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4<head>
5 <title>LLVM Programmer's Manual</title>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]6 <link rel="stylesheet" href="llvm.css" type="text/css">
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]7</head>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]8<body>
9
10<div class="doc_title">
11 LLVM Programmer's Manual
12</div>
13
Chris Lattner9355b472002-09-06 02:50:58 +0000[diff] [blame]14<ol>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]15 <li><a href="#introduction">Introduction</a></li>
Chris Lattner9355b472002-09-06 02:50:58 +0000[diff] [blame]16 <li><a href="#general">General Information</a>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]17 <ul>
Reid Spencerfe8f4ff2004-11-01 09:02:53 +0000[diff] [blame]18 <li><a href="#stl">The C++ Standard Template Library</a></li>
19<!--
20 <li>The <tt>-time-passes</tt> option</li>
21 <li>How to use the LLVM Makefile system</li>
22 <li>How to write a regression test</li>
Chris Lattner61db4652004-12-08 19:05:44 +0000[diff] [blame]23
Reid Spencerfe8f4ff2004-11-01 09:02:53 +0000[diff] [blame]24-->
Chris Lattner84b7f8d2003-08-01 22:20:59 +0000[diff] [blame]25 </ul>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]26 </li>
27 <li><a href="#apis">Important and useful LLVM APIs</a>
28 <ul>
29 <li><a href="#isa">The <tt>isa&lt;&gt;</tt>, <tt>cast&lt;&gt;</tt>
30and <tt>dyn_cast&lt;&gt;</tt> templates</a> </li>
Misha Brukman2c122ce2005-11-01 21:12:49 +0000[diff] [blame]31 <li><a href="#DEBUG">The <tt>DEBUG()</tt> macro and <tt>-debug</tt>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]32option</a>
33 <ul>
34 <li><a href="#DEBUG_TYPE">Fine grained debug info with <tt>DEBUG_TYPE</tt>
35and the <tt>-debug-only</tt> option</a> </li>
36 </ul>
37 </li>
Chris Lattner0be6fdf2006-12-19 21:46:21 +0000[diff] [blame]38 <li><a href="#Statistic">The <tt>Statistic</tt> class &amp; <tt>-stats</tt>
Reid Spencerfe8f4ff2004-11-01 09:02:53 +0000[diff] [blame]39option</a></li>
40<!--
41 <li>The <tt>InstVisitor</tt> template
42 <li>The general graph API
43-->
Chris Lattnerf623a082005-10-17 01:36:23 +0000[diff] [blame]44 <li><a href="#ViewGraph">Viewing graphs while debugging code</a></li>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]45 </ul>
46 </li>
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]47 <li><a href="#datastructure">Picking the Right Data Structure for a Task</a>
48 <ul>
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]49 <li><a href="#ds_sequential">Sequential Containers (std::vector, std::list, etc)</a>
50 <ul>
51 <li><a href="#dss_fixedarrays">Fixed Size Arrays</a></li>
52 <li><a href="#dss_heaparrays">Heap Allocated Arrays</a></li>
53 <li><a href="#dss_smallvector">"llvm/ADT/SmallVector.h"</a></li>
54 <li><a href="#dss_vector">&lt;vector&gt;</a></li>
55 <li><a href="#dss_deque">&lt;deque&gt;</a></li>
56 <li><a href="#dss_list">&lt;list&gt;</a></li>
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>
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame^]138 <li><a href="#Module">The <tt>Module</tt> class</a></li>
Reid Spencerfe8f4ff2004-11-01 09:02:53 +0000[diff] [blame]139 <li><a href="#Value">The <tt>Value</tt> class</a>
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame^]140 <ul>
141 <li><a href="#User">The <tt>User</tt> class</a>
Chris Lattner9355b472002-09-06 02:50:58 +0000[diff] [blame]142 <ul>
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame^]143 <li><a href="#Instruction">The <tt>Instruction</tt> class</a></li>
144 <li><a href="#Constant">The <tt>Constant</tt> class</a>
145 <ul>
146 <li><a href="#GlobalValue">The <tt>GlobalValue</tt> class</a>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]147 <ul>
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame^]148 <li><a href="#Function">The <tt>Function</tt> class</a></li>
149 <li><a href="#GlobalVariable">The <tt>GlobalVariable</tt> class</a></li>
150 </ul>
151 </li>
152 </ul>
153 </li>
Reid Spencerfe8f4ff2004-11-01 09:02:53 +0000[diff] [blame]154 </ul>
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame^]155 </li>
156 <li><a href="#BasicBlock">The <tt>BasicBlock</tt> class</a></li>
157 <li><a href="#Argument">The <tt>Argument</tt> class</a></li>
158 </ul>
Reid Spencerfe8f4ff2004-11-01 09:02:53 +0000[diff] [blame]159 </li>
160 </ul>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]161 </li>
Chris Lattner9355b472002-09-06 02:50:58 +0000[diff] [blame]162</ol>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]163
Chris Lattner69bf8a92004-05-23 21:06:58 +0000[diff] [blame]164<div class="doc_author">
165 <p>Written by <a href="mailto:sabre@nondot.org">Chris Lattner</a>,
Chris Lattner94c43592004-05-26 16:52:55 +0000[diff] [blame]166 <a href="mailto:dhurjati@cs.uiuc.edu">Dinakar Dhurjati</a>,
167 <a href="mailto:jstanley@cs.uiuc.edu">Joel Stanley</a>, and
168 <a href="mailto:rspencer@x10sys.com">Reid Spencer</a></p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]169</div>
170
Chris Lattner9355b472002-09-06 02:50:58 +0000[diff] [blame]171<!-- *********************************************************************** -->
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]172<div class="doc_section">
173 <a name="introduction">Introduction </a>
174</div>
Chris Lattner9355b472002-09-06 02:50:58 +0000[diff] [blame]175<!-- *********************************************************************** -->
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]176
177<div class="doc_text">
178
179<p>This document is meant to highlight some of the important classes and
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]180interfaces available in the LLVM source-base. This manual is not
181intended to explain what LLVM is, how it works, and what LLVM code looks
182like. It assumes that you know the basics of LLVM and are interested
183in writing transformations or otherwise analyzing or manipulating the
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]184code.</p>
185
186<p>This document should get you oriented so that you can find your
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]187way in the continuously growing source code that makes up the LLVM
188infrastructure. Note that this manual is not intended to serve as a
189replacement for reading the source code, so if you think there should be
190a method in one of these classes to do something, but it's not listed,
191check the source. Links to the <a href="/doxygen/">doxygen</a> sources
192are provided to make this as easy as possible.</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]193
194<p>The first section of this document describes general information that is
195useful to know when working in the LLVM infrastructure, and the second describes
196the Core LLVM classes. In the future this manual will be extended with
197information describing how to use extension libraries, such as dominator
198information, CFG traversal routines, and useful utilities like the <tt><a
199href="/doxygen/InstVisitor_8h-source.html">InstVisitor</a></tt> template.</p>
200
201</div>
202
Chris Lattner9355b472002-09-06 02:50:58 +0000[diff] [blame]203<!-- *********************************************************************** -->
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]204<div class="doc_section">
205 <a name="general">General Information</a>
206</div>
207<!-- *********************************************************************** -->
208
209<div class="doc_text">
210
211<p>This section contains general information that is useful if you are working
212in the LLVM source-base, but that isn't specific to any particular API.</p>
213
214</div>
215
216<!-- ======================================================================= -->
217<div class="doc_subsection">
218 <a name="stl">The C++ Standard Template Library</a>
219</div>
220
221<div class="doc_text">
222
223<p>LLVM makes heavy use of the C++ Standard Template Library (STL),
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]224perhaps much more than you are used to, or have seen before. Because of
225this, you might want to do a little background reading in the
226techniques used and capabilities of the library. There are many good
227pages that discuss the STL, and several books on the subject that you
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]228can get, so it will not be discussed in this document.</p>
229
230<p>Here are some useful links:</p>
231
232<ol>
233
234<li><a href="http://www.dinkumware.com/refxcpp.html">Dinkumware C++ Library
235reference</a> - an excellent reference for the STL and other parts of the
236standard C++ library.</li>
237
238<li><a href="http://www.tempest-sw.com/cpp/">C++ In a Nutshell</a> - This is an
Tanya Lattner09cf73c2004-06-22 04:24:55 +0000[diff] [blame]239O'Reilly book in the making. It has a decent
240Standard Library
241Reference that rivals Dinkumware's, and is unfortunately no longer free since the book has been
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]242published.</li>
243
244<li><a href="http://www.parashift.com/c++-faq-lite/">C++ Frequently Asked
245Questions</a></li>
246
247<li><a href="http://www.sgi.com/tech/stl/">SGI's STL Programmer's Guide</a> -
248Contains a useful <a
249href="http://www.sgi.com/tech/stl/stl_introduction.html">Introduction to the
250STL</a>.</li>
251
252<li><a href="http://www.research.att.com/%7Ebs/C++.html">Bjarne Stroustrup's C++
253Page</a></li>
254
Tanya Lattner79445ba2004-12-08 18:34:56 +0000[diff] [blame]255<li><a href="http://64.78.49.204/">
Reid Spencer096603a2004-05-26 08:41:35 +0000[diff] [blame]256Bruce Eckel's Thinking in C++, 2nd ed. Volume 2 Revision 4.0 (even better, get
257the book).</a></li>
258
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]259</ol>
260
261<p>You are also encouraged to take a look at the <a
262href="CodingStandards.html">LLVM Coding Standards</a> guide which focuses on how
263to write maintainable code more than where to put your curly braces.</p>
264
265</div>
266
267<!-- ======================================================================= -->
268<div class="doc_subsection">
269 <a name="stl">Other useful references</a>
270</div>
271
272<div class="doc_text">
273
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]274<ol>
275<li><a href="http://www.psc.edu/%7Esemke/cvs_branches.html">CVS
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]276Branch and Tag Primer</a></li>
Misha Brukmana0f71e42004-06-18 18:39:00 +0000[diff] [blame]277<li><a href="http://www.fortran-2000.com/ArnaudRecipes/sharedlib.html">Using
278static and shared libraries across platforms</a></li>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]279</ol>
280
281</div>
282
Chris Lattner9355b472002-09-06 02:50:58 +0000[diff] [blame]283<!-- *********************************************************************** -->
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]284<div class="doc_section">
285 <a name="apis">Important and useful LLVM APIs</a>
286</div>
287<!-- *********************************************************************** -->
288
289<div class="doc_text">
290
291<p>Here we highlight some LLVM APIs that are generally useful and good to
292know about when writing transformations.</p>
293
294</div>
295
296<!-- ======================================================================= -->
297<div class="doc_subsection">
Misha Brukman2c122ce2005-11-01 21:12:49 +0000[diff] [blame]298 <a name="isa">The <tt>isa&lt;&gt;</tt>, <tt>cast&lt;&gt;</tt> and
299 <tt>dyn_cast&lt;&gt;</tt> templates</a>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]300</div>
301
302<div class="doc_text">
303
304<p>The LLVM source-base makes extensive use of a custom form of RTTI.
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]305These templates have many similarities to the C++ <tt>dynamic_cast&lt;&gt;</tt>
306operator, but they don't have some drawbacks (primarily stemming from
307the fact that <tt>dynamic_cast&lt;&gt;</tt> only works on classes that
308have a v-table). Because they are used so often, you must know what they
309do and how they work. All of these templates are defined in the <a
Chris Lattner695b78b2005-04-26 22:56:16 +0000[diff] [blame]310 href="/doxygen/Casting_8h-source.html"><tt>llvm/Support/Casting.h</tt></a>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]311file (note that you very rarely have to include this file directly).</p>
312
313<dl>
314 <dt><tt>isa&lt;&gt;</tt>: </dt>
315
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]316 <dd><p>The <tt>isa&lt;&gt;</tt> operator works exactly like the Java
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]317 "<tt>instanceof</tt>" operator. It returns true or false depending on whether
318 a reference or pointer points to an instance of the specified class. This can
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]319 be very useful for constraint checking of various sorts (example below).</p>
320 </dd>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]321
322 <dt><tt>cast&lt;&gt;</tt>: </dt>
323
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]324 <dd><p>The <tt>cast&lt;&gt;</tt> operator is a "checked cast" operation. It
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]325 converts a pointer or reference from a base class to a derived cast, causing
326 an assertion failure if it is not really an instance of the right type. This
327 should be used in cases where you have some information that makes you believe
328 that something is of the right type. An example of the <tt>isa&lt;&gt;</tt>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]329 and <tt>cast&lt;&gt;</tt> template is:</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]330
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]331<div class="doc_code">
332<pre>
333static bool isLoopInvariant(const <a href="#Value">Value</a> *V, const Loop *L) {
334 if (isa&lt;<a href="#Constant">Constant</a>&gt;(V) || isa&lt;<a href="#Argument">Argument</a>&gt;(V) || isa&lt;<a href="#GlobalValue">GlobalValue</a>&gt;(V))
335 return true;
Chris Lattner69bf8a92004-05-23 21:06:58 +0000[diff] [blame]336
Bill Wendling82e2eea2006-10-11 18:00:22 +0000[diff] [blame]337 // <i>Otherwise, it must be an instruction...</i>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]338 return !L-&gt;contains(cast&lt;<a href="#Instruction">Instruction</a>&gt;(V)-&gt;getParent());
339}
340</pre>
341</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]342
343 <p>Note that you should <b>not</b> use an <tt>isa&lt;&gt;</tt> test followed
344 by a <tt>cast&lt;&gt;</tt>, for that use the <tt>dyn_cast&lt;&gt;</tt>
345 operator.</p>
346
347 </dd>
348
349 <dt><tt>dyn_cast&lt;&gt;</tt>:</dt>
350
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]351 <dd><p>The <tt>dyn_cast&lt;&gt;</tt> operator is a "checking cast" operation.
352 It checks to see if the operand is of the specified type, and if so, returns a
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]353 pointer to it (this operator does not work with references). If the operand is
354 not of the correct type, a null pointer is returned. Thus, this works very
Misha Brukman2c122ce2005-11-01 21:12:49 +0000[diff] [blame]355 much like the <tt>dynamic_cast&lt;&gt;</tt> operator in C++, and should be
356 used in the same circumstances. Typically, the <tt>dyn_cast&lt;&gt;</tt>
357 operator is used in an <tt>if</tt> statement or some other flow control
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]358 statement like this:</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]359
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]360<div class="doc_code">
361<pre>
362if (<a href="#AllocationInst">AllocationInst</a> *AI = dyn_cast&lt;<a href="#AllocationInst">AllocationInst</a>&gt;(Val)) {
Bill Wendling82e2eea2006-10-11 18:00:22 +0000[diff] [blame]363 // <i>...</i>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]364}
365</pre>
366</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]367
Misha Brukman2c122ce2005-11-01 21:12:49 +0000[diff] [blame]368 <p>This form of the <tt>if</tt> statement effectively combines together a call
369 to <tt>isa&lt;&gt;</tt> and a call to <tt>cast&lt;&gt;</tt> into one
370 statement, which is very convenient.</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]371
Misha Brukman2c122ce2005-11-01 21:12:49 +0000[diff] [blame]372 <p>Note that the <tt>dyn_cast&lt;&gt;</tt> operator, like C++'s
373 <tt>dynamic_cast&lt;&gt;</tt> or Java's <tt>instanceof</tt> operator, can be
374 abused. In particular, you should not use big chained <tt>if/then/else</tt>
375 blocks to check for lots of different variants of classes. If you find
376 yourself wanting to do this, it is much cleaner and more efficient to use the
377 <tt>InstVisitor</tt> class to dispatch over the instruction type directly.</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]378
Misha Brukman2c122ce2005-11-01 21:12:49 +0000[diff] [blame]379 </dd>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]380
Misha Brukman2c122ce2005-11-01 21:12:49 +0000[diff] [blame]381 <dt><tt>cast_or_null&lt;&gt;</tt>: </dt>
382
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]383 <dd><p>The <tt>cast_or_null&lt;&gt;</tt> operator works just like the
Misha Brukman2c122ce2005-11-01 21:12:49 +0000[diff] [blame]384 <tt>cast&lt;&gt;</tt> operator, except that it allows for a null pointer as an
385 argument (which it then propagates). This can sometimes be useful, allowing
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]386 you to combine several null checks into one.</p></dd>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]387
Misha Brukman2c122ce2005-11-01 21:12:49 +0000[diff] [blame]388 <dt><tt>dyn_cast_or_null&lt;&gt;</tt>: </dt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]389
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]390 <dd><p>The <tt>dyn_cast_or_null&lt;&gt;</tt> operator works just like the
Misha Brukman2c122ce2005-11-01 21:12:49 +0000[diff] [blame]391 <tt>dyn_cast&lt;&gt;</tt> operator, except that it allows for a null pointer
392 as an argument (which it then propagates). This can sometimes be useful,
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]393 allowing you to combine several null checks into one.</p></dd>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]394
Misha Brukman2c122ce2005-11-01 21:12:49 +0000[diff] [blame]395</dl>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]396
397<p>These five templates can be used with any classes, whether they have a
398v-table or not. To add support for these templates, you simply need to add
399<tt>classof</tt> static methods to the class you are interested casting
400to. Describing this is currently outside the scope of this document, but there
401are lots of examples in the LLVM source base.</p>
402
403</div>
404
405<!-- ======================================================================= -->
406<div class="doc_subsection">
Misha Brukman2c122ce2005-11-01 21:12:49 +0000[diff] [blame]407 <a name="DEBUG">The <tt>DEBUG()</tt> macro and <tt>-debug</tt> option</a>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]408</div>
409
410<div class="doc_text">
411
412<p>Often when working on your pass you will put a bunch of debugging printouts
413and other code into your pass. After you get it working, you want to remove
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]414it, but you may need it again in the future (to work out new bugs that you run
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]415across).</p>
416
417<p> Naturally, because of this, you don't want to delete the debug printouts,
418but you don't want them to always be noisy. A standard compromise is to comment
419them out, allowing you to enable them if you need them in the future.</p>
420
Chris Lattner695b78b2005-04-26 22:56:16 +0000[diff] [blame]421<p>The "<tt><a href="/doxygen/Debug_8h-source.html">llvm/Support/Debug.h</a></tt>"
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]422file provides a macro named <tt>DEBUG()</tt> that is a much nicer solution to
423this problem. Basically, you can put arbitrary code into the argument of the
424<tt>DEBUG</tt> macro, and it is only executed if '<tt>opt</tt>' (or any other
425tool) is run with the '<tt>-debug</tt>' command line argument:</p>
426
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]427<div class="doc_code">
428<pre>
Bill Wendling832171c2006-12-07 20:04:42 +0000[diff] [blame]429DOUT &lt;&lt; "I am here!\n";
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]430</pre>
431</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]432
433<p>Then you can run your pass like this:</p>
434
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]435<div class="doc_code">
436<pre>
437$ opt &lt; a.bc &gt; /dev/null -mypass
Bill Wendling82e2eea2006-10-11 18:00:22 +0000[diff] [blame]438<i>&lt;no output&gt;</i>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]439$ opt &lt; a.bc &gt; /dev/null -mypass -debug
440I am here!
441</pre>
442</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]443
444<p>Using the <tt>DEBUG()</tt> macro instead of a home-brewed solution allows you
445to not have to create "yet another" command line option for the debug output for
446your pass. Note that <tt>DEBUG()</tt> macros are disabled for optimized builds,
447so they do not cause a performance impact at all (for the same reason, they
448should also not contain side-effects!).</p>
449
450<p>One additional nice thing about the <tt>DEBUG()</tt> macro is that you can
451enable or disable it directly in gdb. Just use "<tt>set DebugFlag=0</tt>" or
452"<tt>set DebugFlag=1</tt>" from the gdb if the program is running. If the
453program hasn't been started yet, you can always just run it with
454<tt>-debug</tt>.</p>
455
456</div>
457
458<!-- _______________________________________________________________________ -->
459<div class="doc_subsubsection">
Chris Lattnerc9151082005-04-26 22:57:07 +0000[diff] [blame]460 <a name="DEBUG_TYPE">Fine grained debug info with <tt>DEBUG_TYPE</tt> and
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]461 the <tt>-debug-only</tt> option</a>
462</div>
463
464<div class="doc_text">
465
466<p>Sometimes you may find yourself in a situation where enabling <tt>-debug</tt>
467just turns on <b>too much</b> information (such as when working on the code
468generator). If you want to enable debug information with more fine-grained
469control, you define the <tt>DEBUG_TYPE</tt> macro and the <tt>-debug</tt> only
470option as follows:</p>
471
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]472<div class="doc_code">
473<pre>
Bill Wendling832171c2006-12-07 20:04:42 +0000[diff] [blame]474DOUT &lt;&lt; "No debug type\n";
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]475#undef DEBUG_TYPE
476#define DEBUG_TYPE "foo"
Bill Wendling832171c2006-12-07 20:04:42 +0000[diff] [blame]477DOUT &lt;&lt; "'foo' debug type\n";
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]478#undef DEBUG_TYPE
479#define DEBUG_TYPE "bar"
Bill Wendling832171c2006-12-07 20:04:42 +0000[diff] [blame]480DOUT &lt;&lt; "'bar' debug type\n";
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]481#undef DEBUG_TYPE
482#define DEBUG_TYPE ""
Bill Wendling832171c2006-12-07 20:04:42 +0000[diff] [blame]483DOUT &lt;&lt; "No debug type (2)\n";
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]484</pre>
485</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]486
487<p>Then you can run your pass like this:</p>
488
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]489<div class="doc_code">
490<pre>
491$ opt &lt; a.bc &gt; /dev/null -mypass
Bill Wendling82e2eea2006-10-11 18:00:22 +0000[diff] [blame]492<i>&lt;no output&gt;</i>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]493$ opt &lt; a.bc &gt; /dev/null -mypass -debug
494No debug type
495'foo' debug type
496'bar' debug type
497No debug type (2)
498$ opt &lt; a.bc &gt; /dev/null -mypass -debug-only=foo
499'foo' debug type
500$ opt &lt; a.bc &gt; /dev/null -mypass -debug-only=bar
501'bar' debug type
502</pre>
503</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]504
505<p>Of course, in practice, you should only set <tt>DEBUG_TYPE</tt> at the top of
506a file, to specify the debug type for the entire module (if you do this before
Chris Lattner695b78b2005-04-26 22:56:16 +0000[diff] [blame]507you <tt>#include "llvm/Support/Debug.h"</tt>, you don't have to insert the ugly
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]508<tt>#undef</tt>'s). Also, you should use names more meaningful than "foo" and
509"bar", because there is no system in place to ensure that names do not
510conflict. If two different modules use the same string, they will all be turned
511on when the name is specified. This allows, for example, all debug information
512for instruction scheduling to be enabled with <tt>-debug-type=InstrSched</tt>,
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]513even if the source lives in multiple files.</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]514
515</div>
516
517<!-- ======================================================================= -->
518<div class="doc_subsection">
Chris Lattner0be6fdf2006-12-19 21:46:21 +0000[diff] [blame]519 <a name="Statistic">The <tt>Statistic</tt> class &amp; <tt>-stats</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]520 option</a>
521</div>
522
523<div class="doc_text">
524
525<p>The "<tt><a
Chris Lattner695b78b2005-04-26 22:56:16 +0000[diff] [blame]526href="/doxygen/Statistic_8h-source.html">llvm/ADT/Statistic.h</a></tt>" file
Chris Lattner0be6fdf2006-12-19 21:46:21 +0000[diff] [blame]527provides a class named <tt>Statistic</tt> that is used as a unified way to
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]528keep track of what the LLVM compiler is doing and how effective various
529optimizations are. It is useful to see what optimizations are contributing to
530making a particular program run faster.</p>
531
532<p>Often you may run your pass on some big program, and you're interested to see
533how many times it makes a certain transformation. Although you can do this with
534hand inspection, or some ad-hoc method, this is a real pain and not very useful
Chris Lattner0be6fdf2006-12-19 21:46:21 +0000[diff] [blame]535for big programs. Using the <tt>Statistic</tt> class makes it very easy to
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]536keep track of this information, and the calculated information is presented in a
537uniform manner with the rest of the passes being executed.</p>
538
539<p>There are many examples of <tt>Statistic</tt> uses, but the basics of using
540it are as follows:</p>
541
542<ol>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]543 <li><p>Define your statistic like this:</p>
544
545<div class="doc_code">
546<pre>
Chris Lattner0be6fdf2006-12-19 21:46:21 +0000[diff] [blame]547#define <a href="#DEBUG_TYPE">DEBUG_TYPE</a> "mypassname" <i>// This goes before any #includes.</i>
548STATISTIC(NumXForms, "The # of times I did stuff");
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]549</pre>
550</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]551
Chris Lattner0be6fdf2006-12-19 21:46:21 +0000[diff] [blame]552 <p>The <tt>STATISTIC</tt> macro defines a static variable, whose name is
553 specified by the first argument. The pass name is taken from the DEBUG_TYPE
554 macro, and the description is taken from the second argument. The variable
Reid Spencer06565dc2007-01-12 17:11:23 +0000[diff] [blame]555 defined ("NumXForms" in this case) acts like an unsigned integer.</p></li>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]556
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]557 <li><p>Whenever you make a transformation, bump the counter:</p>
558
559<div class="doc_code">
560<pre>
Bill Wendling82e2eea2006-10-11 18:00:22 +0000[diff] [blame]561++NumXForms; // <i>I did stuff!</i>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]562</pre>
563</div>
564
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]565 </li>
566 </ol>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]567
568 <p>That's all you have to do. To get '<tt>opt</tt>' to print out the
569 statistics gathered, use the '<tt>-stats</tt>' option:</p>
570
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]571<div class="doc_code">
572<pre>
573$ opt -stats -mypassname &lt; program.bc &gt; /dev/null
Bill Wendling82e2eea2006-10-11 18:00:22 +0000[diff] [blame]574<i>... statistics output ...</i>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]575</pre>
576</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]577
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]578 <p> When running <tt>gccas</tt> on a C file from the SPEC benchmark
579suite, it gives a report that looks like this:</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]580
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]581<div class="doc_code">
582<pre>
583 7646 bytecodewriter - Number of normal instructions
584 725 bytecodewriter - Number of oversized instructions
585 129996 bytecodewriter - Number of bytecode bytes written
586 2817 raise - Number of insts DCEd or constprop'd
587 3213 raise - Number of cast-of-self removed
588 5046 raise - Number of expression trees converted
589 75 raise - Number of other getelementptr's formed
590 138 raise - Number of load/store peepholes
591 42 deadtypeelim - Number of unused typenames removed from symtab
592 392 funcresolve - Number of varargs functions resolved
593 27 globaldce - Number of global variables removed
594 2 adce - Number of basic blocks removed
595 134 cee - Number of branches revectored
596 49 cee - Number of setcc instruction eliminated
597 532 gcse - Number of loads removed
598 2919 gcse - Number of instructions removed
599 86 indvars - Number of canonical indvars added
600 87 indvars - Number of aux indvars removed
601 25 instcombine - Number of dead inst eliminate
602 434 instcombine - Number of insts combined
603 248 licm - Number of load insts hoisted
604 1298 licm - Number of insts hoisted to a loop pre-header
605 3 licm - Number of insts hoisted to multiple loop preds (bad, no loop pre-header)
606 75 mem2reg - Number of alloca's promoted
607 1444 cfgsimplify - Number of blocks simplified
608</pre>
609</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]610
611<p>Obviously, with so many optimizations, having a unified framework for this
612stuff is very nice. Making your pass fit well into the framework makes it more
613maintainable and useful.</p>
614
615</div>
616
Chris Lattnerf623a082005-10-17 01:36:23 +0000[diff] [blame]617<!-- ======================================================================= -->
618<div class="doc_subsection">
619 <a name="ViewGraph">Viewing graphs while debugging code</a>
620</div>
621
622<div class="doc_text">
623
624<p>Several of the important data structures in LLVM are graphs: for example
625CFGs made out of LLVM <a href="#BasicBlock">BasicBlock</a>s, CFGs made out of
626LLVM <a href="CodeGenerator.html#machinebasicblock">MachineBasicBlock</a>s, and
627<a href="CodeGenerator.html#selectiondag_intro">Instruction Selection
628DAGs</a>. In many cases, while debugging various parts of the compiler, it is
629nice to instantly visualize these graphs.</p>
630
631<p>LLVM provides several callbacks that are available in a debug build to do
632exactly that. If you call the <tt>Function::viewCFG()</tt> method, for example,
633the current LLVM tool will pop up a window containing the CFG for the function
634where each basic block is a node in the graph, and each node contains the
635instructions in the block. Similarly, there also exists
636<tt>Function::viewCFGOnly()</tt> (does not include the instructions), the
637<tt>MachineFunction::viewCFG()</tt> and <tt>MachineFunction::viewCFGOnly()</tt>,
638and the <tt>SelectionDAG::viewGraph()</tt> methods. Within GDB, for example,
Jim Laskey543a0ee2006-10-02 12:28:07 +0000[diff] [blame]639you can usually use something like <tt>call DAG.viewGraph()</tt> to pop
Chris Lattnerf623a082005-10-17 01:36:23 +0000[diff] [blame]640up a window. Alternatively, you can sprinkle calls to these functions in your
641code in places you want to debug.</p>
642
643<p>Getting this to work requires a small amount of configuration. On Unix
644systems with X11, install the <a href="http://www.graphviz.org">graphviz</a>
645toolkit, and make sure 'dot' and 'gv' are in your path. If you are running on
646Mac OS/X, download and install the Mac OS/X <a
647href="http://www.pixelglow.com/graphviz/">Graphviz program</a>, and add
648<tt>/Applications/Graphviz.app/Contents/MacOS/</tt> (or whereever you install
649it) to your path. Once in your system and path are set up, rerun the LLVM
650configure script and rebuild LLVM to enable this functionality.</p>
651
Jim Laskey543a0ee2006-10-02 12:28:07 +0000[diff] [blame]652<p><tt>SelectionDAG</tt> has been extended to make it easier to locate
653<i>interesting</i> nodes in large complex graphs. From gdb, if you
654<tt>call DAG.setGraphColor(<i>node</i>, "<i>color</i>")</tt>, then the
655next <tt>call DAG.viewGraph()</tt> would hilight the node in the
656specified color (choices of colors can be found at <a
Chris Lattner302da1e2007-02-03 03:05:57 +0000[diff] [blame]657href="http://www.graphviz.org/doc/info/colors.html">colors</a>.) More
Jim Laskey543a0ee2006-10-02 12:28:07 +0000[diff] [blame]658complex node attributes can be provided with <tt>call
659DAG.setGraphAttrs(<i>node</i>, "<i>attributes</i>")</tt> (choices can be
660found at <a href="http://www.graphviz.org/doc/info/attrs.html">Graph
661Attributes</a>.) If you want to restart and clear all the current graph
662attributes, then you can <tt>call DAG.clearGraphAttrs()</tt>. </p>
663
Chris Lattnerf623a082005-10-17 01:36:23 +0000[diff] [blame]664</div>
665
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]666<!-- *********************************************************************** -->
667<div class="doc_section">
668 <a name="datastructure">Picking the Right Data Structure for a Task</a>
669</div>
670<!-- *********************************************************************** -->
671
672<div class="doc_text">
673
674<p>LLVM has a plethora of datastructures in the <tt>llvm/ADT/</tt> directory,
675 and we commonly use STL datastructures. This section describes the tradeoffs
676 you should consider when you pick one.</p>
677
678<p>
679The first step is a choose your own adventure: do you want a sequential
680container, a set-like container, or a map-like container? The most important
681thing when choosing a container is the algorithmic properties of how you plan to
682access the container. Based on that, you should use:</p>
683
684<ul>
685<li>a <a href="#ds_map">map-like</a> container if you need efficient lookup
686 of an value based on another value. Map-like containers also support
687 efficient queries for containment (whether a key is in the map). Map-like
688 containers generally do not support efficient reverse mapping (values to
689 keys). If you need that, use two maps. Some map-like containers also
690 support efficient iteration through the keys in sorted order. Map-like
691 containers are the most expensive sort, only use them if you need one of
692 these capabilities.</li>
693
694<li>a <a href="#ds_set">set-like</a> container if you need to put a bunch of
695 stuff into a container that automatically eliminates duplicates. Some
696 set-like containers support efficient iteration through the elements in
697 sorted order. Set-like containers are more expensive than sequential
698 containers.
699</li>
700
701<li>a <a href="#ds_sequential">sequential</a> container provides
702 the most efficient way to add elements and keeps track of the order they are
703 added to the collection. They permit duplicates and support efficient
704 iteration, but do not support efficient lookup based on a key.
705</li>
706
707</ul>
708
709<p>
710Once the proper catagory of container is determined, you can fine tune the
711memory use, constant factors, and cache behaviors of access by intelligently
712picking a member of the catagory. Note that constant factors and cache behavior
713can be a big deal. If you have a vector that usually only contains a few
714elements (but could contain many), for example, it's much better to use
715<a href="#dss_smallvector">SmallVector</a> than <a href="#dss_vector">vector</a>
716. Doing so avoids (relatively) expensive malloc/free calls, which dwarf the
717cost of adding the elements to the container. </p>
718
719</div>
720
721<!-- ======================================================================= -->
722<div class="doc_subsection">
723 <a name="ds_sequential">Sequential Containers (std::vector, std::list, etc)</a>
724</div>
725
726<div class="doc_text">
727There are a variety of sequential containers available for you, based on your
728needs. Pick the first in this section that will do what you want.
729</div>
730
731<!-- _______________________________________________________________________ -->
732<div class="doc_subsubsection">
733 <a name="dss_fixedarrays">Fixed Size Arrays</a>
734</div>
735
736<div class="doc_text">
737<p>Fixed size arrays are very simple and very fast. They are good if you know
738exactly how many elements you have, or you have a (low) upper bound on how many
739you have.</p>
740</div>
741
742<!-- _______________________________________________________________________ -->
743<div class="doc_subsubsection">
744 <a name="dss_heaparrays">Heap Allocated Arrays</a>
745</div>
746
747<div class="doc_text">
748<p>Heap allocated arrays (new[] + delete[]) are also simple. They are good if
749the number of elements is variable, if you know how many elements you will need
750before the array is allocated, and if the array is usually large (if not,
751consider a <a href="#dss_smallvector">SmallVector</a>). The cost of a heap
752allocated array is the cost of the new/delete (aka malloc/free). Also note that
753if you are allocating an array of a type with a constructor, the constructor and
754destructors will be run for every element in the array (resizable vectors only
755construct those elements actually used).</p>
756</div>
757
758<!-- _______________________________________________________________________ -->
759<div class="doc_subsubsection">
760 <a name="dss_smallvector">"llvm/ADT/SmallVector.h"</a>
761</div>
762
763<div class="doc_text">
764<p><tt>SmallVector&lt;Type, N&gt;</tt> is a simple class that looks and smells
765just like <tt>vector&lt;Type&gt;</tt>:
766it supports efficient iteration, lays out elements in memory order (so you can
767do pointer arithmetic between elements), supports efficient push_back/pop_back
768operations, supports efficient random access to its elements, etc.</p>
769
770<p>The advantage of SmallVector is that it allocates space for
771some number of elements (N) <b>in the object itself</b>. Because of this, if
772the SmallVector is dynamically smaller than N, no malloc is performed. This can
773be a big win in cases where the malloc/free call is far more expensive than the
774code that fiddles around with the elements.</p>
775
776<p>This is good for vectors that are "usually small" (e.g. the number of
777predecessors/successors of a block is usually less than 8). On the other hand,
778this makes the size of the SmallVector itself large, so you don't want to
779allocate lots of them (doing so will waste a lot of space). As such,
780SmallVectors are most useful when on the stack.</p>
781
782<p>SmallVector also provides a nice portable and efficient replacement for
783<tt>alloca</tt>.</p>
784
785</div>
786
787<!-- _______________________________________________________________________ -->
788<div class="doc_subsubsection">
789 <a name="dss_vector">&lt;vector&gt;</a>
790</div>
791
792<div class="doc_text">
793<p>
794std::vector is well loved and respected. It is useful when SmallVector isn't:
795when the size of the vector is often large (thus the small optimization will
796rarely be a benefit) or if you will be allocating many instances of the vector
797itself (which would waste space for elements that aren't in the container).
798vector is also useful when interfacing with code that expects vectors :).
799</p>
800</div>
801
802<!-- _______________________________________________________________________ -->
803<div class="doc_subsubsection">
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]804 <a name="dss_deque">&lt;deque&gt;</a>
805</div>
806
807<div class="doc_text">
808<p>std::deque is, in some senses, a generalized version of std::vector. Like
809std::vector, it provides constant time random access and other similar
810properties, but it also provides efficient access to the front of the list. It
811does not guarantee continuity of elements within memory.</p>
812
813<p>In exchange for this extra flexibility, std::deque has significantly higher
814constant factor costs than std::vector. If possible, use std::vector or
815something cheaper.</p>
816</div>
817
818<!-- _______________________________________________________________________ -->
819<div class="doc_subsubsection">
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]820 <a name="dss_list">&lt;list&gt;</a>
821</div>
822
823<div class="doc_text">
824<p>std::list is an extremely inefficient class that is rarely useful.
825It performs a heap allocation for every element inserted into it, thus having an
826extremely high constant factor, particularly for small data types. std::list
827also only supports bidirectional iteration, not random access iteration.</p>
828
829<p>In exchange for this high cost, std::list supports efficient access to both
830ends of the list (like std::deque, but unlike std::vector or SmallVector). In
831addition, the iterator invalidation characteristics of std::list are stronger
832than that of a vector class: inserting or removing an element into the list does
833not invalidate iterator or pointers to other elements in the list.</p>
834</div>
835
836<!-- _______________________________________________________________________ -->
837<div class="doc_subsubsection">
838 <a name="dss_ilist">llvm/ADT/ilist</a>
839</div>
840
841<div class="doc_text">
842<p><tt>ilist&lt;T&gt;</tt> implements an 'intrusive' doubly-linked list. It is
843intrusive, because it requires the element to store and provide access to the
844prev/next pointers for the list.</p>
845
846<p>ilist has the same drawbacks as std::list, and additionally requires an
847ilist_traits implementation for the element type, but it provides some novel
848characteristics. In particular, it can efficiently store polymorphic objects,
849the traits class is informed when an element is inserted or removed from the
850list, and ilists are guaranteed to support a constant-time splice operation.
851</p>
852
853<p>These properties are exactly what we want for things like Instructions and
854basic blocks, which is why these are implemented with ilists.</p>
855</div>
856
857<!-- _______________________________________________________________________ -->
858<div class="doc_subsubsection">
Chris Lattnerc5722432007-02-03 19:49:31 +0000[diff] [blame]859 <a name="dss_other">Other Sequential Container options</a>
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]860</div>
861
862<div class="doc_text">
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]863<p>Other STL containers are available, such as std::string.</p>
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]864
865<p>There are also various STL adapter classes such as std::queue,
866std::priority_queue, std::stack, etc. These provide simplified access to an
867underlying container but don't affect the cost of the container itself.</p>
868
869</div>
870
871
872<!-- ======================================================================= -->
873<div class="doc_subsection">
874 <a name="ds_set">Set-Like Containers (std::set, SmallSet, SetVector, etc)</a>
875</div>
876
877<div class="doc_text">
878
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]879<p>Set-like containers are useful when you need to canonicalize multiple values
880into a single representation. There are several different choices for how to do
881this, providing various trade-offs.</p>
882
883</div>
884
885
886<!-- _______________________________________________________________________ -->
887<div class="doc_subsubsection">
888 <a name="dss_sortedvectorset">A sorted 'vector'</a>
889</div>
890
891<div class="doc_text">
892
Chris Lattner3b23a8c2007-02-03 08:10:45 +0000[diff] [blame]893<p>If you intend to insert a lot of elements, then do a lot of queries, a
894great approach is to use a vector (or other sequential container) with
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]895std::sort+std::unique to remove duplicates. This approach works really well if
Chris Lattner3b23a8c2007-02-03 08:10:45 +0000[diff] [blame]896your usage pattern has these two distinct phases (insert then query), and can be
897coupled with a good choice of <a href="#ds_sequential">sequential container</a>.
898</p>
899
900<p>
901This combination provides the several nice properties: the result data is
902contiguous in memory (good for cache locality), has few allocations, is easy to
903address (iterators in the final vector are just indices or pointers), and can be
904efficiently queried with a standard binary or radix search.</p>
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]905
906</div>
907
908<!-- _______________________________________________________________________ -->
909<div class="doc_subsubsection">
910 <a name="dss_smallset">"llvm/ADT/SmallSet.h"</a>
911</div>
912
913<div class="doc_text">
914
915<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]916are 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]917has space for N elements in place (thus, if the set is dynamically smaller than
Chris Lattner14868db2007-02-03 08:20:15 +0000[diff] [blame]918N, no malloc traffic is required) and accesses them with a simple linear search.
919When the set grows beyond 'N' elements, it allocates a more expensive representation that
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]920guarantees efficient access (for most types, it falls back to std::set, but for
Chris Lattner14868db2007-02-03 08:20:15 +0000[diff] [blame]921pointers it uses something far better, <a
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]922href="#dss_smallptrset">SmallPtrSet</a>).</p>
923
924<p>The magic of this class is that it handles small sets extremely efficiently,
925but gracefully handles extremely large sets without loss of efficiency. The
926drawback is that the interface is quite small: it supports insertion, queries
927and erasing, but does not support iteration.</p>
928
929</div>
930
931<!-- _______________________________________________________________________ -->
932<div class="doc_subsubsection">
933 <a name="dss_smallptrset">"llvm/ADT/SmallPtrSet.h"</a>
934</div>
935
936<div class="doc_text">
937
938<p>SmallPtrSet has all the advantages of SmallSet (and a SmallSet of pointers is
939transparently implemented with a SmallPtrSet), but also suports iterators. If
Chris Lattner14868db2007-02-03 08:20:15 +0000[diff] [blame]940more than 'N' insertions are performed, a single quadratically
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]941probed hash table is allocated and grows as needed, providing extremely
942efficient access (constant time insertion/deleting/queries with low constant
943factors) and is very stingy with malloc traffic.</p>
944
945<p>Note that, unlike std::set, the iterators of SmallPtrSet are invalidated
946whenever an insertion occurs. Also, the values visited by the iterators are not
947visited in sorted order.</p>
948
949</div>
950
951<!-- _______________________________________________________________________ -->
952<div class="doc_subsubsection">
953 <a name="dss_FoldingSet">"llvm/ADT/FoldingSet.h"</a>
954</div>
955
956<div class="doc_text">
957
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]958<p>
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]959FoldingSet is an aggregate class that is really good at uniquing
960expensive-to-create or polymorphic objects. It is a combination of a chained
961hash table with intrusive links (uniqued objects are required to inherit from
Chris Lattner14868db2007-02-03 08:20:15 +0000[diff] [blame]962FoldingSetNode) that uses <a href="#dss_smallvector">SmallVector</a> as part of
963its ID process.</p>
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]964
Chris Lattner14868db2007-02-03 08:20:15 +0000[diff] [blame]965<p>Consider a case where you want to implement a "getOrCreateFoo" method for
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]966a complex object (for example, a node in the code generator). The client has a
967description of *what* it wants to generate (it knows the opcode and all the
968operands), 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]969only to find out it already exists, at which point we would have to delete it
970and return the node that already exists.
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]971</p>
972
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]973<p>To support this style of client, FoldingSet perform a query with a
974FoldingSetNodeID (which wraps SmallVector) that can be used to describe the
975element that we want to query for. The query either returns the element
976matching the ID or it returns an opaque ID that indicates where insertion should
Chris Lattner14868db2007-02-03 08:20:15 +0000[diff] [blame]977take place. Construction of the ID usually does not require heap traffic.</p>
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]978
979<p>Because FoldingSet uses intrusive links, it can support polymorphic objects
980in the set (for example, you can have SDNode instances mixed with LoadSDNodes).
981Because the elements are individually allocated, pointers to the elements are
982stable: inserting or removing elements does not invalidate any pointers to other
983elements.
984</p>
985
986</div>
987
988<!-- _______________________________________________________________________ -->
989<div class="doc_subsubsection">
990 <a name="dss_set">&lt;set&gt;</a>
991</div>
992
993<div class="doc_text">
994
Chris Lattnerc5722432007-02-03 19:49:31 +0000[diff] [blame]995<p><tt>std::set</tt> is a reasonable all-around set class, which is decent at
996many things but great at nothing. std::set allocates memory for each element
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]997inserted (thus it is very malloc intensive) and typically stores three pointers
Chris Lattner14868db2007-02-03 08:20:15 +0000[diff] [blame]998per element in the set (thus adding a large amount of per-element space
999overhead). It offers guaranteed log(n) performance, which is not particularly
Chris Lattnerc5722432007-02-03 19:49:31 +0000[diff] [blame]1000fast from a complexity standpoint (particularly if the elements of the set are
1001expensive to compare, like strings), and has extremely high constant factors for
1002lookup, insertion and removal.</p>
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1003
Chris Lattner14868db2007-02-03 08:20:15 +0000[diff] [blame]1004<p>The advantages of std::set are that its iterators are stable (deleting or
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1005inserting an element from the set does not affect iterators or pointers to other
1006elements) and that iteration over the set is guaranteed to be in sorted order.
1007If the elements in the set are large, then the relative overhead of the pointers
1008and malloc traffic is not a big deal, but if the elements of the set are small,
1009std::set is almost never a good choice.</p>
1010
1011</div>
1012
1013<!-- _______________________________________________________________________ -->
1014<div class="doc_subsubsection">
1015 <a name="dss_setvector">"llvm/ADT/SetVector.h"</a>
1016</div>
1017
1018<div class="doc_text">
1019<p>LLVM's SetVector&lt;Type&gt; is actually a combination of a set along with
1020a <a href="#ds_sequential">Sequential Container</a>. The important property
1021that this provides is efficient insertion with uniquing (duplicate elements are
1022ignored) with iteration support. It implements this by inserting elements into
1023both a set-like container and the sequential container, using the set-like
1024container for uniquing and the sequential container for iteration.
1025</p>
1026
1027<p>The difference between SetVector and other sets is that the order of
1028iteration is guaranteed to match the order of insertion into the SetVector.
1029This property is really important for things like sets of pointers. Because
1030pointer values are non-deterministic (e.g. vary across runs of the program on
1031different machines), iterating over the pointers in a std::set or other set will
1032not be in a well-defined order.</p>
1033
1034<p>
1035The drawback of SetVector is that it requires twice as much space as a normal
1036set and has the sum of constant factors from the set-like container and the
1037sequential container that it uses. Use it *only* if you need to iterate over
1038the elements in a deterministic order. SetVector is also expensive to delete
1039elements out of (linear time).
1040</p>
1041
1042</div>
1043
1044<!-- _______________________________________________________________________ -->
1045<div class="doc_subsubsection">
Chris Lattnerc5722432007-02-03 19:49:31 +0000[diff] [blame]1046 <a name="dss_uniquevector">"llvm/ADT/UniqueVector.h"</a>
1047</div>
1048
1049<div class="doc_text">
1050
1051<p>
1052UniqueVector is similar to <a href="#dss_setvector">SetVector</a>, but it
1053retains a unique ID for each element inserted into the set. It internally
1054contains a map and a vector, and it assigns a unique ID for each value inserted
1055into the set.</p>
1056
1057<p>UniqueVector is very expensive: its cost is the sum of the cost of
1058maintaining both the map and vector, it has high complexity, high constant
1059factors, and produces a lot of malloc traffic. It should be avoided.</p>
1060
1061</div>
1062
1063
1064<!-- _______________________________________________________________________ -->
1065<div class="doc_subsubsection">
1066 <a name="dss_otherset">Other Set-Like Container Options</a>
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1067</div>
1068
1069<div class="doc_text">
1070
1071<p>
1072The STL provides several other options, such as std::multiset and the various
Chris Lattnerc5722432007-02-03 19:49:31 +0000[diff] [blame]1073"hash_set" like containers (whether from C++ TR1 or from the SGI library).</p>
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1074
1075<p>std::multiset is useful if you're not interested in elimination of
Chris Lattner14868db2007-02-03 08:20:15 +0000[diff] [blame]1076duplicates, but has all the drawbacks of std::set. A sorted vector (where you
1077don't delete duplicate entries) or some other approach is almost always
1078better.</p>
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1079
1080<p>The various hash_set implementations (exposed portably by
Chris Lattner14868db2007-02-03 08:20:15 +0000[diff] [blame]1081"llvm/ADT/hash_set") is a simple chained hashtable. This algorithm is as malloc
1082intensive as std::set (performing an allocation for each element inserted,
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1083thus having really high constant factors) but (usually) provides O(1)
1084insertion/deletion of elements. This can be useful if your elements are large
Chris Lattner14868db2007-02-03 08:20:15 +0000[diff] [blame]1085(thus making the constant-factor cost relatively low) or if comparisons are
1086expensive. Element iteration does not visit elements in a useful order.</p>
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1087
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]1088</div>
1089
1090<!-- ======================================================================= -->
1091<div class="doc_subsection">
1092 <a name="ds_map">Map-Like Containers (std::map, DenseMap, etc)</a>
1093</div>
1094
1095<div class="doc_text">
Chris Lattnerc5722432007-02-03 19:49:31 +0000[diff] [blame]1096Map-like containers are useful when you want to associate data to a key. As
1097usual, there are a lot of different ways to do this. :)
1098</div>
1099
1100<!-- _______________________________________________________________________ -->
1101<div class="doc_subsubsection">
1102 <a name="dss_sortedvectormap">A sorted 'vector'</a>
1103</div>
1104
1105<div class="doc_text">
1106
1107<p>
1108If your usage pattern follows a strict insert-then-query approach, you can
1109trivially use the same approach as <a href="#dss_sortedvectorset">sorted vectors
1110for set-like containers</a>. The only difference is that your query function
1111(which uses std::lower_bound to get efficient log(n) lookup) should only compare
1112the key, not both the key and value. This yields the same advantages as sorted
1113vectors for sets.
1114</p>
1115</div>
1116
1117<!-- _______________________________________________________________________ -->
1118<div class="doc_subsubsection">
1119 <a name="dss_cstringmap">"llvm/ADT/CStringMap.h"</a>
1120</div>
1121
1122<div class="doc_text">
1123
1124<p>
1125Strings are commonly used as keys in maps, and they are difficult to support
1126efficiently: they are variable length, inefficient to hash and compare when
1127long, expensive to copy, etc. CStringMap is a specialized container designed to
1128cope with these issues. It supports mapping an arbitrary range of bytes that
1129does not have an embedded nul character in it ("C strings") to an arbitrary
1130other object.</p>
1131
1132<p>The CStringMap implementation uses a quadratically-probed hash table, where
1133the buckets store a pointer to the heap allocated entries (and some other
1134stuff). The entries in the map must be heap allocated because the strings are
1135variable length. The string data (key) and the element object (value) are
1136stored in the same allocation with the string data immediately after the element
1137object. This container guarantees the "<tt>(char*)(&amp;Value+1)</tt>" points
1138to the key string for a value.</p>
1139
1140<p>The CStringMap is very fast for several reasons: quadratic probing is very
1141cache efficient for lookups, the hash value of strings in buckets is not
1142recomputed when lookup up an element, CStringMap rarely has to touch the
1143memory for unrelated objects when looking up a value (even when hash collisions
1144happen), hash table growth does not recompute the hash values for strings
1145already in the table, and each pair in the map is store in a single allocation
1146(the string data is stored in the same allocation as the Value of a pair).</p>
1147
1148<p>CStringMap also provides query methods that take byte ranges, so it only ever
1149copies a string if a value is inserted into the table.</p>
1150</div>
1151
1152<!-- _______________________________________________________________________ -->
1153<div class="doc_subsubsection">
1154 <a name="dss_indexedmap">"llvm/ADT/IndexedMap.h"</a>
1155</div>
1156
1157<div class="doc_text">
1158<p>
1159IndexedMap is a specialized container for mapping small dense integers (or
1160values that can be mapped to small dense integers) to some other type. It is
1161internally implemented as a vector with a mapping function that maps the keys to
1162the dense integer range.
1163</p>
1164
1165<p>
1166This is useful for cases like virtual registers in the LLVM code generator: they
1167have a dense mapping that is offset by a compile-time constant (the first
1168virtual register ID).</p>
1169
1170</div>
1171
1172<!-- _______________________________________________________________________ -->
1173<div class="doc_subsubsection">
1174 <a name="dss_densemap">"llvm/ADT/DenseMap.h"</a>
1175</div>
1176
1177<div class="doc_text">
1178
1179<p>
1180DenseMap is a simple quadratically probed hash table. It excels at supporting
1181small keys and values: it uses a single allocation to hold all of the pairs that
1182are currently inserted in the map. DenseMap is a great way to map pointers to
1183pointers, or map other small types to each other.
1184</p>
1185
1186<p>
1187There are several aspects of DenseMap that you should be aware of, however. The
1188iterators in a densemap are invalidated whenever an insertion occurs, unlike
1189map. Also, because DenseMap allocates space for a large number of key/value
1190pairs (it starts with 64 by default) if you have large keys or values, it can
1191waste a lot of space. Finally, you must implement a partial specialization of
1192DenseMapKeyInfo for the key that you want, if it isn't already supported. This
1193is required to tell DenseMap about two special marker values (which can never be
1194inserted into the map).</p>
1195
1196</div>
1197
1198<!-- _______________________________________________________________________ -->
1199<div class="doc_subsubsection">
1200 <a name="dss_map">&lt;map&gt;</a>
1201</div>
1202
1203<div class="doc_text">
1204
1205<p>
1206std::map has similar characteristics to <a href="#dss_set">std::set</a>: it uses
1207a single allocation per pair inserted into the map, it offers log(n) lookup with
1208an extremely large constant factor, imposes a space penalty of 3 pointers per
1209pair in the map, etc.</p>
1210
1211<p>std::map is most useful when your keys or values are very large, if you need
1212to iterate over the collection in sorted order, or if you need stable iterators
1213into the map (i.e. they don't get invalidated if an insertion or deletion of
1214another element takes place).</p>
1215
1216</div>
1217
1218<!-- _______________________________________________________________________ -->
1219<div class="doc_subsubsection">
1220 <a name="dss_othermap">Other Map-Like Container Options</a>
1221</div>
1222
1223<div class="doc_text">
1224
1225<p>
1226The STL provides several other options, such as std::multimap and the various
1227"hash_map" like containers (whether from C++ TR1 or from the SGI library).</p>
1228
1229<p>std::multimap is useful if you want to map a key to multiple values, but has
1230all the drawbacks of std::map. A sorted vector or some other approach is almost
1231always better.</p>
1232
1233<p>The various hash_map implementations (exposed portably by
1234"llvm/ADT/hash_map") are simple chained hash tables. This algorithm is as
1235malloc intensive as std::map (performing an allocation for each element
1236inserted, thus having really high constant factors) but (usually) provides O(1)
1237insertion/deletion of elements. This can be useful if your elements are large
1238(thus making the constant-factor cost relatively low) or if comparisons are
1239expensive. Element iteration does not visit elements in a useful order.</p>
1240
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]1241</div>
1242
Chris Lattnerf623a082005-10-17 01:36:23 +0000[diff] [blame]1243
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1244<!-- *********************************************************************** -->
1245<div class="doc_section">
1246 <a name="common">Helpful Hints for Common Operations</a>
1247</div>
1248<!-- *********************************************************************** -->
1249
1250<div class="doc_text">
1251
1252<p>This section describes how to perform some very simple transformations of
1253LLVM code. This is meant to give examples of common idioms used, showing the
1254practical side of LLVM transformations. <p> Because this is a "how-to" section,
1255you should also read about the main classes that you will be working with. The
1256<a href="#coreclasses">Core LLVM Class Hierarchy Reference</a> contains details
1257and descriptions of the main classes that you should know about.</p>
1258
1259</div>
1260
1261<!-- NOTE: this section should be heavy on example code -->
1262<!-- ======================================================================= -->
1263<div class="doc_subsection">
1264 <a name="inspection">Basic Inspection and Traversal Routines</a>
1265</div>
1266
1267<div class="doc_text">
1268
1269<p>The LLVM compiler infrastructure have many different data structures that may
1270be traversed. Following the example of the C++ standard template library, the
1271techniques used to traverse these various data structures are all basically the
1272same. For a enumerable sequence of values, the <tt>XXXbegin()</tt> function (or
1273method) returns an iterator to the start of the sequence, the <tt>XXXend()</tt>
1274function returns an iterator pointing to one past the last valid element of the
1275sequence, and there is some <tt>XXXiterator</tt> data type that is common
1276between the two operations.</p>
1277
1278<p>Because the pattern for iteration is common across many different aspects of
1279the program representation, the standard template library algorithms may be used
1280on them, and it is easier to remember how to iterate. First we show a few common
1281examples of the data structures that need to be traversed. Other data
1282structures are traversed in very similar ways.</p>
1283
1284</div>
1285
1286<!-- _______________________________________________________________________ -->
Chris Lattner69bf8a92004-05-23 21:06:58 +0000[diff] [blame]1287<div class="doc_subsubsection">
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1288 <a name="iterate_function">Iterating over the </a><a
1289 href="#BasicBlock"><tt>BasicBlock</tt></a>s in a <a
1290 href="#Function"><tt>Function</tt></a>
1291</div>
1292
1293<div class="doc_text">
1294
1295<p>It's quite common to have a <tt>Function</tt> instance that you'd like to
1296transform in some way; in particular, you'd like to manipulate its
1297<tt>BasicBlock</tt>s. To facilitate this, you'll need to iterate over all of
1298the <tt>BasicBlock</tt>s that constitute the <tt>Function</tt>. The following is
1299an example that prints the name of a <tt>BasicBlock</tt> and the number of
1300<tt>Instruction</tt>s it contains:</p>
1301
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1302<div class="doc_code">
1303<pre>
Bill Wendling82e2eea2006-10-11 18:00:22 +0000[diff] [blame]1304// <i>func is a pointer to a Function instance</i>
1305for (Function::iterator i = func-&gt;begin(), e = func-&gt;end(); i != e; ++i)
1306 // <i>Print out the name of the basic block if it has one, and then the</i>
1307 // <i>number of instructions that it contains</i>
Bill Wendling832171c2006-12-07 20:04:42 +0000[diff] [blame]1308 llvm::cerr &lt;&lt; "Basic block (name=" &lt;&lt; i-&gt;getName() &lt;&lt; ") has "
1309 &lt;&lt; i-&gt;size() &lt;&lt; " instructions.\n";
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1310</pre>
1311</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1312
1313<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]1314invoking member functions of the <tt>Instruction</tt> class. This is
1315because the indirection operator is overloaded for the iterator
Chris Lattner7496ec52003-08-05 22:54:23 +0000[diff] [blame]1316classes. In the above code, the expression <tt>i-&gt;size()</tt> is
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1317exactly equivalent to <tt>(*i).size()</tt> just like you'd expect.</p>
1318
1319</div>
1320
1321<!-- _______________________________________________________________________ -->
Chris Lattner69bf8a92004-05-23 21:06:58 +0000[diff] [blame]1322<div class="doc_subsubsection">
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1323 <a name="iterate_basicblock">Iterating over the </a><a
1324 href="#Instruction"><tt>Instruction</tt></a>s in a <a
1325 href="#BasicBlock"><tt>BasicBlock</tt></a>
1326</div>
1327
1328<div class="doc_text">
1329
1330<p>Just like when dealing with <tt>BasicBlock</tt>s in <tt>Function</tt>s, it's
1331easy to iterate over the individual instructions that make up
1332<tt>BasicBlock</tt>s. Here's a code snippet that prints out each instruction in
1333a <tt>BasicBlock</tt>:</p>
1334
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1335<div class="doc_code">
Chris Lattner55c04612005-03-06 06:00:13 +0000[diff] [blame]1336<pre>
Bill Wendling82e2eea2006-10-11 18:00:22 +0000[diff] [blame]1337// <i>blk is a pointer to a BasicBlock instance</i>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1338for (BasicBlock::iterator i = blk-&gt;begin(), e = blk-&gt;end(); i != e; ++i)
Bill Wendling82e2eea2006-10-11 18:00:22 +0000[diff] [blame]1339 // <i>The next statement works since operator&lt;&lt;(ostream&amp;,...)</i>
1340 // <i>is overloaded for Instruction&amp;</i>
Bill Wendling832171c2006-12-07 20:04:42 +0000[diff] [blame]1341 llvm::cerr &lt;&lt; *i &lt;&lt; "\n";
Chris Lattner55c04612005-03-06 06:00:13 +0000[diff] [blame]1342</pre>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1343</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1344
1345<p>However, this isn't really the best way to print out the contents of a
1346<tt>BasicBlock</tt>! Since the ostream operators are overloaded for virtually
1347anything you'll care about, you could have just invoked the print routine on the
Bill Wendling832171c2006-12-07 20:04:42 +0000[diff] [blame]1348basic block itself: <tt>llvm::cerr &lt;&lt; *blk &lt;&lt; "\n";</tt>.</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1349
1350</div>
1351
1352<!-- _______________________________________________________________________ -->
Chris Lattner69bf8a92004-05-23 21:06:58 +0000[diff] [blame]1353<div class="doc_subsubsection">
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1354 <a name="iterate_institer">Iterating over the </a><a
1355 href="#Instruction"><tt>Instruction</tt></a>s in a <a
1356 href="#Function"><tt>Function</tt></a>
1357</div>
1358
1359<div class="doc_text">
1360
1361<p>If you're finding that you commonly iterate over a <tt>Function</tt>'s
1362<tt>BasicBlock</tt>s and then that <tt>BasicBlock</tt>'s <tt>Instruction</tt>s,
1363<tt>InstIterator</tt> should be used instead. You'll need to include <a
1364href="/doxygen/InstIterator_8h-source.html"><tt>llvm/Support/InstIterator.h</tt></a>,
1365and then instantiate <tt>InstIterator</tt>s explicitly in your code. Here's a
Chris Lattner69bf8a92004-05-23 21:06:58 +0000[diff] [blame]1366small 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]1367
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1368<div class="doc_code">
1369<pre>
1370#include "<a href="/doxygen/InstIterator_8h-source.html">llvm/Support/InstIterator.h</a>"
1371
Bill Wendling82e2eea2006-10-11 18:00:22 +0000[diff] [blame]1372// <i>F is a ptr to a Function instance</i>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1373for (inst_iterator i = inst_begin(F), e = inst_end(F); i != e; ++i)
Bill Wendling832171c2006-12-07 20:04:42 +0000[diff] [blame]1374 llvm::cerr &lt;&lt; *i &lt;&lt; "\n";
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1375</pre>
1376</div>
1377
1378<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]1379worklist with its initial contents. For example, if you wanted to
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]1380initialize a worklist to contain all instructions in a <tt>Function</tt>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1381F, all you would need to do is something like:</p>
1382
1383<div class="doc_code">
1384<pre>
1385std::set&lt;Instruction*&gt; worklist;
1386worklist.insert(inst_begin(F), inst_end(F));
1387</pre>
1388</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1389
1390<p>The STL set <tt>worklist</tt> would now contain all instructions in the
1391<tt>Function</tt> pointed to by F.</p>
1392
1393</div>
1394
1395<!-- _______________________________________________________________________ -->
1396<div class="doc_subsubsection">
1397 <a name="iterate_convert">Turning an iterator into a class pointer (and
1398 vice-versa)</a>
1399</div>
1400
1401<div class="doc_text">
1402
1403<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]1404instance when all you've got at hand is an iterator. Well, extracting
Chris Lattner69bf8a92004-05-23 21:06:58 +0000[diff] [blame]1405a reference or a pointer from an iterator is very straight-forward.
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]1406Assuming that <tt>i</tt> is a <tt>BasicBlock::iterator</tt> and <tt>j</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1407is a <tt>BasicBlock::const_iterator</tt>:</p>
1408
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1409<div class="doc_code">
1410<pre>
Bill Wendling82e2eea2006-10-11 18:00:22 +0000[diff] [blame]1411Instruction&amp; inst = *i; // <i>Grab reference to instruction reference</i>
1412Instruction* pinst = &amp;*i; // <i>Grab pointer to instruction reference</i>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1413const Instruction&amp; inst = *j;
1414</pre>
1415</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1416
1417<p>However, the iterators you'll be working with in the LLVM framework are
1418special: they will automatically convert to a ptr-to-instance type whenever they
1419need to. Instead of dereferencing the iterator and then taking the address of
1420the result, you can simply assign the iterator to the proper pointer type and
1421you get the dereference and address-of operation as a result of the assignment
1422(behind the scenes, this is a result of overloading casting mechanisms). Thus
1423the last line of the last example,</p>
1424
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1425<div class="doc_code">
1426<pre>
1427Instruction* pinst = &amp;*i;
1428</pre>
1429</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1430
1431<p>is semantically equivalent to</p>
1432
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1433<div class="doc_code">
1434<pre>
1435Instruction* pinst = i;
1436</pre>
1437</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1438
Chris Lattner69bf8a92004-05-23 21:06:58 +0000[diff] [blame]1439<p>It's also possible to turn a class pointer into the corresponding iterator,
1440and this is a constant time operation (very efficient). The following code
1441snippet illustrates use of the conversion constructors provided by LLVM
1442iterators. By using these, you can explicitly grab the iterator of something
1443without actually obtaining it via iteration over some structure:</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1444
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1445<div class="doc_code">
1446<pre>
1447void printNextInstruction(Instruction* inst) {
1448 BasicBlock::iterator it(inst);
Bill Wendling82e2eea2006-10-11 18:00:22 +0000[diff] [blame]1449 ++it; // <i>After this line, it refers to the instruction after *inst</i>
Bill Wendling832171c2006-12-07 20:04:42 +0000[diff] [blame]1450 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]1451}
1452</pre>
1453</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1454
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1455</div>
1456
1457<!--_______________________________________________________________________-->
1458<div class="doc_subsubsection">
1459 <a name="iterate_complex">Finding call sites: a slightly more complex
1460 example</a>
1461</div>
1462
1463<div class="doc_text">
1464
1465<p>Say that you're writing a FunctionPass and would like to count all the
1466locations in the entire module (that is, across every <tt>Function</tt>) where a
1467certain function (i.e., some <tt>Function</tt>*) is already in scope. As you'll
1468learn 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]1469much more straight-forward manner, but this example will allow us to explore how
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1470you'd do it if you didn't have <tt>InstVisitor</tt> around. In pseudocode, this
1471is what we want to do:</p>
1472
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1473<div class="doc_code">
1474<pre>
1475initialize callCounter to zero
1476for each Function f in the Module
1477 for each BasicBlock b in f
1478 for each Instruction i in b
1479 if (i is a CallInst and calls the given function)
1480 increment callCounter
1481</pre>
1482</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1483
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1484<p>And the actual code is (remember, because we're writing a
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1485<tt>FunctionPass</tt>, our <tt>FunctionPass</tt>-derived class simply has to
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1486override the <tt>runOnFunction</tt> method):</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1487
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1488<div class="doc_code">
1489<pre>
1490Function* targetFunc = ...;
1491
1492class OurFunctionPass : public FunctionPass {
1493 public:
1494 OurFunctionPass(): callCounter(0) { }
1495
1496 virtual runOnFunction(Function&amp; F) {
1497 for (Function::iterator b = F.begin(), be = F.end(); b != be; ++b) {
1498 for (BasicBlock::iterator i = b-&gt;begin(); ie = b-&gt;end(); i != ie; ++i) {
1499 if (<a href="#CallInst">CallInst</a>* callInst = <a href="#isa">dyn_cast</a>&lt;<a
1500 href="#CallInst">CallInst</a>&gt;(&amp;*i)) {
Bill Wendling82e2eea2006-10-11 18:00:22 +0000[diff] [blame]1501 // <i>We know we've encountered a call instruction, so we</i>
1502 // <i>need to determine if it's a call to the</i>
1503 // <i>function pointed to by m_func or not</i>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1504
1505 if (callInst-&gt;getCalledFunction() == targetFunc)
1506 ++callCounter;
1507 }
1508 }
1509 }
Bill Wendling82e2eea2006-10-11 18:00:22 +0000[diff] [blame]1510 }
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1511
1512 private:
1513 unsigned callCounter;
1514};
1515</pre>
1516</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1517
1518</div>
1519
Brian Gaekef1972c62003-11-07 19:25:45 +0000[diff] [blame]1520<!--_______________________________________________________________________-->
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1521<div class="doc_subsubsection">
1522 <a name="calls_and_invokes">Treating calls and invokes the same way</a>
1523</div>
1524
1525<div class="doc_text">
1526
1527<p>You may have noticed that the previous example was a bit oversimplified in
1528that it did not deal with call sites generated by 'invoke' instructions. In
1529this, and in other situations, you may find that you want to treat
1530<tt>CallInst</tt>s and <tt>InvokeInst</tt>s the same way, even though their
1531most-specific common base class is <tt>Instruction</tt>, which includes lots of
1532less closely-related things. For these cases, LLVM provides a handy wrapper
1533class called <a
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]1534href="http://llvm.org/doxygen/classllvm_1_1CallSite.html"><tt>CallSite</tt></a>.
Chris Lattner69bf8a92004-05-23 21:06:58 +0000[diff] [blame]1535It is essentially a wrapper around an <tt>Instruction</tt> pointer, with some
1536methods that provide functionality common to <tt>CallInst</tt>s and
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1537<tt>InvokeInst</tt>s.</p>
1538
Chris Lattner69bf8a92004-05-23 21:06:58 +0000[diff] [blame]1539<p>This class has "value semantics": it should be passed by value, not by
1540reference and it should not be dynamically allocated or deallocated using
1541<tt>operator new</tt> or <tt>operator delete</tt>. It is efficiently copyable,
1542assignable and constructable, with costs equivalents to that of a bare pointer.
1543If you look at its definition, it has only a single pointer member.</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1544
1545</div>
1546
Chris Lattner1a3105b2002-09-09 05:49:39 +0000[diff] [blame]1547<!--_______________________________________________________________________-->
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1548<div class="doc_subsubsection">
1549 <a name="iterate_chains">Iterating over def-use &amp; use-def chains</a>
1550</div>
1551
1552<div class="doc_text">
1553
1554<p>Frequently, we might have an instance of the <a
Chris Lattner00815172007-01-04 22:01:45 +0000[diff] [blame]1555href="/doxygen/classllvm_1_1Value.html">Value Class</a> and we want to
Misha Brukman384047f2004-06-03 23:29:12 +0000[diff] [blame]1556determine which <tt>User</tt>s use the <tt>Value</tt>. The list of all
1557<tt>User</tt>s of a particular <tt>Value</tt> is called a <i>def-use</i> chain.
1558For example, let's say we have a <tt>Function*</tt> named <tt>F</tt> to a
1559particular function <tt>foo</tt>. Finding all of the instructions that
1560<i>use</i> <tt>foo</tt> is as simple as iterating over the <i>def-use</i> chain
1561of <tt>F</tt>:</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1562
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1563<div class="doc_code">
1564<pre>
1565Function* F = ...;
1566
Bill Wendling82e2eea2006-10-11 18:00:22 +0000[diff] [blame]1567for (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]1568 if (Instruction *Inst = dyn_cast&lt;Instruction&gt;(*i)) {
Bill Wendling832171c2006-12-07 20:04:42 +0000[diff] [blame]1569 llvm::cerr &lt;&lt; "F is used in instruction:\n";
1570 llvm::cerr &lt;&lt; *Inst &lt;&lt; "\n";
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1571 }
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1572</pre>
1573</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1574
1575<p>Alternately, it's common to have an instance of the <a
Misha Brukman384047f2004-06-03 23:29:12 +0000[diff] [blame]1576href="/doxygen/classllvm_1_1User.html">User Class</a> and need to know what
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1577<tt>Value</tt>s are used by it. The list of all <tt>Value</tt>s used by a
1578<tt>User</tt> is known as a <i>use-def</i> chain. Instances of class
1579<tt>Instruction</tt> are common <tt>User</tt>s, so we might want to iterate over
1580all of the values that a particular instruction uses (that is, the operands of
1581the particular <tt>Instruction</tt>):</p>
1582
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1583<div class="doc_code">
1584<pre>
1585Instruction* pi = ...;
1586
1587for (User::op_iterator i = pi-&gt;op_begin(), e = pi-&gt;op_end(); i != e; ++i) {
1588 Value* v = *i;
Bill Wendling82e2eea2006-10-11 18:00:22 +0000[diff] [blame]1589 // <i>...</i>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1590}
1591</pre>
1592</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1593
Chris Lattner1a3105b2002-09-09 05:49:39 +0000[diff] [blame]1594<!--
1595 def-use chains ("finding all users of"): Value::use_begin/use_end
1596 use-def chains ("finding all values used"): User::op_begin/op_end [op=operand]
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1597-->
1598
1599</div>
1600
1601<!-- ======================================================================= -->
1602<div class="doc_subsection">
1603 <a name="simplechanges">Making simple changes</a>
1604</div>
1605
1606<div class="doc_text">
1607
1608<p>There are some primitive transformation operations present in the LLVM
Joel Stanley753eb712002-09-11 22:32:24 +0000[diff] [blame]1609infrastructure that are worth knowing about. When performing
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]1610transformations, it's fairly common to manipulate the contents of basic
1611blocks. This section describes some of the common methods for doing so
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1612and gives example code.</p>
1613
1614</div>
1615
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]1616<!--_______________________________________________________________________-->
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1617<div class="doc_subsubsection">
1618 <a name="schanges_creating">Creating and inserting new
1619 <tt>Instruction</tt>s</a>
1620</div>
1621
1622<div class="doc_text">
1623
1624<p><i>Instantiating Instructions</i></p>
1625
Chris Lattner69bf8a92004-05-23 21:06:58 +0000[diff] [blame]1626<p>Creation of <tt>Instruction</tt>s is straight-forward: simply call the
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1627constructor for the kind of instruction to instantiate and provide the necessary
1628parameters. For example, an <tt>AllocaInst</tt> only <i>requires</i> a
1629(const-ptr-to) <tt>Type</tt>. Thus:</p>
1630
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1631<div class="doc_code">
1632<pre>
1633AllocaInst* ai = new AllocaInst(Type::IntTy);
1634</pre>
1635</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1636
1637<p>will create an <tt>AllocaInst</tt> instance that represents the allocation of
1638one integer in the current stack frame, at runtime. Each <tt>Instruction</tt>
1639subclass is likely to have varying default parameters which change the semantics
1640of the instruction, so refer to the <a
Misha Brukman31ca1de2004-06-03 23:35:54 +0000[diff] [blame]1641href="/doxygen/classllvm_1_1Instruction.html">doxygen documentation for the subclass of
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1642Instruction</a> that you're interested in instantiating.</p>
1643
1644<p><i>Naming values</i></p>
1645
1646<p>It is very useful to name the values of instructions when you're able to, as
1647this facilitates the debugging of your transformations. If you end up looking
1648at generated LLVM machine code, you definitely want to have logical names
1649associated with the results of instructions! By supplying a value for the
1650<tt>Name</tt> (default) parameter of the <tt>Instruction</tt> constructor, you
1651associate a logical name with the result of the instruction's execution at
1652runtime. For example, say that I'm writing a transformation that dynamically
1653allocates space for an integer on the stack, and that integer is going to be
1654used as some kind of index by some other code. To accomplish this, I place an
1655<tt>AllocaInst</tt> at the first point in the first <tt>BasicBlock</tt> of some
1656<tt>Function</tt>, and I'm intending to use it within the same
1657<tt>Function</tt>. I might do:</p>
1658
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1659<div class="doc_code">
1660<pre>
1661AllocaInst* pa = new AllocaInst(Type::IntTy, 0, "indexLoc");
1662</pre>
1663</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1664
1665<p>where <tt>indexLoc</tt> is now the logical name of the instruction's
1666execution value, which is a pointer to an integer on the runtime stack.</p>
1667
1668<p><i>Inserting instructions</i></p>
1669
1670<p>There are essentially two ways to insert an <tt>Instruction</tt>
1671into an existing sequence of instructions that form a <tt>BasicBlock</tt>:</p>
1672
Joel Stanley9dd1ad62002-09-18 03:17:23 +0000[diff] [blame]1673<ul>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1674 <li>Insertion into an explicit instruction list
1675
1676 <p>Given a <tt>BasicBlock* pb</tt>, an <tt>Instruction* pi</tt> within that
1677 <tt>BasicBlock</tt>, and a newly-created instruction we wish to insert
1678 before <tt>*pi</tt>, we do the following: </p>
1679
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1680<div class="doc_code">
1681<pre>
1682BasicBlock *pb = ...;
1683Instruction *pi = ...;
1684Instruction *newInst = new Instruction(...);
1685
Bill Wendling82e2eea2006-10-11 18:00:22 +0000[diff] [blame]1686pb-&gt;getInstList().insert(pi, newInst); // <i>Inserts newInst before pi in pb</i>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1687</pre>
1688</div>
Alkis Evlogimenos9a5dc4f2004-05-27 00:57:51 +0000[diff] [blame]1689
1690 <p>Appending to the end of a <tt>BasicBlock</tt> is so common that
1691 the <tt>Instruction</tt> class and <tt>Instruction</tt>-derived
1692 classes provide constructors which take a pointer to a
1693 <tt>BasicBlock</tt> to be appended to. For example code that
1694 looked like: </p>
1695
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1696<div class="doc_code">
1697<pre>
1698BasicBlock *pb = ...;
1699Instruction *newInst = new Instruction(...);
1700
Bill Wendling82e2eea2006-10-11 18:00:22 +0000[diff] [blame]1701pb-&gt;getInstList().push_back(newInst); // <i>Appends newInst to pb</i>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1702</pre>
1703</div>
Alkis Evlogimenos9a5dc4f2004-05-27 00:57:51 +0000[diff] [blame]1704
1705 <p>becomes: </p>
1706
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1707<div class="doc_code">
1708<pre>
1709BasicBlock *pb = ...;
1710Instruction *newInst = new Instruction(..., pb);
1711</pre>
1712</div>
Alkis Evlogimenos9a5dc4f2004-05-27 00:57:51 +0000[diff] [blame]1713
1714 <p>which is much cleaner, especially if you are creating
1715 long instruction streams.</p></li>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1716
1717 <li>Insertion into an implicit instruction list
1718
1719 <p><tt>Instruction</tt> instances that are already in <tt>BasicBlock</tt>s
1720 are implicitly associated with an existing instruction list: the instruction
1721 list of the enclosing basic block. Thus, we could have accomplished the same
1722 thing as the above code without being given a <tt>BasicBlock</tt> by doing:
1723 </p>
1724
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1725<div class="doc_code">
1726<pre>
1727Instruction *pi = ...;
1728Instruction *newInst = new Instruction(...);
1729
1730pi-&gt;getParent()-&gt;getInstList().insert(pi, newInst);
1731</pre>
1732</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1733
1734 <p>In fact, this sequence of steps occurs so frequently that the
1735 <tt>Instruction</tt> class and <tt>Instruction</tt>-derived classes provide
1736 constructors which take (as a default parameter) a pointer to an
1737 <tt>Instruction</tt> which the newly-created <tt>Instruction</tt> should
1738 precede. That is, <tt>Instruction</tt> constructors are capable of
1739 inserting the newly-created instance into the <tt>BasicBlock</tt> of a
1740 provided instruction, immediately before that instruction. Using an
1741 <tt>Instruction</tt> constructor with a <tt>insertBefore</tt> (default)
1742 parameter, the above code becomes:</p>
1743
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1744<div class="doc_code">
1745<pre>
1746Instruction* pi = ...;
1747Instruction* newInst = new Instruction(..., pi);
1748</pre>
1749</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1750
1751 <p>which is much cleaner, especially if you're creating a lot of
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1752 instructions and adding them to <tt>BasicBlock</tt>s.</p></li>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1753</ul>
1754
1755</div>
1756
1757<!--_______________________________________________________________________-->
1758<div class="doc_subsubsection">
1759 <a name="schanges_deleting">Deleting <tt>Instruction</tt>s</a>
1760</div>
1761
1762<div class="doc_text">
1763
1764<p>Deleting an instruction from an existing sequence of instructions that form a
Chris Lattner69bf8a92004-05-23 21:06:58 +0000[diff] [blame]1765<a href="#BasicBlock"><tt>BasicBlock</tt></a> is very straight-forward. First,
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1766you must have a pointer to the instruction that you wish to delete. Second, you
1767need to obtain the pointer to that instruction's basic block. You use the
1768pointer to the basic block to get its list of instructions and then use the
1769erase function to remove your instruction. For example:</p>
1770
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1771<div class="doc_code">
1772<pre>
1773<a href="#Instruction">Instruction</a> *I = .. ;
1774<a href="#BasicBlock">BasicBlock</a> *BB = I-&gt;getParent();
1775
1776BB-&gt;getInstList().erase(I);
1777</pre>
1778</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1779
1780</div>
1781
1782<!--_______________________________________________________________________-->
1783<div class="doc_subsubsection">
1784 <a name="schanges_replacing">Replacing an <tt>Instruction</tt> with another
1785 <tt>Value</tt></a>
1786</div>
1787
1788<div class="doc_text">
1789
1790<p><i>Replacing individual instructions</i></p>
1791
1792<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]1793permits use of two very useful replace functions: <tt>ReplaceInstWithValue</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1794and <tt>ReplaceInstWithInst</tt>.</p>
1795
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]1796<h4><a name="schanges_deleting">Deleting <tt>Instruction</tt>s</a></h4>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1797
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]1798<ul>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1799 <li><tt>ReplaceInstWithValue</tt>
1800
1801 <p>This function replaces all uses (within a basic block) of a given
1802 instruction with a value, and then removes the original instruction. The
1803 following example illustrates the replacement of the result of a particular
Chris Lattner58360822005-01-17 00:12:04 +0000[diff] [blame]1804 <tt>AllocaInst</tt> that allocates memory for a single integer with a null
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1805 pointer to an integer.</p>
1806
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1807<div class="doc_code">
1808<pre>
1809AllocaInst* instToReplace = ...;
1810BasicBlock::iterator ii(instToReplace);
1811
1812ReplaceInstWithValue(instToReplace-&gt;getParent()-&gt;getInstList(), ii,
1813 Constant::getNullValue(PointerType::get(Type::IntTy)));
1814</pre></div></li>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1815
1816 <li><tt>ReplaceInstWithInst</tt>
1817
1818 <p>This function replaces a particular instruction with another
1819 instruction. The following example illustrates the replacement of one
1820 <tt>AllocaInst</tt> with another.</p>
1821
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1822<div class="doc_code">
1823<pre>
1824AllocaInst* instToReplace = ...;
1825BasicBlock::iterator ii(instToReplace);
1826
1827ReplaceInstWithInst(instToReplace-&gt;getParent()-&gt;getInstList(), ii,
1828 new AllocaInst(Type::IntTy, 0, "ptrToReplacedInt"));
1829</pre></div></li>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]1830</ul>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1831
1832<p><i>Replacing multiple uses of <tt>User</tt>s and <tt>Value</tt>s</i></p>
1833
1834<p>You can use <tt>Value::replaceAllUsesWith</tt> and
1835<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]1836doxygen documentation for the <a href="/doxygen/classllvm_1_1Value.html">Value Class</a>
Misha Brukman384047f2004-06-03 23:29:12 +0000[diff] [blame]1837and <a href="/doxygen/classllvm_1_1User.html">User Class</a>, respectively, for more
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1838information.</p>
1839
1840<!-- Value::replaceAllUsesWith User::replaceUsesOfWith Point out:
1841include/llvm/Transforms/Utils/ especially BasicBlockUtils.h with:
1842ReplaceInstWithValue, ReplaceInstWithInst -->
1843
1844</div>
1845
Chris Lattner9355b472002-09-06 02:50:58 +0000[diff] [blame]1846<!-- *********************************************************************** -->
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1847<div class="doc_section">
Chris Lattnerd9d6e102005-04-23 16:10:52 +0000[diff] [blame]1848 <a name="advanced">Advanced Topics</a>
1849</div>
1850<!-- *********************************************************************** -->
1851
1852<div class="doc_text">
Chris Lattnerf1b200b2005-04-23 17:27:36 +0000[diff] [blame]1853<p>
1854This section describes some of the advanced or obscure API's that most clients
1855do not need to be aware of. These API's tend manage the inner workings of the
1856LLVM system, and only need to be accessed in unusual circumstances.
1857</p>
1858</div>
Chris Lattnerd9d6e102005-04-23 16:10:52 +0000[diff] [blame]1859
Chris Lattnerf1b200b2005-04-23 17:27:36 +0000[diff] [blame]1860<!-- ======================================================================= -->
1861<div class="doc_subsection">
1862 <a name="TypeResolve">LLVM Type Resolution</a>
1863</div>
Chris Lattnerd9d6e102005-04-23 16:10:52 +0000[diff] [blame]1864
Chris Lattnerf1b200b2005-04-23 17:27:36 +0000[diff] [blame]1865<div class="doc_text">
1866
1867<p>
1868The LLVM type system has a very simple goal: allow clients to compare types for
1869structural equality with a simple pointer comparison (aka a shallow compare).
1870This goal makes clients much simpler and faster, and is used throughout the LLVM
1871system.
1872</p>
1873
1874<p>
1875Unfortunately achieving this goal is not a simple matter. In particular,
1876recursive types and late resolution of opaque types makes the situation very
1877difficult to handle. Fortunately, for the most part, our implementation makes
1878most clients able to be completely unaware of the nasty internal details. The
1879primary case where clients are exposed to the inner workings of it are when
1880building a recursive type. In addition to this case, the LLVM bytecode reader,
1881assembly parser, and linker also have to be aware of the inner workings of this
1882system.
1883</p>
1884
Chris Lattner0f876db2005-04-25 15:47:57 +0000[diff] [blame]1885<p>
1886For our purposes below, we need three concepts. First, an "Opaque Type" is
1887exactly as defined in the <a href="LangRef.html#t_opaque">language
1888reference</a>. Second an "Abstract Type" is any type which includes an
Reid Spencer06565dc2007-01-12 17:11:23 +0000[diff] [blame]1889opaque type as part of its type graph (for example "<tt>{ opaque, i32 }</tt>").
1890Third, 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]1891float }</tt>").
1892</p>
1893
Chris Lattnerf1b200b2005-04-23 17:27:36 +0000[diff] [blame]1894</div>
1895
1896<!-- ______________________________________________________________________ -->
1897<div class="doc_subsubsection">
1898 <a name="BuildRecType">Basic Recursive Type Construction</a>
1899</div>
1900
1901<div class="doc_text">
1902
1903<p>
1904Because the most common question is "how do I build a recursive type with LLVM",
1905we answer it now and explain it as we go. Here we include enough to cause this
1906to be emitted to an output .ll file:
1907</p>
1908
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1909<div class="doc_code">
Chris Lattnerf1b200b2005-04-23 17:27:36 +0000[diff] [blame]1910<pre>
Reid Spencer06565dc2007-01-12 17:11:23 +0000[diff] [blame]1911%mylist = type { %mylist*, i32 }
Chris Lattnerf1b200b2005-04-23 17:27:36 +0000[diff] [blame]1912</pre>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1913</div>
Chris Lattnerf1b200b2005-04-23 17:27:36 +0000[diff] [blame]1914
1915<p>
1916To build this, use the following LLVM APIs:
1917</p>
1918
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1919<div class="doc_code">
Chris Lattnerf1b200b2005-04-23 17:27:36 +0000[diff] [blame]1920<pre>
Bill Wendling82e2eea2006-10-11 18:00:22 +0000[diff] [blame]1921// <i>Create the initial outer struct</i>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1922<a href="#PATypeHolder">PATypeHolder</a> StructTy = OpaqueType::get();
1923std::vector&lt;const Type*&gt; Elts;
1924Elts.push_back(PointerType::get(StructTy));
1925Elts.push_back(Type::IntTy);
1926StructType *NewSTy = StructType::get(Elts);
Chris Lattnerf1b200b2005-04-23 17:27:36 +0000[diff] [blame]1927
Reid Spencer06565dc2007-01-12 17:11:23 +0000[diff] [blame]1928// <i>At this point, NewSTy = "{ opaque*, i32 }". Tell VMCore that</i>
Bill Wendling82e2eea2006-10-11 18:00:22 +0000[diff] [blame]1929// <i>the struct and the opaque type are actually the same.</i>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1930cast&lt;OpaqueType&gt;(StructTy.get())-&gt;<a href="#refineAbstractTypeTo">refineAbstractTypeTo</a>(NewSTy);
Chris Lattnerf1b200b2005-04-23 17:27:36 +0000[diff] [blame]1931
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1932// <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]1933// <i>kept up-to-date</i>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1934NewSTy = cast&lt;StructType&gt;(StructTy.get());
Chris Lattnerf1b200b2005-04-23 17:27:36 +0000[diff] [blame]1935
Bill Wendling82e2eea2006-10-11 18:00:22 +0000[diff] [blame]1936// <i>Add a name for the type to the module symbol table (optional)</i>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1937MyModule-&gt;addTypeName("mylist", NewSTy);
Chris Lattnerf1b200b2005-04-23 17:27:36 +0000[diff] [blame]1938</pre>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1939</div>
Chris Lattnerf1b200b2005-04-23 17:27:36 +0000[diff] [blame]1940
1941<p>
1942This code shows the basic approach used to build recursive types: build a
1943non-recursive type using 'opaque', then use type unification to close the cycle.
1944The type unification step is performed by the <tt><a
Chris Lattneraff26d12007-02-03 03:06:52 +0000[diff] [blame]1945href="#refineAbstractTypeTo">refineAbstractTypeTo</a></tt> method, which is
Chris Lattnerf1b200b2005-04-23 17:27:36 +0000[diff] [blame]1946described next. After that, we describe the <a
1947href="#PATypeHolder">PATypeHolder class</a>.
1948</p>
1949
1950</div>
1951
1952<!-- ______________________________________________________________________ -->
1953<div class="doc_subsubsection">
1954 <a name="refineAbstractTypeTo">The <tt>refineAbstractTypeTo</tt> method</a>
1955</div>
1956
1957<div class="doc_text">
1958<p>
1959The <tt>refineAbstractTypeTo</tt> method starts the type unification process.
1960While this method is actually a member of the DerivedType class, it is most
1961often used on OpaqueType instances. Type unification is actually a recursive
1962process. After unification, types can become structurally isomorphic to
1963existing types, and all duplicates are deleted (to preserve pointer equality).
1964</p>
1965
1966<p>
1967In the example above, the OpaqueType object is definitely deleted.
Reid Spencer06565dc2007-01-12 17:11:23 +0000[diff] [blame]1968Additionally, if there is an "{ \2*, i32}" type already created in the system,
Chris Lattnerf1b200b2005-04-23 17:27:36 +0000[diff] [blame]1969the pointer and struct type created are <b>also</b> deleted. Obviously whenever
1970a type is deleted, any "Type*" pointers in the program are invalidated. As
1971such, it is safest to avoid having <i>any</i> "Type*" pointers to abstract types
1972live across a call to <tt>refineAbstractTypeTo</tt> (note that non-abstract
1973types can never move or be deleted). To deal with this, the <a
1974href="#PATypeHolder">PATypeHolder</a> class is used to maintain a stable
1975reference to a possibly refined type, and the <a
1976href="#AbstractTypeUser">AbstractTypeUser</a> class is used to update more
1977complex datastructures.
1978</p>
1979
1980</div>
1981
1982<!-- ______________________________________________________________________ -->
1983<div class="doc_subsubsection">
1984 <a name="PATypeHolder">The PATypeHolder Class</a>
1985</div>
1986
1987<div class="doc_text">
1988<p>
1989PATypeHolder is a form of a "smart pointer" for Type objects. When VMCore
1990happily goes about nuking types that become isomorphic to existing types, it
1991automatically updates all PATypeHolder objects to point to the new type. In the
1992example above, this allows the code to maintain a pointer to the resultant
1993resolved recursive type, even though the Type*'s are potentially invalidated.
1994</p>
1995
1996<p>
1997PATypeHolder is an extremely light-weight object that uses a lazy union-find
1998implementation to update pointers. For example the pointer from a Value to its
1999Type is maintained by PATypeHolder objects.
2000</p>
2001
2002</div>
2003
2004<!-- ______________________________________________________________________ -->
2005<div class="doc_subsubsection">
2006 <a name="AbstractTypeUser">The AbstractTypeUser Class</a>
2007</div>
2008
2009<div class="doc_text">
2010
2011<p>
2012Some data structures need more to perform more complex updates when types get
2013resolved. The <a href="#SymbolTable">SymbolTable</a> class, for example, needs
2014move and potentially merge type planes in its representation when a pointer
2015changes.</p>
2016
2017<p>
2018To support this, a class can derive from the AbstractTypeUser class. This class
2019allows it to get callbacks when certain types are resolved. To register to get
2020callbacks for a particular type, the DerivedType::{add/remove}AbstractTypeUser
Chris Lattner0f876db2005-04-25 15:47:57 +0000[diff] [blame]2021methods can be called on a type. Note that these methods only work for <i>
Reid Spencer06565dc2007-01-12 17:11:23 +0000[diff] [blame]2022 abstract</i> types. Concrete types (those that do not include any opaque
2023objects) can never be refined.
Chris Lattnerf1b200b2005-04-23 17:27:36 +0000[diff] [blame]2024</p>
Chris Lattnerd9d6e102005-04-23 16:10:52 +0000[diff] [blame]2025</div>
2026
2027
2028<!-- ======================================================================= -->
2029<div class="doc_subsection">
2030 <a name="SymbolTable">The <tt>SymbolTable</tt> class</a>
2031</div>
Chris Lattnerf1b200b2005-04-23 17:27:36 +0000[diff] [blame]2032
Chris Lattnerd9d6e102005-04-23 16:10:52 +0000[diff] [blame]2033<div class="doc_text">
2034<p>This class provides a symbol table that the <a
2035href="#Function"><tt>Function</tt></a> and <a href="#Module">
2036<tt>Module</tt></a> classes use for naming definitions. The symbol table can
Reid Spencera6362242007-01-07 00:41:39 +0000[diff] [blame]2037provide a name for any <a href="#Value"><tt>Value</tt></a>.
2038<tt>SymbolTable</tt> is an abstract data type. It hides the data it contains
2039and provides access to it through a controlled interface.</p>
Chris Lattnerd9d6e102005-04-23 16:10:52 +0000[diff] [blame]2040
Reid Spencera6362242007-01-07 00:41:39 +0000[diff] [blame]2041<p>Note that the <tt>SymbolTable</tt> class should not be directly accessed
2042by most clients. It should only be used when iteration over the symbol table
2043names themselves are required, which is very special purpose. Note that not
2044all LLVM
Chris Lattnerd9d6e102005-04-23 16:10:52 +0000[diff] [blame]2045<a href="#Value">Value</a>s have names, and those without names (i.e. they have
2046an empty name) do not exist in the symbol table.
2047</p>
2048
2049<p>To use the <tt>SymbolTable</tt> well, you need to understand the
2050structure of the information it holds. The class contains two
2051<tt>std::map</tt> objects. The first, <tt>pmap</tt>, is a map of
2052<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]2053Thus, Values are stored in two-dimensions and accessed by <tt>Type</tt> and
2054name.</p>
Chris Lattnerd9d6e102005-04-23 16:10:52 +0000[diff] [blame]2055
2056<p>The interface of this class provides three basic types of operations:
2057<ol>
2058 <li><em>Accessors</em>. Accessors provide read-only access to information
2059 such as finding a value for a name with the
2060 <a href="#SymbolTable_lookup">lookup</a> method.</li>
2061 <li><em>Mutators</em>. Mutators allow the user to add information to the
2062 <tt>SymbolTable</tt> with methods like
2063 <a href="#SymbolTable_insert"><tt>insert</tt></a>.</li>
2064 <li><em>Iterators</em>. Iterators allow the user to traverse the content
2065 of the symbol table in well defined ways, such as the method
Reid Spencera6362242007-01-07 00:41:39 +0000[diff] [blame]2066 <a href="#SymbolTable_plane_begin"><tt>plane_begin</tt></a>.</li>
Chris Lattnerd9d6e102005-04-23 16:10:52 +0000[diff] [blame]2067</ol>
2068
2069<h3>Accessors</h3>
2070<dl>
2071 <dt><tt>Value* lookup(const Type* Ty, const std::string&amp; name) const</tt>:
2072 </dt>
2073 <dd>The <tt>lookup</tt> method searches the type plane given by the
2074 <tt>Ty</tt> parameter for a <tt>Value</tt> with the provided <tt>name</tt>.
2075 If a suitable <tt>Value</tt> is not found, null is returned.</dd>
2076
Chris Lattnerd9d6e102005-04-23 16:10:52 +0000[diff] [blame]2077 <dt><tt>bool isEmpty() const</tt>:</dt>
2078 <dd>This function returns true if both the value and types maps are
2079 empty</dd>
2080</dl>
2081
2082<h3>Mutators</h3>
2083<dl>
2084 <dt><tt>void insert(Value *Val)</tt>:</dt>
2085 <dd>This method adds the provided value to the symbol table. The Value must
2086 have both a name and a type which are extracted and used to place the value
2087 in the correct type plane under the value's name.</dd>
2088
2089 <dt><tt>void insert(const std::string&amp; Name, Value *Val)</tt>:</dt>
2090 <dd> Inserts a constant or type into the symbol table with the specified
2091 name. There can be a many to one mapping between names and constants
2092 or types.</dd>
2093
Chris Lattnerd9d6e102005-04-23 16:10:52 +0000[diff] [blame]2094 <dt><tt>void remove(Value* Val)</tt>:</dt>
2095 <dd> This method removes a named value from the symbol table. The
2096 type and name of the Value are extracted from \p N and used to
2097 lookup the Value in the correct type plane. If the Value is
2098 not in the symbol table, this method silently ignores the
2099 request.</dd>
2100
Chris Lattnerd9d6e102005-04-23 16:10:52 +0000[diff] [blame]2101 <dt><tt>Value* remove(const std::string&amp; Name, Value *Val)</tt>:</dt>
2102 <dd> Remove a constant or type with the specified name from the
2103 symbol table.</dd>
2104
Reid Spencera6362242007-01-07 00:41:39 +0000[diff] [blame]2105 <dt><tt>Value *remove(const value_iterator&amp; It)</tt>:</dt>
Chris Lattnerd9d6e102005-04-23 16:10:52 +0000[diff] [blame]2106 <dd> Removes a specific value from the symbol table.
2107 Returns the removed value.</dd>
2108
2109 <dt><tt>bool strip()</tt>:</dt>
2110 <dd> This method will strip the symbol table of its names leaving
2111 the type and values. </dd>
2112
2113 <dt><tt>void clear()</tt>:</dt>
2114 <dd>Empty the symbol table completely.</dd>
2115</dl>
2116
2117<h3>Iteration</h3>
2118<p>The following functions describe three types of iterators you can obtain
2119the beginning or end of the sequence for both const and non-const. It is
2120important to keep track of the different kinds of iterators. There are
2121three idioms worth pointing out:</p>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2122
Chris Lattnerd9d6e102005-04-23 16:10:52 +0000[diff] [blame]2123<table>
2124 <tr><th>Units</th><th>Iterator</th><th>Idiom</th></tr>
2125 <tr>
2126 <td align="left">Planes Of name/Value maps</td><td>PI</td>
2127 <td align="left"><pre><tt>
2128for (SymbolTable::plane_const_iterator PI = ST.plane_begin(),
2129 PE = ST.plane_end(); PI != PE; ++PI ) {
Bill Wendling82e2eea2006-10-11 18:00:22 +0000[diff] [blame]2130 PI-&gt;first // <i>This is the Type* of the plane</i>
2131 PI-&gt;second // <i>This is the SymbolTable::ValueMap of name/Value pairs</i>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2132}
Chris Lattnerd9d6e102005-04-23 16:10:52 +0000[diff] [blame]2133 </tt></pre></td>
2134 </tr>
2135 <tr>
Chris Lattnerd9d6e102005-04-23 16:10:52 +0000[diff] [blame]2136 <td align="left">name/Value pairs in a plane</td><td>VI</td>
2137 <td align="left"><pre><tt>
2138for (SymbolTable::value_const_iterator VI = ST.value_begin(SomeType),
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2139 VE = ST.value_end(SomeType); VI != VE; ++VI ) {
Bill Wendling82e2eea2006-10-11 18:00:22 +0000[diff] [blame]2140 VI-&gt;first // <i>This is the name of the Value</i>
2141 VI-&gt;second // <i>This is the Value* value associated with the name</i>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2142}
Chris Lattnerd9d6e102005-04-23 16:10:52 +0000[diff] [blame]2143 </tt></pre></td>
2144 </tr>
2145</table>
2146
2147<p>Using the recommended iterator names and idioms will help you avoid
2148making mistakes. Of particular note, make sure that whenever you use
2149value_begin(SomeType) that you always compare the resulting iterator
2150with value_end(SomeType) not value_end(SomeOtherType) or else you
2151will loop infinitely.</p>
2152
2153<dl>
2154
2155 <dt><tt>plane_iterator plane_begin()</tt>:</dt>
2156 <dd>Get an iterator that starts at the beginning of the type planes.
2157 The iterator will iterate over the Type/ValueMap pairs in the
2158 type planes. </dd>
2159
2160 <dt><tt>plane_const_iterator plane_begin() const</tt>:</dt>
2161 <dd>Get a const_iterator that starts at the beginning of the type
2162 planes. The iterator will iterate over the Type/ValueMap pairs
2163 in the type planes. </dd>
2164
2165 <dt><tt>plane_iterator plane_end()</tt>:</dt>
2166 <dd>Get an iterator at the end of the type planes. This serves as
2167 the marker for end of iteration over the type planes.</dd>
2168
2169 <dt><tt>plane_const_iterator plane_end() const</tt>:</dt>
2170 <dd>Get a const_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>value_iterator value_begin(const Type *Typ)</tt>:</dt>
2174 <dd>Get an iterator that starts at the beginning of a type plane.
2175 The iterator will iterate over the name/value pairs in the type plane.
2176 Note: The type plane must already exist before using this.</dd>
2177
2178 <dt><tt>value_const_iterator value_begin(const Type *Typ) const</tt>:</dt>
2179 <dd>Get a const_iterator that starts at the beginning of a type plane.
2180 The iterator will iterate over the name/value pairs in the type plane.
2181 Note: The type plane must already exist before using this.</dd>
2182
2183 <dt><tt>value_iterator value_end(const Type *Typ)</tt>:</dt>
2184 <dd>Get an iterator to the end of a type plane. This serves as the marker
2185 for end of iteration of the type plane.
2186 Note: The type plane must already exist before using this.</dd>
2187
2188 <dt><tt>value_const_iterator value_end(const Type *Typ) const</tt>:</dt>
2189 <dd>Get a const_iterator to the end of a type plane. This serves as the
2190 marker for end of iteration of the type plane.
2191 Note: the type plane must already exist before using this.</dd>
2192
Chris Lattnerd9d6e102005-04-23 16:10:52 +0000[diff] [blame]2193 <dt><tt>plane_const_iterator find(const Type* Typ ) const</tt>:</dt>
2194 <dd>This method returns a plane_const_iterator for iteration over
2195 the type planes starting at a specific plane, given by \p Ty.</dd>
2196
2197 <dt><tt>plane_iterator find( const Type* Typ </tt>:</dt>
2198 <dd>This method returns a plane_iterator for iteration over the
2199 type planes starting at a specific plane, given by \p Ty.</dd>
2200
2201</dl>
2202</div>
2203
2204
2205
2206<!-- *********************************************************************** -->
2207<div class="doc_section">
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2208 <a name="coreclasses">The Core LLVM Class Hierarchy Reference </a>
2209</div>
2210<!-- *********************************************************************** -->
2211
2212<div class="doc_text">
Reid Spencer303c4b42007-01-12 17:26:25 +0000[diff] [blame]2213<p><tt>#include "<a href="/doxygen/Type_8h-source.html">llvm/Type.h</a>"</tt>
2214<br>doxygen info: <a href="/doxygen/classllvm_1_1Type.html">Type Class</a></p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2215
2216<p>The Core LLVM classes are the primary means of representing the program
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]2217being inspected or transformed. The core LLVM classes are defined in
2218header files in the <tt>include/llvm/</tt> directory, and implemented in
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2219the <tt>lib/VMCore</tt> directory.</p>
2220
2221</div>
2222
2223<!-- ======================================================================= -->
2224<div class="doc_subsection">
Reid Spencer303c4b42007-01-12 17:26:25 +0000[diff] [blame]2225 <a name="Type">The <tt>Type</tt> class and Derived Types</a>
2226</div>
2227
2228<div class="doc_text">
2229
2230 <p><tt>Type</tt> is a superclass of all type classes. Every <tt>Value</tt> has
2231 a <tt>Type</tt>. <tt>Type</tt> cannot be instantiated directly but only
2232 through its subclasses. Certain primitive types (<tt>VoidType</tt>,
2233 <tt>LabelType</tt>, <tt>FloatType</tt> and <tt>DoubleType</tt>) have hidden
2234 subclasses. They are hidden because they offer no useful functionality beyond
2235 what the <tt>Type</tt> class offers except to distinguish themselves from
2236 other subclasses of <tt>Type</tt>.</p>
2237 <p>All other types are subclasses of <tt>DerivedType</tt>. Types can be
2238 named, but this is not a requirement. There exists exactly
2239 one instance of a given shape at any one time. This allows type equality to
2240 be performed with address equality of the Type Instance. That is, given two
2241 <tt>Type*</tt> values, the types are identical if the pointers are identical.
2242 </p>
2243</div>
2244
2245<!-- _______________________________________________________________________ -->
2246<div class="doc_subsubsection">
2247 <a name="m_Value">Important Public Methods</a>
2248</div>
2249
2250<div class="doc_text">
2251
2252<ul>
Chris Lattner8f79df32007-01-15 01:55:32 +0000[diff] [blame]2253 <li><tt>bool isInteger() const</tt>: Returns true for any integer type.</li>
Reid Spencer303c4b42007-01-12 17:26:25 +0000[diff] [blame]2254
2255 <li><tt>bool isFloatingPoint()</tt>: Return true if this is one of the two
2256 floating point types.</li>
2257
2258 <li><tt>bool isAbstract()</tt>: Return true if the type is abstract (contains
2259 an OpaqueType anywhere in its definition).</li>
2260
2261 <li><tt>bool isSized()</tt>: Return true if the type has known size. Things
2262 that don't have a size are abstract types, labels and void.</li>
2263
2264</ul>
2265</div>
2266
2267<!-- _______________________________________________________________________ -->
2268<div class="doc_subsubsection">
2269 <a name="m_Value">Important Derived Types</a>
2270</div>
2271<div class="doc_text">
2272<dl>
2273 <dt><tt>IntegerType</tt></dt>
2274 <dd>Subclass of DerivedType that represents integer types of any bit width.
2275 Any bit width between <tt>IntegerType::MIN_INT_BITS</tt> (1) and
2276 <tt>IntegerType::MAX_INT_BITS</tt> (~8 million) can be represented.
2277 <ul>
2278 <li><tt>static const IntegerType* get(unsigned NumBits)</tt>: get an integer
2279 type of a specific bit width.</li>
2280 <li><tt>unsigned getBitWidth() const</tt>: Get the bit width of an integer
2281 type.</li>
2282 </ul>
2283 </dd>
2284 <dt><tt>SequentialType</tt></dt>
2285 <dd>This is subclassed by ArrayType and PointerType
2286 <ul>
2287 <li><tt>const Type * getElementType() const</tt>: Returns the type of each
2288 of the elements in the sequential type. </li>
2289 </ul>
2290 </dd>
2291 <dt><tt>ArrayType</tt></dt>
2292 <dd>This is a subclass of SequentialType and defines the interface for array
2293 types.
2294 <ul>
2295 <li><tt>unsigned getNumElements() const</tt>: Returns the number of
2296 elements in the array. </li>
2297 </ul>
2298 </dd>
2299 <dt><tt>PointerType</tt></dt>
Chris Lattner302da1e2007-02-03 03:05:57 +0000[diff] [blame]2300 <dd>Subclass of SequentialType for pointer types.</dd>
Reid Spencer303c4b42007-01-12 17:26:25 +0000[diff] [blame]2301 <dt><tt>PackedType</tt></dt>
2302 <dd>Subclass of SequentialType for packed (vector) types. A
2303 packed type is similar to an ArrayType but is distinguished because it is
2304 a first class type wherease ArrayType is not. Packed types are used for
2305 vector operations and are usually small vectors of of an integer or floating
2306 point type.</dd>
2307 <dt><tt>StructType</tt></dt>
2308 <dd>Subclass of DerivedTypes for struct types.</dd>
2309 <dt><tt>FunctionType</tt></dt>
2310 <dd>Subclass of DerivedTypes for function types.
2311 <ul>
2312 <li><tt>bool isVarArg() const</tt>: Returns true if its a vararg
2313 function</li>
2314 <li><tt> const Type * getReturnType() const</tt>: Returns the
2315 return type of the function.</li>
2316 <li><tt>const Type * getParamType (unsigned i)</tt>: Returns
2317 the type of the ith parameter.</li>
2318 <li><tt> const unsigned getNumParams() const</tt>: Returns the
2319 number of formal parameters.</li>
2320 </ul>
2321 </dd>
2322 <dt><tt>OpaqueType</tt></dt>
2323 <dd>Sublcass of DerivedType for abstract types. This class
2324 defines no content and is used as a placeholder for some other type. Note
2325 that OpaqueType is used (temporarily) during type resolution for forward
2326 references of types. Once the referenced type is resolved, the OpaqueType
2327 is replaced with the actual type. OpaqueType can also be used for data
2328 abstraction. At link time opaque types can be resolved to actual types
2329 of the same name.</dd>
2330</dl>
2331</div>
2332
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame^]2333
2334
2335<!-- ======================================================================= -->
2336<div class="doc_subsection">
2337 <a name="Module">The <tt>Module</tt> class</a>
2338</div>
2339
2340<div class="doc_text">
2341
2342<p><tt>#include "<a
2343href="/doxygen/Module_8h-source.html">llvm/Module.h</a>"</tt><br> doxygen info:
2344<a href="/doxygen/classllvm_1_1Module.html">Module Class</a></p>
2345
2346<p>The <tt>Module</tt> class represents the top level structure present in LLVM
2347programs. An LLVM module is effectively either a translation unit of the
2348original program or a combination of several translation units merged by the
2349linker. The <tt>Module</tt> class keeps track of a list of <a
2350href="#Function"><tt>Function</tt></a>s, a list of <a
2351href="#GlobalVariable"><tt>GlobalVariable</tt></a>s, and a <a
2352href="#SymbolTable"><tt>SymbolTable</tt></a>. Additionally, it contains a few
2353helpful member functions that try to make common operations easy.</p>
2354
2355</div>
2356
2357<!-- _______________________________________________________________________ -->
2358<div class="doc_subsubsection">
2359 <a name="m_Module">Important Public Members of the <tt>Module</tt> class</a>
2360</div>
2361
2362<div class="doc_text">
2363
2364<ul>
2365 <li><tt>Module::Module(std::string name = "")</tt></li>
2366</ul>
2367
2368<p>Constructing a <a href="#Module">Module</a> is easy. You can optionally
2369provide a name for it (probably based on the name of the translation unit).</p>
2370
2371<ul>
2372 <li><tt>Module::iterator</tt> - Typedef for function list iterator<br>
2373 <tt>Module::const_iterator</tt> - Typedef for const_iterator.<br>
2374
2375 <tt>begin()</tt>, <tt>end()</tt>
2376 <tt>size()</tt>, <tt>empty()</tt>
2377
2378 <p>These are forwarding methods that make it easy to access the contents of
2379 a <tt>Module</tt> object's <a href="#Function"><tt>Function</tt></a>
2380 list.</p></li>
2381
2382 <li><tt>Module::FunctionListType &amp;getFunctionList()</tt>
2383
2384 <p> Returns the list of <a href="#Function"><tt>Function</tt></a>s. This is
2385 necessary to use when you need to update the list or perform a complex
2386 action that doesn't have a forwarding method.</p>
2387
2388 <p><!-- Global Variable --></p></li>
2389</ul>
2390
2391<hr>
2392
2393<ul>
2394 <li><tt>Module::global_iterator</tt> - Typedef for global variable list iterator<br>
2395
2396 <tt>Module::const_global_iterator</tt> - Typedef for const_iterator.<br>
2397
2398 <tt>global_begin()</tt>, <tt>global_end()</tt>
2399 <tt>global_size()</tt>, <tt>global_empty()</tt>
2400
2401 <p> These are forwarding methods that make it easy to access the contents of
2402 a <tt>Module</tt> object's <a
2403 href="#GlobalVariable"><tt>GlobalVariable</tt></a> list.</p></li>
2404
2405 <li><tt>Module::GlobalListType &amp;getGlobalList()</tt>
2406
2407 <p>Returns the list of <a
2408 href="#GlobalVariable"><tt>GlobalVariable</tt></a>s. This is necessary to
2409 use when you need to update the list or perform a complex action that
2410 doesn't have a forwarding method.</p>
2411
2412 <p><!-- Symbol table stuff --> </p></li>
2413</ul>
2414
2415<hr>
2416
2417<ul>
2418 <li><tt><a href="#SymbolTable">SymbolTable</a> *getSymbolTable()</tt>
2419
2420 <p>Return a reference to the <a href="#SymbolTable"><tt>SymbolTable</tt></a>
2421 for this <tt>Module</tt>.</p>
2422
2423 <p><!-- Convenience methods --></p></li>
2424</ul>
2425
2426<hr>
2427
2428<ul>
2429 <li><tt><a href="#Function">Function</a> *getFunction(const std::string
2430 &amp;Name, const <a href="#FunctionType">FunctionType</a> *Ty)</tt>
2431
2432 <p>Look up the specified function in the <tt>Module</tt> <a
2433 href="#SymbolTable"><tt>SymbolTable</tt></a>. If it does not exist, return
2434 <tt>null</tt>.</p></li>
2435
2436 <li><tt><a href="#Function">Function</a> *getOrInsertFunction(const
2437 std::string &amp;Name, const <a href="#FunctionType">FunctionType</a> *T)</tt>
2438
2439 <p>Look up the specified function in the <tt>Module</tt> <a
2440 href="#SymbolTable"><tt>SymbolTable</tt></a>. If it does not exist, add an
2441 external declaration for the function and return it.</p></li>
2442
2443 <li><tt>std::string getTypeName(const <a href="#Type">Type</a> *Ty)</tt>
2444
2445 <p>If there is at least one entry in the <a
2446 href="#SymbolTable"><tt>SymbolTable</tt></a> for the specified <a
2447 href="#Type"><tt>Type</tt></a>, return it. Otherwise return the empty
2448 string.</p></li>
2449
2450 <li><tt>bool addTypeName(const std::string &amp;Name, const <a
2451 href="#Type">Type</a> *Ty)</tt>
2452
2453 <p>Insert an entry in the <a href="#SymbolTable"><tt>SymbolTable</tt></a>
2454 mapping <tt>Name</tt> to <tt>Ty</tt>. If there is already an entry for this
2455 name, true is returned and the <a
2456 href="#SymbolTable"><tt>SymbolTable</tt></a> is not modified.</p></li>
2457</ul>
2458
2459</div>
2460
2461
Reid Spencer303c4b42007-01-12 17:26:25 +0000[diff] [blame]2462<!-- ======================================================================= -->
2463<div class="doc_subsection">
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2464 <a name="Value">The <tt>Value</tt> class</a>
2465</div>
2466
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame^]2467<div class="doc_text">
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2468
2469<p><tt>#include "<a href="/doxygen/Value_8h-source.html">llvm/Value.h</a>"</tt>
2470<br>
Chris Lattner00815172007-01-04 22:01:45 +0000[diff] [blame]2471doxygen info: <a href="/doxygen/classllvm_1_1Value.html">Value Class</a></p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2472
2473<p>The <tt>Value</tt> class is the most important class in the LLVM Source
2474base. It represents a typed value that may be used (among other things) as an
2475operand to an instruction. There are many different types of <tt>Value</tt>s,
2476such as <a href="#Constant"><tt>Constant</tt></a>s,<a
2477href="#Argument"><tt>Argument</tt></a>s. Even <a
2478href="#Instruction"><tt>Instruction</tt></a>s and <a
2479href="#Function"><tt>Function</tt></a>s are <tt>Value</tt>s.</p>
2480
2481<p>A particular <tt>Value</tt> may be used many times in the LLVM representation
2482for a program. For example, an incoming argument to a function (represented
2483with an instance of the <a href="#Argument">Argument</a> class) is "used" by
2484every instruction in the function that references the argument. To keep track
2485of this relationship, the <tt>Value</tt> class keeps a list of all of the <a
2486href="#User"><tt>User</tt></a>s that is using it (the <a
2487href="#User"><tt>User</tt></a> class is a base class for all nodes in the LLVM
2488graph that can refer to <tt>Value</tt>s). This use list is how LLVM represents
2489def-use information in the program, and is accessible through the <tt>use_</tt>*
2490methods, shown below.</p>
2491
2492<p>Because LLVM is a typed representation, every LLVM <tt>Value</tt> is typed,
2493and this <a href="#Type">Type</a> is available through the <tt>getType()</tt>
2494method. In addition, all LLVM values can be named. The "name" of the
2495<tt>Value</tt> is a symbolic string printed in the LLVM code:</p>
2496
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2497<div class="doc_code">
2498<pre>
Reid Spencer06565dc2007-01-12 17:11:23 +0000[diff] [blame]2499%<b>foo</b> = add i32 1, 2
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2500</pre>
2501</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2502
2503<p><a name="#nameWarning">The name of this instruction is "foo".</a> <b>NOTE</b>
2504that the name of any value may be missing (an empty string), so names should
2505<b>ONLY</b> be used for debugging (making the source code easier to read,
2506debugging printouts), they should not be used to keep track of values or map
2507between them. For this purpose, use a <tt>std::map</tt> of pointers to the
2508<tt>Value</tt> itself instead.</p>
2509
2510<p>One important aspect of LLVM is that there is no distinction between an SSA
2511variable and the operation that produces it. Because of this, any reference to
2512the value produced by an instruction (or the value available as an incoming
Chris Lattnerd5fc4fc2004-03-18 14:58:55 +0000[diff] [blame]2513argument, for example) is represented as a direct pointer to the instance of
2514the class that
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2515represents this value. Although this may take some getting used to, it
2516simplifies the representation and makes it easier to manipulate.</p>
2517
2518</div>
2519
2520<!-- _______________________________________________________________________ -->
2521<div class="doc_subsubsection">
2522 <a name="m_Value">Important Public Members of the <tt>Value</tt> class</a>
2523</div>
2524
2525<div class="doc_text">
2526
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]2527<ul>
2528 <li><tt>Value::use_iterator</tt> - Typedef for iterator over the
2529use-list<br>
2530 <tt>Value::use_const_iterator</tt> - Typedef for const_iterator over
2531the use-list<br>
2532 <tt>unsigned use_size()</tt> - Returns the number of users of the
2533value.<br>
Chris Lattner9355b472002-09-06 02:50:58 +0000[diff] [blame]2534 <tt>bool use_empty()</tt> - Returns true if there are no users.<br>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]2535 <tt>use_iterator use_begin()</tt> - Get an iterator to the start of
2536the use-list.<br>
2537 <tt>use_iterator use_end()</tt> - Get an iterator to the end of the
2538use-list.<br>
2539 <tt><a href="#User">User</a> *use_back()</tt> - Returns the last
2540element in the list.
2541 <p> These methods are the interface to access the def-use
2542information in LLVM. As with all other iterators in LLVM, the naming
2543conventions follow the conventions defined by the <a href="#stl">STL</a>.</p>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]2544 </li>
2545 <li><tt><a href="#Type">Type</a> *getType() const</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2546 <p>This method returns the Type of the Value.</p>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]2547 </li>
2548 <li><tt>bool hasName() const</tt><br>
Chris Lattner9355b472002-09-06 02:50:58 +0000[diff] [blame]2549 <tt>std::string getName() const</tt><br>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]2550 <tt>void setName(const std::string &amp;Name)</tt>
2551 <p> This family of methods is used to access and assign a name to a <tt>Value</tt>,
2552be aware of the <a href="#nameWarning">precaution above</a>.</p>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]2553 </li>
2554 <li><tt>void replaceAllUsesWith(Value *V)</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2555
2556 <p>This method traverses the use list of a <tt>Value</tt> changing all <a
2557 href="#User"><tt>User</tt>s</a> of the current value to refer to
2558 "<tt>V</tt>" instead. For example, if you detect that an instruction always
2559 produces a constant value (for example through constant folding), you can
2560 replace all uses of the instruction with the constant like this:</p>
2561
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2562<div class="doc_code">
2563<pre>
2564Inst-&gt;replaceAllUsesWith(ConstVal);
2565</pre>
2566</div>
2567
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]2568</ul>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2569
2570</div>
2571
2572<!-- ======================================================================= -->
2573<div class="doc_subsection">
2574 <a name="User">The <tt>User</tt> class</a>
2575</div>
2576
2577<div class="doc_text">
2578
2579<p>
2580<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]2581doxygen info: <a href="/doxygen/classllvm_1_1User.html">User Class</a><br>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2582Superclass: <a href="#Value"><tt>Value</tt></a></p>
2583
2584<p>The <tt>User</tt> class is the common base class of all LLVM nodes that may
2585refer to <a href="#Value"><tt>Value</tt></a>s. It exposes a list of "Operands"
2586that are all of the <a href="#Value"><tt>Value</tt></a>s that the User is
2587referring to. The <tt>User</tt> class itself is a subclass of
2588<tt>Value</tt>.</p>
2589
2590<p>The operands of a <tt>User</tt> point directly to the LLVM <a
2591href="#Value"><tt>Value</tt></a> that it refers to. Because LLVM uses Static
2592Single Assignment (SSA) form, there can only be one definition referred to,
2593allowing this direct connection. This connection provides the use-def
2594information in LLVM.</p>
2595
2596</div>
2597
2598<!-- _______________________________________________________________________ -->
2599<div class="doc_subsubsection">
2600 <a name="m_User">Important Public Members of the <tt>User</tt> class</a>
2601</div>
2602
2603<div class="doc_text">
2604
2605<p>The <tt>User</tt> class exposes the operand list in two ways: through
2606an index access interface and through an iterator based interface.</p>
2607
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]2608<ul>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]2609 <li><tt>Value *getOperand(unsigned i)</tt><br>
2610 <tt>unsigned getNumOperands()</tt>
2611 <p> These two methods expose the operands of the <tt>User</tt> in a
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2612convenient form for direct access.</p></li>
2613
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]2614 <li><tt>User::op_iterator</tt> - Typedef for iterator over the operand
2615list<br>
Chris Lattner58360822005-01-17 00:12:04 +0000[diff] [blame]2616 <tt>op_iterator op_begin()</tt> - Get an iterator to the start of
2617the operand list.<br>
2618 <tt>op_iterator op_end()</tt> - Get an iterator to the end of the
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]2619operand list.
2620 <p> Together, these methods make up the iterator based interface to
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2621the operands of a <tt>User</tt>.</p></li>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]2622</ul>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2623
2624</div>
2625
2626<!-- ======================================================================= -->
2627<div class="doc_subsection">
2628 <a name="Instruction">The <tt>Instruction</tt> class</a>
2629</div>
2630
2631<div class="doc_text">
2632
2633<p><tt>#include "</tt><tt><a
2634href="/doxygen/Instruction_8h-source.html">llvm/Instruction.h</a>"</tt><br>
Misha Brukman31ca1de2004-06-03 23:35:54 +0000[diff] [blame]2635doxygen info: <a href="/doxygen/classllvm_1_1Instruction.html">Instruction Class</a><br>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2636Superclasses: <a href="#User"><tt>User</tt></a>, <a
2637href="#Value"><tt>Value</tt></a></p>
2638
2639<p>The <tt>Instruction</tt> class is the common base class for all LLVM
2640instructions. It provides only a few methods, but is a very commonly used
2641class. The primary data tracked by the <tt>Instruction</tt> class itself is the
2642opcode (instruction type) and the parent <a
2643href="#BasicBlock"><tt>BasicBlock</tt></a> the <tt>Instruction</tt> is embedded
2644into. To represent a specific type of instruction, one of many subclasses of
2645<tt>Instruction</tt> are used.</p>
2646
2647<p> Because the <tt>Instruction</tt> class subclasses the <a
2648href="#User"><tt>User</tt></a> class, its operands can be accessed in the same
2649way as for other <a href="#User"><tt>User</tt></a>s (with the
2650<tt>getOperand()</tt>/<tt>getNumOperands()</tt> and
2651<tt>op_begin()</tt>/<tt>op_end()</tt> methods).</p> <p> An important file for
2652the <tt>Instruction</tt> class is the <tt>llvm/Instruction.def</tt> file. This
2653file contains some meta-data about the various different types of instructions
2654in LLVM. It describes the enum values that are used as opcodes (for example
Reid Spencerc92d25d2006-12-19 19:47:19 +0000[diff] [blame]2655<tt>Instruction::Add</tt> and <tt>Instruction::ICmp</tt>), as well as the
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2656concrete sub-classes of <tt>Instruction</tt> that implement the instruction (for
2657example <tt><a href="#BinaryOperator">BinaryOperator</a></tt> and <tt><a
Reid Spencerc92d25d2006-12-19 19:47:19 +0000[diff] [blame]2658href="#CmpInst">CmpInst</a></tt>). Unfortunately, the use of macros in
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2659this file confuses doxygen, so these enum values don't show up correctly in the
Misha Brukman31ca1de2004-06-03 23:35:54 +0000[diff] [blame]2660<a href="/doxygen/classllvm_1_1Instruction.html">doxygen output</a>.</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2661
2662</div>
2663
2664<!-- _______________________________________________________________________ -->
2665<div class="doc_subsubsection">
Reid Spencerc92d25d2006-12-19 19:47:19 +0000[diff] [blame]2666 <a name="s_Instruction">Important Subclasses of the <tt>Instruction</tt>
2667 class</a>
2668</div>
2669<div class="doc_text">
2670 <ul>
2671 <li><tt><a name="BinaryOperator">BinaryOperator</a></tt>
2672 <p>This subclasses represents all two operand instructions whose operands
2673 must be the same type, except for the comparison instructions.</p></li>
2674 <li><tt><a name="CastInst">CastInst</a></tt>
2675 <p>This subclass is the parent of the 12 casting instructions. It provides
2676 common operations on cast instructions.</p>
2677 <li><tt><a name="CmpInst">CmpInst</a></tt>
2678 <p>This subclass respresents the two comparison instructions,
2679 <a href="LangRef.html#i_icmp">ICmpInst</a> (integer opreands), and
2680 <a href="LangRef.html#i_fcmp">FCmpInst</a> (floating point operands).</p>
2681 <li><tt><a name="TerminatorInst">TerminatorInst</a></tt>
2682 <p>This subclass is the parent of all terminator instructions (those which
2683 can terminate a block).</p>
2684 </ul>
2685 </div>
2686
2687<!-- _______________________________________________________________________ -->
2688<div class="doc_subsubsection">
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2689 <a name="m_Instruction">Important Public Members of the <tt>Instruction</tt>
2690 class</a>
2691</div>
2692
2693<div class="doc_text">
2694
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]2695<ul>
2696 <li><tt><a href="#BasicBlock">BasicBlock</a> *getParent()</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2697 <p>Returns the <a href="#BasicBlock"><tt>BasicBlock</tt></a> that
2698this <tt>Instruction</tt> is embedded into.</p></li>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]2699 <li><tt>bool mayWriteToMemory()</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2700 <p>Returns true if the instruction writes to memory, i.e. it is a
2701 <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]2702 <li><tt>unsigned getOpcode()</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2703 <p>Returns the opcode for the <tt>Instruction</tt>.</p></li>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]2704 <li><tt><a href="#Instruction">Instruction</a> *clone() const</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2705 <p>Returns another instance of the specified instruction, identical
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]2706in all ways to the original except that the instruction has no parent
2707(ie it's not embedded into a <a href="#BasicBlock"><tt>BasicBlock</tt></a>),
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2708and it has no name</p></li>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]2709</ul>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2710
2711</div>
2712
2713<!-- ======================================================================= -->
2714<div class="doc_subsection">
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame^]2715 <a name="Constant">The <tt>Constant</tt> class and subclasses</a>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2716</div>
2717
2718<div class="doc_text">
2719
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame^]2720<p>Constant represents a base class for different types of constants. It
2721is subclassed by ConstantInt, ConstantArray, etc. for representing
2722the various types of Constants. <a href="#GlobalValue">GlobalValue</a> is also
2723a subclass, which represents the address of a global variable or function.
2724</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2725
2726</div>
2727
2728<!-- _______________________________________________________________________ -->
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame^]2729<div class="doc_subsubsection">Important Subclasses of Constant </div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2730<div class="doc_text">
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]2731<ul>
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame^]2732 <li>ConstantInt : This subclass of Constant represents an integer constant of
2733 any width.
2734 <ul>
2735 <li><tt>int64_t getSExtValue() const</tt>: Returns the underlying value of
2736 this constant as a sign extended signed integer value.</li>
2737 <li><tt>uint64_t getZExtValue() const</tt>: Returns the underlying value
2738 of this constant as a zero extended unsigned integer value.</li>
2739 <li><tt>static ConstantInt* get(const Type *Ty, uint64_t Val)</tt>:
2740 Returns the ConstantInt object that represents the value provided by
2741 <tt>Val</tt> for integer type <tt>Ty</tt>.</li>
2742 </ul>
2743 </li>
2744 <li>ConstantFP : This class represents a floating point constant.
2745 <ul>
2746 <li><tt>double getValue() const</tt>: Returns the underlying value of
2747 this constant. </li>
2748 </ul>
2749 </li>
2750 <li>ConstantArray : This represents a constant array.
2751 <ul>
2752 <li><tt>const std::vector&lt;Use&gt; &amp;getValues() const</tt>: Returns
2753 a vector of component constants that makeup this array. </li>
2754 </ul>
2755 </li>
2756 <li>ConstantStruct : This represents a constant struct.
2757 <ul>
2758 <li><tt>const std::vector&lt;Use&gt; &amp;getValues() const</tt>: Returns
2759 a vector of component constants that makeup this array. </li>
2760 </ul>
2761 </li>
2762 <li>GlobalValue : This represents either a global variable or a function. In
2763 either case, the value is a constant fixed address (after linking).
2764 </li>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]2765</ul>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2766</div>
2767
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame^]2768
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2769<!-- ======================================================================= -->
2770<div class="doc_subsection">
2771 <a name="GlobalValue">The <tt>GlobalValue</tt> class</a>
2772</div>
2773
2774<div class="doc_text">
2775
2776<p><tt>#include "<a
2777href="/doxygen/GlobalValue_8h-source.html">llvm/GlobalValue.h</a>"</tt><br>
Misha Brukman384047f2004-06-03 23:29:12 +0000[diff] [blame]2778doxygen info: <a href="/doxygen/classllvm_1_1GlobalValue.html">GlobalValue
2779Class</a><br>
Reid Spencerbe5e85e2006-04-14 14:11:48 +0000[diff] [blame]2780Superclasses: <a href="#Constant"><tt>Constant</tt></a>,
2781<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]2782
2783<p>Global values (<a href="#GlobalVariable"><tt>GlobalVariable</tt></a>s or <a
2784href="#Function"><tt>Function</tt></a>s) are the only LLVM values that are
2785visible in the bodies of all <a href="#Function"><tt>Function</tt></a>s.
2786Because they are visible at global scope, they are also subject to linking with
2787other globals defined in different translation units. To control the linking
2788process, <tt>GlobalValue</tt>s know their linkage rules. Specifically,
2789<tt>GlobalValue</tt>s know whether they have internal or external linkage, as
Reid Spencer8b2da7a2004-07-18 13:10:31 +0000[diff] [blame]2790defined by the <tt>LinkageTypes</tt> enumeration.</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2791
2792<p>If a <tt>GlobalValue</tt> has internal linkage (equivalent to being
2793<tt>static</tt> in C), it is not visible to code outside the current translation
2794unit, and does not participate in linking. If it has external linkage, it is
2795visible to external code, and does participate in linking. In addition to
2796linkage information, <tt>GlobalValue</tt>s keep track of which <a
2797href="#Module"><tt>Module</tt></a> they are currently part of.</p>
2798
2799<p>Because <tt>GlobalValue</tt>s are memory objects, they are always referred to
2800by their <b>address</b>. As such, the <a href="#Type"><tt>Type</tt></a> of a
2801global is always a pointer to its contents. It is important to remember this
2802when using the <tt>GetElementPtrInst</tt> instruction because this pointer must
2803be dereferenced first. For example, if you have a <tt>GlobalVariable</tt> (a
2804subclass 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]2805i32]</tt>, then the <tt>GlobalVariable</tt> is a pointer to that array. Although
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2806the address of the first element of this array and the value of the
2807<tt>GlobalVariable</tt> are the same, they have different types. The
Reid Spencer06565dc2007-01-12 17:11:23 +0000[diff] [blame]2808<tt>GlobalVariable</tt>'s type is <tt>[24 x i32]</tt>. The first element's type
2809is <tt>i32.</tt> Because of this, accessing a global value requires you to
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2810dereference the pointer with <tt>GetElementPtrInst</tt> first, then its elements
2811can be accessed. This is explained in the <a href="LangRef.html#globalvars">LLVM
2812Language Reference Manual</a>.</p>
2813
2814</div>
2815
2816<!-- _______________________________________________________________________ -->
2817<div class="doc_subsubsection">
2818 <a name="m_GlobalValue">Important Public Members of the <tt>GlobalValue</tt>
2819 class</a>
2820</div>
2821
2822<div class="doc_text">
2823
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]2824<ul>
2825 <li><tt>bool hasInternalLinkage() const</tt><br>
Chris Lattner9355b472002-09-06 02:50:58 +0000[diff] [blame]2826 <tt>bool hasExternalLinkage() const</tt><br>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]2827 <tt>void setInternalLinkage(bool HasInternalLinkage)</tt>
2828 <p> These methods manipulate the linkage characteristics of the <tt>GlobalValue</tt>.</p>
2829 <p> </p>
2830 </li>
2831 <li><tt><a href="#Module">Module</a> *getParent()</tt>
2832 <p> This returns the <a href="#Module"><tt>Module</tt></a> that the
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2833GlobalValue is currently embedded into.</p></li>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]2834</ul>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2835
2836</div>
2837
2838<!-- ======================================================================= -->
2839<div class="doc_subsection">
2840 <a name="Function">The <tt>Function</tt> class</a>
2841</div>
2842
2843<div class="doc_text">
2844
2845<p><tt>#include "<a
2846href="/doxygen/Function_8h-source.html">llvm/Function.h</a>"</tt><br> doxygen
Misha Brukman31ca1de2004-06-03 23:35:54 +0000[diff] [blame]2847info: <a href="/doxygen/classllvm_1_1Function.html">Function Class</a><br>
Reid Spencerbe5e85e2006-04-14 14:11:48 +0000[diff] [blame]2848Superclasses: <a href="#GlobalValue"><tt>GlobalValue</tt></a>,
2849<a href="#Constant"><tt>Constant</tt></a>,
2850<a href="#User"><tt>User</tt></a>,
2851<a href="#Value"><tt>Value</tt></a></p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2852
2853<p>The <tt>Function</tt> class represents a single procedure in LLVM. It is
2854actually one of the more complex classes in the LLVM heirarchy because it must
2855keep track of a large amount of data. The <tt>Function</tt> class keeps track
Reid Spencerbe5e85e2006-04-14 14:11:48 +0000[diff] [blame]2856of a list of <a href="#BasicBlock"><tt>BasicBlock</tt></a>s, a list of formal
2857<a href="#Argument"><tt>Argument</tt></a>s, and a
2858<a href="#SymbolTable"><tt>SymbolTable</tt></a>.</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2859
2860<p>The list of <a href="#BasicBlock"><tt>BasicBlock</tt></a>s is the most
2861commonly used part of <tt>Function</tt> objects. The list imposes an implicit
2862ordering of the blocks in the function, which indicate how the code will be
2863layed out by the backend. Additionally, the first <a
2864href="#BasicBlock"><tt>BasicBlock</tt></a> is the implicit entry node for the
2865<tt>Function</tt>. It is not legal in LLVM to explicitly branch to this initial
2866block. There are no implicit exit nodes, and in fact there may be multiple exit
2867nodes from a single <tt>Function</tt>. If the <a
2868href="#BasicBlock"><tt>BasicBlock</tt></a> list is empty, this indicates that
2869the <tt>Function</tt> is actually a function declaration: the actual body of the
2870function hasn't been linked in yet.</p>
2871
2872<p>In addition to a list of <a href="#BasicBlock"><tt>BasicBlock</tt></a>s, the
2873<tt>Function</tt> class also keeps track of the list of formal <a
2874href="#Argument"><tt>Argument</tt></a>s that the function receives. This
2875container manages the lifetime of the <a href="#Argument"><tt>Argument</tt></a>
2876nodes, just like the <a href="#BasicBlock"><tt>BasicBlock</tt></a> list does for
2877the <a href="#BasicBlock"><tt>BasicBlock</tt></a>s.</p>
2878
2879<p>The <a href="#SymbolTable"><tt>SymbolTable</tt></a> is a very rarely used
2880LLVM feature that is only used when you have to look up a value by name. Aside
2881from that, the <a href="#SymbolTable"><tt>SymbolTable</tt></a> is used
2882internally to make sure that there are not conflicts between the names of <a
2883href="#Instruction"><tt>Instruction</tt></a>s, <a
2884href="#BasicBlock"><tt>BasicBlock</tt></a>s, or <a
2885href="#Argument"><tt>Argument</tt></a>s in the function body.</p>
2886
Reid Spencer8b2da7a2004-07-18 13:10:31 +0000[diff] [blame]2887<p>Note that <tt>Function</tt> is a <a href="#GlobalValue">GlobalValue</a>
2888and therefore also a <a href="#Constant">Constant</a>. The value of the function
2889is its address (after linking) which is guaranteed to be constant.</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2890</div>
2891
2892<!-- _______________________________________________________________________ -->
2893<div class="doc_subsubsection">
2894 <a name="m_Function">Important Public Members of the <tt>Function</tt>
2895 class</a>
2896</div>
2897
2898<div class="doc_text">
2899
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]2900<ul>
2901 <li><tt>Function(const </tt><tt><a href="#FunctionType">FunctionType</a>
Chris Lattnerac479e52004-08-04 05:10:48 +0000[diff] [blame]2902 *Ty, LinkageTypes Linkage, const std::string &amp;N = "", Module* Parent = 0)</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2903
2904 <p>Constructor used when you need to create new <tt>Function</tt>s to add
2905 the the program. The constructor must specify the type of the function to
Chris Lattnerac479e52004-08-04 05:10:48 +0000[diff] [blame]2906 create and what type of linkage the function should have. The <a
2907 href="#FunctionType"><tt>FunctionType</tt></a> argument
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2908 specifies the formal arguments and return value for the function. The same
2909 <a href="#FunctionTypel"><tt>FunctionType</tt></a> value can be used to
2910 create multiple functions. The <tt>Parent</tt> argument specifies the Module
2911 in which the function is defined. If this argument is provided, the function
2912 will automatically be inserted into that module's list of
2913 functions.</p></li>
2914
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]2915 <li><tt>bool isExternal()</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2916
2917 <p>Return whether or not the <tt>Function</tt> has a body defined. If the
2918 function is "external", it does not have a body, and thus must be resolved
2919 by linking with a function defined in a different translation unit.</p></li>
2920
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]2921 <li><tt>Function::iterator</tt> - Typedef for basic block list iterator<br>
Chris Lattner9355b472002-09-06 02:50:58 +0000[diff] [blame]2922 <tt>Function::const_iterator</tt> - Typedef for const_iterator.<br>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2923
Chris Lattner77d69242005-03-15 05:19:20 +0000[diff] [blame]2924 <tt>begin()</tt>, <tt>end()</tt>
2925 <tt>size()</tt>, <tt>empty()</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2926
2927 <p>These are forwarding methods that make it easy to access the contents of
2928 a <tt>Function</tt> object's <a href="#BasicBlock"><tt>BasicBlock</tt></a>
2929 list.</p></li>
2930
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]2931 <li><tt>Function::BasicBlockListType &amp;getBasicBlockList()</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2932
2933 <p>Returns the list of <a href="#BasicBlock"><tt>BasicBlock</tt></a>s. This
2934 is necessary to use when you need to update the list or perform a complex
2935 action that doesn't have a forwarding method.</p></li>
2936
Chris Lattner89cc2652005-03-15 04:48:32 +0000[diff] [blame]2937 <li><tt>Function::arg_iterator</tt> - Typedef for the argument list
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]2938iterator<br>
Chris Lattner89cc2652005-03-15 04:48:32 +0000[diff] [blame]2939 <tt>Function::const_arg_iterator</tt> - Typedef for const_iterator.<br>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2940
Chris Lattner77d69242005-03-15 05:19:20 +0000[diff] [blame]2941 <tt>arg_begin()</tt>, <tt>arg_end()</tt>
Chris Lattner89cc2652005-03-15 04:48:32 +0000[diff] [blame]2942 <tt>arg_size()</tt>, <tt>arg_empty()</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2943
2944 <p>These are forwarding methods that make it easy to access the contents of
2945 a <tt>Function</tt> object's <a href="#Argument"><tt>Argument</tt></a>
2946 list.</p></li>
2947
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]2948 <li><tt>Function::ArgumentListType &amp;getArgumentList()</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2949
2950 <p>Returns the list of <a href="#Argument"><tt>Argument</tt></a>s. This is
2951 necessary to use when you need to update the list or perform a complex
2952 action that doesn't have a forwarding method.</p></li>
2953
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]2954 <li><tt><a href="#BasicBlock">BasicBlock</a> &amp;getEntryBlock()</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2955
2956 <p>Returns the entry <a href="#BasicBlock"><tt>BasicBlock</tt></a> for the
2957 function. Because the entry block for the function is always the first
2958 block, this returns the first block of the <tt>Function</tt>.</p></li>
2959
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]2960 <li><tt><a href="#Type">Type</a> *getReturnType()</tt><br>
2961 <tt><a href="#FunctionType">FunctionType</a> *getFunctionType()</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2962
2963 <p>This traverses the <a href="#Type"><tt>Type</tt></a> of the
2964 <tt>Function</tt> and returns the return type of the function, or the <a
2965 href="#FunctionType"><tt>FunctionType</tt></a> of the actual
2966 function.</p></li>
2967
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]2968 <li><tt><a href="#SymbolTable">SymbolTable</a> *getSymbolTable()</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2969
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]2970 <p> Return a pointer to the <a href="#SymbolTable"><tt>SymbolTable</tt></a>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2971 for this <tt>Function</tt>.</p></li>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]2972</ul>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2973
2974</div>
2975
2976<!-- ======================================================================= -->
2977<div class="doc_subsection">
2978 <a name="GlobalVariable">The <tt>GlobalVariable</tt> class</a>
2979</div>
2980
2981<div class="doc_text">
2982
2983<p><tt>#include "<a
2984href="/doxygen/GlobalVariable_8h-source.html">llvm/GlobalVariable.h</a>"</tt>
2985<br>
Tanya Lattnera3da7772004-06-22 08:02:25 +0000[diff] [blame]2986doxygen info: <a href="/doxygen/classllvm_1_1GlobalVariable.html">GlobalVariable
Reid Spencerbe5e85e2006-04-14 14:11:48 +0000[diff] [blame]2987 Class</a><br>
2988Superclasses: <a href="#GlobalValue"><tt>GlobalValue</tt></a>,
2989<a href="#Constant"><tt>Constant</tt></a>,
2990<a href="#User"><tt>User</tt></a>,
2991<a href="#Value"><tt>Value</tt></a></p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2992
2993<p>Global variables are represented with the (suprise suprise)
2994<tt>GlobalVariable</tt> class. Like functions, <tt>GlobalVariable</tt>s are also
2995subclasses of <a href="#GlobalValue"><tt>GlobalValue</tt></a>, and as such are
2996always referenced by their address (global values must live in memory, so their
Reid Spencerbe5e85e2006-04-14 14:11:48 +0000[diff] [blame]2997"name" refers to their constant address). See
2998<a href="#GlobalValue"><tt>GlobalValue</tt></a> for more on this. Global
2999variables may have an initial value (which must be a
3000<a href="#Constant"><tt>Constant</tt></a>), and if they have an initializer,
3001they may be marked as "constant" themselves (indicating that their contents
3002never change at runtime).</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3003</div>
3004
3005<!-- _______________________________________________________________________ -->
3006<div class="doc_subsubsection">
3007 <a name="m_GlobalVariable">Important Public Members of the
3008 <tt>GlobalVariable</tt> class</a>
3009</div>
3010
3011<div class="doc_text">
3012
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3013<ul>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3014 <li><tt>GlobalVariable(const </tt><tt><a href="#Type">Type</a> *Ty, bool
3015 isConstant, LinkageTypes&amp; Linkage, <a href="#Constant">Constant</a>
3016 *Initializer = 0, const std::string &amp;Name = "", Module* Parent = 0)</tt>
3017
3018 <p>Create a new global variable of the specified type. If
3019 <tt>isConstant</tt> is true then the global variable will be marked as
3020 unchanging for the program. The Linkage parameter specifies the type of
3021 linkage (internal, external, weak, linkonce, appending) for the variable. If
3022 the linkage is InternalLinkage, WeakLinkage, or LinkOnceLinkage,&nbsp; then
3023 the resultant global variable will have internal linkage. AppendingLinkage
3024 concatenates together all instances (in different translation units) of the
3025 variable into a single variable but is only applicable to arrays. &nbsp;See
3026 the <a href="LangRef.html#modulestructure">LLVM Language Reference</a> for
3027 further details on linkage types. Optionally an initializer, a name, and the
3028 module to put the variable into may be specified for the global variable as
3029 well.</p></li>
3030
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3031 <li><tt>bool isConstant() const</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3032
3033 <p>Returns true if this is a global variable that is known not to
3034 be modified at runtime.</p></li>
3035
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3036 <li><tt>bool hasInitializer()</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3037
3038 <p>Returns true if this <tt>GlobalVariable</tt> has an intializer.</p></li>
3039
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3040 <li><tt><a href="#Constant">Constant</a> *getInitializer()</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3041
3042 <p>Returns the intial value for a <tt>GlobalVariable</tt>. It is not legal
3043 to call this method if there is no initializer.</p></li>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3044</ul>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3045
3046</div>
3047
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame^]3048
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3049<!-- ======================================================================= -->
3050<div class="doc_subsection">
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame^]3051 <a name="BasicBlock">The <tt>BasicBlock</tt> class</a>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3052</div>
3053
3054<div class="doc_text">
3055
3056<p><tt>#include "<a
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame^]3057href="/doxygen/BasicBlock_8h-source.html">llvm/BasicBlock.h</a>"</tt><br>
3058doxygen info: <a href="/doxygen/structllvm_1_1BasicBlock.html">BasicBlock
3059Class</a><br>
3060Superclass: <a href="#Value"><tt>Value</tt></a></p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3061
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame^]3062<p>This class represents a single entry multiple exit section of the code,
3063commonly known as a basic block by the compiler community. The
3064<tt>BasicBlock</tt> class maintains a list of <a
3065href="#Instruction"><tt>Instruction</tt></a>s, which form the body of the block.
3066Matching the language definition, the last element of this list of instructions
3067is always a terminator instruction (a subclass of the <a
3068href="#TerminatorInst"><tt>TerminatorInst</tt></a> class).</p>
3069
3070<p>In addition to tracking the list of instructions that make up the block, the
3071<tt>BasicBlock</tt> class also keeps track of the <a
3072href="#Function"><tt>Function</tt></a> that it is embedded into.</p>
3073
3074<p>Note that <tt>BasicBlock</tt>s themselves are <a
3075href="#Value"><tt>Value</tt></a>s, because they are referenced by instructions
3076like branches and can go in the switch tables. <tt>BasicBlock</tt>s have type
3077<tt>label</tt>.</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3078
3079</div>
3080
3081<!-- _______________________________________________________________________ -->
3082<div class="doc_subsubsection">
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame^]3083 <a name="m_BasicBlock">Important Public Members of the <tt>BasicBlock</tt>
3084 class</a>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3085</div>
3086
3087<div class="doc_text">
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3088<ul>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3089
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame^]3090<li><tt>BasicBlock(const std::string &amp;Name = "", </tt><tt><a
3091 href="#Function">Function</a> *Parent = 0)</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3092
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame^]3093<p>The <tt>BasicBlock</tt> constructor is used to create new basic blocks for
3094insertion into a function. The constructor optionally takes a name for the new
3095block, and a <a href="#Function"><tt>Function</tt></a> to insert it into. If
3096the <tt>Parent</tt> parameter is specified, the new <tt>BasicBlock</tt> is
3097automatically inserted at the end of the specified <a
3098href="#Function"><tt>Function</tt></a>, if not specified, the BasicBlock must be
3099manually inserted into the <a href="#Function"><tt>Function</tt></a>.</p></li>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3100
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame^]3101<li><tt>BasicBlock::iterator</tt> - Typedef for instruction list iterator<br>
3102<tt>BasicBlock::const_iterator</tt> - Typedef for const_iterator.<br>
3103<tt>begin()</tt>, <tt>end()</tt>, <tt>front()</tt>, <tt>back()</tt>,
3104<tt>size()</tt>, <tt>empty()</tt>
3105STL-style functions for accessing the instruction list.
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3106
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame^]3107<p>These methods and typedefs are forwarding functions that have the same
3108semantics as the standard library methods of the same names. These methods
3109expose the underlying instruction list of a basic block in a way that is easy to
3110manipulate. To get the full complement of container operations (including
3111operations to update the list), you must use the <tt>getInstList()</tt>
3112method.</p></li>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3113
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame^]3114<li><tt>BasicBlock::InstListType &amp;getInstList()</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3115
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame^]3116<p>This method is used to get access to the underlying container that actually
3117holds the Instructions. This method must be used when there isn't a forwarding
3118function in the <tt>BasicBlock</tt> class for the operation that you would like
3119to perform. Because there are no forwarding functions for "updating"
3120operations, you need to use this if you want to update the contents of a
3121<tt>BasicBlock</tt>.</p></li>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3122
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame^]3123<li><tt><a href="#Function">Function</a> *getParent()</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3124
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame^]3125<p> Returns a pointer to <a href="#Function"><tt>Function</tt></a> the block is
3126embedded into, or a null pointer if it is homeless.</p></li>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3127
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame^]3128<li><tt><a href="#TerminatorInst">TerminatorInst</a> *getTerminator()</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3129
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame^]3130<p> Returns a pointer to the terminator instruction that appears at the end of
3131the <tt>BasicBlock</tt>. If there is no terminator instruction, or if the last
3132instruction in the block is not a terminator, then a null pointer is
3133returned.</p></li>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3134
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3135</ul>
3136
3137</div>
3138
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3139
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3140<!-- ======================================================================= -->
3141<div class="doc_subsection">
3142 <a name="Argument">The <tt>Argument</tt> class</a>
3143</div>
3144
3145<div class="doc_text">
3146
3147<p>This subclass of Value defines the interface for incoming formal
Chris Lattner58360822005-01-17 00:12:04 +0000[diff] [blame]3148arguments to a function. A Function maintains a list of its formal
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3149arguments. An argument has a pointer to the parent Function.</p>
3150
3151</div>
3152
Chris Lattner9355b472002-09-06 02:50:58 +0000[diff] [blame]3153<!-- *********************************************************************** -->
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3154<hr>
3155<address>
3156 <a href="http://jigsaw.w3.org/css-validator/check/referer"><img
3157 src="http://jigsaw.w3.org/css-validator/images/vcss" alt="Valid CSS!"></a>
3158 <a href="http://validator.w3.org/check/referer"><img
3159 src="http://www.w3.org/Icons/valid-html401" alt="Valid HTML 4.01!" /></a>
3160
3161 <a href="mailto:dhurjati@cs.uiuc.edu">Dinakar Dhurjati</a> and
3162 <a href="mailto:sabre@nondot.org">Chris Lattner</a><br>
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]3163 <a href="http://llvm.org">The LLVM Compiler Infrastructure</a><br>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3164 Last modified: $Date$
3165</address>
3166
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3167</body>
3168</html>