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				4	<head>
				5	<title>LLVM Programmer's Manual</title>
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				7	</head>
				8	<body>
				9
				10	<div class="doc_title">
				11	LLVM Programmer's Manual
				12	</div>
				13
				14	<ol>
				15	<li><a href="#introduction">Introduction</a></li>
				16	<li><a href="#general">General Information</a>
				17	<ul>
				18	<li><a href="#stl">The C++ Standard Template Library</a></li>
				19	<!--
				20	<li>The <tt>-time-passes</tt> option</li>
				21	<li>How to use the LLVM Makefile system</li>
				22	<li>How to write a regression test</li>
				23
				24	-->
				25	</ul>
				26	</li>
				27	<li><a href="#apis">Important and useful LLVM APIs</a>
				28	<ul>
				29	<li><a href="#isa">The <tt>isa<></tt>, <tt>cast<></tt>
				30	and <tt>dyn_cast<></tt> templates</a> </li>
				31	<li><a href="#DEBUG">The <tt>DEBUG()</tt> macro and <tt>-debug</tt>
				32	option</a>
				33	<ul>
				34	<li><a href="#DEBUG_TYPE">Fine grained debug info with <tt>DEBUG_TYPE</tt>
				35	and the <tt>-debug-only</tt> option</a> </li>
				36	</ul>
				37	</li>
				38	<li><a href="#Statistic">The <tt>Statistic</tt> class & <tt>-stats</tt>
				39	option</a></li>
				40	<!--
				41	<li>The <tt>InstVisitor</tt> template
				42	<li>The general graph API
				43	-->
				44	<li><a href="#ViewGraph">Viewing graphs while debugging code</a></li>
				45	</ul>
				46	</li>
				47	<li><a href="#datastructure">Picking the Right Data Structure for a Task</a>
				48	<ul>
				49	<li><a href="#ds_sequential">Sequential Containers (std::vector, std::list, etc)</a>
				50	<ul>
				51	<li><a href="#dss_fixedarrays">Fixed Size Arrays</a></li>
				52	<li><a href="#dss_heaparrays">Heap Allocated Arrays</a></li>
				53	<li><a href="#dss_smallvector">"llvm/ADT/SmallVector.h"</a></li>
				54	<li><a href="#dss_vector"><vector></a></li>
				55	<li><a href="#dss_deque"><deque></a></li>
				56	<li><a href="#dss_list"><list></a></li>
				57	<li><a href="#dss_ilist">llvm/ADT/ilist</a></li>
				58	<li><a href="#dss_other">Other Sequential Container Options</a></li>
				59	</ul></li>
				60	<li><a href="#ds_set">Set-Like Containers (std::set, SmallSet, SetVector, etc)</a>
				61	<ul>
				62	<li><a href="#dss_sortedvectorset">A sorted 'vector'</a></li>
				63	<li><a href="#dss_smallset">"llvm/ADT/SmallSet.h"</a></li>
				64	<li><a href="#dss_smallptrset">"llvm/ADT/SmallPtrSet.h"</a></li>
Chris Lattner	77ab46d	2007-09-30 00:58:59 +0000	[diff] [blame]	65	<li><a href="#dss_denseset">"llvm/ADT/DenseSet.h"</a></li>
Dan Gohman	f17a25c	2007-07-18 16:29:46 +0000	[diff] [blame]	66	<li><a href="#dss_FoldingSet">"llvm/ADT/FoldingSet.h"</a></li>
				67	<li><a href="#dss_set"><set></a></li>
				68	<li><a href="#dss_setvector">"llvm/ADT/SetVector.h"</a></li>
				69	<li><a href="#dss_uniquevector">"llvm/ADT/UniqueVector.h"</a></li>
				70	<li><a href="#dss_otherset">Other Set-Like ContainerOptions</a></li>
				71	</ul></li>
				72	<li><a href="#ds_map">Map-Like Containers (std::map, DenseMap, etc)</a>
				73	<ul>
				74	<li><a href="#dss_sortedvectormap">A sorted 'vector'</a></li>
				75	<li><a href="#dss_stringmap">"llvm/ADT/StringMap.h"</a></li>
				76	<li><a href="#dss_indexedmap">"llvm/ADT/IndexedMap.h"</a></li>
				77	<li><a href="#dss_densemap">"llvm/ADT/DenseMap.h"</a></li>
				78	<li><a href="#dss_map"><map></a></li>
				79	<li><a href="#dss_othermap">Other Map-Like Container Options</a></li>
				80	</ul></li>
Daniel Berlin	7ea44dc	2007-09-24 17:52:25 +0000	[diff] [blame]	81	<li><a href="#ds_bit">BitVector-like containers</a>
				82	<ul>
				83	<li><a href="#dss_bitvector">A dense bitvector</a></li>
				84	<li><a href="#dss_sparsebitvector">A sparse bitvector</a></li>
				85	</ul></li>
Dan Gohman	f17a25c	2007-07-18 16:29:46 +0000	[diff] [blame]	86	</ul>
				87	</li>
				88	<li><a href="#common">Helpful Hints for Common Operations</a>
				89	<ul>
				90	<li><a href="#inspection">Basic Inspection and Traversal Routines</a>
				91	<ul>
				92	<li><a href="#iterate_function">Iterating over the <tt>BasicBlock</tt>s
				93	in a <tt>Function</tt></a> </li>
				94	<li><a href="#iterate_basicblock">Iterating over the <tt>Instruction</tt>s
				95	in a <tt>BasicBlock</tt></a> </li>
				96	<li><a href="#iterate_institer">Iterating over the <tt>Instruction</tt>s
				97	in a <tt>Function</tt></a> </li>
				98	<li><a href="#iterate_convert">Turning an iterator into a
				99	class pointer</a> </li>
				100	<li><a href="#iterate_complex">Finding call sites: a more
				101	complex example</a> </li>
				102	<li><a href="#calls_and_invokes">Treating calls and invokes
				103	the same way</a> </li>
				104	<li><a href="#iterate_chains">Iterating over def-use &
				105	use-def chains</a> </li>
Chris Lattner	0665e1f	2008-01-03 16:56:04 +0000	[diff] [blame]	106	<li><a href="#iterate_preds">Iterating over predecessors &
				107	successors of blocks</a></li>
Dan Gohman	f17a25c	2007-07-18 16:29:46 +0000	[diff] [blame]	108	</ul>
				109	</li>
				110	<li><a href="#simplechanges">Making simple changes</a>
				111	<ul>
				112	<li><a href="#schanges_creating">Creating and inserting new
				113	<tt>Instruction</tt>s</a> </li>
				114	<li><a href="#schanges_deleting">Deleting <tt>Instruction</tt>s</a> </li>
				115	<li><a href="#schanges_replacing">Replacing an <tt>Instruction</tt>
				116	with another <tt>Value</tt></a> </li>
				117	<li><a href="#schanges_deletingGV">Deleting <tt>GlobalVariable</tt>s</a> </li>
				118	</ul>
				119	</li>
				120	<!--
				121	<li>Working with the Control Flow Graph
				122	<ul>
				123	<li>Accessing predecessors and successors of a <tt>BasicBlock</tt>
				124	<li>
				125	<li>
				126	</ul>
				127	-->
				128	</ul>
				129	</li>
				130
				131	<li><a href="#advanced">Advanced Topics</a>
				132	<ul>
				133	<li><a href="#TypeResolve">LLVM Type Resolution</a>
				134	<ul>
				135	<li><a href="#BuildRecType">Basic Recursive Type Construction</a></li>
				136	<li><a href="#refineAbstractTypeTo">The <tt>refineAbstractTypeTo</tt> method</a></li>
				137	<li><a href="#PATypeHolder">The PATypeHolder Class</a></li>
				138	<li><a href="#AbstractTypeUser">The AbstractTypeUser Class</a></li>
				139	</ul></li>
				140
Gabor Greif	92e8776	2008-06-16 21:06:12 +0000	[diff] [blame]	141	<li><a href="#SymbolTable">The <tt>ValueSymbolTable</tt> and <tt>TypeSymbolTable</tt> classes</a></li>
				142	<li><a href="#UserLayout">The <tt>User</tt> and owned <tt>Use</tt> classes' memory layout</a></li>
Dan Gohman	f17a25c	2007-07-18 16:29:46 +0000	[diff] [blame]	143	</ul></li>
				144
				145	<li><a href="#coreclasses">The Core LLVM Class Hierarchy Reference</a>
				146	<ul>
				147	<li><a href="#Type">The <tt>Type</tt> class</a> </li>
				148	<li><a href="#Module">The <tt>Module</tt> class</a></li>
				149	<li><a href="#Value">The <tt>Value</tt> class</a>
				150	<ul>
				151	<li><a href="#User">The <tt>User</tt> class</a>
				152	<ul>
				153	<li><a href="#Instruction">The <tt>Instruction</tt> class</a></li>
				154	<li><a href="#Constant">The <tt>Constant</tt> class</a>
				155	<ul>
				156	<li><a href="#GlobalValue">The <tt>GlobalValue</tt> class</a>
				157	<ul>
				158	<li><a href="#Function">The <tt>Function</tt> class</a></li>
				159	<li><a href="#GlobalVariable">The <tt>GlobalVariable</tt> class</a></li>
				160	</ul>
				161	</li>
				162	</ul>
				163	</li>
				164	</ul>
				165	</li>
				166	<li><a href="#BasicBlock">The <tt>BasicBlock</tt> class</a></li>
				167	<li><a href="#Argument">The <tt>Argument</tt> class</a></li>
				168	</ul>
				169	</li>
				170	</ul>
				171	</li>
				172	</ol>
				173
				174	<div class="doc_author">
				175	<p>Written by <a href="mailto:sabre@nondot.org">Chris Lattner</a>,
				176	<a href="mailto:dhurjati@cs.uiuc.edu">Dinakar Dhurjati</a>,
Gabor Greif	92e8776	2008-06-16 21:06:12 +0000	[diff] [blame]	177	<a href="mailto:ggreif@gmail.com">Gabor Greif</a>,
				178	<a href="mailto:jstanley@cs.uiuc.edu">Joel Stanley</a> and
Dan Gohman	f17a25c	2007-07-18 16:29:46 +0000	[diff] [blame]	179	<a href="mailto:rspencer@x10sys.com">Reid Spencer</a></p>
				180	</div>
				181
				182	<!-- *********************************************************************** -->
				183	<div class="doc_section">
				184	<a name="introduction">Introduction </a>
				185	</div>
				186	<!-- *********************************************************************** -->
				187
				188	<div class="doc_text">
				189
				190	<p>This document is meant to highlight some of the important classes and
				191	interfaces available in the LLVM source-base. This manual is not
				192	intended to explain what LLVM is, how it works, and what LLVM code looks
				193	like. It assumes that you know the basics of LLVM and are interested
				194	in writing transformations or otherwise analyzing or manipulating the
				195	code.</p>
				196
				197	<p>This document should get you oriented so that you can find your
				198	way in the continuously growing source code that makes up the LLVM
				199	infrastructure. Note that this manual is not intended to serve as a
				200	replacement for reading the source code, so if you think there should be
				201	a method in one of these classes to do something, but it's not listed,
				202	check the source. Links to the <a href="/doxygen/">doxygen</a> sources
				203	are provided to make this as easy as possible.</p>
				204
				205	<p>The first section of this document describes general information that is
				206	useful to know when working in the LLVM infrastructure, and the second describes
				207	the Core LLVM classes. In the future this manual will be extended with
				208	information describing how to use extension libraries, such as dominator
				209	information, CFG traversal routines, and useful utilities like the <tt><a
				210	href="/doxygen/InstVisitor_8h-source.html">InstVisitor</a></tt> template.</p>
				211
				212	</div>
				213
				214	<!-- *********************************************************************** -->
				215	<div class="doc_section">
				216	<a name="general">General Information</a>
				217	</div>
				218	<!-- *********************************************************************** -->
				219
				220	<div class="doc_text">
				221
				222	<p>This section contains general information that is useful if you are working
				223	in the LLVM source-base, but that isn't specific to any particular API.</p>
				224
				225	</div>
				226
				227	<!-- ======================================================================= -->
				228	<div class="doc_subsection">
				229	<a name="stl">The C++ Standard Template Library</a>
				230	</div>
				231
				232	<div class="doc_text">
				233
				234	<p>LLVM makes heavy use of the C++ Standard Template Library (STL),
				235	perhaps much more than you are used to, or have seen before. Because of
				236	this, you might want to do a little background reading in the
				237	techniques used and capabilities of the library. There are many good
				238	pages that discuss the STL, and several books on the subject that you
				239	can get, so it will not be discussed in this document.</p>
				240
				241	<p>Here are some useful links:</p>
				242
				243	<ol>
				244
				245	<li><a href="http://www.dinkumware.com/refxcpp.html">Dinkumware C++ Library
				246	reference</a> - an excellent reference for the STL and other parts of the
				247	standard C++ library.</li>
				248
				249	<li><a href="http://www.tempest-sw.com/cpp/">C++ In a Nutshell</a> - This is an
				250	O'Reilly book in the making. It has a decent
				251	Standard Library
				252	Reference that rivals Dinkumware's, and is unfortunately no longer free since the book has been
				253	published.</li>
				254
				255	<li><a href="http://www.parashift.com/c++-faq-lite/">C++ Frequently Asked
				256	Questions</a></li>
				257
				258	<li><a href="http://www.sgi.com/tech/stl/">SGI's STL Programmer's Guide</a> -
				259	Contains a useful <a
				260	href="http://www.sgi.com/tech/stl/stl_introduction.html">Introduction to the
				261	STL</a>.</li>
				262
				263	<li><a href="http://www.research.att.com/%7Ebs/C++.html">Bjarne Stroustrup's C++
				264	Page</a></li>
				265
				266	<li><a href="http://64.78.49.204/">
				267	Bruce Eckel's Thinking in C++, 2nd ed. Volume 2 Revision 4.0 (even better, get
				268	the book).</a></li>
				269
				270	</ol>
				271
				272	<p>You are also encouraged to take a look at the <a
				273	href="CodingStandards.html">LLVM Coding Standards</a> guide which focuses on how
				274	to write maintainable code more than where to put your curly braces.</p>
				275
				276	</div>
				277
				278	<!-- ======================================================================= -->
				279	<div class="doc_subsection">
				280	<a name="stl">Other useful references</a>
				281	</div>
				282
				283	<div class="doc_text">
				284
				285	<ol>
				286	<li><a href="http://www.psc.edu/%7Esemke/cvs_branches.html">CVS
				287	Branch and Tag Primer</a></li>
				288	<li><a href="http://www.fortran-2000.com/ArnaudRecipes/sharedlib.html">Using
				289	static and shared libraries across platforms</a></li>
				290	</ol>
				291
				292	</div>
				293
				294	<!-- *********************************************************************** -->
				295	<div class="doc_section">
				296	<a name="apis">Important and useful LLVM APIs</a>
				297	</div>
				298	<!-- *********************************************************************** -->
				299
				300	<div class="doc_text">
				301
				302	<p>Here we highlight some LLVM APIs that are generally useful and good to
				303	know about when writing transformations.</p>
				304
				305	</div>
				306
				307	<!-- ======================================================================= -->
				308	<div class="doc_subsection">
				309	<a name="isa">The <tt>isa<></tt>, <tt>cast<></tt> and
				310	<tt>dyn_cast<></tt> templates</a>
				311	</div>
				312
				313	<div class="doc_text">
				314
				315	<p>The LLVM source-base makes extensive use of a custom form of RTTI.
				316	These templates have many similarities to the C++ <tt>dynamic_cast<></tt>
				317	operator, but they don't have some drawbacks (primarily stemming from
				318	the fact that <tt>dynamic_cast<></tt> only works on classes that
				319	have a v-table). Because they are used so often, you must know what they
				320	do and how they work. All of these templates are defined in the <a
				321	href="/doxygen/Casting_8h-source.html"><tt>llvm/Support/Casting.h</tt></a>
				322	file (note that you very rarely have to include this file directly).</p>
				323
				324	<dl>
				325	<dt><tt>isa<></tt>: </dt>
				326
				327	<dd><p>The <tt>isa<></tt> operator works exactly like the Java
				328	"<tt>instanceof</tt>" operator. It returns true or false depending on whether
				329	a reference or pointer points to an instance of the specified class. This can
				330	be very useful for constraint checking of various sorts (example below).</p>
				331	</dd>
				332
				333	<dt><tt>cast<></tt>: </dt>
				334
				335	<dd><p>The <tt>cast<></tt> operator is a "checked cast" operation. It
Chris Lattner	1d5610a	2008-06-20 05:03:17 +0000	[diff] [blame]	336	converts a pointer or reference from a base class to a derived class, causing
Dan Gohman	f17a25c	2007-07-18 16:29:46 +0000	[diff] [blame]	337	an assertion failure if it is not really an instance of the right type. This
				338	should be used in cases where you have some information that makes you believe
				339	that something is of the right type. An example of the <tt>isa<></tt>
				340	and <tt>cast<></tt> template is:</p>
				341
				342	<div class="doc_code">
				343	<pre>
				344	static bool isLoopInvariant(const <a href="#Value">Value</a> V, const Loop L) {
				345	if (isa<<a href="#Constant">Constant</a>>(V) \|\| isa<<a href="#Argument">Argument</a>>(V) \|\| isa<<a href="#GlobalValue">GlobalValue</a>>(V))
				346	return true;
				347
				348	// <i>Otherwise, it must be an instruction...</i>
				349	return !L->contains(cast<<a href="#Instruction">Instruction</a>>(V)->getParent());
				350	}
				351	</pre>
				352	</div>
				353
				354	<p>Note that you should <b>not</b> use an <tt>isa<></tt> test followed
				355	by a <tt>cast<></tt>, for that use the <tt>dyn_cast<></tt>
				356	operator.</p>
				357
				358	</dd>
				359
				360	<dt><tt>dyn_cast<></tt>:</dt>
				361
				362	<dd><p>The <tt>dyn_cast<></tt> operator is a "checking cast" operation.
				363	It checks to see if the operand is of the specified type, and if so, returns a
				364	pointer to it (this operator does not work with references). If the operand is
				365	not of the correct type, a null pointer is returned. Thus, this works very
				366	much like the <tt>dynamic_cast<></tt> operator in C++, and should be
				367	used in the same circumstances. Typically, the <tt>dyn_cast<></tt>
				368	operator is used in an <tt>if</tt> statement or some other flow control
				369	statement like this:</p>
				370
				371	<div class="doc_code">
				372	<pre>
				373	if (<a href="#AllocationInst">AllocationInst</a> *AI = dyn_cast<<a href="#AllocationInst">AllocationInst</a>>(Val)) {
				374	// <i>...</i>
				375	}
				376	</pre>
				377	</div>
				378
				379	<p>This form of the <tt>if</tt> statement effectively combines together a call
				380	to <tt>isa<></tt> and a call to <tt>cast<></tt> into one
				381	statement, which is very convenient.</p>
				382
				383	<p>Note that the <tt>dyn_cast<></tt> operator, like C++'s
				384	<tt>dynamic_cast<></tt> or Java's <tt>instanceof</tt> operator, can be
				385	abused. In particular, you should not use big chained <tt>if/then/else</tt>
				386	blocks to check for lots of different variants of classes. If you find
				387	yourself wanting to do this, it is much cleaner and more efficient to use the
				388	<tt>InstVisitor</tt> class to dispatch over the instruction type directly.</p>
				389
				390	</dd>
				391
				392	<dt><tt>cast_or_null<></tt>: </dt>
				393
				394	<dd><p>The <tt>cast_or_null<></tt> operator works just like the
				395	<tt>cast<></tt> operator, except that it allows for a null pointer as an
				396	argument (which it then propagates). This can sometimes be useful, allowing
				397	you to combine several null checks into one.</p></dd>
				398
				399	<dt><tt>dyn_cast_or_null<></tt>: </dt>
				400
				401	<dd><p>The <tt>dyn_cast_or_null<></tt> operator works just like the
				402	<tt>dyn_cast<></tt> operator, except that it allows for a null pointer
				403	as an argument (which it then propagates). This can sometimes be useful,
				404	allowing you to combine several null checks into one.</p></dd>
				405
				406	</dl>
				407
				408	<p>These five templates can be used with any classes, whether they have a
				409	v-table or not. To add support for these templates, you simply need to add
				410	<tt>classof</tt> static methods to the class you are interested casting
				411	to. Describing this is currently outside the scope of this document, but there
				412	are lots of examples in the LLVM source base.</p>
				413
				414	</div>
				415
				416	<!-- ======================================================================= -->
				417	<div class="doc_subsection">
				418	<a name="DEBUG">The <tt>DEBUG()</tt> macro and <tt>-debug</tt> option</a>
				419	</div>
				420
				421	<div class="doc_text">
				422
				423	<p>Often when working on your pass you will put a bunch of debugging printouts
				424	and other code into your pass. After you get it working, you want to remove
				425	it, but you may need it again in the future (to work out new bugs that you run
				426	across).</p>
				427
				428	<p> Naturally, because of this, you don't want to delete the debug printouts,
				429	but you don't want them to always be noisy. A standard compromise is to comment
				430	them out, allowing you to enable them if you need them in the future.</p>
				431
				432	<p>The "<tt><a href="/doxygen/Debug_8h-source.html">llvm/Support/Debug.h</a></tt>"
				433	file provides a macro named <tt>DEBUG()</tt> that is a much nicer solution to
				434	this problem. Basically, you can put arbitrary code into the argument of the
				435	<tt>DEBUG</tt> macro, and it is only executed if '<tt>opt</tt>' (or any other
				436	tool) is run with the '<tt>-debug</tt>' command line argument:</p>
				437
				438	<div class="doc_code">
				439	<pre>
				440	DOUT << "I am here!\n";
				441	</pre>
				442	</div>
				443
				444	<p>Then you can run your pass like this:</p>
				445
				446	<div class="doc_code">
				447	<pre>
				448	$ opt < a.bc > /dev/null -mypass
				449	<i><no output></i>
				450	$ opt < a.bc > /dev/null -mypass -debug
				451	I am here!
				452	</pre>
				453	</div>
				454
				455	<p>Using the <tt>DEBUG()</tt> macro instead of a home-brewed solution allows you
				456	to not have to create "yet another" command line option for the debug output for
				457	your pass. Note that <tt>DEBUG()</tt> macros are disabled for optimized builds,
				458	so they do not cause a performance impact at all (for the same reason, they
				459	should also not contain side-effects!).</p>
				460
				461	<p>One additional nice thing about the <tt>DEBUG()</tt> macro is that you can
				462	enable or disable it directly in gdb. Just use "<tt>set DebugFlag=0</tt>" or
				463	"<tt>set DebugFlag=1</tt>" from the gdb if the program is running. If the
				464	program hasn't been started yet, you can always just run it with
				465	<tt>-debug</tt>.</p>
				466
				467	</div>
				468
				469	<!-- _______________________________________________________________________ -->
				470	<div class="doc_subsubsection">
				471	<a name="DEBUG_TYPE">Fine grained debug info with <tt>DEBUG_TYPE</tt> and
				472	the <tt>-debug-only</tt> option</a>
				473	</div>
				474
				475	<div class="doc_text">
				476
				477	<p>Sometimes you may find yourself in a situation where enabling <tt>-debug</tt>
				478	just turns on <b>too much</b> information (such as when working on the code
				479	generator). If you want to enable debug information with more fine-grained
				480	control, you define the <tt>DEBUG_TYPE</tt> macro and the <tt>-debug</tt> only
				481	option as follows:</p>
				482
				483	<div class="doc_code">
				484	<pre>
				485	DOUT << "No debug type\n";
				486	#undef DEBUG_TYPE
				487	#define DEBUG_TYPE "foo"
				488	DOUT << "'foo' debug type\n";
				489	#undef DEBUG_TYPE
				490	#define DEBUG_TYPE "bar"
				491	DOUT << "'bar' debug type\n";
				492	#undef DEBUG_TYPE
				493	#define DEBUG_TYPE ""
				494	DOUT << "No debug type (2)\n";
				495	</pre>
				496	</div>
				497
				498	<p>Then you can run your pass like this:</p>
				499
				500	<div class="doc_code">
				501	<pre>
				502	$ opt < a.bc > /dev/null -mypass
				503	<i><no output></i>
				504	$ opt < a.bc > /dev/null -mypass -debug
				505	No debug type
				506	'foo' debug type
				507	'bar' debug type
				508	No debug type (2)
				509	$ opt < a.bc > /dev/null -mypass -debug-only=foo
				510	'foo' debug type
				511	$ opt < a.bc > /dev/null -mypass -debug-only=bar
				512	'bar' debug type
				513	</pre>
				514	</div>
				515
				516	<p>Of course, in practice, you should only set <tt>DEBUG_TYPE</tt> at the top of
				517	a file, to specify the debug type for the entire module (if you do this before
				518	you <tt>#include "llvm/Support/Debug.h"</tt>, you don't have to insert the ugly
				519	<tt>#undef</tt>'s). Also, you should use names more meaningful than "foo" and
				520	"bar", because there is no system in place to ensure that names do not
				521	conflict. If two different modules use the same string, they will all be turned
				522	on when the name is specified. This allows, for example, all debug information
				523	for instruction scheduling to be enabled with <tt>-debug-type=InstrSched</tt>,
				524	even if the source lives in multiple files.</p>
				525
				526	</div>
				527
				528	<!-- ======================================================================= -->
				529	<div class="doc_subsection">
				530	<a name="Statistic">The <tt>Statistic</tt> class & <tt>-stats</tt>
				531	option</a>
				532	</div>
				533
				534	<div class="doc_text">
				535
				536	<p>The "<tt><a
				537	href="/doxygen/Statistic_8h-source.html">llvm/ADT/Statistic.h</a></tt>" file
				538	provides a class named <tt>Statistic</tt> that is used as a unified way to
				539	keep track of what the LLVM compiler is doing and how effective various
				540	optimizations are. It is useful to see what optimizations are contributing to
				541	making a particular program run faster.</p>
				542
				543	<p>Often you may run your pass on some big program, and you're interested to see
				544	how many times it makes a certain transformation. Although you can do this with
				545	hand inspection, or some ad-hoc method, this is a real pain and not very useful
				546	for big programs. Using the <tt>Statistic</tt> class makes it very easy to
				547	keep track of this information, and the calculated information is presented in a
				548	uniform manner with the rest of the passes being executed.</p>
				549
				550	<p>There are many examples of <tt>Statistic</tt> uses, but the basics of using
				551	it are as follows:</p>
				552
				553	<ol>
				554	<li><p>Define your statistic like this:</p>
				555
				556	<div class="doc_code">
				557	<pre>
				558	#define <a href="#DEBUG_TYPE">DEBUG_TYPE</a> "mypassname" <i>// This goes before any #includes.</i>
				559	STATISTIC(NumXForms, "The # of times I did stuff");
				560	</pre>
				561	</div>
				562
				563	<p>The <tt>STATISTIC</tt> macro defines a static variable, whose name is
				564	specified by the first argument. The pass name is taken from the DEBUG_TYPE
				565	macro, and the description is taken from the second argument. The variable
				566	defined ("NumXForms" in this case) acts like an unsigned integer.</p></li>
				567
				568	<li><p>Whenever you make a transformation, bump the counter:</p>
				569
				570	<div class="doc_code">
				571	<pre>
				572	++NumXForms; // <i>I did stuff!</i>
				573	</pre>
				574	</div>
				575
				576	</li>
				577	</ol>
				578
				579	<p>That's all you have to do. To get '<tt>opt</tt>' to print out the
				580	statistics gathered, use the '<tt>-stats</tt>' option:</p>
				581
				582	<div class="doc_code">
				583	<pre>
				584	$ opt -stats -mypassname < program.bc > /dev/null
				585	<i>... statistics output ...</i>
				586	</pre>
				587	</div>
				588
				589	<p> When running <tt>opt</tt> on a C file from the SPEC benchmark
				590	suite, it gives a report that looks like this:</p>
				591
				592	<div class="doc_code">
				593	<pre>
				594	7646 bitcodewriter - Number of normal instructions
				595	725 bitcodewriter - Number of oversized instructions
				596	129996 bitcodewriter - Number of bitcode bytes written
				597	2817 raise - Number of insts DCEd or constprop'd
				598	3213 raise - Number of cast-of-self removed
				599	5046 raise - Number of expression trees converted
				600	75 raise - Number of other getelementptr's formed
				601	138 raise - Number of load/store peepholes
				602	42 deadtypeelim - Number of unused typenames removed from symtab
				603	392 funcresolve - Number of varargs functions resolved
				604	27 globaldce - Number of global variables removed
				605	2 adce - Number of basic blocks removed
				606	134 cee - Number of branches revectored
				607	49 cee - Number of setcc instruction eliminated
				608	532 gcse - Number of loads removed
				609	2919 gcse - Number of instructions removed
				610	86 indvars - Number of canonical indvars added
				611	87 indvars - Number of aux indvars removed
				612	25 instcombine - Number of dead inst eliminate
				613	434 instcombine - Number of insts combined
				614	248 licm - Number of load insts hoisted
				615	1298 licm - Number of insts hoisted to a loop pre-header
				616	3 licm - Number of insts hoisted to multiple loop preds (bad, no loop pre-header)
				617	75 mem2reg - Number of alloca's promoted
				618	1444 cfgsimplify - Number of blocks simplified
				619	</pre>
				620	</div>
				621
				622	<p>Obviously, with so many optimizations, having a unified framework for this
				623	stuff is very nice. Making your pass fit well into the framework makes it more
				624	maintainable and useful.</p>
				625
				626	</div>
				627
				628	<!-- ======================================================================= -->
				629	<div class="doc_subsection">
				630	<a name="ViewGraph">Viewing graphs while debugging code</a>
				631	</div>
				632
				633	<div class="doc_text">
				634
				635	<p>Several of the important data structures in LLVM are graphs: for example
				636	CFGs made out of LLVM <a href="#BasicBlock">BasicBlock</a>s, CFGs made out of
				637	LLVM <a href="CodeGenerator.html#machinebasicblock">MachineBasicBlock</a>s, and
				638	<a href="CodeGenerator.html#selectiondag_intro">Instruction Selection
				639	DAGs</a>. In many cases, while debugging various parts of the compiler, it is
				640	nice to instantly visualize these graphs.</p>
				641
				642	<p>LLVM provides several callbacks that are available in a debug build to do
				643	exactly that. If you call the <tt>Function::viewCFG()</tt> method, for example,
				644	the current LLVM tool will pop up a window containing the CFG for the function
				645	where each basic block is a node in the graph, and each node contains the
				646	instructions in the block. Similarly, there also exists
				647	<tt>Function::viewCFGOnly()</tt> (does not include the instructions), the
				648	<tt>MachineFunction::viewCFG()</tt> and <tt>MachineFunction::viewCFGOnly()</tt>,
				649	and the <tt>SelectionDAG::viewGraph()</tt> methods. Within GDB, for example,
				650	you can usually use something like <tt>call DAG.viewGraph()</tt> to pop
				651	up a window. Alternatively, you can sprinkle calls to these functions in your
				652	code in places you want to debug.</p>
				653
				654	<p>Getting this to work requires a small amount of configuration. On Unix
				655	systems with X11, install the <a href="http://www.graphviz.org">graphviz</a>
				656	toolkit, and make sure 'dot' and 'gv' are in your path. If you are running on
				657	Mac OS/X, download and install the Mac OS/X <a
				658	href="http://www.pixelglow.com/graphviz/">Graphviz program</a>, and add
				659	<tt>/Applications/Graphviz.app/Contents/MacOS/</tt> (or wherever you install
				660	it) to your path. Once in your system and path are set up, rerun the LLVM
				661	configure script and rebuild LLVM to enable this functionality.</p>
				662
				663	<p><tt>SelectionDAG</tt> has been extended to make it easier to locate
				664	<i>interesting</i> nodes in large complex graphs. From gdb, if you
				665	<tt>call DAG.setGraphColor(<i>node</i>, "<i>color</i>")</tt>, then the
				666	next <tt>call DAG.viewGraph()</tt> would highlight the node in the
				667	specified color (choices of colors can be found at <a
				668	href="http://www.graphviz.org/doc/info/colors.html">colors</a>.) More
				669	complex node attributes can be provided with <tt>call
				670	DAG.setGraphAttrs(<i>node</i>, "<i>attributes</i>")</tt> (choices can be
				671	found at <a href="http://www.graphviz.org/doc/info/attrs.html">Graph
				672	Attributes</a>.) If you want to restart and clear all the current graph
				673	attributes, then you can <tt>call DAG.clearGraphAttrs()</tt>. </p>
				674
				675	</div>
				676
				677	<!-- *********************************************************************** -->
				678	<div class="doc_section">
				679	<a name="datastructure">Picking the Right Data Structure for a Task</a>
				680	</div>
				681	<!-- *********************************************************************** -->
				682
				683	<div class="doc_text">
				684
				685	<p>LLVM has a plethora of data structures in the <tt>llvm/ADT/</tt> directory,
				686	and we commonly use STL data structures. This section describes the trade-offs
				687	you should consider when you pick one.</p>
				688
				689	<p>
				690	The first step is a choose your own adventure: do you want a sequential
				691	container, a set-like container, or a map-like container? The most important
				692	thing when choosing a container is the algorithmic properties of how you plan to
				693	access the container. Based on that, you should use:</p>
				694
				695	<ul>
				696	<li>a <a href="#ds_map">map-like</a> container if you need efficient look-up
				697	of an value based on another value. Map-like containers also support
				698	efficient queries for containment (whether a key is in the map). Map-like
				699	containers generally do not support efficient reverse mapping (values to
				700	keys). If you need that, use two maps. Some map-like containers also
				701	support efficient iteration through the keys in sorted order. Map-like
				702	containers are the most expensive sort, only use them if you need one of
				703	these capabilities.</li>
				704
				705	<li>a <a href="#ds_set">set-like</a> container if you need to put a bunch of
				706	stuff into a container that automatically eliminates duplicates. Some
				707	set-like containers support efficient iteration through the elements in
				708	sorted order. Set-like containers are more expensive than sequential
				709	containers.
				710	</li>
				711
				712	<li>a <a href="#ds_sequential">sequential</a> container provides
				713	the most efficient way to add elements and keeps track of the order they are
				714	added to the collection. They permit duplicates and support efficient
				715	iteration, but do not support efficient look-up based on a key.
				716	</li>
				717
Daniel Berlin	7ea44dc	2007-09-24 17:52:25 +0000	[diff] [blame]	718	<li>a <a href="#ds_bit">bit</a> container provides an efficient way to store and
				719	perform set operations on sets of numeric id's, while automatically
				720	eliminating duplicates. Bit containers require a maximum of 1 bit for each
				721	identifier you want to store.
				722	</li>
Dan Gohman	f17a25c	2007-07-18 16:29:46 +0000	[diff] [blame]	723	</ul>
				724
				725	<p>
				726	Once the proper category of container is determined, you can fine tune the
				727	memory use, constant factors, and cache behaviors of access by intelligently
				728	picking a member of the category. Note that constant factors and cache behavior
				729	can be a big deal. If you have a vector that usually only contains a few
				730	elements (but could contain many), for example, it's much better to use
				731	<a href="#dss_smallvector">SmallVector</a> than <a href="#dss_vector">vector</a>
				732	. Doing so avoids (relatively) expensive malloc/free calls, which dwarf the
				733	cost of adding the elements to the container. </p>
				734
				735	</div>
				736
				737	<!-- ======================================================================= -->
				738	<div class="doc_subsection">
				739	<a name="ds_sequential">Sequential Containers (std::vector, std::list, etc)</a>
				740	</div>
				741
				742	<div class="doc_text">
				743	There are a variety of sequential containers available for you, based on your
				744	needs. Pick the first in this section that will do what you want.
				745	</div>
				746
				747	<!-- _______________________________________________________________________ -->
				748	<div class="doc_subsubsection">
				749	<a name="dss_fixedarrays">Fixed Size Arrays</a>
				750	</div>
				751
				752	<div class="doc_text">
				753	<p>Fixed size arrays are very simple and very fast. They are good if you know
				754	exactly how many elements you have, or you have a (low) upper bound on how many
				755	you have.</p>
				756	</div>
				757
				758	<!-- _______________________________________________________________________ -->
				759	<div class="doc_subsubsection">
				760	<a name="dss_heaparrays">Heap Allocated Arrays</a>
				761	</div>
				762
				763	<div class="doc_text">
				764	<p>Heap allocated arrays (new[] + delete[]) are also simple. They are good if
				765	the number of elements is variable, if you know how many elements you will need
				766	before the array is allocated, and if the array is usually large (if not,
				767	consider a <a href="#dss_smallvector">SmallVector</a>). The cost of a heap
				768	allocated array is the cost of the new/delete (aka malloc/free). Also note that
				769	if you are allocating an array of a type with a constructor, the constructor and
				770	destructors will be run for every element in the array (re-sizable vectors only
				771	construct those elements actually used).</p>
				772	</div>
				773
				774	<!-- _______________________________________________________________________ -->
				775	<div class="doc_subsubsection">
				776	<a name="dss_smallvector">"llvm/ADT/SmallVector.h"</a>
				777	</div>
				778
				779	<div class="doc_text">
				780	<p><tt>SmallVector<Type, N></tt> is a simple class that looks and smells
				781	just like <tt>vector<Type></tt>:
				782	it supports efficient iteration, lays out elements in memory order (so you can
				783	do pointer arithmetic between elements), supports efficient push_back/pop_back
				784	operations, supports efficient random access to its elements, etc.</p>
				785
				786	<p>The advantage of SmallVector is that it allocates space for
				787	some number of elements (N) <b>in the object itself</b>. Because of this, if
				788	the SmallVector is dynamically smaller than N, no malloc is performed. This can
				789	be a big win in cases where the malloc/free call is far more expensive than the
				790	code that fiddles around with the elements.</p>
				791
				792	<p>This is good for vectors that are "usually small" (e.g. the number of
				793	predecessors/successors of a block is usually less than 8). On the other hand,
				794	this makes the size of the SmallVector itself large, so you don't want to
				795	allocate lots of them (doing so will waste a lot of space). As such,
				796	SmallVectors are most useful when on the stack.</p>
				797
				798	<p>SmallVector also provides a nice portable and efficient replacement for
				799	<tt>alloca</tt>.</p>
				800
				801	</div>
				802
				803	<!-- _______________________________________________________________________ -->
				804	<div class="doc_subsubsection">
				805	<a name="dss_vector"><vector></a>
				806	</div>
				807
				808	<div class="doc_text">
				809	<p>
				810	std::vector is well loved and respected. It is useful when SmallVector isn't:
				811	when the size of the vector is often large (thus the small optimization will
				812	rarely be a benefit) or if you will be allocating many instances of the vector
				813	itself (which would waste space for elements that aren't in the container).
				814	vector is also useful when interfacing with code that expects vectors :).
				815	</p>
				816
				817	<p>One worthwhile note about std::vector: avoid code like this:</p>
				818
				819	<div class="doc_code">
				820	<pre>
				821	for ( ... ) {
				822	std::vector<foo> V;
				823	use V;
				824	}
				825	</pre>
				826	</div>
				827
				828	<p>Instead, write this as:</p>
				829
				830	<div class="doc_code">
				831	<pre>
				832	std::vector<foo> V;
				833	for ( ... ) {
				834	use V;
				835	V.clear();
				836	}
				837	</pre>
				838	</div>
				839
				840	<p>Doing so will save (at least) one heap allocation and free per iteration of
				841	the loop.</p>
				842
				843	</div>
				844
				845	<!-- _______________________________________________________________________ -->
				846	<div class="doc_subsubsection">
				847	<a name="dss_deque"><deque></a>
				848	</div>
				849
				850	<div class="doc_text">
				851	<p>std::deque is, in some senses, a generalized version of std::vector. Like
				852	std::vector, it provides constant time random access and other similar
				853	properties, but it also provides efficient access to the front of the list. It
				854	does not guarantee continuity of elements within memory.</p>
				855
				856	<p>In exchange for this extra flexibility, std::deque has significantly higher
				857	constant factor costs than std::vector. If possible, use std::vector or
				858	something cheaper.</p>
				859	</div>
				860
				861	<!-- _______________________________________________________________________ -->
				862	<div class="doc_subsubsection">
				863	<a name="dss_list"><list></a>
				864	</div>
				865
				866	<div class="doc_text">
				867	<p>std::list is an extremely inefficient class that is rarely useful.
				868	It performs a heap allocation for every element inserted into it, thus having an
				869	extremely high constant factor, particularly for small data types. std::list
				870	also only supports bidirectional iteration, not random access iteration.</p>
				871
				872	<p>In exchange for this high cost, std::list supports efficient access to both
				873	ends of the list (like std::deque, but unlike std::vector or SmallVector). In
				874	addition, the iterator invalidation characteristics of std::list are stronger
				875	than that of a vector class: inserting or removing an element into the list does
				876	not invalidate iterator or pointers to other elements in the list.</p>
				877	</div>
				878
				879	<!-- _______________________________________________________________________ -->
				880	<div class="doc_subsubsection">
				881	<a name="dss_ilist">llvm/ADT/ilist</a>
				882	</div>
				883
				884	<div class="doc_text">
				885	<p><tt>ilist<T></tt> implements an 'intrusive' doubly-linked list. It is
				886	intrusive, because it requires the element to store and provide access to the
				887	prev/next pointers for the list.</p>
				888
				889	<p>ilist has the same drawbacks as std::list, and additionally requires an
				890	ilist_traits implementation for the element type, but it provides some novel
				891	characteristics. In particular, it can efficiently store polymorphic objects,
				892	the traits class is informed when an element is inserted or removed from the
				893	list, and ilists are guaranteed to support a constant-time splice operation.
				894	</p>
				895
				896	<p>These properties are exactly what we want for things like Instructions and
				897	basic blocks, which is why these are implemented with ilists.</p>
				898	</div>
				899
				900	<!-- _______________________________________________________________________ -->
				901	<div class="doc_subsubsection">
				902	<a name="dss_other">Other Sequential Container options</a>
				903	</div>
				904
				905	<div class="doc_text">
				906	<p>Other STL containers are available, such as std::string.</p>
				907
				908	<p>There are also various STL adapter classes such as std::queue,
				909	std::priority_queue, std::stack, etc. These provide simplified access to an
				910	underlying container but don't affect the cost of the container itself.</p>
				911
				912	</div>
				913
				914
				915	<!-- ======================================================================= -->
				916	<div class="doc_subsection">
				917	<a name="ds_set">Set-Like Containers (std::set, SmallSet, SetVector, etc)</a>
				918	</div>
				919
				920	<div class="doc_text">
				921
				922	<p>Set-like containers are useful when you need to canonicalize multiple values
				923	into a single representation. There are several different choices for how to do
				924	this, providing various trade-offs.</p>
				925
				926	</div>
				927
				928
				929	<!-- _______________________________________________________________________ -->
				930	<div class="doc_subsubsection">
				931	<a name="dss_sortedvectorset">A sorted 'vector'</a>
				932	</div>
				933
				934	<div class="doc_text">
				935
				936	<p>If you intend to insert a lot of elements, then do a lot of queries, a
				937	great approach is to use a vector (or other sequential container) with
				938	std::sort+std::unique to remove duplicates. This approach works really well if
				939	your usage pattern has these two distinct phases (insert then query), and can be
				940	coupled with a good choice of <a href="#ds_sequential">sequential container</a>.
				941	</p>
				942
				943	<p>
				944	This combination provides the several nice properties: the result data is
				945	contiguous in memory (good for cache locality), has few allocations, is easy to
				946	address (iterators in the final vector are just indices or pointers), and can be
				947	efficiently queried with a standard binary or radix search.</p>
				948
				949	</div>
				950
				951	<!-- _______________________________________________________________________ -->
				952	<div class="doc_subsubsection">
				953	<a name="dss_smallset">"llvm/ADT/SmallSet.h"</a>
				954	</div>
				955
				956	<div class="doc_text">
				957
				958	<p>If you have a set-like data structure that is usually small and whose elements
				959	are reasonably small, a <tt>SmallSet<Type, N></tt> is a good choice. This set
				960	has space for N elements in place (thus, if the set is dynamically smaller than
				961	N, no malloc traffic is required) and accesses them with a simple linear search.
				962	When the set grows beyond 'N' elements, it allocates a more expensive representation that
				963	guarantees efficient access (for most types, it falls back to std::set, but for
				964	pointers it uses something far better, <a
				965	href="#dss_smallptrset">SmallPtrSet</a>).</p>
				966
				967	<p>The magic of this class is that it handles small sets extremely efficiently,
				968	but gracefully handles extremely large sets without loss of efficiency. The
				969	drawback is that the interface is quite small: it supports insertion, queries
				970	and erasing, but does not support iteration.</p>
				971
				972	</div>
				973
				974	<!-- _______________________________________________________________________ -->
				975	<div class="doc_subsubsection">
				976	<a name="dss_smallptrset">"llvm/ADT/SmallPtrSet.h"</a>
				977	</div>
				978
				979	<div class="doc_text">
				980
				981	<p>SmallPtrSet has all the advantages of SmallSet (and a SmallSet of pointers is
				982	transparently implemented with a SmallPtrSet), but also supports iterators. If
				983	more than 'N' insertions are performed, a single quadratically
				984	probed hash table is allocated and grows as needed, providing extremely
				985	efficient access (constant time insertion/deleting/queries with low constant
				986	factors) and is very stingy with malloc traffic.</p>
				987
				988	<p>Note that, unlike std::set, the iterators of SmallPtrSet are invalidated
				989	whenever an insertion occurs. Also, the values visited by the iterators are not
				990	visited in sorted order.</p>
				991
				992	</div>
				993
				994	<!-- _______________________________________________________________________ -->
				995	<div class="doc_subsubsection">
Chris Lattner	77ab46d	2007-09-30 00:58:59 +0000	[diff] [blame]	996	<a name="dss_denseset">"llvm/ADT/DenseSet.h"</a>
				997	</div>
				998
				999	<div class="doc_text">
				1000
				1001	<p>
				1002	DenseSet is a simple quadratically probed hash table. It excels at supporting
				1003	small values: it uses a single allocation to hold all of the pairs that
				1004	are currently inserted in the set. DenseSet is a great way to unique small
				1005	values that are not simple pointers (use <a
				1006	href="#dss_smallptrset">SmallPtrSet</a> for pointers). Note that DenseSet has
				1007	the same requirements for the value type that <a
				1008	href="#dss_densemap">DenseMap</a> has.
				1009	</p>
				1010
				1011	</div>
				1012
				1013	<!-- _______________________________________________________________________ -->
				1014	<div class="doc_subsubsection">
Dan Gohman	f17a25c	2007-07-18 16:29:46 +0000	[diff] [blame]	1015	<a name="dss_FoldingSet">"llvm/ADT/FoldingSet.h"</a>
				1016	</div>
				1017
				1018	<div class="doc_text">
				1019
				1020	<p>
				1021	FoldingSet is an aggregate class that is really good at uniquing
				1022	expensive-to-create or polymorphic objects. It is a combination of a chained
				1023	hash table with intrusive links (uniqued objects are required to inherit from
				1024	FoldingSetNode) that uses <a href="#dss_smallvector">SmallVector</a> as part of
				1025	its ID process.</p>
				1026
				1027	<p>Consider a case where you want to implement a "getOrCreateFoo" method for
				1028	a complex object (for example, a node in the code generator). The client has a
				1029	description of what it wants to generate (it knows the opcode and all the
				1030	operands), but we don't want to 'new' a node, then try inserting it into a set
				1031	only to find out it already exists, at which point we would have to delete it
				1032	and return the node that already exists.
				1033	</p>
				1034
				1035	<p>To support this style of client, FoldingSet perform a query with a
				1036	FoldingSetNodeID (which wraps SmallVector) that can be used to describe the
				1037	element that we want to query for. The query either returns the element
				1038	matching the ID or it returns an opaque ID that indicates where insertion should
				1039	take place. Construction of the ID usually does not require heap traffic.</p>
				1040
				1041	<p>Because FoldingSet uses intrusive links, it can support polymorphic objects
				1042	in the set (for example, you can have SDNode instances mixed with LoadSDNodes).
				1043	Because the elements are individually allocated, pointers to the elements are
				1044	stable: inserting or removing elements does not invalidate any pointers to other
				1045	elements.
				1046	</p>
				1047
				1048	</div>
				1049
				1050	<!-- _______________________________________________________________________ -->
				1051	<div class="doc_subsubsection">
				1052	<a name="dss_set"><set></a>
				1053	</div>
				1054
				1055	<div class="doc_text">
				1056
				1057	<p><tt>std::set</tt> is a reasonable all-around set class, which is decent at
				1058	many things but great at nothing. std::set allocates memory for each element
				1059	inserted (thus it is very malloc intensive) and typically stores three pointers
				1060	per element in the set (thus adding a large amount of per-element space
				1061	overhead). It offers guaranteed log(n) performance, which is not particularly
				1062	fast from a complexity standpoint (particularly if the elements of the set are
				1063	expensive to compare, like strings), and has extremely high constant factors for
				1064	lookup, insertion and removal.</p>
				1065
				1066	<p>The advantages of std::set are that its iterators are stable (deleting or
				1067	inserting an element from the set does not affect iterators or pointers to other
				1068	elements) and that iteration over the set is guaranteed to be in sorted order.
				1069	If the elements in the set are large, then the relative overhead of the pointers
				1070	and malloc traffic is not a big deal, but if the elements of the set are small,
				1071	std::set is almost never a good choice.</p>
				1072
				1073	</div>
				1074
				1075	<!-- _______________________________________________________________________ -->
				1076	<div class="doc_subsubsection">
				1077	<a name="dss_setvector">"llvm/ADT/SetVector.h"</a>
				1078	</div>
				1079
				1080	<div class="doc_text">
				1081	<p>LLVM's SetVector<Type> is an adapter class that combines your choice of
				1082	a set-like container along with a <a href="#ds_sequential">Sequential
				1083	Container</a>. The important property
				1084	that this provides is efficient insertion with uniquing (duplicate elements are
				1085	ignored) with iteration support. It implements this by inserting elements into
				1086	both a set-like container and the sequential container, using the set-like
				1087	container for uniquing and the sequential container for iteration.
				1088	</p>
				1089
				1090	<p>The difference between SetVector and other sets is that the order of
				1091	iteration is guaranteed to match the order of insertion into the SetVector.
				1092	This property is really important for things like sets of pointers. Because
				1093	pointer values are non-deterministic (e.g. vary across runs of the program on
				1094	different machines), iterating over the pointers in the set will
				1095	not be in a well-defined order.</p>
				1096
				1097	<p>
				1098	The drawback of SetVector is that it requires twice as much space as a normal
				1099	set and has the sum of constant factors from the set-like container and the
				1100	sequential container that it uses. Use it only if you need to iterate over
				1101	the elements in a deterministic order. SetVector is also expensive to delete
				1102	elements out of (linear time), unless you use it's "pop_back" method, which is
				1103	faster.
				1104	</p>
				1105
				1106	<p>SetVector is an adapter class that defaults to using std::vector and std::set
				1107	for the underlying containers, so it is quite expensive. However,
				1108	<tt>"llvm/ADT/SetVector.h"</tt> also provides a SmallSetVector class, which
				1109	defaults to using a SmallVector and SmallSet of a specified size. If you use
				1110	this, and if your sets are dynamically smaller than N, you will save a lot of
				1111	heap traffic.</p>
				1112
				1113	</div>
				1114
				1115	<!-- _______________________________________________________________________ -->
				1116	<div class="doc_subsubsection">
				1117	<a name="dss_uniquevector">"llvm/ADT/UniqueVector.h"</a>
				1118	</div>
				1119
				1120	<div class="doc_text">
				1121
				1122	<p>
				1123	UniqueVector is similar to <a href="#dss_setvector">SetVector</a>, but it
				1124	retains a unique ID for each element inserted into the set. It internally
				1125	contains a map and a vector, and it assigns a unique ID for each value inserted
				1126	into the set.</p>
				1127
				1128	<p>UniqueVector is very expensive: its cost is the sum of the cost of
				1129	maintaining both the map and vector, it has high complexity, high constant
				1130	factors, and produces a lot of malloc traffic. It should be avoided.</p>
				1131
				1132	</div>
				1133
				1134
				1135	<!-- _______________________________________________________________________ -->
				1136	<div class="doc_subsubsection">
				1137	<a name="dss_otherset">Other Set-Like Container Options</a>
				1138	</div>
				1139
				1140	<div class="doc_text">
				1141
				1142	<p>
				1143	The STL provides several other options, such as std::multiset and the various
				1144	"hash_set" like containers (whether from C++ TR1 or from the SGI library).</p>
				1145
				1146	<p>std::multiset is useful if you're not interested in elimination of
				1147	duplicates, but has all the drawbacks of std::set. A sorted vector (where you
				1148	don't delete duplicate entries) or some other approach is almost always
				1149	better.</p>
				1150
				1151	<p>The various hash_set implementations (exposed portably by
				1152	"llvm/ADT/hash_set") is a simple chained hashtable. This algorithm is as malloc
				1153	intensive as std::set (performing an allocation for each element inserted,
				1154	thus having really high constant factors) but (usually) provides O(1)
				1155	insertion/deletion of elements. This can be useful if your elements are large
				1156	(thus making the constant-factor cost relatively low) or if comparisons are
				1157	expensive. Element iteration does not visit elements in a useful order.</p>
				1158
				1159	</div>
				1160
				1161	<!-- ======================================================================= -->
				1162	<div class="doc_subsection">
				1163	<a name="ds_map">Map-Like Containers (std::map, DenseMap, etc)</a>
				1164	</div>
				1165
				1166	<div class="doc_text">
				1167	Map-like containers are useful when you want to associate data to a key. As
				1168	usual, there are a lot of different ways to do this. :)
				1169	</div>
				1170
				1171	<!-- _______________________________________________________________________ -->
				1172	<div class="doc_subsubsection">
				1173	<a name="dss_sortedvectormap">A sorted 'vector'</a>
				1174	</div>
				1175
				1176	<div class="doc_text">
				1177
				1178	<p>
				1179	If your usage pattern follows a strict insert-then-query approach, you can
				1180	trivially use the same approach as <a href="#dss_sortedvectorset">sorted vectors
				1181	for set-like containers</a>. The only difference is that your query function
				1182	(which uses std::lower_bound to get efficient log(n) lookup) should only compare
				1183	the key, not both the key and value. This yields the same advantages as sorted
				1184	vectors for sets.
				1185	</p>
				1186	</div>
				1187
				1188	<!-- _______________________________________________________________________ -->
				1189	<div class="doc_subsubsection">
				1190	<a name="dss_stringmap">"llvm/ADT/StringMap.h"</a>
				1191	</div>
				1192
				1193	<div class="doc_text">
				1194
				1195	<p>
				1196	Strings are commonly used as keys in maps, and they are difficult to support
				1197	efficiently: they are variable length, inefficient to hash and compare when
				1198	long, expensive to copy, etc. StringMap is a specialized container designed to
				1199	cope with these issues. It supports mapping an arbitrary range of bytes to an
				1200	arbitrary other object.</p>
				1201
				1202	<p>The StringMap implementation uses a quadratically-probed hash table, where
				1203	the buckets store a pointer to the heap allocated entries (and some other
				1204	stuff). The entries in the map must be heap allocated because the strings are
				1205	variable length. The string data (key) and the element object (value) are
				1206	stored in the same allocation with the string data immediately after the element
				1207	object. This container guarantees the "<tt>(char*)(&Value+1)</tt>" points
				1208	to the key string for a value.</p>
				1209
				1210	<p>The StringMap is very fast for several reasons: quadratic probing is very
				1211	cache efficient for lookups, the hash value of strings in buckets is not
				1212	recomputed when lookup up an element, StringMap rarely has to touch the
				1213	memory for unrelated objects when looking up a value (even when hash collisions
				1214	happen), hash table growth does not recompute the hash values for strings
				1215	already in the table, and each pair in the map is store in a single allocation
				1216	(the string data is stored in the same allocation as the Value of a pair).</p>
				1217
				1218	<p>StringMap also provides query methods that take byte ranges, so it only ever
				1219	copies a string if a value is inserted into the table.</p>
				1220	</div>
				1221
				1222	<!-- _______________________________________________________________________ -->
				1223	<div class="doc_subsubsection">
				1224	<a name="dss_indexedmap">"llvm/ADT/IndexedMap.h"</a>
				1225	</div>
				1226
				1227	<div class="doc_text">
				1228	<p>
				1229	IndexedMap is a specialized container for mapping small dense integers (or
				1230	values that can be mapped to small dense integers) to some other type. It is
				1231	internally implemented as a vector with a mapping function that maps the keys to
				1232	the dense integer range.
				1233	</p>
				1234
				1235	<p>
				1236	This is useful for cases like virtual registers in the LLVM code generator: they
				1237	have a dense mapping that is offset by a compile-time constant (the first
				1238	virtual register ID).</p>
				1239
				1240	</div>
				1241
				1242	<!-- _______________________________________________________________________ -->
				1243	<div class="doc_subsubsection">
				1244	<a name="dss_densemap">"llvm/ADT/DenseMap.h"</a>
				1245	</div>
				1246
				1247	<div class="doc_text">
				1248
				1249	<p>
				1250	DenseMap is a simple quadratically probed hash table. It excels at supporting
				1251	small keys and values: it uses a single allocation to hold all of the pairs that
				1252	are currently inserted in the map. DenseMap is a great way to map pointers to
				1253	pointers, or map other small types to each other.
				1254	</p>
				1255
				1256	<p>
				1257	There are several aspects of DenseMap that you should be aware of, however. The
				1258	iterators in a densemap are invalidated whenever an insertion occurs, unlike
				1259	map. Also, because DenseMap allocates space for a large number of key/value
				1260	pairs (it starts with 64 by default), it will waste a lot of space if your keys
				1261	or values are large. Finally, you must implement a partial specialization of
Chris Lattner	92eea07	2007-09-17 18:34:04 +0000	[diff] [blame]	1262	DenseMapInfo for the key that you want, if it isn't already supported. This
Dan Gohman	f17a25c	2007-07-18 16:29:46 +0000	[diff] [blame]	1263	is required to tell DenseMap about two special marker values (which can never be
				1264	inserted into the map) that it needs internally.</p>
				1265
				1266	</div>
				1267
				1268	<!-- _______________________________________________________________________ -->
				1269	<div class="doc_subsubsection">
				1270	<a name="dss_map"><map></a>
				1271	</div>
				1272
				1273	<div class="doc_text">
				1274
				1275	<p>
				1276	std::map has similar characteristics to <a href="#dss_set">std::set</a>: it uses
				1277	a single allocation per pair inserted into the map, it offers log(n) lookup with
				1278	an extremely large constant factor, imposes a space penalty of 3 pointers per
				1279	pair in the map, etc.</p>
				1280
				1281	<p>std::map is most useful when your keys or values are very large, if you need
				1282	to iterate over the collection in sorted order, or if you need stable iterators
				1283	into the map (i.e. they don't get invalidated if an insertion or deletion of
				1284	another element takes place).</p>
				1285
				1286	</div>
				1287
				1288	<!-- _______________________________________________________________________ -->
				1289	<div class="doc_subsubsection">
				1290	<a name="dss_othermap">Other Map-Like Container Options</a>
				1291	</div>
				1292
				1293	<div class="doc_text">
				1294
				1295	<p>
				1296	The STL provides several other options, such as std::multimap and the various
				1297	"hash_map" like containers (whether from C++ TR1 or from the SGI library).</p>
				1298
				1299	<p>std::multimap is useful if you want to map a key to multiple values, but has
				1300	all the drawbacks of std::map. A sorted vector or some other approach is almost
				1301	always better.</p>
				1302
				1303	<p>The various hash_map implementations (exposed portably by
				1304	"llvm/ADT/hash_map") are simple chained hash tables. This algorithm is as
				1305	malloc intensive as std::map (performing an allocation for each element
				1306	inserted, thus having really high constant factors) but (usually) provides O(1)
				1307	insertion/deletion of elements. This can be useful if your elements are large
				1308	(thus making the constant-factor cost relatively low) or if comparisons are
				1309	expensive. Element iteration does not visit elements in a useful order.</p>
				1310
				1311	</div>
				1312
Daniel Berlin	7ea44dc	2007-09-24 17:52:25 +0000	[diff] [blame]	1313	<!-- ======================================================================= -->
				1314	<div class="doc_subsection">
				1315	<a name="ds_bit">Bit storage containers (BitVector, SparseBitVector)</a>
				1316	</div>
				1317
				1318	<div class="doc_text">
Chris Lattner	62a4eae	2007-09-25 22:37:50 +0000	[diff] [blame]	1319	<p>Unlike the other containers, there are only two bit storage containers, and
				1320	choosing when to use each is relatively straightforward.</p>
				1321
				1322	<p>One additional option is
				1323	<tt>std::vector<bool></tt>: we discourage its use for two reasons 1) the
				1324	implementation in many common compilers (e.g. commonly available versions of
				1325	GCC) is extremely inefficient and 2) the C++ standards committee is likely to
				1326	deprecate this container and/or change it significantly somehow. In any case,
				1327	please don't use it.</p>
Daniel Berlin	7ea44dc	2007-09-24 17:52:25 +0000	[diff] [blame]	1328	</div>
				1329
				1330	<!-- _______________________________________________________________________ -->
				1331	<div class="doc_subsubsection">
				1332	<a name="dss_bitvector">BitVector</a>
				1333	</div>
				1334
				1335	<div class="doc_text">
				1336	<p> The BitVector container provides a fixed size set of bits for manipulation.
				1337	It supports individual bit setting/testing, as well as set operations. The set
				1338	operations take time O(size of bitvector), but operations are performed one word
				1339	at a time, instead of one bit at a time. This makes the BitVector very fast for
				1340	set operations compared to other containers. Use the BitVector when you expect
				1341	the number of set bits to be high (IE a dense set).
				1342	</p>
				1343	</div>
				1344
				1345	<!-- _______________________________________________________________________ -->
				1346	<div class="doc_subsubsection">
				1347	<a name="dss_sparsebitvector">SparseBitVector</a>
				1348	</div>
				1349
				1350	<div class="doc_text">
				1351	<p> The SparseBitVector container is much like BitVector, with one major
				1352	difference: Only the bits that are set, are stored. This makes the
				1353	SparseBitVector much more space efficient than BitVector when the set is sparse,
				1354	as well as making set operations O(number of set bits) instead of O(size of
				1355	universe). 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
				1356	(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).
				1357	</p>
				1358	</div>
Dan Gohman	f17a25c	2007-07-18 16:29:46 +0000	[diff] [blame]	1359
				1360	<!-- *********************************************************************** -->
				1361	<div class="doc_section">
				1362	<a name="common">Helpful Hints for Common Operations</a>
				1363	</div>
				1364	<!-- *********************************************************************** -->
				1365
				1366	<div class="doc_text">
				1367
				1368	<p>This section describes how to perform some very simple transformations of
				1369	LLVM code. This is meant to give examples of common idioms used, showing the
				1370	practical side of LLVM transformations. <p> Because this is a "how-to" section,
				1371	you should also read about the main classes that you will be working with. The
				1372	<a href="#coreclasses">Core LLVM Class Hierarchy Reference</a> contains details
				1373	and descriptions of the main classes that you should know about.</p>
				1374
				1375	</div>
				1376
				1377	<!-- NOTE: this section should be heavy on example code -->
				1378	<!-- ======================================================================= -->
				1379	<div class="doc_subsection">
				1380	<a name="inspection">Basic Inspection and Traversal Routines</a>
				1381	</div>
				1382
				1383	<div class="doc_text">
				1384
				1385	<p>The LLVM compiler infrastructure have many different data structures that may
				1386	be traversed. Following the example of the C++ standard template library, the
				1387	techniques used to traverse these various data structures are all basically the
				1388	same. For a enumerable sequence of values, the <tt>XXXbegin()</tt> function (or
				1389	method) returns an iterator to the start of the sequence, the <tt>XXXend()</tt>
				1390	function returns an iterator pointing to one past the last valid element of the
				1391	sequence, and there is some <tt>XXXiterator</tt> data type that is common
				1392	between the two operations.</p>
				1393
				1394	<p>Because the pattern for iteration is common across many different aspects of
				1395	the program representation, the standard template library algorithms may be used
				1396	on them, and it is easier to remember how to iterate. First we show a few common
				1397	examples of the data structures that need to be traversed. Other data
				1398	structures are traversed in very similar ways.</p>
				1399
				1400	</div>
				1401
				1402	<!-- _______________________________________________________________________ -->
				1403	<div class="doc_subsubsection">
				1404	<a name="iterate_function">Iterating over the </a><a
				1405	href="#BasicBlock"><tt>BasicBlock</tt></a>s in a <a
				1406	href="#Function"><tt>Function</tt></a>
				1407	</div>
				1408
				1409	<div class="doc_text">
				1410
				1411	<p>It's quite common to have a <tt>Function</tt> instance that you'd like to
				1412	transform in some way; in particular, you'd like to manipulate its
				1413	<tt>BasicBlock</tt>s. To facilitate this, you'll need to iterate over all of
				1414	the <tt>BasicBlock</tt>s that constitute the <tt>Function</tt>. The following is
				1415	an example that prints the name of a <tt>BasicBlock</tt> and the number of
				1416	<tt>Instruction</tt>s it contains:</p>
				1417
				1418	<div class="doc_code">
				1419	<pre>
				1420	// <i>func is a pointer to a Function instance</i>
				1421	for (Function::iterator i = func->begin(), e = func->end(); i != e; ++i)
				1422	// <i>Print out the name of the basic block if it has one, and then the</i>
				1423	// <i>number of instructions that it contains</i>
				1424	llvm::cerr << "Basic block (name=" << i->getName() << ") has "
				1425	<< i->size() << " instructions.\n";
				1426	</pre>
				1427	</div>
				1428
				1429	<p>Note that i can be used as if it were a pointer for the purposes of
				1430	invoking member functions of the <tt>Instruction</tt> class. This is
				1431	because the indirection operator is overloaded for the iterator
				1432	classes. In the above code, the expression <tt>i->size()</tt> is
				1433	exactly equivalent to <tt>(*i).size()</tt> just like you'd expect.</p>
				1434
				1435	</div>
				1436
				1437	<!-- _______________________________________________________________________ -->
				1438	<div class="doc_subsubsection">
				1439	<a name="iterate_basicblock">Iterating over the </a><a
				1440	href="#Instruction"><tt>Instruction</tt></a>s in a <a
				1441	href="#BasicBlock"><tt>BasicBlock</tt></a>
				1442	</div>
				1443
				1444	<div class="doc_text">
				1445
				1446	<p>Just like when dealing with <tt>BasicBlock</tt>s in <tt>Function</tt>s, it's
				1447	easy to iterate over the individual instructions that make up
				1448	<tt>BasicBlock</tt>s. Here's a code snippet that prints out each instruction in
				1449	a <tt>BasicBlock</tt>:</p>
				1450
				1451	<div class="doc_code">
				1452	<pre>
				1453	// <i>blk is a pointer to a BasicBlock instance</i>
				1454	for (BasicBlock::iterator i = blk->begin(), e = blk->end(); i != e; ++i)
				1455	// <i>The next statement works since operator<<(ostream&,...)</i>
				1456	// <i>is overloaded for Instruction&</i>
				1457	llvm::cerr << *i << "\n";
				1458	</pre>
				1459	</div>
				1460
				1461	<p>However, this isn't really the best way to print out the contents of a
				1462	<tt>BasicBlock</tt>! Since the ostream operators are overloaded for virtually
				1463	anything you'll care about, you could have just invoked the print routine on the
				1464	basic block itself: <tt>llvm::cerr << *blk << "\n";</tt>.</p>
				1465
				1466	</div>
				1467
				1468	<!-- _______________________________________________________________________ -->
				1469	<div class="doc_subsubsection">
				1470	<a name="iterate_institer">Iterating over the </a><a
				1471	href="#Instruction"><tt>Instruction</tt></a>s in a <a
				1472	href="#Function"><tt>Function</tt></a>
				1473	</div>
				1474
				1475	<div class="doc_text">
				1476
				1477	<p>If you're finding that you commonly iterate over a <tt>Function</tt>'s
				1478	<tt>BasicBlock</tt>s and then that <tt>BasicBlock</tt>'s <tt>Instruction</tt>s,
				1479	<tt>InstIterator</tt> should be used instead. You'll need to include <a
				1480	href="/doxygen/InstIterator_8h-source.html"><tt>llvm/Support/InstIterator.h</tt></a>,
				1481	and then instantiate <tt>InstIterator</tt>s explicitly in your code. Here's a
				1482	small example that shows how to dump all instructions in a function to the standard error stream:<p>
				1483
				1484	<div class="doc_code">
				1485	<pre>
				1486	#include "<a href="/doxygen/InstIterator_8h-source.html">llvm/Support/InstIterator.h</a>"
				1487
				1488	// <i>F is a pointer to a Function instance</i>
Chris Lattner	fd62ee7	2008-06-04 18:20:42 +0000	[diff] [blame]	1489	for (inst_iterator I = inst_begin(F), E = inst_end(F); I != E; ++I)
				1490	llvm::cerr << *I << "\n";
Dan Gohman	f17a25c	2007-07-18 16:29:46 +0000	[diff] [blame]	1491	</pre>
				1492	</div>
				1493
				1494	<p>Easy, isn't it? You can also use <tt>InstIterator</tt>s to fill a
				1495	work list with its initial contents. For example, if you wanted to
				1496	initialize a work list to contain all instructions in a <tt>Function</tt>
				1497	F, all you would need to do is something like:</p>
				1498
				1499	<div class="doc_code">
				1500	<pre>
				1501	std::set<Instruction*> worklist;
Chris Lattner	fd62ee7	2008-06-04 18:20:42 +0000	[diff] [blame]	1502	// or better yet, SmallPtrSet<Instruction*, 64> worklist;
				1503
				1504	for (inst_iterator I = inst_begin(F), E = inst_end(F); I != E; ++I)
				1505	worklist.insert(&*I);
Dan Gohman	f17a25c	2007-07-18 16:29:46 +0000	[diff] [blame]	1506	</pre>
				1507	</div>
				1508
				1509	<p>The STL set <tt>worklist</tt> would now contain all instructions in the
				1510	<tt>Function</tt> pointed to by F.</p>
				1511
				1512	</div>
				1513
				1514	<!-- _______________________________________________________________________ -->
				1515	<div class="doc_subsubsection">
				1516	<a name="iterate_convert">Turning an iterator into a class pointer (and
				1517	vice-versa)</a>
				1518	</div>
				1519
				1520	<div class="doc_text">
				1521
				1522	<p>Sometimes, it'll be useful to grab a reference (or pointer) to a class
				1523	instance when all you've got at hand is an iterator. Well, extracting
				1524	a reference or a pointer from an iterator is very straight-forward.
				1525	Assuming that <tt>i</tt> is a <tt>BasicBlock::iterator</tt> and <tt>j</tt>
				1526	is a <tt>BasicBlock::const_iterator</tt>:</p>
				1527
				1528	<div class="doc_code">
				1529	<pre>
				1530	Instruction& inst = *i; // <i>Grab reference to instruction reference</i>
				1531	Instruction* pinst = &*i; // <i>Grab pointer to instruction reference</i>
				1532	const Instruction& inst = *j;
				1533	</pre>
				1534	</div>
				1535
				1536	<p>However, the iterators you'll be working with in the LLVM framework are
				1537	special: they will automatically convert to a ptr-to-instance type whenever they
				1538	need to. Instead of dereferencing the iterator and then taking the address of
				1539	the result, you can simply assign the iterator to the proper pointer type and
				1540	you get the dereference and address-of operation as a result of the assignment
				1541	(behind the scenes, this is a result of overloading casting mechanisms). Thus
				1542	the last line of the last example,</p>
				1543
				1544	<div class="doc_code">
				1545	<pre>
Chris Lattner	0665e1f	2008-01-03 16:56:04 +0000	[diff] [blame]	1546	Instruction pinst = &i;
Dan Gohman	f17a25c	2007-07-18 16:29:46 +0000	[diff] [blame]	1547	</pre>
				1548	</div>
				1549
				1550	<p>is semantically equivalent to</p>
				1551
				1552	<div class="doc_code">
				1553	<pre>
Chris Lattner	0665e1f	2008-01-03 16:56:04 +0000	[diff] [blame]	1554	Instruction *pinst = i;
Dan Gohman	f17a25c	2007-07-18 16:29:46 +0000	[diff] [blame]	1555	</pre>
				1556	</div>
				1557
				1558	<p>It's also possible to turn a class pointer into the corresponding iterator,
				1559	and this is a constant time operation (very efficient). The following code
				1560	snippet illustrates use of the conversion constructors provided by LLVM
				1561	iterators. By using these, you can explicitly grab the iterator of something
				1562	without actually obtaining it via iteration over some structure:</p>
				1563
				1564	<div class="doc_code">
				1565	<pre>
				1566	void printNextInstruction(Instruction* inst) {
				1567	BasicBlock::iterator it(inst);
				1568	++it; // <i>After this line, it refers to the instruction after *inst</i>
				1569	if (it != inst->getParent()->end()) llvm::cerr << *it << "\n";
				1570	}
				1571	</pre>
				1572	</div>
				1573
				1574	</div>
				1575
				1576	<!--_______________________________________________________________________-->
				1577	<div class="doc_subsubsection">
				1578	<a name="iterate_complex">Finding call sites: a slightly more complex
				1579	example</a>
				1580	</div>
				1581
				1582	<div class="doc_text">
				1583
				1584	<p>Say that you're writing a FunctionPass and would like to count all the
				1585	locations in the entire module (that is, across every <tt>Function</tt>) where a
				1586	certain function (i.e., some <tt>Function</tt>*) is already in scope. As you'll
				1587	learn later, you may want to use an <tt>InstVisitor</tt> to accomplish this in a
				1588	much more straight-forward manner, but this example will allow us to explore how
				1589	you'd do it if you didn't have <tt>InstVisitor</tt> around. In pseudo-code, this
				1590	is what we want to do:</p>
				1591
				1592	<div class="doc_code">
				1593	<pre>
				1594	initialize callCounter to zero
				1595	for each Function f in the Module
				1596	for each BasicBlock b in f
				1597	for each Instruction i in b
				1598	if (i is a CallInst and calls the given function)
				1599	increment callCounter
				1600	</pre>
				1601	</div>
				1602
				1603	<p>And the actual code is (remember, because we're writing a
				1604	<tt>FunctionPass</tt>, our <tt>FunctionPass</tt>-derived class simply has to
				1605	override the <tt>runOnFunction</tt> method):</p>
				1606
				1607	<div class="doc_code">
				1608	<pre>
				1609	Function* targetFunc = ...;
				1610
				1611	class OurFunctionPass : public FunctionPass {
				1612	public:
				1613	OurFunctionPass(): callCounter(0) { }
				1614
				1615	virtual runOnFunction(Function& F) {
				1616	for (Function::iterator b = F.begin(), be = F.end(); b != be; ++b) {
				1617	for (BasicBlock::iterator i = b->begin(); ie = b->end(); i != ie; ++i) {
				1618	if (<a href="#CallInst">CallInst</a>* callInst = <a href="#isa">dyn_cast</a><<a
				1619	href="#CallInst">CallInst</a>>(&*i)) {
				1620	// <i>We know we've encountered a call instruction, so we</i>
				1621	// <i>need to determine if it's a call to the</i>
Chris Lattner	0665e1f	2008-01-03 16:56:04 +0000	[diff] [blame]	1622	// <i>function pointed to by m_func or not.</i>
Dan Gohman	f17a25c	2007-07-18 16:29:46 +0000	[diff] [blame]	1623	if (callInst->getCalledFunction() == targetFunc)
				1624	++callCounter;
				1625	}
				1626	}
				1627	}
				1628	}
				1629
				1630	private:
Chris Lattner	0665e1f	2008-01-03 16:56:04 +0000	[diff] [blame]	1631	unsigned callCounter;
Dan Gohman	f17a25c	2007-07-18 16:29:46 +0000	[diff] [blame]	1632	};
				1633	</pre>
				1634	</div>
				1635
				1636	</div>
				1637
				1638	<!--_______________________________________________________________________-->
				1639	<div class="doc_subsubsection">
				1640	<a name="calls_and_invokes">Treating calls and invokes the same way</a>
				1641	</div>
				1642
				1643	<div class="doc_text">
				1644
				1645	<p>You may have noticed that the previous example was a bit oversimplified in
				1646	that it did not deal with call sites generated by 'invoke' instructions. In
				1647	this, and in other situations, you may find that you want to treat
				1648	<tt>CallInst</tt>s and <tt>InvokeInst</tt>s the same way, even though their
				1649	most-specific common base class is <tt>Instruction</tt>, which includes lots of
				1650	less closely-related things. For these cases, LLVM provides a handy wrapper
				1651	class called <a
				1652	href="http://llvm.org/doxygen/classllvm_1_1CallSite.html"><tt>CallSite</tt></a>.
				1653	It is essentially a wrapper around an <tt>Instruction</tt> pointer, with some
				1654	methods that provide functionality common to <tt>CallInst</tt>s and
				1655	<tt>InvokeInst</tt>s.</p>
				1656
				1657	<p>This class has "value semantics": it should be passed by value, not by
				1658	reference and it should not be dynamically allocated or deallocated using
				1659	<tt>operator new</tt> or <tt>operator delete</tt>. It is efficiently copyable,
				1660	assignable and constructable, with costs equivalents to that of a bare pointer.
				1661	If you look at its definition, it has only a single pointer member.</p>
				1662
				1663	</div>
				1664
				1665	<!--_______________________________________________________________________-->
				1666	<div class="doc_subsubsection">
				1667	<a name="iterate_chains">Iterating over def-use & use-def chains</a>
				1668	</div>
				1669
				1670	<div class="doc_text">
				1671
				1672	<p>Frequently, we might have an instance of the <a
				1673	href="/doxygen/classllvm_1_1Value.html">Value Class</a> and we want to
				1674	determine which <tt>User</tt>s use the <tt>Value</tt>. The list of all
				1675	<tt>User</tt>s of a particular <tt>Value</tt> is called a <i>def-use</i> chain.
				1676	For example, let's say we have a <tt>Function*</tt> named <tt>F</tt> to a
				1677	particular function <tt>foo</tt>. Finding all of the instructions that
				1678	<i>use</i> <tt>foo</tt> is as simple as iterating over the <i>def-use</i> chain
				1679	of <tt>F</tt>:</p>
				1680
				1681	<div class="doc_code">
				1682	<pre>
Chris Lattner	0665e1f	2008-01-03 16:56:04 +0000	[diff] [blame]	1683	Function *F = ...;
Dan Gohman	f17a25c	2007-07-18 16:29:46 +0000	[diff] [blame]	1684
				1685	for (Value::use_iterator i = F->use_begin(), e = F->use_end(); i != e; ++i)
				1686	if (Instruction Inst = dyn_cast<Instruction>(i)) {
				1687	llvm::cerr << "F is used in instruction:\n";
				1688	llvm::cerr << *Inst << "\n";
				1689	}
				1690	</pre>
				1691	</div>
				1692
				1693	<p>Alternately, it's common to have an instance of the <a
				1694	href="/doxygen/classllvm_1_1User.html">User Class</a> and need to know what
				1695	<tt>Value</tt>s are used by it. The list of all <tt>Value</tt>s used by a
				1696	<tt>User</tt> is known as a <i>use-def</i> chain. Instances of class
				1697	<tt>Instruction</tt> are common <tt>User</tt>s, so we might want to iterate over
				1698	all of the values that a particular instruction uses (that is, the operands of
				1699	the particular <tt>Instruction</tt>):</p>
				1700
				1701	<div class="doc_code">
				1702	<pre>
Chris Lattner	0665e1f	2008-01-03 16:56:04 +0000	[diff] [blame]	1703	Instruction *pi = ...;
Dan Gohman	f17a25c	2007-07-18 16:29:46 +0000	[diff] [blame]	1704
				1705	for (User::op_iterator i = pi->op_begin(), e = pi->op_end(); i != e; ++i) {
Chris Lattner	0665e1f	2008-01-03 16:56:04 +0000	[diff] [blame]	1706	Value v = i;
Dan Gohman	f17a25c	2007-07-18 16:29:46 +0000	[diff] [blame]	1707	// <i>...</i>
				1708	}
				1709	</pre>
				1710	</div>
				1711
				1712	<!--
				1713	def-use chains ("finding all users of"): Value::use_begin/use_end
				1714	use-def chains ("finding all values used"): User::op_begin/op_end [op=operand]
				1715	-->
				1716
				1717	</div>
				1718
Chris Lattner	0665e1f	2008-01-03 16:56:04 +0000	[diff] [blame]	1719	<!--_______________________________________________________________________-->
				1720	<div class="doc_subsubsection">
				1721	<a name="iterate_preds">Iterating over predecessors &
				1722	successors of blocks</a>
				1723	</div>
				1724
				1725	<div class="doc_text">
				1726
				1727	<p>Iterating over the predecessors and successors of a block is quite easy
				1728	with the routines defined in <tt>"llvm/Support/CFG.h"</tt>. Just use code like
				1729	this to iterate over all predecessors of BB:</p>
				1730
				1731	<div class="doc_code">
				1732	<pre>
				1733	#include "llvm/Support/CFG.h"
				1734	BasicBlock *BB = ...;
				1735
				1736	for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI) {
				1737	BasicBlock Pred = PI;
				1738	// <i>...</i>
				1739	}
				1740	</pre>
				1741	</div>
				1742
				1743	<p>Similarly, to iterate over successors use
				1744	succ_iterator/succ_begin/succ_end.</p>
				1745
				1746	</div>
				1747
				1748
Dan Gohman	f17a25c	2007-07-18 16:29:46 +0000	[diff] [blame]	1749	<!-- ======================================================================= -->
				1750	<div class="doc_subsection">
				1751	<a name="simplechanges">Making simple changes</a>
				1752	</div>
				1753
				1754	<div class="doc_text">
				1755
				1756	<p>There are some primitive transformation operations present in the LLVM
				1757	infrastructure that are worth knowing about. When performing
				1758	transformations, it's fairly common to manipulate the contents of basic
				1759	blocks. This section describes some of the common methods for doing so
				1760	and gives example code.</p>
				1761
				1762	</div>
				1763
				1764	<!--_______________________________________________________________________-->
				1765	<div class="doc_subsubsection">
				1766	<a name="schanges_creating">Creating and inserting new
				1767	<tt>Instruction</tt>s</a>
				1768	</div>
				1769
				1770	<div class="doc_text">
				1771
				1772	<p><i>Instantiating Instructions</i></p>
				1773
				1774	<p>Creation of <tt>Instruction</tt>s is straight-forward: simply call the
				1775	constructor for the kind of instruction to instantiate and provide the necessary
				1776	parameters. For example, an <tt>AllocaInst</tt> only <i>requires</i> a
				1777	(const-ptr-to) <tt>Type</tt>. Thus:</p>
				1778
				1779	<div class="doc_code">
				1780	<pre>
Nick Lewycky	c004e5b	2007-12-03 01:52:52 +0000	[diff] [blame]	1781	AllocaInst* ai = new AllocaInst(Type::Int32Ty);
Dan Gohman	f17a25c	2007-07-18 16:29:46 +0000	[diff] [blame]	1782	</pre>
				1783	</div>
				1784
				1785	<p>will create an <tt>AllocaInst</tt> instance that represents the allocation of
				1786	one integer in the current stack frame, at run time. Each <tt>Instruction</tt>
				1787	subclass is likely to have varying default parameters which change the semantics
				1788	of the instruction, so refer to the <a
				1789	href="/doxygen/classllvm_1_1Instruction.html">doxygen documentation for the subclass of
				1790	Instruction</a> that you're interested in instantiating.</p>
				1791
				1792	<p><i>Naming values</i></p>
				1793
				1794	<p>It is very useful to name the values of instructions when you're able to, as
				1795	this facilitates the debugging of your transformations. If you end up looking
				1796	at generated LLVM machine code, you definitely want to have logical names
				1797	associated with the results of instructions! By supplying a value for the
				1798	<tt>Name</tt> (default) parameter of the <tt>Instruction</tt> constructor, you
				1799	associate a logical name with the result of the instruction's execution at
				1800	run time. For example, say that I'm writing a transformation that dynamically
				1801	allocates space for an integer on the stack, and that integer is going to be
				1802	used as some kind of index by some other code. To accomplish this, I place an
				1803	<tt>AllocaInst</tt> at the first point in the first <tt>BasicBlock</tt> of some
				1804	<tt>Function</tt>, and I'm intending to use it within the same
				1805	<tt>Function</tt>. I might do:</p>
				1806
				1807	<div class="doc_code">
				1808	<pre>
Nick Lewycky	c004e5b	2007-12-03 01:52:52 +0000	[diff] [blame]	1809	AllocaInst* pa = new AllocaInst(Type::Int32Ty, 0, "indexLoc");
Dan Gohman	f17a25c	2007-07-18 16:29:46 +0000	[diff] [blame]	1810	</pre>
				1811	</div>
				1812
				1813	<p>where <tt>indexLoc</tt> is now the logical name of the instruction's
				1814	execution value, which is a pointer to an integer on the run time stack.</p>
				1815
				1816	<p><i>Inserting instructions</i></p>
				1817
				1818	<p>There are essentially two ways to insert an <tt>Instruction</tt>
				1819	into an existing sequence of instructions that form a <tt>BasicBlock</tt>:</p>
				1820
				1821	<ul>
				1822	<li>Insertion into an explicit instruction list
				1823
				1824	<p>Given a <tt>BasicBlock* pb</tt>, an <tt>Instruction* pi</tt> within that
				1825	<tt>BasicBlock</tt>, and a newly-created instruction we wish to insert
				1826	before <tt>*pi</tt>, we do the following: </p>
				1827
				1828	<div class="doc_code">
				1829	<pre>
				1830	BasicBlock *pb = ...;
				1831	Instruction *pi = ...;
				1832	Instruction *newInst = new Instruction(...);
				1833
				1834	pb->getInstList().insert(pi, newInst); // <i>Inserts newInst before pi in pb</i>
				1835	</pre>
				1836	</div>
				1837
				1838	<p>Appending to the end of a <tt>BasicBlock</tt> is so common that
				1839	the <tt>Instruction</tt> class and <tt>Instruction</tt>-derived
				1840	classes provide constructors which take a pointer to a
				1841	<tt>BasicBlock</tt> to be appended to. For example code that
				1842	looked like: </p>
				1843
				1844	<div class="doc_code">
				1845	<pre>
				1846	BasicBlock *pb = ...;
				1847	Instruction *newInst = new Instruction(...);
				1848
				1849	pb->getInstList().push_back(newInst); // <i>Appends newInst to pb</i>
				1850	</pre>
				1851	</div>
				1852
				1853	<p>becomes: </p>
				1854
				1855	<div class="doc_code">
				1856	<pre>
				1857	BasicBlock *pb = ...;
				1858	Instruction *newInst = new Instruction(..., pb);
				1859	</pre>
				1860	</div>
				1861
				1862	<p>which is much cleaner, especially if you are creating
				1863	long instruction streams.</p></li>
				1864
				1865	<li>Insertion into an implicit instruction list
				1866
				1867	<p><tt>Instruction</tt> instances that are already in <tt>BasicBlock</tt>s
				1868	are implicitly associated with an existing instruction list: the instruction
				1869	list of the enclosing basic block. Thus, we could have accomplished the same
				1870	thing as the above code without being given a <tt>BasicBlock</tt> by doing:
				1871	</p>
				1872
				1873	<div class="doc_code">
				1874	<pre>
				1875	Instruction *pi = ...;
				1876	Instruction *newInst = new Instruction(...);
				1877
				1878	pi->getParent()->getInstList().insert(pi, newInst);
				1879	</pre>
				1880	</div>
				1881
				1882	<p>In fact, this sequence of steps occurs so frequently that the
				1883	<tt>Instruction</tt> class and <tt>Instruction</tt>-derived classes provide
				1884	constructors which take (as a default parameter) a pointer to an
				1885	<tt>Instruction</tt> which the newly-created <tt>Instruction</tt> should
				1886	precede. That is, <tt>Instruction</tt> constructors are capable of
				1887	inserting the newly-created instance into the <tt>BasicBlock</tt> of a
				1888	provided instruction, immediately before that instruction. Using an
				1889	<tt>Instruction</tt> constructor with a <tt>insertBefore</tt> (default)
				1890	parameter, the above code becomes:</p>
				1891
				1892	<div class="doc_code">
				1893	<pre>
				1894	Instruction* pi = ...;
				1895	Instruction* newInst = new Instruction(..., pi);
				1896	</pre>
				1897	</div>
				1898
				1899	<p>which is much cleaner, especially if you're creating a lot of
				1900	instructions and adding them to <tt>BasicBlock</tt>s.</p></li>
				1901	</ul>
				1902
				1903	</div>
				1904
				1905	<!--_______________________________________________________________________-->
				1906	<div class="doc_subsubsection">
				1907	<a name="schanges_deleting">Deleting <tt>Instruction</tt>s</a>
				1908	</div>
				1909
				1910	<div class="doc_text">
				1911
				1912	<p>Deleting an instruction from an existing sequence of instructions that form a
				1913	<a href="#BasicBlock"><tt>BasicBlock</tt></a> is very straight-forward. First,
				1914	you must have a pointer to the instruction that you wish to delete. Second, you
				1915	need to obtain the pointer to that instruction's basic block. You use the
				1916	pointer to the basic block to get its list of instructions and then use the
				1917	erase function to remove your instruction. For example:</p>
				1918
				1919	<div class="doc_code">
				1920	<pre>
				1921	<a href="#Instruction">Instruction</a> *I = .. ;
Chris Lattner	3db8f77	2008-02-15 22:57:17 +0000	[diff] [blame]	1922	I->eraseFromParent();
Dan Gohman	f17a25c	2007-07-18 16:29:46 +0000	[diff] [blame]	1923	</pre>
				1924	</div>
				1925
				1926	</div>
				1927
				1928	<!--_______________________________________________________________________-->
				1929	<div class="doc_subsubsection">
				1930	<a name="schanges_replacing">Replacing an <tt>Instruction</tt> with another
				1931	<tt>Value</tt></a>
				1932	</div>
				1933
				1934	<div class="doc_text">
				1935
				1936	<p><i>Replacing individual instructions</i></p>
				1937
				1938	<p>Including "<a href="/doxygen/BasicBlockUtils_8h-source.html">llvm/Transforms/Utils/BasicBlockUtils.h</a>"
				1939	permits use of two very useful replace functions: <tt>ReplaceInstWithValue</tt>
				1940	and <tt>ReplaceInstWithInst</tt>.</p>
				1941
				1942	<h4><a name="schanges_deleting">Deleting <tt>Instruction</tt>s</a></h4>
				1943
				1944	<ul>
				1945	<li><tt>ReplaceInstWithValue</tt>
				1946
				1947	<p>This function replaces all uses (within a basic block) of a given
				1948	instruction with a value, and then removes the original instruction. The
				1949	following example illustrates the replacement of the result of a particular
				1950	<tt>AllocaInst</tt> that allocates memory for a single integer with a null
				1951	pointer to an integer.</p>
				1952
				1953	<div class="doc_code">
				1954	<pre>
				1955	AllocaInst* instToReplace = ...;
				1956	BasicBlock::iterator ii(instToReplace);
				1957
				1958	ReplaceInstWithValue(instToReplace->getParent()->getInstList(), ii,
Nick Lewycky	c004e5b	2007-12-03 01:52:52 +0000	[diff] [blame]	1959	Constant::getNullValue(PointerType::get(Type::Int32Ty)));
Dan Gohman	f17a25c	2007-07-18 16:29:46 +0000	[diff] [blame]	1960	</pre></div></li>
				1961
				1962	<li><tt>ReplaceInstWithInst</tt>
				1963
				1964	<p>This function replaces a particular instruction with another
				1965	instruction. The following example illustrates the replacement of one
				1966	<tt>AllocaInst</tt> with another.</p>
				1967
				1968	<div class="doc_code">
				1969	<pre>
				1970	AllocaInst* instToReplace = ...;
				1971	BasicBlock::iterator ii(instToReplace);
				1972
				1973	ReplaceInstWithInst(instToReplace->getParent()->getInstList(), ii,
Nick Lewycky	c004e5b	2007-12-03 01:52:52 +0000	[diff] [blame]	1974	new AllocaInst(Type::Int32Ty, 0, "ptrToReplacedInt"));
Dan Gohman	f17a25c	2007-07-18 16:29:46 +0000	[diff] [blame]	1975	</pre></div></li>
				1976	</ul>
				1977
				1978	<p><i>Replacing multiple uses of <tt>User</tt>s and <tt>Value</tt>s</i></p>
				1979
				1980	<p>You can use <tt>Value::replaceAllUsesWith</tt> and
				1981	<tt>User::replaceUsesOfWith</tt> to change more than one use at a time. See the
				1982	doxygen documentation for the <a href="/doxygen/classllvm_1_1Value.html">Value Class</a>
				1983	and <a href="/doxygen/classllvm_1_1User.html">User Class</a>, respectively, for more
				1984	information.</p>
				1985
				1986	<!-- Value::replaceAllUsesWith User::replaceUsesOfWith Point out:
				1987	include/llvm/Transforms/Utils/ especially BasicBlockUtils.h with:
				1988	ReplaceInstWithValue, ReplaceInstWithInst -->
				1989
				1990	</div>
				1991
				1992	<!--_______________________________________________________________________-->
				1993	<div class="doc_subsubsection">
				1994	<a name="schanges_deletingGV">Deleting <tt>GlobalVariable</tt>s</a>
				1995	</div>
				1996
				1997	<div class="doc_text">
				1998
				1999	<p>Deleting a global variable from a module is just as easy as deleting an
				2000	Instruction. First, you must have a pointer to the global variable that you wish
				2001	to delete. You use this pointer to erase it from its parent, the module.
				2002	For example:</p>
				2003
				2004	<div class="doc_code">
				2005	<pre>
				2006	<a href="#GlobalVariable">GlobalVariable</a> *GV = .. ;
				2007
				2008	GV->eraseFromParent();
				2009	</pre>
				2010	</div>
				2011
				2012	</div>
				2013
				2014	<!-- *********************************************************************** -->
				2015	<div class="doc_section">
				2016	<a name="advanced">Advanced Topics</a>
				2017	</div>
				2018	<!-- *********************************************************************** -->
				2019
				2020	<div class="doc_text">
				2021	<p>
				2022	This section describes some of the advanced or obscure API's that most clients
				2023	do not need to be aware of. These API's tend manage the inner workings of the
				2024	LLVM system, and only need to be accessed in unusual circumstances.
				2025	</p>
				2026	</div>
				2027
				2028	<!-- ======================================================================= -->
				2029	<div class="doc_subsection">
				2030	<a name="TypeResolve">LLVM Type Resolution</a>
				2031	</div>
				2032
				2033	<div class="doc_text">
				2034
				2035	<p>
				2036	The LLVM type system has a very simple goal: allow clients to compare types for
				2037	structural equality with a simple pointer comparison (aka a shallow compare).
				2038	This goal makes clients much simpler and faster, and is used throughout the LLVM
				2039	system.
				2040	</p>
				2041
				2042	<p>
				2043	Unfortunately achieving this goal is not a simple matter. In particular,
				2044	recursive types and late resolution of opaque types makes the situation very
				2045	difficult to handle. Fortunately, for the most part, our implementation makes
				2046	most clients able to be completely unaware of the nasty internal details. The
				2047	primary case where clients are exposed to the inner workings of it are when
				2048	building a recursive type. In addition to this case, the LLVM bitcode reader,
				2049	assembly parser, and linker also have to be aware of the inner workings of this
				2050	system.
				2051	</p>
				2052
				2053	<p>
				2054	For our purposes below, we need three concepts. First, an "Opaque Type" is
				2055	exactly as defined in the <a href="LangRef.html#t_opaque">language
				2056	reference</a>. Second an "Abstract Type" is any type which includes an
				2057	opaque type as part of its type graph (for example "<tt>{ opaque, i32 }</tt>").
				2058	Third, a concrete type is a type that is not an abstract type (e.g. "<tt>{ i32,
				2059	float }</tt>").
				2060	</p>
				2061
				2062	</div>
				2063
				2064	<!-- ______________________________________________________________________ -->
				2065	<div class="doc_subsubsection">
				2066	<a name="BuildRecType">Basic Recursive Type Construction</a>
				2067	</div>
				2068
				2069	<div class="doc_text">
				2070
				2071	<p>
				2072	Because the most common question is "how do I build a recursive type with LLVM",
				2073	we answer it now and explain it as we go. Here we include enough to cause this
				2074	to be emitted to an output .ll file:
				2075	</p>
				2076
				2077	<div class="doc_code">
				2078	<pre>
				2079	%mylist = type { %mylist*, i32 }
				2080	</pre>
				2081	</div>
				2082
				2083	<p>
				2084	To build this, use the following LLVM APIs:
				2085	</p>
				2086
				2087	<div class="doc_code">
				2088	<pre>
				2089	// <i>Create the initial outer struct</i>
				2090	<a href="#PATypeHolder">PATypeHolder</a> StructTy = OpaqueType::get();
				2091	std::vector<const Type*> Elts;
				2092	Elts.push_back(PointerType::get(StructTy));
Nick Lewycky	c004e5b	2007-12-03 01:52:52 +0000	[diff] [blame]	2093	Elts.push_back(Type::Int32Ty);
Dan Gohman	f17a25c	2007-07-18 16:29:46 +0000	[diff] [blame]	2094	StructType *NewSTy = StructType::get(Elts);
				2095
				2096	// <i>At this point, NewSTy = "{ opaque*, i32 }". Tell VMCore that</i>
				2097	// <i>the struct and the opaque type are actually the same.</i>
				2098	cast<OpaqueType>(StructTy.get())-><a href="#refineAbstractTypeTo">refineAbstractTypeTo</a>(NewSTy);
				2099
				2100	// <i>NewSTy is potentially invalidated, but StructTy (a <a href="#PATypeHolder">PATypeHolder</a>) is</i>
				2101	// <i>kept up-to-date</i>
				2102	NewSTy = cast<StructType>(StructTy.get());
				2103
				2104	// <i>Add a name for the type to the module symbol table (optional)</i>
				2105	MyModule->addTypeName("mylist", NewSTy);
				2106	</pre>
				2107	</div>
				2108
				2109	<p>
				2110	This code shows the basic approach used to build recursive types: build a
				2111	non-recursive type using 'opaque', then use type unification to close the cycle.
				2112	The type unification step is performed by the <tt><a
				2113	href="#refineAbstractTypeTo">refineAbstractTypeTo</a></tt> method, which is
				2114	described next. After that, we describe the <a
				2115	href="#PATypeHolder">PATypeHolder class</a>.
				2116	</p>
				2117
				2118	</div>
				2119
				2120	<!-- ______________________________________________________________________ -->
				2121	<div class="doc_subsubsection">
				2122	<a name="refineAbstractTypeTo">The <tt>refineAbstractTypeTo</tt> method</a>
				2123	</div>
				2124
				2125	<div class="doc_text">
				2126	<p>
				2127	The <tt>refineAbstractTypeTo</tt> method starts the type unification process.
				2128	While this method is actually a member of the DerivedType class, it is most
				2129	often used on OpaqueType instances. Type unification is actually a recursive
				2130	process. After unification, types can become structurally isomorphic to
				2131	existing types, and all duplicates are deleted (to preserve pointer equality).
				2132	</p>
				2133
				2134	<p>
				2135	In the example above, the OpaqueType object is definitely deleted.
				2136	Additionally, if there is an "{ \2*, i32}" type already created in the system,
				2137	the pointer and struct type created are <b>also</b> deleted. Obviously whenever
				2138	a type is deleted, any "Type*" pointers in the program are invalidated. As
				2139	such, it is safest to avoid having <i>any</i> "Type*" pointers to abstract types
				2140	live across a call to <tt>refineAbstractTypeTo</tt> (note that non-abstract
				2141	types can never move or be deleted). To deal with this, the <a
				2142	href="#PATypeHolder">PATypeHolder</a> class is used to maintain a stable
				2143	reference to a possibly refined type, and the <a
				2144	href="#AbstractTypeUser">AbstractTypeUser</a> class is used to update more
				2145	complex datastructures.
				2146	</p>
				2147
				2148	</div>
				2149
				2150	<!-- ______________________________________________________________________ -->
				2151	<div class="doc_subsubsection">
				2152	<a name="PATypeHolder">The PATypeHolder Class</a>
				2153	</div>
				2154
				2155	<div class="doc_text">
				2156	<p>
				2157	PATypeHolder is a form of a "smart pointer" for Type objects. When VMCore
				2158	happily goes about nuking types that become isomorphic to existing types, it
				2159	automatically updates all PATypeHolder objects to point to the new type. In the
				2160	example above, this allows the code to maintain a pointer to the resultant
				2161	resolved recursive type, even though the Type*'s are potentially invalidated.
				2162	</p>
				2163
				2164	<p>
				2165	PATypeHolder is an extremely light-weight object that uses a lazy union-find
				2166	implementation to update pointers. For example the pointer from a Value to its
				2167	Type is maintained by PATypeHolder objects.
				2168	</p>
				2169
				2170	</div>
				2171
				2172	<!-- ______________________________________________________________________ -->
				2173	<div class="doc_subsubsection">
				2174	<a name="AbstractTypeUser">The AbstractTypeUser Class</a>
				2175	</div>
				2176
				2177	<div class="doc_text">
				2178
				2179	<p>
				2180	Some data structures need more to perform more complex updates when types get
				2181	resolved. To support this, a class can derive from the AbstractTypeUser class.
				2182	This class
				2183	allows it to get callbacks when certain types are resolved. To register to get
				2184	callbacks for a particular type, the DerivedType::{add/remove}AbstractTypeUser
				2185	methods can be called on a type. Note that these methods only work for <i>
				2186	abstract</i> types. Concrete types (those that do not include any opaque
				2187	objects) can never be refined.
				2188	</p>
				2189	</div>
				2190
				2191
				2192	<!-- ======================================================================= -->
				2193	<div class="doc_subsection">
				2194	<a name="SymbolTable">The <tt>ValueSymbolTable</tt> and
				2195	<tt>TypeSymbolTable</tt> classes</a>
				2196	</div>
				2197
				2198	<div class="doc_text">
				2199	<p>The <tt><a href="http://llvm.org/doxygen/classllvm_1_1ValueSymbolTable.html">
				2200	ValueSymbolTable</a></tt> class provides a symbol table that the <a
				2201	href="#Function"><tt>Function</tt></a> and <a href="#Module">
				2202	<tt>Module</tt></a> classes use for naming value definitions. The symbol table
				2203	can provide a name for any <a href="#Value"><tt>Value</tt></a>.
				2204	The <tt><a href="http://llvm.org/doxygen/classllvm_1_1TypeSymbolTable.html">
				2205	TypeSymbolTable</a></tt> class is used by the <tt>Module</tt> class to store
				2206	names for types.</p>
				2207
				2208	<p>Note that the <tt>SymbolTable</tt> class should not be directly accessed
				2209	by most clients. It should only be used when iteration over the symbol table
				2210	names themselves are required, which is very special purpose. Note that not
				2211	all LLVM
Gabor Greif	92e8776	2008-06-16 21:06:12 +0000	[diff] [blame]	2212	<tt><a href="#Value">Value</a></tt>s have names, and those without names (i.e. they have
Dan Gohman	f17a25c	2007-07-18 16:29:46 +0000	[diff] [blame]	2213	an empty name) do not exist in the symbol table.
				2214	</p>
				2215
				2216	<p>These symbol tables support iteration over the values/types in the symbol
				2217	table with <tt>begin/end/iterator</tt> and supports querying to see if a
				2218	specific name is in the symbol table (with <tt>lookup</tt>). The
				2219	<tt>ValueSymbolTable</tt> class exposes no public mutator methods, instead,
				2220	simply call <tt>setName</tt> on a value, which will autoinsert it into the
				2221	appropriate symbol table. For types, use the Module::addTypeName method to
				2222	insert entries into the symbol table.</p>
				2223
				2224	</div>
				2225
				2226
				2227
Gabor Greif	92e8776	2008-06-16 21:06:12 +0000	[diff] [blame]	2228	<!-- ======================================================================= -->
				2229	<div class="doc_subsection">
				2230	<a name="UserLayout">The <tt>User</tt> and owned <tt>Use</tt> classes' memory layout</a>
				2231	</div>
				2232
				2233	<div class="doc_text">
				2234	<p>The <tt><a href="http://llvm.org/doxygen/classllvm_1_1User.html">
				2235	User</a></tt> class provides a base for expressing the ownership of <tt>User</tt>
				2236	towards other <tt><a href="http://llvm.org/doxygen/classllvm_1_1Value.html">
				2237	Value</a></tt>s. The <tt><a href="http://llvm.org/doxygen/classllvm_1_1Use.html">
Gabor Greif	93b462b	2008-06-18 13:44:57 +0000	[diff] [blame]	2238	Use</a></tt> helper class is employed to do the bookkeeping and to facilitate <i>O(1)</i>
Gabor Greif	92e8776	2008-06-16 21:06:12 +0000	[diff] [blame]	2239	addition and removal.</p>
				2240
Gabor Greif	93b462b	2008-06-18 13:44:57 +0000	[diff] [blame]	2241	<!-- ______________________________________________________________________ -->
				2242	<div class="doc_subsubsection">
				2243	<a name="PATypeHolder">Interaction and relationship between <tt>User</tt> and <tt>Use</tt> objects</a>
				2244	</div>
Gabor Greif	92e8776	2008-06-16 21:06:12 +0000	[diff] [blame]	2245
Gabor Greif	93b462b	2008-06-18 13:44:57 +0000	[diff] [blame]	2246	<div class="doc_text">
				2247	<p>
				2248	A subclass of <tt>User</tt> can choose between incorporating its <tt>Use</tt> objects
Gabor Greif	92e8776	2008-06-16 21:06:12 +0000	[diff] [blame]	2249	or refer to them out-of-line by means of a pointer. A mixed variant
Gabor Greif	93b462b	2008-06-18 13:44:57 +0000	[diff] [blame]	2250	(some <tt>Use</tt>s inline others hung off) is impractical and breaks the invariant
				2251	that the <tt>Use</tt> objects belonging to the same <tt>User</tt> form a contiguous array.
				2252	</p>
				2253	</div>
Gabor Greif	92e8776	2008-06-16 21:06:12 +0000	[diff] [blame]	2254
Gabor Greif	93b462b	2008-06-18 13:44:57 +0000	[diff] [blame]	2255	<p>
				2256	We have 2 different layouts in the <tt>User</tt> (sub)classes:
				2257	<ul>
				2258	<li><p>Layout a)
				2259	The <tt>Use</tt> object(s) are inside (resp. at fixed offset) of the <tt>User</tt>
				2260	object and there are a fixed number of them.</p>
Gabor Greif	92e8776	2008-06-16 21:06:12 +0000	[diff] [blame]	2261
Gabor Greif	93b462b	2008-06-18 13:44:57 +0000	[diff] [blame]	2262	<li><p>Layout b)
				2263	The <tt>Use</tt> object(s) are referenced by a pointer to an
				2264	array from the <tt>User</tt> object and there may be a variable
				2265	number of them.</p>
				2266	</ul>
				2267	<p>
Gabor Greif	92e8776	2008-06-16 21:06:12 +0000	[diff] [blame]	2268	Initially each layout will possess a direct pointer to the
Gabor Greif	93b462b	2008-06-18 13:44:57 +0000	[diff] [blame]	2269	start of the array of <tt>Use</tt>s. Though not mandatory for layout a),
Gabor Greif	92e8776	2008-06-16 21:06:12 +0000	[diff] [blame]	2270	we stick to this redundancy for the sake of simplicity.
Gabor Greif	93b462b	2008-06-18 13:44:57 +0000	[diff] [blame]	2271	The <tt>User</tt> object will also store the number of <tt>Use</tt> objects it
Gabor Greif	92e8776	2008-06-16 21:06:12 +0000	[diff] [blame]	2272	has. (Theoretically this information can also be calculated
Gabor Greif	93b462b	2008-06-18 13:44:57 +0000	[diff] [blame]	2273	given the scheme presented below.)</p>
				2274	<p>
				2275	Special forms of allocation operators (<tt>operator new</tt>)
				2276	will enforce the following memory layouts:</p>
Gabor Greif	92e8776	2008-06-16 21:06:12 +0000	[diff] [blame]	2277
Gabor Greif	93b462b	2008-06-18 13:44:57 +0000	[diff] [blame]	2278	<ul>
				2279	<li><p>Layout a) will be modelled by prepending the <tt>User</tt> object by the <tt>Use[]</tt> array.</p>
Gabor Greif	92e8776	2008-06-16 21:06:12 +0000	[diff] [blame]	2280
Gabor Greif	93b462b	2008-06-18 13:44:57 +0000	[diff] [blame]	2281	<pre>
				2282	...---.---.---.---.-------...
				2283	\| P \| P \| P \| P \| User
				2284	'''---'---'---'---'-------'''
				2285	</pre>
Gabor Greif	92e8776	2008-06-16 21:06:12 +0000	[diff] [blame]	2286
Gabor Greif	93b462b	2008-06-18 13:44:57 +0000	[diff] [blame]	2287	<li><p>Layout b) will be modelled by pointing at the Use[] array.</p>
				2288	<pre>
				2289	.-------...
				2290	\| User
				2291	'-------'''
				2292	\|
				2293	v
				2294	.---.---.---.---...
				2295	\| P \| P \| P \| P \|
				2296	'---'---'---'---'''
				2297	</pre>
				2298	</ul>
				2299	<i>(In the above figures '<tt>P</tt>' stands for the <tt>Use**</tt> that
				2300	is stored in each <tt>Use</tt> object in the member <tt>Use::Prev</tt>)</i>
Gabor Greif	92e8776	2008-06-16 21:06:12 +0000	[diff] [blame]	2301
Gabor Greif	93b462b	2008-06-18 13:44:57 +0000	[diff] [blame]	2302	<!-- ______________________________________________________________________ -->
				2303	<div class="doc_subsubsection">
				2304	<a name="PATypeHolder">The waymarking algorithm</a>
				2305	</div>
Gabor Greif	92e8776	2008-06-16 21:06:12 +0000	[diff] [blame]	2306
Gabor Greif	93b462b	2008-06-18 13:44:57 +0000	[diff] [blame]	2307	<div class="doc_text">
				2308	<p>
				2309	Since the <tt>Use</tt> objects will be deprived of the direct pointer to
				2310	their <tt>User</tt> objects, there must be a fast and exact method to
				2311	recover it. This is accomplished by the following scheme:</p>
				2312	</div>
Gabor Greif	92e8776	2008-06-16 21:06:12 +0000	[diff] [blame]	2313
Gabor Greif	93b462b	2008-06-18 13:44:57 +0000	[diff] [blame]	2314	A bit-encoding in the 2 LSBits (least significant bits) of the <tt>Use::Prev</tt> will allow to find the
				2315	start of the <tt>User</tt> object:
				2316	<ul>
				2317	<li><tt>00</tt> —> binary digit 0</li>
				2318	<li><tt>01</tt> —> binary digit 1</li>
				2319	<li><tt>10</tt> —> stop and calculate (<tt>s</tt>)</li>
				2320	<li><tt>11</tt> —> full stop (<tt>S</tt>)</li>
				2321	</ul>
				2322	<p>
				2323	Given a <tt>Use*</tt>, all we have to do is to walk till we get
				2324	a stop and we either have a <tt>User</tt> immediately behind or
Gabor Greif	92e8776	2008-06-16 21:06:12 +0000	[diff] [blame]	2325	we have to walk to the next stop picking up digits
Gabor Greif	93b462b	2008-06-18 13:44:57 +0000	[diff] [blame]	2326	and calculating the offset:</p>
				2327	<pre>
Gabor Greif	92e8776	2008-06-16 21:06:12 +0000	[diff] [blame]	2328	.---.---.---.---.---.---.---.---.---.---.---.---.---.---.---.---.----------------
				2329	\| 1 \| s \| 1 \| 0 \| 1 \| 0 \| s \| 1 \| 1 \| 0 \| s \| 1 \| 1 \| s \| 1 \| S \| User (or User*)
				2330	'---'---'---'---'---'---'---'---'---'---'---'---'---'---'---'---'----------------
				2331	\|+15 \|+10 \|+6 \|+3 \|+1
				2332	\| \| \| \| \|__>
				2333	\| \| \| \|__________>
				2334	\| \| \|______________________>
				2335	\| \|______________________________________>
				2336	\|__________________________________________________________>
Gabor Greif	93b462b	2008-06-18 13:44:57 +0000	[diff] [blame]	2337	</pre>
				2338	<p>
Gabor Greif	92e8776	2008-06-16 21:06:12 +0000	[diff] [blame]	2339	Only the significant number of bits need to be stored between the
Gabor Greif	93b462b	2008-06-18 13:44:57 +0000	[diff] [blame]	2340	stops, so that the <i>worst case is 20 memory accesses</i> when there are
				2341	1000 <tt>Use</tt> objects associated with a <tt>User</tt>.</p>
Gabor Greif	92e8776	2008-06-16 21:06:12 +0000	[diff] [blame]	2342
Gabor Greif	93b462b	2008-06-18 13:44:57 +0000	[diff] [blame]	2343	<!-- ______________________________________________________________________ -->
				2344	<div class="doc_subsubsection">
				2345	<a name="PATypeHolder">Reference implementation</a>
				2346	</div>
Gabor Greif	92e8776	2008-06-16 21:06:12 +0000	[diff] [blame]	2347
Gabor Greif	93b462b	2008-06-18 13:44:57 +0000	[diff] [blame]	2348	<div class="doc_text">
				2349	<p>
				2350	The following literate Haskell fragment demonstrates the concept:</p>
				2351	</div>
				2352
				2353	<div class="doc_code">
				2354	<pre>
Gabor Greif	92e8776	2008-06-16 21:06:12 +0000	[diff] [blame]	2355	> import Test.QuickCheck
				2356	>
				2357	> digits :: Int -> [Char] -> [Char]
				2358	> digits 0 acc = '0' : acc
				2359	> digits 1 acc = '1' : acc
				2360	> digits n acc = digits (n `div` 2) $ digits (n `mod` 2) acc
				2361	>
				2362	> dist :: Int -> [Char] -> [Char]
				2363	> dist 0 [] = ['S']
				2364	> dist 0 acc = acc
				2365	> dist 1 acc = let r = dist 0 acc in 's' : digits (length r) r
				2366	> dist n acc = dist (n - 1) $ dist 1 acc
				2367	>
				2368	> takeLast n ss = reverse $ take n $ reverse ss
				2369	>
				2370	> test = takeLast 40 $ dist 20 []
				2371	>
Gabor Greif	93b462b	2008-06-18 13:44:57 +0000	[diff] [blame]	2372	</pre>
				2373	</div>
				2374	<p>
				2375	Printing <test> gives: <tt>"1s100000s11010s10100s1111s1010s110s11s1S"</tt></p>
				2376	<p>
				2377	The reverse algorithm computes the length of the string just by examining
				2378	a certain prefix:</p>
Gabor Greif	92e8776	2008-06-16 21:06:12 +0000	[diff] [blame]	2379
Gabor Greif	93b462b	2008-06-18 13:44:57 +0000	[diff] [blame]	2380	<div class="doc_code">
				2381	<pre>
Gabor Greif	92e8776	2008-06-16 21:06:12 +0000	[diff] [blame]	2382	> pref :: [Char] -> Int
				2383	> pref "S" = 1
				2384	> pref ('s':'1':rest) = decode 2 1 rest
				2385	> pref (_:rest) = 1 + pref rest
				2386	>
				2387	> decode walk acc ('0':rest) = decode (walk + 1) (acc * 2) rest
				2388	> decode walk acc ('1':rest) = decode (walk + 1) (acc * 2 + 1) rest
				2389	> decode walk acc _ = walk + acc
				2390	>
Gabor Greif	93b462b	2008-06-18 13:44:57 +0000	[diff] [blame]	2391	</pre>
				2392	</div>
				2393	<p>
				2394	Now, as expected, printing <pref test> gives <tt>40</tt>.</p>
				2395	<p>
				2396	We can <i>quickCheck</i> this with following property:</p>
Gabor Greif	92e8776	2008-06-16 21:06:12 +0000	[diff] [blame]	2397
Gabor Greif	93b462b	2008-06-18 13:44:57 +0000	[diff] [blame]	2398	<div class="doc_code">
				2399	<pre>
Gabor Greif	92e8776	2008-06-16 21:06:12 +0000	[diff] [blame]	2400	> testcase = dist 2000 []
				2401	> testcaseLength = length testcase
				2402	>
				2403	> identityProp n = n > 0 && n <= testcaseLength ==> length arr == pref arr
				2404	> where arr = takeLast n testcase
Gabor Greif	93b462b	2008-06-18 13:44:57 +0000	[diff] [blame]	2405	>
				2406	</pre>
				2407	</div>
				2408	<p>
				2409	As expected <quickCheck identityProp> gives:</p>
Gabor Greif	92e8776	2008-06-16 21:06:12 +0000	[diff] [blame]	2410
Gabor Greif	93b462b	2008-06-18 13:44:57 +0000	[diff] [blame]	2411	<pre>
Gabor Greif	92e8776	2008-06-16 21:06:12 +0000	[diff] [blame]	2412	*Main> quickCheck identityProp
				2413	OK, passed 100 tests.
Gabor Greif	93b462b	2008-06-18 13:44:57 +0000	[diff] [blame]	2414	</pre>
				2415	<p>
				2416	Let's be a bit more exhaustive:</p>
Gabor Greif	92e8776	2008-06-16 21:06:12 +0000	[diff] [blame]	2417
Gabor Greif	93b462b	2008-06-18 13:44:57 +0000	[diff] [blame]	2418	<div class="doc_code">
				2419	<pre>
Gabor Greif	92e8776	2008-06-16 21:06:12 +0000	[diff] [blame]	2420	>
				2421	> deepCheck p = check (defaultConfig { configMaxTest = 500 }) p
				2422	>
Gabor Greif	93b462b	2008-06-18 13:44:57 +0000	[diff] [blame]	2423	</pre>
				2424	</div>
				2425	<p>
				2426	And here is the result of <deepCheck identityProp>:</p>
Gabor Greif	92e8776	2008-06-16 21:06:12 +0000	[diff] [blame]	2427
Gabor Greif	93b462b	2008-06-18 13:44:57 +0000	[diff] [blame]	2428	<pre>
Gabor Greif	92e8776	2008-06-16 21:06:12 +0000	[diff] [blame]	2429	*Main> deepCheck identityProp
				2430	OK, passed 500 tests.
Gabor Greif	92e8776	2008-06-16 21:06:12 +0000	[diff] [blame]	2431	</pre>
				2432
Gabor Greif	93b462b	2008-06-18 13:44:57 +0000	[diff] [blame]	2433	<!-- ______________________________________________________________________ -->
				2434	<div class="doc_subsubsection">
				2435	<a name="PATypeHolder">Tagging considerations</a>
				2436	</div>
				2437
				2438	<p>
				2439	To maintain the invariant that the 2 LSBits of each <tt>Use**</tt> in <tt>Use</tt>
				2440	never change after being set up, setters of <tt>Use::Prev</tt> must re-tag the
				2441	new <tt>Use**</tt> on every modification. Accordingly getters must strip the
				2442	tag bits.</p>
				2443	<p>
				2444	For layout b) instead of the <tt>User</tt> we will find a pointer (<tt>User*</tt> with LSBit set).
				2445	Following this pointer brings us to the <tt>User</tt>. A portable trick will ensure
				2446	that the first bytes of <tt>User</tt> (if interpreted as a pointer) will never have
				2447	the LSBit set.</p>
				2448
Gabor Greif	92e8776	2008-06-16 21:06:12 +0000	[diff] [blame]	2449	</div>
				2450
				2451	<!-- *********************************************************************** -->
Dan Gohman	f17a25c	2007-07-18 16:29:46 +0000	[diff] [blame]	2452	<div class="doc_section">
				2453	<a name="coreclasses">The Core LLVM Class Hierarchy Reference </a>
				2454	</div>
				2455	<!-- *********************************************************************** -->
				2456
				2457	<div class="doc_text">
				2458	<p><tt>#include "<a href="/doxygen/Type_8h-source.html">llvm/Type.h</a>"</tt>
				2459	<br>doxygen info: <a href="/doxygen/classllvm_1_1Type.html">Type Class</a></p>
				2460
				2461	<p>The Core LLVM classes are the primary means of representing the program
				2462	being inspected or transformed. The core LLVM classes are defined in
				2463	header files in the <tt>include/llvm/</tt> directory, and implemented in
				2464	the <tt>lib/VMCore</tt> directory.</p>
				2465
				2466	</div>
				2467
				2468	<!-- ======================================================================= -->
				2469	<div class="doc_subsection">
				2470	<a name="Type">The <tt>Type</tt> class and Derived Types</a>
				2471	</div>
				2472
				2473	<div class="doc_text">
				2474
				2475	<p><tt>Type</tt> is a superclass of all type classes. Every <tt>Value</tt> has
				2476	a <tt>Type</tt>. <tt>Type</tt> cannot be instantiated directly but only
				2477	through its subclasses. Certain primitive types (<tt>VoidType</tt>,
				2478	<tt>LabelType</tt>, <tt>FloatType</tt> and <tt>DoubleType</tt>) have hidden
				2479	subclasses. They are hidden because they offer no useful functionality beyond
				2480	what the <tt>Type</tt> class offers except to distinguish themselves from
				2481	other subclasses of <tt>Type</tt>.</p>
				2482	<p>All other types are subclasses of <tt>DerivedType</tt>. Types can be
				2483	named, but this is not a requirement. There exists exactly
				2484	one instance of a given shape at any one time. This allows type equality to
				2485	be performed with address equality of the Type Instance. That is, given two
				2486	<tt>Type*</tt> values, the types are identical if the pointers are identical.
				2487	</p>
				2488	</div>
				2489
				2490	<!-- _______________________________________________________________________ -->
				2491	<div class="doc_subsubsection">
				2492	<a name="m_Value">Important Public Methods</a>
				2493	</div>
				2494
				2495	<div class="doc_text">
				2496
				2497	<ul>
				2498	<li><tt>bool isInteger() const</tt>: Returns true for any integer type.</li>
				2499
				2500	<li><tt>bool isFloatingPoint()</tt>: Return true if this is one of the two
				2501	floating point types.</li>
				2502
				2503	<li><tt>bool isAbstract()</tt>: Return true if the type is abstract (contains
				2504	an OpaqueType anywhere in its definition).</li>
				2505
				2506	<li><tt>bool isSized()</tt>: Return true if the type has known size. Things
				2507	that don't have a size are abstract types, labels and void.</li>
				2508
				2509	</ul>
				2510	</div>
				2511
				2512	<!-- _______________________________________________________________________ -->
				2513	<div class="doc_subsubsection">
				2514	<a name="m_Value">Important Derived Types</a>
				2515	</div>
				2516	<div class="doc_text">
				2517	<dl>
				2518	<dt><tt>IntegerType</tt></dt>
				2519	<dd>Subclass of DerivedType that represents integer types of any bit width.
				2520	Any bit width between <tt>IntegerType::MIN_INT_BITS</tt> (1) and
				2521	<tt>IntegerType::MAX_INT_BITS</tt> (~8 million) can be represented.
				2522	<ul>
				2523	<li><tt>static const IntegerType* get(unsigned NumBits)</tt>: get an integer
				2524	type of a specific bit width.</li>
				2525	<li><tt>unsigned getBitWidth() const</tt>: Get the bit width of an integer
				2526	type.</li>
				2527	</ul>
				2528	</dd>
				2529	<dt><tt>SequentialType</tt></dt>
				2530	<dd>This is subclassed by ArrayType and PointerType
				2531	<ul>
				2532	<li><tt>const Type * getElementType() const</tt>: Returns the type of each
				2533	of the elements in the sequential type. </li>
				2534	</ul>
				2535	</dd>
				2536	<dt><tt>ArrayType</tt></dt>
				2537	<dd>This is a subclass of SequentialType and defines the interface for array
				2538	types.
				2539	<ul>
				2540	<li><tt>unsigned getNumElements() const</tt>: Returns the number of
				2541	elements in the array. </li>
				2542	</ul>
				2543	</dd>
				2544	<dt><tt>PointerType</tt></dt>
				2545	<dd>Subclass of SequentialType for pointer types.</dd>
				2546	<dt><tt>VectorType</tt></dt>
				2547	<dd>Subclass of SequentialType for vector types. A
				2548	vector type is similar to an ArrayType but is distinguished because it is
				2549	a first class type wherease ArrayType is not. Vector types are used for
				2550	vector operations and are usually small vectors of of an integer or floating
				2551	point type.</dd>
				2552	<dt><tt>StructType</tt></dt>
				2553	<dd>Subclass of DerivedTypes for struct types.</dd>
				2554	<dt><tt><a name="FunctionType">FunctionType</a></tt></dt>
				2555	<dd>Subclass of DerivedTypes for function types.
				2556	<ul>
				2557	<li><tt>bool isVarArg() const</tt>: Returns true if its a vararg
				2558	function</li>
				2559	<li><tt> const Type * getReturnType() const</tt>: Returns the
				2560	return type of the function.</li>
				2561	<li><tt>const Type * getParamType (unsigned i)</tt>: Returns
				2562	the type of the ith parameter.</li>
				2563	<li><tt> const unsigned getNumParams() const</tt>: Returns the
				2564	number of formal parameters.</li>
				2565	</ul>
				2566	</dd>
				2567	<dt><tt>OpaqueType</tt></dt>
				2568	<dd>Sublcass of DerivedType for abstract types. This class
				2569	defines no content and is used as a placeholder for some other type. Note
				2570	that OpaqueType is used (temporarily) during type resolution for forward
				2571	references of types. Once the referenced type is resolved, the OpaqueType
				2572	is replaced with the actual type. OpaqueType can also be used for data
				2573	abstraction. At link time opaque types can be resolved to actual types
				2574	of the same name.</dd>
				2575	</dl>
				2576	</div>
				2577
				2578
				2579
				2580	<!-- ======================================================================= -->
				2581	<div class="doc_subsection">
				2582	<a name="Module">The <tt>Module</tt> class</a>
				2583	</div>
				2584
				2585	<div class="doc_text">
				2586
				2587	<p><tt>#include "<a
				2588	href="/doxygen/Module_8h-source.html">llvm/Module.h</a>"</tt><br> doxygen info:
				2589	<a href="/doxygen/classllvm_1_1Module.html">Module Class</a></p>
				2590
				2591	<p>The <tt>Module</tt> class represents the top level structure present in LLVM
				2592	programs. An LLVM module is effectively either a translation unit of the
				2593	original program or a combination of several translation units merged by the
				2594	linker. The <tt>Module</tt> class keeps track of a list of <a
				2595	href="#Function"><tt>Function</tt></a>s, a list of <a
				2596	href="#GlobalVariable"><tt>GlobalVariable</tt></a>s, and a <a
				2597	href="#SymbolTable"><tt>SymbolTable</tt></a>. Additionally, it contains a few
				2598	helpful member functions that try to make common operations easy.</p>
				2599
				2600	</div>
				2601
				2602	<!-- _______________________________________________________________________ -->
				2603	<div class="doc_subsubsection">
				2604	<a name="m_Module">Important Public Members of the <tt>Module</tt> class</a>
				2605	</div>
				2606
				2607	<div class="doc_text">
				2608
				2609	<ul>
				2610	<li><tt>Module::Module(std::string name = "")</tt></li>
				2611	</ul>
				2612
				2613	<p>Constructing a <a href="#Module">Module</a> is easy. You can optionally
				2614	provide a name for it (probably based on the name of the translation unit).</p>
				2615
				2616	<ul>
				2617	<li><tt>Module::iterator</tt> - Typedef for function list iterator<br>
				2618	<tt>Module::const_iterator</tt> - Typedef for const_iterator.<br>
				2619
				2620	<tt>begin()</tt>, <tt>end()</tt>
				2621	<tt>size()</tt>, <tt>empty()</tt>
				2622
				2623	<p>These are forwarding methods that make it easy to access the contents of
				2624	a <tt>Module</tt> object's <a href="#Function"><tt>Function</tt></a>
				2625	list.</p></li>
				2626
				2627	<li><tt>Module::FunctionListType &getFunctionList()</tt>
				2628
				2629	<p> Returns the list of <a href="#Function"><tt>Function</tt></a>s. This is
				2630	necessary to use when you need to update the list or perform a complex
				2631	action that doesn't have a forwarding method.</p>
				2632
				2633	<p><!-- Global Variable --></p></li>
				2634	</ul>
				2635
				2636	<hr>
				2637
				2638	<ul>
				2639	<li><tt>Module::global_iterator</tt> - Typedef for global variable list iterator<br>
				2640
				2641	<tt>Module::const_global_iterator</tt> - Typedef for const_iterator.<br>
				2642
				2643	<tt>global_begin()</tt>, <tt>global_end()</tt>
				2644	<tt>global_size()</tt>, <tt>global_empty()</tt>
				2645
				2646	<p> These are forwarding methods that make it easy to access the contents of
				2647	a <tt>Module</tt> object's <a
				2648	href="#GlobalVariable"><tt>GlobalVariable</tt></a> list.</p></li>
				2649
				2650	<li><tt>Module::GlobalListType &getGlobalList()</tt>
				2651
				2652	<p>Returns the list of <a
				2653	href="#GlobalVariable"><tt>GlobalVariable</tt></a>s. This is necessary to
				2654	use when you need to update the list or perform a complex action that
				2655	doesn't have a forwarding method.</p>
				2656
				2657	<p><!-- Symbol table stuff --> </p></li>
				2658	</ul>
				2659
				2660	<hr>
				2661
				2662	<ul>
				2663	<li><tt><a href="#SymbolTable">SymbolTable</a> *getSymbolTable()</tt>
				2664
				2665	<p>Return a reference to the <a href="#SymbolTable"><tt>SymbolTable</tt></a>
				2666	for this <tt>Module</tt>.</p>
				2667
				2668	<p><!-- Convenience methods --></p></li>
				2669	</ul>
				2670
				2671	<hr>
				2672
				2673	<ul>
				2674	<li><tt><a href="#Function">Function</a> *getFunction(const std::string
				2675	&Name, const <a href="#FunctionType">FunctionType</a> *Ty)</tt>
				2676
				2677	<p>Look up the specified function in the <tt>Module</tt> <a
				2678	href="#SymbolTable"><tt>SymbolTable</tt></a>. If it does not exist, return
				2679	<tt>null</tt>.</p></li>
				2680
				2681	<li><tt><a href="#Function">Function</a> *getOrInsertFunction(const
				2682	std::string &Name, const <a href="#FunctionType">FunctionType</a> *T)</tt>
				2683
				2684	<p>Look up the specified function in the <tt>Module</tt> <a
				2685	href="#SymbolTable"><tt>SymbolTable</tt></a>. If it does not exist, add an
				2686	external declaration for the function and return it.</p></li>
				2687
				2688	<li><tt>std::string getTypeName(const <a href="#Type">Type</a> *Ty)</tt>
				2689
				2690	<p>If there is at least one entry in the <a
				2691	href="#SymbolTable"><tt>SymbolTable</tt></a> for the specified <a
				2692	href="#Type"><tt>Type</tt></a>, return it. Otherwise return the empty
				2693	string.</p></li>
				2694
				2695	<li><tt>bool addTypeName(const std::string &Name, const <a
				2696	href="#Type">Type</a> *Ty)</tt>
				2697
				2698	<p>Insert an entry in the <a href="#SymbolTable"><tt>SymbolTable</tt></a>
				2699	mapping <tt>Name</tt> to <tt>Ty</tt>. If there is already an entry for this
				2700	name, true is returned and the <a
				2701	href="#SymbolTable"><tt>SymbolTable</tt></a> is not modified.</p></li>
				2702	</ul>
				2703
				2704	</div>
				2705
				2706
				2707	<!-- ======================================================================= -->
				2708	<div class="doc_subsection">
				2709	<a name="Value">The <tt>Value</tt> class</a>
				2710	</div>
				2711
				2712	<div class="doc_text">
				2713
				2714	<p><tt>#include "<a href="/doxygen/Value_8h-source.html">llvm/Value.h</a>"</tt>
				2715	<br>
				2716	doxygen info: <a href="/doxygen/classllvm_1_1Value.html">Value Class</a></p>
				2717
				2718	<p>The <tt>Value</tt> class is the most important class in the LLVM Source
				2719	base. It represents a typed value that may be used (among other things) as an
				2720	operand to an instruction. There are many different types of <tt>Value</tt>s,
				2721	such as <a href="#Constant"><tt>Constant</tt></a>s,<a
				2722	href="#Argument"><tt>Argument</tt></a>s. Even <a
				2723	href="#Instruction"><tt>Instruction</tt></a>s and <a
				2724	href="#Function"><tt>Function</tt></a>s are <tt>Value</tt>s.</p>
				2725
				2726	<p>A particular <tt>Value</tt> may be used many times in the LLVM representation
				2727	for a program. For example, an incoming argument to a function (represented
				2728	with an instance of the <a href="#Argument">Argument</a> class) is "used" by
				2729	every instruction in the function that references the argument. To keep track
				2730	of this relationship, the <tt>Value</tt> class keeps a list of all of the <a
				2731	href="#User"><tt>User</tt></a>s that is using it (the <a
				2732	href="#User"><tt>User</tt></a> class is a base class for all nodes in the LLVM
				2733	graph that can refer to <tt>Value</tt>s). This use list is how LLVM represents
				2734	def-use information in the program, and is accessible through the <tt>use_</tt>*
				2735	methods, shown below.</p>
				2736
				2737	<p>Because LLVM is a typed representation, every LLVM <tt>Value</tt> is typed,
				2738	and this <a href="#Type">Type</a> is available through the <tt>getType()</tt>
				2739	method. In addition, all LLVM values can be named. The "name" of the
				2740	<tt>Value</tt> is a symbolic string printed in the LLVM code:</p>
				2741
				2742	<div class="doc_code">
				2743	<pre>
				2744	%<b>foo</b> = add i32 1, 2
				2745	</pre>
				2746	</div>
				2747
				2748	<p><a name="nameWarning">The name of this instruction is "foo".</a> <b>NOTE</b>
				2749	that the name of any value may be missing (an empty string), so names should
				2750	<b>ONLY</b> be used for debugging (making the source code easier to read,
				2751	debugging printouts), they should not be used to keep track of values or map
				2752	between them. For this purpose, use a <tt>std::map</tt> of pointers to the
				2753	<tt>Value</tt> itself instead.</p>
				2754
				2755	<p>One important aspect of LLVM is that there is no distinction between an SSA
				2756	variable and the operation that produces it. Because of this, any reference to
				2757	the value produced by an instruction (or the value available as an incoming
				2758	argument, for example) is represented as a direct pointer to the instance of
				2759	the class that
				2760	represents this value. Although this may take some getting used to, it
				2761	simplifies the representation and makes it easier to manipulate.</p>
				2762
				2763	</div>
				2764
				2765	<!-- _______________________________________________________________________ -->
				2766	<div class="doc_subsubsection">
				2767	<a name="m_Value">Important Public Members of the <tt>Value</tt> class</a>
				2768	</div>
				2769
				2770	<div class="doc_text">
				2771
				2772	<ul>
				2773	<li><tt>Value::use_iterator</tt> - Typedef for iterator over the
				2774	use-list<br>
				2775	<tt>Value::use_const_iterator</tt> - Typedef for const_iterator over
				2776	the use-list<br>
				2777	<tt>unsigned use_size()</tt> - Returns the number of users of the
				2778	value.<br>
				2779	<tt>bool use_empty()</tt> - Returns true if there are no users.<br>
				2780	<tt>use_iterator use_begin()</tt> - Get an iterator to the start of
				2781	the use-list.<br>
				2782	<tt>use_iterator use_end()</tt> - Get an iterator to the end of the
				2783	use-list.<br>
				2784	<tt><a href="#User">User</a> *use_back()</tt> - Returns the last
				2785	element in the list.
				2786	<p> These methods are the interface to access the def-use
				2787	information in LLVM. As with all other iterators in LLVM, the naming
				2788	conventions follow the conventions defined by the <a href="#stl">STL</a>.</p>
				2789	</li>
				2790	<li><tt><a href="#Type">Type</a> *getType() const</tt>
				2791	<p>This method returns the Type of the Value.</p>
				2792	</li>
				2793	<li><tt>bool hasName() const</tt><br>
				2794	<tt>std::string getName() const</tt><br>
				2795	<tt>void setName(const std::string &Name)</tt>
				2796	<p> This family of methods is used to access and assign a name to a <tt>Value</tt>,
				2797	be aware of the <a href="#nameWarning">precaution above</a>.</p>
				2798	</li>
				2799	<li><tt>void replaceAllUsesWith(Value *V)</tt>
				2800
				2801	<p>This method traverses the use list of a <tt>Value</tt> changing all <a
				2802	href="#User"><tt>User</tt>s</a> of the current value to refer to
				2803	"<tt>V</tt>" instead. For example, if you detect that an instruction always
				2804	produces a constant value (for example through constant folding), you can
				2805	replace all uses of the instruction with the constant like this:</p>
				2806
				2807	<div class="doc_code">
				2808	<pre>
				2809	Inst->replaceAllUsesWith(ConstVal);
				2810	</pre>
				2811	</div>
				2812
				2813	</ul>
				2814
				2815	</div>
				2816
				2817	<!-- ======================================================================= -->
				2818	<div class="doc_subsection">
				2819	<a name="User">The <tt>User</tt> class</a>
				2820	</div>
				2821
				2822	<div class="doc_text">
				2823
				2824	<p>
				2825	<tt>#include "<a href="/doxygen/User_8h-source.html">llvm/User.h</a>"</tt><br>
				2826	doxygen info: <a href="/doxygen/classllvm_1_1User.html">User Class</a><br>
				2827	Superclass: <a href="#Value"><tt>Value</tt></a></p>
				2828
				2829	<p>The <tt>User</tt> class is the common base class of all LLVM nodes that may
				2830	refer to <a href="#Value"><tt>Value</tt></a>s. It exposes a list of "Operands"
				2831	that are all of the <a href="#Value"><tt>Value</tt></a>s that the User is
				2832	referring to. The <tt>User</tt> class itself is a subclass of
				2833	<tt>Value</tt>.</p>
				2834
				2835	<p>The operands of a <tt>User</tt> point directly to the LLVM <a
				2836	href="#Value"><tt>Value</tt></a> that it refers to. Because LLVM uses Static
				2837	Single Assignment (SSA) form, there can only be one definition referred to,
				2838	allowing this direct connection. This connection provides the use-def
				2839	information in LLVM.</p>
				2840
				2841	</div>
				2842
				2843	<!-- _______________________________________________________________________ -->
				2844	<div class="doc_subsubsection">
				2845	<a name="m_User">Important Public Members of the <tt>User</tt> class</a>
				2846	</div>
				2847
				2848	<div class="doc_text">
				2849
				2850	<p>The <tt>User</tt> class exposes the operand list in two ways: through
				2851	an index access interface and through an iterator based interface.</p>
				2852
				2853	<ul>
				2854	<li><tt>Value *getOperand(unsigned i)</tt><br>
				2855	<tt>unsigned getNumOperands()</tt>
				2856	<p> These two methods expose the operands of the <tt>User</tt> in a
				2857	convenient form for direct access.</p></li>
				2858
				2859	<li><tt>User::op_iterator</tt> - Typedef for iterator over the operand
				2860	list<br>
				2861	<tt>op_iterator op_begin()</tt> - Get an iterator to the start of
				2862	the operand list.<br>
				2863	<tt>op_iterator op_end()</tt> - Get an iterator to the end of the
				2864	operand list.
				2865	<p> Together, these methods make up the iterator based interface to
				2866	the operands of a <tt>User</tt>.</p></li>
				2867	</ul>
				2868
				2869	</div>
				2870
				2871	<!-- ======================================================================= -->
				2872	<div class="doc_subsection">
				2873	<a name="Instruction">The <tt>Instruction</tt> class</a>
				2874	</div>
				2875
				2876	<div class="doc_text">
				2877
				2878	<p><tt>#include "</tt><tt><a
				2879	href="/doxygen/Instruction_8h-source.html">llvm/Instruction.h</a>"</tt><br>
				2880	doxygen info: <a href="/doxygen/classllvm_1_1Instruction.html">Instruction Class</a><br>
				2881	Superclasses: <a href="#User"><tt>User</tt></a>, <a
				2882	href="#Value"><tt>Value</tt></a></p>
				2883
				2884	<p>The <tt>Instruction</tt> class is the common base class for all LLVM
				2885	instructions. It provides only a few methods, but is a very commonly used
				2886	class. The primary data tracked by the <tt>Instruction</tt> class itself is the
				2887	opcode (instruction type) and the parent <a
				2888	href="#BasicBlock"><tt>BasicBlock</tt></a> the <tt>Instruction</tt> is embedded
				2889	into. To represent a specific type of instruction, one of many subclasses of
				2890	<tt>Instruction</tt> are used.</p>
				2891
				2892	<p> Because the <tt>Instruction</tt> class subclasses the <a
				2893	href="#User"><tt>User</tt></a> class, its operands can be accessed in the same
				2894	way as for other <a href="#User"><tt>User</tt></a>s (with the
				2895	<tt>getOperand()</tt>/<tt>getNumOperands()</tt> and
				2896	<tt>op_begin()</tt>/<tt>op_end()</tt> methods).</p> <p> An important file for
				2897	the <tt>Instruction</tt> class is the <tt>llvm/Instruction.def</tt> file. This
				2898	file contains some meta-data about the various different types of instructions
				2899	in LLVM. It describes the enum values that are used as opcodes (for example
				2900	<tt>Instruction::Add</tt> and <tt>Instruction::ICmp</tt>), as well as the
				2901	concrete sub-classes of <tt>Instruction</tt> that implement the instruction (for
				2902	example <tt><a href="#BinaryOperator">BinaryOperator</a></tt> and <tt><a
				2903	href="#CmpInst">CmpInst</a></tt>). Unfortunately, the use of macros in
				2904	this file confuses doxygen, so these enum values don't show up correctly in the
				2905	<a href="/doxygen/classllvm_1_1Instruction.html">doxygen output</a>.</p>
				2906
				2907	</div>
				2908
				2909	<!-- _______________________________________________________________________ -->
				2910	<div class="doc_subsubsection">
				2911	<a name="s_Instruction">Important Subclasses of the <tt>Instruction</tt>
				2912	class</a>
				2913	</div>
				2914	<div class="doc_text">
				2915	<ul>
				2916	<li><tt><a name="BinaryOperator">BinaryOperator</a></tt>
				2917	<p>This subclasses represents all two operand instructions whose operands
				2918	must be the same type, except for the comparison instructions.</p></li>
				2919	<li><tt><a name="CastInst">CastInst</a></tt>
				2920	<p>This subclass is the parent of the 12 casting instructions. It provides
				2921	common operations on cast instructions.</p>
				2922	<li><tt><a name="CmpInst">CmpInst</a></tt>
				2923	<p>This subclass respresents the two comparison instructions,
				2924	<a href="LangRef.html#i_icmp">ICmpInst</a> (integer opreands), and
				2925	<a href="LangRef.html#i_fcmp">FCmpInst</a> (floating point operands).</p>
				2926	<li><tt><a name="TerminatorInst">TerminatorInst</a></tt>
				2927	<p>This subclass is the parent of all terminator instructions (those which
				2928	can terminate a block).</p>
				2929	</ul>
				2930	</div>
				2931
				2932	<!-- _______________________________________________________________________ -->
				2933	<div class="doc_subsubsection">
				2934	<a name="m_Instruction">Important Public Members of the <tt>Instruction</tt>
				2935	class</a>
				2936	</div>
				2937
				2938	<div class="doc_text">
				2939
				2940	<ul>
				2941	<li><tt><a href="#BasicBlock">BasicBlock</a> *getParent()</tt>
				2942	<p>Returns the <a href="#BasicBlock"><tt>BasicBlock</tt></a> that
				2943	this <tt>Instruction</tt> is embedded into.</p></li>
				2944	<li><tt>bool mayWriteToMemory()</tt>
				2945	<p>Returns true if the instruction writes to memory, i.e. it is a
				2946	<tt>call</tt>,<tt>free</tt>,<tt>invoke</tt>, or <tt>store</tt>.</p></li>
				2947	<li><tt>unsigned getOpcode()</tt>
				2948	<p>Returns the opcode for the <tt>Instruction</tt>.</p></li>
				2949	<li><tt><a href="#Instruction">Instruction</a> *clone() const</tt>
				2950	<p>Returns another instance of the specified instruction, identical
				2951	in all ways to the original except that the instruction has no parent
				2952	(ie it's not embedded into a <a href="#BasicBlock"><tt>BasicBlock</tt></a>),
				2953	and it has no name</p></li>
				2954	</ul>
				2955
				2956	</div>
				2957
				2958	<!-- ======================================================================= -->
				2959	<div class="doc_subsection">
				2960	<a name="Constant">The <tt>Constant</tt> class and subclasses</a>
				2961	</div>
				2962
				2963	<div class="doc_text">
				2964
				2965	<p>Constant represents a base class for different types of constants. It
				2966	is subclassed by ConstantInt, ConstantArray, etc. for representing
				2967	the various types of Constants. <a href="#GlobalValue">GlobalValue</a> is also
				2968	a subclass, which represents the address of a global variable or function.
				2969	</p>
				2970
				2971	</div>
				2972
				2973	<!-- _______________________________________________________________________ -->
				2974	<div class="doc_subsubsection">Important Subclasses of Constant </div>
				2975	<div class="doc_text">
				2976	<ul>
				2977	<li>ConstantInt : This subclass of Constant represents an integer constant of
				2978	any width.
				2979	<ul>
				2980	<li><tt>const APInt& getValue() const</tt>: Returns the underlying
				2981	value of this constant, an APInt value.</li>
				2982	<li><tt>int64_t getSExtValue() const</tt>: Converts the underlying APInt
				2983	value to an int64_t via sign extension. If the value (not the bit width)
				2984	of the APInt is too large to fit in an int64_t, an assertion will result.
				2985	For this reason, use of this method is discouraged.</li>
				2986	<li><tt>uint64_t getZExtValue() const</tt>: Converts the underlying APInt
				2987	value to a uint64_t via zero extension. IF the value (not the bit width)
				2988	of the APInt is too large to fit in a uint64_t, an assertion will result.
				2989	For this reason, use of this method is discouraged.</li>
				2990	<li><tt>static ConstantInt* get(const APInt& Val)</tt>: Returns the
				2991	ConstantInt object that represents the value provided by <tt>Val</tt>.
				2992	The type is implied as the IntegerType that corresponds to the bit width
				2993	of <tt>Val</tt>.</li>
				2994	<li><tt>static ConstantInt* get(const Type *Ty, uint64_t Val)</tt>:
				2995	Returns the ConstantInt object that represents the value provided by
				2996	<tt>Val</tt> for integer type <tt>Ty</tt>.</li>
				2997	</ul>
				2998	</li>
				2999	<li>ConstantFP : This class represents a floating point constant.
				3000	<ul>
				3001	<li><tt>double getValue() const</tt>: Returns the underlying value of
				3002	this constant. </li>
				3003	</ul>
				3004	</li>
				3005	<li>ConstantArray : This represents a constant array.
				3006	<ul>
				3007	<li><tt>const std::vector<Use> &getValues() const</tt>: Returns
				3008	a vector of component constants that makeup this array. </li>
				3009	</ul>
				3010	</li>
				3011	<li>ConstantStruct : This represents a constant struct.
				3012	<ul>
				3013	<li><tt>const std::vector<Use> &getValues() const</tt>: Returns
				3014	a vector of component constants that makeup this array. </li>
				3015	</ul>
				3016	</li>
				3017	<li>GlobalValue : This represents either a global variable or a function. In
				3018	either case, the value is a constant fixed address (after linking).
				3019	</li>
				3020	</ul>
				3021	</div>
				3022
				3023
				3024	<!-- ======================================================================= -->
				3025	<div class="doc_subsection">
				3026	<a name="GlobalValue">The <tt>GlobalValue</tt> class</a>
				3027	</div>
				3028
				3029	<div class="doc_text">
				3030
				3031	<p><tt>#include "<a
				3032	href="/doxygen/GlobalValue_8h-source.html">llvm/GlobalValue.h</a>"</tt><br>
				3033	doxygen info: <a href="/doxygen/classllvm_1_1GlobalValue.html">GlobalValue
				3034	Class</a><br>
				3035	Superclasses: <a href="#Constant"><tt>Constant</tt></a>,
				3036	<a href="#User"><tt>User</tt></a>, <a href="#Value"><tt>Value</tt></a></p>
				3037
				3038	<p>Global values (<a href="#GlobalVariable"><tt>GlobalVariable</tt></a>s or <a
				3039	href="#Function"><tt>Function</tt></a>s) are the only LLVM values that are
				3040	visible in the bodies of all <a href="#Function"><tt>Function</tt></a>s.
				3041	Because they are visible at global scope, they are also subject to linking with
				3042	other globals defined in different translation units. To control the linking
				3043	process, <tt>GlobalValue</tt>s know their linkage rules. Specifically,
				3044	<tt>GlobalValue</tt>s know whether they have internal or external linkage, as
				3045	defined by the <tt>LinkageTypes</tt> enumeration.</p>
				3046
				3047	<p>If a <tt>GlobalValue</tt> has internal linkage (equivalent to being
				3048	<tt>static</tt> in C), it is not visible to code outside the current translation
				3049	unit, and does not participate in linking. If it has external linkage, it is
				3050	visible to external code, and does participate in linking. In addition to
				3051	linkage information, <tt>GlobalValue</tt>s keep track of which <a
				3052	href="#Module"><tt>Module</tt></a> they are currently part of.</p>
				3053
				3054	<p>Because <tt>GlobalValue</tt>s are memory objects, they are always referred to
				3055	by their <b>address</b>. As such, the <a href="#Type"><tt>Type</tt></a> of a
				3056	global is always a pointer to its contents. It is important to remember this
				3057	when using the <tt>GetElementPtrInst</tt> instruction because this pointer must
				3058	be dereferenced first. For example, if you have a <tt>GlobalVariable</tt> (a
				3059	subclass of <tt>GlobalValue)</tt> that is an array of 24 ints, type <tt>[24 x
				3060	i32]</tt>, then the <tt>GlobalVariable</tt> is a pointer to that array. Although
				3061	the address of the first element of this array and the value of the
				3062	<tt>GlobalVariable</tt> are the same, they have different types. The
				3063	<tt>GlobalVariable</tt>'s type is <tt>[24 x i32]</tt>. The first element's type
				3064	is <tt>i32.</tt> Because of this, accessing a global value requires you to
				3065	dereference the pointer with <tt>GetElementPtrInst</tt> first, then its elements
				3066	can be accessed. This is explained in the <a href="LangRef.html#globalvars">LLVM
				3067	Language Reference Manual</a>.</p>
				3068
				3069	</div>
				3070
				3071	<!-- _______________________________________________________________________ -->
				3072	<div class="doc_subsubsection">
				3073	<a name="m_GlobalValue">Important Public Members of the <tt>GlobalValue</tt>
				3074	class</a>
				3075	</div>
				3076
				3077	<div class="doc_text">
				3078
				3079	<ul>
				3080	<li><tt>bool hasInternalLinkage() const</tt><br>
				3081	<tt>bool hasExternalLinkage() const</tt><br>
				3082	<tt>void setInternalLinkage(bool HasInternalLinkage)</tt>
				3083	<p> These methods manipulate the linkage characteristics of the <tt>GlobalValue</tt>.</p>
				3084	<p> </p>
				3085	</li>
				3086	<li><tt><a href="#Module">Module</a> *getParent()</tt>
				3087	<p> This returns the <a href="#Module"><tt>Module</tt></a> that the
				3088	GlobalValue is currently embedded into.</p></li>
				3089	</ul>
				3090
				3091	</div>
				3092
				3093	<!-- ======================================================================= -->
				3094	<div class="doc_subsection">
				3095	<a name="Function">The <tt>Function</tt> class</a>
				3096	</div>
				3097
				3098	<div class="doc_text">
				3099
				3100	<p><tt>#include "<a
				3101	href="/doxygen/Function_8h-source.html">llvm/Function.h</a>"</tt><br> doxygen
				3102	info: <a href="/doxygen/classllvm_1_1Function.html">Function Class</a><br>
				3103	Superclasses: <a href="#GlobalValue"><tt>GlobalValue</tt></a>,
				3104	<a href="#Constant"><tt>Constant</tt></a>,
				3105	<a href="#User"><tt>User</tt></a>,
				3106	<a href="#Value"><tt>Value</tt></a></p>
				3107
				3108	<p>The <tt>Function</tt> class represents a single procedure in LLVM. It is
				3109	actually one of the more complex classes in the LLVM heirarchy because it must
				3110	keep track of a large amount of data. The <tt>Function</tt> class keeps track
				3111	of a list of <a href="#BasicBlock"><tt>BasicBlock</tt></a>s, a list of formal
				3112	<a href="#Argument"><tt>Argument</tt></a>s, and a
				3113	<a href="#SymbolTable"><tt>SymbolTable</tt></a>.</p>
				3114
				3115	<p>The list of <a href="#BasicBlock"><tt>BasicBlock</tt></a>s is the most
				3116	commonly used part of <tt>Function</tt> objects. The list imposes an implicit
				3117	ordering of the blocks in the function, which indicate how the code will be
				3118	layed out by the backend. Additionally, the first <a
				3119	href="#BasicBlock"><tt>BasicBlock</tt></a> is the implicit entry node for the
				3120	<tt>Function</tt>. It is not legal in LLVM to explicitly branch to this initial
				3121	block. There are no implicit exit nodes, and in fact there may be multiple exit
				3122	nodes from a single <tt>Function</tt>. If the <a
				3123	href="#BasicBlock"><tt>BasicBlock</tt></a> list is empty, this indicates that
				3124	the <tt>Function</tt> is actually a function declaration: the actual body of the
				3125	function hasn't been linked in yet.</p>
				3126
				3127	<p>In addition to a list of <a href="#BasicBlock"><tt>BasicBlock</tt></a>s, the
				3128	<tt>Function</tt> class also keeps track of the list of formal <a
				3129	href="#Argument"><tt>Argument</tt></a>s that the function receives. This
				3130	container manages the lifetime of the <a href="#Argument"><tt>Argument</tt></a>
				3131	nodes, just like the <a href="#BasicBlock"><tt>BasicBlock</tt></a> list does for
				3132	the <a href="#BasicBlock"><tt>BasicBlock</tt></a>s.</p>
				3133
				3134	<p>The <a href="#SymbolTable"><tt>SymbolTable</tt></a> is a very rarely used
				3135	LLVM feature that is only used when you have to look up a value by name. Aside
				3136	from that, the <a href="#SymbolTable"><tt>SymbolTable</tt></a> is used
				3137	internally to make sure that there are not conflicts between the names of <a
				3138	href="#Instruction"><tt>Instruction</tt></a>s, <a
				3139	href="#BasicBlock"><tt>BasicBlock</tt></a>s, or <a
				3140	href="#Argument"><tt>Argument</tt></a>s in the function body.</p>
				3141
				3142	<p>Note that <tt>Function</tt> is a <a href="#GlobalValue">GlobalValue</a>
				3143	and therefore also a <a href="#Constant">Constant</a>. The value of the function
				3144	is its address (after linking) which is guaranteed to be constant.</p>
				3145	</div>
				3146
				3147	<!-- _______________________________________________________________________ -->
				3148	<div class="doc_subsubsection">
				3149	<a name="m_Function">Important Public Members of the <tt>Function</tt>
				3150	class</a>
				3151	</div>
				3152
				3153	<div class="doc_text">
				3154
				3155	<ul>
				3156	<li><tt>Function(const </tt><tt><a href="#FunctionType">FunctionType</a>
				3157	Ty, LinkageTypes Linkage, const std::string &N = "", Module Parent = 0)</tt>
				3158
				3159	<p>Constructor used when you need to create new <tt>Function</tt>s to add
				3160	the the program. The constructor must specify the type of the function to
				3161	create and what type of linkage the function should have. The <a
				3162	href="#FunctionType"><tt>FunctionType</tt></a> argument
				3163	specifies the formal arguments and return value for the function. The same
				3164	<a href="#FunctionType"><tt>FunctionType</tt></a> value can be used to
				3165	create multiple functions. The <tt>Parent</tt> argument specifies the Module
				3166	in which the function is defined. If this argument is provided, the function
				3167	will automatically be inserted into that module's list of
				3168	functions.</p></li>
				3169
				3170	<li><tt>bool isExternal()</tt>
				3171
				3172	<p>Return whether or not the <tt>Function</tt> has a body defined. If the
				3173	function is "external", it does not have a body, and thus must be resolved
				3174	by linking with a function defined in a different translation unit.</p></li>
				3175
				3176	<li><tt>Function::iterator</tt> - Typedef for basic block list iterator<br>
				3177	<tt>Function::const_iterator</tt> - Typedef for const_iterator.<br>
				3178
				3179	<tt>begin()</tt>, <tt>end()</tt>
				3180	<tt>size()</tt>, <tt>empty()</tt>
				3181
				3182	<p>These are forwarding methods that make it easy to access the contents of
				3183	a <tt>Function</tt> object's <a href="#BasicBlock"><tt>BasicBlock</tt></a>
				3184	list.</p></li>
				3185
				3186	<li><tt>Function::BasicBlockListType &getBasicBlockList()</tt>
				3187
				3188	<p>Returns the list of <a href="#BasicBlock"><tt>BasicBlock</tt></a>s. This
				3189	is necessary to use when you need to update the list or perform a complex
				3190	action that doesn't have a forwarding method.</p></li>
				3191
				3192	<li><tt>Function::arg_iterator</tt> - Typedef for the argument list
				3193	iterator<br>
				3194	<tt>Function::const_arg_iterator</tt> - Typedef for const_iterator.<br>
				3195
				3196	<tt>arg_begin()</tt>, <tt>arg_end()</tt>
				3197	<tt>arg_size()</tt>, <tt>arg_empty()</tt>
				3198
				3199	<p>These are forwarding methods that make it easy to access the contents of
				3200	a <tt>Function</tt> object's <a href="#Argument"><tt>Argument</tt></a>
				3201	list.</p></li>
				3202
				3203	<li><tt>Function::ArgumentListType &getArgumentList()</tt>
				3204
				3205	<p>Returns the list of <a href="#Argument"><tt>Argument</tt></a>s. This is
				3206	necessary to use when you need to update the list or perform a complex
				3207	action that doesn't have a forwarding method.</p></li>
				3208
				3209	<li><tt><a href="#BasicBlock">BasicBlock</a> &getEntryBlock()</tt>
				3210
				3211	<p>Returns the entry <a href="#BasicBlock"><tt>BasicBlock</tt></a> for the
				3212	function. Because the entry block for the function is always the first
				3213	block, this returns the first block of the <tt>Function</tt>.</p></li>
				3214
				3215	<li><tt><a href="#Type">Type</a> *getReturnType()</tt><br>
				3216	<tt><a href="#FunctionType">FunctionType</a> *getFunctionType()</tt>
				3217
				3218	<p>This traverses the <a href="#Type"><tt>Type</tt></a> of the
				3219	<tt>Function</tt> and returns the return type of the function, or the <a
				3220	href="#FunctionType"><tt>FunctionType</tt></a> of the actual
				3221	function.</p></li>
				3222
				3223	<li><tt><a href="#SymbolTable">SymbolTable</a> *getSymbolTable()</tt>
				3224
				3225	<p> Return a pointer to the <a href="#SymbolTable"><tt>SymbolTable</tt></a>
				3226	for this <tt>Function</tt>.</p></li>
				3227	</ul>
				3228
				3229	</div>
				3230
				3231	<!-- ======================================================================= -->
				3232	<div class="doc_subsection">
				3233	<a name="GlobalVariable">The <tt>GlobalVariable</tt> class</a>
				3234	</div>
				3235
				3236	<div class="doc_text">
				3237
				3238	<p><tt>#include "<a
				3239	href="/doxygen/GlobalVariable_8h-source.html">llvm/GlobalVariable.h</a>"</tt>
				3240	<br>
				3241	doxygen info: <a href="/doxygen/classllvm_1_1GlobalVariable.html">GlobalVariable
				3242	Class</a><br>
				3243	Superclasses: <a href="#GlobalValue"><tt>GlobalValue</tt></a>,
				3244	<a href="#Constant"><tt>Constant</tt></a>,
				3245	<a href="#User"><tt>User</tt></a>,
				3246	<a href="#Value"><tt>Value</tt></a></p>
				3247
				3248	<p>Global variables are represented with the (suprise suprise)
				3249	<tt>GlobalVariable</tt> class. Like functions, <tt>GlobalVariable</tt>s are also
				3250	subclasses of <a href="#GlobalValue"><tt>GlobalValue</tt></a>, and as such are
				3251	always referenced by their address (global values must live in memory, so their
				3252	"name" refers to their constant address). See
				3253	<a href="#GlobalValue"><tt>GlobalValue</tt></a> for more on this. Global
				3254	variables may have an initial value (which must be a
				3255	<a href="#Constant"><tt>Constant</tt></a>), and if they have an initializer,
				3256	they may be marked as "constant" themselves (indicating that their contents
				3257	never change at runtime).</p>
				3258	</div>
				3259
				3260	<!-- _______________________________________________________________________ -->
				3261	<div class="doc_subsubsection">
				3262	<a name="m_GlobalVariable">Important Public Members of the
				3263	<tt>GlobalVariable</tt> class</a>
				3264	</div>
				3265
				3266	<div class="doc_text">
				3267
				3268	<ul>
				3269	<li><tt>GlobalVariable(const </tt><tt><a href="#Type">Type</a> *Ty, bool
				3270	isConstant, LinkageTypes& Linkage, <a href="#Constant">Constant</a>
				3271	Initializer = 0, const std::string &Name = "", Module Parent = 0)</tt>
				3272
				3273	<p>Create a new global variable of the specified type. If
				3274	<tt>isConstant</tt> is true then the global variable will be marked as
				3275	unchanging for the program. The Linkage parameter specifies the type of
				3276	linkage (internal, external, weak, linkonce, appending) for the variable. If
				3277	the linkage is InternalLinkage, WeakLinkage, or LinkOnceLinkage,  then
				3278	the resultant global variable will have internal linkage. AppendingLinkage
				3279	concatenates together all instances (in different translation units) of the
				3280	variable into a single variable but is only applicable to arrays.  See
				3281	the <a href="LangRef.html#modulestructure">LLVM Language Reference</a> for
				3282	further details on linkage types. Optionally an initializer, a name, and the
				3283	module to put the variable into may be specified for the global variable as
				3284	well.</p></li>
				3285
				3286	<li><tt>bool isConstant() const</tt>
				3287
				3288	<p>Returns true if this is a global variable that is known not to
				3289	be modified at runtime.</p></li>
				3290
				3291	<li><tt>bool hasInitializer()</tt>
				3292
				3293	<p>Returns true if this <tt>GlobalVariable</tt> has an intializer.</p></li>
				3294
				3295	<li><tt><a href="#Constant">Constant</a> *getInitializer()</tt>
				3296
				3297	<p>Returns the intial value for a <tt>GlobalVariable</tt>. It is not legal
				3298	to call this method if there is no initializer.</p></li>
				3299	</ul>
				3300
				3301	</div>
				3302
				3303
				3304	<!-- ======================================================================= -->
				3305	<div class="doc_subsection">
				3306	<a name="BasicBlock">The <tt>BasicBlock</tt> class</a>
				3307	</div>
				3308
				3309	<div class="doc_text">
				3310
				3311	<p><tt>#include "<a
				3312	href="/doxygen/BasicBlock_8h-source.html">llvm/BasicBlock.h</a>"</tt><br>
				3313	doxygen info: <a href="/doxygen/structllvm_1_1BasicBlock.html">BasicBlock
				3314	Class</a><br>
				3315	Superclass: <a href="#Value"><tt>Value</tt></a></p>
				3316
				3317	<p>This class represents a single entry multiple exit section of the code,
				3318	commonly known as a basic block by the compiler community. The
				3319	<tt>BasicBlock</tt> class maintains a list of <a
				3320	href="#Instruction"><tt>Instruction</tt></a>s, which form the body of the block.
				3321	Matching the language definition, the last element of this list of instructions
				3322	is always a terminator instruction (a subclass of the <a
				3323	href="#TerminatorInst"><tt>TerminatorInst</tt></a> class).</p>
				3324
				3325	<p>In addition to tracking the list of instructions that make up the block, the
				3326	<tt>BasicBlock</tt> class also keeps track of the <a
				3327	href="#Function"><tt>Function</tt></a> that it is embedded into.</p>
				3328
				3329	<p>Note that <tt>BasicBlock</tt>s themselves are <a
				3330	href="#Value"><tt>Value</tt></a>s, because they are referenced by instructions
				3331	like branches and can go in the switch tables. <tt>BasicBlock</tt>s have type
				3332	<tt>label</tt>.</p>
				3333
				3334	</div>
				3335
				3336	<!-- _______________________________________________________________________ -->
				3337	<div class="doc_subsubsection">
				3338	<a name="m_BasicBlock">Important Public Members of the <tt>BasicBlock</tt>
				3339	class</a>
				3340	</div>
				3341
				3342	<div class="doc_text">
				3343	<ul>
				3344
				3345	<li><tt>BasicBlock(const std::string &Name = "", </tt><tt><a
				3346	href="#Function">Function</a> *Parent = 0)</tt>
				3347
				3348	<p>The <tt>BasicBlock</tt> constructor is used to create new basic blocks for
				3349	insertion into a function. The constructor optionally takes a name for the new
				3350	block, and a <a href="#Function"><tt>Function</tt></a> to insert it into. If
				3351	the <tt>Parent</tt> parameter is specified, the new <tt>BasicBlock</tt> is
				3352	automatically inserted at the end of the specified <a
				3353	href="#Function"><tt>Function</tt></a>, if not specified, the BasicBlock must be
				3354	manually inserted into the <a href="#Function"><tt>Function</tt></a>.</p></li>
				3355
				3356	<li><tt>BasicBlock::iterator</tt> - Typedef for instruction list iterator<br>
				3357	<tt>BasicBlock::const_iterator</tt> - Typedef for const_iterator.<br>
				3358	<tt>begin()</tt>, <tt>end()</tt>, <tt>front()</tt>, <tt>back()</tt>,
				3359	<tt>size()</tt>, <tt>empty()</tt>
				3360	STL-style functions for accessing the instruction list.
				3361
				3362	<p>These methods and typedefs are forwarding functions that have the same
				3363	semantics as the standard library methods of the same names. These methods
				3364	expose the underlying instruction list of a basic block in a way that is easy to
				3365	manipulate. To get the full complement of container operations (including
				3366	operations to update the list), you must use the <tt>getInstList()</tt>
				3367	method.</p></li>
				3368
				3369	<li><tt>BasicBlock::InstListType &getInstList()</tt>
				3370
				3371	<p>This method is used to get access to the underlying container that actually
				3372	holds the Instructions. This method must be used when there isn't a forwarding
				3373	function in the <tt>BasicBlock</tt> class for the operation that you would like
				3374	to perform. Because there are no forwarding functions for "updating"
				3375	operations, you need to use this if you want to update the contents of a
				3376	<tt>BasicBlock</tt>.</p></li>
				3377
				3378	<li><tt><a href="#Function">Function</a> *getParent()</tt>
				3379
				3380	<p> Returns a pointer to <a href="#Function"><tt>Function</tt></a> the block is
				3381	embedded into, or a null pointer if it is homeless.</p></li>
				3382
				3383	<li><tt><a href="#TerminatorInst">TerminatorInst</a> *getTerminator()</tt>
				3384
				3385	<p> Returns a pointer to the terminator instruction that appears at the end of
				3386	the <tt>BasicBlock</tt>. If there is no terminator instruction, or if the last
				3387	instruction in the block is not a terminator, then a null pointer is
				3388	returned.</p></li>
				3389
				3390	</ul>
				3391
				3392	</div>
				3393
				3394
				3395	<!-- ======================================================================= -->
				3396	<div class="doc_subsection">
				3397	<a name="Argument">The <tt>Argument</tt> class</a>
				3398	</div>
				3399
				3400	<div class="doc_text">
				3401
				3402	<p>This subclass of Value defines the interface for incoming formal
				3403	arguments to a function. A Function maintains a list of its formal
				3404	arguments. An argument has a pointer to the parent Function.</p>
				3405
				3406	</div>
				3407
				3408	<!-- *********************************************************************** -->
				3409	<hr>
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				3417	<a href="mailto:sabre@nondot.org">Chris Lattner</a><br>
				3418	<a href="http://llvm.org">The LLVM Compiler Infrastructure</a><br>
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