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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>
Jakob Stoklund Olesenaca0da62010-12-14 00:55:51 +0000[diff] [blame]87 <li><a href="#dss_intervalmap">"llvm/ADT/IntervalMap.h"</a></li>
Chris Lattnerf3692522007-02-03 19:51:56 +0000[diff] [blame]88 <li><a href="#dss_map">&lt;map&gt;</a></li>
Jakob Stoklund Olesen4359e5e2011-04-05 20:56:08 +0000[diff] [blame^]89 <li><a href="#dss_inteqclasses">"llvm/ADT/IntEqClasses.h"</a></li>
Chris Lattnerf3692522007-02-03 19:51:56 +0000[diff] [blame]90 <li><a href="#dss_othermap">Other Map-Like Container Options</a></li>
91 </ul></li>
Chris Lattnerdced9fb2009-07-25 07:22:20 +0000[diff] [blame]92 <li><a href="#ds_string">String-like containers</a>
Benjamin Kramere15192b2009-08-05 15:42:44 +0000[diff] [blame]93 <!--<ul>
94 todo
95 </ul>--></li>
Daniel Berlin1939ace2007-09-24 17:52:25 +0000[diff] [blame]96 <li><a href="#ds_bit">BitVector-like containers</a>
97 <ul>
98 <li><a href="#dss_bitvector">A dense bitvector</a></li>
Dan Gohman5f7775c2010-01-05 18:24:00 +0000[diff] [blame]99 <li><a href="#dss_smallbitvector">A "small" dense bitvector</a></li>
Daniel Berlin1939ace2007-09-24 17:52:25 +0000[diff] [blame]100 <li><a href="#dss_sparsebitvector">A sparse bitvector</a></li>
101 </ul></li>
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]102 </ul>
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]103 </li>
Chris Lattnerae7f7592002-09-06 18:31:18 +0000[diff] [blame]104 <li><a href="#common">Helpful Hints for Common Operations</a>
Chris Lattnerae7f7592002-09-06 18:31:18 +0000[diff] [blame]105 <ul>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]106 <li><a href="#inspection">Basic Inspection and Traversal Routines</a>
107 <ul>
108 <li><a href="#iterate_function">Iterating over the <tt>BasicBlock</tt>s
109in a <tt>Function</tt></a> </li>
110 <li><a href="#iterate_basicblock">Iterating over the <tt>Instruction</tt>s
111in a <tt>BasicBlock</tt></a> </li>
112 <li><a href="#iterate_institer">Iterating over the <tt>Instruction</tt>s
113in a <tt>Function</tt></a> </li>
114 <li><a href="#iterate_convert">Turning an iterator into a
115class pointer</a> </li>
116 <li><a href="#iterate_complex">Finding call sites: a more
117complex example</a> </li>
118 <li><a href="#calls_and_invokes">Treating calls and invokes
119the same way</a> </li>
120 <li><a href="#iterate_chains">Iterating over def-use &amp;
121use-def chains</a> </li>
Chris Lattner2e438ca2008-01-03 16:56:04 +0000[diff] [blame]122 <li><a href="#iterate_preds">Iterating over predecessors &amp;
123successors of blocks</a></li>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]124 </ul>
125 </li>
126 <li><a href="#simplechanges">Making simple changes</a>
127 <ul>
128 <li><a href="#schanges_creating">Creating and inserting new
129 <tt>Instruction</tt>s</a> </li>
130 <li><a href="#schanges_deleting">Deleting <tt>Instruction</tt>s</a> </li>
131 <li><a href="#schanges_replacing">Replacing an <tt>Instruction</tt>
132with another <tt>Value</tt></a> </li>
Tanya Lattnerb011c662007-06-20 18:33:15 +0000[diff] [blame]133 <li><a href="#schanges_deletingGV">Deleting <tt>GlobalVariable</tt>s</a> </li>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]134 </ul>
Reid Spencerfe8f4ff2004-11-01 09:02:53 +0000[diff] [blame]135 </li>
Jeffrey Yasskin714257f2009-04-30 22:33:41 +0000[diff] [blame]136 <li><a href="#create_types">How to Create Types</a></li>
Chris Lattnerae7f7592002-09-06 18:31:18 +0000[diff] [blame]137<!--
138 <li>Working with the Control Flow Graph
139 <ul>
140 <li>Accessing predecessors and successors of a <tt>BasicBlock</tt>
141 <li>
142 <li>
143 </ul>
Reid Spencerfe8f4ff2004-11-01 09:02:53 +0000[diff] [blame]144-->
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]145 </ul>
146 </li>
Chris Lattnerd9d6e102005-04-23 16:10:52 +0000[diff] [blame]147
Owen Anderson8bc1b3b2009-06-16 01:17:16 +0000[diff] [blame]148 <li><a href="#threading">Threads and LLVM</a>
149 <ul>
Owen Anderson1ad70e32009-06-16 18:04:19 +0000[diff] [blame]150 <li><a href="#startmultithreaded">Entering and Exiting Multithreaded Mode
151 </a></li>
Owen Anderson8bc1b3b2009-06-16 01:17:16 +0000[diff] [blame]152 <li><a href="#shutdown">Ending execution with <tt>llvm_shutdown()</tt></a></li>
153 <li><a href="#managedstatic">Lazy initialization with <tt>ManagedStatic</tt></a></li>
Owen Andersone0c951a2009-08-19 17:58:52 +0000[diff] [blame]154 <li><a href="#llvmcontext">Achieving Isolation with <tt>LLVMContext</tt></a></li>
Jeffrey Yasskin01eba392010-01-29 19:10:38 +0000[diff] [blame]155 <li><a href="#jitthreading">Threads and the JIT</a></li>
Owen Anderson8bc1b3b2009-06-16 01:17:16 +0000[diff] [blame]156 </ul>
157 </li>
158
Chris Lattnerd9d6e102005-04-23 16:10:52 +0000[diff] [blame]159 <li><a href="#advanced">Advanced Topics</a>
160 <ul>
Chris Lattnerf1b200b2005-04-23 17:27:36 +0000[diff] [blame]161 <li><a href="#TypeResolve">LLVM Type Resolution</a>
162 <ul>
163 <li><a href="#BuildRecType">Basic Recursive Type Construction</a></li>
164 <li><a href="#refineAbstractTypeTo">The <tt>refineAbstractTypeTo</tt> method</a></li>
165 <li><a href="#PATypeHolder">The PATypeHolder Class</a></li>
166 <li><a href="#AbstractTypeUser">The AbstractTypeUser Class</a></li>
167 </ul></li>
168
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]169 <li><a href="#SymbolTable">The <tt>ValueSymbolTable</tt> and <tt>TypeSymbolTable</tt> classes</a></li>
170 <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]171 </ul></li>
172
Joel Stanley9b96c442002-09-06 21:55:13 +0000[diff] [blame]173 <li><a href="#coreclasses">The Core LLVM Class Hierarchy Reference</a>
Chris Lattner9355b472002-09-06 02:50:58 +0000[diff] [blame]174 <ul>
Reid Spencer303c4b42007-01-12 17:26:25 +0000[diff] [blame]175 <li><a href="#Type">The <tt>Type</tt> class</a> </li>
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]176 <li><a href="#Module">The <tt>Module</tt> class</a></li>
Reid Spencerfe8f4ff2004-11-01 09:02:53 +0000[diff] [blame]177 <li><a href="#Value">The <tt>Value</tt> class</a>
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]178 <ul>
179 <li><a href="#User">The <tt>User</tt> class</a>
Chris Lattner9355b472002-09-06 02:50:58 +0000[diff] [blame]180 <ul>
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]181 <li><a href="#Instruction">The <tt>Instruction</tt> class</a></li>
182 <li><a href="#Constant">The <tt>Constant</tt> class</a>
183 <ul>
184 <li><a href="#GlobalValue">The <tt>GlobalValue</tt> class</a>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]185 <ul>
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]186 <li><a href="#Function">The <tt>Function</tt> class</a></li>
187 <li><a href="#GlobalVariable">The <tt>GlobalVariable</tt> class</a></li>
188 </ul>
189 </li>
190 </ul>
191 </li>
Reid Spencerfe8f4ff2004-11-01 09:02:53 +0000[diff] [blame]192 </ul>
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]193 </li>
194 <li><a href="#BasicBlock">The <tt>BasicBlock</tt> class</a></li>
195 <li><a href="#Argument">The <tt>Argument</tt> class</a></li>
196 </ul>
Reid Spencerfe8f4ff2004-11-01 09:02:53 +0000[diff] [blame]197 </li>
198 </ul>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]199 </li>
Chris Lattner9355b472002-09-06 02:50:58 +0000[diff] [blame]200</ol>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]201
Chris Lattner69bf8a92004-05-23 21:06:58 +0000[diff] [blame]202<div class="doc_author">
203 <p>Written by <a href="mailto:sabre@nondot.org">Chris Lattner</a>,
Chris Lattner94c43592004-05-26 16:52:55 +0000[diff] [blame]204 <a href="mailto:dhurjati@cs.uiuc.edu">Dinakar Dhurjati</a>,
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]205 <a href="mailto:ggreif@gmail.com">Gabor Greif</a>,
Owen Anderson8bc1b3b2009-06-16 01:17:16 +0000[diff] [blame]206 <a href="mailto:jstanley@cs.uiuc.edu">Joel Stanley</a>,
207 <a href="mailto:rspencer@x10sys.com">Reid Spencer</a> and
208 <a href="mailto:owen@apple.com">Owen Anderson</a></p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]209</div>
210
Chris Lattner9355b472002-09-06 02:50:58 +0000[diff] [blame]211<!-- *********************************************************************** -->
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]212<div class="doc_section">
213 <a name="introduction">Introduction </a>
214</div>
Chris Lattner9355b472002-09-06 02:50:58 +0000[diff] [blame]215<!-- *********************************************************************** -->
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]216
217<div class="doc_text">
218
219<p>This document is meant to highlight some of the important classes and
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]220interfaces available in the LLVM source-base. This manual is not
221intended to explain what LLVM is, how it works, and what LLVM code looks
222like. It assumes that you know the basics of LLVM and are interested
223in writing transformations or otherwise analyzing or manipulating the
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]224code.</p>
225
226<p>This document should get you oriented so that you can find your
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]227way in the continuously growing source code that makes up the LLVM
228infrastructure. Note that this manual is not intended to serve as a
229replacement for reading the source code, so if you think there should be
230a method in one of these classes to do something, but it's not listed,
231check the source. Links to the <a href="/doxygen/">doxygen</a> sources
232are provided to make this as easy as possible.</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]233
234<p>The first section of this document describes general information that is
235useful to know when working in the LLVM infrastructure, and the second describes
236the Core LLVM classes. In the future this manual will be extended with
237information describing how to use extension libraries, such as dominator
238information, CFG traversal routines, and useful utilities like the <tt><a
239href="/doxygen/InstVisitor_8h-source.html">InstVisitor</a></tt> template.</p>
240
241</div>
242
Chris Lattner9355b472002-09-06 02:50:58 +0000[diff] [blame]243<!-- *********************************************************************** -->
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]244<div class="doc_section">
245 <a name="general">General Information</a>
246</div>
247<!-- *********************************************************************** -->
248
249<div class="doc_text">
250
251<p>This section contains general information that is useful if you are working
252in the LLVM source-base, but that isn't specific to any particular API.</p>
253
254</div>
255
256<!-- ======================================================================= -->
257<div class="doc_subsection">
258 <a name="stl">The C++ Standard Template Library</a>
259</div>
260
261<div class="doc_text">
262
263<p>LLVM makes heavy use of the C++ Standard Template Library (STL),
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]264perhaps much more than you are used to, or have seen before. Because of
265this, you might want to do a little background reading in the
266techniques used and capabilities of the library. There are many good
267pages that discuss the STL, and several books on the subject that you
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]268can get, so it will not be discussed in this document.</p>
269
270<p>Here are some useful links:</p>
271
272<ol>
273
Nick Lewyckyea1fe2c2010-10-09 21:12:29 +0000[diff] [blame]274<li><a href="http://www.dinkumware.com/manuals/#Standard C++ Library">Dinkumware
275C++ Library reference</a> - an excellent reference for the STL and other parts
276of the standard C++ library.</li>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]277
278<li><a href="http://www.tempest-sw.com/cpp/">C++ In a Nutshell</a> - This is an
Gabor Greif0cbcabe2009-03-12 09:47:03 +0000[diff] [blame]279O'Reilly book in the making. It has a decent Standard Library
280Reference that rivals Dinkumware's, and is unfortunately no longer free since the
281book has been published.</li>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]282
283<li><a href="http://www.parashift.com/c++-faq-lite/">C++ Frequently Asked
284Questions</a></li>
285
286<li><a href="http://www.sgi.com/tech/stl/">SGI's STL Programmer's Guide</a> -
287Contains a useful <a
288href="http://www.sgi.com/tech/stl/stl_introduction.html">Introduction to the
289STL</a>.</li>
290
291<li><a href="http://www.research.att.com/%7Ebs/C++.html">Bjarne Stroustrup's C++
292Page</a></li>
293
Tanya Lattner79445ba2004-12-08 18:34:56 +0000[diff] [blame]294<li><a href="http://64.78.49.204/">
Reid Spencer096603a2004-05-26 08:41:35 +0000[diff] [blame]295Bruce Eckel's Thinking in C++, 2nd ed. Volume 2 Revision 4.0 (even better, get
296the book).</a></li>
297
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]298</ol>
299
300<p>You are also encouraged to take a look at the <a
301href="CodingStandards.html">LLVM Coding Standards</a> guide which focuses on how
302to write maintainable code more than where to put your curly braces.</p>
303
304</div>
305
306<!-- ======================================================================= -->
307<div class="doc_subsection">
308 <a name="stl">Other useful references</a>
309</div>
310
311<div class="doc_text">
312
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]313<ol>
Misha Brukmana0f71e42004-06-18 18:39:00 +0000[diff] [blame]314<li><a href="http://www.fortran-2000.com/ArnaudRecipes/sharedlib.html">Using
315static and shared libraries across platforms</a></li>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]316</ol>
317
318</div>
319
Chris Lattner9355b472002-09-06 02:50:58 +0000[diff] [blame]320<!-- *********************************************************************** -->
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]321<div class="doc_section">
322 <a name="apis">Important and useful LLVM APIs</a>
323</div>
324<!-- *********************************************************************** -->
325
326<div class="doc_text">
327
328<p>Here we highlight some LLVM APIs that are generally useful and good to
329know about when writing transformations.</p>
330
331</div>
332
333<!-- ======================================================================= -->
334<div class="doc_subsection">
Misha Brukman2c122ce2005-11-01 21:12:49 +0000[diff] [blame]335 <a name="isa">The <tt>isa&lt;&gt;</tt>, <tt>cast&lt;&gt;</tt> and
336 <tt>dyn_cast&lt;&gt;</tt> templates</a>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]337</div>
338
339<div class="doc_text">
340
341<p>The LLVM source-base makes extensive use of a custom form of RTTI.
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]342These templates have many similarities to the C++ <tt>dynamic_cast&lt;&gt;</tt>
343operator, but they don't have some drawbacks (primarily stemming from
344the fact that <tt>dynamic_cast&lt;&gt;</tt> only works on classes that
345have a v-table). Because they are used so often, you must know what they
346do and how they work. All of these templates are defined in the <a
Chris Lattner695b78b2005-04-26 22:56:16 +0000[diff] [blame]347 href="/doxygen/Casting_8h-source.html"><tt>llvm/Support/Casting.h</tt></a>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]348file (note that you very rarely have to include this file directly).</p>
349
350<dl>
351 <dt><tt>isa&lt;&gt;</tt>: </dt>
352
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]353 <dd><p>The <tt>isa&lt;&gt;</tt> operator works exactly like the Java
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]354 "<tt>instanceof</tt>" operator. It returns true or false depending on whether
355 a reference or pointer points to an instance of the specified class. This can
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]356 be very useful for constraint checking of various sorts (example below).</p>
357 </dd>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]358
359 <dt><tt>cast&lt;&gt;</tt>: </dt>
360
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]361 <dd><p>The <tt>cast&lt;&gt;</tt> operator is a "checked cast" operation. It
Chris Lattner28e6ff52008-06-20 05:03:17 +0000[diff] [blame]362 converts a pointer or reference from a base class to a derived class, causing
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]363 an assertion failure if it is not really an instance of the right type. This
364 should be used in cases where you have some information that makes you believe
365 that something is of the right type. An example of the <tt>isa&lt;&gt;</tt>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]366 and <tt>cast&lt;&gt;</tt> template is:</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]367
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]368<div class="doc_code">
369<pre>
370static bool isLoopInvariant(const <a href="#Value">Value</a> *V, const Loop *L) {
371 if (isa&lt;<a href="#Constant">Constant</a>&gt;(V) || isa&lt;<a href="#Argument">Argument</a>&gt;(V) || isa&lt;<a href="#GlobalValue">GlobalValue</a>&gt;(V))
372 return true;
Chris Lattner69bf8a92004-05-23 21:06:58 +0000[diff] [blame]373
Bill Wendling82e2eea2006-10-11 18:00:22 +0000[diff] [blame]374 // <i>Otherwise, it must be an instruction...</i>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]375 return !L-&gt;contains(cast&lt;<a href="#Instruction">Instruction</a>&gt;(V)-&gt;getParent());
376}
377</pre>
378</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]379
380 <p>Note that you should <b>not</b> use an <tt>isa&lt;&gt;</tt> test followed
381 by a <tt>cast&lt;&gt;</tt>, for that use the <tt>dyn_cast&lt;&gt;</tt>
382 operator.</p>
383
384 </dd>
385
386 <dt><tt>dyn_cast&lt;&gt;</tt>:</dt>
387
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]388 <dd><p>The <tt>dyn_cast&lt;&gt;</tt> operator is a "checking cast" operation.
389 It checks to see if the operand is of the specified type, and if so, returns a
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]390 pointer to it (this operator does not work with references). If the operand is
391 not of the correct type, a null pointer is returned. Thus, this works very
Misha Brukman2c122ce2005-11-01 21:12:49 +0000[diff] [blame]392 much like the <tt>dynamic_cast&lt;&gt;</tt> operator in C++, and should be
393 used in the same circumstances. Typically, the <tt>dyn_cast&lt;&gt;</tt>
394 operator is used in an <tt>if</tt> statement or some other flow control
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]395 statement like this:</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]396
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]397<div class="doc_code">
398<pre>
399if (<a href="#AllocationInst">AllocationInst</a> *AI = dyn_cast&lt;<a href="#AllocationInst">AllocationInst</a>&gt;(Val)) {
Bill Wendling82e2eea2006-10-11 18:00:22 +0000[diff] [blame]400 // <i>...</i>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]401}
402</pre>
403</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]404
Misha Brukman2c122ce2005-11-01 21:12:49 +0000[diff] [blame]405 <p>This form of the <tt>if</tt> statement effectively combines together a call
406 to <tt>isa&lt;&gt;</tt> and a call to <tt>cast&lt;&gt;</tt> into one
407 statement, which is very convenient.</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]408
Misha Brukman2c122ce2005-11-01 21:12:49 +0000[diff] [blame]409 <p>Note that the <tt>dyn_cast&lt;&gt;</tt> operator, like C++'s
410 <tt>dynamic_cast&lt;&gt;</tt> or Java's <tt>instanceof</tt> operator, can be
411 abused. In particular, you should not use big chained <tt>if/then/else</tt>
412 blocks to check for lots of different variants of classes. If you find
413 yourself wanting to do this, it is much cleaner and more efficient to use the
414 <tt>InstVisitor</tt> class to dispatch over the instruction type directly.</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]415
Misha Brukman2c122ce2005-11-01 21:12:49 +0000[diff] [blame]416 </dd>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]417
Misha Brukman2c122ce2005-11-01 21:12:49 +0000[diff] [blame]418 <dt><tt>cast_or_null&lt;&gt;</tt>: </dt>
419
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]420 <dd><p>The <tt>cast_or_null&lt;&gt;</tt> operator works just like the
Misha Brukman2c122ce2005-11-01 21:12:49 +0000[diff] [blame]421 <tt>cast&lt;&gt;</tt> operator, except that it allows for a null pointer as an
422 argument (which it then propagates). This can sometimes be useful, allowing
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]423 you to combine several null checks into one.</p></dd>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]424
Misha Brukman2c122ce2005-11-01 21:12:49 +0000[diff] [blame]425 <dt><tt>dyn_cast_or_null&lt;&gt;</tt>: </dt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]426
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]427 <dd><p>The <tt>dyn_cast_or_null&lt;&gt;</tt> operator works just like the
Misha Brukman2c122ce2005-11-01 21:12:49 +0000[diff] [blame]428 <tt>dyn_cast&lt;&gt;</tt> operator, except that it allows for a null pointer
429 as an argument (which it then propagates). This can sometimes be useful,
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]430 allowing you to combine several null checks into one.</p></dd>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]431
Misha Brukman2c122ce2005-11-01 21:12:49 +0000[diff] [blame]432</dl>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]433
434<p>These five templates can be used with any classes, whether they have a
435v-table or not. To add support for these templates, you simply need to add
436<tt>classof</tt> static methods to the class you are interested casting
437to. Describing this is currently outside the scope of this document, but there
438are lots of examples in the LLVM source base.</p>
439
440</div>
441
Daniel Dunbar6e0d1cb2009-07-25 04:41:11 +0000[diff] [blame]442
443<!-- ======================================================================= -->
444<div class="doc_subsection">
445 <a name="string_apis">Passing strings (the <tt>StringRef</tt>
446and <tt>Twine</tt> classes)</a>
447</div>
448
449<div class="doc_text">
450
451<p>Although LLVM generally does not do much string manipulation, we do have
Chris Lattner81187ae2009-07-25 07:16:59 +0000[diff] [blame]452several important APIs which take strings. Two important examples are the
Daniel Dunbar6e0d1cb2009-07-25 04:41:11 +0000[diff] [blame]453Value class -- which has names for instructions, functions, etc. -- and the
454StringMap class which is used extensively in LLVM and Clang.</p>
455
456<p>These are generic classes, and they need to be able to accept strings which
457may have embedded null characters. Therefore, they cannot simply take
Chris Lattner81187ae2009-07-25 07:16:59 +0000[diff] [blame]458a <tt>const char *</tt>, and taking a <tt>const std::string&amp;</tt> requires
Daniel Dunbar6e0d1cb2009-07-25 04:41:11 +0000[diff] [blame]459clients to perform a heap allocation which is usually unnecessary. Instead,
Benjamin Kramer38e59892010-07-14 22:38:02 +0000[diff] [blame]460many LLVM APIs use a <tt>StringRef</tt> or a <tt>const Twine&amp;</tt> for
461passing strings efficiently.</p>
Daniel Dunbar6e0d1cb2009-07-25 04:41:11 +0000[diff] [blame]462
463</div>
464
465<!-- _______________________________________________________________________ -->
466<div class="doc_subsubsection">
467 <a name="StringRef">The <tt>StringRef</tt> class</a>
468</div>
469
470<div class="doc_text">
471
472<p>The <tt>StringRef</tt> data type represents a reference to a constant string
473(a character array and a length) and supports the common operations available
474on <tt>std:string</tt>, but does not require heap allocation.</p>
475
Chris Lattner81187ae2009-07-25 07:16:59 +0000[diff] [blame]476<p>It can be implicitly constructed using a C style null-terminated string,
477an <tt>std::string</tt>, or explicitly with a character pointer and length.
Daniel Dunbar6e0d1cb2009-07-25 04:41:11 +0000[diff] [blame]478For example, the <tt>StringRef</tt> find function is declared as:</p>
Chris Lattner81187ae2009-07-25 07:16:59 +0000[diff] [blame]479
Benjamin Kramer38e59892010-07-14 22:38:02 +0000[diff] [blame]480<pre class="doc_code">
481 iterator find(StringRef Key);
482</pre>
Daniel Dunbar6e0d1cb2009-07-25 04:41:11 +0000[diff] [blame]483
484<p>and clients can call it using any one of:</p>
485
Benjamin Kramer38e59892010-07-14 22:38:02 +0000[diff] [blame]486<pre class="doc_code">
Daniel Dunbar6e0d1cb2009-07-25 04:41:11 +0000[diff] [blame]487 Map.find("foo"); <i>// Lookup "foo"</i>
488 Map.find(std::string("bar")); <i>// Lookup "bar"</i>
489 Map.find(StringRef("\0baz", 4)); <i>// Lookup "\0baz"</i>
490</pre>
Daniel Dunbar6e0d1cb2009-07-25 04:41:11 +0000[diff] [blame]491
492<p>Similarly, APIs which need to return a string may return a <tt>StringRef</tt>
493instance, which can be used directly or converted to an <tt>std::string</tt>
494using the <tt>str</tt> member function. See
495"<tt><a href="/doxygen/classllvm_1_1StringRef_8h-source.html">llvm/ADT/StringRef.h</a></tt>"
496for more information.</p>
497
498<p>You should rarely use the <tt>StringRef</tt> class directly, because it contains
499pointers to external memory it is not generally safe to store an instance of the
Benjamin Kramer38e59892010-07-14 22:38:02 +0000[diff] [blame]500class (unless you know that the external storage will not be freed). StringRef is
501small and pervasive enough in LLVM that it should always be passed by value.</p>
Daniel Dunbar6e0d1cb2009-07-25 04:41:11 +0000[diff] [blame]502
503</div>
504
505<!-- _______________________________________________________________________ -->
506<div class="doc_subsubsection">
507 <a name="Twine">The <tt>Twine</tt> class</a>
508</div>
509
510<div class="doc_text">
511
512<p>The <tt>Twine</tt> class is an efficient way for APIs to accept concatenated
513strings. For example, a common LLVM paradigm is to name one instruction based on
514the name of another instruction with a suffix, for example:</p>
515
516<div class="doc_code">
517<pre>
518 New = CmpInst::Create(<i>...</i>, SO->getName() + ".cmp");
519</pre>
520</div>
521
522<p>The <tt>Twine</tt> class is effectively a
523lightweight <a href="http://en.wikipedia.org/wiki/Rope_(computer_science)">rope</a>
524which points to temporary (stack allocated) objects. Twines can be implicitly
525constructed as the result of the plus operator applied to strings (i.e., a C
526strings, an <tt>std::string</tt>, or a <tt>StringRef</tt>). The twine delays the
Dan Gohmancf0c9bc2010-02-25 23:51:27 +0000[diff] [blame]527actual concatenation of strings until it is actually required, at which point
Daniel Dunbar6e0d1cb2009-07-25 04:41:11 +0000[diff] [blame]528it can be efficiently rendered directly into a character array. This avoids
529unnecessary heap allocation involved in constructing the temporary results of
530string concatenation. See
531"<tt><a href="/doxygen/classllvm_1_1Twine_8h-source.html">llvm/ADT/Twine.h</a></tt>"
Benjamin Kramere15192b2009-08-05 15:42:44 +0000[diff] [blame]532for more information.</p>
Daniel Dunbar6e0d1cb2009-07-25 04:41:11 +0000[diff] [blame]533
534<p>As with a <tt>StringRef</tt>, <tt>Twine</tt> objects point to external memory
535and should almost never be stored or mentioned directly. They are intended
536solely for use when defining a function which should be able to efficiently
537accept concatenated strings.</p>
538
539</div>
540
541
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]542<!-- ======================================================================= -->
543<div class="doc_subsection">
Misha Brukman2c122ce2005-11-01 21:12:49 +0000[diff] [blame]544 <a name="DEBUG">The <tt>DEBUG()</tt> macro and <tt>-debug</tt> option</a>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]545</div>
546
547<div class="doc_text">
548
549<p>Often when working on your pass you will put a bunch of debugging printouts
550and other code into your pass. After you get it working, you want to remove
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]551it, but you may need it again in the future (to work out new bugs that you run
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]552across).</p>
553
554<p> Naturally, because of this, you don't want to delete the debug printouts,
555but you don't want them to always be noisy. A standard compromise is to comment
556them out, allowing you to enable them if you need them in the future.</p>
557
Chris Lattner695b78b2005-04-26 22:56:16 +0000[diff] [blame]558<p>The "<tt><a href="/doxygen/Debug_8h-source.html">llvm/Support/Debug.h</a></tt>"
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]559file provides a macro named <tt>DEBUG()</tt> that is a much nicer solution to
560this problem. Basically, you can put arbitrary code into the argument of the
561<tt>DEBUG</tt> macro, and it is only executed if '<tt>opt</tt>' (or any other
562tool) is run with the '<tt>-debug</tt>' command line argument:</p>
563
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]564<div class="doc_code">
565<pre>
Daniel Dunbar06388ae2009-07-25 01:55:32 +0000[diff] [blame]566DEBUG(errs() &lt;&lt; "I am here!\n");
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]567</pre>
568</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]569
570<p>Then you can run your pass like this:</p>
571
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]572<div class="doc_code">
573<pre>
574$ opt &lt; a.bc &gt; /dev/null -mypass
Bill Wendling82e2eea2006-10-11 18:00:22 +0000[diff] [blame]575<i>&lt;no output&gt;</i>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]576$ opt &lt; a.bc &gt; /dev/null -mypass -debug
577I am here!
578</pre>
579</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]580
581<p>Using the <tt>DEBUG()</tt> macro instead of a home-brewed solution allows you
582to not have to create "yet another" command line option for the debug output for
583your pass. Note that <tt>DEBUG()</tt> macros are disabled for optimized builds,
584so they do not cause a performance impact at all (for the same reason, they
585should also not contain side-effects!).</p>
586
587<p>One additional nice thing about the <tt>DEBUG()</tt> macro is that you can
588enable or disable it directly in gdb. Just use "<tt>set DebugFlag=0</tt>" or
589"<tt>set DebugFlag=1</tt>" from the gdb if the program is running. If the
590program hasn't been started yet, you can always just run it with
591<tt>-debug</tt>.</p>
592
593</div>
594
595<!-- _______________________________________________________________________ -->
596<div class="doc_subsubsection">
Chris Lattnerc9151082005-04-26 22:57:07 +0000[diff] [blame]597 <a name="DEBUG_TYPE">Fine grained debug info with <tt>DEBUG_TYPE</tt> and
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]598 the <tt>-debug-only</tt> option</a>
599</div>
600
601<div class="doc_text">
602
603<p>Sometimes you may find yourself in a situation where enabling <tt>-debug</tt>
604just turns on <b>too much</b> information (such as when working on the code
605generator). If you want to enable debug information with more fine-grained
606control, you define the <tt>DEBUG_TYPE</tt> macro and the <tt>-debug</tt> only
607option as follows:</p>
608
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]609<div class="doc_code">
610<pre>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]611#undef DEBUG_TYPE
Daniel Dunbar06388ae2009-07-25 01:55:32 +0000[diff] [blame]612DEBUG(errs() &lt;&lt; "No debug type\n");
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]613#define DEBUG_TYPE "foo"
Daniel Dunbar06388ae2009-07-25 01:55:32 +0000[diff] [blame]614DEBUG(errs() &lt;&lt; "'foo' debug type\n");
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]615#undef DEBUG_TYPE
616#define DEBUG_TYPE "bar"
Daniel Dunbar06388ae2009-07-25 01:55:32 +0000[diff] [blame]617DEBUG(errs() &lt;&lt; "'bar' debug type\n"));
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]618#undef DEBUG_TYPE
619#define DEBUG_TYPE ""
Daniel Dunbar06388ae2009-07-25 01:55:32 +0000[diff] [blame]620DEBUG(errs() &lt;&lt; "No debug type (2)\n");
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]621</pre>
622</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]623
624<p>Then you can run your pass like this:</p>
625
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]626<div class="doc_code">
627<pre>
628$ opt &lt; a.bc &gt; /dev/null -mypass
Bill Wendling82e2eea2006-10-11 18:00:22 +0000[diff] [blame]629<i>&lt;no output&gt;</i>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]630$ opt &lt; a.bc &gt; /dev/null -mypass -debug
631No debug type
632'foo' debug type
633'bar' debug type
634No debug type (2)
635$ opt &lt; a.bc &gt; /dev/null -mypass -debug-only=foo
636'foo' debug type
637$ opt &lt; a.bc &gt; /dev/null -mypass -debug-only=bar
638'bar' debug type
639</pre>
640</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]641
642<p>Of course, in practice, you should only set <tt>DEBUG_TYPE</tt> at the top of
643a file, to specify the debug type for the entire module (if you do this before
Chris Lattner695b78b2005-04-26 22:56:16 +0000[diff] [blame]644you <tt>#include "llvm/Support/Debug.h"</tt>, you don't have to insert the ugly
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]645<tt>#undef</tt>'s). Also, you should use names more meaningful than "foo" and
646"bar", because there is no system in place to ensure that names do not
647conflict. If two different modules use the same string, they will all be turned
648on when the name is specified. This allows, for example, all debug information
649for instruction scheduling to be enabled with <tt>-debug-type=InstrSched</tt>,
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]650even if the source lives in multiple files.</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]651
Daniel Dunbarc3c92392009-08-07 23:48:59 +0000[diff] [blame]652<p>The <tt>DEBUG_WITH_TYPE</tt> macro is also available for situations where you
653would like to set <tt>DEBUG_TYPE</tt>, but only for one specific <tt>DEBUG</tt>
654statement. It takes an additional first parameter, which is the type to use. For
Benjamin Kramer8040cd32009-10-12 14:46:08 +0000[diff] [blame]655example, the preceding example could be written as:</p>
Daniel Dunbarc3c92392009-08-07 23:48:59 +0000[diff] [blame]656
657
658<div class="doc_code">
659<pre>
660DEBUG_WITH_TYPE("", errs() &lt;&lt; "No debug type\n");
661DEBUG_WITH_TYPE("foo", errs() &lt;&lt; "'foo' debug type\n");
662DEBUG_WITH_TYPE("bar", errs() &lt;&lt; "'bar' debug type\n"));
663DEBUG_WITH_TYPE("", errs() &lt;&lt; "No debug type (2)\n");
664</pre>
665</div>
666
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]667</div>
668
669<!-- ======================================================================= -->
670<div class="doc_subsection">
Chris Lattner0be6fdf2006-12-19 21:46:21 +0000[diff] [blame]671 <a name="Statistic">The <tt>Statistic</tt> class &amp; <tt>-stats</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]672 option</a>
673</div>
674
675<div class="doc_text">
676
677<p>The "<tt><a
Chris Lattner695b78b2005-04-26 22:56:16 +0000[diff] [blame]678href="/doxygen/Statistic_8h-source.html">llvm/ADT/Statistic.h</a></tt>" file
Chris Lattner0be6fdf2006-12-19 21:46:21 +0000[diff] [blame]679provides a class named <tt>Statistic</tt> that is used as a unified way to
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]680keep track of what the LLVM compiler is doing and how effective various
681optimizations are. It is useful to see what optimizations are contributing to
682making a particular program run faster.</p>
683
684<p>Often you may run your pass on some big program, and you're interested to see
685how many times it makes a certain transformation. Although you can do this with
686hand inspection, or some ad-hoc method, this is a real pain and not very useful
Chris Lattner0be6fdf2006-12-19 21:46:21 +0000[diff] [blame]687for big programs. Using the <tt>Statistic</tt> class makes it very easy to
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]688keep track of this information, and the calculated information is presented in a
689uniform manner with the rest of the passes being executed.</p>
690
691<p>There are many examples of <tt>Statistic</tt> uses, but the basics of using
692it are as follows:</p>
693
694<ol>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]695 <li><p>Define your statistic like this:</p>
696
697<div class="doc_code">
698<pre>
Chris Lattner0be6fdf2006-12-19 21:46:21 +0000[diff] [blame]699#define <a href="#DEBUG_TYPE">DEBUG_TYPE</a> "mypassname" <i>// This goes before any #includes.</i>
700STATISTIC(NumXForms, "The # of times I did stuff");
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]701</pre>
702</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]703
Chris Lattner0be6fdf2006-12-19 21:46:21 +0000[diff] [blame]704 <p>The <tt>STATISTIC</tt> macro defines a static variable, whose name is
705 specified by the first argument. The pass name is taken from the DEBUG_TYPE
706 macro, and the description is taken from the second argument. The variable
Reid Spencer06565dc2007-01-12 17:11:23 +0000[diff] [blame]707 defined ("NumXForms" in this case) acts like an unsigned integer.</p></li>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]708
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]709 <li><p>Whenever you make a transformation, bump the counter:</p>
710
711<div class="doc_code">
712<pre>
Bill Wendling82e2eea2006-10-11 18:00:22 +0000[diff] [blame]713++NumXForms; // <i>I did stuff!</i>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]714</pre>
715</div>
716
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]717 </li>
718 </ol>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]719
720 <p>That's all you have to do. To get '<tt>opt</tt>' to print out the
721 statistics gathered, use the '<tt>-stats</tt>' option:</p>
722
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]723<div class="doc_code">
724<pre>
725$ opt -stats -mypassname &lt; program.bc &gt; /dev/null
Bill Wendling82e2eea2006-10-11 18:00:22 +0000[diff] [blame]726<i>... statistics output ...</i>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]727</pre>
728</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]729
Reid Spencer6b6c73e2007-02-09 16:00:28 +0000[diff] [blame]730 <p> When running <tt>opt</tt> on a C file from the SPEC benchmark
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]731suite, it gives a report that looks like this:</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]732
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]733<div class="doc_code">
734<pre>
Gabor Greif04367bf2007-07-06 22:07:22 +0000[diff] [blame]735 7646 bitcodewriter - Number of normal instructions
736 725 bitcodewriter - Number of oversized instructions
737 129996 bitcodewriter - Number of bitcode bytes written
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]738 2817 raise - Number of insts DCEd or constprop'd
739 3213 raise - Number of cast-of-self removed
740 5046 raise - Number of expression trees converted
741 75 raise - Number of other getelementptr's formed
742 138 raise - Number of load/store peepholes
743 42 deadtypeelim - Number of unused typenames removed from symtab
744 392 funcresolve - Number of varargs functions resolved
745 27 globaldce - Number of global variables removed
746 2 adce - Number of basic blocks removed
747 134 cee - Number of branches revectored
748 49 cee - Number of setcc instruction eliminated
749 532 gcse - Number of loads removed
750 2919 gcse - Number of instructions removed
751 86 indvars - Number of canonical indvars added
752 87 indvars - Number of aux indvars removed
753 25 instcombine - Number of dead inst eliminate
754 434 instcombine - Number of insts combined
755 248 licm - Number of load insts hoisted
756 1298 licm - Number of insts hoisted to a loop pre-header
757 3 licm - Number of insts hoisted to multiple loop preds (bad, no loop pre-header)
758 75 mem2reg - Number of alloca's promoted
759 1444 cfgsimplify - Number of blocks simplified
760</pre>
761</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]762
763<p>Obviously, with so many optimizations, having a unified framework for this
764stuff is very nice. Making your pass fit well into the framework makes it more
765maintainable and useful.</p>
766
767</div>
768
Chris Lattnerf623a082005-10-17 01:36:23 +0000[diff] [blame]769<!-- ======================================================================= -->
770<div class="doc_subsection">
771 <a name="ViewGraph">Viewing graphs while debugging code</a>
772</div>
773
774<div class="doc_text">
775
776<p>Several of the important data structures in LLVM are graphs: for example
777CFGs made out of LLVM <a href="#BasicBlock">BasicBlock</a>s, CFGs made out of
778LLVM <a href="CodeGenerator.html#machinebasicblock">MachineBasicBlock</a>s, and
779<a href="CodeGenerator.html#selectiondag_intro">Instruction Selection
780DAGs</a>. In many cases, while debugging various parts of the compiler, it is
781nice to instantly visualize these graphs.</p>
782
783<p>LLVM provides several callbacks that are available in a debug build to do
784exactly that. If you call the <tt>Function::viewCFG()</tt> method, for example,
785the current LLVM tool will pop up a window containing the CFG for the function
786where each basic block is a node in the graph, and each node contains the
787instructions in the block. Similarly, there also exists
788<tt>Function::viewCFGOnly()</tt> (does not include the instructions), the
789<tt>MachineFunction::viewCFG()</tt> and <tt>MachineFunction::viewCFGOnly()</tt>,
790and the <tt>SelectionDAG::viewGraph()</tt> methods. Within GDB, for example,
Jim Laskey543a0ee2006-10-02 12:28:07 +0000[diff] [blame]791you can usually use something like <tt>call DAG.viewGraph()</tt> to pop
Chris Lattnerf623a082005-10-17 01:36:23 +0000[diff] [blame]792up a window. Alternatively, you can sprinkle calls to these functions in your
793code in places you want to debug.</p>
794
795<p>Getting this to work requires a small amount of configuration. On Unix
796systems with X11, install the <a href="http://www.graphviz.org">graphviz</a>
797toolkit, and make sure 'dot' and 'gv' are in your path. If you are running on
798Mac OS/X, download and install the Mac OS/X <a
799href="http://www.pixelglow.com/graphviz/">Graphviz program</a>, and add
Reid Spencer128a7a72007-02-03 21:06:43 +0000[diff] [blame]800<tt>/Applications/Graphviz.app/Contents/MacOS/</tt> (or wherever you install
Chris Lattnerf623a082005-10-17 01:36:23 +0000[diff] [blame]801it) to your path. Once in your system and path are set up, rerun the LLVM
802configure script and rebuild LLVM to enable this functionality.</p>
803
Jim Laskey543a0ee2006-10-02 12:28:07 +0000[diff] [blame]804<p><tt>SelectionDAG</tt> has been extended to make it easier to locate
805<i>interesting</i> nodes in large complex graphs. From gdb, if you
806<tt>call DAG.setGraphColor(<i>node</i>, "<i>color</i>")</tt>, then the
Reid Spencer128a7a72007-02-03 21:06:43 +0000[diff] [blame]807next <tt>call DAG.viewGraph()</tt> would highlight the node in the
Jim Laskey543a0ee2006-10-02 12:28:07 +0000[diff] [blame]808specified color (choices of colors can be found at <a
Chris Lattner302da1e2007-02-03 03:05:57 +0000[diff] [blame]809href="http://www.graphviz.org/doc/info/colors.html">colors</a>.) More
Jim Laskey543a0ee2006-10-02 12:28:07 +0000[diff] [blame]810complex node attributes can be provided with <tt>call
811DAG.setGraphAttrs(<i>node</i>, "<i>attributes</i>")</tt> (choices can be
812found at <a href="http://www.graphviz.org/doc/info/attrs.html">Graph
813Attributes</a>.) If you want to restart and clear all the current graph
814attributes, then you can <tt>call DAG.clearGraphAttrs()</tt>. </p>
815
Chris Lattnerf623a082005-10-17 01:36:23 +0000[diff] [blame]816</div>
817
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]818<!-- *********************************************************************** -->
819<div class="doc_section">
820 <a name="datastructure">Picking the Right Data Structure for a Task</a>
821</div>
822<!-- *********************************************************************** -->
823
824<div class="doc_text">
825
Reid Spencer128a7a72007-02-03 21:06:43 +0000[diff] [blame]826<p>LLVM has a plethora of data structures in the <tt>llvm/ADT/</tt> directory,
827 and we commonly use STL data structures. This section describes the trade-offs
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]828 you should consider when you pick one.</p>
829
830<p>
831The first step is a choose your own adventure: do you want a sequential
832container, a set-like container, or a map-like container? The most important
833thing when choosing a container is the algorithmic properties of how you plan to
834access the container. Based on that, you should use:</p>
835
836<ul>
Reid Spencer128a7a72007-02-03 21:06:43 +0000[diff] [blame]837<li>a <a href="#ds_map">map-like</a> container if you need efficient look-up
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]838 of an value based on another value. Map-like containers also support
839 efficient queries for containment (whether a key is in the map). Map-like
840 containers generally do not support efficient reverse mapping (values to
841 keys). If you need that, use two maps. Some map-like containers also
842 support efficient iteration through the keys in sorted order. Map-like
843 containers are the most expensive sort, only use them if you need one of
844 these capabilities.</li>
845
846<li>a <a href="#ds_set">set-like</a> container if you need to put a bunch of
847 stuff into a container that automatically eliminates duplicates. Some
848 set-like containers support efficient iteration through the elements in
849 sorted order. Set-like containers are more expensive than sequential
850 containers.
851</li>
852
853<li>a <a href="#ds_sequential">sequential</a> container provides
854 the most efficient way to add elements and keeps track of the order they are
855 added to the collection. They permit duplicates and support efficient
Reid Spencer128a7a72007-02-03 21:06:43 +0000[diff] [blame]856 iteration, but do not support efficient look-up based on a key.
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]857</li>
858
Chris Lattnerdced9fb2009-07-25 07:22:20 +0000[diff] [blame]859<li>a <a href="#ds_string">string</a> container is a specialized sequential
860 container or reference structure that is used for character or byte
861 arrays.</li>
862
Daniel Berlin1939ace2007-09-24 17:52:25 +0000[diff] [blame]863<li>a <a href="#ds_bit">bit</a> container provides an efficient way to store and
864 perform set operations on sets of numeric id's, while automatically
865 eliminating duplicates. Bit containers require a maximum of 1 bit for each
866 identifier you want to store.
867</li>
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]868</ul>
869
870<p>
Reid Spencer128a7a72007-02-03 21:06:43 +0000[diff] [blame]871Once the proper category of container is determined, you can fine tune the
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]872memory use, constant factors, and cache behaviors of access by intelligently
Reid Spencer128a7a72007-02-03 21:06:43 +0000[diff] [blame]873picking a member of the category. Note that constant factors and cache behavior
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]874can be a big deal. If you have a vector that usually only contains a few
875elements (but could contain many), for example, it's much better to use
876<a href="#dss_smallvector">SmallVector</a> than <a href="#dss_vector">vector</a>
877. Doing so avoids (relatively) expensive malloc/free calls, which dwarf the
878cost of adding the elements to the container. </p>
879
880</div>
881
882<!-- ======================================================================= -->
883<div class="doc_subsection">
884 <a name="ds_sequential">Sequential Containers (std::vector, std::list, etc)</a>
885</div>
886
887<div class="doc_text">
888There are a variety of sequential containers available for you, based on your
889needs. Pick the first in this section that will do what you want.
890</div>
891
892<!-- _______________________________________________________________________ -->
893<div class="doc_subsubsection">
894 <a name="dss_fixedarrays">Fixed Size Arrays</a>
895</div>
896
897<div class="doc_text">
898<p>Fixed size arrays are very simple and very fast. They are good if you know
899exactly how many elements you have, or you have a (low) upper bound on how many
900you have.</p>
901</div>
902
903<!-- _______________________________________________________________________ -->
904<div class="doc_subsubsection">
905 <a name="dss_heaparrays">Heap Allocated Arrays</a>
906</div>
907
908<div class="doc_text">
909<p>Heap allocated arrays (new[] + delete[]) are also simple. They are good if
910the number of elements is variable, if you know how many elements you will need
911before the array is allocated, and if the array is usually large (if not,
912consider a <a href="#dss_smallvector">SmallVector</a>). The cost of a heap
913allocated array is the cost of the new/delete (aka malloc/free). Also note that
914if you are allocating an array of a type with a constructor, the constructor and
Reid Spencer128a7a72007-02-03 21:06:43 +0000[diff] [blame]915destructors will be run for every element in the array (re-sizable vectors only
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]916construct those elements actually used).</p>
917</div>
918
919<!-- _______________________________________________________________________ -->
920<div class="doc_subsubsection">
921 <a name="dss_smallvector">"llvm/ADT/SmallVector.h"</a>
922</div>
923
924<div class="doc_text">
925<p><tt>SmallVector&lt;Type, N&gt;</tt> is a simple class that looks and smells
926just like <tt>vector&lt;Type&gt;</tt>:
927it supports efficient iteration, lays out elements in memory order (so you can
928do pointer arithmetic between elements), supports efficient push_back/pop_back
929operations, supports efficient random access to its elements, etc.</p>
930
931<p>The advantage of SmallVector is that it allocates space for
932some number of elements (N) <b>in the object itself</b>. Because of this, if
933the SmallVector is dynamically smaller than N, no malloc is performed. This can
934be a big win in cases where the malloc/free call is far more expensive than the
935code that fiddles around with the elements.</p>
936
937<p>This is good for vectors that are "usually small" (e.g. the number of
938predecessors/successors of a block is usually less than 8). On the other hand,
939this makes the size of the SmallVector itself large, so you don't want to
940allocate lots of them (doing so will waste a lot of space). As such,
941SmallVectors are most useful when on the stack.</p>
942
943<p>SmallVector also provides a nice portable and efficient replacement for
944<tt>alloca</tt>.</p>
945
946</div>
947
948<!-- _______________________________________________________________________ -->
949<div class="doc_subsubsection">
950 <a name="dss_vector">&lt;vector&gt;</a>
951</div>
952
953<div class="doc_text">
954<p>
955std::vector is well loved and respected. It is useful when SmallVector isn't:
956when the size of the vector is often large (thus the small optimization will
957rarely be a benefit) or if you will be allocating many instances of the vector
958itself (which would waste space for elements that aren't in the container).
959vector is also useful when interfacing with code that expects vectors :).
960</p>
Chris Lattner32d84762007-02-05 06:30:51 +0000[diff] [blame]961
962<p>One worthwhile note about std::vector: avoid code like this:</p>
963
964<div class="doc_code">
965<pre>
966for ( ... ) {
Chris Lattner9bb3dbb2007-03-28 18:27:57 +0000[diff] [blame]967 std::vector&lt;foo&gt; V;
Chris Lattner32d84762007-02-05 06:30:51 +0000[diff] [blame]968 use V;
969}
970</pre>
971</div>
972
973<p>Instead, write this as:</p>
974
975<div class="doc_code">
976<pre>
Chris Lattner9bb3dbb2007-03-28 18:27:57 +0000[diff] [blame]977std::vector&lt;foo&gt; V;
Chris Lattner32d84762007-02-05 06:30:51 +0000[diff] [blame]978for ( ... ) {
979 use V;
980 V.clear();
981}
982</pre>
983</div>
984
985<p>Doing so will save (at least) one heap allocation and free per iteration of
986the loop.</p>
987
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]988</div>
989
990<!-- _______________________________________________________________________ -->
991<div class="doc_subsubsection">
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]992 <a name="dss_deque">&lt;deque&gt;</a>
993</div>
994
995<div class="doc_text">
996<p>std::deque is, in some senses, a generalized version of std::vector. Like
997std::vector, it provides constant time random access and other similar
998properties, but it also provides efficient access to the front of the list. It
999does not guarantee continuity of elements within memory.</p>
1000
1001<p>In exchange for this extra flexibility, std::deque has significantly higher
1002constant factor costs than std::vector. If possible, use std::vector or
1003something cheaper.</p>
1004</div>
1005
1006<!-- _______________________________________________________________________ -->
1007<div class="doc_subsubsection">
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]1008 <a name="dss_list">&lt;list&gt;</a>
1009</div>
1010
1011<div class="doc_text">
1012<p>std::list is an extremely inefficient class that is rarely useful.
1013It performs a heap allocation for every element inserted into it, thus having an
1014extremely high constant factor, particularly for small data types. std::list
1015also only supports bidirectional iteration, not random access iteration.</p>
1016
1017<p>In exchange for this high cost, std::list supports efficient access to both
1018ends of the list (like std::deque, but unlike std::vector or SmallVector). In
1019addition, the iterator invalidation characteristics of std::list are stronger
1020than that of a vector class: inserting or removing an element into the list does
1021not invalidate iterator or pointers to other elements in the list.</p>
1022</div>
1023
1024<!-- _______________________________________________________________________ -->
1025<div class="doc_subsubsection">
Gabor Greif3899e492009-02-27 11:37:41 +0000[diff] [blame]1026 <a name="dss_ilist">llvm/ADT/ilist.h</a>
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]1027</div>
1028
1029<div class="doc_text">
1030<p><tt>ilist&lt;T&gt;</tt> implements an 'intrusive' doubly-linked list. It is
1031intrusive, because it requires the element to store and provide access to the
1032prev/next pointers for the list.</p>
1033
Gabor Greif2946d1c2009-02-27 12:02:19 +0000[diff] [blame]1034<p><tt>ilist</tt> has the same drawbacks as <tt>std::list</tt>, and additionally
1035requires an <tt>ilist_traits</tt> implementation for the element type, but it
1036provides some novel characteristics. In particular, it can efficiently store
1037polymorphic objects, the traits class is informed when an element is inserted or
Gabor Greif0cbcabe2009-03-12 09:47:03 +0000[diff] [blame]1038removed from the list, and <tt>ilist</tt>s are guaranteed to support a
1039constant-time splice operation.</p>
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]1040
Gabor Greif0cbcabe2009-03-12 09:47:03 +0000[diff] [blame]1041<p>These properties are exactly what we want for things like
1042<tt>Instruction</tt>s and basic blocks, which is why these are implemented with
1043<tt>ilist</tt>s.</p>
Gabor Greif3899e492009-02-27 11:37:41 +0000[diff] [blame]1044
1045Related classes of interest are explained in the following subsections:
1046 <ul>
Gabor Greif01862502009-02-27 13:28:07 +0000[diff] [blame]1047 <li><a href="#dss_ilist_traits">ilist_traits</a></li>
Gabor Greif2946d1c2009-02-27 12:02:19 +0000[diff] [blame]1048 <li><a href="#dss_iplist">iplist</a></li>
Gabor Greif3899e492009-02-27 11:37:41 +0000[diff] [blame]1049 <li><a href="#dss_ilist_node">llvm/ADT/ilist_node.h</a></li>
Gabor Greif6a65f422009-03-12 10:30:31 +0000[diff] [blame]1050 <li><a href="#dss_ilist_sentinel">Sentinels</a></li>
Gabor Greif3899e492009-02-27 11:37:41 +0000[diff] [blame]1051 </ul>
1052</div>
1053
1054<!-- _______________________________________________________________________ -->
1055<div class="doc_subsubsection">
Gabor Greif01862502009-02-27 13:28:07 +0000[diff] [blame]1056 <a name="dss_ilist_traits">ilist_traits</a>
1057</div>
1058
1059<div class="doc_text">
1060<p><tt>ilist_traits&lt;T&gt;</tt> is <tt>ilist&lt;T&gt;</tt>'s customization
1061mechanism. <tt>iplist&lt;T&gt;</tt> (and consequently <tt>ilist&lt;T&gt;</tt>)
1062publicly derive from this traits class.</p>
1063</div>
1064
1065<!-- _______________________________________________________________________ -->
1066<div class="doc_subsubsection">
Gabor Greif2946d1c2009-02-27 12:02:19 +0000[diff] [blame]1067 <a name="dss_iplist">iplist</a>
1068</div>
1069
1070<div class="doc_text">
1071<p><tt>iplist&lt;T&gt;</tt> is <tt>ilist&lt;T&gt;</tt>'s base and as such
Gabor Greif0cbcabe2009-03-12 09:47:03 +0000[diff] [blame]1072supports a slightly narrower interface. Notably, inserters from
1073<tt>T&amp;</tt> are absent.</p>
Gabor Greif01862502009-02-27 13:28:07 +0000[diff] [blame]1074
1075<p><tt>ilist_traits&lt;T&gt;</tt> is a public base of this class and can be
1076used for a wide variety of customizations.</p>
Gabor Greif2946d1c2009-02-27 12:02:19 +0000[diff] [blame]1077</div>
1078
1079<!-- _______________________________________________________________________ -->
1080<div class="doc_subsubsection">
Gabor Greif3899e492009-02-27 11:37:41 +0000[diff] [blame]1081 <a name="dss_ilist_node">llvm/ADT/ilist_node.h</a>
1082</div>
1083
1084<div class="doc_text">
1085<p><tt>ilist_node&lt;T&gt;</tt> implements a the forward and backward links
1086that are expected by the <tt>ilist&lt;T&gt;</tt> (and analogous containers)
1087in the default manner.</p>
1088
1089<p><tt>ilist_node&lt;T&gt;</tt>s are meant to be embedded in the node type
Gabor Greif0cbcabe2009-03-12 09:47:03 +0000[diff] [blame]1090<tt>T</tt>, usually <tt>T</tt> publicly derives from
1091<tt>ilist_node&lt;T&gt;</tt>.</p>
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]1092</div>
1093
1094<!-- _______________________________________________________________________ -->
1095<div class="doc_subsubsection">
Gabor Greif6a65f422009-03-12 10:30:31 +0000[diff] [blame]1096 <a name="dss_ilist_sentinel">Sentinels</a>
1097</div>
1098
1099<div class="doc_text">
Dan Gohmancf0c9bc2010-02-25 23:51:27 +0000[diff] [blame]1100<p><tt>ilist</tt>s have another specialty that must be considered. To be a good
Gabor Greif6a65f422009-03-12 10:30:31 +0000[diff] [blame]1101citizen in the C++ ecosystem, it needs to support the standard container
1102operations, such as <tt>begin</tt> and <tt>end</tt> iterators, etc. Also, the
1103<tt>operator--</tt> must work correctly on the <tt>end</tt> iterator in the
1104case of non-empty <tt>ilist</tt>s.</p>
1105
1106<p>The only sensible solution to this problem is to allocate a so-called
1107<i>sentinel</i> along with the intrusive list, which serves as the <tt>end</tt>
1108iterator, providing the back-link to the last element. However conforming to the
1109C++ convention it is illegal to <tt>operator++</tt> beyond the sentinel and it
1110also must not be dereferenced.</p>
1111
1112<p>These constraints allow for some implementation freedom to the <tt>ilist</tt>
1113how to allocate and store the sentinel. The corresponding policy is dictated
1114by <tt>ilist_traits&lt;T&gt;</tt>. By default a <tt>T</tt> gets heap-allocated
1115whenever the need for a sentinel arises.</p>
1116
1117<p>While the default policy is sufficient in most cases, it may break down when
1118<tt>T</tt> does not provide a default constructor. Also, in the case of many
1119instances of <tt>ilist</tt>s, the memory overhead of the associated sentinels
1120is wasted. To alleviate the situation with numerous and voluminous
1121<tt>T</tt>-sentinels, sometimes a trick is employed, leading to <i>ghostly
1122sentinels</i>.</p>
1123
1124<p>Ghostly sentinels are obtained by specially-crafted <tt>ilist_traits&lt;T&gt;</tt>
1125which superpose the sentinel with the <tt>ilist</tt> instance in memory. Pointer
1126arithmetic is used to obtain the sentinel, which is relative to the
1127<tt>ilist</tt>'s <tt>this</tt> pointer. The <tt>ilist</tt> is augmented by an
1128extra pointer, which serves as the back-link of the sentinel. This is the only
1129field in the ghostly sentinel which can be legally accessed.</p>
1130</div>
1131
1132<!-- _______________________________________________________________________ -->
1133<div class="doc_subsubsection">
Chris Lattnerc5722432007-02-03 19:49:31 +0000[diff] [blame]1134 <a name="dss_other">Other Sequential Container options</a>
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]1135</div>
1136
1137<div class="doc_text">
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1138<p>Other STL containers are available, such as std::string.</p>
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]1139
1140<p>There are also various STL adapter classes such as std::queue,
1141std::priority_queue, std::stack, etc. These provide simplified access to an
1142underlying container but don't affect the cost of the container itself.</p>
1143
1144</div>
1145
1146
1147<!-- ======================================================================= -->
1148<div class="doc_subsection">
1149 <a name="ds_set">Set-Like Containers (std::set, SmallSet, SetVector, etc)</a>
1150</div>
1151
1152<div class="doc_text">
1153
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1154<p>Set-like containers are useful when you need to canonicalize multiple values
1155into a single representation. There are several different choices for how to do
1156this, providing various trade-offs.</p>
1157
1158</div>
1159
1160
1161<!-- _______________________________________________________________________ -->
1162<div class="doc_subsubsection">
1163 <a name="dss_sortedvectorset">A sorted 'vector'</a>
1164</div>
1165
1166<div class="doc_text">
1167
Chris Lattner3b23a8c2007-02-03 08:10:45 +0000[diff] [blame]1168<p>If you intend to insert a lot of elements, then do a lot of queries, a
1169great approach is to use a vector (or other sequential container) with
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1170std::sort+std::unique to remove duplicates. This approach works really well if
Chris Lattner3b23a8c2007-02-03 08:10:45 +0000[diff] [blame]1171your usage pattern has these two distinct phases (insert then query), and can be
1172coupled with a good choice of <a href="#ds_sequential">sequential container</a>.
1173</p>
1174
1175<p>
1176This combination provides the several nice properties: the result data is
1177contiguous in memory (good for cache locality), has few allocations, is easy to
1178address (iterators in the final vector are just indices or pointers), and can be
1179efficiently queried with a standard binary or radix search.</p>
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1180
1181</div>
1182
1183<!-- _______________________________________________________________________ -->
1184<div class="doc_subsubsection">
1185 <a name="dss_smallset">"llvm/ADT/SmallSet.h"</a>
1186</div>
1187
1188<div class="doc_text">
1189
Reid Spencer128a7a72007-02-03 21:06:43 +0000[diff] [blame]1190<p>If you have a set-like data structure that is usually small and whose elements
Chris Lattner4ddfac12007-02-03 07:59:51 +0000[diff] [blame]1191are reasonably small, a <tt>SmallSet&lt;Type, N&gt;</tt> is a good choice. This set
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1192has space for N elements in place (thus, if the set is dynamically smaller than
Chris Lattner14868db2007-02-03 08:20:15 +0000[diff] [blame]1193N, no malloc traffic is required) and accesses them with a simple linear search.
1194When the set grows beyond 'N' elements, it allocates a more expensive representation that
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1195guarantees efficient access (for most types, it falls back to std::set, but for
Chris Lattner14868db2007-02-03 08:20:15 +0000[diff] [blame]1196pointers it uses something far better, <a
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1197href="#dss_smallptrset">SmallPtrSet</a>).</p>
1198
1199<p>The magic of this class is that it handles small sets extremely efficiently,
1200but gracefully handles extremely large sets without loss of efficiency. The
1201drawback is that the interface is quite small: it supports insertion, queries
1202and erasing, but does not support iteration.</p>
1203
1204</div>
1205
1206<!-- _______________________________________________________________________ -->
1207<div class="doc_subsubsection">
1208 <a name="dss_smallptrset">"llvm/ADT/SmallPtrSet.h"</a>
1209</div>
1210
1211<div class="doc_text">
1212
Gabor Greif4de73682010-03-26 19:30:47 +0000[diff] [blame]1213<p>SmallPtrSet has all the advantages of <tt>SmallSet</tt> (and a <tt>SmallSet</tt> of pointers is
1214transparently implemented with a <tt>SmallPtrSet</tt>), but also supports iterators. If
Chris Lattner14868db2007-02-03 08:20:15 +0000[diff] [blame]1215more than 'N' insertions are performed, a single quadratically
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1216probed hash table is allocated and grows as needed, providing extremely
1217efficient access (constant time insertion/deleting/queries with low constant
1218factors) and is very stingy with malloc traffic.</p>
1219
Gabor Greif4de73682010-03-26 19:30:47 +0000[diff] [blame]1220<p>Note that, unlike <tt>std::set</tt>, the iterators of <tt>SmallPtrSet</tt> are invalidated
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1221whenever an insertion occurs. Also, the values visited by the iterators are not
1222visited in sorted order.</p>
1223
1224</div>
1225
1226<!-- _______________________________________________________________________ -->
1227<div class="doc_subsubsection">
Chris Lattnerc28476f2007-09-30 00:58:59 +0000[diff] [blame]1228 <a name="dss_denseset">"llvm/ADT/DenseSet.h"</a>
1229</div>
1230
1231<div class="doc_text">
1232
1233<p>
1234DenseSet is a simple quadratically probed hash table. It excels at supporting
1235small values: it uses a single allocation to hold all of the pairs that
1236are currently inserted in the set. DenseSet is a great way to unique small
1237values that are not simple pointers (use <a
1238href="#dss_smallptrset">SmallPtrSet</a> for pointers). Note that DenseSet has
1239the same requirements for the value type that <a
1240href="#dss_densemap">DenseMap</a> has.
1241</p>
1242
1243</div>
1244
1245<!-- _______________________________________________________________________ -->
1246<div class="doc_subsubsection">
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1247 <a name="dss_FoldingSet">"llvm/ADT/FoldingSet.h"</a>
1248</div>
1249
1250<div class="doc_text">
1251
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]1252<p>
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1253FoldingSet is an aggregate class that is really good at uniquing
1254expensive-to-create or polymorphic objects. It is a combination of a chained
1255hash table with intrusive links (uniqued objects are required to inherit from
Chris Lattner14868db2007-02-03 08:20:15 +0000[diff] [blame]1256FoldingSetNode) that uses <a href="#dss_smallvector">SmallVector</a> as part of
1257its ID process.</p>
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1258
Chris Lattner14868db2007-02-03 08:20:15 +0000[diff] [blame]1259<p>Consider a case where you want to implement a "getOrCreateFoo" method for
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1260a complex object (for example, a node in the code generator). The client has a
1261description of *what* it wants to generate (it knows the opcode and all the
1262operands), but we don't want to 'new' a node, then try inserting it into a set
Chris Lattner14868db2007-02-03 08:20:15 +0000[diff] [blame]1263only to find out it already exists, at which point we would have to delete it
1264and return the node that already exists.
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]1265</p>
1266
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1267<p>To support this style of client, FoldingSet perform a query with a
1268FoldingSetNodeID (which wraps SmallVector) that can be used to describe the
1269element that we want to query for. The query either returns the element
1270matching the ID or it returns an opaque ID that indicates where insertion should
Chris Lattner14868db2007-02-03 08:20:15 +0000[diff] [blame]1271take place. Construction of the ID usually does not require heap traffic.</p>
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1272
1273<p>Because FoldingSet uses intrusive links, it can support polymorphic objects
1274in the set (for example, you can have SDNode instances mixed with LoadSDNodes).
1275Because the elements are individually allocated, pointers to the elements are
1276stable: inserting or removing elements does not invalidate any pointers to other
1277elements.
1278</p>
1279
1280</div>
1281
1282<!-- _______________________________________________________________________ -->
1283<div class="doc_subsubsection">
1284 <a name="dss_set">&lt;set&gt;</a>
1285</div>
1286
1287<div class="doc_text">
1288
Chris Lattnerc5722432007-02-03 19:49:31 +0000[diff] [blame]1289<p><tt>std::set</tt> is a reasonable all-around set class, which is decent at
1290many things but great at nothing. std::set allocates memory for each element
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1291inserted (thus it is very malloc intensive) and typically stores three pointers
Chris Lattner14868db2007-02-03 08:20:15 +0000[diff] [blame]1292per element in the set (thus adding a large amount of per-element space
1293overhead). It offers guaranteed log(n) performance, which is not particularly
Chris Lattnerc5722432007-02-03 19:49:31 +0000[diff] [blame]1294fast from a complexity standpoint (particularly if the elements of the set are
1295expensive to compare, like strings), and has extremely high constant factors for
1296lookup, insertion and removal.</p>
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1297
Chris Lattner14868db2007-02-03 08:20:15 +0000[diff] [blame]1298<p>The advantages of std::set are that its iterators are stable (deleting or
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1299inserting an element from the set does not affect iterators or pointers to other
1300elements) and that iteration over the set is guaranteed to be in sorted order.
1301If the elements in the set are large, then the relative overhead of the pointers
1302and malloc traffic is not a big deal, but if the elements of the set are small,
1303std::set is almost never a good choice.</p>
1304
1305</div>
1306
1307<!-- _______________________________________________________________________ -->
1308<div class="doc_subsubsection">
1309 <a name="dss_setvector">"llvm/ADT/SetVector.h"</a>
1310</div>
1311
1312<div class="doc_text">
Chris Lattneredca3c52007-02-04 00:00:26 +0000[diff] [blame]1313<p>LLVM's SetVector&lt;Type&gt; is an adapter class that combines your choice of
1314a set-like container along with a <a href="#ds_sequential">Sequential
1315Container</a>. The important property
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1316that this provides is efficient insertion with uniquing (duplicate elements are
1317ignored) with iteration support. It implements this by inserting elements into
1318both a set-like container and the sequential container, using the set-like
1319container for uniquing and the sequential container for iteration.
1320</p>
1321
1322<p>The difference between SetVector and other sets is that the order of
1323iteration is guaranteed to match the order of insertion into the SetVector.
1324This property is really important for things like sets of pointers. Because
1325pointer values are non-deterministic (e.g. vary across runs of the program on
Chris Lattneredca3c52007-02-04 00:00:26 +0000[diff] [blame]1326different machines), iterating over the pointers in the set will
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1327not be in a well-defined order.</p>
1328
1329<p>
1330The drawback of SetVector is that it requires twice as much space as a normal
1331set and has the sum of constant factors from the set-like container and the
1332sequential container that it uses. Use it *only* if you need to iterate over
1333the elements in a deterministic order. SetVector is also expensive to delete
Chris Lattneredca3c52007-02-04 00:00:26 +0000[diff] [blame]1334elements out of (linear time), unless you use it's "pop_back" method, which is
1335faster.
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1336</p>
1337
Chris Lattneredca3c52007-02-04 00:00:26 +0000[diff] [blame]1338<p>SetVector is an adapter class that defaults to using std::vector and std::set
1339for the underlying containers, so it is quite expensive. However,
1340<tt>"llvm/ADT/SetVector.h"</tt> also provides a SmallSetVector class, which
1341defaults to using a SmallVector and SmallSet of a specified size. If you use
1342this, and if your sets are dynamically smaller than N, you will save a lot of
1343heap traffic.</p>
1344
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1345</div>
1346
1347<!-- _______________________________________________________________________ -->
1348<div class="doc_subsubsection">
Chris Lattnerc5722432007-02-03 19:49:31 +0000[diff] [blame]1349 <a name="dss_uniquevector">"llvm/ADT/UniqueVector.h"</a>
1350</div>
1351
1352<div class="doc_text">
1353
1354<p>
1355UniqueVector is similar to <a href="#dss_setvector">SetVector</a>, but it
1356retains a unique ID for each element inserted into the set. It internally
1357contains a map and a vector, and it assigns a unique ID for each value inserted
1358into the set.</p>
1359
1360<p>UniqueVector is very expensive: its cost is the sum of the cost of
1361maintaining both the map and vector, it has high complexity, high constant
1362factors, and produces a lot of malloc traffic. It should be avoided.</p>
1363
1364</div>
1365
1366
1367<!-- _______________________________________________________________________ -->
1368<div class="doc_subsubsection">
1369 <a name="dss_otherset">Other Set-Like Container Options</a>
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1370</div>
1371
1372<div class="doc_text">
1373
1374<p>
1375The STL provides several other options, such as std::multiset and the various
Chris Lattnerf1a30822009-03-09 05:20:45 +0000[diff] [blame]1376"hash_set" like containers (whether from C++ TR1 or from the SGI library). We
1377never use hash_set and unordered_set because they are generally very expensive
1378(each insertion requires a malloc) and very non-portable.
1379</p>
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1380
1381<p>std::multiset is useful if you're not interested in elimination of
Chris Lattner14868db2007-02-03 08:20:15 +0000[diff] [blame]1382duplicates, but has all the drawbacks of std::set. A sorted vector (where you
1383don't delete duplicate entries) or some other approach is almost always
1384better.</p>
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1385
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]1386</div>
1387
1388<!-- ======================================================================= -->
1389<div class="doc_subsection">
1390 <a name="ds_map">Map-Like Containers (std::map, DenseMap, etc)</a>
1391</div>
1392
1393<div class="doc_text">
Chris Lattnerc5722432007-02-03 19:49:31 +0000[diff] [blame]1394Map-like containers are useful when you want to associate data to a key. As
1395usual, there are a lot of different ways to do this. :)
1396</div>
1397
1398<!-- _______________________________________________________________________ -->
1399<div class="doc_subsubsection">
1400 <a name="dss_sortedvectormap">A sorted 'vector'</a>
1401</div>
1402
1403<div class="doc_text">
1404
1405<p>
1406If your usage pattern follows a strict insert-then-query approach, you can
1407trivially use the same approach as <a href="#dss_sortedvectorset">sorted vectors
1408for set-like containers</a>. The only difference is that your query function
1409(which uses std::lower_bound to get efficient log(n) lookup) should only compare
1410the key, not both the key and value. This yields the same advantages as sorted
1411vectors for sets.
1412</p>
1413</div>
1414
1415<!-- _______________________________________________________________________ -->
1416<div class="doc_subsubsection">
Chris Lattner796f9fa2007-02-08 19:14:21 +0000[diff] [blame]1417 <a name="dss_stringmap">"llvm/ADT/StringMap.h"</a>
Chris Lattnerc5722432007-02-03 19:49:31 +0000[diff] [blame]1418</div>
1419
1420<div class="doc_text">
1421
1422<p>
1423Strings are commonly used as keys in maps, and they are difficult to support
1424efficiently: they are variable length, inefficient to hash and compare when
Chris Lattner796f9fa2007-02-08 19:14:21 +0000[diff] [blame]1425long, expensive to copy, etc. StringMap is a specialized container designed to
1426cope with these issues. It supports mapping an arbitrary range of bytes to an
1427arbitrary other object.</p>
Chris Lattnerc5722432007-02-03 19:49:31 +0000[diff] [blame]1428
Chris Lattner796f9fa2007-02-08 19:14:21 +0000[diff] [blame]1429<p>The StringMap implementation uses a quadratically-probed hash table, where
Chris Lattnerc5722432007-02-03 19:49:31 +0000[diff] [blame]1430the buckets store a pointer to the heap allocated entries (and some other
1431stuff). The entries in the map must be heap allocated because the strings are
1432variable length. The string data (key) and the element object (value) are
1433stored in the same allocation with the string data immediately after the element
1434object. This container guarantees the "<tt>(char*)(&amp;Value+1)</tt>" points
1435to the key string for a value.</p>
1436
Chris Lattner796f9fa2007-02-08 19:14:21 +0000[diff] [blame]1437<p>The StringMap is very fast for several reasons: quadratic probing is very
Chris Lattnerc5722432007-02-03 19:49:31 +0000[diff] [blame]1438cache efficient for lookups, the hash value of strings in buckets is not
Nick Lewycky2a80aca2010-08-01 23:18:45 +0000[diff] [blame]1439recomputed when looking up an element, StringMap rarely has to touch the
Chris Lattnerc5722432007-02-03 19:49:31 +0000[diff] [blame]1440memory for unrelated objects when looking up a value (even when hash collisions
1441happen), hash table growth does not recompute the hash values for strings
1442already in the table, and each pair in the map is store in a single allocation
1443(the string data is stored in the same allocation as the Value of a pair).</p>
1444
Chris Lattner796f9fa2007-02-08 19:14:21 +0000[diff] [blame]1445<p>StringMap also provides query methods that take byte ranges, so it only ever
Chris Lattnerc5722432007-02-03 19:49:31 +0000[diff] [blame]1446copies a string if a value is inserted into the table.</p>
1447</div>
1448
1449<!-- _______________________________________________________________________ -->
1450<div class="doc_subsubsection">
1451 <a name="dss_indexedmap">"llvm/ADT/IndexedMap.h"</a>
1452</div>
1453
1454<div class="doc_text">
1455<p>
1456IndexedMap is a specialized container for mapping small dense integers (or
1457values that can be mapped to small dense integers) to some other type. It is
1458internally implemented as a vector with a mapping function that maps the keys to
1459the dense integer range.
1460</p>
1461
1462<p>
1463This is useful for cases like virtual registers in the LLVM code generator: they
1464have a dense mapping that is offset by a compile-time constant (the first
1465virtual register ID).</p>
1466
1467</div>
1468
1469<!-- _______________________________________________________________________ -->
1470<div class="doc_subsubsection">
1471 <a name="dss_densemap">"llvm/ADT/DenseMap.h"</a>
1472</div>
1473
1474<div class="doc_text">
1475
1476<p>
1477DenseMap is a simple quadratically probed hash table. It excels at supporting
1478small keys and values: it uses a single allocation to hold all of the pairs that
1479are currently inserted in the map. DenseMap is a great way to map pointers to
1480pointers, or map other small types to each other.
1481</p>
1482
1483<p>
1484There are several aspects of DenseMap that you should be aware of, however. The
1485iterators in a densemap are invalidated whenever an insertion occurs, unlike
1486map. Also, because DenseMap allocates space for a large number of key/value
Chris Lattnera4a264d2007-02-03 20:17:53 +0000[diff] [blame]1487pairs (it starts with 64 by default), it will waste a lot of space if your keys
1488or values are large. Finally, you must implement a partial specialization of
Chris Lattner76c1b972007-09-17 18:34:04 +0000[diff] [blame]1489DenseMapInfo for the key that you want, if it isn't already supported. This
Chris Lattnerc5722432007-02-03 19:49:31 +0000[diff] [blame]1490is required to tell DenseMap about two special marker values (which can never be
Chris Lattnera4a264d2007-02-03 20:17:53 +0000[diff] [blame]1491inserted into the map) that it needs internally.</p>
Chris Lattnerc5722432007-02-03 19:49:31 +0000[diff] [blame]1492
1493</div>
1494
1495<!-- _______________________________________________________________________ -->
1496<div class="doc_subsubsection">
Jeffrey Yasskin71a5c222009-10-22 22:11:22 +0000[diff] [blame]1497 <a name="dss_valuemap">"llvm/ADT/ValueMap.h"</a>
1498</div>
1499
1500<div class="doc_text">
1501
1502<p>
1503ValueMap is a wrapper around a <a href="#dss_densemap">DenseMap</a> mapping
1504Value*s (or subclasses) to another type. When a Value is deleted or RAUW'ed,
1505ValueMap will update itself so the new version of the key is mapped to the same
1506value, just as if the key were a WeakVH. You can configure exactly how this
1507happens, and what else happens on these two events, by passing
1508a <code>Config</code> parameter to the ValueMap template.</p>
1509
1510</div>
1511
1512<!-- _______________________________________________________________________ -->
1513<div class="doc_subsubsection">
Jakob Stoklund Olesenaca0da62010-12-14 00:55:51 +0000[diff] [blame]1514 <a name="dss_intervalmap">"llvm/ADT/IntervalMap.h"</a>
1515</div>
1516
1517<div class="doc_text">
1518
1519<p> IntervalMap is a compact map for small keys and values. It maps key
1520intervals instead of single keys, and it will automatically coalesce adjacent
1521intervals. When then map only contains a few intervals, they are stored in the
1522map object itself to avoid allocations.</p>
1523
1524<p> The IntervalMap iterators are quite big, so they should not be passed around
1525as STL iterators. The heavyweight iterators allow a smaller data structure.</p>
1526
1527</div>
1528
1529<!-- _______________________________________________________________________ -->
1530<div class="doc_subsubsection">
Chris Lattnerc5722432007-02-03 19:49:31 +0000[diff] [blame]1531 <a name="dss_map">&lt;map&gt;</a>
1532</div>
1533
1534<div class="doc_text">
1535
1536<p>
1537std::map has similar characteristics to <a href="#dss_set">std::set</a>: it uses
1538a single allocation per pair inserted into the map, it offers log(n) lookup with
1539an extremely large constant factor, imposes a space penalty of 3 pointers per
1540pair in the map, etc.</p>
1541
1542<p>std::map is most useful when your keys or values are very large, if you need
1543to iterate over the collection in sorted order, or if you need stable iterators
1544into the map (i.e. they don't get invalidated if an insertion or deletion of
1545another element takes place).</p>
1546
1547</div>
1548
1549<!-- _______________________________________________________________________ -->
1550<div class="doc_subsubsection">
Jakob Stoklund Olesen4359e5e2011-04-05 20:56:08 +0000[diff] [blame^]1551 <a name="dss_inteqclasses">"llvm/ADT/IntEqClasses.h"</a>
1552</div>
1553
1554<div class="doc_text">
1555
1556<p>IntEqClasses provides a compact representation of equivalence classes of
1557small integers. Initially, each integer in the range 0..n-1 has its own
1558equivalence class. Classes can be joined by passing two class representatives to
1559the join(a, b) method. Two integers are in the same class when findLeader()
1560returns the same representative.</p>
1561
1562<p>Once all equivalence classes are formed, the map can be compressed so each
1563integer 0..n-1 maps to an equivalence class number in the range 0..m-1, where m
1564is the total number of equivalence classes. The map must be uncompressed before
1565it can be edited again.</p>
1566
1567</div>
1568
1569<!-- _______________________________________________________________________ -->
1570<div class="doc_subsubsection">
Chris Lattnerc5722432007-02-03 19:49:31 +0000[diff] [blame]1571 <a name="dss_othermap">Other Map-Like Container Options</a>
1572</div>
1573
1574<div class="doc_text">
1575
1576<p>
1577The STL provides several other options, such as std::multimap and the various
Chris Lattnerf1a30822009-03-09 05:20:45 +0000[diff] [blame]1578"hash_map" like containers (whether from C++ TR1 or from the SGI library). We
1579never use hash_set and unordered_set because they are generally very expensive
1580(each insertion requires a malloc) and very non-portable.</p>
Chris Lattnerc5722432007-02-03 19:49:31 +0000[diff] [blame]1581
1582<p>std::multimap is useful if you want to map a key to multiple values, but has
1583all the drawbacks of std::map. A sorted vector or some other approach is almost
1584always better.</p>
1585
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]1586</div>
1587
Daniel Berlin1939ace2007-09-24 17:52:25 +0000[diff] [blame]1588<!-- ======================================================================= -->
1589<div class="doc_subsection">
Chris Lattnerdced9fb2009-07-25 07:22:20 +0000[diff] [blame]1590 <a name="ds_string">String-like containers</a>
1591</div>
1592
1593<div class="doc_text">
1594
1595<p>
1596TODO: const char* vs stringref vs smallstring vs std::string. Describe twine,
1597xref to #string_apis.
1598</p>
1599
1600</div>
1601
1602<!-- ======================================================================= -->
1603<div class="doc_subsection">
Daniel Berlin1939ace2007-09-24 17:52:25 +0000[diff] [blame]1604 <a name="ds_bit">Bit storage containers (BitVector, SparseBitVector)</a>
1605</div>
1606
1607<div class="doc_text">
Chris Lattner7086ce72007-09-25 22:37:50 +0000[diff] [blame]1608<p>Unlike the other containers, there are only two bit storage containers, and
1609choosing when to use each is relatively straightforward.</p>
1610
1611<p>One additional option is
1612<tt>std::vector&lt;bool&gt;</tt>: we discourage its use for two reasons 1) the
1613implementation in many common compilers (e.g. commonly available versions of
1614GCC) is extremely inefficient and 2) the C++ standards committee is likely to
1615deprecate this container and/or change it significantly somehow. In any case,
1616please don't use it.</p>
Daniel Berlin1939ace2007-09-24 17:52:25 +0000[diff] [blame]1617</div>
1618
1619<!-- _______________________________________________________________________ -->
1620<div class="doc_subsubsection">
1621 <a name="dss_bitvector">BitVector</a>
1622</div>
1623
1624<div class="doc_text">
Dan Gohman5f7775c2010-01-05 18:24:00 +0000[diff] [blame]1625<p> The BitVector container provides a dynamic size set of bits for manipulation.
Daniel Berlin1939ace2007-09-24 17:52:25 +0000[diff] [blame]1626It supports individual bit setting/testing, as well as set operations. The set
1627operations take time O(size of bitvector), but operations are performed one word
1628at a time, instead of one bit at a time. This makes the BitVector very fast for
1629set operations compared to other containers. Use the BitVector when you expect
1630the number of set bits to be high (IE a dense set).
1631</p>
1632</div>
1633
1634<!-- _______________________________________________________________________ -->
1635<div class="doc_subsubsection">
Dan Gohman5f7775c2010-01-05 18:24:00 +0000[diff] [blame]1636 <a name="dss_smallbitvector">SmallBitVector</a>
1637</div>
1638
1639<div class="doc_text">
1640<p> The SmallBitVector container provides the same interface as BitVector, but
1641it is optimized for the case where only a small number of bits, less than
164225 or so, are needed. It also transparently supports larger bit counts, but
1643slightly less efficiently than a plain BitVector, so SmallBitVector should
1644only be used when larger counts are rare.
1645</p>
1646
1647<p>
1648At this time, SmallBitVector does not support set operations (and, or, xor),
1649and its operator[] does not provide an assignable lvalue.
1650</p>
1651</div>
1652
1653<!-- _______________________________________________________________________ -->
1654<div class="doc_subsubsection">
Daniel Berlin1939ace2007-09-24 17:52:25 +0000[diff] [blame]1655 <a name="dss_sparsebitvector">SparseBitVector</a>
1656</div>
1657
1658<div class="doc_text">
1659<p> The SparseBitVector container is much like BitVector, with one major
1660difference: Only the bits that are set, are stored. This makes the
1661SparseBitVector much more space efficient than BitVector when the set is sparse,
1662as well as making set operations O(number of set bits) instead of O(size of
1663universe). 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
1664(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).
1665</p>
1666</div>
Chris Lattnerf623a082005-10-17 01:36:23 +0000[diff] [blame]1667
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1668<!-- *********************************************************************** -->
1669<div class="doc_section">
1670 <a name="common">Helpful Hints for Common Operations</a>
1671</div>
1672<!-- *********************************************************************** -->
1673
1674<div class="doc_text">
1675
1676<p>This section describes how to perform some very simple transformations of
1677LLVM code. This is meant to give examples of common idioms used, showing the
1678practical side of LLVM transformations. <p> Because this is a "how-to" section,
1679you should also read about the main classes that you will be working with. The
1680<a href="#coreclasses">Core LLVM Class Hierarchy Reference</a> contains details
1681and descriptions of the main classes that you should know about.</p>
1682
1683</div>
1684
1685<!-- NOTE: this section should be heavy on example code -->
1686<!-- ======================================================================= -->
1687<div class="doc_subsection">
1688 <a name="inspection">Basic Inspection and Traversal Routines</a>
1689</div>
1690
1691<div class="doc_text">
1692
1693<p>The LLVM compiler infrastructure have many different data structures that may
1694be traversed. Following the example of the C++ standard template library, the
1695techniques used to traverse these various data structures are all basically the
1696same. For a enumerable sequence of values, the <tt>XXXbegin()</tt> function (or
1697method) returns an iterator to the start of the sequence, the <tt>XXXend()</tt>
1698function returns an iterator pointing to one past the last valid element of the
1699sequence, and there is some <tt>XXXiterator</tt> data type that is common
1700between the two operations.</p>
1701
1702<p>Because the pattern for iteration is common across many different aspects of
1703the program representation, the standard template library algorithms may be used
1704on them, and it is easier to remember how to iterate. First we show a few common
1705examples of the data structures that need to be traversed. Other data
1706structures are traversed in very similar ways.</p>
1707
1708</div>
1709
1710<!-- _______________________________________________________________________ -->
Chris Lattner69bf8a92004-05-23 21:06:58 +0000[diff] [blame]1711<div class="doc_subsubsection">
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1712 <a name="iterate_function">Iterating over the </a><a
1713 href="#BasicBlock"><tt>BasicBlock</tt></a>s in a <a
1714 href="#Function"><tt>Function</tt></a>
1715</div>
1716
1717<div class="doc_text">
1718
1719<p>It's quite common to have a <tt>Function</tt> instance that you'd like to
1720transform in some way; in particular, you'd like to manipulate its
1721<tt>BasicBlock</tt>s. To facilitate this, you'll need to iterate over all of
1722the <tt>BasicBlock</tt>s that constitute the <tt>Function</tt>. The following is
1723an example that prints the name of a <tt>BasicBlock</tt> and the number of
1724<tt>Instruction</tt>s it contains:</p>
1725
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1726<div class="doc_code">
1727<pre>
Bill Wendling82e2eea2006-10-11 18:00:22 +0000[diff] [blame]1728// <i>func is a pointer to a Function instance</i>
1729for (Function::iterator i = func-&gt;begin(), e = func-&gt;end(); i != e; ++i)
1730 // <i>Print out the name of the basic block if it has one, and then the</i>
1731 // <i>number of instructions that it contains</i>
Chris Lattner3fee6ed2009-09-08 05:15:50 +0000[diff] [blame]1732 errs() &lt;&lt; "Basic block (name=" &lt;&lt; i-&gt;getName() &lt;&lt; ") has "
Bill Wendling832171c2006-12-07 20:04:42 +0000[diff] [blame]1733 &lt;&lt; i-&gt;size() &lt;&lt; " instructions.\n";
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1734</pre>
1735</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1736
1737<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]1738invoking member functions of the <tt>Instruction</tt> class. This is
1739because the indirection operator is overloaded for the iterator
Chris Lattner7496ec52003-08-05 22:54:23 +0000[diff] [blame]1740classes. In the above code, the expression <tt>i-&gt;size()</tt> is
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1741exactly equivalent to <tt>(*i).size()</tt> just like you'd expect.</p>
1742
1743</div>
1744
1745<!-- _______________________________________________________________________ -->
Chris Lattner69bf8a92004-05-23 21:06:58 +0000[diff] [blame]1746<div class="doc_subsubsection">
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1747 <a name="iterate_basicblock">Iterating over the </a><a
1748 href="#Instruction"><tt>Instruction</tt></a>s in a <a
1749 href="#BasicBlock"><tt>BasicBlock</tt></a>
1750</div>
1751
1752<div class="doc_text">
1753
1754<p>Just like when dealing with <tt>BasicBlock</tt>s in <tt>Function</tt>s, it's
1755easy to iterate over the individual instructions that make up
1756<tt>BasicBlock</tt>s. Here's a code snippet that prints out each instruction in
1757a <tt>BasicBlock</tt>:</p>
1758
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1759<div class="doc_code">
Chris Lattner55c04612005-03-06 06:00:13 +0000[diff] [blame]1760<pre>
Bill Wendling82e2eea2006-10-11 18:00:22 +0000[diff] [blame]1761// <i>blk is a pointer to a BasicBlock instance</i>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1762for (BasicBlock::iterator i = blk-&gt;begin(), e = blk-&gt;end(); i != e; ++i)
Bill Wendling82e2eea2006-10-11 18:00:22 +0000[diff] [blame]1763 // <i>The next statement works since operator&lt;&lt;(ostream&amp;,...)</i>
1764 // <i>is overloaded for Instruction&amp;</i>
Chris Lattner3fee6ed2009-09-08 05:15:50 +0000[diff] [blame]1765 errs() &lt;&lt; *i &lt;&lt; "\n";
Chris Lattner55c04612005-03-06 06:00:13 +0000[diff] [blame]1766</pre>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1767</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1768
1769<p>However, this isn't really the best way to print out the contents of a
1770<tt>BasicBlock</tt>! Since the ostream operators are overloaded for virtually
1771anything you'll care about, you could have just invoked the print routine on the
Chris Lattner3fee6ed2009-09-08 05:15:50 +0000[diff] [blame]1772basic block itself: <tt>errs() &lt;&lt; *blk &lt;&lt; "\n";</tt>.</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1773
1774</div>
1775
1776<!-- _______________________________________________________________________ -->
Chris Lattner69bf8a92004-05-23 21:06:58 +0000[diff] [blame]1777<div class="doc_subsubsection">
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1778 <a name="iterate_institer">Iterating over the </a><a
1779 href="#Instruction"><tt>Instruction</tt></a>s in a <a
1780 href="#Function"><tt>Function</tt></a>
1781</div>
1782
1783<div class="doc_text">
1784
1785<p>If you're finding that you commonly iterate over a <tt>Function</tt>'s
1786<tt>BasicBlock</tt>s and then that <tt>BasicBlock</tt>'s <tt>Instruction</tt>s,
1787<tt>InstIterator</tt> should be used instead. You'll need to include <a
1788href="/doxygen/InstIterator_8h-source.html"><tt>llvm/Support/InstIterator.h</tt></a>,
1789and then instantiate <tt>InstIterator</tt>s explicitly in your code. Here's a
Chris Lattner69bf8a92004-05-23 21:06:58 +0000[diff] [blame]1790small 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]1791
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1792<div class="doc_code">
1793<pre>
1794#include "<a href="/doxygen/InstIterator_8h-source.html">llvm/Support/InstIterator.h</a>"
1795
Reid Spencer128a7a72007-02-03 21:06:43 +0000[diff] [blame]1796// <i>F is a pointer to a Function instance</i>
Chris Lattnerda021aa2008-06-04 18:20:42 +0000[diff] [blame]1797for (inst_iterator I = inst_begin(F), E = inst_end(F); I != E; ++I)
Chris Lattner3fee6ed2009-09-08 05:15:50 +0000[diff] [blame]1798 errs() &lt;&lt; *I &lt;&lt; "\n";
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1799</pre>
1800</div>
1801
1802<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]1803work list with its initial contents. For example, if you wanted to
1804initialize a work list to contain all instructions in a <tt>Function</tt>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1805F, all you would need to do is something like:</p>
1806
1807<div class="doc_code">
1808<pre>
1809std::set&lt;Instruction*&gt; worklist;
Chris Lattnerda021aa2008-06-04 18:20:42 +0000[diff] [blame]1810// or better yet, SmallPtrSet&lt;Instruction*, 64&gt; worklist;
1811
1812for (inst_iterator I = inst_begin(F), E = inst_end(F); I != E; ++I)
1813 worklist.insert(&amp;*I);
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1814</pre>
1815</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1816
1817<p>The STL set <tt>worklist</tt> would now contain all instructions in the
1818<tt>Function</tt> pointed to by F.</p>
1819
1820</div>
1821
1822<!-- _______________________________________________________________________ -->
1823<div class="doc_subsubsection">
1824 <a name="iterate_convert">Turning an iterator into a class pointer (and
1825 vice-versa)</a>
1826</div>
1827
1828<div class="doc_text">
1829
1830<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]1831instance when all you've got at hand is an iterator. Well, extracting
Chris Lattner69bf8a92004-05-23 21:06:58 +0000[diff] [blame]1832a reference or a pointer from an iterator is very straight-forward.
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]1833Assuming that <tt>i</tt> is a <tt>BasicBlock::iterator</tt> and <tt>j</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1834is a <tt>BasicBlock::const_iterator</tt>:</p>
1835
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1836<div class="doc_code">
1837<pre>
Bill Wendling82e2eea2006-10-11 18:00:22 +0000[diff] [blame]1838Instruction&amp; inst = *i; // <i>Grab reference to instruction reference</i>
1839Instruction* pinst = &amp;*i; // <i>Grab pointer to instruction reference</i>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1840const Instruction&amp; inst = *j;
1841</pre>
1842</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1843
1844<p>However, the iterators you'll be working with in the LLVM framework are
1845special: they will automatically convert to a ptr-to-instance type whenever they
1846need to. Instead of dereferencing the iterator and then taking the address of
1847the result, you can simply assign the iterator to the proper pointer type and
1848you get the dereference and address-of operation as a result of the assignment
1849(behind the scenes, this is a result of overloading casting mechanisms). Thus
1850the last line of the last example,</p>
1851
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1852<div class="doc_code">
1853<pre>
Chris Lattner2e438ca2008-01-03 16:56:04 +0000[diff] [blame]1854Instruction *pinst = &amp;*i;
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1855</pre>
1856</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1857
1858<p>is semantically equivalent to</p>
1859
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1860<div class="doc_code">
1861<pre>
Chris Lattner2e438ca2008-01-03 16:56:04 +0000[diff] [blame]1862Instruction *pinst = i;
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1863</pre>
1864</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1865
Chris Lattner69bf8a92004-05-23 21:06:58 +0000[diff] [blame]1866<p>It's also possible to turn a class pointer into the corresponding iterator,
1867and this is a constant time operation (very efficient). The following code
1868snippet illustrates use of the conversion constructors provided by LLVM
1869iterators. By using these, you can explicitly grab the iterator of something
1870without actually obtaining it via iteration over some structure:</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1871
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1872<div class="doc_code">
1873<pre>
1874void printNextInstruction(Instruction* inst) {
1875 BasicBlock::iterator it(inst);
Bill Wendling82e2eea2006-10-11 18:00:22 +0000[diff] [blame]1876 ++it; // <i>After this line, it refers to the instruction after *inst</i>
Chris Lattner3fee6ed2009-09-08 05:15:50 +0000[diff] [blame]1877 if (it != inst-&gt;getParent()-&gt;end()) errs() &lt;&lt; *it &lt;&lt; "\n";
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1878}
1879</pre>
1880</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1881
Dan Gohman525bf8e2010-03-26 19:39:05 +0000[diff] [blame]1882<p>Unfortunately, these implicit conversions come at a cost; they prevent
1883these iterators from conforming to standard iterator conventions, and thus
Dan Gohman0d91c112010-03-26 19:51:14 +0000[diff] [blame]1884from being usable with standard algorithms and containers. For example, they
1885prevent the following code, where <tt>B</tt> is a <tt>BasicBlock</tt>,
Dan Gohman525bf8e2010-03-26 19:39:05 +0000[diff] [blame]1886from compiling:</p>
1887
1888<div class="doc_code">
1889<pre>
1890 llvm::SmallVector&lt;llvm::Instruction *, 16&gt;(B-&gt;begin(), B-&gt;end());
1891</pre>
1892</div>
1893
1894<p>Because of this, these implicit conversions may be removed some day,
Dan Gohman0d91c112010-03-26 19:51:14 +0000[diff] [blame]1895and <tt>operator*</tt> changed to return a pointer instead of a reference.</p>
Dan Gohman525bf8e2010-03-26 19:39:05 +0000[diff] [blame]1896
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1897</div>
1898
1899<!--_______________________________________________________________________-->
1900<div class="doc_subsubsection">
1901 <a name="iterate_complex">Finding call sites: a slightly more complex
1902 example</a>
1903</div>
1904
1905<div class="doc_text">
1906
1907<p>Say that you're writing a FunctionPass and would like to count all the
1908locations in the entire module (that is, across every <tt>Function</tt>) where a
1909certain function (i.e., some <tt>Function</tt>*) is already in scope. As you'll
1910learn 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]1911much more straight-forward manner, but this example will allow us to explore how
Reid Spencer128a7a72007-02-03 21:06:43 +0000[diff] [blame]1912you'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]1913is what we want to do:</p>
1914
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1915<div class="doc_code">
1916<pre>
1917initialize callCounter to zero
1918for each Function f in the Module
1919 for each BasicBlock b in f
1920 for each Instruction i in b
1921 if (i is a CallInst and calls the given function)
1922 increment callCounter
1923</pre>
1924</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1925
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1926<p>And the actual code is (remember, because we're writing a
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1927<tt>FunctionPass</tt>, our <tt>FunctionPass</tt>-derived class simply has to
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1928override the <tt>runOnFunction</tt> method):</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1929
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1930<div class="doc_code">
1931<pre>
1932Function* targetFunc = ...;
1933
1934class OurFunctionPass : public FunctionPass {
1935 public:
1936 OurFunctionPass(): callCounter(0) { }
1937
1938 virtual runOnFunction(Function&amp; F) {
1939 for (Function::iterator b = F.begin(), be = F.end(); b != be; ++b) {
Eric Christopher203e71d2008-11-08 08:20:49 +0000[diff] [blame]1940 for (BasicBlock::iterator i = b-&gt;begin(), ie = b-&gt;end(); i != ie; ++i) {
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1941 if (<a href="#CallInst">CallInst</a>* callInst = <a href="#isa">dyn_cast</a>&lt;<a
1942 href="#CallInst">CallInst</a>&gt;(&amp;*i)) {
Bill Wendling82e2eea2006-10-11 18:00:22 +0000[diff] [blame]1943 // <i>We know we've encountered a call instruction, so we</i>
1944 // <i>need to determine if it's a call to the</i>
Chris Lattner2e438ca2008-01-03 16:56:04 +0000[diff] [blame]1945 // <i>function pointed to by m_func or not.</i>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1946 if (callInst-&gt;getCalledFunction() == targetFunc)
1947 ++callCounter;
1948 }
1949 }
1950 }
Bill Wendling82e2eea2006-10-11 18:00:22 +0000[diff] [blame]1951 }
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1952
1953 private:
Chris Lattner2e438ca2008-01-03 16:56:04 +0000[diff] [blame]1954 unsigned callCounter;
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1955};
1956</pre>
1957</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1958
1959</div>
1960
Brian Gaekef1972c62003-11-07 19:25:45 +0000[diff] [blame]1961<!--_______________________________________________________________________-->
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1962<div class="doc_subsubsection">
1963 <a name="calls_and_invokes">Treating calls and invokes the same way</a>
1964</div>
1965
1966<div class="doc_text">
1967
1968<p>You may have noticed that the previous example was a bit oversimplified in
1969that it did not deal with call sites generated by 'invoke' instructions. In
1970this, and in other situations, you may find that you want to treat
1971<tt>CallInst</tt>s and <tt>InvokeInst</tt>s the same way, even though their
1972most-specific common base class is <tt>Instruction</tt>, which includes lots of
1973less closely-related things. For these cases, LLVM provides a handy wrapper
1974class called <a
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]1975href="http://llvm.org/doxygen/classllvm_1_1CallSite.html"><tt>CallSite</tt></a>.
Chris Lattner69bf8a92004-05-23 21:06:58 +0000[diff] [blame]1976It is essentially a wrapper around an <tt>Instruction</tt> pointer, with some
1977methods that provide functionality common to <tt>CallInst</tt>s and
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1978<tt>InvokeInst</tt>s.</p>
1979
Chris Lattner69bf8a92004-05-23 21:06:58 +0000[diff] [blame]1980<p>This class has "value semantics": it should be passed by value, not by
1981reference and it should not be dynamically allocated or deallocated using
1982<tt>operator new</tt> or <tt>operator delete</tt>. It is efficiently copyable,
1983assignable and constructable, with costs equivalents to that of a bare pointer.
1984If you look at its definition, it has only a single pointer member.</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1985
1986</div>
1987
Chris Lattner1a3105b2002-09-09 05:49:39 +0000[diff] [blame]1988<!--_______________________________________________________________________-->
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1989<div class="doc_subsubsection">
1990 <a name="iterate_chains">Iterating over def-use &amp; use-def chains</a>
1991</div>
1992
1993<div class="doc_text">
1994
1995<p>Frequently, we might have an instance of the <a
Chris Lattner00815172007-01-04 22:01:45 +0000[diff] [blame]1996href="/doxygen/classllvm_1_1Value.html">Value Class</a> and we want to
Misha Brukman384047f2004-06-03 23:29:12 +0000[diff] [blame]1997determine which <tt>User</tt>s use the <tt>Value</tt>. The list of all
1998<tt>User</tt>s of a particular <tt>Value</tt> is called a <i>def-use</i> chain.
1999For example, let's say we have a <tt>Function*</tt> named <tt>F</tt> to a
2000particular function <tt>foo</tt>. Finding all of the instructions that
2001<i>use</i> <tt>foo</tt> is as simple as iterating over the <i>def-use</i> chain
2002of <tt>F</tt>:</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2003
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2004<div class="doc_code">
2005<pre>
Chris Lattner2e438ca2008-01-03 16:56:04 +0000[diff] [blame]2006Function *F = ...;
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2007
Bill Wendling82e2eea2006-10-11 18:00:22 +0000[diff] [blame]2008for (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]2009 if (Instruction *Inst = dyn_cast&lt;Instruction&gt;(*i)) {
Chris Lattner3fee6ed2009-09-08 05:15:50 +0000[diff] [blame]2010 errs() &lt;&lt; "F is used in instruction:\n";
2011 errs() &lt;&lt; *Inst &lt;&lt; "\n";
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2012 }
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2013</pre>
Gabor Greif394fdfb2010-03-26 19:35:48 +0000[diff] [blame]2014</div>
2015
Gabor Greifce94319532010-03-26 19:40:38 +0000[diff] [blame]2016<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]2017operation. Instead of performing <tt>*i</tt> above several times, consider
Gabor Greifce94319532010-03-26 19:40:38 +0000[diff] [blame]2018doing it only once in the loop body and reusing its result.</p>
Gabor Greif4de73682010-03-26 19:30:47 +0000[diff] [blame]2019
Gabor Greif6091ff32010-03-26 19:04:42 +0000[diff] [blame]2020<p>Alternatively, it's common to have an instance of the <a
Misha Brukman384047f2004-06-03 23:29:12 +0000[diff] [blame]2021href="/doxygen/classllvm_1_1User.html">User Class</a> and need to know what
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2022<tt>Value</tt>s are used by it. The list of all <tt>Value</tt>s used by a
2023<tt>User</tt> is known as a <i>use-def</i> chain. Instances of class
2024<tt>Instruction</tt> are common <tt>User</tt>s, so we might want to iterate over
2025all of the values that a particular instruction uses (that is, the operands of
2026the particular <tt>Instruction</tt>):</p>
2027
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2028<div class="doc_code">
2029<pre>
Chris Lattner2e438ca2008-01-03 16:56:04 +0000[diff] [blame]2030Instruction *pi = ...;
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2031
2032for (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]2033 Value *v = *i;
Bill Wendling82e2eea2006-10-11 18:00:22 +0000[diff] [blame]2034 // <i>...</i>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2035}
2036</pre>
2037</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2038
Gabor Greif4de73682010-03-26 19:30:47 +0000[diff] [blame]2039<p>Declaring objects as <tt>const</tt> is an important tool of enforcing
Gabor Greifce94319532010-03-26 19:40:38 +0000[diff] [blame]2040mutation free algorithms (such as analyses, etc.). For this purpose above
Gabor Greif4de73682010-03-26 19:30:47 +0000[diff] [blame]2041iterators come in constant flavors as <tt>Value::const_use_iterator</tt>
2042and <tt>Value::const_op_iterator</tt>. They automatically arise when
2043calling <tt>use/op_begin()</tt> on <tt>const Value*</tt>s or
2044<tt>const User*</tt>s respectively. Upon dereferencing, they return
Gabor Greifce94319532010-03-26 19:40:38 +0000[diff] [blame]2045<tt>const Use*</tt>s. Otherwise the above patterns remain unchanged.</p>
2046
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2047</div>
2048
Chris Lattner2e438ca2008-01-03 16:56:04 +0000[diff] [blame]2049<!--_______________________________________________________________________-->
2050<div class="doc_subsubsection">
2051 <a name="iterate_preds">Iterating over predecessors &amp;
2052successors of blocks</a>
2053</div>
2054
2055<div class="doc_text">
2056
2057<p>Iterating over the predecessors and successors of a block is quite easy
2058with the routines defined in <tt>"llvm/Support/CFG.h"</tt>. Just use code like
2059this to iterate over all predecessors of BB:</p>
2060
2061<div class="doc_code">
2062<pre>
2063#include "llvm/Support/CFG.h"
2064BasicBlock *BB = ...;
2065
2066for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI) {
2067 BasicBlock *Pred = *PI;
2068 // <i>...</i>
2069}
2070</pre>
2071</div>
2072
2073<p>Similarly, to iterate over successors use
2074succ_iterator/succ_begin/succ_end.</p>
2075
2076</div>
2077
2078
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2079<!-- ======================================================================= -->
2080<div class="doc_subsection">
2081 <a name="simplechanges">Making simple changes</a>
2082</div>
2083
2084<div class="doc_text">
2085
2086<p>There are some primitive transformation operations present in the LLVM
Joel Stanley753eb712002-09-11 22:32:24 +0000[diff] [blame]2087infrastructure that are worth knowing about. When performing
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]2088transformations, it's fairly common to manipulate the contents of basic
2089blocks. This section describes some of the common methods for doing so
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2090and gives example code.</p>
2091
2092</div>
2093
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]2094<!--_______________________________________________________________________-->
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2095<div class="doc_subsubsection">
2096 <a name="schanges_creating">Creating and inserting new
2097 <tt>Instruction</tt>s</a>
2098</div>
2099
2100<div class="doc_text">
2101
2102<p><i>Instantiating Instructions</i></p>
2103
Chris Lattner69bf8a92004-05-23 21:06:58 +0000[diff] [blame]2104<p>Creation of <tt>Instruction</tt>s is straight-forward: simply call the
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2105constructor for the kind of instruction to instantiate and provide the necessary
2106parameters. For example, an <tt>AllocaInst</tt> only <i>requires</i> a
2107(const-ptr-to) <tt>Type</tt>. Thus:</p>
2108
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2109<div class="doc_code">
2110<pre>
Nick Lewycky10d64b92007-12-03 01:52:52 +0000[diff] [blame]2111AllocaInst* ai = new AllocaInst(Type::Int32Ty);
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2112</pre>
2113</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2114
2115<p>will create an <tt>AllocaInst</tt> instance that represents the allocation of
Reid Spencer128a7a72007-02-03 21:06:43 +0000[diff] [blame]2116one integer in the current stack frame, at run time. Each <tt>Instruction</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2117subclass is likely to have varying default parameters which change the semantics
2118of the instruction, so refer to the <a
Misha Brukman31ca1de2004-06-03 23:35:54 +0000[diff] [blame]2119href="/doxygen/classllvm_1_1Instruction.html">doxygen documentation for the subclass of
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2120Instruction</a> that you're interested in instantiating.</p>
2121
2122<p><i>Naming values</i></p>
2123
2124<p>It is very useful to name the values of instructions when you're able to, as
2125this facilitates the debugging of your transformations. If you end up looking
2126at generated LLVM machine code, you definitely want to have logical names
2127associated with the results of instructions! By supplying a value for the
2128<tt>Name</tt> (default) parameter of the <tt>Instruction</tt> constructor, you
2129associate a logical name with the result of the instruction's execution at
Reid Spencer128a7a72007-02-03 21:06:43 +0000[diff] [blame]2130run time. For example, say that I'm writing a transformation that dynamically
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2131allocates space for an integer on the stack, and that integer is going to be
2132used as some kind of index by some other code. To accomplish this, I place an
2133<tt>AllocaInst</tt> at the first point in the first <tt>BasicBlock</tt> of some
2134<tt>Function</tt>, and I'm intending to use it within the same
2135<tt>Function</tt>. I might do:</p>
2136
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2137<div class="doc_code">
2138<pre>
Nick Lewycky10d64b92007-12-03 01:52:52 +0000[diff] [blame]2139AllocaInst* pa = new AllocaInst(Type::Int32Ty, 0, "indexLoc");
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2140</pre>
2141</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2142
2143<p>where <tt>indexLoc</tt> is now the logical name of the instruction's
Reid Spencer128a7a72007-02-03 21:06:43 +0000[diff] [blame]2144execution value, which is a pointer to an integer on the run time stack.</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2145
2146<p><i>Inserting instructions</i></p>
2147
2148<p>There are essentially two ways to insert an <tt>Instruction</tt>
2149into an existing sequence of instructions that form a <tt>BasicBlock</tt>:</p>
2150
Joel Stanley9dd1ad62002-09-18 03:17:23 +0000[diff] [blame]2151<ul>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2152 <li>Insertion into an explicit instruction list
2153
2154 <p>Given a <tt>BasicBlock* pb</tt>, an <tt>Instruction* pi</tt> within that
2155 <tt>BasicBlock</tt>, and a newly-created instruction we wish to insert
2156 before <tt>*pi</tt>, we do the following: </p>
2157
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2158<div class="doc_code">
2159<pre>
2160BasicBlock *pb = ...;
2161Instruction *pi = ...;
2162Instruction *newInst = new Instruction(...);
2163
Bill Wendling82e2eea2006-10-11 18:00:22 +0000[diff] [blame]2164pb-&gt;getInstList().insert(pi, newInst); // <i>Inserts newInst before pi in pb</i>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2165</pre>
2166</div>
Alkis Evlogimenos9a5dc4f2004-05-27 00:57:51 +0000[diff] [blame]2167
2168 <p>Appending to the end of a <tt>BasicBlock</tt> is so common that
2169 the <tt>Instruction</tt> class and <tt>Instruction</tt>-derived
2170 classes provide constructors which take a pointer to a
2171 <tt>BasicBlock</tt> to be appended to. For example code that
2172 looked like: </p>
2173
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2174<div class="doc_code">
2175<pre>
2176BasicBlock *pb = ...;
2177Instruction *newInst = new Instruction(...);
2178
Bill Wendling82e2eea2006-10-11 18:00:22 +0000[diff] [blame]2179pb-&gt;getInstList().push_back(newInst); // <i>Appends newInst to pb</i>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2180</pre>
2181</div>
Alkis Evlogimenos9a5dc4f2004-05-27 00:57:51 +0000[diff] [blame]2182
2183 <p>becomes: </p>
2184
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2185<div class="doc_code">
2186<pre>
2187BasicBlock *pb = ...;
2188Instruction *newInst = new Instruction(..., pb);
2189</pre>
2190</div>
Alkis Evlogimenos9a5dc4f2004-05-27 00:57:51 +0000[diff] [blame]2191
2192 <p>which is much cleaner, especially if you are creating
2193 long instruction streams.</p></li>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2194
2195 <li>Insertion into an implicit instruction list
2196
2197 <p><tt>Instruction</tt> instances that are already in <tt>BasicBlock</tt>s
2198 are implicitly associated with an existing instruction list: the instruction
2199 list of the enclosing basic block. Thus, we could have accomplished the same
2200 thing as the above code without being given a <tt>BasicBlock</tt> by doing:
2201 </p>
2202
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2203<div class="doc_code">
2204<pre>
2205Instruction *pi = ...;
2206Instruction *newInst = new Instruction(...);
2207
2208pi-&gt;getParent()-&gt;getInstList().insert(pi, newInst);
2209</pre>
2210</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2211
2212 <p>In fact, this sequence of steps occurs so frequently that the
2213 <tt>Instruction</tt> class and <tt>Instruction</tt>-derived classes provide
2214 constructors which take (as a default parameter) a pointer to an
2215 <tt>Instruction</tt> which the newly-created <tt>Instruction</tt> should
2216 precede. That is, <tt>Instruction</tt> constructors are capable of
2217 inserting the newly-created instance into the <tt>BasicBlock</tt> of a
2218 provided instruction, immediately before that instruction. Using an
2219 <tt>Instruction</tt> constructor with a <tt>insertBefore</tt> (default)
2220 parameter, the above code becomes:</p>
2221
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2222<div class="doc_code">
2223<pre>
2224Instruction* pi = ...;
2225Instruction* newInst = new Instruction(..., pi);
2226</pre>
2227</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2228
2229 <p>which is much cleaner, especially if you're creating a lot of
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2230 instructions and adding them to <tt>BasicBlock</tt>s.</p></li>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2231</ul>
2232
2233</div>
2234
2235<!--_______________________________________________________________________-->
2236<div class="doc_subsubsection">
2237 <a name="schanges_deleting">Deleting <tt>Instruction</tt>s</a>
2238</div>
2239
2240<div class="doc_text">
2241
2242<p>Deleting an instruction from an existing sequence of instructions that form a
Chris Lattner49e0ccf2011-03-24 16:13:31 +0000[diff] [blame]2243<a href="#BasicBlock"><tt>BasicBlock</tt></a> is very straight-forward: just
2244call the instruction's eraseFromParent() method. For example:</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2245
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2246<div class="doc_code">
2247<pre>
2248<a href="#Instruction">Instruction</a> *I = .. ;
Chris Lattner9f8ec252008-02-15 22:57:17 +0000[diff] [blame]2249I-&gt;eraseFromParent();
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2250</pre>
2251</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2252
Chris Lattner49e0ccf2011-03-24 16:13:31 +0000[diff] [blame]2253<p>This unlinks the instruction from its containing basic block and deletes
2254it. If you'd just like to unlink the instruction from its containing basic
2255block but not delete it, you can use the <tt>removeFromParent()</tt> method.</p>
2256
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2257</div>
2258
2259<!--_______________________________________________________________________-->
2260<div class="doc_subsubsection">
2261 <a name="schanges_replacing">Replacing an <tt>Instruction</tt> with another
2262 <tt>Value</tt></a>
2263</div>
2264
2265<div class="doc_text">
2266
2267<p><i>Replacing individual instructions</i></p>
2268
2269<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]2270permits use of two very useful replace functions: <tt>ReplaceInstWithValue</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2271and <tt>ReplaceInstWithInst</tt>.</p>
2272
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]2273<h4><a name="schanges_deleting">Deleting <tt>Instruction</tt>s</a></h4>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2274
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]2275<ul>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2276 <li><tt>ReplaceInstWithValue</tt>
2277
Nick Lewyckyb6d1f392008-09-15 06:31:52 +0000[diff] [blame]2278 <p>This function replaces all uses of a given instruction with a value,
2279 and then removes the original instruction. The following example
2280 illustrates the replacement of the result of a particular
Chris Lattner58360822005-01-17 00:12:04 +0000[diff] [blame]2281 <tt>AllocaInst</tt> that allocates memory for a single integer with a null
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2282 pointer to an integer.</p>
2283
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2284<div class="doc_code">
2285<pre>
2286AllocaInst* instToReplace = ...;
2287BasicBlock::iterator ii(instToReplace);
2288
2289ReplaceInstWithValue(instToReplace-&gt;getParent()-&gt;getInstList(), ii,
Daniel Dunbar58c2ac02008-10-03 22:17:25 +0000[diff] [blame]2290 Constant::getNullValue(PointerType::getUnqual(Type::Int32Ty)));
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2291</pre></div></li>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2292
2293 <li><tt>ReplaceInstWithInst</tt>
2294
2295 <p>This function replaces a particular instruction with another
Nick Lewyckyb6d1f392008-09-15 06:31:52 +0000[diff] [blame]2296 instruction, inserting the new instruction into the basic block at the
2297 location where the old instruction was, and replacing any uses of the old
2298 instruction with the new instruction. The following example illustrates
2299 the replacement of one <tt>AllocaInst</tt> with another.</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2300
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2301<div class="doc_code">
2302<pre>
2303AllocaInst* instToReplace = ...;
2304BasicBlock::iterator ii(instToReplace);
2305
2306ReplaceInstWithInst(instToReplace-&gt;getParent()-&gt;getInstList(), ii,
Nick Lewycky10d64b92007-12-03 01:52:52 +0000[diff] [blame]2307 new AllocaInst(Type::Int32Ty, 0, "ptrToReplacedInt"));
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2308</pre></div></li>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]2309</ul>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2310
2311<p><i>Replacing multiple uses of <tt>User</tt>s and <tt>Value</tt>s</i></p>
2312
2313<p>You can use <tt>Value::replaceAllUsesWith</tt> and
2314<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]2315doxygen documentation for the <a href="/doxygen/classllvm_1_1Value.html">Value Class</a>
Misha Brukman384047f2004-06-03 23:29:12 +0000[diff] [blame]2316and <a href="/doxygen/classllvm_1_1User.html">User Class</a>, respectively, for more
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2317information.</p>
2318
2319<!-- Value::replaceAllUsesWith User::replaceUsesOfWith Point out:
2320include/llvm/Transforms/Utils/ especially BasicBlockUtils.h with:
2321ReplaceInstWithValue, ReplaceInstWithInst -->
2322
2323</div>
2324
Tanya Lattnerb011c662007-06-20 18:33:15 +0000[diff] [blame]2325<!--_______________________________________________________________________-->
2326<div class="doc_subsubsection">
2327 <a name="schanges_deletingGV">Deleting <tt>GlobalVariable</tt>s</a>
2328</div>
2329
2330<div class="doc_text">
2331
Tanya Lattnerc5dfcdb2007-06-20 20:46:37 +0000[diff] [blame]2332<p>Deleting a global variable from a module is just as easy as deleting an
2333Instruction. First, you must have a pointer to the global variable that you wish
2334 to delete. You use this pointer to erase it from its parent, the module.
Tanya Lattnerb011c662007-06-20 18:33:15 +0000[diff] [blame]2335 For example:</p>
2336
2337<div class="doc_code">
2338<pre>
2339<a href="#GlobalVariable">GlobalVariable</a> *GV = .. ;
Tanya Lattnerb011c662007-06-20 18:33:15 +0000[diff] [blame]2340
Tanya Lattnerc5dfcdb2007-06-20 20:46:37 +0000[diff] [blame]2341GV-&gt;eraseFromParent();
Tanya Lattnerb011c662007-06-20 18:33:15 +0000[diff] [blame]2342</pre>
2343</div>
2344
2345</div>
2346
Jeffrey Yasskin714257f2009-04-30 22:33:41 +0000[diff] [blame]2347<!-- ======================================================================= -->
2348<div class="doc_subsection">
2349 <a name="create_types">How to Create Types</a>
2350</div>
2351
2352<div class="doc_text">
2353
2354<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]2355statically, you can use <tt>TypeBuilder&lt;...&gt;::get()</tt>, defined
Jeffrey Yasskin714257f2009-04-30 22:33:41 +0000[diff] [blame]2356in <tt>llvm/Support/TypeBuilder.h</tt>, to retrieve them. <tt>TypeBuilder</tt>
2357has two forms depending on whether you're building types for cross-compilation
Misha Brukman1af789f2009-05-01 20:40:51 +0000[diff] [blame]2358or native library use. <tt>TypeBuilder&lt;T, true&gt;</tt> requires
Jeffrey Yasskin714257f2009-04-30 22:33:41 +0000[diff] [blame]2359that <tt>T</tt> be independent of the host environment, meaning that it's built
2360out of types from
2361the <a href="/doxygen/namespacellvm_1_1types.html"><tt>llvm::types</tt></a>
2362namespace and pointers, functions, arrays, etc. built of
Misha Brukman1af789f2009-05-01 20:40:51 +0000[diff] [blame]2363those. <tt>TypeBuilder&lt;T, false&gt;</tt> additionally allows native C types
Jeffrey Yasskin714257f2009-04-30 22:33:41 +0000[diff] [blame]2364whose size may depend on the host compiler. For example,</p>
2365
2366<div class="doc_code">
2367<pre>
Misha Brukman1af789f2009-05-01 20:40:51 +0000[diff] [blame]2368FunctionType *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]2369</pre>
2370</div>
2371
2372<p>is easier to read and write than the equivalent</p>
2373
2374<div class="doc_code">
2375<pre>
Owen Anderson5e8c50e2009-06-16 17:40:28 +0000[diff] [blame]2376std::vector&lt;const Type*&gt; params;
Jeffrey Yasskin714257f2009-04-30 22:33:41 +0000[diff] [blame]2377params.push_back(PointerType::getUnqual(Type::Int32Ty));
2378FunctionType *ft = FunctionType::get(Type::Int8Ty, params, false);
2379</pre>
2380</div>
2381
2382<p>See the <a href="/doxygen/TypeBuilder_8h-source.html#l00001">class
2383comment</a> for more details.</p>
2384
2385</div>
2386
Chris Lattner9355b472002-09-06 02:50:58 +0000[diff] [blame]2387<!-- *********************************************************************** -->
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2388<div class="doc_section">
Owen Anderson8bc1b3b2009-06-16 01:17:16 +0000[diff] [blame]2389 <a name="threading">Threads and LLVM</a>
2390</div>
2391<!-- *********************************************************************** -->
2392
2393<div class="doc_text">
2394<p>
2395This section describes the interaction of the LLVM APIs with multithreading,
2396both on the part of client applications, and in the JIT, in the hosted
2397application.
2398</p>
2399
2400<p>
2401Note that LLVM's support for multithreading is still relatively young. Up
2402through version 2.5, the execution of threaded hosted applications was
2403supported, but not threaded client access to the APIs. While this use case is
2404now supported, clients <em>must</em> adhere to the guidelines specified below to
2405ensure proper operation in multithreaded mode.
2406</p>
2407
2408<p>
2409Note that, on Unix-like platforms, LLVM requires the presence of GCC's atomic
2410intrinsics in order to support threaded operation. If you need a
2411multhreading-capable LLVM on a platform without a suitably modern system
2412compiler, consider compiling LLVM and LLVM-GCC in single-threaded mode, and
2413using the resultant compiler to build a copy of LLVM with multithreading
2414support.
2415</p>
2416</div>
2417
2418<!-- ======================================================================= -->
2419<div class="doc_subsection">
Owen Anderson1ad70e32009-06-16 18:04:19 +0000[diff] [blame]2420 <a name="startmultithreaded">Entering and Exiting Multithreaded Mode</a>
Owen Anderson8bc1b3b2009-06-16 01:17:16 +0000[diff] [blame]2421</div>
2422
2423<div class="doc_text">
2424
2425<p>
2426In order to properly protect its internal data structures while avoiding
Owen Anderson1ad70e32009-06-16 18:04:19 +0000[diff] [blame]2427excessive locking overhead in the single-threaded case, the LLVM must intialize
2428certain data structures necessary to provide guards around its internals. To do
2429so, the client program must invoke <tt>llvm_start_multithreaded()</tt> before
2430making any concurrent LLVM API calls. To subsequently tear down these
2431structures, use the <tt>llvm_stop_multithreaded()</tt> call. You can also use
2432the <tt>llvm_is_multithreaded()</tt> call to check the status of multithreaded
2433mode.
Owen Anderson8bc1b3b2009-06-16 01:17:16 +0000[diff] [blame]2434</p>
2435
2436<p>
Owen Anderson1ad70e32009-06-16 18:04:19 +0000[diff] [blame]2437Note that both of these calls must be made <em>in isolation</em>. That is to
2438say that no other LLVM API calls may be executing at any time during the
2439execution of <tt>llvm_start_multithreaded()</tt> or <tt>llvm_stop_multithreaded
2440</tt>. It's is the client's responsibility to enforce this isolation.
2441</p>
2442
2443<p>
2444The return value of <tt>llvm_start_multithreaded()</tt> indicates the success or
2445failure of the initialization. Failure typically indicates that your copy of
2446LLVM was built without multithreading support, typically because GCC atomic
2447intrinsics were not found in your system compiler. In this case, the LLVM API
2448will not be safe for concurrent calls. However, it <em>will</em> be safe for
Jeffrey Yasskin01eba392010-01-29 19:10:38 +0000[diff] [blame]2449hosting threaded applications in the JIT, though <a href="#jitthreading">care
2450must be taken</a> to ensure that side exits and the like do not accidentally
2451result in concurrent LLVM API calls.
Owen Anderson8bc1b3b2009-06-16 01:17:16 +0000[diff] [blame]2452</p>
2453</div>
2454
2455<!-- ======================================================================= -->
2456<div class="doc_subsection">
2457 <a name="shutdown">Ending Execution with <tt>llvm_shutdown()</tt></a>
2458</div>
2459
2460<div class="doc_text">
2461<p>
2462When you are done using the LLVM APIs, you should call <tt>llvm_shutdown()</tt>
Owen Anderson1ad70e32009-06-16 18:04:19 +0000[diff] [blame]2463to deallocate memory used for internal structures. This will also invoke
2464<tt>llvm_stop_multithreaded()</tt> if LLVM is operating in multithreaded mode.
2465As such, <tt>llvm_shutdown()</tt> requires the same isolation guarantees as
2466<tt>llvm_stop_multithreaded()</tt>.
Owen Anderson8bc1b3b2009-06-16 01:17:16 +0000[diff] [blame]2467</p>
2468
2469<p>
2470Note that, if you use scope-based shutdown, you can use the
2471<tt>llvm_shutdown_obj</tt> class, which calls <tt>llvm_shutdown()</tt> in its
2472destructor.
2473</div>
2474
2475<!-- ======================================================================= -->
2476<div class="doc_subsection">
2477 <a name="managedstatic">Lazy Initialization with <tt>ManagedStatic</tt></a>
2478</div>
2479
2480<div class="doc_text">
2481<p>
2482<tt>ManagedStatic</tt> is a utility class in LLVM used to implement static
2483initialization of static resources, such as the global type tables. Before the
2484invocation of <tt>llvm_shutdown()</tt>, it implements a simple lazy
2485initialization scheme. Once <tt>llvm_start_multithreaded()</tt> returns,
2486however, it uses double-checked locking to implement thread-safe lazy
2487initialization.
2488</p>
2489
2490<p>
2491Note that, because no other threads are allowed to issue LLVM API calls before
2492<tt>llvm_start_multithreaded()</tt> returns, it is possible to have
2493<tt>ManagedStatic</tt>s of <tt>llvm::sys::Mutex</tt>s.
2494</p>
Owen Anderson1ad70e32009-06-16 18:04:19 +0000[diff] [blame]2495
2496<p>
2497The <tt>llvm_acquire_global_lock()</tt> and <tt>llvm_release_global_lock</tt>
2498APIs provide access to the global lock used to implement the double-checked
2499locking for lazy initialization. These should only be used internally to LLVM,
2500and only if you know what you're doing!
2501</p>
Owen Anderson8bc1b3b2009-06-16 01:17:16 +0000[diff] [blame]2502</div>
2503
Owen Andersone0c951a2009-08-19 17:58:52 +0000[diff] [blame]2504<!-- ======================================================================= -->
2505<div class="doc_subsection">
2506 <a name="llvmcontext">Achieving Isolation with <tt>LLVMContext</tt></a>
2507</div>
2508
2509<div class="doc_text">
2510<p>
2511<tt>LLVMContext</tt> is an opaque class in the LLVM API which clients can use
2512to operate multiple, isolated instances of LLVM concurrently within the same
2513address space. For instance, in a hypothetical compile-server, the compilation
2514of an individual translation unit is conceptually independent from all the
2515others, and it would be desirable to be able to compile incoming translation
2516units concurrently on independent server threads. Fortunately,
2517<tt>LLVMContext</tt> exists to enable just this kind of scenario!
2518</p>
2519
2520<p>
2521Conceptually, <tt>LLVMContext</tt> provides isolation. Every LLVM entity
2522(<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]2523in LLVM's in-memory IR belongs to an <tt>LLVMContext</tt>. Entities in
Owen Andersone0c951a2009-08-19 17:58:52 +0000[diff] [blame]2524different contexts <em>cannot</em> interact with each other: <tt>Module</tt>s in
2525different contexts cannot be linked together, <tt>Function</tt>s cannot be added
2526to <tt>Module</tt>s in different contexts, etc. What this means is that is is
2527safe to compile on multiple threads simultaneously, as long as no two threads
2528operate on entities within the same context.
2529</p>
2530
2531<p>
2532In practice, very few places in the API require the explicit specification of a
2533<tt>LLVMContext</tt>, other than the <tt>Type</tt> creation/lookup APIs.
2534Because every <tt>Type</tt> carries a reference to its owning context, most
2535other entities can determine what context they belong to by looking at their
2536own <tt>Type</tt>. If you are adding new entities to LLVM IR, please try to
2537maintain this interface design.
2538</p>
2539
2540<p>
2541For clients that do <em>not</em> require the benefits of isolation, LLVM
2542provides a convenience API <tt>getGlobalContext()</tt>. This returns a global,
2543lazily initialized <tt>LLVMContext</tt> that may be used in situations where
2544isolation is not a concern.
2545</p>
2546</div>
2547
Jeffrey Yasskin01eba392010-01-29 19:10:38 +0000[diff] [blame]2548<!-- ======================================================================= -->
2549<div class="doc_subsection">
2550 <a name="jitthreading">Threads and the JIT</a>
2551</div>
2552
2553<div class="doc_text">
2554<p>
2555LLVM's "eager" JIT compiler is safe to use in threaded programs. Multiple
2556threads can call <tt>ExecutionEngine::getPointerToFunction()</tt> or
2557<tt>ExecutionEngine::runFunction()</tt> concurrently, and multiple threads can
2558run code output by the JIT concurrently. The user must still ensure that only
2559one thread accesses IR in a given <tt>LLVMContext</tt> while another thread
2560might be modifying it. One way to do that is to always hold the JIT lock while
2561accessing IR outside the JIT (the JIT <em>modifies</em> the IR by adding
2562<tt>CallbackVH</tt>s). Another way is to only
2563call <tt>getPointerToFunction()</tt> from the <tt>LLVMContext</tt>'s thread.
2564</p>
2565
2566<p>When the JIT is configured to compile lazily (using
2567<tt>ExecutionEngine::DisableLazyCompilation(false)</tt>), there is currently a
2568<a href="http://llvm.org/bugs/show_bug.cgi?id=5184">race condition</a> in
2569updating call sites after a function is lazily-jitted. It's still possible to
2570use the lazy JIT in a threaded program if you ensure that only one thread at a
2571time can call any particular lazy stub and that the JIT lock guards any IR
2572access, but we suggest using only the eager JIT in threaded programs.
2573</p>
2574</div>
2575
Owen Anderson8bc1b3b2009-06-16 01:17:16 +0000[diff] [blame]2576<!-- *********************************************************************** -->
2577<div class="doc_section">
Chris Lattnerd9d6e102005-04-23 16:10:52 +0000[diff] [blame]2578 <a name="advanced">Advanced Topics</a>
2579</div>
2580<!-- *********************************************************************** -->
2581
2582<div class="doc_text">
Chris Lattnerf1b200b2005-04-23 17:27:36 +0000[diff] [blame]2583<p>
2584This section describes some of the advanced or obscure API's that most clients
2585do not need to be aware of. These API's tend manage the inner workings of the
2586LLVM system, and only need to be accessed in unusual circumstances.
2587</p>
2588</div>
Chris Lattnerd9d6e102005-04-23 16:10:52 +0000[diff] [blame]2589
Chris Lattnerf1b200b2005-04-23 17:27:36 +0000[diff] [blame]2590<!-- ======================================================================= -->
2591<div class="doc_subsection">
2592 <a name="TypeResolve">LLVM Type Resolution</a>
2593</div>
Chris Lattnerd9d6e102005-04-23 16:10:52 +0000[diff] [blame]2594
Chris Lattnerf1b200b2005-04-23 17:27:36 +0000[diff] [blame]2595<div class="doc_text">
2596
2597<p>
2598The LLVM type system has a very simple goal: allow clients to compare types for
2599structural equality with a simple pointer comparison (aka a shallow compare).
2600This goal makes clients much simpler and faster, and is used throughout the LLVM
2601system.
2602</p>
2603
2604<p>
2605Unfortunately achieving this goal is not a simple matter. In particular,
2606recursive types and late resolution of opaque types makes the situation very
2607difficult to handle. Fortunately, for the most part, our implementation makes
2608most clients able to be completely unaware of the nasty internal details. The
2609primary case where clients are exposed to the inner workings of it are when
Gabor Greif04367bf2007-07-06 22:07:22 +0000[diff] [blame]2610building a recursive type. In addition to this case, the LLVM bitcode reader,
Chris Lattnerf1b200b2005-04-23 17:27:36 +0000[diff] [blame]2611assembly parser, and linker also have to be aware of the inner workings of this
2612system.
2613</p>
2614
Chris Lattner0f876db2005-04-25 15:47:57 +0000[diff] [blame]2615<p>
2616For our purposes below, we need three concepts. First, an "Opaque Type" is
2617exactly as defined in the <a href="LangRef.html#t_opaque">language
2618reference</a>. Second an "Abstract Type" is any type which includes an
Reid Spencer06565dc2007-01-12 17:11:23 +0000[diff] [blame]2619opaque type as part of its type graph (for example "<tt>{ opaque, i32 }</tt>").
2620Third, 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]2621float }</tt>").
2622</p>
2623
Chris Lattnerf1b200b2005-04-23 17:27:36 +0000[diff] [blame]2624</div>
2625
2626<!-- ______________________________________________________________________ -->
2627<div class="doc_subsubsection">
2628 <a name="BuildRecType">Basic Recursive Type Construction</a>
2629</div>
2630
2631<div class="doc_text">
2632
2633<p>
2634Because the most common question is "how do I build a recursive type with LLVM",
2635we answer it now and explain it as we go. Here we include enough to cause this
2636to be emitted to an output .ll file:
2637</p>
2638
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2639<div class="doc_code">
Chris Lattnerf1b200b2005-04-23 17:27:36 +0000[diff] [blame]2640<pre>
Reid Spencer06565dc2007-01-12 17:11:23 +0000[diff] [blame]2641%mylist = type { %mylist*, i32 }
Chris Lattnerf1b200b2005-04-23 17:27:36 +0000[diff] [blame]2642</pre>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2643</div>
Chris Lattnerf1b200b2005-04-23 17:27:36 +0000[diff] [blame]2644
2645<p>
2646To build this, use the following LLVM APIs:
2647</p>
2648
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2649<div class="doc_code">
Chris Lattnerf1b200b2005-04-23 17:27:36 +0000[diff] [blame]2650<pre>
Bill Wendling82e2eea2006-10-11 18:00:22 +0000[diff] [blame]2651// <i>Create the initial outer struct</i>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2652<a href="#PATypeHolder">PATypeHolder</a> StructTy = OpaqueType::get();
2653std::vector&lt;const Type*&gt; Elts;
Daniel Dunbar58c2ac02008-10-03 22:17:25 +0000[diff] [blame]2654Elts.push_back(PointerType::getUnqual(StructTy));
Nick Lewycky10d64b92007-12-03 01:52:52 +0000[diff] [blame]2655Elts.push_back(Type::Int32Ty);
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2656StructType *NewSTy = StructType::get(Elts);
Chris Lattnerf1b200b2005-04-23 17:27:36 +0000[diff] [blame]2657
Reid Spencer06565dc2007-01-12 17:11:23 +0000[diff] [blame]2658// <i>At this point, NewSTy = "{ opaque*, i32 }". Tell VMCore that</i>
Bill Wendling82e2eea2006-10-11 18:00:22 +0000[diff] [blame]2659// <i>the struct and the opaque type are actually the same.</i>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2660cast&lt;OpaqueType&gt;(StructTy.get())-&gt;<a href="#refineAbstractTypeTo">refineAbstractTypeTo</a>(NewSTy);
Chris Lattnerf1b200b2005-04-23 17:27:36 +0000[diff] [blame]2661
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2662// <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]2663// <i>kept up-to-date</i>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2664NewSTy = cast&lt;StructType&gt;(StructTy.get());
Chris Lattnerf1b200b2005-04-23 17:27:36 +0000[diff] [blame]2665
Bill Wendling82e2eea2006-10-11 18:00:22 +0000[diff] [blame]2666// <i>Add a name for the type to the module symbol table (optional)</i>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2667MyModule-&gt;addTypeName("mylist", NewSTy);
Chris Lattnerf1b200b2005-04-23 17:27:36 +0000[diff] [blame]2668</pre>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2669</div>
Chris Lattnerf1b200b2005-04-23 17:27:36 +0000[diff] [blame]2670
2671<p>
2672This code shows the basic approach used to build recursive types: build a
2673non-recursive type using 'opaque', then use type unification to close the cycle.
2674The type unification step is performed by the <tt><a
Chris Lattneraff26d12007-02-03 03:06:52 +0000[diff] [blame]2675href="#refineAbstractTypeTo">refineAbstractTypeTo</a></tt> method, which is
Chris Lattnerf1b200b2005-04-23 17:27:36 +0000[diff] [blame]2676described next. After that, we describe the <a
2677href="#PATypeHolder">PATypeHolder class</a>.
2678</p>
2679
2680</div>
2681
2682<!-- ______________________________________________________________________ -->
2683<div class="doc_subsubsection">
2684 <a name="refineAbstractTypeTo">The <tt>refineAbstractTypeTo</tt> method</a>
2685</div>
2686
2687<div class="doc_text">
2688<p>
2689The <tt>refineAbstractTypeTo</tt> method starts the type unification process.
2690While this method is actually a member of the DerivedType class, it is most
2691often used on OpaqueType instances. Type unification is actually a recursive
2692process. After unification, types can become structurally isomorphic to
2693existing types, and all duplicates are deleted (to preserve pointer equality).
2694</p>
2695
2696<p>
2697In the example above, the OpaqueType object is definitely deleted.
Reid Spencer06565dc2007-01-12 17:11:23 +0000[diff] [blame]2698Additionally, if there is an "{ \2*, i32}" type already created in the system,
Chris Lattnerf1b200b2005-04-23 17:27:36 +0000[diff] [blame]2699the pointer and struct type created are <b>also</b> deleted. Obviously whenever
2700a type is deleted, any "Type*" pointers in the program are invalidated. As
2701such, it is safest to avoid having <i>any</i> "Type*" pointers to abstract types
2702live across a call to <tt>refineAbstractTypeTo</tt> (note that non-abstract
2703types can never move or be deleted). To deal with this, the <a
2704href="#PATypeHolder">PATypeHolder</a> class is used to maintain a stable
2705reference to a possibly refined type, and the <a
2706href="#AbstractTypeUser">AbstractTypeUser</a> class is used to update more
2707complex datastructures.
2708</p>
2709
2710</div>
2711
2712<!-- ______________________________________________________________________ -->
2713<div class="doc_subsubsection">
2714 <a name="PATypeHolder">The PATypeHolder Class</a>
2715</div>
2716
2717<div class="doc_text">
2718<p>
2719PATypeHolder is a form of a "smart pointer" for Type objects. When VMCore
2720happily goes about nuking types that become isomorphic to existing types, it
2721automatically updates all PATypeHolder objects to point to the new type. In the
2722example above, this allows the code to maintain a pointer to the resultant
2723resolved recursive type, even though the Type*'s are potentially invalidated.
2724</p>
2725
2726<p>
2727PATypeHolder is an extremely light-weight object that uses a lazy union-find
2728implementation to update pointers. For example the pointer from a Value to its
2729Type is maintained by PATypeHolder objects.
2730</p>
2731
2732</div>
2733
2734<!-- ______________________________________________________________________ -->
2735<div class="doc_subsubsection">
2736 <a name="AbstractTypeUser">The AbstractTypeUser Class</a>
2737</div>
2738
2739<div class="doc_text">
2740
2741<p>
2742Some data structures need more to perform more complex updates when types get
Chris Lattner263a98e2007-02-16 04:37:31 +0000[diff] [blame]2743resolved. To support this, a class can derive from the AbstractTypeUser class.
2744This class
Chris Lattnerf1b200b2005-04-23 17:27:36 +0000[diff] [blame]2745allows it to get callbacks when certain types are resolved. To register to get
2746callbacks for a particular type, the DerivedType::{add/remove}AbstractTypeUser
Chris Lattner0f876db2005-04-25 15:47:57 +0000[diff] [blame]2747methods can be called on a type. Note that these methods only work for <i>
Reid Spencer06565dc2007-01-12 17:11:23 +0000[diff] [blame]2748 abstract</i> types. Concrete types (those that do not include any opaque
2749objects) can never be refined.
Chris Lattnerf1b200b2005-04-23 17:27:36 +0000[diff] [blame]2750</p>
Chris Lattnerd9d6e102005-04-23 16:10:52 +0000[diff] [blame]2751</div>
2752
2753
2754<!-- ======================================================================= -->
2755<div class="doc_subsection">
Chris Lattner263a98e2007-02-16 04:37:31 +0000[diff] [blame]2756 <a name="SymbolTable">The <tt>ValueSymbolTable</tt> and
2757 <tt>TypeSymbolTable</tt> classes</a>
Chris Lattnerd9d6e102005-04-23 16:10:52 +0000[diff] [blame]2758</div>
Chris Lattnerf1b200b2005-04-23 17:27:36 +0000[diff] [blame]2759
Chris Lattnerd9d6e102005-04-23 16:10:52 +0000[diff] [blame]2760<div class="doc_text">
Chris Lattner263a98e2007-02-16 04:37:31 +0000[diff] [blame]2761<p>The <tt><a href="http://llvm.org/doxygen/classllvm_1_1ValueSymbolTable.html">
2762ValueSymbolTable</a></tt> class provides a symbol table that the <a
Chris Lattnerd9d6e102005-04-23 16:10:52 +0000[diff] [blame]2763href="#Function"><tt>Function</tt></a> and <a href="#Module">
Chris Lattner263a98e2007-02-16 04:37:31 +0000[diff] [blame]2764<tt>Module</tt></a> classes use for naming value definitions. The symbol table
2765can provide a name for any <a href="#Value"><tt>Value</tt></a>.
2766The <tt><a href="http://llvm.org/doxygen/classllvm_1_1TypeSymbolTable.html">
2767TypeSymbolTable</a></tt> class is used by the <tt>Module</tt> class to store
2768names for types.</p>
Chris Lattnerd9d6e102005-04-23 16:10:52 +0000[diff] [blame]2769
Reid Spencera6362242007-01-07 00:41:39 +0000[diff] [blame]2770<p>Note that the <tt>SymbolTable</tt> class should not be directly accessed
2771by most clients. It should only be used when iteration over the symbol table
2772names themselves are required, which is very special purpose. Note that not
2773all LLVM
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2774<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]2775an empty name) do not exist in the symbol table.
2776</p>
2777
Chris Lattner263a98e2007-02-16 04:37:31 +0000[diff] [blame]2778<p>These symbol tables support iteration over the values/types in the symbol
2779table with <tt>begin/end/iterator</tt> and supports querying to see if a
2780specific name is in the symbol table (with <tt>lookup</tt>). The
2781<tt>ValueSymbolTable</tt> class exposes no public mutator methods, instead,
2782simply call <tt>setName</tt> on a value, which will autoinsert it into the
2783appropriate symbol table. For types, use the Module::addTypeName method to
2784insert entries into the symbol table.</p>
Chris Lattnerd9d6e102005-04-23 16:10:52 +0000[diff] [blame]2785
Chris Lattnerd9d6e102005-04-23 16:10:52 +0000[diff] [blame]2786</div>
2787
2788
2789
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2790<!-- ======================================================================= -->
2791<div class="doc_subsection">
2792 <a name="UserLayout">The <tt>User</tt> and owned <tt>Use</tt> classes' memory layout</a>
2793</div>
2794
2795<div class="doc_text">
2796<p>The <tt><a href="http://llvm.org/doxygen/classllvm_1_1User.html">
Gabor Greiffd095b62009-01-05 16:05:32 +0000[diff] [blame]2797User</a></tt> class provides a basis for expressing the ownership of <tt>User</tt>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2798towards other <tt><a href="http://llvm.org/doxygen/classllvm_1_1Value.html">
2799Value</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]2800Use</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]2801addition and removal.</p>
2802
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2803<!-- ______________________________________________________________________ -->
2804<div class="doc_subsubsection">
Gabor Greiffd095b62009-01-05 16:05:32 +0000[diff] [blame]2805 <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]2806</div>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2807
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2808<div class="doc_text">
2809<p>
2810A subclass of <tt>User</tt> can choose between incorporating its <tt>Use</tt> objects
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2811or refer to them out-of-line by means of a pointer. A mixed variant
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2812(some <tt>Use</tt>s inline others hung off) is impractical and breaks the invariant
2813that the <tt>Use</tt> objects belonging to the same <tt>User</tt> form a contiguous array.
2814</p>
2815</div>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2816
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2817<p>
2818We have 2 different layouts in the <tt>User</tt> (sub)classes:
2819<ul>
2820<li><p>Layout a)
2821The <tt>Use</tt> object(s) are inside (resp. at fixed offset) of the <tt>User</tt>
2822object and there are a fixed number of them.</p>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2823
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2824<li><p>Layout b)
2825The <tt>Use</tt> object(s) are referenced by a pointer to an
2826array from the <tt>User</tt> object and there may be a variable
2827number of them.</p>
2828</ul>
2829<p>
Gabor Greifd41720a2008-06-25 00:10:22 +0000[diff] [blame]2830As of v2.4 each layout still possesses a direct pointer to the
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2831start of the array of <tt>Use</tt>s. Though not mandatory for layout a),
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2832we stick to this redundancy for the sake of simplicity.
Gabor Greifd41720a2008-06-25 00:10:22 +0000[diff] [blame]2833The <tt>User</tt> object also stores the number of <tt>Use</tt> objects it
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2834has. (Theoretically this information can also be calculated
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2835given the scheme presented below.)</p>
2836<p>
2837Special forms of allocation operators (<tt>operator new</tt>)
Gabor Greifd41720a2008-06-25 00:10:22 +0000[diff] [blame]2838enforce the following memory layouts:</p>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2839
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2840<ul>
Gabor Greifd41720a2008-06-25 00:10:22 +0000[diff] [blame]2841<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]2842
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2843<pre>
2844...---.---.---.---.-------...
2845 | P | P | P | P | User
2846'''---'---'---'---'-------'''
2847</pre>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2848
Gabor Greifd41720a2008-06-25 00:10:22 +0000[diff] [blame]2849<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]2850<pre>
2851.-------...
2852| User
2853'-------'''
2854 |
2855 v
2856 .---.---.---.---...
2857 | P | P | P | P |
2858 '---'---'---'---'''
2859</pre>
2860</ul>
2861<i>(In the above figures '<tt>P</tt>' stands for the <tt>Use**</tt> that
2862 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]2863
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2864<!-- ______________________________________________________________________ -->
2865<div class="doc_subsubsection">
Gabor Greiffd095b62009-01-05 16:05:32 +0000[diff] [blame]2866 <a name="Waymarking">The waymarking algorithm</a>
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2867</div>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2868
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2869<div class="doc_text">
2870<p>
Gabor Greifd41720a2008-06-25 00:10:22 +0000[diff] [blame]2871Since the <tt>Use</tt> objects are deprived of the direct (back)pointer to
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2872their <tt>User</tt> objects, there must be a fast and exact method to
2873recover it. This is accomplished by the following scheme:</p>
2874</div>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2875
Gabor Greifd41720a2008-06-25 00:10:22 +0000[diff] [blame]2876A 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]2877start of the <tt>User</tt> object:
2878<ul>
2879<li><tt>00</tt> &mdash;&gt; binary digit 0</li>
2880<li><tt>01</tt> &mdash;&gt; binary digit 1</li>
2881<li><tt>10</tt> &mdash;&gt; stop and calculate (<tt>s</tt>)</li>
2882<li><tt>11</tt> &mdash;&gt; full stop (<tt>S</tt>)</li>
2883</ul>
2884<p>
2885Given a <tt>Use*</tt>, all we have to do is to walk till we get
2886a stop and we either have a <tt>User</tt> immediately behind or
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2887we have to walk to the next stop picking up digits
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2888and calculating the offset:</p>
2889<pre>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2890.---.---.---.---.---.---.---.---.---.---.---.---.---.---.---.---.----------------
2891| 1 | s | 1 | 0 | 1 | 0 | s | 1 | 1 | 0 | s | 1 | 1 | s | 1 | S | User (or User*)
2892'---'---'---'---'---'---'---'---'---'---'---'---'---'---'---'---'----------------
2893 |+15 |+10 |+6 |+3 |+1
2894 | | | | |__>
2895 | | | |__________>
2896 | | |______________________>
2897 | |______________________________________>
2898 |__________________________________________________________>
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2899</pre>
2900<p>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2901Only the significant number of bits need to be stored between the
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2902stops, so that the <i>worst case is 20 memory accesses</i> when there are
29031000 <tt>Use</tt> objects associated with a <tt>User</tt>.</p>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2904
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2905<!-- ______________________________________________________________________ -->
2906<div class="doc_subsubsection">
Gabor Greiffd095b62009-01-05 16:05:32 +0000[diff] [blame]2907 <a name="ReferenceImpl">Reference implementation</a>
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2908</div>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2909
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2910<div class="doc_text">
2911<p>
2912The following literate Haskell fragment demonstrates the concept:</p>
2913</div>
2914
2915<div class="doc_code">
2916<pre>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2917> import Test.QuickCheck
2918>
2919> digits :: Int -> [Char] -> [Char]
2920> digits 0 acc = '0' : acc
2921> digits 1 acc = '1' : acc
2922> digits n acc = digits (n `div` 2) $ digits (n `mod` 2) acc
2923>
2924> dist :: Int -> [Char] -> [Char]
2925> dist 0 [] = ['S']
2926> dist 0 acc = acc
2927> dist 1 acc = let r = dist 0 acc in 's' : digits (length r) r
2928> dist n acc = dist (n - 1) $ dist 1 acc
2929>
2930> takeLast n ss = reverse $ take n $ reverse ss
2931>
2932> test = takeLast 40 $ dist 20 []
2933>
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2934</pre>
2935</div>
2936<p>
2937Printing &lt;test&gt; gives: <tt>"1s100000s11010s10100s1111s1010s110s11s1S"</tt></p>
2938<p>
2939The reverse algorithm computes the length of the string just by examining
2940a certain prefix:</p>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2941
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2942<div class="doc_code">
2943<pre>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2944> pref :: [Char] -> Int
2945> pref "S" = 1
2946> pref ('s':'1':rest) = decode 2 1 rest
2947> pref (_:rest) = 1 + pref rest
2948>
2949> decode walk acc ('0':rest) = decode (walk + 1) (acc * 2) rest
2950> decode walk acc ('1':rest) = decode (walk + 1) (acc * 2 + 1) rest
2951> decode walk acc _ = walk + acc
2952>
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2953</pre>
2954</div>
2955<p>
2956Now, as expected, printing &lt;pref test&gt; gives <tt>40</tt>.</p>
2957<p>
2958We can <i>quickCheck</i> this with following property:</p>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2959
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2960<div class="doc_code">
2961<pre>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2962> testcase = dist 2000 []
2963> testcaseLength = length testcase
2964>
2965> identityProp n = n > 0 && n <= testcaseLength ==> length arr == pref arr
2966> where arr = takeLast n testcase
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2967>
2968</pre>
2969</div>
2970<p>
2971As expected &lt;quickCheck identityProp&gt; gives:</p>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2972
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2973<pre>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2974*Main> quickCheck identityProp
2975OK, passed 100 tests.
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2976</pre>
2977<p>
2978Let's be a bit more exhaustive:</p>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2979
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2980<div class="doc_code">
2981<pre>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2982>
2983> deepCheck p = check (defaultConfig { configMaxTest = 500 }) p
2984>
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2985</pre>
2986</div>
2987<p>
2988And here is the result of &lt;deepCheck identityProp&gt;:</p>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2989
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2990<pre>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2991*Main> deepCheck identityProp
2992OK, passed 500 tests.
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2993</pre>
2994
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2995<!-- ______________________________________________________________________ -->
2996<div class="doc_subsubsection">
Gabor Greiffd095b62009-01-05 16:05:32 +0000[diff] [blame]2997 <a name="Tagging">Tagging considerations</a>
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2998</div>
2999
3000<p>
3001To maintain the invariant that the 2 LSBits of each <tt>Use**</tt> in <tt>Use</tt>
3002never change after being set up, setters of <tt>Use::Prev</tt> must re-tag the
3003new <tt>Use**</tt> on every modification. Accordingly getters must strip the
3004tag bits.</p>
3005<p>
Gabor Greifd41720a2008-06-25 00:10:22 +0000[diff] [blame]3006For layout b) instead of the <tt>User</tt> we find a pointer (<tt>User*</tt> with LSBit set).
3007Following this pointer brings us to the <tt>User</tt>. A portable trick ensures
3008that the first bytes of <tt>User</tt> (if interpreted as a pointer) never has
Gabor Greiffd095b62009-01-05 16:05:32 +0000[diff] [blame]3009the LSBit set. (Portability is relying on the fact that all known compilers place the
3010<tt>vptr</tt> in the first word of the instances.)</p>
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]3011
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]3012</div>
3013
3014 <!-- *********************************************************************** -->
Chris Lattnerd9d6e102005-04-23 16:10:52 +0000[diff] [blame]3015<div class="doc_section">
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3016 <a name="coreclasses">The Core LLVM Class Hierarchy Reference </a>
3017</div>
3018<!-- *********************************************************************** -->
3019
3020<div class="doc_text">
Reid Spencer303c4b42007-01-12 17:26:25 +0000[diff] [blame]3021<p><tt>#include "<a href="/doxygen/Type_8h-source.html">llvm/Type.h</a>"</tt>
3022<br>doxygen info: <a href="/doxygen/classllvm_1_1Type.html">Type Class</a></p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3023
3024<p>The Core LLVM classes are the primary means of representing the program
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3025being inspected or transformed. The core LLVM classes are defined in
3026header files in the <tt>include/llvm/</tt> directory, and implemented in
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3027the <tt>lib/VMCore</tt> directory.</p>
3028
3029</div>
3030
3031<!-- ======================================================================= -->
3032<div class="doc_subsection">
Reid Spencer303c4b42007-01-12 17:26:25 +0000[diff] [blame]3033 <a name="Type">The <tt>Type</tt> class and Derived Types</a>
3034</div>
3035
3036<div class="doc_text">
3037
3038 <p><tt>Type</tt> is a superclass of all type classes. Every <tt>Value</tt> has
3039 a <tt>Type</tt>. <tt>Type</tt> cannot be instantiated directly but only
3040 through its subclasses. Certain primitive types (<tt>VoidType</tt>,
3041 <tt>LabelType</tt>, <tt>FloatType</tt> and <tt>DoubleType</tt>) have hidden
3042 subclasses. They are hidden because they offer no useful functionality beyond
3043 what the <tt>Type</tt> class offers except to distinguish themselves from
3044 other subclasses of <tt>Type</tt>.</p>
3045 <p>All other types are subclasses of <tt>DerivedType</tt>. Types can be
3046 named, but this is not a requirement. There exists exactly
3047 one instance of a given shape at any one time. This allows type equality to
3048 be performed with address equality of the Type Instance. That is, given two
3049 <tt>Type*</tt> values, the types are identical if the pointers are identical.
3050 </p>
3051</div>
3052
3053<!-- _______________________________________________________________________ -->
3054<div class="doc_subsubsection">
Gabor Greiffd095b62009-01-05 16:05:32 +0000[diff] [blame]3055 <a name="m_Type">Important Public Methods</a>
Reid Spencer303c4b42007-01-12 17:26:25 +0000[diff] [blame]3056</div>
3057
3058<div class="doc_text">
3059
3060<ul>
Duncan Sandsb0bc6c32010-02-15 16:12:20 +0000[diff] [blame]3061 <li><tt>bool isIntegerTy() const</tt>: Returns true for any integer type.</li>
Reid Spencer303c4b42007-01-12 17:26:25 +0000[diff] [blame]3062
Duncan Sandsb0bc6c32010-02-15 16:12:20 +0000[diff] [blame]3063 <li><tt>bool isFloatingPointTy()</tt>: Return true if this is one of the five
Reid Spencer303c4b42007-01-12 17:26:25 +0000[diff] [blame]3064 floating point types.</li>
3065
3066 <li><tt>bool isAbstract()</tt>: Return true if the type is abstract (contains
3067 an OpaqueType anywhere in its definition).</li>
3068
3069 <li><tt>bool isSized()</tt>: Return true if the type has known size. Things
3070 that don't have a size are abstract types, labels and void.</li>
3071
3072</ul>
3073</div>
3074
3075<!-- _______________________________________________________________________ -->
3076<div class="doc_subsubsection">
Gabor Greiffd095b62009-01-05 16:05:32 +0000[diff] [blame]3077 <a name="derivedtypes">Important Derived Types</a>
Reid Spencer303c4b42007-01-12 17:26:25 +0000[diff] [blame]3078</div>
3079<div class="doc_text">
3080<dl>
3081 <dt><tt>IntegerType</tt></dt>
3082 <dd>Subclass of DerivedType that represents integer types of any bit width.
3083 Any bit width between <tt>IntegerType::MIN_INT_BITS</tt> (1) and
3084 <tt>IntegerType::MAX_INT_BITS</tt> (~8 million) can be represented.
3085 <ul>
3086 <li><tt>static const IntegerType* get(unsigned NumBits)</tt>: get an integer
3087 type of a specific bit width.</li>
3088 <li><tt>unsigned getBitWidth() const</tt>: Get the bit width of an integer
3089 type.</li>
3090 </ul>
3091 </dd>
3092 <dt><tt>SequentialType</tt></dt>
3093 <dd>This is subclassed by ArrayType and PointerType
3094 <ul>
3095 <li><tt>const Type * getElementType() const</tt>: Returns the type of each
3096 of the elements in the sequential type. </li>
3097 </ul>
3098 </dd>
3099 <dt><tt>ArrayType</tt></dt>
3100 <dd>This is a subclass of SequentialType and defines the interface for array
3101 types.
3102 <ul>
3103 <li><tt>unsigned getNumElements() const</tt>: Returns the number of
3104 elements in the array. </li>
3105 </ul>
3106 </dd>
3107 <dt><tt>PointerType</tt></dt>
Chris Lattner302da1e2007-02-03 03:05:57 +0000[diff] [blame]3108 <dd>Subclass of SequentialType for pointer types.</dd>
Reid Spencer9d6565a2007-02-15 02:26:10 +0000[diff] [blame]3109 <dt><tt>VectorType</tt></dt>
Reid Spencer485bad12007-02-15 03:07:05 +0000[diff] [blame]3110 <dd>Subclass of SequentialType for vector types. A
3111 vector type is similar to an ArrayType but is distinguished because it is
Benjamin Kramer8040cd32009-10-12 14:46:08 +0000[diff] [blame]3112 a first class type whereas ArrayType is not. Vector types are used for
Reid Spencer303c4b42007-01-12 17:26:25 +0000[diff] [blame]3113 vector operations and are usually small vectors of of an integer or floating
3114 point type.</dd>
3115 <dt><tt>StructType</tt></dt>
3116 <dd>Subclass of DerivedTypes for struct types.</dd>
Duncan Sands8036ca42007-03-30 12:22:09 +0000[diff] [blame]3117 <dt><tt><a name="FunctionType">FunctionType</a></tt></dt>
Reid Spencer303c4b42007-01-12 17:26:25 +0000[diff] [blame]3118 <dd>Subclass of DerivedTypes for function types.
3119 <ul>
Dan Gohman4bb31bf2010-03-30 20:04:57 +0000[diff] [blame]3120 <li><tt>bool isVarArg() const</tt>: Returns true if it's a vararg
Reid Spencer303c4b42007-01-12 17:26:25 +0000[diff] [blame]3121 function</li>
3122 <li><tt> const Type * getReturnType() const</tt>: Returns the
3123 return type of the function.</li>
3124 <li><tt>const Type * getParamType (unsigned i)</tt>: Returns
3125 the type of the ith parameter.</li>
3126 <li><tt> const unsigned getNumParams() const</tt>: Returns the
3127 number of formal parameters.</li>
3128 </ul>
3129 </dd>
3130 <dt><tt>OpaqueType</tt></dt>
3131 <dd>Sublcass of DerivedType for abstract types. This class
3132 defines no content and is used as a placeholder for some other type. Note
3133 that OpaqueType is used (temporarily) during type resolution for forward
3134 references of types. Once the referenced type is resolved, the OpaqueType
3135 is replaced with the actual type. OpaqueType can also be used for data
3136 abstraction. At link time opaque types can be resolved to actual types
3137 of the same name.</dd>
3138</dl>
3139</div>
3140
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]3141
3142
3143<!-- ======================================================================= -->
3144<div class="doc_subsection">
3145 <a name="Module">The <tt>Module</tt> class</a>
3146</div>
3147
3148<div class="doc_text">
3149
3150<p><tt>#include "<a
3151href="/doxygen/Module_8h-source.html">llvm/Module.h</a>"</tt><br> doxygen info:
3152<a href="/doxygen/classllvm_1_1Module.html">Module Class</a></p>
3153
3154<p>The <tt>Module</tt> class represents the top level structure present in LLVM
3155programs. An LLVM module is effectively either a translation unit of the
3156original program or a combination of several translation units merged by the
3157linker. The <tt>Module</tt> class keeps track of a list of <a
3158href="#Function"><tt>Function</tt></a>s, a list of <a
3159href="#GlobalVariable"><tt>GlobalVariable</tt></a>s, and a <a
3160href="#SymbolTable"><tt>SymbolTable</tt></a>. Additionally, it contains a few
3161helpful member functions that try to make common operations easy.</p>
3162
3163</div>
3164
3165<!-- _______________________________________________________________________ -->
3166<div class="doc_subsubsection">
3167 <a name="m_Module">Important Public Members of the <tt>Module</tt> class</a>
3168</div>
3169
3170<div class="doc_text">
3171
3172<ul>
3173 <li><tt>Module::Module(std::string name = "")</tt></li>
3174</ul>
3175
3176<p>Constructing a <a href="#Module">Module</a> is easy. You can optionally
3177provide a name for it (probably based on the name of the translation unit).</p>
3178
3179<ul>
3180 <li><tt>Module::iterator</tt> - Typedef for function list iterator<br>
3181 <tt>Module::const_iterator</tt> - Typedef for const_iterator.<br>
3182
3183 <tt>begin()</tt>, <tt>end()</tt>
3184 <tt>size()</tt>, <tt>empty()</tt>
3185
3186 <p>These are forwarding methods that make it easy to access the contents of
3187 a <tt>Module</tt> object's <a href="#Function"><tt>Function</tt></a>
3188 list.</p></li>
3189
3190 <li><tt>Module::FunctionListType &amp;getFunctionList()</tt>
3191
3192 <p> Returns the list of <a href="#Function"><tt>Function</tt></a>s. This is
3193 necessary to use when you need to update the list or perform a complex
3194 action that doesn't have a forwarding method.</p>
3195
3196 <p><!-- Global Variable --></p></li>
3197</ul>
3198
3199<hr>
3200
3201<ul>
3202 <li><tt>Module::global_iterator</tt> - Typedef for global variable list iterator<br>
3203
3204 <tt>Module::const_global_iterator</tt> - Typedef for const_iterator.<br>
3205
3206 <tt>global_begin()</tt>, <tt>global_end()</tt>
3207 <tt>global_size()</tt>, <tt>global_empty()</tt>
3208
3209 <p> These are forwarding methods that make it easy to access the contents of
3210 a <tt>Module</tt> object's <a
3211 href="#GlobalVariable"><tt>GlobalVariable</tt></a> list.</p></li>
3212
3213 <li><tt>Module::GlobalListType &amp;getGlobalList()</tt>
3214
3215 <p>Returns the list of <a
3216 href="#GlobalVariable"><tt>GlobalVariable</tt></a>s. This is necessary to
3217 use when you need to update the list or perform a complex action that
3218 doesn't have a forwarding method.</p>
3219
3220 <p><!-- Symbol table stuff --> </p></li>
3221</ul>
3222
3223<hr>
3224
3225<ul>
3226 <li><tt><a href="#SymbolTable">SymbolTable</a> *getSymbolTable()</tt>
3227
3228 <p>Return a reference to the <a href="#SymbolTable"><tt>SymbolTable</tt></a>
3229 for this <tt>Module</tt>.</p>
3230
3231 <p><!-- Convenience methods --></p></li>
3232</ul>
3233
3234<hr>
3235
3236<ul>
3237 <li><tt><a href="#Function">Function</a> *getFunction(const std::string
3238 &amp;Name, const <a href="#FunctionType">FunctionType</a> *Ty)</tt>
3239
3240 <p>Look up the specified function in the <tt>Module</tt> <a
3241 href="#SymbolTable"><tt>SymbolTable</tt></a>. If it does not exist, return
3242 <tt>null</tt>.</p></li>
3243
3244 <li><tt><a href="#Function">Function</a> *getOrInsertFunction(const
3245 std::string &amp;Name, const <a href="#FunctionType">FunctionType</a> *T)</tt>
3246
3247 <p>Look up the specified function in the <tt>Module</tt> <a
3248 href="#SymbolTable"><tt>SymbolTable</tt></a>. If it does not exist, add an
3249 external declaration for the function and return it.</p></li>
3250
3251 <li><tt>std::string getTypeName(const <a href="#Type">Type</a> *Ty)</tt>
3252
3253 <p>If there is at least one entry in the <a
3254 href="#SymbolTable"><tt>SymbolTable</tt></a> for the specified <a
3255 href="#Type"><tt>Type</tt></a>, return it. Otherwise return the empty
3256 string.</p></li>
3257
3258 <li><tt>bool addTypeName(const std::string &amp;Name, const <a
3259 href="#Type">Type</a> *Ty)</tt>
3260
3261 <p>Insert an entry in the <a href="#SymbolTable"><tt>SymbolTable</tt></a>
3262 mapping <tt>Name</tt> to <tt>Ty</tt>. If there is already an entry for this
3263 name, true is returned and the <a
3264 href="#SymbolTable"><tt>SymbolTable</tt></a> is not modified.</p></li>
3265</ul>
3266
3267</div>
3268
3269
Reid Spencer303c4b42007-01-12 17:26:25 +0000[diff] [blame]3270<!-- ======================================================================= -->
3271<div class="doc_subsection">
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3272 <a name="Value">The <tt>Value</tt> class</a>
3273</div>
3274
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]3275<div class="doc_text">
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3276
3277<p><tt>#include "<a href="/doxygen/Value_8h-source.html">llvm/Value.h</a>"</tt>
3278<br>
Chris Lattner00815172007-01-04 22:01:45 +0000[diff] [blame]3279doxygen info: <a href="/doxygen/classllvm_1_1Value.html">Value Class</a></p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3280
3281<p>The <tt>Value</tt> class is the most important class in the LLVM Source
3282base. It represents a typed value that may be used (among other things) as an
3283operand to an instruction. There are many different types of <tt>Value</tt>s,
3284such as <a href="#Constant"><tt>Constant</tt></a>s,<a
3285href="#Argument"><tt>Argument</tt></a>s. Even <a
3286href="#Instruction"><tt>Instruction</tt></a>s and <a
3287href="#Function"><tt>Function</tt></a>s are <tt>Value</tt>s.</p>
3288
3289<p>A particular <tt>Value</tt> may be used many times in the LLVM representation
3290for a program. For example, an incoming argument to a function (represented
3291with an instance of the <a href="#Argument">Argument</a> class) is "used" by
3292every instruction in the function that references the argument. To keep track
3293of this relationship, the <tt>Value</tt> class keeps a list of all of the <a
3294href="#User"><tt>User</tt></a>s that is using it (the <a
3295href="#User"><tt>User</tt></a> class is a base class for all nodes in the LLVM
3296graph that can refer to <tt>Value</tt>s). This use list is how LLVM represents
3297def-use information in the program, and is accessible through the <tt>use_</tt>*
3298methods, shown below.</p>
3299
3300<p>Because LLVM is a typed representation, every LLVM <tt>Value</tt> is typed,
3301and this <a href="#Type">Type</a> is available through the <tt>getType()</tt>
3302method. In addition, all LLVM values can be named. The "name" of the
3303<tt>Value</tt> is a symbolic string printed in the LLVM code:</p>
3304
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]3305<div class="doc_code">
3306<pre>
Reid Spencer06565dc2007-01-12 17:11:23 +0000[diff] [blame]3307%<b>foo</b> = add i32 1, 2
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]3308</pre>
3309</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3310
Duncan Sands8036ca42007-03-30 12:22:09 +0000[diff] [blame]3311<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]3312that the name of any value may be missing (an empty string), so names should
3313<b>ONLY</b> be used for debugging (making the source code easier to read,
3314debugging printouts), they should not be used to keep track of values or map
3315between them. For this purpose, use a <tt>std::map</tt> of pointers to the
3316<tt>Value</tt> itself instead.</p>
3317
3318<p>One important aspect of LLVM is that there is no distinction between an SSA
3319variable and the operation that produces it. Because of this, any reference to
3320the value produced by an instruction (or the value available as an incoming
Chris Lattnerd5fc4fc2004-03-18 14:58:55 +0000[diff] [blame]3321argument, for example) is represented as a direct pointer to the instance of
3322the class that
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3323represents this value. Although this may take some getting used to, it
3324simplifies the representation and makes it easier to manipulate.</p>
3325
3326</div>
3327
3328<!-- _______________________________________________________________________ -->
3329<div class="doc_subsubsection">
3330 <a name="m_Value">Important Public Members of the <tt>Value</tt> class</a>
3331</div>
3332
3333<div class="doc_text">
3334
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3335<ul>
3336 <li><tt>Value::use_iterator</tt> - Typedef for iterator over the
3337use-list<br>
Gabor Greifbbbf9a22010-03-26 19:59:25 +0000[diff] [blame]3338 <tt>Value::const_use_iterator</tt> - Typedef for const_iterator over
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3339the use-list<br>
3340 <tt>unsigned use_size()</tt> - Returns the number of users of the
3341value.<br>
Chris Lattner9355b472002-09-06 02:50:58 +0000[diff] [blame]3342 <tt>bool use_empty()</tt> - Returns true if there are no users.<br>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3343 <tt>use_iterator use_begin()</tt> - Get an iterator to the start of
3344the use-list.<br>
3345 <tt>use_iterator use_end()</tt> - Get an iterator to the end of the
3346use-list.<br>
3347 <tt><a href="#User">User</a> *use_back()</tt> - Returns the last
3348element in the list.
3349 <p> These methods are the interface to access the def-use
3350information in LLVM. As with all other iterators in LLVM, the naming
3351conventions follow the conventions defined by the <a href="#stl">STL</a>.</p>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3352 </li>
3353 <li><tt><a href="#Type">Type</a> *getType() const</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3354 <p>This method returns the Type of the Value.</p>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3355 </li>
3356 <li><tt>bool hasName() const</tt><br>
Chris Lattner9355b472002-09-06 02:50:58 +0000[diff] [blame]3357 <tt>std::string getName() const</tt><br>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3358 <tt>void setName(const std::string &amp;Name)</tt>
3359 <p> This family of methods is used to access and assign a name to a <tt>Value</tt>,
3360be aware of the <a href="#nameWarning">precaution above</a>.</p>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3361 </li>
3362 <li><tt>void replaceAllUsesWith(Value *V)</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3363
3364 <p>This method traverses the use list of a <tt>Value</tt> changing all <a
3365 href="#User"><tt>User</tt>s</a> of the current value to refer to
3366 "<tt>V</tt>" instead. For example, if you detect that an instruction always
3367 produces a constant value (for example through constant folding), you can
3368 replace all uses of the instruction with the constant like this:</p>
3369
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]3370<div class="doc_code">
3371<pre>
3372Inst-&gt;replaceAllUsesWith(ConstVal);
3373</pre>
3374</div>
3375
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3376</ul>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3377
3378</div>
3379
3380<!-- ======================================================================= -->
3381<div class="doc_subsection">
3382 <a name="User">The <tt>User</tt> class</a>
3383</div>
3384
3385<div class="doc_text">
3386
3387<p>
3388<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]3389doxygen info: <a href="/doxygen/classllvm_1_1User.html">User Class</a><br>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3390Superclass: <a href="#Value"><tt>Value</tt></a></p>
3391
3392<p>The <tt>User</tt> class is the common base class of all LLVM nodes that may
3393refer to <a href="#Value"><tt>Value</tt></a>s. It exposes a list of "Operands"
3394that are all of the <a href="#Value"><tt>Value</tt></a>s that the User is
3395referring to. The <tt>User</tt> class itself is a subclass of
3396<tt>Value</tt>.</p>
3397
3398<p>The operands of a <tt>User</tt> point directly to the LLVM <a
3399href="#Value"><tt>Value</tt></a> that it refers to. Because LLVM uses Static
3400Single Assignment (SSA) form, there can only be one definition referred to,
3401allowing this direct connection. This connection provides the use-def
3402information in LLVM.</p>
3403
3404</div>
3405
3406<!-- _______________________________________________________________________ -->
3407<div class="doc_subsubsection">
3408 <a name="m_User">Important Public Members of the <tt>User</tt> class</a>
3409</div>
3410
3411<div class="doc_text">
3412
3413<p>The <tt>User</tt> class exposes the operand list in two ways: through
3414an index access interface and through an iterator based interface.</p>
3415
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3416<ul>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3417 <li><tt>Value *getOperand(unsigned i)</tt><br>
3418 <tt>unsigned getNumOperands()</tt>
3419 <p> These two methods expose the operands of the <tt>User</tt> in a
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3420convenient form for direct access.</p></li>
3421
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3422 <li><tt>User::op_iterator</tt> - Typedef for iterator over the operand
3423list<br>
Chris Lattner58360822005-01-17 00:12:04 +0000[diff] [blame]3424 <tt>op_iterator op_begin()</tt> - Get an iterator to the start of
3425the operand list.<br>
3426 <tt>op_iterator op_end()</tt> - Get an iterator to the end of the
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3427operand list.
3428 <p> Together, these methods make up the iterator based interface to
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3429the operands of a <tt>User</tt>.</p></li>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3430</ul>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3431
3432</div>
3433
3434<!-- ======================================================================= -->
3435<div class="doc_subsection">
3436 <a name="Instruction">The <tt>Instruction</tt> class</a>
3437</div>
3438
3439<div class="doc_text">
3440
3441<p><tt>#include "</tt><tt><a
3442href="/doxygen/Instruction_8h-source.html">llvm/Instruction.h</a>"</tt><br>
Misha Brukman31ca1de2004-06-03 23:35:54 +0000[diff] [blame]3443doxygen info: <a href="/doxygen/classllvm_1_1Instruction.html">Instruction Class</a><br>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3444Superclasses: <a href="#User"><tt>User</tt></a>, <a
3445href="#Value"><tt>Value</tt></a></p>
3446
3447<p>The <tt>Instruction</tt> class is the common base class for all LLVM
3448instructions. It provides only a few methods, but is a very commonly used
3449class. The primary data tracked by the <tt>Instruction</tt> class itself is the
3450opcode (instruction type) and the parent <a
3451href="#BasicBlock"><tt>BasicBlock</tt></a> the <tt>Instruction</tt> is embedded
3452into. To represent a specific type of instruction, one of many subclasses of
3453<tt>Instruction</tt> are used.</p>
3454
3455<p> Because the <tt>Instruction</tt> class subclasses the <a
3456href="#User"><tt>User</tt></a> class, its operands can be accessed in the same
3457way as for other <a href="#User"><tt>User</tt></a>s (with the
3458<tt>getOperand()</tt>/<tt>getNumOperands()</tt> and
3459<tt>op_begin()</tt>/<tt>op_end()</tt> methods).</p> <p> An important file for
3460the <tt>Instruction</tt> class is the <tt>llvm/Instruction.def</tt> file. This
3461file contains some meta-data about the various different types of instructions
3462in LLVM. It describes the enum values that are used as opcodes (for example
Reid Spencerc92d25d2006-12-19 19:47:19 +0000[diff] [blame]3463<tt>Instruction::Add</tt> and <tt>Instruction::ICmp</tt>), as well as the
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3464concrete sub-classes of <tt>Instruction</tt> that implement the instruction (for
3465example <tt><a href="#BinaryOperator">BinaryOperator</a></tt> and <tt><a
Reid Spencerc92d25d2006-12-19 19:47:19 +0000[diff] [blame]3466href="#CmpInst">CmpInst</a></tt>). Unfortunately, the use of macros in
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3467this file confuses doxygen, so these enum values don't show up correctly in the
Misha Brukman31ca1de2004-06-03 23:35:54 +0000[diff] [blame]3468<a href="/doxygen/classllvm_1_1Instruction.html">doxygen output</a>.</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3469
3470</div>
3471
3472<!-- _______________________________________________________________________ -->
3473<div class="doc_subsubsection">
Reid Spencerc92d25d2006-12-19 19:47:19 +0000[diff] [blame]3474 <a name="s_Instruction">Important Subclasses of the <tt>Instruction</tt>
3475 class</a>
3476</div>
3477<div class="doc_text">
3478 <ul>
3479 <li><tt><a name="BinaryOperator">BinaryOperator</a></tt>
3480 <p>This subclasses represents all two operand instructions whose operands
3481 must be the same type, except for the comparison instructions.</p></li>
3482 <li><tt><a name="CastInst">CastInst</a></tt>
3483 <p>This subclass is the parent of the 12 casting instructions. It provides
3484 common operations on cast instructions.</p>
3485 <li><tt><a name="CmpInst">CmpInst</a></tt>
3486 <p>This subclass respresents the two comparison instructions,
3487 <a href="LangRef.html#i_icmp">ICmpInst</a> (integer opreands), and
3488 <a href="LangRef.html#i_fcmp">FCmpInst</a> (floating point operands).</p>
3489 <li><tt><a name="TerminatorInst">TerminatorInst</a></tt>
3490 <p>This subclass is the parent of all terminator instructions (those which
3491 can terminate a block).</p>
3492 </ul>
3493 </div>
3494
3495<!-- _______________________________________________________________________ -->
3496<div class="doc_subsubsection">
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3497 <a name="m_Instruction">Important Public Members of the <tt>Instruction</tt>
3498 class</a>
3499</div>
3500
3501<div class="doc_text">
3502
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3503<ul>
3504 <li><tt><a href="#BasicBlock">BasicBlock</a> *getParent()</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3505 <p>Returns the <a href="#BasicBlock"><tt>BasicBlock</tt></a> that
3506this <tt>Instruction</tt> is embedded into.</p></li>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3507 <li><tt>bool mayWriteToMemory()</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3508 <p>Returns true if the instruction writes to memory, i.e. it is a
3509 <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]3510 <li><tt>unsigned getOpcode()</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3511 <p>Returns the opcode for the <tt>Instruction</tt>.</p></li>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3512 <li><tt><a href="#Instruction">Instruction</a> *clone() const</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3513 <p>Returns another instance of the specified instruction, identical
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3514in all ways to the original except that the instruction has no parent
3515(ie it's not embedded into a <a href="#BasicBlock"><tt>BasicBlock</tt></a>),
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3516and it has no name</p></li>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3517</ul>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3518
3519</div>
3520
3521<!-- ======================================================================= -->
3522<div class="doc_subsection">
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]3523 <a name="Constant">The <tt>Constant</tt> class and subclasses</a>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3524</div>
3525
3526<div class="doc_text">
3527
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]3528<p>Constant represents a base class for different types of constants. It
3529is subclassed by ConstantInt, ConstantArray, etc. for representing
3530the various types of Constants. <a href="#GlobalValue">GlobalValue</a> is also
3531a subclass, which represents the address of a global variable or function.
3532</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3533
3534</div>
3535
3536<!-- _______________________________________________________________________ -->
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]3537<div class="doc_subsubsection">Important Subclasses of Constant </div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3538<div class="doc_text">
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3539<ul>
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]3540 <li>ConstantInt : This subclass of Constant represents an integer constant of
3541 any width.
3542 <ul>
Reid Spencer97b4ee32007-03-01 21:05:33 +0000[diff] [blame]3543 <li><tt>const APInt&amp; getValue() const</tt>: Returns the underlying
3544 value of this constant, an APInt value.</li>
3545 <li><tt>int64_t getSExtValue() const</tt>: Converts the underlying APInt
3546 value to an int64_t via sign extension. If the value (not the bit width)
3547 of the APInt is too large to fit in an int64_t, an assertion will result.
3548 For this reason, use of this method is discouraged.</li>
3549 <li><tt>uint64_t getZExtValue() const</tt>: Converts the underlying APInt
3550 value to a uint64_t via zero extension. IF the value (not the bit width)
3551 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]3552 For this reason, use of this method is discouraged.</li>
Reid Spencer97b4ee32007-03-01 21:05:33 +0000[diff] [blame]3553 <li><tt>static ConstantInt* get(const APInt&amp; Val)</tt>: Returns the
3554 ConstantInt object that represents the value provided by <tt>Val</tt>.
3555 The type is implied as the IntegerType that corresponds to the bit width
3556 of <tt>Val</tt>.</li>
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]3557 <li><tt>static ConstantInt* get(const Type *Ty, uint64_t Val)</tt>:
3558 Returns the ConstantInt object that represents the value provided by
3559 <tt>Val</tt> for integer type <tt>Ty</tt>.</li>
3560 </ul>
3561 </li>
3562 <li>ConstantFP : This class represents a floating point constant.
3563 <ul>
3564 <li><tt>double getValue() const</tt>: Returns the underlying value of
3565 this constant. </li>
3566 </ul>
3567 </li>
3568 <li>ConstantArray : This represents a constant array.
3569 <ul>
3570 <li><tt>const std::vector&lt;Use&gt; &amp;getValues() const</tt>: Returns
3571 a vector of component constants that makeup this array. </li>
3572 </ul>
3573 </li>
3574 <li>ConstantStruct : This represents a constant struct.
3575 <ul>
3576 <li><tt>const std::vector&lt;Use&gt; &amp;getValues() const</tt>: Returns
3577 a vector of component constants that makeup this array. </li>
3578 </ul>
3579 </li>
3580 <li>GlobalValue : This represents either a global variable or a function. In
3581 either case, the value is a constant fixed address (after linking).
3582 </li>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3583</ul>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3584</div>
3585
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]3586
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3587<!-- ======================================================================= -->
3588<div class="doc_subsection">
3589 <a name="GlobalValue">The <tt>GlobalValue</tt> class</a>
3590</div>
3591
3592<div class="doc_text">
3593
3594<p><tt>#include "<a
3595href="/doxygen/GlobalValue_8h-source.html">llvm/GlobalValue.h</a>"</tt><br>
Misha Brukman384047f2004-06-03 23:29:12 +0000[diff] [blame]3596doxygen info: <a href="/doxygen/classllvm_1_1GlobalValue.html">GlobalValue
3597Class</a><br>
Reid Spencerbe5e85e2006-04-14 14:11:48 +0000[diff] [blame]3598Superclasses: <a href="#Constant"><tt>Constant</tt></a>,
3599<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]3600
3601<p>Global values (<a href="#GlobalVariable"><tt>GlobalVariable</tt></a>s or <a
3602href="#Function"><tt>Function</tt></a>s) are the only LLVM values that are
3603visible in the bodies of all <a href="#Function"><tt>Function</tt></a>s.
3604Because they are visible at global scope, they are also subject to linking with
3605other globals defined in different translation units. To control the linking
3606process, <tt>GlobalValue</tt>s know their linkage rules. Specifically,
3607<tt>GlobalValue</tt>s know whether they have internal or external linkage, as
Reid Spencer8b2da7a2004-07-18 13:10:31 +0000[diff] [blame]3608defined by the <tt>LinkageTypes</tt> enumeration.</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3609
3610<p>If a <tt>GlobalValue</tt> has internal linkage (equivalent to being
3611<tt>static</tt> in C), it is not visible to code outside the current translation
3612unit, and does not participate in linking. If it has external linkage, it is
3613visible to external code, and does participate in linking. In addition to
3614linkage information, <tt>GlobalValue</tt>s keep track of which <a
3615href="#Module"><tt>Module</tt></a> they are currently part of.</p>
3616
3617<p>Because <tt>GlobalValue</tt>s are memory objects, they are always referred to
3618by their <b>address</b>. As such, the <a href="#Type"><tt>Type</tt></a> of a
3619global is always a pointer to its contents. It is important to remember this
3620when using the <tt>GetElementPtrInst</tt> instruction because this pointer must
3621be dereferenced first. For example, if you have a <tt>GlobalVariable</tt> (a
3622subclass 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]3623i32]</tt>, then the <tt>GlobalVariable</tt> is a pointer to that array. Although
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3624the address of the first element of this array and the value of the
3625<tt>GlobalVariable</tt> are the same, they have different types. The
Reid Spencer06565dc2007-01-12 17:11:23 +0000[diff] [blame]3626<tt>GlobalVariable</tt>'s type is <tt>[24 x i32]</tt>. The first element's type
3627is <tt>i32.</tt> Because of this, accessing a global value requires you to
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3628dereference the pointer with <tt>GetElementPtrInst</tt> first, then its elements
3629can be accessed. This is explained in the <a href="LangRef.html#globalvars">LLVM
3630Language Reference Manual</a>.</p>
3631
3632</div>
3633
3634<!-- _______________________________________________________________________ -->
3635<div class="doc_subsubsection">
3636 <a name="m_GlobalValue">Important Public Members of the <tt>GlobalValue</tt>
3637 class</a>
3638</div>
3639
3640<div class="doc_text">
3641
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3642<ul>
3643 <li><tt>bool hasInternalLinkage() const</tt><br>
Chris Lattner9355b472002-09-06 02:50:58 +0000[diff] [blame]3644 <tt>bool hasExternalLinkage() const</tt><br>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3645 <tt>void setInternalLinkage(bool HasInternalLinkage)</tt>
3646 <p> These methods manipulate the linkage characteristics of the <tt>GlobalValue</tt>.</p>
3647 <p> </p>
3648 </li>
3649 <li><tt><a href="#Module">Module</a> *getParent()</tt>
3650 <p> This returns the <a href="#Module"><tt>Module</tt></a> that the
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3651GlobalValue is currently embedded into.</p></li>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3652</ul>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3653
3654</div>
3655
3656<!-- ======================================================================= -->
3657<div class="doc_subsection">
3658 <a name="Function">The <tt>Function</tt> class</a>
3659</div>
3660
3661<div class="doc_text">
3662
3663<p><tt>#include "<a
3664href="/doxygen/Function_8h-source.html">llvm/Function.h</a>"</tt><br> doxygen
Misha Brukman31ca1de2004-06-03 23:35:54 +0000[diff] [blame]3665info: <a href="/doxygen/classllvm_1_1Function.html">Function Class</a><br>
Reid Spencerbe5e85e2006-04-14 14:11:48 +0000[diff] [blame]3666Superclasses: <a href="#GlobalValue"><tt>GlobalValue</tt></a>,
3667<a href="#Constant"><tt>Constant</tt></a>,
3668<a href="#User"><tt>User</tt></a>,
3669<a href="#Value"><tt>Value</tt></a></p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3670
3671<p>The <tt>Function</tt> class represents a single procedure in LLVM. It is
Torok Edwin87469292009-10-12 13:37:29 +0000[diff] [blame]3672actually one of the more complex classes in the LLVM hierarchy because it must
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3673keep track of a large amount of data. The <tt>Function</tt> class keeps track
Reid Spencerbe5e85e2006-04-14 14:11:48 +0000[diff] [blame]3674of a list of <a href="#BasicBlock"><tt>BasicBlock</tt></a>s, a list of formal
3675<a href="#Argument"><tt>Argument</tt></a>s, and a
3676<a href="#SymbolTable"><tt>SymbolTable</tt></a>.</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3677
3678<p>The list of <a href="#BasicBlock"><tt>BasicBlock</tt></a>s is the most
3679commonly used part of <tt>Function</tt> objects. The list imposes an implicit
3680ordering of the blocks in the function, which indicate how the code will be
Benjamin Kramer8040cd32009-10-12 14:46:08 +0000[diff] [blame]3681laid out by the backend. Additionally, the first <a
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3682href="#BasicBlock"><tt>BasicBlock</tt></a> is the implicit entry node for the
3683<tt>Function</tt>. It is not legal in LLVM to explicitly branch to this initial
3684block. There are no implicit exit nodes, and in fact there may be multiple exit
3685nodes from a single <tt>Function</tt>. If the <a
3686href="#BasicBlock"><tt>BasicBlock</tt></a> list is empty, this indicates that
3687the <tt>Function</tt> is actually a function declaration: the actual body of the
3688function hasn't been linked in yet.</p>
3689
3690<p>In addition to a list of <a href="#BasicBlock"><tt>BasicBlock</tt></a>s, the
3691<tt>Function</tt> class also keeps track of the list of formal <a
3692href="#Argument"><tt>Argument</tt></a>s that the function receives. This
3693container manages the lifetime of the <a href="#Argument"><tt>Argument</tt></a>
3694nodes, just like the <a href="#BasicBlock"><tt>BasicBlock</tt></a> list does for
3695the <a href="#BasicBlock"><tt>BasicBlock</tt></a>s.</p>
3696
3697<p>The <a href="#SymbolTable"><tt>SymbolTable</tt></a> is a very rarely used
3698LLVM feature that is only used when you have to look up a value by name. Aside
3699from that, the <a href="#SymbolTable"><tt>SymbolTable</tt></a> is used
3700internally to make sure that there are not conflicts between the names of <a
3701href="#Instruction"><tt>Instruction</tt></a>s, <a
3702href="#BasicBlock"><tt>BasicBlock</tt></a>s, or <a
3703href="#Argument"><tt>Argument</tt></a>s in the function body.</p>
3704
Reid Spencer8b2da7a2004-07-18 13:10:31 +0000[diff] [blame]3705<p>Note that <tt>Function</tt> is a <a href="#GlobalValue">GlobalValue</a>
3706and therefore also a <a href="#Constant">Constant</a>. The value of the function
3707is its address (after linking) which is guaranteed to be constant.</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3708</div>
3709
3710<!-- _______________________________________________________________________ -->
3711<div class="doc_subsubsection">
3712 <a name="m_Function">Important Public Members of the <tt>Function</tt>
3713 class</a>
3714</div>
3715
3716<div class="doc_text">
3717
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3718<ul>
3719 <li><tt>Function(const </tt><tt><a href="#FunctionType">FunctionType</a>
Chris Lattnerac479e52004-08-04 05:10:48 +0000[diff] [blame]3720 *Ty, LinkageTypes Linkage, const std::string &amp;N = "", Module* Parent = 0)</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3721
3722 <p>Constructor used when you need to create new <tt>Function</tt>s to add
3723 the the program. The constructor must specify the type of the function to
Chris Lattnerac479e52004-08-04 05:10:48 +0000[diff] [blame]3724 create and what type of linkage the function should have. The <a
3725 href="#FunctionType"><tt>FunctionType</tt></a> argument
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3726 specifies the formal arguments and return value for the function. The same
Duncan Sands8036ca42007-03-30 12:22:09 +0000[diff] [blame]3727 <a href="#FunctionType"><tt>FunctionType</tt></a> value can be used to
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3728 create multiple functions. The <tt>Parent</tt> argument specifies the Module
3729 in which the function is defined. If this argument is provided, the function
3730 will automatically be inserted into that module's list of
3731 functions.</p></li>
3732
Chris Lattner62810e32008-11-25 18:34:50 +0000[diff] [blame]3733 <li><tt>bool isDeclaration()</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3734
3735 <p>Return whether or not the <tt>Function</tt> has a body defined. If the
3736 function is "external", it does not have a body, and thus must be resolved
3737 by linking with a function defined in a different translation unit.</p></li>
3738
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3739 <li><tt>Function::iterator</tt> - Typedef for basic block list iterator<br>
Chris Lattner9355b472002-09-06 02:50:58 +0000[diff] [blame]3740 <tt>Function::const_iterator</tt> - Typedef for const_iterator.<br>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3741
Chris Lattner77d69242005-03-15 05:19:20 +0000[diff] [blame]3742 <tt>begin()</tt>, <tt>end()</tt>
3743 <tt>size()</tt>, <tt>empty()</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3744
3745 <p>These are forwarding methods that make it easy to access the contents of
3746 a <tt>Function</tt> object's <a href="#BasicBlock"><tt>BasicBlock</tt></a>
3747 list.</p></li>
3748
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3749 <li><tt>Function::BasicBlockListType &amp;getBasicBlockList()</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3750
3751 <p>Returns the list of <a href="#BasicBlock"><tt>BasicBlock</tt></a>s. This
3752 is necessary to use when you need to update the list or perform a complex
3753 action that doesn't have a forwarding method.</p></li>
3754
Chris Lattner89cc2652005-03-15 04:48:32 +0000[diff] [blame]3755 <li><tt>Function::arg_iterator</tt> - Typedef for the argument list
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3756iterator<br>
Chris Lattner89cc2652005-03-15 04:48:32 +0000[diff] [blame]3757 <tt>Function::const_arg_iterator</tt> - Typedef for const_iterator.<br>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3758
Chris Lattner77d69242005-03-15 05:19:20 +0000[diff] [blame]3759 <tt>arg_begin()</tt>, <tt>arg_end()</tt>
Chris Lattner89cc2652005-03-15 04:48:32 +0000[diff] [blame]3760 <tt>arg_size()</tt>, <tt>arg_empty()</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3761
3762 <p>These are forwarding methods that make it easy to access the contents of
3763 a <tt>Function</tt> object's <a href="#Argument"><tt>Argument</tt></a>
3764 list.</p></li>
3765
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3766 <li><tt>Function::ArgumentListType &amp;getArgumentList()</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3767
3768 <p>Returns the list of <a href="#Argument"><tt>Argument</tt></a>s. This is
3769 necessary to use when you need to update the list or perform a complex
3770 action that doesn't have a forwarding method.</p></li>
3771
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3772 <li><tt><a href="#BasicBlock">BasicBlock</a> &amp;getEntryBlock()</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3773
3774 <p>Returns the entry <a href="#BasicBlock"><tt>BasicBlock</tt></a> for the
3775 function. Because the entry block for the function is always the first
3776 block, this returns the first block of the <tt>Function</tt>.</p></li>
3777
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3778 <li><tt><a href="#Type">Type</a> *getReturnType()</tt><br>
3779 <tt><a href="#FunctionType">FunctionType</a> *getFunctionType()</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3780
3781 <p>This traverses the <a href="#Type"><tt>Type</tt></a> of the
3782 <tt>Function</tt> and returns the return type of the function, or the <a
3783 href="#FunctionType"><tt>FunctionType</tt></a> of the actual
3784 function.</p></li>
3785
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3786 <li><tt><a href="#SymbolTable">SymbolTable</a> *getSymbolTable()</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3787
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3788 <p> Return a pointer to the <a href="#SymbolTable"><tt>SymbolTable</tt></a>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3789 for this <tt>Function</tt>.</p></li>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3790</ul>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3791
3792</div>
3793
3794<!-- ======================================================================= -->
3795<div class="doc_subsection">
3796 <a name="GlobalVariable">The <tt>GlobalVariable</tt> class</a>
3797</div>
3798
3799<div class="doc_text">
3800
3801<p><tt>#include "<a
3802href="/doxygen/GlobalVariable_8h-source.html">llvm/GlobalVariable.h</a>"</tt>
3803<br>
Tanya Lattnera3da7772004-06-22 08:02:25 +0000[diff] [blame]3804doxygen info: <a href="/doxygen/classllvm_1_1GlobalVariable.html">GlobalVariable
Reid Spencerbe5e85e2006-04-14 14:11:48 +0000[diff] [blame]3805 Class</a><br>
3806Superclasses: <a href="#GlobalValue"><tt>GlobalValue</tt></a>,
3807<a href="#Constant"><tt>Constant</tt></a>,
3808<a href="#User"><tt>User</tt></a>,
3809<a href="#Value"><tt>Value</tt></a></p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3810
Benjamin Kramer8040cd32009-10-12 14:46:08 +0000[diff] [blame]3811<p>Global variables are represented with the (surprise surprise)
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3812<tt>GlobalVariable</tt> class. Like functions, <tt>GlobalVariable</tt>s are also
3813subclasses of <a href="#GlobalValue"><tt>GlobalValue</tt></a>, and as such are
3814always referenced by their address (global values must live in memory, so their
Reid Spencerbe5e85e2006-04-14 14:11:48 +0000[diff] [blame]3815"name" refers to their constant address). See
3816<a href="#GlobalValue"><tt>GlobalValue</tt></a> for more on this. Global
3817variables may have an initial value (which must be a
3818<a href="#Constant"><tt>Constant</tt></a>), and if they have an initializer,
3819they may be marked as "constant" themselves (indicating that their contents
3820never change at runtime).</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3821</div>
3822
3823<!-- _______________________________________________________________________ -->
3824<div class="doc_subsubsection">
3825 <a name="m_GlobalVariable">Important Public Members of the
3826 <tt>GlobalVariable</tt> class</a>
3827</div>
3828
3829<div class="doc_text">
3830
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3831<ul>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3832 <li><tt>GlobalVariable(const </tt><tt><a href="#Type">Type</a> *Ty, bool
3833 isConstant, LinkageTypes&amp; Linkage, <a href="#Constant">Constant</a>
3834 *Initializer = 0, const std::string &amp;Name = "", Module* Parent = 0)</tt>
3835
3836 <p>Create a new global variable of the specified type. If
3837 <tt>isConstant</tt> is true then the global variable will be marked as
3838 unchanging for the program. The Linkage parameter specifies the type of
Duncan Sands667d4b82009-03-07 15:45:40 +0000[diff] [blame]3839 linkage (internal, external, weak, linkonce, appending) for the variable.
3840 If the linkage is InternalLinkage, WeakAnyLinkage, WeakODRLinkage,
3841 LinkOnceAnyLinkage or LinkOnceODRLinkage,&nbsp; then the resultant
3842 global variable will have internal linkage. AppendingLinkage concatenates
3843 together all instances (in different translation units) of the variable
3844 into a single variable but is only applicable to arrays. &nbsp;See
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3845 the <a href="LangRef.html#modulestructure">LLVM Language Reference</a> for
3846 further details on linkage types. Optionally an initializer, a name, and the
3847 module to put the variable into may be specified for the global variable as
3848 well.</p></li>
3849
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3850 <li><tt>bool isConstant() const</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3851
3852 <p>Returns true if this is a global variable that is known not to
3853 be modified at runtime.</p></li>
3854
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3855 <li><tt>bool hasInitializer()</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3856
3857 <p>Returns true if this <tt>GlobalVariable</tt> has an intializer.</p></li>
3858
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3859 <li><tt><a href="#Constant">Constant</a> *getInitializer()</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3860
Benjamin Kramer8040cd32009-10-12 14:46:08 +0000[diff] [blame]3861 <p>Returns the initial value for a <tt>GlobalVariable</tt>. It is not legal
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3862 to call this method if there is no initializer.</p></li>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3863</ul>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3864
3865</div>
3866
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]3867
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3868<!-- ======================================================================= -->
3869<div class="doc_subsection">
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]3870 <a name="BasicBlock">The <tt>BasicBlock</tt> class</a>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3871</div>
3872
3873<div class="doc_text">
3874
3875<p><tt>#include "<a
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]3876href="/doxygen/BasicBlock_8h-source.html">llvm/BasicBlock.h</a>"</tt><br>
Stefanus Du Toit24e04112009-06-17 21:12:26 +0000[diff] [blame]3877doxygen info: <a href="/doxygen/classllvm_1_1BasicBlock.html">BasicBlock
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]3878Class</a><br>
3879Superclass: <a href="#Value"><tt>Value</tt></a></p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3880
Nick Lewyckyccd279d2011-02-17 02:19:22 +0000[diff] [blame]3881<p>This class represents a single entry single exit section of the code,
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]3882commonly known as a basic block by the compiler community. The
3883<tt>BasicBlock</tt> class maintains a list of <a
3884href="#Instruction"><tt>Instruction</tt></a>s, which form the body of the block.
3885Matching the language definition, the last element of this list of instructions
3886is always a terminator instruction (a subclass of the <a
3887href="#TerminatorInst"><tt>TerminatorInst</tt></a> class).</p>
3888
3889<p>In addition to tracking the list of instructions that make up the block, the
3890<tt>BasicBlock</tt> class also keeps track of the <a
3891href="#Function"><tt>Function</tt></a> that it is embedded into.</p>
3892
3893<p>Note that <tt>BasicBlock</tt>s themselves are <a
3894href="#Value"><tt>Value</tt></a>s, because they are referenced by instructions
3895like branches and can go in the switch tables. <tt>BasicBlock</tt>s have type
3896<tt>label</tt>.</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3897
3898</div>
3899
3900<!-- _______________________________________________________________________ -->
3901<div class="doc_subsubsection">
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]3902 <a name="m_BasicBlock">Important Public Members of the <tt>BasicBlock</tt>
3903 class</a>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3904</div>
3905
3906<div class="doc_text">
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3907<ul>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3908
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]3909<li><tt>BasicBlock(const std::string &amp;Name = "", </tt><tt><a
3910 href="#Function">Function</a> *Parent = 0)</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3911
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]3912<p>The <tt>BasicBlock</tt> constructor is used to create new basic blocks for
3913insertion into a function. The constructor optionally takes a name for the new
3914block, and a <a href="#Function"><tt>Function</tt></a> to insert it into. If
3915the <tt>Parent</tt> parameter is specified, the new <tt>BasicBlock</tt> is
3916automatically inserted at the end of the specified <a
3917href="#Function"><tt>Function</tt></a>, if not specified, the BasicBlock must be
3918manually inserted into the <a href="#Function"><tt>Function</tt></a>.</p></li>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3919
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]3920<li><tt>BasicBlock::iterator</tt> - Typedef for instruction list iterator<br>
3921<tt>BasicBlock::const_iterator</tt> - Typedef for const_iterator.<br>
3922<tt>begin()</tt>, <tt>end()</tt>, <tt>front()</tt>, <tt>back()</tt>,
3923<tt>size()</tt>, <tt>empty()</tt>
3924STL-style functions for accessing the instruction list.
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3925
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]3926<p>These methods and typedefs are forwarding functions that have the same
3927semantics as the standard library methods of the same names. These methods
3928expose the underlying instruction list of a basic block in a way that is easy to
3929manipulate. To get the full complement of container operations (including
3930operations to update the list), you must use the <tt>getInstList()</tt>
3931method.</p></li>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3932
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]3933<li><tt>BasicBlock::InstListType &amp;getInstList()</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3934
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]3935<p>This method is used to get access to the underlying container that actually
3936holds the Instructions. This method must be used when there isn't a forwarding
3937function in the <tt>BasicBlock</tt> class for the operation that you would like
3938to perform. Because there are no forwarding functions for "updating"
3939operations, you need to use this if you want to update the contents of a
3940<tt>BasicBlock</tt>.</p></li>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3941
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]3942<li><tt><a href="#Function">Function</a> *getParent()</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3943
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]3944<p> Returns a pointer to <a href="#Function"><tt>Function</tt></a> the block is
3945embedded into, or a null pointer if it is homeless.</p></li>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3946
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]3947<li><tt><a href="#TerminatorInst">TerminatorInst</a> *getTerminator()</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3948
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]3949<p> Returns a pointer to the terminator instruction that appears at the end of
3950the <tt>BasicBlock</tt>. If there is no terminator instruction, or if the last
3951instruction in the block is not a terminator, then a null pointer is
3952returned.</p></li>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3953
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3954</ul>
3955
3956</div>
3957
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3958
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3959<!-- ======================================================================= -->
3960<div class="doc_subsection">
3961 <a name="Argument">The <tt>Argument</tt> class</a>
3962</div>
3963
3964<div class="doc_text">
3965
3966<p>This subclass of Value defines the interface for incoming formal
Chris Lattner58360822005-01-17 00:12:04 +0000[diff] [blame]3967arguments to a function. A Function maintains a list of its formal
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3968arguments. An argument has a pointer to the parent Function.</p>
3969
3970</div>
3971
Chris Lattner9355b472002-09-06 02:50:58 +0000[diff] [blame]3972<!-- *********************************************************************** -->
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3973<hr>
3974<address>
3975 <a href="http://jigsaw.w3.org/css-validator/check/referer"><img
Misha Brukman44408702008-12-11 17:34:48 +0000[diff] [blame]3976 src="http://jigsaw.w3.org/css-validator/images/vcss-blue" alt="Valid CSS"></a>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3977 <a href="http://validator.w3.org/check/referer"><img
Gabor Greifa9c0f2b2008-06-18 14:05:31 +0000[diff] [blame]3978 src="http://www.w3.org/Icons/valid-html401" alt="Valid HTML 4.01 Strict"></a>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3979
3980 <a href="mailto:dhurjati@cs.uiuc.edu">Dinakar Dhurjati</a> and
3981 <a href="mailto:sabre@nondot.org">Chris Lattner</a><br>
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]3982 <a href="http://llvm.org">The LLVM Compiler Infrastructure</a><br>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3983 Last modified: $Date$
3984</address>
3985
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3986</body>
3987</html>