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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
Gabor Greif0cbcabe2009-03-12 09:47:03 +0000[diff] [blame^]250O'Reilly book in the making. It has a decent Standard Library
251Reference that rivals Dinkumware's, and is unfortunately no longer free since the
252book has been published.</li>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]253
254<li><a href="http://www.parashift.com/c++-faq-lite/">C++ Frequently Asked
255Questions</a></li>
256
257<li><a href="http://www.sgi.com/tech/stl/">SGI's STL Programmer's Guide</a> -
258Contains a useful <a
259href="http://www.sgi.com/tech/stl/stl_introduction.html">Introduction to the
260STL</a>.</li>
261
262<li><a href="http://www.research.att.com/%7Ebs/C++.html">Bjarne Stroustrup's C++
263Page</a></li>
264
Tanya Lattner79445ba2004-12-08 18:34:56 +0000[diff] [blame]265<li><a href="http://64.78.49.204/">
Reid Spencer096603a2004-05-26 08:41:35 +0000[diff] [blame]266Bruce Eckel's Thinking in C++, 2nd ed. Volume 2 Revision 4.0 (even better, get
267the book).</a></li>
268
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]269</ol>
270
271<p>You are also encouraged to take a look at the <a
272href="CodingStandards.html">LLVM Coding Standards</a> guide which focuses on how
273to write maintainable code more than where to put your curly braces.</p>
274
275</div>
276
277<!-- ======================================================================= -->
278<div class="doc_subsection">
279 <a name="stl">Other useful references</a>
280</div>
281
282<div class="doc_text">
283
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]284<ol>
285<li><a href="http://www.psc.edu/%7Esemke/cvs_branches.html">CVS
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]286Branch and Tag Primer</a></li>
Misha Brukmana0f71e42004-06-18 18:39:00 +0000[diff] [blame]287<li><a href="http://www.fortran-2000.com/ArnaudRecipes/sharedlib.html">Using
288static and shared libraries across platforms</a></li>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]289</ol>
290
291</div>
292
Chris Lattner9355b472002-09-06 02:50:58 +0000[diff] [blame]293<!-- *********************************************************************** -->
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]294<div class="doc_section">
295 <a name="apis">Important and useful LLVM APIs</a>
296</div>
297<!-- *********************************************************************** -->
298
299<div class="doc_text">
300
301<p>Here we highlight some LLVM APIs that are generally useful and good to
302know about when writing transformations.</p>
303
304</div>
305
306<!-- ======================================================================= -->
307<div class="doc_subsection">
Misha Brukman2c122ce2005-11-01 21:12:49 +0000[diff] [blame]308 <a name="isa">The <tt>isa&lt;&gt;</tt>, <tt>cast&lt;&gt;</tt> and
309 <tt>dyn_cast&lt;&gt;</tt> templates</a>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]310</div>
311
312<div class="doc_text">
313
314<p>The LLVM source-base makes extensive use of a custom form of RTTI.
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]315These templates have many similarities to the C++ <tt>dynamic_cast&lt;&gt;</tt>
316operator, but they don't have some drawbacks (primarily stemming from
317the fact that <tt>dynamic_cast&lt;&gt;</tt> only works on classes that
318have a v-table). Because they are used so often, you must know what they
319do and how they work. All of these templates are defined in the <a
Chris Lattner695b78b2005-04-26 22:56:16 +0000[diff] [blame]320 href="/doxygen/Casting_8h-source.html"><tt>llvm/Support/Casting.h</tt></a>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]321file (note that you very rarely have to include this file directly).</p>
322
323<dl>
324 <dt><tt>isa&lt;&gt;</tt>: </dt>
325
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]326 <dd><p>The <tt>isa&lt;&gt;</tt> operator works exactly like the Java
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]327 "<tt>instanceof</tt>" operator. It returns true or false depending on whether
328 a reference or pointer points to an instance of the specified class. This can
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]329 be very useful for constraint checking of various sorts (example below).</p>
330 </dd>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]331
332 <dt><tt>cast&lt;&gt;</tt>: </dt>
333
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]334 <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]335 converts a pointer or reference from a base class to a derived class, causing
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]336 an assertion failure if it is not really an instance of the right type. This
337 should be used in cases where you have some information that makes you believe
338 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]339 and <tt>cast&lt;&gt;</tt> template is:</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]340
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]341<div class="doc_code">
342<pre>
343static bool isLoopInvariant(const <a href="#Value">Value</a> *V, const Loop *L) {
344 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))
345 return true;
Chris Lattner69bf8a92004-05-23 21:06:58 +0000[diff] [blame]346
Bill Wendling82e2eea2006-10-11 18:00:22 +0000[diff] [blame]347 // <i>Otherwise, it must be an instruction...</i>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]348 return !L-&gt;contains(cast&lt;<a href="#Instruction">Instruction</a>&gt;(V)-&gt;getParent());
349}
350</pre>
351</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]352
353 <p>Note that you should <b>not</b> use an <tt>isa&lt;&gt;</tt> test followed
354 by a <tt>cast&lt;&gt;</tt>, for that use the <tt>dyn_cast&lt;&gt;</tt>
355 operator.</p>
356
357 </dd>
358
359 <dt><tt>dyn_cast&lt;&gt;</tt>:</dt>
360
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]361 <dd><p>The <tt>dyn_cast&lt;&gt;</tt> operator is a "checking cast" operation.
362 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]363 pointer to it (this operator does not work with references). If the operand is
364 not of the correct type, a null pointer is returned. Thus, this works very
Misha Brukman2c122ce2005-11-01 21:12:49 +0000[diff] [blame]365 much like the <tt>dynamic_cast&lt;&gt;</tt> operator in C++, and should be
366 used in the same circumstances. Typically, the <tt>dyn_cast&lt;&gt;</tt>
367 operator is used in an <tt>if</tt> statement or some other flow control
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]368 statement like this:</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]369
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]370<div class="doc_code">
371<pre>
372if (<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]373 // <i>...</i>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]374}
375</pre>
376</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]377
Misha Brukman2c122ce2005-11-01 21:12:49 +0000[diff] [blame]378 <p>This form of the <tt>if</tt> statement effectively combines together a call
379 to <tt>isa&lt;&gt;</tt> and a call to <tt>cast&lt;&gt;</tt> into one
380 statement, which is very convenient.</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]381
Misha Brukman2c122ce2005-11-01 21:12:49 +0000[diff] [blame]382 <p>Note that the <tt>dyn_cast&lt;&gt;</tt> operator, like C++'s
383 <tt>dynamic_cast&lt;&gt;</tt> or Java's <tt>instanceof</tt> operator, can be
384 abused. In particular, you should not use big chained <tt>if/then/else</tt>
385 blocks to check for lots of different variants of classes. If you find
386 yourself wanting to do this, it is much cleaner and more efficient to use the
387 <tt>InstVisitor</tt> class to dispatch over the instruction type directly.</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]388
Misha Brukman2c122ce2005-11-01 21:12:49 +0000[diff] [blame]389 </dd>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]390
Misha Brukman2c122ce2005-11-01 21:12:49 +0000[diff] [blame]391 <dt><tt>cast_or_null&lt;&gt;</tt>: </dt>
392
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]393 <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]394 <tt>cast&lt;&gt;</tt> operator, except that it allows for a null pointer as an
395 argument (which it then propagates). This can sometimes be useful, allowing
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]396 you to combine several null checks into one.</p></dd>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]397
Misha Brukman2c122ce2005-11-01 21:12:49 +0000[diff] [blame]398 <dt><tt>dyn_cast_or_null&lt;&gt;</tt>: </dt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]399
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]400 <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]401 <tt>dyn_cast&lt;&gt;</tt> operator, except that it allows for a null pointer
402 as an argument (which it then propagates). This can sometimes be useful,
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]403 allowing you to combine several null checks into one.</p></dd>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]404
Misha Brukman2c122ce2005-11-01 21:12:49 +0000[diff] [blame]405</dl>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]406
407<p>These five templates can be used with any classes, whether they have a
408v-table or not. To add support for these templates, you simply need to add
409<tt>classof</tt> static methods to the class you are interested casting
410to. Describing this is currently outside the scope of this document, but there
411are lots of examples in the LLVM source base.</p>
412
413</div>
414
415<!-- ======================================================================= -->
416<div class="doc_subsection">
Misha Brukman2c122ce2005-11-01 21:12:49 +0000[diff] [blame]417 <a name="DEBUG">The <tt>DEBUG()</tt> macro and <tt>-debug</tt> option</a>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]418</div>
419
420<div class="doc_text">
421
422<p>Often when working on your pass you will put a bunch of debugging printouts
423and other code into your pass. After you get it working, you want to remove
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]424it, 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]425across).</p>
426
427<p> Naturally, because of this, you don't want to delete the debug printouts,
428but you don't want them to always be noisy. A standard compromise is to comment
429them out, allowing you to enable them if you need them in the future.</p>
430
Chris Lattner695b78b2005-04-26 22:56:16 +0000[diff] [blame]431<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]432file provides a macro named <tt>DEBUG()</tt> that is a much nicer solution to
433this problem. Basically, you can put arbitrary code into the argument of the
434<tt>DEBUG</tt> macro, and it is only executed if '<tt>opt</tt>' (or any other
435tool) is run with the '<tt>-debug</tt>' command line argument:</p>
436
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]437<div class="doc_code">
438<pre>
Bill Wendling832171c2006-12-07 20:04:42 +0000[diff] [blame]439DOUT &lt;&lt; "I am here!\n";
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]440</pre>
441</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]442
443<p>Then you can run your pass like this:</p>
444
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]445<div class="doc_code">
446<pre>
447$ opt &lt; a.bc &gt; /dev/null -mypass
Bill Wendling82e2eea2006-10-11 18:00:22 +0000[diff] [blame]448<i>&lt;no output&gt;</i>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]449$ opt &lt; a.bc &gt; /dev/null -mypass -debug
450I am here!
451</pre>
452</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]453
454<p>Using the <tt>DEBUG()</tt> macro instead of a home-brewed solution allows you
455to not have to create "yet another" command line option for the debug output for
456your pass. Note that <tt>DEBUG()</tt> macros are disabled for optimized builds,
457so they do not cause a performance impact at all (for the same reason, they
458should also not contain side-effects!).</p>
459
460<p>One additional nice thing about the <tt>DEBUG()</tt> macro is that you can
461enable or disable it directly in gdb. Just use "<tt>set DebugFlag=0</tt>" or
462"<tt>set DebugFlag=1</tt>" from the gdb if the program is running. If the
463program hasn't been started yet, you can always just run it with
464<tt>-debug</tt>.</p>
465
466</div>
467
468<!-- _______________________________________________________________________ -->
469<div class="doc_subsubsection">
Chris Lattnerc9151082005-04-26 22:57:07 +0000[diff] [blame]470 <a name="DEBUG_TYPE">Fine grained debug info with <tt>DEBUG_TYPE</tt> and
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]471 the <tt>-debug-only</tt> option</a>
472</div>
473
474<div class="doc_text">
475
476<p>Sometimes you may find yourself in a situation where enabling <tt>-debug</tt>
477just turns on <b>too much</b> information (such as when working on the code
478generator). If you want to enable debug information with more fine-grained
479control, you define the <tt>DEBUG_TYPE</tt> macro and the <tt>-debug</tt> only
480option as follows:</p>
481
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]482<div class="doc_code">
483<pre>
Bill Wendling832171c2006-12-07 20:04:42 +0000[diff] [blame]484DOUT &lt;&lt; "No debug type\n";
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]485#undef DEBUG_TYPE
486#define DEBUG_TYPE "foo"
Bill Wendling832171c2006-12-07 20:04:42 +0000[diff] [blame]487DOUT &lt;&lt; "'foo' debug type\n";
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]488#undef DEBUG_TYPE
489#define DEBUG_TYPE "bar"
Bill Wendling832171c2006-12-07 20:04:42 +0000[diff] [blame]490DOUT &lt;&lt; "'bar' debug type\n";
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]491#undef DEBUG_TYPE
492#define DEBUG_TYPE ""
Bill Wendling832171c2006-12-07 20:04:42 +0000[diff] [blame]493DOUT &lt;&lt; "No debug type (2)\n";
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]494</pre>
495</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]496
497<p>Then you can run your pass like this:</p>
498
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]499<div class="doc_code">
500<pre>
501$ opt &lt; a.bc &gt; /dev/null -mypass
Bill Wendling82e2eea2006-10-11 18:00:22 +0000[diff] [blame]502<i>&lt;no output&gt;</i>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]503$ opt &lt; a.bc &gt; /dev/null -mypass -debug
504No debug type
505'foo' debug type
506'bar' debug type
507No debug type (2)
508$ opt &lt; a.bc &gt; /dev/null -mypass -debug-only=foo
509'foo' debug type
510$ opt &lt; a.bc &gt; /dev/null -mypass -debug-only=bar
511'bar' debug type
512</pre>
513</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]514
515<p>Of course, in practice, you should only set <tt>DEBUG_TYPE</tt> at the top of
516a 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]517you <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]518<tt>#undef</tt>'s). Also, you should use names more meaningful than "foo" and
519"bar", because there is no system in place to ensure that names do not
520conflict. If two different modules use the same string, they will all be turned
521on when the name is specified. This allows, for example, all debug information
522for instruction scheduling to be enabled with <tt>-debug-type=InstrSched</tt>,
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]523even if the source lives in multiple files.</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]524
525</div>
526
527<!-- ======================================================================= -->
528<div class="doc_subsection">
Chris Lattner0be6fdf2006-12-19 21:46:21 +0000[diff] [blame]529 <a name="Statistic">The <tt>Statistic</tt> class &amp; <tt>-stats</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]530 option</a>
531</div>
532
533<div class="doc_text">
534
535<p>The "<tt><a
Chris Lattner695b78b2005-04-26 22:56:16 +0000[diff] [blame]536href="/doxygen/Statistic_8h-source.html">llvm/ADT/Statistic.h</a></tt>" file
Chris Lattner0be6fdf2006-12-19 21:46:21 +0000[diff] [blame]537provides a class named <tt>Statistic</tt> that is used as a unified way to
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]538keep track of what the LLVM compiler is doing and how effective various
539optimizations are. It is useful to see what optimizations are contributing to
540making a particular program run faster.</p>
541
542<p>Often you may run your pass on some big program, and you're interested to see
543how many times it makes a certain transformation. Although you can do this with
544hand 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]545for big programs. Using the <tt>Statistic</tt> class makes it very easy to
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]546keep track of this information, and the calculated information is presented in a
547uniform manner with the rest of the passes being executed.</p>
548
549<p>There are many examples of <tt>Statistic</tt> uses, but the basics of using
550it are as follows:</p>
551
552<ol>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]553 <li><p>Define your statistic like this:</p>
554
555<div class="doc_code">
556<pre>
Chris Lattner0be6fdf2006-12-19 21:46:21 +0000[diff] [blame]557#define <a href="#DEBUG_TYPE">DEBUG_TYPE</a> "mypassname" <i>// This goes before any #includes.</i>
558STATISTIC(NumXForms, "The # of times I did stuff");
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]559</pre>
560</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]561
Chris Lattner0be6fdf2006-12-19 21:46:21 +0000[diff] [blame]562 <p>The <tt>STATISTIC</tt> macro defines a static variable, whose name is
563 specified by the first argument. The pass name is taken from the DEBUG_TYPE
564 macro, and the description is taken from the second argument. The variable
Reid Spencer06565dc2007-01-12 17:11:23 +0000[diff] [blame]565 defined ("NumXForms" in this case) acts like an unsigned integer.</p></li>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]566
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]567 <li><p>Whenever you make a transformation, bump the counter:</p>
568
569<div class="doc_code">
570<pre>
Bill Wendling82e2eea2006-10-11 18:00:22 +0000[diff] [blame]571++NumXForms; // <i>I did stuff!</i>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]572</pre>
573</div>
574
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]575 </li>
576 </ol>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]577
578 <p>That's all you have to do. To get '<tt>opt</tt>' to print out the
579 statistics gathered, use the '<tt>-stats</tt>' option:</p>
580
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]581<div class="doc_code">
582<pre>
583$ opt -stats -mypassname &lt; program.bc &gt; /dev/null
Bill Wendling82e2eea2006-10-11 18:00:22 +0000[diff] [blame]584<i>... statistics output ...</i>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]585</pre>
586</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]587
Reid Spencer6b6c73e2007-02-09 16:00:28 +0000[diff] [blame]588 <p> When running <tt>opt</tt> on a C file from the SPEC benchmark
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]589suite, it gives a report that looks like this:</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]590
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]591<div class="doc_code">
592<pre>
Gabor Greif04367bf2007-07-06 22:07:22 +0000[diff] [blame]593 7646 bitcodewriter - Number of normal instructions
594 725 bitcodewriter - Number of oversized instructions
595 129996 bitcodewriter - Number of bitcode bytes written
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]596 2817 raise - Number of insts DCEd or constprop'd
597 3213 raise - Number of cast-of-self removed
598 5046 raise - Number of expression trees converted
599 75 raise - Number of other getelementptr's formed
600 138 raise - Number of load/store peepholes
601 42 deadtypeelim - Number of unused typenames removed from symtab
602 392 funcresolve - Number of varargs functions resolved
603 27 globaldce - Number of global variables removed
604 2 adce - Number of basic blocks removed
605 134 cee - Number of branches revectored
606 49 cee - Number of setcc instruction eliminated
607 532 gcse - Number of loads removed
608 2919 gcse - Number of instructions removed
609 86 indvars - Number of canonical indvars added
610 87 indvars - Number of aux indvars removed
611 25 instcombine - Number of dead inst eliminate
612 434 instcombine - Number of insts combined
613 248 licm - Number of load insts hoisted
614 1298 licm - Number of insts hoisted to a loop pre-header
615 3 licm - Number of insts hoisted to multiple loop preds (bad, no loop pre-header)
616 75 mem2reg - Number of alloca's promoted
617 1444 cfgsimplify - Number of blocks simplified
618</pre>
619</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]620
621<p>Obviously, with so many optimizations, having a unified framework for this
622stuff is very nice. Making your pass fit well into the framework makes it more
623maintainable and useful.</p>
624
625</div>
626
Chris Lattnerf623a082005-10-17 01:36:23 +0000[diff] [blame]627<!-- ======================================================================= -->
628<div class="doc_subsection">
629 <a name="ViewGraph">Viewing graphs while debugging code</a>
630</div>
631
632<div class="doc_text">
633
634<p>Several of the important data structures in LLVM are graphs: for example
635CFGs made out of LLVM <a href="#BasicBlock">BasicBlock</a>s, CFGs made out of
636LLVM <a href="CodeGenerator.html#machinebasicblock">MachineBasicBlock</a>s, and
637<a href="CodeGenerator.html#selectiondag_intro">Instruction Selection
638DAGs</a>. In many cases, while debugging various parts of the compiler, it is
639nice to instantly visualize these graphs.</p>
640
641<p>LLVM provides several callbacks that are available in a debug build to do
642exactly that. If you call the <tt>Function::viewCFG()</tt> method, for example,
643the current LLVM tool will pop up a window containing the CFG for the function
644where each basic block is a node in the graph, and each node contains the
645instructions in the block. Similarly, there also exists
646<tt>Function::viewCFGOnly()</tt> (does not include the instructions), the
647<tt>MachineFunction::viewCFG()</tt> and <tt>MachineFunction::viewCFGOnly()</tt>,
648and the <tt>SelectionDAG::viewGraph()</tt> methods. Within GDB, for example,
Jim Laskey543a0ee2006-10-02 12:28:07 +0000[diff] [blame]649you can usually use something like <tt>call DAG.viewGraph()</tt> to pop
Chris Lattnerf623a082005-10-17 01:36:23 +0000[diff] [blame]650up a window. Alternatively, you can sprinkle calls to these functions in your
651code in places you want to debug.</p>
652
653<p>Getting this to work requires a small amount of configuration. On Unix
654systems with X11, install the <a href="http://www.graphviz.org">graphviz</a>
655toolkit, and make sure 'dot' and 'gv' are in your path. If you are running on
656Mac OS/X, download and install the Mac OS/X <a
657href="http://www.pixelglow.com/graphviz/">Graphviz program</a>, and add
Reid Spencer128a7a72007-02-03 21:06:43 +0000[diff] [blame]658<tt>/Applications/Graphviz.app/Contents/MacOS/</tt> (or wherever you install
Chris Lattnerf623a082005-10-17 01:36:23 +0000[diff] [blame]659it) to your path. Once in your system and path are set up, rerun the LLVM
660configure script and rebuild LLVM to enable this functionality.</p>
661
Jim Laskey543a0ee2006-10-02 12:28:07 +0000[diff] [blame]662<p><tt>SelectionDAG</tt> has been extended to make it easier to locate
663<i>interesting</i> nodes in large complex graphs. From gdb, if you
664<tt>call DAG.setGraphColor(<i>node</i>, "<i>color</i>")</tt>, then the
Reid Spencer128a7a72007-02-03 21:06:43 +0000[diff] [blame]665next <tt>call DAG.viewGraph()</tt> would highlight the node in the
Jim Laskey543a0ee2006-10-02 12:28:07 +0000[diff] [blame]666specified color (choices of colors can be found at <a
Chris Lattner302da1e2007-02-03 03:05:57 +0000[diff] [blame]667href="http://www.graphviz.org/doc/info/colors.html">colors</a>.) More
Jim Laskey543a0ee2006-10-02 12:28:07 +0000[diff] [blame]668complex node attributes can be provided with <tt>call
669DAG.setGraphAttrs(<i>node</i>, "<i>attributes</i>")</tt> (choices can be
670found at <a href="http://www.graphviz.org/doc/info/attrs.html">Graph
671Attributes</a>.) If you want to restart and clear all the current graph
672attributes, then you can <tt>call DAG.clearGraphAttrs()</tt>. </p>
673
Chris Lattnerf623a082005-10-17 01:36:23 +0000[diff] [blame]674</div>
675
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]676<!-- *********************************************************************** -->
677<div class="doc_section">
678 <a name="datastructure">Picking the Right Data Structure for a Task</a>
679</div>
680<!-- *********************************************************************** -->
681
682<div class="doc_text">
683
Reid Spencer128a7a72007-02-03 21:06:43 +0000[diff] [blame]684<p>LLVM has a plethora of data structures in the <tt>llvm/ADT/</tt> directory,
685 and we commonly use STL data structures. This section describes the trade-offs
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]686 you should consider when you pick one.</p>
687
688<p>
689The first step is a choose your own adventure: do you want a sequential
690container, a set-like container, or a map-like container? The most important
691thing when choosing a container is the algorithmic properties of how you plan to
692access the container. Based on that, you should use:</p>
693
694<ul>
Reid Spencer128a7a72007-02-03 21:06:43 +0000[diff] [blame]695<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]696 of an value based on another value. Map-like containers also support
697 efficient queries for containment (whether a key is in the map). Map-like
698 containers generally do not support efficient reverse mapping (values to
699 keys). If you need that, use two maps. Some map-like containers also
700 support efficient iteration through the keys in sorted order. Map-like
701 containers are the most expensive sort, only use them if you need one of
702 these capabilities.</li>
703
704<li>a <a href="#ds_set">set-like</a> container if you need to put a bunch of
705 stuff into a container that automatically eliminates duplicates. Some
706 set-like containers support efficient iteration through the elements in
707 sorted order. Set-like containers are more expensive than sequential
708 containers.
709</li>
710
711<li>a <a href="#ds_sequential">sequential</a> container provides
712 the most efficient way to add elements and keeps track of the order they are
713 added to the collection. They permit duplicates and support efficient
Reid Spencer128a7a72007-02-03 21:06:43 +0000[diff] [blame]714 iteration, but do not support efficient look-up based on a key.
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]715</li>
716
Daniel Berlin1939ace2007-09-24 17:52:25 +0000[diff] [blame]717<li>a <a href="#ds_bit">bit</a> container provides an efficient way to store and
718 perform set operations on sets of numeric id's, while automatically
719 eliminating duplicates. Bit containers require a maximum of 1 bit for each
720 identifier you want to store.
721</li>
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]722</ul>
723
724<p>
Reid Spencer128a7a72007-02-03 21:06:43 +0000[diff] [blame]725Once the proper category of container is determined, you can fine tune the
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]726memory use, constant factors, and cache behaviors of access by intelligently
Reid Spencer128a7a72007-02-03 21:06:43 +0000[diff] [blame]727picking a member of the category. Note that constant factors and cache behavior
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]728can be a big deal. If you have a vector that usually only contains a few
729elements (but could contain many), for example, it's much better to use
730<a href="#dss_smallvector">SmallVector</a> than <a href="#dss_vector">vector</a>
731. Doing so avoids (relatively) expensive malloc/free calls, which dwarf the
732cost of adding the elements to the container. </p>
733
734</div>
735
736<!-- ======================================================================= -->
737<div class="doc_subsection">
738 <a name="ds_sequential">Sequential Containers (std::vector, std::list, etc)</a>
739</div>
740
741<div class="doc_text">
742There are a variety of sequential containers available for you, based on your
743needs. Pick the first in this section that will do what you want.
744</div>
745
746<!-- _______________________________________________________________________ -->
747<div class="doc_subsubsection">
748 <a name="dss_fixedarrays">Fixed Size Arrays</a>
749</div>
750
751<div class="doc_text">
752<p>Fixed size arrays are very simple and very fast. They are good if you know
753exactly how many elements you have, or you have a (low) upper bound on how many
754you have.</p>
755</div>
756
757<!-- _______________________________________________________________________ -->
758<div class="doc_subsubsection">
759 <a name="dss_heaparrays">Heap Allocated Arrays</a>
760</div>
761
762<div class="doc_text">
763<p>Heap allocated arrays (new[] + delete[]) are also simple. They are good if
764the number of elements is variable, if you know how many elements you will need
765before the array is allocated, and if the array is usually large (if not,
766consider a <a href="#dss_smallvector">SmallVector</a>). The cost of a heap
767allocated array is the cost of the new/delete (aka malloc/free). Also note that
768if you are allocating an array of a type with a constructor, the constructor and
Reid Spencer128a7a72007-02-03 21:06:43 +0000[diff] [blame]769destructors will be run for every element in the array (re-sizable vectors only
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]770construct those elements actually used).</p>
771</div>
772
773<!-- _______________________________________________________________________ -->
774<div class="doc_subsubsection">
775 <a name="dss_smallvector">"llvm/ADT/SmallVector.h"</a>
776</div>
777
778<div class="doc_text">
779<p><tt>SmallVector&lt;Type, N&gt;</tt> is a simple class that looks and smells
780just like <tt>vector&lt;Type&gt;</tt>:
781it supports efficient iteration, lays out elements in memory order (so you can
782do pointer arithmetic between elements), supports efficient push_back/pop_back
783operations, supports efficient random access to its elements, etc.</p>
784
785<p>The advantage of SmallVector is that it allocates space for
786some number of elements (N) <b>in the object itself</b>. Because of this, if
787the SmallVector is dynamically smaller than N, no malloc is performed. This can
788be a big win in cases where the malloc/free call is far more expensive than the
789code that fiddles around with the elements.</p>
790
791<p>This is good for vectors that are "usually small" (e.g. the number of
792predecessors/successors of a block is usually less than 8). On the other hand,
793this makes the size of the SmallVector itself large, so you don't want to
794allocate lots of them (doing so will waste a lot of space). As such,
795SmallVectors are most useful when on the stack.</p>
796
797<p>SmallVector also provides a nice portable and efficient replacement for
798<tt>alloca</tt>.</p>
799
800</div>
801
802<!-- _______________________________________________________________________ -->
803<div class="doc_subsubsection">
804 <a name="dss_vector">&lt;vector&gt;</a>
805</div>
806
807<div class="doc_text">
808<p>
809std::vector is well loved and respected. It is useful when SmallVector isn't:
810when the size of the vector is often large (thus the small optimization will
811rarely be a benefit) or if you will be allocating many instances of the vector
812itself (which would waste space for elements that aren't in the container).
813vector is also useful when interfacing with code that expects vectors :).
814</p>
Chris Lattner32d84762007-02-05 06:30:51 +0000[diff] [blame]815
816<p>One worthwhile note about std::vector: avoid code like this:</p>
817
818<div class="doc_code">
819<pre>
820for ( ... ) {
Chris Lattner9bb3dbb2007-03-28 18:27:57 +0000[diff] [blame]821 std::vector&lt;foo&gt; V;
Chris Lattner32d84762007-02-05 06:30:51 +0000[diff] [blame]822 use V;
823}
824</pre>
825</div>
826
827<p>Instead, write this as:</p>
828
829<div class="doc_code">
830<pre>
Chris Lattner9bb3dbb2007-03-28 18:27:57 +0000[diff] [blame]831std::vector&lt;foo&gt; V;
Chris Lattner32d84762007-02-05 06:30:51 +0000[diff] [blame]832for ( ... ) {
833 use V;
834 V.clear();
835}
836</pre>
837</div>
838
839<p>Doing so will save (at least) one heap allocation and free per iteration of
840the loop.</p>
841
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]842</div>
843
844<!-- _______________________________________________________________________ -->
845<div class="doc_subsubsection">
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]846 <a name="dss_deque">&lt;deque&gt;</a>
847</div>
848
849<div class="doc_text">
850<p>std::deque is, in some senses, a generalized version of std::vector. Like
851std::vector, it provides constant time random access and other similar
852properties, but it also provides efficient access to the front of the list. It
853does not guarantee continuity of elements within memory.</p>
854
855<p>In exchange for this extra flexibility, std::deque has significantly higher
856constant factor costs than std::vector. If possible, use std::vector or
857something cheaper.</p>
858</div>
859
860<!-- _______________________________________________________________________ -->
861<div class="doc_subsubsection">
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]862 <a name="dss_list">&lt;list&gt;</a>
863</div>
864
865<div class="doc_text">
866<p>std::list is an extremely inefficient class that is rarely useful.
867It performs a heap allocation for every element inserted into it, thus having an
868extremely high constant factor, particularly for small data types. std::list
869also only supports bidirectional iteration, not random access iteration.</p>
870
871<p>In exchange for this high cost, std::list supports efficient access to both
872ends of the list (like std::deque, but unlike std::vector or SmallVector). In
873addition, the iterator invalidation characteristics of std::list are stronger
874than that of a vector class: inserting or removing an element into the list does
875not invalidate iterator or pointers to other elements in the list.</p>
876</div>
877
878<!-- _______________________________________________________________________ -->
879<div class="doc_subsubsection">
Gabor Greif3899e492009-02-27 11:37:41 +0000[diff] [blame]880 <a name="dss_ilist">llvm/ADT/ilist.h</a>
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]881</div>
882
883<div class="doc_text">
884<p><tt>ilist&lt;T&gt;</tt> implements an 'intrusive' doubly-linked list. It is
885intrusive, because it requires the element to store and provide access to the
886prev/next pointers for the list.</p>
887
Gabor Greif2946d1c2009-02-27 12:02:19 +0000[diff] [blame]888<p><tt>ilist</tt> has the same drawbacks as <tt>std::list</tt>, and additionally
889requires an <tt>ilist_traits</tt> implementation for the element type, but it
890provides some novel characteristics. In particular, it can efficiently store
891polymorphic objects, the traits class is informed when an element is inserted or
Gabor Greif0cbcabe2009-03-12 09:47:03 +0000[diff] [blame^]892removed from the list, and <tt>ilist</tt>s are guaranteed to support a
893constant-time splice operation.</p>
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]894
Gabor Greif0cbcabe2009-03-12 09:47:03 +0000[diff] [blame^]895<p>These properties are exactly what we want for things like
896<tt>Instruction</tt>s and basic blocks, which is why these are implemented with
897<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
Gabor Greif0cbcabe2009-03-12 09:47:03 +0000[diff] [blame^]925supports a slightly narrower interface. Notably, inserters from
926<tt>T&amp;</tt> are 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
Gabor Greif0cbcabe2009-03-12 09:47:03 +0000[diff] [blame^]943<tt>T</tt>, usually <tt>T</tt> publicly derives from
944<tt>ilist_node&lt;T&gt;</tt>.</p>
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]945</div>
946
947<!-- _______________________________________________________________________ -->
948<div class="doc_subsubsection">
Chris Lattnerc5722432007-02-03 19:49:31 +0000[diff] [blame]949 <a name="dss_other">Other Sequential Container options</a>
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]950</div>
951
952<div class="doc_text">
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]953<p>Other STL containers are available, such as std::string.</p>
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]954
955<p>There are also various STL adapter classes such as std::queue,
956std::priority_queue, std::stack, etc. These provide simplified access to an
957underlying container but don't affect the cost of the container itself.</p>
958
959</div>
960
961
962<!-- ======================================================================= -->
963<div class="doc_subsection">
964 <a name="ds_set">Set-Like Containers (std::set, SmallSet, SetVector, etc)</a>
965</div>
966
967<div class="doc_text">
968
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]969<p>Set-like containers are useful when you need to canonicalize multiple values
970into a single representation. There are several different choices for how to do
971this, providing various trade-offs.</p>
972
973</div>
974
975
976<!-- _______________________________________________________________________ -->
977<div class="doc_subsubsection">
978 <a name="dss_sortedvectorset">A sorted 'vector'</a>
979</div>
980
981<div class="doc_text">
982
Chris Lattner3b23a8c2007-02-03 08:10:45 +0000[diff] [blame]983<p>If you intend to insert a lot of elements, then do a lot of queries, a
984great approach is to use a vector (or other sequential container) with
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]985std::sort+std::unique to remove duplicates. This approach works really well if
Chris Lattner3b23a8c2007-02-03 08:10:45 +0000[diff] [blame]986your usage pattern has these two distinct phases (insert then query), and can be
987coupled with a good choice of <a href="#ds_sequential">sequential container</a>.
988</p>
989
990<p>
991This combination provides the several nice properties: the result data is
992contiguous in memory (good for cache locality), has few allocations, is easy to
993address (iterators in the final vector are just indices or pointers), and can be
994efficiently queried with a standard binary or radix search.</p>
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]995
996</div>
997
998<!-- _______________________________________________________________________ -->
999<div class="doc_subsubsection">
1000 <a name="dss_smallset">"llvm/ADT/SmallSet.h"</a>
1001</div>
1002
1003<div class="doc_text">
1004
Reid Spencer128a7a72007-02-03 21:06:43 +0000[diff] [blame]1005<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]1006are 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]1007has space for N elements in place (thus, if the set is dynamically smaller than
Chris Lattner14868db2007-02-03 08:20:15 +0000[diff] [blame]1008N, no malloc traffic is required) and accesses them with a simple linear search.
1009When the set grows beyond 'N' elements, it allocates a more expensive representation that
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1010guarantees efficient access (for most types, it falls back to std::set, but for
Chris Lattner14868db2007-02-03 08:20:15 +0000[diff] [blame]1011pointers it uses something far better, <a
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1012href="#dss_smallptrset">SmallPtrSet</a>).</p>
1013
1014<p>The magic of this class is that it handles small sets extremely efficiently,
1015but gracefully handles extremely large sets without loss of efficiency. The
1016drawback is that the interface is quite small: it supports insertion, queries
1017and erasing, but does not support iteration.</p>
1018
1019</div>
1020
1021<!-- _______________________________________________________________________ -->
1022<div class="doc_subsubsection">
1023 <a name="dss_smallptrset">"llvm/ADT/SmallPtrSet.h"</a>
1024</div>
1025
1026<div class="doc_text">
1027
1028<p>SmallPtrSet has all the advantages of SmallSet (and a SmallSet of pointers is
Reid Spencer128a7a72007-02-03 21:06:43 +0000[diff] [blame]1029transparently implemented with a SmallPtrSet), but also supports iterators. If
Chris Lattner14868db2007-02-03 08:20:15 +0000[diff] [blame]1030more than 'N' insertions are performed, a single quadratically
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1031probed hash table is allocated and grows as needed, providing extremely
1032efficient access (constant time insertion/deleting/queries with low constant
1033factors) and is very stingy with malloc traffic.</p>
1034
1035<p>Note that, unlike std::set, the iterators of SmallPtrSet are invalidated
1036whenever an insertion occurs. Also, the values visited by the iterators are not
1037visited in sorted order.</p>
1038
1039</div>
1040
1041<!-- _______________________________________________________________________ -->
1042<div class="doc_subsubsection">
Chris Lattnerc28476f2007-09-30 00:58:59 +0000[diff] [blame]1043 <a name="dss_denseset">"llvm/ADT/DenseSet.h"</a>
1044</div>
1045
1046<div class="doc_text">
1047
1048<p>
1049DenseSet is a simple quadratically probed hash table. It excels at supporting
1050small values: it uses a single allocation to hold all of the pairs that
1051are currently inserted in the set. DenseSet is a great way to unique small
1052values that are not simple pointers (use <a
1053href="#dss_smallptrset">SmallPtrSet</a> for pointers). Note that DenseSet has
1054the same requirements for the value type that <a
1055href="#dss_densemap">DenseMap</a> has.
1056</p>
1057
1058</div>
1059
1060<!-- _______________________________________________________________________ -->
1061<div class="doc_subsubsection">
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1062 <a name="dss_FoldingSet">"llvm/ADT/FoldingSet.h"</a>
1063</div>
1064
1065<div class="doc_text">
1066
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]1067<p>
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1068FoldingSet is an aggregate class that is really good at uniquing
1069expensive-to-create or polymorphic objects. It is a combination of a chained
1070hash table with intrusive links (uniqued objects are required to inherit from
Chris Lattner14868db2007-02-03 08:20:15 +0000[diff] [blame]1071FoldingSetNode) that uses <a href="#dss_smallvector">SmallVector</a> as part of
1072its ID process.</p>
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1073
Chris Lattner14868db2007-02-03 08:20:15 +0000[diff] [blame]1074<p>Consider a case where you want to implement a "getOrCreateFoo" method for
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1075a complex object (for example, a node in the code generator). The client has a
1076description of *what* it wants to generate (it knows the opcode and all the
1077operands), 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]1078only to find out it already exists, at which point we would have to delete it
1079and return the node that already exists.
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]1080</p>
1081
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1082<p>To support this style of client, FoldingSet perform a query with a
1083FoldingSetNodeID (which wraps SmallVector) that can be used to describe the
1084element that we want to query for. The query either returns the element
1085matching the ID or it returns an opaque ID that indicates where insertion should
Chris Lattner14868db2007-02-03 08:20:15 +0000[diff] [blame]1086take place. Construction of the ID usually does not require heap traffic.</p>
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1087
1088<p>Because FoldingSet uses intrusive links, it can support polymorphic objects
1089in the set (for example, you can have SDNode instances mixed with LoadSDNodes).
1090Because the elements are individually allocated, pointers to the elements are
1091stable: inserting or removing elements does not invalidate any pointers to other
1092elements.
1093</p>
1094
1095</div>
1096
1097<!-- _______________________________________________________________________ -->
1098<div class="doc_subsubsection">
1099 <a name="dss_set">&lt;set&gt;</a>
1100</div>
1101
1102<div class="doc_text">
1103
Chris Lattnerc5722432007-02-03 19:49:31 +0000[diff] [blame]1104<p><tt>std::set</tt> is a reasonable all-around set class, which is decent at
1105many things but great at nothing. std::set allocates memory for each element
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1106inserted (thus it is very malloc intensive) and typically stores three pointers
Chris Lattner14868db2007-02-03 08:20:15 +0000[diff] [blame]1107per element in the set (thus adding a large amount of per-element space
1108overhead). It offers guaranteed log(n) performance, which is not particularly
Chris Lattnerc5722432007-02-03 19:49:31 +0000[diff] [blame]1109fast from a complexity standpoint (particularly if the elements of the set are
1110expensive to compare, like strings), and has extremely high constant factors for
1111lookup, insertion and removal.</p>
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1112
Chris Lattner14868db2007-02-03 08:20:15 +0000[diff] [blame]1113<p>The advantages of std::set are that its iterators are stable (deleting or
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1114inserting an element from the set does not affect iterators or pointers to other
1115elements) and that iteration over the set is guaranteed to be in sorted order.
1116If the elements in the set are large, then the relative overhead of the pointers
1117and malloc traffic is not a big deal, but if the elements of the set are small,
1118std::set is almost never a good choice.</p>
1119
1120</div>
1121
1122<!-- _______________________________________________________________________ -->
1123<div class="doc_subsubsection">
1124 <a name="dss_setvector">"llvm/ADT/SetVector.h"</a>
1125</div>
1126
1127<div class="doc_text">
Chris Lattneredca3c52007-02-04 00:00:26 +0000[diff] [blame]1128<p>LLVM's SetVector&lt;Type&gt; is an adapter class that combines your choice of
1129a set-like container along with a <a href="#ds_sequential">Sequential
1130Container</a>. The important property
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1131that this provides is efficient insertion with uniquing (duplicate elements are
1132ignored) with iteration support. It implements this by inserting elements into
1133both a set-like container and the sequential container, using the set-like
1134container for uniquing and the sequential container for iteration.
1135</p>
1136
1137<p>The difference between SetVector and other sets is that the order of
1138iteration is guaranteed to match the order of insertion into the SetVector.
1139This property is really important for things like sets of pointers. Because
1140pointer values are non-deterministic (e.g. vary across runs of the program on
Chris Lattneredca3c52007-02-04 00:00:26 +0000[diff] [blame]1141different machines), iterating over the pointers in the set will
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1142not be in a well-defined order.</p>
1143
1144<p>
1145The drawback of SetVector is that it requires twice as much space as a normal
1146set and has the sum of constant factors from the set-like container and the
1147sequential container that it uses. Use it *only* if you need to iterate over
1148the elements in a deterministic order. SetVector is also expensive to delete
Chris Lattneredca3c52007-02-04 00:00:26 +0000[diff] [blame]1149elements out of (linear time), unless you use it's "pop_back" method, which is
1150faster.
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1151</p>
1152
Chris Lattneredca3c52007-02-04 00:00:26 +0000[diff] [blame]1153<p>SetVector is an adapter class that defaults to using std::vector and std::set
1154for the underlying containers, so it is quite expensive. However,
1155<tt>"llvm/ADT/SetVector.h"</tt> also provides a SmallSetVector class, which
1156defaults to using a SmallVector and SmallSet of a specified size. If you use
1157this, and if your sets are dynamically smaller than N, you will save a lot of
1158heap traffic.</p>
1159
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1160</div>
1161
1162<!-- _______________________________________________________________________ -->
1163<div class="doc_subsubsection">
Chris Lattnerc5722432007-02-03 19:49:31 +0000[diff] [blame]1164 <a name="dss_uniquevector">"llvm/ADT/UniqueVector.h"</a>
1165</div>
1166
1167<div class="doc_text">
1168
1169<p>
1170UniqueVector is similar to <a href="#dss_setvector">SetVector</a>, but it
1171retains a unique ID for each element inserted into the set. It internally
1172contains a map and a vector, and it assigns a unique ID for each value inserted
1173into the set.</p>
1174
1175<p>UniqueVector is very expensive: its cost is the sum of the cost of
1176maintaining both the map and vector, it has high complexity, high constant
1177factors, and produces a lot of malloc traffic. It should be avoided.</p>
1178
1179</div>
1180
1181
1182<!-- _______________________________________________________________________ -->
1183<div class="doc_subsubsection">
1184 <a name="dss_otherset">Other Set-Like Container Options</a>
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1185</div>
1186
1187<div class="doc_text">
1188
1189<p>
1190The STL provides several other options, such as std::multiset and the various
Chris Lattnerf1a30822009-03-09 05:20:45 +0000[diff] [blame]1191"hash_set" like containers (whether from C++ TR1 or from the SGI library). We
1192never use hash_set and unordered_set because they are generally very expensive
1193(each insertion requires a malloc) and very non-portable.
1194</p>
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1195
1196<p>std::multiset is useful if you're not interested in elimination of
Chris Lattner14868db2007-02-03 08:20:15 +0000[diff] [blame]1197duplicates, but has all the drawbacks of std::set. A sorted vector (where you
1198don't delete duplicate entries) or some other approach is almost always
1199better.</p>
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1200
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]1201</div>
1202
1203<!-- ======================================================================= -->
1204<div class="doc_subsection">
1205 <a name="ds_map">Map-Like Containers (std::map, DenseMap, etc)</a>
1206</div>
1207
1208<div class="doc_text">
Chris Lattnerc5722432007-02-03 19:49:31 +0000[diff] [blame]1209Map-like containers are useful when you want to associate data to a key. As
1210usual, there are a lot of different ways to do this. :)
1211</div>
1212
1213<!-- _______________________________________________________________________ -->
1214<div class="doc_subsubsection">
1215 <a name="dss_sortedvectormap">A sorted 'vector'</a>
1216</div>
1217
1218<div class="doc_text">
1219
1220<p>
1221If your usage pattern follows a strict insert-then-query approach, you can
1222trivially use the same approach as <a href="#dss_sortedvectorset">sorted vectors
1223for set-like containers</a>. The only difference is that your query function
1224(which uses std::lower_bound to get efficient log(n) lookup) should only compare
1225the key, not both the key and value. This yields the same advantages as sorted
1226vectors for sets.
1227</p>
1228</div>
1229
1230<!-- _______________________________________________________________________ -->
1231<div class="doc_subsubsection">
Chris Lattner796f9fa2007-02-08 19:14:21 +0000[diff] [blame]1232 <a name="dss_stringmap">"llvm/ADT/StringMap.h"</a>
Chris Lattnerc5722432007-02-03 19:49:31 +0000[diff] [blame]1233</div>
1234
1235<div class="doc_text">
1236
1237<p>
1238Strings are commonly used as keys in maps, and they are difficult to support
1239efficiently: they are variable length, inefficient to hash and compare when
Chris Lattner796f9fa2007-02-08 19:14:21 +0000[diff] [blame]1240long, expensive to copy, etc. StringMap is a specialized container designed to
1241cope with these issues. It supports mapping an arbitrary range of bytes to an
1242arbitrary other object.</p>
Chris Lattnerc5722432007-02-03 19:49:31 +0000[diff] [blame]1243
Chris Lattner796f9fa2007-02-08 19:14:21 +0000[diff] [blame]1244<p>The StringMap implementation uses a quadratically-probed hash table, where
Chris Lattnerc5722432007-02-03 19:49:31 +0000[diff] [blame]1245the buckets store a pointer to the heap allocated entries (and some other
1246stuff). The entries in the map must be heap allocated because the strings are
1247variable length. The string data (key) and the element object (value) are
1248stored in the same allocation with the string data immediately after the element
1249object. This container guarantees the "<tt>(char*)(&amp;Value+1)</tt>" points
1250to the key string for a value.</p>
1251
Chris Lattner796f9fa2007-02-08 19:14:21 +0000[diff] [blame]1252<p>The StringMap is very fast for several reasons: quadratic probing is very
Chris Lattnerc5722432007-02-03 19:49:31 +0000[diff] [blame]1253cache efficient for lookups, the hash value of strings in buckets is not
Chris Lattner796f9fa2007-02-08 19:14:21 +0000[diff] [blame]1254recomputed when lookup up an element, StringMap rarely has to touch the
Chris Lattnerc5722432007-02-03 19:49:31 +0000[diff] [blame]1255memory for unrelated objects when looking up a value (even when hash collisions
1256happen), hash table growth does not recompute the hash values for strings
1257already in the table, and each pair in the map is store in a single allocation
1258(the string data is stored in the same allocation as the Value of a pair).</p>
1259
Chris Lattner796f9fa2007-02-08 19:14:21 +0000[diff] [blame]1260<p>StringMap also provides query methods that take byte ranges, so it only ever
Chris Lattnerc5722432007-02-03 19:49:31 +0000[diff] [blame]1261copies a string if a value is inserted into the table.</p>
1262</div>
1263
1264<!-- _______________________________________________________________________ -->
1265<div class="doc_subsubsection">
1266 <a name="dss_indexedmap">"llvm/ADT/IndexedMap.h"</a>
1267</div>
1268
1269<div class="doc_text">
1270<p>
1271IndexedMap is a specialized container for mapping small dense integers (or
1272values that can be mapped to small dense integers) to some other type. It is
1273internally implemented as a vector with a mapping function that maps the keys to
1274the dense integer range.
1275</p>
1276
1277<p>
1278This is useful for cases like virtual registers in the LLVM code generator: they
1279have a dense mapping that is offset by a compile-time constant (the first
1280virtual register ID).</p>
1281
1282</div>
1283
1284<!-- _______________________________________________________________________ -->
1285<div class="doc_subsubsection">
1286 <a name="dss_densemap">"llvm/ADT/DenseMap.h"</a>
1287</div>
1288
1289<div class="doc_text">
1290
1291<p>
1292DenseMap is a simple quadratically probed hash table. It excels at supporting
1293small keys and values: it uses a single allocation to hold all of the pairs that
1294are currently inserted in the map. DenseMap is a great way to map pointers to
1295pointers, or map other small types to each other.
1296</p>
1297
1298<p>
1299There are several aspects of DenseMap that you should be aware of, however. The
1300iterators in a densemap are invalidated whenever an insertion occurs, unlike
1301map. Also, because DenseMap allocates space for a large number of key/value
Chris Lattnera4a264d2007-02-03 20:17:53 +0000[diff] [blame]1302pairs (it starts with 64 by default), it will waste a lot of space if your keys
1303or values are large. Finally, you must implement a partial specialization of
Chris Lattner76c1b972007-09-17 18:34:04 +0000[diff] [blame]1304DenseMapInfo for the key that you want, if it isn't already supported. This
Chris Lattnerc5722432007-02-03 19:49:31 +0000[diff] [blame]1305is required to tell DenseMap about two special marker values (which can never be
Chris Lattnera4a264d2007-02-03 20:17:53 +0000[diff] [blame]1306inserted into the map) that it needs internally.</p>
Chris Lattnerc5722432007-02-03 19:49:31 +0000[diff] [blame]1307
1308</div>
1309
1310<!-- _______________________________________________________________________ -->
1311<div class="doc_subsubsection">
1312 <a name="dss_map">&lt;map&gt;</a>
1313</div>
1314
1315<div class="doc_text">
1316
1317<p>
1318std::map has similar characteristics to <a href="#dss_set">std::set</a>: it uses
1319a single allocation per pair inserted into the map, it offers log(n) lookup with
1320an extremely large constant factor, imposes a space penalty of 3 pointers per
1321pair in the map, etc.</p>
1322
1323<p>std::map is most useful when your keys or values are very large, if you need
1324to iterate over the collection in sorted order, or if you need stable iterators
1325into the map (i.e. they don't get invalidated if an insertion or deletion of
1326another element takes place).</p>
1327
1328</div>
1329
1330<!-- _______________________________________________________________________ -->
1331<div class="doc_subsubsection">
1332 <a name="dss_othermap">Other Map-Like Container Options</a>
1333</div>
1334
1335<div class="doc_text">
1336
1337<p>
1338The STL provides several other options, such as std::multimap and the various
Chris Lattnerf1a30822009-03-09 05:20:45 +0000[diff] [blame]1339"hash_map" like containers (whether from C++ TR1 or from the SGI library). We
1340never use hash_set and unordered_set because they are generally very expensive
1341(each insertion requires a malloc) and very non-portable.</p>
Chris Lattnerc5722432007-02-03 19:49:31 +0000[diff] [blame]1342
1343<p>std::multimap is useful if you want to map a key to multiple values, but has
1344all the drawbacks of std::map. A sorted vector or some other approach is almost
1345always better.</p>
1346
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]1347</div>
1348
Daniel Berlin1939ace2007-09-24 17:52:25 +0000[diff] [blame]1349<!-- ======================================================================= -->
1350<div class="doc_subsection">
1351 <a name="ds_bit">Bit storage containers (BitVector, SparseBitVector)</a>
1352</div>
1353
1354<div class="doc_text">
Chris Lattner7086ce72007-09-25 22:37:50 +0000[diff] [blame]1355<p>Unlike the other containers, there are only two bit storage containers, and
1356choosing when to use each is relatively straightforward.</p>
1357
1358<p>One additional option is
1359<tt>std::vector&lt;bool&gt;</tt>: we discourage its use for two reasons 1) the
1360implementation in many common compilers (e.g. commonly available versions of
1361GCC) is extremely inefficient and 2) the C++ standards committee is likely to
1362deprecate this container and/or change it significantly somehow. In any case,
1363please don't use it.</p>
Daniel Berlin1939ace2007-09-24 17:52:25 +0000[diff] [blame]1364</div>
1365
1366<!-- _______________________________________________________________________ -->
1367<div class="doc_subsubsection">
1368 <a name="dss_bitvector">BitVector</a>
1369</div>
1370
1371<div class="doc_text">
1372<p> The BitVector container provides a fixed size set of bits for manipulation.
1373It supports individual bit setting/testing, as well as set operations. The set
1374operations take time O(size of bitvector), but operations are performed one word
1375at a time, instead of one bit at a time. This makes the BitVector very fast for
1376set operations compared to other containers. Use the BitVector when you expect
1377the number of set bits to be high (IE a dense set).
1378</p>
1379</div>
1380
1381<!-- _______________________________________________________________________ -->
1382<div class="doc_subsubsection">
1383 <a name="dss_sparsebitvector">SparseBitVector</a>
1384</div>
1385
1386<div class="doc_text">
1387<p> The SparseBitVector container is much like BitVector, with one major
1388difference: Only the bits that are set, are stored. This makes the
1389SparseBitVector much more space efficient than BitVector when the set is sparse,
1390as well as making set operations O(number of set bits) instead of O(size of
1391universe). 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
1392(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).
1393</p>
1394</div>
Chris Lattnerf623a082005-10-17 01:36:23 +0000[diff] [blame]1395
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1396<!-- *********************************************************************** -->
1397<div class="doc_section">
1398 <a name="common">Helpful Hints for Common Operations</a>
1399</div>
1400<!-- *********************************************************************** -->
1401
1402<div class="doc_text">
1403
1404<p>This section describes how to perform some very simple transformations of
1405LLVM code. This is meant to give examples of common idioms used, showing the
1406practical side of LLVM transformations. <p> Because this is a "how-to" section,
1407you should also read about the main classes that you will be working with. The
1408<a href="#coreclasses">Core LLVM Class Hierarchy Reference</a> contains details
1409and descriptions of the main classes that you should know about.</p>
1410
1411</div>
1412
1413<!-- NOTE: this section should be heavy on example code -->
1414<!-- ======================================================================= -->
1415<div class="doc_subsection">
1416 <a name="inspection">Basic Inspection and Traversal Routines</a>
1417</div>
1418
1419<div class="doc_text">
1420
1421<p>The LLVM compiler infrastructure have many different data structures that may
1422be traversed. Following the example of the C++ standard template library, the
1423techniques used to traverse these various data structures are all basically the
1424same. For a enumerable sequence of values, the <tt>XXXbegin()</tt> function (or
1425method) returns an iterator to the start of the sequence, the <tt>XXXend()</tt>
1426function returns an iterator pointing to one past the last valid element of the
1427sequence, and there is some <tt>XXXiterator</tt> data type that is common
1428between the two operations.</p>
1429
1430<p>Because the pattern for iteration is common across many different aspects of
1431the program representation, the standard template library algorithms may be used
1432on them, and it is easier to remember how to iterate. First we show a few common
1433examples of the data structures that need to be traversed. Other data
1434structures are traversed in very similar ways.</p>
1435
1436</div>
1437
1438<!-- _______________________________________________________________________ -->
Chris Lattner69bf8a92004-05-23 21:06:58 +0000[diff] [blame]1439<div class="doc_subsubsection">
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1440 <a name="iterate_function">Iterating over the </a><a
1441 href="#BasicBlock"><tt>BasicBlock</tt></a>s in a <a
1442 href="#Function"><tt>Function</tt></a>
1443</div>
1444
1445<div class="doc_text">
1446
1447<p>It's quite common to have a <tt>Function</tt> instance that you'd like to
1448transform in some way; in particular, you'd like to manipulate its
1449<tt>BasicBlock</tt>s. To facilitate this, you'll need to iterate over all of
1450the <tt>BasicBlock</tt>s that constitute the <tt>Function</tt>. The following is
1451an example that prints the name of a <tt>BasicBlock</tt> and the number of
1452<tt>Instruction</tt>s it contains:</p>
1453
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1454<div class="doc_code">
1455<pre>
Bill Wendling82e2eea2006-10-11 18:00:22 +0000[diff] [blame]1456// <i>func is a pointer to a Function instance</i>
1457for (Function::iterator i = func-&gt;begin(), e = func-&gt;end(); i != e; ++i)
1458 // <i>Print out the name of the basic block if it has one, and then the</i>
1459 // <i>number of instructions that it contains</i>
Bill Wendling832171c2006-12-07 20:04:42 +0000[diff] [blame]1460 llvm::cerr &lt;&lt; "Basic block (name=" &lt;&lt; i-&gt;getName() &lt;&lt; ") has "
1461 &lt;&lt; i-&gt;size() &lt;&lt; " instructions.\n";
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1462</pre>
1463</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1464
1465<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]1466invoking member functions of the <tt>Instruction</tt> class. This is
1467because the indirection operator is overloaded for the iterator
Chris Lattner7496ec52003-08-05 22:54:23 +0000[diff] [blame]1468classes. In the above code, the expression <tt>i-&gt;size()</tt> is
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1469exactly equivalent to <tt>(*i).size()</tt> just like you'd expect.</p>
1470
1471</div>
1472
1473<!-- _______________________________________________________________________ -->
Chris Lattner69bf8a92004-05-23 21:06:58 +0000[diff] [blame]1474<div class="doc_subsubsection">
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1475 <a name="iterate_basicblock">Iterating over the </a><a
1476 href="#Instruction"><tt>Instruction</tt></a>s in a <a
1477 href="#BasicBlock"><tt>BasicBlock</tt></a>
1478</div>
1479
1480<div class="doc_text">
1481
1482<p>Just like when dealing with <tt>BasicBlock</tt>s in <tt>Function</tt>s, it's
1483easy to iterate over the individual instructions that make up
1484<tt>BasicBlock</tt>s. Here's a code snippet that prints out each instruction in
1485a <tt>BasicBlock</tt>:</p>
1486
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1487<div class="doc_code">
Chris Lattner55c04612005-03-06 06:00:13 +0000[diff] [blame]1488<pre>
Bill Wendling82e2eea2006-10-11 18:00:22 +0000[diff] [blame]1489// <i>blk is a pointer to a BasicBlock instance</i>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1490for (BasicBlock::iterator i = blk-&gt;begin(), e = blk-&gt;end(); i != e; ++i)
Bill Wendling82e2eea2006-10-11 18:00:22 +0000[diff] [blame]1491 // <i>The next statement works since operator&lt;&lt;(ostream&amp;,...)</i>
1492 // <i>is overloaded for Instruction&amp;</i>
Bill Wendling832171c2006-12-07 20:04:42 +0000[diff] [blame]1493 llvm::cerr &lt;&lt; *i &lt;&lt; "\n";
Chris Lattner55c04612005-03-06 06:00:13 +0000[diff] [blame]1494</pre>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1495</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1496
1497<p>However, this isn't really the best way to print out the contents of a
1498<tt>BasicBlock</tt>! Since the ostream operators are overloaded for virtually
1499anything you'll care about, you could have just invoked the print routine on the
Bill Wendling832171c2006-12-07 20:04:42 +0000[diff] [blame]1500basic block itself: <tt>llvm::cerr &lt;&lt; *blk &lt;&lt; "\n";</tt>.</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1501
1502</div>
1503
1504<!-- _______________________________________________________________________ -->
Chris Lattner69bf8a92004-05-23 21:06:58 +0000[diff] [blame]1505<div class="doc_subsubsection">
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1506 <a name="iterate_institer">Iterating over the </a><a
1507 href="#Instruction"><tt>Instruction</tt></a>s in a <a
1508 href="#Function"><tt>Function</tt></a>
1509</div>
1510
1511<div class="doc_text">
1512
1513<p>If you're finding that you commonly iterate over a <tt>Function</tt>'s
1514<tt>BasicBlock</tt>s and then that <tt>BasicBlock</tt>'s <tt>Instruction</tt>s,
1515<tt>InstIterator</tt> should be used instead. You'll need to include <a
1516href="/doxygen/InstIterator_8h-source.html"><tt>llvm/Support/InstIterator.h</tt></a>,
1517and then instantiate <tt>InstIterator</tt>s explicitly in your code. Here's a
Chris Lattner69bf8a92004-05-23 21:06:58 +0000[diff] [blame]1518small 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]1519
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1520<div class="doc_code">
1521<pre>
1522#include "<a href="/doxygen/InstIterator_8h-source.html">llvm/Support/InstIterator.h</a>"
1523
Reid Spencer128a7a72007-02-03 21:06:43 +0000[diff] [blame]1524// <i>F is a pointer to a Function instance</i>
Chris Lattnerda021aa2008-06-04 18:20:42 +0000[diff] [blame]1525for (inst_iterator I = inst_begin(F), E = inst_end(F); I != E; ++I)
1526 llvm::cerr &lt;&lt; *I &lt;&lt; "\n";
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1527</pre>
1528</div>
1529
1530<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]1531work list with its initial contents. For example, if you wanted to
1532initialize a work list to contain all instructions in a <tt>Function</tt>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1533F, all you would need to do is something like:</p>
1534
1535<div class="doc_code">
1536<pre>
1537std::set&lt;Instruction*&gt; worklist;
Chris Lattnerda021aa2008-06-04 18:20:42 +0000[diff] [blame]1538// or better yet, SmallPtrSet&lt;Instruction*, 64&gt; worklist;
1539
1540for (inst_iterator I = inst_begin(F), E = inst_end(F); I != E; ++I)
1541 worklist.insert(&amp;*I);
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1542</pre>
1543</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1544
1545<p>The STL set <tt>worklist</tt> would now contain all instructions in the
1546<tt>Function</tt> pointed to by F.</p>
1547
1548</div>
1549
1550<!-- _______________________________________________________________________ -->
1551<div class="doc_subsubsection">
1552 <a name="iterate_convert">Turning an iterator into a class pointer (and
1553 vice-versa)</a>
1554</div>
1555
1556<div class="doc_text">
1557
1558<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]1559instance when all you've got at hand is an iterator. Well, extracting
Chris Lattner69bf8a92004-05-23 21:06:58 +0000[diff] [blame]1560a reference or a pointer from an iterator is very straight-forward.
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]1561Assuming that <tt>i</tt> is a <tt>BasicBlock::iterator</tt> and <tt>j</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1562is a <tt>BasicBlock::const_iterator</tt>:</p>
1563
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1564<div class="doc_code">
1565<pre>
Bill Wendling82e2eea2006-10-11 18:00:22 +0000[diff] [blame]1566Instruction&amp; inst = *i; // <i>Grab reference to instruction reference</i>
1567Instruction* pinst = &amp;*i; // <i>Grab pointer to instruction reference</i>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1568const Instruction&amp; inst = *j;
1569</pre>
1570</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1571
1572<p>However, the iterators you'll be working with in the LLVM framework are
1573special: they will automatically convert to a ptr-to-instance type whenever they
1574need to. Instead of dereferencing the iterator and then taking the address of
1575the result, you can simply assign the iterator to the proper pointer type and
1576you get the dereference and address-of operation as a result of the assignment
1577(behind the scenes, this is a result of overloading casting mechanisms). Thus
1578the last line of the last example,</p>
1579
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1580<div class="doc_code">
1581<pre>
Chris Lattner2e438ca2008-01-03 16:56:04 +0000[diff] [blame]1582Instruction *pinst = &amp;*i;
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1583</pre>
1584</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1585
1586<p>is semantically equivalent to</p>
1587
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1588<div class="doc_code">
1589<pre>
Chris Lattner2e438ca2008-01-03 16:56:04 +0000[diff] [blame]1590Instruction *pinst = i;
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1591</pre>
1592</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1593
Chris Lattner69bf8a92004-05-23 21:06:58 +0000[diff] [blame]1594<p>It's also possible to turn a class pointer into the corresponding iterator,
1595and this is a constant time operation (very efficient). The following code
1596snippet illustrates use of the conversion constructors provided by LLVM
1597iterators. By using these, you can explicitly grab the iterator of something
1598without actually obtaining it via iteration over some structure:</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1599
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1600<div class="doc_code">
1601<pre>
1602void printNextInstruction(Instruction* inst) {
1603 BasicBlock::iterator it(inst);
Bill Wendling82e2eea2006-10-11 18:00:22 +0000[diff] [blame]1604 ++it; // <i>After this line, it refers to the instruction after *inst</i>
Bill Wendling832171c2006-12-07 20:04:42 +0000[diff] [blame]1605 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]1606}
1607</pre>
1608</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1609
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1610</div>
1611
1612<!--_______________________________________________________________________-->
1613<div class="doc_subsubsection">
1614 <a name="iterate_complex">Finding call sites: a slightly more complex
1615 example</a>
1616</div>
1617
1618<div class="doc_text">
1619
1620<p>Say that you're writing a FunctionPass and would like to count all the
1621locations in the entire module (that is, across every <tt>Function</tt>) where a
1622certain function (i.e., some <tt>Function</tt>*) is already in scope. As you'll
1623learn 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]1624much more straight-forward manner, but this example will allow us to explore how
Reid Spencer128a7a72007-02-03 21:06:43 +0000[diff] [blame]1625you'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]1626is what we want to do:</p>
1627
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1628<div class="doc_code">
1629<pre>
1630initialize callCounter to zero
1631for each Function f in the Module
1632 for each BasicBlock b in f
1633 for each Instruction i in b
1634 if (i is a CallInst and calls the given function)
1635 increment callCounter
1636</pre>
1637</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1638
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1639<p>And the actual code is (remember, because we're writing a
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1640<tt>FunctionPass</tt>, our <tt>FunctionPass</tt>-derived class simply has to
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1641override the <tt>runOnFunction</tt> method):</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1642
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1643<div class="doc_code">
1644<pre>
1645Function* targetFunc = ...;
1646
1647class OurFunctionPass : public FunctionPass {
1648 public:
1649 OurFunctionPass(): callCounter(0) { }
1650
1651 virtual runOnFunction(Function&amp; F) {
1652 for (Function::iterator b = F.begin(), be = F.end(); b != be; ++b) {
Eric Christopher203e71d2008-11-08 08:20:49 +0000[diff] [blame]1653 for (BasicBlock::iterator i = b-&gt;begin(), ie = b-&gt;end(); i != ie; ++i) {
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1654 if (<a href="#CallInst">CallInst</a>* callInst = <a href="#isa">dyn_cast</a>&lt;<a
1655 href="#CallInst">CallInst</a>&gt;(&amp;*i)) {
Bill Wendling82e2eea2006-10-11 18:00:22 +0000[diff] [blame]1656 // <i>We know we've encountered a call instruction, so we</i>
1657 // <i>need to determine if it's a call to the</i>
Chris Lattner2e438ca2008-01-03 16:56:04 +0000[diff] [blame]1658 // <i>function pointed to by m_func or not.</i>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1659 if (callInst-&gt;getCalledFunction() == targetFunc)
1660 ++callCounter;
1661 }
1662 }
1663 }
Bill Wendling82e2eea2006-10-11 18:00:22 +0000[diff] [blame]1664 }
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1665
1666 private:
Chris Lattner2e438ca2008-01-03 16:56:04 +0000[diff] [blame]1667 unsigned callCounter;
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1668};
1669</pre>
1670</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1671
1672</div>
1673
Brian Gaekef1972c62003-11-07 19:25:45 +0000[diff] [blame]1674<!--_______________________________________________________________________-->
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1675<div class="doc_subsubsection">
1676 <a name="calls_and_invokes">Treating calls and invokes the same way</a>
1677</div>
1678
1679<div class="doc_text">
1680
1681<p>You may have noticed that the previous example was a bit oversimplified in
1682that it did not deal with call sites generated by 'invoke' instructions. In
1683this, and in other situations, you may find that you want to treat
1684<tt>CallInst</tt>s and <tt>InvokeInst</tt>s the same way, even though their
1685most-specific common base class is <tt>Instruction</tt>, which includes lots of
1686less closely-related things. For these cases, LLVM provides a handy wrapper
1687class called <a
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]1688href="http://llvm.org/doxygen/classllvm_1_1CallSite.html"><tt>CallSite</tt></a>.
Chris Lattner69bf8a92004-05-23 21:06:58 +0000[diff] [blame]1689It is essentially a wrapper around an <tt>Instruction</tt> pointer, with some
1690methods that provide functionality common to <tt>CallInst</tt>s and
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1691<tt>InvokeInst</tt>s.</p>
1692
Chris Lattner69bf8a92004-05-23 21:06:58 +0000[diff] [blame]1693<p>This class has "value semantics": it should be passed by value, not by
1694reference and it should not be dynamically allocated or deallocated using
1695<tt>operator new</tt> or <tt>operator delete</tt>. It is efficiently copyable,
1696assignable and constructable, with costs equivalents to that of a bare pointer.
1697If you look at its definition, it has only a single pointer member.</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1698
1699</div>
1700
Chris Lattner1a3105b2002-09-09 05:49:39 +0000[diff] [blame]1701<!--_______________________________________________________________________-->
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1702<div class="doc_subsubsection">
1703 <a name="iterate_chains">Iterating over def-use &amp; use-def chains</a>
1704</div>
1705
1706<div class="doc_text">
1707
1708<p>Frequently, we might have an instance of the <a
Chris Lattner00815172007-01-04 22:01:45 +0000[diff] [blame]1709href="/doxygen/classllvm_1_1Value.html">Value Class</a> and we want to
Misha Brukman384047f2004-06-03 23:29:12 +0000[diff] [blame]1710determine which <tt>User</tt>s use the <tt>Value</tt>. The list of all
1711<tt>User</tt>s of a particular <tt>Value</tt> is called a <i>def-use</i> chain.
1712For example, let's say we have a <tt>Function*</tt> named <tt>F</tt> to a
1713particular function <tt>foo</tt>. Finding all of the instructions that
1714<i>use</i> <tt>foo</tt> is as simple as iterating over the <i>def-use</i> chain
1715of <tt>F</tt>:</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1716
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1717<div class="doc_code">
1718<pre>
Chris Lattner2e438ca2008-01-03 16:56:04 +0000[diff] [blame]1719Function *F = ...;
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1720
Bill Wendling82e2eea2006-10-11 18:00:22 +0000[diff] [blame]1721for (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]1722 if (Instruction *Inst = dyn_cast&lt;Instruction&gt;(*i)) {
Bill Wendling832171c2006-12-07 20:04:42 +0000[diff] [blame]1723 llvm::cerr &lt;&lt; "F is used in instruction:\n";
1724 llvm::cerr &lt;&lt; *Inst &lt;&lt; "\n";
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1725 }
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1726</pre>
1727</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1728
1729<p>Alternately, it's common to have an instance of the <a
Misha Brukman384047f2004-06-03 23:29:12 +0000[diff] [blame]1730href="/doxygen/classllvm_1_1User.html">User Class</a> and need to know what
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1731<tt>Value</tt>s are used by it. The list of all <tt>Value</tt>s used by a
1732<tt>User</tt> is known as a <i>use-def</i> chain. Instances of class
1733<tt>Instruction</tt> are common <tt>User</tt>s, so we might want to iterate over
1734all of the values that a particular instruction uses (that is, the operands of
1735the particular <tt>Instruction</tt>):</p>
1736
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1737<div class="doc_code">
1738<pre>
Chris Lattner2e438ca2008-01-03 16:56:04 +0000[diff] [blame]1739Instruction *pi = ...;
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1740
1741for (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]1742 Value *v = *i;
Bill Wendling82e2eea2006-10-11 18:00:22 +0000[diff] [blame]1743 // <i>...</i>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1744}
1745</pre>
1746</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1747
Chris Lattner1a3105b2002-09-09 05:49:39 +0000[diff] [blame]1748<!--
1749 def-use chains ("finding all users of"): Value::use_begin/use_end
1750 use-def chains ("finding all values used"): User::op_begin/op_end [op=operand]
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1751-->
1752
1753</div>
1754
Chris Lattner2e438ca2008-01-03 16:56:04 +0000[diff] [blame]1755<!--_______________________________________________________________________-->
1756<div class="doc_subsubsection">
1757 <a name="iterate_preds">Iterating over predecessors &amp;
1758successors of blocks</a>
1759</div>
1760
1761<div class="doc_text">
1762
1763<p>Iterating over the predecessors and successors of a block is quite easy
1764with the routines defined in <tt>"llvm/Support/CFG.h"</tt>. Just use code like
1765this to iterate over all predecessors of BB:</p>
1766
1767<div class="doc_code">
1768<pre>
1769#include "llvm/Support/CFG.h"
1770BasicBlock *BB = ...;
1771
1772for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI) {
1773 BasicBlock *Pred = *PI;
1774 // <i>...</i>
1775}
1776</pre>
1777</div>
1778
1779<p>Similarly, to iterate over successors use
1780succ_iterator/succ_begin/succ_end.</p>
1781
1782</div>
1783
1784
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1785<!-- ======================================================================= -->
1786<div class="doc_subsection">
1787 <a name="simplechanges">Making simple changes</a>
1788</div>
1789
1790<div class="doc_text">
1791
1792<p>There are some primitive transformation operations present in the LLVM
Joel Stanley753eb712002-09-11 22:32:24 +0000[diff] [blame]1793infrastructure that are worth knowing about. When performing
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]1794transformations, it's fairly common to manipulate the contents of basic
1795blocks. This section describes some of the common methods for doing so
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1796and gives example code.</p>
1797
1798</div>
1799
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]1800<!--_______________________________________________________________________-->
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1801<div class="doc_subsubsection">
1802 <a name="schanges_creating">Creating and inserting new
1803 <tt>Instruction</tt>s</a>
1804</div>
1805
1806<div class="doc_text">
1807
1808<p><i>Instantiating Instructions</i></p>
1809
Chris Lattner69bf8a92004-05-23 21:06:58 +0000[diff] [blame]1810<p>Creation of <tt>Instruction</tt>s is straight-forward: simply call the
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1811constructor for the kind of instruction to instantiate and provide the necessary
1812parameters. For example, an <tt>AllocaInst</tt> only <i>requires</i> a
1813(const-ptr-to) <tt>Type</tt>. Thus:</p>
1814
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1815<div class="doc_code">
1816<pre>
Nick Lewycky10d64b92007-12-03 01:52:52 +0000[diff] [blame]1817AllocaInst* ai = new AllocaInst(Type::Int32Ty);
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1818</pre>
1819</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1820
1821<p>will create an <tt>AllocaInst</tt> instance that represents the allocation of
Reid Spencer128a7a72007-02-03 21:06:43 +0000[diff] [blame]1822one integer in the current stack frame, at run time. Each <tt>Instruction</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1823subclass is likely to have varying default parameters which change the semantics
1824of the instruction, so refer to the <a
Misha Brukman31ca1de2004-06-03 23:35:54 +0000[diff] [blame]1825href="/doxygen/classllvm_1_1Instruction.html">doxygen documentation for the subclass of
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1826Instruction</a> that you're interested in instantiating.</p>
1827
1828<p><i>Naming values</i></p>
1829
1830<p>It is very useful to name the values of instructions when you're able to, as
1831this facilitates the debugging of your transformations. If you end up looking
1832at generated LLVM machine code, you definitely want to have logical names
1833associated with the results of instructions! By supplying a value for the
1834<tt>Name</tt> (default) parameter of the <tt>Instruction</tt> constructor, you
1835associate a logical name with the result of the instruction's execution at
Reid Spencer128a7a72007-02-03 21:06:43 +0000[diff] [blame]1836run time. For example, say that I'm writing a transformation that dynamically
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1837allocates space for an integer on the stack, and that integer is going to be
1838used as some kind of index by some other code. To accomplish this, I place an
1839<tt>AllocaInst</tt> at the first point in the first <tt>BasicBlock</tt> of some
1840<tt>Function</tt>, and I'm intending to use it within the same
1841<tt>Function</tt>. I might do:</p>
1842
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1843<div class="doc_code">
1844<pre>
Nick Lewycky10d64b92007-12-03 01:52:52 +0000[diff] [blame]1845AllocaInst* pa = new AllocaInst(Type::Int32Ty, 0, "indexLoc");
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1846</pre>
1847</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1848
1849<p>where <tt>indexLoc</tt> is now the logical name of the instruction's
Reid Spencer128a7a72007-02-03 21:06:43 +0000[diff] [blame]1850execution value, which is a pointer to an integer on the run time stack.</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1851
1852<p><i>Inserting instructions</i></p>
1853
1854<p>There are essentially two ways to insert an <tt>Instruction</tt>
1855into an existing sequence of instructions that form a <tt>BasicBlock</tt>:</p>
1856
Joel Stanley9dd1ad62002-09-18 03:17:23 +0000[diff] [blame]1857<ul>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1858 <li>Insertion into an explicit instruction list
1859
1860 <p>Given a <tt>BasicBlock* pb</tt>, an <tt>Instruction* pi</tt> within that
1861 <tt>BasicBlock</tt>, and a newly-created instruction we wish to insert
1862 before <tt>*pi</tt>, we do the following: </p>
1863
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1864<div class="doc_code">
1865<pre>
1866BasicBlock *pb = ...;
1867Instruction *pi = ...;
1868Instruction *newInst = new Instruction(...);
1869
Bill Wendling82e2eea2006-10-11 18:00:22 +0000[diff] [blame]1870pb-&gt;getInstList().insert(pi, newInst); // <i>Inserts newInst before pi in pb</i>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1871</pre>
1872</div>
Alkis Evlogimenos9a5dc4f2004-05-27 00:57:51 +0000[diff] [blame]1873
1874 <p>Appending to the end of a <tt>BasicBlock</tt> is so common that
1875 the <tt>Instruction</tt> class and <tt>Instruction</tt>-derived
1876 classes provide constructors which take a pointer to a
1877 <tt>BasicBlock</tt> to be appended to. For example code that
1878 looked like: </p>
1879
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1880<div class="doc_code">
1881<pre>
1882BasicBlock *pb = ...;
1883Instruction *newInst = new Instruction(...);
1884
Bill Wendling82e2eea2006-10-11 18:00:22 +0000[diff] [blame]1885pb-&gt;getInstList().push_back(newInst); // <i>Appends newInst to pb</i>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1886</pre>
1887</div>
Alkis Evlogimenos9a5dc4f2004-05-27 00:57:51 +0000[diff] [blame]1888
1889 <p>becomes: </p>
1890
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1891<div class="doc_code">
1892<pre>
1893BasicBlock *pb = ...;
1894Instruction *newInst = new Instruction(..., pb);
1895</pre>
1896</div>
Alkis Evlogimenos9a5dc4f2004-05-27 00:57:51 +0000[diff] [blame]1897
1898 <p>which is much cleaner, especially if you are creating
1899 long instruction streams.</p></li>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1900
1901 <li>Insertion into an implicit instruction list
1902
1903 <p><tt>Instruction</tt> instances that are already in <tt>BasicBlock</tt>s
1904 are implicitly associated with an existing instruction list: the instruction
1905 list of the enclosing basic block. Thus, we could have accomplished the same
1906 thing as the above code without being given a <tt>BasicBlock</tt> by doing:
1907 </p>
1908
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1909<div class="doc_code">
1910<pre>
1911Instruction *pi = ...;
1912Instruction *newInst = new Instruction(...);
1913
1914pi-&gt;getParent()-&gt;getInstList().insert(pi, newInst);
1915</pre>
1916</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1917
1918 <p>In fact, this sequence of steps occurs so frequently that the
1919 <tt>Instruction</tt> class and <tt>Instruction</tt>-derived classes provide
1920 constructors which take (as a default parameter) a pointer to an
1921 <tt>Instruction</tt> which the newly-created <tt>Instruction</tt> should
1922 precede. That is, <tt>Instruction</tt> constructors are capable of
1923 inserting the newly-created instance into the <tt>BasicBlock</tt> of a
1924 provided instruction, immediately before that instruction. Using an
1925 <tt>Instruction</tt> constructor with a <tt>insertBefore</tt> (default)
1926 parameter, the above code becomes:</p>
1927
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1928<div class="doc_code">
1929<pre>
1930Instruction* pi = ...;
1931Instruction* newInst = new Instruction(..., pi);
1932</pre>
1933</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1934
1935 <p>which is much cleaner, especially if you're creating a lot of
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1936 instructions and adding them to <tt>BasicBlock</tt>s.</p></li>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1937</ul>
1938
1939</div>
1940
1941<!--_______________________________________________________________________-->
1942<div class="doc_subsubsection">
1943 <a name="schanges_deleting">Deleting <tt>Instruction</tt>s</a>
1944</div>
1945
1946<div class="doc_text">
1947
1948<p>Deleting an instruction from an existing sequence of instructions that form a
Chris Lattner69bf8a92004-05-23 21:06:58 +0000[diff] [blame]1949<a href="#BasicBlock"><tt>BasicBlock</tt></a> is very straight-forward. First,
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1950you must have a pointer to the instruction that you wish to delete. Second, you
1951need to obtain the pointer to that instruction's basic block. You use the
1952pointer to the basic block to get its list of instructions and then use the
1953erase function to remove your instruction. For example:</p>
1954
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1955<div class="doc_code">
1956<pre>
1957<a href="#Instruction">Instruction</a> *I = .. ;
Chris Lattner9f8ec252008-02-15 22:57:17 +0000[diff] [blame]1958I-&gt;eraseFromParent();
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1959</pre>
1960</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1961
1962</div>
1963
1964<!--_______________________________________________________________________-->
1965<div class="doc_subsubsection">
1966 <a name="schanges_replacing">Replacing an <tt>Instruction</tt> with another
1967 <tt>Value</tt></a>
1968</div>
1969
1970<div class="doc_text">
1971
1972<p><i>Replacing individual instructions</i></p>
1973
1974<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]1975permits use of two very useful replace functions: <tt>ReplaceInstWithValue</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1976and <tt>ReplaceInstWithInst</tt>.</p>
1977
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]1978<h4><a name="schanges_deleting">Deleting <tt>Instruction</tt>s</a></h4>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1979
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]1980<ul>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1981 <li><tt>ReplaceInstWithValue</tt>
1982
Nick Lewyckyb6d1f392008-09-15 06:31:52 +0000[diff] [blame]1983 <p>This function replaces all uses of a given instruction with a value,
1984 and then removes the original instruction. The following example
1985 illustrates the replacement of the result of a particular
Chris Lattner58360822005-01-17 00:12:04 +0000[diff] [blame]1986 <tt>AllocaInst</tt> that allocates memory for a single integer with a null
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1987 pointer to an integer.</p>
1988
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1989<div class="doc_code">
1990<pre>
1991AllocaInst* instToReplace = ...;
1992BasicBlock::iterator ii(instToReplace);
1993
1994ReplaceInstWithValue(instToReplace-&gt;getParent()-&gt;getInstList(), ii,
Daniel Dunbar58c2ac02008-10-03 22:17:25 +0000[diff] [blame]1995 Constant::getNullValue(PointerType::getUnqual(Type::Int32Ty)));
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1996</pre></div></li>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1997
1998 <li><tt>ReplaceInstWithInst</tt>
1999
2000 <p>This function replaces a particular instruction with another
Nick Lewyckyb6d1f392008-09-15 06:31:52 +0000[diff] [blame]2001 instruction, inserting the new instruction into the basic block at the
2002 location where the old instruction was, and replacing any uses of the old
2003 instruction with the new instruction. The following example illustrates
2004 the replacement of one <tt>AllocaInst</tt> with another.</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2005
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2006<div class="doc_code">
2007<pre>
2008AllocaInst* instToReplace = ...;
2009BasicBlock::iterator ii(instToReplace);
2010
2011ReplaceInstWithInst(instToReplace-&gt;getParent()-&gt;getInstList(), ii,
Nick Lewycky10d64b92007-12-03 01:52:52 +0000[diff] [blame]2012 new AllocaInst(Type::Int32Ty, 0, "ptrToReplacedInt"));
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2013</pre></div></li>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]2014</ul>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2015
2016<p><i>Replacing multiple uses of <tt>User</tt>s and <tt>Value</tt>s</i></p>
2017
2018<p>You can use <tt>Value::replaceAllUsesWith</tt> and
2019<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]2020doxygen documentation for the <a href="/doxygen/classllvm_1_1Value.html">Value Class</a>
Misha Brukman384047f2004-06-03 23:29:12 +0000[diff] [blame]2021and <a href="/doxygen/classllvm_1_1User.html">User Class</a>, respectively, for more
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2022information.</p>
2023
2024<!-- Value::replaceAllUsesWith User::replaceUsesOfWith Point out:
2025include/llvm/Transforms/Utils/ especially BasicBlockUtils.h with:
2026ReplaceInstWithValue, ReplaceInstWithInst -->
2027
2028</div>
2029
Tanya Lattnerb011c662007-06-20 18:33:15 +0000[diff] [blame]2030<!--_______________________________________________________________________-->
2031<div class="doc_subsubsection">
2032 <a name="schanges_deletingGV">Deleting <tt>GlobalVariable</tt>s</a>
2033</div>
2034
2035<div class="doc_text">
2036
Tanya Lattnerc5dfcdb2007-06-20 20:46:37 +0000[diff] [blame]2037<p>Deleting a global variable from a module is just as easy as deleting an
2038Instruction. First, you must have a pointer to the global variable that you wish
2039 to delete. You use this pointer to erase it from its parent, the module.
Tanya Lattnerb011c662007-06-20 18:33:15 +0000[diff] [blame]2040 For example:</p>
2041
2042<div class="doc_code">
2043<pre>
2044<a href="#GlobalVariable">GlobalVariable</a> *GV = .. ;
Tanya Lattnerb011c662007-06-20 18:33:15 +0000[diff] [blame]2045
Tanya Lattnerc5dfcdb2007-06-20 20:46:37 +0000[diff] [blame]2046GV-&gt;eraseFromParent();
Tanya Lattnerb011c662007-06-20 18:33:15 +0000[diff] [blame]2047</pre>
2048</div>
2049
2050</div>
2051
Chris Lattner9355b472002-09-06 02:50:58 +0000[diff] [blame]2052<!-- *********************************************************************** -->
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2053<div class="doc_section">
Chris Lattnerd9d6e102005-04-23 16:10:52 +0000[diff] [blame]2054 <a name="advanced">Advanced Topics</a>
2055</div>
2056<!-- *********************************************************************** -->
2057
2058<div class="doc_text">
Chris Lattnerf1b200b2005-04-23 17:27:36 +0000[diff] [blame]2059<p>
2060This section describes some of the advanced or obscure API's that most clients
2061do not need to be aware of. These API's tend manage the inner workings of the
2062LLVM system, and only need to be accessed in unusual circumstances.
2063</p>
2064</div>
Chris Lattnerd9d6e102005-04-23 16:10:52 +0000[diff] [blame]2065
Chris Lattnerf1b200b2005-04-23 17:27:36 +0000[diff] [blame]2066<!-- ======================================================================= -->
2067<div class="doc_subsection">
2068 <a name="TypeResolve">LLVM Type Resolution</a>
2069</div>
Chris Lattnerd9d6e102005-04-23 16:10:52 +0000[diff] [blame]2070
Chris Lattnerf1b200b2005-04-23 17:27:36 +0000[diff] [blame]2071<div class="doc_text">
2072
2073<p>
2074The LLVM type system has a very simple goal: allow clients to compare types for
2075structural equality with a simple pointer comparison (aka a shallow compare).
2076This goal makes clients much simpler and faster, and is used throughout the LLVM
2077system.
2078</p>
2079
2080<p>
2081Unfortunately achieving this goal is not a simple matter. In particular,
2082recursive types and late resolution of opaque types makes the situation very
2083difficult to handle. Fortunately, for the most part, our implementation makes
2084most clients able to be completely unaware of the nasty internal details. The
2085primary case where clients are exposed to the inner workings of it are when
Gabor Greif04367bf2007-07-06 22:07:22 +0000[diff] [blame]2086building a recursive type. In addition to this case, the LLVM bitcode reader,
Chris Lattnerf1b200b2005-04-23 17:27:36 +0000[diff] [blame]2087assembly parser, and linker also have to be aware of the inner workings of this
2088system.
2089</p>
2090
Chris Lattner0f876db2005-04-25 15:47:57 +0000[diff] [blame]2091<p>
2092For our purposes below, we need three concepts. First, an "Opaque Type" is
2093exactly as defined in the <a href="LangRef.html#t_opaque">language
2094reference</a>. Second an "Abstract Type" is any type which includes an
Reid Spencer06565dc2007-01-12 17:11:23 +0000[diff] [blame]2095opaque type as part of its type graph (for example "<tt>{ opaque, i32 }</tt>").
2096Third, 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]2097float }</tt>").
2098</p>
2099
Chris Lattnerf1b200b2005-04-23 17:27:36 +0000[diff] [blame]2100</div>
2101
2102<!-- ______________________________________________________________________ -->
2103<div class="doc_subsubsection">
2104 <a name="BuildRecType">Basic Recursive Type Construction</a>
2105</div>
2106
2107<div class="doc_text">
2108
2109<p>
2110Because the most common question is "how do I build a recursive type with LLVM",
2111we answer it now and explain it as we go. Here we include enough to cause this
2112to be emitted to an output .ll file:
2113</p>
2114
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2115<div class="doc_code">
Chris Lattnerf1b200b2005-04-23 17:27:36 +0000[diff] [blame]2116<pre>
Reid Spencer06565dc2007-01-12 17:11:23 +0000[diff] [blame]2117%mylist = type { %mylist*, i32 }
Chris Lattnerf1b200b2005-04-23 17:27:36 +0000[diff] [blame]2118</pre>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2119</div>
Chris Lattnerf1b200b2005-04-23 17:27:36 +0000[diff] [blame]2120
2121<p>
2122To build this, use the following LLVM APIs:
2123</p>
2124
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2125<div class="doc_code">
Chris Lattnerf1b200b2005-04-23 17:27:36 +0000[diff] [blame]2126<pre>
Bill Wendling82e2eea2006-10-11 18:00:22 +0000[diff] [blame]2127// <i>Create the initial outer struct</i>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2128<a href="#PATypeHolder">PATypeHolder</a> StructTy = OpaqueType::get();
2129std::vector&lt;const Type*&gt; Elts;
Daniel Dunbar58c2ac02008-10-03 22:17:25 +0000[diff] [blame]2130Elts.push_back(PointerType::getUnqual(StructTy));
Nick Lewycky10d64b92007-12-03 01:52:52 +0000[diff] [blame]2131Elts.push_back(Type::Int32Ty);
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2132StructType *NewSTy = StructType::get(Elts);
Chris Lattnerf1b200b2005-04-23 17:27:36 +0000[diff] [blame]2133
Reid Spencer06565dc2007-01-12 17:11:23 +0000[diff] [blame]2134// <i>At this point, NewSTy = "{ opaque*, i32 }". Tell VMCore that</i>
Bill Wendling82e2eea2006-10-11 18:00:22 +0000[diff] [blame]2135// <i>the struct and the opaque type are actually the same.</i>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2136cast&lt;OpaqueType&gt;(StructTy.get())-&gt;<a href="#refineAbstractTypeTo">refineAbstractTypeTo</a>(NewSTy);
Chris Lattnerf1b200b2005-04-23 17:27:36 +0000[diff] [blame]2137
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2138// <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]2139// <i>kept up-to-date</i>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2140NewSTy = cast&lt;StructType&gt;(StructTy.get());
Chris Lattnerf1b200b2005-04-23 17:27:36 +0000[diff] [blame]2141
Bill Wendling82e2eea2006-10-11 18:00:22 +0000[diff] [blame]2142// <i>Add a name for the type to the module symbol table (optional)</i>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2143MyModule-&gt;addTypeName("mylist", NewSTy);
Chris Lattnerf1b200b2005-04-23 17:27:36 +0000[diff] [blame]2144</pre>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2145</div>
Chris Lattnerf1b200b2005-04-23 17:27:36 +0000[diff] [blame]2146
2147<p>
2148This code shows the basic approach used to build recursive types: build a
2149non-recursive type using 'opaque', then use type unification to close the cycle.
2150The type unification step is performed by the <tt><a
Chris Lattneraff26d12007-02-03 03:06:52 +0000[diff] [blame]2151href="#refineAbstractTypeTo">refineAbstractTypeTo</a></tt> method, which is
Chris Lattnerf1b200b2005-04-23 17:27:36 +0000[diff] [blame]2152described next. After that, we describe the <a
2153href="#PATypeHolder">PATypeHolder class</a>.
2154</p>
2155
2156</div>
2157
2158<!-- ______________________________________________________________________ -->
2159<div class="doc_subsubsection">
2160 <a name="refineAbstractTypeTo">The <tt>refineAbstractTypeTo</tt> method</a>
2161</div>
2162
2163<div class="doc_text">
2164<p>
2165The <tt>refineAbstractTypeTo</tt> method starts the type unification process.
2166While this method is actually a member of the DerivedType class, it is most
2167often used on OpaqueType instances. Type unification is actually a recursive
2168process. After unification, types can become structurally isomorphic to
2169existing types, and all duplicates are deleted (to preserve pointer equality).
2170</p>
2171
2172<p>
2173In the example above, the OpaqueType object is definitely deleted.
Reid Spencer06565dc2007-01-12 17:11:23 +0000[diff] [blame]2174Additionally, if there is an "{ \2*, i32}" type already created in the system,
Chris Lattnerf1b200b2005-04-23 17:27:36 +0000[diff] [blame]2175the pointer and struct type created are <b>also</b> deleted. Obviously whenever
2176a type is deleted, any "Type*" pointers in the program are invalidated. As
2177such, it is safest to avoid having <i>any</i> "Type*" pointers to abstract types
2178live across a call to <tt>refineAbstractTypeTo</tt> (note that non-abstract
2179types can never move or be deleted). To deal with this, the <a
2180href="#PATypeHolder">PATypeHolder</a> class is used to maintain a stable
2181reference to a possibly refined type, and the <a
2182href="#AbstractTypeUser">AbstractTypeUser</a> class is used to update more
2183complex datastructures.
2184</p>
2185
2186</div>
2187
2188<!-- ______________________________________________________________________ -->
2189<div class="doc_subsubsection">
2190 <a name="PATypeHolder">The PATypeHolder Class</a>
2191</div>
2192
2193<div class="doc_text">
2194<p>
2195PATypeHolder is a form of a "smart pointer" for Type objects. When VMCore
2196happily goes about nuking types that become isomorphic to existing types, it
2197automatically updates all PATypeHolder objects to point to the new type. In the
2198example above, this allows the code to maintain a pointer to the resultant
2199resolved recursive type, even though the Type*'s are potentially invalidated.
2200</p>
2201
2202<p>
2203PATypeHolder is an extremely light-weight object that uses a lazy union-find
2204implementation to update pointers. For example the pointer from a Value to its
2205Type is maintained by PATypeHolder objects.
2206</p>
2207
2208</div>
2209
2210<!-- ______________________________________________________________________ -->
2211<div class="doc_subsubsection">
2212 <a name="AbstractTypeUser">The AbstractTypeUser Class</a>
2213</div>
2214
2215<div class="doc_text">
2216
2217<p>
2218Some data structures need more to perform more complex updates when types get
Chris Lattner263a98e2007-02-16 04:37:31 +0000[diff] [blame]2219resolved. To support this, a class can derive from the AbstractTypeUser class.
2220This class
Chris Lattnerf1b200b2005-04-23 17:27:36 +0000[diff] [blame]2221allows it to get callbacks when certain types are resolved. To register to get
2222callbacks for a particular type, the DerivedType::{add/remove}AbstractTypeUser
Chris Lattner0f876db2005-04-25 15:47:57 +0000[diff] [blame]2223methods can be called on a type. Note that these methods only work for <i>
Reid Spencer06565dc2007-01-12 17:11:23 +0000[diff] [blame]2224 abstract</i> types. Concrete types (those that do not include any opaque
2225objects) can never be refined.
Chris Lattnerf1b200b2005-04-23 17:27:36 +0000[diff] [blame]2226</p>
Chris Lattnerd9d6e102005-04-23 16:10:52 +0000[diff] [blame]2227</div>
2228
2229
2230<!-- ======================================================================= -->
2231<div class="doc_subsection">
Chris Lattner263a98e2007-02-16 04:37:31 +0000[diff] [blame]2232 <a name="SymbolTable">The <tt>ValueSymbolTable</tt> and
2233 <tt>TypeSymbolTable</tt> classes</a>
Chris Lattnerd9d6e102005-04-23 16:10:52 +0000[diff] [blame]2234</div>
Chris Lattnerf1b200b2005-04-23 17:27:36 +0000[diff] [blame]2235
Chris Lattnerd9d6e102005-04-23 16:10:52 +0000[diff] [blame]2236<div class="doc_text">
Chris Lattner263a98e2007-02-16 04:37:31 +0000[diff] [blame]2237<p>The <tt><a href="http://llvm.org/doxygen/classllvm_1_1ValueSymbolTable.html">
2238ValueSymbolTable</a></tt> class provides a symbol table that the <a
Chris Lattnerd9d6e102005-04-23 16:10:52 +0000[diff] [blame]2239href="#Function"><tt>Function</tt></a> and <a href="#Module">
Chris Lattner263a98e2007-02-16 04:37:31 +0000[diff] [blame]2240<tt>Module</tt></a> classes use for naming value definitions. The symbol table
2241can provide a name for any <a href="#Value"><tt>Value</tt></a>.
2242The <tt><a href="http://llvm.org/doxygen/classllvm_1_1TypeSymbolTable.html">
2243TypeSymbolTable</a></tt> class is used by the <tt>Module</tt> class to store
2244names for types.</p>
Chris Lattnerd9d6e102005-04-23 16:10:52 +0000[diff] [blame]2245
Reid Spencera6362242007-01-07 00:41:39 +0000[diff] [blame]2246<p>Note that the <tt>SymbolTable</tt> class should not be directly accessed
2247by most clients. It should only be used when iteration over the symbol table
2248names themselves are required, which is very special purpose. Note that not
2249all LLVM
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2250<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]2251an empty name) do not exist in the symbol table.
2252</p>
2253
Chris Lattner263a98e2007-02-16 04:37:31 +0000[diff] [blame]2254<p>These symbol tables support iteration over the values/types in the symbol
2255table with <tt>begin/end/iterator</tt> and supports querying to see if a
2256specific name is in the symbol table (with <tt>lookup</tt>). The
2257<tt>ValueSymbolTable</tt> class exposes no public mutator methods, instead,
2258simply call <tt>setName</tt> on a value, which will autoinsert it into the
2259appropriate symbol table. For types, use the Module::addTypeName method to
2260insert entries into the symbol table.</p>
Chris Lattnerd9d6e102005-04-23 16:10:52 +0000[diff] [blame]2261
Chris Lattnerd9d6e102005-04-23 16:10:52 +0000[diff] [blame]2262</div>
2263
2264
2265
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2266<!-- ======================================================================= -->
2267<div class="doc_subsection">
2268 <a name="UserLayout">The <tt>User</tt> and owned <tt>Use</tt> classes' memory layout</a>
2269</div>
2270
2271<div class="doc_text">
2272<p>The <tt><a href="http://llvm.org/doxygen/classllvm_1_1User.html">
Gabor Greiffd095b62009-01-05 16:05:32 +0000[diff] [blame]2273User</a></tt> class provides a basis for expressing the ownership of <tt>User</tt>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2274towards other <tt><a href="http://llvm.org/doxygen/classllvm_1_1Value.html">
2275Value</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]2276Use</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]2277addition and removal.</p>
2278
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2279<!-- ______________________________________________________________________ -->
2280<div class="doc_subsubsection">
Gabor Greiffd095b62009-01-05 16:05:32 +0000[diff] [blame]2281 <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]2282</div>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2283
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2284<div class="doc_text">
2285<p>
2286A subclass of <tt>User</tt> can choose between incorporating its <tt>Use</tt> objects
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2287or refer to them out-of-line by means of a pointer. A mixed variant
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2288(some <tt>Use</tt>s inline others hung off) is impractical and breaks the invariant
2289that the <tt>Use</tt> objects belonging to the same <tt>User</tt> form a contiguous array.
2290</p>
2291</div>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2292
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2293<p>
2294We have 2 different layouts in the <tt>User</tt> (sub)classes:
2295<ul>
2296<li><p>Layout a)
2297The <tt>Use</tt> object(s) are inside (resp. at fixed offset) of the <tt>User</tt>
2298object and there are a fixed number of them.</p>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2299
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2300<li><p>Layout b)
2301The <tt>Use</tt> object(s) are referenced by a pointer to an
2302array from the <tt>User</tt> object and there may be a variable
2303number of them.</p>
2304</ul>
2305<p>
Gabor Greifd41720a2008-06-25 00:10:22 +0000[diff] [blame]2306As of v2.4 each layout still possesses a direct pointer to the
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2307start of the array of <tt>Use</tt>s. Though not mandatory for layout a),
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2308we stick to this redundancy for the sake of simplicity.
Gabor Greifd41720a2008-06-25 00:10:22 +0000[diff] [blame]2309The <tt>User</tt> object also stores the number of <tt>Use</tt> objects it
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2310has. (Theoretically this information can also be calculated
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2311given the scheme presented below.)</p>
2312<p>
2313Special forms of allocation operators (<tt>operator new</tt>)
Gabor Greifd41720a2008-06-25 00:10:22 +0000[diff] [blame]2314enforce the following memory layouts:</p>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2315
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2316<ul>
Gabor Greifd41720a2008-06-25 00:10:22 +0000[diff] [blame]2317<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]2318
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2319<pre>
2320...---.---.---.---.-------...
2321 | P | P | P | P | User
2322'''---'---'---'---'-------'''
2323</pre>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2324
Gabor Greifd41720a2008-06-25 00:10:22 +0000[diff] [blame]2325<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]2326<pre>
2327.-------...
2328| User
2329'-------'''
2330 |
2331 v
2332 .---.---.---.---...
2333 | P | P | P | P |
2334 '---'---'---'---'''
2335</pre>
2336</ul>
2337<i>(In the above figures '<tt>P</tt>' stands for the <tt>Use**</tt> that
2338 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]2339
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2340<!-- ______________________________________________________________________ -->
2341<div class="doc_subsubsection">
Gabor Greiffd095b62009-01-05 16:05:32 +0000[diff] [blame]2342 <a name="Waymarking">The waymarking algorithm</a>
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2343</div>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2344
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2345<div class="doc_text">
2346<p>
Gabor Greifd41720a2008-06-25 00:10:22 +0000[diff] [blame]2347Since the <tt>Use</tt> objects are deprived of the direct (back)pointer to
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2348their <tt>User</tt> objects, there must be a fast and exact method to
2349recover it. This is accomplished by the following scheme:</p>
2350</div>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2351
Gabor Greifd41720a2008-06-25 00:10:22 +0000[diff] [blame]2352A 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]2353start of the <tt>User</tt> object:
2354<ul>
2355<li><tt>00</tt> &mdash;&gt; binary digit 0</li>
2356<li><tt>01</tt> &mdash;&gt; binary digit 1</li>
2357<li><tt>10</tt> &mdash;&gt; stop and calculate (<tt>s</tt>)</li>
2358<li><tt>11</tt> &mdash;&gt; full stop (<tt>S</tt>)</li>
2359</ul>
2360<p>
2361Given a <tt>Use*</tt>, all we have to do is to walk till we get
2362a stop and we either have a <tt>User</tt> immediately behind or
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2363we have to walk to the next stop picking up digits
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2364and calculating the offset:</p>
2365<pre>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2366.---.---.---.---.---.---.---.---.---.---.---.---.---.---.---.---.----------------
2367| 1 | s | 1 | 0 | 1 | 0 | s | 1 | 1 | 0 | s | 1 | 1 | s | 1 | S | User (or User*)
2368'---'---'---'---'---'---'---'---'---'---'---'---'---'---'---'---'----------------
2369 |+15 |+10 |+6 |+3 |+1
2370 | | | | |__>
2371 | | | |__________>
2372 | | |______________________>
2373 | |______________________________________>
2374 |__________________________________________________________>
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2375</pre>
2376<p>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2377Only the significant number of bits need to be stored between the
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2378stops, so that the <i>worst case is 20 memory accesses</i> when there are
23791000 <tt>Use</tt> objects associated with a <tt>User</tt>.</p>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2380
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2381<!-- ______________________________________________________________________ -->
2382<div class="doc_subsubsection">
Gabor Greiffd095b62009-01-05 16:05:32 +0000[diff] [blame]2383 <a name="ReferenceImpl">Reference implementation</a>
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2384</div>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2385
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2386<div class="doc_text">
2387<p>
2388The following literate Haskell fragment demonstrates the concept:</p>
2389</div>
2390
2391<div class="doc_code">
2392<pre>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2393> import Test.QuickCheck
2394>
2395> digits :: Int -> [Char] -> [Char]
2396> digits 0 acc = '0' : acc
2397> digits 1 acc = '1' : acc
2398> digits n acc = digits (n `div` 2) $ digits (n `mod` 2) acc
2399>
2400> dist :: Int -> [Char] -> [Char]
2401> dist 0 [] = ['S']
2402> dist 0 acc = acc
2403> dist 1 acc = let r = dist 0 acc in 's' : digits (length r) r
2404> dist n acc = dist (n - 1) $ dist 1 acc
2405>
2406> takeLast n ss = reverse $ take n $ reverse ss
2407>
2408> test = takeLast 40 $ dist 20 []
2409>
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2410</pre>
2411</div>
2412<p>
2413Printing &lt;test&gt; gives: <tt>"1s100000s11010s10100s1111s1010s110s11s1S"</tt></p>
2414<p>
2415The reverse algorithm computes the length of the string just by examining
2416a certain prefix:</p>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2417
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2418<div class="doc_code">
2419<pre>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2420> pref :: [Char] -> Int
2421> pref "S" = 1
2422> pref ('s':'1':rest) = decode 2 1 rest
2423> pref (_:rest) = 1 + pref rest
2424>
2425> decode walk acc ('0':rest) = decode (walk + 1) (acc * 2) rest
2426> decode walk acc ('1':rest) = decode (walk + 1) (acc * 2 + 1) rest
2427> decode walk acc _ = walk + acc
2428>
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2429</pre>
2430</div>
2431<p>
2432Now, as expected, printing &lt;pref test&gt; gives <tt>40</tt>.</p>
2433<p>
2434We can <i>quickCheck</i> this with following property:</p>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2435
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2436<div class="doc_code">
2437<pre>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2438> testcase = dist 2000 []
2439> testcaseLength = length testcase
2440>
2441> identityProp n = n > 0 && n <= testcaseLength ==> length arr == pref arr
2442> where arr = takeLast n testcase
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2443>
2444</pre>
2445</div>
2446<p>
2447As expected &lt;quickCheck identityProp&gt; gives:</p>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2448
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2449<pre>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2450*Main> quickCheck identityProp
2451OK, passed 100 tests.
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2452</pre>
2453<p>
2454Let's be a bit more exhaustive:</p>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2455
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2456<div class="doc_code">
2457<pre>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2458>
2459> deepCheck p = check (defaultConfig { configMaxTest = 500 }) p
2460>
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2461</pre>
2462</div>
2463<p>
2464And here is the result of &lt;deepCheck identityProp&gt;:</p>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2465
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2466<pre>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2467*Main> deepCheck identityProp
2468OK, passed 500 tests.
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2469</pre>
2470
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2471<!-- ______________________________________________________________________ -->
2472<div class="doc_subsubsection">
Gabor Greiffd095b62009-01-05 16:05:32 +0000[diff] [blame]2473 <a name="Tagging">Tagging considerations</a>
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2474</div>
2475
2476<p>
2477To maintain the invariant that the 2 LSBits of each <tt>Use**</tt> in <tt>Use</tt>
2478never change after being set up, setters of <tt>Use::Prev</tt> must re-tag the
2479new <tt>Use**</tt> on every modification. Accordingly getters must strip the
2480tag bits.</p>
2481<p>
Gabor Greifd41720a2008-06-25 00:10:22 +0000[diff] [blame]2482For layout b) instead of the <tt>User</tt> we find a pointer (<tt>User*</tt> with LSBit set).
2483Following this pointer brings us to the <tt>User</tt>. A portable trick ensures
2484that the first bytes of <tt>User</tt> (if interpreted as a pointer) never has
Gabor Greiffd095b62009-01-05 16:05:32 +0000[diff] [blame]2485the LSBit set. (Portability is relying on the fact that all known compilers place the
2486<tt>vptr</tt> in the first word of the instances.)</p>
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2487
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2488</div>
2489
2490 <!-- *********************************************************************** -->
Chris Lattnerd9d6e102005-04-23 16:10:52 +0000[diff] [blame]2491<div class="doc_section">
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2492 <a name="coreclasses">The Core LLVM Class Hierarchy Reference </a>
2493</div>
2494<!-- *********************************************************************** -->
2495
2496<div class="doc_text">
Reid Spencer303c4b42007-01-12 17:26:25 +0000[diff] [blame]2497<p><tt>#include "<a href="/doxygen/Type_8h-source.html">llvm/Type.h</a>"</tt>
2498<br>doxygen info: <a href="/doxygen/classllvm_1_1Type.html">Type Class</a></p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2499
2500<p>The Core LLVM classes are the primary means of representing the program
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]2501being inspected or transformed. The core LLVM classes are defined in
2502header files in the <tt>include/llvm/</tt> directory, and implemented in
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2503the <tt>lib/VMCore</tt> directory.</p>
2504
2505</div>
2506
2507<!-- ======================================================================= -->
2508<div class="doc_subsection">
Reid Spencer303c4b42007-01-12 17:26:25 +0000[diff] [blame]2509 <a name="Type">The <tt>Type</tt> class and Derived Types</a>
2510</div>
2511
2512<div class="doc_text">
2513
2514 <p><tt>Type</tt> is a superclass of all type classes. Every <tt>Value</tt> has
2515 a <tt>Type</tt>. <tt>Type</tt> cannot be instantiated directly but only
2516 through its subclasses. Certain primitive types (<tt>VoidType</tt>,
2517 <tt>LabelType</tt>, <tt>FloatType</tt> and <tt>DoubleType</tt>) have hidden
2518 subclasses. They are hidden because they offer no useful functionality beyond
2519 what the <tt>Type</tt> class offers except to distinguish themselves from
2520 other subclasses of <tt>Type</tt>.</p>
2521 <p>All other types are subclasses of <tt>DerivedType</tt>. Types can be
2522 named, but this is not a requirement. There exists exactly
2523 one instance of a given shape at any one time. This allows type equality to
2524 be performed with address equality of the Type Instance. That is, given two
2525 <tt>Type*</tt> values, the types are identical if the pointers are identical.
2526 </p>
2527</div>
2528
2529<!-- _______________________________________________________________________ -->
2530<div class="doc_subsubsection">
Gabor Greiffd095b62009-01-05 16:05:32 +0000[diff] [blame]2531 <a name="m_Type">Important Public Methods</a>
Reid Spencer303c4b42007-01-12 17:26:25 +0000[diff] [blame]2532</div>
2533
2534<div class="doc_text">
2535
2536<ul>
Chris Lattner8f79df32007-01-15 01:55:32 +0000[diff] [blame]2537 <li><tt>bool isInteger() const</tt>: Returns true for any integer type.</li>
Reid Spencer303c4b42007-01-12 17:26:25 +0000[diff] [blame]2538
2539 <li><tt>bool isFloatingPoint()</tt>: Return true if this is one of the two
2540 floating point types.</li>
2541
2542 <li><tt>bool isAbstract()</tt>: Return true if the type is abstract (contains
2543 an OpaqueType anywhere in its definition).</li>
2544
2545 <li><tt>bool isSized()</tt>: Return true if the type has known size. Things
2546 that don't have a size are abstract types, labels and void.</li>
2547
2548</ul>
2549</div>
2550
2551<!-- _______________________________________________________________________ -->
2552<div class="doc_subsubsection">
Gabor Greiffd095b62009-01-05 16:05:32 +0000[diff] [blame]2553 <a name="derivedtypes">Important Derived Types</a>
Reid Spencer303c4b42007-01-12 17:26:25 +0000[diff] [blame]2554</div>
2555<div class="doc_text">
2556<dl>
2557 <dt><tt>IntegerType</tt></dt>
2558 <dd>Subclass of DerivedType that represents integer types of any bit width.
2559 Any bit width between <tt>IntegerType::MIN_INT_BITS</tt> (1) and
2560 <tt>IntegerType::MAX_INT_BITS</tt> (~8 million) can be represented.
2561 <ul>
2562 <li><tt>static const IntegerType* get(unsigned NumBits)</tt>: get an integer
2563 type of a specific bit width.</li>
2564 <li><tt>unsigned getBitWidth() const</tt>: Get the bit width of an integer
2565 type.</li>
2566 </ul>
2567 </dd>
2568 <dt><tt>SequentialType</tt></dt>
2569 <dd>This is subclassed by ArrayType and PointerType
2570 <ul>
2571 <li><tt>const Type * getElementType() const</tt>: Returns the type of each
2572 of the elements in the sequential type. </li>
2573 </ul>
2574 </dd>
2575 <dt><tt>ArrayType</tt></dt>
2576 <dd>This is a subclass of SequentialType and defines the interface for array
2577 types.
2578 <ul>
2579 <li><tt>unsigned getNumElements() const</tt>: Returns the number of
2580 elements in the array. </li>
2581 </ul>
2582 </dd>
2583 <dt><tt>PointerType</tt></dt>
Chris Lattner302da1e2007-02-03 03:05:57 +0000[diff] [blame]2584 <dd>Subclass of SequentialType for pointer types.</dd>
Reid Spencer9d6565a2007-02-15 02:26:10 +0000[diff] [blame]2585 <dt><tt>VectorType</tt></dt>
Reid Spencer485bad12007-02-15 03:07:05 +0000[diff] [blame]2586 <dd>Subclass of SequentialType for vector types. A
2587 vector type is similar to an ArrayType but is distinguished because it is
2588 a first class type wherease ArrayType is not. Vector types are used for
Reid Spencer303c4b42007-01-12 17:26:25 +0000[diff] [blame]2589 vector operations and are usually small vectors of of an integer or floating
2590 point type.</dd>
2591 <dt><tt>StructType</tt></dt>
2592 <dd>Subclass of DerivedTypes for struct types.</dd>
Duncan Sands8036ca42007-03-30 12:22:09 +0000[diff] [blame]2593 <dt><tt><a name="FunctionType">FunctionType</a></tt></dt>
Reid Spencer303c4b42007-01-12 17:26:25 +0000[diff] [blame]2594 <dd>Subclass of DerivedTypes for function types.
2595 <ul>
2596 <li><tt>bool isVarArg() const</tt>: Returns true if its a vararg
2597 function</li>
2598 <li><tt> const Type * getReturnType() const</tt>: Returns the
2599 return type of the function.</li>
2600 <li><tt>const Type * getParamType (unsigned i)</tt>: Returns
2601 the type of the ith parameter.</li>
2602 <li><tt> const unsigned getNumParams() const</tt>: Returns the
2603 number of formal parameters.</li>
2604 </ul>
2605 </dd>
2606 <dt><tt>OpaqueType</tt></dt>
2607 <dd>Sublcass of DerivedType for abstract types. This class
2608 defines no content and is used as a placeholder for some other type. Note
2609 that OpaqueType is used (temporarily) during type resolution for forward
2610 references of types. Once the referenced type is resolved, the OpaqueType
2611 is replaced with the actual type. OpaqueType can also be used for data
2612 abstraction. At link time opaque types can be resolved to actual types
2613 of the same name.</dd>
2614</dl>
2615</div>
2616
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]2617
2618
2619<!-- ======================================================================= -->
2620<div class="doc_subsection">
2621 <a name="Module">The <tt>Module</tt> class</a>
2622</div>
2623
2624<div class="doc_text">
2625
2626<p><tt>#include "<a
2627href="/doxygen/Module_8h-source.html">llvm/Module.h</a>"</tt><br> doxygen info:
2628<a href="/doxygen/classllvm_1_1Module.html">Module Class</a></p>
2629
2630<p>The <tt>Module</tt> class represents the top level structure present in LLVM
2631programs. An LLVM module is effectively either a translation unit of the
2632original program or a combination of several translation units merged by the
2633linker. The <tt>Module</tt> class keeps track of a list of <a
2634href="#Function"><tt>Function</tt></a>s, a list of <a
2635href="#GlobalVariable"><tt>GlobalVariable</tt></a>s, and a <a
2636href="#SymbolTable"><tt>SymbolTable</tt></a>. Additionally, it contains a few
2637helpful member functions that try to make common operations easy.</p>
2638
2639</div>
2640
2641<!-- _______________________________________________________________________ -->
2642<div class="doc_subsubsection">
2643 <a name="m_Module">Important Public Members of the <tt>Module</tt> class</a>
2644</div>
2645
2646<div class="doc_text">
2647
2648<ul>
2649 <li><tt>Module::Module(std::string name = "")</tt></li>
2650</ul>
2651
2652<p>Constructing a <a href="#Module">Module</a> is easy. You can optionally
2653provide a name for it (probably based on the name of the translation unit).</p>
2654
2655<ul>
2656 <li><tt>Module::iterator</tt> - Typedef for function list iterator<br>
2657 <tt>Module::const_iterator</tt> - Typedef for const_iterator.<br>
2658
2659 <tt>begin()</tt>, <tt>end()</tt>
2660 <tt>size()</tt>, <tt>empty()</tt>
2661
2662 <p>These are forwarding methods that make it easy to access the contents of
2663 a <tt>Module</tt> object's <a href="#Function"><tt>Function</tt></a>
2664 list.</p></li>
2665
2666 <li><tt>Module::FunctionListType &amp;getFunctionList()</tt>
2667
2668 <p> Returns the list of <a href="#Function"><tt>Function</tt></a>s. This is
2669 necessary to use when you need to update the list or perform a complex
2670 action that doesn't have a forwarding method.</p>
2671
2672 <p><!-- Global Variable --></p></li>
2673</ul>
2674
2675<hr>
2676
2677<ul>
2678 <li><tt>Module::global_iterator</tt> - Typedef for global variable list iterator<br>
2679
2680 <tt>Module::const_global_iterator</tt> - Typedef for const_iterator.<br>
2681
2682 <tt>global_begin()</tt>, <tt>global_end()</tt>
2683 <tt>global_size()</tt>, <tt>global_empty()</tt>
2684
2685 <p> These are forwarding methods that make it easy to access the contents of
2686 a <tt>Module</tt> object's <a
2687 href="#GlobalVariable"><tt>GlobalVariable</tt></a> list.</p></li>
2688
2689 <li><tt>Module::GlobalListType &amp;getGlobalList()</tt>
2690
2691 <p>Returns the list of <a
2692 href="#GlobalVariable"><tt>GlobalVariable</tt></a>s. This is necessary to
2693 use when you need to update the list or perform a complex action that
2694 doesn't have a forwarding method.</p>
2695
2696 <p><!-- Symbol table stuff --> </p></li>
2697</ul>
2698
2699<hr>
2700
2701<ul>
2702 <li><tt><a href="#SymbolTable">SymbolTable</a> *getSymbolTable()</tt>
2703
2704 <p>Return a reference to the <a href="#SymbolTable"><tt>SymbolTable</tt></a>
2705 for this <tt>Module</tt>.</p>
2706
2707 <p><!-- Convenience methods --></p></li>
2708</ul>
2709
2710<hr>
2711
2712<ul>
2713 <li><tt><a href="#Function">Function</a> *getFunction(const std::string
2714 &amp;Name, const <a href="#FunctionType">FunctionType</a> *Ty)</tt>
2715
2716 <p>Look up the specified function in the <tt>Module</tt> <a
2717 href="#SymbolTable"><tt>SymbolTable</tt></a>. If it does not exist, return
2718 <tt>null</tt>.</p></li>
2719
2720 <li><tt><a href="#Function">Function</a> *getOrInsertFunction(const
2721 std::string &amp;Name, const <a href="#FunctionType">FunctionType</a> *T)</tt>
2722
2723 <p>Look up the specified function in the <tt>Module</tt> <a
2724 href="#SymbolTable"><tt>SymbolTable</tt></a>. If it does not exist, add an
2725 external declaration for the function and return it.</p></li>
2726
2727 <li><tt>std::string getTypeName(const <a href="#Type">Type</a> *Ty)</tt>
2728
2729 <p>If there is at least one entry in the <a
2730 href="#SymbolTable"><tt>SymbolTable</tt></a> for the specified <a
2731 href="#Type"><tt>Type</tt></a>, return it. Otherwise return the empty
2732 string.</p></li>
2733
2734 <li><tt>bool addTypeName(const std::string &amp;Name, const <a
2735 href="#Type">Type</a> *Ty)</tt>
2736
2737 <p>Insert an entry in the <a href="#SymbolTable"><tt>SymbolTable</tt></a>
2738 mapping <tt>Name</tt> to <tt>Ty</tt>. If there is already an entry for this
2739 name, true is returned and the <a
2740 href="#SymbolTable"><tt>SymbolTable</tt></a> is not modified.</p></li>
2741</ul>
2742
2743</div>
2744
2745
Reid Spencer303c4b42007-01-12 17:26:25 +0000[diff] [blame]2746<!-- ======================================================================= -->
2747<div class="doc_subsection">
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2748 <a name="Value">The <tt>Value</tt> class</a>
2749</div>
2750
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]2751<div class="doc_text">
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2752
2753<p><tt>#include "<a href="/doxygen/Value_8h-source.html">llvm/Value.h</a>"</tt>
2754<br>
Chris Lattner00815172007-01-04 22:01:45 +0000[diff] [blame]2755doxygen info: <a href="/doxygen/classllvm_1_1Value.html">Value Class</a></p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2756
2757<p>The <tt>Value</tt> class is the most important class in the LLVM Source
2758base. It represents a typed value that may be used (among other things) as an
2759operand to an instruction. There are many different types of <tt>Value</tt>s,
2760such as <a href="#Constant"><tt>Constant</tt></a>s,<a
2761href="#Argument"><tt>Argument</tt></a>s. Even <a
2762href="#Instruction"><tt>Instruction</tt></a>s and <a
2763href="#Function"><tt>Function</tt></a>s are <tt>Value</tt>s.</p>
2764
2765<p>A particular <tt>Value</tt> may be used many times in the LLVM representation
2766for a program. For example, an incoming argument to a function (represented
2767with an instance of the <a href="#Argument">Argument</a> class) is "used" by
2768every instruction in the function that references the argument. To keep track
2769of this relationship, the <tt>Value</tt> class keeps a list of all of the <a
2770href="#User"><tt>User</tt></a>s that is using it (the <a
2771href="#User"><tt>User</tt></a> class is a base class for all nodes in the LLVM
2772graph that can refer to <tt>Value</tt>s). This use list is how LLVM represents
2773def-use information in the program, and is accessible through the <tt>use_</tt>*
2774methods, shown below.</p>
2775
2776<p>Because LLVM is a typed representation, every LLVM <tt>Value</tt> is typed,
2777and this <a href="#Type">Type</a> is available through the <tt>getType()</tt>
2778method. In addition, all LLVM values can be named. The "name" of the
2779<tt>Value</tt> is a symbolic string printed in the LLVM code:</p>
2780
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2781<div class="doc_code">
2782<pre>
Reid Spencer06565dc2007-01-12 17:11:23 +0000[diff] [blame]2783%<b>foo</b> = add i32 1, 2
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2784</pre>
2785</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2786
Duncan Sands8036ca42007-03-30 12:22:09 +0000[diff] [blame]2787<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]2788that the name of any value may be missing (an empty string), so names should
2789<b>ONLY</b> be used for debugging (making the source code easier to read,
2790debugging printouts), they should not be used to keep track of values or map
2791between them. For this purpose, use a <tt>std::map</tt> of pointers to the
2792<tt>Value</tt> itself instead.</p>
2793
2794<p>One important aspect of LLVM is that there is no distinction between an SSA
2795variable and the operation that produces it. Because of this, any reference to
2796the value produced by an instruction (or the value available as an incoming
Chris Lattnerd5fc4fc2004-03-18 14:58:55 +0000[diff] [blame]2797argument, for example) is represented as a direct pointer to the instance of
2798the class that
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2799represents this value. Although this may take some getting used to, it
2800simplifies the representation and makes it easier to manipulate.</p>
2801
2802</div>
2803
2804<!-- _______________________________________________________________________ -->
2805<div class="doc_subsubsection">
2806 <a name="m_Value">Important Public Members of the <tt>Value</tt> class</a>
2807</div>
2808
2809<div class="doc_text">
2810
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]2811<ul>
2812 <li><tt>Value::use_iterator</tt> - Typedef for iterator over the
2813use-list<br>
2814 <tt>Value::use_const_iterator</tt> - Typedef for const_iterator over
2815the use-list<br>
2816 <tt>unsigned use_size()</tt> - Returns the number of users of the
2817value.<br>
Chris Lattner9355b472002-09-06 02:50:58 +0000[diff] [blame]2818 <tt>bool use_empty()</tt> - Returns true if there are no users.<br>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]2819 <tt>use_iterator use_begin()</tt> - Get an iterator to the start of
2820the use-list.<br>
2821 <tt>use_iterator use_end()</tt> - Get an iterator to the end of the
2822use-list.<br>
2823 <tt><a href="#User">User</a> *use_back()</tt> - Returns the last
2824element in the list.
2825 <p> These methods are the interface to access the def-use
2826information in LLVM. As with all other iterators in LLVM, the naming
2827conventions follow the conventions defined by the <a href="#stl">STL</a>.</p>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]2828 </li>
2829 <li><tt><a href="#Type">Type</a> *getType() const</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2830 <p>This method returns the Type of the Value.</p>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]2831 </li>
2832 <li><tt>bool hasName() const</tt><br>
Chris Lattner9355b472002-09-06 02:50:58 +0000[diff] [blame]2833 <tt>std::string getName() const</tt><br>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]2834 <tt>void setName(const std::string &amp;Name)</tt>
2835 <p> This family of methods is used to access and assign a name to a <tt>Value</tt>,
2836be aware of the <a href="#nameWarning">precaution above</a>.</p>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]2837 </li>
2838 <li><tt>void replaceAllUsesWith(Value *V)</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2839
2840 <p>This method traverses the use list of a <tt>Value</tt> changing all <a
2841 href="#User"><tt>User</tt>s</a> of the current value to refer to
2842 "<tt>V</tt>" instead. For example, if you detect that an instruction always
2843 produces a constant value (for example through constant folding), you can
2844 replace all uses of the instruction with the constant like this:</p>
2845
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2846<div class="doc_code">
2847<pre>
2848Inst-&gt;replaceAllUsesWith(ConstVal);
2849</pre>
2850</div>
2851
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]2852</ul>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2853
2854</div>
2855
2856<!-- ======================================================================= -->
2857<div class="doc_subsection">
2858 <a name="User">The <tt>User</tt> class</a>
2859</div>
2860
2861<div class="doc_text">
2862
2863<p>
2864<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]2865doxygen info: <a href="/doxygen/classllvm_1_1User.html">User Class</a><br>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2866Superclass: <a href="#Value"><tt>Value</tt></a></p>
2867
2868<p>The <tt>User</tt> class is the common base class of all LLVM nodes that may
2869refer to <a href="#Value"><tt>Value</tt></a>s. It exposes a list of "Operands"
2870that are all of the <a href="#Value"><tt>Value</tt></a>s that the User is
2871referring to. The <tt>User</tt> class itself is a subclass of
2872<tt>Value</tt>.</p>
2873
2874<p>The operands of a <tt>User</tt> point directly to the LLVM <a
2875href="#Value"><tt>Value</tt></a> that it refers to. Because LLVM uses Static
2876Single Assignment (SSA) form, there can only be one definition referred to,
2877allowing this direct connection. This connection provides the use-def
2878information in LLVM.</p>
2879
2880</div>
2881
2882<!-- _______________________________________________________________________ -->
2883<div class="doc_subsubsection">
2884 <a name="m_User">Important Public Members of the <tt>User</tt> class</a>
2885</div>
2886
2887<div class="doc_text">
2888
2889<p>The <tt>User</tt> class exposes the operand list in two ways: through
2890an index access interface and through an iterator based interface.</p>
2891
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]2892<ul>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]2893 <li><tt>Value *getOperand(unsigned i)</tt><br>
2894 <tt>unsigned getNumOperands()</tt>
2895 <p> These two methods expose the operands of the <tt>User</tt> in a
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2896convenient form for direct access.</p></li>
2897
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]2898 <li><tt>User::op_iterator</tt> - Typedef for iterator over the operand
2899list<br>
Chris Lattner58360822005-01-17 00:12:04 +0000[diff] [blame]2900 <tt>op_iterator op_begin()</tt> - Get an iterator to the start of
2901the operand list.<br>
2902 <tt>op_iterator op_end()</tt> - Get an iterator to the end of the
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]2903operand list.
2904 <p> Together, these methods make up the iterator based interface to
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2905the operands of a <tt>User</tt>.</p></li>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]2906</ul>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2907
2908</div>
2909
2910<!-- ======================================================================= -->
2911<div class="doc_subsection">
2912 <a name="Instruction">The <tt>Instruction</tt> class</a>
2913</div>
2914
2915<div class="doc_text">
2916
2917<p><tt>#include "</tt><tt><a
2918href="/doxygen/Instruction_8h-source.html">llvm/Instruction.h</a>"</tt><br>
Misha Brukman31ca1de2004-06-03 23:35:54 +0000[diff] [blame]2919doxygen info: <a href="/doxygen/classllvm_1_1Instruction.html">Instruction Class</a><br>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2920Superclasses: <a href="#User"><tt>User</tt></a>, <a
2921href="#Value"><tt>Value</tt></a></p>
2922
2923<p>The <tt>Instruction</tt> class is the common base class for all LLVM
2924instructions. It provides only a few methods, but is a very commonly used
2925class. The primary data tracked by the <tt>Instruction</tt> class itself is the
2926opcode (instruction type) and the parent <a
2927href="#BasicBlock"><tt>BasicBlock</tt></a> the <tt>Instruction</tt> is embedded
2928into. To represent a specific type of instruction, one of many subclasses of
2929<tt>Instruction</tt> are used.</p>
2930
2931<p> Because the <tt>Instruction</tt> class subclasses the <a
2932href="#User"><tt>User</tt></a> class, its operands can be accessed in the same
2933way as for other <a href="#User"><tt>User</tt></a>s (with the
2934<tt>getOperand()</tt>/<tt>getNumOperands()</tt> and
2935<tt>op_begin()</tt>/<tt>op_end()</tt> methods).</p> <p> An important file for
2936the <tt>Instruction</tt> class is the <tt>llvm/Instruction.def</tt> file. This
2937file contains some meta-data about the various different types of instructions
2938in LLVM. It describes the enum values that are used as opcodes (for example
Reid Spencerc92d25d2006-12-19 19:47:19 +0000[diff] [blame]2939<tt>Instruction::Add</tt> and <tt>Instruction::ICmp</tt>), as well as the
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2940concrete sub-classes of <tt>Instruction</tt> that implement the instruction (for
2941example <tt><a href="#BinaryOperator">BinaryOperator</a></tt> and <tt><a
Reid Spencerc92d25d2006-12-19 19:47:19 +0000[diff] [blame]2942href="#CmpInst">CmpInst</a></tt>). Unfortunately, the use of macros in
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2943this file confuses doxygen, so these enum values don't show up correctly in the
Misha Brukman31ca1de2004-06-03 23:35:54 +0000[diff] [blame]2944<a href="/doxygen/classllvm_1_1Instruction.html">doxygen output</a>.</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2945
2946</div>
2947
2948<!-- _______________________________________________________________________ -->
2949<div class="doc_subsubsection">
Reid Spencerc92d25d2006-12-19 19:47:19 +0000[diff] [blame]2950 <a name="s_Instruction">Important Subclasses of the <tt>Instruction</tt>
2951 class</a>
2952</div>
2953<div class="doc_text">
2954 <ul>
2955 <li><tt><a name="BinaryOperator">BinaryOperator</a></tt>
2956 <p>This subclasses represents all two operand instructions whose operands
2957 must be the same type, except for the comparison instructions.</p></li>
2958 <li><tt><a name="CastInst">CastInst</a></tt>
2959 <p>This subclass is the parent of the 12 casting instructions. It provides
2960 common operations on cast instructions.</p>
2961 <li><tt><a name="CmpInst">CmpInst</a></tt>
2962 <p>This subclass respresents the two comparison instructions,
2963 <a href="LangRef.html#i_icmp">ICmpInst</a> (integer opreands), and
2964 <a href="LangRef.html#i_fcmp">FCmpInst</a> (floating point operands).</p>
2965 <li><tt><a name="TerminatorInst">TerminatorInst</a></tt>
2966 <p>This subclass is the parent of all terminator instructions (those which
2967 can terminate a block).</p>
2968 </ul>
2969 </div>
2970
2971<!-- _______________________________________________________________________ -->
2972<div class="doc_subsubsection">
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2973 <a name="m_Instruction">Important Public Members of the <tt>Instruction</tt>
2974 class</a>
2975</div>
2976
2977<div class="doc_text">
2978
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]2979<ul>
2980 <li><tt><a href="#BasicBlock">BasicBlock</a> *getParent()</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2981 <p>Returns the <a href="#BasicBlock"><tt>BasicBlock</tt></a> that
2982this <tt>Instruction</tt> is embedded into.</p></li>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]2983 <li><tt>bool mayWriteToMemory()</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2984 <p>Returns true if the instruction writes to memory, i.e. it is a
2985 <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]2986 <li><tt>unsigned getOpcode()</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2987 <p>Returns the opcode for the <tt>Instruction</tt>.</p></li>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]2988 <li><tt><a href="#Instruction">Instruction</a> *clone() const</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2989 <p>Returns another instance of the specified instruction, identical
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]2990in all ways to the original except that the instruction has no parent
2991(ie it's not embedded into a <a href="#BasicBlock"><tt>BasicBlock</tt></a>),
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2992and it has no name</p></li>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]2993</ul>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2994
2995</div>
2996
2997<!-- ======================================================================= -->
2998<div class="doc_subsection">
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]2999 <a name="Constant">The <tt>Constant</tt> class and subclasses</a>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3000</div>
3001
3002<div class="doc_text">
3003
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]3004<p>Constant represents a base class for different types of constants. It
3005is subclassed by ConstantInt, ConstantArray, etc. for representing
3006the various types of Constants. <a href="#GlobalValue">GlobalValue</a> is also
3007a subclass, which represents the address of a global variable or function.
3008</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3009
3010</div>
3011
3012<!-- _______________________________________________________________________ -->
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]3013<div class="doc_subsubsection">Important Subclasses of Constant </div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3014<div class="doc_text">
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3015<ul>
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]3016 <li>ConstantInt : This subclass of Constant represents an integer constant of
3017 any width.
3018 <ul>
Reid Spencer97b4ee32007-03-01 21:05:33 +0000[diff] [blame]3019 <li><tt>const APInt&amp; getValue() const</tt>: Returns the underlying
3020 value of this constant, an APInt value.</li>
3021 <li><tt>int64_t getSExtValue() const</tt>: Converts the underlying APInt
3022 value to an int64_t via sign extension. If the value (not the bit width)
3023 of the APInt is too large to fit in an int64_t, an assertion will result.
3024 For this reason, use of this method is discouraged.</li>
3025 <li><tt>uint64_t getZExtValue() const</tt>: Converts the underlying APInt
3026 value to a uint64_t via zero extension. IF the value (not the bit width)
3027 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]3028 For this reason, use of this method is discouraged.</li>
Reid Spencer97b4ee32007-03-01 21:05:33 +0000[diff] [blame]3029 <li><tt>static ConstantInt* get(const APInt&amp; Val)</tt>: Returns the
3030 ConstantInt object that represents the value provided by <tt>Val</tt>.
3031 The type is implied as the IntegerType that corresponds to the bit width
3032 of <tt>Val</tt>.</li>
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]3033 <li><tt>static ConstantInt* get(const Type *Ty, uint64_t Val)</tt>:
3034 Returns the ConstantInt object that represents the value provided by
3035 <tt>Val</tt> for integer type <tt>Ty</tt>.</li>
3036 </ul>
3037 </li>
3038 <li>ConstantFP : This class represents a floating point constant.
3039 <ul>
3040 <li><tt>double getValue() const</tt>: Returns the underlying value of
3041 this constant. </li>
3042 </ul>
3043 </li>
3044 <li>ConstantArray : This represents a constant array.
3045 <ul>
3046 <li><tt>const std::vector&lt;Use&gt; &amp;getValues() const</tt>: Returns
3047 a vector of component constants that makeup this array. </li>
3048 </ul>
3049 </li>
3050 <li>ConstantStruct : This represents a constant struct.
3051 <ul>
3052 <li><tt>const std::vector&lt;Use&gt; &amp;getValues() const</tt>: Returns
3053 a vector of component constants that makeup this array. </li>
3054 </ul>
3055 </li>
3056 <li>GlobalValue : This represents either a global variable or a function. In
3057 either case, the value is a constant fixed address (after linking).
3058 </li>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3059</ul>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3060</div>
3061
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]3062
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3063<!-- ======================================================================= -->
3064<div class="doc_subsection">
3065 <a name="GlobalValue">The <tt>GlobalValue</tt> class</a>
3066</div>
3067
3068<div class="doc_text">
3069
3070<p><tt>#include "<a
3071href="/doxygen/GlobalValue_8h-source.html">llvm/GlobalValue.h</a>"</tt><br>
Misha Brukman384047f2004-06-03 23:29:12 +0000[diff] [blame]3072doxygen info: <a href="/doxygen/classllvm_1_1GlobalValue.html">GlobalValue
3073Class</a><br>
Reid Spencerbe5e85e2006-04-14 14:11:48 +0000[diff] [blame]3074Superclasses: <a href="#Constant"><tt>Constant</tt></a>,
3075<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]3076
3077<p>Global values (<a href="#GlobalVariable"><tt>GlobalVariable</tt></a>s or <a
3078href="#Function"><tt>Function</tt></a>s) are the only LLVM values that are
3079visible in the bodies of all <a href="#Function"><tt>Function</tt></a>s.
3080Because they are visible at global scope, they are also subject to linking with
3081other globals defined in different translation units. To control the linking
3082process, <tt>GlobalValue</tt>s know their linkage rules. Specifically,
3083<tt>GlobalValue</tt>s know whether they have internal or external linkage, as
Reid Spencer8b2da7a2004-07-18 13:10:31 +0000[diff] [blame]3084defined by the <tt>LinkageTypes</tt> enumeration.</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3085
3086<p>If a <tt>GlobalValue</tt> has internal linkage (equivalent to being
3087<tt>static</tt> in C), it is not visible to code outside the current translation
3088unit, and does not participate in linking. If it has external linkage, it is
3089visible to external code, and does participate in linking. In addition to
3090linkage information, <tt>GlobalValue</tt>s keep track of which <a
3091href="#Module"><tt>Module</tt></a> they are currently part of.</p>
3092
3093<p>Because <tt>GlobalValue</tt>s are memory objects, they are always referred to
3094by their <b>address</b>. As such, the <a href="#Type"><tt>Type</tt></a> of a
3095global is always a pointer to its contents. It is important to remember this
3096when using the <tt>GetElementPtrInst</tt> instruction because this pointer must
3097be dereferenced first. For example, if you have a <tt>GlobalVariable</tt> (a
3098subclass 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]3099i32]</tt>, then the <tt>GlobalVariable</tt> is a pointer to that array. Although
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3100the address of the first element of this array and the value of the
3101<tt>GlobalVariable</tt> are the same, they have different types. The
Reid Spencer06565dc2007-01-12 17:11:23 +0000[diff] [blame]3102<tt>GlobalVariable</tt>'s type is <tt>[24 x i32]</tt>. The first element's type
3103is <tt>i32.</tt> Because of this, accessing a global value requires you to
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3104dereference the pointer with <tt>GetElementPtrInst</tt> first, then its elements
3105can be accessed. This is explained in the <a href="LangRef.html#globalvars">LLVM
3106Language Reference Manual</a>.</p>
3107
3108</div>
3109
3110<!-- _______________________________________________________________________ -->
3111<div class="doc_subsubsection">
3112 <a name="m_GlobalValue">Important Public Members of the <tt>GlobalValue</tt>
3113 class</a>
3114</div>
3115
3116<div class="doc_text">
3117
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3118<ul>
3119 <li><tt>bool hasInternalLinkage() const</tt><br>
Chris Lattner9355b472002-09-06 02:50:58 +0000[diff] [blame]3120 <tt>bool hasExternalLinkage() const</tt><br>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3121 <tt>void setInternalLinkage(bool HasInternalLinkage)</tt>
3122 <p> These methods manipulate the linkage characteristics of the <tt>GlobalValue</tt>.</p>
3123 <p> </p>
3124 </li>
3125 <li><tt><a href="#Module">Module</a> *getParent()</tt>
3126 <p> This returns the <a href="#Module"><tt>Module</tt></a> that the
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3127GlobalValue is currently embedded into.</p></li>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3128</ul>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3129
3130</div>
3131
3132<!-- ======================================================================= -->
3133<div class="doc_subsection">
3134 <a name="Function">The <tt>Function</tt> class</a>
3135</div>
3136
3137<div class="doc_text">
3138
3139<p><tt>#include "<a
3140href="/doxygen/Function_8h-source.html">llvm/Function.h</a>"</tt><br> doxygen
Misha Brukman31ca1de2004-06-03 23:35:54 +0000[diff] [blame]3141info: <a href="/doxygen/classllvm_1_1Function.html">Function Class</a><br>
Reid Spencerbe5e85e2006-04-14 14:11:48 +0000[diff] [blame]3142Superclasses: <a href="#GlobalValue"><tt>GlobalValue</tt></a>,
3143<a href="#Constant"><tt>Constant</tt></a>,
3144<a href="#User"><tt>User</tt></a>,
3145<a href="#Value"><tt>Value</tt></a></p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3146
3147<p>The <tt>Function</tt> class represents a single procedure in LLVM. It is
3148actually one of the more complex classes in the LLVM heirarchy because it must
3149keep track of a large amount of data. The <tt>Function</tt> class keeps track
Reid Spencerbe5e85e2006-04-14 14:11:48 +0000[diff] [blame]3150of a list of <a href="#BasicBlock"><tt>BasicBlock</tt></a>s, a list of formal
3151<a href="#Argument"><tt>Argument</tt></a>s, and a
3152<a href="#SymbolTable"><tt>SymbolTable</tt></a>.</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3153
3154<p>The list of <a href="#BasicBlock"><tt>BasicBlock</tt></a>s is the most
3155commonly used part of <tt>Function</tt> objects. The list imposes an implicit
3156ordering of the blocks in the function, which indicate how the code will be
3157layed out by the backend. Additionally, the first <a
3158href="#BasicBlock"><tt>BasicBlock</tt></a> is the implicit entry node for the
3159<tt>Function</tt>. It is not legal in LLVM to explicitly branch to this initial
3160block. There are no implicit exit nodes, and in fact there may be multiple exit
3161nodes from a single <tt>Function</tt>. If the <a
3162href="#BasicBlock"><tt>BasicBlock</tt></a> list is empty, this indicates that
3163the <tt>Function</tt> is actually a function declaration: the actual body of the
3164function hasn't been linked in yet.</p>
3165
3166<p>In addition to a list of <a href="#BasicBlock"><tt>BasicBlock</tt></a>s, the
3167<tt>Function</tt> class also keeps track of the list of formal <a
3168href="#Argument"><tt>Argument</tt></a>s that the function receives. This
3169container manages the lifetime of the <a href="#Argument"><tt>Argument</tt></a>
3170nodes, just like the <a href="#BasicBlock"><tt>BasicBlock</tt></a> list does for
3171the <a href="#BasicBlock"><tt>BasicBlock</tt></a>s.</p>
3172
3173<p>The <a href="#SymbolTable"><tt>SymbolTable</tt></a> is a very rarely used
3174LLVM feature that is only used when you have to look up a value by name. Aside
3175from that, the <a href="#SymbolTable"><tt>SymbolTable</tt></a> is used
3176internally to make sure that there are not conflicts between the names of <a
3177href="#Instruction"><tt>Instruction</tt></a>s, <a
3178href="#BasicBlock"><tt>BasicBlock</tt></a>s, or <a
3179href="#Argument"><tt>Argument</tt></a>s in the function body.</p>
3180
Reid Spencer8b2da7a2004-07-18 13:10:31 +0000[diff] [blame]3181<p>Note that <tt>Function</tt> is a <a href="#GlobalValue">GlobalValue</a>
3182and therefore also a <a href="#Constant">Constant</a>. The value of the function
3183is its address (after linking) which is guaranteed to be constant.</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3184</div>
3185
3186<!-- _______________________________________________________________________ -->
3187<div class="doc_subsubsection">
3188 <a name="m_Function">Important Public Members of the <tt>Function</tt>
3189 class</a>
3190</div>
3191
3192<div class="doc_text">
3193
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3194<ul>
3195 <li><tt>Function(const </tt><tt><a href="#FunctionType">FunctionType</a>
Chris Lattnerac479e52004-08-04 05:10:48 +0000[diff] [blame]3196 *Ty, LinkageTypes Linkage, const std::string &amp;N = "", Module* Parent = 0)</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3197
3198 <p>Constructor used when you need to create new <tt>Function</tt>s to add
3199 the the program. The constructor must specify the type of the function to
Chris Lattnerac479e52004-08-04 05:10:48 +0000[diff] [blame]3200 create and what type of linkage the function should have. The <a
3201 href="#FunctionType"><tt>FunctionType</tt></a> argument
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3202 specifies the formal arguments and return value for the function. The same
Duncan Sands8036ca42007-03-30 12:22:09 +0000[diff] [blame]3203 <a href="#FunctionType"><tt>FunctionType</tt></a> value can be used to
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3204 create multiple functions. The <tt>Parent</tt> argument specifies the Module
3205 in which the function is defined. If this argument is provided, the function
3206 will automatically be inserted into that module's list of
3207 functions.</p></li>
3208
Chris Lattner62810e32008-11-25 18:34:50 +0000[diff] [blame]3209 <li><tt>bool isDeclaration()</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3210
3211 <p>Return whether or not the <tt>Function</tt> has a body defined. If the
3212 function is "external", it does not have a body, and thus must be resolved
3213 by linking with a function defined in a different translation unit.</p></li>
3214
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3215 <li><tt>Function::iterator</tt> - Typedef for basic block list iterator<br>
Chris Lattner9355b472002-09-06 02:50:58 +0000[diff] [blame]3216 <tt>Function::const_iterator</tt> - Typedef for const_iterator.<br>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3217
Chris Lattner77d69242005-03-15 05:19:20 +0000[diff] [blame]3218 <tt>begin()</tt>, <tt>end()</tt>
3219 <tt>size()</tt>, <tt>empty()</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3220
3221 <p>These are forwarding methods that make it easy to access the contents of
3222 a <tt>Function</tt> object's <a href="#BasicBlock"><tt>BasicBlock</tt></a>
3223 list.</p></li>
3224
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3225 <li><tt>Function::BasicBlockListType &amp;getBasicBlockList()</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3226
3227 <p>Returns the list of <a href="#BasicBlock"><tt>BasicBlock</tt></a>s. This
3228 is necessary to use when you need to update the list or perform a complex
3229 action that doesn't have a forwarding method.</p></li>
3230
Chris Lattner89cc2652005-03-15 04:48:32 +0000[diff] [blame]3231 <li><tt>Function::arg_iterator</tt> - Typedef for the argument list
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3232iterator<br>
Chris Lattner89cc2652005-03-15 04:48:32 +0000[diff] [blame]3233 <tt>Function::const_arg_iterator</tt> - Typedef for const_iterator.<br>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3234
Chris Lattner77d69242005-03-15 05:19:20 +0000[diff] [blame]3235 <tt>arg_begin()</tt>, <tt>arg_end()</tt>
Chris Lattner89cc2652005-03-15 04:48:32 +0000[diff] [blame]3236 <tt>arg_size()</tt>, <tt>arg_empty()</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3237
3238 <p>These are forwarding methods that make it easy to access the contents of
3239 a <tt>Function</tt> object's <a href="#Argument"><tt>Argument</tt></a>
3240 list.</p></li>
3241
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3242 <li><tt>Function::ArgumentListType &amp;getArgumentList()</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3243
3244 <p>Returns the list of <a href="#Argument"><tt>Argument</tt></a>s. This is
3245 necessary to use when you need to update the list or perform a complex
3246 action that doesn't have a forwarding method.</p></li>
3247
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3248 <li><tt><a href="#BasicBlock">BasicBlock</a> &amp;getEntryBlock()</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3249
3250 <p>Returns the entry <a href="#BasicBlock"><tt>BasicBlock</tt></a> for the
3251 function. Because the entry block for the function is always the first
3252 block, this returns the first block of the <tt>Function</tt>.</p></li>
3253
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3254 <li><tt><a href="#Type">Type</a> *getReturnType()</tt><br>
3255 <tt><a href="#FunctionType">FunctionType</a> *getFunctionType()</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3256
3257 <p>This traverses the <a href="#Type"><tt>Type</tt></a> of the
3258 <tt>Function</tt> and returns the return type of the function, or the <a
3259 href="#FunctionType"><tt>FunctionType</tt></a> of the actual
3260 function.</p></li>
3261
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3262 <li><tt><a href="#SymbolTable">SymbolTable</a> *getSymbolTable()</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3263
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3264 <p> Return a pointer to the <a href="#SymbolTable"><tt>SymbolTable</tt></a>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3265 for this <tt>Function</tt>.</p></li>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3266</ul>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3267
3268</div>
3269
3270<!-- ======================================================================= -->
3271<div class="doc_subsection">
3272 <a name="GlobalVariable">The <tt>GlobalVariable</tt> class</a>
3273</div>
3274
3275<div class="doc_text">
3276
3277<p><tt>#include "<a
3278href="/doxygen/GlobalVariable_8h-source.html">llvm/GlobalVariable.h</a>"</tt>
3279<br>
Tanya Lattnera3da7772004-06-22 08:02:25 +0000[diff] [blame]3280doxygen info: <a href="/doxygen/classllvm_1_1GlobalVariable.html">GlobalVariable
Reid Spencerbe5e85e2006-04-14 14:11:48 +0000[diff] [blame]3281 Class</a><br>
3282Superclasses: <a href="#GlobalValue"><tt>GlobalValue</tt></a>,
3283<a href="#Constant"><tt>Constant</tt></a>,
3284<a href="#User"><tt>User</tt></a>,
3285<a href="#Value"><tt>Value</tt></a></p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3286
3287<p>Global variables are represented with the (suprise suprise)
3288<tt>GlobalVariable</tt> class. Like functions, <tt>GlobalVariable</tt>s are also
3289subclasses of <a href="#GlobalValue"><tt>GlobalValue</tt></a>, and as such are
3290always referenced by their address (global values must live in memory, so their
Reid Spencerbe5e85e2006-04-14 14:11:48 +0000[diff] [blame]3291"name" refers to their constant address). See
3292<a href="#GlobalValue"><tt>GlobalValue</tt></a> for more on this. Global
3293variables may have an initial value (which must be a
3294<a href="#Constant"><tt>Constant</tt></a>), and if they have an initializer,
3295they may be marked as "constant" themselves (indicating that their contents
3296never change at runtime).</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3297</div>
3298
3299<!-- _______________________________________________________________________ -->
3300<div class="doc_subsubsection">
3301 <a name="m_GlobalVariable">Important Public Members of the
3302 <tt>GlobalVariable</tt> class</a>
3303</div>
3304
3305<div class="doc_text">
3306
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3307<ul>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3308 <li><tt>GlobalVariable(const </tt><tt><a href="#Type">Type</a> *Ty, bool
3309 isConstant, LinkageTypes&amp; Linkage, <a href="#Constant">Constant</a>
3310 *Initializer = 0, const std::string &amp;Name = "", Module* Parent = 0)</tt>
3311
3312 <p>Create a new global variable of the specified type. If
3313 <tt>isConstant</tt> is true then the global variable will be marked as
3314 unchanging for the program. The Linkage parameter specifies the type of
Duncan Sands667d4b82009-03-07 15:45:40 +0000[diff] [blame]3315 linkage (internal, external, weak, linkonce, appending) for the variable.
3316 If the linkage is InternalLinkage, WeakAnyLinkage, WeakODRLinkage,
3317 LinkOnceAnyLinkage or LinkOnceODRLinkage,&nbsp; then the resultant
3318 global variable will have internal linkage. AppendingLinkage concatenates
3319 together all instances (in different translation units) of the variable
3320 into a single variable but is only applicable to arrays. &nbsp;See
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3321 the <a href="LangRef.html#modulestructure">LLVM Language Reference</a> for
3322 further details on linkage types. Optionally an initializer, a name, and the
3323 module to put the variable into may be specified for the global variable as
3324 well.</p></li>
3325
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3326 <li><tt>bool isConstant() const</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3327
3328 <p>Returns true if this is a global variable that is known not to
3329 be modified at runtime.</p></li>
3330
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3331 <li><tt>bool hasInitializer()</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3332
3333 <p>Returns true if this <tt>GlobalVariable</tt> has an intializer.</p></li>
3334
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3335 <li><tt><a href="#Constant">Constant</a> *getInitializer()</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3336
3337 <p>Returns the intial value for a <tt>GlobalVariable</tt>. It is not legal
3338 to call this method if there is no initializer.</p></li>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3339</ul>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3340
3341</div>
3342
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]3343
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3344<!-- ======================================================================= -->
3345<div class="doc_subsection">
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]3346 <a name="BasicBlock">The <tt>BasicBlock</tt> class</a>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3347</div>
3348
3349<div class="doc_text">
3350
3351<p><tt>#include "<a
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]3352href="/doxygen/BasicBlock_8h-source.html">llvm/BasicBlock.h</a>"</tt><br>
3353doxygen info: <a href="/doxygen/structllvm_1_1BasicBlock.html">BasicBlock
3354Class</a><br>
3355Superclass: <a href="#Value"><tt>Value</tt></a></p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3356
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]3357<p>This class represents a single entry multiple exit section of the code,
3358commonly known as a basic block by the compiler community. The
3359<tt>BasicBlock</tt> class maintains a list of <a
3360href="#Instruction"><tt>Instruction</tt></a>s, which form the body of the block.
3361Matching the language definition, the last element of this list of instructions
3362is always a terminator instruction (a subclass of the <a
3363href="#TerminatorInst"><tt>TerminatorInst</tt></a> class).</p>
3364
3365<p>In addition to tracking the list of instructions that make up the block, the
3366<tt>BasicBlock</tt> class also keeps track of the <a
3367href="#Function"><tt>Function</tt></a> that it is embedded into.</p>
3368
3369<p>Note that <tt>BasicBlock</tt>s themselves are <a
3370href="#Value"><tt>Value</tt></a>s, because they are referenced by instructions
3371like branches and can go in the switch tables. <tt>BasicBlock</tt>s have type
3372<tt>label</tt>.</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3373
3374</div>
3375
3376<!-- _______________________________________________________________________ -->
3377<div class="doc_subsubsection">
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]3378 <a name="m_BasicBlock">Important Public Members of the <tt>BasicBlock</tt>
3379 class</a>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3380</div>
3381
3382<div class="doc_text">
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3383<ul>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3384
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]3385<li><tt>BasicBlock(const std::string &amp;Name = "", </tt><tt><a
3386 href="#Function">Function</a> *Parent = 0)</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3387
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]3388<p>The <tt>BasicBlock</tt> constructor is used to create new basic blocks for
3389insertion into a function. The constructor optionally takes a name for the new
3390block, and a <a href="#Function"><tt>Function</tt></a> to insert it into. If
3391the <tt>Parent</tt> parameter is specified, the new <tt>BasicBlock</tt> is
3392automatically inserted at the end of the specified <a
3393href="#Function"><tt>Function</tt></a>, if not specified, the BasicBlock must be
3394manually inserted into the <a href="#Function"><tt>Function</tt></a>.</p></li>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3395
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]3396<li><tt>BasicBlock::iterator</tt> - Typedef for instruction list iterator<br>
3397<tt>BasicBlock::const_iterator</tt> - Typedef for const_iterator.<br>
3398<tt>begin()</tt>, <tt>end()</tt>, <tt>front()</tt>, <tt>back()</tt>,
3399<tt>size()</tt>, <tt>empty()</tt>
3400STL-style functions for accessing the instruction list.
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3401
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]3402<p>These methods and typedefs are forwarding functions that have the same
3403semantics as the standard library methods of the same names. These methods
3404expose the underlying instruction list of a basic block in a way that is easy to
3405manipulate. To get the full complement of container operations (including
3406operations to update the list), you must use the <tt>getInstList()</tt>
3407method.</p></li>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3408
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]3409<li><tt>BasicBlock::InstListType &amp;getInstList()</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3410
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]3411<p>This method is used to get access to the underlying container that actually
3412holds the Instructions. This method must be used when there isn't a forwarding
3413function in the <tt>BasicBlock</tt> class for the operation that you would like
3414to perform. Because there are no forwarding functions for "updating"
3415operations, you need to use this if you want to update the contents of a
3416<tt>BasicBlock</tt>.</p></li>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3417
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]3418<li><tt><a href="#Function">Function</a> *getParent()</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3419
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]3420<p> Returns a pointer to <a href="#Function"><tt>Function</tt></a> the block is
3421embedded into, or a null pointer if it is homeless.</p></li>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3422
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]3423<li><tt><a href="#TerminatorInst">TerminatorInst</a> *getTerminator()</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3424
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]3425<p> Returns a pointer to the terminator instruction that appears at the end of
3426the <tt>BasicBlock</tt>. If there is no terminator instruction, or if the last
3427instruction in the block is not a terminator, then a null pointer is
3428returned.</p></li>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3429
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3430</ul>
3431
3432</div>
3433
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3434
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3435<!-- ======================================================================= -->
3436<div class="doc_subsection">
3437 <a name="Argument">The <tt>Argument</tt> class</a>
3438</div>
3439
3440<div class="doc_text">
3441
3442<p>This subclass of Value defines the interface for incoming formal
Chris Lattner58360822005-01-17 00:12:04 +0000[diff] [blame]3443arguments to a function. A Function maintains a list of its formal
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3444arguments. An argument has a pointer to the parent Function.</p>
3445
3446</div>
3447
Chris Lattner9355b472002-09-06 02:50:58 +0000[diff] [blame]3448<!-- *********************************************************************** -->
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3449<hr>
3450<address>
3451 <a href="http://jigsaw.w3.org/css-validator/check/referer"><img
Misha Brukman44408702008-12-11 17:34:48 +0000[diff] [blame]3452 src="http://jigsaw.w3.org/css-validator/images/vcss-blue" alt="Valid CSS"></a>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3453 <a href="http://validator.w3.org/check/referer"><img
Gabor Greifa9c0f2b2008-06-18 14:05:31 +0000[diff] [blame]3454 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]3455
3456 <a href="mailto:dhurjati@cs.uiuc.edu">Dinakar Dhurjati</a> and
3457 <a href="mailto:sabre@nondot.org">Chris Lattner</a><br>
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]3458 <a href="http://llvm.org">The LLVM Compiler Infrastructure</a><br>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3459 Last modified: $Date$
3460</address>
3461
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3462</body>
3463</html>