-02-27 12:02:19 +0000[diff] [blame]1046 <li><a href="#dss_iplist">iplist</a></li>
Gabor Greif3899e492009-02-27 11:37:41 +0000[diff] [blame]1047 <li><a href="#dss_ilist_node">llvm/ADT/ilist_node.h</a></li>
Gabor Greif6a65f422009-03-12 10:30:31 +0000[diff] [blame]1048 <li><a href="#dss_ilist_sentinel">Sentinels</a></li>
Gabor Greif3899e492009-02-27 11:37:41 +0000[diff] [blame]1049 </ul>
1050</div>
1051
1052<!-- _______________________________________________________________________ -->
1053<div class="doc_subsubsection">
Gabor Greif01862502009-02-27 13:28:07 +0000[diff] [blame]1054 <a name="dss_ilist_traits">ilist_traits</a>
1055</div>
1056
1057<div class="doc_text">
1058<p><tt>ilist_traits&lt;T&gt;</tt> is <tt>ilist&lt;T&gt;</tt>'s customization
1059mechanism. <tt>iplist&lt;T&gt;</tt> (and consequently <tt>ilist&lt;T&gt;</tt>)
1060publicly derive from this traits class.</p>
1061</div>
1062
1063<!-- _______________________________________________________________________ -->
1064<div class="doc_subsubsection">
Gabor Greif2946d1c2009-02-27 12:02:19 +0000[diff] [blame]1065 <a name="dss_iplist">iplist</a>
1066</div>
1067
1068<div class="doc_text">
1069<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]1070supports a slightly narrower interface. Notably, inserters from
1071<tt>T&amp;</tt> are absent.</p>
Gabor Greif01862502009-02-27 13:28:07 +0000[diff] [blame]1072
1073<p><tt>ilist_traits&lt;T&gt;</tt> is a public base of this class and can be
1074used for a wide variety of customizations.</p>
Gabor Greif2946d1c2009-02-27 12:02:19 +0000[diff] [blame]1075</div>
1076
1077<!-- _______________________________________________________________________ -->
1078<div class="doc_subsubsection">
Gabor Greif3899e492009-02-27 11:37:41 +0000[diff] [blame]1079 <a name="dss_ilist_node">llvm/ADT/ilist_node.h</a>
1080</div>
1081
1082<div class="doc_text">
1083<p><tt>ilist_node&lt;T&gt;</tt> implements a the forward and backward links
1084that are expected by the <tt>ilist&lt;T&gt;</tt> (and analogous containers)
1085in the default manner.</p>
1086
1087<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]1088<tt>T</tt>, usually <tt>T</tt> publicly derives from
1089<tt>ilist_node&lt;T&gt;</tt>.</p>
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]1090</div>
1091
1092<!-- _______________________________________________________________________ -->
1093<div class="doc_subsubsection">
Gabor Greif6a65f422009-03-12 10:30:31 +0000[diff] [blame]1094 <a name="dss_ilist_sentinel">Sentinels</a>
1095</div>
1096
1097<div class="doc_text">
Dan Gohmancf0c9bc2010-02-25 23:51:27 +0000[diff] [blame]1098<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]1099citizen in the C++ ecosystem, it needs to support the standard container
1100operations, such as <tt>begin</tt> and <tt>end</tt> iterators, etc. Also, the
1101<tt>operator--</tt> must work correctly on the <tt>end</tt> iterator in the
1102case of non-empty <tt>ilist</tt>s.</p>
1103
1104<p>The only sensible solution to this problem is to allocate a so-called
1105<i>sentinel</i> along with the intrusive list, which serves as the <tt>end</tt>
1106iterator, providing the back-link to the last element. However conforming to the
1107C++ convention it is illegal to <tt>operator++</tt> beyond the sentinel and it
1108also must not be dereferenced.</p>
1109
1110<p>These constraints allow for some implementation freedom to the <tt>ilist</tt>
1111how to allocate and store the sentinel. The corresponding policy is dictated
1112by <tt>ilist_traits&lt;T&gt;</tt>. By default a <tt>T</tt> gets heap-allocated
1113whenever the need for a sentinel arises.</p>
1114
1115<p>While the default policy is sufficient in most cases, it may break down when
1116<tt>T</tt> does not provide a default constructor. Also, in the case of many
1117instances of <tt>ilist</tt>s, the memory overhead of the associated sentinels
1118is wasted. To alleviate the situation with numerous and voluminous
1119<tt>T</tt>-sentinels, sometimes a trick is employed, leading to <i>ghostly
1120sentinels</i>.</p>
1121
1122<p>Ghostly sentinels are obtained by specially-crafted <tt>ilist_traits&lt;T&gt;</tt>
1123which superpose the sentinel with the <tt>ilist</tt> instance in memory. Pointer
1124arithmetic is used to obtain the sentinel, which is relative to the
1125<tt>ilist</tt>'s <tt>this</tt> pointer. The <tt>ilist</tt> is augmented by an
1126extra pointer, which serves as the back-link of the sentinel. This is the only
1127field in the ghostly sentinel which can be legally accessed.</p>
1128</div>
1129
1130<!-- _______________________________________________________________________ -->
1131<div class="doc_subsubsection">
Chris Lattnerc5722432007-02-03 19:49:31 +0000[diff] [blame]1132 <a name="dss_other">Other Sequential Container options</a>
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]1133</div>
1134
1135<div class="doc_text">
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1136<p>Other STL containers are available, such as std::string.</p>
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]1137
1138<p>There are also various STL adapter classes such as std::queue,
1139std::priority_queue, std::stack, etc. These provide simplified access to an
1140underlying container but don't affect the cost of the container itself.</p>
1141
1142</div>
1143
1144
1145<!-- ======================================================================= -->
1146<div class="doc_subsection">
1147 <a name="ds_set">Set-Like Containers (std::set, SmallSet, SetVector, etc)</a>
1148</div>
1149
1150<div class="doc_text">
1151
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1152<p>Set-like containers are useful when you need to canonicalize multiple values
1153into a single representation. There are several different choices for how to do
1154this, providing various trade-offs.</p>
1155
1156</div>
1157
1158
1159<!-- _______________________________________________________________________ -->
1160<div class="doc_subsubsection">
1161 <a name="dss_sortedvectorset">A sorted 'vector'</a>
1162</div>
1163
1164<div class="doc_text">
1165
Chris Lattner3b23a8c2007-02-03 08:10:45 +0000[diff] [blame]1166<p>If you intend to insert a lot of elements, then do a lot of queries, a
1167great approach is to use a vector (or other sequential container) with
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1168std::sort+std::unique to remove duplicates. This approach works really well if
Chris Lattner3b23a8c2007-02-03 08:10:45 +0000[diff] [blame]1169your usage pattern has these two distinct phases (insert then query), and can be
1170coupled with a good choice of <a href="#ds_sequential">sequential container</a>.
1171</p>
1172
1173<p>
1174This combination provides the several nice properties: the result data is
1175contiguous in memory (good for cache locality), has few allocations, is easy to
1176address (iterators in the final vector are just indices or pointers), and can be
1177efficiently queried with a standard binary or radix search.</p>
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1178
1179</div>
1180
1181<!-- _______________________________________________________________________ -->
1182<div class="doc_subsubsection">
1183 <a name="dss_smallset">"llvm/ADT/SmallSet.h"</a>
1184</div>
1185
1186<div class="doc_text">
1187
Reid Spencer128a7a72007-02-03 21:06:43 +0000[diff] [blame]1188<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]1189are 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]1190has space for N elements in place (thus, if the set is dynamically smaller than
Chris Lattner14868db2007-02-03 08:20:15 +0000[diff] [blame]1191N, no malloc traffic is required) and accesses them with a simple linear search.
1192When the set grows beyond 'N' elements, it allocates a more expensive representation that
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1193guarantees efficient access (for most types, it falls back to std::set, but for
Chris Lattner14868db2007-02-03 08:20:15 +0000[diff] [blame]1194pointers it uses something far better, <a
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1195href="#dss_smallptrset">SmallPtrSet</a>).</p>
1196
1197<p>The magic of this class is that it handles small sets extremely efficiently,
1198but gracefully handles extremely large sets without loss of efficiency. The
1199drawback is that the interface is quite small: it supports insertion, queries
1200and erasing, but does not support iteration.</p>
1201
1202</div>
1203
1204<!-- _______________________________________________________________________ -->
1205<div class="doc_subsubsection">
1206 <a name="dss_smallptrset">"llvm/ADT/SmallPtrSet.h"</a>
1207</div>
1208
1209<div class="doc_text">
1210
Gabor Greif4de73682010-03-26 19:30:47 +0000[diff] [blame]1211<p>SmallPtrSet has all the advantages of <tt>SmallSet</tt> (and a <tt>SmallSet</tt> of pointers is
1212transparently implemented with a <tt>SmallPtrSet</tt>), but also supports iterators. If
Chris Lattner14868db2007-02-03 08:20:15 +0000[diff] [blame]1213more than 'N' insertions are performed, a single quadratically
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1214probed hash table is allocated and grows as needed, providing extremely
1215efficient access (constant time insertion/deleting/queries with low constant
1216factors) and is very stingy with malloc traffic.</p>
1217
Gabor Greif4de73682010-03-26 19:30:47 +0000[diff] [blame]1218<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]1219whenever an insertion occurs. Also, the values visited by the iterators are not
1220visited in sorted order.</p>
1221
1222</div>
1223
1224<!-- _______________________________________________________________________ -->
1225<div class="doc_subsubsection">
Chris Lattnerc28476f2007-09-30 00:58:59 +0000[diff] [blame]1226 <a name="dss_denseset">"llvm/ADT/DenseSet.h"</a>
1227</div>
1228
1229<div class="doc_text">
1230
1231<p>
1232DenseSet is a simple quadratically probed hash table. It excels at supporting
1233small values: it uses a single allocation to hold all of the pairs that
1234are currently inserted in the set. DenseSet is a great way to unique small
1235values that are not simple pointers (use <a
1236href="#dss_smallptrset">SmallPtrSet</a> for pointers). Note that DenseSet has
1237the same requirements for the value type that <a
1238href="#dss_densemap">DenseMap</a> has.
1239</p>
1240
1241</div>
1242
1243<!-- _______________________________________________________________________ -->
1244<div class="doc_subsubsection">
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1245 <a name="dss_FoldingSet">"llvm/ADT/FoldingSet.h"</a>
1246</div>
1247
1248<div class="doc_text">
1249
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]1250<p>
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1251FoldingSet is an aggregate class that is really good at uniquing
1252expensive-to-create or polymorphic objects. It is a combination of a chained
1253hash table with intrusive links (uniqued objects are required to inherit from
Chris Lattner14868db2007-02-03 08:20:15 +0000[diff] [blame]1254FoldingSetNode) that uses <a href="#dss_smallvector">SmallVector</a> as part of
1255its ID process.</p>
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1256
Chris Lattner14868db2007-02-03 08:20:15 +0000[diff] [blame]1257<p>Consider a case where you want to implement a "getOrCreateFoo" method for
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1258a complex object (for example, a node in the code generator). The client has a
1259description of *what* it wants to generate (it knows the opcode and all the
1260operands), 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]1261only to find out it already exists, at which point we would have to delete it
1262and return the node that already exists.
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]1263</p>
1264
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1265<p>To support this style of client, FoldingSet perform a query with a
1266FoldingSetNodeID (which wraps SmallVector) that can be used to describe the
1267element that we want to query for. The query either returns the element
1268matching the ID or it returns an opaque ID that indicates where insertion should
Chris Lattner14868db2007-02-03 08:20:15 +0000[diff] [blame]1269take place. Construction of the ID usually does not require heap traffic.</p>
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1270
1271<p>Because FoldingSet uses intrusive links, it can support polymorphic objects
1272in the set (for example, you can have SDNode instances mixed with LoadSDNodes).
1273Because the elements are individually allocated, pointers to the elements are
1274stable: inserting or removing elements does not invalidate any pointers to other
1275elements.
1276</p>
1277
1278</div>
1279
1280<!-- _______________________________________________________________________ -->
1281<div class="doc_subsubsection">
1282 <a name="dss_set">&lt;set&gt;</a>
1283</div>
1284
1285<div class="doc_text">
1286
Chris Lattnerc5722432007-02-03 19:49:31 +0000[diff] [blame]1287<p><tt>std::set</tt> is a reasonable all-around set class, which is decent at
1288many things but great at nothing. std::set allocates memory for each element
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1289inserted (thus it is very malloc intensive) and typically stores three pointers
Chris Lattner14868db2007-02-03 08:20:15 +0000[diff] [blame]1290per element in the set (thus adding a large amount of per-element space
1291overhead). It offers guaranteed log(n) performance, which is not particularly
Chris Lattnerc5722432007-02-03 19:49:31 +0000[diff] [blame]1292fast from a complexity standpoint (particularly if the elements of the set are
1293expensive to compare, like strings), and has extremely high constant factors for
1294lookup, insertion and removal.</p>
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1295
Chris Lattner14868db2007-02-03 08:20:15 +0000[diff] [blame]1296<p>The advantages of std::set are that its iterators are stable (deleting or
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1297inserting an element from the set does not affect iterators or pointers to other
1298elements) and that iteration over the set is guaranteed to be in sorted order.
1299If the elements in the set are large, then the relative overhead of the pointers
1300and malloc traffic is not a big deal, but if the elements of the set are small,
1301std::set is almost never a good choice.</p>
1302
1303</div>
1304
1305<!-- _______________________________________________________________________ -->
1306<div class="doc_subsubsection">
1307 <a name="dss_setvector">"llvm/ADT/SetVector.h"</a>
1308</div>
1309
1310<div class="doc_text">
Chris Lattneredca3c52007-02-04 00:00:26 +0000[diff] [blame]1311<p>LLVM's SetVector&lt;Type&gt; is an adapter class that combines your choice of
1312a set-like container along with a <a href="#ds_sequential">Sequential
1313Container</a>. The important property
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1314that this provides is efficient insertion with uniquing (duplicate elements are
1315ignored) with iteration support. It implements this by inserting elements into
1316both a set-like container and the sequential container, using the set-like
1317container for uniquing and the sequential container for iteration.
1318</p>
1319
1320<p>The difference between SetVector and other sets is that the order of
1321iteration is guaranteed to match the order of insertion into the SetVector.
1322This property is really important for things like sets of pointers. Because
1323pointer values are non-deterministic (e.g. vary across runs of the program on
Chris Lattneredca3c52007-02-04 00:00:26 +0000[diff] [blame]1324different machines), iterating over the pointers in the set will
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1325not be in a well-defined order.</p>
1326
1327<p>
1328The drawback of SetVector is that it requires twice as much space as a normal
1329set and has the sum of constant factors from the set-like container and the
1330sequential container that it uses. Use it *only* if you need to iterate over
1331the elements in a deterministic order. SetVector is also expensive to delete
Chris Lattneredca3c52007-02-04 00:00:26 +0000[diff] [blame]1332elements out of (linear time), unless you use it's "pop_back" method, which is
1333faster.
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1334</p>
1335
Chris Lattneredca3c52007-02-04 00:00:26 +0000[diff] [blame]1336<p>SetVector is an adapter class that defaults to using std::vector and std::set
1337for the underlying containers, so it is quite expensive. However,
1338<tt>"llvm/ADT/SetVector.h"</tt> also provides a SmallSetVector class, which
1339defaults to using a SmallVector and SmallSet of a specified size. If you use
1340this, and if your sets are dynamically smaller than N, you will save a lot of
1341heap traffic.</p>
1342
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1343</div>
1344
1345<!-- _______________________________________________________________________ -->
1346<div class="doc_subsubsection">
Chris Lattnerc5722432007-02-03 19:49:31 +0000[diff] [blame]1347 <a name="dss_uniquevector">"llvm/ADT/UniqueVector.h"</a>
1348</div>
1349
1350<div class="doc_text">
1351
1352<p>
1353UniqueVector is similar to <a href="#dss_setvector">SetVector</a>, but it
1354retains a unique ID for each element inserted into the set. It internally
1355contains a map and a vector, and it assigns a unique ID for each value inserted
1356into the set.</p>
1357
1358<p>UniqueVector is very expensive: its cost is the sum of the cost of
1359maintaining both the map and vector, it has high complexity, high constant
1360factors, and produces a lot of malloc traffic. It should be avoided.</p>
1361
1362</div>
1363
1364
1365<!-- _______________________________________________________________________ -->
1366<div class="doc_subsubsection">
1367 <a name="dss_otherset">Other Set-Like Container Options</a>
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1368</div>
1369
1370<div class="doc_text">
1371
1372<p>
1373The STL provides several other options, such as std::multiset and the various
Chris Lattnerf1a30822009-03-09 05:20:45 +0000[diff] [blame]1374"hash_set" like containers (whether from C++ TR1 or from the SGI library). We
1375never use hash_set and unordered_set because they are generally very expensive
1376(each insertion requires a malloc) and very non-portable.
1377</p>
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1378
1379<p>std::multiset is useful if you're not interested in elimination of
Chris Lattner14868db2007-02-03 08:20:15 +0000[diff] [blame]1380duplicates, but has all the drawbacks of std::set. A sorted vector (where you
1381don't delete duplicate entries) or some other approach is almost always
1382better.</p>
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1383
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]1384</div>
1385
1386<!-- ======================================================================= -->
1387<div class="doc_subsection">
1388 <a name="ds_map">Map-Like Containers (std::map, DenseMap, etc)</a>
1389</div>
1390
1391<div class="doc_text">
Chris Lattnerc5722432007-02-03 19:49:31 +0000[diff] [blame]1392Map-like containers are useful when you want to associate data to a key. As
1393usual, there are a lot of different ways to do this. :)
1394</div>
1395
1396<!-- _______________________________________________________________________ -->
1397<div class="doc_subsubsection">
1398 <a name="dss_sortedvectormap">A sorted 'vector'</a>
1399</div>
1400
1401<div class="doc_text">
1402
1403<p>
1404If your usage pattern follows a strict insert-then-query approach, you can
1405trivially use the same approach as <a href="#dss_sortedvectorset">sorted vectors
1406for set-like containers</a>. The only difference is that your query function
1407(which uses std::lower_bound to get efficient log(n) lookup) should only compare
1408the key, not both the key and value. This yields the same advantages as sorted
1409vectors for sets.
1410</p>
1411</div>
1412
1413<!-- _______________________________________________________________________ -->
1414<div class="doc_subsubsection">
Chris Lattner796f9fa2007-02-08 19:14:21 +0000[diff] [blame]1415 <a name="dss_stringmap">"llvm/ADT/StringMap.h"</a>
Chris Lattnerc5722432007-02-03 19:49:31 +0000[diff] [blame]1416</div>
1417
1418<div class="doc_text">
1419
1420<p>
1421Strings are commonly used as keys in maps, and they are difficult to support
1422efficiently: they are variable length, inefficient to hash and compare when
Chris Lattner796f9fa2007-02-08 19:14:21 +0000[diff] [blame]1423long, expensive to copy, etc. StringMap is a specialized container designed to
1424cope with these issues. It supports mapping an arbitrary range of bytes to an
1425arbitrary other object.</p>
Chris Lattnerc5722432007-02-03 19:49:31 +0000[diff] [blame]1426
Chris Lattner796f9fa2007-02-08 19:14:21 +0000[diff] [blame]1427<p>The StringMap implementation uses a quadratically-probed hash table, where
Chris Lattnerc5722432007-02-03 19:49:31 +0000[diff] [blame]1428the buckets store a pointer to the heap allocated entries (and some other
1429stuff). The entries in the map must be heap allocated because the strings are
1430variable length. The string data (key) and the element object (value) are
1431stored in the same allocation with the string data immediately after the element
1432object. This container guarantees the "<tt>(char*)(&amp;Value+1)</tt>" points
1433to the key string for a value.</p>
1434
Chris Lattner796f9fa2007-02-08 19:14:21 +0000[diff] [blame]1435<p>The StringMap is very fast for several reasons: quadratic probing is very
Chris Lattnerc5722432007-02-03 19:49:31 +0000[diff] [blame]1436cache efficient for lookups, the hash value of strings in buckets is not
Nick Lewycky2a80aca2010-08-01 23:18:45 +0000[diff] [blame]1437recomputed when looking up an element, StringMap rarely has to touch the
Chris Lattnerc5722432007-02-03 19:49:31 +0000[diff] [blame]1438memory for unrelated objects when looking up a value (even when hash collisions
1439happen), hash table growth does not recompute the hash values for strings
1440already in the table, and each pair in the map is store in a single allocation
1441(the string data is stored in the same allocation as the Value of a pair).</p>
1442
Chris Lattner796f9fa2007-02-08 19:14:21 +0000[diff] [blame]1443<p>StringMap also provides query methods that take byte ranges, so it only ever
Chris Lattnerc5722432007-02-03 19:49:31 +0000[diff] [blame]1444copies a string if a value is inserted into the table.</p>
1445</div>
1446
1447<!-- _______________________________________________________________________ -->
1448<div class="doc_subsubsection">
1449 <a name="dss_indexedmap">"llvm/ADT/IndexedMap.h"</a>
1450</div>
1451
1452<div class="doc_text">
1453<p>
1454IndexedMap is a specialized container for mapping small dense integers (or
1455values that can be mapped to small dense integers) to some other type. It is
1456internally implemented as a vector with a mapping function that maps the keys to
1457the dense integer range.
1458</p>
1459
1460<p>
1461This is useful for cases like virtual registers in the LLVM code generator: they
1462have a dense mapping that is offset by a compile-time constant (the first
1463virtual register ID).</p>
1464
1465</div>
1466
1467<!-- _______________________________________________________________________ -->
1468<div class="doc_subsubsection">
1469 <a name="dss_densemap">"llvm/ADT/DenseMap.h"</a>
1470</div>
1471
1472<div class="doc_text">
1473
1474<p>
1475DenseMap is a simple quadratically probed hash table. It excels at supporting
1476small keys and values: it uses a single allocation to hold all of the pairs that
1477are currently inserted in the map. DenseMap is a great way to map pointers to
1478pointers, or map other small types to each other.
1479</p>
1480
1481<p>
1482There are several aspects of DenseMap that you should be aware of, however. The
1483iterators in a densemap are invalidated whenever an insertion occurs, unlike
1484map. Also, because DenseMap allocates space for a large number of key/value
Chris Lattnera4a264d2007-02-03 20:17:53 +0000[diff] [blame]1485pairs (it starts with 64 by default), it will waste a lot of space if your keys
1486or values are large. Finally, you must implement a partial specialization of
Chris Lattner76c1b972007-09-17 18:34:04 +0000[diff] [blame]1487DenseMapInfo for the key that you want, if it isn't already supported. This
Chris Lattnerc5722432007-02-03 19:49:31 +0000[diff] [blame]1488is required to tell DenseMap about two special marker values (which can never be
Chris Lattnera4a264d2007-02-03 20:17:53 +0000[diff] [blame]1489inserted into the map) that it needs internally.</p>
Chris Lattnerc5722432007-02-03 19:49:31 +0000[diff] [blame]1490
1491</div>
1492
1493<!-- _______________________________________________________________________ -->
1494<div class="doc_subsubsection">
Jeffrey Yasskin71a5c222009-10-22 22:11:22 +0000[diff] [blame]1495 <a name="dss_valuemap">"llvm/ADT/ValueMap.h"</a>
1496</div>
1497
1498<div class="doc_text">
1499
1500<p>
1501ValueMap is a wrapper around a <a href="#dss_densemap">DenseMap</a> mapping
1502Value*s (or subclasses) to another type. When a Value is deleted or RAUW'ed,
1503ValueMap will update itself so the new version of the key is mapped to the same
1504value, just as if the key were a WeakVH. You can configure exactly how this
1505happens, and what else happens on these two events, by passing
1506a <code>Config</code> parameter to the ValueMap template.</p>
1507
1508</div>
1509
1510<!-- _______________________________________________________________________ -->
1511<div class="doc_subsubsection">
Chris Lattnerc5722432007-02-03 19:49:31 +0000[diff] [blame]1512 <a name="dss_map">&lt;map&gt;</a>
1513</div>
1514
1515<div class="doc_text">
1516
1517<p>
1518std::map has similar characteristics to <a href="#dss_set">std::set</a>: it uses
1519a single allocation per pair inserted into the map, it offers log(n) lookup with
1520an extremely large constant factor, imposes a space penalty of 3 pointers per
1521pair in the map, etc.</p>
1522
1523<p>std::map is most useful when your keys or values are very large, if you need
1524to iterate over the collection in sorted order, or if you need stable iterators
1525into the map (i.e. they don't get invalidated if an insertion or deletion of
1526another element takes place).</p>
1527
1528</div>
1529
1530<!-- _______________________________________________________________________ -->
1531<div class="doc_subsubsection">
1532 <a name="dss_othermap">Other Map-Like Container Options</a>
1533</div>
1534
1535<div class="doc_text">
1536
1537<p>
1538The STL provides several other options, such as std::multimap and the various
Chris Lattnerf1a30822009-03-09 05:20:45 +0000[diff] [blame]1539"hash_map" like containers (whether from C++ TR1 or from the SGI library). We
1540never use hash_set and unordered_set because they are generally very expensive
1541(each insertion requires a malloc) and very non-portable.</p>
Chris Lattnerc5722432007-02-03 19:49:31 +0000[diff] [blame]1542
1543<p>std::multimap is useful if you want to map a key to multiple values, but has
1544all the drawbacks of std::map. A sorted vector or some other approach is almost
1545always better.</p>
1546
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]1547</div>
1548
Daniel Berlin1939ace2007-09-24 17:52:25 +0000[diff] [blame]1549<!-- ======================================================================= -->
1550<div class="doc_subsection">
Chris Lattnerdced9fb2009-07-25 07:22:20 +0000[diff] [blame]1551 <a name="ds_string">String-like containers</a>
1552</div>
1553
1554<div class="doc_text">
1555
1556<p>
1557TODO: const char* vs stringref vs smallstring vs std::string. Describe twine,
1558xref to #string_apis.
1559</p>
1560
1561</div>
1562
1563<!-- ======================================================================= -->
1564<div class="doc_subsection">
Daniel Berlin1939ace2007-09-24 17:52:25 +0000[diff] [blame]1565 <a name="ds_bit">Bit storage containers (BitVector, SparseBitVector)</a>
1566</div>
1567
1568<div class="doc_text">
Chris Lattner7086ce72007-09-25 22:37:50 +0000[diff] [blame]1569<p>Unlike the other containers, there are only two bit storage containers, and
1570choosing when to use each is relatively straightforward.</p>
1571
1572<p>One additional option is
1573<tt>std::vector&lt;bool&gt;</tt>: we discourage its use for two reasons 1) the
1574implementation in many common compilers (e.g. commonly available versions of
1575GCC) is extremely inefficient and 2) the C++ standards committee is likely to
1576deprecate this container and/or change it significantly somehow. In any case,
1577please don't use it.</p>
Daniel Berlin1939ace2007-09-24 17:52:25 +0000[diff] [blame]1578</div>
1579
1580<!-- _______________________________________________________________________ -->
1581<div class="doc_subsubsection">
1582 <a name="dss_bitvector">BitVector</a>
1583</div>
1584
1585<div class="doc_text">
Dan Gohman5f7775c2010-01-05 18:24:00 +0000[diff] [blame]1586<p> The BitVector container provides a dynamic size set of bits for manipulation.
Daniel Berlin1939ace2007-09-24 17:52:25 +0000[diff] [blame]1587It supports individual bit setting/testing, as well as set operations. The set
1588operations take time O(size of bitvector), but operations are performed one word
1589at a time, instead of one bit at a time. This makes the BitVector very fast for
1590set operations compared to other containers. Use the BitVector when you expect
1591the number of set bits to be high (IE a dense set).
1592</p>
1593</div>
1594
1595<!-- _______________________________________________________________________ -->
1596<div class="doc_subsubsection">
Dan Gohman5f7775c2010-01-05 18:24:00 +0000[diff] [blame]1597 <a name="dss_smallbitvector">SmallBitVector</a>
1598</div>
1599
1600<div class="doc_text">
1601<p> The SmallBitVector container provides the same interface as BitVector, but
1602it is optimized for the case where only a small number of bits, less than
160325 or so, are needed. It also transparently supports larger bit counts, but
1604slightly less efficiently than a plain BitVector, so SmallBitVector should
1605only be used when larger counts are rare.
1606</p>
1607
1608<p>
1609At this time, SmallBitVector does not support set operations (and, or, xor),
1610and its operator[] does not provide an assignable lvalue.
1611</p>
1612</div>
1613
1614<!-- _______________________________________________________________________ -->
1615<div class="doc_subsubsection">
Daniel Berlin1939ace2007-09-24 17:52:25 +0000[diff] [blame]1616 <a name="dss_sparsebitvector">SparseBitVector</a>
1617</div>
1618
1619<div class="doc_text">
1620<p> The SparseBitVector container is much like BitVector, with one major
1621difference: Only the bits that are set, are stored. This makes the
1622SparseBitVector much more space efficient than BitVector when the set is sparse,
1623as well as making set operations O(number of set bits) instead of O(size of
1624universe). 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
1625(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).
1626</p>
1627</div>
Chris Lattnerf623a082005-10-17 01:36:23 +0000[diff] [blame]1628
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1629<!-- *********************************************************************** -->
1630<div class="doc_section">
1631 <a name="common">Helpful Hints for Common Operations</a>
1632</div>
1633<!-- *********************************************************************** -->
1634
1635<div class="doc_text">
1636
1637<p>This section describes how to perform some very simple transformations of
1638LLVM code. This is meant to give examples of common idioms used, showing the
1639practical side of LLVM transformations. <p> Because this is a "how-to" section,
1640you should also read about the main classes that you will be working with. The
1641<a href="#coreclasses">Core LLVM Class Hierarchy Reference</a> contains details
1642and descriptions of the main classes that you should know about.</p>
1643
1644</div>
1645
1646<!-- NOTE: this section should be heavy on example code -->
1647<!-- ======================================================================= -->
1648<div class="doc_subsection">
1649 <a name="inspection">Basic Inspection and Traversal Routines</a>
1650</div>
1651
1652<div class="doc_text">
1653
1654<p>The LLVM compiler infrastructure have many different data structures that may
1655be traversed. Following the example of the C++ standard template library, the
1656techniques used to traverse these various data structures are all basically the
1657same. For a enumerable sequence of values, the <tt>XXXbegin()</tt> function (or
1658method) returns an iterator to the start of the sequence, the <tt>XXXend()</tt>
1659function returns an iterator pointing to one past the last valid element of the
1660sequence, and there is some <tt>XXXiterator</tt> data type that is common
1661between the two operations.</p>
1662
1663<p>Because the pattern for iteration is common across many different aspects of
1664the program representation, the standard template library algorithms may be used
1665on them, and it is easier to remember how to iterate. First we show a few common
1666examples of the data structures that need to be traversed. Other data
1667structures are traversed in very similar ways.</p>
1668
1669</div>
1670
1671<!-- _______________________________________________________________________ -->
Chris Lattner69bf8a92004-05-23 21:06:58 +0000[diff] [blame]1672<div class="doc_subsubsection">
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1673 <a name="iterate_function">Iterating over the </a><a
1674 href="#BasicBlock"><tt>BasicBlock</tt></a>s in a <a
1675 href="#Function"><tt>Function</tt></a>
1676</div>
1677
1678<div class="doc_text">
1679
1680<p>It's quite common to have a <tt>Function</tt> instance that you'd like to
1681transform in some way; in particular, you'd like to manipulate its
1682<tt>BasicBlock</tt>s. To facilitate this, you'll need to iterate over all of
1683the <tt>BasicBlock</tt>s that constitute the <tt>Function</tt>. The following is
1684an example that prints the name of a <tt>BasicBlock</tt> and the number of
1685<tt>Instruction</tt>s it contains:</p>
1686
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1687<div class="doc_code">
1688<pre>
Bill Wendling82e2eea2006-10-11 18:00:22 +0000[diff] [blame]1689// <i>func is a pointer to a Function instance</i>
1690for (Function::iterator i = func-&gt;begin(), e = func-&gt;end(); i != e; ++i)
1691 // <i>Print out the name of the basic block if it has one, and then the</i>
1692 // <i>number of instructions that it contains</i>
Chris Lattner3fee6ed2009-09-08 05:15:50 +0000[diff] [blame]1693 errs() &lt;&lt; "Basic block (name=" &lt;&lt; i-&gt;getName() &lt;&lt; ") has "
Bill Wendling832171c2006-12-07 20:04:42 +0000[diff] [blame]1694 &lt;&lt; i-&gt;size() &lt;&lt; " instructions.\n";
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1695</pre>
1696</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1697
1698<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]1699invoking member functions of the <tt>Instruction</tt> class. This is
1700because the indirection operator is overloaded for the iterator
Chris Lattner7496ec52003-08-05 22:54:23 +0000[diff] [blame]1701classes. In the above code, the expression <tt>i-&gt;size()</tt> is
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1702exactly equivalent to <tt>(*i).size()</tt> just like you'd expect.</p>
1703
1704</div>
1705
1706<!-- _______________________________________________________________________ -->
Chris Lattner69bf8a92004-05-23 21:06:58 +0000[diff] [blame]1707<div class="doc_subsubsection">
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1708 <a name="iterate_basicblock">Iterating over the </a><a
1709 href="#Instruction"><tt>Instruction</tt></a>s in a <a
1710 href="#BasicBlock"><tt>BasicBlock</tt></a>
1711</div>
1712
1713<div class="doc_text">
1714
1715<p>Just like when dealing with <tt>BasicBlock</tt>s in <tt>Function</tt>s, it's
1716easy to iterate over the individual instructions that make up
1717<tt>BasicBlock</tt>s. Here's a code snippet that prints out each instruction in
1718a <tt>BasicBlock</tt>:</p>
1719
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1720<div class="doc_code">
Chris Lattner55c04612005-03-06 06:00:13 +0000[diff] [blame]1721<pre>
Bill Wendling82e2eea2006-10-11 18:00:22 +0000[diff] [blame]1722// <i>blk is a pointer to a BasicBlock instance</i>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1723for (BasicBlock::iterator i = blk-&gt;begin(), e = blk-&gt;end(); i != e; ++i)
Bill Wendling82e2eea2006-10-11 18:00:22 +0000[diff] [blame]1724 // <i>The next statement works since operator&lt;&lt;(ostream&amp;,...)</i>
1725 // <i>is overloaded for Instruction&amp;</i>
Chris Lattner3fee6ed2009-09-08 05:15:50 +0000[diff] [blame]1726 errs() &lt;&lt; *i &lt;&lt; "\n";
Chris Lattner55c04612005-03-06 06:00:13 +0000[diff] [blame]1727</pre>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1728</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1729
1730<p>However, this isn't really the best way to print out the contents of a
1731<tt>BasicBlock</tt>! Since the ostream operators are overloaded for virtually
1732anything you'll care about, you could have just invoked the print routine on the
Chris Lattner3fee6ed2009-09-08 05:15:50 +0000[diff] [blame]1733basic block itself: <tt>errs() &lt;&lt; *blk &lt;&lt; "\n";</tt>.</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1734
1735</div>
1736
1737<!-- _______________________________________________________________________ -->
Chris Lattner69bf8a92004-05-23 21:06:58 +0000[diff] [blame]1738<div class="doc_subsubsection">
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1739 <a name="iterate_institer">Iterating over the </a><a
1740 href="#Instruction"><tt>Instruction</tt></a>s in a <a
1741 href="#Function"><tt>Function</tt></a>
1742</div>
1743
1744<div class="doc_text">
1745
1746<p>If you're finding that you commonly iterate over a <tt>Function</tt>'s
1747<tt>BasicBlock</tt>s and then that <tt>BasicBlock</tt>'s <tt>Instruction</tt>s,
1748<tt>InstIterator</tt> should be used instead. You'll need to include <a
1749href="/doxygen/InstIterator_8h-source.html"><tt>llvm/Support/InstIterator.h</tt></a>,
1750and then instantiate <tt>InstIterator</tt>s explicitly in your code. Here's a
Chris Lattner69bf8a92004-05-23 21:06:58 +0000[diff] [blame]1751small 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]1752
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1753<div class="doc_code">
1754<pre>
1755#include "<a href="/doxygen/InstIterator_8h-source.html">llvm/Support/InstIterator.h</a>"
1756
Reid Spencer128a7a72007-02-03 21:06:43 +0000[diff] [blame]1757// <i>F is a pointer to a Function instance</i>
Chris Lattnerda021aa2008-06-04 18:20:42 +0000[diff] [blame]1758for (inst_iterator I = inst_begin(F), E = inst_end(F); I != E; ++I)
Chris Lattner3fee6ed2009-09-08 05:15:50 +0000[diff] [blame]1759 errs() &lt;&lt; *I &lt;&lt; "\n";
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1760</pre>
1761</div>
1762
1763<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]1764work list with its initial contents. For example, if you wanted to
1765initialize a work list to contain all instructions in a <tt>Function</tt>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1766F, all you would need to do is something like:</p>
1767
1768<div class="doc_code">
1769<pre>
1770std::set&lt;Instruction*&gt; worklist;
Chris Lattnerda021aa2008-06-04 18:20:42 +0000[diff] [blame]1771// or better yet, SmallPtrSet&lt;Instruction*, 64&gt; worklist;
1772
1773for (inst_iterator I = inst_begin(F), E = inst_end(F); I != E; ++I)
1774 worklist.insert(&amp;*I);
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1775</pre>
1776</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1777
1778<p>The STL set <tt>worklist</tt> would now contain all instructions in the
1779<tt>Function</tt> pointed to by F.</p>
1780
1781</div>
1782
1783<!-- _______________________________________________________________________ -->
1784<div class="doc_subsubsection">
1785 <a name="iterate_convert">Turning an iterator into a class pointer (and
1786 vice-versa)</a>
1787</div>
1788
1789<div class="doc_text">
1790
1791<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]1792instance when all you've got at hand is an iterator. Well, extracting
Chris Lattner69bf8a92004-05-23 21:06:58 +0000[diff] [blame]1793a reference or a pointer from an iterator is very straight-forward.
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]1794Assuming that <tt>i</tt> is a <tt>BasicBlock::iterator</tt> and <tt>j</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1795is a <tt>BasicBlock::const_iterator</tt>:</p>
1796
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1797<div class="doc_code">
1798<pre>
Bill Wendling82e2eea2006-10-11 18:00:22 +0000[diff] [blame]1799Instruction&amp; inst = *i; // <i>Grab reference to instruction reference</i>
1800Instruction* pinst = &amp;*i; // <i>Grab pointer to instruction reference</i>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1801const Instruction&amp; inst = *j;
1802</pre>
1803</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1804
1805<p>However, the iterators you'll be working with in the LLVM framework are
1806special: they will automatically convert to a ptr-to-instance type whenever they
1807need to. Instead of dereferencing the iterator and then taking the address of
1808the result, you can simply assign the iterator to the proper pointer type and
1809you get the dereference and address-of operation as a result of the assignment
1810(behind the scenes, this is a result of overloading casting mechanisms). Thus
1811the last line of the last example,</p>
1812
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1813<div class="doc_code">
1814<pre>
Chris Lattner2e438ca2008-01-03 16:56:04 +0000[diff] [blame]1815Instruction *pinst = &amp;*i;
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1816</pre>
1817</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1818
1819<p>is semantically equivalent to</p>
1820
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1821<div class="doc_code">
1822<pre>
Chris Lattner2e438ca2008-01-03 16:56:04 +0000[diff] [blame]1823Instruction *pinst = i;
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1824</pre>
1825</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1826
Chris Lattner69bf8a92004-05-23 21:06:58 +0000[diff] [blame]1827<p>It's also possible to turn a class pointer into the corresponding iterator,
1828and this is a constant time operation (very efficient). The following code
1829snippet illustrates use of the conversion constructors provided by LLVM
1830iterators. By using these, you can explicitly grab the iterator of something
1831without actually obtaining it via iteration over some structure:</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1832
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1833<div class="doc_code">
1834<pre>
1835void printNextInstruction(Instruction* inst) {
1836 BasicBlock::iterator it(inst);
Bill Wendling82e2eea2006-10-11 18:00:22 +0000[diff] [blame]1837 ++it; // <i>After this line, it refers to the instruction after *inst</i>
Chris Lattner3fee6ed2009-09-08 05:15:50 +0000[diff] [blame]1838 if (it != inst-&gt;getParent()-&gt;end()) errs() &lt;&lt; *it &lt;&lt; "\n";
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1839}
1840</pre>
1841</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1842
Dan Gohman525bf8e2010-03-26 19:39:05 +0000[diff] [blame]1843<p>Unfortunately, these implicit conversions come at a cost; they prevent
1844these iterators from conforming to standard iterator conventions, and thus
Dan Gohman0d91c112010-03-26 19:51:14 +0000[diff] [blame]1845from being usable with standard algorithms and containers. For example, they
1846prevent the following code, where <tt>B</tt> is a <tt>BasicBlock</tt>,
Dan Gohman525bf8e2010-03-26 19:39:05 +0000[diff] [blame]1847from compiling:</p>
1848
1849<div class="doc_code">
1850<pre>
1851 llvm::SmallVector&lt;llvm::Instruction *, 16&gt;(B-&gt;begin(), B-&gt;end());
1852</pre>
1853</div>
1854
1855<p>Because of this, these implicit conversions may be removed some day,
Dan Gohman0d91c112010-03-26 19:51:14 +0000[diff] [blame]1856and <tt>operator*</tt> changed to return a pointer instead of a reference.</p>
Dan Gohman525bf8e2010-03-26 19:39:05 +0000[diff] [blame]1857
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1858</div>
1859
1860<!--_______________________________________________________________________-->
1861<div class="doc_subsubsection">
1862 <a name="iterate_complex">Finding call sites: a slightly more complex
1863 example</a>
1864</div>
1865
1866<div class="doc_text">
1867
1868<p>Say that you're writing a FunctionPass and would like to count all the
1869locations in the entire module (that is, across every <tt>Function</tt>) where a
1870certain function (i.e., some <tt>Function</tt>*) is already in scope. As you'll
1871learn 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]1872much more straight-forward manner, but this example will allow us to explore how
Reid Spencer128a7a72007-02-03 21:06:43 +0000[diff] [blame]1873you'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]1874is what we want to do:</p>
1875
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1876<div class="doc_code">
1877<pre>
1878initialize callCounter to zero
1879for each Function f in the Module
1880 for each BasicBlock b in f
1881 for each Instruction i in b
1882 if (i is a CallInst and calls the given function)
1883 increment callCounter
1884</pre>
1885</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1886
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1887<p>And the actual code is (remember, because we're writing a
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1888<tt>FunctionPass</tt>, our <tt>FunctionPass</tt>-derived class simply has to
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1889override the <tt>runOnFunction</tt> method):</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1890
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1891<div class="doc_code">
1892<pre>
1893Function* targetFunc = ...;
1894
1895class OurFunctionPass : public FunctionPass {
1896 public:
1897 OurFunctionPass(): callCounter(0) { }
1898
1899 virtual runOnFunction(Function&amp; F) {
1900 for (Function::iterator b = F.begin(), be = F.end(); b != be; ++b) {
Eric Christopher203e71d2008-11-08 08:20:49 +0000[diff] [blame]1901 for (BasicBlock::iterator i = b-&gt;begin(), ie = b-&gt;end(); i != ie; ++i) {
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1902 if (<a href="#CallInst">CallInst</a>* callInst = <a href="#isa">dyn_cast</a>&lt;<a
1903 href="#CallInst">CallInst</a>&gt;(&amp;*i)) {
Bill Wendling82e2eea2006-10-11 18:00:22 +0000[diff] [blame]1904 // <i>We know we've encountered a call instruction, so we</i>
1905 // <i>need to determine if it's a call to the</i>
Chris Lattner2e438ca2008-01-03 16:56:04 +0000[diff] [blame]1906 // <i>function pointed to by m_func or not.</i>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1907 if (callInst-&gt;getCalledFunction() == targetFunc)
1908 ++callCounter;
1909 }
1910 }
1911 }
Bill Wendling82e2eea2006-10-11 18:00:22 +0000[diff] [blame]1912 }
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1913
1914 private:
Chris Lattner2e438ca2008-01-03 16:56:04 +0000[diff] [blame]1915 unsigned callCounter;
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1916};
1917</pre>
1918</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1919
1920</div>
1921
Brian Gaekef1972c62003-11-07 19:25:45 +0000[diff] [blame]1922<!--_______________________________________________________________________-->
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1923<div class="doc_subsubsection">
1924 <a name="calls_and_invokes">Treating calls and invokes the same way</a>
1925</div>
1926
1927<div class="doc_text">
1928
1929<p>You may have noticed that the previous example was a bit oversimplified in
1930that it did not deal with call sites generated by 'invoke' instructions. In
1931this, and in other situations, you may find that you want to treat
1932<tt>CallInst</tt>s and <tt>InvokeInst</tt>s the same way, even though their
1933most-specific common base class is <tt>Instruction</tt>, which includes lots of
1934less closely-related things. For these cases, LLVM provides a handy wrapper
1935class called <a
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]1936href="http://llvm.org/doxygen/classllvm_1_1CallSite.html"><tt>CallSite</tt></a>.
Chris Lattner69bf8a92004-05-23 21:06:58 +0000[diff] [blame]1937It is essentially a wrapper around an <tt>Instruction</tt> pointer, with some
1938methods that provide functionality common to <tt>CallInst</tt>s and
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1939<tt>InvokeInst</tt>s.</p>
1940
Chris Lattner69bf8a92004-05-23 21:06:58 +0000[diff] [blame]1941<p>This class has "value semantics": it should be passed by value, not by
1942reference and it should not be dynamically allocated or deallocated using
1943<tt>operator new</tt> or <tt>operator delete</tt>. It is efficiently copyable,
1944assignable and constructable, with costs equivalents to that of a bare pointer.
1945If you look at its definition, it has only a single pointer member.</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1946
1947</div>
1948
Chris Lattner1a3105b2002-09-09 05:49:39 +0000[diff] [blame]1949<!--_______________________________________________________________________-->
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1950<div class="doc_subsubsection">
1951 <a name="iterate_chains">Iterating over def-use &amp; use-def chains</a>
1952</div>
1953
1954<div class="doc_text">
1955
1956<p>Frequently, we might have an instance of the <a
Chris Lattner00815172007-01-04 22:01:45 +0000[diff] [blame]1957href="/doxygen/classllvm_1_1Value.html">Value Class</a> and we want to
Misha Brukman384047f2004-06-03 23:29:12 +0000[diff] [blame]1958determine which <tt>User</tt>s use the <tt>Value</tt>. The list of all
1959<tt>User</tt>s of a particular <tt>Value</tt> is called a <i>def-use</i> chain.
1960For example, let's say we have a <tt>Function*</tt> named <tt>F</tt> to a
1961particular function <tt>foo</tt>. Finding all of the instructions that
1962<i>use</i> <tt>foo</tt> is as simple as iterating over the <i>def-use</i> chain
1963of <tt>F</tt>:</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1964
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1965<div class="doc_code">
1966<pre>
Chris Lattner2e438ca2008-01-03 16:56:04 +0000[diff] [blame]1967Function *F = ...;
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1968
Bill Wendling82e2eea2006-10-11 18:00:22 +0000[diff] [blame]1969for (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]1970 if (Instruction *Inst = dyn_cast&lt;Instruction&gt;(*i)) {
Chris Lattner3fee6ed2009-09-08 05:15:50 +0000[diff] [blame]1971 errs() &lt;&lt; "F is used in instruction:\n";
1972 errs() &lt;&lt; *Inst &lt;&lt; "\n";
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1973 }
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1974</pre>
Gabor Greif394fdfb2010-03-26 19:35:48 +0000[diff] [blame]1975</div>
1976
Gabor Greifce94319532010-03-26 19:40:38 +0000[diff] [blame]1977<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]1978operation. Instead of performing <tt>*i</tt> above several times, consider
Gabor Greifce94319532010-03-26 19:40:38 +0000[diff] [blame]1979doing it only once in the loop body and reusing its result.</p>
Gabor Greif4de73682010-03-26 19:30:47 +0000[diff] [blame]1980
Gabor Greif6091ff32010-03-26 19:04:42 +0000[diff] [blame]1981<p>Alternatively, it's common to have an instance of the <a
Misha Brukman384047f2004-06-03 23:29:12 +0000[diff] [blame]1982href="/doxygen/classllvm_1_1User.html">User Class</a> and need to know what
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1983<tt>Value</tt>s are used by it. The list of all <tt>Value</tt>s used by a
1984<tt>User</tt> is known as a <i>use-def</i> chain. Instances of class
1985<tt>Instruction</tt> are common <tt>User</tt>s, so we might want to iterate over
1986all of the values that a particular instruction uses (that is, the operands of
1987the particular <tt>Instruction</tt>):</p>
1988
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1989<div class="doc_code">
1990<pre>
Chris Lattner2e438ca2008-01-03 16:56:04 +0000[diff] [blame]1991Instruction *pi = ...;
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1992
1993for (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]1994 Value *v = *i;
Bill Wendling82e2eea2006-10-11 18:00:22 +0000[diff] [blame]1995 // <i>...</i>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1996}
1997</pre>
1998</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1999
Gabor Greif4de73682010-03-26 19:30:47 +0000[diff] [blame]2000<p>Declaring objects as <tt>const</tt> is an important tool of enforcing
Gabor Greifce94319532010-03-26 19:40:38 +0000[diff] [blame]2001mutation free algorithms (such as analyses, etc.). For this purpose above
Gabor Greif4de73682010-03-26 19:30:47 +0000[diff] [blame]2002iterators come in constant flavors as <tt>Value::const_use_iterator</tt>
2003and <tt>Value::const_op_iterator</tt>. They automatically arise when
2004calling <tt>use/op_begin()</tt> on <tt>const Value*</tt>s or
2005<tt>const User*</tt>s respectively. Upon dereferencing, they return
Gabor Greifce94319532010-03-26 19:40:38 +0000[diff] [blame]2006<tt>const Use*</tt>s. Otherwise the above patterns remain unchanged.</p>
2007
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2008</div>
2009
Chris Lattner2e438ca2008-01-03 16:56:04 +0000[diff] [blame]2010<!--_______________________________________________________________________-->
2011<div class="doc_subsubsection">
2012 <a name="iterate_preds">Iterating over predecessors &amp;
2013successors of blocks</a>
2014</div>
2015
2016<div class="doc_text">
2017
2018<p>Iterating over the predecessors and successors of a block is quite easy
2019with the routines defined in <tt>"llvm/Support/CFG.h"</tt>. Just use code like
2020this to iterate over all predecessors of BB:</p>
2021
2022<div class="doc_code">
2023<pre>
2024#include "llvm/Support/CFG.h"
2025BasicBlock *BB = ...;
2026
2027for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI) {
2028 BasicBlock *Pred = *PI;
2029 // <i>...</i>
2030}
2031</pre>
2032</div>
2033
2034<p>Similarly, to iterate over successors use
2035succ_iterator/succ_begin/succ_end.</p>
2036
2037</div>
2038
2039
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2040<!-- ======================================================================= -->
2041<div class="doc_subsection">
2042 <a name="simplechanges">Making simple changes</a>
2043</div>
2044
2045<div class="doc_text">
2046
2047<p>There are some primitive transformation operations present in the LLVM
Joel Stanley753eb712002-09-11 22:32:24 +0000[diff] [blame]2048infrastructure that are worth knowing about. When performing
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]2049transformations, it's fairly common to manipulate the contents of basic
2050blocks. This section describes some of the common methods for doing so
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2051and gives example code.</p>
2052
2053</div>
2054
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]2055<!--_______________________________________________________________________-->
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2056<div class="doc_subsubsection">
2057 <a name="schanges_creating">Creating and inserting new
2058 <tt>Instruction</tt>s</a>
2059</div>
2060
2061<div class="doc_text">
2062
2063<p><i>Instantiating Instructions</i></p>
2064
Chris Lattner69bf8a92004-05-23 21:06:58 +0000[diff] [blame]2065<p>Creation of <tt>Instruction</tt>s is straight-forward: simply call the
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2066constructor for the kind of instruction to instantiate and provide the necessary
2067parameters. For example, an <tt>AllocaInst</tt> only <i>requires</i> a
2068(const-ptr-to) <tt>Type</tt>. Thus:</p>
2069
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2070<div class="doc_code">
2071<pre>
Nick Lewycky10d64b92007-12-03 01:52:52 +0000[diff] [blame]2072AllocaInst* ai = new AllocaInst(Type::Int32Ty);
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2073</pre>
2074</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2075
2076<p>will create an <tt>AllocaInst</tt> instance that represents the allocation of
Reid Spencer128a7a72007-02-03 21:06:43 +0000[diff] [blame]2077one integer in the current stack frame, at run time. Each <tt>Instruction</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2078subclass is likely to have varying default parameters which change the semantics
2079of the instruction, so refer to the <a
Misha Brukman31ca1de2004-06-03 23:35:54 +0000[diff] [blame]2080href="/doxygen/classllvm_1_1Instruction.html">doxygen documentation for the subclass of
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2081Instruction</a> that you're interested in instantiating.</p>
2082
2083<p><i>Naming values</i></p>
2084
2085<p>It is very useful to name the values of instructions when you're able to, as
2086this facilitates the debugging of your transformations. If you end up looking
2087at generated LLVM machine code, you definitely want to have logical names
2088associated with the results of instructions! By supplying a value for the
2089<tt>Name</tt> (default) parameter of the <tt>Instruction</tt> constructor, you
2090associate a logical name with the result of the instruction's execution at
Reid Spencer128a7a72007-02-03 21:06:43 +0000[diff] [blame]2091run time. For example, say that I'm writing a transformation that dynamically
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2092allocates space for an integer on the stack, and that integer is going to be
2093used as some kind of index by some other code. To accomplish this, I place an
2094<tt>AllocaInst</tt> at the first point in the first <tt>BasicBlock</tt> of some
2095<tt>Function</tt>, and I'm intending to use it within the same
2096<tt>Function</tt>. I might do:</p>
2097
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2098<div class="doc_code">
2099<pre>
Nick Lewycky10d64b92007-12-03 01:52:52 +0000[diff] [blame]2100AllocaInst* pa = new AllocaInst(Type::Int32Ty, 0, "indexLoc");
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2101</pre>
2102</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2103
2104<p>where <tt>indexLoc</tt> is now the logical name of the instruction's
Reid Spencer128a7a72007-02-03 21:06:43 +0000[diff] [blame]2105execution value, which is a pointer to an integer on the run time stack.</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2106
2107<p><i>Inserting instructions</i></p>
2108
2109<p>There are essentially two ways to insert an <tt>Instruction</tt>
2110into an existing sequence of instructions that form a <tt>BasicBlock</tt>:</p>
2111
Joel Stanley9dd1ad62002-09-18 03:17:23 +0000[diff] [blame]2112<ul>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2113 <li>Insertion into an explicit instruction list
2114
2115 <p>Given a <tt>BasicBlock* pb</tt>, an <tt>Instruction* pi</tt> within that
2116 <tt>BasicBlock</tt>, and a newly-created instruction we wish to insert
2117 before <tt>*pi</tt>, we do the following: </p>
2118
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2119<div class="doc_code">
2120<pre>
2121BasicBlock *pb = ...;
2122Instruction *pi = ...;
2123Instruction *newInst = new Instruction(...);
2124
Bill Wendling82e2eea2006-10-11 18:00:22 +0000[diff] [blame]2125pb-&gt;getInstList().insert(pi, newInst); // <i>Inserts newInst before pi in pb</i>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2126</pre>
2127</div>
Alkis Evlogimenos9a5dc4f2004-05-27 00:57:51 +0000[diff] [blame]2128
2129 <p>Appending to the end of a <tt>BasicBlock</tt> is so common that
2130 the <tt>Instruction</tt> class and <tt>Instruction</tt>-derived
2131 classes provide constructors which take a pointer to a
2132 <tt>BasicBlock</tt> to be appended to. For example code that
2133 looked like: </p>
2134
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2135<div class="doc_code">
2136<pre>
2137BasicBlock *pb = ...;
2138Instruction *newInst = new Instruction(...);
2139
Bill Wendling82e2eea2006-10-11 18:00:22 +0000[diff] [blame]2140pb-&gt;getInstList().push_back(newInst); // <i>Appends newInst to pb</i>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2141</pre>
2142</div>
Alkis Evlogimenos9a5dc4f2004-05-27 00:57:51 +0000[diff] [blame]2143
2144 <p>becomes: </p>
2145
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2146<div class="doc_code">
2147<pre>
2148BasicBlock *pb = ...;
2149Instruction *newInst = new Instruction(..., pb);
2150</pre>
2151</div>
Alkis Evlogimenos9a5dc4f2004-05-27 00:57:51 +0000[diff] [blame]2152
2153 <p>which is much cleaner, especially if you are creating
2154 long instruction streams.</p></li>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2155
2156 <li>Insertion into an implicit instruction list
2157
2158 <p><tt>Instruction</tt> instances that are already in <tt>BasicBlock</tt>s
2159 are implicitly associated with an existing instruction list: the instruction
2160 list of the enclosing basic block. Thus, we could have accomplished the same
2161 thing as the above code without being given a <tt>BasicBlock</tt> by doing:
2162 </p>
2163
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2164<div class="doc_code">
2165<pre>
2166Instruction *pi = ...;
2167Instruction *newInst = new Instruction(...);
2168
2169pi-&gt;getParent()-&gt;getInstList().insert(pi, newInst);
2170</pre>
2171</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2172
2173 <p>In fact, this sequence of steps occurs so frequently that the
2174 <tt>Instruction</tt> class and <tt>Instruction</tt>-derived classes provide
2175 constructors which take (as a default parameter) a pointer to an
2176 <tt>Instruction</tt> which the newly-created <tt>Instruction</tt> should
2177 precede. That is, <tt>Instruction</tt> constructors are capable of
2178 inserting the newly-created instance into the <tt>BasicBlock</tt> of a
2179 provided instruction, immediately before that instruction. Using an
2180 <tt>Instruction</tt> constructor with a <tt>insertBefore</tt> (default)
2181 parameter, the above code becomes:</p>
2182
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2183<div class="doc_code">
2184<pre>
2185Instruction* pi = ...;
2186Instruction* newInst = new Instruction(..., pi);
2187</pre>
2188</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2189
2190 <p>which is much cleaner, especially if you're creating a lot of
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2191 instructions and adding them to <tt>BasicBlock</tt>s.</p></li>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2192</ul>
2193
2194</div>
2195
2196<!--_______________________________________________________________________-->
2197<div class="doc_subsubsection">
2198 <a name="schanges_deleting">Deleting <tt>Instruction</tt>s</a>
2199</div>
2200
2201<div class="doc_text">
2202
2203<p>Deleting an instruction from an existing sequence of instructions that form a
Chris Lattner69bf8a92004-05-23 21:06:58 +0000[diff] [blame]2204<a href="#BasicBlock"><tt>BasicBlock</tt></a> is very straight-forward. First,
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2205you must have a pointer to the instruction that you wish to delete. Second, you
2206need to obtain the pointer to that instruction's basic block. You use the
2207pointer to the basic block to get its list of instructions and then use the
2208erase function to remove your instruction. For example:</p>
2209
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2210<div class="doc_code">
2211<pre>
2212<a href="#Instruction">Instruction</a> *I = .. ;
Chris Lattner9f8ec252008-02-15 22:57:17 +0000[diff] [blame]2213I-&gt;eraseFromParent();
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2214</pre>
2215</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2216
2217</div>
2218
2219<!--_______________________________________________________________________-->
2220<div class="doc_subsubsection">
2221 <a name="schanges_replacing">Replacing an <tt>Instruction</tt> with another
2222 <tt>Value</tt></a>
2223</div>
2224
2225<div class="doc_text">
2226
2227<p><i>Replacing individual instructions</i></p>
2228
2229<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]2230permits use of two very useful replace functions: <tt>ReplaceInstWithValue</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2231and <tt>ReplaceInstWithInst</tt>.</p>
2232
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]2233<h4><a name="schanges_deleting">Deleting <tt>Instruction</tt>s</a></h4>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2234
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]2235<ul>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2236 <li><tt>ReplaceInstWithValue</tt>
2237
Nick Lewyckyb6d1f392008-09-15 06:31:52 +0000[diff] [blame]2238 <p>This function replaces all uses of a given instruction with a value,
2239 and then removes the original instruction. The following example
2240 illustrates the replacement of the result of a particular
Chris Lattner58360822005-01-17 00:12:04 +0000[diff] [blame]2241 <tt>AllocaInst</tt> that allocates memory for a single integer with a null
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2242 pointer to an integer.</p>
2243
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2244<div class="doc_code">
2245<pre>
2246AllocaInst* instToReplace = ...;
2247BasicBlock::iterator ii(instToReplace);
2248
2249ReplaceInstWithValue(instToReplace-&gt;getParent()-&gt;getInstList(), ii,
Daniel Dunbar58c2ac02008-10-03 22:17:25 +0000[diff] [blame]2250 Constant::getNullValue(PointerType::getUnqual(Type::Int32Ty)));
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2251</pre></div></li>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2252
2253 <li><tt>ReplaceInstWithInst</tt>
2254
2255 <p>This function replaces a particular instruction with another
Nick Lewyckyb6d1f392008-09-15 06:31:52 +0000[diff] [blame]2256 instruction, inserting the new instruction into the basic block at the
2257 location where the old instruction was, and replacing any uses of the old
2258 instruction with the new instruction. The following example illustrates
2259 the replacement of one <tt>AllocaInst</tt> with another.</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2260
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2261<div class="doc_code">
2262<pre>
2263AllocaInst* instToReplace = ...;
2264BasicBlock::iterator ii(instToReplace);
2265
2266ReplaceInstWithInst(instToReplace-&gt;getParent()-&gt;getInstList(), ii,
Nick Lewycky10d64b92007-12-03 01:52:52 +0000[diff] [blame]2267 new AllocaInst(Type::Int32Ty, 0, "ptrToReplacedInt"));
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2268</pre></div></li>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]2269</ul>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2270
2271<p><i>Replacing multiple uses of <tt>User</tt>s and <tt>Value</tt>s</i></p>
2272
2273<p>You can use <tt>Value::replaceAllUsesWith</tt> and
2274<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]2275doxygen documentation for the <a href="/doxygen/classllvm_1_1Value.html">Value Class</a>
Misha Brukman384047f2004-06-03 23:29:12 +0000[diff] [blame]2276and <a href="/doxygen/classllvm_1_1User.html">User Class</a>, respectively, for more
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2277information.</p>
2278
2279<!-- Value::replaceAllUsesWith User::replaceUsesOfWith Point out:
2280include/llvm/Transforms/Utils/ especially BasicBlockUtils.h with:
2281ReplaceInstWithValue, ReplaceInstWithInst -->
2282
2283</div>
2284
Tanya Lattnerb011c662007-06-20 18:33:15 +0000[diff] [blame]2285<!--_______________________________________________________________________-->
2286<div class="doc_subsubsection">
2287 <a name="schanges_deletingGV">Deleting <tt>GlobalVariable</tt>s</a>
2288</div>
2289
2290<div class="doc_text">
2291
Tanya Lattnerc5dfcdb2007-06-20 20:46:37 +0000[diff] [blame]2292<p>Deleting a global variable from a module is just as easy as deleting an
2293Instruction. First, you must have a pointer to the global variable that you wish
2294 to delete. You use this pointer to erase it from its parent, the module.
Tanya Lattnerb011c662007-06-20 18:33:15 +0000[diff] [blame]2295 For example:</p>
2296
2297<div class="doc_code">
2298<pre>
2299<a href="#GlobalVariable">GlobalVariable</a> *GV = .. ;
Tanya Lattnerb011c662007-06-20 18:33:15 +0000[diff] [blame]2300
Tanya Lattnerc5dfcdb2007-06-20 20:46:37 +0000[diff] [blame]2301GV-&gt;eraseFromParent();
Tanya Lattnerb011c662007-06-20 18:33:15 +0000[diff] [blame]2302</pre>
2303</div>
2304
2305</div>
2306
Jeffrey Yasskin714257f2009-04-30 22:33:41 +0000[diff] [blame]2307<!-- ======================================================================= -->
2308<div class="doc_subsection">
2309 <a name="create_types">How to Create Types</a>
2310</div>
2311
2312<div class="doc_text">
2313
2314<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]2315statically, you can use <tt>TypeBuilder&lt;...&gt;::get()</tt>, defined
Jeffrey Yasskin714257f2009-04-30 22:33:41 +0000[diff] [blame]2316in <tt>llvm/Support/TypeBuilder.h</tt>, to retrieve them. <tt>TypeBuilder</tt>
2317has two forms depending on whether you're building types for cross-compilation
Misha Brukman1af789f2009-05-01 20:40:51 +0000[diff] [blame]2318or native library use. <tt>TypeBuilder&lt;T, true&gt;</tt> requires
Jeffrey Yasskin714257f2009-04-30 22:33:41 +0000[diff] [blame]2319that <tt>T</tt> be independent of the host environment, meaning that it's built
2320out of types from
2321the <a href="/doxygen/namespacellvm_1_1types.html"><tt>llvm::types</tt></a>
2322namespace and pointers, functions, arrays, etc. built of
Misha Brukman1af789f2009-05-01 20:40:51 +0000[diff] [blame]2323those. <tt>TypeBuilder&lt;T, false&gt;</tt> additionally allows native C types
Jeffrey Yasskin714257f2009-04-30 22:33:41 +0000[diff] [blame]2324whose size may depend on the host compiler. For example,</p>
2325
2326<div class="doc_code">
2327<pre>
Misha Brukman1af789f2009-05-01 20:40:51 +0000[diff] [blame]2328FunctionType *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]2329</pre>
2330</div>
2331
2332<p>is easier to read and write than the equivalent</p>
2333
2334<div class="doc_code">
2335<pre>
Owen Anderson5e8c50e2009-06-16 17:40:28 +0000[diff] [blame]2336std::vector&lt;const Type*&gt; params;
Jeffrey Yasskin714257f2009-04-30 22:33:41 +0000[diff] [blame]2337params.push_back(PointerType::getUnqual(Type::Int32Ty));
2338FunctionType *ft = FunctionType::get(Type::Int8Ty, params, false);
2339</pre>
2340</div>
2341
2342<p>See the <a href="/doxygen/TypeBuilder_8h-source.html#l00001">class
2343comment</a> for more details.</p>
2344
2345</div>
2346
Chris Lattner9355b472002-09-06 02:50:58 +0000[diff] [blame]2347<!-- *********************************************************************** -->
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2348<div class="doc_section">
Owen Anderson8bc1b3b2009-06-16 01:17:16 +0000[diff] [blame]2349 <a name="threading">Threads and LLVM</a>
2350</div>
2351<!-- *********************************************************************** -->
2352
2353<div class="doc_text">
2354<p>
2355This section describes the interaction of the LLVM APIs with multithreading,
2356both on the part of client applications, and in the JIT, in the hosted
2357application.
2358</p>
2359
2360<p>
2361Note that LLVM's support for multithreading is still relatively young. Up
2362through version 2.5, the execution of threaded hosted applications was
2363supported, but not threaded client access to the APIs. While this use case is
2364now supported, clients <em>must</em> adhere to the guidelines specified below to
2365ensure proper operation in multithreaded mode.
2366</p>
2367
2368<p>
2369Note that, on Unix-like platforms, LLVM requires the presence of GCC's atomic
2370intrinsics in order to support threaded operation. If you need a
2371multhreading-capable LLVM on a platform without a suitably modern system
2372compiler, consider compiling LLVM and LLVM-GCC in single-threaded mode, and
2373using the resultant compiler to build a copy of LLVM with multithreading
2374support.
2375</p>
2376</div>
2377
2378<!-- ======================================================================= -->
2379<div class="doc_subsection">
Owen Anderson1ad70e32009-06-16 18:04:19 +0000[diff] [blame]2380 <a name="startmultithreaded">Entering and Exiting Multithreaded Mode</a>
Owen Anderson8bc1b3b2009-06-16 01:17:16 +0000[diff] [blame]2381</div>
2382
2383<div class="doc_text">
2384
2385<p>
2386In order to properly protect its internal data structures while avoiding
Owen Anderson1ad70e32009-06-16 18:04:19 +0000[diff] [blame]2387excessive locking overhead in the single-threaded case, the LLVM must intialize
2388certain data structures necessary to provide guards around its internals. To do
2389so, the client program must invoke <tt>llvm_start_multithreaded()</tt> before
2390making any concurrent LLVM API calls. To subsequently tear down these
2391structures, use the <tt>llvm_stop_multithreaded()</tt> call. You can also use
2392the <tt>llvm_is_multithreaded()</tt> call to check the status of multithreaded
2393mode.
Owen Anderson8bc1b3b2009-06-16 01:17:16 +0000[diff] [blame]2394</p>
2395
2396<p>
Owen Anderson1ad70e32009-06-16 18:04:19 +0000[diff] [blame]2397Note that both of these calls must be made <em>in isolation</em>. That is to
2398say that no other LLVM API calls may be executing at any time during the
2399execution of <tt>llvm_start_multithreaded()</tt> or <tt>llvm_stop_multithreaded
2400</tt>. It's is the client's responsibility to enforce this isolation.
2401</p>
2402
2403<p>
2404The return value of <tt>llvm_start_multithreaded()</tt> indicates the success or
2405failure of the initialization. Failure typically indicates that your copy of
2406LLVM was built without multithreading support, typically because GCC atomic
2407intrinsics were not found in your system compiler. In this case, the LLVM API
2408will not be safe for concurrent calls. However, it <em>will</em> be safe for
Jeffrey Yasskin01eba392010-01-29 19:10:38 +0000[diff] [blame]2409hosting threaded applications in the JIT, though <a href="#jitthreading">care
2410must be taken</a> to ensure that side exits and the like do not accidentally
2411result in concurrent LLVM API calls.
Owen Anderson8bc1b3b2009-06-16 01:17:16 +0000[diff] [blame]2412</p>
2413</div>
2414
2415<!-- ======================================================================= -->
2416<div class="doc_subsection">
2417 <a name="shutdown">Ending Execution with <tt>llvm_shutdown()</tt></a>
2418</div>
2419
2420<div class="doc_text">
2421<p>
2422When you are done using the LLVM APIs, you should call <tt>llvm_shutdown()</tt>
Owen Anderson1ad70e32009-06-16 18:04:19 +0000[diff] [blame]2423to deallocate memory used for internal structures. This will also invoke
2424<tt>llvm_stop_multithreaded()</tt> if LLVM is operating in multithreaded mode.
2425As such, <tt>llvm_shutdown()</tt> requires the same isolation guarantees as
2426<tt>llvm_stop_multithreaded()</tt>.
Owen Anderson8bc1b3b2009-06-16 01:17:16 +0000[diff] [blame]2427</p>
2428
2429<p>
2430Note that, if you use scope-based shutdown, you can use the
2431<tt>llvm_shutdown_obj</tt> class, which calls <tt>llvm_shutdown()</tt> in its
2432destructor.
2433</div>
2434
2435<!-- ======================================================================= -->
2436<div class="doc_subsection">
2437 <a name="managedstatic">Lazy Initialization with <tt>ManagedStatic</tt></a>
2438</div>
2439
2440<div class="doc_text">
2441<p>
2442<tt>ManagedStatic</tt> is a utility class in LLVM used to implement static
2443initialization of static resources, such as the global type tables. Before the
2444invocation of <tt>llvm_shutdown()</tt>, it implements a simple lazy
2445initialization scheme. Once <tt>llvm_start_multithreaded()</tt> returns,
2446however, it uses double-checked locking to implement thread-safe lazy
2447initialization.
2448</p>
2449
2450<p>
2451Note that, because no other threads are allowed to issue LLVM API calls before
2452<tt>llvm_start_multithreaded()</tt> returns, it is possible to have
2453<tt>ManagedStatic</tt>s of <tt>llvm::sys::Mutex</tt>s.
2454</p>
Owen Anderson1ad70e32009-06-16 18:04:19 +0000[diff] [blame]2455
2456<p>
2457The <tt>llvm_acquire_global_lock()</tt> and <tt>llvm_release_global_lock</tt>
2458APIs provide access to the global lock used to implement the double-checked
2459locking for lazy initialization. These should only be used internally to LLVM,
2460and only if you know what you're doing!
2461</p>
Owen Anderson8bc1b3b2009-06-16 01:17:16 +0000[diff] [blame]2462</div>
2463
Owen Andersone0c951a2009-08-19 17:58:52 +0000[diff] [blame]2464<!-- ======================================================================= -->
2465<div class="doc_subsection">
2466 <a name="llvmcontext">Achieving Isolation with <tt>LLVMContext</tt></a>
2467</div>
2468
2469<div class="doc_text">
2470<p>
2471<tt>LLVMContext</tt> is an opaque class in the LLVM API which clients can use
2472to operate multiple, isolated instances of LLVM concurrently within the same
2473address space. For instance, in a hypothetical compile-server, the compilation
2474of an individual translation unit is conceptually independent from all the
2475others, and it would be desirable to be able to compile incoming translation
2476units concurrently on independent server threads. Fortunately,
2477<tt>LLVMContext</tt> exists to enable just this kind of scenario!
2478</p>
2479
2480<p>
2481Conceptually, <tt>LLVMContext</tt> provides isolation. Every LLVM entity
2482(<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]2483in LLVM's in-memory IR belongs to an <tt>LLVMContext</tt>. Entities in
Owen Andersone0c951a2009-08-19 17:58:52 +0000[diff] [blame]2484different contexts <em>cannot</em> interact with each other: <tt>Module</tt>s in
2485different contexts cannot be linked together, <tt>Function</tt>s cannot be added
2486to <tt>Module</tt>s in different contexts, etc. What this means is that is is
2487safe to compile on multiple threads simultaneously, as long as no two threads
2488operate on entities within the same context.
2489</p>
2490
2491<p>
2492In practice, very few places in the API require the explicit specification of a
2493<tt>LLVMContext</tt>, other than the <tt>Type</tt> creation/lookup APIs.
2494Because every <tt>Type</tt> carries a reference to its owning context, most
2495other entities can determine what context they belong to by looking at their
2496own <tt>Type</tt>. If you are adding new entities to LLVM IR, please try to
2497maintain this interface design.
2498</p>
2499
2500<p>
2501For clients that do <em>not</em> require the benefits of isolation, LLVM
2502provides a convenience API <tt>getGlobalContext()</tt>. This returns a global,
2503lazily initialized <tt>LLVMContext</tt> that may be used in situations where
2504isolation is not a concern.
2505</p>
2506</div>
2507
Jeffrey Yasskin01eba392010-01-29 19:10:38 +0000[diff] [blame]2508<!-- ======================================================================= -->
2509<div class="doc_subsection">
2510 <a name="jitthreading">Threads and the JIT</a>
2511</div>
2512
2513<div class="doc_text">
2514<p>
2515LLVM's "eager" JIT compiler is safe to use in threaded programs. Multiple
2516threads can call <tt>ExecutionEngine::getPointerToFunction()</tt> or
2517<tt>ExecutionEngine::runFunction()</tt> concurrently, and multiple threads can
2518run code output by the JIT concurrently. The user must still ensure that only
2519one thread accesses IR in a given <tt>LLVMContext</tt> while another thread
2520might be modifying it. One way to do that is to always hold the JIT lock while
2521accessing IR outside the JIT (the JIT <em>modifies</em> the IR by adding
2522<tt>CallbackVH</tt>s). Another way is to only
2523call <tt>getPointerToFunction()</tt> from the <tt>LLVMContext</tt>'s thread.
2524</p>
2525
2526<p>When the JIT is configured to compile lazily (using
2527<tt>ExecutionEngine::DisableLazyCompilation(false)</tt>), there is currently a
2528<a href="http://llvm.org/bugs/show_bug.cgi?id=5184">race condition</a> in
2529updating call sites after a function is lazily-jitted. It's still possible to
2530use the lazy JIT in a threaded program if you ensure that only one thread at a
2531time can call any particular lazy stub and that the JIT lock guards any IR
2532access, but we suggest using only the eager JIT in threaded programs.
2533</p>
2534</div>
2535
Owen Anderson8bc1b3b2009-06-16 01:17:16 +0000[diff] [blame]2536<!-- *********************************************************************** -->
2537<div class="doc_section">
Chris Lattnerd9d6e102005-04-23 16:10:52 +0000[diff] [blame]2538 <a name="advanced">Advanced Topics</a>
2539</div>
2540<!-- *********************************************************************** -->
2541
2542<div class="doc_text">
Chris Lattnerf1b200b2005-04-23 17:27:36 +0000[diff] [blame]2543<p>
2544This section describes some of the advanced or obscure API's that most clients
2545do not need to be aware of. These API's tend manage the inner workings of the
2546LLVM system, and only need to be accessed in unusual circumstances.
2547</p>
2548</div>
Chris Lattnerd9d6e102005-04-23 16:10:52 +0000[diff] [blame]2549
Chris Lattnerf1b200b2005-04-23 17:27:36 +0000[diff] [blame]2550<!-- ======================================================================= -->
2551<div class="doc_subsection">
2552 <a name="TypeResolve">LLVM Type Resolution</a>
2553</div>
Chris Lattnerd9d6e102005-04-23 16:10:52 +0000[diff] [blame]2554
Chris Lattnerf1b200b2005-04-23 17:27:36 +0000[diff] [blame]2555<div class="doc_text">
2556
2557<p>
2558The LLVM type system has a very simple goal: allow clients to compare types for
2559structural equality with a simple pointer comparison (aka a shallow compare).
2560This goal makes clients much simpler and faster, and is used throughout the LLVM
2561system.
2562</p>
2563
2564<p>
2565Unfortunately achieving this goal is not a simple matter. In particular,
2566recursive types and late resolution of opaque types makes the situation very
2567difficult to handle. Fortunately, for the most part, our implementation makes
2568most clients able to be completely unaware of the nasty internal details. The
2569primary case where clients are exposed to the inner workings of it are when
Gabor Greif04367bf2007-07-06 22:07:22 +0000[diff] [blame]2570building a recursive type. In addition to this case, the LLVM bitcode reader,
Chris Lattnerf1b200b2005-04-23 17:27:36 +0000[diff] [blame]2571assembly parser, and linker also have to be aware of the inner workings of this
2572system.
2573</p>
2574
Chris Lattner0f876db2005-04-25 15:47:57 +0000[diff] [blame]2575<p>
2576For our purposes below, we need three concepts. First, an "Opaque Type" is
2577exactly as defined in the <a href="LangRef.html#t_opaque">language
2578reference</a>. Second an "Abstract Type" is any type which includes an
Reid Spencer06565dc2007-01-12 17:11:23 +0000[diff] [blame]2579opaque type as part of its type graph (for example "<tt>{ opaque, i32 }</tt>").
2580Third, 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]2581float }</tt>").
2582</p>
2583
Chris Lattnerf1b200b2005-04-23 17:27:36 +0000[diff] [blame]2584</div>
2585
2586<!-- ______________________________________________________________________ -->
2587<div class="doc_subsubsection">
2588 <a name="BuildRecType">Basic Recursive Type Construction</a>
2589</div>
2590
2591<div class="doc_text">
2592
2593<p>
2594Because the most common question is "how do I build a recursive type with LLVM",
2595we answer it now and explain it as we go. Here we include enough to cause this
2596to be emitted to an output .ll file:
2597</p>
2598
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2599<div class="doc_code">
Chris Lattnerf1b200b2005-04-23 17:27:36 +0000[diff] [blame]2600<pre>
Reid Spencer06565dc2007-01-12 17:11:23 +0000[diff] [blame]2601%mylist = type { %mylist*, i32 }
Chris Lattnerf1b200b2005-04-23 17:27:36 +0000[diff] [blame]2602</pre>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2603</div>
Chris Lattnerf1b200b2005-04-23 17:27:36 +0000[diff] [blame]2604
2605<p>
2606To build this, use the following LLVM APIs:
2607</p>
2608
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2609<div class="doc_code">
Chris Lattnerf1b200b2005-04-23 17:27:36 +0000[diff] [blame]2610<pre>
Bill Wendling82e2eea2006-10-11 18:00:22 +0000[diff] [blame]2611// <i>Create the initial outer struct</i>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2612<a href="#PATypeHolder">PATypeHolder</a> StructTy = OpaqueType::get();
2613std::vector&lt;const Type*&gt; Elts;
Daniel Dunbar58c2ac02008-10-03 22:17:25 +0000[diff] [blame]2614Elts.push_back(PointerType::getUnqual(StructTy));
Nick Lewycky10d64b92007-12-03 01:52:52 +0000[diff] [blame]2615Elts.push_back(Type::Int32Ty);
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2616StructType *NewSTy = StructType::get(Elts);
Chris Lattnerf1b200b2005-04-23 17:27:36 +0000[diff] [blame]2617
Reid Spencer06565dc2007-01-12 17:11:23 +0000[diff] [blame]2618// <i>At this point, NewSTy = "{ opaque*, i32 }". Tell VMCore that</i>
Bill Wendling82e2eea2006-10-11 18:00:22 +0000[diff] [blame]2619// <i>the struct and the opaque type are actually the same.</i>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2620cast&lt;OpaqueType&gt;(StructTy.get())-&gt;<a href="#refineAbstractTypeTo">refineAbstractTypeTo</a>(NewSTy);
Chris Lattnerf1b200b2005-04-23 17:27:36 +0000[diff] [blame]2621
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2622// <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]2623// <i>kept up-to-date</i>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2624NewSTy = cast&lt;StructType&gt;(StructTy.get());
Chris Lattnerf1b200b2005-04-23 17:27:36 +0000[diff] [blame]2625
Bill Wendling82e2eea2006-10-11 18:00:22 +0000[diff] [blame]2626// <i>Add a name for the type to the module symbol table (optional)</i>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2627MyModule-&gt;addTypeName("mylist", NewSTy);
Chris Lattnerf1b200b2005-04-23 17:27:36 +0000[diff] [blame]2628</pre>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2629</div>
Chris Lattnerf1b200b2005-04-23 17:27:36 +0000[diff] [blame]2630
2631<p>
2632This code shows the basic approach used to build recursive types: build a
2633non-recursive type using 'opaque', then use type unification to close the cycle.
2634The type unification step is performed by the <tt><a
Chris Lattneraff26d12007-02-03 03:06:52 +0000[diff] [blame]2635href="#refineAbstractTypeTo">refineAbstractTypeTo</a></tt> method, which is
Chris Lattnerf1b200b2005-04-23 17:27:36 +0000[diff] [blame]2636described next. After that, we describe the <a
2637href="#PATypeHolder">PATypeHolder class</a>.
2638</p>
2639
2640</div>
2641
2642<!-- ______________________________________________________________________ -->
2643<div class="doc_subsubsection">
2644 <a name="refineAbstractTypeTo">The <tt>refineAbstractTypeTo</tt> method</a>
2645</div>
2646
2647<div class="doc_text">
2648<p>
2649The <tt>refineAbstractTypeTo</tt> method starts the type unification process.
2650While this method is actually a member of the DerivedType class, it is most
2651often used on OpaqueType instances. Type unification is actually a recursive
2652process. After unification, types can become structurally isomorphic to
2653existing types, and all duplicates are deleted (to preserve pointer equality).
2654</p>
2655
2656<p>
2657In the example above, the OpaqueType object is definitely deleted.
Reid Spencer06565dc2007-01-12 17:11:23 +0000[diff] [blame]2658Additionally, if there is an "{ \2*, i32}" type already created in the system,
Chris Lattnerf1b200b2005-04-23 17:27:36 +0000[diff] [blame]2659the pointer and struct type created are <b>also</b> deleted. Obviously whenever
2660a type is deleted, any "Type*" pointers in the program are invalidated. As
2661such, it is safest to avoid having <i>any</i> "Type*" pointers to abstract types
2662live across a call to <tt>refineAbstractTypeTo</tt> (note that non-abstract
2663types can never move or be deleted). To deal with this, the <a
2664href="#PATypeHolder">PATypeHolder</a> class is used to maintain a stable
2665reference to a possibly refined type, and the <a
2666href="#AbstractTypeUser">AbstractTypeUser</a> class is used to update more
2667complex datastructures.
2668</p>
2669
2670</div>
2671
2672<!-- ______________________________________________________________________ -->
2673<div class="doc_subsubsection">
2674 <a name="PATypeHolder">The PATypeHolder Class</a>
2675</div>
2676
2677<div class="doc_text">
2678<p>
2679PATypeHolder is a form of a "smart pointer" for Type objects. When VMCore
2680happily goes about nuking types that become isomorphic to existing types, it
2681automatically updates all PATypeHolder objects to point to the new type. In the
2682example above, this allows the code to maintain a pointer to the resultant
2683resolved recursive type, even though the Type*'s are potentially invalidated.
2684</p>
2685
2686<p>
2687PATypeHolder is an extremely light-weight object that uses a lazy union-find
2688implementation to update pointers. For example the pointer from a Value to its
2689Type is maintained by PATypeHolder objects.
2690</p>
2691
2692</div>
2693
2694<!-- ______________________________________________________________________ -->
2695<div class="doc_subsubsection">
2696 <a name="AbstractTypeUser">The AbstractTypeUser Class</a>
2697</div>
2698
2699<div class="doc_text">
2700
2701<p>
2702Some data structures need more to perform more complex updates when types get
Chris Lattner263a98e2007-02-16 04:37:31 +0000[diff] [blame]2703resolved. To support this, a class can derive from the AbstractTypeUser class.
2704This class
Chris Lattnerf1b200b2005-04-23 17:27:36 +0000[diff] [blame]2705allows it to get callbacks when certain types are resolved. To register to get
2706callbacks for a particular type, the DerivedType::{add/remove}AbstractTypeUser
Chris Lattner0f876db2005-04-25 15:47:57 +0000[diff] [blame]2707methods can be called on a type. Note that these methods only work for <i>
Reid Spencer06565dc2007-01-12 17:11:23 +0000[diff] [blame]2708 abstract</i> types. Concrete types (those that do not include any opaque
2709objects) can never be refined.
Chris Lattnerf1b200b2005-04-23 17:27:36 +0000[diff] [blame]2710</p>
Chris Lattnerd9d6e102005-04-23 16:10:52 +0000[diff] [blame]2711</div>
2712
2713
2714<!-- ======================================================================= -->
2715<div class="doc_subsection">
Chris Lattner263a98e2007-02-16 04:37:31 +0000[diff] [blame]2716 <a name="SymbolTable">The <tt>ValueSymbolTable</tt> and
2717 <tt>TypeSymbolTable</tt> classes</a>
Chris Lattnerd9d6e102005-04-23 16:10:52 +0000[diff] [blame]2718</div>
Chris Lattnerf1b200b2005-04-23 17:27:36 +0000[diff] [blame]2719
Chris Lattnerd9d6e102005-04-23 16:10:52 +0000[diff] [blame]2720<div class="doc_text">
Chris Lattner263a98e2007-02-16 04:37:31 +0000[diff] [blame]2721<p>The <tt><a href="http://llvm.org/doxygen/classllvm_1_1ValueSymbolTable.html">
2722ValueSymbolTable</a></tt> class provides a symbol table that the <a
Chris Lattnerd9d6e102005-04-23 16:10:52 +0000[diff] [blame]2723href="#Function"><tt>Function</tt></a> and <a href="#Module">
Chris Lattner263a98e2007-02-16 04:37:31 +0000[diff] [blame]2724<tt>Module</tt></a> classes use for naming value definitions. The symbol table
2725can provide a name for any <a href="#Value"><tt>Value</tt></a>.
2726The <tt><a href="http://llvm.org/doxygen/classllvm_1_1TypeSymbolTable.html">
2727TypeSymbolTable</a></tt> class is used by the <tt>Module</tt> class to store
2728names for types.</p>
Chris Lattnerd9d6e102005-04-23 16:10:52 +0000[diff] [blame]2729
Reid Spencera6362242007-01-07 00:41:39 +0000[diff] [blame]2730<p>Note that the <tt>SymbolTable</tt> class should not be directly accessed
2731by most clients. It should only be used when iteration over the symbol table
2732names themselves are required, which is very special purpose. Note that not
2733all LLVM
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2734<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]2735an empty name) do not exist in the symbol table.
2736</p>
2737
Chris Lattner263a98e2007-02-16 04:37:31 +0000[diff] [blame]2738<p>These symbol tables support iteration over the values/types in the symbol
2739table with <tt>begin/end/iterator</tt> and supports querying to see if a
2740specific name is in the symbol table (with <tt>lookup</tt>). The
2741<tt>ValueSymbolTable</tt> class exposes no public mutator methods, instead,
2742simply call <tt>setName</tt> on a value, which will autoinsert it into the
2743appropriate symbol table. For types, use the Module::addTypeName method to
2744insert entries into the symbol table.</p>
Chris Lattnerd9d6e102005-04-23 16:10:52 +0000[diff] [blame]2745
Chris Lattnerd9d6e102005-04-23 16:10:52 +0000[diff] [blame]2746</div>
2747
2748
2749
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2750<!-- ======================================================================= -->
2751<div class="doc_subsection">
2752 <a name="UserLayout">The <tt>User</tt> and owned <tt>Use</tt> classes' memory layout</a>
2753</div>
2754
2755<div class="doc_text">
2756<p>The <tt><a href="http://llvm.org/doxygen/classllvm_1_1User.html">
Gabor Greiffd095b62009-01-05 16:05:32 +0000[diff] [blame]2757User</a></tt> class provides a basis for expressing the ownership of <tt>User</tt>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2758towards other <tt><a href="http://llvm.org/doxygen/classllvm_1_1Value.html">
2759Value</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]2760Use</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]2761addition and removal.</p>
2762
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2763<!-- ______________________________________________________________________ -->
2764<div class="doc_subsubsection">
Gabor Greiffd095b62009-01-05 16:05:32 +0000[diff] [blame]2765 <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]2766</div>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2767
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2768<div class="doc_text">
2769<p>
2770A subclass of <tt>User</tt> can choose between incorporating its <tt>Use</tt> objects
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2771or refer to them out-of-line by means of a pointer. A mixed variant
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2772(some <tt>Use</tt>s inline others hung off) is impractical and breaks the invariant
2773that the <tt>Use</tt> objects belonging to the same <tt>User</tt> form a contiguous array.
2774</p>
2775</div>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2776
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2777<p>
2778We have 2 different layouts in the <tt>User</tt> (sub)classes:
2779<ul>
2780<li><p>Layout a)
2781The <tt>Use</tt> object(s) are inside (resp. at fixed offset) of the <tt>User</tt>
2782object and there are a fixed number of them.</p>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2783
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2784<li><p>Layout b)
2785The <tt>Use</tt> object(s) are referenced by a pointer to an
2786array from the <tt>User</tt> object and there may be a variable
2787number of them.</p>
2788</ul>
2789<p>
Gabor Greifd41720a2008-06-25 00:10:22 +0000[diff] [blame]2790As of v2.4 each layout still possesses a direct pointer to the
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2791start of the array of <tt>Use</tt>s. Though not mandatory for layout a),
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2792we stick to this redundancy for the sake of simplicity.
Gabor Greifd41720a2008-06-25 00:10:22 +0000[diff] [blame]2793The <tt>User</tt> object also stores the number of <tt>Use</tt> objects it
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2794has. (Theoretically this information can also be calculated
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2795given the scheme presented below.)</p>
2796<p>
2797Special forms of allocation operators (<tt>operator new</tt>)
Gabor Greifd41720a2008-06-25 00:10:22 +0000[diff] [blame]2798enforce the following memory layouts:</p>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2799
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2800<ul>
Gabor Greifd41720a2008-06-25 00:10:22 +0000[diff] [blame]2801<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]2802
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2803<pre>
2804...---.---.---.---.-------...
2805 | P | P | P | P | User
2806'''---'---'---'---'-------'''
2807</pre>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2808
Gabor Greifd41720a2008-06-25 00:10:22 +0000[diff] [blame]2809<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]2810<pre>
2811.-------...
2812| User
2813'-------'''
2814 |
2815 v
2816 .---.---.---.---...
2817 | P | P | P | P |
2818 '---'---'---'---'''
2819</pre>
2820</ul>
2821<i>(In the above figures '<tt>P</tt>' stands for the <tt>Use**</tt> that
2822 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]2823
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2824<!-- ______________________________________________________________________ -->
2825<div class="doc_subsubsection">
Gabor Greiffd095b62009-01-05 16:05:32 +0000[diff] [blame]2826 <a name="Waymarking">The waymarking algorithm</a>
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2827</div>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2828
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2829<div class="doc_text">
2830<p>
Gabor Greifd41720a2008-06-25 00:10:22 +0000[diff] [blame]2831Since the <tt>Use</tt> objects are deprived of the direct (back)pointer to
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2832their <tt>User</tt> objects, there must be a fast and exact method to
2833recover it. This is accomplished by the following scheme:</p>
2834</div>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2835
Gabor Greifd41720a2008-06-25 00:10:22 +0000[diff] [blame]2836A 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]2837start of the <tt>User</tt> object:
2838<ul>
2839<li><tt>00</tt> &mdash;&gt; binary digit 0</li>
2840<li><tt>01</tt> &mdash;&gt; binary digit 1</li>
2841<li><tt>10</tt> &mdash;&gt; stop and calculate (<tt>s</tt>)</li>
2842<li><tt>11</tt> &mdash;&gt; full stop (<tt>S</tt>)</li>
2843</ul>
2844<p>
2845Given a <tt>Use*</tt>, all we have to do is to walk till we get
2846a stop and we either have a <tt>User</tt> immediately behind or
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2847we have to walk to the next stop picking up digits
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2848and calculating the offset:</p>
2849<pre>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2850.---.---.---.---.---.---.---.---.---.---.---.---.---.---.---.---.----------------
2851| 1 | s | 1 | 0 | 1 | 0 | s | 1 | 1 | 0 | s | 1 | 1 | s | 1 | S | User (or User*)
2852'---'---'---'---'---'---'---'---'---'---'---'---'---'---'---'---'----------------
2853 |+15 |+10 |+6 |+3 |+1
2854 | | | | |__>
2855 | | | |__________>
2856 | | |______________________>
2857 | |______________________________________>
2858 |__________________________________________________________>
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2859</pre>
2860<p>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2861Only the significant number of bits need to be stored between the
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2862stops, so that the <i>worst case is 20 memory accesses</i> when there are
28631000 <tt>Use</tt> objects associated with a <tt>User</tt>.</p>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2864
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2865<!-- ______________________________________________________________________ -->
2866<div class="doc_subsubsection">
Gabor Greiffd095b62009-01-05 16:05:32 +0000[diff] [blame]2867 <a name="ReferenceImpl">Reference implementation</a>
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2868</div>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2869
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2870<div class="doc_text">
2871<p>
2872The following literate Haskell fragment demonstrates the concept:</p>
2873</div>
2874
2875<div class="doc_code">
2876<pre>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2877> import Test.QuickCheck
2878>
2879> digits :: Int -> [Char] -> [Char]
2880> digits 0 acc = '0' : acc
2881> digits 1 acc = '1' : acc
2882> digits n acc = digits (n `div` 2) $ digits (n `mod` 2) acc
2883>
2884> dist :: Int -> [Char] -> [Char]
2885> dist 0 [] = ['S']
2886> dist 0 acc = acc
2887> dist 1 acc = let r = dist 0 acc in 's' : digits (length r) r
2888> dist n acc = dist (n - 1) $ dist 1 acc
2889>
2890> takeLast n ss = reverse $ take n $ reverse ss
2891>
2892> test = takeLast 40 $ dist 20 []
2893>
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2894</pre>
2895</div>
2896<p>
2897Printing &lt;test&gt; gives: <tt>"1s100000s11010s10100s1111s1010s110s11s1S"</tt></p>
2898<p>
2899The reverse algorithm computes the length of the string just by examining
2900a certain prefix:</p>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2901
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2902<div class="doc_code">
2903<pre>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2904> pref :: [Char] -> Int
2905> pref "S" = 1
2906> pref ('s':'1':rest) = decode 2 1 rest
2907> pref (_:rest) = 1 + pref rest
2908>
2909> decode walk acc ('0':rest) = decode (walk + 1) (acc * 2) rest
2910> decode walk acc ('1':rest) = decode (walk + 1) (acc * 2 + 1) rest
2911> decode walk acc _ = walk + acc
2912>
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2913</pre>
2914</div>
2915<p>
2916Now, as expected, printing &lt;pref test&gt; gives <tt>40</tt>.</p>
2917<p>
2918We can <i>quickCheck</i> this with following property:</p>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2919
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2920<div class="doc_code">
2921<pre>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2922> testcase = dist 2000 []
2923> testcaseLength = length testcase
2924>
2925> identityProp n = n > 0 && n <= testcaseLength ==> length arr == pref arr
2926> where arr = takeLast n testcase
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2927>
2928</pre>
2929</div>
2930<p>
2931As expected &lt;quickCheck identityProp&gt; gives:</p>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2932
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2933<pre>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2934*Main> quickCheck identityProp
2935OK, passed 100 tests.
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2936</pre>
2937<p>
2938Let's be a bit more exhaustive:</p>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2939
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2940<div class="doc_code">
2941<pre>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2942>
2943> deepCheck p = check (defaultConfig { configMaxTest = 500 }) p
2944>
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2945</pre>
2946</div>
2947<p>
2948And here is the result of &lt;deepCheck identityProp&gt;:</p>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2949
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2950<pre>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2951*Main> deepCheck identityProp
2952OK, passed 500 tests.
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2953</pre>
2954
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2955<!-- ______________________________________________________________________ -->
2956<div class="doc_subsubsection">
Gabor Greiffd095b62009-01-05 16:05:32 +0000[diff] [blame]2957 <a name="Tagging">Tagging considerations</a>
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2958</div>
2959
2960<p>
2961To maintain the invariant that the 2 LSBits of each <tt>Use**</tt> in <tt>Use</tt>
2962never change after being set up, setters of <tt>Use::Prev</tt> must re-tag the
2963new <tt>Use**</tt> on every modification. Accordingly getters must strip the
2964tag bits.</p>
2965<p>
Gabor Greifd41720a2008-06-25 00:10:22 +0000[diff] [blame]2966For layout b) instead of the <tt>User</tt> we find a pointer (<tt>User*</tt> with LSBit set).
2967Following this pointer brings us to the <tt>User</tt>. A portable trick ensures
2968that the first bytes of <tt>User</tt> (if interpreted as a pointer) never has
Gabor Greiffd095b62009-01-05 16:05:32 +0000[diff] [blame]2969the LSBit set. (Portability is relying on the fact that all known compilers place the
2970<tt>vptr</tt> in the first word of the instances.)</p>
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2971
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2972</div>
2973
2974 <!-- *********************************************************************** -->
Chris Lattnerd9d6e102005-04-23 16:10:52 +0000[diff] [blame]2975<div class="doc_section">
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2976 <a name="coreclasses">The Core LLVM Class Hierarchy Reference </a>
2977</div>
2978<!-- *********************************************************************** -->
2979
2980<div class="doc_text">
Reid Spencer303c4b42007-01-12 17:26:25 +0000[diff] [blame]2981<p><tt>#include "<a href="/doxygen/Type_8h-source.html">llvm/Type.h</a>"</tt>
2982<br>doxygen info: <a href="/doxygen/classllvm_1_1Type.html">Type Class</a></p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2983
2984<p>The Core LLVM classes are the primary means of representing the program
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]2985being inspected or transformed. The core LLVM classes are defined in
2986header files in the <tt>include/llvm/</tt> directory, and implemented in
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2987the <tt>lib/VMCore</tt> directory.</p>
2988
2989</div>
2990
2991<!-- ======================================================================= -->
2992<div class="doc_subsection">
Reid Spencer303c4b42007-01-12 17:26:25 +0000[diff] [blame]2993 <a name="Type">The <tt>Type</tt> class and Derived Types</a>
2994</div>
2995
2996<div class="doc_text">
2997
2998 <p><tt>Type</tt> is a superclass of all type classes. Every <tt>Value</tt> has
2999 a <tt>Type</tt>. <tt>Type</tt> cannot be instantiated directly but only
3000 through its subclasses. Certain primitive types (<tt>VoidType</tt>,
3001 <tt>LabelType</tt>, <tt>FloatType</tt> and <tt>DoubleType</tt>) have hidden
3002 subclasses. They are hidden because they offer no useful functionality beyond
3003 what the <tt>Type</tt> class offers except to distinguish themselves from
3004 other subclasses of <tt>Type</tt>.</p>
3005 <p>All other types are subclasses of <tt>DerivedType</tt>. Types can be
3006 named, but this is not a requirement. There exists exactly
3007 one instance of a given shape at any one time. This allows type equality to
3008 be performed with address equality of the Type Instance. That is, given two
3009 <tt>Type*</tt> values, the types are identical if the pointers are identical.
3010 </p>
3011</div>
3012
3013<!-- _______________________________________________________________________ -->
3014<div class="doc_subsubsection">
Gabor Greiffd095b62009-01-05 16:05:32 +0000[diff] [blame]3015 <a name="m_Type">Important Public Methods</a>
Reid Spencer303c4b42007-01-12 17:26:25 +0000[diff] [blame]3016</div>
3017
3018<div class="doc_text">
3019
3020<ul>
Duncan Sandsb0bc6c32010-02-15 16:12:20 +0000[diff] [blame]3021 <li><tt>bool isIntegerTy() const</tt>: Returns true for any integer type.</li>
Reid Spencer303c4b42007-01-12 17:26:25 +0000[diff] [blame]3022
Duncan Sandsb0bc6c32010-02-15 16:12:20 +0000[diff] [blame]3023 <li><tt>bool isFloatingPointTy()</tt>: Return true if this is one of the five
Reid Spencer303c4b42007-01-12 17:26:25 +0000[diff] [blame]3024 floating point types.</li>
3025
3026 <li><tt>bool isAbstract()</tt>: Return true if the type is abstract (contains
3027 an OpaqueType anywhere in its definition).</li>
3028
3029 <li><tt>bool isSized()</tt>: Return true if the type has known size. Things
3030 that don't have a size are abstract types, labels and void.</li>
3031
3032</ul>
3033</div>
3034
3035<!-- _______________________________________________________________________ -->
3036<div class="doc_subsubsection">
Gabor Greiffd095b62009-01-05 16:05:32 +0000[diff] [blame]3037 <a name="derivedtypes">Important Derived Types</a>
Reid Spencer303c4b42007-01-12 17:26:25 +0000[diff] [blame]3038</div>
3039<div class="doc_text">
3040<dl>
3041 <dt><tt>IntegerType</tt></dt>
3042 <dd>Subclass of DerivedType that represents integer types of any bit width.
3043 Any bit width between <tt>IntegerType::MIN_INT_BITS</tt> (1) and
3044 <tt>IntegerType::MAX_INT_BITS</tt> (~8 million) can be represented.
3045 <ul>
3046 <li><tt>static const IntegerType* get(unsigned NumBits)</tt>: get an integer
3047 type of a specific bit width.</li>
3048 <li><tt>unsigned getBitWidth() const</tt>: Get the bit width of an integer
3049 type.</li>
3050 </ul>
3051 </dd>
3052 <dt><tt>SequentialType</tt></dt>
3053 <dd>This is subclassed by ArrayType and PointerType
3054 <ul>
3055 <li><tt>const Type * getElementType() const</tt>: Returns the type of each
3056 of the elements in the sequential type. </li>
3057 </ul>
3058 </dd>
3059 <dt><tt>ArrayType</tt></dt>
3060 <dd>This is a subclass of SequentialType and defines the interface for array
3061 types.
3062 <ul>
3063 <li><tt>unsigned getNumElements() const</tt>: Returns the number of
3064 elements in the array. </li>
3065 </ul>
3066 </dd>
3067 <dt><tt>PointerType</tt></dt>
Chris Lattner302da1e2007-02-03 03:05:57 +0000[diff] [blame]3068 <dd>Subclass of SequentialType for pointer types.</dd>
Reid Spencer9d6565a2007-02-15 02:26:10 +0000[diff] [blame]3069 <dt><tt>VectorType</tt></dt>
Reid Spencer485bad12007-02-15 03:07:05 +0000[diff] [blame]3070 <dd>Subclass of SequentialType for vector types. A
3071 vector type is similar to an ArrayType but is distinguished because it is
Benjamin Kramer8040cd32009-10-12 14:46:08 +0000[diff] [blame]3072 a first class type whereas ArrayType is not. Vector types are used for
Reid Spencer303c4b42007-01-12 17:26:25 +0000[diff] [blame]3073 vector operations and are usually small vectors of of an integer or floating
3074 point type.</dd>
3075 <dt><tt>StructType</tt></dt>
3076 <dd>Subclass of DerivedTypes for struct types.</dd>
Duncan Sands8036ca42007-03-30 12:22:09 +0000[diff] [blame]3077 <dt><tt><a name="FunctionType">FunctionType</a></tt></dt>
Reid Spencer303c4b42007-01-12 17:26:25 +0000[diff] [blame]3078 <dd>Subclass of DerivedTypes for function types.
3079 <ul>
Dan Gohman4bb31bf2010-03-30 20:04:57 +0000[diff] [blame]3080 <li><tt>bool isVarArg() const</tt>: Returns true if it's a vararg
Reid Spencer303c4b42007-01-12 17:26:25 +0000[diff] [blame]3081 function</li>
3082 <li><tt> const Type * getReturnType() const</tt>: Returns the
3083 return type of the function.</li>
3084 <li><tt>const Type * getParamType (unsigned i)</tt>: Returns
3085 the type of the ith parameter.</li>
3086 <li><tt> const unsigned getNumParams() const</tt>: Returns the
3087 number of formal parameters.</li>
3088 </ul>
3089 </dd>
3090 <dt><tt>OpaqueType</tt></dt>
3091 <dd>Sublcass of DerivedType for abstract types. This class
3092 defines no content and is used as a placeholder for some other type. Note
3093 that OpaqueType is used (temporarily) during type resolution for forward
3094 references of types. Once the referenced type is resolved, the OpaqueType
3095 is replaced with the actual type. OpaqueType can also be used for data
3096 abstraction. At link time opaque types can be resolved to actual types
3097 of the same name.</dd>
3098</dl>
3099</div>
3100
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]3101
3102
3103<!-- ======================================================================= -->
3104<div class="doc_subsection">
3105 <a name="Module">The <tt>Module</tt> class</a>
3106</div>
3107
3108<div class="doc_text">
3109
3110<p><tt>#include "<a
3111href="/doxygen/Module_8h-source.html">llvm/Module.h</a>"</tt><br> doxygen info:
3112<a href="/doxygen/classllvm_1_1Module.html">Module Class</a></p>
3113
3114<p>The <tt>Module</tt> class represents the top level structure present in LLVM
3115programs. An LLVM module is effectively either a translation unit of the
3116original program or a combination of several translation units merged by the
3117linker. The <tt>Module</tt> class keeps track of a list of <a
3118href="#Function"><tt>Function</tt></a>s, a list of <a
3119href="#GlobalVariable"><tt>GlobalVariable</tt></a>s, and a <a
3120href="#SymbolTable"><tt>SymbolTable</tt></a>. Additionally, it contains a few
3121helpful member functions that try to make common operations easy.</p>
3122
3123</div>
3124
3125<!-- _______________________________________________________________________ -->
3126<div class="doc_subsubsection">
3127 <a name="m_Module">Important Public Members of the <tt>Module</tt> class</a>
3128</div>
3129
3130<div class="doc_text">
3131
3132<ul>
3133 <li><tt>Module::Module(std::string name = "")</tt></li>
3134</ul>
3135
3136<p>Constructing a <a href="#Module">Module</a> is easy. You can optionally
3137provide a name for it (probably based on the name of the translation unit).</p>
3138
3139<ul>
3140 <li><tt>Module::iterator</tt> - Typedef for function list iterator<br>
3141 <tt>Module::const_iterator</tt> - Typedef for const_iterator.<br>
3142
3143 <tt>begin()</tt>, <tt>end()</tt>
3144 <tt>size()</tt>, <tt>empty()</tt>
3145
3146 <p>These are forwarding methods that make it easy to access the contents of
3147 a <tt>Module</tt> object's <a href="#Function"><tt>Function</tt></a>
3148 list.</p></li>
3149
3150 <li><tt>Module::FunctionListType &amp;getFunctionList()</tt>
3151
3152 <p> Returns the list of <a href="#Function"><tt>Function</tt></a>s. This is
3153 necessary to use when you need to update the list or perform a complex
3154 action that doesn't have a forwarding method.</p>
3155
3156 <p><!-- Global Variable --></p></li>
3157</ul>
3158
3159<hr>
3160
3161<ul>
3162 <li><tt>Module::global_iterator</tt> - Typedef for global variable list iterator<br>
3163
3164 <tt>Module::const_global_iterator</tt> - Typedef for const_iterator.<br>
3165
3166 <tt>global_begin()</tt>, <tt>global_end()</tt>
3167 <tt>global_size()</tt>, <tt>global_empty()</tt>
3168
3169 <p> These are forwarding methods that make it easy to access the contents of
3170 a <tt>Module</tt> object's <a
3171 href="#GlobalVariable"><tt>GlobalVariable</tt></a> list.</p></li>
3172
3173 <li><tt>Module::GlobalListType &amp;getGlobalList()</tt>
3174
3175 <p>Returns the list of <a
3176 href="#GlobalVariable"><tt>GlobalVariable</tt></a>s. This is necessary to
3177 use when you need to update the list or perform a complex action that
3178 doesn't have a forwarding method.</p>
3179
3180 <p><!-- Symbol table stuff --> </p></li>
3181</ul>
3182
3183<hr>
3184
3185<ul>
3186 <li><tt><a href="#SymbolTable">SymbolTable</a> *getSymbolTable()</tt>
3187
3188 <p>Return a reference to the <a href="#SymbolTable"><tt>SymbolTable</tt></a>
3189 for this <tt>Module</tt>.</p>
3190
3191 <p><!-- Convenience methods --></p></li>
3192</ul>
3193
3194<hr>
3195
3196<ul>
3197 <li><tt><a href="#Function">Function</a> *getFunction(const std::string
3198 &amp;Name, const <a href="#FunctionType">FunctionType</a> *Ty)</tt>
3199
3200 <p>Look up the specified function in the <tt>Module</tt> <a
3201 href="#SymbolTable"><tt>SymbolTable</tt></a>. If it does not exist, return
3202 <tt>null</tt>.</p></li>
3203
3204 <li><tt><a href="#Function">Function</a> *getOrInsertFunction(const
3205 std::string &amp;Name, const <a href="#FunctionType">FunctionType</a> *T)</tt>
3206
3207 <p>Look up the specified function in the <tt>Module</tt> <a
3208 href="#SymbolTable"><tt>SymbolTable</tt></a>. If it does not exist, add an
3209 external declaration for the function and return it.</p></li>
3210
3211 <li><tt>std::string getTypeName(const <a href="#Type">Type</a> *Ty)</tt>
3212
3213 <p>If there is at least one entry in the <a
3214 href="#SymbolTable"><tt>SymbolTable</tt></a> for the specified <a
3215 href="#Type"><tt>Type</tt></a>, return it. Otherwise return the empty
3216 string.</p></li>
3217
3218 <li><tt>bool addTypeName(const std::string &amp;Name, const <a
3219 href="#Type">Type</a> *Ty)</tt>
3220
3221 <p>Insert an entry in the <a href="#SymbolTable"><tt>SymbolTable</tt></a>
3222 mapping <tt>Name</tt> to <tt>Ty</tt>. If there is already an entry for this
3223 name, true is returned and the <a
3224 href="#SymbolTable"><tt>SymbolTable</tt></a> is not modified.</p></li>
3225</ul>
3226
3227</div>
3228
3229
Reid Spencer303c4b42007-01-12 17:26:25 +0000[diff] [blame]3230<!-- ======================================================================= -->
3231<div class="doc_subsection">
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3232 <a name="Value">The <tt>Value</tt> class</a>
3233</div>
3234
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]3235<div class="doc_text">
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3236
3237<p><tt>#include "<a href="/doxygen/Value_8h-source.html">llvm/Value.h</a>"</tt>
3238<br>
Chris Lattner00815172007-01-04 22:01:45 +0000[diff] [blame]3239doxygen info: <a href="/doxygen/classllvm_1_1Value.html">Value Class</a></p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3240
3241<p>The <tt>Value</tt> class is the most important class in the LLVM Source
3242base. It represents a typed value that may be used (among other things) as an
3243operand to an instruction. There are many different types of <tt>Value</tt>s,
3244such as <a href="#Constant"><tt>Constant</tt></a>s,<a
3245href="#Argument"><tt>Argument</tt></a>s. Even <a
3246href="#Instruction"><tt>Instruction</tt></a>s and <a
3247href="#Function"><tt>Function</tt></a>s are <tt>Value</tt>s.</p>
3248
3249<p>A particular <tt>Value</tt> may be used many times in the LLVM representation
3250for a program. For example, an incoming argument to a function (represented
3251with an instance of the <a href="#Argument">Argument</a> class) is "used" by
3252every instruction in the function that references the argument. To keep track
3253of this relationship, the <tt>Value</tt> class keeps a list of all of the <a
3254href="#User"><tt>User</tt></a>s that is using it (the <a
3255href="#User"><tt>User</tt></a> class is a base class for all nodes in the LLVM
3256graph that can refer to <tt>Value</tt>s). This use list is how LLVM represents
3257def-use information in the program, and is accessible through the <tt>use_</tt>*
3258methods, shown below.</p>
3259
3260<p>Because LLVM is a typed representation, every LLVM <tt>Value</tt> is typed,
3261and this <a href="#Type">Type</a> is available through the <tt>getType()</tt>
3262method. In addition, all LLVM values can be named. The "name" of the
3263<tt>Value</tt> is a symbolic string printed in the LLVM code:</p>
3264
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]3265<div class="doc_code">
3266<pre>
Reid Spencer06565dc2007-01-12 17:11:23 +0000[diff] [blame]3267%<b>foo</b> = add i32 1, 2
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]3268</pre>
3269</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3270
Duncan Sands8036ca42007-03-30 12:22:09 +0000[diff] [blame]3271<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]3272that the name of any value may be missing (an empty string), so names should
3273<b>ONLY</b> be used for debugging (making the source code easier to read,
3274debugging printouts), they should not be used to keep track of values or map
3275between them. For this purpose, use a <tt>std::map</tt> of pointers to the
3276<tt>Value</tt> itself instead.</p>
3277
3278<p>One important aspect of LLVM is that there is no distinction between an SSA
3279variable and the operation that produces it. Because of this, any reference to
3280the value produced by an instruction (or the value available as an incoming
Chris Lattnerd5fc4fc2004-03-18 14:58:55 +0000[diff] [blame]3281argument, for example) is represented as a direct pointer to the instance of
3282the class that
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3283represents this value. Although this may take some getting used to, it
3284simplifies the representation and makes it easier to manipulate.</p>
3285
3286</div>
3287
3288<!-- _______________________________________________________________________ -->
3289<div class="doc_subsubsection">
3290 <a name="m_Value">Important Public Members of the <tt>Value</tt> class</a>
3291</div>
3292
3293<div class="doc_text">
3294
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3295<ul>
3296 <li><tt>Value::use_iterator</tt> - Typedef for iterator over the
3297use-list<br>
Gabor Greifbbbf9a22010-03-26 19:59:25 +0000[diff] [blame]3298 <tt>Value::const_use_iterator</tt> - Typedef for const_iterator over
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3299the use-list<br>
3300 <tt>unsigned use_size()</tt> - Returns the number of users of the
3301value.<br>
Chris Lattner9355b472002-09-06 02:50:58 +0000[diff] [blame]3302 <tt>bool use_empty()</tt> - Returns true if there are no users.<br>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3303 <tt>use_iterator use_begin()</tt> - Get an iterator to the start of
3304the use-list.<br>
3305 <tt>use_iterator use_end()</tt> - Get an iterator to the end of the
3306use-list.<br>
3307 <tt><a href="#User">User</a> *use_back()</tt> - Returns the last
3308element in the list.
3309 <p> These methods are the interface to access the def-use
3310information in LLVM. As with all other iterators in LLVM, the naming
3311conventions follow the conventions defined by the <a href="#stl">STL</a>.</p>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3312 </li>
3313 <li><tt><a href="#Type">Type</a> *getType() const</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3314 <p>This method returns the Type of the Value.</p>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3315 </li>
3316 <li><tt>bool hasName() const</tt><br>
Chris Lattner9355b472002-09-06 02:50:58 +0000[diff] [blame]3317 <tt>std::string getName() const</tt><br>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3318 <tt>void setName(const std::string &amp;Name)</tt>
3319 <p> This family of methods is used to access and assign a name to a <tt>Value</tt>,
3320be aware of the <a href="#nameWarning">precaution above</a>.</p>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3321 </li>
3322 <li><tt>void replaceAllUsesWith(Value *V)</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3323
3324 <p>This method traverses the use list of a <tt>Value</tt> changing all <a
3325 href="#User"><tt>User</tt>s</a> of the current value to refer to
3326 "<tt>V</tt>" instead. For example, if you detect that an instruction always
3327 produces a constant value (for example through constant folding), you can
3328 replace all uses of the instruction with the constant like this:</p>
3329
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]3330<div class="doc_code">
3331<pre>
3332Inst-&gt;replaceAllUsesWith(ConstVal);
3333</pre>
3334</div>
3335
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3336</ul>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3337
3338</div>
3339
3340<!-- ======================================================================= -->
3341<div class="doc_subsection">
3342 <a name="User">The <tt>User</tt> class</a>
3343</div>
3344
3345<div class="doc_text">
3346
3347<p>
3348<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]3349doxygen info: <a href="/doxygen/classllvm_1_1User.html">User Class</a><br>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3350Superclass: <a href="#Value"><tt>Value</tt></a></p>
3351
3352<p>The <tt>User</tt> class is the common base class of all LLVM nodes that may
3353refer to <a href="#Value"><tt>Value</tt></a>s. It exposes a list of "Operands"
3354that are all of the <a href="#Value"><tt>Value</tt></a>s that the User is
3355referring to. The <tt>User</tt> class itself is a subclass of
3356<tt>Value</tt>.</p>
3357
3358<p>The operands of a <tt>User</tt> point directly to the LLVM <a
3359href="#Value"><tt>Value</tt></a> that it refers to. Because LLVM uses Static
3360Single Assignment (SSA) form, there can only be one definition referred to,
3361allowing this direct connection. This connection provides the use-def
3362information in LLVM.</p>
3363
3364</div>
3365
3366<!-- _______________________________________________________________________ -->
3367<div class="doc_subsubsection">
3368 <a name="m_User">Important Public Members of the <tt>User</tt> class</a>
3369</div>
3370
3371<div class="doc_text">
3372
3373<p>The <tt>User</tt> class exposes the operand list in two ways: through
3374an index access interface and through an iterator based interface.</p>
3375
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3376<ul>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3377 <li><tt>Value *getOperand(unsigned i)</tt><br>
3378 <tt>unsigned getNumOperands()</tt>
3379 <p> These two methods expose the operands of the <tt>User</tt> in a
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3380convenient form for direct access.</p></li>
3381
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3382 <li><tt>User::op_iterator</tt> - Typedef for iterator over the operand
3383list<br>
Chris Lattner58360822005-01-17 00:12:04 +0000[diff] [blame]3384 <tt>op_iterator op_begin()</tt> - Get an iterator to the start of
3385the operand list.<br>
3386 <tt>op_iterator op_end()</tt> - Get an iterator to the end of the
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3387operand list.
3388 <p> Together, these methods make up the iterator based interface to
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3389the operands of a <tt>User</tt>.</p></li>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3390</ul>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3391
3392</div>
3393
3394<!-- ======================================================================= -->
3395<div class="doc_subsection">
3396 <a name="Instruction">The <tt>Instruction</tt> class</a>
3397</div>
3398
3399<div class="doc_text">
3400
3401<p><tt>#include "</tt><tt><a
3402href="/doxygen/Instruction_8h-source.html">llvm/Instruction.h</a>"</tt><br>
Misha Brukman31ca1de2004-06-03 23:35:54 +0000[diff] [blame]3403doxygen info: <a href="/doxygen/classllvm_1_1Instruction.html">Instruction Class</a><br>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3404Superclasses: <a href="#User"><tt>User</tt></a>, <a
3405href="#Value"><tt>Value</tt></a></p>
3406
3407<p>The <tt>Instruction</tt> class is the common base class for all LLVM
3408instructions. It provides only a few methods, but is a very commonly used
3409class. The primary data tracked by the <tt>Instruction</tt> class itself is the
3410opcode (instruction type) and the parent <a
3411href="#BasicBlock"><tt>BasicBlock</tt></a> the <tt>Instruction</tt> is embedded
3412into. To represent a specific type of instruction, one of many subclasses of
3413<tt>Instruction</tt> are used.</p>
3414
3415<p> Because the <tt>Instruction</tt> class subclasses the <a
3416href="#User"><tt>User</tt></a> class, its operands can be accessed in the same
3417way as for other <a href="#User"><tt>User</tt></a>s (with the
3418<tt>getOperand()</tt>/<tt>getNumOperands()</tt> and
3419<tt>op_begin()</tt>/<tt>op_end()</tt> methods).</p> <p> An important file for
3420the <tt>Instruction</tt> class is the <tt>llvm/Instruction.def</tt> file. This
3421file contains some meta-data about the various different types of instructions
3422in LLVM. It describes the enum values that are used as opcodes (for example
Reid Spencerc92d25d2006-12-19 19:47:19 +0000[diff] [blame]3423<tt>Instruction::Add</tt> and <tt>Instruction::ICmp</tt>), as well as the
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3424concrete sub-classes of <tt>Instruction</tt> that implement the instruction (for
3425example <tt><a href="#BinaryOperator">BinaryOperator</a></tt> and <tt><a
Reid Spencerc92d25d2006-12-19 19:47:19 +0000[diff] [blame]3426href="#CmpInst">CmpInst</a></tt>). Unfortunately, the use of macros in
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3427this file confuses doxygen, so these enum values don't show up correctly in the
Misha Brukman31ca1de2004-06-03 23:35:54 +0000[diff] [blame]3428<a href="/doxygen/classllvm_1_1Instruction.html">doxygen output</a>.</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3429
3430</div>
3431
3432<!-- _______________________________________________________________________ -->
3433<div class="doc_subsubsection">
Reid Spencerc92d25d2006-12-19 19:47:19 +0000[diff] [blame]3434 <a name="s_Instruction">Important Subclasses of the <tt>Instruction</tt>
3435 class</a>
3436</div>
3437<div class="doc_text">
3438 <ul>
3439 <li><tt><a name="BinaryOperator">BinaryOperator</a></tt>
3440 <p>This subclasses represents all two operand instructions whose operands
3441 must be the same type, except for the comparison instructions.</p></li>
3442 <li><tt><a name="CastInst">CastInst</a></tt>
3443 <p>This subclass is the parent of the 12 casting instructions. It provides
3444 common operations on cast instructions.</p>
3445 <li><tt><a name="CmpInst">CmpInst</a></tt>
3446 <p>This subclass respresents the two comparison instructions,
3447 <a href="LangRef.html#i_icmp">ICmpInst</a> (integer opreands), and
3448 <a href="LangRef.html#i_fcmp">FCmpInst</a> (floating point operands).</p>
3449 <li><tt><a name="TerminatorInst">TerminatorInst</a></tt>
3450 <p>This subclass is the parent of all terminator instructions (those which
3451 can terminate a block).</p>
3452 </ul>
3453 </div>
3454
3455<!-- _______________________________________________________________________ -->
3456<div class="doc_subsubsection">
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3457 <a name="m_Instruction">Important Public Members of the <tt>Instruction</tt>
3458 class</a>
3459</div>
3460
3461<div class="doc_text">
3462
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3463<ul>
3464 <li><tt><a href="#BasicBlock">BasicBlock</a> *getParent()</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3465 <p>Returns the <a href="#BasicBlock"><tt>BasicBlock</tt></a> that
3466this <tt>Instruction</tt> is embedded into.</p></li>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3467 <li><tt>bool mayWriteToMemory()</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3468 <p>Returns true if the instruction writes to memory, i.e. it is a
3469 <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]3470 <li><tt>unsigned getOpcode()</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3471 <p>Returns the opcode for the <tt>Instruction</tt>.</p></li>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3472 <li><tt><a href="#Instruction">Instruction</a> *clone() const</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3473 <p>Returns another instance of the specified instruction, identical
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3474in all ways to the original except that the instruction has no parent
3475(ie it's not embedded into a <a href="#BasicBlock"><tt>BasicBlock</tt></a>),
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3476and it has no name</p></li>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3477</ul>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3478
3479</div>
3480
3481<!-- ======================================================================= -->
3482<div class="doc_subsection">
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]3483 <a name="Constant">The <tt>Constant</tt> class and subclasses</a>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3484</div>
3485
3486<div class="doc_text">
3487
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]3488<p>Constant represents a base class for different types of constants. It
3489is subclassed by ConstantInt, ConstantArray, etc. for representing
3490the various types of Constants. <a href="#GlobalValue">GlobalValue</a> is also
3491a subclass, which represents the address of a global variable or function.
3492</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3493
3494</div>
3495
3496<!-- _______________________________________________________________________ -->
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]3497<div class="doc_subsubsection">Important Subclasses of Constant </div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3498<div class="doc_text">
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3499<ul>
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]3500 <li>ConstantInt : This subclass of Constant represents an integer constant of
3501 any width.
3502 <ul>
Reid Spencer97b4ee32007-03-01 21:05:33 +0000[diff] [blame]3503 <li><tt>const APInt&amp; getValue() const</tt>: Returns the underlying
3504 value of this constant, an APInt value.</li>
3505 <li><tt>int64_t getSExtValue() const</tt>: Converts the underlying APInt
3506 value to an int64_t via sign extension. If the value (not the bit width)
3507 of the APInt is too large to fit in an int64_t, an assertion will result.
3508 For this reason, use of this method is discouraged.</li>
3509 <li><tt>uint64_t getZExtValue() const</tt>: Converts the underlying APInt
3510 value to a uint64_t via zero extension. IF the value (not the bit width)
3511 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]3512 For this reason, use of this method is discouraged.</li>
Reid Spencer97b4ee32007-03-01 21:05:33 +0000[diff] [blame]3513 <li><tt>static ConstantInt* get(const APInt&amp; Val)</tt>: Returns the
3514 ConstantInt object that represents the value provided by <tt>Val</tt>.
3515 The type is implied as the IntegerType that corresponds to the bit width
3516 of <tt>Val</tt>.</li>
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]3517 <li><tt>static ConstantInt* get(const Type *Ty, uint64_t Val)</tt>:
3518 Returns the ConstantInt object that represents the value provided by
3519 <tt>Val</tt> for integer type <tt>Ty</tt>.</li>
3520 </ul>
3521 </li>
3522 <li>ConstantFP : This class represents a floating point constant.
3523 <ul>
3524 <li><tt>double getValue() const</tt>: Returns the underlying value of
3525 this constant. </li>
3526 </ul>
3527 </li>
3528 <li>ConstantArray : This represents a constant array.
3529 <ul>
3530 <li><tt>const std::vector&lt;Use&gt; &amp;getValues() const</tt>: Returns
3531 a vector of component constants that makeup this array. </li>
3532 </ul>
3533 </li>
3534 <li>ConstantStruct : This represents a constant struct.
3535 <ul>
3536 <li><tt>const std::vector&lt;Use&gt; &amp;getValues() const</tt>: Returns
3537 a vector of component constants that makeup this array. </li>
3538 </ul>
3539 </li>
3540 <li>GlobalValue : This represents either a global variable or a function. In
3541 either case, the value is a constant fixed address (after linking).
3542 </li>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3543</ul>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3544</div>
3545
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]3546
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3547<!-- ======================================================================= -->
3548<div class="doc_subsection">
3549 <a name="GlobalValue">The <tt>GlobalValue</tt> class</a>
3550</div>
3551
3552<div class="doc_text">
3553
3554<p><tt>#include "<a
3555href="/doxygen/GlobalValue_8h-source.html">llvm/GlobalValue.h</a>"</tt><br>
Misha Brukman384047f2004-06-03 23:29:12 +0000[diff] [blame]3556doxygen info: <a href="/doxygen/classllvm_1_1GlobalValue.html">GlobalValue
3557Class</a><br>
Reid Spencerbe5e85e2006-04-14 14:11:48 +0000[diff] [blame]3558Superclasses: <a href="#Constant"><tt>Constant</tt></a>,
3559<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]3560
3561<p>Global values (<a href="#GlobalVariable"><tt>GlobalVariable</tt></a>s or <a
3562href="#Function"><tt>Function</tt></a>s) are the only LLVM values that are
3563visible in the bodies of all <a href="#Function"><tt>Function</tt></a>s.
3564Because they are visible at global scope, they are also subject to linking with
3565other globals defined in different translation units. To control the linking
3566process, <tt>GlobalValue</tt>s know their linkage rules. Specifically,
3567<tt>GlobalValue</tt>s know whether they have internal or external linkage, as
Reid Spencer8b2da7a2004-07-18 13:10:31 +0000[diff] [blame]3568defined by the <tt>LinkageTypes</tt> enumeration.</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3569
3570<p>If a <tt>GlobalValue</tt> has internal linkage (equivalent to being
3571<tt>static</tt> in C), it is not visible to code outside the current translation
3572unit, and does not participate in linking. If it has external linkage, it is
3573visible to external code, and does participate in linking. In addition to
3574linkage information, <tt>GlobalValue</tt>s keep track of which <a
3575href="#Module"><tt>Module</tt></a> they are currently part of.</p>
3576
3577<p>Because <tt>GlobalValue</tt>s are memory objects, they are always referred to
3578by their <b>address</b>. As such, the <a href="#Type"><tt>Type</tt></a> of a
3579global is always a pointer to its contents. It is important to remember this
3580when using the <tt>GetElementPtrInst</tt> instruction because this pointer must
3581be dereferenced first. For example, if you have a <tt>GlobalVariable</tt> (a
3582subclass 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]3583i32]</tt>, then the <tt>GlobalVariable</tt> is a pointer to that array. Although
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3584the address of the first element of this array and the value of the
3585<tt>GlobalVariable</tt> are the same, they have different types. The
Reid Spencer06565dc2007-01-12 17:11:23 +0000[diff] [blame]3586<tt>GlobalVariable</tt>'s type is <tt>[24 x i32]</tt>. The first element's type
3587is <tt>i32.</tt> Because of this, accessing a global value requires you to
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3588dereference the pointer with <tt>GetElementPtrInst</tt> first, then its elements
3589can be accessed. This is explained in the <a href="LangRef.html#globalvars">LLVM
3590Language Reference Manual</a>.</p>
3591
3592</div>
3593
3594<!-- _______________________________________________________________________ -->
3595<div class="doc_subsubsection">
3596 <a name="m_GlobalValue">Important Public Members of the <tt>GlobalValue</tt>
3597 class</a>
3598</div>
3599
3600<div class="doc_text">
3601
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3602<ul>
3603 <li><tt>bool hasInternalLinkage() const</tt><br>
Chris Lattner9355b472002-09-06 02:50:58 +0000[diff] [blame]3604 <tt>bool hasExternalLinkage() const</tt><br>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3605 <tt>void setInternalLinkage(bool HasInternalLinkage)</tt>
3606 <p> These methods manipulate the linkage characteristics of the <tt>GlobalValue</tt>.</p>
3607 <p> </p>
3608 </li>
3609 <li><tt><a href="#Module">Module</a> *getParent()</tt>
3610 <p> This returns the <a href="#Module"><tt>Module</tt></a> that the
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3611GlobalValue is currently embedded into.</p></li>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3612</ul>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3613
3614</div>
3615
3616<!-- ======================================================================= -->
3617<div class="doc_subsection">
3618 <a name="Function">The <tt>Function</tt> class</a>
3619</div>
3620
3621<div class="doc_text">
3622
3623<p><tt>#include "<a
3624href="/doxygen/Function_8h-source.html">llvm/Function.h</a>"</tt><br> doxygen
Misha Brukman31ca1de2004-06-03 23:35:54 +0000[diff] [blame]3625info: <a href="/doxygen/classllvm_1_1Function.html">Function Class</a><br>
Reid Spencerbe5e85e2006-04-14 14:11:48 +0000[diff] [blame]3626Superclasses: <a href="#GlobalValue"><tt>GlobalValue</tt></a>,
3627<a href="#Constant"><tt>Constant</tt></a>,
3628<a href="#User"><tt>User</tt></a>,
3629<a href="#Value"><tt>Value</tt></a></p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3630
3631<p>The <tt>Function</tt> class represents a single procedure in LLVM. It is
Torok Edwin87469292009-10-12 13:37:29 +0000[diff] [blame]3632actually one of the more complex classes in the LLVM hierarchy because it must
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3633keep track of a large amount of data. The <tt>Function</tt> class keeps track
Reid Spencerbe5e85e2006-04-14 14:11:48 +0000[diff] [blame]3634of a list of <a href="#BasicBlock"><tt>BasicBlock</tt></a>s, a list of formal
3635<a href="#Argument"><tt>Argument</tt></a>s, and a
3636<a href="#SymbolTable"><tt>SymbolTable</tt></a>.</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3637
3638<p>The list of <a href="#BasicBlock"><tt>BasicBlock</tt></a>s is the most
3639commonly used part of <tt>Function</tt> objects. The list imposes an implicit
3640ordering of the blocks in the function, which indicate how the code will be
Benjamin Kramer8040cd32009-10-12 14:46:08 +0000[diff] [blame]3641laid out by the backend. Additionally, the first <a
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3642href="#BasicBlock"><tt>BasicBlock</tt></a> is the implicit entry node for the
3643<tt>Function</tt>. It is not legal in LLVM to explicitly branch to this initial
3644block. There are no implicit exit nodes, and in fact there may be multiple exit
3645nodes from a single <tt>Function</tt>. If the <a
3646href="#BasicBlock"><tt>BasicBlock</tt></a> list is empty, this indicates that
3647the <tt>Function</tt> is actually a function declaration: the actual body of the
3648function hasn't been linked in yet.</p>
3649
3650<p>In addition to a list of <a href="#BasicBlock"><tt>BasicBlock</tt></a>s, the
3651<tt>Function</tt> class also keeps track of the list of formal <a
3652href="#Argument"><tt>Argument</tt></a>s that the function receives. This
3653container manages the lifetime of the <a href="#Argument"><tt>Argument</tt></a>
3654nodes, just like the <a href="#BasicBlock"><tt>BasicBlock</tt></a> list does for
3655the <a href="#BasicBlock"><tt>BasicBlock</tt></a>s.</p>
3656
3657<p>The <a href="#SymbolTable"><tt>SymbolTable</tt></a> is a very rarely used
3658LLVM feature that is only used when you have to look up a value by name. Aside
3659from that, the <a href="#SymbolTable"><tt>SymbolTable</tt></a> is used
3660internally to make sure that there are not conflicts between the names of <a
3661href="#Instruction"><tt>Instruction</tt></a>s, <a
3662href="#BasicBlock"><tt>BasicBlock</tt></a>s, or <a
3663href="#Argument"><tt>Argument</tt></a>s in the function body.</p>
3664
Reid Spencer8b2da7a2004-07-18 13:10:31 +0000[diff] [blame]3665<p>Note that <tt>Function</tt> is a <a href="#GlobalValue">GlobalValue</a>
3666and therefore also a <a href="#Constant">Constant</a>. The value of the function
3667is its address (after linking) which is guaranteed to be constant.</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3668</div>
3669
3670<!-- _______________________________________________________________________ -->
3671<div class="doc_subsubsection">
3672 <a name="m_Function">Important Public Members of the <tt>Function</tt>
3673 class</a>
3674</div>
3675
3676<div class="doc_text">
3677
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3678<ul>
3679 <li><tt>Function(const </tt><tt><a href="#FunctionType">FunctionType</a>
Chris Lattnerac479e52004-08-04 05:10:48 +0000[diff] [blame]3680 *Ty, LinkageTypes Linkage, const std::string &amp;N = "", Module* Parent = 0)</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3681
3682 <p>Constructor used when you need to create new <tt>Function</tt>s to add
3683 the the program. The constructor must specify the type of the function to
Chris Lattnerac479e52004-08-04 05:10:48 +0000[diff] [blame]3684 create and what type of linkage the function should have. The <a
3685 href="#FunctionType"><tt>FunctionType</tt></a> argument
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3686 specifies the formal arguments and return value for the function. The same
Duncan Sands8036ca42007-03-30 12:22:09 +0000[diff] [blame]3687 <a href="#FunctionType"><tt>FunctionType</tt></a> value can be used to
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3688 create multiple functions. The <tt>Parent</tt> argument specifies the Module
3689 in which the function is defined. If this argument is provided, the function
3690 will automatically be inserted into that module's list of
3691 functions.</p></li>
3692
Chris Lattner62810e32008-11-25 18:34:50 +0000[diff] [blame]3693 <li><tt>bool isDeclaration()</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3694
3695 <p>Return whether or not the <tt>Function</tt> has a body defined. If the
3696 function is "external", it does not have a body, and thus must be resolved
3697 by linking with a function defined in a different translation unit.</p></li>
3698
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3699 <li><tt>Function::iterator</tt> - Typedef for basic block list iterator<br>
Chris Lattner9355b472002-09-06 02:50:58 +0000[diff] [blame]3700 <tt>Function::const_iterator</tt> - Typedef for const_iterator.<br>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3701
Chris Lattner77d69242005-03-15 05:19:20 +0000[diff] [blame]3702 <tt>begin()</tt>, <tt>end()</tt>
3703 <tt>size()</tt>, <tt>empty()</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3704
3705 <p>These are forwarding methods that make it easy to access the contents of
3706 a <tt>Function</tt> object's <a href="#BasicBlock"><tt>BasicBlock</tt></a>
3707 list.</p></li>
3708
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3709 <li><tt>Function::BasicBlockListType &amp;getBasicBlockList()</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3710
3711 <p>Returns the list of <a href="#BasicBlock"><tt>BasicBlock</tt></a>s. This
3712 is necessary to use when you need to update the list or perform a complex
3713 action that doesn't have a forwarding method.</p></li>
3714
Chris Lattner89cc2652005-03-15 04:48:32 +0000[diff] [blame]3715 <li><tt>Function::arg_iterator</tt> - Typedef for the argument list
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3716iterator<br>
Chris Lattner89cc2652005-03-15 04:48:32 +0000[diff] [blame]3717 <tt>Function::const_arg_iterator</tt> - Typedef for const_iterator.<br>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3718
Chris Lattner77d69242005-03-15 05:19:20 +0000[diff] [blame]3719 <tt>arg_begin()</tt>, <tt>arg_end()</tt>
Chris Lattner89cc2652005-03-15 04:48:32 +0000[diff] [blame]3720 <tt>arg_size()</tt>, <tt>arg_empty()</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3721
3722 <p>These are forwarding methods that make it easy to access the contents of
3723 a <tt>Function</tt> object's <a href="#Argument"><tt>Argument</tt></a>
3724 list.</p></li>
3725
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3726 <li><tt>Function::ArgumentListType &amp;getArgumentList()</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3727
3728 <p>Returns the list of <a href="#Argument"><tt>Argument</tt></a>s. This is
3729 necessary to use when you need to update the list or perform a complex
3730 action that doesn't have a forwarding method.</p></li>
3731
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3732 <li><tt><a href="#BasicBlock">BasicBlock</a> &amp;getEntryBlock()</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3733
3734 <p>Returns the entry <a href="#BasicBlock"><tt>BasicBlock</tt></a> for the
3735 function. Because the entry block for the function is always the first
3736 block, this returns the first block of the <tt>Function</tt>.</p></li>
3737
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3738 <li><tt><a href="#Type">Type</a> *getReturnType()</tt><br>
3739 <tt><a href="#FunctionType">FunctionType</a> *getFunctionType()</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3740
3741 <p>This traverses the <a href="#Type"><tt>Type</tt></a> of the
3742 <tt>Function</tt> and returns the return type of the function, or the <a
3743 href="#FunctionType"><tt>FunctionType</tt></a> of the actual
3744 function.</p></li>
3745
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3746 <li><tt><a href="#SymbolTable">SymbolTable</a> *getSymbolTable()</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3747
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3748 <p> Return a pointer to the <a href="#SymbolTable"><tt>SymbolTable</tt></a>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3749 for this <tt>Function</tt>.</p></li>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3750</ul>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3751
3752</div>
3753
3754<!-- ======================================================================= -->
3755<div class="doc_subsection">
3756 <a name="GlobalVariable">The <tt>GlobalVariable</tt> class</a>
3757</div>
3758
3759<div class="doc_text">
3760
3761<p><tt>#include "<a
3762href="/doxygen/GlobalVariable_8h-source.html">llvm/GlobalVariable.h</a>"</tt>
3763<br>
Tanya Lattnera3da7772004-06-22 08:02:25 +0000[diff] [blame]3764doxygen info: <a href="/doxygen/classllvm_1_1GlobalVariable.html">GlobalVariable
Reid Spencerbe5e85e2006-04-14 14:11:48 +0000[diff] [blame]3765 Class</a><br>
3766Superclasses: <a href="#GlobalValue"><tt>GlobalValue</tt></a>,
3767<a href="#Constant"><tt>Constant</tt></a>,
3768<a href="#User"><tt>User</tt></a>,
3769<a href="#Value"><tt>Value</tt></a></p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3770
Benjamin Kramer8040cd32009-10-12 14:46:08 +0000[diff] [blame]3771<p>Global variables are represented with the (surprise surprise)
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3772<tt>GlobalVariable</tt> class. Like functions, <tt>GlobalVariable</tt>s are also
3773subclasses of <a href="#GlobalValue"><tt>GlobalValue</tt></a>, and as such are
3774always referenced by their address (global values must live in memory, so their
Reid Spencerbe5e85e2006-04-14 14:11:48 +0000[diff] [blame]3775"name" refers to their constant address). See
3776<a href="#GlobalValue"><tt>GlobalValue</tt></a> for more on this. Global
3777variables may have an initial value (which must be a
3778<a href="#Constant"><tt>Constant</tt></a>), and if they have an initializer,
3779they may be marked as "constant" themselves (indicating that their contents
3780never change at runtime).</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3781</div>
3782
3783<!-- _______________________________________________________________________ -->
3784<div class="doc_subsubsection">
3785 <a name="m_GlobalVariable">Important Public Members of the
3786 <tt>GlobalVariable</tt> class</a>
3787</div>
3788
3789<div class="doc_text">
3790
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3791<ul>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3792 <li><tt>GlobalVariable(const </tt><tt><a href="#Type">Type</a> *Ty, bool
3793 isConstant, LinkageTypes&amp; Linkage, <a href="#Constant">Constant</a>
3794 *Initializer = 0, const std::string &amp;Name = "", Module* Parent = 0)</tt>
3795
3796 <p>Create a new global variable of the specified type. If
3797 <tt>isConstant</tt> is true then the global variable will be marked as
3798 unchanging for the program. The Linkage parameter specifies the type of
Duncan Sands667d4b82009-03-07 15:45:40 +0000[diff] [blame]3799 linkage (internal, external, weak, linkonce, appending) for the variable.
3800 If the linkage is InternalLinkage, WeakAnyLinkage, WeakODRLinkage,
3801 LinkOnceAnyLinkage or LinkOnceODRLinkage,&nbsp; then the resultant
3802 global variable will have internal linkage. AppendingLinkage concatenates
3803 together all instances (in different translation units) of the variable
3804 into a single variable but is only applicable to arrays. &nbsp;See
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3805 the <a href="LangRef.html#modulestructure">LLVM Language Reference</a> for
3806 further details on linkage types. Optionally an initializer, a name, and the
3807 module to put the variable into may be specified for the global variable as
3808 well.</p></li>
3809
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3810 <li><tt>bool isConstant() const</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3811
3812 <p>Returns true if this is a global variable that is known not to
3813 be modified at runtime.</p></li>
3814
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3815 <li><tt>bool hasInitializer()</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3816
3817 <p>Returns true if this <tt>GlobalVariable</tt> has an intializer.</p></li>
3818
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3819 <li><tt><a href="#Constant">Constant</a> *getInitializer()</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3820
Benjamin Kramer8040cd32009-10-12 14:46:08 +0000[diff] [blame]3821 <p>Returns the initial value for a <tt>GlobalVariable</tt>. It is not legal
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3822 to call this method if there is no initializer.</p></li>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3823</ul>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3824
3825</div>
3826
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]3827
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3828<!-- ======================================================================= -->
3829<div class="doc_subsection">
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]3830 <a name="BasicBlock">The <tt>BasicBlock</tt> class</a>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3831</div>
3832
3833<div class="doc_text">
3834
3835<p><tt>#include "<a
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]3836href="/doxygen/BasicBlock_8h-source.html">llvm/BasicBlock.h</a>"</tt><br>
Stefanus Du Toit24e04112009-06-17 21:12:26 +0000[diff] [blame]3837doxygen info: <a href="/doxygen/classllvm_1_1BasicBlock.html">BasicBlock
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]3838Class</a><br>
3839Superclass: <a href="#Value"><tt>Value</tt></a></p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3840
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]3841<p>This class represents a single entry multiple exit section of the code,
3842commonly known as a basic block by the compiler community. The
3843<tt>BasicBlock</tt> class maintains a list of <a
3844href="#Instruction"><tt>Instruction</tt></a>s, which form the body of the block.
3845Matching the language definition, the last element of this list of instructions
3846is always a terminator instruction (a subclass of the <a
3847href="#TerminatorInst"><tt>TerminatorInst</tt></a> class).</p>
3848
3849<p>In addition to tracking the list of instructions that make up the block, the
3850<tt>BasicBlock</tt> class also keeps track of the <a
3851href="#Function"><tt>Function</tt></a> that it is embedded into.</p>
3852
3853<p>Note that <tt>BasicBlock</tt>s themselves are <a
3854href="#Value"><tt>Value</tt></a>s, because they are referenced by instructions
3855like branches and can go in the switch tables. <tt>BasicBlock</tt>s have type
3856<tt>label</tt>.</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3857
3858</div>
3859
3860<!-- _______________________________________________________________________ -->
3861<div class="doc_subsubsection">
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]3862 <a name="m_BasicBlock">Important Public Members of the <tt>BasicBlock</tt>
3863 class</a>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3864</div>
3865
3866<div class="doc_text">
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3867<ul>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3868
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]3869<li><tt>BasicBlock(const std::string &amp;Name = "", </tt><tt><a
3870 href="#Function">Function</a> *Parent = 0)</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3871
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]3872<p>The <tt>BasicBlock</tt> constructor is used to create new basic blocks for
3873insertion into a function. The constructor optionally takes a name for the new
3874block, and a <a href="#Function"><tt>Function</tt></a> to insert it into. If
3875the <tt>Parent</tt> parameter is specified, the new <tt>BasicBlock</tt> is
3876automatically inserted at the end of the specified <a
3877href="#Function"><tt>Function</tt></a>, if not specified, the BasicBlock must be
3878manually inserted into the <a href="#Function"><tt>Function</tt></a>.</p></li>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3879
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]3880<li><tt>BasicBlock::iterator</tt> - Typedef for instruction list iterator<br>
3881<tt>BasicBlock::const_iterator</tt> - Typedef for const_iterator.<br>
3882<tt>begin()</tt>, <tt>end()</tt>, <tt>front()</tt>, <tt>back()</tt>,
3883<tt>size()</tt>, <tt>empty()</tt>
3884STL-style functions for accessing the instruction list.
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3885
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]3886<p>These methods and typedefs are forwarding functions that have the same
3887semantics as the standard library methods of the same names. These methods
3888expose the underlying instruction list of a basic block in a way that is easy to
3889manipulate. To get the full complement of container operations (including
3890operations to update the list), you must use the <tt>getInstList()</tt>
3891method.</p></li>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3892
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]3893<li><tt>BasicBlock::InstListType &amp;getInstList()</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3894
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]3895<p>This method is used to get access to the underlying container that actually
3896holds the Instructions. This method must be used when there isn't a forwarding
3897function in the <tt>BasicBlock</tt> class for the operation that you would like
3898to perform. Because there are no forwarding functions for "updating"
3899operations, you need to use this if you want to update the contents of a
3900<tt>BasicBlock</tt>.</p></li>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3901
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]3902<li><tt><a href="#Function">Function</a> *getParent()</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3903
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]3904<p> Returns a pointer to <a href="#Function"><tt>Function</tt></a> the block is
3905embedded into, or a null pointer if it is homeless.</p></li>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3906
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]3907<li><tt><a href="#TerminatorInst">TerminatorInst</a> *getTerminator()</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3908
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]3909<p> Returns a pointer to the terminator instruction that appears at the end of
3910the <tt>BasicBlock</tt>. If there is no terminator instruction, or if the last
3911instruction in the block is not a terminator, then a null pointer is
3912returned.</p></li>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3913
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3914</ul>
3915
3916</div>
3917
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3918
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3919<!-- ======================================================================= -->
3920<div class="doc_subsection">
3921 <a name="Argument">The <tt>Argument</tt> class</a>
3922</div>
3923
3924<div class="doc_text">
3925
3926<p>This subclass of Value defines the interface for incoming formal
Chris Lattner58360822005-01-17 00:12:04 +0000[diff] [blame]3927arguments to a function. A Function maintains a list of its formal
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3928arguments. An argument has a pointer to the parent Function.</p>
3929
3930</div>
3931
Chris Lattner9355b472002-09-06 02:50:58 +0000[diff] [blame]3932<!-- *********************************************************************** -->
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3933<hr>
3934<address>
3935 <a href="http://jigsaw.w3.org/css-validator/check/referer"><img
Misha Brukman44408702008-12-11 17:34:48 +0000[diff] [blame]3936 src="http://jigsaw.w3.org/css-validator/images/vcss-blue" alt="Valid CSS"></a>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3937 <a href="http://validator.w3.org/check/referer"><img
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Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3939
3940 <a href="mailto:dhurjati@cs.uiuc.edu">Dinakar Dhurjati</a> and
3941 <a href="mailto:sabre@nondot.org">Chris Lattner</a><br>
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]3942 <a href="http://llvm.org">The LLVM Compiler Infrastructure</a><br>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3943 Last modified: $Date$
3944</address>
3945
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3946</body>
3947</html>