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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>
86 <li><a href="#dss_map">&lt;map&gt;</a></li>
87 <li><a href="#dss_othermap">Other Map-Like Container Options</a></li>
88 </ul></li>
Chris Lattnerdced9fb2009-07-25 07:22:20 +0000[diff] [blame]89 <li><a href="#ds_string">String-like containers</a>
Benjamin Kramere15192b2009-08-05 15:42:44 +0000[diff] [blame^]90 <!--<ul>
91 todo
92 </ul>--></li>
Daniel Berlin1939ace2007-09-24 17:52:25 +0000[diff] [blame]93 <li><a href="#ds_bit">BitVector-like containers</a>
94 <ul>
95 <li><a href="#dss_bitvector">A dense bitvector</a></li>
96 <li><a href="#dss_sparsebitvector">A sparse bitvector</a></li>
97 </ul></li>
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]98 </ul>
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]99 </li>
Chris Lattnerae7f7592002-09-06 18:31:18 +0000[diff] [blame]100 <li><a href="#common">Helpful Hints for Common Operations</a>
Chris Lattnerae7f7592002-09-06 18:31:18 +0000[diff] [blame]101 <ul>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]102 <li><a href="#inspection">Basic Inspection and Traversal Routines</a>
103 <ul>
104 <li><a href="#iterate_function">Iterating over the <tt>BasicBlock</tt>s
105in a <tt>Function</tt></a> </li>
106 <li><a href="#iterate_basicblock">Iterating over the <tt>Instruction</tt>s
107in a <tt>BasicBlock</tt></a> </li>
108 <li><a href="#iterate_institer">Iterating over the <tt>Instruction</tt>s
109in a <tt>Function</tt></a> </li>
110 <li><a href="#iterate_convert">Turning an iterator into a
111class pointer</a> </li>
112 <li><a href="#iterate_complex">Finding call sites: a more
113complex example</a> </li>
114 <li><a href="#calls_and_invokes">Treating calls and invokes
115the same way</a> </li>
116 <li><a href="#iterate_chains">Iterating over def-use &amp;
117use-def chains</a> </li>
Chris Lattner2e438ca2008-01-03 16:56:04 +0000[diff] [blame]118 <li><a href="#iterate_preds">Iterating over predecessors &amp;
119successors of blocks</a></li>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]120 </ul>
121 </li>
122 <li><a href="#simplechanges">Making simple changes</a>
123 <ul>
124 <li><a href="#schanges_creating">Creating and inserting new
125 <tt>Instruction</tt>s</a> </li>
126 <li><a href="#schanges_deleting">Deleting <tt>Instruction</tt>s</a> </li>
127 <li><a href="#schanges_replacing">Replacing an <tt>Instruction</tt>
128with another <tt>Value</tt></a> </li>
Tanya Lattnerb011c662007-06-20 18:33:15 +0000[diff] [blame]129 <li><a href="#schanges_deletingGV">Deleting <tt>GlobalVariable</tt>s</a> </li>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]130 </ul>
Reid Spencerfe8f4ff2004-11-01 09:02:53 +0000[diff] [blame]131 </li>
Jeffrey Yasskin714257f2009-04-30 22:33:41 +0000[diff] [blame]132 <li><a href="#create_types">How to Create Types</a></li>
Chris Lattnerae7f7592002-09-06 18:31:18 +0000[diff] [blame]133<!--
134 <li>Working with the Control Flow Graph
135 <ul>
136 <li>Accessing predecessors and successors of a <tt>BasicBlock</tt>
137 <li>
138 <li>
139 </ul>
Reid Spencerfe8f4ff2004-11-01 09:02:53 +0000[diff] [blame]140-->
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]141 </ul>
142 </li>
Chris Lattnerd9d6e102005-04-23 16:10:52 +0000[diff] [blame]143
Owen Anderson8bc1b3b2009-06-16 01:17:16 +0000[diff] [blame]144 <li><a href="#threading">Threads and LLVM</a>
145 <ul>
Owen Anderson1ad70e32009-06-16 18:04:19 +0000[diff] [blame]146 <li><a href="#startmultithreaded">Entering and Exiting Multithreaded Mode
147 </a></li>
Owen Anderson8bc1b3b2009-06-16 01:17:16 +0000[diff] [blame]148 <li><a href="#shutdown">Ending execution with <tt>llvm_shutdown()</tt></a></li>
149 <li><a href="#managedstatic">Lazy initialization with <tt>ManagedStatic</tt></a></li>
150 </ul>
151 </li>
152
Chris Lattnerd9d6e102005-04-23 16:10:52 +0000[diff] [blame]153 <li><a href="#advanced">Advanced Topics</a>
154 <ul>
Chris Lattnerf1b200b2005-04-23 17:27:36 +0000[diff] [blame]155 <li><a href="#TypeResolve">LLVM Type Resolution</a>
156 <ul>
157 <li><a href="#BuildRecType">Basic Recursive Type Construction</a></li>
158 <li><a href="#refineAbstractTypeTo">The <tt>refineAbstractTypeTo</tt> method</a></li>
159 <li><a href="#PATypeHolder">The PATypeHolder Class</a></li>
160 <li><a href="#AbstractTypeUser">The AbstractTypeUser Class</a></li>
161 </ul></li>
162
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]163 <li><a href="#SymbolTable">The <tt>ValueSymbolTable</tt> and <tt>TypeSymbolTable</tt> classes</a></li>
164 <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]165 </ul></li>
166
Joel Stanley9b96c442002-09-06 21:55:13 +0000[diff] [blame]167 <li><a href="#coreclasses">The Core LLVM Class Hierarchy Reference</a>
Chris Lattner9355b472002-09-06 02:50:58 +0000[diff] [blame]168 <ul>
Reid Spencer303c4b42007-01-12 17:26:25 +0000[diff] [blame]169 <li><a href="#Type">The <tt>Type</tt> class</a> </li>
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]170 <li><a href="#Module">The <tt>Module</tt> class</a></li>
Reid Spencerfe8f4ff2004-11-01 09:02:53 +0000[diff] [blame]171 <li><a href="#Value">The <tt>Value</tt> class</a>
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]172 <ul>
173 <li><a href="#User">The <tt>User</tt> class</a>
Chris Lattner9355b472002-09-06 02:50:58 +0000[diff] [blame]174 <ul>
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]175 <li><a href="#Instruction">The <tt>Instruction</tt> class</a></li>
176 <li><a href="#Constant">The <tt>Constant</tt> class</a>
177 <ul>
178 <li><a href="#GlobalValue">The <tt>GlobalValue</tt> class</a>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]179 <ul>
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]180 <li><a href="#Function">The <tt>Function</tt> class</a></li>
181 <li><a href="#GlobalVariable">The <tt>GlobalVariable</tt> class</a></li>
182 </ul>
183 </li>
184 </ul>
185 </li>
Reid Spencerfe8f4ff2004-11-01 09:02:53 +0000[diff] [blame]186 </ul>
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]187 </li>
188 <li><a href="#BasicBlock">The <tt>BasicBlock</tt> class</a></li>
189 <li><a href="#Argument">The <tt>Argument</tt> class</a></li>
190 </ul>
Reid Spencerfe8f4ff2004-11-01 09:02:53 +0000[diff] [blame]191 </li>
192 </ul>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]193 </li>
Chris Lattner9355b472002-09-06 02:50:58 +0000[diff] [blame]194</ol>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]195
Chris Lattner69bf8a92004-05-23 21:06:58 +0000[diff] [blame]196<div class="doc_author">
197 <p>Written by <a href="mailto:sabre@nondot.org">Chris Lattner</a>,
Chris Lattner94c43592004-05-26 16:52:55 +0000[diff] [blame]198 <a href="mailto:dhurjati@cs.uiuc.edu">Dinakar Dhurjati</a>,
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]199 <a href="mailto:ggreif@gmail.com">Gabor Greif</a>,
Owen Anderson8bc1b3b2009-06-16 01:17:16 +0000[diff] [blame]200 <a href="mailto:jstanley@cs.uiuc.edu">Joel Stanley</a>,
201 <a href="mailto:rspencer@x10sys.com">Reid Spencer</a> and
202 <a href="mailto:owen@apple.com">Owen Anderson</a></p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]203</div>
204
Chris Lattner9355b472002-09-06 02:50:58 +0000[diff] [blame]205<!-- *********************************************************************** -->
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]206<div class="doc_section">
207 <a name="introduction">Introduction </a>
208</div>
Chris Lattner9355b472002-09-06 02:50:58 +0000[diff] [blame]209<!-- *********************************************************************** -->
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]210
211<div class="doc_text">
212
213<p>This document is meant to highlight some of the important classes and
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]214interfaces available in the LLVM source-base. This manual is not
215intended to explain what LLVM is, how it works, and what LLVM code looks
216like. It assumes that you know the basics of LLVM and are interested
217in writing transformations or otherwise analyzing or manipulating the
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]218code.</p>
219
220<p>This document should get you oriented so that you can find your
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]221way in the continuously growing source code that makes up the LLVM
222infrastructure. Note that this manual is not intended to serve as a
223replacement for reading the source code, so if you think there should be
224a method in one of these classes to do something, but it's not listed,
225check the source. Links to the <a href="/doxygen/">doxygen</a> sources
226are provided to make this as easy as possible.</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]227
228<p>The first section of this document describes general information that is
229useful to know when working in the LLVM infrastructure, and the second describes
230the Core LLVM classes. In the future this manual will be extended with
231information describing how to use extension libraries, such as dominator
232information, CFG traversal routines, and useful utilities like the <tt><a
233href="/doxygen/InstVisitor_8h-source.html">InstVisitor</a></tt> template.</p>
234
235</div>
236
Chris Lattner9355b472002-09-06 02:50:58 +0000[diff] [blame]237<!-- *********************************************************************** -->
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]238<div class="doc_section">
239 <a name="general">General Information</a>
240</div>
241<!-- *********************************************************************** -->
242
243<div class="doc_text">
244
245<p>This section contains general information that is useful if you are working
246in the LLVM source-base, but that isn't specific to any particular API.</p>
247
248</div>
249
250<!-- ======================================================================= -->
251<div class="doc_subsection">
252 <a name="stl">The C++ Standard Template Library</a>
253</div>
254
255<div class="doc_text">
256
257<p>LLVM makes heavy use of the C++ Standard Template Library (STL),
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]258perhaps much more than you are used to, or have seen before. Because of
259this, you might want to do a little background reading in the
260techniques used and capabilities of the library. There are many good
261pages that discuss the STL, and several books on the subject that you
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]262can get, so it will not be discussed in this document.</p>
263
264<p>Here are some useful links:</p>
265
266<ol>
267
268<li><a href="http://www.dinkumware.com/refxcpp.html">Dinkumware C++ Library
269reference</a> - an excellent reference for the STL and other parts of the
270standard C++ library.</li>
271
272<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]273O'Reilly book in the making. It has a decent Standard Library
274Reference that rivals Dinkumware's, and is unfortunately no longer free since the
275book has been published.</li>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]276
277<li><a href="http://www.parashift.com/c++-faq-lite/">C++ Frequently Asked
278Questions</a></li>
279
280<li><a href="http://www.sgi.com/tech/stl/">SGI's STL Programmer's Guide</a> -
281Contains a useful <a
282href="http://www.sgi.com/tech/stl/stl_introduction.html">Introduction to the
283STL</a>.</li>
284
285<li><a href="http://www.research.att.com/%7Ebs/C++.html">Bjarne Stroustrup's C++
286Page</a></li>
287
Tanya Lattner79445ba2004-12-08 18:34:56 +0000[diff] [blame]288<li><a href="http://64.78.49.204/">
Reid Spencer096603a2004-05-26 08:41:35 +0000[diff] [blame]289Bruce Eckel's Thinking in C++, 2nd ed. Volume 2 Revision 4.0 (even better, get
290the book).</a></li>
291
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]292</ol>
293
294<p>You are also encouraged to take a look at the <a
295href="CodingStandards.html">LLVM Coding Standards</a> guide which focuses on how
296to write maintainable code more than where to put your curly braces.</p>
297
298</div>
299
300<!-- ======================================================================= -->
301<div class="doc_subsection">
302 <a name="stl">Other useful references</a>
303</div>
304
305<div class="doc_text">
306
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]307<ol>
308<li><a href="http://www.psc.edu/%7Esemke/cvs_branches.html">CVS
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]309Branch and Tag Primer</a></li>
Misha Brukmana0f71e42004-06-18 18:39:00 +0000[diff] [blame]310<li><a href="http://www.fortran-2000.com/ArnaudRecipes/sharedlib.html">Using
311static and shared libraries across platforms</a></li>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]312</ol>
313
314</div>
315
Chris Lattner9355b472002-09-06 02:50:58 +0000[diff] [blame]316<!-- *********************************************************************** -->
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]317<div class="doc_section">
318 <a name="apis">Important and useful LLVM APIs</a>
319</div>
320<!-- *********************************************************************** -->
321
322<div class="doc_text">
323
324<p>Here we highlight some LLVM APIs that are generally useful and good to
325know about when writing transformations.</p>
326
327</div>
328
329<!-- ======================================================================= -->
330<div class="doc_subsection">
Misha Brukman2c122ce2005-11-01 21:12:49 +0000[diff] [blame]331 <a name="isa">The <tt>isa&lt;&gt;</tt>, <tt>cast&lt;&gt;</tt> and
332 <tt>dyn_cast&lt;&gt;</tt> templates</a>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]333</div>
334
335<div class="doc_text">
336
337<p>The LLVM source-base makes extensive use of a custom form of RTTI.
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]338These templates have many similarities to the C++ <tt>dynamic_cast&lt;&gt;</tt>
339operator, but they don't have some drawbacks (primarily stemming from
340the fact that <tt>dynamic_cast&lt;&gt;</tt> only works on classes that
341have a v-table). Because they are used so often, you must know what they
342do and how they work. All of these templates are defined in the <a
Chris Lattner695b78b2005-04-26 22:56:16 +0000[diff] [blame]343 href="/doxygen/Casting_8h-source.html"><tt>llvm/Support/Casting.h</tt></a>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]344file (note that you very rarely have to include this file directly).</p>
345
346<dl>
347 <dt><tt>isa&lt;&gt;</tt>: </dt>
348
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]349 <dd><p>The <tt>isa&lt;&gt;</tt> operator works exactly like the Java
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]350 "<tt>instanceof</tt>" operator. It returns true or false depending on whether
351 a reference or pointer points to an instance of the specified class. This can
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]352 be very useful for constraint checking of various sorts (example below).</p>
353 </dd>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]354
355 <dt><tt>cast&lt;&gt;</tt>: </dt>
356
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]357 <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]358 converts a pointer or reference from a base class to a derived class, causing
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]359 an assertion failure if it is not really an instance of the right type. This
360 should be used in cases where you have some information that makes you believe
361 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]362 and <tt>cast&lt;&gt;</tt> template is:</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]363
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]364<div class="doc_code">
365<pre>
366static bool isLoopInvariant(const <a href="#Value">Value</a> *V, const Loop *L) {
367 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))
368 return true;
Chris Lattner69bf8a92004-05-23 21:06:58 +0000[diff] [blame]369
Bill Wendling82e2eea2006-10-11 18:00:22 +0000[diff] [blame]370 // <i>Otherwise, it must be an instruction...</i>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]371 return !L-&gt;contains(cast&lt;<a href="#Instruction">Instruction</a>&gt;(V)-&gt;getParent());
372}
373</pre>
374</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]375
376 <p>Note that you should <b>not</b> use an <tt>isa&lt;&gt;</tt> test followed
377 by a <tt>cast&lt;&gt;</tt>, for that use the <tt>dyn_cast&lt;&gt;</tt>
378 operator.</p>
379
380 </dd>
381
382 <dt><tt>dyn_cast&lt;&gt;</tt>:</dt>
383
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]384 <dd><p>The <tt>dyn_cast&lt;&gt;</tt> operator is a "checking cast" operation.
385 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]386 pointer to it (this operator does not work with references). If the operand is
387 not of the correct type, a null pointer is returned. Thus, this works very
Misha Brukman2c122ce2005-11-01 21:12:49 +0000[diff] [blame]388 much like the <tt>dynamic_cast&lt;&gt;</tt> operator in C++, and should be
389 used in the same circumstances. Typically, the <tt>dyn_cast&lt;&gt;</tt>
390 operator is used in an <tt>if</tt> statement or some other flow control
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]391 statement like this:</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]392
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]393<div class="doc_code">
394<pre>
395if (<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]396 // <i>...</i>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]397}
398</pre>
399</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]400
Misha Brukman2c122ce2005-11-01 21:12:49 +0000[diff] [blame]401 <p>This form of the <tt>if</tt> statement effectively combines together a call
402 to <tt>isa&lt;&gt;</tt> and a call to <tt>cast&lt;&gt;</tt> into one
403 statement, which is very convenient.</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]404
Misha Brukman2c122ce2005-11-01 21:12:49 +0000[diff] [blame]405 <p>Note that the <tt>dyn_cast&lt;&gt;</tt> operator, like C++'s
406 <tt>dynamic_cast&lt;&gt;</tt> or Java's <tt>instanceof</tt> operator, can be
407 abused. In particular, you should not use big chained <tt>if/then/else</tt>
408 blocks to check for lots of different variants of classes. If you find
409 yourself wanting to do this, it is much cleaner and more efficient to use the
410 <tt>InstVisitor</tt> class to dispatch over the instruction type directly.</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]411
Misha Brukman2c122ce2005-11-01 21:12:49 +0000[diff] [blame]412 </dd>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]413
Misha Brukman2c122ce2005-11-01 21:12:49 +0000[diff] [blame]414 <dt><tt>cast_or_null&lt;&gt;</tt>: </dt>
415
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]416 <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]417 <tt>cast&lt;&gt;</tt> operator, except that it allows for a null pointer as an
418 argument (which it then propagates). This can sometimes be useful, allowing
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]419 you to combine several null checks into one.</p></dd>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]420
Misha Brukman2c122ce2005-11-01 21:12:49 +0000[diff] [blame]421 <dt><tt>dyn_cast_or_null&lt;&gt;</tt>: </dt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]422
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]423 <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]424 <tt>dyn_cast&lt;&gt;</tt> operator, except that it allows for a null pointer
425 as an argument (which it then propagates). This can sometimes be useful,
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]426 allowing you to combine several null checks into one.</p></dd>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]427
Misha Brukman2c122ce2005-11-01 21:12:49 +0000[diff] [blame]428</dl>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]429
430<p>These five templates can be used with any classes, whether they have a
431v-table or not. To add support for these templates, you simply need to add
432<tt>classof</tt> static methods to the class you are interested casting
433to. Describing this is currently outside the scope of this document, but there
434are lots of examples in the LLVM source base.</p>
435
436</div>
437
Daniel Dunbar6e0d1cb2009-07-25 04:41:11 +0000[diff] [blame]438
439<!-- ======================================================================= -->
440<div class="doc_subsection">
441 <a name="string_apis">Passing strings (the <tt>StringRef</tt>
442and <tt>Twine</tt> classes)</a>
443</div>
444
445<div class="doc_text">
446
447<p>Although LLVM generally does not do much string manipulation, we do have
Chris Lattner81187ae2009-07-25 07:16:59 +0000[diff] [blame]448several important APIs which take strings. Two important examples are the
Daniel Dunbar6e0d1cb2009-07-25 04:41:11 +0000[diff] [blame]449Value class -- which has names for instructions, functions, etc. -- and the
450StringMap class which is used extensively in LLVM and Clang.</p>
451
452<p>These are generic classes, and they need to be able to accept strings which
453may have embedded null characters. Therefore, they cannot simply take
Chris Lattner81187ae2009-07-25 07:16:59 +0000[diff] [blame]454a <tt>const char *</tt>, and taking a <tt>const std::string&amp;</tt> requires
Daniel Dunbar6e0d1cb2009-07-25 04:41:11 +0000[diff] [blame]455clients to perform a heap allocation which is usually unnecessary. Instead,
Chris Lattner81187ae2009-07-25 07:16:59 +0000[diff] [blame]456many LLVM APIs use a <tt>const StringRef&amp;</tt> or a <tt>const
457Twine&amp;</tt> for passing strings efficiently.</p>
Daniel Dunbar6e0d1cb2009-07-25 04:41:11 +0000[diff] [blame]458
459</div>
460
461<!-- _______________________________________________________________________ -->
462<div class="doc_subsubsection">
463 <a name="StringRef">The <tt>StringRef</tt> class</a>
464</div>
465
466<div class="doc_text">
467
468<p>The <tt>StringRef</tt> data type represents a reference to a constant string
469(a character array and a length) and supports the common operations available
470on <tt>std:string</tt>, but does not require heap allocation.</p>
471
Chris Lattner81187ae2009-07-25 07:16:59 +0000[diff] [blame]472<p>It can be implicitly constructed using a C style null-terminated string,
473an <tt>std::string</tt>, or explicitly with a character pointer and length.
Daniel Dunbar6e0d1cb2009-07-25 04:41:11 +0000[diff] [blame]474For example, the <tt>StringRef</tt> find function is declared as:</p>
Chris Lattner81187ae2009-07-25 07:16:59 +0000[diff] [blame]475
Daniel Dunbar6e0d1cb2009-07-25 04:41:11 +0000[diff] [blame]476<div class="doc_code">
Chris Lattner81187ae2009-07-25 07:16:59 +0000[diff] [blame]477 iterator find(const StringRef &amp;Key);
Daniel Dunbar6e0d1cb2009-07-25 04:41:11 +0000[diff] [blame]478</div>
479
480<p>and clients can call it using any one of:</p>
481
482<div class="doc_code">
483<pre>
484 Map.find("foo"); <i>// Lookup "foo"</i>
485 Map.find(std::string("bar")); <i>// Lookup "bar"</i>
486 Map.find(StringRef("\0baz", 4)); <i>// Lookup "\0baz"</i>
487</pre>
488</div>
489
490<p>Similarly, APIs which need to return a string may return a <tt>StringRef</tt>
491instance, which can be used directly or converted to an <tt>std::string</tt>
492using the <tt>str</tt> member function. See
493"<tt><a href="/doxygen/classllvm_1_1StringRef_8h-source.html">llvm/ADT/StringRef.h</a></tt>"
494for more information.</p>
495
496<p>You should rarely use the <tt>StringRef</tt> class directly, because it contains
497pointers to external memory it is not generally safe to store an instance of the
Chris Lattner81187ae2009-07-25 07:16:59 +0000[diff] [blame]498class (unless you know that the external storage will not be freed).</p>
Daniel Dunbar6e0d1cb2009-07-25 04:41:11 +0000[diff] [blame]499
500</div>
501
502<!-- _______________________________________________________________________ -->
503<div class="doc_subsubsection">
504 <a name="Twine">The <tt>Twine</tt> class</a>
505</div>
506
507<div class="doc_text">
508
509<p>The <tt>Twine</tt> class is an efficient way for APIs to accept concatenated
510strings. For example, a common LLVM paradigm is to name one instruction based on
511the name of another instruction with a suffix, for example:</p>
512
513<div class="doc_code">
514<pre>
515 New = CmpInst::Create(<i>...</i>, SO->getName() + ".cmp");
516</pre>
517</div>
518
519<p>The <tt>Twine</tt> class is effectively a
520lightweight <a href="http://en.wikipedia.org/wiki/Rope_(computer_science)">rope</a>
521which points to temporary (stack allocated) objects. Twines can be implicitly
522constructed as the result of the plus operator applied to strings (i.e., a C
523strings, an <tt>std::string</tt>, or a <tt>StringRef</tt>). The twine delays the
524actual concatentation of strings until it is actually required, at which point
525it can be efficiently rendered directly into a character array. This avoids
526unnecessary heap allocation involved in constructing the temporary results of
527string concatenation. See
528"<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^]529for more information.</p>
Daniel Dunbar6e0d1cb2009-07-25 04:41:11 +0000[diff] [blame]530
531<p>As with a <tt>StringRef</tt>, <tt>Twine</tt> objects point to external memory
532and should almost never be stored or mentioned directly. They are intended
533solely for use when defining a function which should be able to efficiently
534accept concatenated strings.</p>
535
536</div>
537
538
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]539<!-- ======================================================================= -->
540<div class="doc_subsection">
Misha Brukman2c122ce2005-11-01 21:12:49 +0000[diff] [blame]541 <a name="DEBUG">The <tt>DEBUG()</tt> macro and <tt>-debug</tt> option</a>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]542</div>
543
544<div class="doc_text">
545
546<p>Often when working on your pass you will put a bunch of debugging printouts
547and other code into your pass. After you get it working, you want to remove
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]548it, 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]549across).</p>
550
551<p> Naturally, because of this, you don't want to delete the debug printouts,
552but you don't want them to always be noisy. A standard compromise is to comment
553them out, allowing you to enable them if you need them in the future.</p>
554
Chris Lattner695b78b2005-04-26 22:56:16 +0000[diff] [blame]555<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]556file provides a macro named <tt>DEBUG()</tt> that is a much nicer solution to
557this problem. Basically, you can put arbitrary code into the argument of the
558<tt>DEBUG</tt> macro, and it is only executed if '<tt>opt</tt>' (or any other
559tool) is run with the '<tt>-debug</tt>' command line argument:</p>
560
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]561<div class="doc_code">
562<pre>
Daniel Dunbar06388ae2009-07-25 01:55:32 +0000[diff] [blame]563DEBUG(errs() &lt;&lt; "I am here!\n");
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]564</pre>
565</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]566
567<p>Then you can run your pass like this:</p>
568
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]569<div class="doc_code">
570<pre>
571$ opt &lt; a.bc &gt; /dev/null -mypass
Bill Wendling82e2eea2006-10-11 18:00:22 +0000[diff] [blame]572<i>&lt;no output&gt;</i>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]573$ opt &lt; a.bc &gt; /dev/null -mypass -debug
574I am here!
575</pre>
576</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]577
578<p>Using the <tt>DEBUG()</tt> macro instead of a home-brewed solution allows you
579to not have to create "yet another" command line option for the debug output for
580your pass. Note that <tt>DEBUG()</tt> macros are disabled for optimized builds,
581so they do not cause a performance impact at all (for the same reason, they
582should also not contain side-effects!).</p>
583
584<p>One additional nice thing about the <tt>DEBUG()</tt> macro is that you can
585enable or disable it directly in gdb. Just use "<tt>set DebugFlag=0</tt>" or
586"<tt>set DebugFlag=1</tt>" from the gdb if the program is running. If the
587program hasn't been started yet, you can always just run it with
588<tt>-debug</tt>.</p>
589
590</div>
591
592<!-- _______________________________________________________________________ -->
593<div class="doc_subsubsection">
Chris Lattnerc9151082005-04-26 22:57:07 +0000[diff] [blame]594 <a name="DEBUG_TYPE">Fine grained debug info with <tt>DEBUG_TYPE</tt> and
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]595 the <tt>-debug-only</tt> option</a>
596</div>
597
598<div class="doc_text">
599
600<p>Sometimes you may find yourself in a situation where enabling <tt>-debug</tt>
601just turns on <b>too much</b> information (such as when working on the code
602generator). If you want to enable debug information with more fine-grained
603control, you define the <tt>DEBUG_TYPE</tt> macro and the <tt>-debug</tt> only
604option as follows:</p>
605
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]606<div class="doc_code">
607<pre>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]608#undef DEBUG_TYPE
Daniel Dunbar06388ae2009-07-25 01:55:32 +0000[diff] [blame]609DEBUG(errs() &lt;&lt; "No debug type\n");
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]610#define DEBUG_TYPE "foo"
Daniel Dunbar06388ae2009-07-25 01:55:32 +0000[diff] [blame]611DEBUG(errs() &lt;&lt; "'foo' debug type\n");
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]612#undef DEBUG_TYPE
613#define DEBUG_TYPE "bar"
Daniel Dunbar06388ae2009-07-25 01:55:32 +0000[diff] [blame]614DEBUG(errs() &lt;&lt; "'bar' debug type\n"));
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]615#undef DEBUG_TYPE
616#define DEBUG_TYPE ""
Daniel Dunbar06388ae2009-07-25 01:55:32 +0000[diff] [blame]617DEBUG(errs() &lt;&lt; "No debug type (2)\n");
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]618</pre>
619</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]620
621<p>Then you can run your pass like this:</p>
622
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]623<div class="doc_code">
624<pre>
625$ opt &lt; a.bc &gt; /dev/null -mypass
Bill Wendling82e2eea2006-10-11 18:00:22 +0000[diff] [blame]626<i>&lt;no output&gt;</i>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]627$ opt &lt; a.bc &gt; /dev/null -mypass -debug
628No debug type
629'foo' debug type
630'bar' debug type
631No debug type (2)
632$ opt &lt; a.bc &gt; /dev/null -mypass -debug-only=foo
633'foo' debug type
634$ opt &lt; a.bc &gt; /dev/null -mypass -debug-only=bar
635'bar' debug type
636</pre>
637</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]638
639<p>Of course, in practice, you should only set <tt>DEBUG_TYPE</tt> at the top of
640a 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]641you <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]642<tt>#undef</tt>'s). Also, you should use names more meaningful than "foo" and
643"bar", because there is no system in place to ensure that names do not
644conflict. If two different modules use the same string, they will all be turned
645on when the name is specified. This allows, for example, all debug information
646for instruction scheduling to be enabled with <tt>-debug-type=InstrSched</tt>,
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]647even if the source lives in multiple files.</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]648
649</div>
650
651<!-- ======================================================================= -->
652<div class="doc_subsection">
Chris Lattner0be6fdf2006-12-19 21:46:21 +0000[diff] [blame]653 <a name="Statistic">The <tt>Statistic</tt> class &amp; <tt>-stats</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]654 option</a>
655</div>
656
657<div class="doc_text">
658
659<p>The "<tt><a
Chris Lattner695b78b2005-04-26 22:56:16 +0000[diff] [blame]660href="/doxygen/Statistic_8h-source.html">llvm/ADT/Statistic.h</a></tt>" file
Chris Lattner0be6fdf2006-12-19 21:46:21 +0000[diff] [blame]661provides a class named <tt>Statistic</tt> that is used as a unified way to
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]662keep track of what the LLVM compiler is doing and how effective various
663optimizations are. It is useful to see what optimizations are contributing to
664making a particular program run faster.</p>
665
666<p>Often you may run your pass on some big program, and you're interested to see
667how many times it makes a certain transformation. Although you can do this with
668hand 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]669for big programs. Using the <tt>Statistic</tt> class makes it very easy to
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]670keep track of this information, and the calculated information is presented in a
671uniform manner with the rest of the passes being executed.</p>
672
673<p>There are many examples of <tt>Statistic</tt> uses, but the basics of using
674it are as follows:</p>
675
676<ol>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]677 <li><p>Define your statistic like this:</p>
678
679<div class="doc_code">
680<pre>
Chris Lattner0be6fdf2006-12-19 21:46:21 +0000[diff] [blame]681#define <a href="#DEBUG_TYPE">DEBUG_TYPE</a> "mypassname" <i>// This goes before any #includes.</i>
682STATISTIC(NumXForms, "The # of times I did stuff");
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]683</pre>
684</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]685
Chris Lattner0be6fdf2006-12-19 21:46:21 +0000[diff] [blame]686 <p>The <tt>STATISTIC</tt> macro defines a static variable, whose name is
687 specified by the first argument. The pass name is taken from the DEBUG_TYPE
688 macro, and the description is taken from the second argument. The variable
Reid Spencer06565dc2007-01-12 17:11:23 +0000[diff] [blame]689 defined ("NumXForms" in this case) acts like an unsigned integer.</p></li>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]690
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]691 <li><p>Whenever you make a transformation, bump the counter:</p>
692
693<div class="doc_code">
694<pre>
Bill Wendling82e2eea2006-10-11 18:00:22 +0000[diff] [blame]695++NumXForms; // <i>I did stuff!</i>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]696</pre>
697</div>
698
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]699 </li>
700 </ol>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]701
702 <p>That's all you have to do. To get '<tt>opt</tt>' to print out the
703 statistics gathered, use the '<tt>-stats</tt>' option:</p>
704
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]705<div class="doc_code">
706<pre>
707$ opt -stats -mypassname &lt; program.bc &gt; /dev/null
Bill Wendling82e2eea2006-10-11 18:00:22 +0000[diff] [blame]708<i>... statistics output ...</i>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]709</pre>
710</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]711
Reid Spencer6b6c73e2007-02-09 16:00:28 +0000[diff] [blame]712 <p> When running <tt>opt</tt> on a C file from the SPEC benchmark
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]713suite, it gives a report that looks like this:</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]714
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]715<div class="doc_code">
716<pre>
Gabor Greif04367bf2007-07-06 22:07:22 +0000[diff] [blame]717 7646 bitcodewriter - Number of normal instructions
718 725 bitcodewriter - Number of oversized instructions
719 129996 bitcodewriter - Number of bitcode bytes written
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]720 2817 raise - Number of insts DCEd or constprop'd
721 3213 raise - Number of cast-of-self removed
722 5046 raise - Number of expression trees converted
723 75 raise - Number of other getelementptr's formed
724 138 raise - Number of load/store peepholes
725 42 deadtypeelim - Number of unused typenames removed from symtab
726 392 funcresolve - Number of varargs functions resolved
727 27 globaldce - Number of global variables removed
728 2 adce - Number of basic blocks removed
729 134 cee - Number of branches revectored
730 49 cee - Number of setcc instruction eliminated
731 532 gcse - Number of loads removed
732 2919 gcse - Number of instructions removed
733 86 indvars - Number of canonical indvars added
734 87 indvars - Number of aux indvars removed
735 25 instcombine - Number of dead inst eliminate
736 434 instcombine - Number of insts combined
737 248 licm - Number of load insts hoisted
738 1298 licm - Number of insts hoisted to a loop pre-header
739 3 licm - Number of insts hoisted to multiple loop preds (bad, no loop pre-header)
740 75 mem2reg - Number of alloca's promoted
741 1444 cfgsimplify - Number of blocks simplified
742</pre>
743</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]744
745<p>Obviously, with so many optimizations, having a unified framework for this
746stuff is very nice. Making your pass fit well into the framework makes it more
747maintainable and useful.</p>
748
749</div>
750
Chris Lattnerf623a082005-10-17 01:36:23 +0000[diff] [blame]751<!-- ======================================================================= -->
752<div class="doc_subsection">
753 <a name="ViewGraph">Viewing graphs while debugging code</a>
754</div>
755
756<div class="doc_text">
757
758<p>Several of the important data structures in LLVM are graphs: for example
759CFGs made out of LLVM <a href="#BasicBlock">BasicBlock</a>s, CFGs made out of
760LLVM <a href="CodeGenerator.html#machinebasicblock">MachineBasicBlock</a>s, and
761<a href="CodeGenerator.html#selectiondag_intro">Instruction Selection
762DAGs</a>. In many cases, while debugging various parts of the compiler, it is
763nice to instantly visualize these graphs.</p>
764
765<p>LLVM provides several callbacks that are available in a debug build to do
766exactly that. If you call the <tt>Function::viewCFG()</tt> method, for example,
767the current LLVM tool will pop up a window containing the CFG for the function
768where each basic block is a node in the graph, and each node contains the
769instructions in the block. Similarly, there also exists
770<tt>Function::viewCFGOnly()</tt> (does not include the instructions), the
771<tt>MachineFunction::viewCFG()</tt> and <tt>MachineFunction::viewCFGOnly()</tt>,
772and the <tt>SelectionDAG::viewGraph()</tt> methods. Within GDB, for example,
Jim Laskey543a0ee2006-10-02 12:28:07 +0000[diff] [blame]773you can usually use something like <tt>call DAG.viewGraph()</tt> to pop
Chris Lattnerf623a082005-10-17 01:36:23 +0000[diff] [blame]774up a window. Alternatively, you can sprinkle calls to these functions in your
775code in places you want to debug.</p>
776
777<p>Getting this to work requires a small amount of configuration. On Unix
778systems with X11, install the <a href="http://www.graphviz.org">graphviz</a>
779toolkit, and make sure 'dot' and 'gv' are in your path. If you are running on
780Mac OS/X, download and install the Mac OS/X <a
781href="http://www.pixelglow.com/graphviz/">Graphviz program</a>, and add
Reid Spencer128a7a72007-02-03 21:06:43 +0000[diff] [blame]782<tt>/Applications/Graphviz.app/Contents/MacOS/</tt> (or wherever you install
Chris Lattnerf623a082005-10-17 01:36:23 +0000[diff] [blame]783it) to your path. Once in your system and path are set up, rerun the LLVM
784configure script and rebuild LLVM to enable this functionality.</p>
785
Jim Laskey543a0ee2006-10-02 12:28:07 +0000[diff] [blame]786<p><tt>SelectionDAG</tt> has been extended to make it easier to locate
787<i>interesting</i> nodes in large complex graphs. From gdb, if you
788<tt>call DAG.setGraphColor(<i>node</i>, "<i>color</i>")</tt>, then the
Reid Spencer128a7a72007-02-03 21:06:43 +0000[diff] [blame]789next <tt>call DAG.viewGraph()</tt> would highlight the node in the
Jim Laskey543a0ee2006-10-02 12:28:07 +0000[diff] [blame]790specified color (choices of colors can be found at <a
Chris Lattner302da1e2007-02-03 03:05:57 +0000[diff] [blame]791href="http://www.graphviz.org/doc/info/colors.html">colors</a>.) More
Jim Laskey543a0ee2006-10-02 12:28:07 +0000[diff] [blame]792complex node attributes can be provided with <tt>call
793DAG.setGraphAttrs(<i>node</i>, "<i>attributes</i>")</tt> (choices can be
794found at <a href="http://www.graphviz.org/doc/info/attrs.html">Graph
795Attributes</a>.) If you want to restart and clear all the current graph
796attributes, then you can <tt>call DAG.clearGraphAttrs()</tt>. </p>
797
Chris Lattnerf623a082005-10-17 01:36:23 +0000[diff] [blame]798</div>
799
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]800<!-- *********************************************************************** -->
801<div class="doc_section">
802 <a name="datastructure">Picking the Right Data Structure for a Task</a>
803</div>
804<!-- *********************************************************************** -->
805
806<div class="doc_text">
807
Reid Spencer128a7a72007-02-03 21:06:43 +0000[diff] [blame]808<p>LLVM has a plethora of data structures in the <tt>llvm/ADT/</tt> directory,
809 and we commonly use STL data structures. This section describes the trade-offs
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]810 you should consider when you pick one.</p>
811
812<p>
813The first step is a choose your own adventure: do you want a sequential
814container, a set-like container, or a map-like container? The most important
815thing when choosing a container is the algorithmic properties of how you plan to
816access the container. Based on that, you should use:</p>
817
818<ul>
Reid Spencer128a7a72007-02-03 21:06:43 +0000[diff] [blame]819<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]820 of an value based on another value. Map-like containers also support
821 efficient queries for containment (whether a key is in the map). Map-like
822 containers generally do not support efficient reverse mapping (values to
823 keys). If you need that, use two maps. Some map-like containers also
824 support efficient iteration through the keys in sorted order. Map-like
825 containers are the most expensive sort, only use them if you need one of
826 these capabilities.</li>
827
828<li>a <a href="#ds_set">set-like</a> container if you need to put a bunch of
829 stuff into a container that automatically eliminates duplicates. Some
830 set-like containers support efficient iteration through the elements in
831 sorted order. Set-like containers are more expensive than sequential
832 containers.
833</li>
834
835<li>a <a href="#ds_sequential">sequential</a> container provides
836 the most efficient way to add elements and keeps track of the order they are
837 added to the collection. They permit duplicates and support efficient
Reid Spencer128a7a72007-02-03 21:06:43 +0000[diff] [blame]838 iteration, but do not support efficient look-up based on a key.
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]839</li>
840
Chris Lattnerdced9fb2009-07-25 07:22:20 +0000[diff] [blame]841<li>a <a href="#ds_string">string</a> container is a specialized sequential
842 container or reference structure that is used for character or byte
843 arrays.</li>
844
Daniel Berlin1939ace2007-09-24 17:52:25 +0000[diff] [blame]845<li>a <a href="#ds_bit">bit</a> container provides an efficient way to store and
846 perform set operations on sets of numeric id's, while automatically
847 eliminating duplicates. Bit containers require a maximum of 1 bit for each
848 identifier you want to store.
849</li>
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]850</ul>
851
852<p>
Reid Spencer128a7a72007-02-03 21:06:43 +0000[diff] [blame]853Once the proper category of container is determined, you can fine tune the
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]854memory use, constant factors, and cache behaviors of access by intelligently
Reid Spencer128a7a72007-02-03 21:06:43 +0000[diff] [blame]855picking a member of the category. Note that constant factors and cache behavior
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]856can be a big deal. If you have a vector that usually only contains a few
857elements (but could contain many), for example, it's much better to use
858<a href="#dss_smallvector">SmallVector</a> than <a href="#dss_vector">vector</a>
859. Doing so avoids (relatively) expensive malloc/free calls, which dwarf the
860cost of adding the elements to the container. </p>
861
862</div>
863
864<!-- ======================================================================= -->
865<div class="doc_subsection">
866 <a name="ds_sequential">Sequential Containers (std::vector, std::list, etc)</a>
867</div>
868
869<div class="doc_text">
870There are a variety of sequential containers available for you, based on your
871needs. Pick the first in this section that will do what you want.
872</div>
873
874<!-- _______________________________________________________________________ -->
875<div class="doc_subsubsection">
876 <a name="dss_fixedarrays">Fixed Size Arrays</a>
877</div>
878
879<div class="doc_text">
880<p>Fixed size arrays are very simple and very fast. They are good if you know
881exactly how many elements you have, or you have a (low) upper bound on how many
882you have.</p>
883</div>
884
885<!-- _______________________________________________________________________ -->
886<div class="doc_subsubsection">
887 <a name="dss_heaparrays">Heap Allocated Arrays</a>
888</div>
889
890<div class="doc_text">
891<p>Heap allocated arrays (new[] + delete[]) are also simple. They are good if
892the number of elements is variable, if you know how many elements you will need
893before the array is allocated, and if the array is usually large (if not,
894consider a <a href="#dss_smallvector">SmallVector</a>). The cost of a heap
895allocated array is the cost of the new/delete (aka malloc/free). Also note that
896if you are allocating an array of a type with a constructor, the constructor and
Reid Spencer128a7a72007-02-03 21:06:43 +0000[diff] [blame]897destructors will be run for every element in the array (re-sizable vectors only
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]898construct those elements actually used).</p>
899</div>
900
901<!-- _______________________________________________________________________ -->
902<div class="doc_subsubsection">
903 <a name="dss_smallvector">"llvm/ADT/SmallVector.h"</a>
904</div>
905
906<div class="doc_text">
907<p><tt>SmallVector&lt;Type, N&gt;</tt> is a simple class that looks and smells
908just like <tt>vector&lt;Type&gt;</tt>:
909it supports efficient iteration, lays out elements in memory order (so you can
910do pointer arithmetic between elements), supports efficient push_back/pop_back
911operations, supports efficient random access to its elements, etc.</p>
912
913<p>The advantage of SmallVector is that it allocates space for
914some number of elements (N) <b>in the object itself</b>. Because of this, if
915the SmallVector is dynamically smaller than N, no malloc is performed. This can
916be a big win in cases where the malloc/free call is far more expensive than the
917code that fiddles around with the elements.</p>
918
919<p>This is good for vectors that are "usually small" (e.g. the number of
920predecessors/successors of a block is usually less than 8). On the other hand,
921this makes the size of the SmallVector itself large, so you don't want to
922allocate lots of them (doing so will waste a lot of space). As such,
923SmallVectors are most useful when on the stack.</p>
924
925<p>SmallVector also provides a nice portable and efficient replacement for
926<tt>alloca</tt>.</p>
927
928</div>
929
930<!-- _______________________________________________________________________ -->
931<div class="doc_subsubsection">
932 <a name="dss_vector">&lt;vector&gt;</a>
933</div>
934
935<div class="doc_text">
936<p>
937std::vector is well loved and respected. It is useful when SmallVector isn't:
938when the size of the vector is often large (thus the small optimization will
939rarely be a benefit) or if you will be allocating many instances of the vector
940itself (which would waste space for elements that aren't in the container).
941vector is also useful when interfacing with code that expects vectors :).
942</p>
Chris Lattner32d84762007-02-05 06:30:51 +0000[diff] [blame]943
944<p>One worthwhile note about std::vector: avoid code like this:</p>
945
946<div class="doc_code">
947<pre>
948for ( ... ) {
Chris Lattner9bb3dbb2007-03-28 18:27:57 +0000[diff] [blame]949 std::vector&lt;foo&gt; V;
Chris Lattner32d84762007-02-05 06:30:51 +0000[diff] [blame]950 use V;
951}
952</pre>
953</div>
954
955<p>Instead, write this as:</p>
956
957<div class="doc_code">
958<pre>
Chris Lattner9bb3dbb2007-03-28 18:27:57 +0000[diff] [blame]959std::vector&lt;foo&gt; V;
Chris Lattner32d84762007-02-05 06:30:51 +0000[diff] [blame]960for ( ... ) {
961 use V;
962 V.clear();
963}
964</pre>
965</div>
966
967<p>Doing so will save (at least) one heap allocation and free per iteration of
968the loop.</p>
969
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]970</div>
971
972<!-- _______________________________________________________________________ -->
973<div class="doc_subsubsection">
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]974 <a name="dss_deque">&lt;deque&gt;</a>
975</div>
976
977<div class="doc_text">
978<p>std::deque is, in some senses, a generalized version of std::vector. Like
979std::vector, it provides constant time random access and other similar
980properties, but it also provides efficient access to the front of the list. It
981does not guarantee continuity of elements within memory.</p>
982
983<p>In exchange for this extra flexibility, std::deque has significantly higher
984constant factor costs than std::vector. If possible, use std::vector or
985something cheaper.</p>
986</div>
987
988<!-- _______________________________________________________________________ -->
989<div class="doc_subsubsection">
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]990 <a name="dss_list">&lt;list&gt;</a>
991</div>
992
993<div class="doc_text">
994<p>std::list is an extremely inefficient class that is rarely useful.
995It performs a heap allocation for every element inserted into it, thus having an
996extremely high constant factor, particularly for small data types. std::list
997also only supports bidirectional iteration, not random access iteration.</p>
998
999<p>In exchange for this high cost, std::list supports efficient access to both
1000ends of the list (like std::deque, but unlike std::vector or SmallVector). In
1001addition, the iterator invalidation characteristics of std::list are stronger
1002than that of a vector class: inserting or removing an element into the list does
1003not invalidate iterator or pointers to other elements in the list.</p>
1004</div>
1005
1006<!-- _______________________________________________________________________ -->
1007<div class="doc_subsubsection">
Gabor Greif3899e492009-02-27 11:37:41 +0000[diff] [blame]1008 <a name="dss_ilist">llvm/ADT/ilist.h</a>
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]1009</div>
1010
1011<div class="doc_text">
1012<p><tt>ilist&lt;T&gt;</tt> implements an 'intrusive' doubly-linked list. It is
1013intrusive, because it requires the element to store and provide access to the
1014prev/next pointers for the list.</p>
1015
Gabor Greif2946d1c2009-02-27 12:02:19 +0000[diff] [blame]1016<p><tt>ilist</tt> has the same drawbacks as <tt>std::list</tt>, and additionally
1017requires an <tt>ilist_traits</tt> implementation for the element type, but it
1018provides some novel characteristics. In particular, it can efficiently store
1019polymorphic objects, the traits class is informed when an element is inserted or
Gabor Greif0cbcabe2009-03-12 09:47:03 +0000[diff] [blame]1020removed from the list, and <tt>ilist</tt>s are guaranteed to support a
1021constant-time splice operation.</p>
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]1022
Gabor Greif0cbcabe2009-03-12 09:47:03 +0000[diff] [blame]1023<p>These properties are exactly what we want for things like
1024<tt>Instruction</tt>s and basic blocks, which is why these are implemented with
1025<tt>ilist</tt>s.</p>
Gabor Greif3899e492009-02-27 11:37:41 +0000[diff] [blame]1026
1027Related classes of interest are explained in the following subsections:
1028 <ul>
Gabor Greif01862502009-02-27 13:28:07 +0000[diff] [blame]1029 <li><a href="#dss_ilist_traits">ilist_traits</a></li>
Gabor Greif2946d1c2009-02-27 12:02:19 +0000[diff] [blame]1030 <li><a href="#dss_iplist">iplist</a></li>
Gabor Greif3899e492009-02-27 11:37:41 +0000[diff] [blame]1031 <li><a href="#dss_ilist_node">llvm/ADT/ilist_node.h</a></li>
Gabor Greif6a65f422009-03-12 10:30:31 +0000[diff] [blame]1032 <li><a href="#dss_ilist_sentinel">Sentinels</a></li>
Gabor Greif3899e492009-02-27 11:37:41 +0000[diff] [blame]1033 </ul>
1034</div>
1035
1036<!-- _______________________________________________________________________ -->
1037<div class="doc_subsubsection">
Gabor Greif01862502009-02-27 13:28:07 +0000[diff] [blame]1038 <a name="dss_ilist_traits">ilist_traits</a>
1039</div>
1040
1041<div class="doc_text">
1042<p><tt>ilist_traits&lt;T&gt;</tt> is <tt>ilist&lt;T&gt;</tt>'s customization
1043mechanism. <tt>iplist&lt;T&gt;</tt> (and consequently <tt>ilist&lt;T&gt;</tt>)
1044publicly derive from this traits class.</p>
1045</div>
1046
1047<!-- _______________________________________________________________________ -->
1048<div class="doc_subsubsection">
Gabor Greif2946d1c2009-02-27 12:02:19 +0000[diff] [blame]1049 <a name="dss_iplist">iplist</a>
1050</div>
1051
1052<div class="doc_text">
1053<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]1054supports a slightly narrower interface. Notably, inserters from
1055<tt>T&amp;</tt> are absent.</p>
Gabor Greif01862502009-02-27 13:28:07 +0000[diff] [blame]1056
1057<p><tt>ilist_traits&lt;T&gt;</tt> is a public base of this class and can be
1058used for a wide variety of customizations.</p>
Gabor Greif2946d1c2009-02-27 12:02:19 +0000[diff] [blame]1059</div>
1060
1061<!-- _______________________________________________________________________ -->
1062<div class="doc_subsubsection">
Gabor Greif3899e492009-02-27 11:37:41 +0000[diff] [blame]1063 <a name="dss_ilist_node">llvm/ADT/ilist_node.h</a>
1064</div>
1065
1066<div class="doc_text">
1067<p><tt>ilist_node&lt;T&gt;</tt> implements a the forward and backward links
1068that are expected by the <tt>ilist&lt;T&gt;</tt> (and analogous containers)
1069in the default manner.</p>
1070
1071<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]1072<tt>T</tt>, usually <tt>T</tt> publicly derives from
1073<tt>ilist_node&lt;T&gt;</tt>.</p>
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]1074</div>
1075
1076<!-- _______________________________________________________________________ -->
1077<div class="doc_subsubsection">
Gabor Greif6a65f422009-03-12 10:30:31 +0000[diff] [blame]1078 <a name="dss_ilist_sentinel">Sentinels</a>
1079</div>
1080
1081<div class="doc_text">
1082<p><tt>ilist</tt>s have another speciality that must be considered. To be a good
1083citizen in the C++ ecosystem, it needs to support the standard container
1084operations, such as <tt>begin</tt> and <tt>end</tt> iterators, etc. Also, the
1085<tt>operator--</tt> must work correctly on the <tt>end</tt> iterator in the
1086case of non-empty <tt>ilist</tt>s.</p>
1087
1088<p>The only sensible solution to this problem is to allocate a so-called
1089<i>sentinel</i> along with the intrusive list, which serves as the <tt>end</tt>
1090iterator, providing the back-link to the last element. However conforming to the
1091C++ convention it is illegal to <tt>operator++</tt> beyond the sentinel and it
1092also must not be dereferenced.</p>
1093
1094<p>These constraints allow for some implementation freedom to the <tt>ilist</tt>
1095how to allocate and store the sentinel. The corresponding policy is dictated
1096by <tt>ilist_traits&lt;T&gt;</tt>. By default a <tt>T</tt> gets heap-allocated
1097whenever the need for a sentinel arises.</p>
1098
1099<p>While the default policy is sufficient in most cases, it may break down when
1100<tt>T</tt> does not provide a default constructor. Also, in the case of many
1101instances of <tt>ilist</tt>s, the memory overhead of the associated sentinels
1102is wasted. To alleviate the situation with numerous and voluminous
1103<tt>T</tt>-sentinels, sometimes a trick is employed, leading to <i>ghostly
1104sentinels</i>.</p>
1105
1106<p>Ghostly sentinels are obtained by specially-crafted <tt>ilist_traits&lt;T&gt;</tt>
1107which superpose the sentinel with the <tt>ilist</tt> instance in memory. Pointer
1108arithmetic is used to obtain the sentinel, which is relative to the
1109<tt>ilist</tt>'s <tt>this</tt> pointer. The <tt>ilist</tt> is augmented by an
1110extra pointer, which serves as the back-link of the sentinel. This is the only
1111field in the ghostly sentinel which can be legally accessed.</p>
1112</div>
1113
1114<!-- _______________________________________________________________________ -->
1115<div class="doc_subsubsection">
Chris Lattnerc5722432007-02-03 19:49:31 +0000[diff] [blame]1116 <a name="dss_other">Other Sequential Container options</a>
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]1117</div>
1118
1119<div class="doc_text">
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1120<p>Other STL containers are available, such as std::string.</p>
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]1121
1122<p>There are also various STL adapter classes such as std::queue,
1123std::priority_queue, std::stack, etc. These provide simplified access to an
1124underlying container but don't affect the cost of the container itself.</p>
1125
1126</div>
1127
1128
1129<!-- ======================================================================= -->
1130<div class="doc_subsection">
1131 <a name="ds_set">Set-Like Containers (std::set, SmallSet, SetVector, etc)</a>
1132</div>
1133
1134<div class="doc_text">
1135
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1136<p>Set-like containers are useful when you need to canonicalize multiple values
1137into a single representation. There are several different choices for how to do
1138this, providing various trade-offs.</p>
1139
1140</div>
1141
1142
1143<!-- _______________________________________________________________________ -->
1144<div class="doc_subsubsection">
1145 <a name="dss_sortedvectorset">A sorted 'vector'</a>
1146</div>
1147
1148<div class="doc_text">
1149
Chris Lattner3b23a8c2007-02-03 08:10:45 +0000[diff] [blame]1150<p>If you intend to insert a lot of elements, then do a lot of queries, a
1151great approach is to use a vector (or other sequential container) with
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1152std::sort+std::unique to remove duplicates. This approach works really well if
Chris Lattner3b23a8c2007-02-03 08:10:45 +0000[diff] [blame]1153your usage pattern has these two distinct phases (insert then query), and can be
1154coupled with a good choice of <a href="#ds_sequential">sequential container</a>.
1155</p>
1156
1157<p>
1158This combination provides the several nice properties: the result data is
1159contiguous in memory (good for cache locality), has few allocations, is easy to
1160address (iterators in the final vector are just indices or pointers), and can be
1161efficiently queried with a standard binary or radix search.</p>
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1162
1163</div>
1164
1165<!-- _______________________________________________________________________ -->
1166<div class="doc_subsubsection">
1167 <a name="dss_smallset">"llvm/ADT/SmallSet.h"</a>
1168</div>
1169
1170<div class="doc_text">
1171
Reid Spencer128a7a72007-02-03 21:06:43 +0000[diff] [blame]1172<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]1173are 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]1174has space for N elements in place (thus, if the set is dynamically smaller than
Chris Lattner14868db2007-02-03 08:20:15 +0000[diff] [blame]1175N, no malloc traffic is required) and accesses them with a simple linear search.
1176When the set grows beyond 'N' elements, it allocates a more expensive representation that
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1177guarantees efficient access (for most types, it falls back to std::set, but for
Chris Lattner14868db2007-02-03 08:20:15 +0000[diff] [blame]1178pointers it uses something far better, <a
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1179href="#dss_smallptrset">SmallPtrSet</a>).</p>
1180
1181<p>The magic of this class is that it handles small sets extremely efficiently,
1182but gracefully handles extremely large sets without loss of efficiency. The
1183drawback is that the interface is quite small: it supports insertion, queries
1184and erasing, but does not support iteration.</p>
1185
1186</div>
1187
1188<!-- _______________________________________________________________________ -->
1189<div class="doc_subsubsection">
1190 <a name="dss_smallptrset">"llvm/ADT/SmallPtrSet.h"</a>
1191</div>
1192
1193<div class="doc_text">
1194
1195<p>SmallPtrSet has all the advantages of SmallSet (and a SmallSet of pointers is
Reid Spencer128a7a72007-02-03 21:06:43 +0000[diff] [blame]1196transparently implemented with a SmallPtrSet), but also supports iterators. If
Chris Lattner14868db2007-02-03 08:20:15 +0000[diff] [blame]1197more than 'N' insertions are performed, a single quadratically
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1198probed hash table is allocated and grows as needed, providing extremely
1199efficient access (constant time insertion/deleting/queries with low constant
1200factors) and is very stingy with malloc traffic.</p>
1201
1202<p>Note that, unlike std::set, the iterators of SmallPtrSet are invalidated
1203whenever an insertion occurs. Also, the values visited by the iterators are not
1204visited in sorted order.</p>
1205
1206</div>
1207
1208<!-- _______________________________________________________________________ -->
1209<div class="doc_subsubsection">
Chris Lattnerc28476f2007-09-30 00:58:59 +0000[diff] [blame]1210 <a name="dss_denseset">"llvm/ADT/DenseSet.h"</a>
1211</div>
1212
1213<div class="doc_text">
1214
1215<p>
1216DenseSet is a simple quadratically probed hash table. It excels at supporting
1217small values: it uses a single allocation to hold all of the pairs that
1218are currently inserted in the set. DenseSet is a great way to unique small
1219values that are not simple pointers (use <a
1220href="#dss_smallptrset">SmallPtrSet</a> for pointers). Note that DenseSet has
1221the same requirements for the value type that <a
1222href="#dss_densemap">DenseMap</a> has.
1223</p>
1224
1225</div>
1226
1227<!-- _______________________________________________________________________ -->
1228<div class="doc_subsubsection">
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1229 <a name="dss_FoldingSet">"llvm/ADT/FoldingSet.h"</a>
1230</div>
1231
1232<div class="doc_text">
1233
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]1234<p>
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1235FoldingSet is an aggregate class that is really good at uniquing
1236expensive-to-create or polymorphic objects. It is a combination of a chained
1237hash table with intrusive links (uniqued objects are required to inherit from
Chris Lattner14868db2007-02-03 08:20:15 +0000[diff] [blame]1238FoldingSetNode) that uses <a href="#dss_smallvector">SmallVector</a> as part of
1239its ID process.</p>
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1240
Chris Lattner14868db2007-02-03 08:20:15 +0000[diff] [blame]1241<p>Consider a case where you want to implement a "getOrCreateFoo" method for
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1242a complex object (for example, a node in the code generator). The client has a
1243description of *what* it wants to generate (it knows the opcode and all the
1244operands), 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]1245only to find out it already exists, at which point we would have to delete it
1246and return the node that already exists.
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]1247</p>
1248
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1249<p>To support this style of client, FoldingSet perform a query with a
1250FoldingSetNodeID (which wraps SmallVector) that can be used to describe the
1251element that we want to query for. The query either returns the element
1252matching the ID or it returns an opaque ID that indicates where insertion should
Chris Lattner14868db2007-02-03 08:20:15 +0000[diff] [blame]1253take place. Construction of the ID usually does not require heap traffic.</p>
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1254
1255<p>Because FoldingSet uses intrusive links, it can support polymorphic objects
1256in the set (for example, you can have SDNode instances mixed with LoadSDNodes).
1257Because the elements are individually allocated, pointers to the elements are
1258stable: inserting or removing elements does not invalidate any pointers to other
1259elements.
1260</p>
1261
1262</div>
1263
1264<!-- _______________________________________________________________________ -->
1265<div class="doc_subsubsection">
1266 <a name="dss_set">&lt;set&gt;</a>
1267</div>
1268
1269<div class="doc_text">
1270
Chris Lattnerc5722432007-02-03 19:49:31 +0000[diff] [blame]1271<p><tt>std::set</tt> is a reasonable all-around set class, which is decent at
1272many things but great at nothing. std::set allocates memory for each element
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1273inserted (thus it is very malloc intensive) and typically stores three pointers
Chris Lattner14868db2007-02-03 08:20:15 +0000[diff] [blame]1274per element in the set (thus adding a large amount of per-element space
1275overhead). It offers guaranteed log(n) performance, which is not particularly
Chris Lattnerc5722432007-02-03 19:49:31 +0000[diff] [blame]1276fast from a complexity standpoint (particularly if the elements of the set are
1277expensive to compare, like strings), and has extremely high constant factors for
1278lookup, insertion and removal.</p>
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1279
Chris Lattner14868db2007-02-03 08:20:15 +0000[diff] [blame]1280<p>The advantages of std::set are that its iterators are stable (deleting or
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1281inserting an element from the set does not affect iterators or pointers to other
1282elements) and that iteration over the set is guaranteed to be in sorted order.
1283If the elements in the set are large, then the relative overhead of the pointers
1284and malloc traffic is not a big deal, but if the elements of the set are small,
1285std::set is almost never a good choice.</p>
1286
1287</div>
1288
1289<!-- _______________________________________________________________________ -->
1290<div class="doc_subsubsection">
1291 <a name="dss_setvector">"llvm/ADT/SetVector.h"</a>
1292</div>
1293
1294<div class="doc_text">
Chris Lattneredca3c52007-02-04 00:00:26 +0000[diff] [blame]1295<p>LLVM's SetVector&lt;Type&gt; is an adapter class that combines your choice of
1296a set-like container along with a <a href="#ds_sequential">Sequential
1297Container</a>. The important property
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1298that this provides is efficient insertion with uniquing (duplicate elements are
1299ignored) with iteration support. It implements this by inserting elements into
1300both a set-like container and the sequential container, using the set-like
1301container for uniquing and the sequential container for iteration.
1302</p>
1303
1304<p>The difference between SetVector and other sets is that the order of
1305iteration is guaranteed to match the order of insertion into the SetVector.
1306This property is really important for things like sets of pointers. Because
1307pointer values are non-deterministic (e.g. vary across runs of the program on
Chris Lattneredca3c52007-02-04 00:00:26 +0000[diff] [blame]1308different machines), iterating over the pointers in the set will
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1309not be in a well-defined order.</p>
1310
1311<p>
1312The drawback of SetVector is that it requires twice as much space as a normal
1313set and has the sum of constant factors from the set-like container and the
1314sequential container that it uses. Use it *only* if you need to iterate over
1315the elements in a deterministic order. SetVector is also expensive to delete
Chris Lattneredca3c52007-02-04 00:00:26 +0000[diff] [blame]1316elements out of (linear time), unless you use it's "pop_back" method, which is
1317faster.
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1318</p>
1319
Chris Lattneredca3c52007-02-04 00:00:26 +0000[diff] [blame]1320<p>SetVector is an adapter class that defaults to using std::vector and std::set
1321for the underlying containers, so it is quite expensive. However,
1322<tt>"llvm/ADT/SetVector.h"</tt> also provides a SmallSetVector class, which
1323defaults to using a SmallVector and SmallSet of a specified size. If you use
1324this, and if your sets are dynamically smaller than N, you will save a lot of
1325heap traffic.</p>
1326
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1327</div>
1328
1329<!-- _______________________________________________________________________ -->
1330<div class="doc_subsubsection">
Chris Lattnerc5722432007-02-03 19:49:31 +0000[diff] [blame]1331 <a name="dss_uniquevector">"llvm/ADT/UniqueVector.h"</a>
1332</div>
1333
1334<div class="doc_text">
1335
1336<p>
1337UniqueVector is similar to <a href="#dss_setvector">SetVector</a>, but it
1338retains a unique ID for each element inserted into the set. It internally
1339contains a map and a vector, and it assigns a unique ID for each value inserted
1340into the set.</p>
1341
1342<p>UniqueVector is very expensive: its cost is the sum of the cost of
1343maintaining both the map and vector, it has high complexity, high constant
1344factors, and produces a lot of malloc traffic. It should be avoided.</p>
1345
1346</div>
1347
1348
1349<!-- _______________________________________________________________________ -->
1350<div class="doc_subsubsection">
1351 <a name="dss_otherset">Other Set-Like Container Options</a>
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1352</div>
1353
1354<div class="doc_text">
1355
1356<p>
1357The STL provides several other options, such as std::multiset and the various
Chris Lattnerf1a30822009-03-09 05:20:45 +0000[diff] [blame]1358"hash_set" like containers (whether from C++ TR1 or from the SGI library). We
1359never use hash_set and unordered_set because they are generally very expensive
1360(each insertion requires a malloc) and very non-portable.
1361</p>
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1362
1363<p>std::multiset is useful if you're not interested in elimination of
Chris Lattner14868db2007-02-03 08:20:15 +0000[diff] [blame]1364duplicates, but has all the drawbacks of std::set. A sorted vector (where you
1365don't delete duplicate entries) or some other approach is almost always
1366better.</p>
Chris Lattner74c4ca12007-02-03 07:59:07 +0000[diff] [blame]1367
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]1368</div>
1369
1370<!-- ======================================================================= -->
1371<div class="doc_subsection">
1372 <a name="ds_map">Map-Like Containers (std::map, DenseMap, etc)</a>
1373</div>
1374
1375<div class="doc_text">
Chris Lattnerc5722432007-02-03 19:49:31 +0000[diff] [blame]1376Map-like containers are useful when you want to associate data to a key. As
1377usual, there are a lot of different ways to do this. :)
1378</div>
1379
1380<!-- _______________________________________________________________________ -->
1381<div class="doc_subsubsection">
1382 <a name="dss_sortedvectormap">A sorted 'vector'</a>
1383</div>
1384
1385<div class="doc_text">
1386
1387<p>
1388If your usage pattern follows a strict insert-then-query approach, you can
1389trivially use the same approach as <a href="#dss_sortedvectorset">sorted vectors
1390for set-like containers</a>. The only difference is that your query function
1391(which uses std::lower_bound to get efficient log(n) lookup) should only compare
1392the key, not both the key and value. This yields the same advantages as sorted
1393vectors for sets.
1394</p>
1395</div>
1396
1397<!-- _______________________________________________________________________ -->
1398<div class="doc_subsubsection">
Chris Lattner796f9fa2007-02-08 19:14:21 +0000[diff] [blame]1399 <a name="dss_stringmap">"llvm/ADT/StringMap.h"</a>
Chris Lattnerc5722432007-02-03 19:49:31 +0000[diff] [blame]1400</div>
1401
1402<div class="doc_text">
1403
1404<p>
1405Strings are commonly used as keys in maps, and they are difficult to support
1406efficiently: they are variable length, inefficient to hash and compare when
Chris Lattner796f9fa2007-02-08 19:14:21 +0000[diff] [blame]1407long, expensive to copy, etc. StringMap is a specialized container designed to
1408cope with these issues. It supports mapping an arbitrary range of bytes to an
1409arbitrary other object.</p>
Chris Lattnerc5722432007-02-03 19:49:31 +0000[diff] [blame]1410
Chris Lattner796f9fa2007-02-08 19:14:21 +0000[diff] [blame]1411<p>The StringMap implementation uses a quadratically-probed hash table, where
Chris Lattnerc5722432007-02-03 19:49:31 +0000[diff] [blame]1412the buckets store a pointer to the heap allocated entries (and some other
1413stuff). The entries in the map must be heap allocated because the strings are
1414variable length. The string data (key) and the element object (value) are
1415stored in the same allocation with the string data immediately after the element
1416object. This container guarantees the "<tt>(char*)(&amp;Value+1)</tt>" points
1417to the key string for a value.</p>
1418
Chris Lattner796f9fa2007-02-08 19:14:21 +0000[diff] [blame]1419<p>The StringMap is very fast for several reasons: quadratic probing is very
Chris Lattnerc5722432007-02-03 19:49:31 +0000[diff] [blame]1420cache efficient for lookups, the hash value of strings in buckets is not
Chris Lattner796f9fa2007-02-08 19:14:21 +0000[diff] [blame]1421recomputed when lookup up an element, StringMap rarely has to touch the
Chris Lattnerc5722432007-02-03 19:49:31 +0000[diff] [blame]1422memory for unrelated objects when looking up a value (even when hash collisions
1423happen), hash table growth does not recompute the hash values for strings
1424already in the table, and each pair in the map is store in a single allocation
1425(the string data is stored in the same allocation as the Value of a pair).</p>
1426
Chris Lattner796f9fa2007-02-08 19:14:21 +0000[diff] [blame]1427<p>StringMap also provides query methods that take byte ranges, so it only ever
Chris Lattnerc5722432007-02-03 19:49:31 +0000[diff] [blame]1428copies a string if a value is inserted into the table.</p>
1429</div>
1430
1431<!-- _______________________________________________________________________ -->
1432<div class="doc_subsubsection">
1433 <a name="dss_indexedmap">"llvm/ADT/IndexedMap.h"</a>
1434</div>
1435
1436<div class="doc_text">
1437<p>
1438IndexedMap is a specialized container for mapping small dense integers (or
1439values that can be mapped to small dense integers) to some other type. It is
1440internally implemented as a vector with a mapping function that maps the keys to
1441the dense integer range.
1442</p>
1443
1444<p>
1445This is useful for cases like virtual registers in the LLVM code generator: they
1446have a dense mapping that is offset by a compile-time constant (the first
1447virtual register ID).</p>
1448
1449</div>
1450
1451<!-- _______________________________________________________________________ -->
1452<div class="doc_subsubsection">
1453 <a name="dss_densemap">"llvm/ADT/DenseMap.h"</a>
1454</div>
1455
1456<div class="doc_text">
1457
1458<p>
1459DenseMap is a simple quadratically probed hash table. It excels at supporting
1460small keys and values: it uses a single allocation to hold all of the pairs that
1461are currently inserted in the map. DenseMap is a great way to map pointers to
1462pointers, or map other small types to each other.
1463</p>
1464
1465<p>
1466There are several aspects of DenseMap that you should be aware of, however. The
1467iterators in a densemap are invalidated whenever an insertion occurs, unlike
1468map. Also, because DenseMap allocates space for a large number of key/value
Chris Lattnera4a264d2007-02-03 20:17:53 +0000[diff] [blame]1469pairs (it starts with 64 by default), it will waste a lot of space if your keys
1470or values are large. Finally, you must implement a partial specialization of
Chris Lattner76c1b972007-09-17 18:34:04 +0000[diff] [blame]1471DenseMapInfo for the key that you want, if it isn't already supported. This
Chris Lattnerc5722432007-02-03 19:49:31 +0000[diff] [blame]1472is required to tell DenseMap about two special marker values (which can never be
Chris Lattnera4a264d2007-02-03 20:17:53 +0000[diff] [blame]1473inserted into the map) that it needs internally.</p>
Chris Lattnerc5722432007-02-03 19:49:31 +0000[diff] [blame]1474
1475</div>
1476
1477<!-- _______________________________________________________________________ -->
1478<div class="doc_subsubsection">
1479 <a name="dss_map">&lt;map&gt;</a>
1480</div>
1481
1482<div class="doc_text">
1483
1484<p>
1485std::map has similar characteristics to <a href="#dss_set">std::set</a>: it uses
1486a single allocation per pair inserted into the map, it offers log(n) lookup with
1487an extremely large constant factor, imposes a space penalty of 3 pointers per
1488pair in the map, etc.</p>
1489
1490<p>std::map is most useful when your keys or values are very large, if you need
1491to iterate over the collection in sorted order, or if you need stable iterators
1492into the map (i.e. they don't get invalidated if an insertion or deletion of
1493another element takes place).</p>
1494
1495</div>
1496
1497<!-- _______________________________________________________________________ -->
1498<div class="doc_subsubsection">
1499 <a name="dss_othermap">Other Map-Like Container Options</a>
1500</div>
1501
1502<div class="doc_text">
1503
1504<p>
1505The STL provides several other options, such as std::multimap and the various
Chris Lattnerf1a30822009-03-09 05:20:45 +0000[diff] [blame]1506"hash_map" like containers (whether from C++ TR1 or from the SGI library). We
1507never use hash_set and unordered_set because they are generally very expensive
1508(each insertion requires a malloc) and very non-portable.</p>
Chris Lattnerc5722432007-02-03 19:49:31 +0000[diff] [blame]1509
1510<p>std::multimap is useful if you want to map a key to multiple values, but has
1511all the drawbacks of std::map. A sorted vector or some other approach is almost
1512always better.</p>
1513
Chris Lattner098129a2007-02-03 03:04:03 +0000[diff] [blame]1514</div>
1515
Daniel Berlin1939ace2007-09-24 17:52:25 +0000[diff] [blame]1516<!-- ======================================================================= -->
1517<div class="doc_subsection">
Chris Lattnerdced9fb2009-07-25 07:22:20 +0000[diff] [blame]1518 <a name="ds_string">String-like containers</a>
1519</div>
1520
1521<div class="doc_text">
1522
1523<p>
1524TODO: const char* vs stringref vs smallstring vs std::string. Describe twine,
1525xref to #string_apis.
1526</p>
1527
1528</div>
1529
1530<!-- ======================================================================= -->
1531<div class="doc_subsection">
Daniel Berlin1939ace2007-09-24 17:52:25 +0000[diff] [blame]1532 <a name="ds_bit">Bit storage containers (BitVector, SparseBitVector)</a>
1533</div>
1534
1535<div class="doc_text">
Chris Lattner7086ce72007-09-25 22:37:50 +0000[diff] [blame]1536<p>Unlike the other containers, there are only two bit storage containers, and
1537choosing when to use each is relatively straightforward.</p>
1538
1539<p>One additional option is
1540<tt>std::vector&lt;bool&gt;</tt>: we discourage its use for two reasons 1) the
1541implementation in many common compilers (e.g. commonly available versions of
1542GCC) is extremely inefficient and 2) the C++ standards committee is likely to
1543deprecate this container and/or change it significantly somehow. In any case,
1544please don't use it.</p>
Daniel Berlin1939ace2007-09-24 17:52:25 +0000[diff] [blame]1545</div>
1546
1547<!-- _______________________________________________________________________ -->
1548<div class="doc_subsubsection">
1549 <a name="dss_bitvector">BitVector</a>
1550</div>
1551
1552<div class="doc_text">
1553<p> The BitVector container provides a fixed size set of bits for manipulation.
1554It supports individual bit setting/testing, as well as set operations. The set
1555operations take time O(size of bitvector), but operations are performed one word
1556at a time, instead of one bit at a time. This makes the BitVector very fast for
1557set operations compared to other containers. Use the BitVector when you expect
1558the number of set bits to be high (IE a dense set).
1559</p>
1560</div>
1561
1562<!-- _______________________________________________________________________ -->
1563<div class="doc_subsubsection">
1564 <a name="dss_sparsebitvector">SparseBitVector</a>
1565</div>
1566
1567<div class="doc_text">
1568<p> The SparseBitVector container is much like BitVector, with one major
1569difference: Only the bits that are set, are stored. This makes the
1570SparseBitVector much more space efficient than BitVector when the set is sparse,
1571as well as making set operations O(number of set bits) instead of O(size of
1572universe). 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
1573(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).
1574</p>
1575</div>
Chris Lattnerf623a082005-10-17 01:36:23 +0000[diff] [blame]1576
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1577<!-- *********************************************************************** -->
1578<div class="doc_section">
1579 <a name="common">Helpful Hints for Common Operations</a>
1580</div>
1581<!-- *********************************************************************** -->
1582
1583<div class="doc_text">
1584
1585<p>This section describes how to perform some very simple transformations of
1586LLVM code. This is meant to give examples of common idioms used, showing the
1587practical side of LLVM transformations. <p> Because this is a "how-to" section,
1588you should also read about the main classes that you will be working with. The
1589<a href="#coreclasses">Core LLVM Class Hierarchy Reference</a> contains details
1590and descriptions of the main classes that you should know about.</p>
1591
1592</div>
1593
1594<!-- NOTE: this section should be heavy on example code -->
1595<!-- ======================================================================= -->
1596<div class="doc_subsection">
1597 <a name="inspection">Basic Inspection and Traversal Routines</a>
1598</div>
1599
1600<div class="doc_text">
1601
1602<p>The LLVM compiler infrastructure have many different data structures that may
1603be traversed. Following the example of the C++ standard template library, the
1604techniques used to traverse these various data structures are all basically the
1605same. For a enumerable sequence of values, the <tt>XXXbegin()</tt> function (or
1606method) returns an iterator to the start of the sequence, the <tt>XXXend()</tt>
1607function returns an iterator pointing to one past the last valid element of the
1608sequence, and there is some <tt>XXXiterator</tt> data type that is common
1609between the two operations.</p>
1610
1611<p>Because the pattern for iteration is common across many different aspects of
1612the program representation, the standard template library algorithms may be used
1613on them, and it is easier to remember how to iterate. First we show a few common
1614examples of the data structures that need to be traversed. Other data
1615structures are traversed in very similar ways.</p>
1616
1617</div>
1618
1619<!-- _______________________________________________________________________ -->
Chris Lattner69bf8a92004-05-23 21:06:58 +0000[diff] [blame]1620<div class="doc_subsubsection">
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1621 <a name="iterate_function">Iterating over the </a><a
1622 href="#BasicBlock"><tt>BasicBlock</tt></a>s in a <a
1623 href="#Function"><tt>Function</tt></a>
1624</div>
1625
1626<div class="doc_text">
1627
1628<p>It's quite common to have a <tt>Function</tt> instance that you'd like to
1629transform in some way; in particular, you'd like to manipulate its
1630<tt>BasicBlock</tt>s. To facilitate this, you'll need to iterate over all of
1631the <tt>BasicBlock</tt>s that constitute the <tt>Function</tt>. The following is
1632an example that prints the name of a <tt>BasicBlock</tt> and the number of
1633<tt>Instruction</tt>s it contains:</p>
1634
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1635<div class="doc_code">
1636<pre>
Bill Wendling82e2eea2006-10-11 18:00:22 +0000[diff] [blame]1637// <i>func is a pointer to a Function instance</i>
1638for (Function::iterator i = func-&gt;begin(), e = func-&gt;end(); i != e; ++i)
1639 // <i>Print out the name of the basic block if it has one, and then the</i>
1640 // <i>number of instructions that it contains</i>
Bill Wendling832171c2006-12-07 20:04:42 +0000[diff] [blame]1641 llvm::cerr &lt;&lt; "Basic block (name=" &lt;&lt; i-&gt;getName() &lt;&lt; ") has "
1642 &lt;&lt; i-&gt;size() &lt;&lt; " instructions.\n";
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1643</pre>
1644</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1645
1646<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]1647invoking member functions of the <tt>Instruction</tt> class. This is
1648because the indirection operator is overloaded for the iterator
Chris Lattner7496ec52003-08-05 22:54:23 +0000[diff] [blame]1649classes. In the above code, the expression <tt>i-&gt;size()</tt> is
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1650exactly equivalent to <tt>(*i).size()</tt> just like you'd expect.</p>
1651
1652</div>
1653
1654<!-- _______________________________________________________________________ -->
Chris Lattner69bf8a92004-05-23 21:06:58 +0000[diff] [blame]1655<div class="doc_subsubsection">
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1656 <a name="iterate_basicblock">Iterating over the </a><a
1657 href="#Instruction"><tt>Instruction</tt></a>s in a <a
1658 href="#BasicBlock"><tt>BasicBlock</tt></a>
1659</div>
1660
1661<div class="doc_text">
1662
1663<p>Just like when dealing with <tt>BasicBlock</tt>s in <tt>Function</tt>s, it's
1664easy to iterate over the individual instructions that make up
1665<tt>BasicBlock</tt>s. Here's a code snippet that prints out each instruction in
1666a <tt>BasicBlock</tt>:</p>
1667
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1668<div class="doc_code">
Chris Lattner55c04612005-03-06 06:00:13 +0000[diff] [blame]1669<pre>
Bill Wendling82e2eea2006-10-11 18:00:22 +0000[diff] [blame]1670// <i>blk is a pointer to a BasicBlock instance</i>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1671for (BasicBlock::iterator i = blk-&gt;begin(), e = blk-&gt;end(); i != e; ++i)
Bill Wendling82e2eea2006-10-11 18:00:22 +0000[diff] [blame]1672 // <i>The next statement works since operator&lt;&lt;(ostream&amp;,...)</i>
1673 // <i>is overloaded for Instruction&amp;</i>
Bill Wendling832171c2006-12-07 20:04:42 +0000[diff] [blame]1674 llvm::cerr &lt;&lt; *i &lt;&lt; "\n";
Chris Lattner55c04612005-03-06 06:00:13 +0000[diff] [blame]1675</pre>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1676</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1677
1678<p>However, this isn't really the best way to print out the contents of a
1679<tt>BasicBlock</tt>! Since the ostream operators are overloaded for virtually
1680anything you'll care about, you could have just invoked the print routine on the
Bill Wendling832171c2006-12-07 20:04:42 +0000[diff] [blame]1681basic block itself: <tt>llvm::cerr &lt;&lt; *blk &lt;&lt; "\n";</tt>.</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1682
1683</div>
1684
1685<!-- _______________________________________________________________________ -->
Chris Lattner69bf8a92004-05-23 21:06:58 +0000[diff] [blame]1686<div class="doc_subsubsection">
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1687 <a name="iterate_institer">Iterating over the </a><a
1688 href="#Instruction"><tt>Instruction</tt></a>s in a <a
1689 href="#Function"><tt>Function</tt></a>
1690</div>
1691
1692<div class="doc_text">
1693
1694<p>If you're finding that you commonly iterate over a <tt>Function</tt>'s
1695<tt>BasicBlock</tt>s and then that <tt>BasicBlock</tt>'s <tt>Instruction</tt>s,
1696<tt>InstIterator</tt> should be used instead. You'll need to include <a
1697href="/doxygen/InstIterator_8h-source.html"><tt>llvm/Support/InstIterator.h</tt></a>,
1698and then instantiate <tt>InstIterator</tt>s explicitly in your code. Here's a
Chris Lattner69bf8a92004-05-23 21:06:58 +0000[diff] [blame]1699small 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]1700
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1701<div class="doc_code">
1702<pre>
1703#include "<a href="/doxygen/InstIterator_8h-source.html">llvm/Support/InstIterator.h</a>"
1704
Reid Spencer128a7a72007-02-03 21:06:43 +0000[diff] [blame]1705// <i>F is a pointer to a Function instance</i>
Chris Lattnerda021aa2008-06-04 18:20:42 +0000[diff] [blame]1706for (inst_iterator I = inst_begin(F), E = inst_end(F); I != E; ++I)
1707 llvm::cerr &lt;&lt; *I &lt;&lt; "\n";
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1708</pre>
1709</div>
1710
1711<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]1712work list with its initial contents. For example, if you wanted to
1713initialize a work list to contain all instructions in a <tt>Function</tt>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1714F, all you would need to do is something like:</p>
1715
1716<div class="doc_code">
1717<pre>
1718std::set&lt;Instruction*&gt; worklist;
Chris Lattnerda021aa2008-06-04 18:20:42 +0000[diff] [blame]1719// or better yet, SmallPtrSet&lt;Instruction*, 64&gt; worklist;
1720
1721for (inst_iterator I = inst_begin(F), E = inst_end(F); I != E; ++I)
1722 worklist.insert(&amp;*I);
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1723</pre>
1724</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1725
1726<p>The STL set <tt>worklist</tt> would now contain all instructions in the
1727<tt>Function</tt> pointed to by F.</p>
1728
1729</div>
1730
1731<!-- _______________________________________________________________________ -->
1732<div class="doc_subsubsection">
1733 <a name="iterate_convert">Turning an iterator into a class pointer (and
1734 vice-versa)</a>
1735</div>
1736
1737<div class="doc_text">
1738
1739<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]1740instance when all you've got at hand is an iterator. Well, extracting
Chris Lattner69bf8a92004-05-23 21:06:58 +0000[diff] [blame]1741a reference or a pointer from an iterator is very straight-forward.
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]1742Assuming that <tt>i</tt> is a <tt>BasicBlock::iterator</tt> and <tt>j</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1743is a <tt>BasicBlock::const_iterator</tt>:</p>
1744
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1745<div class="doc_code">
1746<pre>
Bill Wendling82e2eea2006-10-11 18:00:22 +0000[diff] [blame]1747Instruction&amp; inst = *i; // <i>Grab reference to instruction reference</i>
1748Instruction* pinst = &amp;*i; // <i>Grab pointer to instruction reference</i>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1749const Instruction&amp; inst = *j;
1750</pre>
1751</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1752
1753<p>However, the iterators you'll be working with in the LLVM framework are
1754special: they will automatically convert to a ptr-to-instance type whenever they
1755need to. Instead of dereferencing the iterator and then taking the address of
1756the result, you can simply assign the iterator to the proper pointer type and
1757you get the dereference and address-of operation as a result of the assignment
1758(behind the scenes, this is a result of overloading casting mechanisms). Thus
1759the last line of the last example,</p>
1760
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1761<div class="doc_code">
1762<pre>
Chris Lattner2e438ca2008-01-03 16:56:04 +0000[diff] [blame]1763Instruction *pinst = &amp;*i;
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1764</pre>
1765</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1766
1767<p>is semantically equivalent to</p>
1768
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1769<div class="doc_code">
1770<pre>
Chris Lattner2e438ca2008-01-03 16:56:04 +0000[diff] [blame]1771Instruction *pinst = i;
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1772</pre>
1773</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1774
Chris Lattner69bf8a92004-05-23 21:06:58 +0000[diff] [blame]1775<p>It's also possible to turn a class pointer into the corresponding iterator,
1776and this is a constant time operation (very efficient). The following code
1777snippet illustrates use of the conversion constructors provided by LLVM
1778iterators. By using these, you can explicitly grab the iterator of something
1779without actually obtaining it via iteration over some structure:</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1780
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1781<div class="doc_code">
1782<pre>
1783void printNextInstruction(Instruction* inst) {
1784 BasicBlock::iterator it(inst);
Bill Wendling82e2eea2006-10-11 18:00:22 +0000[diff] [blame]1785 ++it; // <i>After this line, it refers to the instruction after *inst</i>
Bill Wendling832171c2006-12-07 20:04:42 +0000[diff] [blame]1786 if (it != inst-&gt;getParent()-&gt;end()) llvm::cerr &lt;&lt; *it &lt;&lt; "\n";
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1787}
1788</pre>
1789</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1790
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1791</div>
1792
1793<!--_______________________________________________________________________-->
1794<div class="doc_subsubsection">
1795 <a name="iterate_complex">Finding call sites: a slightly more complex
1796 example</a>
1797</div>
1798
1799<div class="doc_text">
1800
1801<p>Say that you're writing a FunctionPass and would like to count all the
1802locations in the entire module (that is, across every <tt>Function</tt>) where a
1803certain function (i.e., some <tt>Function</tt>*) is already in scope. As you'll
1804learn 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]1805much more straight-forward manner, but this example will allow us to explore how
Reid Spencer128a7a72007-02-03 21:06:43 +0000[diff] [blame]1806you'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]1807is what we want to do:</p>
1808
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1809<div class="doc_code">
1810<pre>
1811initialize callCounter to zero
1812for each Function f in the Module
1813 for each BasicBlock b in f
1814 for each Instruction i in b
1815 if (i is a CallInst and calls the given function)
1816 increment callCounter
1817</pre>
1818</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1819
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1820<p>And the actual code is (remember, because we're writing a
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1821<tt>FunctionPass</tt>, our <tt>FunctionPass</tt>-derived class simply has to
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1822override the <tt>runOnFunction</tt> method):</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1823
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1824<div class="doc_code">
1825<pre>
1826Function* targetFunc = ...;
1827
1828class OurFunctionPass : public FunctionPass {
1829 public:
1830 OurFunctionPass(): callCounter(0) { }
1831
1832 virtual runOnFunction(Function&amp; F) {
1833 for (Function::iterator b = F.begin(), be = F.end(); b != be; ++b) {
Eric Christopher203e71d2008-11-08 08:20:49 +0000[diff] [blame]1834 for (BasicBlock::iterator i = b-&gt;begin(), ie = b-&gt;end(); i != ie; ++i) {
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1835 if (<a href="#CallInst">CallInst</a>* callInst = <a href="#isa">dyn_cast</a>&lt;<a
1836 href="#CallInst">CallInst</a>&gt;(&amp;*i)) {
Bill Wendling82e2eea2006-10-11 18:00:22 +0000[diff] [blame]1837 // <i>We know we've encountered a call instruction, so we</i>
1838 // <i>need to determine if it's a call to the</i>
Chris Lattner2e438ca2008-01-03 16:56:04 +0000[diff] [blame]1839 // <i>function pointed to by m_func or not.</i>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1840 if (callInst-&gt;getCalledFunction() == targetFunc)
1841 ++callCounter;
1842 }
1843 }
1844 }
Bill Wendling82e2eea2006-10-11 18:00:22 +0000[diff] [blame]1845 }
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1846
1847 private:
Chris Lattner2e438ca2008-01-03 16:56:04 +0000[diff] [blame]1848 unsigned callCounter;
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1849};
1850</pre>
1851</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1852
1853</div>
1854
Brian Gaekef1972c62003-11-07 19:25:45 +0000[diff] [blame]1855<!--_______________________________________________________________________-->
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1856<div class="doc_subsubsection">
1857 <a name="calls_and_invokes">Treating calls and invokes the same way</a>
1858</div>
1859
1860<div class="doc_text">
1861
1862<p>You may have noticed that the previous example was a bit oversimplified in
1863that it did not deal with call sites generated by 'invoke' instructions. In
1864this, and in other situations, you may find that you want to treat
1865<tt>CallInst</tt>s and <tt>InvokeInst</tt>s the same way, even though their
1866most-specific common base class is <tt>Instruction</tt>, which includes lots of
1867less closely-related things. For these cases, LLVM provides a handy wrapper
1868class called <a
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]1869href="http://llvm.org/doxygen/classllvm_1_1CallSite.html"><tt>CallSite</tt></a>.
Chris Lattner69bf8a92004-05-23 21:06:58 +0000[diff] [blame]1870It is essentially a wrapper around an <tt>Instruction</tt> pointer, with some
1871methods that provide functionality common to <tt>CallInst</tt>s and
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1872<tt>InvokeInst</tt>s.</p>
1873
Chris Lattner69bf8a92004-05-23 21:06:58 +0000[diff] [blame]1874<p>This class has "value semantics": it should be passed by value, not by
1875reference and it should not be dynamically allocated or deallocated using
1876<tt>operator new</tt> or <tt>operator delete</tt>. It is efficiently copyable,
1877assignable and constructable, with costs equivalents to that of a bare pointer.
1878If you look at its definition, it has only a single pointer member.</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1879
1880</div>
1881
Chris Lattner1a3105b2002-09-09 05:49:39 +0000[diff] [blame]1882<!--_______________________________________________________________________-->
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1883<div class="doc_subsubsection">
1884 <a name="iterate_chains">Iterating over def-use &amp; use-def chains</a>
1885</div>
1886
1887<div class="doc_text">
1888
1889<p>Frequently, we might have an instance of the <a
Chris Lattner00815172007-01-04 22:01:45 +0000[diff] [blame]1890href="/doxygen/classllvm_1_1Value.html">Value Class</a> and we want to
Misha Brukman384047f2004-06-03 23:29:12 +0000[diff] [blame]1891determine which <tt>User</tt>s use the <tt>Value</tt>. The list of all
1892<tt>User</tt>s of a particular <tt>Value</tt> is called a <i>def-use</i> chain.
1893For example, let's say we have a <tt>Function*</tt> named <tt>F</tt> to a
1894particular function <tt>foo</tt>. Finding all of the instructions that
1895<i>use</i> <tt>foo</tt> is as simple as iterating over the <i>def-use</i> chain
1896of <tt>F</tt>:</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1897
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1898<div class="doc_code">
1899<pre>
Chris Lattner2e438ca2008-01-03 16:56:04 +0000[diff] [blame]1900Function *F = ...;
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1901
Bill Wendling82e2eea2006-10-11 18:00:22 +0000[diff] [blame]1902for (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]1903 if (Instruction *Inst = dyn_cast&lt;Instruction&gt;(*i)) {
Bill Wendling832171c2006-12-07 20:04:42 +0000[diff] [blame]1904 llvm::cerr &lt;&lt; "F is used in instruction:\n";
1905 llvm::cerr &lt;&lt; *Inst &lt;&lt; "\n";
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1906 }
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1907</pre>
1908</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1909
1910<p>Alternately, it's common to have an instance of the <a
Misha Brukman384047f2004-06-03 23:29:12 +0000[diff] [blame]1911href="/doxygen/classllvm_1_1User.html">User Class</a> and need to know what
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1912<tt>Value</tt>s are used by it. The list of all <tt>Value</tt>s used by a
1913<tt>User</tt> is known as a <i>use-def</i> chain. Instances of class
1914<tt>Instruction</tt> are common <tt>User</tt>s, so we might want to iterate over
1915all of the values that a particular instruction uses (that is, the operands of
1916the particular <tt>Instruction</tt>):</p>
1917
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1918<div class="doc_code">
1919<pre>
Chris Lattner2e438ca2008-01-03 16:56:04 +0000[diff] [blame]1920Instruction *pi = ...;
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1921
1922for (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]1923 Value *v = *i;
Bill Wendling82e2eea2006-10-11 18:00:22 +0000[diff] [blame]1924 // <i>...</i>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1925}
1926</pre>
1927</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1928
Chris Lattner1a3105b2002-09-09 05:49:39 +0000[diff] [blame]1929<!--
1930 def-use chains ("finding all users of"): Value::use_begin/use_end
1931 use-def chains ("finding all values used"): User::op_begin/op_end [op=operand]
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1932-->
1933
1934</div>
1935
Chris Lattner2e438ca2008-01-03 16:56:04 +0000[diff] [blame]1936<!--_______________________________________________________________________-->
1937<div class="doc_subsubsection">
1938 <a name="iterate_preds">Iterating over predecessors &amp;
1939successors of blocks</a>
1940</div>
1941
1942<div class="doc_text">
1943
1944<p>Iterating over the predecessors and successors of a block is quite easy
1945with the routines defined in <tt>"llvm/Support/CFG.h"</tt>. Just use code like
1946this to iterate over all predecessors of BB:</p>
1947
1948<div class="doc_code">
1949<pre>
1950#include "llvm/Support/CFG.h"
1951BasicBlock *BB = ...;
1952
1953for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI) {
1954 BasicBlock *Pred = *PI;
1955 // <i>...</i>
1956}
1957</pre>
1958</div>
1959
1960<p>Similarly, to iterate over successors use
1961succ_iterator/succ_begin/succ_end.</p>
1962
1963</div>
1964
1965
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1966<!-- ======================================================================= -->
1967<div class="doc_subsection">
1968 <a name="simplechanges">Making simple changes</a>
1969</div>
1970
1971<div class="doc_text">
1972
1973<p>There are some primitive transformation operations present in the LLVM
Joel Stanley753eb712002-09-11 22:32:24 +0000[diff] [blame]1974infrastructure that are worth knowing about. When performing
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]1975transformations, it's fairly common to manipulate the contents of basic
1976blocks. This section describes some of the common methods for doing so
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1977and gives example code.</p>
1978
1979</div>
1980
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]1981<!--_______________________________________________________________________-->
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1982<div class="doc_subsubsection">
1983 <a name="schanges_creating">Creating and inserting new
1984 <tt>Instruction</tt>s</a>
1985</div>
1986
1987<div class="doc_text">
1988
1989<p><i>Instantiating Instructions</i></p>
1990
Chris Lattner69bf8a92004-05-23 21:06:58 +0000[diff] [blame]1991<p>Creation of <tt>Instruction</tt>s is straight-forward: simply call the
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]1992constructor for the kind of instruction to instantiate and provide the necessary
1993parameters. For example, an <tt>AllocaInst</tt> only <i>requires</i> a
1994(const-ptr-to) <tt>Type</tt>. Thus:</p>
1995
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1996<div class="doc_code">
1997<pre>
Nick Lewycky10d64b92007-12-03 01:52:52 +0000[diff] [blame]1998AllocaInst* ai = new AllocaInst(Type::Int32Ty);
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]1999</pre>
2000</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2001
2002<p>will create an <tt>AllocaInst</tt> instance that represents the allocation of
Reid Spencer128a7a72007-02-03 21:06:43 +0000[diff] [blame]2003one integer in the current stack frame, at run time. Each <tt>Instruction</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2004subclass is likely to have varying default parameters which change the semantics
2005of the instruction, so refer to the <a
Misha Brukman31ca1de2004-06-03 23:35:54 +0000[diff] [blame]2006href="/doxygen/classllvm_1_1Instruction.html">doxygen documentation for the subclass of
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2007Instruction</a> that you're interested in instantiating.</p>
2008
2009<p><i>Naming values</i></p>
2010
2011<p>It is very useful to name the values of instructions when you're able to, as
2012this facilitates the debugging of your transformations. If you end up looking
2013at generated LLVM machine code, you definitely want to have logical names
2014associated with the results of instructions! By supplying a value for the
2015<tt>Name</tt> (default) parameter of the <tt>Instruction</tt> constructor, you
2016associate a logical name with the result of the instruction's execution at
Reid Spencer128a7a72007-02-03 21:06:43 +0000[diff] [blame]2017run time. For example, say that I'm writing a transformation that dynamically
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2018allocates space for an integer on the stack, and that integer is going to be
2019used as some kind of index by some other code. To accomplish this, I place an
2020<tt>AllocaInst</tt> at the first point in the first <tt>BasicBlock</tt> of some
2021<tt>Function</tt>, and I'm intending to use it within the same
2022<tt>Function</tt>. I might do:</p>
2023
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2024<div class="doc_code">
2025<pre>
Nick Lewycky10d64b92007-12-03 01:52:52 +0000[diff] [blame]2026AllocaInst* pa = new AllocaInst(Type::Int32Ty, 0, "indexLoc");
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2027</pre>
2028</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2029
2030<p>where <tt>indexLoc</tt> is now the logical name of the instruction's
Reid Spencer128a7a72007-02-03 21:06:43 +0000[diff] [blame]2031execution value, which is a pointer to an integer on the run time stack.</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2032
2033<p><i>Inserting instructions</i></p>
2034
2035<p>There are essentially two ways to insert an <tt>Instruction</tt>
2036into an existing sequence of instructions that form a <tt>BasicBlock</tt>:</p>
2037
Joel Stanley9dd1ad62002-09-18 03:17:23 +0000[diff] [blame]2038<ul>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2039 <li>Insertion into an explicit instruction list
2040
2041 <p>Given a <tt>BasicBlock* pb</tt>, an <tt>Instruction* pi</tt> within that
2042 <tt>BasicBlock</tt>, and a newly-created instruction we wish to insert
2043 before <tt>*pi</tt>, we do the following: </p>
2044
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2045<div class="doc_code">
2046<pre>
2047BasicBlock *pb = ...;
2048Instruction *pi = ...;
2049Instruction *newInst = new Instruction(...);
2050
Bill Wendling82e2eea2006-10-11 18:00:22 +0000[diff] [blame]2051pb-&gt;getInstList().insert(pi, newInst); // <i>Inserts newInst before pi in pb</i>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2052</pre>
2053</div>
Alkis Evlogimenos9a5dc4f2004-05-27 00:57:51 +0000[diff] [blame]2054
2055 <p>Appending to the end of a <tt>BasicBlock</tt> is so common that
2056 the <tt>Instruction</tt> class and <tt>Instruction</tt>-derived
2057 classes provide constructors which take a pointer to a
2058 <tt>BasicBlock</tt> to be appended to. For example code that
2059 looked like: </p>
2060
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2061<div class="doc_code">
2062<pre>
2063BasicBlock *pb = ...;
2064Instruction *newInst = new Instruction(...);
2065
Bill Wendling82e2eea2006-10-11 18:00:22 +0000[diff] [blame]2066pb-&gt;getInstList().push_back(newInst); // <i>Appends newInst to pb</i>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2067</pre>
2068</div>
Alkis Evlogimenos9a5dc4f2004-05-27 00:57:51 +0000[diff] [blame]2069
2070 <p>becomes: </p>
2071
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2072<div class="doc_code">
2073<pre>
2074BasicBlock *pb = ...;
2075Instruction *newInst = new Instruction(..., pb);
2076</pre>
2077</div>
Alkis Evlogimenos9a5dc4f2004-05-27 00:57:51 +0000[diff] [blame]2078
2079 <p>which is much cleaner, especially if you are creating
2080 long instruction streams.</p></li>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2081
2082 <li>Insertion into an implicit instruction list
2083
2084 <p><tt>Instruction</tt> instances that are already in <tt>BasicBlock</tt>s
2085 are implicitly associated with an existing instruction list: the instruction
2086 list of the enclosing basic block. Thus, we could have accomplished the same
2087 thing as the above code without being given a <tt>BasicBlock</tt> by doing:
2088 </p>
2089
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2090<div class="doc_code">
2091<pre>
2092Instruction *pi = ...;
2093Instruction *newInst = new Instruction(...);
2094
2095pi-&gt;getParent()-&gt;getInstList().insert(pi, newInst);
2096</pre>
2097</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2098
2099 <p>In fact, this sequence of steps occurs so frequently that the
2100 <tt>Instruction</tt> class and <tt>Instruction</tt>-derived classes provide
2101 constructors which take (as a default parameter) a pointer to an
2102 <tt>Instruction</tt> which the newly-created <tt>Instruction</tt> should
2103 precede. That is, <tt>Instruction</tt> constructors are capable of
2104 inserting the newly-created instance into the <tt>BasicBlock</tt> of a
2105 provided instruction, immediately before that instruction. Using an
2106 <tt>Instruction</tt> constructor with a <tt>insertBefore</tt> (default)
2107 parameter, the above code becomes:</p>
2108
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2109<div class="doc_code">
2110<pre>
2111Instruction* pi = ...;
2112Instruction* newInst = new Instruction(..., pi);
2113</pre>
2114</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2115
2116 <p>which is much cleaner, especially if you're creating a lot of
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2117 instructions and adding them to <tt>BasicBlock</tt>s.</p></li>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2118</ul>
2119
2120</div>
2121
2122<!--_______________________________________________________________________-->
2123<div class="doc_subsubsection">
2124 <a name="schanges_deleting">Deleting <tt>Instruction</tt>s</a>
2125</div>
2126
2127<div class="doc_text">
2128
2129<p>Deleting an instruction from an existing sequence of instructions that form a
Chris Lattner69bf8a92004-05-23 21:06:58 +0000[diff] [blame]2130<a href="#BasicBlock"><tt>BasicBlock</tt></a> is very straight-forward. First,
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2131you must have a pointer to the instruction that you wish to delete. Second, you
2132need to obtain the pointer to that instruction's basic block. You use the
2133pointer to the basic block to get its list of instructions and then use the
2134erase function to remove your instruction. For example:</p>
2135
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2136<div class="doc_code">
2137<pre>
2138<a href="#Instruction">Instruction</a> *I = .. ;
Chris Lattner9f8ec252008-02-15 22:57:17 +0000[diff] [blame]2139I-&gt;eraseFromParent();
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2140</pre>
2141</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2142
2143</div>
2144
2145<!--_______________________________________________________________________-->
2146<div class="doc_subsubsection">
2147 <a name="schanges_replacing">Replacing an <tt>Instruction</tt> with another
2148 <tt>Value</tt></a>
2149</div>
2150
2151<div class="doc_text">
2152
2153<p><i>Replacing individual instructions</i></p>
2154
2155<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]2156permits use of two very useful replace functions: <tt>ReplaceInstWithValue</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2157and <tt>ReplaceInstWithInst</tt>.</p>
2158
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]2159<h4><a name="schanges_deleting">Deleting <tt>Instruction</tt>s</a></h4>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2160
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]2161<ul>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2162 <li><tt>ReplaceInstWithValue</tt>
2163
Nick Lewyckyb6d1f392008-09-15 06:31:52 +0000[diff] [blame]2164 <p>This function replaces all uses of a given instruction with a value,
2165 and then removes the original instruction. The following example
2166 illustrates the replacement of the result of a particular
Chris Lattner58360822005-01-17 00:12:04 +0000[diff] [blame]2167 <tt>AllocaInst</tt> that allocates memory for a single integer with a null
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2168 pointer to an integer.</p>
2169
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2170<div class="doc_code">
2171<pre>
2172AllocaInst* instToReplace = ...;
2173BasicBlock::iterator ii(instToReplace);
2174
2175ReplaceInstWithValue(instToReplace-&gt;getParent()-&gt;getInstList(), ii,
Daniel Dunbar58c2ac02008-10-03 22:17:25 +0000[diff] [blame]2176 Constant::getNullValue(PointerType::getUnqual(Type::Int32Ty)));
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2177</pre></div></li>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2178
2179 <li><tt>ReplaceInstWithInst</tt>
2180
2181 <p>This function replaces a particular instruction with another
Nick Lewyckyb6d1f392008-09-15 06:31:52 +0000[diff] [blame]2182 instruction, inserting the new instruction into the basic block at the
2183 location where the old instruction was, and replacing any uses of the old
2184 instruction with the new instruction. The following example illustrates
2185 the replacement of one <tt>AllocaInst</tt> with another.</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2186
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2187<div class="doc_code">
2188<pre>
2189AllocaInst* instToReplace = ...;
2190BasicBlock::iterator ii(instToReplace);
2191
2192ReplaceInstWithInst(instToReplace-&gt;getParent()-&gt;getInstList(), ii,
Nick Lewycky10d64b92007-12-03 01:52:52 +0000[diff] [blame]2193 new AllocaInst(Type::Int32Ty, 0, "ptrToReplacedInt"));
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2194</pre></div></li>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]2195</ul>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2196
2197<p><i>Replacing multiple uses of <tt>User</tt>s and <tt>Value</tt>s</i></p>
2198
2199<p>You can use <tt>Value::replaceAllUsesWith</tt> and
2200<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]2201doxygen documentation for the <a href="/doxygen/classllvm_1_1Value.html">Value Class</a>
Misha Brukman384047f2004-06-03 23:29:12 +0000[diff] [blame]2202and <a href="/doxygen/classllvm_1_1User.html">User Class</a>, respectively, for more
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2203information.</p>
2204
2205<!-- Value::replaceAllUsesWith User::replaceUsesOfWith Point out:
2206include/llvm/Transforms/Utils/ especially BasicBlockUtils.h with:
2207ReplaceInstWithValue, ReplaceInstWithInst -->
2208
2209</div>
2210
Tanya Lattnerb011c662007-06-20 18:33:15 +0000[diff] [blame]2211<!--_______________________________________________________________________-->
2212<div class="doc_subsubsection">
2213 <a name="schanges_deletingGV">Deleting <tt>GlobalVariable</tt>s</a>
2214</div>
2215
2216<div class="doc_text">
2217
Tanya Lattnerc5dfcdb2007-06-20 20:46:37 +0000[diff] [blame]2218<p>Deleting a global variable from a module is just as easy as deleting an
2219Instruction. First, you must have a pointer to the global variable that you wish
2220 to delete. You use this pointer to erase it from its parent, the module.
Tanya Lattnerb011c662007-06-20 18:33:15 +0000[diff] [blame]2221 For example:</p>
2222
2223<div class="doc_code">
2224<pre>
2225<a href="#GlobalVariable">GlobalVariable</a> *GV = .. ;
Tanya Lattnerb011c662007-06-20 18:33:15 +0000[diff] [blame]2226
Tanya Lattnerc5dfcdb2007-06-20 20:46:37 +0000[diff] [blame]2227GV-&gt;eraseFromParent();
Tanya Lattnerb011c662007-06-20 18:33:15 +0000[diff] [blame]2228</pre>
2229</div>
2230
2231</div>
2232
Jeffrey Yasskin714257f2009-04-30 22:33:41 +0000[diff] [blame]2233<!-- ======================================================================= -->
2234<div class="doc_subsection">
2235 <a name="create_types">How to Create Types</a>
2236</div>
2237
2238<div class="doc_text">
2239
2240<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]2241statically, you can use <tt>TypeBuilder&lt;...&gt;::get()</tt>, defined
Jeffrey Yasskin714257f2009-04-30 22:33:41 +0000[diff] [blame]2242in <tt>llvm/Support/TypeBuilder.h</tt>, to retrieve them. <tt>TypeBuilder</tt>
2243has two forms depending on whether you're building types for cross-compilation
Misha Brukman1af789f2009-05-01 20:40:51 +0000[diff] [blame]2244or native library use. <tt>TypeBuilder&lt;T, true&gt;</tt> requires
Jeffrey Yasskin714257f2009-04-30 22:33:41 +0000[diff] [blame]2245that <tt>T</tt> be independent of the host environment, meaning that it's built
2246out of types from
2247the <a href="/doxygen/namespacellvm_1_1types.html"><tt>llvm::types</tt></a>
2248namespace and pointers, functions, arrays, etc. built of
Misha Brukman1af789f2009-05-01 20:40:51 +0000[diff] [blame]2249those. <tt>TypeBuilder&lt;T, false&gt;</tt> additionally allows native C types
Jeffrey Yasskin714257f2009-04-30 22:33:41 +0000[diff] [blame]2250whose size may depend on the host compiler. For example,</p>
2251
2252<div class="doc_code">
2253<pre>
Misha Brukman1af789f2009-05-01 20:40:51 +0000[diff] [blame]2254FunctionType *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]2255</pre>
2256</div>
2257
2258<p>is easier to read and write than the equivalent</p>
2259
2260<div class="doc_code">
2261<pre>
Owen Anderson5e8c50e2009-06-16 17:40:28 +0000[diff] [blame]2262std::vector&lt;const Type*&gt; params;
Jeffrey Yasskin714257f2009-04-30 22:33:41 +0000[diff] [blame]2263params.push_back(PointerType::getUnqual(Type::Int32Ty));
2264FunctionType *ft = FunctionType::get(Type::Int8Ty, params, false);
2265</pre>
2266</div>
2267
2268<p>See the <a href="/doxygen/TypeBuilder_8h-source.html#l00001">class
2269comment</a> for more details.</p>
2270
2271</div>
2272
Chris Lattner9355b472002-09-06 02:50:58 +0000[diff] [blame]2273<!-- *********************************************************************** -->
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2274<div class="doc_section">
Owen Anderson8bc1b3b2009-06-16 01:17:16 +0000[diff] [blame]2275 <a name="threading">Threads and LLVM</a>
2276</div>
2277<!-- *********************************************************************** -->
2278
2279<div class="doc_text">
2280<p>
2281This section describes the interaction of the LLVM APIs with multithreading,
2282both on the part of client applications, and in the JIT, in the hosted
2283application.
2284</p>
2285
2286<p>
2287Note that LLVM's support for multithreading is still relatively young. Up
2288through version 2.5, the execution of threaded hosted applications was
2289supported, but not threaded client access to the APIs. While this use case is
2290now supported, clients <em>must</em> adhere to the guidelines specified below to
2291ensure proper operation in multithreaded mode.
2292</p>
2293
2294<p>
2295Note that, on Unix-like platforms, LLVM requires the presence of GCC's atomic
2296intrinsics in order to support threaded operation. If you need a
2297multhreading-capable LLVM on a platform without a suitably modern system
2298compiler, consider compiling LLVM and LLVM-GCC in single-threaded mode, and
2299using the resultant compiler to build a copy of LLVM with multithreading
2300support.
2301</p>
2302</div>
2303
2304<!-- ======================================================================= -->
2305<div class="doc_subsection">
Owen Anderson1ad70e32009-06-16 18:04:19 +0000[diff] [blame]2306 <a name="startmultithreaded">Entering and Exiting Multithreaded Mode</a>
Owen Anderson8bc1b3b2009-06-16 01:17:16 +0000[diff] [blame]2307</div>
2308
2309<div class="doc_text">
2310
2311<p>
2312In order to properly protect its internal data structures while avoiding
Owen Anderson1ad70e32009-06-16 18:04:19 +0000[diff] [blame]2313excessive locking overhead in the single-threaded case, the LLVM must intialize
2314certain data structures necessary to provide guards around its internals. To do
2315so, the client program must invoke <tt>llvm_start_multithreaded()</tt> before
2316making any concurrent LLVM API calls. To subsequently tear down these
2317structures, use the <tt>llvm_stop_multithreaded()</tt> call. You can also use
2318the <tt>llvm_is_multithreaded()</tt> call to check the status of multithreaded
2319mode.
Owen Anderson8bc1b3b2009-06-16 01:17:16 +0000[diff] [blame]2320</p>
2321
2322<p>
Owen Anderson1ad70e32009-06-16 18:04:19 +0000[diff] [blame]2323Note that both of these calls must be made <em>in isolation</em>. That is to
2324say that no other LLVM API calls may be executing at any time during the
2325execution of <tt>llvm_start_multithreaded()</tt> or <tt>llvm_stop_multithreaded
2326</tt>. It's is the client's responsibility to enforce this isolation.
2327</p>
2328
2329<p>
2330The return value of <tt>llvm_start_multithreaded()</tt> indicates the success or
2331failure of the initialization. Failure typically indicates that your copy of
2332LLVM was built without multithreading support, typically because GCC atomic
2333intrinsics were not found in your system compiler. In this case, the LLVM API
2334will not be safe for concurrent calls. However, it <em>will</em> be safe for
2335hosting threaded applications in the JIT, though care must be taken to ensure
2336that side exits and the like do not accidentally result in concurrent LLVM API
2337calls.
Owen Anderson8bc1b3b2009-06-16 01:17:16 +0000[diff] [blame]2338</p>
2339</div>
2340
2341<!-- ======================================================================= -->
2342<div class="doc_subsection">
2343 <a name="shutdown">Ending Execution with <tt>llvm_shutdown()</tt></a>
2344</div>
2345
2346<div class="doc_text">
2347<p>
2348When you are done using the LLVM APIs, you should call <tt>llvm_shutdown()</tt>
Owen Anderson1ad70e32009-06-16 18:04:19 +0000[diff] [blame]2349to deallocate memory used for internal structures. This will also invoke
2350<tt>llvm_stop_multithreaded()</tt> if LLVM is operating in multithreaded mode.
2351As such, <tt>llvm_shutdown()</tt> requires the same isolation guarantees as
2352<tt>llvm_stop_multithreaded()</tt>.
Owen Anderson8bc1b3b2009-06-16 01:17:16 +0000[diff] [blame]2353</p>
2354
2355<p>
2356Note that, if you use scope-based shutdown, you can use the
2357<tt>llvm_shutdown_obj</tt> class, which calls <tt>llvm_shutdown()</tt> in its
2358destructor.
2359</div>
2360
2361<!-- ======================================================================= -->
2362<div class="doc_subsection">
2363 <a name="managedstatic">Lazy Initialization with <tt>ManagedStatic</tt></a>
2364</div>
2365
2366<div class="doc_text">
2367<p>
2368<tt>ManagedStatic</tt> is a utility class in LLVM used to implement static
2369initialization of static resources, such as the global type tables. Before the
2370invocation of <tt>llvm_shutdown()</tt>, it implements a simple lazy
2371initialization scheme. Once <tt>llvm_start_multithreaded()</tt> returns,
2372however, it uses double-checked locking to implement thread-safe lazy
2373initialization.
2374</p>
2375
2376<p>
2377Note that, because no other threads are allowed to issue LLVM API calls before
2378<tt>llvm_start_multithreaded()</tt> returns, it is possible to have
2379<tt>ManagedStatic</tt>s of <tt>llvm::sys::Mutex</tt>s.
2380</p>
Owen Anderson1ad70e32009-06-16 18:04:19 +0000[diff] [blame]2381
2382<p>
2383The <tt>llvm_acquire_global_lock()</tt> and <tt>llvm_release_global_lock</tt>
2384APIs provide access to the global lock used to implement the double-checked
2385locking for lazy initialization. These should only be used internally to LLVM,
2386and only if you know what you're doing!
2387</p>
Owen Anderson8bc1b3b2009-06-16 01:17:16 +0000[diff] [blame]2388</div>
2389
2390<!-- *********************************************************************** -->
2391<div class="doc_section">
Chris Lattnerd9d6e102005-04-23 16:10:52 +0000[diff] [blame]2392 <a name="advanced">Advanced Topics</a>
2393</div>
2394<!-- *********************************************************************** -->
2395
2396<div class="doc_text">
Chris Lattnerf1b200b2005-04-23 17:27:36 +0000[diff] [blame]2397<p>
2398This section describes some of the advanced or obscure API's that most clients
2399do not need to be aware of. These API's tend manage the inner workings of the
2400LLVM system, and only need to be accessed in unusual circumstances.
2401</p>
2402</div>
Chris Lattnerd9d6e102005-04-23 16:10:52 +0000[diff] [blame]2403
Chris Lattnerf1b200b2005-04-23 17:27:36 +0000[diff] [blame]2404<!-- ======================================================================= -->
2405<div class="doc_subsection">
2406 <a name="TypeResolve">LLVM Type Resolution</a>
2407</div>
Chris Lattnerd9d6e102005-04-23 16:10:52 +0000[diff] [blame]2408
Chris Lattnerf1b200b2005-04-23 17:27:36 +0000[diff] [blame]2409<div class="doc_text">
2410
2411<p>
2412The LLVM type system has a very simple goal: allow clients to compare types for
2413structural equality with a simple pointer comparison (aka a shallow compare).
2414This goal makes clients much simpler and faster, and is used throughout the LLVM
2415system.
2416</p>
2417
2418<p>
2419Unfortunately achieving this goal is not a simple matter. In particular,
2420recursive types and late resolution of opaque types makes the situation very
2421difficult to handle. Fortunately, for the most part, our implementation makes
2422most clients able to be completely unaware of the nasty internal details. The
2423primary case where clients are exposed to the inner workings of it are when
Gabor Greif04367bf2007-07-06 22:07:22 +0000[diff] [blame]2424building a recursive type. In addition to this case, the LLVM bitcode reader,
Chris Lattnerf1b200b2005-04-23 17:27:36 +0000[diff] [blame]2425assembly parser, and linker also have to be aware of the inner workings of this
2426system.
2427</p>
2428
Chris Lattner0f876db2005-04-25 15:47:57 +0000[diff] [blame]2429<p>
2430For our purposes below, we need three concepts. First, an "Opaque Type" is
2431exactly as defined in the <a href="LangRef.html#t_opaque">language
2432reference</a>. Second an "Abstract Type" is any type which includes an
Reid Spencer06565dc2007-01-12 17:11:23 +0000[diff] [blame]2433opaque type as part of its type graph (for example "<tt>{ opaque, i32 }</tt>").
2434Third, 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]2435float }</tt>").
2436</p>
2437
Chris Lattnerf1b200b2005-04-23 17:27:36 +0000[diff] [blame]2438</div>
2439
2440<!-- ______________________________________________________________________ -->
2441<div class="doc_subsubsection">
2442 <a name="BuildRecType">Basic Recursive Type Construction</a>
2443</div>
2444
2445<div class="doc_text">
2446
2447<p>
2448Because the most common question is "how do I build a recursive type with LLVM",
2449we answer it now and explain it as we go. Here we include enough to cause this
2450to be emitted to an output .ll file:
2451</p>
2452
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2453<div class="doc_code">
Chris Lattnerf1b200b2005-04-23 17:27:36 +0000[diff] [blame]2454<pre>
Reid Spencer06565dc2007-01-12 17:11:23 +0000[diff] [blame]2455%mylist = type { %mylist*, i32 }
Chris Lattnerf1b200b2005-04-23 17:27:36 +0000[diff] [blame]2456</pre>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2457</div>
Chris Lattnerf1b200b2005-04-23 17:27:36 +0000[diff] [blame]2458
2459<p>
2460To build this, use the following LLVM APIs:
2461</p>
2462
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2463<div class="doc_code">
Chris Lattnerf1b200b2005-04-23 17:27:36 +0000[diff] [blame]2464<pre>
Bill Wendling82e2eea2006-10-11 18:00:22 +0000[diff] [blame]2465// <i>Create the initial outer struct</i>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2466<a href="#PATypeHolder">PATypeHolder</a> StructTy = OpaqueType::get();
2467std::vector&lt;const Type*&gt; Elts;
Daniel Dunbar58c2ac02008-10-03 22:17:25 +0000[diff] [blame]2468Elts.push_back(PointerType::getUnqual(StructTy));
Nick Lewycky10d64b92007-12-03 01:52:52 +0000[diff] [blame]2469Elts.push_back(Type::Int32Ty);
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2470StructType *NewSTy = StructType::get(Elts);
Chris Lattnerf1b200b2005-04-23 17:27:36 +0000[diff] [blame]2471
Reid Spencer06565dc2007-01-12 17:11:23 +0000[diff] [blame]2472// <i>At this point, NewSTy = "{ opaque*, i32 }". Tell VMCore that</i>
Bill Wendling82e2eea2006-10-11 18:00:22 +0000[diff] [blame]2473// <i>the struct and the opaque type are actually the same.</i>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2474cast&lt;OpaqueType&gt;(StructTy.get())-&gt;<a href="#refineAbstractTypeTo">refineAbstractTypeTo</a>(NewSTy);
Chris Lattnerf1b200b2005-04-23 17:27:36 +0000[diff] [blame]2475
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2476// <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]2477// <i>kept up-to-date</i>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2478NewSTy = cast&lt;StructType&gt;(StructTy.get());
Chris Lattnerf1b200b2005-04-23 17:27:36 +0000[diff] [blame]2479
Bill Wendling82e2eea2006-10-11 18:00:22 +0000[diff] [blame]2480// <i>Add a name for the type to the module symbol table (optional)</i>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2481MyModule-&gt;addTypeName("mylist", NewSTy);
Chris Lattnerf1b200b2005-04-23 17:27:36 +0000[diff] [blame]2482</pre>
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]2483</div>
Chris Lattnerf1b200b2005-04-23 17:27:36 +0000[diff] [blame]2484
2485<p>
2486This code shows the basic approach used to build recursive types: build a
2487non-recursive type using 'opaque', then use type unification to close the cycle.
2488The type unification step is performed by the <tt><a
Chris Lattneraff26d12007-02-03 03:06:52 +0000[diff] [blame]2489href="#refineAbstractTypeTo">refineAbstractTypeTo</a></tt> method, which is
Chris Lattnerf1b200b2005-04-23 17:27:36 +0000[diff] [blame]2490described next. After that, we describe the <a
2491href="#PATypeHolder">PATypeHolder class</a>.
2492</p>
2493
2494</div>
2495
2496<!-- ______________________________________________________________________ -->
2497<div class="doc_subsubsection">
2498 <a name="refineAbstractTypeTo">The <tt>refineAbstractTypeTo</tt> method</a>
2499</div>
2500
2501<div class="doc_text">
2502<p>
2503The <tt>refineAbstractTypeTo</tt> method starts the type unification process.
2504While this method is actually a member of the DerivedType class, it is most
2505often used on OpaqueType instances. Type unification is actually a recursive
2506process. After unification, types can become structurally isomorphic to
2507existing types, and all duplicates are deleted (to preserve pointer equality).
2508</p>
2509
2510<p>
2511In the example above, the OpaqueType object is definitely deleted.
Reid Spencer06565dc2007-01-12 17:11:23 +0000[diff] [blame]2512Additionally, if there is an "{ \2*, i32}" type already created in the system,
Chris Lattnerf1b200b2005-04-23 17:27:36 +0000[diff] [blame]2513the pointer and struct type created are <b>also</b> deleted. Obviously whenever
2514a type is deleted, any "Type*" pointers in the program are invalidated. As
2515such, it is safest to avoid having <i>any</i> "Type*" pointers to abstract types
2516live across a call to <tt>refineAbstractTypeTo</tt> (note that non-abstract
2517types can never move or be deleted). To deal with this, the <a
2518href="#PATypeHolder">PATypeHolder</a> class is used to maintain a stable
2519reference to a possibly refined type, and the <a
2520href="#AbstractTypeUser">AbstractTypeUser</a> class is used to update more
2521complex datastructures.
2522</p>
2523
2524</div>
2525
2526<!-- ______________________________________________________________________ -->
2527<div class="doc_subsubsection">
2528 <a name="PATypeHolder">The PATypeHolder Class</a>
2529</div>
2530
2531<div class="doc_text">
2532<p>
2533PATypeHolder is a form of a "smart pointer" for Type objects. When VMCore
2534happily goes about nuking types that become isomorphic to existing types, it
2535automatically updates all PATypeHolder objects to point to the new type. In the
2536example above, this allows the code to maintain a pointer to the resultant
2537resolved recursive type, even though the Type*'s are potentially invalidated.
2538</p>
2539
2540<p>
2541PATypeHolder is an extremely light-weight object that uses a lazy union-find
2542implementation to update pointers. For example the pointer from a Value to its
2543Type is maintained by PATypeHolder objects.
2544</p>
2545
2546</div>
2547
2548<!-- ______________________________________________________________________ -->
2549<div class="doc_subsubsection">
2550 <a name="AbstractTypeUser">The AbstractTypeUser Class</a>
2551</div>
2552
2553<div class="doc_text">
2554
2555<p>
2556Some data structures need more to perform more complex updates when types get
Chris Lattner263a98e2007-02-16 04:37:31 +0000[diff] [blame]2557resolved. To support this, a class can derive from the AbstractTypeUser class.
2558This class
Chris Lattnerf1b200b2005-04-23 17:27:36 +0000[diff] [blame]2559allows it to get callbacks when certain types are resolved. To register to get
2560callbacks for a particular type, the DerivedType::{add/remove}AbstractTypeUser
Chris Lattner0f876db2005-04-25 15:47:57 +0000[diff] [blame]2561methods can be called on a type. Note that these methods only work for <i>
Reid Spencer06565dc2007-01-12 17:11:23 +0000[diff] [blame]2562 abstract</i> types. Concrete types (those that do not include any opaque
2563objects) can never be refined.
Chris Lattnerf1b200b2005-04-23 17:27:36 +0000[diff] [blame]2564</p>
Chris Lattnerd9d6e102005-04-23 16:10:52 +0000[diff] [blame]2565</div>
2566
2567
2568<!-- ======================================================================= -->
2569<div class="doc_subsection">
Chris Lattner263a98e2007-02-16 04:37:31 +0000[diff] [blame]2570 <a name="SymbolTable">The <tt>ValueSymbolTable</tt> and
2571 <tt>TypeSymbolTable</tt> classes</a>
Chris Lattnerd9d6e102005-04-23 16:10:52 +0000[diff] [blame]2572</div>
Chris Lattnerf1b200b2005-04-23 17:27:36 +0000[diff] [blame]2573
Chris Lattnerd9d6e102005-04-23 16:10:52 +0000[diff] [blame]2574<div class="doc_text">
Chris Lattner263a98e2007-02-16 04:37:31 +0000[diff] [blame]2575<p>The <tt><a href="http://llvm.org/doxygen/classllvm_1_1ValueSymbolTable.html">
2576ValueSymbolTable</a></tt> class provides a symbol table that the <a
Chris Lattnerd9d6e102005-04-23 16:10:52 +0000[diff] [blame]2577href="#Function"><tt>Function</tt></a> and <a href="#Module">
Chris Lattner263a98e2007-02-16 04:37:31 +0000[diff] [blame]2578<tt>Module</tt></a> classes use for naming value definitions. The symbol table
2579can provide a name for any <a href="#Value"><tt>Value</tt></a>.
2580The <tt><a href="http://llvm.org/doxygen/classllvm_1_1TypeSymbolTable.html">
2581TypeSymbolTable</a></tt> class is used by the <tt>Module</tt> class to store
2582names for types.</p>
Chris Lattnerd9d6e102005-04-23 16:10:52 +0000[diff] [blame]2583
Reid Spencera6362242007-01-07 00:41:39 +0000[diff] [blame]2584<p>Note that the <tt>SymbolTable</tt> class should not be directly accessed
2585by most clients. It should only be used when iteration over the symbol table
2586names themselves are required, which is very special purpose. Note that not
2587all LLVM
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2588<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]2589an empty name) do not exist in the symbol table.
2590</p>
2591
Chris Lattner263a98e2007-02-16 04:37:31 +0000[diff] [blame]2592<p>These symbol tables support iteration over the values/types in the symbol
2593table with <tt>begin/end/iterator</tt> and supports querying to see if a
2594specific name is in the symbol table (with <tt>lookup</tt>). The
2595<tt>ValueSymbolTable</tt> class exposes no public mutator methods, instead,
2596simply call <tt>setName</tt> on a value, which will autoinsert it into the
2597appropriate symbol table. For types, use the Module::addTypeName method to
2598insert entries into the symbol table.</p>
Chris Lattnerd9d6e102005-04-23 16:10:52 +0000[diff] [blame]2599
Chris Lattnerd9d6e102005-04-23 16:10:52 +0000[diff] [blame]2600</div>
2601
2602
2603
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2604<!-- ======================================================================= -->
2605<div class="doc_subsection">
2606 <a name="UserLayout">The <tt>User</tt> and owned <tt>Use</tt> classes' memory layout</a>
2607</div>
2608
2609<div class="doc_text">
2610<p>The <tt><a href="http://llvm.org/doxygen/classllvm_1_1User.html">
Gabor Greiffd095b62009-01-05 16:05:32 +0000[diff] [blame]2611User</a></tt> class provides a basis for expressing the ownership of <tt>User</tt>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2612towards other <tt><a href="http://llvm.org/doxygen/classllvm_1_1Value.html">
2613Value</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]2614Use</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]2615addition and removal.</p>
2616
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2617<!-- ______________________________________________________________________ -->
2618<div class="doc_subsubsection">
Gabor Greiffd095b62009-01-05 16:05:32 +0000[diff] [blame]2619 <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]2620</div>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2621
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2622<div class="doc_text">
2623<p>
2624A subclass of <tt>User</tt> can choose between incorporating its <tt>Use</tt> objects
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2625or refer to them out-of-line by means of a pointer. A mixed variant
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2626(some <tt>Use</tt>s inline others hung off) is impractical and breaks the invariant
2627that the <tt>Use</tt> objects belonging to the same <tt>User</tt> form a contiguous array.
2628</p>
2629</div>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2630
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2631<p>
2632We have 2 different layouts in the <tt>User</tt> (sub)classes:
2633<ul>
2634<li><p>Layout a)
2635The <tt>Use</tt> object(s) are inside (resp. at fixed offset) of the <tt>User</tt>
2636object and there are a fixed number of them.</p>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2637
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2638<li><p>Layout b)
2639The <tt>Use</tt> object(s) are referenced by a pointer to an
2640array from the <tt>User</tt> object and there may be a variable
2641number of them.</p>
2642</ul>
2643<p>
Gabor Greifd41720a2008-06-25 00:10:22 +0000[diff] [blame]2644As of v2.4 each layout still possesses a direct pointer to the
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2645start of the array of <tt>Use</tt>s. Though not mandatory for layout a),
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2646we stick to this redundancy for the sake of simplicity.
Gabor Greifd41720a2008-06-25 00:10:22 +0000[diff] [blame]2647The <tt>User</tt> object also stores the number of <tt>Use</tt> objects it
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2648has. (Theoretically this information can also be calculated
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2649given the scheme presented below.)</p>
2650<p>
2651Special forms of allocation operators (<tt>operator new</tt>)
Gabor Greifd41720a2008-06-25 00:10:22 +0000[diff] [blame]2652enforce the following memory layouts:</p>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2653
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2654<ul>
Gabor Greifd41720a2008-06-25 00:10:22 +0000[diff] [blame]2655<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]2656
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2657<pre>
2658...---.---.---.---.-------...
2659 | P | P | P | P | User
2660'''---'---'---'---'-------'''
2661</pre>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2662
Gabor Greifd41720a2008-06-25 00:10:22 +0000[diff] [blame]2663<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]2664<pre>
2665.-------...
2666| User
2667'-------'''
2668 |
2669 v
2670 .---.---.---.---...
2671 | P | P | P | P |
2672 '---'---'---'---'''
2673</pre>
2674</ul>
2675<i>(In the above figures '<tt>P</tt>' stands for the <tt>Use**</tt> that
2676 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]2677
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2678<!-- ______________________________________________________________________ -->
2679<div class="doc_subsubsection">
Gabor Greiffd095b62009-01-05 16:05:32 +0000[diff] [blame]2680 <a name="Waymarking">The waymarking algorithm</a>
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2681</div>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2682
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2683<div class="doc_text">
2684<p>
Gabor Greifd41720a2008-06-25 00:10:22 +0000[diff] [blame]2685Since the <tt>Use</tt> objects are deprived of the direct (back)pointer to
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2686their <tt>User</tt> objects, there must be a fast and exact method to
2687recover it. This is accomplished by the following scheme:</p>
2688</div>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2689
Gabor Greifd41720a2008-06-25 00:10:22 +0000[diff] [blame]2690A 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]2691start of the <tt>User</tt> object:
2692<ul>
2693<li><tt>00</tt> &mdash;&gt; binary digit 0</li>
2694<li><tt>01</tt> &mdash;&gt; binary digit 1</li>
2695<li><tt>10</tt> &mdash;&gt; stop and calculate (<tt>s</tt>)</li>
2696<li><tt>11</tt> &mdash;&gt; full stop (<tt>S</tt>)</li>
2697</ul>
2698<p>
2699Given a <tt>Use*</tt>, all we have to do is to walk till we get
2700a stop and we either have a <tt>User</tt> immediately behind or
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2701we have to walk to the next stop picking up digits
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2702and calculating the offset:</p>
2703<pre>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2704.---.---.---.---.---.---.---.---.---.---.---.---.---.---.---.---.----------------
2705| 1 | s | 1 | 0 | 1 | 0 | s | 1 | 1 | 0 | s | 1 | 1 | s | 1 | S | User (or User*)
2706'---'---'---'---'---'---'---'---'---'---'---'---'---'---'---'---'----------------
2707 |+15 |+10 |+6 |+3 |+1
2708 | | | | |__>
2709 | | | |__________>
2710 | | |______________________>
2711 | |______________________________________>
2712 |__________________________________________________________>
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2713</pre>
2714<p>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2715Only the significant number of bits need to be stored between the
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2716stops, so that the <i>worst case is 20 memory accesses</i> when there are
27171000 <tt>Use</tt> objects associated with a <tt>User</tt>.</p>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2718
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2719<!-- ______________________________________________________________________ -->
2720<div class="doc_subsubsection">
Gabor Greiffd095b62009-01-05 16:05:32 +0000[diff] [blame]2721 <a name="ReferenceImpl">Reference implementation</a>
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2722</div>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2723
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2724<div class="doc_text">
2725<p>
2726The following literate Haskell fragment demonstrates the concept:</p>
2727</div>
2728
2729<div class="doc_code">
2730<pre>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2731> import Test.QuickCheck
2732>
2733> digits :: Int -> [Char] -> [Char]
2734> digits 0 acc = '0' : acc
2735> digits 1 acc = '1' : acc
2736> digits n acc = digits (n `div` 2) $ digits (n `mod` 2) acc
2737>
2738> dist :: Int -> [Char] -> [Char]
2739> dist 0 [] = ['S']
2740> dist 0 acc = acc
2741> dist 1 acc = let r = dist 0 acc in 's' : digits (length r) r
2742> dist n acc = dist (n - 1) $ dist 1 acc
2743>
2744> takeLast n ss = reverse $ take n $ reverse ss
2745>
2746> test = takeLast 40 $ dist 20 []
2747>
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2748</pre>
2749</div>
2750<p>
2751Printing &lt;test&gt; gives: <tt>"1s100000s11010s10100s1111s1010s110s11s1S"</tt></p>
2752<p>
2753The reverse algorithm computes the length of the string just by examining
2754a certain prefix:</p>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2755
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2756<div class="doc_code">
2757<pre>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2758> pref :: [Char] -> Int
2759> pref "S" = 1
2760> pref ('s':'1':rest) = decode 2 1 rest
2761> pref (_:rest) = 1 + pref rest
2762>
2763> decode walk acc ('0':rest) = decode (walk + 1) (acc * 2) rest
2764> decode walk acc ('1':rest) = decode (walk + 1) (acc * 2 + 1) rest
2765> decode walk acc _ = walk + acc
2766>
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2767</pre>
2768</div>
2769<p>
2770Now, as expected, printing &lt;pref test&gt; gives <tt>40</tt>.</p>
2771<p>
2772We can <i>quickCheck</i> this with following property:</p>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2773
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2774<div class="doc_code">
2775<pre>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2776> testcase = dist 2000 []
2777> testcaseLength = length testcase
2778>
2779> identityProp n = n > 0 && n <= testcaseLength ==> length arr == pref arr
2780> where arr = takeLast n testcase
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2781>
2782</pre>
2783</div>
2784<p>
2785As expected &lt;quickCheck identityProp&gt; gives:</p>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2786
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2787<pre>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2788*Main> quickCheck identityProp
2789OK, passed 100 tests.
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2790</pre>
2791<p>
2792Let's be a bit more exhaustive:</p>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2793
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2794<div class="doc_code">
2795<pre>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2796>
2797> deepCheck p = check (defaultConfig { configMaxTest = 500 }) p
2798>
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2799</pre>
2800</div>
2801<p>
2802And here is the result of &lt;deepCheck identityProp&gt;:</p>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2803
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2804<pre>
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2805*Main> deepCheck identityProp
2806OK, passed 500 tests.
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2807</pre>
2808
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2809<!-- ______________________________________________________________________ -->
2810<div class="doc_subsubsection">
Gabor Greiffd095b62009-01-05 16:05:32 +0000[diff] [blame]2811 <a name="Tagging">Tagging considerations</a>
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2812</div>
2813
2814<p>
2815To maintain the invariant that the 2 LSBits of each <tt>Use**</tt> in <tt>Use</tt>
2816never change after being set up, setters of <tt>Use::Prev</tt> must re-tag the
2817new <tt>Use**</tt> on every modification. Accordingly getters must strip the
2818tag bits.</p>
2819<p>
Gabor Greifd41720a2008-06-25 00:10:22 +0000[diff] [blame]2820For layout b) instead of the <tt>User</tt> we find a pointer (<tt>User*</tt> with LSBit set).
2821Following this pointer brings us to the <tt>User</tt>. A portable trick ensures
2822that the first bytes of <tt>User</tt> (if interpreted as a pointer) never has
Gabor Greiffd095b62009-01-05 16:05:32 +0000[diff] [blame]2823the LSBit set. (Portability is relying on the fact that all known compilers place the
2824<tt>vptr</tt> in the first word of the instances.)</p>
Gabor Greifdfed1182008-06-18 13:44:57 +0000[diff] [blame]2825
Gabor Greife98fc272008-06-16 21:06:12 +0000[diff] [blame]2826</div>
2827
2828 <!-- *********************************************************************** -->
Chris Lattnerd9d6e102005-04-23 16:10:52 +0000[diff] [blame]2829<div class="doc_section">
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2830 <a name="coreclasses">The Core LLVM Class Hierarchy Reference </a>
2831</div>
2832<!-- *********************************************************************** -->
2833
2834<div class="doc_text">
Reid Spencer303c4b42007-01-12 17:26:25 +0000[diff] [blame]2835<p><tt>#include "<a href="/doxygen/Type_8h-source.html">llvm/Type.h</a>"</tt>
2836<br>doxygen info: <a href="/doxygen/classllvm_1_1Type.html">Type Class</a></p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2837
2838<p>The Core LLVM classes are the primary means of representing the program
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]2839being inspected or transformed. The core LLVM classes are defined in
2840header files in the <tt>include/llvm/</tt> directory, and implemented in
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]2841the <tt>lib/VMCore</tt> directory.</p>
2842
2843</div>
2844
2845<!-- ======================================================================= -->
2846<div class="doc_subsection">
Reid Spencer303c4b42007-01-12 17:26:25 +0000[diff] [blame]2847 <a name="Type">The <tt>Type</tt> class and Derived Types</a>
2848</div>
2849
2850<div class="doc_text">
2851
2852 <p><tt>Type</tt> is a superclass of all type classes. Every <tt>Value</tt> has
2853 a <tt>Type</tt>. <tt>Type</tt> cannot be instantiated directly but only
2854 through its subclasses. Certain primitive types (<tt>VoidType</tt>,
2855 <tt>LabelType</tt>, <tt>FloatType</tt> and <tt>DoubleType</tt>) have hidden
2856 subclasses. They are hidden because they offer no useful functionality beyond
2857 what the <tt>Type</tt> class offers except to distinguish themselves from
2858 other subclasses of <tt>Type</tt>.</p>
2859 <p>All other types are subclasses of <tt>DerivedType</tt>. Types can be
2860 named, but this is not a requirement. There exists exactly
2861 one instance of a given shape at any one time. This allows type equality to
2862 be performed with address equality of the Type Instance. That is, given two
2863 <tt>Type*</tt> values, the types are identical if the pointers are identical.
2864 </p>
2865</div>
2866
2867<!-- _______________________________________________________________________ -->
2868<div class="doc_subsubsection">
Gabor Greiffd095b62009-01-05 16:05:32 +0000[diff] [blame]2869 <a name="m_Type">Important Public Methods</a>
Reid Spencer303c4b42007-01-12 17:26:25 +0000[diff] [blame]2870</div>
2871
2872<div class="doc_text">
2873
2874<ul>
Chris Lattner8f79df32007-01-15 01:55:32 +0000[diff] [blame]2875 <li><tt>bool isInteger() const</tt>: Returns true for any integer type.</li>
Reid Spencer303c4b42007-01-12 17:26:25 +0000[diff] [blame]2876
2877 <li><tt>bool isFloatingPoint()</tt>: Return true if this is one of the two
2878 floating point types.</li>
2879
2880 <li><tt>bool isAbstract()</tt>: Return true if the type is abstract (contains
2881 an OpaqueType anywhere in its definition).</li>
2882
2883 <li><tt>bool isSized()</tt>: Return true if the type has known size. Things
2884 that don't have a size are abstract types, labels and void.</li>
2885
2886</ul>
2887</div>
2888
2889<!-- _______________________________________________________________________ -->
2890<div class="doc_subsubsection">
Gabor Greiffd095b62009-01-05 16:05:32 +0000[diff] [blame]2891 <a name="derivedtypes">Important Derived Types</a>
Reid Spencer303c4b42007-01-12 17:26:25 +0000[diff] [blame]2892</div>
2893<div class="doc_text">
2894<dl>
2895 <dt><tt>IntegerType</tt></dt>
2896 <dd>Subclass of DerivedType that represents integer types of any bit width.
2897 Any bit width between <tt>IntegerType::MIN_INT_BITS</tt> (1) and
2898 <tt>IntegerType::MAX_INT_BITS</tt> (~8 million) can be represented.
2899 <ul>
2900 <li><tt>static const IntegerType* get(unsigned NumBits)</tt>: get an integer
2901 type of a specific bit width.</li>
2902 <li><tt>unsigned getBitWidth() const</tt>: Get the bit width of an integer
2903 type.</li>
2904 </ul>
2905 </dd>
2906 <dt><tt>SequentialType</tt></dt>
2907 <dd>This is subclassed by ArrayType and PointerType
2908 <ul>
2909 <li><tt>const Type * getElementType() const</tt>: Returns the type of each
2910 of the elements in the sequential type. </li>
2911 </ul>
2912 </dd>
2913 <dt><tt>ArrayType</tt></dt>
2914 <dd>This is a subclass of SequentialType and defines the interface for array
2915 types.
2916 <ul>
2917 <li><tt>unsigned getNumElements() const</tt>: Returns the number of
2918 elements in the array. </li>
2919 </ul>
2920 </dd>
2921 <dt><tt>PointerType</tt></dt>
Chris Lattner302da1e2007-02-03 03:05:57 +0000[diff] [blame]2922 <dd>Subclass of SequentialType for pointer types.</dd>
Reid Spencer9d6565a2007-02-15 02:26:10 +0000[diff] [blame]2923 <dt><tt>VectorType</tt></dt>
Reid Spencer485bad12007-02-15 03:07:05 +0000[diff] [blame]2924 <dd>Subclass of SequentialType for vector types. A
2925 vector type is similar to an ArrayType but is distinguished because it is
2926 a first class type wherease ArrayType is not. Vector types are used for
Reid Spencer303c4b42007-01-12 17:26:25 +0000[diff] [blame]2927 vector operations and are usually small vectors of of an integer or floating
2928 point type.</dd>
2929 <dt><tt>StructType</tt></dt>
2930 <dd>Subclass of DerivedTypes for struct types.</dd>
Duncan Sands8036ca42007-03-30 12:22:09 +0000[diff] [blame]2931 <dt><tt><a name="FunctionType">FunctionType</a></tt></dt>
Reid Spencer303c4b42007-01-12 17:26:25 +0000[diff] [blame]2932 <dd>Subclass of DerivedTypes for function types.
2933 <ul>
2934 <li><tt>bool isVarArg() const</tt>: Returns true if its a vararg
2935 function</li>
2936 <li><tt> const Type * getReturnType() const</tt>: Returns the
2937 return type of the function.</li>
2938 <li><tt>const Type * getParamType (unsigned i)</tt>: Returns
2939 the type of the ith parameter.</li>
2940 <li><tt> const unsigned getNumParams() const</tt>: Returns the
2941 number of formal parameters.</li>
2942 </ul>
2943 </dd>
2944 <dt><tt>OpaqueType</tt></dt>
2945 <dd>Sublcass of DerivedType for abstract types. This class
2946 defines no content and is used as a placeholder for some other type. Note
2947 that OpaqueType is used (temporarily) during type resolution for forward
2948 references of types. Once the referenced type is resolved, the OpaqueType
2949 is replaced with the actual type. OpaqueType can also be used for data
2950 abstraction. At link time opaque types can be resolved to actual types
2951 of the same name.</dd>
2952</dl>
2953</div>
2954
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]2955
2956
2957<!-- ======================================================================= -->
2958<div class="doc_subsection">
2959 <a name="Module">The <tt>Module</tt> class</a>
2960</div>
2961
2962<div class="doc_text">
2963
2964<p><tt>#include "<a
2965href="/doxygen/Module_8h-source.html">llvm/Module.h</a>"</tt><br> doxygen info:
2966<a href="/doxygen/classllvm_1_1Module.html">Module Class</a></p>
2967
2968<p>The <tt>Module</tt> class represents the top level structure present in LLVM
2969programs. An LLVM module is effectively either a translation unit of the
2970original program or a combination of several translation units merged by the
2971linker. The <tt>Module</tt> class keeps track of a list of <a
2972href="#Function"><tt>Function</tt></a>s, a list of <a
2973href="#GlobalVariable"><tt>GlobalVariable</tt></a>s, and a <a
2974href="#SymbolTable"><tt>SymbolTable</tt></a>. Additionally, it contains a few
2975helpful member functions that try to make common operations easy.</p>
2976
2977</div>
2978
2979<!-- _______________________________________________________________________ -->
2980<div class="doc_subsubsection">
2981 <a name="m_Module">Important Public Members of the <tt>Module</tt> class</a>
2982</div>
2983
2984<div class="doc_text">
2985
2986<ul>
2987 <li><tt>Module::Module(std::string name = "")</tt></li>
2988</ul>
2989
2990<p>Constructing a <a href="#Module">Module</a> is easy. You can optionally
2991provide a name for it (probably based on the name of the translation unit).</p>
2992
2993<ul>
2994 <li><tt>Module::iterator</tt> - Typedef for function list iterator<br>
2995 <tt>Module::const_iterator</tt> - Typedef for const_iterator.<br>
2996
2997 <tt>begin()</tt>, <tt>end()</tt>
2998 <tt>size()</tt>, <tt>empty()</tt>
2999
3000 <p>These are forwarding methods that make it easy to access the contents of
3001 a <tt>Module</tt> object's <a href="#Function"><tt>Function</tt></a>
3002 list.</p></li>
3003
3004 <li><tt>Module::FunctionListType &amp;getFunctionList()</tt>
3005
3006 <p> Returns the list of <a href="#Function"><tt>Function</tt></a>s. This is
3007 necessary to use when you need to update the list or perform a complex
3008 action that doesn't have a forwarding method.</p>
3009
3010 <p><!-- Global Variable --></p></li>
3011</ul>
3012
3013<hr>
3014
3015<ul>
3016 <li><tt>Module::global_iterator</tt> - Typedef for global variable list iterator<br>
3017
3018 <tt>Module::const_global_iterator</tt> - Typedef for const_iterator.<br>
3019
3020 <tt>global_begin()</tt>, <tt>global_end()</tt>
3021 <tt>global_size()</tt>, <tt>global_empty()</tt>
3022
3023 <p> These are forwarding methods that make it easy to access the contents of
3024 a <tt>Module</tt> object's <a
3025 href="#GlobalVariable"><tt>GlobalVariable</tt></a> list.</p></li>
3026
3027 <li><tt>Module::GlobalListType &amp;getGlobalList()</tt>
3028
3029 <p>Returns the list of <a
3030 href="#GlobalVariable"><tt>GlobalVariable</tt></a>s. This is necessary to
3031 use when you need to update the list or perform a complex action that
3032 doesn't have a forwarding method.</p>
3033
3034 <p><!-- Symbol table stuff --> </p></li>
3035</ul>
3036
3037<hr>
3038
3039<ul>
3040 <li><tt><a href="#SymbolTable">SymbolTable</a> *getSymbolTable()</tt>
3041
3042 <p>Return a reference to the <a href="#SymbolTable"><tt>SymbolTable</tt></a>
3043 for this <tt>Module</tt>.</p>
3044
3045 <p><!-- Convenience methods --></p></li>
3046</ul>
3047
3048<hr>
3049
3050<ul>
3051 <li><tt><a href="#Function">Function</a> *getFunction(const std::string
3052 &amp;Name, const <a href="#FunctionType">FunctionType</a> *Ty)</tt>
3053
3054 <p>Look up the specified function in the <tt>Module</tt> <a
3055 href="#SymbolTable"><tt>SymbolTable</tt></a>. If it does not exist, return
3056 <tt>null</tt>.</p></li>
3057
3058 <li><tt><a href="#Function">Function</a> *getOrInsertFunction(const
3059 std::string &amp;Name, const <a href="#FunctionType">FunctionType</a> *T)</tt>
3060
3061 <p>Look up the specified function in the <tt>Module</tt> <a
3062 href="#SymbolTable"><tt>SymbolTable</tt></a>. If it does not exist, add an
3063 external declaration for the function and return it.</p></li>
3064
3065 <li><tt>std::string getTypeName(const <a href="#Type">Type</a> *Ty)</tt>
3066
3067 <p>If there is at least one entry in the <a
3068 href="#SymbolTable"><tt>SymbolTable</tt></a> for the specified <a
3069 href="#Type"><tt>Type</tt></a>, return it. Otherwise return the empty
3070 string.</p></li>
3071
3072 <li><tt>bool addTypeName(const std::string &amp;Name, const <a
3073 href="#Type">Type</a> *Ty)</tt>
3074
3075 <p>Insert an entry in the <a href="#SymbolTable"><tt>SymbolTable</tt></a>
3076 mapping <tt>Name</tt> to <tt>Ty</tt>. If there is already an entry for this
3077 name, true is returned and the <a
3078 href="#SymbolTable"><tt>SymbolTable</tt></a> is not modified.</p></li>
3079</ul>
3080
3081</div>
3082
3083
Reid Spencer303c4b42007-01-12 17:26:25 +0000[diff] [blame]3084<!-- ======================================================================= -->
3085<div class="doc_subsection">
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3086 <a name="Value">The <tt>Value</tt> class</a>
3087</div>
3088
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]3089<div class="doc_text">
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3090
3091<p><tt>#include "<a href="/doxygen/Value_8h-source.html">llvm/Value.h</a>"</tt>
3092<br>
Chris Lattner00815172007-01-04 22:01:45 +0000[diff] [blame]3093doxygen info: <a href="/doxygen/classllvm_1_1Value.html">Value Class</a></p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3094
3095<p>The <tt>Value</tt> class is the most important class in the LLVM Source
3096base. It represents a typed value that may be used (among other things) as an
3097operand to an instruction. There are many different types of <tt>Value</tt>s,
3098such as <a href="#Constant"><tt>Constant</tt></a>s,<a
3099href="#Argument"><tt>Argument</tt></a>s. Even <a
3100href="#Instruction"><tt>Instruction</tt></a>s and <a
3101href="#Function"><tt>Function</tt></a>s are <tt>Value</tt>s.</p>
3102
3103<p>A particular <tt>Value</tt> may be used many times in the LLVM representation
3104for a program. For example, an incoming argument to a function (represented
3105with an instance of the <a href="#Argument">Argument</a> class) is "used" by
3106every instruction in the function that references the argument. To keep track
3107of this relationship, the <tt>Value</tt> class keeps a list of all of the <a
3108href="#User"><tt>User</tt></a>s that is using it (the <a
3109href="#User"><tt>User</tt></a> class is a base class for all nodes in the LLVM
3110graph that can refer to <tt>Value</tt>s). This use list is how LLVM represents
3111def-use information in the program, and is accessible through the <tt>use_</tt>*
3112methods, shown below.</p>
3113
3114<p>Because LLVM is a typed representation, every LLVM <tt>Value</tt> is typed,
3115and this <a href="#Type">Type</a> is available through the <tt>getType()</tt>
3116method. In addition, all LLVM values can be named. The "name" of the
3117<tt>Value</tt> is a symbolic string printed in the LLVM code:</p>
3118
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]3119<div class="doc_code">
3120<pre>
Reid Spencer06565dc2007-01-12 17:11:23 +0000[diff] [blame]3121%<b>foo</b> = add i32 1, 2
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]3122</pre>
3123</div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3124
Duncan Sands8036ca42007-03-30 12:22:09 +0000[diff] [blame]3125<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]3126that the name of any value may be missing (an empty string), so names should
3127<b>ONLY</b> be used for debugging (making the source code easier to read,
3128debugging printouts), they should not be used to keep track of values or map
3129between them. For this purpose, use a <tt>std::map</tt> of pointers to the
3130<tt>Value</tt> itself instead.</p>
3131
3132<p>One important aspect of LLVM is that there is no distinction between an SSA
3133variable and the operation that produces it. Because of this, any reference to
3134the value produced by an instruction (or the value available as an incoming
Chris Lattnerd5fc4fc2004-03-18 14:58:55 +0000[diff] [blame]3135argument, for example) is represented as a direct pointer to the instance of
3136the class that
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3137represents this value. Although this may take some getting used to, it
3138simplifies the representation and makes it easier to manipulate.</p>
3139
3140</div>
3141
3142<!-- _______________________________________________________________________ -->
3143<div class="doc_subsubsection">
3144 <a name="m_Value">Important Public Members of the <tt>Value</tt> class</a>
3145</div>
3146
3147<div class="doc_text">
3148
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3149<ul>
3150 <li><tt>Value::use_iterator</tt> - Typedef for iterator over the
3151use-list<br>
3152 <tt>Value::use_const_iterator</tt> - Typedef for const_iterator over
3153the use-list<br>
3154 <tt>unsigned use_size()</tt> - Returns the number of users of the
3155value.<br>
Chris Lattner9355b472002-09-06 02:50:58 +0000[diff] [blame]3156 <tt>bool use_empty()</tt> - Returns true if there are no users.<br>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3157 <tt>use_iterator use_begin()</tt> - Get an iterator to the start of
3158the use-list.<br>
3159 <tt>use_iterator use_end()</tt> - Get an iterator to the end of the
3160use-list.<br>
3161 <tt><a href="#User">User</a> *use_back()</tt> - Returns the last
3162element in the list.
3163 <p> These methods are the interface to access the def-use
3164information in LLVM. As with all other iterators in LLVM, the naming
3165conventions follow the conventions defined by the <a href="#stl">STL</a>.</p>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3166 </li>
3167 <li><tt><a href="#Type">Type</a> *getType() const</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3168 <p>This method returns the Type of the Value.</p>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3169 </li>
3170 <li><tt>bool hasName() const</tt><br>
Chris Lattner9355b472002-09-06 02:50:58 +0000[diff] [blame]3171 <tt>std::string getName() const</tt><br>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3172 <tt>void setName(const std::string &amp;Name)</tt>
3173 <p> This family of methods is used to access and assign a name to a <tt>Value</tt>,
3174be aware of the <a href="#nameWarning">precaution above</a>.</p>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3175 </li>
3176 <li><tt>void replaceAllUsesWith(Value *V)</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3177
3178 <p>This method traverses the use list of a <tt>Value</tt> changing all <a
3179 href="#User"><tt>User</tt>s</a> of the current value to refer to
3180 "<tt>V</tt>" instead. For example, if you detect that an instruction always
3181 produces a constant value (for example through constant folding), you can
3182 replace all uses of the instruction with the constant like this:</p>
3183
Bill Wendling3cd5ca62006-10-11 06:30:10 +0000[diff] [blame]3184<div class="doc_code">
3185<pre>
3186Inst-&gt;replaceAllUsesWith(ConstVal);
3187</pre>
3188</div>
3189
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3190</ul>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3191
3192</div>
3193
3194<!-- ======================================================================= -->
3195<div class="doc_subsection">
3196 <a name="User">The <tt>User</tt> class</a>
3197</div>
3198
3199<div class="doc_text">
3200
3201<p>
3202<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]3203doxygen info: <a href="/doxygen/classllvm_1_1User.html">User Class</a><br>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3204Superclass: <a href="#Value"><tt>Value</tt></a></p>
3205
3206<p>The <tt>User</tt> class is the common base class of all LLVM nodes that may
3207refer to <a href="#Value"><tt>Value</tt></a>s. It exposes a list of "Operands"
3208that are all of the <a href="#Value"><tt>Value</tt></a>s that the User is
3209referring to. The <tt>User</tt> class itself is a subclass of
3210<tt>Value</tt>.</p>
3211
3212<p>The operands of a <tt>User</tt> point directly to the LLVM <a
3213href="#Value"><tt>Value</tt></a> that it refers to. Because LLVM uses Static
3214Single Assignment (SSA) form, there can only be one definition referred to,
3215allowing this direct connection. This connection provides the use-def
3216information in LLVM.</p>
3217
3218</div>
3219
3220<!-- _______________________________________________________________________ -->
3221<div class="doc_subsubsection">
3222 <a name="m_User">Important Public Members of the <tt>User</tt> class</a>
3223</div>
3224
3225<div class="doc_text">
3226
3227<p>The <tt>User</tt> class exposes the operand list in two ways: through
3228an index access interface and through an iterator based interface.</p>
3229
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3230<ul>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3231 <li><tt>Value *getOperand(unsigned i)</tt><br>
3232 <tt>unsigned getNumOperands()</tt>
3233 <p> These two methods expose the operands of the <tt>User</tt> in a
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3234convenient form for direct access.</p></li>
3235
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3236 <li><tt>User::op_iterator</tt> - Typedef for iterator over the operand
3237list<br>
Chris Lattner58360822005-01-17 00:12:04 +0000[diff] [blame]3238 <tt>op_iterator op_begin()</tt> - Get an iterator to the start of
3239the operand list.<br>
3240 <tt>op_iterator op_end()</tt> - Get an iterator to the end of the
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3241operand list.
3242 <p> Together, these methods make up the iterator based interface to
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3243the operands of a <tt>User</tt>.</p></li>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3244</ul>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3245
3246</div>
3247
3248<!-- ======================================================================= -->
3249<div class="doc_subsection">
3250 <a name="Instruction">The <tt>Instruction</tt> class</a>
3251</div>
3252
3253<div class="doc_text">
3254
3255<p><tt>#include "</tt><tt><a
3256href="/doxygen/Instruction_8h-source.html">llvm/Instruction.h</a>"</tt><br>
Misha Brukman31ca1de2004-06-03 23:35:54 +0000[diff] [blame]3257doxygen info: <a href="/doxygen/classllvm_1_1Instruction.html">Instruction Class</a><br>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3258Superclasses: <a href="#User"><tt>User</tt></a>, <a
3259href="#Value"><tt>Value</tt></a></p>
3260
3261<p>The <tt>Instruction</tt> class is the common base class for all LLVM
3262instructions. It provides only a few methods, but is a very commonly used
3263class. The primary data tracked by the <tt>Instruction</tt> class itself is the
3264opcode (instruction type) and the parent <a
3265href="#BasicBlock"><tt>BasicBlock</tt></a> the <tt>Instruction</tt> is embedded
3266into. To represent a specific type of instruction, one of many subclasses of
3267<tt>Instruction</tt> are used.</p>
3268
3269<p> Because the <tt>Instruction</tt> class subclasses the <a
3270href="#User"><tt>User</tt></a> class, its operands can be accessed in the same
3271way as for other <a href="#User"><tt>User</tt></a>s (with the
3272<tt>getOperand()</tt>/<tt>getNumOperands()</tt> and
3273<tt>op_begin()</tt>/<tt>op_end()</tt> methods).</p> <p> An important file for
3274the <tt>Instruction</tt> class is the <tt>llvm/Instruction.def</tt> file. This
3275file contains some meta-data about the various different types of instructions
3276in LLVM. It describes the enum values that are used as opcodes (for example
Reid Spencerc92d25d2006-12-19 19:47:19 +0000[diff] [blame]3277<tt>Instruction::Add</tt> and <tt>Instruction::ICmp</tt>), as well as the
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3278concrete sub-classes of <tt>Instruction</tt> that implement the instruction (for
3279example <tt><a href="#BinaryOperator">BinaryOperator</a></tt> and <tt><a
Reid Spencerc92d25d2006-12-19 19:47:19 +0000[diff] [blame]3280href="#CmpInst">CmpInst</a></tt>). Unfortunately, the use of macros in
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3281this file confuses doxygen, so these enum values don't show up correctly in the
Misha Brukman31ca1de2004-06-03 23:35:54 +0000[diff] [blame]3282<a href="/doxygen/classllvm_1_1Instruction.html">doxygen output</a>.</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3283
3284</div>
3285
3286<!-- _______________________________________________________________________ -->
3287<div class="doc_subsubsection">
Reid Spencerc92d25d2006-12-19 19:47:19 +0000[diff] [blame]3288 <a name="s_Instruction">Important Subclasses of the <tt>Instruction</tt>
3289 class</a>
3290</div>
3291<div class="doc_text">
3292 <ul>
3293 <li><tt><a name="BinaryOperator">BinaryOperator</a></tt>
3294 <p>This subclasses represents all two operand instructions whose operands
3295 must be the same type, except for the comparison instructions.</p></li>
3296 <li><tt><a name="CastInst">CastInst</a></tt>
3297 <p>This subclass is the parent of the 12 casting instructions. It provides
3298 common operations on cast instructions.</p>
3299 <li><tt><a name="CmpInst">CmpInst</a></tt>
3300 <p>This subclass respresents the two comparison instructions,
3301 <a href="LangRef.html#i_icmp">ICmpInst</a> (integer opreands), and
3302 <a href="LangRef.html#i_fcmp">FCmpInst</a> (floating point operands).</p>
3303 <li><tt><a name="TerminatorInst">TerminatorInst</a></tt>
3304 <p>This subclass is the parent of all terminator instructions (those which
3305 can terminate a block).</p>
3306 </ul>
3307 </div>
3308
3309<!-- _______________________________________________________________________ -->
3310<div class="doc_subsubsection">
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3311 <a name="m_Instruction">Important Public Members of the <tt>Instruction</tt>
3312 class</a>
3313</div>
3314
3315<div class="doc_text">
3316
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3317<ul>
3318 <li><tt><a href="#BasicBlock">BasicBlock</a> *getParent()</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3319 <p>Returns the <a href="#BasicBlock"><tt>BasicBlock</tt></a> that
3320this <tt>Instruction</tt> is embedded into.</p></li>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3321 <li><tt>bool mayWriteToMemory()</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3322 <p>Returns true if the instruction writes to memory, i.e. it is a
3323 <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]3324 <li><tt>unsigned getOpcode()</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3325 <p>Returns the opcode for the <tt>Instruction</tt>.</p></li>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3326 <li><tt><a href="#Instruction">Instruction</a> *clone() const</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3327 <p>Returns another instance of the specified instruction, identical
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3328in all ways to the original except that the instruction has no parent
3329(ie it's not embedded into a <a href="#BasicBlock"><tt>BasicBlock</tt></a>),
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3330and it has no name</p></li>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3331</ul>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3332
3333</div>
3334
3335<!-- ======================================================================= -->
3336<div class="doc_subsection">
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]3337 <a name="Constant">The <tt>Constant</tt> class and subclasses</a>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3338</div>
3339
3340<div class="doc_text">
3341
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]3342<p>Constant represents a base class for different types of constants. It
3343is subclassed by ConstantInt, ConstantArray, etc. for representing
3344the various types of Constants. <a href="#GlobalValue">GlobalValue</a> is also
3345a subclass, which represents the address of a global variable or function.
3346</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3347
3348</div>
3349
3350<!-- _______________________________________________________________________ -->
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]3351<div class="doc_subsubsection">Important Subclasses of Constant </div>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3352<div class="doc_text">
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3353<ul>
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]3354 <li>ConstantInt : This subclass of Constant represents an integer constant of
3355 any width.
3356 <ul>
Reid Spencer97b4ee32007-03-01 21:05:33 +0000[diff] [blame]3357 <li><tt>const APInt&amp; getValue() const</tt>: Returns the underlying
3358 value of this constant, an APInt value.</li>
3359 <li><tt>int64_t getSExtValue() const</tt>: Converts the underlying APInt
3360 value to an int64_t via sign extension. If the value (not the bit width)
3361 of the APInt is too large to fit in an int64_t, an assertion will result.
3362 For this reason, use of this method is discouraged.</li>
3363 <li><tt>uint64_t getZExtValue() const</tt>: Converts the underlying APInt
3364 value to a uint64_t via zero extension. IF the value (not the bit width)
3365 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]3366 For this reason, use of this method is discouraged.</li>
Reid Spencer97b4ee32007-03-01 21:05:33 +0000[diff] [blame]3367 <li><tt>static ConstantInt* get(const APInt&amp; Val)</tt>: Returns the
3368 ConstantInt object that represents the value provided by <tt>Val</tt>.
3369 The type is implied as the IntegerType that corresponds to the bit width
3370 of <tt>Val</tt>.</li>
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]3371 <li><tt>static ConstantInt* get(const Type *Ty, uint64_t Val)</tt>:
3372 Returns the ConstantInt object that represents the value provided by
3373 <tt>Val</tt> for integer type <tt>Ty</tt>.</li>
3374 </ul>
3375 </li>
3376 <li>ConstantFP : This class represents a floating point constant.
3377 <ul>
3378 <li><tt>double getValue() const</tt>: Returns the underlying value of
3379 this constant. </li>
3380 </ul>
3381 </li>
3382 <li>ConstantArray : This represents a constant array.
3383 <ul>
3384 <li><tt>const std::vector&lt;Use&gt; &amp;getValues() const</tt>: Returns
3385 a vector of component constants that makeup this array. </li>
3386 </ul>
3387 </li>
3388 <li>ConstantStruct : This represents a constant struct.
3389 <ul>
3390 <li><tt>const std::vector&lt;Use&gt; &amp;getValues() const</tt>: Returns
3391 a vector of component constants that makeup this array. </li>
3392 </ul>
3393 </li>
3394 <li>GlobalValue : This represents either a global variable or a function. In
3395 either case, the value is a constant fixed address (after linking).
3396 </li>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3397</ul>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3398</div>
3399
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]3400
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3401<!-- ======================================================================= -->
3402<div class="doc_subsection">
3403 <a name="GlobalValue">The <tt>GlobalValue</tt> class</a>
3404</div>
3405
3406<div class="doc_text">
3407
3408<p><tt>#include "<a
3409href="/doxygen/GlobalValue_8h-source.html">llvm/GlobalValue.h</a>"</tt><br>
Misha Brukman384047f2004-06-03 23:29:12 +0000[diff] [blame]3410doxygen info: <a href="/doxygen/classllvm_1_1GlobalValue.html">GlobalValue
3411Class</a><br>
Reid Spencerbe5e85e2006-04-14 14:11:48 +0000[diff] [blame]3412Superclasses: <a href="#Constant"><tt>Constant</tt></a>,
3413<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]3414
3415<p>Global values (<a href="#GlobalVariable"><tt>GlobalVariable</tt></a>s or <a
3416href="#Function"><tt>Function</tt></a>s) are the only LLVM values that are
3417visible in the bodies of all <a href="#Function"><tt>Function</tt></a>s.
3418Because they are visible at global scope, they are also subject to linking with
3419other globals defined in different translation units. To control the linking
3420process, <tt>GlobalValue</tt>s know their linkage rules. Specifically,
3421<tt>GlobalValue</tt>s know whether they have internal or external linkage, as
Reid Spencer8b2da7a2004-07-18 13:10:31 +0000[diff] [blame]3422defined by the <tt>LinkageTypes</tt> enumeration.</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3423
3424<p>If a <tt>GlobalValue</tt> has internal linkage (equivalent to being
3425<tt>static</tt> in C), it is not visible to code outside the current translation
3426unit, and does not participate in linking. If it has external linkage, it is
3427visible to external code, and does participate in linking. In addition to
3428linkage information, <tt>GlobalValue</tt>s keep track of which <a
3429href="#Module"><tt>Module</tt></a> they are currently part of.</p>
3430
3431<p>Because <tt>GlobalValue</tt>s are memory objects, they are always referred to
3432by their <b>address</b>. As such, the <a href="#Type"><tt>Type</tt></a> of a
3433global is always a pointer to its contents. It is important to remember this
3434when using the <tt>GetElementPtrInst</tt> instruction because this pointer must
3435be dereferenced first. For example, if you have a <tt>GlobalVariable</tt> (a
3436subclass 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]3437i32]</tt>, then the <tt>GlobalVariable</tt> is a pointer to that array. Although
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3438the address of the first element of this array and the value of the
3439<tt>GlobalVariable</tt> are the same, they have different types. The
Reid Spencer06565dc2007-01-12 17:11:23 +0000[diff] [blame]3440<tt>GlobalVariable</tt>'s type is <tt>[24 x i32]</tt>. The first element's type
3441is <tt>i32.</tt> Because of this, accessing a global value requires you to
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3442dereference the pointer with <tt>GetElementPtrInst</tt> first, then its elements
3443can be accessed. This is explained in the <a href="LangRef.html#globalvars">LLVM
3444Language Reference Manual</a>.</p>
3445
3446</div>
3447
3448<!-- _______________________________________________________________________ -->
3449<div class="doc_subsubsection">
3450 <a name="m_GlobalValue">Important Public Members of the <tt>GlobalValue</tt>
3451 class</a>
3452</div>
3453
3454<div class="doc_text">
3455
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3456<ul>
3457 <li><tt>bool hasInternalLinkage() const</tt><br>
Chris Lattner9355b472002-09-06 02:50:58 +0000[diff] [blame]3458 <tt>bool hasExternalLinkage() const</tt><br>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3459 <tt>void setInternalLinkage(bool HasInternalLinkage)</tt>
3460 <p> These methods manipulate the linkage characteristics of the <tt>GlobalValue</tt>.</p>
3461 <p> </p>
3462 </li>
3463 <li><tt><a href="#Module">Module</a> *getParent()</tt>
3464 <p> This returns the <a href="#Module"><tt>Module</tt></a> that the
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3465GlobalValue is currently embedded into.</p></li>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3466</ul>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3467
3468</div>
3469
3470<!-- ======================================================================= -->
3471<div class="doc_subsection">
3472 <a name="Function">The <tt>Function</tt> class</a>
3473</div>
3474
3475<div class="doc_text">
3476
3477<p><tt>#include "<a
3478href="/doxygen/Function_8h-source.html">llvm/Function.h</a>"</tt><br> doxygen
Misha Brukman31ca1de2004-06-03 23:35:54 +0000[diff] [blame]3479info: <a href="/doxygen/classllvm_1_1Function.html">Function Class</a><br>
Reid Spencerbe5e85e2006-04-14 14:11:48 +0000[diff] [blame]3480Superclasses: <a href="#GlobalValue"><tt>GlobalValue</tt></a>,
3481<a href="#Constant"><tt>Constant</tt></a>,
3482<a href="#User"><tt>User</tt></a>,
3483<a href="#Value"><tt>Value</tt></a></p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3484
3485<p>The <tt>Function</tt> class represents a single procedure in LLVM. It is
3486actually one of the more complex classes in the LLVM heirarchy because it must
3487keep track of a large amount of data. The <tt>Function</tt> class keeps track
Reid Spencerbe5e85e2006-04-14 14:11:48 +0000[diff] [blame]3488of a list of <a href="#BasicBlock"><tt>BasicBlock</tt></a>s, a list of formal
3489<a href="#Argument"><tt>Argument</tt></a>s, and a
3490<a href="#SymbolTable"><tt>SymbolTable</tt></a>.</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3491
3492<p>The list of <a href="#BasicBlock"><tt>BasicBlock</tt></a>s is the most
3493commonly used part of <tt>Function</tt> objects. The list imposes an implicit
3494ordering of the blocks in the function, which indicate how the code will be
3495layed out by the backend. Additionally, the first <a
3496href="#BasicBlock"><tt>BasicBlock</tt></a> is the implicit entry node for the
3497<tt>Function</tt>. It is not legal in LLVM to explicitly branch to this initial
3498block. There are no implicit exit nodes, and in fact there may be multiple exit
3499nodes from a single <tt>Function</tt>. If the <a
3500href="#BasicBlock"><tt>BasicBlock</tt></a> list is empty, this indicates that
3501the <tt>Function</tt> is actually a function declaration: the actual body of the
3502function hasn't been linked in yet.</p>
3503
3504<p>In addition to a list of <a href="#BasicBlock"><tt>BasicBlock</tt></a>s, the
3505<tt>Function</tt> class also keeps track of the list of formal <a
3506href="#Argument"><tt>Argument</tt></a>s that the function receives. This
3507container manages the lifetime of the <a href="#Argument"><tt>Argument</tt></a>
3508nodes, just like the <a href="#BasicBlock"><tt>BasicBlock</tt></a> list does for
3509the <a href="#BasicBlock"><tt>BasicBlock</tt></a>s.</p>
3510
3511<p>The <a href="#SymbolTable"><tt>SymbolTable</tt></a> is a very rarely used
3512LLVM feature that is only used when you have to look up a value by name. Aside
3513from that, the <a href="#SymbolTable"><tt>SymbolTable</tt></a> is used
3514internally to make sure that there are not conflicts between the names of <a
3515href="#Instruction"><tt>Instruction</tt></a>s, <a
3516href="#BasicBlock"><tt>BasicBlock</tt></a>s, or <a
3517href="#Argument"><tt>Argument</tt></a>s in the function body.</p>
3518
Reid Spencer8b2da7a2004-07-18 13:10:31 +0000[diff] [blame]3519<p>Note that <tt>Function</tt> is a <a href="#GlobalValue">GlobalValue</a>
3520and therefore also a <a href="#Constant">Constant</a>. The value of the function
3521is its address (after linking) which is guaranteed to be constant.</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3522</div>
3523
3524<!-- _______________________________________________________________________ -->
3525<div class="doc_subsubsection">
3526 <a name="m_Function">Important Public Members of the <tt>Function</tt>
3527 class</a>
3528</div>
3529
3530<div class="doc_text">
3531
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3532<ul>
3533 <li><tt>Function(const </tt><tt><a href="#FunctionType">FunctionType</a>
Chris Lattnerac479e52004-08-04 05:10:48 +0000[diff] [blame]3534 *Ty, LinkageTypes Linkage, const std::string &amp;N = "", Module* Parent = 0)</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3535
3536 <p>Constructor used when you need to create new <tt>Function</tt>s to add
3537 the the program. The constructor must specify the type of the function to
Chris Lattnerac479e52004-08-04 05:10:48 +0000[diff] [blame]3538 create and what type of linkage the function should have. The <a
3539 href="#FunctionType"><tt>FunctionType</tt></a> argument
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3540 specifies the formal arguments and return value for the function. The same
Duncan Sands8036ca42007-03-30 12:22:09 +0000[diff] [blame]3541 <a href="#FunctionType"><tt>FunctionType</tt></a> value can be used to
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3542 create multiple functions. The <tt>Parent</tt> argument specifies the Module
3543 in which the function is defined. If this argument is provided, the function
3544 will automatically be inserted into that module's list of
3545 functions.</p></li>
3546
Chris Lattner62810e32008-11-25 18:34:50 +0000[diff] [blame]3547 <li><tt>bool isDeclaration()</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3548
3549 <p>Return whether or not the <tt>Function</tt> has a body defined. If the
3550 function is "external", it does not have a body, and thus must be resolved
3551 by linking with a function defined in a different translation unit.</p></li>
3552
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3553 <li><tt>Function::iterator</tt> - Typedef for basic block list iterator<br>
Chris Lattner9355b472002-09-06 02:50:58 +0000[diff] [blame]3554 <tt>Function::const_iterator</tt> - Typedef for const_iterator.<br>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3555
Chris Lattner77d69242005-03-15 05:19:20 +0000[diff] [blame]3556 <tt>begin()</tt>, <tt>end()</tt>
3557 <tt>size()</tt>, <tt>empty()</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3558
3559 <p>These are forwarding methods that make it easy to access the contents of
3560 a <tt>Function</tt> object's <a href="#BasicBlock"><tt>BasicBlock</tt></a>
3561 list.</p></li>
3562
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3563 <li><tt>Function::BasicBlockListType &amp;getBasicBlockList()</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3564
3565 <p>Returns the list of <a href="#BasicBlock"><tt>BasicBlock</tt></a>s. This
3566 is necessary to use when you need to update the list or perform a complex
3567 action that doesn't have a forwarding method.</p></li>
3568
Chris Lattner89cc2652005-03-15 04:48:32 +0000[diff] [blame]3569 <li><tt>Function::arg_iterator</tt> - Typedef for the argument list
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3570iterator<br>
Chris Lattner89cc2652005-03-15 04:48:32 +0000[diff] [blame]3571 <tt>Function::const_arg_iterator</tt> - Typedef for const_iterator.<br>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3572
Chris Lattner77d69242005-03-15 05:19:20 +0000[diff] [blame]3573 <tt>arg_begin()</tt>, <tt>arg_end()</tt>
Chris Lattner89cc2652005-03-15 04:48:32 +0000[diff] [blame]3574 <tt>arg_size()</tt>, <tt>arg_empty()</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3575
3576 <p>These are forwarding methods that make it easy to access the contents of
3577 a <tt>Function</tt> object's <a href="#Argument"><tt>Argument</tt></a>
3578 list.</p></li>
3579
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3580 <li><tt>Function::ArgumentListType &amp;getArgumentList()</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3581
3582 <p>Returns the list of <a href="#Argument"><tt>Argument</tt></a>s. This is
3583 necessary to use when you need to update the list or perform a complex
3584 action that doesn't have a forwarding method.</p></li>
3585
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3586 <li><tt><a href="#BasicBlock">BasicBlock</a> &amp;getEntryBlock()</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3587
3588 <p>Returns the entry <a href="#BasicBlock"><tt>BasicBlock</tt></a> for the
3589 function. Because the entry block for the function is always the first
3590 block, this returns the first block of the <tt>Function</tt>.</p></li>
3591
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3592 <li><tt><a href="#Type">Type</a> *getReturnType()</tt><br>
3593 <tt><a href="#FunctionType">FunctionType</a> *getFunctionType()</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3594
3595 <p>This traverses the <a href="#Type"><tt>Type</tt></a> of the
3596 <tt>Function</tt> and returns the return type of the function, or the <a
3597 href="#FunctionType"><tt>FunctionType</tt></a> of the actual
3598 function.</p></li>
3599
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3600 <li><tt><a href="#SymbolTable">SymbolTable</a> *getSymbolTable()</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3601
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3602 <p> Return a pointer to the <a href="#SymbolTable"><tt>SymbolTable</tt></a>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3603 for this <tt>Function</tt>.</p></li>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3604</ul>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3605
3606</div>
3607
3608<!-- ======================================================================= -->
3609<div class="doc_subsection">
3610 <a name="GlobalVariable">The <tt>GlobalVariable</tt> class</a>
3611</div>
3612
3613<div class="doc_text">
3614
3615<p><tt>#include "<a
3616href="/doxygen/GlobalVariable_8h-source.html">llvm/GlobalVariable.h</a>"</tt>
3617<br>
Tanya Lattnera3da7772004-06-22 08:02:25 +0000[diff] [blame]3618doxygen info: <a href="/doxygen/classllvm_1_1GlobalVariable.html">GlobalVariable
Reid Spencerbe5e85e2006-04-14 14:11:48 +0000[diff] [blame]3619 Class</a><br>
3620Superclasses: <a href="#GlobalValue"><tt>GlobalValue</tt></a>,
3621<a href="#Constant"><tt>Constant</tt></a>,
3622<a href="#User"><tt>User</tt></a>,
3623<a href="#Value"><tt>Value</tt></a></p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3624
3625<p>Global variables are represented with the (suprise suprise)
3626<tt>GlobalVariable</tt> class. Like functions, <tt>GlobalVariable</tt>s are also
3627subclasses of <a href="#GlobalValue"><tt>GlobalValue</tt></a>, and as such are
3628always referenced by their address (global values must live in memory, so their
Reid Spencerbe5e85e2006-04-14 14:11:48 +0000[diff] [blame]3629"name" refers to their constant address). See
3630<a href="#GlobalValue"><tt>GlobalValue</tt></a> for more on this. Global
3631variables may have an initial value (which must be a
3632<a href="#Constant"><tt>Constant</tt></a>), and if they have an initializer,
3633they may be marked as "constant" themselves (indicating that their contents
3634never change at runtime).</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3635</div>
3636
3637<!-- _______________________________________________________________________ -->
3638<div class="doc_subsubsection">
3639 <a name="m_GlobalVariable">Important Public Members of the
3640 <tt>GlobalVariable</tt> class</a>
3641</div>
3642
3643<div class="doc_text">
3644
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3645<ul>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3646 <li><tt>GlobalVariable(const </tt><tt><a href="#Type">Type</a> *Ty, bool
3647 isConstant, LinkageTypes&amp; Linkage, <a href="#Constant">Constant</a>
3648 *Initializer = 0, const std::string &amp;Name = "", Module* Parent = 0)</tt>
3649
3650 <p>Create a new global variable of the specified type. If
3651 <tt>isConstant</tt> is true then the global variable will be marked as
3652 unchanging for the program. The Linkage parameter specifies the type of
Duncan Sands667d4b82009-03-07 15:45:40 +0000[diff] [blame]3653 linkage (internal, external, weak, linkonce, appending) for the variable.
3654 If the linkage is InternalLinkage, WeakAnyLinkage, WeakODRLinkage,
3655 LinkOnceAnyLinkage or LinkOnceODRLinkage,&nbsp; then the resultant
3656 global variable will have internal linkage. AppendingLinkage concatenates
3657 together all instances (in different translation units) of the variable
3658 into a single variable but is only applicable to arrays. &nbsp;See
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3659 the <a href="LangRef.html#modulestructure">LLVM Language Reference</a> for
3660 further details on linkage types. Optionally an initializer, a name, and the
3661 module to put the variable into may be specified for the global variable as
3662 well.</p></li>
3663
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3664 <li><tt>bool isConstant() const</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3665
3666 <p>Returns true if this is a global variable that is known not to
3667 be modified at runtime.</p></li>
3668
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3669 <li><tt>bool hasInitializer()</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3670
3671 <p>Returns true if this <tt>GlobalVariable</tt> has an intializer.</p></li>
3672
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3673 <li><tt><a href="#Constant">Constant</a> *getInitializer()</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3674
3675 <p>Returns the intial value for a <tt>GlobalVariable</tt>. It is not legal
3676 to call this method if there is no initializer.</p></li>
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3677</ul>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3678
3679</div>
3680
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]3681
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3682<!-- ======================================================================= -->
3683<div class="doc_subsection">
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]3684 <a name="BasicBlock">The <tt>BasicBlock</tt> class</a>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3685</div>
3686
3687<div class="doc_text">
3688
3689<p><tt>#include "<a
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]3690href="/doxygen/BasicBlock_8h-source.html">llvm/BasicBlock.h</a>"</tt><br>
Stefanus Du Toit24e04112009-06-17 21:12:26 +0000[diff] [blame]3691doxygen info: <a href="/doxygen/classllvm_1_1BasicBlock.html">BasicBlock
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]3692Class</a><br>
3693Superclass: <a href="#Value"><tt>Value</tt></a></p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3694
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]3695<p>This class represents a single entry multiple exit section of the code,
3696commonly known as a basic block by the compiler community. The
3697<tt>BasicBlock</tt> class maintains a list of <a
3698href="#Instruction"><tt>Instruction</tt></a>s, which form the body of the block.
3699Matching the language definition, the last element of this list of instructions
3700is always a terminator instruction (a subclass of the <a
3701href="#TerminatorInst"><tt>TerminatorInst</tt></a> class).</p>
3702
3703<p>In addition to tracking the list of instructions that make up the block, the
3704<tt>BasicBlock</tt> class also keeps track of the <a
3705href="#Function"><tt>Function</tt></a> that it is embedded into.</p>
3706
3707<p>Note that <tt>BasicBlock</tt>s themselves are <a
3708href="#Value"><tt>Value</tt></a>s, because they are referenced by instructions
3709like branches and can go in the switch tables. <tt>BasicBlock</tt>s have type
3710<tt>label</tt>.</p>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3711
3712</div>
3713
3714<!-- _______________________________________________________________________ -->
3715<div class="doc_subsubsection">
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]3716 <a name="m_BasicBlock">Important Public Members of the <tt>BasicBlock</tt>
3717 class</a>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3718</div>
3719
3720<div class="doc_text">
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3721<ul>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3722
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]3723<li><tt>BasicBlock(const std::string &amp;Name = "", </tt><tt><a
3724 href="#Function">Function</a> *Parent = 0)</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3725
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]3726<p>The <tt>BasicBlock</tt> constructor is used to create new basic blocks for
3727insertion into a function. The constructor optionally takes a name for the new
3728block, and a <a href="#Function"><tt>Function</tt></a> to insert it into. If
3729the <tt>Parent</tt> parameter is specified, the new <tt>BasicBlock</tt> is
3730automatically inserted at the end of the specified <a
3731href="#Function"><tt>Function</tt></a>, if not specified, the BasicBlock must be
3732manually inserted into the <a href="#Function"><tt>Function</tt></a>.</p></li>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3733
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]3734<li><tt>BasicBlock::iterator</tt> - Typedef for instruction list iterator<br>
3735<tt>BasicBlock::const_iterator</tt> - Typedef for const_iterator.<br>
3736<tt>begin()</tt>, <tt>end()</tt>, <tt>front()</tt>, <tt>back()</tt>,
3737<tt>size()</tt>, <tt>empty()</tt>
3738STL-style functions for accessing the instruction list.
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3739
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]3740<p>These methods and typedefs are forwarding functions that have the same
3741semantics as the standard library methods of the same names. These methods
3742expose the underlying instruction list of a basic block in a way that is easy to
3743manipulate. To get the full complement of container operations (including
3744operations to update the list), you must use the <tt>getInstList()</tt>
3745method.</p></li>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3746
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]3747<li><tt>BasicBlock::InstListType &amp;getInstList()</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3748
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]3749<p>This method is used to get access to the underlying container that actually
3750holds the Instructions. This method must be used when there isn't a forwarding
3751function in the <tt>BasicBlock</tt> class for the operation that you would like
3752to perform. Because there are no forwarding functions for "updating"
3753operations, you need to use this if you want to update the contents of a
3754<tt>BasicBlock</tt>.</p></li>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3755
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]3756<li><tt><a href="#Function">Function</a> *getParent()</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3757
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]3758<p> Returns a pointer to <a href="#Function"><tt>Function</tt></a> the block is
3759embedded into, or a null pointer if it is homeless.</p></li>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3760
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]3761<li><tt><a href="#TerminatorInst">TerminatorInst</a> *getTerminator()</tt>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3762
Chris Lattner2b78d962007-02-03 20:02:25 +0000[diff] [blame]3763<p> Returns a pointer to the terminator instruction that appears at the end of
3764the <tt>BasicBlock</tt>. If there is no terminator instruction, or if the last
3765instruction in the block is not a terminator, then a null pointer is
3766returned.</p></li>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3767
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3768</ul>
3769
3770</div>
3771
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3772
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3773<!-- ======================================================================= -->
3774<div class="doc_subsection">
3775 <a name="Argument">The <tt>Argument</tt> class</a>
3776</div>
3777
3778<div class="doc_text">
3779
3780<p>This subclass of Value defines the interface for incoming formal
Chris Lattner58360822005-01-17 00:12:04 +0000[diff] [blame]3781arguments to a function. A Function maintains a list of its formal
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3782arguments. An argument has a pointer to the parent Function.</p>
3783
3784</div>
3785
Chris Lattner9355b472002-09-06 02:50:58 +0000[diff] [blame]3786<!-- *********************************************************************** -->
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3787<hr>
3788<address>
3789 <a href="http://jigsaw.w3.org/css-validator/check/referer"><img
Misha Brukman44408702008-12-11 17:34:48 +0000[diff] [blame]3790 src="http://jigsaw.w3.org/css-validator/images/vcss-blue" alt="Valid CSS"></a>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3791 <a href="http://validator.w3.org/check/referer"><img
Gabor Greifa9c0f2b2008-06-18 14:05:31 +0000[diff] [blame]3792 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]3793
3794 <a href="mailto:dhurjati@cs.uiuc.edu">Dinakar Dhurjati</a> and
3795 <a href="mailto:sabre@nondot.org">Chris Lattner</a><br>
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]3796 <a href="http://llvm.org">The LLVM Compiler Infrastructure</a><br>
Misha Brukman13fd15c2004-01-15 00:14:41 +0000[diff] [blame]3797 Last modified: $Date$
3798</address>
3799
Chris Lattner261efe92003-11-25 01:02:51 +0000[diff] [blame]3800</body>
3801</html>