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4<head>
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Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]6 <title>LLVM Programmer's Manual</title>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]7 <link rel="stylesheet" href="llvm.css" type="text/css">
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]8</head>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]9<body>
10
11<div class="doc_title">
12 LLVM Programmer's Manual
13</div>
14
Chris Lattner9355b472002-09-06 02:50:58 +0000[diff] [blame]15<ol>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]16 <li><a href="#introduction">Introduction</a></li>
Chris Lattner9355b472002-09-06 02:50:58 +0000[diff] [blame]17 <li><a href="#general">General Information</a>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]18 <ul>
Reid Spencerfe8f4ff2004-11-01 09:02:53 +0000[diff] [blame]19 <li><a href="#stl">The C++ Standard Template Library</a></li>
20<!--
21 <li>The <tt>-time-passes</tt> option</li>
22 <li>How to use the LLVM Makefile system</li>
23 <li>How to write a regression test</li>
Chris Lattner61db4652004-12-08 19:05:44 +0000[diff] [blame]24
Reid Spencerfe8f4ff2004-11-01 09:02:53 +0000[diff] [blame]25-->
Chris Lattner84b7f8d2003-08-01 22:20:59 +0000[diff] [blame]26 </ul>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]27 </li>
28 <li><a href="#apis">Important and useful LLVM APIs</a>
29 <ul>
30 <li><a href="#isa">The <tt>isa&lt;&gt;</tt>, <tt>cast&lt;&gt;</tt>
31and <tt>dyn_cast&lt;&gt;</tt> templates</a> </li>
Misha Brukman2c122ce2005-11-01 21:12:49 +0000[diff] [blame]32 <li><a href="#DEBUG">The <tt>DEBUG()</tt> macro and <tt>-debug</tt>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]33option</a>
34 <ul>
35 <li><a href="#DEBUG_TYPE">Fine grained debug info with <tt>DEBUG_TYPE</tt>
36and the <tt>-debug-only</tt> option</a> </li>
37 </ul>
38 </li>
Chris Lattner0be6fdf2006-12-19 21:46:21 +0000[diff] [blame]39 <li><a href="#Statistic">The <tt>Statistic</tt> class &amp; <tt>-stats</tt>
Reid Spencerfe8f4ff2004-11-01 09:02:53 +0000[diff] [blame]40option</a></li>
41<!--
42 <li>The <tt>InstVisitor</tt> template
43 <li>The general graph API
44-->
Chris Lattnerf623a082005-10-17 01:36:23 +0000[diff] [blame]45 <li><a href="#ViewGraph">Viewing graphs while debugging code</a></li>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]46 </ul>
47 </li>
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]48 <li><a href="#datastructure">Picking the Right Data Structure for a Task</a>
49 <ul>
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]50 <li><a href="#ds_sequential">Sequential Containers (std::vector, std::list, etc)</a>
51 <ul>
52 <li><a href="#dss_fixedarrays">Fixed Size Arrays</a></li>
53 <li><a href="#dss_heaparrays">Heap Allocated Arrays</a></li>
54 <li><a href="#dss_smallvector">"llvm/ADT/SmallVector.h"</a></li>
55 <li><a href="#dss_vector">&lt;vector&gt;</a></li>
56 <li><a href="#dss_deque">&lt;deque&gt;</a></li>
57 <li><a href="#dss_list">&lt;list&gt;</a></li>
Gabor Greif3899e492009-02-27 11:37:41 +0000[diff] [blame]58 <li><a href="#dss_ilist">llvm/ADT/ilist.h</a></li>
Chris Lattnerc5722432007-02-03 19:49:31 +0000[diff] [blame]59 <li><a href="#dss_other">Other Sequential Container Options</a></li>
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]60 </ul></li>
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]61 <li><a href="#ds_set">Set-Like Containers (std::set, SmallSet, SetVector, etc)</a>
62 <ul>
63 <li><a href="#dss_sortedvectorset">A sorted 'vector'</a></li>
64 <li><a href="#dss_smallset">"llvm/ADT/SmallSet.h"</a></li>
65 <li><a href="#dss_smallptrset">"llvm/ADT/SmallPtrSet.h"</a></li>
Chris Lattnerc28476f2007-09-30 00:58:59 +0000[diff] [blame]66 <li><a href="#dss_denseset">"llvm/ADT/DenseSet.h"</a></li>
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]67 <li><a href="#dss_FoldingSet">"llvm/ADT/FoldingSet.h"</a></li>
68 <li><a href="#dss_set">&lt;set&gt;</a></li>
69 <li><a href="#dss_setvector">"llvm/ADT/SetVector.h"</a></li>
Chris Lattnerc5722432007-02-03 19:49:31 +0000[diff] [blame]70 <li><a href="#dss_uniquevector">"llvm/ADT/UniqueVector.h"</a></li>
71 <li><a href="#dss_otherset">Other Set-Like ContainerOptions</a></li>
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]72 </ul></li>
Chris Lattnerf3692522007-02-03 19:51:56 +0000[diff] [blame]73 <li><a href="#ds_map">Map-Like Containers (std::map, DenseMap, etc)</a>
74 <ul>
75 <li><a href="#dss_sortedvectormap">A sorted 'vector'</a></li>
Chris Lattner796f9fa2007-02-08 19:14:21 +0000[diff] [blame]76 <li><a href="#dss_stringmap">"llvm/ADT/StringMap.h"</a></li>
Chris Lattnerf3692522007-02-03 19:51:56 +0000[diff] [blame]77 <li><a href="#dss_indexedmap">"llvm/ADT/IndexedMap.h"</a></li>
78 <li><a href="#dss_densemap">"llvm/ADT/DenseMap.h"</a></li>
79 <li><a href="#dss_map">&lt;map&gt;</a></li>
80 <li><a href="#dss_othermap">Other Map-Like Container Options</a></li>
81 </ul></li>
Daniel Berlin1939ace2007-09-24 17:52:25 +0000[diff] [blame]82 <li><a href="#ds_bit">BitVector-like containers</a>
83 <ul>
84 <li><a href="#dss_bitvector">A dense bitvector</a></li>
85 <li><a href="#dss_sparsebitvector">A sparse bitvector</a></li>
86 </ul></li>
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]87 </ul>
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]88 </li>
Chris Lattnerae7f7592002-09-06 18:31:18 +0000[diff] [blame]89 <li><a href="#common">Helpful Hints for Common Operations</a>
Chris Lattnerae7f7592002-09-06 18:31:18 +0000[diff] [blame]90 <ul>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]91 <li><a href="#inspection">Basic Inspection and Traversal Routines</a>
92 <ul>
93 <li><a href="#iterate_function">Iterating over the <tt>BasicBlock</tt>s
94in a <tt>Function</tt></a> </li>
95 <li><a href="#iterate_basicblock">Iterating over the <tt>Instruction</tt>s
96in a <tt>BasicBlock</tt></a> </li>
97 <li><a href="#iterate_institer">Iterating over the <tt>Instruction</tt>s
98in a <tt>Function</tt></a> </li>
99 <li><a href="#iterate_convert">Turning an iterator into a
100class pointer</a> </li>
101 <li><a href="#iterate_complex">Finding call sites: a more
102complex example</a> </li>
103 <li><a href="#calls_and_invokes">Treating calls and invokes
104the same way</a> </li>
105 <li><a href="#iterate_chains">Iterating over def-use &amp;
106use-def chains</a> </li>
Chris Lattner2e438ca2008-01-03 16:56:04 +0000[diff] [blame]107 <li><a href="#iterate_preds">Iterating over predecessors &amp;
108successors of blocks</a></li>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]109 </ul>
110 </li>
111 <li><a href="#simplechanges">Making simple changes</a>
112 <ul>
113 <li><a href="#schanges_creating">Creating and inserting new
114 <tt>Instruction</tt>s</a> </li>
115 <li><a href="#schanges_deleting">Deleting <tt>Instruction</tt>s</a> </li>
116 <li><a href="#schanges_replacing">Replacing an <tt>Instruction</tt>
117with another <tt>Value</tt></a> </li>
Tanya Lattnerb011c662007-06-20 18:33:15 +0000[diff] [blame]118 <li><a href="#schanges_deletingGV">Deleting <tt>GlobalVariable</tt>s</a> </li>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]119 </ul>
Reid Spencerfe8f4ff2004-11-01 09:02:53 +0000[diff] [blame]120 </li>
Jeffrey Yasskin714257f2009-04-30 22:33:41 +0000[diff] [blame]121 <li><a href="#create_types">How to Create Types</a></li>
Chris Lattnerae7f7592002-09-06 18:31:18 +0000[diff] [blame]122<!--
123 <li>Working with the Control Flow Graph
124 <ul>
125 <li>Accessing predecessors and successors of a <tt>BasicBlock</tt>
126 <li>
127 <li>
128 </ul>
Reid Spencerfe8f4ff2004-11-01 09:02:53 +0000[diff] [blame]129-->
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]130 </ul>
131 </li>
Chris Lattnerd9d6e102005-04-23 16:10:52 +0000[diff] [blame]132
Owen Anderson8bc1b3b2009-06-16 01:17:16 +0000[diff] [blame]133 <li><a href="#threading">Threads and LLVM</a>
134 <ul>
Owen Anderson5e8c50e2009-06-16 17:40:28 +0000[diff] [blame^]135 <li><a href="#startmultithreaded">Entering threaded mode with <tt>llvm_start_multithreaded()</tt></a></li>
Owen Anderson8bc1b3b2009-06-16 01:17:16 +0000[diff] [blame]136 <li><a href="#shutdown">Ending execution with <tt>llvm_shutdown()</tt></a></li>
137 <li><a href="#managedstatic">Lazy initialization with <tt>ManagedStatic</tt></a></li>
138 </ul>
139 </li>
140
Chris Lattnerd9d6e102005-04-23 16:10:52 +0000[diff] [blame]141 <li><a href="#advanced">Advanced Topics</a>
142 <ul>
Chris Lattnerf1b200b2005-04-23 17:27:36 +0000[diff] [blame]143 <li><a href="#TypeResolve">LLVM Type Resolution</a>
144 <ul>
145 <li><a href="#BuildRecType">Basic Recursive Type Construction</a></li>
146 <li><a href="#refineAbstractTypeTo">The <tt>refineAbstractTypeTo</tt> method</a></li>
147 <li><a href="#PATypeHolder">The PATypeHolder Class</a></li>
148 <li><a href="#AbstractTypeUser">The AbstractTypeUser Class</a></li>
149 </ul></li>
150
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]151 <li><a href="#SymbolTable">The <tt>ValueSymbolTable</tt> and <tt>TypeSymbolTable</tt> classes</a></li>
152 <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]153 </ul></li>
154
Joel Stanley9b96c442002-09-06 21:55:13 +0000[diff] [blame]155 <li><a href="#coreclasses">The Core LLVM Class Hierarchy Reference</a>
Chris Lattner9355b472002-09-06 02:50:58 +0000[diff] [blame]156 <ul>
Reid Spencer303c4b42007-01-12 17:26:25 +0000[diff] [blame]157 <li><a href="#Type">The <tt>Type</tt> class</a> </li>
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]158 <li><a href="#Module">The <tt>Module</tt> class</a></li>
Reid Spencerfe8f4ff2004-11-01 09:02:53 +0000[diff] [blame]159 <li><a href="#Value">The <tt>Value</tt> class</a>
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]160 <ul>
161 <li><a href="#User">The <tt>User</tt> class</a>
Chris Lattner9355b472002-09-06 02:50:58 +0000[diff] [blame]162 <ul>
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]163 <li><a href="#Instruction">The <tt>Instruction</tt> class</a></li>
164 <li><a href="#Constant">The <tt>Constant</tt> class</a>
165 <ul>
166 <li><a href="#GlobalValue">The <tt>GlobalValue</tt> class</a>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]167 <ul>
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]168 <li><a href="#Function">The <tt>Function</tt> class</a></li>
169 <li><a href="#GlobalVariable">The <tt>GlobalVariable</tt> class</a></li>
170 </ul>
171 </li>
172 </ul>
173 </li>
Reid Spencerfe8f4ff2004-11-01 09:02:53 +0000[diff] [blame]174 </ul>
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]175 </li>
176 <li><a href="#BasicBlock">The <tt>BasicBlock</tt> class</a></li>
177 <li><a href="#Argument">The <tt>Argument</tt> class</a></li>
178 </ul>
Reid Spencerfe8f4ff2004-11-01 09:02:53 +0000[diff] [blame]179 </li>
180 </ul>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]181 </li>
Chris Lattner9355b472002-09-06 02:50:58 +0000[diff] [blame]182</ol>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]183
Chris Lattner69bf8a92004-05-23 21:06:58 +0000[diff] [blame]184<div class="doc_author">
185 <p>Written by <a href="mailto:sabre@nondot.org">Chris Lattner</a>,
Chris Lattner94c43592004-05-26 16:52:55 +0000[diff] [blame]186 <a href="mailto:dhurjati@cs.uiuc.edu">Dinakar Dhurjati</a>,
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]187 <a href="mailto:ggreif@gmail.com">Gabor Greif</a>,
Owen Anderson8bc1b3b2009-06-16 01:17:16 +0000[diff] [blame]188 <a href="mailto:jstanley@cs.uiuc.edu">Joel Stanley</a>,
189 <a href="mailto:rspencer@x10sys.com">Reid Spencer</a> and
190 <a href="mailto:owen@apple.com">Owen Anderson</a></p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]191</div>
192
Chris Lattner9355b472002-09-06 02:50:58 +0000[diff] [blame]193<!-- *********************************************************************** -->
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]194<div class="doc_section">
195 <a name="introduction">Introduction </a>
196</div>
Chris Lattner9355b472002-09-06 02:50:58 +0000[diff] [blame]197<!-- *********************************************************************** -->
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]198
199<div class="doc_text">
200
201<p>This document is meant to highlight some of the important classes and
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]202interfaces available in the LLVM source-base. This manual is not
203intended to explain what LLVM is, how it works, and what LLVM code looks
204like. It assumes that you know the basics of LLVM and are interested
205in writing transformations or otherwise analyzing or manipulating the
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]206code.</p>
207
208<p>This document should get you oriented so that you can find your
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]209way in the continuously growing source code that makes up the LLVM
210infrastructure. Note that this manual is not intended to serve as a
211replacement for reading the source code, so if you think there should be
212a method in one of these classes to do something, but it's not listed,
213check the source. Links to the <a href="/doxygen/">doxygen</a> sources
214are provided to make this as easy as possible.</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]215
216<p>The first section of this document describes general information that is
217useful to know when working in the LLVM infrastructure, and the second describes
218the Core LLVM classes. In the future this manual will be extended with
219information describing how to use extension libraries, such as dominator
220information, CFG traversal routines, and useful utilities like the <tt><a
221href="/doxygen/InstVisitor_8h-source.html">InstVisitor</a></tt> template.</p>
222
223</div>
224
Chris Lattner9355b472002-09-06 02:50:58 +0000[diff] [blame]225<!-- *********************************************************************** -->
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]226<div class="doc_section">
227 <a name="general">General Information</a>
228</div>
229<!-- *********************************************************************** -->
230
231<div class="doc_text">
232
233<p>This section contains general information that is useful if you are working
234in the LLVM source-base, but that isn't specific to any particular API.</p>
235
236</div>
237
238<!-- ======================================================================= -->
239<div class="doc_subsection">
240 <a name="stl">The C++ Standard Template Library</a>
241</div>
242
243<div class="doc_text">
244
245<p>LLVM makes heavy use of the C++ Standard Template Library (STL),
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]246perhaps much more than you are used to, or have seen before. Because of
247this, you might want to do a little background reading in the
248techniques used and capabilities of the library. There are many good
249pages that discuss the STL, and several books on the subject that you
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]250can get, so it will not be discussed in this document.</p>
251
252<p>Here are some useful links:</p>
253
254<ol>
255
256<li><a href="http://www.dinkumware.com/refxcpp.html">Dinkumware C++ Library
257reference</a> - an excellent reference for the STL and other parts of the
258standard C++ library.</li>
259
260<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]261O'Reilly book in the making. It has a decent Standard Library
262Reference that rivals Dinkumware's, and is unfortunately no longer free since the
263book has been published.</li>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]264
265<li><a href="http://www.parashift.com/c++-faq-lite/">C++ Frequently Asked
266Questions</a></li>
267
268<li><a href="http://www.sgi.com/tech/stl/">SGI's STL Programmer's Guide</a> -
269Contains a useful <a
270href="http://www.sgi.com/tech/stl/stl_introduction.html">Introduction to the
271STL</a>.</li>
272
273<li><a href="http://www.research.att.com/%7Ebs/C++.html">Bjarne Stroustrup's C++
274Page</a></li>
275
Tanya Lattner79445ba2004-12-08 18:34:56 +0000[diff] [blame]276<li><a href="http://64.78.49.204/">
Reid Spencer096603a2004-05-26 08:41:35 +0000[diff] [blame]277Bruce Eckel's Thinking in C++, 2nd ed. Volume 2 Revision 4.0 (even better, get
278the book).</a></li>
279
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]280</ol>
281
282<p>You are also encouraged to take a look at the <a
283href="CodingStandards.html">LLVM Coding Standards</a> guide which focuses on how
284to write maintainable code more than where to put your curly braces.</p>
285
286</div>
287
288<!-- ======================================================================= -->
289<div class="doc_subsection">
290 <a name="stl">Other useful references</a>
291</div>
292
293<div class="doc_text">
294
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]295<ol>
296<li><a href="http://www.psc.edu/%7Esemke/cvs_branches.html">CVS
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]297Branch and Tag Primer</a></li>
Misha Brukmana0f71e42004-06-18 18:39:00 +0000[diff] [blame]298<li><a href="http://www.fortran-2000.com/ArnaudRecipes/sharedlib.html">Using
299static and shared libraries across platforms</a></li>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]300</ol>
301
302</div>
303
Chris Lattner9355b472002-09-06 02:50:58 +0000[diff] [blame]304<!-- *********************************************************************** -->
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]305<div class="doc_section">
306 <a name="apis">Important and useful LLVM APIs</a>
307</div>
308<!-- *********************************************************************** -->
309
310<div class="doc_text">
311
312<p>Here we highlight some LLVM APIs that are generally useful and good to
313know about when writing transformations.</p>
314
315</div>
316
317<!-- ======================================================================= -->
318<div class="doc_subsection">
Misha Brukman2c122ce2005-11-01 21:12:49 +0000[diff] [blame]319 <a name="isa">The <tt>isa&lt;&gt;</tt>, <tt>cast&lt;&gt;</tt> and
320 <tt>dyn_cast&lt;&gt;</tt> templates</a>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]321</div>
322
323<div class="doc_text">
324
325<p>The LLVM source-base makes extensive use of a custom form of RTTI.
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]326These templates have many similarities to the C++ <tt>dynamic_cast&lt;&gt;</tt>
327operator, but they don't have some drawbacks (primarily stemming from
328the fact that <tt>dynamic_cast&lt;&gt;</tt> only works on classes that
329have a v-table). Because they are used so often, you must know what they
330do and how they work. All of these templates are defined in the <a
Chris Lattner695b78b2005-04-26 22:56:16 +0000[diff] [blame]331 href="/doxygen/Casting_8h-source.html"><tt>llvm/Support/Casting.h</tt></a>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]332file (note that you very rarely have to include this file directly).</p>
333
334<dl>
335 <dt><tt>isa&lt;&gt;</tt>: </dt>
336
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]337 <dd><p>The <tt>isa&lt;&gt;</tt> operator works exactly like the Java
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]338 "<tt>instanceof</tt>" operator. It returns true or false depending on whether
339 a reference or pointer points to an instance of the specified class. This can
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]340 be very useful for constraint checking of various sorts (example below).</p>
341 </dd>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]342
343 <dt><tt>cast&lt;&gt;</tt>: </dt>
344
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]345 <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]346 converts a pointer or reference from a base class to a derived class, causing
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]347 an assertion failure if it is not really an instance of the right type. This
348 should be used in cases where you have some information that makes you believe
349 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]350 and <tt>cast&lt;&gt;</tt> template is:</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]351
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]352<div class="doc_code">
353<pre>
354static bool isLoopInvariant(const <a href="#Value">Value</a> *V, const Loop *L) {
355 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))
356 return true;
Chris Lattner69bf8a92004-05-23 21:06:58 +0000[diff] [blame]357
Bill Wendling82e2eea2006-10-11 18:00:22 +0000[diff] [blame]358 // <i>Otherwise, it must be an instruction...</i>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]359 return !L-&gt;contains(cast&lt;<a href="#Instruction">Instruction</a>&gt;(V)-&gt;getParent());
360}
361</pre>
362</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]363
364 <p>Note that you should <b>not</b> use an <tt>isa&lt;&gt;</tt> test followed
365 by a <tt>cast&lt;&gt;</tt>, for that use the <tt>dyn_cast&lt;&gt;</tt>
366 operator.</p>
367
368 </dd>
369
370 <dt><tt>dyn_cast&lt;&gt;</tt>:</dt>
371
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]372 <dd><p>The <tt>dyn_cast&lt;&gt;</tt> operator is a "checking cast" operation.
373 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]374 pointer to it (this operator does not work with references). If the operand is
375 not of the correct type, a null pointer is returned. Thus, this works very
Misha Brukman2c122ce2005-11-01 21:12:49 +0000[diff] [blame]376 much like the <tt>dynamic_cast&lt;&gt;</tt> operator in C++, and should be
377 used in the same circumstances. Typically, the <tt>dyn_cast&lt;&gt;</tt>
378 operator is used in an <tt>if</tt> statement or some other flow control
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]379 statement like this:</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]380
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]381<div class="doc_code">
382<pre>
383if (<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]384 // <i>...</i>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]385}
386</pre>
387</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]388
Misha Brukman2c122ce2005-11-01 21:12:49 +0000[diff] [blame]389 <p>This form of the <tt>if</tt> statement effectively combines together a call
390 to <tt>isa&lt;&gt;</tt> and a call to <tt>cast&lt;&gt;</tt> into one
391 statement, which is very convenient.</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]392
Misha Brukman2c122ce2005-11-01 21:12:49 +0000[diff] [blame]393 <p>Note that the <tt>dyn_cast&lt;&gt;</tt> operator, like C++'s
394 <tt>dynamic_cast&lt;&gt;</tt> or Java's <tt>instanceof</tt> operator, can be
395 abused. In particular, you should not use big chained <tt>if/then/else</tt>
396 blocks to check for lots of different variants of classes. If you find
397 yourself wanting to do this, it is much cleaner and more efficient to use the
398 <tt>InstVisitor</tt> class to dispatch over the instruction type directly.</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]399
Misha Brukman2c122ce2005-11-01 21:12:49 +0000[diff] [blame]400 </dd>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]401
Misha Brukman2c122ce2005-11-01 21:12:49 +0000[diff] [blame]402 <dt><tt>cast_or_null&lt;&gt;</tt>: </dt>
403
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]404 <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]405 <tt>cast&lt;&gt;</tt> operator, except that it allows for a null pointer as an
406 argument (which it then propagates). This can sometimes be useful, allowing
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]407 you to combine several null checks into one.</p></dd>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]408
Misha Brukman2c122ce2005-11-01 21:12:49 +0000[diff] [blame]409 <dt><tt>dyn_cast_or_null&lt;&gt;</tt>: </dt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]410
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]411 <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]412 <tt>dyn_cast&lt;&gt;</tt> operator, except that it allows for a null pointer
413 as an argument (which it then propagates). This can sometimes be useful,
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]414 allowing you to combine several null checks into one.</p></dd>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]415
Misha Brukman2c122ce2005-11-01 21:12:49 +0000[diff] [blame]416</dl>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]417
418<p>These five templates can be used with any classes, whether they have a
419v-table or not. To add support for these templates, you simply need to add
420<tt>classof</tt> static methods to the class you are interested casting
421to. Describing this is currently outside the scope of this document, but there
422are lots of examples in the LLVM source base.</p>
423
424</div>
425
426<!-- ======================================================================= -->
427<div class="doc_subsection">
Misha Brukman2c122ce2005-11-01 21:12:49 +0000[diff] [blame]428 <a name="DEBUG">The <tt>DEBUG()</tt> macro and <tt>-debug</tt> option</a>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]429</div>
430
431<div class="doc_text">
432
433<p>Often when working on your pass you will put a bunch of debugging printouts
434and other code into your pass. After you get it working, you want to remove
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]435it, 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]436across).</p>
437
438<p> Naturally, because of this, you don't want to delete the debug printouts,
439but you don't want them to always be noisy. A standard compromise is to comment
440them out, allowing you to enable them if you need them in the future.</p>
441
Chris Lattner695b78b2005-04-26 22:56:16 +0000[diff] [blame]442<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]443file provides a macro named <tt>DEBUG()</tt> that is a much nicer solution to
444this problem. Basically, you can put arbitrary code into the argument of the
445<tt>DEBUG</tt> macro, and it is only executed if '<tt>opt</tt>' (or any other
446tool) is run with the '<tt>-debug</tt>' command line argument:</p>
447
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]448<div class="doc_code">
449<pre>
Bill Wendling832171c2006-12-07 20:04:42 +0000[diff] [blame]450DOUT &lt;&lt; "I am here!\n";
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]451</pre>
452</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]453
454<p>Then you can run your pass like this:</p>
455
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]456<div class="doc_code">
457<pre>
458$ opt &lt; a.bc &gt; /dev/null -mypass
Bill Wendling82e2eea2006-10-11 18:00:22 +0000[diff] [blame]459<i>&lt;no output&gt;</i>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]460$ opt &lt; a.bc &gt; /dev/null -mypass -debug
461I am here!
462</pre>
463</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]464
465<p>Using the <tt>DEBUG()</tt> macro instead of a home-brewed solution allows you
466to not have to create "yet another" command line option for the debug output for
467your pass. Note that <tt>DEBUG()</tt> macros are disabled for optimized builds,
468so they do not cause a performance impact at all (for the same reason, they
469should also not contain side-effects!).</p>
470
471<p>One additional nice thing about the <tt>DEBUG()</tt> macro is that you can
472enable or disable it directly in gdb. Just use "<tt>set DebugFlag=0</tt>" or
473"<tt>set DebugFlag=1</tt>" from the gdb if the program is running. If the
474program hasn't been started yet, you can always just run it with
475<tt>-debug</tt>.</p>
476
477</div>
478
479<!-- _______________________________________________________________________ -->
480<div class="doc_subsubsection">
Chris Lattnerc9151082005-04-26 22:57:07 +0000[diff] [blame]481 <a name="DEBUG_TYPE">Fine grained debug info with <tt>DEBUG_TYPE</tt> and
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]482 the <tt>-debug-only</tt> option</a>
483</div>
484
485<div class="doc_text">
486
487<p>Sometimes you may find yourself in a situation where enabling <tt>-debug</tt>
488just turns on <b>too much</b> information (such as when working on the code
489generator). If you want to enable debug information with more fine-grained
490control, you define the <tt>DEBUG_TYPE</tt> macro and the <tt>-debug</tt> only
491option as follows:</p>
492
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]493<div class="doc_code">
494<pre>
Bill Wendling832171c2006-12-07 20:04:42 +0000[diff] [blame]495DOUT &lt;&lt; "No debug type\n";
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]496#undef DEBUG_TYPE
497#define DEBUG_TYPE "foo"
Bill Wendling832171c2006-12-07 20:04:42 +0000[diff] [blame]498DOUT &lt;&lt; "'foo' debug type\n";
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]499#undef DEBUG_TYPE
500#define DEBUG_TYPE "bar"
Bill Wendling832171c2006-12-07 20:04:42 +0000[diff] [blame]501DOUT &lt;&lt; "'bar' debug type\n";
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]502#undef DEBUG_TYPE
503#define DEBUG_TYPE ""
Bill Wendling832171c2006-12-07 20:04:42 +0000[diff] [blame]504DOUT &lt;&lt; "No debug type (2)\n";
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]505</pre>
506</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]507
508<p>Then you can run your pass like this:</p>
509
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]510<div class="doc_code">
511<pre>
512$ opt &lt; a.bc &gt; /dev/null -mypass
Bill Wendling82e2eea2006-10-11 18:00:22 +0000[diff] [blame]513<i>&lt;no output&gt;</i>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]514$ opt &lt; a.bc &gt; /dev/null -mypass -debug
515No debug type
516'foo' debug type
517'bar' debug type
518No debug type (2)
519$ opt &lt; a.bc &gt; /dev/null -mypass -debug-only=foo
520'foo' debug type
521$ opt &lt; a.bc &gt; /dev/null -mypass -debug-only=bar
522'bar' debug type
523</pre>
524</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]525
526<p>Of course, in practice, you should only set <tt>DEBUG_TYPE</tt> at the top of
527a 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]528you <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]529<tt>#undef</tt>'s). Also, you should use names more meaningful than "foo" and
530"bar", because there is no system in place to ensure that names do not
531conflict. If two different modules use the same string, they will all be turned
532on when the name is specified. This allows, for example, all debug information
533for instruction scheduling to be enabled with <tt>-debug-type=InstrSched</tt>,
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]534even if the source lives in multiple files.</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]535
536</div>
537
538<!-- ======================================================================= -->
539<div class="doc_subsection">
Chris Lattner0be6fdf2006-12-19 21:46:21 +0000[diff] [blame]540 <a name="Statistic">The <tt>Statistic</tt> class &amp; <tt>-stats</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]541 option</a>
542</div>
543
544<div class="doc_text">
545
546<p>The "<tt><a
Chris Lattner695b78b2005-04-26 22:56:16 +0000[diff] [blame]547href="/doxygen/Statistic_8h-source.html">llvm/ADT/Statistic.h</a></tt>" file
Chris Lattner0be6fdf2006-12-19 21:46:21 +0000[diff] [blame]548provides a class named <tt>Statistic</tt> that is used as a unified way to
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]549keep track of what the LLVM compiler is doing and how effective various
550optimizations are. It is useful to see what optimizations are contributing to
551making a particular program run faster.</p>
552
553<p>Often you may run your pass on some big program, and you're interested to see
554how many times it makes a certain transformation. Although you can do this with
555hand 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]556for big programs. Using the <tt>Statistic</tt> class makes it very easy to
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]557keep track of this information, and the calculated information is presented in a
558uniform manner with the rest of the passes being executed.</p>
559
560<p>There are many examples of <tt>Statistic</tt> uses, but the basics of using
561it are as follows:</p>
562
563<ol>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]564 <li><p>Define your statistic like this:</p>
565
566<div class="doc_code">
567<pre>
Chris Lattner0be6fdf2006-12-19 21:46:21 +0000[diff] [blame]568#define <a href="#DEBUG_TYPE">DEBUG_TYPE</a> "mypassname" <i>// This goes before any #includes.</i>
569STATISTIC(NumXForms, "The # of times I did stuff");
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]570</pre>
571</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]572
Chris Lattner0be6fdf2006-12-19 21:46:21 +0000[diff] [blame]573 <p>The <tt>STATISTIC</tt> macro defines a static variable, whose name is
574 specified by the first argument. The pass name is taken from the DEBUG_TYPE
575 macro, and the description is taken from the second argument. The variable
Reid Spencer06565dc2007-01-12 17:11:23 +0000[diff] [blame]576 defined ("NumXForms" in this case) acts like an unsigned integer.</p></li>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]577
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]578 <li><p>Whenever you make a transformation, bump the counter:</p>
579
580<div class="doc_code">
581<pre>
Bill Wendling82e2eea2006-10-11 18:00:22 +0000[diff] [blame]582++NumXForms; // <i>I did stuff!</i>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]583</pre>
584</div>
585
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]586 </li>
587 </ol>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]588
589 <p>That's all you have to do. To get '<tt>opt</tt>' to print out the
590 statistics gathered, use the '<tt>-stats</tt>' option:</p>
591
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]592<div class="doc_code">
593<pre>
594$ opt -stats -mypassname &lt; program.bc &gt; /dev/null
Bill Wendling82e2eea2006-10-11 18:00:22 +0000[diff] [blame]595<i>... statistics output ...</i>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]596</pre>
597</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]598
Reid Spencer6b6c73e2007-02-09 16:00:28 +0000[diff] [blame]599 <p> When running <tt>opt</tt> on a C file from the SPEC benchmark
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]600suite, it gives a report that looks like this:</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]601
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]602<div class="doc_code">
603<pre>
Gabor Greif04367bf2007-07-06 22:07:22 +0000[diff] [blame]604 7646 bitcodewriter - Number of normal instructions
605 725 bitcodewriter - Number of oversized instructions
606 129996 bitcodewriter - Number of bitcode bytes written
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]607 2817 raise - Number of insts DCEd or constprop'd
608 3213 raise - Number of cast-of-self removed
609 5046 raise - Number of expression trees converted
610 75 raise - Number of other getelementptr's formed
611 138 raise - Number of load/store peepholes
612 42 deadtypeelim - Number of unused typenames removed from symtab
613 392 funcresolve - Number of varargs functions resolved
614 27 globaldce - Number of global variables removed
615 2 adce - Number of basic blocks removed
616 134 cee - Number of branches revectored
617 49 cee - Number of setcc instruction eliminated
618 532 gcse - Number of loads removed
619 2919 gcse - Number of instructions removed
620 86 indvars - Number of canonical indvars added
621 87 indvars - Number of aux indvars removed
622 25 instcombine - Number of dead inst eliminate
623 434 instcombine - Number of insts combined
624 248 licm - Number of load insts hoisted
625 1298 licm - Number of insts hoisted to a loop pre-header
626 3 licm - Number of insts hoisted to multiple loop preds (bad, no loop pre-header)
627 75 mem2reg - Number of alloca's promoted
628 1444 cfgsimplify - Number of blocks simplified
629</pre>
630</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]631
632<p>Obviously, with so many optimizations, having a unified framework for this
633stuff is very nice. Making your pass fit well into the framework makes it more
634maintainable and useful.</p>
635
636</div>
637
Chris Lattnerf623a082005-10-17 01:36:23 +0000[diff] [blame]638<!-- ======================================================================= -->
639<div class="doc_subsection">
640 <a name="ViewGraph">Viewing graphs while debugging code</a>
641</div>
642
643<div class="doc_text">
644
645<p>Several of the important data structures in LLVM are graphs: for example
646CFGs made out of LLVM <a href="#BasicBlock">BasicBlock</a>s, CFGs made out of
647LLVM <a href="CodeGenerator.html#machinebasicblock">MachineBasicBlock</a>s, and
648<a href="CodeGenerator.html#selectiondag_intro">Instruction Selection
649DAGs</a>. In many cases, while debugging various parts of the compiler, it is
650nice to instantly visualize these graphs.</p>
651
652<p>LLVM provides several callbacks that are available in a debug build to do
653exactly that. If you call the <tt>Function::viewCFG()</tt> method, for example,
654the current LLVM tool will pop up a window containing the CFG for the function
655where each basic block is a node in the graph, and each node contains the
656instructions in the block. Similarly, there also exists
657<tt>Function::viewCFGOnly()</tt> (does not include the instructions), the
658<tt>MachineFunction::viewCFG()</tt> and <tt>MachineFunction::viewCFGOnly()</tt>,
659and the <tt>SelectionDAG::viewGraph()</tt> methods. Within GDB, for example,
Jim Laskey543a0ee2006-10-02 12:28:07 +0000[diff] [blame]660you can usually use something like <tt>call DAG.viewGraph()</tt> to pop
Chris Lattnerf623a082005-10-17 01:36:23 +0000[diff] [blame]661up a window. Alternatively, you can sprinkle calls to these functions in your
662code in places you want to debug.</p>
663
664<p>Getting this to work requires a small amount of configuration. On Unix
665systems with X11, install the <a href="http://www.graphviz.org">graphviz</a>
666toolkit, and make sure 'dot' and 'gv' are in your path. If you are running on
667Mac OS/X, download and install the Mac OS/X <a
668href="http://www.pixelglow.com/graphviz/">Graphviz program</a>, and add
Reid Spencer128a7a72007-02-03 21:06:43 +0000[diff] [blame]669<tt>/Applications/Graphviz.app/Contents/MacOS/</tt> (or wherever you install
Chris Lattnerf623a082005-10-17 01:36:23 +0000[diff] [blame]670it) to your path. Once in your system and path are set up, rerun the LLVM
671configure script and rebuild LLVM to enable this functionality.</p>
672
Jim Laskey543a0ee2006-10-02 12:28:07 +0000[diff] [blame]673<p><tt>SelectionDAG</tt> has been extended to make it easier to locate
674<i>interesting</i> nodes in large complex graphs. From gdb, if you
675<tt>call DAG.setGraphColor(<i>node</i>, "<i>color</i>")</tt>, then the
Reid Spencer128a7a72007-02-03 21:06:43 +0000[diff] [blame]676next <tt>call DAG.viewGraph()</tt> would highlight the node in the
Jim Laskey543a0ee2006-10-02 12:28:07 +0000[diff] [blame]677specified color (choices of colors can be found at <a
Chris Lattner302da1e2007-02-03 03:05:57 +0000[diff] [blame]678href="http://www.graphviz.org/doc/info/colors.html">colors</a>.) More
Jim Laskey543a0ee2006-10-02 12:28:07 +0000[diff] [blame]679complex node attributes can be provided with <tt>call
680DAG.setGraphAttrs(<i>node</i>, "<i>attributes</i>")</tt> (choices can be
681found at <a href="http://www.graphviz.org/doc/info/attrs.html">Graph
682Attributes</a>.) If you want to restart and clear all the current graph
683attributes, then you can <tt>call DAG.clearGraphAttrs()</tt>. </p>
684
Chris Lattnerf623a082005-10-17 01:36:23 +0000[diff] [blame]685</div>
686
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]687<!-- *********************************************************************** -->
688<div class="doc_section">
689 <a name="datastructure">Picking the Right Data Structure for a Task</a>
690</div>
691<!-- *********************************************************************** -->
692
693<div class="doc_text">
694
Reid Spencer128a7a72007-02-03 21:06:43 +0000[diff] [blame]695<p>LLVM has a plethora of data structures in the <tt>llvm/ADT/</tt> directory,
696 and we commonly use STL data structures. This section describes the trade-offs
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]697 you should consider when you pick one.</p>
698
699<p>
700The first step is a choose your own adventure: do you want a sequential
701container, a set-like container, or a map-like container? The most important
702thing when choosing a container is the algorithmic properties of how you plan to
703access the container. Based on that, you should use:</p>
704
705<ul>
Reid Spencer128a7a72007-02-03 21:06:43 +0000[diff] [blame]706<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]707 of an value based on another value. Map-like containers also support
708 efficient queries for containment (whether a key is in the map). Map-like
709 containers generally do not support efficient reverse mapping (values to
710 keys). If you need that, use two maps. Some map-like containers also
711 support efficient iteration through the keys in sorted order. Map-like
712 containers are the most expensive sort, only use them if you need one of
713 these capabilities.</li>
714
715<li>a <a href="#ds_set">set-like</a> container if you need to put a bunch of
716 stuff into a container that automatically eliminates duplicates. Some
717 set-like containers support efficient iteration through the elements in
718 sorted order. Set-like containers are more expensive than sequential
719 containers.
720</li>
721
722<li>a <a href="#ds_sequential">sequential</a> container provides
723 the most efficient way to add elements and keeps track of the order they are
724 added to the collection. They permit duplicates and support efficient
Reid Spencer128a7a72007-02-03 21:06:43 +0000[diff] [blame]725 iteration, but do not support efficient look-up based on a key.
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]726</li>
727
Daniel Berlin1939ace2007-09-24 17:52:25 +0000[diff] [blame]728<li>a <a href="#ds_bit">bit</a> container provides an efficient way to store and
729 perform set operations on sets of numeric id's, while automatically
730 eliminating duplicates. Bit containers require a maximum of 1 bit for each
731 identifier you want to store.
732</li>
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]733</ul>
734
735<p>
Reid Spencer128a7a72007-02-03 21:06:43 +0000[diff] [blame]736Once the proper category of container is determined, you can fine tune the
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]737memory use, constant factors, and cache behaviors of access by intelligently
Reid Spencer128a7a72007-02-03 21:06:43 +0000[diff] [blame]738picking a member of the category. Note that constant factors and cache behavior
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]739can be a big deal. If you have a vector that usually only contains a few
740elements (but could contain many), for example, it's much better to use
741<a href="#dss_smallvector">SmallVector</a> than <a href="#dss_vector">vector</a>
742. Doing so avoids (relatively) expensive malloc/free calls, which dwarf the
743cost of adding the elements to the container. </p>
744
745</div>
746
747<!-- ======================================================================= -->
748<div class="doc_subsection">
749 <a name="ds_sequential">Sequential Containers (std::vector, std::list, etc)</a>
750</div>
751
752<div class="doc_text">
753There are a variety of sequential containers available for you, based on your
754needs. Pick the first in this section that will do what you want.
755</div>
756
757<!-- _______________________________________________________________________ -->
758<div class="doc_subsubsection">
759 <a name="dss_fixedarrays">Fixed Size Arrays</a>
760</div>
761
762<div class="doc_text">
763<p>Fixed size arrays are very simple and very fast. They are good if you know
764exactly how many elements you have, or you have a (low) upper bound on how many
765you have.</p>
766</div>
767
768<!-- _______________________________________________________________________ -->
769<div class="doc_subsubsection">
770 <a name="dss_heaparrays">Heap Allocated Arrays</a>
771</div>
772
773<div class="doc_text">
774<p>Heap allocated arrays (new[] + delete[]) are also simple. They are good if
775the number of elements is variable, if you know how many elements you will need
776before the array is allocated, and if the array is usually large (if not,
777consider a <a href="#dss_smallvector">SmallVector</a>). The cost of a heap
778allocated array is the cost of the new/delete (aka malloc/free). Also note that
779if you are allocating an array of a type with a constructor, the constructor and
Reid Spencer128a7a72007-02-03 21:06:43 +0000[diff] [blame]780destructors will be run for every element in the array (re-sizable vectors only
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]781construct those elements actually used).</p>
782</div>
783
784<!-- _______________________________________________________________________ -->
785<div class="doc_subsubsection">
786 <a name="dss_smallvector">"llvm/ADT/SmallVector.h"</a>
787</div>
788
789<div class="doc_text">
790<p><tt>SmallVector&lt;Type, N&gt;</tt> is a simple class that looks and smells
791just like <tt>vector&lt;Type&gt;</tt>:
792it supports efficient iteration, lays out elements in memory order (so you can
793do pointer arithmetic between elements), supports efficient push_back/pop_back
794operations, supports efficient random access to its elements, etc.</p>
795
796<p>The advantage of SmallVector is that it allocates space for
797some number of elements (N) <b>in the object itself</b>. Because of this, if
798the SmallVector is dynamically smaller than N, no malloc is performed. This can
799be a big win in cases where the malloc/free call is far more expensive than the
800code that fiddles around with the elements.</p>
801
802<p>This is good for vectors that are "usually small" (e.g. the number of
803predecessors/successors of a block is usually less than 8). On the other hand,
804this makes the size of the SmallVector itself large, so you don't want to
805allocate lots of them (doing so will waste a lot of space). As such,
806SmallVectors are most useful when on the stack.</p>
807
808<p>SmallVector also provides a nice portable and efficient replacement for
809<tt>alloca</tt>.</p>
810
811</div>
812
813<!-- _______________________________________________________________________ -->
814<div class="doc_subsubsection">
815 <a name="dss_vector">&lt;vector&gt;</a>
816</div>
817
818<div class="doc_text">
819<p>
820std::vector is well loved and respected. It is useful when SmallVector isn't:
821when the size of the vector is often large (thus the small optimization will
822rarely be a benefit) or if you will be allocating many instances of the vector
823itself (which would waste space for elements that aren't in the container).
824vector is also useful when interfacing with code that expects vectors :).
825</p>
Chris Lattner32d84762007-02-05 06:30:51 +0000[diff] [blame]826
827<p>One worthwhile note about std::vector: avoid code like this:</p>
828
829<div class="doc_code">
830<pre>
831for ( ... ) {
Chris Lattner9bb3dbb2007-03-28 18:27:57 +0000[diff] [blame]832 std::vector&lt;foo&gt; V;
Chris Lattner32d84762007-02-05 06:30:51 +0000[diff] [blame]833 use V;
834}
835</pre>
836</div>
837
838<p>Instead, write this as:</p>
839
840<div class="doc_code">
841<pre>
Chris Lattner9bb3dbb2007-03-28 18:27:57 +0000[diff] [blame]842std::vector&lt;foo&gt; V;
Chris Lattner32d84762007-02-05 06:30:51 +0000[diff] [blame]843for ( ... ) {
844 use V;
845 V.clear();
846}
847</pre>
848</div>
849
850<p>Doing so will save (at least) one heap allocation and free per iteration of
851the loop.</p>
852
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]853</div>
854
855<!-- _______________________________________________________________________ -->
856<div class="doc_subsubsection">
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]857 <a name="dss_deque">&lt;deque&gt;</a>
858</div>
859
860<div class="doc_text">
861<p>std::deque is, in some senses, a generalized version of std::vector. Like
862std::vector, it provides constant time random access and other similar
863properties, but it also provides efficient access to the front of the list. It
864does not guarantee continuity of elements within memory.</p>
865
866<p>In exchange for this extra flexibility, std::deque has significantly higher
867constant factor costs than std::vector. If possible, use std::vector or
868something cheaper.</p>
869</div>
870
871<!-- _______________________________________________________________________ -->
872<div class="doc_subsubsection">
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]873 <a name="dss_list">&lt;list&gt;</a>
874</div>
875
876<div class="doc_text">
877<p>std::list is an extremely inefficient class that is rarely useful.
878It performs a heap allocation for every element inserted into it, thus having an
879extremely high constant factor, particularly for small data types. std::list
880also only supports bidirectional iteration, not random access iteration.</p>
881
882<p>In exchange for this high cost, std::list supports efficient access to both
883ends of the list (like std::deque, but unlike std::vector or SmallVector). In
884addition, the iterator invalidation characteristics of std::list are stronger
885than that of a vector class: inserting or removing an element into the list does
886not invalidate iterator or pointers to other elements in the list.</p>
887</div>
888
889<!-- _______________________________________________________________________ -->
890<div class="doc_subsubsection">
Gabor Greif3899e492009-02-27 11:37:41 +0000[diff] [blame]891 <a name="dss_ilist">llvm/ADT/ilist.h</a>
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]892</div>
893
894<div class="doc_text">
895<p><tt>ilist&lt;T&gt;</tt> implements an 'intrusive' doubly-linked list. It is
896intrusive, because it requires the element to store and provide access to the
897prev/next pointers for the list.</p>
898
Gabor Greif2946d1c2009-02-27 12:02:19 +0000[diff] [blame]899<p><tt>ilist</tt> has the same drawbacks as <tt>std::list</tt>, and additionally
900requires an <tt>ilist_traits</tt> implementation for the element type, but it
901provides some novel characteristics. In particular, it can efficiently store
902polymorphic objects, the traits class is informed when an element is inserted or
Gabor Greif0cbcabe2009-03-12 09:47:03 +0000[diff] [blame]903removed from the list, and <tt>ilist</tt>s are guaranteed to support a
904constant-time splice operation.</p>
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]905
Gabor Greif0cbcabe2009-03-12 09:47:03 +0000[diff] [blame]906<p>These properties are exactly what we want for things like
907<tt>Instruction</tt>s and basic blocks, which is why these are implemented with
908<tt>ilist</tt>s.</p>
Gabor Greif3899e492009-02-27 11:37:41 +0000[diff] [blame]909
910Related classes of interest are explained in the following subsections:
911 <ul>
Gabor Greif01862502009-02-27 13:28:07 +0000[diff] [blame]912 <li><a href="#dss_ilist_traits">ilist_traits</a></li>
Gabor Greif2946d1c2009-02-27 12:02:19 +0000[diff] [blame]913 <li><a href="#dss_iplist">iplist</a></li>
Gabor Greif3899e492009-02-27 11:37:41 +0000[diff] [blame]914 <li><a href="#dss_ilist_node">llvm/ADT/ilist_node.h</a></li>
Gabor Greif6a65f422009-03-12 10:30:31 +0000[diff] [blame]915 <li><a href="#dss_ilist_sentinel">Sentinels</a></li>
Gabor Greif3899e492009-02-27 11:37:41 +0000[diff] [blame]916 </ul>
917</div>
918
919<!-- _______________________________________________________________________ -->
920<div class="doc_subsubsection">
Gabor Greif01862502009-02-27 13:28:07 +0000[diff] [blame]921 <a name="dss_ilist_traits">ilist_traits</a>
922</div>
923
924<div class="doc_text">
925<p><tt>ilist_traits&lt;T&gt;</tt> is <tt>ilist&lt;T&gt;</tt>'s customization
926mechanism. <tt>iplist&lt;T&gt;</tt> (and consequently <tt>ilist&lt;T&gt;</tt>)
927publicly derive from this traits class.</p>
928</div>
929
930<!-- _______________________________________________________________________ -->
931<div class="doc_subsubsection">
Gabor Greif2946d1c2009-02-27 12:02:19 +0000[diff] [blame]932 <a name="dss_iplist">iplist</a>
933</div>
934
935<div class="doc_text">
936<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]937supports a slightly narrower interface. Notably, inserters from
938<tt>T&amp;</tt> are absent.</p>
Gabor Greif01862502009-02-27 13:28:07 +0000[diff] [blame]939
940<p><tt>ilist_traits&lt;T&gt;</tt> is a public base of this class and can be
941used for a wide variety of customizations.</p>
Gabor Greif2946d1c2009-02-27 12:02:19 +0000[diff] [blame]942</div>
943
944<!-- _______________________________________________________________________ -->
945<div class="doc_subsubsection">
Gabor Greif3899e492009-02-27 11:37:41 +0000[diff] [blame]946 <a name="dss_ilist_node">llvm/ADT/ilist_node.h</a>
947</div>
948
949<div class="doc_text">
950<p><tt>ilist_node&lt;T&gt;</tt> implements a the forward and backward links
951that are expected by the <tt>ilist&lt;T&gt;</tt> (and analogous containers)
952in the default manner.</p>
953
954<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]955<tt>T</tt>, usually <tt>T</tt> publicly derives from
956<tt>ilist_node&lt;T&gt;</tt>.</p>
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]957</div>
958
959<!-- _______________________________________________________________________ -->
960<div class="doc_subsubsection">
Gabor Greif6a65f422009-03-12 10:30:31 +0000[diff] [blame]961 <a name="dss_ilist_sentinel">Sentinels</a>
962</div>
963
964<div class="doc_text">
965<p><tt>ilist</tt>s have another speciality that must be considered. To be a good
966citizen in the C++ ecosystem, it needs to support the standard container
967operations, such as <tt>begin</tt> and <tt>end</tt> iterators, etc. Also, the
968<tt>operator--</tt> must work correctly on the <tt>end</tt> iterator in the
969case of non-empty <tt>ilist</tt>s.</p>
970
971<p>The only sensible solution to this problem is to allocate a so-called
972<i>sentinel</i> along with the intrusive list, which serves as the <tt>end</tt>
973iterator, providing the back-link to the last element. However conforming to the
974C++ convention it is illegal to <tt>operator++</tt> beyond the sentinel and it
975also must not be dereferenced.</p>
976
977<p>These constraints allow for some implementation freedom to the <tt>ilist</tt>
978how to allocate and store the sentinel. The corresponding policy is dictated
979by <tt>ilist_traits&lt;T&gt;</tt>. By default a <tt>T</tt> gets heap-allocated
980whenever the need for a sentinel arises.</p>
981
982<p>While the default policy is sufficient in most cases, it may break down when
983<tt>T</tt> does not provide a default constructor. Also, in the case of many
984instances of <tt>ilist</tt>s, the memory overhead of the associated sentinels
985is wasted. To alleviate the situation with numerous and voluminous
986<tt>T</tt>-sentinels, sometimes a trick is employed, leading to <i>ghostly
987sentinels</i>.</p>
988
989<p>Ghostly sentinels are obtained by specially-crafted <tt>ilist_traits&lt;T&gt;</tt>
990which superpose the sentinel with the <tt>ilist</tt> instance in memory. Pointer
991arithmetic is used to obtain the sentinel, which is relative to the
992<tt>ilist</tt>'s <tt>this</tt> pointer. The <tt>ilist</tt> is augmented by an
993extra pointer, which serves as the back-link of the sentinel. This is the only
994field in the ghostly sentinel which can be legally accessed.</p>
995</div>
996
997<!-- _______________________________________________________________________ -->
998<div class="doc_subsubsection">
Chris Lattnerc5722432007-02-03 19:49:31 +0000[diff] [blame]999 <a name="dss_other">Other Sequential Container options</a>
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]1000</div>
1001
1002<div class="doc_text">
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1003<p>Other STL containers are available, such as std::string.</p>
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]1004
1005<p>There are also various STL adapter classes such as std::queue,
1006std::priority_queue, std::stack, etc. These provide simplified access to an
1007underlying container but don't affect the cost of the container itself.</p>
1008
1009</div>
1010
1011
1012<!-- ======================================================================= -->
1013<div class="doc_subsection">
1014 <a name="ds_set">Set-Like Containers (std::set, SmallSet, SetVector, etc)</a>
1015</div>
1016
1017<div class="doc_text">
1018
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1019<p>Set-like containers are useful when you need to canonicalize multiple values
1020into a single representation. There are several different choices for how to do
1021this, providing various trade-offs.</p>
1022
1023</div>
1024
1025
1026<!-- _______________________________________________________________________ -->
1027<div class="doc_subsubsection">
1028 <a name="dss_sortedvectorset">A sorted 'vector'</a>
1029</div>
1030
1031<div class="doc_text">
1032
Chris Lattner3b23a8c2007-02-03 08:10:45 +0000[diff] [blame]1033<p>If you intend to insert a lot of elements, then do a lot of queries, a
1034great approach is to use a vector (or other sequential container) with
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1035std::sort+std::unique to remove duplicates. This approach works really well if
Chris Lattner3b23a8c2007-02-03 08:10:45 +0000[diff] [blame]1036your usage pattern has these two distinct phases (insert then query), and can be
1037coupled with a good choice of <a href="#ds_sequential">sequential container</a>.
1038</p>
1039
1040<p>
1041This combination provides the several nice properties: the result data is
1042contiguous in memory (good for cache locality), has few allocations, is easy to
1043address (iterators in the final vector are just indices or pointers), and can be
1044efficiently queried with a standard binary or radix search.</p>
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1045
1046</div>
1047
1048<!-- _______________________________________________________________________ -->
1049<div class="doc_subsubsection">
1050 <a name="dss_smallset">"llvm/ADT/SmallSet.h"</a>
1051</div>
1052
1053<div class="doc_text">
1054
Reid Spencer128a7a72007-02-03 21:06:43 +0000[diff] [blame]1055<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]1056are 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]1057has space for N elements in place (thus, if the set is dynamically smaller than
Chris Lattner14868db2007-02-03 08:20:15 +0000[diff] [blame]1058N, no malloc traffic is required) and accesses them with a simple linear search.
1059When the set grows beyond 'N' elements, it allocates a more expensive representation that
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1060guarantees efficient access (for most types, it falls back to std::set, but for
Chris Lattner14868db2007-02-03 08:20:15 +0000[diff] [blame]1061pointers it uses something far better, <a
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1062href="#dss_smallptrset">SmallPtrSet</a>).</p>
1063
1064<p>The magic of this class is that it handles small sets extremely efficiently,
1065but gracefully handles extremely large sets without loss of efficiency. The
1066drawback is that the interface is quite small: it supports insertion, queries
1067and erasing, but does not support iteration.</p>
1068
1069</div>
1070
1071<!-- _______________________________________________________________________ -->
1072<div class="doc_subsubsection">
1073 <a name="dss_smallptrset">"llvm/ADT/SmallPtrSet.h"</a>
1074</div>
1075
1076<div class="doc_text">
1077
1078<p>SmallPtrSet has all the advantages of SmallSet (and a SmallSet of pointers is
Reid Spencer128a7a72007-02-03 21:06:43 +0000[diff] [blame]1079transparently implemented with a SmallPtrSet), but also supports iterators. If
Chris Lattner14868db2007-02-03 08:20:15 +0000[diff] [blame]1080more than 'N' insertions are performed, a single quadratically
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1081probed hash table is allocated and grows as needed, providing extremely
1082efficient access (constant time insertion/deleting/queries with low constant
1083factors) and is very stingy with malloc traffic.</p>
1084
1085<p>Note that, unlike std::set, the iterators of SmallPtrSet are invalidated
1086whenever an insertion occurs. Also, the values visited by the iterators are not
1087visited in sorted order.</p>
1088
1089</div>
1090
1091<!-- _______________________________________________________________________ -->
1092<div class="doc_subsubsection">
Chris Lattnerc28476f2007-09-30 00:58:59 +0000[diff] [blame]1093 <a name="dss_denseset">"llvm/ADT/DenseSet.h"</a>
1094</div>
1095
1096<div class="doc_text">
1097
1098<p>
1099DenseSet is a simple quadratically probed hash table. It excels at supporting
1100small values: it uses a single allocation to hold all of the pairs that
1101are currently inserted in the set. DenseSet is a great way to unique small
1102values that are not simple pointers (use <a
1103href="#dss_smallptrset">SmallPtrSet</a> for pointers). Note that DenseSet has
1104the same requirements for the value type that <a
1105href="#dss_densemap">DenseMap</a> has.
1106</p>
1107
1108</div>
1109
1110<!-- _______________________________________________________________________ -->
1111<div class="doc_subsubsection">
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1112 <a name="dss_FoldingSet">"llvm/ADT/FoldingSet.h"</a>
1113</div>
1114
1115<div class="doc_text">
1116
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]1117<p>
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1118FoldingSet is an aggregate class that is really good at uniquing
1119expensive-to-create or polymorphic objects. It is a combination of a chained
1120hash table with intrusive links (uniqued objects are required to inherit from
Chris Lattner14868db2007-02-03 08:20:15 +0000[diff] [blame]1121FoldingSetNode) that uses <a href="#dss_smallvector">SmallVector</a> as part of
1122its ID process.</p>
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1123
Chris Lattner14868db2007-02-03 08:20:15 +0000[diff] [blame]1124<p>Consider a case where you want to implement a "getOrCreateFoo" method for
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1125a complex object (for example, a node in the code generator). The client has a
1126description of *what* it wants to generate (it knows the opcode and all the
1127operands), 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]1128only to find out it already exists, at which point we would have to delete it
1129and return the node that already exists.
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]1130</p>
1131
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1132<p>To support this style of client, FoldingSet perform a query with a
1133FoldingSetNodeID (which wraps SmallVector) that can be used to describe the
1134element that we want to query for. The query either returns the element
1135matching the ID or it returns an opaque ID that indicates where insertion should
Chris Lattner14868db2007-02-03 08:20:15 +0000[diff] [blame]1136take place. Construction of the ID usually does not require heap traffic.</p>
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1137
1138<p>Because FoldingSet uses intrusive links, it can support polymorphic objects
1139in the set (for example, you can have SDNode instances mixed with LoadSDNodes).
1140Because the elements are individually allocated, pointers to the elements are
1141stable: inserting or removing elements does not invalidate any pointers to other
1142elements.
1143</p>
1144
1145</div>
1146
1147<!-- _______________________________________________________________________ -->
1148<div class="doc_subsubsection">
1149 <a name="dss_set">&lt;set&gt;</a>
1150</div>
1151
1152<div class="doc_text">
1153
Chris Lattnerc5722432007-02-03 19:49:31 +0000[diff] [blame]1154<p><tt>std::set</tt> is a reasonable all-around set class, which is decent at
1155many things but great at nothing. std::set allocates memory for each element
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1156inserted (thus it is very malloc intensive) and typically stores three pointers
Chris Lattner14868db2007-02-03 08:20:15 +0000[diff] [blame]1157per element in the set (thus adding a large amount of per-element space
1158overhead). It offers guaranteed log(n) performance, which is not particularly
Chris Lattnerc5722432007-02-03 19:49:31 +0000[diff] [blame]1159fast from a complexity standpoint (particularly if the elements of the set are
1160expensive to compare, like strings), and has extremely high constant factors for
1161lookup, insertion and removal.</p>
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1162
Chris Lattner14868db2007-02-03 08:20:15 +0000[diff] [blame]1163<p>The advantages of std::set are that its iterators are stable (deleting or
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1164inserting an element from the set does not affect iterators or pointers to other
1165elements) and that iteration over the set is guaranteed to be in sorted order.
1166If the elements in the set are large, then the relative overhead of the pointers
1167and malloc traffic is not a big deal, but if the elements of the set are small,
1168std::set is almost never a good choice.</p>
1169
1170</div>
1171
1172<!-- _______________________________________________________________________ -->
1173<div class="doc_subsubsection">
1174 <a name="dss_setvector">"llvm/ADT/SetVector.h"</a>
1175</div>
1176
1177<div class="doc_text">
Chris Lattneredca3c52007-02-04 00:00:26 +0000[diff] [blame]1178<p>LLVM's SetVector&lt;Type&gt; is an adapter class that combines your choice of
1179a set-like container along with a <a href="#ds_sequential">Sequential
1180Container</a>. The important property
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1181that this provides is efficient insertion with uniquing (duplicate elements are
1182ignored) with iteration support. It implements this by inserting elements into
1183both a set-like container and the sequential container, using the set-like
1184container for uniquing and the sequential container for iteration.
1185</p>
1186
1187<p>The difference between SetVector and other sets is that the order of
1188iteration is guaranteed to match the order of insertion into the SetVector.
1189This property is really important for things like sets of pointers. Because
1190pointer values are non-deterministic (e.g. vary across runs of the program on
Chris Lattneredca3c52007-02-04 00:00:26 +0000[diff] [blame]1191different machines), iterating over the pointers in the set will
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1192not be in a well-defined order.</p>
1193
1194<p>
1195The drawback of SetVector is that it requires twice as much space as a normal
1196set and has the sum of constant factors from the set-like container and the
1197sequential container that it uses. Use it *only* if you need to iterate over
1198the elements in a deterministic order. SetVector is also expensive to delete
Chris Lattneredca3c52007-02-04 00:00:26 +0000[diff] [blame]1199elements out of (linear time), unless you use it's "pop_back" method, which is
1200faster.
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1201</p>
1202
Chris Lattneredca3c52007-02-04 00:00:26 +0000[diff] [blame]1203<p>SetVector is an adapter class that defaults to using std::vector and std::set
1204for the underlying containers, so it is quite expensive. However,
1205<tt>"llvm/ADT/SetVector.h"</tt> also provides a SmallSetVector class, which
1206defaults to using a SmallVector and SmallSet of a specified size. If you use
1207this, and if your sets are dynamically smaller than N, you will save a lot of
1208heap traffic.</p>
1209
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1210</div>
1211
1212<!-- _______________________________________________________________________ -->
1213<div class="doc_subsubsection">
Chris Lattnerc5722432007-02-03 19:49:31 +0000[diff] [blame]1214 <a name="dss_uniquevector">"llvm/ADT/UniqueVector.h"</a>
1215</div>
1216
1217<div class="doc_text">
1218
1219<p>
1220UniqueVector is similar to <a href="#dss_setvector">SetVector</a>, but it
1221retains a unique ID for each element inserted into the set. It internally
1222contains a map and a vector, and it assigns a unique ID for each value inserted
1223into the set.</p>
1224
1225<p>UniqueVector is very expensive: its cost is the sum of the cost of
1226maintaining both the map and vector, it has high complexity, high constant
1227factors, and produces a lot of malloc traffic. It should be avoided.</p>
1228
1229</div>
1230
1231
1232<!-- _______________________________________________________________________ -->
1233<div class="doc_subsubsection">
1234 <a name="dss_otherset">Other Set-Like Container Options</a>
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1235</div>
1236
1237<div class="doc_text">
1238
1239<p>
1240The STL provides several other options, such as std::multiset and the various
Chris Lattnerf1a30822009-03-09 05:20:45 +0000[diff] [blame]1241"hash_set" like containers (whether from C++ TR1 or from the SGI library). We
1242never use hash_set and unordered_set because they are generally very expensive
1243(each insertion requires a malloc) and very non-portable.
1244</p>
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1245
1246<p>std::multiset is useful if you're not interested in elimination of
Chris Lattner14868db2007-02-03 08:20:15 +0000[diff] [blame]1247duplicates, but has all the drawbacks of std::set. A sorted vector (where you
1248don't delete duplicate entries) or some other approach is almost always
1249better.</p>
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1250
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]1251</div>
1252
1253<!-- ======================================================================= -->
1254<div class="doc_subsection">
1255 <a name="ds_map">Map-Like Containers (std::map, DenseMap, etc)</a>
1256</div>
1257
1258<div class="doc_text">
Chris Lattnerc5722432007-02-03 19:49:31 +0000[diff] [blame]1259Map-like containers are useful when you want to associate data to a key. As
1260usual, there are a lot of different ways to do this. :)
1261</div>
1262
1263<!-- _______________________________________________________________________ -->
1264<div class="doc_subsubsection">
1265 <a name="dss_sortedvectormap">A sorted 'vector'</a>
1266</div>
1267
1268<div class="doc_text">
1269
1270<p>
1271If your usage pattern follows a strict insert-then-query approach, you can
1272trivially use the same approach as <a href="#dss_sortedvectorset">sorted vectors
1273for set-like containers</a>. The only difference is that your query function
1274(which uses std::lower_bound to get efficient log(n) lookup) should only compare
1275the key, not both the key and value. This yields the same advantages as sorted
1276vectors for sets.
1277</p>
1278</div>
1279
1280<!-- _______________________________________________________________________ -->
1281<div class="doc_subsubsection">
Chris Lattner796f9fa2007-02-08 19:14:21 +0000[diff] [blame]1282 <a name="dss_stringmap">"llvm/ADT/StringMap.h"</a>
Chris Lattnerc5722432007-02-03 19:49:31 +0000[diff] [blame]1283</div>
1284
1285<div class="doc_text">
1286
1287<p>
1288Strings are commonly used as keys in maps, and they are difficult to support
1289efficiently: they are variable length, inefficient to hash and compare when
Chris Lattner796f9fa2007-02-08 19:14:21 +0000[diff] [blame]1290long, expensive to copy, etc. StringMap is a specialized container designed to
1291cope with these issues. It supports mapping an arbitrary range of bytes to an
1292arbitrary other object.</p>
Chris Lattnerc5722432007-02-03 19:49:31 +0000[diff] [blame]1293
Chris Lattner796f9fa2007-02-08 19:14:21 +0000[diff] [blame]1294<p>The StringMap implementation uses a quadratically-probed hash table, where
Chris Lattnerc5722432007-02-03 19:49:31 +0000[diff] [blame]1295the buckets store a pointer to the heap allocated entries (and some other
1296stuff). The entries in the map must be heap allocated because the strings are
1297variable length. The string data (key) and the element object (value) are
1298stored in the same allocation with the string data immediately after the element
1299object. This container guarantees the "<tt>(char*)(&amp;Value+1)</tt>" points
1300to the key string for a value.</p>
1301
Chris Lattner796f9fa2007-02-08 19:14:21 +0000[diff] [blame]1302<p>The StringMap is very fast for several reasons: quadratic probing is very
Chris Lattnerc5722432007-02-03 19:49:31 +0000[diff] [blame]1303cache efficient for lookups, the hash value of strings in buckets is not
Chris Lattner796f9fa2007-02-08 19:14:21 +0000[diff] [blame]1304recomputed when lookup up an element, StringMap rarely has to touch the
Chris Lattnerc5722432007-02-03 19:49:31 +0000[diff] [blame]1305memory for unrelated objects when looking up a value (even when hash collisions
1306happen), hash table growth does not recompute the hash values for strings
1307already in the table, and each pair in the map is store in a single allocation
1308(the string data is stored in the same allocation as the Value of a pair).</p>
1309
Chris Lattner796f9fa2007-02-08 19:14:21 +0000[diff] [blame]1310<p>StringMap also provides query methods that take byte ranges, so it only ever
Chris Lattnerc5722432007-02-03 19:49:31 +0000[diff] [blame]1311copies a string if a value is inserted into the table.</p>
1312</div>
1313
1314<!-- _______________________________________________________________________ -->
1315<div class="doc_subsubsection">
1316 <a name="dss_indexedmap">"llvm/ADT/IndexedMap.h"</a>
1317</div>
1318
1319<div class="doc_text">
1320<p>
1321IndexedMap is a specialized container for mapping small dense integers (or
1322values that can be mapped to small dense integers) to some other type. It is
1323internally implemented as a vector with a mapping function that maps the keys to
1324the dense integer range.
1325</p>
1326
1327<p>
1328This is useful for cases like virtual registers in the LLVM code generator: they
1329have a dense mapping that is offset by a compile-time constant (the first
1330virtual register ID).</p>
1331
1332</div>
1333
1334<!-- _______________________________________________________________________ -->
1335<div class="doc_subsubsection">
1336 <a name="dss_densemap">"llvm/ADT/DenseMap.h"</a>
1337</div>
1338
1339<div class="doc_text">
1340
1341<p>
1342DenseMap is a simple quadratically probed hash table. It excels at supporting
1343small keys and values: it uses a single allocation to hold all of the pairs that
1344are currently inserted in the map. DenseMap is a great way to map pointers to
1345pointers, or map other small types to each other.
1346</p>
1347
1348<p>
1349There are several aspects of DenseMap that you should be aware of, however. The
1350iterators in a densemap are invalidated whenever an insertion occurs, unlike
1351map. Also, because DenseMap allocates space for a large number of key/value
Chris Lattnera4a264d2007-02-03 20:17:53 +0000[diff] [blame]1352pairs (it starts with 64 by default), it will waste a lot of space if your keys
1353or values are large. Finally, you must implement a partial specialization of
Chris Lattner76c1b972007-09-17 18:34:04 +0000[diff] [blame]1354DenseMapInfo for the key that you want, if it isn't already supported. This
Chris Lattnerc5722432007-02-03 19:49:31 +0000[diff] [blame]1355is required to tell DenseMap about two special marker values (which can never be
Chris Lattnera4a264d2007-02-03 20:17:53 +0000[diff] [blame]1356inserted into the map) that it needs internally.</p>
Chris Lattnerc5722432007-02-03 19:49:31 +0000[diff] [blame]1357
1358</div>
1359
1360<!-- _______________________________________________________________________ -->
1361<div class="doc_subsubsection">
1362 <a name="dss_map">&lt;map&gt;</a>
1363</div>
1364
1365<div class="doc_text">
1366
1367<p>
1368std::map has similar characteristics to <a href="#dss_set">std::set</a>: it uses
1369a single allocation per pair inserted into the map, it offers log(n) lookup with
1370an extremely large constant factor, imposes a space penalty of 3 pointers per
1371pair in the map, etc.</p>
1372
1373<p>std::map is most useful when your keys or values are very large, if you need
1374to iterate over the collection in sorted order, or if you need stable iterators
1375into the map (i.e. they don't get invalidated if an insertion or deletion of
1376another element takes place).</p>
1377
1378</div>
1379
1380<!-- _______________________________________________________________________ -->
1381<div class="doc_subsubsection">
1382 <a name="dss_othermap">Other Map-Like Container Options</a>
1383</div>
1384
1385<div class="doc_text">
1386
1387<p>
1388The STL provides several other options, such as std::multimap and the various
Chris Lattnerf1a30822009-03-09 05:20:45 +0000[diff] [blame]1389"hash_map" like containers (whether from C++ TR1 or from the SGI library). We
1390never use hash_set and unordered_set because they are generally very expensive
1391(each insertion requires a malloc) and very non-portable.</p>
Chris Lattnerc5722432007-02-03 19:49:31 +0000[diff] [blame]1392
1393<p>std::multimap is useful if you want to map a key to multiple values, but has
1394all the drawbacks of std::map. A sorted vector or some other approach is almost
1395always better.</p>
1396
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]1397</div>
1398
Daniel Berlin1939ace2007-09-24 17:52:25 +0000[diff] [blame]1399<!-- ======================================================================= -->
1400<div class="doc_subsection">
1401 <a name="ds_bit">Bit storage containers (BitVector, SparseBitVector)</a>
1402</div>
1403
1404<div class="doc_text">
Chris Lattner7086ce72007-09-25 22:37:50 +0000[diff] [blame]1405<p>Unlike the other containers, there are only two bit storage containers, and
1406choosing when to use each is relatively straightforward.</p>
1407
1408<p>One additional option is
1409<tt>std::vector&lt;bool&gt;</tt>: we discourage its use for two reasons 1) the
1410implementation in many common compilers (e.g. commonly available versions of
1411GCC) is extremely inefficient and 2) the C++ standards committee is likely to
1412deprecate this container and/or change it significantly somehow. In any case,
1413please don't use it.</p>
Daniel Berlin1939ace2007-09-24 17:52:25 +0000[diff] [blame]1414</div>
1415
1416<!-- _______________________________________________________________________ -->
1417<div class="doc_subsubsection">
1418 <a name="dss_bitvector">BitVector</a>
1419</div>
1420
1421<div class="doc_text">
1422<p> The BitVector container provides a fixed size set of bits for manipulation.
1423It supports individual bit setting/testing, as well as set operations. The set
1424operations take time O(size of bitvector), but operations are performed one word
1425at a time, instead of one bit at a time. This makes the BitVector very fast for
1426set operations compared to other containers. Use the BitVector when you expect
1427the number of set bits to be high (IE a dense set).
1428</p>
1429</div>
1430
1431<!-- _______________________________________________________________________ -->
1432<div class="doc_subsubsection">
1433 <a name="dss_sparsebitvector">SparseBitVector</a>
1434</div>
1435
1436<div class="doc_text">
1437<p> The SparseBitVector container is much like BitVector, with one major
1438difference: Only the bits that are set, are stored. This makes the
1439SparseBitVector much more space efficient than BitVector when the set is sparse,
1440as well as making set operations O(number of set bits) instead of O(size of
1441universe). 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
1442(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).
1443</p>
1444</div>
Chris Lattnerf623a082005-10-17 01:36:23 +0000[diff] [blame]1445
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1446<!-- *********************************************************************** -->
1447<div class="doc_section">
1448 <a name="common">Helpful Hints for Common Operations</a>
1449</div>
1450<!-- *********************************************************************** -->
1451
1452<div class="doc_text">
1453
1454<p>This section describes how to perform some very simple transformations of
1455LLVM code. This is meant to give examples of common idioms used, showing the
1456practical side of LLVM transformations. <p> Because this is a "how-to" section,
1457you should also read about the main classes that you will be working with. The
1458<a href="#coreclasses">Core LLVM Class Hierarchy Reference</a> contains details
1459and descriptions of the main classes that you should know about.</p>
1460
1461</div>
1462
1463<!-- NOTE: this section should be heavy on example code -->
1464<!-- ======================================================================= -->
1465<div class="doc_subsection">
1466 <a name="inspection">Basic Inspection and Traversal Routines</a>
1467</div>
1468
1469<div class="doc_text">
1470
1471<p>The LLVM compiler infrastructure have many different data structures that may
1472be traversed. Following the example of the C++ standard template library, the
1473techniques used to traverse these various data structures are all basically the
1474same. For a enumerable sequence of values, the <tt>XXXbegin()</tt> function (or
1475method) returns an iterator to the start of the sequence, the <tt>XXXend()</tt>
1476function returns an iterator pointing to one past the last valid element of the
1477sequence, and there is some <tt>XXXiterator</tt> data type that is common
1478between the two operations.</p>
1479
1480<p>Because the pattern for iteration is common across many different aspects of
1481the program representation, the standard template library algorithms may be used
1482on them, and it is easier to remember how to iterate. First we show a few common
1483examples of the data structures that need to be traversed. Other data
1484structures are traversed in very similar ways.</p>
1485
1486</div>
1487
1488<!-- _______________________________________________________________________ -->
Chris Lattner69bf8a92004-05-23 21:06:58 +0000[diff] [blame]1489<div class="doc_subsubsection">
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1490 <a name="iterate_function">Iterating over the </a><a
1491 href="#BasicBlock"><tt>BasicBlock</tt></a>s in a <a
1492 href="#Function"><tt>Function</tt></a>
1493</div>
1494
1495<div class="doc_text">
1496
1497<p>It's quite common to have a <tt>Function</tt> instance that you'd like to
1498transform in some way; in particular, you'd like to manipulate its
1499<tt>BasicBlock</tt>s. To facilitate this, you'll need to iterate over all of
1500the <tt>BasicBlock</tt>s that constitute the <tt>Function</tt>. The following is
1501an example that prints the name of a <tt>BasicBlock</tt> and the number of
1502<tt>Instruction</tt>s it contains:</p>
1503
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1504<div class="doc_code">
1505<pre>
Bill Wendling82e2eea2006-10-11 18:00:22 +0000[diff] [blame]1506// <i>func is a pointer to a Function instance</i>
1507for (Function::iterator i = func-&gt;begin(), e = func-&gt;end(); i != e; ++i)
1508 // <i>Print out the name of the basic block if it has one, and then the</i>
1509 // <i>number of instructions that it contains</i>
Bill Wendling832171c2006-12-07 20:04:42 +0000[diff] [blame]1510 llvm::cerr &lt;&lt; "Basic block (name=" &lt;&lt; i-&gt;getName() &lt;&lt; ") has "
1511 &lt;&lt; i-&gt;size() &lt;&lt; " instructions.\n";
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1512</pre>
1513</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1514
1515<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]1516invoking member functions of the <tt>Instruction</tt> class. This is
1517because the indirection operator is overloaded for the iterator
Chris Lattner7496ec52003-08-05 22:54:23 +0000[diff] [blame]1518classes. In the above code, the expression <tt>i-&gt;size()</tt> is
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1519exactly equivalent to <tt>(*i).size()</tt> just like you'd expect.</p>
1520
1521</div>
1522
1523<!-- _______________________________________________________________________ -->
Chris Lattner69bf8a92004-05-23 21:06:58 +0000[diff] [blame]1524<div class="doc_subsubsection">
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1525 <a name="iterate_basicblock">Iterating over the </a><a
1526 href="#Instruction"><tt>Instruction</tt></a>s in a <a
1527 href="#BasicBlock"><tt>BasicBlock</tt></a>
1528</div>
1529
1530<div class="doc_text">
1531
1532<p>Just like when dealing with <tt>BasicBlock</tt>s in <tt>Function</tt>s, it's
1533easy to iterate over the individual instructions that make up
1534<tt>BasicBlock</tt>s. Here's a code snippet that prints out each instruction in
1535a <tt>BasicBlock</tt>:</p>
1536
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1537<div class="doc_code">
Chris Lattner55c04612005-03-06 06:00:13 +0000[diff] [blame]1538<pre>
Bill Wendling82e2eea2006-10-11 18:00:22 +0000[diff] [blame]1539// <i>blk is a pointer to a BasicBlock instance</i>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1540for (BasicBlock::iterator i = blk-&gt;begin(), e = blk-&gt;end(); i != e; ++i)
Bill Wendling82e2eea2006-10-11 18:00:22 +0000[diff] [blame]1541 // <i>The next statement works since operator&lt;&lt;(ostream&amp;,...)</i>
1542 // <i>is overloaded for Instruction&amp;</i>
Bill Wendling832171c2006-12-07 20:04:42 +0000[diff] [blame]1543 llvm::cerr &lt;&lt; *i &lt;&lt; "\n";
Chris Lattner55c04612005-03-06 06:00:13 +0000[diff] [blame]1544</pre>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1545</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1546
1547<p>However, this isn't really the best way to print out the contents of a
1548<tt>BasicBlock</tt>! Since the ostream operators are overloaded for virtually
1549anything you'll care about, you could have just invoked the print routine on the
Bill Wendling832171c2006-12-07 20:04:42 +0000[diff] [blame]1550basic block itself: <tt>llvm::cerr &lt;&lt; *blk &lt;&lt; "\n";</tt>.</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1551
1552</div>
1553
1554<!-- _______________________________________________________________________ -->
Chris Lattner69bf8a92004-05-23 21:06:58 +0000[diff] [blame]1555<div class="doc_subsubsection">
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1556 <a name="iterate_institer">Iterating over the </a><a
1557 href="#Instruction"><tt>Instruction</tt></a>s in a <a
1558 href="#Function"><tt>Function</tt></a>
1559</div>
1560
1561<div class="doc_text">
1562
1563<p>If you're finding that you commonly iterate over a <tt>Function</tt>'s
1564<tt>BasicBlock</tt>s and then that <tt>BasicBlock</tt>'s <tt>Instruction</tt>s,
1565<tt>InstIterator</tt> should be used instead. You'll need to include <a
1566href="/doxygen/InstIterator_8h-source.html"><tt>llvm/Support/InstIterator.h</tt></a>,
1567and then instantiate <tt>InstIterator</tt>s explicitly in your code. Here's a
Chris Lattner69bf8a92004-05-23 21:06:58 +0000[diff] [blame]1568small 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]1569
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1570<div class="doc_code">
1571<pre>
1572#include "<a href="/doxygen/InstIterator_8h-source.html">llvm/Support/InstIterator.h</a>"
1573
Reid Spencer128a7a72007-02-03 21:06:43 +0000[diff] [blame]1574// <i>F is a pointer to a Function instance</i>
Chris Lattnerda021aa2008-06-04 18:20:42 +0000[diff] [blame]1575for (inst_iterator I = inst_begin(F), E = inst_end(F); I != E; ++I)
1576 llvm::cerr &lt;&lt; *I &lt;&lt; "\n";
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1577</pre>
1578</div>
1579
1580<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]1581work list with its initial contents. For example, if you wanted to
1582initialize a work list to contain all instructions in a <tt>Function</tt>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1583F, all you would need to do is something like:</p>
1584
1585<div class="doc_code">
1586<pre>
1587std::set&lt;Instruction*&gt; worklist;
Chris Lattnerda021aa2008-06-04 18:20:42 +0000[diff] [blame]1588// or better yet, SmallPtrSet&lt;Instruction*, 64&gt; worklist;
1589
1590for (inst_iterator I = inst_begin(F), E = inst_end(F); I != E; ++I)
1591 worklist.insert(&amp;*I);
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1592</pre>
1593</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1594
1595<p>The STL set <tt>worklist</tt> would now contain all instructions in the
1596<tt>Function</tt> pointed to by F.</p>
1597
1598</div>
1599
1600<!-- _______________________________________________________________________ -->
1601<div class="doc_subsubsection">
1602 <a name="iterate_convert">Turning an iterator into a class pointer (and
1603 vice-versa)</a>
1604</div>
1605
1606<div class="doc_text">
1607
1608<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]1609instance when all you've got at hand is an iterator. Well, extracting
Chris Lattner69bf8a92004-05-23 21:06:58 +0000[diff] [blame]1610a reference or a pointer from an iterator is very straight-forward.
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]1611Assuming that <tt>i</tt> is a <tt>BasicBlock::iterator</tt> and <tt>j</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1612is a <tt>BasicBlock::const_iterator</tt>:</p>
1613
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1614<div class="doc_code">
1615<pre>
Bill Wendling82e2eea2006-10-11 18:00:22 +0000[diff] [blame]1616Instruction&amp; inst = *i; // <i>Grab reference to instruction reference</i>
1617Instruction* pinst = &amp;*i; // <i>Grab pointer to instruction reference</i>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1618const Instruction&amp; inst = *j;
1619</pre>
1620</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1621
1622<p>However, the iterators you'll be working with in the LLVM framework are
1623special: they will automatically convert to a ptr-to-instance type whenever they
1624need to. Instead of dereferencing the iterator and then taking the address of
1625the result, you can simply assign the iterator to the proper pointer type and
1626you get the dereference and address-of operation as a result of the assignment
1627(behind the scenes, this is a result of overloading casting mechanisms). Thus
1628the last line of the last example,</p>
1629
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1630<div class="doc_code">
1631<pre>
Chris Lattner2e438ca2008-01-03 16:56:04 +0000[diff] [blame]1632Instruction *pinst = &amp;*i;
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1633</pre>
1634</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1635
1636<p>is semantically equivalent to</p>
1637
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1638<div class="doc_code">
1639<pre>
Chris Lattner2e438ca2008-01-03 16:56:04 +0000[diff] [blame]1640Instruction *pinst = i;
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1641</pre>
1642</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1643
Chris Lattner69bf8a92004-05-23 21:06:58 +0000[diff] [blame]1644<p>It's also possible to turn a class pointer into the corresponding iterator,
1645and this is a constant time operation (very efficient). The following code
1646snippet illustrates use of the conversion constructors provided by LLVM
1647iterators. By using these, you can explicitly grab the iterator of something
1648without actually obtaining it via iteration over some structure:</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1649
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1650<div class="doc_code">
1651<pre>
1652void printNextInstruction(Instruction* inst) {
1653 BasicBlock::iterator it(inst);
Bill Wendling82e2eea2006-10-11 18:00:22 +0000[diff] [blame]1654 ++it; // <i>After this line, it refers to the instruction after *inst</i>
Bill Wendling832171c2006-12-07 20:04:42 +0000[diff] [blame]1655 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]1656}
1657</pre>
1658</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1659
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1660</div>
1661
1662<!--_______________________________________________________________________-->
1663<div class="doc_subsubsection">
1664 <a name="iterate_complex">Finding call sites: a slightly more complex
1665 example</a>
1666</div>
1667
1668<div class="doc_text">
1669
1670<p>Say that you're writing a FunctionPass and would like to count all the
1671locations in the entire module (that is, across every <tt>Function</tt>) where a
1672certain function (i.e., some <tt>Function</tt>*) is already in scope. As you'll
1673learn 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]1674much more straight-forward manner, but this example will allow us to explore how
Reid Spencer128a7a72007-02-03 21:06:43 +0000[diff] [blame]1675you'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]1676is what we want to do:</p>
1677
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1678<div class="doc_code">
1679<pre>
1680initialize callCounter to zero
1681for each Function f in the Module
1682 for each BasicBlock b in f
1683 for each Instruction i in b
1684 if (i is a CallInst and calls the given function)
1685 increment callCounter
1686</pre>
1687</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1688
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1689<p>And the actual code is (remember, because we're writing a
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1690<tt>FunctionPass</tt>, our <tt>FunctionPass</tt>-derived class simply has to
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1691override the <tt>runOnFunction</tt> method):</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1692
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1693<div class="doc_code">
1694<pre>
1695Function* targetFunc = ...;
1696
1697class OurFunctionPass : public FunctionPass {
1698 public:
1699 OurFunctionPass(): callCounter(0) { }
1700
1701 virtual runOnFunction(Function&amp; F) {
1702 for (Function::iterator b = F.begin(), be = F.end(); b != be; ++b) {
Eric Christopher203e71d2008-11-08 08:20:49 +0000[diff] [blame]1703 for (BasicBlock::iterator i = b-&gt;begin(), ie = b-&gt;end(); i != ie; ++i) {
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1704 if (<a href="#CallInst">CallInst</a>* callInst = <a href="#isa">dyn_cast</a>&lt;<a
1705 href="#CallInst">CallInst</a>&gt;(&amp;*i)) {
Bill Wendling82e2eea2006-10-11 18:00:22 +0000[diff] [blame]1706 // <i>We know we've encountered a call instruction, so we</i>
1707 // <i>need to determine if it's a call to the</i>
Chris Lattner2e438ca2008-01-03 16:56:04 +0000[diff] [blame]1708 // <i>function pointed to by m_func or not.</i>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1709 if (callInst-&gt;getCalledFunction() == targetFunc)
1710 ++callCounter;
1711 }
1712 }
1713 }
Bill Wendling82e2eea2006-10-11 18:00:22 +0000[diff] [blame]1714 }
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1715
1716 private:
Chris Lattner2e438ca2008-01-03 16:56:04 +0000[diff] [blame]1717 unsigned callCounter;
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1718};
1719</pre>
1720</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1721
1722</div>
1723
Brian Gaekef1972c62003-11-07 19:25:45 +0000[diff] [blame]1724<!--_______________________________________________________________________-->
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1725<div class="doc_subsubsection">
1726 <a name="calls_and_invokes">Treating calls and invokes the same way</a>
1727</div>
1728
1729<div class="doc_text">
1730
1731<p>You may have noticed that the previous example was a bit oversimplified in
1732that it did not deal with call sites generated by 'invoke' instructions. In
1733this, and in other situations, you may find that you want to treat
1734<tt>CallInst</tt>s and <tt>InvokeInst</tt>s the same way, even though their
1735most-specific common base class is <tt>Instruction</tt>, which includes lots of
1736less closely-related things. For these cases, LLVM provides a handy wrapper
1737class called <a
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]1738href="http://llvm.org/doxygen/classllvm_1_1CallSite.html"><tt>CallSite</tt></a>.
Chris Lattner69bf8a92004-05-23 21:06:58 +0000[diff] [blame]1739It is essentially a wrapper around an <tt>Instruction</tt> pointer, with some
1740methods that provide functionality common to <tt>CallInst</tt>s and
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1741<tt>InvokeInst</tt>s.</p>
1742
Chris Lattner69bf8a92004-05-23 21:06:58 +0000[diff] [blame]1743<p>This class has "value semantics": it should be passed by value, not by
1744reference and it should not be dynamically allocated or deallocated using
1745<tt>operator new</tt> or <tt>operator delete</tt>. It is efficiently copyable,
1746assignable and constructable, with costs equivalents to that of a bare pointer.
1747If you look at its definition, it has only a single pointer member.</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1748
1749</div>
1750
Chris Lattner1a3105b2002-09-09 05:49:39 +0000[diff] [blame]1751<!--_______________________________________________________________________-->
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1752<div class="doc_subsubsection">
1753 <a name="iterate_chains">Iterating over def-use &amp; use-def chains</a>
1754</div>
1755
1756<div class="doc_text">
1757
1758<p>Frequently, we might have an instance of the <a
Chris Lattner00815172007-01-04 22:01:45 +0000[diff] [blame]1759href="/doxygen/classllvm_1_1Value.html">Value Class</a> and we want to
Misha Brukman384047f2004-06-03 23:29:12 +0000[diff] [blame]1760determine which <tt>User</tt>s use the <tt>Value</tt>. The list of all
1761<tt>User</tt>s of a particular <tt>Value</tt> is called a <i>def-use</i> chain.
1762For example, let's say we have a <tt>Function*</tt> named <tt>F</tt> to a
1763particular function <tt>foo</tt>. Finding all of the instructions that
1764<i>use</i> <tt>foo</tt> is as simple as iterating over the <i>def-use</i> chain
1765of <tt>F</tt>:</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1766
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1767<div class="doc_code">
1768<pre>
Chris Lattner2e438ca2008-01-03 16:56:04 +0000[diff] [blame]1769Function *F = ...;
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1770
Bill Wendling82e2eea2006-10-11 18:00:22 +0000[diff] [blame]1771for (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]1772 if (Instruction *Inst = dyn_cast&lt;Instruction&gt;(*i)) {
Bill Wendling832171c2006-12-07 20:04:42 +0000[diff] [blame]1773 llvm::cerr &lt;&lt; "F is used in instruction:\n";
1774 llvm::cerr &lt;&lt; *Inst &lt;&lt; "\n";
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1775 }
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1776</pre>
1777</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1778
1779<p>Alternately, it's common to have an instance of the <a
Misha Brukman384047f2004-06-03 23:29:12 +0000[diff] [blame]1780href="/doxygen/classllvm_1_1User.html">User Class</a> and need to know what
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1781<tt>Value</tt>s are used by it. The list of all <tt>Value</tt>s used by a
1782<tt>User</tt> is known as a <i>use-def</i> chain. Instances of class
1783<tt>Instruction</tt> are common <tt>User</tt>s, so we might want to iterate over
1784all of the values that a particular instruction uses (that is, the operands of
1785the particular <tt>Instruction</tt>):</p>
1786
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1787<div class="doc_code">
1788<pre>
Chris Lattner2e438ca2008-01-03 16:56:04 +0000[diff] [blame]1789Instruction *pi = ...;
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1790
1791for (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]1792 Value *v = *i;
Bill Wendling82e2eea2006-10-11 18:00:22 +0000[diff] [blame]1793 // <i>...</i>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1794}
1795</pre>
1796</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1797
Chris Lattner1a3105b2002-09-09 05:49:39 +0000[diff] [blame]1798<!--
1799 def-use chains ("finding all users of"): Value::use_begin/use_end
1800 use-def chains ("finding all values used"): User::op_begin/op_end [op=operand]
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1801-->
1802
1803</div>
1804
Chris Lattner2e438ca2008-01-03 16:56:04 +0000[diff] [blame]1805<!--_______________________________________________________________________-->
1806<div class="doc_subsubsection">
1807 <a name="iterate_preds">Iterating over predecessors &amp;
1808successors of blocks</a>
1809</div>
1810
1811<div class="doc_text">
1812
1813<p>Iterating over the predecessors and successors of a block is quite easy
1814with the routines defined in <tt>"llvm/Support/CFG.h"</tt>. Just use code like
1815this to iterate over all predecessors of BB:</p>
1816
1817<div class="doc_code">
1818<pre>
1819#include "llvm/Support/CFG.h"
1820BasicBlock *BB = ...;
1821
1822for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI) {
1823 BasicBlock *Pred = *PI;
1824 // <i>...</i>
1825}
1826</pre>
1827</div>
1828
1829<p>Similarly, to iterate over successors use
1830succ_iterator/succ_begin/succ_end.</p>
1831
1832</div>
1833
1834
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1835<!-- ======================================================================= -->
1836<div class="doc_subsection">
1837 <a name="simplechanges">Making simple changes</a>
1838</div>
1839
1840<div class="doc_text">
1841
1842<p>There are some primitive transformation operations present in the LLVM
Joel Stanley753eb712002-09-11 22:32:24 +0000[diff] [blame]1843infrastructure that are worth knowing about. When performing
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]1844transformations, it's fairly common to manipulate the contents of basic
1845blocks. This section describes some of the common methods for doing so
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1846and gives example code.</p>
1847
1848</div>
1849
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]1850<!--_______________________________________________________________________-->
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1851<div class="doc_subsubsection">
1852 <a name="schanges_creating">Creating and inserting new
1853 <tt>Instruction</tt>s</a>
1854</div>
1855
1856<div class="doc_text">
1857
1858<p><i>Instantiating Instructions</i></p>
1859
Chris Lattner69bf8a92004-05-23 21:06:58 +0000[diff] [blame]1860<p>Creation of <tt>Instruction</tt>s is straight-forward: simply call the
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1861constructor for the kind of instruction to instantiate and provide the necessary
1862parameters. For example, an <tt>AllocaInst</tt> only <i>requires</i> a
1863(const-ptr-to) <tt>Type</tt>. Thus:</p>
1864
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1865<div class="doc_code">
1866<pre>
Nick Lewycky10d64b92007-12-03 01:52:52 +0000[diff] [blame]1867AllocaInst* ai = new AllocaInst(Type::Int32Ty);
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1868</pre>
1869</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1870
1871<p>will create an <tt>AllocaInst</tt> instance that represents the allocation of
Reid Spencer128a7a72007-02-03 21:06:43 +0000[diff] [blame]1872one integer in the current stack frame, at run time. Each <tt>Instruction</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1873subclass is likely to have varying default parameters which change the semantics
1874of the instruction, so refer to the <a
Misha Brukman31ca1de2004-06-03 23:35:54 +0000[diff] [blame]1875href="/doxygen/classllvm_1_1Instruction.html">doxygen documentation for the subclass of
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1876Instruction</a> that you're interested in instantiating.</p>
1877
1878<p><i>Naming values</i></p>
1879
1880<p>It is very useful to name the values of instructions when you're able to, as
1881this facilitates the debugging of your transformations. If you end up looking
1882at generated LLVM machine code, you definitely want to have logical names
1883associated with the results of instructions! By supplying a value for the
1884<tt>Name</tt> (default) parameter of the <tt>Instruction</tt> constructor, you
1885associate a logical name with the result of the instruction's execution at
Reid Spencer128a7a72007-02-03 21:06:43 +0000[diff] [blame]1886run time. For example, say that I'm writing a transformation that dynamically
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1887allocates space for an integer on the stack, and that integer is going to be
1888used as some kind of index by some other code. To accomplish this, I place an
1889<tt>AllocaInst</tt> at the first point in the first <tt>BasicBlock</tt> of some
1890<tt>Function</tt>, and I'm intending to use it within the same
1891<tt>Function</tt>. I might do:</p>
1892
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1893<div class="doc_code">
1894<pre>
Nick Lewycky10d64b92007-12-03 01:52:52 +0000[diff] [blame]1895AllocaInst* pa = new AllocaInst(Type::Int32Ty, 0, "indexLoc");
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1896</pre>
1897</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1898
1899<p>where <tt>indexLoc</tt> is now the logical name of the instruction's
Reid Spencer128a7a72007-02-03 21:06:43 +0000[diff] [blame]1900execution value, which is a pointer to an integer on the run time stack.</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1901
1902<p><i>Inserting instructions</i></p>
1903
1904<p>There are essentially two ways to insert an <tt>Instruction</tt>
1905into an existing sequence of instructions that form a <tt>BasicBlock</tt>:</p>
1906
Joel Stanley9dd1ad62002-09-18 03:17:23 +0000[diff] [blame]1907<ul>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1908 <li>Insertion into an explicit instruction list
1909
1910 <p>Given a <tt>BasicBlock* pb</tt>, an <tt>Instruction* pi</tt> within that
1911 <tt>BasicBlock</tt>, and a newly-created instruction we wish to insert
1912 before <tt>*pi</tt>, we do the following: </p>
1913
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1914<div class="doc_code">
1915<pre>
1916BasicBlock *pb = ...;
1917Instruction *pi = ...;
1918Instruction *newInst = new Instruction(...);
1919
Bill Wendling82e2eea2006-10-11 18:00:22 +0000[diff] [blame]1920pb-&gt;getInstList().insert(pi, newInst); // <i>Inserts newInst before pi in pb</i>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1921</pre>
1922</div>
Alkis Evlogimenos9a5dc4f2004-05-27 00:57:51 +0000[diff] [blame]1923
1924 <p>Appending to the end of a <tt>BasicBlock</tt> is so common that
1925 the <tt>Instruction</tt> class and <tt>Instruction</tt>-derived
1926 classes provide constructors which take a pointer to a
1927 <tt>BasicBlock</tt> to be appended to. For example code that
1928 looked like: </p>
1929
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1930<div class="doc_code">
1931<pre>
1932BasicBlock *pb = ...;
1933Instruction *newInst = new Instruction(...);
1934
Bill Wendling82e2eea2006-10-11 18:00:22 +0000[diff] [blame]1935pb-&gt;getInstList().push_back(newInst); // <i>Appends newInst to pb</i>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1936</pre>
1937</div>
Alkis Evlogimenos9a5dc4f2004-05-27 00:57:51 +0000[diff] [blame]1938
1939 <p>becomes: </p>
1940
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1941<div class="doc_code">
1942<pre>
1943BasicBlock *pb = ...;
1944Instruction *newInst = new Instruction(..., pb);
1945</pre>
1946</div>
Alkis Evlogimenos9a5dc4f2004-05-27 00:57:51 +0000[diff] [blame]1947
1948 <p>which is much cleaner, especially if you are creating
1949 long instruction streams.</p></li>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1950
1951 <li>Insertion into an implicit instruction list
1952
1953 <p><tt>Instruction</tt> instances that are already in <tt>BasicBlock</tt>s
1954 are implicitly associated with an existing instruction list: the instruction
1955 list of the enclosing basic block. Thus, we could have accomplished the same
1956 thing as the above code without being given a <tt>BasicBlock</tt> by doing:
1957 </p>
1958
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1959<div class="doc_code">
1960<pre>
1961Instruction *pi = ...;
1962Instruction *newInst = new Instruction(...);
1963
1964pi-&gt;getParent()-&gt;getInstList().insert(pi, newInst);
1965</pre>
1966</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1967
1968 <p>In fact, this sequence of steps occurs so frequently that the
1969 <tt>Instruction</tt> class and <tt>Instruction</tt>-derived classes provide
1970 constructors which take (as a default parameter) a pointer to an
1971 <tt>Instruction</tt> which the newly-created <tt>Instruction</tt> should
1972 precede. That is, <tt>Instruction</tt> constructors are capable of
1973 inserting the newly-created instance into the <tt>BasicBlock</tt> of a
1974 provided instruction, immediately before that instruction. Using an
1975 <tt>Instruction</tt> constructor with a <tt>insertBefore</tt> (default)
1976 parameter, the above code becomes:</p>
1977
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1978<div class="doc_code">
1979<pre>
1980Instruction* pi = ...;
1981Instruction* newInst = new Instruction(..., pi);
1982</pre>
1983</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1984
1985 <p>which is much cleaner, especially if you're creating a lot of
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1986 instructions and adding them to <tt>BasicBlock</tt>s.</p></li>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1987</ul>
1988
1989</div>
1990
1991<!--_______________________________________________________________________-->
1992<div class="doc_subsubsection">
1993 <a name="schanges_deleting">Deleting <tt>Instruction</tt>s</a>
1994</div>
1995
1996<div class="doc_text">
1997
1998<p>Deleting an instruction from an existing sequence of instructions that form a
Chris Lattner69bf8a92004-05-23 21:06:58 +0000[diff] [blame]1999<a href="#BasicBlock"><tt>BasicBlock</tt></a> is very straight-forward. First,
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2000you must have a pointer to the instruction that you wish to delete. Second, you
2001need to obtain the pointer to that instruction's basic block. You use the
2002pointer to the basic block to get its list of instructions and then use the
2003erase function to remove your instruction. For example:</p>
2004
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2005<div class="doc_code">
2006<pre>
2007<a href="#Instruction">Instruction</a> *I = .. ;
Chris Lattner9f8ec252008-02-15 22:57:17 +0000[diff] [blame]2008I-&gt;eraseFromParent();
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2009</pre>
2010</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2011
2012</div>
2013
2014<!--_______________________________________________________________________-->
2015<div class="doc_subsubsection">
2016 <a name="schanges_replacing">Replacing an <tt>Instruction</tt> with another
2017 <tt>Value</tt></a>
2018</div>
2019
2020<div class="doc_text">
2021
2022<p><i>Replacing individual instructions</i></p>
2023
2024<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]2025permits use of two very useful replace functions: <tt>ReplaceInstWithValue</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2026and <tt>ReplaceInstWithInst</tt>.</p>
2027
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]2028<h4><a name="schanges_deleting">Deleting <tt>Instruction</tt>s</a></h4>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2029
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]2030<ul>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2031 <li><tt>ReplaceInstWithValue</tt>
2032
Nick Lewyckyb6d1f392008-09-15 06:31:52 +0000[diff] [blame]2033 <p>This function replaces all uses of a given instruction with a value,
2034 and then removes the original instruction. The following example
2035 illustrates the replacement of the result of a particular
Chris Lattner58360822005-01-17 00:12:04 +0000[diff] [blame]2036 <tt>AllocaInst</tt> that allocates memory for a single integer with a null
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2037 pointer to an integer.</p>
2038
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2039<div class="doc_code">
2040<pre>
2041AllocaInst* instToReplace = ...;
2042BasicBlock::iterator ii(instToReplace);
2043
2044ReplaceInstWithValue(instToReplace-&gt;getParent()-&gt;getInstList(), ii,
Daniel Dunbar58c2ac02008-10-03 22:17:25 +0000[diff] [blame]2045 Constant::getNullValue(PointerType::getUnqual(Type::Int32Ty)));
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2046</pre></div></li>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2047
2048 <li><tt>ReplaceInstWithInst</tt>
2049
2050 <p>This function replaces a particular instruction with another
Nick Lewyckyb6d1f392008-09-15 06:31:52 +0000[diff] [blame]2051 instruction, inserting the new instruction into the basic block at the
2052 location where the old instruction was, and replacing any uses of the old
2053 instruction with the new instruction. The following example illustrates
2054 the replacement of one <tt>AllocaInst</tt> with another.</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2055
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2056<div class="doc_code">
2057<pre>
2058AllocaInst* instToReplace = ...;
2059BasicBlock::iterator ii(instToReplace);
2060
2061ReplaceInstWithInst(instToReplace-&gt;getParent()-&gt;getInstList(), ii,
Nick Lewycky10d64b92007-12-03 01:52:52 +0000[diff] [blame]2062 new AllocaInst(Type::Int32Ty, 0, "ptrToReplacedInt"));
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2063</pre></div></li>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]2064</ul>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2065
2066<p><i>Replacing multiple uses of <tt>User</tt>s and <tt>Value</tt>s</i></p>
2067
2068<p>You can use <tt>Value::replaceAllUsesWith</tt> and
2069<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]2070doxygen documentation for the <a href="/doxygen/classllvm_1_1Value.html">Value Class</a>
Misha Brukman384047f2004-06-03 23:29:12 +0000[diff] [blame]2071and <a href="/doxygen/classllvm_1_1User.html">User Class</a>, respectively, for more
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2072information.</p>
2073
2074<!-- Value::replaceAllUsesWith User::replaceUsesOfWith Point out:
2075include/llvm/Transforms/Utils/ especially BasicBlockUtils.h with:
2076ReplaceInstWithValue, ReplaceInstWithInst -->
2077
2078</div>
2079
Tanya Lattnerb011c662007-06-20 18:33:15 +0000[diff] [blame]2080<!--_______________________________________________________________________-->
2081<div class="doc_subsubsection">
2082 <a name="schanges_deletingGV">Deleting <tt>GlobalVariable</tt>s</a>
2083</div>
2084
2085<div class="doc_text">
2086
Tanya Lattnerc5dfcdb2007-06-20 20:46:37 +0000[diff] [blame]2087<p>Deleting a global variable from a module is just as easy as deleting an
2088Instruction. First, you must have a pointer to the global variable that you wish
2089 to delete. You use this pointer to erase it from its parent, the module.
Tanya Lattnerb011c662007-06-20 18:33:15 +0000[diff] [blame]2090 For example:</p>
2091
2092<div class="doc_code">
2093<pre>
2094<a href="#GlobalVariable">GlobalVariable</a> *GV = .. ;
Tanya Lattnerb011c662007-06-20 18:33:15 +0000[diff] [blame]2095
Tanya Lattnerc5dfcdb2007-06-20 20:46:37 +0000[diff] [blame]2096GV-&gt;eraseFromParent();
Tanya Lattnerb011c662007-06-20 18:33:15 +0000[diff] [blame]2097</pre>
2098</div>
2099
2100</div>
2101
Jeffrey Yasskin714257f2009-04-30 22:33:41 +0000[diff] [blame]2102<!-- ======================================================================= -->
2103<div class="doc_subsection">
2104 <a name="create_types">How to Create Types</a>
2105</div>
2106
2107<div class="doc_text">
2108
2109<p>In generating IR, you may need some complex types. If you know these types
Misha Brukman1af789f2009-05-01 20:40:51 +0000[diff] [blame]2110statically, you can use <tt>TypeBuilder&lt;...&gt;::get()</tt>, defined
Jeffrey Yasskin714257f2009-04-30 22:33:41 +0000[diff] [blame]2111in <tt>llvm/Support/TypeBuilder.h</tt>, to retrieve them. <tt>TypeBuilder</tt>
2112has two forms depending on whether you're building types for cross-compilation
Misha Brukman1af789f2009-05-01 20:40:51 +0000[diff] [blame]2113or native library use. <tt>TypeBuilder&lt;T, true&gt;</tt> requires
Jeffrey Yasskin714257f2009-04-30 22:33:41 +0000[diff] [blame]2114that <tt>T</tt> be independent of the host environment, meaning that it's built
2115out of types from
2116the <a href="/doxygen/namespacellvm_1_1types.html"><tt>llvm::types</tt></a>
2117namespace and pointers, functions, arrays, etc. built of
Misha Brukman1af789f2009-05-01 20:40:51 +0000[diff] [blame]2118those. <tt>TypeBuilder&lt;T, false&gt;</tt> additionally allows native C types
Jeffrey Yasskin714257f2009-04-30 22:33:41 +0000[diff] [blame]2119whose size may depend on the host compiler. For example,</p>
2120
2121<div class="doc_code">
2122<pre>
Misha Brukman1af789f2009-05-01 20:40:51 +0000[diff] [blame]2123FunctionType *ft = TypeBuilder&lt;types::i&lt;8&gt;(types::i&lt;32&gt;*), true&gt;::get();
Jeffrey Yasskin714257f2009-04-30 22:33:41 +0000[diff] [blame]2124</pre>
2125</div>
2126
2127<p>is easier to read and write than the equivalent</p>
2128
2129<div class="doc_code">
2130<pre>
Owen Anderson5e8c50e2009-06-16 17:40:28 +0000[diff] [blame^]2131std::vector&lt;const Type*&gt; params;
Jeffrey Yasskin714257f2009-04-30 22:33:41 +0000[diff] [blame]2132params.push_back(PointerType::getUnqual(Type::Int32Ty));
2133FunctionType *ft = FunctionType::get(Type::Int8Ty, params, false);
2134</pre>
2135</div>
2136
2137<p>See the <a href="/doxygen/TypeBuilder_8h-source.html#l00001">class
2138comment</a> for more details.</p>
2139
2140</div>
2141
Chris Lattner9355b472002-09-06 02:50:58 +0000[diff] [blame]2142<!-- *********************************************************************** -->
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2143<div class="doc_section">
Owen Anderson8bc1b3b2009-06-16 01:17:16 +0000[diff] [blame]2144 <a name="threading">Threads and LLVM</a>
2145</div>
2146<!-- *********************************************************************** -->
2147
2148<div class="doc_text">
2149<p>
2150This section describes the interaction of the LLVM APIs with multithreading,
2151both on the part of client applications, and in the JIT, in the hosted
2152application.
2153</p>
2154
2155<p>
2156Note that LLVM's support for multithreading is still relatively young. Up
2157through version 2.5, the execution of threaded hosted applications was
2158supported, but not threaded client access to the APIs. While this use case is
2159now supported, clients <em>must</em> adhere to the guidelines specified below to
2160ensure proper operation in multithreaded mode.
2161</p>
2162
2163<p>
2164Note that, on Unix-like platforms, LLVM requires the presence of GCC's atomic
2165intrinsics in order to support threaded operation. If you need a
2166multhreading-capable LLVM on a platform without a suitably modern system
2167compiler, consider compiling LLVM and LLVM-GCC in single-threaded mode, and
2168using the resultant compiler to build a copy of LLVM with multithreading
2169support.
2170</p>
2171</div>
2172
2173<!-- ======================================================================= -->
2174<div class="doc_subsection">
2175 <a name="startmultithreaded">Entering Threaded Mode with
2176 <tt>llvm_start_multithreaded()</tt></a>
2177</div>
2178
2179<div class="doc_text">
2180
2181<p>
2182In order to properly protect its internal data structures while avoiding
2183excessive locking overhead in the single-threaded case, the LLVM APIs require
2184that the client invoke <tt>llvm_start_multithreaded()</tt>. This call must
2185complete <em>before</em> any other threads attempt to invoke LLVM APIs. Any
2186attempts to call LLVM APIs from multiple threads before
2187<tt>llvm_start_multithreaded</tt> returns can and will cause corruption of
2188LLVM's internal data.
2189</p>
2190
2191<p>
2192A caveat: before <tt>llvm_start_multithreaded()</tt> has been invoked, all
2193<tt>llvm::sys::Mutex</tt> acquisitions and releases will become no-ops. This
2194means that <tt>llvm_start_multithreaded()</tt> must be invoked before a threaded
2195application can be executed in the JIT.
2196</p>
2197</div>
2198
2199<!-- ======================================================================= -->
2200<div class="doc_subsection">
2201 <a name="shutdown">Ending Execution with <tt>llvm_shutdown()</tt></a>
2202</div>
2203
2204<div class="doc_text">
2205<p>
2206When you are done using the LLVM APIs, you should call <tt>llvm_shutdown()</tt>
2207to deallocate memory used for internal structures. This call must not begin
2208while any other threads are still issuing LLVM API calls. Doing so is likely
2209to result in garbage data or crashes.
2210</p>
2211
2212<p>
2213Note that, if you use scope-based shutdown, you can use the
2214<tt>llvm_shutdown_obj</tt> class, which calls <tt>llvm_shutdown()</tt> in its
2215destructor.
2216</div>
2217
2218<!-- ======================================================================= -->
2219<div class="doc_subsection">
2220 <a name="managedstatic">Lazy Initialization with <tt>ManagedStatic</tt></a>
2221</div>
2222
2223<div class="doc_text">
2224<p>
2225<tt>ManagedStatic</tt> is a utility class in LLVM used to implement static
2226initialization of static resources, such as the global type tables. Before the
2227invocation of <tt>llvm_shutdown()</tt>, it implements a simple lazy
2228initialization scheme. Once <tt>llvm_start_multithreaded()</tt> returns,
2229however, it uses double-checked locking to implement thread-safe lazy
2230initialization.
2231</p>
2232
2233<p>
2234Note that, because no other threads are allowed to issue LLVM API calls before
2235<tt>llvm_start_multithreaded()</tt> returns, it is possible to have
2236<tt>ManagedStatic</tt>s of <tt>llvm::sys::Mutex</tt>s.
2237</p>
2238</div>
2239
2240<!-- *********************************************************************** -->
2241<div class="doc_section">
Chris Lattnerd9d6e102005-04-23 16:10:52 +0000[diff] [blame]2242 <a name="advanced">Advanced Topics</a>
2243</div>
2244<!-- *********************************************************************** -->
2245
2246<div class="doc_text">
Chris Lattnerf1b200b2005-04-23 17:27:36 +0000[diff] [blame]2247<p>
2248This section describes some of the advanced or obscure API's that most clients
2249do not need to be aware of. These API's tend manage the inner workings of the
2250LLVM system, and only need to be accessed in unusual circumstances.
2251</p>
2252</div>
Chris Lattnerd9d6e102005-04-23 16:10:52 +0000[diff] [blame]2253
Chris Lattnerf1b200b2005-04-23 17:27:36 +0000[diff] [blame]2254<!-- ======================================================================= -->
2255<div class="doc_subsection">
2256 <a name="TypeResolve">LLVM Type Resolution</a>
2257</div>
Chris Lattnerd9d6e102005-04-23 16:10:52 +0000[diff] [blame]2258
Chris Lattnerf1b200b2005-04-23 17:27:36 +0000[diff] [blame]2259<div class="doc_text">
2260
2261<p>
2262The LLVM type system has a very simple goal: allow clients to compare types for
2263structural equality with a simple pointer comparison (aka a shallow compare).
2264This goal makes clients much simpler and faster, and is used throughout the LLVM
2265system.
2266</p>
2267
2268<p>
2269Unfortunately achieving this goal is not a simple matter. In particular,
2270recursive types and late resolution of opaque types makes the situation very
2271difficult to handle. Fortunately, for the most part, our implementation makes
2272most clients able to be completely unaware of the nasty internal details. The
2273primary case where clients are exposed to the inner workings of it are when
Gabor Greif04367bf2007-07-06 22:07:22 +0000[diff] [blame]2274building a recursive type. In addition to this case, the LLVM bitcode reader,
Chris Lattnerf1b200b2005-04-23 17:27:36 +0000[diff] [blame]2275assembly parser, and linker also have to be aware of the inner workings of this
2276system.
2277</p>
2278
Chris Lattner0f876db2005-04-25 15:47:57 +0000[diff] [blame]2279<p>
2280For our purposes below, we need three concepts. First, an "Opaque Type" is
2281exactly as defined in the <a href="LangRef.html#t_opaque">language
2282reference</a>. Second an "Abstract Type" is any type which includes an
Reid Spencer06565dc2007-01-12 17:11:23 +0000[diff] [blame]2283opaque type as part of its type graph (for example "<tt>{ opaque, i32 }</tt>").
2284Third, 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]2285float }</tt>").
2286</p>
2287
Chris Lattnerf1b200b2005-04-23 17:27:36 +0000[diff] [blame]2288</div>
2289
2290<!-- ______________________________________________________________________ -->
2291<div class="doc_subsubsection">
2292 <a name="BuildRecType">Basic Recursive Type Construction</a>
2293</div>
2294
2295<div class="doc_text">
2296
2297<p>
2298Because the most common question is "how do I build a recursive type with LLVM",
2299we answer it now and explain it as we go. Here we include enough to cause this
2300to be emitted to an output .ll file:
2301</p>
2302
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2303<div class="doc_code">
Chris Lattnerf1b200b2005-04-23 17:27:36 +0000[diff] [blame]2304<pre>
Reid Spencer06565dc2007-01-12 17:11:23 +0000[diff] [blame]2305%mylist = type { %mylist*, i32 }
Chris Lattnerf1b200b2005-04-23 17:27:36 +0000[diff] [blame]2306</pre>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2307</div>
Chris Lattnerf1b200b2005-04-23 17:27:36 +0000[diff] [blame]2308
2309<p>
2310To build this, use the following LLVM APIs:
2311</p>
2312
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2313<div class="doc_code">
Chris Lattnerf1b200b2005-04-23 17:27:36 +0000[diff] [blame]2314<pre>
Bill Wendling82e2eea2006-10-11 18:00:22 +0000[diff] [blame]2315// <i>Create the initial outer struct</i>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2316<a href="#PATypeHolder">PATypeHolder</a> StructTy = OpaqueType::get();
2317std::vector&lt;const Type*&gt; Elts;
Daniel Dunbar58c2ac02008-10-03 22:17:25 +0000[diff] [blame]2318Elts.push_back(PointerType::getUnqual(StructTy));
Nick Lewycky10d64b92007-12-03 01:52:52 +0000[diff] [blame]2319Elts.push_back(Type::Int32Ty);
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2320StructType *NewSTy = StructType::get(Elts);
Chris Lattnerf1b200b2005-04-23 17:27:36 +0000[diff] [blame]2321
Reid Spencer06565dc2007-01-12 17:11:23 +0000[diff] [blame]2322// <i>At this point, NewSTy = "{ opaque*, i32 }". Tell VMCore that</i>
Bill Wendling82e2eea2006-10-11 18:00:22 +0000[diff] [blame]2323// <i>the struct and the opaque type are actually the same.</i>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2324cast&lt;OpaqueType&gt;(StructTy.get())-&gt;<a href="#refineAbstractTypeTo">refineAbstractTypeTo</a>(NewSTy);
Chris Lattnerf1b200b2005-04-23 17:27:36 +0000[diff] [blame]2325
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2326// <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]2327// <i>kept up-to-date</i>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2328NewSTy = cast&lt;StructType&gt;(StructTy.get());
Chris Lattnerf1b200b2005-04-23 17:27:36 +0000[diff] [blame]2329
Bill Wendling82e2eea2006-10-11 18:00:22 +0000[diff] [blame]2330// <i>Add a name for the type to the module symbol table (optional)</i>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2331MyModule-&gt;addTypeName("mylist", NewSTy);
Chris Lattnerf1b200b2005-04-23 17:27:36 +0000[diff] [blame]2332</pre>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2333</div>
Chris Lattnerf1b200b2005-04-23 17:27:36 +0000[diff] [blame]2334
2335<p>
2336This code shows the basic approach used to build recursive types: build a
2337non-recursive type using 'opaque', then use type unification to close the cycle.
2338The type unification step is performed by the <tt><a
Chris Lattneraff26d12007-02-03 03:06:52 +0000[diff] [blame]2339href="#refineAbstractTypeTo">refineAbstractTypeTo</a></tt> method, which is
Chris Lattnerf1b200b2005-04-23 17:27:36 +0000[diff] [blame]2340described next. After that, we describe the <a
2341href="#PATypeHolder">PATypeHolder class</a>.
2342</p>
2343
2344</div>
2345
2346<!-- ______________________________________________________________________ -->
2347<div class="doc_subsubsection">
2348 <a name="refineAbstractTypeTo">The <tt>refineAbstractTypeTo</tt> method</a>
2349</div>
2350
2351<div class="doc_text">
2352<p>
2353The <tt>refineAbstractTypeTo</tt> method starts the type unification process.
2354While this method is actually a member of the DerivedType class, it is most
2355often used on OpaqueType instances. Type unification is actually a recursive
2356process. After unification, types can become structurally isomorphic to
2357existing types, and all duplicates are deleted (to preserve pointer equality).
2358</p>
2359
2360<p>
2361In the example above, the OpaqueType object is definitely deleted.
Reid Spencer06565dc2007-01-12 17:11:23 +0000[diff] [blame]2362Additionally, if there is an "{ \2*, i32}" type already created in the system,
Chris Lattnerf1b200b2005-04-23 17:27:36 +0000[diff] [blame]2363the pointer and struct type created are <b>also</b> deleted. Obviously whenever
2364a type is deleted, any "Type*" pointers in the program are invalidated. As
2365such, it is safest to avoid having <i>any</i> "Type*" pointers to abstract types
2366live across a call to <tt>refineAbstractTypeTo</tt> (note that non-abstract
2367types can never move or be deleted). To deal with this, the <a
2368href="#PATypeHolder">PATypeHolder</a> class is used to maintain a stable
2369reference to a possibly refined type, and the <a
2370href="#AbstractTypeUser">AbstractTypeUser</a> class is used to update more
2371complex datastructures.
2372</p>
2373
2374</div>
2375
2376<!-- ______________________________________________________________________ -->
2377<div class="doc_subsubsection">
2378 <a name="PATypeHolder">The PATypeHolder Class</a>
2379</div>
2380
2381<div class="doc_text">
2382<p>
2383PATypeHolder is a form of a "smart pointer" for Type objects. When VMCore
2384happily goes about nuking types that become isomorphic to existing types, it
2385automatically updates all PATypeHolder objects to point to the new type. In the
2386example above, this allows the code to maintain a pointer to the resultant
2387resolved recursive type, even though the Type*'s are potentially invalidated.
2388</p>
2389
2390<p>
2391PATypeHolder is an extremely light-weight object that uses a lazy union-find
2392implementation to update pointers. For example the pointer from a Value to its
2393Type is maintained by PATypeHolder objects.
2394</p>
2395
2396</div>
2397
2398<!-- ______________________________________________________________________ -->
2399<div class="doc_subsubsection">
2400 <a name="AbstractTypeUser">The AbstractTypeUser Class</a>
2401</div>
2402
2403<div class="doc_text">
2404
2405<p>
2406Some data structures need more to perform more complex updates when types get
Chris Lattner263a98e2007-02-16 04:37:31 +0000[diff] [blame]2407resolved. To support this, a class can derive from the AbstractTypeUser class.
2408This class
Chris Lattnerf1b200b2005-04-23 17:27:36 +0000[diff] [blame]2409allows it to get callbacks when certain types are resolved. To register to get
2410callbacks for a particular type, the DerivedType::{add/remove}AbstractTypeUser
Chris Lattner0f876db2005-04-25 15:47:57 +0000[diff] [blame]2411methods can be called on a type. Note that these methods only work for <i>
Reid Spencer06565dc2007-01-12 17:11:23 +0000[diff] [blame]2412 abstract</i> types. Concrete types (those that do not include any opaque
2413objects) can never be refined.
Chris Lattnerf1b200b2005-04-23 17:27:36 +0000[diff] [blame]2414</p>
Chris Lattnerd9d6e102005-04-23 16:10:52 +0000[diff] [blame]2415</div>
2416
2417
2418<!-- ======================================================================= -->
2419<div class="doc_subsection">
Chris Lattner263a98e2007-02-16 04:37:31 +0000[diff] [blame]2420 <a name="SymbolTable">The <tt>ValueSymbolTable</tt> and
2421 <tt>TypeSymbolTable</tt> classes</a>
Chris Lattnerd9d6e102005-04-23 16:10:52 +0000[diff] [blame]2422</div>
Chris Lattnerf1b200b2005-04-23 17:27:36 +0000[diff] [blame]2423
Chris Lattnerd9d6e102005-04-23 16:10:52 +0000[diff] [blame]2424<div class="doc_text">
Chris Lattner263a98e2007-02-16 04:37:31 +0000[diff] [blame]2425<p>The <tt><a href="http://llvm.org/doxygen/classllvm_1_1ValueSymbolTable.html">
2426ValueSymbolTable</a></tt> class provides a symbol table that the <a
Chris Lattnerd9d6e102005-04-23 16:10:52 +0000[diff] [blame]2427href="#Function"><tt>Function</tt></a> and <a href="#Module">
Chris Lattner263a98e2007-02-16 04:37:31 +0000[diff] [blame]2428<tt>Module</tt></a> classes use for naming value definitions. The symbol table
2429can provide a name for any <a href="#Value"><tt>Value</tt></a>.
2430The <tt><a href="http://llvm.org/doxygen/classllvm_1_1TypeSymbolTable.html">
2431TypeSymbolTable</a></tt> class is used by the <tt>Module</tt> class to store
2432names for types.</p>
Chris Lattnerd9d6e102005-04-23 16:10:52 +0000[diff] [blame]2433
Reid Spencera6362242007-01-07 00:41:39 +0000[diff] [blame]2434<p>Note that the <tt>SymbolTable</tt> class should not be directly accessed
2435by most clients. It should only be used when iteration over the symbol table
2436names themselves are required, which is very special purpose. Note that not
2437all LLVM
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2438<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]2439an empty name) do not exist in the symbol table.
2440</p>
2441
Chris Lattner263a98e2007-02-16 04:37:31 +0000[diff] [blame]2442<p>These symbol tables support iteration over the values/types in the symbol
2443table with <tt>begin/end/iterator</tt> and supports querying to see if a
2444specific name is in the symbol table (with <tt>lookup</tt>). The
2445<tt>ValueSymbolTable</tt> class exposes no public mutator methods, instead,
2446simply call <tt>setName</tt> on a value, which will autoinsert it into the
2447appropriate symbol table. For types, use the Module::addTypeName method to
2448insert entries into the symbol table.</p>
Chris Lattnerd9d6e102005-04-23 16:10:52 +0000[diff] [blame]2449
Chris Lattnerd9d6e102005-04-23 16:10:52 +0000[diff] [blame]2450</div>
2451
2452
2453
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2454<!-- ======================================================================= -->
2455<div class="doc_subsection">
2456 <a name="UserLayout">The <tt>User</tt> and owned <tt>Use</tt> classes' memory layout</a>
2457</div>
2458
2459<div class="doc_text">
2460<p>The <tt><a href="http://llvm.org/doxygen/classllvm_1_1User.html">
Gabor Greiffd095b62009-01-05 16:05:32 +0000[diff] [blame]2461User</a></tt> class provides a basis for expressing the ownership of <tt>User</tt>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2462towards other <tt><a href="http://llvm.org/doxygen/classllvm_1_1Value.html">
2463Value</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]2464Use</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]2465addition and removal.</p>
2466
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2467<!-- ______________________________________________________________________ -->
2468<div class="doc_subsubsection">
Gabor Greiffd095b62009-01-05 16:05:32 +0000[diff] [blame]2469 <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]2470</div>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2471
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2472<div class="doc_text">
2473<p>
2474A subclass of <tt>User</tt> can choose between incorporating its <tt>Use</tt> objects
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2475or refer to them out-of-line by means of a pointer. A mixed variant
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2476(some <tt>Use</tt>s inline others hung off) is impractical and breaks the invariant
2477that the <tt>Use</tt> objects belonging to the same <tt>User</tt> form a contiguous array.
2478</p>
2479</div>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2480
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2481<p>
2482We have 2 different layouts in the <tt>User</tt> (sub)classes:
2483<ul>
2484<li><p>Layout a)
2485The <tt>Use</tt> object(s) are inside (resp. at fixed offset) of the <tt>User</tt>
2486object and there are a fixed number of them.</p>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2487
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2488<li><p>Layout b)
2489The <tt>Use</tt> object(s) are referenced by a pointer to an
2490array from the <tt>User</tt> object and there may be a variable
2491number of them.</p>
2492</ul>
2493<p>
Gabor Greifd41720a2008-06-25 00:10:22 +0000[diff] [blame]2494As of v2.4 each layout still possesses a direct pointer to the
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2495start of the array of <tt>Use</tt>s. Though not mandatory for layout a),
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2496we stick to this redundancy for the sake of simplicity.
Gabor Greifd41720a2008-06-25 00:10:22 +0000[diff] [blame]2497The <tt>User</tt> object also stores the number of <tt>Use</tt> objects it
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2498has. (Theoretically this information can also be calculated
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2499given the scheme presented below.)</p>
2500<p>
2501Special forms of allocation operators (<tt>operator new</tt>)
Gabor Greifd41720a2008-06-25 00:10:22 +0000[diff] [blame]2502enforce the following memory layouts:</p>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2503
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2504<ul>
Gabor Greifd41720a2008-06-25 00:10:22 +0000[diff] [blame]2505<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]2506
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2507<pre>
2508...---.---.---.---.-------...
2509 | P | P | P | P | User
2510'''---'---'---'---'-------'''
2511</pre>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2512
Gabor Greifd41720a2008-06-25 00:10:22 +0000[diff] [blame]2513<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]2514<pre>
2515.-------...
2516| User
2517'-------'''
2518 |
2519 v
2520 .---.---.---.---...
2521 | P | P | P | P |
2522 '---'---'---'---'''
2523</pre>
2524</ul>
2525<i>(In the above figures '<tt>P</tt>' stands for the <tt>Use**</tt> that
2526 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]2527
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2528<!-- ______________________________________________________________________ -->
2529<div class="doc_subsubsection">
Gabor Greiffd095b62009-01-05 16:05:32 +0000[diff] [blame]2530 <a name="Waymarking">The waymarking algorithm</a>
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2531</div>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2532
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2533<div class="doc_text">
2534<p>
Gabor Greifd41720a2008-06-25 00:10:22 +0000[diff] [blame]2535Since the <tt>Use</tt> objects are deprived of the direct (back)pointer to
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2536their <tt>User</tt> objects, there must be a fast and exact method to
2537recover it. This is accomplished by the following scheme:</p>
2538</div>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2539
Gabor Greifd41720a2008-06-25 00:10:22 +0000[diff] [blame]2540A 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]2541start of the <tt>User</tt> object:
2542<ul>
2543<li><tt>00</tt> &mdash;&gt; binary digit 0</li>
2544<li><tt>01</tt> &mdash;&gt; binary digit 1</li>
2545<li><tt>10</tt> &mdash;&gt; stop and calculate (<tt>s</tt>)</li>
2546<li><tt>11</tt> &mdash;&gt; full stop (<tt>S</tt>)</li>
2547</ul>
2548<p>
2549Given a <tt>Use*</tt>, all we have to do is to walk till we get
2550a stop and we either have a <tt>User</tt> immediately behind or
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2551we have to walk to the next stop picking up digits
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2552and calculating the offset:</p>
2553<pre>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2554.---.---.---.---.---.---.---.---.---.---.---.---.---.---.---.---.----------------
2555| 1 | s | 1 | 0 | 1 | 0 | s | 1 | 1 | 0 | s | 1 | 1 | s | 1 | S | User (or User*)
2556'---'---'---'---'---'---'---'---'---'---'---'---'---'---'---'---'----------------
2557 |+15 |+10 |+6 |+3 |+1
2558 | | | | |__>
2559 | | | |__________>
2560 | | |______________________>
2561 | |______________________________________>
2562 |__________________________________________________________>
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2563</pre>
2564<p>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2565Only the significant number of bits need to be stored between the
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2566stops, so that the <i>worst case is 20 memory accesses</i> when there are
25671000 <tt>Use</tt> objects associated with a <tt>User</tt>.</p>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2568
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2569<!-- ______________________________________________________________________ -->
2570<div class="doc_subsubsection">
Gabor Greiffd095b62009-01-05 16:05:32 +0000[diff] [blame]2571 <a name="ReferenceImpl">Reference implementation</a>
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2572</div>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2573
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2574<div class="doc_text">
2575<p>
2576The following literate Haskell fragment demonstrates the concept:</p>
2577</div>
2578
2579<div class="doc_code">
2580<pre>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2581> import Test.QuickCheck
2582>
2583> digits :: Int -> [Char] -> [Char]
2584> digits 0 acc = '0' : acc
2585> digits 1 acc = '1' : acc
2586> digits n acc = digits (n `div` 2) $ digits (n `mod` 2) acc
2587>
2588> dist :: Int -> [Char] -> [Char]
2589> dist 0 [] = ['S']
2590> dist 0 acc = acc
2591> dist 1 acc = let r = dist 0 acc in 's' : digits (length r) r
2592> dist n acc = dist (n - 1) $ dist 1 acc
2593>
2594> takeLast n ss = reverse $ take n $ reverse ss
2595>
2596> test = takeLast 40 $ dist 20 []
2597>
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2598</pre>
2599</div>
2600<p>
2601Printing &lt;test&gt; gives: <tt>"1s100000s11010s10100s1111s1010s110s11s1S"</tt></p>
2602<p>
2603The reverse algorithm computes the length of the string just by examining
2604a certain prefix:</p>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2605
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2606<div class="doc_code">
2607<pre>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2608> pref :: [Char] -> Int
2609> pref "S" = 1
2610> pref ('s':'1':rest) = decode 2 1 rest
2611> pref (_:rest) = 1 + pref rest
2612>
2613> decode walk acc ('0':rest) = decode (walk + 1) (acc * 2) rest
2614> decode walk acc ('1':rest) = decode (walk + 1) (acc * 2 + 1) rest
2615> decode walk acc _ = walk + acc
2616>
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2617</pre>
2618</div>
2619<p>
2620Now, as expected, printing &lt;pref test&gt; gives <tt>40</tt>.</p>
2621<p>
2622We can <i>quickCheck</i> this with following property:</p>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2623
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2624<div class="doc_code">
2625<pre>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2626> testcase = dist 2000 []
2627> testcaseLength = length testcase
2628>
2629> identityProp n = n > 0 && n <= testcaseLength ==> length arr == pref arr
2630> where arr = takeLast n testcase
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2631>
2632</pre>
2633</div>
2634<p>
2635As expected &lt;quickCheck identityProp&gt; gives:</p>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2636
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2637<pre>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2638*Main> quickCheck identityProp
2639OK, passed 100 tests.
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2640</pre>
2641<p>
2642Let's be a bit more exhaustive:</p>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2643
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2644<div class="doc_code">
2645<pre>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2646>
2647> deepCheck p = check (defaultConfig { configMaxTest = 500 }) p
2648>
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2649</pre>
2650</div>
2651<p>
2652And here is the result of &lt;deepCheck identityProp&gt;:</p>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2653
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2654<pre>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2655*Main> deepCheck identityProp
2656OK, passed 500 tests.
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2657</pre>
2658
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2659<!-- ______________________________________________________________________ -->
2660<div class="doc_subsubsection">
Gabor Greiffd095b62009-01-05 16:05:32 +0000[diff] [blame]2661 <a name="Tagging">Tagging considerations</a>
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2662</div>
2663
2664<p>
2665To maintain the invariant that the 2 LSBits of each <tt>Use**</tt> in <tt>Use</tt>
2666never change after being set up, setters of <tt>Use::Prev</tt> must re-tag the
2667new <tt>Use**</tt> on every modification. Accordingly getters must strip the
2668tag bits.</p>
2669<p>
Gabor Greifd41720a2008-06-25 00:10:22 +0000[diff] [blame]2670For layout b) instead of the <tt>User</tt> we find a pointer (<tt>User*</tt> with LSBit set).
2671Following this pointer brings us to the <tt>User</tt>. A portable trick ensures
2672that the first bytes of <tt>User</tt> (if interpreted as a pointer) never has
Gabor Greiffd095b62009-01-05 16:05:32 +0000[diff] [blame]2673the LSBit set. (Portability is relying on the fact that all known compilers place the
2674<tt>vptr</tt> in the first word of the instances.)</p>
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2675
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2676</div>
2677
2678 <!-- *********************************************************************** -->
Chris Lattnerd9d6e102005-04-23 16:10:52 +0000[diff] [blame]2679<div class="doc_section">
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2680 <a name="coreclasses">The Core LLVM Class Hierarchy Reference </a>
2681</div>
2682<!-- *********************************************************************** -->
2683
2684<div class="doc_text">
Reid Spencer303c4b42007-01-12 17:26:25 +0000[diff] [blame]2685<p><tt>#include "<a href="/doxygen/Type_8h-source.html">llvm/Type.h</a>"</tt>
2686<br>doxygen info: <a href="/doxygen/classllvm_1_1Type.html">Type Class</a></p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2687
2688<p>The Core LLVM classes are the primary means of representing the program
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]2689being inspected or transformed. The core LLVM classes are defined in
2690header files in the <tt>include/llvm/</tt> directory, and implemented in
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2691the <tt>lib/VMCore</tt> directory.</p>
2692
2693</div>
2694
2695<!-- ======================================================================= -->
2696<div class="doc_subsection">
Reid Spencer303c4b42007-01-12 17:26:25 +0000[diff] [blame]2697 <a name="Type">The <tt>Type</tt> class and Derived Types</a>
2698</div>
2699
2700<div class="doc_text">
2701
2702 <p><tt>Type</tt> is a superclass of all type classes. Every <tt>Value</tt> has
2703 a <tt>Type</tt>. <tt>Type</tt> cannot be instantiated directly but only
2704 through its subclasses. Certain primitive types (<tt>VoidType</tt>,
2705 <tt>LabelType</tt>, <tt>FloatType</tt> and <tt>DoubleType</tt>) have hidden
2706 subclasses. They are hidden because they offer no useful functionality beyond
2707 what the <tt>Type</tt> class offers except to distinguish themselves from
2708 other subclasses of <tt>Type</tt>.</p>
2709 <p>All other types are subclasses of <tt>DerivedType</tt>. Types can be
2710 named, but this is not a requirement. There exists exactly
2711 one instance of a given shape at any one time. This allows type equality to
2712 be performed with address equality of the Type Instance. That is, given two
2713 <tt>Type*</tt> values, the types are identical if the pointers are identical.
2714 </p>
2715</div>
2716
2717<!-- _______________________________________________________________________ -->
2718<div class="doc_subsubsection">
Gabor Greiffd095b62009-01-05 16:05:32 +0000[diff] [blame]2719 <a name="m_Type">Important Public Methods</a>
Reid Spencer303c4b42007-01-12 17:26:25 +0000[diff] [blame]2720</div>
2721
2722<div class="doc_text">
2723
2724<ul>
Chris Lattner8f79df32007-01-15 01:55:32 +0000[diff] [blame]2725 <li><tt>bool isInteger() const</tt>: Returns true for any integer type.</li>
Reid Spencer303c4b42007-01-12 17:26:25 +0000[diff] [blame]2726
2727 <li><tt>bool isFloatingPoint()</tt>: Return true if this is one of the two
2728 floating point types.</li>
2729
2730 <li><tt>bool isAbstract()</tt>: Return true if the type is abstract (contains
2731 an OpaqueType anywhere in its definition).</li>
2732
2733 <li><tt>bool isSized()</tt>: Return true if the type has known size. Things
2734 that don't have a size are abstract types, labels and void.</li>
2735
2736</ul>
2737</div>
2738
2739<!-- _______________________________________________________________________ -->
2740<div class="doc_subsubsection">
Gabor Greiffd095b62009-01-05 16:05:32 +0000[diff] [blame]2741 <a name="derivedtypes">Important Derived Types</a>
Reid Spencer303c4b42007-01-12 17:26:25 +0000[diff] [blame]2742</div>
2743<div class="doc_text">
2744<dl>
2745 <dt><tt>IntegerType</tt></dt>
2746 <dd>Subclass of DerivedType that represents integer types of any bit width.
2747 Any bit width between <tt>IntegerType::MIN_INT_BITS</tt> (1) and
2748 <tt>IntegerType::MAX_INT_BITS</tt> (~8 million) can be represented.
2749 <ul>
2750 <li><tt>static const IntegerType* get(unsigned NumBits)</tt>: get an integer
2751 type of a specific bit width.</li>
2752 <li><tt>unsigned getBitWidth() const</tt>: Get the bit width of an integer
2753 type.</li>
2754 </ul>
2755 </dd>
2756 <dt><tt>SequentialType</tt></dt>
2757 <dd>This is subclassed by ArrayType and PointerType
2758 <ul>
2759 <li><tt>const Type * getElementType() const</tt>: Returns the type of each
2760 of the elements in the sequential type. </li>
2761 </ul>
2762 </dd>
2763 <dt><tt>ArrayType</tt></dt>
2764 <dd>This is a subclass of SequentialType and defines the interface for array
2765 types.
2766 <ul>
2767 <li><tt>unsigned getNumElements() const</tt>: Returns the number of
2768 elements in the array. </li>
2769 </ul>
2770 </dd>
2771 <dt><tt>PointerType</tt></dt>
Chris Lattner302da1e2007-02-03 03:05:57 +0000[diff] [blame]2772 <dd>Subclass of SequentialType for pointer types.</dd>
Reid Spencer9d6565a2007-02-15 02:26:10 +0000[diff] [blame]2773 <dt><tt>VectorType</tt></dt>
Reid Spencer485bad12007-02-15 03:07:05 +0000[diff] [blame]2774 <dd>Subclass of SequentialType for vector types. A
2775 vector type is similar to an ArrayType but is distinguished because it is
2776 a first class type wherease ArrayType is not. Vector types are used for
Reid Spencer303c4b42007-01-12 17:26:25 +0000[diff] [blame]2777 vector operations and are usually small vectors of of an integer or floating
2778 point type.</dd>
2779 <dt><tt>StructType</tt></dt>
2780 <dd>Subclass of DerivedTypes for struct types.</dd>
Duncan Sands8036ca42007-03-30 12:22:09 +0000[diff] [blame]2781 <dt><tt><a name="FunctionType">FunctionType</a></tt></dt>
Reid Spencer303c4b42007-01-12 17:26:25 +0000[diff] [blame]2782 <dd>Subclass of DerivedTypes for function types.
2783 <ul>
2784 <li><tt>bool isVarArg() const</tt>: Returns true if its a vararg
2785 function</li>
2786 <li><tt> const Type * getReturnType() const</tt>: Returns the
2787 return type of the function.</li>
2788 <li><tt>const Type * getParamType (unsigned i)</tt>: Returns
2789 the type of the ith parameter.</li>
2790 <li><tt> const unsigned getNumParams() const</tt>: Returns the
2791 number of formal parameters.</li>
2792 </ul>
2793 </dd>
2794 <dt><tt>OpaqueType</tt></dt>
2795 <dd>Sublcass of DerivedType for abstract types. This class
2796 defines no content and is used as a placeholder for some other type. Note
2797 that OpaqueType is used (temporarily) during type resolution for forward
2798 references of types. Once the referenced type is resolved, the OpaqueType
2799 is replaced with the actual type. OpaqueType can also be used for data
2800 abstraction. At link time opaque types can be resolved to actual types
2801 of the same name.</dd>
2802</dl>
2803</div>
2804
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]2805
2806
2807<!-- ======================================================================= -->
2808<div class="doc_subsection">
2809 <a name="Module">The <tt>Module</tt> class</a>
2810</div>
2811
2812<div class="doc_text">
2813
2814<p><tt>#include "<a
2815href="/doxygen/Module_8h-source.html">llvm/Module.h</a>"</tt><br> doxygen info:
2816<a href="/doxygen/classllvm_1_1Module.html">Module Class</a></p>
2817
2818<p>The <tt>Module</tt> class represents the top level structure present in LLVM
2819programs. An LLVM module is effectively either a translation unit of the
2820original program or a combination of several translation units merged by the
2821linker. The <tt>Module</tt> class keeps track of a list of <a
2822href="#Function"><tt>Function</tt></a>s, a list of <a
2823href="#GlobalVariable"><tt>GlobalVariable</tt></a>s, and a <a
2824href="#SymbolTable"><tt>SymbolTable</tt></a>. Additionally, it contains a few
2825helpful member functions that try to make common operations easy.</p>
2826
2827</div>
2828
2829<!-- _______________________________________________________________________ -->
2830<div class="doc_subsubsection">
2831 <a name="m_Module">Important Public Members of the <tt>Module</tt> class</a>
2832</div>
2833
2834<div class="doc_text">
2835
2836<ul>
2837 <li><tt>Module::Module(std::string name = "")</tt></li>
2838</ul>
2839
2840<p>Constructing a <a href="#Module">Module</a> is easy. You can optionally
2841provide a name for it (probably based on the name of the translation unit).</p>
2842
2843<ul>
2844 <li><tt>Module::iterator</tt> - Typedef for function list iterator<br>
2845 <tt>Module::const_iterator</tt> - Typedef for const_iterator.<br>
2846
2847 <tt>begin()</tt>, <tt>end()</tt>
2848 <tt>size()</tt>, <tt>empty()</tt>
2849
2850 <p>These are forwarding methods that make it easy to access the contents of
2851 a <tt>Module</tt> object's <a href="#Function"><tt>Function</tt></a>
2852 list.</p></li>
2853
2854 <li><tt>Module::FunctionListType &amp;getFunctionList()</tt>
2855
2856 <p> Returns the list of <a href="#Function"><tt>Function</tt></a>s. This is
2857 necessary to use when you need to update the list or perform a complex
2858 action that doesn't have a forwarding method.</p>
2859
2860 <p><!-- Global Variable --></p></li>
2861</ul>
2862
2863<hr>
2864
2865<ul>
2866 <li><tt>Module::global_iterator</tt> - Typedef for global variable list iterator<br>
2867
2868 <tt>Module::const_global_iterator</tt> - Typedef for const_iterator.<br>
2869
2870 <tt>global_begin()</tt>, <tt>global_end()</tt>
2871 <tt>global_size()</tt>, <tt>global_empty()</tt>
2872
2873 <p> These are forwarding methods that make it easy to access the contents of
2874 a <tt>Module</tt> object's <a
2875 href="#GlobalVariable"><tt>GlobalVariable</tt></a> list.</p></li>
2876
2877 <li><tt>Module::GlobalListType &amp;getGlobalList()</tt>
2878
2879 <p>Returns the list of <a
2880 href="#GlobalVariable"><tt>GlobalVariable</tt></a>s. This is necessary to
2881 use when you need to update the list or perform a complex action that
2882 doesn't have a forwarding method.</p>
2883
2884 <p><!-- Symbol table stuff --> </p></li>
2885</ul>
2886
2887<hr>
2888
2889<ul>
2890 <li><tt><a href="#SymbolTable">SymbolTable</a> *getSymbolTable()</tt>
2891
2892 <p>Return a reference to the <a href="#SymbolTable"><tt>SymbolTable</tt></a>
2893 for this <tt>Module</tt>.</p>
2894
2895 <p><!-- Convenience methods --></p></li>
2896</ul>
2897
2898<hr>
2899
2900<ul>
2901 <li><tt><a href="#Function">Function</a> *getFunction(const std::string
2902 &amp;Name, const <a href="#FunctionType">FunctionType</a> *Ty)</tt>
2903
2904 <p>Look up the specified function in the <tt>Module</tt> <a
2905 href="#SymbolTable"><tt>SymbolTable</tt></a>. If it does not exist, return
2906 <tt>null</tt>.</p></li>
2907
2908 <li><tt><a href="#Function">Function</a> *getOrInsertFunction(const
2909 std::string &amp;Name, const <a href="#FunctionType">FunctionType</a> *T)</tt>
2910
2911 <p>Look up the specified function in the <tt>Module</tt> <a
2912 href="#SymbolTable"><tt>SymbolTable</tt></a>. If it does not exist, add an
2913 external declaration for the function and return it.</p></li>
2914
2915 <li><tt>std::string getTypeName(const <a href="#Type">Type</a> *Ty)</tt>
2916
2917 <p>If there is at least one entry in the <a
2918 href="#SymbolTable"><tt>SymbolTable</tt></a> for the specified <a
2919 href="#Type"><tt>Type</tt></a>, return it. Otherwise return the empty
2920 string.</p></li>
2921
2922 <li><tt>bool addTypeName(const std::string &amp;Name, const <a
2923 href="#Type">Type</a> *Ty)</tt>
2924
2925 <p>Insert an entry in the <a href="#SymbolTable"><tt>SymbolTable</tt></a>
2926 mapping <tt>Name</tt> to <tt>Ty</tt>. If there is already an entry for this
2927 name, true is returned and the <a
2928 href="#SymbolTable"><tt>SymbolTable</tt></a> is not modified.</p></li>
2929</ul>
2930
2931</div>
2932
2933
Reid Spencer303c4b42007-01-12 17:26:25 +0000[diff] [blame]2934<!-- ======================================================================= -->
2935<div class="doc_subsection">
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2936 <a name="Value">The <tt>Value</tt> class</a>
2937</div>
2938
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]2939<div class="doc_text">
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2940
2941<p><tt>#include "<a href="/doxygen/Value_8h-source.html">llvm/Value.h</a>"</tt>
2942<br>
Chris Lattner00815172007-01-04 22:01:45 +0000[diff] [blame]2943doxygen info: <a href="/doxygen/classllvm_1_1Value.html">Value Class</a></p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2944
2945<p>The <tt>Value</tt> class is the most important class in the LLVM Source
2946base. It represents a typed value that may be used (among other things) as an
2947operand to an instruction. There are many different types of <tt>Value</tt>s,
2948such as <a href="#Constant"><tt>Constant</tt></a>s,<a
2949href="#Argument"><tt>Argument</tt></a>s. Even <a
2950href="#Instruction"><tt>Instruction</tt></a>s and <a
2951href="#Function"><tt>Function</tt></a>s are <tt>Value</tt>s.</p>
2952
2953<p>A particular <tt>Value</tt> may be used many times in the LLVM representation
2954for a program. For example, an incoming argument to a function (represented
2955with an instance of the <a href="#Argument">Argument</a> class) is "used" by
2956every instruction in the function that references the argument. To keep track
2957of this relationship, the <tt>Value</tt> class keeps a list of all of the <a
2958href="#User"><tt>User</tt></a>s that is using it (the <a
2959href="#User"><tt>User</tt></a> class is a base class for all nodes in the LLVM
2960graph that can refer to <tt>Value</tt>s). This use list is how LLVM represents
2961def-use information in the program, and is accessible through the <tt>use_</tt>*
2962methods, shown below.</p>
2963
2964<p>Because LLVM is a typed representation, every LLVM <tt>Value</tt> is typed,
2965and this <a href="#Type">Type</a> is available through the <tt>getType()</tt>
2966method. In addition, all LLVM values can be named. The "name" of the
2967<tt>Value</tt> is a symbolic string printed in the LLVM code:</p>
2968
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2969<div class="doc_code">
2970<pre>
Reid Spencer06565dc2007-01-12 17:11:23 +0000[diff] [blame]2971%<b>foo</b> = add i32 1, 2
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2972</pre>
2973</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2974
Duncan Sands8036ca42007-03-30 12:22:09 +0000[diff] [blame]2975<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]2976that the name of any value may be missing (an empty string), so names should
2977<b>ONLY</b> be used for debugging (making the source code easier to read,
2978debugging printouts), they should not be used to keep track of values or map
2979between them. For this purpose, use a <tt>std::map</tt> of pointers to the
2980<tt>Value</tt> itself instead.</p>
2981
2982<p>One important aspect of LLVM is that there is no distinction between an SSA
2983variable and the operation that produces it. Because of this, any reference to
2984the value produced by an instruction (or the value available as an incoming
Chris Lattnerd5fc4fc2004-03-18 14:58:55 +0000[diff] [blame]2985argument, for example) is represented as a direct pointer to the instance of
2986the class that
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2987represents this value. Although this may take some getting used to, it
2988simplifies the representation and makes it easier to manipulate.</p>
2989
2990</div>
2991
2992<!-- _______________________________________________________________________ -->
2993<div class="doc_subsubsection">
2994 <a name="m_Value">Important Public Members of the <tt>Value</tt> class</a>
2995</div>
2996
2997<div class="doc_text">
2998
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]2999<ul>
3000 <li><tt>Value::use_iterator</tt> - Typedef for iterator over the
3001use-list<br>
3002 <tt>Value::use_const_iterator</tt> - Typedef for const_iterator over
3003the use-list<br>
3004 <tt>unsigned use_size()</tt> - Returns the number of users of the
3005value.<br>
Chris Lattner9355b472002-09-06 02:50:58 +0000[diff] [blame]3006 <tt>bool use_empty()</tt> - Returns true if there are no users.<br>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3007 <tt>use_iterator use_begin()</tt> - Get an iterator to the start of
3008the use-list.<br>
3009 <tt>use_iterator use_end()</tt> - Get an iterator to the end of the
3010use-list.<br>
3011 <tt><a href="#User">User</a> *use_back()</tt> - Returns the last
3012element in the list.
3013 <p> These methods are the interface to access the def-use
3014information in LLVM. As with all other iterators in LLVM, the naming
3015conventions follow the conventions defined by the <a href="#stl">STL</a>.</p>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3016 </li>
3017 <li><tt><a href="#Type">Type</a> *getType() const</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3018 <p>This method returns the Type of the Value.</p>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3019 </li>
3020 <li><tt>bool hasName() const</tt><br>
Chris Lattner9355b472002-09-06 02:50:58 +0000[diff] [blame]3021 <tt>std::string getName() const</tt><br>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3022 <tt>void setName(const std::string &amp;Name)</tt>
3023 <p> This family of methods is used to access and assign a name to a <tt>Value</tt>,
3024be aware of the <a href="#nameWarning">precaution above</a>.</p>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3025 </li>
3026 <li><tt>void replaceAllUsesWith(Value *V)</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3027
3028 <p>This method traverses the use list of a <tt>Value</tt> changing all <a
3029 href="#User"><tt>User</tt>s</a> of the current value to refer to
3030 "<tt>V</tt>" instead. For example, if you detect that an instruction always
3031 produces a constant value (for example through constant folding), you can
3032 replace all uses of the instruction with the constant like this:</p>
3033
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]3034<div class="doc_code">
3035<pre>
3036Inst-&gt;replaceAllUsesWith(ConstVal);
3037</pre>
3038</div>
3039
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3040</ul>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3041
3042</div>
3043
3044<!-- ======================================================================= -->
3045<div class="doc_subsection">
3046 <a name="User">The <tt>User</tt> class</a>
3047</div>
3048
3049<div class="doc_text">
3050
3051<p>
3052<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]3053doxygen info: <a href="/doxygen/classllvm_1_1User.html">User Class</a><br>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3054Superclass: <a href="#Value"><tt>Value</tt></a></p>
3055
3056<p>The <tt>User</tt> class is the common base class of all LLVM nodes that may
3057refer to <a href="#Value"><tt>Value</tt></a>s. It exposes a list of "Operands"
3058that are all of the <a href="#Value"><tt>Value</tt></a>s that the User is
3059referring to. The <tt>User</tt> class itself is a subclass of
3060<tt>Value</tt>.</p>
3061
3062<p>The operands of a <tt>User</tt> point directly to the LLVM <a
3063href="#Value"><tt>Value</tt></a> that it refers to. Because LLVM uses Static
3064Single Assignment (SSA) form, there can only be one definition referred to,
3065allowing this direct connection. This connection provides the use-def
3066information in LLVM.</p>
3067
3068</div>
3069
3070<!-- _______________________________________________________________________ -->
3071<div class="doc_subsubsection">
3072 <a name="m_User">Important Public Members of the <tt>User</tt> class</a>
3073</div>
3074
3075<div class="doc_text">
3076
3077<p>The <tt>User</tt> class exposes the operand list in two ways: through
3078an index access interface and through an iterator based interface.</p>
3079
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3080<ul>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3081 <li><tt>Value *getOperand(unsigned i)</tt><br>
3082 <tt>unsigned getNumOperands()</tt>
3083 <p> These two methods expose the operands of the <tt>User</tt> in a
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3084convenient form for direct access.</p></li>
3085
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3086 <li><tt>User::op_iterator</tt> - Typedef for iterator over the operand
3087list<br>
Chris Lattner58360822005-01-17 00:12:04 +0000[diff] [blame]3088 <tt>op_iterator op_begin()</tt> - Get an iterator to the start of
3089the operand list.<br>
3090 <tt>op_iterator op_end()</tt> - Get an iterator to the end of the
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3091operand list.
3092 <p> Together, these methods make up the iterator based interface to
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3093the operands of a <tt>User</tt>.</p></li>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3094</ul>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3095
3096</div>
3097
3098<!-- ======================================================================= -->
3099<div class="doc_subsection">
3100 <a name="Instruction">The <tt>Instruction</tt> class</a>
3101</div>
3102
3103<div class="doc_text">
3104
3105<p><tt>#include "</tt><tt><a
3106href="/doxygen/Instruction_8h-source.html">llvm/Instruction.h</a>"</tt><br>
Misha Brukman31ca1de2004-06-03 23:35:54 +0000[diff] [blame]3107doxygen info: <a href="/doxygen/classllvm_1_1Instruction.html">Instruction Class</a><br>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3108Superclasses: <a href="#User"><tt>User</tt></a>, <a
3109href="#Value"><tt>Value</tt></a></p>
3110
3111<p>The <tt>Instruction</tt> class is the common base class for all LLVM
3112instructions. It provides only a few methods, but is a very commonly used
3113class. The primary data tracked by the <tt>Instruction</tt> class itself is the
3114opcode (instruction type) and the parent <a
3115href="#BasicBlock"><tt>BasicBlock</tt></a> the <tt>Instruction</tt> is embedded
3116into. To represent a specific type of instruction, one of many subclasses of
3117<tt>Instruction</tt> are used.</p>
3118
3119<p> Because the <tt>Instruction</tt> class subclasses the <a
3120href="#User"><tt>User</tt></a> class, its operands can be accessed in the same
3121way as for other <a href="#User"><tt>User</tt></a>s (with the
3122<tt>getOperand()</tt>/<tt>getNumOperands()</tt> and
3123<tt>op_begin()</tt>/<tt>op_end()</tt> methods).</p> <p> An important file for
3124the <tt>Instruction</tt> class is the <tt>llvm/Instruction.def</tt> file. This
3125file contains some meta-data about the various different types of instructions
3126in LLVM. It describes the enum values that are used as opcodes (for example
Reid Spencerc92d25d2006-12-19 19:47:19 +0000[diff] [blame]3127<tt>Instruction::Add</tt> and <tt>Instruction::ICmp</tt>), as well as the
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3128concrete sub-classes of <tt>Instruction</tt> that implement the instruction (for
3129example <tt><a href="#BinaryOperator">BinaryOperator</a></tt> and <tt><a
Reid Spencerc92d25d2006-12-19 19:47:19 +0000[diff] [blame]3130href="#CmpInst">CmpInst</a></tt>). Unfortunately, the use of macros in
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3131this file confuses doxygen, so these enum values don't show up correctly in the
Misha Brukman31ca1de2004-06-03 23:35:54 +0000[diff] [blame]3132<a href="/doxygen/classllvm_1_1Instruction.html">doxygen output</a>.</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3133
3134</div>
3135
3136<!-- _______________________________________________________________________ -->
3137<div class="doc_subsubsection">
Reid Spencerc92d25d2006-12-19 19:47:19 +0000[diff] [blame]3138 <a name="s_Instruction">Important Subclasses of the <tt>Instruction</tt>
3139 class</a>
3140</div>
3141<div class="doc_text">
3142 <ul>
3143 <li><tt><a name="BinaryOperator">BinaryOperator</a></tt>
3144 <p>This subclasses represents all two operand instructions whose operands
3145 must be the same type, except for the comparison instructions.</p></li>
3146 <li><tt><a name="CastInst">CastInst</a></tt>
3147 <p>This subclass is the parent of the 12 casting instructions. It provides
3148 common operations on cast instructions.</p>
3149 <li><tt><a name="CmpInst">CmpInst</a></tt>
3150 <p>This subclass respresents the two comparison instructions,
3151 <a href="LangRef.html#i_icmp">ICmpInst</a> (integer opreands), and
3152 <a href="LangRef.html#i_fcmp">FCmpInst</a> (floating point operands).</p>
3153 <li><tt><a name="TerminatorInst">TerminatorInst</a></tt>
3154 <p>This subclass is the parent of all terminator instructions (those which
3155 can terminate a block).</p>
3156 </ul>
3157 </div>
3158
3159<!-- _______________________________________________________________________ -->
3160<div class="doc_subsubsection">
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3161 <a name="m_Instruction">Important Public Members of the <tt>Instruction</tt>
3162 class</a>
3163</div>
3164
3165<div class="doc_text">
3166
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3167<ul>
3168 <li><tt><a href="#BasicBlock">BasicBlock</a> *getParent()</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3169 <p>Returns the <a href="#BasicBlock"><tt>BasicBlock</tt></a> that
3170this <tt>Instruction</tt> is embedded into.</p></li>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3171 <li><tt>bool mayWriteToMemory()</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3172 <p>Returns true if the instruction writes to memory, i.e. it is a
3173 <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]3174 <li><tt>unsigned getOpcode()</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3175 <p>Returns the opcode for the <tt>Instruction</tt>.</p></li>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3176 <li><tt><a href="#Instruction">Instruction</a> *clone() const</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3177 <p>Returns another instance of the specified instruction, identical
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3178in all ways to the original except that the instruction has no parent
3179(ie it's not embedded into a <a href="#BasicBlock"><tt>BasicBlock</tt></a>),
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3180and it has no name</p></li>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3181</ul>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3182
3183</div>
3184
3185<!-- ======================================================================= -->
3186<div class="doc_subsection">
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]3187 <a name="Constant">The <tt>Constant</tt> class and subclasses</a>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3188</div>
3189
3190<div class="doc_text">
3191
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]3192<p>Constant represents a base class for different types of constants. It
3193is subclassed by ConstantInt, ConstantArray, etc. for representing
3194the various types of Constants. <a href="#GlobalValue">GlobalValue</a> is also
3195a subclass, which represents the address of a global variable or function.
3196</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3197
3198</div>
3199
3200<!-- _______________________________________________________________________ -->
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]3201<div class="doc_subsubsection">Important Subclasses of Constant </div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3202<div class="doc_text">
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3203<ul>
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]3204 <li>ConstantInt : This subclass of Constant represents an integer constant of
3205 any width.
3206 <ul>
Reid Spencer97b4ee32007-03-01 21:05:33 +0000[diff] [blame]3207 <li><tt>const APInt&amp; getValue() const</tt>: Returns the underlying
3208 value of this constant, an APInt value.</li>
3209 <li><tt>int64_t getSExtValue() const</tt>: Converts the underlying APInt
3210 value to an int64_t via sign extension. If the value (not the bit width)
3211 of the APInt is too large to fit in an int64_t, an assertion will result.
3212 For this reason, use of this method is discouraged.</li>
3213 <li><tt>uint64_t getZExtValue() const</tt>: Converts the underlying APInt
3214 value to a uint64_t via zero extension. IF the value (not the bit width)
3215 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]3216 For this reason, use of this method is discouraged.</li>
Reid Spencer97b4ee32007-03-01 21:05:33 +0000[diff] [blame]3217 <li><tt>static ConstantInt* get(const APInt&amp; Val)</tt>: Returns the
3218 ConstantInt object that represents the value provided by <tt>Val</tt>.
3219 The type is implied as the IntegerType that corresponds to the bit width
3220 of <tt>Val</tt>.</li>
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]3221 <li><tt>static ConstantInt* get(const Type *Ty, uint64_t Val)</tt>:
3222 Returns the ConstantInt object that represents the value provided by
3223 <tt>Val</tt> for integer type <tt>Ty</tt>.</li>
3224 </ul>
3225 </li>
3226 <li>ConstantFP : This class represents a floating point constant.
3227 <ul>
3228 <li><tt>double getValue() const</tt>: Returns the underlying value of
3229 this constant. </li>
3230 </ul>
3231 </li>
3232 <li>ConstantArray : This represents a constant array.
3233 <ul>
3234 <li><tt>const std::vector&lt;Use&gt; &amp;getValues() const</tt>: Returns
3235 a vector of component constants that makeup this array. </li>
3236 </ul>
3237 </li>
3238 <li>ConstantStruct : This represents a constant struct.
3239 <ul>
3240 <li><tt>const std::vector&lt;Use&gt; &amp;getValues() const</tt>: Returns
3241 a vector of component constants that makeup this array. </li>
3242 </ul>
3243 </li>
3244 <li>GlobalValue : This represents either a global variable or a function. In
3245 either case, the value is a constant fixed address (after linking).
3246 </li>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3247</ul>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3248</div>
3249
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]3250
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3251<!-- ======================================================================= -->
3252<div class="doc_subsection">
3253 <a name="GlobalValue">The <tt>GlobalValue</tt> class</a>
3254</div>
3255
3256<div class="doc_text">
3257
3258<p><tt>#include "<a
3259href="/doxygen/GlobalValue_8h-source.html">llvm/GlobalValue.h</a>"</tt><br>
Misha Brukman384047f2004-06-03 23:29:12 +0000[diff] [blame]3260doxygen info: <a href="/doxygen/classllvm_1_1GlobalValue.html">GlobalValue
3261Class</a><br>
Reid Spencerbe5e85e2006-04-14 14:11:48 +0000[diff] [blame]3262Superclasses: <a href="#Constant"><tt>Constant</tt></a>,
3263<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]3264
3265<p>Global values (<a href="#GlobalVariable"><tt>GlobalVariable</tt></a>s or <a
3266href="#Function"><tt>Function</tt></a>s) are the only LLVM values that are
3267visible in the bodies of all <a href="#Function"><tt>Function</tt></a>s.
3268Because they are visible at global scope, they are also subject to linking with
3269other globals defined in different translation units. To control the linking
3270process, <tt>GlobalValue</tt>s know their linkage rules. Specifically,
3271<tt>GlobalValue</tt>s know whether they have internal or external linkage, as
Reid Spencer8b2da7a2004-07-18 13:10:31 +0000[diff] [blame]3272defined by the <tt>LinkageTypes</tt> enumeration.</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3273
3274<p>If a <tt>GlobalValue</tt> has internal linkage (equivalent to being
3275<tt>static</tt> in C), it is not visible to code outside the current translation
3276unit, and does not participate in linking. If it has external linkage, it is
3277visible to external code, and does participate in linking. In addition to
3278linkage information, <tt>GlobalValue</tt>s keep track of which <a
3279href="#Module"><tt>Module</tt></a> they are currently part of.</p>
3280
3281<p>Because <tt>GlobalValue</tt>s are memory objects, they are always referred to
3282by their <b>address</b>. As such, the <a href="#Type"><tt>Type</tt></a> of a
3283global is always a pointer to its contents. It is important to remember this
3284when using the <tt>GetElementPtrInst</tt> instruction because this pointer must
3285be dereferenced first. For example, if you have a <tt>GlobalVariable</tt> (a
3286subclass 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]3287i32]</tt>, then the <tt>GlobalVariable</tt> is a pointer to that array. Although
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3288the address of the first element of this array and the value of the
3289<tt>GlobalVariable</tt> are the same, they have different types. The
Reid Spencer06565dc2007-01-12 17:11:23 +0000[diff] [blame]3290<tt>GlobalVariable</tt>'s type is <tt>[24 x i32]</tt>. The first element's type
3291is <tt>i32.</tt> Because of this, accessing a global value requires you to
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3292dereference the pointer with <tt>GetElementPtrInst</tt> first, then its elements
3293can be accessed. This is explained in the <a href="LangRef.html#globalvars">LLVM
3294Language Reference Manual</a>.</p>
3295
3296</div>
3297
3298<!-- _______________________________________________________________________ -->
3299<div class="doc_subsubsection">
3300 <a name="m_GlobalValue">Important Public Members of the <tt>GlobalValue</tt>
3301 class</a>
3302</div>
3303
3304<div class="doc_text">
3305
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3306<ul>
3307 <li><tt>bool hasInternalLinkage() const</tt><br>
Chris Lattner9355b472002-09-06 02:50:58 +0000[diff] [blame]3308 <tt>bool hasExternalLinkage() const</tt><br>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3309 <tt>void setInternalLinkage(bool HasInternalLinkage)</tt>
3310 <p> These methods manipulate the linkage characteristics of the <tt>GlobalValue</tt>.</p>
3311 <p> </p>
3312 </li>
3313 <li><tt><a href="#Module">Module</a> *getParent()</tt>
3314 <p> This returns the <a href="#Module"><tt>Module</tt></a> that the
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3315GlobalValue is currently embedded into.</p></li>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3316</ul>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3317
3318</div>
3319
3320<!-- ======================================================================= -->
3321<div class="doc_subsection">
3322 <a name="Function">The <tt>Function</tt> class</a>
3323</div>
3324
3325<div class="doc_text">
3326
3327<p><tt>#include "<a
3328href="/doxygen/Function_8h-source.html">llvm/Function.h</a>"</tt><br> doxygen
Misha Brukman31ca1de2004-06-03 23:35:54 +0000[diff] [blame]3329info: <a href="/doxygen/classllvm_1_1Function.html">Function Class</a><br>
Reid Spencerbe5e85e2006-04-14 14:11:48 +0000[diff] [blame]3330Superclasses: <a href="#GlobalValue"><tt>GlobalValue</tt></a>,
3331<a href="#Constant"><tt>Constant</tt></a>,
3332<a href="#User"><tt>User</tt></a>,
3333<a href="#Value"><tt>Value</tt></a></p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3334
3335<p>The <tt>Function</tt> class represents a single procedure in LLVM. It is
3336actually one of the more complex classes in the LLVM heirarchy because it must
3337keep track of a large amount of data. The <tt>Function</tt> class keeps track
Reid Spencerbe5e85e2006-04-14 14:11:48 +0000[diff] [blame]3338of a list of <a href="#BasicBlock"><tt>BasicBlock</tt></a>s, a list of formal
3339<a href="#Argument"><tt>Argument</tt></a>s, and a
3340<a href="#SymbolTable"><tt>SymbolTable</tt></a>.</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3341
3342<p>The list of <a href="#BasicBlock"><tt>BasicBlock</tt></a>s is the most
3343commonly used part of <tt>Function</tt> objects. The list imposes an implicit
3344ordering of the blocks in the function, which indicate how the code will be
3345layed out by the backend. Additionally, the first <a
3346href="#BasicBlock"><tt>BasicBlock</tt></a> is the implicit entry node for the
3347<tt>Function</tt>. It is not legal in LLVM to explicitly branch to this initial
3348block. There are no implicit exit nodes, and in fact there may be multiple exit
3349nodes from a single <tt>Function</tt>. If the <a
3350href="#BasicBlock"><tt>BasicBlock</tt></a> list is empty, this indicates that
3351the <tt>Function</tt> is actually a function declaration: the actual body of the
3352function hasn't been linked in yet.</p>
3353
3354<p>In addition to a list of <a href="#BasicBlock"><tt>BasicBlock</tt></a>s, the
3355<tt>Function</tt> class also keeps track of the list of formal <a
3356href="#Argument"><tt>Argument</tt></a>s that the function receives. This
3357container manages the lifetime of the <a href="#Argument"><tt>Argument</tt></a>
3358nodes, just like the <a href="#BasicBlock"><tt>BasicBlock</tt></a> list does for
3359the <a href="#BasicBlock"><tt>BasicBlock</tt></a>s.</p>
3360
3361<p>The <a href="#SymbolTable"><tt>SymbolTable</tt></a> is a very rarely used
3362LLVM feature that is only used when you have to look up a value by name. Aside
3363from that, the <a href="#SymbolTable"><tt>SymbolTable</tt></a> is used
3364internally to make sure that there are not conflicts between the names of <a
3365href="#Instruction"><tt>Instruction</tt></a>s, <a
3366href="#BasicBlock"><tt>BasicBlock</tt></a>s, or <a
3367href="#Argument"><tt>Argument</tt></a>s in the function body.</p>
3368
Reid Spencer8b2da7a2004-07-18 13:10:31 +0000[diff] [blame]3369<p>Note that <tt>Function</tt> is a <a href="#GlobalValue">GlobalValue</a>
3370and therefore also a <a href="#Constant">Constant</a>. The value of the function
3371is its address (after linking) which is guaranteed to be constant.</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3372</div>
3373
3374<!-- _______________________________________________________________________ -->
3375<div class="doc_subsubsection">
3376 <a name="m_Function">Important Public Members of the <tt>Function</tt>
3377 class</a>
3378</div>
3379
3380<div class="doc_text">
3381
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3382<ul>
3383 <li><tt>Function(const </tt><tt><a href="#FunctionType">FunctionType</a>
Chris Lattnerac479e52004-08-04 05:10:48 +0000[diff] [blame]3384 *Ty, LinkageTypes Linkage, const std::string &amp;N = "", Module* Parent = 0)</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3385
3386 <p>Constructor used when you need to create new <tt>Function</tt>s to add
3387 the the program. The constructor must specify the type of the function to
Chris Lattnerac479e52004-08-04 05:10:48 +0000[diff] [blame]3388 create and what type of linkage the function should have. The <a
3389 href="#FunctionType"><tt>FunctionType</tt></a> argument
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3390 specifies the formal arguments and return value for the function. The same
Duncan Sands8036ca42007-03-30 12:22:09 +0000[diff] [blame]3391 <a href="#FunctionType"><tt>FunctionType</tt></a> value can be used to
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3392 create multiple functions. The <tt>Parent</tt> argument specifies the Module
3393 in which the function is defined. If this argument is provided, the function
3394 will automatically be inserted into that module's list of
3395 functions.</p></li>
3396
Chris Lattner62810e32008-11-25 18:34:50 +0000[diff] [blame]3397 <li><tt>bool isDeclaration()</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3398
3399 <p>Return whether or not the <tt>Function</tt> has a body defined. If the
3400 function is "external", it does not have a body, and thus must be resolved
3401 by linking with a function defined in a different translation unit.</p></li>
3402
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3403 <li><tt>Function::iterator</tt> - Typedef for basic block list iterator<br>
Chris Lattner9355b472002-09-06 02:50:58 +0000[diff] [blame]3404 <tt>Function::const_iterator</tt> - Typedef for const_iterator.<br>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3405
Chris Lattner77d69242005-03-15 05:19:20 +0000[diff] [blame]3406 <tt>begin()</tt>, <tt>end()</tt>
3407 <tt>size()</tt>, <tt>empty()</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3408
3409 <p>These are forwarding methods that make it easy to access the contents of
3410 a <tt>Function</tt> object's <a href="#BasicBlock"><tt>BasicBlock</tt></a>
3411 list.</p></li>
3412
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3413 <li><tt>Function::BasicBlockListType &amp;getBasicBlockList()</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3414
3415 <p>Returns the list of <a href="#BasicBlock"><tt>BasicBlock</tt></a>s. This
3416 is necessary to use when you need to update the list or perform a complex
3417 action that doesn't have a forwarding method.</p></li>
3418
Chris Lattner89cc2652005-03-15 04:48:32 +0000[diff] [blame]3419 <li><tt>Function::arg_iterator</tt> - Typedef for the argument list
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3420iterator<br>
Chris Lattner89cc2652005-03-15 04:48:32 +0000[diff] [blame]3421 <tt>Function::const_arg_iterator</tt> - Typedef for const_iterator.<br>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3422
Chris Lattner77d69242005-03-15 05:19:20 +0000[diff] [blame]3423 <tt>arg_begin()</tt>, <tt>arg_end()</tt>
Chris Lattner89cc2652005-03-15 04:48:32 +0000[diff] [blame]3424 <tt>arg_size()</tt>, <tt>arg_empty()</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3425
3426 <p>These are forwarding methods that make it easy to access the contents of
3427 a <tt>Function</tt> object's <a href="#Argument"><tt>Argument</tt></a>
3428 list.</p></li>
3429
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3430 <li><tt>Function::ArgumentListType &amp;getArgumentList()</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3431
3432 <p>Returns the list of <a href="#Argument"><tt>Argument</tt></a>s. This is
3433 necessary to use when you need to update the list or perform a complex
3434 action that doesn't have a forwarding method.</p></li>
3435
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3436 <li><tt><a href="#BasicBlock">BasicBlock</a> &amp;getEntryBlock()</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3437
3438 <p>Returns the entry <a href="#BasicBlock"><tt>BasicBlock</tt></a> for the
3439 function. Because the entry block for the function is always the first
3440 block, this returns the first block of the <tt>Function</tt>.</p></li>
3441
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3442 <li><tt><a href="#Type">Type</a> *getReturnType()</tt><br>
3443 <tt><a href="#FunctionType">FunctionType</a> *getFunctionType()</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3444
3445 <p>This traverses the <a href="#Type"><tt>Type</tt></a> of the
3446 <tt>Function</tt> and returns the return type of the function, or the <a
3447 href="#FunctionType"><tt>FunctionType</tt></a> of the actual
3448 function.</p></li>
3449
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3450 <li><tt><a href="#SymbolTable">SymbolTable</a> *getSymbolTable()</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3451
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3452 <p> Return a pointer to the <a href="#SymbolTable"><tt>SymbolTable</tt></a>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3453 for this <tt>Function</tt>.</p></li>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3454</ul>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3455
3456</div>
3457
3458<!-- ======================================================================= -->
3459<div class="doc_subsection">
3460 <a name="GlobalVariable">The <tt>GlobalVariable</tt> class</a>
3461</div>
3462
3463<div class="doc_text">
3464
3465<p><tt>#include "<a
3466href="/doxygen/GlobalVariable_8h-source.html">llvm/GlobalVariable.h</a>"</tt>
3467<br>
Tanya Lattnera3da7772004-06-22 08:02:25 +0000[diff] [blame]3468doxygen info: <a href="/doxygen/classllvm_1_1GlobalVariable.html">GlobalVariable
Reid Spencerbe5e85e2006-04-14 14:11:48 +0000[diff] [blame]3469 Class</a><br>
3470Superclasses: <a href="#GlobalValue"><tt>GlobalValue</tt></a>,
3471<a href="#Constant"><tt>Constant</tt></a>,
3472<a href="#User"><tt>User</tt></a>,
3473<a href="#Value"><tt>Value</tt></a></p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3474
3475<p>Global variables are represented with the (suprise suprise)
3476<tt>GlobalVariable</tt> class. Like functions, <tt>GlobalVariable</tt>s are also
3477subclasses of <a href="#GlobalValue"><tt>GlobalValue</tt></a>, and as such are
3478always referenced by their address (global values must live in memory, so their
Reid Spencerbe5e85e2006-04-14 14:11:48 +0000[diff] [blame]3479"name" refers to their constant address). See
3480<a href="#GlobalValue"><tt>GlobalValue</tt></a> for more on this. Global
3481variables may have an initial value (which must be a
3482<a href="#Constant"><tt>Constant</tt></a>), and if they have an initializer,
3483they may be marked as "constant" themselves (indicating that their contents
3484never change at runtime).</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3485</div>
3486
3487<!-- _______________________________________________________________________ -->
3488<div class="doc_subsubsection">
3489 <a name="m_GlobalVariable">Important Public Members of the
3490 <tt>GlobalVariable</tt> class</a>
3491</div>
3492
3493<div class="doc_text">
3494
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3495<ul>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3496 <li><tt>GlobalVariable(const </tt><tt><a href="#Type">Type</a> *Ty, bool
3497 isConstant, LinkageTypes&amp; Linkage, <a href="#Constant">Constant</a>
3498 *Initializer = 0, const std::string &amp;Name = "", Module* Parent = 0)</tt>
3499
3500 <p>Create a new global variable of the specified type. If
3501 <tt>isConstant</tt> is true then the global variable will be marked as
3502 unchanging for the program. The Linkage parameter specifies the type of
Duncan Sands667d4b82009-03-07 15:45:40 +0000[diff] [blame]3503 linkage (internal, external, weak, linkonce, appending) for the variable.
3504 If the linkage is InternalLinkage, WeakAnyLinkage, WeakODRLinkage,
3505 LinkOnceAnyLinkage or LinkOnceODRLinkage,&nbsp; then the resultant
3506 global variable will have internal linkage. AppendingLinkage concatenates
3507 together all instances (in different translation units) of the variable
3508 into a single variable but is only applicable to arrays. &nbsp;See
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3509 the <a href="LangRef.html#modulestructure">LLVM Language Reference</a> for
3510 further details on linkage types. Optionally an initializer, a name, and the
3511 module to put the variable into may be specified for the global variable as
3512 well.</p></li>
3513
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3514 <li><tt>bool isConstant() const</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3515
3516 <p>Returns true if this is a global variable that is known not to
3517 be modified at runtime.</p></li>
3518
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3519 <li><tt>bool hasInitializer()</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3520
3521 <p>Returns true if this <tt>GlobalVariable</tt> has an intializer.</p></li>
3522
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3523 <li><tt><a href="#Constant">Constant</a> *getInitializer()</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3524
3525 <p>Returns the intial value for a <tt>GlobalVariable</tt>. It is not legal
3526 to call this method if there is no initializer.</p></li>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3527</ul>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3528
3529</div>
3530
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]3531
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3532<!-- ======================================================================= -->
3533<div class="doc_subsection">
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]3534 <a name="BasicBlock">The <tt>BasicBlock</tt> class</a>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3535</div>
3536
3537<div class="doc_text">
3538
3539<p><tt>#include "<a
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]3540href="/doxygen/BasicBlock_8h-source.html">llvm/BasicBlock.h</a>"</tt><br>
3541doxygen info: <a href="/doxygen/structllvm_1_1BasicBlock.html">BasicBlock
3542Class</a><br>
3543Superclass: <a href="#Value"><tt>Value</tt></a></p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3544
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]3545<p>This class represents a single entry multiple exit section of the code,
3546commonly known as a basic block by the compiler community. The
3547<tt>BasicBlock</tt> class maintains a list of <a
3548href="#Instruction"><tt>Instruction</tt></a>s, which form the body of the block.
3549Matching the language definition, the last element of this list of instructions
3550is always a terminator instruction (a subclass of the <a
3551href="#TerminatorInst"><tt>TerminatorInst</tt></a> class).</p>
3552
3553<p>In addition to tracking the list of instructions that make up the block, the
3554<tt>BasicBlock</tt> class also keeps track of the <a
3555href="#Function"><tt>Function</tt></a> that it is embedded into.</p>
3556
3557<p>Note that <tt>BasicBlock</tt>s themselves are <a
3558href="#Value"><tt>Value</tt></a>s, because they are referenced by instructions
3559like branches and can go in the switch tables. <tt>BasicBlock</tt>s have type
3560<tt>label</tt>.</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3561
3562</div>
3563
3564<!-- _______________________________________________________________________ -->
3565<div class="doc_subsubsection">
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]3566 <a name="m_BasicBlock">Important Public Members of the <tt>BasicBlock</tt>
3567 class</a>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3568</div>
3569
3570<div class="doc_text">
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3571<ul>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3572
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]3573<li><tt>BasicBlock(const std::string &amp;Name = "", </tt><tt><a
3574 href="#Function">Function</a> *Parent = 0)</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3575
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]3576<p>The <tt>BasicBlock</tt> constructor is used to create new basic blocks for
3577insertion into a function. The constructor optionally takes a name for the new
3578block, and a <a href="#Function"><tt>Function</tt></a> to insert it into. If
3579the <tt>Parent</tt> parameter is specified, the new <tt>BasicBlock</tt> is
3580automatically inserted at the end of the specified <a
3581href="#Function"><tt>Function</tt></a>, if not specified, the BasicBlock must be
3582manually inserted into the <a href="#Function"><tt>Function</tt></a>.</p></li>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3583
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]3584<li><tt>BasicBlock::iterator</tt> - Typedef for instruction list iterator<br>
3585<tt>BasicBlock::const_iterator</tt> - Typedef for const_iterator.<br>
3586<tt>begin()</tt>, <tt>end()</tt>, <tt>front()</tt>, <tt>back()</tt>,
3587<tt>size()</tt>, <tt>empty()</tt>
3588STL-style functions for accessing the instruction list.
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3589
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]3590<p>These methods and typedefs are forwarding functions that have the same
3591semantics as the standard library methods of the same names. These methods
3592expose the underlying instruction list of a basic block in a way that is easy to
3593manipulate. To get the full complement of container operations (including
3594operations to update the list), you must use the <tt>getInstList()</tt>
3595method.</p></li>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3596
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]3597<li><tt>BasicBlock::InstListType &amp;getInstList()</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3598
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]3599<p>This method is used to get access to the underlying container that actually
3600holds the Instructions. This method must be used when there isn't a forwarding
3601function in the <tt>BasicBlock</tt> class for the operation that you would like
3602to perform. Because there are no forwarding functions for "updating"
3603operations, you need to use this if you want to update the contents of a
3604<tt>BasicBlock</tt>.</p></li>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3605
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]3606<li><tt><a href="#Function">Function</a> *getParent()</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3607
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]3608<p> Returns a pointer to <a href="#Function"><tt>Function</tt></a> the block is
3609embedded into, or a null pointer if it is homeless.</p></li>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3610
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]3611<li><tt><a href="#TerminatorInst">TerminatorInst</a> *getTerminator()</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3612
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]3613<p> Returns a pointer to the terminator instruction that appears at the end of
3614the <tt>BasicBlock</tt>. If there is no terminator instruction, or if the last
3615instruction in the block is not a terminator, then a null pointer is
3616returned.</p></li>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3617
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3618</ul>
3619
3620</div>
3621
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3622
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3623<!-- ======================================================================= -->
3624<div class="doc_subsection">
3625 <a name="Argument">The <tt>Argument</tt> class</a>
3626</div>
3627
3628<div class="doc_text">
3629
3630<p>This subclass of Value defines the interface for incoming formal
Chris Lattner58360822005-01-17 00:12:04 +0000[diff] [blame]3631arguments to a function. A Function maintains a list of its formal
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3632arguments. An argument has a pointer to the parent Function.</p>
3633
3634</div>
3635
Chris Lattner9355b472002-09-06 02:50:58 +0000[diff] [blame]3636<!-- *********************************************************************** -->
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3637<hr>
3638<address>
3639 <a href="http://jigsaw.w3.org/css-validator/check/referer"><img
Misha Brukman44408702008-12-11 17:34:48 +0000[diff] [blame]3640 src="http://jigsaw.w3.org/css-validator/images/vcss-blue" alt="Valid CSS"></a>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3641 <a href="http://validator.w3.org/check/referer"><img
Gabor Greifa9c0f2b2008-06-18 14:05:31 +0000[diff] [blame]3642 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]3643
3644 <a href="mailto:dhurjati@cs.uiuc.edu">Dinakar Dhurjati</a> and
3645 <a href="mailto:sabre@nondot.org">Chris Lattner</a><br>
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]3646 <a href="http://llvm.org">The LLVM Compiler Infrastructure</a><br>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3647 Last modified: $Date$
3648</address>
3649
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3650</body>
3651</html>