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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>
Chris Lattnerae7f7592002-09-06 18:31:18 +0000[diff] [blame]120<!--
121 <li>Working with the Control Flow Graph
122 <ul>
123 <li>Accessing predecessors and successors of a <tt>BasicBlock</tt>
124 <li>
125 <li>
126 </ul>
Reid Spencerfe8f4ff2004-11-01 09:02:53 +0000[diff] [blame]127-->
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]128 </ul>
129 </li>
Chris Lattnerd9d6e102005-04-23 16:10:52 +0000[diff] [blame]130
131 <li><a href="#advanced">Advanced Topics</a>
132 <ul>
Chris Lattnerf1b200b2005-04-23 17:27:36 +0000[diff] [blame]133 <li><a href="#TypeResolve">LLVM Type Resolution</a>
134 <ul>
135 <li><a href="#BuildRecType">Basic Recursive Type Construction</a></li>
136 <li><a href="#refineAbstractTypeTo">The <tt>refineAbstractTypeTo</tt> method</a></li>
137 <li><a href="#PATypeHolder">The PATypeHolder Class</a></li>
138 <li><a href="#AbstractTypeUser">The AbstractTypeUser Class</a></li>
139 </ul></li>
140
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]141 <li><a href="#SymbolTable">The <tt>ValueSymbolTable</tt> and <tt>TypeSymbolTable</tt> classes</a></li>
142 <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]143 </ul></li>
144
Joel Stanley9b96c442002-09-06 21:55:13 +0000[diff] [blame]145 <li><a href="#coreclasses">The Core LLVM Class Hierarchy Reference</a>
Chris Lattner9355b472002-09-06 02:50:58 +0000[diff] [blame]146 <ul>
Reid Spencer303c4b42007-01-12 17:26:25 +0000[diff] [blame]147 <li><a href="#Type">The <tt>Type</tt> class</a> </li>
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]148 <li><a href="#Module">The <tt>Module</tt> class</a></li>
Reid Spencerfe8f4ff2004-11-01 09:02:53 +0000[diff] [blame]149 <li><a href="#Value">The <tt>Value</tt> class</a>
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]150 <ul>
151 <li><a href="#User">The <tt>User</tt> class</a>
Chris Lattner9355b472002-09-06 02:50:58 +0000[diff] [blame]152 <ul>
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]153 <li><a href="#Instruction">The <tt>Instruction</tt> class</a></li>
154 <li><a href="#Constant">The <tt>Constant</tt> class</a>
155 <ul>
156 <li><a href="#GlobalValue">The <tt>GlobalValue</tt> class</a>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]157 <ul>
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]158 <li><a href="#Function">The <tt>Function</tt> class</a></li>
159 <li><a href="#GlobalVariable">The <tt>GlobalVariable</tt> class</a></li>
160 </ul>
161 </li>
162 </ul>
163 </li>
Reid Spencerfe8f4ff2004-11-01 09:02:53 +0000[diff] [blame]164 </ul>
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]165 </li>
166 <li><a href="#BasicBlock">The <tt>BasicBlock</tt> class</a></li>
167 <li><a href="#Argument">The <tt>Argument</tt> class</a></li>
168 </ul>
Reid Spencerfe8f4ff2004-11-01 09:02:53 +0000[diff] [blame]169 </li>
170 </ul>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]171 </li>
Chris Lattner9355b472002-09-06 02:50:58 +0000[diff] [blame]172</ol>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]173
Chris Lattner69bf8a92004-05-23 21:06:58 +0000[diff] [blame]174<div class="doc_author">
175 <p>Written by <a href="mailto:sabre@nondot.org">Chris Lattner</a>,
Chris Lattner94c43592004-05-26 16:52:55 +0000[diff] [blame]176 <a href="mailto:dhurjati@cs.uiuc.edu">Dinakar Dhurjati</a>,
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]177 <a href="mailto:ggreif@gmail.com">Gabor Greif</a>,
178 <a href="mailto:jstanley@cs.uiuc.edu">Joel Stanley</a> and
Chris Lattner94c43592004-05-26 16:52:55 +0000[diff] [blame]179 <a href="mailto:rspencer@x10sys.com">Reid Spencer</a></p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]180</div>
181
Chris Lattner9355b472002-09-06 02:50:58 +0000[diff] [blame]182<!-- *********************************************************************** -->
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]183<div class="doc_section">
184 <a name="introduction">Introduction </a>
185</div>
Chris Lattner9355b472002-09-06 02:50:58 +0000[diff] [blame]186<!-- *********************************************************************** -->
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]187
188<div class="doc_text">
189
190<p>This document is meant to highlight some of the important classes and
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]191interfaces available in the LLVM source-base. This manual is not
192intended to explain what LLVM is, how it works, and what LLVM code looks
193like. It assumes that you know the basics of LLVM and are interested
194in writing transformations or otherwise analyzing or manipulating the
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]195code.</p>
196
197<p>This document should get you oriented so that you can find your
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]198way in the continuously growing source code that makes up the LLVM
199infrastructure. Note that this manual is not intended to serve as a
200replacement for reading the source code, so if you think there should be
201a method in one of these classes to do something, but it's not listed,
202check the source. Links to the <a href="/doxygen/">doxygen</a> sources
203are provided to make this as easy as possible.</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]204
205<p>The first section of this document describes general information that is
206useful to know when working in the LLVM infrastructure, and the second describes
207the Core LLVM classes. In the future this manual will be extended with
208information describing how to use extension libraries, such as dominator
209information, CFG traversal routines, and useful utilities like the <tt><a
210href="/doxygen/InstVisitor_8h-source.html">InstVisitor</a></tt> template.</p>
211
212</div>
213
Chris Lattner9355b472002-09-06 02:50:58 +0000[diff] [blame]214<!-- *********************************************************************** -->
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]215<div class="doc_section">
216 <a name="general">General Information</a>
217</div>
218<!-- *********************************************************************** -->
219
220<div class="doc_text">
221
222<p>This section contains general information that is useful if you are working
223in the LLVM source-base, but that isn't specific to any particular API.</p>
224
225</div>
226
227<!-- ======================================================================= -->
228<div class="doc_subsection">
229 <a name="stl">The C++ Standard Template Library</a>
230</div>
231
232<div class="doc_text">
233
234<p>LLVM makes heavy use of the C++ Standard Template Library (STL),
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]235perhaps much more than you are used to, or have seen before. Because of
236this, you might want to do a little background reading in the
237techniques used and capabilities of the library. There are many good
238pages that discuss the STL, and several books on the subject that you
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]239can get, so it will not be discussed in this document.</p>
240
241<p>Here are some useful links:</p>
242
243<ol>
244
245<li><a href="http://www.dinkumware.com/refxcpp.html">Dinkumware C++ Library
246reference</a> - an excellent reference for the STL and other parts of the
247standard C++ library.</li>
248
249<li><a href="http://www.tempest-sw.com/cpp/">C++ In a Nutshell</a> - This is an
Tanya Lattner09cf73c2004-06-22 04:24:55 +0000[diff] [blame]250O'Reilly book in the making. It has a decent
251Standard Library
252Reference that rivals Dinkumware's, and is unfortunately no longer free since the book has been
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]253published.</li>
254
255<li><a href="http://www.parashift.com/c++-faq-lite/">C++ Frequently Asked
256Questions</a></li>
257
258<li><a href="http://www.sgi.com/tech/stl/">SGI's STL Programmer's Guide</a> -
259Contains a useful <a
260href="http://www.sgi.com/tech/stl/stl_introduction.html">Introduction to the
261STL</a>.</li>
262
263<li><a href="http://www.research.att.com/%7Ebs/C++.html">Bjarne Stroustrup's C++
264Page</a></li>
265
Tanya Lattner79445ba2004-12-08 18:34:56 +0000[diff] [blame]266<li><a href="http://64.78.49.204/">
Reid Spencer096603a2004-05-26 08:41:35 +0000[diff] [blame]267Bruce Eckel's Thinking in C++, 2nd ed. Volume 2 Revision 4.0 (even better, get
268the book).</a></li>
269
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]270</ol>
271
272<p>You are also encouraged to take a look at the <a
273href="CodingStandards.html">LLVM Coding Standards</a> guide which focuses on how
274to write maintainable code more than where to put your curly braces.</p>
275
276</div>
277
278<!-- ======================================================================= -->
279<div class="doc_subsection">
280 <a name="stl">Other useful references</a>
281</div>
282
283<div class="doc_text">
284
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]285<ol>
286<li><a href="http://www.psc.edu/%7Esemke/cvs_branches.html">CVS
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]287Branch and Tag Primer</a></li>
Misha Brukmana0f71e42004-06-18 18:39:00 +0000[diff] [blame]288<li><a href="http://www.fortran-2000.com/ArnaudRecipes/sharedlib.html">Using
289static and shared libraries across platforms</a></li>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]290</ol>
291
292</div>
293
Chris Lattner9355b472002-09-06 02:50:58 +0000[diff] [blame]294<!-- *********************************************************************** -->
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]295<div class="doc_section">
296 <a name="apis">Important and useful LLVM APIs</a>
297</div>
298<!-- *********************************************************************** -->
299
300<div class="doc_text">
301
302<p>Here we highlight some LLVM APIs that are generally useful and good to
303know about when writing transformations.</p>
304
305</div>
306
307<!-- ======================================================================= -->
308<div class="doc_subsection">
Misha Brukman2c122ce2005-11-01 21:12:49 +0000[diff] [blame]309 <a name="isa">The <tt>isa&lt;&gt;</tt>, <tt>cast&lt;&gt;</tt> and
310 <tt>dyn_cast&lt;&gt;</tt> templates</a>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]311</div>
312
313<div class="doc_text">
314
315<p>The LLVM source-base makes extensive use of a custom form of RTTI.
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]316These templates have many similarities to the C++ <tt>dynamic_cast&lt;&gt;</tt>
317operator, but they don't have some drawbacks (primarily stemming from
318the fact that <tt>dynamic_cast&lt;&gt;</tt> only works on classes that
319have a v-table). Because they are used so often, you must know what they
320do and how they work. All of these templates are defined in the <a
Chris Lattner695b78b2005-04-26 22:56:16 +0000[diff] [blame]321 href="/doxygen/Casting_8h-source.html"><tt>llvm/Support/Casting.h</tt></a>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]322file (note that you very rarely have to include this file directly).</p>
323
324<dl>
325 <dt><tt>isa&lt;&gt;</tt>: </dt>
326
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]327 <dd><p>The <tt>isa&lt;&gt;</tt> operator works exactly like the Java
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]328 "<tt>instanceof</tt>" operator. It returns true or false depending on whether
329 a reference or pointer points to an instance of the specified class. This can
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]330 be very useful for constraint checking of various sorts (example below).</p>
331 </dd>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]332
333 <dt><tt>cast&lt;&gt;</tt>: </dt>
334
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]335 <dd><p>The <tt>cast&lt;&gt;</tt> operator is a "checked cast" operation. It
Chris Lattner28e6ff52008-06-20 05:03:17 +0000[diff] [blame]336 converts a pointer or reference from a base class to a derived class, causing
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]337 an assertion failure if it is not really an instance of the right type. This
338 should be used in cases where you have some information that makes you believe
339 that something is of the right type. An example of the <tt>isa&lt;&gt;</tt>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]340 and <tt>cast&lt;&gt;</tt> template is:</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]341
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]342<div class="doc_code">
343<pre>
344static bool isLoopInvariant(const <a href="#Value">Value</a> *V, const Loop *L) {
345 if (isa&lt;<a href="#Constant">Constant</a>&gt;(V) || isa&lt;<a href="#Argument">Argument</a>&gt;(V) || isa&lt;<a href="#GlobalValue">GlobalValue</a>&gt;(V))
346 return true;
Chris Lattner69bf8a92004-05-23 21:06:58 +0000[diff] [blame]347
Bill Wendling82e2eea2006-10-11 18:00:22 +0000[diff] [blame]348 // <i>Otherwise, it must be an instruction...</i>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]349 return !L-&gt;contains(cast&lt;<a href="#Instruction">Instruction</a>&gt;(V)-&gt;getParent());
350}
351</pre>
352</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]353
354 <p>Note that you should <b>not</b> use an <tt>isa&lt;&gt;</tt> test followed
355 by a <tt>cast&lt;&gt;</tt>, for that use the <tt>dyn_cast&lt;&gt;</tt>
356 operator.</p>
357
358 </dd>
359
360 <dt><tt>dyn_cast&lt;&gt;</tt>:</dt>
361
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]362 <dd><p>The <tt>dyn_cast&lt;&gt;</tt> operator is a "checking cast" operation.
363 It checks to see if the operand is of the specified type, and if so, returns a
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]364 pointer to it (this operator does not work with references). If the operand is
365 not of the correct type, a null pointer is returned. Thus, this works very
Misha Brukman2c122ce2005-11-01 21:12:49 +0000[diff] [blame]366 much like the <tt>dynamic_cast&lt;&gt;</tt> operator in C++, and should be
367 used in the same circumstances. Typically, the <tt>dyn_cast&lt;&gt;</tt>
368 operator is used in an <tt>if</tt> statement or some other flow control
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]369 statement like this:</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]370
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]371<div class="doc_code">
372<pre>
373if (<a href="#AllocationInst">AllocationInst</a> *AI = dyn_cast&lt;<a href="#AllocationInst">AllocationInst</a>&gt;(Val)) {
Bill Wendling82e2eea2006-10-11 18:00:22 +0000[diff] [blame]374 // <i>...</i>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]375}
376</pre>
377</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]378
Misha Brukman2c122ce2005-11-01 21:12:49 +0000[diff] [blame]379 <p>This form of the <tt>if</tt> statement effectively combines together a call
380 to <tt>isa&lt;&gt;</tt> and a call to <tt>cast&lt;&gt;</tt> into one
381 statement, which is very convenient.</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]382
Misha Brukman2c122ce2005-11-01 21:12:49 +0000[diff] [blame]383 <p>Note that the <tt>dyn_cast&lt;&gt;</tt> operator, like C++'s
384 <tt>dynamic_cast&lt;&gt;</tt> or Java's <tt>instanceof</tt> operator, can be
385 abused. In particular, you should not use big chained <tt>if/then/else</tt>
386 blocks to check for lots of different variants of classes. If you find
387 yourself wanting to do this, it is much cleaner and more efficient to use the
388 <tt>InstVisitor</tt> class to dispatch over the instruction type directly.</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]389
Misha Brukman2c122ce2005-11-01 21:12:49 +0000[diff] [blame]390 </dd>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]391
Misha Brukman2c122ce2005-11-01 21:12:49 +0000[diff] [blame]392 <dt><tt>cast_or_null&lt;&gt;</tt>: </dt>
393
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]394 <dd><p>The <tt>cast_or_null&lt;&gt;</tt> operator works just like the
Misha Brukman2c122ce2005-11-01 21:12:49 +0000[diff] [blame]395 <tt>cast&lt;&gt;</tt> operator, except that it allows for a null pointer as an
396 argument (which it then propagates). This can sometimes be useful, allowing
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]397 you to combine several null checks into one.</p></dd>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]398
Misha Brukman2c122ce2005-11-01 21:12:49 +0000[diff] [blame]399 <dt><tt>dyn_cast_or_null&lt;&gt;</tt>: </dt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]400
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]401 <dd><p>The <tt>dyn_cast_or_null&lt;&gt;</tt> operator works just like the
Misha Brukman2c122ce2005-11-01 21:12:49 +0000[diff] [blame]402 <tt>dyn_cast&lt;&gt;</tt> operator, except that it allows for a null pointer
403 as an argument (which it then propagates). This can sometimes be useful,
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]404 allowing you to combine several null checks into one.</p></dd>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]405
Misha Brukman2c122ce2005-11-01 21:12:49 +0000[diff] [blame]406</dl>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]407
408<p>These five templates can be used with any classes, whether they have a
409v-table or not. To add support for these templates, you simply need to add
410<tt>classof</tt> static methods to the class you are interested casting
411to. Describing this is currently outside the scope of this document, but there
412are lots of examples in the LLVM source base.</p>
413
414</div>
415
416<!-- ======================================================================= -->
417<div class="doc_subsection">
Misha Brukman2c122ce2005-11-01 21:12:49 +0000[diff] [blame]418 <a name="DEBUG">The <tt>DEBUG()</tt> macro and <tt>-debug</tt> option</a>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]419</div>
420
421<div class="doc_text">
422
423<p>Often when working on your pass you will put a bunch of debugging printouts
424and other code into your pass. After you get it working, you want to remove
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]425it, but you may need it again in the future (to work out new bugs that you run
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]426across).</p>
427
428<p> Naturally, because of this, you don't want to delete the debug printouts,
429but you don't want them to always be noisy. A standard compromise is to comment
430them out, allowing you to enable them if you need them in the future.</p>
431
Chris Lattner695b78b2005-04-26 22:56:16 +0000[diff] [blame]432<p>The "<tt><a href="/doxygen/Debug_8h-source.html">llvm/Support/Debug.h</a></tt>"
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]433file provides a macro named <tt>DEBUG()</tt> that is a much nicer solution to
434this problem. Basically, you can put arbitrary code into the argument of the
435<tt>DEBUG</tt> macro, and it is only executed if '<tt>opt</tt>' (or any other
436tool) is run with the '<tt>-debug</tt>' command line argument:</p>
437
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]438<div class="doc_code">
439<pre>
Bill Wendling832171c2006-12-07 20:04:42 +0000[diff] [blame]440DOUT &lt;&lt; "I am here!\n";
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]441</pre>
442</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]443
444<p>Then you can run your pass like this:</p>
445
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]446<div class="doc_code">
447<pre>
448$ opt &lt; a.bc &gt; /dev/null -mypass
Bill Wendling82e2eea2006-10-11 18:00:22 +0000[diff] [blame]449<i>&lt;no output&gt;</i>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]450$ opt &lt; a.bc &gt; /dev/null -mypass -debug
451I am here!
452</pre>
453</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]454
455<p>Using the <tt>DEBUG()</tt> macro instead of a home-brewed solution allows you
456to not have to create "yet another" command line option for the debug output for
457your pass. Note that <tt>DEBUG()</tt> macros are disabled for optimized builds,
458so they do not cause a performance impact at all (for the same reason, they
459should also not contain side-effects!).</p>
460
461<p>One additional nice thing about the <tt>DEBUG()</tt> macro is that you can
462enable or disable it directly in gdb. Just use "<tt>set DebugFlag=0</tt>" or
463"<tt>set DebugFlag=1</tt>" from the gdb if the program is running. If the
464program hasn't been started yet, you can always just run it with
465<tt>-debug</tt>.</p>
466
467</div>
468
469<!-- _______________________________________________________________________ -->
470<div class="doc_subsubsection">
Chris Lattnerc9151082005-04-26 22:57:07 +0000[diff] [blame]471 <a name="DEBUG_TYPE">Fine grained debug info with <tt>DEBUG_TYPE</tt> and
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]472 the <tt>-debug-only</tt> option</a>
473</div>
474
475<div class="doc_text">
476
477<p>Sometimes you may find yourself in a situation where enabling <tt>-debug</tt>
478just turns on <b>too much</b> information (such as when working on the code
479generator). If you want to enable debug information with more fine-grained
480control, you define the <tt>DEBUG_TYPE</tt> macro and the <tt>-debug</tt> only
481option as follows:</p>
482
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]483<div class="doc_code">
484<pre>
Bill Wendling832171c2006-12-07 20:04:42 +0000[diff] [blame]485DOUT &lt;&lt; "No debug type\n";
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]486#undef DEBUG_TYPE
487#define DEBUG_TYPE "foo"
Bill Wendling832171c2006-12-07 20:04:42 +0000[diff] [blame]488DOUT &lt;&lt; "'foo' debug type\n";
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]489#undef DEBUG_TYPE
490#define DEBUG_TYPE "bar"
Bill Wendling832171c2006-12-07 20:04:42 +0000[diff] [blame]491DOUT &lt;&lt; "'bar' debug type\n";
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]492#undef DEBUG_TYPE
493#define DEBUG_TYPE ""
Bill Wendling832171c2006-12-07 20:04:42 +0000[diff] [blame]494DOUT &lt;&lt; "No debug type (2)\n";
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]495</pre>
496</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]497
498<p>Then you can run your pass like this:</p>
499
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]500<div class="doc_code">
501<pre>
502$ opt &lt; a.bc &gt; /dev/null -mypass
Bill Wendling82e2eea2006-10-11 18:00:22 +0000[diff] [blame]503<i>&lt;no output&gt;</i>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]504$ opt &lt; a.bc &gt; /dev/null -mypass -debug
505No debug type
506'foo' debug type
507'bar' debug type
508No debug type (2)
509$ opt &lt; a.bc &gt; /dev/null -mypass -debug-only=foo
510'foo' debug type
511$ opt &lt; a.bc &gt; /dev/null -mypass -debug-only=bar
512'bar' debug type
513</pre>
514</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]515
516<p>Of course, in practice, you should only set <tt>DEBUG_TYPE</tt> at the top of
517a file, to specify the debug type for the entire module (if you do this before
Chris Lattner695b78b2005-04-26 22:56:16 +0000[diff] [blame]518you <tt>#include "llvm/Support/Debug.h"</tt>, you don't have to insert the ugly
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]519<tt>#undef</tt>'s). Also, you should use names more meaningful than "foo" and
520"bar", because there is no system in place to ensure that names do not
521conflict. If two different modules use the same string, they will all be turned
522on when the name is specified. This allows, for example, all debug information
523for instruction scheduling to be enabled with <tt>-debug-type=InstrSched</tt>,
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]524even if the source lives in multiple files.</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]525
526</div>
527
528<!-- ======================================================================= -->
529<div class="doc_subsection">
Chris Lattner0be6fdf2006-12-19 21:46:21 +0000[diff] [blame]530 <a name="Statistic">The <tt>Statistic</tt> class &amp; <tt>-stats</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]531 option</a>
532</div>
533
534<div class="doc_text">
535
536<p>The "<tt><a
Chris Lattner695b78b2005-04-26 22:56:16 +0000[diff] [blame]537href="/doxygen/Statistic_8h-source.html">llvm/ADT/Statistic.h</a></tt>" file
Chris Lattner0be6fdf2006-12-19 21:46:21 +0000[diff] [blame]538provides a class named <tt>Statistic</tt> that is used as a unified way to
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]539keep track of what the LLVM compiler is doing and how effective various
540optimizations are. It is useful to see what optimizations are contributing to
541making a particular program run faster.</p>
542
543<p>Often you may run your pass on some big program, and you're interested to see
544how many times it makes a certain transformation. Although you can do this with
545hand inspection, or some ad-hoc method, this is a real pain and not very useful
Chris Lattner0be6fdf2006-12-19 21:46:21 +0000[diff] [blame]546for big programs. Using the <tt>Statistic</tt> class makes it very easy to
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]547keep track of this information, and the calculated information is presented in a
548uniform manner with the rest of the passes being executed.</p>
549
550<p>There are many examples of <tt>Statistic</tt> uses, but the basics of using
551it are as follows:</p>
552
553<ol>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]554 <li><p>Define your statistic like this:</p>
555
556<div class="doc_code">
557<pre>
Chris Lattner0be6fdf2006-12-19 21:46:21 +0000[diff] [blame]558#define <a href="#DEBUG_TYPE">DEBUG_TYPE</a> "mypassname" <i>// This goes before any #includes.</i>
559STATISTIC(NumXForms, "The # of times I did stuff");
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]560</pre>
561</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]562
Chris Lattner0be6fdf2006-12-19 21:46:21 +0000[diff] [blame]563 <p>The <tt>STATISTIC</tt> macro defines a static variable, whose name is
564 specified by the first argument. The pass name is taken from the DEBUG_TYPE
565 macro, and the description is taken from the second argument. The variable
Reid Spencer06565dc2007-01-12 17:11:23 +0000[diff] [blame]566 defined ("NumXForms" in this case) acts like an unsigned integer.</p></li>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]567
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]568 <li><p>Whenever you make a transformation, bump the counter:</p>
569
570<div class="doc_code">
571<pre>
Bill Wendling82e2eea2006-10-11 18:00:22 +0000[diff] [blame]572++NumXForms; // <i>I did stuff!</i>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]573</pre>
574</div>
575
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]576 </li>
577 </ol>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]578
579 <p>That's all you have to do. To get '<tt>opt</tt>' to print out the
580 statistics gathered, use the '<tt>-stats</tt>' option:</p>
581
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]582<div class="doc_code">
583<pre>
584$ opt -stats -mypassname &lt; program.bc &gt; /dev/null
Bill Wendling82e2eea2006-10-11 18:00:22 +0000[diff] [blame]585<i>... statistics output ...</i>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]586</pre>
587</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]588
Reid Spencer6b6c73e2007-02-09 16:00:28 +0000[diff] [blame]589 <p> When running <tt>opt</tt> on a C file from the SPEC benchmark
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]590suite, it gives a report that looks like this:</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]591
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]592<div class="doc_code">
593<pre>
Gabor Greif04367bf2007-07-06 22:07:22 +0000[diff] [blame]594 7646 bitcodewriter - Number of normal instructions
595 725 bitcodewriter - Number of oversized instructions
596 129996 bitcodewriter - Number of bitcode bytes written
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]597 2817 raise - Number of insts DCEd or constprop'd
598 3213 raise - Number of cast-of-self removed
599 5046 raise - Number of expression trees converted
600 75 raise - Number of other getelementptr's formed
601 138 raise - Number of load/store peepholes
602 42 deadtypeelim - Number of unused typenames removed from symtab
603 392 funcresolve - Number of varargs functions resolved
604 27 globaldce - Number of global variables removed
605 2 adce - Number of basic blocks removed
606 134 cee - Number of branches revectored
607 49 cee - Number of setcc instruction eliminated
608 532 gcse - Number of loads removed
609 2919 gcse - Number of instructions removed
610 86 indvars - Number of canonical indvars added
611 87 indvars - Number of aux indvars removed
612 25 instcombine - Number of dead inst eliminate
613 434 instcombine - Number of insts combined
614 248 licm - Number of load insts hoisted
615 1298 licm - Number of insts hoisted to a loop pre-header
616 3 licm - Number of insts hoisted to multiple loop preds (bad, no loop pre-header)
617 75 mem2reg - Number of alloca's promoted
618 1444 cfgsimplify - Number of blocks simplified
619</pre>
620</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]621
622<p>Obviously, with so many optimizations, having a unified framework for this
623stuff is very nice. Making your pass fit well into the framework makes it more
624maintainable and useful.</p>
625
626</div>
627
Chris Lattnerf623a082005-10-17 01:36:23 +0000[diff] [blame]628<!-- ======================================================================= -->
629<div class="doc_subsection">
630 <a name="ViewGraph">Viewing graphs while debugging code</a>
631</div>
632
633<div class="doc_text">
634
635<p>Several of the important data structures in LLVM are graphs: for example
636CFGs made out of LLVM <a href="#BasicBlock">BasicBlock</a>s, CFGs made out of
637LLVM <a href="CodeGenerator.html#machinebasicblock">MachineBasicBlock</a>s, and
638<a href="CodeGenerator.html#selectiondag_intro">Instruction Selection
639DAGs</a>. In many cases, while debugging various parts of the compiler, it is
640nice to instantly visualize these graphs.</p>
641
642<p>LLVM provides several callbacks that are available in a debug build to do
643exactly that. If you call the <tt>Function::viewCFG()</tt> method, for example,
644the current LLVM tool will pop up a window containing the CFG for the function
645where each basic block is a node in the graph, and each node contains the
646instructions in the block. Similarly, there also exists
647<tt>Function::viewCFGOnly()</tt> (does not include the instructions), the
648<tt>MachineFunction::viewCFG()</tt> and <tt>MachineFunction::viewCFGOnly()</tt>,
649and the <tt>SelectionDAG::viewGraph()</tt> methods. Within GDB, for example,
Jim Laskey543a0ee2006-10-02 12:28:07 +0000[diff] [blame]650you can usually use something like <tt>call DAG.viewGraph()</tt> to pop
Chris Lattnerf623a082005-10-17 01:36:23 +0000[diff] [blame]651up a window. Alternatively, you can sprinkle calls to these functions in your
652code in places you want to debug.</p>
653
654<p>Getting this to work requires a small amount of configuration. On Unix
655systems with X11, install the <a href="http://www.graphviz.org">graphviz</a>
656toolkit, and make sure 'dot' and 'gv' are in your path. If you are running on
657Mac OS/X, download and install the Mac OS/X <a
658href="http://www.pixelglow.com/graphviz/">Graphviz program</a>, and add
Reid Spencer128a7a72007-02-03 21:06:43 +0000[diff] [blame]659<tt>/Applications/Graphviz.app/Contents/MacOS/</tt> (or wherever you install
Chris Lattnerf623a082005-10-17 01:36:23 +0000[diff] [blame]660it) to your path. Once in your system and path are set up, rerun the LLVM
661configure script and rebuild LLVM to enable this functionality.</p>
662
Jim Laskey543a0ee2006-10-02 12:28:07 +0000[diff] [blame]663<p><tt>SelectionDAG</tt> has been extended to make it easier to locate
664<i>interesting</i> nodes in large complex graphs. From gdb, if you
665<tt>call DAG.setGraphColor(<i>node</i>, "<i>color</i>")</tt>, then the
Reid Spencer128a7a72007-02-03 21:06:43 +0000[diff] [blame]666next <tt>call DAG.viewGraph()</tt> would highlight the node in the
Jim Laskey543a0ee2006-10-02 12:28:07 +0000[diff] [blame]667specified color (choices of colors can be found at <a
Chris Lattner302da1e2007-02-03 03:05:57 +0000[diff] [blame]668href="http://www.graphviz.org/doc/info/colors.html">colors</a>.) More
Jim Laskey543a0ee2006-10-02 12:28:07 +0000[diff] [blame]669complex node attributes can be provided with <tt>call
670DAG.setGraphAttrs(<i>node</i>, "<i>attributes</i>")</tt> (choices can be
671found at <a href="http://www.graphviz.org/doc/info/attrs.html">Graph
672Attributes</a>.) If you want to restart and clear all the current graph
673attributes, then you can <tt>call DAG.clearGraphAttrs()</tt>. </p>
674
Chris Lattnerf623a082005-10-17 01:36:23 +0000[diff] [blame]675</div>
676
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]677<!-- *********************************************************************** -->
678<div class="doc_section">
679 <a name="datastructure">Picking the Right Data Structure for a Task</a>
680</div>
681<!-- *********************************************************************** -->
682
683<div class="doc_text">
684
Reid Spencer128a7a72007-02-03 21:06:43 +0000[diff] [blame]685<p>LLVM has a plethora of data structures in the <tt>llvm/ADT/</tt> directory,
686 and we commonly use STL data structures. This section describes the trade-offs
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]687 you should consider when you pick one.</p>
688
689<p>
690The first step is a choose your own adventure: do you want a sequential
691container, a set-like container, or a map-like container? The most important
692thing when choosing a container is the algorithmic properties of how you plan to
693access the container. Based on that, you should use:</p>
694
695<ul>
Reid Spencer128a7a72007-02-03 21:06:43 +0000[diff] [blame]696<li>a <a href="#ds_map">map-like</a> container if you need efficient look-up
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]697 of an value based on another value. Map-like containers also support
698 efficient queries for containment (whether a key is in the map). Map-like
699 containers generally do not support efficient reverse mapping (values to
700 keys). If you need that, use two maps. Some map-like containers also
701 support efficient iteration through the keys in sorted order. Map-like
702 containers are the most expensive sort, only use them if you need one of
703 these capabilities.</li>
704
705<li>a <a href="#ds_set">set-like</a> container if you need to put a bunch of
706 stuff into a container that automatically eliminates duplicates. Some
707 set-like containers support efficient iteration through the elements in
708 sorted order. Set-like containers are more expensive than sequential
709 containers.
710</li>
711
712<li>a <a href="#ds_sequential">sequential</a> container provides
713 the most efficient way to add elements and keeps track of the order they are
714 added to the collection. They permit duplicates and support efficient
Reid Spencer128a7a72007-02-03 21:06:43 +0000[diff] [blame]715 iteration, but do not support efficient look-up based on a key.
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]716</li>
717
Daniel Berlin1939ace2007-09-24 17:52:25 +0000[diff] [blame]718<li>a <a href="#ds_bit">bit</a> container provides an efficient way to store and
719 perform set operations on sets of numeric id's, while automatically
720 eliminating duplicates. Bit containers require a maximum of 1 bit for each
721 identifier you want to store.
722</li>
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]723</ul>
724
725<p>
Reid Spencer128a7a72007-02-03 21:06:43 +0000[diff] [blame]726Once the proper category of container is determined, you can fine tune the
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]727memory use, constant factors, and cache behaviors of access by intelligently
Reid Spencer128a7a72007-02-03 21:06:43 +0000[diff] [blame]728picking a member of the category. Note that constant factors and cache behavior
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]729can be a big deal. If you have a vector that usually only contains a few
730elements (but could contain many), for example, it's much better to use
731<a href="#dss_smallvector">SmallVector</a> than <a href="#dss_vector">vector</a>
732. Doing so avoids (relatively) expensive malloc/free calls, which dwarf the
733cost of adding the elements to the container. </p>
734
735</div>
736
737<!-- ======================================================================= -->
738<div class="doc_subsection">
739 <a name="ds_sequential">Sequential Containers (std::vector, std::list, etc)</a>
740</div>
741
742<div class="doc_text">
743There are a variety of sequential containers available for you, based on your
744needs. Pick the first in this section that will do what you want.
745</div>
746
747<!-- _______________________________________________________________________ -->
748<div class="doc_subsubsection">
749 <a name="dss_fixedarrays">Fixed Size Arrays</a>
750</div>
751
752<div class="doc_text">
753<p>Fixed size arrays are very simple and very fast. They are good if you know
754exactly how many elements you have, or you have a (low) upper bound on how many
755you have.</p>
756</div>
757
758<!-- _______________________________________________________________________ -->
759<div class="doc_subsubsection">
760 <a name="dss_heaparrays">Heap Allocated Arrays</a>
761</div>
762
763<div class="doc_text">
764<p>Heap allocated arrays (new[] + delete[]) are also simple. They are good if
765the number of elements is variable, if you know how many elements you will need
766before the array is allocated, and if the array is usually large (if not,
767consider a <a href="#dss_smallvector">SmallVector</a>). The cost of a heap
768allocated array is the cost of the new/delete (aka malloc/free). Also note that
769if you are allocating an array of a type with a constructor, the constructor and
Reid Spencer128a7a72007-02-03 21:06:43 +0000[diff] [blame]770destructors will be run for every element in the array (re-sizable vectors only
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]771construct those elements actually used).</p>
772</div>
773
774<!-- _______________________________________________________________________ -->
775<div class="doc_subsubsection">
776 <a name="dss_smallvector">"llvm/ADT/SmallVector.h"</a>
777</div>
778
779<div class="doc_text">
780<p><tt>SmallVector&lt;Type, N&gt;</tt> is a simple class that looks and smells
781just like <tt>vector&lt;Type&gt;</tt>:
782it supports efficient iteration, lays out elements in memory order (so you can
783do pointer arithmetic between elements), supports efficient push_back/pop_back
784operations, supports efficient random access to its elements, etc.</p>
785
786<p>The advantage of SmallVector is that it allocates space for
787some number of elements (N) <b>in the object itself</b>. Because of this, if
788the SmallVector is dynamically smaller than N, no malloc is performed. This can
789be a big win in cases where the malloc/free call is far more expensive than the
790code that fiddles around with the elements.</p>
791
792<p>This is good for vectors that are "usually small" (e.g. the number of
793predecessors/successors of a block is usually less than 8). On the other hand,
794this makes the size of the SmallVector itself large, so you don't want to
795allocate lots of them (doing so will waste a lot of space). As such,
796SmallVectors are most useful when on the stack.</p>
797
798<p>SmallVector also provides a nice portable and efficient replacement for
799<tt>alloca</tt>.</p>
800
801</div>
802
803<!-- _______________________________________________________________________ -->
804<div class="doc_subsubsection">
805 <a name="dss_vector">&lt;vector&gt;</a>
806</div>
807
808<div class="doc_text">
809<p>
810std::vector is well loved and respected. It is useful when SmallVector isn't:
811when the size of the vector is often large (thus the small optimization will
812rarely be a benefit) or if you will be allocating many instances of the vector
813itself (which would waste space for elements that aren't in the container).
814vector is also useful when interfacing with code that expects vectors :).
815</p>
Chris Lattner32d84762007-02-05 06:30:51 +0000[diff] [blame]816
817<p>One worthwhile note about std::vector: avoid code like this:</p>
818
819<div class="doc_code">
820<pre>
821for ( ... ) {
Chris Lattner9bb3dbb2007-03-28 18:27:57 +0000[diff] [blame]822 std::vector&lt;foo&gt; V;
Chris Lattner32d84762007-02-05 06:30:51 +0000[diff] [blame]823 use V;
824}
825</pre>
826</div>
827
828<p>Instead, write this as:</p>
829
830<div class="doc_code">
831<pre>
Chris Lattner9bb3dbb2007-03-28 18:27:57 +0000[diff] [blame]832std::vector&lt;foo&gt; V;
Chris Lattner32d84762007-02-05 06:30:51 +0000[diff] [blame]833for ( ... ) {
834 use V;
835 V.clear();
836}
837</pre>
838</div>
839
840<p>Doing so will save (at least) one heap allocation and free per iteration of
841the loop.</p>
842
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]843</div>
844
845<!-- _______________________________________________________________________ -->
846<div class="doc_subsubsection">
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]847 <a name="dss_deque">&lt;deque&gt;</a>
848</div>
849
850<div class="doc_text">
851<p>std::deque is, in some senses, a generalized version of std::vector. Like
852std::vector, it provides constant time random access and other similar
853properties, but it also provides efficient access to the front of the list. It
854does not guarantee continuity of elements within memory.</p>
855
856<p>In exchange for this extra flexibility, std::deque has significantly higher
857constant factor costs than std::vector. If possible, use std::vector or
858something cheaper.</p>
859</div>
860
861<!-- _______________________________________________________________________ -->
862<div class="doc_subsubsection">
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]863 <a name="dss_list">&lt;list&gt;</a>
864</div>
865
866<div class="doc_text">
867<p>std::list is an extremely inefficient class that is rarely useful.
868It performs a heap allocation for every element inserted into it, thus having an
869extremely high constant factor, particularly for small data types. std::list
870also only supports bidirectional iteration, not random access iteration.</p>
871
872<p>In exchange for this high cost, std::list supports efficient access to both
873ends of the list (like std::deque, but unlike std::vector or SmallVector). In
874addition, the iterator invalidation characteristics of std::list are stronger
875than that of a vector class: inserting or removing an element into the list does
876not invalidate iterator or pointers to other elements in the list.</p>
877</div>
878
879<!-- _______________________________________________________________________ -->
880<div class="doc_subsubsection">
Gabor Greif3899e492009-02-27 11:37:41 +0000[diff] [blame]881 <a name="dss_ilist">llvm/ADT/ilist.h</a>
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]882</div>
883
884<div class="doc_text">
885<p><tt>ilist&lt;T&gt;</tt> implements an 'intrusive' doubly-linked list. It is
886intrusive, because it requires the element to store and provide access to the
887prev/next pointers for the list.</p>
888
Gabor Greif2946d1c2009-02-27 12:02:19 +0000[diff] [blame^]889<p><tt>ilist</tt> has the same drawbacks as <tt>std::list</tt>, and additionally
890requires an <tt>ilist_traits</tt> implementation for the element type, but it
891provides some novel characteristics. In particular, it can efficiently store
892polymorphic objects, the traits class is informed when an element is inserted or
893removed from the list, and ilists are guaranteed to support a constant-time splice
894operation.</p>
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]895
Gabor Greif2946d1c2009-02-27 12:02:19 +0000[diff] [blame^]896<p>These properties are exactly what we want for things like <tt>Instruction</tt>s
897and basic blocks, which is why these are implemented with <tt>ilist</tt>s.</p>
Gabor Greif3899e492009-02-27 11:37:41 +0000[diff] [blame]898
899Related classes of interest are explained in the following subsections:
900 <ul>
Gabor Greif2946d1c2009-02-27 12:02:19 +0000[diff] [blame^]901 <li><a href="#dss_iplist">iplist</a></li>
Gabor Greif3899e492009-02-27 11:37:41 +0000[diff] [blame]902 <li><a href="#dss_ilist_node">llvm/ADT/ilist_node.h</a></li>
903 </ul>
904</div>
905
906<!-- _______________________________________________________________________ -->
907<div class="doc_subsubsection">
Gabor Greif2946d1c2009-02-27 12:02:19 +0000[diff] [blame^]908 <a name="dss_iplist">iplist</a>
909</div>
910
911<div class="doc_text">
912<p><tt>iplist&lt;T&gt;</tt> is <tt>ilist&lt;T&gt;</tt>'s base and as such
913supports a slightly narrower interface. Notably, inserters from <tt>T&amp;</tt>
914are absent.</p>
915</div>
916
917<!-- _______________________________________________________________________ -->
918<div class="doc_subsubsection">
Gabor Greif3899e492009-02-27 11:37:41 +0000[diff] [blame]919 <a name="dss_ilist_node">llvm/ADT/ilist_node.h</a>
920</div>
921
922<div class="doc_text">
923<p><tt>ilist_node&lt;T&gt;</tt> implements a the forward and backward links
924that are expected by the <tt>ilist&lt;T&gt;</tt> (and analogous containers)
925in the default manner.</p>
926
927<p><tt>ilist_node&lt;T&gt;</tt>s are meant to be embedded in the node type
928<tt>T</tt>.</p>
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]929</div>
930
931<!-- _______________________________________________________________________ -->
932<div class="doc_subsubsection">
Chris Lattnerc5722432007-02-03 19:49:31 +0000[diff] [blame]933 <a name="dss_other">Other Sequential Container options</a>
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]934</div>
935
936<div class="doc_text">
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]937<p>Other STL containers are available, such as std::string.</p>
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]938
939<p>There are also various STL adapter classes such as std::queue,
940std::priority_queue, std::stack, etc. These provide simplified access to an
941underlying container but don't affect the cost of the container itself.</p>
942
943</div>
944
945
946<!-- ======================================================================= -->
947<div class="doc_subsection">
948 <a name="ds_set">Set-Like Containers (std::set, SmallSet, SetVector, etc)</a>
949</div>
950
951<div class="doc_text">
952
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]953<p>Set-like containers are useful when you need to canonicalize multiple values
954into a single representation. There are several different choices for how to do
955this, providing various trade-offs.</p>
956
957</div>
958
959
960<!-- _______________________________________________________________________ -->
961<div class="doc_subsubsection">
962 <a name="dss_sortedvectorset">A sorted 'vector'</a>
963</div>
964
965<div class="doc_text">
966
Chris Lattner3b23a8c2007-02-03 08:10:45 +0000[diff] [blame]967<p>If you intend to insert a lot of elements, then do a lot of queries, a
968great approach is to use a vector (or other sequential container) with
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]969std::sort+std::unique to remove duplicates. This approach works really well if
Chris Lattner3b23a8c2007-02-03 08:10:45 +0000[diff] [blame]970your usage pattern has these two distinct phases (insert then query), and can be
971coupled with a good choice of <a href="#ds_sequential">sequential container</a>.
972</p>
973
974<p>
975This combination provides the several nice properties: the result data is
976contiguous in memory (good for cache locality), has few allocations, is easy to
977address (iterators in the final vector are just indices or pointers), and can be
978efficiently queried with a standard binary or radix search.</p>
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]979
980</div>
981
982<!-- _______________________________________________________________________ -->
983<div class="doc_subsubsection">
984 <a name="dss_smallset">"llvm/ADT/SmallSet.h"</a>
985</div>
986
987<div class="doc_text">
988
Reid Spencer128a7a72007-02-03 21:06:43 +0000[diff] [blame]989<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]990are 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]991has space for N elements in place (thus, if the set is dynamically smaller than
Chris Lattner14868db2007-02-03 08:20:15 +0000[diff] [blame]992N, no malloc traffic is required) and accesses them with a simple linear search.
993When the set grows beyond 'N' elements, it allocates a more expensive representation that
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]994guarantees efficient access (for most types, it falls back to std::set, but for
Chris Lattner14868db2007-02-03 08:20:15 +0000[diff] [blame]995pointers it uses something far better, <a
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]996href="#dss_smallptrset">SmallPtrSet</a>).</p>
997
998<p>The magic of this class is that it handles small sets extremely efficiently,
999but gracefully handles extremely large sets without loss of efficiency. The
1000drawback is that the interface is quite small: it supports insertion, queries
1001and erasing, but does not support iteration.</p>
1002
1003</div>
1004
1005<!-- _______________________________________________________________________ -->
1006<div class="doc_subsubsection">
1007 <a name="dss_smallptrset">"llvm/ADT/SmallPtrSet.h"</a>
1008</div>
1009
1010<div class="doc_text">
1011
1012<p>SmallPtrSet has all the advantages of SmallSet (and a SmallSet of pointers is
Reid Spencer128a7a72007-02-03 21:06:43 +0000[diff] [blame]1013transparently implemented with a SmallPtrSet), but also supports iterators. If
Chris Lattner14868db2007-02-03 08:20:15 +0000[diff] [blame]1014more than 'N' insertions are performed, a single quadratically
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1015probed hash table is allocated and grows as needed, providing extremely
1016efficient access (constant time insertion/deleting/queries with low constant
1017factors) and is very stingy with malloc traffic.</p>
1018
1019<p>Note that, unlike std::set, the iterators of SmallPtrSet are invalidated
1020whenever an insertion occurs. Also, the values visited by the iterators are not
1021visited in sorted order.</p>
1022
1023</div>
1024
1025<!-- _______________________________________________________________________ -->
1026<div class="doc_subsubsection">
Chris Lattnerc28476f2007-09-30 00:58:59 +0000[diff] [blame]1027 <a name="dss_denseset">"llvm/ADT/DenseSet.h"</a>
1028</div>
1029
1030<div class="doc_text">
1031
1032<p>
1033DenseSet is a simple quadratically probed hash table. It excels at supporting
1034small values: it uses a single allocation to hold all of the pairs that
1035are currently inserted in the set. DenseSet is a great way to unique small
1036values that are not simple pointers (use <a
1037href="#dss_smallptrset">SmallPtrSet</a> for pointers). Note that DenseSet has
1038the same requirements for the value type that <a
1039href="#dss_densemap">DenseMap</a> has.
1040</p>
1041
1042</div>
1043
1044<!-- _______________________________________________________________________ -->
1045<div class="doc_subsubsection">
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1046 <a name="dss_FoldingSet">"llvm/ADT/FoldingSet.h"</a>
1047</div>
1048
1049<div class="doc_text">
1050
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]1051<p>
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1052FoldingSet is an aggregate class that is really good at uniquing
1053expensive-to-create or polymorphic objects. It is a combination of a chained
1054hash table with intrusive links (uniqued objects are required to inherit from
Chris Lattner14868db2007-02-03 08:20:15 +0000[diff] [blame]1055FoldingSetNode) that uses <a href="#dss_smallvector">SmallVector</a> as part of
1056its ID process.</p>
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1057
Chris Lattner14868db2007-02-03 08:20:15 +0000[diff] [blame]1058<p>Consider a case where you want to implement a "getOrCreateFoo" method for
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1059a complex object (for example, a node in the code generator). The client has a
1060description of *what* it wants to generate (it knows the opcode and all the
1061operands), 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]1062only to find out it already exists, at which point we would have to delete it
1063and return the node that already exists.
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]1064</p>
1065
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1066<p>To support this style of client, FoldingSet perform a query with a
1067FoldingSetNodeID (which wraps SmallVector) that can be used to describe the
1068element that we want to query for. The query either returns the element
1069matching the ID or it returns an opaque ID that indicates where insertion should
Chris Lattner14868db2007-02-03 08:20:15 +0000[diff] [blame]1070take place. Construction of the ID usually does not require heap traffic.</p>
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1071
1072<p>Because FoldingSet uses intrusive links, it can support polymorphic objects
1073in the set (for example, you can have SDNode instances mixed with LoadSDNodes).
1074Because the elements are individually allocated, pointers to the elements are
1075stable: inserting or removing elements does not invalidate any pointers to other
1076elements.
1077</p>
1078
1079</div>
1080
1081<!-- _______________________________________________________________________ -->
1082<div class="doc_subsubsection">
1083 <a name="dss_set">&lt;set&gt;</a>
1084</div>
1085
1086<div class="doc_text">
1087
Chris Lattnerc5722432007-02-03 19:49:31 +0000[diff] [blame]1088<p><tt>std::set</tt> is a reasonable all-around set class, which is decent at
1089many things but great at nothing. std::set allocates memory for each element
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1090inserted (thus it is very malloc intensive) and typically stores three pointers
Chris Lattner14868db2007-02-03 08:20:15 +0000[diff] [blame]1091per element in the set (thus adding a large amount of per-element space
1092overhead). It offers guaranteed log(n) performance, which is not particularly
Chris Lattnerc5722432007-02-03 19:49:31 +0000[diff] [blame]1093fast from a complexity standpoint (particularly if the elements of the set are
1094expensive to compare, like strings), and has extremely high constant factors for
1095lookup, insertion and removal.</p>
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1096
Chris Lattner14868db2007-02-03 08:20:15 +0000[diff] [blame]1097<p>The advantages of std::set are that its iterators are stable (deleting or
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1098inserting an element from the set does not affect iterators or pointers to other
1099elements) and that iteration over the set is guaranteed to be in sorted order.
1100If the elements in the set are large, then the relative overhead of the pointers
1101and malloc traffic is not a big deal, but if the elements of the set are small,
1102std::set is almost never a good choice.</p>
1103
1104</div>
1105
1106<!-- _______________________________________________________________________ -->
1107<div class="doc_subsubsection">
1108 <a name="dss_setvector">"llvm/ADT/SetVector.h"</a>
1109</div>
1110
1111<div class="doc_text">
Chris Lattneredca3c52007-02-04 00:00:26 +0000[diff] [blame]1112<p>LLVM's SetVector&lt;Type&gt; is an adapter class that combines your choice of
1113a set-like container along with a <a href="#ds_sequential">Sequential
1114Container</a>. The important property
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1115that this provides is efficient insertion with uniquing (duplicate elements are
1116ignored) with iteration support. It implements this by inserting elements into
1117both a set-like container and the sequential container, using the set-like
1118container for uniquing and the sequential container for iteration.
1119</p>
1120
1121<p>The difference between SetVector and other sets is that the order of
1122iteration is guaranteed to match the order of insertion into the SetVector.
1123This property is really important for things like sets of pointers. Because
1124pointer values are non-deterministic (e.g. vary across runs of the program on
Chris Lattneredca3c52007-02-04 00:00:26 +0000[diff] [blame]1125different machines), iterating over the pointers in the set will
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1126not be in a well-defined order.</p>
1127
1128<p>
1129The drawback of SetVector is that it requires twice as much space as a normal
1130set and has the sum of constant factors from the set-like container and the
1131sequential container that it uses. Use it *only* if you need to iterate over
1132the elements in a deterministic order. SetVector is also expensive to delete
Chris Lattneredca3c52007-02-04 00:00:26 +0000[diff] [blame]1133elements out of (linear time), unless you use it's "pop_back" method, which is
1134faster.
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1135</p>
1136
Chris Lattneredca3c52007-02-04 00:00:26 +0000[diff] [blame]1137<p>SetVector is an adapter class that defaults to using std::vector and std::set
1138for the underlying containers, so it is quite expensive. However,
1139<tt>"llvm/ADT/SetVector.h"</tt> also provides a SmallSetVector class, which
1140defaults to using a SmallVector and SmallSet of a specified size. If you use
1141this, and if your sets are dynamically smaller than N, you will save a lot of
1142heap traffic.</p>
1143
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1144</div>
1145
1146<!-- _______________________________________________________________________ -->
1147<div class="doc_subsubsection">
Chris Lattnerc5722432007-02-03 19:49:31 +0000[diff] [blame]1148 <a name="dss_uniquevector">"llvm/ADT/UniqueVector.h"</a>
1149</div>
1150
1151<div class="doc_text">
1152
1153<p>
1154UniqueVector is similar to <a href="#dss_setvector">SetVector</a>, but it
1155retains a unique ID for each element inserted into the set. It internally
1156contains a map and a vector, and it assigns a unique ID for each value inserted
1157into the set.</p>
1158
1159<p>UniqueVector is very expensive: its cost is the sum of the cost of
1160maintaining both the map and vector, it has high complexity, high constant
1161factors, and produces a lot of malloc traffic. It should be avoided.</p>
1162
1163</div>
1164
1165
1166<!-- _______________________________________________________________________ -->
1167<div class="doc_subsubsection">
1168 <a name="dss_otherset">Other Set-Like Container Options</a>
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1169</div>
1170
1171<div class="doc_text">
1172
1173<p>
1174The STL provides several other options, such as std::multiset and the various
Chris Lattnerc5722432007-02-03 19:49:31 +0000[diff] [blame]1175"hash_set" like containers (whether from C++ TR1 or from the SGI library).</p>
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1176
1177<p>std::multiset is useful if you're not interested in elimination of
Chris Lattner14868db2007-02-03 08:20:15 +0000[diff] [blame]1178duplicates, but has all the drawbacks of std::set. A sorted vector (where you
1179don't delete duplicate entries) or some other approach is almost always
1180better.</p>
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1181
1182<p>The various hash_set implementations (exposed portably by
Chris Lattner14868db2007-02-03 08:20:15 +0000[diff] [blame]1183"llvm/ADT/hash_set") is a simple chained hashtable. This algorithm is as malloc
1184intensive as std::set (performing an allocation for each element inserted,
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1185thus having really high constant factors) but (usually) provides O(1)
1186insertion/deletion of elements. This can be useful if your elements are large
Chris Lattner14868db2007-02-03 08:20:15 +0000[diff] [blame]1187(thus making the constant-factor cost relatively low) or if comparisons are
1188expensive. Element iteration does not visit elements in a useful order.</p>
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1189
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]1190</div>
1191
1192<!-- ======================================================================= -->
1193<div class="doc_subsection">
1194 <a name="ds_map">Map-Like Containers (std::map, DenseMap, etc)</a>
1195</div>
1196
1197<div class="doc_text">
Chris Lattnerc5722432007-02-03 19:49:31 +0000[diff] [blame]1198Map-like containers are useful when you want to associate data to a key. As
1199usual, there are a lot of different ways to do this. :)
1200</div>
1201
1202<!-- _______________________________________________________________________ -->
1203<div class="doc_subsubsection">
1204 <a name="dss_sortedvectormap">A sorted 'vector'</a>
1205</div>
1206
1207<div class="doc_text">
1208
1209<p>
1210If your usage pattern follows a strict insert-then-query approach, you can
1211trivially use the same approach as <a href="#dss_sortedvectorset">sorted vectors
1212for set-like containers</a>. The only difference is that your query function
1213(which uses std::lower_bound to get efficient log(n) lookup) should only compare
1214the key, not both the key and value. This yields the same advantages as sorted
1215vectors for sets.
1216</p>
1217</div>
1218
1219<!-- _______________________________________________________________________ -->
1220<div class="doc_subsubsection">
Chris Lattner796f9fa2007-02-08 19:14:21 +0000[diff] [blame]1221 <a name="dss_stringmap">"llvm/ADT/StringMap.h"</a>
Chris Lattnerc5722432007-02-03 19:49:31 +0000[diff] [blame]1222</div>
1223
1224<div class="doc_text">
1225
1226<p>
1227Strings are commonly used as keys in maps, and they are difficult to support
1228efficiently: they are variable length, inefficient to hash and compare when
Chris Lattner796f9fa2007-02-08 19:14:21 +0000[diff] [blame]1229long, expensive to copy, etc. StringMap is a specialized container designed to
1230cope with these issues. It supports mapping an arbitrary range of bytes to an
1231arbitrary other object.</p>
Chris Lattnerc5722432007-02-03 19:49:31 +0000[diff] [blame]1232
Chris Lattner796f9fa2007-02-08 19:14:21 +0000[diff] [blame]1233<p>The StringMap implementation uses a quadratically-probed hash table, where
Chris Lattnerc5722432007-02-03 19:49:31 +0000[diff] [blame]1234the buckets store a pointer to the heap allocated entries (and some other
1235stuff). The entries in the map must be heap allocated because the strings are
1236variable length. The string data (key) and the element object (value) are
1237stored in the same allocation with the string data immediately after the element
1238object. This container guarantees the "<tt>(char*)(&amp;Value+1)</tt>" points
1239to the key string for a value.</p>
1240
Chris Lattner796f9fa2007-02-08 19:14:21 +0000[diff] [blame]1241<p>The StringMap is very fast for several reasons: quadratic probing is very
Chris Lattnerc5722432007-02-03 19:49:31 +0000[diff] [blame]1242cache efficient for lookups, the hash value of strings in buckets is not
Chris Lattner796f9fa2007-02-08 19:14:21 +0000[diff] [blame]1243recomputed when lookup up an element, StringMap rarely has to touch the
Chris Lattnerc5722432007-02-03 19:49:31 +0000[diff] [blame]1244memory for unrelated objects when looking up a value (even when hash collisions
1245happen), hash table growth does not recompute the hash values for strings
1246already in the table, and each pair in the map is store in a single allocation
1247(the string data is stored in the same allocation as the Value of a pair).</p>
1248
Chris Lattner796f9fa2007-02-08 19:14:21 +0000[diff] [blame]1249<p>StringMap also provides query methods that take byte ranges, so it only ever
Chris Lattnerc5722432007-02-03 19:49:31 +0000[diff] [blame]1250copies a string if a value is inserted into the table.</p>
1251</div>
1252
1253<!-- _______________________________________________________________________ -->
1254<div class="doc_subsubsection">
1255 <a name="dss_indexedmap">"llvm/ADT/IndexedMap.h"</a>
1256</div>
1257
1258<div class="doc_text">
1259<p>
1260IndexedMap is a specialized container for mapping small dense integers (or
1261values that can be mapped to small dense integers) to some other type. It is
1262internally implemented as a vector with a mapping function that maps the keys to
1263the dense integer range.
1264</p>
1265
1266<p>
1267This is useful for cases like virtual registers in the LLVM code generator: they
1268have a dense mapping that is offset by a compile-time constant (the first
1269virtual register ID).</p>
1270
1271</div>
1272
1273<!-- _______________________________________________________________________ -->
1274<div class="doc_subsubsection">
1275 <a name="dss_densemap">"llvm/ADT/DenseMap.h"</a>
1276</div>
1277
1278<div class="doc_text">
1279
1280<p>
1281DenseMap is a simple quadratically probed hash table. It excels at supporting
1282small keys and values: it uses a single allocation to hold all of the pairs that
1283are currently inserted in the map. DenseMap is a great way to map pointers to
1284pointers, or map other small types to each other.
1285</p>
1286
1287<p>
1288There are several aspects of DenseMap that you should be aware of, however. The
1289iterators in a densemap are invalidated whenever an insertion occurs, unlike
1290map. Also, because DenseMap allocates space for a large number of key/value
Chris Lattnera4a264d2007-02-03 20:17:53 +0000[diff] [blame]1291pairs (it starts with 64 by default), it will waste a lot of space if your keys
1292or values are large. Finally, you must implement a partial specialization of
Chris Lattner76c1b972007-09-17 18:34:04 +0000[diff] [blame]1293DenseMapInfo for the key that you want, if it isn't already supported. This
Chris Lattnerc5722432007-02-03 19:49:31 +0000[diff] [blame]1294is required to tell DenseMap about two special marker values (which can never be
Chris Lattnera4a264d2007-02-03 20:17:53 +0000[diff] [blame]1295inserted into the map) that it needs internally.</p>
Chris Lattnerc5722432007-02-03 19:49:31 +0000[diff] [blame]1296
1297</div>
1298
1299<!-- _______________________________________________________________________ -->
1300<div class="doc_subsubsection">
1301 <a name="dss_map">&lt;map&gt;</a>
1302</div>
1303
1304<div class="doc_text">
1305
1306<p>
1307std::map has similar characteristics to <a href="#dss_set">std::set</a>: it uses
1308a single allocation per pair inserted into the map, it offers log(n) lookup with
1309an extremely large constant factor, imposes a space penalty of 3 pointers per
1310pair in the map, etc.</p>
1311
1312<p>std::map is most useful when your keys or values are very large, if you need
1313to iterate over the collection in sorted order, or if you need stable iterators
1314into the map (i.e. they don't get invalidated if an insertion or deletion of
1315another element takes place).</p>
1316
1317</div>
1318
1319<!-- _______________________________________________________________________ -->
1320<div class="doc_subsubsection">
1321 <a name="dss_othermap">Other Map-Like Container Options</a>
1322</div>
1323
1324<div class="doc_text">
1325
1326<p>
1327The STL provides several other options, such as std::multimap and the various
1328"hash_map" like containers (whether from C++ TR1 or from the SGI library).</p>
1329
1330<p>std::multimap is useful if you want to map a key to multiple values, but has
1331all the drawbacks of std::map. A sorted vector or some other approach is almost
1332always better.</p>
1333
1334<p>The various hash_map implementations (exposed portably by
1335"llvm/ADT/hash_map") are simple chained hash tables. This algorithm is as
1336malloc intensive as std::map (performing an allocation for each element
1337inserted, thus having really high constant factors) but (usually) provides O(1)
1338insertion/deletion of elements. This can be useful if your elements are large
1339(thus making the constant-factor cost relatively low) or if comparisons are
1340expensive. Element iteration does not visit elements in a useful order.</p>
1341
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]1342</div>
1343
Daniel Berlin1939ace2007-09-24 17:52:25 +0000[diff] [blame]1344<!-- ======================================================================= -->
1345<div class="doc_subsection">
1346 <a name="ds_bit">Bit storage containers (BitVector, SparseBitVector)</a>
1347</div>
1348
1349<div class="doc_text">
Chris Lattner7086ce72007-09-25 22:37:50 +0000[diff] [blame]1350<p>Unlike the other containers, there are only two bit storage containers, and
1351choosing when to use each is relatively straightforward.</p>
1352
1353<p>One additional option is
1354<tt>std::vector&lt;bool&gt;</tt>: we discourage its use for two reasons 1) the
1355implementation in many common compilers (e.g. commonly available versions of
1356GCC) is extremely inefficient and 2) the C++ standards committee is likely to
1357deprecate this container and/or change it significantly somehow. In any case,
1358please don't use it.</p>
Daniel Berlin1939ace2007-09-24 17:52:25 +0000[diff] [blame]1359</div>
1360
1361<!-- _______________________________________________________________________ -->
1362<div class="doc_subsubsection">
1363 <a name="dss_bitvector">BitVector</a>
1364</div>
1365
1366<div class="doc_text">
1367<p> The BitVector container provides a fixed size set of bits for manipulation.
1368It supports individual bit setting/testing, as well as set operations. The set
1369operations take time O(size of bitvector), but operations are performed one word
1370at a time, instead of one bit at a time. This makes the BitVector very fast for
1371set operations compared to other containers. Use the BitVector when you expect
1372the number of set bits to be high (IE a dense set).
1373</p>
1374</div>
1375
1376<!-- _______________________________________________________________________ -->
1377<div class="doc_subsubsection">
1378 <a name="dss_sparsebitvector">SparseBitVector</a>
1379</div>
1380
1381<div class="doc_text">
1382<p> The SparseBitVector container is much like BitVector, with one major
1383difference: Only the bits that are set, are stored. This makes the
1384SparseBitVector much more space efficient than BitVector when the set is sparse,
1385as well as making set operations O(number of set bits) instead of O(size of
1386universe). 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
1387(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).
1388</p>
1389</div>
Chris Lattnerf623a082005-10-17 01:36:23 +0000[diff] [blame]1390
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1391<!-- *********************************************************************** -->
1392<div class="doc_section">
1393 <a name="common">Helpful Hints for Common Operations</a>
1394</div>
1395<!-- *********************************************************************** -->
1396
1397<div class="doc_text">
1398
1399<p>This section describes how to perform some very simple transformations of
1400LLVM code. This is meant to give examples of common idioms used, showing the
1401practical side of LLVM transformations. <p> Because this is a "how-to" section,
1402you should also read about the main classes that you will be working with. The
1403<a href="#coreclasses">Core LLVM Class Hierarchy Reference</a> contains details
1404and descriptions of the main classes that you should know about.</p>
1405
1406</div>
1407
1408<!-- NOTE: this section should be heavy on example code -->
1409<!-- ======================================================================= -->
1410<div class="doc_subsection">
1411 <a name="inspection">Basic Inspection and Traversal Routines</a>
1412</div>
1413
1414<div class="doc_text">
1415
1416<p>The LLVM compiler infrastructure have many different data structures that may
1417be traversed. Following the example of the C++ standard template library, the
1418techniques used to traverse these various data structures are all basically the
1419same. For a enumerable sequence of values, the <tt>XXXbegin()</tt> function (or
1420method) returns an iterator to the start of the sequence, the <tt>XXXend()</tt>
1421function returns an iterator pointing to one past the last valid element of the
1422sequence, and there is some <tt>XXXiterator</tt> data type that is common
1423between the two operations.</p>
1424
1425<p>Because the pattern for iteration is common across many different aspects of
1426the program representation, the standard template library algorithms may be used
1427on them, and it is easier to remember how to iterate. First we show a few common
1428examples of the data structures that need to be traversed. Other data
1429structures are traversed in very similar ways.</p>
1430
1431</div>
1432
1433<!-- _______________________________________________________________________ -->
Chris Lattner69bf8a92004-05-23 21:06:58 +0000[diff] [blame]1434<div class="doc_subsubsection">
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1435 <a name="iterate_function">Iterating over the </a><a
1436 href="#BasicBlock"><tt>BasicBlock</tt></a>s in a <a
1437 href="#Function"><tt>Function</tt></a>
1438</div>
1439
1440<div class="doc_text">
1441
1442<p>It's quite common to have a <tt>Function</tt> instance that you'd like to
1443transform in some way; in particular, you'd like to manipulate its
1444<tt>BasicBlock</tt>s. To facilitate this, you'll need to iterate over all of
1445the <tt>BasicBlock</tt>s that constitute the <tt>Function</tt>. The following is
1446an example that prints the name of a <tt>BasicBlock</tt> and the number of
1447<tt>Instruction</tt>s it contains:</p>
1448
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1449<div class="doc_code">
1450<pre>
Bill Wendling82e2eea2006-10-11 18:00:22 +0000[diff] [blame]1451// <i>func is a pointer to a Function instance</i>
1452for (Function::iterator i = func-&gt;begin(), e = func-&gt;end(); i != e; ++i)
1453 // <i>Print out the name of the basic block if it has one, and then the</i>
1454 // <i>number of instructions that it contains</i>
Bill Wendling832171c2006-12-07 20:04:42 +0000[diff] [blame]1455 llvm::cerr &lt;&lt; "Basic block (name=" &lt;&lt; i-&gt;getName() &lt;&lt; ") has "
1456 &lt;&lt; i-&gt;size() &lt;&lt; " instructions.\n";
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1457</pre>
1458</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1459
1460<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]1461invoking member functions of the <tt>Instruction</tt> class. This is
1462because the indirection operator is overloaded for the iterator
Chris Lattner7496ec52003-08-05 22:54:23 +0000[diff] [blame]1463classes. In the above code, the expression <tt>i-&gt;size()</tt> is
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1464exactly equivalent to <tt>(*i).size()</tt> just like you'd expect.</p>
1465
1466</div>
1467
1468<!-- _______________________________________________________________________ -->
Chris Lattner69bf8a92004-05-23 21:06:58 +0000[diff] [blame]1469<div class="doc_subsubsection">
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1470 <a name="iterate_basicblock">Iterating over the </a><a
1471 href="#Instruction"><tt>Instruction</tt></a>s in a <a
1472 href="#BasicBlock"><tt>BasicBlock</tt></a>
1473</div>
1474
1475<div class="doc_text">
1476
1477<p>Just like when dealing with <tt>BasicBlock</tt>s in <tt>Function</tt>s, it's
1478easy to iterate over the individual instructions that make up
1479<tt>BasicBlock</tt>s. Here's a code snippet that prints out each instruction in
1480a <tt>BasicBlock</tt>:</p>
1481
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1482<div class="doc_code">
Chris Lattner55c04612005-03-06 06:00:13 +0000[diff] [blame]1483<pre>
Bill Wendling82e2eea2006-10-11 18:00:22 +0000[diff] [blame]1484// <i>blk is a pointer to a BasicBlock instance</i>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1485for (BasicBlock::iterator i = blk-&gt;begin(), e = blk-&gt;end(); i != e; ++i)
Bill Wendling82e2eea2006-10-11 18:00:22 +0000[diff] [blame]1486 // <i>The next statement works since operator&lt;&lt;(ostream&amp;,...)</i>
1487 // <i>is overloaded for Instruction&amp;</i>
Bill Wendling832171c2006-12-07 20:04:42 +0000[diff] [blame]1488 llvm::cerr &lt;&lt; *i &lt;&lt; "\n";
Chris Lattner55c04612005-03-06 06:00:13 +0000[diff] [blame]1489</pre>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1490</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1491
1492<p>However, this isn't really the best way to print out the contents of a
1493<tt>BasicBlock</tt>! Since the ostream operators are overloaded for virtually
1494anything you'll care about, you could have just invoked the print routine on the
Bill Wendling832171c2006-12-07 20:04:42 +0000[diff] [blame]1495basic block itself: <tt>llvm::cerr &lt;&lt; *blk &lt;&lt; "\n";</tt>.</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1496
1497</div>
1498
1499<!-- _______________________________________________________________________ -->
Chris Lattner69bf8a92004-05-23 21:06:58 +0000[diff] [blame]1500<div class="doc_subsubsection">
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1501 <a name="iterate_institer">Iterating over the </a><a
1502 href="#Instruction"><tt>Instruction</tt></a>s in a <a
1503 href="#Function"><tt>Function</tt></a>
1504</div>
1505
1506<div class="doc_text">
1507
1508<p>If you're finding that you commonly iterate over a <tt>Function</tt>'s
1509<tt>BasicBlock</tt>s and then that <tt>BasicBlock</tt>'s <tt>Instruction</tt>s,
1510<tt>InstIterator</tt> should be used instead. You'll need to include <a
1511href="/doxygen/InstIterator_8h-source.html"><tt>llvm/Support/InstIterator.h</tt></a>,
1512and then instantiate <tt>InstIterator</tt>s explicitly in your code. Here's a
Chris Lattner69bf8a92004-05-23 21:06:58 +0000[diff] [blame]1513small 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]1514
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1515<div class="doc_code">
1516<pre>
1517#include "<a href="/doxygen/InstIterator_8h-source.html">llvm/Support/InstIterator.h</a>"
1518
Reid Spencer128a7a72007-02-03 21:06:43 +0000[diff] [blame]1519// <i>F is a pointer to a Function instance</i>
Chris Lattnerda021aa2008-06-04 18:20:42 +0000[diff] [blame]1520for (inst_iterator I = inst_begin(F), E = inst_end(F); I != E; ++I)
1521 llvm::cerr &lt;&lt; *I &lt;&lt; "\n";
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1522</pre>
1523</div>
1524
1525<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]1526work list with its initial contents. For example, if you wanted to
1527initialize a work list to contain all instructions in a <tt>Function</tt>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1528F, all you would need to do is something like:</p>
1529
1530<div class="doc_code">
1531<pre>
1532std::set&lt;Instruction*&gt; worklist;
Chris Lattnerda021aa2008-06-04 18:20:42 +0000[diff] [blame]1533// or better yet, SmallPtrSet&lt;Instruction*, 64&gt; worklist;
1534
1535for (inst_iterator I = inst_begin(F), E = inst_end(F); I != E; ++I)
1536 worklist.insert(&amp;*I);
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1537</pre>
1538</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1539
1540<p>The STL set <tt>worklist</tt> would now contain all instructions in the
1541<tt>Function</tt> pointed to by F.</p>
1542
1543</div>
1544
1545<!-- _______________________________________________________________________ -->
1546<div class="doc_subsubsection">
1547 <a name="iterate_convert">Turning an iterator into a class pointer (and
1548 vice-versa)</a>
1549</div>
1550
1551<div class="doc_text">
1552
1553<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]1554instance when all you've got at hand is an iterator. Well, extracting
Chris Lattner69bf8a92004-05-23 21:06:58 +0000[diff] [blame]1555a reference or a pointer from an iterator is very straight-forward.
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]1556Assuming that <tt>i</tt> is a <tt>BasicBlock::iterator</tt> and <tt>j</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1557is a <tt>BasicBlock::const_iterator</tt>:</p>
1558
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1559<div class="doc_code">
1560<pre>
Bill Wendling82e2eea2006-10-11 18:00:22 +0000[diff] [blame]1561Instruction&amp; inst = *i; // <i>Grab reference to instruction reference</i>
1562Instruction* pinst = &amp;*i; // <i>Grab pointer to instruction reference</i>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1563const Instruction&amp; inst = *j;
1564</pre>
1565</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1566
1567<p>However, the iterators you'll be working with in the LLVM framework are
1568special: they will automatically convert to a ptr-to-instance type whenever they
1569need to. Instead of dereferencing the iterator and then taking the address of
1570the result, you can simply assign the iterator to the proper pointer type and
1571you get the dereference and address-of operation as a result of the assignment
1572(behind the scenes, this is a result of overloading casting mechanisms). Thus
1573the last line of the last example,</p>
1574
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1575<div class="doc_code">
1576<pre>
Chris Lattner2e438ca2008-01-03 16:56:04 +0000[diff] [blame]1577Instruction *pinst = &amp;*i;
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1578</pre>
1579</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1580
1581<p>is semantically equivalent to</p>
1582
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1583<div class="doc_code">
1584<pre>
Chris Lattner2e438ca2008-01-03 16:56:04 +0000[diff] [blame]1585Instruction *pinst = i;
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1586</pre>
1587</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1588
Chris Lattner69bf8a92004-05-23 21:06:58 +0000[diff] [blame]1589<p>It's also possible to turn a class pointer into the corresponding iterator,
1590and this is a constant time operation (very efficient). The following code
1591snippet illustrates use of the conversion constructors provided by LLVM
1592iterators. By using these, you can explicitly grab the iterator of something
1593without actually obtaining it via iteration over some structure:</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1594
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1595<div class="doc_code">
1596<pre>
1597void printNextInstruction(Instruction* inst) {
1598 BasicBlock::iterator it(inst);
Bill Wendling82e2eea2006-10-11 18:00:22 +0000[diff] [blame]1599 ++it; // <i>After this line, it refers to the instruction after *inst</i>
Bill Wendling832171c2006-12-07 20:04:42 +0000[diff] [blame]1600 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]1601}
1602</pre>
1603</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1604
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1605</div>
1606
1607<!--_______________________________________________________________________-->
1608<div class="doc_subsubsection">
1609 <a name="iterate_complex">Finding call sites: a slightly more complex
1610 example</a>
1611</div>
1612
1613<div class="doc_text">
1614
1615<p>Say that you're writing a FunctionPass and would like to count all the
1616locations in the entire module (that is, across every <tt>Function</tt>) where a
1617certain function (i.e., some <tt>Function</tt>*) is already in scope. As you'll
1618learn 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]1619much more straight-forward manner, but this example will allow us to explore how
Reid Spencer128a7a72007-02-03 21:06:43 +0000[diff] [blame]1620you'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]1621is what we want to do:</p>
1622
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1623<div class="doc_code">
1624<pre>
1625initialize callCounter to zero
1626for each Function f in the Module
1627 for each BasicBlock b in f
1628 for each Instruction i in b
1629 if (i is a CallInst and calls the given function)
1630 increment callCounter
1631</pre>
1632</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1633
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1634<p>And the actual code is (remember, because we're writing a
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1635<tt>FunctionPass</tt>, our <tt>FunctionPass</tt>-derived class simply has to
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1636override the <tt>runOnFunction</tt> method):</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1637
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1638<div class="doc_code">
1639<pre>
1640Function* targetFunc = ...;
1641
1642class OurFunctionPass : public FunctionPass {
1643 public:
1644 OurFunctionPass(): callCounter(0) { }
1645
1646 virtual runOnFunction(Function&amp; F) {
1647 for (Function::iterator b = F.begin(), be = F.end(); b != be; ++b) {
Eric Christopher203e71d2008-11-08 08:20:49 +0000[diff] [blame]1648 for (BasicBlock::iterator i = b-&gt;begin(), ie = b-&gt;end(); i != ie; ++i) {
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1649 if (<a href="#CallInst">CallInst</a>* callInst = <a href="#isa">dyn_cast</a>&lt;<a
1650 href="#CallInst">CallInst</a>&gt;(&amp;*i)) {
Bill Wendling82e2eea2006-10-11 18:00:22 +0000[diff] [blame]1651 // <i>We know we've encountered a call instruction, so we</i>
1652 // <i>need to determine if it's a call to the</i>
Chris Lattner2e438ca2008-01-03 16:56:04 +0000[diff] [blame]1653 // <i>function pointed to by m_func or not.</i>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1654 if (callInst-&gt;getCalledFunction() == targetFunc)
1655 ++callCounter;
1656 }
1657 }
1658 }
Bill Wendling82e2eea2006-10-11 18:00:22 +0000[diff] [blame]1659 }
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1660
1661 private:
Chris Lattner2e438ca2008-01-03 16:56:04 +0000[diff] [blame]1662 unsigned callCounter;
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1663};
1664</pre>
1665</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1666
1667</div>
1668
Brian Gaekef1972c62003-11-07 19:25:45 +0000[diff] [blame]1669<!--_______________________________________________________________________-->
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1670<div class="doc_subsubsection">
1671 <a name="calls_and_invokes">Treating calls and invokes the same way</a>
1672</div>
1673
1674<div class="doc_text">
1675
1676<p>You may have noticed that the previous example was a bit oversimplified in
1677that it did not deal with call sites generated by 'invoke' instructions. In
1678this, and in other situations, you may find that you want to treat
1679<tt>CallInst</tt>s and <tt>InvokeInst</tt>s the same way, even though their
1680most-specific common base class is <tt>Instruction</tt>, which includes lots of
1681less closely-related things. For these cases, LLVM provides a handy wrapper
1682class called <a
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]1683href="http://llvm.org/doxygen/classllvm_1_1CallSite.html"><tt>CallSite</tt></a>.
Chris Lattner69bf8a92004-05-23 21:06:58 +0000[diff] [blame]1684It is essentially a wrapper around an <tt>Instruction</tt> pointer, with some
1685methods that provide functionality common to <tt>CallInst</tt>s and
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1686<tt>InvokeInst</tt>s.</p>
1687
Chris Lattner69bf8a92004-05-23 21:06:58 +0000[diff] [blame]1688<p>This class has "value semantics": it should be passed by value, not by
1689reference and it should not be dynamically allocated or deallocated using
1690<tt>operator new</tt> or <tt>operator delete</tt>. It is efficiently copyable,
1691assignable and constructable, with costs equivalents to that of a bare pointer.
1692If you look at its definition, it has only a single pointer member.</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1693
1694</div>
1695
Chris Lattner1a3105b2002-09-09 05:49:39 +0000[diff] [blame]1696<!--_______________________________________________________________________-->
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1697<div class="doc_subsubsection">
1698 <a name="iterate_chains">Iterating over def-use &amp; use-def chains</a>
1699</div>
1700
1701<div class="doc_text">
1702
1703<p>Frequently, we might have an instance of the <a
Chris Lattner00815172007-01-04 22:01:45 +0000[diff] [blame]1704href="/doxygen/classllvm_1_1Value.html">Value Class</a> and we want to
Misha Brukman384047f2004-06-03 23:29:12 +0000[diff] [blame]1705determine which <tt>User</tt>s use the <tt>Value</tt>. The list of all
1706<tt>User</tt>s of a particular <tt>Value</tt> is called a <i>def-use</i> chain.
1707For example, let's say we have a <tt>Function*</tt> named <tt>F</tt> to a
1708particular function <tt>foo</tt>. Finding all of the instructions that
1709<i>use</i> <tt>foo</tt> is as simple as iterating over the <i>def-use</i> chain
1710of <tt>F</tt>:</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1711
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1712<div class="doc_code">
1713<pre>
Chris Lattner2e438ca2008-01-03 16:56:04 +0000[diff] [blame]1714Function *F = ...;
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1715
Bill Wendling82e2eea2006-10-11 18:00:22 +0000[diff] [blame]1716for (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]1717 if (Instruction *Inst = dyn_cast&lt;Instruction&gt;(*i)) {
Bill Wendling832171c2006-12-07 20:04:42 +0000[diff] [blame]1718 llvm::cerr &lt;&lt; "F is used in instruction:\n";
1719 llvm::cerr &lt;&lt; *Inst &lt;&lt; "\n";
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1720 }
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1721</pre>
1722</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1723
1724<p>Alternately, it's common to have an instance of the <a
Misha Brukman384047f2004-06-03 23:29:12 +0000[diff] [blame]1725href="/doxygen/classllvm_1_1User.html">User Class</a> and need to know what
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1726<tt>Value</tt>s are used by it. The list of all <tt>Value</tt>s used by a
1727<tt>User</tt> is known as a <i>use-def</i> chain. Instances of class
1728<tt>Instruction</tt> are common <tt>User</tt>s, so we might want to iterate over
1729all of the values that a particular instruction uses (that is, the operands of
1730the particular <tt>Instruction</tt>):</p>
1731
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1732<div class="doc_code">
1733<pre>
Chris Lattner2e438ca2008-01-03 16:56:04 +0000[diff] [blame]1734Instruction *pi = ...;
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1735
1736for (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]1737 Value *v = *i;
Bill Wendling82e2eea2006-10-11 18:00:22 +0000[diff] [blame]1738 // <i>...</i>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1739}
1740</pre>
1741</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1742
Chris Lattner1a3105b2002-09-09 05:49:39 +0000[diff] [blame]1743<!--
1744 def-use chains ("finding all users of"): Value::use_begin/use_end
1745 use-def chains ("finding all values used"): User::op_begin/op_end [op=operand]
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1746-->
1747
1748</div>
1749
Chris Lattner2e438ca2008-01-03 16:56:04 +0000[diff] [blame]1750<!--_______________________________________________________________________-->
1751<div class="doc_subsubsection">
1752 <a name="iterate_preds">Iterating over predecessors &amp;
1753successors of blocks</a>
1754</div>
1755
1756<div class="doc_text">
1757
1758<p>Iterating over the predecessors and successors of a block is quite easy
1759with the routines defined in <tt>"llvm/Support/CFG.h"</tt>. Just use code like
1760this to iterate over all predecessors of BB:</p>
1761
1762<div class="doc_code">
1763<pre>
1764#include "llvm/Support/CFG.h"
1765BasicBlock *BB = ...;
1766
1767for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI) {
1768 BasicBlock *Pred = *PI;
1769 // <i>...</i>
1770}
1771</pre>
1772</div>
1773
1774<p>Similarly, to iterate over successors use
1775succ_iterator/succ_begin/succ_end.</p>
1776
1777</div>
1778
1779
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1780<!-- ======================================================================= -->
1781<div class="doc_subsection">
1782 <a name="simplechanges">Making simple changes</a>
1783</div>
1784
1785<div class="doc_text">
1786
1787<p>There are some primitive transformation operations present in the LLVM
Joel Stanley753eb712002-09-11 22:32:24 +0000[diff] [blame]1788infrastructure that are worth knowing about. When performing
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]1789transformations, it's fairly common to manipulate the contents of basic
1790blocks. This section describes some of the common methods for doing so
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1791and gives example code.</p>
1792
1793</div>
1794
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]1795<!--_______________________________________________________________________-->
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1796<div class="doc_subsubsection">
1797 <a name="schanges_creating">Creating and inserting new
1798 <tt>Instruction</tt>s</a>
1799</div>
1800
1801<div class="doc_text">
1802
1803<p><i>Instantiating Instructions</i></p>
1804
Chris Lattner69bf8a92004-05-23 21:06:58 +0000[diff] [blame]1805<p>Creation of <tt>Instruction</tt>s is straight-forward: simply call the
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1806constructor for the kind of instruction to instantiate and provide the necessary
1807parameters. For example, an <tt>AllocaInst</tt> only <i>requires</i> a
1808(const-ptr-to) <tt>Type</tt>. Thus:</p>
1809
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1810<div class="doc_code">
1811<pre>
Nick Lewycky10d64b92007-12-03 01:52:52 +0000[diff] [blame]1812AllocaInst* ai = new AllocaInst(Type::Int32Ty);
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1813</pre>
1814</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1815
1816<p>will create an <tt>AllocaInst</tt> instance that represents the allocation of
Reid Spencer128a7a72007-02-03 21:06:43 +0000[diff] [blame]1817one integer in the current stack frame, at run time. Each <tt>Instruction</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1818subclass is likely to have varying default parameters which change the semantics
1819of the instruction, so refer to the <a
Misha Brukman31ca1de2004-06-03 23:35:54 +0000[diff] [blame]1820href="/doxygen/classllvm_1_1Instruction.html">doxygen documentation for the subclass of
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1821Instruction</a> that you're interested in instantiating.</p>
1822
1823<p><i>Naming values</i></p>
1824
1825<p>It is very useful to name the values of instructions when you're able to, as
1826this facilitates the debugging of your transformations. If you end up looking
1827at generated LLVM machine code, you definitely want to have logical names
1828associated with the results of instructions! By supplying a value for the
1829<tt>Name</tt> (default) parameter of the <tt>Instruction</tt> constructor, you
1830associate a logical name with the result of the instruction's execution at
Reid Spencer128a7a72007-02-03 21:06:43 +0000[diff] [blame]1831run time. For example, say that I'm writing a transformation that dynamically
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1832allocates space for an integer on the stack, and that integer is going to be
1833used as some kind of index by some other code. To accomplish this, I place an
1834<tt>AllocaInst</tt> at the first point in the first <tt>BasicBlock</tt> of some
1835<tt>Function</tt>, and I'm intending to use it within the same
1836<tt>Function</tt>. I might do:</p>
1837
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1838<div class="doc_code">
1839<pre>
Nick Lewycky10d64b92007-12-03 01:52:52 +0000[diff] [blame]1840AllocaInst* pa = new AllocaInst(Type::Int32Ty, 0, "indexLoc");
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1841</pre>
1842</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1843
1844<p>where <tt>indexLoc</tt> is now the logical name of the instruction's
Reid Spencer128a7a72007-02-03 21:06:43 +0000[diff] [blame]1845execution value, which is a pointer to an integer on the run time stack.</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1846
1847<p><i>Inserting instructions</i></p>
1848
1849<p>There are essentially two ways to insert an <tt>Instruction</tt>
1850into an existing sequence of instructions that form a <tt>BasicBlock</tt>:</p>
1851
Joel Stanley9dd1ad62002-09-18 03:17:23 +0000[diff] [blame]1852<ul>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1853 <li>Insertion into an explicit instruction list
1854
1855 <p>Given a <tt>BasicBlock* pb</tt>, an <tt>Instruction* pi</tt> within that
1856 <tt>BasicBlock</tt>, and a newly-created instruction we wish to insert
1857 before <tt>*pi</tt>, we do the following: </p>
1858
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1859<div class="doc_code">
1860<pre>
1861BasicBlock *pb = ...;
1862Instruction *pi = ...;
1863Instruction *newInst = new Instruction(...);
1864
Bill Wendling82e2eea2006-10-11 18:00:22 +0000[diff] [blame]1865pb-&gt;getInstList().insert(pi, newInst); // <i>Inserts newInst before pi in pb</i>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1866</pre>
1867</div>
Alkis Evlogimenos9a5dc4f2004-05-27 00:57:51 +0000[diff] [blame]1868
1869 <p>Appending to the end of a <tt>BasicBlock</tt> is so common that
1870 the <tt>Instruction</tt> class and <tt>Instruction</tt>-derived
1871 classes provide constructors which take a pointer to a
1872 <tt>BasicBlock</tt> to be appended to. For example code that
1873 looked like: </p>
1874
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1875<div class="doc_code">
1876<pre>
1877BasicBlock *pb = ...;
1878Instruction *newInst = new Instruction(...);
1879
Bill Wendling82e2eea2006-10-11 18:00:22 +0000[diff] [blame]1880pb-&gt;getInstList().push_back(newInst); // <i>Appends newInst to pb</i>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1881</pre>
1882</div>
Alkis Evlogimenos9a5dc4f2004-05-27 00:57:51 +0000[diff] [blame]1883
1884 <p>becomes: </p>
1885
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1886<div class="doc_code">
1887<pre>
1888BasicBlock *pb = ...;
1889Instruction *newInst = new Instruction(..., pb);
1890</pre>
1891</div>
Alkis Evlogimenos9a5dc4f2004-05-27 00:57:51 +0000[diff] [blame]1892
1893 <p>which is much cleaner, especially if you are creating
1894 long instruction streams.</p></li>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1895
1896 <li>Insertion into an implicit instruction list
1897
1898 <p><tt>Instruction</tt> instances that are already in <tt>BasicBlock</tt>s
1899 are implicitly associated with an existing instruction list: the instruction
1900 list of the enclosing basic block. Thus, we could have accomplished the same
1901 thing as the above code without being given a <tt>BasicBlock</tt> by doing:
1902 </p>
1903
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1904<div class="doc_code">
1905<pre>
1906Instruction *pi = ...;
1907Instruction *newInst = new Instruction(...);
1908
1909pi-&gt;getParent()-&gt;getInstList().insert(pi, newInst);
1910</pre>
1911</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1912
1913 <p>In fact, this sequence of steps occurs so frequently that the
1914 <tt>Instruction</tt> class and <tt>Instruction</tt>-derived classes provide
1915 constructors which take (as a default parameter) a pointer to an
1916 <tt>Instruction</tt> which the newly-created <tt>Instruction</tt> should
1917 precede. That is, <tt>Instruction</tt> constructors are capable of
1918 inserting the newly-created instance into the <tt>BasicBlock</tt> of a
1919 provided instruction, immediately before that instruction. Using an
1920 <tt>Instruction</tt> constructor with a <tt>insertBefore</tt> (default)
1921 parameter, the above code becomes:</p>
1922
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1923<div class="doc_code">
1924<pre>
1925Instruction* pi = ...;
1926Instruction* newInst = new Instruction(..., pi);
1927</pre>
1928</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1929
1930 <p>which is much cleaner, especially if you're creating a lot of
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1931 instructions and adding them to <tt>BasicBlock</tt>s.</p></li>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1932</ul>
1933
1934</div>
1935
1936<!--_______________________________________________________________________-->
1937<div class="doc_subsubsection">
1938 <a name="schanges_deleting">Deleting <tt>Instruction</tt>s</a>
1939</div>
1940
1941<div class="doc_text">
1942
1943<p>Deleting an instruction from an existing sequence of instructions that form a
Chris Lattner69bf8a92004-05-23 21:06:58 +0000[diff] [blame]1944<a href="#BasicBlock"><tt>BasicBlock</tt></a> is very straight-forward. First,
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1945you must have a pointer to the instruction that you wish to delete. Second, you
1946need to obtain the pointer to that instruction's basic block. You use the
1947pointer to the basic block to get its list of instructions and then use the
1948erase function to remove your instruction. For example:</p>
1949
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1950<div class="doc_code">
1951<pre>
1952<a href="#Instruction">Instruction</a> *I = .. ;
Chris Lattner9f8ec252008-02-15 22:57:17 +0000[diff] [blame]1953I-&gt;eraseFromParent();
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1954</pre>
1955</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1956
1957</div>
1958
1959<!--_______________________________________________________________________-->
1960<div class="doc_subsubsection">
1961 <a name="schanges_replacing">Replacing an <tt>Instruction</tt> with another
1962 <tt>Value</tt></a>
1963</div>
1964
1965<div class="doc_text">
1966
1967<p><i>Replacing individual instructions</i></p>
1968
1969<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]1970permits use of two very useful replace functions: <tt>ReplaceInstWithValue</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1971and <tt>ReplaceInstWithInst</tt>.</p>
1972
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]1973<h4><a name="schanges_deleting">Deleting <tt>Instruction</tt>s</a></h4>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1974
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]1975<ul>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1976 <li><tt>ReplaceInstWithValue</tt>
1977
Nick Lewyckyb6d1f392008-09-15 06:31:52 +0000[diff] [blame]1978 <p>This function replaces all uses of a given instruction with a value,
1979 and then removes the original instruction. The following example
1980 illustrates the replacement of the result of a particular
Chris Lattner58360822005-01-17 00:12:04 +0000[diff] [blame]1981 <tt>AllocaInst</tt> that allocates memory for a single integer with a null
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1982 pointer to an integer.</p>
1983
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1984<div class="doc_code">
1985<pre>
1986AllocaInst* instToReplace = ...;
1987BasicBlock::iterator ii(instToReplace);
1988
1989ReplaceInstWithValue(instToReplace-&gt;getParent()-&gt;getInstList(), ii,
Daniel Dunbar58c2ac02008-10-03 22:17:25 +0000[diff] [blame]1990 Constant::getNullValue(PointerType::getUnqual(Type::Int32Ty)));
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1991</pre></div></li>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1992
1993 <li><tt>ReplaceInstWithInst</tt>
1994
1995 <p>This function replaces a particular instruction with another
Nick Lewyckyb6d1f392008-09-15 06:31:52 +0000[diff] [blame]1996 instruction, inserting the new instruction into the basic block at the
1997 location where the old instruction was, and replacing any uses of the old
1998 instruction with the new instruction. The following example illustrates
1999 the replacement of one <tt>AllocaInst</tt> with another.</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2000
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2001<div class="doc_code">
2002<pre>
2003AllocaInst* instToReplace = ...;
2004BasicBlock::iterator ii(instToReplace);
2005
2006ReplaceInstWithInst(instToReplace-&gt;getParent()-&gt;getInstList(), ii,
Nick Lewycky10d64b92007-12-03 01:52:52 +0000[diff] [blame]2007 new AllocaInst(Type::Int32Ty, 0, "ptrToReplacedInt"));
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2008</pre></div></li>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]2009</ul>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2010
2011<p><i>Replacing multiple uses of <tt>User</tt>s and <tt>Value</tt>s</i></p>
2012
2013<p>You can use <tt>Value::replaceAllUsesWith</tt> and
2014<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]2015doxygen documentation for the <a href="/doxygen/classllvm_1_1Value.html">Value Class</a>
Misha Brukman384047f2004-06-03 23:29:12 +0000[diff] [blame]2016and <a href="/doxygen/classllvm_1_1User.html">User Class</a>, respectively, for more
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2017information.</p>
2018
2019<!-- Value::replaceAllUsesWith User::replaceUsesOfWith Point out:
2020include/llvm/Transforms/Utils/ especially BasicBlockUtils.h with:
2021ReplaceInstWithValue, ReplaceInstWithInst -->
2022
2023</div>
2024
Tanya Lattnerb011c662007-06-20 18:33:15 +0000[diff] [blame]2025<!--_______________________________________________________________________-->
2026<div class="doc_subsubsection">
2027 <a name="schanges_deletingGV">Deleting <tt>GlobalVariable</tt>s</a>
2028</div>
2029
2030<div class="doc_text">
2031
Tanya Lattnerc5dfcdb2007-06-20 20:46:37 +0000[diff] [blame]2032<p>Deleting a global variable from a module is just as easy as deleting an
2033Instruction. First, you must have a pointer to the global variable that you wish
2034 to delete. You use this pointer to erase it from its parent, the module.
Tanya Lattnerb011c662007-06-20 18:33:15 +0000[diff] [blame]2035 For example:</p>
2036
2037<div class="doc_code">
2038<pre>
2039<a href="#GlobalVariable">GlobalVariable</a> *GV = .. ;
Tanya Lattnerb011c662007-06-20 18:33:15 +0000[diff] [blame]2040
Tanya Lattnerc5dfcdb2007-06-20 20:46:37 +0000[diff] [blame]2041GV-&gt;eraseFromParent();
Tanya Lattnerb011c662007-06-20 18:33:15 +0000[diff] [blame]2042</pre>
2043</div>
2044
2045</div>
2046
Chris Lattner9355b472002-09-06 02:50:58 +0000[diff] [blame]2047<!-- *********************************************************************** -->
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2048<div class="doc_section">
Chris Lattnerd9d6e102005-04-23 16:10:52 +0000[diff] [blame]2049 <a name="advanced">Advanced Topics</a>
2050</div>
2051<!-- *********************************************************************** -->
2052
2053<div class="doc_text">
Chris Lattnerf1b200b2005-04-23 17:27:36 +0000[diff] [blame]2054<p>
2055This section describes some of the advanced or obscure API's that most clients
2056do not need to be aware of. These API's tend manage the inner workings of the
2057LLVM system, and only need to be accessed in unusual circumstances.
2058</p>
2059</div>
Chris Lattnerd9d6e102005-04-23 16:10:52 +0000[diff] [blame]2060
Chris Lattnerf1b200b2005-04-23 17:27:36 +0000[diff] [blame]2061<!-- ======================================================================= -->
2062<div class="doc_subsection">
2063 <a name="TypeResolve">LLVM Type Resolution</a>
2064</div>
Chris Lattnerd9d6e102005-04-23 16:10:52 +0000[diff] [blame]2065
Chris Lattnerf1b200b2005-04-23 17:27:36 +0000[diff] [blame]2066<div class="doc_text">
2067
2068<p>
2069The LLVM type system has a very simple goal: allow clients to compare types for
2070structural equality with a simple pointer comparison (aka a shallow compare).
2071This goal makes clients much simpler and faster, and is used throughout the LLVM
2072system.
2073</p>
2074
2075<p>
2076Unfortunately achieving this goal is not a simple matter. In particular,
2077recursive types and late resolution of opaque types makes the situation very
2078difficult to handle. Fortunately, for the most part, our implementation makes
2079most clients able to be completely unaware of the nasty internal details. The
2080primary case where clients are exposed to the inner workings of it are when
Gabor Greif04367bf2007-07-06 22:07:22 +0000[diff] [blame]2081building a recursive type. In addition to this case, the LLVM bitcode reader,
Chris Lattnerf1b200b2005-04-23 17:27:36 +0000[diff] [blame]2082assembly parser, and linker also have to be aware of the inner workings of this
2083system.
2084</p>
2085
Chris Lattner0f876db2005-04-25 15:47:57 +0000[diff] [blame]2086<p>
2087For our purposes below, we need three concepts. First, an "Opaque Type" is
2088exactly as defined in the <a href="LangRef.html#t_opaque">language
2089reference</a>. Second an "Abstract Type" is any type which includes an
Reid Spencer06565dc2007-01-12 17:11:23 +0000[diff] [blame]2090opaque type as part of its type graph (for example "<tt>{ opaque, i32 }</tt>").
2091Third, 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]2092float }</tt>").
2093</p>
2094
Chris Lattnerf1b200b2005-04-23 17:27:36 +0000[diff] [blame]2095</div>
2096
2097<!-- ______________________________________________________________________ -->
2098<div class="doc_subsubsection">
2099 <a name="BuildRecType">Basic Recursive Type Construction</a>
2100</div>
2101
2102<div class="doc_text">
2103
2104<p>
2105Because the most common question is "how do I build a recursive type with LLVM",
2106we answer it now and explain it as we go. Here we include enough to cause this
2107to be emitted to an output .ll file:
2108</p>
2109
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2110<div class="doc_code">
Chris Lattnerf1b200b2005-04-23 17:27:36 +0000[diff] [blame]2111<pre>
Reid Spencer06565dc2007-01-12 17:11:23 +0000[diff] [blame]2112%mylist = type { %mylist*, i32 }
Chris Lattnerf1b200b2005-04-23 17:27:36 +0000[diff] [blame]2113</pre>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2114</div>
Chris Lattnerf1b200b2005-04-23 17:27:36 +0000[diff] [blame]2115
2116<p>
2117To build this, use the following LLVM APIs:
2118</p>
2119
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2120<div class="doc_code">
Chris Lattnerf1b200b2005-04-23 17:27:36 +0000[diff] [blame]2121<pre>
Bill Wendling82e2eea2006-10-11 18:00:22 +0000[diff] [blame]2122// <i>Create the initial outer struct</i>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2123<a href="#PATypeHolder">PATypeHolder</a> StructTy = OpaqueType::get();
2124std::vector&lt;const Type*&gt; Elts;
Daniel Dunbar58c2ac02008-10-03 22:17:25 +0000[diff] [blame]2125Elts.push_back(PointerType::getUnqual(StructTy));
Nick Lewycky10d64b92007-12-03 01:52:52 +0000[diff] [blame]2126Elts.push_back(Type::Int32Ty);
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2127StructType *NewSTy = StructType::get(Elts);
Chris Lattnerf1b200b2005-04-23 17:27:36 +0000[diff] [blame]2128
Reid Spencer06565dc2007-01-12 17:11:23 +0000[diff] [blame]2129// <i>At this point, NewSTy = "{ opaque*, i32 }". Tell VMCore that</i>
Bill Wendling82e2eea2006-10-11 18:00:22 +0000[diff] [blame]2130// <i>the struct and the opaque type are actually the same.</i>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2131cast&lt;OpaqueType&gt;(StructTy.get())-&gt;<a href="#refineAbstractTypeTo">refineAbstractTypeTo</a>(NewSTy);
Chris Lattnerf1b200b2005-04-23 17:27:36 +0000[diff] [blame]2132
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2133// <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]2134// <i>kept up-to-date</i>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2135NewSTy = cast&lt;StructType&gt;(StructTy.get());
Chris Lattnerf1b200b2005-04-23 17:27:36 +0000[diff] [blame]2136
Bill Wendling82e2eea2006-10-11 18:00:22 +0000[diff] [blame]2137// <i>Add a name for the type to the module symbol table (optional)</i>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2138MyModule-&gt;addTypeName("mylist", NewSTy);
Chris Lattnerf1b200b2005-04-23 17:27:36 +0000[diff] [blame]2139</pre>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2140</div>
Chris Lattnerf1b200b2005-04-23 17:27:36 +0000[diff] [blame]2141
2142<p>
2143This code shows the basic approach used to build recursive types: build a
2144non-recursive type using 'opaque', then use type unification to close the cycle.
2145The type unification step is performed by the <tt><a
Chris Lattneraff26d12007-02-03 03:06:52 +0000[diff] [blame]2146href="#refineAbstractTypeTo">refineAbstractTypeTo</a></tt> method, which is
Chris Lattnerf1b200b2005-04-23 17:27:36 +0000[diff] [blame]2147described next. After that, we describe the <a
2148href="#PATypeHolder">PATypeHolder class</a>.
2149</p>
2150
2151</div>
2152
2153<!-- ______________________________________________________________________ -->
2154<div class="doc_subsubsection">
2155 <a name="refineAbstractTypeTo">The <tt>refineAbstractTypeTo</tt> method</a>
2156</div>
2157
2158<div class="doc_text">
2159<p>
2160The <tt>refineAbstractTypeTo</tt> method starts the type unification process.
2161While this method is actually a member of the DerivedType class, it is most
2162often used on OpaqueType instances. Type unification is actually a recursive
2163process. After unification, types can become structurally isomorphic to
2164existing types, and all duplicates are deleted (to preserve pointer equality).
2165</p>
2166
2167<p>
2168In the example above, the OpaqueType object is definitely deleted.
Reid Spencer06565dc2007-01-12 17:11:23 +0000[diff] [blame]2169Additionally, if there is an "{ \2*, i32}" type already created in the system,
Chris Lattnerf1b200b2005-04-23 17:27:36 +0000[diff] [blame]2170the pointer and struct type created are <b>also</b> deleted. Obviously whenever
2171a type is deleted, any "Type*" pointers in the program are invalidated. As
2172such, it is safest to avoid having <i>any</i> "Type*" pointers to abstract types
2173live across a call to <tt>refineAbstractTypeTo</tt> (note that non-abstract
2174types can never move or be deleted). To deal with this, the <a
2175href="#PATypeHolder">PATypeHolder</a> class is used to maintain a stable
2176reference to a possibly refined type, and the <a
2177href="#AbstractTypeUser">AbstractTypeUser</a> class is used to update more
2178complex datastructures.
2179</p>
2180
2181</div>
2182
2183<!-- ______________________________________________________________________ -->
2184<div class="doc_subsubsection">
2185 <a name="PATypeHolder">The PATypeHolder Class</a>
2186</div>
2187
2188<div class="doc_text">
2189<p>
2190PATypeHolder is a form of a "smart pointer" for Type objects. When VMCore
2191happily goes about nuking types that become isomorphic to existing types, it
2192automatically updates all PATypeHolder objects to point to the new type. In the
2193example above, this allows the code to maintain a pointer to the resultant
2194resolved recursive type, even though the Type*'s are potentially invalidated.
2195</p>
2196
2197<p>
2198PATypeHolder is an extremely light-weight object that uses a lazy union-find
2199implementation to update pointers. For example the pointer from a Value to its
2200Type is maintained by PATypeHolder objects.
2201</p>
2202
2203</div>
2204
2205<!-- ______________________________________________________________________ -->
2206<div class="doc_subsubsection">
2207 <a name="AbstractTypeUser">The AbstractTypeUser Class</a>
2208</div>
2209
2210<div class="doc_text">
2211
2212<p>
2213Some data structures need more to perform more complex updates when types get
Chris Lattner263a98e2007-02-16 04:37:31 +0000[diff] [blame]2214resolved. To support this, a class can derive from the AbstractTypeUser class.
2215This class
Chris Lattnerf1b200b2005-04-23 17:27:36 +0000[diff] [blame]2216allows it to get callbacks when certain types are resolved. To register to get
2217callbacks for a particular type, the DerivedType::{add/remove}AbstractTypeUser
Chris Lattner0f876db2005-04-25 15:47:57 +0000[diff] [blame]2218methods can be called on a type. Note that these methods only work for <i>
Reid Spencer06565dc2007-01-12 17:11:23 +0000[diff] [blame]2219 abstract</i> types. Concrete types (those that do not include any opaque
2220objects) can never be refined.
Chris Lattnerf1b200b2005-04-23 17:27:36 +0000[diff] [blame]2221</p>
Chris Lattnerd9d6e102005-04-23 16:10:52 +0000[diff] [blame]2222</div>
2223
2224
2225<!-- ======================================================================= -->
2226<div class="doc_subsection">
Chris Lattner263a98e2007-02-16 04:37:31 +0000[diff] [blame]2227 <a name="SymbolTable">The <tt>ValueSymbolTable</tt> and
2228 <tt>TypeSymbolTable</tt> classes</a>
Chris Lattnerd9d6e102005-04-23 16:10:52 +0000[diff] [blame]2229</div>
Chris Lattnerf1b200b2005-04-23 17:27:36 +0000[diff] [blame]2230
Chris Lattnerd9d6e102005-04-23 16:10:52 +0000[diff] [blame]2231<div class="doc_text">
Chris Lattner263a98e2007-02-16 04:37:31 +0000[diff] [blame]2232<p>The <tt><a href="http://llvm.org/doxygen/classllvm_1_1ValueSymbolTable.html">
2233ValueSymbolTable</a></tt> class provides a symbol table that the <a
Chris Lattnerd9d6e102005-04-23 16:10:52 +0000[diff] [blame]2234href="#Function"><tt>Function</tt></a> and <a href="#Module">
Chris Lattner263a98e2007-02-16 04:37:31 +0000[diff] [blame]2235<tt>Module</tt></a> classes use for naming value definitions. The symbol table
2236can provide a name for any <a href="#Value"><tt>Value</tt></a>.
2237The <tt><a href="http://llvm.org/doxygen/classllvm_1_1TypeSymbolTable.html">
2238TypeSymbolTable</a></tt> class is used by the <tt>Module</tt> class to store
2239names for types.</p>
Chris Lattnerd9d6e102005-04-23 16:10:52 +0000[diff] [blame]2240
Reid Spencera6362242007-01-07 00:41:39 +0000[diff] [blame]2241<p>Note that the <tt>SymbolTable</tt> class should not be directly accessed
2242by most clients. It should only be used when iteration over the symbol table
2243names themselves are required, which is very special purpose. Note that not
2244all LLVM
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2245<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]2246an empty name) do not exist in the symbol table.
2247</p>
2248
Chris Lattner263a98e2007-02-16 04:37:31 +0000[diff] [blame]2249<p>These symbol tables support iteration over the values/types in the symbol
2250table with <tt>begin/end/iterator</tt> and supports querying to see if a
2251specific name is in the symbol table (with <tt>lookup</tt>). The
2252<tt>ValueSymbolTable</tt> class exposes no public mutator methods, instead,
2253simply call <tt>setName</tt> on a value, which will autoinsert it into the
2254appropriate symbol table. For types, use the Module::addTypeName method to
2255insert entries into the symbol table.</p>
Chris Lattnerd9d6e102005-04-23 16:10:52 +0000[diff] [blame]2256
Chris Lattnerd9d6e102005-04-23 16:10:52 +0000[diff] [blame]2257</div>
2258
2259
2260
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2261<!-- ======================================================================= -->
2262<div class="doc_subsection">
2263 <a name="UserLayout">The <tt>User</tt> and owned <tt>Use</tt> classes' memory layout</a>
2264</div>
2265
2266<div class="doc_text">
2267<p>The <tt><a href="http://llvm.org/doxygen/classllvm_1_1User.html">
Gabor Greiffd095b62009-01-05 16:05:32 +0000[diff] [blame]2268User</a></tt> class provides a basis for expressing the ownership of <tt>User</tt>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2269towards other <tt><a href="http://llvm.org/doxygen/classllvm_1_1Value.html">
2270Value</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]2271Use</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]2272addition and removal.</p>
2273
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2274<!-- ______________________________________________________________________ -->
2275<div class="doc_subsubsection">
Gabor Greiffd095b62009-01-05 16:05:32 +0000[diff] [blame]2276 <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]2277</div>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2278
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2279<div class="doc_text">
2280<p>
2281A subclass of <tt>User</tt> can choose between incorporating its <tt>Use</tt> objects
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2282or refer to them out-of-line by means of a pointer. A mixed variant
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2283(some <tt>Use</tt>s inline others hung off) is impractical and breaks the invariant
2284that the <tt>Use</tt> objects belonging to the same <tt>User</tt> form a contiguous array.
2285</p>
2286</div>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2287
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2288<p>
2289We have 2 different layouts in the <tt>User</tt> (sub)classes:
2290<ul>
2291<li><p>Layout a)
2292The <tt>Use</tt> object(s) are inside (resp. at fixed offset) of the <tt>User</tt>
2293object and there are a fixed number of them.</p>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2294
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2295<li><p>Layout b)
2296The <tt>Use</tt> object(s) are referenced by a pointer to an
2297array from the <tt>User</tt> object and there may be a variable
2298number of them.</p>
2299</ul>
2300<p>
Gabor Greifd41720a2008-06-25 00:10:22 +0000[diff] [blame]2301As of v2.4 each layout still possesses a direct pointer to the
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2302start of the array of <tt>Use</tt>s. Though not mandatory for layout a),
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2303we stick to this redundancy for the sake of simplicity.
Gabor Greifd41720a2008-06-25 00:10:22 +0000[diff] [blame]2304The <tt>User</tt> object also stores the number of <tt>Use</tt> objects it
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2305has. (Theoretically this information can also be calculated
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2306given the scheme presented below.)</p>
2307<p>
2308Special forms of allocation operators (<tt>operator new</tt>)
Gabor Greifd41720a2008-06-25 00:10:22 +0000[diff] [blame]2309enforce the following memory layouts:</p>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2310
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2311<ul>
Gabor Greifd41720a2008-06-25 00:10:22 +0000[diff] [blame]2312<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]2313
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2314<pre>
2315...---.---.---.---.-------...
2316 | P | P | P | P | User
2317'''---'---'---'---'-------'''
2318</pre>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2319
Gabor Greifd41720a2008-06-25 00:10:22 +0000[diff] [blame]2320<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]2321<pre>
2322.-------...
2323| User
2324'-------'''
2325 |
2326 v
2327 .---.---.---.---...
2328 | P | P | P | P |
2329 '---'---'---'---'''
2330</pre>
2331</ul>
2332<i>(In the above figures '<tt>P</tt>' stands for the <tt>Use**</tt> that
2333 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]2334
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2335<!-- ______________________________________________________________________ -->
2336<div class="doc_subsubsection">
Gabor Greiffd095b62009-01-05 16:05:32 +0000[diff] [blame]2337 <a name="Waymarking">The waymarking algorithm</a>
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2338</div>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2339
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2340<div class="doc_text">
2341<p>
Gabor Greifd41720a2008-06-25 00:10:22 +0000[diff] [blame]2342Since the <tt>Use</tt> objects are deprived of the direct (back)pointer to
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2343their <tt>User</tt> objects, there must be a fast and exact method to
2344recover it. This is accomplished by the following scheme:</p>
2345</div>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2346
Gabor Greifd41720a2008-06-25 00:10:22 +0000[diff] [blame]2347A 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]2348start of the <tt>User</tt> object:
2349<ul>
2350<li><tt>00</tt> &mdash;&gt; binary digit 0</li>
2351<li><tt>01</tt> &mdash;&gt; binary digit 1</li>
2352<li><tt>10</tt> &mdash;&gt; stop and calculate (<tt>s</tt>)</li>
2353<li><tt>11</tt> &mdash;&gt; full stop (<tt>S</tt>)</li>
2354</ul>
2355<p>
2356Given a <tt>Use*</tt>, all we have to do is to walk till we get
2357a stop and we either have a <tt>User</tt> immediately behind or
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2358we have to walk to the next stop picking up digits
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2359and calculating the offset:</p>
2360<pre>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2361.---.---.---.---.---.---.---.---.---.---.---.---.---.---.---.---.----------------
2362| 1 | s | 1 | 0 | 1 | 0 | s | 1 | 1 | 0 | s | 1 | 1 | s | 1 | S | User (or User*)
2363'---'---'---'---'---'---'---'---'---'---'---'---'---'---'---'---'----------------
2364 |+15 |+10 |+6 |+3 |+1
2365 | | | | |__>
2366 | | | |__________>
2367 | | |______________________>
2368 | |______________________________________>
2369 |__________________________________________________________>
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2370</pre>
2371<p>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2372Only the significant number of bits need to be stored between the
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2373stops, so that the <i>worst case is 20 memory accesses</i> when there are
23741000 <tt>Use</tt> objects associated with a <tt>User</tt>.</p>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2375
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2376<!-- ______________________________________________________________________ -->
2377<div class="doc_subsubsection">
Gabor Greiffd095b62009-01-05 16:05:32 +0000[diff] [blame]2378 <a name="ReferenceImpl">Reference implementation</a>
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2379</div>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2380
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2381<div class="doc_text">
2382<p>
2383The following literate Haskell fragment demonstrates the concept:</p>
2384</div>
2385
2386<div class="doc_code">
2387<pre>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2388> import Test.QuickCheck
2389>
2390> digits :: Int -> [Char] -> [Char]
2391> digits 0 acc = '0' : acc
2392> digits 1 acc = '1' : acc
2393> digits n acc = digits (n `div` 2) $ digits (n `mod` 2) acc
2394>
2395> dist :: Int -> [Char] -> [Char]
2396> dist 0 [] = ['S']
2397> dist 0 acc = acc
2398> dist 1 acc = let r = dist 0 acc in 's' : digits (length r) r
2399> dist n acc = dist (n - 1) $ dist 1 acc
2400>
2401> takeLast n ss = reverse $ take n $ reverse ss
2402>
2403> test = takeLast 40 $ dist 20 []
2404>
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2405</pre>
2406</div>
2407<p>
2408Printing &lt;test&gt; gives: <tt>"1s100000s11010s10100s1111s1010s110s11s1S"</tt></p>
2409<p>
2410The reverse algorithm computes the length of the string just by examining
2411a certain prefix:</p>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2412
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2413<div class="doc_code">
2414<pre>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2415> pref :: [Char] -> Int
2416> pref "S" = 1
2417> pref ('s':'1':rest) = decode 2 1 rest
2418> pref (_:rest) = 1 + pref rest
2419>
2420> decode walk acc ('0':rest) = decode (walk + 1) (acc * 2) rest
2421> decode walk acc ('1':rest) = decode (walk + 1) (acc * 2 + 1) rest
2422> decode walk acc _ = walk + acc
2423>
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2424</pre>
2425</div>
2426<p>
2427Now, as expected, printing &lt;pref test&gt; gives <tt>40</tt>.</p>
2428<p>
2429We can <i>quickCheck</i> this with following property:</p>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2430
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2431<div class="doc_code">
2432<pre>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2433> testcase = dist 2000 []
2434> testcaseLength = length testcase
2435>
2436> identityProp n = n > 0 && n <= testcaseLength ==> length arr == pref arr
2437> where arr = takeLast n testcase
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2438>
2439</pre>
2440</div>
2441<p>
2442As expected &lt;quickCheck identityProp&gt; gives:</p>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2443
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2444<pre>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2445*Main> quickCheck identityProp
2446OK, passed 100 tests.
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2447</pre>
2448<p>
2449Let's be a bit more exhaustive:</p>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2450
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2451<div class="doc_code">
2452<pre>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2453>
2454> deepCheck p = check (defaultConfig { configMaxTest = 500 }) p
2455>
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2456</pre>
2457</div>
2458<p>
2459And here is the result of &lt;deepCheck identityProp&gt;:</p>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2460
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2461<pre>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2462*Main> deepCheck identityProp
2463OK, passed 500 tests.
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2464</pre>
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="Tagging">Tagging considerations</a>
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2469</div>
2470
2471<p>
2472To maintain the invariant that the 2 LSBits of each <tt>Use**</tt> in <tt>Use</tt>
2473never change after being set up, setters of <tt>Use::Prev</tt> must re-tag the
2474new <tt>Use**</tt> on every modification. Accordingly getters must strip the
2475tag bits.</p>
2476<p>
Gabor Greifd41720a2008-06-25 00:10:22 +0000[diff] [blame]2477For layout b) instead of the <tt>User</tt> we find a pointer (<tt>User*</tt> with LSBit set).
2478Following this pointer brings us to the <tt>User</tt>. A portable trick ensures
2479that the first bytes of <tt>User</tt> (if interpreted as a pointer) never has
Gabor Greiffd095b62009-01-05 16:05:32 +0000[diff] [blame]2480the LSBit set. (Portability is relying on the fact that all known compilers place the
2481<tt>vptr</tt> in the first word of the instances.)</p>
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2482
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2483</div>
2484
2485 <!-- *********************************************************************** -->
Chris Lattnerd9d6e102005-04-23 16:10:52 +0000[diff] [blame]2486<div class="doc_section">
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2487 <a name="coreclasses">The Core LLVM Class Hierarchy Reference </a>
2488</div>
2489<!-- *********************************************************************** -->
2490
2491<div class="doc_text">
Reid Spencer303c4b42007-01-12 17:26:25 +0000[diff] [blame]2492<p><tt>#include "<a href="/doxygen/Type_8h-source.html">llvm/Type.h</a>"</tt>
2493<br>doxygen info: <a href="/doxygen/classllvm_1_1Type.html">Type Class</a></p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2494
2495<p>The Core LLVM classes are the primary means of representing the program
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]2496being inspected or transformed. The core LLVM classes are defined in
2497header files in the <tt>include/llvm/</tt> directory, and implemented in
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2498the <tt>lib/VMCore</tt> directory.</p>
2499
2500</div>
2501
2502<!-- ======================================================================= -->
2503<div class="doc_subsection">
Reid Spencer303c4b42007-01-12 17:26:25 +0000[diff] [blame]2504 <a name="Type">The <tt>Type</tt> class and Derived Types</a>
2505</div>
2506
2507<div class="doc_text">
2508
2509 <p><tt>Type</tt> is a superclass of all type classes. Every <tt>Value</tt> has
2510 a <tt>Type</tt>. <tt>Type</tt> cannot be instantiated directly but only
2511 through its subclasses. Certain primitive types (<tt>VoidType</tt>,
2512 <tt>LabelType</tt>, <tt>FloatType</tt> and <tt>DoubleType</tt>) have hidden
2513 subclasses. They are hidden because they offer no useful functionality beyond
2514 what the <tt>Type</tt> class offers except to distinguish themselves from
2515 other subclasses of <tt>Type</tt>.</p>
2516 <p>All other types are subclasses of <tt>DerivedType</tt>. Types can be
2517 named, but this is not a requirement. There exists exactly
2518 one instance of a given shape at any one time. This allows type equality to
2519 be performed with address equality of the Type Instance. That is, given two
2520 <tt>Type*</tt> values, the types are identical if the pointers are identical.
2521 </p>
2522</div>
2523
2524<!-- _______________________________________________________________________ -->
2525<div class="doc_subsubsection">
Gabor Greiffd095b62009-01-05 16:05:32 +0000[diff] [blame]2526 <a name="m_Type">Important Public Methods</a>
Reid Spencer303c4b42007-01-12 17:26:25 +0000[diff] [blame]2527</div>
2528
2529<div class="doc_text">
2530
2531<ul>
Chris Lattner8f79df32007-01-15 01:55:32 +0000[diff] [blame]2532 <li><tt>bool isInteger() const</tt>: Returns true for any integer type.</li>
Reid Spencer303c4b42007-01-12 17:26:25 +0000[diff] [blame]2533
2534 <li><tt>bool isFloatingPoint()</tt>: Return true if this is one of the two
2535 floating point types.</li>
2536
2537 <li><tt>bool isAbstract()</tt>: Return true if the type is abstract (contains
2538 an OpaqueType anywhere in its definition).</li>
2539
2540 <li><tt>bool isSized()</tt>: Return true if the type has known size. Things
2541 that don't have a size are abstract types, labels and void.</li>
2542
2543</ul>
2544</div>
2545
2546<!-- _______________________________________________________________________ -->
2547<div class="doc_subsubsection">
Gabor Greiffd095b62009-01-05 16:05:32 +0000[diff] [blame]2548 <a name="derivedtypes">Important Derived Types</a>
Reid Spencer303c4b42007-01-12 17:26:25 +0000[diff] [blame]2549</div>
2550<div class="doc_text">
2551<dl>
2552 <dt><tt>IntegerType</tt></dt>
2553 <dd>Subclass of DerivedType that represents integer types of any bit width.
2554 Any bit width between <tt>IntegerType::MIN_INT_BITS</tt> (1) and
2555 <tt>IntegerType::MAX_INT_BITS</tt> (~8 million) can be represented.
2556 <ul>
2557 <li><tt>static const IntegerType* get(unsigned NumBits)</tt>: get an integer
2558 type of a specific bit width.</li>
2559 <li><tt>unsigned getBitWidth() const</tt>: Get the bit width of an integer
2560 type.</li>
2561 </ul>
2562 </dd>
2563 <dt><tt>SequentialType</tt></dt>
2564 <dd>This is subclassed by ArrayType and PointerType
2565 <ul>
2566 <li><tt>const Type * getElementType() const</tt>: Returns the type of each
2567 of the elements in the sequential type. </li>
2568 </ul>
2569 </dd>
2570 <dt><tt>ArrayType</tt></dt>
2571 <dd>This is a subclass of SequentialType and defines the interface for array
2572 types.
2573 <ul>
2574 <li><tt>unsigned getNumElements() const</tt>: Returns the number of
2575 elements in the array. </li>
2576 </ul>
2577 </dd>
2578 <dt><tt>PointerType</tt></dt>
Chris Lattner302da1e2007-02-03 03:05:57 +0000[diff] [blame]2579 <dd>Subclass of SequentialType for pointer types.</dd>
Reid Spencer9d6565a2007-02-15 02:26:10 +0000[diff] [blame]2580 <dt><tt>VectorType</tt></dt>
Reid Spencer485bad12007-02-15 03:07:05 +0000[diff] [blame]2581 <dd>Subclass of SequentialType for vector types. A
2582 vector type is similar to an ArrayType but is distinguished because it is
2583 a first class type wherease ArrayType is not. Vector types are used for
Reid Spencer303c4b42007-01-12 17:26:25 +0000[diff] [blame]2584 vector operations and are usually small vectors of of an integer or floating
2585 point type.</dd>
2586 <dt><tt>StructType</tt></dt>
2587 <dd>Subclass of DerivedTypes for struct types.</dd>
Duncan Sands8036ca42007-03-30 12:22:09 +0000[diff] [blame]2588 <dt><tt><a name="FunctionType">FunctionType</a></tt></dt>
Reid Spencer303c4b42007-01-12 17:26:25 +0000[diff] [blame]2589 <dd>Subclass of DerivedTypes for function types.
2590 <ul>
2591 <li><tt>bool isVarArg() const</tt>: Returns true if its a vararg
2592 function</li>
2593 <li><tt> const Type * getReturnType() const</tt>: Returns the
2594 return type of the function.</li>
2595 <li><tt>const Type * getParamType (unsigned i)</tt>: Returns
2596 the type of the ith parameter.</li>
2597 <li><tt> const unsigned getNumParams() const</tt>: Returns the
2598 number of formal parameters.</li>
2599 </ul>
2600 </dd>
2601 <dt><tt>OpaqueType</tt></dt>
2602 <dd>Sublcass of DerivedType for abstract types. This class
2603 defines no content and is used as a placeholder for some other type. Note
2604 that OpaqueType is used (temporarily) during type resolution for forward
2605 references of types. Once the referenced type is resolved, the OpaqueType
2606 is replaced with the actual type. OpaqueType can also be used for data
2607 abstraction. At link time opaque types can be resolved to actual types
2608 of the same name.</dd>
2609</dl>
2610</div>
2611
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]2612
2613
2614<!-- ======================================================================= -->
2615<div class="doc_subsection">
2616 <a name="Module">The <tt>Module</tt> class</a>
2617</div>
2618
2619<div class="doc_text">
2620
2621<p><tt>#include "<a
2622href="/doxygen/Module_8h-source.html">llvm/Module.h</a>"</tt><br> doxygen info:
2623<a href="/doxygen/classllvm_1_1Module.html">Module Class</a></p>
2624
2625<p>The <tt>Module</tt> class represents the top level structure present in LLVM
2626programs. An LLVM module is effectively either a translation unit of the
2627original program or a combination of several translation units merged by the
2628linker. The <tt>Module</tt> class keeps track of a list of <a
2629href="#Function"><tt>Function</tt></a>s, a list of <a
2630href="#GlobalVariable"><tt>GlobalVariable</tt></a>s, and a <a
2631href="#SymbolTable"><tt>SymbolTable</tt></a>. Additionally, it contains a few
2632helpful member functions that try to make common operations easy.</p>
2633
2634</div>
2635
2636<!-- _______________________________________________________________________ -->
2637<div class="doc_subsubsection">
2638 <a name="m_Module">Important Public Members of the <tt>Module</tt> class</a>
2639</div>
2640
2641<div class="doc_text">
2642
2643<ul>
2644 <li><tt>Module::Module(std::string name = "")</tt></li>
2645</ul>
2646
2647<p>Constructing a <a href="#Module">Module</a> is easy. You can optionally
2648provide a name for it (probably based on the name of the translation unit).</p>
2649
2650<ul>
2651 <li><tt>Module::iterator</tt> - Typedef for function list iterator<br>
2652 <tt>Module::const_iterator</tt> - Typedef for const_iterator.<br>
2653
2654 <tt>begin()</tt>, <tt>end()</tt>
2655 <tt>size()</tt>, <tt>empty()</tt>
2656
2657 <p>These are forwarding methods that make it easy to access the contents of
2658 a <tt>Module</tt> object's <a href="#Function"><tt>Function</tt></a>
2659 list.</p></li>
2660
2661 <li><tt>Module::FunctionListType &amp;getFunctionList()</tt>
2662
2663 <p> Returns the list of <a href="#Function"><tt>Function</tt></a>s. This is
2664 necessary to use when you need to update the list or perform a complex
2665 action that doesn't have a forwarding method.</p>
2666
2667 <p><!-- Global Variable --></p></li>
2668</ul>
2669
2670<hr>
2671
2672<ul>
2673 <li><tt>Module::global_iterator</tt> - Typedef for global variable list iterator<br>
2674
2675 <tt>Module::const_global_iterator</tt> - Typedef for const_iterator.<br>
2676
2677 <tt>global_begin()</tt>, <tt>global_end()</tt>
2678 <tt>global_size()</tt>, <tt>global_empty()</tt>
2679
2680 <p> These are forwarding methods that make it easy to access the contents of
2681 a <tt>Module</tt> object's <a
2682 href="#GlobalVariable"><tt>GlobalVariable</tt></a> list.</p></li>
2683
2684 <li><tt>Module::GlobalListType &amp;getGlobalList()</tt>
2685
2686 <p>Returns the list of <a
2687 href="#GlobalVariable"><tt>GlobalVariable</tt></a>s. This is necessary to
2688 use when you need to update the list or perform a complex action that
2689 doesn't have a forwarding method.</p>
2690
2691 <p><!-- Symbol table stuff --> </p></li>
2692</ul>
2693
2694<hr>
2695
2696<ul>
2697 <li><tt><a href="#SymbolTable">SymbolTable</a> *getSymbolTable()</tt>
2698
2699 <p>Return a reference to the <a href="#SymbolTable"><tt>SymbolTable</tt></a>
2700 for this <tt>Module</tt>.</p>
2701
2702 <p><!-- Convenience methods --></p></li>
2703</ul>
2704
2705<hr>
2706
2707<ul>
2708 <li><tt><a href="#Function">Function</a> *getFunction(const std::string
2709 &amp;Name, const <a href="#FunctionType">FunctionType</a> *Ty)</tt>
2710
2711 <p>Look up the specified function in the <tt>Module</tt> <a
2712 href="#SymbolTable"><tt>SymbolTable</tt></a>. If it does not exist, return
2713 <tt>null</tt>.</p></li>
2714
2715 <li><tt><a href="#Function">Function</a> *getOrInsertFunction(const
2716 std::string &amp;Name, const <a href="#FunctionType">FunctionType</a> *T)</tt>
2717
2718 <p>Look up the specified function in the <tt>Module</tt> <a
2719 href="#SymbolTable"><tt>SymbolTable</tt></a>. If it does not exist, add an
2720 external declaration for the function and return it.</p></li>
2721
2722 <li><tt>std::string getTypeName(const <a href="#Type">Type</a> *Ty)</tt>
2723
2724 <p>If there is at least one entry in the <a
2725 href="#SymbolTable"><tt>SymbolTable</tt></a> for the specified <a
2726 href="#Type"><tt>Type</tt></a>, return it. Otherwise return the empty
2727 string.</p></li>
2728
2729 <li><tt>bool addTypeName(const std::string &amp;Name, const <a
2730 href="#Type">Type</a> *Ty)</tt>
2731
2732 <p>Insert an entry in the <a href="#SymbolTable"><tt>SymbolTable</tt></a>
2733 mapping <tt>Name</tt> to <tt>Ty</tt>. If there is already an entry for this
2734 name, true is returned and the <a
2735 href="#SymbolTable"><tt>SymbolTable</tt></a> is not modified.</p></li>
2736</ul>
2737
2738</div>
2739
2740
Reid Spencer303c4b42007-01-12 17:26:25 +0000[diff] [blame]2741<!-- ======================================================================= -->
2742<div class="doc_subsection">
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2743 <a name="Value">The <tt>Value</tt> class</a>
2744</div>
2745
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]2746<div class="doc_text">
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2747
2748<p><tt>#include "<a href="/doxygen/Value_8h-source.html">llvm/Value.h</a>"</tt>
2749<br>
Chris Lattner00815172007-01-04 22:01:45 +0000[diff] [blame]2750doxygen info: <a href="/doxygen/classllvm_1_1Value.html">Value Class</a></p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2751
2752<p>The <tt>Value</tt> class is the most important class in the LLVM Source
2753base. It represents a typed value that may be used (among other things) as an
2754operand to an instruction. There are many different types of <tt>Value</tt>s,
2755such as <a href="#Constant"><tt>Constant</tt></a>s,<a
2756href="#Argument"><tt>Argument</tt></a>s. Even <a
2757href="#Instruction"><tt>Instruction</tt></a>s and <a
2758href="#Function"><tt>Function</tt></a>s are <tt>Value</tt>s.</p>
2759
2760<p>A particular <tt>Value</tt> may be used many times in the LLVM representation
2761for a program. For example, an incoming argument to a function (represented
2762with an instance of the <a href="#Argument">Argument</a> class) is "used" by
2763every instruction in the function that references the argument. To keep track
2764of this relationship, the <tt>Value</tt> class keeps a list of all of the <a
2765href="#User"><tt>User</tt></a>s that is using it (the <a
2766href="#User"><tt>User</tt></a> class is a base class for all nodes in the LLVM
2767graph that can refer to <tt>Value</tt>s). This use list is how LLVM represents
2768def-use information in the program, and is accessible through the <tt>use_</tt>*
2769methods, shown below.</p>
2770
2771<p>Because LLVM is a typed representation, every LLVM <tt>Value</tt> is typed,
2772and this <a href="#Type">Type</a> is available through the <tt>getType()</tt>
2773method. In addition, all LLVM values can be named. The "name" of the
2774<tt>Value</tt> is a symbolic string printed in the LLVM code:</p>
2775
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2776<div class="doc_code">
2777<pre>
Reid Spencer06565dc2007-01-12 17:11:23 +0000[diff] [blame]2778%<b>foo</b> = add i32 1, 2
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2779</pre>
2780</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2781
Duncan Sands8036ca42007-03-30 12:22:09 +0000[diff] [blame]2782<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]2783that the name of any value may be missing (an empty string), so names should
2784<b>ONLY</b> be used for debugging (making the source code easier to read,
2785debugging printouts), they should not be used to keep track of values or map
2786between them. For this purpose, use a <tt>std::map</tt> of pointers to the
2787<tt>Value</tt> itself instead.</p>
2788
2789<p>One important aspect of LLVM is that there is no distinction between an SSA
2790variable and the operation that produces it. Because of this, any reference to
2791the value produced by an instruction (or the value available as an incoming
Chris Lattnerd5fc4fc2004-03-18 14:58:55 +0000[diff] [blame]2792argument, for example) is represented as a direct pointer to the instance of
2793the class that
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2794represents this value. Although this may take some getting used to, it
2795simplifies the representation and makes it easier to manipulate.</p>
2796
2797</div>
2798
2799<!-- _______________________________________________________________________ -->
2800<div class="doc_subsubsection">
2801 <a name="m_Value">Important Public Members of the <tt>Value</tt> class</a>
2802</div>
2803
2804<div class="doc_text">
2805
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]2806<ul>
2807 <li><tt>Value::use_iterator</tt> - Typedef for iterator over the
2808use-list<br>
2809 <tt>Value::use_const_iterator</tt> - Typedef for const_iterator over
2810the use-list<br>
2811 <tt>unsigned use_size()</tt> - Returns the number of users of the
2812value.<br>
Chris Lattner9355b472002-09-06 02:50:58 +0000[diff] [blame]2813 <tt>bool use_empty()</tt> - Returns true if there are no users.<br>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]2814 <tt>use_iterator use_begin()</tt> - Get an iterator to the start of
2815the use-list.<br>
2816 <tt>use_iterator use_end()</tt> - Get an iterator to the end of the
2817use-list.<br>
2818 <tt><a href="#User">User</a> *use_back()</tt> - Returns the last
2819element in the list.
2820 <p> These methods are the interface to access the def-use
2821information in LLVM. As with all other iterators in LLVM, the naming
2822conventions follow the conventions defined by the <a href="#stl">STL</a>.</p>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]2823 </li>
2824 <li><tt><a href="#Type">Type</a> *getType() const</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2825 <p>This method returns the Type of the Value.</p>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]2826 </li>
2827 <li><tt>bool hasName() const</tt><br>
Chris Lattner9355b472002-09-06 02:50:58 +0000[diff] [blame]2828 <tt>std::string getName() const</tt><br>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]2829 <tt>void setName(const std::string &amp;Name)</tt>
2830 <p> This family of methods is used to access and assign a name to a <tt>Value</tt>,
2831be aware of the <a href="#nameWarning">precaution above</a>.</p>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]2832 </li>
2833 <li><tt>void replaceAllUsesWith(Value *V)</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2834
2835 <p>This method traverses the use list of a <tt>Value</tt> changing all <a
2836 href="#User"><tt>User</tt>s</a> of the current value to refer to
2837 "<tt>V</tt>" instead. For example, if you detect that an instruction always
2838 produces a constant value (for example through constant folding), you can
2839 replace all uses of the instruction with the constant like this:</p>
2840
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2841<div class="doc_code">
2842<pre>
2843Inst-&gt;replaceAllUsesWith(ConstVal);
2844</pre>
2845</div>
2846
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]2847</ul>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2848
2849</div>
2850
2851<!-- ======================================================================= -->
2852<div class="doc_subsection">
2853 <a name="User">The <tt>User</tt> class</a>
2854</div>
2855
2856<div class="doc_text">
2857
2858<p>
2859<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]2860doxygen info: <a href="/doxygen/classllvm_1_1User.html">User Class</a><br>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2861Superclass: <a href="#Value"><tt>Value</tt></a></p>
2862
2863<p>The <tt>User</tt> class is the common base class of all LLVM nodes that may
2864refer to <a href="#Value"><tt>Value</tt></a>s. It exposes a list of "Operands"
2865that are all of the <a href="#Value"><tt>Value</tt></a>s that the User is
2866referring to. The <tt>User</tt> class itself is a subclass of
2867<tt>Value</tt>.</p>
2868
2869<p>The operands of a <tt>User</tt> point directly to the LLVM <a
2870href="#Value"><tt>Value</tt></a> that it refers to. Because LLVM uses Static
2871Single Assignment (SSA) form, there can only be one definition referred to,
2872allowing this direct connection. This connection provides the use-def
2873information in LLVM.</p>
2874
2875</div>
2876
2877<!-- _______________________________________________________________________ -->
2878<div class="doc_subsubsection">
2879 <a name="m_User">Important Public Members of the <tt>User</tt> class</a>
2880</div>
2881
2882<div class="doc_text">
2883
2884<p>The <tt>User</tt> class exposes the operand list in two ways: through
2885an index access interface and through an iterator based interface.</p>
2886
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]2887<ul>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]2888 <li><tt>Value *getOperand(unsigned i)</tt><br>
2889 <tt>unsigned getNumOperands()</tt>
2890 <p> These two methods expose the operands of the <tt>User</tt> in a
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2891convenient form for direct access.</p></li>
2892
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]2893 <li><tt>User::op_iterator</tt> - Typedef for iterator over the operand
2894list<br>
Chris Lattner58360822005-01-17 00:12:04 +0000[diff] [blame]2895 <tt>op_iterator op_begin()</tt> - Get an iterator to the start of
2896the operand list.<br>
2897 <tt>op_iterator op_end()</tt> - Get an iterator to the end of the
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]2898operand list.
2899 <p> Together, these methods make up the iterator based interface to
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2900the operands of a <tt>User</tt>.</p></li>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]2901</ul>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2902
2903</div>
2904
2905<!-- ======================================================================= -->
2906<div class="doc_subsection">
2907 <a name="Instruction">The <tt>Instruction</tt> class</a>
2908</div>
2909
2910<div class="doc_text">
2911
2912<p><tt>#include "</tt><tt><a
2913href="/doxygen/Instruction_8h-source.html">llvm/Instruction.h</a>"</tt><br>
Misha Brukman31ca1de2004-06-03 23:35:54 +0000[diff] [blame]2914doxygen info: <a href="/doxygen/classllvm_1_1Instruction.html">Instruction Class</a><br>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2915Superclasses: <a href="#User"><tt>User</tt></a>, <a
2916href="#Value"><tt>Value</tt></a></p>
2917
2918<p>The <tt>Instruction</tt> class is the common base class for all LLVM
2919instructions. It provides only a few methods, but is a very commonly used
2920class. The primary data tracked by the <tt>Instruction</tt> class itself is the
2921opcode (instruction type) and the parent <a
2922href="#BasicBlock"><tt>BasicBlock</tt></a> the <tt>Instruction</tt> is embedded
2923into. To represent a specific type of instruction, one of many subclasses of
2924<tt>Instruction</tt> are used.</p>
2925
2926<p> Because the <tt>Instruction</tt> class subclasses the <a
2927href="#User"><tt>User</tt></a> class, its operands can be accessed in the same
2928way as for other <a href="#User"><tt>User</tt></a>s (with the
2929<tt>getOperand()</tt>/<tt>getNumOperands()</tt> and
2930<tt>op_begin()</tt>/<tt>op_end()</tt> methods).</p> <p> An important file for
2931the <tt>Instruction</tt> class is the <tt>llvm/Instruction.def</tt> file. This
2932file contains some meta-data about the various different types of instructions
2933in LLVM. It describes the enum values that are used as opcodes (for example
Reid Spencerc92d25d2006-12-19 19:47:19 +0000[diff] [blame]2934<tt>Instruction::Add</tt> and <tt>Instruction::ICmp</tt>), as well as the
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2935concrete sub-classes of <tt>Instruction</tt> that implement the instruction (for
2936example <tt><a href="#BinaryOperator">BinaryOperator</a></tt> and <tt><a
Reid Spencerc92d25d2006-12-19 19:47:19 +0000[diff] [blame]2937href="#CmpInst">CmpInst</a></tt>). Unfortunately, the use of macros in
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2938this file confuses doxygen, so these enum values don't show up correctly in the
Misha Brukman31ca1de2004-06-03 23:35:54 +0000[diff] [blame]2939<a href="/doxygen/classllvm_1_1Instruction.html">doxygen output</a>.</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2940
2941</div>
2942
2943<!-- _______________________________________________________________________ -->
2944<div class="doc_subsubsection">
Reid Spencerc92d25d2006-12-19 19:47:19 +0000[diff] [blame]2945 <a name="s_Instruction">Important Subclasses of the <tt>Instruction</tt>
2946 class</a>
2947</div>
2948<div class="doc_text">
2949 <ul>
2950 <li><tt><a name="BinaryOperator">BinaryOperator</a></tt>
2951 <p>This subclasses represents all two operand instructions whose operands
2952 must be the same type, except for the comparison instructions.</p></li>
2953 <li><tt><a name="CastInst">CastInst</a></tt>
2954 <p>This subclass is the parent of the 12 casting instructions. It provides
2955 common operations on cast instructions.</p>
2956 <li><tt><a name="CmpInst">CmpInst</a></tt>
2957 <p>This subclass respresents the two comparison instructions,
2958 <a href="LangRef.html#i_icmp">ICmpInst</a> (integer opreands), and
2959 <a href="LangRef.html#i_fcmp">FCmpInst</a> (floating point operands).</p>
2960 <li><tt><a name="TerminatorInst">TerminatorInst</a></tt>
2961 <p>This subclass is the parent of all terminator instructions (those which
2962 can terminate a block).</p>
2963 </ul>
2964 </div>
2965
2966<!-- _______________________________________________________________________ -->
2967<div class="doc_subsubsection">
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2968 <a name="m_Instruction">Important Public Members of the <tt>Instruction</tt>
2969 class</a>
2970</div>
2971
2972<div class="doc_text">
2973
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]2974<ul>
2975 <li><tt><a href="#BasicBlock">BasicBlock</a> *getParent()</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2976 <p>Returns the <a href="#BasicBlock"><tt>BasicBlock</tt></a> that
2977this <tt>Instruction</tt> is embedded into.</p></li>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]2978 <li><tt>bool mayWriteToMemory()</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2979 <p>Returns true if the instruction writes to memory, i.e. it is a
2980 <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]2981 <li><tt>unsigned getOpcode()</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2982 <p>Returns the opcode for the <tt>Instruction</tt>.</p></li>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]2983 <li><tt><a href="#Instruction">Instruction</a> *clone() const</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2984 <p>Returns another instance of the specified instruction, identical
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]2985in all ways to the original except that the instruction has no parent
2986(ie it's not embedded into a <a href="#BasicBlock"><tt>BasicBlock</tt></a>),
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2987and it has no name</p></li>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]2988</ul>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2989
2990</div>
2991
2992<!-- ======================================================================= -->
2993<div class="doc_subsection">
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]2994 <a name="Constant">The <tt>Constant</tt> class and subclasses</a>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2995</div>
2996
2997<div class="doc_text">
2998
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]2999<p>Constant represents a base class for different types of constants. It
3000is subclassed by ConstantInt, ConstantArray, etc. for representing
3001the various types of Constants. <a href="#GlobalValue">GlobalValue</a> is also
3002a subclass, which represents the address of a global variable or function.
3003</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3004
3005</div>
3006
3007<!-- _______________________________________________________________________ -->
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]3008<div class="doc_subsubsection">Important Subclasses of Constant </div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3009<div class="doc_text">
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3010<ul>
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]3011 <li>ConstantInt : This subclass of Constant represents an integer constant of
3012 any width.
3013 <ul>
Reid Spencer97b4ee32007-03-01 21:05:33 +0000[diff] [blame]3014 <li><tt>const APInt&amp; getValue() const</tt>: Returns the underlying
3015 value of this constant, an APInt value.</li>
3016 <li><tt>int64_t getSExtValue() const</tt>: Converts the underlying APInt
3017 value to an int64_t via sign extension. If the value (not the bit width)
3018 of the APInt is too large to fit in an int64_t, an assertion will result.
3019 For this reason, use of this method is discouraged.</li>
3020 <li><tt>uint64_t getZExtValue() const</tt>: Converts the underlying APInt
3021 value to a uint64_t via zero extension. IF the value (not the bit width)
3022 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]3023 For this reason, use of this method is discouraged.</li>
Reid Spencer97b4ee32007-03-01 21:05:33 +0000[diff] [blame]3024 <li><tt>static ConstantInt* get(const APInt&amp; Val)</tt>: Returns the
3025 ConstantInt object that represents the value provided by <tt>Val</tt>.
3026 The type is implied as the IntegerType that corresponds to the bit width
3027 of <tt>Val</tt>.</li>
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]3028 <li><tt>static ConstantInt* get(const Type *Ty, uint64_t Val)</tt>:
3029 Returns the ConstantInt object that represents the value provided by
3030 <tt>Val</tt> for integer type <tt>Ty</tt>.</li>
3031 </ul>
3032 </li>
3033 <li>ConstantFP : This class represents a floating point constant.
3034 <ul>
3035 <li><tt>double getValue() const</tt>: Returns the underlying value of
3036 this constant. </li>
3037 </ul>
3038 </li>
3039 <li>ConstantArray : This represents a constant array.
3040 <ul>
3041 <li><tt>const std::vector&lt;Use&gt; &amp;getValues() const</tt>: Returns
3042 a vector of component constants that makeup this array. </li>
3043 </ul>
3044 </li>
3045 <li>ConstantStruct : This represents a constant struct.
3046 <ul>
3047 <li><tt>const std::vector&lt;Use&gt; &amp;getValues() const</tt>: Returns
3048 a vector of component constants that makeup this array. </li>
3049 </ul>
3050 </li>
3051 <li>GlobalValue : This represents either a global variable or a function. In
3052 either case, the value is a constant fixed address (after linking).
3053 </li>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3054</ul>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3055</div>
3056
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]3057
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3058<!-- ======================================================================= -->
3059<div class="doc_subsection">
3060 <a name="GlobalValue">The <tt>GlobalValue</tt> class</a>
3061</div>
3062
3063<div class="doc_text">
3064
3065<p><tt>#include "<a
3066href="/doxygen/GlobalValue_8h-source.html">llvm/GlobalValue.h</a>"</tt><br>
Misha Brukman384047f2004-06-03 23:29:12 +0000[diff] [blame]3067doxygen info: <a href="/doxygen/classllvm_1_1GlobalValue.html">GlobalValue
3068Class</a><br>
Reid Spencerbe5e85e2006-04-14 14:11:48 +0000[diff] [blame]3069Superclasses: <a href="#Constant"><tt>Constant</tt></a>,
3070<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]3071
3072<p>Global values (<a href="#GlobalVariable"><tt>GlobalVariable</tt></a>s or <a
3073href="#Function"><tt>Function</tt></a>s) are the only LLVM values that are
3074visible in the bodies of all <a href="#Function"><tt>Function</tt></a>s.
3075Because they are visible at global scope, they are also subject to linking with
3076other globals defined in different translation units. To control the linking
3077process, <tt>GlobalValue</tt>s know their linkage rules. Specifically,
3078<tt>GlobalValue</tt>s know whether they have internal or external linkage, as
Reid Spencer8b2da7a2004-07-18 13:10:31 +0000[diff] [blame]3079defined by the <tt>LinkageTypes</tt> enumeration.</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3080
3081<p>If a <tt>GlobalValue</tt> has internal linkage (equivalent to being
3082<tt>static</tt> in C), it is not visible to code outside the current translation
3083unit, and does not participate in linking. If it has external linkage, it is
3084visible to external code, and does participate in linking. In addition to
3085linkage information, <tt>GlobalValue</tt>s keep track of which <a
3086href="#Module"><tt>Module</tt></a> they are currently part of.</p>
3087
3088<p>Because <tt>GlobalValue</tt>s are memory objects, they are always referred to
3089by their <b>address</b>. As such, the <a href="#Type"><tt>Type</tt></a> of a
3090global is always a pointer to its contents. It is important to remember this
3091when using the <tt>GetElementPtrInst</tt> instruction because this pointer must
3092be dereferenced first. For example, if you have a <tt>GlobalVariable</tt> (a
3093subclass 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]3094i32]</tt>, then the <tt>GlobalVariable</tt> is a pointer to that array. Although
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3095the address of the first element of this array and the value of the
3096<tt>GlobalVariable</tt> are the same, they have different types. The
Reid Spencer06565dc2007-01-12 17:11:23 +0000[diff] [blame]3097<tt>GlobalVariable</tt>'s type is <tt>[24 x i32]</tt>. The first element's type
3098is <tt>i32.</tt> Because of this, accessing a global value requires you to
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3099dereference the pointer with <tt>GetElementPtrInst</tt> first, then its elements
3100can be accessed. This is explained in the <a href="LangRef.html#globalvars">LLVM
3101Language Reference Manual</a>.</p>
3102
3103</div>
3104
3105<!-- _______________________________________________________________________ -->
3106<div class="doc_subsubsection">
3107 <a name="m_GlobalValue">Important Public Members of the <tt>GlobalValue</tt>
3108 class</a>
3109</div>
3110
3111<div class="doc_text">
3112
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3113<ul>
3114 <li><tt>bool hasInternalLinkage() const</tt><br>
Chris Lattner9355b472002-09-06 02:50:58 +0000[diff] [blame]3115 <tt>bool hasExternalLinkage() const</tt><br>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3116 <tt>void setInternalLinkage(bool HasInternalLinkage)</tt>
3117 <p> These methods manipulate the linkage characteristics of the <tt>GlobalValue</tt>.</p>
3118 <p> </p>
3119 </li>
3120 <li><tt><a href="#Module">Module</a> *getParent()</tt>
3121 <p> This returns the <a href="#Module"><tt>Module</tt></a> that the
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3122GlobalValue is currently embedded into.</p></li>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3123</ul>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3124
3125</div>
3126
3127<!-- ======================================================================= -->
3128<div class="doc_subsection">
3129 <a name="Function">The <tt>Function</tt> class</a>
3130</div>
3131
3132<div class="doc_text">
3133
3134<p><tt>#include "<a
3135href="/doxygen/Function_8h-source.html">llvm/Function.h</a>"</tt><br> doxygen
Misha Brukman31ca1de2004-06-03 23:35:54 +0000[diff] [blame]3136info: <a href="/doxygen/classllvm_1_1Function.html">Function Class</a><br>
Reid Spencerbe5e85e2006-04-14 14:11:48 +0000[diff] [blame]3137Superclasses: <a href="#GlobalValue"><tt>GlobalValue</tt></a>,
3138<a href="#Constant"><tt>Constant</tt></a>,
3139<a href="#User"><tt>User</tt></a>,
3140<a href="#Value"><tt>Value</tt></a></p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3141
3142<p>The <tt>Function</tt> class represents a single procedure in LLVM. It is
3143actually one of the more complex classes in the LLVM heirarchy because it must
3144keep track of a large amount of data. The <tt>Function</tt> class keeps track
Reid Spencerbe5e85e2006-04-14 14:11:48 +0000[diff] [blame]3145of a list of <a href="#BasicBlock"><tt>BasicBlock</tt></a>s, a list of formal
3146<a href="#Argument"><tt>Argument</tt></a>s, and a
3147<a href="#SymbolTable"><tt>SymbolTable</tt></a>.</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3148
3149<p>The list of <a href="#BasicBlock"><tt>BasicBlock</tt></a>s is the most
3150commonly used part of <tt>Function</tt> objects. The list imposes an implicit
3151ordering of the blocks in the function, which indicate how the code will be
3152layed out by the backend. Additionally, the first <a
3153href="#BasicBlock"><tt>BasicBlock</tt></a> is the implicit entry node for the
3154<tt>Function</tt>. It is not legal in LLVM to explicitly branch to this initial
3155block. There are no implicit exit nodes, and in fact there may be multiple exit
3156nodes from a single <tt>Function</tt>. If the <a
3157href="#BasicBlock"><tt>BasicBlock</tt></a> list is empty, this indicates that
3158the <tt>Function</tt> is actually a function declaration: the actual body of the
3159function hasn't been linked in yet.</p>
3160
3161<p>In addition to a list of <a href="#BasicBlock"><tt>BasicBlock</tt></a>s, the
3162<tt>Function</tt> class also keeps track of the list of formal <a
3163href="#Argument"><tt>Argument</tt></a>s that the function receives. This
3164container manages the lifetime of the <a href="#Argument"><tt>Argument</tt></a>
3165nodes, just like the <a href="#BasicBlock"><tt>BasicBlock</tt></a> list does for
3166the <a href="#BasicBlock"><tt>BasicBlock</tt></a>s.</p>
3167
3168<p>The <a href="#SymbolTable"><tt>SymbolTable</tt></a> is a very rarely used
3169LLVM feature that is only used when you have to look up a value by name. Aside
3170from that, the <a href="#SymbolTable"><tt>SymbolTable</tt></a> is used
3171internally to make sure that there are not conflicts between the names of <a
3172href="#Instruction"><tt>Instruction</tt></a>s, <a
3173href="#BasicBlock"><tt>BasicBlock</tt></a>s, or <a
3174href="#Argument"><tt>Argument</tt></a>s in the function body.</p>
3175
Reid Spencer8b2da7a2004-07-18 13:10:31 +0000[diff] [blame]3176<p>Note that <tt>Function</tt> is a <a href="#GlobalValue">GlobalValue</a>
3177and therefore also a <a href="#Constant">Constant</a>. The value of the function
3178is its address (after linking) which is guaranteed to be constant.</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3179</div>
3180
3181<!-- _______________________________________________________________________ -->
3182<div class="doc_subsubsection">
3183 <a name="m_Function">Important Public Members of the <tt>Function</tt>
3184 class</a>
3185</div>
3186
3187<div class="doc_text">
3188
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3189<ul>
3190 <li><tt>Function(const </tt><tt><a href="#FunctionType">FunctionType</a>
Chris Lattnerac479e52004-08-04 05:10:48 +0000[diff] [blame]3191 *Ty, LinkageTypes Linkage, const std::string &amp;N = "", Module* Parent = 0)</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3192
3193 <p>Constructor used when you need to create new <tt>Function</tt>s to add
3194 the the program. The constructor must specify the type of the function to
Chris Lattnerac479e52004-08-04 05:10:48 +0000[diff] [blame]3195 create and what type of linkage the function should have. The <a
3196 href="#FunctionType"><tt>FunctionType</tt></a> argument
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3197 specifies the formal arguments and return value for the function. The same
Duncan Sands8036ca42007-03-30 12:22:09 +0000[diff] [blame]3198 <a href="#FunctionType"><tt>FunctionType</tt></a> value can be used to
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3199 create multiple functions. The <tt>Parent</tt> argument specifies the Module
3200 in which the function is defined. If this argument is provided, the function
3201 will automatically be inserted into that module's list of
3202 functions.</p></li>
3203
Chris Lattner62810e32008-11-25 18:34:50 +0000[diff] [blame]3204 <li><tt>bool isDeclaration()</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3205
3206 <p>Return whether or not the <tt>Function</tt> has a body defined. If the
3207 function is "external", it does not have a body, and thus must be resolved
3208 by linking with a function defined in a different translation unit.</p></li>
3209
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3210 <li><tt>Function::iterator</tt> - Typedef for basic block list iterator<br>
Chris Lattner9355b472002-09-06 02:50:58 +0000[diff] [blame]3211 <tt>Function::const_iterator</tt> - Typedef for const_iterator.<br>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3212
Chris Lattner77d69242005-03-15 05:19:20 +0000[diff] [blame]3213 <tt>begin()</tt>, <tt>end()</tt>
3214 <tt>size()</tt>, <tt>empty()</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3215
3216 <p>These are forwarding methods that make it easy to access the contents of
3217 a <tt>Function</tt> object's <a href="#BasicBlock"><tt>BasicBlock</tt></a>
3218 list.</p></li>
3219
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3220 <li><tt>Function::BasicBlockListType &amp;getBasicBlockList()</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3221
3222 <p>Returns the list of <a href="#BasicBlock"><tt>BasicBlock</tt></a>s. This
3223 is necessary to use when you need to update the list or perform a complex
3224 action that doesn't have a forwarding method.</p></li>
3225
Chris Lattner89cc2652005-03-15 04:48:32 +0000[diff] [blame]3226 <li><tt>Function::arg_iterator</tt> - Typedef for the argument list
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3227iterator<br>
Chris Lattner89cc2652005-03-15 04:48:32 +0000[diff] [blame]3228 <tt>Function::const_arg_iterator</tt> - Typedef for const_iterator.<br>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3229
Chris Lattner77d69242005-03-15 05:19:20 +0000[diff] [blame]3230 <tt>arg_begin()</tt>, <tt>arg_end()</tt>
Chris Lattner89cc2652005-03-15 04:48:32 +0000[diff] [blame]3231 <tt>arg_size()</tt>, <tt>arg_empty()</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3232
3233 <p>These are forwarding methods that make it easy to access the contents of
3234 a <tt>Function</tt> object's <a href="#Argument"><tt>Argument</tt></a>
3235 list.</p></li>
3236
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3237 <li><tt>Function::ArgumentListType &amp;getArgumentList()</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3238
3239 <p>Returns the list of <a href="#Argument"><tt>Argument</tt></a>s. This is
3240 necessary to use when you need to update the list or perform a complex
3241 action that doesn't have a forwarding method.</p></li>
3242
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3243 <li><tt><a href="#BasicBlock">BasicBlock</a> &amp;getEntryBlock()</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3244
3245 <p>Returns the entry <a href="#BasicBlock"><tt>BasicBlock</tt></a> for the
3246 function. Because the entry block for the function is always the first
3247 block, this returns the first block of the <tt>Function</tt>.</p></li>
3248
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3249 <li><tt><a href="#Type">Type</a> *getReturnType()</tt><br>
3250 <tt><a href="#FunctionType">FunctionType</a> *getFunctionType()</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3251
3252 <p>This traverses the <a href="#Type"><tt>Type</tt></a> of the
3253 <tt>Function</tt> and returns the return type of the function, or the <a
3254 href="#FunctionType"><tt>FunctionType</tt></a> of the actual
3255 function.</p></li>
3256
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3257 <li><tt><a href="#SymbolTable">SymbolTable</a> *getSymbolTable()</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3258
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3259 <p> Return a pointer to the <a href="#SymbolTable"><tt>SymbolTable</tt></a>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3260 for this <tt>Function</tt>.</p></li>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3261</ul>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3262
3263</div>
3264
3265<!-- ======================================================================= -->
3266<div class="doc_subsection">
3267 <a name="GlobalVariable">The <tt>GlobalVariable</tt> class</a>
3268</div>
3269
3270<div class="doc_text">
3271
3272<p><tt>#include "<a
3273href="/doxygen/GlobalVariable_8h-source.html">llvm/GlobalVariable.h</a>"</tt>
3274<br>
Tanya Lattnera3da7772004-06-22 08:02:25 +0000[diff] [blame]3275doxygen info: <a href="/doxygen/classllvm_1_1GlobalVariable.html">GlobalVariable
Reid Spencerbe5e85e2006-04-14 14:11:48 +0000[diff] [blame]3276 Class</a><br>
3277Superclasses: <a href="#GlobalValue"><tt>GlobalValue</tt></a>,
3278<a href="#Constant"><tt>Constant</tt></a>,
3279<a href="#User"><tt>User</tt></a>,
3280<a href="#Value"><tt>Value</tt></a></p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3281
3282<p>Global variables are represented with the (suprise suprise)
3283<tt>GlobalVariable</tt> class. Like functions, <tt>GlobalVariable</tt>s are also
3284subclasses of <a href="#GlobalValue"><tt>GlobalValue</tt></a>, and as such are
3285always referenced by their address (global values must live in memory, so their
Reid Spencerbe5e85e2006-04-14 14:11:48 +0000[diff] [blame]3286"name" refers to their constant address). See
3287<a href="#GlobalValue"><tt>GlobalValue</tt></a> for more on this. Global
3288variables may have an initial value (which must be a
3289<a href="#Constant"><tt>Constant</tt></a>), and if they have an initializer,
3290they may be marked as "constant" themselves (indicating that their contents
3291never change at runtime).</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3292</div>
3293
3294<!-- _______________________________________________________________________ -->
3295<div class="doc_subsubsection">
3296 <a name="m_GlobalVariable">Important Public Members of the
3297 <tt>GlobalVariable</tt> class</a>
3298</div>
3299
3300<div class="doc_text">
3301
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3302<ul>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3303 <li><tt>GlobalVariable(const </tt><tt><a href="#Type">Type</a> *Ty, bool
3304 isConstant, LinkageTypes&amp; Linkage, <a href="#Constant">Constant</a>
3305 *Initializer = 0, const std::string &amp;Name = "", Module* Parent = 0)</tt>
3306
3307 <p>Create a new global variable of the specified type. If
3308 <tt>isConstant</tt> is true then the global variable will be marked as
3309 unchanging for the program. The Linkage parameter specifies the type of
3310 linkage (internal, external, weak, linkonce, appending) for the variable. If
3311 the linkage is InternalLinkage, WeakLinkage, or LinkOnceLinkage,&nbsp; then
3312 the resultant global variable will have internal linkage. AppendingLinkage
3313 concatenates together all instances (in different translation units) of the
3314 variable into a single variable but is only applicable to arrays. &nbsp;See
3315 the <a href="LangRef.html#modulestructure">LLVM Language Reference</a> for
3316 further details on linkage types. Optionally an initializer, a name, and the
3317 module to put the variable into may be specified for the global variable as
3318 well.</p></li>
3319
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3320 <li><tt>bool isConstant() const</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3321
3322 <p>Returns true if this is a global variable that is known not to
3323 be modified at runtime.</p></li>
3324
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3325 <li><tt>bool hasInitializer()</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3326
3327 <p>Returns true if this <tt>GlobalVariable</tt> has an intializer.</p></li>
3328
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3329 <li><tt><a href="#Constant">Constant</a> *getInitializer()</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3330
3331 <p>Returns the intial value for a <tt>GlobalVariable</tt>. It is not legal
3332 to call this method if there is no initializer.</p></li>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3333</ul>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3334
3335</div>
3336
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]3337
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3338<!-- ======================================================================= -->
3339<div class="doc_subsection">
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]3340 <a name="BasicBlock">The <tt>BasicBlock</tt> class</a>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3341</div>
3342
3343<div class="doc_text">
3344
3345<p><tt>#include "<a
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]3346href="/doxygen/BasicBlock_8h-source.html">llvm/BasicBlock.h</a>"</tt><br>
3347doxygen info: <a href="/doxygen/structllvm_1_1BasicBlock.html">BasicBlock
3348Class</a><br>
3349Superclass: <a href="#Value"><tt>Value</tt></a></p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3350
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]3351<p>This class represents a single entry multiple exit section of the code,
3352commonly known as a basic block by the compiler community. The
3353<tt>BasicBlock</tt> class maintains a list of <a
3354href="#Instruction"><tt>Instruction</tt></a>s, which form the body of the block.
3355Matching the language definition, the last element of this list of instructions
3356is always a terminator instruction (a subclass of the <a
3357href="#TerminatorInst"><tt>TerminatorInst</tt></a> class).</p>
3358
3359<p>In addition to tracking the list of instructions that make up the block, the
3360<tt>BasicBlock</tt> class also keeps track of the <a
3361href="#Function"><tt>Function</tt></a> that it is embedded into.</p>
3362
3363<p>Note that <tt>BasicBlock</tt>s themselves are <a
3364href="#Value"><tt>Value</tt></a>s, because they are referenced by instructions
3365like branches and can go in the switch tables. <tt>BasicBlock</tt>s have type
3366<tt>label</tt>.</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3367
3368</div>
3369
3370<!-- _______________________________________________________________________ -->
3371<div class="doc_subsubsection">
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]3372 <a name="m_BasicBlock">Important Public Members of the <tt>BasicBlock</tt>
3373 class</a>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3374</div>
3375
3376<div class="doc_text">
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3377<ul>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3378
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]3379<li><tt>BasicBlock(const std::string &amp;Name = "", </tt><tt><a
3380 href="#Function">Function</a> *Parent = 0)</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3381
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]3382<p>The <tt>BasicBlock</tt> constructor is used to create new basic blocks for
3383insertion into a function. The constructor optionally takes a name for the new
3384block, and a <a href="#Function"><tt>Function</tt></a> to insert it into. If
3385the <tt>Parent</tt> parameter is specified, the new <tt>BasicBlock</tt> is
3386automatically inserted at the end of the specified <a
3387href="#Function"><tt>Function</tt></a>, if not specified, the BasicBlock must be
3388manually inserted into the <a href="#Function"><tt>Function</tt></a>.</p></li>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3389
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]3390<li><tt>BasicBlock::iterator</tt> - Typedef for instruction list iterator<br>
3391<tt>BasicBlock::const_iterator</tt> - Typedef for const_iterator.<br>
3392<tt>begin()</tt>, <tt>end()</tt>, <tt>front()</tt>, <tt>back()</tt>,
3393<tt>size()</tt>, <tt>empty()</tt>
3394STL-style functions for accessing the instruction list.
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3395
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]3396<p>These methods and typedefs are forwarding functions that have the same
3397semantics as the standard library methods of the same names. These methods
3398expose the underlying instruction list of a basic block in a way that is easy to
3399manipulate. To get the full complement of container operations (including
3400operations to update the list), you must use the <tt>getInstList()</tt>
3401method.</p></li>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3402
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]3403<li><tt>BasicBlock::InstListType &amp;getInstList()</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3404
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]3405<p>This method is used to get access to the underlying container that actually
3406holds the Instructions. This method must be used when there isn't a forwarding
3407function in the <tt>BasicBlock</tt> class for the operation that you would like
3408to perform. Because there are no forwarding functions for "updating"
3409operations, you need to use this if you want to update the contents of a
3410<tt>BasicBlock</tt>.</p></li>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3411
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]3412<li><tt><a href="#Function">Function</a> *getParent()</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3413
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]3414<p> Returns a pointer to <a href="#Function"><tt>Function</tt></a> the block is
3415embedded into, or a null pointer if it is homeless.</p></li>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3416
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]3417<li><tt><a href="#TerminatorInst">TerminatorInst</a> *getTerminator()</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3418
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]3419<p> Returns a pointer to the terminator instruction that appears at the end of
3420the <tt>BasicBlock</tt>. If there is no terminator instruction, or if the last
3421instruction in the block is not a terminator, then a null pointer is
3422returned.</p></li>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3423
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3424</ul>
3425
3426</div>
3427
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3428
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3429<!-- ======================================================================= -->
3430<div class="doc_subsection">
3431 <a name="Argument">The <tt>Argument</tt> class</a>
3432</div>
3433
3434<div class="doc_text">
3435
3436<p>This subclass of Value defines the interface for incoming formal
Chris Lattner58360822005-01-17 00:12:04 +0000[diff] [blame]3437arguments to a function. A Function maintains a list of its formal
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3438arguments. An argument has a pointer to the parent Function.</p>
3439
3440</div>
3441
Chris Lattner9355b472002-09-06 02:50:58 +0000[diff] [blame]3442<!-- *********************************************************************** -->
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3443<hr>
3444<address>
3445 <a href="http://jigsaw.w3.org/css-validator/check/referer"><img
Misha Brukman44408702008-12-11 17:34:48 +0000[diff] [blame]3446 src="http://jigsaw.w3.org/css-validator/images/vcss-blue" alt="Valid CSS"></a>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3447 <a href="http://validator.w3.org/check/referer"><img
Gabor Greifa9c0f2b2008-06-18 14:05:31 +0000[diff] [blame]3448 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]3449
3450 <a href="mailto:dhurjati@cs.uiuc.edu">Dinakar Dhurjati</a> and
3451 <a href="mailto:sabre@nondot.org">Chris Lattner</a><br>
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]3452 <a href="http://llvm.org">The LLVM Compiler Infrastructure</a><br>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3453 Last modified: $Date$
3454</address>
3455
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3456</body>
3457</html>