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4<head>
5 <title>LLVM Programmer's Manual</title>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]6 <link rel="stylesheet" href="llvm.css" type="text/css">
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]7</head>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]8<body>
9
10<div class="doc_title">
11 LLVM Programmer's Manual
12</div>
13
Chris Lattner9355b472002-09-06 02:50:58 +0000[diff] [blame]14<ol>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]15 <li><a href="#introduction">Introduction</a></li>
Chris Lattner9355b472002-09-06 02:50:58 +0000[diff] [blame]16 <li><a href="#general">General Information</a>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]17 <ul>
Reid Spencerfe8f4ff2004-11-01 09:02:53 +0000[diff] [blame]18 <li><a href="#stl">The C++ Standard Template Library</a></li>
19<!--
20 <li>The <tt>-time-passes</tt> option</li>
21 <li>How to use the LLVM Makefile system</li>
22 <li>How to write a regression test</li>
Chris Lattner61db4652004-12-08 19:05:44 +0000[diff] [blame]23
Reid Spencerfe8f4ff2004-11-01 09:02:53 +0000[diff] [blame]24-->
Chris Lattner84b7f8d2003-08-01 22:20:59 +0000[diff] [blame]25 </ul>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]26 </li>
27 <li><a href="#apis">Important and useful LLVM APIs</a>
28 <ul>
29 <li><a href="#isa">The <tt>isa&lt;&gt;</tt>, <tt>cast&lt;&gt;</tt>
30and <tt>dyn_cast&lt;&gt;</tt> templates</a> </li>
Misha Brukman2c122ce2005-11-01 21:12:49 +0000[diff] [blame]31 <li><a href="#DEBUG">The <tt>DEBUG()</tt> macro and <tt>-debug</tt>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]32option</a>
33 <ul>
34 <li><a href="#DEBUG_TYPE">Fine grained debug info with <tt>DEBUG_TYPE</tt>
35and the <tt>-debug-only</tt> option</a> </li>
36 </ul>
37 </li>
Chris Lattner0be6fdf2006-12-19 21:46:21 +0000[diff] [blame]38 <li><a href="#Statistic">The <tt>Statistic</tt> class &amp; <tt>-stats</tt>
Reid Spencerfe8f4ff2004-11-01 09:02:53 +0000[diff] [blame]39option</a></li>
40<!--
41 <li>The <tt>InstVisitor</tt> template
42 <li>The general graph API
43-->
Chris Lattnerf623a082005-10-17 01:36:23 +0000[diff] [blame]44 <li><a href="#ViewGraph">Viewing graphs while debugging code</a></li>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]45 </ul>
46 </li>
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]47 <li><a href="#datastructure">Picking the Right Data Structure for a Task</a>
48 <ul>
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]49 <li><a href="#ds_sequential">Sequential Containers (std::vector, std::list, etc)</a>
50 <ul>
51 <li><a href="#dss_fixedarrays">Fixed Size Arrays</a></li>
52 <li><a href="#dss_heaparrays">Heap Allocated Arrays</a></li>
53 <li><a href="#dss_smallvector">"llvm/ADT/SmallVector.h"</a></li>
54 <li><a href="#dss_vector">&lt;vector&gt;</a></li>
55 <li><a href="#dss_deque">&lt;deque&gt;</a></li>
56 <li><a href="#dss_list">&lt;list&gt;</a></li>
Gabor Greif3899e492009-02-27 11:37:41 +0000[diff] [blame]57 <li><a href="#dss_ilist">llvm/ADT/ilist.h</a></li>
Chris Lattnerc5722432007-02-03 19:49:31 +0000[diff] [blame]58 <li><a href="#dss_other">Other Sequential Container Options</a></li>
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]59 </ul></li>
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]60 <li><a href="#ds_set">Set-Like Containers (std::set, SmallSet, SetVector, etc)</a>
61 <ul>
62 <li><a href="#dss_sortedvectorset">A sorted 'vector'</a></li>
63 <li><a href="#dss_smallset">"llvm/ADT/SmallSet.h"</a></li>
64 <li><a href="#dss_smallptrset">"llvm/ADT/SmallPtrSet.h"</a></li>
Chris Lattnerc28476f2007-09-30 00:58:59 +0000[diff] [blame]65 <li><a href="#dss_denseset">"llvm/ADT/DenseSet.h"</a></li>
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]66 <li><a href="#dss_FoldingSet">"llvm/ADT/FoldingSet.h"</a></li>
67 <li><a href="#dss_set">&lt;set&gt;</a></li>
68 <li><a href="#dss_setvector">"llvm/ADT/SetVector.h"</a></li>
Chris Lattnerc5722432007-02-03 19:49:31 +0000[diff] [blame]69 <li><a href="#dss_uniquevector">"llvm/ADT/UniqueVector.h"</a></li>
70 <li><a href="#dss_otherset">Other Set-Like ContainerOptions</a></li>
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]71 </ul></li>
Chris Lattnerf3692522007-02-03 19:51:56 +0000[diff] [blame]72 <li><a href="#ds_map">Map-Like Containers (std::map, DenseMap, etc)</a>
73 <ul>
74 <li><a href="#dss_sortedvectormap">A sorted 'vector'</a></li>
Chris Lattner796f9fa2007-02-08 19:14:21 +0000[diff] [blame]75 <li><a href="#dss_stringmap">"llvm/ADT/StringMap.h"</a></li>
Chris Lattnerf3692522007-02-03 19:51:56 +0000[diff] [blame]76 <li><a href="#dss_indexedmap">"llvm/ADT/IndexedMap.h"</a></li>
77 <li><a href="#dss_densemap">"llvm/ADT/DenseMap.h"</a></li>
78 <li><a href="#dss_map">&lt;map&gt;</a></li>
79 <li><a href="#dss_othermap">Other Map-Like Container Options</a></li>
80 </ul></li>
Daniel Berlin1939ace2007-09-24 17:52:25 +0000[diff] [blame]81 <li><a href="#ds_bit">BitVector-like containers</a>
82 <ul>
83 <li><a href="#dss_bitvector">A dense bitvector</a></li>
84 <li><a href="#dss_sparsebitvector">A sparse bitvector</a></li>
85 </ul></li>
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]86 </ul>
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]87 </li>
Chris Lattnerae7f7592002-09-06 18:31:18 +0000[diff] [blame]88 <li><a href="#common">Helpful Hints for Common Operations</a>
Chris Lattnerae7f7592002-09-06 18:31:18 +0000[diff] [blame]89 <ul>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]90 <li><a href="#inspection">Basic Inspection and Traversal Routines</a>
91 <ul>
92 <li><a href="#iterate_function">Iterating over the <tt>BasicBlock</tt>s
93in a <tt>Function</tt></a> </li>
94 <li><a href="#iterate_basicblock">Iterating over the <tt>Instruction</tt>s
95in a <tt>BasicBlock</tt></a> </li>
96 <li><a href="#iterate_institer">Iterating over the <tt>Instruction</tt>s
97in a <tt>Function</tt></a> </li>
98 <li><a href="#iterate_convert">Turning an iterator into a
99class pointer</a> </li>
100 <li><a href="#iterate_complex">Finding call sites: a more
101complex example</a> </li>
102 <li><a href="#calls_and_invokes">Treating calls and invokes
103the same way</a> </li>
104 <li><a href="#iterate_chains">Iterating over def-use &amp;
105use-def chains</a> </li>
Chris Lattner2e438ca2008-01-03 16:56:04 +0000[diff] [blame]106 <li><a href="#iterate_preds">Iterating over predecessors &amp;
107successors of blocks</a></li>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]108 </ul>
109 </li>
110 <li><a href="#simplechanges">Making simple changes</a>
111 <ul>
112 <li><a href="#schanges_creating">Creating and inserting new
113 <tt>Instruction</tt>s</a> </li>
114 <li><a href="#schanges_deleting">Deleting <tt>Instruction</tt>s</a> </li>
115 <li><a href="#schanges_replacing">Replacing an <tt>Instruction</tt>
116with another <tt>Value</tt></a> </li>
Tanya Lattnerb011c662007-06-20 18:33:15 +0000[diff] [blame]117 <li><a href="#schanges_deletingGV">Deleting <tt>GlobalVariable</tt>s</a> </li>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]118 </ul>
Reid Spencerfe8f4ff2004-11-01 09:02:53 +0000[diff] [blame]119 </li>
Jeffrey Yasskin714257f2009-04-30 22:33:41 +0000[diff] [blame]120 <li><a href="#create_types">How to Create Types</a></li>
Chris Lattnerae7f7592002-09-06 18:31:18 +0000[diff] [blame]121<!--
122 <li>Working with the Control Flow Graph
123 <ul>
124 <li>Accessing predecessors and successors of a <tt>BasicBlock</tt>
125 <li>
126 <li>
127 </ul>
Reid Spencerfe8f4ff2004-11-01 09:02:53 +0000[diff] [blame]128-->
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]129 </ul>
130 </li>
Chris Lattnerd9d6e102005-04-23 16:10:52 +0000[diff] [blame]131
Owen Anderson8bc1b3b2009-06-16 01:17:16 +0000[diff] [blame^]132 <li><a href="#threading">Threads and LLVM</a>
133 <ul>
134 <li><a href="#startmultithreaded">Entering threaded mode with <tt>llvm_start_multithreaded()</tt><a/></li>
135 <li><a href="#shutdown">Ending execution with <tt>llvm_shutdown()</tt></a></li>
136 <li><a href="#managedstatic">Lazy initialization with <tt>ManagedStatic</tt></a></li>
137 </ul>
138 </li>
139
Chris Lattnerd9d6e102005-04-23 16:10:52 +0000[diff] [blame]140 <li><a href="#advanced">Advanced Topics</a>
141 <ul>
Chris Lattnerf1b200b2005-04-23 17:27:36 +0000[diff] [blame]142 <li><a href="#TypeResolve">LLVM Type Resolution</a>
143 <ul>
144 <li><a href="#BuildRecType">Basic Recursive Type Construction</a></li>
145 <li><a href="#refineAbstractTypeTo">The <tt>refineAbstractTypeTo</tt> method</a></li>
146 <li><a href="#PATypeHolder">The PATypeHolder Class</a></li>
147 <li><a href="#AbstractTypeUser">The AbstractTypeUser Class</a></li>
148 </ul></li>
149
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]150 <li><a href="#SymbolTable">The <tt>ValueSymbolTable</tt> and <tt>TypeSymbolTable</tt> classes</a></li>
151 <li><a href="#UserLayout">The <tt>User</tt> and owned <tt>Use</tt> classes' memory layout</a></li>
Chris Lattnerd9d6e102005-04-23 16:10:52 +0000[diff] [blame]152 </ul></li>
153
Joel Stanley9b96c442002-09-06 21:55:13 +0000[diff] [blame]154 <li><a href="#coreclasses">The Core LLVM Class Hierarchy Reference</a>
Chris Lattner9355b472002-09-06 02:50:58 +0000[diff] [blame]155 <ul>
Reid Spencer303c4b42007-01-12 17:26:25 +0000[diff] [blame]156 <li><a href="#Type">The <tt>Type</tt> class</a> </li>
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]157 <li><a href="#Module">The <tt>Module</tt> class</a></li>
Reid Spencerfe8f4ff2004-11-01 09:02:53 +0000[diff] [blame]158 <li><a href="#Value">The <tt>Value</tt> class</a>
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]159 <ul>
160 <li><a href="#User">The <tt>User</tt> class</a>
Chris Lattner9355b472002-09-06 02:50:58 +0000[diff] [blame]161 <ul>
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]162 <li><a href="#Instruction">The <tt>Instruction</tt> class</a></li>
163 <li><a href="#Constant">The <tt>Constant</tt> class</a>
164 <ul>
165 <li><a href="#GlobalValue">The <tt>GlobalValue</tt> class</a>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]166 <ul>
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]167 <li><a href="#Function">The <tt>Function</tt> class</a></li>
168 <li><a href="#GlobalVariable">The <tt>GlobalVariable</tt> class</a></li>
169 </ul>
170 </li>
171 </ul>
172 </li>
Reid Spencerfe8f4ff2004-11-01 09:02:53 +0000[diff] [blame]173 </ul>
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]174 </li>
175 <li><a href="#BasicBlock">The <tt>BasicBlock</tt> class</a></li>
176 <li><a href="#Argument">The <tt>Argument</tt> class</a></li>
177 </ul>
Reid Spencerfe8f4ff2004-11-01 09:02:53 +0000[diff] [blame]178 </li>
179 </ul>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]180 </li>
Chris Lattner9355b472002-09-06 02:50:58 +0000[diff] [blame]181</ol>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]182
Chris Lattner69bf8a92004-05-23 21:06:58 +0000[diff] [blame]183<div class="doc_author">
184 <p>Written by <a href="mailto:sabre@nondot.org">Chris Lattner</a>,
Chris Lattner94c43592004-05-26 16:52:55 +0000[diff] [blame]185 <a href="mailto:dhurjati@cs.uiuc.edu">Dinakar Dhurjati</a>,
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]186 <a href="mailto:ggreif@gmail.com">Gabor Greif</a>,
Owen Anderson8bc1b3b2009-06-16 01:17:16 +0000[diff] [blame^]187 <a href="mailto:jstanley@cs.uiuc.edu">Joel Stanley</a>,
188 <a href="mailto:rspencer@x10sys.com">Reid Spencer</a> and
189 <a href="mailto:owen@apple.com">Owen Anderson</a></p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]190</div>
191
Chris Lattner9355b472002-09-06 02:50:58 +0000[diff] [blame]192<!-- *********************************************************************** -->
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]193<div class="doc_section">
194 <a name="introduction">Introduction </a>
195</div>
Chris Lattner9355b472002-09-06 02:50:58 +0000[diff] [blame]196<!-- *********************************************************************** -->
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]197
198<div class="doc_text">
199
200<p>This document is meant to highlight some of the important classes and
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]201interfaces available in the LLVM source-base. This manual is not
202intended to explain what LLVM is, how it works, and what LLVM code looks
203like. It assumes that you know the basics of LLVM and are interested
204in writing transformations or otherwise analyzing or manipulating the
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]205code.</p>
206
207<p>This document should get you oriented so that you can find your
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]208way in the continuously growing source code that makes up the LLVM
209infrastructure. Note that this manual is not intended to serve as a
210replacement for reading the source code, so if you think there should be
211a method in one of these classes to do something, but it's not listed,
212check the source. Links to the <a href="/doxygen/">doxygen</a> sources
213are provided to make this as easy as possible.</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]214
215<p>The first section of this document describes general information that is
216useful to know when working in the LLVM infrastructure, and the second describes
217the Core LLVM classes. In the future this manual will be extended with
218information describing how to use extension libraries, such as dominator
219information, CFG traversal routines, and useful utilities like the <tt><a
220href="/doxygen/InstVisitor_8h-source.html">InstVisitor</a></tt> template.</p>
221
222</div>
223
Chris Lattner9355b472002-09-06 02:50:58 +0000[diff] [blame]224<!-- *********************************************************************** -->
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]225<div class="doc_section">
226 <a name="general">General Information</a>
227</div>
228<!-- *********************************************************************** -->
229
230<div class="doc_text">
231
232<p>This section contains general information that is useful if you are working
233in the LLVM source-base, but that isn't specific to any particular API.</p>
234
235</div>
236
237<!-- ======================================================================= -->
238<div class="doc_subsection">
239 <a name="stl">The C++ Standard Template Library</a>
240</div>
241
242<div class="doc_text">
243
244<p>LLVM makes heavy use of the C++ Standard Template Library (STL),
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]245perhaps much more than you are used to, or have seen before. Because of
246this, you might want to do a little background reading in the
247techniques used and capabilities of the library. There are many good
248pages that discuss the STL, and several books on the subject that you
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]249can get, so it will not be discussed in this document.</p>
250
251<p>Here are some useful links:</p>
252
253<ol>
254
255<li><a href="http://www.dinkumware.com/refxcpp.html">Dinkumware C++ Library
256reference</a> - an excellent reference for the STL and other parts of the
257standard C++ library.</li>
258
259<li><a href="http://www.tempest-sw.com/cpp/">C++ In a Nutshell</a> - This is an
Gabor Greif0cbcabe2009-03-12 09:47:03 +0000[diff] [blame]260O'Reilly book in the making. It has a decent Standard Library
261Reference that rivals Dinkumware's, and is unfortunately no longer free since the
262book has been published.</li>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]263
264<li><a href="http://www.parashift.com/c++-faq-lite/">C++ Frequently Asked
265Questions</a></li>
266
267<li><a href="http://www.sgi.com/tech/stl/">SGI's STL Programmer's Guide</a> -
268Contains a useful <a
269href="http://www.sgi.com/tech/stl/stl_introduction.html">Introduction to the
270STL</a>.</li>
271
272<li><a href="http://www.research.att.com/%7Ebs/C++.html">Bjarne Stroustrup's C++
273Page</a></li>
274
Tanya Lattner79445ba2004-12-08 18:34:56 +0000[diff] [blame]275<li><a href="http://64.78.49.204/">
Reid Spencer096603a2004-05-26 08:41:35 +0000[diff] [blame]276Bruce Eckel's Thinking in C++, 2nd ed. Volume 2 Revision 4.0 (even better, get
277the book).</a></li>
278
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]279</ol>
280
281<p>You are also encouraged to take a look at the <a
282href="CodingStandards.html">LLVM Coding Standards</a> guide which focuses on how
283to write maintainable code more than where to put your curly braces.</p>
284
285</div>
286
287<!-- ======================================================================= -->
288<div class="doc_subsection">
289 <a name="stl">Other useful references</a>
290</div>
291
292<div class="doc_text">
293
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]294<ol>
295<li><a href="http://www.psc.edu/%7Esemke/cvs_branches.html">CVS
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]296Branch and Tag Primer</a></li>
Misha Brukmana0f71e42004-06-18 18:39:00 +0000[diff] [blame]297<li><a href="http://www.fortran-2000.com/ArnaudRecipes/sharedlib.html">Using
298static and shared libraries across platforms</a></li>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]299</ol>
300
301</div>
302
Chris Lattner9355b472002-09-06 02:50:58 +0000[diff] [blame]303<!-- *********************************************************************** -->
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]304<div class="doc_section">
305 <a name="apis">Important and useful LLVM APIs</a>
306</div>
307<!-- *********************************************************************** -->
308
309<div class="doc_text">
310
311<p>Here we highlight some LLVM APIs that are generally useful and good to
312know about when writing transformations.</p>
313
314</div>
315
316<!-- ======================================================================= -->
317<div class="doc_subsection">
Misha Brukman2c122ce2005-11-01 21:12:49 +0000[diff] [blame]318 <a name="isa">The <tt>isa&lt;&gt;</tt>, <tt>cast&lt;&gt;</tt> and
319 <tt>dyn_cast&lt;&gt;</tt> templates</a>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]320</div>
321
322<div class="doc_text">
323
324<p>The LLVM source-base makes extensive use of a custom form of RTTI.
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]325These templates have many similarities to the C++ <tt>dynamic_cast&lt;&gt;</tt>
326operator, but they don't have some drawbacks (primarily stemming from
327the fact that <tt>dynamic_cast&lt;&gt;</tt> only works on classes that
328have a v-table). Because they are used so often, you must know what they
329do and how they work. All of these templates are defined in the <a
Chris Lattner695b78b2005-04-26 22:56:16 +0000[diff] [blame]330 href="/doxygen/Casting_8h-source.html"><tt>llvm/Support/Casting.h</tt></a>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]331file (note that you very rarely have to include this file directly).</p>
332
333<dl>
334 <dt><tt>isa&lt;&gt;</tt>: </dt>
335
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]336 <dd><p>The <tt>isa&lt;&gt;</tt> operator works exactly like the Java
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]337 "<tt>instanceof</tt>" operator. It returns true or false depending on whether
338 a reference or pointer points to an instance of the specified class. This can
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]339 be very useful for constraint checking of various sorts (example below).</p>
340 </dd>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]341
342 <dt><tt>cast&lt;&gt;</tt>: </dt>
343
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]344 <dd><p>The <tt>cast&lt;&gt;</tt> operator is a "checked cast" operation. It
Chris Lattner28e6ff52008-06-20 05:03:17 +0000[diff] [blame]345 converts a pointer or reference from a base class to a derived class, causing
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]346 an assertion failure if it is not really an instance of the right type. This
347 should be used in cases where you have some information that makes you believe
348 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]349 and <tt>cast&lt;&gt;</tt> template is:</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]350
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]351<div class="doc_code">
352<pre>
353static bool isLoopInvariant(const <a href="#Value">Value</a> *V, const Loop *L) {
354 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))
355 return true;
Chris Lattner69bf8a92004-05-23 21:06:58 +0000[diff] [blame]356
Bill Wendling82e2eea2006-10-11 18:00:22 +0000[diff] [blame]357 // <i>Otherwise, it must be an instruction...</i>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]358 return !L-&gt;contains(cast&lt;<a href="#Instruction">Instruction</a>&gt;(V)-&gt;getParent());
359}
360</pre>
361</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]362
363 <p>Note that you should <b>not</b> use an <tt>isa&lt;&gt;</tt> test followed
364 by a <tt>cast&lt;&gt;</tt>, for that use the <tt>dyn_cast&lt;&gt;</tt>
365 operator.</p>
366
367 </dd>
368
369 <dt><tt>dyn_cast&lt;&gt;</tt>:</dt>
370
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]371 <dd><p>The <tt>dyn_cast&lt;&gt;</tt> operator is a "checking cast" operation.
372 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]373 pointer to it (this operator does not work with references). If the operand is
374 not of the correct type, a null pointer is returned. Thus, this works very
Misha Brukman2c122ce2005-11-01 21:12:49 +0000[diff] [blame]375 much like the <tt>dynamic_cast&lt;&gt;</tt> operator in C++, and should be
376 used in the same circumstances. Typically, the <tt>dyn_cast&lt;&gt;</tt>
377 operator is used in an <tt>if</tt> statement or some other flow control
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]378 statement like this:</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]379
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]380<div class="doc_code">
381<pre>
382if (<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]383 // <i>...</i>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]384}
385</pre>
386</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]387
Misha Brukman2c122ce2005-11-01 21:12:49 +0000[diff] [blame]388 <p>This form of the <tt>if</tt> statement effectively combines together a call
389 to <tt>isa&lt;&gt;</tt> and a call to <tt>cast&lt;&gt;</tt> into one
390 statement, which is very convenient.</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]391
Misha Brukman2c122ce2005-11-01 21:12:49 +0000[diff] [blame]392 <p>Note that the <tt>dyn_cast&lt;&gt;</tt> operator, like C++'s
393 <tt>dynamic_cast&lt;&gt;</tt> or Java's <tt>instanceof</tt> operator, can be
394 abused. In particular, you should not use big chained <tt>if/then/else</tt>
395 blocks to check for lots of different variants of classes. If you find
396 yourself wanting to do this, it is much cleaner and more efficient to use the
397 <tt>InstVisitor</tt> class to dispatch over the instruction type directly.</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]398
Misha Brukman2c122ce2005-11-01 21:12:49 +0000[diff] [blame]399 </dd>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]400
Misha Brukman2c122ce2005-11-01 21:12:49 +0000[diff] [blame]401 <dt><tt>cast_or_null&lt;&gt;</tt>: </dt>
402
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]403 <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]404 <tt>cast&lt;&gt;</tt> operator, except that it allows for a null pointer as an
405 argument (which it then propagates). This can sometimes be useful, allowing
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]406 you to combine several null checks into one.</p></dd>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]407
Misha Brukman2c122ce2005-11-01 21:12:49 +0000[diff] [blame]408 <dt><tt>dyn_cast_or_null&lt;&gt;</tt>: </dt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]409
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]410 <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]411 <tt>dyn_cast&lt;&gt;</tt> operator, except that it allows for a null pointer
412 as an argument (which it then propagates). This can sometimes be useful,
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]413 allowing you to combine several null checks into one.</p></dd>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]414
Misha Brukman2c122ce2005-11-01 21:12:49 +0000[diff] [blame]415</dl>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]416
417<p>These five templates can be used with any classes, whether they have a
418v-table or not. To add support for these templates, you simply need to add
419<tt>classof</tt> static methods to the class you are interested casting
420to. Describing this is currently outside the scope of this document, but there
421are lots of examples in the LLVM source base.</p>
422
423</div>
424
425<!-- ======================================================================= -->
426<div class="doc_subsection">
Misha Brukman2c122ce2005-11-01 21:12:49 +0000[diff] [blame]427 <a name="DEBUG">The <tt>DEBUG()</tt> macro and <tt>-debug</tt> option</a>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]428</div>
429
430<div class="doc_text">
431
432<p>Often when working on your pass you will put a bunch of debugging printouts
433and other code into your pass. After you get it working, you want to remove
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]434it, 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]435across).</p>
436
437<p> Naturally, because of this, you don't want to delete the debug printouts,
438but you don't want them to always be noisy. A standard compromise is to comment
439them out, allowing you to enable them if you need them in the future.</p>
440
Chris Lattner695b78b2005-04-26 22:56:16 +0000[diff] [blame]441<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]442file provides a macro named <tt>DEBUG()</tt> that is a much nicer solution to
443this problem. Basically, you can put arbitrary code into the argument of the
444<tt>DEBUG</tt> macro, and it is only executed if '<tt>opt</tt>' (or any other
445tool) is run with the '<tt>-debug</tt>' command line argument:</p>
446
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]447<div class="doc_code">
448<pre>
Bill Wendling832171c2006-12-07 20:04:42 +0000[diff] [blame]449DOUT &lt;&lt; "I am here!\n";
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]450</pre>
451</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]452
453<p>Then you can run your pass like this:</p>
454
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]455<div class="doc_code">
456<pre>
457$ opt &lt; a.bc &gt; /dev/null -mypass
Bill Wendling82e2eea2006-10-11 18:00:22 +0000[diff] [blame]458<i>&lt;no output&gt;</i>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]459$ opt &lt; a.bc &gt; /dev/null -mypass -debug
460I am here!
461</pre>
462</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]463
464<p>Using the <tt>DEBUG()</tt> macro instead of a home-brewed solution allows you
465to not have to create "yet another" command line option for the debug output for
466your pass. Note that <tt>DEBUG()</tt> macros are disabled for optimized builds,
467so they do not cause a performance impact at all (for the same reason, they
468should also not contain side-effects!).</p>
469
470<p>One additional nice thing about the <tt>DEBUG()</tt> macro is that you can
471enable or disable it directly in gdb. Just use "<tt>set DebugFlag=0</tt>" or
472"<tt>set DebugFlag=1</tt>" from the gdb if the program is running. If the
473program hasn't been started yet, you can always just run it with
474<tt>-debug</tt>.</p>
475
476</div>
477
478<!-- _______________________________________________________________________ -->
479<div class="doc_subsubsection">
Chris Lattnerc9151082005-04-26 22:57:07 +0000[diff] [blame]480 <a name="DEBUG_TYPE">Fine grained debug info with <tt>DEBUG_TYPE</tt> and
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]481 the <tt>-debug-only</tt> option</a>
482</div>
483
484<div class="doc_text">
485
486<p>Sometimes you may find yourself in a situation where enabling <tt>-debug</tt>
487just turns on <b>too much</b> information (such as when working on the code
488generator). If you want to enable debug information with more fine-grained
489control, you define the <tt>DEBUG_TYPE</tt> macro and the <tt>-debug</tt> only
490option as follows:</p>
491
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]492<div class="doc_code">
493<pre>
Bill Wendling832171c2006-12-07 20:04:42 +0000[diff] [blame]494DOUT &lt;&lt; "No debug type\n";
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]495#undef DEBUG_TYPE
496#define DEBUG_TYPE "foo"
Bill Wendling832171c2006-12-07 20:04:42 +0000[diff] [blame]497DOUT &lt;&lt; "'foo' debug type\n";
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]498#undef DEBUG_TYPE
499#define DEBUG_TYPE "bar"
Bill Wendling832171c2006-12-07 20:04:42 +0000[diff] [blame]500DOUT &lt;&lt; "'bar' debug type\n";
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]501#undef DEBUG_TYPE
502#define DEBUG_TYPE ""
Bill Wendling832171c2006-12-07 20:04:42 +0000[diff] [blame]503DOUT &lt;&lt; "No debug type (2)\n";
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]504</pre>
505</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]506
507<p>Then you can run your pass like this:</p>
508
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]509<div class="doc_code">
510<pre>
511$ opt &lt; a.bc &gt; /dev/null -mypass
Bill Wendling82e2eea2006-10-11 18:00:22 +0000[diff] [blame]512<i>&lt;no output&gt;</i>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]513$ opt &lt; a.bc &gt; /dev/null -mypass -debug
514No debug type
515'foo' debug type
516'bar' debug type
517No debug type (2)
518$ opt &lt; a.bc &gt; /dev/null -mypass -debug-only=foo
519'foo' debug type
520$ opt &lt; a.bc &gt; /dev/null -mypass -debug-only=bar
521'bar' debug type
522</pre>
523</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]524
525<p>Of course, in practice, you should only set <tt>DEBUG_TYPE</tt> at the top of
526a 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]527you <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]528<tt>#undef</tt>'s). Also, you should use names more meaningful than "foo" and
529"bar", because there is no system in place to ensure that names do not
530conflict. If two different modules use the same string, they will all be turned
531on when the name is specified. This allows, for example, all debug information
532for instruction scheduling to be enabled with <tt>-debug-type=InstrSched</tt>,
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]533even if the source lives in multiple files.</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]534
535</div>
536
537<!-- ======================================================================= -->
538<div class="doc_subsection">
Chris Lattner0be6fdf2006-12-19 21:46:21 +0000[diff] [blame]539 <a name="Statistic">The <tt>Statistic</tt> class &amp; <tt>-stats</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]540 option</a>
541</div>
542
543<div class="doc_text">
544
545<p>The "<tt><a
Chris Lattner695b78b2005-04-26 22:56:16 +0000[diff] [blame]546href="/doxygen/Statistic_8h-source.html">llvm/ADT/Statistic.h</a></tt>" file
Chris Lattner0be6fdf2006-12-19 21:46:21 +0000[diff] [blame]547provides a class named <tt>Statistic</tt> that is used as a unified way to
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]548keep track of what the LLVM compiler is doing and how effective various
549optimizations are. It is useful to see what optimizations are contributing to
550making a particular program run faster.</p>
551
552<p>Often you may run your pass on some big program, and you're interested to see
553how many times it makes a certain transformation. Although you can do this with
554hand 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]555for big programs. Using the <tt>Statistic</tt> class makes it very easy to
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]556keep track of this information, and the calculated information is presented in a
557uniform manner with the rest of the passes being executed.</p>
558
559<p>There are many examples of <tt>Statistic</tt> uses, but the basics of using
560it are as follows:</p>
561
562<ol>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]563 <li><p>Define your statistic like this:</p>
564
565<div class="doc_code">
566<pre>
Chris Lattner0be6fdf2006-12-19 21:46:21 +0000[diff] [blame]567#define <a href="#DEBUG_TYPE">DEBUG_TYPE</a> "mypassname" <i>// This goes before any #includes.</i>
568STATISTIC(NumXForms, "The # of times I did stuff");
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]569</pre>
570</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]571
Chris Lattner0be6fdf2006-12-19 21:46:21 +0000[diff] [blame]572 <p>The <tt>STATISTIC</tt> macro defines a static variable, whose name is
573 specified by the first argument. The pass name is taken from the DEBUG_TYPE
574 macro, and the description is taken from the second argument. The variable
Reid Spencer06565dc2007-01-12 17:11:23 +0000[diff] [blame]575 defined ("NumXForms" in this case) acts like an unsigned integer.</p></li>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]576
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]577 <li><p>Whenever you make a transformation, bump the counter:</p>
578
579<div class="doc_code">
580<pre>
Bill Wendling82e2eea2006-10-11 18:00:22 +0000[diff] [blame]581++NumXForms; // <i>I did stuff!</i>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]582</pre>
583</div>
584
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]585 </li>
586 </ol>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]587
588 <p>That's all you have to do. To get '<tt>opt</tt>' to print out the
589 statistics gathered, use the '<tt>-stats</tt>' option:</p>
590
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]591<div class="doc_code">
592<pre>
593$ opt -stats -mypassname &lt; program.bc &gt; /dev/null
Bill Wendling82e2eea2006-10-11 18:00:22 +0000[diff] [blame]594<i>... statistics output ...</i>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]595</pre>
596</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]597
Reid Spencer6b6c73e2007-02-09 16:00:28 +0000[diff] [blame]598 <p> When running <tt>opt</tt> on a C file from the SPEC benchmark
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]599suite, it gives a report that looks like this:</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]600
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]601<div class="doc_code">
602<pre>
Gabor Greif04367bf2007-07-06 22:07:22 +0000[diff] [blame]603 7646 bitcodewriter - Number of normal instructions
604 725 bitcodewriter - Number of oversized instructions
605 129996 bitcodewriter - Number of bitcode bytes written
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]606 2817 raise - Number of insts DCEd or constprop'd
607 3213 raise - Number of cast-of-self removed
608 5046 raise - Number of expression trees converted
609 75 raise - Number of other getelementptr's formed
610 138 raise - Number of load/store peepholes
611 42 deadtypeelim - Number of unused typenames removed from symtab
612 392 funcresolve - Number of varargs functions resolved
613 27 globaldce - Number of global variables removed
614 2 adce - Number of basic blocks removed
615 134 cee - Number of branches revectored
616 49 cee - Number of setcc instruction eliminated
617 532 gcse - Number of loads removed
618 2919 gcse - Number of instructions removed
619 86 indvars - Number of canonical indvars added
620 87 indvars - Number of aux indvars removed
621 25 instcombine - Number of dead inst eliminate
622 434 instcombine - Number of insts combined
623 248 licm - Number of load insts hoisted
624 1298 licm - Number of insts hoisted to a loop pre-header
625 3 licm - Number of insts hoisted to multiple loop preds (bad, no loop pre-header)
626 75 mem2reg - Number of alloca's promoted
627 1444 cfgsimplify - Number of blocks simplified
628</pre>
629</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]630
631<p>Obviously, with so many optimizations, having a unified framework for this
632stuff is very nice. Making your pass fit well into the framework makes it more
633maintainable and useful.</p>
634
635</div>
636
Chris Lattnerf623a082005-10-17 01:36:23 +0000[diff] [blame]637<!-- ======================================================================= -->
638<div class="doc_subsection">
639 <a name="ViewGraph">Viewing graphs while debugging code</a>
640</div>
641
642<div class="doc_text">
643
644<p>Several of the important data structures in LLVM are graphs: for example
645CFGs made out of LLVM <a href="#BasicBlock">BasicBlock</a>s, CFGs made out of
646LLVM <a href="CodeGenerator.html#machinebasicblock">MachineBasicBlock</a>s, and
647<a href="CodeGenerator.html#selectiondag_intro">Instruction Selection
648DAGs</a>. In many cases, while debugging various parts of the compiler, it is
649nice to instantly visualize these graphs.</p>
650
651<p>LLVM provides several callbacks that are available in a debug build to do
652exactly that. If you call the <tt>Function::viewCFG()</tt> method, for example,
653the current LLVM tool will pop up a window containing the CFG for the function
654where each basic block is a node in the graph, and each node contains the
655instructions in the block. Similarly, there also exists
656<tt>Function::viewCFGOnly()</tt> (does not include the instructions), the
657<tt>MachineFunction::viewCFG()</tt> and <tt>MachineFunction::viewCFGOnly()</tt>,
658and the <tt>SelectionDAG::viewGraph()</tt> methods. Within GDB, for example,
Jim Laskey543a0ee2006-10-02 12:28:07 +0000[diff] [blame]659you can usually use something like <tt>call DAG.viewGraph()</tt> to pop
Chris Lattnerf623a082005-10-17 01:36:23 +0000[diff] [blame]660up a window. Alternatively, you can sprinkle calls to these functions in your
661code in places you want to debug.</p>
662
663<p>Getting this to work requires a small amount of configuration. On Unix
664systems with X11, install the <a href="http://www.graphviz.org">graphviz</a>
665toolkit, and make sure 'dot' and 'gv' are in your path. If you are running on
666Mac OS/X, download and install the Mac OS/X <a
667href="http://www.pixelglow.com/graphviz/">Graphviz program</a>, and add
Reid Spencer128a7a72007-02-03 21:06:43 +0000[diff] [blame]668<tt>/Applications/Graphviz.app/Contents/MacOS/</tt> (or wherever you install
Chris Lattnerf623a082005-10-17 01:36:23 +0000[diff] [blame]669it) to your path. Once in your system and path are set up, rerun the LLVM
670configure script and rebuild LLVM to enable this functionality.</p>
671
Jim Laskey543a0ee2006-10-02 12:28:07 +0000[diff] [blame]672<p><tt>SelectionDAG</tt> has been extended to make it easier to locate
673<i>interesting</i> nodes in large complex graphs. From gdb, if you
674<tt>call DAG.setGraphColor(<i>node</i>, "<i>color</i>")</tt>, then the
Reid Spencer128a7a72007-02-03 21:06:43 +0000[diff] [blame]675next <tt>call DAG.viewGraph()</tt> would highlight the node in the
Jim Laskey543a0ee2006-10-02 12:28:07 +0000[diff] [blame]676specified color (choices of colors can be found at <a
Chris Lattner302da1e2007-02-03 03:05:57 +0000[diff] [blame]677href="http://www.graphviz.org/doc/info/colors.html">colors</a>.) More
Jim Laskey543a0ee2006-10-02 12:28:07 +0000[diff] [blame]678complex node attributes can be provided with <tt>call
679DAG.setGraphAttrs(<i>node</i>, "<i>attributes</i>")</tt> (choices can be
680found at <a href="http://www.graphviz.org/doc/info/attrs.html">Graph
681Attributes</a>.) If you want to restart and clear all the current graph
682attributes, then you can <tt>call DAG.clearGraphAttrs()</tt>. </p>
683
Chris Lattnerf623a082005-10-17 01:36:23 +0000[diff] [blame]684</div>
685
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]686<!-- *********************************************************************** -->
687<div class="doc_section">
688 <a name="datastructure">Picking the Right Data Structure for a Task</a>
689</div>
690<!-- *********************************************************************** -->
691
692<div class="doc_text">
693
Reid Spencer128a7a72007-02-03 21:06:43 +0000[diff] [blame]694<p>LLVM has a plethora of data structures in the <tt>llvm/ADT/</tt> directory,
695 and we commonly use STL data structures. This section describes the trade-offs
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]696 you should consider when you pick one.</p>
697
698<p>
699The first step is a choose your own adventure: do you want a sequential
700container, a set-like container, or a map-like container? The most important
701thing when choosing a container is the algorithmic properties of how you plan to
702access the container. Based on that, you should use:</p>
703
704<ul>
Reid Spencer128a7a72007-02-03 21:06:43 +0000[diff] [blame]705<li>a <a href="#ds_map">map-like</a> container if you need efficient look-up
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]706 of an value based on another value. Map-like containers also support
707 efficient queries for containment (whether a key is in the map). Map-like
708 containers generally do not support efficient reverse mapping (values to
709 keys). If you need that, use two maps. Some map-like containers also
710 support efficient iteration through the keys in sorted order. Map-like
711 containers are the most expensive sort, only use them if you need one of
712 these capabilities.</li>
713
714<li>a <a href="#ds_set">set-like</a> container if you need to put a bunch of
715 stuff into a container that automatically eliminates duplicates. Some
716 set-like containers support efficient iteration through the elements in
717 sorted order. Set-like containers are more expensive than sequential
718 containers.
719</li>
720
721<li>a <a href="#ds_sequential">sequential</a> container provides
722 the most efficient way to add elements and keeps track of the order they are
723 added to the collection. They permit duplicates and support efficient
Reid Spencer128a7a72007-02-03 21:06:43 +0000[diff] [blame]724 iteration, but do not support efficient look-up based on a key.
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]725</li>
726
Daniel Berlin1939ace2007-09-24 17:52:25 +0000[diff] [blame]727<li>a <a href="#ds_bit">bit</a> container provides an efficient way to store and
728 perform set operations on sets of numeric id's, while automatically
729 eliminating duplicates. Bit containers require a maximum of 1 bit for each
730 identifier you want to store.
731</li>
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]732</ul>
733
734<p>
Reid Spencer128a7a72007-02-03 21:06:43 +0000[diff] [blame]735Once the proper category of container is determined, you can fine tune the
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]736memory use, constant factors, and cache behaviors of access by intelligently
Reid Spencer128a7a72007-02-03 21:06:43 +0000[diff] [blame]737picking a member of the category. Note that constant factors and cache behavior
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]738can be a big deal. If you have a vector that usually only contains a few
739elements (but could contain many), for example, it's much better to use
740<a href="#dss_smallvector">SmallVector</a> than <a href="#dss_vector">vector</a>
741. Doing so avoids (relatively) expensive malloc/free calls, which dwarf the
742cost of adding the elements to the container. </p>
743
744</div>
745
746<!-- ======================================================================= -->
747<div class="doc_subsection">
748 <a name="ds_sequential">Sequential Containers (std::vector, std::list, etc)</a>
749</div>
750
751<div class="doc_text">
752There are a variety of sequential containers available for you, based on your
753needs. Pick the first in this section that will do what you want.
754</div>
755
756<!-- _______________________________________________________________________ -->
757<div class="doc_subsubsection">
758 <a name="dss_fixedarrays">Fixed Size Arrays</a>
759</div>
760
761<div class="doc_text">
762<p>Fixed size arrays are very simple and very fast. They are good if you know
763exactly how many elements you have, or you have a (low) upper bound on how many
764you have.</p>
765</div>
766
767<!-- _______________________________________________________________________ -->
768<div class="doc_subsubsection">
769 <a name="dss_heaparrays">Heap Allocated Arrays</a>
770</div>
771
772<div class="doc_text">
773<p>Heap allocated arrays (new[] + delete[]) are also simple. They are good if
774the number of elements is variable, if you know how many elements you will need
775before the array is allocated, and if the array is usually large (if not,
776consider a <a href="#dss_smallvector">SmallVector</a>). The cost of a heap
777allocated array is the cost of the new/delete (aka malloc/free). Also note that
778if you are allocating an array of a type with a constructor, the constructor and
Reid Spencer128a7a72007-02-03 21:06:43 +0000[diff] [blame]779destructors will be run for every element in the array (re-sizable vectors only
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]780construct those elements actually used).</p>
781</div>
782
783<!-- _______________________________________________________________________ -->
784<div class="doc_subsubsection">
785 <a name="dss_smallvector">"llvm/ADT/SmallVector.h"</a>
786</div>
787
788<div class="doc_text">
789<p><tt>SmallVector&lt;Type, N&gt;</tt> is a simple class that looks and smells
790just like <tt>vector&lt;Type&gt;</tt>:
791it supports efficient iteration, lays out elements in memory order (so you can
792do pointer arithmetic between elements), supports efficient push_back/pop_back
793operations, supports efficient random access to its elements, etc.</p>
794
795<p>The advantage of SmallVector is that it allocates space for
796some number of elements (N) <b>in the object itself</b>. Because of this, if
797the SmallVector is dynamically smaller than N, no malloc is performed. This can
798be a big win in cases where the malloc/free call is far more expensive than the
799code that fiddles around with the elements.</p>
800
801<p>This is good for vectors that are "usually small" (e.g. the number of
802predecessors/successors of a block is usually less than 8). On the other hand,
803this makes the size of the SmallVector itself large, so you don't want to
804allocate lots of them (doing so will waste a lot of space). As such,
805SmallVectors are most useful when on the stack.</p>
806
807<p>SmallVector also provides a nice portable and efficient replacement for
808<tt>alloca</tt>.</p>
809
810</div>
811
812<!-- _______________________________________________________________________ -->
813<div class="doc_subsubsection">
814 <a name="dss_vector">&lt;vector&gt;</a>
815</div>
816
817<div class="doc_text">
818<p>
819std::vector is well loved and respected. It is useful when SmallVector isn't:
820when the size of the vector is often large (thus the small optimization will
821rarely be a benefit) or if you will be allocating many instances of the vector
822itself (which would waste space for elements that aren't in the container).
823vector is also useful when interfacing with code that expects vectors :).
824</p>
Chris Lattner32d84762007-02-05 06:30:51 +0000[diff] [blame]825
826<p>One worthwhile note about std::vector: avoid code like this:</p>
827
828<div class="doc_code">
829<pre>
830for ( ... ) {
Chris Lattner9bb3dbb2007-03-28 18:27:57 +0000[diff] [blame]831 std::vector&lt;foo&gt; V;
Chris Lattner32d84762007-02-05 06:30:51 +0000[diff] [blame]832 use V;
833}
834</pre>
835</div>
836
837<p>Instead, write this as:</p>
838
839<div class="doc_code">
840<pre>
Chris Lattner9bb3dbb2007-03-28 18:27:57 +0000[diff] [blame]841std::vector&lt;foo&gt; V;
Chris Lattner32d84762007-02-05 06:30:51 +0000[diff] [blame]842for ( ... ) {
843 use V;
844 V.clear();
845}
846</pre>
847</div>
848
849<p>Doing so will save (at least) one heap allocation and free per iteration of
850the loop.</p>
851
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]852</div>
853
854<!-- _______________________________________________________________________ -->
855<div class="doc_subsubsection">
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]856 <a name="dss_deque">&lt;deque&gt;</a>
857</div>
858
859<div class="doc_text">
860<p>std::deque is, in some senses, a generalized version of std::vector. Like
861std::vector, it provides constant time random access and other similar
862properties, but it also provides efficient access to the front of the list. It
863does not guarantee continuity of elements within memory.</p>
864
865<p>In exchange for this extra flexibility, std::deque has significantly higher
866constant factor costs than std::vector. If possible, use std::vector or
867something cheaper.</p>
868</div>
869
870<!-- _______________________________________________________________________ -->
871<div class="doc_subsubsection">
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]872 <a name="dss_list">&lt;list&gt;</a>
873</div>
874
875<div class="doc_text">
876<p>std::list is an extremely inefficient class that is rarely useful.
877It performs a heap allocation for every element inserted into it, thus having an
878extremely high constant factor, particularly for small data types. std::list
879also only supports bidirectional iteration, not random access iteration.</p>
880
881<p>In exchange for this high cost, std::list supports efficient access to both
882ends of the list (like std::deque, but unlike std::vector or SmallVector). In
883addition, the iterator invalidation characteristics of std::list are stronger
884than that of a vector class: inserting or removing an element into the list does
885not invalidate iterator or pointers to other elements in the list.</p>
886</div>
887
888<!-- _______________________________________________________________________ -->
889<div class="doc_subsubsection">
Gabor Greif3899e492009-02-27 11:37:41 +0000[diff] [blame]890 <a name="dss_ilist">llvm/ADT/ilist.h</a>
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]891</div>
892
893<div class="doc_text">
894<p><tt>ilist&lt;T&gt;</tt> implements an 'intrusive' doubly-linked list. It is
895intrusive, because it requires the element to store and provide access to the
896prev/next pointers for the list.</p>
897
Gabor Greif2946d1c2009-02-27 12:02:19 +0000[diff] [blame]898<p><tt>ilist</tt> has the same drawbacks as <tt>std::list</tt>, and additionally
899requires an <tt>ilist_traits</tt> implementation for the element type, but it
900provides some novel characteristics. In particular, it can efficiently store
901polymorphic objects, the traits class is informed when an element is inserted or
Gabor Greif0cbcabe2009-03-12 09:47:03 +0000[diff] [blame]902removed from the list, and <tt>ilist</tt>s are guaranteed to support a
903constant-time splice operation.</p>
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]904
Gabor Greif0cbcabe2009-03-12 09:47:03 +0000[diff] [blame]905<p>These properties are exactly what we want for things like
906<tt>Instruction</tt>s and basic blocks, which is why these are implemented with
907<tt>ilist</tt>s.</p>
Gabor Greif3899e492009-02-27 11:37:41 +0000[diff] [blame]908
909Related classes of interest are explained in the following subsections:
910 <ul>
Gabor Greif01862502009-02-27 13:28:07 +0000[diff] [blame]911 <li><a href="#dss_ilist_traits">ilist_traits</a></li>
Gabor Greif2946d1c2009-02-27 12:02:19 +0000[diff] [blame]912 <li><a href="#dss_iplist">iplist</a></li>
Gabor Greif3899e492009-02-27 11:37:41 +0000[diff] [blame]913 <li><a href="#dss_ilist_node">llvm/ADT/ilist_node.h</a></li>
Gabor Greif6a65f422009-03-12 10:30:31 +0000[diff] [blame]914 <li><a href="#dss_ilist_sentinel">Sentinels</a></li>
Gabor Greif3899e492009-02-27 11:37:41 +0000[diff] [blame]915 </ul>
916</div>
917
918<!-- _______________________________________________________________________ -->
919<div class="doc_subsubsection">
Gabor Greif01862502009-02-27 13:28:07 +0000[diff] [blame]920 <a name="dss_ilist_traits">ilist_traits</a>
921</div>
922
923<div class="doc_text">
924<p><tt>ilist_traits&lt;T&gt;</tt> is <tt>ilist&lt;T&gt;</tt>'s customization
925mechanism. <tt>iplist&lt;T&gt;</tt> (and consequently <tt>ilist&lt;T&gt;</tt>)
926publicly derive from this traits class.</p>
927</div>
928
929<!-- _______________________________________________________________________ -->
930<div class="doc_subsubsection">
Gabor Greif2946d1c2009-02-27 12:02:19 +0000[diff] [blame]931 <a name="dss_iplist">iplist</a>
932</div>
933
934<div class="doc_text">
935<p><tt>iplist&lt;T&gt;</tt> is <tt>ilist&lt;T&gt;</tt>'s base and as such
Gabor Greif0cbcabe2009-03-12 09:47:03 +0000[diff] [blame]936supports a slightly narrower interface. Notably, inserters from
937<tt>T&amp;</tt> are absent.</p>
Gabor Greif01862502009-02-27 13:28:07 +0000[diff] [blame]938
939<p><tt>ilist_traits&lt;T&gt;</tt> is a public base of this class and can be
940used for a wide variety of customizations.</p>
Gabor Greif2946d1c2009-02-27 12:02:19 +0000[diff] [blame]941</div>
942
943<!-- _______________________________________________________________________ -->
944<div class="doc_subsubsection">
Gabor Greif3899e492009-02-27 11:37:41 +0000[diff] [blame]945 <a name="dss_ilist_node">llvm/ADT/ilist_node.h</a>
946</div>
947
948<div class="doc_text">
949<p><tt>ilist_node&lt;T&gt;</tt> implements a the forward and backward links
950that are expected by the <tt>ilist&lt;T&gt;</tt> (and analogous containers)
951in the default manner.</p>
952
953<p><tt>ilist_node&lt;T&gt;</tt>s are meant to be embedded in the node type
Gabor Greif0cbcabe2009-03-12 09:47:03 +0000[diff] [blame]954<tt>T</tt>, usually <tt>T</tt> publicly derives from
955<tt>ilist_node&lt;T&gt;</tt>.</p>
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]956</div>
957
958<!-- _______________________________________________________________________ -->
959<div class="doc_subsubsection">
Gabor Greif6a65f422009-03-12 10:30:31 +0000[diff] [blame]960 <a name="dss_ilist_sentinel">Sentinels</a>
961</div>
962
963<div class="doc_text">
964<p><tt>ilist</tt>s have another speciality that must be considered. To be a good
965citizen in the C++ ecosystem, it needs to support the standard container
966operations, such as <tt>begin</tt> and <tt>end</tt> iterators, etc. Also, the
967<tt>operator--</tt> must work correctly on the <tt>end</tt> iterator in the
968case of non-empty <tt>ilist</tt>s.</p>
969
970<p>The only sensible solution to this problem is to allocate a so-called
971<i>sentinel</i> along with the intrusive list, which serves as the <tt>end</tt>
972iterator, providing the back-link to the last element. However conforming to the
973C++ convention it is illegal to <tt>operator++</tt> beyond the sentinel and it
974also must not be dereferenced.</p>
975
976<p>These constraints allow for some implementation freedom to the <tt>ilist</tt>
977how to allocate and store the sentinel. The corresponding policy is dictated
978by <tt>ilist_traits&lt;T&gt;</tt>. By default a <tt>T</tt> gets heap-allocated
979whenever the need for a sentinel arises.</p>
980
981<p>While the default policy is sufficient in most cases, it may break down when
982<tt>T</tt> does not provide a default constructor. Also, in the case of many
983instances of <tt>ilist</tt>s, the memory overhead of the associated sentinels
984is wasted. To alleviate the situation with numerous and voluminous
985<tt>T</tt>-sentinels, sometimes a trick is employed, leading to <i>ghostly
986sentinels</i>.</p>
987
988<p>Ghostly sentinels are obtained by specially-crafted <tt>ilist_traits&lt;T&gt;</tt>
989which superpose the sentinel with the <tt>ilist</tt> instance in memory. Pointer
990arithmetic is used to obtain the sentinel, which is relative to the
991<tt>ilist</tt>'s <tt>this</tt> pointer. The <tt>ilist</tt> is augmented by an
992extra pointer, which serves as the back-link of the sentinel. This is the only
993field in the ghostly sentinel which can be legally accessed.</p>
994</div>
995
996<!-- _______________________________________________________________________ -->
997<div class="doc_subsubsection">
Chris Lattnerc5722432007-02-03 19:49:31 +0000[diff] [blame]998 <a name="dss_other">Other Sequential Container options</a>
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]999</div>
1000
1001<div class="doc_text">
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1002<p>Other STL containers are available, such as std::string.</p>
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]1003
1004<p>There are also various STL adapter classes such as std::queue,
1005std::priority_queue, std::stack, etc. These provide simplified access to an
1006underlying container but don't affect the cost of the container itself.</p>
1007
1008</div>
1009
1010
1011<!-- ======================================================================= -->
1012<div class="doc_subsection">
1013 <a name="ds_set">Set-Like Containers (std::set, SmallSet, SetVector, etc)</a>
1014</div>
1015
1016<div class="doc_text">
1017
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1018<p>Set-like containers are useful when you need to canonicalize multiple values
1019into a single representation. There are several different choices for how to do
1020this, providing various trade-offs.</p>
1021
1022</div>
1023
1024
1025<!-- _______________________________________________________________________ -->
1026<div class="doc_subsubsection">
1027 <a name="dss_sortedvectorset">A sorted 'vector'</a>
1028</div>
1029
1030<div class="doc_text">
1031
Chris Lattner3b23a8c2007-02-03 08:10:45 +0000[diff] [blame]1032<p>If you intend to insert a lot of elements, then do a lot of queries, a
1033great approach is to use a vector (or other sequential container) with
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1034std::sort+std::unique to remove duplicates. This approach works really well if
Chris Lattner3b23a8c2007-02-03 08:10:45 +0000[diff] [blame]1035your usage pattern has these two distinct phases (insert then query), and can be
1036coupled with a good choice of <a href="#ds_sequential">sequential container</a>.
1037</p>
1038
1039<p>
1040This combination provides the several nice properties: the result data is
1041contiguous in memory (good for cache locality), has few allocations, is easy to
1042address (iterators in the final vector are just indices or pointers), and can be
1043efficiently queried with a standard binary or radix search.</p>
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1044
1045</div>
1046
1047<!-- _______________________________________________________________________ -->
1048<div class="doc_subsubsection">
1049 <a name="dss_smallset">"llvm/ADT/SmallSet.h"</a>
1050</div>
1051
1052<div class="doc_text">
1053
Reid Spencer128a7a72007-02-03 21:06:43 +0000[diff] [blame]1054<p>If you have a set-like data structure that is usually small and whose elements
Chris Lattner4ddfac12007-02-03 07:59:51 +0000[diff] [blame]1055are 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]1056has space for N elements in place (thus, if the set is dynamically smaller than
Chris Lattner14868db2007-02-03 08:20:15 +0000[diff] [blame]1057N, no malloc traffic is required) and accesses them with a simple linear search.
1058When the set grows beyond 'N' elements, it allocates a more expensive representation that
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1059guarantees efficient access (for most types, it falls back to std::set, but for
Chris Lattner14868db2007-02-03 08:20:15 +0000[diff] [blame]1060pointers it uses something far better, <a
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1061href="#dss_smallptrset">SmallPtrSet</a>).</p>
1062
1063<p>The magic of this class is that it handles small sets extremely efficiently,
1064but gracefully handles extremely large sets without loss of efficiency. The
1065drawback is that the interface is quite small: it supports insertion, queries
1066and erasing, but does not support iteration.</p>
1067
1068</div>
1069
1070<!-- _______________________________________________________________________ -->
1071<div class="doc_subsubsection">
1072 <a name="dss_smallptrset">"llvm/ADT/SmallPtrSet.h"</a>
1073</div>
1074
1075<div class="doc_text">
1076
1077<p>SmallPtrSet has all the advantages of SmallSet (and a SmallSet of pointers is
Reid Spencer128a7a72007-02-03 21:06:43 +0000[diff] [blame]1078transparently implemented with a SmallPtrSet), but also supports iterators. If
Chris Lattner14868db2007-02-03 08:20:15 +0000[diff] [blame]1079more than 'N' insertions are performed, a single quadratically
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1080probed hash table is allocated and grows as needed, providing extremely
1081efficient access (constant time insertion/deleting/queries with low constant
1082factors) and is very stingy with malloc traffic.</p>
1083
1084<p>Note that, unlike std::set, the iterators of SmallPtrSet are invalidated
1085whenever an insertion occurs. Also, the values visited by the iterators are not
1086visited in sorted order.</p>
1087
1088</div>
1089
1090<!-- _______________________________________________________________________ -->
1091<div class="doc_subsubsection">
Chris Lattnerc28476f2007-09-30 00:58:59 +0000[diff] [blame]1092 <a name="dss_denseset">"llvm/ADT/DenseSet.h"</a>
1093</div>
1094
1095<div class="doc_text">
1096
1097<p>
1098DenseSet is a simple quadratically probed hash table. It excels at supporting
1099small values: it uses a single allocation to hold all of the pairs that
1100are currently inserted in the set. DenseSet is a great way to unique small
1101values that are not simple pointers (use <a
1102href="#dss_smallptrset">SmallPtrSet</a> for pointers). Note that DenseSet has
1103the same requirements for the value type that <a
1104href="#dss_densemap">DenseMap</a> has.
1105</p>
1106
1107</div>
1108
1109<!-- _______________________________________________________________________ -->
1110<div class="doc_subsubsection">
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1111 <a name="dss_FoldingSet">"llvm/ADT/FoldingSet.h"</a>
1112</div>
1113
1114<div class="doc_text">
1115
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]1116<p>
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1117FoldingSet is an aggregate class that is really good at uniquing
1118expensive-to-create or polymorphic objects. It is a combination of a chained
1119hash table with intrusive links (uniqued objects are required to inherit from
Chris Lattner14868db2007-02-03 08:20:15 +0000[diff] [blame]1120FoldingSetNode) that uses <a href="#dss_smallvector">SmallVector</a> as part of
1121its ID process.</p>
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1122
Chris Lattner14868db2007-02-03 08:20:15 +0000[diff] [blame]1123<p>Consider a case where you want to implement a "getOrCreateFoo" method for
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1124a complex object (for example, a node in the code generator). The client has a
1125description of *what* it wants to generate (it knows the opcode and all the
1126operands), 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]1127only to find out it already exists, at which point we would have to delete it
1128and return the node that already exists.
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]1129</p>
1130
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1131<p>To support this style of client, FoldingSet perform a query with a
1132FoldingSetNodeID (which wraps SmallVector) that can be used to describe the
1133element that we want to query for. The query either returns the element
1134matching the ID or it returns an opaque ID that indicates where insertion should
Chris Lattner14868db2007-02-03 08:20:15 +0000[diff] [blame]1135take place. Construction of the ID usually does not require heap traffic.</p>
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1136
1137<p>Because FoldingSet uses intrusive links, it can support polymorphic objects
1138in the set (for example, you can have SDNode instances mixed with LoadSDNodes).
1139Because the elements are individually allocated, pointers to the elements are
1140stable: inserting or removing elements does not invalidate any pointers to other
1141elements.
1142</p>
1143
1144</div>
1145
1146<!-- _______________________________________________________________________ -->
1147<div class="doc_subsubsection">
1148 <a name="dss_set">&lt;set&gt;</a>
1149</div>
1150
1151<div class="doc_text">
1152
Chris Lattnerc5722432007-02-03 19:49:31 +0000[diff] [blame]1153<p><tt>std::set</tt> is a reasonable all-around set class, which is decent at
1154many things but great at nothing. std::set allocates memory for each element
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1155inserted (thus it is very malloc intensive) and typically stores three pointers
Chris Lattner14868db2007-02-03 08:20:15 +0000[diff] [blame]1156per element in the set (thus adding a large amount of per-element space
1157overhead). It offers guaranteed log(n) performance, which is not particularly
Chris Lattnerc5722432007-02-03 19:49:31 +0000[diff] [blame]1158fast from a complexity standpoint (particularly if the elements of the set are
1159expensive to compare, like strings), and has extremely high constant factors for
1160lookup, insertion and removal.</p>
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1161
Chris Lattner14868db2007-02-03 08:20:15 +0000[diff] [blame]1162<p>The advantages of std::set are that its iterators are stable (deleting or
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1163inserting an element from the set does not affect iterators or pointers to other
1164elements) and that iteration over the set is guaranteed to be in sorted order.
1165If the elements in the set are large, then the relative overhead of the pointers
1166and malloc traffic is not a big deal, but if the elements of the set are small,
1167std::set is almost never a good choice.</p>
1168
1169</div>
1170
1171<!-- _______________________________________________________________________ -->
1172<div class="doc_subsubsection">
1173 <a name="dss_setvector">"llvm/ADT/SetVector.h"</a>
1174</div>
1175
1176<div class="doc_text">
Chris Lattneredca3c52007-02-04 00:00:26 +0000[diff] [blame]1177<p>LLVM's SetVector&lt;Type&gt; is an adapter class that combines your choice of
1178a set-like container along with a <a href="#ds_sequential">Sequential
1179Container</a>. The important property
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1180that this provides is efficient insertion with uniquing (duplicate elements are
1181ignored) with iteration support. It implements this by inserting elements into
1182both a set-like container and the sequential container, using the set-like
1183container for uniquing and the sequential container for iteration.
1184</p>
1185
1186<p>The difference between SetVector and other sets is that the order of
1187iteration is guaranteed to match the order of insertion into the SetVector.
1188This property is really important for things like sets of pointers. Because
1189pointer values are non-deterministic (e.g. vary across runs of the program on
Chris Lattneredca3c52007-02-04 00:00:26 +0000[diff] [blame]1190different machines), iterating over the pointers in the set will
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1191not be in a well-defined order.</p>
1192
1193<p>
1194The drawback of SetVector is that it requires twice as much space as a normal
1195set and has the sum of constant factors from the set-like container and the
1196sequential container that it uses. Use it *only* if you need to iterate over
1197the elements in a deterministic order. SetVector is also expensive to delete
Chris Lattneredca3c52007-02-04 00:00:26 +0000[diff] [blame]1198elements out of (linear time), unless you use it's "pop_back" method, which is
1199faster.
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1200</p>
1201
Chris Lattneredca3c52007-02-04 00:00:26 +0000[diff] [blame]1202<p>SetVector is an adapter class that defaults to using std::vector and std::set
1203for the underlying containers, so it is quite expensive. However,
1204<tt>"llvm/ADT/SetVector.h"</tt> also provides a SmallSetVector class, which
1205defaults to using a SmallVector and SmallSet of a specified size. If you use
1206this, and if your sets are dynamically smaller than N, you will save a lot of
1207heap traffic.</p>
1208
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1209</div>
1210
1211<!-- _______________________________________________________________________ -->
1212<div class="doc_subsubsection">
Chris Lattnerc5722432007-02-03 19:49:31 +0000[diff] [blame]1213 <a name="dss_uniquevector">"llvm/ADT/UniqueVector.h"</a>
1214</div>
1215
1216<div class="doc_text">
1217
1218<p>
1219UniqueVector is similar to <a href="#dss_setvector">SetVector</a>, but it
1220retains a unique ID for each element inserted into the set. It internally
1221contains a map and a vector, and it assigns a unique ID for each value inserted
1222into the set.</p>
1223
1224<p>UniqueVector is very expensive: its cost is the sum of the cost of
1225maintaining both the map and vector, it has high complexity, high constant
1226factors, and produces a lot of malloc traffic. It should be avoided.</p>
1227
1228</div>
1229
1230
1231<!-- _______________________________________________________________________ -->
1232<div class="doc_subsubsection">
1233 <a name="dss_otherset">Other Set-Like Container Options</a>
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1234</div>
1235
1236<div class="doc_text">
1237
1238<p>
1239The STL provides several other options, such as std::multiset and the various
Chris Lattnerf1a30822009-03-09 05:20:45 +0000[diff] [blame]1240"hash_set" like containers (whether from C++ TR1 or from the SGI library). We
1241never use hash_set and unordered_set because they are generally very expensive
1242(each insertion requires a malloc) and very non-portable.
1243</p>
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1244
1245<p>std::multiset is useful if you're not interested in elimination of
Chris Lattner14868db2007-02-03 08:20:15 +0000[diff] [blame]1246duplicates, but has all the drawbacks of std::set. A sorted vector (where you
1247don't delete duplicate entries) or some other approach is almost always
1248better.</p>
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1249
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]1250</div>
1251
1252<!-- ======================================================================= -->
1253<div class="doc_subsection">
1254 <a name="ds_map">Map-Like Containers (std::map, DenseMap, etc)</a>
1255</div>
1256
1257<div class="doc_text">
Chris Lattnerc5722432007-02-03 19:49:31 +0000[diff] [blame]1258Map-like containers are useful when you want to associate data to a key. As
1259usual, there are a lot of different ways to do this. :)
1260</div>
1261
1262<!-- _______________________________________________________________________ -->
1263<div class="doc_subsubsection">
1264 <a name="dss_sortedvectormap">A sorted 'vector'</a>
1265</div>
1266
1267<div class="doc_text">
1268
1269<p>
1270If your usage pattern follows a strict insert-then-query approach, you can
1271trivially use the same approach as <a href="#dss_sortedvectorset">sorted vectors
1272for set-like containers</a>. The only difference is that your query function
1273(which uses std::lower_bound to get efficient log(n) lookup) should only compare
1274the key, not both the key and value. This yields the same advantages as sorted
1275vectors for sets.
1276</p>
1277</div>
1278
1279<!-- _______________________________________________________________________ -->
1280<div class="doc_subsubsection">
Chris Lattner796f9fa2007-02-08 19:14:21 +0000[diff] [blame]1281 <a name="dss_stringmap">"llvm/ADT/StringMap.h"</a>
Chris Lattnerc5722432007-02-03 19:49:31 +0000[diff] [blame]1282</div>
1283
1284<div class="doc_text">
1285
1286<p>
1287Strings are commonly used as keys in maps, and they are difficult to support
1288efficiently: they are variable length, inefficient to hash and compare when
Chris Lattner796f9fa2007-02-08 19:14:21 +0000[diff] [blame]1289long, expensive to copy, etc. StringMap is a specialized container designed to
1290cope with these issues. It supports mapping an arbitrary range of bytes to an
1291arbitrary other object.</p>
Chris Lattnerc5722432007-02-03 19:49:31 +0000[diff] [blame]1292
Chris Lattner796f9fa2007-02-08 19:14:21 +0000[diff] [blame]1293<p>The StringMap implementation uses a quadratically-probed hash table, where
Chris Lattnerc5722432007-02-03 19:49:31 +0000[diff] [blame]1294the buckets store a pointer to the heap allocated entries (and some other
1295stuff). The entries in the map must be heap allocated because the strings are
1296variable length. The string data (key) and the element object (value) are
1297stored in the same allocation with the string data immediately after the element
1298object. This container guarantees the "<tt>(char*)(&amp;Value+1)</tt>" points
1299to the key string for a value.</p>
1300
Chris Lattner796f9fa2007-02-08 19:14:21 +0000[diff] [blame]1301<p>The StringMap is very fast for several reasons: quadratic probing is very
Chris Lattnerc5722432007-02-03 19:49:31 +0000[diff] [blame]1302cache efficient for lookups, the hash value of strings in buckets is not
Chris Lattner796f9fa2007-02-08 19:14:21 +0000[diff] [blame]1303recomputed when lookup up an element, StringMap rarely has to touch the
Chris Lattnerc5722432007-02-03 19:49:31 +0000[diff] [blame]1304memory for unrelated objects when looking up a value (even when hash collisions
1305happen), hash table growth does not recompute the hash values for strings
1306already in the table, and each pair in the map is store in a single allocation
1307(the string data is stored in the same allocation as the Value of a pair).</p>
1308
Chris Lattner796f9fa2007-02-08 19:14:21 +0000[diff] [blame]1309<p>StringMap also provides query methods that take byte ranges, so it only ever
Chris Lattnerc5722432007-02-03 19:49:31 +0000[diff] [blame]1310copies a string if a value is inserted into the table.</p>
1311</div>
1312
1313<!-- _______________________________________________________________________ -->
1314<div class="doc_subsubsection">
1315 <a name="dss_indexedmap">"llvm/ADT/IndexedMap.h"</a>
1316</div>
1317
1318<div class="doc_text">
1319<p>
1320IndexedMap is a specialized container for mapping small dense integers (or
1321values that can be mapped to small dense integers) to some other type. It is
1322internally implemented as a vector with a mapping function that maps the keys to
1323the dense integer range.
1324</p>
1325
1326<p>
1327This is useful for cases like virtual registers in the LLVM code generator: they
1328have a dense mapping that is offset by a compile-time constant (the first
1329virtual register ID).</p>
1330
1331</div>
1332
1333<!-- _______________________________________________________________________ -->
1334<div class="doc_subsubsection">
1335 <a name="dss_densemap">"llvm/ADT/DenseMap.h"</a>
1336</div>
1337
1338<div class="doc_text">
1339
1340<p>
1341DenseMap is a simple quadratically probed hash table. It excels at supporting
1342small keys and values: it uses a single allocation to hold all of the pairs that
1343are currently inserted in the map. DenseMap is a great way to map pointers to
1344pointers, or map other small types to each other.
1345</p>
1346
1347<p>
1348There are several aspects of DenseMap that you should be aware of, however. The
1349iterators in a densemap are invalidated whenever an insertion occurs, unlike
1350map. Also, because DenseMap allocates space for a large number of key/value
Chris Lattnera4a264d2007-02-03 20:17:53 +0000[diff] [blame]1351pairs (it starts with 64 by default), it will waste a lot of space if your keys
1352or values are large. Finally, you must implement a partial specialization of
Chris Lattner76c1b972007-09-17 18:34:04 +0000[diff] [blame]1353DenseMapInfo for the key that you want, if it isn't already supported. This
Chris Lattnerc5722432007-02-03 19:49:31 +0000[diff] [blame]1354is required to tell DenseMap about two special marker values (which can never be
Chris Lattnera4a264d2007-02-03 20:17:53 +0000[diff] [blame]1355inserted into the map) that it needs internally.</p>
Chris Lattnerc5722432007-02-03 19:49:31 +0000[diff] [blame]1356
1357</div>
1358
1359<!-- _______________________________________________________________________ -->
1360<div class="doc_subsubsection">
1361 <a name="dss_map">&lt;map&gt;</a>
1362</div>
1363
1364<div class="doc_text">
1365
1366<p>
1367std::map has similar characteristics to <a href="#dss_set">std::set</a>: it uses
1368a single allocation per pair inserted into the map, it offers log(n) lookup with
1369an extremely large constant factor, imposes a space penalty of 3 pointers per
1370pair in the map, etc.</p>
1371
1372<p>std::map is most useful when your keys or values are very large, if you need
1373to iterate over the collection in sorted order, or if you need stable iterators
1374into the map (i.e. they don't get invalidated if an insertion or deletion of
1375another element takes place).</p>
1376
1377</div>
1378
1379<!-- _______________________________________________________________________ -->
1380<div class="doc_subsubsection">
1381 <a name="dss_othermap">Other Map-Like Container Options</a>
1382</div>
1383
1384<div class="doc_text">
1385
1386<p>
1387The STL provides several other options, such as std::multimap and the various
Chris Lattnerf1a30822009-03-09 05:20:45 +0000[diff] [blame]1388"hash_map" like containers (whether from C++ TR1 or from the SGI library). We
1389never use hash_set and unordered_set because they are generally very expensive
1390(each insertion requires a malloc) and very non-portable.</p>
Chris Lattnerc5722432007-02-03 19:49:31 +0000[diff] [blame]1391
1392<p>std::multimap is useful if you want to map a key to multiple values, but has
1393all the drawbacks of std::map. A sorted vector or some other approach is almost
1394always better.</p>
1395
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]1396</div>
1397
Daniel Berlin1939ace2007-09-24 17:52:25 +0000[diff] [blame]1398<!-- ======================================================================= -->
1399<div class="doc_subsection">
1400 <a name="ds_bit">Bit storage containers (BitVector, SparseBitVector)</a>
1401</div>
1402
1403<div class="doc_text">
Chris Lattner7086ce72007-09-25 22:37:50 +0000[diff] [blame]1404<p>Unlike the other containers, there are only two bit storage containers, and
1405choosing when to use each is relatively straightforward.</p>
1406
1407<p>One additional option is
1408<tt>std::vector&lt;bool&gt;</tt>: we discourage its use for two reasons 1) the
1409implementation in many common compilers (e.g. commonly available versions of
1410GCC) is extremely inefficient and 2) the C++ standards committee is likely to
1411deprecate this container and/or change it significantly somehow. In any case,
1412please don't use it.</p>
Daniel Berlin1939ace2007-09-24 17:52:25 +0000[diff] [blame]1413</div>
1414
1415<!-- _______________________________________________________________________ -->
1416<div class="doc_subsubsection">
1417 <a name="dss_bitvector">BitVector</a>
1418</div>
1419
1420<div class="doc_text">
1421<p> The BitVector container provides a fixed size set of bits for manipulation.
1422It supports individual bit setting/testing, as well as set operations. The set
1423operations take time O(size of bitvector), but operations are performed one word
1424at a time, instead of one bit at a time. This makes the BitVector very fast for
1425set operations compared to other containers. Use the BitVector when you expect
1426the number of set bits to be high (IE a dense set).
1427</p>
1428</div>
1429
1430<!-- _______________________________________________________________________ -->
1431<div class="doc_subsubsection">
1432 <a name="dss_sparsebitvector">SparseBitVector</a>
1433</div>
1434
1435<div class="doc_text">
1436<p> The SparseBitVector container is much like BitVector, with one major
1437difference: Only the bits that are set, are stored. This makes the
1438SparseBitVector much more space efficient than BitVector when the set is sparse,
1439as well as making set operations O(number of set bits) instead of O(size of
1440universe). The downside to the SparseBitVector is that setting and testing of random bits is O(N), and on large SparseBitVectors, this can be slower than BitVector. In our implementation, setting or testing bits in sorted order
1441(either forwards or reverse) is O(1) worst case. Testing and setting bits within 128 bits (depends on size) of the current bit is also O(1). As a general statement, testing/setting bits in a SparseBitVector is O(distance away from last set bit).
1442</p>
1443</div>
Chris Lattnerf623a082005-10-17 01:36:23 +0000[diff] [blame]1444
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1445<!-- *********************************************************************** -->
1446<div class="doc_section">
1447 <a name="common">Helpful Hints for Common Operations</a>
1448</div>
1449<!-- *********************************************************************** -->
1450
1451<div class="doc_text">
1452
1453<p>This section describes how to perform some very simple transformations of
1454LLVM code. This is meant to give examples of common idioms used, showing the
1455practical side of LLVM transformations. <p> Because this is a "how-to" section,
1456you should also read about the main classes that you will be working with. The
1457<a href="#coreclasses">Core LLVM Class Hierarchy Reference</a> contains details
1458and descriptions of the main classes that you should know about.</p>
1459
1460</div>
1461
1462<!-- NOTE: this section should be heavy on example code -->
1463<!-- ======================================================================= -->
1464<div class="doc_subsection">
1465 <a name="inspection">Basic Inspection and Traversal Routines</a>
1466</div>
1467
1468<div class="doc_text">
1469
1470<p>The LLVM compiler infrastructure have many different data structures that may
1471be traversed. Following the example of the C++ standard template library, the
1472techniques used to traverse these various data structures are all basically the
1473same. For a enumerable sequence of values, the <tt>XXXbegin()</tt> function (or
1474method) returns an iterator to the start of the sequence, the <tt>XXXend()</tt>
1475function returns an iterator pointing to one past the last valid element of the
1476sequence, and there is some <tt>XXXiterator</tt> data type that is common
1477between the two operations.</p>
1478
1479<p>Because the pattern for iteration is common across many different aspects of
1480the program representation, the standard template library algorithms may be used
1481on them, and it is easier to remember how to iterate. First we show a few common
1482examples of the data structures that need to be traversed. Other data
1483structures are traversed in very similar ways.</p>
1484
1485</div>
1486
1487<!-- _______________________________________________________________________ -->
Chris Lattner69bf8a92004-05-23 21:06:58 +0000[diff] [blame]1488<div class="doc_subsubsection">
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1489 <a name="iterate_function">Iterating over the </a><a
1490 href="#BasicBlock"><tt>BasicBlock</tt></a>s in a <a
1491 href="#Function"><tt>Function</tt></a>
1492</div>
1493
1494<div class="doc_text">
1495
1496<p>It's quite common to have a <tt>Function</tt> instance that you'd like to
1497transform in some way; in particular, you'd like to manipulate its
1498<tt>BasicBlock</tt>s. To facilitate this, you'll need to iterate over all of
1499the <tt>BasicBlock</tt>s that constitute the <tt>Function</tt>. The following is
1500an example that prints the name of a <tt>BasicBlock</tt> and the number of
1501<tt>Instruction</tt>s it contains:</p>
1502
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1503<div class="doc_code">
1504<pre>
Bill Wendling82e2eea2006-10-11 18:00:22 +0000[diff] [blame]1505// <i>func is a pointer to a Function instance</i>
1506for (Function::iterator i = func-&gt;begin(), e = func-&gt;end(); i != e; ++i)
1507 // <i>Print out the name of the basic block if it has one, and then the</i>
1508 // <i>number of instructions that it contains</i>
Bill Wendling832171c2006-12-07 20:04:42 +0000[diff] [blame]1509 llvm::cerr &lt;&lt; "Basic block (name=" &lt;&lt; i-&gt;getName() &lt;&lt; ") has "
1510 &lt;&lt; i-&gt;size() &lt;&lt; " instructions.\n";
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1511</pre>
1512</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1513
1514<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]1515invoking member functions of the <tt>Instruction</tt> class. This is
1516because the indirection operator is overloaded for the iterator
Chris Lattner7496ec52003-08-05 22:54:23 +0000[diff] [blame]1517classes. In the above code, the expression <tt>i-&gt;size()</tt> is
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1518exactly equivalent to <tt>(*i).size()</tt> just like you'd expect.</p>
1519
1520</div>
1521
1522<!-- _______________________________________________________________________ -->
Chris Lattner69bf8a92004-05-23 21:06:58 +0000[diff] [blame]1523<div class="doc_subsubsection">
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1524 <a name="iterate_basicblock">Iterating over the </a><a
1525 href="#Instruction"><tt>Instruction</tt></a>s in a <a
1526 href="#BasicBlock"><tt>BasicBlock</tt></a>
1527</div>
1528
1529<div class="doc_text">
1530
1531<p>Just like when dealing with <tt>BasicBlock</tt>s in <tt>Function</tt>s, it's
1532easy to iterate over the individual instructions that make up
1533<tt>BasicBlock</tt>s. Here's a code snippet that prints out each instruction in
1534a <tt>BasicBlock</tt>:</p>
1535
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1536<div class="doc_code">
Chris Lattner55c04612005-03-06 06:00:13 +0000[diff] [blame]1537<pre>
Bill Wendling82e2eea2006-10-11 18:00:22 +0000[diff] [blame]1538// <i>blk is a pointer to a BasicBlock instance</i>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1539for (BasicBlock::iterator i = blk-&gt;begin(), e = blk-&gt;end(); i != e; ++i)
Bill Wendling82e2eea2006-10-11 18:00:22 +0000[diff] [blame]1540 // <i>The next statement works since operator&lt;&lt;(ostream&amp;,...)</i>
1541 // <i>is overloaded for Instruction&amp;</i>
Bill Wendling832171c2006-12-07 20:04:42 +0000[diff] [blame]1542 llvm::cerr &lt;&lt; *i &lt;&lt; "\n";
Chris Lattner55c04612005-03-06 06:00:13 +0000[diff] [blame]1543</pre>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1544</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1545
1546<p>However, this isn't really the best way to print out the contents of a
1547<tt>BasicBlock</tt>! Since the ostream operators are overloaded for virtually
1548anything you'll care about, you could have just invoked the print routine on the
Bill Wendling832171c2006-12-07 20:04:42 +0000[diff] [blame]1549basic block itself: <tt>llvm::cerr &lt;&lt; *blk &lt;&lt; "\n";</tt>.</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1550
1551</div>
1552
1553<!-- _______________________________________________________________________ -->
Chris Lattner69bf8a92004-05-23 21:06:58 +0000[diff] [blame]1554<div class="doc_subsubsection">
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1555 <a name="iterate_institer">Iterating over the </a><a
1556 href="#Instruction"><tt>Instruction</tt></a>s in a <a
1557 href="#Function"><tt>Function</tt></a>
1558</div>
1559
1560<div class="doc_text">
1561
1562<p>If you're finding that you commonly iterate over a <tt>Function</tt>'s
1563<tt>BasicBlock</tt>s and then that <tt>BasicBlock</tt>'s <tt>Instruction</tt>s,
1564<tt>InstIterator</tt> should be used instead. You'll need to include <a
1565href="/doxygen/InstIterator_8h-source.html"><tt>llvm/Support/InstIterator.h</tt></a>,
1566and then instantiate <tt>InstIterator</tt>s explicitly in your code. Here's a
Chris Lattner69bf8a92004-05-23 21:06:58 +0000[diff] [blame]1567small 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]1568
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1569<div class="doc_code">
1570<pre>
1571#include "<a href="/doxygen/InstIterator_8h-source.html">llvm/Support/InstIterator.h</a>"
1572
Reid Spencer128a7a72007-02-03 21:06:43 +0000[diff] [blame]1573// <i>F is a pointer to a Function instance</i>
Chris Lattnerda021aa2008-06-04 18:20:42 +0000[diff] [blame]1574for (inst_iterator I = inst_begin(F), E = inst_end(F); I != E; ++I)
1575 llvm::cerr &lt;&lt; *I &lt;&lt; "\n";
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1576</pre>
1577</div>
1578
1579<p>Easy, isn't it? You can also use <tt>InstIterator</tt>s to fill a
Reid Spencer128a7a72007-02-03 21:06:43 +0000[diff] [blame]1580work list with its initial contents. For example, if you wanted to
1581initialize a work list to contain all instructions in a <tt>Function</tt>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1582F, all you would need to do is something like:</p>
1583
1584<div class="doc_code">
1585<pre>
1586std::set&lt;Instruction*&gt; worklist;
Chris Lattnerda021aa2008-06-04 18:20:42 +0000[diff] [blame]1587// or better yet, SmallPtrSet&lt;Instruction*, 64&gt; worklist;
1588
1589for (inst_iterator I = inst_begin(F), E = inst_end(F); I != E; ++I)
1590 worklist.insert(&amp;*I);
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1591</pre>
1592</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1593
1594<p>The STL set <tt>worklist</tt> would now contain all instructions in the
1595<tt>Function</tt> pointed to by F.</p>
1596
1597</div>
1598
1599<!-- _______________________________________________________________________ -->
1600<div class="doc_subsubsection">
1601 <a name="iterate_convert">Turning an iterator into a class pointer (and
1602 vice-versa)</a>
1603</div>
1604
1605<div class="doc_text">
1606
1607<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]1608instance when all you've got at hand is an iterator. Well, extracting
Chris Lattner69bf8a92004-05-23 21:06:58 +0000[diff] [blame]1609a reference or a pointer from an iterator is very straight-forward.
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]1610Assuming that <tt>i</tt> is a <tt>BasicBlock::iterator</tt> and <tt>j</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1611is a <tt>BasicBlock::const_iterator</tt>:</p>
1612
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1613<div class="doc_code">
1614<pre>
Bill Wendling82e2eea2006-10-11 18:00:22 +0000[diff] [blame]1615Instruction&amp; inst = *i; // <i>Grab reference to instruction reference</i>
1616Instruction* pinst = &amp;*i; // <i>Grab pointer to instruction reference</i>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1617const Instruction&amp; inst = *j;
1618</pre>
1619</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1620
1621<p>However, the iterators you'll be working with in the LLVM framework are
1622special: they will automatically convert to a ptr-to-instance type whenever they
1623need to. Instead of dereferencing the iterator and then taking the address of
1624the result, you can simply assign the iterator to the proper pointer type and
1625you get the dereference and address-of operation as a result of the assignment
1626(behind the scenes, this is a result of overloading casting mechanisms). Thus
1627the last line of the last example,</p>
1628
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1629<div class="doc_code">
1630<pre>
Chris Lattner2e438ca2008-01-03 16:56:04 +0000[diff] [blame]1631Instruction *pinst = &amp;*i;
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1632</pre>
1633</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1634
1635<p>is semantically equivalent to</p>
1636
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1637<div class="doc_code">
1638<pre>
Chris Lattner2e438ca2008-01-03 16:56:04 +0000[diff] [blame]1639Instruction *pinst = i;
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1640</pre>
1641</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1642
Chris Lattner69bf8a92004-05-23 21:06:58 +0000[diff] [blame]1643<p>It's also possible to turn a class pointer into the corresponding iterator,
1644and this is a constant time operation (very efficient). The following code
1645snippet illustrates use of the conversion constructors provided by LLVM
1646iterators. By using these, you can explicitly grab the iterator of something
1647without actually obtaining it via iteration over some structure:</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1648
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1649<div class="doc_code">
1650<pre>
1651void printNextInstruction(Instruction* inst) {
1652 BasicBlock::iterator it(inst);
Bill Wendling82e2eea2006-10-11 18:00:22 +0000[diff] [blame]1653 ++it; // <i>After this line, it refers to the instruction after *inst</i>
Bill Wendling832171c2006-12-07 20:04:42 +0000[diff] [blame]1654 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]1655}
1656</pre>
1657</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1658
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1659</div>
1660
1661<!--_______________________________________________________________________-->
1662<div class="doc_subsubsection">
1663 <a name="iterate_complex">Finding call sites: a slightly more complex
1664 example</a>
1665</div>
1666
1667<div class="doc_text">
1668
1669<p>Say that you're writing a FunctionPass and would like to count all the
1670locations in the entire module (that is, across every <tt>Function</tt>) where a
1671certain function (i.e., some <tt>Function</tt>*) is already in scope. As you'll
1672learn 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]1673much more straight-forward manner, but this example will allow us to explore how
Reid Spencer128a7a72007-02-03 21:06:43 +0000[diff] [blame]1674you'd do it if you didn't have <tt>InstVisitor</tt> around. In pseudo-code, this
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1675is what we want to do:</p>
1676
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1677<div class="doc_code">
1678<pre>
1679initialize callCounter to zero
1680for each Function f in the Module
1681 for each BasicBlock b in f
1682 for each Instruction i in b
1683 if (i is a CallInst and calls the given function)
1684 increment callCounter
1685</pre>
1686</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1687
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1688<p>And the actual code is (remember, because we're writing a
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1689<tt>FunctionPass</tt>, our <tt>FunctionPass</tt>-derived class simply has to
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1690override the <tt>runOnFunction</tt> method):</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1691
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1692<div class="doc_code">
1693<pre>
1694Function* targetFunc = ...;
1695
1696class OurFunctionPass : public FunctionPass {
1697 public:
1698 OurFunctionPass(): callCounter(0) { }
1699
1700 virtual runOnFunction(Function&amp; F) {
1701 for (Function::iterator b = F.begin(), be = F.end(); b != be; ++b) {
Eric Christopher203e71d2008-11-08 08:20:49 +0000[diff] [blame]1702 for (BasicBlock::iterator i = b-&gt;begin(), ie = b-&gt;end(); i != ie; ++i) {
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1703 if (<a href="#CallInst">CallInst</a>* callInst = <a href="#isa">dyn_cast</a>&lt;<a
1704 href="#CallInst">CallInst</a>&gt;(&amp;*i)) {
Bill Wendling82e2eea2006-10-11 18:00:22 +0000[diff] [blame]1705 // <i>We know we've encountered a call instruction, so we</i>
1706 // <i>need to determine if it's a call to the</i>
Chris Lattner2e438ca2008-01-03 16:56:04 +0000[diff] [blame]1707 // <i>function pointed to by m_func or not.</i>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1708 if (callInst-&gt;getCalledFunction() == targetFunc)
1709 ++callCounter;
1710 }
1711 }
1712 }
Bill Wendling82e2eea2006-10-11 18:00:22 +0000[diff] [blame]1713 }
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1714
1715 private:
Chris Lattner2e438ca2008-01-03 16:56:04 +0000[diff] [blame]1716 unsigned callCounter;
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1717};
1718</pre>
1719</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1720
1721</div>
1722
Brian Gaekef1972c62003-11-07 19:25:45 +0000[diff] [blame]1723<!--_______________________________________________________________________-->
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1724<div class="doc_subsubsection">
1725 <a name="calls_and_invokes">Treating calls and invokes the same way</a>
1726</div>
1727
1728<div class="doc_text">
1729
1730<p>You may have noticed that the previous example was a bit oversimplified in
1731that it did not deal with call sites generated by 'invoke' instructions. In
1732this, and in other situations, you may find that you want to treat
1733<tt>CallInst</tt>s and <tt>InvokeInst</tt>s the same way, even though their
1734most-specific common base class is <tt>Instruction</tt>, which includes lots of
1735less closely-related things. For these cases, LLVM provides a handy wrapper
1736class called <a
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]1737href="http://llvm.org/doxygen/classllvm_1_1CallSite.html"><tt>CallSite</tt></a>.
Chris Lattner69bf8a92004-05-23 21:06:58 +0000[diff] [blame]1738It is essentially a wrapper around an <tt>Instruction</tt> pointer, with some
1739methods that provide functionality common to <tt>CallInst</tt>s and
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1740<tt>InvokeInst</tt>s.</p>
1741
Chris Lattner69bf8a92004-05-23 21:06:58 +0000[diff] [blame]1742<p>This class has "value semantics": it should be passed by value, not by
1743reference and it should not be dynamically allocated or deallocated using
1744<tt>operator new</tt> or <tt>operator delete</tt>. It is efficiently copyable,
1745assignable and constructable, with costs equivalents to that of a bare pointer.
1746If you look at its definition, it has only a single pointer member.</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1747
1748</div>
1749
Chris Lattner1a3105b2002-09-09 05:49:39 +0000[diff] [blame]1750<!--_______________________________________________________________________-->
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1751<div class="doc_subsubsection">
1752 <a name="iterate_chains">Iterating over def-use &amp; use-def chains</a>
1753</div>
1754
1755<div class="doc_text">
1756
1757<p>Frequently, we might have an instance of the <a
Chris Lattner00815172007-01-04 22:01:45 +0000[diff] [blame]1758href="/doxygen/classllvm_1_1Value.html">Value Class</a> and we want to
Misha Brukman384047f2004-06-03 23:29:12 +0000[diff] [blame]1759determine which <tt>User</tt>s use the <tt>Value</tt>. The list of all
1760<tt>User</tt>s of a particular <tt>Value</tt> is called a <i>def-use</i> chain.
1761For example, let's say we have a <tt>Function*</tt> named <tt>F</tt> to a
1762particular function <tt>foo</tt>. Finding all of the instructions that
1763<i>use</i> <tt>foo</tt> is as simple as iterating over the <i>def-use</i> chain
1764of <tt>F</tt>:</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1765
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1766<div class="doc_code">
1767<pre>
Chris Lattner2e438ca2008-01-03 16:56:04 +0000[diff] [blame]1768Function *F = ...;
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1769
Bill Wendling82e2eea2006-10-11 18:00:22 +0000[diff] [blame]1770for (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]1771 if (Instruction *Inst = dyn_cast&lt;Instruction&gt;(*i)) {
Bill Wendling832171c2006-12-07 20:04:42 +0000[diff] [blame]1772 llvm::cerr &lt;&lt; "F is used in instruction:\n";
1773 llvm::cerr &lt;&lt; *Inst &lt;&lt; "\n";
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1774 }
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1775</pre>
1776</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1777
1778<p>Alternately, it's common to have an instance of the <a
Misha Brukman384047f2004-06-03 23:29:12 +0000[diff] [blame]1779href="/doxygen/classllvm_1_1User.html">User Class</a> and need to know what
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1780<tt>Value</tt>s are used by it. The list of all <tt>Value</tt>s used by a
1781<tt>User</tt> is known as a <i>use-def</i> chain. Instances of class
1782<tt>Instruction</tt> are common <tt>User</tt>s, so we might want to iterate over
1783all of the values that a particular instruction uses (that is, the operands of
1784the particular <tt>Instruction</tt>):</p>
1785
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1786<div class="doc_code">
1787<pre>
Chris Lattner2e438ca2008-01-03 16:56:04 +0000[diff] [blame]1788Instruction *pi = ...;
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1789
1790for (User::op_iterator i = pi-&gt;op_begin(), e = pi-&gt;op_end(); i != e; ++i) {
Chris Lattner2e438ca2008-01-03 16:56:04 +0000[diff] [blame]1791 Value *v = *i;
Bill Wendling82e2eea2006-10-11 18:00:22 +0000[diff] [blame]1792 // <i>...</i>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1793}
1794</pre>
1795</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1796
Chris Lattner1a3105b2002-09-09 05:49:39 +0000[diff] [blame]1797<!--
1798 def-use chains ("finding all users of"): Value::use_begin/use_end
1799 use-def chains ("finding all values used"): User::op_begin/op_end [op=operand]
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1800-->
1801
1802</div>
1803
Chris Lattner2e438ca2008-01-03 16:56:04 +0000[diff] [blame]1804<!--_______________________________________________________________________-->
1805<div class="doc_subsubsection">
1806 <a name="iterate_preds">Iterating over predecessors &amp;
1807successors of blocks</a>
1808</div>
1809
1810<div class="doc_text">
1811
1812<p>Iterating over the predecessors and successors of a block is quite easy
1813with the routines defined in <tt>"llvm/Support/CFG.h"</tt>. Just use code like
1814this to iterate over all predecessors of BB:</p>
1815
1816<div class="doc_code">
1817<pre>
1818#include "llvm/Support/CFG.h"
1819BasicBlock *BB = ...;
1820
1821for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI) {
1822 BasicBlock *Pred = *PI;
1823 // <i>...</i>
1824}
1825</pre>
1826</div>
1827
1828<p>Similarly, to iterate over successors use
1829succ_iterator/succ_begin/succ_end.</p>
1830
1831</div>
1832
1833
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1834<!-- ======================================================================= -->
1835<div class="doc_subsection">
1836 <a name="simplechanges">Making simple changes</a>
1837</div>
1838
1839<div class="doc_text">
1840
1841<p>There are some primitive transformation operations present in the LLVM
Joel Stanley753eb712002-09-11 22:32:24 +0000[diff] [blame]1842infrastructure that are worth knowing about. When performing
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]1843transformations, it's fairly common to manipulate the contents of basic
1844blocks. This section describes some of the common methods for doing so
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1845and gives example code.</p>
1846
1847</div>
1848
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]1849<!--_______________________________________________________________________-->
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1850<div class="doc_subsubsection">
1851 <a name="schanges_creating">Creating and inserting new
1852 <tt>Instruction</tt>s</a>
1853</div>
1854
1855<div class="doc_text">
1856
1857<p><i>Instantiating Instructions</i></p>
1858
Chris Lattner69bf8a92004-05-23 21:06:58 +0000[diff] [blame]1859<p>Creation of <tt>Instruction</tt>s is straight-forward: simply call the
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1860constructor for the kind of instruction to instantiate and provide the necessary
1861parameters. For example, an <tt>AllocaInst</tt> only <i>requires</i> a
1862(const-ptr-to) <tt>Type</tt>. Thus:</p>
1863
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1864<div class="doc_code">
1865<pre>
Nick Lewycky10d64b92007-12-03 01:52:52 +0000[diff] [blame]1866AllocaInst* ai = new AllocaInst(Type::Int32Ty);
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1867</pre>
1868</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1869
1870<p>will create an <tt>AllocaInst</tt> instance that represents the allocation of
Reid Spencer128a7a72007-02-03 21:06:43 +0000[diff] [blame]1871one integer in the current stack frame, at run time. Each <tt>Instruction</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1872subclass is likely to have varying default parameters which change the semantics
1873of the instruction, so refer to the <a
Misha Brukman31ca1de2004-06-03 23:35:54 +0000[diff] [blame]1874href="/doxygen/classllvm_1_1Instruction.html">doxygen documentation for the subclass of
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1875Instruction</a> that you're interested in instantiating.</p>
1876
1877<p><i>Naming values</i></p>
1878
1879<p>It is very useful to name the values of instructions when you're able to, as
1880this facilitates the debugging of your transformations. If you end up looking
1881at generated LLVM machine code, you definitely want to have logical names
1882associated with the results of instructions! By supplying a value for the
1883<tt>Name</tt> (default) parameter of the <tt>Instruction</tt> constructor, you
1884associate a logical name with the result of the instruction's execution at
Reid Spencer128a7a72007-02-03 21:06:43 +0000[diff] [blame]1885run time. For example, say that I'm writing a transformation that dynamically
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1886allocates space for an integer on the stack, and that integer is going to be
1887used as some kind of index by some other code. To accomplish this, I place an
1888<tt>AllocaInst</tt> at the first point in the first <tt>BasicBlock</tt> of some
1889<tt>Function</tt>, and I'm intending to use it within the same
1890<tt>Function</tt>. I might do:</p>
1891
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1892<div class="doc_code">
1893<pre>
Nick Lewycky10d64b92007-12-03 01:52:52 +0000[diff] [blame]1894AllocaInst* pa = new AllocaInst(Type::Int32Ty, 0, "indexLoc");
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1895</pre>
1896</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1897
1898<p>where <tt>indexLoc</tt> is now the logical name of the instruction's
Reid Spencer128a7a72007-02-03 21:06:43 +0000[diff] [blame]1899execution value, which is a pointer to an integer on the run time stack.</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1900
1901<p><i>Inserting instructions</i></p>
1902
1903<p>There are essentially two ways to insert an <tt>Instruction</tt>
1904into an existing sequence of instructions that form a <tt>BasicBlock</tt>:</p>
1905
Joel Stanley9dd1ad62002-09-18 03:17:23 +0000[diff] [blame]1906<ul>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1907 <li>Insertion into an explicit instruction list
1908
1909 <p>Given a <tt>BasicBlock* pb</tt>, an <tt>Instruction* pi</tt> within that
1910 <tt>BasicBlock</tt>, and a newly-created instruction we wish to insert
1911 before <tt>*pi</tt>, we do the following: </p>
1912
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1913<div class="doc_code">
1914<pre>
1915BasicBlock *pb = ...;
1916Instruction *pi = ...;
1917Instruction *newInst = new Instruction(...);
1918
Bill Wendling82e2eea2006-10-11 18:00:22 +0000[diff] [blame]1919pb-&gt;getInstList().insert(pi, newInst); // <i>Inserts newInst before pi in pb</i>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1920</pre>
1921</div>
Alkis Evlogimenos9a5dc4f2004-05-27 00:57:51 +0000[diff] [blame]1922
1923 <p>Appending to the end of a <tt>BasicBlock</tt> is so common that
1924 the <tt>Instruction</tt> class and <tt>Instruction</tt>-derived
1925 classes provide constructors which take a pointer to a
1926 <tt>BasicBlock</tt> to be appended to. For example code that
1927 looked like: </p>
1928
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1929<div class="doc_code">
1930<pre>
1931BasicBlock *pb = ...;
1932Instruction *newInst = new Instruction(...);
1933
Bill Wendling82e2eea2006-10-11 18:00:22 +0000[diff] [blame]1934pb-&gt;getInstList().push_back(newInst); // <i>Appends newInst to pb</i>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1935</pre>
1936</div>
Alkis Evlogimenos9a5dc4f2004-05-27 00:57:51 +0000[diff] [blame]1937
1938 <p>becomes: </p>
1939
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1940<div class="doc_code">
1941<pre>
1942BasicBlock *pb = ...;
1943Instruction *newInst = new Instruction(..., pb);
1944</pre>
1945</div>
Alkis Evlogimenos9a5dc4f2004-05-27 00:57:51 +0000[diff] [blame]1946
1947 <p>which is much cleaner, especially if you are creating
1948 long instruction streams.</p></li>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1949
1950 <li>Insertion into an implicit instruction list
1951
1952 <p><tt>Instruction</tt> instances that are already in <tt>BasicBlock</tt>s
1953 are implicitly associated with an existing instruction list: the instruction
1954 list of the enclosing basic block. Thus, we could have accomplished the same
1955 thing as the above code without being given a <tt>BasicBlock</tt> by doing:
1956 </p>
1957
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1958<div class="doc_code">
1959<pre>
1960Instruction *pi = ...;
1961Instruction *newInst = new Instruction(...);
1962
1963pi-&gt;getParent()-&gt;getInstList().insert(pi, newInst);
1964</pre>
1965</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1966
1967 <p>In fact, this sequence of steps occurs so frequently that the
1968 <tt>Instruction</tt> class and <tt>Instruction</tt>-derived classes provide
1969 constructors which take (as a default parameter) a pointer to an
1970 <tt>Instruction</tt> which the newly-created <tt>Instruction</tt> should
1971 precede. That is, <tt>Instruction</tt> constructors are capable of
1972 inserting the newly-created instance into the <tt>BasicBlock</tt> of a
1973 provided instruction, immediately before that instruction. Using an
1974 <tt>Instruction</tt> constructor with a <tt>insertBefore</tt> (default)
1975 parameter, the above code becomes:</p>
1976
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1977<div class="doc_code">
1978<pre>
1979Instruction* pi = ...;
1980Instruction* newInst = new Instruction(..., pi);
1981</pre>
1982</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1983
1984 <p>which is much cleaner, especially if you're creating a lot of
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1985 instructions and adding them to <tt>BasicBlock</tt>s.</p></li>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1986</ul>
1987
1988</div>
1989
1990<!--_______________________________________________________________________-->
1991<div class="doc_subsubsection">
1992 <a name="schanges_deleting">Deleting <tt>Instruction</tt>s</a>
1993</div>
1994
1995<div class="doc_text">
1996
1997<p>Deleting an instruction from an existing sequence of instructions that form a
Chris Lattner69bf8a92004-05-23 21:06:58 +0000[diff] [blame]1998<a href="#BasicBlock"><tt>BasicBlock</tt></a> is very straight-forward. First,
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1999you must have a pointer to the instruction that you wish to delete. Second, you
2000need to obtain the pointer to that instruction's basic block. You use the
2001pointer to the basic block to get its list of instructions and then use the
2002erase function to remove your instruction. For example:</p>
2003
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2004<div class="doc_code">
2005<pre>
2006<a href="#Instruction">Instruction</a> *I = .. ;
Chris Lattner9f8ec252008-02-15 22:57:17 +0000[diff] [blame]2007I-&gt;eraseFromParent();
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2008</pre>
2009</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2010
2011</div>
2012
2013<!--_______________________________________________________________________-->
2014<div class="doc_subsubsection">
2015 <a name="schanges_replacing">Replacing an <tt>Instruction</tt> with another
2016 <tt>Value</tt></a>
2017</div>
2018
2019<div class="doc_text">
2020
2021<p><i>Replacing individual instructions</i></p>
2022
2023<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]2024permits use of two very useful replace functions: <tt>ReplaceInstWithValue</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2025and <tt>ReplaceInstWithInst</tt>.</p>
2026
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]2027<h4><a name="schanges_deleting">Deleting <tt>Instruction</tt>s</a></h4>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2028
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]2029<ul>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2030 <li><tt>ReplaceInstWithValue</tt>
2031
Nick Lewyckyb6d1f392008-09-15 06:31:52 +0000[diff] [blame]2032 <p>This function replaces all uses of a given instruction with a value,
2033 and then removes the original instruction. The following example
2034 illustrates the replacement of the result of a particular
Chris Lattner58360822005-01-17 00:12:04 +0000[diff] [blame]2035 <tt>AllocaInst</tt> that allocates memory for a single integer with a null
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2036 pointer to an integer.</p>
2037
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2038<div class="doc_code">
2039<pre>
2040AllocaInst* instToReplace = ...;
2041BasicBlock::iterator ii(instToReplace);
2042
2043ReplaceInstWithValue(instToReplace-&gt;getParent()-&gt;getInstList(), ii,
Daniel Dunbar58c2ac02008-10-03 22:17:25 +0000[diff] [blame]2044 Constant::getNullValue(PointerType::getUnqual(Type::Int32Ty)));
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2045</pre></div></li>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2046
2047 <li><tt>ReplaceInstWithInst</tt>
2048
2049 <p>This function replaces a particular instruction with another
Nick Lewyckyb6d1f392008-09-15 06:31:52 +0000[diff] [blame]2050 instruction, inserting the new instruction into the basic block at the
2051 location where the old instruction was, and replacing any uses of the old
2052 instruction with the new instruction. The following example illustrates
2053 the replacement of one <tt>AllocaInst</tt> with another.</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2054
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2055<div class="doc_code">
2056<pre>
2057AllocaInst* instToReplace = ...;
2058BasicBlock::iterator ii(instToReplace);
2059
2060ReplaceInstWithInst(instToReplace-&gt;getParent()-&gt;getInstList(), ii,
Nick Lewycky10d64b92007-12-03 01:52:52 +0000[diff] [blame]2061 new AllocaInst(Type::Int32Ty, 0, "ptrToReplacedInt"));
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2062</pre></div></li>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]2063</ul>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2064
2065<p><i>Replacing multiple uses of <tt>User</tt>s and <tt>Value</tt>s</i></p>
2066
2067<p>You can use <tt>Value::replaceAllUsesWith</tt> and
2068<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]2069doxygen documentation for the <a href="/doxygen/classllvm_1_1Value.html">Value Class</a>
Misha Brukman384047f2004-06-03 23:29:12 +0000[diff] [blame]2070and <a href="/doxygen/classllvm_1_1User.html">User Class</a>, respectively, for more
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2071information.</p>
2072
2073<!-- Value::replaceAllUsesWith User::replaceUsesOfWith Point out:
2074include/llvm/Transforms/Utils/ especially BasicBlockUtils.h with:
2075ReplaceInstWithValue, ReplaceInstWithInst -->
2076
2077</div>
2078
Tanya Lattnerb011c662007-06-20 18:33:15 +0000[diff] [blame]2079<!--_______________________________________________________________________-->
2080<div class="doc_subsubsection">
2081 <a name="schanges_deletingGV">Deleting <tt>GlobalVariable</tt>s</a>
2082</div>
2083
2084<div class="doc_text">
2085
Tanya Lattnerc5dfcdb2007-06-20 20:46:37 +0000[diff] [blame]2086<p>Deleting a global variable from a module is just as easy as deleting an
2087Instruction. First, you must have a pointer to the global variable that you wish
2088 to delete. You use this pointer to erase it from its parent, the module.
Tanya Lattnerb011c662007-06-20 18:33:15 +0000[diff] [blame]2089 For example:</p>
2090
2091<div class="doc_code">
2092<pre>
2093<a href="#GlobalVariable">GlobalVariable</a> *GV = .. ;
Tanya Lattnerb011c662007-06-20 18:33:15 +0000[diff] [blame]2094
Tanya Lattnerc5dfcdb2007-06-20 20:46:37 +0000[diff] [blame]2095GV-&gt;eraseFromParent();
Tanya Lattnerb011c662007-06-20 18:33:15 +0000[diff] [blame]2096</pre>
2097</div>
2098
2099</div>
2100
Jeffrey Yasskin714257f2009-04-30 22:33:41 +0000[diff] [blame]2101<!-- ======================================================================= -->
2102<div class="doc_subsection">
2103 <a name="create_types">How to Create Types</a>
2104</div>
2105
2106<div class="doc_text">
2107
2108<p>In generating IR, you may need some complex types. If you know these types
Misha Brukman1af789f2009-05-01 20:40:51 +0000[diff] [blame]2109statically, you can use <tt>TypeBuilder&lt;...&gt;::get()</tt>, defined
Jeffrey Yasskin714257f2009-04-30 22:33:41 +0000[diff] [blame]2110in <tt>llvm/Support/TypeBuilder.h</tt>, to retrieve them. <tt>TypeBuilder</tt>
2111has two forms depending on whether you're building types for cross-compilation
Misha Brukman1af789f2009-05-01 20:40:51 +0000[diff] [blame]2112or native library use. <tt>TypeBuilder&lt;T, true&gt;</tt> requires
Jeffrey Yasskin714257f2009-04-30 22:33:41 +0000[diff] [blame]2113that <tt>T</tt> be independent of the host environment, meaning that it's built
2114out of types from
2115the <a href="/doxygen/namespacellvm_1_1types.html"><tt>llvm::types</tt></a>
2116namespace and pointers, functions, arrays, etc. built of
Misha Brukman1af789f2009-05-01 20:40:51 +0000[diff] [blame]2117those. <tt>TypeBuilder&lt;T, false&gt;</tt> additionally allows native C types
Jeffrey Yasskin714257f2009-04-30 22:33:41 +0000[diff] [blame]2118whose size may depend on the host compiler. For example,</p>
2119
2120<div class="doc_code">
2121<pre>
Misha Brukman1af789f2009-05-01 20:40:51 +0000[diff] [blame]2122FunctionType *ft = TypeBuilder&lt;types::i&lt;8&gt;(types::i&lt;32&gt;*), true&gt;::get();
Jeffrey Yasskin714257f2009-04-30 22:33:41 +0000[diff] [blame]2123</pre>
2124</div>
2125
2126<p>is easier to read and write than the equivalent</p>
2127
2128<div class="doc_code">
2129<pre>
2130std::vector<const Type*> params;
2131params.push_back(PointerType::getUnqual(Type::Int32Ty));
2132FunctionType *ft = FunctionType::get(Type::Int8Ty, params, false);
2133</pre>
2134</div>
2135
2136<p>See the <a href="/doxygen/TypeBuilder_8h-source.html#l00001">class
2137comment</a> for more details.</p>
2138
2139</div>
2140
Chris Lattner9355b472002-09-06 02:50:58 +0000[diff] [blame]2141<!-- *********************************************************************** -->
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2142<div class="doc_section">
Owen Anderson8bc1b3b2009-06-16 01:17:16 +0000[diff] [blame^]2143 <a name="threading">Threads and LLVM</a>
2144</div>
2145<!-- *********************************************************************** -->
2146
2147<div class="doc_text">
2148<p>
2149This section describes the interaction of the LLVM APIs with multithreading,
2150both on the part of client applications, and in the JIT, in the hosted
2151application.
2152</p>
2153
2154<p>
2155Note that LLVM's support for multithreading is still relatively young. Up
2156through version 2.5, the execution of threaded hosted applications was
2157supported, but not threaded client access to the APIs. While this use case is
2158now supported, clients <em>must</em> adhere to the guidelines specified below to
2159ensure proper operation in multithreaded mode.
2160</p>
2161
2162<p>
2163Note that, on Unix-like platforms, LLVM requires the presence of GCC's atomic
2164intrinsics in order to support threaded operation. If you need a
2165multhreading-capable LLVM on a platform without a suitably modern system
2166compiler, consider compiling LLVM and LLVM-GCC in single-threaded mode, and
2167using the resultant compiler to build a copy of LLVM with multithreading
2168support.
2169</p>
2170</div>
2171
2172<!-- ======================================================================= -->
2173<div class="doc_subsection">
2174 <a name="startmultithreaded">Entering Threaded Mode with
2175 <tt>llvm_start_multithreaded()</tt></a>
2176</div>
2177
2178<div class="doc_text">
2179
2180<p>
2181In order to properly protect its internal data structures while avoiding
2182excessive locking overhead in the single-threaded case, the LLVM APIs require
2183that the client invoke <tt>llvm_start_multithreaded()</tt>. This call must
2184complete <em>before</em> any other threads attempt to invoke LLVM APIs. Any
2185attempts to call LLVM APIs from multiple threads before
2186<tt>llvm_start_multithreaded</tt> returns can and will cause corruption of
2187LLVM's internal data.
2188</p>
2189
2190<p>
2191A caveat: before <tt>llvm_start_multithreaded()</tt> has been invoked, all
2192<tt>llvm::sys::Mutex</tt> acquisitions and releases will become no-ops. This
2193means that <tt>llvm_start_multithreaded()</tt> must be invoked before a threaded
2194application can be executed in the JIT.
2195</p>
2196</div>
2197
2198<!-- ======================================================================= -->
2199<div class="doc_subsection">
2200 <a name="shutdown">Ending Execution with <tt>llvm_shutdown()</tt></a>
2201</div>
2202
2203<div class="doc_text">
2204<p>
2205When you are done using the LLVM APIs, you should call <tt>llvm_shutdown()</tt>
2206to deallocate memory used for internal structures. This call must not begin
2207while any other threads are still issuing LLVM API calls. Doing so is likely
2208to result in garbage data or crashes.
2209</p>
2210
2211<p>
2212Note that, if you use scope-based shutdown, you can use the
2213<tt>llvm_shutdown_obj</tt> class, which calls <tt>llvm_shutdown()</tt> in its
2214destructor.
2215</div>
2216
2217<!-- ======================================================================= -->
2218<div class="doc_subsection">
2219 <a name="managedstatic">Lazy Initialization with <tt>ManagedStatic</tt></a>
2220</div>
2221
2222<div class="doc_text">
2223<p>
2224<tt>ManagedStatic</tt> is a utility class in LLVM used to implement static
2225initialization of static resources, such as the global type tables. Before the
2226invocation of <tt>llvm_shutdown()</tt>, it implements a simple lazy
2227initialization scheme. Once <tt>llvm_start_multithreaded()</tt> returns,
2228however, it uses double-checked locking to implement thread-safe lazy
2229initialization.
2230</p>
2231
2232<p>
2233Note that, because no other threads are allowed to issue LLVM API calls before
2234<tt>llvm_start_multithreaded()</tt> returns, it is possible to have
2235<tt>ManagedStatic</tt>s of <tt>llvm::sys::Mutex</tt>s.
2236</p>
2237</div>
2238
2239<!-- *********************************************************************** -->
2240<div class="doc_section">
Chris Lattnerd9d6e102005-04-23 16:10:52 +0000[diff] [blame]2241 <a name="advanced">Advanced Topics</a>
2242</div>
2243<!-- *********************************************************************** -->
2244
2245<div class="doc_text">
Chris Lattnerf1b200b2005-04-23 17:27:36 +0000[diff] [blame]2246<p>
2247This section describes some of the advanced or obscure API's that most clients
2248do not need to be aware of. These API's tend manage the inner workings of the
2249LLVM system, and only need to be accessed in unusual circumstances.
2250</p>
2251</div>
Chris Lattnerd9d6e102005-04-23 16:10:52 +0000[diff] [blame]2252
Chris Lattnerf1b200b2005-04-23 17:27:36 +0000[diff] [blame]2253<!-- ======================================================================= -->
2254<div class="doc_subsection">
2255 <a name="TypeResolve">LLVM Type Resolution</a>
2256</div>
Chris Lattnerd9d6e102005-04-23 16:10:52 +0000[diff] [blame]2257
Chris Lattnerf1b200b2005-04-23 17:27:36 +0000[diff] [blame]2258<div class="doc_text">
2259
2260<p>
2261The LLVM type system has a very simple goal: allow clients to compare types for
2262structural equality with a simple pointer comparison (aka a shallow compare).
2263This goal makes clients much simpler and faster, and is used throughout the LLVM
2264system.
2265</p>
2266
2267<p>
2268Unfortunately achieving this goal is not a simple matter. In particular,
2269recursive types and late resolution of opaque types makes the situation very
2270difficult to handle. Fortunately, for the most part, our implementation makes
2271most clients able to be completely unaware of the nasty internal details. The
2272primary case where clients are exposed to the inner workings of it are when
Gabor Greif04367bf2007-07-06 22:07:22 +0000[diff] [blame]2273building a recursive type. In addition to this case, the LLVM bitcode reader,
Chris Lattnerf1b200b2005-04-23 17:27:36 +0000[diff] [blame]2274assembly parser, and linker also have to be aware of the inner workings of this
2275system.
2276</p>
2277
Chris Lattner0f876db2005-04-25 15:47:57 +0000[diff] [blame]2278<p>
2279For our purposes below, we need three concepts. First, an "Opaque Type" is
2280exactly as defined in the <a href="LangRef.html#t_opaque">language
2281reference</a>. Second an "Abstract Type" is any type which includes an
Reid Spencer06565dc2007-01-12 17:11:23 +0000[diff] [blame]2282opaque type as part of its type graph (for example "<tt>{ opaque, i32 }</tt>").
2283Third, 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]2284float }</tt>").
2285</p>
2286
Chris Lattnerf1b200b2005-04-23 17:27:36 +0000[diff] [blame]2287</div>
2288
2289<!-- ______________________________________________________________________ -->
2290<div class="doc_subsubsection">
2291 <a name="BuildRecType">Basic Recursive Type Construction</a>
2292</div>
2293
2294<div class="doc_text">
2295
2296<p>
2297Because the most common question is "how do I build a recursive type with LLVM",
2298we answer it now and explain it as we go. Here we include enough to cause this
2299to be emitted to an output .ll file:
2300</p>
2301
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2302<div class="doc_code">
Chris Lattnerf1b200b2005-04-23 17:27:36 +0000[diff] [blame]2303<pre>
Reid Spencer06565dc2007-01-12 17:11:23 +0000[diff] [blame]2304%mylist = type { %mylist*, i32 }
Chris Lattnerf1b200b2005-04-23 17:27:36 +0000[diff] [blame]2305</pre>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2306</div>
Chris Lattnerf1b200b2005-04-23 17:27:36 +0000[diff] [blame]2307
2308<p>
2309To build this, use the following LLVM APIs:
2310</p>
2311
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2312<div class="doc_code">
Chris Lattnerf1b200b2005-04-23 17:27:36 +0000[diff] [blame]2313<pre>
Bill Wendling82e2eea2006-10-11 18:00:22 +0000[diff] [blame]2314// <i>Create the initial outer struct</i>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2315<a href="#PATypeHolder">PATypeHolder</a> StructTy = OpaqueType::get();
2316std::vector&lt;const Type*&gt; Elts;
Daniel Dunbar58c2ac02008-10-03 22:17:25 +0000[diff] [blame]2317Elts.push_back(PointerType::getUnqual(StructTy));
Nick Lewycky10d64b92007-12-03 01:52:52 +0000[diff] [blame]2318Elts.push_back(Type::Int32Ty);
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2319StructType *NewSTy = StructType::get(Elts);
Chris Lattnerf1b200b2005-04-23 17:27:36 +0000[diff] [blame]2320
Reid Spencer06565dc2007-01-12 17:11:23 +0000[diff] [blame]2321// <i>At this point, NewSTy = "{ opaque*, i32 }". Tell VMCore that</i>
Bill Wendling82e2eea2006-10-11 18:00:22 +0000[diff] [blame]2322// <i>the struct and the opaque type are actually the same.</i>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2323cast&lt;OpaqueType&gt;(StructTy.get())-&gt;<a href="#refineAbstractTypeTo">refineAbstractTypeTo</a>(NewSTy);
Chris Lattnerf1b200b2005-04-23 17:27:36 +0000[diff] [blame]2324
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2325// <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]2326// <i>kept up-to-date</i>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2327NewSTy = cast&lt;StructType&gt;(StructTy.get());
Chris Lattnerf1b200b2005-04-23 17:27:36 +0000[diff] [blame]2328
Bill Wendling82e2eea2006-10-11 18:00:22 +0000[diff] [blame]2329// <i>Add a name for the type to the module symbol table (optional)</i>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2330MyModule-&gt;addTypeName("mylist", NewSTy);
Chris Lattnerf1b200b2005-04-23 17:27:36 +0000[diff] [blame]2331</pre>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2332</div>
Chris Lattnerf1b200b2005-04-23 17:27:36 +0000[diff] [blame]2333
2334<p>
2335This code shows the basic approach used to build recursive types: build a
2336non-recursive type using 'opaque', then use type unification to close the cycle.
2337The type unification step is performed by the <tt><a
Chris Lattneraff26d12007-02-03 03:06:52 +0000[diff] [blame]2338href="#refineAbstractTypeTo">refineAbstractTypeTo</a></tt> method, which is
Chris Lattnerf1b200b2005-04-23 17:27:36 +0000[diff] [blame]2339described next. After that, we describe the <a
2340href="#PATypeHolder">PATypeHolder class</a>.
2341</p>
2342
2343</div>
2344
2345<!-- ______________________________________________________________________ -->
2346<div class="doc_subsubsection">
2347 <a name="refineAbstractTypeTo">The <tt>refineAbstractTypeTo</tt> method</a>
2348</div>
2349
2350<div class="doc_text">
2351<p>
2352The <tt>refineAbstractTypeTo</tt> method starts the type unification process.
2353While this method is actually a member of the DerivedType class, it is most
2354often used on OpaqueType instances. Type unification is actually a recursive
2355process. After unification, types can become structurally isomorphic to
2356existing types, and all duplicates are deleted (to preserve pointer equality).
2357</p>
2358
2359<p>
2360In the example above, the OpaqueType object is definitely deleted.
Reid Spencer06565dc2007-01-12 17:11:23 +0000[diff] [blame]2361Additionally, if there is an "{ \2*, i32}" type already created in the system,
Chris Lattnerf1b200b2005-04-23 17:27:36 +0000[diff] [blame]2362the pointer and struct type created are <b>also</b> deleted. Obviously whenever
2363a type is deleted, any "Type*" pointers in the program are invalidated. As
2364such, it is safest to avoid having <i>any</i> "Type*" pointers to abstract types
2365live across a call to <tt>refineAbstractTypeTo</tt> (note that non-abstract
2366types can never move or be deleted). To deal with this, the <a
2367href="#PATypeHolder">PATypeHolder</a> class is used to maintain a stable
2368reference to a possibly refined type, and the <a
2369href="#AbstractTypeUser">AbstractTypeUser</a> class is used to update more
2370complex datastructures.
2371</p>
2372
2373</div>
2374
2375<!-- ______________________________________________________________________ -->
2376<div class="doc_subsubsection">
2377 <a name="PATypeHolder">The PATypeHolder Class</a>
2378</div>
2379
2380<div class="doc_text">
2381<p>
2382PATypeHolder is a form of a "smart pointer" for Type objects. When VMCore
2383happily goes about nuking types that become isomorphic to existing types, it
2384automatically updates all PATypeHolder objects to point to the new type. In the
2385example above, this allows the code to maintain a pointer to the resultant
2386resolved recursive type, even though the Type*'s are potentially invalidated.
2387</p>
2388
2389<p>
2390PATypeHolder is an extremely light-weight object that uses a lazy union-find
2391implementation to update pointers. For example the pointer from a Value to its
2392Type is maintained by PATypeHolder objects.
2393</p>
2394
2395</div>
2396
2397<!-- ______________________________________________________________________ -->
2398<div class="doc_subsubsection">
2399 <a name="AbstractTypeUser">The AbstractTypeUser Class</a>
2400</div>
2401
2402<div class="doc_text">
2403
2404<p>
2405Some data structures need more to perform more complex updates when types get
Chris Lattner263a98e2007-02-16 04:37:31 +0000[diff] [blame]2406resolved. To support this, a class can derive from the AbstractTypeUser class.
2407This class
Chris Lattnerf1b200b2005-04-23 17:27:36 +0000[diff] [blame]2408allows it to get callbacks when certain types are resolved. To register to get
2409callbacks for a particular type, the DerivedType::{add/remove}AbstractTypeUser
Chris Lattner0f876db2005-04-25 15:47:57 +0000[diff] [blame]2410methods can be called on a type. Note that these methods only work for <i>
Reid Spencer06565dc2007-01-12 17:11:23 +0000[diff] [blame]2411 abstract</i> types. Concrete types (those that do not include any opaque
2412objects) can never be refined.
Chris Lattnerf1b200b2005-04-23 17:27:36 +0000[diff] [blame]2413</p>
Chris Lattnerd9d6e102005-04-23 16:10:52 +0000[diff] [blame]2414</div>
2415
2416
2417<!-- ======================================================================= -->
2418<div class="doc_subsection">
Chris Lattner263a98e2007-02-16 04:37:31 +0000[diff] [blame]2419 <a name="SymbolTable">The <tt>ValueSymbolTable</tt> and
2420 <tt>TypeSymbolTable</tt> classes</a>
Chris Lattnerd9d6e102005-04-23 16:10:52 +0000[diff] [blame]2421</div>
Chris Lattnerf1b200b2005-04-23 17:27:36 +0000[diff] [blame]2422
Chris Lattnerd9d6e102005-04-23 16:10:52 +0000[diff] [blame]2423<div class="doc_text">
Chris Lattner263a98e2007-02-16 04:37:31 +0000[diff] [blame]2424<p>The <tt><a href="http://llvm.org/doxygen/classllvm_1_1ValueSymbolTable.html">
2425ValueSymbolTable</a></tt> class provides a symbol table that the <a
Chris Lattnerd9d6e102005-04-23 16:10:52 +0000[diff] [blame]2426href="#Function"><tt>Function</tt></a> and <a href="#Module">
Chris Lattner263a98e2007-02-16 04:37:31 +0000[diff] [blame]2427<tt>Module</tt></a> classes use for naming value definitions. The symbol table
2428can provide a name for any <a href="#Value"><tt>Value</tt></a>.
2429The <tt><a href="http://llvm.org/doxygen/classllvm_1_1TypeSymbolTable.html">
2430TypeSymbolTable</a></tt> class is used by the <tt>Module</tt> class to store
2431names for types.</p>
Chris Lattnerd9d6e102005-04-23 16:10:52 +0000[diff] [blame]2432
Reid Spencera6362242007-01-07 00:41:39 +0000[diff] [blame]2433<p>Note that the <tt>SymbolTable</tt> class should not be directly accessed
2434by most clients. It should only be used when iteration over the symbol table
2435names themselves are required, which is very special purpose. Note that not
2436all LLVM
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2437<tt><a href="#Value">Value</a></tt>s have names, and those without names (i.e. they have
Chris Lattnerd9d6e102005-04-23 16:10:52 +0000[diff] [blame]2438an empty name) do not exist in the symbol table.
2439</p>
2440
Chris Lattner263a98e2007-02-16 04:37:31 +0000[diff] [blame]2441<p>These symbol tables support iteration over the values/types in the symbol
2442table with <tt>begin/end/iterator</tt> and supports querying to see if a
2443specific name is in the symbol table (with <tt>lookup</tt>). The
2444<tt>ValueSymbolTable</tt> class exposes no public mutator methods, instead,
2445simply call <tt>setName</tt> on a value, which will autoinsert it into the
2446appropriate symbol table. For types, use the Module::addTypeName method to
2447insert entries into the symbol table.</p>
Chris Lattnerd9d6e102005-04-23 16:10:52 +0000[diff] [blame]2448
Chris Lattnerd9d6e102005-04-23 16:10:52 +0000[diff] [blame]2449</div>
2450
2451
2452
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2453<!-- ======================================================================= -->
2454<div class="doc_subsection">
2455 <a name="UserLayout">The <tt>User</tt> and owned <tt>Use</tt> classes' memory layout</a>
2456</div>
2457
2458<div class="doc_text">
2459<p>The <tt><a href="http://llvm.org/doxygen/classllvm_1_1User.html">
Gabor Greiffd095b62009-01-05 16:05:32 +0000[diff] [blame]2460User</a></tt> class provides a basis for expressing the ownership of <tt>User</tt>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2461towards other <tt><a href="http://llvm.org/doxygen/classllvm_1_1Value.html">
2462Value</a></tt>s. The <tt><a href="http://llvm.org/doxygen/classllvm_1_1Use.html">
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2463Use</a></tt> helper class is employed to do the bookkeeping and to facilitate <i>O(1)</i>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2464addition and removal.</p>
2465
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2466<!-- ______________________________________________________________________ -->
2467<div class="doc_subsubsection">
Gabor Greiffd095b62009-01-05 16:05:32 +0000[diff] [blame]2468 <a name="Use2User">Interaction and relationship between <tt>User</tt> and <tt>Use</tt> objects</a>
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2469</div>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2470
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2471<div class="doc_text">
2472<p>
2473A subclass of <tt>User</tt> can choose between incorporating its <tt>Use</tt> objects
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2474or refer to them out-of-line by means of a pointer. A mixed variant
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2475(some <tt>Use</tt>s inline others hung off) is impractical and breaks the invariant
2476that the <tt>Use</tt> objects belonging to the same <tt>User</tt> form a contiguous array.
2477</p>
2478</div>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2479
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2480<p>
2481We have 2 different layouts in the <tt>User</tt> (sub)classes:
2482<ul>
2483<li><p>Layout a)
2484The <tt>Use</tt> object(s) are inside (resp. at fixed offset) of the <tt>User</tt>
2485object and there are a fixed number of them.</p>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2486
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2487<li><p>Layout b)
2488The <tt>Use</tt> object(s) are referenced by a pointer to an
2489array from the <tt>User</tt> object and there may be a variable
2490number of them.</p>
2491</ul>
2492<p>
Gabor Greifd41720a2008-06-25 00:10:22 +0000[diff] [blame]2493As of v2.4 each layout still possesses a direct pointer to the
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2494start of the array of <tt>Use</tt>s. Though not mandatory for layout a),
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2495we stick to this redundancy for the sake of simplicity.
Gabor Greifd41720a2008-06-25 00:10:22 +0000[diff] [blame]2496The <tt>User</tt> object also stores the number of <tt>Use</tt> objects it
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2497has. (Theoretically this information can also be calculated
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2498given the scheme presented below.)</p>
2499<p>
2500Special forms of allocation operators (<tt>operator new</tt>)
Gabor Greifd41720a2008-06-25 00:10:22 +0000[diff] [blame]2501enforce the following memory layouts:</p>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2502
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2503<ul>
Gabor Greifd41720a2008-06-25 00:10:22 +0000[diff] [blame]2504<li><p>Layout a) is modelled by prepending the <tt>User</tt> object by the <tt>Use[]</tt> array.</p>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2505
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2506<pre>
2507...---.---.---.---.-------...
2508 | P | P | P | P | User
2509'''---'---'---'---'-------'''
2510</pre>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2511
Gabor Greifd41720a2008-06-25 00:10:22 +0000[diff] [blame]2512<li><p>Layout b) is modelled by pointing at the <tt>Use[]</tt> array.</p>
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2513<pre>
2514.-------...
2515| User
2516'-------'''
2517 |
2518 v
2519 .---.---.---.---...
2520 | P | P | P | P |
2521 '---'---'---'---'''
2522</pre>
2523</ul>
2524<i>(In the above figures '<tt>P</tt>' stands for the <tt>Use**</tt> that
2525 is stored in each <tt>Use</tt> object in the member <tt>Use::Prev</tt>)</i>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2526
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2527<!-- ______________________________________________________________________ -->
2528<div class="doc_subsubsection">
Gabor Greiffd095b62009-01-05 16:05:32 +0000[diff] [blame]2529 <a name="Waymarking">The waymarking algorithm</a>
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2530</div>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2531
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2532<div class="doc_text">
2533<p>
Gabor Greifd41720a2008-06-25 00:10:22 +0000[diff] [blame]2534Since the <tt>Use</tt> objects are deprived of the direct (back)pointer to
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2535their <tt>User</tt> objects, there must be a fast and exact method to
2536recover it. This is accomplished by the following scheme:</p>
2537</div>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2538
Gabor Greifd41720a2008-06-25 00:10:22 +0000[diff] [blame]2539A bit-encoding in the 2 LSBits (least significant bits) of the <tt>Use::Prev</tt> allows to find the
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2540start of the <tt>User</tt> object:
2541<ul>
2542<li><tt>00</tt> &mdash;&gt; binary digit 0</li>
2543<li><tt>01</tt> &mdash;&gt; binary digit 1</li>
2544<li><tt>10</tt> &mdash;&gt; stop and calculate (<tt>s</tt>)</li>
2545<li><tt>11</tt> &mdash;&gt; full stop (<tt>S</tt>)</li>
2546</ul>
2547<p>
2548Given a <tt>Use*</tt>, all we have to do is to walk till we get
2549a stop and we either have a <tt>User</tt> immediately behind or
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2550we have to walk to the next stop picking up digits
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2551and calculating the offset:</p>
2552<pre>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2553.---.---.---.---.---.---.---.---.---.---.---.---.---.---.---.---.----------------
2554| 1 | s | 1 | 0 | 1 | 0 | s | 1 | 1 | 0 | s | 1 | 1 | s | 1 | S | User (or User*)
2555'---'---'---'---'---'---'---'---'---'---'---'---'---'---'---'---'----------------
2556 |+15 |+10 |+6 |+3 |+1
2557 | | | | |__>
2558 | | | |__________>
2559 | | |______________________>
2560 | |______________________________________>
2561 |__________________________________________________________>
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2562</pre>
2563<p>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2564Only the significant number of bits need to be stored between the
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2565stops, so that the <i>worst case is 20 memory accesses</i> when there are
25661000 <tt>Use</tt> objects associated with a <tt>User</tt>.</p>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2567
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2568<!-- ______________________________________________________________________ -->
2569<div class="doc_subsubsection">
Gabor Greiffd095b62009-01-05 16:05:32 +0000[diff] [blame]2570 <a name="ReferenceImpl">Reference implementation</a>
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2571</div>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2572
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2573<div class="doc_text">
2574<p>
2575The following literate Haskell fragment demonstrates the concept:</p>
2576</div>
2577
2578<div class="doc_code">
2579<pre>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2580> import Test.QuickCheck
2581>
2582> digits :: Int -> [Char] -> [Char]
2583> digits 0 acc = '0' : acc
2584> digits 1 acc = '1' : acc
2585> digits n acc = digits (n `div` 2) $ digits (n `mod` 2) acc
2586>
2587> dist :: Int -> [Char] -> [Char]
2588> dist 0 [] = ['S']
2589> dist 0 acc = acc
2590> dist 1 acc = let r = dist 0 acc in 's' : digits (length r) r
2591> dist n acc = dist (n - 1) $ dist 1 acc
2592>
2593> takeLast n ss = reverse $ take n $ reverse ss
2594>
2595> test = takeLast 40 $ dist 20 []
2596>
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2597</pre>
2598</div>
2599<p>
2600Printing &lt;test&gt; gives: <tt>"1s100000s11010s10100s1111s1010s110s11s1S"</tt></p>
2601<p>
2602The reverse algorithm computes the length of the string just by examining
2603a certain prefix:</p>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2604
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2605<div class="doc_code">
2606<pre>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2607> pref :: [Char] -> Int
2608> pref "S" = 1
2609> pref ('s':'1':rest) = decode 2 1 rest
2610> pref (_:rest) = 1 + pref rest
2611>
2612> decode walk acc ('0':rest) = decode (walk + 1) (acc * 2) rest
2613> decode walk acc ('1':rest) = decode (walk + 1) (acc * 2 + 1) rest
2614> decode walk acc _ = walk + acc
2615>
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2616</pre>
2617</div>
2618<p>
2619Now, as expected, printing &lt;pref test&gt; gives <tt>40</tt>.</p>
2620<p>
2621We can <i>quickCheck</i> this with following property:</p>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2622
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2623<div class="doc_code">
2624<pre>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2625> testcase = dist 2000 []
2626> testcaseLength = length testcase
2627>
2628> identityProp n = n > 0 && n <= testcaseLength ==> length arr == pref arr
2629> where arr = takeLast n testcase
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2630>
2631</pre>
2632</div>
2633<p>
2634As expected &lt;quickCheck identityProp&gt; gives:</p>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2635
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2636<pre>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2637*Main> quickCheck identityProp
2638OK, passed 100 tests.
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2639</pre>
2640<p>
2641Let's be a bit more exhaustive:</p>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2642
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2643<div class="doc_code">
2644<pre>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2645>
2646> deepCheck p = check (defaultConfig { configMaxTest = 500 }) p
2647>
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2648</pre>
2649</div>
2650<p>
2651And here is the result of &lt;deepCheck identityProp&gt;:</p>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2652
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2653<pre>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2654*Main> deepCheck identityProp
2655OK, passed 500 tests.
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2656</pre>
2657
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2658<!-- ______________________________________________________________________ -->
2659<div class="doc_subsubsection">
Gabor Greiffd095b62009-01-05 16:05:32 +0000[diff] [blame]2660 <a name="Tagging">Tagging considerations</a>
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2661</div>
2662
2663<p>
2664To maintain the invariant that the 2 LSBits of each <tt>Use**</tt> in <tt>Use</tt>
2665never change after being set up, setters of <tt>Use::Prev</tt> must re-tag the
2666new <tt>Use**</tt> on every modification. Accordingly getters must strip the
2667tag bits.</p>
2668<p>
Gabor Greifd41720a2008-06-25 00:10:22 +0000[diff] [blame]2669For layout b) instead of the <tt>User</tt> we find a pointer (<tt>User*</tt> with LSBit set).
2670Following this pointer brings us to the <tt>User</tt>. A portable trick ensures
2671that the first bytes of <tt>User</tt> (if interpreted as a pointer) never has
Gabor Greiffd095b62009-01-05 16:05:32 +0000[diff] [blame]2672the LSBit set. (Portability is relying on the fact that all known compilers place the
2673<tt>vptr</tt> in the first word of the instances.)</p>
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2674
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2675</div>
2676
2677 <!-- *********************************************************************** -->
Chris Lattnerd9d6e102005-04-23 16:10:52 +0000[diff] [blame]2678<div class="doc_section">
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2679 <a name="coreclasses">The Core LLVM Class Hierarchy Reference </a>
2680</div>
2681<!-- *********************************************************************** -->
2682
2683<div class="doc_text">
Reid Spencer303c4b42007-01-12 17:26:25 +0000[diff] [blame]2684<p><tt>#include "<a href="/doxygen/Type_8h-source.html">llvm/Type.h</a>"</tt>
2685<br>doxygen info: <a href="/doxygen/classllvm_1_1Type.html">Type Class</a></p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2686
2687<p>The Core LLVM classes are the primary means of representing the program
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]2688being inspected or transformed. The core LLVM classes are defined in
2689header files in the <tt>include/llvm/</tt> directory, and implemented in
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2690the <tt>lib/VMCore</tt> directory.</p>
2691
2692</div>
2693
2694<!-- ======================================================================= -->
2695<div class="doc_subsection">
Reid Spencer303c4b42007-01-12 17:26:25 +0000[diff] [blame]2696 <a name="Type">The <tt>Type</tt> class and Derived Types</a>
2697</div>
2698
2699<div class="doc_text">
2700
2701 <p><tt>Type</tt> is a superclass of all type classes. Every <tt>Value</tt> has
2702 a <tt>Type</tt>. <tt>Type</tt> cannot be instantiated directly but only
2703 through its subclasses. Certain primitive types (<tt>VoidType</tt>,
2704 <tt>LabelType</tt>, <tt>FloatType</tt> and <tt>DoubleType</tt>) have hidden
2705 subclasses. They are hidden because they offer no useful functionality beyond
2706 what the <tt>Type</tt> class offers except to distinguish themselves from
2707 other subclasses of <tt>Type</tt>.</p>
2708 <p>All other types are subclasses of <tt>DerivedType</tt>. Types can be
2709 named, but this is not a requirement. There exists exactly
2710 one instance of a given shape at any one time. This allows type equality to
2711 be performed with address equality of the Type Instance. That is, given two
2712 <tt>Type*</tt> values, the types are identical if the pointers are identical.
2713 </p>
2714</div>
2715
2716<!-- _______________________________________________________________________ -->
2717<div class="doc_subsubsection">
Gabor Greiffd095b62009-01-05 16:05:32 +0000[diff] [blame]2718 <a name="m_Type">Important Public Methods</a>
Reid Spencer303c4b42007-01-12 17:26:25 +0000[diff] [blame]2719</div>
2720
2721<div class="doc_text">
2722
2723<ul>
Chris Lattner8f79df32007-01-15 01:55:32 +0000[diff] [blame]2724 <li><tt>bool isInteger() const</tt>: Returns true for any integer type.</li>
Reid Spencer303c4b42007-01-12 17:26:25 +0000[diff] [blame]2725
2726 <li><tt>bool isFloatingPoint()</tt>: Return true if this is one of the two
2727 floating point types.</li>
2728
2729 <li><tt>bool isAbstract()</tt>: Return true if the type is abstract (contains
2730 an OpaqueType anywhere in its definition).</li>
2731
2732 <li><tt>bool isSized()</tt>: Return true if the type has known size. Things
2733 that don't have a size are abstract types, labels and void.</li>
2734
2735</ul>
2736</div>
2737
2738<!-- _______________________________________________________________________ -->
2739<div class="doc_subsubsection">
Gabor Greiffd095b62009-01-05 16:05:32 +0000[diff] [blame]2740 <a name="derivedtypes">Important Derived Types</a>
Reid Spencer303c4b42007-01-12 17:26:25 +0000[diff] [blame]2741</div>
2742<div class="doc_text">
2743<dl>
2744 <dt><tt>IntegerType</tt></dt>
2745 <dd>Subclass of DerivedType that represents integer types of any bit width.
2746 Any bit width between <tt>IntegerType::MIN_INT_BITS</tt> (1) and
2747 <tt>IntegerType::MAX_INT_BITS</tt> (~8 million) can be represented.
2748 <ul>
2749 <li><tt>static const IntegerType* get(unsigned NumBits)</tt>: get an integer
2750 type of a specific bit width.</li>
2751 <li><tt>unsigned getBitWidth() const</tt>: Get the bit width of an integer
2752 type.</li>
2753 </ul>
2754 </dd>
2755 <dt><tt>SequentialType</tt></dt>
2756 <dd>This is subclassed by ArrayType and PointerType
2757 <ul>
2758 <li><tt>const Type * getElementType() const</tt>: Returns the type of each
2759 of the elements in the sequential type. </li>
2760 </ul>
2761 </dd>
2762 <dt><tt>ArrayType</tt></dt>
2763 <dd>This is a subclass of SequentialType and defines the interface for array
2764 types.
2765 <ul>
2766 <li><tt>unsigned getNumElements() const</tt>: Returns the number of
2767 elements in the array. </li>
2768 </ul>
2769 </dd>
2770 <dt><tt>PointerType</tt></dt>
Chris Lattner302da1e2007-02-03 03:05:57 +0000[diff] [blame]2771 <dd>Subclass of SequentialType for pointer types.</dd>
Reid Spencer9d6565a2007-02-15 02:26:10 +0000[diff] [blame]2772 <dt><tt>VectorType</tt></dt>
Reid Spencer485bad12007-02-15 03:07:05 +0000[diff] [blame]2773 <dd>Subclass of SequentialType for vector types. A
2774 vector type is similar to an ArrayType but is distinguished because it is
2775 a first class type wherease ArrayType is not. Vector types are used for
Reid Spencer303c4b42007-01-12 17:26:25 +0000[diff] [blame]2776 vector operations and are usually small vectors of of an integer or floating
2777 point type.</dd>
2778 <dt><tt>StructType</tt></dt>
2779 <dd>Subclass of DerivedTypes for struct types.</dd>
Duncan Sands8036ca42007-03-30 12:22:09 +0000[diff] [blame]2780 <dt><tt><a name="FunctionType">FunctionType</a></tt></dt>
Reid Spencer303c4b42007-01-12 17:26:25 +0000[diff] [blame]2781 <dd>Subclass of DerivedTypes for function types.
2782 <ul>
2783 <li><tt>bool isVarArg() const</tt>: Returns true if its a vararg
2784 function</li>
2785 <li><tt> const Type * getReturnType() const</tt>: Returns the
2786 return type of the function.</li>
2787 <li><tt>const Type * getParamType (unsigned i)</tt>: Returns
2788 the type of the ith parameter.</li>
2789 <li><tt> const unsigned getNumParams() const</tt>: Returns the
2790 number of formal parameters.</li>
2791 </ul>
2792 </dd>
2793 <dt><tt>OpaqueType</tt></dt>
2794 <dd>Sublcass of DerivedType for abstract types. This class
2795 defines no content and is used as a placeholder for some other type. Note
2796 that OpaqueType is used (temporarily) during type resolution for forward
2797 references of types. Once the referenced type is resolved, the OpaqueType
2798 is replaced with the actual type. OpaqueType can also be used for data
2799 abstraction. At link time opaque types can be resolved to actual types
2800 of the same name.</dd>
2801</dl>
2802</div>
2803
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]2804
2805
2806<!-- ======================================================================= -->
2807<div class="doc_subsection">
2808 <a name="Module">The <tt>Module</tt> class</a>
2809</div>
2810
2811<div class="doc_text">
2812
2813<p><tt>#include "<a
2814href="/doxygen/Module_8h-source.html">llvm/Module.h</a>"</tt><br> doxygen info:
2815<a href="/doxygen/classllvm_1_1Module.html">Module Class</a></p>
2816
2817<p>The <tt>Module</tt> class represents the top level structure present in LLVM
2818programs. An LLVM module is effectively either a translation unit of the
2819original program or a combination of several translation units merged by the
2820linker. The <tt>Module</tt> class keeps track of a list of <a
2821href="#Function"><tt>Function</tt></a>s, a list of <a
2822href="#GlobalVariable"><tt>GlobalVariable</tt></a>s, and a <a
2823href="#SymbolTable"><tt>SymbolTable</tt></a>. Additionally, it contains a few
2824helpful member functions that try to make common operations easy.</p>
2825
2826</div>
2827
2828<!-- _______________________________________________________________________ -->
2829<div class="doc_subsubsection">
2830 <a name="m_Module">Important Public Members of the <tt>Module</tt> class</a>
2831</div>
2832
2833<div class="doc_text">
2834
2835<ul>
2836 <li><tt>Module::Module(std::string name = "")</tt></li>
2837</ul>
2838
2839<p>Constructing a <a href="#Module">Module</a> is easy. You can optionally
2840provide a name for it (probably based on the name of the translation unit).</p>
2841
2842<ul>
2843 <li><tt>Module::iterator</tt> - Typedef for function list iterator<br>
2844 <tt>Module::const_iterator</tt> - Typedef for const_iterator.<br>
2845
2846 <tt>begin()</tt>, <tt>end()</tt>
2847 <tt>size()</tt>, <tt>empty()</tt>
2848
2849 <p>These are forwarding methods that make it easy to access the contents of
2850 a <tt>Module</tt> object's <a href="#Function"><tt>Function</tt></a>
2851 list.</p></li>
2852
2853 <li><tt>Module::FunctionListType &amp;getFunctionList()</tt>
2854
2855 <p> Returns the list of <a href="#Function"><tt>Function</tt></a>s. This is
2856 necessary to use when you need to update the list or perform a complex
2857 action that doesn't have a forwarding method.</p>
2858
2859 <p><!-- Global Variable --></p></li>
2860</ul>
2861
2862<hr>
2863
2864<ul>
2865 <li><tt>Module::global_iterator</tt> - Typedef for global variable list iterator<br>
2866
2867 <tt>Module::const_global_iterator</tt> - Typedef for const_iterator.<br>
2868
2869 <tt>global_begin()</tt>, <tt>global_end()</tt>
2870 <tt>global_size()</tt>, <tt>global_empty()</tt>
2871
2872 <p> These are forwarding methods that make it easy to access the contents of
2873 a <tt>Module</tt> object's <a
2874 href="#GlobalVariable"><tt>GlobalVariable</tt></a> list.</p></li>
2875
2876 <li><tt>Module::GlobalListType &amp;getGlobalList()</tt>
2877
2878 <p>Returns the list of <a
2879 href="#GlobalVariable"><tt>GlobalVariable</tt></a>s. This is necessary to
2880 use when you need to update the list or perform a complex action that
2881 doesn't have a forwarding method.</p>
2882
2883 <p><!-- Symbol table stuff --> </p></li>
2884</ul>
2885
2886<hr>
2887
2888<ul>
2889 <li><tt><a href="#SymbolTable">SymbolTable</a> *getSymbolTable()</tt>
2890
2891 <p>Return a reference to the <a href="#SymbolTable"><tt>SymbolTable</tt></a>
2892 for this <tt>Module</tt>.</p>
2893
2894 <p><!-- Convenience methods --></p></li>
2895</ul>
2896
2897<hr>
2898
2899<ul>
2900 <li><tt><a href="#Function">Function</a> *getFunction(const std::string
2901 &amp;Name, const <a href="#FunctionType">FunctionType</a> *Ty)</tt>
2902
2903 <p>Look up the specified function in the <tt>Module</tt> <a
2904 href="#SymbolTable"><tt>SymbolTable</tt></a>. If it does not exist, return
2905 <tt>null</tt>.</p></li>
2906
2907 <li><tt><a href="#Function">Function</a> *getOrInsertFunction(const
2908 std::string &amp;Name, const <a href="#FunctionType">FunctionType</a> *T)</tt>
2909
2910 <p>Look up the specified function in the <tt>Module</tt> <a
2911 href="#SymbolTable"><tt>SymbolTable</tt></a>. If it does not exist, add an
2912 external declaration for the function and return it.</p></li>
2913
2914 <li><tt>std::string getTypeName(const <a href="#Type">Type</a> *Ty)</tt>
2915
2916 <p>If there is at least one entry in the <a
2917 href="#SymbolTable"><tt>SymbolTable</tt></a> for the specified <a
2918 href="#Type"><tt>Type</tt></a>, return it. Otherwise return the empty
2919 string.</p></li>
2920
2921 <li><tt>bool addTypeName(const std::string &amp;Name, const <a
2922 href="#Type">Type</a> *Ty)</tt>
2923
2924 <p>Insert an entry in the <a href="#SymbolTable"><tt>SymbolTable</tt></a>
2925 mapping <tt>Name</tt> to <tt>Ty</tt>. If there is already an entry for this
2926 name, true is returned and the <a
2927 href="#SymbolTable"><tt>SymbolTable</tt></a> is not modified.</p></li>
2928</ul>
2929
2930</div>
2931
2932
Reid Spencer303c4b42007-01-12 17:26:25 +0000[diff] [blame]2933<!-- ======================================================================= -->
2934<div class="doc_subsection">
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2935 <a name="Value">The <tt>Value</tt> class</a>
2936</div>
2937
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]2938<div class="doc_text">
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2939
2940<p><tt>#include "<a href="/doxygen/Value_8h-source.html">llvm/Value.h</a>"</tt>
2941<br>
Chris Lattner00815172007-01-04 22:01:45 +0000[diff] [blame]2942doxygen info: <a href="/doxygen/classllvm_1_1Value.html">Value Class</a></p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2943
2944<p>The <tt>Value</tt> class is the most important class in the LLVM Source
2945base. It represents a typed value that may be used (among other things) as an
2946operand to an instruction. There are many different types of <tt>Value</tt>s,
2947such as <a href="#Constant"><tt>Constant</tt></a>s,<a
2948href="#Argument"><tt>Argument</tt></a>s. Even <a
2949href="#Instruction"><tt>Instruction</tt></a>s and <a
2950href="#Function"><tt>Function</tt></a>s are <tt>Value</tt>s.</p>
2951
2952<p>A particular <tt>Value</tt> may be used many times in the LLVM representation
2953for a program. For example, an incoming argument to a function (represented
2954with an instance of the <a href="#Argument">Argument</a> class) is "used" by
2955every instruction in the function that references the argument. To keep track
2956of this relationship, the <tt>Value</tt> class keeps a list of all of the <a
2957href="#User"><tt>User</tt></a>s that is using it (the <a
2958href="#User"><tt>User</tt></a> class is a base class for all nodes in the LLVM
2959graph that can refer to <tt>Value</tt>s). This use list is how LLVM represents
2960def-use information in the program, and is accessible through the <tt>use_</tt>*
2961methods, shown below.</p>
2962
2963<p>Because LLVM is a typed representation, every LLVM <tt>Value</tt> is typed,
2964and this <a href="#Type">Type</a> is available through the <tt>getType()</tt>
2965method. In addition, all LLVM values can be named. The "name" of the
2966<tt>Value</tt> is a symbolic string printed in the LLVM code:</p>
2967
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2968<div class="doc_code">
2969<pre>
Reid Spencer06565dc2007-01-12 17:11:23 +0000[diff] [blame]2970%<b>foo</b> = add i32 1, 2
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2971</pre>
2972</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2973
Duncan Sands8036ca42007-03-30 12:22:09 +0000[diff] [blame]2974<p><a name="nameWarning">The name of this instruction is "foo".</a> <b>NOTE</b>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2975that the name of any value may be missing (an empty string), so names should
2976<b>ONLY</b> be used for debugging (making the source code easier to read,
2977debugging printouts), they should not be used to keep track of values or map
2978between them. For this purpose, use a <tt>std::map</tt> of pointers to the
2979<tt>Value</tt> itself instead.</p>
2980
2981<p>One important aspect of LLVM is that there is no distinction between an SSA
2982variable and the operation that produces it. Because of this, any reference to
2983the value produced by an instruction (or the value available as an incoming
Chris Lattnerd5fc4fc2004-03-18 14:58:55 +0000[diff] [blame]2984argument, for example) is represented as a direct pointer to the instance of
2985the class that
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2986represents this value. Although this may take some getting used to, it
2987simplifies the representation and makes it easier to manipulate.</p>
2988
2989</div>
2990
2991<!-- _______________________________________________________________________ -->
2992<div class="doc_subsubsection">
2993 <a name="m_Value">Important Public Members of the <tt>Value</tt> class</a>
2994</div>
2995
2996<div class="doc_text">
2997
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]2998<ul>
2999 <li><tt>Value::use_iterator</tt> - Typedef for iterator over the
3000use-list<br>
3001 <tt>Value::use_const_iterator</tt> - Typedef for const_iterator over
3002the use-list<br>
3003 <tt>unsigned use_size()</tt> - Returns the number of users of the
3004value.<br>
Chris Lattner9355b472002-09-06 02:50:58 +0000[diff] [blame]3005 <tt>bool use_empty()</tt> - Returns true if there are no users.<br>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3006 <tt>use_iterator use_begin()</tt> - Get an iterator to the start of
3007the use-list.<br>
3008 <tt>use_iterator use_end()</tt> - Get an iterator to the end of the
3009use-list.<br>
3010 <tt><a href="#User">User</a> *use_back()</tt> - Returns the last
3011element in the list.
3012 <p> These methods are the interface to access the def-use
3013information in LLVM. As with all other iterators in LLVM, the naming
3014conventions follow the conventions defined by the <a href="#stl">STL</a>.</p>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3015 </li>
3016 <li><tt><a href="#Type">Type</a> *getType() const</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3017 <p>This method returns the Type of the Value.</p>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3018 </li>
3019 <li><tt>bool hasName() const</tt><br>
Chris Lattner9355b472002-09-06 02:50:58 +0000[diff] [blame]3020 <tt>std::string getName() const</tt><br>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3021 <tt>void setName(const std::string &amp;Name)</tt>
3022 <p> This family of methods is used to access and assign a name to a <tt>Value</tt>,
3023be aware of the <a href="#nameWarning">precaution above</a>.</p>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3024 </li>
3025 <li><tt>void replaceAllUsesWith(Value *V)</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3026
3027 <p>This method traverses the use list of a <tt>Value</tt> changing all <a
3028 href="#User"><tt>User</tt>s</a> of the current value to refer to
3029 "<tt>V</tt>" instead. For example, if you detect that an instruction always
3030 produces a constant value (for example through constant folding), you can
3031 replace all uses of the instruction with the constant like this:</p>
3032
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]3033<div class="doc_code">
3034<pre>
3035Inst-&gt;replaceAllUsesWith(ConstVal);
3036</pre>
3037</div>
3038
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3039</ul>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3040
3041</div>
3042
3043<!-- ======================================================================= -->
3044<div class="doc_subsection">
3045 <a name="User">The <tt>User</tt> class</a>
3046</div>
3047
3048<div class="doc_text">
3049
3050<p>
3051<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]3052doxygen info: <a href="/doxygen/classllvm_1_1User.html">User Class</a><br>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3053Superclass: <a href="#Value"><tt>Value</tt></a></p>
3054
3055<p>The <tt>User</tt> class is the common base class of all LLVM nodes that may
3056refer to <a href="#Value"><tt>Value</tt></a>s. It exposes a list of "Operands"
3057that are all of the <a href="#Value"><tt>Value</tt></a>s that the User is
3058referring to. The <tt>User</tt> class itself is a subclass of
3059<tt>Value</tt>.</p>
3060
3061<p>The operands of a <tt>User</tt> point directly to the LLVM <a
3062href="#Value"><tt>Value</tt></a> that it refers to. Because LLVM uses Static
3063Single Assignment (SSA) form, there can only be one definition referred to,
3064allowing this direct connection. This connection provides the use-def
3065information in LLVM.</p>
3066
3067</div>
3068
3069<!-- _______________________________________________________________________ -->
3070<div class="doc_subsubsection">
3071 <a name="m_User">Important Public Members of the <tt>User</tt> class</a>
3072</div>
3073
3074<div class="doc_text">
3075
3076<p>The <tt>User</tt> class exposes the operand list in two ways: through
3077an index access interface and through an iterator based interface.</p>
3078
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3079<ul>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3080 <li><tt>Value *getOperand(unsigned i)</tt><br>
3081 <tt>unsigned getNumOperands()</tt>
3082 <p> These two methods expose the operands of the <tt>User</tt> in a
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3083convenient form for direct access.</p></li>
3084
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3085 <li><tt>User::op_iterator</tt> - Typedef for iterator over the operand
3086list<br>
Chris Lattner58360822005-01-17 00:12:04 +0000[diff] [blame]3087 <tt>op_iterator op_begin()</tt> - Get an iterator to the start of
3088the operand list.<br>
3089 <tt>op_iterator op_end()</tt> - Get an iterator to the end of the
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3090operand list.
3091 <p> Together, these methods make up the iterator based interface to
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3092the operands of a <tt>User</tt>.</p></li>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3093</ul>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3094
3095</div>
3096
3097<!-- ======================================================================= -->
3098<div class="doc_subsection">
3099 <a name="Instruction">The <tt>Instruction</tt> class</a>
3100</div>
3101
3102<div class="doc_text">
3103
3104<p><tt>#include "</tt><tt><a
3105href="/doxygen/Instruction_8h-source.html">llvm/Instruction.h</a>"</tt><br>
Misha Brukman31ca1de2004-06-03 23:35:54 +0000[diff] [blame]3106doxygen info: <a href="/doxygen/classllvm_1_1Instruction.html">Instruction Class</a><br>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3107Superclasses: <a href="#User"><tt>User</tt></a>, <a
3108href="#Value"><tt>Value</tt></a></p>
3109
3110<p>The <tt>Instruction</tt> class is the common base class for all LLVM
3111instructions. It provides only a few methods, but is a very commonly used
3112class. The primary data tracked by the <tt>Instruction</tt> class itself is the
3113opcode (instruction type) and the parent <a
3114href="#BasicBlock"><tt>BasicBlock</tt></a> the <tt>Instruction</tt> is embedded
3115into. To represent a specific type of instruction, one of many subclasses of
3116<tt>Instruction</tt> are used.</p>
3117
3118<p> Because the <tt>Instruction</tt> class subclasses the <a
3119href="#User"><tt>User</tt></a> class, its operands can be accessed in the same
3120way as for other <a href="#User"><tt>User</tt></a>s (with the
3121<tt>getOperand()</tt>/<tt>getNumOperands()</tt> and
3122<tt>op_begin()</tt>/<tt>op_end()</tt> methods).</p> <p> An important file for
3123the <tt>Instruction</tt> class is the <tt>llvm/Instruction.def</tt> file. This
3124file contains some meta-data about the various different types of instructions
3125in LLVM. It describes the enum values that are used as opcodes (for example
Reid Spencerc92d25d2006-12-19 19:47:19 +0000[diff] [blame]3126<tt>Instruction::Add</tt> and <tt>Instruction::ICmp</tt>), as well as the
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3127concrete sub-classes of <tt>Instruction</tt> that implement the instruction (for
3128example <tt><a href="#BinaryOperator">BinaryOperator</a></tt> and <tt><a
Reid Spencerc92d25d2006-12-19 19:47:19 +0000[diff] [blame]3129href="#CmpInst">CmpInst</a></tt>). Unfortunately, the use of macros in
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3130this file confuses doxygen, so these enum values don't show up correctly in the
Misha Brukman31ca1de2004-06-03 23:35:54 +0000[diff] [blame]3131<a href="/doxygen/classllvm_1_1Instruction.html">doxygen output</a>.</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3132
3133</div>
3134
3135<!-- _______________________________________________________________________ -->
3136<div class="doc_subsubsection">
Reid Spencerc92d25d2006-12-19 19:47:19 +0000[diff] [blame]3137 <a name="s_Instruction">Important Subclasses of the <tt>Instruction</tt>
3138 class</a>
3139</div>
3140<div class="doc_text">
3141 <ul>
3142 <li><tt><a name="BinaryOperator">BinaryOperator</a></tt>
3143 <p>This subclasses represents all two operand instructions whose operands
3144 must be the same type, except for the comparison instructions.</p></li>
3145 <li><tt><a name="CastInst">CastInst</a></tt>
3146 <p>This subclass is the parent of the 12 casting instructions. It provides
3147 common operations on cast instructions.</p>
3148 <li><tt><a name="CmpInst">CmpInst</a></tt>
3149 <p>This subclass respresents the two comparison instructions,
3150 <a href="LangRef.html#i_icmp">ICmpInst</a> (integer opreands), and
3151 <a href="LangRef.html#i_fcmp">FCmpInst</a> (floating point operands).</p>
3152 <li><tt><a name="TerminatorInst">TerminatorInst</a></tt>
3153 <p>This subclass is the parent of all terminator instructions (those which
3154 can terminate a block).</p>
3155 </ul>
3156 </div>
3157
3158<!-- _______________________________________________________________________ -->
3159<div class="doc_subsubsection">
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3160 <a name="m_Instruction">Important Public Members of the <tt>Instruction</tt>
3161 class</a>
3162</div>
3163
3164<div class="doc_text">
3165
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3166<ul>
3167 <li><tt><a href="#BasicBlock">BasicBlock</a> *getParent()</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3168 <p>Returns the <a href="#BasicBlock"><tt>BasicBlock</tt></a> that
3169this <tt>Instruction</tt> is embedded into.</p></li>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3170 <li><tt>bool mayWriteToMemory()</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3171 <p>Returns true if the instruction writes to memory, i.e. it is a
3172 <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]3173 <li><tt>unsigned getOpcode()</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3174 <p>Returns the opcode for the <tt>Instruction</tt>.</p></li>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3175 <li><tt><a href="#Instruction">Instruction</a> *clone() const</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3176 <p>Returns another instance of the specified instruction, identical
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3177in all ways to the original except that the instruction has no parent
3178(ie it's not embedded into a <a href="#BasicBlock"><tt>BasicBlock</tt></a>),
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3179and it has no name</p></li>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3180</ul>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3181
3182</div>
3183
3184<!-- ======================================================================= -->
3185<div class="doc_subsection">
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]3186 <a name="Constant">The <tt>Constant</tt> class and subclasses</a>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3187</div>
3188
3189<div class="doc_text">
3190
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]3191<p>Constant represents a base class for different types of constants. It
3192is subclassed by ConstantInt, ConstantArray, etc. for representing
3193the various types of Constants. <a href="#GlobalValue">GlobalValue</a> is also
3194a subclass, which represents the address of a global variable or function.
3195</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3196
3197</div>
3198
3199<!-- _______________________________________________________________________ -->
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]3200<div class="doc_subsubsection">Important Subclasses of Constant </div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3201<div class="doc_text">
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3202<ul>
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]3203 <li>ConstantInt : This subclass of Constant represents an integer constant of
3204 any width.
3205 <ul>
Reid Spencer97b4ee32007-03-01 21:05:33 +0000[diff] [blame]3206 <li><tt>const APInt&amp; getValue() const</tt>: Returns the underlying
3207 value of this constant, an APInt value.</li>
3208 <li><tt>int64_t getSExtValue() const</tt>: Converts the underlying APInt
3209 value to an int64_t via sign extension. If the value (not the bit width)
3210 of the APInt is too large to fit in an int64_t, an assertion will result.
3211 For this reason, use of this method is discouraged.</li>
3212 <li><tt>uint64_t getZExtValue() const</tt>: Converts the underlying APInt
3213 value to a uint64_t via zero extension. IF the value (not the bit width)
3214 of the APInt is too large to fit in a uint64_t, an assertion will result.
Reid Spencer4474d872007-03-02 01:31:31 +0000[diff] [blame]3215 For this reason, use of this method is discouraged.</li>
Reid Spencer97b4ee32007-03-01 21:05:33 +0000[diff] [blame]3216 <li><tt>static ConstantInt* get(const APInt&amp; Val)</tt>: Returns the
3217 ConstantInt object that represents the value provided by <tt>Val</tt>.
3218 The type is implied as the IntegerType that corresponds to the bit width
3219 of <tt>Val</tt>.</li>
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]3220 <li><tt>static ConstantInt* get(const Type *Ty, uint64_t Val)</tt>:
3221 Returns the ConstantInt object that represents the value provided by
3222 <tt>Val</tt> for integer type <tt>Ty</tt>.</li>
3223 </ul>
3224 </li>
3225 <li>ConstantFP : This class represents a floating point constant.
3226 <ul>
3227 <li><tt>double getValue() const</tt>: Returns the underlying value of
3228 this constant. </li>
3229 </ul>
3230 </li>
3231 <li>ConstantArray : This represents a constant array.
3232 <ul>
3233 <li><tt>const std::vector&lt;Use&gt; &amp;getValues() const</tt>: Returns
3234 a vector of component constants that makeup this array. </li>
3235 </ul>
3236 </li>
3237 <li>ConstantStruct : This represents a constant struct.
3238 <ul>
3239 <li><tt>const std::vector&lt;Use&gt; &amp;getValues() const</tt>: Returns
3240 a vector of component constants that makeup this array. </li>
3241 </ul>
3242 </li>
3243 <li>GlobalValue : This represents either a global variable or a function. In
3244 either case, the value is a constant fixed address (after linking).
3245 </li>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3246</ul>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3247</div>
3248
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]3249
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3250<!-- ======================================================================= -->
3251<div class="doc_subsection">
3252 <a name="GlobalValue">The <tt>GlobalValue</tt> class</a>
3253</div>
3254
3255<div class="doc_text">
3256
3257<p><tt>#include "<a
3258href="/doxygen/GlobalValue_8h-source.html">llvm/GlobalValue.h</a>"</tt><br>
Misha Brukman384047f2004-06-03 23:29:12 +0000[diff] [blame]3259doxygen info: <a href="/doxygen/classllvm_1_1GlobalValue.html">GlobalValue
3260Class</a><br>
Reid Spencerbe5e85e2006-04-14 14:11:48 +0000[diff] [blame]3261Superclasses: <a href="#Constant"><tt>Constant</tt></a>,
3262<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]3263
3264<p>Global values (<a href="#GlobalVariable"><tt>GlobalVariable</tt></a>s or <a
3265href="#Function"><tt>Function</tt></a>s) are the only LLVM values that are
3266visible in the bodies of all <a href="#Function"><tt>Function</tt></a>s.
3267Because they are visible at global scope, they are also subject to linking with
3268other globals defined in different translation units. To control the linking
3269process, <tt>GlobalValue</tt>s know their linkage rules. Specifically,
3270<tt>GlobalValue</tt>s know whether they have internal or external linkage, as
Reid Spencer8b2da7a2004-07-18 13:10:31 +0000[diff] [blame]3271defined by the <tt>LinkageTypes</tt> enumeration.</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3272
3273<p>If a <tt>GlobalValue</tt> has internal linkage (equivalent to being
3274<tt>static</tt> in C), it is not visible to code outside the current translation
3275unit, and does not participate in linking. If it has external linkage, it is
3276visible to external code, and does participate in linking. In addition to
3277linkage information, <tt>GlobalValue</tt>s keep track of which <a
3278href="#Module"><tt>Module</tt></a> they are currently part of.</p>
3279
3280<p>Because <tt>GlobalValue</tt>s are memory objects, they are always referred to
3281by their <b>address</b>. As such, the <a href="#Type"><tt>Type</tt></a> of a
3282global is always a pointer to its contents. It is important to remember this
3283when using the <tt>GetElementPtrInst</tt> instruction because this pointer must
3284be dereferenced first. For example, if you have a <tt>GlobalVariable</tt> (a
3285subclass 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]3286i32]</tt>, then the <tt>GlobalVariable</tt> is a pointer to that array. Although
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3287the address of the first element of this array and the value of the
3288<tt>GlobalVariable</tt> are the same, they have different types. The
Reid Spencer06565dc2007-01-12 17:11:23 +0000[diff] [blame]3289<tt>GlobalVariable</tt>'s type is <tt>[24 x i32]</tt>. The first element's type
3290is <tt>i32.</tt> Because of this, accessing a global value requires you to
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3291dereference the pointer with <tt>GetElementPtrInst</tt> first, then its elements
3292can be accessed. This is explained in the <a href="LangRef.html#globalvars">LLVM
3293Language Reference Manual</a>.</p>
3294
3295</div>
3296
3297<!-- _______________________________________________________________________ -->
3298<div class="doc_subsubsection">
3299 <a name="m_GlobalValue">Important Public Members of the <tt>GlobalValue</tt>
3300 class</a>
3301</div>
3302
3303<div class="doc_text">
3304
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3305<ul>
3306 <li><tt>bool hasInternalLinkage() const</tt><br>
Chris Lattner9355b472002-09-06 02:50:58 +0000[diff] [blame]3307 <tt>bool hasExternalLinkage() const</tt><br>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3308 <tt>void setInternalLinkage(bool HasInternalLinkage)</tt>
3309 <p> These methods manipulate the linkage characteristics of the <tt>GlobalValue</tt>.</p>
3310 <p> </p>
3311 </li>
3312 <li><tt><a href="#Module">Module</a> *getParent()</tt>
3313 <p> This returns the <a href="#Module"><tt>Module</tt></a> that the
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3314GlobalValue is currently embedded into.</p></li>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3315</ul>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3316
3317</div>
3318
3319<!-- ======================================================================= -->
3320<div class="doc_subsection">
3321 <a name="Function">The <tt>Function</tt> class</a>
3322</div>
3323
3324<div class="doc_text">
3325
3326<p><tt>#include "<a
3327href="/doxygen/Function_8h-source.html">llvm/Function.h</a>"</tt><br> doxygen
Misha Brukman31ca1de2004-06-03 23:35:54 +0000[diff] [blame]3328info: <a href="/doxygen/classllvm_1_1Function.html">Function Class</a><br>
Reid Spencerbe5e85e2006-04-14 14:11:48 +0000[diff] [blame]3329Superclasses: <a href="#GlobalValue"><tt>GlobalValue</tt></a>,
3330<a href="#Constant"><tt>Constant</tt></a>,
3331<a href="#User"><tt>User</tt></a>,
3332<a href="#Value"><tt>Value</tt></a></p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3333
3334<p>The <tt>Function</tt> class represents a single procedure in LLVM. It is
3335actually one of the more complex classes in the LLVM heirarchy because it must
3336keep track of a large amount of data. The <tt>Function</tt> class keeps track
Reid Spencerbe5e85e2006-04-14 14:11:48 +0000[diff] [blame]3337of a list of <a href="#BasicBlock"><tt>BasicBlock</tt></a>s, a list of formal
3338<a href="#Argument"><tt>Argument</tt></a>s, and a
3339<a href="#SymbolTable"><tt>SymbolTable</tt></a>.</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3340
3341<p>The list of <a href="#BasicBlock"><tt>BasicBlock</tt></a>s is the most
3342commonly used part of <tt>Function</tt> objects. The list imposes an implicit
3343ordering of the blocks in the function, which indicate how the code will be
3344layed out by the backend. Additionally, the first <a
3345href="#BasicBlock"><tt>BasicBlock</tt></a> is the implicit entry node for the
3346<tt>Function</tt>. It is not legal in LLVM to explicitly branch to this initial
3347block. There are no implicit exit nodes, and in fact there may be multiple exit
3348nodes from a single <tt>Function</tt>. If the <a
3349href="#BasicBlock"><tt>BasicBlock</tt></a> list is empty, this indicates that
3350the <tt>Function</tt> is actually a function declaration: the actual body of the
3351function hasn't been linked in yet.</p>
3352
3353<p>In addition to a list of <a href="#BasicBlock"><tt>BasicBlock</tt></a>s, the
3354<tt>Function</tt> class also keeps track of the list of formal <a
3355href="#Argument"><tt>Argument</tt></a>s that the function receives. This
3356container manages the lifetime of the <a href="#Argument"><tt>Argument</tt></a>
3357nodes, just like the <a href="#BasicBlock"><tt>BasicBlock</tt></a> list does for
3358the <a href="#BasicBlock"><tt>BasicBlock</tt></a>s.</p>
3359
3360<p>The <a href="#SymbolTable"><tt>SymbolTable</tt></a> is a very rarely used
3361LLVM feature that is only used when you have to look up a value by name. Aside
3362from that, the <a href="#SymbolTable"><tt>SymbolTable</tt></a> is used
3363internally to make sure that there are not conflicts between the names of <a
3364href="#Instruction"><tt>Instruction</tt></a>s, <a
3365href="#BasicBlock"><tt>BasicBlock</tt></a>s, or <a
3366href="#Argument"><tt>Argument</tt></a>s in the function body.</p>
3367
Reid Spencer8b2da7a2004-07-18 13:10:31 +0000[diff] [blame]3368<p>Note that <tt>Function</tt> is a <a href="#GlobalValue">GlobalValue</a>
3369and therefore also a <a href="#Constant">Constant</a>. The value of the function
3370is its address (after linking) which is guaranteed to be constant.</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3371</div>
3372
3373<!-- _______________________________________________________________________ -->
3374<div class="doc_subsubsection">
3375 <a name="m_Function">Important Public Members of the <tt>Function</tt>
3376 class</a>
3377</div>
3378
3379<div class="doc_text">
3380
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3381<ul>
3382 <li><tt>Function(const </tt><tt><a href="#FunctionType">FunctionType</a>
Chris Lattnerac479e52004-08-04 05:10:48 +0000[diff] [blame]3383 *Ty, LinkageTypes Linkage, const std::string &amp;N = "", Module* Parent = 0)</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3384
3385 <p>Constructor used when you need to create new <tt>Function</tt>s to add
3386 the the program. The constructor must specify the type of the function to
Chris Lattnerac479e52004-08-04 05:10:48 +0000[diff] [blame]3387 create and what type of linkage the function should have. The <a
3388 href="#FunctionType"><tt>FunctionType</tt></a> argument
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3389 specifies the formal arguments and return value for the function. The same
Duncan Sands8036ca42007-03-30 12:22:09 +0000[diff] [blame]3390 <a href="#FunctionType"><tt>FunctionType</tt></a> value can be used to
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3391 create multiple functions. The <tt>Parent</tt> argument specifies the Module
3392 in which the function is defined. If this argument is provided, the function
3393 will automatically be inserted into that module's list of
3394 functions.</p></li>
3395
Chris Lattner62810e32008-11-25 18:34:50 +0000[diff] [blame]3396 <li><tt>bool isDeclaration()</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3397
3398 <p>Return whether or not the <tt>Function</tt> has a body defined. If the
3399 function is "external", it does not have a body, and thus must be resolved
3400 by linking with a function defined in a different translation unit.</p></li>
3401
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3402 <li><tt>Function::iterator</tt> - Typedef for basic block list iterator<br>
Chris Lattner9355b472002-09-06 02:50:58 +0000[diff] [blame]3403 <tt>Function::const_iterator</tt> - Typedef for const_iterator.<br>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3404
Chris Lattner77d69242005-03-15 05:19:20 +0000[diff] [blame]3405 <tt>begin()</tt>, <tt>end()</tt>
3406 <tt>size()</tt>, <tt>empty()</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3407
3408 <p>These are forwarding methods that make it easy to access the contents of
3409 a <tt>Function</tt> object's <a href="#BasicBlock"><tt>BasicBlock</tt></a>
3410 list.</p></li>
3411
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3412 <li><tt>Function::BasicBlockListType &amp;getBasicBlockList()</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3413
3414 <p>Returns the list of <a href="#BasicBlock"><tt>BasicBlock</tt></a>s. This
3415 is necessary to use when you need to update the list or perform a complex
3416 action that doesn't have a forwarding method.</p></li>
3417
Chris Lattner89cc2652005-03-15 04:48:32 +0000[diff] [blame]3418 <li><tt>Function::arg_iterator</tt> - Typedef for the argument list
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3419iterator<br>
Chris Lattner89cc2652005-03-15 04:48:32 +0000[diff] [blame]3420 <tt>Function::const_arg_iterator</tt> - Typedef for const_iterator.<br>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3421
Chris Lattner77d69242005-03-15 05:19:20 +0000[diff] [blame]3422 <tt>arg_begin()</tt>, <tt>arg_end()</tt>
Chris Lattner89cc2652005-03-15 04:48:32 +0000[diff] [blame]3423 <tt>arg_size()</tt>, <tt>arg_empty()</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3424
3425 <p>These are forwarding methods that make it easy to access the contents of
3426 a <tt>Function</tt> object's <a href="#Argument"><tt>Argument</tt></a>
3427 list.</p></li>
3428
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3429 <li><tt>Function::ArgumentListType &amp;getArgumentList()</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3430
3431 <p>Returns the list of <a href="#Argument"><tt>Argument</tt></a>s. This is
3432 necessary to use when you need to update the list or perform a complex
3433 action that doesn't have a forwarding method.</p></li>
3434
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3435 <li><tt><a href="#BasicBlock">BasicBlock</a> &amp;getEntryBlock()</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3436
3437 <p>Returns the entry <a href="#BasicBlock"><tt>BasicBlock</tt></a> for the
3438 function. Because the entry block for the function is always the first
3439 block, this returns the first block of the <tt>Function</tt>.</p></li>
3440
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3441 <li><tt><a href="#Type">Type</a> *getReturnType()</tt><br>
3442 <tt><a href="#FunctionType">FunctionType</a> *getFunctionType()</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3443
3444 <p>This traverses the <a href="#Type"><tt>Type</tt></a> of the
3445 <tt>Function</tt> and returns the return type of the function, or the <a
3446 href="#FunctionType"><tt>FunctionType</tt></a> of the actual
3447 function.</p></li>
3448
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3449 <li><tt><a href="#SymbolTable">SymbolTable</a> *getSymbolTable()</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3450
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3451 <p> Return a pointer to the <a href="#SymbolTable"><tt>SymbolTable</tt></a>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3452 for this <tt>Function</tt>.</p></li>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3453</ul>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3454
3455</div>
3456
3457<!-- ======================================================================= -->
3458<div class="doc_subsection">
3459 <a name="GlobalVariable">The <tt>GlobalVariable</tt> class</a>
3460</div>
3461
3462<div class="doc_text">
3463
3464<p><tt>#include "<a
3465href="/doxygen/GlobalVariable_8h-source.html">llvm/GlobalVariable.h</a>"</tt>
3466<br>
Tanya Lattnera3da7772004-06-22 08:02:25 +0000[diff] [blame]3467doxygen info: <a href="/doxygen/classllvm_1_1GlobalVariable.html">GlobalVariable
Reid Spencerbe5e85e2006-04-14 14:11:48 +0000[diff] [blame]3468 Class</a><br>
3469Superclasses: <a href="#GlobalValue"><tt>GlobalValue</tt></a>,
3470<a href="#Constant"><tt>Constant</tt></a>,
3471<a href="#User"><tt>User</tt></a>,
3472<a href="#Value"><tt>Value</tt></a></p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3473
3474<p>Global variables are represented with the (suprise suprise)
3475<tt>GlobalVariable</tt> class. Like functions, <tt>GlobalVariable</tt>s are also
3476subclasses of <a href="#GlobalValue"><tt>GlobalValue</tt></a>, and as such are
3477always referenced by their address (global values must live in memory, so their
Reid Spencerbe5e85e2006-04-14 14:11:48 +0000[diff] [blame]3478"name" refers to their constant address). See
3479<a href="#GlobalValue"><tt>GlobalValue</tt></a> for more on this. Global
3480variables may have an initial value (which must be a
3481<a href="#Constant"><tt>Constant</tt></a>), and if they have an initializer,
3482they may be marked as "constant" themselves (indicating that their contents
3483never change at runtime).</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3484</div>
3485
3486<!-- _______________________________________________________________________ -->
3487<div class="doc_subsubsection">
3488 <a name="m_GlobalVariable">Important Public Members of the
3489 <tt>GlobalVariable</tt> class</a>
3490</div>
3491
3492<div class="doc_text">
3493
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3494<ul>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3495 <li><tt>GlobalVariable(const </tt><tt><a href="#Type">Type</a> *Ty, bool
3496 isConstant, LinkageTypes&amp; Linkage, <a href="#Constant">Constant</a>
3497 *Initializer = 0, const std::string &amp;Name = "", Module* Parent = 0)</tt>
3498
3499 <p>Create a new global variable of the specified type. If
3500 <tt>isConstant</tt> is true then the global variable will be marked as
3501 unchanging for the program. The Linkage parameter specifies the type of
Duncan Sands667d4b82009-03-07 15:45:40 +0000[diff] [blame]3502 linkage (internal, external, weak, linkonce, appending) for the variable.
3503 If the linkage is InternalLinkage, WeakAnyLinkage, WeakODRLinkage,
3504 LinkOnceAnyLinkage or LinkOnceODRLinkage,&nbsp; then the resultant
3505 global variable will have internal linkage. AppendingLinkage concatenates
3506 together all instances (in different translation units) of the variable
3507 into a single variable but is only applicable to arrays. &nbsp;See
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3508 the <a href="LangRef.html#modulestructure">LLVM Language Reference</a> for
3509 further details on linkage types. Optionally an initializer, a name, and the
3510 module to put the variable into may be specified for the global variable as
3511 well.</p></li>
3512
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3513 <li><tt>bool isConstant() const</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3514
3515 <p>Returns true if this is a global variable that is known not to
3516 be modified at runtime.</p></li>
3517
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3518 <li><tt>bool hasInitializer()</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3519
3520 <p>Returns true if this <tt>GlobalVariable</tt> has an intializer.</p></li>
3521
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3522 <li><tt><a href="#Constant">Constant</a> *getInitializer()</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3523
3524 <p>Returns the intial value for a <tt>GlobalVariable</tt>. It is not legal
3525 to call this method if there is no initializer.</p></li>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3526</ul>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3527
3528</div>
3529
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]3530
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3531<!-- ======================================================================= -->
3532<div class="doc_subsection">
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]3533 <a name="BasicBlock">The <tt>BasicBlock</tt> class</a>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3534</div>
3535
3536<div class="doc_text">
3537
3538<p><tt>#include "<a
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]3539href="/doxygen/BasicBlock_8h-source.html">llvm/BasicBlock.h</a>"</tt><br>
3540doxygen info: <a href="/doxygen/structllvm_1_1BasicBlock.html">BasicBlock
3541Class</a><br>
3542Superclass: <a href="#Value"><tt>Value</tt></a></p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3543
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]3544<p>This class represents a single entry multiple exit section of the code,
3545commonly known as a basic block by the compiler community. The
3546<tt>BasicBlock</tt> class maintains a list of <a
3547href="#Instruction"><tt>Instruction</tt></a>s, which form the body of the block.
3548Matching the language definition, the last element of this list of instructions
3549is always a terminator instruction (a subclass of the <a
3550href="#TerminatorInst"><tt>TerminatorInst</tt></a> class).</p>
3551
3552<p>In addition to tracking the list of instructions that make up the block, the
3553<tt>BasicBlock</tt> class also keeps track of the <a
3554href="#Function"><tt>Function</tt></a> that it is embedded into.</p>
3555
3556<p>Note that <tt>BasicBlock</tt>s themselves are <a
3557href="#Value"><tt>Value</tt></a>s, because they are referenced by instructions
3558like branches and can go in the switch tables. <tt>BasicBlock</tt>s have type
3559<tt>label</tt>.</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3560
3561</div>
3562
3563<!-- _______________________________________________________________________ -->
3564<div class="doc_subsubsection">
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]3565 <a name="m_BasicBlock">Important Public Members of the <tt>BasicBlock</tt>
3566 class</a>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3567</div>
3568
3569<div class="doc_text">
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3570<ul>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3571
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]3572<li><tt>BasicBlock(const std::string &amp;Name = "", </tt><tt><a
3573 href="#Function">Function</a> *Parent = 0)</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3574
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]3575<p>The <tt>BasicBlock</tt> constructor is used to create new basic blocks for
3576insertion into a function. The constructor optionally takes a name for the new
3577block, and a <a href="#Function"><tt>Function</tt></a> to insert it into. If
3578the <tt>Parent</tt> parameter is specified, the new <tt>BasicBlock</tt> is
3579automatically inserted at the end of the specified <a
3580href="#Function"><tt>Function</tt></a>, if not specified, the BasicBlock must be
3581manually inserted into the <a href="#Function"><tt>Function</tt></a>.</p></li>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3582
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]3583<li><tt>BasicBlock::iterator</tt> - Typedef for instruction list iterator<br>
3584<tt>BasicBlock::const_iterator</tt> - Typedef for const_iterator.<br>
3585<tt>begin()</tt>, <tt>end()</tt>, <tt>front()</tt>, <tt>back()</tt>,
3586<tt>size()</tt>, <tt>empty()</tt>
3587STL-style functions for accessing the instruction list.
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3588
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]3589<p>These methods and typedefs are forwarding functions that have the same
3590semantics as the standard library methods of the same names. These methods
3591expose the underlying instruction list of a basic block in a way that is easy to
3592manipulate. To get the full complement of container operations (including
3593operations to update the list), you must use the <tt>getInstList()</tt>
3594method.</p></li>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3595
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]3596<li><tt>BasicBlock::InstListType &amp;getInstList()</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3597
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]3598<p>This method is used to get access to the underlying container that actually
3599holds the Instructions. This method must be used when there isn't a forwarding
3600function in the <tt>BasicBlock</tt> class for the operation that you would like
3601to perform. Because there are no forwarding functions for "updating"
3602operations, you need to use this if you want to update the contents of a
3603<tt>BasicBlock</tt>.</p></li>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3604
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]3605<li><tt><a href="#Function">Function</a> *getParent()</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3606
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]3607<p> Returns a pointer to <a href="#Function"><tt>Function</tt></a> the block is
3608embedded into, or a null pointer if it is homeless.</p></li>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3609
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]3610<li><tt><a href="#TerminatorInst">TerminatorInst</a> *getTerminator()</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3611
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]3612<p> Returns a pointer to the terminator instruction that appears at the end of
3613the <tt>BasicBlock</tt>. If there is no terminator instruction, or if the last
3614instruction in the block is not a terminator, then a null pointer is
3615returned.</p></li>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3616
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3617</ul>
3618
3619</div>
3620
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3621
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3622<!-- ======================================================================= -->
3623<div class="doc_subsection">
3624 <a name="Argument">The <tt>Argument</tt> class</a>
3625</div>
3626
3627<div class="doc_text">
3628
3629<p>This subclass of Value defines the interface for incoming formal
Chris Lattner58360822005-01-17 00:12:04 +0000[diff] [blame]3630arguments to a function. A Function maintains a list of its formal
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3631arguments. An argument has a pointer to the parent Function.</p>
3632
3633</div>
3634
Chris Lattner9355b472002-09-06 02:50:58 +0000[diff] [blame]3635<!-- *********************************************************************** -->
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3636<hr>
3637<address>
3638 <a href="http://jigsaw.w3.org/css-validator/check/referer"><img
Misha Brukman44408702008-12-11 17:34:48 +0000[diff] [blame]3639 src="http://jigsaw.w3.org/css-validator/images/vcss-blue" alt="Valid CSS"></a>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3640 <a href="http://validator.w3.org/check/referer"><img
Gabor Greifa9c0f2b2008-06-18 14:05:31 +0000[diff] [blame]3641 src="http://www.w3.org/Icons/valid-html401" alt="Valid HTML 4.01 Strict"></a>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3642
3643 <a href="mailto:dhurjati@cs.uiuc.edu">Dinakar Dhurjati</a> and
3644 <a href="mailto:sabre@nondot.org">Chris Lattner</a><br>
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]3645 <a href="http://llvm.org">The LLVM Compiler Infrastructure</a><br>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3646 Last modified: $Date$
3647</address>
3648
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3649</body>
3650</html>