Gitiles
Code Review Sign In
gerrit-public.fairphone.software / platform / external / llvm / 9d6565a5b1fbc4286d6ee638d8f47a3171a9ed7e / . / docs / ProgrammersManual.html
blob: a96a676c600237c1e21897562e9cf9898bfd14b1 [file] [log] [blame]
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN"
2 "http://www.w3.org/TR/html4/strict.dtd">
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3<html>
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>
57 <li><a href="#dss_ilist">llvm/ADT/ilist</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>
65 <li><a href="#dss_FoldingSet">"llvm/ADT/FoldingSet.h"</a></li>
66 <li><a href="#dss_set">&lt;set&gt;</a></li>
67 <li><a href="#dss_setvector">"llvm/ADT/SetVector.h"</a></li>
Chris Lattnerc5722432007-02-03 19:49:31 +0000[diff] [blame]68 <li><a href="#dss_uniquevector">"llvm/ADT/UniqueVector.h"</a></li>
69 <li><a href="#dss_otherset">Other Set-Like ContainerOptions</a></li>
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]70 </ul></li>
Chris Lattnerf3692522007-02-03 19:51:56 +0000[diff] [blame]71 <li><a href="#ds_map">Map-Like Containers (std::map, DenseMap, etc)</a>
72 <ul>
73 <li><a href="#dss_sortedvectormap">A sorted 'vector'</a></li>
Chris Lattner796f9fa2007-02-08 19:14:21 +0000[diff] [blame]74 <li><a href="#dss_stringmap">"llvm/ADT/StringMap.h"</a></li>
Chris Lattnerf3692522007-02-03 19:51:56 +0000[diff] [blame]75 <li><a href="#dss_indexedmap">"llvm/ADT/IndexedMap.h"</a></li>
76 <li><a href="#dss_densemap">"llvm/ADT/DenseMap.h"</a></li>
77 <li><a href="#dss_map">&lt;map&gt;</a></li>
78 <li><a href="#dss_othermap">Other Map-Like Container Options</a></li>
79 </ul></li>
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]80 </ul>
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]81 </li>
Chris Lattnerae7f7592002-09-06 18:31:18 +0000[diff] [blame]82 <li><a href="#common">Helpful Hints for Common Operations</a>
Chris Lattnerae7f7592002-09-06 18:31:18 +0000[diff] [blame]83 <ul>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]84 <li><a href="#inspection">Basic Inspection and Traversal Routines</a>
85 <ul>
86 <li><a href="#iterate_function">Iterating over the <tt>BasicBlock</tt>s
87in a <tt>Function</tt></a> </li>
88 <li><a href="#iterate_basicblock">Iterating over the <tt>Instruction</tt>s
89in a <tt>BasicBlock</tt></a> </li>
90 <li><a href="#iterate_institer">Iterating over the <tt>Instruction</tt>s
91in a <tt>Function</tt></a> </li>
92 <li><a href="#iterate_convert">Turning an iterator into a
93class pointer</a> </li>
94 <li><a href="#iterate_complex">Finding call sites: a more
95complex example</a> </li>
96 <li><a href="#calls_and_invokes">Treating calls and invokes
97the same way</a> </li>
98 <li><a href="#iterate_chains">Iterating over def-use &amp;
99use-def chains</a> </li>
100 </ul>
101 </li>
102 <li><a href="#simplechanges">Making simple changes</a>
103 <ul>
104 <li><a href="#schanges_creating">Creating and inserting new
105 <tt>Instruction</tt>s</a> </li>
106 <li><a href="#schanges_deleting">Deleting <tt>Instruction</tt>s</a> </li>
107 <li><a href="#schanges_replacing">Replacing an <tt>Instruction</tt>
108with another <tt>Value</tt></a> </li>
109 </ul>
Reid Spencerfe8f4ff2004-11-01 09:02:53 +0000[diff] [blame]110 </li>
Chris Lattnerae7f7592002-09-06 18:31:18 +0000[diff] [blame]111<!--
112 <li>Working with the Control Flow Graph
113 <ul>
114 <li>Accessing predecessors and successors of a <tt>BasicBlock</tt>
115 <li>
116 <li>
117 </ul>
Reid Spencerfe8f4ff2004-11-01 09:02:53 +0000[diff] [blame]118-->
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]119 </ul>
120 </li>
Chris Lattnerd9d6e102005-04-23 16:10:52 +0000[diff] [blame]121
122 <li><a href="#advanced">Advanced Topics</a>
123 <ul>
Chris Lattnerf1b200b2005-04-23 17:27:36 +0000[diff] [blame]124 <li><a href="#TypeResolve">LLVM Type Resolution</a>
125 <ul>
126 <li><a href="#BuildRecType">Basic Recursive Type Construction</a></li>
127 <li><a href="#refineAbstractTypeTo">The <tt>refineAbstractTypeTo</tt> method</a></li>
128 <li><a href="#PATypeHolder">The PATypeHolder Class</a></li>
129 <li><a href="#AbstractTypeUser">The AbstractTypeUser Class</a></li>
130 </ul></li>
131
Chris Lattnerd9d6e102005-04-23 16:10:52 +0000[diff] [blame]132 <li><a href="#SymbolTable">The <tt>SymbolTable</tt> class </a></li>
133 </ul></li>
134
Joel Stanley9b96c442002-09-06 21:55:13 +0000[diff] [blame]135 <li><a href="#coreclasses">The Core LLVM Class Hierarchy Reference</a>
Chris Lattner9355b472002-09-06 02:50:58 +0000[diff] [blame]136 <ul>
Reid Spencer303c4b42007-01-12 17:26:25 +0000[diff] [blame]137 <li><a href="#Type">The <tt>Type</tt> class</a> </li>
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]138 <li><a href="#Module">The <tt>Module</tt> class</a></li>
Reid Spencerfe8f4ff2004-11-01 09:02:53 +0000[diff] [blame]139 <li><a href="#Value">The <tt>Value</tt> class</a>
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]140 <ul>
141 <li><a href="#User">The <tt>User</tt> class</a>
Chris Lattner9355b472002-09-06 02:50:58 +0000[diff] [blame]142 <ul>
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]143 <li><a href="#Instruction">The <tt>Instruction</tt> class</a></li>
144 <li><a href="#Constant">The <tt>Constant</tt> class</a>
145 <ul>
146 <li><a href="#GlobalValue">The <tt>GlobalValue</tt> class</a>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]147 <ul>
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]148 <li><a href="#Function">The <tt>Function</tt> class</a></li>
149 <li><a href="#GlobalVariable">The <tt>GlobalVariable</tt> class</a></li>
150 </ul>
151 </li>
152 </ul>
153 </li>
Reid Spencerfe8f4ff2004-11-01 09:02:53 +0000[diff] [blame]154 </ul>
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]155 </li>
156 <li><a href="#BasicBlock">The <tt>BasicBlock</tt> class</a></li>
157 <li><a href="#Argument">The <tt>Argument</tt> class</a></li>
158 </ul>
Reid Spencerfe8f4ff2004-11-01 09:02:53 +0000[diff] [blame]159 </li>
160 </ul>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]161 </li>
Chris Lattner9355b472002-09-06 02:50:58 +0000[diff] [blame]162</ol>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]163
Chris Lattner69bf8a92004-05-23 21:06:58 +0000[diff] [blame]164<div class="doc_author">
165 <p>Written by <a href="mailto:sabre@nondot.org">Chris Lattner</a>,
Chris Lattner94c43592004-05-26 16:52:55 +0000[diff] [blame]166 <a href="mailto:dhurjati@cs.uiuc.edu">Dinakar Dhurjati</a>,
167 <a href="mailto:jstanley@cs.uiuc.edu">Joel Stanley</a>, and
168 <a href="mailto:rspencer@x10sys.com">Reid Spencer</a></p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]169</div>
170
Chris Lattner9355b472002-09-06 02:50:58 +0000[diff] [blame]171<!-- *********************************************************************** -->
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]172<div class="doc_section">
173 <a name="introduction">Introduction </a>
174</div>
Chris Lattner9355b472002-09-06 02:50:58 +0000[diff] [blame]175<!-- *********************************************************************** -->
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]176
177<div class="doc_text">
178
179<p>This document is meant to highlight some of the important classes and
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]180interfaces available in the LLVM source-base. This manual is not
181intended to explain what LLVM is, how it works, and what LLVM code looks
182like. It assumes that you know the basics of LLVM and are interested
183in writing transformations or otherwise analyzing or manipulating the
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]184code.</p>
185
186<p>This document should get you oriented so that you can find your
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]187way in the continuously growing source code that makes up the LLVM
188infrastructure. Note that this manual is not intended to serve as a
189replacement for reading the source code, so if you think there should be
190a method in one of these classes to do something, but it's not listed,
191check the source. Links to the <a href="/doxygen/">doxygen</a> sources
192are provided to make this as easy as possible.</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]193
194<p>The first section of this document describes general information that is
195useful to know when working in the LLVM infrastructure, and the second describes
196the Core LLVM classes. In the future this manual will be extended with
197information describing how to use extension libraries, such as dominator
198information, CFG traversal routines, and useful utilities like the <tt><a
199href="/doxygen/InstVisitor_8h-source.html">InstVisitor</a></tt> template.</p>
200
201</div>
202
Chris Lattner9355b472002-09-06 02:50:58 +0000[diff] [blame]203<!-- *********************************************************************** -->
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]204<div class="doc_section">
205 <a name="general">General Information</a>
206</div>
207<!-- *********************************************************************** -->
208
209<div class="doc_text">
210
211<p>This section contains general information that is useful if you are working
212in the LLVM source-base, but that isn't specific to any particular API.</p>
213
214</div>
215
216<!-- ======================================================================= -->
217<div class="doc_subsection">
218 <a name="stl">The C++ Standard Template Library</a>
219</div>
220
221<div class="doc_text">
222
223<p>LLVM makes heavy use of the C++ Standard Template Library (STL),
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]224perhaps much more than you are used to, or have seen before. Because of
225this, you might want to do a little background reading in the
226techniques used and capabilities of the library. There are many good
227pages that discuss the STL, and several books on the subject that you
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]228can get, so it will not be discussed in this document.</p>
229
230<p>Here are some useful links:</p>
231
232<ol>
233
234<li><a href="http://www.dinkumware.com/refxcpp.html">Dinkumware C++ Library
235reference</a> - an excellent reference for the STL and other parts of the
236standard C++ library.</li>
237
238<li><a href="http://www.tempest-sw.com/cpp/">C++ In a Nutshell</a> - This is an
Tanya Lattner09cf73c2004-06-22 04:24:55 +0000[diff] [blame]239O'Reilly book in the making. It has a decent
240Standard Library
241Reference that rivals Dinkumware's, and is unfortunately no longer free since the book has been
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]242published.</li>
243
244<li><a href="http://www.parashift.com/c++-faq-lite/">C++ Frequently Asked
245Questions</a></li>
246
247<li><a href="http://www.sgi.com/tech/stl/">SGI's STL Programmer's Guide</a> -
248Contains a useful <a
249href="http://www.sgi.com/tech/stl/stl_introduction.html">Introduction to the
250STL</a>.</li>
251
252<li><a href="http://www.research.att.com/%7Ebs/C++.html">Bjarne Stroustrup's C++
253Page</a></li>
254
Tanya Lattner79445ba2004-12-08 18:34:56 +0000[diff] [blame]255<li><a href="http://64.78.49.204/">
Reid Spencer096603a2004-05-26 08:41:35 +0000[diff] [blame]256Bruce Eckel's Thinking in C++, 2nd ed. Volume 2 Revision 4.0 (even better, get
257the book).</a></li>
258
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]259</ol>
260
261<p>You are also encouraged to take a look at the <a
262href="CodingStandards.html">LLVM Coding Standards</a> guide which focuses on how
263to write maintainable code more than where to put your curly braces.</p>
264
265</div>
266
267<!-- ======================================================================= -->
268<div class="doc_subsection">
269 <a name="stl">Other useful references</a>
270</div>
271
272<div class="doc_text">
273
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]274<ol>
275<li><a href="http://www.psc.edu/%7Esemke/cvs_branches.html">CVS
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]276Branch and Tag Primer</a></li>
Misha Brukmana0f71e42004-06-18 18:39:00 +0000[diff] [blame]277<li><a href="http://www.fortran-2000.com/ArnaudRecipes/sharedlib.html">Using
278static and shared libraries across platforms</a></li>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]279</ol>
280
281</div>
282
Chris Lattner9355b472002-09-06 02:50:58 +0000[diff] [blame]283<!-- *********************************************************************** -->
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]284<div class="doc_section">
285 <a name="apis">Important and useful LLVM APIs</a>
286</div>
287<!-- *********************************************************************** -->
288
289<div class="doc_text">
290
291<p>Here we highlight some LLVM APIs that are generally useful and good to
292know about when writing transformations.</p>
293
294</div>
295
296<!-- ======================================================================= -->
297<div class="doc_subsection">
Misha Brukman2c122ce2005-11-01 21:12:49 +0000[diff] [blame]298 <a name="isa">The <tt>isa&lt;&gt;</tt>, <tt>cast&lt;&gt;</tt> and
299 <tt>dyn_cast&lt;&gt;</tt> templates</a>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]300</div>
301
302<div class="doc_text">
303
304<p>The LLVM source-base makes extensive use of a custom form of RTTI.
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]305These templates have many similarities to the C++ <tt>dynamic_cast&lt;&gt;</tt>
306operator, but they don't have some drawbacks (primarily stemming from
307the fact that <tt>dynamic_cast&lt;&gt;</tt> only works on classes that
308have a v-table). Because they are used so often, you must know what they
309do and how they work. All of these templates are defined in the <a
Chris Lattner695b78b2005-04-26 22:56:16 +0000[diff] [blame]310 href="/doxygen/Casting_8h-source.html"><tt>llvm/Support/Casting.h</tt></a>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]311file (note that you very rarely have to include this file directly).</p>
312
313<dl>
314 <dt><tt>isa&lt;&gt;</tt>: </dt>
315
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]316 <dd><p>The <tt>isa&lt;&gt;</tt> operator works exactly like the Java
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]317 "<tt>instanceof</tt>" operator. It returns true or false depending on whether
318 a reference or pointer points to an instance of the specified class. This can
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]319 be very useful for constraint checking of various sorts (example below).</p>
320 </dd>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]321
322 <dt><tt>cast&lt;&gt;</tt>: </dt>
323
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]324 <dd><p>The <tt>cast&lt;&gt;</tt> operator is a "checked cast" operation. It
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]325 converts a pointer or reference from a base class to a derived cast, causing
326 an assertion failure if it is not really an instance of the right type. This
327 should be used in cases where you have some information that makes you believe
328 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]329 and <tt>cast&lt;&gt;</tt> template is:</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]330
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]331<div class="doc_code">
332<pre>
333static bool isLoopInvariant(const <a href="#Value">Value</a> *V, const Loop *L) {
334 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))
335 return true;
Chris Lattner69bf8a92004-05-23 21:06:58 +0000[diff] [blame]336
Bill Wendling82e2eea2006-10-11 18:00:22 +0000[diff] [blame]337 // <i>Otherwise, it must be an instruction...</i>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]338 return !L-&gt;contains(cast&lt;<a href="#Instruction">Instruction</a>&gt;(V)-&gt;getParent());
339}
340</pre>
341</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]342
343 <p>Note that you should <b>not</b> use an <tt>isa&lt;&gt;</tt> test followed
344 by a <tt>cast&lt;&gt;</tt>, for that use the <tt>dyn_cast&lt;&gt;</tt>
345 operator.</p>
346
347 </dd>
348
349 <dt><tt>dyn_cast&lt;&gt;</tt>:</dt>
350
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]351 <dd><p>The <tt>dyn_cast&lt;&gt;</tt> operator is a "checking cast" operation.
352 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]353 pointer to it (this operator does not work with references). If the operand is
354 not of the correct type, a null pointer is returned. Thus, this works very
Misha Brukman2c122ce2005-11-01 21:12:49 +0000[diff] [blame]355 much like the <tt>dynamic_cast&lt;&gt;</tt> operator in C++, and should be
356 used in the same circumstances. Typically, the <tt>dyn_cast&lt;&gt;</tt>
357 operator is used in an <tt>if</tt> statement or some other flow control
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]358 statement like this:</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]359
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]360<div class="doc_code">
361<pre>
362if (<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]363 // <i>...</i>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]364}
365</pre>
366</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]367
Misha Brukman2c122ce2005-11-01 21:12:49 +0000[diff] [blame]368 <p>This form of the <tt>if</tt> statement effectively combines together a call
369 to <tt>isa&lt;&gt;</tt> and a call to <tt>cast&lt;&gt;</tt> into one
370 statement, which is very convenient.</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]371
Misha Brukman2c122ce2005-11-01 21:12:49 +0000[diff] [blame]372 <p>Note that the <tt>dyn_cast&lt;&gt;</tt> operator, like C++'s
373 <tt>dynamic_cast&lt;&gt;</tt> or Java's <tt>instanceof</tt> operator, can be
374 abused. In particular, you should not use big chained <tt>if/then/else</tt>
375 blocks to check for lots of different variants of classes. If you find
376 yourself wanting to do this, it is much cleaner and more efficient to use the
377 <tt>InstVisitor</tt> class to dispatch over the instruction type directly.</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]378
Misha Brukman2c122ce2005-11-01 21:12:49 +0000[diff] [blame]379 </dd>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]380
Misha Brukman2c122ce2005-11-01 21:12:49 +0000[diff] [blame]381 <dt><tt>cast_or_null&lt;&gt;</tt>: </dt>
382
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]383 <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]384 <tt>cast&lt;&gt;</tt> operator, except that it allows for a null pointer as an
385 argument (which it then propagates). This can sometimes be useful, allowing
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]386 you to combine several null checks into one.</p></dd>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]387
Misha Brukman2c122ce2005-11-01 21:12:49 +0000[diff] [blame]388 <dt><tt>dyn_cast_or_null&lt;&gt;</tt>: </dt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]389
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]390 <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]391 <tt>dyn_cast&lt;&gt;</tt> operator, except that it allows for a null pointer
392 as an argument (which it then propagates). This can sometimes be useful,
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]393 allowing you to combine several null checks into one.</p></dd>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]394
Misha Brukman2c122ce2005-11-01 21:12:49 +0000[diff] [blame]395</dl>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]396
397<p>These five templates can be used with any classes, whether they have a
398v-table or not. To add support for these templates, you simply need to add
399<tt>classof</tt> static methods to the class you are interested casting
400to. Describing this is currently outside the scope of this document, but there
401are lots of examples in the LLVM source base.</p>
402
403</div>
404
405<!-- ======================================================================= -->
406<div class="doc_subsection">
Misha Brukman2c122ce2005-11-01 21:12:49 +0000[diff] [blame]407 <a name="DEBUG">The <tt>DEBUG()</tt> macro and <tt>-debug</tt> option</a>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]408</div>
409
410<div class="doc_text">
411
412<p>Often when working on your pass you will put a bunch of debugging printouts
413and other code into your pass. After you get it working, you want to remove
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]414it, 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]415across).</p>
416
417<p> Naturally, because of this, you don't want to delete the debug printouts,
418but you don't want them to always be noisy. A standard compromise is to comment
419them out, allowing you to enable them if you need them in the future.</p>
420
Chris Lattner695b78b2005-04-26 22:56:16 +0000[diff] [blame]421<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]422file provides a macro named <tt>DEBUG()</tt> that is a much nicer solution to
423this problem. Basically, you can put arbitrary code into the argument of the
424<tt>DEBUG</tt> macro, and it is only executed if '<tt>opt</tt>' (or any other
425tool) is run with the '<tt>-debug</tt>' command line argument:</p>
426
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]427<div class="doc_code">
428<pre>
Bill Wendling832171c2006-12-07 20:04:42 +0000[diff] [blame]429DOUT &lt;&lt; "I am here!\n";
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]430</pre>
431</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]432
433<p>Then you can run your pass like this:</p>
434
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]435<div class="doc_code">
436<pre>
437$ opt &lt; a.bc &gt; /dev/null -mypass
Bill Wendling82e2eea2006-10-11 18:00:22 +0000[diff] [blame]438<i>&lt;no output&gt;</i>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]439$ opt &lt; a.bc &gt; /dev/null -mypass -debug
440I am here!
441</pre>
442</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]443
444<p>Using the <tt>DEBUG()</tt> macro instead of a home-brewed solution allows you
445to not have to create "yet another" command line option for the debug output for
446your pass. Note that <tt>DEBUG()</tt> macros are disabled for optimized builds,
447so they do not cause a performance impact at all (for the same reason, they
448should also not contain side-effects!).</p>
449
450<p>One additional nice thing about the <tt>DEBUG()</tt> macro is that you can
451enable or disable it directly in gdb. Just use "<tt>set DebugFlag=0</tt>" or
452"<tt>set DebugFlag=1</tt>" from the gdb if the program is running. If the
453program hasn't been started yet, you can always just run it with
454<tt>-debug</tt>.</p>
455
456</div>
457
458<!-- _______________________________________________________________________ -->
459<div class="doc_subsubsection">
Chris Lattnerc9151082005-04-26 22:57:07 +0000[diff] [blame]460 <a name="DEBUG_TYPE">Fine grained debug info with <tt>DEBUG_TYPE</tt> and
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]461 the <tt>-debug-only</tt> option</a>
462</div>
463
464<div class="doc_text">
465
466<p>Sometimes you may find yourself in a situation where enabling <tt>-debug</tt>
467just turns on <b>too much</b> information (such as when working on the code
468generator). If you want to enable debug information with more fine-grained
469control, you define the <tt>DEBUG_TYPE</tt> macro and the <tt>-debug</tt> only
470option as follows:</p>
471
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]472<div class="doc_code">
473<pre>
Bill Wendling832171c2006-12-07 20:04:42 +0000[diff] [blame]474DOUT &lt;&lt; "No debug type\n";
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]475#undef DEBUG_TYPE
476#define DEBUG_TYPE "foo"
Bill Wendling832171c2006-12-07 20:04:42 +0000[diff] [blame]477DOUT &lt;&lt; "'foo' debug type\n";
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]478#undef DEBUG_TYPE
479#define DEBUG_TYPE "bar"
Bill Wendling832171c2006-12-07 20:04:42 +0000[diff] [blame]480DOUT &lt;&lt; "'bar' debug type\n";
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]481#undef DEBUG_TYPE
482#define DEBUG_TYPE ""
Bill Wendling832171c2006-12-07 20:04:42 +0000[diff] [blame]483DOUT &lt;&lt; "No debug type (2)\n";
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]484</pre>
485</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]486
487<p>Then you can run your pass like this:</p>
488
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]489<div class="doc_code">
490<pre>
491$ opt &lt; a.bc &gt; /dev/null -mypass
Bill Wendling82e2eea2006-10-11 18:00:22 +0000[diff] [blame]492<i>&lt;no output&gt;</i>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]493$ opt &lt; a.bc &gt; /dev/null -mypass -debug
494No debug type
495'foo' debug type
496'bar' debug type
497No debug type (2)
498$ opt &lt; a.bc &gt; /dev/null -mypass -debug-only=foo
499'foo' debug type
500$ opt &lt; a.bc &gt; /dev/null -mypass -debug-only=bar
501'bar' debug type
502</pre>
503</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]504
505<p>Of course, in practice, you should only set <tt>DEBUG_TYPE</tt> at the top of
506a 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]507you <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]508<tt>#undef</tt>'s). Also, you should use names more meaningful than "foo" and
509"bar", because there is no system in place to ensure that names do not
510conflict. If two different modules use the same string, they will all be turned
511on when the name is specified. This allows, for example, all debug information
512for instruction scheduling to be enabled with <tt>-debug-type=InstrSched</tt>,
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]513even if the source lives in multiple files.</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]514
515</div>
516
517<!-- ======================================================================= -->
518<div class="doc_subsection">
Chris Lattner0be6fdf2006-12-19 21:46:21 +0000[diff] [blame]519 <a name="Statistic">The <tt>Statistic</tt> class &amp; <tt>-stats</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]520 option</a>
521</div>
522
523<div class="doc_text">
524
525<p>The "<tt><a
Chris Lattner695b78b2005-04-26 22:56:16 +0000[diff] [blame]526href="/doxygen/Statistic_8h-source.html">llvm/ADT/Statistic.h</a></tt>" file
Chris Lattner0be6fdf2006-12-19 21:46:21 +0000[diff] [blame]527provides a class named <tt>Statistic</tt> that is used as a unified way to
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]528keep track of what the LLVM compiler is doing and how effective various
529optimizations are. It is useful to see what optimizations are contributing to
530making a particular program run faster.</p>
531
532<p>Often you may run your pass on some big program, and you're interested to see
533how many times it makes a certain transformation. Although you can do this with
534hand 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]535for big programs. Using the <tt>Statistic</tt> class makes it very easy to
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]536keep track of this information, and the calculated information is presented in a
537uniform manner with the rest of the passes being executed.</p>
538
539<p>There are many examples of <tt>Statistic</tt> uses, but the basics of using
540it are as follows:</p>
541
542<ol>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]543 <li><p>Define your statistic like this:</p>
544
545<div class="doc_code">
546<pre>
Chris Lattner0be6fdf2006-12-19 21:46:21 +0000[diff] [blame]547#define <a href="#DEBUG_TYPE">DEBUG_TYPE</a> "mypassname" <i>// This goes before any #includes.</i>
548STATISTIC(NumXForms, "The # of times I did stuff");
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]549</pre>
550</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]551
Chris Lattner0be6fdf2006-12-19 21:46:21 +0000[diff] [blame]552 <p>The <tt>STATISTIC</tt> macro defines a static variable, whose name is
553 specified by the first argument. The pass name is taken from the DEBUG_TYPE
554 macro, and the description is taken from the second argument. The variable
Reid Spencer06565dc2007-01-12 17:11:23 +0000[diff] [blame]555 defined ("NumXForms" in this case) acts like an unsigned integer.</p></li>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]556
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]557 <li><p>Whenever you make a transformation, bump the counter:</p>
558
559<div class="doc_code">
560<pre>
Bill Wendling82e2eea2006-10-11 18:00:22 +0000[diff] [blame]561++NumXForms; // <i>I did stuff!</i>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]562</pre>
563</div>
564
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]565 </li>
566 </ol>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]567
568 <p>That's all you have to do. To get '<tt>opt</tt>' to print out the
569 statistics gathered, use the '<tt>-stats</tt>' option:</p>
570
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]571<div class="doc_code">
572<pre>
573$ opt -stats -mypassname &lt; program.bc &gt; /dev/null
Bill Wendling82e2eea2006-10-11 18:00:22 +0000[diff] [blame]574<i>... statistics output ...</i>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]575</pre>
576</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]577
Reid Spencer6b6c73e2007-02-09 16:00:28 +0000[diff] [blame]578 <p> When running <tt>opt</tt> on a C file from the SPEC benchmark
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]579suite, it gives a report that looks like this:</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]580
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]581<div class="doc_code">
582<pre>
583 7646 bytecodewriter - Number of normal instructions
584 725 bytecodewriter - Number of oversized instructions
585 129996 bytecodewriter - Number of bytecode bytes written
586 2817 raise - Number of insts DCEd or constprop'd
587 3213 raise - Number of cast-of-self removed
588 5046 raise - Number of expression trees converted
589 75 raise - Number of other getelementptr's formed
590 138 raise - Number of load/store peepholes
591 42 deadtypeelim - Number of unused typenames removed from symtab
592 392 funcresolve - Number of varargs functions resolved
593 27 globaldce - Number of global variables removed
594 2 adce - Number of basic blocks removed
595 134 cee - Number of branches revectored
596 49 cee - Number of setcc instruction eliminated
597 532 gcse - Number of loads removed
598 2919 gcse - Number of instructions removed
599 86 indvars - Number of canonical indvars added
600 87 indvars - Number of aux indvars removed
601 25 instcombine - Number of dead inst eliminate
602 434 instcombine - Number of insts combined
603 248 licm - Number of load insts hoisted
604 1298 licm - Number of insts hoisted to a loop pre-header
605 3 licm - Number of insts hoisted to multiple loop preds (bad, no loop pre-header)
606 75 mem2reg - Number of alloca's promoted
607 1444 cfgsimplify - Number of blocks simplified
608</pre>
609</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]610
611<p>Obviously, with so many optimizations, having a unified framework for this
612stuff is very nice. Making your pass fit well into the framework makes it more
613maintainable and useful.</p>
614
615</div>
616
Chris Lattnerf623a082005-10-17 01:36:23 +0000[diff] [blame]617<!-- ======================================================================= -->
618<div class="doc_subsection">
619 <a name="ViewGraph">Viewing graphs while debugging code</a>
620</div>
621
622<div class="doc_text">
623
624<p>Several of the important data structures in LLVM are graphs: for example
625CFGs made out of LLVM <a href="#BasicBlock">BasicBlock</a>s, CFGs made out of
626LLVM <a href="CodeGenerator.html#machinebasicblock">MachineBasicBlock</a>s, and
627<a href="CodeGenerator.html#selectiondag_intro">Instruction Selection
628DAGs</a>. In many cases, while debugging various parts of the compiler, it is
629nice to instantly visualize these graphs.</p>
630
631<p>LLVM provides several callbacks that are available in a debug build to do
632exactly that. If you call the <tt>Function::viewCFG()</tt> method, for example,
633the current LLVM tool will pop up a window containing the CFG for the function
634where each basic block is a node in the graph, and each node contains the
635instructions in the block. Similarly, there also exists
636<tt>Function::viewCFGOnly()</tt> (does not include the instructions), the
637<tt>MachineFunction::viewCFG()</tt> and <tt>MachineFunction::viewCFGOnly()</tt>,
638and the <tt>SelectionDAG::viewGraph()</tt> methods. Within GDB, for example,
Jim Laskey543a0ee2006-10-02 12:28:07 +0000[diff] [blame]639you can usually use something like <tt>call DAG.viewGraph()</tt> to pop
Chris Lattnerf623a082005-10-17 01:36:23 +0000[diff] [blame]640up a window. Alternatively, you can sprinkle calls to these functions in your
641code in places you want to debug.</p>
642
643<p>Getting this to work requires a small amount of configuration. On Unix
644systems with X11, install the <a href="http://www.graphviz.org">graphviz</a>
645toolkit, and make sure 'dot' and 'gv' are in your path. If you are running on
646Mac OS/X, download and install the Mac OS/X <a
647href="http://www.pixelglow.com/graphviz/">Graphviz program</a>, and add
Reid Spencer128a7a72007-02-03 21:06:43 +0000[diff] [blame]648<tt>/Applications/Graphviz.app/Contents/MacOS/</tt> (or wherever you install
Chris Lattnerf623a082005-10-17 01:36:23 +0000[diff] [blame]649it) to your path. Once in your system and path are set up, rerun the LLVM
650configure script and rebuild LLVM to enable this functionality.</p>
651
Jim Laskey543a0ee2006-10-02 12:28:07 +0000[diff] [blame]652<p><tt>SelectionDAG</tt> has been extended to make it easier to locate
653<i>interesting</i> nodes in large complex graphs. From gdb, if you
654<tt>call DAG.setGraphColor(<i>node</i>, "<i>color</i>")</tt>, then the
Reid Spencer128a7a72007-02-03 21:06:43 +0000[diff] [blame]655next <tt>call DAG.viewGraph()</tt> would highlight the node in the
Jim Laskey543a0ee2006-10-02 12:28:07 +0000[diff] [blame]656specified color (choices of colors can be found at <a
Chris Lattner302da1e2007-02-03 03:05:57 +0000[diff] [blame]657href="http://www.graphviz.org/doc/info/colors.html">colors</a>.) More
Jim Laskey543a0ee2006-10-02 12:28:07 +0000[diff] [blame]658complex node attributes can be provided with <tt>call
659DAG.setGraphAttrs(<i>node</i>, "<i>attributes</i>")</tt> (choices can be
660found at <a href="http://www.graphviz.org/doc/info/attrs.html">Graph
661Attributes</a>.) If you want to restart and clear all the current graph
662attributes, then you can <tt>call DAG.clearGraphAttrs()</tt>. </p>
663
Chris Lattnerf623a082005-10-17 01:36:23 +0000[diff] [blame]664</div>
665
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]666<!-- *********************************************************************** -->
667<div class="doc_section">
668 <a name="datastructure">Picking the Right Data Structure for a Task</a>
669</div>
670<!-- *********************************************************************** -->
671
672<div class="doc_text">
673
Reid Spencer128a7a72007-02-03 21:06:43 +0000[diff] [blame]674<p>LLVM has a plethora of data structures in the <tt>llvm/ADT/</tt> directory,
675 and we commonly use STL data structures. This section describes the trade-offs
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]676 you should consider when you pick one.</p>
677
678<p>
679The first step is a choose your own adventure: do you want a sequential
680container, a set-like container, or a map-like container? The most important
681thing when choosing a container is the algorithmic properties of how you plan to
682access the container. Based on that, you should use:</p>
683
684<ul>
Reid Spencer128a7a72007-02-03 21:06:43 +0000[diff] [blame]685<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]686 of an value based on another value. Map-like containers also support
687 efficient queries for containment (whether a key is in the map). Map-like
688 containers generally do not support efficient reverse mapping (values to
689 keys). If you need that, use two maps. Some map-like containers also
690 support efficient iteration through the keys in sorted order. Map-like
691 containers are the most expensive sort, only use them if you need one of
692 these capabilities.</li>
693
694<li>a <a href="#ds_set">set-like</a> container if you need to put a bunch of
695 stuff into a container that automatically eliminates duplicates. Some
696 set-like containers support efficient iteration through the elements in
697 sorted order. Set-like containers are more expensive than sequential
698 containers.
699</li>
700
701<li>a <a href="#ds_sequential">sequential</a> container provides
702 the most efficient way to add elements and keeps track of the order they are
703 added to the collection. They permit duplicates and support efficient
Reid Spencer128a7a72007-02-03 21:06:43 +0000[diff] [blame]704 iteration, but do not support efficient look-up based on a key.
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]705</li>
706
707</ul>
708
709<p>
Reid Spencer128a7a72007-02-03 21:06:43 +0000[diff] [blame]710Once the proper category of container is determined, you can fine tune the
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]711memory use, constant factors, and cache behaviors of access by intelligently
Reid Spencer128a7a72007-02-03 21:06:43 +0000[diff] [blame]712picking a member of the category. Note that constant factors and cache behavior
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]713can be a big deal. If you have a vector that usually only contains a few
714elements (but could contain many), for example, it's much better to use
715<a href="#dss_smallvector">SmallVector</a> than <a href="#dss_vector">vector</a>
716. Doing so avoids (relatively) expensive malloc/free calls, which dwarf the
717cost of adding the elements to the container. </p>
718
719</div>
720
721<!-- ======================================================================= -->
722<div class="doc_subsection">
723 <a name="ds_sequential">Sequential Containers (std::vector, std::list, etc)</a>
724</div>
725
726<div class="doc_text">
727There are a variety of sequential containers available for you, based on your
728needs. Pick the first in this section that will do what you want.
729</div>
730
731<!-- _______________________________________________________________________ -->
732<div class="doc_subsubsection">
733 <a name="dss_fixedarrays">Fixed Size Arrays</a>
734</div>
735
736<div class="doc_text">
737<p>Fixed size arrays are very simple and very fast. They are good if you know
738exactly how many elements you have, or you have a (low) upper bound on how many
739you have.</p>
740</div>
741
742<!-- _______________________________________________________________________ -->
743<div class="doc_subsubsection">
744 <a name="dss_heaparrays">Heap Allocated Arrays</a>
745</div>
746
747<div class="doc_text">
748<p>Heap allocated arrays (new[] + delete[]) are also simple. They are good if
749the number of elements is variable, if you know how many elements you will need
750before the array is allocated, and if the array is usually large (if not,
751consider a <a href="#dss_smallvector">SmallVector</a>). The cost of a heap
752allocated array is the cost of the new/delete (aka malloc/free). Also note that
753if you are allocating an array of a type with a constructor, the constructor and
Reid Spencer128a7a72007-02-03 21:06:43 +0000[diff] [blame]754destructors will be run for every element in the array (re-sizable vectors only
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]755construct those elements actually used).</p>
756</div>
757
758<!-- _______________________________________________________________________ -->
759<div class="doc_subsubsection">
760 <a name="dss_smallvector">"llvm/ADT/SmallVector.h"</a>
761</div>
762
763<div class="doc_text">
764<p><tt>SmallVector&lt;Type, N&gt;</tt> is a simple class that looks and smells
765just like <tt>vector&lt;Type&gt;</tt>:
766it supports efficient iteration, lays out elements in memory order (so you can
767do pointer arithmetic between elements), supports efficient push_back/pop_back
768operations, supports efficient random access to its elements, etc.</p>
769
770<p>The advantage of SmallVector is that it allocates space for
771some number of elements (N) <b>in the object itself</b>. Because of this, if
772the SmallVector is dynamically smaller than N, no malloc is performed. This can
773be a big win in cases where the malloc/free call is far more expensive than the
774code that fiddles around with the elements.</p>
775
776<p>This is good for vectors that are "usually small" (e.g. the number of
777predecessors/successors of a block is usually less than 8). On the other hand,
778this makes the size of the SmallVector itself large, so you don't want to
779allocate lots of them (doing so will waste a lot of space). As such,
780SmallVectors are most useful when on the stack.</p>
781
782<p>SmallVector also provides a nice portable and efficient replacement for
783<tt>alloca</tt>.</p>
784
785</div>
786
787<!-- _______________________________________________________________________ -->
788<div class="doc_subsubsection">
789 <a name="dss_vector">&lt;vector&gt;</a>
790</div>
791
792<div class="doc_text">
793<p>
794std::vector is well loved and respected. It is useful when SmallVector isn't:
795when the size of the vector is often large (thus the small optimization will
796rarely be a benefit) or if you will be allocating many instances of the vector
797itself (which would waste space for elements that aren't in the container).
798vector is also useful when interfacing with code that expects vectors :).
799</p>
Chris Lattner32d84762007-02-05 06:30:51 +0000[diff] [blame]800
801<p>One worthwhile note about std::vector: avoid code like this:</p>
802
803<div class="doc_code">
804<pre>
805for ( ... ) {
806 std::vector<foo> V;
807 use V;
808}
809</pre>
810</div>
811
812<p>Instead, write this as:</p>
813
814<div class="doc_code">
815<pre>
816std::vector<foo> V;
817for ( ... ) {
818 use V;
819 V.clear();
820}
821</pre>
822</div>
823
824<p>Doing so will save (at least) one heap allocation and free per iteration of
825the loop.</p>
826
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]827</div>
828
829<!-- _______________________________________________________________________ -->
830<div class="doc_subsubsection">
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]831 <a name="dss_deque">&lt;deque&gt;</a>
832</div>
833
834<div class="doc_text">
835<p>std::deque is, in some senses, a generalized version of std::vector. Like
836std::vector, it provides constant time random access and other similar
837properties, but it also provides efficient access to the front of the list. It
838does not guarantee continuity of elements within memory.</p>
839
840<p>In exchange for this extra flexibility, std::deque has significantly higher
841constant factor costs than std::vector. If possible, use std::vector or
842something cheaper.</p>
843</div>
844
845<!-- _______________________________________________________________________ -->
846<div class="doc_subsubsection">
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]847 <a name="dss_list">&lt;list&gt;</a>
848</div>
849
850<div class="doc_text">
851<p>std::list is an extremely inefficient class that is rarely useful.
852It performs a heap allocation for every element inserted into it, thus having an
853extremely high constant factor, particularly for small data types. std::list
854also only supports bidirectional iteration, not random access iteration.</p>
855
856<p>In exchange for this high cost, std::list supports efficient access to both
857ends of the list (like std::deque, but unlike std::vector or SmallVector). In
858addition, the iterator invalidation characteristics of std::list are stronger
859than that of a vector class: inserting or removing an element into the list does
860not invalidate iterator or pointers to other elements in the list.</p>
861</div>
862
863<!-- _______________________________________________________________________ -->
864<div class="doc_subsubsection">
865 <a name="dss_ilist">llvm/ADT/ilist</a>
866</div>
867
868<div class="doc_text">
869<p><tt>ilist&lt;T&gt;</tt> implements an 'intrusive' doubly-linked list. It is
870intrusive, because it requires the element to store and provide access to the
871prev/next pointers for the list.</p>
872
873<p>ilist has the same drawbacks as std::list, and additionally requires an
874ilist_traits implementation for the element type, but it provides some novel
875characteristics. In particular, it can efficiently store polymorphic objects,
876the traits class is informed when an element is inserted or removed from the
877list, and ilists are guaranteed to support a constant-time splice operation.
878</p>
879
880<p>These properties are exactly what we want for things like Instructions and
881basic blocks, which is why these are implemented with ilists.</p>
882</div>
883
884<!-- _______________________________________________________________________ -->
885<div class="doc_subsubsection">
Chris Lattnerc5722432007-02-03 19:49:31 +0000[diff] [blame]886 <a name="dss_other">Other Sequential Container options</a>
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]887</div>
888
889<div class="doc_text">
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]890<p>Other STL containers are available, such as std::string.</p>
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]891
892<p>There are also various STL adapter classes such as std::queue,
893std::priority_queue, std::stack, etc. These provide simplified access to an
894underlying container but don't affect the cost of the container itself.</p>
895
896</div>
897
898
899<!-- ======================================================================= -->
900<div class="doc_subsection">
901 <a name="ds_set">Set-Like Containers (std::set, SmallSet, SetVector, etc)</a>
902</div>
903
904<div class="doc_text">
905
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]906<p>Set-like containers are useful when you need to canonicalize multiple values
907into a single representation. There are several different choices for how to do
908this, providing various trade-offs.</p>
909
910</div>
911
912
913<!-- _______________________________________________________________________ -->
914<div class="doc_subsubsection">
915 <a name="dss_sortedvectorset">A sorted 'vector'</a>
916</div>
917
918<div class="doc_text">
919
Chris Lattner3b23a8c2007-02-03 08:10:45 +0000[diff] [blame]920<p>If you intend to insert a lot of elements, then do a lot of queries, a
921great approach is to use a vector (or other sequential container) with
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]922std::sort+std::unique to remove duplicates. This approach works really well if
Chris Lattner3b23a8c2007-02-03 08:10:45 +0000[diff] [blame]923your usage pattern has these two distinct phases (insert then query), and can be
924coupled with a good choice of <a href="#ds_sequential">sequential container</a>.
925</p>
926
927<p>
928This combination provides the several nice properties: the result data is
929contiguous in memory (good for cache locality), has few allocations, is easy to
930address (iterators in the final vector are just indices or pointers), and can be
931efficiently queried with a standard binary or radix search.</p>
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]932
933</div>
934
935<!-- _______________________________________________________________________ -->
936<div class="doc_subsubsection">
937 <a name="dss_smallset">"llvm/ADT/SmallSet.h"</a>
938</div>
939
940<div class="doc_text">
941
Reid Spencer128a7a72007-02-03 21:06:43 +0000[diff] [blame]942<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]943are 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]944has space for N elements in place (thus, if the set is dynamically smaller than
Chris Lattner14868db2007-02-03 08:20:15 +0000[diff] [blame]945N, no malloc traffic is required) and accesses them with a simple linear search.
946When the set grows beyond 'N' elements, it allocates a more expensive representation that
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]947guarantees efficient access (for most types, it falls back to std::set, but for
Chris Lattner14868db2007-02-03 08:20:15 +0000[diff] [blame]948pointers it uses something far better, <a
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]949href="#dss_smallptrset">SmallPtrSet</a>).</p>
950
951<p>The magic of this class is that it handles small sets extremely efficiently,
952but gracefully handles extremely large sets without loss of efficiency. The
953drawback is that the interface is quite small: it supports insertion, queries
954and erasing, but does not support iteration.</p>
955
956</div>
957
958<!-- _______________________________________________________________________ -->
959<div class="doc_subsubsection">
960 <a name="dss_smallptrset">"llvm/ADT/SmallPtrSet.h"</a>
961</div>
962
963<div class="doc_text">
964
965<p>SmallPtrSet has all the advantages of SmallSet (and a SmallSet of pointers is
Reid Spencer128a7a72007-02-03 21:06:43 +0000[diff] [blame]966transparently implemented with a SmallPtrSet), but also supports iterators. If
Chris Lattner14868db2007-02-03 08:20:15 +0000[diff] [blame]967more than 'N' insertions are performed, a single quadratically
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]968probed hash table is allocated and grows as needed, providing extremely
969efficient access (constant time insertion/deleting/queries with low constant
970factors) and is very stingy with malloc traffic.</p>
971
972<p>Note that, unlike std::set, the iterators of SmallPtrSet are invalidated
973whenever an insertion occurs. Also, the values visited by the iterators are not
974visited in sorted order.</p>
975
976</div>
977
978<!-- _______________________________________________________________________ -->
979<div class="doc_subsubsection">
980 <a name="dss_FoldingSet">"llvm/ADT/FoldingSet.h"</a>
981</div>
982
983<div class="doc_text">
984
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]985<p>
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]986FoldingSet is an aggregate class that is really good at uniquing
987expensive-to-create or polymorphic objects. It is a combination of a chained
988hash table with intrusive links (uniqued objects are required to inherit from
Chris Lattner14868db2007-02-03 08:20:15 +0000[diff] [blame]989FoldingSetNode) that uses <a href="#dss_smallvector">SmallVector</a> as part of
990its ID process.</p>
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]991
Chris Lattner14868db2007-02-03 08:20:15 +0000[diff] [blame]992<p>Consider a case where you want to implement a "getOrCreateFoo" method for
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]993a complex object (for example, a node in the code generator). The client has a
994description of *what* it wants to generate (it knows the opcode and all the
995operands), 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]996only to find out it already exists, at which point we would have to delete it
997and return the node that already exists.
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]998</p>
999
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1000<p>To support this style of client, FoldingSet perform a query with a
1001FoldingSetNodeID (which wraps SmallVector) that can be used to describe the
1002element that we want to query for. The query either returns the element
1003matching the ID or it returns an opaque ID that indicates where insertion should
Chris Lattner14868db2007-02-03 08:20:15 +0000[diff] [blame]1004take place. Construction of the ID usually does not require heap traffic.</p>
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1005
1006<p>Because FoldingSet uses intrusive links, it can support polymorphic objects
1007in the set (for example, you can have SDNode instances mixed with LoadSDNodes).
1008Because the elements are individually allocated, pointers to the elements are
1009stable: inserting or removing elements does not invalidate any pointers to other
1010elements.
1011</p>
1012
1013</div>
1014
1015<!-- _______________________________________________________________________ -->
1016<div class="doc_subsubsection">
1017 <a name="dss_set">&lt;set&gt;</a>
1018</div>
1019
1020<div class="doc_text">
1021
Chris Lattnerc5722432007-02-03 19:49:31 +0000[diff] [blame]1022<p><tt>std::set</tt> is a reasonable all-around set class, which is decent at
1023many things but great at nothing. std::set allocates memory for each element
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1024inserted (thus it is very malloc intensive) and typically stores three pointers
Chris Lattner14868db2007-02-03 08:20:15 +0000[diff] [blame]1025per element in the set (thus adding a large amount of per-element space
1026overhead). It offers guaranteed log(n) performance, which is not particularly
Chris Lattnerc5722432007-02-03 19:49:31 +0000[diff] [blame]1027fast from a complexity standpoint (particularly if the elements of the set are
1028expensive to compare, like strings), and has extremely high constant factors for
1029lookup, insertion and removal.</p>
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1030
Chris Lattner14868db2007-02-03 08:20:15 +0000[diff] [blame]1031<p>The advantages of std::set are that its iterators are stable (deleting or
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1032inserting an element from the set does not affect iterators or pointers to other
1033elements) and that iteration over the set is guaranteed to be in sorted order.
1034If the elements in the set are large, then the relative overhead of the pointers
1035and malloc traffic is not a big deal, but if the elements of the set are small,
1036std::set is almost never a good choice.</p>
1037
1038</div>
1039
1040<!-- _______________________________________________________________________ -->
1041<div class="doc_subsubsection">
1042 <a name="dss_setvector">"llvm/ADT/SetVector.h"</a>
1043</div>
1044
1045<div class="doc_text">
Chris Lattneredca3c52007-02-04 00:00:26 +0000[diff] [blame]1046<p>LLVM's SetVector&lt;Type&gt; is an adapter class that combines your choice of
1047a set-like container along with a <a href="#ds_sequential">Sequential
1048Container</a>. The important property
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1049that this provides is efficient insertion with uniquing (duplicate elements are
1050ignored) with iteration support. It implements this by inserting elements into
1051both a set-like container and the sequential container, using the set-like
1052container for uniquing and the sequential container for iteration.
1053</p>
1054
1055<p>The difference between SetVector and other sets is that the order of
1056iteration is guaranteed to match the order of insertion into the SetVector.
1057This property is really important for things like sets of pointers. Because
1058pointer values are non-deterministic (e.g. vary across runs of the program on
Chris Lattneredca3c52007-02-04 00:00:26 +0000[diff] [blame]1059different machines), iterating over the pointers in the set will
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1060not be in a well-defined order.</p>
1061
1062<p>
1063The drawback of SetVector is that it requires twice as much space as a normal
1064set and has the sum of constant factors from the set-like container and the
1065sequential container that it uses. Use it *only* if you need to iterate over
1066the elements in a deterministic order. SetVector is also expensive to delete
Chris Lattneredca3c52007-02-04 00:00:26 +0000[diff] [blame]1067elements out of (linear time), unless you use it's "pop_back" method, which is
1068faster.
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1069</p>
1070
Chris Lattneredca3c52007-02-04 00:00:26 +0000[diff] [blame]1071<p>SetVector is an adapter class that defaults to using std::vector and std::set
1072for the underlying containers, so it is quite expensive. However,
1073<tt>"llvm/ADT/SetVector.h"</tt> also provides a SmallSetVector class, which
1074defaults to using a SmallVector and SmallSet of a specified size. If you use
1075this, and if your sets are dynamically smaller than N, you will save a lot of
1076heap traffic.</p>
1077
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1078</div>
1079
1080<!-- _______________________________________________________________________ -->
1081<div class="doc_subsubsection">
Chris Lattnerc5722432007-02-03 19:49:31 +0000[diff] [blame]1082 <a name="dss_uniquevector">"llvm/ADT/UniqueVector.h"</a>
1083</div>
1084
1085<div class="doc_text">
1086
1087<p>
1088UniqueVector is similar to <a href="#dss_setvector">SetVector</a>, but it
1089retains a unique ID for each element inserted into the set. It internally
1090contains a map and a vector, and it assigns a unique ID for each value inserted
1091into the set.</p>
1092
1093<p>UniqueVector is very expensive: its cost is the sum of the cost of
1094maintaining both the map and vector, it has high complexity, high constant
1095factors, and produces a lot of malloc traffic. It should be avoided.</p>
1096
1097</div>
1098
1099
1100<!-- _______________________________________________________________________ -->
1101<div class="doc_subsubsection">
1102 <a name="dss_otherset">Other Set-Like Container Options</a>
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1103</div>
1104
1105<div class="doc_text">
1106
1107<p>
1108The STL provides several other options, such as std::multiset and the various
Chris Lattnerc5722432007-02-03 19:49:31 +0000[diff] [blame]1109"hash_set" like containers (whether from C++ TR1 or from the SGI library).</p>
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1110
1111<p>std::multiset is useful if you're not interested in elimination of
Chris Lattner14868db2007-02-03 08:20:15 +0000[diff] [blame]1112duplicates, but has all the drawbacks of std::set. A sorted vector (where you
1113don't delete duplicate entries) or some other approach is almost always
1114better.</p>
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1115
1116<p>The various hash_set implementations (exposed portably by
Chris Lattner14868db2007-02-03 08:20:15 +0000[diff] [blame]1117"llvm/ADT/hash_set") is a simple chained hashtable. This algorithm is as malloc
1118intensive as std::set (performing an allocation for each element inserted,
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1119thus having really high constant factors) but (usually) provides O(1)
1120insertion/deletion of elements. This can be useful if your elements are large
Chris Lattner14868db2007-02-03 08:20:15 +0000[diff] [blame]1121(thus making the constant-factor cost relatively low) or if comparisons are
1122expensive. Element iteration does not visit elements in a useful order.</p>
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1123
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]1124</div>
1125
1126<!-- ======================================================================= -->
1127<div class="doc_subsection">
1128 <a name="ds_map">Map-Like Containers (std::map, DenseMap, etc)</a>
1129</div>
1130
1131<div class="doc_text">
Chris Lattnerc5722432007-02-03 19:49:31 +0000[diff] [blame]1132Map-like containers are useful when you want to associate data to a key. As
1133usual, there are a lot of different ways to do this. :)
1134</div>
1135
1136<!-- _______________________________________________________________________ -->
1137<div class="doc_subsubsection">
1138 <a name="dss_sortedvectormap">A sorted 'vector'</a>
1139</div>
1140
1141<div class="doc_text">
1142
1143<p>
1144If your usage pattern follows a strict insert-then-query approach, you can
1145trivially use the same approach as <a href="#dss_sortedvectorset">sorted vectors
1146for set-like containers</a>. The only difference is that your query function
1147(which uses std::lower_bound to get efficient log(n) lookup) should only compare
1148the key, not both the key and value. This yields the same advantages as sorted
1149vectors for sets.
1150</p>
1151</div>
1152
1153<!-- _______________________________________________________________________ -->
1154<div class="doc_subsubsection">
Chris Lattner796f9fa2007-02-08 19:14:21 +0000[diff] [blame]1155 <a name="dss_stringmap">"llvm/ADT/StringMap.h"</a>
Chris Lattnerc5722432007-02-03 19:49:31 +0000[diff] [blame]1156</div>
1157
1158<div class="doc_text">
1159
1160<p>
1161Strings are commonly used as keys in maps, and they are difficult to support
1162efficiently: they are variable length, inefficient to hash and compare when
Chris Lattner796f9fa2007-02-08 19:14:21 +0000[diff] [blame]1163long, expensive to copy, etc. StringMap is a specialized container designed to
1164cope with these issues. It supports mapping an arbitrary range of bytes to an
1165arbitrary other object.</p>
Chris Lattnerc5722432007-02-03 19:49:31 +0000[diff] [blame]1166
Chris Lattner796f9fa2007-02-08 19:14:21 +0000[diff] [blame]1167<p>The StringMap implementation uses a quadratically-probed hash table, where
Chris Lattnerc5722432007-02-03 19:49:31 +0000[diff] [blame]1168the buckets store a pointer to the heap allocated entries (and some other
1169stuff). The entries in the map must be heap allocated because the strings are
1170variable length. The string data (key) and the element object (value) are
1171stored in the same allocation with the string data immediately after the element
1172object. This container guarantees the "<tt>(char*)(&amp;Value+1)</tt>" points
1173to the key string for a value.</p>
1174
Chris Lattner796f9fa2007-02-08 19:14:21 +0000[diff] [blame]1175<p>The StringMap is very fast for several reasons: quadratic probing is very
Chris Lattnerc5722432007-02-03 19:49:31 +0000[diff] [blame]1176cache efficient for lookups, the hash value of strings in buckets is not
Chris Lattner796f9fa2007-02-08 19:14:21 +0000[diff] [blame]1177recomputed when lookup up an element, StringMap rarely has to touch the
Chris Lattnerc5722432007-02-03 19:49:31 +0000[diff] [blame]1178memory for unrelated objects when looking up a value (even when hash collisions
1179happen), hash table growth does not recompute the hash values for strings
1180already in the table, and each pair in the map is store in a single allocation
1181(the string data is stored in the same allocation as the Value of a pair).</p>
1182
Chris Lattner796f9fa2007-02-08 19:14:21 +0000[diff] [blame]1183<p>StringMap also provides query methods that take byte ranges, so it only ever
Chris Lattnerc5722432007-02-03 19:49:31 +0000[diff] [blame]1184copies a string if a value is inserted into the table.</p>
1185</div>
1186
1187<!-- _______________________________________________________________________ -->
1188<div class="doc_subsubsection">
1189 <a name="dss_indexedmap">"llvm/ADT/IndexedMap.h"</a>
1190</div>
1191
1192<div class="doc_text">
1193<p>
1194IndexedMap is a specialized container for mapping small dense integers (or
1195values that can be mapped to small dense integers) to some other type. It is
1196internally implemented as a vector with a mapping function that maps the keys to
1197the dense integer range.
1198</p>
1199
1200<p>
1201This is useful for cases like virtual registers in the LLVM code generator: they
1202have a dense mapping that is offset by a compile-time constant (the first
1203virtual register ID).</p>
1204
1205</div>
1206
1207<!-- _______________________________________________________________________ -->
1208<div class="doc_subsubsection">
1209 <a name="dss_densemap">"llvm/ADT/DenseMap.h"</a>
1210</div>
1211
1212<div class="doc_text">
1213
1214<p>
1215DenseMap is a simple quadratically probed hash table. It excels at supporting
1216small keys and values: it uses a single allocation to hold all of the pairs that
1217are currently inserted in the map. DenseMap is a great way to map pointers to
1218pointers, or map other small types to each other.
1219</p>
1220
1221<p>
1222There are several aspects of DenseMap that you should be aware of, however. The
1223iterators in a densemap are invalidated whenever an insertion occurs, unlike
1224map. Also, because DenseMap allocates space for a large number of key/value
Chris Lattnera4a264d2007-02-03 20:17:53 +0000[diff] [blame]1225pairs (it starts with 64 by default), it will waste a lot of space if your keys
1226or values are large. Finally, you must implement a partial specialization of
Chris Lattnerc5722432007-02-03 19:49:31 +0000[diff] [blame]1227DenseMapKeyInfo for the key that you want, if it isn't already supported. This
1228is required to tell DenseMap about two special marker values (which can never be
Chris Lattnera4a264d2007-02-03 20:17:53 +0000[diff] [blame]1229inserted into the map) that it needs internally.</p>
Chris Lattnerc5722432007-02-03 19:49:31 +0000[diff] [blame]1230
1231</div>
1232
1233<!-- _______________________________________________________________________ -->
1234<div class="doc_subsubsection">
1235 <a name="dss_map">&lt;map&gt;</a>
1236</div>
1237
1238<div class="doc_text">
1239
1240<p>
1241std::map has similar characteristics to <a href="#dss_set">std::set</a>: it uses
1242a single allocation per pair inserted into the map, it offers log(n) lookup with
1243an extremely large constant factor, imposes a space penalty of 3 pointers per
1244pair in the map, etc.</p>
1245
1246<p>std::map is most useful when your keys or values are very large, if you need
1247to iterate over the collection in sorted order, or if you need stable iterators
1248into the map (i.e. they don't get invalidated if an insertion or deletion of
1249another element takes place).</p>
1250
1251</div>
1252
1253<!-- _______________________________________________________________________ -->
1254<div class="doc_subsubsection">
1255 <a name="dss_othermap">Other Map-Like Container Options</a>
1256</div>
1257
1258<div class="doc_text">
1259
1260<p>
1261The STL provides several other options, such as std::multimap and the various
1262"hash_map" like containers (whether from C++ TR1 or from the SGI library).</p>
1263
1264<p>std::multimap is useful if you want to map a key to multiple values, but has
1265all the drawbacks of std::map. A sorted vector or some other approach is almost
1266always better.</p>
1267
1268<p>The various hash_map implementations (exposed portably by
1269"llvm/ADT/hash_map") are simple chained hash tables. This algorithm is as
1270malloc intensive as std::map (performing an allocation for each element
1271inserted, thus having really high constant factors) but (usually) provides O(1)
1272insertion/deletion of elements. This can be useful if your elements are large
1273(thus making the constant-factor cost relatively low) or if comparisons are
1274expensive. Element iteration does not visit elements in a useful order.</p>
1275
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]1276</div>
1277
Chris Lattnerf623a082005-10-17 01:36:23 +0000[diff] [blame]1278
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1279<!-- *********************************************************************** -->
1280<div class="doc_section">
1281 <a name="common">Helpful Hints for Common Operations</a>
1282</div>
1283<!-- *********************************************************************** -->
1284
1285<div class="doc_text">
1286
1287<p>This section describes how to perform some very simple transformations of
1288LLVM code. This is meant to give examples of common idioms used, showing the
1289practical side of LLVM transformations. <p> Because this is a "how-to" section,
1290you should also read about the main classes that you will be working with. The
1291<a href="#coreclasses">Core LLVM Class Hierarchy Reference</a> contains details
1292and descriptions of the main classes that you should know about.</p>
1293
1294</div>
1295
1296<!-- NOTE: this section should be heavy on example code -->
1297<!-- ======================================================================= -->
1298<div class="doc_subsection">
1299 <a name="inspection">Basic Inspection and Traversal Routines</a>
1300</div>
1301
1302<div class="doc_text">
1303
1304<p>The LLVM compiler infrastructure have many different data structures that may
1305be traversed. Following the example of the C++ standard template library, the
1306techniques used to traverse these various data structures are all basically the
1307same. For a enumerable sequence of values, the <tt>XXXbegin()</tt> function (or
1308method) returns an iterator to the start of the sequence, the <tt>XXXend()</tt>
1309function returns an iterator pointing to one past the last valid element of the
1310sequence, and there is some <tt>XXXiterator</tt> data type that is common
1311between the two operations.</p>
1312
1313<p>Because the pattern for iteration is common across many different aspects of
1314the program representation, the standard template library algorithms may be used
1315on them, and it is easier to remember how to iterate. First we show a few common
1316examples of the data structures that need to be traversed. Other data
1317structures are traversed in very similar ways.</p>
1318
1319</div>
1320
1321<!-- _______________________________________________________________________ -->
Chris Lattner69bf8a92004-05-23 21:06:58 +0000[diff] [blame]1322<div class="doc_subsubsection">
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1323 <a name="iterate_function">Iterating over the </a><a
1324 href="#BasicBlock"><tt>BasicBlock</tt></a>s in a <a
1325 href="#Function"><tt>Function</tt></a>
1326</div>
1327
1328<div class="doc_text">
1329
1330<p>It's quite common to have a <tt>Function</tt> instance that you'd like to
1331transform in some way; in particular, you'd like to manipulate its
1332<tt>BasicBlock</tt>s. To facilitate this, you'll need to iterate over all of
1333the <tt>BasicBlock</tt>s that constitute the <tt>Function</tt>. The following is
1334an example that prints the name of a <tt>BasicBlock</tt> and the number of
1335<tt>Instruction</tt>s it contains:</p>
1336
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1337<div class="doc_code">
1338<pre>
Bill Wendling82e2eea2006-10-11 18:00:22 +0000[diff] [blame]1339// <i>func is a pointer to a Function instance</i>
1340for (Function::iterator i = func-&gt;begin(), e = func-&gt;end(); i != e; ++i)
1341 // <i>Print out the name of the basic block if it has one, and then the</i>
1342 // <i>number of instructions that it contains</i>
Bill Wendling832171c2006-12-07 20:04:42 +0000[diff] [blame]1343 llvm::cerr &lt;&lt; "Basic block (name=" &lt;&lt; i-&gt;getName() &lt;&lt; ") has "
1344 &lt;&lt; i-&gt;size() &lt;&lt; " instructions.\n";
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1345</pre>
1346</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1347
1348<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]1349invoking member functions of the <tt>Instruction</tt> class. This is
1350because the indirection operator is overloaded for the iterator
Chris Lattner7496ec52003-08-05 22:54:23 +0000[diff] [blame]1351classes. In the above code, the expression <tt>i-&gt;size()</tt> is
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1352exactly equivalent to <tt>(*i).size()</tt> just like you'd expect.</p>
1353
1354</div>
1355
1356<!-- _______________________________________________________________________ -->
Chris Lattner69bf8a92004-05-23 21:06:58 +0000[diff] [blame]1357<div class="doc_subsubsection">
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1358 <a name="iterate_basicblock">Iterating over the </a><a
1359 href="#Instruction"><tt>Instruction</tt></a>s in a <a
1360 href="#BasicBlock"><tt>BasicBlock</tt></a>
1361</div>
1362
1363<div class="doc_text">
1364
1365<p>Just like when dealing with <tt>BasicBlock</tt>s in <tt>Function</tt>s, it's
1366easy to iterate over the individual instructions that make up
1367<tt>BasicBlock</tt>s. Here's a code snippet that prints out each instruction in
1368a <tt>BasicBlock</tt>:</p>
1369
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1370<div class="doc_code">
Chris Lattner55c04612005-03-06 06:00:13 +0000[diff] [blame]1371<pre>
Bill Wendling82e2eea2006-10-11 18:00:22 +0000[diff] [blame]1372// <i>blk is a pointer to a BasicBlock instance</i>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1373for (BasicBlock::iterator i = blk-&gt;begin(), e = blk-&gt;end(); i != e; ++i)
Bill Wendling82e2eea2006-10-11 18:00:22 +0000[diff] [blame]1374 // <i>The next statement works since operator&lt;&lt;(ostream&amp;,...)</i>
1375 // <i>is overloaded for Instruction&amp;</i>
Bill Wendling832171c2006-12-07 20:04:42 +0000[diff] [blame]1376 llvm::cerr &lt;&lt; *i &lt;&lt; "\n";
Chris Lattner55c04612005-03-06 06:00:13 +0000[diff] [blame]1377</pre>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1378</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1379
1380<p>However, this isn't really the best way to print out the contents of a
1381<tt>BasicBlock</tt>! Since the ostream operators are overloaded for virtually
1382anything you'll care about, you could have just invoked the print routine on the
Bill Wendling832171c2006-12-07 20:04:42 +0000[diff] [blame]1383basic block itself: <tt>llvm::cerr &lt;&lt; *blk &lt;&lt; "\n";</tt>.</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1384
1385</div>
1386
1387<!-- _______________________________________________________________________ -->
Chris Lattner69bf8a92004-05-23 21:06:58 +0000[diff] [blame]1388<div class="doc_subsubsection">
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1389 <a name="iterate_institer">Iterating over the </a><a
1390 href="#Instruction"><tt>Instruction</tt></a>s in a <a
1391 href="#Function"><tt>Function</tt></a>
1392</div>
1393
1394<div class="doc_text">
1395
1396<p>If you're finding that you commonly iterate over a <tt>Function</tt>'s
1397<tt>BasicBlock</tt>s and then that <tt>BasicBlock</tt>'s <tt>Instruction</tt>s,
1398<tt>InstIterator</tt> should be used instead. You'll need to include <a
1399href="/doxygen/InstIterator_8h-source.html"><tt>llvm/Support/InstIterator.h</tt></a>,
1400and then instantiate <tt>InstIterator</tt>s explicitly in your code. Here's a
Chris Lattner69bf8a92004-05-23 21:06:58 +0000[diff] [blame]1401small 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]1402
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1403<div class="doc_code">
1404<pre>
1405#include "<a href="/doxygen/InstIterator_8h-source.html">llvm/Support/InstIterator.h</a>"
1406
Reid Spencer128a7a72007-02-03 21:06:43 +0000[diff] [blame]1407// <i>F is a pointer to a Function instance</i>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1408for (inst_iterator i = inst_begin(F), e = inst_end(F); i != e; ++i)
Bill Wendling832171c2006-12-07 20:04:42 +0000[diff] [blame]1409 llvm::cerr &lt;&lt; *i &lt;&lt; "\n";
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1410</pre>
1411</div>
1412
1413<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]1414work list with its initial contents. For example, if you wanted to
1415initialize a work list to contain all instructions in a <tt>Function</tt>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1416F, all you would need to do is something like:</p>
1417
1418<div class="doc_code">
1419<pre>
1420std::set&lt;Instruction*&gt; worklist;
1421worklist.insert(inst_begin(F), inst_end(F));
1422</pre>
1423</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1424
1425<p>The STL set <tt>worklist</tt> would now contain all instructions in the
1426<tt>Function</tt> pointed to by F.</p>
1427
1428</div>
1429
1430<!-- _______________________________________________________________________ -->
1431<div class="doc_subsubsection">
1432 <a name="iterate_convert">Turning an iterator into a class pointer (and
1433 vice-versa)</a>
1434</div>
1435
1436<div class="doc_text">
1437
1438<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]1439instance when all you've got at hand is an iterator. Well, extracting
Chris Lattner69bf8a92004-05-23 21:06:58 +0000[diff] [blame]1440a reference or a pointer from an iterator is very straight-forward.
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]1441Assuming that <tt>i</tt> is a <tt>BasicBlock::iterator</tt> and <tt>j</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1442is a <tt>BasicBlock::const_iterator</tt>:</p>
1443
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1444<div class="doc_code">
1445<pre>
Bill Wendling82e2eea2006-10-11 18:00:22 +0000[diff] [blame]1446Instruction&amp; inst = *i; // <i>Grab reference to instruction reference</i>
1447Instruction* pinst = &amp;*i; // <i>Grab pointer to instruction reference</i>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1448const Instruction&amp; inst = *j;
1449</pre>
1450</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1451
1452<p>However, the iterators you'll be working with in the LLVM framework are
1453special: they will automatically convert to a ptr-to-instance type whenever they
1454need to. Instead of dereferencing the iterator and then taking the address of
1455the result, you can simply assign the iterator to the proper pointer type and
1456you get the dereference and address-of operation as a result of the assignment
1457(behind the scenes, this is a result of overloading casting mechanisms). Thus
1458the last line of the last example,</p>
1459
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1460<div class="doc_code">
1461<pre>
1462Instruction* pinst = &amp;*i;
1463</pre>
1464</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1465
1466<p>is semantically equivalent to</p>
1467
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1468<div class="doc_code">
1469<pre>
1470Instruction* pinst = i;
1471</pre>
1472</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1473
Chris Lattner69bf8a92004-05-23 21:06:58 +0000[diff] [blame]1474<p>It's also possible to turn a class pointer into the corresponding iterator,
1475and this is a constant time operation (very efficient). The following code
1476snippet illustrates use of the conversion constructors provided by LLVM
1477iterators. By using these, you can explicitly grab the iterator of something
1478without actually obtaining it via iteration over some structure:</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1479
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1480<div class="doc_code">
1481<pre>
1482void printNextInstruction(Instruction* inst) {
1483 BasicBlock::iterator it(inst);
Bill Wendling82e2eea2006-10-11 18:00:22 +0000[diff] [blame]1484 ++it; // <i>After this line, it refers to the instruction after *inst</i>
Bill Wendling832171c2006-12-07 20:04:42 +0000[diff] [blame]1485 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]1486}
1487</pre>
1488</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1489
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1490</div>
1491
1492<!--_______________________________________________________________________-->
1493<div class="doc_subsubsection">
1494 <a name="iterate_complex">Finding call sites: a slightly more complex
1495 example</a>
1496</div>
1497
1498<div class="doc_text">
1499
1500<p>Say that you're writing a FunctionPass and would like to count all the
1501locations in the entire module (that is, across every <tt>Function</tt>) where a
1502certain function (i.e., some <tt>Function</tt>*) is already in scope. As you'll
1503learn 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]1504much more straight-forward manner, but this example will allow us to explore how
Reid Spencer128a7a72007-02-03 21:06:43 +0000[diff] [blame]1505you'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]1506is what we want to do:</p>
1507
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1508<div class="doc_code">
1509<pre>
1510initialize callCounter to zero
1511for each Function f in the Module
1512 for each BasicBlock b in f
1513 for each Instruction i in b
1514 if (i is a CallInst and calls the given function)
1515 increment callCounter
1516</pre>
1517</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1518
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1519<p>And the actual code is (remember, because we're writing a
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1520<tt>FunctionPass</tt>, our <tt>FunctionPass</tt>-derived class simply has to
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1521override the <tt>runOnFunction</tt> method):</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1522
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1523<div class="doc_code">
1524<pre>
1525Function* targetFunc = ...;
1526
1527class OurFunctionPass : public FunctionPass {
1528 public:
1529 OurFunctionPass(): callCounter(0) { }
1530
1531 virtual runOnFunction(Function&amp; F) {
1532 for (Function::iterator b = F.begin(), be = F.end(); b != be; ++b) {
1533 for (BasicBlock::iterator i = b-&gt;begin(); ie = b-&gt;end(); i != ie; ++i) {
1534 if (<a href="#CallInst">CallInst</a>* callInst = <a href="#isa">dyn_cast</a>&lt;<a
1535 href="#CallInst">CallInst</a>&gt;(&amp;*i)) {
Bill Wendling82e2eea2006-10-11 18:00:22 +0000[diff] [blame]1536 // <i>We know we've encountered a call instruction, so we</i>
1537 // <i>need to determine if it's a call to the</i>
1538 // <i>function pointed to by m_func or not</i>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1539
1540 if (callInst-&gt;getCalledFunction() == targetFunc)
1541 ++callCounter;
1542 }
1543 }
1544 }
Bill Wendling82e2eea2006-10-11 18:00:22 +0000[diff] [blame]1545 }
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1546
1547 private:
1548 unsigned callCounter;
1549};
1550</pre>
1551</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1552
1553</div>
1554
Brian Gaekef1972c62003-11-07 19:25:45 +0000[diff] [blame]1555<!--_______________________________________________________________________-->
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1556<div class="doc_subsubsection">
1557 <a name="calls_and_invokes">Treating calls and invokes the same way</a>
1558</div>
1559
1560<div class="doc_text">
1561
1562<p>You may have noticed that the previous example was a bit oversimplified in
1563that it did not deal with call sites generated by 'invoke' instructions. In
1564this, and in other situations, you may find that you want to treat
1565<tt>CallInst</tt>s and <tt>InvokeInst</tt>s the same way, even though their
1566most-specific common base class is <tt>Instruction</tt>, which includes lots of
1567less closely-related things. For these cases, LLVM provides a handy wrapper
1568class called <a
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]1569href="http://llvm.org/doxygen/classllvm_1_1CallSite.html"><tt>CallSite</tt></a>.
Chris Lattner69bf8a92004-05-23 21:06:58 +0000[diff] [blame]1570It is essentially a wrapper around an <tt>Instruction</tt> pointer, with some
1571methods that provide functionality common to <tt>CallInst</tt>s and
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1572<tt>InvokeInst</tt>s.</p>
1573
Chris Lattner69bf8a92004-05-23 21:06:58 +0000[diff] [blame]1574<p>This class has "value semantics": it should be passed by value, not by
1575reference and it should not be dynamically allocated or deallocated using
1576<tt>operator new</tt> or <tt>operator delete</tt>. It is efficiently copyable,
1577assignable and constructable, with costs equivalents to that of a bare pointer.
1578If you look at its definition, it has only a single pointer member.</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1579
1580</div>
1581
Chris Lattner1a3105b2002-09-09 05:49:39 +0000[diff] [blame]1582<!--_______________________________________________________________________-->
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1583<div class="doc_subsubsection">
1584 <a name="iterate_chains">Iterating over def-use &amp; use-def chains</a>
1585</div>
1586
1587<div class="doc_text">
1588
1589<p>Frequently, we might have an instance of the <a
Chris Lattner00815172007-01-04 22:01:45 +0000[diff] [blame]1590href="/doxygen/classllvm_1_1Value.html">Value Class</a> and we want to
Misha Brukman384047f2004-06-03 23:29:12 +0000[diff] [blame]1591determine which <tt>User</tt>s use the <tt>Value</tt>. The list of all
1592<tt>User</tt>s of a particular <tt>Value</tt> is called a <i>def-use</i> chain.
1593For example, let's say we have a <tt>Function*</tt> named <tt>F</tt> to a
1594particular function <tt>foo</tt>. Finding all of the instructions that
1595<i>use</i> <tt>foo</tt> is as simple as iterating over the <i>def-use</i> chain
1596of <tt>F</tt>:</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1597
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1598<div class="doc_code">
1599<pre>
1600Function* F = ...;
1601
Bill Wendling82e2eea2006-10-11 18:00:22 +0000[diff] [blame]1602for (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]1603 if (Instruction *Inst = dyn_cast&lt;Instruction&gt;(*i)) {
Bill Wendling832171c2006-12-07 20:04:42 +0000[diff] [blame]1604 llvm::cerr &lt;&lt; "F is used in instruction:\n";
1605 llvm::cerr &lt;&lt; *Inst &lt;&lt; "\n";
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1606 }
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1607</pre>
1608</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1609
1610<p>Alternately, it's common to have an instance of the <a
Misha Brukman384047f2004-06-03 23:29:12 +0000[diff] [blame]1611href="/doxygen/classllvm_1_1User.html">User Class</a> and need to know what
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1612<tt>Value</tt>s are used by it. The list of all <tt>Value</tt>s used by a
1613<tt>User</tt> is known as a <i>use-def</i> chain. Instances of class
1614<tt>Instruction</tt> are common <tt>User</tt>s, so we might want to iterate over
1615all of the values that a particular instruction uses (that is, the operands of
1616the particular <tt>Instruction</tt>):</p>
1617
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1618<div class="doc_code">
1619<pre>
1620Instruction* pi = ...;
1621
1622for (User::op_iterator i = pi-&gt;op_begin(), e = pi-&gt;op_end(); i != e; ++i) {
1623 Value* v = *i;
Bill Wendling82e2eea2006-10-11 18:00:22 +0000[diff] [blame]1624 // <i>...</i>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1625}
1626</pre>
1627</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1628
Chris Lattner1a3105b2002-09-09 05:49:39 +0000[diff] [blame]1629<!--
1630 def-use chains ("finding all users of"): Value::use_begin/use_end
1631 use-def chains ("finding all values used"): User::op_begin/op_end [op=operand]
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1632-->
1633
1634</div>
1635
1636<!-- ======================================================================= -->
1637<div class="doc_subsection">
1638 <a name="simplechanges">Making simple changes</a>
1639</div>
1640
1641<div class="doc_text">
1642
1643<p>There are some primitive transformation operations present in the LLVM
Joel Stanley753eb712002-09-11 22:32:24 +0000[diff] [blame]1644infrastructure that are worth knowing about. When performing
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]1645transformations, it's fairly common to manipulate the contents of basic
1646blocks. This section describes some of the common methods for doing so
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1647and gives example code.</p>
1648
1649</div>
1650
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]1651<!--_______________________________________________________________________-->
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1652<div class="doc_subsubsection">
1653 <a name="schanges_creating">Creating and inserting new
1654 <tt>Instruction</tt>s</a>
1655</div>
1656
1657<div class="doc_text">
1658
1659<p><i>Instantiating Instructions</i></p>
1660
Chris Lattner69bf8a92004-05-23 21:06:58 +0000[diff] [blame]1661<p>Creation of <tt>Instruction</tt>s is straight-forward: simply call the
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1662constructor for the kind of instruction to instantiate and provide the necessary
1663parameters. For example, an <tt>AllocaInst</tt> only <i>requires</i> a
1664(const-ptr-to) <tt>Type</tt>. Thus:</p>
1665
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1666<div class="doc_code">
1667<pre>
1668AllocaInst* ai = new AllocaInst(Type::IntTy);
1669</pre>
1670</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1671
1672<p>will create an <tt>AllocaInst</tt> instance that represents the allocation of
Reid Spencer128a7a72007-02-03 21:06:43 +0000[diff] [blame]1673one integer in the current stack frame, at run time. Each <tt>Instruction</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1674subclass is likely to have varying default parameters which change the semantics
1675of the instruction, so refer to the <a
Misha Brukman31ca1de2004-06-03 23:35:54 +0000[diff] [blame]1676href="/doxygen/classllvm_1_1Instruction.html">doxygen documentation for the subclass of
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1677Instruction</a> that you're interested in instantiating.</p>
1678
1679<p><i>Naming values</i></p>
1680
1681<p>It is very useful to name the values of instructions when you're able to, as
1682this facilitates the debugging of your transformations. If you end up looking
1683at generated LLVM machine code, you definitely want to have logical names
1684associated with the results of instructions! By supplying a value for the
1685<tt>Name</tt> (default) parameter of the <tt>Instruction</tt> constructor, you
1686associate a logical name with the result of the instruction's execution at
Reid Spencer128a7a72007-02-03 21:06:43 +0000[diff] [blame]1687run time. For example, say that I'm writing a transformation that dynamically
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1688allocates space for an integer on the stack, and that integer is going to be
1689used as some kind of index by some other code. To accomplish this, I place an
1690<tt>AllocaInst</tt> at the first point in the first <tt>BasicBlock</tt> of some
1691<tt>Function</tt>, and I'm intending to use it within the same
1692<tt>Function</tt>. I might do:</p>
1693
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1694<div class="doc_code">
1695<pre>
1696AllocaInst* pa = new AllocaInst(Type::IntTy, 0, "indexLoc");
1697</pre>
1698</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1699
1700<p>where <tt>indexLoc</tt> is now the logical name of the instruction's
Reid Spencer128a7a72007-02-03 21:06:43 +0000[diff] [blame]1701execution value, which is a pointer to an integer on the run time stack.</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1702
1703<p><i>Inserting instructions</i></p>
1704
1705<p>There are essentially two ways to insert an <tt>Instruction</tt>
1706into an existing sequence of instructions that form a <tt>BasicBlock</tt>:</p>
1707
Joel Stanley9dd1ad62002-09-18 03:17:23 +0000[diff] [blame]1708<ul>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1709 <li>Insertion into an explicit instruction list
1710
1711 <p>Given a <tt>BasicBlock* pb</tt>, an <tt>Instruction* pi</tt> within that
1712 <tt>BasicBlock</tt>, and a newly-created instruction we wish to insert
1713 before <tt>*pi</tt>, we do the following: </p>
1714
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1715<div class="doc_code">
1716<pre>
1717BasicBlock *pb = ...;
1718Instruction *pi = ...;
1719Instruction *newInst = new Instruction(...);
1720
Bill Wendling82e2eea2006-10-11 18:00:22 +0000[diff] [blame]1721pb-&gt;getInstList().insert(pi, newInst); // <i>Inserts newInst before pi in pb</i>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1722</pre>
1723</div>
Alkis Evlogimenos9a5dc4f2004-05-27 00:57:51 +0000[diff] [blame]1724
1725 <p>Appending to the end of a <tt>BasicBlock</tt> is so common that
1726 the <tt>Instruction</tt> class and <tt>Instruction</tt>-derived
1727 classes provide constructors which take a pointer to a
1728 <tt>BasicBlock</tt> to be appended to. For example code that
1729 looked like: </p>
1730
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1731<div class="doc_code">
1732<pre>
1733BasicBlock *pb = ...;
1734Instruction *newInst = new Instruction(...);
1735
Bill Wendling82e2eea2006-10-11 18:00:22 +0000[diff] [blame]1736pb-&gt;getInstList().push_back(newInst); // <i>Appends newInst to pb</i>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1737</pre>
1738</div>
Alkis Evlogimenos9a5dc4f2004-05-27 00:57:51 +0000[diff] [blame]1739
1740 <p>becomes: </p>
1741
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1742<div class="doc_code">
1743<pre>
1744BasicBlock *pb = ...;
1745Instruction *newInst = new Instruction(..., pb);
1746</pre>
1747</div>
Alkis Evlogimenos9a5dc4f2004-05-27 00:57:51 +0000[diff] [blame]1748
1749 <p>which is much cleaner, especially if you are creating
1750 long instruction streams.</p></li>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1751
1752 <li>Insertion into an implicit instruction list
1753
1754 <p><tt>Instruction</tt> instances that are already in <tt>BasicBlock</tt>s
1755 are implicitly associated with an existing instruction list: the instruction
1756 list of the enclosing basic block. Thus, we could have accomplished the same
1757 thing as the above code without being given a <tt>BasicBlock</tt> by doing:
1758 </p>
1759
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1760<div class="doc_code">
1761<pre>
1762Instruction *pi = ...;
1763Instruction *newInst = new Instruction(...);
1764
1765pi-&gt;getParent()-&gt;getInstList().insert(pi, newInst);
1766</pre>
1767</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1768
1769 <p>In fact, this sequence of steps occurs so frequently that the
1770 <tt>Instruction</tt> class and <tt>Instruction</tt>-derived classes provide
1771 constructors which take (as a default parameter) a pointer to an
1772 <tt>Instruction</tt> which the newly-created <tt>Instruction</tt> should
1773 precede. That is, <tt>Instruction</tt> constructors are capable of
1774 inserting the newly-created instance into the <tt>BasicBlock</tt> of a
1775 provided instruction, immediately before that instruction. Using an
1776 <tt>Instruction</tt> constructor with a <tt>insertBefore</tt> (default)
1777 parameter, the above code becomes:</p>
1778
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1779<div class="doc_code">
1780<pre>
1781Instruction* pi = ...;
1782Instruction* newInst = new Instruction(..., pi);
1783</pre>
1784</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1785
1786 <p>which is much cleaner, especially if you're creating a lot of
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1787 instructions and adding them to <tt>BasicBlock</tt>s.</p></li>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1788</ul>
1789
1790</div>
1791
1792<!--_______________________________________________________________________-->
1793<div class="doc_subsubsection">
1794 <a name="schanges_deleting">Deleting <tt>Instruction</tt>s</a>
1795</div>
1796
1797<div class="doc_text">
1798
1799<p>Deleting an instruction from an existing sequence of instructions that form a
Chris Lattner69bf8a92004-05-23 21:06:58 +0000[diff] [blame]1800<a href="#BasicBlock"><tt>BasicBlock</tt></a> is very straight-forward. First,
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1801you must have a pointer to the instruction that you wish to delete. Second, you
1802need to obtain the pointer to that instruction's basic block. You use the
1803pointer to the basic block to get its list of instructions and then use the
1804erase function to remove your instruction. For example:</p>
1805
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1806<div class="doc_code">
1807<pre>
1808<a href="#Instruction">Instruction</a> *I = .. ;
1809<a href="#BasicBlock">BasicBlock</a> *BB = I-&gt;getParent();
1810
1811BB-&gt;getInstList().erase(I);
1812</pre>
1813</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1814
1815</div>
1816
1817<!--_______________________________________________________________________-->
1818<div class="doc_subsubsection">
1819 <a name="schanges_replacing">Replacing an <tt>Instruction</tt> with another
1820 <tt>Value</tt></a>
1821</div>
1822
1823<div class="doc_text">
1824
1825<p><i>Replacing individual instructions</i></p>
1826
1827<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]1828permits use of two very useful replace functions: <tt>ReplaceInstWithValue</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1829and <tt>ReplaceInstWithInst</tt>.</p>
1830
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]1831<h4><a name="schanges_deleting">Deleting <tt>Instruction</tt>s</a></h4>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1832
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]1833<ul>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1834 <li><tt>ReplaceInstWithValue</tt>
1835
1836 <p>This function replaces all uses (within a basic block) of a given
1837 instruction with a value, and then removes the original instruction. The
1838 following example illustrates the replacement of the result of a particular
Chris Lattner58360822005-01-17 00:12:04 +0000[diff] [blame]1839 <tt>AllocaInst</tt> that allocates memory for a single integer with a null
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1840 pointer to an integer.</p>
1841
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1842<div class="doc_code">
1843<pre>
1844AllocaInst* instToReplace = ...;
1845BasicBlock::iterator ii(instToReplace);
1846
1847ReplaceInstWithValue(instToReplace-&gt;getParent()-&gt;getInstList(), ii,
1848 Constant::getNullValue(PointerType::get(Type::IntTy)));
1849</pre></div></li>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1850
1851 <li><tt>ReplaceInstWithInst</tt>
1852
1853 <p>This function replaces a particular instruction with another
1854 instruction. The following example illustrates the replacement of one
1855 <tt>AllocaInst</tt> with another.</p>
1856
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1857<div class="doc_code">
1858<pre>
1859AllocaInst* instToReplace = ...;
1860BasicBlock::iterator ii(instToReplace);
1861
1862ReplaceInstWithInst(instToReplace-&gt;getParent()-&gt;getInstList(), ii,
1863 new AllocaInst(Type::IntTy, 0, "ptrToReplacedInt"));
1864</pre></div></li>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]1865</ul>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1866
1867<p><i>Replacing multiple uses of <tt>User</tt>s and <tt>Value</tt>s</i></p>
1868
1869<p>You can use <tt>Value::replaceAllUsesWith</tt> and
1870<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]1871doxygen documentation for the <a href="/doxygen/classllvm_1_1Value.html">Value Class</a>
Misha Brukman384047f2004-06-03 23:29:12 +0000[diff] [blame]1872and <a href="/doxygen/classllvm_1_1User.html">User Class</a>, respectively, for more
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1873information.</p>
1874
1875<!-- Value::replaceAllUsesWith User::replaceUsesOfWith Point out:
1876include/llvm/Transforms/Utils/ especially BasicBlockUtils.h with:
1877ReplaceInstWithValue, ReplaceInstWithInst -->
1878
1879</div>
1880
Chris Lattner9355b472002-09-06 02:50:58 +0000[diff] [blame]1881<!-- *********************************************************************** -->
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1882<div class="doc_section">
Chris Lattnerd9d6e102005-04-23 16:10:52 +0000[diff] [blame]1883 <a name="advanced">Advanced Topics</a>
1884</div>
1885<!-- *********************************************************************** -->
1886
1887<div class="doc_text">
Chris Lattnerf1b200b2005-04-23 17:27:36 +0000[diff] [blame]1888<p>
1889This section describes some of the advanced or obscure API's that most clients
1890do not need to be aware of. These API's tend manage the inner workings of the
1891LLVM system, and only need to be accessed in unusual circumstances.
1892</p>
1893</div>
Chris Lattnerd9d6e102005-04-23 16:10:52 +0000[diff] [blame]1894
Chris Lattnerf1b200b2005-04-23 17:27:36 +0000[diff] [blame]1895<!-- ======================================================================= -->
1896<div class="doc_subsection">
1897 <a name="TypeResolve">LLVM Type Resolution</a>
1898</div>
Chris Lattnerd9d6e102005-04-23 16:10:52 +0000[diff] [blame]1899
Chris Lattnerf1b200b2005-04-23 17:27:36 +0000[diff] [blame]1900<div class="doc_text">
1901
1902<p>
1903The LLVM type system has a very simple goal: allow clients to compare types for
1904structural equality with a simple pointer comparison (aka a shallow compare).
1905This goal makes clients much simpler and faster, and is used throughout the LLVM
1906system.
1907</p>
1908
1909<p>
1910Unfortunately achieving this goal is not a simple matter. In particular,
1911recursive types and late resolution of opaque types makes the situation very
1912difficult to handle. Fortunately, for the most part, our implementation makes
1913most clients able to be completely unaware of the nasty internal details. The
1914primary case where clients are exposed to the inner workings of it are when
1915building a recursive type. In addition to this case, the LLVM bytecode reader,
1916assembly parser, and linker also have to be aware of the inner workings of this
1917system.
1918</p>
1919
Chris Lattner0f876db2005-04-25 15:47:57 +0000[diff] [blame]1920<p>
1921For our purposes below, we need three concepts. First, an "Opaque Type" is
1922exactly as defined in the <a href="LangRef.html#t_opaque">language
1923reference</a>. Second an "Abstract Type" is any type which includes an
Reid Spencer06565dc2007-01-12 17:11:23 +0000[diff] [blame]1924opaque type as part of its type graph (for example "<tt>{ opaque, i32 }</tt>").
1925Third, 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]1926float }</tt>").
1927</p>
1928
Chris Lattnerf1b200b2005-04-23 17:27:36 +0000[diff] [blame]1929</div>
1930
1931<!-- ______________________________________________________________________ -->
1932<div class="doc_subsubsection">
1933 <a name="BuildRecType">Basic Recursive Type Construction</a>
1934</div>
1935
1936<div class="doc_text">
1937
1938<p>
1939Because the most common question is "how do I build a recursive type with LLVM",
1940we answer it now and explain it as we go. Here we include enough to cause this
1941to be emitted to an output .ll file:
1942</p>
1943
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1944<div class="doc_code">
Chris Lattnerf1b200b2005-04-23 17:27:36 +0000[diff] [blame]1945<pre>
Reid Spencer06565dc2007-01-12 17:11:23 +0000[diff] [blame]1946%mylist = type { %mylist*, i32 }
Chris Lattnerf1b200b2005-04-23 17:27:36 +0000[diff] [blame]1947</pre>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1948</div>
Chris Lattnerf1b200b2005-04-23 17:27:36 +0000[diff] [blame]1949
1950<p>
1951To build this, use the following LLVM APIs:
1952</p>
1953
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1954<div class="doc_code">
Chris Lattnerf1b200b2005-04-23 17:27:36 +0000[diff] [blame]1955<pre>
Bill Wendling82e2eea2006-10-11 18:00:22 +0000[diff] [blame]1956// <i>Create the initial outer struct</i>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1957<a href="#PATypeHolder">PATypeHolder</a> StructTy = OpaqueType::get();
1958std::vector&lt;const Type*&gt; Elts;
1959Elts.push_back(PointerType::get(StructTy));
1960Elts.push_back(Type::IntTy);
1961StructType *NewSTy = StructType::get(Elts);
Chris Lattnerf1b200b2005-04-23 17:27:36 +0000[diff] [blame]1962
Reid Spencer06565dc2007-01-12 17:11:23 +0000[diff] [blame]1963// <i>At this point, NewSTy = "{ opaque*, i32 }". Tell VMCore that</i>
Bill Wendling82e2eea2006-10-11 18:00:22 +0000[diff] [blame]1964// <i>the struct and the opaque type are actually the same.</i>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1965cast&lt;OpaqueType&gt;(StructTy.get())-&gt;<a href="#refineAbstractTypeTo">refineAbstractTypeTo</a>(NewSTy);
Chris Lattnerf1b200b2005-04-23 17:27:36 +0000[diff] [blame]1966
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1967// <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]1968// <i>kept up-to-date</i>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1969NewSTy = cast&lt;StructType&gt;(StructTy.get());
Chris Lattnerf1b200b2005-04-23 17:27:36 +0000[diff] [blame]1970
Bill Wendling82e2eea2006-10-11 18:00:22 +0000[diff] [blame]1971// <i>Add a name for the type to the module symbol table (optional)</i>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1972MyModule-&gt;addTypeName("mylist", NewSTy);
Chris Lattnerf1b200b2005-04-23 17:27:36 +0000[diff] [blame]1973</pre>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1974</div>
Chris Lattnerf1b200b2005-04-23 17:27:36 +0000[diff] [blame]1975
1976<p>
1977This code shows the basic approach used to build recursive types: build a
1978non-recursive type using 'opaque', then use type unification to close the cycle.
1979The type unification step is performed by the <tt><a
Chris Lattneraff26d12007-02-03 03:06:52 +0000[diff] [blame]1980href="#refineAbstractTypeTo">refineAbstractTypeTo</a></tt> method, which is
Chris Lattnerf1b200b2005-04-23 17:27:36 +0000[diff] [blame]1981described next. After that, we describe the <a
1982href="#PATypeHolder">PATypeHolder class</a>.
1983</p>
1984
1985</div>
1986
1987<!-- ______________________________________________________________________ -->
1988<div class="doc_subsubsection">
1989 <a name="refineAbstractTypeTo">The <tt>refineAbstractTypeTo</tt> method</a>
1990</div>
1991
1992<div class="doc_text">
1993<p>
1994The <tt>refineAbstractTypeTo</tt> method starts the type unification process.
1995While this method is actually a member of the DerivedType class, it is most
1996often used on OpaqueType instances. Type unification is actually a recursive
1997process. After unification, types can become structurally isomorphic to
1998existing types, and all duplicates are deleted (to preserve pointer equality).
1999</p>
2000
2001<p>
2002In the example above, the OpaqueType object is definitely deleted.
Reid Spencer06565dc2007-01-12 17:11:23 +0000[diff] [blame]2003Additionally, if there is an "{ \2*, i32}" type already created in the system,
Chris Lattnerf1b200b2005-04-23 17:27:36 +0000[diff] [blame]2004the pointer and struct type created are <b>also</b> deleted. Obviously whenever
2005a type is deleted, any "Type*" pointers in the program are invalidated. As
2006such, it is safest to avoid having <i>any</i> "Type*" pointers to abstract types
2007live across a call to <tt>refineAbstractTypeTo</tt> (note that non-abstract
2008types can never move or be deleted). To deal with this, the <a
2009href="#PATypeHolder">PATypeHolder</a> class is used to maintain a stable
2010reference to a possibly refined type, and the <a
2011href="#AbstractTypeUser">AbstractTypeUser</a> class is used to update more
2012complex datastructures.
2013</p>
2014
2015</div>
2016
2017<!-- ______________________________________________________________________ -->
2018<div class="doc_subsubsection">
2019 <a name="PATypeHolder">The PATypeHolder Class</a>
2020</div>
2021
2022<div class="doc_text">
2023<p>
2024PATypeHolder is a form of a "smart pointer" for Type objects. When VMCore
2025happily goes about nuking types that become isomorphic to existing types, it
2026automatically updates all PATypeHolder objects to point to the new type. In the
2027example above, this allows the code to maintain a pointer to the resultant
2028resolved recursive type, even though the Type*'s are potentially invalidated.
2029</p>
2030
2031<p>
2032PATypeHolder is an extremely light-weight object that uses a lazy union-find
2033implementation to update pointers. For example the pointer from a Value to its
2034Type is maintained by PATypeHolder objects.
2035</p>
2036
2037</div>
2038
2039<!-- ______________________________________________________________________ -->
2040<div class="doc_subsubsection">
2041 <a name="AbstractTypeUser">The AbstractTypeUser Class</a>
2042</div>
2043
2044<div class="doc_text">
2045
2046<p>
2047Some data structures need more to perform more complex updates when types get
2048resolved. The <a href="#SymbolTable">SymbolTable</a> class, for example, needs
2049move and potentially merge type planes in its representation when a pointer
2050changes.</p>
2051
2052<p>
2053To support this, a class can derive from the AbstractTypeUser class. This class
2054allows it to get callbacks when certain types are resolved. To register to get
2055callbacks for a particular type, the DerivedType::{add/remove}AbstractTypeUser
Chris Lattner0f876db2005-04-25 15:47:57 +0000[diff] [blame]2056methods can be called on a type. Note that these methods only work for <i>
Reid Spencer06565dc2007-01-12 17:11:23 +0000[diff] [blame]2057 abstract</i> types. Concrete types (those that do not include any opaque
2058objects) can never be refined.
Chris Lattnerf1b200b2005-04-23 17:27:36 +0000[diff] [blame]2059</p>
Chris Lattnerd9d6e102005-04-23 16:10:52 +0000[diff] [blame]2060</div>
2061
2062
2063<!-- ======================================================================= -->
2064<div class="doc_subsection">
2065 <a name="SymbolTable">The <tt>SymbolTable</tt> class</a>
2066</div>
Chris Lattnerf1b200b2005-04-23 17:27:36 +0000[diff] [blame]2067
Chris Lattnerd9d6e102005-04-23 16:10:52 +0000[diff] [blame]2068<div class="doc_text">
2069<p>This class provides a symbol table that the <a
2070href="#Function"><tt>Function</tt></a> and <a href="#Module">
2071<tt>Module</tt></a> classes use for naming definitions. The symbol table can
Reid Spencera6362242007-01-07 00:41:39 +0000[diff] [blame]2072provide a name for any <a href="#Value"><tt>Value</tt></a>.
2073<tt>SymbolTable</tt> is an abstract data type. It hides the data it contains
2074and provides access to it through a controlled interface.</p>
Chris Lattnerd9d6e102005-04-23 16:10:52 +0000[diff] [blame]2075
Reid Spencera6362242007-01-07 00:41:39 +0000[diff] [blame]2076<p>Note that the <tt>SymbolTable</tt> class should not be directly accessed
2077by most clients. It should only be used when iteration over the symbol table
2078names themselves are required, which is very special purpose. Note that not
2079all LLVM
Chris Lattnerd9d6e102005-04-23 16:10:52 +0000[diff] [blame]2080<a href="#Value">Value</a>s have names, and those without names (i.e. they have
2081an empty name) do not exist in the symbol table.
2082</p>
2083
2084<p>To use the <tt>SymbolTable</tt> well, you need to understand the
2085structure of the information it holds. The class contains two
2086<tt>std::map</tt> objects. The first, <tt>pmap</tt>, is a map of
2087<tt>Type*</tt> to maps of name (<tt>std::string</tt>) to <tt>Value*</tt>.
Reid Spencera6362242007-01-07 00:41:39 +0000[diff] [blame]2088Thus, Values are stored in two-dimensions and accessed by <tt>Type</tt> and
2089name.</p>
Chris Lattnerd9d6e102005-04-23 16:10:52 +0000[diff] [blame]2090
2091<p>The interface of this class provides three basic types of operations:
2092<ol>
2093 <li><em>Accessors</em>. Accessors provide read-only access to information
2094 such as finding a value for a name with the
2095 <a href="#SymbolTable_lookup">lookup</a> method.</li>
2096 <li><em>Mutators</em>. Mutators allow the user to add information to the
2097 <tt>SymbolTable</tt> with methods like
2098 <a href="#SymbolTable_insert"><tt>insert</tt></a>.</li>
2099 <li><em>Iterators</em>. Iterators allow the user to traverse the content
2100 of the symbol table in well defined ways, such as the method
Reid Spencera6362242007-01-07 00:41:39 +0000[diff] [blame]2101 <a href="#SymbolTable_plane_begin"><tt>plane_begin</tt></a>.</li>
Chris Lattnerd9d6e102005-04-23 16:10:52 +0000[diff] [blame]2102</ol>
2103
2104<h3>Accessors</h3>
2105<dl>
2106 <dt><tt>Value* lookup(const Type* Ty, const std::string&amp; name) const</tt>:
2107 </dt>
2108 <dd>The <tt>lookup</tt> method searches the type plane given by the
2109 <tt>Ty</tt> parameter for a <tt>Value</tt> with the provided <tt>name</tt>.
2110 If a suitable <tt>Value</tt> is not found, null is returned.</dd>
2111
Chris Lattnerd9d6e102005-04-23 16:10:52 +0000[diff] [blame]2112 <dt><tt>bool isEmpty() const</tt>:</dt>
2113 <dd>This function returns true if both the value and types maps are
2114 empty</dd>
2115</dl>
2116
2117<h3>Mutators</h3>
2118<dl>
2119 <dt><tt>void insert(Value *Val)</tt>:</dt>
2120 <dd>This method adds the provided value to the symbol table. The Value must
2121 have both a name and a type which are extracted and used to place the value
2122 in the correct type plane under the value's name.</dd>
2123
Chris Lattnerd9d6e102005-04-23 16:10:52 +0000[diff] [blame]2124 <dt><tt>void remove(Value* Val)</tt>:</dt>
2125 <dd> This method removes a named value from the symbol table. The
2126 type and name of the Value are extracted from \p N and used to
2127 lookup the Value in the correct type plane. If the Value is
2128 not in the symbol table, this method silently ignores the
2129 request.</dd>
2130
Chris Lattnerd9d6e102005-04-23 16:10:52 +0000[diff] [blame]2131</dl>
2132
2133<h3>Iteration</h3>
2134<p>The following functions describe three types of iterators you can obtain
2135the beginning or end of the sequence for both const and non-const. It is
2136important to keep track of the different kinds of iterators. There are
2137three idioms worth pointing out:</p>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2138
Chris Lattnerd9d6e102005-04-23 16:10:52 +0000[diff] [blame]2139<table>
2140 <tr><th>Units</th><th>Iterator</th><th>Idiom</th></tr>
2141 <tr>
2142 <td align="left">Planes Of name/Value maps</td><td>PI</td>
2143 <td align="left"><pre><tt>
2144for (SymbolTable::plane_const_iterator PI = ST.plane_begin(),
2145 PE = ST.plane_end(); PI != PE; ++PI ) {
Bill Wendling82e2eea2006-10-11 18:00:22 +0000[diff] [blame]2146 PI-&gt;first // <i>This is the Type* of the plane</i>
2147 PI-&gt;second // <i>This is the SymbolTable::ValueMap of name/Value pairs</i>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2148}
Chris Lattnerd9d6e102005-04-23 16:10:52 +0000[diff] [blame]2149 </tt></pre></td>
2150 </tr>
2151 <tr>
Chris Lattnerd9d6e102005-04-23 16:10:52 +0000[diff] [blame]2152 <td align="left">name/Value pairs in a plane</td><td>VI</td>
2153 <td align="left"><pre><tt>
2154for (SymbolTable::value_const_iterator VI = ST.value_begin(SomeType),
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2155 VE = ST.value_end(SomeType); VI != VE; ++VI ) {
Bill Wendling82e2eea2006-10-11 18:00:22 +0000[diff] [blame]2156 VI-&gt;first // <i>This is the name of the Value</i>
2157 VI-&gt;second // <i>This is the Value* value associated with the name</i>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2158}
Chris Lattnerd9d6e102005-04-23 16:10:52 +0000[diff] [blame]2159 </tt></pre></td>
2160 </tr>
2161</table>
2162
2163<p>Using the recommended iterator names and idioms will help you avoid
2164making mistakes. Of particular note, make sure that whenever you use
2165value_begin(SomeType) that you always compare the resulting iterator
2166with value_end(SomeType) not value_end(SomeOtherType) or else you
2167will loop infinitely.</p>
2168
2169<dl>
2170
2171 <dt><tt>plane_iterator plane_begin()</tt>:</dt>
2172 <dd>Get an iterator that starts at the beginning of the type planes.
2173 The iterator will iterate over the Type/ValueMap pairs in the
2174 type planes. </dd>
2175
2176 <dt><tt>plane_const_iterator plane_begin() const</tt>:</dt>
2177 <dd>Get a const_iterator that starts at the beginning of the type
2178 planes. The iterator will iterate over the Type/ValueMap pairs
2179 in the type planes. </dd>
2180
2181 <dt><tt>plane_iterator plane_end()</tt>:</dt>
2182 <dd>Get an iterator at the end of the type planes. This serves as
2183 the marker for end of iteration over the type planes.</dd>
2184
2185 <dt><tt>plane_const_iterator plane_end() const</tt>:</dt>
2186 <dd>Get a const_iterator at the end of the type planes. This serves as
2187 the marker for end of iteration over the type planes.</dd>
2188
2189 <dt><tt>value_iterator value_begin(const Type *Typ)</tt>:</dt>
2190 <dd>Get an iterator that starts at the beginning of a type plane.
2191 The iterator will iterate over the name/value pairs in the type plane.
2192 Note: The type plane must already exist before using this.</dd>
2193
2194 <dt><tt>value_const_iterator value_begin(const Type *Typ) const</tt>:</dt>
2195 <dd>Get a const_iterator that starts at the beginning of a type plane.
2196 The iterator will iterate over the name/value pairs in the type plane.
2197 Note: The type plane must already exist before using this.</dd>
2198
2199 <dt><tt>value_iterator value_end(const Type *Typ)</tt>:</dt>
2200 <dd>Get an iterator to the end of a type plane. This serves as the marker
2201 for end of iteration of the type plane.
2202 Note: The type plane must already exist before using this.</dd>
2203
2204 <dt><tt>value_const_iterator value_end(const Type *Typ) const</tt>:</dt>
2205 <dd>Get a const_iterator to the end of a type plane. This serves as the
2206 marker for end of iteration of the type plane.
2207 Note: the type plane must already exist before using this.</dd>
2208
Chris Lattnerd9d6e102005-04-23 16:10:52 +0000[diff] [blame]2209 <dt><tt>plane_const_iterator find(const Type* Typ ) const</tt>:</dt>
2210 <dd>This method returns a plane_const_iterator for iteration over
2211 the type planes starting at a specific plane, given by \p Ty.</dd>
2212
2213 <dt><tt>plane_iterator find( const Type* Typ </tt>:</dt>
2214 <dd>This method returns a plane_iterator for iteration over the
2215 type planes starting at a specific plane, given by \p Ty.</dd>
2216
2217</dl>
2218</div>
2219
2220
2221
2222<!-- *********************************************************************** -->
2223<div class="doc_section">
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2224 <a name="coreclasses">The Core LLVM Class Hierarchy Reference </a>
2225</div>
2226<!-- *********************************************************************** -->
2227
2228<div class="doc_text">
Reid Spencer303c4b42007-01-12 17:26:25 +0000[diff] [blame]2229<p><tt>#include "<a href="/doxygen/Type_8h-source.html">llvm/Type.h</a>"</tt>
2230<br>doxygen info: <a href="/doxygen/classllvm_1_1Type.html">Type Class</a></p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2231
2232<p>The Core LLVM classes are the primary means of representing the program
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]2233being inspected or transformed. The core LLVM classes are defined in
2234header files in the <tt>include/llvm/</tt> directory, and implemented in
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2235the <tt>lib/VMCore</tt> directory.</p>
2236
2237</div>
2238
2239<!-- ======================================================================= -->
2240<div class="doc_subsection">
Reid Spencer303c4b42007-01-12 17:26:25 +0000[diff] [blame]2241 <a name="Type">The <tt>Type</tt> class and Derived Types</a>
2242</div>
2243
2244<div class="doc_text">
2245
2246 <p><tt>Type</tt> is a superclass of all type classes. Every <tt>Value</tt> has
2247 a <tt>Type</tt>. <tt>Type</tt> cannot be instantiated directly but only
2248 through its subclasses. Certain primitive types (<tt>VoidType</tt>,
2249 <tt>LabelType</tt>, <tt>FloatType</tt> and <tt>DoubleType</tt>) have hidden
2250 subclasses. They are hidden because they offer no useful functionality beyond
2251 what the <tt>Type</tt> class offers except to distinguish themselves from
2252 other subclasses of <tt>Type</tt>.</p>
2253 <p>All other types are subclasses of <tt>DerivedType</tt>. Types can be
2254 named, but this is not a requirement. There exists exactly
2255 one instance of a given shape at any one time. This allows type equality to
2256 be performed with address equality of the Type Instance. That is, given two
2257 <tt>Type*</tt> values, the types are identical if the pointers are identical.
2258 </p>
2259</div>
2260
2261<!-- _______________________________________________________________________ -->
2262<div class="doc_subsubsection">
2263 <a name="m_Value">Important Public Methods</a>
2264</div>
2265
2266<div class="doc_text">
2267
2268<ul>
Chris Lattner8f79df32007-01-15 01:55:32 +0000[diff] [blame]2269 <li><tt>bool isInteger() const</tt>: Returns true for any integer type.</li>
Reid Spencer303c4b42007-01-12 17:26:25 +0000[diff] [blame]2270
2271 <li><tt>bool isFloatingPoint()</tt>: Return true if this is one of the two
2272 floating point types.</li>
2273
2274 <li><tt>bool isAbstract()</tt>: Return true if the type is abstract (contains
2275 an OpaqueType anywhere in its definition).</li>
2276
2277 <li><tt>bool isSized()</tt>: Return true if the type has known size. Things
2278 that don't have a size are abstract types, labels and void.</li>
2279
2280</ul>
2281</div>
2282
2283<!-- _______________________________________________________________________ -->
2284<div class="doc_subsubsection">
2285 <a name="m_Value">Important Derived Types</a>
2286</div>
2287<div class="doc_text">
2288<dl>
2289 <dt><tt>IntegerType</tt></dt>
2290 <dd>Subclass of DerivedType that represents integer types of any bit width.
2291 Any bit width between <tt>IntegerType::MIN_INT_BITS</tt> (1) and
2292 <tt>IntegerType::MAX_INT_BITS</tt> (~8 million) can be represented.
2293 <ul>
2294 <li><tt>static const IntegerType* get(unsigned NumBits)</tt>: get an integer
2295 type of a specific bit width.</li>
2296 <li><tt>unsigned getBitWidth() const</tt>: Get the bit width of an integer
2297 type.</li>
2298 </ul>
2299 </dd>
2300 <dt><tt>SequentialType</tt></dt>
2301 <dd>This is subclassed by ArrayType and PointerType
2302 <ul>
2303 <li><tt>const Type * getElementType() const</tt>: Returns the type of each
2304 of the elements in the sequential type. </li>
2305 </ul>
2306 </dd>
2307 <dt><tt>ArrayType</tt></dt>
2308 <dd>This is a subclass of SequentialType and defines the interface for array
2309 types.
2310 <ul>
2311 <li><tt>unsigned getNumElements() const</tt>: Returns the number of
2312 elements in the array. </li>
2313 </ul>
2314 </dd>
2315 <dt><tt>PointerType</tt></dt>
Chris Lattner302da1e2007-02-03 03:05:57 +0000[diff] [blame]2316 <dd>Subclass of SequentialType for pointer types.</dd>
Reid Spencer9d6565a2007-02-15 02:26:10 +0000[diff] [blame^]2317 <dt><tt>VectorType</tt></dt>
Reid Spencer303c4b42007-01-12 17:26:25 +0000[diff] [blame]2318 <dd>Subclass of SequentialType for packed (vector) types. A
2319 packed type is similar to an ArrayType but is distinguished because it is
2320 a first class type wherease ArrayType is not. Packed types are used for
2321 vector operations and are usually small vectors of of an integer or floating
2322 point type.</dd>
2323 <dt><tt>StructType</tt></dt>
2324 <dd>Subclass of DerivedTypes for struct types.</dd>
2325 <dt><tt>FunctionType</tt></dt>
2326 <dd>Subclass of DerivedTypes for function types.
2327 <ul>
2328 <li><tt>bool isVarArg() const</tt>: Returns true if its a vararg
2329 function</li>
2330 <li><tt> const Type * getReturnType() const</tt>: Returns the
2331 return type of the function.</li>
2332 <li><tt>const Type * getParamType (unsigned i)</tt>: Returns
2333 the type of the ith parameter.</li>
2334 <li><tt> const unsigned getNumParams() const</tt>: Returns the
2335 number of formal parameters.</li>
2336 </ul>
2337 </dd>
2338 <dt><tt>OpaqueType</tt></dt>
2339 <dd>Sublcass of DerivedType for abstract types. This class
2340 defines no content and is used as a placeholder for some other type. Note
2341 that OpaqueType is used (temporarily) during type resolution for forward
2342 references of types. Once the referenced type is resolved, the OpaqueType
2343 is replaced with the actual type. OpaqueType can also be used for data
2344 abstraction. At link time opaque types can be resolved to actual types
2345 of the same name.</dd>
2346</dl>
2347</div>
2348
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]2349
2350
2351<!-- ======================================================================= -->
2352<div class="doc_subsection">
2353 <a name="Module">The <tt>Module</tt> class</a>
2354</div>
2355
2356<div class="doc_text">
2357
2358<p><tt>#include "<a
2359href="/doxygen/Module_8h-source.html">llvm/Module.h</a>"</tt><br> doxygen info:
2360<a href="/doxygen/classllvm_1_1Module.html">Module Class</a></p>
2361
2362<p>The <tt>Module</tt> class represents the top level structure present in LLVM
2363programs. An LLVM module is effectively either a translation unit of the
2364original program or a combination of several translation units merged by the
2365linker. The <tt>Module</tt> class keeps track of a list of <a
2366href="#Function"><tt>Function</tt></a>s, a list of <a
2367href="#GlobalVariable"><tt>GlobalVariable</tt></a>s, and a <a
2368href="#SymbolTable"><tt>SymbolTable</tt></a>. Additionally, it contains a few
2369helpful member functions that try to make common operations easy.</p>
2370
2371</div>
2372
2373<!-- _______________________________________________________________________ -->
2374<div class="doc_subsubsection">
2375 <a name="m_Module">Important Public Members of the <tt>Module</tt> class</a>
2376</div>
2377
2378<div class="doc_text">
2379
2380<ul>
2381 <li><tt>Module::Module(std::string name = "")</tt></li>
2382</ul>
2383
2384<p>Constructing a <a href="#Module">Module</a> is easy. You can optionally
2385provide a name for it (probably based on the name of the translation unit).</p>
2386
2387<ul>
2388 <li><tt>Module::iterator</tt> - Typedef for function list iterator<br>
2389 <tt>Module::const_iterator</tt> - Typedef for const_iterator.<br>
2390
2391 <tt>begin()</tt>, <tt>end()</tt>
2392 <tt>size()</tt>, <tt>empty()</tt>
2393
2394 <p>These are forwarding methods that make it easy to access the contents of
2395 a <tt>Module</tt> object's <a href="#Function"><tt>Function</tt></a>
2396 list.</p></li>
2397
2398 <li><tt>Module::FunctionListType &amp;getFunctionList()</tt>
2399
2400 <p> Returns the list of <a href="#Function"><tt>Function</tt></a>s. This is
2401 necessary to use when you need to update the list or perform a complex
2402 action that doesn't have a forwarding method.</p>
2403
2404 <p><!-- Global Variable --></p></li>
2405</ul>
2406
2407<hr>
2408
2409<ul>
2410 <li><tt>Module::global_iterator</tt> - Typedef for global variable list iterator<br>
2411
2412 <tt>Module::const_global_iterator</tt> - Typedef for const_iterator.<br>
2413
2414 <tt>global_begin()</tt>, <tt>global_end()</tt>
2415 <tt>global_size()</tt>, <tt>global_empty()</tt>
2416
2417 <p> These are forwarding methods that make it easy to access the contents of
2418 a <tt>Module</tt> object's <a
2419 href="#GlobalVariable"><tt>GlobalVariable</tt></a> list.</p></li>
2420
2421 <li><tt>Module::GlobalListType &amp;getGlobalList()</tt>
2422
2423 <p>Returns the list of <a
2424 href="#GlobalVariable"><tt>GlobalVariable</tt></a>s. This is necessary to
2425 use when you need to update the list or perform a complex action that
2426 doesn't have a forwarding method.</p>
2427
2428 <p><!-- Symbol table stuff --> </p></li>
2429</ul>
2430
2431<hr>
2432
2433<ul>
2434 <li><tt><a href="#SymbolTable">SymbolTable</a> *getSymbolTable()</tt>
2435
2436 <p>Return a reference to the <a href="#SymbolTable"><tt>SymbolTable</tt></a>
2437 for this <tt>Module</tt>.</p>
2438
2439 <p><!-- Convenience methods --></p></li>
2440</ul>
2441
2442<hr>
2443
2444<ul>
2445 <li><tt><a href="#Function">Function</a> *getFunction(const std::string
2446 &amp;Name, const <a href="#FunctionType">FunctionType</a> *Ty)</tt>
2447
2448 <p>Look up the specified function in the <tt>Module</tt> <a
2449 href="#SymbolTable"><tt>SymbolTable</tt></a>. If it does not exist, return
2450 <tt>null</tt>.</p></li>
2451
2452 <li><tt><a href="#Function">Function</a> *getOrInsertFunction(const
2453 std::string &amp;Name, const <a href="#FunctionType">FunctionType</a> *T)</tt>
2454
2455 <p>Look up the specified function in the <tt>Module</tt> <a
2456 href="#SymbolTable"><tt>SymbolTable</tt></a>. If it does not exist, add an
2457 external declaration for the function and return it.</p></li>
2458
2459 <li><tt>std::string getTypeName(const <a href="#Type">Type</a> *Ty)</tt>
2460
2461 <p>If there is at least one entry in the <a
2462 href="#SymbolTable"><tt>SymbolTable</tt></a> for the specified <a
2463 href="#Type"><tt>Type</tt></a>, return it. Otherwise return the empty
2464 string.</p></li>
2465
2466 <li><tt>bool addTypeName(const std::string &amp;Name, const <a
2467 href="#Type">Type</a> *Ty)</tt>
2468
2469 <p>Insert an entry in the <a href="#SymbolTable"><tt>SymbolTable</tt></a>
2470 mapping <tt>Name</tt> to <tt>Ty</tt>. If there is already an entry for this
2471 name, true is returned and the <a
2472 href="#SymbolTable"><tt>SymbolTable</tt></a> is not modified.</p></li>
2473</ul>
2474
2475</div>
2476
2477
Reid Spencer303c4b42007-01-12 17:26:25 +0000[diff] [blame]2478<!-- ======================================================================= -->
2479<div class="doc_subsection">
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2480 <a name="Value">The <tt>Value</tt> class</a>
2481</div>
2482
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]2483<div class="doc_text">
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2484
2485<p><tt>#include "<a href="/doxygen/Value_8h-source.html">llvm/Value.h</a>"</tt>
2486<br>
Chris Lattner00815172007-01-04 22:01:45 +0000[diff] [blame]2487doxygen info: <a href="/doxygen/classllvm_1_1Value.html">Value Class</a></p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2488
2489<p>The <tt>Value</tt> class is the most important class in the LLVM Source
2490base. It represents a typed value that may be used (among other things) as an
2491operand to an instruction. There are many different types of <tt>Value</tt>s,
2492such as <a href="#Constant"><tt>Constant</tt></a>s,<a
2493href="#Argument"><tt>Argument</tt></a>s. Even <a
2494href="#Instruction"><tt>Instruction</tt></a>s and <a
2495href="#Function"><tt>Function</tt></a>s are <tt>Value</tt>s.</p>
2496
2497<p>A particular <tt>Value</tt> may be used many times in the LLVM representation
2498for a program. For example, an incoming argument to a function (represented
2499with an instance of the <a href="#Argument">Argument</a> class) is "used" by
2500every instruction in the function that references the argument. To keep track
2501of this relationship, the <tt>Value</tt> class keeps a list of all of the <a
2502href="#User"><tt>User</tt></a>s that is using it (the <a
2503href="#User"><tt>User</tt></a> class is a base class for all nodes in the LLVM
2504graph that can refer to <tt>Value</tt>s). This use list is how LLVM represents
2505def-use information in the program, and is accessible through the <tt>use_</tt>*
2506methods, shown below.</p>
2507
2508<p>Because LLVM is a typed representation, every LLVM <tt>Value</tt> is typed,
2509and this <a href="#Type">Type</a> is available through the <tt>getType()</tt>
2510method. In addition, all LLVM values can be named. The "name" of the
2511<tt>Value</tt> is a symbolic string printed in the LLVM code:</p>
2512
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2513<div class="doc_code">
2514<pre>
Reid Spencer06565dc2007-01-12 17:11:23 +0000[diff] [blame]2515%<b>foo</b> = add i32 1, 2
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2516</pre>
2517</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2518
2519<p><a name="#nameWarning">The name of this instruction is "foo".</a> <b>NOTE</b>
2520that the name of any value may be missing (an empty string), so names should
2521<b>ONLY</b> be used for debugging (making the source code easier to read,
2522debugging printouts), they should not be used to keep track of values or map
2523between them. For this purpose, use a <tt>std::map</tt> of pointers to the
2524<tt>Value</tt> itself instead.</p>
2525
2526<p>One important aspect of LLVM is that there is no distinction between an SSA
2527variable and the operation that produces it. Because of this, any reference to
2528the value produced by an instruction (or the value available as an incoming
Chris Lattnerd5fc4fc2004-03-18 14:58:55 +0000[diff] [blame]2529argument, for example) is represented as a direct pointer to the instance of
2530the class that
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2531represents this value. Although this may take some getting used to, it
2532simplifies the representation and makes it easier to manipulate.</p>
2533
2534</div>
2535
2536<!-- _______________________________________________________________________ -->
2537<div class="doc_subsubsection">
2538 <a name="m_Value">Important Public Members of the <tt>Value</tt> class</a>
2539</div>
2540
2541<div class="doc_text">
2542
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]2543<ul>
2544 <li><tt>Value::use_iterator</tt> - Typedef for iterator over the
2545use-list<br>
2546 <tt>Value::use_const_iterator</tt> - Typedef for const_iterator over
2547the use-list<br>
2548 <tt>unsigned use_size()</tt> - Returns the number of users of the
2549value.<br>
Chris Lattner9355b472002-09-06 02:50:58 +0000[diff] [blame]2550 <tt>bool use_empty()</tt> - Returns true if there are no users.<br>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]2551 <tt>use_iterator use_begin()</tt> - Get an iterator to the start of
2552the use-list.<br>
2553 <tt>use_iterator use_end()</tt> - Get an iterator to the end of the
2554use-list.<br>
2555 <tt><a href="#User">User</a> *use_back()</tt> - Returns the last
2556element in the list.
2557 <p> These methods are the interface to access the def-use
2558information in LLVM. As with all other iterators in LLVM, the naming
2559conventions follow the conventions defined by the <a href="#stl">STL</a>.</p>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]2560 </li>
2561 <li><tt><a href="#Type">Type</a> *getType() const</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2562 <p>This method returns the Type of the Value.</p>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]2563 </li>
2564 <li><tt>bool hasName() const</tt><br>
Chris Lattner9355b472002-09-06 02:50:58 +0000[diff] [blame]2565 <tt>std::string getName() const</tt><br>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]2566 <tt>void setName(const std::string &amp;Name)</tt>
2567 <p> This family of methods is used to access and assign a name to a <tt>Value</tt>,
2568be aware of the <a href="#nameWarning">precaution above</a>.</p>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]2569 </li>
2570 <li><tt>void replaceAllUsesWith(Value *V)</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2571
2572 <p>This method traverses the use list of a <tt>Value</tt> changing all <a
2573 href="#User"><tt>User</tt>s</a> of the current value to refer to
2574 "<tt>V</tt>" instead. For example, if you detect that an instruction always
2575 produces a constant value (for example through constant folding), you can
2576 replace all uses of the instruction with the constant like this:</p>
2577
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2578<div class="doc_code">
2579<pre>
2580Inst-&gt;replaceAllUsesWith(ConstVal);
2581</pre>
2582</div>
2583
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]2584</ul>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2585
2586</div>
2587
2588<!-- ======================================================================= -->
2589<div class="doc_subsection">
2590 <a name="User">The <tt>User</tt> class</a>
2591</div>
2592
2593<div class="doc_text">
2594
2595<p>
2596<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]2597doxygen info: <a href="/doxygen/classllvm_1_1User.html">User Class</a><br>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2598Superclass: <a href="#Value"><tt>Value</tt></a></p>
2599
2600<p>The <tt>User</tt> class is the common base class of all LLVM nodes that may
2601refer to <a href="#Value"><tt>Value</tt></a>s. It exposes a list of "Operands"
2602that are all of the <a href="#Value"><tt>Value</tt></a>s that the User is
2603referring to. The <tt>User</tt> class itself is a subclass of
2604<tt>Value</tt>.</p>
2605
2606<p>The operands of a <tt>User</tt> point directly to the LLVM <a
2607href="#Value"><tt>Value</tt></a> that it refers to. Because LLVM uses Static
2608Single Assignment (SSA) form, there can only be one definition referred to,
2609allowing this direct connection. This connection provides the use-def
2610information in LLVM.</p>
2611
2612</div>
2613
2614<!-- _______________________________________________________________________ -->
2615<div class="doc_subsubsection">
2616 <a name="m_User">Important Public Members of the <tt>User</tt> class</a>
2617</div>
2618
2619<div class="doc_text">
2620
2621<p>The <tt>User</tt> class exposes the operand list in two ways: through
2622an index access interface and through an iterator based interface.</p>
2623
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]2624<ul>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]2625 <li><tt>Value *getOperand(unsigned i)</tt><br>
2626 <tt>unsigned getNumOperands()</tt>
2627 <p> These two methods expose the operands of the <tt>User</tt> in a
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2628convenient form for direct access.</p></li>
2629
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]2630 <li><tt>User::op_iterator</tt> - Typedef for iterator over the operand
2631list<br>
Chris Lattner58360822005-01-17 00:12:04 +0000[diff] [blame]2632 <tt>op_iterator op_begin()</tt> - Get an iterator to the start of
2633the operand list.<br>
2634 <tt>op_iterator op_end()</tt> - Get an iterator to the end of the
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]2635operand list.
2636 <p> Together, these methods make up the iterator based interface to
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2637the operands of a <tt>User</tt>.</p></li>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]2638</ul>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2639
2640</div>
2641
2642<!-- ======================================================================= -->
2643<div class="doc_subsection">
2644 <a name="Instruction">The <tt>Instruction</tt> class</a>
2645</div>
2646
2647<div class="doc_text">
2648
2649<p><tt>#include "</tt><tt><a
2650href="/doxygen/Instruction_8h-source.html">llvm/Instruction.h</a>"</tt><br>
Misha Brukman31ca1de2004-06-03 23:35:54 +0000[diff] [blame]2651doxygen info: <a href="/doxygen/classllvm_1_1Instruction.html">Instruction Class</a><br>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2652Superclasses: <a href="#User"><tt>User</tt></a>, <a
2653href="#Value"><tt>Value</tt></a></p>
2654
2655<p>The <tt>Instruction</tt> class is the common base class for all LLVM
2656instructions. It provides only a few methods, but is a very commonly used
2657class. The primary data tracked by the <tt>Instruction</tt> class itself is the
2658opcode (instruction type) and the parent <a
2659href="#BasicBlock"><tt>BasicBlock</tt></a> the <tt>Instruction</tt> is embedded
2660into. To represent a specific type of instruction, one of many subclasses of
2661<tt>Instruction</tt> are used.</p>
2662
2663<p> Because the <tt>Instruction</tt> class subclasses the <a
2664href="#User"><tt>User</tt></a> class, its operands can be accessed in the same
2665way as for other <a href="#User"><tt>User</tt></a>s (with the
2666<tt>getOperand()</tt>/<tt>getNumOperands()</tt> and
2667<tt>op_begin()</tt>/<tt>op_end()</tt> methods).</p> <p> An important file for
2668the <tt>Instruction</tt> class is the <tt>llvm/Instruction.def</tt> file. This
2669file contains some meta-data about the various different types of instructions
2670in LLVM. It describes the enum values that are used as opcodes (for example
Reid Spencerc92d25d2006-12-19 19:47:19 +0000[diff] [blame]2671<tt>Instruction::Add</tt> and <tt>Instruction::ICmp</tt>), as well as the
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2672concrete sub-classes of <tt>Instruction</tt> that implement the instruction (for
2673example <tt><a href="#BinaryOperator">BinaryOperator</a></tt> and <tt><a
Reid Spencerc92d25d2006-12-19 19:47:19 +0000[diff] [blame]2674href="#CmpInst">CmpInst</a></tt>). Unfortunately, the use of macros in
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2675this file confuses doxygen, so these enum values don't show up correctly in the
Misha Brukman31ca1de2004-06-03 23:35:54 +0000[diff] [blame]2676<a href="/doxygen/classllvm_1_1Instruction.html">doxygen output</a>.</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2677
2678</div>
2679
2680<!-- _______________________________________________________________________ -->
2681<div class="doc_subsubsection">
Reid Spencerc92d25d2006-12-19 19:47:19 +0000[diff] [blame]2682 <a name="s_Instruction">Important Subclasses of the <tt>Instruction</tt>
2683 class</a>
2684</div>
2685<div class="doc_text">
2686 <ul>
2687 <li><tt><a name="BinaryOperator">BinaryOperator</a></tt>
2688 <p>This subclasses represents all two operand instructions whose operands
2689 must be the same type, except for the comparison instructions.</p></li>
2690 <li><tt><a name="CastInst">CastInst</a></tt>
2691 <p>This subclass is the parent of the 12 casting instructions. It provides
2692 common operations on cast instructions.</p>
2693 <li><tt><a name="CmpInst">CmpInst</a></tt>
2694 <p>This subclass respresents the two comparison instructions,
2695 <a href="LangRef.html#i_icmp">ICmpInst</a> (integer opreands), and
2696 <a href="LangRef.html#i_fcmp">FCmpInst</a> (floating point operands).</p>
2697 <li><tt><a name="TerminatorInst">TerminatorInst</a></tt>
2698 <p>This subclass is the parent of all terminator instructions (those which
2699 can terminate a block).</p>
2700 </ul>
2701 </div>
2702
2703<!-- _______________________________________________________________________ -->
2704<div class="doc_subsubsection">
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2705 <a name="m_Instruction">Important Public Members of the <tt>Instruction</tt>
2706 class</a>
2707</div>
2708
2709<div class="doc_text">
2710
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]2711<ul>
2712 <li><tt><a href="#BasicBlock">BasicBlock</a> *getParent()</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2713 <p>Returns the <a href="#BasicBlock"><tt>BasicBlock</tt></a> that
2714this <tt>Instruction</tt> is embedded into.</p></li>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]2715 <li><tt>bool mayWriteToMemory()</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2716 <p>Returns true if the instruction writes to memory, i.e. it is a
2717 <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]2718 <li><tt>unsigned getOpcode()</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2719 <p>Returns the opcode for the <tt>Instruction</tt>.</p></li>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]2720 <li><tt><a href="#Instruction">Instruction</a> *clone() const</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2721 <p>Returns another instance of the specified instruction, identical
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]2722in all ways to the original except that the instruction has no parent
2723(ie it's not embedded into a <a href="#BasicBlock"><tt>BasicBlock</tt></a>),
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2724and it has no name</p></li>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]2725</ul>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2726
2727</div>
2728
2729<!-- ======================================================================= -->
2730<div class="doc_subsection">
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]2731 <a name="Constant">The <tt>Constant</tt> class and subclasses</a>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2732</div>
2733
2734<div class="doc_text">
2735
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]2736<p>Constant represents a base class for different types of constants. It
2737is subclassed by ConstantInt, ConstantArray, etc. for representing
2738the various types of Constants. <a href="#GlobalValue">GlobalValue</a> is also
2739a subclass, which represents the address of a global variable or function.
2740</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2741
2742</div>
2743
2744<!-- _______________________________________________________________________ -->
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]2745<div class="doc_subsubsection">Important Subclasses of Constant </div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2746<div class="doc_text">
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]2747<ul>
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]2748 <li>ConstantInt : This subclass of Constant represents an integer constant of
2749 any width.
2750 <ul>
2751 <li><tt>int64_t getSExtValue() const</tt>: Returns the underlying value of
2752 this constant as a sign extended signed integer value.</li>
2753 <li><tt>uint64_t getZExtValue() const</tt>: Returns the underlying value
2754 of this constant as a zero extended unsigned integer value.</li>
2755 <li><tt>static ConstantInt* get(const Type *Ty, uint64_t Val)</tt>:
2756 Returns the ConstantInt object that represents the value provided by
2757 <tt>Val</tt> for integer type <tt>Ty</tt>.</li>
2758 </ul>
2759 </li>
2760 <li>ConstantFP : This class represents a floating point constant.
2761 <ul>
2762 <li><tt>double getValue() const</tt>: Returns the underlying value of
2763 this constant. </li>
2764 </ul>
2765 </li>
2766 <li>ConstantArray : This represents a constant array.
2767 <ul>
2768 <li><tt>const std::vector&lt;Use&gt; &amp;getValues() const</tt>: Returns
2769 a vector of component constants that makeup this array. </li>
2770 </ul>
2771 </li>
2772 <li>ConstantStruct : This represents a constant struct.
2773 <ul>
2774 <li><tt>const std::vector&lt;Use&gt; &amp;getValues() const</tt>: Returns
2775 a vector of component constants that makeup this array. </li>
2776 </ul>
2777 </li>
2778 <li>GlobalValue : This represents either a global variable or a function. In
2779 either case, the value is a constant fixed address (after linking).
2780 </li>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]2781</ul>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2782</div>
2783
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]2784
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2785<!-- ======================================================================= -->
2786<div class="doc_subsection">
2787 <a name="GlobalValue">The <tt>GlobalValue</tt> class</a>
2788</div>
2789
2790<div class="doc_text">
2791
2792<p><tt>#include "<a
2793href="/doxygen/GlobalValue_8h-source.html">llvm/GlobalValue.h</a>"</tt><br>
Misha Brukman384047f2004-06-03 23:29:12 +0000[diff] [blame]2794doxygen info: <a href="/doxygen/classllvm_1_1GlobalValue.html">GlobalValue
2795Class</a><br>
Reid Spencerbe5e85e2006-04-14 14:11:48 +0000[diff] [blame]2796Superclasses: <a href="#Constant"><tt>Constant</tt></a>,
2797<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]2798
2799<p>Global values (<a href="#GlobalVariable"><tt>GlobalVariable</tt></a>s or <a
2800href="#Function"><tt>Function</tt></a>s) are the only LLVM values that are
2801visible in the bodies of all <a href="#Function"><tt>Function</tt></a>s.
2802Because they are visible at global scope, they are also subject to linking with
2803other globals defined in different translation units. To control the linking
2804process, <tt>GlobalValue</tt>s know their linkage rules. Specifically,
2805<tt>GlobalValue</tt>s know whether they have internal or external linkage, as
Reid Spencer8b2da7a2004-07-18 13:10:31 +0000[diff] [blame]2806defined by the <tt>LinkageTypes</tt> enumeration.</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2807
2808<p>If a <tt>GlobalValue</tt> has internal linkage (equivalent to being
2809<tt>static</tt> in C), it is not visible to code outside the current translation
2810unit, and does not participate in linking. If it has external linkage, it is
2811visible to external code, and does participate in linking. In addition to
2812linkage information, <tt>GlobalValue</tt>s keep track of which <a
2813href="#Module"><tt>Module</tt></a> they are currently part of.</p>
2814
2815<p>Because <tt>GlobalValue</tt>s are memory objects, they are always referred to
2816by their <b>address</b>. As such, the <a href="#Type"><tt>Type</tt></a> of a
2817global is always a pointer to its contents. It is important to remember this
2818when using the <tt>GetElementPtrInst</tt> instruction because this pointer must
2819be dereferenced first. For example, if you have a <tt>GlobalVariable</tt> (a
2820subclass 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]2821i32]</tt>, then the <tt>GlobalVariable</tt> is a pointer to that array. Although
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2822the address of the first element of this array and the value of the
2823<tt>GlobalVariable</tt> are the same, they have different types. The
Reid Spencer06565dc2007-01-12 17:11:23 +0000[diff] [blame]2824<tt>GlobalVariable</tt>'s type is <tt>[24 x i32]</tt>. The first element's type
2825is <tt>i32.</tt> Because of this, accessing a global value requires you to
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2826dereference the pointer with <tt>GetElementPtrInst</tt> first, then its elements
2827can be accessed. This is explained in the <a href="LangRef.html#globalvars">LLVM
2828Language Reference Manual</a>.</p>
2829
2830</div>
2831
2832<!-- _______________________________________________________________________ -->
2833<div class="doc_subsubsection">
2834 <a name="m_GlobalValue">Important Public Members of the <tt>GlobalValue</tt>
2835 class</a>
2836</div>
2837
2838<div class="doc_text">
2839
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]2840<ul>
2841 <li><tt>bool hasInternalLinkage() const</tt><br>
Chris Lattner9355b472002-09-06 02:50:58 +0000[diff] [blame]2842 <tt>bool hasExternalLinkage() const</tt><br>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]2843 <tt>void setInternalLinkage(bool HasInternalLinkage)</tt>
2844 <p> These methods manipulate the linkage characteristics of the <tt>GlobalValue</tt>.</p>
2845 <p> </p>
2846 </li>
2847 <li><tt><a href="#Module">Module</a> *getParent()</tt>
2848 <p> This returns the <a href="#Module"><tt>Module</tt></a> that the
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2849GlobalValue is currently embedded into.</p></li>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]2850</ul>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2851
2852</div>
2853
2854<!-- ======================================================================= -->
2855<div class="doc_subsection">
2856 <a name="Function">The <tt>Function</tt> class</a>
2857</div>
2858
2859<div class="doc_text">
2860
2861<p><tt>#include "<a
2862href="/doxygen/Function_8h-source.html">llvm/Function.h</a>"</tt><br> doxygen
Misha Brukman31ca1de2004-06-03 23:35:54 +0000[diff] [blame]2863info: <a href="/doxygen/classllvm_1_1Function.html">Function Class</a><br>
Reid Spencerbe5e85e2006-04-14 14:11:48 +0000[diff] [blame]2864Superclasses: <a href="#GlobalValue"><tt>GlobalValue</tt></a>,
2865<a href="#Constant"><tt>Constant</tt></a>,
2866<a href="#User"><tt>User</tt></a>,
2867<a href="#Value"><tt>Value</tt></a></p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2868
2869<p>The <tt>Function</tt> class represents a single procedure in LLVM. It is
2870actually one of the more complex classes in the LLVM heirarchy because it must
2871keep track of a large amount of data. The <tt>Function</tt> class keeps track
Reid Spencerbe5e85e2006-04-14 14:11:48 +0000[diff] [blame]2872of a list of <a href="#BasicBlock"><tt>BasicBlock</tt></a>s, a list of formal
2873<a href="#Argument"><tt>Argument</tt></a>s, and a
2874<a href="#SymbolTable"><tt>SymbolTable</tt></a>.</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2875
2876<p>The list of <a href="#BasicBlock"><tt>BasicBlock</tt></a>s is the most
2877commonly used part of <tt>Function</tt> objects. The list imposes an implicit
2878ordering of the blocks in the function, which indicate how the code will be
2879layed out by the backend. Additionally, the first <a
2880href="#BasicBlock"><tt>BasicBlock</tt></a> is the implicit entry node for the
2881<tt>Function</tt>. It is not legal in LLVM to explicitly branch to this initial
2882block. There are no implicit exit nodes, and in fact there may be multiple exit
2883nodes from a single <tt>Function</tt>. If the <a
2884href="#BasicBlock"><tt>BasicBlock</tt></a> list is empty, this indicates that
2885the <tt>Function</tt> is actually a function declaration: the actual body of the
2886function hasn't been linked in yet.</p>
2887
2888<p>In addition to a list of <a href="#BasicBlock"><tt>BasicBlock</tt></a>s, the
2889<tt>Function</tt> class also keeps track of the list of formal <a
2890href="#Argument"><tt>Argument</tt></a>s that the function receives. This
2891container manages the lifetime of the <a href="#Argument"><tt>Argument</tt></a>
2892nodes, just like the <a href="#BasicBlock"><tt>BasicBlock</tt></a> list does for
2893the <a href="#BasicBlock"><tt>BasicBlock</tt></a>s.</p>
2894
2895<p>The <a href="#SymbolTable"><tt>SymbolTable</tt></a> is a very rarely used
2896LLVM feature that is only used when you have to look up a value by name. Aside
2897from that, the <a href="#SymbolTable"><tt>SymbolTable</tt></a> is used
2898internally to make sure that there are not conflicts between the names of <a
2899href="#Instruction"><tt>Instruction</tt></a>s, <a
2900href="#BasicBlock"><tt>BasicBlock</tt></a>s, or <a
2901href="#Argument"><tt>Argument</tt></a>s in the function body.</p>
2902
Reid Spencer8b2da7a2004-07-18 13:10:31 +0000[diff] [blame]2903<p>Note that <tt>Function</tt> is a <a href="#GlobalValue">GlobalValue</a>
2904and therefore also a <a href="#Constant">Constant</a>. The value of the function
2905is its address (after linking) which is guaranteed to be constant.</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2906</div>
2907
2908<!-- _______________________________________________________________________ -->
2909<div class="doc_subsubsection">
2910 <a name="m_Function">Important Public Members of the <tt>Function</tt>
2911 class</a>
2912</div>
2913
2914<div class="doc_text">
2915
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]2916<ul>
2917 <li><tt>Function(const </tt><tt><a href="#FunctionType">FunctionType</a>
Chris Lattnerac479e52004-08-04 05:10:48 +0000[diff] [blame]2918 *Ty, LinkageTypes Linkage, const std::string &amp;N = "", Module* Parent = 0)</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2919
2920 <p>Constructor used when you need to create new <tt>Function</tt>s to add
2921 the the program. The constructor must specify the type of the function to
Chris Lattnerac479e52004-08-04 05:10:48 +0000[diff] [blame]2922 create and what type of linkage the function should have. The <a
2923 href="#FunctionType"><tt>FunctionType</tt></a> argument
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2924 specifies the formal arguments and return value for the function. The same
2925 <a href="#FunctionTypel"><tt>FunctionType</tt></a> value can be used to
2926 create multiple functions. The <tt>Parent</tt> argument specifies the Module
2927 in which the function is defined. If this argument is provided, the function
2928 will automatically be inserted into that module's list of
2929 functions.</p></li>
2930
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]2931 <li><tt>bool isExternal()</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2932
2933 <p>Return whether or not the <tt>Function</tt> has a body defined. If the
2934 function is "external", it does not have a body, and thus must be resolved
2935 by linking with a function defined in a different translation unit.</p></li>
2936
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]2937 <li><tt>Function::iterator</tt> - Typedef for basic block list iterator<br>
Chris Lattner9355b472002-09-06 02:50:58 +0000[diff] [blame]2938 <tt>Function::const_iterator</tt> - Typedef for const_iterator.<br>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2939
Chris Lattner77d69242005-03-15 05:19:20 +0000[diff] [blame]2940 <tt>begin()</tt>, <tt>end()</tt>
2941 <tt>size()</tt>, <tt>empty()</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2942
2943 <p>These are forwarding methods that make it easy to access the contents of
2944 a <tt>Function</tt> object's <a href="#BasicBlock"><tt>BasicBlock</tt></a>
2945 list.</p></li>
2946
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]2947 <li><tt>Function::BasicBlockListType &amp;getBasicBlockList()</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2948
2949 <p>Returns the list of <a href="#BasicBlock"><tt>BasicBlock</tt></a>s. This
2950 is necessary to use when you need to update the list or perform a complex
2951 action that doesn't have a forwarding method.</p></li>
2952
Chris Lattner89cc2652005-03-15 04:48:32 +0000[diff] [blame]2953 <li><tt>Function::arg_iterator</tt> - Typedef for the argument list
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]2954iterator<br>
Chris Lattner89cc2652005-03-15 04:48:32 +0000[diff] [blame]2955 <tt>Function::const_arg_iterator</tt> - Typedef for const_iterator.<br>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2956
Chris Lattner77d69242005-03-15 05:19:20 +0000[diff] [blame]2957 <tt>arg_begin()</tt>, <tt>arg_end()</tt>
Chris Lattner89cc2652005-03-15 04:48:32 +0000[diff] [blame]2958 <tt>arg_size()</tt>, <tt>arg_empty()</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2959
2960 <p>These are forwarding methods that make it easy to access the contents of
2961 a <tt>Function</tt> object's <a href="#Argument"><tt>Argument</tt></a>
2962 list.</p></li>
2963
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]2964 <li><tt>Function::ArgumentListType &amp;getArgumentList()</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2965
2966 <p>Returns the list of <a href="#Argument"><tt>Argument</tt></a>s. This is
2967 necessary to use when you need to update the list or perform a complex
2968 action that doesn't have a forwarding method.</p></li>
2969
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]2970 <li><tt><a href="#BasicBlock">BasicBlock</a> &amp;getEntryBlock()</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2971
2972 <p>Returns the entry <a href="#BasicBlock"><tt>BasicBlock</tt></a> for the
2973 function. Because the entry block for the function is always the first
2974 block, this returns the first block of the <tt>Function</tt>.</p></li>
2975
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]2976 <li><tt><a href="#Type">Type</a> *getReturnType()</tt><br>
2977 <tt><a href="#FunctionType">FunctionType</a> *getFunctionType()</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2978
2979 <p>This traverses the <a href="#Type"><tt>Type</tt></a> of the
2980 <tt>Function</tt> and returns the return type of the function, or the <a
2981 href="#FunctionType"><tt>FunctionType</tt></a> of the actual
2982 function.</p></li>
2983
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]2984 <li><tt><a href="#SymbolTable">SymbolTable</a> *getSymbolTable()</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2985
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]2986 <p> Return a pointer to the <a href="#SymbolTable"><tt>SymbolTable</tt></a>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2987 for this <tt>Function</tt>.</p></li>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]2988</ul>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2989
2990</div>
2991
2992<!-- ======================================================================= -->
2993<div class="doc_subsection">
2994 <a name="GlobalVariable">The <tt>GlobalVariable</tt> class</a>
2995</div>
2996
2997<div class="doc_text">
2998
2999<p><tt>#include "<a
3000href="/doxygen/GlobalVariable_8h-source.html">llvm/GlobalVariable.h</a>"</tt>
3001<br>
Tanya Lattnera3da7772004-06-22 08:02:25 +0000[diff] [blame]3002doxygen info: <a href="/doxygen/classllvm_1_1GlobalVariable.html">GlobalVariable
Reid Spencerbe5e85e2006-04-14 14:11:48 +0000[diff] [blame]3003 Class</a><br>
3004Superclasses: <a href="#GlobalValue"><tt>GlobalValue</tt></a>,
3005<a href="#Constant"><tt>Constant</tt></a>,
3006<a href="#User"><tt>User</tt></a>,
3007<a href="#Value"><tt>Value</tt></a></p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3008
3009<p>Global variables are represented with the (suprise suprise)
3010<tt>GlobalVariable</tt> class. Like functions, <tt>GlobalVariable</tt>s are also
3011subclasses of <a href="#GlobalValue"><tt>GlobalValue</tt></a>, and as such are
3012always referenced by their address (global values must live in memory, so their
Reid Spencerbe5e85e2006-04-14 14:11:48 +0000[diff] [blame]3013"name" refers to their constant address). See
3014<a href="#GlobalValue"><tt>GlobalValue</tt></a> for more on this. Global
3015variables may have an initial value (which must be a
3016<a href="#Constant"><tt>Constant</tt></a>), and if they have an initializer,
3017they may be marked as "constant" themselves (indicating that their contents
3018never change at runtime).</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3019</div>
3020
3021<!-- _______________________________________________________________________ -->
3022<div class="doc_subsubsection">
3023 <a name="m_GlobalVariable">Important Public Members of the
3024 <tt>GlobalVariable</tt> class</a>
3025</div>
3026
3027<div class="doc_text">
3028
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3029<ul>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3030 <li><tt>GlobalVariable(const </tt><tt><a href="#Type">Type</a> *Ty, bool
3031 isConstant, LinkageTypes&amp; Linkage, <a href="#Constant">Constant</a>
3032 *Initializer = 0, const std::string &amp;Name = "", Module* Parent = 0)</tt>
3033
3034 <p>Create a new global variable of the specified type. If
3035 <tt>isConstant</tt> is true then the global variable will be marked as
3036 unchanging for the program. The Linkage parameter specifies the type of
3037 linkage (internal, external, weak, linkonce, appending) for the variable. If
3038 the linkage is InternalLinkage, WeakLinkage, or LinkOnceLinkage,&nbsp; then
3039 the resultant global variable will have internal linkage. AppendingLinkage
3040 concatenates together all instances (in different translation units) of the
3041 variable into a single variable but is only applicable to arrays. &nbsp;See
3042 the <a href="LangRef.html#modulestructure">LLVM Language Reference</a> for
3043 further details on linkage types. Optionally an initializer, a name, and the
3044 module to put the variable into may be specified for the global variable as
3045 well.</p></li>
3046
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3047 <li><tt>bool isConstant() const</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3048
3049 <p>Returns true if this is a global variable that is known not to
3050 be modified at runtime.</p></li>
3051
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3052 <li><tt>bool hasInitializer()</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3053
3054 <p>Returns true if this <tt>GlobalVariable</tt> has an intializer.</p></li>
3055
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3056 <li><tt><a href="#Constant">Constant</a> *getInitializer()</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3057
3058 <p>Returns the intial value for a <tt>GlobalVariable</tt>. It is not legal
3059 to call this method if there is no initializer.</p></li>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3060</ul>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3061
3062</div>
3063
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]3064
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3065<!-- ======================================================================= -->
3066<div class="doc_subsection">
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]3067 <a name="BasicBlock">The <tt>BasicBlock</tt> class</a>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3068</div>
3069
3070<div class="doc_text">
3071
3072<p><tt>#include "<a
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]3073href="/doxygen/BasicBlock_8h-source.html">llvm/BasicBlock.h</a>"</tt><br>
3074doxygen info: <a href="/doxygen/structllvm_1_1BasicBlock.html">BasicBlock
3075Class</a><br>
3076Superclass: <a href="#Value"><tt>Value</tt></a></p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3077
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]3078<p>This class represents a single entry multiple exit section of the code,
3079commonly known as a basic block by the compiler community. The
3080<tt>BasicBlock</tt> class maintains a list of <a
3081href="#Instruction"><tt>Instruction</tt></a>s, which form the body of the block.
3082Matching the language definition, the last element of this list of instructions
3083is always a terminator instruction (a subclass of the <a
3084href="#TerminatorInst"><tt>TerminatorInst</tt></a> class).</p>
3085
3086<p>In addition to tracking the list of instructions that make up the block, the
3087<tt>BasicBlock</tt> class also keeps track of the <a
3088href="#Function"><tt>Function</tt></a> that it is embedded into.</p>
3089
3090<p>Note that <tt>BasicBlock</tt>s themselves are <a
3091href="#Value"><tt>Value</tt></a>s, because they are referenced by instructions
3092like branches and can go in the switch tables. <tt>BasicBlock</tt>s have type
3093<tt>label</tt>.</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3094
3095</div>
3096
3097<!-- _______________________________________________________________________ -->
3098<div class="doc_subsubsection">
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]3099 <a name="m_BasicBlock">Important Public Members of the <tt>BasicBlock</tt>
3100 class</a>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3101</div>
3102
3103<div class="doc_text">
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3104<ul>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3105
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]3106<li><tt>BasicBlock(const std::string &amp;Name = "", </tt><tt><a
3107 href="#Function">Function</a> *Parent = 0)</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3108
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]3109<p>The <tt>BasicBlock</tt> constructor is used to create new basic blocks for
3110insertion into a function. The constructor optionally takes a name for the new
3111block, and a <a href="#Function"><tt>Function</tt></a> to insert it into. If
3112the <tt>Parent</tt> parameter is specified, the new <tt>BasicBlock</tt> is
3113automatically inserted at the end of the specified <a
3114href="#Function"><tt>Function</tt></a>, if not specified, the BasicBlock must be
3115manually inserted into the <a href="#Function"><tt>Function</tt></a>.</p></li>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3116
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]3117<li><tt>BasicBlock::iterator</tt> - Typedef for instruction list iterator<br>
3118<tt>BasicBlock::const_iterator</tt> - Typedef for const_iterator.<br>
3119<tt>begin()</tt>, <tt>end()</tt>, <tt>front()</tt>, <tt>back()</tt>,
3120<tt>size()</tt>, <tt>empty()</tt>
3121STL-style functions for accessing the instruction list.
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3122
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]3123<p>These methods and typedefs are forwarding functions that have the same
3124semantics as the standard library methods of the same names. These methods
3125expose the underlying instruction list of a basic block in a way that is easy to
3126manipulate. To get the full complement of container operations (including
3127operations to update the list), you must use the <tt>getInstList()</tt>
3128method.</p></li>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3129
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]3130<li><tt>BasicBlock::InstListType &amp;getInstList()</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3131
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]3132<p>This method is used to get access to the underlying container that actually
3133holds the Instructions. This method must be used when there isn't a forwarding
3134function in the <tt>BasicBlock</tt> class for the operation that you would like
3135to perform. Because there are no forwarding functions for "updating"
3136operations, you need to use this if you want to update the contents of a
3137<tt>BasicBlock</tt>.</p></li>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3138
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]3139<li><tt><a href="#Function">Function</a> *getParent()</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3140
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]3141<p> Returns a pointer to <a href="#Function"><tt>Function</tt></a> the block is
3142embedded into, or a null pointer if it is homeless.</p></li>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3143
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]3144<li><tt><a href="#TerminatorInst">TerminatorInst</a> *getTerminator()</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3145
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]3146<p> Returns a pointer to the terminator instruction that appears at the end of
3147the <tt>BasicBlock</tt>. If there is no terminator instruction, or if the last
3148instruction in the block is not a terminator, then a null pointer is
3149returned.</p></li>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3150
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3151</ul>
3152
3153</div>
3154
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3155
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3156<!-- ======================================================================= -->
3157<div class="doc_subsection">
3158 <a name="Argument">The <tt>Argument</tt> class</a>
3159</div>
3160
3161<div class="doc_text">
3162
3163<p>This subclass of Value defines the interface for incoming formal
Chris Lattner58360822005-01-17 00:12:04 +0000[diff] [blame]3164arguments to a function. A Function maintains a list of its formal
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3165arguments. An argument has a pointer to the parent Function.</p>
3166
3167</div>
3168
Chris Lattner9355b472002-09-06 02:50:58 +0000[diff] [blame]3169<!-- *********************************************************************** -->
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3170<hr>
3171<address>
3172 <a href="http://jigsaw.w3.org/css-validator/check/referer"><img
3173 src="http://jigsaw.w3.org/css-validator/images/vcss" alt="Valid CSS!"></a>
3174 <a href="http://validator.w3.org/check/referer"><img
3175 src="http://www.w3.org/Icons/valid-html401" alt="Valid HTML 4.01!" /></a>
3176
3177 <a href="mailto:dhurjati@cs.uiuc.edu">Dinakar Dhurjati</a> and
3178 <a href="mailto:sabre@nondot.org">Chris Lattner</a><br>
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]3179 <a href="http://llvm.org">The LLVM Compiler Infrastructure</a><br>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3180 Last modified: $Date$
3181</address>
3182
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3183</body>
3184</html>