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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>
Daniel Dunbar6e0d1cb2009-07-25 04:41:11 +0000[diff] [blame]32 <li><a href="#string_apis">Passing strings (the <tt>StringRef</tt>
Benjamin Kramere15192b2009-08-05 15:42:44 +0000[diff] [blame]33and <tt>Twine</tt> classes)</a>
Daniel Dunbar6e0d1cb2009-07-25 04:41:11 +0000[diff] [blame]34 <ul>
35 <li><a href="#StringRef">The <tt>StringRef</tt> class</a> </li>
36 <li><a href="#Twine">The <tt>Twine</tt> class</a> </li>
37 </ul>
Benjamin Kramere15192b2009-08-05 15:42:44 +0000[diff] [blame]38 </li>
Misha Brukman2c122ce2005-11-01 21:12:49 +0000[diff] [blame]39 <li><a href="#DEBUG">The <tt>DEBUG()</tt> macro and <tt>-debug</tt>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]40option</a>
41 <ul>
42 <li><a href="#DEBUG_TYPE">Fine grained debug info with <tt>DEBUG_TYPE</tt>
43and the <tt>-debug-only</tt> option</a> </li>
44 </ul>
45 </li>
Chris Lattner0be6fdf2006-12-19 21:46:21 +0000[diff] [blame]46 <li><a href="#Statistic">The <tt>Statistic</tt> class &amp; <tt>-stats</tt>
Reid Spencerfe8f4ff2004-11-01 09:02:53 +0000[diff] [blame]47option</a></li>
48<!--
49 <li>The <tt>InstVisitor</tt> template
50 <li>The general graph API
51-->
Chris Lattnerf623a082005-10-17 01:36:23 +0000[diff] [blame]52 <li><a href="#ViewGraph">Viewing graphs while debugging code</a></li>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]53 </ul>
54 </li>
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]55 <li><a href="#datastructure">Picking the Right Data Structure for a Task</a>
56 <ul>
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]57 <li><a href="#ds_sequential">Sequential Containers (std::vector, std::list, etc)</a>
58 <ul>
59 <li><a href="#dss_fixedarrays">Fixed Size Arrays</a></li>
60 <li><a href="#dss_heaparrays">Heap Allocated Arrays</a></li>
61 <li><a href="#dss_smallvector">"llvm/ADT/SmallVector.h"</a></li>
62 <li><a href="#dss_vector">&lt;vector&gt;</a></li>
63 <li><a href="#dss_deque">&lt;deque&gt;</a></li>
64 <li><a href="#dss_list">&lt;list&gt;</a></li>
Gabor Greif3899e492009-02-27 11:37:41 +0000[diff] [blame]65 <li><a href="#dss_ilist">llvm/ADT/ilist.h</a></li>
Chris Lattnerc5722432007-02-03 19:49:31 +0000[diff] [blame]66 <li><a href="#dss_other">Other Sequential Container Options</a></li>
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]67 </ul></li>
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]68 <li><a href="#ds_set">Set-Like Containers (std::set, SmallSet, SetVector, etc)</a>
69 <ul>
70 <li><a href="#dss_sortedvectorset">A sorted 'vector'</a></li>
71 <li><a href="#dss_smallset">"llvm/ADT/SmallSet.h"</a></li>
72 <li><a href="#dss_smallptrset">"llvm/ADT/SmallPtrSet.h"</a></li>
Chris Lattnerc28476f2007-09-30 00:58:59 +0000[diff] [blame]73 <li><a href="#dss_denseset">"llvm/ADT/DenseSet.h"</a></li>
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]74 <li><a href="#dss_FoldingSet">"llvm/ADT/FoldingSet.h"</a></li>
75 <li><a href="#dss_set">&lt;set&gt;</a></li>
76 <li><a href="#dss_setvector">"llvm/ADT/SetVector.h"</a></li>
Chris Lattnerc5722432007-02-03 19:49:31 +0000[diff] [blame]77 <li><a href="#dss_uniquevector">"llvm/ADT/UniqueVector.h"</a></li>
78 <li><a href="#dss_otherset">Other Set-Like ContainerOptions</a></li>
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]79 </ul></li>
Chris Lattnerf3692522007-02-03 19:51:56 +0000[diff] [blame]80 <li><a href="#ds_map">Map-Like Containers (std::map, DenseMap, etc)</a>
81 <ul>
82 <li><a href="#dss_sortedvectormap">A sorted 'vector'</a></li>
Chris Lattner796f9fa2007-02-08 19:14:21 +0000[diff] [blame]83 <li><a href="#dss_stringmap">"llvm/ADT/StringMap.h"</a></li>
Chris Lattnerf3692522007-02-03 19:51:56 +0000[diff] [blame]84 <li><a href="#dss_indexedmap">"llvm/ADT/IndexedMap.h"</a></li>
85 <li><a href="#dss_densemap">"llvm/ADT/DenseMap.h"</a></li>
Jeffrey Yasskin71a5c222009-10-22 22:11:22 +0000[diff] [blame]86 <li><a href="#dss_valuemap">"llvm/ADT/ValueMap.h"</a></li>
Jakob Stoklund Olesenaca0da62010-12-14 00:55:51 +0000[diff] [blame]87 <li><a href="#dss_intervalmap">"llvm/ADT/IntervalMap.h"</a></li>
Chris Lattnerf3692522007-02-03 19:51:56 +0000[diff] [blame]88 <li><a href="#dss_map">&lt;map&gt;</a></li>
89 <li><a href="#dss_othermap">Other Map-Like Container Options</a></li>
90 </ul></li>
Chris Lattnerdced9fb2009-07-25 07:22:20 +0000[diff] [blame]91 <li><a href="#ds_string">String-like containers</a>
Benjamin Kramere15192b2009-08-05 15:42:44 +0000[diff] [blame]92 <!--<ul>
93 todo
94 </ul>--></li>
Daniel Berlin1939ace2007-09-24 17:52:25 +0000[diff] [blame]95 <li><a href="#ds_bit">BitVector-like containers</a>
96 <ul>
97 <li><a href="#dss_bitvector">A dense bitvector</a></li>
Dan Gohman5f7775c2010-01-05 18:24:00 +0000[diff] [blame]98 <li><a href="#dss_smallbitvector">A "small" dense bitvector</a></li>
Daniel Berlin1939ace2007-09-24 17:52:25 +0000[diff] [blame]99 <li><a href="#dss_sparsebitvector">A sparse bitvector</a></li>
100 </ul></li>
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]101 </ul>
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]102 </li>
Chris Lattnerae7f7592002-09-06 18:31:18 +0000[diff] [blame]103 <li><a href="#common">Helpful Hints for Common Operations</a>
Chris Lattnerae7f7592002-09-06 18:31:18 +0000[diff] [blame]104 <ul>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]105 <li><a href="#inspection">Basic Inspection and Traversal Routines</a>
106 <ul>
107 <li><a href="#iterate_function">Iterating over the <tt>BasicBlock</tt>s
108in a <tt>Function</tt></a> </li>
109 <li><a href="#iterate_basicblock">Iterating over the <tt>Instruction</tt>s
110in a <tt>BasicBlock</tt></a> </li>
111 <li><a href="#iterate_institer">Iterating over the <tt>Instruction</tt>s
112in a <tt>Function</tt></a> </li>
113 <li><a href="#iterate_convert">Turning an iterator into a
114class pointer</a> </li>
115 <li><a href="#iterate_complex">Finding call sites: a more
116complex example</a> </li>
117 <li><a href="#calls_and_invokes">Treating calls and invokes
118the same way</a> </li>
119 <li><a href="#iterate_chains">Iterating over def-use &amp;
120use-def chains</a> </li>
Chris Lattner2e438ca2008-01-03 16:56:04 +0000[diff] [blame]121 <li><a href="#iterate_preds">Iterating over predecessors &amp;
122successors of blocks</a></li>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]123 </ul>
124 </li>
125 <li><a href="#simplechanges">Making simple changes</a>
126 <ul>
127 <li><a href="#schanges_creating">Creating and inserting new
128 <tt>Instruction</tt>s</a> </li>
129 <li><a href="#schanges_deleting">Deleting <tt>Instruction</tt>s</a> </li>
130 <li><a href="#schanges_replacing">Replacing an <tt>Instruction</tt>
131with another <tt>Value</tt></a> </li>
Tanya Lattnerb011c662007-06-20 18:33:15 +0000[diff] [blame]132 <li><a href="#schanges_deletingGV">Deleting <tt>GlobalVariable</tt>s</a> </li>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]133 </ul>
Reid Spencerfe8f4ff2004-11-01 09:02:53 +0000[diff] [blame]134 </li>
Jeffrey Yasskin714257f2009-04-30 22:33:41 +0000[diff] [blame]135 <li><a href="#create_types">How to Create Types</a></li>
Chris Lattnerae7f7592002-09-06 18:31:18 +0000[diff] [blame]136<!--
137 <li>Working with the Control Flow Graph
138 <ul>
139 <li>Accessing predecessors and successors of a <tt>BasicBlock</tt>
140 <li>
141 <li>
142 </ul>
Reid Spencerfe8f4ff2004-11-01 09:02:53 +0000[diff] [blame]143-->
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]144 </ul>
145 </li>
Chris Lattnerd9d6e102005-04-23 16:10:52 +0000[diff] [blame]146
Owen Anderson8bc1b3b2009-06-16 01:17:16 +0000[diff] [blame]147 <li><a href="#threading">Threads and LLVM</a>
148 <ul>
Owen Anderson1ad70e32009-06-16 18:04:19 +0000[diff] [blame]149 <li><a href="#startmultithreaded">Entering and Exiting Multithreaded Mode
150 </a></li>
Owen Anderson8bc1b3b2009-06-16 01:17:16 +0000[diff] [blame]151 <li><a href="#shutdown">Ending execution with <tt>llvm_shutdown()</tt></a></li>
152 <li><a href="#managedstatic">Lazy initialization with <tt>ManagedStatic</tt></a></li>
Owen Andersone0c951a2009-08-19 17:58:52 +0000[diff] [blame]153 <li><a href="#llvmcontext">Achieving Isolation with <tt>LLVMContext</tt></a></li>
Jeffrey Yasskin01eba392010-01-29 19:10:38 +0000[diff] [blame]154 <li><a href="#jitthreading">Threads and the JIT</a></li>
Owen Anderson8bc1b3b2009-06-16 01:17:16 +0000[diff] [blame]155 </ul>
156 </li>
157
Chris Lattnerd9d6e102005-04-23 16:10:52 +0000[diff] [blame]158 <li><a href="#advanced">Advanced Topics</a>
159 <ul>
Chris Lattnerf1b200b2005-04-23 17:27:36 +0000[diff] [blame]160 <li><a href="#TypeResolve">LLVM Type Resolution</a>
161 <ul>
162 <li><a href="#BuildRecType">Basic Recursive Type Construction</a></li>
163 <li><a href="#refineAbstractTypeTo">The <tt>refineAbstractTypeTo</tt> method</a></li>
164 <li><a href="#PATypeHolder">The PATypeHolder Class</a></li>
165 <li><a href="#AbstractTypeUser">The AbstractTypeUser Class</a></li>
166 </ul></li>
167
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]168 <li><a href="#SymbolTable">The <tt>ValueSymbolTable</tt> and <tt>TypeSymbolTable</tt> classes</a></li>
169 <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]170 </ul></li>
171
Joel Stanley9b96c442002-09-06 21:55:13 +0000[diff] [blame]172 <li><a href="#coreclasses">The Core LLVM Class Hierarchy Reference</a>
Chris Lattner9355b472002-09-06 02:50:58 +0000[diff] [blame]173 <ul>
Reid Spencer303c4b42007-01-12 17:26:25 +0000[diff] [blame]174 <li><a href="#Type">The <tt>Type</tt> class</a> </li>
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]175 <li><a href="#Module">The <tt>Module</tt> class</a></li>
Reid Spencerfe8f4ff2004-11-01 09:02:53 +0000[diff] [blame]176 <li><a href="#Value">The <tt>Value</tt> class</a>
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]177 <ul>
178 <li><a href="#User">The <tt>User</tt> class</a>
Chris Lattner9355b472002-09-06 02:50:58 +0000[diff] [blame]179 <ul>
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]180 <li><a href="#Instruction">The <tt>Instruction</tt> class</a></li>
181 <li><a href="#Constant">The <tt>Constant</tt> class</a>
182 <ul>
183 <li><a href="#GlobalValue">The <tt>GlobalValue</tt> class</a>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]184 <ul>
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]185 <li><a href="#Function">The <tt>Function</tt> class</a></li>
186 <li><a href="#GlobalVariable">The <tt>GlobalVariable</tt> class</a></li>
187 </ul>
188 </li>
189 </ul>
190 </li>
Reid Spencerfe8f4ff2004-11-01 09:02:53 +0000[diff] [blame]191 </ul>
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]192 </li>
193 <li><a href="#BasicBlock">The <tt>BasicBlock</tt> class</a></li>
194 <li><a href="#Argument">The <tt>Argument</tt> class</a></li>
195 </ul>
Reid Spencerfe8f4ff2004-11-01 09:02:53 +0000[diff] [blame]196 </li>
197 </ul>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]198 </li>
Chris Lattner9355b472002-09-06 02:50:58 +0000[diff] [blame]199</ol>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]200
Chris Lattner69bf8a92004-05-23 21:06:58 +0000[diff] [blame]201<div class="doc_author">
202 <p>Written by <a href="mailto:sabre@nondot.org">Chris Lattner</a>,
Chris Lattner94c43592004-05-26 16:52:55 +0000[diff] [blame]203 <a href="mailto:dhurjati@cs.uiuc.edu">Dinakar Dhurjati</a>,
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]204 <a href="mailto:ggreif@gmail.com">Gabor Greif</a>,
Owen Anderson8bc1b3b2009-06-16 01:17:16 +0000[diff] [blame]205 <a href="mailto:jstanley@cs.uiuc.edu">Joel Stanley</a>,
206 <a href="mailto:rspencer@x10sys.com">Reid Spencer</a> and
207 <a href="mailto:owen@apple.com">Owen Anderson</a></p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]208</div>
209
Chris Lattner9355b472002-09-06 02:50:58 +0000[diff] [blame]210<!-- *********************************************************************** -->
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]211<div class="doc_section">
212 <a name="introduction">Introduction </a>
213</div>
Chris Lattner9355b472002-09-06 02:50:58 +0000[diff] [blame]214<!-- *********************************************************************** -->
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]215
216<div class="doc_text">
217
218<p>This document is meant to highlight some of the important classes and
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]219interfaces available in the LLVM source-base. This manual is not
220intended to explain what LLVM is, how it works, and what LLVM code looks
221like. It assumes that you know the basics of LLVM and are interested
222in writing transformations or otherwise analyzing or manipulating the
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]223code.</p>
224
225<p>This document should get you oriented so that you can find your
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]226way in the continuously growing source code that makes up the LLVM
227infrastructure. Note that this manual is not intended to serve as a
228replacement for reading the source code, so if you think there should be
229a method in one of these classes to do something, but it's not listed,
230check the source. Links to the <a href="/doxygen/">doxygen</a> sources
231are provided to make this as easy as possible.</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]232
233<p>The first section of this document describes general information that is
234useful to know when working in the LLVM infrastructure, and the second describes
235the Core LLVM classes. In the future this manual will be extended with
236information describing how to use extension libraries, such as dominator
237information, CFG traversal routines, and useful utilities like the <tt><a
238href="/doxygen/InstVisitor_8h-source.html">InstVisitor</a></tt> template.</p>
239
240</div>
241
Chris Lattner9355b472002-09-06 02:50:58 +0000[diff] [blame]242<!-- *********************************************************************** -->
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]243<div class="doc_section">
244 <a name="general">General Information</a>
245</div>
246<!-- *********************************************************************** -->
247
248<div class="doc_text">
249
250<p>This section contains general information that is useful if you are working
251in the LLVM source-base, but that isn't specific to any particular API.</p>
252
253</div>
254
255<!-- ======================================================================= -->
256<div class="doc_subsection">
257 <a name="stl">The C++ Standard Template Library</a>
258</div>
259
260<div class="doc_text">
261
262<p>LLVM makes heavy use of the C++ Standard Template Library (STL),
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]263perhaps much more than you are used to, or have seen before. Because of
264this, you might want to do a little background reading in the
265techniques used and capabilities of the library. There are many good
266pages that discuss the STL, and several books on the subject that you
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]267can get, so it will not be discussed in this document.</p>
268
269<p>Here are some useful links:</p>
270
271<ol>
272
Nick Lewyckyea1fe2c2010-10-09 21:12:29 +0000[diff] [blame]273<li><a href="http://www.dinkumware.com/manuals/#Standard C++ Library">Dinkumware
274C++ Library reference</a> - an excellent reference for the STL and other parts
275of the standard C++ library.</li>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]276
277<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]278O'Reilly book in the making. It has a decent Standard Library
279Reference that rivals Dinkumware's, and is unfortunately no longer free since the
280book has been published.</li>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]281
282<li><a href="http://www.parashift.com/c++-faq-lite/">C++ Frequently Asked
283Questions</a></li>
284
285<li><a href="http://www.sgi.com/tech/stl/">SGI's STL Programmer's Guide</a> -
286Contains a useful <a
287href="http://www.sgi.com/tech/stl/stl_introduction.html">Introduction to the
288STL</a>.</li>
289
290<li><a href="http://www.research.att.com/%7Ebs/C++.html">Bjarne Stroustrup's C++
291Page</a></li>
292
Tanya Lattner79445ba2004-12-08 18:34:56 +0000[diff] [blame]293<li><a href="http://64.78.49.204/">
Reid Spencer096603a2004-05-26 08:41:35 +0000[diff] [blame]294Bruce Eckel's Thinking in C++, 2nd ed. Volume 2 Revision 4.0 (even better, get
295the book).</a></li>
296
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]297</ol>
298
299<p>You are also encouraged to take a look at the <a
300href="CodingStandards.html">LLVM Coding Standards</a> guide which focuses on how
301to write maintainable code more than where to put your curly braces.</p>
302
303</div>
304
305<!-- ======================================================================= -->
306<div class="doc_subsection">
307 <a name="stl">Other useful references</a>
308</div>
309
310<div class="doc_text">
311
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]312<ol>
Misha Brukmana0f71e42004-06-18 18:39:00 +0000[diff] [blame]313<li><a href="http://www.fortran-2000.com/ArnaudRecipes/sharedlib.html">Using
314static and shared libraries across platforms</a></li>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]315</ol>
316
317</div>
318
Chris Lattner9355b472002-09-06 02:50:58 +0000[diff] [blame]319<!-- *********************************************************************** -->
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]320<div class="doc_section">
321 <a name="apis">Important and useful LLVM APIs</a>
322</div>
323<!-- *********************************************************************** -->
324
325<div class="doc_text">
326
327<p>Here we highlight some LLVM APIs that are generally useful and good to
328know about when writing transformations.</p>
329
330</div>
331
332<!-- ======================================================================= -->
333<div class="doc_subsection">
Misha Brukman2c122ce2005-11-01 21:12:49 +0000[diff] [blame]334 <a name="isa">The <tt>isa&lt;&gt;</tt>, <tt>cast&lt;&gt;</tt> and
335 <tt>dyn_cast&lt;&gt;</tt> templates</a>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]336</div>
337
338<div class="doc_text">
339
340<p>The LLVM source-base makes extensive use of a custom form of RTTI.
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]341These templates have many similarities to the C++ <tt>dynamic_cast&lt;&gt;</tt>
342operator, but they don't have some drawbacks (primarily stemming from
343the fact that <tt>dynamic_cast&lt;&gt;</tt> only works on classes that
344have a v-table). Because they are used so often, you must know what they
345do and how they work. All of these templates are defined in the <a
Chris Lattner695b78b2005-04-26 22:56:16 +0000[diff] [blame]346 href="/doxygen/Casting_8h-source.html"><tt>llvm/Support/Casting.h</tt></a>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]347file (note that you very rarely have to include this file directly).</p>
348
349<dl>
350 <dt><tt>isa&lt;&gt;</tt>: </dt>
351
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]352 <dd><p>The <tt>isa&lt;&gt;</tt> operator works exactly like the Java
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]353 "<tt>instanceof</tt>" operator. It returns true or false depending on whether
354 a reference or pointer points to an instance of the specified class. This can
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]355 be very useful for constraint checking of various sorts (example below).</p>
356 </dd>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]357
358 <dt><tt>cast&lt;&gt;</tt>: </dt>
359
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]360 <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]361 converts a pointer or reference from a base class to a derived class, causing
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]362 an assertion failure if it is not really an instance of the right type. This
363 should be used in cases where you have some information that makes you believe
364 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]365 and <tt>cast&lt;&gt;</tt> template is:</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]366
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]367<div class="doc_code">
368<pre>
369static bool isLoopInvariant(const <a href="#Value">Value</a> *V, const Loop *L) {
370 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))
371 return true;
Chris Lattner69bf8a92004-05-23 21:06:58 +0000[diff] [blame]372
Bill Wendling82e2eea2006-10-11 18:00:22 +0000[diff] [blame]373 // <i>Otherwise, it must be an instruction...</i>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]374 return !L-&gt;contains(cast&lt;<a href="#Instruction">Instruction</a>&gt;(V)-&gt;getParent());
375}
376</pre>
377</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]378
379 <p>Note that you should <b>not</b> use an <tt>isa&lt;&gt;</tt> test followed
380 by a <tt>cast&lt;&gt;</tt>, for that use the <tt>dyn_cast&lt;&gt;</tt>
381 operator.</p>
382
383 </dd>
384
385 <dt><tt>dyn_cast&lt;&gt;</tt>:</dt>
386
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]387 <dd><p>The <tt>dyn_cast&lt;&gt;</tt> operator is a "checking cast" operation.
388 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]389 pointer to it (this operator does not work with references). If the operand is
390 not of the correct type, a null pointer is returned. Thus, this works very
Misha Brukman2c122ce2005-11-01 21:12:49 +0000[diff] [blame]391 much like the <tt>dynamic_cast&lt;&gt;</tt> operator in C++, and should be
392 used in the same circumstances. Typically, the <tt>dyn_cast&lt;&gt;</tt>
393 operator is used in an <tt>if</tt> statement or some other flow control
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]394 statement like this:</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]395
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]396<div class="doc_code">
397<pre>
398if (<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]399 // <i>...</i>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]400}
401</pre>
402</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]403
Misha Brukman2c122ce2005-11-01 21:12:49 +0000[diff] [blame]404 <p>This form of the <tt>if</tt> statement effectively combines together a call
405 to <tt>isa&lt;&gt;</tt> and a call to <tt>cast&lt;&gt;</tt> into one
406 statement, which is very convenient.</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]407
Misha Brukman2c122ce2005-11-01 21:12:49 +0000[diff] [blame]408 <p>Note that the <tt>dyn_cast&lt;&gt;</tt> operator, like C++'s
409 <tt>dynamic_cast&lt;&gt;</tt> or Java's <tt>instanceof</tt> operator, can be
410 abused. In particular, you should not use big chained <tt>if/then/else</tt>
411 blocks to check for lots of different variants of classes. If you find
412 yourself wanting to do this, it is much cleaner and more efficient to use the
413 <tt>InstVisitor</tt> class to dispatch over the instruction type directly.</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]414
Misha Brukman2c122ce2005-11-01 21:12:49 +0000[diff] [blame]415 </dd>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]416
Misha Brukman2c122ce2005-11-01 21:12:49 +0000[diff] [blame]417 <dt><tt>cast_or_null&lt;&gt;</tt>: </dt>
418
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]419 <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]420 <tt>cast&lt;&gt;</tt> operator, except that it allows for a null pointer as an
421 argument (which it then propagates). This can sometimes be useful, allowing
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]422 you to combine several null checks into one.</p></dd>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]423
Misha Brukman2c122ce2005-11-01 21:12:49 +0000[diff] [blame]424 <dt><tt>dyn_cast_or_null&lt;&gt;</tt>: </dt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]425
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]426 <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]427 <tt>dyn_cast&lt;&gt;</tt> operator, except that it allows for a null pointer
428 as an argument (which it then propagates). This can sometimes be useful,
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]429 allowing you to combine several null checks into one.</p></dd>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]430
Misha Brukman2c122ce2005-11-01 21:12:49 +0000[diff] [blame]431</dl>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]432
433<p>These five templates can be used with any classes, whether they have a
434v-table or not. To add support for these templates, you simply need to add
435<tt>classof</tt> static methods to the class you are interested casting
436to. Describing this is currently outside the scope of this document, but there
437are lots of examples in the LLVM source base.</p>
438
439</div>
440
Daniel Dunbar6e0d1cb2009-07-25 04:41:11 +0000[diff] [blame]441
442<!-- ======================================================================= -->
443<div class="doc_subsection">
444 <a name="string_apis">Passing strings (the <tt>StringRef</tt>
445and <tt>Twine</tt> classes)</a>
446</div>
447
448<div class="doc_text">
449
450<p>Although LLVM generally does not do much string manipulation, we do have
Chris Lattner81187ae2009-07-25 07:16:59 +0000[diff] [blame]451several important APIs which take strings. Two important examples are the
Daniel Dunbar6e0d1cb2009-07-25 04:41:11 +0000[diff] [blame]452Value class -- which has names for instructions, functions, etc. -- and the
453StringMap class which is used extensively in LLVM and Clang.</p>
454
455<p>These are generic classes, and they need to be able to accept strings which
456may have embedded null characters. Therefore, they cannot simply take
Chris Lattner81187ae2009-07-25 07:16:59 +0000[diff] [blame]457a <tt>const char *</tt>, and taking a <tt>const std::string&amp;</tt> requires
Daniel Dunbar6e0d1cb2009-07-25 04:41:11 +0000[diff] [blame]458clients to perform a heap allocation which is usually unnecessary. Instead,
Benjamin Kramer38e59892010-07-14 22:38:02 +0000[diff] [blame]459many LLVM APIs use a <tt>StringRef</tt> or a <tt>const Twine&amp;</tt> for
460passing strings efficiently.</p>
Daniel Dunbar6e0d1cb2009-07-25 04:41:11 +0000[diff] [blame]461
462</div>
463
464<!-- _______________________________________________________________________ -->
465<div class="doc_subsubsection">
466 <a name="StringRef">The <tt>StringRef</tt> class</a>
467</div>
468
469<div class="doc_text">
470
471<p>The <tt>StringRef</tt> data type represents a reference to a constant string
472(a character array and a length) and supports the common operations available
473on <tt>std:string</tt>, but does not require heap allocation.</p>
474
Chris Lattner81187ae2009-07-25 07:16:59 +0000[diff] [blame]475<p>It can be implicitly constructed using a C style null-terminated string,
476an <tt>std::string</tt>, or explicitly with a character pointer and length.
Daniel Dunbar6e0d1cb2009-07-25 04:41:11 +0000[diff] [blame]477For example, the <tt>StringRef</tt> find function is declared as:</p>
Chris Lattner81187ae2009-07-25 07:16:59 +0000[diff] [blame]478
Benjamin Kramer38e59892010-07-14 22:38:02 +0000[diff] [blame]479<pre class="doc_code">
480 iterator find(StringRef Key);
481</pre>
Daniel Dunbar6e0d1cb2009-07-25 04:41:11 +0000[diff] [blame]482
483<p>and clients can call it using any one of:</p>
484
Benjamin Kramer38e59892010-07-14 22:38:02 +0000[diff] [blame]485<pre class="doc_code">
Daniel Dunbar6e0d1cb2009-07-25 04:41:11 +0000[diff] [blame]486 Map.find("foo"); <i>// Lookup "foo"</i>
487 Map.find(std::string("bar")); <i>// Lookup "bar"</i>
488 Map.find(StringRef("\0baz", 4)); <i>// Lookup "\0baz"</i>
489</pre>
Daniel Dunbar6e0d1cb2009-07-25 04:41:11 +0000[diff] [blame]490
491<p>Similarly, APIs which need to return a string may return a <tt>StringRef</tt>
492instance, which can be used directly or converted to an <tt>std::string</tt>
493using the <tt>str</tt> member function. See
494"<tt><a href="/doxygen/classllvm_1_1StringRef_8h-source.html">llvm/ADT/StringRef.h</a></tt>"
495for more information.</p>
496
497<p>You should rarely use the <tt>StringRef</tt> class directly, because it contains
498pointers to external memory it is not generally safe to store an instance of the
Benjamin Kramer38e59892010-07-14 22:38:02 +0000[diff] [blame]499class (unless you know that the external storage will not be freed). StringRef is
500small and pervasive enough in LLVM that it should always be passed by value.</p>
Daniel Dunbar6e0d1cb2009-07-25 04:41:11 +0000[diff] [blame]501
502</div>
503
504<!-- _______________________________________________________________________ -->
505<div class="doc_subsubsection">
506 <a name="Twine">The <tt>Twine</tt> class</a>
507</div>
508
509<div class="doc_text">
510
511<p>The <tt>Twine</tt> class is an efficient way for APIs to accept concatenated
512strings. For example, a common LLVM paradigm is to name one instruction based on
513the name of another instruction with a suffix, for example:</p>
514
515<div class="doc_code">
516<pre>
517 New = CmpInst::Create(<i>...</i>, SO->getName() + ".cmp");
518</pre>
519</div>
520
521<p>The <tt>Twine</tt> class is effectively a
522lightweight <a href="http://en.wikipedia.org/wiki/Rope_(computer_science)">rope</a>
523which points to temporary (stack allocated) objects. Twines can be implicitly
524constructed as the result of the plus operator applied to strings (i.e., a C
525strings, an <tt>std::string</tt>, or a <tt>StringRef</tt>). The twine delays the
Dan Gohmancf0c9bc2010-02-25 23:51:27 +0000[diff] [blame]526actual concatenation of strings until it is actually required, at which point
Daniel Dunbar6e0d1cb2009-07-25 04:41:11 +0000[diff] [blame]527it can be efficiently rendered directly into a character array. This avoids
528unnecessary heap allocation involved in constructing the temporary results of
529string concatenation. See
530"<tt><a href="/doxygen/classllvm_1_1Twine_8h-source.html">llvm/ADT/Twine.h</a></tt>"
Benjamin Kramere15192b2009-08-05 15:42:44 +0000[diff] [blame]531for more information.</p>
Daniel Dunbar6e0d1cb2009-07-25 04:41:11 +0000[diff] [blame]532
533<p>As with a <tt>StringRef</tt>, <tt>Twine</tt> objects point to external memory
534and should almost never be stored or mentioned directly. They are intended
535solely for use when defining a function which should be able to efficiently
536accept concatenated strings.</p>
537
538</div>
539
540
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]541<!-- ======================================================================= -->
542<div class="doc_subsection">
Misha Brukman2c122ce2005-11-01 21:12:49 +0000[diff] [blame]543 <a name="DEBUG">The <tt>DEBUG()</tt> macro and <tt>-debug</tt> option</a>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]544</div>
545
546<div class="doc_text">
547
548<p>Often when working on your pass you will put a bunch of debugging printouts
549and other code into your pass. After you get it working, you want to remove
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]550it, 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]551across).</p>
552
553<p> Naturally, because of this, you don't want to delete the debug printouts,
554but you don't want them to always be noisy. A standard compromise is to comment
555them out, allowing you to enable them if you need them in the future.</p>
556
Chris Lattner695b78b2005-04-26 22:56:16 +0000[diff] [blame]557<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]558file provides a macro named <tt>DEBUG()</tt> that is a much nicer solution to
559this problem. Basically, you can put arbitrary code into the argument of the
560<tt>DEBUG</tt> macro, and it is only executed if '<tt>opt</tt>' (or any other
561tool) is run with the '<tt>-debug</tt>' command line argument:</p>
562
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]563<div class="doc_code">
564<pre>
Daniel Dunbar06388ae2009-07-25 01:55:32 +0000[diff] [blame]565DEBUG(errs() &lt;&lt; "I am here!\n");
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]566</pre>
567</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]568
569<p>Then you can run your pass like this:</p>
570
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]571<div class="doc_code">
572<pre>
573$ opt &lt; a.bc &gt; /dev/null -mypass
Bill Wendling82e2eea2006-10-11 18:00:22 +0000[diff] [blame]574<i>&lt;no output&gt;</i>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]575$ opt &lt; a.bc &gt; /dev/null -mypass -debug
576I am here!
577</pre>
578</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]579
580<p>Using the <tt>DEBUG()</tt> macro instead of a home-brewed solution allows you
581to not have to create "yet another" command line option for the debug output for
582your pass. Note that <tt>DEBUG()</tt> macros are disabled for optimized builds,
583so they do not cause a performance impact at all (for the same reason, they
584should also not contain side-effects!).</p>
585
586<p>One additional nice thing about the <tt>DEBUG()</tt> macro is that you can
587enable or disable it directly in gdb. Just use "<tt>set DebugFlag=0</tt>" or
588"<tt>set DebugFlag=1</tt>" from the gdb if the program is running. If the
589program hasn't been started yet, you can always just run it with
590<tt>-debug</tt>.</p>
591
592</div>
593
594<!-- _______________________________________________________________________ -->
595<div class="doc_subsubsection">
Chris Lattnerc9151082005-04-26 22:57:07 +0000[diff] [blame]596 <a name="DEBUG_TYPE">Fine grained debug info with <tt>DEBUG_TYPE</tt> and
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]597 the <tt>-debug-only</tt> option</a>
598</div>
599
600<div class="doc_text">
601
602<p>Sometimes you may find yourself in a situation where enabling <tt>-debug</tt>
603just turns on <b>too much</b> information (such as when working on the code
604generator). If you want to enable debug information with more fine-grained
605control, you define the <tt>DEBUG_TYPE</tt> macro and the <tt>-debug</tt> only
606option as follows:</p>
607
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]608<div class="doc_code">
609<pre>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]610#undef DEBUG_TYPE
Daniel Dunbar06388ae2009-07-25 01:55:32 +0000[diff] [blame]611DEBUG(errs() &lt;&lt; "No debug type\n");
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]612#define DEBUG_TYPE "foo"
Daniel Dunbar06388ae2009-07-25 01:55:32 +0000[diff] [blame]613DEBUG(errs() &lt;&lt; "'foo' debug type\n");
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]614#undef DEBUG_TYPE
615#define DEBUG_TYPE "bar"
Daniel Dunbar06388ae2009-07-25 01:55:32 +0000[diff] [blame]616DEBUG(errs() &lt;&lt; "'bar' debug type\n"));
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]617#undef DEBUG_TYPE
618#define DEBUG_TYPE ""
Daniel Dunbar06388ae2009-07-25 01:55:32 +0000[diff] [blame]619DEBUG(errs() &lt;&lt; "No debug type (2)\n");
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]620</pre>
621</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]622
623<p>Then you can run your pass like this:</p>
624
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]625<div class="doc_code">
626<pre>
627$ opt &lt; a.bc &gt; /dev/null -mypass
Bill Wendling82e2eea2006-10-11 18:00:22 +0000[diff] [blame]628<i>&lt;no output&gt;</i>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]629$ opt &lt; a.bc &gt; /dev/null -mypass -debug
630No debug type
631'foo' debug type
632'bar' debug type
633No debug type (2)
634$ opt &lt; a.bc &gt; /dev/null -mypass -debug-only=foo
635'foo' debug type
636$ opt &lt; a.bc &gt; /dev/null -mypass -debug-only=bar
637'bar' debug type
638</pre>
639</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]640
641<p>Of course, in practice, you should only set <tt>DEBUG_TYPE</tt> at the top of
642a 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]643you <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]644<tt>#undef</tt>'s). Also, you should use names more meaningful than "foo" and
645"bar", because there is no system in place to ensure that names do not
646conflict. If two different modules use the same string, they will all be turned
647on when the name is specified. This allows, for example, all debug information
648for instruction scheduling to be enabled with <tt>-debug-type=InstrSched</tt>,
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]649even if the source lives in multiple files.</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]650
Daniel Dunbarc3c92392009-08-07 23:48:59 +0000[diff] [blame]651<p>The <tt>DEBUG_WITH_TYPE</tt> macro is also available for situations where you
652would like to set <tt>DEBUG_TYPE</tt>, but only for one specific <tt>DEBUG</tt>
653statement. It takes an additional first parameter, which is the type to use. For
Benjamin Kramer8040cd32009-10-12 14:46:08 +0000[diff] [blame]654example, the preceding example could be written as:</p>
Daniel Dunbarc3c92392009-08-07 23:48:59 +0000[diff] [blame]655
656
657<div class="doc_code">
658<pre>
659DEBUG_WITH_TYPE("", errs() &lt;&lt; "No debug type\n");
660DEBUG_WITH_TYPE("foo", errs() &lt;&lt; "'foo' debug type\n");
661DEBUG_WITH_TYPE("bar", errs() &lt;&lt; "'bar' debug type\n"));
662DEBUG_WITH_TYPE("", errs() &lt;&lt; "No debug type (2)\n");
663</pre>
664</div>
665
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]666</div>
667
668<!-- ======================================================================= -->
669<div class="doc_subsection">
Chris Lattner0be6fdf2006-12-19 21:46:21 +0000[diff] [blame]670 <a name="Statistic">The <tt>Statistic</tt> class &amp; <tt>-stats</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]671 option</a>
672</div>
673
674<div class="doc_text">
675
676<p>The "<tt><a
Chris Lattner695b78b2005-04-26 22:56:16 +0000[diff] [blame]677href="/doxygen/Statistic_8h-source.html">llvm/ADT/Statistic.h</a></tt>" file
Chris Lattner0be6fdf2006-12-19 21:46:21 +0000[diff] [blame]678provides a class named <tt>Statistic</tt> that is used as a unified way to
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]679keep track of what the LLVM compiler is doing and how effective various
680optimizations are. It is useful to see what optimizations are contributing to
681making a particular program run faster.</p>
682
683<p>Often you may run your pass on some big program, and you're interested to see
684how many times it makes a certain transformation. Although you can do this with
685hand 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]686for big programs. Using the <tt>Statistic</tt> class makes it very easy to
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]687keep track of this information, and the calculated information is presented in a
688uniform manner with the rest of the passes being executed.</p>
689
690<p>There are many examples of <tt>Statistic</tt> uses, but the basics of using
691it are as follows:</p>
692
693<ol>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]694 <li><p>Define your statistic like this:</p>
695
696<div class="doc_code">
697<pre>
Chris Lattner0be6fdf2006-12-19 21:46:21 +0000[diff] [blame]698#define <a href="#DEBUG_TYPE">DEBUG_TYPE</a> "mypassname" <i>// This goes before any #includes.</i>
699STATISTIC(NumXForms, "The # of times I did stuff");
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]700</pre>
701</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]702
Chris Lattner0be6fdf2006-12-19 21:46:21 +0000[diff] [blame]703 <p>The <tt>STATISTIC</tt> macro defines a static variable, whose name is
704 specified by the first argument. The pass name is taken from the DEBUG_TYPE
705 macro, and the description is taken from the second argument. The variable
Reid Spencer06565dc2007-01-12 17:11:23 +0000[diff] [blame]706 defined ("NumXForms" in this case) acts like an unsigned integer.</p></li>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]707
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]708 <li><p>Whenever you make a transformation, bump the counter:</p>
709
710<div class="doc_code">
711<pre>
Bill Wendling82e2eea2006-10-11 18:00:22 +0000[diff] [blame]712++NumXForms; // <i>I did stuff!</i>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]713</pre>
714</div>
715
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]716 </li>
717 </ol>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]718
719 <p>That's all you have to do. To get '<tt>opt</tt>' to print out the
720 statistics gathered, use the '<tt>-stats</tt>' option:</p>
721
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]722<div class="doc_code">
723<pre>
724$ opt -stats -mypassname &lt; program.bc &gt; /dev/null
Bill Wendling82e2eea2006-10-11 18:00:22 +0000[diff] [blame]725<i>... statistics output ...</i>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]726</pre>
727</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]728
Reid Spencer6b6c73e2007-02-09 16:00:28 +0000[diff] [blame]729 <p> When running <tt>opt</tt> on a C file from the SPEC benchmark
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]730suite, it gives a report that looks like this:</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]731
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]732<div class="doc_code">
733<pre>
Gabor Greif04367bf2007-07-06 22:07:22 +0000[diff] [blame]734 7646 bitcodewriter - Number of normal instructions
735 725 bitcodewriter - Number of oversized instructions
736 129996 bitcodewriter - Number of bitcode bytes written
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]737 2817 raise - Number of insts DCEd or constprop'd
738 3213 raise - Number of cast-of-self removed
739 5046 raise - Number of expression trees converted
740 75 raise - Number of other getelementptr's formed
741 138 raise - Number of load/store peepholes
742 42 deadtypeelim - Number of unused typenames removed from symtab
743 392 funcresolve - Number of varargs functions resolved
744 27 globaldce - Number of global variables removed
745 2 adce - Number of basic blocks removed
746 134 cee - Number of branches revectored
747 49 cee - Number of setcc instruction eliminated
748 532 gcse - Number of loads removed
749 2919 gcse - Number of instructions removed
750 86 indvars - Number of canonical indvars added
751 87 indvars - Number of aux indvars removed
752 25 instcombine - Number of dead inst eliminate
753 434 instcombine - Number of insts combined
754 248 licm - Number of load insts hoisted
755 1298 licm - Number of insts hoisted to a loop pre-header
756 3 licm - Number of insts hoisted to multiple loop preds (bad, no loop pre-header)
757 75 mem2reg - Number of alloca's promoted
758 1444 cfgsimplify - Number of blocks simplified
759</pre>
760</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]761
762<p>Obviously, with so many optimizations, having a unified framework for this
763stuff is very nice. Making your pass fit well into the framework makes it more
764maintainable and useful.</p>
765
766</div>
767
Chris Lattnerf623a082005-10-17 01:36:23 +0000[diff] [blame]768<!-- ======================================================================= -->
769<div class="doc_subsection">
770 <a name="ViewGraph">Viewing graphs while debugging code</a>
771</div>
772
773<div class="doc_text">
774
775<p>Several of the important data structures in LLVM are graphs: for example
776CFGs made out of LLVM <a href="#BasicBlock">BasicBlock</a>s, CFGs made out of
777LLVM <a href="CodeGenerator.html#machinebasicblock">MachineBasicBlock</a>s, and
778<a href="CodeGenerator.html#selectiondag_intro">Instruction Selection
779DAGs</a>. In many cases, while debugging various parts of the compiler, it is
780nice to instantly visualize these graphs.</p>
781
782<p>LLVM provides several callbacks that are available in a debug build to do
783exactly that. If you call the <tt>Function::viewCFG()</tt> method, for example,
784the current LLVM tool will pop up a window containing the CFG for the function
785where each basic block is a node in the graph, and each node contains the
786instructions in the block. Similarly, there also exists
787<tt>Function::viewCFGOnly()</tt> (does not include the instructions), the
788<tt>MachineFunction::viewCFG()</tt> and <tt>MachineFunction::viewCFGOnly()</tt>,
789and the <tt>SelectionDAG::viewGraph()</tt> methods. Within GDB, for example,
Jim Laskey543a0ee2006-10-02 12:28:07 +0000[diff] [blame]790you can usually use something like <tt>call DAG.viewGraph()</tt> to pop
Chris Lattnerf623a082005-10-17 01:36:23 +0000[diff] [blame]791up a window. Alternatively, you can sprinkle calls to these functions in your
792code in places you want to debug.</p>
793
794<p>Getting this to work requires a small amount of configuration. On Unix
795systems with X11, install the <a href="http://www.graphviz.org">graphviz</a>
796toolkit, and make sure 'dot' and 'gv' are in your path. If you are running on
797Mac OS/X, download and install the Mac OS/X <a
798href="http://www.pixelglow.com/graphviz/">Graphviz program</a>, and add
Reid Spencer128a7a72007-02-03 21:06:43 +0000[diff] [blame]799<tt>/Applications/Graphviz.app/Contents/MacOS/</tt> (or wherever you install
Chris Lattnerf623a082005-10-17 01:36:23 +0000[diff] [blame]800it) to your path. Once in your system and path are set up, rerun the LLVM
801configure script and rebuild LLVM to enable this functionality.</p>
802
Jim Laskey543a0ee2006-10-02 12:28:07 +0000[diff] [blame]803<p><tt>SelectionDAG</tt> has been extended to make it easier to locate
804<i>interesting</i> nodes in large complex graphs. From gdb, if you
805<tt>call DAG.setGraphColor(<i>node</i>, "<i>color</i>")</tt>, then the
Reid Spencer128a7a72007-02-03 21:06:43 +0000[diff] [blame]806next <tt>call DAG.viewGraph()</tt> would highlight the node in the
Jim Laskey543a0ee2006-10-02 12:28:07 +0000[diff] [blame]807specified color (choices of colors can be found at <a
Chris Lattner302da1e2007-02-03 03:05:57 +0000[diff] [blame]808href="http://www.graphviz.org/doc/info/colors.html">colors</a>.) More
Jim Laskey543a0ee2006-10-02 12:28:07 +0000[diff] [blame]809complex node attributes can be provided with <tt>call
810DAG.setGraphAttrs(<i>node</i>, "<i>attributes</i>")</tt> (choices can be
811found at <a href="http://www.graphviz.org/doc/info/attrs.html">Graph
812Attributes</a>.) If you want to restart and clear all the current graph
813attributes, then you can <tt>call DAG.clearGraphAttrs()</tt>. </p>
814
Chris Lattnerf623a082005-10-17 01:36:23 +0000[diff] [blame]815</div>
816
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]817<!-- *********************************************************************** -->
818<div class="doc_section">
819 <a name="datastructure">Picking the Right Data Structure for a Task</a>
820</div>
821<!-- *********************************************************************** -->
822
823<div class="doc_text">
824
Reid Spencer128a7a72007-02-03 21:06:43 +0000[diff] [blame]825<p>LLVM has a plethora of data structures in the <tt>llvm/ADT/</tt> directory,
826 and we commonly use STL data structures. This section describes the trade-offs
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]827 you should consider when you pick one.</p>
828
829<p>
830The first step is a choose your own adventure: do you want a sequential
831container, a set-like container, or a map-like container? The most important
832thing when choosing a container is the algorithmic properties of how you plan to
833access the container. Based on that, you should use:</p>
834
835<ul>
Reid Spencer128a7a72007-02-03 21:06:43 +0000[diff] [blame]836<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]837 of an value based on another value. Map-like containers also support
838 efficient queries for containment (whether a key is in the map). Map-like
839 containers generally do not support efficient reverse mapping (values to
840 keys). If you need that, use two maps. Some map-like containers also
841 support efficient iteration through the keys in sorted order. Map-like
842 containers are the most expensive sort, only use them if you need one of
843 these capabilities.</li>
844
845<li>a <a href="#ds_set">set-like</a> container if you need to put a bunch of
846 stuff into a container that automatically eliminates duplicates. Some
847 set-like containers support efficient iteration through the elements in
848 sorted order. Set-like containers are more expensive than sequential
849 containers.
850</li>
851
852<li>a <a href="#ds_sequential">sequential</a> container provides
853 the most efficient way to add elements and keeps track of the order they are
854 added to the collection. They permit duplicates and support efficient
Reid Spencer128a7a72007-02-03 21:06:43 +0000[diff] [blame]855 iteration, but do not support efficient look-up based on a key.
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]856</li>
857
Chris Lattnerdced9fb2009-07-25 07:22:20 +0000[diff] [blame]858<li>a <a href="#ds_string">string</a> container is a specialized sequential
859 container or reference structure that is used for character or byte
860 arrays.</li>
861
Daniel Berlin1939ace2007-09-24 17:52:25 +0000[diff] [blame]862<li>a <a href="#ds_bit">bit</a> container provides an efficient way to store and
863 perform set operations on sets of numeric id's, while automatically
864 eliminating duplicates. Bit containers require a maximum of 1 bit for each
865 identifier you want to store.
866</li>
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]867</ul>
868
869<p>
Reid Spencer128a7a72007-02-03 21:06:43 +0000[diff] [blame]870Once the proper category of container is determined, you can fine tune the
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]871memory use, constant factors, and cache behaviors of access by intelligently
Reid Spencer128a7a72007-02-03 21:06:43 +0000[diff] [blame]872picking a member of the category. Note that constant factors and cache behavior
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]873can be a big deal. If you have a vector that usually only contains a few
874elements (but could contain many), for example, it's much better to use
875<a href="#dss_smallvector">SmallVector</a> than <a href="#dss_vector">vector</a>
876. Doing so avoids (relatively) expensive malloc/free calls, which dwarf the
877cost of adding the elements to the container. </p>
878
879</div>
880
881<!-- ======================================================================= -->
882<div class="doc_subsection">
883 <a name="ds_sequential">Sequential Containers (std::vector, std::list, etc)</a>
884</div>
885
886<div class="doc_text">
887There are a variety of sequential containers available for you, based on your
888needs. Pick the first in this section that will do what you want.
889</div>
890
891<!-- _______________________________________________________________________ -->
892<div class="doc_subsubsection">
893 <a name="dss_fixedarrays">Fixed Size Arrays</a>
894</div>
895
896<div class="doc_text">
897<p>Fixed size arrays are very simple and very fast. They are good if you know
898exactly how many elements you have, or you have a (low) upper bound on how many
899you have.</p>
900</div>
901
902<!-- _______________________________________________________________________ -->
903<div class="doc_subsubsection">
904 <a name="dss_heaparrays">Heap Allocated Arrays</a>
905</div>
906
907<div class="doc_text">
908<p>Heap allocated arrays (new[] + delete[]) are also simple. They are good if
909the number of elements is variable, if you know how many elements you will need
910before the array is allocated, and if the array is usually large (if not,
911consider a <a href="#dss_smallvector">SmallVector</a>). The cost of a heap
912allocated array is the cost of the new/delete (aka malloc/free). Also note that
913if you are allocating an array of a type with a constructor, the constructor and
Reid Spencer128a7a72007-02-03 21:06:43 +0000[diff] [blame]914destructors will be run for every element in the array (re-sizable vectors only
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]915construct those elements actually used).</p>
916</div>
917
918<!-- _______________________________________________________________________ -->
919<div class="doc_subsubsection">
920 <a name="dss_smallvector">"llvm/ADT/SmallVector.h"</a>
921</div>
922
923<div class="doc_text">
924<p><tt>SmallVector&lt;Type, N&gt;</tt> is a simple class that looks and smells
925just like <tt>vector&lt;Type&gt;</tt>:
926it supports efficient iteration, lays out elements in memory order (so you can
927do pointer arithmetic between elements), supports efficient push_back/pop_back
928operations, supports efficient random access to its elements, etc.</p>
929
930<p>The advantage of SmallVector is that it allocates space for
931some number of elements (N) <b>in the object itself</b>. Because of this, if
932the SmallVector is dynamically smaller than N, no malloc is performed. This can
933be a big win in cases where the malloc/free call is far more expensive than the
934code that fiddles around with the elements.</p>
935
936<p>This is good for vectors that are "usually small" (e.g. the number of
937predecessors/successors of a block is usually less than 8). On the other hand,
938this makes the size of the SmallVector itself large, so you don't want to
939allocate lots of them (doing so will waste a lot of space). As such,
940SmallVectors are most useful when on the stack.</p>
941
942<p>SmallVector also provides a nice portable and efficient replacement for
943<tt>alloca</tt>.</p>
944
945</div>
946
947<!-- _______________________________________________________________________ -->
948<div class="doc_subsubsection">
949 <a name="dss_vector">&lt;vector&gt;</a>
950</div>
951
952<div class="doc_text">
953<p>
954std::vector is well loved and respected. It is useful when SmallVector isn't:
955when the size of the vector is often large (thus the small optimization will
956rarely be a benefit) or if you will be allocating many instances of the vector
957itself (which would waste space for elements that aren't in the container).
958vector is also useful when interfacing with code that expects vectors :).
959</p>
Chris Lattner32d84762007-02-05 06:30:51 +0000[diff] [blame]960
961<p>One worthwhile note about std::vector: avoid code like this:</p>
962
963<div class="doc_code">
964<pre>
965for ( ... ) {
Chris Lattner9bb3dbb2007-03-28 18:27:57 +0000[diff] [blame]966 std::vector&lt;foo&gt; V;
Chris Lattner32d84762007-02-05 06:30:51 +0000[diff] [blame]967 use V;
968}
969</pre>
970</div>
971
972<p>Instead, write this as:</p>
973
974<div class="doc_code">
975<pre>
Chris Lattner9bb3dbb2007-03-28 18:27:57 +0000[diff] [blame]976std::vector&lt;foo&gt; V;
Chris Lattner32d84762007-02-05 06:30:51 +0000[diff] [blame]977for ( ... ) {
978 use V;
979 V.clear();
980}
981</pre>
982</div>
983
984<p>Doing so will save (at least) one heap allocation and free per iteration of
985the loop.</p>
986
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]987</div>
988
989<!-- _______________________________________________________________________ -->
990<div class="doc_subsubsection">
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]991 <a name="dss_deque">&lt;deque&gt;</a>
992</div>
993
994<div class="doc_text">
995<p>std::deque is, in some senses, a generalized version of std::vector. Like
996std::vector, it provides constant time random access and other similar
997properties, but it also provides efficient access to the front of the list. It
998does not guarantee continuity of elements within memory.</p>
999
1000<p>In exchange for this extra flexibility, std::deque has significantly higher
1001constant factor costs than std::vector. If possible, use std::vector or
1002something cheaper.</p>
1003</div>
1004
1005<!-- _______________________________________________________________________ -->
1006<div class="doc_subsubsection">
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]1007 <a name="dss_list">&lt;list&gt;</a>
1008</div>
1009
1010<div class="doc_text">
1011<p>std::list is an extremely inefficient class that is rarely useful.
1012It performs a heap allocation for every element inserted into it, thus having an
1013extremely high constant factor, particularly for small data types. std::list
1014also only supports bidirectional iteration, not random access iteration.</p>
1015
1016<p>In exchange for this high cost, std::list supports efficient access to both
1017ends of the list (like std::deque, but unlike std::vector or SmallVector). In
1018addition, the iterator invalidation characteristics of std::list are stronger
1019than that of a vector class: inserting or removing an element into the list does
1020not invalidate iterator or pointers to other elements in the list.</p>
1021</div>
1022
1023<!-- _______________________________________________________________________ -->
1024<div class="doc_subsubsection">
Gabor Greif3899e492009-02-27 11:37:41 +0000[diff] [blame]1025 <a name="dss_ilist">llvm/ADT/ilist.h</a>
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]1026</div>
1027
1028<div class="doc_text">
1029<p><tt>ilist&lt;T&gt;</tt> implements an 'intrusive' doubly-linked list. It is
1030intrusive, because it requires the element to store and provide access to the
1031prev/next pointers for the list.</p>
1032
Gabor Greif2946d1c2009-02-27 12:02:19 +0000[diff] [blame]1033<p><tt>ilist</tt> has the same drawbacks as <tt>std::list</tt>, and additionally
1034requires an <tt>ilist_traits</tt> implementation for the element type, but it
1035provides some novel characteristics. In particular, it can efficiently store
1036polymorphic objects, the traits class is informed when an element is inserted or
Gabor Greif0cbcabe2009-03-12 09:47:03 +0000[diff] [blame]1037removed from the list, and <tt>ilist</tt>s are guaranteed to support a
1038constant-time splice operation.</p>
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]1039
Gabor Greif0cbcabe2009-03-12 09:47:03 +0000[diff] [blame]1040<p>These properties are exactly what we want for things like
1041<tt>Instruction</tt>s and basic blocks, which is why these are implemented with
1042<tt>ilist</tt>s.</p>
Gabor Greif3899e492009-02-27 11:37:41 +0000[diff] [blame]1043
1044Related classes of interest are explained in the following subsections:
1045 <ul>
Gabor Greif01862502009-02-27 13:28:07 +0000[diff] [blame]1046 <li><a href="#dss_ilist_traits">ilist_traits</a></li>
Gabor Greif2946d1c2009-02-27 12:02:19 +0000[diff] [blame]1047 <li><a href="#dss_iplist">iplist</a></li>
Gabor Greif3899e492009-02-27 11:37:41 +0000[diff] [blame]1048 <li><a href="#dss_ilist_node">llvm/ADT/ilist_node.h</a></li>
Gabor Greif6a65f422009-03-12 10:30:31 +0000[diff] [blame]1049 <li><a href="#dss_ilist_sentinel">Sentinels</a></li>
Gabor Greif3899e492009-02-27 11:37:41 +0000[diff] [blame]1050 </ul>
1051</div>
1052
1053<!-- _______________________________________________________________________ -->
1054<div class="doc_subsubsection">
Gabor Greif01862502009-02-27 13:28:07 +0000[diff] [blame]1055 <a name="dss_ilist_traits">ilist_traits</a>
1056</div>
1057
1058<div class="doc_text">
1059<p><tt>ilist_traits&lt;T&gt;</tt> is <tt>ilist&lt;T&gt;</tt>'s customization
1060mechanism. <tt>iplist&lt;T&gt;</tt> (and consequently <tt>ilist&lt;T&gt;</tt>)
1061publicly derive from this traits class.</p>
1062</div>
1063
1064<!-- _______________________________________________________________________ -->
1065<div class="doc_subsubsection">
Gabor Greif2946d1c2009-02-27 12:02:19 +0000[diff] [blame]1066 <a name="dss_iplist">iplist</a>
1067</div>
1068
1069<div class="doc_text">
1070<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]1071supports a slightly narrower interface. Notably, inserters from
1072<tt>T&amp;</tt> are absent.</p>
Gabor Greif01862502009-02-27 13:28:07 +0000[diff] [blame]1073
1074<p><tt>ilist_traits&lt;T&gt;</tt> is a public base of this class and can be
1075used for a wide variety of customizations.</p>
Gabor Greif2946d1c2009-02-27 12:02:19 +0000[diff] [blame]1076</div>
1077
1078<!-- _______________________________________________________________________ -->
1079<div class="doc_subsubsection">
Gabor Greif3899e492009-02-27 11:37:41 +0000[diff] [blame]1080 <a name="dss_ilist_node">llvm/ADT/ilist_node.h</a>
1081</div>
1082
1083<div class="doc_text">
1084<p><tt>ilist_node&lt;T&gt;</tt> implements a the forward and backward links
1085that are expected by the <tt>ilist&lt;T&gt;</tt> (and analogous containers)
1086in the default manner.</p>
1087
1088<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]1089<tt>T</tt>, usually <tt>T</tt> publicly derives from
1090<tt>ilist_node&lt;T&gt;</tt>.</p>
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]1091</div>
1092
1093<!-- _______________________________________________________________________ -->
1094<div class="doc_subsubsection">
Gabor Greif6a65f422009-03-12 10:30:31 +0000[diff] [blame]1095 <a name="dss_ilist_sentinel">Sentinels</a>
1096</div>
1097
1098<div class="doc_text">
Dan Gohmancf0c9bc2010-02-25 23:51:27 +0000[diff] [blame]1099<p><tt>ilist</tt>s have another specialty that must be considered. To be a good
Gabor Greif6a65f422009-03-12 10:30:31 +0000[diff] [blame]1100citizen in the C++ ecosystem, it needs to support the standard container
1101operations, such as <tt>begin</tt> and <tt>end</tt> iterators, etc. Also, the
1102<tt>operator--</tt> must work correctly on the <tt>end</tt> iterator in the
1103case of non-empty <tt>ilist</tt>s.</p>
1104
1105<p>The only sensible solution to this problem is to allocate a so-called
1106<i>sentinel</i> along with the intrusive list, which serves as the <tt>end</tt>
1107iterator, providing the back-link to the last element. However conforming to the
1108C++ convention it is illegal to <tt>operator++</tt> beyond the sentinel and it
1109also must not be dereferenced.</p>
1110
1111<p>These constraints allow for some implementation freedom to the <tt>ilist</tt>
1112how to allocate and store the sentinel. The corresponding policy is dictated
1113by <tt>ilist_traits&lt;T&gt;</tt>. By default a <tt>T</tt> gets heap-allocated
1114whenever the need for a sentinel arises.</p>
1115
1116<p>While the default policy is sufficient in most cases, it may break down when
1117<tt>T</tt> does not provide a default constructor. Also, in the case of many
1118instances of <tt>ilist</tt>s, the memory overhead of the associated sentinels
1119is wasted. To alleviate the situation with numerous and voluminous
1120<tt>T</tt>-sentinels, sometimes a trick is employed, leading to <i>ghostly
1121sentinels</i>.</p>
1122
1123<p>Ghostly sentinels are obtained by specially-crafted <tt>ilist_traits&lt;T&gt;</tt>
1124which superpose the sentinel with the <tt>ilist</tt> instance in memory. Pointer
1125arithmetic is used to obtain the sentinel, which is relative to the
1126<tt>ilist</tt>'s <tt>this</tt> pointer. The <tt>ilist</tt> is augmented by an
1127extra pointer, which serves as the back-link of the sentinel. This is the only
1128field in the ghostly sentinel which can be legally accessed.</p>
1129</div>
1130
1131<!-- _______________________________________________________________________ -->
1132<div class="doc_subsubsection">
Chris Lattnerc5722432007-02-03 19:49:31 +0000[diff] [blame]1133 <a name="dss_other">Other Sequential Container options</a>
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]1134</div>
1135
1136<div class="doc_text">
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1137<p>Other STL containers are available, such as std::string.</p>
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]1138
1139<p>There are also various STL adapter classes such as std::queue,
1140std::priority_queue, std::stack, etc. These provide simplified access to an
1141underlying container but don't affect the cost of the container itself.</p>
1142
1143</div>
1144
1145
1146<!-- ======================================================================= -->
1147<div class="doc_subsection">
1148 <a name="ds_set">Set-Like Containers (std::set, SmallSet, SetVector, etc)</a>
1149</div>
1150
1151<div class="doc_text">
1152
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1153<p>Set-like containers are useful when you need to canonicalize multiple values
1154into a single representation. There are several different choices for how to do
1155this, providing various trade-offs.</p>
1156
1157</div>
1158
1159
1160<!-- _______________________________________________________________________ -->
1161<div class="doc_subsubsection">
1162 <a name="dss_sortedvectorset">A sorted 'vector'</a>
1163</div>
1164
1165<div class="doc_text">
1166
Chris Lattner3b23a8c2007-02-03 08:10:45 +0000[diff] [blame]1167<p>If you intend to insert a lot of elements, then do a lot of queries, a
1168great approach is to use a vector (or other sequential container) with
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1169std::sort+std::unique to remove duplicates. This approach works really well if
Chris Lattner3b23a8c2007-02-03 08:10:45 +0000[diff] [blame]1170your usage pattern has these two distinct phases (insert then query), and can be
1171coupled with a good choice of <a href="#ds_sequential">sequential container</a>.
1172</p>
1173
1174<p>
1175This combination provides the several nice properties: the result data is
1176contiguous in memory (good for cache locality), has few allocations, is easy to
1177address (iterators in the final vector are just indices or pointers), and can be
1178efficiently queried with a standard binary or radix search.</p>
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1179
1180</div>
1181
1182<!-- _______________________________________________________________________ -->
1183<div class="doc_subsubsection">
1184 <a name="dss_smallset">"llvm/ADT/SmallSet.h"</a>
1185</div>
1186
1187<div class="doc_text">
1188
Reid Spencer128a7a72007-02-03 21:06:43 +0000[diff] [blame]1189<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]1190are 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]1191has space for N elements in place (thus, if the set is dynamically smaller than
Chris Lattner14868db2007-02-03 08:20:15 +0000[diff] [blame]1192N, no malloc traffic is required) and accesses them with a simple linear search.
1193When the set grows beyond 'N' elements, it allocates a more expensive representation that
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1194guarantees efficient access (for most types, it falls back to std::set, but for
Chris Lattner14868db2007-02-03 08:20:15 +0000[diff] [blame]1195pointers it uses something far better, <a
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1196href="#dss_smallptrset">SmallPtrSet</a>).</p>
1197
1198<p>The magic of this class is that it handles small sets extremely efficiently,
1199but gracefully handles extremely large sets without loss of efficiency. The
1200drawback is that the interface is quite small: it supports insertion, queries
1201and erasing, but does not support iteration.</p>
1202
1203</div>
1204
1205<!-- _______________________________________________________________________ -->
1206<div class="doc_subsubsection">
1207 <a name="dss_smallptrset">"llvm/ADT/SmallPtrSet.h"</a>
1208</div>
1209
1210<div class="doc_text">
1211
Gabor Greif4de73682010-03-26 19:30:47 +0000[diff] [blame]1212<p>SmallPtrSet has all the advantages of <tt>SmallSet</tt> (and a <tt>SmallSet</tt> of pointers is
1213transparently implemented with a <tt>SmallPtrSet</tt>), but also supports iterators. If
Chris Lattner14868db2007-02-03 08:20:15 +0000[diff] [blame]1214more than 'N' insertions are performed, a single quadratically
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1215probed hash table is allocated and grows as needed, providing extremely
1216efficient access (constant time insertion/deleting/queries with low constant
1217factors) and is very stingy with malloc traffic.</p>
1218
Gabor Greif4de73682010-03-26 19:30:47 +0000[diff] [blame]1219<p>Note that, unlike <tt>std::set</tt>, the iterators of <tt>SmallPtrSet</tt> are invalidated
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1220whenever an insertion occurs. Also, the values visited by the iterators are not
1221visited in sorted order.</p>
1222
1223</div>
1224
1225<!-- _______________________________________________________________________ -->
1226<div class="doc_subsubsection">
Chris Lattnerc28476f2007-09-30 00:58:59 +0000[diff] [blame]1227 <a name="dss_denseset">"llvm/ADT/DenseSet.h"</a>
1228</div>
1229
1230<div class="doc_text">
1231
1232<p>
1233DenseSet is a simple quadratically probed hash table. It excels at supporting
1234small values: it uses a single allocation to hold all of the pairs that
1235are currently inserted in the set. DenseSet is a great way to unique small
1236values that are not simple pointers (use <a
1237href="#dss_smallptrset">SmallPtrSet</a> for pointers). Note that DenseSet has
1238the same requirements for the value type that <a
1239href="#dss_densemap">DenseMap</a> has.
1240</p>
1241
1242</div>
1243
1244<!-- _______________________________________________________________________ -->
1245<div class="doc_subsubsection">
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1246 <a name="dss_FoldingSet">"llvm/ADT/FoldingSet.h"</a>
1247</div>
1248
1249<div class="doc_text">
1250
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]1251<p>
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1252FoldingSet is an aggregate class that is really good at uniquing
1253expensive-to-create or polymorphic objects. It is a combination of a chained
1254hash table with intrusive links (uniqued objects are required to inherit from
Chris Lattner14868db2007-02-03 08:20:15 +0000[diff] [blame]1255FoldingSetNode) that uses <a href="#dss_smallvector">SmallVector</a> as part of
1256its ID process.</p>
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1257
Chris Lattner14868db2007-02-03 08:20:15 +0000[diff] [blame]1258<p>Consider a case where you want to implement a "getOrCreateFoo" method for
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1259a complex object (for example, a node in the code generator). The client has a
1260description of *what* it wants to generate (it knows the opcode and all the
1261operands), 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]1262only to find out it already exists, at which point we would have to delete it
1263and return the node that already exists.
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]1264</p>
1265
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1266<p>To support this style of client, FoldingSet perform a query with a
1267FoldingSetNodeID (which wraps SmallVector) that can be used to describe the
1268element that we want to query for. The query either returns the element
1269matching the ID or it returns an opaque ID that indicates where insertion should
Chris Lattner14868db2007-02-03 08:20:15 +0000[diff] [blame]1270take place. Construction of the ID usually does not require heap traffic.</p>
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1271
1272<p>Because FoldingSet uses intrusive links, it can support polymorphic objects
1273in the set (for example, you can have SDNode instances mixed with LoadSDNodes).
1274Because the elements are individually allocated, pointers to the elements are
1275stable: inserting or removing elements does not invalidate any pointers to other
1276elements.
1277</p>
1278
1279</div>
1280
1281<!-- _______________________________________________________________________ -->
1282<div class="doc_subsubsection">
1283 <a name="dss_set">&lt;set&gt;</a>
1284</div>
1285
1286<div class="doc_text">
1287
Chris Lattnerc5722432007-02-03 19:49:31 +0000[diff] [blame]1288<p><tt>std::set</tt> is a reasonable all-around set class, which is decent at
1289many things but great at nothing. std::set allocates memory for each element
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1290inserted (thus it is very malloc intensive) and typically stores three pointers
Chris Lattner14868db2007-02-03 08:20:15 +0000[diff] [blame]1291per element in the set (thus adding a large amount of per-element space
1292overhead). It offers guaranteed log(n) performance, which is not particularly
Chris Lattnerc5722432007-02-03 19:49:31 +0000[diff] [blame]1293fast from a complexity standpoint (particularly if the elements of the set are
1294expensive to compare, like strings), and has extremely high constant factors for
1295lookup, insertion and removal.</p>
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1296
Chris Lattner14868db2007-02-03 08:20:15 +0000[diff] [blame]1297<p>The advantages of std::set are that its iterators are stable (deleting or
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1298inserting an element from the set does not affect iterators or pointers to other
1299elements) and that iteration over the set is guaranteed to be in sorted order.
1300If the elements in the set are large, then the relative overhead of the pointers
1301and malloc traffic is not a big deal, but if the elements of the set are small,
1302std::set is almost never a good choice.</p>
1303
1304</div>
1305
1306<!-- _______________________________________________________________________ -->
1307<div class="doc_subsubsection">
1308 <a name="dss_setvector">"llvm/ADT/SetVector.h"</a>
1309</div>
1310
1311<div class="doc_text">
Chris Lattneredca3c52007-02-04 00:00:26 +0000[diff] [blame]1312<p>LLVM's SetVector&lt;Type&gt; is an adapter class that combines your choice of
1313a set-like container along with a <a href="#ds_sequential">Sequential
1314Container</a>. The important property
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1315that this provides is efficient insertion with uniquing (duplicate elements are
1316ignored) with iteration support. It implements this by inserting elements into
1317both a set-like container and the sequential container, using the set-like
1318container for uniquing and the sequential container for iteration.
1319</p>
1320
1321<p>The difference between SetVector and other sets is that the order of
1322iteration is guaranteed to match the order of insertion into the SetVector.
1323This property is really important for things like sets of pointers. Because
1324pointer values are non-deterministic (e.g. vary across runs of the program on
Chris Lattneredca3c52007-02-04 00:00:26 +0000[diff] [blame]1325different machines), iterating over the pointers in the set will
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1326not be in a well-defined order.</p>
1327
1328<p>
1329The drawback of SetVector is that it requires twice as much space as a normal
1330set and has the sum of constant factors from the set-like container and the
1331sequential container that it uses. Use it *only* if you need to iterate over
1332the elements in a deterministic order. SetVector is also expensive to delete
Chris Lattneredca3c52007-02-04 00:00:26 +0000[diff] [blame]1333elements out of (linear time), unless you use it's "pop_back" method, which is
1334faster.
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1335</p>
1336
Chris Lattneredca3c52007-02-04 00:00:26 +0000[diff] [blame]1337<p>SetVector is an adapter class that defaults to using std::vector and std::set
1338for the underlying containers, so it is quite expensive. However,
1339<tt>"llvm/ADT/SetVector.h"</tt> also provides a SmallSetVector class, which
1340defaults to using a SmallVector and SmallSet of a specified size. If you use
1341this, and if your sets are dynamically smaller than N, you will save a lot of
1342heap traffic.</p>
1343
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1344</div>
1345
1346<!-- _______________________________________________________________________ -->
1347<div class="doc_subsubsection">
Chris Lattnerc5722432007-02-03 19:49:31 +0000[diff] [blame]1348 <a name="dss_uniquevector">"llvm/ADT/UniqueVector.h"</a>
1349</div>
1350
1351<div class="doc_text">
1352
1353<p>
1354UniqueVector is similar to <a href="#dss_setvector">SetVector</a>, but it
1355retains a unique ID for each element inserted into the set. It internally
1356contains a map and a vector, and it assigns a unique ID for each value inserted
1357into the set.</p>
1358
1359<p>UniqueVector is very expensive: its cost is the sum of the cost of
1360maintaining both the map and vector, it has high complexity, high constant
1361factors, and produces a lot of malloc traffic. It should be avoided.</p>
1362
1363</div>
1364
1365
1366<!-- _______________________________________________________________________ -->
1367<div class="doc_subsubsection">
1368 <a name="dss_otherset">Other Set-Like Container Options</a>
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1369</div>
1370
1371<div class="doc_text">
1372
1373<p>
1374The STL provides several other options, such as std::multiset and the various
Chris Lattnerf1a30822009-03-09 05:20:45 +0000[diff] [blame]1375"hash_set" like containers (whether from C++ TR1 or from the SGI library). We
1376never use hash_set and unordered_set because they are generally very expensive
1377(each insertion requires a malloc) and very non-portable.
1378</p>
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1379
1380<p>std::multiset is useful if you're not interested in elimination of
Chris Lattner14868db2007-02-03 08:20:15 +0000[diff] [blame]1381duplicates, but has all the drawbacks of std::set. A sorted vector (where you
1382don't delete duplicate entries) or some other approach is almost always
1383better.</p>
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1384
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]1385</div>
1386
1387<!-- ======================================================================= -->
1388<div class="doc_subsection">
1389 <a name="ds_map">Map-Like Containers (std::map, DenseMap, etc)</a>
1390</div>
1391
1392<div class="doc_text">
Chris Lattnerc5722432007-02-03 19:49:31 +0000[diff] [blame]1393Map-like containers are useful when you want to associate data to a key. As
1394usual, there are a lot of different ways to do this. :)
1395</div>
1396
1397<!-- _______________________________________________________________________ -->
1398<div class="doc_subsubsection">
1399 <a name="dss_sortedvectormap">A sorted 'vector'</a>
1400</div>
1401
1402<div class="doc_text">
1403
1404<p>
1405If your usage pattern follows a strict insert-then-query approach, you can
1406trivially use the same approach as <a href="#dss_sortedvectorset">sorted vectors
1407for set-like containers</a>. The only difference is that your query function
1408(which uses std::lower_bound to get efficient log(n) lookup) should only compare
1409the key, not both the key and value. This yields the same advantages as sorted
1410vectors for sets.
1411</p>
1412</div>
1413
1414<!-- _______________________________________________________________________ -->
1415<div class="doc_subsubsection">
Chris Lattner796f9fa2007-02-08 19:14:21 +0000[diff] [blame]1416 <a name="dss_stringmap">"llvm/ADT/StringMap.h"</a>
Chris Lattnerc5722432007-02-03 19:49:31 +0000[diff] [blame]1417</div>
1418
1419<div class="doc_text">
1420
1421<p>
1422Strings are commonly used as keys in maps, and they are difficult to support
1423efficiently: they are variable length, inefficient to hash and compare when
Chris Lattner796f9fa2007-02-08 19:14:21 +0000[diff] [blame]1424long, expensive to copy, etc. StringMap is a specialized container designed to
1425cope with these issues. It supports mapping an arbitrary range of bytes to an
1426arbitrary other object.</p>
Chris Lattnerc5722432007-02-03 19:49:31 +0000[diff] [blame]1427
Chris Lattner796f9fa2007-02-08 19:14:21 +0000[diff] [blame]1428<p>The StringMap implementation uses a quadratically-probed hash table, where
Chris Lattnerc5722432007-02-03 19:49:31 +0000[diff] [blame]1429the buckets store a pointer to the heap allocated entries (and some other
1430stuff). The entries in the map must be heap allocated because the strings are
1431variable length. The string data (key) and the element object (value) are
1432stored in the same allocation with the string data immediately after the element
1433object. This container guarantees the "<tt>(char*)(&amp;Value+1)</tt>" points
1434to the key string for a value.</p>
1435
Chris Lattner796f9fa2007-02-08 19:14:21 +0000[diff] [blame]1436<p>The StringMap is very fast for several reasons: quadratic probing is very
Chris Lattnerc5722432007-02-03 19:49:31 +0000[diff] [blame]1437cache efficient for lookups, the hash value of strings in buckets is not
Nick Lewycky2a80aca2010-08-01 23:18:45 +0000[diff] [blame]1438recomputed when looking up an element, StringMap rarely has to touch the
Chris Lattnerc5722432007-02-03 19:49:31 +0000[diff] [blame]1439memory for unrelated objects when looking up a value (even when hash collisions
1440happen), hash table growth does not recompute the hash values for strings
1441already in the table, and each pair in the map is store in a single allocation
1442(the string data is stored in the same allocation as the Value of a pair).</p>
1443
Chris Lattner796f9fa2007-02-08 19:14:21 +0000[diff] [blame]1444<p>StringMap also provides query methods that take byte ranges, so it only ever
Chris Lattnerc5722432007-02-03 19:49:31 +0000[diff] [blame]1445copies a string if a value is inserted into the table.</p>
1446</div>
1447
1448<!-- _______________________________________________________________________ -->
1449<div class="doc_subsubsection">
1450 <a name="dss_indexedmap">"llvm/ADT/IndexedMap.h"</a>
1451</div>
1452
1453<div class="doc_text">
1454<p>
1455IndexedMap is a specialized container for mapping small dense integers (or
1456values that can be mapped to small dense integers) to some other type. It is
1457internally implemented as a vector with a mapping function that maps the keys to
1458the dense integer range.
1459</p>
1460
1461<p>
1462This is useful for cases like virtual registers in the LLVM code generator: they
1463have a dense mapping that is offset by a compile-time constant (the first
1464virtual register ID).</p>
1465
1466</div>
1467
1468<!-- _______________________________________________________________________ -->
1469<div class="doc_subsubsection">
1470 <a name="dss_densemap">"llvm/ADT/DenseMap.h"</a>
1471</div>
1472
1473<div class="doc_text">
1474
1475<p>
1476DenseMap is a simple quadratically probed hash table. It excels at supporting
1477small keys and values: it uses a single allocation to hold all of the pairs that
1478are currently inserted in the map. DenseMap is a great way to map pointers to
1479pointers, or map other small types to each other.
1480</p>
1481
1482<p>
1483There are several aspects of DenseMap that you should be aware of, however. The
1484iterators in a densemap are invalidated whenever an insertion occurs, unlike
1485map. Also, because DenseMap allocates space for a large number of key/value
Chris Lattnera4a264d2007-02-03 20:17:53 +0000[diff] [blame]1486pairs (it starts with 64 by default), it will waste a lot of space if your keys
1487or values are large. Finally, you must implement a partial specialization of
Chris Lattner76c1b972007-09-17 18:34:04 +0000[diff] [blame]1488DenseMapInfo for the key that you want, if it isn't already supported. This
Chris Lattnerc5722432007-02-03 19:49:31 +0000[diff] [blame]1489is required to tell DenseMap about two special marker values (which can never be
Chris Lattnera4a264d2007-02-03 20:17:53 +0000[diff] [blame]1490inserted into the map) that it needs internally.</p>
Chris Lattnerc5722432007-02-03 19:49:31 +0000[diff] [blame]1491
1492</div>
1493
1494<!-- _______________________________________________________________________ -->
1495<div class="doc_subsubsection">
Jeffrey Yasskin71a5c222009-10-22 22:11:22 +0000[diff] [blame]1496 <a name="dss_valuemap">"llvm/ADT/ValueMap.h"</a>
1497</div>
1498
1499<div class="doc_text">
1500
1501<p>
1502ValueMap is a wrapper around a <a href="#dss_densemap">DenseMap</a> mapping
1503Value*s (or subclasses) to another type. When a Value is deleted or RAUW'ed,
1504ValueMap will update itself so the new version of the key is mapped to the same
1505value, just as if the key were a WeakVH. You can configure exactly how this
1506happens, and what else happens on these two events, by passing
1507a <code>Config</code> parameter to the ValueMap template.</p>
1508
1509</div>
1510
1511<!-- _______________________________________________________________________ -->
1512<div class="doc_subsubsection">
Jakob Stoklund Olesenaca0da62010-12-14 00:55:51 +0000[diff] [blame]1513 <a name="dss_intervalmap">"llvm/ADT/IntervalMap.h"</a>
1514</div>
1515
1516<div class="doc_text">
1517
1518<p> IntervalMap is a compact map for small keys and values. It maps key
1519intervals instead of single keys, and it will automatically coalesce adjacent
1520intervals. When then map only contains a few intervals, they are stored in the
1521map object itself to avoid allocations.</p>
1522
1523<p> The IntervalMap iterators are quite big, so they should not be passed around
1524as STL iterators. The heavyweight iterators allow a smaller data structure.</p>
1525
1526</div>
1527
1528<!-- _______________________________________________________________________ -->
1529<div class="doc_subsubsection">
Chris Lattnerc5722432007-02-03 19:49:31 +0000[diff] [blame]1530 <a name="dss_map">&lt;map&gt;</a>
1531</div>
1532
1533<div class="doc_text">
1534
1535<p>
1536std::map has similar characteristics to <a href="#dss_set">std::set</a>: it uses
1537a single allocation per pair inserted into the map, it offers log(n) lookup with
1538an extremely large constant factor, imposes a space penalty of 3 pointers per
1539pair in the map, etc.</p>
1540
1541<p>std::map is most useful when your keys or values are very large, if you need
1542to iterate over the collection in sorted order, or if you need stable iterators
1543into the map (i.e. they don't get invalidated if an insertion or deletion of
1544another element takes place).</p>
1545
1546</div>
1547
1548<!-- _______________________________________________________________________ -->
1549<div class="doc_subsubsection">
1550 <a name="dss_othermap">Other Map-Like Container Options</a>
1551</div>
1552
1553<div class="doc_text">
1554
1555<p>
1556The STL provides several other options, such as std::multimap and the various
Chris Lattnerf1a30822009-03-09 05:20:45 +0000[diff] [blame]1557"hash_map" like containers (whether from C++ TR1 or from the SGI library). We
1558never use hash_set and unordered_set because they are generally very expensive
1559(each insertion requires a malloc) and very non-portable.</p>
Chris Lattnerc5722432007-02-03 19:49:31 +0000[diff] [blame]1560
1561<p>std::multimap is useful if you want to map a key to multiple values, but has
1562all the drawbacks of std::map. A sorted vector or some other approach is almost
1563always better.</p>
1564
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]1565</div>
1566
Daniel Berlin1939ace2007-09-24 17:52:25 +0000[diff] [blame]1567<!-- ======================================================================= -->
1568<div class="doc_subsection">
Chris Lattnerdced9fb2009-07-25 07:22:20 +0000[diff] [blame]1569 <a name="ds_string">String-like containers</a>
1570</div>
1571
1572<div class="doc_text">
1573
1574<p>
1575TODO: const char* vs stringref vs smallstring vs std::string. Describe twine,
1576xref to #string_apis.
1577</p>
1578
1579</div>
1580
1581<!-- ======================================================================= -->
1582<div class="doc_subsection">
Daniel Berlin1939ace2007-09-24 17:52:25 +0000[diff] [blame]1583 <a name="ds_bit">Bit storage containers (BitVector, SparseBitVector)</a>
1584</div>
1585
1586<div class="doc_text">
Chris Lattner7086ce72007-09-25 22:37:50 +0000[diff] [blame]1587<p>Unlike the other containers, there are only two bit storage containers, and
1588choosing when to use each is relatively straightforward.</p>
1589
1590<p>One additional option is
1591<tt>std::vector&lt;bool&gt;</tt>: we discourage its use for two reasons 1) the
1592implementation in many common compilers (e.g. commonly available versions of
1593GCC) is extremely inefficient and 2) the C++ standards committee is likely to
1594deprecate this container and/or change it significantly somehow. In any case,
1595please don't use it.</p>
Daniel Berlin1939ace2007-09-24 17:52:25 +0000[diff] [blame]1596</div>
1597
1598<!-- _______________________________________________________________________ -->
1599<div class="doc_subsubsection">
1600 <a name="dss_bitvector">BitVector</a>
1601</div>
1602
1603<div class="doc_text">
Dan Gohman5f7775c2010-01-05 18:24:00 +0000[diff] [blame]1604<p> The BitVector container provides a dynamic size set of bits for manipulation.
Daniel Berlin1939ace2007-09-24 17:52:25 +0000[diff] [blame]1605It supports individual bit setting/testing, as well as set operations. The set
1606operations take time O(size of bitvector), but operations are performed one word
1607at a time, instead of one bit at a time. This makes the BitVector very fast for
1608set operations compared to other containers. Use the BitVector when you expect
1609the number of set bits to be high (IE a dense set).
1610</p>
1611</div>
1612
1613<!-- _______________________________________________________________________ -->
1614<div class="doc_subsubsection">
Dan Gohman5f7775c2010-01-05 18:24:00 +0000[diff] [blame]1615 <a name="dss_smallbitvector">SmallBitVector</a>
1616</div>
1617
1618<div class="doc_text">
1619<p> The SmallBitVector container provides the same interface as BitVector, but
1620it is optimized for the case where only a small number of bits, less than
162125 or so, are needed. It also transparently supports larger bit counts, but
1622slightly less efficiently than a plain BitVector, so SmallBitVector should
1623only be used when larger counts are rare.
1624</p>
1625
1626<p>
1627At this time, SmallBitVector does not support set operations (and, or, xor),
1628and its operator[] does not provide an assignable lvalue.
1629</p>
1630</div>
1631
1632<!-- _______________________________________________________________________ -->
1633<div class="doc_subsubsection">
Daniel Berlin1939ace2007-09-24 17:52:25 +0000[diff] [blame]1634 <a name="dss_sparsebitvector">SparseBitVector</a>
1635</div>
1636
1637<div class="doc_text">
1638<p> The SparseBitVector container is much like BitVector, with one major
1639difference: Only the bits that are set, are stored. This makes the
1640SparseBitVector much more space efficient than BitVector when the set is sparse,
1641as well as making set operations O(number of set bits) instead of O(size of
1642universe). 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
1643(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).
1644</p>
1645</div>
Chris Lattnerf623a082005-10-17 01:36:23 +0000[diff] [blame]1646
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1647<!-- *********************************************************************** -->
1648<div class="doc_section">
1649 <a name="common">Helpful Hints for Common Operations</a>
1650</div>
1651<!-- *********************************************************************** -->
1652
1653<div class="doc_text">
1654
1655<p>This section describes how to perform some very simple transformations of
1656LLVM code. This is meant to give examples of common idioms used, showing the
1657practical side of LLVM transformations. <p> Because this is a "how-to" section,
1658you should also read about the main classes that you will be working with. The
1659<a href="#coreclasses">Core LLVM Class Hierarchy Reference</a> contains details
1660and descriptions of the main classes that you should know about.</p>
1661
1662</div>
1663
1664<!-- NOTE: this section should be heavy on example code -->
1665<!-- ======================================================================= -->
1666<div class="doc_subsection">
1667 <a name="inspection">Basic Inspection and Traversal Routines</a>
1668</div>
1669
1670<div class="doc_text">
1671
1672<p>The LLVM compiler infrastructure have many different data structures that may
1673be traversed. Following the example of the C++ standard template library, the
1674techniques used to traverse these various data structures are all basically the
1675same. For a enumerable sequence of values, the <tt>XXXbegin()</tt> function (or
1676method) returns an iterator to the start of the sequence, the <tt>XXXend()</tt>
1677function returns an iterator pointing to one past the last valid element of the
1678sequence, and there is some <tt>XXXiterator</tt> data type that is common
1679between the two operations.</p>
1680
1681<p>Because the pattern for iteration is common across many different aspects of
1682the program representation, the standard template library algorithms may be used
1683on them, and it is easier to remember how to iterate. First we show a few common
1684examples of the data structures that need to be traversed. Other data
1685structures are traversed in very similar ways.</p>
1686
1687</div>
1688
1689<!-- _______________________________________________________________________ -->
Chris Lattner69bf8a92004-05-23 21:06:58 +0000[diff] [blame]1690<div class="doc_subsubsection">
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1691 <a name="iterate_function">Iterating over the </a><a
1692 href="#BasicBlock"><tt>BasicBlock</tt></a>s in a <a
1693 href="#Function"><tt>Function</tt></a>
1694</div>
1695
1696<div class="doc_text">
1697
1698<p>It's quite common to have a <tt>Function</tt> instance that you'd like to
1699transform in some way; in particular, you'd like to manipulate its
1700<tt>BasicBlock</tt>s. To facilitate this, you'll need to iterate over all of
1701the <tt>BasicBlock</tt>s that constitute the <tt>Function</tt>. The following is
1702an example that prints the name of a <tt>BasicBlock</tt> and the number of
1703<tt>Instruction</tt>s it contains:</p>
1704
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1705<div class="doc_code">
1706<pre>
Bill Wendling82e2eea2006-10-11 18:00:22 +0000[diff] [blame]1707// <i>func is a pointer to a Function instance</i>
1708for (Function::iterator i = func-&gt;begin(), e = func-&gt;end(); i != e; ++i)
1709 // <i>Print out the name of the basic block if it has one, and then the</i>
1710 // <i>number of instructions that it contains</i>
Chris Lattner3fee6ed2009-09-08 05:15:50 +0000[diff] [blame]1711 errs() &lt;&lt; "Basic block (name=" &lt;&lt; i-&gt;getName() &lt;&lt; ") has "
Bill Wendling832171c2006-12-07 20:04:42 +0000[diff] [blame]1712 &lt;&lt; i-&gt;size() &lt;&lt; " instructions.\n";
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1713</pre>
1714</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1715
1716<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]1717invoking member functions of the <tt>Instruction</tt> class. This is
1718because the indirection operator is overloaded for the iterator
Chris Lattner7496ec52003-08-05 22:54:23 +0000[diff] [blame]1719classes. In the above code, the expression <tt>i-&gt;size()</tt> is
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1720exactly equivalent to <tt>(*i).size()</tt> just like you'd expect.</p>
1721
1722</div>
1723
1724<!-- _______________________________________________________________________ -->
Chris Lattner69bf8a92004-05-23 21:06:58 +0000[diff] [blame]1725<div class="doc_subsubsection">
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1726 <a name="iterate_basicblock">Iterating over the </a><a
1727 href="#Instruction"><tt>Instruction</tt></a>s in a <a
1728 href="#BasicBlock"><tt>BasicBlock</tt></a>
1729</div>
1730
1731<div class="doc_text">
1732
1733<p>Just like when dealing with <tt>BasicBlock</tt>s in <tt>Function</tt>s, it's
1734easy to iterate over the individual instructions that make up
1735<tt>BasicBlock</tt>s. Here's a code snippet that prints out each instruction in
1736a <tt>BasicBlock</tt>:</p>
1737
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1738<div class="doc_code">
Chris Lattner55c04612005-03-06 06:00:13 +0000[diff] [blame]1739<pre>
Bill Wendling82e2eea2006-10-11 18:00:22 +0000[diff] [blame]1740// <i>blk is a pointer to a BasicBlock instance</i>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1741for (BasicBlock::iterator i = blk-&gt;begin(), e = blk-&gt;end(); i != e; ++i)
Bill Wendling82e2eea2006-10-11 18:00:22 +0000[diff] [blame]1742 // <i>The next statement works since operator&lt;&lt;(ostream&amp;,...)</i>
1743 // <i>is overloaded for Instruction&amp;</i>
Chris Lattner3fee6ed2009-09-08 05:15:50 +0000[diff] [blame]1744 errs() &lt;&lt; *i &lt;&lt; "\n";
Chris Lattner55c04612005-03-06 06:00:13 +0000[diff] [blame]1745</pre>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1746</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1747
1748<p>However, this isn't really the best way to print out the contents of a
1749<tt>BasicBlock</tt>! Since the ostream operators are overloaded for virtually
1750anything you'll care about, you could have just invoked the print routine on the
Chris Lattner3fee6ed2009-09-08 05:15:50 +0000[diff] [blame]1751basic block itself: <tt>errs() &lt;&lt; *blk &lt;&lt; "\n";</tt>.</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1752
1753</div>
1754
1755<!-- _______________________________________________________________________ -->
Chris Lattner69bf8a92004-05-23 21:06:58 +0000[diff] [blame]1756<div class="doc_subsubsection">
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1757 <a name="iterate_institer">Iterating over the </a><a
1758 href="#Instruction"><tt>Instruction</tt></a>s in a <a
1759 href="#Function"><tt>Function</tt></a>
1760</div>
1761
1762<div class="doc_text">
1763
1764<p>If you're finding that you commonly iterate over a <tt>Function</tt>'s
1765<tt>BasicBlock</tt>s and then that <tt>BasicBlock</tt>'s <tt>Instruction</tt>s,
1766<tt>InstIterator</tt> should be used instead. You'll need to include <a
1767href="/doxygen/InstIterator_8h-source.html"><tt>llvm/Support/InstIterator.h</tt></a>,
1768and then instantiate <tt>InstIterator</tt>s explicitly in your code. Here's a
Chris Lattner69bf8a92004-05-23 21:06:58 +0000[diff] [blame]1769small 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]1770
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1771<div class="doc_code">
1772<pre>
1773#include "<a href="/doxygen/InstIterator_8h-source.html">llvm/Support/InstIterator.h</a>"
1774
Reid Spencer128a7a72007-02-03 21:06:43 +0000[diff] [blame]1775// <i>F is a pointer to a Function instance</i>
Chris Lattnerda021aa2008-06-04 18:20:42 +0000[diff] [blame]1776for (inst_iterator I = inst_begin(F), E = inst_end(F); I != E; ++I)
Chris Lattner3fee6ed2009-09-08 05:15:50 +0000[diff] [blame]1777 errs() &lt;&lt; *I &lt;&lt; "\n";
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1778</pre>
1779</div>
1780
1781<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]1782work list with its initial contents. For example, if you wanted to
1783initialize a work list to contain all instructions in a <tt>Function</tt>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1784F, all you would need to do is something like:</p>
1785
1786<div class="doc_code">
1787<pre>
1788std::set&lt;Instruction*&gt; worklist;
Chris Lattnerda021aa2008-06-04 18:20:42 +0000[diff] [blame]1789// or better yet, SmallPtrSet&lt;Instruction*, 64&gt; worklist;
1790
1791for (inst_iterator I = inst_begin(F), E = inst_end(F); I != E; ++I)
1792 worklist.insert(&amp;*I);
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1793</pre>
1794</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1795
1796<p>The STL set <tt>worklist</tt> would now contain all instructions in the
1797<tt>Function</tt> pointed to by F.</p>
1798
1799</div>
1800
1801<!-- _______________________________________________________________________ -->
1802<div class="doc_subsubsection">
1803 <a name="iterate_convert">Turning an iterator into a class pointer (and
1804 vice-versa)</a>
1805</div>
1806
1807<div class="doc_text">
1808
1809<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]1810instance when all you've got at hand is an iterator. Well, extracting
Chris Lattner69bf8a92004-05-23 21:06:58 +0000[diff] [blame]1811a reference or a pointer from an iterator is very straight-forward.
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]1812Assuming that <tt>i</tt> is a <tt>BasicBlock::iterator</tt> and <tt>j</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1813is a <tt>BasicBlock::const_iterator</tt>:</p>
1814
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1815<div class="doc_code">
1816<pre>
Bill Wendling82e2eea2006-10-11 18:00:22 +0000[diff] [blame]1817Instruction&amp; inst = *i; // <i>Grab reference to instruction reference</i>
1818Instruction* pinst = &amp;*i; // <i>Grab pointer to instruction reference</i>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1819const Instruction&amp; inst = *j;
1820</pre>
1821</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1822
1823<p>However, the iterators you'll be working with in the LLVM framework are
1824special: they will automatically convert to a ptr-to-instance type whenever they
1825need to. Instead of dereferencing the iterator and then taking the address of
1826the result, you can simply assign the iterator to the proper pointer type and
1827you get the dereference and address-of operation as a result of the assignment
1828(behind the scenes, this is a result of overloading casting mechanisms). Thus
1829the last line of the last example,</p>
1830
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1831<div class="doc_code">
1832<pre>
Chris Lattner2e438ca2008-01-03 16:56:04 +0000[diff] [blame]1833Instruction *pinst = &amp;*i;
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1834</pre>
1835</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1836
1837<p>is semantically equivalent to</p>
1838
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1839<div class="doc_code">
1840<pre>
Chris Lattner2e438ca2008-01-03 16:56:04 +0000[diff] [blame]1841Instruction *pinst = i;
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1842</pre>
1843</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1844
Chris Lattner69bf8a92004-05-23 21:06:58 +0000[diff] [blame]1845<p>It's also possible to turn a class pointer into the corresponding iterator,
1846and this is a constant time operation (very efficient). The following code
1847snippet illustrates use of the conversion constructors provided by LLVM
1848iterators. By using these, you can explicitly grab the iterator of something
1849without actually obtaining it via iteration over some structure:</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1850
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1851<div class="doc_code">
1852<pre>
1853void printNextInstruction(Instruction* inst) {
1854 BasicBlock::iterator it(inst);
Bill Wendling82e2eea2006-10-11 18:00:22 +0000[diff] [blame]1855 ++it; // <i>After this line, it refers to the instruction after *inst</i>
Chris Lattner3fee6ed2009-09-08 05:15:50 +0000[diff] [blame]1856 if (it != inst-&gt;getParent()-&gt;end()) errs() &lt;&lt; *it &lt;&lt; "\n";
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1857}
1858</pre>
1859</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1860
Dan Gohman525bf8e2010-03-26 19:39:05 +0000[diff] [blame]1861<p>Unfortunately, these implicit conversions come at a cost; they prevent
1862these iterators from conforming to standard iterator conventions, and thus
Dan Gohman0d91c112010-03-26 19:51:14 +0000[diff] [blame]1863from being usable with standard algorithms and containers. For example, they
1864prevent the following code, where <tt>B</tt> is a <tt>BasicBlock</tt>,
Dan Gohman525bf8e2010-03-26 19:39:05 +0000[diff] [blame]1865from compiling:</p>
1866
1867<div class="doc_code">
1868<pre>
1869 llvm::SmallVector&lt;llvm::Instruction *, 16&gt;(B-&gt;begin(), B-&gt;end());
1870</pre>
1871</div>
1872
1873<p>Because of this, these implicit conversions may be removed some day,
Dan Gohman0d91c112010-03-26 19:51:14 +0000[diff] [blame]1874and <tt>operator*</tt> changed to return a pointer instead of a reference.</p>
Dan Gohman525bf8e2010-03-26 19:39:05 +0000[diff] [blame]1875
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1876</div>
1877
1878<!--_______________________________________________________________________-->
1879<div class="doc_subsubsection">
1880 <a name="iterate_complex">Finding call sites: a slightly more complex
1881 example</a>
1882</div>
1883
1884<div class="doc_text">
1885
1886<p>Say that you're writing a FunctionPass and would like to count all the
1887locations in the entire module (that is, across every <tt>Function</tt>) where a
1888certain function (i.e., some <tt>Function</tt>*) is already in scope. As you'll
1889learn 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]1890much more straight-forward manner, but this example will allow us to explore how
Reid Spencer128a7a72007-02-03 21:06:43 +0000[diff] [blame]1891you'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]1892is what we want to do:</p>
1893
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1894<div class="doc_code">
1895<pre>
1896initialize callCounter to zero
1897for each Function f in the Module
1898 for each BasicBlock b in f
1899 for each Instruction i in b
1900 if (i is a CallInst and calls the given function)
1901 increment callCounter
1902</pre>
1903</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1904
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1905<p>And the actual code is (remember, because we're writing a
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1906<tt>FunctionPass</tt>, our <tt>FunctionPass</tt>-derived class simply has to
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1907override the <tt>runOnFunction</tt> method):</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1908
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1909<div class="doc_code">
1910<pre>
1911Function* targetFunc = ...;
1912
1913class OurFunctionPass : public FunctionPass {
1914 public:
1915 OurFunctionPass(): callCounter(0) { }
1916
1917 virtual runOnFunction(Function&amp; F) {
1918 for (Function::iterator b = F.begin(), be = F.end(); b != be; ++b) {
Eric Christopher203e71d2008-11-08 08:20:49 +0000[diff] [blame]1919 for (BasicBlock::iterator i = b-&gt;begin(), ie = b-&gt;end(); i != ie; ++i) {
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1920 if (<a href="#CallInst">CallInst</a>* callInst = <a href="#isa">dyn_cast</a>&lt;<a
1921 href="#CallInst">CallInst</a>&gt;(&amp;*i)) {
Bill Wendling82e2eea2006-10-11 18:00:22 +0000[diff] [blame]1922 // <i>We know we've encountered a call instruction, so we</i>
1923 // <i>need to determine if it's a call to the</i>
Chris Lattner2e438ca2008-01-03 16:56:04 +0000[diff] [blame]1924 // <i>function pointed to by m_func or not.</i>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1925 if (callInst-&gt;getCalledFunction() == targetFunc)
1926 ++callCounter;
1927 }
1928 }
1929 }
Bill Wendling82e2eea2006-10-11 18:00:22 +0000[diff] [blame]1930 }
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1931
1932 private:
Chris Lattner2e438ca2008-01-03 16:56:04 +0000[diff] [blame]1933 unsigned callCounter;
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1934};
1935</pre>
1936</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1937
1938</div>
1939
Brian Gaekef1972c62003-11-07 19:25:45 +0000[diff] [blame]1940<!--_______________________________________________________________________-->
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1941<div class="doc_subsubsection">
1942 <a name="calls_and_invokes">Treating calls and invokes the same way</a>
1943</div>
1944
1945<div class="doc_text">
1946
1947<p>You may have noticed that the previous example was a bit oversimplified in
1948that it did not deal with call sites generated by 'invoke' instructions. In
1949this, and in other situations, you may find that you want to treat
1950<tt>CallInst</tt>s and <tt>InvokeInst</tt>s the same way, even though their
1951most-specific common base class is <tt>Instruction</tt>, which includes lots of
1952less closely-related things. For these cases, LLVM provides a handy wrapper
1953class called <a
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]1954href="http://llvm.org/doxygen/classllvm_1_1CallSite.html"><tt>CallSite</tt></a>.
Chris Lattner69bf8a92004-05-23 21:06:58 +0000[diff] [blame]1955It is essentially a wrapper around an <tt>Instruction</tt> pointer, with some
1956methods that provide functionality common to <tt>CallInst</tt>s and
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1957<tt>InvokeInst</tt>s.</p>
1958
Chris Lattner69bf8a92004-05-23 21:06:58 +0000[diff] [blame]1959<p>This class has "value semantics": it should be passed by value, not by
1960reference and it should not be dynamically allocated or deallocated using
1961<tt>operator new</tt> or <tt>operator delete</tt>. It is efficiently copyable,
1962assignable and constructable, with costs equivalents to that of a bare pointer.
1963If you look at its definition, it has only a single pointer member.</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1964
1965</div>
1966
Chris Lattner1a3105b2002-09-09 05:49:39 +0000[diff] [blame]1967<!--_______________________________________________________________________-->
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1968<div class="doc_subsubsection">
1969 <a name="iterate_chains">Iterating over def-use &amp; use-def chains</a>
1970</div>
1971
1972<div class="doc_text">
1973
1974<p>Frequently, we might have an instance of the <a
Chris Lattner00815172007-01-04 22:01:45 +0000[diff] [blame]1975href="/doxygen/classllvm_1_1Value.html">Value Class</a> and we want to
Misha Brukman384047f2004-06-03 23:29:12 +0000[diff] [blame]1976determine which <tt>User</tt>s use the <tt>Value</tt>. The list of all
1977<tt>User</tt>s of a particular <tt>Value</tt> is called a <i>def-use</i> chain.
1978For example, let's say we have a <tt>Function*</tt> named <tt>F</tt> to a
1979particular function <tt>foo</tt>. Finding all of the instructions that
1980<i>use</i> <tt>foo</tt> is as simple as iterating over the <i>def-use</i> chain
1981of <tt>F</tt>:</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1982
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1983<div class="doc_code">
1984<pre>
Chris Lattner2e438ca2008-01-03 16:56:04 +0000[diff] [blame]1985Function *F = ...;
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1986
Bill Wendling82e2eea2006-10-11 18:00:22 +0000[diff] [blame]1987for (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]1988 if (Instruction *Inst = dyn_cast&lt;Instruction&gt;(*i)) {
Chris Lattner3fee6ed2009-09-08 05:15:50 +0000[diff] [blame]1989 errs() &lt;&lt; "F is used in instruction:\n";
1990 errs() &lt;&lt; *Inst &lt;&lt; "\n";
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1991 }
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1992</pre>
Gabor Greif394fdfb2010-03-26 19:35:48 +0000[diff] [blame]1993</div>
1994
Gabor Greifce94319532010-03-26 19:40:38 +0000[diff] [blame]1995<p>Note that dereferencing a <tt>Value::use_iterator</tt> is not a very cheap
Gabor Greif4de73682010-03-26 19:30:47 +0000[diff] [blame]1996operation. Instead of performing <tt>*i</tt> above several times, consider
Gabor Greifce94319532010-03-26 19:40:38 +0000[diff] [blame]1997doing it only once in the loop body and reusing its result.</p>
Gabor Greif4de73682010-03-26 19:30:47 +0000[diff] [blame]1998
Gabor Greif6091ff32010-03-26 19:04:42 +0000[diff] [blame]1999<p>Alternatively, it's common to have an instance of the <a
Misha Brukman384047f2004-06-03 23:29:12 +0000[diff] [blame]2000href="/doxygen/classllvm_1_1User.html">User Class</a> and need to know what
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2001<tt>Value</tt>s are used by it. The list of all <tt>Value</tt>s used by a
2002<tt>User</tt> is known as a <i>use-def</i> chain. Instances of class
2003<tt>Instruction</tt> are common <tt>User</tt>s, so we might want to iterate over
2004all of the values that a particular instruction uses (that is, the operands of
2005the particular <tt>Instruction</tt>):</p>
2006
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2007<div class="doc_code">
2008<pre>
Chris Lattner2e438ca2008-01-03 16:56:04 +0000[diff] [blame]2009Instruction *pi = ...;
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2010
2011for (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]2012 Value *v = *i;
Bill Wendling82e2eea2006-10-11 18:00:22 +0000[diff] [blame]2013 // <i>...</i>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2014}
2015</pre>
2016</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2017
Gabor Greif4de73682010-03-26 19:30:47 +0000[diff] [blame]2018<p>Declaring objects as <tt>const</tt> is an important tool of enforcing
Gabor Greifce94319532010-03-26 19:40:38 +0000[diff] [blame]2019mutation free algorithms (such as analyses, etc.). For this purpose above
Gabor Greif4de73682010-03-26 19:30:47 +0000[diff] [blame]2020iterators come in constant flavors as <tt>Value::const_use_iterator</tt>
2021and <tt>Value::const_op_iterator</tt>. They automatically arise when
2022calling <tt>use/op_begin()</tt> on <tt>const Value*</tt>s or
2023<tt>const User*</tt>s respectively. Upon dereferencing, they return
Gabor Greifce94319532010-03-26 19:40:38 +0000[diff] [blame]2024<tt>const Use*</tt>s. Otherwise the above patterns remain unchanged.</p>
2025
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2026</div>
2027
Chris Lattner2e438ca2008-01-03 16:56:04 +0000[diff] [blame]2028<!--_______________________________________________________________________-->
2029<div class="doc_subsubsection">
2030 <a name="iterate_preds">Iterating over predecessors &amp;
2031successors of blocks</a>
2032</div>
2033
2034<div class="doc_text">
2035
2036<p>Iterating over the predecessors and successors of a block is quite easy
2037with the routines defined in <tt>"llvm/Support/CFG.h"</tt>. Just use code like
2038this to iterate over all predecessors of BB:</p>
2039
2040<div class="doc_code">
2041<pre>
2042#include "llvm/Support/CFG.h"
2043BasicBlock *BB = ...;
2044
2045for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI) {
2046 BasicBlock *Pred = *PI;
2047 // <i>...</i>
2048}
2049</pre>
2050</div>
2051
2052<p>Similarly, to iterate over successors use
2053succ_iterator/succ_begin/succ_end.</p>
2054
2055</div>
2056
2057
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2058<!-- ======================================================================= -->
2059<div class="doc_subsection">
2060 <a name="simplechanges">Making simple changes</a>
2061</div>
2062
2063<div class="doc_text">
2064
2065<p>There are some primitive transformation operations present in the LLVM
Joel Stanley753eb712002-09-11 22:32:24 +0000[diff] [blame]2066infrastructure that are worth knowing about. When performing
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]2067transformations, it's fairly common to manipulate the contents of basic
2068blocks. This section describes some of the common methods for doing so
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2069and gives example code.</p>
2070
2071</div>
2072
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]2073<!--_______________________________________________________________________-->
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2074<div class="doc_subsubsection">
2075 <a name="schanges_creating">Creating and inserting new
2076 <tt>Instruction</tt>s</a>
2077</div>
2078
2079<div class="doc_text">
2080
2081<p><i>Instantiating Instructions</i></p>
2082
Chris Lattner69bf8a92004-05-23 21:06:58 +0000[diff] [blame]2083<p>Creation of <tt>Instruction</tt>s is straight-forward: simply call the
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2084constructor for the kind of instruction to instantiate and provide the necessary
2085parameters. For example, an <tt>AllocaInst</tt> only <i>requires</i> a
2086(const-ptr-to) <tt>Type</tt>. Thus:</p>
2087
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2088<div class="doc_code">
2089<pre>
Nick Lewycky10d64b92007-12-03 01:52:52 +0000[diff] [blame]2090AllocaInst* ai = new AllocaInst(Type::Int32Ty);
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2091</pre>
2092</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2093
2094<p>will create an <tt>AllocaInst</tt> instance that represents the allocation of
Reid Spencer128a7a72007-02-03 21:06:43 +0000[diff] [blame]2095one integer in the current stack frame, at run time. Each <tt>Instruction</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2096subclass is likely to have varying default parameters which change the semantics
2097of the instruction, so refer to the <a
Misha Brukman31ca1de2004-06-03 23:35:54 +0000[diff] [blame]2098href="/doxygen/classllvm_1_1Instruction.html">doxygen documentation for the subclass of
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2099Instruction</a> that you're interested in instantiating.</p>
2100
2101<p><i>Naming values</i></p>
2102
2103<p>It is very useful to name the values of instructions when you're able to, as
2104this facilitates the debugging of your transformations. If you end up looking
2105at generated LLVM machine code, you definitely want to have logical names
2106associated with the results of instructions! By supplying a value for the
2107<tt>Name</tt> (default) parameter of the <tt>Instruction</tt> constructor, you
2108associate a logical name with the result of the instruction's execution at
Reid Spencer128a7a72007-02-03 21:06:43 +0000[diff] [blame]2109run time. For example, say that I'm writing a transformation that dynamically
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2110allocates space for an integer on the stack, and that integer is going to be
2111used as some kind of index by some other code. To accomplish this, I place an
2112<tt>AllocaInst</tt> at the first point in the first <tt>BasicBlock</tt> of some
2113<tt>Function</tt>, and I'm intending to use it within the same
2114<tt>Function</tt>. I might do:</p>
2115
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2116<div class="doc_code">
2117<pre>
Nick Lewycky10d64b92007-12-03 01:52:52 +0000[diff] [blame]2118AllocaInst* pa = new AllocaInst(Type::Int32Ty, 0, "indexLoc");
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2119</pre>
2120</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2121
2122<p>where <tt>indexLoc</tt> is now the logical name of the instruction's
Reid Spencer128a7a72007-02-03 21:06:43 +0000[diff] [blame]2123execution value, which is a pointer to an integer on the run time stack.</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2124
2125<p><i>Inserting instructions</i></p>
2126
2127<p>There are essentially two ways to insert an <tt>Instruction</tt>
2128into an existing sequence of instructions that form a <tt>BasicBlock</tt>:</p>
2129
Joel Stanley9dd1ad62002-09-18 03:17:23 +0000[diff] [blame]2130<ul>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2131 <li>Insertion into an explicit instruction list
2132
2133 <p>Given a <tt>BasicBlock* pb</tt>, an <tt>Instruction* pi</tt> within that
2134 <tt>BasicBlock</tt>, and a newly-created instruction we wish to insert
2135 before <tt>*pi</tt>, we do the following: </p>
2136
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2137<div class="doc_code">
2138<pre>
2139BasicBlock *pb = ...;
2140Instruction *pi = ...;
2141Instruction *newInst = new Instruction(...);
2142
Bill Wendling82e2eea2006-10-11 18:00:22 +0000[diff] [blame]2143pb-&gt;getInstList().insert(pi, newInst); // <i>Inserts newInst before pi in pb</i>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2144</pre>
2145</div>
Alkis Evlogimenos9a5dc4f2004-05-27 00:57:51 +0000[diff] [blame]2146
2147 <p>Appending to the end of a <tt>BasicBlock</tt> is so common that
2148 the <tt>Instruction</tt> class and <tt>Instruction</tt>-derived
2149 classes provide constructors which take a pointer to a
2150 <tt>BasicBlock</tt> to be appended to. For example code that
2151 looked like: </p>
2152
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2153<div class="doc_code">
2154<pre>
2155BasicBlock *pb = ...;
2156Instruction *newInst = new Instruction(...);
2157
Bill Wendling82e2eea2006-10-11 18:00:22 +0000[diff] [blame]2158pb-&gt;getInstList().push_back(newInst); // <i>Appends newInst to pb</i>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2159</pre>
2160</div>
Alkis Evlogimenos9a5dc4f2004-05-27 00:57:51 +0000[diff] [blame]2161
2162 <p>becomes: </p>
2163
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2164<div class="doc_code">
2165<pre>
2166BasicBlock *pb = ...;
2167Instruction *newInst = new Instruction(..., pb);
2168</pre>
2169</div>
Alkis Evlogimenos9a5dc4f2004-05-27 00:57:51 +0000[diff] [blame]2170
2171 <p>which is much cleaner, especially if you are creating
2172 long instruction streams.</p></li>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2173
2174 <li>Insertion into an implicit instruction list
2175
2176 <p><tt>Instruction</tt> instances that are already in <tt>BasicBlock</tt>s
2177 are implicitly associated with an existing instruction list: the instruction
2178 list of the enclosing basic block. Thus, we could have accomplished the same
2179 thing as the above code without being given a <tt>BasicBlock</tt> by doing:
2180 </p>
2181
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2182<div class="doc_code">
2183<pre>
2184Instruction *pi = ...;
2185Instruction *newInst = new Instruction(...);
2186
2187pi-&gt;getParent()-&gt;getInstList().insert(pi, newInst);
2188</pre>
2189</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2190
2191 <p>In fact, this sequence of steps occurs so frequently that the
2192 <tt>Instruction</tt> class and <tt>Instruction</tt>-derived classes provide
2193 constructors which take (as a default parameter) a pointer to an
2194 <tt>Instruction</tt> which the newly-created <tt>Instruction</tt> should
2195 precede. That is, <tt>Instruction</tt> constructors are capable of
2196 inserting the newly-created instance into the <tt>BasicBlock</tt> of a
2197 provided instruction, immediately before that instruction. Using an
2198 <tt>Instruction</tt> constructor with a <tt>insertBefore</tt> (default)
2199 parameter, the above code becomes:</p>
2200
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2201<div class="doc_code">
2202<pre>
2203Instruction* pi = ...;
2204Instruction* newInst = new Instruction(..., pi);
2205</pre>
2206</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2207
2208 <p>which is much cleaner, especially if you're creating a lot of
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2209 instructions and adding them to <tt>BasicBlock</tt>s.</p></li>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2210</ul>
2211
2212</div>
2213
2214<!--_______________________________________________________________________-->
2215<div class="doc_subsubsection">
2216 <a name="schanges_deleting">Deleting <tt>Instruction</tt>s</a>
2217</div>
2218
2219<div class="doc_text">
2220
2221<p>Deleting an instruction from an existing sequence of instructions that form a
Chris Lattner69bf8a92004-05-23 21:06:58 +0000[diff] [blame]2222<a href="#BasicBlock"><tt>BasicBlock</tt></a> is very straight-forward. First,
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2223you must have a pointer to the instruction that you wish to delete. Second, you
2224need to obtain the pointer to that instruction's basic block. You use the
2225pointer to the basic block to get its list of instructions and then use the
2226erase function to remove your instruction. For example:</p>
2227
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2228<div class="doc_code">
2229<pre>
2230<a href="#Instruction">Instruction</a> *I = .. ;
Chris Lattner9f8ec252008-02-15 22:57:17 +0000[diff] [blame]2231I-&gt;eraseFromParent();
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2232</pre>
2233</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2234
2235</div>
2236
2237<!--_______________________________________________________________________-->
2238<div class="doc_subsubsection">
2239 <a name="schanges_replacing">Replacing an <tt>Instruction</tt> with another
2240 <tt>Value</tt></a>
2241</div>
2242
2243<div class="doc_text">
2244
2245<p><i>Replacing individual instructions</i></p>
2246
2247<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]2248permits use of two very useful replace functions: <tt>ReplaceInstWithValue</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2249and <tt>ReplaceInstWithInst</tt>.</p>
2250
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]2251<h4><a name="schanges_deleting">Deleting <tt>Instruction</tt>s</a></h4>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2252
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]2253<ul>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2254 <li><tt>ReplaceInstWithValue</tt>
2255
Nick Lewyckyb6d1f392008-09-15 06:31:52 +0000[diff] [blame]2256 <p>This function replaces all uses of a given instruction with a value,
2257 and then removes the original instruction. The following example
2258 illustrates the replacement of the result of a particular
Chris Lattner58360822005-01-17 00:12:04 +0000[diff] [blame]2259 <tt>AllocaInst</tt> that allocates memory for a single integer with a null
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2260 pointer to an integer.</p>
2261
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2262<div class="doc_code">
2263<pre>
2264AllocaInst* instToReplace = ...;
2265BasicBlock::iterator ii(instToReplace);
2266
2267ReplaceInstWithValue(instToReplace-&gt;getParent()-&gt;getInstList(), ii,
Daniel Dunbar58c2ac02008-10-03 22:17:25 +0000[diff] [blame]2268 Constant::getNullValue(PointerType::getUnqual(Type::Int32Ty)));
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2269</pre></div></li>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2270
2271 <li><tt>ReplaceInstWithInst</tt>
2272
2273 <p>This function replaces a particular instruction with another
Nick Lewyckyb6d1f392008-09-15 06:31:52 +0000[diff] [blame]2274 instruction, inserting the new instruction into the basic block at the
2275 location where the old instruction was, and replacing any uses of the old
2276 instruction with the new instruction. The following example illustrates
2277 the replacement of one <tt>AllocaInst</tt> with another.</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2278
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2279<div class="doc_code">
2280<pre>
2281AllocaInst* instToReplace = ...;
2282BasicBlock::iterator ii(instToReplace);
2283
2284ReplaceInstWithInst(instToReplace-&gt;getParent()-&gt;getInstList(), ii,
Nick Lewycky10d64b92007-12-03 01:52:52 +0000[diff] [blame]2285 new AllocaInst(Type::Int32Ty, 0, "ptrToReplacedInt"));
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2286</pre></div></li>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]2287</ul>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2288
2289<p><i>Replacing multiple uses of <tt>User</tt>s and <tt>Value</tt>s</i></p>
2290
2291<p>You can use <tt>Value::replaceAllUsesWith</tt> and
2292<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]2293doxygen documentation for the <a href="/doxygen/classllvm_1_1Value.html">Value Class</a>
Misha Brukman384047f2004-06-03 23:29:12 +0000[diff] [blame]2294and <a href="/doxygen/classllvm_1_1User.html">User Class</a>, respectively, for more
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2295information.</p>
2296
2297<!-- Value::replaceAllUsesWith User::replaceUsesOfWith Point out:
2298include/llvm/Transforms/Utils/ especially BasicBlockUtils.h with:
2299ReplaceInstWithValue, ReplaceInstWithInst -->
2300
2301</div>
2302
Tanya Lattnerb011c662007-06-20 18:33:15 +0000[diff] [blame]2303<!--_______________________________________________________________________-->
2304<div class="doc_subsubsection">
2305 <a name="schanges_deletingGV">Deleting <tt>GlobalVariable</tt>s</a>
2306</div>
2307
2308<div class="doc_text">
2309
Tanya Lattnerc5dfcdb2007-06-20 20:46:37 +0000[diff] [blame]2310<p>Deleting a global variable from a module is just as easy as deleting an
2311Instruction. First, you must have a pointer to the global variable that you wish
2312 to delete. You use this pointer to erase it from its parent, the module.
Tanya Lattnerb011c662007-06-20 18:33:15 +0000[diff] [blame]2313 For example:</p>
2314
2315<div class="doc_code">
2316<pre>
2317<a href="#GlobalVariable">GlobalVariable</a> *GV = .. ;
Tanya Lattnerb011c662007-06-20 18:33:15 +0000[diff] [blame]2318
Tanya Lattnerc5dfcdb2007-06-20 20:46:37 +0000[diff] [blame]2319GV-&gt;eraseFromParent();
Tanya Lattnerb011c662007-06-20 18:33:15 +0000[diff] [blame]2320</pre>
2321</div>
2322
2323</div>
2324
Jeffrey Yasskin714257f2009-04-30 22:33:41 +0000[diff] [blame]2325<!-- ======================================================================= -->
2326<div class="doc_subsection">
2327 <a name="create_types">How to Create Types</a>
2328</div>
2329
2330<div class="doc_text">
2331
2332<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]2333statically, you can use <tt>TypeBuilder&lt;...&gt;::get()</tt>, defined
Jeffrey Yasskin714257f2009-04-30 22:33:41 +0000[diff] [blame]2334in <tt>llvm/Support/TypeBuilder.h</tt>, to retrieve them. <tt>TypeBuilder</tt>
2335has two forms depending on whether you're building types for cross-compilation
Misha Brukman1af789f2009-05-01 20:40:51 +0000[diff] [blame]2336or native library use. <tt>TypeBuilder&lt;T, true&gt;</tt> requires
Jeffrey Yasskin714257f2009-04-30 22:33:41 +0000[diff] [blame]2337that <tt>T</tt> be independent of the host environment, meaning that it's built
2338out of types from
2339the <a href="/doxygen/namespacellvm_1_1types.html"><tt>llvm::types</tt></a>
2340namespace and pointers, functions, arrays, etc. built of
Misha Brukman1af789f2009-05-01 20:40:51 +0000[diff] [blame]2341those. <tt>TypeBuilder&lt;T, false&gt;</tt> additionally allows native C types
Jeffrey Yasskin714257f2009-04-30 22:33:41 +0000[diff] [blame]2342whose size may depend on the host compiler. For example,</p>
2343
2344<div class="doc_code">
2345<pre>
Misha Brukman1af789f2009-05-01 20:40:51 +0000[diff] [blame]2346FunctionType *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]2347</pre>
2348</div>
2349
2350<p>is easier to read and write than the equivalent</p>
2351
2352<div class="doc_code">
2353<pre>
Owen Anderson5e8c50e2009-06-16 17:40:28 +0000[diff] [blame]2354std::vector&lt;const Type*&gt; params;
Jeffrey Yasskin714257f2009-04-30 22:33:41 +0000[diff] [blame]2355params.push_back(PointerType::getUnqual(Type::Int32Ty));
2356FunctionType *ft = FunctionType::get(Type::Int8Ty, params, false);
2357</pre>
2358</div>
2359
2360<p>See the <a href="/doxygen/TypeBuilder_8h-source.html#l00001">class
2361comment</a> for more details.</p>
2362
2363</div>
2364
Chris Lattner9355b472002-09-06 02:50:58 +0000[diff] [blame]2365<!-- *********************************************************************** -->
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2366<div class="doc_section">
Owen Anderson8bc1b3b2009-06-16 01:17:16 +0000[diff] [blame]2367 <a name="threading">Threads and LLVM</a>
2368</div>
2369<!-- *********************************************************************** -->
2370
2371<div class="doc_text">
2372<p>
2373This section describes the interaction of the LLVM APIs with multithreading,
2374both on the part of client applications, and in the JIT, in the hosted
2375application.
2376</p>
2377
2378<p>
2379Note that LLVM's support for multithreading is still relatively young. Up
2380through version 2.5, the execution of threaded hosted applications was
2381supported, but not threaded client access to the APIs. While this use case is
2382now supported, clients <em>must</em> adhere to the guidelines specified below to
2383ensure proper operation in multithreaded mode.
2384</p>
2385
2386<p>
2387Note that, on Unix-like platforms, LLVM requires the presence of GCC's atomic
2388intrinsics in order to support threaded operation. If you need a
2389multhreading-capable LLVM on a platform without a suitably modern system
2390compiler, consider compiling LLVM and LLVM-GCC in single-threaded mode, and
2391using the resultant compiler to build a copy of LLVM with multithreading
2392support.
2393</p>
2394</div>
2395
2396<!-- ======================================================================= -->
2397<div class="doc_subsection">
Owen Anderson1ad70e32009-06-16 18:04:19 +0000[diff] [blame]2398 <a name="startmultithreaded">Entering and Exiting Multithreaded Mode</a>
Owen Anderson8bc1b3b2009-06-16 01:17:16 +0000[diff] [blame]2399</div>
2400
2401<div class="doc_text">
2402
2403<p>
2404In order to properly protect its internal data structures while avoiding
Owen Anderson1ad70e32009-06-16 18:04:19 +0000[diff] [blame]2405excessive locking overhead in the single-threaded case, the LLVM must intialize
2406certain data structures necessary to provide guards around its internals. To do
2407so, the client program must invoke <tt>llvm_start_multithreaded()</tt> before
2408making any concurrent LLVM API calls. To subsequently tear down these
2409structures, use the <tt>llvm_stop_multithreaded()</tt> call. You can also use
2410the <tt>llvm_is_multithreaded()</tt> call to check the status of multithreaded
2411mode.
Owen Anderson8bc1b3b2009-06-16 01:17:16 +0000[diff] [blame]2412</p>
2413
2414<p>
Owen Anderson1ad70e32009-06-16 18:04:19 +0000[diff] [blame]2415Note that both of these calls must be made <em>in isolation</em>. That is to
2416say that no other LLVM API calls may be executing at any time during the
2417execution of <tt>llvm_start_multithreaded()</tt> or <tt>llvm_stop_multithreaded
2418</tt>. It's is the client's responsibility to enforce this isolation.
2419</p>
2420
2421<p>
2422The return value of <tt>llvm_start_multithreaded()</tt> indicates the success or
2423failure of the initialization. Failure typically indicates that your copy of
2424LLVM was built without multithreading support, typically because GCC atomic
2425intrinsics were not found in your system compiler. In this case, the LLVM API
2426will not be safe for concurrent calls. However, it <em>will</em> be safe for
Jeffrey Yasskin01eba392010-01-29 19:10:38 +0000[diff] [blame]2427hosting threaded applications in the JIT, though <a href="#jitthreading">care
2428must be taken</a> to ensure that side exits and the like do not accidentally
2429result in concurrent LLVM API calls.
Owen Anderson8bc1b3b2009-06-16 01:17:16 +0000[diff] [blame]2430</p>
2431</div>
2432
2433<!-- ======================================================================= -->
2434<div class="doc_subsection">
2435 <a name="shutdown">Ending Execution with <tt>llvm_shutdown()</tt></a>
2436</div>
2437
2438<div class="doc_text">
2439<p>
2440When you are done using the LLVM APIs, you should call <tt>llvm_shutdown()</tt>
Owen Anderson1ad70e32009-06-16 18:04:19 +0000[diff] [blame]2441to deallocate memory used for internal structures. This will also invoke
2442<tt>llvm_stop_multithreaded()</tt> if LLVM is operating in multithreaded mode.
2443As such, <tt>llvm_shutdown()</tt> requires the same isolation guarantees as
2444<tt>llvm_stop_multithreaded()</tt>.
Owen Anderson8bc1b3b2009-06-16 01:17:16 +0000[diff] [blame]2445</p>
2446
2447<p>
2448Note that, if you use scope-based shutdown, you can use the
2449<tt>llvm_shutdown_obj</tt> class, which calls <tt>llvm_shutdown()</tt> in its
2450destructor.
2451</div>
2452
2453<!-- ======================================================================= -->
2454<div class="doc_subsection">
2455 <a name="managedstatic">Lazy Initialization with <tt>ManagedStatic</tt></a>
2456</div>
2457
2458<div class="doc_text">
2459<p>
2460<tt>ManagedStatic</tt> is a utility class in LLVM used to implement static
2461initialization of static resources, such as the global type tables. Before the
2462invocation of <tt>llvm_shutdown()</tt>, it implements a simple lazy
2463initialization scheme. Once <tt>llvm_start_multithreaded()</tt> returns,
2464however, it uses double-checked locking to implement thread-safe lazy
2465initialization.
2466</p>
2467
2468<p>
2469Note that, because no other threads are allowed to issue LLVM API calls before
2470<tt>llvm_start_multithreaded()</tt> returns, it is possible to have
2471<tt>ManagedStatic</tt>s of <tt>llvm::sys::Mutex</tt>s.
2472</p>
Owen Anderson1ad70e32009-06-16 18:04:19 +0000[diff] [blame]2473
2474<p>
2475The <tt>llvm_acquire_global_lock()</tt> and <tt>llvm_release_global_lock</tt>
2476APIs provide access to the global lock used to implement the double-checked
2477locking for lazy initialization. These should only be used internally to LLVM,
2478and only if you know what you're doing!
2479</p>
Owen Anderson8bc1b3b2009-06-16 01:17:16 +0000[diff] [blame]2480</div>
2481
Owen Andersone0c951a2009-08-19 17:58:52 +0000[diff] [blame]2482<!-- ======================================================================= -->
2483<div class="doc_subsection">
2484 <a name="llvmcontext">Achieving Isolation with <tt>LLVMContext</tt></a>
2485</div>
2486
2487<div class="doc_text">
2488<p>
2489<tt>LLVMContext</tt> is an opaque class in the LLVM API which clients can use
2490to operate multiple, isolated instances of LLVM concurrently within the same
2491address space. For instance, in a hypothetical compile-server, the compilation
2492of an individual translation unit is conceptually independent from all the
2493others, and it would be desirable to be able to compile incoming translation
2494units concurrently on independent server threads. Fortunately,
2495<tt>LLVMContext</tt> exists to enable just this kind of scenario!
2496</p>
2497
2498<p>
2499Conceptually, <tt>LLVMContext</tt> provides isolation. Every LLVM entity
2500(<tt>Module</tt>s, <tt>Value</tt>s, <tt>Type</tt>s, <tt>Constant</tt>s, etc.)
Chris Lattner38eee3c2009-08-20 03:10:14 +0000[diff] [blame]2501in LLVM's in-memory IR belongs to an <tt>LLVMContext</tt>. Entities in
Owen Andersone0c951a2009-08-19 17:58:52 +0000[diff] [blame]2502different contexts <em>cannot</em> interact with each other: <tt>Module</tt>s in
2503different contexts cannot be linked together, <tt>Function</tt>s cannot be added
2504to <tt>Module</tt>s in different contexts, etc. What this means is that is is
2505safe to compile on multiple threads simultaneously, as long as no two threads
2506operate on entities within the same context.
2507</p>
2508
2509<p>
2510In practice, very few places in the API require the explicit specification of a
2511<tt>LLVMContext</tt>, other than the <tt>Type</tt> creation/lookup APIs.
2512Because every <tt>Type</tt> carries a reference to its owning context, most
2513other entities can determine what context they belong to by looking at their
2514own <tt>Type</tt>. If you are adding new entities to LLVM IR, please try to
2515maintain this interface design.
2516</p>
2517
2518<p>
2519For clients that do <em>not</em> require the benefits of isolation, LLVM
2520provides a convenience API <tt>getGlobalContext()</tt>. This returns a global,
2521lazily initialized <tt>LLVMContext</tt> that may be used in situations where
2522isolation is not a concern.
2523</p>
2524</div>
2525
Jeffrey Yasskin01eba392010-01-29 19:10:38 +0000[diff] [blame]2526<!-- ======================================================================= -->
2527<div class="doc_subsection">
2528 <a name="jitthreading">Threads and the JIT</a>
2529</div>
2530
2531<div class="doc_text">
2532<p>
2533LLVM's "eager" JIT compiler is safe to use in threaded programs. Multiple
2534threads can call <tt>ExecutionEngine::getPointerToFunction()</tt> or
2535<tt>ExecutionEngine::runFunction()</tt> concurrently, and multiple threads can
2536run code output by the JIT concurrently. The user must still ensure that only
2537one thread accesses IR in a given <tt>LLVMContext</tt> while another thread
2538might be modifying it. One way to do that is to always hold the JIT lock while
2539accessing IR outside the JIT (the JIT <em>modifies</em> the IR by adding
2540<tt>CallbackVH</tt>s). Another way is to only
2541call <tt>getPointerToFunction()</tt> from the <tt>LLVMContext</tt>'s thread.
2542</p>
2543
2544<p>When the JIT is configured to compile lazily (using
2545<tt>ExecutionEngine::DisableLazyCompilation(false)</tt>), there is currently a
2546<a href="http://llvm.org/bugs/show_bug.cgi?id=5184">race condition</a> in
2547updating call sites after a function is lazily-jitted. It's still possible to
2548use the lazy JIT in a threaded program if you ensure that only one thread at a
2549time can call any particular lazy stub and that the JIT lock guards any IR
2550access, but we suggest using only the eager JIT in threaded programs.
2551</p>
2552</div>
2553
Owen Anderson8bc1b3b2009-06-16 01:17:16 +0000[diff] [blame]2554<!-- *********************************************************************** -->
2555<div class="doc_section">
Chris Lattnerd9d6e102005-04-23 16:10:52 +0000[diff] [blame]2556 <a name="advanced">Advanced Topics</a>
2557</div>
2558<!-- *********************************************************************** -->
2559
2560<div class="doc_text">
Chris Lattnerf1b200b2005-04-23 17:27:36 +0000[diff] [blame]2561<p>
2562This section describes some of the advanced or obscure API's that most clients
2563do not need to be aware of. These API's tend manage the inner workings of the
2564LLVM system, and only need to be accessed in unusual circumstances.
2565</p>
2566</div>
Chris Lattnerd9d6e102005-04-23 16:10:52 +0000[diff] [blame]2567
Chris Lattnerf1b200b2005-04-23 17:27:36 +0000[diff] [blame]2568<!-- ======================================================================= -->
2569<div class="doc_subsection">
2570 <a name="TypeResolve">LLVM Type Resolution</a>
2571</div>
Chris Lattnerd9d6e102005-04-23 16:10:52 +0000[diff] [blame]2572
Chris Lattnerf1b200b2005-04-23 17:27:36 +0000[diff] [blame]2573<div class="doc_text">
2574
2575<p>
2576The LLVM type system has a very simple goal: allow clients to compare types for
2577structural equality with a simple pointer comparison (aka a shallow compare).
2578This goal makes clients much simpler and faster, and is used throughout the LLVM
2579system.
2580</p>
2581
2582<p>
2583Unfortunately achieving this goal is not a simple matter. In particular,
2584recursive types and late resolution of opaque types makes the situation very
2585difficult to handle. Fortunately, for the most part, our implementation makes
2586most clients able to be completely unaware of the nasty internal details. The
2587primary case where clients are exposed to the inner workings of it are when
Gabor Greif04367bf2007-07-06 22:07:22 +0000[diff] [blame]2588building a recursive type. In addition to this case, the LLVM bitcode reader,
Chris Lattnerf1b200b2005-04-23 17:27:36 +0000[diff] [blame]2589assembly parser, and linker also have to be aware of the inner workings of this
2590system.
2591</p>
2592
Chris Lattner0f876db2005-04-25 15:47:57 +0000[diff] [blame]2593<p>
2594For our purposes below, we need three concepts. First, an "Opaque Type" is
2595exactly as defined in the <a href="LangRef.html#t_opaque">language
2596reference</a>. Second an "Abstract Type" is any type which includes an
Reid Spencer06565dc2007-01-12 17:11:23 +0000[diff] [blame]2597opaque type as part of its type graph (for example "<tt>{ opaque, i32 }</tt>").
2598Third, 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]2599float }</tt>").
2600</p>
2601
Chris Lattnerf1b200b2005-04-23 17:27:36 +0000[diff] [blame]2602</div>
2603
2604<!-- ______________________________________________________________________ -->
2605<div class="doc_subsubsection">
2606 <a name="BuildRecType">Basic Recursive Type Construction</a>
2607</div>
2608
2609<div class="doc_text">
2610
2611<p>
2612Because the most common question is "how do I build a recursive type with LLVM",
2613we answer it now and explain it as we go. Here we include enough to cause this
2614to be emitted to an output .ll file:
2615</p>
2616
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2617<div class="doc_code">
Chris Lattnerf1b200b2005-04-23 17:27:36 +0000[diff] [blame]2618<pre>
Reid Spencer06565dc2007-01-12 17:11:23 +0000[diff] [blame]2619%mylist = type { %mylist*, i32 }
Chris Lattnerf1b200b2005-04-23 17:27:36 +0000[diff] [blame]2620</pre>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2621</div>
Chris Lattnerf1b200b2005-04-23 17:27:36 +0000[diff] [blame]2622
2623<p>
2624To build this, use the following LLVM APIs:
2625</p>
2626
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2627<div class="doc_code">
Chris Lattnerf1b200b2005-04-23 17:27:36 +0000[diff] [blame]2628<pre>
Bill Wendling82e2eea2006-10-11 18:00:22 +0000[diff] [blame]2629// <i>Create the initial outer struct</i>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2630<a href="#PATypeHolder">PATypeHolder</a> StructTy = OpaqueType::get();
2631std::vector&lt;const Type*&gt; Elts;
Daniel Dunbar58c2ac02008-10-03 22:17:25 +0000[diff] [blame]2632Elts.push_back(PointerType::getUnqual(StructTy));
Nick Lewycky10d64b92007-12-03 01:52:52 +0000[diff] [blame]2633Elts.push_back(Type::Int32Ty);
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2634StructType *NewSTy = StructType::get(Elts);
Chris Lattnerf1b200b2005-04-23 17:27:36 +0000[diff] [blame]2635
Reid Spencer06565dc2007-01-12 17:11:23 +0000[diff] [blame]2636// <i>At this point, NewSTy = "{ opaque*, i32 }". Tell VMCore that</i>
Bill Wendling82e2eea2006-10-11 18:00:22 +0000[diff] [blame]2637// <i>the struct and the opaque type are actually the same.</i>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2638cast&lt;OpaqueType&gt;(StructTy.get())-&gt;<a href="#refineAbstractTypeTo">refineAbstractTypeTo</a>(NewSTy);
Chris Lattnerf1b200b2005-04-23 17:27:36 +0000[diff] [blame]2639
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2640// <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]2641// <i>kept up-to-date</i>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2642NewSTy = cast&lt;StructType&gt;(StructTy.get());
Chris Lattnerf1b200b2005-04-23 17:27:36 +0000[diff] [blame]2643
Bill Wendling82e2eea2006-10-11 18:00:22 +0000[diff] [blame]2644// <i>Add a name for the type to the module symbol table (optional)</i>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2645MyModule-&gt;addTypeName("mylist", NewSTy);
Chris Lattnerf1b200b2005-04-23 17:27:36 +0000[diff] [blame]2646</pre>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2647</div>
Chris Lattnerf1b200b2005-04-23 17:27:36 +0000[diff] [blame]2648
2649<p>
2650This code shows the basic approach used to build recursive types: build a
2651non-recursive type using 'opaque', then use type unification to close the cycle.
2652The type unification step is performed by the <tt><a
Chris Lattneraff26d12007-02-03 03:06:52 +0000[diff] [blame]2653href="#refineAbstractTypeTo">refineAbstractTypeTo</a></tt> method, which is
Chris Lattnerf1b200b2005-04-23 17:27:36 +0000[diff] [blame]2654described next. After that, we describe the <a
2655href="#PATypeHolder">PATypeHolder class</a>.
2656</p>
2657
2658</div>
2659
2660<!-- ______________________________________________________________________ -->
2661<div class="doc_subsubsection">
2662 <a name="refineAbstractTypeTo">The <tt>refineAbstractTypeTo</tt> method</a>
2663</div>
2664
2665<div class="doc_text">
2666<p>
2667The <tt>refineAbstractTypeTo</tt> method starts the type unification process.
2668While this method is actually a member of the DerivedType class, it is most
2669often used on OpaqueType instances. Type unification is actually a recursive
2670process. After unification, types can become structurally isomorphic to
2671existing types, and all duplicates are deleted (to preserve pointer equality).
2672</p>
2673
2674<p>
2675In the example above, the OpaqueType object is definitely deleted.
Reid Spencer06565dc2007-01-12 17:11:23 +0000[diff] [blame]2676Additionally, if there is an "{ \2*, i32}" type already created in the system,
Chris Lattnerf1b200b2005-04-23 17:27:36 +0000[diff] [blame]2677the pointer and struct type created are <b>also</b> deleted. Obviously whenever
2678a type is deleted, any "Type*" pointers in the program are invalidated. As
2679such, it is safest to avoid having <i>any</i> "Type*" pointers to abstract types
2680live across a call to <tt>refineAbstractTypeTo</tt> (note that non-abstract
2681types can never move or be deleted). To deal with this, the <a
2682href="#PATypeHolder">PATypeHolder</a> class is used to maintain a stable
2683reference to a possibly refined type, and the <a
2684href="#AbstractTypeUser">AbstractTypeUser</a> class is used to update more
2685complex datastructures.
2686</p>
2687
2688</div>
2689
2690<!-- ______________________________________________________________________ -->
2691<div class="doc_subsubsection">
2692 <a name="PATypeHolder">The PATypeHolder Class</a>
2693</div>
2694
2695<div class="doc_text">
2696<p>
2697PATypeHolder is a form of a "smart pointer" for Type objects. When VMCore
2698happily goes about nuking types that become isomorphic to existing types, it
2699automatically updates all PATypeHolder objects to point to the new type. In the
2700example above, this allows the code to maintain a pointer to the resultant
2701resolved recursive type, even though the Type*'s are potentially invalidated.
2702</p>
2703
2704<p>
2705PATypeHolder is an extremely light-weight object that uses a lazy union-find
2706implementation to update pointers. For example the pointer from a Value to its
2707Type is maintained by PATypeHolder objects.
2708</p>
2709
2710</div>
2711
2712<!-- ______________________________________________________________________ -->
2713<div class="doc_subsubsection">
2714 <a name="AbstractTypeUser">The AbstractTypeUser Class</a>
2715</div>
2716
2717<div class="doc_text">
2718
2719<p>
2720Some data structures need more to perform more complex updates when types get
Chris Lattner263a98e2007-02-16 04:37:31 +0000[diff] [blame]2721resolved. To support this, a class can derive from the AbstractTypeUser class.
2722This class
Chris Lattnerf1b200b2005-04-23 17:27:36 +0000[diff] [blame]2723allows it to get callbacks when certain types are resolved. To register to get
2724callbacks for a particular type, the DerivedType::{add/remove}AbstractTypeUser
Chris Lattner0f876db2005-04-25 15:47:57 +0000[diff] [blame]2725methods can be called on a type. Note that these methods only work for <i>
Reid Spencer06565dc2007-01-12 17:11:23 +0000[diff] [blame]2726 abstract</i> types. Concrete types (those that do not include any opaque
2727objects) can never be refined.
Chris Lattnerf1b200b2005-04-23 17:27:36 +0000[diff] [blame]2728</p>
Chris Lattnerd9d6e102005-04-23 16:10:52 +0000[diff] [blame]2729</div>
2730
2731
2732<!-- ======================================================================= -->
2733<div class="doc_subsection">
Chris Lattner263a98e2007-02-16 04:37:31 +0000[diff] [blame]2734 <a name="SymbolTable">The <tt>ValueSymbolTable</tt> and
2735 <tt>TypeSymbolTable</tt> classes</a>
Chris Lattnerd9d6e102005-04-23 16:10:52 +0000[diff] [blame]2736</div>
Chris Lattnerf1b200b2005-04-23 17:27:36 +0000[diff] [blame]2737
Chris Lattnerd9d6e102005-04-23 16:10:52 +0000[diff] [blame]2738<div class="doc_text">
Chris Lattner263a98e2007-02-16 04:37:31 +0000[diff] [blame]2739<p>The <tt><a href="http://llvm.org/doxygen/classllvm_1_1ValueSymbolTable.html">
2740ValueSymbolTable</a></tt> class provides a symbol table that the <a
Chris Lattnerd9d6e102005-04-23 16:10:52 +0000[diff] [blame]2741href="#Function"><tt>Function</tt></a> and <a href="#Module">
Chris Lattner263a98e2007-02-16 04:37:31 +0000[diff] [blame]2742<tt>Module</tt></a> classes use for naming value definitions. The symbol table
2743can provide a name for any <a href="#Value"><tt>Value</tt></a>.
2744The <tt><a href="http://llvm.org/doxygen/classllvm_1_1TypeSymbolTable.html">
2745TypeSymbolTable</a></tt> class is used by the <tt>Module</tt> class to store
2746names for types.</p>
Chris Lattnerd9d6e102005-04-23 16:10:52 +0000[diff] [blame]2747
Reid Spencera6362242007-01-07 00:41:39 +0000[diff] [blame]2748<p>Note that the <tt>SymbolTable</tt> class should not be directly accessed
2749by most clients. It should only be used when iteration over the symbol table
2750names themselves are required, which is very special purpose. Note that not
2751all LLVM
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2752<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]2753an empty name) do not exist in the symbol table.
2754</p>
2755
Chris Lattner263a98e2007-02-16 04:37:31 +0000[diff] [blame]2756<p>These symbol tables support iteration over the values/types in the symbol
2757table with <tt>begin/end/iterator</tt> and supports querying to see if a
2758specific name is in the symbol table (with <tt>lookup</tt>). The
2759<tt>ValueSymbolTable</tt> class exposes no public mutator methods, instead,
2760simply call <tt>setName</tt> on a value, which will autoinsert it into the
2761appropriate symbol table. For types, use the Module::addTypeName method to
2762insert entries into the symbol table.</p>
Chris Lattnerd9d6e102005-04-23 16:10:52 +0000[diff] [blame]2763
Chris Lattnerd9d6e102005-04-23 16:10:52 +0000[diff] [blame]2764</div>
2765
2766
2767
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2768<!-- ======================================================================= -->
2769<div class="doc_subsection">
2770 <a name="UserLayout">The <tt>User</tt> and owned <tt>Use</tt> classes' memory layout</a>
2771</div>
2772
2773<div class="doc_text">
2774<p>The <tt><a href="http://llvm.org/doxygen/classllvm_1_1User.html">
Gabor Greiffd095b62009-01-05 16:05:32 +0000[diff] [blame]2775User</a></tt> class provides a basis for expressing the ownership of <tt>User</tt>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2776towards other <tt><a href="http://llvm.org/doxygen/classllvm_1_1Value.html">
2777Value</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]2778Use</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]2779addition and removal.</p>
2780
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2781<!-- ______________________________________________________________________ -->
2782<div class="doc_subsubsection">
Gabor Greiffd095b62009-01-05 16:05:32 +0000[diff] [blame]2783 <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]2784</div>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2785
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2786<div class="doc_text">
2787<p>
2788A subclass of <tt>User</tt> can choose between incorporating its <tt>Use</tt> objects
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2789or refer to them out-of-line by means of a pointer. A mixed variant
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2790(some <tt>Use</tt>s inline others hung off) is impractical and breaks the invariant
2791that the <tt>Use</tt> objects belonging to the same <tt>User</tt> form a contiguous array.
2792</p>
2793</div>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2794
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2795<p>
2796We have 2 different layouts in the <tt>User</tt> (sub)classes:
2797<ul>
2798<li><p>Layout a)
2799The <tt>Use</tt> object(s) are inside (resp. at fixed offset) of the <tt>User</tt>
2800object and there are a fixed number of them.</p>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2801
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2802<li><p>Layout b)
2803The <tt>Use</tt> object(s) are referenced by a pointer to an
2804array from the <tt>User</tt> object and there may be a variable
2805number of them.</p>
2806</ul>
2807<p>
Gabor Greifd41720a2008-06-25 00:10:22 +0000[diff] [blame]2808As of v2.4 each layout still possesses a direct pointer to the
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2809start of the array of <tt>Use</tt>s. Though not mandatory for layout a),
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2810we stick to this redundancy for the sake of simplicity.
Gabor Greifd41720a2008-06-25 00:10:22 +0000[diff] [blame]2811The <tt>User</tt> object also stores the number of <tt>Use</tt> objects it
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2812has. (Theoretically this information can also be calculated
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2813given the scheme presented below.)</p>
2814<p>
2815Special forms of allocation operators (<tt>operator new</tt>)
Gabor Greifd41720a2008-06-25 00:10:22 +0000[diff] [blame]2816enforce the following memory layouts:</p>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2817
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2818<ul>
Gabor Greifd41720a2008-06-25 00:10:22 +0000[diff] [blame]2819<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]2820
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2821<pre>
2822...---.---.---.---.-------...
2823 | P | P | P | P | User
2824'''---'---'---'---'-------'''
2825</pre>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2826
Gabor Greifd41720a2008-06-25 00:10:22 +0000[diff] [blame]2827<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]2828<pre>
2829.-------...
2830| User
2831'-------'''
2832 |
2833 v
2834 .---.---.---.---...
2835 | P | P | P | P |
2836 '---'---'---'---'''
2837</pre>
2838</ul>
2839<i>(In the above figures '<tt>P</tt>' stands for the <tt>Use**</tt> that
2840 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]2841
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2842<!-- ______________________________________________________________________ -->
2843<div class="doc_subsubsection">
Gabor Greiffd095b62009-01-05 16:05:32 +0000[diff] [blame]2844 <a name="Waymarking">The waymarking algorithm</a>
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2845</div>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2846
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2847<div class="doc_text">
2848<p>
Gabor Greifd41720a2008-06-25 00:10:22 +0000[diff] [blame]2849Since the <tt>Use</tt> objects are deprived of the direct (back)pointer to
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2850their <tt>User</tt> objects, there must be a fast and exact method to
2851recover it. This is accomplished by the following scheme:</p>
2852</div>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2853
Gabor Greifd41720a2008-06-25 00:10:22 +0000[diff] [blame]2854A 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]2855start of the <tt>User</tt> object:
2856<ul>
2857<li><tt>00</tt> &mdash;&gt; binary digit 0</li>
2858<li><tt>01</tt> &mdash;&gt; binary digit 1</li>
2859<li><tt>10</tt> &mdash;&gt; stop and calculate (<tt>s</tt>)</li>
2860<li><tt>11</tt> &mdash;&gt; full stop (<tt>S</tt>)</li>
2861</ul>
2862<p>
2863Given a <tt>Use*</tt>, all we have to do is to walk till we get
2864a stop and we either have a <tt>User</tt> immediately behind or
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2865we have to walk to the next stop picking up digits
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2866and calculating the offset:</p>
2867<pre>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2868.---.---.---.---.---.---.---.---.---.---.---.---.---.---.---.---.----------------
2869| 1 | s | 1 | 0 | 1 | 0 | s | 1 | 1 | 0 | s | 1 | 1 | s | 1 | S | User (or User*)
2870'---'---'---'---'---'---'---'---'---'---'---'---'---'---'---'---'----------------
2871 |+15 |+10 |+6 |+3 |+1
2872 | | | | |__>
2873 | | | |__________>
2874 | | |______________________>
2875 | |______________________________________>
2876 |__________________________________________________________>
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2877</pre>
2878<p>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2879Only the significant number of bits need to be stored between the
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2880stops, so that the <i>worst case is 20 memory accesses</i> when there are
28811000 <tt>Use</tt> objects associated with a <tt>User</tt>.</p>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2882
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2883<!-- ______________________________________________________________________ -->
2884<div class="doc_subsubsection">
Gabor Greiffd095b62009-01-05 16:05:32 +0000[diff] [blame]2885 <a name="ReferenceImpl">Reference implementation</a>
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2886</div>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2887
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2888<div class="doc_text">
2889<p>
2890The following literate Haskell fragment demonstrates the concept:</p>
2891</div>
2892
2893<div class="doc_code">
2894<pre>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2895> import Test.QuickCheck
2896>
2897> digits :: Int -> [Char] -> [Char]
2898> digits 0 acc = '0' : acc
2899> digits 1 acc = '1' : acc
2900> digits n acc = digits (n `div` 2) $ digits (n `mod` 2) acc
2901>
2902> dist :: Int -> [Char] -> [Char]
2903> dist 0 [] = ['S']
2904> dist 0 acc = acc
2905> dist 1 acc = let r = dist 0 acc in 's' : digits (length r) r
2906> dist n acc = dist (n - 1) $ dist 1 acc
2907>
2908> takeLast n ss = reverse $ take n $ reverse ss
2909>
2910> test = takeLast 40 $ dist 20 []
2911>
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2912</pre>
2913</div>
2914<p>
2915Printing &lt;test&gt; gives: <tt>"1s100000s11010s10100s1111s1010s110s11s1S"</tt></p>
2916<p>
2917The reverse algorithm computes the length of the string just by examining
2918a certain prefix:</p>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2919
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2920<div class="doc_code">
2921<pre>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2922> pref :: [Char] -> Int
2923> pref "S" = 1
2924> pref ('s':'1':rest) = decode 2 1 rest
2925> pref (_:rest) = 1 + pref rest
2926>
2927> decode walk acc ('0':rest) = decode (walk + 1) (acc * 2) rest
2928> decode walk acc ('1':rest) = decode (walk + 1) (acc * 2 + 1) rest
2929> decode walk acc _ = walk + acc
2930>
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2931</pre>
2932</div>
2933<p>
2934Now, as expected, printing &lt;pref test&gt; gives <tt>40</tt>.</p>
2935<p>
2936We can <i>quickCheck</i> this with following property:</p>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2937
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2938<div class="doc_code">
2939<pre>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2940> testcase = dist 2000 []
2941> testcaseLength = length testcase
2942>
2943> identityProp n = n > 0 && n <= testcaseLength ==> length arr == pref arr
2944> where arr = takeLast n testcase
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2945>
2946</pre>
2947</div>
2948<p>
2949As expected &lt;quickCheck identityProp&gt; gives:</p>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2950
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2951<pre>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2952*Main> quickCheck identityProp
2953OK, passed 100 tests.
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2954</pre>
2955<p>
2956Let's be a bit more exhaustive:</p>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2957
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2958<div class="doc_code">
2959<pre>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2960>
2961> deepCheck p = check (defaultConfig { configMaxTest = 500 }) p
2962>
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2963</pre>
2964</div>
2965<p>
2966And here is the result of &lt;deepCheck identityProp&gt;:</p>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2967
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2968<pre>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2969*Main> deepCheck identityProp
2970OK, passed 500 tests.
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2971</pre>
2972
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2973<!-- ______________________________________________________________________ -->
2974<div class="doc_subsubsection">
Gabor Greiffd095b62009-01-05 16:05:32 +0000[diff] [blame]2975 <a name="Tagging">Tagging considerations</a>
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2976</div>
2977
2978<p>
2979To maintain the invariant that the 2 LSBits of each <tt>Use**</tt> in <tt>Use</tt>
2980never change after being set up, setters of <tt>Use::Prev</tt> must re-tag the
2981new <tt>Use**</tt> on every modification. Accordingly getters must strip the
2982tag bits.</p>
2983<p>
Gabor Greifd41720a2008-06-25 00:10:22 +0000[diff] [blame]2984For layout b) instead of the <tt>User</tt> we find a pointer (<tt>User*</tt> with LSBit set).
2985Following this pointer brings us to the <tt>User</tt>. A portable trick ensures
2986that the first bytes of <tt>User</tt> (if interpreted as a pointer) never has
Gabor Greiffd095b62009-01-05 16:05:32 +0000[diff] [blame]2987the LSBit set. (Portability is relying on the fact that all known compilers place the
2988<tt>vptr</tt> in the first word of the instances.)</p>
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2989
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2990</div>
2991
2992 <!-- *********************************************************************** -->
Chris Lattnerd9d6e102005-04-23 16:10:52 +0000[diff] [blame]2993<div class="doc_section">
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2994 <a name="coreclasses">The Core LLVM Class Hierarchy Reference </a>
2995</div>
2996<!-- *********************************************************************** -->
2997
2998<div class="doc_text">
Reid Spencer303c4b42007-01-12 17:26:25 +0000[diff] [blame]2999<p><tt>#include "<a href="/doxygen/Type_8h-source.html">llvm/Type.h</a>"</tt>
3000<br>doxygen info: <a href="/doxygen/classllvm_1_1Type.html">Type Class</a></p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3001
3002<p>The Core LLVM classes are the primary means of representing the program
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3003being inspected or transformed. The core LLVM classes are defined in
3004header files in the <tt>include/llvm/</tt> directory, and implemented in
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3005the <tt>lib/VMCore</tt> directory.</p>
3006
3007</div>
3008
3009<!-- ======================================================================= -->
3010<div class="doc_subsection">
Reid Spencer303c4b42007-01-12 17:26:25 +0000[diff] [blame]3011 <a name="Type">The <tt>Type</tt> class and Derived Types</a>
3012</div>
3013
3014<div class="doc_text">
3015
3016 <p><tt>Type</tt> is a superclass of all type classes. Every <tt>Value</tt> has
3017 a <tt>Type</tt>. <tt>Type</tt> cannot be instantiated directly but only
3018 through its subclasses. Certain primitive types (<tt>VoidType</tt>,
3019 <tt>LabelType</tt>, <tt>FloatType</tt> and <tt>DoubleType</tt>) have hidden
3020 subclasses. They are hidden because they offer no useful functionality beyond
3021 what the <tt>Type</tt> class offers except to distinguish themselves from
3022 other subclasses of <tt>Type</tt>.</p>
3023 <p>All other types are subclasses of <tt>DerivedType</tt>. Types can be
3024 named, but this is not a requirement. There exists exactly
3025 one instance of a given shape at any one time. This allows type equality to
3026 be performed with address equality of the Type Instance. That is, given two
3027 <tt>Type*</tt> values, the types are identical if the pointers are identical.
3028 </p>
3029</div>
3030
3031<!-- _______________________________________________________________________ -->
3032<div class="doc_subsubsection">
Gabor Greiffd095b62009-01-05 16:05:32 +0000[diff] [blame]3033 <a name="m_Type">Important Public Methods</a>
Reid Spencer303c4b42007-01-12 17:26:25 +0000[diff] [blame]3034</div>
3035
3036<div class="doc_text">
3037
3038<ul>
Duncan Sandsb0bc6c32010-02-15 16:12:20 +0000[diff] [blame]3039 <li><tt>bool isIntegerTy() const</tt>: Returns true for any integer type.</li>
Reid Spencer303c4b42007-01-12 17:26:25 +0000[diff] [blame]3040
Duncan Sandsb0bc6c32010-02-15 16:12:20 +0000[diff] [blame]3041 <li><tt>bool isFloatingPointTy()</tt>: Return true if this is one of the five
Reid Spencer303c4b42007-01-12 17:26:25 +0000[diff] [blame]3042 floating point types.</li>
3043
3044 <li><tt>bool isAbstract()</tt>: Return true if the type is abstract (contains
3045 an OpaqueType anywhere in its definition).</li>
3046
3047 <li><tt>bool isSized()</tt>: Return true if the type has known size. Things
3048 that don't have a size are abstract types, labels and void.</li>
3049
3050</ul>
3051</div>
3052
3053<!-- _______________________________________________________________________ -->
3054<div class="doc_subsubsection">
Gabor Greiffd095b62009-01-05 16:05:32 +0000[diff] [blame]3055 <a name="derivedtypes">Important Derived Types</a>
Reid Spencer303c4b42007-01-12 17:26:25 +0000[diff] [blame]3056</div>
3057<div class="doc_text">
3058<dl>
3059 <dt><tt>IntegerType</tt></dt>
3060 <dd>Subclass of DerivedType that represents integer types of any bit width.
3061 Any bit width between <tt>IntegerType::MIN_INT_BITS</tt> (1) and
3062 <tt>IntegerType::MAX_INT_BITS</tt> (~8 million) can be represented.
3063 <ul>
3064 <li><tt>static const IntegerType* get(unsigned NumBits)</tt>: get an integer
3065 type of a specific bit width.</li>
3066 <li><tt>unsigned getBitWidth() const</tt>: Get the bit width of an integer
3067 type.</li>
3068 </ul>
3069 </dd>
3070 <dt><tt>SequentialType</tt></dt>
3071 <dd>This is subclassed by ArrayType and PointerType
3072 <ul>
3073 <li><tt>const Type * getElementType() const</tt>: Returns the type of each
3074 of the elements in the sequential type. </li>
3075 </ul>
3076 </dd>
3077 <dt><tt>ArrayType</tt></dt>
3078 <dd>This is a subclass of SequentialType and defines the interface for array
3079 types.
3080 <ul>
3081 <li><tt>unsigned getNumElements() const</tt>: Returns the number of
3082 elements in the array. </li>
3083 </ul>
3084 </dd>
3085 <dt><tt>PointerType</tt></dt>
Chris Lattner302da1e2007-02-03 03:05:57 +0000[diff] [blame]3086 <dd>Subclass of SequentialType for pointer types.</dd>
Reid Spencer9d6565a2007-02-15 02:26:10 +0000[diff] [blame]3087 <dt><tt>VectorType</tt></dt>
Reid Spencer485bad12007-02-15 03:07:05 +0000[diff] [blame]3088 <dd>Subclass of SequentialType for vector types. A
3089 vector type is similar to an ArrayType but is distinguished because it is
Benjamin Kramer8040cd32009-10-12 14:46:08 +0000[diff] [blame]3090 a first class type whereas ArrayType is not. Vector types are used for
Reid Spencer303c4b42007-01-12 17:26:25 +0000[diff] [blame]3091 vector operations and are usually small vectors of of an integer or floating
3092 point type.</dd>
3093 <dt><tt>StructType</tt></dt>
3094 <dd>Subclass of DerivedTypes for struct types.</dd>
Duncan Sands8036ca42007-03-30 12:22:09 +0000[diff] [blame]3095 <dt><tt><a name="FunctionType">FunctionType</a></tt></dt>
Reid Spencer303c4b42007-01-12 17:26:25 +0000[diff] [blame]3096 <dd>Subclass of DerivedTypes for function types.
3097 <ul>
Dan Gohman4bb31bf2010-03-30 20:04:57 +0000[diff] [blame]3098 <li><tt>bool isVarArg() const</tt>: Returns true if it's a vararg
Reid Spencer303c4b42007-01-12 17:26:25 +0000[diff] [blame]3099 function</li>
3100 <li><tt> const Type * getReturnType() const</tt>: Returns the
3101 return type of the function.</li>
3102 <li><tt>const Type * getParamType (unsigned i)</tt>: Returns
3103 the type of the ith parameter.</li>
3104 <li><tt> const unsigned getNumParams() const</tt>: Returns the
3105 number of formal parameters.</li>
3106 </ul>
3107 </dd>
3108 <dt><tt>OpaqueType</tt></dt>
3109 <dd>Sublcass of DerivedType for abstract types. This class
3110 defines no content and is used as a placeholder for some other type. Note
3111 that OpaqueType is used (temporarily) during type resolution for forward
3112 references of types. Once the referenced type is resolved, the OpaqueType
3113 is replaced with the actual type. OpaqueType can also be used for data
3114 abstraction. At link time opaque types can be resolved to actual types
3115 of the same name.</dd>
3116</dl>
3117</div>
3118
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]3119
3120
3121<!-- ======================================================================= -->
3122<div class="doc_subsection">
3123 <a name="Module">The <tt>Module</tt> class</a>
3124</div>
3125
3126<div class="doc_text">
3127
3128<p><tt>#include "<a
3129href="/doxygen/Module_8h-source.html">llvm/Module.h</a>"</tt><br> doxygen info:
3130<a href="/doxygen/classllvm_1_1Module.html">Module Class</a></p>
3131
3132<p>The <tt>Module</tt> class represents the top level structure present in LLVM
3133programs. An LLVM module is effectively either a translation unit of the
3134original program or a combination of several translation units merged by the
3135linker. The <tt>Module</tt> class keeps track of a list of <a
3136href="#Function"><tt>Function</tt></a>s, a list of <a
3137href="#GlobalVariable"><tt>GlobalVariable</tt></a>s, and a <a
3138href="#SymbolTable"><tt>SymbolTable</tt></a>. Additionally, it contains a few
3139helpful member functions that try to make common operations easy.</p>
3140
3141</div>
3142
3143<!-- _______________________________________________________________________ -->
3144<div class="doc_subsubsection">
3145 <a name="m_Module">Important Public Members of the <tt>Module</tt> class</a>
3146</div>
3147
3148<div class="doc_text">
3149
3150<ul>
3151 <li><tt>Module::Module(std::string name = "")</tt></li>
3152</ul>
3153
3154<p>Constructing a <a href="#Module">Module</a> is easy. You can optionally
3155provide a name for it (probably based on the name of the translation unit).</p>
3156
3157<ul>
3158 <li><tt>Module::iterator</tt> - Typedef for function list iterator<br>
3159 <tt>Module::const_iterator</tt> - Typedef for const_iterator.<br>
3160
3161 <tt>begin()</tt>, <tt>end()</tt>
3162 <tt>size()</tt>, <tt>empty()</tt>
3163
3164 <p>These are forwarding methods that make it easy to access the contents of
3165 a <tt>Module</tt> object's <a href="#Function"><tt>Function</tt></a>
3166 list.</p></li>
3167
3168 <li><tt>Module::FunctionListType &amp;getFunctionList()</tt>
3169
3170 <p> Returns the list of <a href="#Function"><tt>Function</tt></a>s. This is
3171 necessary to use when you need to update the list or perform a complex
3172 action that doesn't have a forwarding method.</p>
3173
3174 <p><!-- Global Variable --></p></li>
3175</ul>
3176
3177<hr>
3178
3179<ul>
3180 <li><tt>Module::global_iterator</tt> - Typedef for global variable list iterator<br>
3181
3182 <tt>Module::const_global_iterator</tt> - Typedef for const_iterator.<br>
3183
3184 <tt>global_begin()</tt>, <tt>global_end()</tt>
3185 <tt>global_size()</tt>, <tt>global_empty()</tt>
3186
3187 <p> These are forwarding methods that make it easy to access the contents of
3188 a <tt>Module</tt> object's <a
3189 href="#GlobalVariable"><tt>GlobalVariable</tt></a> list.</p></li>
3190
3191 <li><tt>Module::GlobalListType &amp;getGlobalList()</tt>
3192
3193 <p>Returns the list of <a
3194 href="#GlobalVariable"><tt>GlobalVariable</tt></a>s. This is necessary to
3195 use when you need to update the list or perform a complex action that
3196 doesn't have a forwarding method.</p>
3197
3198 <p><!-- Symbol table stuff --> </p></li>
3199</ul>
3200
3201<hr>
3202
3203<ul>
3204 <li><tt><a href="#SymbolTable">SymbolTable</a> *getSymbolTable()</tt>
3205
3206 <p>Return a reference to the <a href="#SymbolTable"><tt>SymbolTable</tt></a>
3207 for this <tt>Module</tt>.</p>
3208
3209 <p><!-- Convenience methods --></p></li>
3210</ul>
3211
3212<hr>
3213
3214<ul>
3215 <li><tt><a href="#Function">Function</a> *getFunction(const std::string
3216 &amp;Name, const <a href="#FunctionType">FunctionType</a> *Ty)</tt>
3217
3218 <p>Look up the specified function in the <tt>Module</tt> <a
3219 href="#SymbolTable"><tt>SymbolTable</tt></a>. If it does not exist, return
3220 <tt>null</tt>.</p></li>
3221
3222 <li><tt><a href="#Function">Function</a> *getOrInsertFunction(const
3223 std::string &amp;Name, const <a href="#FunctionType">FunctionType</a> *T)</tt>
3224
3225 <p>Look up the specified function in the <tt>Module</tt> <a
3226 href="#SymbolTable"><tt>SymbolTable</tt></a>. If it does not exist, add an
3227 external declaration for the function and return it.</p></li>
3228
3229 <li><tt>std::string getTypeName(const <a href="#Type">Type</a> *Ty)</tt>
3230
3231 <p>If there is at least one entry in the <a
3232 href="#SymbolTable"><tt>SymbolTable</tt></a> for the specified <a
3233 href="#Type"><tt>Type</tt></a>, return it. Otherwise return the empty
3234 string.</p></li>
3235
3236 <li><tt>bool addTypeName(const std::string &amp;Name, const <a
3237 href="#Type">Type</a> *Ty)</tt>
3238
3239 <p>Insert an entry in the <a href="#SymbolTable"><tt>SymbolTable</tt></a>
3240 mapping <tt>Name</tt> to <tt>Ty</tt>. If there is already an entry for this
3241 name, true is returned and the <a
3242 href="#SymbolTable"><tt>SymbolTable</tt></a> is not modified.</p></li>
3243</ul>
3244
3245</div>
3246
3247
Reid Spencer303c4b42007-01-12 17:26:25 +0000[diff] [blame]3248<!-- ======================================================================= -->
3249<div class="doc_subsection">
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3250 <a name="Value">The <tt>Value</tt> class</a>
3251</div>
3252
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]3253<div class="doc_text">
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3254
3255<p><tt>#include "<a href="/doxygen/Value_8h-source.html">llvm/Value.h</a>"</tt>
3256<br>
Chris Lattner00815172007-01-04 22:01:45 +0000[diff] [blame]3257doxygen info: <a href="/doxygen/classllvm_1_1Value.html">Value Class</a></p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3258
3259<p>The <tt>Value</tt> class is the most important class in the LLVM Source
3260base. It represents a typed value that may be used (among other things) as an
3261operand to an instruction. There are many different types of <tt>Value</tt>s,
3262such as <a href="#Constant"><tt>Constant</tt></a>s,<a
3263href="#Argument"><tt>Argument</tt></a>s. Even <a
3264href="#Instruction"><tt>Instruction</tt></a>s and <a
3265href="#Function"><tt>Function</tt></a>s are <tt>Value</tt>s.</p>
3266
3267<p>A particular <tt>Value</tt> may be used many times in the LLVM representation
3268for a program. For example, an incoming argument to a function (represented
3269with an instance of the <a href="#Argument">Argument</a> class) is "used" by
3270every instruction in the function that references the argument. To keep track
3271of this relationship, the <tt>Value</tt> class keeps a list of all of the <a
3272href="#User"><tt>User</tt></a>s that is using it (the <a
3273href="#User"><tt>User</tt></a> class is a base class for all nodes in the LLVM
3274graph that can refer to <tt>Value</tt>s). This use list is how LLVM represents
3275def-use information in the program, and is accessible through the <tt>use_</tt>*
3276methods, shown below.</p>
3277
3278<p>Because LLVM is a typed representation, every LLVM <tt>Value</tt> is typed,
3279and this <a href="#Type">Type</a> is available through the <tt>getType()</tt>
3280method. In addition, all LLVM values can be named. The "name" of the
3281<tt>Value</tt> is a symbolic string printed in the LLVM code:</p>
3282
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]3283<div class="doc_code">
3284<pre>
Reid Spencer06565dc2007-01-12 17:11:23 +0000[diff] [blame]3285%<b>foo</b> = add i32 1, 2
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]3286</pre>
3287</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3288
Duncan Sands8036ca42007-03-30 12:22:09 +0000[diff] [blame]3289<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]3290that the name of any value may be missing (an empty string), so names should
3291<b>ONLY</b> be used for debugging (making the source code easier to read,
3292debugging printouts), they should not be used to keep track of values or map
3293between them. For this purpose, use a <tt>std::map</tt> of pointers to the
3294<tt>Value</tt> itself instead.</p>
3295
3296<p>One important aspect of LLVM is that there is no distinction between an SSA
3297variable and the operation that produces it. Because of this, any reference to
3298the value produced by an instruction (or the value available as an incoming
Chris Lattnerd5fc4fc2004-03-18 14:58:55 +0000[diff] [blame]3299argument, for example) is represented as a direct pointer to the instance of
3300the class that
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3301represents this value. Although this may take some getting used to, it
3302simplifies the representation and makes it easier to manipulate.</p>
3303
3304</div>
3305
3306<!-- _______________________________________________________________________ -->
3307<div class="doc_subsubsection">
3308 <a name="m_Value">Important Public Members of the <tt>Value</tt> class</a>
3309</div>
3310
3311<div class="doc_text">
3312
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3313<ul>
3314 <li><tt>Value::use_iterator</tt> - Typedef for iterator over the
3315use-list<br>
Gabor Greifbbbf9a22010-03-26 19:59:25 +0000[diff] [blame]3316 <tt>Value::const_use_iterator</tt> - Typedef for const_iterator over
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3317the use-list<br>
3318 <tt>unsigned use_size()</tt> - Returns the number of users of the
3319value.<br>
Chris Lattner9355b472002-09-06 02:50:58 +0000[diff] [blame]3320 <tt>bool use_empty()</tt> - Returns true if there are no users.<br>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3321 <tt>use_iterator use_begin()</tt> - Get an iterator to the start of
3322the use-list.<br>
3323 <tt>use_iterator use_end()</tt> - Get an iterator to the end of the
3324use-list.<br>
3325 <tt><a href="#User">User</a> *use_back()</tt> - Returns the last
3326element in the list.
3327 <p> These methods are the interface to access the def-use
3328information in LLVM. As with all other iterators in LLVM, the naming
3329conventions follow the conventions defined by the <a href="#stl">STL</a>.</p>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3330 </li>
3331 <li><tt><a href="#Type">Type</a> *getType() const</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3332 <p>This method returns the Type of the Value.</p>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3333 </li>
3334 <li><tt>bool hasName() const</tt><br>
Chris Lattner9355b472002-09-06 02:50:58 +0000[diff] [blame]3335 <tt>std::string getName() const</tt><br>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3336 <tt>void setName(const std::string &amp;Name)</tt>
3337 <p> This family of methods is used to access and assign a name to a <tt>Value</tt>,
3338be aware of the <a href="#nameWarning">precaution above</a>.</p>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3339 </li>
3340 <li><tt>void replaceAllUsesWith(Value *V)</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3341
3342 <p>This method traverses the use list of a <tt>Value</tt> changing all <a
3343 href="#User"><tt>User</tt>s</a> of the current value to refer to
3344 "<tt>V</tt>" instead. For example, if you detect that an instruction always
3345 produces a constant value (for example through constant folding), you can
3346 replace all uses of the instruction with the constant like this:</p>
3347
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]3348<div class="doc_code">
3349<pre>
3350Inst-&gt;replaceAllUsesWith(ConstVal);
3351</pre>
3352</div>
3353
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3354</ul>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3355
3356</div>
3357
3358<!-- ======================================================================= -->
3359<div class="doc_subsection">
3360 <a name="User">The <tt>User</tt> class</a>
3361</div>
3362
3363<div class="doc_text">
3364
3365<p>
3366<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]3367doxygen info: <a href="/doxygen/classllvm_1_1User.html">User Class</a><br>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3368Superclass: <a href="#Value"><tt>Value</tt></a></p>
3369
3370<p>The <tt>User</tt> class is the common base class of all LLVM nodes that may
3371refer to <a href="#Value"><tt>Value</tt></a>s. It exposes a list of "Operands"
3372that are all of the <a href="#Value"><tt>Value</tt></a>s that the User is
3373referring to. The <tt>User</tt> class itself is a subclass of
3374<tt>Value</tt>.</p>
3375
3376<p>The operands of a <tt>User</tt> point directly to the LLVM <a
3377href="#Value"><tt>Value</tt></a> that it refers to. Because LLVM uses Static
3378Single Assignment (SSA) form, there can only be one definition referred to,
3379allowing this direct connection. This connection provides the use-def
3380information in LLVM.</p>
3381
3382</div>
3383
3384<!-- _______________________________________________________________________ -->
3385<div class="doc_subsubsection">
3386 <a name="m_User">Important Public Members of the <tt>User</tt> class</a>
3387</div>
3388
3389<div class="doc_text">
3390
3391<p>The <tt>User</tt> class exposes the operand list in two ways: through
3392an index access interface and through an iterator based interface.</p>
3393
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3394<ul>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3395 <li><tt>Value *getOperand(unsigned i)</tt><br>
3396 <tt>unsigned getNumOperands()</tt>
3397 <p> These two methods expose the operands of the <tt>User</tt> in a
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3398convenient form for direct access.</p></li>
3399
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3400 <li><tt>User::op_iterator</tt> - Typedef for iterator over the operand
3401list<br>
Chris Lattner58360822005-01-17 00:12:04 +0000[diff] [blame]3402 <tt>op_iterator op_begin()</tt> - Get an iterator to the start of
3403the operand list.<br>
3404 <tt>op_iterator op_end()</tt> - Get an iterator to the end of the
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3405operand list.
3406 <p> Together, these methods make up the iterator based interface to
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3407the operands of a <tt>User</tt>.</p></li>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3408</ul>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3409
3410</div>
3411
3412<!-- ======================================================================= -->
3413<div class="doc_subsection">
3414 <a name="Instruction">The <tt>Instruction</tt> class</a>
3415</div>
3416
3417<div class="doc_text">
3418
3419<p><tt>#include "</tt><tt><a
3420href="/doxygen/Instruction_8h-source.html">llvm/Instruction.h</a>"</tt><br>
Misha Brukman31ca1de2004-06-03 23:35:54 +0000[diff] [blame]3421doxygen info: <a href="/doxygen/classllvm_1_1Instruction.html">Instruction Class</a><br>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3422Superclasses: <a href="#User"><tt>User</tt></a>, <a
3423href="#Value"><tt>Value</tt></a></p>
3424
3425<p>The <tt>Instruction</tt> class is the common base class for all LLVM
3426instructions. It provides only a few methods, but is a very commonly used
3427class. The primary data tracked by the <tt>Instruction</tt> class itself is the
3428opcode (instruction type) and the parent <a
3429href="#BasicBlock"><tt>BasicBlock</tt></a> the <tt>Instruction</tt> is embedded
3430into. To represent a specific type of instruction, one of many subclasses of
3431<tt>Instruction</tt> are used.</p>
3432
3433<p> Because the <tt>Instruction</tt> class subclasses the <a
3434href="#User"><tt>User</tt></a> class, its operands can be accessed in the same
3435way as for other <a href="#User"><tt>User</tt></a>s (with the
3436<tt>getOperand()</tt>/<tt>getNumOperands()</tt> and
3437<tt>op_begin()</tt>/<tt>op_end()</tt> methods).</p> <p> An important file for
3438the <tt>Instruction</tt> class is the <tt>llvm/Instruction.def</tt> file. This
3439file contains some meta-data about the various different types of instructions
3440in LLVM. It describes the enum values that are used as opcodes (for example
Reid Spencerc92d25d2006-12-19 19:47:19 +0000[diff] [blame]3441<tt>Instruction::Add</tt> and <tt>Instruction::ICmp</tt>), as well as the
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3442concrete sub-classes of <tt>Instruction</tt> that implement the instruction (for
3443example <tt><a href="#BinaryOperator">BinaryOperator</a></tt> and <tt><a
Reid Spencerc92d25d2006-12-19 19:47:19 +0000[diff] [blame]3444href="#CmpInst">CmpInst</a></tt>). Unfortunately, the use of macros in
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3445this file confuses doxygen, so these enum values don't show up correctly in the
Misha Brukman31ca1de2004-06-03 23:35:54 +0000[diff] [blame]3446<a href="/doxygen/classllvm_1_1Instruction.html">doxygen output</a>.</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3447
3448</div>
3449
3450<!-- _______________________________________________________________________ -->
3451<div class="doc_subsubsection">
Reid Spencerc92d25d2006-12-19 19:47:19 +0000[diff] [blame]3452 <a name="s_Instruction">Important Subclasses of the <tt>Instruction</tt>
3453 class</a>
3454</div>
3455<div class="doc_text">
3456 <ul>
3457 <li><tt><a name="BinaryOperator">BinaryOperator</a></tt>
3458 <p>This subclasses represents all two operand instructions whose operands
3459 must be the same type, except for the comparison instructions.</p></li>
3460 <li><tt><a name="CastInst">CastInst</a></tt>
3461 <p>This subclass is the parent of the 12 casting instructions. It provides
3462 common operations on cast instructions.</p>
3463 <li><tt><a name="CmpInst">CmpInst</a></tt>
3464 <p>This subclass respresents the two comparison instructions,
3465 <a href="LangRef.html#i_icmp">ICmpInst</a> (integer opreands), and
3466 <a href="LangRef.html#i_fcmp">FCmpInst</a> (floating point operands).</p>
3467 <li><tt><a name="TerminatorInst">TerminatorInst</a></tt>
3468 <p>This subclass is the parent of all terminator instructions (those which
3469 can terminate a block).</p>
3470 </ul>
3471 </div>
3472
3473<!-- _______________________________________________________________________ -->
3474<div class="doc_subsubsection">
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3475 <a name="m_Instruction">Important Public Members of the <tt>Instruction</tt>
3476 class</a>
3477</div>
3478
3479<div class="doc_text">
3480
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3481<ul>
3482 <li><tt><a href="#BasicBlock">BasicBlock</a> *getParent()</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3483 <p>Returns the <a href="#BasicBlock"><tt>BasicBlock</tt></a> that
3484this <tt>Instruction</tt> is embedded into.</p></li>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3485 <li><tt>bool mayWriteToMemory()</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3486 <p>Returns true if the instruction writes to memory, i.e. it is a
3487 <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]3488 <li><tt>unsigned getOpcode()</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3489 <p>Returns the opcode for the <tt>Instruction</tt>.</p></li>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3490 <li><tt><a href="#Instruction">Instruction</a> *clone() const</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3491 <p>Returns another instance of the specified instruction, identical
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3492in all ways to the original except that the instruction has no parent
3493(ie it's not embedded into a <a href="#BasicBlock"><tt>BasicBlock</tt></a>),
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3494and it has no name</p></li>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3495</ul>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3496
3497</div>
3498
3499<!-- ======================================================================= -->
3500<div class="doc_subsection">
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]3501 <a name="Constant">The <tt>Constant</tt> class and subclasses</a>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3502</div>
3503
3504<div class="doc_text">
3505
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]3506<p>Constant represents a base class for different types of constants. It
3507is subclassed by ConstantInt, ConstantArray, etc. for representing
3508the various types of Constants. <a href="#GlobalValue">GlobalValue</a> is also
3509a subclass, which represents the address of a global variable or function.
3510</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3511
3512</div>
3513
3514<!-- _______________________________________________________________________ -->
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]3515<div class="doc_subsubsection">Important Subclasses of Constant </div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3516<div class="doc_text">
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3517<ul>
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]3518 <li>ConstantInt : This subclass of Constant represents an integer constant of
3519 any width.
3520 <ul>
Reid Spencer97b4ee32007-03-01 21:05:33 +0000[diff] [blame]3521 <li><tt>const APInt&amp; getValue() const</tt>: Returns the underlying
3522 value of this constant, an APInt value.</li>
3523 <li><tt>int64_t getSExtValue() const</tt>: Converts the underlying APInt
3524 value to an int64_t via sign extension. If the value (not the bit width)
3525 of the APInt is too large to fit in an int64_t, an assertion will result.
3526 For this reason, use of this method is discouraged.</li>
3527 <li><tt>uint64_t getZExtValue() const</tt>: Converts the underlying APInt
3528 value to a uint64_t via zero extension. IF the value (not the bit width)
3529 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]3530 For this reason, use of this method is discouraged.</li>
Reid Spencer97b4ee32007-03-01 21:05:33 +0000[diff] [blame]3531 <li><tt>static ConstantInt* get(const APInt&amp; Val)</tt>: Returns the
3532 ConstantInt object that represents the value provided by <tt>Val</tt>.
3533 The type is implied as the IntegerType that corresponds to the bit width
3534 of <tt>Val</tt>.</li>
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]3535 <li><tt>static ConstantInt* get(const Type *Ty, uint64_t Val)</tt>:
3536 Returns the ConstantInt object that represents the value provided by
3537 <tt>Val</tt> for integer type <tt>Ty</tt>.</li>
3538 </ul>
3539 </li>
3540 <li>ConstantFP : This class represents a floating point constant.
3541 <ul>
3542 <li><tt>double getValue() const</tt>: Returns the underlying value of
3543 this constant. </li>
3544 </ul>
3545 </li>
3546 <li>ConstantArray : This represents a constant array.
3547 <ul>
3548 <li><tt>const std::vector&lt;Use&gt; &amp;getValues() const</tt>: Returns
3549 a vector of component constants that makeup this array. </li>
3550 </ul>
3551 </li>
3552 <li>ConstantStruct : This represents a constant struct.
3553 <ul>
3554 <li><tt>const std::vector&lt;Use&gt; &amp;getValues() const</tt>: Returns
3555 a vector of component constants that makeup this array. </li>
3556 </ul>
3557 </li>
3558 <li>GlobalValue : This represents either a global variable or a function. In
3559 either case, the value is a constant fixed address (after linking).
3560 </li>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3561</ul>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3562</div>
3563
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]3564
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3565<!-- ======================================================================= -->
3566<div class="doc_subsection">
3567 <a name="GlobalValue">The <tt>GlobalValue</tt> class</a>
3568</div>
3569
3570<div class="doc_text">
3571
3572<p><tt>#include "<a
3573href="/doxygen/GlobalValue_8h-source.html">llvm/GlobalValue.h</a>"</tt><br>
Misha Brukman384047f2004-06-03 23:29:12 +0000[diff] [blame]3574doxygen info: <a href="/doxygen/classllvm_1_1GlobalValue.html">GlobalValue
3575Class</a><br>
Reid Spencerbe5e85e2006-04-14 14:11:48 +0000[diff] [blame]3576Superclasses: <a href="#Constant"><tt>Constant</tt></a>,
3577<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]3578
3579<p>Global values (<a href="#GlobalVariable"><tt>GlobalVariable</tt></a>s or <a
3580href="#Function"><tt>Function</tt></a>s) are the only LLVM values that are
3581visible in the bodies of all <a href="#Function"><tt>Function</tt></a>s.
3582Because they are visible at global scope, they are also subject to linking with
3583other globals defined in different translation units. To control the linking
3584process, <tt>GlobalValue</tt>s know their linkage rules. Specifically,
3585<tt>GlobalValue</tt>s know whether they have internal or external linkage, as
Reid Spencer8b2da7a2004-07-18 13:10:31 +0000[diff] [blame]3586defined by the <tt>LinkageTypes</tt> enumeration.</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3587
3588<p>If a <tt>GlobalValue</tt> has internal linkage (equivalent to being
3589<tt>static</tt> in C), it is not visible to code outside the current translation
3590unit, and does not participate in linking. If it has external linkage, it is
3591visible to external code, and does participate in linking. In addition to
3592linkage information, <tt>GlobalValue</tt>s keep track of which <a
3593href="#Module"><tt>Module</tt></a> they are currently part of.</p>
3594
3595<p>Because <tt>GlobalValue</tt>s are memory objects, they are always referred to
3596by their <b>address</b>. As such, the <a href="#Type"><tt>Type</tt></a> of a
3597global is always a pointer to its contents. It is important to remember this
3598when using the <tt>GetElementPtrInst</tt> instruction because this pointer must
3599be dereferenced first. For example, if you have a <tt>GlobalVariable</tt> (a
3600subclass 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]3601i32]</tt>, then the <tt>GlobalVariable</tt> is a pointer to that array. Although
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3602the address of the first element of this array and the value of the
3603<tt>GlobalVariable</tt> are the same, they have different types. The
Reid Spencer06565dc2007-01-12 17:11:23 +0000[diff] [blame]3604<tt>GlobalVariable</tt>'s type is <tt>[24 x i32]</tt>. The first element's type
3605is <tt>i32.</tt> Because of this, accessing a global value requires you to
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3606dereference the pointer with <tt>GetElementPtrInst</tt> first, then its elements
3607can be accessed. This is explained in the <a href="LangRef.html#globalvars">LLVM
3608Language Reference Manual</a>.</p>
3609
3610</div>
3611
3612<!-- _______________________________________________________________________ -->
3613<div class="doc_subsubsection">
3614 <a name="m_GlobalValue">Important Public Members of the <tt>GlobalValue</tt>
3615 class</a>
3616</div>
3617
3618<div class="doc_text">
3619
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3620<ul>
3621 <li><tt>bool hasInternalLinkage() const</tt><br>
Chris Lattner9355b472002-09-06 02:50:58 +0000[diff] [blame]3622 <tt>bool hasExternalLinkage() const</tt><br>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3623 <tt>void setInternalLinkage(bool HasInternalLinkage)</tt>
3624 <p> These methods manipulate the linkage characteristics of the <tt>GlobalValue</tt>.</p>
3625 <p> </p>
3626 </li>
3627 <li><tt><a href="#Module">Module</a> *getParent()</tt>
3628 <p> This returns the <a href="#Module"><tt>Module</tt></a> that the
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3629GlobalValue is currently embedded into.</p></li>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3630</ul>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3631
3632</div>
3633
3634<!-- ======================================================================= -->
3635<div class="doc_subsection">
3636 <a name="Function">The <tt>Function</tt> class</a>
3637</div>
3638
3639<div class="doc_text">
3640
3641<p><tt>#include "<a
3642href="/doxygen/Function_8h-source.html">llvm/Function.h</a>"</tt><br> doxygen
Misha Brukman31ca1de2004-06-03 23:35:54 +0000[diff] [blame]3643info: <a href="/doxygen/classllvm_1_1Function.html">Function Class</a><br>
Reid Spencerbe5e85e2006-04-14 14:11:48 +0000[diff] [blame]3644Superclasses: <a href="#GlobalValue"><tt>GlobalValue</tt></a>,
3645<a href="#Constant"><tt>Constant</tt></a>,
3646<a href="#User"><tt>User</tt></a>,
3647<a href="#Value"><tt>Value</tt></a></p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3648
3649<p>The <tt>Function</tt> class represents a single procedure in LLVM. It is
Torok Edwin87469292009-10-12 13:37:29 +0000[diff] [blame]3650actually one of the more complex classes in the LLVM hierarchy because it must
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3651keep track of a large amount of data. The <tt>Function</tt> class keeps track
Reid Spencerbe5e85e2006-04-14 14:11:48 +0000[diff] [blame]3652of a list of <a href="#BasicBlock"><tt>BasicBlock</tt></a>s, a list of formal
3653<a href="#Argument"><tt>Argument</tt></a>s, and a
3654<a href="#SymbolTable"><tt>SymbolTable</tt></a>.</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3655
3656<p>The list of <a href="#BasicBlock"><tt>BasicBlock</tt></a>s is the most
3657commonly used part of <tt>Function</tt> objects. The list imposes an implicit
3658ordering of the blocks in the function, which indicate how the code will be
Benjamin Kramer8040cd32009-10-12 14:46:08 +0000[diff] [blame]3659laid out by the backend. Additionally, the first <a
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3660href="#BasicBlock"><tt>BasicBlock</tt></a> is the implicit entry node for the
3661<tt>Function</tt>. It is not legal in LLVM to explicitly branch to this initial
3662block. There are no implicit exit nodes, and in fact there may be multiple exit
3663nodes from a single <tt>Function</tt>. If the <a
3664href="#BasicBlock"><tt>BasicBlock</tt></a> list is empty, this indicates that
3665the <tt>Function</tt> is actually a function declaration: the actual body of the
3666function hasn't been linked in yet.</p>
3667
3668<p>In addition to a list of <a href="#BasicBlock"><tt>BasicBlock</tt></a>s, the
3669<tt>Function</tt> class also keeps track of the list of formal <a
3670href="#Argument"><tt>Argument</tt></a>s that the function receives. This
3671container manages the lifetime of the <a href="#Argument"><tt>Argument</tt></a>
3672nodes, just like the <a href="#BasicBlock"><tt>BasicBlock</tt></a> list does for
3673the <a href="#BasicBlock"><tt>BasicBlock</tt></a>s.</p>
3674
3675<p>The <a href="#SymbolTable"><tt>SymbolTable</tt></a> is a very rarely used
3676LLVM feature that is only used when you have to look up a value by name. Aside
3677from that, the <a href="#SymbolTable"><tt>SymbolTable</tt></a> is used
3678internally to make sure that there are not conflicts between the names of <a
3679href="#Instruction"><tt>Instruction</tt></a>s, <a
3680href="#BasicBlock"><tt>BasicBlock</tt></a>s, or <a
3681href="#Argument"><tt>Argument</tt></a>s in the function body.</p>
3682
Reid Spencer8b2da7a2004-07-18 13:10:31 +0000[diff] [blame]3683<p>Note that <tt>Function</tt> is a <a href="#GlobalValue">GlobalValue</a>
3684and therefore also a <a href="#Constant">Constant</a>. The value of the function
3685is its address (after linking) which is guaranteed to be constant.</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3686</div>
3687
3688<!-- _______________________________________________________________________ -->
3689<div class="doc_subsubsection">
3690 <a name="m_Function">Important Public Members of the <tt>Function</tt>
3691 class</a>
3692</div>
3693
3694<div class="doc_text">
3695
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3696<ul>
3697 <li><tt>Function(const </tt><tt><a href="#FunctionType">FunctionType</a>
Chris Lattnerac479e52004-08-04 05:10:48 +0000[diff] [blame]3698 *Ty, LinkageTypes Linkage, const std::string &amp;N = "", Module* Parent = 0)</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3699
3700 <p>Constructor used when you need to create new <tt>Function</tt>s to add
3701 the the program. The constructor must specify the type of the function to
Chris Lattnerac479e52004-08-04 05:10:48 +0000[diff] [blame]3702 create and what type of linkage the function should have. The <a
3703 href="#FunctionType"><tt>FunctionType</tt></a> argument
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3704 specifies the formal arguments and return value for the function. The same
Duncan Sands8036ca42007-03-30 12:22:09 +0000[diff] [blame]3705 <a href="#FunctionType"><tt>FunctionType</tt></a> value can be used to
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3706 create multiple functions. The <tt>Parent</tt> argument specifies the Module
3707 in which the function is defined. If this argument is provided, the function
3708 will automatically be inserted into that module's list of
3709 functions.</p></li>
3710
Chris Lattner62810e32008-11-25 18:34:50 +0000[diff] [blame]3711 <li><tt>bool isDeclaration()</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3712
3713 <p>Return whether or not the <tt>Function</tt> has a body defined. If the
3714 function is "external", it does not have a body, and thus must be resolved
3715 by linking with a function defined in a different translation unit.</p></li>
3716
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3717 <li><tt>Function::iterator</tt> - Typedef for basic block list iterator<br>
Chris Lattner9355b472002-09-06 02:50:58 +0000[diff] [blame]3718 <tt>Function::const_iterator</tt> - Typedef for const_iterator.<br>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3719
Chris Lattner77d69242005-03-15 05:19:20 +0000[diff] [blame]3720 <tt>begin()</tt>, <tt>end()</tt>
3721 <tt>size()</tt>, <tt>empty()</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3722
3723 <p>These are forwarding methods that make it easy to access the contents of
3724 a <tt>Function</tt> object's <a href="#BasicBlock"><tt>BasicBlock</tt></a>
3725 list.</p></li>
3726
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3727 <li><tt>Function::BasicBlockListType &amp;getBasicBlockList()</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3728
3729 <p>Returns the list of <a href="#BasicBlock"><tt>BasicBlock</tt></a>s. This
3730 is necessary to use when you need to update the list or perform a complex
3731 action that doesn't have a forwarding method.</p></li>
3732
Chris Lattner89cc2652005-03-15 04:48:32 +0000[diff] [blame]3733 <li><tt>Function::arg_iterator</tt> - Typedef for the argument list
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3734iterator<br>
Chris Lattner89cc2652005-03-15 04:48:32 +0000[diff] [blame]3735 <tt>Function::const_arg_iterator</tt> - Typedef for const_iterator.<br>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3736
Chris Lattner77d69242005-03-15 05:19:20 +0000[diff] [blame]3737 <tt>arg_begin()</tt>, <tt>arg_end()</tt>
Chris Lattner89cc2652005-03-15 04:48:32 +0000[diff] [blame]3738 <tt>arg_size()</tt>, <tt>arg_empty()</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3739
3740 <p>These are forwarding methods that make it easy to access the contents of
3741 a <tt>Function</tt> object's <a href="#Argument"><tt>Argument</tt></a>
3742 list.</p></li>
3743
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3744 <li><tt>Function::ArgumentListType &amp;getArgumentList()</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3745
3746 <p>Returns the list of <a href="#Argument"><tt>Argument</tt></a>s. This is
3747 necessary to use when you need to update the list or perform a complex
3748 action that doesn't have a forwarding method.</p></li>
3749
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3750 <li><tt><a href="#BasicBlock">BasicBlock</a> &amp;getEntryBlock()</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3751
3752 <p>Returns the entry <a href="#BasicBlock"><tt>BasicBlock</tt></a> for the
3753 function. Because the entry block for the function is always the first
3754 block, this returns the first block of the <tt>Function</tt>.</p></li>
3755
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3756 <li><tt><a href="#Type">Type</a> *getReturnType()</tt><br>
3757 <tt><a href="#FunctionType">FunctionType</a> *getFunctionType()</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3758
3759 <p>This traverses the <a href="#Type"><tt>Type</tt></a> of the
3760 <tt>Function</tt> and returns the return type of the function, or the <a
3761 href="#FunctionType"><tt>FunctionType</tt></a> of the actual
3762 function.</p></li>
3763
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3764 <li><tt><a href="#SymbolTable">SymbolTable</a> *getSymbolTable()</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3765
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3766 <p> Return a pointer to the <a href="#SymbolTable"><tt>SymbolTable</tt></a>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3767 for this <tt>Function</tt>.</p></li>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3768</ul>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3769
3770</div>
3771
3772<!-- ======================================================================= -->
3773<div class="doc_subsection">
3774 <a name="GlobalVariable">The <tt>GlobalVariable</tt> class</a>
3775</div>
3776
3777<div class="doc_text">
3778
3779<p><tt>#include "<a
3780href="/doxygen/GlobalVariable_8h-source.html">llvm/GlobalVariable.h</a>"</tt>
3781<br>
Tanya Lattnera3da7772004-06-22 08:02:25 +0000[diff] [blame]3782doxygen info: <a href="/doxygen/classllvm_1_1GlobalVariable.html">GlobalVariable
Reid Spencerbe5e85e2006-04-14 14:11:48 +0000[diff] [blame]3783 Class</a><br>
3784Superclasses: <a href="#GlobalValue"><tt>GlobalValue</tt></a>,
3785<a href="#Constant"><tt>Constant</tt></a>,
3786<a href="#User"><tt>User</tt></a>,
3787<a href="#Value"><tt>Value</tt></a></p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3788
Benjamin Kramer8040cd32009-10-12 14:46:08 +0000[diff] [blame]3789<p>Global variables are represented with the (surprise surprise)
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3790<tt>GlobalVariable</tt> class. Like functions, <tt>GlobalVariable</tt>s are also
3791subclasses of <a href="#GlobalValue"><tt>GlobalValue</tt></a>, and as such are
3792always referenced by their address (global values must live in memory, so their
Reid Spencerbe5e85e2006-04-14 14:11:48 +0000[diff] [blame]3793"name" refers to their constant address). See
3794<a href="#GlobalValue"><tt>GlobalValue</tt></a> for more on this. Global
3795variables may have an initial value (which must be a
3796<a href="#Constant"><tt>Constant</tt></a>), and if they have an initializer,
3797they may be marked as "constant" themselves (indicating that their contents
3798never change at runtime).</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3799</div>
3800
3801<!-- _______________________________________________________________________ -->
3802<div class="doc_subsubsection">
3803 <a name="m_GlobalVariable">Important Public Members of the
3804 <tt>GlobalVariable</tt> class</a>
3805</div>
3806
3807<div class="doc_text">
3808
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3809<ul>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3810 <li><tt>GlobalVariable(const </tt><tt><a href="#Type">Type</a> *Ty, bool
3811 isConstant, LinkageTypes&amp; Linkage, <a href="#Constant">Constant</a>
3812 *Initializer = 0, const std::string &amp;Name = "", Module* Parent = 0)</tt>
3813
3814 <p>Create a new global variable of the specified type. If
3815 <tt>isConstant</tt> is true then the global variable will be marked as
3816 unchanging for the program. The Linkage parameter specifies the type of
Duncan Sands667d4b82009-03-07 15:45:40 +0000[diff] [blame]3817 linkage (internal, external, weak, linkonce, appending) for the variable.
3818 If the linkage is InternalLinkage, WeakAnyLinkage, WeakODRLinkage,
3819 LinkOnceAnyLinkage or LinkOnceODRLinkage,&nbsp; then the resultant
3820 global variable will have internal linkage. AppendingLinkage concatenates
3821 together all instances (in different translation units) of the variable
3822 into a single variable but is only applicable to arrays. &nbsp;See
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3823 the <a href="LangRef.html#modulestructure">LLVM Language Reference</a> for
3824 further details on linkage types. Optionally an initializer, a name, and the
3825 module to put the variable into may be specified for the global variable as
3826 well.</p></li>
3827
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3828 <li><tt>bool isConstant() const</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3829
3830 <p>Returns true if this is a global variable that is known not to
3831 be modified at runtime.</p></li>
3832
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3833 <li><tt>bool hasInitializer()</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3834
3835 <p>Returns true if this <tt>GlobalVariable</tt> has an intializer.</p></li>
3836
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3837 <li><tt><a href="#Constant">Constant</a> *getInitializer()</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3838
Benjamin Kramer8040cd32009-10-12 14:46:08 +0000[diff] [blame]3839 <p>Returns the initial value for a <tt>GlobalVariable</tt>. It is not legal
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3840 to call this method if there is no initializer.</p></li>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3841</ul>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3842
3843</div>
3844
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]3845
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3846<!-- ======================================================================= -->
3847<div class="doc_subsection">
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]3848 <a name="BasicBlock">The <tt>BasicBlock</tt> class</a>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3849</div>
3850
3851<div class="doc_text">
3852
3853<p><tt>#include "<a
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]3854href="/doxygen/BasicBlock_8h-source.html">llvm/BasicBlock.h</a>"</tt><br>
Stefanus Du Toit24e04112009-06-17 21:12:26 +0000[diff] [blame]3855doxygen info: <a href="/doxygen/classllvm_1_1BasicBlock.html">BasicBlock
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]3856Class</a><br>
3857Superclass: <a href="#Value"><tt>Value</tt></a></p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3858
Nick Lewyckyccd279d2011-02-17 02:19:22 +0000[diff] [blame^]3859<p>This class represents a single entry single exit section of the code,
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]3860commonly known as a basic block by the compiler community. The
3861<tt>BasicBlock</tt> class maintains a list of <a
3862href="#Instruction"><tt>Instruction</tt></a>s, which form the body of the block.
3863Matching the language definition, the last element of this list of instructions
3864is always a terminator instruction (a subclass of the <a
3865href="#TerminatorInst"><tt>TerminatorInst</tt></a> class).</p>
3866
3867<p>In addition to tracking the list of instructions that make up the block, the
3868<tt>BasicBlock</tt> class also keeps track of the <a
3869href="#Function"><tt>Function</tt></a> that it is embedded into.</p>
3870
3871<p>Note that <tt>BasicBlock</tt>s themselves are <a
3872href="#Value"><tt>Value</tt></a>s, because they are referenced by instructions
3873like branches and can go in the switch tables. <tt>BasicBlock</tt>s have type
3874<tt>label</tt>.</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3875
3876</div>
3877
3878<!-- _______________________________________________________________________ -->
3879<div class="doc_subsubsection">
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]3880 <a name="m_BasicBlock">Important Public Members of the <tt>BasicBlock</tt>
3881 class</a>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3882</div>
3883
3884<div class="doc_text">
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3885<ul>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3886
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]3887<li><tt>BasicBlock(const std::string &amp;Name = "", </tt><tt><a
3888 href="#Function">Function</a> *Parent = 0)</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3889
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]3890<p>The <tt>BasicBlock</tt> constructor is used to create new basic blocks for
3891insertion into a function. The constructor optionally takes a name for the new
3892block, and a <a href="#Function"><tt>Function</tt></a> to insert it into. If
3893the <tt>Parent</tt> parameter is specified, the new <tt>BasicBlock</tt> is
3894automatically inserted at the end of the specified <a
3895href="#Function"><tt>Function</tt></a>, if not specified, the BasicBlock must be
3896manually inserted into the <a href="#Function"><tt>Function</tt></a>.</p></li>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3897
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]3898<li><tt>BasicBlock::iterator</tt> - Typedef for instruction list iterator<br>
3899<tt>BasicBlock::const_iterator</tt> - Typedef for const_iterator.<br>
3900<tt>begin()</tt>, <tt>end()</tt>, <tt>front()</tt>, <tt>back()</tt>,
3901<tt>size()</tt>, <tt>empty()</tt>
3902STL-style functions for accessing the instruction list.
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3903
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]3904<p>These methods and typedefs are forwarding functions that have the same
3905semantics as the standard library methods of the same names. These methods
3906expose the underlying instruction list of a basic block in a way that is easy to
3907manipulate. To get the full complement of container operations (including
3908operations to update the list), you must use the <tt>getInstList()</tt>
3909method.</p></li>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3910
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]3911<li><tt>BasicBlock::InstListType &amp;getInstList()</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3912
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]3913<p>This method is used to get access to the underlying container that actually
3914holds the Instructions. This method must be used when there isn't a forwarding
3915function in the <tt>BasicBlock</tt> class for the operation that you would like
3916to perform. Because there are no forwarding functions for "updating"
3917operations, you need to use this if you want to update the contents of a
3918<tt>BasicBlock</tt>.</p></li>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3919
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]3920<li><tt><a href="#Function">Function</a> *getParent()</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3921
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]3922<p> Returns a pointer to <a href="#Function"><tt>Function</tt></a> the block is
3923embedded into, or a null pointer if it is homeless.</p></li>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3924
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]3925<li><tt><a href="#TerminatorInst">TerminatorInst</a> *getTerminator()</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3926
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]3927<p> Returns a pointer to the terminator instruction that appears at the end of
3928the <tt>BasicBlock</tt>. If there is no terminator instruction, or if the last
3929instruction in the block is not a terminator, then a null pointer is
3930returned.</p></li>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3931
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3932</ul>
3933
3934</div>
3935
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3936
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3937<!-- ======================================================================= -->
3938<div class="doc_subsection">
3939 <a name="Argument">The <tt>Argument</tt> class</a>
3940</div>
3941
3942<div class="doc_text">
3943
3944<p>This subclass of Value defines the interface for incoming formal
Chris Lattner58360822005-01-17 00:12:04 +0000[diff] [blame]3945arguments to a function. A Function maintains a list of its formal
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3946arguments. An argument has a pointer to the parent Function.</p>
3947
3948</div>
3949
Chris Lattner9355b472002-09-06 02:50:58 +0000[diff] [blame]3950<!-- *********************************************************************** -->
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3951<hr>
3952<address>
3953 <a href="http://jigsaw.w3.org/css-validator/check/referer"><img
Misha Brukman44408702008-12-11 17:34:48 +0000[diff] [blame]3954 src="http://jigsaw.w3.org/css-validator/images/vcss-blue" alt="Valid CSS"></a>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3955 <a href="http://validator.w3.org/check/referer"><img
Gabor Greifa9c0f2b2008-06-18 14:05:31 +0000[diff] [blame]3956 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]3957
3958 <a href="mailto:dhurjati@cs.uiuc.edu">Dinakar Dhurjati</a> and
3959 <a href="mailto:sabre@nondot.org">Chris Lattner</a><br>
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]3960 <a href="http://llvm.org">The LLVM Compiler Infrastructure</a><br>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3961 Last modified: $Date$
3962</address>
3963
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3964</body>
3965</html>