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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>
Chris Lattner8ae42612011-04-05 23:18:20 +0000[diff] [blame]59 <li><a href="#dss_arrayref">llvm/ADT/ArrayRef.h</a></li>
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]60 <li><a href="#dss_fixedarrays">Fixed Size Arrays</a></li>
61 <li><a href="#dss_heaparrays">Heap Allocated Arrays</a></li>
62 <li><a href="#dss_smallvector">"llvm/ADT/SmallVector.h"</a></li>
63 <li><a href="#dss_vector">&lt;vector&gt;</a></li>
64 <li><a href="#dss_deque">&lt;deque&gt;</a></li>
65 <li><a href="#dss_list">&lt;list&gt;</a></li>
Gabor Greif3899e492009-02-27 11:37:41 +0000[diff] [blame]66 <li><a href="#dss_ilist">llvm/ADT/ilist.h</a></li>
Chris Lattnerc5722432007-02-03 19:49:31 +0000[diff] [blame]67 <li><a href="#dss_other">Other Sequential Container Options</a></li>
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]68 </ul></li>
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]69 <li><a href="#ds_set">Set-Like Containers (std::set, SmallSet, SetVector, etc)</a>
70 <ul>
71 <li><a href="#dss_sortedvectorset">A sorted 'vector'</a></li>
72 <li><a href="#dss_smallset">"llvm/ADT/SmallSet.h"</a></li>
73 <li><a href="#dss_smallptrset">"llvm/ADT/SmallPtrSet.h"</a></li>
Chris Lattnerc28476f2007-09-30 00:58:59 +0000[diff] [blame]74 <li><a href="#dss_denseset">"llvm/ADT/DenseSet.h"</a></li>
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]75 <li><a href="#dss_FoldingSet">"llvm/ADT/FoldingSet.h"</a></li>
76 <li><a href="#dss_set">&lt;set&gt;</a></li>
77 <li><a href="#dss_setvector">"llvm/ADT/SetVector.h"</a></li>
Chris Lattnerc5722432007-02-03 19:49:31 +0000[diff] [blame]78 <li><a href="#dss_uniquevector">"llvm/ADT/UniqueVector.h"</a></li>
79 <li><a href="#dss_otherset">Other Set-Like ContainerOptions</a></li>
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]80 </ul></li>
Chris Lattnerf3692522007-02-03 19:51:56 +0000[diff] [blame]81 <li><a href="#ds_map">Map-Like Containers (std::map, DenseMap, etc)</a>
82 <ul>
83 <li><a href="#dss_sortedvectormap">A sorted 'vector'</a></li>
Chris Lattner796f9fa2007-02-08 19:14:21 +0000[diff] [blame]84 <li><a href="#dss_stringmap">"llvm/ADT/StringMap.h"</a></li>
Chris Lattnerf3692522007-02-03 19:51:56 +0000[diff] [blame]85 <li><a href="#dss_indexedmap">"llvm/ADT/IndexedMap.h"</a></li>
86 <li><a href="#dss_densemap">"llvm/ADT/DenseMap.h"</a></li>
Jeffrey Yasskin71a5c222009-10-22 22:11:22 +0000[diff] [blame]87 <li><a href="#dss_valuemap">"llvm/ADT/ValueMap.h"</a></li>
Jakob Stoklund Olesenaca0da62010-12-14 00:55:51 +0000[diff] [blame]88 <li><a href="#dss_intervalmap">"llvm/ADT/IntervalMap.h"</a></li>
Chris Lattnerf3692522007-02-03 19:51:56 +0000[diff] [blame]89 <li><a href="#dss_map">&lt;map&gt;</a></li>
Jakob Stoklund Olesen4359e5e2011-04-05 20:56:08 +0000[diff] [blame]90 <li><a href="#dss_inteqclasses">"llvm/ADT/IntEqClasses.h"</a></li>
Chris Lattnerf3692522007-02-03 19:51:56 +0000[diff] [blame]91 <li><a href="#dss_othermap">Other Map-Like Container Options</a></li>
92 </ul></li>
Chris Lattnerdced9fb2009-07-25 07:22:20 +0000[diff] [blame]93 <li><a href="#ds_string">String-like containers</a>
Benjamin Kramere15192b2009-08-05 15:42:44 +0000[diff] [blame]94 <!--<ul>
95 todo
96 </ul>--></li>
Daniel Berlin1939ace2007-09-24 17:52:25 +0000[diff] [blame]97 <li><a href="#ds_bit">BitVector-like containers</a>
98 <ul>
99 <li><a href="#dss_bitvector">A dense bitvector</a></li>
Dan Gohman5f7775c2010-01-05 18:24:00 +0000[diff] [blame]100 <li><a href="#dss_smallbitvector">A "small" dense bitvector</a></li>
Daniel Berlin1939ace2007-09-24 17:52:25 +0000[diff] [blame]101 <li><a href="#dss_sparsebitvector">A sparse bitvector</a></li>
102 </ul></li>
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]103 </ul>
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]104 </li>
Chris Lattnerae7f7592002-09-06 18:31:18 +0000[diff] [blame]105 <li><a href="#common">Helpful Hints for Common Operations</a>
Chris Lattnerae7f7592002-09-06 18:31:18 +0000[diff] [blame]106 <ul>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]107 <li><a href="#inspection">Basic Inspection and Traversal Routines</a>
108 <ul>
109 <li><a href="#iterate_function">Iterating over the <tt>BasicBlock</tt>s
110in a <tt>Function</tt></a> </li>
111 <li><a href="#iterate_basicblock">Iterating over the <tt>Instruction</tt>s
112in a <tt>BasicBlock</tt></a> </li>
113 <li><a href="#iterate_institer">Iterating over the <tt>Instruction</tt>s
114in a <tt>Function</tt></a> </li>
115 <li><a href="#iterate_convert">Turning an iterator into a
116class pointer</a> </li>
117 <li><a href="#iterate_complex">Finding call sites: a more
118complex example</a> </li>
119 <li><a href="#calls_and_invokes">Treating calls and invokes
120the same way</a> </li>
121 <li><a href="#iterate_chains">Iterating over def-use &amp;
122use-def chains</a> </li>
Chris Lattner2e438ca2008-01-03 16:56:04 +0000[diff] [blame]123 <li><a href="#iterate_preds">Iterating over predecessors &amp;
124successors of blocks</a></li>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]125 </ul>
126 </li>
127 <li><a href="#simplechanges">Making simple changes</a>
128 <ul>
129 <li><a href="#schanges_creating">Creating and inserting new
130 <tt>Instruction</tt>s</a> </li>
131 <li><a href="#schanges_deleting">Deleting <tt>Instruction</tt>s</a> </li>
132 <li><a href="#schanges_replacing">Replacing an <tt>Instruction</tt>
133with another <tt>Value</tt></a> </li>
Tanya Lattnerb011c662007-06-20 18:33:15 +0000[diff] [blame]134 <li><a href="#schanges_deletingGV">Deleting <tt>GlobalVariable</tt>s</a> </li>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]135 </ul>
Reid Spencerfe8f4ff2004-11-01 09:02:53 +0000[diff] [blame]136 </li>
Jeffrey Yasskin714257f2009-04-30 22:33:41 +0000[diff] [blame]137 <li><a href="#create_types">How to Create Types</a></li>
Chris Lattnerae7f7592002-09-06 18:31:18 +0000[diff] [blame]138<!--
139 <li>Working with the Control Flow Graph
140 <ul>
141 <li>Accessing predecessors and successors of a <tt>BasicBlock</tt>
142 <li>
143 <li>
144 </ul>
Reid Spencerfe8f4ff2004-11-01 09:02:53 +0000[diff] [blame]145-->
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]146 </ul>
147 </li>
Chris Lattnerd9d6e102005-04-23 16:10:52 +0000[diff] [blame]148
Owen Anderson8bc1b3b2009-06-16 01:17:16 +0000[diff] [blame]149 <li><a href="#threading">Threads and LLVM</a>
150 <ul>
Owen Anderson1ad70e32009-06-16 18:04:19 +0000[diff] [blame]151 <li><a href="#startmultithreaded">Entering and Exiting Multithreaded Mode
152 </a></li>
Owen Anderson8bc1b3b2009-06-16 01:17:16 +0000[diff] [blame]153 <li><a href="#shutdown">Ending execution with <tt>llvm_shutdown()</tt></a></li>
154 <li><a href="#managedstatic">Lazy initialization with <tt>ManagedStatic</tt></a></li>
Owen Andersone0c951a2009-08-19 17:58:52 +0000[diff] [blame]155 <li><a href="#llvmcontext">Achieving Isolation with <tt>LLVMContext</tt></a></li>
Jeffrey Yasskin01eba392010-01-29 19:10:38 +0000[diff] [blame]156 <li><a href="#jitthreading">Threads and the JIT</a></li>
Owen Anderson8bc1b3b2009-06-16 01:17:16 +0000[diff] [blame]157 </ul>
158 </li>
159
Chris Lattnerd9d6e102005-04-23 16:10:52 +0000[diff] [blame]160 <li><a href="#advanced">Advanced Topics</a>
161 <ul>
Chris Lattnerf1b200b2005-04-23 17:27:36 +0000[diff] [blame]162 <li><a href="#TypeResolve">LLVM Type Resolution</a>
163 <ul>
164 <li><a href="#BuildRecType">Basic Recursive Type Construction</a></li>
165 <li><a href="#refineAbstractTypeTo">The <tt>refineAbstractTypeTo</tt> method</a></li>
166 <li><a href="#PATypeHolder">The PATypeHolder Class</a></li>
167 <li><a href="#AbstractTypeUser">The AbstractTypeUser Class</a></li>
168 </ul></li>
169
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]170 <li><a href="#SymbolTable">The <tt>ValueSymbolTable</tt> and <tt>TypeSymbolTable</tt> classes</a></li>
171 <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]172 </ul></li>
173
Joel Stanley9b96c442002-09-06 21:55:13 +0000[diff] [blame]174 <li><a href="#coreclasses">The Core LLVM Class Hierarchy Reference</a>
Chris Lattner9355b472002-09-06 02:50:58 +0000[diff] [blame]175 <ul>
Reid Spencer303c4b42007-01-12 17:26:25 +0000[diff] [blame]176 <li><a href="#Type">The <tt>Type</tt> class</a> </li>
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]177 <li><a href="#Module">The <tt>Module</tt> class</a></li>
Reid Spencerfe8f4ff2004-11-01 09:02:53 +0000[diff] [blame]178 <li><a href="#Value">The <tt>Value</tt> class</a>
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]179 <ul>
180 <li><a href="#User">The <tt>User</tt> class</a>
Chris Lattner9355b472002-09-06 02:50:58 +0000[diff] [blame]181 <ul>
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]182 <li><a href="#Instruction">The <tt>Instruction</tt> class</a></li>
183 <li><a href="#Constant">The <tt>Constant</tt> class</a>
184 <ul>
185 <li><a href="#GlobalValue">The <tt>GlobalValue</tt> class</a>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]186 <ul>
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]187 <li><a href="#Function">The <tt>Function</tt> class</a></li>
188 <li><a href="#GlobalVariable">The <tt>GlobalVariable</tt> class</a></li>
189 </ul>
190 </li>
191 </ul>
192 </li>
Reid Spencerfe8f4ff2004-11-01 09:02:53 +0000[diff] [blame]193 </ul>
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]194 </li>
195 <li><a href="#BasicBlock">The <tt>BasicBlock</tt> class</a></li>
196 <li><a href="#Argument">The <tt>Argument</tt> class</a></li>
197 </ul>
Reid Spencerfe8f4ff2004-11-01 09:02:53 +0000[diff] [blame]198 </li>
199 </ul>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]200 </li>
Chris Lattner9355b472002-09-06 02:50:58 +0000[diff] [blame]201</ol>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]202
Chris Lattner69bf8a92004-05-23 21:06:58 +0000[diff] [blame]203<div class="doc_author">
204 <p>Written by <a href="mailto:sabre@nondot.org">Chris Lattner</a>,
Chris Lattner94c43592004-05-26 16:52:55 +0000[diff] [blame]205 <a href="mailto:dhurjati@cs.uiuc.edu">Dinakar Dhurjati</a>,
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]206 <a href="mailto:ggreif@gmail.com">Gabor Greif</a>,
Owen Anderson8bc1b3b2009-06-16 01:17:16 +0000[diff] [blame]207 <a href="mailto:jstanley@cs.uiuc.edu">Joel Stanley</a>,
208 <a href="mailto:rspencer@x10sys.com">Reid Spencer</a> and
209 <a href="mailto:owen@apple.com">Owen Anderson</a></p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]210</div>
211
Chris Lattner9355b472002-09-06 02:50:58 +0000[diff] [blame]212<!-- *********************************************************************** -->
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]213<div class="doc_section">
214 <a name="introduction">Introduction </a>
215</div>
Chris Lattner9355b472002-09-06 02:50:58 +0000[diff] [blame]216<!-- *********************************************************************** -->
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]217
218<div class="doc_text">
219
220<p>This document is meant to highlight some of the important classes and
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]221interfaces available in the LLVM source-base. This manual is not
222intended to explain what LLVM is, how it works, and what LLVM code looks
223like. It assumes that you know the basics of LLVM and are interested
224in writing transformations or otherwise analyzing or manipulating the
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]225code.</p>
226
227<p>This document should get you oriented so that you can find your
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]228way in the continuously growing source code that makes up the LLVM
229infrastructure. Note that this manual is not intended to serve as a
230replacement for reading the source code, so if you think there should be
231a method in one of these classes to do something, but it's not listed,
232check the source. Links to the <a href="/doxygen/">doxygen</a> sources
233are provided to make this as easy as possible.</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]234
235<p>The first section of this document describes general information that is
236useful to know when working in the LLVM infrastructure, and the second describes
237the Core LLVM classes. In the future this manual will be extended with
238information describing how to use extension libraries, such as dominator
239information, CFG traversal routines, and useful utilities like the <tt><a
240href="/doxygen/InstVisitor_8h-source.html">InstVisitor</a></tt> template.</p>
241
242</div>
243
Chris Lattner9355b472002-09-06 02:50:58 +0000[diff] [blame]244<!-- *********************************************************************** -->
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]245<div class="doc_section">
246 <a name="general">General Information</a>
247</div>
248<!-- *********************************************************************** -->
249
250<div class="doc_text">
251
252<p>This section contains general information that is useful if you are working
253in the LLVM source-base, but that isn't specific to any particular API.</p>
254
255</div>
256
257<!-- ======================================================================= -->
258<div class="doc_subsection">
259 <a name="stl">The C++ Standard Template Library</a>
260</div>
261
262<div class="doc_text">
263
264<p>LLVM makes heavy use of the C++ Standard Template Library (STL),
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]265perhaps much more than you are used to, or have seen before. Because of
266this, you might want to do a little background reading in the
267techniques used and capabilities of the library. There are many good
268pages that discuss the STL, and several books on the subject that you
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]269can get, so it will not be discussed in this document.</p>
270
271<p>Here are some useful links:</p>
272
273<ol>
274
Nick Lewyckyea1fe2c2010-10-09 21:12:29 +0000[diff] [blame]275<li><a href="http://www.dinkumware.com/manuals/#Standard C++ Library">Dinkumware
276C++ Library reference</a> - an excellent reference for the STL and other parts
277of the standard C++ library.</li>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]278
279<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]280O'Reilly book in the making. It has a decent Standard Library
281Reference that rivals Dinkumware's, and is unfortunately no longer free since the
282book has been published.</li>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]283
284<li><a href="http://www.parashift.com/c++-faq-lite/">C++ Frequently Asked
285Questions</a></li>
286
287<li><a href="http://www.sgi.com/tech/stl/">SGI's STL Programmer's Guide</a> -
288Contains a useful <a
289href="http://www.sgi.com/tech/stl/stl_introduction.html">Introduction to the
290STL</a>.</li>
291
292<li><a href="http://www.research.att.com/%7Ebs/C++.html">Bjarne Stroustrup's C++
293Page</a></li>
294
Tanya Lattner79445ba2004-12-08 18:34:56 +0000[diff] [blame]295<li><a href="http://64.78.49.204/">
Reid Spencer096603a2004-05-26 08:41:35 +0000[diff] [blame]296Bruce Eckel's Thinking in C++, 2nd ed. Volume 2 Revision 4.0 (even better, get
297the book).</a></li>
298
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]299</ol>
300
301<p>You are also encouraged to take a look at the <a
302href="CodingStandards.html">LLVM Coding Standards</a> guide which focuses on how
303to write maintainable code more than where to put your curly braces.</p>
304
305</div>
306
307<!-- ======================================================================= -->
308<div class="doc_subsection">
309 <a name="stl">Other useful references</a>
310</div>
311
312<div class="doc_text">
313
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]314<ol>
Misha Brukmana0f71e42004-06-18 18:39:00 +0000[diff] [blame]315<li><a href="http://www.fortran-2000.com/ArnaudRecipes/sharedlib.html">Using
316static and shared libraries across platforms</a></li>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]317</ol>
318
319</div>
320
Chris Lattner9355b472002-09-06 02:50:58 +0000[diff] [blame]321<!-- *********************************************************************** -->
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]322<div class="doc_section">
323 <a name="apis">Important and useful LLVM APIs</a>
324</div>
325<!-- *********************************************************************** -->
326
327<div class="doc_text">
328
329<p>Here we highlight some LLVM APIs that are generally useful and good to
330know about when writing transformations.</p>
331
332</div>
333
334<!-- ======================================================================= -->
335<div class="doc_subsection">
Misha Brukman2c122ce2005-11-01 21:12:49 +0000[diff] [blame]336 <a name="isa">The <tt>isa&lt;&gt;</tt>, <tt>cast&lt;&gt;</tt> and
337 <tt>dyn_cast&lt;&gt;</tt> templates</a>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]338</div>
339
340<div class="doc_text">
341
342<p>The LLVM source-base makes extensive use of a custom form of RTTI.
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]343These templates have many similarities to the C++ <tt>dynamic_cast&lt;&gt;</tt>
344operator, but they don't have some drawbacks (primarily stemming from
345the fact that <tt>dynamic_cast&lt;&gt;</tt> only works on classes that
346have a v-table). Because they are used so often, you must know what they
347do and how they work. All of these templates are defined in the <a
Chris Lattner695b78b2005-04-26 22:56:16 +0000[diff] [blame]348 href="/doxygen/Casting_8h-source.html"><tt>llvm/Support/Casting.h</tt></a>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]349file (note that you very rarely have to include this file directly).</p>
350
351<dl>
352 <dt><tt>isa&lt;&gt;</tt>: </dt>
353
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]354 <dd><p>The <tt>isa&lt;&gt;</tt> operator works exactly like the Java
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]355 "<tt>instanceof</tt>" operator. It returns true or false depending on whether
356 a reference or pointer points to an instance of the specified class. This can
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]357 be very useful for constraint checking of various sorts (example below).</p>
358 </dd>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]359
360 <dt><tt>cast&lt;&gt;</tt>: </dt>
361
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]362 <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]363 converts a pointer or reference from a base class to a derived class, causing
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]364 an assertion failure if it is not really an instance of the right type. This
365 should be used in cases where you have some information that makes you believe
366 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]367 and <tt>cast&lt;&gt;</tt> template is:</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]368
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]369<div class="doc_code">
370<pre>
371static bool isLoopInvariant(const <a href="#Value">Value</a> *V, const Loop *L) {
372 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))
373 return true;
Chris Lattner69bf8a92004-05-23 21:06:58 +0000[diff] [blame]374
Bill Wendling82e2eea2006-10-11 18:00:22 +0000[diff] [blame]375 // <i>Otherwise, it must be an instruction...</i>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]376 return !L-&gt;contains(cast&lt;<a href="#Instruction">Instruction</a>&gt;(V)-&gt;getParent());
377}
378</pre>
379</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]380
381 <p>Note that you should <b>not</b> use an <tt>isa&lt;&gt;</tt> test followed
382 by a <tt>cast&lt;&gt;</tt>, for that use the <tt>dyn_cast&lt;&gt;</tt>
383 operator.</p>
384
385 </dd>
386
387 <dt><tt>dyn_cast&lt;&gt;</tt>:</dt>
388
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]389 <dd><p>The <tt>dyn_cast&lt;&gt;</tt> operator is a "checking cast" operation.
390 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]391 pointer to it (this operator does not work with references). If the operand is
392 not of the correct type, a null pointer is returned. Thus, this works very
Misha Brukman2c122ce2005-11-01 21:12:49 +0000[diff] [blame]393 much like the <tt>dynamic_cast&lt;&gt;</tt> operator in C++, and should be
394 used in the same circumstances. Typically, the <tt>dyn_cast&lt;&gt;</tt>
395 operator is used in an <tt>if</tt> statement or some other flow control
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]396 statement like this:</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]397
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]398<div class="doc_code">
399<pre>
400if (<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]401 // <i>...</i>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]402}
403</pre>
404</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]405
Misha Brukman2c122ce2005-11-01 21:12:49 +0000[diff] [blame]406 <p>This form of the <tt>if</tt> statement effectively combines together a call
407 to <tt>isa&lt;&gt;</tt> and a call to <tt>cast&lt;&gt;</tt> into one
408 statement, which is very convenient.</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]409
Misha Brukman2c122ce2005-11-01 21:12:49 +0000[diff] [blame]410 <p>Note that the <tt>dyn_cast&lt;&gt;</tt> operator, like C++'s
411 <tt>dynamic_cast&lt;&gt;</tt> or Java's <tt>instanceof</tt> operator, can be
412 abused. In particular, you should not use big chained <tt>if/then/else</tt>
413 blocks to check for lots of different variants of classes. If you find
414 yourself wanting to do this, it is much cleaner and more efficient to use the
415 <tt>InstVisitor</tt> class to dispatch over the instruction type directly.</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]416
Misha Brukman2c122ce2005-11-01 21:12:49 +0000[diff] [blame]417 </dd>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]418
Misha Brukman2c122ce2005-11-01 21:12:49 +0000[diff] [blame]419 <dt><tt>cast_or_null&lt;&gt;</tt>: </dt>
420
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]421 <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]422 <tt>cast&lt;&gt;</tt> operator, except that it allows for a null pointer as an
423 argument (which it then propagates). This can sometimes be useful, allowing
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]424 you to combine several null checks into one.</p></dd>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]425
Misha Brukman2c122ce2005-11-01 21:12:49 +0000[diff] [blame]426 <dt><tt>dyn_cast_or_null&lt;&gt;</tt>: </dt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]427
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]428 <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]429 <tt>dyn_cast&lt;&gt;</tt> operator, except that it allows for a null pointer
430 as an argument (which it then propagates). This can sometimes be useful,
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]431 allowing you to combine several null checks into one.</p></dd>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]432
Misha Brukman2c122ce2005-11-01 21:12:49 +0000[diff] [blame]433</dl>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]434
435<p>These five templates can be used with any classes, whether they have a
436v-table or not. To add support for these templates, you simply need to add
437<tt>classof</tt> static methods to the class you are interested casting
438to. Describing this is currently outside the scope of this document, but there
439are lots of examples in the LLVM source base.</p>
440
441</div>
442
Daniel Dunbar6e0d1cb2009-07-25 04:41:11 +0000[diff] [blame]443
444<!-- ======================================================================= -->
445<div class="doc_subsection">
446 <a name="string_apis">Passing strings (the <tt>StringRef</tt>
447and <tt>Twine</tt> classes)</a>
448</div>
449
450<div class="doc_text">
451
452<p>Although LLVM generally does not do much string manipulation, we do have
Chris Lattner81187ae2009-07-25 07:16:59 +0000[diff] [blame]453several important APIs which take strings. Two important examples are the
Daniel Dunbar6e0d1cb2009-07-25 04:41:11 +0000[diff] [blame]454Value class -- which has names for instructions, functions, etc. -- and the
455StringMap class which is used extensively in LLVM and Clang.</p>
456
457<p>These are generic classes, and they need to be able to accept strings which
458may have embedded null characters. Therefore, they cannot simply take
Chris Lattner81187ae2009-07-25 07:16:59 +0000[diff] [blame]459a <tt>const char *</tt>, and taking a <tt>const std::string&amp;</tt> requires
Daniel Dunbar6e0d1cb2009-07-25 04:41:11 +0000[diff] [blame]460clients to perform a heap allocation which is usually unnecessary. Instead,
Benjamin Kramer38e59892010-07-14 22:38:02 +0000[diff] [blame]461many LLVM APIs use a <tt>StringRef</tt> or a <tt>const Twine&amp;</tt> for
462passing strings efficiently.</p>
Daniel Dunbar6e0d1cb2009-07-25 04:41:11 +0000[diff] [blame]463
464</div>
465
466<!-- _______________________________________________________________________ -->
467<div class="doc_subsubsection">
468 <a name="StringRef">The <tt>StringRef</tt> class</a>
469</div>
470
471<div class="doc_text">
472
473<p>The <tt>StringRef</tt> data type represents a reference to a constant string
474(a character array and a length) and supports the common operations available
475on <tt>std:string</tt>, but does not require heap allocation.</p>
476
Chris Lattner81187ae2009-07-25 07:16:59 +0000[diff] [blame]477<p>It can be implicitly constructed using a C style null-terminated string,
478an <tt>std::string</tt>, or explicitly with a character pointer and length.
Daniel Dunbar6e0d1cb2009-07-25 04:41:11 +0000[diff] [blame]479For example, the <tt>StringRef</tt> find function is declared as:</p>
Chris Lattner81187ae2009-07-25 07:16:59 +0000[diff] [blame]480
Benjamin Kramer38e59892010-07-14 22:38:02 +0000[diff] [blame]481<pre class="doc_code">
482 iterator find(StringRef Key);
483</pre>
Daniel Dunbar6e0d1cb2009-07-25 04:41:11 +0000[diff] [blame]484
485<p>and clients can call it using any one of:</p>
486
Benjamin Kramer38e59892010-07-14 22:38:02 +0000[diff] [blame]487<pre class="doc_code">
Daniel Dunbar6e0d1cb2009-07-25 04:41:11 +0000[diff] [blame]488 Map.find("foo"); <i>// Lookup "foo"</i>
489 Map.find(std::string("bar")); <i>// Lookup "bar"</i>
490 Map.find(StringRef("\0baz", 4)); <i>// Lookup "\0baz"</i>
491</pre>
Daniel Dunbar6e0d1cb2009-07-25 04:41:11 +0000[diff] [blame]492
493<p>Similarly, APIs which need to return a string may return a <tt>StringRef</tt>
494instance, which can be used directly or converted to an <tt>std::string</tt>
495using the <tt>str</tt> member function. See
496"<tt><a href="/doxygen/classllvm_1_1StringRef_8h-source.html">llvm/ADT/StringRef.h</a></tt>"
497for more information.</p>
498
499<p>You should rarely use the <tt>StringRef</tt> class directly, because it contains
500pointers to external memory it is not generally safe to store an instance of the
Benjamin Kramer38e59892010-07-14 22:38:02 +0000[diff] [blame]501class (unless you know that the external storage will not be freed). StringRef is
502small and pervasive enough in LLVM that it should always be passed by value.</p>
Daniel Dunbar6e0d1cb2009-07-25 04:41:11 +0000[diff] [blame]503
504</div>
505
506<!-- _______________________________________________________________________ -->
507<div class="doc_subsubsection">
508 <a name="Twine">The <tt>Twine</tt> class</a>
509</div>
510
511<div class="doc_text">
512
513<p>The <tt>Twine</tt> class is an efficient way for APIs to accept concatenated
514strings. For example, a common LLVM paradigm is to name one instruction based on
515the name of another instruction with a suffix, for example:</p>
516
517<div class="doc_code">
518<pre>
519 New = CmpInst::Create(<i>...</i>, SO->getName() + ".cmp");
520</pre>
521</div>
522
523<p>The <tt>Twine</tt> class is effectively a
524lightweight <a href="http://en.wikipedia.org/wiki/Rope_(computer_science)">rope</a>
525which points to temporary (stack allocated) objects. Twines can be implicitly
526constructed as the result of the plus operator applied to strings (i.e., a C
527strings, an <tt>std::string</tt>, or a <tt>StringRef</tt>). The twine delays the
Dan Gohmancf0c9bc2010-02-25 23:51:27 +0000[diff] [blame]528actual concatenation of strings until it is actually required, at which point
Daniel Dunbar6e0d1cb2009-07-25 04:41:11 +0000[diff] [blame]529it can be efficiently rendered directly into a character array. This avoids
530unnecessary heap allocation involved in constructing the temporary results of
531string concatenation. See
532"<tt><a href="/doxygen/classllvm_1_1Twine_8h-source.html">llvm/ADT/Twine.h</a></tt>"
Benjamin Kramere15192b2009-08-05 15:42:44 +0000[diff] [blame]533for more information.</p>
Daniel Dunbar6e0d1cb2009-07-25 04:41:11 +0000[diff] [blame]534
535<p>As with a <tt>StringRef</tt>, <tt>Twine</tt> objects point to external memory
536and should almost never be stored or mentioned directly. They are intended
537solely for use when defining a function which should be able to efficiently
538accept concatenated strings.</p>
539
540</div>
541
542
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]543<!-- ======================================================================= -->
544<div class="doc_subsection">
Misha Brukman2c122ce2005-11-01 21:12:49 +0000[diff] [blame]545 <a name="DEBUG">The <tt>DEBUG()</tt> macro and <tt>-debug</tt> option</a>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]546</div>
547
548<div class="doc_text">
549
550<p>Often when working on your pass you will put a bunch of debugging printouts
551and other code into your pass. After you get it working, you want to remove
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]552it, but you may need it again in the future (to work out new bugs that you run
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]553across).</p>
554
555<p> Naturally, because of this, you don't want to delete the debug printouts,
556but you don't want them to always be noisy. A standard compromise is to comment
557them out, allowing you to enable them if you need them in the future.</p>
558
Chris Lattner695b78b2005-04-26 22:56:16 +0000[diff] [blame]559<p>The "<tt><a href="/doxygen/Debug_8h-source.html">llvm/Support/Debug.h</a></tt>"
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]560file provides a macro named <tt>DEBUG()</tt> that is a much nicer solution to
561this problem. Basically, you can put arbitrary code into the argument of the
562<tt>DEBUG</tt> macro, and it is only executed if '<tt>opt</tt>' (or any other
563tool) is run with the '<tt>-debug</tt>' command line argument:</p>
564
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]565<div class="doc_code">
566<pre>
Daniel Dunbar06388ae2009-07-25 01:55:32 +0000[diff] [blame]567DEBUG(errs() &lt;&lt; "I am here!\n");
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]568</pre>
569</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]570
571<p>Then you can run your pass like this:</p>
572
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]573<div class="doc_code">
574<pre>
575$ opt &lt; a.bc &gt; /dev/null -mypass
Bill Wendling82e2eea2006-10-11 18:00:22 +0000[diff] [blame]576<i>&lt;no output&gt;</i>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]577$ opt &lt; a.bc &gt; /dev/null -mypass -debug
578I am here!
579</pre>
580</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]581
582<p>Using the <tt>DEBUG()</tt> macro instead of a home-brewed solution allows you
583to not have to create "yet another" command line option for the debug output for
584your pass. Note that <tt>DEBUG()</tt> macros are disabled for optimized builds,
585so they do not cause a performance impact at all (for the same reason, they
586should also not contain side-effects!).</p>
587
588<p>One additional nice thing about the <tt>DEBUG()</tt> macro is that you can
589enable or disable it directly in gdb. Just use "<tt>set DebugFlag=0</tt>" or
590"<tt>set DebugFlag=1</tt>" from the gdb if the program is running. If the
591program hasn't been started yet, you can always just run it with
592<tt>-debug</tt>.</p>
593
594</div>
595
596<!-- _______________________________________________________________________ -->
597<div class="doc_subsubsection">
Chris Lattnerc9151082005-04-26 22:57:07 +0000[diff] [blame]598 <a name="DEBUG_TYPE">Fine grained debug info with <tt>DEBUG_TYPE</tt> and
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]599 the <tt>-debug-only</tt> option</a>
600</div>
601
602<div class="doc_text">
603
604<p>Sometimes you may find yourself in a situation where enabling <tt>-debug</tt>
605just turns on <b>too much</b> information (such as when working on the code
606generator). If you want to enable debug information with more fine-grained
607control, you define the <tt>DEBUG_TYPE</tt> macro and the <tt>-debug</tt> only
608option as follows:</p>
609
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]610<div class="doc_code">
611<pre>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]612#undef DEBUG_TYPE
Daniel Dunbar06388ae2009-07-25 01:55:32 +0000[diff] [blame]613DEBUG(errs() &lt;&lt; "No debug type\n");
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]614#define DEBUG_TYPE "foo"
Daniel Dunbar06388ae2009-07-25 01:55:32 +0000[diff] [blame]615DEBUG(errs() &lt;&lt; "'foo' debug type\n");
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]616#undef DEBUG_TYPE
617#define DEBUG_TYPE "bar"
Daniel Dunbar06388ae2009-07-25 01:55:32 +0000[diff] [blame]618DEBUG(errs() &lt;&lt; "'bar' debug type\n"));
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]619#undef DEBUG_TYPE
620#define DEBUG_TYPE ""
Daniel Dunbar06388ae2009-07-25 01:55:32 +0000[diff] [blame]621DEBUG(errs() &lt;&lt; "No debug type (2)\n");
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]622</pre>
623</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]624
625<p>Then you can run your pass like this:</p>
626
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]627<div class="doc_code">
628<pre>
629$ opt &lt; a.bc &gt; /dev/null -mypass
Bill Wendling82e2eea2006-10-11 18:00:22 +0000[diff] [blame]630<i>&lt;no output&gt;</i>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]631$ opt &lt; a.bc &gt; /dev/null -mypass -debug
632No debug type
633'foo' debug type
634'bar' debug type
635No debug type (2)
636$ opt &lt; a.bc &gt; /dev/null -mypass -debug-only=foo
637'foo' debug type
638$ opt &lt; a.bc &gt; /dev/null -mypass -debug-only=bar
639'bar' debug type
640</pre>
641</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]642
643<p>Of course, in practice, you should only set <tt>DEBUG_TYPE</tt> at the top of
644a file, to specify the debug type for the entire module (if you do this before
Chris Lattner695b78b2005-04-26 22:56:16 +0000[diff] [blame]645you <tt>#include "llvm/Support/Debug.h"</tt>, you don't have to insert the ugly
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]646<tt>#undef</tt>'s). Also, you should use names more meaningful than "foo" and
647"bar", because there is no system in place to ensure that names do not
648conflict. If two different modules use the same string, they will all be turned
649on when the name is specified. This allows, for example, all debug information
650for instruction scheduling to be enabled with <tt>-debug-type=InstrSched</tt>,
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]651even if the source lives in multiple files.</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]652
Daniel Dunbarc3c92392009-08-07 23:48:59 +0000[diff] [blame]653<p>The <tt>DEBUG_WITH_TYPE</tt> macro is also available for situations where you
654would like to set <tt>DEBUG_TYPE</tt>, but only for one specific <tt>DEBUG</tt>
655statement. It takes an additional first parameter, which is the type to use. For
Benjamin Kramer8040cd32009-10-12 14:46:08 +0000[diff] [blame]656example, the preceding example could be written as:</p>
Daniel Dunbarc3c92392009-08-07 23:48:59 +0000[diff] [blame]657
658
659<div class="doc_code">
660<pre>
661DEBUG_WITH_TYPE("", errs() &lt;&lt; "No debug type\n");
662DEBUG_WITH_TYPE("foo", errs() &lt;&lt; "'foo' debug type\n");
663DEBUG_WITH_TYPE("bar", errs() &lt;&lt; "'bar' debug type\n"));
664DEBUG_WITH_TYPE("", errs() &lt;&lt; "No debug type (2)\n");
665</pre>
666</div>
667
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]668</div>
669
670<!-- ======================================================================= -->
671<div class="doc_subsection">
Chris Lattner0be6fdf2006-12-19 21:46:21 +0000[diff] [blame]672 <a name="Statistic">The <tt>Statistic</tt> class &amp; <tt>-stats</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]673 option</a>
674</div>
675
676<div class="doc_text">
677
678<p>The "<tt><a
Chris Lattner695b78b2005-04-26 22:56:16 +0000[diff] [blame]679href="/doxygen/Statistic_8h-source.html">llvm/ADT/Statistic.h</a></tt>" file
Chris Lattner0be6fdf2006-12-19 21:46:21 +0000[diff] [blame]680provides a class named <tt>Statistic</tt> that is used as a unified way to
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]681keep track of what the LLVM compiler is doing and how effective various
682optimizations are. It is useful to see what optimizations are contributing to
683making a particular program run faster.</p>
684
685<p>Often you may run your pass on some big program, and you're interested to see
686how many times it makes a certain transformation. Although you can do this with
687hand inspection, or some ad-hoc method, this is a real pain and not very useful
Chris Lattner0be6fdf2006-12-19 21:46:21 +0000[diff] [blame]688for big programs. Using the <tt>Statistic</tt> class makes it very easy to
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]689keep track of this information, and the calculated information is presented in a
690uniform manner with the rest of the passes being executed.</p>
691
692<p>There are many examples of <tt>Statistic</tt> uses, but the basics of using
693it are as follows:</p>
694
695<ol>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]696 <li><p>Define your statistic like this:</p>
697
698<div class="doc_code">
699<pre>
Chris Lattner0be6fdf2006-12-19 21:46:21 +0000[diff] [blame]700#define <a href="#DEBUG_TYPE">DEBUG_TYPE</a> "mypassname" <i>// This goes before any #includes.</i>
701STATISTIC(NumXForms, "The # of times I did stuff");
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]702</pre>
703</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]704
Chris Lattner0be6fdf2006-12-19 21:46:21 +0000[diff] [blame]705 <p>The <tt>STATISTIC</tt> macro defines a static variable, whose name is
706 specified by the first argument. The pass name is taken from the DEBUG_TYPE
707 macro, and the description is taken from the second argument. The variable
Reid Spencer06565dc2007-01-12 17:11:23 +0000[diff] [blame]708 defined ("NumXForms" in this case) acts like an unsigned integer.</p></li>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]709
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]710 <li><p>Whenever you make a transformation, bump the counter:</p>
711
712<div class="doc_code">
713<pre>
Bill Wendling82e2eea2006-10-11 18:00:22 +0000[diff] [blame]714++NumXForms; // <i>I did stuff!</i>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]715</pre>
716</div>
717
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]718 </li>
719 </ol>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]720
721 <p>That's all you have to do. To get '<tt>opt</tt>' to print out the
722 statistics gathered, use the '<tt>-stats</tt>' option:</p>
723
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]724<div class="doc_code">
725<pre>
726$ opt -stats -mypassname &lt; program.bc &gt; /dev/null
Bill Wendling82e2eea2006-10-11 18:00:22 +0000[diff] [blame]727<i>... statistics output ...</i>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]728</pre>
729</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]730
Reid Spencer6b6c73e2007-02-09 16:00:28 +0000[diff] [blame]731 <p> When running <tt>opt</tt> on a C file from the SPEC benchmark
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]732suite, it gives a report that looks like this:</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]733
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]734<div class="doc_code">
735<pre>
Gabor Greif04367bf2007-07-06 22:07:22 +0000[diff] [blame]736 7646 bitcodewriter - Number of normal instructions
737 725 bitcodewriter - Number of oversized instructions
738 129996 bitcodewriter - Number of bitcode bytes written
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]739 2817 raise - Number of insts DCEd or constprop'd
740 3213 raise - Number of cast-of-self removed
741 5046 raise - Number of expression trees converted
742 75 raise - Number of other getelementptr's formed
743 138 raise - Number of load/store peepholes
744 42 deadtypeelim - Number of unused typenames removed from symtab
745 392 funcresolve - Number of varargs functions resolved
746 27 globaldce - Number of global variables removed
747 2 adce - Number of basic blocks removed
748 134 cee - Number of branches revectored
749 49 cee - Number of setcc instruction eliminated
750 532 gcse - Number of loads removed
751 2919 gcse - Number of instructions removed
752 86 indvars - Number of canonical indvars added
753 87 indvars - Number of aux indvars removed
754 25 instcombine - Number of dead inst eliminate
755 434 instcombine - Number of insts combined
756 248 licm - Number of load insts hoisted
757 1298 licm - Number of insts hoisted to a loop pre-header
758 3 licm - Number of insts hoisted to multiple loop preds (bad, no loop pre-header)
759 75 mem2reg - Number of alloca's promoted
760 1444 cfgsimplify - Number of blocks simplified
761</pre>
762</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]763
764<p>Obviously, with so many optimizations, having a unified framework for this
765stuff is very nice. Making your pass fit well into the framework makes it more
766maintainable and useful.</p>
767
768</div>
769
Chris Lattnerf623a082005-10-17 01:36:23 +0000[diff] [blame]770<!-- ======================================================================= -->
771<div class="doc_subsection">
772 <a name="ViewGraph">Viewing graphs while debugging code</a>
773</div>
774
775<div class="doc_text">
776
777<p>Several of the important data structures in LLVM are graphs: for example
778CFGs made out of LLVM <a href="#BasicBlock">BasicBlock</a>s, CFGs made out of
779LLVM <a href="CodeGenerator.html#machinebasicblock">MachineBasicBlock</a>s, and
780<a href="CodeGenerator.html#selectiondag_intro">Instruction Selection
781DAGs</a>. In many cases, while debugging various parts of the compiler, it is
782nice to instantly visualize these graphs.</p>
783
784<p>LLVM provides several callbacks that are available in a debug build to do
785exactly that. If you call the <tt>Function::viewCFG()</tt> method, for example,
786the current LLVM tool will pop up a window containing the CFG for the function
787where each basic block is a node in the graph, and each node contains the
788instructions in the block. Similarly, there also exists
789<tt>Function::viewCFGOnly()</tt> (does not include the instructions), the
790<tt>MachineFunction::viewCFG()</tt> and <tt>MachineFunction::viewCFGOnly()</tt>,
791and the <tt>SelectionDAG::viewGraph()</tt> methods. Within GDB, for example,
Jim Laskey543a0ee2006-10-02 12:28:07 +0000[diff] [blame]792you can usually use something like <tt>call DAG.viewGraph()</tt> to pop
Chris Lattnerf623a082005-10-17 01:36:23 +0000[diff] [blame]793up a window. Alternatively, you can sprinkle calls to these functions in your
794code in places you want to debug.</p>
795
796<p>Getting this to work requires a small amount of configuration. On Unix
797systems with X11, install the <a href="http://www.graphviz.org">graphviz</a>
798toolkit, and make sure 'dot' and 'gv' are in your path. If you are running on
799Mac OS/X, download and install the Mac OS/X <a
800href="http://www.pixelglow.com/graphviz/">Graphviz program</a>, and add
Reid Spencer128a7a72007-02-03 21:06:43 +0000[diff] [blame]801<tt>/Applications/Graphviz.app/Contents/MacOS/</tt> (or wherever you install
Chris Lattnerf623a082005-10-17 01:36:23 +0000[diff] [blame]802it) to your path. Once in your system and path are set up, rerun the LLVM
803configure script and rebuild LLVM to enable this functionality.</p>
804
Jim Laskey543a0ee2006-10-02 12:28:07 +0000[diff] [blame]805<p><tt>SelectionDAG</tt> has been extended to make it easier to locate
806<i>interesting</i> nodes in large complex graphs. From gdb, if you
807<tt>call DAG.setGraphColor(<i>node</i>, "<i>color</i>")</tt>, then the
Reid Spencer128a7a72007-02-03 21:06:43 +0000[diff] [blame]808next <tt>call DAG.viewGraph()</tt> would highlight the node in the
Jim Laskey543a0ee2006-10-02 12:28:07 +0000[diff] [blame]809specified color (choices of colors can be found at <a
Chris Lattner302da1e2007-02-03 03:05:57 +0000[diff] [blame]810href="http://www.graphviz.org/doc/info/colors.html">colors</a>.) More
Jim Laskey543a0ee2006-10-02 12:28:07 +0000[diff] [blame]811complex node attributes can be provided with <tt>call
812DAG.setGraphAttrs(<i>node</i>, "<i>attributes</i>")</tt> (choices can be
813found at <a href="http://www.graphviz.org/doc/info/attrs.html">Graph
814Attributes</a>.) If you want to restart and clear all the current graph
815attributes, then you can <tt>call DAG.clearGraphAttrs()</tt>. </p>
816
Chris Lattnerf623a082005-10-17 01:36:23 +0000[diff] [blame]817</div>
818
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]819<!-- *********************************************************************** -->
820<div class="doc_section">
821 <a name="datastructure">Picking the Right Data Structure for a Task</a>
822</div>
823<!-- *********************************************************************** -->
824
825<div class="doc_text">
826
Reid Spencer128a7a72007-02-03 21:06:43 +0000[diff] [blame]827<p>LLVM has a plethora of data structures in the <tt>llvm/ADT/</tt> directory,
828 and we commonly use STL data structures. This section describes the trade-offs
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]829 you should consider when you pick one.</p>
830
831<p>
832The first step is a choose your own adventure: do you want a sequential
833container, a set-like container, or a map-like container? The most important
834thing when choosing a container is the algorithmic properties of how you plan to
835access the container. Based on that, you should use:</p>
836
837<ul>
Reid Spencer128a7a72007-02-03 21:06:43 +0000[diff] [blame]838<li>a <a href="#ds_map">map-like</a> container if you need efficient look-up
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]839 of an value based on another value. Map-like containers also support
840 efficient queries for containment (whether a key is in the map). Map-like
841 containers generally do not support efficient reverse mapping (values to
842 keys). If you need that, use two maps. Some map-like containers also
843 support efficient iteration through the keys in sorted order. Map-like
844 containers are the most expensive sort, only use them if you need one of
845 these capabilities.</li>
846
847<li>a <a href="#ds_set">set-like</a> container if you need to put a bunch of
848 stuff into a container that automatically eliminates duplicates. Some
849 set-like containers support efficient iteration through the elements in
850 sorted order. Set-like containers are more expensive than sequential
851 containers.
852</li>
853
854<li>a <a href="#ds_sequential">sequential</a> container provides
855 the most efficient way to add elements and keeps track of the order they are
856 added to the collection. They permit duplicates and support efficient
Reid Spencer128a7a72007-02-03 21:06:43 +0000[diff] [blame]857 iteration, but do not support efficient look-up based on a key.
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]858</li>
859
Chris Lattnerdced9fb2009-07-25 07:22:20 +0000[diff] [blame]860<li>a <a href="#ds_string">string</a> container is a specialized sequential
861 container or reference structure that is used for character or byte
862 arrays.</li>
863
Daniel Berlin1939ace2007-09-24 17:52:25 +0000[diff] [blame]864<li>a <a href="#ds_bit">bit</a> container provides an efficient way to store and
865 perform set operations on sets of numeric id's, while automatically
866 eliminating duplicates. Bit containers require a maximum of 1 bit for each
867 identifier you want to store.
868</li>
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]869</ul>
870
871<p>
Reid Spencer128a7a72007-02-03 21:06:43 +0000[diff] [blame]872Once the proper category of container is determined, you can fine tune the
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]873memory use, constant factors, and cache behaviors of access by intelligently
Reid Spencer128a7a72007-02-03 21:06:43 +0000[diff] [blame]874picking a member of the category. Note that constant factors and cache behavior
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]875can be a big deal. If you have a vector that usually only contains a few
876elements (but could contain many), for example, it's much better to use
877<a href="#dss_smallvector">SmallVector</a> than <a href="#dss_vector">vector</a>
878. Doing so avoids (relatively) expensive malloc/free calls, which dwarf the
879cost of adding the elements to the container. </p>
880
881</div>
882
883<!-- ======================================================================= -->
884<div class="doc_subsection">
885 <a name="ds_sequential">Sequential Containers (std::vector, std::list, etc)</a>
886</div>
887
888<div class="doc_text">
889There are a variety of sequential containers available for you, based on your
890needs. Pick the first in this section that will do what you want.
891</div>
892
893<!-- _______________________________________________________________________ -->
894<div class="doc_subsubsection">
Chris Lattner8ae42612011-04-05 23:18:20 +0000[diff] [blame]895 <a name="dss_arrayref">llvm/ADT/ArrayRef.h</a>
896</div>
897
898<div class="doc_text">
899<p>The llvm::ArrayRef class is the preferred class to use in an interface that
900 accepts a sequential list of elements in memory and just reads from them. By
901 taking an ArrayRef, the API can be passed a fixed size array, an std::vector,
902 an llvm::SmallVector and anything else that is contiguous in memory.
903</p>
904</div>
905
906
907
908<!-- _______________________________________________________________________ -->
909<div class="doc_subsubsection">
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]910 <a name="dss_fixedarrays">Fixed Size Arrays</a>
911</div>
912
913<div class="doc_text">
914<p>Fixed size arrays are very simple and very fast. They are good if you know
915exactly how many elements you have, or you have a (low) upper bound on how many
916you have.</p>
917</div>
918
919<!-- _______________________________________________________________________ -->
920<div class="doc_subsubsection">
921 <a name="dss_heaparrays">Heap Allocated Arrays</a>
922</div>
923
924<div class="doc_text">
925<p>Heap allocated arrays (new[] + delete[]) are also simple. They are good if
926the number of elements is variable, if you know how many elements you will need
927before the array is allocated, and if the array is usually large (if not,
928consider a <a href="#dss_smallvector">SmallVector</a>). The cost of a heap
929allocated array is the cost of the new/delete (aka malloc/free). Also note that
930if you are allocating an array of a type with a constructor, the constructor and
Reid Spencer128a7a72007-02-03 21:06:43 +0000[diff] [blame]931destructors will be run for every element in the array (re-sizable vectors only
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]932construct those elements actually used).</p>
933</div>
934
935<!-- _______________________________________________________________________ -->
936<div class="doc_subsubsection">
937 <a name="dss_smallvector">"llvm/ADT/SmallVector.h"</a>
938</div>
939
940<div class="doc_text">
941<p><tt>SmallVector&lt;Type, N&gt;</tt> is a simple class that looks and smells
942just like <tt>vector&lt;Type&gt;</tt>:
943it supports efficient iteration, lays out elements in memory order (so you can
944do pointer arithmetic between elements), supports efficient push_back/pop_back
945operations, supports efficient random access to its elements, etc.</p>
946
947<p>The advantage of SmallVector is that it allocates space for
948some number of elements (N) <b>in the object itself</b>. Because of this, if
949the SmallVector is dynamically smaller than N, no malloc is performed. This can
950be a big win in cases where the malloc/free call is far more expensive than the
951code that fiddles around with the elements.</p>
952
953<p>This is good for vectors that are "usually small" (e.g. the number of
954predecessors/successors of a block is usually less than 8). On the other hand,
955this makes the size of the SmallVector itself large, so you don't want to
956allocate lots of them (doing so will waste a lot of space). As such,
957SmallVectors are most useful when on the stack.</p>
958
959<p>SmallVector also provides a nice portable and efficient replacement for
960<tt>alloca</tt>.</p>
961
962</div>
963
964<!-- _______________________________________________________________________ -->
965<div class="doc_subsubsection">
966 <a name="dss_vector">&lt;vector&gt;</a>
967</div>
968
969<div class="doc_text">
970<p>
971std::vector is well loved and respected. It is useful when SmallVector isn't:
972when the size of the vector is often large (thus the small optimization will
973rarely be a benefit) or if you will be allocating many instances of the vector
974itself (which would waste space for elements that aren't in the container).
975vector is also useful when interfacing with code that expects vectors :).
976</p>
Chris Lattner32d84762007-02-05 06:30:51 +0000[diff] [blame]977
978<p>One worthwhile note about std::vector: avoid code like this:</p>
979
980<div class="doc_code">
981<pre>
982for ( ... ) {
Chris Lattner9bb3dbb2007-03-28 18:27:57 +0000[diff] [blame]983 std::vector&lt;foo&gt; V;
Chris Lattner32d84762007-02-05 06:30:51 +0000[diff] [blame]984 use V;
985}
986</pre>
987</div>
988
989<p>Instead, write this as:</p>
990
991<div class="doc_code">
992<pre>
Chris Lattner9bb3dbb2007-03-28 18:27:57 +0000[diff] [blame]993std::vector&lt;foo&gt; V;
Chris Lattner32d84762007-02-05 06:30:51 +0000[diff] [blame]994for ( ... ) {
995 use V;
996 V.clear();
997}
998</pre>
999</div>
1000
1001<p>Doing so will save (at least) one heap allocation and free per iteration of
1002the loop.</p>
1003
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]1004</div>
1005
1006<!-- _______________________________________________________________________ -->
1007<div class="doc_subsubsection">
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1008 <a name="dss_deque">&lt;deque&gt;</a>
1009</div>
1010
1011<div class="doc_text">
1012<p>std::deque is, in some senses, a generalized version of std::vector. Like
1013std::vector, it provides constant time random access and other similar
1014properties, but it also provides efficient access to the front of the list. It
1015does not guarantee continuity of elements within memory.</p>
1016
1017<p>In exchange for this extra flexibility, std::deque has significantly higher
1018constant factor costs than std::vector. If possible, use std::vector or
1019something cheaper.</p>
1020</div>
1021
1022<!-- _______________________________________________________________________ -->
1023<div class="doc_subsubsection">
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]1024 <a name="dss_list">&lt;list&gt;</a>
1025</div>
1026
1027<div class="doc_text">
1028<p>std::list is an extremely inefficient class that is rarely useful.
1029It performs a heap allocation for every element inserted into it, thus having an
1030extremely high constant factor, particularly for small data types. std::list
1031also only supports bidirectional iteration, not random access iteration.</p>
1032
1033<p>In exchange for this high cost, std::list supports efficient access to both
1034ends of the list (like std::deque, but unlike std::vector or SmallVector). In
1035addition, the iterator invalidation characteristics of std::list are stronger
1036than that of a vector class: inserting or removing an element into the list does
1037not invalidate iterator or pointers to other elements in the list.</p>
1038</div>
1039
1040<!-- _______________________________________________________________________ -->
1041<div class="doc_subsubsection">
Gabor Greif3899e492009-02-27 11:37:41 +0000[diff] [blame]1042 <a name="dss_ilist">llvm/ADT/ilist.h</a>
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]1043</div>
1044
1045<div class="doc_text">
1046<p><tt>ilist&lt;T&gt;</tt> implements an 'intrusive' doubly-linked list. It is
1047intrusive, because it requires the element to store and provide access to the
1048prev/next pointers for the list.</p>
1049
Gabor Greif2946d1c2009-02-27 12:02:19 +0000[diff] [blame]1050<p><tt>ilist</tt> has the same drawbacks as <tt>std::list</tt>, and additionally
1051requires an <tt>ilist_traits</tt> implementation for the element type, but it
1052provides some novel characteristics. In particular, it can efficiently store
1053polymorphic objects, the traits class is informed when an element is inserted or
Gabor Greif0cbcabe2009-03-12 09:47:03 +0000[diff] [blame]1054removed from the list, and <tt>ilist</tt>s are guaranteed to support a
1055constant-time splice operation.</p>
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]1056
Gabor Greif0cbcabe2009-03-12 09:47:03 +0000[diff] [blame]1057<p>These properties are exactly what we want for things like
1058<tt>Instruction</tt>s and basic blocks, which is why these are implemented with
1059<tt>ilist</tt>s.</p>
Gabor Greif3899e492009-02-27 11:37:41 +0000[diff] [blame]1060
1061Related classes of interest are explained in the following subsections:
1062 <ul>
Gabor Greif01862502009-02-27 13:28:07 +0000[diff] [blame]1063 <li><a href="#dss_ilist_traits">ilist_traits</a></li>
Gabor Greif2946d1c2009-02-27 12:02:19 +0000[diff] [blame]1064 <li><a href="#dss_iplist">iplist</a></li>
Gabor Greif3899e492009-02-27 11:37:41 +0000[diff] [blame]1065 <li><a href="#dss_ilist_node">llvm/ADT/ilist_node.h</a></li>
Gabor Greif6a65f422009-03-12 10:30:31 +0000[diff] [blame]1066 <li><a href="#dss_ilist_sentinel">Sentinels</a></li>
Gabor Greif3899e492009-02-27 11:37:41 +0000[diff] [blame]1067 </ul>
1068</div>
1069
1070<!-- _______________________________________________________________________ -->
1071<div class="doc_subsubsection">
Gabor Greif01862502009-02-27 13:28:07 +0000[diff] [blame]1072 <a name="dss_ilist_traits">ilist_traits</a>
1073</div>
1074
1075<div class="doc_text">
1076<p><tt>ilist_traits&lt;T&gt;</tt> is <tt>ilist&lt;T&gt;</tt>'s customization
1077mechanism. <tt>iplist&lt;T&gt;</tt> (and consequently <tt>ilist&lt;T&gt;</tt>)
1078publicly derive from this traits class.</p>
1079</div>
1080
1081<!-- _______________________________________________________________________ -->
1082<div class="doc_subsubsection">
Gabor Greif2946d1c2009-02-27 12:02:19 +0000[diff] [blame]1083 <a name="dss_iplist">iplist</a>
1084</div>
1085
1086<div class="doc_text">
1087<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]1088supports a slightly narrower interface. Notably, inserters from
1089<tt>T&amp;</tt> are absent.</p>
Gabor Greif01862502009-02-27 13:28:07 +0000[diff] [blame]1090
1091<p><tt>ilist_traits&lt;T&gt;</tt> is a public base of this class and can be
1092used for a wide variety of customizations.</p>
Gabor Greif2946d1c2009-02-27 12:02:19 +0000[diff] [blame]1093</div>
1094
1095<!-- _______________________________________________________________________ -->
1096<div class="doc_subsubsection">
Gabor Greif3899e492009-02-27 11:37:41 +0000[diff] [blame]1097 <a name="dss_ilist_node">llvm/ADT/ilist_node.h</a>
1098</div>
1099
1100<div class="doc_text">
1101<p><tt>ilist_node&lt;T&gt;</tt> implements a the forward and backward links
1102that are expected by the <tt>ilist&lt;T&gt;</tt> (and analogous containers)
1103in the default manner.</p>
1104
1105<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]1106<tt>T</tt>, usually <tt>T</tt> publicly derives from
1107<tt>ilist_node&lt;T&gt;</tt>.</p>
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]1108</div>
1109
1110<!-- _______________________________________________________________________ -->
1111<div class="doc_subsubsection">
Gabor Greif6a65f422009-03-12 10:30:31 +0000[diff] [blame]1112 <a name="dss_ilist_sentinel">Sentinels</a>
1113</div>
1114
1115<div class="doc_text">
Dan Gohmancf0c9bc2010-02-25 23:51:27 +0000[diff] [blame]1116<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]1117citizen in the C++ ecosystem, it needs to support the standard container
1118operations, such as <tt>begin</tt> and <tt>end</tt> iterators, etc. Also, the
1119<tt>operator--</tt> must work correctly on the <tt>end</tt> iterator in the
1120case of non-empty <tt>ilist</tt>s.</p>
1121
1122<p>The only sensible solution to this problem is to allocate a so-called
1123<i>sentinel</i> along with the intrusive list, which serves as the <tt>end</tt>
1124iterator, providing the back-link to the last element. However conforming to the
1125C++ convention it is illegal to <tt>operator++</tt> beyond the sentinel and it
1126also must not be dereferenced.</p>
1127
1128<p>These constraints allow for some implementation freedom to the <tt>ilist</tt>
1129how to allocate and store the sentinel. The corresponding policy is dictated
1130by <tt>ilist_traits&lt;T&gt;</tt>. By default a <tt>T</tt> gets heap-allocated
1131whenever the need for a sentinel arises.</p>
1132
1133<p>While the default policy is sufficient in most cases, it may break down when
1134<tt>T</tt> does not provide a default constructor. Also, in the case of many
1135instances of <tt>ilist</tt>s, the memory overhead of the associated sentinels
1136is wasted. To alleviate the situation with numerous and voluminous
1137<tt>T</tt>-sentinels, sometimes a trick is employed, leading to <i>ghostly
1138sentinels</i>.</p>
1139
1140<p>Ghostly sentinels are obtained by specially-crafted <tt>ilist_traits&lt;T&gt;</tt>
1141which superpose the sentinel with the <tt>ilist</tt> instance in memory. Pointer
1142arithmetic is used to obtain the sentinel, which is relative to the
1143<tt>ilist</tt>'s <tt>this</tt> pointer. The <tt>ilist</tt> is augmented by an
1144extra pointer, which serves as the back-link of the sentinel. This is the only
1145field in the ghostly sentinel which can be legally accessed.</p>
1146</div>
1147
1148<!-- _______________________________________________________________________ -->
1149<div class="doc_subsubsection">
Chris Lattnerc5722432007-02-03 19:49:31 +0000[diff] [blame]1150 <a name="dss_other">Other Sequential Container options</a>
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]1151</div>
1152
1153<div class="doc_text">
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1154<p>Other STL containers are available, such as std::string.</p>
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]1155
1156<p>There are also various STL adapter classes such as std::queue,
1157std::priority_queue, std::stack, etc. These provide simplified access to an
1158underlying container but don't affect the cost of the container itself.</p>
1159
1160</div>
1161
1162
1163<!-- ======================================================================= -->
1164<div class="doc_subsection">
1165 <a name="ds_set">Set-Like Containers (std::set, SmallSet, SetVector, etc)</a>
1166</div>
1167
1168<div class="doc_text">
1169
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1170<p>Set-like containers are useful when you need to canonicalize multiple values
1171into a single representation. There are several different choices for how to do
1172this, providing various trade-offs.</p>
1173
1174</div>
1175
1176
1177<!-- _______________________________________________________________________ -->
1178<div class="doc_subsubsection">
1179 <a name="dss_sortedvectorset">A sorted 'vector'</a>
1180</div>
1181
1182<div class="doc_text">
1183
Chris Lattner3b23a8c2007-02-03 08:10:45 +0000[diff] [blame]1184<p>If you intend to insert a lot of elements, then do a lot of queries, a
1185great approach is to use a vector (or other sequential container) with
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1186std::sort+std::unique to remove duplicates. This approach works really well if
Chris Lattner3b23a8c2007-02-03 08:10:45 +0000[diff] [blame]1187your usage pattern has these two distinct phases (insert then query), and can be
1188coupled with a good choice of <a href="#ds_sequential">sequential container</a>.
1189</p>
1190
1191<p>
1192This combination provides the several nice properties: the result data is
1193contiguous in memory (good for cache locality), has few allocations, is easy to
1194address (iterators in the final vector are just indices or pointers), and can be
1195efficiently queried with a standard binary or radix search.</p>
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1196
1197</div>
1198
1199<!-- _______________________________________________________________________ -->
1200<div class="doc_subsubsection">
1201 <a name="dss_smallset">"llvm/ADT/SmallSet.h"</a>
1202</div>
1203
1204<div class="doc_text">
1205
Reid Spencer128a7a72007-02-03 21:06:43 +0000[diff] [blame]1206<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]1207are 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]1208has space for N elements in place (thus, if the set is dynamically smaller than
Chris Lattner14868db2007-02-03 08:20:15 +0000[diff] [blame]1209N, no malloc traffic is required) and accesses them with a simple linear search.
1210When the set grows beyond 'N' elements, it allocates a more expensive representation that
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1211guarantees efficient access (for most types, it falls back to std::set, but for
Chris Lattner14868db2007-02-03 08:20:15 +0000[diff] [blame]1212pointers it uses something far better, <a
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1213href="#dss_smallptrset">SmallPtrSet</a>).</p>
1214
1215<p>The magic of this class is that it handles small sets extremely efficiently,
1216but gracefully handles extremely large sets without loss of efficiency. The
1217drawback is that the interface is quite small: it supports insertion, queries
1218and erasing, but does not support iteration.</p>
1219
1220</div>
1221
1222<!-- _______________________________________________________________________ -->
1223<div class="doc_subsubsection">
1224 <a name="dss_smallptrset">"llvm/ADT/SmallPtrSet.h"</a>
1225</div>
1226
1227<div class="doc_text">
1228
Gabor Greif4de73682010-03-26 19:30:47 +0000[diff] [blame]1229<p>SmallPtrSet has all the advantages of <tt>SmallSet</tt> (and a <tt>SmallSet</tt> of pointers is
1230transparently implemented with a <tt>SmallPtrSet</tt>), but also supports iterators. If
Chris Lattner14868db2007-02-03 08:20:15 +0000[diff] [blame]1231more than 'N' insertions are performed, a single quadratically
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1232probed hash table is allocated and grows as needed, providing extremely
1233efficient access (constant time insertion/deleting/queries with low constant
1234factors) and is very stingy with malloc traffic.</p>
1235
Gabor Greif4de73682010-03-26 19:30:47 +0000[diff] [blame]1236<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]1237whenever an insertion occurs. Also, the values visited by the iterators are not
1238visited in sorted order.</p>
1239
1240</div>
1241
1242<!-- _______________________________________________________________________ -->
1243<div class="doc_subsubsection">
Chris Lattnerc28476f2007-09-30 00:58:59 +0000[diff] [blame]1244 <a name="dss_denseset">"llvm/ADT/DenseSet.h"</a>
1245</div>
1246
1247<div class="doc_text">
1248
1249<p>
1250DenseSet is a simple quadratically probed hash table. It excels at supporting
1251small values: it uses a single allocation to hold all of the pairs that
1252are currently inserted in the set. DenseSet is a great way to unique small
1253values that are not simple pointers (use <a
1254href="#dss_smallptrset">SmallPtrSet</a> for pointers). Note that DenseSet has
1255the same requirements for the value type that <a
1256href="#dss_densemap">DenseMap</a> has.
1257</p>
1258
1259</div>
1260
1261<!-- _______________________________________________________________________ -->
1262<div class="doc_subsubsection">
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1263 <a name="dss_FoldingSet">"llvm/ADT/FoldingSet.h"</a>
1264</div>
1265
1266<div class="doc_text">
1267
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]1268<p>
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1269FoldingSet is an aggregate class that is really good at uniquing
1270expensive-to-create or polymorphic objects. It is a combination of a chained
1271hash table with intrusive links (uniqued objects are required to inherit from
Chris Lattner14868db2007-02-03 08:20:15 +0000[diff] [blame]1272FoldingSetNode) that uses <a href="#dss_smallvector">SmallVector</a> as part of
1273its ID process.</p>
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1274
Chris Lattner14868db2007-02-03 08:20:15 +0000[diff] [blame]1275<p>Consider a case where you want to implement a "getOrCreateFoo" method for
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1276a complex object (for example, a node in the code generator). The client has a
1277description of *what* it wants to generate (it knows the opcode and all the
1278operands), 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]1279only to find out it already exists, at which point we would have to delete it
1280and return the node that already exists.
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]1281</p>
1282
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1283<p>To support this style of client, FoldingSet perform a query with a
1284FoldingSetNodeID (which wraps SmallVector) that can be used to describe the
1285element that we want to query for. The query either returns the element
1286matching the ID or it returns an opaque ID that indicates where insertion should
Chris Lattner14868db2007-02-03 08:20:15 +0000[diff] [blame]1287take place. Construction of the ID usually does not require heap traffic.</p>
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1288
1289<p>Because FoldingSet uses intrusive links, it can support polymorphic objects
1290in the set (for example, you can have SDNode instances mixed with LoadSDNodes).
1291Because the elements are individually allocated, pointers to the elements are
1292stable: inserting or removing elements does not invalidate any pointers to other
1293elements.
1294</p>
1295
1296</div>
1297
1298<!-- _______________________________________________________________________ -->
1299<div class="doc_subsubsection">
1300 <a name="dss_set">&lt;set&gt;</a>
1301</div>
1302
1303<div class="doc_text">
1304
Chris Lattnerc5722432007-02-03 19:49:31 +0000[diff] [blame]1305<p><tt>std::set</tt> is a reasonable all-around set class, which is decent at
1306many things but great at nothing. std::set allocates memory for each element
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1307inserted (thus it is very malloc intensive) and typically stores three pointers
Chris Lattner14868db2007-02-03 08:20:15 +0000[diff] [blame]1308per element in the set (thus adding a large amount of per-element space
1309overhead). It offers guaranteed log(n) performance, which is not particularly
Chris Lattnerc5722432007-02-03 19:49:31 +0000[diff] [blame]1310fast from a complexity standpoint (particularly if the elements of the set are
1311expensive to compare, like strings), and has extremely high constant factors for
1312lookup, insertion and removal.</p>
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1313
Chris Lattner14868db2007-02-03 08:20:15 +0000[diff] [blame]1314<p>The advantages of std::set are that its iterators are stable (deleting or
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1315inserting an element from the set does not affect iterators or pointers to other
1316elements) and that iteration over the set is guaranteed to be in sorted order.
1317If the elements in the set are large, then the relative overhead of the pointers
1318and malloc traffic is not a big deal, but if the elements of the set are small,
1319std::set is almost never a good choice.</p>
1320
1321</div>
1322
1323<!-- _______________________________________________________________________ -->
1324<div class="doc_subsubsection">
1325 <a name="dss_setvector">"llvm/ADT/SetVector.h"</a>
1326</div>
1327
1328<div class="doc_text">
Chris Lattneredca3c52007-02-04 00:00:26 +0000[diff] [blame]1329<p>LLVM's SetVector&lt;Type&gt; is an adapter class that combines your choice of
1330a set-like container along with a <a href="#ds_sequential">Sequential
1331Container</a>. The important property
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1332that this provides is efficient insertion with uniquing (duplicate elements are
1333ignored) with iteration support. It implements this by inserting elements into
1334both a set-like container and the sequential container, using the set-like
1335container for uniquing and the sequential container for iteration.
1336</p>
1337
1338<p>The difference between SetVector and other sets is that the order of
1339iteration is guaranteed to match the order of insertion into the SetVector.
1340This property is really important for things like sets of pointers. Because
1341pointer values are non-deterministic (e.g. vary across runs of the program on
Chris Lattneredca3c52007-02-04 00:00:26 +0000[diff] [blame]1342different machines), iterating over the pointers in the set will
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1343not be in a well-defined order.</p>
1344
1345<p>
1346The drawback of SetVector is that it requires twice as much space as a normal
1347set and has the sum of constant factors from the set-like container and the
1348sequential container that it uses. Use it *only* if you need to iterate over
1349the elements in a deterministic order. SetVector is also expensive to delete
Chris Lattneredca3c52007-02-04 00:00:26 +0000[diff] [blame]1350elements out of (linear time), unless you use it's "pop_back" method, which is
1351faster.
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1352</p>
1353
Chris Lattneredca3c52007-02-04 00:00:26 +0000[diff] [blame]1354<p>SetVector is an adapter class that defaults to using std::vector and std::set
1355for the underlying containers, so it is quite expensive. However,
1356<tt>"llvm/ADT/SetVector.h"</tt> also provides a SmallSetVector class, which
1357defaults to using a SmallVector and SmallSet of a specified size. If you use
1358this, and if your sets are dynamically smaller than N, you will save a lot of
1359heap traffic.</p>
1360
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1361</div>
1362
1363<!-- _______________________________________________________________________ -->
1364<div class="doc_subsubsection">
Chris Lattnerc5722432007-02-03 19:49:31 +0000[diff] [blame]1365 <a name="dss_uniquevector">"llvm/ADT/UniqueVector.h"</a>
1366</div>
1367
1368<div class="doc_text">
1369
1370<p>
1371UniqueVector is similar to <a href="#dss_setvector">SetVector</a>, but it
1372retains a unique ID for each element inserted into the set. It internally
1373contains a map and a vector, and it assigns a unique ID for each value inserted
1374into the set.</p>
1375
1376<p>UniqueVector is very expensive: its cost is the sum of the cost of
1377maintaining both the map and vector, it has high complexity, high constant
1378factors, and produces a lot of malloc traffic. It should be avoided.</p>
1379
1380</div>
1381
1382
1383<!-- _______________________________________________________________________ -->
1384<div class="doc_subsubsection">
1385 <a name="dss_otherset">Other Set-Like Container Options</a>
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1386</div>
1387
1388<div class="doc_text">
1389
1390<p>
1391The STL provides several other options, such as std::multiset and the various
Chris Lattnerf1a30822009-03-09 05:20:45 +0000[diff] [blame]1392"hash_set" like containers (whether from C++ TR1 or from the SGI library). We
1393never use hash_set and unordered_set because they are generally very expensive
1394(each insertion requires a malloc) and very non-portable.
1395</p>
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1396
1397<p>std::multiset is useful if you're not interested in elimination of
Chris Lattner14868db2007-02-03 08:20:15 +0000[diff] [blame]1398duplicates, but has all the drawbacks of std::set. A sorted vector (where you
1399don't delete duplicate entries) or some other approach is almost always
1400better.</p>
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1401
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]1402</div>
1403
1404<!-- ======================================================================= -->
1405<div class="doc_subsection">
1406 <a name="ds_map">Map-Like Containers (std::map, DenseMap, etc)</a>
1407</div>
1408
1409<div class="doc_text">
Chris Lattnerc5722432007-02-03 19:49:31 +0000[diff] [blame]1410Map-like containers are useful when you want to associate data to a key. As
1411usual, there are a lot of different ways to do this. :)
1412</div>
1413
1414<!-- _______________________________________________________________________ -->
1415<div class="doc_subsubsection">
1416 <a name="dss_sortedvectormap">A sorted 'vector'</a>
1417</div>
1418
1419<div class="doc_text">
1420
1421<p>
1422If your usage pattern follows a strict insert-then-query approach, you can
1423trivially use the same approach as <a href="#dss_sortedvectorset">sorted vectors
1424for set-like containers</a>. The only difference is that your query function
1425(which uses std::lower_bound to get efficient log(n) lookup) should only compare
1426the key, not both the key and value. This yields the same advantages as sorted
1427vectors for sets.
1428</p>
1429</div>
1430
1431<!-- _______________________________________________________________________ -->
1432<div class="doc_subsubsection">
Chris Lattner796f9fa2007-02-08 19:14:21 +0000[diff] [blame]1433 <a name="dss_stringmap">"llvm/ADT/StringMap.h"</a>
Chris Lattnerc5722432007-02-03 19:49:31 +0000[diff] [blame]1434</div>
1435
1436<div class="doc_text">
1437
1438<p>
1439Strings are commonly used as keys in maps, and they are difficult to support
1440efficiently: they are variable length, inefficient to hash and compare when
Chris Lattner796f9fa2007-02-08 19:14:21 +0000[diff] [blame]1441long, expensive to copy, etc. StringMap is a specialized container designed to
1442cope with these issues. It supports mapping an arbitrary range of bytes to an
1443arbitrary other object.</p>
Chris Lattnerc5722432007-02-03 19:49:31 +0000[diff] [blame]1444
Chris Lattner796f9fa2007-02-08 19:14:21 +0000[diff] [blame]1445<p>The StringMap implementation uses a quadratically-probed hash table, where
Chris Lattnerc5722432007-02-03 19:49:31 +0000[diff] [blame]1446the buckets store a pointer to the heap allocated entries (and some other
1447stuff). The entries in the map must be heap allocated because the strings are
1448variable length. The string data (key) and the element object (value) are
1449stored in the same allocation with the string data immediately after the element
1450object. This container guarantees the "<tt>(char*)(&amp;Value+1)</tt>" points
1451to the key string for a value.</p>
1452
Chris Lattner796f9fa2007-02-08 19:14:21 +0000[diff] [blame]1453<p>The StringMap is very fast for several reasons: quadratic probing is very
Chris Lattnerc5722432007-02-03 19:49:31 +0000[diff] [blame]1454cache efficient for lookups, the hash value of strings in buckets is not
Nick Lewycky2a80aca2010-08-01 23:18:45 +0000[diff] [blame]1455recomputed when looking up an element, StringMap rarely has to touch the
Chris Lattnerc5722432007-02-03 19:49:31 +0000[diff] [blame]1456memory for unrelated objects when looking up a value (even when hash collisions
1457happen), hash table growth does not recompute the hash values for strings
1458already in the table, and each pair in the map is store in a single allocation
1459(the string data is stored in the same allocation as the Value of a pair).</p>
1460
Chris Lattner796f9fa2007-02-08 19:14:21 +0000[diff] [blame]1461<p>StringMap also provides query methods that take byte ranges, so it only ever
Chris Lattnerc5722432007-02-03 19:49:31 +0000[diff] [blame]1462copies a string if a value is inserted into the table.</p>
1463</div>
1464
1465<!-- _______________________________________________________________________ -->
1466<div class="doc_subsubsection">
1467 <a name="dss_indexedmap">"llvm/ADT/IndexedMap.h"</a>
1468</div>
1469
1470<div class="doc_text">
1471<p>
1472IndexedMap is a specialized container for mapping small dense integers (or
1473values that can be mapped to small dense integers) to some other type. It is
1474internally implemented as a vector with a mapping function that maps the keys to
1475the dense integer range.
1476</p>
1477
1478<p>
1479This is useful for cases like virtual registers in the LLVM code generator: they
1480have a dense mapping that is offset by a compile-time constant (the first
1481virtual register ID).</p>
1482
1483</div>
1484
1485<!-- _______________________________________________________________________ -->
1486<div class="doc_subsubsection">
1487 <a name="dss_densemap">"llvm/ADT/DenseMap.h"</a>
1488</div>
1489
1490<div class="doc_text">
1491
1492<p>
1493DenseMap is a simple quadratically probed hash table. It excels at supporting
1494small keys and values: it uses a single allocation to hold all of the pairs that
1495are currently inserted in the map. DenseMap is a great way to map pointers to
1496pointers, or map other small types to each other.
1497</p>
1498
1499<p>
1500There are several aspects of DenseMap that you should be aware of, however. The
1501iterators in a densemap are invalidated whenever an insertion occurs, unlike
1502map. Also, because DenseMap allocates space for a large number of key/value
Chris Lattnera4a264d2007-02-03 20:17:53 +0000[diff] [blame]1503pairs (it starts with 64 by default), it will waste a lot of space if your keys
1504or values are large. Finally, you must implement a partial specialization of
Chris Lattner76c1b972007-09-17 18:34:04 +0000[diff] [blame]1505DenseMapInfo for the key that you want, if it isn't already supported. This
Chris Lattnerc5722432007-02-03 19:49:31 +0000[diff] [blame]1506is required to tell DenseMap about two special marker values (which can never be
Chris Lattnera4a264d2007-02-03 20:17:53 +0000[diff] [blame]1507inserted into the map) that it needs internally.</p>
Chris Lattnerc5722432007-02-03 19:49:31 +0000[diff] [blame]1508
1509</div>
1510
1511<!-- _______________________________________________________________________ -->
1512<div class="doc_subsubsection">
Jeffrey Yasskin71a5c222009-10-22 22:11:22 +0000[diff] [blame]1513 <a name="dss_valuemap">"llvm/ADT/ValueMap.h"</a>
1514</div>
1515
1516<div class="doc_text">
1517
1518<p>
1519ValueMap is a wrapper around a <a href="#dss_densemap">DenseMap</a> mapping
1520Value*s (or subclasses) to another type. When a Value is deleted or RAUW'ed,
1521ValueMap will update itself so the new version of the key is mapped to the same
1522value, just as if the key were a WeakVH. You can configure exactly how this
1523happens, and what else happens on these two events, by passing
1524a <code>Config</code> parameter to the ValueMap template.</p>
1525
1526</div>
1527
1528<!-- _______________________________________________________________________ -->
1529<div class="doc_subsubsection">
Jakob Stoklund Olesenaca0da62010-12-14 00:55:51 +0000[diff] [blame]1530 <a name="dss_intervalmap">"llvm/ADT/IntervalMap.h"</a>
1531</div>
1532
1533<div class="doc_text">
1534
1535<p> IntervalMap is a compact map for small keys and values. It maps key
1536intervals instead of single keys, and it will automatically coalesce adjacent
1537intervals. When then map only contains a few intervals, they are stored in the
1538map object itself to avoid allocations.</p>
1539
1540<p> The IntervalMap iterators are quite big, so they should not be passed around
1541as STL iterators. The heavyweight iterators allow a smaller data structure.</p>
1542
1543</div>
1544
1545<!-- _______________________________________________________________________ -->
1546<div class="doc_subsubsection">
Chris Lattnerc5722432007-02-03 19:49:31 +0000[diff] [blame]1547 <a name="dss_map">&lt;map&gt;</a>
1548</div>
1549
1550<div class="doc_text">
1551
1552<p>
1553std::map has similar characteristics to <a href="#dss_set">std::set</a>: it uses
1554a single allocation per pair inserted into the map, it offers log(n) lookup with
1555an extremely large constant factor, imposes a space penalty of 3 pointers per
1556pair in the map, etc.</p>
1557
1558<p>std::map is most useful when your keys or values are very large, if you need
1559to iterate over the collection in sorted order, or if you need stable iterators
1560into the map (i.e. they don't get invalidated if an insertion or deletion of
1561another element takes place).</p>
1562
1563</div>
1564
1565<!-- _______________________________________________________________________ -->
1566<div class="doc_subsubsection">
Jakob Stoklund Olesen4359e5e2011-04-05 20:56:08 +0000[diff] [blame]1567 <a name="dss_inteqclasses">"llvm/ADT/IntEqClasses.h"</a>
1568</div>
1569
1570<div class="doc_text">
1571
1572<p>IntEqClasses provides a compact representation of equivalence classes of
1573small integers. Initially, each integer in the range 0..n-1 has its own
1574equivalence class. Classes can be joined by passing two class representatives to
1575the join(a, b) method. Two integers are in the same class when findLeader()
1576returns the same representative.</p>
1577
1578<p>Once all equivalence classes are formed, the map can be compressed so each
1579integer 0..n-1 maps to an equivalence class number in the range 0..m-1, where m
1580is the total number of equivalence classes. The map must be uncompressed before
1581it can be edited again.</p>
1582
1583</div>
1584
1585<!-- _______________________________________________________________________ -->
1586<div class="doc_subsubsection">
Chris Lattnerc5722432007-02-03 19:49:31 +0000[diff] [blame]1587 <a name="dss_othermap">Other Map-Like Container Options</a>
1588</div>
1589
1590<div class="doc_text">
1591
1592<p>
1593The STL provides several other options, such as std::multimap and the various
Chris Lattnerf1a30822009-03-09 05:20:45 +0000[diff] [blame]1594"hash_map" like containers (whether from C++ TR1 or from the SGI library). We
1595never use hash_set and unordered_set because they are generally very expensive
1596(each insertion requires a malloc) and very non-portable.</p>
Chris Lattnerc5722432007-02-03 19:49:31 +0000[diff] [blame]1597
1598<p>std::multimap is useful if you want to map a key to multiple values, but has
1599all the drawbacks of std::map. A sorted vector or some other approach is almost
1600always better.</p>
1601
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]1602</div>
1603
Daniel Berlin1939ace2007-09-24 17:52:25 +0000[diff] [blame]1604<!-- ======================================================================= -->
1605<div class="doc_subsection">
Chris Lattnerdced9fb2009-07-25 07:22:20 +0000[diff] [blame]1606 <a name="ds_string">String-like containers</a>
1607</div>
1608
1609<div class="doc_text">
1610
1611<p>
1612TODO: const char* vs stringref vs smallstring vs std::string. Describe twine,
1613xref to #string_apis.
1614</p>
1615
1616</div>
1617
1618<!-- ======================================================================= -->
1619<div class="doc_subsection">
Daniel Berlin1939ace2007-09-24 17:52:25 +0000[diff] [blame]1620 <a name="ds_bit">Bit storage containers (BitVector, SparseBitVector)</a>
1621</div>
1622
1623<div class="doc_text">
Chris Lattner7086ce72007-09-25 22:37:50 +0000[diff] [blame]1624<p>Unlike the other containers, there are only two bit storage containers, and
1625choosing when to use each is relatively straightforward.</p>
1626
1627<p>One additional option is
1628<tt>std::vector&lt;bool&gt;</tt>: we discourage its use for two reasons 1) the
1629implementation in many common compilers (e.g. commonly available versions of
1630GCC) is extremely inefficient and 2) the C++ standards committee is likely to
1631deprecate this container and/or change it significantly somehow. In any case,
1632please don't use it.</p>
Daniel Berlin1939ace2007-09-24 17:52:25 +0000[diff] [blame]1633</div>
1634
1635<!-- _______________________________________________________________________ -->
1636<div class="doc_subsubsection">
1637 <a name="dss_bitvector">BitVector</a>
1638</div>
1639
1640<div class="doc_text">
Dan Gohman5f7775c2010-01-05 18:24:00 +0000[diff] [blame]1641<p> The BitVector container provides a dynamic size set of bits for manipulation.
Daniel Berlin1939ace2007-09-24 17:52:25 +0000[diff] [blame]1642It supports individual bit setting/testing, as well as set operations. The set
1643operations take time O(size of bitvector), but operations are performed one word
1644at a time, instead of one bit at a time. This makes the BitVector very fast for
1645set operations compared to other containers. Use the BitVector when you expect
1646the number of set bits to be high (IE a dense set).
1647</p>
1648</div>
1649
1650<!-- _______________________________________________________________________ -->
1651<div class="doc_subsubsection">
Dan Gohman5f7775c2010-01-05 18:24:00 +0000[diff] [blame]1652 <a name="dss_smallbitvector">SmallBitVector</a>
1653</div>
1654
1655<div class="doc_text">
1656<p> The SmallBitVector container provides the same interface as BitVector, but
1657it is optimized for the case where only a small number of bits, less than
165825 or so, are needed. It also transparently supports larger bit counts, but
1659slightly less efficiently than a plain BitVector, so SmallBitVector should
1660only be used when larger counts are rare.
1661</p>
1662
1663<p>
1664At this time, SmallBitVector does not support set operations (and, or, xor),
1665and its operator[] does not provide an assignable lvalue.
1666</p>
1667</div>
1668
1669<!-- _______________________________________________________________________ -->
1670<div class="doc_subsubsection">
Daniel Berlin1939ace2007-09-24 17:52:25 +0000[diff] [blame]1671 <a name="dss_sparsebitvector">SparseBitVector</a>
1672</div>
1673
1674<div class="doc_text">
1675<p> The SparseBitVector container is much like BitVector, with one major
1676difference: Only the bits that are set, are stored. This makes the
1677SparseBitVector much more space efficient than BitVector when the set is sparse,
1678as well as making set operations O(number of set bits) instead of O(size of
1679universe). 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
1680(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).
1681</p>
1682</div>
Chris Lattnerf623a082005-10-17 01:36:23 +0000[diff] [blame]1683
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1684<!-- *********************************************************************** -->
1685<div class="doc_section">
1686 <a name="common">Helpful Hints for Common Operations</a>
1687</div>
1688<!-- *********************************************************************** -->
1689
1690<div class="doc_text">
1691
1692<p>This section describes how to perform some very simple transformations of
1693LLVM code. This is meant to give examples of common idioms used, showing the
1694practical side of LLVM transformations. <p> Because this is a "how-to" section,
1695you should also read about the main classes that you will be working with. The
1696<a href="#coreclasses">Core LLVM Class Hierarchy Reference</a> contains details
1697and descriptions of the main classes that you should know about.</p>
1698
1699</div>
1700
1701<!-- NOTE: this section should be heavy on example code -->
1702<!-- ======================================================================= -->
1703<div class="doc_subsection">
1704 <a name="inspection">Basic Inspection and Traversal Routines</a>
1705</div>
1706
1707<div class="doc_text">
1708
1709<p>The LLVM compiler infrastructure have many different data structures that may
1710be traversed. Following the example of the C++ standard template library, the
1711techniques used to traverse these various data structures are all basically the
1712same. For a enumerable sequence of values, the <tt>XXXbegin()</tt> function (or
1713method) returns an iterator to the start of the sequence, the <tt>XXXend()</tt>
1714function returns an iterator pointing to one past the last valid element of the
1715sequence, and there is some <tt>XXXiterator</tt> data type that is common
1716between the two operations.</p>
1717
1718<p>Because the pattern for iteration is common across many different aspects of
1719the program representation, the standard template library algorithms may be used
1720on them, and it is easier to remember how to iterate. First we show a few common
1721examples of the data structures that need to be traversed. Other data
1722structures are traversed in very similar ways.</p>
1723
1724</div>
1725
1726<!-- _______________________________________________________________________ -->
Chris Lattner69bf8a92004-05-23 21:06:58 +0000[diff] [blame]1727<div class="doc_subsubsection">
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1728 <a name="iterate_function">Iterating over the </a><a
1729 href="#BasicBlock"><tt>BasicBlock</tt></a>s in a <a
1730 href="#Function"><tt>Function</tt></a>
1731</div>
1732
1733<div class="doc_text">
1734
1735<p>It's quite common to have a <tt>Function</tt> instance that you'd like to
1736transform in some way; in particular, you'd like to manipulate its
1737<tt>BasicBlock</tt>s. To facilitate this, you'll need to iterate over all of
1738the <tt>BasicBlock</tt>s that constitute the <tt>Function</tt>. The following is
1739an example that prints the name of a <tt>BasicBlock</tt> and the number of
1740<tt>Instruction</tt>s it contains:</p>
1741
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1742<div class="doc_code">
1743<pre>
Bill Wendling82e2eea2006-10-11 18:00:22 +0000[diff] [blame]1744// <i>func is a pointer to a Function instance</i>
1745for (Function::iterator i = func-&gt;begin(), e = func-&gt;end(); i != e; ++i)
1746 // <i>Print out the name of the basic block if it has one, and then the</i>
1747 // <i>number of instructions that it contains</i>
Chris Lattner3fee6ed2009-09-08 05:15:50 +0000[diff] [blame]1748 errs() &lt;&lt; "Basic block (name=" &lt;&lt; i-&gt;getName() &lt;&lt; ") has "
Bill Wendling832171c2006-12-07 20:04:42 +0000[diff] [blame]1749 &lt;&lt; i-&gt;size() &lt;&lt; " instructions.\n";
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1750</pre>
1751</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1752
1753<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]1754invoking member functions of the <tt>Instruction</tt> class. This is
1755because the indirection operator is overloaded for the iterator
Chris Lattner7496ec52003-08-05 22:54:23 +0000[diff] [blame]1756classes. In the above code, the expression <tt>i-&gt;size()</tt> is
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1757exactly equivalent to <tt>(*i).size()</tt> just like you'd expect.</p>
1758
1759</div>
1760
1761<!-- _______________________________________________________________________ -->
Chris Lattner69bf8a92004-05-23 21:06:58 +0000[diff] [blame]1762<div class="doc_subsubsection">
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1763 <a name="iterate_basicblock">Iterating over the </a><a
1764 href="#Instruction"><tt>Instruction</tt></a>s in a <a
1765 href="#BasicBlock"><tt>BasicBlock</tt></a>
1766</div>
1767
1768<div class="doc_text">
1769
1770<p>Just like when dealing with <tt>BasicBlock</tt>s in <tt>Function</tt>s, it's
1771easy to iterate over the individual instructions that make up
1772<tt>BasicBlock</tt>s. Here's a code snippet that prints out each instruction in
1773a <tt>BasicBlock</tt>:</p>
1774
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1775<div class="doc_code">
Chris Lattner55c04612005-03-06 06:00:13 +0000[diff] [blame]1776<pre>
Bill Wendling82e2eea2006-10-11 18:00:22 +0000[diff] [blame]1777// <i>blk is a pointer to a BasicBlock instance</i>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1778for (BasicBlock::iterator i = blk-&gt;begin(), e = blk-&gt;end(); i != e; ++i)
Bill Wendling82e2eea2006-10-11 18:00:22 +0000[diff] [blame]1779 // <i>The next statement works since operator&lt;&lt;(ostream&amp;,...)</i>
1780 // <i>is overloaded for Instruction&amp;</i>
Chris Lattner3fee6ed2009-09-08 05:15:50 +0000[diff] [blame]1781 errs() &lt;&lt; *i &lt;&lt; "\n";
Chris Lattner55c04612005-03-06 06:00:13 +0000[diff] [blame]1782</pre>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1783</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1784
1785<p>However, this isn't really the best way to print out the contents of a
1786<tt>BasicBlock</tt>! Since the ostream operators are overloaded for virtually
1787anything you'll care about, you could have just invoked the print routine on the
Chris Lattner3fee6ed2009-09-08 05:15:50 +0000[diff] [blame]1788basic block itself: <tt>errs() &lt;&lt; *blk &lt;&lt; "\n";</tt>.</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1789
1790</div>
1791
1792<!-- _______________________________________________________________________ -->
Chris Lattner69bf8a92004-05-23 21:06:58 +0000[diff] [blame]1793<div class="doc_subsubsection">
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1794 <a name="iterate_institer">Iterating over the </a><a
1795 href="#Instruction"><tt>Instruction</tt></a>s in a <a
1796 href="#Function"><tt>Function</tt></a>
1797</div>
1798
1799<div class="doc_text">
1800
1801<p>If you're finding that you commonly iterate over a <tt>Function</tt>'s
1802<tt>BasicBlock</tt>s and then that <tt>BasicBlock</tt>'s <tt>Instruction</tt>s,
1803<tt>InstIterator</tt> should be used instead. You'll need to include <a
1804href="/doxygen/InstIterator_8h-source.html"><tt>llvm/Support/InstIterator.h</tt></a>,
1805and then instantiate <tt>InstIterator</tt>s explicitly in your code. Here's a
Chris Lattner69bf8a92004-05-23 21:06:58 +0000[diff] [blame]1806small 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]1807
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1808<div class="doc_code">
1809<pre>
1810#include "<a href="/doxygen/InstIterator_8h-source.html">llvm/Support/InstIterator.h</a>"
1811
Reid Spencer128a7a72007-02-03 21:06:43 +0000[diff] [blame]1812// <i>F is a pointer to a Function instance</i>
Chris Lattnerda021aa2008-06-04 18:20:42 +0000[diff] [blame]1813for (inst_iterator I = inst_begin(F), E = inst_end(F); I != E; ++I)
Chris Lattner3fee6ed2009-09-08 05:15:50 +0000[diff] [blame]1814 errs() &lt;&lt; *I &lt;&lt; "\n";
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1815</pre>
1816</div>
1817
1818<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]1819work list with its initial contents. For example, if you wanted to
1820initialize a work list to contain all instructions in a <tt>Function</tt>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1821F, all you would need to do is something like:</p>
1822
1823<div class="doc_code">
1824<pre>
1825std::set&lt;Instruction*&gt; worklist;
Chris Lattnerda021aa2008-06-04 18:20:42 +0000[diff] [blame]1826// or better yet, SmallPtrSet&lt;Instruction*, 64&gt; worklist;
1827
1828for (inst_iterator I = inst_begin(F), E = inst_end(F); I != E; ++I)
1829 worklist.insert(&amp;*I);
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1830</pre>
1831</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1832
1833<p>The STL set <tt>worklist</tt> would now contain all instructions in the
1834<tt>Function</tt> pointed to by F.</p>
1835
1836</div>
1837
1838<!-- _______________________________________________________________________ -->
1839<div class="doc_subsubsection">
1840 <a name="iterate_convert">Turning an iterator into a class pointer (and
1841 vice-versa)</a>
1842</div>
1843
1844<div class="doc_text">
1845
1846<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]1847instance when all you've got at hand is an iterator. Well, extracting
Chris Lattner69bf8a92004-05-23 21:06:58 +0000[diff] [blame]1848a reference or a pointer from an iterator is very straight-forward.
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]1849Assuming that <tt>i</tt> is a <tt>BasicBlock::iterator</tt> and <tt>j</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1850is a <tt>BasicBlock::const_iterator</tt>:</p>
1851
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1852<div class="doc_code">
1853<pre>
Bill Wendling82e2eea2006-10-11 18:00:22 +0000[diff] [blame]1854Instruction&amp; inst = *i; // <i>Grab reference to instruction reference</i>
1855Instruction* pinst = &amp;*i; // <i>Grab pointer to instruction reference</i>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1856const Instruction&amp; inst = *j;
1857</pre>
1858</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1859
1860<p>However, the iterators you'll be working with in the LLVM framework are
1861special: they will automatically convert to a ptr-to-instance type whenever they
1862need to. Instead of dereferencing the iterator and then taking the address of
1863the result, you can simply assign the iterator to the proper pointer type and
1864you get the dereference and address-of operation as a result of the assignment
1865(behind the scenes, this is a result of overloading casting mechanisms). Thus
1866the last line of the last example,</p>
1867
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1868<div class="doc_code">
1869<pre>
Chris Lattner2e438ca2008-01-03 16:56:04 +0000[diff] [blame]1870Instruction *pinst = &amp;*i;
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1871</pre>
1872</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1873
1874<p>is semantically equivalent to</p>
1875
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1876<div class="doc_code">
1877<pre>
Chris Lattner2e438ca2008-01-03 16:56:04 +0000[diff] [blame]1878Instruction *pinst = i;
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1879</pre>
1880</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1881
Chris Lattner69bf8a92004-05-23 21:06:58 +0000[diff] [blame]1882<p>It's also possible to turn a class pointer into the corresponding iterator,
1883and this is a constant time operation (very efficient). The following code
1884snippet illustrates use of the conversion constructors provided by LLVM
1885iterators. By using these, you can explicitly grab the iterator of something
1886without actually obtaining it via iteration over some structure:</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1887
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1888<div class="doc_code">
1889<pre>
1890void printNextInstruction(Instruction* inst) {
1891 BasicBlock::iterator it(inst);
Bill Wendling82e2eea2006-10-11 18:00:22 +0000[diff] [blame]1892 ++it; // <i>After this line, it refers to the instruction after *inst</i>
Chris Lattner3fee6ed2009-09-08 05:15:50 +0000[diff] [blame]1893 if (it != inst-&gt;getParent()-&gt;end()) errs() &lt;&lt; *it &lt;&lt; "\n";
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1894}
1895</pre>
1896</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1897
Dan Gohman525bf8e2010-03-26 19:39:05 +0000[diff] [blame]1898<p>Unfortunately, these implicit conversions come at a cost; they prevent
1899these iterators from conforming to standard iterator conventions, and thus
Dan Gohman0d91c112010-03-26 19:51:14 +0000[diff] [blame]1900from being usable with standard algorithms and containers. For example, they
1901prevent the following code, where <tt>B</tt> is a <tt>BasicBlock</tt>,
Dan Gohman525bf8e2010-03-26 19:39:05 +0000[diff] [blame]1902from compiling:</p>
1903
1904<div class="doc_code">
1905<pre>
1906 llvm::SmallVector&lt;llvm::Instruction *, 16&gt;(B-&gt;begin(), B-&gt;end());
1907</pre>
1908</div>
1909
1910<p>Because of this, these implicit conversions may be removed some day,
Dan Gohman0d91c112010-03-26 19:51:14 +0000[diff] [blame]1911and <tt>operator*</tt> changed to return a pointer instead of a reference.</p>
Dan Gohman525bf8e2010-03-26 19:39:05 +0000[diff] [blame]1912
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1913</div>
1914
1915<!--_______________________________________________________________________-->
1916<div class="doc_subsubsection">
1917 <a name="iterate_complex">Finding call sites: a slightly more complex
1918 example</a>
1919</div>
1920
1921<div class="doc_text">
1922
1923<p>Say that you're writing a FunctionPass and would like to count all the
1924locations in the entire module (that is, across every <tt>Function</tt>) where a
1925certain function (i.e., some <tt>Function</tt>*) is already in scope. As you'll
1926learn 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]1927much more straight-forward manner, but this example will allow us to explore how
Reid Spencer128a7a72007-02-03 21:06:43 +0000[diff] [blame]1928you'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]1929is what we want to do:</p>
1930
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1931<div class="doc_code">
1932<pre>
1933initialize callCounter to zero
1934for each Function f in the Module
1935 for each BasicBlock b in f
1936 for each Instruction i in b
1937 if (i is a CallInst and calls the given function)
1938 increment callCounter
1939</pre>
1940</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1941
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1942<p>And the actual code is (remember, because we're writing a
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1943<tt>FunctionPass</tt>, our <tt>FunctionPass</tt>-derived class simply has to
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1944override the <tt>runOnFunction</tt> method):</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1945
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1946<div class="doc_code">
1947<pre>
1948Function* targetFunc = ...;
1949
1950class OurFunctionPass : public FunctionPass {
1951 public:
1952 OurFunctionPass(): callCounter(0) { }
1953
1954 virtual runOnFunction(Function&amp; F) {
1955 for (Function::iterator b = F.begin(), be = F.end(); b != be; ++b) {
Eric Christopher203e71d2008-11-08 08:20:49 +0000[diff] [blame]1956 for (BasicBlock::iterator i = b-&gt;begin(), ie = b-&gt;end(); i != ie; ++i) {
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1957 if (<a href="#CallInst">CallInst</a>* callInst = <a href="#isa">dyn_cast</a>&lt;<a
1958 href="#CallInst">CallInst</a>&gt;(&amp;*i)) {
Bill Wendling82e2eea2006-10-11 18:00:22 +0000[diff] [blame]1959 // <i>We know we've encountered a call instruction, so we</i>
1960 // <i>need to determine if it's a call to the</i>
Chris Lattner2e438ca2008-01-03 16:56:04 +0000[diff] [blame]1961 // <i>function pointed to by m_func or not.</i>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1962 if (callInst-&gt;getCalledFunction() == targetFunc)
1963 ++callCounter;
1964 }
1965 }
1966 }
Bill Wendling82e2eea2006-10-11 18:00:22 +0000[diff] [blame]1967 }
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1968
1969 private:
Chris Lattner2e438ca2008-01-03 16:56:04 +0000[diff] [blame]1970 unsigned callCounter;
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1971};
1972</pre>
1973</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1974
1975</div>
1976
Brian Gaekef1972c62003-11-07 19:25:45 +0000[diff] [blame]1977<!--_______________________________________________________________________-->
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1978<div class="doc_subsubsection">
1979 <a name="calls_and_invokes">Treating calls and invokes the same way</a>
1980</div>
1981
1982<div class="doc_text">
1983
1984<p>You may have noticed that the previous example was a bit oversimplified in
1985that it did not deal with call sites generated by 'invoke' instructions. In
1986this, and in other situations, you may find that you want to treat
1987<tt>CallInst</tt>s and <tt>InvokeInst</tt>s the same way, even though their
1988most-specific common base class is <tt>Instruction</tt>, which includes lots of
1989less closely-related things. For these cases, LLVM provides a handy wrapper
1990class called <a
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]1991href="http://llvm.org/doxygen/classllvm_1_1CallSite.html"><tt>CallSite</tt></a>.
Chris Lattner69bf8a92004-05-23 21:06:58 +0000[diff] [blame]1992It is essentially a wrapper around an <tt>Instruction</tt> pointer, with some
1993methods that provide functionality common to <tt>CallInst</tt>s and
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1994<tt>InvokeInst</tt>s.</p>
1995
Chris Lattner69bf8a92004-05-23 21:06:58 +0000[diff] [blame]1996<p>This class has "value semantics": it should be passed by value, not by
1997reference and it should not be dynamically allocated or deallocated using
1998<tt>operator new</tt> or <tt>operator delete</tt>. It is efficiently copyable,
1999assignable and constructable, with costs equivalents to that of a bare pointer.
2000If you look at its definition, it has only a single pointer member.</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2001
2002</div>
2003
Chris Lattner1a3105b2002-09-09 05:49:39 +0000[diff] [blame]2004<!--_______________________________________________________________________-->
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2005<div class="doc_subsubsection">
2006 <a name="iterate_chains">Iterating over def-use &amp; use-def chains</a>
2007</div>
2008
2009<div class="doc_text">
2010
2011<p>Frequently, we might have an instance of the <a
Chris Lattner00815172007-01-04 22:01:45 +0000[diff] [blame]2012href="/doxygen/classllvm_1_1Value.html">Value Class</a> and we want to
Misha Brukman384047f2004-06-03 23:29:12 +0000[diff] [blame]2013determine which <tt>User</tt>s use the <tt>Value</tt>. The list of all
2014<tt>User</tt>s of a particular <tt>Value</tt> is called a <i>def-use</i> chain.
2015For example, let's say we have a <tt>Function*</tt> named <tt>F</tt> to a
2016particular function <tt>foo</tt>. Finding all of the instructions that
2017<i>use</i> <tt>foo</tt> is as simple as iterating over the <i>def-use</i> chain
2018of <tt>F</tt>:</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2019
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2020<div class="doc_code">
2021<pre>
Chris Lattner2e438ca2008-01-03 16:56:04 +0000[diff] [blame]2022Function *F = ...;
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2023
Bill Wendling82e2eea2006-10-11 18:00:22 +0000[diff] [blame]2024for (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]2025 if (Instruction *Inst = dyn_cast&lt;Instruction&gt;(*i)) {
Chris Lattner3fee6ed2009-09-08 05:15:50 +0000[diff] [blame]2026 errs() &lt;&lt; "F is used in instruction:\n";
2027 errs() &lt;&lt; *Inst &lt;&lt; "\n";
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2028 }
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2029</pre>
Gabor Greif394fdfb2010-03-26 19:35:48 +0000[diff] [blame]2030</div>
2031
Gabor Greifce94319532010-03-26 19:40:38 +0000[diff] [blame]2032<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]2033operation. Instead of performing <tt>*i</tt> above several times, consider
Gabor Greifce94319532010-03-26 19:40:38 +0000[diff] [blame]2034doing it only once in the loop body and reusing its result.</p>
Gabor Greif4de73682010-03-26 19:30:47 +0000[diff] [blame]2035
Gabor Greif6091ff32010-03-26 19:04:42 +0000[diff] [blame]2036<p>Alternatively, it's common to have an instance of the <a
Misha Brukman384047f2004-06-03 23:29:12 +0000[diff] [blame]2037href="/doxygen/classllvm_1_1User.html">User Class</a> and need to know what
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2038<tt>Value</tt>s are used by it. The list of all <tt>Value</tt>s used by a
2039<tt>User</tt> is known as a <i>use-def</i> chain. Instances of class
2040<tt>Instruction</tt> are common <tt>User</tt>s, so we might want to iterate over
2041all of the values that a particular instruction uses (that is, the operands of
2042the particular <tt>Instruction</tt>):</p>
2043
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2044<div class="doc_code">
2045<pre>
Chris Lattner2e438ca2008-01-03 16:56:04 +0000[diff] [blame]2046Instruction *pi = ...;
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2047
2048for (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]2049 Value *v = *i;
Bill Wendling82e2eea2006-10-11 18:00:22 +0000[diff] [blame]2050 // <i>...</i>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2051}
2052</pre>
2053</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2054
Gabor Greif4de73682010-03-26 19:30:47 +0000[diff] [blame]2055<p>Declaring objects as <tt>const</tt> is an important tool of enforcing
Gabor Greifce94319532010-03-26 19:40:38 +0000[diff] [blame]2056mutation free algorithms (such as analyses, etc.). For this purpose above
Gabor Greif4de73682010-03-26 19:30:47 +0000[diff] [blame]2057iterators come in constant flavors as <tt>Value::const_use_iterator</tt>
2058and <tt>Value::const_op_iterator</tt>. They automatically arise when
2059calling <tt>use/op_begin()</tt> on <tt>const Value*</tt>s or
2060<tt>const User*</tt>s respectively. Upon dereferencing, they return
Gabor Greifce94319532010-03-26 19:40:38 +0000[diff] [blame]2061<tt>const Use*</tt>s. Otherwise the above patterns remain unchanged.</p>
2062
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2063</div>
2064
Chris Lattner2e438ca2008-01-03 16:56:04 +0000[diff] [blame]2065<!--_______________________________________________________________________-->
2066<div class="doc_subsubsection">
2067 <a name="iterate_preds">Iterating over predecessors &amp;
2068successors of blocks</a>
2069</div>
2070
2071<div class="doc_text">
2072
2073<p>Iterating over the predecessors and successors of a block is quite easy
2074with the routines defined in <tt>"llvm/Support/CFG.h"</tt>. Just use code like
2075this to iterate over all predecessors of BB:</p>
2076
2077<div class="doc_code">
2078<pre>
2079#include "llvm/Support/CFG.h"
2080BasicBlock *BB = ...;
2081
2082for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI) {
2083 BasicBlock *Pred = *PI;
2084 // <i>...</i>
2085}
2086</pre>
2087</div>
2088
2089<p>Similarly, to iterate over successors use
2090succ_iterator/succ_begin/succ_end.</p>
2091
2092</div>
2093
2094
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2095<!-- ======================================================================= -->
2096<div class="doc_subsection">
2097 <a name="simplechanges">Making simple changes</a>
2098</div>
2099
2100<div class="doc_text">
2101
2102<p>There are some primitive transformation operations present in the LLVM
Joel Stanley753eb712002-09-11 22:32:24 +0000[diff] [blame]2103infrastructure that are worth knowing about. When performing
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]2104transformations, it's fairly common to manipulate the contents of basic
2105blocks. This section describes some of the common methods for doing so
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2106and gives example code.</p>
2107
2108</div>
2109
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]2110<!--_______________________________________________________________________-->
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2111<div class="doc_subsubsection">
2112 <a name="schanges_creating">Creating and inserting new
2113 <tt>Instruction</tt>s</a>
2114</div>
2115
2116<div class="doc_text">
2117
2118<p><i>Instantiating Instructions</i></p>
2119
Chris Lattner69bf8a92004-05-23 21:06:58 +0000[diff] [blame]2120<p>Creation of <tt>Instruction</tt>s is straight-forward: simply call the
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2121constructor for the kind of instruction to instantiate and provide the necessary
2122parameters. For example, an <tt>AllocaInst</tt> only <i>requires</i> a
2123(const-ptr-to) <tt>Type</tt>. Thus:</p>
2124
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2125<div class="doc_code">
2126<pre>
Nick Lewycky10d64b92007-12-03 01:52:52 +0000[diff] [blame]2127AllocaInst* ai = new AllocaInst(Type::Int32Ty);
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2128</pre>
2129</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2130
2131<p>will create an <tt>AllocaInst</tt> instance that represents the allocation of
Reid Spencer128a7a72007-02-03 21:06:43 +0000[diff] [blame]2132one integer in the current stack frame, at run time. Each <tt>Instruction</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2133subclass is likely to have varying default parameters which change the semantics
2134of the instruction, so refer to the <a
Misha Brukman31ca1de2004-06-03 23:35:54 +0000[diff] [blame]2135href="/doxygen/classllvm_1_1Instruction.html">doxygen documentation for the subclass of
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2136Instruction</a> that you're interested in instantiating.</p>
2137
2138<p><i>Naming values</i></p>
2139
2140<p>It is very useful to name the values of instructions when you're able to, as
2141this facilitates the debugging of your transformations. If you end up looking
2142at generated LLVM machine code, you definitely want to have logical names
2143associated with the results of instructions! By supplying a value for the
2144<tt>Name</tt> (default) parameter of the <tt>Instruction</tt> constructor, you
2145associate a logical name with the result of the instruction's execution at
Reid Spencer128a7a72007-02-03 21:06:43 +0000[diff] [blame]2146run time. For example, say that I'm writing a transformation that dynamically
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2147allocates space for an integer on the stack, and that integer is going to be
2148used as some kind of index by some other code. To accomplish this, I place an
2149<tt>AllocaInst</tt> at the first point in the first <tt>BasicBlock</tt> of some
2150<tt>Function</tt>, and I'm intending to use it within the same
2151<tt>Function</tt>. I might do:</p>
2152
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2153<div class="doc_code">
2154<pre>
Nick Lewycky10d64b92007-12-03 01:52:52 +0000[diff] [blame]2155AllocaInst* pa = new AllocaInst(Type::Int32Ty, 0, "indexLoc");
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2156</pre>
2157</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2158
2159<p>where <tt>indexLoc</tt> is now the logical name of the instruction's
Reid Spencer128a7a72007-02-03 21:06:43 +0000[diff] [blame]2160execution value, which is a pointer to an integer on the run time stack.</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2161
2162<p><i>Inserting instructions</i></p>
2163
2164<p>There are essentially two ways to insert an <tt>Instruction</tt>
2165into an existing sequence of instructions that form a <tt>BasicBlock</tt>:</p>
2166
Joel Stanley9dd1ad62002-09-18 03:17:23 +0000[diff] [blame]2167<ul>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2168 <li>Insertion into an explicit instruction list
2169
2170 <p>Given a <tt>BasicBlock* pb</tt>, an <tt>Instruction* pi</tt> within that
2171 <tt>BasicBlock</tt>, and a newly-created instruction we wish to insert
2172 before <tt>*pi</tt>, we do the following: </p>
2173
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2174<div class="doc_code">
2175<pre>
2176BasicBlock *pb = ...;
2177Instruction *pi = ...;
2178Instruction *newInst = new Instruction(...);
2179
Bill Wendling82e2eea2006-10-11 18:00:22 +0000[diff] [blame]2180pb-&gt;getInstList().insert(pi, newInst); // <i>Inserts newInst before pi in pb</i>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2181</pre>
2182</div>
Alkis Evlogimenos9a5dc4f2004-05-27 00:57:51 +0000[diff] [blame]2183
2184 <p>Appending to the end of a <tt>BasicBlock</tt> is so common that
2185 the <tt>Instruction</tt> class and <tt>Instruction</tt>-derived
2186 classes provide constructors which take a pointer to a
2187 <tt>BasicBlock</tt> to be appended to. For example code that
2188 looked like: </p>
2189
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2190<div class="doc_code">
2191<pre>
2192BasicBlock *pb = ...;
2193Instruction *newInst = new Instruction(...);
2194
Bill Wendling82e2eea2006-10-11 18:00:22 +0000[diff] [blame]2195pb-&gt;getInstList().push_back(newInst); // <i>Appends newInst to pb</i>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2196</pre>
2197</div>
Alkis Evlogimenos9a5dc4f2004-05-27 00:57:51 +0000[diff] [blame]2198
2199 <p>becomes: </p>
2200
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2201<div class="doc_code">
2202<pre>
2203BasicBlock *pb = ...;
2204Instruction *newInst = new Instruction(..., pb);
2205</pre>
2206</div>
Alkis Evlogimenos9a5dc4f2004-05-27 00:57:51 +0000[diff] [blame]2207
2208 <p>which is much cleaner, especially if you are creating
2209 long instruction streams.</p></li>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2210
2211 <li>Insertion into an implicit instruction list
2212
2213 <p><tt>Instruction</tt> instances that are already in <tt>BasicBlock</tt>s
2214 are implicitly associated with an existing instruction list: the instruction
2215 list of the enclosing basic block. Thus, we could have accomplished the same
2216 thing as the above code without being given a <tt>BasicBlock</tt> by doing:
2217 </p>
2218
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2219<div class="doc_code">
2220<pre>
2221Instruction *pi = ...;
2222Instruction *newInst = new Instruction(...);
2223
2224pi-&gt;getParent()-&gt;getInstList().insert(pi, newInst);
2225</pre>
2226</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2227
2228 <p>In fact, this sequence of steps occurs so frequently that the
2229 <tt>Instruction</tt> class and <tt>Instruction</tt>-derived classes provide
2230 constructors which take (as a default parameter) a pointer to an
2231 <tt>Instruction</tt> which the newly-created <tt>Instruction</tt> should
2232 precede. That is, <tt>Instruction</tt> constructors are capable of
2233 inserting the newly-created instance into the <tt>BasicBlock</tt> of a
2234 provided instruction, immediately before that instruction. Using an
2235 <tt>Instruction</tt> constructor with a <tt>insertBefore</tt> (default)
2236 parameter, the above code becomes:</p>
2237
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2238<div class="doc_code">
2239<pre>
2240Instruction* pi = ...;
2241Instruction* newInst = new Instruction(..., pi);
2242</pre>
2243</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2244
2245 <p>which is much cleaner, especially if you're creating a lot of
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2246 instructions and adding them to <tt>BasicBlock</tt>s.</p></li>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2247</ul>
2248
2249</div>
2250
2251<!--_______________________________________________________________________-->
2252<div class="doc_subsubsection">
2253 <a name="schanges_deleting">Deleting <tt>Instruction</tt>s</a>
2254</div>
2255
2256<div class="doc_text">
2257
2258<p>Deleting an instruction from an existing sequence of instructions that form a
Chris Lattner49e0ccf2011-03-24 16:13:31 +0000[diff] [blame]2259<a href="#BasicBlock"><tt>BasicBlock</tt></a> is very straight-forward: just
2260call the instruction's eraseFromParent() method. For example:</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2261
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2262<div class="doc_code">
2263<pre>
2264<a href="#Instruction">Instruction</a> *I = .. ;
Chris Lattner9f8ec252008-02-15 22:57:17 +0000[diff] [blame]2265I-&gt;eraseFromParent();
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2266</pre>
2267</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2268
Chris Lattner49e0ccf2011-03-24 16:13:31 +0000[diff] [blame]2269<p>This unlinks the instruction from its containing basic block and deletes
2270it. If you'd just like to unlink the instruction from its containing basic
2271block but not delete it, you can use the <tt>removeFromParent()</tt> method.</p>
2272
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2273</div>
2274
2275<!--_______________________________________________________________________-->
2276<div class="doc_subsubsection">
2277 <a name="schanges_replacing">Replacing an <tt>Instruction</tt> with another
2278 <tt>Value</tt></a>
2279</div>
2280
2281<div class="doc_text">
2282
2283<p><i>Replacing individual instructions</i></p>
2284
2285<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]2286permits use of two very useful replace functions: <tt>ReplaceInstWithValue</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2287and <tt>ReplaceInstWithInst</tt>.</p>
2288
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]2289<h4><a name="schanges_deleting">Deleting <tt>Instruction</tt>s</a></h4>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2290
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]2291<ul>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2292 <li><tt>ReplaceInstWithValue</tt>
2293
Nick Lewyckyb6d1f392008-09-15 06:31:52 +0000[diff] [blame]2294 <p>This function replaces all uses of a given instruction with a value,
2295 and then removes the original instruction. The following example
2296 illustrates the replacement of the result of a particular
Chris Lattner58360822005-01-17 00:12:04 +0000[diff] [blame]2297 <tt>AllocaInst</tt> that allocates memory for a single integer with a null
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2298 pointer to an integer.</p>
2299
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2300<div class="doc_code">
2301<pre>
2302AllocaInst* instToReplace = ...;
2303BasicBlock::iterator ii(instToReplace);
2304
2305ReplaceInstWithValue(instToReplace-&gt;getParent()-&gt;getInstList(), ii,
Daniel Dunbar58c2ac02008-10-03 22:17:25 +0000[diff] [blame]2306 Constant::getNullValue(PointerType::getUnqual(Type::Int32Ty)));
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2307</pre></div></li>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2308
2309 <li><tt>ReplaceInstWithInst</tt>
2310
2311 <p>This function replaces a particular instruction with another
Nick Lewyckyb6d1f392008-09-15 06:31:52 +0000[diff] [blame]2312 instruction, inserting the new instruction into the basic block at the
2313 location where the old instruction was, and replacing any uses of the old
2314 instruction with the new instruction. The following example illustrates
2315 the replacement of one <tt>AllocaInst</tt> with another.</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2316
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2317<div class="doc_code">
2318<pre>
2319AllocaInst* instToReplace = ...;
2320BasicBlock::iterator ii(instToReplace);
2321
2322ReplaceInstWithInst(instToReplace-&gt;getParent()-&gt;getInstList(), ii,
Nick Lewycky10d64b92007-12-03 01:52:52 +0000[diff] [blame]2323 new AllocaInst(Type::Int32Ty, 0, "ptrToReplacedInt"));
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2324</pre></div></li>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]2325</ul>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2326
2327<p><i>Replacing multiple uses of <tt>User</tt>s and <tt>Value</tt>s</i></p>
2328
2329<p>You can use <tt>Value::replaceAllUsesWith</tt> and
2330<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]2331doxygen documentation for the <a href="/doxygen/classllvm_1_1Value.html">Value Class</a>
Misha Brukman384047f2004-06-03 23:29:12 +0000[diff] [blame]2332and <a href="/doxygen/classllvm_1_1User.html">User Class</a>, respectively, for more
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2333information.</p>
2334
2335<!-- Value::replaceAllUsesWith User::replaceUsesOfWith Point out:
2336include/llvm/Transforms/Utils/ especially BasicBlockUtils.h with:
2337ReplaceInstWithValue, ReplaceInstWithInst -->
2338
2339</div>
2340
Tanya Lattnerb011c662007-06-20 18:33:15 +0000[diff] [blame]2341<!--_______________________________________________________________________-->
2342<div class="doc_subsubsection">
2343 <a name="schanges_deletingGV">Deleting <tt>GlobalVariable</tt>s</a>
2344</div>
2345
2346<div class="doc_text">
2347
Tanya Lattnerc5dfcdb2007-06-20 20:46:37 +0000[diff] [blame]2348<p>Deleting a global variable from a module is just as easy as deleting an
2349Instruction. First, you must have a pointer to the global variable that you wish
2350 to delete. You use this pointer to erase it from its parent, the module.
Tanya Lattnerb011c662007-06-20 18:33:15 +0000[diff] [blame]2351 For example:</p>
2352
2353<div class="doc_code">
2354<pre>
2355<a href="#GlobalVariable">GlobalVariable</a> *GV = .. ;
Tanya Lattnerb011c662007-06-20 18:33:15 +0000[diff] [blame]2356
Tanya Lattnerc5dfcdb2007-06-20 20:46:37 +0000[diff] [blame]2357GV-&gt;eraseFromParent();
Tanya Lattnerb011c662007-06-20 18:33:15 +0000[diff] [blame]2358</pre>
2359</div>
2360
2361</div>
2362
Jeffrey Yasskin714257f2009-04-30 22:33:41 +0000[diff] [blame]2363<!-- ======================================================================= -->
2364<div class="doc_subsection">
2365 <a name="create_types">How to Create Types</a>
2366</div>
2367
2368<div class="doc_text">
2369
2370<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]2371statically, you can use <tt>TypeBuilder&lt;...&gt;::get()</tt>, defined
Jeffrey Yasskin714257f2009-04-30 22:33:41 +0000[diff] [blame]2372in <tt>llvm/Support/TypeBuilder.h</tt>, to retrieve them. <tt>TypeBuilder</tt>
2373has two forms depending on whether you're building types for cross-compilation
Misha Brukman1af789f2009-05-01 20:40:51 +0000[diff] [blame]2374or native library use. <tt>TypeBuilder&lt;T, true&gt;</tt> requires
Jeffrey Yasskin714257f2009-04-30 22:33:41 +0000[diff] [blame]2375that <tt>T</tt> be independent of the host environment, meaning that it's built
2376out of types from
2377the <a href="/doxygen/namespacellvm_1_1types.html"><tt>llvm::types</tt></a>
2378namespace and pointers, functions, arrays, etc. built of
Misha Brukman1af789f2009-05-01 20:40:51 +0000[diff] [blame]2379those. <tt>TypeBuilder&lt;T, false&gt;</tt> additionally allows native C types
Jeffrey Yasskin714257f2009-04-30 22:33:41 +0000[diff] [blame]2380whose size may depend on the host compiler. For example,</p>
2381
2382<div class="doc_code">
2383<pre>
Misha Brukman1af789f2009-05-01 20:40:51 +0000[diff] [blame]2384FunctionType *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]2385</pre>
2386</div>
2387
2388<p>is easier to read and write than the equivalent</p>
2389
2390<div class="doc_code">
2391<pre>
Owen Anderson5e8c50e2009-06-16 17:40:28 +0000[diff] [blame]2392std::vector&lt;const Type*&gt; params;
Jeffrey Yasskin714257f2009-04-30 22:33:41 +0000[diff] [blame]2393params.push_back(PointerType::getUnqual(Type::Int32Ty));
2394FunctionType *ft = FunctionType::get(Type::Int8Ty, params, false);
2395</pre>
2396</div>
2397
2398<p>See the <a href="/doxygen/TypeBuilder_8h-source.html#l00001">class
2399comment</a> for more details.</p>
2400
2401</div>
2402
Chris Lattner9355b472002-09-06 02:50:58 +0000[diff] [blame]2403<!-- *********************************************************************** -->
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2404<div class="doc_section">
Owen Anderson8bc1b3b2009-06-16 01:17:16 +0000[diff] [blame]2405 <a name="threading">Threads and LLVM</a>
2406</div>
2407<!-- *********************************************************************** -->
2408
2409<div class="doc_text">
2410<p>
2411This section describes the interaction of the LLVM APIs with multithreading,
2412both on the part of client applications, and in the JIT, in the hosted
2413application.
2414</p>
2415
2416<p>
2417Note that LLVM's support for multithreading is still relatively young. Up
2418through version 2.5, the execution of threaded hosted applications was
2419supported, but not threaded client access to the APIs. While this use case is
2420now supported, clients <em>must</em> adhere to the guidelines specified below to
2421ensure proper operation in multithreaded mode.
2422</p>
2423
2424<p>
2425Note that, on Unix-like platforms, LLVM requires the presence of GCC's atomic
2426intrinsics in order to support threaded operation. If you need a
2427multhreading-capable LLVM on a platform without a suitably modern system
2428compiler, consider compiling LLVM and LLVM-GCC in single-threaded mode, and
2429using the resultant compiler to build a copy of LLVM with multithreading
2430support.
2431</p>
2432</div>
2433
2434<!-- ======================================================================= -->
2435<div class="doc_subsection">
Owen Anderson1ad70e32009-06-16 18:04:19 +0000[diff] [blame]2436 <a name="startmultithreaded">Entering and Exiting Multithreaded Mode</a>
Owen Anderson8bc1b3b2009-06-16 01:17:16 +0000[diff] [blame]2437</div>
2438
2439<div class="doc_text">
2440
2441<p>
2442In order to properly protect its internal data structures while avoiding
Owen Anderson1ad70e32009-06-16 18:04:19 +0000[diff] [blame]2443excessive locking overhead in the single-threaded case, the LLVM must intialize
2444certain data structures necessary to provide guards around its internals. To do
2445so, the client program must invoke <tt>llvm_start_multithreaded()</tt> before
2446making any concurrent LLVM API calls. To subsequently tear down these
2447structures, use the <tt>llvm_stop_multithreaded()</tt> call. You can also use
2448the <tt>llvm_is_multithreaded()</tt> call to check the status of multithreaded
2449mode.
Owen Anderson8bc1b3b2009-06-16 01:17:16 +0000[diff] [blame]2450</p>
2451
2452<p>
Owen Anderson1ad70e32009-06-16 18:04:19 +0000[diff] [blame]2453Note that both of these calls must be made <em>in isolation</em>. That is to
2454say that no other LLVM API calls may be executing at any time during the
2455execution of <tt>llvm_start_multithreaded()</tt> or <tt>llvm_stop_multithreaded
2456</tt>. It's is the client's responsibility to enforce this isolation.
2457</p>
2458
2459<p>
2460The return value of <tt>llvm_start_multithreaded()</tt> indicates the success or
2461failure of the initialization. Failure typically indicates that your copy of
2462LLVM was built without multithreading support, typically because GCC atomic
2463intrinsics were not found in your system compiler. In this case, the LLVM API
2464will not be safe for concurrent calls. However, it <em>will</em> be safe for
Jeffrey Yasskin01eba392010-01-29 19:10:38 +0000[diff] [blame]2465hosting threaded applications in the JIT, though <a href="#jitthreading">care
2466must be taken</a> to ensure that side exits and the like do not accidentally
2467result in concurrent LLVM API calls.
Owen Anderson8bc1b3b2009-06-16 01:17:16 +0000[diff] [blame]2468</p>
2469</div>
2470
2471<!-- ======================================================================= -->
2472<div class="doc_subsection">
2473 <a name="shutdown">Ending Execution with <tt>llvm_shutdown()</tt></a>
2474</div>
2475
2476<div class="doc_text">
2477<p>
2478When you are done using the LLVM APIs, you should call <tt>llvm_shutdown()</tt>
Owen Anderson1ad70e32009-06-16 18:04:19 +0000[diff] [blame]2479to deallocate memory used for internal structures. This will also invoke
2480<tt>llvm_stop_multithreaded()</tt> if LLVM is operating in multithreaded mode.
2481As such, <tt>llvm_shutdown()</tt> requires the same isolation guarantees as
2482<tt>llvm_stop_multithreaded()</tt>.
Owen Anderson8bc1b3b2009-06-16 01:17:16 +0000[diff] [blame]2483</p>
2484
2485<p>
2486Note that, if you use scope-based shutdown, you can use the
2487<tt>llvm_shutdown_obj</tt> class, which calls <tt>llvm_shutdown()</tt> in its
2488destructor.
2489</div>
2490
2491<!-- ======================================================================= -->
2492<div class="doc_subsection">
2493 <a name="managedstatic">Lazy Initialization with <tt>ManagedStatic</tt></a>
2494</div>
2495
2496<div class="doc_text">
2497<p>
2498<tt>ManagedStatic</tt> is a utility class in LLVM used to implement static
2499initialization of static resources, such as the global type tables. Before the
2500invocation of <tt>llvm_shutdown()</tt>, it implements a simple lazy
2501initialization scheme. Once <tt>llvm_start_multithreaded()</tt> returns,
2502however, it uses double-checked locking to implement thread-safe lazy
2503initialization.
2504</p>
2505
2506<p>
2507Note that, because no other threads are allowed to issue LLVM API calls before
2508<tt>llvm_start_multithreaded()</tt> returns, it is possible to have
2509<tt>ManagedStatic</tt>s of <tt>llvm::sys::Mutex</tt>s.
2510</p>
Owen Anderson1ad70e32009-06-16 18:04:19 +0000[diff] [blame]2511
2512<p>
2513The <tt>llvm_acquire_global_lock()</tt> and <tt>llvm_release_global_lock</tt>
2514APIs provide access to the global lock used to implement the double-checked
2515locking for lazy initialization. These should only be used internally to LLVM,
2516and only if you know what you're doing!
2517</p>
Owen Anderson8bc1b3b2009-06-16 01:17:16 +0000[diff] [blame]2518</div>
2519
Owen Andersone0c951a2009-08-19 17:58:52 +0000[diff] [blame]2520<!-- ======================================================================= -->
2521<div class="doc_subsection">
2522 <a name="llvmcontext">Achieving Isolation with <tt>LLVMContext</tt></a>
2523</div>
2524
2525<div class="doc_text">
2526<p>
2527<tt>LLVMContext</tt> is an opaque class in the LLVM API which clients can use
2528to operate multiple, isolated instances of LLVM concurrently within the same
2529address space. For instance, in a hypothetical compile-server, the compilation
2530of an individual translation unit is conceptually independent from all the
2531others, and it would be desirable to be able to compile incoming translation
2532units concurrently on independent server threads. Fortunately,
2533<tt>LLVMContext</tt> exists to enable just this kind of scenario!
2534</p>
2535
2536<p>
2537Conceptually, <tt>LLVMContext</tt> provides isolation. Every LLVM entity
2538(<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]2539in LLVM's in-memory IR belongs to an <tt>LLVMContext</tt>. Entities in
Owen Andersone0c951a2009-08-19 17:58:52 +0000[diff] [blame]2540different contexts <em>cannot</em> interact with each other: <tt>Module</tt>s in
2541different contexts cannot be linked together, <tt>Function</tt>s cannot be added
2542to <tt>Module</tt>s in different contexts, etc. What this means is that is is
2543safe to compile on multiple threads simultaneously, as long as no two threads
2544operate on entities within the same context.
2545</p>
2546
2547<p>
2548In practice, very few places in the API require the explicit specification of a
2549<tt>LLVMContext</tt>, other than the <tt>Type</tt> creation/lookup APIs.
2550Because every <tt>Type</tt> carries a reference to its owning context, most
2551other entities can determine what context they belong to by looking at their
2552own <tt>Type</tt>. If you are adding new entities to LLVM IR, please try to
2553maintain this interface design.
2554</p>
2555
2556<p>
2557For clients that do <em>not</em> require the benefits of isolation, LLVM
2558provides a convenience API <tt>getGlobalContext()</tt>. This returns a global,
2559lazily initialized <tt>LLVMContext</tt> that may be used in situations where
2560isolation is not a concern.
2561</p>
2562</div>
2563
Jeffrey Yasskin01eba392010-01-29 19:10:38 +0000[diff] [blame]2564<!-- ======================================================================= -->
2565<div class="doc_subsection">
2566 <a name="jitthreading">Threads and the JIT</a>
2567</div>
2568
2569<div class="doc_text">
2570<p>
2571LLVM's "eager" JIT compiler is safe to use in threaded programs. Multiple
2572threads can call <tt>ExecutionEngine::getPointerToFunction()</tt> or
2573<tt>ExecutionEngine::runFunction()</tt> concurrently, and multiple threads can
2574run code output by the JIT concurrently. The user must still ensure that only
2575one thread accesses IR in a given <tt>LLVMContext</tt> while another thread
2576might be modifying it. One way to do that is to always hold the JIT lock while
2577accessing IR outside the JIT (the JIT <em>modifies</em> the IR by adding
2578<tt>CallbackVH</tt>s). Another way is to only
2579call <tt>getPointerToFunction()</tt> from the <tt>LLVMContext</tt>'s thread.
2580</p>
2581
2582<p>When the JIT is configured to compile lazily (using
2583<tt>ExecutionEngine::DisableLazyCompilation(false)</tt>), there is currently a
2584<a href="http://llvm.org/bugs/show_bug.cgi?id=5184">race condition</a> in
2585updating call sites after a function is lazily-jitted. It's still possible to
2586use the lazy JIT in a threaded program if you ensure that only one thread at a
2587time can call any particular lazy stub and that the JIT lock guards any IR
2588access, but we suggest using only the eager JIT in threaded programs.
2589</p>
2590</div>
2591
Owen Anderson8bc1b3b2009-06-16 01:17:16 +0000[diff] [blame]2592<!-- *********************************************************************** -->
2593<div class="doc_section">
Chris Lattnerd9d6e102005-04-23 16:10:52 +0000[diff] [blame]2594 <a name="advanced">Advanced Topics</a>
2595</div>
2596<!-- *********************************************************************** -->
2597
2598<div class="doc_text">
Chris Lattnerf1b200b2005-04-23 17:27:36 +0000[diff] [blame]2599<p>
2600This section describes some of the advanced or obscure API's that most clients
2601do not need to be aware of. These API's tend manage the inner workings of the
2602LLVM system, and only need to be accessed in unusual circumstances.
2603</p>
2604</div>
Chris Lattnerd9d6e102005-04-23 16:10:52 +0000[diff] [blame]2605
Chris Lattnerf1b200b2005-04-23 17:27:36 +0000[diff] [blame]2606<!-- ======================================================================= -->
2607<div class="doc_subsection">
2608 <a name="TypeResolve">LLVM Type Resolution</a>
2609</div>
Chris Lattnerd9d6e102005-04-23 16:10:52 +0000[diff] [blame]2610
Chris Lattnerf1b200b2005-04-23 17:27:36 +0000[diff] [blame]2611<div class="doc_text">
2612
2613<p>
2614The LLVM type system has a very simple goal: allow clients to compare types for
2615structural equality with a simple pointer comparison (aka a shallow compare).
2616This goal makes clients much simpler and faster, and is used throughout the LLVM
2617system.
2618</p>
2619
2620<p>
2621Unfortunately achieving this goal is not a simple matter. In particular,
2622recursive types and late resolution of opaque types makes the situation very
2623difficult to handle. Fortunately, for the most part, our implementation makes
2624most clients able to be completely unaware of the nasty internal details. The
2625primary case where clients are exposed to the inner workings of it are when
Gabor Greif04367bf2007-07-06 22:07:22 +0000[diff] [blame]2626building a recursive type. In addition to this case, the LLVM bitcode reader,
Chris Lattnerf1b200b2005-04-23 17:27:36 +0000[diff] [blame]2627assembly parser, and linker also have to be aware of the inner workings of this
2628system.
2629</p>
2630
Chris Lattner0f876db2005-04-25 15:47:57 +0000[diff] [blame]2631<p>
2632For our purposes below, we need three concepts. First, an "Opaque Type" is
2633exactly as defined in the <a href="LangRef.html#t_opaque">language
2634reference</a>. Second an "Abstract Type" is any type which includes an
Reid Spencer06565dc2007-01-12 17:11:23 +0000[diff] [blame]2635opaque type as part of its type graph (for example "<tt>{ opaque, i32 }</tt>").
2636Third, 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]2637float }</tt>").
2638</p>
2639
Chris Lattnerf1b200b2005-04-23 17:27:36 +0000[diff] [blame]2640</div>
2641
2642<!-- ______________________________________________________________________ -->
2643<div class="doc_subsubsection">
2644 <a name="BuildRecType">Basic Recursive Type Construction</a>
2645</div>
2646
2647<div class="doc_text">
2648
2649<p>
2650Because the most common question is "how do I build a recursive type with LLVM",
2651we answer it now and explain it as we go. Here we include enough to cause this
2652to be emitted to an output .ll file:
2653</p>
2654
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2655<div class="doc_code">
Chris Lattnerf1b200b2005-04-23 17:27:36 +0000[diff] [blame]2656<pre>
Reid Spencer06565dc2007-01-12 17:11:23 +0000[diff] [blame]2657%mylist = type { %mylist*, i32 }
Chris Lattnerf1b200b2005-04-23 17:27:36 +0000[diff] [blame]2658</pre>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2659</div>
Chris Lattnerf1b200b2005-04-23 17:27:36 +0000[diff] [blame]2660
2661<p>
2662To build this, use the following LLVM APIs:
2663</p>
2664
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2665<div class="doc_code">
Chris Lattnerf1b200b2005-04-23 17:27:36 +0000[diff] [blame]2666<pre>
Bill Wendling82e2eea2006-10-11 18:00:22 +0000[diff] [blame]2667// <i>Create the initial outer struct</i>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2668<a href="#PATypeHolder">PATypeHolder</a> StructTy = OpaqueType::get();
2669std::vector&lt;const Type*&gt; Elts;
Daniel Dunbar58c2ac02008-10-03 22:17:25 +0000[diff] [blame]2670Elts.push_back(PointerType::getUnqual(StructTy));
Nick Lewycky10d64b92007-12-03 01:52:52 +0000[diff] [blame]2671Elts.push_back(Type::Int32Ty);
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2672StructType *NewSTy = StructType::get(Elts);
Chris Lattnerf1b200b2005-04-23 17:27:36 +0000[diff] [blame]2673
Reid Spencer06565dc2007-01-12 17:11:23 +0000[diff] [blame]2674// <i>At this point, NewSTy = "{ opaque*, i32 }". Tell VMCore that</i>
Bill Wendling82e2eea2006-10-11 18:00:22 +0000[diff] [blame]2675// <i>the struct and the opaque type are actually the same.</i>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2676cast&lt;OpaqueType&gt;(StructTy.get())-&gt;<a href="#refineAbstractTypeTo">refineAbstractTypeTo</a>(NewSTy);
Chris Lattnerf1b200b2005-04-23 17:27:36 +0000[diff] [blame]2677
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2678// <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]2679// <i>kept up-to-date</i>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2680NewSTy = cast&lt;StructType&gt;(StructTy.get());
Chris Lattnerf1b200b2005-04-23 17:27:36 +0000[diff] [blame]2681
Bill Wendling82e2eea2006-10-11 18:00:22 +0000[diff] [blame]2682// <i>Add a name for the type to the module symbol table (optional)</i>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2683MyModule-&gt;addTypeName("mylist", NewSTy);
Chris Lattnerf1b200b2005-04-23 17:27:36 +0000[diff] [blame]2684</pre>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2685</div>
Chris Lattnerf1b200b2005-04-23 17:27:36 +0000[diff] [blame]2686
2687<p>
2688This code shows the basic approach used to build recursive types: build a
2689non-recursive type using 'opaque', then use type unification to close the cycle.
2690The type unification step is performed by the <tt><a
Chris Lattneraff26d12007-02-03 03:06:52 +0000[diff] [blame]2691href="#refineAbstractTypeTo">refineAbstractTypeTo</a></tt> method, which is
Chris Lattnerf1b200b2005-04-23 17:27:36 +0000[diff] [blame]2692described next. After that, we describe the <a
2693href="#PATypeHolder">PATypeHolder class</a>.
2694</p>
2695
2696</div>
2697
2698<!-- ______________________________________________________________________ -->
2699<div class="doc_subsubsection">
2700 <a name="refineAbstractTypeTo">The <tt>refineAbstractTypeTo</tt> method</a>
2701</div>
2702
2703<div class="doc_text">
2704<p>
2705The <tt>refineAbstractTypeTo</tt> method starts the type unification process.
2706While this method is actually a member of the DerivedType class, it is most
2707often used on OpaqueType instances. Type unification is actually a recursive
2708process. After unification, types can become structurally isomorphic to
2709existing types, and all duplicates are deleted (to preserve pointer equality).
2710</p>
2711
2712<p>
2713In the example above, the OpaqueType object is definitely deleted.
Reid Spencer06565dc2007-01-12 17:11:23 +0000[diff] [blame]2714Additionally, if there is an "{ \2*, i32}" type already created in the system,
Chris Lattnerf1b200b2005-04-23 17:27:36 +0000[diff] [blame]2715the pointer and struct type created are <b>also</b> deleted. Obviously whenever
2716a type is deleted, any "Type*" pointers in the program are invalidated. As
2717such, it is safest to avoid having <i>any</i> "Type*" pointers to abstract types
2718live across a call to <tt>refineAbstractTypeTo</tt> (note that non-abstract
2719types can never move or be deleted). To deal with this, the <a
2720href="#PATypeHolder">PATypeHolder</a> class is used to maintain a stable
2721reference to a possibly refined type, and the <a
2722href="#AbstractTypeUser">AbstractTypeUser</a> class is used to update more
2723complex datastructures.
2724</p>
2725
2726</div>
2727
2728<!-- ______________________________________________________________________ -->
2729<div class="doc_subsubsection">
2730 <a name="PATypeHolder">The PATypeHolder Class</a>
2731</div>
2732
2733<div class="doc_text">
2734<p>
2735PATypeHolder is a form of a "smart pointer" for Type objects. When VMCore
2736happily goes about nuking types that become isomorphic to existing types, it
2737automatically updates all PATypeHolder objects to point to the new type. In the
2738example above, this allows the code to maintain a pointer to the resultant
2739resolved recursive type, even though the Type*'s are potentially invalidated.
2740</p>
2741
2742<p>
2743PATypeHolder is an extremely light-weight object that uses a lazy union-find
2744implementation to update pointers. For example the pointer from a Value to its
2745Type is maintained by PATypeHolder objects.
2746</p>
2747
2748</div>
2749
2750<!-- ______________________________________________________________________ -->
2751<div class="doc_subsubsection">
2752 <a name="AbstractTypeUser">The AbstractTypeUser Class</a>
2753</div>
2754
2755<div class="doc_text">
2756
2757<p>
2758Some data structures need more to perform more complex updates when types get
Chris Lattner263a98e2007-02-16 04:37:31 +0000[diff] [blame]2759resolved. To support this, a class can derive from the AbstractTypeUser class.
2760This class
Chris Lattnerf1b200b2005-04-23 17:27:36 +0000[diff] [blame]2761allows it to get callbacks when certain types are resolved. To register to get
2762callbacks for a particular type, the DerivedType::{add/remove}AbstractTypeUser
Chris Lattner0f876db2005-04-25 15:47:57 +0000[diff] [blame]2763methods can be called on a type. Note that these methods only work for <i>
Reid Spencer06565dc2007-01-12 17:11:23 +0000[diff] [blame]2764 abstract</i> types. Concrete types (those that do not include any opaque
2765objects) can never be refined.
Chris Lattnerf1b200b2005-04-23 17:27:36 +0000[diff] [blame]2766</p>
Chris Lattnerd9d6e102005-04-23 16:10:52 +0000[diff] [blame]2767</div>
2768
2769
2770<!-- ======================================================================= -->
2771<div class="doc_subsection">
Chris Lattner263a98e2007-02-16 04:37:31 +0000[diff] [blame]2772 <a name="SymbolTable">The <tt>ValueSymbolTable</tt> and
2773 <tt>TypeSymbolTable</tt> classes</a>
Chris Lattnerd9d6e102005-04-23 16:10:52 +0000[diff] [blame]2774</div>
Chris Lattnerf1b200b2005-04-23 17:27:36 +0000[diff] [blame]2775
Chris Lattnerd9d6e102005-04-23 16:10:52 +0000[diff] [blame]2776<div class="doc_text">
Chris Lattner263a98e2007-02-16 04:37:31 +0000[diff] [blame]2777<p>The <tt><a href="http://llvm.org/doxygen/classllvm_1_1ValueSymbolTable.html">
2778ValueSymbolTable</a></tt> class provides a symbol table that the <a
Chris Lattnerd9d6e102005-04-23 16:10:52 +0000[diff] [blame]2779href="#Function"><tt>Function</tt></a> and <a href="#Module">
Chris Lattner263a98e2007-02-16 04:37:31 +0000[diff] [blame]2780<tt>Module</tt></a> classes use for naming value definitions. The symbol table
2781can provide a name for any <a href="#Value"><tt>Value</tt></a>.
2782The <tt><a href="http://llvm.org/doxygen/classllvm_1_1TypeSymbolTable.html">
2783TypeSymbolTable</a></tt> class is used by the <tt>Module</tt> class to store
2784names for types.</p>
Chris Lattnerd9d6e102005-04-23 16:10:52 +0000[diff] [blame]2785
Reid Spencera6362242007-01-07 00:41:39 +0000[diff] [blame]2786<p>Note that the <tt>SymbolTable</tt> class should not be directly accessed
2787by most clients. It should only be used when iteration over the symbol table
2788names themselves are required, which is very special purpose. Note that not
2789all LLVM
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2790<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]2791an empty name) do not exist in the symbol table.
2792</p>
2793
Chris Lattner263a98e2007-02-16 04:37:31 +0000[diff] [blame]2794<p>These symbol tables support iteration over the values/types in the symbol
2795table with <tt>begin/end/iterator</tt> and supports querying to see if a
2796specific name is in the symbol table (with <tt>lookup</tt>). The
2797<tt>ValueSymbolTable</tt> class exposes no public mutator methods, instead,
2798simply call <tt>setName</tt> on a value, which will autoinsert it into the
2799appropriate symbol table. For types, use the Module::addTypeName method to
2800insert entries into the symbol table.</p>
Chris Lattnerd9d6e102005-04-23 16:10:52 +0000[diff] [blame]2801
Chris Lattnerd9d6e102005-04-23 16:10:52 +0000[diff] [blame]2802</div>
2803
2804
2805
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2806<!-- ======================================================================= -->
2807<div class="doc_subsection">
2808 <a name="UserLayout">The <tt>User</tt> and owned <tt>Use</tt> classes' memory layout</a>
2809</div>
2810
2811<div class="doc_text">
2812<p>The <tt><a href="http://llvm.org/doxygen/classllvm_1_1User.html">
Gabor Greiffd095b62009-01-05 16:05:32 +0000[diff] [blame]2813User</a></tt> class provides a basis for expressing the ownership of <tt>User</tt>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2814towards other <tt><a href="http://llvm.org/doxygen/classllvm_1_1Value.html">
2815Value</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]2816Use</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]2817addition and removal.</p>
2818
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2819<!-- ______________________________________________________________________ -->
2820<div class="doc_subsubsection">
Gabor Greiffd095b62009-01-05 16:05:32 +0000[diff] [blame]2821 <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]2822</div>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2823
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2824<div class="doc_text">
2825<p>
2826A subclass of <tt>User</tt> can choose between incorporating its <tt>Use</tt> objects
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2827or refer to them out-of-line by means of a pointer. A mixed variant
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2828(some <tt>Use</tt>s inline others hung off) is impractical and breaks the invariant
2829that the <tt>Use</tt> objects belonging to the same <tt>User</tt> form a contiguous array.
2830</p>
2831</div>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2832
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2833<p>
2834We have 2 different layouts in the <tt>User</tt> (sub)classes:
2835<ul>
2836<li><p>Layout a)
2837The <tt>Use</tt> object(s) are inside (resp. at fixed offset) of the <tt>User</tt>
2838object and there are a fixed number of them.</p>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2839
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2840<li><p>Layout b)
2841The <tt>Use</tt> object(s) are referenced by a pointer to an
2842array from the <tt>User</tt> object and there may be a variable
2843number of them.</p>
2844</ul>
2845<p>
Gabor Greifd41720a2008-06-25 00:10:22 +0000[diff] [blame]2846As of v2.4 each layout still possesses a direct pointer to the
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2847start of the array of <tt>Use</tt>s. Though not mandatory for layout a),
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2848we stick to this redundancy for the sake of simplicity.
Gabor Greifd41720a2008-06-25 00:10:22 +0000[diff] [blame]2849The <tt>User</tt> object also stores the number of <tt>Use</tt> objects it
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2850has. (Theoretically this information can also be calculated
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2851given the scheme presented below.)</p>
2852<p>
2853Special forms of allocation operators (<tt>operator new</tt>)
Gabor Greifd41720a2008-06-25 00:10:22 +0000[diff] [blame]2854enforce the following memory layouts:</p>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2855
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2856<ul>
Gabor Greifd41720a2008-06-25 00:10:22 +0000[diff] [blame]2857<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]2858
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2859<pre>
2860...---.---.---.---.-------...
2861 | P | P | P | P | User
2862'''---'---'---'---'-------'''
2863</pre>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2864
Gabor Greifd41720a2008-06-25 00:10:22 +0000[diff] [blame]2865<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]2866<pre>
2867.-------...
2868| User
2869'-------'''
2870 |
2871 v
2872 .---.---.---.---...
2873 | P | P | P | P |
2874 '---'---'---'---'''
2875</pre>
2876</ul>
2877<i>(In the above figures '<tt>P</tt>' stands for the <tt>Use**</tt> that
2878 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]2879
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2880<!-- ______________________________________________________________________ -->
2881<div class="doc_subsubsection">
Gabor Greiffd095b62009-01-05 16:05:32 +0000[diff] [blame]2882 <a name="Waymarking">The waymarking algorithm</a>
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2883</div>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2884
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2885<div class="doc_text">
2886<p>
Gabor Greifd41720a2008-06-25 00:10:22 +0000[diff] [blame]2887Since the <tt>Use</tt> objects are deprived of the direct (back)pointer to
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2888their <tt>User</tt> objects, there must be a fast and exact method to
2889recover it. This is accomplished by the following scheme:</p>
2890</div>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2891
Gabor Greifd41720a2008-06-25 00:10:22 +0000[diff] [blame]2892A 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]2893start of the <tt>User</tt> object:
2894<ul>
2895<li><tt>00</tt> &mdash;&gt; binary digit 0</li>
2896<li><tt>01</tt> &mdash;&gt; binary digit 1</li>
2897<li><tt>10</tt> &mdash;&gt; stop and calculate (<tt>s</tt>)</li>
2898<li><tt>11</tt> &mdash;&gt; full stop (<tt>S</tt>)</li>
2899</ul>
2900<p>
2901Given a <tt>Use*</tt>, all we have to do is to walk till we get
2902a stop and we either have a <tt>User</tt> immediately behind or
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2903we have to walk to the next stop picking up digits
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2904and calculating the offset:</p>
2905<pre>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2906.---.---.---.---.---.---.---.---.---.---.---.---.---.---.---.---.----------------
2907| 1 | s | 1 | 0 | 1 | 0 | s | 1 | 1 | 0 | s | 1 | 1 | s | 1 | S | User (or User*)
2908'---'---'---'---'---'---'---'---'---'---'---'---'---'---'---'---'----------------
2909 |+15 |+10 |+6 |+3 |+1
2910 | | | | |__>
2911 | | | |__________>
2912 | | |______________________>
2913 | |______________________________________>
2914 |__________________________________________________________>
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2915</pre>
2916<p>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2917Only the significant number of bits need to be stored between the
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2918stops, so that the <i>worst case is 20 memory accesses</i> when there are
29191000 <tt>Use</tt> objects associated with a <tt>User</tt>.</p>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2920
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2921<!-- ______________________________________________________________________ -->
2922<div class="doc_subsubsection">
Gabor Greiffd095b62009-01-05 16:05:32 +0000[diff] [blame]2923 <a name="ReferenceImpl">Reference implementation</a>
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2924</div>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2925
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2926<div class="doc_text">
2927<p>
2928The following literate Haskell fragment demonstrates the concept:</p>
2929</div>
2930
2931<div class="doc_code">
2932<pre>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2933> import Test.QuickCheck
2934>
2935> digits :: Int -> [Char] -> [Char]
2936> digits 0 acc = '0' : acc
2937> digits 1 acc = '1' : acc
2938> digits n acc = digits (n `div` 2) $ digits (n `mod` 2) acc
2939>
2940> dist :: Int -> [Char] -> [Char]
2941> dist 0 [] = ['S']
2942> dist 0 acc = acc
2943> dist 1 acc = let r = dist 0 acc in 's' : digits (length r) r
2944> dist n acc = dist (n - 1) $ dist 1 acc
2945>
2946> takeLast n ss = reverse $ take n $ reverse ss
2947>
2948> test = takeLast 40 $ dist 20 []
2949>
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2950</pre>
2951</div>
2952<p>
2953Printing &lt;test&gt; gives: <tt>"1s100000s11010s10100s1111s1010s110s11s1S"</tt></p>
2954<p>
2955The reverse algorithm computes the length of the string just by examining
2956a certain prefix:</p>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2957
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2958<div class="doc_code">
2959<pre>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2960> pref :: [Char] -> Int
2961> pref "S" = 1
2962> pref ('s':'1':rest) = decode 2 1 rest
2963> pref (_:rest) = 1 + pref rest
2964>
2965> decode walk acc ('0':rest) = decode (walk + 1) (acc * 2) rest
2966> decode walk acc ('1':rest) = decode (walk + 1) (acc * 2 + 1) rest
2967> decode walk acc _ = walk + acc
2968>
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2969</pre>
2970</div>
2971<p>
2972Now, as expected, printing &lt;pref test&gt; gives <tt>40</tt>.</p>
2973<p>
2974We can <i>quickCheck</i> this with following property:</p>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2975
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2976<div class="doc_code">
2977<pre>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2978> testcase = dist 2000 []
2979> testcaseLength = length testcase
2980>
2981> identityProp n = n > 0 && n <= testcaseLength ==> length arr == pref arr
2982> where arr = takeLast n testcase
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2983>
2984</pre>
2985</div>
2986<p>
2987As expected &lt;quickCheck identityProp&gt; gives:</p>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2988
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2989<pre>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2990*Main> quickCheck identityProp
2991OK, passed 100 tests.
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2992</pre>
2993<p>
2994Let's be a bit more exhaustive:</p>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2995
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2996<div class="doc_code">
2997<pre>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2998>
2999> deepCheck p = check (defaultConfig { configMaxTest = 500 }) p
3000>
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]3001</pre>
3002</div>
3003<p>
3004And here is the result of &lt;deepCheck identityProp&gt;:</p>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]3005
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]3006<pre>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]3007*Main> deepCheck identityProp
3008OK, passed 500 tests.
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]3009</pre>
3010
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]3011<!-- ______________________________________________________________________ -->
3012<div class="doc_subsubsection">
Gabor Greiffd095b62009-01-05 16:05:32 +0000[diff] [blame]3013 <a name="Tagging">Tagging considerations</a>
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]3014</div>
3015
3016<p>
3017To maintain the invariant that the 2 LSBits of each <tt>Use**</tt> in <tt>Use</tt>
3018never change after being set up, setters of <tt>Use::Prev</tt> must re-tag the
3019new <tt>Use**</tt> on every modification. Accordingly getters must strip the
3020tag bits.</p>
3021<p>
Gabor Greifd41720a2008-06-25 00:10:22 +0000[diff] [blame]3022For layout b) instead of the <tt>User</tt> we find a pointer (<tt>User*</tt> with LSBit set).
3023Following this pointer brings us to the <tt>User</tt>. A portable trick ensures
3024that the first bytes of <tt>User</tt> (if interpreted as a pointer) never has
Gabor Greiffd095b62009-01-05 16:05:32 +0000[diff] [blame]3025the LSBit set. (Portability is relying on the fact that all known compilers place the
3026<tt>vptr</tt> in the first word of the instances.)</p>
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]3027
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]3028</div>
3029
3030 <!-- *********************************************************************** -->
Chris Lattnerd9d6e102005-04-23 16:10:52 +0000[diff] [blame]3031<div class="doc_section">
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3032 <a name="coreclasses">The Core LLVM Class Hierarchy Reference </a>
3033</div>
3034<!-- *********************************************************************** -->
3035
3036<div class="doc_text">
Reid Spencer303c4b42007-01-12 17:26:25 +0000[diff] [blame]3037<p><tt>#include "<a href="/doxygen/Type_8h-source.html">llvm/Type.h</a>"</tt>
3038<br>doxygen info: <a href="/doxygen/classllvm_1_1Type.html">Type Class</a></p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3039
3040<p>The Core LLVM classes are the primary means of representing the program
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3041being inspected or transformed. The core LLVM classes are defined in
3042header files in the <tt>include/llvm/</tt> directory, and implemented in
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3043the <tt>lib/VMCore</tt> directory.</p>
3044
3045</div>
3046
3047<!-- ======================================================================= -->
3048<div class="doc_subsection">
Reid Spencer303c4b42007-01-12 17:26:25 +0000[diff] [blame]3049 <a name="Type">The <tt>Type</tt> class and Derived Types</a>
3050</div>
3051
3052<div class="doc_text">
3053
3054 <p><tt>Type</tt> is a superclass of all type classes. Every <tt>Value</tt> has
3055 a <tt>Type</tt>. <tt>Type</tt> cannot be instantiated directly but only
3056 through its subclasses. Certain primitive types (<tt>VoidType</tt>,
3057 <tt>LabelType</tt>, <tt>FloatType</tt> and <tt>DoubleType</tt>) have hidden
3058 subclasses. They are hidden because they offer no useful functionality beyond
3059 what the <tt>Type</tt> class offers except to distinguish themselves from
3060 other subclasses of <tt>Type</tt>.</p>
3061 <p>All other types are subclasses of <tt>DerivedType</tt>. Types can be
3062 named, but this is not a requirement. There exists exactly
3063 one instance of a given shape at any one time. This allows type equality to
3064 be performed with address equality of the Type Instance. That is, given two
3065 <tt>Type*</tt> values, the types are identical if the pointers are identical.
3066 </p>
3067</div>
3068
3069<!-- _______________________________________________________________________ -->
3070<div class="doc_subsubsection">
Gabor Greiffd095b62009-01-05 16:05:32 +0000[diff] [blame]3071 <a name="m_Type">Important Public Methods</a>
Reid Spencer303c4b42007-01-12 17:26:25 +0000[diff] [blame]3072</div>
3073
3074<div class="doc_text">
3075
3076<ul>
Duncan Sandsb0bc6c32010-02-15 16:12:20 +0000[diff] [blame]3077 <li><tt>bool isIntegerTy() const</tt>: Returns true for any integer type.</li>
Reid Spencer303c4b42007-01-12 17:26:25 +0000[diff] [blame]3078
Duncan Sandsb0bc6c32010-02-15 16:12:20 +0000[diff] [blame]3079 <li><tt>bool isFloatingPointTy()</tt>: Return true if this is one of the five
Reid Spencer303c4b42007-01-12 17:26:25 +0000[diff] [blame]3080 floating point types.</li>
3081
3082 <li><tt>bool isAbstract()</tt>: Return true if the type is abstract (contains
3083 an OpaqueType anywhere in its definition).</li>
3084
3085 <li><tt>bool isSized()</tt>: Return true if the type has known size. Things
3086 that don't have a size are abstract types, labels and void.</li>
3087
3088</ul>
3089</div>
3090
3091<!-- _______________________________________________________________________ -->
3092<div class="doc_subsubsection">
Gabor Greiffd095b62009-01-05 16:05:32 +0000[diff] [blame]3093 <a name="derivedtypes">Important Derived Types</a>
Reid Spencer303c4b42007-01-12 17:26:25 +0000[diff] [blame]3094</div>
3095<div class="doc_text">
3096<dl>
3097 <dt><tt>IntegerType</tt></dt>
3098 <dd>Subclass of DerivedType that represents integer types of any bit width.
3099 Any bit width between <tt>IntegerType::MIN_INT_BITS</tt> (1) and
3100 <tt>IntegerType::MAX_INT_BITS</tt> (~8 million) can be represented.
3101 <ul>
3102 <li><tt>static const IntegerType* get(unsigned NumBits)</tt>: get an integer
3103 type of a specific bit width.</li>
3104 <li><tt>unsigned getBitWidth() const</tt>: Get the bit width of an integer
3105 type.</li>
3106 </ul>
3107 </dd>
3108 <dt><tt>SequentialType</tt></dt>
3109 <dd>This is subclassed by ArrayType and PointerType
3110 <ul>
3111 <li><tt>const Type * getElementType() const</tt>: Returns the type of each
3112 of the elements in the sequential type. </li>
3113 </ul>
3114 </dd>
3115 <dt><tt>ArrayType</tt></dt>
3116 <dd>This is a subclass of SequentialType and defines the interface for array
3117 types.
3118 <ul>
3119 <li><tt>unsigned getNumElements() const</tt>: Returns the number of
3120 elements in the array. </li>
3121 </ul>
3122 </dd>
3123 <dt><tt>PointerType</tt></dt>
Chris Lattner302da1e2007-02-03 03:05:57 +0000[diff] [blame]3124 <dd>Subclass of SequentialType for pointer types.</dd>
Reid Spencer9d6565a2007-02-15 02:26:10 +0000[diff] [blame]3125 <dt><tt>VectorType</tt></dt>
Reid Spencer485bad12007-02-15 03:07:05 +0000[diff] [blame]3126 <dd>Subclass of SequentialType for vector types. A
3127 vector type is similar to an ArrayType but is distinguished because it is
Benjamin Kramer8040cd32009-10-12 14:46:08 +0000[diff] [blame]3128 a first class type whereas ArrayType is not. Vector types are used for
Reid Spencer303c4b42007-01-12 17:26:25 +0000[diff] [blame]3129 vector operations and are usually small vectors of of an integer or floating
3130 point type.</dd>
3131 <dt><tt>StructType</tt></dt>
3132 <dd>Subclass of DerivedTypes for struct types.</dd>
Duncan Sands8036ca42007-03-30 12:22:09 +0000[diff] [blame]3133 <dt><tt><a name="FunctionType">FunctionType</a></tt></dt>
Reid Spencer303c4b42007-01-12 17:26:25 +0000[diff] [blame]3134 <dd>Subclass of DerivedTypes for function types.
3135 <ul>
Dan Gohman4bb31bf2010-03-30 20:04:57 +0000[diff] [blame]3136 <li><tt>bool isVarArg() const</tt>: Returns true if it's a vararg
Reid Spencer303c4b42007-01-12 17:26:25 +0000[diff] [blame]3137 function</li>
3138 <li><tt> const Type * getReturnType() const</tt>: Returns the
3139 return type of the function.</li>
3140 <li><tt>const Type * getParamType (unsigned i)</tt>: Returns
3141 the type of the ith parameter.</li>
3142 <li><tt> const unsigned getNumParams() const</tt>: Returns the
3143 number of formal parameters.</li>
3144 </ul>
3145 </dd>
3146 <dt><tt>OpaqueType</tt></dt>
3147 <dd>Sublcass of DerivedType for abstract types. This class
3148 defines no content and is used as a placeholder for some other type. Note
3149 that OpaqueType is used (temporarily) during type resolution for forward
3150 references of types. Once the referenced type is resolved, the OpaqueType
3151 is replaced with the actual type. OpaqueType can also be used for data
3152 abstraction. At link time opaque types can be resolved to actual types
3153 of the same name.</dd>
3154</dl>
3155</div>
3156
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]3157
3158
3159<!-- ======================================================================= -->
3160<div class="doc_subsection">
3161 <a name="Module">The <tt>Module</tt> class</a>
3162</div>
3163
3164<div class="doc_text">
3165
3166<p><tt>#include "<a
3167href="/doxygen/Module_8h-source.html">llvm/Module.h</a>"</tt><br> doxygen info:
3168<a href="/doxygen/classllvm_1_1Module.html">Module Class</a></p>
3169
3170<p>The <tt>Module</tt> class represents the top level structure present in LLVM
3171programs. An LLVM module is effectively either a translation unit of the
3172original program or a combination of several translation units merged by the
3173linker. The <tt>Module</tt> class keeps track of a list of <a
3174href="#Function"><tt>Function</tt></a>s, a list of <a
3175href="#GlobalVariable"><tt>GlobalVariable</tt></a>s, and a <a
3176href="#SymbolTable"><tt>SymbolTable</tt></a>. Additionally, it contains a few
3177helpful member functions that try to make common operations easy.</p>
3178
3179</div>
3180
3181<!-- _______________________________________________________________________ -->
3182<div class="doc_subsubsection">
3183 <a name="m_Module">Important Public Members of the <tt>Module</tt> class</a>
3184</div>
3185
3186<div class="doc_text">
3187
3188<ul>
3189 <li><tt>Module::Module(std::string name = "")</tt></li>
3190</ul>
3191
3192<p>Constructing a <a href="#Module">Module</a> is easy. You can optionally
3193provide a name for it (probably based on the name of the translation unit).</p>
3194
3195<ul>
3196 <li><tt>Module::iterator</tt> - Typedef for function list iterator<br>
3197 <tt>Module::const_iterator</tt> - Typedef for const_iterator.<br>
3198
3199 <tt>begin()</tt>, <tt>end()</tt>
3200 <tt>size()</tt>, <tt>empty()</tt>
3201
3202 <p>These are forwarding methods that make it easy to access the contents of
3203 a <tt>Module</tt> object's <a href="#Function"><tt>Function</tt></a>
3204 list.</p></li>
3205
3206 <li><tt>Module::FunctionListType &amp;getFunctionList()</tt>
3207
3208 <p> Returns the list of <a href="#Function"><tt>Function</tt></a>s. This is
3209 necessary to use when you need to update the list or perform a complex
3210 action that doesn't have a forwarding method.</p>
3211
3212 <p><!-- Global Variable --></p></li>
3213</ul>
3214
3215<hr>
3216
3217<ul>
3218 <li><tt>Module::global_iterator</tt> - Typedef for global variable list iterator<br>
3219
3220 <tt>Module::const_global_iterator</tt> - Typedef for const_iterator.<br>
3221
3222 <tt>global_begin()</tt>, <tt>global_end()</tt>
3223 <tt>global_size()</tt>, <tt>global_empty()</tt>
3224
3225 <p> These are forwarding methods that make it easy to access the contents of
3226 a <tt>Module</tt> object's <a
3227 href="#GlobalVariable"><tt>GlobalVariable</tt></a> list.</p></li>
3228
3229 <li><tt>Module::GlobalListType &amp;getGlobalList()</tt>
3230
3231 <p>Returns the list of <a
3232 href="#GlobalVariable"><tt>GlobalVariable</tt></a>s. This is necessary to
3233 use when you need to update the list or perform a complex action that
3234 doesn't have a forwarding method.</p>
3235
3236 <p><!-- Symbol table stuff --> </p></li>
3237</ul>
3238
3239<hr>
3240
3241<ul>
3242 <li><tt><a href="#SymbolTable">SymbolTable</a> *getSymbolTable()</tt>
3243
3244 <p>Return a reference to the <a href="#SymbolTable"><tt>SymbolTable</tt></a>
3245 for this <tt>Module</tt>.</p>
3246
3247 <p><!-- Convenience methods --></p></li>
3248</ul>
3249
3250<hr>
3251
3252<ul>
3253 <li><tt><a href="#Function">Function</a> *getFunction(const std::string
3254 &amp;Name, const <a href="#FunctionType">FunctionType</a> *Ty)</tt>
3255
3256 <p>Look up the specified function in the <tt>Module</tt> <a
3257 href="#SymbolTable"><tt>SymbolTable</tt></a>. If it does not exist, return
3258 <tt>null</tt>.</p></li>
3259
3260 <li><tt><a href="#Function">Function</a> *getOrInsertFunction(const
3261 std::string &amp;Name, const <a href="#FunctionType">FunctionType</a> *T)</tt>
3262
3263 <p>Look up the specified function in the <tt>Module</tt> <a
3264 href="#SymbolTable"><tt>SymbolTable</tt></a>. If it does not exist, add an
3265 external declaration for the function and return it.</p></li>
3266
3267 <li><tt>std::string getTypeName(const <a href="#Type">Type</a> *Ty)</tt>
3268
3269 <p>If there is at least one entry in the <a
3270 href="#SymbolTable"><tt>SymbolTable</tt></a> for the specified <a
3271 href="#Type"><tt>Type</tt></a>, return it. Otherwise return the empty
3272 string.</p></li>
3273
3274 <li><tt>bool addTypeName(const std::string &amp;Name, const <a
3275 href="#Type">Type</a> *Ty)</tt>
3276
3277 <p>Insert an entry in the <a href="#SymbolTable"><tt>SymbolTable</tt></a>
3278 mapping <tt>Name</tt> to <tt>Ty</tt>. If there is already an entry for this
3279 name, true is returned and the <a
3280 href="#SymbolTable"><tt>SymbolTable</tt></a> is not modified.</p></li>
3281</ul>
3282
3283</div>
3284
3285
Reid Spencer303c4b42007-01-12 17:26:25 +0000[diff] [blame]3286<!-- ======================================================================= -->
3287<div class="doc_subsection">
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3288 <a name="Value">The <tt>Value</tt> class</a>
3289</div>
3290
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]3291<div class="doc_text">
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3292
3293<p><tt>#include "<a href="/doxygen/Value_8h-source.html">llvm/Value.h</a>"</tt>
3294<br>
Chris Lattner00815172007-01-04 22:01:45 +0000[diff] [blame]3295doxygen info: <a href="/doxygen/classllvm_1_1Value.html">Value Class</a></p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3296
3297<p>The <tt>Value</tt> class is the most important class in the LLVM Source
3298base. It represents a typed value that may be used (among other things) as an
3299operand to an instruction. There are many different types of <tt>Value</tt>s,
3300such as <a href="#Constant"><tt>Constant</tt></a>s,<a
3301href="#Argument"><tt>Argument</tt></a>s. Even <a
3302href="#Instruction"><tt>Instruction</tt></a>s and <a
3303href="#Function"><tt>Function</tt></a>s are <tt>Value</tt>s.</p>
3304
3305<p>A particular <tt>Value</tt> may be used many times in the LLVM representation
3306for a program. For example, an incoming argument to a function (represented
3307with an instance of the <a href="#Argument">Argument</a> class) is "used" by
3308every instruction in the function that references the argument. To keep track
3309of this relationship, the <tt>Value</tt> class keeps a list of all of the <a
3310href="#User"><tt>User</tt></a>s that is using it (the <a
3311href="#User"><tt>User</tt></a> class is a base class for all nodes in the LLVM
3312graph that can refer to <tt>Value</tt>s). This use list is how LLVM represents
3313def-use information in the program, and is accessible through the <tt>use_</tt>*
3314methods, shown below.</p>
3315
3316<p>Because LLVM is a typed representation, every LLVM <tt>Value</tt> is typed,
3317and this <a href="#Type">Type</a> is available through the <tt>getType()</tt>
3318method. In addition, all LLVM values can be named. The "name" of the
3319<tt>Value</tt> is a symbolic string printed in the LLVM code:</p>
3320
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]3321<div class="doc_code">
3322<pre>
Reid Spencer06565dc2007-01-12 17:11:23 +0000[diff] [blame]3323%<b>foo</b> = add i32 1, 2
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]3324</pre>
3325</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3326
Duncan Sands8036ca42007-03-30 12:22:09 +0000[diff] [blame]3327<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]3328that the name of any value may be missing (an empty string), so names should
3329<b>ONLY</b> be used for debugging (making the source code easier to read,
3330debugging printouts), they should not be used to keep track of values or map
3331between them. For this purpose, use a <tt>std::map</tt> of pointers to the
3332<tt>Value</tt> itself instead.</p>
3333
3334<p>One important aspect of LLVM is that there is no distinction between an SSA
3335variable and the operation that produces it. Because of this, any reference to
3336the value produced by an instruction (or the value available as an incoming
Chris Lattnerd5fc4fc2004-03-18 14:58:55 +0000[diff] [blame]3337argument, for example) is represented as a direct pointer to the instance of
3338the class that
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3339represents this value. Although this may take some getting used to, it
3340simplifies the representation and makes it easier to manipulate.</p>
3341
3342</div>
3343
3344<!-- _______________________________________________________________________ -->
3345<div class="doc_subsubsection">
3346 <a name="m_Value">Important Public Members of the <tt>Value</tt> class</a>
3347</div>
3348
3349<div class="doc_text">
3350
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3351<ul>
3352 <li><tt>Value::use_iterator</tt> - Typedef for iterator over the
3353use-list<br>
Gabor Greifbbbf9a22010-03-26 19:59:25 +0000[diff] [blame]3354 <tt>Value::const_use_iterator</tt> - Typedef for const_iterator over
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3355the use-list<br>
3356 <tt>unsigned use_size()</tt> - Returns the number of users of the
3357value.<br>
Chris Lattner9355b472002-09-06 02:50:58 +0000[diff] [blame]3358 <tt>bool use_empty()</tt> - Returns true if there are no users.<br>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3359 <tt>use_iterator use_begin()</tt> - Get an iterator to the start of
3360the use-list.<br>
3361 <tt>use_iterator use_end()</tt> - Get an iterator to the end of the
3362use-list.<br>
3363 <tt><a href="#User">User</a> *use_back()</tt> - Returns the last
3364element in the list.
3365 <p> These methods are the interface to access the def-use
3366information in LLVM. As with all other iterators in LLVM, the naming
3367conventions follow the conventions defined by the <a href="#stl">STL</a>.</p>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3368 </li>
3369 <li><tt><a href="#Type">Type</a> *getType() const</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3370 <p>This method returns the Type of the Value.</p>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3371 </li>
3372 <li><tt>bool hasName() const</tt><br>
Chris Lattner9355b472002-09-06 02:50:58 +0000[diff] [blame]3373 <tt>std::string getName() const</tt><br>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3374 <tt>void setName(const std::string &amp;Name)</tt>
3375 <p> This family of methods is used to access and assign a name to a <tt>Value</tt>,
3376be aware of the <a href="#nameWarning">precaution above</a>.</p>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3377 </li>
3378 <li><tt>void replaceAllUsesWith(Value *V)</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3379
3380 <p>This method traverses the use list of a <tt>Value</tt> changing all <a
3381 href="#User"><tt>User</tt>s</a> of the current value to refer to
3382 "<tt>V</tt>" instead. For example, if you detect that an instruction always
3383 produces a constant value (for example through constant folding), you can
3384 replace all uses of the instruction with the constant like this:</p>
3385
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]3386<div class="doc_code">
3387<pre>
3388Inst-&gt;replaceAllUsesWith(ConstVal);
3389</pre>
3390</div>
3391
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3392</ul>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3393
3394</div>
3395
3396<!-- ======================================================================= -->
3397<div class="doc_subsection">
3398 <a name="User">The <tt>User</tt> class</a>
3399</div>
3400
3401<div class="doc_text">
3402
3403<p>
3404<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]3405doxygen info: <a href="/doxygen/classllvm_1_1User.html">User Class</a><br>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3406Superclass: <a href="#Value"><tt>Value</tt></a></p>
3407
3408<p>The <tt>User</tt> class is the common base class of all LLVM nodes that may
3409refer to <a href="#Value"><tt>Value</tt></a>s. It exposes a list of "Operands"
3410that are all of the <a href="#Value"><tt>Value</tt></a>s that the User is
3411referring to. The <tt>User</tt> class itself is a subclass of
3412<tt>Value</tt>.</p>
3413
3414<p>The operands of a <tt>User</tt> point directly to the LLVM <a
3415href="#Value"><tt>Value</tt></a> that it refers to. Because LLVM uses Static
3416Single Assignment (SSA) form, there can only be one definition referred to,
3417allowing this direct connection. This connection provides the use-def
3418information in LLVM.</p>
3419
3420</div>
3421
3422<!-- _______________________________________________________________________ -->
3423<div class="doc_subsubsection">
3424 <a name="m_User">Important Public Members of the <tt>User</tt> class</a>
3425</div>
3426
3427<div class="doc_text">
3428
3429<p>The <tt>User</tt> class exposes the operand list in two ways: through
3430an index access interface and through an iterator based interface.</p>
3431
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3432<ul>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3433 <li><tt>Value *getOperand(unsigned i)</tt><br>
3434 <tt>unsigned getNumOperands()</tt>
3435 <p> These two methods expose the operands of the <tt>User</tt> in a
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3436convenient form for direct access.</p></li>
3437
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3438 <li><tt>User::op_iterator</tt> - Typedef for iterator over the operand
3439list<br>
Chris Lattner58360822005-01-17 00:12:04 +0000[diff] [blame]3440 <tt>op_iterator op_begin()</tt> - Get an iterator to the start of
3441the operand list.<br>
3442 <tt>op_iterator op_end()</tt> - Get an iterator to the end of the
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3443operand list.
3444 <p> Together, these methods make up the iterator based interface to
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3445the operands of a <tt>User</tt>.</p></li>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3446</ul>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3447
3448</div>
3449
3450<!-- ======================================================================= -->
3451<div class="doc_subsection">
3452 <a name="Instruction">The <tt>Instruction</tt> class</a>
3453</div>
3454
3455<div class="doc_text">
3456
3457<p><tt>#include "</tt><tt><a
3458href="/doxygen/Instruction_8h-source.html">llvm/Instruction.h</a>"</tt><br>
Misha Brukman31ca1de2004-06-03 23:35:54 +0000[diff] [blame]3459doxygen info: <a href="/doxygen/classllvm_1_1Instruction.html">Instruction Class</a><br>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3460Superclasses: <a href="#User"><tt>User</tt></a>, <a
3461href="#Value"><tt>Value</tt></a></p>
3462
3463<p>The <tt>Instruction</tt> class is the common base class for all LLVM
3464instructions. It provides only a few methods, but is a very commonly used
3465class. The primary data tracked by the <tt>Instruction</tt> class itself is the
3466opcode (instruction type) and the parent <a
3467href="#BasicBlock"><tt>BasicBlock</tt></a> the <tt>Instruction</tt> is embedded
3468into. To represent a specific type of instruction, one of many subclasses of
3469<tt>Instruction</tt> are used.</p>
3470
3471<p> Because the <tt>Instruction</tt> class subclasses the <a
3472href="#User"><tt>User</tt></a> class, its operands can be accessed in the same
3473way as for other <a href="#User"><tt>User</tt></a>s (with the
3474<tt>getOperand()</tt>/<tt>getNumOperands()</tt> and
3475<tt>op_begin()</tt>/<tt>op_end()</tt> methods).</p> <p> An important file for
3476the <tt>Instruction</tt> class is the <tt>llvm/Instruction.def</tt> file. This
3477file contains some meta-data about the various different types of instructions
3478in LLVM. It describes the enum values that are used as opcodes (for example
Reid Spencerc92d25d2006-12-19 19:47:19 +0000[diff] [blame]3479<tt>Instruction::Add</tt> and <tt>Instruction::ICmp</tt>), as well as the
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3480concrete sub-classes of <tt>Instruction</tt> that implement the instruction (for
3481example <tt><a href="#BinaryOperator">BinaryOperator</a></tt> and <tt><a
Reid Spencerc92d25d2006-12-19 19:47:19 +0000[diff] [blame]3482href="#CmpInst">CmpInst</a></tt>). Unfortunately, the use of macros in
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3483this file confuses doxygen, so these enum values don't show up correctly in the
Misha Brukman31ca1de2004-06-03 23:35:54 +0000[diff] [blame]3484<a href="/doxygen/classllvm_1_1Instruction.html">doxygen output</a>.</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3485
3486</div>
3487
3488<!-- _______________________________________________________________________ -->
3489<div class="doc_subsubsection">
Reid Spencerc92d25d2006-12-19 19:47:19 +0000[diff] [blame]3490 <a name="s_Instruction">Important Subclasses of the <tt>Instruction</tt>
3491 class</a>
3492</div>
3493<div class="doc_text">
3494 <ul>
3495 <li><tt><a name="BinaryOperator">BinaryOperator</a></tt>
3496 <p>This subclasses represents all two operand instructions whose operands
3497 must be the same type, except for the comparison instructions.</p></li>
3498 <li><tt><a name="CastInst">CastInst</a></tt>
3499 <p>This subclass is the parent of the 12 casting instructions. It provides
3500 common operations on cast instructions.</p>
3501 <li><tt><a name="CmpInst">CmpInst</a></tt>
3502 <p>This subclass respresents the two comparison instructions,
3503 <a href="LangRef.html#i_icmp">ICmpInst</a> (integer opreands), and
3504 <a href="LangRef.html#i_fcmp">FCmpInst</a> (floating point operands).</p>
3505 <li><tt><a name="TerminatorInst">TerminatorInst</a></tt>
3506 <p>This subclass is the parent of all terminator instructions (those which
3507 can terminate a block).</p>
3508 </ul>
3509 </div>
3510
3511<!-- _______________________________________________________________________ -->
3512<div class="doc_subsubsection">
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3513 <a name="m_Instruction">Important Public Members of the <tt>Instruction</tt>
3514 class</a>
3515</div>
3516
3517<div class="doc_text">
3518
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3519<ul>
3520 <li><tt><a href="#BasicBlock">BasicBlock</a> *getParent()</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3521 <p>Returns the <a href="#BasicBlock"><tt>BasicBlock</tt></a> that
3522this <tt>Instruction</tt> is embedded into.</p></li>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3523 <li><tt>bool mayWriteToMemory()</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3524 <p>Returns true if the instruction writes to memory, i.e. it is a
3525 <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]3526 <li><tt>unsigned getOpcode()</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3527 <p>Returns the opcode for the <tt>Instruction</tt>.</p></li>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3528 <li><tt><a href="#Instruction">Instruction</a> *clone() const</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3529 <p>Returns another instance of the specified instruction, identical
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3530in all ways to the original except that the instruction has no parent
3531(ie it's not embedded into a <a href="#BasicBlock"><tt>BasicBlock</tt></a>),
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3532and it has no name</p></li>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3533</ul>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3534
3535</div>
3536
3537<!-- ======================================================================= -->
3538<div class="doc_subsection">
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]3539 <a name="Constant">The <tt>Constant</tt> class and subclasses</a>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3540</div>
3541
3542<div class="doc_text">
3543
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]3544<p>Constant represents a base class for different types of constants. It
3545is subclassed by ConstantInt, ConstantArray, etc. for representing
3546the various types of Constants. <a href="#GlobalValue">GlobalValue</a> is also
3547a subclass, which represents the address of a global variable or function.
3548</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3549
3550</div>
3551
3552<!-- _______________________________________________________________________ -->
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]3553<div class="doc_subsubsection">Important Subclasses of Constant </div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3554<div class="doc_text">
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3555<ul>
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]3556 <li>ConstantInt : This subclass of Constant represents an integer constant of
3557 any width.
3558 <ul>
Reid Spencer97b4ee32007-03-01 21:05:33 +0000[diff] [blame]3559 <li><tt>const APInt&amp; getValue() const</tt>: Returns the underlying
3560 value of this constant, an APInt value.</li>
3561 <li><tt>int64_t getSExtValue() const</tt>: Converts the underlying APInt
3562 value to an int64_t via sign extension. If the value (not the bit width)
3563 of the APInt is too large to fit in an int64_t, an assertion will result.
3564 For this reason, use of this method is discouraged.</li>
3565 <li><tt>uint64_t getZExtValue() const</tt>: Converts the underlying APInt
3566 value to a uint64_t via zero extension. IF the value (not the bit width)
3567 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]3568 For this reason, use of this method is discouraged.</li>
Reid Spencer97b4ee32007-03-01 21:05:33 +0000[diff] [blame]3569 <li><tt>static ConstantInt* get(const APInt&amp; Val)</tt>: Returns the
3570 ConstantInt object that represents the value provided by <tt>Val</tt>.
3571 The type is implied as the IntegerType that corresponds to the bit width
3572 of <tt>Val</tt>.</li>
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]3573 <li><tt>static ConstantInt* get(const Type *Ty, uint64_t Val)</tt>:
3574 Returns the ConstantInt object that represents the value provided by
3575 <tt>Val</tt> for integer type <tt>Ty</tt>.</li>
3576 </ul>
3577 </li>
3578 <li>ConstantFP : This class represents a floating point constant.
3579 <ul>
3580 <li><tt>double getValue() const</tt>: Returns the underlying value of
3581 this constant. </li>
3582 </ul>
3583 </li>
3584 <li>ConstantArray : This represents a constant array.
3585 <ul>
3586 <li><tt>const std::vector&lt;Use&gt; &amp;getValues() const</tt>: Returns
3587 a vector of component constants that makeup this array. </li>
3588 </ul>
3589 </li>
3590 <li>ConstantStruct : This represents a constant struct.
3591 <ul>
3592 <li><tt>const std::vector&lt;Use&gt; &amp;getValues() const</tt>: Returns
3593 a vector of component constants that makeup this array. </li>
3594 </ul>
3595 </li>
3596 <li>GlobalValue : This represents either a global variable or a function. In
3597 either case, the value is a constant fixed address (after linking).
3598 </li>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3599</ul>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3600</div>
3601
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]3602
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3603<!-- ======================================================================= -->
3604<div class="doc_subsection">
3605 <a name="GlobalValue">The <tt>GlobalValue</tt> class</a>
3606</div>
3607
3608<div class="doc_text">
3609
3610<p><tt>#include "<a
3611href="/doxygen/GlobalValue_8h-source.html">llvm/GlobalValue.h</a>"</tt><br>
Misha Brukman384047f2004-06-03 23:29:12 +0000[diff] [blame]3612doxygen info: <a href="/doxygen/classllvm_1_1GlobalValue.html">GlobalValue
3613Class</a><br>
Reid Spencerbe5e85e2006-04-14 14:11:48 +0000[diff] [blame]3614Superclasses: <a href="#Constant"><tt>Constant</tt></a>,
3615<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]3616
3617<p>Global values (<a href="#GlobalVariable"><tt>GlobalVariable</tt></a>s or <a
3618href="#Function"><tt>Function</tt></a>s) are the only LLVM values that are
3619visible in the bodies of all <a href="#Function"><tt>Function</tt></a>s.
3620Because they are visible at global scope, they are also subject to linking with
3621other globals defined in different translation units. To control the linking
3622process, <tt>GlobalValue</tt>s know their linkage rules. Specifically,
3623<tt>GlobalValue</tt>s know whether they have internal or external linkage, as
Reid Spencer8b2da7a2004-07-18 13:10:31 +0000[diff] [blame]3624defined by the <tt>LinkageTypes</tt> enumeration.</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3625
3626<p>If a <tt>GlobalValue</tt> has internal linkage (equivalent to being
3627<tt>static</tt> in C), it is not visible to code outside the current translation
3628unit, and does not participate in linking. If it has external linkage, it is
3629visible to external code, and does participate in linking. In addition to
3630linkage information, <tt>GlobalValue</tt>s keep track of which <a
3631href="#Module"><tt>Module</tt></a> they are currently part of.</p>
3632
3633<p>Because <tt>GlobalValue</tt>s are memory objects, they are always referred to
3634by their <b>address</b>. As such, the <a href="#Type"><tt>Type</tt></a> of a
3635global is always a pointer to its contents. It is important to remember this
3636when using the <tt>GetElementPtrInst</tt> instruction because this pointer must
3637be dereferenced first. For example, if you have a <tt>GlobalVariable</tt> (a
3638subclass 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]3639i32]</tt>, then the <tt>GlobalVariable</tt> is a pointer to that array. Although
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3640the address of the first element of this array and the value of the
3641<tt>GlobalVariable</tt> are the same, they have different types. The
Reid Spencer06565dc2007-01-12 17:11:23 +0000[diff] [blame]3642<tt>GlobalVariable</tt>'s type is <tt>[24 x i32]</tt>. The first element's type
3643is <tt>i32.</tt> Because of this, accessing a global value requires you to
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3644dereference the pointer with <tt>GetElementPtrInst</tt> first, then its elements
3645can be accessed. This is explained in the <a href="LangRef.html#globalvars">LLVM
3646Language Reference Manual</a>.</p>
3647
3648</div>
3649
3650<!-- _______________________________________________________________________ -->
3651<div class="doc_subsubsection">
3652 <a name="m_GlobalValue">Important Public Members of the <tt>GlobalValue</tt>
3653 class</a>
3654</div>
3655
3656<div class="doc_text">
3657
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3658<ul>
3659 <li><tt>bool hasInternalLinkage() const</tt><br>
Chris Lattner9355b472002-09-06 02:50:58 +0000[diff] [blame]3660 <tt>bool hasExternalLinkage() const</tt><br>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3661 <tt>void setInternalLinkage(bool HasInternalLinkage)</tt>
3662 <p> These methods manipulate the linkage characteristics of the <tt>GlobalValue</tt>.</p>
3663 <p> </p>
3664 </li>
3665 <li><tt><a href="#Module">Module</a> *getParent()</tt>
3666 <p> This returns the <a href="#Module"><tt>Module</tt></a> that the
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3667GlobalValue is currently embedded into.</p></li>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3668</ul>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3669
3670</div>
3671
3672<!-- ======================================================================= -->
3673<div class="doc_subsection">
3674 <a name="Function">The <tt>Function</tt> class</a>
3675</div>
3676
3677<div class="doc_text">
3678
3679<p><tt>#include "<a
3680href="/doxygen/Function_8h-source.html">llvm/Function.h</a>"</tt><br> doxygen
Misha Brukman31ca1de2004-06-03 23:35:54 +0000[diff] [blame]3681info: <a href="/doxygen/classllvm_1_1Function.html">Function Class</a><br>
Reid Spencerbe5e85e2006-04-14 14:11:48 +0000[diff] [blame]3682Superclasses: <a href="#GlobalValue"><tt>GlobalValue</tt></a>,
3683<a href="#Constant"><tt>Constant</tt></a>,
3684<a href="#User"><tt>User</tt></a>,
3685<a href="#Value"><tt>Value</tt></a></p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3686
3687<p>The <tt>Function</tt> class represents a single procedure in LLVM. It is
Torok Edwin87469292009-10-12 13:37:29 +0000[diff] [blame]3688actually one of the more complex classes in the LLVM hierarchy because it must
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3689keep track of a large amount of data. The <tt>Function</tt> class keeps track
Reid Spencerbe5e85e2006-04-14 14:11:48 +0000[diff] [blame]3690of a list of <a href="#BasicBlock"><tt>BasicBlock</tt></a>s, a list of formal
3691<a href="#Argument"><tt>Argument</tt></a>s, and a
3692<a href="#SymbolTable"><tt>SymbolTable</tt></a>.</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3693
3694<p>The list of <a href="#BasicBlock"><tt>BasicBlock</tt></a>s is the most
3695commonly used part of <tt>Function</tt> objects. The list imposes an implicit
3696ordering of the blocks in the function, which indicate how the code will be
Benjamin Kramer8040cd32009-10-12 14:46:08 +0000[diff] [blame]3697laid out by the backend. Additionally, the first <a
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3698href="#BasicBlock"><tt>BasicBlock</tt></a> is the implicit entry node for the
3699<tt>Function</tt>. It is not legal in LLVM to explicitly branch to this initial
3700block. There are no implicit exit nodes, and in fact there may be multiple exit
3701nodes from a single <tt>Function</tt>. If the <a
3702href="#BasicBlock"><tt>BasicBlock</tt></a> list is empty, this indicates that
3703the <tt>Function</tt> is actually a function declaration: the actual body of the
3704function hasn't been linked in yet.</p>
3705
3706<p>In addition to a list of <a href="#BasicBlock"><tt>BasicBlock</tt></a>s, the
3707<tt>Function</tt> class also keeps track of the list of formal <a
3708href="#Argument"><tt>Argument</tt></a>s that the function receives. This
3709container manages the lifetime of the <a href="#Argument"><tt>Argument</tt></a>
3710nodes, just like the <a href="#BasicBlock"><tt>BasicBlock</tt></a> list does for
3711the <a href="#BasicBlock"><tt>BasicBlock</tt></a>s.</p>
3712
3713<p>The <a href="#SymbolTable"><tt>SymbolTable</tt></a> is a very rarely used
3714LLVM feature that is only used when you have to look up a value by name. Aside
3715from that, the <a href="#SymbolTable"><tt>SymbolTable</tt></a> is used
3716internally to make sure that there are not conflicts between the names of <a
3717href="#Instruction"><tt>Instruction</tt></a>s, <a
3718href="#BasicBlock"><tt>BasicBlock</tt></a>s, or <a
3719href="#Argument"><tt>Argument</tt></a>s in the function body.</p>
3720
Reid Spencer8b2da7a2004-07-18 13:10:31 +0000[diff] [blame]3721<p>Note that <tt>Function</tt> is a <a href="#GlobalValue">GlobalValue</a>
3722and therefore also a <a href="#Constant">Constant</a>. The value of the function
3723is its address (after linking) which is guaranteed to be constant.</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3724</div>
3725
3726<!-- _______________________________________________________________________ -->
3727<div class="doc_subsubsection">
3728 <a name="m_Function">Important Public Members of the <tt>Function</tt>
3729 class</a>
3730</div>
3731
3732<div class="doc_text">
3733
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3734<ul>
3735 <li><tt>Function(const </tt><tt><a href="#FunctionType">FunctionType</a>
Chris Lattnerac479e52004-08-04 05:10:48 +0000[diff] [blame]3736 *Ty, LinkageTypes Linkage, const std::string &amp;N = "", Module* Parent = 0)</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3737
3738 <p>Constructor used when you need to create new <tt>Function</tt>s to add
3739 the the program. The constructor must specify the type of the function to
Chris Lattnerac479e52004-08-04 05:10:48 +0000[diff] [blame]3740 create and what type of linkage the function should have. The <a
3741 href="#FunctionType"><tt>FunctionType</tt></a> argument
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3742 specifies the formal arguments and return value for the function. The same
Duncan Sands8036ca42007-03-30 12:22:09 +0000[diff] [blame]3743 <a href="#FunctionType"><tt>FunctionType</tt></a> value can be used to
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3744 create multiple functions. The <tt>Parent</tt> argument specifies the Module
3745 in which the function is defined. If this argument is provided, the function
3746 will automatically be inserted into that module's list of
3747 functions.</p></li>
3748
Chris Lattner62810e32008-11-25 18:34:50 +0000[diff] [blame]3749 <li><tt>bool isDeclaration()</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3750
3751 <p>Return whether or not the <tt>Function</tt> has a body defined. If the
3752 function is "external", it does not have a body, and thus must be resolved
3753 by linking with a function defined in a different translation unit.</p></li>
3754
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3755 <li><tt>Function::iterator</tt> - Typedef for basic block list iterator<br>
Chris Lattner9355b472002-09-06 02:50:58 +0000[diff] [blame]3756 <tt>Function::const_iterator</tt> - Typedef for const_iterator.<br>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3757
Chris Lattner77d69242005-03-15 05:19:20 +0000[diff] [blame]3758 <tt>begin()</tt>, <tt>end()</tt>
3759 <tt>size()</tt>, <tt>empty()</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3760
3761 <p>These are forwarding methods that make it easy to access the contents of
3762 a <tt>Function</tt> object's <a href="#BasicBlock"><tt>BasicBlock</tt></a>
3763 list.</p></li>
3764
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3765 <li><tt>Function::BasicBlockListType &amp;getBasicBlockList()</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3766
3767 <p>Returns the list of <a href="#BasicBlock"><tt>BasicBlock</tt></a>s. This
3768 is necessary to use when you need to update the list or perform a complex
3769 action that doesn't have a forwarding method.</p></li>
3770
Chris Lattner89cc2652005-03-15 04:48:32 +0000[diff] [blame]3771 <li><tt>Function::arg_iterator</tt> - Typedef for the argument list
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3772iterator<br>
Chris Lattner89cc2652005-03-15 04:48:32 +0000[diff] [blame]3773 <tt>Function::const_arg_iterator</tt> - Typedef for const_iterator.<br>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3774
Chris Lattner77d69242005-03-15 05:19:20 +0000[diff] [blame]3775 <tt>arg_begin()</tt>, <tt>arg_end()</tt>
Chris Lattner89cc2652005-03-15 04:48:32 +0000[diff] [blame]3776 <tt>arg_size()</tt>, <tt>arg_empty()</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3777
3778 <p>These are forwarding methods that make it easy to access the contents of
3779 a <tt>Function</tt> object's <a href="#Argument"><tt>Argument</tt></a>
3780 list.</p></li>
3781
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3782 <li><tt>Function::ArgumentListType &amp;getArgumentList()</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3783
3784 <p>Returns the list of <a href="#Argument"><tt>Argument</tt></a>s. This is
3785 necessary to use when you need to update the list or perform a complex
3786 action that doesn't have a forwarding method.</p></li>
3787
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3788 <li><tt><a href="#BasicBlock">BasicBlock</a> &amp;getEntryBlock()</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3789
3790 <p>Returns the entry <a href="#BasicBlock"><tt>BasicBlock</tt></a> for the
3791 function. Because the entry block for the function is always the first
3792 block, this returns the first block of the <tt>Function</tt>.</p></li>
3793
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3794 <li><tt><a href="#Type">Type</a> *getReturnType()</tt><br>
3795 <tt><a href="#FunctionType">FunctionType</a> *getFunctionType()</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3796
3797 <p>This traverses the <a href="#Type"><tt>Type</tt></a> of the
3798 <tt>Function</tt> and returns the return type of the function, or the <a
3799 href="#FunctionType"><tt>FunctionType</tt></a> of the actual
3800 function.</p></li>
3801
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3802 <li><tt><a href="#SymbolTable">SymbolTable</a> *getSymbolTable()</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3803
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3804 <p> Return a pointer to the <a href="#SymbolTable"><tt>SymbolTable</tt></a>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3805 for this <tt>Function</tt>.</p></li>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3806</ul>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3807
3808</div>
3809
3810<!-- ======================================================================= -->
3811<div class="doc_subsection">
3812 <a name="GlobalVariable">The <tt>GlobalVariable</tt> class</a>
3813</div>
3814
3815<div class="doc_text">
3816
3817<p><tt>#include "<a
3818href="/doxygen/GlobalVariable_8h-source.html">llvm/GlobalVariable.h</a>"</tt>
3819<br>
Tanya Lattnera3da7772004-06-22 08:02:25 +0000[diff] [blame]3820doxygen info: <a href="/doxygen/classllvm_1_1GlobalVariable.html">GlobalVariable
Reid Spencerbe5e85e2006-04-14 14:11:48 +0000[diff] [blame]3821 Class</a><br>
3822Superclasses: <a href="#GlobalValue"><tt>GlobalValue</tt></a>,
3823<a href="#Constant"><tt>Constant</tt></a>,
3824<a href="#User"><tt>User</tt></a>,
3825<a href="#Value"><tt>Value</tt></a></p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3826
Benjamin Kramer8040cd32009-10-12 14:46:08 +0000[diff] [blame]3827<p>Global variables are represented with the (surprise surprise)
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3828<tt>GlobalVariable</tt> class. Like functions, <tt>GlobalVariable</tt>s are also
3829subclasses of <a href="#GlobalValue"><tt>GlobalValue</tt></a>, and as such are
3830always referenced by their address (global values must live in memory, so their
Reid Spencerbe5e85e2006-04-14 14:11:48 +0000[diff] [blame]3831"name" refers to their constant address). See
3832<a href="#GlobalValue"><tt>GlobalValue</tt></a> for more on this. Global
3833variables may have an initial value (which must be a
3834<a href="#Constant"><tt>Constant</tt></a>), and if they have an initializer,
3835they may be marked as "constant" themselves (indicating that their contents
3836never change at runtime).</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3837</div>
3838
3839<!-- _______________________________________________________________________ -->
3840<div class="doc_subsubsection">
3841 <a name="m_GlobalVariable">Important Public Members of the
3842 <tt>GlobalVariable</tt> class</a>
3843</div>
3844
3845<div class="doc_text">
3846
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3847<ul>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3848 <li><tt>GlobalVariable(const </tt><tt><a href="#Type">Type</a> *Ty, bool
3849 isConstant, LinkageTypes&amp; Linkage, <a href="#Constant">Constant</a>
3850 *Initializer = 0, const std::string &amp;Name = "", Module* Parent = 0)</tt>
3851
3852 <p>Create a new global variable of the specified type. If
3853 <tt>isConstant</tt> is true then the global variable will be marked as
3854 unchanging for the program. The Linkage parameter specifies the type of
Duncan Sands667d4b82009-03-07 15:45:40 +0000[diff] [blame]3855 linkage (internal, external, weak, linkonce, appending) for the variable.
3856 If the linkage is InternalLinkage, WeakAnyLinkage, WeakODRLinkage,
3857 LinkOnceAnyLinkage or LinkOnceODRLinkage,&nbsp; then the resultant
3858 global variable will have internal linkage. AppendingLinkage concatenates
3859 together all instances (in different translation units) of the variable
3860 into a single variable but is only applicable to arrays. &nbsp;See
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3861 the <a href="LangRef.html#modulestructure">LLVM Language Reference</a> for
3862 further details on linkage types. Optionally an initializer, a name, and the
3863 module to put the variable into may be specified for the global variable as
3864 well.</p></li>
3865
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3866 <li><tt>bool isConstant() const</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3867
3868 <p>Returns true if this is a global variable that is known not to
3869 be modified at runtime.</p></li>
3870
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3871 <li><tt>bool hasInitializer()</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3872
3873 <p>Returns true if this <tt>GlobalVariable</tt> has an intializer.</p></li>
3874
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3875 <li><tt><a href="#Constant">Constant</a> *getInitializer()</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3876
Benjamin Kramer8040cd32009-10-12 14:46:08 +0000[diff] [blame]3877 <p>Returns the initial value for a <tt>GlobalVariable</tt>. It is not legal
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3878 to call this method if there is no initializer.</p></li>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3879</ul>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3880
3881</div>
3882
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]3883
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3884<!-- ======================================================================= -->
3885<div class="doc_subsection">
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]3886 <a name="BasicBlock">The <tt>BasicBlock</tt> class</a>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3887</div>
3888
3889<div class="doc_text">
3890
3891<p><tt>#include "<a
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]3892href="/doxygen/BasicBlock_8h-source.html">llvm/BasicBlock.h</a>"</tt><br>
Stefanus Du Toit24e04112009-06-17 21:12:26 +0000[diff] [blame]3893doxygen info: <a href="/doxygen/classllvm_1_1BasicBlock.html">BasicBlock
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]3894Class</a><br>
3895Superclass: <a href="#Value"><tt>Value</tt></a></p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3896
Nick Lewyckyccd279d2011-02-17 02:19:22 +0000[diff] [blame]3897<p>This class represents a single entry single exit section of the code,
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]3898commonly known as a basic block by the compiler community. The
3899<tt>BasicBlock</tt> class maintains a list of <a
3900href="#Instruction"><tt>Instruction</tt></a>s, which form the body of the block.
3901Matching the language definition, the last element of this list of instructions
3902is always a terminator instruction (a subclass of the <a
3903href="#TerminatorInst"><tt>TerminatorInst</tt></a> class).</p>
3904
3905<p>In addition to tracking the list of instructions that make up the block, the
3906<tt>BasicBlock</tt> class also keeps track of the <a
3907href="#Function"><tt>Function</tt></a> that it is embedded into.</p>
3908
3909<p>Note that <tt>BasicBlock</tt>s themselves are <a
3910href="#Value"><tt>Value</tt></a>s, because they are referenced by instructions
3911like branches and can go in the switch tables. <tt>BasicBlock</tt>s have type
3912<tt>label</tt>.</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3913
3914</div>
3915
3916<!-- _______________________________________________________________________ -->
3917<div class="doc_subsubsection">
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]3918 <a name="m_BasicBlock">Important Public Members of the <tt>BasicBlock</tt>
3919 class</a>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3920</div>
3921
3922<div class="doc_text">
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3923<ul>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3924
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]3925<li><tt>BasicBlock(const std::string &amp;Name = "", </tt><tt><a
3926 href="#Function">Function</a> *Parent = 0)</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3927
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]3928<p>The <tt>BasicBlock</tt> constructor is used to create new basic blocks for
3929insertion into a function. The constructor optionally takes a name for the new
3930block, and a <a href="#Function"><tt>Function</tt></a> to insert it into. If
3931the <tt>Parent</tt> parameter is specified, the new <tt>BasicBlock</tt> is
3932automatically inserted at the end of the specified <a
3933href="#Function"><tt>Function</tt></a>, if not specified, the BasicBlock must be
3934manually inserted into the <a href="#Function"><tt>Function</tt></a>.</p></li>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3935
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]3936<li><tt>BasicBlock::iterator</tt> - Typedef for instruction list iterator<br>
3937<tt>BasicBlock::const_iterator</tt> - Typedef for const_iterator.<br>
3938<tt>begin()</tt>, <tt>end()</tt>, <tt>front()</tt>, <tt>back()</tt>,
3939<tt>size()</tt>, <tt>empty()</tt>
3940STL-style functions for accessing the instruction list.
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3941
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]3942<p>These methods and typedefs are forwarding functions that have the same
3943semantics as the standard library methods of the same names. These methods
3944expose the underlying instruction list of a basic block in a way that is easy to
3945manipulate. To get the full complement of container operations (including
3946operations to update the list), you must use the <tt>getInstList()</tt>
3947method.</p></li>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3948
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]3949<li><tt>BasicBlock::InstListType &amp;getInstList()</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3950
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]3951<p>This method is used to get access to the underlying container that actually
3952holds the Instructions. This method must be used when there isn't a forwarding
3953function in the <tt>BasicBlock</tt> class for the operation that you would like
3954to perform. Because there are no forwarding functions for "updating"
3955operations, you need to use this if you want to update the contents of a
3956<tt>BasicBlock</tt>.</p></li>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3957
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]3958<li><tt><a href="#Function">Function</a> *getParent()</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3959
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]3960<p> Returns a pointer to <a href="#Function"><tt>Function</tt></a> the block is
3961embedded into, or a null pointer if it is homeless.</p></li>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3962
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]3963<li><tt><a href="#TerminatorInst">TerminatorInst</a> *getTerminator()</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3964
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]3965<p> Returns a pointer to the terminator instruction that appears at the end of
3966the <tt>BasicBlock</tt>. If there is no terminator instruction, or if the last
3967instruction in the block is not a terminator, then a null pointer is
3968returned.</p></li>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3969
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3970</ul>
3971
3972</div>
3973
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3974
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3975<!-- ======================================================================= -->
3976<div class="doc_subsection">
3977 <a name="Argument">The <tt>Argument</tt> class</a>
3978</div>
3979
3980<div class="doc_text">
3981
3982<p>This subclass of Value defines the interface for incoming formal
Chris Lattner58360822005-01-17 00:12:04 +0000[diff] [blame]3983arguments to a function. A Function maintains a list of its formal
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3984arguments. An argument has a pointer to the parent Function.</p>
3985
3986</div>
3987
Chris Lattner9355b472002-09-06 02:50:58 +0000[diff] [blame]3988<!-- *********************************************************************** -->
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3989<hr>
3990<address>
3991 <a href="http://jigsaw.w3.org/css-validator/check/referer"><img
Misha Brukman44408702008-12-11 17:34:48 +0000[diff] [blame]3992 src="http://jigsaw.w3.org/css-validator/images/vcss-blue" alt="Valid CSS"></a>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3993 <a href="http://validator.w3.org/check/referer"><img
Gabor Greifa9c0f2b2008-06-18 14:05:31 +0000[diff] [blame]3994 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]3995
3996 <a href="mailto:dhurjati@cs.uiuc.edu">Dinakar Dhurjati</a> and
3997 <a href="mailto:sabre@nondot.org">Chris Lattner</a><br>
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]3998 <a href="http://llvm.org">The LLVM Compiler Infrastructure</a><br>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3999 Last modified: $Date$
4000</address>
4001
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]4002</body>
4003</html>