Gitiles
Code Review Sign In
gerrit-public.fairphone.software / fp2-dev / platform / external / llvm / f369252d039c48ea063d459319214502f5f8ba4c / . / docs / ProgrammersManual.html
blob: 67b240ae8871ef710e5c6175dcabaa0c7f684c7d [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>
74 <li><a href="#dss_cstringmap">"llvm/ADT/CStringMap.h"</a></li>
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>
Reid Spencerfe8f4ff2004-11-01 09:02:53 +0000[diff] [blame]138 <li><a href="#Value">The <tt>Value</tt> class</a>
Chris Lattner9355b472002-09-06 02:50:58 +0000[diff] [blame]139 <ul>
Reid Spencerfe8f4ff2004-11-01 09:02:53 +0000[diff] [blame]140 <li><a href="#User">The <tt>User</tt> class</a>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]141 <ul>
Reid Spencerfe8f4ff2004-11-01 09:02:53 +0000[diff] [blame]142 <li><a href="#Instruction">The <tt>Instruction</tt> class</a>
143 <ul>
144 <li><a href="#GetElementPtrInst">The <tt>GetElementPtrInst</tt> class</a></li>
145 </ul>
146 </li>
147 <li><a href="#Module">The <tt>Module</tt> class</a></li>
148 <li><a href="#Constant">The <tt>Constant</tt> class</a>
149 <ul>
150 <li><a href="#GlobalValue">The <tt>GlobalValue</tt> class</a>
151 <ul>
152 <li><a href="#BasicBlock">The <tt>BasicBlock</tt>class</a></li>
153 <li><a href="#Function">The <tt>Function</tt> class</a></li>
154 <li><a href="#GlobalVariable">The <tt>GlobalVariable</tt> class</a></li>
155 </ul>
156 </li>
157 </ul>
158 </li>
Reid Spencer8b2da7a2004-07-18 13:10:31 +0000[diff] [blame]159 </ul>
160 </li>
Reid Spencer096603a2004-05-26 08:41:35 +0000[diff] [blame]161 <li><a href="#Argument">The <tt>Argument</tt> class</a></li>
Reid Spencerfe8f4ff2004-11-01 09:02:53 +0000[diff] [blame]162 </ul>
163 </li>
164 </ul>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]165 </li>
Chris Lattner9355b472002-09-06 02:50:58 +0000[diff] [blame]166</ol>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]167
Chris Lattner69bf8a92004-05-23 21:06:58 +0000[diff] [blame]168<div class="doc_author">
169 <p>Written by <a href="mailto:sabre@nondot.org">Chris Lattner</a>,
Chris Lattner94c43592004-05-26 16:52:55 +0000[diff] [blame]170 <a href="mailto:dhurjati@cs.uiuc.edu">Dinakar Dhurjati</a>,
171 <a href="mailto:jstanley@cs.uiuc.edu">Joel Stanley</a>, and
172 <a href="mailto:rspencer@x10sys.com">Reid Spencer</a></p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]173</div>
174
Chris Lattner9355b472002-09-06 02:50:58 +0000[diff] [blame]175<!-- *********************************************************************** -->
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]176<div class="doc_section">
177 <a name="introduction">Introduction </a>
178</div>
Chris Lattner9355b472002-09-06 02:50:58 +0000[diff] [blame]179<!-- *********************************************************************** -->
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]180
181<div class="doc_text">
182
183<p>This document is meant to highlight some of the important classes and
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]184interfaces available in the LLVM source-base. This manual is not
185intended to explain what LLVM is, how it works, and what LLVM code looks
186like. It assumes that you know the basics of LLVM and are interested
187in writing transformations or otherwise analyzing or manipulating the
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]188code.</p>
189
190<p>This document should get you oriented so that you can find your
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]191way in the continuously growing source code that makes up the LLVM
192infrastructure. Note that this manual is not intended to serve as a
193replacement for reading the source code, so if you think there should be
194a method in one of these classes to do something, but it's not listed,
195check the source. Links to the <a href="/doxygen/">doxygen</a> sources
196are provided to make this as easy as possible.</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]197
198<p>The first section of this document describes general information that is
199useful to know when working in the LLVM infrastructure, and the second describes
200the Core LLVM classes. In the future this manual will be extended with
201information describing how to use extension libraries, such as dominator
202information, CFG traversal routines, and useful utilities like the <tt><a
203href="/doxygen/InstVisitor_8h-source.html">InstVisitor</a></tt> template.</p>
204
205</div>
206
Chris Lattner9355b472002-09-06 02:50:58 +0000[diff] [blame]207<!-- *********************************************************************** -->
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]208<div class="doc_section">
209 <a name="general">General Information</a>
210</div>
211<!-- *********************************************************************** -->
212
213<div class="doc_text">
214
215<p>This section contains general information that is useful if you are working
216in the LLVM source-base, but that isn't specific to any particular API.</p>
217
218</div>
219
220<!-- ======================================================================= -->
221<div class="doc_subsection">
222 <a name="stl">The C++ Standard Template Library</a>
223</div>
224
225<div class="doc_text">
226
227<p>LLVM makes heavy use of the C++ Standard Template Library (STL),
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]228perhaps much more than you are used to, or have seen before. Because of
229this, you might want to do a little background reading in the
230techniques used and capabilities of the library. There are many good
231pages that discuss the STL, and several books on the subject that you
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]232can get, so it will not be discussed in this document.</p>
233
234<p>Here are some useful links:</p>
235
236<ol>
237
238<li><a href="http://www.dinkumware.com/refxcpp.html">Dinkumware C++ Library
239reference</a> - an excellent reference for the STL and other parts of the
240standard C++ library.</li>
241
242<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]243O'Reilly book in the making. It has a decent
244Standard Library
245Reference 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]246published.</li>
247
248<li><a href="http://www.parashift.com/c++-faq-lite/">C++ Frequently Asked
249Questions</a></li>
250
251<li><a href="http://www.sgi.com/tech/stl/">SGI's STL Programmer's Guide</a> -
252Contains a useful <a
253href="http://www.sgi.com/tech/stl/stl_introduction.html">Introduction to the
254STL</a>.</li>
255
256<li><a href="http://www.research.att.com/%7Ebs/C++.html">Bjarne Stroustrup's C++
257Page</a></li>
258
Tanya Lattner79445ba2004-12-08 18:34:56 +0000[diff] [blame]259<li><a href="http://64.78.49.204/">
Reid Spencer096603a2004-05-26 08:41:35 +0000[diff] [blame]260Bruce Eckel's Thinking in C++, 2nd ed. Volume 2 Revision 4.0 (even better, get
261the book).</a></li>
262
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]263</ol>
264
265<p>You are also encouraged to take a look at the <a
266href="CodingStandards.html">LLVM Coding Standards</a> guide which focuses on how
267to write maintainable code more than where to put your curly braces.</p>
268
269</div>
270
271<!-- ======================================================================= -->
272<div class="doc_subsection">
273 <a name="stl">Other useful references</a>
274</div>
275
276<div class="doc_text">
277
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]278<ol>
279<li><a href="http://www.psc.edu/%7Esemke/cvs_branches.html">CVS
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]280Branch and Tag Primer</a></li>
Misha Brukmana0f71e42004-06-18 18:39:00 +0000[diff] [blame]281<li><a href="http://www.fortran-2000.com/ArnaudRecipes/sharedlib.html">Using
282static and shared libraries across platforms</a></li>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]283</ol>
284
285</div>
286
Chris Lattner9355b472002-09-06 02:50:58 +0000[diff] [blame]287<!-- *********************************************************************** -->
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]288<div class="doc_section">
289 <a name="apis">Important and useful LLVM APIs</a>
290</div>
291<!-- *********************************************************************** -->
292
293<div class="doc_text">
294
295<p>Here we highlight some LLVM APIs that are generally useful and good to
296know about when writing transformations.</p>
297
298</div>
299
300<!-- ======================================================================= -->
301<div class="doc_subsection">
Misha Brukman2c122ce2005-11-01 21:12:49 +0000[diff] [blame]302 <a name="isa">The <tt>isa&lt;&gt;</tt>, <tt>cast&lt;&gt;</tt> and
303 <tt>dyn_cast&lt;&gt;</tt> templates</a>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]304</div>
305
306<div class="doc_text">
307
308<p>The LLVM source-base makes extensive use of a custom form of RTTI.
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]309These templates have many similarities to the C++ <tt>dynamic_cast&lt;&gt;</tt>
310operator, but they don't have some drawbacks (primarily stemming from
311the fact that <tt>dynamic_cast&lt;&gt;</tt> only works on classes that
312have a v-table). Because they are used so often, you must know what they
313do and how they work. All of these templates are defined in the <a
Chris Lattner695b78b2005-04-26 22:56:16 +0000[diff] [blame]314 href="/doxygen/Casting_8h-source.html"><tt>llvm/Support/Casting.h</tt></a>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]315file (note that you very rarely have to include this file directly).</p>
316
317<dl>
318 <dt><tt>isa&lt;&gt;</tt>: </dt>
319
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]320 <dd><p>The <tt>isa&lt;&gt;</tt> operator works exactly like the Java
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]321 "<tt>instanceof</tt>" operator. It returns true or false depending on whether
322 a reference or pointer points to an instance of the specified class. This can
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]323 be very useful for constraint checking of various sorts (example below).</p>
324 </dd>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]325
326 <dt><tt>cast&lt;&gt;</tt>: </dt>
327
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]328 <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]329 converts a pointer or reference from a base class to a derived cast, causing
330 an assertion failure if it is not really an instance of the right type. This
331 should be used in cases where you have some information that makes you believe
332 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]333 and <tt>cast&lt;&gt;</tt> template is:</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]334
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]335<div class="doc_code">
336<pre>
337static bool isLoopInvariant(const <a href="#Value">Value</a> *V, const Loop *L) {
338 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))
339 return true;
Chris Lattner69bf8a92004-05-23 21:06:58 +0000[diff] [blame]340
Bill Wendling82e2eea2006-10-11 18:00:22 +0000[diff] [blame]341 // <i>Otherwise, it must be an instruction...</i>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]342 return !L-&gt;contains(cast&lt;<a href="#Instruction">Instruction</a>&gt;(V)-&gt;getParent());
343}
344</pre>
345</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]346
347 <p>Note that you should <b>not</b> use an <tt>isa&lt;&gt;</tt> test followed
348 by a <tt>cast&lt;&gt;</tt>, for that use the <tt>dyn_cast&lt;&gt;</tt>
349 operator.</p>
350
351 </dd>
352
353 <dt><tt>dyn_cast&lt;&gt;</tt>:</dt>
354
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]355 <dd><p>The <tt>dyn_cast&lt;&gt;</tt> operator is a "checking cast" operation.
356 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]357 pointer to it (this operator does not work with references). If the operand is
358 not of the correct type, a null pointer is returned. Thus, this works very
Misha Brukman2c122ce2005-11-01 21:12:49 +0000[diff] [blame]359 much like the <tt>dynamic_cast&lt;&gt;</tt> operator in C++, and should be
360 used in the same circumstances. Typically, the <tt>dyn_cast&lt;&gt;</tt>
361 operator is used in an <tt>if</tt> statement or some other flow control
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]362 statement like this:</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]363
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]364<div class="doc_code">
365<pre>
366if (<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]367 // <i>...</i>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]368}
369</pre>
370</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]371
Misha Brukman2c122ce2005-11-01 21:12:49 +0000[diff] [blame]372 <p>This form of the <tt>if</tt> statement effectively combines together a call
373 to <tt>isa&lt;&gt;</tt> and a call to <tt>cast&lt;&gt;</tt> into one
374 statement, which is very convenient.</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]375
Misha Brukman2c122ce2005-11-01 21:12:49 +0000[diff] [blame]376 <p>Note that the <tt>dyn_cast&lt;&gt;</tt> operator, like C++'s
377 <tt>dynamic_cast&lt;&gt;</tt> or Java's <tt>instanceof</tt> operator, can be
378 abused. In particular, you should not use big chained <tt>if/then/else</tt>
379 blocks to check for lots of different variants of classes. If you find
380 yourself wanting to do this, it is much cleaner and more efficient to use the
381 <tt>InstVisitor</tt> class to dispatch over the instruction type directly.</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]382
Misha Brukman2c122ce2005-11-01 21:12:49 +0000[diff] [blame]383 </dd>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]384
Misha Brukman2c122ce2005-11-01 21:12:49 +0000[diff] [blame]385 <dt><tt>cast_or_null&lt;&gt;</tt>: </dt>
386
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]387 <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]388 <tt>cast&lt;&gt;</tt> operator, except that it allows for a null pointer as an
389 argument (which it then propagates). This can sometimes be useful, allowing
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]390 you to combine several null checks into one.</p></dd>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]391
Misha Brukman2c122ce2005-11-01 21:12:49 +0000[diff] [blame]392 <dt><tt>dyn_cast_or_null&lt;&gt;</tt>: </dt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]393
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]394 <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]395 <tt>dyn_cast&lt;&gt;</tt> operator, except that it allows for a null pointer
396 as an argument (which it then propagates). This can sometimes be useful,
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]397 allowing you to combine several null checks into one.</p></dd>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]398
Misha Brukman2c122ce2005-11-01 21:12:49 +0000[diff] [blame]399</dl>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]400
401<p>These five templates can be used with any classes, whether they have a
402v-table or not. To add support for these templates, you simply need to add
403<tt>classof</tt> static methods to the class you are interested casting
404to. Describing this is currently outside the scope of this document, but there
405are lots of examples in the LLVM source base.</p>
406
407</div>
408
409<!-- ======================================================================= -->
410<div class="doc_subsection">
Misha Brukman2c122ce2005-11-01 21:12:49 +0000[diff] [blame]411 <a name="DEBUG">The <tt>DEBUG()</tt> macro and <tt>-debug</tt> option</a>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]412</div>
413
414<div class="doc_text">
415
416<p>Often when working on your pass you will put a bunch of debugging printouts
417and other code into your pass. After you get it working, you want to remove
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]418it, 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]419across).</p>
420
421<p> Naturally, because of this, you don't want to delete the debug printouts,
422but you don't want them to always be noisy. A standard compromise is to comment
423them out, allowing you to enable them if you need them in the future.</p>
424
Chris Lattner695b78b2005-04-26 22:56:16 +0000[diff] [blame]425<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]426file provides a macro named <tt>DEBUG()</tt> that is a much nicer solution to
427this problem. Basically, you can put arbitrary code into the argument of the
428<tt>DEBUG</tt> macro, and it is only executed if '<tt>opt</tt>' (or any other
429tool) is run with the '<tt>-debug</tt>' command line argument:</p>
430
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]431<div class="doc_code">
432<pre>
Bill Wendling832171c2006-12-07 20:04:42 +0000[diff] [blame]433DOUT &lt;&lt; "I am here!\n";
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]434</pre>
435</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]436
437<p>Then you can run your pass like this:</p>
438
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]439<div class="doc_code">
440<pre>
441$ opt &lt; a.bc &gt; /dev/null -mypass
Bill Wendling82e2eea2006-10-11 18:00:22 +0000[diff] [blame]442<i>&lt;no output&gt;</i>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]443$ opt &lt; a.bc &gt; /dev/null -mypass -debug
444I am here!
445</pre>
446</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]447
448<p>Using the <tt>DEBUG()</tt> macro instead of a home-brewed solution allows you
449to not have to create "yet another" command line option for the debug output for
450your pass. Note that <tt>DEBUG()</tt> macros are disabled for optimized builds,
451so they do not cause a performance impact at all (for the same reason, they
452should also not contain side-effects!).</p>
453
454<p>One additional nice thing about the <tt>DEBUG()</tt> macro is that you can
455enable or disable it directly in gdb. Just use "<tt>set DebugFlag=0</tt>" or
456"<tt>set DebugFlag=1</tt>" from the gdb if the program is running. If the
457program hasn't been started yet, you can always just run it with
458<tt>-debug</tt>.</p>
459
460</div>
461
462<!-- _______________________________________________________________________ -->
463<div class="doc_subsubsection">
Chris Lattnerc9151082005-04-26 22:57:07 +0000[diff] [blame]464 <a name="DEBUG_TYPE">Fine grained debug info with <tt>DEBUG_TYPE</tt> and
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]465 the <tt>-debug-only</tt> option</a>
466</div>
467
468<div class="doc_text">
469
470<p>Sometimes you may find yourself in a situation where enabling <tt>-debug</tt>
471just turns on <b>too much</b> information (such as when working on the code
472generator). If you want to enable debug information with more fine-grained
473control, you define the <tt>DEBUG_TYPE</tt> macro and the <tt>-debug</tt> only
474option as follows:</p>
475
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]476<div class="doc_code">
477<pre>
Bill Wendling832171c2006-12-07 20:04:42 +0000[diff] [blame]478DOUT &lt;&lt; "No debug type\n";
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]479#undef DEBUG_TYPE
480#define DEBUG_TYPE "foo"
Bill Wendling832171c2006-12-07 20:04:42 +0000[diff] [blame]481DOUT &lt;&lt; "'foo' debug type\n";
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]482#undef DEBUG_TYPE
483#define DEBUG_TYPE "bar"
Bill Wendling832171c2006-12-07 20:04:42 +0000[diff] [blame]484DOUT &lt;&lt; "'bar' debug type\n";
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]485#undef DEBUG_TYPE
486#define DEBUG_TYPE ""
Bill Wendling832171c2006-12-07 20:04:42 +0000[diff] [blame]487DOUT &lt;&lt; "No debug type (2)\n";
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]488</pre>
489</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]490
491<p>Then you can run your pass like this:</p>
492
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]493<div class="doc_code">
494<pre>
495$ opt &lt; a.bc &gt; /dev/null -mypass
Bill Wendling82e2eea2006-10-11 18:00:22 +0000[diff] [blame]496<i>&lt;no output&gt;</i>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]497$ opt &lt; a.bc &gt; /dev/null -mypass -debug
498No debug type
499'foo' debug type
500'bar' debug type
501No debug type (2)
502$ opt &lt; a.bc &gt; /dev/null -mypass -debug-only=foo
503'foo' debug type
504$ opt &lt; a.bc &gt; /dev/null -mypass -debug-only=bar
505'bar' debug type
506</pre>
507</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]508
509<p>Of course, in practice, you should only set <tt>DEBUG_TYPE</tt> at the top of
510a 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]511you <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]512<tt>#undef</tt>'s). Also, you should use names more meaningful than "foo" and
513"bar", because there is no system in place to ensure that names do not
514conflict. If two different modules use the same string, they will all be turned
515on when the name is specified. This allows, for example, all debug information
516for instruction scheduling to be enabled with <tt>-debug-type=InstrSched</tt>,
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]517even if the source lives in multiple files.</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]518
519</div>
520
521<!-- ======================================================================= -->
522<div class="doc_subsection">
Chris Lattner0be6fdf2006-12-19 21:46:21 +0000[diff] [blame]523 <a name="Statistic">The <tt>Statistic</tt> class &amp; <tt>-stats</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]524 option</a>
525</div>
526
527<div class="doc_text">
528
529<p>The "<tt><a
Chris Lattner695b78b2005-04-26 22:56:16 +0000[diff] [blame]530href="/doxygen/Statistic_8h-source.html">llvm/ADT/Statistic.h</a></tt>" file
Chris Lattner0be6fdf2006-12-19 21:46:21 +0000[diff] [blame]531provides a class named <tt>Statistic</tt> that is used as a unified way to
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]532keep track of what the LLVM compiler is doing and how effective various
533optimizations are. It is useful to see what optimizations are contributing to
534making a particular program run faster.</p>
535
536<p>Often you may run your pass on some big program, and you're interested to see
537how many times it makes a certain transformation. Although you can do this with
538hand 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]539for big programs. Using the <tt>Statistic</tt> class makes it very easy to
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]540keep track of this information, and the calculated information is presented in a
541uniform manner with the rest of the passes being executed.</p>
542
543<p>There are many examples of <tt>Statistic</tt> uses, but the basics of using
544it are as follows:</p>
545
546<ol>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]547 <li><p>Define your statistic like this:</p>
548
549<div class="doc_code">
550<pre>
Chris Lattner0be6fdf2006-12-19 21:46:21 +0000[diff] [blame]551#define <a href="#DEBUG_TYPE">DEBUG_TYPE</a> "mypassname" <i>// This goes before any #includes.</i>
552STATISTIC(NumXForms, "The # of times I did stuff");
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]553</pre>
554</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]555
Chris Lattner0be6fdf2006-12-19 21:46:21 +0000[diff] [blame]556 <p>The <tt>STATISTIC</tt> macro defines a static variable, whose name is
557 specified by the first argument. The pass name is taken from the DEBUG_TYPE
558 macro, and the description is taken from the second argument. The variable
Reid Spencer06565dc2007-01-12 17:11:23 +0000[diff] [blame]559 defined ("NumXForms" in this case) acts like an unsigned integer.</p></li>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]560
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]561 <li><p>Whenever you make a transformation, bump the counter:</p>
562
563<div class="doc_code">
564<pre>
Bill Wendling82e2eea2006-10-11 18:00:22 +0000[diff] [blame]565++NumXForms; // <i>I did stuff!</i>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]566</pre>
567</div>
568
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]569 </li>
570 </ol>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]571
572 <p>That's all you have to do. To get '<tt>opt</tt>' to print out the
573 statistics gathered, use the '<tt>-stats</tt>' option:</p>
574
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]575<div class="doc_code">
576<pre>
577$ opt -stats -mypassname &lt; program.bc &gt; /dev/null
Bill Wendling82e2eea2006-10-11 18:00:22 +0000[diff] [blame]578<i>... statistics output ...</i>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]579</pre>
580</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]581
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]582 <p> When running <tt>gccas</tt> on a C file from the SPEC benchmark
583suite, it gives a report that looks like this:</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]584
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]585<div class="doc_code">
586<pre>
587 7646 bytecodewriter - Number of normal instructions
588 725 bytecodewriter - Number of oversized instructions
589 129996 bytecodewriter - Number of bytecode bytes written
590 2817 raise - Number of insts DCEd or constprop'd
591 3213 raise - Number of cast-of-self removed
592 5046 raise - Number of expression trees converted
593 75 raise - Number of other getelementptr's formed
594 138 raise - Number of load/store peepholes
595 42 deadtypeelim - Number of unused typenames removed from symtab
596 392 funcresolve - Number of varargs functions resolved
597 27 globaldce - Number of global variables removed
598 2 adce - Number of basic blocks removed
599 134 cee - Number of branches revectored
600 49 cee - Number of setcc instruction eliminated
601 532 gcse - Number of loads removed
602 2919 gcse - Number of instructions removed
603 86 indvars - Number of canonical indvars added
604 87 indvars - Number of aux indvars removed
605 25 instcombine - Number of dead inst eliminate
606 434 instcombine - Number of insts combined
607 248 licm - Number of load insts hoisted
608 1298 licm - Number of insts hoisted to a loop pre-header
609 3 licm - Number of insts hoisted to multiple loop preds (bad, no loop pre-header)
610 75 mem2reg - Number of alloca's promoted
611 1444 cfgsimplify - Number of blocks simplified
612</pre>
613</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]614
615<p>Obviously, with so many optimizations, having a unified framework for this
616stuff is very nice. Making your pass fit well into the framework makes it more
617maintainable and useful.</p>
618
619</div>
620
Chris Lattnerf623a082005-10-17 01:36:23 +0000[diff] [blame]621<!-- ======================================================================= -->
622<div class="doc_subsection">
623 <a name="ViewGraph">Viewing graphs while debugging code</a>
624</div>
625
626<div class="doc_text">
627
628<p>Several of the important data structures in LLVM are graphs: for example
629CFGs made out of LLVM <a href="#BasicBlock">BasicBlock</a>s, CFGs made out of
630LLVM <a href="CodeGenerator.html#machinebasicblock">MachineBasicBlock</a>s, and
631<a href="CodeGenerator.html#selectiondag_intro">Instruction Selection
632DAGs</a>. In many cases, while debugging various parts of the compiler, it is
633nice to instantly visualize these graphs.</p>
634
635<p>LLVM provides several callbacks that are available in a debug build to do
636exactly that. If you call the <tt>Function::viewCFG()</tt> method, for example,
637the current LLVM tool will pop up a window containing the CFG for the function
638where each basic block is a node in the graph, and each node contains the
639instructions in the block. Similarly, there also exists
640<tt>Function::viewCFGOnly()</tt> (does not include the instructions), the
641<tt>MachineFunction::viewCFG()</tt> and <tt>MachineFunction::viewCFGOnly()</tt>,
642and the <tt>SelectionDAG::viewGraph()</tt> methods. Within GDB, for example,
Jim Laskey543a0ee2006-10-02 12:28:07 +0000[diff] [blame]643you can usually use something like <tt>call DAG.viewGraph()</tt> to pop
Chris Lattnerf623a082005-10-17 01:36:23 +0000[diff] [blame]644up a window. Alternatively, you can sprinkle calls to these functions in your
645code in places you want to debug.</p>
646
647<p>Getting this to work requires a small amount of configuration. On Unix
648systems with X11, install the <a href="http://www.graphviz.org">graphviz</a>
649toolkit, and make sure 'dot' and 'gv' are in your path. If you are running on
650Mac OS/X, download and install the Mac OS/X <a
651href="http://www.pixelglow.com/graphviz/">Graphviz program</a>, and add
652<tt>/Applications/Graphviz.app/Contents/MacOS/</tt> (or whereever you install
653it) to your path. Once in your system and path are set up, rerun the LLVM
654configure script and rebuild LLVM to enable this functionality.</p>
655
Jim Laskey543a0ee2006-10-02 12:28:07 +0000[diff] [blame]656<p><tt>SelectionDAG</tt> has been extended to make it easier to locate
657<i>interesting</i> nodes in large complex graphs. From gdb, if you
658<tt>call DAG.setGraphColor(<i>node</i>, "<i>color</i>")</tt>, then the
659next <tt>call DAG.viewGraph()</tt> would hilight the node in the
660specified color (choices of colors can be found at <a
Chris Lattner302da1e2007-02-03 03:05:57 +0000[diff] [blame]661href="http://www.graphviz.org/doc/info/colors.html">colors</a>.) More
Jim Laskey543a0ee2006-10-02 12:28:07 +0000[diff] [blame]662complex node attributes can be provided with <tt>call
663DAG.setGraphAttrs(<i>node</i>, "<i>attributes</i>")</tt> (choices can be
664found at <a href="http://www.graphviz.org/doc/info/attrs.html">Graph
665Attributes</a>.) If you want to restart and clear all the current graph
666attributes, then you can <tt>call DAG.clearGraphAttrs()</tt>. </p>
667
Chris Lattnerf623a082005-10-17 01:36:23 +0000[diff] [blame]668</div>
669
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]670<!-- *********************************************************************** -->
671<div class="doc_section">
672 <a name="datastructure">Picking the Right Data Structure for a Task</a>
673</div>
674<!-- *********************************************************************** -->
675
676<div class="doc_text">
677
678<p>LLVM has a plethora of datastructures in the <tt>llvm/ADT/</tt> directory,
679 and we commonly use STL datastructures. This section describes the tradeoffs
680 you should consider when you pick one.</p>
681
682<p>
683The first step is a choose your own adventure: do you want a sequential
684container, a set-like container, or a map-like container? The most important
685thing when choosing a container is the algorithmic properties of how you plan to
686access the container. Based on that, you should use:</p>
687
688<ul>
689<li>a <a href="#ds_map">map-like</a> container if you need efficient lookup
690 of an value based on another value. Map-like containers also support
691 efficient queries for containment (whether a key is in the map). Map-like
692 containers generally do not support efficient reverse mapping (values to
693 keys). If you need that, use two maps. Some map-like containers also
694 support efficient iteration through the keys in sorted order. Map-like
695 containers are the most expensive sort, only use them if you need one of
696 these capabilities.</li>
697
698<li>a <a href="#ds_set">set-like</a> container if you need to put a bunch of
699 stuff into a container that automatically eliminates duplicates. Some
700 set-like containers support efficient iteration through the elements in
701 sorted order. Set-like containers are more expensive than sequential
702 containers.
703</li>
704
705<li>a <a href="#ds_sequential">sequential</a> container provides
706 the most efficient way to add elements and keeps track of the order they are
707 added to the collection. They permit duplicates and support efficient
708 iteration, but do not support efficient lookup based on a key.
709</li>
710
711</ul>
712
713<p>
714Once the proper catagory of container is determined, you can fine tune the
715memory use, constant factors, and cache behaviors of access by intelligently
716picking a member of the catagory. Note that constant factors and cache behavior
717can be a big deal. If you have a vector that usually only contains a few
718elements (but could contain many), for example, it's much better to use
719<a href="#dss_smallvector">SmallVector</a> than <a href="#dss_vector">vector</a>
720. Doing so avoids (relatively) expensive malloc/free calls, which dwarf the
721cost of adding the elements to the container. </p>
722
723</div>
724
725<!-- ======================================================================= -->
726<div class="doc_subsection">
727 <a name="ds_sequential">Sequential Containers (std::vector, std::list, etc)</a>
728</div>
729
730<div class="doc_text">
731There are a variety of sequential containers available for you, based on your
732needs. Pick the first in this section that will do what you want.
733</div>
734
735<!-- _______________________________________________________________________ -->
736<div class="doc_subsubsection">
737 <a name="dss_fixedarrays">Fixed Size Arrays</a>
738</div>
739
740<div class="doc_text">
741<p>Fixed size arrays are very simple and very fast. They are good if you know
742exactly how many elements you have, or you have a (low) upper bound on how many
743you have.</p>
744</div>
745
746<!-- _______________________________________________________________________ -->
747<div class="doc_subsubsection">
748 <a name="dss_heaparrays">Heap Allocated Arrays</a>
749</div>
750
751<div class="doc_text">
752<p>Heap allocated arrays (new[] + delete[]) are also simple. They are good if
753the number of elements is variable, if you know how many elements you will need
754before the array is allocated, and if the array is usually large (if not,
755consider a <a href="#dss_smallvector">SmallVector</a>). The cost of a heap
756allocated array is the cost of the new/delete (aka malloc/free). Also note that
757if you are allocating an array of a type with a constructor, the constructor and
758destructors will be run for every element in the array (resizable vectors only
759construct those elements actually used).</p>
760</div>
761
762<!-- _______________________________________________________________________ -->
763<div class="doc_subsubsection">
764 <a name="dss_smallvector">"llvm/ADT/SmallVector.h"</a>
765</div>
766
767<div class="doc_text">
768<p><tt>SmallVector&lt;Type, N&gt;</tt> is a simple class that looks and smells
769just like <tt>vector&lt;Type&gt;</tt>:
770it supports efficient iteration, lays out elements in memory order (so you can
771do pointer arithmetic between elements), supports efficient push_back/pop_back
772operations, supports efficient random access to its elements, etc.</p>
773
774<p>The advantage of SmallVector is that it allocates space for
775some number of elements (N) <b>in the object itself</b>. Because of this, if
776the SmallVector is dynamically smaller than N, no malloc is performed. This can
777be a big win in cases where the malloc/free call is far more expensive than the
778code that fiddles around with the elements.</p>
779
780<p>This is good for vectors that are "usually small" (e.g. the number of
781predecessors/successors of a block is usually less than 8). On the other hand,
782this makes the size of the SmallVector itself large, so you don't want to
783allocate lots of them (doing so will waste a lot of space). As such,
784SmallVectors are most useful when on the stack.</p>
785
786<p>SmallVector also provides a nice portable and efficient replacement for
787<tt>alloca</tt>.</p>
788
789</div>
790
791<!-- _______________________________________________________________________ -->
792<div class="doc_subsubsection">
793 <a name="dss_vector">&lt;vector&gt;</a>
794</div>
795
796<div class="doc_text">
797<p>
798std::vector is well loved and respected. It is useful when SmallVector isn't:
799when the size of the vector is often large (thus the small optimization will
800rarely be a benefit) or if you will be allocating many instances of the vector
801itself (which would waste space for elements that aren't in the container).
802vector is also useful when interfacing with code that expects vectors :).
803</p>
804</div>
805
806<!-- _______________________________________________________________________ -->
807<div class="doc_subsubsection">
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]808 <a name="dss_deque">&lt;deque&gt;</a>
809</div>
810
811<div class="doc_text">
812<p>std::deque is, in some senses, a generalized version of std::vector. Like
813std::vector, it provides constant time random access and other similar
814properties, but it also provides efficient access to the front of the list. It
815does not guarantee continuity of elements within memory.</p>
816
817<p>In exchange for this extra flexibility, std::deque has significantly higher
818constant factor costs than std::vector. If possible, use std::vector or
819something cheaper.</p>
820</div>
821
822<!-- _______________________________________________________________________ -->
823<div class="doc_subsubsection">
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]824 <a name="dss_list">&lt;list&gt;</a>
825</div>
826
827<div class="doc_text">
828<p>std::list is an extremely inefficient class that is rarely useful.
829It performs a heap allocation for every element inserted into it, thus having an
830extremely high constant factor, particularly for small data types. std::list
831also only supports bidirectional iteration, not random access iteration.</p>
832
833<p>In exchange for this high cost, std::list supports efficient access to both
834ends of the list (like std::deque, but unlike std::vector or SmallVector). In
835addition, the iterator invalidation characteristics of std::list are stronger
836than that of a vector class: inserting or removing an element into the list does
837not invalidate iterator or pointers to other elements in the list.</p>
838</div>
839
840<!-- _______________________________________________________________________ -->
841<div class="doc_subsubsection">
842 <a name="dss_ilist">llvm/ADT/ilist</a>
843</div>
844
845<div class="doc_text">
846<p><tt>ilist&lt;T&gt;</tt> implements an 'intrusive' doubly-linked list. It is
847intrusive, because it requires the element to store and provide access to the
848prev/next pointers for the list.</p>
849
850<p>ilist has the same drawbacks as std::list, and additionally requires an
851ilist_traits implementation for the element type, but it provides some novel
852characteristics. In particular, it can efficiently store polymorphic objects,
853the traits class is informed when an element is inserted or removed from the
854list, and ilists are guaranteed to support a constant-time splice operation.
855</p>
856
857<p>These properties are exactly what we want for things like Instructions and
858basic blocks, which is why these are implemented with ilists.</p>
859</div>
860
861<!-- _______________________________________________________________________ -->
862<div class="doc_subsubsection">
Chris Lattnerc5722432007-02-03 19:49:31 +0000[diff] [blame]863 <a name="dss_other">Other Sequential Container options</a>
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]864</div>
865
866<div class="doc_text">
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]867<p>Other STL containers are available, such as std::string.</p>
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]868
869<p>There are also various STL adapter classes such as std::queue,
870std::priority_queue, std::stack, etc. These provide simplified access to an
871underlying container but don't affect the cost of the container itself.</p>
872
873</div>
874
875
876<!-- ======================================================================= -->
877<div class="doc_subsection">
878 <a name="ds_set">Set-Like Containers (std::set, SmallSet, SetVector, etc)</a>
879</div>
880
881<div class="doc_text">
882
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]883<p>Set-like containers are useful when you need to canonicalize multiple values
884into a single representation. There are several different choices for how to do
885this, providing various trade-offs.</p>
886
887</div>
888
889
890<!-- _______________________________________________________________________ -->
891<div class="doc_subsubsection">
892 <a name="dss_sortedvectorset">A sorted 'vector'</a>
893</div>
894
895<div class="doc_text">
896
Chris Lattner3b23a8c2007-02-03 08:10:45 +0000[diff] [blame]897<p>If you intend to insert a lot of elements, then do a lot of queries, a
898great approach is to use a vector (or other sequential container) with
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]899std::sort+std::unique to remove duplicates. This approach works really well if
Chris Lattner3b23a8c2007-02-03 08:10:45 +0000[diff] [blame]900your usage pattern has these two distinct phases (insert then query), and can be
901coupled with a good choice of <a href="#ds_sequential">sequential container</a>.
902</p>
903
904<p>
905This combination provides the several nice properties: the result data is
906contiguous in memory (good for cache locality), has few allocations, is easy to
907address (iterators in the final vector are just indices or pointers), and can be
908efficiently queried with a standard binary or radix search.</p>
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]909
910</div>
911
912<!-- _______________________________________________________________________ -->
913<div class="doc_subsubsection">
914 <a name="dss_smallset">"llvm/ADT/SmallSet.h"</a>
915</div>
916
917<div class="doc_text">
918
919<p>If you have a set-like datastructure that is usually small and whose elements
Chris Lattner4ddfac12007-02-03 07:59:51 +0000[diff] [blame]920are 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]921has space for N elements in place (thus, if the set is dynamically smaller than
Chris Lattner14868db2007-02-03 08:20:15 +0000[diff] [blame]922N, no malloc traffic is required) and accesses them with a simple linear search.
923When the set grows beyond 'N' elements, it allocates a more expensive representation that
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]924guarantees efficient access (for most types, it falls back to std::set, but for
Chris Lattner14868db2007-02-03 08:20:15 +0000[diff] [blame]925pointers it uses something far better, <a
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]926href="#dss_smallptrset">SmallPtrSet</a>).</p>
927
928<p>The magic of this class is that it handles small sets extremely efficiently,
929but gracefully handles extremely large sets without loss of efficiency. The
930drawback is that the interface is quite small: it supports insertion, queries
931and erasing, but does not support iteration.</p>
932
933</div>
934
935<!-- _______________________________________________________________________ -->
936<div class="doc_subsubsection">
937 <a name="dss_smallptrset">"llvm/ADT/SmallPtrSet.h"</a>
938</div>
939
940<div class="doc_text">
941
942<p>SmallPtrSet has all the advantages of SmallSet (and a SmallSet of pointers is
943transparently implemented with a SmallPtrSet), but also suports iterators. If
Chris Lattner14868db2007-02-03 08:20:15 +0000[diff] [blame]944more than 'N' insertions are performed, a single quadratically
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]945probed hash table is allocated and grows as needed, providing extremely
946efficient access (constant time insertion/deleting/queries with low constant
947factors) and is very stingy with malloc traffic.</p>
948
949<p>Note that, unlike std::set, the iterators of SmallPtrSet are invalidated
950whenever an insertion occurs. Also, the values visited by the iterators are not
951visited in sorted order.</p>
952
953</div>
954
955<!-- _______________________________________________________________________ -->
956<div class="doc_subsubsection">
957 <a name="dss_FoldingSet">"llvm/ADT/FoldingSet.h"</a>
958</div>
959
960<div class="doc_text">
961
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]962<p>
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]963FoldingSet is an aggregate class that is really good at uniquing
964expensive-to-create or polymorphic objects. It is a combination of a chained
965hash table with intrusive links (uniqued objects are required to inherit from
Chris Lattner14868db2007-02-03 08:20:15 +0000[diff] [blame]966FoldingSetNode) that uses <a href="#dss_smallvector">SmallVector</a> as part of
967its ID process.</p>
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]968
Chris Lattner14868db2007-02-03 08:20:15 +0000[diff] [blame]969<p>Consider a case where you want to implement a "getOrCreateFoo" method for
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]970a complex object (for example, a node in the code generator). The client has a
971description of *what* it wants to generate (it knows the opcode and all the
972operands), 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]973only to find out it already exists, at which point we would have to delete it
974and return the node that already exists.
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]975</p>
976
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]977<p>To support this style of client, FoldingSet perform a query with a
978FoldingSetNodeID (which wraps SmallVector) that can be used to describe the
979element that we want to query for. The query either returns the element
980matching the ID or it returns an opaque ID that indicates where insertion should
Chris Lattner14868db2007-02-03 08:20:15 +0000[diff] [blame]981take place. Construction of the ID usually does not require heap traffic.</p>
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]982
983<p>Because FoldingSet uses intrusive links, it can support polymorphic objects
984in the set (for example, you can have SDNode instances mixed with LoadSDNodes).
985Because the elements are individually allocated, pointers to the elements are
986stable: inserting or removing elements does not invalidate any pointers to other
987elements.
988</p>
989
990</div>
991
992<!-- _______________________________________________________________________ -->
993<div class="doc_subsubsection">
994 <a name="dss_set">&lt;set&gt;</a>
995</div>
996
997<div class="doc_text">
998
Chris Lattnerc5722432007-02-03 19:49:31 +0000[diff] [blame]999<p><tt>std::set</tt> is a reasonable all-around set class, which is decent at
1000many things but great at nothing. std::set allocates memory for each element
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1001inserted (thus it is very malloc intensive) and typically stores three pointers
Chris Lattner14868db2007-02-03 08:20:15 +0000[diff] [blame]1002per element in the set (thus adding a large amount of per-element space
1003overhead). It offers guaranteed log(n) performance, which is not particularly
Chris Lattnerc5722432007-02-03 19:49:31 +0000[diff] [blame]1004fast from a complexity standpoint (particularly if the elements of the set are
1005expensive to compare, like strings), and has extremely high constant factors for
1006lookup, insertion and removal.</p>
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1007
Chris Lattner14868db2007-02-03 08:20:15 +0000[diff] [blame]1008<p>The advantages of std::set are that its iterators are stable (deleting or
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1009inserting an element from the set does not affect iterators or pointers to other
1010elements) and that iteration over the set is guaranteed to be in sorted order.
1011If the elements in the set are large, then the relative overhead of the pointers
1012and malloc traffic is not a big deal, but if the elements of the set are small,
1013std::set is almost never a good choice.</p>
1014
1015</div>
1016
1017<!-- _______________________________________________________________________ -->
1018<div class="doc_subsubsection">
1019 <a name="dss_setvector">"llvm/ADT/SetVector.h"</a>
1020</div>
1021
1022<div class="doc_text">
1023<p>LLVM's SetVector&lt;Type&gt; is actually a combination of a set along with
1024a <a href="#ds_sequential">Sequential Container</a>. The important property
1025that this provides is efficient insertion with uniquing (duplicate elements are
1026ignored) with iteration support. It implements this by inserting elements into
1027both a set-like container and the sequential container, using the set-like
1028container for uniquing and the sequential container for iteration.
1029</p>
1030
1031<p>The difference between SetVector and other sets is that the order of
1032iteration is guaranteed to match the order of insertion into the SetVector.
1033This property is really important for things like sets of pointers. Because
1034pointer values are non-deterministic (e.g. vary across runs of the program on
1035different machines), iterating over the pointers in a std::set or other set will
1036not be in a well-defined order.</p>
1037
1038<p>
1039The drawback of SetVector is that it requires twice as much space as a normal
1040set and has the sum of constant factors from the set-like container and the
1041sequential container that it uses. Use it *only* if you need to iterate over
1042the elements in a deterministic order. SetVector is also expensive to delete
1043elements out of (linear time).
1044</p>
1045
1046</div>
1047
1048<!-- _______________________________________________________________________ -->
1049<div class="doc_subsubsection">
Chris Lattnerc5722432007-02-03 19:49:31 +0000[diff] [blame]1050 <a name="dss_uniquevector">"llvm/ADT/UniqueVector.h"</a>
1051</div>
1052
1053<div class="doc_text">
1054
1055<p>
1056UniqueVector is similar to <a href="#dss_setvector">SetVector</a>, but it
1057retains a unique ID for each element inserted into the set. It internally
1058contains a map and a vector, and it assigns a unique ID for each value inserted
1059into the set.</p>
1060
1061<p>UniqueVector is very expensive: its cost is the sum of the cost of
1062maintaining both the map and vector, it has high complexity, high constant
1063factors, and produces a lot of malloc traffic. It should be avoided.</p>
1064
1065</div>
1066
1067
1068<!-- _______________________________________________________________________ -->
1069<div class="doc_subsubsection">
1070 <a name="dss_otherset">Other Set-Like Container Options</a>
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1071</div>
1072
1073<div class="doc_text">
1074
1075<p>
1076The STL provides several other options, such as std::multiset and the various
Chris Lattnerc5722432007-02-03 19:49:31 +0000[diff] [blame]1077"hash_set" like containers (whether from C++ TR1 or from the SGI library).</p>
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1078
1079<p>std::multiset is useful if you're not interested in elimination of
Chris Lattner14868db2007-02-03 08:20:15 +0000[diff] [blame]1080duplicates, but has all the drawbacks of std::set. A sorted vector (where you
1081don't delete duplicate entries) or some other approach is almost always
1082better.</p>
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1083
1084<p>The various hash_set implementations (exposed portably by
Chris Lattner14868db2007-02-03 08:20:15 +0000[diff] [blame]1085"llvm/ADT/hash_set") is a simple chained hashtable. This algorithm is as malloc
1086intensive as std::set (performing an allocation for each element inserted,
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1087thus having really high constant factors) but (usually) provides O(1)
1088insertion/deletion of elements. This can be useful if your elements are large
Chris Lattner14868db2007-02-03 08:20:15 +0000[diff] [blame]1089(thus making the constant-factor cost relatively low) or if comparisons are
1090expensive. Element iteration does not visit elements in a useful order.</p>
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1091
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]1092</div>
1093
1094<!-- ======================================================================= -->
1095<div class="doc_subsection">
1096 <a name="ds_map">Map-Like Containers (std::map, DenseMap, etc)</a>
1097</div>
1098
1099<div class="doc_text">
Chris Lattnerc5722432007-02-03 19:49:31 +0000[diff] [blame]1100Map-like containers are useful when you want to associate data to a key. As
1101usual, there are a lot of different ways to do this. :)
1102</div>
1103
1104<!-- _______________________________________________________________________ -->
1105<div class="doc_subsubsection">
1106 <a name="dss_sortedvectormap">A sorted 'vector'</a>
1107</div>
1108
1109<div class="doc_text">
1110
1111<p>
1112If your usage pattern follows a strict insert-then-query approach, you can
1113trivially use the same approach as <a href="#dss_sortedvectorset">sorted vectors
1114for set-like containers</a>. The only difference is that your query function
1115(which uses std::lower_bound to get efficient log(n) lookup) should only compare
1116the key, not both the key and value. This yields the same advantages as sorted
1117vectors for sets.
1118</p>
1119</div>
1120
1121<!-- _______________________________________________________________________ -->
1122<div class="doc_subsubsection">
1123 <a name="dss_cstringmap">"llvm/ADT/CStringMap.h"</a>
1124</div>
1125
1126<div class="doc_text">
1127
1128<p>
1129Strings are commonly used as keys in maps, and they are difficult to support
1130efficiently: they are variable length, inefficient to hash and compare when
1131long, expensive to copy, etc. CStringMap is a specialized container designed to
1132cope with these issues. It supports mapping an arbitrary range of bytes that
1133does not have an embedded nul character in it ("C strings") to an arbitrary
1134other object.</p>
1135
1136<p>The CStringMap implementation uses a quadratically-probed hash table, where
1137the buckets store a pointer to the heap allocated entries (and some other
1138stuff). The entries in the map must be heap allocated because the strings are
1139variable length. The string data (key) and the element object (value) are
1140stored in the same allocation with the string data immediately after the element
1141object. This container guarantees the "<tt>(char*)(&amp;Value+1)</tt>" points
1142to the key string for a value.</p>
1143
1144<p>The CStringMap is very fast for several reasons: quadratic probing is very
1145cache efficient for lookups, the hash value of strings in buckets is not
1146recomputed when lookup up an element, CStringMap rarely has to touch the
1147memory for unrelated objects when looking up a value (even when hash collisions
1148happen), hash table growth does not recompute the hash values for strings
1149already in the table, and each pair in the map is store in a single allocation
1150(the string data is stored in the same allocation as the Value of a pair).</p>
1151
1152<p>CStringMap also provides query methods that take byte ranges, so it only ever
1153copies a string if a value is inserted into the table.</p>
1154</div>
1155
1156<!-- _______________________________________________________________________ -->
1157<div class="doc_subsubsection">
1158 <a name="dss_indexedmap">"llvm/ADT/IndexedMap.h"</a>
1159</div>
1160
1161<div class="doc_text">
1162<p>
1163IndexedMap is a specialized container for mapping small dense integers (or
1164values that can be mapped to small dense integers) to some other type. It is
1165internally implemented as a vector with a mapping function that maps the keys to
1166the dense integer range.
1167</p>
1168
1169<p>
1170This is useful for cases like virtual registers in the LLVM code generator: they
1171have a dense mapping that is offset by a compile-time constant (the first
1172virtual register ID).</p>
1173
1174</div>
1175
1176<!-- _______________________________________________________________________ -->
1177<div class="doc_subsubsection">
1178 <a name="dss_densemap">"llvm/ADT/DenseMap.h"</a>
1179</div>
1180
1181<div class="doc_text">
1182
1183<p>
1184DenseMap is a simple quadratically probed hash table. It excels at supporting
1185small keys and values: it uses a single allocation to hold all of the pairs that
1186are currently inserted in the map. DenseMap is a great way to map pointers to
1187pointers, or map other small types to each other.
1188</p>
1189
1190<p>
1191There are several aspects of DenseMap that you should be aware of, however. The
1192iterators in a densemap are invalidated whenever an insertion occurs, unlike
1193map. Also, because DenseMap allocates space for a large number of key/value
1194pairs (it starts with 64 by default) if you have large keys or values, it can
1195waste a lot of space. Finally, you must implement a partial specialization of
1196DenseMapKeyInfo for the key that you want, if it isn't already supported. This
1197is required to tell DenseMap about two special marker values (which can never be
1198inserted into the map).</p>
1199
1200</div>
1201
1202<!-- _______________________________________________________________________ -->
1203<div class="doc_subsubsection">
1204 <a name="dss_map">&lt;map&gt;</a>
1205</div>
1206
1207<div class="doc_text">
1208
1209<p>
1210std::map has similar characteristics to <a href="#dss_set">std::set</a>: it uses
1211a single allocation per pair inserted into the map, it offers log(n) lookup with
1212an extremely large constant factor, imposes a space penalty of 3 pointers per
1213pair in the map, etc.</p>
1214
1215<p>std::map is most useful when your keys or values are very large, if you need
1216to iterate over the collection in sorted order, or if you need stable iterators
1217into the map (i.e. they don't get invalidated if an insertion or deletion of
1218another element takes place).</p>
1219
1220</div>
1221
1222<!-- _______________________________________________________________________ -->
1223<div class="doc_subsubsection">
1224 <a name="dss_othermap">Other Map-Like Container Options</a>
1225</div>
1226
1227<div class="doc_text">
1228
1229<p>
1230The STL provides several other options, such as std::multimap and the various
1231"hash_map" like containers (whether from C++ TR1 or from the SGI library).</p>
1232
1233<p>std::multimap is useful if you want to map a key to multiple values, but has
1234all the drawbacks of std::map. A sorted vector or some other approach is almost
1235always better.</p>
1236
1237<p>The various hash_map implementations (exposed portably by
1238"llvm/ADT/hash_map") are simple chained hash tables. This algorithm is as
1239malloc intensive as std::map (performing an allocation for each element
1240inserted, thus having really high constant factors) but (usually) provides O(1)
1241insertion/deletion of elements. This can be useful if your elements are large
1242(thus making the constant-factor cost relatively low) or if comparisons are
1243expensive. Element iteration does not visit elements in a useful order.</p>
1244
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]1245</div>
1246
Chris Lattnerf623a082005-10-17 01:36:23 +0000[diff] [blame]1247
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1248<!-- *********************************************************************** -->
1249<div class="doc_section">
1250 <a name="common">Helpful Hints for Common Operations</a>
1251</div>
1252<!-- *********************************************************************** -->
1253
1254<div class="doc_text">
1255
1256<p>This section describes how to perform some very simple transformations of
1257LLVM code. This is meant to give examples of common idioms used, showing the
1258practical side of LLVM transformations. <p> Because this is a "how-to" section,
1259you should also read about the main classes that you will be working with. The
1260<a href="#coreclasses">Core LLVM Class Hierarchy Reference</a> contains details
1261and descriptions of the main classes that you should know about.</p>
1262
1263</div>
1264
1265<!-- NOTE: this section should be heavy on example code -->
1266<!-- ======================================================================= -->
1267<div class="doc_subsection">
1268 <a name="inspection">Basic Inspection and Traversal Routines</a>
1269</div>
1270
1271<div class="doc_text">
1272
1273<p>The LLVM compiler infrastructure have many different data structures that may
1274be traversed. Following the example of the C++ standard template library, the
1275techniques used to traverse these various data structures are all basically the
1276same. For a enumerable sequence of values, the <tt>XXXbegin()</tt> function (or
1277method) returns an iterator to the start of the sequence, the <tt>XXXend()</tt>
1278function returns an iterator pointing to one past the last valid element of the
1279sequence, and there is some <tt>XXXiterator</tt> data type that is common
1280between the two operations.</p>
1281
1282<p>Because the pattern for iteration is common across many different aspects of
1283the program representation, the standard template library algorithms may be used
1284on them, and it is easier to remember how to iterate. First we show a few common
1285examples of the data structures that need to be traversed. Other data
1286structures are traversed in very similar ways.</p>
1287
1288</div>
1289
1290<!-- _______________________________________________________________________ -->
Chris Lattner69bf8a92004-05-23 21:06:58 +0000[diff] [blame]1291<div class="doc_subsubsection">
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1292 <a name="iterate_function">Iterating over the </a><a
1293 href="#BasicBlock"><tt>BasicBlock</tt></a>s in a <a
1294 href="#Function"><tt>Function</tt></a>
1295</div>
1296
1297<div class="doc_text">
1298
1299<p>It's quite common to have a <tt>Function</tt> instance that you'd like to
1300transform in some way; in particular, you'd like to manipulate its
1301<tt>BasicBlock</tt>s. To facilitate this, you'll need to iterate over all of
1302the <tt>BasicBlock</tt>s that constitute the <tt>Function</tt>. The following is
1303an example that prints the name of a <tt>BasicBlock</tt> and the number of
1304<tt>Instruction</tt>s it contains:</p>
1305
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1306<div class="doc_code">
1307<pre>
Bill Wendling82e2eea2006-10-11 18:00:22 +0000[diff] [blame]1308// <i>func is a pointer to a Function instance</i>
1309for (Function::iterator i = func-&gt;begin(), e = func-&gt;end(); i != e; ++i)
1310 // <i>Print out the name of the basic block if it has one, and then the</i>
1311 // <i>number of instructions that it contains</i>
Bill Wendling832171c2006-12-07 20:04:42 +0000[diff] [blame]1312 llvm::cerr &lt;&lt; "Basic block (name=" &lt;&lt; i-&gt;getName() &lt;&lt; ") has "
1313 &lt;&lt; i-&gt;size() &lt;&lt; " instructions.\n";
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1314</pre>
1315</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1316
1317<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]1318invoking member functions of the <tt>Instruction</tt> class. This is
1319because the indirection operator is overloaded for the iterator
Chris Lattner7496ec52003-08-05 22:54:23 +0000[diff] [blame]1320classes. In the above code, the expression <tt>i-&gt;size()</tt> is
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1321exactly equivalent to <tt>(*i).size()</tt> just like you'd expect.</p>
1322
1323</div>
1324
1325<!-- _______________________________________________________________________ -->
Chris Lattner69bf8a92004-05-23 21:06:58 +0000[diff] [blame]1326<div class="doc_subsubsection">
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1327 <a name="iterate_basicblock">Iterating over the </a><a
1328 href="#Instruction"><tt>Instruction</tt></a>s in a <a
1329 href="#BasicBlock"><tt>BasicBlock</tt></a>
1330</div>
1331
1332<div class="doc_text">
1333
1334<p>Just like when dealing with <tt>BasicBlock</tt>s in <tt>Function</tt>s, it's
1335easy to iterate over the individual instructions that make up
1336<tt>BasicBlock</tt>s. Here's a code snippet that prints out each instruction in
1337a <tt>BasicBlock</tt>:</p>
1338
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1339<div class="doc_code">
Chris Lattner55c04612005-03-06 06:00:13 +0000[diff] [blame]1340<pre>
Bill Wendling82e2eea2006-10-11 18:00:22 +0000[diff] [blame]1341// <i>blk is a pointer to a BasicBlock instance</i>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1342for (BasicBlock::iterator i = blk-&gt;begin(), e = blk-&gt;end(); i != e; ++i)
Bill Wendling82e2eea2006-10-11 18:00:22 +0000[diff] [blame]1343 // <i>The next statement works since operator&lt;&lt;(ostream&amp;,...)</i>
1344 // <i>is overloaded for Instruction&amp;</i>
Bill Wendling832171c2006-12-07 20:04:42 +0000[diff] [blame]1345 llvm::cerr &lt;&lt; *i &lt;&lt; "\n";
Chris Lattner55c04612005-03-06 06:00:13 +0000[diff] [blame]1346</pre>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1347</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1348
1349<p>However, this isn't really the best way to print out the contents of a
1350<tt>BasicBlock</tt>! Since the ostream operators are overloaded for virtually
1351anything you'll care about, you could have just invoked the print routine on the
Bill Wendling832171c2006-12-07 20:04:42 +0000[diff] [blame]1352basic block itself: <tt>llvm::cerr &lt;&lt; *blk &lt;&lt; "\n";</tt>.</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]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_institer">Iterating over the </a><a
1359 href="#Instruction"><tt>Instruction</tt></a>s in a <a
1360 href="#Function"><tt>Function</tt></a>
1361</div>
1362
1363<div class="doc_text">
1364
1365<p>If you're finding that you commonly iterate over a <tt>Function</tt>'s
1366<tt>BasicBlock</tt>s and then that <tt>BasicBlock</tt>'s <tt>Instruction</tt>s,
1367<tt>InstIterator</tt> should be used instead. You'll need to include <a
1368href="/doxygen/InstIterator_8h-source.html"><tt>llvm/Support/InstIterator.h</tt></a>,
1369and then instantiate <tt>InstIterator</tt>s explicitly in your code. Here's a
Chris Lattner69bf8a92004-05-23 21:06:58 +0000[diff] [blame]1370small 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]1371
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1372<div class="doc_code">
1373<pre>
1374#include "<a href="/doxygen/InstIterator_8h-source.html">llvm/Support/InstIterator.h</a>"
1375
Bill Wendling82e2eea2006-10-11 18:00:22 +0000[diff] [blame]1376// <i>F is a ptr to a Function instance</i>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1377for (inst_iterator i = inst_begin(F), e = inst_end(F); i != e; ++i)
Bill Wendling832171c2006-12-07 20:04:42 +0000[diff] [blame]1378 llvm::cerr &lt;&lt; *i &lt;&lt; "\n";
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1379</pre>
1380</div>
1381
1382<p>Easy, isn't it? You can also use <tt>InstIterator</tt>s to fill a
Joel Stanleye7be6502002-09-09 15:50:33 +0000[diff] [blame]1383worklist with its initial contents. For example, if you wanted to
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]1384initialize a worklist to contain all instructions in a <tt>Function</tt>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1385F, all you would need to do is something like:</p>
1386
1387<div class="doc_code">
1388<pre>
1389std::set&lt;Instruction*&gt; worklist;
1390worklist.insert(inst_begin(F), inst_end(F));
1391</pre>
1392</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1393
1394<p>The STL set <tt>worklist</tt> would now contain all instructions in the
1395<tt>Function</tt> pointed to by F.</p>
1396
1397</div>
1398
1399<!-- _______________________________________________________________________ -->
1400<div class="doc_subsubsection">
1401 <a name="iterate_convert">Turning an iterator into a class pointer (and
1402 vice-versa)</a>
1403</div>
1404
1405<div class="doc_text">
1406
1407<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]1408instance when all you've got at hand is an iterator. Well, extracting
Chris Lattner69bf8a92004-05-23 21:06:58 +0000[diff] [blame]1409a reference or a pointer from an iterator is very straight-forward.
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]1410Assuming that <tt>i</tt> is a <tt>BasicBlock::iterator</tt> and <tt>j</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1411is a <tt>BasicBlock::const_iterator</tt>:</p>
1412
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1413<div class="doc_code">
1414<pre>
Bill Wendling82e2eea2006-10-11 18:00:22 +0000[diff] [blame]1415Instruction&amp; inst = *i; // <i>Grab reference to instruction reference</i>
1416Instruction* pinst = &amp;*i; // <i>Grab pointer to instruction reference</i>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1417const Instruction&amp; inst = *j;
1418</pre>
1419</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1420
1421<p>However, the iterators you'll be working with in the LLVM framework are
1422special: they will automatically convert to a ptr-to-instance type whenever they
1423need to. Instead of dereferencing the iterator and then taking the address of
1424the result, you can simply assign the iterator to the proper pointer type and
1425you get the dereference and address-of operation as a result of the assignment
1426(behind the scenes, this is a result of overloading casting mechanisms). Thus
1427the last line of the last example,</p>
1428
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1429<div class="doc_code">
1430<pre>
1431Instruction* pinst = &amp;*i;
1432</pre>
1433</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1434
1435<p>is semantically equivalent to</p>
1436
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1437<div class="doc_code">
1438<pre>
1439Instruction* pinst = i;
1440</pre>
1441</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1442
Chris Lattner69bf8a92004-05-23 21:06:58 +0000[diff] [blame]1443<p>It's also possible to turn a class pointer into the corresponding iterator,
1444and this is a constant time operation (very efficient). The following code
1445snippet illustrates use of the conversion constructors provided by LLVM
1446iterators. By using these, you can explicitly grab the iterator of something
1447without actually obtaining it via iteration over some structure:</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1448
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1449<div class="doc_code">
1450<pre>
1451void printNextInstruction(Instruction* inst) {
1452 BasicBlock::iterator it(inst);
Bill Wendling82e2eea2006-10-11 18:00:22 +0000[diff] [blame]1453 ++it; // <i>After this line, it refers to the instruction after *inst</i>
Bill Wendling832171c2006-12-07 20:04:42 +0000[diff] [blame]1454 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]1455}
1456</pre>
1457</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1458
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1459</div>
1460
1461<!--_______________________________________________________________________-->
1462<div class="doc_subsubsection">
1463 <a name="iterate_complex">Finding call sites: a slightly more complex
1464 example</a>
1465</div>
1466
1467<div class="doc_text">
1468
1469<p>Say that you're writing a FunctionPass and would like to count all the
1470locations in the entire module (that is, across every <tt>Function</tt>) where a
1471certain function (i.e., some <tt>Function</tt>*) is already in scope. As you'll
1472learn 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]1473much more straight-forward manner, but this example will allow us to explore how
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1474you'd do it if you didn't have <tt>InstVisitor</tt> around. In pseudocode, this
1475is what we want to do:</p>
1476
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1477<div class="doc_code">
1478<pre>
1479initialize callCounter to zero
1480for each Function f in the Module
1481 for each BasicBlock b in f
1482 for each Instruction i in b
1483 if (i is a CallInst and calls the given function)
1484 increment callCounter
1485</pre>
1486</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1487
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1488<p>And the actual code is (remember, because we're writing a
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1489<tt>FunctionPass</tt>, our <tt>FunctionPass</tt>-derived class simply has to
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1490override the <tt>runOnFunction</tt> method):</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1491
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1492<div class="doc_code">
1493<pre>
1494Function* targetFunc = ...;
1495
1496class OurFunctionPass : public FunctionPass {
1497 public:
1498 OurFunctionPass(): callCounter(0) { }
1499
1500 virtual runOnFunction(Function&amp; F) {
1501 for (Function::iterator b = F.begin(), be = F.end(); b != be; ++b) {
1502 for (BasicBlock::iterator i = b-&gt;begin(); ie = b-&gt;end(); i != ie; ++i) {
1503 if (<a href="#CallInst">CallInst</a>* callInst = <a href="#isa">dyn_cast</a>&lt;<a
1504 href="#CallInst">CallInst</a>&gt;(&amp;*i)) {
Bill Wendling82e2eea2006-10-11 18:00:22 +0000[diff] [blame]1505 // <i>We know we've encountered a call instruction, so we</i>
1506 // <i>need to determine if it's a call to the</i>
1507 // <i>function pointed to by m_func or not</i>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1508
1509 if (callInst-&gt;getCalledFunction() == targetFunc)
1510 ++callCounter;
1511 }
1512 }
1513 }
Bill Wendling82e2eea2006-10-11 18:00:22 +0000[diff] [blame]1514 }
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1515
1516 private:
1517 unsigned callCounter;
1518};
1519</pre>
1520</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1521
1522</div>
1523
Brian Gaekef1972c62003-11-07 19:25:45 +0000[diff] [blame]1524<!--_______________________________________________________________________-->
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1525<div class="doc_subsubsection">
1526 <a name="calls_and_invokes">Treating calls and invokes the same way</a>
1527</div>
1528
1529<div class="doc_text">
1530
1531<p>You may have noticed that the previous example was a bit oversimplified in
1532that it did not deal with call sites generated by 'invoke' instructions. In
1533this, and in other situations, you may find that you want to treat
1534<tt>CallInst</tt>s and <tt>InvokeInst</tt>s the same way, even though their
1535most-specific common base class is <tt>Instruction</tt>, which includes lots of
1536less closely-related things. For these cases, LLVM provides a handy wrapper
1537class called <a
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]1538href="http://llvm.org/doxygen/classllvm_1_1CallSite.html"><tt>CallSite</tt></a>.
Chris Lattner69bf8a92004-05-23 21:06:58 +0000[diff] [blame]1539It is essentially a wrapper around an <tt>Instruction</tt> pointer, with some
1540methods that provide functionality common to <tt>CallInst</tt>s and
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1541<tt>InvokeInst</tt>s.</p>
1542
Chris Lattner69bf8a92004-05-23 21:06:58 +0000[diff] [blame]1543<p>This class has "value semantics": it should be passed by value, not by
1544reference and it should not be dynamically allocated or deallocated using
1545<tt>operator new</tt> or <tt>operator delete</tt>. It is efficiently copyable,
1546assignable and constructable, with costs equivalents to that of a bare pointer.
1547If you look at its definition, it has only a single pointer member.</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1548
1549</div>
1550
Chris Lattner1a3105b2002-09-09 05:49:39 +0000[diff] [blame]1551<!--_______________________________________________________________________-->
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1552<div class="doc_subsubsection">
1553 <a name="iterate_chains">Iterating over def-use &amp; use-def chains</a>
1554</div>
1555
1556<div class="doc_text">
1557
1558<p>Frequently, we might have an instance of the <a
Chris Lattner00815172007-01-04 22:01:45 +0000[diff] [blame]1559href="/doxygen/classllvm_1_1Value.html">Value Class</a> and we want to
Misha Brukman384047f2004-06-03 23:29:12 +0000[diff] [blame]1560determine which <tt>User</tt>s use the <tt>Value</tt>. The list of all
1561<tt>User</tt>s of a particular <tt>Value</tt> is called a <i>def-use</i> chain.
1562For example, let's say we have a <tt>Function*</tt> named <tt>F</tt> to a
1563particular function <tt>foo</tt>. Finding all of the instructions that
1564<i>use</i> <tt>foo</tt> is as simple as iterating over the <i>def-use</i> chain
1565of <tt>F</tt>:</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1566
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1567<div class="doc_code">
1568<pre>
1569Function* F = ...;
1570
Bill Wendling82e2eea2006-10-11 18:00:22 +0000[diff] [blame]1571for (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]1572 if (Instruction *Inst = dyn_cast&lt;Instruction&gt;(*i)) {
Bill Wendling832171c2006-12-07 20:04:42 +0000[diff] [blame]1573 llvm::cerr &lt;&lt; "F is used in instruction:\n";
1574 llvm::cerr &lt;&lt; *Inst &lt;&lt; "\n";
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1575 }
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1576</pre>
1577</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1578
1579<p>Alternately, it's common to have an instance of the <a
Misha Brukman384047f2004-06-03 23:29:12 +0000[diff] [blame]1580href="/doxygen/classllvm_1_1User.html">User Class</a> and need to know what
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1581<tt>Value</tt>s are used by it. The list of all <tt>Value</tt>s used by a
1582<tt>User</tt> is known as a <i>use-def</i> chain. Instances of class
1583<tt>Instruction</tt> are common <tt>User</tt>s, so we might want to iterate over
1584all of the values that a particular instruction uses (that is, the operands of
1585the particular <tt>Instruction</tt>):</p>
1586
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1587<div class="doc_code">
1588<pre>
1589Instruction* pi = ...;
1590
1591for (User::op_iterator i = pi-&gt;op_begin(), e = pi-&gt;op_end(); i != e; ++i) {
1592 Value* v = *i;
Bill Wendling82e2eea2006-10-11 18:00:22 +0000[diff] [blame]1593 // <i>...</i>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1594}
1595</pre>
1596</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1597
Chris Lattner1a3105b2002-09-09 05:49:39 +0000[diff] [blame]1598<!--
1599 def-use chains ("finding all users of"): Value::use_begin/use_end
1600 use-def chains ("finding all values used"): User::op_begin/op_end [op=operand]
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1601-->
1602
1603</div>
1604
1605<!-- ======================================================================= -->
1606<div class="doc_subsection">
1607 <a name="simplechanges">Making simple changes</a>
1608</div>
1609
1610<div class="doc_text">
1611
1612<p>There are some primitive transformation operations present in the LLVM
Joel Stanley753eb712002-09-11 22:32:24 +0000[diff] [blame]1613infrastructure that are worth knowing about. When performing
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]1614transformations, it's fairly common to manipulate the contents of basic
1615blocks. This section describes some of the common methods for doing so
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1616and gives example code.</p>
1617
1618</div>
1619
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]1620<!--_______________________________________________________________________-->
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1621<div class="doc_subsubsection">
1622 <a name="schanges_creating">Creating and inserting new
1623 <tt>Instruction</tt>s</a>
1624</div>
1625
1626<div class="doc_text">
1627
1628<p><i>Instantiating Instructions</i></p>
1629
Chris Lattner69bf8a92004-05-23 21:06:58 +0000[diff] [blame]1630<p>Creation of <tt>Instruction</tt>s is straight-forward: simply call the
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1631constructor for the kind of instruction to instantiate and provide the necessary
1632parameters. For example, an <tt>AllocaInst</tt> only <i>requires</i> a
1633(const-ptr-to) <tt>Type</tt>. Thus:</p>
1634
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1635<div class="doc_code">
1636<pre>
1637AllocaInst* ai = new AllocaInst(Type::IntTy);
1638</pre>
1639</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1640
1641<p>will create an <tt>AllocaInst</tt> instance that represents the allocation of
1642one integer in the current stack frame, at runtime. Each <tt>Instruction</tt>
1643subclass is likely to have varying default parameters which change the semantics
1644of the instruction, so refer to the <a
Misha Brukman31ca1de2004-06-03 23:35:54 +0000[diff] [blame]1645href="/doxygen/classllvm_1_1Instruction.html">doxygen documentation for the subclass of
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1646Instruction</a> that you're interested in instantiating.</p>
1647
1648<p><i>Naming values</i></p>
1649
1650<p>It is very useful to name the values of instructions when you're able to, as
1651this facilitates the debugging of your transformations. If you end up looking
1652at generated LLVM machine code, you definitely want to have logical names
1653associated with the results of instructions! By supplying a value for the
1654<tt>Name</tt> (default) parameter of the <tt>Instruction</tt> constructor, you
1655associate a logical name with the result of the instruction's execution at
1656runtime. For example, say that I'm writing a transformation that dynamically
1657allocates space for an integer on the stack, and that integer is going to be
1658used as some kind of index by some other code. To accomplish this, I place an
1659<tt>AllocaInst</tt> at the first point in the first <tt>BasicBlock</tt> of some
1660<tt>Function</tt>, and I'm intending to use it within the same
1661<tt>Function</tt>. I might do:</p>
1662
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1663<div class="doc_code">
1664<pre>
1665AllocaInst* pa = new AllocaInst(Type::IntTy, 0, "indexLoc");
1666</pre>
1667</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1668
1669<p>where <tt>indexLoc</tt> is now the logical name of the instruction's
1670execution value, which is a pointer to an integer on the runtime stack.</p>
1671
1672<p><i>Inserting instructions</i></p>
1673
1674<p>There are essentially two ways to insert an <tt>Instruction</tt>
1675into an existing sequence of instructions that form a <tt>BasicBlock</tt>:</p>
1676
Joel Stanley9dd1ad62002-09-18 03:17:23 +0000[diff] [blame]1677<ul>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1678 <li>Insertion into an explicit instruction list
1679
1680 <p>Given a <tt>BasicBlock* pb</tt>, an <tt>Instruction* pi</tt> within that
1681 <tt>BasicBlock</tt>, and a newly-created instruction we wish to insert
1682 before <tt>*pi</tt>, we do the following: </p>
1683
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1684<div class="doc_code">
1685<pre>
1686BasicBlock *pb = ...;
1687Instruction *pi = ...;
1688Instruction *newInst = new Instruction(...);
1689
Bill Wendling82e2eea2006-10-11 18:00:22 +0000[diff] [blame]1690pb-&gt;getInstList().insert(pi, newInst); // <i>Inserts newInst before pi in pb</i>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1691</pre>
1692</div>
Alkis Evlogimenos9a5dc4f2004-05-27 00:57:51 +0000[diff] [blame]1693
1694 <p>Appending to the end of a <tt>BasicBlock</tt> is so common that
1695 the <tt>Instruction</tt> class and <tt>Instruction</tt>-derived
1696 classes provide constructors which take a pointer to a
1697 <tt>BasicBlock</tt> to be appended to. For example code that
1698 looked like: </p>
1699
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1700<div class="doc_code">
1701<pre>
1702BasicBlock *pb = ...;
1703Instruction *newInst = new Instruction(...);
1704
Bill Wendling82e2eea2006-10-11 18:00:22 +0000[diff] [blame]1705pb-&gt;getInstList().push_back(newInst); // <i>Appends newInst to pb</i>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1706</pre>
1707</div>
Alkis Evlogimenos9a5dc4f2004-05-27 00:57:51 +0000[diff] [blame]1708
1709 <p>becomes: </p>
1710
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1711<div class="doc_code">
1712<pre>
1713BasicBlock *pb = ...;
1714Instruction *newInst = new Instruction(..., pb);
1715</pre>
1716</div>
Alkis Evlogimenos9a5dc4f2004-05-27 00:57:51 +0000[diff] [blame]1717
1718 <p>which is much cleaner, especially if you are creating
1719 long instruction streams.</p></li>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1720
1721 <li>Insertion into an implicit instruction list
1722
1723 <p><tt>Instruction</tt> instances that are already in <tt>BasicBlock</tt>s
1724 are implicitly associated with an existing instruction list: the instruction
1725 list of the enclosing basic block. Thus, we could have accomplished the same
1726 thing as the above code without being given a <tt>BasicBlock</tt> by doing:
1727 </p>
1728
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1729<div class="doc_code">
1730<pre>
1731Instruction *pi = ...;
1732Instruction *newInst = new Instruction(...);
1733
1734pi-&gt;getParent()-&gt;getInstList().insert(pi, newInst);
1735</pre>
1736</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1737
1738 <p>In fact, this sequence of steps occurs so frequently that the
1739 <tt>Instruction</tt> class and <tt>Instruction</tt>-derived classes provide
1740 constructors which take (as a default parameter) a pointer to an
1741 <tt>Instruction</tt> which the newly-created <tt>Instruction</tt> should
1742 precede. That is, <tt>Instruction</tt> constructors are capable of
1743 inserting the newly-created instance into the <tt>BasicBlock</tt> of a
1744 provided instruction, immediately before that instruction. Using an
1745 <tt>Instruction</tt> constructor with a <tt>insertBefore</tt> (default)
1746 parameter, the above code becomes:</p>
1747
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1748<div class="doc_code">
1749<pre>
1750Instruction* pi = ...;
1751Instruction* newInst = new Instruction(..., pi);
1752</pre>
1753</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1754
1755 <p>which is much cleaner, especially if you're creating a lot of
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1756 instructions and adding them to <tt>BasicBlock</tt>s.</p></li>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1757</ul>
1758
1759</div>
1760
1761<!--_______________________________________________________________________-->
1762<div class="doc_subsubsection">
1763 <a name="schanges_deleting">Deleting <tt>Instruction</tt>s</a>
1764</div>
1765
1766<div class="doc_text">
1767
1768<p>Deleting an instruction from an existing sequence of instructions that form a
Chris Lattner69bf8a92004-05-23 21:06:58 +0000[diff] [blame]1769<a href="#BasicBlock"><tt>BasicBlock</tt></a> is very straight-forward. First,
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1770you must have a pointer to the instruction that you wish to delete. Second, you
1771need to obtain the pointer to that instruction's basic block. You use the
1772pointer to the basic block to get its list of instructions and then use the
1773erase function to remove your instruction. For example:</p>
1774
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1775<div class="doc_code">
1776<pre>
1777<a href="#Instruction">Instruction</a> *I = .. ;
1778<a href="#BasicBlock">BasicBlock</a> *BB = I-&gt;getParent();
1779
1780BB-&gt;getInstList().erase(I);
1781</pre>
1782</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1783
1784</div>
1785
1786<!--_______________________________________________________________________-->
1787<div class="doc_subsubsection">
1788 <a name="schanges_replacing">Replacing an <tt>Instruction</tt> with another
1789 <tt>Value</tt></a>
1790</div>
1791
1792<div class="doc_text">
1793
1794<p><i>Replacing individual instructions</i></p>
1795
1796<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]1797permits use of two very useful replace functions: <tt>ReplaceInstWithValue</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1798and <tt>ReplaceInstWithInst</tt>.</p>
1799
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]1800<h4><a name="schanges_deleting">Deleting <tt>Instruction</tt>s</a></h4>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1801
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]1802<ul>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1803 <li><tt>ReplaceInstWithValue</tt>
1804
1805 <p>This function replaces all uses (within a basic block) of a given
1806 instruction with a value, and then removes the original instruction. The
1807 following example illustrates the replacement of the result of a particular
Chris Lattner58360822005-01-17 00:12:04 +0000[diff] [blame]1808 <tt>AllocaInst</tt> that allocates memory for a single integer with a null
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1809 pointer to an integer.</p>
1810
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1811<div class="doc_code">
1812<pre>
1813AllocaInst* instToReplace = ...;
1814BasicBlock::iterator ii(instToReplace);
1815
1816ReplaceInstWithValue(instToReplace-&gt;getParent()-&gt;getInstList(), ii,
1817 Constant::getNullValue(PointerType::get(Type::IntTy)));
1818</pre></div></li>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1819
1820 <li><tt>ReplaceInstWithInst</tt>
1821
1822 <p>This function replaces a particular instruction with another
1823 instruction. The following example illustrates the replacement of one
1824 <tt>AllocaInst</tt> with another.</p>
1825
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1826<div class="doc_code">
1827<pre>
1828AllocaInst* instToReplace = ...;
1829BasicBlock::iterator ii(instToReplace);
1830
1831ReplaceInstWithInst(instToReplace-&gt;getParent()-&gt;getInstList(), ii,
1832 new AllocaInst(Type::IntTy, 0, "ptrToReplacedInt"));
1833</pre></div></li>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]1834</ul>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1835
1836<p><i>Replacing multiple uses of <tt>User</tt>s and <tt>Value</tt>s</i></p>
1837
1838<p>You can use <tt>Value::replaceAllUsesWith</tt> and
1839<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]1840doxygen documentation for the <a href="/doxygen/classllvm_1_1Value.html">Value Class</a>
Misha Brukman384047f2004-06-03 23:29:12 +0000[diff] [blame]1841and <a href="/doxygen/classllvm_1_1User.html">User Class</a>, respectively, for more
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1842information.</p>
1843
1844<!-- Value::replaceAllUsesWith User::replaceUsesOfWith Point out:
1845include/llvm/Transforms/Utils/ especially BasicBlockUtils.h with:
1846ReplaceInstWithValue, ReplaceInstWithInst -->
1847
1848</div>
1849
Chris Lattner9355b472002-09-06 02:50:58 +0000[diff] [blame]1850<!-- *********************************************************************** -->
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1851<div class="doc_section">
Chris Lattnerd9d6e102005-04-23 16:10:52 +0000[diff] [blame]1852 <a name="advanced">Advanced Topics</a>
1853</div>
1854<!-- *********************************************************************** -->
1855
1856<div class="doc_text">
Chris Lattnerf1b200b2005-04-23 17:27:36 +0000[diff] [blame]1857<p>
1858This section describes some of the advanced or obscure API's that most clients
1859do not need to be aware of. These API's tend manage the inner workings of the
1860LLVM system, and only need to be accessed in unusual circumstances.
1861</p>
1862</div>
Chris Lattnerd9d6e102005-04-23 16:10:52 +0000[diff] [blame]1863
Chris Lattnerf1b200b2005-04-23 17:27:36 +0000[diff] [blame]1864<!-- ======================================================================= -->
1865<div class="doc_subsection">
1866 <a name="TypeResolve">LLVM Type Resolution</a>
1867</div>
Chris Lattnerd9d6e102005-04-23 16:10:52 +0000[diff] [blame]1868
Chris Lattnerf1b200b2005-04-23 17:27:36 +0000[diff] [blame]1869<div class="doc_text">
1870
1871<p>
1872The LLVM type system has a very simple goal: allow clients to compare types for
1873structural equality with a simple pointer comparison (aka a shallow compare).
1874This goal makes clients much simpler and faster, and is used throughout the LLVM
1875system.
1876</p>
1877
1878<p>
1879Unfortunately achieving this goal is not a simple matter. In particular,
1880recursive types and late resolution of opaque types makes the situation very
1881difficult to handle. Fortunately, for the most part, our implementation makes
1882most clients able to be completely unaware of the nasty internal details. The
1883primary case where clients are exposed to the inner workings of it are when
1884building a recursive type. In addition to this case, the LLVM bytecode reader,
1885assembly parser, and linker also have to be aware of the inner workings of this
1886system.
1887</p>
1888
Chris Lattner0f876db2005-04-25 15:47:57 +0000[diff] [blame]1889<p>
1890For our purposes below, we need three concepts. First, an "Opaque Type" is
1891exactly as defined in the <a href="LangRef.html#t_opaque">language
1892reference</a>. Second an "Abstract Type" is any type which includes an
Reid Spencer06565dc2007-01-12 17:11:23 +0000[diff] [blame]1893opaque type as part of its type graph (for example "<tt>{ opaque, i32 }</tt>").
1894Third, 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]1895float }</tt>").
1896</p>
1897
Chris Lattnerf1b200b2005-04-23 17:27:36 +0000[diff] [blame]1898</div>
1899
1900<!-- ______________________________________________________________________ -->
1901<div class="doc_subsubsection">
1902 <a name="BuildRecType">Basic Recursive Type Construction</a>
1903</div>
1904
1905<div class="doc_text">
1906
1907<p>
1908Because the most common question is "how do I build a recursive type with LLVM",
1909we answer it now and explain it as we go. Here we include enough to cause this
1910to be emitted to an output .ll file:
1911</p>
1912
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1913<div class="doc_code">
Chris Lattnerf1b200b2005-04-23 17:27:36 +0000[diff] [blame]1914<pre>
Reid Spencer06565dc2007-01-12 17:11:23 +0000[diff] [blame]1915%mylist = type { %mylist*, i32 }
Chris Lattnerf1b200b2005-04-23 17:27:36 +0000[diff] [blame]1916</pre>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1917</div>
Chris Lattnerf1b200b2005-04-23 17:27:36 +0000[diff] [blame]1918
1919<p>
1920To build this, use the following LLVM APIs:
1921</p>
1922
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1923<div class="doc_code">
Chris Lattnerf1b200b2005-04-23 17:27:36 +0000[diff] [blame]1924<pre>
Bill Wendling82e2eea2006-10-11 18:00:22 +0000[diff] [blame]1925// <i>Create the initial outer struct</i>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1926<a href="#PATypeHolder">PATypeHolder</a> StructTy = OpaqueType::get();
1927std::vector&lt;const Type*&gt; Elts;
1928Elts.push_back(PointerType::get(StructTy));
1929Elts.push_back(Type::IntTy);
1930StructType *NewSTy = StructType::get(Elts);
Chris Lattnerf1b200b2005-04-23 17:27:36 +0000[diff] [blame]1931
Reid Spencer06565dc2007-01-12 17:11:23 +0000[diff] [blame]1932// <i>At this point, NewSTy = "{ opaque*, i32 }". Tell VMCore that</i>
Bill Wendling82e2eea2006-10-11 18:00:22 +0000[diff] [blame]1933// <i>the struct and the opaque type are actually the same.</i>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1934cast&lt;OpaqueType&gt;(StructTy.get())-&gt;<a href="#refineAbstractTypeTo">refineAbstractTypeTo</a>(NewSTy);
Chris Lattnerf1b200b2005-04-23 17:27:36 +0000[diff] [blame]1935
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1936// <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]1937// <i>kept up-to-date</i>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1938NewSTy = cast&lt;StructType&gt;(StructTy.get());
Chris Lattnerf1b200b2005-04-23 17:27:36 +0000[diff] [blame]1939
Bill Wendling82e2eea2006-10-11 18:00:22 +0000[diff] [blame]1940// <i>Add a name for the type to the module symbol table (optional)</i>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1941MyModule-&gt;addTypeName("mylist", NewSTy);
Chris Lattnerf1b200b2005-04-23 17:27:36 +0000[diff] [blame]1942</pre>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1943</div>
Chris Lattnerf1b200b2005-04-23 17:27:36 +0000[diff] [blame]1944
1945<p>
1946This code shows the basic approach used to build recursive types: build a
1947non-recursive type using 'opaque', then use type unification to close the cycle.
1948The type unification step is performed by the <tt><a
Chris Lattneraff26d12007-02-03 03:06:52 +0000[diff] [blame]1949href="#refineAbstractTypeTo">refineAbstractTypeTo</a></tt> method, which is
Chris Lattnerf1b200b2005-04-23 17:27:36 +0000[diff] [blame]1950described next. After that, we describe the <a
1951href="#PATypeHolder">PATypeHolder class</a>.
1952</p>
1953
1954</div>
1955
1956<!-- ______________________________________________________________________ -->
1957<div class="doc_subsubsection">
1958 <a name="refineAbstractTypeTo">The <tt>refineAbstractTypeTo</tt> method</a>
1959</div>
1960
1961<div class="doc_text">
1962<p>
1963The <tt>refineAbstractTypeTo</tt> method starts the type unification process.
1964While this method is actually a member of the DerivedType class, it is most
1965often used on OpaqueType instances. Type unification is actually a recursive
1966process. After unification, types can become structurally isomorphic to
1967existing types, and all duplicates are deleted (to preserve pointer equality).
1968</p>
1969
1970<p>
1971In the example above, the OpaqueType object is definitely deleted.
Reid Spencer06565dc2007-01-12 17:11:23 +0000[diff] [blame]1972Additionally, if there is an "{ \2*, i32}" type already created in the system,
Chris Lattnerf1b200b2005-04-23 17:27:36 +0000[diff] [blame]1973the pointer and struct type created are <b>also</b> deleted. Obviously whenever
1974a type is deleted, any "Type*" pointers in the program are invalidated. As
1975such, it is safest to avoid having <i>any</i> "Type*" pointers to abstract types
1976live across a call to <tt>refineAbstractTypeTo</tt> (note that non-abstract
1977types can never move or be deleted). To deal with this, the <a
1978href="#PATypeHolder">PATypeHolder</a> class is used to maintain a stable
1979reference to a possibly refined type, and the <a
1980href="#AbstractTypeUser">AbstractTypeUser</a> class is used to update more
1981complex datastructures.
1982</p>
1983
1984</div>
1985
1986<!-- ______________________________________________________________________ -->
1987<div class="doc_subsubsection">
1988 <a name="PATypeHolder">The PATypeHolder Class</a>
1989</div>
1990
1991<div class="doc_text">
1992<p>
1993PATypeHolder is a form of a "smart pointer" for Type objects. When VMCore
1994happily goes about nuking types that become isomorphic to existing types, it
1995automatically updates all PATypeHolder objects to point to the new type. In the
1996example above, this allows the code to maintain a pointer to the resultant
1997resolved recursive type, even though the Type*'s are potentially invalidated.
1998</p>
1999
2000<p>
2001PATypeHolder is an extremely light-weight object that uses a lazy union-find
2002implementation to update pointers. For example the pointer from a Value to its
2003Type is maintained by PATypeHolder objects.
2004</p>
2005
2006</div>
2007
2008<!-- ______________________________________________________________________ -->
2009<div class="doc_subsubsection">
2010 <a name="AbstractTypeUser">The AbstractTypeUser Class</a>
2011</div>
2012
2013<div class="doc_text">
2014
2015<p>
2016Some data structures need more to perform more complex updates when types get
2017resolved. The <a href="#SymbolTable">SymbolTable</a> class, for example, needs
2018move and potentially merge type planes in its representation when a pointer
2019changes.</p>
2020
2021<p>
2022To support this, a class can derive from the AbstractTypeUser class. This class
2023allows it to get callbacks when certain types are resolved. To register to get
2024callbacks for a particular type, the DerivedType::{add/remove}AbstractTypeUser
Chris Lattner0f876db2005-04-25 15:47:57 +0000[diff] [blame]2025methods can be called on a type. Note that these methods only work for <i>
Reid Spencer06565dc2007-01-12 17:11:23 +0000[diff] [blame]2026 abstract</i> types. Concrete types (those that do not include any opaque
2027objects) can never be refined.
Chris Lattnerf1b200b2005-04-23 17:27:36 +0000[diff] [blame]2028</p>
Chris Lattnerd9d6e102005-04-23 16:10:52 +0000[diff] [blame]2029</div>
2030
2031
2032<!-- ======================================================================= -->
2033<div class="doc_subsection">
2034 <a name="SymbolTable">The <tt>SymbolTable</tt> class</a>
2035</div>
Chris Lattnerf1b200b2005-04-23 17:27:36 +0000[diff] [blame]2036
Chris Lattnerd9d6e102005-04-23 16:10:52 +0000[diff] [blame]2037<div class="doc_text">
2038<p>This class provides a symbol table that the <a
2039href="#Function"><tt>Function</tt></a> and <a href="#Module">
2040<tt>Module</tt></a> classes use for naming definitions. The symbol table can
Reid Spencera6362242007-01-07 00:41:39 +0000[diff] [blame]2041provide a name for any <a href="#Value"><tt>Value</tt></a>.
2042<tt>SymbolTable</tt> is an abstract data type. It hides the data it contains
2043and provides access to it through a controlled interface.</p>
Chris Lattnerd9d6e102005-04-23 16:10:52 +0000[diff] [blame]2044
Reid Spencera6362242007-01-07 00:41:39 +0000[diff] [blame]2045<p>Note that the <tt>SymbolTable</tt> class should not be directly accessed
2046by most clients. It should only be used when iteration over the symbol table
2047names themselves are required, which is very special purpose. Note that not
2048all LLVM
Chris Lattnerd9d6e102005-04-23 16:10:52 +0000[diff] [blame]2049<a href="#Value">Value</a>s have names, and those without names (i.e. they have
2050an empty name) do not exist in the symbol table.
2051</p>
2052
2053<p>To use the <tt>SymbolTable</tt> well, you need to understand the
2054structure of the information it holds. The class contains two
2055<tt>std::map</tt> objects. The first, <tt>pmap</tt>, is a map of
2056<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]2057Thus, Values are stored in two-dimensions and accessed by <tt>Type</tt> and
2058name.</p>
Chris Lattnerd9d6e102005-04-23 16:10:52 +0000[diff] [blame]2059
2060<p>The interface of this class provides three basic types of operations:
2061<ol>
2062 <li><em>Accessors</em>. Accessors provide read-only access to information
2063 such as finding a value for a name with the
2064 <a href="#SymbolTable_lookup">lookup</a> method.</li>
2065 <li><em>Mutators</em>. Mutators allow the user to add information to the
2066 <tt>SymbolTable</tt> with methods like
2067 <a href="#SymbolTable_insert"><tt>insert</tt></a>.</li>
2068 <li><em>Iterators</em>. Iterators allow the user to traverse the content
2069 of the symbol table in well defined ways, such as the method
Reid Spencera6362242007-01-07 00:41:39 +0000[diff] [blame]2070 <a href="#SymbolTable_plane_begin"><tt>plane_begin</tt></a>.</li>
Chris Lattnerd9d6e102005-04-23 16:10:52 +0000[diff] [blame]2071</ol>
2072
2073<h3>Accessors</h3>
2074<dl>
2075 <dt><tt>Value* lookup(const Type* Ty, const std::string&amp; name) const</tt>:
2076 </dt>
2077 <dd>The <tt>lookup</tt> method searches the type plane given by the
2078 <tt>Ty</tt> parameter for a <tt>Value</tt> with the provided <tt>name</tt>.
2079 If a suitable <tt>Value</tt> is not found, null is returned.</dd>
2080
Chris Lattnerd9d6e102005-04-23 16:10:52 +0000[diff] [blame]2081 <dt><tt>bool isEmpty() const</tt>:</dt>
2082 <dd>This function returns true if both the value and types maps are
2083 empty</dd>
2084</dl>
2085
2086<h3>Mutators</h3>
2087<dl>
2088 <dt><tt>void insert(Value *Val)</tt>:</dt>
2089 <dd>This method adds the provided value to the symbol table. The Value must
2090 have both a name and a type which are extracted and used to place the value
2091 in the correct type plane under the value's name.</dd>
2092
2093 <dt><tt>void insert(const std::string&amp; Name, Value *Val)</tt>:</dt>
2094 <dd> Inserts a constant or type into the symbol table with the specified
2095 name. There can be a many to one mapping between names and constants
2096 or types.</dd>
2097
Chris Lattnerd9d6e102005-04-23 16:10:52 +0000[diff] [blame]2098 <dt><tt>void remove(Value* Val)</tt>:</dt>
2099 <dd> This method removes a named value from the symbol table. The
2100 type and name of the Value are extracted from \p N and used to
2101 lookup the Value in the correct type plane. If the Value is
2102 not in the symbol table, this method silently ignores the
2103 request.</dd>
2104
Chris Lattnerd9d6e102005-04-23 16:10:52 +0000[diff] [blame]2105 <dt><tt>Value* remove(const std::string&amp; Name, Value *Val)</tt>:</dt>
2106 <dd> Remove a constant or type with the specified name from the
2107 symbol table.</dd>
2108
Reid Spencera6362242007-01-07 00:41:39 +0000[diff] [blame]2109 <dt><tt>Value *remove(const value_iterator&amp; It)</tt>:</dt>
Chris Lattnerd9d6e102005-04-23 16:10:52 +0000[diff] [blame]2110 <dd> Removes a specific value from the symbol table.
2111 Returns the removed value.</dd>
2112
2113 <dt><tt>bool strip()</tt>:</dt>
2114 <dd> This method will strip the symbol table of its names leaving
2115 the type and values. </dd>
2116
2117 <dt><tt>void clear()</tt>:</dt>
2118 <dd>Empty the symbol table completely.</dd>
2119</dl>
2120
2121<h3>Iteration</h3>
2122<p>The following functions describe three types of iterators you can obtain
2123the beginning or end of the sequence for both const and non-const. It is
2124important to keep track of the different kinds of iterators. There are
2125three idioms worth pointing out:</p>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2126
Chris Lattnerd9d6e102005-04-23 16:10:52 +0000[diff] [blame]2127<table>
2128 <tr><th>Units</th><th>Iterator</th><th>Idiom</th></tr>
2129 <tr>
2130 <td align="left">Planes Of name/Value maps</td><td>PI</td>
2131 <td align="left"><pre><tt>
2132for (SymbolTable::plane_const_iterator PI = ST.plane_begin(),
2133 PE = ST.plane_end(); PI != PE; ++PI ) {
Bill Wendling82e2eea2006-10-11 18:00:22 +0000[diff] [blame]2134 PI-&gt;first // <i>This is the Type* of the plane</i>
2135 PI-&gt;second // <i>This is the SymbolTable::ValueMap of name/Value pairs</i>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2136}
Chris Lattnerd9d6e102005-04-23 16:10:52 +0000[diff] [blame]2137 </tt></pre></td>
2138 </tr>
2139 <tr>
Chris Lattnerd9d6e102005-04-23 16:10:52 +0000[diff] [blame]2140 <td align="left">name/Value pairs in a plane</td><td>VI</td>
2141 <td align="left"><pre><tt>
2142for (SymbolTable::value_const_iterator VI = ST.value_begin(SomeType),
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2143 VE = ST.value_end(SomeType); VI != VE; ++VI ) {
Bill Wendling82e2eea2006-10-11 18:00:22 +0000[diff] [blame]2144 VI-&gt;first // <i>This is the name of the Value</i>
2145 VI-&gt;second // <i>This is the Value* value associated with the name</i>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2146}
Chris Lattnerd9d6e102005-04-23 16:10:52 +0000[diff] [blame]2147 </tt></pre></td>
2148 </tr>
2149</table>
2150
2151<p>Using the recommended iterator names and idioms will help you avoid
2152making mistakes. Of particular note, make sure that whenever you use
2153value_begin(SomeType) that you always compare the resulting iterator
2154with value_end(SomeType) not value_end(SomeOtherType) or else you
2155will loop infinitely.</p>
2156
2157<dl>
2158
2159 <dt><tt>plane_iterator plane_begin()</tt>:</dt>
2160 <dd>Get an iterator that starts at the beginning of the type planes.
2161 The iterator will iterate over the Type/ValueMap pairs in the
2162 type planes. </dd>
2163
2164 <dt><tt>plane_const_iterator plane_begin() const</tt>:</dt>
2165 <dd>Get a const_iterator that starts at the beginning of the type
2166 planes. The iterator will iterate over the Type/ValueMap pairs
2167 in the type planes. </dd>
2168
2169 <dt><tt>plane_iterator plane_end()</tt>:</dt>
2170 <dd>Get an iterator at the end of the type planes. This serves as
2171 the marker for end of iteration over the type planes.</dd>
2172
2173 <dt><tt>plane_const_iterator plane_end() const</tt>:</dt>
2174 <dd>Get a const_iterator at the end of the type planes. This serves as
2175 the marker for end of iteration over the type planes.</dd>
2176
2177 <dt><tt>value_iterator value_begin(const Type *Typ)</tt>:</dt>
2178 <dd>Get an iterator that starts at the beginning of a type plane.
2179 The iterator will iterate over the name/value pairs in the type plane.
2180 Note: The type plane must already exist before using this.</dd>
2181
2182 <dt><tt>value_const_iterator value_begin(const Type *Typ) const</tt>:</dt>
2183 <dd>Get a const_iterator that starts at the beginning of a type plane.
2184 The iterator will iterate over the name/value pairs in the type plane.
2185 Note: The type plane must already exist before using this.</dd>
2186
2187 <dt><tt>value_iterator value_end(const Type *Typ)</tt>:</dt>
2188 <dd>Get an iterator to the end of a type plane. This serves as the marker
2189 for end of iteration of the type plane.
2190 Note: The type plane must already exist before using this.</dd>
2191
2192 <dt><tt>value_const_iterator value_end(const Type *Typ) const</tt>:</dt>
2193 <dd>Get a const_iterator to the end of a type plane. This serves as the
2194 marker for end of iteration of the type plane.
2195 Note: the type plane must already exist before using this.</dd>
2196
Chris Lattnerd9d6e102005-04-23 16:10:52 +0000[diff] [blame]2197 <dt><tt>plane_const_iterator find(const Type* Typ ) const</tt>:</dt>
2198 <dd>This method returns a plane_const_iterator for iteration over
2199 the type planes starting at a specific plane, given by \p Ty.</dd>
2200
2201 <dt><tt>plane_iterator find( const Type* Typ </tt>:</dt>
2202 <dd>This method returns a plane_iterator for iteration over the
2203 type planes starting at a specific plane, given by \p Ty.</dd>
2204
2205</dl>
2206</div>
2207
2208
2209
2210<!-- *********************************************************************** -->
2211<div class="doc_section">
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2212 <a name="coreclasses">The Core LLVM Class Hierarchy Reference </a>
2213</div>
2214<!-- *********************************************************************** -->
2215
2216<div class="doc_text">
Reid Spencer303c4b42007-01-12 17:26:25 +0000[diff] [blame]2217<p><tt>#include "<a href="/doxygen/Type_8h-source.html">llvm/Type.h</a>"</tt>
2218<br>doxygen info: <a href="/doxygen/classllvm_1_1Type.html">Type Class</a></p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2219
2220<p>The Core LLVM classes are the primary means of representing the program
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]2221being inspected or transformed. The core LLVM classes are defined in
2222header files in the <tt>include/llvm/</tt> directory, and implemented in
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2223the <tt>lib/VMCore</tt> directory.</p>
2224
2225</div>
2226
2227<!-- ======================================================================= -->
2228<div class="doc_subsection">
Reid Spencer303c4b42007-01-12 17:26:25 +0000[diff] [blame]2229 <a name="Type">The <tt>Type</tt> class and Derived Types</a>
2230</div>
2231
2232<div class="doc_text">
2233
2234 <p><tt>Type</tt> is a superclass of all type classes. Every <tt>Value</tt> has
2235 a <tt>Type</tt>. <tt>Type</tt> cannot be instantiated directly but only
2236 through its subclasses. Certain primitive types (<tt>VoidType</tt>,
2237 <tt>LabelType</tt>, <tt>FloatType</tt> and <tt>DoubleType</tt>) have hidden
2238 subclasses. They are hidden because they offer no useful functionality beyond
2239 what the <tt>Type</tt> class offers except to distinguish themselves from
2240 other subclasses of <tt>Type</tt>.</p>
2241 <p>All other types are subclasses of <tt>DerivedType</tt>. Types can be
2242 named, but this is not a requirement. There exists exactly
2243 one instance of a given shape at any one time. This allows type equality to
2244 be performed with address equality of the Type Instance. That is, given two
2245 <tt>Type*</tt> values, the types are identical if the pointers are identical.
2246 </p>
2247</div>
2248
2249<!-- _______________________________________________________________________ -->
2250<div class="doc_subsubsection">
2251 <a name="m_Value">Important Public Methods</a>
2252</div>
2253
2254<div class="doc_text">
2255
2256<ul>
Chris Lattner8f79df32007-01-15 01:55:32 +0000[diff] [blame]2257 <li><tt>bool isInteger() const</tt>: Returns true for any integer type.</li>
Reid Spencer303c4b42007-01-12 17:26:25 +0000[diff] [blame]2258
2259 <li><tt>bool isFloatingPoint()</tt>: Return true if this is one of the two
2260 floating point types.</li>
2261
2262 <li><tt>bool isAbstract()</tt>: Return true if the type is abstract (contains
2263 an OpaqueType anywhere in its definition).</li>
2264
2265 <li><tt>bool isSized()</tt>: Return true if the type has known size. Things
2266 that don't have a size are abstract types, labels and void.</li>
2267
2268</ul>
2269</div>
2270
2271<!-- _______________________________________________________________________ -->
2272<div class="doc_subsubsection">
2273 <a name="m_Value">Important Derived Types</a>
2274</div>
2275<div class="doc_text">
2276<dl>
2277 <dt><tt>IntegerType</tt></dt>
2278 <dd>Subclass of DerivedType that represents integer types of any bit width.
2279 Any bit width between <tt>IntegerType::MIN_INT_BITS</tt> (1) and
2280 <tt>IntegerType::MAX_INT_BITS</tt> (~8 million) can be represented.
2281 <ul>
2282 <li><tt>static const IntegerType* get(unsigned NumBits)</tt>: get an integer
2283 type of a specific bit width.</li>
2284 <li><tt>unsigned getBitWidth() const</tt>: Get the bit width of an integer
2285 type.</li>
2286 </ul>
2287 </dd>
2288 <dt><tt>SequentialType</tt></dt>
2289 <dd>This is subclassed by ArrayType and PointerType
2290 <ul>
2291 <li><tt>const Type * getElementType() const</tt>: Returns the type of each
2292 of the elements in the sequential type. </li>
2293 </ul>
2294 </dd>
2295 <dt><tt>ArrayType</tt></dt>
2296 <dd>This is a subclass of SequentialType and defines the interface for array
2297 types.
2298 <ul>
2299 <li><tt>unsigned getNumElements() const</tt>: Returns the number of
2300 elements in the array. </li>
2301 </ul>
2302 </dd>
2303 <dt><tt>PointerType</tt></dt>
Chris Lattner302da1e2007-02-03 03:05:57 +0000[diff] [blame]2304 <dd>Subclass of SequentialType for pointer types.</dd>
Reid Spencer303c4b42007-01-12 17:26:25 +0000[diff] [blame]2305 <dt><tt>PackedType</tt></dt>
2306 <dd>Subclass of SequentialType for packed (vector) types. A
2307 packed type is similar to an ArrayType but is distinguished because it is
2308 a first class type wherease ArrayType is not. Packed types are used for
2309 vector operations and are usually small vectors of of an integer or floating
2310 point type.</dd>
2311 <dt><tt>StructType</tt></dt>
2312 <dd>Subclass of DerivedTypes for struct types.</dd>
2313 <dt><tt>FunctionType</tt></dt>
2314 <dd>Subclass of DerivedTypes for function types.
2315 <ul>
2316 <li><tt>bool isVarArg() const</tt>: Returns true if its a vararg
2317 function</li>
2318 <li><tt> const Type * getReturnType() const</tt>: Returns the
2319 return type of the function.</li>
2320 <li><tt>const Type * getParamType (unsigned i)</tt>: Returns
2321 the type of the ith parameter.</li>
2322 <li><tt> const unsigned getNumParams() const</tt>: Returns the
2323 number of formal parameters.</li>
2324 </ul>
2325 </dd>
2326 <dt><tt>OpaqueType</tt></dt>
2327 <dd>Sublcass of DerivedType for abstract types. This class
2328 defines no content and is used as a placeholder for some other type. Note
2329 that OpaqueType is used (temporarily) during type resolution for forward
2330 references of types. Once the referenced type is resolved, the OpaqueType
2331 is replaced with the actual type. OpaqueType can also be used for data
2332 abstraction. At link time opaque types can be resolved to actual types
2333 of the same name.</dd>
2334</dl>
2335</div>
2336
2337<!-- ======================================================================= -->
2338<div class="doc_subsection">
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2339 <a name="Value">The <tt>Value</tt> class</a>
2340</div>
2341
2342<div>
2343
2344<p><tt>#include "<a href="/doxygen/Value_8h-source.html">llvm/Value.h</a>"</tt>
2345<br>
Chris Lattner00815172007-01-04 22:01:45 +0000[diff] [blame]2346doxygen info: <a href="/doxygen/classllvm_1_1Value.html">Value Class</a></p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2347
2348<p>The <tt>Value</tt> class is the most important class in the LLVM Source
2349base. It represents a typed value that may be used (among other things) as an
2350operand to an instruction. There are many different types of <tt>Value</tt>s,
2351such as <a href="#Constant"><tt>Constant</tt></a>s,<a
2352href="#Argument"><tt>Argument</tt></a>s. Even <a
2353href="#Instruction"><tt>Instruction</tt></a>s and <a
2354href="#Function"><tt>Function</tt></a>s are <tt>Value</tt>s.</p>
2355
2356<p>A particular <tt>Value</tt> may be used many times in the LLVM representation
2357for a program. For example, an incoming argument to a function (represented
2358with an instance of the <a href="#Argument">Argument</a> class) is "used" by
2359every instruction in the function that references the argument. To keep track
2360of this relationship, the <tt>Value</tt> class keeps a list of all of the <a
2361href="#User"><tt>User</tt></a>s that is using it (the <a
2362href="#User"><tt>User</tt></a> class is a base class for all nodes in the LLVM
2363graph that can refer to <tt>Value</tt>s). This use list is how LLVM represents
2364def-use information in the program, and is accessible through the <tt>use_</tt>*
2365methods, shown below.</p>
2366
2367<p>Because LLVM is a typed representation, every LLVM <tt>Value</tt> is typed,
2368and this <a href="#Type">Type</a> is available through the <tt>getType()</tt>
2369method. In addition, all LLVM values can be named. The "name" of the
2370<tt>Value</tt> is a symbolic string printed in the LLVM code:</p>
2371
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2372<div class="doc_code">
2373<pre>
Reid Spencer06565dc2007-01-12 17:11:23 +0000[diff] [blame]2374%<b>foo</b> = add i32 1, 2
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2375</pre>
2376</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2377
2378<p><a name="#nameWarning">The name of this instruction is "foo".</a> <b>NOTE</b>
2379that the name of any value may be missing (an empty string), so names should
2380<b>ONLY</b> be used for debugging (making the source code easier to read,
2381debugging printouts), they should not be used to keep track of values or map
2382between them. For this purpose, use a <tt>std::map</tt> of pointers to the
2383<tt>Value</tt> itself instead.</p>
2384
2385<p>One important aspect of LLVM is that there is no distinction between an SSA
2386variable and the operation that produces it. Because of this, any reference to
2387the value produced by an instruction (or the value available as an incoming
Chris Lattnerd5fc4fc2004-03-18 14:58:55 +0000[diff] [blame]2388argument, for example) is represented as a direct pointer to the instance of
2389the class that
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2390represents this value. Although this may take some getting used to, it
2391simplifies the representation and makes it easier to manipulate.</p>
2392
2393</div>
2394
2395<!-- _______________________________________________________________________ -->
2396<div class="doc_subsubsection">
2397 <a name="m_Value">Important Public Members of the <tt>Value</tt> class</a>
2398</div>
2399
2400<div class="doc_text">
2401
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]2402<ul>
2403 <li><tt>Value::use_iterator</tt> - Typedef for iterator over the
2404use-list<br>
2405 <tt>Value::use_const_iterator</tt> - Typedef for const_iterator over
2406the use-list<br>
2407 <tt>unsigned use_size()</tt> - Returns the number of users of the
2408value.<br>
Chris Lattner9355b472002-09-06 02:50:58 +0000[diff] [blame]2409 <tt>bool use_empty()</tt> - Returns true if there are no users.<br>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]2410 <tt>use_iterator use_begin()</tt> - Get an iterator to the start of
2411the use-list.<br>
2412 <tt>use_iterator use_end()</tt> - Get an iterator to the end of the
2413use-list.<br>
2414 <tt><a href="#User">User</a> *use_back()</tt> - Returns the last
2415element in the list.
2416 <p> These methods are the interface to access the def-use
2417information in LLVM. As with all other iterators in LLVM, the naming
2418conventions follow the conventions defined by the <a href="#stl">STL</a>.</p>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]2419 </li>
2420 <li><tt><a href="#Type">Type</a> *getType() const</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2421 <p>This method returns the Type of the Value.</p>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]2422 </li>
2423 <li><tt>bool hasName() const</tt><br>
Chris Lattner9355b472002-09-06 02:50:58 +0000[diff] [blame]2424 <tt>std::string getName() const</tt><br>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]2425 <tt>void setName(const std::string &amp;Name)</tt>
2426 <p> This family of methods is used to access and assign a name to a <tt>Value</tt>,
2427be aware of the <a href="#nameWarning">precaution above</a>.</p>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]2428 </li>
2429 <li><tt>void replaceAllUsesWith(Value *V)</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2430
2431 <p>This method traverses the use list of a <tt>Value</tt> changing all <a
2432 href="#User"><tt>User</tt>s</a> of the current value to refer to
2433 "<tt>V</tt>" instead. For example, if you detect that an instruction always
2434 produces a constant value (for example through constant folding), you can
2435 replace all uses of the instruction with the constant like this:</p>
2436
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2437<div class="doc_code">
2438<pre>
2439Inst-&gt;replaceAllUsesWith(ConstVal);
2440</pre>
2441</div>
2442
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]2443</ul>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2444
2445</div>
2446
2447<!-- ======================================================================= -->
2448<div class="doc_subsection">
2449 <a name="User">The <tt>User</tt> class</a>
2450</div>
2451
2452<div class="doc_text">
2453
2454<p>
2455<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]2456doxygen info: <a href="/doxygen/classllvm_1_1User.html">User Class</a><br>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2457Superclass: <a href="#Value"><tt>Value</tt></a></p>
2458
2459<p>The <tt>User</tt> class is the common base class of all LLVM nodes that may
2460refer to <a href="#Value"><tt>Value</tt></a>s. It exposes a list of "Operands"
2461that are all of the <a href="#Value"><tt>Value</tt></a>s that the User is
2462referring to. The <tt>User</tt> class itself is a subclass of
2463<tt>Value</tt>.</p>
2464
2465<p>The operands of a <tt>User</tt> point directly to the LLVM <a
2466href="#Value"><tt>Value</tt></a> that it refers to. Because LLVM uses Static
2467Single Assignment (SSA) form, there can only be one definition referred to,
2468allowing this direct connection. This connection provides the use-def
2469information in LLVM.</p>
2470
2471</div>
2472
2473<!-- _______________________________________________________________________ -->
2474<div class="doc_subsubsection">
2475 <a name="m_User">Important Public Members of the <tt>User</tt> class</a>
2476</div>
2477
2478<div class="doc_text">
2479
2480<p>The <tt>User</tt> class exposes the operand list in two ways: through
2481an index access interface and through an iterator based interface.</p>
2482
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]2483<ul>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]2484 <li><tt>Value *getOperand(unsigned i)</tt><br>
2485 <tt>unsigned getNumOperands()</tt>
2486 <p> These two methods expose the operands of the <tt>User</tt> in a
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2487convenient form for direct access.</p></li>
2488
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]2489 <li><tt>User::op_iterator</tt> - Typedef for iterator over the operand
2490list<br>
Chris Lattner58360822005-01-17 00:12:04 +0000[diff] [blame]2491 <tt>op_iterator op_begin()</tt> - Get an iterator to the start of
2492the operand list.<br>
2493 <tt>op_iterator op_end()</tt> - Get an iterator to the end of the
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]2494operand list.
2495 <p> Together, these methods make up the iterator based interface to
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2496the operands of a <tt>User</tt>.</p></li>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]2497</ul>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2498
2499</div>
2500
2501<!-- ======================================================================= -->
2502<div class="doc_subsection">
2503 <a name="Instruction">The <tt>Instruction</tt> class</a>
2504</div>
2505
2506<div class="doc_text">
2507
2508<p><tt>#include "</tt><tt><a
2509href="/doxygen/Instruction_8h-source.html">llvm/Instruction.h</a>"</tt><br>
Misha Brukman31ca1de2004-06-03 23:35:54 +0000[diff] [blame]2510doxygen info: <a href="/doxygen/classllvm_1_1Instruction.html">Instruction Class</a><br>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2511Superclasses: <a href="#User"><tt>User</tt></a>, <a
2512href="#Value"><tt>Value</tt></a></p>
2513
2514<p>The <tt>Instruction</tt> class is the common base class for all LLVM
2515instructions. It provides only a few methods, but is a very commonly used
2516class. The primary data tracked by the <tt>Instruction</tt> class itself is the
2517opcode (instruction type) and the parent <a
2518href="#BasicBlock"><tt>BasicBlock</tt></a> the <tt>Instruction</tt> is embedded
2519into. To represent a specific type of instruction, one of many subclasses of
2520<tt>Instruction</tt> are used.</p>
2521
2522<p> Because the <tt>Instruction</tt> class subclasses the <a
2523href="#User"><tt>User</tt></a> class, its operands can be accessed in the same
2524way as for other <a href="#User"><tt>User</tt></a>s (with the
2525<tt>getOperand()</tt>/<tt>getNumOperands()</tt> and
2526<tt>op_begin()</tt>/<tt>op_end()</tt> methods).</p> <p> An important file for
2527the <tt>Instruction</tt> class is the <tt>llvm/Instruction.def</tt> file. This
2528file contains some meta-data about the various different types of instructions
2529in LLVM. It describes the enum values that are used as opcodes (for example
Reid Spencerc92d25d2006-12-19 19:47:19 +0000[diff] [blame]2530<tt>Instruction::Add</tt> and <tt>Instruction::ICmp</tt>), as well as the
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2531concrete sub-classes of <tt>Instruction</tt> that implement the instruction (for
2532example <tt><a href="#BinaryOperator">BinaryOperator</a></tt> and <tt><a
Reid Spencerc92d25d2006-12-19 19:47:19 +0000[diff] [blame]2533href="#CmpInst">CmpInst</a></tt>). Unfortunately, the use of macros in
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2534this file confuses doxygen, so these enum values don't show up correctly in the
Misha Brukman31ca1de2004-06-03 23:35:54 +0000[diff] [blame]2535<a href="/doxygen/classllvm_1_1Instruction.html">doxygen output</a>.</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2536
2537</div>
2538
2539<!-- _______________________________________________________________________ -->
2540<div class="doc_subsubsection">
Reid Spencerc92d25d2006-12-19 19:47:19 +0000[diff] [blame]2541 <a name="s_Instruction">Important Subclasses of the <tt>Instruction</tt>
2542 class</a>
2543</div>
2544<div class="doc_text">
2545 <ul>
2546 <li><tt><a name="BinaryOperator">BinaryOperator</a></tt>
2547 <p>This subclasses represents all two operand instructions whose operands
2548 must be the same type, except for the comparison instructions.</p></li>
2549 <li><tt><a name="CastInst">CastInst</a></tt>
2550 <p>This subclass is the parent of the 12 casting instructions. It provides
2551 common operations on cast instructions.</p>
2552 <li><tt><a name="CmpInst">CmpInst</a></tt>
2553 <p>This subclass respresents the two comparison instructions,
2554 <a href="LangRef.html#i_icmp">ICmpInst</a> (integer opreands), and
2555 <a href="LangRef.html#i_fcmp">FCmpInst</a> (floating point operands).</p>
2556 <li><tt><a name="TerminatorInst">TerminatorInst</a></tt>
2557 <p>This subclass is the parent of all terminator instructions (those which
2558 can terminate a block).</p>
2559 </ul>
2560 </div>
2561
2562<!-- _______________________________________________________________________ -->
2563<div class="doc_subsubsection">
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2564 <a name="m_Instruction">Important Public Members of the <tt>Instruction</tt>
2565 class</a>
2566</div>
2567
2568<div class="doc_text">
2569
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]2570<ul>
2571 <li><tt><a href="#BasicBlock">BasicBlock</a> *getParent()</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2572 <p>Returns the <a href="#BasicBlock"><tt>BasicBlock</tt></a> that
2573this <tt>Instruction</tt> is embedded into.</p></li>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]2574 <li><tt>bool mayWriteToMemory()</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2575 <p>Returns true if the instruction writes to memory, i.e. it is a
2576 <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]2577 <li><tt>unsigned getOpcode()</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2578 <p>Returns the opcode for the <tt>Instruction</tt>.</p></li>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]2579 <li><tt><a href="#Instruction">Instruction</a> *clone() const</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2580 <p>Returns another instance of the specified instruction, identical
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]2581in all ways to the original except that the instruction has no parent
2582(ie it's not embedded into a <a href="#BasicBlock"><tt>BasicBlock</tt></a>),
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2583and it has no name</p></li>
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="BasicBlock">The <tt>BasicBlock</tt> class</a>
2591</div>
2592
2593<div class="doc_text">
2594
Misha Brukman384047f2004-06-03 23:29:12 +0000[diff] [blame]2595<p><tt>#include "<a
2596href="/doxygen/BasicBlock_8h-source.html">llvm/BasicBlock.h</a>"</tt><br>
2597doxygen info: <a href="/doxygen/structllvm_1_1BasicBlock.html">BasicBlock
2598Class</a><br>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2599Superclass: <a href="#Value"><tt>Value</tt></a></p>
2600
2601<p>This class represents a single entry multiple exit section of the code,
2602commonly known as a basic block by the compiler community. The
2603<tt>BasicBlock</tt> class maintains a list of <a
2604href="#Instruction"><tt>Instruction</tt></a>s, which form the body of the block.
2605Matching the language definition, the last element of this list of instructions
2606is always a terminator instruction (a subclass of the <a
2607href="#TerminatorInst"><tt>TerminatorInst</tt></a> class).</p>
2608
2609<p>In addition to tracking the list of instructions that make up the block, the
2610<tt>BasicBlock</tt> class also keeps track of the <a
2611href="#Function"><tt>Function</tt></a> that it is embedded into.</p>
2612
2613<p>Note that <tt>BasicBlock</tt>s themselves are <a
2614href="#Value"><tt>Value</tt></a>s, because they are referenced by instructions
2615like branches and can go in the switch tables. <tt>BasicBlock</tt>s have type
2616<tt>label</tt>.</p>
2617
2618</div>
2619
2620<!-- _______________________________________________________________________ -->
2621<div class="doc_subsubsection">
2622 <a name="m_BasicBlock">Important Public Members of the <tt>BasicBlock</tt>
2623 class</a>
2624</div>
2625
2626<div class="doc_text">
2627
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]2628<ul>
Misha Brukmanb0e7e452004-10-29 04:33:19 +0000[diff] [blame]2629
2630<li><tt>BasicBlock(const std::string &amp;Name = "", </tt><tt><a
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]2631 href="#Function">Function</a> *Parent = 0)</tt>
Misha Brukmanb0e7e452004-10-29 04:33:19 +0000[diff] [blame]2632
2633<p>The <tt>BasicBlock</tt> constructor is used to create new basic blocks for
2634insertion into a function. The constructor optionally takes a name for the new
2635block, and a <a href="#Function"><tt>Function</tt></a> to insert it into. If
2636the <tt>Parent</tt> parameter is specified, the new <tt>BasicBlock</tt> is
2637automatically inserted at the end of the specified <a
2638href="#Function"><tt>Function</tt></a>, if not specified, the BasicBlock must be
2639manually inserted into the <a href="#Function"><tt>Function</tt></a>.</p></li>
2640
2641<li><tt>BasicBlock::iterator</tt> - Typedef for instruction list iterator<br>
2642<tt>BasicBlock::const_iterator</tt> - Typedef for const_iterator.<br>
2643<tt>begin()</tt>, <tt>end()</tt>, <tt>front()</tt>, <tt>back()</tt>,
Chris Lattner77d69242005-03-15 05:19:20 +0000[diff] [blame]2644<tt>size()</tt>, <tt>empty()</tt>
Misha Brukmanb0e7e452004-10-29 04:33:19 +0000[diff] [blame]2645STL-style functions for accessing the instruction list.
2646
2647<p>These methods and typedefs are forwarding functions that have the same
2648semantics as the standard library methods of the same names. These methods
2649expose the underlying instruction list of a basic block in a way that is easy to
2650manipulate. To get the full complement of container operations (including
2651operations to update the list), you must use the <tt>getInstList()</tt>
2652method.</p></li>
2653
2654<li><tt>BasicBlock::InstListType &amp;getInstList()</tt>
2655
2656<p>This method is used to get access to the underlying container that actually
2657holds the Instructions. This method must be used when there isn't a forwarding
2658function in the <tt>BasicBlock</tt> class for the operation that you would like
2659to perform. Because there are no forwarding functions for "updating"
2660operations, you need to use this if you want to update the contents of a
2661<tt>BasicBlock</tt>.</p></li>
2662
2663<li><tt><a href="#Function">Function</a> *getParent()</tt>
2664
2665<p> Returns a pointer to <a href="#Function"><tt>Function</tt></a> the block is
2666embedded into, or a null pointer if it is homeless.</p></li>
2667
2668<li><tt><a href="#TerminatorInst">TerminatorInst</a> *getTerminator()</tt>
2669
2670<p> Returns a pointer to the terminator instruction that appears at the end of
2671the <tt>BasicBlock</tt>. If there is no terminator instruction, or if the last
2672instruction in the block is not a terminator, then a null pointer is
2673returned.</p></li>
2674
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]2675</ul>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2676
2677</div>
2678
2679<!-- ======================================================================= -->
2680<div class="doc_subsection">
2681 <a name="GlobalValue">The <tt>GlobalValue</tt> class</a>
2682</div>
2683
2684<div class="doc_text">
2685
2686<p><tt>#include "<a
2687href="/doxygen/GlobalValue_8h-source.html">llvm/GlobalValue.h</a>"</tt><br>
Misha Brukman384047f2004-06-03 23:29:12 +0000[diff] [blame]2688doxygen info: <a href="/doxygen/classllvm_1_1GlobalValue.html">GlobalValue
2689Class</a><br>
Reid Spencerbe5e85e2006-04-14 14:11:48 +0000[diff] [blame]2690Superclasses: <a href="#Constant"><tt>Constant</tt></a>,
2691<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]2692
2693<p>Global values (<a href="#GlobalVariable"><tt>GlobalVariable</tt></a>s or <a
2694href="#Function"><tt>Function</tt></a>s) are the only LLVM values that are
2695visible in the bodies of all <a href="#Function"><tt>Function</tt></a>s.
2696Because they are visible at global scope, they are also subject to linking with
2697other globals defined in different translation units. To control the linking
2698process, <tt>GlobalValue</tt>s know their linkage rules. Specifically,
2699<tt>GlobalValue</tt>s know whether they have internal or external linkage, as
Reid Spencer8b2da7a2004-07-18 13:10:31 +0000[diff] [blame]2700defined by the <tt>LinkageTypes</tt> enumeration.</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2701
2702<p>If a <tt>GlobalValue</tt> has internal linkage (equivalent to being
2703<tt>static</tt> in C), it is not visible to code outside the current translation
2704unit, and does not participate in linking. If it has external linkage, it is
2705visible to external code, and does participate in linking. In addition to
2706linkage information, <tt>GlobalValue</tt>s keep track of which <a
2707href="#Module"><tt>Module</tt></a> they are currently part of.</p>
2708
2709<p>Because <tt>GlobalValue</tt>s are memory objects, they are always referred to
2710by their <b>address</b>. As such, the <a href="#Type"><tt>Type</tt></a> of a
2711global is always a pointer to its contents. It is important to remember this
2712when using the <tt>GetElementPtrInst</tt> instruction because this pointer must
2713be dereferenced first. For example, if you have a <tt>GlobalVariable</tt> (a
2714subclass 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]2715i32]</tt>, then the <tt>GlobalVariable</tt> is a pointer to that array. Although
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2716the address of the first element of this array and the value of the
2717<tt>GlobalVariable</tt> are the same, they have different types. The
Reid Spencer06565dc2007-01-12 17:11:23 +0000[diff] [blame]2718<tt>GlobalVariable</tt>'s type is <tt>[24 x i32]</tt>. The first element's type
2719is <tt>i32.</tt> Because of this, accessing a global value requires you to
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2720dereference the pointer with <tt>GetElementPtrInst</tt> first, then its elements
2721can be accessed. This is explained in the <a href="LangRef.html#globalvars">LLVM
2722Language Reference Manual</a>.</p>
2723
2724</div>
2725
2726<!-- _______________________________________________________________________ -->
2727<div class="doc_subsubsection">
2728 <a name="m_GlobalValue">Important Public Members of the <tt>GlobalValue</tt>
2729 class</a>
2730</div>
2731
2732<div class="doc_text">
2733
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]2734<ul>
2735 <li><tt>bool hasInternalLinkage() const</tt><br>
Chris Lattner9355b472002-09-06 02:50:58 +0000[diff] [blame]2736 <tt>bool hasExternalLinkage() const</tt><br>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]2737 <tt>void setInternalLinkage(bool HasInternalLinkage)</tt>
2738 <p> These methods manipulate the linkage characteristics of the <tt>GlobalValue</tt>.</p>
2739 <p> </p>
2740 </li>
2741 <li><tt><a href="#Module">Module</a> *getParent()</tt>
2742 <p> This returns the <a href="#Module"><tt>Module</tt></a> that the
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2743GlobalValue is currently embedded into.</p></li>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]2744</ul>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2745
2746</div>
2747
2748<!-- ======================================================================= -->
2749<div class="doc_subsection">
2750 <a name="Function">The <tt>Function</tt> class</a>
2751</div>
2752
2753<div class="doc_text">
2754
2755<p><tt>#include "<a
2756href="/doxygen/Function_8h-source.html">llvm/Function.h</a>"</tt><br> doxygen
Misha Brukman31ca1de2004-06-03 23:35:54 +0000[diff] [blame]2757info: <a href="/doxygen/classllvm_1_1Function.html">Function Class</a><br>
Reid Spencerbe5e85e2006-04-14 14:11:48 +0000[diff] [blame]2758Superclasses: <a href="#GlobalValue"><tt>GlobalValue</tt></a>,
2759<a href="#Constant"><tt>Constant</tt></a>,
2760<a href="#User"><tt>User</tt></a>,
2761<a href="#Value"><tt>Value</tt></a></p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2762
2763<p>The <tt>Function</tt> class represents a single procedure in LLVM. It is
2764actually one of the more complex classes in the LLVM heirarchy because it must
2765keep track of a large amount of data. The <tt>Function</tt> class keeps track
Reid Spencerbe5e85e2006-04-14 14:11:48 +0000[diff] [blame]2766of a list of <a href="#BasicBlock"><tt>BasicBlock</tt></a>s, a list of formal
2767<a href="#Argument"><tt>Argument</tt></a>s, and a
2768<a href="#SymbolTable"><tt>SymbolTable</tt></a>.</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2769
2770<p>The list of <a href="#BasicBlock"><tt>BasicBlock</tt></a>s is the most
2771commonly used part of <tt>Function</tt> objects. The list imposes an implicit
2772ordering of the blocks in the function, which indicate how the code will be
2773layed out by the backend. Additionally, the first <a
2774href="#BasicBlock"><tt>BasicBlock</tt></a> is the implicit entry node for the
2775<tt>Function</tt>. It is not legal in LLVM to explicitly branch to this initial
2776block. There are no implicit exit nodes, and in fact there may be multiple exit
2777nodes from a single <tt>Function</tt>. If the <a
2778href="#BasicBlock"><tt>BasicBlock</tt></a> list is empty, this indicates that
2779the <tt>Function</tt> is actually a function declaration: the actual body of the
2780function hasn't been linked in yet.</p>
2781
2782<p>In addition to a list of <a href="#BasicBlock"><tt>BasicBlock</tt></a>s, the
2783<tt>Function</tt> class also keeps track of the list of formal <a
2784href="#Argument"><tt>Argument</tt></a>s that the function receives. This
2785container manages the lifetime of the <a href="#Argument"><tt>Argument</tt></a>
2786nodes, just like the <a href="#BasicBlock"><tt>BasicBlock</tt></a> list does for
2787the <a href="#BasicBlock"><tt>BasicBlock</tt></a>s.</p>
2788
2789<p>The <a href="#SymbolTable"><tt>SymbolTable</tt></a> is a very rarely used
2790LLVM feature that is only used when you have to look up a value by name. Aside
2791from that, the <a href="#SymbolTable"><tt>SymbolTable</tt></a> is used
2792internally to make sure that there are not conflicts between the names of <a
2793href="#Instruction"><tt>Instruction</tt></a>s, <a
2794href="#BasicBlock"><tt>BasicBlock</tt></a>s, or <a
2795href="#Argument"><tt>Argument</tt></a>s in the function body.</p>
2796
Reid Spencer8b2da7a2004-07-18 13:10:31 +0000[diff] [blame]2797<p>Note that <tt>Function</tt> is a <a href="#GlobalValue">GlobalValue</a>
2798and therefore also a <a href="#Constant">Constant</a>. The value of the function
2799is its address (after linking) which is guaranteed to be constant.</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2800</div>
2801
2802<!-- _______________________________________________________________________ -->
2803<div class="doc_subsubsection">
2804 <a name="m_Function">Important Public Members of the <tt>Function</tt>
2805 class</a>
2806</div>
2807
2808<div class="doc_text">
2809
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]2810<ul>
2811 <li><tt>Function(const </tt><tt><a href="#FunctionType">FunctionType</a>
Chris Lattnerac479e52004-08-04 05:10:48 +0000[diff] [blame]2812 *Ty, LinkageTypes Linkage, const std::string &amp;N = "", Module* Parent = 0)</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2813
2814 <p>Constructor used when you need to create new <tt>Function</tt>s to add
2815 the the program. The constructor must specify the type of the function to
Chris Lattnerac479e52004-08-04 05:10:48 +0000[diff] [blame]2816 create and what type of linkage the function should have. The <a
2817 href="#FunctionType"><tt>FunctionType</tt></a> argument
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2818 specifies the formal arguments and return value for the function. The same
2819 <a href="#FunctionTypel"><tt>FunctionType</tt></a> value can be used to
2820 create multiple functions. The <tt>Parent</tt> argument specifies the Module
2821 in which the function is defined. If this argument is provided, the function
2822 will automatically be inserted into that module's list of
2823 functions.</p></li>
2824
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]2825 <li><tt>bool isExternal()</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2826
2827 <p>Return whether or not the <tt>Function</tt> has a body defined. If the
2828 function is "external", it does not have a body, and thus must be resolved
2829 by linking with a function defined in a different translation unit.</p></li>
2830
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]2831 <li><tt>Function::iterator</tt> - Typedef for basic block list iterator<br>
Chris Lattner9355b472002-09-06 02:50:58 +0000[diff] [blame]2832 <tt>Function::const_iterator</tt> - Typedef for const_iterator.<br>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2833
Chris Lattner77d69242005-03-15 05:19:20 +0000[diff] [blame]2834 <tt>begin()</tt>, <tt>end()</tt>
2835 <tt>size()</tt>, <tt>empty()</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2836
2837 <p>These are forwarding methods that make it easy to access the contents of
2838 a <tt>Function</tt> object's <a href="#BasicBlock"><tt>BasicBlock</tt></a>
2839 list.</p></li>
2840
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]2841 <li><tt>Function::BasicBlockListType &amp;getBasicBlockList()</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2842
2843 <p>Returns the list of <a href="#BasicBlock"><tt>BasicBlock</tt></a>s. This
2844 is necessary to use when you need to update the list or perform a complex
2845 action that doesn't have a forwarding method.</p></li>
2846
Chris Lattner89cc2652005-03-15 04:48:32 +0000[diff] [blame]2847 <li><tt>Function::arg_iterator</tt> - Typedef for the argument list
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]2848iterator<br>
Chris Lattner89cc2652005-03-15 04:48:32 +0000[diff] [blame]2849 <tt>Function::const_arg_iterator</tt> - Typedef for const_iterator.<br>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2850
Chris Lattner77d69242005-03-15 05:19:20 +0000[diff] [blame]2851 <tt>arg_begin()</tt>, <tt>arg_end()</tt>
Chris Lattner89cc2652005-03-15 04:48:32 +0000[diff] [blame]2852 <tt>arg_size()</tt>, <tt>arg_empty()</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2853
2854 <p>These are forwarding methods that make it easy to access the contents of
2855 a <tt>Function</tt> object's <a href="#Argument"><tt>Argument</tt></a>
2856 list.</p></li>
2857
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]2858 <li><tt>Function::ArgumentListType &amp;getArgumentList()</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2859
2860 <p>Returns the list of <a href="#Argument"><tt>Argument</tt></a>s. This is
2861 necessary to use when you need to update the list or perform a complex
2862 action that doesn't have a forwarding method.</p></li>
2863
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]2864 <li><tt><a href="#BasicBlock">BasicBlock</a> &amp;getEntryBlock()</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2865
2866 <p>Returns the entry <a href="#BasicBlock"><tt>BasicBlock</tt></a> for the
2867 function. Because the entry block for the function is always the first
2868 block, this returns the first block of the <tt>Function</tt>.</p></li>
2869
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]2870 <li><tt><a href="#Type">Type</a> *getReturnType()</tt><br>
2871 <tt><a href="#FunctionType">FunctionType</a> *getFunctionType()</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2872
2873 <p>This traverses the <a href="#Type"><tt>Type</tt></a> of the
2874 <tt>Function</tt> and returns the return type of the function, or the <a
2875 href="#FunctionType"><tt>FunctionType</tt></a> of the actual
2876 function.</p></li>
2877
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]2878 <li><tt><a href="#SymbolTable">SymbolTable</a> *getSymbolTable()</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2879
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]2880 <p> Return a pointer to the <a href="#SymbolTable"><tt>SymbolTable</tt></a>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2881 for this <tt>Function</tt>.</p></li>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]2882</ul>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2883
2884</div>
2885
2886<!-- ======================================================================= -->
2887<div class="doc_subsection">
2888 <a name="GlobalVariable">The <tt>GlobalVariable</tt> class</a>
2889</div>
2890
2891<div class="doc_text">
2892
2893<p><tt>#include "<a
2894href="/doxygen/GlobalVariable_8h-source.html">llvm/GlobalVariable.h</a>"</tt>
2895<br>
Tanya Lattnera3da7772004-06-22 08:02:25 +0000[diff] [blame]2896doxygen info: <a href="/doxygen/classllvm_1_1GlobalVariable.html">GlobalVariable
Reid Spencerbe5e85e2006-04-14 14:11:48 +0000[diff] [blame]2897 Class</a><br>
2898Superclasses: <a href="#GlobalValue"><tt>GlobalValue</tt></a>,
2899<a href="#Constant"><tt>Constant</tt></a>,
2900<a href="#User"><tt>User</tt></a>,
2901<a href="#Value"><tt>Value</tt></a></p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2902
2903<p>Global variables are represented with the (suprise suprise)
2904<tt>GlobalVariable</tt> class. Like functions, <tt>GlobalVariable</tt>s are also
2905subclasses of <a href="#GlobalValue"><tt>GlobalValue</tt></a>, and as such are
2906always referenced by their address (global values must live in memory, so their
Reid Spencerbe5e85e2006-04-14 14:11:48 +0000[diff] [blame]2907"name" refers to their constant address). See
2908<a href="#GlobalValue"><tt>GlobalValue</tt></a> for more on this. Global
2909variables may have an initial value (which must be a
2910<a href="#Constant"><tt>Constant</tt></a>), and if they have an initializer,
2911they may be marked as "constant" themselves (indicating that their contents
2912never change at runtime).</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2913</div>
2914
2915<!-- _______________________________________________________________________ -->
2916<div class="doc_subsubsection">
2917 <a name="m_GlobalVariable">Important Public Members of the
2918 <tt>GlobalVariable</tt> class</a>
2919</div>
2920
2921<div class="doc_text">
2922
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]2923<ul>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2924 <li><tt>GlobalVariable(const </tt><tt><a href="#Type">Type</a> *Ty, bool
2925 isConstant, LinkageTypes&amp; Linkage, <a href="#Constant">Constant</a>
2926 *Initializer = 0, const std::string &amp;Name = "", Module* Parent = 0)</tt>
2927
2928 <p>Create a new global variable of the specified type. If
2929 <tt>isConstant</tt> is true then the global variable will be marked as
2930 unchanging for the program. The Linkage parameter specifies the type of
2931 linkage (internal, external, weak, linkonce, appending) for the variable. If
2932 the linkage is InternalLinkage, WeakLinkage, or LinkOnceLinkage,&nbsp; then
2933 the resultant global variable will have internal linkage. AppendingLinkage
2934 concatenates together all instances (in different translation units) of the
2935 variable into a single variable but is only applicable to arrays. &nbsp;See
2936 the <a href="LangRef.html#modulestructure">LLVM Language Reference</a> for
2937 further details on linkage types. Optionally an initializer, a name, and the
2938 module to put the variable into may be specified for the global variable as
2939 well.</p></li>
2940
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]2941 <li><tt>bool isConstant() const</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2942
2943 <p>Returns true if this is a global variable that is known not to
2944 be modified at runtime.</p></li>
2945
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]2946 <li><tt>bool hasInitializer()</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2947
2948 <p>Returns true if this <tt>GlobalVariable</tt> has an intializer.</p></li>
2949
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]2950 <li><tt><a href="#Constant">Constant</a> *getInitializer()</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2951
2952 <p>Returns the intial value for a <tt>GlobalVariable</tt>. It is not legal
2953 to call this method if there is no initializer.</p></li>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]2954</ul>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2955
2956</div>
2957
2958<!-- ======================================================================= -->
2959<div class="doc_subsection">
2960 <a name="Module">The <tt>Module</tt> class</a>
2961</div>
2962
2963<div class="doc_text">
2964
2965<p><tt>#include "<a
2966href="/doxygen/Module_8h-source.html">llvm/Module.h</a>"</tt><br> doxygen info:
Tanya Lattnera3da7772004-06-22 08:02:25 +0000[diff] [blame]2967<a href="/doxygen/classllvm_1_1Module.html">Module Class</a></p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2968
2969<p>The <tt>Module</tt> class represents the top level structure present in LLVM
2970programs. An LLVM module is effectively either a translation unit of the
2971original program or a combination of several translation units merged by the
2972linker. The <tt>Module</tt> class keeps track of a list of <a
2973href="#Function"><tt>Function</tt></a>s, a list of <a
2974href="#GlobalVariable"><tt>GlobalVariable</tt></a>s, and a <a
2975href="#SymbolTable"><tt>SymbolTable</tt></a>. Additionally, it contains a few
2976helpful member functions that try to make common operations easy.</p>
2977
2978</div>
2979
2980<!-- _______________________________________________________________________ -->
2981<div class="doc_subsubsection">
2982 <a name="m_Module">Important Public Members of the <tt>Module</tt> class</a>
2983</div>
2984
2985<div class="doc_text">
2986
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]2987<ul>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2988 <li><tt>Module::Module(std::string name = "")</tt></li>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]2989</ul>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2990
2991<p>Constructing a <a href="#Module">Module</a> is easy. You can optionally
2992provide a name for it (probably based on the name of the translation unit).</p>
2993
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]2994<ul>
2995 <li><tt>Module::iterator</tt> - Typedef for function list iterator<br>
Chris Lattner0377de42002-09-06 14:50:55 +0000[diff] [blame]2996 <tt>Module::const_iterator</tt> - Typedef for const_iterator.<br>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2997
Chris Lattner77d69242005-03-15 05:19:20 +0000[diff] [blame]2998 <tt>begin()</tt>, <tt>end()</tt>
2999 <tt>size()</tt>, <tt>empty()</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3000
3001 <p>These are forwarding methods that make it easy to access the contents of
3002 a <tt>Module</tt> object's <a href="#Function"><tt>Function</tt></a>
3003 list.</p></li>
3004
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3005 <li><tt>Module::FunctionListType &amp;getFunctionList()</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3006
3007 <p> Returns the list of <a href="#Function"><tt>Function</tt></a>s. This is
3008 necessary to use when you need to update the list or perform a complex
3009 action that doesn't have a forwarding method.</p>
3010
3011 <p><!-- Global Variable --></p></li>
Chris Lattnerc75ff9a2002-10-01 23:17:09 +0000[diff] [blame]3012</ul>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3013
3014<hr>
3015
Chris Lattnerc75ff9a2002-10-01 23:17:09 +0000[diff] [blame]3016<ul>
Chris Lattner89cc2652005-03-15 04:48:32 +0000[diff] [blame]3017 <li><tt>Module::global_iterator</tt> - Typedef for global variable list iterator<br>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3018
Chris Lattner89cc2652005-03-15 04:48:32 +0000[diff] [blame]3019 <tt>Module::const_global_iterator</tt> - Typedef for const_iterator.<br>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3020
Chris Lattner77d69242005-03-15 05:19:20 +0000[diff] [blame]3021 <tt>global_begin()</tt>, <tt>global_end()</tt>
Chris Lattner89cc2652005-03-15 04:48:32 +0000[diff] [blame]3022 <tt>global_size()</tt>, <tt>global_empty()</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3023
3024 <p> These are forwarding methods that make it easy to access the contents of
3025 a <tt>Module</tt> object's <a
3026 href="#GlobalVariable"><tt>GlobalVariable</tt></a> list.</p></li>
3027
3028 <li><tt>Module::GlobalListType &amp;getGlobalList()</tt>
3029
3030 <p>Returns the list of <a
3031 href="#GlobalVariable"><tt>GlobalVariable</tt></a>s. This is necessary to
3032 use when you need to update the list or perform a complex action that
3033 doesn't have a forwarding method.</p>
3034
3035 <p><!-- Symbol table stuff --> </p></li>
Chris Lattnerc75ff9a2002-10-01 23:17:09 +0000[diff] [blame]3036</ul>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3037
3038<hr>
3039
3040<ul>
3041 <li><tt><a href="#SymbolTable">SymbolTable</a> *getSymbolTable()</tt>
3042
3043 <p>Return a reference to the <a href="#SymbolTable"><tt>SymbolTable</tt></a>
3044 for this <tt>Module</tt>.</p>
3045
3046 <p><!-- Convenience methods --></p></li>
3047</ul>
3048
3049<hr>
3050
3051<ul>
3052 <li><tt><a href="#Function">Function</a> *getFunction(const std::string
3053 &amp;Name, const <a href="#FunctionType">FunctionType</a> *Ty)</tt>
3054
3055 <p>Look up the specified function in the <tt>Module</tt> <a
3056 href="#SymbolTable"><tt>SymbolTable</tt></a>. If it does not exist, return
3057 <tt>null</tt>.</p></li>
3058
3059 <li><tt><a href="#Function">Function</a> *getOrInsertFunction(const
3060 std::string &amp;Name, const <a href="#FunctionType">FunctionType</a> *T)</tt>
3061
3062 <p>Look up the specified function in the <tt>Module</tt> <a
3063 href="#SymbolTable"><tt>SymbolTable</tt></a>. If it does not exist, add an
3064 external declaration for the function and return it.</p></li>
3065
3066 <li><tt>std::string getTypeName(const <a href="#Type">Type</a> *Ty)</tt>
3067
3068 <p>If there is at least one entry in the <a
3069 href="#SymbolTable"><tt>SymbolTable</tt></a> for the specified <a
3070 href="#Type"><tt>Type</tt></a>, return it. Otherwise return the empty
3071 string.</p></li>
3072
3073 <li><tt>bool addTypeName(const std::string &amp;Name, const <a
3074 href="#Type">Type</a> *Ty)</tt>
3075
3076 <p>Insert an entry in the <a href="#SymbolTable"><tt>SymbolTable</tt></a>
3077 mapping <tt>Name</tt> to <tt>Ty</tt>. If there is already an entry for this
3078 name, true is returned and the <a
3079 href="#SymbolTable"><tt>SymbolTable</tt></a> is not modified.</p></li>
3080</ul>
3081
3082</div>
3083
3084<!-- ======================================================================= -->
3085<div class="doc_subsection">
3086 <a name="Constant">The <tt>Constant</tt> class and subclasses</a>
3087</div>
3088
3089<div class="doc_text">
3090
3091<p>Constant represents a base class for different types of constants. It
Reid Spencer53bfebc2007-01-12 03:36:33 +0000[diff] [blame]3092is subclassed by ConstantInt, ConstantArray, etc. for representing
Reid Spencerb83eb642006-10-20 07:07:24 +0000[diff] [blame]3093the various types of Constants.</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3094
3095</div>
3096
3097<!-- _______________________________________________________________________ -->
3098<div class="doc_subsubsection">
Reid Spencerfe8f4ff2004-11-01 09:02:53 +0000[diff] [blame]3099 <a name="m_Constant">Important Public Methods</a>
3100</div>
3101<div class="doc_text">
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3102</div>
3103
Reid Spencerfe8f4ff2004-11-01 09:02:53 +0000[diff] [blame]3104<!-- _______________________________________________________________________ -->
3105<div class="doc_subsubsection">Important Subclasses of Constant </div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3106<div class="doc_text">
Chris Lattnerc75ff9a2002-10-01 23:17:09 +0000[diff] [blame]3107<ul>
Reid Spencer53bfebc2007-01-12 03:36:33 +0000[diff] [blame]3108 <li>ConstantInt : This subclass of Constant represents an integer constant of
3109 any width, including boolean (1 bit integer).
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3110 <ul>
Reid Spencerb83eb642006-10-20 07:07:24 +0000[diff] [blame]3111 <li><tt>int64_t getSExtValue() const</tt>: Returns the underlying value of
3112 this constant as a sign extended signed integer value.</li>
3113 <li><tt>uint64_t getZExtValue() const</tt>: Returns the underlying value
3114 of this constant as a zero extended unsigned integer value.</li>
Reid Spencer53bfebc2007-01-12 03:36:33 +0000[diff] [blame]3115 <li><tt>static ConstantInt* get(const Type *Ty, uint64_t Val)</tt>:
3116 Returns the ConstantInt object that represents the value provided by
3117 <tt>Val</tt> for integer type <tt>Ty</tt>.</li>
Reid Spencerfe8f4ff2004-11-01 09:02:53 +0000[diff] [blame]3118 </ul>
3119 </li>
3120 <li>ConstantFP : This class represents a floating point constant.
3121 <ul>
3122 <li><tt>double getValue() const</tt>: Returns the underlying value of
3123 this constant. </li>
3124 </ul>
3125 </li>
Reid Spencerfe8f4ff2004-11-01 09:02:53 +0000[diff] [blame]3126 <li>ConstantArray : This represents a constant array.
3127 <ul>
3128 <li><tt>const std::vector&lt;Use&gt; &amp;getValues() const</tt>: Returns
Chris Lattner58360822005-01-17 00:12:04 +0000[diff] [blame]3129 a vector of component constants that makeup this array. </li>
Reid Spencerfe8f4ff2004-11-01 09:02:53 +0000[diff] [blame]3130 </ul>
3131 </li>
3132 <li>ConstantStruct : This represents a constant struct.
3133 <ul>
3134 <li><tt>const std::vector&lt;Use&gt; &amp;getValues() const</tt>: Returns
Chris Lattner58360822005-01-17 00:12:04 +0000[diff] [blame]3135 a vector of component constants that makeup this array. </li>
Reid Spencerfe8f4ff2004-11-01 09:02:53 +0000[diff] [blame]3136 </ul>
3137 </li>
3138 <li>GlobalValue : This represents either a global variable or a function. In
3139 either case, the value is a constant fixed address (after linking).
3140 </li>
Chris Lattnerc75ff9a2002-10-01 23:17:09 +0000[diff] [blame]3141</ul>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3142</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3143<!-- ======================================================================= -->
3144<div class="doc_subsection">
3145 <a name="Argument">The <tt>Argument</tt> class</a>
3146</div>
3147
3148<div class="doc_text">
3149
3150<p>This subclass of Value defines the interface for incoming formal
Chris Lattner58360822005-01-17 00:12:04 +0000[diff] [blame]3151arguments to a function. A Function maintains a list of its formal
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3152arguments. An argument has a pointer to the parent Function.</p>
3153
3154</div>
3155
Chris Lattner9355b472002-09-06 02:50:58 +0000[diff] [blame]3156<!-- *********************************************************************** -->
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3157<hr>
3158<address>
3159 <a href="http://jigsaw.w3.org/css-validator/check/referer"><img
3160 src="http://jigsaw.w3.org/css-validator/images/vcss" alt="Valid CSS!"></a>
3161 <a href="http://validator.w3.org/check/referer"><img
3162 src="http://www.w3.org/Icons/valid-html401" alt="Valid HTML 4.01!" /></a>
3163
3164 <a href="mailto:dhurjati@cs.uiuc.edu">Dinakar Dhurjati</a> and
3165 <a href="mailto:sabre@nondot.org">Chris Lattner</a><br>
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]3166 <a href="http://llvm.org">The LLVM Compiler Infrastructure</a><br>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3167 Last modified: $Date$
3168</address>
3169
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3170</body>
3171</html>