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4<head>
5 <title>LLVM Programmer's Manual</title>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]6 <link rel="stylesheet" href="llvm.css" type="text/css">
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]7</head>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]8<body>
9
10<div class="doc_title">
11 LLVM Programmer's Manual
12</div>
13
Chris Lattner9355b472002-09-06 02:50:58 +0000[diff] [blame]14<ol>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]15 <li><a href="#introduction">Introduction</a></li>
Chris Lattner9355b472002-09-06 02:50:58 +0000[diff] [blame]16 <li><a href="#general">General Information</a>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]17 <ul>
Reid Spencerfe8f4ff2004-11-01 09:02:53 +0000[diff] [blame]18 <li><a href="#stl">The C++ Standard Template Library</a></li>
19<!--
20 <li>The <tt>-time-passes</tt> option</li>
21 <li>How to use the LLVM Makefile system</li>
22 <li>How to write a regression test</li>
Chris Lattner61db4652004-12-08 19:05:44 +0000[diff] [blame]23
Reid Spencerfe8f4ff2004-11-01 09:02:53 +0000[diff] [blame]24-->
Chris Lattner84b7f8d2003-08-01 22:20:59 +0000[diff] [blame]25 </ul>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]26 </li>
27 <li><a href="#apis">Important and useful LLVM APIs</a>
28 <ul>
29 <li><a href="#isa">The <tt>isa&lt;&gt;</tt>, <tt>cast&lt;&gt;</tt>
30and <tt>dyn_cast&lt;&gt;</tt> templates</a> </li>
Misha Brukman2c122ce2005-11-01 21:12:49 +0000[diff] [blame]31 <li><a href="#DEBUG">The <tt>DEBUG()</tt> macro and <tt>-debug</tt>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]32option</a>
33 <ul>
34 <li><a href="#DEBUG_TYPE">Fine grained debug info with <tt>DEBUG_TYPE</tt>
35and the <tt>-debug-only</tt> option</a> </li>
36 </ul>
37 </li>
Chris Lattner0be6fdf2006-12-19 21:46:21 +0000[diff] [blame]38 <li><a href="#Statistic">The <tt>Statistic</tt> class &amp; <tt>-stats</tt>
Reid Spencerfe8f4ff2004-11-01 09:02:53 +0000[diff] [blame]39option</a></li>
40<!--
41 <li>The <tt>InstVisitor</tt> template
42 <li>The general graph API
43-->
Chris Lattnerf623a082005-10-17 01:36:23 +0000[diff] [blame]44 <li><a href="#ViewGraph">Viewing graphs while debugging code</a></li>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]45 </ul>
46 </li>
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]47 <li><a href="#datastructure">Picking the Right Data Structure for a Task</a>
48 <ul>
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]49 <li><a href="#ds_sequential">Sequential Containers (std::vector, std::list, etc)</a>
50 <ul>
51 <li><a href="#dss_fixedarrays">Fixed Size Arrays</a></li>
52 <li><a href="#dss_heaparrays">Heap Allocated Arrays</a></li>
53 <li><a href="#dss_smallvector">"llvm/ADT/SmallVector.h"</a></li>
54 <li><a href="#dss_vector">&lt;vector&gt;</a></li>
55 <li><a href="#dss_deque">&lt;deque&gt;</a></li>
56 <li><a href="#dss_list">&lt;list&gt;</a></li>
Gabor Greif3899e492009-02-27 11:37:41 +0000[diff] [blame]57 <li><a href="#dss_ilist">llvm/ADT/ilist.h</a></li>
Chris Lattnerc5722432007-02-03 19:49:31 +0000[diff] [blame]58 <li><a href="#dss_other">Other Sequential Container Options</a></li>
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]59 </ul></li>
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]60 <li><a href="#ds_set">Set-Like Containers (std::set, SmallSet, SetVector, etc)</a>
61 <ul>
62 <li><a href="#dss_sortedvectorset">A sorted 'vector'</a></li>
63 <li><a href="#dss_smallset">"llvm/ADT/SmallSet.h"</a></li>
64 <li><a href="#dss_smallptrset">"llvm/ADT/SmallPtrSet.h"</a></li>
Chris Lattnerc28476f2007-09-30 00:58:59 +0000[diff] [blame]65 <li><a href="#dss_denseset">"llvm/ADT/DenseSet.h"</a></li>
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]66 <li><a href="#dss_FoldingSet">"llvm/ADT/FoldingSet.h"</a></li>
67 <li><a href="#dss_set">&lt;set&gt;</a></li>
68 <li><a href="#dss_setvector">"llvm/ADT/SetVector.h"</a></li>
Chris Lattnerc5722432007-02-03 19:49:31 +0000[diff] [blame]69 <li><a href="#dss_uniquevector">"llvm/ADT/UniqueVector.h"</a></li>
70 <li><a href="#dss_otherset">Other Set-Like ContainerOptions</a></li>
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]71 </ul></li>
Chris Lattnerf3692522007-02-03 19:51:56 +0000[diff] [blame]72 <li><a href="#ds_map">Map-Like Containers (std::map, DenseMap, etc)</a>
73 <ul>
74 <li><a href="#dss_sortedvectormap">A sorted 'vector'</a></li>
Chris Lattner796f9fa2007-02-08 19:14:21 +0000[diff] [blame]75 <li><a href="#dss_stringmap">"llvm/ADT/StringMap.h"</a></li>
Chris Lattnerf3692522007-02-03 19:51:56 +0000[diff] [blame]76 <li><a href="#dss_indexedmap">"llvm/ADT/IndexedMap.h"</a></li>
77 <li><a href="#dss_densemap">"llvm/ADT/DenseMap.h"</a></li>
78 <li><a href="#dss_map">&lt;map&gt;</a></li>
79 <li><a href="#dss_othermap">Other Map-Like Container Options</a></li>
80 </ul></li>
Daniel Berlin1939ace2007-09-24 17:52:25 +0000[diff] [blame]81 <li><a href="#ds_bit">BitVector-like containers</a>
82 <ul>
83 <li><a href="#dss_bitvector">A dense bitvector</a></li>
84 <li><a href="#dss_sparsebitvector">A sparse bitvector</a></li>
85 </ul></li>
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]86 </ul>
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]87 </li>
Chris Lattnerae7f7592002-09-06 18:31:18 +0000[diff] [blame]88 <li><a href="#common">Helpful Hints for Common Operations</a>
Chris Lattnerae7f7592002-09-06 18:31:18 +0000[diff] [blame]89 <ul>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]90 <li><a href="#inspection">Basic Inspection and Traversal Routines</a>
91 <ul>
92 <li><a href="#iterate_function">Iterating over the <tt>BasicBlock</tt>s
93in a <tt>Function</tt></a> </li>
94 <li><a href="#iterate_basicblock">Iterating over the <tt>Instruction</tt>s
95in a <tt>BasicBlock</tt></a> </li>
96 <li><a href="#iterate_institer">Iterating over the <tt>Instruction</tt>s
97in a <tt>Function</tt></a> </li>
98 <li><a href="#iterate_convert">Turning an iterator into a
99class pointer</a> </li>
100 <li><a href="#iterate_complex">Finding call sites: a more
101complex example</a> </li>
102 <li><a href="#calls_and_invokes">Treating calls and invokes
103the same way</a> </li>
104 <li><a href="#iterate_chains">Iterating over def-use &amp;
105use-def chains</a> </li>
Chris Lattner2e438ca2008-01-03 16:56:04 +0000[diff] [blame]106 <li><a href="#iterate_preds">Iterating over predecessors &amp;
107successors of blocks</a></li>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]108 </ul>
109 </li>
110 <li><a href="#simplechanges">Making simple changes</a>
111 <ul>
112 <li><a href="#schanges_creating">Creating and inserting new
113 <tt>Instruction</tt>s</a> </li>
114 <li><a href="#schanges_deleting">Deleting <tt>Instruction</tt>s</a> </li>
115 <li><a href="#schanges_replacing">Replacing an <tt>Instruction</tt>
116with another <tt>Value</tt></a> </li>
Tanya Lattnerb011c662007-06-20 18:33:15 +0000[diff] [blame]117 <li><a href="#schanges_deletingGV">Deleting <tt>GlobalVariable</tt>s</a> </li>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]118 </ul>
Reid Spencerfe8f4ff2004-11-01 09:02:53 +0000[diff] [blame]119 </li>
Chris Lattnerae7f7592002-09-06 18:31:18 +0000[diff] [blame]120<!--
121 <li>Working with the Control Flow Graph
122 <ul>
123 <li>Accessing predecessors and successors of a <tt>BasicBlock</tt>
124 <li>
125 <li>
126 </ul>
Reid Spencerfe8f4ff2004-11-01 09:02:53 +0000[diff] [blame]127-->
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]128 </ul>
129 </li>
Chris Lattnerd9d6e102005-04-23 16:10:52 +0000[diff] [blame]130
131 <li><a href="#advanced">Advanced Topics</a>
132 <ul>
Chris Lattnerf1b200b2005-04-23 17:27:36 +0000[diff] [blame]133 <li><a href="#TypeResolve">LLVM Type Resolution</a>
134 <ul>
135 <li><a href="#BuildRecType">Basic Recursive Type Construction</a></li>
136 <li><a href="#refineAbstractTypeTo">The <tt>refineAbstractTypeTo</tt> method</a></li>
137 <li><a href="#PATypeHolder">The PATypeHolder Class</a></li>
138 <li><a href="#AbstractTypeUser">The AbstractTypeUser Class</a></li>
139 </ul></li>
140
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]141 <li><a href="#SymbolTable">The <tt>ValueSymbolTable</tt> and <tt>TypeSymbolTable</tt> classes</a></li>
142 <li><a href="#UserLayout">The <tt>User</tt> and owned <tt>Use</tt> classes' memory layout</a></li>
Chris Lattnerd9d6e102005-04-23 16:10:52 +0000[diff] [blame]143 </ul></li>
144
Joel Stanley9b96c442002-09-06 21:55:13 +0000[diff] [blame]145 <li><a href="#coreclasses">The Core LLVM Class Hierarchy Reference</a>
Chris Lattner9355b472002-09-06 02:50:58 +0000[diff] [blame]146 <ul>
Reid Spencer303c4b42007-01-12 17:26:25 +0000[diff] [blame]147 <li><a href="#Type">The <tt>Type</tt> class</a> </li>
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]148 <li><a href="#Module">The <tt>Module</tt> class</a></li>
Reid Spencerfe8f4ff2004-11-01 09:02:53 +0000[diff] [blame]149 <li><a href="#Value">The <tt>Value</tt> class</a>
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]150 <ul>
151 <li><a href="#User">The <tt>User</tt> class</a>
Chris Lattner9355b472002-09-06 02:50:58 +0000[diff] [blame]152 <ul>
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]153 <li><a href="#Instruction">The <tt>Instruction</tt> class</a></li>
154 <li><a href="#Constant">The <tt>Constant</tt> class</a>
155 <ul>
156 <li><a href="#GlobalValue">The <tt>GlobalValue</tt> class</a>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]157 <ul>
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]158 <li><a href="#Function">The <tt>Function</tt> class</a></li>
159 <li><a href="#GlobalVariable">The <tt>GlobalVariable</tt> class</a></li>
160 </ul>
161 </li>
162 </ul>
163 </li>
Reid Spencerfe8f4ff2004-11-01 09:02:53 +0000[diff] [blame]164 </ul>
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]165 </li>
166 <li><a href="#BasicBlock">The <tt>BasicBlock</tt> class</a></li>
167 <li><a href="#Argument">The <tt>Argument</tt> class</a></li>
168 </ul>
Reid Spencerfe8f4ff2004-11-01 09:02:53 +0000[diff] [blame]169 </li>
170 </ul>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]171 </li>
Chris Lattner9355b472002-09-06 02:50:58 +0000[diff] [blame]172</ol>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]173
Chris Lattner69bf8a92004-05-23 21:06:58 +0000[diff] [blame]174<div class="doc_author">
175 <p>Written by <a href="mailto:sabre@nondot.org">Chris Lattner</a>,
Chris Lattner94c43592004-05-26 16:52:55 +0000[diff] [blame]176 <a href="mailto:dhurjati@cs.uiuc.edu">Dinakar Dhurjati</a>,
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]177 <a href="mailto:ggreif@gmail.com">Gabor Greif</a>,
178 <a href="mailto:jstanley@cs.uiuc.edu">Joel Stanley</a> and
Chris Lattner94c43592004-05-26 16:52:55 +0000[diff] [blame]179 <a href="mailto:rspencer@x10sys.com">Reid Spencer</a></p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]180</div>
181
Chris Lattner9355b472002-09-06 02:50:58 +0000[diff] [blame]182<!-- *********************************************************************** -->
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]183<div class="doc_section">
184 <a name="introduction">Introduction </a>
185</div>
Chris Lattner9355b472002-09-06 02:50:58 +0000[diff] [blame]186<!-- *********************************************************************** -->
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]187
188<div class="doc_text">
189
190<p>This document is meant to highlight some of the important classes and
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]191interfaces available in the LLVM source-base. This manual is not
192intended to explain what LLVM is, how it works, and what LLVM code looks
193like. It assumes that you know the basics of LLVM and are interested
194in writing transformations or otherwise analyzing or manipulating the
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]195code.</p>
196
197<p>This document should get you oriented so that you can find your
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]198way in the continuously growing source code that makes up the LLVM
199infrastructure. Note that this manual is not intended to serve as a
200replacement for reading the source code, so if you think there should be
201a method in one of these classes to do something, but it's not listed,
202check the source. Links to the <a href="/doxygen/">doxygen</a> sources
203are provided to make this as easy as possible.</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]204
205<p>The first section of this document describes general information that is
206useful to know when working in the LLVM infrastructure, and the second describes
207the Core LLVM classes. In the future this manual will be extended with
208information describing how to use extension libraries, such as dominator
209information, CFG traversal routines, and useful utilities like the <tt><a
210href="/doxygen/InstVisitor_8h-source.html">InstVisitor</a></tt> template.</p>
211
212</div>
213
Chris Lattner9355b472002-09-06 02:50:58 +0000[diff] [blame]214<!-- *********************************************************************** -->
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]215<div class="doc_section">
216 <a name="general">General Information</a>
217</div>
218<!-- *********************************************************************** -->
219
220<div class="doc_text">
221
222<p>This section contains general information that is useful if you are working
223in the LLVM source-base, but that isn't specific to any particular API.</p>
224
225</div>
226
227<!-- ======================================================================= -->
228<div class="doc_subsection">
229 <a name="stl">The C++ Standard Template Library</a>
230</div>
231
232<div class="doc_text">
233
234<p>LLVM makes heavy use of the C++ Standard Template Library (STL),
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]235perhaps much more than you are used to, or have seen before. Because of
236this, you might want to do a little background reading in the
237techniques used and capabilities of the library. There are many good
238pages that discuss the STL, and several books on the subject that you
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]239can get, so it will not be discussed in this document.</p>
240
241<p>Here are some useful links:</p>
242
243<ol>
244
245<li><a href="http://www.dinkumware.com/refxcpp.html">Dinkumware C++ Library
246reference</a> - an excellent reference for the STL and other parts of the
247standard C++ library.</li>
248
249<li><a href="http://www.tempest-sw.com/cpp/">C++ In a Nutshell</a> - This is an
Tanya Lattner09cf73c2004-06-22 04:24:55 +0000[diff] [blame]250O'Reilly book in the making. It has a decent
251Standard Library
252Reference that rivals Dinkumware's, and is unfortunately no longer free since the book has been
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]253published.</li>
254
255<li><a href="http://www.parashift.com/c++-faq-lite/">C++ Frequently Asked
256Questions</a></li>
257
258<li><a href="http://www.sgi.com/tech/stl/">SGI's STL Programmer's Guide</a> -
259Contains a useful <a
260href="http://www.sgi.com/tech/stl/stl_introduction.html">Introduction to the
261STL</a>.</li>
262
263<li><a href="http://www.research.att.com/%7Ebs/C++.html">Bjarne Stroustrup's C++
264Page</a></li>
265
Tanya Lattner79445ba2004-12-08 18:34:56 +0000[diff] [blame]266<li><a href="http://64.78.49.204/">
Reid Spencer096603a2004-05-26 08:41:35 +0000[diff] [blame]267Bruce Eckel's Thinking in C++, 2nd ed. Volume 2 Revision 4.0 (even better, get
268the book).</a></li>
269
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]270</ol>
271
272<p>You are also encouraged to take a look at the <a
273href="CodingStandards.html">LLVM Coding Standards</a> guide which focuses on how
274to write maintainable code more than where to put your curly braces.</p>
275
276</div>
277
278<!-- ======================================================================= -->
279<div class="doc_subsection">
280 <a name="stl">Other useful references</a>
281</div>
282
283<div class="doc_text">
284
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]285<ol>
286<li><a href="http://www.psc.edu/%7Esemke/cvs_branches.html">CVS
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]287Branch and Tag Primer</a></li>
Misha Brukmana0f71e42004-06-18 18:39:00 +0000[diff] [blame]288<li><a href="http://www.fortran-2000.com/ArnaudRecipes/sharedlib.html">Using
289static and shared libraries across platforms</a></li>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]290</ol>
291
292</div>
293
Chris Lattner9355b472002-09-06 02:50:58 +0000[diff] [blame]294<!-- *********************************************************************** -->
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]295<div class="doc_section">
296 <a name="apis">Important and useful LLVM APIs</a>
297</div>
298<!-- *********************************************************************** -->
299
300<div class="doc_text">
301
302<p>Here we highlight some LLVM APIs that are generally useful and good to
303know about when writing transformations.</p>
304
305</div>
306
307<!-- ======================================================================= -->
308<div class="doc_subsection">
Misha Brukman2c122ce2005-11-01 21:12:49 +0000[diff] [blame]309 <a name="isa">The <tt>isa&lt;&gt;</tt>, <tt>cast&lt;&gt;</tt> and
310 <tt>dyn_cast&lt;&gt;</tt> templates</a>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]311</div>
312
313<div class="doc_text">
314
315<p>The LLVM source-base makes extensive use of a custom form of RTTI.
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]316These templates have many similarities to the C++ <tt>dynamic_cast&lt;&gt;</tt>
317operator, but they don't have some drawbacks (primarily stemming from
318the fact that <tt>dynamic_cast&lt;&gt;</tt> only works on classes that
319have a v-table). Because they are used so often, you must know what they
320do and how they work. All of these templates are defined in the <a
Chris Lattner695b78b2005-04-26 22:56:16 +0000[diff] [blame]321 href="/doxygen/Casting_8h-source.html"><tt>llvm/Support/Casting.h</tt></a>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]322file (note that you very rarely have to include this file directly).</p>
323
324<dl>
325 <dt><tt>isa&lt;&gt;</tt>: </dt>
326
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]327 <dd><p>The <tt>isa&lt;&gt;</tt> operator works exactly like the Java
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]328 "<tt>instanceof</tt>" operator. It returns true or false depending on whether
329 a reference or pointer points to an instance of the specified class. This can
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]330 be very useful for constraint checking of various sorts (example below).</p>
331 </dd>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]332
333 <dt><tt>cast&lt;&gt;</tt>: </dt>
334
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]335 <dd><p>The <tt>cast&lt;&gt;</tt> operator is a "checked cast" operation. It
Chris Lattner28e6ff52008-06-20 05:03:17 +0000[diff] [blame]336 converts a pointer or reference from a base class to a derived class, causing
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]337 an assertion failure if it is not really an instance of the right type. This
338 should be used in cases where you have some information that makes you believe
339 that something is of the right type. An example of the <tt>isa&lt;&gt;</tt>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]340 and <tt>cast&lt;&gt;</tt> template is:</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]341
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]342<div class="doc_code">
343<pre>
344static bool isLoopInvariant(const <a href="#Value">Value</a> *V, const Loop *L) {
345 if (isa&lt;<a href="#Constant">Constant</a>&gt;(V) || isa&lt;<a href="#Argument">Argument</a>&gt;(V) || isa&lt;<a href="#GlobalValue">GlobalValue</a>&gt;(V))
346 return true;
Chris Lattner69bf8a92004-05-23 21:06:58 +0000[diff] [blame]347
Bill Wendling82e2eea2006-10-11 18:00:22 +0000[diff] [blame]348 // <i>Otherwise, it must be an instruction...</i>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]349 return !L-&gt;contains(cast&lt;<a href="#Instruction">Instruction</a>&gt;(V)-&gt;getParent());
350}
351</pre>
352</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]353
354 <p>Note that you should <b>not</b> use an <tt>isa&lt;&gt;</tt> test followed
355 by a <tt>cast&lt;&gt;</tt>, for that use the <tt>dyn_cast&lt;&gt;</tt>
356 operator.</p>
357
358 </dd>
359
360 <dt><tt>dyn_cast&lt;&gt;</tt>:</dt>
361
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]362 <dd><p>The <tt>dyn_cast&lt;&gt;</tt> operator is a "checking cast" operation.
363 It checks to see if the operand is of the specified type, and if so, returns a
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]364 pointer to it (this operator does not work with references). If the operand is
365 not of the correct type, a null pointer is returned. Thus, this works very
Misha Brukman2c122ce2005-11-01 21:12:49 +0000[diff] [blame]366 much like the <tt>dynamic_cast&lt;&gt;</tt> operator in C++, and should be
367 used in the same circumstances. Typically, the <tt>dyn_cast&lt;&gt;</tt>
368 operator is used in an <tt>if</tt> statement or some other flow control
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]369 statement like this:</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]370
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]371<div class="doc_code">
372<pre>
373if (<a href="#AllocationInst">AllocationInst</a> *AI = dyn_cast&lt;<a href="#AllocationInst">AllocationInst</a>&gt;(Val)) {
Bill Wendling82e2eea2006-10-11 18:00:22 +0000[diff] [blame]374 // <i>...</i>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]375}
376</pre>
377</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]378
Misha Brukman2c122ce2005-11-01 21:12:49 +0000[diff] [blame]379 <p>This form of the <tt>if</tt> statement effectively combines together a call
380 to <tt>isa&lt;&gt;</tt> and a call to <tt>cast&lt;&gt;</tt> into one
381 statement, which is very convenient.</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]382
Misha Brukman2c122ce2005-11-01 21:12:49 +0000[diff] [blame]383 <p>Note that the <tt>dyn_cast&lt;&gt;</tt> operator, like C++'s
384 <tt>dynamic_cast&lt;&gt;</tt> or Java's <tt>instanceof</tt> operator, can be
385 abused. In particular, you should not use big chained <tt>if/then/else</tt>
386 blocks to check for lots of different variants of classes. If you find
387 yourself wanting to do this, it is much cleaner and more efficient to use the
388 <tt>InstVisitor</tt> class to dispatch over the instruction type directly.</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]389
Misha Brukman2c122ce2005-11-01 21:12:49 +0000[diff] [blame]390 </dd>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]391
Misha Brukman2c122ce2005-11-01 21:12:49 +0000[diff] [blame]392 <dt><tt>cast_or_null&lt;&gt;</tt>: </dt>
393
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]394 <dd><p>The <tt>cast_or_null&lt;&gt;</tt> operator works just like the
Misha Brukman2c122ce2005-11-01 21:12:49 +0000[diff] [blame]395 <tt>cast&lt;&gt;</tt> operator, except that it allows for a null pointer as an
396 argument (which it then propagates). This can sometimes be useful, allowing
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]397 you to combine several null checks into one.</p></dd>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]398
Misha Brukman2c122ce2005-11-01 21:12:49 +0000[diff] [blame]399 <dt><tt>dyn_cast_or_null&lt;&gt;</tt>: </dt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]400
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]401 <dd><p>The <tt>dyn_cast_or_null&lt;&gt;</tt> operator works just like the
Misha Brukman2c122ce2005-11-01 21:12:49 +0000[diff] [blame]402 <tt>dyn_cast&lt;&gt;</tt> operator, except that it allows for a null pointer
403 as an argument (which it then propagates). This can sometimes be useful,
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]404 allowing you to combine several null checks into one.</p></dd>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]405
Misha Brukman2c122ce2005-11-01 21:12:49 +0000[diff] [blame]406</dl>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]407
408<p>These five templates can be used with any classes, whether they have a
409v-table or not. To add support for these templates, you simply need to add
410<tt>classof</tt> static methods to the class you are interested casting
411to. Describing this is currently outside the scope of this document, but there
412are lots of examples in the LLVM source base.</p>
413
414</div>
415
416<!-- ======================================================================= -->
417<div class="doc_subsection">
Misha Brukman2c122ce2005-11-01 21:12:49 +0000[diff] [blame]418 <a name="DEBUG">The <tt>DEBUG()</tt> macro and <tt>-debug</tt> option</a>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]419</div>
420
421<div class="doc_text">
422
423<p>Often when working on your pass you will put a bunch of debugging printouts
424and other code into your pass. After you get it working, you want to remove
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]425it, but you may need it again in the future (to work out new bugs that you run
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]426across).</p>
427
428<p> Naturally, because of this, you don't want to delete the debug printouts,
429but you don't want them to always be noisy. A standard compromise is to comment
430them out, allowing you to enable them if you need them in the future.</p>
431
Chris Lattner695b78b2005-04-26 22:56:16 +0000[diff] [blame]432<p>The "<tt><a href="/doxygen/Debug_8h-source.html">llvm/Support/Debug.h</a></tt>"
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]433file provides a macro named <tt>DEBUG()</tt> that is a much nicer solution to
434this problem. Basically, you can put arbitrary code into the argument of the
435<tt>DEBUG</tt> macro, and it is only executed if '<tt>opt</tt>' (or any other
436tool) is run with the '<tt>-debug</tt>' command line argument:</p>
437
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]438<div class="doc_code">
439<pre>
Bill Wendling832171c2006-12-07 20:04:42 +0000[diff] [blame]440DOUT &lt;&lt; "I am here!\n";
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]441</pre>
442</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]443
444<p>Then you can run your pass like this:</p>
445
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]446<div class="doc_code">
447<pre>
448$ opt &lt; a.bc &gt; /dev/null -mypass
Bill Wendling82e2eea2006-10-11 18:00:22 +0000[diff] [blame]449<i>&lt;no output&gt;</i>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]450$ opt &lt; a.bc &gt; /dev/null -mypass -debug
451I am here!
452</pre>
453</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]454
455<p>Using the <tt>DEBUG()</tt> macro instead of a home-brewed solution allows you
456to not have to create "yet another" command line option for the debug output for
457your pass. Note that <tt>DEBUG()</tt> macros are disabled for optimized builds,
458so they do not cause a performance impact at all (for the same reason, they
459should also not contain side-effects!).</p>
460
461<p>One additional nice thing about the <tt>DEBUG()</tt> macro is that you can
462enable or disable it directly in gdb. Just use "<tt>set DebugFlag=0</tt>" or
463"<tt>set DebugFlag=1</tt>" from the gdb if the program is running. If the
464program hasn't been started yet, you can always just run it with
465<tt>-debug</tt>.</p>
466
467</div>
468
469<!-- _______________________________________________________________________ -->
470<div class="doc_subsubsection">
Chris Lattnerc9151082005-04-26 22:57:07 +0000[diff] [blame]471 <a name="DEBUG_TYPE">Fine grained debug info with <tt>DEBUG_TYPE</tt> and
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]472 the <tt>-debug-only</tt> option</a>
473</div>
474
475<div class="doc_text">
476
477<p>Sometimes you may find yourself in a situation where enabling <tt>-debug</tt>
478just turns on <b>too much</b> information (such as when working on the code
479generator). If you want to enable debug information with more fine-grained
480control, you define the <tt>DEBUG_TYPE</tt> macro and the <tt>-debug</tt> only
481option as follows:</p>
482
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]483<div class="doc_code">
484<pre>
Bill Wendling832171c2006-12-07 20:04:42 +0000[diff] [blame]485DOUT &lt;&lt; "No debug type\n";
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]486#undef DEBUG_TYPE
487#define DEBUG_TYPE "foo"
Bill Wendling832171c2006-12-07 20:04:42 +0000[diff] [blame]488DOUT &lt;&lt; "'foo' debug type\n";
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]489#undef DEBUG_TYPE
490#define DEBUG_TYPE "bar"
Bill Wendling832171c2006-12-07 20:04:42 +0000[diff] [blame]491DOUT &lt;&lt; "'bar' debug type\n";
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]492#undef DEBUG_TYPE
493#define DEBUG_TYPE ""
Bill Wendling832171c2006-12-07 20:04:42 +0000[diff] [blame]494DOUT &lt;&lt; "No debug type (2)\n";
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]495</pre>
496</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]497
498<p>Then you can run your pass like this:</p>
499
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]500<div class="doc_code">
501<pre>
502$ opt &lt; a.bc &gt; /dev/null -mypass
Bill Wendling82e2eea2006-10-11 18:00:22 +0000[diff] [blame]503<i>&lt;no output&gt;</i>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]504$ opt &lt; a.bc &gt; /dev/null -mypass -debug
505No debug type
506'foo' debug type
507'bar' debug type
508No debug type (2)
509$ opt &lt; a.bc &gt; /dev/null -mypass -debug-only=foo
510'foo' debug type
511$ opt &lt; a.bc &gt; /dev/null -mypass -debug-only=bar
512'bar' debug type
513</pre>
514</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]515
516<p>Of course, in practice, you should only set <tt>DEBUG_TYPE</tt> at the top of
517a file, to specify the debug type for the entire module (if you do this before
Chris Lattner695b78b2005-04-26 22:56:16 +0000[diff] [blame]518you <tt>#include "llvm/Support/Debug.h"</tt>, you don't have to insert the ugly
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]519<tt>#undef</tt>'s). Also, you should use names more meaningful than "foo" and
520"bar", because there is no system in place to ensure that names do not
521conflict. If two different modules use the same string, they will all be turned
522on when the name is specified. This allows, for example, all debug information
523for instruction scheduling to be enabled with <tt>-debug-type=InstrSched</tt>,
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]524even if the source lives in multiple files.</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]525
526</div>
527
528<!-- ======================================================================= -->
529<div class="doc_subsection">
Chris Lattner0be6fdf2006-12-19 21:46:21 +0000[diff] [blame]530 <a name="Statistic">The <tt>Statistic</tt> class &amp; <tt>-stats</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]531 option</a>
532</div>
533
534<div class="doc_text">
535
536<p>The "<tt><a
Chris Lattner695b78b2005-04-26 22:56:16 +0000[diff] [blame]537href="/doxygen/Statistic_8h-source.html">llvm/ADT/Statistic.h</a></tt>" file
Chris Lattner0be6fdf2006-12-19 21:46:21 +0000[diff] [blame]538provides a class named <tt>Statistic</tt> that is used as a unified way to
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]539keep track of what the LLVM compiler is doing and how effective various
540optimizations are. It is useful to see what optimizations are contributing to
541making a particular program run faster.</p>
542
543<p>Often you may run your pass on some big program, and you're interested to see
544how many times it makes a certain transformation. Although you can do this with
545hand inspection, or some ad-hoc method, this is a real pain and not very useful
Chris Lattner0be6fdf2006-12-19 21:46:21 +0000[diff] [blame]546for big programs. Using the <tt>Statistic</tt> class makes it very easy to
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]547keep track of this information, and the calculated information is presented in a
548uniform manner with the rest of the passes being executed.</p>
549
550<p>There are many examples of <tt>Statistic</tt> uses, but the basics of using
551it are as follows:</p>
552
553<ol>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]554 <li><p>Define your statistic like this:</p>
555
556<div class="doc_code">
557<pre>
Chris Lattner0be6fdf2006-12-19 21:46:21 +0000[diff] [blame]558#define <a href="#DEBUG_TYPE">DEBUG_TYPE</a> "mypassname" <i>// This goes before any #includes.</i>
559STATISTIC(NumXForms, "The # of times I did stuff");
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]560</pre>
561</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]562
Chris Lattner0be6fdf2006-12-19 21:46:21 +0000[diff] [blame]563 <p>The <tt>STATISTIC</tt> macro defines a static variable, whose name is
564 specified by the first argument. The pass name is taken from the DEBUG_TYPE
565 macro, and the description is taken from the second argument. The variable
Reid Spencer06565dc2007-01-12 17:11:23 +0000[diff] [blame]566 defined ("NumXForms" in this case) acts like an unsigned integer.</p></li>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]567
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]568 <li><p>Whenever you make a transformation, bump the counter:</p>
569
570<div class="doc_code">
571<pre>
Bill Wendling82e2eea2006-10-11 18:00:22 +0000[diff] [blame]572++NumXForms; // <i>I did stuff!</i>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]573</pre>
574</div>
575
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]576 </li>
577 </ol>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]578
579 <p>That's all you have to do. To get '<tt>opt</tt>' to print out the
580 statistics gathered, use the '<tt>-stats</tt>' option:</p>
581
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]582<div class="doc_code">
583<pre>
584$ opt -stats -mypassname &lt; program.bc &gt; /dev/null
Bill Wendling82e2eea2006-10-11 18:00:22 +0000[diff] [blame]585<i>... statistics output ...</i>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]586</pre>
587</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]588
Reid Spencer6b6c73e2007-02-09 16:00:28 +0000[diff] [blame]589 <p> When running <tt>opt</tt> on a C file from the SPEC benchmark
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]590suite, it gives a report that looks like this:</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]591
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]592<div class="doc_code">
593<pre>
Gabor Greif04367bf2007-07-06 22:07:22 +0000[diff] [blame]594 7646 bitcodewriter - Number of normal instructions
595 725 bitcodewriter - Number of oversized instructions
596 129996 bitcodewriter - Number of bitcode bytes written
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]597 2817 raise - Number of insts DCEd or constprop'd
598 3213 raise - Number of cast-of-self removed
599 5046 raise - Number of expression trees converted
600 75 raise - Number of other getelementptr's formed
601 138 raise - Number of load/store peepholes
602 42 deadtypeelim - Number of unused typenames removed from symtab
603 392 funcresolve - Number of varargs functions resolved
604 27 globaldce - Number of global variables removed
605 2 adce - Number of basic blocks removed
606 134 cee - Number of branches revectored
607 49 cee - Number of setcc instruction eliminated
608 532 gcse - Number of loads removed
609 2919 gcse - Number of instructions removed
610 86 indvars - Number of canonical indvars added
611 87 indvars - Number of aux indvars removed
612 25 instcombine - Number of dead inst eliminate
613 434 instcombine - Number of insts combined
614 248 licm - Number of load insts hoisted
615 1298 licm - Number of insts hoisted to a loop pre-header
616 3 licm - Number of insts hoisted to multiple loop preds (bad, no loop pre-header)
617 75 mem2reg - Number of alloca's promoted
618 1444 cfgsimplify - Number of blocks simplified
619</pre>
620</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]621
622<p>Obviously, with so many optimizations, having a unified framework for this
623stuff is very nice. Making your pass fit well into the framework makes it more
624maintainable and useful.</p>
625
626</div>
627
Chris Lattnerf623a082005-10-17 01:36:23 +0000[diff] [blame]628<!-- ======================================================================= -->
629<div class="doc_subsection">
630 <a name="ViewGraph">Viewing graphs while debugging code</a>
631</div>
632
633<div class="doc_text">
634
635<p>Several of the important data structures in LLVM are graphs: for example
636CFGs made out of LLVM <a href="#BasicBlock">BasicBlock</a>s, CFGs made out of
637LLVM <a href="CodeGenerator.html#machinebasicblock">MachineBasicBlock</a>s, and
638<a href="CodeGenerator.html#selectiondag_intro">Instruction Selection
639DAGs</a>. In many cases, while debugging various parts of the compiler, it is
640nice to instantly visualize these graphs.</p>
641
642<p>LLVM provides several callbacks that are available in a debug build to do
643exactly that. If you call the <tt>Function::viewCFG()</tt> method, for example,
644the current LLVM tool will pop up a window containing the CFG for the function
645where each basic block is a node in the graph, and each node contains the
646instructions in the block. Similarly, there also exists
647<tt>Function::viewCFGOnly()</tt> (does not include the instructions), the
648<tt>MachineFunction::viewCFG()</tt> and <tt>MachineFunction::viewCFGOnly()</tt>,
649and the <tt>SelectionDAG::viewGraph()</tt> methods. Within GDB, for example,
Jim Laskey543a0ee2006-10-02 12:28:07 +0000[diff] [blame]650you can usually use something like <tt>call DAG.viewGraph()</tt> to pop
Chris Lattnerf623a082005-10-17 01:36:23 +0000[diff] [blame]651up a window. Alternatively, you can sprinkle calls to these functions in your
652code in places you want to debug.</p>
653
654<p>Getting this to work requires a small amount of configuration. On Unix
655systems with X11, install the <a href="http://www.graphviz.org">graphviz</a>
656toolkit, and make sure 'dot' and 'gv' are in your path. If you are running on
657Mac OS/X, download and install the Mac OS/X <a
658href="http://www.pixelglow.com/graphviz/">Graphviz program</a>, and add
Reid Spencer128a7a72007-02-03 21:06:43 +0000[diff] [blame]659<tt>/Applications/Graphviz.app/Contents/MacOS/</tt> (or wherever you install
Chris Lattnerf623a082005-10-17 01:36:23 +0000[diff] [blame]660it) to your path. Once in your system and path are set up, rerun the LLVM
661configure script and rebuild LLVM to enable this functionality.</p>
662
Jim Laskey543a0ee2006-10-02 12:28:07 +0000[diff] [blame]663<p><tt>SelectionDAG</tt> has been extended to make it easier to locate
664<i>interesting</i> nodes in large complex graphs. From gdb, if you
665<tt>call DAG.setGraphColor(<i>node</i>, "<i>color</i>")</tt>, then the
Reid Spencer128a7a72007-02-03 21:06:43 +0000[diff] [blame]666next <tt>call DAG.viewGraph()</tt> would highlight the node in the
Jim Laskey543a0ee2006-10-02 12:28:07 +0000[diff] [blame]667specified color (choices of colors can be found at <a
Chris Lattner302da1e2007-02-03 03:05:57 +0000[diff] [blame]668href="http://www.graphviz.org/doc/info/colors.html">colors</a>.) More
Jim Laskey543a0ee2006-10-02 12:28:07 +0000[diff] [blame]669complex node attributes can be provided with <tt>call
670DAG.setGraphAttrs(<i>node</i>, "<i>attributes</i>")</tt> (choices can be
671found at <a href="http://www.graphviz.org/doc/info/attrs.html">Graph
672Attributes</a>.) If you want to restart and clear all the current graph
673attributes, then you can <tt>call DAG.clearGraphAttrs()</tt>. </p>
674
Chris Lattnerf623a082005-10-17 01:36:23 +0000[diff] [blame]675</div>
676
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]677<!-- *********************************************************************** -->
678<div class="doc_section">
679 <a name="datastructure">Picking the Right Data Structure for a Task</a>
680</div>
681<!-- *********************************************************************** -->
682
683<div class="doc_text">
684
Reid Spencer128a7a72007-02-03 21:06:43 +0000[diff] [blame]685<p>LLVM has a plethora of data structures in the <tt>llvm/ADT/</tt> directory,
686 and we commonly use STL data structures. This section describes the trade-offs
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]687 you should consider when you pick one.</p>
688
689<p>
690The first step is a choose your own adventure: do you want a sequential
691container, a set-like container, or a map-like container? The most important
692thing when choosing a container is the algorithmic properties of how you plan to
693access the container. Based on that, you should use:</p>
694
695<ul>
Reid Spencer128a7a72007-02-03 21:06:43 +0000[diff] [blame]696<li>a <a href="#ds_map">map-like</a> container if you need efficient look-up
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]697 of an value based on another value. Map-like containers also support
698 efficient queries for containment (whether a key is in the map). Map-like
699 containers generally do not support efficient reverse mapping (values to
700 keys). If you need that, use two maps. Some map-like containers also
701 support efficient iteration through the keys in sorted order. Map-like
702 containers are the most expensive sort, only use them if you need one of
703 these capabilities.</li>
704
705<li>a <a href="#ds_set">set-like</a> container if you need to put a bunch of
706 stuff into a container that automatically eliminates duplicates. Some
707 set-like containers support efficient iteration through the elements in
708 sorted order. Set-like containers are more expensive than sequential
709 containers.
710</li>
711
712<li>a <a href="#ds_sequential">sequential</a> container provides
713 the most efficient way to add elements and keeps track of the order they are
714 added to the collection. They permit duplicates and support efficient
Reid Spencer128a7a72007-02-03 21:06:43 +0000[diff] [blame]715 iteration, but do not support efficient look-up based on a key.
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]716</li>
717
Daniel Berlin1939ace2007-09-24 17:52:25 +0000[diff] [blame]718<li>a <a href="#ds_bit">bit</a> container provides an efficient way to store and
719 perform set operations on sets of numeric id's, while automatically
720 eliminating duplicates. Bit containers require a maximum of 1 bit for each
721 identifier you want to store.
722</li>
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]723</ul>
724
725<p>
Reid Spencer128a7a72007-02-03 21:06:43 +0000[diff] [blame]726Once the proper category of container is determined, you can fine tune the
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]727memory use, constant factors, and cache behaviors of access by intelligently
Reid Spencer128a7a72007-02-03 21:06:43 +0000[diff] [blame]728picking a member of the category. Note that constant factors and cache behavior
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]729can be a big deal. If you have a vector that usually only contains a few
730elements (but could contain many), for example, it's much better to use
731<a href="#dss_smallvector">SmallVector</a> than <a href="#dss_vector">vector</a>
732. Doing so avoids (relatively) expensive malloc/free calls, which dwarf the
733cost of adding the elements to the container. </p>
734
735</div>
736
737<!-- ======================================================================= -->
738<div class="doc_subsection">
739 <a name="ds_sequential">Sequential Containers (std::vector, std::list, etc)</a>
740</div>
741
742<div class="doc_text">
743There are a variety of sequential containers available for you, based on your
744needs. Pick the first in this section that will do what you want.
745</div>
746
747<!-- _______________________________________________________________________ -->
748<div class="doc_subsubsection">
749 <a name="dss_fixedarrays">Fixed Size Arrays</a>
750</div>
751
752<div class="doc_text">
753<p>Fixed size arrays are very simple and very fast. They are good if you know
754exactly how many elements you have, or you have a (low) upper bound on how many
755you have.</p>
756</div>
757
758<!-- _______________________________________________________________________ -->
759<div class="doc_subsubsection">
760 <a name="dss_heaparrays">Heap Allocated Arrays</a>
761</div>
762
763<div class="doc_text">
764<p>Heap allocated arrays (new[] + delete[]) are also simple. They are good if
765the number of elements is variable, if you know how many elements you will need
766before the array is allocated, and if the array is usually large (if not,
767consider a <a href="#dss_smallvector">SmallVector</a>). The cost of a heap
768allocated array is the cost of the new/delete (aka malloc/free). Also note that
769if you are allocating an array of a type with a constructor, the constructor and
Reid Spencer128a7a72007-02-03 21:06:43 +0000[diff] [blame]770destructors will be run for every element in the array (re-sizable vectors only
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]771construct those elements actually used).</p>
772</div>
773
774<!-- _______________________________________________________________________ -->
775<div class="doc_subsubsection">
776 <a name="dss_smallvector">"llvm/ADT/SmallVector.h"</a>
777</div>
778
779<div class="doc_text">
780<p><tt>SmallVector&lt;Type, N&gt;</tt> is a simple class that looks and smells
781just like <tt>vector&lt;Type&gt;</tt>:
782it supports efficient iteration, lays out elements in memory order (so you can
783do pointer arithmetic between elements), supports efficient push_back/pop_back
784operations, supports efficient random access to its elements, etc.</p>
785
786<p>The advantage of SmallVector is that it allocates space for
787some number of elements (N) <b>in the object itself</b>. Because of this, if
788the SmallVector is dynamically smaller than N, no malloc is performed. This can
789be a big win in cases where the malloc/free call is far more expensive than the
790code that fiddles around with the elements.</p>
791
792<p>This is good for vectors that are "usually small" (e.g. the number of
793predecessors/successors of a block is usually less than 8). On the other hand,
794this makes the size of the SmallVector itself large, so you don't want to
795allocate lots of them (doing so will waste a lot of space). As such,
796SmallVectors are most useful when on the stack.</p>
797
798<p>SmallVector also provides a nice portable and efficient replacement for
799<tt>alloca</tt>.</p>
800
801</div>
802
803<!-- _______________________________________________________________________ -->
804<div class="doc_subsubsection">
805 <a name="dss_vector">&lt;vector&gt;</a>
806</div>
807
808<div class="doc_text">
809<p>
810std::vector is well loved and respected. It is useful when SmallVector isn't:
811when the size of the vector is often large (thus the small optimization will
812rarely be a benefit) or if you will be allocating many instances of the vector
813itself (which would waste space for elements that aren't in the container).
814vector is also useful when interfacing with code that expects vectors :).
815</p>
Chris Lattner32d84762007-02-05 06:30:51 +0000[diff] [blame]816
817<p>One worthwhile note about std::vector: avoid code like this:</p>
818
819<div class="doc_code">
820<pre>
821for ( ... ) {
Chris Lattner9bb3dbb2007-03-28 18:27:57 +0000[diff] [blame]822 std::vector&lt;foo&gt; V;
Chris Lattner32d84762007-02-05 06:30:51 +0000[diff] [blame]823 use V;
824}
825</pre>
826</div>
827
828<p>Instead, write this as:</p>
829
830<div class="doc_code">
831<pre>
Chris Lattner9bb3dbb2007-03-28 18:27:57 +0000[diff] [blame]832std::vector&lt;foo&gt; V;
Chris Lattner32d84762007-02-05 06:30:51 +0000[diff] [blame]833for ( ... ) {
834 use V;
835 V.clear();
836}
837</pre>
838</div>
839
840<p>Doing so will save (at least) one heap allocation and free per iteration of
841the loop.</p>
842
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]843</div>
844
845<!-- _______________________________________________________________________ -->
846<div class="doc_subsubsection">
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]847 <a name="dss_deque">&lt;deque&gt;</a>
848</div>
849
850<div class="doc_text">
851<p>std::deque is, in some senses, a generalized version of std::vector. Like
852std::vector, it provides constant time random access and other similar
853properties, but it also provides efficient access to the front of the list. It
854does not guarantee continuity of elements within memory.</p>
855
856<p>In exchange for this extra flexibility, std::deque has significantly higher
857constant factor costs than std::vector. If possible, use std::vector or
858something cheaper.</p>
859</div>
860
861<!-- _______________________________________________________________________ -->
862<div class="doc_subsubsection">
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]863 <a name="dss_list">&lt;list&gt;</a>
864</div>
865
866<div class="doc_text">
867<p>std::list is an extremely inefficient class that is rarely useful.
868It performs a heap allocation for every element inserted into it, thus having an
869extremely high constant factor, particularly for small data types. std::list
870also only supports bidirectional iteration, not random access iteration.</p>
871
872<p>In exchange for this high cost, std::list supports efficient access to both
873ends of the list (like std::deque, but unlike std::vector or SmallVector). In
874addition, the iterator invalidation characteristics of std::list are stronger
875than that of a vector class: inserting or removing an element into the list does
876not invalidate iterator or pointers to other elements in the list.</p>
877</div>
878
879<!-- _______________________________________________________________________ -->
880<div class="doc_subsubsection">
Gabor Greif3899e492009-02-27 11:37:41 +0000[diff] [blame]881 <a name="dss_ilist">llvm/ADT/ilist.h</a>
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]882</div>
883
884<div class="doc_text">
885<p><tt>ilist&lt;T&gt;</tt> implements an 'intrusive' doubly-linked list. It is
886intrusive, because it requires the element to store and provide access to the
887prev/next pointers for the list.</p>
888
Gabor Greif2946d1c2009-02-27 12:02:19 +0000[diff] [blame]889<p><tt>ilist</tt> has the same drawbacks as <tt>std::list</tt>, and additionally
890requires an <tt>ilist_traits</tt> implementation for the element type, but it
891provides some novel characteristics. In particular, it can efficiently store
892polymorphic objects, the traits class is informed when an element is inserted or
893removed from the list, and ilists are guaranteed to support a constant-time splice
894operation.</p>
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]895
Gabor Greif2946d1c2009-02-27 12:02:19 +0000[diff] [blame]896<p>These properties are exactly what we want for things like <tt>Instruction</tt>s
897and basic blocks, which is why these are implemented with <tt>ilist</tt>s.</p>
Gabor Greif3899e492009-02-27 11:37:41 +0000[diff] [blame]898
899Related classes of interest are explained in the following subsections:
900 <ul>
Gabor Greif01862502009-02-27 13:28:07 +0000[diff] [blame]901 <li><a href="#dss_ilist_traits">ilist_traits</a></li>
Gabor Greif2946d1c2009-02-27 12:02:19 +0000[diff] [blame]902 <li><a href="#dss_iplist">iplist</a></li>
Gabor Greif3899e492009-02-27 11:37:41 +0000[diff] [blame]903 <li><a href="#dss_ilist_node">llvm/ADT/ilist_node.h</a></li>
904 </ul>
905</div>
906
907<!-- _______________________________________________________________________ -->
908<div class="doc_subsubsection">
Gabor Greif01862502009-02-27 13:28:07 +0000[diff] [blame]909 <a name="dss_ilist_traits">ilist_traits</a>
910</div>
911
912<div class="doc_text">
913<p><tt>ilist_traits&lt;T&gt;</tt> is <tt>ilist&lt;T&gt;</tt>'s customization
914mechanism. <tt>iplist&lt;T&gt;</tt> (and consequently <tt>ilist&lt;T&gt;</tt>)
915publicly derive from this traits class.</p>
916</div>
917
918<!-- _______________________________________________________________________ -->
919<div class="doc_subsubsection">
Gabor Greif2946d1c2009-02-27 12:02:19 +0000[diff] [blame]920 <a name="dss_iplist">iplist</a>
921</div>
922
923<div class="doc_text">
924<p><tt>iplist&lt;T&gt;</tt> is <tt>ilist&lt;T&gt;</tt>'s base and as such
925supports a slightly narrower interface. Notably, inserters from <tt>T&amp;</tt>
926are absent.</p>
Gabor Greif01862502009-02-27 13:28:07 +0000[diff] [blame]927
928<p><tt>ilist_traits&lt;T&gt;</tt> is a public base of this class and can be
929used for a wide variety of customizations.</p>
Gabor Greif2946d1c2009-02-27 12:02:19 +0000[diff] [blame]930</div>
931
932<!-- _______________________________________________________________________ -->
933<div class="doc_subsubsection">
Gabor Greif3899e492009-02-27 11:37:41 +0000[diff] [blame]934 <a name="dss_ilist_node">llvm/ADT/ilist_node.h</a>
935</div>
936
937<div class="doc_text">
938<p><tt>ilist_node&lt;T&gt;</tt> implements a the forward and backward links
939that are expected by the <tt>ilist&lt;T&gt;</tt> (and analogous containers)
940in the default manner.</p>
941
942<p><tt>ilist_node&lt;T&gt;</tt>s are meant to be embedded in the node type
943<tt>T</tt>.</p>
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]944</div>
945
946<!-- _______________________________________________________________________ -->
947<div class="doc_subsubsection">
Chris Lattnerc5722432007-02-03 19:49:31 +0000[diff] [blame]948 <a name="dss_other">Other Sequential Container options</a>
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]949</div>
950
951<div class="doc_text">
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]952<p>Other STL containers are available, such as std::string.</p>
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]953
954<p>There are also various STL adapter classes such as std::queue,
955std::priority_queue, std::stack, etc. These provide simplified access to an
956underlying container but don't affect the cost of the container itself.</p>
957
958</div>
959
960
961<!-- ======================================================================= -->
962<div class="doc_subsection">
963 <a name="ds_set">Set-Like Containers (std::set, SmallSet, SetVector, etc)</a>
964</div>
965
966<div class="doc_text">
967
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]968<p>Set-like containers are useful when you need to canonicalize multiple values
969into a single representation. There are several different choices for how to do
970this, providing various trade-offs.</p>
971
972</div>
973
974
975<!-- _______________________________________________________________________ -->
976<div class="doc_subsubsection">
977 <a name="dss_sortedvectorset">A sorted 'vector'</a>
978</div>
979
980<div class="doc_text">
981
Chris Lattner3b23a8c2007-02-03 08:10:45 +0000[diff] [blame]982<p>If you intend to insert a lot of elements, then do a lot of queries, a
983great approach is to use a vector (or other sequential container) with
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]984std::sort+std::unique to remove duplicates. This approach works really well if
Chris Lattner3b23a8c2007-02-03 08:10:45 +0000[diff] [blame]985your usage pattern has these two distinct phases (insert then query), and can be
986coupled with a good choice of <a href="#ds_sequential">sequential container</a>.
987</p>
988
989<p>
990This combination provides the several nice properties: the result data is
991contiguous in memory (good for cache locality), has few allocations, is easy to
992address (iterators in the final vector are just indices or pointers), and can be
993efficiently queried with a standard binary or radix search.</p>
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]994
995</div>
996
997<!-- _______________________________________________________________________ -->
998<div class="doc_subsubsection">
999 <a name="dss_smallset">"llvm/ADT/SmallSet.h"</a>
1000</div>
1001
1002<div class="doc_text">
1003
Reid Spencer128a7a72007-02-03 21:06:43 +0000[diff] [blame]1004<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]1005are 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]1006has space for N elements in place (thus, if the set is dynamically smaller than
Chris Lattner14868db2007-02-03 08:20:15 +0000[diff] [blame]1007N, no malloc traffic is required) and accesses them with a simple linear search.
1008When the set grows beyond 'N' elements, it allocates a more expensive representation that
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1009guarantees efficient access (for most types, it falls back to std::set, but for
Chris Lattner14868db2007-02-03 08:20:15 +0000[diff] [blame]1010pointers it uses something far better, <a
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1011href="#dss_smallptrset">SmallPtrSet</a>).</p>
1012
1013<p>The magic of this class is that it handles small sets extremely efficiently,
1014but gracefully handles extremely large sets without loss of efficiency. The
1015drawback is that the interface is quite small: it supports insertion, queries
1016and erasing, but does not support iteration.</p>
1017
1018</div>
1019
1020<!-- _______________________________________________________________________ -->
1021<div class="doc_subsubsection">
1022 <a name="dss_smallptrset">"llvm/ADT/SmallPtrSet.h"</a>
1023</div>
1024
1025<div class="doc_text">
1026
1027<p>SmallPtrSet has all the advantages of SmallSet (and a SmallSet of pointers is
Reid Spencer128a7a72007-02-03 21:06:43 +0000[diff] [blame]1028transparently implemented with a SmallPtrSet), but also supports iterators. If
Chris Lattner14868db2007-02-03 08:20:15 +0000[diff] [blame]1029more than 'N' insertions are performed, a single quadratically
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1030probed hash table is allocated and grows as needed, providing extremely
1031efficient access (constant time insertion/deleting/queries with low constant
1032factors) and is very stingy with malloc traffic.</p>
1033
1034<p>Note that, unlike std::set, the iterators of SmallPtrSet are invalidated
1035whenever an insertion occurs. Also, the values visited by the iterators are not
1036visited in sorted order.</p>
1037
1038</div>
1039
1040<!-- _______________________________________________________________________ -->
1041<div class="doc_subsubsection">
Chris Lattnerc28476f2007-09-30 00:58:59 +0000[diff] [blame]1042 <a name="dss_denseset">"llvm/ADT/DenseSet.h"</a>
1043</div>
1044
1045<div class="doc_text">
1046
1047<p>
1048DenseSet is a simple quadratically probed hash table. It excels at supporting
1049small values: it uses a single allocation to hold all of the pairs that
1050are currently inserted in the set. DenseSet is a great way to unique small
1051values that are not simple pointers (use <a
1052href="#dss_smallptrset">SmallPtrSet</a> for pointers). Note that DenseSet has
1053the same requirements for the value type that <a
1054href="#dss_densemap">DenseMap</a> has.
1055</p>
1056
1057</div>
1058
1059<!-- _______________________________________________________________________ -->
1060<div class="doc_subsubsection">
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1061 <a name="dss_FoldingSet">"llvm/ADT/FoldingSet.h"</a>
1062</div>
1063
1064<div class="doc_text">
1065
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]1066<p>
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1067FoldingSet is an aggregate class that is really good at uniquing
1068expensive-to-create or polymorphic objects. It is a combination of a chained
1069hash table with intrusive links (uniqued objects are required to inherit from
Chris Lattner14868db2007-02-03 08:20:15 +0000[diff] [blame]1070FoldingSetNode) that uses <a href="#dss_smallvector">SmallVector</a> as part of
1071its ID process.</p>
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1072
Chris Lattner14868db2007-02-03 08:20:15 +0000[diff] [blame]1073<p>Consider a case where you want to implement a "getOrCreateFoo" method for
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1074a complex object (for example, a node in the code generator). The client has a
1075description of *what* it wants to generate (it knows the opcode and all the
1076operands), 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]1077only to find out it already exists, at which point we would have to delete it
1078and return the node that already exists.
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]1079</p>
1080
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1081<p>To support this style of client, FoldingSet perform a query with a
1082FoldingSetNodeID (which wraps SmallVector) that can be used to describe the
1083element that we want to query for. The query either returns the element
1084matching the ID or it returns an opaque ID that indicates where insertion should
Chris Lattner14868db2007-02-03 08:20:15 +0000[diff] [blame]1085take place. Construction of the ID usually does not require heap traffic.</p>
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1086
1087<p>Because FoldingSet uses intrusive links, it can support polymorphic objects
1088in the set (for example, you can have SDNode instances mixed with LoadSDNodes).
1089Because the elements are individually allocated, pointers to the elements are
1090stable: inserting or removing elements does not invalidate any pointers to other
1091elements.
1092</p>
1093
1094</div>
1095
1096<!-- _______________________________________________________________________ -->
1097<div class="doc_subsubsection">
1098 <a name="dss_set">&lt;set&gt;</a>
1099</div>
1100
1101<div class="doc_text">
1102
Chris Lattnerc5722432007-02-03 19:49:31 +0000[diff] [blame]1103<p><tt>std::set</tt> is a reasonable all-around set class, which is decent at
1104many things but great at nothing. std::set allocates memory for each element
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1105inserted (thus it is very malloc intensive) and typically stores three pointers
Chris Lattner14868db2007-02-03 08:20:15 +0000[diff] [blame]1106per element in the set (thus adding a large amount of per-element space
1107overhead). It offers guaranteed log(n) performance, which is not particularly
Chris Lattnerc5722432007-02-03 19:49:31 +0000[diff] [blame]1108fast from a complexity standpoint (particularly if the elements of the set are
1109expensive to compare, like strings), and has extremely high constant factors for
1110lookup, insertion and removal.</p>
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1111
Chris Lattner14868db2007-02-03 08:20:15 +0000[diff] [blame]1112<p>The advantages of std::set are that its iterators are stable (deleting or
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1113inserting an element from the set does not affect iterators or pointers to other
1114elements) and that iteration over the set is guaranteed to be in sorted order.
1115If the elements in the set are large, then the relative overhead of the pointers
1116and malloc traffic is not a big deal, but if the elements of the set are small,
1117std::set is almost never a good choice.</p>
1118
1119</div>
1120
1121<!-- _______________________________________________________________________ -->
1122<div class="doc_subsubsection">
1123 <a name="dss_setvector">"llvm/ADT/SetVector.h"</a>
1124</div>
1125
1126<div class="doc_text">
Chris Lattneredca3c52007-02-04 00:00:26 +0000[diff] [blame]1127<p>LLVM's SetVector&lt;Type&gt; is an adapter class that combines your choice of
1128a set-like container along with a <a href="#ds_sequential">Sequential
1129Container</a>. The important property
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1130that this provides is efficient insertion with uniquing (duplicate elements are
1131ignored) with iteration support. It implements this by inserting elements into
1132both a set-like container and the sequential container, using the set-like
1133container for uniquing and the sequential container for iteration.
1134</p>
1135
1136<p>The difference between SetVector and other sets is that the order of
1137iteration is guaranteed to match the order of insertion into the SetVector.
1138This property is really important for things like sets of pointers. Because
1139pointer values are non-deterministic (e.g. vary across runs of the program on
Chris Lattneredca3c52007-02-04 00:00:26 +0000[diff] [blame]1140different machines), iterating over the pointers in the set will
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1141not be in a well-defined order.</p>
1142
1143<p>
1144The drawback of SetVector is that it requires twice as much space as a normal
1145set and has the sum of constant factors from the set-like container and the
1146sequential container that it uses. Use it *only* if you need to iterate over
1147the elements in a deterministic order. SetVector is also expensive to delete
Chris Lattneredca3c52007-02-04 00:00:26 +0000[diff] [blame]1148elements out of (linear time), unless you use it's "pop_back" method, which is
1149faster.
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1150</p>
1151
Chris Lattneredca3c52007-02-04 00:00:26 +0000[diff] [blame]1152<p>SetVector is an adapter class that defaults to using std::vector and std::set
1153for the underlying containers, so it is quite expensive. However,
1154<tt>"llvm/ADT/SetVector.h"</tt> also provides a SmallSetVector class, which
1155defaults to using a SmallVector and SmallSet of a specified size. If you use
1156this, and if your sets are dynamically smaller than N, you will save a lot of
1157heap traffic.</p>
1158
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1159</div>
1160
1161<!-- _______________________________________________________________________ -->
1162<div class="doc_subsubsection">
Chris Lattnerc5722432007-02-03 19:49:31 +0000[diff] [blame]1163 <a name="dss_uniquevector">"llvm/ADT/UniqueVector.h"</a>
1164</div>
1165
1166<div class="doc_text">
1167
1168<p>
1169UniqueVector is similar to <a href="#dss_setvector">SetVector</a>, but it
1170retains a unique ID for each element inserted into the set. It internally
1171contains a map and a vector, and it assigns a unique ID for each value inserted
1172into the set.</p>
1173
1174<p>UniqueVector is very expensive: its cost is the sum of the cost of
1175maintaining both the map and vector, it has high complexity, high constant
1176factors, and produces a lot of malloc traffic. It should be avoided.</p>
1177
1178</div>
1179
1180
1181<!-- _______________________________________________________________________ -->
1182<div class="doc_subsubsection">
1183 <a name="dss_otherset">Other Set-Like Container Options</a>
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1184</div>
1185
1186<div class="doc_text">
1187
1188<p>
1189The STL provides several other options, such as std::multiset and the various
Chris Lattnerf1a30822009-03-09 05:20:45 +0000[diff] [blame^]1190"hash_set" like containers (whether from C++ TR1 or from the SGI library). We
1191never use hash_set and unordered_set because they are generally very expensive
1192(each insertion requires a malloc) and very non-portable.
1193</p>
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1194
1195<p>std::multiset is useful if you're not interested in elimination of
Chris Lattner14868db2007-02-03 08:20:15 +0000[diff] [blame]1196duplicates, but has all the drawbacks of std::set. A sorted vector (where you
1197don't delete duplicate entries) or some other approach is almost always
1198better.</p>
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1199
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]1200</div>
1201
1202<!-- ======================================================================= -->
1203<div class="doc_subsection">
1204 <a name="ds_map">Map-Like Containers (std::map, DenseMap, etc)</a>
1205</div>
1206
1207<div class="doc_text">
Chris Lattnerc5722432007-02-03 19:49:31 +0000[diff] [blame]1208Map-like containers are useful when you want to associate data to a key. As
1209usual, there are a lot of different ways to do this. :)
1210</div>
1211
1212<!-- _______________________________________________________________________ -->
1213<div class="doc_subsubsection">
1214 <a name="dss_sortedvectormap">A sorted 'vector'</a>
1215</div>
1216
1217<div class="doc_text">
1218
1219<p>
1220If your usage pattern follows a strict insert-then-query approach, you can
1221trivially use the same approach as <a href="#dss_sortedvectorset">sorted vectors
1222for set-like containers</a>. The only difference is that your query function
1223(which uses std::lower_bound to get efficient log(n) lookup) should only compare
1224the key, not both the key and value. This yields the same advantages as sorted
1225vectors for sets.
1226</p>
1227</div>
1228
1229<!-- _______________________________________________________________________ -->
1230<div class="doc_subsubsection">
Chris Lattner796f9fa2007-02-08 19:14:21 +0000[diff] [blame]1231 <a name="dss_stringmap">"llvm/ADT/StringMap.h"</a>
Chris Lattnerc5722432007-02-03 19:49:31 +0000[diff] [blame]1232</div>
1233
1234<div class="doc_text">
1235
1236<p>
1237Strings are commonly used as keys in maps, and they are difficult to support
1238efficiently: they are variable length, inefficient to hash and compare when
Chris Lattner796f9fa2007-02-08 19:14:21 +0000[diff] [blame]1239long, expensive to copy, etc. StringMap is a specialized container designed to
1240cope with these issues. It supports mapping an arbitrary range of bytes to an
1241arbitrary other object.</p>
Chris Lattnerc5722432007-02-03 19:49:31 +0000[diff] [blame]1242
Chris Lattner796f9fa2007-02-08 19:14:21 +0000[diff] [blame]1243<p>The StringMap implementation uses a quadratically-probed hash table, where
Chris Lattnerc5722432007-02-03 19:49:31 +0000[diff] [blame]1244the buckets store a pointer to the heap allocated entries (and some other
1245stuff). The entries in the map must be heap allocated because the strings are
1246variable length. The string data (key) and the element object (value) are
1247stored in the same allocation with the string data immediately after the element
1248object. This container guarantees the "<tt>(char*)(&amp;Value+1)</tt>" points
1249to the key string for a value.</p>
1250
Chris Lattner796f9fa2007-02-08 19:14:21 +0000[diff] [blame]1251<p>The StringMap is very fast for several reasons: quadratic probing is very
Chris Lattnerc5722432007-02-03 19:49:31 +0000[diff] [blame]1252cache efficient for lookups, the hash value of strings in buckets is not
Chris Lattner796f9fa2007-02-08 19:14:21 +0000[diff] [blame]1253recomputed when lookup up an element, StringMap rarely has to touch the
Chris Lattnerc5722432007-02-03 19:49:31 +0000[diff] [blame]1254memory for unrelated objects when looking up a value (even when hash collisions
1255happen), hash table growth does not recompute the hash values for strings
1256already in the table, and each pair in the map is store in a single allocation
1257(the string data is stored in the same allocation as the Value of a pair).</p>
1258
Chris Lattner796f9fa2007-02-08 19:14:21 +0000[diff] [blame]1259<p>StringMap also provides query methods that take byte ranges, so it only ever
Chris Lattnerc5722432007-02-03 19:49:31 +0000[diff] [blame]1260copies a string if a value is inserted into the table.</p>
1261</div>
1262
1263<!-- _______________________________________________________________________ -->
1264<div class="doc_subsubsection">
1265 <a name="dss_indexedmap">"llvm/ADT/IndexedMap.h"</a>
1266</div>
1267
1268<div class="doc_text">
1269<p>
1270IndexedMap is a specialized container for mapping small dense integers (or
1271values that can be mapped to small dense integers) to some other type. It is
1272internally implemented as a vector with a mapping function that maps the keys to
1273the dense integer range.
1274</p>
1275
1276<p>
1277This is useful for cases like virtual registers in the LLVM code generator: they
1278have a dense mapping that is offset by a compile-time constant (the first
1279virtual register ID).</p>
1280
1281</div>
1282
1283<!-- _______________________________________________________________________ -->
1284<div class="doc_subsubsection">
1285 <a name="dss_densemap">"llvm/ADT/DenseMap.h"</a>
1286</div>
1287
1288<div class="doc_text">
1289
1290<p>
1291DenseMap is a simple quadratically probed hash table. It excels at supporting
1292small keys and values: it uses a single allocation to hold all of the pairs that
1293are currently inserted in the map. DenseMap is a great way to map pointers to
1294pointers, or map other small types to each other.
1295</p>
1296
1297<p>
1298There are several aspects of DenseMap that you should be aware of, however. The
1299iterators in a densemap are invalidated whenever an insertion occurs, unlike
1300map. Also, because DenseMap allocates space for a large number of key/value
Chris Lattnera4a264d2007-02-03 20:17:53 +0000[diff] [blame]1301pairs (it starts with 64 by default), it will waste a lot of space if your keys
1302or values are large. Finally, you must implement a partial specialization of
Chris Lattner76c1b972007-09-17 18:34:04 +0000[diff] [blame]1303DenseMapInfo for the key that you want, if it isn't already supported. This
Chris Lattnerc5722432007-02-03 19:49:31 +0000[diff] [blame]1304is required to tell DenseMap about two special marker values (which can never be
Chris Lattnera4a264d2007-02-03 20:17:53 +0000[diff] [blame]1305inserted into the map) that it needs internally.</p>
Chris Lattnerc5722432007-02-03 19:49:31 +0000[diff] [blame]1306
1307</div>
1308
1309<!-- _______________________________________________________________________ -->
1310<div class="doc_subsubsection">
1311 <a name="dss_map">&lt;map&gt;</a>
1312</div>
1313
1314<div class="doc_text">
1315
1316<p>
1317std::map has similar characteristics to <a href="#dss_set">std::set</a>: it uses
1318a single allocation per pair inserted into the map, it offers log(n) lookup with
1319an extremely large constant factor, imposes a space penalty of 3 pointers per
1320pair in the map, etc.</p>
1321
1322<p>std::map is most useful when your keys or values are very large, if you need
1323to iterate over the collection in sorted order, or if you need stable iterators
1324into the map (i.e. they don't get invalidated if an insertion or deletion of
1325another element takes place).</p>
1326
1327</div>
1328
1329<!-- _______________________________________________________________________ -->
1330<div class="doc_subsubsection">
1331 <a name="dss_othermap">Other Map-Like Container Options</a>
1332</div>
1333
1334<div class="doc_text">
1335
1336<p>
1337The STL provides several other options, such as std::multimap and the various
Chris Lattnerf1a30822009-03-09 05:20:45 +0000[diff] [blame^]1338"hash_map" like containers (whether from C++ TR1 or from the SGI library). We
1339never use hash_set and unordered_set because they are generally very expensive
1340(each insertion requires a malloc) and very non-portable.</p>
Chris Lattnerc5722432007-02-03 19:49:31 +0000[diff] [blame]1341
1342<p>std::multimap is useful if you want to map a key to multiple values, but has
1343all the drawbacks of std::map. A sorted vector or some other approach is almost
1344always better.</p>
1345
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]1346</div>
1347
Daniel Berlin1939ace2007-09-24 17:52:25 +0000[diff] [blame]1348<!-- ======================================================================= -->
1349<div class="doc_subsection">
1350 <a name="ds_bit">Bit storage containers (BitVector, SparseBitVector)</a>
1351</div>
1352
1353<div class="doc_text">
Chris Lattner7086ce72007-09-25 22:37:50 +0000[diff] [blame]1354<p>Unlike the other containers, there are only two bit storage containers, and
1355choosing when to use each is relatively straightforward.</p>
1356
1357<p>One additional option is
1358<tt>std::vector&lt;bool&gt;</tt>: we discourage its use for two reasons 1) the
1359implementation in many common compilers (e.g. commonly available versions of
1360GCC) is extremely inefficient and 2) the C++ standards committee is likely to
1361deprecate this container and/or change it significantly somehow. In any case,
1362please don't use it.</p>
Daniel Berlin1939ace2007-09-24 17:52:25 +0000[diff] [blame]1363</div>
1364
1365<!-- _______________________________________________________________________ -->
1366<div class="doc_subsubsection">
1367 <a name="dss_bitvector">BitVector</a>
1368</div>
1369
1370<div class="doc_text">
1371<p> The BitVector container provides a fixed size set of bits for manipulation.
1372It supports individual bit setting/testing, as well as set operations. The set
1373operations take time O(size of bitvector), but operations are performed one word
1374at a time, instead of one bit at a time. This makes the BitVector very fast for
1375set operations compared to other containers. Use the BitVector when you expect
1376the number of set bits to be high (IE a dense set).
1377</p>
1378</div>
1379
1380<!-- _______________________________________________________________________ -->
1381<div class="doc_subsubsection">
1382 <a name="dss_sparsebitvector">SparseBitVector</a>
1383</div>
1384
1385<div class="doc_text">
1386<p> The SparseBitVector container is much like BitVector, with one major
1387difference: Only the bits that are set, are stored. This makes the
1388SparseBitVector much more space efficient than BitVector when the set is sparse,
1389as well as making set operations O(number of set bits) instead of O(size of
1390universe). 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
1391(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).
1392</p>
1393</div>
Chris Lattnerf623a082005-10-17 01:36:23 +0000[diff] [blame]1394
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1395<!-- *********************************************************************** -->
1396<div class="doc_section">
1397 <a name="common">Helpful Hints for Common Operations</a>
1398</div>
1399<!-- *********************************************************************** -->
1400
1401<div class="doc_text">
1402
1403<p>This section describes how to perform some very simple transformations of
1404LLVM code. This is meant to give examples of common idioms used, showing the
1405practical side of LLVM transformations. <p> Because this is a "how-to" section,
1406you should also read about the main classes that you will be working with. The
1407<a href="#coreclasses">Core LLVM Class Hierarchy Reference</a> contains details
1408and descriptions of the main classes that you should know about.</p>
1409
1410</div>
1411
1412<!-- NOTE: this section should be heavy on example code -->
1413<!-- ======================================================================= -->
1414<div class="doc_subsection">
1415 <a name="inspection">Basic Inspection and Traversal Routines</a>
1416</div>
1417
1418<div class="doc_text">
1419
1420<p>The LLVM compiler infrastructure have many different data structures that may
1421be traversed. Following the example of the C++ standard template library, the
1422techniques used to traverse these various data structures are all basically the
1423same. For a enumerable sequence of values, the <tt>XXXbegin()</tt> function (or
1424method) returns an iterator to the start of the sequence, the <tt>XXXend()</tt>
1425function returns an iterator pointing to one past the last valid element of the
1426sequence, and there is some <tt>XXXiterator</tt> data type that is common
1427between the two operations.</p>
1428
1429<p>Because the pattern for iteration is common across many different aspects of
1430the program representation, the standard template library algorithms may be used
1431on them, and it is easier to remember how to iterate. First we show a few common
1432examples of the data structures that need to be traversed. Other data
1433structures are traversed in very similar ways.</p>
1434
1435</div>
1436
1437<!-- _______________________________________________________________________ -->
Chris Lattner69bf8a92004-05-23 21:06:58 +0000[diff] [blame]1438<div class="doc_subsubsection">
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1439 <a name="iterate_function">Iterating over the </a><a
1440 href="#BasicBlock"><tt>BasicBlock</tt></a>s in a <a
1441 href="#Function"><tt>Function</tt></a>
1442</div>
1443
1444<div class="doc_text">
1445
1446<p>It's quite common to have a <tt>Function</tt> instance that you'd like to
1447transform in some way; in particular, you'd like to manipulate its
1448<tt>BasicBlock</tt>s. To facilitate this, you'll need to iterate over all of
1449the <tt>BasicBlock</tt>s that constitute the <tt>Function</tt>. The following is
1450an example that prints the name of a <tt>BasicBlock</tt> and the number of
1451<tt>Instruction</tt>s it contains:</p>
1452
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1453<div class="doc_code">
1454<pre>
Bill Wendling82e2eea2006-10-11 18:00:22 +0000[diff] [blame]1455// <i>func is a pointer to a Function instance</i>
1456for (Function::iterator i = func-&gt;begin(), e = func-&gt;end(); i != e; ++i)
1457 // <i>Print out the name of the basic block if it has one, and then the</i>
1458 // <i>number of instructions that it contains</i>
Bill Wendling832171c2006-12-07 20:04:42 +0000[diff] [blame]1459 llvm::cerr &lt;&lt; "Basic block (name=" &lt;&lt; i-&gt;getName() &lt;&lt; ") has "
1460 &lt;&lt; i-&gt;size() &lt;&lt; " instructions.\n";
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1461</pre>
1462</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1463
1464<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]1465invoking member functions of the <tt>Instruction</tt> class. This is
1466because the indirection operator is overloaded for the iterator
Chris Lattner7496ec52003-08-05 22:54:23 +0000[diff] [blame]1467classes. In the above code, the expression <tt>i-&gt;size()</tt> is
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1468exactly equivalent to <tt>(*i).size()</tt> just like you'd expect.</p>
1469
1470</div>
1471
1472<!-- _______________________________________________________________________ -->
Chris Lattner69bf8a92004-05-23 21:06:58 +0000[diff] [blame]1473<div class="doc_subsubsection">
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1474 <a name="iterate_basicblock">Iterating over the </a><a
1475 href="#Instruction"><tt>Instruction</tt></a>s in a <a
1476 href="#BasicBlock"><tt>BasicBlock</tt></a>
1477</div>
1478
1479<div class="doc_text">
1480
1481<p>Just like when dealing with <tt>BasicBlock</tt>s in <tt>Function</tt>s, it's
1482easy to iterate over the individual instructions that make up
1483<tt>BasicBlock</tt>s. Here's a code snippet that prints out each instruction in
1484a <tt>BasicBlock</tt>:</p>
1485
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1486<div class="doc_code">
Chris Lattner55c04612005-03-06 06:00:13 +0000[diff] [blame]1487<pre>
Bill Wendling82e2eea2006-10-11 18:00:22 +0000[diff] [blame]1488// <i>blk is a pointer to a BasicBlock instance</i>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1489for (BasicBlock::iterator i = blk-&gt;begin(), e = blk-&gt;end(); i != e; ++i)
Bill Wendling82e2eea2006-10-11 18:00:22 +0000[diff] [blame]1490 // <i>The next statement works since operator&lt;&lt;(ostream&amp;,...)</i>
1491 // <i>is overloaded for Instruction&amp;</i>
Bill Wendling832171c2006-12-07 20:04:42 +0000[diff] [blame]1492 llvm::cerr &lt;&lt; *i &lt;&lt; "\n";
Chris Lattner55c04612005-03-06 06:00:13 +0000[diff] [blame]1493</pre>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1494</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1495
1496<p>However, this isn't really the best way to print out the contents of a
1497<tt>BasicBlock</tt>! Since the ostream operators are overloaded for virtually
1498anything you'll care about, you could have just invoked the print routine on the
Bill Wendling832171c2006-12-07 20:04:42 +0000[diff] [blame]1499basic block itself: <tt>llvm::cerr &lt;&lt; *blk &lt;&lt; "\n";</tt>.</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1500
1501</div>
1502
1503<!-- _______________________________________________________________________ -->
Chris Lattner69bf8a92004-05-23 21:06:58 +0000[diff] [blame]1504<div class="doc_subsubsection">
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1505 <a name="iterate_institer">Iterating over the </a><a
1506 href="#Instruction"><tt>Instruction</tt></a>s in a <a
1507 href="#Function"><tt>Function</tt></a>
1508</div>
1509
1510<div class="doc_text">
1511
1512<p>If you're finding that you commonly iterate over a <tt>Function</tt>'s
1513<tt>BasicBlock</tt>s and then that <tt>BasicBlock</tt>'s <tt>Instruction</tt>s,
1514<tt>InstIterator</tt> should be used instead. You'll need to include <a
1515href="/doxygen/InstIterator_8h-source.html"><tt>llvm/Support/InstIterator.h</tt></a>,
1516and then instantiate <tt>InstIterator</tt>s explicitly in your code. Here's a
Chris Lattner69bf8a92004-05-23 21:06:58 +0000[diff] [blame]1517small 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]1518
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1519<div class="doc_code">
1520<pre>
1521#include "<a href="/doxygen/InstIterator_8h-source.html">llvm/Support/InstIterator.h</a>"
1522
Reid Spencer128a7a72007-02-03 21:06:43 +0000[diff] [blame]1523// <i>F is a pointer to a Function instance</i>
Chris Lattnerda021aa2008-06-04 18:20:42 +0000[diff] [blame]1524for (inst_iterator I = inst_begin(F), E = inst_end(F); I != E; ++I)
1525 llvm::cerr &lt;&lt; *I &lt;&lt; "\n";
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1526</pre>
1527</div>
1528
1529<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]1530work list with its initial contents. For example, if you wanted to
1531initialize a work list to contain all instructions in a <tt>Function</tt>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1532F, all you would need to do is something like:</p>
1533
1534<div class="doc_code">
1535<pre>
1536std::set&lt;Instruction*&gt; worklist;
Chris Lattnerda021aa2008-06-04 18:20:42 +0000[diff] [blame]1537// or better yet, SmallPtrSet&lt;Instruction*, 64&gt; worklist;
1538
1539for (inst_iterator I = inst_begin(F), E = inst_end(F); I != E; ++I)
1540 worklist.insert(&amp;*I);
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1541</pre>
1542</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1543
1544<p>The STL set <tt>worklist</tt> would now contain all instructions in the
1545<tt>Function</tt> pointed to by F.</p>
1546
1547</div>
1548
1549<!-- _______________________________________________________________________ -->
1550<div class="doc_subsubsection">
1551 <a name="iterate_convert">Turning an iterator into a class pointer (and
1552 vice-versa)</a>
1553</div>
1554
1555<div class="doc_text">
1556
1557<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]1558instance when all you've got at hand is an iterator. Well, extracting
Chris Lattner69bf8a92004-05-23 21:06:58 +0000[diff] [blame]1559a reference or a pointer from an iterator is very straight-forward.
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]1560Assuming that <tt>i</tt> is a <tt>BasicBlock::iterator</tt> and <tt>j</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1561is a <tt>BasicBlock::const_iterator</tt>:</p>
1562
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1563<div class="doc_code">
1564<pre>
Bill Wendling82e2eea2006-10-11 18:00:22 +0000[diff] [blame]1565Instruction&amp; inst = *i; // <i>Grab reference to instruction reference</i>
1566Instruction* pinst = &amp;*i; // <i>Grab pointer to instruction reference</i>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1567const Instruction&amp; inst = *j;
1568</pre>
1569</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1570
1571<p>However, the iterators you'll be working with in the LLVM framework are
1572special: they will automatically convert to a ptr-to-instance type whenever they
1573need to. Instead of dereferencing the iterator and then taking the address of
1574the result, you can simply assign the iterator to the proper pointer type and
1575you get the dereference and address-of operation as a result of the assignment
1576(behind the scenes, this is a result of overloading casting mechanisms). Thus
1577the last line of the last example,</p>
1578
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1579<div class="doc_code">
1580<pre>
Chris Lattner2e438ca2008-01-03 16:56:04 +0000[diff] [blame]1581Instruction *pinst = &amp;*i;
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1582</pre>
1583</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1584
1585<p>is semantically equivalent to</p>
1586
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1587<div class="doc_code">
1588<pre>
Chris Lattner2e438ca2008-01-03 16:56:04 +0000[diff] [blame]1589Instruction *pinst = i;
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1590</pre>
1591</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1592
Chris Lattner69bf8a92004-05-23 21:06:58 +0000[diff] [blame]1593<p>It's also possible to turn a class pointer into the corresponding iterator,
1594and this is a constant time operation (very efficient). The following code
1595snippet illustrates use of the conversion constructors provided by LLVM
1596iterators. By using these, you can explicitly grab the iterator of something
1597without actually obtaining it via iteration over some structure:</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1598
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1599<div class="doc_code">
1600<pre>
1601void printNextInstruction(Instruction* inst) {
1602 BasicBlock::iterator it(inst);
Bill Wendling82e2eea2006-10-11 18:00:22 +0000[diff] [blame]1603 ++it; // <i>After this line, it refers to the instruction after *inst</i>
Bill Wendling832171c2006-12-07 20:04:42 +0000[diff] [blame]1604 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]1605}
1606</pre>
1607</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1608
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1609</div>
1610
1611<!--_______________________________________________________________________-->
1612<div class="doc_subsubsection">
1613 <a name="iterate_complex">Finding call sites: a slightly more complex
1614 example</a>
1615</div>
1616
1617<div class="doc_text">
1618
1619<p>Say that you're writing a FunctionPass and would like to count all the
1620locations in the entire module (that is, across every <tt>Function</tt>) where a
1621certain function (i.e., some <tt>Function</tt>*) is already in scope. As you'll
1622learn 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]1623much more straight-forward manner, but this example will allow us to explore how
Reid Spencer128a7a72007-02-03 21:06:43 +0000[diff] [blame]1624you'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]1625is what we want to do:</p>
1626
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1627<div class="doc_code">
1628<pre>
1629initialize callCounter to zero
1630for each Function f in the Module
1631 for each BasicBlock b in f
1632 for each Instruction i in b
1633 if (i is a CallInst and calls the given function)
1634 increment callCounter
1635</pre>
1636</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1637
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1638<p>And the actual code is (remember, because we're writing a
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1639<tt>FunctionPass</tt>, our <tt>FunctionPass</tt>-derived class simply has to
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1640override the <tt>runOnFunction</tt> method):</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1641
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1642<div class="doc_code">
1643<pre>
1644Function* targetFunc = ...;
1645
1646class OurFunctionPass : public FunctionPass {
1647 public:
1648 OurFunctionPass(): callCounter(0) { }
1649
1650 virtual runOnFunction(Function&amp; F) {
1651 for (Function::iterator b = F.begin(), be = F.end(); b != be; ++b) {
Eric Christopher203e71d2008-11-08 08:20:49 +0000[diff] [blame]1652 for (BasicBlock::iterator i = b-&gt;begin(), ie = b-&gt;end(); i != ie; ++i) {
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1653 if (<a href="#CallInst">CallInst</a>* callInst = <a href="#isa">dyn_cast</a>&lt;<a
1654 href="#CallInst">CallInst</a>&gt;(&amp;*i)) {
Bill Wendling82e2eea2006-10-11 18:00:22 +0000[diff] [blame]1655 // <i>We know we've encountered a call instruction, so we</i>
1656 // <i>need to determine if it's a call to the</i>
Chris Lattner2e438ca2008-01-03 16:56:04 +0000[diff] [blame]1657 // <i>function pointed to by m_func or not.</i>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1658 if (callInst-&gt;getCalledFunction() == targetFunc)
1659 ++callCounter;
1660 }
1661 }
1662 }
Bill Wendling82e2eea2006-10-11 18:00:22 +0000[diff] [blame]1663 }
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1664
1665 private:
Chris Lattner2e438ca2008-01-03 16:56:04 +0000[diff] [blame]1666 unsigned callCounter;
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1667};
1668</pre>
1669</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1670
1671</div>
1672
Brian Gaekef1972c62003-11-07 19:25:45 +0000[diff] [blame]1673<!--_______________________________________________________________________-->
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1674<div class="doc_subsubsection">
1675 <a name="calls_and_invokes">Treating calls and invokes the same way</a>
1676</div>
1677
1678<div class="doc_text">
1679
1680<p>You may have noticed that the previous example was a bit oversimplified in
1681that it did not deal with call sites generated by 'invoke' instructions. In
1682this, and in other situations, you may find that you want to treat
1683<tt>CallInst</tt>s and <tt>InvokeInst</tt>s the same way, even though their
1684most-specific common base class is <tt>Instruction</tt>, which includes lots of
1685less closely-related things. For these cases, LLVM provides a handy wrapper
1686class called <a
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]1687href="http://llvm.org/doxygen/classllvm_1_1CallSite.html"><tt>CallSite</tt></a>.
Chris Lattner69bf8a92004-05-23 21:06:58 +0000[diff] [blame]1688It is essentially a wrapper around an <tt>Instruction</tt> pointer, with some
1689methods that provide functionality common to <tt>CallInst</tt>s and
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1690<tt>InvokeInst</tt>s.</p>
1691
Chris Lattner69bf8a92004-05-23 21:06:58 +0000[diff] [blame]1692<p>This class has "value semantics": it should be passed by value, not by
1693reference and it should not be dynamically allocated or deallocated using
1694<tt>operator new</tt> or <tt>operator delete</tt>. It is efficiently copyable,
1695assignable and constructable, with costs equivalents to that of a bare pointer.
1696If you look at its definition, it has only a single pointer member.</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1697
1698</div>
1699
Chris Lattner1a3105b2002-09-09 05:49:39 +0000[diff] [blame]1700<!--_______________________________________________________________________-->
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1701<div class="doc_subsubsection">
1702 <a name="iterate_chains">Iterating over def-use &amp; use-def chains</a>
1703</div>
1704
1705<div class="doc_text">
1706
1707<p>Frequently, we might have an instance of the <a
Chris Lattner00815172007-01-04 22:01:45 +0000[diff] [blame]1708href="/doxygen/classllvm_1_1Value.html">Value Class</a> and we want to
Misha Brukman384047f2004-06-03 23:29:12 +0000[diff] [blame]1709determine which <tt>User</tt>s use the <tt>Value</tt>. The list of all
1710<tt>User</tt>s of a particular <tt>Value</tt> is called a <i>def-use</i> chain.
1711For example, let's say we have a <tt>Function*</tt> named <tt>F</tt> to a
1712particular function <tt>foo</tt>. Finding all of the instructions that
1713<i>use</i> <tt>foo</tt> is as simple as iterating over the <i>def-use</i> chain
1714of <tt>F</tt>:</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1715
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1716<div class="doc_code">
1717<pre>
Chris Lattner2e438ca2008-01-03 16:56:04 +0000[diff] [blame]1718Function *F = ...;
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1719
Bill Wendling82e2eea2006-10-11 18:00:22 +0000[diff] [blame]1720for (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]1721 if (Instruction *Inst = dyn_cast&lt;Instruction&gt;(*i)) {
Bill Wendling832171c2006-12-07 20:04:42 +0000[diff] [blame]1722 llvm::cerr &lt;&lt; "F is used in instruction:\n";
1723 llvm::cerr &lt;&lt; *Inst &lt;&lt; "\n";
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1724 }
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1725</pre>
1726</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1727
1728<p>Alternately, it's common to have an instance of the <a
Misha Brukman384047f2004-06-03 23:29:12 +0000[diff] [blame]1729href="/doxygen/classllvm_1_1User.html">User Class</a> and need to know what
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1730<tt>Value</tt>s are used by it. The list of all <tt>Value</tt>s used by a
1731<tt>User</tt> is known as a <i>use-def</i> chain. Instances of class
1732<tt>Instruction</tt> are common <tt>User</tt>s, so we might want to iterate over
1733all of the values that a particular instruction uses (that is, the operands of
1734the particular <tt>Instruction</tt>):</p>
1735
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1736<div class="doc_code">
1737<pre>
Chris Lattner2e438ca2008-01-03 16:56:04 +0000[diff] [blame]1738Instruction *pi = ...;
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1739
1740for (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]1741 Value *v = *i;
Bill Wendling82e2eea2006-10-11 18:00:22 +0000[diff] [blame]1742 // <i>...</i>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1743}
1744</pre>
1745</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1746
Chris Lattner1a3105b2002-09-09 05:49:39 +0000[diff] [blame]1747<!--
1748 def-use chains ("finding all users of"): Value::use_begin/use_end
1749 use-def chains ("finding all values used"): User::op_begin/op_end [op=operand]
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1750-->
1751
1752</div>
1753
Chris Lattner2e438ca2008-01-03 16:56:04 +0000[diff] [blame]1754<!--_______________________________________________________________________-->
1755<div class="doc_subsubsection">
1756 <a name="iterate_preds">Iterating over predecessors &amp;
1757successors of blocks</a>
1758</div>
1759
1760<div class="doc_text">
1761
1762<p>Iterating over the predecessors and successors of a block is quite easy
1763with the routines defined in <tt>"llvm/Support/CFG.h"</tt>. Just use code like
1764this to iterate over all predecessors of BB:</p>
1765
1766<div class="doc_code">
1767<pre>
1768#include "llvm/Support/CFG.h"
1769BasicBlock *BB = ...;
1770
1771for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI) {
1772 BasicBlock *Pred = *PI;
1773 // <i>...</i>
1774}
1775</pre>
1776</div>
1777
1778<p>Similarly, to iterate over successors use
1779succ_iterator/succ_begin/succ_end.</p>
1780
1781</div>
1782
1783
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1784<!-- ======================================================================= -->
1785<div class="doc_subsection">
1786 <a name="simplechanges">Making simple changes</a>
1787</div>
1788
1789<div class="doc_text">
1790
1791<p>There are some primitive transformation operations present in the LLVM
Joel Stanley753eb712002-09-11 22:32:24 +0000[diff] [blame]1792infrastructure that are worth knowing about. When performing
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]1793transformations, it's fairly common to manipulate the contents of basic
1794blocks. This section describes some of the common methods for doing so
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1795and gives example code.</p>
1796
1797</div>
1798
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]1799<!--_______________________________________________________________________-->
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1800<div class="doc_subsubsection">
1801 <a name="schanges_creating">Creating and inserting new
1802 <tt>Instruction</tt>s</a>
1803</div>
1804
1805<div class="doc_text">
1806
1807<p><i>Instantiating Instructions</i></p>
1808
Chris Lattner69bf8a92004-05-23 21:06:58 +0000[diff] [blame]1809<p>Creation of <tt>Instruction</tt>s is straight-forward: simply call the
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1810constructor for the kind of instruction to instantiate and provide the necessary
1811parameters. For example, an <tt>AllocaInst</tt> only <i>requires</i> a
1812(const-ptr-to) <tt>Type</tt>. Thus:</p>
1813
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1814<div class="doc_code">
1815<pre>
Nick Lewycky10d64b92007-12-03 01:52:52 +0000[diff] [blame]1816AllocaInst* ai = new AllocaInst(Type::Int32Ty);
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1817</pre>
1818</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1819
1820<p>will create an <tt>AllocaInst</tt> instance that represents the allocation of
Reid Spencer128a7a72007-02-03 21:06:43 +0000[diff] [blame]1821one integer in the current stack frame, at run time. Each <tt>Instruction</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1822subclass is likely to have varying default parameters which change the semantics
1823of the instruction, so refer to the <a
Misha Brukman31ca1de2004-06-03 23:35:54 +0000[diff] [blame]1824href="/doxygen/classllvm_1_1Instruction.html">doxygen documentation for the subclass of
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1825Instruction</a> that you're interested in instantiating.</p>
1826
1827<p><i>Naming values</i></p>
1828
1829<p>It is very useful to name the values of instructions when you're able to, as
1830this facilitates the debugging of your transformations. If you end up looking
1831at generated LLVM machine code, you definitely want to have logical names
1832associated with the results of instructions! By supplying a value for the
1833<tt>Name</tt> (default) parameter of the <tt>Instruction</tt> constructor, you
1834associate a logical name with the result of the instruction's execution at
Reid Spencer128a7a72007-02-03 21:06:43 +0000[diff] [blame]1835run time. For example, say that I'm writing a transformation that dynamically
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1836allocates space for an integer on the stack, and that integer is going to be
1837used as some kind of index by some other code. To accomplish this, I place an
1838<tt>AllocaInst</tt> at the first point in the first <tt>BasicBlock</tt> of some
1839<tt>Function</tt>, and I'm intending to use it within the same
1840<tt>Function</tt>. I might do:</p>
1841
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1842<div class="doc_code">
1843<pre>
Nick Lewycky10d64b92007-12-03 01:52:52 +0000[diff] [blame]1844AllocaInst* pa = new AllocaInst(Type::Int32Ty, 0, "indexLoc");
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1845</pre>
1846</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1847
1848<p>where <tt>indexLoc</tt> is now the logical name of the instruction's
Reid Spencer128a7a72007-02-03 21:06:43 +0000[diff] [blame]1849execution value, which is a pointer to an integer on the run time stack.</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1850
1851<p><i>Inserting instructions</i></p>
1852
1853<p>There are essentially two ways to insert an <tt>Instruction</tt>
1854into an existing sequence of instructions that form a <tt>BasicBlock</tt>:</p>
1855
Joel Stanley9dd1ad62002-09-18 03:17:23 +0000[diff] [blame]1856<ul>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1857 <li>Insertion into an explicit instruction list
1858
1859 <p>Given a <tt>BasicBlock* pb</tt>, an <tt>Instruction* pi</tt> within that
1860 <tt>BasicBlock</tt>, and a newly-created instruction we wish to insert
1861 before <tt>*pi</tt>, we do the following: </p>
1862
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1863<div class="doc_code">
1864<pre>
1865BasicBlock *pb = ...;
1866Instruction *pi = ...;
1867Instruction *newInst = new Instruction(...);
1868
Bill Wendling82e2eea2006-10-11 18:00:22 +0000[diff] [blame]1869pb-&gt;getInstList().insert(pi, newInst); // <i>Inserts newInst before pi in pb</i>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1870</pre>
1871</div>
Alkis Evlogimenos9a5dc4f2004-05-27 00:57:51 +0000[diff] [blame]1872
1873 <p>Appending to the end of a <tt>BasicBlock</tt> is so common that
1874 the <tt>Instruction</tt> class and <tt>Instruction</tt>-derived
1875 classes provide constructors which take a pointer to a
1876 <tt>BasicBlock</tt> to be appended to. For example code that
1877 looked like: </p>
1878
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1879<div class="doc_code">
1880<pre>
1881BasicBlock *pb = ...;
1882Instruction *newInst = new Instruction(...);
1883
Bill Wendling82e2eea2006-10-11 18:00:22 +0000[diff] [blame]1884pb-&gt;getInstList().push_back(newInst); // <i>Appends newInst to pb</i>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1885</pre>
1886</div>
Alkis Evlogimenos9a5dc4f2004-05-27 00:57:51 +0000[diff] [blame]1887
1888 <p>becomes: </p>
1889
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1890<div class="doc_code">
1891<pre>
1892BasicBlock *pb = ...;
1893Instruction *newInst = new Instruction(..., pb);
1894</pre>
1895</div>
Alkis Evlogimenos9a5dc4f2004-05-27 00:57:51 +0000[diff] [blame]1896
1897 <p>which is much cleaner, especially if you are creating
1898 long instruction streams.</p></li>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1899
1900 <li>Insertion into an implicit instruction list
1901
1902 <p><tt>Instruction</tt> instances that are already in <tt>BasicBlock</tt>s
1903 are implicitly associated with an existing instruction list: the instruction
1904 list of the enclosing basic block. Thus, we could have accomplished the same
1905 thing as the above code without being given a <tt>BasicBlock</tt> by doing:
1906 </p>
1907
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1908<div class="doc_code">
1909<pre>
1910Instruction *pi = ...;
1911Instruction *newInst = new Instruction(...);
1912
1913pi-&gt;getParent()-&gt;getInstList().insert(pi, newInst);
1914</pre>
1915</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1916
1917 <p>In fact, this sequence of steps occurs so frequently that the
1918 <tt>Instruction</tt> class and <tt>Instruction</tt>-derived classes provide
1919 constructors which take (as a default parameter) a pointer to an
1920 <tt>Instruction</tt> which the newly-created <tt>Instruction</tt> should
1921 precede. That is, <tt>Instruction</tt> constructors are capable of
1922 inserting the newly-created instance into the <tt>BasicBlock</tt> of a
1923 provided instruction, immediately before that instruction. Using an
1924 <tt>Instruction</tt> constructor with a <tt>insertBefore</tt> (default)
1925 parameter, the above code becomes:</p>
1926
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1927<div class="doc_code">
1928<pre>
1929Instruction* pi = ...;
1930Instruction* newInst = new Instruction(..., pi);
1931</pre>
1932</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1933
1934 <p>which is much cleaner, especially if you're creating a lot of
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1935 instructions and adding them to <tt>BasicBlock</tt>s.</p></li>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1936</ul>
1937
1938</div>
1939
1940<!--_______________________________________________________________________-->
1941<div class="doc_subsubsection">
1942 <a name="schanges_deleting">Deleting <tt>Instruction</tt>s</a>
1943</div>
1944
1945<div class="doc_text">
1946
1947<p>Deleting an instruction from an existing sequence of instructions that form a
Chris Lattner69bf8a92004-05-23 21:06:58 +0000[diff] [blame]1948<a href="#BasicBlock"><tt>BasicBlock</tt></a> is very straight-forward. First,
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1949you must have a pointer to the instruction that you wish to delete. Second, you
1950need to obtain the pointer to that instruction's basic block. You use the
1951pointer to the basic block to get its list of instructions and then use the
1952erase function to remove your instruction. For example:</p>
1953
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1954<div class="doc_code">
1955<pre>
1956<a href="#Instruction">Instruction</a> *I = .. ;
Chris Lattner9f8ec252008-02-15 22:57:17 +0000[diff] [blame]1957I-&gt;eraseFromParent();
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1958</pre>
1959</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1960
1961</div>
1962
1963<!--_______________________________________________________________________-->
1964<div class="doc_subsubsection">
1965 <a name="schanges_replacing">Replacing an <tt>Instruction</tt> with another
1966 <tt>Value</tt></a>
1967</div>
1968
1969<div class="doc_text">
1970
1971<p><i>Replacing individual instructions</i></p>
1972
1973<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]1974permits use of two very useful replace functions: <tt>ReplaceInstWithValue</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1975and <tt>ReplaceInstWithInst</tt>.</p>
1976
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]1977<h4><a name="schanges_deleting">Deleting <tt>Instruction</tt>s</a></h4>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1978
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]1979<ul>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1980 <li><tt>ReplaceInstWithValue</tt>
1981
Nick Lewyckyb6d1f392008-09-15 06:31:52 +0000[diff] [blame]1982 <p>This function replaces all uses of a given instruction with a value,
1983 and then removes the original instruction. The following example
1984 illustrates the replacement of the result of a particular
Chris Lattner58360822005-01-17 00:12:04 +0000[diff] [blame]1985 <tt>AllocaInst</tt> that allocates memory for a single integer with a null
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1986 pointer to an integer.</p>
1987
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1988<div class="doc_code">
1989<pre>
1990AllocaInst* instToReplace = ...;
1991BasicBlock::iterator ii(instToReplace);
1992
1993ReplaceInstWithValue(instToReplace-&gt;getParent()-&gt;getInstList(), ii,
Daniel Dunbar58c2ac02008-10-03 22:17:25 +0000[diff] [blame]1994 Constant::getNullValue(PointerType::getUnqual(Type::Int32Ty)));
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1995</pre></div></li>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1996
1997 <li><tt>ReplaceInstWithInst</tt>
1998
1999 <p>This function replaces a particular instruction with another
Nick Lewyckyb6d1f392008-09-15 06:31:52 +0000[diff] [blame]2000 instruction, inserting the new instruction into the basic block at the
2001 location where the old instruction was, and replacing any uses of the old
2002 instruction with the new instruction. The following example illustrates
2003 the replacement of one <tt>AllocaInst</tt> with another.</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2004
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2005<div class="doc_code">
2006<pre>
2007AllocaInst* instToReplace = ...;
2008BasicBlock::iterator ii(instToReplace);
2009
2010ReplaceInstWithInst(instToReplace-&gt;getParent()-&gt;getInstList(), ii,
Nick Lewycky10d64b92007-12-03 01:52:52 +0000[diff] [blame]2011 new AllocaInst(Type::Int32Ty, 0, "ptrToReplacedInt"));
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2012</pre></div></li>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]2013</ul>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2014
2015<p><i>Replacing multiple uses of <tt>User</tt>s and <tt>Value</tt>s</i></p>
2016
2017<p>You can use <tt>Value::replaceAllUsesWith</tt> and
2018<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]2019doxygen documentation for the <a href="/doxygen/classllvm_1_1Value.html">Value Class</a>
Misha Brukman384047f2004-06-03 23:29:12 +0000[diff] [blame]2020and <a href="/doxygen/classllvm_1_1User.html">User Class</a>, respectively, for more
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2021information.</p>
2022
2023<!-- Value::replaceAllUsesWith User::replaceUsesOfWith Point out:
2024include/llvm/Transforms/Utils/ especially BasicBlockUtils.h with:
2025ReplaceInstWithValue, ReplaceInstWithInst -->
2026
2027</div>
2028
Tanya Lattnerb011c662007-06-20 18:33:15 +0000[diff] [blame]2029<!--_______________________________________________________________________-->
2030<div class="doc_subsubsection">
2031 <a name="schanges_deletingGV">Deleting <tt>GlobalVariable</tt>s</a>
2032</div>
2033
2034<div class="doc_text">
2035
Tanya Lattnerc5dfcdb2007-06-20 20:46:37 +0000[diff] [blame]2036<p>Deleting a global variable from a module is just as easy as deleting an
2037Instruction. First, you must have a pointer to the global variable that you wish
2038 to delete. You use this pointer to erase it from its parent, the module.
Tanya Lattnerb011c662007-06-20 18:33:15 +0000[diff] [blame]2039 For example:</p>
2040
2041<div class="doc_code">
2042<pre>
2043<a href="#GlobalVariable">GlobalVariable</a> *GV = .. ;
Tanya Lattnerb011c662007-06-20 18:33:15 +0000[diff] [blame]2044
Tanya Lattnerc5dfcdb2007-06-20 20:46:37 +0000[diff] [blame]2045GV-&gt;eraseFromParent();
Tanya Lattnerb011c662007-06-20 18:33:15 +0000[diff] [blame]2046</pre>
2047</div>
2048
2049</div>
2050
Chris Lattner9355b472002-09-06 02:50:58 +0000[diff] [blame]2051<!-- *********************************************************************** -->
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2052<div class="doc_section">
Chris Lattnerd9d6e102005-04-23 16:10:52 +0000[diff] [blame]2053 <a name="advanced">Advanced Topics</a>
2054</div>
2055<!-- *********************************************************************** -->
2056
2057<div class="doc_text">
Chris Lattnerf1b200b2005-04-23 17:27:36 +0000[diff] [blame]2058<p>
2059This section describes some of the advanced or obscure API's that most clients
2060do not need to be aware of. These API's tend manage the inner workings of the
2061LLVM system, and only need to be accessed in unusual circumstances.
2062</p>
2063</div>
Chris Lattnerd9d6e102005-04-23 16:10:52 +0000[diff] [blame]2064
Chris Lattnerf1b200b2005-04-23 17:27:36 +0000[diff] [blame]2065<!-- ======================================================================= -->
2066<div class="doc_subsection">
2067 <a name="TypeResolve">LLVM Type Resolution</a>
2068</div>
Chris Lattnerd9d6e102005-04-23 16:10:52 +0000[diff] [blame]2069
Chris Lattnerf1b200b2005-04-23 17:27:36 +0000[diff] [blame]2070<div class="doc_text">
2071
2072<p>
2073The LLVM type system has a very simple goal: allow clients to compare types for
2074structural equality with a simple pointer comparison (aka a shallow compare).
2075This goal makes clients much simpler and faster, and is used throughout the LLVM
2076system.
2077</p>
2078
2079<p>
2080Unfortunately achieving this goal is not a simple matter. In particular,
2081recursive types and late resolution of opaque types makes the situation very
2082difficult to handle. Fortunately, for the most part, our implementation makes
2083most clients able to be completely unaware of the nasty internal details. The
2084primary case where clients are exposed to the inner workings of it are when
Gabor Greif04367bf2007-07-06 22:07:22 +0000[diff] [blame]2085building a recursive type. In addition to this case, the LLVM bitcode reader,
Chris Lattnerf1b200b2005-04-23 17:27:36 +0000[diff] [blame]2086assembly parser, and linker also have to be aware of the inner workings of this
2087system.
2088</p>
2089
Chris Lattner0f876db2005-04-25 15:47:57 +0000[diff] [blame]2090<p>
2091For our purposes below, we need three concepts. First, an "Opaque Type" is
2092exactly as defined in the <a href="LangRef.html#t_opaque">language
2093reference</a>. Second an "Abstract Type" is any type which includes an
Reid Spencer06565dc2007-01-12 17:11:23 +0000[diff] [blame]2094opaque type as part of its type graph (for example "<tt>{ opaque, i32 }</tt>").
2095Third, 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]2096float }</tt>").
2097</p>
2098
Chris Lattnerf1b200b2005-04-23 17:27:36 +0000[diff] [blame]2099</div>
2100
2101<!-- ______________________________________________________________________ -->
2102<div class="doc_subsubsection">
2103 <a name="BuildRecType">Basic Recursive Type Construction</a>
2104</div>
2105
2106<div class="doc_text">
2107
2108<p>
2109Because the most common question is "how do I build a recursive type with LLVM",
2110we answer it now and explain it as we go. Here we include enough to cause this
2111to be emitted to an output .ll file:
2112</p>
2113
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2114<div class="doc_code">
Chris Lattnerf1b200b2005-04-23 17:27:36 +0000[diff] [blame]2115<pre>
Reid Spencer06565dc2007-01-12 17:11:23 +0000[diff] [blame]2116%mylist = type { %mylist*, i32 }
Chris Lattnerf1b200b2005-04-23 17:27:36 +0000[diff] [blame]2117</pre>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2118</div>
Chris Lattnerf1b200b2005-04-23 17:27:36 +0000[diff] [blame]2119
2120<p>
2121To build this, use the following LLVM APIs:
2122</p>
2123
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2124<div class="doc_code">
Chris Lattnerf1b200b2005-04-23 17:27:36 +0000[diff] [blame]2125<pre>
Bill Wendling82e2eea2006-10-11 18:00:22 +0000[diff] [blame]2126// <i>Create the initial outer struct</i>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2127<a href="#PATypeHolder">PATypeHolder</a> StructTy = OpaqueType::get();
2128std::vector&lt;const Type*&gt; Elts;
Daniel Dunbar58c2ac02008-10-03 22:17:25 +0000[diff] [blame]2129Elts.push_back(PointerType::getUnqual(StructTy));
Nick Lewycky10d64b92007-12-03 01:52:52 +0000[diff] [blame]2130Elts.push_back(Type::Int32Ty);
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2131StructType *NewSTy = StructType::get(Elts);
Chris Lattnerf1b200b2005-04-23 17:27:36 +0000[diff] [blame]2132
Reid Spencer06565dc2007-01-12 17:11:23 +0000[diff] [blame]2133// <i>At this point, NewSTy = "{ opaque*, i32 }". Tell VMCore that</i>
Bill Wendling82e2eea2006-10-11 18:00:22 +0000[diff] [blame]2134// <i>the struct and the opaque type are actually the same.</i>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2135cast&lt;OpaqueType&gt;(StructTy.get())-&gt;<a href="#refineAbstractTypeTo">refineAbstractTypeTo</a>(NewSTy);
Chris Lattnerf1b200b2005-04-23 17:27:36 +0000[diff] [blame]2136
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2137// <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]2138// <i>kept up-to-date</i>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2139NewSTy = cast&lt;StructType&gt;(StructTy.get());
Chris Lattnerf1b200b2005-04-23 17:27:36 +0000[diff] [blame]2140
Bill Wendling82e2eea2006-10-11 18:00:22 +0000[diff] [blame]2141// <i>Add a name for the type to the module symbol table (optional)</i>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2142MyModule-&gt;addTypeName("mylist", NewSTy);
Chris Lattnerf1b200b2005-04-23 17:27:36 +0000[diff] [blame]2143</pre>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2144</div>
Chris Lattnerf1b200b2005-04-23 17:27:36 +0000[diff] [blame]2145
2146<p>
2147This code shows the basic approach used to build recursive types: build a
2148non-recursive type using 'opaque', then use type unification to close the cycle.
2149The type unification step is performed by the <tt><a
Chris Lattneraff26d12007-02-03 03:06:52 +0000[diff] [blame]2150href="#refineAbstractTypeTo">refineAbstractTypeTo</a></tt> method, which is
Chris Lattnerf1b200b2005-04-23 17:27:36 +0000[diff] [blame]2151described next. After that, we describe the <a
2152href="#PATypeHolder">PATypeHolder class</a>.
2153</p>
2154
2155</div>
2156
2157<!-- ______________________________________________________________________ -->
2158<div class="doc_subsubsection">
2159 <a name="refineAbstractTypeTo">The <tt>refineAbstractTypeTo</tt> method</a>
2160</div>
2161
2162<div class="doc_text">
2163<p>
2164The <tt>refineAbstractTypeTo</tt> method starts the type unification process.
2165While this method is actually a member of the DerivedType class, it is most
2166often used on OpaqueType instances. Type unification is actually a recursive
2167process. After unification, types can become structurally isomorphic to
2168existing types, and all duplicates are deleted (to preserve pointer equality).
2169</p>
2170
2171<p>
2172In the example above, the OpaqueType object is definitely deleted.
Reid Spencer06565dc2007-01-12 17:11:23 +0000[diff] [blame]2173Additionally, if there is an "{ \2*, i32}" type already created in the system,
Chris Lattnerf1b200b2005-04-23 17:27:36 +0000[diff] [blame]2174the pointer and struct type created are <b>also</b> deleted. Obviously whenever
2175a type is deleted, any "Type*" pointers in the program are invalidated. As
2176such, it is safest to avoid having <i>any</i> "Type*" pointers to abstract types
2177live across a call to <tt>refineAbstractTypeTo</tt> (note that non-abstract
2178types can never move or be deleted). To deal with this, the <a
2179href="#PATypeHolder">PATypeHolder</a> class is used to maintain a stable
2180reference to a possibly refined type, and the <a
2181href="#AbstractTypeUser">AbstractTypeUser</a> class is used to update more
2182complex datastructures.
2183</p>
2184
2185</div>
2186
2187<!-- ______________________________________________________________________ -->
2188<div class="doc_subsubsection">
2189 <a name="PATypeHolder">The PATypeHolder Class</a>
2190</div>
2191
2192<div class="doc_text">
2193<p>
2194PATypeHolder is a form of a "smart pointer" for Type objects. When VMCore
2195happily goes about nuking types that become isomorphic to existing types, it
2196automatically updates all PATypeHolder objects to point to the new type. In the
2197example above, this allows the code to maintain a pointer to the resultant
2198resolved recursive type, even though the Type*'s are potentially invalidated.
2199</p>
2200
2201<p>
2202PATypeHolder is an extremely light-weight object that uses a lazy union-find
2203implementation to update pointers. For example the pointer from a Value to its
2204Type is maintained by PATypeHolder objects.
2205</p>
2206
2207</div>
2208
2209<!-- ______________________________________________________________________ -->
2210<div class="doc_subsubsection">
2211 <a name="AbstractTypeUser">The AbstractTypeUser Class</a>
2212</div>
2213
2214<div class="doc_text">
2215
2216<p>
2217Some data structures need more to perform more complex updates when types get
Chris Lattner263a98e2007-02-16 04:37:31 +0000[diff] [blame]2218resolved. To support this, a class can derive from the AbstractTypeUser class.
2219This class
Chris Lattnerf1b200b2005-04-23 17:27:36 +0000[diff] [blame]2220allows it to get callbacks when certain types are resolved. To register to get
2221callbacks for a particular type, the DerivedType::{add/remove}AbstractTypeUser
Chris Lattner0f876db2005-04-25 15:47:57 +0000[diff] [blame]2222methods can be called on a type. Note that these methods only work for <i>
Reid Spencer06565dc2007-01-12 17:11:23 +0000[diff] [blame]2223 abstract</i> types. Concrete types (those that do not include any opaque
2224objects) can never be refined.
Chris Lattnerf1b200b2005-04-23 17:27:36 +0000[diff] [blame]2225</p>
Chris Lattnerd9d6e102005-04-23 16:10:52 +0000[diff] [blame]2226</div>
2227
2228
2229<!-- ======================================================================= -->
2230<div class="doc_subsection">
Chris Lattner263a98e2007-02-16 04:37:31 +0000[diff] [blame]2231 <a name="SymbolTable">The <tt>ValueSymbolTable</tt> and
2232 <tt>TypeSymbolTable</tt> classes</a>
Chris Lattnerd9d6e102005-04-23 16:10:52 +0000[diff] [blame]2233</div>
Chris Lattnerf1b200b2005-04-23 17:27:36 +0000[diff] [blame]2234
Chris Lattnerd9d6e102005-04-23 16:10:52 +0000[diff] [blame]2235<div class="doc_text">
Chris Lattner263a98e2007-02-16 04:37:31 +0000[diff] [blame]2236<p>The <tt><a href="http://llvm.org/doxygen/classllvm_1_1ValueSymbolTable.html">
2237ValueSymbolTable</a></tt> class provides a symbol table that the <a
Chris Lattnerd9d6e102005-04-23 16:10:52 +0000[diff] [blame]2238href="#Function"><tt>Function</tt></a> and <a href="#Module">
Chris Lattner263a98e2007-02-16 04:37:31 +0000[diff] [blame]2239<tt>Module</tt></a> classes use for naming value definitions. The symbol table
2240can provide a name for any <a href="#Value"><tt>Value</tt></a>.
2241The <tt><a href="http://llvm.org/doxygen/classllvm_1_1TypeSymbolTable.html">
2242TypeSymbolTable</a></tt> class is used by the <tt>Module</tt> class to store
2243names for types.</p>
Chris Lattnerd9d6e102005-04-23 16:10:52 +0000[diff] [blame]2244
Reid Spencera6362242007-01-07 00:41:39 +0000[diff] [blame]2245<p>Note that the <tt>SymbolTable</tt> class should not be directly accessed
2246by most clients. It should only be used when iteration over the symbol table
2247names themselves are required, which is very special purpose. Note that not
2248all LLVM
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2249<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]2250an empty name) do not exist in the symbol table.
2251</p>
2252
Chris Lattner263a98e2007-02-16 04:37:31 +0000[diff] [blame]2253<p>These symbol tables support iteration over the values/types in the symbol
2254table with <tt>begin/end/iterator</tt> and supports querying to see if a
2255specific name is in the symbol table (with <tt>lookup</tt>). The
2256<tt>ValueSymbolTable</tt> class exposes no public mutator methods, instead,
2257simply call <tt>setName</tt> on a value, which will autoinsert it into the
2258appropriate symbol table. For types, use the Module::addTypeName method to
2259insert entries into the symbol table.</p>
Chris Lattnerd9d6e102005-04-23 16:10:52 +0000[diff] [blame]2260
Chris Lattnerd9d6e102005-04-23 16:10:52 +0000[diff] [blame]2261</div>
2262
2263
2264
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2265<!-- ======================================================================= -->
2266<div class="doc_subsection">
2267 <a name="UserLayout">The <tt>User</tt> and owned <tt>Use</tt> classes' memory layout</a>
2268</div>
2269
2270<div class="doc_text">
2271<p>The <tt><a href="http://llvm.org/doxygen/classllvm_1_1User.html">
Gabor Greiffd095b62009-01-05 16:05:32 +0000[diff] [blame]2272User</a></tt> class provides a basis for expressing the ownership of <tt>User</tt>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2273towards other <tt><a href="http://llvm.org/doxygen/classllvm_1_1Value.html">
2274Value</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]2275Use</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]2276addition and removal.</p>
2277
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2278<!-- ______________________________________________________________________ -->
2279<div class="doc_subsubsection">
Gabor Greiffd095b62009-01-05 16:05:32 +0000[diff] [blame]2280 <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]2281</div>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2282
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2283<div class="doc_text">
2284<p>
2285A subclass of <tt>User</tt> can choose between incorporating its <tt>Use</tt> objects
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2286or refer to them out-of-line by means of a pointer. A mixed variant
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2287(some <tt>Use</tt>s inline others hung off) is impractical and breaks the invariant
2288that the <tt>Use</tt> objects belonging to the same <tt>User</tt> form a contiguous array.
2289</p>
2290</div>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2291
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2292<p>
2293We have 2 different layouts in the <tt>User</tt> (sub)classes:
2294<ul>
2295<li><p>Layout a)
2296The <tt>Use</tt> object(s) are inside (resp. at fixed offset) of the <tt>User</tt>
2297object and there are a fixed number of them.</p>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2298
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2299<li><p>Layout b)
2300The <tt>Use</tt> object(s) are referenced by a pointer to an
2301array from the <tt>User</tt> object and there may be a variable
2302number of them.</p>
2303</ul>
2304<p>
Gabor Greifd41720a2008-06-25 00:10:22 +0000[diff] [blame]2305As of v2.4 each layout still possesses a direct pointer to the
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2306start of the array of <tt>Use</tt>s. Though not mandatory for layout a),
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2307we stick to this redundancy for the sake of simplicity.
Gabor Greifd41720a2008-06-25 00:10:22 +0000[diff] [blame]2308The <tt>User</tt> object also stores the number of <tt>Use</tt> objects it
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2309has. (Theoretically this information can also be calculated
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2310given the scheme presented below.)</p>
2311<p>
2312Special forms of allocation operators (<tt>operator new</tt>)
Gabor Greifd41720a2008-06-25 00:10:22 +0000[diff] [blame]2313enforce the following memory layouts:</p>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2314
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2315<ul>
Gabor Greifd41720a2008-06-25 00:10:22 +0000[diff] [blame]2316<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]2317
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2318<pre>
2319...---.---.---.---.-------...
2320 | P | P | P | P | User
2321'''---'---'---'---'-------'''
2322</pre>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2323
Gabor Greifd41720a2008-06-25 00:10:22 +0000[diff] [blame]2324<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]2325<pre>
2326.-------...
2327| User
2328'-------'''
2329 |
2330 v
2331 .---.---.---.---...
2332 | P | P | P | P |
2333 '---'---'---'---'''
2334</pre>
2335</ul>
2336<i>(In the above figures '<tt>P</tt>' stands for the <tt>Use**</tt> that
2337 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]2338
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2339<!-- ______________________________________________________________________ -->
2340<div class="doc_subsubsection">
Gabor Greiffd095b62009-01-05 16:05:32 +0000[diff] [blame]2341 <a name="Waymarking">The waymarking algorithm</a>
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2342</div>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2343
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2344<div class="doc_text">
2345<p>
Gabor Greifd41720a2008-06-25 00:10:22 +0000[diff] [blame]2346Since the <tt>Use</tt> objects are deprived of the direct (back)pointer to
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2347their <tt>User</tt> objects, there must be a fast and exact method to
2348recover it. This is accomplished by the following scheme:</p>
2349</div>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2350
Gabor Greifd41720a2008-06-25 00:10:22 +0000[diff] [blame]2351A 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]2352start of the <tt>User</tt> object:
2353<ul>
2354<li><tt>00</tt> &mdash;&gt; binary digit 0</li>
2355<li><tt>01</tt> &mdash;&gt; binary digit 1</li>
2356<li><tt>10</tt> &mdash;&gt; stop and calculate (<tt>s</tt>)</li>
2357<li><tt>11</tt> &mdash;&gt; full stop (<tt>S</tt>)</li>
2358</ul>
2359<p>
2360Given a <tt>Use*</tt>, all we have to do is to walk till we get
2361a stop and we either have a <tt>User</tt> immediately behind or
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2362we have to walk to the next stop picking up digits
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2363and calculating the offset:</p>
2364<pre>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2365.---.---.---.---.---.---.---.---.---.---.---.---.---.---.---.---.----------------
2366| 1 | s | 1 | 0 | 1 | 0 | s | 1 | 1 | 0 | s | 1 | 1 | s | 1 | S | User (or User*)
2367'---'---'---'---'---'---'---'---'---'---'---'---'---'---'---'---'----------------
2368 |+15 |+10 |+6 |+3 |+1
2369 | | | | |__>
2370 | | | |__________>
2371 | | |______________________>
2372 | |______________________________________>
2373 |__________________________________________________________>
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2374</pre>
2375<p>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2376Only the significant number of bits need to be stored between the
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2377stops, so that the <i>worst case is 20 memory accesses</i> when there are
23781000 <tt>Use</tt> objects associated with a <tt>User</tt>.</p>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2379
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2380<!-- ______________________________________________________________________ -->
2381<div class="doc_subsubsection">
Gabor Greiffd095b62009-01-05 16:05:32 +0000[diff] [blame]2382 <a name="ReferenceImpl">Reference implementation</a>
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2383</div>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2384
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2385<div class="doc_text">
2386<p>
2387The following literate Haskell fragment demonstrates the concept:</p>
2388</div>
2389
2390<div class="doc_code">
2391<pre>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2392> import Test.QuickCheck
2393>
2394> digits :: Int -> [Char] -> [Char]
2395> digits 0 acc = '0' : acc
2396> digits 1 acc = '1' : acc
2397> digits n acc = digits (n `div` 2) $ digits (n `mod` 2) acc
2398>
2399> dist :: Int -> [Char] -> [Char]
2400> dist 0 [] = ['S']
2401> dist 0 acc = acc
2402> dist 1 acc = let r = dist 0 acc in 's' : digits (length r) r
2403> dist n acc = dist (n - 1) $ dist 1 acc
2404>
2405> takeLast n ss = reverse $ take n $ reverse ss
2406>
2407> test = takeLast 40 $ dist 20 []
2408>
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2409</pre>
2410</div>
2411<p>
2412Printing &lt;test&gt; gives: <tt>"1s100000s11010s10100s1111s1010s110s11s1S"</tt></p>
2413<p>
2414The reverse algorithm computes the length of the string just by examining
2415a certain prefix:</p>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2416
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2417<div class="doc_code">
2418<pre>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2419> pref :: [Char] -> Int
2420> pref "S" = 1
2421> pref ('s':'1':rest) = decode 2 1 rest
2422> pref (_:rest) = 1 + pref rest
2423>
2424> decode walk acc ('0':rest) = decode (walk + 1) (acc * 2) rest
2425> decode walk acc ('1':rest) = decode (walk + 1) (acc * 2 + 1) rest
2426> decode walk acc _ = walk + acc
2427>
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2428</pre>
2429</div>
2430<p>
2431Now, as expected, printing &lt;pref test&gt; gives <tt>40</tt>.</p>
2432<p>
2433We can <i>quickCheck</i> this with following property:</p>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2434
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2435<div class="doc_code">
2436<pre>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2437> testcase = dist 2000 []
2438> testcaseLength = length testcase
2439>
2440> identityProp n = n > 0 && n <= testcaseLength ==> length arr == pref arr
2441> where arr = takeLast n testcase
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2442>
2443</pre>
2444</div>
2445<p>
2446As expected &lt;quickCheck identityProp&gt; gives:</p>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2447
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2448<pre>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2449*Main> quickCheck identityProp
2450OK, passed 100 tests.
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2451</pre>
2452<p>
2453Let's be a bit more exhaustive:</p>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2454
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2455<div class="doc_code">
2456<pre>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2457>
2458> deepCheck p = check (defaultConfig { configMaxTest = 500 }) p
2459>
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2460</pre>
2461</div>
2462<p>
2463And here is the result of &lt;deepCheck identityProp&gt;:</p>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2464
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2465<pre>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2466*Main> deepCheck identityProp
2467OK, passed 500 tests.
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2468</pre>
2469
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2470<!-- ______________________________________________________________________ -->
2471<div class="doc_subsubsection">
Gabor Greiffd095b62009-01-05 16:05:32 +0000[diff] [blame]2472 <a name="Tagging">Tagging considerations</a>
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2473</div>
2474
2475<p>
2476To maintain the invariant that the 2 LSBits of each <tt>Use**</tt> in <tt>Use</tt>
2477never change after being set up, setters of <tt>Use::Prev</tt> must re-tag the
2478new <tt>Use**</tt> on every modification. Accordingly getters must strip the
2479tag bits.</p>
2480<p>
Gabor Greifd41720a2008-06-25 00:10:22 +0000[diff] [blame]2481For layout b) instead of the <tt>User</tt> we find a pointer (<tt>User*</tt> with LSBit set).
2482Following this pointer brings us to the <tt>User</tt>. A portable trick ensures
2483that the first bytes of <tt>User</tt> (if interpreted as a pointer) never has
Gabor Greiffd095b62009-01-05 16:05:32 +0000[diff] [blame]2484the LSBit set. (Portability is relying on the fact that all known compilers place the
2485<tt>vptr</tt> in the first word of the instances.)</p>
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2486
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2487</div>
2488
2489 <!-- *********************************************************************** -->
Chris Lattnerd9d6e102005-04-23 16:10:52 +0000[diff] [blame]2490<div class="doc_section">
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2491 <a name="coreclasses">The Core LLVM Class Hierarchy Reference </a>
2492</div>
2493<!-- *********************************************************************** -->
2494
2495<div class="doc_text">
Reid Spencer303c4b42007-01-12 17:26:25 +0000[diff] [blame]2496<p><tt>#include "<a href="/doxygen/Type_8h-source.html">llvm/Type.h</a>"</tt>
2497<br>doxygen info: <a href="/doxygen/classllvm_1_1Type.html">Type Class</a></p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2498
2499<p>The Core LLVM classes are the primary means of representing the program
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]2500being inspected or transformed. The core LLVM classes are defined in
2501header files in the <tt>include/llvm/</tt> directory, and implemented in
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2502the <tt>lib/VMCore</tt> directory.</p>
2503
2504</div>
2505
2506<!-- ======================================================================= -->
2507<div class="doc_subsection">
Reid Spencer303c4b42007-01-12 17:26:25 +0000[diff] [blame]2508 <a name="Type">The <tt>Type</tt> class and Derived Types</a>
2509</div>
2510
2511<div class="doc_text">
2512
2513 <p><tt>Type</tt> is a superclass of all type classes. Every <tt>Value</tt> has
2514 a <tt>Type</tt>. <tt>Type</tt> cannot be instantiated directly but only
2515 through its subclasses. Certain primitive types (<tt>VoidType</tt>,
2516 <tt>LabelType</tt>, <tt>FloatType</tt> and <tt>DoubleType</tt>) have hidden
2517 subclasses. They are hidden because they offer no useful functionality beyond
2518 what the <tt>Type</tt> class offers except to distinguish themselves from
2519 other subclasses of <tt>Type</tt>.</p>
2520 <p>All other types are subclasses of <tt>DerivedType</tt>. Types can be
2521 named, but this is not a requirement. There exists exactly
2522 one instance of a given shape at any one time. This allows type equality to
2523 be performed with address equality of the Type Instance. That is, given two
2524 <tt>Type*</tt> values, the types are identical if the pointers are identical.
2525 </p>
2526</div>
2527
2528<!-- _______________________________________________________________________ -->
2529<div class="doc_subsubsection">
Gabor Greiffd095b62009-01-05 16:05:32 +0000[diff] [blame]2530 <a name="m_Type">Important Public Methods</a>
Reid Spencer303c4b42007-01-12 17:26:25 +0000[diff] [blame]2531</div>
2532
2533<div class="doc_text">
2534
2535<ul>
Chris Lattner8f79df32007-01-15 01:55:32 +0000[diff] [blame]2536 <li><tt>bool isInteger() const</tt>: Returns true for any integer type.</li>
Reid Spencer303c4b42007-01-12 17:26:25 +0000[diff] [blame]2537
2538 <li><tt>bool isFloatingPoint()</tt>: Return true if this is one of the two
2539 floating point types.</li>
2540
2541 <li><tt>bool isAbstract()</tt>: Return true if the type is abstract (contains
2542 an OpaqueType anywhere in its definition).</li>
2543
2544 <li><tt>bool isSized()</tt>: Return true if the type has known size. Things
2545 that don't have a size are abstract types, labels and void.</li>
2546
2547</ul>
2548</div>
2549
2550<!-- _______________________________________________________________________ -->
2551<div class="doc_subsubsection">
Gabor Greiffd095b62009-01-05 16:05:32 +0000[diff] [blame]2552 <a name="derivedtypes">Important Derived Types</a>
Reid Spencer303c4b42007-01-12 17:26:25 +0000[diff] [blame]2553</div>
2554<div class="doc_text">
2555<dl>
2556 <dt><tt>IntegerType</tt></dt>
2557 <dd>Subclass of DerivedType that represents integer types of any bit width.
2558 Any bit width between <tt>IntegerType::MIN_INT_BITS</tt> (1) and
2559 <tt>IntegerType::MAX_INT_BITS</tt> (~8 million) can be represented.
2560 <ul>
2561 <li><tt>static const IntegerType* get(unsigned NumBits)</tt>: get an integer
2562 type of a specific bit width.</li>
2563 <li><tt>unsigned getBitWidth() const</tt>: Get the bit width of an integer
2564 type.</li>
2565 </ul>
2566 </dd>
2567 <dt><tt>SequentialType</tt></dt>
2568 <dd>This is subclassed by ArrayType and PointerType
2569 <ul>
2570 <li><tt>const Type * getElementType() const</tt>: Returns the type of each
2571 of the elements in the sequential type. </li>
2572 </ul>
2573 </dd>
2574 <dt><tt>ArrayType</tt></dt>
2575 <dd>This is a subclass of SequentialType and defines the interface for array
2576 types.
2577 <ul>
2578 <li><tt>unsigned getNumElements() const</tt>: Returns the number of
2579 elements in the array. </li>
2580 </ul>
2581 </dd>
2582 <dt><tt>PointerType</tt></dt>
Chris Lattner302da1e2007-02-03 03:05:57 +0000[diff] [blame]2583 <dd>Subclass of SequentialType for pointer types.</dd>
Reid Spencer9d6565a2007-02-15 02:26:10 +0000[diff] [blame]2584 <dt><tt>VectorType</tt></dt>
Reid Spencer485bad12007-02-15 03:07:05 +0000[diff] [blame]2585 <dd>Subclass of SequentialType for vector types. A
2586 vector type is similar to an ArrayType but is distinguished because it is
2587 a first class type wherease ArrayType is not. Vector types are used for
Reid Spencer303c4b42007-01-12 17:26:25 +0000[diff] [blame]2588 vector operations and are usually small vectors of of an integer or floating
2589 point type.</dd>
2590 <dt><tt>StructType</tt></dt>
2591 <dd>Subclass of DerivedTypes for struct types.</dd>
Duncan Sands8036ca42007-03-30 12:22:09 +0000[diff] [blame]2592 <dt><tt><a name="FunctionType">FunctionType</a></tt></dt>
Reid Spencer303c4b42007-01-12 17:26:25 +0000[diff] [blame]2593 <dd>Subclass of DerivedTypes for function types.
2594 <ul>
2595 <li><tt>bool isVarArg() const</tt>: Returns true if its a vararg
2596 function</li>
2597 <li><tt> const Type * getReturnType() const</tt>: Returns the
2598 return type of the function.</li>
2599 <li><tt>const Type * getParamType (unsigned i)</tt>: Returns
2600 the type of the ith parameter.</li>
2601 <li><tt> const unsigned getNumParams() const</tt>: Returns the
2602 number of formal parameters.</li>
2603 </ul>
2604 </dd>
2605 <dt><tt>OpaqueType</tt></dt>
2606 <dd>Sublcass of DerivedType for abstract types. This class
2607 defines no content and is used as a placeholder for some other type. Note
2608 that OpaqueType is used (temporarily) during type resolution for forward
2609 references of types. Once the referenced type is resolved, the OpaqueType
2610 is replaced with the actual type. OpaqueType can also be used for data
2611 abstraction. At link time opaque types can be resolved to actual types
2612 of the same name.</dd>
2613</dl>
2614</div>
2615
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]2616
2617
2618<!-- ======================================================================= -->
2619<div class="doc_subsection">
2620 <a name="Module">The <tt>Module</tt> class</a>
2621</div>
2622
2623<div class="doc_text">
2624
2625<p><tt>#include "<a
2626href="/doxygen/Module_8h-source.html">llvm/Module.h</a>"</tt><br> doxygen info:
2627<a href="/doxygen/classllvm_1_1Module.html">Module Class</a></p>
2628
2629<p>The <tt>Module</tt> class represents the top level structure present in LLVM
2630programs. An LLVM module is effectively either a translation unit of the
2631original program or a combination of several translation units merged by the
2632linker. The <tt>Module</tt> class keeps track of a list of <a
2633href="#Function"><tt>Function</tt></a>s, a list of <a
2634href="#GlobalVariable"><tt>GlobalVariable</tt></a>s, and a <a
2635href="#SymbolTable"><tt>SymbolTable</tt></a>. Additionally, it contains a few
2636helpful member functions that try to make common operations easy.</p>
2637
2638</div>
2639
2640<!-- _______________________________________________________________________ -->
2641<div class="doc_subsubsection">
2642 <a name="m_Module">Important Public Members of the <tt>Module</tt> class</a>
2643</div>
2644
2645<div class="doc_text">
2646
2647<ul>
2648 <li><tt>Module::Module(std::string name = "")</tt></li>
2649</ul>
2650
2651<p>Constructing a <a href="#Module">Module</a> is easy. You can optionally
2652provide a name for it (probably based on the name of the translation unit).</p>
2653
2654<ul>
2655 <li><tt>Module::iterator</tt> - Typedef for function list iterator<br>
2656 <tt>Module::const_iterator</tt> - Typedef for const_iterator.<br>
2657
2658 <tt>begin()</tt>, <tt>end()</tt>
2659 <tt>size()</tt>, <tt>empty()</tt>
2660
2661 <p>These are forwarding methods that make it easy to access the contents of
2662 a <tt>Module</tt> object's <a href="#Function"><tt>Function</tt></a>
2663 list.</p></li>
2664
2665 <li><tt>Module::FunctionListType &amp;getFunctionList()</tt>
2666
2667 <p> Returns the list of <a href="#Function"><tt>Function</tt></a>s. This is
2668 necessary to use when you need to update the list or perform a complex
2669 action that doesn't have a forwarding method.</p>
2670
2671 <p><!-- Global Variable --></p></li>
2672</ul>
2673
2674<hr>
2675
2676<ul>
2677 <li><tt>Module::global_iterator</tt> - Typedef for global variable list iterator<br>
2678
2679 <tt>Module::const_global_iterator</tt> - Typedef for const_iterator.<br>
2680
2681 <tt>global_begin()</tt>, <tt>global_end()</tt>
2682 <tt>global_size()</tt>, <tt>global_empty()</tt>
2683
2684 <p> These are forwarding methods that make it easy to access the contents of
2685 a <tt>Module</tt> object's <a
2686 href="#GlobalVariable"><tt>GlobalVariable</tt></a> list.</p></li>
2687
2688 <li><tt>Module::GlobalListType &amp;getGlobalList()</tt>
2689
2690 <p>Returns the list of <a
2691 href="#GlobalVariable"><tt>GlobalVariable</tt></a>s. This is necessary to
2692 use when you need to update the list or perform a complex action that
2693 doesn't have a forwarding method.</p>
2694
2695 <p><!-- Symbol table stuff --> </p></li>
2696</ul>
2697
2698<hr>
2699
2700<ul>
2701 <li><tt><a href="#SymbolTable">SymbolTable</a> *getSymbolTable()</tt>
2702
2703 <p>Return a reference to the <a href="#SymbolTable"><tt>SymbolTable</tt></a>
2704 for this <tt>Module</tt>.</p>
2705
2706 <p><!-- Convenience methods --></p></li>
2707</ul>
2708
2709<hr>
2710
2711<ul>
2712 <li><tt><a href="#Function">Function</a> *getFunction(const std::string
2713 &amp;Name, const <a href="#FunctionType">FunctionType</a> *Ty)</tt>
2714
2715 <p>Look up the specified function in the <tt>Module</tt> <a
2716 href="#SymbolTable"><tt>SymbolTable</tt></a>. If it does not exist, return
2717 <tt>null</tt>.</p></li>
2718
2719 <li><tt><a href="#Function">Function</a> *getOrInsertFunction(const
2720 std::string &amp;Name, const <a href="#FunctionType">FunctionType</a> *T)</tt>
2721
2722 <p>Look up the specified function in the <tt>Module</tt> <a
2723 href="#SymbolTable"><tt>SymbolTable</tt></a>. If it does not exist, add an
2724 external declaration for the function and return it.</p></li>
2725
2726 <li><tt>std::string getTypeName(const <a href="#Type">Type</a> *Ty)</tt>
2727
2728 <p>If there is at least one entry in the <a
2729 href="#SymbolTable"><tt>SymbolTable</tt></a> for the specified <a
2730 href="#Type"><tt>Type</tt></a>, return it. Otherwise return the empty
2731 string.</p></li>
2732
2733 <li><tt>bool addTypeName(const std::string &amp;Name, const <a
2734 href="#Type">Type</a> *Ty)</tt>
2735
2736 <p>Insert an entry in the <a href="#SymbolTable"><tt>SymbolTable</tt></a>
2737 mapping <tt>Name</tt> to <tt>Ty</tt>. If there is already an entry for this
2738 name, true is returned and the <a
2739 href="#SymbolTable"><tt>SymbolTable</tt></a> is not modified.</p></li>
2740</ul>
2741
2742</div>
2743
2744
Reid Spencer303c4b42007-01-12 17:26:25 +0000[diff] [blame]2745<!-- ======================================================================= -->
2746<div class="doc_subsection">
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2747 <a name="Value">The <tt>Value</tt> class</a>
2748</div>
2749
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]2750<div class="doc_text">
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2751
2752<p><tt>#include "<a href="/doxygen/Value_8h-source.html">llvm/Value.h</a>"</tt>
2753<br>
Chris Lattner00815172007-01-04 22:01:45 +0000[diff] [blame]2754doxygen info: <a href="/doxygen/classllvm_1_1Value.html">Value Class</a></p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2755
2756<p>The <tt>Value</tt> class is the most important class in the LLVM Source
2757base. It represents a typed value that may be used (among other things) as an
2758operand to an instruction. There are many different types of <tt>Value</tt>s,
2759such as <a href="#Constant"><tt>Constant</tt></a>s,<a
2760href="#Argument"><tt>Argument</tt></a>s. Even <a
2761href="#Instruction"><tt>Instruction</tt></a>s and <a
2762href="#Function"><tt>Function</tt></a>s are <tt>Value</tt>s.</p>
2763
2764<p>A particular <tt>Value</tt> may be used many times in the LLVM representation
2765for a program. For example, an incoming argument to a function (represented
2766with an instance of the <a href="#Argument">Argument</a> class) is "used" by
2767every instruction in the function that references the argument. To keep track
2768of this relationship, the <tt>Value</tt> class keeps a list of all of the <a
2769href="#User"><tt>User</tt></a>s that is using it (the <a
2770href="#User"><tt>User</tt></a> class is a base class for all nodes in the LLVM
2771graph that can refer to <tt>Value</tt>s). This use list is how LLVM represents
2772def-use information in the program, and is accessible through the <tt>use_</tt>*
2773methods, shown below.</p>
2774
2775<p>Because LLVM is a typed representation, every LLVM <tt>Value</tt> is typed,
2776and this <a href="#Type">Type</a> is available through the <tt>getType()</tt>
2777method. In addition, all LLVM values can be named. The "name" of the
2778<tt>Value</tt> is a symbolic string printed in the LLVM code:</p>
2779
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2780<div class="doc_code">
2781<pre>
Reid Spencer06565dc2007-01-12 17:11:23 +0000[diff] [blame]2782%<b>foo</b> = add i32 1, 2
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2783</pre>
2784</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2785
Duncan Sands8036ca42007-03-30 12:22:09 +0000[diff] [blame]2786<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]2787that the name of any value may be missing (an empty string), so names should
2788<b>ONLY</b> be used for debugging (making the source code easier to read,
2789debugging printouts), they should not be used to keep track of values or map
2790between them. For this purpose, use a <tt>std::map</tt> of pointers to the
2791<tt>Value</tt> itself instead.</p>
2792
2793<p>One important aspect of LLVM is that there is no distinction between an SSA
2794variable and the operation that produces it. Because of this, any reference to
2795the value produced by an instruction (or the value available as an incoming
Chris Lattnerd5fc4fc2004-03-18 14:58:55 +0000[diff] [blame]2796argument, for example) is represented as a direct pointer to the instance of
2797the class that
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2798represents this value. Although this may take some getting used to, it
2799simplifies the representation and makes it easier to manipulate.</p>
2800
2801</div>
2802
2803<!-- _______________________________________________________________________ -->
2804<div class="doc_subsubsection">
2805 <a name="m_Value">Important Public Members of the <tt>Value</tt> class</a>
2806</div>
2807
2808<div class="doc_text">
2809
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]2810<ul>
2811 <li><tt>Value::use_iterator</tt> - Typedef for iterator over the
2812use-list<br>
2813 <tt>Value::use_const_iterator</tt> - Typedef for const_iterator over
2814the use-list<br>
2815 <tt>unsigned use_size()</tt> - Returns the number of users of the
2816value.<br>
Chris Lattner9355b472002-09-06 02:50:58 +0000[diff] [blame]2817 <tt>bool use_empty()</tt> - Returns true if there are no users.<br>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]2818 <tt>use_iterator use_begin()</tt> - Get an iterator to the start of
2819the use-list.<br>
2820 <tt>use_iterator use_end()</tt> - Get an iterator to the end of the
2821use-list.<br>
2822 <tt><a href="#User">User</a> *use_back()</tt> - Returns the last
2823element in the list.
2824 <p> These methods are the interface to access the def-use
2825information in LLVM. As with all other iterators in LLVM, the naming
2826conventions follow the conventions defined by the <a href="#stl">STL</a>.</p>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]2827 </li>
2828 <li><tt><a href="#Type">Type</a> *getType() const</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2829 <p>This method returns the Type of the Value.</p>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]2830 </li>
2831 <li><tt>bool hasName() const</tt><br>
Chris Lattner9355b472002-09-06 02:50:58 +0000[diff] [blame]2832 <tt>std::string getName() const</tt><br>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]2833 <tt>void setName(const std::string &amp;Name)</tt>
2834 <p> This family of methods is used to access and assign a name to a <tt>Value</tt>,
2835be aware of the <a href="#nameWarning">precaution above</a>.</p>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]2836 </li>
2837 <li><tt>void replaceAllUsesWith(Value *V)</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2838
2839 <p>This method traverses the use list of a <tt>Value</tt> changing all <a
2840 href="#User"><tt>User</tt>s</a> of the current value to refer to
2841 "<tt>V</tt>" instead. For example, if you detect that an instruction always
2842 produces a constant value (for example through constant folding), you can
2843 replace all uses of the instruction with the constant like this:</p>
2844
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2845<div class="doc_code">
2846<pre>
2847Inst-&gt;replaceAllUsesWith(ConstVal);
2848</pre>
2849</div>
2850
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]2851</ul>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2852
2853</div>
2854
2855<!-- ======================================================================= -->
2856<div class="doc_subsection">
2857 <a name="User">The <tt>User</tt> class</a>
2858</div>
2859
2860<div class="doc_text">
2861
2862<p>
2863<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]2864doxygen info: <a href="/doxygen/classllvm_1_1User.html">User Class</a><br>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2865Superclass: <a href="#Value"><tt>Value</tt></a></p>
2866
2867<p>The <tt>User</tt> class is the common base class of all LLVM nodes that may
2868refer to <a href="#Value"><tt>Value</tt></a>s. It exposes a list of "Operands"
2869that are all of the <a href="#Value"><tt>Value</tt></a>s that the User is
2870referring to. The <tt>User</tt> class itself is a subclass of
2871<tt>Value</tt>.</p>
2872
2873<p>The operands of a <tt>User</tt> point directly to the LLVM <a
2874href="#Value"><tt>Value</tt></a> that it refers to. Because LLVM uses Static
2875Single Assignment (SSA) form, there can only be one definition referred to,
2876allowing this direct connection. This connection provides the use-def
2877information in LLVM.</p>
2878
2879</div>
2880
2881<!-- _______________________________________________________________________ -->
2882<div class="doc_subsubsection">
2883 <a name="m_User">Important Public Members of the <tt>User</tt> class</a>
2884</div>
2885
2886<div class="doc_text">
2887
2888<p>The <tt>User</tt> class exposes the operand list in two ways: through
2889an index access interface and through an iterator based interface.</p>
2890
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]2891<ul>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]2892 <li><tt>Value *getOperand(unsigned i)</tt><br>
2893 <tt>unsigned getNumOperands()</tt>
2894 <p> These two methods expose the operands of the <tt>User</tt> in a
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2895convenient form for direct access.</p></li>
2896
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]2897 <li><tt>User::op_iterator</tt> - Typedef for iterator over the operand
2898list<br>
Chris Lattner58360822005-01-17 00:12:04 +0000[diff] [blame]2899 <tt>op_iterator op_begin()</tt> - Get an iterator to the start of
2900the operand list.<br>
2901 <tt>op_iterator op_end()</tt> - Get an iterator to the end of the
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]2902operand list.
2903 <p> Together, these methods make up the iterator based interface to
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2904the operands of a <tt>User</tt>.</p></li>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]2905</ul>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2906
2907</div>
2908
2909<!-- ======================================================================= -->
2910<div class="doc_subsection">
2911 <a name="Instruction">The <tt>Instruction</tt> class</a>
2912</div>
2913
2914<div class="doc_text">
2915
2916<p><tt>#include "</tt><tt><a
2917href="/doxygen/Instruction_8h-source.html">llvm/Instruction.h</a>"</tt><br>
Misha Brukman31ca1de2004-06-03 23:35:54 +0000[diff] [blame]2918doxygen info: <a href="/doxygen/classllvm_1_1Instruction.html">Instruction Class</a><br>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2919Superclasses: <a href="#User"><tt>User</tt></a>, <a
2920href="#Value"><tt>Value</tt></a></p>
2921
2922<p>The <tt>Instruction</tt> class is the common base class for all LLVM
2923instructions. It provides only a few methods, but is a very commonly used
2924class. The primary data tracked by the <tt>Instruction</tt> class itself is the
2925opcode (instruction type) and the parent <a
2926href="#BasicBlock"><tt>BasicBlock</tt></a> the <tt>Instruction</tt> is embedded
2927into. To represent a specific type of instruction, one of many subclasses of
2928<tt>Instruction</tt> are used.</p>
2929
2930<p> Because the <tt>Instruction</tt> class subclasses the <a
2931href="#User"><tt>User</tt></a> class, its operands can be accessed in the same
2932way as for other <a href="#User"><tt>User</tt></a>s (with the
2933<tt>getOperand()</tt>/<tt>getNumOperands()</tt> and
2934<tt>op_begin()</tt>/<tt>op_end()</tt> methods).</p> <p> An important file for
2935the <tt>Instruction</tt> class is the <tt>llvm/Instruction.def</tt> file. This
2936file contains some meta-data about the various different types of instructions
2937in LLVM. It describes the enum values that are used as opcodes (for example
Reid Spencerc92d25d2006-12-19 19:47:19 +0000[diff] [blame]2938<tt>Instruction::Add</tt> and <tt>Instruction::ICmp</tt>), as well as the
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2939concrete sub-classes of <tt>Instruction</tt> that implement the instruction (for
2940example <tt><a href="#BinaryOperator">BinaryOperator</a></tt> and <tt><a
Reid Spencerc92d25d2006-12-19 19:47:19 +0000[diff] [blame]2941href="#CmpInst">CmpInst</a></tt>). Unfortunately, the use of macros in
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2942this file confuses doxygen, so these enum values don't show up correctly in the
Misha Brukman31ca1de2004-06-03 23:35:54 +0000[diff] [blame]2943<a href="/doxygen/classllvm_1_1Instruction.html">doxygen output</a>.</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2944
2945</div>
2946
2947<!-- _______________________________________________________________________ -->
2948<div class="doc_subsubsection">
Reid Spencerc92d25d2006-12-19 19:47:19 +0000[diff] [blame]2949 <a name="s_Instruction">Important Subclasses of the <tt>Instruction</tt>
2950 class</a>
2951</div>
2952<div class="doc_text">
2953 <ul>
2954 <li><tt><a name="BinaryOperator">BinaryOperator</a></tt>
2955 <p>This subclasses represents all two operand instructions whose operands
2956 must be the same type, except for the comparison instructions.</p></li>
2957 <li><tt><a name="CastInst">CastInst</a></tt>
2958 <p>This subclass is the parent of the 12 casting instructions. It provides
2959 common operations on cast instructions.</p>
2960 <li><tt><a name="CmpInst">CmpInst</a></tt>
2961 <p>This subclass respresents the two comparison instructions,
2962 <a href="LangRef.html#i_icmp">ICmpInst</a> (integer opreands), and
2963 <a href="LangRef.html#i_fcmp">FCmpInst</a> (floating point operands).</p>
2964 <li><tt><a name="TerminatorInst">TerminatorInst</a></tt>
2965 <p>This subclass is the parent of all terminator instructions (those which
2966 can terminate a block).</p>
2967 </ul>
2968 </div>
2969
2970<!-- _______________________________________________________________________ -->
2971<div class="doc_subsubsection">
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2972 <a name="m_Instruction">Important Public Members of the <tt>Instruction</tt>
2973 class</a>
2974</div>
2975
2976<div class="doc_text">
2977
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]2978<ul>
2979 <li><tt><a href="#BasicBlock">BasicBlock</a> *getParent()</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2980 <p>Returns the <a href="#BasicBlock"><tt>BasicBlock</tt></a> that
2981this <tt>Instruction</tt> is embedded into.</p></li>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]2982 <li><tt>bool mayWriteToMemory()</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2983 <p>Returns true if the instruction writes to memory, i.e. it is a
2984 <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]2985 <li><tt>unsigned getOpcode()</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2986 <p>Returns the opcode for the <tt>Instruction</tt>.</p></li>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]2987 <li><tt><a href="#Instruction">Instruction</a> *clone() const</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2988 <p>Returns another instance of the specified instruction, identical
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]2989in all ways to the original except that the instruction has no parent
2990(ie it's not embedded into a <a href="#BasicBlock"><tt>BasicBlock</tt></a>),
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2991and it has no name</p></li>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]2992</ul>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2993
2994</div>
2995
2996<!-- ======================================================================= -->
2997<div class="doc_subsection">
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]2998 <a name="Constant">The <tt>Constant</tt> class and subclasses</a>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2999</div>
3000
3001<div class="doc_text">
3002
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]3003<p>Constant represents a base class for different types of constants. It
3004is subclassed by ConstantInt, ConstantArray, etc. for representing
3005the various types of Constants. <a href="#GlobalValue">GlobalValue</a> is also
3006a subclass, which represents the address of a global variable or function.
3007</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3008
3009</div>
3010
3011<!-- _______________________________________________________________________ -->
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]3012<div class="doc_subsubsection">Important Subclasses of Constant </div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3013<div class="doc_text">
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3014<ul>
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]3015 <li>ConstantInt : This subclass of Constant represents an integer constant of
3016 any width.
3017 <ul>
Reid Spencer97b4ee32007-03-01 21:05:33 +0000[diff] [blame]3018 <li><tt>const APInt&amp; getValue() const</tt>: Returns the underlying
3019 value of this constant, an APInt value.</li>
3020 <li><tt>int64_t getSExtValue() const</tt>: Converts the underlying APInt
3021 value to an int64_t via sign extension. If the value (not the bit width)
3022 of the APInt is too large to fit in an int64_t, an assertion will result.
3023 For this reason, use of this method is discouraged.</li>
3024 <li><tt>uint64_t getZExtValue() const</tt>: Converts the underlying APInt
3025 value to a uint64_t via zero extension. IF the value (not the bit width)
3026 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]3027 For this reason, use of this method is discouraged.</li>
Reid Spencer97b4ee32007-03-01 21:05:33 +0000[diff] [blame]3028 <li><tt>static ConstantInt* get(const APInt&amp; Val)</tt>: Returns the
3029 ConstantInt object that represents the value provided by <tt>Val</tt>.
3030 The type is implied as the IntegerType that corresponds to the bit width
3031 of <tt>Val</tt>.</li>
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]3032 <li><tt>static ConstantInt* get(const Type *Ty, uint64_t Val)</tt>:
3033 Returns the ConstantInt object that represents the value provided by
3034 <tt>Val</tt> for integer type <tt>Ty</tt>.</li>
3035 </ul>
3036 </li>
3037 <li>ConstantFP : This class represents a floating point constant.
3038 <ul>
3039 <li><tt>double getValue() const</tt>: Returns the underlying value of
3040 this constant. </li>
3041 </ul>
3042 </li>
3043 <li>ConstantArray : This represents a constant array.
3044 <ul>
3045 <li><tt>const std::vector&lt;Use&gt; &amp;getValues() const</tt>: Returns
3046 a vector of component constants that makeup this array. </li>
3047 </ul>
3048 </li>
3049 <li>ConstantStruct : This represents a constant struct.
3050 <ul>
3051 <li><tt>const std::vector&lt;Use&gt; &amp;getValues() const</tt>: Returns
3052 a vector of component constants that makeup this array. </li>
3053 </ul>
3054 </li>
3055 <li>GlobalValue : This represents either a global variable or a function. In
3056 either case, the value is a constant fixed address (after linking).
3057 </li>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3058</ul>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3059</div>
3060
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]3061
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3062<!-- ======================================================================= -->
3063<div class="doc_subsection">
3064 <a name="GlobalValue">The <tt>GlobalValue</tt> class</a>
3065</div>
3066
3067<div class="doc_text">
3068
3069<p><tt>#include "<a
3070href="/doxygen/GlobalValue_8h-source.html">llvm/GlobalValue.h</a>"</tt><br>
Misha Brukman384047f2004-06-03 23:29:12 +0000[diff] [blame]3071doxygen info: <a href="/doxygen/classllvm_1_1GlobalValue.html">GlobalValue
3072Class</a><br>
Reid Spencerbe5e85e2006-04-14 14:11:48 +0000[diff] [blame]3073Superclasses: <a href="#Constant"><tt>Constant</tt></a>,
3074<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]3075
3076<p>Global values (<a href="#GlobalVariable"><tt>GlobalVariable</tt></a>s or <a
3077href="#Function"><tt>Function</tt></a>s) are the only LLVM values that are
3078visible in the bodies of all <a href="#Function"><tt>Function</tt></a>s.
3079Because they are visible at global scope, they are also subject to linking with
3080other globals defined in different translation units. To control the linking
3081process, <tt>GlobalValue</tt>s know their linkage rules. Specifically,
3082<tt>GlobalValue</tt>s know whether they have internal or external linkage, as
Reid Spencer8b2da7a2004-07-18 13:10:31 +0000[diff] [blame]3083defined by the <tt>LinkageTypes</tt> enumeration.</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3084
3085<p>If a <tt>GlobalValue</tt> has internal linkage (equivalent to being
3086<tt>static</tt> in C), it is not visible to code outside the current translation
3087unit, and does not participate in linking. If it has external linkage, it is
3088visible to external code, and does participate in linking. In addition to
3089linkage information, <tt>GlobalValue</tt>s keep track of which <a
3090href="#Module"><tt>Module</tt></a> they are currently part of.</p>
3091
3092<p>Because <tt>GlobalValue</tt>s are memory objects, they are always referred to
3093by their <b>address</b>. As such, the <a href="#Type"><tt>Type</tt></a> of a
3094global is always a pointer to its contents. It is important to remember this
3095when using the <tt>GetElementPtrInst</tt> instruction because this pointer must
3096be dereferenced first. For example, if you have a <tt>GlobalVariable</tt> (a
3097subclass 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]3098i32]</tt>, then the <tt>GlobalVariable</tt> is a pointer to that array. Although
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3099the address of the first element of this array and the value of the
3100<tt>GlobalVariable</tt> are the same, they have different types. The
Reid Spencer06565dc2007-01-12 17:11:23 +0000[diff] [blame]3101<tt>GlobalVariable</tt>'s type is <tt>[24 x i32]</tt>. The first element's type
3102is <tt>i32.</tt> Because of this, accessing a global value requires you to
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3103dereference the pointer with <tt>GetElementPtrInst</tt> first, then its elements
3104can be accessed. This is explained in the <a href="LangRef.html#globalvars">LLVM
3105Language Reference Manual</a>.</p>
3106
3107</div>
3108
3109<!-- _______________________________________________________________________ -->
3110<div class="doc_subsubsection">
3111 <a name="m_GlobalValue">Important Public Members of the <tt>GlobalValue</tt>
3112 class</a>
3113</div>
3114
3115<div class="doc_text">
3116
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3117<ul>
3118 <li><tt>bool hasInternalLinkage() const</tt><br>
Chris Lattner9355b472002-09-06 02:50:58 +0000[diff] [blame]3119 <tt>bool hasExternalLinkage() const</tt><br>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3120 <tt>void setInternalLinkage(bool HasInternalLinkage)</tt>
3121 <p> These methods manipulate the linkage characteristics of the <tt>GlobalValue</tt>.</p>
3122 <p> </p>
3123 </li>
3124 <li><tt><a href="#Module">Module</a> *getParent()</tt>
3125 <p> This returns the <a href="#Module"><tt>Module</tt></a> that the
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3126GlobalValue is currently embedded into.</p></li>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3127</ul>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3128
3129</div>
3130
3131<!-- ======================================================================= -->
3132<div class="doc_subsection">
3133 <a name="Function">The <tt>Function</tt> class</a>
3134</div>
3135
3136<div class="doc_text">
3137
3138<p><tt>#include "<a
3139href="/doxygen/Function_8h-source.html">llvm/Function.h</a>"</tt><br> doxygen
Misha Brukman31ca1de2004-06-03 23:35:54 +0000[diff] [blame]3140info: <a href="/doxygen/classllvm_1_1Function.html">Function Class</a><br>
Reid Spencerbe5e85e2006-04-14 14:11:48 +0000[diff] [blame]3141Superclasses: <a href="#GlobalValue"><tt>GlobalValue</tt></a>,
3142<a href="#Constant"><tt>Constant</tt></a>,
3143<a href="#User"><tt>User</tt></a>,
3144<a href="#Value"><tt>Value</tt></a></p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3145
3146<p>The <tt>Function</tt> class represents a single procedure in LLVM. It is
3147actually one of the more complex classes in the LLVM heirarchy because it must
3148keep track of a large amount of data. The <tt>Function</tt> class keeps track
Reid Spencerbe5e85e2006-04-14 14:11:48 +0000[diff] [blame]3149of a list of <a href="#BasicBlock"><tt>BasicBlock</tt></a>s, a list of formal
3150<a href="#Argument"><tt>Argument</tt></a>s, and a
3151<a href="#SymbolTable"><tt>SymbolTable</tt></a>.</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3152
3153<p>The list of <a href="#BasicBlock"><tt>BasicBlock</tt></a>s is the most
3154commonly used part of <tt>Function</tt> objects. The list imposes an implicit
3155ordering of the blocks in the function, which indicate how the code will be
3156layed out by the backend. Additionally, the first <a
3157href="#BasicBlock"><tt>BasicBlock</tt></a> is the implicit entry node for the
3158<tt>Function</tt>. It is not legal in LLVM to explicitly branch to this initial
3159block. There are no implicit exit nodes, and in fact there may be multiple exit
3160nodes from a single <tt>Function</tt>. If the <a
3161href="#BasicBlock"><tt>BasicBlock</tt></a> list is empty, this indicates that
3162the <tt>Function</tt> is actually a function declaration: the actual body of the
3163function hasn't been linked in yet.</p>
3164
3165<p>In addition to a list of <a href="#BasicBlock"><tt>BasicBlock</tt></a>s, the
3166<tt>Function</tt> class also keeps track of the list of formal <a
3167href="#Argument"><tt>Argument</tt></a>s that the function receives. This
3168container manages the lifetime of the <a href="#Argument"><tt>Argument</tt></a>
3169nodes, just like the <a href="#BasicBlock"><tt>BasicBlock</tt></a> list does for
3170the <a href="#BasicBlock"><tt>BasicBlock</tt></a>s.</p>
3171
3172<p>The <a href="#SymbolTable"><tt>SymbolTable</tt></a> is a very rarely used
3173LLVM feature that is only used when you have to look up a value by name. Aside
3174from that, the <a href="#SymbolTable"><tt>SymbolTable</tt></a> is used
3175internally to make sure that there are not conflicts between the names of <a
3176href="#Instruction"><tt>Instruction</tt></a>s, <a
3177href="#BasicBlock"><tt>BasicBlock</tt></a>s, or <a
3178href="#Argument"><tt>Argument</tt></a>s in the function body.</p>
3179
Reid Spencer8b2da7a2004-07-18 13:10:31 +0000[diff] [blame]3180<p>Note that <tt>Function</tt> is a <a href="#GlobalValue">GlobalValue</a>
3181and therefore also a <a href="#Constant">Constant</a>. The value of the function
3182is its address (after linking) which is guaranteed to be constant.</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3183</div>
3184
3185<!-- _______________________________________________________________________ -->
3186<div class="doc_subsubsection">
3187 <a name="m_Function">Important Public Members of the <tt>Function</tt>
3188 class</a>
3189</div>
3190
3191<div class="doc_text">
3192
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3193<ul>
3194 <li><tt>Function(const </tt><tt><a href="#FunctionType">FunctionType</a>
Chris Lattnerac479e52004-08-04 05:10:48 +0000[diff] [blame]3195 *Ty, LinkageTypes Linkage, const std::string &amp;N = "", Module* Parent = 0)</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3196
3197 <p>Constructor used when you need to create new <tt>Function</tt>s to add
3198 the the program. The constructor must specify the type of the function to
Chris Lattnerac479e52004-08-04 05:10:48 +0000[diff] [blame]3199 create and what type of linkage the function should have. The <a
3200 href="#FunctionType"><tt>FunctionType</tt></a> argument
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3201 specifies the formal arguments and return value for the function. The same
Duncan Sands8036ca42007-03-30 12:22:09 +0000[diff] [blame]3202 <a href="#FunctionType"><tt>FunctionType</tt></a> value can be used to
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3203 create multiple functions. The <tt>Parent</tt> argument specifies the Module
3204 in which the function is defined. If this argument is provided, the function
3205 will automatically be inserted into that module's list of
3206 functions.</p></li>
3207
Chris Lattner62810e32008-11-25 18:34:50 +0000[diff] [blame]3208 <li><tt>bool isDeclaration()</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3209
3210 <p>Return whether or not the <tt>Function</tt> has a body defined. If the
3211 function is "external", it does not have a body, and thus must be resolved
3212 by linking with a function defined in a different translation unit.</p></li>
3213
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3214 <li><tt>Function::iterator</tt> - Typedef for basic block list iterator<br>
Chris Lattner9355b472002-09-06 02:50:58 +0000[diff] [blame]3215 <tt>Function::const_iterator</tt> - Typedef for const_iterator.<br>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3216
Chris Lattner77d69242005-03-15 05:19:20 +0000[diff] [blame]3217 <tt>begin()</tt>, <tt>end()</tt>
3218 <tt>size()</tt>, <tt>empty()</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3219
3220 <p>These are forwarding methods that make it easy to access the contents of
3221 a <tt>Function</tt> object's <a href="#BasicBlock"><tt>BasicBlock</tt></a>
3222 list.</p></li>
3223
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3224 <li><tt>Function::BasicBlockListType &amp;getBasicBlockList()</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3225
3226 <p>Returns the list of <a href="#BasicBlock"><tt>BasicBlock</tt></a>s. This
3227 is necessary to use when you need to update the list or perform a complex
3228 action that doesn't have a forwarding method.</p></li>
3229
Chris Lattner89cc2652005-03-15 04:48:32 +0000[diff] [blame]3230 <li><tt>Function::arg_iterator</tt> - Typedef for the argument list
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3231iterator<br>
Chris Lattner89cc2652005-03-15 04:48:32 +0000[diff] [blame]3232 <tt>Function::const_arg_iterator</tt> - Typedef for const_iterator.<br>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3233
Chris Lattner77d69242005-03-15 05:19:20 +0000[diff] [blame]3234 <tt>arg_begin()</tt>, <tt>arg_end()</tt>
Chris Lattner89cc2652005-03-15 04:48:32 +0000[diff] [blame]3235 <tt>arg_size()</tt>, <tt>arg_empty()</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3236
3237 <p>These are forwarding methods that make it easy to access the contents of
3238 a <tt>Function</tt> object's <a href="#Argument"><tt>Argument</tt></a>
3239 list.</p></li>
3240
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3241 <li><tt>Function::ArgumentListType &amp;getArgumentList()</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3242
3243 <p>Returns the list of <a href="#Argument"><tt>Argument</tt></a>s. This is
3244 necessary to use when you need to update the list or perform a complex
3245 action that doesn't have a forwarding method.</p></li>
3246
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3247 <li><tt><a href="#BasicBlock">BasicBlock</a> &amp;getEntryBlock()</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3248
3249 <p>Returns the entry <a href="#BasicBlock"><tt>BasicBlock</tt></a> for the
3250 function. Because the entry block for the function is always the first
3251 block, this returns the first block of the <tt>Function</tt>.</p></li>
3252
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3253 <li><tt><a href="#Type">Type</a> *getReturnType()</tt><br>
3254 <tt><a href="#FunctionType">FunctionType</a> *getFunctionType()</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3255
3256 <p>This traverses the <a href="#Type"><tt>Type</tt></a> of the
3257 <tt>Function</tt> and returns the return type of the function, or the <a
3258 href="#FunctionType"><tt>FunctionType</tt></a> of the actual
3259 function.</p></li>
3260
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3261 <li><tt><a href="#SymbolTable">SymbolTable</a> *getSymbolTable()</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3262
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3263 <p> Return a pointer to the <a href="#SymbolTable"><tt>SymbolTable</tt></a>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3264 for this <tt>Function</tt>.</p></li>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3265</ul>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3266
3267</div>
3268
3269<!-- ======================================================================= -->
3270<div class="doc_subsection">
3271 <a name="GlobalVariable">The <tt>GlobalVariable</tt> class</a>
3272</div>
3273
3274<div class="doc_text">
3275
3276<p><tt>#include "<a
3277href="/doxygen/GlobalVariable_8h-source.html">llvm/GlobalVariable.h</a>"</tt>
3278<br>
Tanya Lattnera3da7772004-06-22 08:02:25 +0000[diff] [blame]3279doxygen info: <a href="/doxygen/classllvm_1_1GlobalVariable.html">GlobalVariable
Reid Spencerbe5e85e2006-04-14 14:11:48 +0000[diff] [blame]3280 Class</a><br>
3281Superclasses: <a href="#GlobalValue"><tt>GlobalValue</tt></a>,
3282<a href="#Constant"><tt>Constant</tt></a>,
3283<a href="#User"><tt>User</tt></a>,
3284<a href="#Value"><tt>Value</tt></a></p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3285
3286<p>Global variables are represented with the (suprise suprise)
3287<tt>GlobalVariable</tt> class. Like functions, <tt>GlobalVariable</tt>s are also
3288subclasses of <a href="#GlobalValue"><tt>GlobalValue</tt></a>, and as such are
3289always referenced by their address (global values must live in memory, so their
Reid Spencerbe5e85e2006-04-14 14:11:48 +0000[diff] [blame]3290"name" refers to their constant address). See
3291<a href="#GlobalValue"><tt>GlobalValue</tt></a> for more on this. Global
3292variables may have an initial value (which must be a
3293<a href="#Constant"><tt>Constant</tt></a>), and if they have an initializer,
3294they may be marked as "constant" themselves (indicating that their contents
3295never change at runtime).</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3296</div>
3297
3298<!-- _______________________________________________________________________ -->
3299<div class="doc_subsubsection">
3300 <a name="m_GlobalVariable">Important Public Members of the
3301 <tt>GlobalVariable</tt> class</a>
3302</div>
3303
3304<div class="doc_text">
3305
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3306<ul>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3307 <li><tt>GlobalVariable(const </tt><tt><a href="#Type">Type</a> *Ty, bool
3308 isConstant, LinkageTypes&amp; Linkage, <a href="#Constant">Constant</a>
3309 *Initializer = 0, const std::string &amp;Name = "", Module* Parent = 0)</tt>
3310
3311 <p>Create a new global variable of the specified type. If
3312 <tt>isConstant</tt> is true then the global variable will be marked as
3313 unchanging for the program. The Linkage parameter specifies the type of
Duncan Sands667d4b82009-03-07 15:45:40 +0000[diff] [blame]3314 linkage (internal, external, weak, linkonce, appending) for the variable.
3315 If the linkage is InternalLinkage, WeakAnyLinkage, WeakODRLinkage,
3316 LinkOnceAnyLinkage or LinkOnceODRLinkage,&nbsp; then the resultant
3317 global variable will have internal linkage. AppendingLinkage concatenates
3318 together all instances (in different translation units) of the variable
3319 into a single variable but is only applicable to arrays. &nbsp;See
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3320 the <a href="LangRef.html#modulestructure">LLVM Language Reference</a> for
3321 further details on linkage types. Optionally an initializer, a name, and the
3322 module to put the variable into may be specified for the global variable as
3323 well.</p></li>
3324
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3325 <li><tt>bool isConstant() const</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3326
3327 <p>Returns true if this is a global variable that is known not to
3328 be modified at runtime.</p></li>
3329
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3330 <li><tt>bool hasInitializer()</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3331
3332 <p>Returns true if this <tt>GlobalVariable</tt> has an intializer.</p></li>
3333
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3334 <li><tt><a href="#Constant">Constant</a> *getInitializer()</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3335
3336 <p>Returns the intial value for a <tt>GlobalVariable</tt>. It is not legal
3337 to call this method if there is no initializer.</p></li>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3338</ul>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3339
3340</div>
3341
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]3342
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3343<!-- ======================================================================= -->
3344<div class="doc_subsection">
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]3345 <a name="BasicBlock">The <tt>BasicBlock</tt> class</a>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3346</div>
3347
3348<div class="doc_text">
3349
3350<p><tt>#include "<a
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]3351href="/doxygen/BasicBlock_8h-source.html">llvm/BasicBlock.h</a>"</tt><br>
3352doxygen info: <a href="/doxygen/structllvm_1_1BasicBlock.html">BasicBlock
3353Class</a><br>
3354Superclass: <a href="#Value"><tt>Value</tt></a></p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3355
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]3356<p>This class represents a single entry multiple exit section of the code,
3357commonly known as a basic block by the compiler community. The
3358<tt>BasicBlock</tt> class maintains a list of <a
3359href="#Instruction"><tt>Instruction</tt></a>s, which form the body of the block.
3360Matching the language definition, the last element of this list of instructions
3361is always a terminator instruction (a subclass of the <a
3362href="#TerminatorInst"><tt>TerminatorInst</tt></a> class).</p>
3363
3364<p>In addition to tracking the list of instructions that make up the block, the
3365<tt>BasicBlock</tt> class also keeps track of the <a
3366href="#Function"><tt>Function</tt></a> that it is embedded into.</p>
3367
3368<p>Note that <tt>BasicBlock</tt>s themselves are <a
3369href="#Value"><tt>Value</tt></a>s, because they are referenced by instructions
3370like branches and can go in the switch tables. <tt>BasicBlock</tt>s have type
3371<tt>label</tt>.</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3372
3373</div>
3374
3375<!-- _______________________________________________________________________ -->
3376<div class="doc_subsubsection">
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]3377 <a name="m_BasicBlock">Important Public Members of the <tt>BasicBlock</tt>
3378 class</a>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3379</div>
3380
3381<div class="doc_text">
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3382<ul>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3383
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]3384<li><tt>BasicBlock(const std::string &amp;Name = "", </tt><tt><a
3385 href="#Function">Function</a> *Parent = 0)</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3386
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]3387<p>The <tt>BasicBlock</tt> constructor is used to create new basic blocks for
3388insertion into a function. The constructor optionally takes a name for the new
3389block, and a <a href="#Function"><tt>Function</tt></a> to insert it into. If
3390the <tt>Parent</tt> parameter is specified, the new <tt>BasicBlock</tt> is
3391automatically inserted at the end of the specified <a
3392href="#Function"><tt>Function</tt></a>, if not specified, the BasicBlock must be
3393manually inserted into the <a href="#Function"><tt>Function</tt></a>.</p></li>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3394
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]3395<li><tt>BasicBlock::iterator</tt> - Typedef for instruction list iterator<br>
3396<tt>BasicBlock::const_iterator</tt> - Typedef for const_iterator.<br>
3397<tt>begin()</tt>, <tt>end()</tt>, <tt>front()</tt>, <tt>back()</tt>,
3398<tt>size()</tt>, <tt>empty()</tt>
3399STL-style functions for accessing the instruction list.
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3400
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]3401<p>These methods and typedefs are forwarding functions that have the same
3402semantics as the standard library methods of the same names. These methods
3403expose the underlying instruction list of a basic block in a way that is easy to
3404manipulate. To get the full complement of container operations (including
3405operations to update the list), you must use the <tt>getInstList()</tt>
3406method.</p></li>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3407
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]3408<li><tt>BasicBlock::InstListType &amp;getInstList()</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3409
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]3410<p>This method is used to get access to the underlying container that actually
3411holds the Instructions. This method must be used when there isn't a forwarding
3412function in the <tt>BasicBlock</tt> class for the operation that you would like
3413to perform. Because there are no forwarding functions for "updating"
3414operations, you need to use this if you want to update the contents of a
3415<tt>BasicBlock</tt>.</p></li>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3416
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]3417<li><tt><a href="#Function">Function</a> *getParent()</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3418
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]3419<p> Returns a pointer to <a href="#Function"><tt>Function</tt></a> the block is
3420embedded into, or a null pointer if it is homeless.</p></li>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3421
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]3422<li><tt><a href="#TerminatorInst">TerminatorInst</a> *getTerminator()</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3423
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]3424<p> Returns a pointer to the terminator instruction that appears at the end of
3425the <tt>BasicBlock</tt>. If there is no terminator instruction, or if the last
3426instruction in the block is not a terminator, then a null pointer is
3427returned.</p></li>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3428
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3429</ul>
3430
3431</div>
3432
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3433
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3434<!-- ======================================================================= -->
3435<div class="doc_subsection">
3436 <a name="Argument">The <tt>Argument</tt> class</a>
3437</div>
3438
3439<div class="doc_text">
3440
3441<p>This subclass of Value defines the interface for incoming formal
Chris Lattner58360822005-01-17 00:12:04 +0000[diff] [blame]3442arguments to a function. A Function maintains a list of its formal
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3443arguments. An argument has a pointer to the parent Function.</p>
3444
3445</div>
3446
Chris Lattner9355b472002-09-06 02:50:58 +0000[diff] [blame]3447<!-- *********************************************************************** -->
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3448<hr>
3449<address>
3450 <a href="http://jigsaw.w3.org/css-validator/check/referer"><img
Misha Brukman44408702008-12-11 17:34:48 +0000[diff] [blame]3451 src="http://jigsaw.w3.org/css-validator/images/vcss-blue" alt="Valid CSS"></a>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3452 <a href="http://validator.w3.org/check/referer"><img
Gabor Greifa9c0f2b2008-06-18 14:05:31 +0000[diff] [blame]3453 src="http://www.w3.org/Icons/valid-html401" alt="Valid HTML 4.01 Strict"></a>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3454
3455 <a href="mailto:dhurjati@cs.uiuc.edu">Dinakar Dhurjati</a> and
3456 <a href="mailto:sabre@nondot.org">Chris Lattner</a><br>
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]3457 <a href="http://llvm.org">The LLVM Compiler Infrastructure</a><br>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3458 Last modified: $Date$
3459</address>
3460
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3461</body>
3462</html>