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4<head>
5 <title>LLVM Programmer's Manual</title>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]6 <link rel="stylesheet" href="llvm.css" type="text/css">
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]7</head>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]8<body>
9
10<div class="doc_title">
11 LLVM Programmer's Manual
12</div>
13
Chris Lattner9355b472002-09-06 02:50:58 +0000[diff] [blame]14<ol>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]15 <li><a href="#introduction">Introduction</a></li>
Chris Lattner9355b472002-09-06 02:50:58 +0000[diff] [blame]16 <li><a href="#general">General Information</a>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]17 <ul>
Reid Spencerfe8f4ff2004-11-01 09:02:53 +0000[diff] [blame]18 <li><a href="#stl">The C++ Standard Template Library</a></li>
19<!--
20 <li>The <tt>-time-passes</tt> option</li>
21 <li>How to use the LLVM Makefile system</li>
22 <li>How to write a regression test</li>
Chris Lattner61db4652004-12-08 19:05:44 +0000[diff] [blame]23
Reid Spencerfe8f4ff2004-11-01 09:02:53 +0000[diff] [blame]24-->
Chris Lattner84b7f8d2003-08-01 22:20:59 +0000[diff] [blame]25 </ul>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]26 </li>
27 <li><a href="#apis">Important and useful LLVM APIs</a>
28 <ul>
29 <li><a href="#isa">The <tt>isa&lt;&gt;</tt>, <tt>cast&lt;&gt;</tt>
30and <tt>dyn_cast&lt;&gt;</tt> templates</a> </li>
Misha Brukman2c122ce2005-11-01 21:12:49 +0000[diff] [blame]31 <li><a href="#DEBUG">The <tt>DEBUG()</tt> macro and <tt>-debug</tt>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]32option</a>
33 <ul>
34 <li><a href="#DEBUG_TYPE">Fine grained debug info with <tt>DEBUG_TYPE</tt>
35and the <tt>-debug-only</tt> option</a> </li>
36 </ul>
37 </li>
Chris Lattner0be6fdf2006-12-19 21:46:21 +0000[diff] [blame]38 <li><a href="#Statistic">The <tt>Statistic</tt> class &amp; <tt>-stats</tt>
Reid Spencerfe8f4ff2004-11-01 09:02:53 +0000[diff] [blame]39option</a></li>
40<!--
41 <li>The <tt>InstVisitor</tt> template
42 <li>The general graph API
43-->
Chris Lattnerf623a082005-10-17 01:36:23 +0000[diff] [blame]44 <li><a href="#ViewGraph">Viewing graphs while debugging code</a></li>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]45 </ul>
46 </li>
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]47 <li><a href="#datastructure">Picking the Right Data Structure for a Task</a>
48 <ul>
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]49 <li><a href="#ds_sequential">Sequential Containers (std::vector, std::list, etc)</a>
50 <ul>
51 <li><a href="#dss_fixedarrays">Fixed Size Arrays</a></li>
52 <li><a href="#dss_heaparrays">Heap Allocated Arrays</a></li>
53 <li><a href="#dss_smallvector">"llvm/ADT/SmallVector.h"</a></li>
54 <li><a href="#dss_vector">&lt;vector&gt;</a></li>
55 <li><a href="#dss_deque">&lt;deque&gt;</a></li>
56 <li><a href="#dss_list">&lt;list&gt;</a></li>
Gabor Greif3899e492009-02-27 11:37:41 +0000[diff] [blame]57 <li><a href="#dss_ilist">llvm/ADT/ilist.h</a></li>
Chris Lattnerc5722432007-02-03 19:49:31 +0000[diff] [blame]58 <li><a href="#dss_other">Other Sequential Container Options</a></li>
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]59 </ul></li>
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]60 <li><a href="#ds_set">Set-Like Containers (std::set, SmallSet, SetVector, etc)</a>
61 <ul>
62 <li><a href="#dss_sortedvectorset">A sorted 'vector'</a></li>
63 <li><a href="#dss_smallset">"llvm/ADT/SmallSet.h"</a></li>
64 <li><a href="#dss_smallptrset">"llvm/ADT/SmallPtrSet.h"</a></li>
Chris Lattnerc28476f2007-09-30 00:58:59 +0000[diff] [blame]65 <li><a href="#dss_denseset">"llvm/ADT/DenseSet.h"</a></li>
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]66 <li><a href="#dss_FoldingSet">"llvm/ADT/FoldingSet.h"</a></li>
67 <li><a href="#dss_set">&lt;set&gt;</a></li>
68 <li><a href="#dss_setvector">"llvm/ADT/SetVector.h"</a></li>
Chris Lattnerc5722432007-02-03 19:49:31 +0000[diff] [blame]69 <li><a href="#dss_uniquevector">"llvm/ADT/UniqueVector.h"</a></li>
70 <li><a href="#dss_otherset">Other Set-Like ContainerOptions</a></li>
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]71 </ul></li>
Chris Lattnerf3692522007-02-03 19:51:56 +0000[diff] [blame]72 <li><a href="#ds_map">Map-Like Containers (std::map, DenseMap, etc)</a>
73 <ul>
74 <li><a href="#dss_sortedvectormap">A sorted 'vector'</a></li>
Chris Lattner796f9fa2007-02-08 19:14:21 +0000[diff] [blame]75 <li><a href="#dss_stringmap">"llvm/ADT/StringMap.h"</a></li>
Chris Lattnerf3692522007-02-03 19:51:56 +0000[diff] [blame]76 <li><a href="#dss_indexedmap">"llvm/ADT/IndexedMap.h"</a></li>
77 <li><a href="#dss_densemap">"llvm/ADT/DenseMap.h"</a></li>
78 <li><a href="#dss_map">&lt;map&gt;</a></li>
79 <li><a href="#dss_othermap">Other Map-Like Container Options</a></li>
80 </ul></li>
Daniel Berlin1939ace2007-09-24 17:52:25 +0000[diff] [blame]81 <li><a href="#ds_bit">BitVector-like containers</a>
82 <ul>
83 <li><a href="#dss_bitvector">A dense bitvector</a></li>
84 <li><a href="#dss_sparsebitvector">A sparse bitvector</a></li>
85 </ul></li>
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]86 </ul>
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]87 </li>
Chris Lattnerae7f7592002-09-06 18:31:18 +0000[diff] [blame]88 <li><a href="#common">Helpful Hints for Common Operations</a>
Chris Lattnerae7f7592002-09-06 18:31:18 +0000[diff] [blame]89 <ul>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]90 <li><a href="#inspection">Basic Inspection and Traversal Routines</a>
91 <ul>
92 <li><a href="#iterate_function">Iterating over the <tt>BasicBlock</tt>s
93in a <tt>Function</tt></a> </li>
94 <li><a href="#iterate_basicblock">Iterating over the <tt>Instruction</tt>s
95in a <tt>BasicBlock</tt></a> </li>
96 <li><a href="#iterate_institer">Iterating over the <tt>Instruction</tt>s
97in a <tt>Function</tt></a> </li>
98 <li><a href="#iterate_convert">Turning an iterator into a
99class pointer</a> </li>
100 <li><a href="#iterate_complex">Finding call sites: a more
101complex example</a> </li>
102 <li><a href="#calls_and_invokes">Treating calls and invokes
103the same way</a> </li>
104 <li><a href="#iterate_chains">Iterating over def-use &amp;
105use-def chains</a> </li>
Chris Lattner2e438ca2008-01-03 16:56:04 +0000[diff] [blame]106 <li><a href="#iterate_preds">Iterating over predecessors &amp;
107successors of blocks</a></li>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]108 </ul>
109 </li>
110 <li><a href="#simplechanges">Making simple changes</a>
111 <ul>
112 <li><a href="#schanges_creating">Creating and inserting new
113 <tt>Instruction</tt>s</a> </li>
114 <li><a href="#schanges_deleting">Deleting <tt>Instruction</tt>s</a> </li>
115 <li><a href="#schanges_replacing">Replacing an <tt>Instruction</tt>
116with another <tt>Value</tt></a> </li>
Tanya Lattnerb011c662007-06-20 18:33:15 +0000[diff] [blame]117 <li><a href="#schanges_deletingGV">Deleting <tt>GlobalVariable</tt>s</a> </li>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]118 </ul>
Reid Spencerfe8f4ff2004-11-01 09:02:53 +0000[diff] [blame]119 </li>
Jeffrey Yasskin714257f2009-04-30 22:33:41 +0000[diff] [blame]120 <li><a href="#create_types">How to Create Types</a></li>
Chris Lattnerae7f7592002-09-06 18:31:18 +0000[diff] [blame]121<!--
122 <li>Working with the Control Flow Graph
123 <ul>
124 <li>Accessing predecessors and successors of a <tt>BasicBlock</tt>
125 <li>
126 <li>
127 </ul>
Reid Spencerfe8f4ff2004-11-01 09:02:53 +0000[diff] [blame]128-->
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]129 </ul>
130 </li>
Chris Lattnerd9d6e102005-04-23 16:10:52 +0000[diff] [blame]131
132 <li><a href="#advanced">Advanced Topics</a>
133 <ul>
Chris Lattnerf1b200b2005-04-23 17:27:36 +0000[diff] [blame]134 <li><a href="#TypeResolve">LLVM Type Resolution</a>
135 <ul>
136 <li><a href="#BuildRecType">Basic Recursive Type Construction</a></li>
137 <li><a href="#refineAbstractTypeTo">The <tt>refineAbstractTypeTo</tt> method</a></li>
138 <li><a href="#PATypeHolder">The PATypeHolder Class</a></li>
139 <li><a href="#AbstractTypeUser">The AbstractTypeUser Class</a></li>
140 </ul></li>
141
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]142 <li><a href="#SymbolTable">The <tt>ValueSymbolTable</tt> and <tt>TypeSymbolTable</tt> classes</a></li>
143 <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]144 </ul></li>
145
Joel Stanley9b96c442002-09-06 21:55:13 +0000[diff] [blame]146 <li><a href="#coreclasses">The Core LLVM Class Hierarchy Reference</a>
Chris Lattner9355b472002-09-06 02:50:58 +0000[diff] [blame]147 <ul>
Reid Spencer303c4b42007-01-12 17:26:25 +0000[diff] [blame]148 <li><a href="#Type">The <tt>Type</tt> class</a> </li>
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]149 <li><a href="#Module">The <tt>Module</tt> class</a></li>
Reid Spencerfe8f4ff2004-11-01 09:02:53 +0000[diff] [blame]150 <li><a href="#Value">The <tt>Value</tt> class</a>
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]151 <ul>
152 <li><a href="#User">The <tt>User</tt> class</a>
Chris Lattner9355b472002-09-06 02:50:58 +0000[diff] [blame]153 <ul>
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]154 <li><a href="#Instruction">The <tt>Instruction</tt> class</a></li>
155 <li><a href="#Constant">The <tt>Constant</tt> class</a>
156 <ul>
157 <li><a href="#GlobalValue">The <tt>GlobalValue</tt> class</a>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]158 <ul>
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]159 <li><a href="#Function">The <tt>Function</tt> class</a></li>
160 <li><a href="#GlobalVariable">The <tt>GlobalVariable</tt> class</a></li>
161 </ul>
162 </li>
163 </ul>
164 </li>
Reid Spencerfe8f4ff2004-11-01 09:02:53 +0000[diff] [blame]165 </ul>
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]166 </li>
167 <li><a href="#BasicBlock">The <tt>BasicBlock</tt> class</a></li>
168 <li><a href="#Argument">The <tt>Argument</tt> class</a></li>
169 </ul>
Reid Spencerfe8f4ff2004-11-01 09:02:53 +0000[diff] [blame]170 </li>
171 </ul>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]172 </li>
Chris Lattner9355b472002-09-06 02:50:58 +0000[diff] [blame]173</ol>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]174
Chris Lattner69bf8a92004-05-23 21:06:58 +0000[diff] [blame]175<div class="doc_author">
176 <p>Written by <a href="mailto:sabre@nondot.org">Chris Lattner</a>,
Chris Lattner94c43592004-05-26 16:52:55 +0000[diff] [blame]177 <a href="mailto:dhurjati@cs.uiuc.edu">Dinakar Dhurjati</a>,
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]178 <a href="mailto:ggreif@gmail.com">Gabor Greif</a>,
179 <a href="mailto:jstanley@cs.uiuc.edu">Joel Stanley</a> and
Chris Lattner94c43592004-05-26 16:52:55 +0000[diff] [blame]180 <a href="mailto:rspencer@x10sys.com">Reid Spencer</a></p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]181</div>
182
Chris Lattner9355b472002-09-06 02:50:58 +0000[diff] [blame]183<!-- *********************************************************************** -->
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]184<div class="doc_section">
185 <a name="introduction">Introduction </a>
186</div>
Chris Lattner9355b472002-09-06 02:50:58 +0000[diff] [blame]187<!-- *********************************************************************** -->
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]188
189<div class="doc_text">
190
191<p>This document is meant to highlight some of the important classes and
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]192interfaces available in the LLVM source-base. This manual is not
193intended to explain what LLVM is, how it works, and what LLVM code looks
194like. It assumes that you know the basics of LLVM and are interested
195in writing transformations or otherwise analyzing or manipulating the
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]196code.</p>
197
198<p>This document should get you oriented so that you can find your
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]199way in the continuously growing source code that makes up the LLVM
200infrastructure. Note that this manual is not intended to serve as a
201replacement for reading the source code, so if you think there should be
202a method in one of these classes to do something, but it's not listed,
203check the source. Links to the <a href="/doxygen/">doxygen</a> sources
204are provided to make this as easy as possible.</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]205
206<p>The first section of this document describes general information that is
207useful to know when working in the LLVM infrastructure, and the second describes
208the Core LLVM classes. In the future this manual will be extended with
209information describing how to use extension libraries, such as dominator
210information, CFG traversal routines, and useful utilities like the <tt><a
211href="/doxygen/InstVisitor_8h-source.html">InstVisitor</a></tt> template.</p>
212
213</div>
214
Chris Lattner9355b472002-09-06 02:50:58 +0000[diff] [blame]215<!-- *********************************************************************** -->
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]216<div class="doc_section">
217 <a name="general">General Information</a>
218</div>
219<!-- *********************************************************************** -->
220
221<div class="doc_text">
222
223<p>This section contains general information that is useful if you are working
224in the LLVM source-base, but that isn't specific to any particular API.</p>
225
226</div>
227
228<!-- ======================================================================= -->
229<div class="doc_subsection">
230 <a name="stl">The C++ Standard Template Library</a>
231</div>
232
233<div class="doc_text">
234
235<p>LLVM makes heavy use of the C++ Standard Template Library (STL),
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]236perhaps much more than you are used to, or have seen before. Because of
237this, you might want to do a little background reading in the
238techniques used and capabilities of the library. There are many good
239pages that discuss the STL, and several books on the subject that you
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]240can get, so it will not be discussed in this document.</p>
241
242<p>Here are some useful links:</p>
243
244<ol>
245
246<li><a href="http://www.dinkumware.com/refxcpp.html">Dinkumware C++ Library
247reference</a> - an excellent reference for the STL and other parts of the
248standard C++ library.</li>
249
250<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]251O'Reilly book in the making. It has a decent Standard Library
252Reference that rivals Dinkumware's, and is unfortunately no longer free since the
253book has been published.</li>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]254
255<li><a href="http://www.parashift.com/c++-faq-lite/">C++ Frequently Asked
256Questions</a></li>
257
258<li><a href="http://www.sgi.com/tech/stl/">SGI's STL Programmer's Guide</a> -
259Contains a useful <a
260href="http://www.sgi.com/tech/stl/stl_introduction.html">Introduction to the
261STL</a>.</li>
262
263<li><a href="http://www.research.att.com/%7Ebs/C++.html">Bjarne Stroustrup's C++
264Page</a></li>
265
Tanya Lattner79445ba2004-12-08 18:34:56 +0000[diff] [blame]266<li><a href="http://64.78.49.204/">
Reid Spencer096603a2004-05-26 08:41:35 +0000[diff] [blame]267Bruce Eckel's Thinking in C++, 2nd ed. Volume 2 Revision 4.0 (even better, get
268the book).</a></li>
269
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]270</ol>
271
272<p>You are also encouraged to take a look at the <a
273href="CodingStandards.html">LLVM Coding Standards</a> guide which focuses on how
274to write maintainable code more than where to put your curly braces.</p>
275
276</div>
277
278<!-- ======================================================================= -->
279<div class="doc_subsection">
280 <a name="stl">Other useful references</a>
281</div>
282
283<div class="doc_text">
284
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]285<ol>
286<li><a href="http://www.psc.edu/%7Esemke/cvs_branches.html">CVS
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]287Branch and Tag Primer</a></li>
Misha Brukmana0f71e42004-06-18 18:39:00 +0000[diff] [blame]288<li><a href="http://www.fortran-2000.com/ArnaudRecipes/sharedlib.html">Using
289static and shared libraries across platforms</a></li>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]290</ol>
291
292</div>
293
Chris Lattner9355b472002-09-06 02:50:58 +0000[diff] [blame]294<!-- *********************************************************************** -->
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]295<div class="doc_section">
296 <a name="apis">Important and useful LLVM APIs</a>
297</div>
298<!-- *********************************************************************** -->
299
300<div class="doc_text">
301
302<p>Here we highlight some LLVM APIs that are generally useful and good to
303know about when writing transformations.</p>
304
305</div>
306
307<!-- ======================================================================= -->
308<div class="doc_subsection">
Misha Brukman2c122ce2005-11-01 21:12:49 +0000[diff] [blame]309 <a name="isa">The <tt>isa&lt;&gt;</tt>, <tt>cast&lt;&gt;</tt> and
310 <tt>dyn_cast&lt;&gt;</tt> templates</a>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]311</div>
312
313<div class="doc_text">
314
315<p>The LLVM source-base makes extensive use of a custom form of RTTI.
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]316These templates have many similarities to the C++ <tt>dynamic_cast&lt;&gt;</tt>
317operator, but they don't have some drawbacks (primarily stemming from
318the fact that <tt>dynamic_cast&lt;&gt;</tt> only works on classes that
319have a v-table). Because they are used so often, you must know what they
320do and how they work. All of these templates are defined in the <a
Chris Lattner695b78b2005-04-26 22:56:16 +0000[diff] [blame]321 href="/doxygen/Casting_8h-source.html"><tt>llvm/Support/Casting.h</tt></a>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]322file (note that you very rarely have to include this file directly).</p>
323
324<dl>
325 <dt><tt>isa&lt;&gt;</tt>: </dt>
326
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]327 <dd><p>The <tt>isa&lt;&gt;</tt> operator works exactly like the Java
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]328 "<tt>instanceof</tt>" operator. It returns true or false depending on whether
329 a reference or pointer points to an instance of the specified class. This can
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]330 be very useful for constraint checking of various sorts (example below).</p>
331 </dd>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]332
333 <dt><tt>cast&lt;&gt;</tt>: </dt>
334
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]335 <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]336 converts a pointer or reference from a base class to a derived class, causing
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]337 an assertion failure if it is not really an instance of the right type. This
338 should be used in cases where you have some information that makes you believe
339 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]340 and <tt>cast&lt;&gt;</tt> template is:</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]341
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]342<div class="doc_code">
343<pre>
344static bool isLoopInvariant(const <a href="#Value">Value</a> *V, const Loop *L) {
345 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))
346 return true;
Chris Lattner69bf8a92004-05-23 21:06:58 +0000[diff] [blame]347
Bill Wendling82e2eea2006-10-11 18:00:22 +0000[diff] [blame]348 // <i>Otherwise, it must be an instruction...</i>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]349 return !L-&gt;contains(cast&lt;<a href="#Instruction">Instruction</a>&gt;(V)-&gt;getParent());
350}
351</pre>
352</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]353
354 <p>Note that you should <b>not</b> use an <tt>isa&lt;&gt;</tt> test followed
355 by a <tt>cast&lt;&gt;</tt>, for that use the <tt>dyn_cast&lt;&gt;</tt>
356 operator.</p>
357
358 </dd>
359
360 <dt><tt>dyn_cast&lt;&gt;</tt>:</dt>
361
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]362 <dd><p>The <tt>dyn_cast&lt;&gt;</tt> operator is a "checking cast" operation.
363 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]364 pointer to it (this operator does not work with references). If the operand is
365 not of the correct type, a null pointer is returned. Thus, this works very
Misha Brukman2c122ce2005-11-01 21:12:49 +0000[diff] [blame]366 much like the <tt>dynamic_cast&lt;&gt;</tt> operator in C++, and should be
367 used in the same circumstances. Typically, the <tt>dyn_cast&lt;&gt;</tt>
368 operator is used in an <tt>if</tt> statement or some other flow control
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]369 statement like this:</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]370
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]371<div class="doc_code">
372<pre>
373if (<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]374 // <i>...</i>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]375}
376</pre>
377</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]378
Misha Brukman2c122ce2005-11-01 21:12:49 +0000[diff] [blame]379 <p>This form of the <tt>if</tt> statement effectively combines together a call
380 to <tt>isa&lt;&gt;</tt> and a call to <tt>cast&lt;&gt;</tt> into one
381 statement, which is very convenient.</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]382
Misha Brukman2c122ce2005-11-01 21:12:49 +0000[diff] [blame]383 <p>Note that the <tt>dyn_cast&lt;&gt;</tt> operator, like C++'s
384 <tt>dynamic_cast&lt;&gt;</tt> or Java's <tt>instanceof</tt> operator, can be
385 abused. In particular, you should not use big chained <tt>if/then/else</tt>
386 blocks to check for lots of different variants of classes. If you find
387 yourself wanting to do this, it is much cleaner and more efficient to use the
388 <tt>InstVisitor</tt> class to dispatch over the instruction type directly.</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]389
Misha Brukman2c122ce2005-11-01 21:12:49 +0000[diff] [blame]390 </dd>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]391
Misha Brukman2c122ce2005-11-01 21:12:49 +0000[diff] [blame]392 <dt><tt>cast_or_null&lt;&gt;</tt>: </dt>
393
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]394 <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]395 <tt>cast&lt;&gt;</tt> operator, except that it allows for a null pointer as an
396 argument (which it then propagates). This can sometimes be useful, allowing
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]397 you to combine several null checks into one.</p></dd>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]398
Misha Brukman2c122ce2005-11-01 21:12:49 +0000[diff] [blame]399 <dt><tt>dyn_cast_or_null&lt;&gt;</tt>: </dt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]400
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]401 <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]402 <tt>dyn_cast&lt;&gt;</tt> operator, except that it allows for a null pointer
403 as an argument (which it then propagates). This can sometimes be useful,
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]404 allowing you to combine several null checks into one.</p></dd>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]405
Misha Brukman2c122ce2005-11-01 21:12:49 +0000[diff] [blame]406</dl>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]407
408<p>These five templates can be used with any classes, whether they have a
409v-table or not. To add support for these templates, you simply need to add
410<tt>classof</tt> static methods to the class you are interested casting
411to. Describing this is currently outside the scope of this document, but there
412are lots of examples in the LLVM source base.</p>
413
414</div>
415
416<!-- ======================================================================= -->
417<div class="doc_subsection">
Misha Brukman2c122ce2005-11-01 21:12:49 +0000[diff] [blame]418 <a name="DEBUG">The <tt>DEBUG()</tt> macro and <tt>-debug</tt> option</a>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]419</div>
420
421<div class="doc_text">
422
423<p>Often when working on your pass you will put a bunch of debugging printouts
424and other code into your pass. After you get it working, you want to remove
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]425it, 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]426across).</p>
427
428<p> Naturally, because of this, you don't want to delete the debug printouts,
429but you don't want them to always be noisy. A standard compromise is to comment
430them out, allowing you to enable them if you need them in the future.</p>
431
Chris Lattner695b78b2005-04-26 22:56:16 +0000[diff] [blame]432<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]433file provides a macro named <tt>DEBUG()</tt> that is a much nicer solution to
434this problem. Basically, you can put arbitrary code into the argument of the
435<tt>DEBUG</tt> macro, and it is only executed if '<tt>opt</tt>' (or any other
436tool) is run with the '<tt>-debug</tt>' command line argument:</p>
437
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]438<div class="doc_code">
439<pre>
Bill Wendling832171c2006-12-07 20:04:42 +0000[diff] [blame]440DOUT &lt;&lt; "I am here!\n";
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]441</pre>
442</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]443
444<p>Then you can run your pass like this:</p>
445
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]446<div class="doc_code">
447<pre>
448$ opt &lt; a.bc &gt; /dev/null -mypass
Bill Wendling82e2eea2006-10-11 18:00:22 +0000[diff] [blame]449<i>&lt;no output&gt;</i>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]450$ opt &lt; a.bc &gt; /dev/null -mypass -debug
451I am here!
452</pre>
453</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]454
455<p>Using the <tt>DEBUG()</tt> macro instead of a home-brewed solution allows you
456to not have to create "yet another" command line option for the debug output for
457your pass. Note that <tt>DEBUG()</tt> macros are disabled for optimized builds,
458so they do not cause a performance impact at all (for the same reason, they
459should also not contain side-effects!).</p>
460
461<p>One additional nice thing about the <tt>DEBUG()</tt> macro is that you can
462enable or disable it directly in gdb. Just use "<tt>set DebugFlag=0</tt>" or
463"<tt>set DebugFlag=1</tt>" from the gdb if the program is running. If the
464program hasn't been started yet, you can always just run it with
465<tt>-debug</tt>.</p>
466
467</div>
468
469<!-- _______________________________________________________________________ -->
470<div class="doc_subsubsection">
Chris Lattnerc9151082005-04-26 22:57:07 +0000[diff] [blame]471 <a name="DEBUG_TYPE">Fine grained debug info with <tt>DEBUG_TYPE</tt> and
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]472 the <tt>-debug-only</tt> option</a>
473</div>
474
475<div class="doc_text">
476
477<p>Sometimes you may find yourself in a situation where enabling <tt>-debug</tt>
478just turns on <b>too much</b> information (such as when working on the code
479generator). If you want to enable debug information with more fine-grained
480control, you define the <tt>DEBUG_TYPE</tt> macro and the <tt>-debug</tt> only
481option as follows:</p>
482
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]483<div class="doc_code">
484<pre>
Bill Wendling832171c2006-12-07 20:04:42 +0000[diff] [blame]485DOUT &lt;&lt; "No debug type\n";
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]486#undef DEBUG_TYPE
487#define DEBUG_TYPE "foo"
Bill Wendling832171c2006-12-07 20:04:42 +0000[diff] [blame]488DOUT &lt;&lt; "'foo' debug type\n";
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]489#undef DEBUG_TYPE
490#define DEBUG_TYPE "bar"
Bill Wendling832171c2006-12-07 20:04:42 +0000[diff] [blame]491DOUT &lt;&lt; "'bar' debug type\n";
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]492#undef DEBUG_TYPE
493#define DEBUG_TYPE ""
Bill Wendling832171c2006-12-07 20:04:42 +0000[diff] [blame]494DOUT &lt;&lt; "No debug type (2)\n";
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]495</pre>
496</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]497
498<p>Then you can run your pass like this:</p>
499
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]500<div class="doc_code">
501<pre>
502$ opt &lt; a.bc &gt; /dev/null -mypass
Bill Wendling82e2eea2006-10-11 18:00:22 +0000[diff] [blame]503<i>&lt;no output&gt;</i>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]504$ opt &lt; a.bc &gt; /dev/null -mypass -debug
505No debug type
506'foo' debug type
507'bar' debug type
508No debug type (2)
509$ opt &lt; a.bc &gt; /dev/null -mypass -debug-only=foo
510'foo' debug type
511$ opt &lt; a.bc &gt; /dev/null -mypass -debug-only=bar
512'bar' debug type
513</pre>
514</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]515
516<p>Of course, in practice, you should only set <tt>DEBUG_TYPE</tt> at the top of
517a 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]518you <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]519<tt>#undef</tt>'s). Also, you should use names more meaningful than "foo" and
520"bar", because there is no system in place to ensure that names do not
521conflict. If two different modules use the same string, they will all be turned
522on when the name is specified. This allows, for example, all debug information
523for instruction scheduling to be enabled with <tt>-debug-type=InstrSched</tt>,
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]524even if the source lives in multiple files.</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]525
526</div>
527
528<!-- ======================================================================= -->
529<div class="doc_subsection">
Chris Lattner0be6fdf2006-12-19 21:46:21 +0000[diff] [blame]530 <a name="Statistic">The <tt>Statistic</tt> class &amp; <tt>-stats</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]531 option</a>
532</div>
533
534<div class="doc_text">
535
536<p>The "<tt><a
Chris Lattner695b78b2005-04-26 22:56:16 +0000[diff] [blame]537href="/doxygen/Statistic_8h-source.html">llvm/ADT/Statistic.h</a></tt>" file
Chris Lattner0be6fdf2006-12-19 21:46:21 +0000[diff] [blame]538provides a class named <tt>Statistic</tt> that is used as a unified way to
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]539keep track of what the LLVM compiler is doing and how effective various
540optimizations are. It is useful to see what optimizations are contributing to
541making a particular program run faster.</p>
542
543<p>Often you may run your pass on some big program, and you're interested to see
544how many times it makes a certain transformation. Although you can do this with
545hand 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]546for big programs. Using the <tt>Statistic</tt> class makes it very easy to
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]547keep track of this information, and the calculated information is presented in a
548uniform manner with the rest of the passes being executed.</p>
549
550<p>There are many examples of <tt>Statistic</tt> uses, but the basics of using
551it are as follows:</p>
552
553<ol>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]554 <li><p>Define your statistic like this:</p>
555
556<div class="doc_code">
557<pre>
Chris Lattner0be6fdf2006-12-19 21:46:21 +0000[diff] [blame]558#define <a href="#DEBUG_TYPE">DEBUG_TYPE</a> "mypassname" <i>// This goes before any #includes.</i>
559STATISTIC(NumXForms, "The # of times I did stuff");
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]560</pre>
561</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]562
Chris Lattner0be6fdf2006-12-19 21:46:21 +0000[diff] [blame]563 <p>The <tt>STATISTIC</tt> macro defines a static variable, whose name is
564 specified by the first argument. The pass name is taken from the DEBUG_TYPE
565 macro, and the description is taken from the second argument. The variable
Reid Spencer06565dc2007-01-12 17:11:23 +0000[diff] [blame]566 defined ("NumXForms" in this case) acts like an unsigned integer.</p></li>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]567
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]568 <li><p>Whenever you make a transformation, bump the counter:</p>
569
570<div class="doc_code">
571<pre>
Bill Wendling82e2eea2006-10-11 18:00:22 +0000[diff] [blame]572++NumXForms; // <i>I did stuff!</i>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]573</pre>
574</div>
575
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]576 </li>
577 </ol>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]578
579 <p>That's all you have to do. To get '<tt>opt</tt>' to print out the
580 statistics gathered, use the '<tt>-stats</tt>' option:</p>
581
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]582<div class="doc_code">
583<pre>
584$ opt -stats -mypassname &lt; program.bc &gt; /dev/null
Bill Wendling82e2eea2006-10-11 18:00:22 +0000[diff] [blame]585<i>... statistics output ...</i>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]586</pre>
587</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]588
Reid Spencer6b6c73e2007-02-09 16:00:28 +0000[diff] [blame]589 <p> When running <tt>opt</tt> on a C file from the SPEC benchmark
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]590suite, it gives a report that looks like this:</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]591
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]592<div class="doc_code">
593<pre>
Gabor Greif04367bf2007-07-06 22:07:22 +0000[diff] [blame]594 7646 bitcodewriter - Number of normal instructions
595 725 bitcodewriter - Number of oversized instructions
596 129996 bitcodewriter - Number of bitcode bytes written
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]597 2817 raise - Number of insts DCEd or constprop'd
598 3213 raise - Number of cast-of-self removed
599 5046 raise - Number of expression trees converted
600 75 raise - Number of other getelementptr's formed
601 138 raise - Number of load/store peepholes
602 42 deadtypeelim - Number of unused typenames removed from symtab
603 392 funcresolve - Number of varargs functions resolved
604 27 globaldce - Number of global variables removed
605 2 adce - Number of basic blocks removed
606 134 cee - Number of branches revectored
607 49 cee - Number of setcc instruction eliminated
608 532 gcse - Number of loads removed
609 2919 gcse - Number of instructions removed
610 86 indvars - Number of canonical indvars added
611 87 indvars - Number of aux indvars removed
612 25 instcombine - Number of dead inst eliminate
613 434 instcombine - Number of insts combined
614 248 licm - Number of load insts hoisted
615 1298 licm - Number of insts hoisted to a loop pre-header
616 3 licm - Number of insts hoisted to multiple loop preds (bad, no loop pre-header)
617 75 mem2reg - Number of alloca's promoted
618 1444 cfgsimplify - Number of blocks simplified
619</pre>
620</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]621
622<p>Obviously, with so many optimizations, having a unified framework for this
623stuff is very nice. Making your pass fit well into the framework makes it more
624maintainable and useful.</p>
625
626</div>
627
Chris Lattnerf623a082005-10-17 01:36:23 +0000[diff] [blame]628<!-- ======================================================================= -->
629<div class="doc_subsection">
630 <a name="ViewGraph">Viewing graphs while debugging code</a>
631</div>
632
633<div class="doc_text">
634
635<p>Several of the important data structures in LLVM are graphs: for example
636CFGs made out of LLVM <a href="#BasicBlock">BasicBlock</a>s, CFGs made out of
637LLVM <a href="CodeGenerator.html#machinebasicblock">MachineBasicBlock</a>s, and
638<a href="CodeGenerator.html#selectiondag_intro">Instruction Selection
639DAGs</a>. In many cases, while debugging various parts of the compiler, it is
640nice to instantly visualize these graphs.</p>
641
642<p>LLVM provides several callbacks that are available in a debug build to do
643exactly that. If you call the <tt>Function::viewCFG()</tt> method, for example,
644the current LLVM tool will pop up a window containing the CFG for the function
645where each basic block is a node in the graph, and each node contains the
646instructions in the block. Similarly, there also exists
647<tt>Function::viewCFGOnly()</tt> (does not include the instructions), the
648<tt>MachineFunction::viewCFG()</tt> and <tt>MachineFunction::viewCFGOnly()</tt>,
649and the <tt>SelectionDAG::viewGraph()</tt> methods. Within GDB, for example,
Jim Laskey543a0ee2006-10-02 12:28:07 +0000[diff] [blame]650you can usually use something like <tt>call DAG.viewGraph()</tt> to pop
Chris Lattnerf623a082005-10-17 01:36:23 +0000[diff] [blame]651up a window. Alternatively, you can sprinkle calls to these functions in your
652code in places you want to debug.</p>
653
654<p>Getting this to work requires a small amount of configuration. On Unix
655systems with X11, install the <a href="http://www.graphviz.org">graphviz</a>
656toolkit, and make sure 'dot' and 'gv' are in your path. If you are running on
657Mac OS/X, download and install the Mac OS/X <a
658href="http://www.pixelglow.com/graphviz/">Graphviz program</a>, and add
Reid Spencer128a7a72007-02-03 21:06:43 +0000[diff] [blame]659<tt>/Applications/Graphviz.app/Contents/MacOS/</tt> (or wherever you install
Chris Lattnerf623a082005-10-17 01:36:23 +0000[diff] [blame]660it) to your path. Once in your system and path are set up, rerun the LLVM
661configure script and rebuild LLVM to enable this functionality.</p>
662
Jim Laskey543a0ee2006-10-02 12:28:07 +0000[diff] [blame]663<p><tt>SelectionDAG</tt> has been extended to make it easier to locate
664<i>interesting</i> nodes in large complex graphs. From gdb, if you
665<tt>call DAG.setGraphColor(<i>node</i>, "<i>color</i>")</tt>, then the
Reid Spencer128a7a72007-02-03 21:06:43 +0000[diff] [blame]666next <tt>call DAG.viewGraph()</tt> would highlight the node in the
Jim Laskey543a0ee2006-10-02 12:28:07 +0000[diff] [blame]667specified color (choices of colors can be found at <a
Chris Lattner302da1e2007-02-03 03:05:57 +0000[diff] [blame]668href="http://www.graphviz.org/doc/info/colors.html">colors</a>.) More
Jim Laskey543a0ee2006-10-02 12:28:07 +0000[diff] [blame]669complex node attributes can be provided with <tt>call
670DAG.setGraphAttrs(<i>node</i>, "<i>attributes</i>")</tt> (choices can be
671found at <a href="http://www.graphviz.org/doc/info/attrs.html">Graph
672Attributes</a>.) If you want to restart and clear all the current graph
673attributes, then you can <tt>call DAG.clearGraphAttrs()</tt>. </p>
674
Chris Lattnerf623a082005-10-17 01:36:23 +0000[diff] [blame]675</div>
676
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]677<!-- *********************************************************************** -->
678<div class="doc_section">
679 <a name="datastructure">Picking the Right Data Structure for a Task</a>
680</div>
681<!-- *********************************************************************** -->
682
683<div class="doc_text">
684
Reid Spencer128a7a72007-02-03 21:06:43 +0000[diff] [blame]685<p>LLVM has a plethora of data structures in the <tt>llvm/ADT/</tt> directory,
686 and we commonly use STL data structures. This section describes the trade-offs
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]687 you should consider when you pick one.</p>
688
689<p>
690The first step is a choose your own adventure: do you want a sequential
691container, a set-like container, or a map-like container? The most important
692thing when choosing a container is the algorithmic properties of how you plan to
693access the container. Based on that, you should use:</p>
694
695<ul>
Reid Spencer128a7a72007-02-03 21:06:43 +0000[diff] [blame]696<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]697 of an value based on another value. Map-like containers also support
698 efficient queries for containment (whether a key is in the map). Map-like
699 containers generally do not support efficient reverse mapping (values to
700 keys). If you need that, use two maps. Some map-like containers also
701 support efficient iteration through the keys in sorted order. Map-like
702 containers are the most expensive sort, only use them if you need one of
703 these capabilities.</li>
704
705<li>a <a href="#ds_set">set-like</a> container if you need to put a bunch of
706 stuff into a container that automatically eliminates duplicates. Some
707 set-like containers support efficient iteration through the elements in
708 sorted order. Set-like containers are more expensive than sequential
709 containers.
710</li>
711
712<li>a <a href="#ds_sequential">sequential</a> container provides
713 the most efficient way to add elements and keeps track of the order they are
714 added to the collection. They permit duplicates and support efficient
Reid Spencer128a7a72007-02-03 21:06:43 +0000[diff] [blame]715 iteration, but do not support efficient look-up based on a key.
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]716</li>
717
Daniel Berlin1939ace2007-09-24 17:52:25 +0000[diff] [blame]718<li>a <a href="#ds_bit">bit</a> container provides an efficient way to store and
719 perform set operations on sets of numeric id's, while automatically
720 eliminating duplicates. Bit containers require a maximum of 1 bit for each
721 identifier you want to store.
722</li>
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]723</ul>
724
725<p>
Reid Spencer128a7a72007-02-03 21:06:43 +0000[diff] [blame]726Once the proper category of container is determined, you can fine tune the
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]727memory use, constant factors, and cache behaviors of access by intelligently
Reid Spencer128a7a72007-02-03 21:06:43 +0000[diff] [blame]728picking a member of the category. Note that constant factors and cache behavior
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]729can be a big deal. If you have a vector that usually only contains a few
730elements (but could contain many), for example, it's much better to use
731<a href="#dss_smallvector">SmallVector</a> than <a href="#dss_vector">vector</a>
732. Doing so avoids (relatively) expensive malloc/free calls, which dwarf the
733cost of adding the elements to the container. </p>
734
735</div>
736
737<!-- ======================================================================= -->
738<div class="doc_subsection">
739 <a name="ds_sequential">Sequential Containers (std::vector, std::list, etc)</a>
740</div>
741
742<div class="doc_text">
743There are a variety of sequential containers available for you, based on your
744needs. Pick the first in this section that will do what you want.
745</div>
746
747<!-- _______________________________________________________________________ -->
748<div class="doc_subsubsection">
749 <a name="dss_fixedarrays">Fixed Size Arrays</a>
750</div>
751
752<div class="doc_text">
753<p>Fixed size arrays are very simple and very fast. They are good if you know
754exactly how many elements you have, or you have a (low) upper bound on how many
755you have.</p>
756</div>
757
758<!-- _______________________________________________________________________ -->
759<div class="doc_subsubsection">
760 <a name="dss_heaparrays">Heap Allocated Arrays</a>
761</div>
762
763<div class="doc_text">
764<p>Heap allocated arrays (new[] + delete[]) are also simple. They are good if
765the number of elements is variable, if you know how many elements you will need
766before the array is allocated, and if the array is usually large (if not,
767consider a <a href="#dss_smallvector">SmallVector</a>). The cost of a heap
768allocated array is the cost of the new/delete (aka malloc/free). Also note that
769if you are allocating an array of a type with a constructor, the constructor and
Reid Spencer128a7a72007-02-03 21:06:43 +0000[diff] [blame]770destructors will be run for every element in the array (re-sizable vectors only
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]771construct those elements actually used).</p>
772</div>
773
774<!-- _______________________________________________________________________ -->
775<div class="doc_subsubsection">
776 <a name="dss_smallvector">"llvm/ADT/SmallVector.h"</a>
777</div>
778
779<div class="doc_text">
780<p><tt>SmallVector&lt;Type, N&gt;</tt> is a simple class that looks and smells
781just like <tt>vector&lt;Type&gt;</tt>:
782it supports efficient iteration, lays out elements in memory order (so you can
783do pointer arithmetic between elements), supports efficient push_back/pop_back
784operations, supports efficient random access to its elements, etc.</p>
785
786<p>The advantage of SmallVector is that it allocates space for
787some number of elements (N) <b>in the object itself</b>. Because of this, if
788the SmallVector is dynamically smaller than N, no malloc is performed. This can
789be a big win in cases where the malloc/free call is far more expensive than the
790code that fiddles around with the elements.</p>
791
792<p>This is good for vectors that are "usually small" (e.g. the number of
793predecessors/successors of a block is usually less than 8). On the other hand,
794this makes the size of the SmallVector itself large, so you don't want to
795allocate lots of them (doing so will waste a lot of space). As such,
796SmallVectors are most useful when on the stack.</p>
797
798<p>SmallVector also provides a nice portable and efficient replacement for
799<tt>alloca</tt>.</p>
800
801</div>
802
803<!-- _______________________________________________________________________ -->
804<div class="doc_subsubsection">
805 <a name="dss_vector">&lt;vector&gt;</a>
806</div>
807
808<div class="doc_text">
809<p>
810std::vector is well loved and respected. It is useful when SmallVector isn't:
811when the size of the vector is often large (thus the small optimization will
812rarely be a benefit) or if you will be allocating many instances of the vector
813itself (which would waste space for elements that aren't in the container).
814vector is also useful when interfacing with code that expects vectors :).
815</p>
Chris Lattner32d84762007-02-05 06:30:51 +0000[diff] [blame]816
817<p>One worthwhile note about std::vector: avoid code like this:</p>
818
819<div class="doc_code">
820<pre>
821for ( ... ) {
Chris Lattner9bb3dbb2007-03-28 18:27:57 +0000[diff] [blame]822 std::vector&lt;foo&gt; V;
Chris Lattner32d84762007-02-05 06:30:51 +0000[diff] [blame]823 use V;
824}
825</pre>
826</div>
827
828<p>Instead, write this as:</p>
829
830<div class="doc_code">
831<pre>
Chris Lattner9bb3dbb2007-03-28 18:27:57 +0000[diff] [blame]832std::vector&lt;foo&gt; V;
Chris Lattner32d84762007-02-05 06:30:51 +0000[diff] [blame]833for ( ... ) {
834 use V;
835 V.clear();
836}
837</pre>
838</div>
839
840<p>Doing so will save (at least) one heap allocation and free per iteration of
841the loop.</p>
842
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]843</div>
844
845<!-- _______________________________________________________________________ -->
846<div class="doc_subsubsection">
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]847 <a name="dss_deque">&lt;deque&gt;</a>
848</div>
849
850<div class="doc_text">
851<p>std::deque is, in some senses, a generalized version of std::vector. Like
852std::vector, it provides constant time random access and other similar
853properties, but it also provides efficient access to the front of the list. It
854does not guarantee continuity of elements within memory.</p>
855
856<p>In exchange for this extra flexibility, std::deque has significantly higher
857constant factor costs than std::vector. If possible, use std::vector or
858something cheaper.</p>
859</div>
860
861<!-- _______________________________________________________________________ -->
862<div class="doc_subsubsection">
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]863 <a name="dss_list">&lt;list&gt;</a>
864</div>
865
866<div class="doc_text">
867<p>std::list is an extremely inefficient class that is rarely useful.
868It performs a heap allocation for every element inserted into it, thus having an
869extremely high constant factor, particularly for small data types. std::list
870also only supports bidirectional iteration, not random access iteration.</p>
871
872<p>In exchange for this high cost, std::list supports efficient access to both
873ends of the list (like std::deque, but unlike std::vector or SmallVector). In
874addition, the iterator invalidation characteristics of std::list are stronger
875than that of a vector class: inserting or removing an element into the list does
876not invalidate iterator or pointers to other elements in the list.</p>
877</div>
878
879<!-- _______________________________________________________________________ -->
880<div class="doc_subsubsection">
Gabor Greif3899e492009-02-27 11:37:41 +0000[diff] [blame]881 <a name="dss_ilist">llvm/ADT/ilist.h</a>
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]882</div>
883
884<div class="doc_text">
885<p><tt>ilist&lt;T&gt;</tt> implements an 'intrusive' doubly-linked list. It is
886intrusive, because it requires the element to store and provide access to the
887prev/next pointers for the list.</p>
888
Gabor Greif2946d1c2009-02-27 12:02:19 +0000[diff] [blame]889<p><tt>ilist</tt> has the same drawbacks as <tt>std::list</tt>, and additionally
890requires an <tt>ilist_traits</tt> implementation for the element type, but it
891provides some novel characteristics. In particular, it can efficiently store
892polymorphic objects, the traits class is informed when an element is inserted or
Gabor Greif0cbcabe2009-03-12 09:47:03 +0000[diff] [blame]893removed from the list, and <tt>ilist</tt>s are guaranteed to support a
894constant-time splice operation.</p>
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]895
Gabor Greif0cbcabe2009-03-12 09:47:03 +0000[diff] [blame]896<p>These properties are exactly what we want for things like
897<tt>Instruction</tt>s and basic blocks, which is why these are implemented with
898<tt>ilist</tt>s.</p>
Gabor Greif3899e492009-02-27 11:37:41 +0000[diff] [blame]899
900Related classes of interest are explained in the following subsections:
901 <ul>
Gabor Greif01862502009-02-27 13:28:07 +0000[diff] [blame]902 <li><a href="#dss_ilist_traits">ilist_traits</a></li>
Gabor Greif2946d1c2009-02-27 12:02:19 +0000[diff] [blame]903 <li><a href="#dss_iplist">iplist</a></li>
Gabor Greif3899e492009-02-27 11:37:41 +0000[diff] [blame]904 <li><a href="#dss_ilist_node">llvm/ADT/ilist_node.h</a></li>
Gabor Greif6a65f422009-03-12 10:30:31 +0000[diff] [blame]905 <li><a href="#dss_ilist_sentinel">Sentinels</a></li>
Gabor Greif3899e492009-02-27 11:37:41 +0000[diff] [blame]906 </ul>
907</div>
908
909<!-- _______________________________________________________________________ -->
910<div class="doc_subsubsection">
Gabor Greif01862502009-02-27 13:28:07 +0000[diff] [blame]911 <a name="dss_ilist_traits">ilist_traits</a>
912</div>
913
914<div class="doc_text">
915<p><tt>ilist_traits&lt;T&gt;</tt> is <tt>ilist&lt;T&gt;</tt>'s customization
916mechanism. <tt>iplist&lt;T&gt;</tt> (and consequently <tt>ilist&lt;T&gt;</tt>)
917publicly derive from this traits class.</p>
918</div>
919
920<!-- _______________________________________________________________________ -->
921<div class="doc_subsubsection">
Gabor Greif2946d1c2009-02-27 12:02:19 +0000[diff] [blame]922 <a name="dss_iplist">iplist</a>
923</div>
924
925<div class="doc_text">
926<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]927supports a slightly narrower interface. Notably, inserters from
928<tt>T&amp;</tt> are absent.</p>
Gabor Greif01862502009-02-27 13:28:07 +0000[diff] [blame]929
930<p><tt>ilist_traits&lt;T&gt;</tt> is a public base of this class and can be
931used for a wide variety of customizations.</p>
Gabor Greif2946d1c2009-02-27 12:02:19 +0000[diff] [blame]932</div>
933
934<!-- _______________________________________________________________________ -->
935<div class="doc_subsubsection">
Gabor Greif3899e492009-02-27 11:37:41 +0000[diff] [blame]936 <a name="dss_ilist_node">llvm/ADT/ilist_node.h</a>
937</div>
938
939<div class="doc_text">
940<p><tt>ilist_node&lt;T&gt;</tt> implements a the forward and backward links
941that are expected by the <tt>ilist&lt;T&gt;</tt> (and analogous containers)
942in the default manner.</p>
943
944<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]945<tt>T</tt>, usually <tt>T</tt> publicly derives from
946<tt>ilist_node&lt;T&gt;</tt>.</p>
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]947</div>
948
949<!-- _______________________________________________________________________ -->
950<div class="doc_subsubsection">
Gabor Greif6a65f422009-03-12 10:30:31 +0000[diff] [blame]951 <a name="dss_ilist_sentinel">Sentinels</a>
952</div>
953
954<div class="doc_text">
955<p><tt>ilist</tt>s have another speciality that must be considered. To be a good
956citizen in the C++ ecosystem, it needs to support the standard container
957operations, such as <tt>begin</tt> and <tt>end</tt> iterators, etc. Also, the
958<tt>operator--</tt> must work correctly on the <tt>end</tt> iterator in the
959case of non-empty <tt>ilist</tt>s.</p>
960
961<p>The only sensible solution to this problem is to allocate a so-called
962<i>sentinel</i> along with the intrusive list, which serves as the <tt>end</tt>
963iterator, providing the back-link to the last element. However conforming to the
964C++ convention it is illegal to <tt>operator++</tt> beyond the sentinel and it
965also must not be dereferenced.</p>
966
967<p>These constraints allow for some implementation freedom to the <tt>ilist</tt>
968how to allocate and store the sentinel. The corresponding policy is dictated
969by <tt>ilist_traits&lt;T&gt;</tt>. By default a <tt>T</tt> gets heap-allocated
970whenever the need for a sentinel arises.</p>
971
972<p>While the default policy is sufficient in most cases, it may break down when
973<tt>T</tt> does not provide a default constructor. Also, in the case of many
974instances of <tt>ilist</tt>s, the memory overhead of the associated sentinels
975is wasted. To alleviate the situation with numerous and voluminous
976<tt>T</tt>-sentinels, sometimes a trick is employed, leading to <i>ghostly
977sentinels</i>.</p>
978
979<p>Ghostly sentinels are obtained by specially-crafted <tt>ilist_traits&lt;T&gt;</tt>
980which superpose the sentinel with the <tt>ilist</tt> instance in memory. Pointer
981arithmetic is used to obtain the sentinel, which is relative to the
982<tt>ilist</tt>'s <tt>this</tt> pointer. The <tt>ilist</tt> is augmented by an
983extra pointer, which serves as the back-link of the sentinel. This is the only
984field in the ghostly sentinel which can be legally accessed.</p>
985</div>
986
987<!-- _______________________________________________________________________ -->
988<div class="doc_subsubsection">
Chris Lattnerc5722432007-02-03 19:49:31 +0000[diff] [blame]989 <a name="dss_other">Other Sequential Container options</a>
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]990</div>
991
992<div class="doc_text">
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]993<p>Other STL containers are available, such as std::string.</p>
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]994
995<p>There are also various STL adapter classes such as std::queue,
996std::priority_queue, std::stack, etc. These provide simplified access to an
997underlying container but don't affect the cost of the container itself.</p>
998
999</div>
1000
1001
1002<!-- ======================================================================= -->
1003<div class="doc_subsection">
1004 <a name="ds_set">Set-Like Containers (std::set, SmallSet, SetVector, etc)</a>
1005</div>
1006
1007<div class="doc_text">
1008
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1009<p>Set-like containers are useful when you need to canonicalize multiple values
1010into a single representation. There are several different choices for how to do
1011this, providing various trade-offs.</p>
1012
1013</div>
1014
1015
1016<!-- _______________________________________________________________________ -->
1017<div class="doc_subsubsection">
1018 <a name="dss_sortedvectorset">A sorted 'vector'</a>
1019</div>
1020
1021<div class="doc_text">
1022
Chris Lattner3b23a8c2007-02-03 08:10:45 +0000[diff] [blame]1023<p>If you intend to insert a lot of elements, then do a lot of queries, a
1024great approach is to use a vector (or other sequential container) with
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1025std::sort+std::unique to remove duplicates. This approach works really well if
Chris Lattner3b23a8c2007-02-03 08:10:45 +0000[diff] [blame]1026your usage pattern has these two distinct phases (insert then query), and can be
1027coupled with a good choice of <a href="#ds_sequential">sequential container</a>.
1028</p>
1029
1030<p>
1031This combination provides the several nice properties: the result data is
1032contiguous in memory (good for cache locality), has few allocations, is easy to
1033address (iterators in the final vector are just indices or pointers), and can be
1034efficiently queried with a standard binary or radix search.</p>
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1035
1036</div>
1037
1038<!-- _______________________________________________________________________ -->
1039<div class="doc_subsubsection">
1040 <a name="dss_smallset">"llvm/ADT/SmallSet.h"</a>
1041</div>
1042
1043<div class="doc_text">
1044
Reid Spencer128a7a72007-02-03 21:06:43 +0000[diff] [blame]1045<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]1046are 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]1047has space for N elements in place (thus, if the set is dynamically smaller than
Chris Lattner14868db2007-02-03 08:20:15 +0000[diff] [blame]1048N, no malloc traffic is required) and accesses them with a simple linear search.
1049When the set grows beyond 'N' elements, it allocates a more expensive representation that
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1050guarantees efficient access (for most types, it falls back to std::set, but for
Chris Lattner14868db2007-02-03 08:20:15 +0000[diff] [blame]1051pointers it uses something far better, <a
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1052href="#dss_smallptrset">SmallPtrSet</a>).</p>
1053
1054<p>The magic of this class is that it handles small sets extremely efficiently,
1055but gracefully handles extremely large sets without loss of efficiency. The
1056drawback is that the interface is quite small: it supports insertion, queries
1057and erasing, but does not support iteration.</p>
1058
1059</div>
1060
1061<!-- _______________________________________________________________________ -->
1062<div class="doc_subsubsection">
1063 <a name="dss_smallptrset">"llvm/ADT/SmallPtrSet.h"</a>
1064</div>
1065
1066<div class="doc_text">
1067
1068<p>SmallPtrSet has all the advantages of SmallSet (and a SmallSet of pointers is
Reid Spencer128a7a72007-02-03 21:06:43 +0000[diff] [blame]1069transparently implemented with a SmallPtrSet), but also supports iterators. If
Chris Lattner14868db2007-02-03 08:20:15 +0000[diff] [blame]1070more than 'N' insertions are performed, a single quadratically
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1071probed hash table is allocated and grows as needed, providing extremely
1072efficient access (constant time insertion/deleting/queries with low constant
1073factors) and is very stingy with malloc traffic.</p>
1074
1075<p>Note that, unlike std::set, the iterators of SmallPtrSet are invalidated
1076whenever an insertion occurs. Also, the values visited by the iterators are not
1077visited in sorted order.</p>
1078
1079</div>
1080
1081<!-- _______________________________________________________________________ -->
1082<div class="doc_subsubsection">
Chris Lattnerc28476f2007-09-30 00:58:59 +0000[diff] [blame]1083 <a name="dss_denseset">"llvm/ADT/DenseSet.h"</a>
1084</div>
1085
1086<div class="doc_text">
1087
1088<p>
1089DenseSet is a simple quadratically probed hash table. It excels at supporting
1090small values: it uses a single allocation to hold all of the pairs that
1091are currently inserted in the set. DenseSet is a great way to unique small
1092values that are not simple pointers (use <a
1093href="#dss_smallptrset">SmallPtrSet</a> for pointers). Note that DenseSet has
1094the same requirements for the value type that <a
1095href="#dss_densemap">DenseMap</a> has.
1096</p>
1097
1098</div>
1099
1100<!-- _______________________________________________________________________ -->
1101<div class="doc_subsubsection">
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1102 <a name="dss_FoldingSet">"llvm/ADT/FoldingSet.h"</a>
1103</div>
1104
1105<div class="doc_text">
1106
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]1107<p>
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1108FoldingSet is an aggregate class that is really good at uniquing
1109expensive-to-create or polymorphic objects. It is a combination of a chained
1110hash table with intrusive links (uniqued objects are required to inherit from
Chris Lattner14868db2007-02-03 08:20:15 +0000[diff] [blame]1111FoldingSetNode) that uses <a href="#dss_smallvector">SmallVector</a> as part of
1112its ID process.</p>
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1113
Chris Lattner14868db2007-02-03 08:20:15 +0000[diff] [blame]1114<p>Consider a case where you want to implement a "getOrCreateFoo" method for
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1115a complex object (for example, a node in the code generator). The client has a
1116description of *what* it wants to generate (it knows the opcode and all the
1117operands), 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]1118only to find out it already exists, at which point we would have to delete it
1119and return the node that already exists.
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]1120</p>
1121
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1122<p>To support this style of client, FoldingSet perform a query with a
1123FoldingSetNodeID (which wraps SmallVector) that can be used to describe the
1124element that we want to query for. The query either returns the element
1125matching the ID or it returns an opaque ID that indicates where insertion should
Chris Lattner14868db2007-02-03 08:20:15 +0000[diff] [blame]1126take place. Construction of the ID usually does not require heap traffic.</p>
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1127
1128<p>Because FoldingSet uses intrusive links, it can support polymorphic objects
1129in the set (for example, you can have SDNode instances mixed with LoadSDNodes).
1130Because the elements are individually allocated, pointers to the elements are
1131stable: inserting or removing elements does not invalidate any pointers to other
1132elements.
1133</p>
1134
1135</div>
1136
1137<!-- _______________________________________________________________________ -->
1138<div class="doc_subsubsection">
1139 <a name="dss_set">&lt;set&gt;</a>
1140</div>
1141
1142<div class="doc_text">
1143
Chris Lattnerc5722432007-02-03 19:49:31 +0000[diff] [blame]1144<p><tt>std::set</tt> is a reasonable all-around set class, which is decent at
1145many things but great at nothing. std::set allocates memory for each element
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1146inserted (thus it is very malloc intensive) and typically stores three pointers
Chris Lattner14868db2007-02-03 08:20:15 +0000[diff] [blame]1147per element in the set (thus adding a large amount of per-element space
1148overhead). It offers guaranteed log(n) performance, which is not particularly
Chris Lattnerc5722432007-02-03 19:49:31 +0000[diff] [blame]1149fast from a complexity standpoint (particularly if the elements of the set are
1150expensive to compare, like strings), and has extremely high constant factors for
1151lookup, insertion and removal.</p>
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1152
Chris Lattner14868db2007-02-03 08:20:15 +0000[diff] [blame]1153<p>The advantages of std::set are that its iterators are stable (deleting or
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1154inserting an element from the set does not affect iterators or pointers to other
1155elements) and that iteration over the set is guaranteed to be in sorted order.
1156If the elements in the set are large, then the relative overhead of the pointers
1157and malloc traffic is not a big deal, but if the elements of the set are small,
1158std::set is almost never a good choice.</p>
1159
1160</div>
1161
1162<!-- _______________________________________________________________________ -->
1163<div class="doc_subsubsection">
1164 <a name="dss_setvector">"llvm/ADT/SetVector.h"</a>
1165</div>
1166
1167<div class="doc_text">
Chris Lattneredca3c52007-02-04 00:00:26 +0000[diff] [blame]1168<p>LLVM's SetVector&lt;Type&gt; is an adapter class that combines your choice of
1169a set-like container along with a <a href="#ds_sequential">Sequential
1170Container</a>. The important property
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1171that this provides is efficient insertion with uniquing (duplicate elements are
1172ignored) with iteration support. It implements this by inserting elements into
1173both a set-like container and the sequential container, using the set-like
1174container for uniquing and the sequential container for iteration.
1175</p>
1176
1177<p>The difference between SetVector and other sets is that the order of
1178iteration is guaranteed to match the order of insertion into the SetVector.
1179This property is really important for things like sets of pointers. Because
1180pointer values are non-deterministic (e.g. vary across runs of the program on
Chris Lattneredca3c52007-02-04 00:00:26 +0000[diff] [blame]1181different machines), iterating over the pointers in the set will
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1182not be in a well-defined order.</p>
1183
1184<p>
1185The drawback of SetVector is that it requires twice as much space as a normal
1186set and has the sum of constant factors from the set-like container and the
1187sequential container that it uses. Use it *only* if you need to iterate over
1188the elements in a deterministic order. SetVector is also expensive to delete
Chris Lattneredca3c52007-02-04 00:00:26 +0000[diff] [blame]1189elements out of (linear time), unless you use it's "pop_back" method, which is
1190faster.
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1191</p>
1192
Chris Lattneredca3c52007-02-04 00:00:26 +0000[diff] [blame]1193<p>SetVector is an adapter class that defaults to using std::vector and std::set
1194for the underlying containers, so it is quite expensive. However,
1195<tt>"llvm/ADT/SetVector.h"</tt> also provides a SmallSetVector class, which
1196defaults to using a SmallVector and SmallSet of a specified size. If you use
1197this, and if your sets are dynamically smaller than N, you will save a lot of
1198heap traffic.</p>
1199
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1200</div>
1201
1202<!-- _______________________________________________________________________ -->
1203<div class="doc_subsubsection">
Chris Lattnerc5722432007-02-03 19:49:31 +0000[diff] [blame]1204 <a name="dss_uniquevector">"llvm/ADT/UniqueVector.h"</a>
1205</div>
1206
1207<div class="doc_text">
1208
1209<p>
1210UniqueVector is similar to <a href="#dss_setvector">SetVector</a>, but it
1211retains a unique ID for each element inserted into the set. It internally
1212contains a map and a vector, and it assigns a unique ID for each value inserted
1213into the set.</p>
1214
1215<p>UniqueVector is very expensive: its cost is the sum of the cost of
1216maintaining both the map and vector, it has high complexity, high constant
1217factors, and produces a lot of malloc traffic. It should be avoided.</p>
1218
1219</div>
1220
1221
1222<!-- _______________________________________________________________________ -->
1223<div class="doc_subsubsection">
1224 <a name="dss_otherset">Other Set-Like Container Options</a>
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1225</div>
1226
1227<div class="doc_text">
1228
1229<p>
1230The STL provides several other options, such as std::multiset and the various
Chris Lattnerf1a30822009-03-09 05:20:45 +0000[diff] [blame]1231"hash_set" like containers (whether from C++ TR1 or from the SGI library). We
1232never use hash_set and unordered_set because they are generally very expensive
1233(each insertion requires a malloc) and very non-portable.
1234</p>
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1235
1236<p>std::multiset is useful if you're not interested in elimination of
Chris Lattner14868db2007-02-03 08:20:15 +0000[diff] [blame]1237duplicates, but has all the drawbacks of std::set. A sorted vector (where you
1238don't delete duplicate entries) or some other approach is almost always
1239better.</p>
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1240
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]1241</div>
1242
1243<!-- ======================================================================= -->
1244<div class="doc_subsection">
1245 <a name="ds_map">Map-Like Containers (std::map, DenseMap, etc)</a>
1246</div>
1247
1248<div class="doc_text">
Chris Lattnerc5722432007-02-03 19:49:31 +0000[diff] [blame]1249Map-like containers are useful when you want to associate data to a key. As
1250usual, there are a lot of different ways to do this. :)
1251</div>
1252
1253<!-- _______________________________________________________________________ -->
1254<div class="doc_subsubsection">
1255 <a name="dss_sortedvectormap">A sorted 'vector'</a>
1256</div>
1257
1258<div class="doc_text">
1259
1260<p>
1261If your usage pattern follows a strict insert-then-query approach, you can
1262trivially use the same approach as <a href="#dss_sortedvectorset">sorted vectors
1263for set-like containers</a>. The only difference is that your query function
1264(which uses std::lower_bound to get efficient log(n) lookup) should only compare
1265the key, not both the key and value. This yields the same advantages as sorted
1266vectors for sets.
1267</p>
1268</div>
1269
1270<!-- _______________________________________________________________________ -->
1271<div class="doc_subsubsection">
Chris Lattner796f9fa2007-02-08 19:14:21 +0000[diff] [blame]1272 <a name="dss_stringmap">"llvm/ADT/StringMap.h"</a>
Chris Lattnerc5722432007-02-03 19:49:31 +0000[diff] [blame]1273</div>
1274
1275<div class="doc_text">
1276
1277<p>
1278Strings are commonly used as keys in maps, and they are difficult to support
1279efficiently: they are variable length, inefficient to hash and compare when
Chris Lattner796f9fa2007-02-08 19:14:21 +0000[diff] [blame]1280long, expensive to copy, etc. StringMap is a specialized container designed to
1281cope with these issues. It supports mapping an arbitrary range of bytes to an
1282arbitrary other object.</p>
Chris Lattnerc5722432007-02-03 19:49:31 +0000[diff] [blame]1283
Chris Lattner796f9fa2007-02-08 19:14:21 +0000[diff] [blame]1284<p>The StringMap implementation uses a quadratically-probed hash table, where
Chris Lattnerc5722432007-02-03 19:49:31 +0000[diff] [blame]1285the buckets store a pointer to the heap allocated entries (and some other
1286stuff). The entries in the map must be heap allocated because the strings are
1287variable length. The string data (key) and the element object (value) are
1288stored in the same allocation with the string data immediately after the element
1289object. This container guarantees the "<tt>(char*)(&amp;Value+1)</tt>" points
1290to the key string for a value.</p>
1291
Chris Lattner796f9fa2007-02-08 19:14:21 +0000[diff] [blame]1292<p>The StringMap is very fast for several reasons: quadratic probing is very
Chris Lattnerc5722432007-02-03 19:49:31 +0000[diff] [blame]1293cache efficient for lookups, the hash value of strings in buckets is not
Chris Lattner796f9fa2007-02-08 19:14:21 +0000[diff] [blame]1294recomputed when lookup up an element, StringMap rarely has to touch the
Chris Lattnerc5722432007-02-03 19:49:31 +0000[diff] [blame]1295memory for unrelated objects when looking up a value (even when hash collisions
1296happen), hash table growth does not recompute the hash values for strings
1297already in the table, and each pair in the map is store in a single allocation
1298(the string data is stored in the same allocation as the Value of a pair).</p>
1299
Chris Lattner796f9fa2007-02-08 19:14:21 +0000[diff] [blame]1300<p>StringMap also provides query methods that take byte ranges, so it only ever
Chris Lattnerc5722432007-02-03 19:49:31 +0000[diff] [blame]1301copies a string if a value is inserted into the table.</p>
1302</div>
1303
1304<!-- _______________________________________________________________________ -->
1305<div class="doc_subsubsection">
1306 <a name="dss_indexedmap">"llvm/ADT/IndexedMap.h"</a>
1307</div>
1308
1309<div class="doc_text">
1310<p>
1311IndexedMap is a specialized container for mapping small dense integers (or
1312values that can be mapped to small dense integers) to some other type. It is
1313internally implemented as a vector with a mapping function that maps the keys to
1314the dense integer range.
1315</p>
1316
1317<p>
1318This is useful for cases like virtual registers in the LLVM code generator: they
1319have a dense mapping that is offset by a compile-time constant (the first
1320virtual register ID).</p>
1321
1322</div>
1323
1324<!-- _______________________________________________________________________ -->
1325<div class="doc_subsubsection">
1326 <a name="dss_densemap">"llvm/ADT/DenseMap.h"</a>
1327</div>
1328
1329<div class="doc_text">
1330
1331<p>
1332DenseMap is a simple quadratically probed hash table. It excels at supporting
1333small keys and values: it uses a single allocation to hold all of the pairs that
1334are currently inserted in the map. DenseMap is a great way to map pointers to
1335pointers, or map other small types to each other.
1336</p>
1337
1338<p>
1339There are several aspects of DenseMap that you should be aware of, however. The
1340iterators in a densemap are invalidated whenever an insertion occurs, unlike
1341map. Also, because DenseMap allocates space for a large number of key/value
Chris Lattnera4a264d2007-02-03 20:17:53 +0000[diff] [blame]1342pairs (it starts with 64 by default), it will waste a lot of space if your keys
1343or values are large. Finally, you must implement a partial specialization of
Chris Lattner76c1b972007-09-17 18:34:04 +0000[diff] [blame]1344DenseMapInfo for the key that you want, if it isn't already supported. This
Chris Lattnerc5722432007-02-03 19:49:31 +0000[diff] [blame]1345is required to tell DenseMap about two special marker values (which can never be
Chris Lattnera4a264d2007-02-03 20:17:53 +0000[diff] [blame]1346inserted into the map) that it needs internally.</p>
Chris Lattnerc5722432007-02-03 19:49:31 +0000[diff] [blame]1347
1348</div>
1349
1350<!-- _______________________________________________________________________ -->
1351<div class="doc_subsubsection">
1352 <a name="dss_map">&lt;map&gt;</a>
1353</div>
1354
1355<div class="doc_text">
1356
1357<p>
1358std::map has similar characteristics to <a href="#dss_set">std::set</a>: it uses
1359a single allocation per pair inserted into the map, it offers log(n) lookup with
1360an extremely large constant factor, imposes a space penalty of 3 pointers per
1361pair in the map, etc.</p>
1362
1363<p>std::map is most useful when your keys or values are very large, if you need
1364to iterate over the collection in sorted order, or if you need stable iterators
1365into the map (i.e. they don't get invalidated if an insertion or deletion of
1366another element takes place).</p>
1367
1368</div>
1369
1370<!-- _______________________________________________________________________ -->
1371<div class="doc_subsubsection">
1372 <a name="dss_othermap">Other Map-Like Container Options</a>
1373</div>
1374
1375<div class="doc_text">
1376
1377<p>
1378The STL provides several other options, such as std::multimap and the various
Chris Lattnerf1a30822009-03-09 05:20:45 +0000[diff] [blame]1379"hash_map" like containers (whether from C++ TR1 or from the SGI library). We
1380never use hash_set and unordered_set because they are generally very expensive
1381(each insertion requires a malloc) and very non-portable.</p>
Chris Lattnerc5722432007-02-03 19:49:31 +0000[diff] [blame]1382
1383<p>std::multimap is useful if you want to map a key to multiple values, but has
1384all the drawbacks of std::map. A sorted vector or some other approach is almost
1385always better.</p>
1386
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]1387</div>
1388
Daniel Berlin1939ace2007-09-24 17:52:25 +0000[diff] [blame]1389<!-- ======================================================================= -->
1390<div class="doc_subsection">
1391 <a name="ds_bit">Bit storage containers (BitVector, SparseBitVector)</a>
1392</div>
1393
1394<div class="doc_text">
Chris Lattner7086ce72007-09-25 22:37:50 +0000[diff] [blame]1395<p>Unlike the other containers, there are only two bit storage containers, and
1396choosing when to use each is relatively straightforward.</p>
1397
1398<p>One additional option is
1399<tt>std::vector&lt;bool&gt;</tt>: we discourage its use for two reasons 1) the
1400implementation in many common compilers (e.g. commonly available versions of
1401GCC) is extremely inefficient and 2) the C++ standards committee is likely to
1402deprecate this container and/or change it significantly somehow. In any case,
1403please don't use it.</p>
Daniel Berlin1939ace2007-09-24 17:52:25 +0000[diff] [blame]1404</div>
1405
1406<!-- _______________________________________________________________________ -->
1407<div class="doc_subsubsection">
1408 <a name="dss_bitvector">BitVector</a>
1409</div>
1410
1411<div class="doc_text">
1412<p> The BitVector container provides a fixed size set of bits for manipulation.
1413It supports individual bit setting/testing, as well as set operations. The set
1414operations take time O(size of bitvector), but operations are performed one word
1415at a time, instead of one bit at a time. This makes the BitVector very fast for
1416set operations compared to other containers. Use the BitVector when you expect
1417the number of set bits to be high (IE a dense set).
1418</p>
1419</div>
1420
1421<!-- _______________________________________________________________________ -->
1422<div class="doc_subsubsection">
1423 <a name="dss_sparsebitvector">SparseBitVector</a>
1424</div>
1425
1426<div class="doc_text">
1427<p> The SparseBitVector container is much like BitVector, with one major
1428difference: Only the bits that are set, are stored. This makes the
1429SparseBitVector much more space efficient than BitVector when the set is sparse,
1430as well as making set operations O(number of set bits) instead of O(size of
1431universe). 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
1432(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).
1433</p>
1434</div>
Chris Lattnerf623a082005-10-17 01:36:23 +0000[diff] [blame]1435
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1436<!-- *********************************************************************** -->
1437<div class="doc_section">
1438 <a name="common">Helpful Hints for Common Operations</a>
1439</div>
1440<!-- *********************************************************************** -->
1441
1442<div class="doc_text">
1443
1444<p>This section describes how to perform some very simple transformations of
1445LLVM code. This is meant to give examples of common idioms used, showing the
1446practical side of LLVM transformations. <p> Because this is a "how-to" section,
1447you should also read about the main classes that you will be working with. The
1448<a href="#coreclasses">Core LLVM Class Hierarchy Reference</a> contains details
1449and descriptions of the main classes that you should know about.</p>
1450
1451</div>
1452
1453<!-- NOTE: this section should be heavy on example code -->
1454<!-- ======================================================================= -->
1455<div class="doc_subsection">
1456 <a name="inspection">Basic Inspection and Traversal Routines</a>
1457</div>
1458
1459<div class="doc_text">
1460
1461<p>The LLVM compiler infrastructure have many different data structures that may
1462be traversed. Following the example of the C++ standard template library, the
1463techniques used to traverse these various data structures are all basically the
1464same. For a enumerable sequence of values, the <tt>XXXbegin()</tt> function (or
1465method) returns an iterator to the start of the sequence, the <tt>XXXend()</tt>
1466function returns an iterator pointing to one past the last valid element of the
1467sequence, and there is some <tt>XXXiterator</tt> data type that is common
1468between the two operations.</p>
1469
1470<p>Because the pattern for iteration is common across many different aspects of
1471the program representation, the standard template library algorithms may be used
1472on them, and it is easier to remember how to iterate. First we show a few common
1473examples of the data structures that need to be traversed. Other data
1474structures are traversed in very similar ways.</p>
1475
1476</div>
1477
1478<!-- _______________________________________________________________________ -->
Chris Lattner69bf8a92004-05-23 21:06:58 +0000[diff] [blame]1479<div class="doc_subsubsection">
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1480 <a name="iterate_function">Iterating over the </a><a
1481 href="#BasicBlock"><tt>BasicBlock</tt></a>s in a <a
1482 href="#Function"><tt>Function</tt></a>
1483</div>
1484
1485<div class="doc_text">
1486
1487<p>It's quite common to have a <tt>Function</tt> instance that you'd like to
1488transform in some way; in particular, you'd like to manipulate its
1489<tt>BasicBlock</tt>s. To facilitate this, you'll need to iterate over all of
1490the <tt>BasicBlock</tt>s that constitute the <tt>Function</tt>. The following is
1491an example that prints the name of a <tt>BasicBlock</tt> and the number of
1492<tt>Instruction</tt>s it contains:</p>
1493
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1494<div class="doc_code">
1495<pre>
Bill Wendling82e2eea2006-10-11 18:00:22 +0000[diff] [blame]1496// <i>func is a pointer to a Function instance</i>
1497for (Function::iterator i = func-&gt;begin(), e = func-&gt;end(); i != e; ++i)
1498 // <i>Print out the name of the basic block if it has one, and then the</i>
1499 // <i>number of instructions that it contains</i>
Bill Wendling832171c2006-12-07 20:04:42 +0000[diff] [blame]1500 llvm::cerr &lt;&lt; "Basic block (name=" &lt;&lt; i-&gt;getName() &lt;&lt; ") has "
1501 &lt;&lt; i-&gt;size() &lt;&lt; " instructions.\n";
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1502</pre>
1503</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1504
1505<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]1506invoking member functions of the <tt>Instruction</tt> class. This is
1507because the indirection operator is overloaded for the iterator
Chris Lattner7496ec52003-08-05 22:54:23 +0000[diff] [blame]1508classes. In the above code, the expression <tt>i-&gt;size()</tt> is
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1509exactly equivalent to <tt>(*i).size()</tt> just like you'd expect.</p>
1510
1511</div>
1512
1513<!-- _______________________________________________________________________ -->
Chris Lattner69bf8a92004-05-23 21:06:58 +0000[diff] [blame]1514<div class="doc_subsubsection">
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1515 <a name="iterate_basicblock">Iterating over the </a><a
1516 href="#Instruction"><tt>Instruction</tt></a>s in a <a
1517 href="#BasicBlock"><tt>BasicBlock</tt></a>
1518</div>
1519
1520<div class="doc_text">
1521
1522<p>Just like when dealing with <tt>BasicBlock</tt>s in <tt>Function</tt>s, it's
1523easy to iterate over the individual instructions that make up
1524<tt>BasicBlock</tt>s. Here's a code snippet that prints out each instruction in
1525a <tt>BasicBlock</tt>:</p>
1526
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1527<div class="doc_code">
Chris Lattner55c04612005-03-06 06:00:13 +0000[diff] [blame]1528<pre>
Bill Wendling82e2eea2006-10-11 18:00:22 +0000[diff] [blame]1529// <i>blk is a pointer to a BasicBlock instance</i>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1530for (BasicBlock::iterator i = blk-&gt;begin(), e = blk-&gt;end(); i != e; ++i)
Bill Wendling82e2eea2006-10-11 18:00:22 +0000[diff] [blame]1531 // <i>The next statement works since operator&lt;&lt;(ostream&amp;,...)</i>
1532 // <i>is overloaded for Instruction&amp;</i>
Bill Wendling832171c2006-12-07 20:04:42 +0000[diff] [blame]1533 llvm::cerr &lt;&lt; *i &lt;&lt; "\n";
Chris Lattner55c04612005-03-06 06:00:13 +0000[diff] [blame]1534</pre>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1535</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1536
1537<p>However, this isn't really the best way to print out the contents of a
1538<tt>BasicBlock</tt>! Since the ostream operators are overloaded for virtually
1539anything you'll care about, you could have just invoked the print routine on the
Bill Wendling832171c2006-12-07 20:04:42 +0000[diff] [blame]1540basic block itself: <tt>llvm::cerr &lt;&lt; *blk &lt;&lt; "\n";</tt>.</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1541
1542</div>
1543
1544<!-- _______________________________________________________________________ -->
Chris Lattner69bf8a92004-05-23 21:06:58 +0000[diff] [blame]1545<div class="doc_subsubsection">
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1546 <a name="iterate_institer">Iterating over the </a><a
1547 href="#Instruction"><tt>Instruction</tt></a>s in a <a
1548 href="#Function"><tt>Function</tt></a>
1549</div>
1550
1551<div class="doc_text">
1552
1553<p>If you're finding that you commonly iterate over a <tt>Function</tt>'s
1554<tt>BasicBlock</tt>s and then that <tt>BasicBlock</tt>'s <tt>Instruction</tt>s,
1555<tt>InstIterator</tt> should be used instead. You'll need to include <a
1556href="/doxygen/InstIterator_8h-source.html"><tt>llvm/Support/InstIterator.h</tt></a>,
1557and then instantiate <tt>InstIterator</tt>s explicitly in your code. Here's a
Chris Lattner69bf8a92004-05-23 21:06:58 +0000[diff] [blame]1558small 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]1559
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1560<div class="doc_code">
1561<pre>
1562#include "<a href="/doxygen/InstIterator_8h-source.html">llvm/Support/InstIterator.h</a>"
1563
Reid Spencer128a7a72007-02-03 21:06:43 +0000[diff] [blame]1564// <i>F is a pointer to a Function instance</i>
Chris Lattnerda021aa2008-06-04 18:20:42 +0000[diff] [blame]1565for (inst_iterator I = inst_begin(F), E = inst_end(F); I != E; ++I)
1566 llvm::cerr &lt;&lt; *I &lt;&lt; "\n";
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1567</pre>
1568</div>
1569
1570<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]1571work list with its initial contents. For example, if you wanted to
1572initialize a work list to contain all instructions in a <tt>Function</tt>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1573F, all you would need to do is something like:</p>
1574
1575<div class="doc_code">
1576<pre>
1577std::set&lt;Instruction*&gt; worklist;
Chris Lattnerda021aa2008-06-04 18:20:42 +0000[diff] [blame]1578// or better yet, SmallPtrSet&lt;Instruction*, 64&gt; worklist;
1579
1580for (inst_iterator I = inst_begin(F), E = inst_end(F); I != E; ++I)
1581 worklist.insert(&amp;*I);
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1582</pre>
1583</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1584
1585<p>The STL set <tt>worklist</tt> would now contain all instructions in the
1586<tt>Function</tt> pointed to by F.</p>
1587
1588</div>
1589
1590<!-- _______________________________________________________________________ -->
1591<div class="doc_subsubsection">
1592 <a name="iterate_convert">Turning an iterator into a class pointer (and
1593 vice-versa)</a>
1594</div>
1595
1596<div class="doc_text">
1597
1598<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]1599instance when all you've got at hand is an iterator. Well, extracting
Chris Lattner69bf8a92004-05-23 21:06:58 +0000[diff] [blame]1600a reference or a pointer from an iterator is very straight-forward.
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]1601Assuming that <tt>i</tt> is a <tt>BasicBlock::iterator</tt> and <tt>j</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1602is a <tt>BasicBlock::const_iterator</tt>:</p>
1603
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1604<div class="doc_code">
1605<pre>
Bill Wendling82e2eea2006-10-11 18:00:22 +0000[diff] [blame]1606Instruction&amp; inst = *i; // <i>Grab reference to instruction reference</i>
1607Instruction* pinst = &amp;*i; // <i>Grab pointer to instruction reference</i>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1608const Instruction&amp; inst = *j;
1609</pre>
1610</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1611
1612<p>However, the iterators you'll be working with in the LLVM framework are
1613special: they will automatically convert to a ptr-to-instance type whenever they
1614need to. Instead of dereferencing the iterator and then taking the address of
1615the result, you can simply assign the iterator to the proper pointer type and
1616you get the dereference and address-of operation as a result of the assignment
1617(behind the scenes, this is a result of overloading casting mechanisms). Thus
1618the last line of the last example,</p>
1619
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1620<div class="doc_code">
1621<pre>
Chris Lattner2e438ca2008-01-03 16:56:04 +0000[diff] [blame]1622Instruction *pinst = &amp;*i;
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1623</pre>
1624</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1625
1626<p>is semantically equivalent to</p>
1627
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1628<div class="doc_code">
1629<pre>
Chris Lattner2e438ca2008-01-03 16:56:04 +0000[diff] [blame]1630Instruction *pinst = i;
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1631</pre>
1632</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1633
Chris Lattner69bf8a92004-05-23 21:06:58 +0000[diff] [blame]1634<p>It's also possible to turn a class pointer into the corresponding iterator,
1635and this is a constant time operation (very efficient). The following code
1636snippet illustrates use of the conversion constructors provided by LLVM
1637iterators. By using these, you can explicitly grab the iterator of something
1638without actually obtaining it via iteration over some structure:</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1639
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1640<div class="doc_code">
1641<pre>
1642void printNextInstruction(Instruction* inst) {
1643 BasicBlock::iterator it(inst);
Bill Wendling82e2eea2006-10-11 18:00:22 +0000[diff] [blame]1644 ++it; // <i>After this line, it refers to the instruction after *inst</i>
Bill Wendling832171c2006-12-07 20:04:42 +0000[diff] [blame]1645 if (it != inst-&gt;getParent()-&gt;end()) llvm::cerr &lt;&lt; *it &lt;&lt; "\n";
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1646}
1647</pre>
1648</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1649
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1650</div>
1651
1652<!--_______________________________________________________________________-->
1653<div class="doc_subsubsection">
1654 <a name="iterate_complex">Finding call sites: a slightly more complex
1655 example</a>
1656</div>
1657
1658<div class="doc_text">
1659
1660<p>Say that you're writing a FunctionPass and would like to count all the
1661locations in the entire module (that is, across every <tt>Function</tt>) where a
1662certain function (i.e., some <tt>Function</tt>*) is already in scope. As you'll
1663learn 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]1664much more straight-forward manner, but this example will allow us to explore how
Reid Spencer128a7a72007-02-03 21:06:43 +0000[diff] [blame]1665you'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]1666is what we want to do:</p>
1667
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1668<div class="doc_code">
1669<pre>
1670initialize callCounter to zero
1671for each Function f in the Module
1672 for each BasicBlock b in f
1673 for each Instruction i in b
1674 if (i is a CallInst and calls the given function)
1675 increment callCounter
1676</pre>
1677</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1678
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1679<p>And the actual code is (remember, because we're writing a
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1680<tt>FunctionPass</tt>, our <tt>FunctionPass</tt>-derived class simply has to
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1681override the <tt>runOnFunction</tt> method):</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1682
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1683<div class="doc_code">
1684<pre>
1685Function* targetFunc = ...;
1686
1687class OurFunctionPass : public FunctionPass {
1688 public:
1689 OurFunctionPass(): callCounter(0) { }
1690
1691 virtual runOnFunction(Function&amp; F) {
1692 for (Function::iterator b = F.begin(), be = F.end(); b != be; ++b) {
Eric Christopher203e71d2008-11-08 08:20:49 +0000[diff] [blame]1693 for (BasicBlock::iterator i = b-&gt;begin(), ie = b-&gt;end(); i != ie; ++i) {
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1694 if (<a href="#CallInst">CallInst</a>* callInst = <a href="#isa">dyn_cast</a>&lt;<a
1695 href="#CallInst">CallInst</a>&gt;(&amp;*i)) {
Bill Wendling82e2eea2006-10-11 18:00:22 +0000[diff] [blame]1696 // <i>We know we've encountered a call instruction, so we</i>
1697 // <i>need to determine if it's a call to the</i>
Chris Lattner2e438ca2008-01-03 16:56:04 +0000[diff] [blame]1698 // <i>function pointed to by m_func or not.</i>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1699 if (callInst-&gt;getCalledFunction() == targetFunc)
1700 ++callCounter;
1701 }
1702 }
1703 }
Bill Wendling82e2eea2006-10-11 18:00:22 +0000[diff] [blame]1704 }
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1705
1706 private:
Chris Lattner2e438ca2008-01-03 16:56:04 +0000[diff] [blame]1707 unsigned callCounter;
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1708};
1709</pre>
1710</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1711
1712</div>
1713
Brian Gaekef1972c62003-11-07 19:25:45 +0000[diff] [blame]1714<!--_______________________________________________________________________-->
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1715<div class="doc_subsubsection">
1716 <a name="calls_and_invokes">Treating calls and invokes the same way</a>
1717</div>
1718
1719<div class="doc_text">
1720
1721<p>You may have noticed that the previous example was a bit oversimplified in
1722that it did not deal with call sites generated by 'invoke' instructions. In
1723this, and in other situations, you may find that you want to treat
1724<tt>CallInst</tt>s and <tt>InvokeInst</tt>s the same way, even though their
1725most-specific common base class is <tt>Instruction</tt>, which includes lots of
1726less closely-related things. For these cases, LLVM provides a handy wrapper
1727class called <a
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]1728href="http://llvm.org/doxygen/classllvm_1_1CallSite.html"><tt>CallSite</tt></a>.
Chris Lattner69bf8a92004-05-23 21:06:58 +0000[diff] [blame]1729It is essentially a wrapper around an <tt>Instruction</tt> pointer, with some
1730methods that provide functionality common to <tt>CallInst</tt>s and
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1731<tt>InvokeInst</tt>s.</p>
1732
Chris Lattner69bf8a92004-05-23 21:06:58 +0000[diff] [blame]1733<p>This class has "value semantics": it should be passed by value, not by
1734reference and it should not be dynamically allocated or deallocated using
1735<tt>operator new</tt> or <tt>operator delete</tt>. It is efficiently copyable,
1736assignable and constructable, with costs equivalents to that of a bare pointer.
1737If you look at its definition, it has only a single pointer member.</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1738
1739</div>
1740
Chris Lattner1a3105b2002-09-09 05:49:39 +0000[diff] [blame]1741<!--_______________________________________________________________________-->
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1742<div class="doc_subsubsection">
1743 <a name="iterate_chains">Iterating over def-use &amp; use-def chains</a>
1744</div>
1745
1746<div class="doc_text">
1747
1748<p>Frequently, we might have an instance of the <a
Chris Lattner00815172007-01-04 22:01:45 +0000[diff] [blame]1749href="/doxygen/classllvm_1_1Value.html">Value Class</a> and we want to
Misha Brukman384047f2004-06-03 23:29:12 +0000[diff] [blame]1750determine which <tt>User</tt>s use the <tt>Value</tt>. The list of all
1751<tt>User</tt>s of a particular <tt>Value</tt> is called a <i>def-use</i> chain.
1752For example, let's say we have a <tt>Function*</tt> named <tt>F</tt> to a
1753particular function <tt>foo</tt>. Finding all of the instructions that
1754<i>use</i> <tt>foo</tt> is as simple as iterating over the <i>def-use</i> chain
1755of <tt>F</tt>:</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1756
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1757<div class="doc_code">
1758<pre>
Chris Lattner2e438ca2008-01-03 16:56:04 +0000[diff] [blame]1759Function *F = ...;
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1760
Bill Wendling82e2eea2006-10-11 18:00:22 +0000[diff] [blame]1761for (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]1762 if (Instruction *Inst = dyn_cast&lt;Instruction&gt;(*i)) {
Bill Wendling832171c2006-12-07 20:04:42 +0000[diff] [blame]1763 llvm::cerr &lt;&lt; "F is used in instruction:\n";
1764 llvm::cerr &lt;&lt; *Inst &lt;&lt; "\n";
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1765 }
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1766</pre>
1767</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1768
1769<p>Alternately, it's common to have an instance of the <a
Misha Brukman384047f2004-06-03 23:29:12 +0000[diff] [blame]1770href="/doxygen/classllvm_1_1User.html">User Class</a> and need to know what
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1771<tt>Value</tt>s are used by it. The list of all <tt>Value</tt>s used by a
1772<tt>User</tt> is known as a <i>use-def</i> chain. Instances of class
1773<tt>Instruction</tt> are common <tt>User</tt>s, so we might want to iterate over
1774all of the values that a particular instruction uses (that is, the operands of
1775the particular <tt>Instruction</tt>):</p>
1776
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1777<div class="doc_code">
1778<pre>
Chris Lattner2e438ca2008-01-03 16:56:04 +0000[diff] [blame]1779Instruction *pi = ...;
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1780
1781for (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]1782 Value *v = *i;
Bill Wendling82e2eea2006-10-11 18:00:22 +0000[diff] [blame]1783 // <i>...</i>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1784}
1785</pre>
1786</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1787
Chris Lattner1a3105b2002-09-09 05:49:39 +0000[diff] [blame]1788<!--
1789 def-use chains ("finding all users of"): Value::use_begin/use_end
1790 use-def chains ("finding all values used"): User::op_begin/op_end [op=operand]
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1791-->
1792
1793</div>
1794
Chris Lattner2e438ca2008-01-03 16:56:04 +0000[diff] [blame]1795<!--_______________________________________________________________________-->
1796<div class="doc_subsubsection">
1797 <a name="iterate_preds">Iterating over predecessors &amp;
1798successors of blocks</a>
1799</div>
1800
1801<div class="doc_text">
1802
1803<p>Iterating over the predecessors and successors of a block is quite easy
1804with the routines defined in <tt>"llvm/Support/CFG.h"</tt>. Just use code like
1805this to iterate over all predecessors of BB:</p>
1806
1807<div class="doc_code">
1808<pre>
1809#include "llvm/Support/CFG.h"
1810BasicBlock *BB = ...;
1811
1812for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI) {
1813 BasicBlock *Pred = *PI;
1814 // <i>...</i>
1815}
1816</pre>
1817</div>
1818
1819<p>Similarly, to iterate over successors use
1820succ_iterator/succ_begin/succ_end.</p>
1821
1822</div>
1823
1824
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1825<!-- ======================================================================= -->
1826<div class="doc_subsection">
1827 <a name="simplechanges">Making simple changes</a>
1828</div>
1829
1830<div class="doc_text">
1831
1832<p>There are some primitive transformation operations present in the LLVM
Joel Stanley753eb712002-09-11 22:32:24 +0000[diff] [blame]1833infrastructure that are worth knowing about. When performing
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]1834transformations, it's fairly common to manipulate the contents of basic
1835blocks. This section describes some of the common methods for doing so
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1836and gives example code.</p>
1837
1838</div>
1839
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]1840<!--_______________________________________________________________________-->
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1841<div class="doc_subsubsection">
1842 <a name="schanges_creating">Creating and inserting new
1843 <tt>Instruction</tt>s</a>
1844</div>
1845
1846<div class="doc_text">
1847
1848<p><i>Instantiating Instructions</i></p>
1849
Chris Lattner69bf8a92004-05-23 21:06:58 +0000[diff] [blame]1850<p>Creation of <tt>Instruction</tt>s is straight-forward: simply call the
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1851constructor for the kind of instruction to instantiate and provide the necessary
1852parameters. For example, an <tt>AllocaInst</tt> only <i>requires</i> a
1853(const-ptr-to) <tt>Type</tt>. Thus:</p>
1854
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1855<div class="doc_code">
1856<pre>
Nick Lewycky10d64b92007-12-03 01:52:52 +0000[diff] [blame]1857AllocaInst* ai = new AllocaInst(Type::Int32Ty);
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1858</pre>
1859</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1860
1861<p>will create an <tt>AllocaInst</tt> instance that represents the allocation of
Reid Spencer128a7a72007-02-03 21:06:43 +0000[diff] [blame]1862one integer in the current stack frame, at run time. Each <tt>Instruction</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1863subclass is likely to have varying default parameters which change the semantics
1864of the instruction, so refer to the <a
Misha Brukman31ca1de2004-06-03 23:35:54 +0000[diff] [blame]1865href="/doxygen/classllvm_1_1Instruction.html">doxygen documentation for the subclass of
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1866Instruction</a> that you're interested in instantiating.</p>
1867
1868<p><i>Naming values</i></p>
1869
1870<p>It is very useful to name the values of instructions when you're able to, as
1871this facilitates the debugging of your transformations. If you end up looking
1872at generated LLVM machine code, you definitely want to have logical names
1873associated with the results of instructions! By supplying a value for the
1874<tt>Name</tt> (default) parameter of the <tt>Instruction</tt> constructor, you
1875associate a logical name with the result of the instruction's execution at
Reid Spencer128a7a72007-02-03 21:06:43 +0000[diff] [blame]1876run time. For example, say that I'm writing a transformation that dynamically
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1877allocates space for an integer on the stack, and that integer is going to be
1878used as some kind of index by some other code. To accomplish this, I place an
1879<tt>AllocaInst</tt> at the first point in the first <tt>BasicBlock</tt> of some
1880<tt>Function</tt>, and I'm intending to use it within the same
1881<tt>Function</tt>. I might do:</p>
1882
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1883<div class="doc_code">
1884<pre>
Nick Lewycky10d64b92007-12-03 01:52:52 +0000[diff] [blame]1885AllocaInst* pa = new AllocaInst(Type::Int32Ty, 0, "indexLoc");
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1886</pre>
1887</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1888
1889<p>where <tt>indexLoc</tt> is now the logical name of the instruction's
Reid Spencer128a7a72007-02-03 21:06:43 +0000[diff] [blame]1890execution value, which is a pointer to an integer on the run time stack.</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1891
1892<p><i>Inserting instructions</i></p>
1893
1894<p>There are essentially two ways to insert an <tt>Instruction</tt>
1895into an existing sequence of instructions that form a <tt>BasicBlock</tt>:</p>
1896
Joel Stanley9dd1ad62002-09-18 03:17:23 +0000[diff] [blame]1897<ul>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1898 <li>Insertion into an explicit instruction list
1899
1900 <p>Given a <tt>BasicBlock* pb</tt>, an <tt>Instruction* pi</tt> within that
1901 <tt>BasicBlock</tt>, and a newly-created instruction we wish to insert
1902 before <tt>*pi</tt>, we do the following: </p>
1903
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1904<div class="doc_code">
1905<pre>
1906BasicBlock *pb = ...;
1907Instruction *pi = ...;
1908Instruction *newInst = new Instruction(...);
1909
Bill Wendling82e2eea2006-10-11 18:00:22 +0000[diff] [blame]1910pb-&gt;getInstList().insert(pi, newInst); // <i>Inserts newInst before pi in pb</i>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1911</pre>
1912</div>
Alkis Evlogimenos9a5dc4f2004-05-27 00:57:51 +0000[diff] [blame]1913
1914 <p>Appending to the end of a <tt>BasicBlock</tt> is so common that
1915 the <tt>Instruction</tt> class and <tt>Instruction</tt>-derived
1916 classes provide constructors which take a pointer to a
1917 <tt>BasicBlock</tt> to be appended to. For example code that
1918 looked like: </p>
1919
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1920<div class="doc_code">
1921<pre>
1922BasicBlock *pb = ...;
1923Instruction *newInst = new Instruction(...);
1924
Bill Wendling82e2eea2006-10-11 18:00:22 +0000[diff] [blame]1925pb-&gt;getInstList().push_back(newInst); // <i>Appends newInst to pb</i>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1926</pre>
1927</div>
Alkis Evlogimenos9a5dc4f2004-05-27 00:57:51 +0000[diff] [blame]1928
1929 <p>becomes: </p>
1930
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1931<div class="doc_code">
1932<pre>
1933BasicBlock *pb = ...;
1934Instruction *newInst = new Instruction(..., pb);
1935</pre>
1936</div>
Alkis Evlogimenos9a5dc4f2004-05-27 00:57:51 +0000[diff] [blame]1937
1938 <p>which is much cleaner, especially if you are creating
1939 long instruction streams.</p></li>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1940
1941 <li>Insertion into an implicit instruction list
1942
1943 <p><tt>Instruction</tt> instances that are already in <tt>BasicBlock</tt>s
1944 are implicitly associated with an existing instruction list: the instruction
1945 list of the enclosing basic block. Thus, we could have accomplished the same
1946 thing as the above code without being given a <tt>BasicBlock</tt> by doing:
1947 </p>
1948
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1949<div class="doc_code">
1950<pre>
1951Instruction *pi = ...;
1952Instruction *newInst = new Instruction(...);
1953
1954pi-&gt;getParent()-&gt;getInstList().insert(pi, newInst);
1955</pre>
1956</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1957
1958 <p>In fact, this sequence of steps occurs so frequently that the
1959 <tt>Instruction</tt> class and <tt>Instruction</tt>-derived classes provide
1960 constructors which take (as a default parameter) a pointer to an
1961 <tt>Instruction</tt> which the newly-created <tt>Instruction</tt> should
1962 precede. That is, <tt>Instruction</tt> constructors are capable of
1963 inserting the newly-created instance into the <tt>BasicBlock</tt> of a
1964 provided instruction, immediately before that instruction. Using an
1965 <tt>Instruction</tt> constructor with a <tt>insertBefore</tt> (default)
1966 parameter, the above code becomes:</p>
1967
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1968<div class="doc_code">
1969<pre>
1970Instruction* pi = ...;
1971Instruction* newInst = new Instruction(..., pi);
1972</pre>
1973</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1974
1975 <p>which is much cleaner, especially if you're creating a lot of
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1976 instructions and adding them to <tt>BasicBlock</tt>s.</p></li>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1977</ul>
1978
1979</div>
1980
1981<!--_______________________________________________________________________-->
1982<div class="doc_subsubsection">
1983 <a name="schanges_deleting">Deleting <tt>Instruction</tt>s</a>
1984</div>
1985
1986<div class="doc_text">
1987
1988<p>Deleting an instruction from an existing sequence of instructions that form a
Chris Lattner69bf8a92004-05-23 21:06:58 +0000[diff] [blame]1989<a href="#BasicBlock"><tt>BasicBlock</tt></a> is very straight-forward. First,
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1990you must have a pointer to the instruction that you wish to delete. Second, you
1991need to obtain the pointer to that instruction's basic block. You use the
1992pointer to the basic block to get its list of instructions and then use the
1993erase function to remove your instruction. For example:</p>
1994
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1995<div class="doc_code">
1996<pre>
1997<a href="#Instruction">Instruction</a> *I = .. ;
Chris Lattner9f8ec252008-02-15 22:57:17 +0000[diff] [blame]1998I-&gt;eraseFromParent();
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1999</pre>
2000</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2001
2002</div>
2003
2004<!--_______________________________________________________________________-->
2005<div class="doc_subsubsection">
2006 <a name="schanges_replacing">Replacing an <tt>Instruction</tt> with another
2007 <tt>Value</tt></a>
2008</div>
2009
2010<div class="doc_text">
2011
2012<p><i>Replacing individual instructions</i></p>
2013
2014<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]2015permits use of two very useful replace functions: <tt>ReplaceInstWithValue</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2016and <tt>ReplaceInstWithInst</tt>.</p>
2017
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]2018<h4><a name="schanges_deleting">Deleting <tt>Instruction</tt>s</a></h4>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2019
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]2020<ul>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2021 <li><tt>ReplaceInstWithValue</tt>
2022
Nick Lewyckyb6d1f392008-09-15 06:31:52 +0000[diff] [blame]2023 <p>This function replaces all uses of a given instruction with a value,
2024 and then removes the original instruction. The following example
2025 illustrates the replacement of the result of a particular
Chris Lattner58360822005-01-17 00:12:04 +0000[diff] [blame]2026 <tt>AllocaInst</tt> that allocates memory for a single integer with a null
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2027 pointer to an integer.</p>
2028
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2029<div class="doc_code">
2030<pre>
2031AllocaInst* instToReplace = ...;
2032BasicBlock::iterator ii(instToReplace);
2033
2034ReplaceInstWithValue(instToReplace-&gt;getParent()-&gt;getInstList(), ii,
Daniel Dunbar58c2ac02008-10-03 22:17:25 +0000[diff] [blame]2035 Constant::getNullValue(PointerType::getUnqual(Type::Int32Ty)));
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2036</pre></div></li>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2037
2038 <li><tt>ReplaceInstWithInst</tt>
2039
2040 <p>This function replaces a particular instruction with another
Nick Lewyckyb6d1f392008-09-15 06:31:52 +0000[diff] [blame]2041 instruction, inserting the new instruction into the basic block at the
2042 location where the old instruction was, and replacing any uses of the old
2043 instruction with the new instruction. The following example illustrates
2044 the replacement of one <tt>AllocaInst</tt> with another.</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2045
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2046<div class="doc_code">
2047<pre>
2048AllocaInst* instToReplace = ...;
2049BasicBlock::iterator ii(instToReplace);
2050
2051ReplaceInstWithInst(instToReplace-&gt;getParent()-&gt;getInstList(), ii,
Nick Lewycky10d64b92007-12-03 01:52:52 +0000[diff] [blame]2052 new AllocaInst(Type::Int32Ty, 0, "ptrToReplacedInt"));
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2053</pre></div></li>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]2054</ul>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2055
2056<p><i>Replacing multiple uses of <tt>User</tt>s and <tt>Value</tt>s</i></p>
2057
2058<p>You can use <tt>Value::replaceAllUsesWith</tt> and
2059<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]2060doxygen documentation for the <a href="/doxygen/classllvm_1_1Value.html">Value Class</a>
Misha Brukman384047f2004-06-03 23:29:12 +0000[diff] [blame]2061and <a href="/doxygen/classllvm_1_1User.html">User Class</a>, respectively, for more
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2062information.</p>
2063
2064<!-- Value::replaceAllUsesWith User::replaceUsesOfWith Point out:
2065include/llvm/Transforms/Utils/ especially BasicBlockUtils.h with:
2066ReplaceInstWithValue, ReplaceInstWithInst -->
2067
2068</div>
2069
Tanya Lattnerb011c662007-06-20 18:33:15 +0000[diff] [blame]2070<!--_______________________________________________________________________-->
2071<div class="doc_subsubsection">
2072 <a name="schanges_deletingGV">Deleting <tt>GlobalVariable</tt>s</a>
2073</div>
2074
2075<div class="doc_text">
2076
Tanya Lattnerc5dfcdb2007-06-20 20:46:37 +0000[diff] [blame]2077<p>Deleting a global variable from a module is just as easy as deleting an
2078Instruction. First, you must have a pointer to the global variable that you wish
2079 to delete. You use this pointer to erase it from its parent, the module.
Tanya Lattnerb011c662007-06-20 18:33:15 +0000[diff] [blame]2080 For example:</p>
2081
2082<div class="doc_code">
2083<pre>
2084<a href="#GlobalVariable">GlobalVariable</a> *GV = .. ;
Tanya Lattnerb011c662007-06-20 18:33:15 +0000[diff] [blame]2085
Tanya Lattnerc5dfcdb2007-06-20 20:46:37 +0000[diff] [blame]2086GV-&gt;eraseFromParent();
Tanya Lattnerb011c662007-06-20 18:33:15 +0000[diff] [blame]2087</pre>
2088</div>
2089
2090</div>
2091
Jeffrey Yasskin714257f2009-04-30 22:33:41 +0000[diff] [blame]2092<!-- ======================================================================= -->
2093<div class="doc_subsection">
2094 <a name="create_types">How to Create Types</a>
2095</div>
2096
2097<div class="doc_text">
2098
2099<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]2100statically, you can use <tt>TypeBuilder&lt;...&gt;::get()</tt>, defined
Jeffrey Yasskin714257f2009-04-30 22:33:41 +0000[diff] [blame]2101in <tt>llvm/Support/TypeBuilder.h</tt>, to retrieve them. <tt>TypeBuilder</tt>
2102has two forms depending on whether you're building types for cross-compilation
Misha Brukman1af789f2009-05-01 20:40:51 +0000[diff] [blame]2103or native library use. <tt>TypeBuilder&lt;T, true&gt;</tt> requires
Jeffrey Yasskin714257f2009-04-30 22:33:41 +0000[diff] [blame]2104that <tt>T</tt> be independent of the host environment, meaning that it's built
2105out of types from
2106the <a href="/doxygen/namespacellvm_1_1types.html"><tt>llvm::types</tt></a>
2107namespace and pointers, functions, arrays, etc. built of
Misha Brukman1af789f2009-05-01 20:40:51 +0000[diff] [blame]2108those. <tt>TypeBuilder&lt;T, false&gt;</tt> additionally allows native C types
Jeffrey Yasskin714257f2009-04-30 22:33:41 +0000[diff] [blame]2109whose size may depend on the host compiler. For example,</p>
2110
2111<div class="doc_code">
2112<pre>
Misha Brukman1af789f2009-05-01 20:40:51 +0000[diff] [blame]2113FunctionType *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]2114</pre>
2115</div>
2116
2117<p>is easier to read and write than the equivalent</p>
2118
2119<div class="doc_code">
2120<pre>
2121std::vector<const Type*> params;
2122params.push_back(PointerType::getUnqual(Type::Int32Ty));
2123FunctionType *ft = FunctionType::get(Type::Int8Ty, params, false);
2124</pre>
2125</div>
2126
2127<p>See the <a href="/doxygen/TypeBuilder_8h-source.html#l00001">class
2128comment</a> for more details.</p>
2129
2130</div>
2131
Chris Lattner9355b472002-09-06 02:50:58 +0000[diff] [blame]2132<!-- *********************************************************************** -->
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2133<div class="doc_section">
Chris Lattnerd9d6e102005-04-23 16:10:52 +0000[diff] [blame]2134 <a name="advanced">Advanced Topics</a>
2135</div>
2136<!-- *********************************************************************** -->
2137
2138<div class="doc_text">
Chris Lattnerf1b200b2005-04-23 17:27:36 +0000[diff] [blame]2139<p>
2140This section describes some of the advanced or obscure API's that most clients
2141do not need to be aware of. These API's tend manage the inner workings of the
2142LLVM system, and only need to be accessed in unusual circumstances.
2143</p>
2144</div>
Chris Lattnerd9d6e102005-04-23 16:10:52 +0000[diff] [blame]2145
Chris Lattnerf1b200b2005-04-23 17:27:36 +0000[diff] [blame]2146<!-- ======================================================================= -->
2147<div class="doc_subsection">
2148 <a name="TypeResolve">LLVM Type Resolution</a>
2149</div>
Chris Lattnerd9d6e102005-04-23 16:10:52 +0000[diff] [blame]2150
Chris Lattnerf1b200b2005-04-23 17:27:36 +0000[diff] [blame]2151<div class="doc_text">
2152
2153<p>
2154The LLVM type system has a very simple goal: allow clients to compare types for
2155structural equality with a simple pointer comparison (aka a shallow compare).
2156This goal makes clients much simpler and faster, and is used throughout the LLVM
2157system.
2158</p>
2159
2160<p>
2161Unfortunately achieving this goal is not a simple matter. In particular,
2162recursive types and late resolution of opaque types makes the situation very
2163difficult to handle. Fortunately, for the most part, our implementation makes
2164most clients able to be completely unaware of the nasty internal details. The
2165primary case where clients are exposed to the inner workings of it are when
Gabor Greif04367bf2007-07-06 22:07:22 +0000[diff] [blame]2166building a recursive type. In addition to this case, the LLVM bitcode reader,
Chris Lattnerf1b200b2005-04-23 17:27:36 +0000[diff] [blame]2167assembly parser, and linker also have to be aware of the inner workings of this
2168system.
2169</p>
2170
Chris Lattner0f876db2005-04-25 15:47:57 +0000[diff] [blame]2171<p>
2172For our purposes below, we need three concepts. First, an "Opaque Type" is
2173exactly as defined in the <a href="LangRef.html#t_opaque">language
2174reference</a>. Second an "Abstract Type" is any type which includes an
Reid Spencer06565dc2007-01-12 17:11:23 +0000[diff] [blame]2175opaque type as part of its type graph (for example "<tt>{ opaque, i32 }</tt>").
2176Third, 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]2177float }</tt>").
2178</p>
2179
Chris Lattnerf1b200b2005-04-23 17:27:36 +0000[diff] [blame]2180</div>
2181
2182<!-- ______________________________________________________________________ -->
2183<div class="doc_subsubsection">
2184 <a name="BuildRecType">Basic Recursive Type Construction</a>
2185</div>
2186
2187<div class="doc_text">
2188
2189<p>
2190Because the most common question is "how do I build a recursive type with LLVM",
2191we answer it now and explain it as we go. Here we include enough to cause this
2192to be emitted to an output .ll file:
2193</p>
2194
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2195<div class="doc_code">
Chris Lattnerf1b200b2005-04-23 17:27:36 +0000[diff] [blame]2196<pre>
Reid Spencer06565dc2007-01-12 17:11:23 +0000[diff] [blame]2197%mylist = type { %mylist*, i32 }
Chris Lattnerf1b200b2005-04-23 17:27:36 +0000[diff] [blame]2198</pre>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2199</div>
Chris Lattnerf1b200b2005-04-23 17:27:36 +0000[diff] [blame]2200
2201<p>
2202To build this, use the following LLVM APIs:
2203</p>
2204
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2205<div class="doc_code">
Chris Lattnerf1b200b2005-04-23 17:27:36 +0000[diff] [blame]2206<pre>
Bill Wendling82e2eea2006-10-11 18:00:22 +0000[diff] [blame]2207// <i>Create the initial outer struct</i>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2208<a href="#PATypeHolder">PATypeHolder</a> StructTy = OpaqueType::get();
2209std::vector&lt;const Type*&gt; Elts;
Daniel Dunbar58c2ac02008-10-03 22:17:25 +0000[diff] [blame]2210Elts.push_back(PointerType::getUnqual(StructTy));
Nick Lewycky10d64b92007-12-03 01:52:52 +0000[diff] [blame]2211Elts.push_back(Type::Int32Ty);
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2212StructType *NewSTy = StructType::get(Elts);
Chris Lattnerf1b200b2005-04-23 17:27:36 +0000[diff] [blame]2213
Reid Spencer06565dc2007-01-12 17:11:23 +0000[diff] [blame]2214// <i>At this point, NewSTy = "{ opaque*, i32 }". Tell VMCore that</i>
Bill Wendling82e2eea2006-10-11 18:00:22 +0000[diff] [blame]2215// <i>the struct and the opaque type are actually the same.</i>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2216cast&lt;OpaqueType&gt;(StructTy.get())-&gt;<a href="#refineAbstractTypeTo">refineAbstractTypeTo</a>(NewSTy);
Chris Lattnerf1b200b2005-04-23 17:27:36 +0000[diff] [blame]2217
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2218// <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]2219// <i>kept up-to-date</i>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2220NewSTy = cast&lt;StructType&gt;(StructTy.get());
Chris Lattnerf1b200b2005-04-23 17:27:36 +0000[diff] [blame]2221
Bill Wendling82e2eea2006-10-11 18:00:22 +0000[diff] [blame]2222// <i>Add a name for the type to the module symbol table (optional)</i>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2223MyModule-&gt;addTypeName("mylist", NewSTy);
Chris Lattnerf1b200b2005-04-23 17:27:36 +0000[diff] [blame]2224</pre>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2225</div>
Chris Lattnerf1b200b2005-04-23 17:27:36 +0000[diff] [blame]2226
2227<p>
2228This code shows the basic approach used to build recursive types: build a
2229non-recursive type using 'opaque', then use type unification to close the cycle.
2230The type unification step is performed by the <tt><a
Chris Lattneraff26d12007-02-03 03:06:52 +0000[diff] [blame]2231href="#refineAbstractTypeTo">refineAbstractTypeTo</a></tt> method, which is
Chris Lattnerf1b200b2005-04-23 17:27:36 +0000[diff] [blame]2232described next. After that, we describe the <a
2233href="#PATypeHolder">PATypeHolder class</a>.
2234</p>
2235
2236</div>
2237
2238<!-- ______________________________________________________________________ -->
2239<div class="doc_subsubsection">
2240 <a name="refineAbstractTypeTo">The <tt>refineAbstractTypeTo</tt> method</a>
2241</div>
2242
2243<div class="doc_text">
2244<p>
2245The <tt>refineAbstractTypeTo</tt> method starts the type unification process.
2246While this method is actually a member of the DerivedType class, it is most
2247often used on OpaqueType instances. Type unification is actually a recursive
2248process. After unification, types can become structurally isomorphic to
2249existing types, and all duplicates are deleted (to preserve pointer equality).
2250</p>
2251
2252<p>
2253In the example above, the OpaqueType object is definitely deleted.
Reid Spencer06565dc2007-01-12 17:11:23 +0000[diff] [blame]2254Additionally, if there is an "{ \2*, i32}" type already created in the system,
Chris Lattnerf1b200b2005-04-23 17:27:36 +0000[diff] [blame]2255the pointer and struct type created are <b>also</b> deleted. Obviously whenever
2256a type is deleted, any "Type*" pointers in the program are invalidated. As
2257such, it is safest to avoid having <i>any</i> "Type*" pointers to abstract types
2258live across a call to <tt>refineAbstractTypeTo</tt> (note that non-abstract
2259types can never move or be deleted). To deal with this, the <a
2260href="#PATypeHolder">PATypeHolder</a> class is used to maintain a stable
2261reference to a possibly refined type, and the <a
2262href="#AbstractTypeUser">AbstractTypeUser</a> class is used to update more
2263complex datastructures.
2264</p>
2265
2266</div>
2267
2268<!-- ______________________________________________________________________ -->
2269<div class="doc_subsubsection">
2270 <a name="PATypeHolder">The PATypeHolder Class</a>
2271</div>
2272
2273<div class="doc_text">
2274<p>
2275PATypeHolder is a form of a "smart pointer" for Type objects. When VMCore
2276happily goes about nuking types that become isomorphic to existing types, it
2277automatically updates all PATypeHolder objects to point to the new type. In the
2278example above, this allows the code to maintain a pointer to the resultant
2279resolved recursive type, even though the Type*'s are potentially invalidated.
2280</p>
2281
2282<p>
2283PATypeHolder is an extremely light-weight object that uses a lazy union-find
2284implementation to update pointers. For example the pointer from a Value to its
2285Type is maintained by PATypeHolder objects.
2286</p>
2287
2288</div>
2289
2290<!-- ______________________________________________________________________ -->
2291<div class="doc_subsubsection">
2292 <a name="AbstractTypeUser">The AbstractTypeUser Class</a>
2293</div>
2294
2295<div class="doc_text">
2296
2297<p>
2298Some data structures need more to perform more complex updates when types get
Chris Lattner263a98e2007-02-16 04:37:31 +0000[diff] [blame]2299resolved. To support this, a class can derive from the AbstractTypeUser class.
2300This class
Chris Lattnerf1b200b2005-04-23 17:27:36 +0000[diff] [blame]2301allows it to get callbacks when certain types are resolved. To register to get
2302callbacks for a particular type, the DerivedType::{add/remove}AbstractTypeUser
Chris Lattner0f876db2005-04-25 15:47:57 +0000[diff] [blame]2303methods can be called on a type. Note that these methods only work for <i>
Reid Spencer06565dc2007-01-12 17:11:23 +0000[diff] [blame]2304 abstract</i> types. Concrete types (those that do not include any opaque
2305objects) can never be refined.
Chris Lattnerf1b200b2005-04-23 17:27:36 +0000[diff] [blame]2306</p>
Chris Lattnerd9d6e102005-04-23 16:10:52 +0000[diff] [blame]2307</div>
2308
2309
2310<!-- ======================================================================= -->
2311<div class="doc_subsection">
Chris Lattner263a98e2007-02-16 04:37:31 +0000[diff] [blame]2312 <a name="SymbolTable">The <tt>ValueSymbolTable</tt> and
2313 <tt>TypeSymbolTable</tt> classes</a>
Chris Lattnerd9d6e102005-04-23 16:10:52 +0000[diff] [blame]2314</div>
Chris Lattnerf1b200b2005-04-23 17:27:36 +0000[diff] [blame]2315
Chris Lattnerd9d6e102005-04-23 16:10:52 +0000[diff] [blame]2316<div class="doc_text">
Chris Lattner263a98e2007-02-16 04:37:31 +0000[diff] [blame]2317<p>The <tt><a href="http://llvm.org/doxygen/classllvm_1_1ValueSymbolTable.html">
2318ValueSymbolTable</a></tt> class provides a symbol table that the <a
Chris Lattnerd9d6e102005-04-23 16:10:52 +0000[diff] [blame]2319href="#Function"><tt>Function</tt></a> and <a href="#Module">
Chris Lattner263a98e2007-02-16 04:37:31 +0000[diff] [blame]2320<tt>Module</tt></a> classes use for naming value definitions. The symbol table
2321can provide a name for any <a href="#Value"><tt>Value</tt></a>.
2322The <tt><a href="http://llvm.org/doxygen/classllvm_1_1TypeSymbolTable.html">
2323TypeSymbolTable</a></tt> class is used by the <tt>Module</tt> class to store
2324names for types.</p>
Chris Lattnerd9d6e102005-04-23 16:10:52 +0000[diff] [blame]2325
Reid Spencera6362242007-01-07 00:41:39 +0000[diff] [blame]2326<p>Note that the <tt>SymbolTable</tt> class should not be directly accessed
2327by most clients. It should only be used when iteration over the symbol table
2328names themselves are required, which is very special purpose. Note that not
2329all LLVM
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2330<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]2331an empty name) do not exist in the symbol table.
2332</p>
2333
Chris Lattner263a98e2007-02-16 04:37:31 +0000[diff] [blame]2334<p>These symbol tables support iteration over the values/types in the symbol
2335table with <tt>begin/end/iterator</tt> and supports querying to see if a
2336specific name is in the symbol table (with <tt>lookup</tt>). The
2337<tt>ValueSymbolTable</tt> class exposes no public mutator methods, instead,
2338simply call <tt>setName</tt> on a value, which will autoinsert it into the
2339appropriate symbol table. For types, use the Module::addTypeName method to
2340insert entries into the symbol table.</p>
Chris Lattnerd9d6e102005-04-23 16:10:52 +0000[diff] [blame]2341
Chris Lattnerd9d6e102005-04-23 16:10:52 +0000[diff] [blame]2342</div>
2343
2344
2345
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2346<!-- ======================================================================= -->
2347<div class="doc_subsection">
2348 <a name="UserLayout">The <tt>User</tt> and owned <tt>Use</tt> classes' memory layout</a>
2349</div>
2350
2351<div class="doc_text">
2352<p>The <tt><a href="http://llvm.org/doxygen/classllvm_1_1User.html">
Gabor Greiffd095b62009-01-05 16:05:32 +0000[diff] [blame]2353User</a></tt> class provides a basis for expressing the ownership of <tt>User</tt>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2354towards other <tt><a href="http://llvm.org/doxygen/classllvm_1_1Value.html">
2355Value</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]2356Use</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]2357addition and removal.</p>
2358
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2359<!-- ______________________________________________________________________ -->
2360<div class="doc_subsubsection">
Gabor Greiffd095b62009-01-05 16:05:32 +0000[diff] [blame]2361 <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]2362</div>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2363
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2364<div class="doc_text">
2365<p>
2366A subclass of <tt>User</tt> can choose between incorporating its <tt>Use</tt> objects
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2367or refer to them out-of-line by means of a pointer. A mixed variant
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2368(some <tt>Use</tt>s inline others hung off) is impractical and breaks the invariant
2369that the <tt>Use</tt> objects belonging to the same <tt>User</tt> form a contiguous array.
2370</p>
2371</div>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2372
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2373<p>
2374We have 2 different layouts in the <tt>User</tt> (sub)classes:
2375<ul>
2376<li><p>Layout a)
2377The <tt>Use</tt> object(s) are inside (resp. at fixed offset) of the <tt>User</tt>
2378object and there are a fixed number of them.</p>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2379
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2380<li><p>Layout b)
2381The <tt>Use</tt> object(s) are referenced by a pointer to an
2382array from the <tt>User</tt> object and there may be a variable
2383number of them.</p>
2384</ul>
2385<p>
Gabor Greifd41720a2008-06-25 00:10:22 +0000[diff] [blame]2386As of v2.4 each layout still possesses a direct pointer to the
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2387start of the array of <tt>Use</tt>s. Though not mandatory for layout a),
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2388we stick to this redundancy for the sake of simplicity.
Gabor Greifd41720a2008-06-25 00:10:22 +0000[diff] [blame]2389The <tt>User</tt> object also stores the number of <tt>Use</tt> objects it
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2390has. (Theoretically this information can also be calculated
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2391given the scheme presented below.)</p>
2392<p>
2393Special forms of allocation operators (<tt>operator new</tt>)
Gabor Greifd41720a2008-06-25 00:10:22 +0000[diff] [blame]2394enforce the following memory layouts:</p>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2395
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2396<ul>
Gabor Greifd41720a2008-06-25 00:10:22 +0000[diff] [blame]2397<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]2398
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2399<pre>
2400...---.---.---.---.-------...
2401 | P | P | P | P | User
2402'''---'---'---'---'-------'''
2403</pre>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2404
Gabor Greifd41720a2008-06-25 00:10:22 +0000[diff] [blame]2405<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]2406<pre>
2407.-------...
2408| User
2409'-------'''
2410 |
2411 v
2412 .---.---.---.---...
2413 | P | P | P | P |
2414 '---'---'---'---'''
2415</pre>
2416</ul>
2417<i>(In the above figures '<tt>P</tt>' stands for the <tt>Use**</tt> that
2418 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]2419
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2420<!-- ______________________________________________________________________ -->
2421<div class="doc_subsubsection">
Gabor Greiffd095b62009-01-05 16:05:32 +0000[diff] [blame]2422 <a name="Waymarking">The waymarking algorithm</a>
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2423</div>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2424
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2425<div class="doc_text">
2426<p>
Gabor Greifd41720a2008-06-25 00:10:22 +0000[diff] [blame]2427Since the <tt>Use</tt> objects are deprived of the direct (back)pointer to
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2428their <tt>User</tt> objects, there must be a fast and exact method to
2429recover it. This is accomplished by the following scheme:</p>
2430</div>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2431
Gabor Greifd41720a2008-06-25 00:10:22 +0000[diff] [blame]2432A 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]2433start of the <tt>User</tt> object:
2434<ul>
2435<li><tt>00</tt> &mdash;&gt; binary digit 0</li>
2436<li><tt>01</tt> &mdash;&gt; binary digit 1</li>
2437<li><tt>10</tt> &mdash;&gt; stop and calculate (<tt>s</tt>)</li>
2438<li><tt>11</tt> &mdash;&gt; full stop (<tt>S</tt>)</li>
2439</ul>
2440<p>
2441Given a <tt>Use*</tt>, all we have to do is to walk till we get
2442a stop and we either have a <tt>User</tt> immediately behind or
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2443we have to walk to the next stop picking up digits
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2444and calculating the offset:</p>
2445<pre>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2446.---.---.---.---.---.---.---.---.---.---.---.---.---.---.---.---.----------------
2447| 1 | s | 1 | 0 | 1 | 0 | s | 1 | 1 | 0 | s | 1 | 1 | s | 1 | S | User (or User*)
2448'---'---'---'---'---'---'---'---'---'---'---'---'---'---'---'---'----------------
2449 |+15 |+10 |+6 |+3 |+1
2450 | | | | |__>
2451 | | | |__________>
2452 | | |______________________>
2453 | |______________________________________>
2454 |__________________________________________________________>
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2455</pre>
2456<p>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2457Only the significant number of bits need to be stored between the
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2458stops, so that the <i>worst case is 20 memory accesses</i> when there are
24591000 <tt>Use</tt> objects associated with a <tt>User</tt>.</p>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2460
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2461<!-- ______________________________________________________________________ -->
2462<div class="doc_subsubsection">
Gabor Greiffd095b62009-01-05 16:05:32 +0000[diff] [blame]2463 <a name="ReferenceImpl">Reference implementation</a>
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2464</div>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2465
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2466<div class="doc_text">
2467<p>
2468The following literate Haskell fragment demonstrates the concept:</p>
2469</div>
2470
2471<div class="doc_code">
2472<pre>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2473> import Test.QuickCheck
2474>
2475> digits :: Int -> [Char] -> [Char]
2476> digits 0 acc = '0' : acc
2477> digits 1 acc = '1' : acc
2478> digits n acc = digits (n `div` 2) $ digits (n `mod` 2) acc
2479>
2480> dist :: Int -> [Char] -> [Char]
2481> dist 0 [] = ['S']
2482> dist 0 acc = acc
2483> dist 1 acc = let r = dist 0 acc in 's' : digits (length r) r
2484> dist n acc = dist (n - 1) $ dist 1 acc
2485>
2486> takeLast n ss = reverse $ take n $ reverse ss
2487>
2488> test = takeLast 40 $ dist 20 []
2489>
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2490</pre>
2491</div>
2492<p>
2493Printing &lt;test&gt; gives: <tt>"1s100000s11010s10100s1111s1010s110s11s1S"</tt></p>
2494<p>
2495The reverse algorithm computes the length of the string just by examining
2496a certain prefix:</p>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2497
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2498<div class="doc_code">
2499<pre>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2500> pref :: [Char] -> Int
2501> pref "S" = 1
2502> pref ('s':'1':rest) = decode 2 1 rest
2503> pref (_:rest) = 1 + pref rest
2504>
2505> decode walk acc ('0':rest) = decode (walk + 1) (acc * 2) rest
2506> decode walk acc ('1':rest) = decode (walk + 1) (acc * 2 + 1) rest
2507> decode walk acc _ = walk + acc
2508>
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2509</pre>
2510</div>
2511<p>
2512Now, as expected, printing &lt;pref test&gt; gives <tt>40</tt>.</p>
2513<p>
2514We can <i>quickCheck</i> this with following property:</p>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2515
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2516<div class="doc_code">
2517<pre>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2518> testcase = dist 2000 []
2519> testcaseLength = length testcase
2520>
2521> identityProp n = n > 0 && n <= testcaseLength ==> length arr == pref arr
2522> where arr = takeLast n testcase
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2523>
2524</pre>
2525</div>
2526<p>
2527As expected &lt;quickCheck identityProp&gt; gives:</p>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2528
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2529<pre>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2530*Main> quickCheck identityProp
2531OK, passed 100 tests.
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2532</pre>
2533<p>
2534Let's be a bit more exhaustive:</p>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2535
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2536<div class="doc_code">
2537<pre>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2538>
2539> deepCheck p = check (defaultConfig { configMaxTest = 500 }) p
2540>
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2541</pre>
2542</div>
2543<p>
2544And here is the result of &lt;deepCheck identityProp&gt;:</p>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2545
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2546<pre>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2547*Main> deepCheck identityProp
2548OK, passed 500 tests.
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2549</pre>
2550
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2551<!-- ______________________________________________________________________ -->
2552<div class="doc_subsubsection">
Gabor Greiffd095b62009-01-05 16:05:32 +0000[diff] [blame]2553 <a name="Tagging">Tagging considerations</a>
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2554</div>
2555
2556<p>
2557To maintain the invariant that the 2 LSBits of each <tt>Use**</tt> in <tt>Use</tt>
2558never change after being set up, setters of <tt>Use::Prev</tt> must re-tag the
2559new <tt>Use**</tt> on every modification. Accordingly getters must strip the
2560tag bits.</p>
2561<p>
Gabor Greifd41720a2008-06-25 00:10:22 +0000[diff] [blame]2562For layout b) instead of the <tt>User</tt> we find a pointer (<tt>User*</tt> with LSBit set).
2563Following this pointer brings us to the <tt>User</tt>. A portable trick ensures
2564that the first bytes of <tt>User</tt> (if interpreted as a pointer) never has
Gabor Greiffd095b62009-01-05 16:05:32 +0000[diff] [blame]2565the LSBit set. (Portability is relying on the fact that all known compilers place the
2566<tt>vptr</tt> in the first word of the instances.)</p>
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2567
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2568</div>
2569
2570 <!-- *********************************************************************** -->
Chris Lattnerd9d6e102005-04-23 16:10:52 +0000[diff] [blame]2571<div class="doc_section">
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2572 <a name="coreclasses">The Core LLVM Class Hierarchy Reference </a>
2573</div>
2574<!-- *********************************************************************** -->
2575
2576<div class="doc_text">
Reid Spencer303c4b42007-01-12 17:26:25 +0000[diff] [blame]2577<p><tt>#include "<a href="/doxygen/Type_8h-source.html">llvm/Type.h</a>"</tt>
2578<br>doxygen info: <a href="/doxygen/classllvm_1_1Type.html">Type Class</a></p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2579
2580<p>The Core LLVM classes are the primary means of representing the program
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]2581being inspected or transformed. The core LLVM classes are defined in
2582header files in the <tt>include/llvm/</tt> directory, and implemented in
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2583the <tt>lib/VMCore</tt> directory.</p>
2584
2585</div>
2586
2587<!-- ======================================================================= -->
2588<div class="doc_subsection">
Reid Spencer303c4b42007-01-12 17:26:25 +0000[diff] [blame]2589 <a name="Type">The <tt>Type</tt> class and Derived Types</a>
2590</div>
2591
2592<div class="doc_text">
2593
2594 <p><tt>Type</tt> is a superclass of all type classes. Every <tt>Value</tt> has
2595 a <tt>Type</tt>. <tt>Type</tt> cannot be instantiated directly but only
2596 through its subclasses. Certain primitive types (<tt>VoidType</tt>,
2597 <tt>LabelType</tt>, <tt>FloatType</tt> and <tt>DoubleType</tt>) have hidden
2598 subclasses. They are hidden because they offer no useful functionality beyond
2599 what the <tt>Type</tt> class offers except to distinguish themselves from
2600 other subclasses of <tt>Type</tt>.</p>
2601 <p>All other types are subclasses of <tt>DerivedType</tt>. Types can be
2602 named, but this is not a requirement. There exists exactly
2603 one instance of a given shape at any one time. This allows type equality to
2604 be performed with address equality of the Type Instance. That is, given two
2605 <tt>Type*</tt> values, the types are identical if the pointers are identical.
2606 </p>
2607</div>
2608
2609<!-- _______________________________________________________________________ -->
2610<div class="doc_subsubsection">
Gabor Greiffd095b62009-01-05 16:05:32 +0000[diff] [blame]2611 <a name="m_Type">Important Public Methods</a>
Reid Spencer303c4b42007-01-12 17:26:25 +0000[diff] [blame]2612</div>
2613
2614<div class="doc_text">
2615
2616<ul>
Chris Lattner8f79df32007-01-15 01:55:32 +0000[diff] [blame]2617 <li><tt>bool isInteger() const</tt>: Returns true for any integer type.</li>
Reid Spencer303c4b42007-01-12 17:26:25 +0000[diff] [blame]2618
2619 <li><tt>bool isFloatingPoint()</tt>: Return true if this is one of the two
2620 floating point types.</li>
2621
2622 <li><tt>bool isAbstract()</tt>: Return true if the type is abstract (contains
2623 an OpaqueType anywhere in its definition).</li>
2624
2625 <li><tt>bool isSized()</tt>: Return true if the type has known size. Things
2626 that don't have a size are abstract types, labels and void.</li>
2627
2628</ul>
2629</div>
2630
2631<!-- _______________________________________________________________________ -->
2632<div class="doc_subsubsection">
Gabor Greiffd095b62009-01-05 16:05:32 +0000[diff] [blame]2633 <a name="derivedtypes">Important Derived Types</a>
Reid Spencer303c4b42007-01-12 17:26:25 +0000[diff] [blame]2634</div>
2635<div class="doc_text">
2636<dl>
2637 <dt><tt>IntegerType</tt></dt>
2638 <dd>Subclass of DerivedType that represents integer types of any bit width.
2639 Any bit width between <tt>IntegerType::MIN_INT_BITS</tt> (1) and
2640 <tt>IntegerType::MAX_INT_BITS</tt> (~8 million) can be represented.
2641 <ul>
2642 <li><tt>static const IntegerType* get(unsigned NumBits)</tt>: get an integer
2643 type of a specific bit width.</li>
2644 <li><tt>unsigned getBitWidth() const</tt>: Get the bit width of an integer
2645 type.</li>
2646 </ul>
2647 </dd>
2648 <dt><tt>SequentialType</tt></dt>
2649 <dd>This is subclassed by ArrayType and PointerType
2650 <ul>
2651 <li><tt>const Type * getElementType() const</tt>: Returns the type of each
2652 of the elements in the sequential type. </li>
2653 </ul>
2654 </dd>
2655 <dt><tt>ArrayType</tt></dt>
2656 <dd>This is a subclass of SequentialType and defines the interface for array
2657 types.
2658 <ul>
2659 <li><tt>unsigned getNumElements() const</tt>: Returns the number of
2660 elements in the array. </li>
2661 </ul>
2662 </dd>
2663 <dt><tt>PointerType</tt></dt>
Chris Lattner302da1e2007-02-03 03:05:57 +0000[diff] [blame]2664 <dd>Subclass of SequentialType for pointer types.</dd>
Reid Spencer9d6565a2007-02-15 02:26:10 +0000[diff] [blame]2665 <dt><tt>VectorType</tt></dt>
Reid Spencer485bad12007-02-15 03:07:05 +0000[diff] [blame]2666 <dd>Subclass of SequentialType for vector types. A
2667 vector type is similar to an ArrayType but is distinguished because it is
2668 a first class type wherease ArrayType is not. Vector types are used for
Reid Spencer303c4b42007-01-12 17:26:25 +0000[diff] [blame]2669 vector operations and are usually small vectors of of an integer or floating
2670 point type.</dd>
2671 <dt><tt>StructType</tt></dt>
2672 <dd>Subclass of DerivedTypes for struct types.</dd>
Duncan Sands8036ca42007-03-30 12:22:09 +0000[diff] [blame]2673 <dt><tt><a name="FunctionType">FunctionType</a></tt></dt>
Reid Spencer303c4b42007-01-12 17:26:25 +0000[diff] [blame]2674 <dd>Subclass of DerivedTypes for function types.
2675 <ul>
2676 <li><tt>bool isVarArg() const</tt>: Returns true if its a vararg
2677 function</li>
2678 <li><tt> const Type * getReturnType() const</tt>: Returns the
2679 return type of the function.</li>
2680 <li><tt>const Type * getParamType (unsigned i)</tt>: Returns
2681 the type of the ith parameter.</li>
2682 <li><tt> const unsigned getNumParams() const</tt>: Returns the
2683 number of formal parameters.</li>
2684 </ul>
2685 </dd>
2686 <dt><tt>OpaqueType</tt></dt>
2687 <dd>Sublcass of DerivedType for abstract types. This class
2688 defines no content and is used as a placeholder for some other type. Note
2689 that OpaqueType is used (temporarily) during type resolution for forward
2690 references of types. Once the referenced type is resolved, the OpaqueType
2691 is replaced with the actual type. OpaqueType can also be used for data
2692 abstraction. At link time opaque types can be resolved to actual types
2693 of the same name.</dd>
2694</dl>
2695</div>
2696
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]2697
2698
2699<!-- ======================================================================= -->
2700<div class="doc_subsection">
2701 <a name="Module">The <tt>Module</tt> class</a>
2702</div>
2703
2704<div class="doc_text">
2705
2706<p><tt>#include "<a
2707href="/doxygen/Module_8h-source.html">llvm/Module.h</a>"</tt><br> doxygen info:
2708<a href="/doxygen/classllvm_1_1Module.html">Module Class</a></p>
2709
2710<p>The <tt>Module</tt> class represents the top level structure present in LLVM
2711programs. An LLVM module is effectively either a translation unit of the
2712original program or a combination of several translation units merged by the
2713linker. The <tt>Module</tt> class keeps track of a list of <a
2714href="#Function"><tt>Function</tt></a>s, a list of <a
2715href="#GlobalVariable"><tt>GlobalVariable</tt></a>s, and a <a
2716href="#SymbolTable"><tt>SymbolTable</tt></a>. Additionally, it contains a few
2717helpful member functions that try to make common operations easy.</p>
2718
2719</div>
2720
2721<!-- _______________________________________________________________________ -->
2722<div class="doc_subsubsection">
2723 <a name="m_Module">Important Public Members of the <tt>Module</tt> class</a>
2724</div>
2725
2726<div class="doc_text">
2727
2728<ul>
2729 <li><tt>Module::Module(std::string name = "")</tt></li>
2730</ul>
2731
2732<p>Constructing a <a href="#Module">Module</a> is easy. You can optionally
2733provide a name for it (probably based on the name of the translation unit).</p>
2734
2735<ul>
2736 <li><tt>Module::iterator</tt> - Typedef for function list iterator<br>
2737 <tt>Module::const_iterator</tt> - Typedef for const_iterator.<br>
2738
2739 <tt>begin()</tt>, <tt>end()</tt>
2740 <tt>size()</tt>, <tt>empty()</tt>
2741
2742 <p>These are forwarding methods that make it easy to access the contents of
2743 a <tt>Module</tt> object's <a href="#Function"><tt>Function</tt></a>
2744 list.</p></li>
2745
2746 <li><tt>Module::FunctionListType &amp;getFunctionList()</tt>
2747
2748 <p> Returns the list of <a href="#Function"><tt>Function</tt></a>s. This is
2749 necessary to use when you need to update the list or perform a complex
2750 action that doesn't have a forwarding method.</p>
2751
2752 <p><!-- Global Variable --></p></li>
2753</ul>
2754
2755<hr>
2756
2757<ul>
2758 <li><tt>Module::global_iterator</tt> - Typedef for global variable list iterator<br>
2759
2760 <tt>Module::const_global_iterator</tt> - Typedef for const_iterator.<br>
2761
2762 <tt>global_begin()</tt>, <tt>global_end()</tt>
2763 <tt>global_size()</tt>, <tt>global_empty()</tt>
2764
2765 <p> These are forwarding methods that make it easy to access the contents of
2766 a <tt>Module</tt> object's <a
2767 href="#GlobalVariable"><tt>GlobalVariable</tt></a> list.</p></li>
2768
2769 <li><tt>Module::GlobalListType &amp;getGlobalList()</tt>
2770
2771 <p>Returns the list of <a
2772 href="#GlobalVariable"><tt>GlobalVariable</tt></a>s. This is necessary to
2773 use when you need to update the list or perform a complex action that
2774 doesn't have a forwarding method.</p>
2775
2776 <p><!-- Symbol table stuff --> </p></li>
2777</ul>
2778
2779<hr>
2780
2781<ul>
2782 <li><tt><a href="#SymbolTable">SymbolTable</a> *getSymbolTable()</tt>
2783
2784 <p>Return a reference to the <a href="#SymbolTable"><tt>SymbolTable</tt></a>
2785 for this <tt>Module</tt>.</p>
2786
2787 <p><!-- Convenience methods --></p></li>
2788</ul>
2789
2790<hr>
2791
2792<ul>
2793 <li><tt><a href="#Function">Function</a> *getFunction(const std::string
2794 &amp;Name, const <a href="#FunctionType">FunctionType</a> *Ty)</tt>
2795
2796 <p>Look up the specified function in the <tt>Module</tt> <a
2797 href="#SymbolTable"><tt>SymbolTable</tt></a>. If it does not exist, return
2798 <tt>null</tt>.</p></li>
2799
2800 <li><tt><a href="#Function">Function</a> *getOrInsertFunction(const
2801 std::string &amp;Name, const <a href="#FunctionType">FunctionType</a> *T)</tt>
2802
2803 <p>Look up the specified function in the <tt>Module</tt> <a
2804 href="#SymbolTable"><tt>SymbolTable</tt></a>. If it does not exist, add an
2805 external declaration for the function and return it.</p></li>
2806
2807 <li><tt>std::string getTypeName(const <a href="#Type">Type</a> *Ty)</tt>
2808
2809 <p>If there is at least one entry in the <a
2810 href="#SymbolTable"><tt>SymbolTable</tt></a> for the specified <a
2811 href="#Type"><tt>Type</tt></a>, return it. Otherwise return the empty
2812 string.</p></li>
2813
2814 <li><tt>bool addTypeName(const std::string &amp;Name, const <a
2815 href="#Type">Type</a> *Ty)</tt>
2816
2817 <p>Insert an entry in the <a href="#SymbolTable"><tt>SymbolTable</tt></a>
2818 mapping <tt>Name</tt> to <tt>Ty</tt>. If there is already an entry for this
2819 name, true is returned and the <a
2820 href="#SymbolTable"><tt>SymbolTable</tt></a> is not modified.</p></li>
2821</ul>
2822
2823</div>
2824
2825
Reid Spencer303c4b42007-01-12 17:26:25 +0000[diff] [blame]2826<!-- ======================================================================= -->
2827<div class="doc_subsection">
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2828 <a name="Value">The <tt>Value</tt> class</a>
2829</div>
2830
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]2831<div class="doc_text">
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2832
2833<p><tt>#include "<a href="/doxygen/Value_8h-source.html">llvm/Value.h</a>"</tt>
2834<br>
Chris Lattner00815172007-01-04 22:01:45 +0000[diff] [blame]2835doxygen info: <a href="/doxygen/classllvm_1_1Value.html">Value Class</a></p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2836
2837<p>The <tt>Value</tt> class is the most important class in the LLVM Source
2838base. It represents a typed value that may be used (among other things) as an
2839operand to an instruction. There are many different types of <tt>Value</tt>s,
2840such as <a href="#Constant"><tt>Constant</tt></a>s,<a
2841href="#Argument"><tt>Argument</tt></a>s. Even <a
2842href="#Instruction"><tt>Instruction</tt></a>s and <a
2843href="#Function"><tt>Function</tt></a>s are <tt>Value</tt>s.</p>
2844
2845<p>A particular <tt>Value</tt> may be used many times in the LLVM representation
2846for a program. For example, an incoming argument to a function (represented
2847with an instance of the <a href="#Argument">Argument</a> class) is "used" by
2848every instruction in the function that references the argument. To keep track
2849of this relationship, the <tt>Value</tt> class keeps a list of all of the <a
2850href="#User"><tt>User</tt></a>s that is using it (the <a
2851href="#User"><tt>User</tt></a> class is a base class for all nodes in the LLVM
2852graph that can refer to <tt>Value</tt>s). This use list is how LLVM represents
2853def-use information in the program, and is accessible through the <tt>use_</tt>*
2854methods, shown below.</p>
2855
2856<p>Because LLVM is a typed representation, every LLVM <tt>Value</tt> is typed,
2857and this <a href="#Type">Type</a> is available through the <tt>getType()</tt>
2858method. In addition, all LLVM values can be named. The "name" of the
2859<tt>Value</tt> is a symbolic string printed in the LLVM code:</p>
2860
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2861<div class="doc_code">
2862<pre>
Reid Spencer06565dc2007-01-12 17:11:23 +0000[diff] [blame]2863%<b>foo</b> = add i32 1, 2
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2864</pre>
2865</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2866
Duncan Sands8036ca42007-03-30 12:22:09 +0000[diff] [blame]2867<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]2868that the name of any value may be missing (an empty string), so names should
2869<b>ONLY</b> be used for debugging (making the source code easier to read,
2870debugging printouts), they should not be used to keep track of values or map
2871between them. For this purpose, use a <tt>std::map</tt> of pointers to the
2872<tt>Value</tt> itself instead.</p>
2873
2874<p>One important aspect of LLVM is that there is no distinction between an SSA
2875variable and the operation that produces it. Because of this, any reference to
2876the value produced by an instruction (or the value available as an incoming
Chris Lattnerd5fc4fc2004-03-18 14:58:55 +0000[diff] [blame]2877argument, for example) is represented as a direct pointer to the instance of
2878the class that
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2879represents this value. Although this may take some getting used to, it
2880simplifies the representation and makes it easier to manipulate.</p>
2881
2882</div>
2883
2884<!-- _______________________________________________________________________ -->
2885<div class="doc_subsubsection">
2886 <a name="m_Value">Important Public Members of the <tt>Value</tt> class</a>
2887</div>
2888
2889<div class="doc_text">
2890
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]2891<ul>
2892 <li><tt>Value::use_iterator</tt> - Typedef for iterator over the
2893use-list<br>
2894 <tt>Value::use_const_iterator</tt> - Typedef for const_iterator over
2895the use-list<br>
2896 <tt>unsigned use_size()</tt> - Returns the number of users of the
2897value.<br>
Chris Lattner9355b472002-09-06 02:50:58 +0000[diff] [blame]2898 <tt>bool use_empty()</tt> - Returns true if there are no users.<br>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]2899 <tt>use_iterator use_begin()</tt> - Get an iterator to the start of
2900the use-list.<br>
2901 <tt>use_iterator use_end()</tt> - Get an iterator to the end of the
2902use-list.<br>
2903 <tt><a href="#User">User</a> *use_back()</tt> - Returns the last
2904element in the list.
2905 <p> These methods are the interface to access the def-use
2906information in LLVM. As with all other iterators in LLVM, the naming
2907conventions follow the conventions defined by the <a href="#stl">STL</a>.</p>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]2908 </li>
2909 <li><tt><a href="#Type">Type</a> *getType() const</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2910 <p>This method returns the Type of the Value.</p>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]2911 </li>
2912 <li><tt>bool hasName() const</tt><br>
Chris Lattner9355b472002-09-06 02:50:58 +0000[diff] [blame]2913 <tt>std::string getName() const</tt><br>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]2914 <tt>void setName(const std::string &amp;Name)</tt>
2915 <p> This family of methods is used to access and assign a name to a <tt>Value</tt>,
2916be aware of the <a href="#nameWarning">precaution above</a>.</p>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]2917 </li>
2918 <li><tt>void replaceAllUsesWith(Value *V)</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2919
2920 <p>This method traverses the use list of a <tt>Value</tt> changing all <a
2921 href="#User"><tt>User</tt>s</a> of the current value to refer to
2922 "<tt>V</tt>" instead. For example, if you detect that an instruction always
2923 produces a constant value (for example through constant folding), you can
2924 replace all uses of the instruction with the constant like this:</p>
2925
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2926<div class="doc_code">
2927<pre>
2928Inst-&gt;replaceAllUsesWith(ConstVal);
2929</pre>
2930</div>
2931
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]2932</ul>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2933
2934</div>
2935
2936<!-- ======================================================================= -->
2937<div class="doc_subsection">
2938 <a name="User">The <tt>User</tt> class</a>
2939</div>
2940
2941<div class="doc_text">
2942
2943<p>
2944<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]2945doxygen info: <a href="/doxygen/classllvm_1_1User.html">User Class</a><br>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2946Superclass: <a href="#Value"><tt>Value</tt></a></p>
2947
2948<p>The <tt>User</tt> class is the common base class of all LLVM nodes that may
2949refer to <a href="#Value"><tt>Value</tt></a>s. It exposes a list of "Operands"
2950that are all of the <a href="#Value"><tt>Value</tt></a>s that the User is
2951referring to. The <tt>User</tt> class itself is a subclass of
2952<tt>Value</tt>.</p>
2953
2954<p>The operands of a <tt>User</tt> point directly to the LLVM <a
2955href="#Value"><tt>Value</tt></a> that it refers to. Because LLVM uses Static
2956Single Assignment (SSA) form, there can only be one definition referred to,
2957allowing this direct connection. This connection provides the use-def
2958information in LLVM.</p>
2959
2960</div>
2961
2962<!-- _______________________________________________________________________ -->
2963<div class="doc_subsubsection">
2964 <a name="m_User">Important Public Members of the <tt>User</tt> class</a>
2965</div>
2966
2967<div class="doc_text">
2968
2969<p>The <tt>User</tt> class exposes the operand list in two ways: through
2970an index access interface and through an iterator based interface.</p>
2971
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]2972<ul>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]2973 <li><tt>Value *getOperand(unsigned i)</tt><br>
2974 <tt>unsigned getNumOperands()</tt>
2975 <p> These two methods expose the operands of the <tt>User</tt> in a
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2976convenient form for direct access.</p></li>
2977
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]2978 <li><tt>User::op_iterator</tt> - Typedef for iterator over the operand
2979list<br>
Chris Lattner58360822005-01-17 00:12:04 +0000[diff] [blame]2980 <tt>op_iterator op_begin()</tt> - Get an iterator to the start of
2981the operand list.<br>
2982 <tt>op_iterator op_end()</tt> - Get an iterator to the end of the
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]2983operand list.
2984 <p> Together, these methods make up the iterator based interface to
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2985the operands of a <tt>User</tt>.</p></li>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]2986</ul>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2987
2988</div>
2989
2990<!-- ======================================================================= -->
2991<div class="doc_subsection">
2992 <a name="Instruction">The <tt>Instruction</tt> class</a>
2993</div>
2994
2995<div class="doc_text">
2996
2997<p><tt>#include "</tt><tt><a
2998href="/doxygen/Instruction_8h-source.html">llvm/Instruction.h</a>"</tt><br>
Misha Brukman31ca1de2004-06-03 23:35:54 +0000[diff] [blame]2999doxygen info: <a href="/doxygen/classllvm_1_1Instruction.html">Instruction Class</a><br>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3000Superclasses: <a href="#User"><tt>User</tt></a>, <a
3001href="#Value"><tt>Value</tt></a></p>
3002
3003<p>The <tt>Instruction</tt> class is the common base class for all LLVM
3004instructions. It provides only a few methods, but is a very commonly used
3005class. The primary data tracked by the <tt>Instruction</tt> class itself is the
3006opcode (instruction type) and the parent <a
3007href="#BasicBlock"><tt>BasicBlock</tt></a> the <tt>Instruction</tt> is embedded
3008into. To represent a specific type of instruction, one of many subclasses of
3009<tt>Instruction</tt> are used.</p>
3010
3011<p> Because the <tt>Instruction</tt> class subclasses the <a
3012href="#User"><tt>User</tt></a> class, its operands can be accessed in the same
3013way as for other <a href="#User"><tt>User</tt></a>s (with the
3014<tt>getOperand()</tt>/<tt>getNumOperands()</tt> and
3015<tt>op_begin()</tt>/<tt>op_end()</tt> methods).</p> <p> An important file for
3016the <tt>Instruction</tt> class is the <tt>llvm/Instruction.def</tt> file. This
3017file contains some meta-data about the various different types of instructions
3018in LLVM. It describes the enum values that are used as opcodes (for example
Reid Spencerc92d25d2006-12-19 19:47:19 +0000[diff] [blame]3019<tt>Instruction::Add</tt> and <tt>Instruction::ICmp</tt>), as well as the
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3020concrete sub-classes of <tt>Instruction</tt> that implement the instruction (for
3021example <tt><a href="#BinaryOperator">BinaryOperator</a></tt> and <tt><a
Reid Spencerc92d25d2006-12-19 19:47:19 +0000[diff] [blame]3022href="#CmpInst">CmpInst</a></tt>). Unfortunately, the use of macros in
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3023this file confuses doxygen, so these enum values don't show up correctly in the
Misha Brukman31ca1de2004-06-03 23:35:54 +0000[diff] [blame]3024<a href="/doxygen/classllvm_1_1Instruction.html">doxygen output</a>.</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3025
3026</div>
3027
3028<!-- _______________________________________________________________________ -->
3029<div class="doc_subsubsection">
Reid Spencerc92d25d2006-12-19 19:47:19 +0000[diff] [blame]3030 <a name="s_Instruction">Important Subclasses of the <tt>Instruction</tt>
3031 class</a>
3032</div>
3033<div class="doc_text">
3034 <ul>
3035 <li><tt><a name="BinaryOperator">BinaryOperator</a></tt>
3036 <p>This subclasses represents all two operand instructions whose operands
3037 must be the same type, except for the comparison instructions.</p></li>
3038 <li><tt><a name="CastInst">CastInst</a></tt>
3039 <p>This subclass is the parent of the 12 casting instructions. It provides
3040 common operations on cast instructions.</p>
3041 <li><tt><a name="CmpInst">CmpInst</a></tt>
3042 <p>This subclass respresents the two comparison instructions,
3043 <a href="LangRef.html#i_icmp">ICmpInst</a> (integer opreands), and
3044 <a href="LangRef.html#i_fcmp">FCmpInst</a> (floating point operands).</p>
3045 <li><tt><a name="TerminatorInst">TerminatorInst</a></tt>
3046 <p>This subclass is the parent of all terminator instructions (those which
3047 can terminate a block).</p>
3048 </ul>
3049 </div>
3050
3051<!-- _______________________________________________________________________ -->
3052<div class="doc_subsubsection">
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3053 <a name="m_Instruction">Important Public Members of the <tt>Instruction</tt>
3054 class</a>
3055</div>
3056
3057<div class="doc_text">
3058
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3059<ul>
3060 <li><tt><a href="#BasicBlock">BasicBlock</a> *getParent()</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3061 <p>Returns the <a href="#BasicBlock"><tt>BasicBlock</tt></a> that
3062this <tt>Instruction</tt> is embedded into.</p></li>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3063 <li><tt>bool mayWriteToMemory()</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3064 <p>Returns true if the instruction writes to memory, i.e. it is a
3065 <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]3066 <li><tt>unsigned getOpcode()</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3067 <p>Returns the opcode for the <tt>Instruction</tt>.</p></li>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3068 <li><tt><a href="#Instruction">Instruction</a> *clone() const</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3069 <p>Returns another instance of the specified instruction, identical
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3070in all ways to the original except that the instruction has no parent
3071(ie it's not embedded into a <a href="#BasicBlock"><tt>BasicBlock</tt></a>),
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3072and it has no name</p></li>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3073</ul>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3074
3075</div>
3076
3077<!-- ======================================================================= -->
3078<div class="doc_subsection">
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]3079 <a name="Constant">The <tt>Constant</tt> class and subclasses</a>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3080</div>
3081
3082<div class="doc_text">
3083
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]3084<p>Constant represents a base class for different types of constants. It
3085is subclassed by ConstantInt, ConstantArray, etc. for representing
3086the various types of Constants. <a href="#GlobalValue">GlobalValue</a> is also
3087a subclass, which represents the address of a global variable or function.
3088</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3089
3090</div>
3091
3092<!-- _______________________________________________________________________ -->
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]3093<div class="doc_subsubsection">Important Subclasses of Constant </div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3094<div class="doc_text">
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3095<ul>
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]3096 <li>ConstantInt : This subclass of Constant represents an integer constant of
3097 any width.
3098 <ul>
Reid Spencer97b4ee32007-03-01 21:05:33 +0000[diff] [blame]3099 <li><tt>const APInt&amp; getValue() const</tt>: Returns the underlying
3100 value of this constant, an APInt value.</li>
3101 <li><tt>int64_t getSExtValue() const</tt>: Converts the underlying APInt
3102 value to an int64_t via sign extension. If the value (not the bit width)
3103 of the APInt is too large to fit in an int64_t, an assertion will result.
3104 For this reason, use of this method is discouraged.</li>
3105 <li><tt>uint64_t getZExtValue() const</tt>: Converts the underlying APInt
3106 value to a uint64_t via zero extension. IF the value (not the bit width)
3107 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]3108 For this reason, use of this method is discouraged.</li>
Reid Spencer97b4ee32007-03-01 21:05:33 +0000[diff] [blame]3109 <li><tt>static ConstantInt* get(const APInt&amp; Val)</tt>: Returns the
3110 ConstantInt object that represents the value provided by <tt>Val</tt>.
3111 The type is implied as the IntegerType that corresponds to the bit width
3112 of <tt>Val</tt>.</li>
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]3113 <li><tt>static ConstantInt* get(const Type *Ty, uint64_t Val)</tt>:
3114 Returns the ConstantInt object that represents the value provided by
3115 <tt>Val</tt> for integer type <tt>Ty</tt>.</li>
3116 </ul>
3117 </li>
3118 <li>ConstantFP : This class represents a floating point constant.
3119 <ul>
3120 <li><tt>double getValue() const</tt>: Returns the underlying value of
3121 this constant. </li>
3122 </ul>
3123 </li>
3124 <li>ConstantArray : This represents a constant array.
3125 <ul>
3126 <li><tt>const std::vector&lt;Use&gt; &amp;getValues() const</tt>: Returns
3127 a vector of component constants that makeup this array. </li>
3128 </ul>
3129 </li>
3130 <li>ConstantStruct : This represents a constant struct.
3131 <ul>
3132 <li><tt>const std::vector&lt;Use&gt; &amp;getValues() const</tt>: Returns
3133 a vector of component constants that makeup this array. </li>
3134 </ul>
3135 </li>
3136 <li>GlobalValue : This represents either a global variable or a function. In
3137 either case, the value is a constant fixed address (after linking).
3138 </li>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3139</ul>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3140</div>
3141
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]3142
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3143<!-- ======================================================================= -->
3144<div class="doc_subsection">
3145 <a name="GlobalValue">The <tt>GlobalValue</tt> class</a>
3146</div>
3147
3148<div class="doc_text">
3149
3150<p><tt>#include "<a
3151href="/doxygen/GlobalValue_8h-source.html">llvm/GlobalValue.h</a>"</tt><br>
Misha Brukman384047f2004-06-03 23:29:12 +0000[diff] [blame]3152doxygen info: <a href="/doxygen/classllvm_1_1GlobalValue.html">GlobalValue
3153Class</a><br>
Reid Spencerbe5e85e2006-04-14 14:11:48 +0000[diff] [blame]3154Superclasses: <a href="#Constant"><tt>Constant</tt></a>,
3155<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]3156
3157<p>Global values (<a href="#GlobalVariable"><tt>GlobalVariable</tt></a>s or <a
3158href="#Function"><tt>Function</tt></a>s) are the only LLVM values that are
3159visible in the bodies of all <a href="#Function"><tt>Function</tt></a>s.
3160Because they are visible at global scope, they are also subject to linking with
3161other globals defined in different translation units. To control the linking
3162process, <tt>GlobalValue</tt>s know their linkage rules. Specifically,
3163<tt>GlobalValue</tt>s know whether they have internal or external linkage, as
Reid Spencer8b2da7a2004-07-18 13:10:31 +0000[diff] [blame]3164defined by the <tt>LinkageTypes</tt> enumeration.</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3165
3166<p>If a <tt>GlobalValue</tt> has internal linkage (equivalent to being
3167<tt>static</tt> in C), it is not visible to code outside the current translation
3168unit, and does not participate in linking. If it has external linkage, it is
3169visible to external code, and does participate in linking. In addition to
3170linkage information, <tt>GlobalValue</tt>s keep track of which <a
3171href="#Module"><tt>Module</tt></a> they are currently part of.</p>
3172
3173<p>Because <tt>GlobalValue</tt>s are memory objects, they are always referred to
3174by their <b>address</b>. As such, the <a href="#Type"><tt>Type</tt></a> of a
3175global is always a pointer to its contents. It is important to remember this
3176when using the <tt>GetElementPtrInst</tt> instruction because this pointer must
3177be dereferenced first. For example, if you have a <tt>GlobalVariable</tt> (a
3178subclass 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]3179i32]</tt>, then the <tt>GlobalVariable</tt> is a pointer to that array. Although
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3180the address of the first element of this array and the value of the
3181<tt>GlobalVariable</tt> are the same, they have different types. The
Reid Spencer06565dc2007-01-12 17:11:23 +0000[diff] [blame]3182<tt>GlobalVariable</tt>'s type is <tt>[24 x i32]</tt>. The first element's type
3183is <tt>i32.</tt> Because of this, accessing a global value requires you to
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3184dereference the pointer with <tt>GetElementPtrInst</tt> first, then its elements
3185can be accessed. This is explained in the <a href="LangRef.html#globalvars">LLVM
3186Language Reference Manual</a>.</p>
3187
3188</div>
3189
3190<!-- _______________________________________________________________________ -->
3191<div class="doc_subsubsection">
3192 <a name="m_GlobalValue">Important Public Members of the <tt>GlobalValue</tt>
3193 class</a>
3194</div>
3195
3196<div class="doc_text">
3197
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3198<ul>
3199 <li><tt>bool hasInternalLinkage() const</tt><br>
Chris Lattner9355b472002-09-06 02:50:58 +0000[diff] [blame]3200 <tt>bool hasExternalLinkage() const</tt><br>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3201 <tt>void setInternalLinkage(bool HasInternalLinkage)</tt>
3202 <p> These methods manipulate the linkage characteristics of the <tt>GlobalValue</tt>.</p>
3203 <p> </p>
3204 </li>
3205 <li><tt><a href="#Module">Module</a> *getParent()</tt>
3206 <p> This returns the <a href="#Module"><tt>Module</tt></a> that the
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3207GlobalValue is currently embedded into.</p></li>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3208</ul>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3209
3210</div>
3211
3212<!-- ======================================================================= -->
3213<div class="doc_subsection">
3214 <a name="Function">The <tt>Function</tt> class</a>
3215</div>
3216
3217<div class="doc_text">
3218
3219<p><tt>#include "<a
3220href="/doxygen/Function_8h-source.html">llvm/Function.h</a>"</tt><br> doxygen
Misha Brukman31ca1de2004-06-03 23:35:54 +0000[diff] [blame]3221info: <a href="/doxygen/classllvm_1_1Function.html">Function Class</a><br>
Reid Spencerbe5e85e2006-04-14 14:11:48 +0000[diff] [blame]3222Superclasses: <a href="#GlobalValue"><tt>GlobalValue</tt></a>,
3223<a href="#Constant"><tt>Constant</tt></a>,
3224<a href="#User"><tt>User</tt></a>,
3225<a href="#Value"><tt>Value</tt></a></p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3226
3227<p>The <tt>Function</tt> class represents a single procedure in LLVM. It is
3228actually one of the more complex classes in the LLVM heirarchy because it must
3229keep track of a large amount of data. The <tt>Function</tt> class keeps track
Reid Spencerbe5e85e2006-04-14 14:11:48 +0000[diff] [blame]3230of a list of <a href="#BasicBlock"><tt>BasicBlock</tt></a>s, a list of formal
3231<a href="#Argument"><tt>Argument</tt></a>s, and a
3232<a href="#SymbolTable"><tt>SymbolTable</tt></a>.</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3233
3234<p>The list of <a href="#BasicBlock"><tt>BasicBlock</tt></a>s is the most
3235commonly used part of <tt>Function</tt> objects. The list imposes an implicit
3236ordering of the blocks in the function, which indicate how the code will be
3237layed out by the backend. Additionally, the first <a
3238href="#BasicBlock"><tt>BasicBlock</tt></a> is the implicit entry node for the
3239<tt>Function</tt>. It is not legal in LLVM to explicitly branch to this initial
3240block. There are no implicit exit nodes, and in fact there may be multiple exit
3241nodes from a single <tt>Function</tt>. If the <a
3242href="#BasicBlock"><tt>BasicBlock</tt></a> list is empty, this indicates that
3243the <tt>Function</tt> is actually a function declaration: the actual body of the
3244function hasn't been linked in yet.</p>
3245
3246<p>In addition to a list of <a href="#BasicBlock"><tt>BasicBlock</tt></a>s, the
3247<tt>Function</tt> class also keeps track of the list of formal <a
3248href="#Argument"><tt>Argument</tt></a>s that the function receives. This
3249container manages the lifetime of the <a href="#Argument"><tt>Argument</tt></a>
3250nodes, just like the <a href="#BasicBlock"><tt>BasicBlock</tt></a> list does for
3251the <a href="#BasicBlock"><tt>BasicBlock</tt></a>s.</p>
3252
3253<p>The <a href="#SymbolTable"><tt>SymbolTable</tt></a> is a very rarely used
3254LLVM feature that is only used when you have to look up a value by name. Aside
3255from that, the <a href="#SymbolTable"><tt>SymbolTable</tt></a> is used
3256internally to make sure that there are not conflicts between the names of <a
3257href="#Instruction"><tt>Instruction</tt></a>s, <a
3258href="#BasicBlock"><tt>BasicBlock</tt></a>s, or <a
3259href="#Argument"><tt>Argument</tt></a>s in the function body.</p>
3260
Reid Spencer8b2da7a2004-07-18 13:10:31 +0000[diff] [blame]3261<p>Note that <tt>Function</tt> is a <a href="#GlobalValue">GlobalValue</a>
3262and therefore also a <a href="#Constant">Constant</a>. The value of the function
3263is its address (after linking) which is guaranteed to be constant.</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3264</div>
3265
3266<!-- _______________________________________________________________________ -->
3267<div class="doc_subsubsection">
3268 <a name="m_Function">Important Public Members of the <tt>Function</tt>
3269 class</a>
3270</div>
3271
3272<div class="doc_text">
3273
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3274<ul>
3275 <li><tt>Function(const </tt><tt><a href="#FunctionType">FunctionType</a>
Chris Lattnerac479e52004-08-04 05:10:48 +0000[diff] [blame]3276 *Ty, LinkageTypes Linkage, const std::string &amp;N = "", Module* Parent = 0)</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3277
3278 <p>Constructor used when you need to create new <tt>Function</tt>s to add
3279 the the program. The constructor must specify the type of the function to
Chris Lattnerac479e52004-08-04 05:10:48 +0000[diff] [blame]3280 create and what type of linkage the function should have. The <a
3281 href="#FunctionType"><tt>FunctionType</tt></a> argument
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3282 specifies the formal arguments and return value for the function. The same
Duncan Sands8036ca42007-03-30 12:22:09 +0000[diff] [blame]3283 <a href="#FunctionType"><tt>FunctionType</tt></a> value can be used to
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3284 create multiple functions. The <tt>Parent</tt> argument specifies the Module
3285 in which the function is defined. If this argument is provided, the function
3286 will automatically be inserted into that module's list of
3287 functions.</p></li>
3288
Chris Lattner62810e32008-11-25 18:34:50 +0000[diff] [blame]3289 <li><tt>bool isDeclaration()</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3290
3291 <p>Return whether or not the <tt>Function</tt> has a body defined. If the
3292 function is "external", it does not have a body, and thus must be resolved
3293 by linking with a function defined in a different translation unit.</p></li>
3294
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3295 <li><tt>Function::iterator</tt> - Typedef for basic block list iterator<br>
Chris Lattner9355b472002-09-06 02:50:58 +0000[diff] [blame]3296 <tt>Function::const_iterator</tt> - Typedef for const_iterator.<br>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3297
Chris Lattner77d69242005-03-15 05:19:20 +0000[diff] [blame]3298 <tt>begin()</tt>, <tt>end()</tt>
3299 <tt>size()</tt>, <tt>empty()</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3300
3301 <p>These are forwarding methods that make it easy to access the contents of
3302 a <tt>Function</tt> object's <a href="#BasicBlock"><tt>BasicBlock</tt></a>
3303 list.</p></li>
3304
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3305 <li><tt>Function::BasicBlockListType &amp;getBasicBlockList()</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3306
3307 <p>Returns the list of <a href="#BasicBlock"><tt>BasicBlock</tt></a>s. This
3308 is necessary to use when you need to update the list or perform a complex
3309 action that doesn't have a forwarding method.</p></li>
3310
Chris Lattner89cc2652005-03-15 04:48:32 +0000[diff] [blame]3311 <li><tt>Function::arg_iterator</tt> - Typedef for the argument list
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3312iterator<br>
Chris Lattner89cc2652005-03-15 04:48:32 +0000[diff] [blame]3313 <tt>Function::const_arg_iterator</tt> - Typedef for const_iterator.<br>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3314
Chris Lattner77d69242005-03-15 05:19:20 +0000[diff] [blame]3315 <tt>arg_begin()</tt>, <tt>arg_end()</tt>
Chris Lattner89cc2652005-03-15 04:48:32 +0000[diff] [blame]3316 <tt>arg_size()</tt>, <tt>arg_empty()</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3317
3318 <p>These are forwarding methods that make it easy to access the contents of
3319 a <tt>Function</tt> object's <a href="#Argument"><tt>Argument</tt></a>
3320 list.</p></li>
3321
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3322 <li><tt>Function::ArgumentListType &amp;getArgumentList()</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3323
3324 <p>Returns the list of <a href="#Argument"><tt>Argument</tt></a>s. This is
3325 necessary to use when you need to update the list or perform a complex
3326 action that doesn't have a forwarding method.</p></li>
3327
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3328 <li><tt><a href="#BasicBlock">BasicBlock</a> &amp;getEntryBlock()</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3329
3330 <p>Returns the entry <a href="#BasicBlock"><tt>BasicBlock</tt></a> for the
3331 function. Because the entry block for the function is always the first
3332 block, this returns the first block of the <tt>Function</tt>.</p></li>
3333
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3334 <li><tt><a href="#Type">Type</a> *getReturnType()</tt><br>
3335 <tt><a href="#FunctionType">FunctionType</a> *getFunctionType()</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3336
3337 <p>This traverses the <a href="#Type"><tt>Type</tt></a> of the
3338 <tt>Function</tt> and returns the return type of the function, or the <a
3339 href="#FunctionType"><tt>FunctionType</tt></a> of the actual
3340 function.</p></li>
3341
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3342 <li><tt><a href="#SymbolTable">SymbolTable</a> *getSymbolTable()</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3343
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3344 <p> Return a pointer to the <a href="#SymbolTable"><tt>SymbolTable</tt></a>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3345 for this <tt>Function</tt>.</p></li>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3346</ul>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3347
3348</div>
3349
3350<!-- ======================================================================= -->
3351<div class="doc_subsection">
3352 <a name="GlobalVariable">The <tt>GlobalVariable</tt> class</a>
3353</div>
3354
3355<div class="doc_text">
3356
3357<p><tt>#include "<a
3358href="/doxygen/GlobalVariable_8h-source.html">llvm/GlobalVariable.h</a>"</tt>
3359<br>
Tanya Lattnera3da7772004-06-22 08:02:25 +0000[diff] [blame]3360doxygen info: <a href="/doxygen/classllvm_1_1GlobalVariable.html">GlobalVariable
Reid Spencerbe5e85e2006-04-14 14:11:48 +0000[diff] [blame]3361 Class</a><br>
3362Superclasses: <a href="#GlobalValue"><tt>GlobalValue</tt></a>,
3363<a href="#Constant"><tt>Constant</tt></a>,
3364<a href="#User"><tt>User</tt></a>,
3365<a href="#Value"><tt>Value</tt></a></p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3366
3367<p>Global variables are represented with the (suprise suprise)
3368<tt>GlobalVariable</tt> class. Like functions, <tt>GlobalVariable</tt>s are also
3369subclasses of <a href="#GlobalValue"><tt>GlobalValue</tt></a>, and as such are
3370always referenced by their address (global values must live in memory, so their
Reid Spencerbe5e85e2006-04-14 14:11:48 +0000[diff] [blame]3371"name" refers to their constant address). See
3372<a href="#GlobalValue"><tt>GlobalValue</tt></a> for more on this. Global
3373variables may have an initial value (which must be a
3374<a href="#Constant"><tt>Constant</tt></a>), and if they have an initializer,
3375they may be marked as "constant" themselves (indicating that their contents
3376never change at runtime).</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3377</div>
3378
3379<!-- _______________________________________________________________________ -->
3380<div class="doc_subsubsection">
3381 <a name="m_GlobalVariable">Important Public Members of the
3382 <tt>GlobalVariable</tt> class</a>
3383</div>
3384
3385<div class="doc_text">
3386
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3387<ul>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3388 <li><tt>GlobalVariable(const </tt><tt><a href="#Type">Type</a> *Ty, bool
3389 isConstant, LinkageTypes&amp; Linkage, <a href="#Constant">Constant</a>
3390 *Initializer = 0, const std::string &amp;Name = "", Module* Parent = 0)</tt>
3391
3392 <p>Create a new global variable of the specified type. If
3393 <tt>isConstant</tt> is true then the global variable will be marked as
3394 unchanging for the program. The Linkage parameter specifies the type of
Duncan Sands667d4b82009-03-07 15:45:40 +0000[diff] [blame]3395 linkage (internal, external, weak, linkonce, appending) for the variable.
3396 If the linkage is InternalLinkage, WeakAnyLinkage, WeakODRLinkage,
3397 LinkOnceAnyLinkage or LinkOnceODRLinkage,&nbsp; then the resultant
3398 global variable will have internal linkage. AppendingLinkage concatenates
3399 together all instances (in different translation units) of the variable
3400 into a single variable but is only applicable to arrays. &nbsp;See
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3401 the <a href="LangRef.html#modulestructure">LLVM Language Reference</a> for
3402 further details on linkage types. Optionally an initializer, a name, and the
3403 module to put the variable into may be specified for the global variable as
3404 well.</p></li>
3405
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3406 <li><tt>bool isConstant() const</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3407
3408 <p>Returns true if this is a global variable that is known not to
3409 be modified at runtime.</p></li>
3410
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3411 <li><tt>bool hasInitializer()</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3412
3413 <p>Returns true if this <tt>GlobalVariable</tt> has an intializer.</p></li>
3414
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3415 <li><tt><a href="#Constant">Constant</a> *getInitializer()</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3416
3417 <p>Returns the intial value for a <tt>GlobalVariable</tt>. It is not legal
3418 to call this method if there is no initializer.</p></li>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3419</ul>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3420
3421</div>
3422
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]3423
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3424<!-- ======================================================================= -->
3425<div class="doc_subsection">
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]3426 <a name="BasicBlock">The <tt>BasicBlock</tt> class</a>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3427</div>
3428
3429<div class="doc_text">
3430
3431<p><tt>#include "<a
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]3432href="/doxygen/BasicBlock_8h-source.html">llvm/BasicBlock.h</a>"</tt><br>
3433doxygen info: <a href="/doxygen/structllvm_1_1BasicBlock.html">BasicBlock
3434Class</a><br>
3435Superclass: <a href="#Value"><tt>Value</tt></a></p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3436
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]3437<p>This class represents a single entry multiple exit section of the code,
3438commonly known as a basic block by the compiler community. The
3439<tt>BasicBlock</tt> class maintains a list of <a
3440href="#Instruction"><tt>Instruction</tt></a>s, which form the body of the block.
3441Matching the language definition, the last element of this list of instructions
3442is always a terminator instruction (a subclass of the <a
3443href="#TerminatorInst"><tt>TerminatorInst</tt></a> class).</p>
3444
3445<p>In addition to tracking the list of instructions that make up the block, the
3446<tt>BasicBlock</tt> class also keeps track of the <a
3447href="#Function"><tt>Function</tt></a> that it is embedded into.</p>
3448
3449<p>Note that <tt>BasicBlock</tt>s themselves are <a
3450href="#Value"><tt>Value</tt></a>s, because they are referenced by instructions
3451like branches and can go in the switch tables. <tt>BasicBlock</tt>s have type
3452<tt>label</tt>.</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3453
3454</div>
3455
3456<!-- _______________________________________________________________________ -->
3457<div class="doc_subsubsection">
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]3458 <a name="m_BasicBlock">Important Public Members of the <tt>BasicBlock</tt>
3459 class</a>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3460</div>
3461
3462<div class="doc_text">
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3463<ul>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3464
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]3465<li><tt>BasicBlock(const std::string &amp;Name = "", </tt><tt><a
3466 href="#Function">Function</a> *Parent = 0)</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3467
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]3468<p>The <tt>BasicBlock</tt> constructor is used to create new basic blocks for
3469insertion into a function. The constructor optionally takes a name for the new
3470block, and a <a href="#Function"><tt>Function</tt></a> to insert it into. If
3471the <tt>Parent</tt> parameter is specified, the new <tt>BasicBlock</tt> is
3472automatically inserted at the end of the specified <a
3473href="#Function"><tt>Function</tt></a>, if not specified, the BasicBlock must be
3474manually inserted into the <a href="#Function"><tt>Function</tt></a>.</p></li>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3475
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]3476<li><tt>BasicBlock::iterator</tt> - Typedef for instruction list iterator<br>
3477<tt>BasicBlock::const_iterator</tt> - Typedef for const_iterator.<br>
3478<tt>begin()</tt>, <tt>end()</tt>, <tt>front()</tt>, <tt>back()</tt>,
3479<tt>size()</tt>, <tt>empty()</tt>
3480STL-style functions for accessing the instruction list.
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3481
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]3482<p>These methods and typedefs are forwarding functions that have the same
3483semantics as the standard library methods of the same names. These methods
3484expose the underlying instruction list of a basic block in a way that is easy to
3485manipulate. To get the full complement of container operations (including
3486operations to update the list), you must use the <tt>getInstList()</tt>
3487method.</p></li>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3488
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]3489<li><tt>BasicBlock::InstListType &amp;getInstList()</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3490
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]3491<p>This method is used to get access to the underlying container that actually
3492holds the Instructions. This method must be used when there isn't a forwarding
3493function in the <tt>BasicBlock</tt> class for the operation that you would like
3494to perform. Because there are no forwarding functions for "updating"
3495operations, you need to use this if you want to update the contents of a
3496<tt>BasicBlock</tt>.</p></li>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3497
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]3498<li><tt><a href="#Function">Function</a> *getParent()</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3499
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]3500<p> Returns a pointer to <a href="#Function"><tt>Function</tt></a> the block is
3501embedded into, or a null pointer if it is homeless.</p></li>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3502
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]3503<li><tt><a href="#TerminatorInst">TerminatorInst</a> *getTerminator()</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3504
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]3505<p> Returns a pointer to the terminator instruction that appears at the end of
3506the <tt>BasicBlock</tt>. If there is no terminator instruction, or if the last
3507instruction in the block is not a terminator, then a null pointer is
3508returned.</p></li>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3509
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3510</ul>
3511
3512</div>
3513
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3514
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3515<!-- ======================================================================= -->
3516<div class="doc_subsection">
3517 <a name="Argument">The <tt>Argument</tt> class</a>
3518</div>
3519
3520<div class="doc_text">
3521
3522<p>This subclass of Value defines the interface for incoming formal
Chris Lattner58360822005-01-17 00:12:04 +0000[diff] [blame]3523arguments to a function. A Function maintains a list of its formal
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3524arguments. An argument has a pointer to the parent Function.</p>
3525
3526</div>
3527
Chris Lattner9355b472002-09-06 02:50:58 +0000[diff] [blame]3528<!-- *********************************************************************** -->
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3529<hr>
3530<address>
3531 <a href="http://jigsaw.w3.org/css-validator/check/referer"><img
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Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3535
3536 <a href="mailto:dhurjati@cs.uiuc.edu">Dinakar Dhurjati</a> and
3537 <a href="mailto:sabre@nondot.org">Chris Lattner</a><br>
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]3538 <a href="http://llvm.org">The LLVM Compiler Infrastructure</a><br>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3539 Last modified: $Date$
3540</address>
3541
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3542</body>
3543</html>