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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
889<p>ilist has the same drawbacks as std::list, and additionally requires an
890ilist_traits implementation for the element type, but it provides some novel
891characteristics. In particular, it can efficiently store polymorphic objects,
892the traits class is informed when an element is inserted or removed from the
893list, and ilists are guaranteed to support a constant-time splice operation.
894</p>
895
896<p>These properties are exactly what we want for things like Instructions and
897basic blocks, which is why these are implemented with ilists.</p>
Gabor Greif3899e492009-02-27 11:37:41 +0000[diff] [blame^]898
899Related classes of interest are explained in the following subsections:
900 <ul>
901 <li><a href="#dss_ilist_node">llvm/ADT/ilist_node.h</a></li>
902 </ul>
903</div>
904
905<!-- _______________________________________________________________________ -->
906<div class="doc_subsubsection">
907 <a name="dss_ilist_node">llvm/ADT/ilist_node.h</a>
908</div>
909
910<div class="doc_text">
911<p><tt>ilist_node&lt;T&gt;</tt> implements a the forward and backward links
912that are expected by the <tt>ilist&lt;T&gt;</tt> (and analogous containers)
913in the default manner.</p>
914
915<p><tt>ilist_node&lt;T&gt;</tt>s are meant to be embedded in the node type
916<tt>T</tt>.</p>
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]917</div>
918
919<!-- _______________________________________________________________________ -->
920<div class="doc_subsubsection">
Chris Lattnerc5722432007-02-03 19:49:31 +0000[diff] [blame]921 <a name="dss_other">Other Sequential Container options</a>
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]922</div>
923
924<div class="doc_text">
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]925<p>Other STL containers are available, such as std::string.</p>
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]926
927<p>There are also various STL adapter classes such as std::queue,
928std::priority_queue, std::stack, etc. These provide simplified access to an
929underlying container but don't affect the cost of the container itself.</p>
930
931</div>
932
933
934<!-- ======================================================================= -->
935<div class="doc_subsection">
936 <a name="ds_set">Set-Like Containers (std::set, SmallSet, SetVector, etc)</a>
937</div>
938
939<div class="doc_text">
940
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]941<p>Set-like containers are useful when you need to canonicalize multiple values
942into a single representation. There are several different choices for how to do
943this, providing various trade-offs.</p>
944
945</div>
946
947
948<!-- _______________________________________________________________________ -->
949<div class="doc_subsubsection">
950 <a name="dss_sortedvectorset">A sorted 'vector'</a>
951</div>
952
953<div class="doc_text">
954
Chris Lattner3b23a8c2007-02-03 08:10:45 +0000[diff] [blame]955<p>If you intend to insert a lot of elements, then do a lot of queries, a
956great approach is to use a vector (or other sequential container) with
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]957std::sort+std::unique to remove duplicates. This approach works really well if
Chris Lattner3b23a8c2007-02-03 08:10:45 +0000[diff] [blame]958your usage pattern has these two distinct phases (insert then query), and can be
959coupled with a good choice of <a href="#ds_sequential">sequential container</a>.
960</p>
961
962<p>
963This combination provides the several nice properties: the result data is
964contiguous in memory (good for cache locality), has few allocations, is easy to
965address (iterators in the final vector are just indices or pointers), and can be
966efficiently queried with a standard binary or radix search.</p>
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]967
968</div>
969
970<!-- _______________________________________________________________________ -->
971<div class="doc_subsubsection">
972 <a name="dss_smallset">"llvm/ADT/SmallSet.h"</a>
973</div>
974
975<div class="doc_text">
976
Reid Spencer128a7a72007-02-03 21:06:43 +0000[diff] [blame]977<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]978are 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]979has space for N elements in place (thus, if the set is dynamically smaller than
Chris Lattner14868db2007-02-03 08:20:15 +0000[diff] [blame]980N, no malloc traffic is required) and accesses them with a simple linear search.
981When the set grows beyond 'N' elements, it allocates a more expensive representation that
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]982guarantees efficient access (for most types, it falls back to std::set, but for
Chris Lattner14868db2007-02-03 08:20:15 +0000[diff] [blame]983pointers it uses something far better, <a
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]984href="#dss_smallptrset">SmallPtrSet</a>).</p>
985
986<p>The magic of this class is that it handles small sets extremely efficiently,
987but gracefully handles extremely large sets without loss of efficiency. The
988drawback is that the interface is quite small: it supports insertion, queries
989and erasing, but does not support iteration.</p>
990
991</div>
992
993<!-- _______________________________________________________________________ -->
994<div class="doc_subsubsection">
995 <a name="dss_smallptrset">"llvm/ADT/SmallPtrSet.h"</a>
996</div>
997
998<div class="doc_text">
999
1000<p>SmallPtrSet has all the advantages of SmallSet (and a SmallSet of pointers is
Reid Spencer128a7a72007-02-03 21:06:43 +0000[diff] [blame]1001transparently implemented with a SmallPtrSet), but also supports iterators. If
Chris Lattner14868db2007-02-03 08:20:15 +0000[diff] [blame]1002more than 'N' insertions are performed, a single quadratically
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1003probed hash table is allocated and grows as needed, providing extremely
1004efficient access (constant time insertion/deleting/queries with low constant
1005factors) and is very stingy with malloc traffic.</p>
1006
1007<p>Note that, unlike std::set, the iterators of SmallPtrSet are invalidated
1008whenever an insertion occurs. Also, the values visited by the iterators are not
1009visited in sorted order.</p>
1010
1011</div>
1012
1013<!-- _______________________________________________________________________ -->
1014<div class="doc_subsubsection">
Chris Lattnerc28476f2007-09-30 00:58:59 +0000[diff] [blame]1015 <a name="dss_denseset">"llvm/ADT/DenseSet.h"</a>
1016</div>
1017
1018<div class="doc_text">
1019
1020<p>
1021DenseSet is a simple quadratically probed hash table. It excels at supporting
1022small values: it uses a single allocation to hold all of the pairs that
1023are currently inserted in the set. DenseSet is a great way to unique small
1024values that are not simple pointers (use <a
1025href="#dss_smallptrset">SmallPtrSet</a> for pointers). Note that DenseSet has
1026the same requirements for the value type that <a
1027href="#dss_densemap">DenseMap</a> has.
1028</p>
1029
1030</div>
1031
1032<!-- _______________________________________________________________________ -->
1033<div class="doc_subsubsection">
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1034 <a name="dss_FoldingSet">"llvm/ADT/FoldingSet.h"</a>
1035</div>
1036
1037<div class="doc_text">
1038
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]1039<p>
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1040FoldingSet is an aggregate class that is really good at uniquing
1041expensive-to-create or polymorphic objects. It is a combination of a chained
1042hash table with intrusive links (uniqued objects are required to inherit from
Chris Lattner14868db2007-02-03 08:20:15 +0000[diff] [blame]1043FoldingSetNode) that uses <a href="#dss_smallvector">SmallVector</a> as part of
1044its ID process.</p>
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1045
Chris Lattner14868db2007-02-03 08:20:15 +0000[diff] [blame]1046<p>Consider a case where you want to implement a "getOrCreateFoo" method for
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1047a complex object (for example, a node in the code generator). The client has a
1048description of *what* it wants to generate (it knows the opcode and all the
1049operands), 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]1050only to find out it already exists, at which point we would have to delete it
1051and return the node that already exists.
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]1052</p>
1053
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1054<p>To support this style of client, FoldingSet perform a query with a
1055FoldingSetNodeID (which wraps SmallVector) that can be used to describe the
1056element that we want to query for. The query either returns the element
1057matching the ID or it returns an opaque ID that indicates where insertion should
Chris Lattner14868db2007-02-03 08:20:15 +0000[diff] [blame]1058take place. Construction of the ID usually does not require heap traffic.</p>
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1059
1060<p>Because FoldingSet uses intrusive links, it can support polymorphic objects
1061in the set (for example, you can have SDNode instances mixed with LoadSDNodes).
1062Because the elements are individually allocated, pointers to the elements are
1063stable: inserting or removing elements does not invalidate any pointers to other
1064elements.
1065</p>
1066
1067</div>
1068
1069<!-- _______________________________________________________________________ -->
1070<div class="doc_subsubsection">
1071 <a name="dss_set">&lt;set&gt;</a>
1072</div>
1073
1074<div class="doc_text">
1075
Chris Lattnerc5722432007-02-03 19:49:31 +0000[diff] [blame]1076<p><tt>std::set</tt> is a reasonable all-around set class, which is decent at
1077many things but great at nothing. std::set allocates memory for each element
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1078inserted (thus it is very malloc intensive) and typically stores three pointers
Chris Lattner14868db2007-02-03 08:20:15 +0000[diff] [blame]1079per element in the set (thus adding a large amount of per-element space
1080overhead). It offers guaranteed log(n) performance, which is not particularly
Chris Lattnerc5722432007-02-03 19:49:31 +0000[diff] [blame]1081fast from a complexity standpoint (particularly if the elements of the set are
1082expensive to compare, like strings), and has extremely high constant factors for
1083lookup, insertion and removal.</p>
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1084
Chris Lattner14868db2007-02-03 08:20:15 +0000[diff] [blame]1085<p>The advantages of std::set are that its iterators are stable (deleting or
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1086inserting an element from the set does not affect iterators or pointers to other
1087elements) and that iteration over the set is guaranteed to be in sorted order.
1088If the elements in the set are large, then the relative overhead of the pointers
1089and malloc traffic is not a big deal, but if the elements of the set are small,
1090std::set is almost never a good choice.</p>
1091
1092</div>
1093
1094<!-- _______________________________________________________________________ -->
1095<div class="doc_subsubsection">
1096 <a name="dss_setvector">"llvm/ADT/SetVector.h"</a>
1097</div>
1098
1099<div class="doc_text">
Chris Lattneredca3c52007-02-04 00:00:26 +0000[diff] [blame]1100<p>LLVM's SetVector&lt;Type&gt; is an adapter class that combines your choice of
1101a set-like container along with a <a href="#ds_sequential">Sequential
1102Container</a>. The important property
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1103that this provides is efficient insertion with uniquing (duplicate elements are
1104ignored) with iteration support. It implements this by inserting elements into
1105both a set-like container and the sequential container, using the set-like
1106container for uniquing and the sequential container for iteration.
1107</p>
1108
1109<p>The difference between SetVector and other sets is that the order of
1110iteration is guaranteed to match the order of insertion into the SetVector.
1111This property is really important for things like sets of pointers. Because
1112pointer values are non-deterministic (e.g. vary across runs of the program on
Chris Lattneredca3c52007-02-04 00:00:26 +0000[diff] [blame]1113different machines), iterating over the pointers in the set will
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1114not be in a well-defined order.</p>
1115
1116<p>
1117The drawback of SetVector is that it requires twice as much space as a normal
1118set and has the sum of constant factors from the set-like container and the
1119sequential container that it uses. Use it *only* if you need to iterate over
1120the elements in a deterministic order. SetVector is also expensive to delete
Chris Lattneredca3c52007-02-04 00:00:26 +0000[diff] [blame]1121elements out of (linear time), unless you use it's "pop_back" method, which is
1122faster.
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1123</p>
1124
Chris Lattneredca3c52007-02-04 00:00:26 +0000[diff] [blame]1125<p>SetVector is an adapter class that defaults to using std::vector and std::set
1126for the underlying containers, so it is quite expensive. However,
1127<tt>"llvm/ADT/SetVector.h"</tt> also provides a SmallSetVector class, which
1128defaults to using a SmallVector and SmallSet of a specified size. If you use
1129this, and if your sets are dynamically smaller than N, you will save a lot of
1130heap traffic.</p>
1131
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1132</div>
1133
1134<!-- _______________________________________________________________________ -->
1135<div class="doc_subsubsection">
Chris Lattnerc5722432007-02-03 19:49:31 +0000[diff] [blame]1136 <a name="dss_uniquevector">"llvm/ADT/UniqueVector.h"</a>
1137</div>
1138
1139<div class="doc_text">
1140
1141<p>
1142UniqueVector is similar to <a href="#dss_setvector">SetVector</a>, but it
1143retains a unique ID for each element inserted into the set. It internally
1144contains a map and a vector, and it assigns a unique ID for each value inserted
1145into the set.</p>
1146
1147<p>UniqueVector is very expensive: its cost is the sum of the cost of
1148maintaining both the map and vector, it has high complexity, high constant
1149factors, and produces a lot of malloc traffic. It should be avoided.</p>
1150
1151</div>
1152
1153
1154<!-- _______________________________________________________________________ -->
1155<div class="doc_subsubsection">
1156 <a name="dss_otherset">Other Set-Like Container Options</a>
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1157</div>
1158
1159<div class="doc_text">
1160
1161<p>
1162The STL provides several other options, such as std::multiset and the various
Chris Lattnerc5722432007-02-03 19:49:31 +0000[diff] [blame]1163"hash_set" like containers (whether from C++ TR1 or from the SGI library).</p>
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1164
1165<p>std::multiset is useful if you're not interested in elimination of
Chris Lattner14868db2007-02-03 08:20:15 +0000[diff] [blame]1166duplicates, but has all the drawbacks of std::set. A sorted vector (where you
1167don't delete duplicate entries) or some other approach is almost always
1168better.</p>
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1169
1170<p>The various hash_set implementations (exposed portably by
Chris Lattner14868db2007-02-03 08:20:15 +0000[diff] [blame]1171"llvm/ADT/hash_set") is a simple chained hashtable. This algorithm is as malloc
1172intensive as std::set (performing an allocation for each element inserted,
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1173thus having really high constant factors) but (usually) provides O(1)
1174insertion/deletion of elements. This can be useful if your elements are large
Chris Lattner14868db2007-02-03 08:20:15 +0000[diff] [blame]1175(thus making the constant-factor cost relatively low) or if comparisons are
1176expensive. Element iteration does not visit elements in a useful order.</p>
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1177
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]1178</div>
1179
1180<!-- ======================================================================= -->
1181<div class="doc_subsection">
1182 <a name="ds_map">Map-Like Containers (std::map, DenseMap, etc)</a>
1183</div>
1184
1185<div class="doc_text">
Chris Lattnerc5722432007-02-03 19:49:31 +0000[diff] [blame]1186Map-like containers are useful when you want to associate data to a key. As
1187usual, there are a lot of different ways to do this. :)
1188</div>
1189
1190<!-- _______________________________________________________________________ -->
1191<div class="doc_subsubsection">
1192 <a name="dss_sortedvectormap">A sorted 'vector'</a>
1193</div>
1194
1195<div class="doc_text">
1196
1197<p>
1198If your usage pattern follows a strict insert-then-query approach, you can
1199trivially use the same approach as <a href="#dss_sortedvectorset">sorted vectors
1200for set-like containers</a>. The only difference is that your query function
1201(which uses std::lower_bound to get efficient log(n) lookup) should only compare
1202the key, not both the key and value. This yields the same advantages as sorted
1203vectors for sets.
1204</p>
1205</div>
1206
1207<!-- _______________________________________________________________________ -->
1208<div class="doc_subsubsection">
Chris Lattner796f9fa2007-02-08 19:14:21 +0000[diff] [blame]1209 <a name="dss_stringmap">"llvm/ADT/StringMap.h"</a>
Chris Lattnerc5722432007-02-03 19:49:31 +0000[diff] [blame]1210</div>
1211
1212<div class="doc_text">
1213
1214<p>
1215Strings are commonly used as keys in maps, and they are difficult to support
1216efficiently: they are variable length, inefficient to hash and compare when
Chris Lattner796f9fa2007-02-08 19:14:21 +0000[diff] [blame]1217long, expensive to copy, etc. StringMap is a specialized container designed to
1218cope with these issues. It supports mapping an arbitrary range of bytes to an
1219arbitrary other object.</p>
Chris Lattnerc5722432007-02-03 19:49:31 +0000[diff] [blame]1220
Chris Lattner796f9fa2007-02-08 19:14:21 +0000[diff] [blame]1221<p>The StringMap implementation uses a quadratically-probed hash table, where
Chris Lattnerc5722432007-02-03 19:49:31 +0000[diff] [blame]1222the buckets store a pointer to the heap allocated entries (and some other
1223stuff). The entries in the map must be heap allocated because the strings are
1224variable length. The string data (key) and the element object (value) are
1225stored in the same allocation with the string data immediately after the element
1226object. This container guarantees the "<tt>(char*)(&amp;Value+1)</tt>" points
1227to the key string for a value.</p>
1228
Chris Lattner796f9fa2007-02-08 19:14:21 +0000[diff] [blame]1229<p>The StringMap is very fast for several reasons: quadratic probing is very
Chris Lattnerc5722432007-02-03 19:49:31 +0000[diff] [blame]1230cache efficient for lookups, the hash value of strings in buckets is not
Chris Lattner796f9fa2007-02-08 19:14:21 +0000[diff] [blame]1231recomputed when lookup up an element, StringMap rarely has to touch the
Chris Lattnerc5722432007-02-03 19:49:31 +0000[diff] [blame]1232memory for unrelated objects when looking up a value (even when hash collisions
1233happen), hash table growth does not recompute the hash values for strings
1234already in the table, and each pair in the map is store in a single allocation
1235(the string data is stored in the same allocation as the Value of a pair).</p>
1236
Chris Lattner796f9fa2007-02-08 19:14:21 +0000[diff] [blame]1237<p>StringMap also provides query methods that take byte ranges, so it only ever
Chris Lattnerc5722432007-02-03 19:49:31 +0000[diff] [blame]1238copies a string if a value is inserted into the table.</p>
1239</div>
1240
1241<!-- _______________________________________________________________________ -->
1242<div class="doc_subsubsection">
1243 <a name="dss_indexedmap">"llvm/ADT/IndexedMap.h"</a>
1244</div>
1245
1246<div class="doc_text">
1247<p>
1248IndexedMap is a specialized container for mapping small dense integers (or
1249values that can be mapped to small dense integers) to some other type. It is
1250internally implemented as a vector with a mapping function that maps the keys to
1251the dense integer range.
1252</p>
1253
1254<p>
1255This is useful for cases like virtual registers in the LLVM code generator: they
1256have a dense mapping that is offset by a compile-time constant (the first
1257virtual register ID).</p>
1258
1259</div>
1260
1261<!-- _______________________________________________________________________ -->
1262<div class="doc_subsubsection">
1263 <a name="dss_densemap">"llvm/ADT/DenseMap.h"</a>
1264</div>
1265
1266<div class="doc_text">
1267
1268<p>
1269DenseMap is a simple quadratically probed hash table. It excels at supporting
1270small keys and values: it uses a single allocation to hold all of the pairs that
1271are currently inserted in the map. DenseMap is a great way to map pointers to
1272pointers, or map other small types to each other.
1273</p>
1274
1275<p>
1276There are several aspects of DenseMap that you should be aware of, however. The
1277iterators in a densemap are invalidated whenever an insertion occurs, unlike
1278map. Also, because DenseMap allocates space for a large number of key/value
Chris Lattnera4a264d2007-02-03 20:17:53 +0000[diff] [blame]1279pairs (it starts with 64 by default), it will waste a lot of space if your keys
1280or values are large. Finally, you must implement a partial specialization of
Chris Lattner76c1b972007-09-17 18:34:04 +0000[diff] [blame]1281DenseMapInfo for the key that you want, if it isn't already supported. This
Chris Lattnerc5722432007-02-03 19:49:31 +0000[diff] [blame]1282is required to tell DenseMap about two special marker values (which can never be
Chris Lattnera4a264d2007-02-03 20:17:53 +0000[diff] [blame]1283inserted into the map) that it needs internally.</p>
Chris Lattnerc5722432007-02-03 19:49:31 +0000[diff] [blame]1284
1285</div>
1286
1287<!-- _______________________________________________________________________ -->
1288<div class="doc_subsubsection">
1289 <a name="dss_map">&lt;map&gt;</a>
1290</div>
1291
1292<div class="doc_text">
1293
1294<p>
1295std::map has similar characteristics to <a href="#dss_set">std::set</a>: it uses
1296a single allocation per pair inserted into the map, it offers log(n) lookup with
1297an extremely large constant factor, imposes a space penalty of 3 pointers per
1298pair in the map, etc.</p>
1299
1300<p>std::map is most useful when your keys or values are very large, if you need
1301to iterate over the collection in sorted order, or if you need stable iterators
1302into the map (i.e. they don't get invalidated if an insertion or deletion of
1303another element takes place).</p>
1304
1305</div>
1306
1307<!-- _______________________________________________________________________ -->
1308<div class="doc_subsubsection">
1309 <a name="dss_othermap">Other Map-Like Container Options</a>
1310</div>
1311
1312<div class="doc_text">
1313
1314<p>
1315The STL provides several other options, such as std::multimap and the various
1316"hash_map" like containers (whether from C++ TR1 or from the SGI library).</p>
1317
1318<p>std::multimap is useful if you want to map a key to multiple values, but has
1319all the drawbacks of std::map. A sorted vector or some other approach is almost
1320always better.</p>
1321
1322<p>The various hash_map implementations (exposed portably by
1323"llvm/ADT/hash_map") are simple chained hash tables. This algorithm is as
1324malloc intensive as std::map (performing an allocation for each element
1325inserted, thus having really high constant factors) but (usually) provides O(1)
1326insertion/deletion of elements. This can be useful if your elements are large
1327(thus making the constant-factor cost relatively low) or if comparisons are
1328expensive. Element iteration does not visit elements in a useful order.</p>
1329
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]1330</div>
1331
Daniel Berlin1939ace2007-09-24 17:52:25 +0000[diff] [blame]1332<!-- ======================================================================= -->
1333<div class="doc_subsection">
1334 <a name="ds_bit">Bit storage containers (BitVector, SparseBitVector)</a>
1335</div>
1336
1337<div class="doc_text">
Chris Lattner7086ce72007-09-25 22:37:50 +0000[diff] [blame]1338<p>Unlike the other containers, there are only two bit storage containers, and
1339choosing when to use each is relatively straightforward.</p>
1340
1341<p>One additional option is
1342<tt>std::vector&lt;bool&gt;</tt>: we discourage its use for two reasons 1) the
1343implementation in many common compilers (e.g. commonly available versions of
1344GCC) is extremely inefficient and 2) the C++ standards committee is likely to
1345deprecate this container and/or change it significantly somehow. In any case,
1346please don't use it.</p>
Daniel Berlin1939ace2007-09-24 17:52:25 +0000[diff] [blame]1347</div>
1348
1349<!-- _______________________________________________________________________ -->
1350<div class="doc_subsubsection">
1351 <a name="dss_bitvector">BitVector</a>
1352</div>
1353
1354<div class="doc_text">
1355<p> The BitVector container provides a fixed size set of bits for manipulation.
1356It supports individual bit setting/testing, as well as set operations. The set
1357operations take time O(size of bitvector), but operations are performed one word
1358at a time, instead of one bit at a time. This makes the BitVector very fast for
1359set operations compared to other containers. Use the BitVector when you expect
1360the number of set bits to be high (IE a dense set).
1361</p>
1362</div>
1363
1364<!-- _______________________________________________________________________ -->
1365<div class="doc_subsubsection">
1366 <a name="dss_sparsebitvector">SparseBitVector</a>
1367</div>
1368
1369<div class="doc_text">
1370<p> The SparseBitVector container is much like BitVector, with one major
1371difference: Only the bits that are set, are stored. This makes the
1372SparseBitVector much more space efficient than BitVector when the set is sparse,
1373as well as making set operations O(number of set bits) instead of O(size of
1374universe). 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
1375(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).
1376</p>
1377</div>
Chris Lattnerf623a082005-10-17 01:36:23 +0000[diff] [blame]1378
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1379<!-- *********************************************************************** -->
1380<div class="doc_section">
1381 <a name="common">Helpful Hints for Common Operations</a>
1382</div>
1383<!-- *********************************************************************** -->
1384
1385<div class="doc_text">
1386
1387<p>This section describes how to perform some very simple transformations of
1388LLVM code. This is meant to give examples of common idioms used, showing the
1389practical side of LLVM transformations. <p> Because this is a "how-to" section,
1390you should also read about the main classes that you will be working with. The
1391<a href="#coreclasses">Core LLVM Class Hierarchy Reference</a> contains details
1392and descriptions of the main classes that you should know about.</p>
1393
1394</div>
1395
1396<!-- NOTE: this section should be heavy on example code -->
1397<!-- ======================================================================= -->
1398<div class="doc_subsection">
1399 <a name="inspection">Basic Inspection and Traversal Routines</a>
1400</div>
1401
1402<div class="doc_text">
1403
1404<p>The LLVM compiler infrastructure have many different data structures that may
1405be traversed. Following the example of the C++ standard template library, the
1406techniques used to traverse these various data structures are all basically the
1407same. For a enumerable sequence of values, the <tt>XXXbegin()</tt> function (or
1408method) returns an iterator to the start of the sequence, the <tt>XXXend()</tt>
1409function returns an iterator pointing to one past the last valid element of the
1410sequence, and there is some <tt>XXXiterator</tt> data type that is common
1411between the two operations.</p>
1412
1413<p>Because the pattern for iteration is common across many different aspects of
1414the program representation, the standard template library algorithms may be used
1415on them, and it is easier to remember how to iterate. First we show a few common
1416examples of the data structures that need to be traversed. Other data
1417structures are traversed in very similar ways.</p>
1418
1419</div>
1420
1421<!-- _______________________________________________________________________ -->
Chris Lattner69bf8a92004-05-23 21:06:58 +0000[diff] [blame]1422<div class="doc_subsubsection">
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1423 <a name="iterate_function">Iterating over the </a><a
1424 href="#BasicBlock"><tt>BasicBlock</tt></a>s in a <a
1425 href="#Function"><tt>Function</tt></a>
1426</div>
1427
1428<div class="doc_text">
1429
1430<p>It's quite common to have a <tt>Function</tt> instance that you'd like to
1431transform in some way; in particular, you'd like to manipulate its
1432<tt>BasicBlock</tt>s. To facilitate this, you'll need to iterate over all of
1433the <tt>BasicBlock</tt>s that constitute the <tt>Function</tt>. The following is
1434an example that prints the name of a <tt>BasicBlock</tt> and the number of
1435<tt>Instruction</tt>s it contains:</p>
1436
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1437<div class="doc_code">
1438<pre>
Bill Wendling82e2eea2006-10-11 18:00:22 +0000[diff] [blame]1439// <i>func is a pointer to a Function instance</i>
1440for (Function::iterator i = func-&gt;begin(), e = func-&gt;end(); i != e; ++i)
1441 // <i>Print out the name of the basic block if it has one, and then the</i>
1442 // <i>number of instructions that it contains</i>
Bill Wendling832171c2006-12-07 20:04:42 +0000[diff] [blame]1443 llvm::cerr &lt;&lt; "Basic block (name=" &lt;&lt; i-&gt;getName() &lt;&lt; ") has "
1444 &lt;&lt; i-&gt;size() &lt;&lt; " instructions.\n";
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1445</pre>
1446</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1447
1448<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]1449invoking member functions of the <tt>Instruction</tt> class. This is
1450because the indirection operator is overloaded for the iterator
Chris Lattner7496ec52003-08-05 22:54:23 +0000[diff] [blame]1451classes. In the above code, the expression <tt>i-&gt;size()</tt> is
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1452exactly equivalent to <tt>(*i).size()</tt> just like you'd expect.</p>
1453
1454</div>
1455
1456<!-- _______________________________________________________________________ -->
Chris Lattner69bf8a92004-05-23 21:06:58 +0000[diff] [blame]1457<div class="doc_subsubsection">
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1458 <a name="iterate_basicblock">Iterating over the </a><a
1459 href="#Instruction"><tt>Instruction</tt></a>s in a <a
1460 href="#BasicBlock"><tt>BasicBlock</tt></a>
1461</div>
1462
1463<div class="doc_text">
1464
1465<p>Just like when dealing with <tt>BasicBlock</tt>s in <tt>Function</tt>s, it's
1466easy to iterate over the individual instructions that make up
1467<tt>BasicBlock</tt>s. Here's a code snippet that prints out each instruction in
1468a <tt>BasicBlock</tt>:</p>
1469
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1470<div class="doc_code">
Chris Lattner55c04612005-03-06 06:00:13 +0000[diff] [blame]1471<pre>
Bill Wendling82e2eea2006-10-11 18:00:22 +0000[diff] [blame]1472// <i>blk is a pointer to a BasicBlock instance</i>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1473for (BasicBlock::iterator i = blk-&gt;begin(), e = blk-&gt;end(); i != e; ++i)
Bill Wendling82e2eea2006-10-11 18:00:22 +0000[diff] [blame]1474 // <i>The next statement works since operator&lt;&lt;(ostream&amp;,...)</i>
1475 // <i>is overloaded for Instruction&amp;</i>
Bill Wendling832171c2006-12-07 20:04:42 +0000[diff] [blame]1476 llvm::cerr &lt;&lt; *i &lt;&lt; "\n";
Chris Lattner55c04612005-03-06 06:00:13 +0000[diff] [blame]1477</pre>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1478</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1479
1480<p>However, this isn't really the best way to print out the contents of a
1481<tt>BasicBlock</tt>! Since the ostream operators are overloaded for virtually
1482anything you'll care about, you could have just invoked the print routine on the
Bill Wendling832171c2006-12-07 20:04:42 +0000[diff] [blame]1483basic block itself: <tt>llvm::cerr &lt;&lt; *blk &lt;&lt; "\n";</tt>.</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1484
1485</div>
1486
1487<!-- _______________________________________________________________________ -->
Chris Lattner69bf8a92004-05-23 21:06:58 +0000[diff] [blame]1488<div class="doc_subsubsection">
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1489 <a name="iterate_institer">Iterating over the </a><a
1490 href="#Instruction"><tt>Instruction</tt></a>s in a <a
1491 href="#Function"><tt>Function</tt></a>
1492</div>
1493
1494<div class="doc_text">
1495
1496<p>If you're finding that you commonly iterate over a <tt>Function</tt>'s
1497<tt>BasicBlock</tt>s and then that <tt>BasicBlock</tt>'s <tt>Instruction</tt>s,
1498<tt>InstIterator</tt> should be used instead. You'll need to include <a
1499href="/doxygen/InstIterator_8h-source.html"><tt>llvm/Support/InstIterator.h</tt></a>,
1500and then instantiate <tt>InstIterator</tt>s explicitly in your code. Here's a
Chris Lattner69bf8a92004-05-23 21:06:58 +0000[diff] [blame]1501small 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]1502
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1503<div class="doc_code">
1504<pre>
1505#include "<a href="/doxygen/InstIterator_8h-source.html">llvm/Support/InstIterator.h</a>"
1506
Reid Spencer128a7a72007-02-03 21:06:43 +0000[diff] [blame]1507// <i>F is a pointer to a Function instance</i>
Chris Lattnerda021aa2008-06-04 18:20:42 +0000[diff] [blame]1508for (inst_iterator I = inst_begin(F), E = inst_end(F); I != E; ++I)
1509 llvm::cerr &lt;&lt; *I &lt;&lt; "\n";
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1510</pre>
1511</div>
1512
1513<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]1514work list with its initial contents. For example, if you wanted to
1515initialize a work list to contain all instructions in a <tt>Function</tt>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1516F, all you would need to do is something like:</p>
1517
1518<div class="doc_code">
1519<pre>
1520std::set&lt;Instruction*&gt; worklist;
Chris Lattnerda021aa2008-06-04 18:20:42 +0000[diff] [blame]1521// or better yet, SmallPtrSet&lt;Instruction*, 64&gt; worklist;
1522
1523for (inst_iterator I = inst_begin(F), E = inst_end(F); I != E; ++I)
1524 worklist.insert(&amp;*I);
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1525</pre>
1526</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1527
1528<p>The STL set <tt>worklist</tt> would now contain all instructions in the
1529<tt>Function</tt> pointed to by F.</p>
1530
1531</div>
1532
1533<!-- _______________________________________________________________________ -->
1534<div class="doc_subsubsection">
1535 <a name="iterate_convert">Turning an iterator into a class pointer (and
1536 vice-versa)</a>
1537</div>
1538
1539<div class="doc_text">
1540
1541<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]1542instance when all you've got at hand is an iterator. Well, extracting
Chris Lattner69bf8a92004-05-23 21:06:58 +0000[diff] [blame]1543a reference or a pointer from an iterator is very straight-forward.
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]1544Assuming that <tt>i</tt> is a <tt>BasicBlock::iterator</tt> and <tt>j</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1545is a <tt>BasicBlock::const_iterator</tt>:</p>
1546
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1547<div class="doc_code">
1548<pre>
Bill Wendling82e2eea2006-10-11 18:00:22 +0000[diff] [blame]1549Instruction&amp; inst = *i; // <i>Grab reference to instruction reference</i>
1550Instruction* pinst = &amp;*i; // <i>Grab pointer to instruction reference</i>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1551const Instruction&amp; inst = *j;
1552</pre>
1553</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1554
1555<p>However, the iterators you'll be working with in the LLVM framework are
1556special: they will automatically convert to a ptr-to-instance type whenever they
1557need to. Instead of dereferencing the iterator and then taking the address of
1558the result, you can simply assign the iterator to the proper pointer type and
1559you get the dereference and address-of operation as a result of the assignment
1560(behind the scenes, this is a result of overloading casting mechanisms). Thus
1561the last line of the last example,</p>
1562
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1563<div class="doc_code">
1564<pre>
Chris Lattner2e438ca2008-01-03 16:56:04 +0000[diff] [blame]1565Instruction *pinst = &amp;*i;
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1566</pre>
1567</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1568
1569<p>is semantically equivalent to</p>
1570
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1571<div class="doc_code">
1572<pre>
Chris Lattner2e438ca2008-01-03 16:56:04 +0000[diff] [blame]1573Instruction *pinst = i;
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1574</pre>
1575</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1576
Chris Lattner69bf8a92004-05-23 21:06:58 +0000[diff] [blame]1577<p>It's also possible to turn a class pointer into the corresponding iterator,
1578and this is a constant time operation (very efficient). The following code
1579snippet illustrates use of the conversion constructors provided by LLVM
1580iterators. By using these, you can explicitly grab the iterator of something
1581without actually obtaining it via iteration over some structure:</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1582
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1583<div class="doc_code">
1584<pre>
1585void printNextInstruction(Instruction* inst) {
1586 BasicBlock::iterator it(inst);
Bill Wendling82e2eea2006-10-11 18:00:22 +0000[diff] [blame]1587 ++it; // <i>After this line, it refers to the instruction after *inst</i>
Bill Wendling832171c2006-12-07 20:04:42 +0000[diff] [blame]1588 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]1589}
1590</pre>
1591</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1592
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1593</div>
1594
1595<!--_______________________________________________________________________-->
1596<div class="doc_subsubsection">
1597 <a name="iterate_complex">Finding call sites: a slightly more complex
1598 example</a>
1599</div>
1600
1601<div class="doc_text">
1602
1603<p>Say that you're writing a FunctionPass and would like to count all the
1604locations in the entire module (that is, across every <tt>Function</tt>) where a
1605certain function (i.e., some <tt>Function</tt>*) is already in scope. As you'll
1606learn 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]1607much more straight-forward manner, but this example will allow us to explore how
Reid Spencer128a7a72007-02-03 21:06:43 +0000[diff] [blame]1608you'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]1609is what we want to do:</p>
1610
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1611<div class="doc_code">
1612<pre>
1613initialize callCounter to zero
1614for each Function f in the Module
1615 for each BasicBlock b in f
1616 for each Instruction i in b
1617 if (i is a CallInst and calls the given function)
1618 increment callCounter
1619</pre>
1620</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1621
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1622<p>And the actual code is (remember, because we're writing a
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1623<tt>FunctionPass</tt>, our <tt>FunctionPass</tt>-derived class simply has to
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1624override the <tt>runOnFunction</tt> method):</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1625
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1626<div class="doc_code">
1627<pre>
1628Function* targetFunc = ...;
1629
1630class OurFunctionPass : public FunctionPass {
1631 public:
1632 OurFunctionPass(): callCounter(0) { }
1633
1634 virtual runOnFunction(Function&amp; F) {
1635 for (Function::iterator b = F.begin(), be = F.end(); b != be; ++b) {
Eric Christopher203e71d2008-11-08 08:20:49 +0000[diff] [blame]1636 for (BasicBlock::iterator i = b-&gt;begin(), ie = b-&gt;end(); i != ie; ++i) {
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1637 if (<a href="#CallInst">CallInst</a>* callInst = <a href="#isa">dyn_cast</a>&lt;<a
1638 href="#CallInst">CallInst</a>&gt;(&amp;*i)) {
Bill Wendling82e2eea2006-10-11 18:00:22 +0000[diff] [blame]1639 // <i>We know we've encountered a call instruction, so we</i>
1640 // <i>need to determine if it's a call to the</i>
Chris Lattner2e438ca2008-01-03 16:56:04 +0000[diff] [blame]1641 // <i>function pointed to by m_func or not.</i>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1642 if (callInst-&gt;getCalledFunction() == targetFunc)
1643 ++callCounter;
1644 }
1645 }
1646 }
Bill Wendling82e2eea2006-10-11 18:00:22 +0000[diff] [blame]1647 }
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1648
1649 private:
Chris Lattner2e438ca2008-01-03 16:56:04 +0000[diff] [blame]1650 unsigned callCounter;
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1651};
1652</pre>
1653</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1654
1655</div>
1656
Brian Gaekef1972c62003-11-07 19:25:45 +0000[diff] [blame]1657<!--_______________________________________________________________________-->
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1658<div class="doc_subsubsection">
1659 <a name="calls_and_invokes">Treating calls and invokes the same way</a>
1660</div>
1661
1662<div class="doc_text">
1663
1664<p>You may have noticed that the previous example was a bit oversimplified in
1665that it did not deal with call sites generated by 'invoke' instructions. In
1666this, and in other situations, you may find that you want to treat
1667<tt>CallInst</tt>s and <tt>InvokeInst</tt>s the same way, even though their
1668most-specific common base class is <tt>Instruction</tt>, which includes lots of
1669less closely-related things. For these cases, LLVM provides a handy wrapper
1670class called <a
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]1671href="http://llvm.org/doxygen/classllvm_1_1CallSite.html"><tt>CallSite</tt></a>.
Chris Lattner69bf8a92004-05-23 21:06:58 +0000[diff] [blame]1672It is essentially a wrapper around an <tt>Instruction</tt> pointer, with some
1673methods that provide functionality common to <tt>CallInst</tt>s and
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1674<tt>InvokeInst</tt>s.</p>
1675
Chris Lattner69bf8a92004-05-23 21:06:58 +0000[diff] [blame]1676<p>This class has "value semantics": it should be passed by value, not by
1677reference and it should not be dynamically allocated or deallocated using
1678<tt>operator new</tt> or <tt>operator delete</tt>. It is efficiently copyable,
1679assignable and constructable, with costs equivalents to that of a bare pointer.
1680If you look at its definition, it has only a single pointer member.</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1681
1682</div>
1683
Chris Lattner1a3105b2002-09-09 05:49:39 +0000[diff] [blame]1684<!--_______________________________________________________________________-->
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1685<div class="doc_subsubsection">
1686 <a name="iterate_chains">Iterating over def-use &amp; use-def chains</a>
1687</div>
1688
1689<div class="doc_text">
1690
1691<p>Frequently, we might have an instance of the <a
Chris Lattner00815172007-01-04 22:01:45 +0000[diff] [blame]1692href="/doxygen/classllvm_1_1Value.html">Value Class</a> and we want to
Misha Brukman384047f2004-06-03 23:29:12 +0000[diff] [blame]1693determine which <tt>User</tt>s use the <tt>Value</tt>. The list of all
1694<tt>User</tt>s of a particular <tt>Value</tt> is called a <i>def-use</i> chain.
1695For example, let's say we have a <tt>Function*</tt> named <tt>F</tt> to a
1696particular function <tt>foo</tt>. Finding all of the instructions that
1697<i>use</i> <tt>foo</tt> is as simple as iterating over the <i>def-use</i> chain
1698of <tt>F</tt>:</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1699
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1700<div class="doc_code">
1701<pre>
Chris Lattner2e438ca2008-01-03 16:56:04 +0000[diff] [blame]1702Function *F = ...;
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1703
Bill Wendling82e2eea2006-10-11 18:00:22 +0000[diff] [blame]1704for (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]1705 if (Instruction *Inst = dyn_cast&lt;Instruction&gt;(*i)) {
Bill Wendling832171c2006-12-07 20:04:42 +0000[diff] [blame]1706 llvm::cerr &lt;&lt; "F is used in instruction:\n";
1707 llvm::cerr &lt;&lt; *Inst &lt;&lt; "\n";
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1708 }
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1709</pre>
1710</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1711
1712<p>Alternately, it's common to have an instance of the <a
Misha Brukman384047f2004-06-03 23:29:12 +0000[diff] [blame]1713href="/doxygen/classllvm_1_1User.html">User Class</a> and need to know what
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1714<tt>Value</tt>s are used by it. The list of all <tt>Value</tt>s used by a
1715<tt>User</tt> is known as a <i>use-def</i> chain. Instances of class
1716<tt>Instruction</tt> are common <tt>User</tt>s, so we might want to iterate over
1717all of the values that a particular instruction uses (that is, the operands of
1718the particular <tt>Instruction</tt>):</p>
1719
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1720<div class="doc_code">
1721<pre>
Chris Lattner2e438ca2008-01-03 16:56:04 +0000[diff] [blame]1722Instruction *pi = ...;
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1723
1724for (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]1725 Value *v = *i;
Bill Wendling82e2eea2006-10-11 18:00:22 +0000[diff] [blame]1726 // <i>...</i>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1727}
1728</pre>
1729</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1730
Chris Lattner1a3105b2002-09-09 05:49:39 +0000[diff] [blame]1731<!--
1732 def-use chains ("finding all users of"): Value::use_begin/use_end
1733 use-def chains ("finding all values used"): User::op_begin/op_end [op=operand]
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1734-->
1735
1736</div>
1737
Chris Lattner2e438ca2008-01-03 16:56:04 +0000[diff] [blame]1738<!--_______________________________________________________________________-->
1739<div class="doc_subsubsection">
1740 <a name="iterate_preds">Iterating over predecessors &amp;
1741successors of blocks</a>
1742</div>
1743
1744<div class="doc_text">
1745
1746<p>Iterating over the predecessors and successors of a block is quite easy
1747with the routines defined in <tt>"llvm/Support/CFG.h"</tt>. Just use code like
1748this to iterate over all predecessors of BB:</p>
1749
1750<div class="doc_code">
1751<pre>
1752#include "llvm/Support/CFG.h"
1753BasicBlock *BB = ...;
1754
1755for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI) {
1756 BasicBlock *Pred = *PI;
1757 // <i>...</i>
1758}
1759</pre>
1760</div>
1761
1762<p>Similarly, to iterate over successors use
1763succ_iterator/succ_begin/succ_end.</p>
1764
1765</div>
1766
1767
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1768<!-- ======================================================================= -->
1769<div class="doc_subsection">
1770 <a name="simplechanges">Making simple changes</a>
1771</div>
1772
1773<div class="doc_text">
1774
1775<p>There are some primitive transformation operations present in the LLVM
Joel Stanley753eb712002-09-11 22:32:24 +0000[diff] [blame]1776infrastructure that are worth knowing about. When performing
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]1777transformations, it's fairly common to manipulate the contents of basic
1778blocks. This section describes some of the common methods for doing so
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1779and gives example code.</p>
1780
1781</div>
1782
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]1783<!--_______________________________________________________________________-->
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1784<div class="doc_subsubsection">
1785 <a name="schanges_creating">Creating and inserting new
1786 <tt>Instruction</tt>s</a>
1787</div>
1788
1789<div class="doc_text">
1790
1791<p><i>Instantiating Instructions</i></p>
1792
Chris Lattner69bf8a92004-05-23 21:06:58 +0000[diff] [blame]1793<p>Creation of <tt>Instruction</tt>s is straight-forward: simply call the
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1794constructor for the kind of instruction to instantiate and provide the necessary
1795parameters. For example, an <tt>AllocaInst</tt> only <i>requires</i> a
1796(const-ptr-to) <tt>Type</tt>. Thus:</p>
1797
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1798<div class="doc_code">
1799<pre>
Nick Lewycky10d64b92007-12-03 01:52:52 +0000[diff] [blame]1800AllocaInst* ai = new AllocaInst(Type::Int32Ty);
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1801</pre>
1802</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1803
1804<p>will create an <tt>AllocaInst</tt> instance that represents the allocation of
Reid Spencer128a7a72007-02-03 21:06:43 +0000[diff] [blame]1805one integer in the current stack frame, at run time. Each <tt>Instruction</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1806subclass is likely to have varying default parameters which change the semantics
1807of the instruction, so refer to the <a
Misha Brukman31ca1de2004-06-03 23:35:54 +0000[diff] [blame]1808href="/doxygen/classllvm_1_1Instruction.html">doxygen documentation for the subclass of
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1809Instruction</a> that you're interested in instantiating.</p>
1810
1811<p><i>Naming values</i></p>
1812
1813<p>It is very useful to name the values of instructions when you're able to, as
1814this facilitates the debugging of your transformations. If you end up looking
1815at generated LLVM machine code, you definitely want to have logical names
1816associated with the results of instructions! By supplying a value for the
1817<tt>Name</tt> (default) parameter of the <tt>Instruction</tt> constructor, you
1818associate a logical name with the result of the instruction's execution at
Reid Spencer128a7a72007-02-03 21:06:43 +0000[diff] [blame]1819run time. For example, say that I'm writing a transformation that dynamically
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1820allocates space for an integer on the stack, and that integer is going to be
1821used as some kind of index by some other code. To accomplish this, I place an
1822<tt>AllocaInst</tt> at the first point in the first <tt>BasicBlock</tt> of some
1823<tt>Function</tt>, and I'm intending to use it within the same
1824<tt>Function</tt>. I might do:</p>
1825
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1826<div class="doc_code">
1827<pre>
Nick Lewycky10d64b92007-12-03 01:52:52 +0000[diff] [blame]1828AllocaInst* pa = new AllocaInst(Type::Int32Ty, 0, "indexLoc");
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1829</pre>
1830</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1831
1832<p>where <tt>indexLoc</tt> is now the logical name of the instruction's
Reid Spencer128a7a72007-02-03 21:06:43 +0000[diff] [blame]1833execution value, which is a pointer to an integer on the run time stack.</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1834
1835<p><i>Inserting instructions</i></p>
1836
1837<p>There are essentially two ways to insert an <tt>Instruction</tt>
1838into an existing sequence of instructions that form a <tt>BasicBlock</tt>:</p>
1839
Joel Stanley9dd1ad62002-09-18 03:17:23 +0000[diff] [blame]1840<ul>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1841 <li>Insertion into an explicit instruction list
1842
1843 <p>Given a <tt>BasicBlock* pb</tt>, an <tt>Instruction* pi</tt> within that
1844 <tt>BasicBlock</tt>, and a newly-created instruction we wish to insert
1845 before <tt>*pi</tt>, we do the following: </p>
1846
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1847<div class="doc_code">
1848<pre>
1849BasicBlock *pb = ...;
1850Instruction *pi = ...;
1851Instruction *newInst = new Instruction(...);
1852
Bill Wendling82e2eea2006-10-11 18:00:22 +0000[diff] [blame]1853pb-&gt;getInstList().insert(pi, newInst); // <i>Inserts newInst before pi in pb</i>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1854</pre>
1855</div>
Alkis Evlogimenos9a5dc4f2004-05-27 00:57:51 +0000[diff] [blame]1856
1857 <p>Appending to the end of a <tt>BasicBlock</tt> is so common that
1858 the <tt>Instruction</tt> class and <tt>Instruction</tt>-derived
1859 classes provide constructors which take a pointer to a
1860 <tt>BasicBlock</tt> to be appended to. For example code that
1861 looked like: </p>
1862
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1863<div class="doc_code">
1864<pre>
1865BasicBlock *pb = ...;
1866Instruction *newInst = new Instruction(...);
1867
Bill Wendling82e2eea2006-10-11 18:00:22 +0000[diff] [blame]1868pb-&gt;getInstList().push_back(newInst); // <i>Appends newInst to pb</i>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1869</pre>
1870</div>
Alkis Evlogimenos9a5dc4f2004-05-27 00:57:51 +0000[diff] [blame]1871
1872 <p>becomes: </p>
1873
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1874<div class="doc_code">
1875<pre>
1876BasicBlock *pb = ...;
1877Instruction *newInst = new Instruction(..., pb);
1878</pre>
1879</div>
Alkis Evlogimenos9a5dc4f2004-05-27 00:57:51 +0000[diff] [blame]1880
1881 <p>which is much cleaner, especially if you are creating
1882 long instruction streams.</p></li>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1883
1884 <li>Insertion into an implicit instruction list
1885
1886 <p><tt>Instruction</tt> instances that are already in <tt>BasicBlock</tt>s
1887 are implicitly associated with an existing instruction list: the instruction
1888 list of the enclosing basic block. Thus, we could have accomplished the same
1889 thing as the above code without being given a <tt>BasicBlock</tt> by doing:
1890 </p>
1891
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1892<div class="doc_code">
1893<pre>
1894Instruction *pi = ...;
1895Instruction *newInst = new Instruction(...);
1896
1897pi-&gt;getParent()-&gt;getInstList().insert(pi, newInst);
1898</pre>
1899</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1900
1901 <p>In fact, this sequence of steps occurs so frequently that the
1902 <tt>Instruction</tt> class and <tt>Instruction</tt>-derived classes provide
1903 constructors which take (as a default parameter) a pointer to an
1904 <tt>Instruction</tt> which the newly-created <tt>Instruction</tt> should
1905 precede. That is, <tt>Instruction</tt> constructors are capable of
1906 inserting the newly-created instance into the <tt>BasicBlock</tt> of a
1907 provided instruction, immediately before that instruction. Using an
1908 <tt>Instruction</tt> constructor with a <tt>insertBefore</tt> (default)
1909 parameter, the above code becomes:</p>
1910
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1911<div class="doc_code">
1912<pre>
1913Instruction* pi = ...;
1914Instruction* newInst = new Instruction(..., pi);
1915</pre>
1916</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1917
1918 <p>which is much cleaner, especially if you're creating a lot of
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1919 instructions and adding them to <tt>BasicBlock</tt>s.</p></li>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1920</ul>
1921
1922</div>
1923
1924<!--_______________________________________________________________________-->
1925<div class="doc_subsubsection">
1926 <a name="schanges_deleting">Deleting <tt>Instruction</tt>s</a>
1927</div>
1928
1929<div class="doc_text">
1930
1931<p>Deleting an instruction from an existing sequence of instructions that form a
Chris Lattner69bf8a92004-05-23 21:06:58 +0000[diff] [blame]1932<a href="#BasicBlock"><tt>BasicBlock</tt></a> is very straight-forward. First,
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1933you must have a pointer to the instruction that you wish to delete. Second, you
1934need to obtain the pointer to that instruction's basic block. You use the
1935pointer to the basic block to get its list of instructions and then use the
1936erase function to remove your instruction. For example:</p>
1937
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1938<div class="doc_code">
1939<pre>
1940<a href="#Instruction">Instruction</a> *I = .. ;
Chris Lattner9f8ec252008-02-15 22:57:17 +0000[diff] [blame]1941I-&gt;eraseFromParent();
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1942</pre>
1943</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1944
1945</div>
1946
1947<!--_______________________________________________________________________-->
1948<div class="doc_subsubsection">
1949 <a name="schanges_replacing">Replacing an <tt>Instruction</tt> with another
1950 <tt>Value</tt></a>
1951</div>
1952
1953<div class="doc_text">
1954
1955<p><i>Replacing individual instructions</i></p>
1956
1957<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]1958permits use of two very useful replace functions: <tt>ReplaceInstWithValue</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1959and <tt>ReplaceInstWithInst</tt>.</p>
1960
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]1961<h4><a name="schanges_deleting">Deleting <tt>Instruction</tt>s</a></h4>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1962
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]1963<ul>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1964 <li><tt>ReplaceInstWithValue</tt>
1965
Nick Lewyckyb6d1f392008-09-15 06:31:52 +0000[diff] [blame]1966 <p>This function replaces all uses of a given instruction with a value,
1967 and then removes the original instruction. The following example
1968 illustrates the replacement of the result of a particular
Chris Lattner58360822005-01-17 00:12:04 +0000[diff] [blame]1969 <tt>AllocaInst</tt> that allocates memory for a single integer with a null
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1970 pointer to an integer.</p>
1971
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1972<div class="doc_code">
1973<pre>
1974AllocaInst* instToReplace = ...;
1975BasicBlock::iterator ii(instToReplace);
1976
1977ReplaceInstWithValue(instToReplace-&gt;getParent()-&gt;getInstList(), ii,
Daniel Dunbar58c2ac02008-10-03 22:17:25 +0000[diff] [blame]1978 Constant::getNullValue(PointerType::getUnqual(Type::Int32Ty)));
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1979</pre></div></li>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1980
1981 <li><tt>ReplaceInstWithInst</tt>
1982
1983 <p>This function replaces a particular instruction with another
Nick Lewyckyb6d1f392008-09-15 06:31:52 +0000[diff] [blame]1984 instruction, inserting the new instruction into the basic block at the
1985 location where the old instruction was, and replacing any uses of the old
1986 instruction with the new instruction. The following example illustrates
1987 the replacement of one <tt>AllocaInst</tt> with another.</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1988
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1989<div class="doc_code">
1990<pre>
1991AllocaInst* instToReplace = ...;
1992BasicBlock::iterator ii(instToReplace);
1993
1994ReplaceInstWithInst(instToReplace-&gt;getParent()-&gt;getInstList(), ii,
Nick Lewycky10d64b92007-12-03 01:52:52 +0000[diff] [blame]1995 new AllocaInst(Type::Int32Ty, 0, "ptrToReplacedInt"));
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1996</pre></div></li>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]1997</ul>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1998
1999<p><i>Replacing multiple uses of <tt>User</tt>s and <tt>Value</tt>s</i></p>
2000
2001<p>You can use <tt>Value::replaceAllUsesWith</tt> and
2002<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]2003doxygen documentation for the <a href="/doxygen/classllvm_1_1Value.html">Value Class</a>
Misha Brukman384047f2004-06-03 23:29:12 +0000[diff] [blame]2004and <a href="/doxygen/classllvm_1_1User.html">User Class</a>, respectively, for more
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2005information.</p>
2006
2007<!-- Value::replaceAllUsesWith User::replaceUsesOfWith Point out:
2008include/llvm/Transforms/Utils/ especially BasicBlockUtils.h with:
2009ReplaceInstWithValue, ReplaceInstWithInst -->
2010
2011</div>
2012
Tanya Lattnerb011c662007-06-20 18:33:15 +0000[diff] [blame]2013<!--_______________________________________________________________________-->
2014<div class="doc_subsubsection">
2015 <a name="schanges_deletingGV">Deleting <tt>GlobalVariable</tt>s</a>
2016</div>
2017
2018<div class="doc_text">
2019
Tanya Lattnerc5dfcdb2007-06-20 20:46:37 +0000[diff] [blame]2020<p>Deleting a global variable from a module is just as easy as deleting an
2021Instruction. First, you must have a pointer to the global variable that you wish
2022 to delete. You use this pointer to erase it from its parent, the module.
Tanya Lattnerb011c662007-06-20 18:33:15 +0000[diff] [blame]2023 For example:</p>
2024
2025<div class="doc_code">
2026<pre>
2027<a href="#GlobalVariable">GlobalVariable</a> *GV = .. ;
Tanya Lattnerb011c662007-06-20 18:33:15 +0000[diff] [blame]2028
Tanya Lattnerc5dfcdb2007-06-20 20:46:37 +0000[diff] [blame]2029GV-&gt;eraseFromParent();
Tanya Lattnerb011c662007-06-20 18:33:15 +0000[diff] [blame]2030</pre>
2031</div>
2032
2033</div>
2034
Chris Lattner9355b472002-09-06 02:50:58 +0000[diff] [blame]2035<!-- *********************************************************************** -->
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2036<div class="doc_section">
Chris Lattnerd9d6e102005-04-23 16:10:52 +0000[diff] [blame]2037 <a name="advanced">Advanced Topics</a>
2038</div>
2039<!-- *********************************************************************** -->
2040
2041<div class="doc_text">
Chris Lattnerf1b200b2005-04-23 17:27:36 +0000[diff] [blame]2042<p>
2043This section describes some of the advanced or obscure API's that most clients
2044do not need to be aware of. These API's tend manage the inner workings of the
2045LLVM system, and only need to be accessed in unusual circumstances.
2046</p>
2047</div>
Chris Lattnerd9d6e102005-04-23 16:10:52 +0000[diff] [blame]2048
Chris Lattnerf1b200b2005-04-23 17:27:36 +0000[diff] [blame]2049<!-- ======================================================================= -->
2050<div class="doc_subsection">
2051 <a name="TypeResolve">LLVM Type Resolution</a>
2052</div>
Chris Lattnerd9d6e102005-04-23 16:10:52 +0000[diff] [blame]2053
Chris Lattnerf1b200b2005-04-23 17:27:36 +0000[diff] [blame]2054<div class="doc_text">
2055
2056<p>
2057The LLVM type system has a very simple goal: allow clients to compare types for
2058structural equality with a simple pointer comparison (aka a shallow compare).
2059This goal makes clients much simpler and faster, and is used throughout the LLVM
2060system.
2061</p>
2062
2063<p>
2064Unfortunately achieving this goal is not a simple matter. In particular,
2065recursive types and late resolution of opaque types makes the situation very
2066difficult to handle. Fortunately, for the most part, our implementation makes
2067most clients able to be completely unaware of the nasty internal details. The
2068primary case where clients are exposed to the inner workings of it are when
Gabor Greif04367bf2007-07-06 22:07:22 +0000[diff] [blame]2069building a recursive type. In addition to this case, the LLVM bitcode reader,
Chris Lattnerf1b200b2005-04-23 17:27:36 +0000[diff] [blame]2070assembly parser, and linker also have to be aware of the inner workings of this
2071system.
2072</p>
2073
Chris Lattner0f876db2005-04-25 15:47:57 +0000[diff] [blame]2074<p>
2075For our purposes below, we need three concepts. First, an "Opaque Type" is
2076exactly as defined in the <a href="LangRef.html#t_opaque">language
2077reference</a>. Second an "Abstract Type" is any type which includes an
Reid Spencer06565dc2007-01-12 17:11:23 +0000[diff] [blame]2078opaque type as part of its type graph (for example "<tt>{ opaque, i32 }</tt>").
2079Third, 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]2080float }</tt>").
2081</p>
2082
Chris Lattnerf1b200b2005-04-23 17:27:36 +0000[diff] [blame]2083</div>
2084
2085<!-- ______________________________________________________________________ -->
2086<div class="doc_subsubsection">
2087 <a name="BuildRecType">Basic Recursive Type Construction</a>
2088</div>
2089
2090<div class="doc_text">
2091
2092<p>
2093Because the most common question is "how do I build a recursive type with LLVM",
2094we answer it now and explain it as we go. Here we include enough to cause this
2095to be emitted to an output .ll file:
2096</p>
2097
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2098<div class="doc_code">
Chris Lattnerf1b200b2005-04-23 17:27:36 +0000[diff] [blame]2099<pre>
Reid Spencer06565dc2007-01-12 17:11:23 +0000[diff] [blame]2100%mylist = type { %mylist*, i32 }
Chris Lattnerf1b200b2005-04-23 17:27:36 +0000[diff] [blame]2101</pre>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2102</div>
Chris Lattnerf1b200b2005-04-23 17:27:36 +0000[diff] [blame]2103
2104<p>
2105To build this, use the following LLVM APIs:
2106</p>
2107
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2108<div class="doc_code">
Chris Lattnerf1b200b2005-04-23 17:27:36 +0000[diff] [blame]2109<pre>
Bill Wendling82e2eea2006-10-11 18:00:22 +0000[diff] [blame]2110// <i>Create the initial outer struct</i>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2111<a href="#PATypeHolder">PATypeHolder</a> StructTy = OpaqueType::get();
2112std::vector&lt;const Type*&gt; Elts;
Daniel Dunbar58c2ac02008-10-03 22:17:25 +0000[diff] [blame]2113Elts.push_back(PointerType::getUnqual(StructTy));
Nick Lewycky10d64b92007-12-03 01:52:52 +0000[diff] [blame]2114Elts.push_back(Type::Int32Ty);
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2115StructType *NewSTy = StructType::get(Elts);
Chris Lattnerf1b200b2005-04-23 17:27:36 +0000[diff] [blame]2116
Reid Spencer06565dc2007-01-12 17:11:23 +0000[diff] [blame]2117// <i>At this point, NewSTy = "{ opaque*, i32 }". Tell VMCore that</i>
Bill Wendling82e2eea2006-10-11 18:00:22 +0000[diff] [blame]2118// <i>the struct and the opaque type are actually the same.</i>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2119cast&lt;OpaqueType&gt;(StructTy.get())-&gt;<a href="#refineAbstractTypeTo">refineAbstractTypeTo</a>(NewSTy);
Chris Lattnerf1b200b2005-04-23 17:27:36 +0000[diff] [blame]2120
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2121// <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]2122// <i>kept up-to-date</i>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2123NewSTy = cast&lt;StructType&gt;(StructTy.get());
Chris Lattnerf1b200b2005-04-23 17:27:36 +0000[diff] [blame]2124
Bill Wendling82e2eea2006-10-11 18:00:22 +0000[diff] [blame]2125// <i>Add a name for the type to the module symbol table (optional)</i>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2126MyModule-&gt;addTypeName("mylist", NewSTy);
Chris Lattnerf1b200b2005-04-23 17:27:36 +0000[diff] [blame]2127</pre>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2128</div>
Chris Lattnerf1b200b2005-04-23 17:27:36 +0000[diff] [blame]2129
2130<p>
2131This code shows the basic approach used to build recursive types: build a
2132non-recursive type using 'opaque', then use type unification to close the cycle.
2133The type unification step is performed by the <tt><a
Chris Lattneraff26d12007-02-03 03:06:52 +0000[diff] [blame]2134href="#refineAbstractTypeTo">refineAbstractTypeTo</a></tt> method, which is
Chris Lattnerf1b200b2005-04-23 17:27:36 +0000[diff] [blame]2135described next. After that, we describe the <a
2136href="#PATypeHolder">PATypeHolder class</a>.
2137</p>
2138
2139</div>
2140
2141<!-- ______________________________________________________________________ -->
2142<div class="doc_subsubsection">
2143 <a name="refineAbstractTypeTo">The <tt>refineAbstractTypeTo</tt> method</a>
2144</div>
2145
2146<div class="doc_text">
2147<p>
2148The <tt>refineAbstractTypeTo</tt> method starts the type unification process.
2149While this method is actually a member of the DerivedType class, it is most
2150often used on OpaqueType instances. Type unification is actually a recursive
2151process. After unification, types can become structurally isomorphic to
2152existing types, and all duplicates are deleted (to preserve pointer equality).
2153</p>
2154
2155<p>
2156In the example above, the OpaqueType object is definitely deleted.
Reid Spencer06565dc2007-01-12 17:11:23 +0000[diff] [blame]2157Additionally, if there is an "{ \2*, i32}" type already created in the system,
Chris Lattnerf1b200b2005-04-23 17:27:36 +0000[diff] [blame]2158the pointer and struct type created are <b>also</b> deleted. Obviously whenever
2159a type is deleted, any "Type*" pointers in the program are invalidated. As
2160such, it is safest to avoid having <i>any</i> "Type*" pointers to abstract types
2161live across a call to <tt>refineAbstractTypeTo</tt> (note that non-abstract
2162types can never move or be deleted). To deal with this, the <a
2163href="#PATypeHolder">PATypeHolder</a> class is used to maintain a stable
2164reference to a possibly refined type, and the <a
2165href="#AbstractTypeUser">AbstractTypeUser</a> class is used to update more
2166complex datastructures.
2167</p>
2168
2169</div>
2170
2171<!-- ______________________________________________________________________ -->
2172<div class="doc_subsubsection">
2173 <a name="PATypeHolder">The PATypeHolder Class</a>
2174</div>
2175
2176<div class="doc_text">
2177<p>
2178PATypeHolder is a form of a "smart pointer" for Type objects. When VMCore
2179happily goes about nuking types that become isomorphic to existing types, it
2180automatically updates all PATypeHolder objects to point to the new type. In the
2181example above, this allows the code to maintain a pointer to the resultant
2182resolved recursive type, even though the Type*'s are potentially invalidated.
2183</p>
2184
2185<p>
2186PATypeHolder is an extremely light-weight object that uses a lazy union-find
2187implementation to update pointers. For example the pointer from a Value to its
2188Type is maintained by PATypeHolder objects.
2189</p>
2190
2191</div>
2192
2193<!-- ______________________________________________________________________ -->
2194<div class="doc_subsubsection">
2195 <a name="AbstractTypeUser">The AbstractTypeUser Class</a>
2196</div>
2197
2198<div class="doc_text">
2199
2200<p>
2201Some data structures need more to perform more complex updates when types get
Chris Lattner263a98e2007-02-16 04:37:31 +0000[diff] [blame]2202resolved. To support this, a class can derive from the AbstractTypeUser class.
2203This class
Chris Lattnerf1b200b2005-04-23 17:27:36 +0000[diff] [blame]2204allows it to get callbacks when certain types are resolved. To register to get
2205callbacks for a particular type, the DerivedType::{add/remove}AbstractTypeUser
Chris Lattner0f876db2005-04-25 15:47:57 +0000[diff] [blame]2206methods can be called on a type. Note that these methods only work for <i>
Reid Spencer06565dc2007-01-12 17:11:23 +0000[diff] [blame]2207 abstract</i> types. Concrete types (those that do not include any opaque
2208objects) can never be refined.
Chris Lattnerf1b200b2005-04-23 17:27:36 +0000[diff] [blame]2209</p>
Chris Lattnerd9d6e102005-04-23 16:10:52 +0000[diff] [blame]2210</div>
2211
2212
2213<!-- ======================================================================= -->
2214<div class="doc_subsection">
Chris Lattner263a98e2007-02-16 04:37:31 +0000[diff] [blame]2215 <a name="SymbolTable">The <tt>ValueSymbolTable</tt> and
2216 <tt>TypeSymbolTable</tt> classes</a>
Chris Lattnerd9d6e102005-04-23 16:10:52 +0000[diff] [blame]2217</div>
Chris Lattnerf1b200b2005-04-23 17:27:36 +0000[diff] [blame]2218
Chris Lattnerd9d6e102005-04-23 16:10:52 +0000[diff] [blame]2219<div class="doc_text">
Chris Lattner263a98e2007-02-16 04:37:31 +0000[diff] [blame]2220<p>The <tt><a href="http://llvm.org/doxygen/classllvm_1_1ValueSymbolTable.html">
2221ValueSymbolTable</a></tt> class provides a symbol table that the <a
Chris Lattnerd9d6e102005-04-23 16:10:52 +0000[diff] [blame]2222href="#Function"><tt>Function</tt></a> and <a href="#Module">
Chris Lattner263a98e2007-02-16 04:37:31 +0000[diff] [blame]2223<tt>Module</tt></a> classes use for naming value definitions. The symbol table
2224can provide a name for any <a href="#Value"><tt>Value</tt></a>.
2225The <tt><a href="http://llvm.org/doxygen/classllvm_1_1TypeSymbolTable.html">
2226TypeSymbolTable</a></tt> class is used by the <tt>Module</tt> class to store
2227names for types.</p>
Chris Lattnerd9d6e102005-04-23 16:10:52 +0000[diff] [blame]2228
Reid Spencera6362242007-01-07 00:41:39 +0000[diff] [blame]2229<p>Note that the <tt>SymbolTable</tt> class should not be directly accessed
2230by most clients. It should only be used when iteration over the symbol table
2231names themselves are required, which is very special purpose. Note that not
2232all LLVM
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2233<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]2234an empty name) do not exist in the symbol table.
2235</p>
2236
Chris Lattner263a98e2007-02-16 04:37:31 +0000[diff] [blame]2237<p>These symbol tables support iteration over the values/types in the symbol
2238table with <tt>begin/end/iterator</tt> and supports querying to see if a
2239specific name is in the symbol table (with <tt>lookup</tt>). The
2240<tt>ValueSymbolTable</tt> class exposes no public mutator methods, instead,
2241simply call <tt>setName</tt> on a value, which will autoinsert it into the
2242appropriate symbol table. For types, use the Module::addTypeName method to
2243insert entries into the symbol table.</p>
Chris Lattnerd9d6e102005-04-23 16:10:52 +0000[diff] [blame]2244
Chris Lattnerd9d6e102005-04-23 16:10:52 +0000[diff] [blame]2245</div>
2246
2247
2248
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2249<!-- ======================================================================= -->
2250<div class="doc_subsection">
2251 <a name="UserLayout">The <tt>User</tt> and owned <tt>Use</tt> classes' memory layout</a>
2252</div>
2253
2254<div class="doc_text">
2255<p>The <tt><a href="http://llvm.org/doxygen/classllvm_1_1User.html">
Gabor Greiffd095b62009-01-05 16:05:32 +0000[diff] [blame]2256User</a></tt> class provides a basis for expressing the ownership of <tt>User</tt>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2257towards other <tt><a href="http://llvm.org/doxygen/classllvm_1_1Value.html">
2258Value</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]2259Use</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]2260addition and removal.</p>
2261
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2262<!-- ______________________________________________________________________ -->
2263<div class="doc_subsubsection">
Gabor Greiffd095b62009-01-05 16:05:32 +0000[diff] [blame]2264 <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]2265</div>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2266
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2267<div class="doc_text">
2268<p>
2269A subclass of <tt>User</tt> can choose between incorporating its <tt>Use</tt> objects
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2270or refer to them out-of-line by means of a pointer. A mixed variant
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2271(some <tt>Use</tt>s inline others hung off) is impractical and breaks the invariant
2272that the <tt>Use</tt> objects belonging to the same <tt>User</tt> form a contiguous array.
2273</p>
2274</div>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2275
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2276<p>
2277We have 2 different layouts in the <tt>User</tt> (sub)classes:
2278<ul>
2279<li><p>Layout a)
2280The <tt>Use</tt> object(s) are inside (resp. at fixed offset) of the <tt>User</tt>
2281object and there are a fixed number of them.</p>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2282
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2283<li><p>Layout b)
2284The <tt>Use</tt> object(s) are referenced by a pointer to an
2285array from the <tt>User</tt> object and there may be a variable
2286number of them.</p>
2287</ul>
2288<p>
Gabor Greifd41720a2008-06-25 00:10:22 +0000[diff] [blame]2289As of v2.4 each layout still possesses a direct pointer to the
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2290start of the array of <tt>Use</tt>s. Though not mandatory for layout a),
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2291we stick to this redundancy for the sake of simplicity.
Gabor Greifd41720a2008-06-25 00:10:22 +0000[diff] [blame]2292The <tt>User</tt> object also stores the number of <tt>Use</tt> objects it
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2293has. (Theoretically this information can also be calculated
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2294given the scheme presented below.)</p>
2295<p>
2296Special forms of allocation operators (<tt>operator new</tt>)
Gabor Greifd41720a2008-06-25 00:10:22 +0000[diff] [blame]2297enforce the following memory layouts:</p>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2298
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2299<ul>
Gabor Greifd41720a2008-06-25 00:10:22 +0000[diff] [blame]2300<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]2301
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2302<pre>
2303...---.---.---.---.-------...
2304 | P | P | P | P | User
2305'''---'---'---'---'-------'''
2306</pre>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2307
Gabor Greifd41720a2008-06-25 00:10:22 +0000[diff] [blame]2308<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]2309<pre>
2310.-------...
2311| User
2312'-------'''
2313 |
2314 v
2315 .---.---.---.---...
2316 | P | P | P | P |
2317 '---'---'---'---'''
2318</pre>
2319</ul>
2320<i>(In the above figures '<tt>P</tt>' stands for the <tt>Use**</tt> that
2321 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]2322
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2323<!-- ______________________________________________________________________ -->
2324<div class="doc_subsubsection">
Gabor Greiffd095b62009-01-05 16:05:32 +0000[diff] [blame]2325 <a name="Waymarking">The waymarking algorithm</a>
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2326</div>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2327
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2328<div class="doc_text">
2329<p>
Gabor Greifd41720a2008-06-25 00:10:22 +0000[diff] [blame]2330Since the <tt>Use</tt> objects are deprived of the direct (back)pointer to
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2331their <tt>User</tt> objects, there must be a fast and exact method to
2332recover it. This is accomplished by the following scheme:</p>
2333</div>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2334
Gabor Greifd41720a2008-06-25 00:10:22 +0000[diff] [blame]2335A 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]2336start of the <tt>User</tt> object:
2337<ul>
2338<li><tt>00</tt> &mdash;&gt; binary digit 0</li>
2339<li><tt>01</tt> &mdash;&gt; binary digit 1</li>
2340<li><tt>10</tt> &mdash;&gt; stop and calculate (<tt>s</tt>)</li>
2341<li><tt>11</tt> &mdash;&gt; full stop (<tt>S</tt>)</li>
2342</ul>
2343<p>
2344Given a <tt>Use*</tt>, all we have to do is to walk till we get
2345a stop and we either have a <tt>User</tt> immediately behind or
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2346we have to walk to the next stop picking up digits
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2347and calculating the offset:</p>
2348<pre>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2349.---.---.---.---.---.---.---.---.---.---.---.---.---.---.---.---.----------------
2350| 1 | s | 1 | 0 | 1 | 0 | s | 1 | 1 | 0 | s | 1 | 1 | s | 1 | S | User (or User*)
2351'---'---'---'---'---'---'---'---'---'---'---'---'---'---'---'---'----------------
2352 |+15 |+10 |+6 |+3 |+1
2353 | | | | |__>
2354 | | | |__________>
2355 | | |______________________>
2356 | |______________________________________>
2357 |__________________________________________________________>
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2358</pre>
2359<p>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2360Only the significant number of bits need to be stored between the
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2361stops, so that the <i>worst case is 20 memory accesses</i> when there are
23621000 <tt>Use</tt> objects associated with a <tt>User</tt>.</p>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2363
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2364<!-- ______________________________________________________________________ -->
2365<div class="doc_subsubsection">
Gabor Greiffd095b62009-01-05 16:05:32 +0000[diff] [blame]2366 <a name="ReferenceImpl">Reference implementation</a>
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2367</div>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2368
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2369<div class="doc_text">
2370<p>
2371The following literate Haskell fragment demonstrates the concept:</p>
2372</div>
2373
2374<div class="doc_code">
2375<pre>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2376> import Test.QuickCheck
2377>
2378> digits :: Int -> [Char] -> [Char]
2379> digits 0 acc = '0' : acc
2380> digits 1 acc = '1' : acc
2381> digits n acc = digits (n `div` 2) $ digits (n `mod` 2) acc
2382>
2383> dist :: Int -> [Char] -> [Char]
2384> dist 0 [] = ['S']
2385> dist 0 acc = acc
2386> dist 1 acc = let r = dist 0 acc in 's' : digits (length r) r
2387> dist n acc = dist (n - 1) $ dist 1 acc
2388>
2389> takeLast n ss = reverse $ take n $ reverse ss
2390>
2391> test = takeLast 40 $ dist 20 []
2392>
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2393</pre>
2394</div>
2395<p>
2396Printing &lt;test&gt; gives: <tt>"1s100000s11010s10100s1111s1010s110s11s1S"</tt></p>
2397<p>
2398The reverse algorithm computes the length of the string just by examining
2399a certain prefix:</p>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2400
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2401<div class="doc_code">
2402<pre>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2403> pref :: [Char] -> Int
2404> pref "S" = 1
2405> pref ('s':'1':rest) = decode 2 1 rest
2406> pref (_:rest) = 1 + pref rest
2407>
2408> decode walk acc ('0':rest) = decode (walk + 1) (acc * 2) rest
2409> decode walk acc ('1':rest) = decode (walk + 1) (acc * 2 + 1) rest
2410> decode walk acc _ = walk + acc
2411>
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2412</pre>
2413</div>
2414<p>
2415Now, as expected, printing &lt;pref test&gt; gives <tt>40</tt>.</p>
2416<p>
2417We can <i>quickCheck</i> this with following property:</p>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2418
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2419<div class="doc_code">
2420<pre>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2421> testcase = dist 2000 []
2422> testcaseLength = length testcase
2423>
2424> identityProp n = n > 0 && n <= testcaseLength ==> length arr == pref arr
2425> where arr = takeLast n testcase
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2426>
2427</pre>
2428</div>
2429<p>
2430As expected &lt;quickCheck identityProp&gt; gives:</p>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2431
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2432<pre>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2433*Main> quickCheck identityProp
2434OK, passed 100 tests.
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2435</pre>
2436<p>
2437Let's be a bit more exhaustive:</p>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2438
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2439<div class="doc_code">
2440<pre>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2441>
2442> deepCheck p = check (defaultConfig { configMaxTest = 500 }) p
2443>
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2444</pre>
2445</div>
2446<p>
2447And here is the result of &lt;deepCheck identityProp&gt;:</p>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2448
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2449<pre>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2450*Main> deepCheck identityProp
2451OK, passed 500 tests.
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2452</pre>
2453
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2454<!-- ______________________________________________________________________ -->
2455<div class="doc_subsubsection">
Gabor Greiffd095b62009-01-05 16:05:32 +0000[diff] [blame]2456 <a name="Tagging">Tagging considerations</a>
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2457</div>
2458
2459<p>
2460To maintain the invariant that the 2 LSBits of each <tt>Use**</tt> in <tt>Use</tt>
2461never change after being set up, setters of <tt>Use::Prev</tt> must re-tag the
2462new <tt>Use**</tt> on every modification. Accordingly getters must strip the
2463tag bits.</p>
2464<p>
Gabor Greifd41720a2008-06-25 00:10:22 +0000[diff] [blame]2465For layout b) instead of the <tt>User</tt> we find a pointer (<tt>User*</tt> with LSBit set).
2466Following this pointer brings us to the <tt>User</tt>. A portable trick ensures
2467that the first bytes of <tt>User</tt> (if interpreted as a pointer) never has
Gabor Greiffd095b62009-01-05 16:05:32 +0000[diff] [blame]2468the LSBit set. (Portability is relying on the fact that all known compilers place the
2469<tt>vptr</tt> in the first word of the instances.)</p>
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2470
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2471</div>
2472
2473 <!-- *********************************************************************** -->
Chris Lattnerd9d6e102005-04-23 16:10:52 +0000[diff] [blame]2474<div class="doc_section">
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2475 <a name="coreclasses">The Core LLVM Class Hierarchy Reference </a>
2476</div>
2477<!-- *********************************************************************** -->
2478
2479<div class="doc_text">
Reid Spencer303c4b42007-01-12 17:26:25 +0000[diff] [blame]2480<p><tt>#include "<a href="/doxygen/Type_8h-source.html">llvm/Type.h</a>"</tt>
2481<br>doxygen info: <a href="/doxygen/classllvm_1_1Type.html">Type Class</a></p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2482
2483<p>The Core LLVM classes are the primary means of representing the program
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]2484being inspected or transformed. The core LLVM classes are defined in
2485header files in the <tt>include/llvm/</tt> directory, and implemented in
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2486the <tt>lib/VMCore</tt> directory.</p>
2487
2488</div>
2489
2490<!-- ======================================================================= -->
2491<div class="doc_subsection">
Reid Spencer303c4b42007-01-12 17:26:25 +0000[diff] [blame]2492 <a name="Type">The <tt>Type</tt> class and Derived Types</a>
2493</div>
2494
2495<div class="doc_text">
2496
2497 <p><tt>Type</tt> is a superclass of all type classes. Every <tt>Value</tt> has
2498 a <tt>Type</tt>. <tt>Type</tt> cannot be instantiated directly but only
2499 through its subclasses. Certain primitive types (<tt>VoidType</tt>,
2500 <tt>LabelType</tt>, <tt>FloatType</tt> and <tt>DoubleType</tt>) have hidden
2501 subclasses. They are hidden because they offer no useful functionality beyond
2502 what the <tt>Type</tt> class offers except to distinguish themselves from
2503 other subclasses of <tt>Type</tt>.</p>
2504 <p>All other types are subclasses of <tt>DerivedType</tt>. Types can be
2505 named, but this is not a requirement. There exists exactly
2506 one instance of a given shape at any one time. This allows type equality to
2507 be performed with address equality of the Type Instance. That is, given two
2508 <tt>Type*</tt> values, the types are identical if the pointers are identical.
2509 </p>
2510</div>
2511
2512<!-- _______________________________________________________________________ -->
2513<div class="doc_subsubsection">
Gabor Greiffd095b62009-01-05 16:05:32 +0000[diff] [blame]2514 <a name="m_Type">Important Public Methods</a>
Reid Spencer303c4b42007-01-12 17:26:25 +0000[diff] [blame]2515</div>
2516
2517<div class="doc_text">
2518
2519<ul>
Chris Lattner8f79df32007-01-15 01:55:32 +0000[diff] [blame]2520 <li><tt>bool isInteger() const</tt>: Returns true for any integer type.</li>
Reid Spencer303c4b42007-01-12 17:26:25 +0000[diff] [blame]2521
2522 <li><tt>bool isFloatingPoint()</tt>: Return true if this is one of the two
2523 floating point types.</li>
2524
2525 <li><tt>bool isAbstract()</tt>: Return true if the type is abstract (contains
2526 an OpaqueType anywhere in its definition).</li>
2527
2528 <li><tt>bool isSized()</tt>: Return true if the type has known size. Things
2529 that don't have a size are abstract types, labels and void.</li>
2530
2531</ul>
2532</div>
2533
2534<!-- _______________________________________________________________________ -->
2535<div class="doc_subsubsection">
Gabor Greiffd095b62009-01-05 16:05:32 +0000[diff] [blame]2536 <a name="derivedtypes">Important Derived Types</a>
Reid Spencer303c4b42007-01-12 17:26:25 +0000[diff] [blame]2537</div>
2538<div class="doc_text">
2539<dl>
2540 <dt><tt>IntegerType</tt></dt>
2541 <dd>Subclass of DerivedType that represents integer types of any bit width.
2542 Any bit width between <tt>IntegerType::MIN_INT_BITS</tt> (1) and
2543 <tt>IntegerType::MAX_INT_BITS</tt> (~8 million) can be represented.
2544 <ul>
2545 <li><tt>static const IntegerType* get(unsigned NumBits)</tt>: get an integer
2546 type of a specific bit width.</li>
2547 <li><tt>unsigned getBitWidth() const</tt>: Get the bit width of an integer
2548 type.</li>
2549 </ul>
2550 </dd>
2551 <dt><tt>SequentialType</tt></dt>
2552 <dd>This is subclassed by ArrayType and PointerType
2553 <ul>
2554 <li><tt>const Type * getElementType() const</tt>: Returns the type of each
2555 of the elements in the sequential type. </li>
2556 </ul>
2557 </dd>
2558 <dt><tt>ArrayType</tt></dt>
2559 <dd>This is a subclass of SequentialType and defines the interface for array
2560 types.
2561 <ul>
2562 <li><tt>unsigned getNumElements() const</tt>: Returns the number of
2563 elements in the array. </li>
2564 </ul>
2565 </dd>
2566 <dt><tt>PointerType</tt></dt>
Chris Lattner302da1e2007-02-03 03:05:57 +0000[diff] [blame]2567 <dd>Subclass of SequentialType for pointer types.</dd>
Reid Spencer9d6565a2007-02-15 02:26:10 +0000[diff] [blame]2568 <dt><tt>VectorType</tt></dt>
Reid Spencer485bad12007-02-15 03:07:05 +0000[diff] [blame]2569 <dd>Subclass of SequentialType for vector types. A
2570 vector type is similar to an ArrayType but is distinguished because it is
2571 a first class type wherease ArrayType is not. Vector types are used for
Reid Spencer303c4b42007-01-12 17:26:25 +0000[diff] [blame]2572 vector operations and are usually small vectors of of an integer or floating
2573 point type.</dd>
2574 <dt><tt>StructType</tt></dt>
2575 <dd>Subclass of DerivedTypes for struct types.</dd>
Duncan Sands8036ca42007-03-30 12:22:09 +0000[diff] [blame]2576 <dt><tt><a name="FunctionType">FunctionType</a></tt></dt>
Reid Spencer303c4b42007-01-12 17:26:25 +0000[diff] [blame]2577 <dd>Subclass of DerivedTypes for function types.
2578 <ul>
2579 <li><tt>bool isVarArg() const</tt>: Returns true if its a vararg
2580 function</li>
2581 <li><tt> const Type * getReturnType() const</tt>: Returns the
2582 return type of the function.</li>
2583 <li><tt>const Type * getParamType (unsigned i)</tt>: Returns
2584 the type of the ith parameter.</li>
2585 <li><tt> const unsigned getNumParams() const</tt>: Returns the
2586 number of formal parameters.</li>
2587 </ul>
2588 </dd>
2589 <dt><tt>OpaqueType</tt></dt>
2590 <dd>Sublcass of DerivedType for abstract types. This class
2591 defines no content and is used as a placeholder for some other type. Note
2592 that OpaqueType is used (temporarily) during type resolution for forward
2593 references of types. Once the referenced type is resolved, the OpaqueType
2594 is replaced with the actual type. OpaqueType can also be used for data
2595 abstraction. At link time opaque types can be resolved to actual types
2596 of the same name.</dd>
2597</dl>
2598</div>
2599
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]2600
2601
2602<!-- ======================================================================= -->
2603<div class="doc_subsection">
2604 <a name="Module">The <tt>Module</tt> class</a>
2605</div>
2606
2607<div class="doc_text">
2608
2609<p><tt>#include "<a
2610href="/doxygen/Module_8h-source.html">llvm/Module.h</a>"</tt><br> doxygen info:
2611<a href="/doxygen/classllvm_1_1Module.html">Module Class</a></p>
2612
2613<p>The <tt>Module</tt> class represents the top level structure present in LLVM
2614programs. An LLVM module is effectively either a translation unit of the
2615original program or a combination of several translation units merged by the
2616linker. The <tt>Module</tt> class keeps track of a list of <a
2617href="#Function"><tt>Function</tt></a>s, a list of <a
2618href="#GlobalVariable"><tt>GlobalVariable</tt></a>s, and a <a
2619href="#SymbolTable"><tt>SymbolTable</tt></a>. Additionally, it contains a few
2620helpful member functions that try to make common operations easy.</p>
2621
2622</div>
2623
2624<!-- _______________________________________________________________________ -->
2625<div class="doc_subsubsection">
2626 <a name="m_Module">Important Public Members of the <tt>Module</tt> class</a>
2627</div>
2628
2629<div class="doc_text">
2630
2631<ul>
2632 <li><tt>Module::Module(std::string name = "")</tt></li>
2633</ul>
2634
2635<p>Constructing a <a href="#Module">Module</a> is easy. You can optionally
2636provide a name for it (probably based on the name of the translation unit).</p>
2637
2638<ul>
2639 <li><tt>Module::iterator</tt> - Typedef for function list iterator<br>
2640 <tt>Module::const_iterator</tt> - Typedef for const_iterator.<br>
2641
2642 <tt>begin()</tt>, <tt>end()</tt>
2643 <tt>size()</tt>, <tt>empty()</tt>
2644
2645 <p>These are forwarding methods that make it easy to access the contents of
2646 a <tt>Module</tt> object's <a href="#Function"><tt>Function</tt></a>
2647 list.</p></li>
2648
2649 <li><tt>Module::FunctionListType &amp;getFunctionList()</tt>
2650
2651 <p> Returns the list of <a href="#Function"><tt>Function</tt></a>s. This is
2652 necessary to use when you need to update the list or perform a complex
2653 action that doesn't have a forwarding method.</p>
2654
2655 <p><!-- Global Variable --></p></li>
2656</ul>
2657
2658<hr>
2659
2660<ul>
2661 <li><tt>Module::global_iterator</tt> - Typedef for global variable list iterator<br>
2662
2663 <tt>Module::const_global_iterator</tt> - Typedef for const_iterator.<br>
2664
2665 <tt>global_begin()</tt>, <tt>global_end()</tt>
2666 <tt>global_size()</tt>, <tt>global_empty()</tt>
2667
2668 <p> These are forwarding methods that make it easy to access the contents of
2669 a <tt>Module</tt> object's <a
2670 href="#GlobalVariable"><tt>GlobalVariable</tt></a> list.</p></li>
2671
2672 <li><tt>Module::GlobalListType &amp;getGlobalList()</tt>
2673
2674 <p>Returns the list of <a
2675 href="#GlobalVariable"><tt>GlobalVariable</tt></a>s. This is necessary to
2676 use when you need to update the list or perform a complex action that
2677 doesn't have a forwarding method.</p>
2678
2679 <p><!-- Symbol table stuff --> </p></li>
2680</ul>
2681
2682<hr>
2683
2684<ul>
2685 <li><tt><a href="#SymbolTable">SymbolTable</a> *getSymbolTable()</tt>
2686
2687 <p>Return a reference to the <a href="#SymbolTable"><tt>SymbolTable</tt></a>
2688 for this <tt>Module</tt>.</p>
2689
2690 <p><!-- Convenience methods --></p></li>
2691</ul>
2692
2693<hr>
2694
2695<ul>
2696 <li><tt><a href="#Function">Function</a> *getFunction(const std::string
2697 &amp;Name, const <a href="#FunctionType">FunctionType</a> *Ty)</tt>
2698
2699 <p>Look up the specified function in the <tt>Module</tt> <a
2700 href="#SymbolTable"><tt>SymbolTable</tt></a>. If it does not exist, return
2701 <tt>null</tt>.</p></li>
2702
2703 <li><tt><a href="#Function">Function</a> *getOrInsertFunction(const
2704 std::string &amp;Name, const <a href="#FunctionType">FunctionType</a> *T)</tt>
2705
2706 <p>Look up the specified function in the <tt>Module</tt> <a
2707 href="#SymbolTable"><tt>SymbolTable</tt></a>. If it does not exist, add an
2708 external declaration for the function and return it.</p></li>
2709
2710 <li><tt>std::string getTypeName(const <a href="#Type">Type</a> *Ty)</tt>
2711
2712 <p>If there is at least one entry in the <a
2713 href="#SymbolTable"><tt>SymbolTable</tt></a> for the specified <a
2714 href="#Type"><tt>Type</tt></a>, return it. Otherwise return the empty
2715 string.</p></li>
2716
2717 <li><tt>bool addTypeName(const std::string &amp;Name, const <a
2718 href="#Type">Type</a> *Ty)</tt>
2719
2720 <p>Insert an entry in the <a href="#SymbolTable"><tt>SymbolTable</tt></a>
2721 mapping <tt>Name</tt> to <tt>Ty</tt>. If there is already an entry for this
2722 name, true is returned and the <a
2723 href="#SymbolTable"><tt>SymbolTable</tt></a> is not modified.</p></li>
2724</ul>
2725
2726</div>
2727
2728
Reid Spencer303c4b42007-01-12 17:26:25 +0000[diff] [blame]2729<!-- ======================================================================= -->
2730<div class="doc_subsection">
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2731 <a name="Value">The <tt>Value</tt> class</a>
2732</div>
2733
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]2734<div class="doc_text">
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2735
2736<p><tt>#include "<a href="/doxygen/Value_8h-source.html">llvm/Value.h</a>"</tt>
2737<br>
Chris Lattner00815172007-01-04 22:01:45 +0000[diff] [blame]2738doxygen info: <a href="/doxygen/classllvm_1_1Value.html">Value Class</a></p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2739
2740<p>The <tt>Value</tt> class is the most important class in the LLVM Source
2741base. It represents a typed value that may be used (among other things) as an
2742operand to an instruction. There are many different types of <tt>Value</tt>s,
2743such as <a href="#Constant"><tt>Constant</tt></a>s,<a
2744href="#Argument"><tt>Argument</tt></a>s. Even <a
2745href="#Instruction"><tt>Instruction</tt></a>s and <a
2746href="#Function"><tt>Function</tt></a>s are <tt>Value</tt>s.</p>
2747
2748<p>A particular <tt>Value</tt> may be used many times in the LLVM representation
2749for a program. For example, an incoming argument to a function (represented
2750with an instance of the <a href="#Argument">Argument</a> class) is "used" by
2751every instruction in the function that references the argument. To keep track
2752of this relationship, the <tt>Value</tt> class keeps a list of all of the <a
2753href="#User"><tt>User</tt></a>s that is using it (the <a
2754href="#User"><tt>User</tt></a> class is a base class for all nodes in the LLVM
2755graph that can refer to <tt>Value</tt>s). This use list is how LLVM represents
2756def-use information in the program, and is accessible through the <tt>use_</tt>*
2757methods, shown below.</p>
2758
2759<p>Because LLVM is a typed representation, every LLVM <tt>Value</tt> is typed,
2760and this <a href="#Type">Type</a> is available through the <tt>getType()</tt>
2761method. In addition, all LLVM values can be named. The "name" of the
2762<tt>Value</tt> is a symbolic string printed in the LLVM code:</p>
2763
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2764<div class="doc_code">
2765<pre>
Reid Spencer06565dc2007-01-12 17:11:23 +0000[diff] [blame]2766%<b>foo</b> = add i32 1, 2
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2767</pre>
2768</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2769
Duncan Sands8036ca42007-03-30 12:22:09 +0000[diff] [blame]2770<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]2771that the name of any value may be missing (an empty string), so names should
2772<b>ONLY</b> be used for debugging (making the source code easier to read,
2773debugging printouts), they should not be used to keep track of values or map
2774between them. For this purpose, use a <tt>std::map</tt> of pointers to the
2775<tt>Value</tt> itself instead.</p>
2776
2777<p>One important aspect of LLVM is that there is no distinction between an SSA
2778variable and the operation that produces it. Because of this, any reference to
2779the value produced by an instruction (or the value available as an incoming
Chris Lattnerd5fc4fc2004-03-18 14:58:55 +0000[diff] [blame]2780argument, for example) is represented as a direct pointer to the instance of
2781the class that
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2782represents this value. Although this may take some getting used to, it
2783simplifies the representation and makes it easier to manipulate.</p>
2784
2785</div>
2786
2787<!-- _______________________________________________________________________ -->
2788<div class="doc_subsubsection">
2789 <a name="m_Value">Important Public Members of the <tt>Value</tt> class</a>
2790</div>
2791
2792<div class="doc_text">
2793
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]2794<ul>
2795 <li><tt>Value::use_iterator</tt> - Typedef for iterator over the
2796use-list<br>
2797 <tt>Value::use_const_iterator</tt> - Typedef for const_iterator over
2798the use-list<br>
2799 <tt>unsigned use_size()</tt> - Returns the number of users of the
2800value.<br>
Chris Lattner9355b472002-09-06 02:50:58 +0000[diff] [blame]2801 <tt>bool use_empty()</tt> - Returns true if there are no users.<br>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]2802 <tt>use_iterator use_begin()</tt> - Get an iterator to the start of
2803the use-list.<br>
2804 <tt>use_iterator use_end()</tt> - Get an iterator to the end of the
2805use-list.<br>
2806 <tt><a href="#User">User</a> *use_back()</tt> - Returns the last
2807element in the list.
2808 <p> These methods are the interface to access the def-use
2809information in LLVM. As with all other iterators in LLVM, the naming
2810conventions follow the conventions defined by the <a href="#stl">STL</a>.</p>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]2811 </li>
2812 <li><tt><a href="#Type">Type</a> *getType() const</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2813 <p>This method returns the Type of the Value.</p>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]2814 </li>
2815 <li><tt>bool hasName() const</tt><br>
Chris Lattner9355b472002-09-06 02:50:58 +0000[diff] [blame]2816 <tt>std::string getName() const</tt><br>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]2817 <tt>void setName(const std::string &amp;Name)</tt>
2818 <p> This family of methods is used to access and assign a name to a <tt>Value</tt>,
2819be aware of the <a href="#nameWarning">precaution above</a>.</p>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]2820 </li>
2821 <li><tt>void replaceAllUsesWith(Value *V)</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2822
2823 <p>This method traverses the use list of a <tt>Value</tt> changing all <a
2824 href="#User"><tt>User</tt>s</a> of the current value to refer to
2825 "<tt>V</tt>" instead. For example, if you detect that an instruction always
2826 produces a constant value (for example through constant folding), you can
2827 replace all uses of the instruction with the constant like this:</p>
2828
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2829<div class="doc_code">
2830<pre>
2831Inst-&gt;replaceAllUsesWith(ConstVal);
2832</pre>
2833</div>
2834
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]2835</ul>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2836
2837</div>
2838
2839<!-- ======================================================================= -->
2840<div class="doc_subsection">
2841 <a name="User">The <tt>User</tt> class</a>
2842</div>
2843
2844<div class="doc_text">
2845
2846<p>
2847<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]2848doxygen info: <a href="/doxygen/classllvm_1_1User.html">User Class</a><br>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2849Superclass: <a href="#Value"><tt>Value</tt></a></p>
2850
2851<p>The <tt>User</tt> class is the common base class of all LLVM nodes that may
2852refer to <a href="#Value"><tt>Value</tt></a>s. It exposes a list of "Operands"
2853that are all of the <a href="#Value"><tt>Value</tt></a>s that the User is
2854referring to. The <tt>User</tt> class itself is a subclass of
2855<tt>Value</tt>.</p>
2856
2857<p>The operands of a <tt>User</tt> point directly to the LLVM <a
2858href="#Value"><tt>Value</tt></a> that it refers to. Because LLVM uses Static
2859Single Assignment (SSA) form, there can only be one definition referred to,
2860allowing this direct connection. This connection provides the use-def
2861information in LLVM.</p>
2862
2863</div>
2864
2865<!-- _______________________________________________________________________ -->
2866<div class="doc_subsubsection">
2867 <a name="m_User">Important Public Members of the <tt>User</tt> class</a>
2868</div>
2869
2870<div class="doc_text">
2871
2872<p>The <tt>User</tt> class exposes the operand list in two ways: through
2873an index access interface and through an iterator based interface.</p>
2874
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]2875<ul>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]2876 <li><tt>Value *getOperand(unsigned i)</tt><br>
2877 <tt>unsigned getNumOperands()</tt>
2878 <p> These two methods expose the operands of the <tt>User</tt> in a
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2879convenient form for direct access.</p></li>
2880
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]2881 <li><tt>User::op_iterator</tt> - Typedef for iterator over the operand
2882list<br>
Chris Lattner58360822005-01-17 00:12:04 +0000[diff] [blame]2883 <tt>op_iterator op_begin()</tt> - Get an iterator to the start of
2884the operand list.<br>
2885 <tt>op_iterator op_end()</tt> - Get an iterator to the end of the
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]2886operand list.
2887 <p> Together, these methods make up the iterator based interface to
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2888the operands of a <tt>User</tt>.</p></li>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]2889</ul>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2890
2891</div>
2892
2893<!-- ======================================================================= -->
2894<div class="doc_subsection">
2895 <a name="Instruction">The <tt>Instruction</tt> class</a>
2896</div>
2897
2898<div class="doc_text">
2899
2900<p><tt>#include "</tt><tt><a
2901href="/doxygen/Instruction_8h-source.html">llvm/Instruction.h</a>"</tt><br>
Misha Brukman31ca1de2004-06-03 23:35:54 +0000[diff] [blame]2902doxygen info: <a href="/doxygen/classllvm_1_1Instruction.html">Instruction Class</a><br>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2903Superclasses: <a href="#User"><tt>User</tt></a>, <a
2904href="#Value"><tt>Value</tt></a></p>
2905
2906<p>The <tt>Instruction</tt> class is the common base class for all LLVM
2907instructions. It provides only a few methods, but is a very commonly used
2908class. The primary data tracked by the <tt>Instruction</tt> class itself is the
2909opcode (instruction type) and the parent <a
2910href="#BasicBlock"><tt>BasicBlock</tt></a> the <tt>Instruction</tt> is embedded
2911into. To represent a specific type of instruction, one of many subclasses of
2912<tt>Instruction</tt> are used.</p>
2913
2914<p> Because the <tt>Instruction</tt> class subclasses the <a
2915href="#User"><tt>User</tt></a> class, its operands can be accessed in the same
2916way as for other <a href="#User"><tt>User</tt></a>s (with the
2917<tt>getOperand()</tt>/<tt>getNumOperands()</tt> and
2918<tt>op_begin()</tt>/<tt>op_end()</tt> methods).</p> <p> An important file for
2919the <tt>Instruction</tt> class is the <tt>llvm/Instruction.def</tt> file. This
2920file contains some meta-data about the various different types of instructions
2921in LLVM. It describes the enum values that are used as opcodes (for example
Reid Spencerc92d25d2006-12-19 19:47:19 +0000[diff] [blame]2922<tt>Instruction::Add</tt> and <tt>Instruction::ICmp</tt>), as well as the
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2923concrete sub-classes of <tt>Instruction</tt> that implement the instruction (for
2924example <tt><a href="#BinaryOperator">BinaryOperator</a></tt> and <tt><a
Reid Spencerc92d25d2006-12-19 19:47:19 +0000[diff] [blame]2925href="#CmpInst">CmpInst</a></tt>). Unfortunately, the use of macros in
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2926this file confuses doxygen, so these enum values don't show up correctly in the
Misha Brukman31ca1de2004-06-03 23:35:54 +0000[diff] [blame]2927<a href="/doxygen/classllvm_1_1Instruction.html">doxygen output</a>.</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2928
2929</div>
2930
2931<!-- _______________________________________________________________________ -->
2932<div class="doc_subsubsection">
Reid Spencerc92d25d2006-12-19 19:47:19 +0000[diff] [blame]2933 <a name="s_Instruction">Important Subclasses of the <tt>Instruction</tt>
2934 class</a>
2935</div>
2936<div class="doc_text">
2937 <ul>
2938 <li><tt><a name="BinaryOperator">BinaryOperator</a></tt>
2939 <p>This subclasses represents all two operand instructions whose operands
2940 must be the same type, except for the comparison instructions.</p></li>
2941 <li><tt><a name="CastInst">CastInst</a></tt>
2942 <p>This subclass is the parent of the 12 casting instructions. It provides
2943 common operations on cast instructions.</p>
2944 <li><tt><a name="CmpInst">CmpInst</a></tt>
2945 <p>This subclass respresents the two comparison instructions,
2946 <a href="LangRef.html#i_icmp">ICmpInst</a> (integer opreands), and
2947 <a href="LangRef.html#i_fcmp">FCmpInst</a> (floating point operands).</p>
2948 <li><tt><a name="TerminatorInst">TerminatorInst</a></tt>
2949 <p>This subclass is the parent of all terminator instructions (those which
2950 can terminate a block).</p>
2951 </ul>
2952 </div>
2953
2954<!-- _______________________________________________________________________ -->
2955<div class="doc_subsubsection">
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2956 <a name="m_Instruction">Important Public Members of the <tt>Instruction</tt>
2957 class</a>
2958</div>
2959
2960<div class="doc_text">
2961
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]2962<ul>
2963 <li><tt><a href="#BasicBlock">BasicBlock</a> *getParent()</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2964 <p>Returns the <a href="#BasicBlock"><tt>BasicBlock</tt></a> that
2965this <tt>Instruction</tt> is embedded into.</p></li>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]2966 <li><tt>bool mayWriteToMemory()</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2967 <p>Returns true if the instruction writes to memory, i.e. it is a
2968 <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]2969 <li><tt>unsigned getOpcode()</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2970 <p>Returns the opcode for the <tt>Instruction</tt>.</p></li>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]2971 <li><tt><a href="#Instruction">Instruction</a> *clone() const</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2972 <p>Returns another instance of the specified instruction, identical
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]2973in all ways to the original except that the instruction has no parent
2974(ie it's not embedded into a <a href="#BasicBlock"><tt>BasicBlock</tt></a>),
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2975and it has no name</p></li>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]2976</ul>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2977
2978</div>
2979
2980<!-- ======================================================================= -->
2981<div class="doc_subsection">
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]2982 <a name="Constant">The <tt>Constant</tt> class and subclasses</a>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2983</div>
2984
2985<div class="doc_text">
2986
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]2987<p>Constant represents a base class for different types of constants. It
2988is subclassed by ConstantInt, ConstantArray, etc. for representing
2989the various types of Constants. <a href="#GlobalValue">GlobalValue</a> is also
2990a subclass, which represents the address of a global variable or function.
2991</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2992
2993</div>
2994
2995<!-- _______________________________________________________________________ -->
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]2996<div class="doc_subsubsection">Important Subclasses of Constant </div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2997<div class="doc_text">
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]2998<ul>
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]2999 <li>ConstantInt : This subclass of Constant represents an integer constant of
3000 any width.
3001 <ul>
Reid Spencer97b4ee32007-03-01 21:05:33 +0000[diff] [blame]3002 <li><tt>const APInt&amp; getValue() const</tt>: Returns the underlying
3003 value of this constant, an APInt value.</li>
3004 <li><tt>int64_t getSExtValue() const</tt>: Converts the underlying APInt
3005 value to an int64_t via sign extension. If the value (not the bit width)
3006 of the APInt is too large to fit in an int64_t, an assertion will result.
3007 For this reason, use of this method is discouraged.</li>
3008 <li><tt>uint64_t getZExtValue() const</tt>: Converts the underlying APInt
3009 value to a uint64_t via zero extension. IF the value (not the bit width)
3010 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]3011 For this reason, use of this method is discouraged.</li>
Reid Spencer97b4ee32007-03-01 21:05:33 +0000[diff] [blame]3012 <li><tt>static ConstantInt* get(const APInt&amp; Val)</tt>: Returns the
3013 ConstantInt object that represents the value provided by <tt>Val</tt>.
3014 The type is implied as the IntegerType that corresponds to the bit width
3015 of <tt>Val</tt>.</li>
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]3016 <li><tt>static ConstantInt* get(const Type *Ty, uint64_t Val)</tt>:
3017 Returns the ConstantInt object that represents the value provided by
3018 <tt>Val</tt> for integer type <tt>Ty</tt>.</li>
3019 </ul>
3020 </li>
3021 <li>ConstantFP : This class represents a floating point constant.
3022 <ul>
3023 <li><tt>double getValue() const</tt>: Returns the underlying value of
3024 this constant. </li>
3025 </ul>
3026 </li>
3027 <li>ConstantArray : This represents a constant array.
3028 <ul>
3029 <li><tt>const std::vector&lt;Use&gt; &amp;getValues() const</tt>: Returns
3030 a vector of component constants that makeup this array. </li>
3031 </ul>
3032 </li>
3033 <li>ConstantStruct : This represents a constant struct.
3034 <ul>
3035 <li><tt>const std::vector&lt;Use&gt; &amp;getValues() const</tt>: Returns
3036 a vector of component constants that makeup this array. </li>
3037 </ul>
3038 </li>
3039 <li>GlobalValue : This represents either a global variable or a function. In
3040 either case, the value is a constant fixed address (after linking).
3041 </li>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3042</ul>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3043</div>
3044
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]3045
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3046<!-- ======================================================================= -->
3047<div class="doc_subsection">
3048 <a name="GlobalValue">The <tt>GlobalValue</tt> class</a>
3049</div>
3050
3051<div class="doc_text">
3052
3053<p><tt>#include "<a
3054href="/doxygen/GlobalValue_8h-source.html">llvm/GlobalValue.h</a>"</tt><br>
Misha Brukman384047f2004-06-03 23:29:12 +0000[diff] [blame]3055doxygen info: <a href="/doxygen/classllvm_1_1GlobalValue.html">GlobalValue
3056Class</a><br>
Reid Spencerbe5e85e2006-04-14 14:11:48 +0000[diff] [blame]3057Superclasses: <a href="#Constant"><tt>Constant</tt></a>,
3058<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]3059
3060<p>Global values (<a href="#GlobalVariable"><tt>GlobalVariable</tt></a>s or <a
3061href="#Function"><tt>Function</tt></a>s) are the only LLVM values that are
3062visible in the bodies of all <a href="#Function"><tt>Function</tt></a>s.
3063Because they are visible at global scope, they are also subject to linking with
3064other globals defined in different translation units. To control the linking
3065process, <tt>GlobalValue</tt>s know their linkage rules. Specifically,
3066<tt>GlobalValue</tt>s know whether they have internal or external linkage, as
Reid Spencer8b2da7a2004-07-18 13:10:31 +0000[diff] [blame]3067defined by the <tt>LinkageTypes</tt> enumeration.</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3068
3069<p>If a <tt>GlobalValue</tt> has internal linkage (equivalent to being
3070<tt>static</tt> in C), it is not visible to code outside the current translation
3071unit, and does not participate in linking. If it has external linkage, it is
3072visible to external code, and does participate in linking. In addition to
3073linkage information, <tt>GlobalValue</tt>s keep track of which <a
3074href="#Module"><tt>Module</tt></a> they are currently part of.</p>
3075
3076<p>Because <tt>GlobalValue</tt>s are memory objects, they are always referred to
3077by their <b>address</b>. As such, the <a href="#Type"><tt>Type</tt></a> of a
3078global is always a pointer to its contents. It is important to remember this
3079when using the <tt>GetElementPtrInst</tt> instruction because this pointer must
3080be dereferenced first. For example, if you have a <tt>GlobalVariable</tt> (a
3081subclass 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]3082i32]</tt>, then the <tt>GlobalVariable</tt> is a pointer to that array. Although
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3083the address of the first element of this array and the value of the
3084<tt>GlobalVariable</tt> are the same, they have different types. The
Reid Spencer06565dc2007-01-12 17:11:23 +0000[diff] [blame]3085<tt>GlobalVariable</tt>'s type is <tt>[24 x i32]</tt>. The first element's type
3086is <tt>i32.</tt> Because of this, accessing a global value requires you to
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3087dereference the pointer with <tt>GetElementPtrInst</tt> first, then its elements
3088can be accessed. This is explained in the <a href="LangRef.html#globalvars">LLVM
3089Language Reference Manual</a>.</p>
3090
3091</div>
3092
3093<!-- _______________________________________________________________________ -->
3094<div class="doc_subsubsection">
3095 <a name="m_GlobalValue">Important Public Members of the <tt>GlobalValue</tt>
3096 class</a>
3097</div>
3098
3099<div class="doc_text">
3100
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3101<ul>
3102 <li><tt>bool hasInternalLinkage() const</tt><br>
Chris Lattner9355b472002-09-06 02:50:58 +0000[diff] [blame]3103 <tt>bool hasExternalLinkage() const</tt><br>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3104 <tt>void setInternalLinkage(bool HasInternalLinkage)</tt>
3105 <p> These methods manipulate the linkage characteristics of the <tt>GlobalValue</tt>.</p>
3106 <p> </p>
3107 </li>
3108 <li><tt><a href="#Module">Module</a> *getParent()</tt>
3109 <p> This returns the <a href="#Module"><tt>Module</tt></a> that the
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3110GlobalValue is currently embedded into.</p></li>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3111</ul>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3112
3113</div>
3114
3115<!-- ======================================================================= -->
3116<div class="doc_subsection">
3117 <a name="Function">The <tt>Function</tt> class</a>
3118</div>
3119
3120<div class="doc_text">
3121
3122<p><tt>#include "<a
3123href="/doxygen/Function_8h-source.html">llvm/Function.h</a>"</tt><br> doxygen
Misha Brukman31ca1de2004-06-03 23:35:54 +0000[diff] [blame]3124info: <a href="/doxygen/classllvm_1_1Function.html">Function Class</a><br>
Reid Spencerbe5e85e2006-04-14 14:11:48 +0000[diff] [blame]3125Superclasses: <a href="#GlobalValue"><tt>GlobalValue</tt></a>,
3126<a href="#Constant"><tt>Constant</tt></a>,
3127<a href="#User"><tt>User</tt></a>,
3128<a href="#Value"><tt>Value</tt></a></p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3129
3130<p>The <tt>Function</tt> class represents a single procedure in LLVM. It is
3131actually one of the more complex classes in the LLVM heirarchy because it must
3132keep track of a large amount of data. The <tt>Function</tt> class keeps track
Reid Spencerbe5e85e2006-04-14 14:11:48 +0000[diff] [blame]3133of a list of <a href="#BasicBlock"><tt>BasicBlock</tt></a>s, a list of formal
3134<a href="#Argument"><tt>Argument</tt></a>s, and a
3135<a href="#SymbolTable"><tt>SymbolTable</tt></a>.</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3136
3137<p>The list of <a href="#BasicBlock"><tt>BasicBlock</tt></a>s is the most
3138commonly used part of <tt>Function</tt> objects. The list imposes an implicit
3139ordering of the blocks in the function, which indicate how the code will be
3140layed out by the backend. Additionally, the first <a
3141href="#BasicBlock"><tt>BasicBlock</tt></a> is the implicit entry node for the
3142<tt>Function</tt>. It is not legal in LLVM to explicitly branch to this initial
3143block. There are no implicit exit nodes, and in fact there may be multiple exit
3144nodes from a single <tt>Function</tt>. If the <a
3145href="#BasicBlock"><tt>BasicBlock</tt></a> list is empty, this indicates that
3146the <tt>Function</tt> is actually a function declaration: the actual body of the
3147function hasn't been linked in yet.</p>
3148
3149<p>In addition to a list of <a href="#BasicBlock"><tt>BasicBlock</tt></a>s, the
3150<tt>Function</tt> class also keeps track of the list of formal <a
3151href="#Argument"><tt>Argument</tt></a>s that the function receives. This
3152container manages the lifetime of the <a href="#Argument"><tt>Argument</tt></a>
3153nodes, just like the <a href="#BasicBlock"><tt>BasicBlock</tt></a> list does for
3154the <a href="#BasicBlock"><tt>BasicBlock</tt></a>s.</p>
3155
3156<p>The <a href="#SymbolTable"><tt>SymbolTable</tt></a> is a very rarely used
3157LLVM feature that is only used when you have to look up a value by name. Aside
3158from that, the <a href="#SymbolTable"><tt>SymbolTable</tt></a> is used
3159internally to make sure that there are not conflicts between the names of <a
3160href="#Instruction"><tt>Instruction</tt></a>s, <a
3161href="#BasicBlock"><tt>BasicBlock</tt></a>s, or <a
3162href="#Argument"><tt>Argument</tt></a>s in the function body.</p>
3163
Reid Spencer8b2da7a2004-07-18 13:10:31 +0000[diff] [blame]3164<p>Note that <tt>Function</tt> is a <a href="#GlobalValue">GlobalValue</a>
3165and therefore also a <a href="#Constant">Constant</a>. The value of the function
3166is its address (after linking) which is guaranteed to be constant.</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3167</div>
3168
3169<!-- _______________________________________________________________________ -->
3170<div class="doc_subsubsection">
3171 <a name="m_Function">Important Public Members of the <tt>Function</tt>
3172 class</a>
3173</div>
3174
3175<div class="doc_text">
3176
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3177<ul>
3178 <li><tt>Function(const </tt><tt><a href="#FunctionType">FunctionType</a>
Chris Lattnerac479e52004-08-04 05:10:48 +0000[diff] [blame]3179 *Ty, LinkageTypes Linkage, const std::string &amp;N = "", Module* Parent = 0)</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3180
3181 <p>Constructor used when you need to create new <tt>Function</tt>s to add
3182 the the program. The constructor must specify the type of the function to
Chris Lattnerac479e52004-08-04 05:10:48 +0000[diff] [blame]3183 create and what type of linkage the function should have. The <a
3184 href="#FunctionType"><tt>FunctionType</tt></a> argument
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3185 specifies the formal arguments and return value for the function. The same
Duncan Sands8036ca42007-03-30 12:22:09 +0000[diff] [blame]3186 <a href="#FunctionType"><tt>FunctionType</tt></a> value can be used to
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3187 create multiple functions. The <tt>Parent</tt> argument specifies the Module
3188 in which the function is defined. If this argument is provided, the function
3189 will automatically be inserted into that module's list of
3190 functions.</p></li>
3191
Chris Lattner62810e32008-11-25 18:34:50 +0000[diff] [blame]3192 <li><tt>bool isDeclaration()</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3193
3194 <p>Return whether or not the <tt>Function</tt> has a body defined. If the
3195 function is "external", it does not have a body, and thus must be resolved
3196 by linking with a function defined in a different translation unit.</p></li>
3197
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3198 <li><tt>Function::iterator</tt> - Typedef for basic block list iterator<br>
Chris Lattner9355b472002-09-06 02:50:58 +0000[diff] [blame]3199 <tt>Function::const_iterator</tt> - Typedef for const_iterator.<br>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3200
Chris Lattner77d69242005-03-15 05:19:20 +0000[diff] [blame]3201 <tt>begin()</tt>, <tt>end()</tt>
3202 <tt>size()</tt>, <tt>empty()</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3203
3204 <p>These are forwarding methods that make it easy to access the contents of
3205 a <tt>Function</tt> object's <a href="#BasicBlock"><tt>BasicBlock</tt></a>
3206 list.</p></li>
3207
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3208 <li><tt>Function::BasicBlockListType &amp;getBasicBlockList()</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3209
3210 <p>Returns the list of <a href="#BasicBlock"><tt>BasicBlock</tt></a>s. This
3211 is necessary to use when you need to update the list or perform a complex
3212 action that doesn't have a forwarding method.</p></li>
3213
Chris Lattner89cc2652005-03-15 04:48:32 +0000[diff] [blame]3214 <li><tt>Function::arg_iterator</tt> - Typedef for the argument list
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3215iterator<br>
Chris Lattner89cc2652005-03-15 04:48:32 +0000[diff] [blame]3216 <tt>Function::const_arg_iterator</tt> - Typedef for const_iterator.<br>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3217
Chris Lattner77d69242005-03-15 05:19:20 +0000[diff] [blame]3218 <tt>arg_begin()</tt>, <tt>arg_end()</tt>
Chris Lattner89cc2652005-03-15 04:48:32 +0000[diff] [blame]3219 <tt>arg_size()</tt>, <tt>arg_empty()</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3220
3221 <p>These are forwarding methods that make it easy to access the contents of
3222 a <tt>Function</tt> object's <a href="#Argument"><tt>Argument</tt></a>
3223 list.</p></li>
3224
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3225 <li><tt>Function::ArgumentListType &amp;getArgumentList()</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3226
3227 <p>Returns the list of <a href="#Argument"><tt>Argument</tt></a>s. This is
3228 necessary to use when you need to update the list or perform a complex
3229 action that doesn't have a forwarding method.</p></li>
3230
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3231 <li><tt><a href="#BasicBlock">BasicBlock</a> &amp;getEntryBlock()</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3232
3233 <p>Returns the entry <a href="#BasicBlock"><tt>BasicBlock</tt></a> for the
3234 function. Because the entry block for the function is always the first
3235 block, this returns the first block of the <tt>Function</tt>.</p></li>
3236
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3237 <li><tt><a href="#Type">Type</a> *getReturnType()</tt><br>
3238 <tt><a href="#FunctionType">FunctionType</a> *getFunctionType()</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3239
3240 <p>This traverses the <a href="#Type"><tt>Type</tt></a> of the
3241 <tt>Function</tt> and returns the return type of the function, or the <a
3242 href="#FunctionType"><tt>FunctionType</tt></a> of the actual
3243 function.</p></li>
3244
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3245 <li><tt><a href="#SymbolTable">SymbolTable</a> *getSymbolTable()</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3246
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3247 <p> Return a pointer to the <a href="#SymbolTable"><tt>SymbolTable</tt></a>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3248 for this <tt>Function</tt>.</p></li>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3249</ul>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3250
3251</div>
3252
3253<!-- ======================================================================= -->
3254<div class="doc_subsection">
3255 <a name="GlobalVariable">The <tt>GlobalVariable</tt> class</a>
3256</div>
3257
3258<div class="doc_text">
3259
3260<p><tt>#include "<a
3261href="/doxygen/GlobalVariable_8h-source.html">llvm/GlobalVariable.h</a>"</tt>
3262<br>
Tanya Lattnera3da7772004-06-22 08:02:25 +0000[diff] [blame]3263doxygen info: <a href="/doxygen/classllvm_1_1GlobalVariable.html">GlobalVariable
Reid Spencerbe5e85e2006-04-14 14:11:48 +0000[diff] [blame]3264 Class</a><br>
3265Superclasses: <a href="#GlobalValue"><tt>GlobalValue</tt></a>,
3266<a href="#Constant"><tt>Constant</tt></a>,
3267<a href="#User"><tt>User</tt></a>,
3268<a href="#Value"><tt>Value</tt></a></p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3269
3270<p>Global variables are represented with the (suprise suprise)
3271<tt>GlobalVariable</tt> class. Like functions, <tt>GlobalVariable</tt>s are also
3272subclasses of <a href="#GlobalValue"><tt>GlobalValue</tt></a>, and as such are
3273always referenced by their address (global values must live in memory, so their
Reid Spencerbe5e85e2006-04-14 14:11:48 +0000[diff] [blame]3274"name" refers to their constant address). See
3275<a href="#GlobalValue"><tt>GlobalValue</tt></a> for more on this. Global
3276variables may have an initial value (which must be a
3277<a href="#Constant"><tt>Constant</tt></a>), and if they have an initializer,
3278they may be marked as "constant" themselves (indicating that their contents
3279never change at runtime).</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3280</div>
3281
3282<!-- _______________________________________________________________________ -->
3283<div class="doc_subsubsection">
3284 <a name="m_GlobalVariable">Important Public Members of the
3285 <tt>GlobalVariable</tt> class</a>
3286</div>
3287
3288<div class="doc_text">
3289
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3290<ul>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3291 <li><tt>GlobalVariable(const </tt><tt><a href="#Type">Type</a> *Ty, bool
3292 isConstant, LinkageTypes&amp; Linkage, <a href="#Constant">Constant</a>
3293 *Initializer = 0, const std::string &amp;Name = "", Module* Parent = 0)</tt>
3294
3295 <p>Create a new global variable of the specified type. If
3296 <tt>isConstant</tt> is true then the global variable will be marked as
3297 unchanging for the program. The Linkage parameter specifies the type of
3298 linkage (internal, external, weak, linkonce, appending) for the variable. If
3299 the linkage is InternalLinkage, WeakLinkage, or LinkOnceLinkage,&nbsp; then
3300 the resultant global variable will have internal linkage. AppendingLinkage
3301 concatenates together all instances (in different translation units) of the
3302 variable into a single variable but is only applicable to arrays. &nbsp;See
3303 the <a href="LangRef.html#modulestructure">LLVM Language Reference</a> for
3304 further details on linkage types. Optionally an initializer, a name, and the
3305 module to put the variable into may be specified for the global variable as
3306 well.</p></li>
3307
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3308 <li><tt>bool isConstant() const</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3309
3310 <p>Returns true if this is a global variable that is known not to
3311 be modified at runtime.</p></li>
3312
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3313 <li><tt>bool hasInitializer()</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3314
3315 <p>Returns true if this <tt>GlobalVariable</tt> has an intializer.</p></li>
3316
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3317 <li><tt><a href="#Constant">Constant</a> *getInitializer()</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3318
3319 <p>Returns the intial value for a <tt>GlobalVariable</tt>. It is not legal
3320 to call this method if there is no initializer.</p></li>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3321</ul>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3322
3323</div>
3324
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]3325
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3326<!-- ======================================================================= -->
3327<div class="doc_subsection">
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]3328 <a name="BasicBlock">The <tt>BasicBlock</tt> class</a>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3329</div>
3330
3331<div class="doc_text">
3332
3333<p><tt>#include "<a
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]3334href="/doxygen/BasicBlock_8h-source.html">llvm/BasicBlock.h</a>"</tt><br>
3335doxygen info: <a href="/doxygen/structllvm_1_1BasicBlock.html">BasicBlock
3336Class</a><br>
3337Superclass: <a href="#Value"><tt>Value</tt></a></p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3338
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]3339<p>This class represents a single entry multiple exit section of the code,
3340commonly known as a basic block by the compiler community. The
3341<tt>BasicBlock</tt> class maintains a list of <a
3342href="#Instruction"><tt>Instruction</tt></a>s, which form the body of the block.
3343Matching the language definition, the last element of this list of instructions
3344is always a terminator instruction (a subclass of the <a
3345href="#TerminatorInst"><tt>TerminatorInst</tt></a> class).</p>
3346
3347<p>In addition to tracking the list of instructions that make up the block, the
3348<tt>BasicBlock</tt> class also keeps track of the <a
3349href="#Function"><tt>Function</tt></a> that it is embedded into.</p>
3350
3351<p>Note that <tt>BasicBlock</tt>s themselves are <a
3352href="#Value"><tt>Value</tt></a>s, because they are referenced by instructions
3353like branches and can go in the switch tables. <tt>BasicBlock</tt>s have type
3354<tt>label</tt>.</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3355
3356</div>
3357
3358<!-- _______________________________________________________________________ -->
3359<div class="doc_subsubsection">
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]3360 <a name="m_BasicBlock">Important Public Members of the <tt>BasicBlock</tt>
3361 class</a>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3362</div>
3363
3364<div class="doc_text">
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3365<ul>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3366
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]3367<li><tt>BasicBlock(const std::string &amp;Name = "", </tt><tt><a
3368 href="#Function">Function</a> *Parent = 0)</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3369
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]3370<p>The <tt>BasicBlock</tt> constructor is used to create new basic blocks for
3371insertion into a function. The constructor optionally takes a name for the new
3372block, and a <a href="#Function"><tt>Function</tt></a> to insert it into. If
3373the <tt>Parent</tt> parameter is specified, the new <tt>BasicBlock</tt> is
3374automatically inserted at the end of the specified <a
3375href="#Function"><tt>Function</tt></a>, if not specified, the BasicBlock must be
3376manually inserted into the <a href="#Function"><tt>Function</tt></a>.</p></li>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3377
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]3378<li><tt>BasicBlock::iterator</tt> - Typedef for instruction list iterator<br>
3379<tt>BasicBlock::const_iterator</tt> - Typedef for const_iterator.<br>
3380<tt>begin()</tt>, <tt>end()</tt>, <tt>front()</tt>, <tt>back()</tt>,
3381<tt>size()</tt>, <tt>empty()</tt>
3382STL-style functions for accessing the instruction list.
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3383
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]3384<p>These methods and typedefs are forwarding functions that have the same
3385semantics as the standard library methods of the same names. These methods
3386expose the underlying instruction list of a basic block in a way that is easy to
3387manipulate. To get the full complement of container operations (including
3388operations to update the list), you must use the <tt>getInstList()</tt>
3389method.</p></li>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3390
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]3391<li><tt>BasicBlock::InstListType &amp;getInstList()</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3392
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]3393<p>This method is used to get access to the underlying container that actually
3394holds the Instructions. This method must be used when there isn't a forwarding
3395function in the <tt>BasicBlock</tt> class for the operation that you would like
3396to perform. Because there are no forwarding functions for "updating"
3397operations, you need to use this if you want to update the contents of a
3398<tt>BasicBlock</tt>.</p></li>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3399
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]3400<li><tt><a href="#Function">Function</a> *getParent()</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3401
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]3402<p> Returns a pointer to <a href="#Function"><tt>Function</tt></a> the block is
3403embedded into, or a null pointer if it is homeless.</p></li>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3404
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]3405<li><tt><a href="#TerminatorInst">TerminatorInst</a> *getTerminator()</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3406
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]3407<p> Returns a pointer to the terminator instruction that appears at the end of
3408the <tt>BasicBlock</tt>. If there is no terminator instruction, or if the last
3409instruction in the block is not a terminator, then a null pointer is
3410returned.</p></li>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3411
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3412</ul>
3413
3414</div>
3415
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3416
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3417<!-- ======================================================================= -->
3418<div class="doc_subsection">
3419 <a name="Argument">The <tt>Argument</tt> class</a>
3420</div>
3421
3422<div class="doc_text">
3423
3424<p>This subclass of Value defines the interface for incoming formal
Chris Lattner58360822005-01-17 00:12:04 +0000[diff] [blame]3425arguments to a function. A Function maintains a list of its formal
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3426arguments. An argument has a pointer to the parent Function.</p>
3427
3428</div>
3429
Chris Lattner9355b472002-09-06 02:50:58 +0000[diff] [blame]3430<!-- *********************************************************************** -->
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3431<hr>
3432<address>
3433 <a href="http://jigsaw.w3.org/css-validator/check/referer"><img
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Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3437
3438 <a href="mailto:dhurjati@cs.uiuc.edu">Dinakar Dhurjati</a> and
3439 <a href="mailto:sabre@nondot.org">Chris Lattner</a><br>
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]3440 <a href="http://llvm.org">The LLVM Compiler Infrastructure</a><br>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3441 Last modified: $Date$
3442</address>
3443
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3445</html>