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				4	<head>
				5	<title>LLVM Programmer's Manual</title>
				6	<link rel="stylesheet" href="llvm.css" type="text/css">
				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>
Gabor Greif	bb17f65	2009-02-27 11:37:41 +0000	[diff] [blame]	57	<li><a href="#dss_ilist">llvm/ADT/ilist.h</a></li>
Dan Gohman	f17a25c	2007-07-18 16:29:46 +0000	[diff] [blame]	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>
Jeffrey Yasskin	7ebb6ac	2009-04-30 22:33:41 +0000	[diff] [blame^]	120	<li><a href="#create_types">How to Create Types</a></li>
Dan Gohman	f17a25c	2007-07-18 16:29:46 +0000	[diff] [blame]	121	<!--
				122	<li>Working with the Control Flow Graph
				123	<ul>
				124	<li>Accessing predecessors and successors of a <tt>BasicBlock</tt>
				125	<li>
				126	<li>
				127	</ul>
				128	-->
				129	</ul>
				130	</li>
				131
				132	<li><a href="#advanced">Advanced Topics</a>
				133	<ul>
				134	<li><a href="#TypeResolve">LLVM Type Resolution</a>
				135	<ul>
				136	<li><a href="#BuildRecType">Basic Recursive Type Construction</a></li>
				137	<li><a href="#refineAbstractTypeTo">The <tt>refineAbstractTypeTo</tt> method</a></li>
				138	<li><a href="#PATypeHolder">The PATypeHolder Class</a></li>
				139	<li><a href="#AbstractTypeUser">The AbstractTypeUser Class</a></li>
				140	</ul></li>
				141
Gabor Greif	92e8776	2008-06-16 21:06:12 +0000	[diff] [blame]	142	<li><a href="#SymbolTable">The <tt>ValueSymbolTable</tt> and <tt>TypeSymbolTable</tt> classes</a></li>
				143	<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]	144	</ul></li>
				145
				146	<li><a href="#coreclasses">The Core LLVM Class Hierarchy Reference</a>
				147	<ul>
				148	<li><a href="#Type">The <tt>Type</tt> class</a> </li>
				149	<li><a href="#Module">The <tt>Module</tt> class</a></li>
				150	<li><a href="#Value">The <tt>Value</tt> class</a>
				151	<ul>
				152	<li><a href="#User">The <tt>User</tt> class</a>
				153	<ul>
				154	<li><a href="#Instruction">The <tt>Instruction</tt> class</a></li>
				155	<li><a href="#Constant">The <tt>Constant</tt> class</a>
				156	<ul>
				157	<li><a href="#GlobalValue">The <tt>GlobalValue</tt> class</a>
				158	<ul>
				159	<li><a href="#Function">The <tt>Function</tt> class</a></li>
				160	<li><a href="#GlobalVariable">The <tt>GlobalVariable</tt> class</a></li>
				161	</ul>
				162	</li>
				163	</ul>
				164	</li>
				165	</ul>
				166	</li>
				167	<li><a href="#BasicBlock">The <tt>BasicBlock</tt> class</a></li>
				168	<li><a href="#Argument">The <tt>Argument</tt> class</a></li>
				169	</ul>
				170	</li>
				171	</ul>
				172	</li>
				173	</ol>
				174
				175	<div class="doc_author">
				176	<p>Written by <a href="mailto:sabre@nondot.org">Chris Lattner</a>,
				177	<a href="mailto:dhurjati@cs.uiuc.edu">Dinakar Dhurjati</a>,
Gabor Greif	92e8776	2008-06-16 21:06:12 +0000	[diff] [blame]	178	<a href="mailto:ggreif@gmail.com">Gabor Greif</a>,
				179	<a href="mailto:jstanley@cs.uiuc.edu">Joel Stanley</a> and
Dan Gohman	f17a25c	2007-07-18 16:29:46 +0000	[diff] [blame]	180	<a href="mailto:rspencer@x10sys.com">Reid Spencer</a></p>
				181	</div>
				182
				183	<!-- *********************************************************************** -->
				184	<div class="doc_section">
				185	<a name="introduction">Introduction </a>
				186	</div>
				187	<!-- *********************************************************************** -->
				188
				189	<div class="doc_text">
				190
				191	<p>This document is meant to highlight some of the important classes and
				192	interfaces available in the LLVM source-base. This manual is not
				193	intended to explain what LLVM is, how it works, and what LLVM code looks
				194	like. It assumes that you know the basics of LLVM and are interested
				195	in writing transformations or otherwise analyzing or manipulating the
				196	code.</p>
				197
				198	<p>This document should get you oriented so that you can find your
				199	way in the continuously growing source code that makes up the LLVM
				200	infrastructure. Note that this manual is not intended to serve as a
				201	replacement for reading the source code, so if you think there should be
				202	a method in one of these classes to do something, but it's not listed,
				203	check the source. Links to the <a href="/doxygen/">doxygen</a> sources
				204	are provided to make this as easy as possible.</p>
				205
				206	<p>The first section of this document describes general information that is
				207	useful to know when working in the LLVM infrastructure, and the second describes
				208	the Core LLVM classes. In the future this manual will be extended with
				209	information describing how to use extension libraries, such as dominator
				210	information, CFG traversal routines, and useful utilities like the <tt><a
				211	href="/doxygen/InstVisitor_8h-source.html">InstVisitor</a></tt> template.</p>
				212
				213	</div>
				214
				215	<!-- *********************************************************************** -->
				216	<div class="doc_section">
				217	<a name="general">General Information</a>
				218	</div>
				219	<!-- *********************************************************************** -->
				220
				221	<div class="doc_text">
				222
				223	<p>This section contains general information that is useful if you are working
				224	in the LLVM source-base, but that isn't specific to any particular API.</p>
				225
				226	</div>
				227
				228	<!-- ======================================================================= -->
				229	<div class="doc_subsection">
				230	<a name="stl">The C++ Standard Template Library</a>
				231	</div>
				232
				233	<div class="doc_text">
				234
				235	<p>LLVM makes heavy use of the C++ Standard Template Library (STL),
				236	perhaps much more than you are used to, or have seen before. Because of
				237	this, you might want to do a little background reading in the
				238	techniques used and capabilities of the library. There are many good
				239	pages that discuss the STL, and several books on the subject that you
				240	can get, so it will not be discussed in this document.</p>
				241
				242	<p>Here are some useful links:</p>
				243
				244	<ol>
				245
				246	<li><a href="http://www.dinkumware.com/refxcpp.html">Dinkumware C++ Library
				247	reference</a> - an excellent reference for the STL and other parts of the
				248	standard C++ library.</li>
				249
				250	<li><a href="http://www.tempest-sw.com/cpp/">C++ In a Nutshell</a> - This is an
Gabor Greif	e39f0e7	2009-03-12 09:47:03 +0000	[diff] [blame]	251	O'Reilly book in the making. It has a decent Standard Library
				252	Reference that rivals Dinkumware's, and is unfortunately no longer free since the
				253	book has been published.</li>
Dan Gohman	f17a25c	2007-07-18 16:29:46 +0000	[diff] [blame]	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">
Gabor Greif	bb17f65	2009-02-27 11:37:41 +0000	[diff] [blame]	881	<a name="dss_ilist">llvm/ADT/ilist.h</a>
Dan Gohman	f17a25c	2007-07-18 16:29:46 +0000	[diff] [blame]	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
Gabor Greif	b6b21ec	2009-02-27 12:02:19 +0000	[diff] [blame]	889	<p><tt>ilist</tt> has the same drawbacks as <tt>std::list</tt>, and additionally
				890	requires an <tt>ilist_traits</tt> implementation for the element type, but it
				891	provides some novel characteristics. In particular, it can efficiently store
				892	polymorphic objects, the traits class is informed when an element is inserted or
Gabor Greif	e39f0e7	2009-03-12 09:47:03 +0000	[diff] [blame]	893	removed from the list, and <tt>ilist</tt>s are guaranteed to support a
				894	constant-time splice operation.</p>
Dan Gohman	f17a25c	2007-07-18 16:29:46 +0000	[diff] [blame]	895
Gabor Greif	e39f0e7	2009-03-12 09:47:03 +0000	[diff] [blame]	896	<p>These properties are exactly what we want for things like
				897	<tt>Instruction</tt>s and basic blocks, which is why these are implemented with
				898	<tt>ilist</tt>s.</p>
Gabor Greif	bb17f65	2009-02-27 11:37:41 +0000	[diff] [blame]	899
				900	Related classes of interest are explained in the following subsections:
				901	<ul>
Gabor Greif	a17abe1	2009-02-27 13:28:07 +0000	[diff] [blame]	902	<li><a href="#dss_ilist_traits">ilist_traits</a></li>
Gabor Greif	b6b21ec	2009-02-27 12:02:19 +0000	[diff] [blame]	903	<li><a href="#dss_iplist">iplist</a></li>
Gabor Greif	bb17f65	2009-02-27 11:37:41 +0000	[diff] [blame]	904	<li><a href="#dss_ilist_node">llvm/ADT/ilist_node.h</a></li>
Gabor Greif	d970d69	2009-03-12 10:30:31 +0000	[diff] [blame]	905	<li><a href="#dss_ilist_sentinel">Sentinels</a></li>
Gabor Greif	bb17f65	2009-02-27 11:37:41 +0000	[diff] [blame]	906	</ul>
				907	</div>
				908
				909	<!-- _______________________________________________________________________ -->
				910	<div class="doc_subsubsection">
Gabor Greif	a17abe1	2009-02-27 13:28:07 +0000	[diff] [blame]	911	<a name="dss_ilist_traits">ilist_traits</a>
				912	</div>
				913
				914	<div class="doc_text">
				915	<p><tt>ilist_traits<T></tt> is <tt>ilist<T></tt>'s customization
				916	mechanism. <tt>iplist<T></tt> (and consequently <tt>ilist<T></tt>)
				917	publicly derive from this traits class.</p>
				918	</div>
				919
				920	<!-- _______________________________________________________________________ -->
				921	<div class="doc_subsubsection">
Gabor Greif	b6b21ec	2009-02-27 12:02:19 +0000	[diff] [blame]	922	<a name="dss_iplist">iplist</a>
				923	</div>
				924
				925	<div class="doc_text">
				926	<p><tt>iplist<T></tt> is <tt>ilist<T></tt>'s base and as such
Gabor Greif	e39f0e7	2009-03-12 09:47:03 +0000	[diff] [blame]	927	supports a slightly narrower interface. Notably, inserters from
				928	<tt>T&</tt> are absent.</p>
Gabor Greif	a17abe1	2009-02-27 13:28:07 +0000	[diff] [blame]	929
				930	<p><tt>ilist_traits<T></tt> is a public base of this class and can be
				931	used for a wide variety of customizations.</p>
Gabor Greif	b6b21ec	2009-02-27 12:02:19 +0000	[diff] [blame]	932	</div>
				933
				934	<!-- _______________________________________________________________________ -->
				935	<div class="doc_subsubsection">
Gabor Greif	bb17f65	2009-02-27 11:37:41 +0000	[diff] [blame]	936	<a name="dss_ilist_node">llvm/ADT/ilist_node.h</a>
				937	</div>
				938
				939	<div class="doc_text">
				940	<p><tt>ilist_node<T></tt> implements a the forward and backward links
				941	that are expected by the <tt>ilist<T></tt> (and analogous containers)
				942	in the default manner.</p>
				943
				944	<p><tt>ilist_node<T></tt>s are meant to be embedded in the node type
Gabor Greif	e39f0e7	2009-03-12 09:47:03 +0000	[diff] [blame]	945	<tt>T</tt>, usually <tt>T</tt> publicly derives from
				946	<tt>ilist_node<T></tt>.</p>
Dan Gohman	f17a25c	2007-07-18 16:29:46 +0000	[diff] [blame]	947	</div>
				948
				949	<!-- _______________________________________________________________________ -->
				950	<div class="doc_subsubsection">
Gabor Greif	d970d69	2009-03-12 10:30:31 +0000	[diff] [blame]	951	<a name="dss_ilist_sentinel">Sentinels</a>
				952	</div>
				953
				954	<div class="doc_text">
				955	<p><tt>ilist</tt>s have another speciality that must be considered. To be a good
				956	citizen in the C++ ecosystem, it needs to support the standard container
				957	operations, such as <tt>begin</tt> and <tt>end</tt> iterators, etc. Also, the
				958	<tt>operator--</tt> must work correctly on the <tt>end</tt> iterator in the
				959	case of non-empty <tt>ilist</tt>s.</p>
				960
				961	<p>The only sensible solution to this problem is to allocate a so-called
				962	<i>sentinel</i> along with the intrusive list, which serves as the <tt>end</tt>
				963	iterator, providing the back-link to the last element. However conforming to the
				964	C++ convention it is illegal to <tt>operator++</tt> beyond the sentinel and it
				965	also must not be dereferenced.</p>
				966
				967	<p>These constraints allow for some implementation freedom to the <tt>ilist</tt>
				968	how to allocate and store the sentinel. The corresponding policy is dictated
				969	by <tt>ilist_traits<T></tt>. By default a <tt>T</tt> gets heap-allocated
				970	whenever the need for a sentinel arises.</p>
				971
				972	<p>While the default policy is sufficient in most cases, it may break down when
				973	<tt>T</tt> does not provide a default constructor. Also, in the case of many
				974	instances of <tt>ilist</tt>s, the memory overhead of the associated sentinels
				975	is wasted. To alleviate the situation with numerous and voluminous
				976	<tt>T</tt>-sentinels, sometimes a trick is employed, leading to <i>ghostly
				977	sentinels</i>.</p>
				978
				979	<p>Ghostly sentinels are obtained by specially-crafted <tt>ilist_traits<T></tt>
				980	which superpose the sentinel with the <tt>ilist</tt> instance in memory. Pointer
				981	arithmetic is used to obtain the sentinel, which is relative to the
				982	<tt>ilist</tt>'s <tt>this</tt> pointer. The <tt>ilist</tt> is augmented by an
				983	extra pointer, which serves as the back-link of the sentinel. This is the only
				984	field in the ghostly sentinel which can be legally accessed.</p>
				985	</div>
				986
				987	<!-- _______________________________________________________________________ -->
				988	<div class="doc_subsubsection">
Dan Gohman	f17a25c	2007-07-18 16:29:46 +0000	[diff] [blame]	989	<a name="dss_other">Other Sequential Container options</a>
				990	</div>
				991
				992	<div class="doc_text">
				993	<p>Other STL containers are available, such as std::string.</p>
				994
				995	<p>There are also various STL adapter classes such as std::queue,
				996	std::priority_queue, std::stack, etc. These provide simplified access to an
				997	underlying container but don't affect the cost of the container itself.</p>
				998
				999	</div>
				1000
				1001
				1002	<!-- ======================================================================= -->
				1003	<div class="doc_subsection">
				1004	<a name="ds_set">Set-Like Containers (std::set, SmallSet, SetVector, etc)</a>
				1005	</div>
				1006
				1007	<div class="doc_text">
				1008
				1009	<p>Set-like containers are useful when you need to canonicalize multiple values
				1010	into a single representation. There are several different choices for how to do
				1011	this, providing various trade-offs.</p>
				1012
				1013	</div>
				1014
				1015
				1016	<!-- _______________________________________________________________________ -->
				1017	<div class="doc_subsubsection">
				1018	<a name="dss_sortedvectorset">A sorted 'vector'</a>
				1019	</div>
				1020
				1021	<div class="doc_text">
				1022
				1023	<p>If you intend to insert a lot of elements, then do a lot of queries, a
				1024	great approach is to use a vector (or other sequential container) with
				1025	std::sort+std::unique to remove duplicates. This approach works really well if
				1026	your usage pattern has these two distinct phases (insert then query), and can be
				1027	coupled with a good choice of <a href="#ds_sequential">sequential container</a>.
				1028	</p>
				1029
				1030	<p>
				1031	This combination provides the several nice properties: the result data is
				1032	contiguous in memory (good for cache locality), has few allocations, is easy to
				1033	address (iterators in the final vector are just indices or pointers), and can be
				1034	efficiently queried with a standard binary or radix search.</p>
				1035
				1036	</div>
				1037
				1038	<!-- _______________________________________________________________________ -->
				1039	<div class="doc_subsubsection">
				1040	<a name="dss_smallset">"llvm/ADT/SmallSet.h"</a>
				1041	</div>
				1042
				1043	<div class="doc_text">
				1044
				1045	<p>If you have a set-like data structure that is usually small and whose elements
				1046	are reasonably small, a <tt>SmallSet<Type, N></tt> is a good choice. This set
				1047	has space for N elements in place (thus, if the set is dynamically smaller than
				1048	N, no malloc traffic is required) and accesses them with a simple linear search.
				1049	When the set grows beyond 'N' elements, it allocates a more expensive representation that
				1050	guarantees efficient access (for most types, it falls back to std::set, but for
				1051	pointers it uses something far better, <a
				1052	href="#dss_smallptrset">SmallPtrSet</a>).</p>
				1053
				1054	<p>The magic of this class is that it handles small sets extremely efficiently,
				1055	but gracefully handles extremely large sets without loss of efficiency. The
				1056	drawback is that the interface is quite small: it supports insertion, queries
				1057	and erasing, but does not support iteration.</p>
				1058
				1059	</div>
				1060
				1061	<!-- _______________________________________________________________________ -->
				1062	<div class="doc_subsubsection">
				1063	<a name="dss_smallptrset">"llvm/ADT/SmallPtrSet.h"</a>
				1064	</div>
				1065
				1066	<div class="doc_text">
				1067
				1068	<p>SmallPtrSet has all the advantages of SmallSet (and a SmallSet of pointers is
				1069	transparently implemented with a SmallPtrSet), but also supports iterators. If
				1070	more than 'N' insertions are performed, a single quadratically
				1071	probed hash table is allocated and grows as needed, providing extremely
				1072	efficient access (constant time insertion/deleting/queries with low constant
				1073	factors) and is very stingy with malloc traffic.</p>
				1074
				1075	<p>Note that, unlike std::set, the iterators of SmallPtrSet are invalidated
				1076	whenever an insertion occurs. Also, the values visited by the iterators are not
				1077	visited in sorted order.</p>
				1078
				1079	</div>
				1080
				1081	<!-- _______________________________________________________________________ -->
				1082	<div class="doc_subsubsection">
Chris Lattner	77ab46d	2007-09-30 00:58:59 +0000	[diff] [blame]	1083	<a name="dss_denseset">"llvm/ADT/DenseSet.h"</a>
				1084	</div>
				1085
				1086	<div class="doc_text">
				1087
				1088	<p>
				1089	DenseSet is a simple quadratically probed hash table. It excels at supporting
				1090	small values: it uses a single allocation to hold all of the pairs that
				1091	are currently inserted in the set. DenseSet is a great way to unique small
				1092	values that are not simple pointers (use <a
				1093	href="#dss_smallptrset">SmallPtrSet</a> for pointers). Note that DenseSet has
				1094	the same requirements for the value type that <a
				1095	href="#dss_densemap">DenseMap</a> has.
				1096	</p>
				1097
				1098	</div>
				1099
				1100	<!-- _______________________________________________________________________ -->
				1101	<div class="doc_subsubsection">
Dan Gohman	f17a25c	2007-07-18 16:29:46 +0000	[diff] [blame]	1102	<a name="dss_FoldingSet">"llvm/ADT/FoldingSet.h"</a>
				1103	</div>
				1104
				1105	<div class="doc_text">
				1106
				1107	<p>
				1108	FoldingSet is an aggregate class that is really good at uniquing
				1109	expensive-to-create or polymorphic objects. It is a combination of a chained
				1110	hash table with intrusive links (uniqued objects are required to inherit from
				1111	FoldingSetNode) that uses <a href="#dss_smallvector">SmallVector</a> as part of
				1112	its ID process.</p>
				1113
				1114	<p>Consider a case where you want to implement a "getOrCreateFoo" method for
				1115	a complex object (for example, a node in the code generator). The client has a
				1116	description of what it wants to generate (it knows the opcode and all the
				1117	operands), but we don't want to 'new' a node, then try inserting it into a set
				1118	only to find out it already exists, at which point we would have to delete it
				1119	and return the node that already exists.
				1120	</p>
				1121
				1122	<p>To support this style of client, FoldingSet perform a query with a
				1123	FoldingSetNodeID (which wraps SmallVector) that can be used to describe the
				1124	element that we want to query for. The query either returns the element
				1125	matching the ID or it returns an opaque ID that indicates where insertion should
				1126	take place. Construction of the ID usually does not require heap traffic.</p>
				1127
				1128	<p>Because FoldingSet uses intrusive links, it can support polymorphic objects
				1129	in the set (for example, you can have SDNode instances mixed with LoadSDNodes).
				1130	Because the elements are individually allocated, pointers to the elements are
				1131	stable: inserting or removing elements does not invalidate any pointers to other
				1132	elements.
				1133	</p>
				1134
				1135	</div>
				1136
				1137	<!-- _______________________________________________________________________ -->
				1138	<div class="doc_subsubsection">
				1139	<a name="dss_set"><set></a>
				1140	</div>
				1141
				1142	<div class="doc_text">
				1143
				1144	<p><tt>std::set</tt> is a reasonable all-around set class, which is decent at
				1145	many things but great at nothing. std::set allocates memory for each element
				1146	inserted (thus it is very malloc intensive) and typically stores three pointers
				1147	per element in the set (thus adding a large amount of per-element space
				1148	overhead). It offers guaranteed log(n) performance, which is not particularly
				1149	fast from a complexity standpoint (particularly if the elements of the set are
				1150	expensive to compare, like strings), and has extremely high constant factors for
				1151	lookup, insertion and removal.</p>
				1152
				1153	<p>The advantages of std::set are that its iterators are stable (deleting or
				1154	inserting an element from the set does not affect iterators or pointers to other
				1155	elements) and that iteration over the set is guaranteed to be in sorted order.
				1156	If the elements in the set are large, then the relative overhead of the pointers
				1157	and malloc traffic is not a big deal, but if the elements of the set are small,
				1158	std::set is almost never a good choice.</p>
				1159
				1160	</div>
				1161
				1162	<!-- _______________________________________________________________________ -->
				1163	<div class="doc_subsubsection">
				1164	<a name="dss_setvector">"llvm/ADT/SetVector.h"</a>
				1165	</div>
				1166
				1167	<div class="doc_text">
				1168	<p>LLVM's SetVector<Type> is an adapter class that combines your choice of
				1169	a set-like container along with a <a href="#ds_sequential">Sequential
				1170	Container</a>. The important property
				1171	that this provides is efficient insertion with uniquing (duplicate elements are
				1172	ignored) with iteration support. It implements this by inserting elements into
				1173	both a set-like container and the sequential container, using the set-like
				1174	container for uniquing and the sequential container for iteration.
				1175	</p>
				1176
				1177	<p>The difference between SetVector and other sets is that the order of
				1178	iteration is guaranteed to match the order of insertion into the SetVector.
				1179	This property is really important for things like sets of pointers. Because
				1180	pointer values are non-deterministic (e.g. vary across runs of the program on
				1181	different machines), iterating over the pointers in the set will
				1182	not be in a well-defined order.</p>
				1183
				1184	<p>
				1185	The drawback of SetVector is that it requires twice as much space as a normal
				1186	set and has the sum of constant factors from the set-like container and the
				1187	sequential container that it uses. Use it only if you need to iterate over
				1188	the elements in a deterministic order. SetVector is also expensive to delete
				1189	elements out of (linear time), unless you use it's "pop_back" method, which is
				1190	faster.
				1191	</p>
				1192
				1193	<p>SetVector is an adapter class that defaults to using std::vector and std::set
				1194	for the underlying containers, so it is quite expensive. However,
				1195	<tt>"llvm/ADT/SetVector.h"</tt> also provides a SmallSetVector class, which
				1196	defaults to using a SmallVector and SmallSet of a specified size. If you use
				1197	this, and if your sets are dynamically smaller than N, you will save a lot of
				1198	heap traffic.</p>
				1199
				1200	</div>
				1201
				1202	<!-- _______________________________________________________________________ -->
				1203	<div class="doc_subsubsection">
				1204	<a name="dss_uniquevector">"llvm/ADT/UniqueVector.h"</a>
				1205	</div>
				1206
				1207	<div class="doc_text">
				1208
				1209	<p>
				1210	UniqueVector is similar to <a href="#dss_setvector">SetVector</a>, but it
				1211	retains a unique ID for each element inserted into the set. It internally
				1212	contains a map and a vector, and it assigns a unique ID for each value inserted
				1213	into the set.</p>
				1214
				1215	<p>UniqueVector is very expensive: its cost is the sum of the cost of
				1216	maintaining both the map and vector, it has high complexity, high constant
				1217	factors, and produces a lot of malloc traffic. It should be avoided.</p>
				1218
				1219	</div>
				1220
				1221
				1222	<!-- _______________________________________________________________________ -->
				1223	<div class="doc_subsubsection">
				1224	<a name="dss_otherset">Other Set-Like Container Options</a>
				1225	</div>
				1226
				1227	<div class="doc_text">
				1228
				1229	<p>
				1230	The STL provides several other options, such as std::multiset and the various
Chris Lattner	86a63d0	2009-03-09 05:20:45 +0000	[diff] [blame]	1231	"hash_set" like containers (whether from C++ TR1 or from the SGI library). We
				1232	never use hash_set and unordered_set because they are generally very expensive
				1233	(each insertion requires a malloc) and very non-portable.
				1234	</p>
Dan Gohman	f17a25c	2007-07-18 16:29:46 +0000	[diff] [blame]	1235
				1236	<p>std::multiset is useful if you're not interested in elimination of
				1237	duplicates, but has all the drawbacks of std::set. A sorted vector (where you
				1238	don't delete duplicate entries) or some other approach is almost always
				1239	better.</p>
				1240
Dan Gohman	f17a25c	2007-07-18 16:29:46 +0000	[diff] [blame]	1241	</div>
				1242
				1243	<!-- ======================================================================= -->
				1244	<div class="doc_subsection">
				1245	<a name="ds_map">Map-Like Containers (std::map, DenseMap, etc)</a>
				1246	</div>
				1247
				1248	<div class="doc_text">
				1249	Map-like containers are useful when you want to associate data to a key. As
				1250	usual, there are a lot of different ways to do this. :)
				1251	</div>
				1252
				1253	<!-- _______________________________________________________________________ -->
				1254	<div class="doc_subsubsection">
				1255	<a name="dss_sortedvectormap">A sorted 'vector'</a>
				1256	</div>
				1257
				1258	<div class="doc_text">
				1259
				1260	<p>
				1261	If your usage pattern follows a strict insert-then-query approach, you can
				1262	trivially use the same approach as <a href="#dss_sortedvectorset">sorted vectors
				1263	for set-like containers</a>. The only difference is that your query function
				1264	(which uses std::lower_bound to get efficient log(n) lookup) should only compare
				1265	the key, not both the key and value. This yields the same advantages as sorted
				1266	vectors for sets.
				1267	</p>
				1268	</div>
				1269
				1270	<!-- _______________________________________________________________________ -->
				1271	<div class="doc_subsubsection">
				1272	<a name="dss_stringmap">"llvm/ADT/StringMap.h"</a>
				1273	</div>
				1274
				1275	<div class="doc_text">
				1276
				1277	<p>
				1278	Strings are commonly used as keys in maps, and they are difficult to support
				1279	efficiently: they are variable length, inefficient to hash and compare when
				1280	long, expensive to copy, etc. StringMap is a specialized container designed to
				1281	cope with these issues. It supports mapping an arbitrary range of bytes to an
				1282	arbitrary other object.</p>
				1283
				1284	<p>The StringMap implementation uses a quadratically-probed hash table, where
				1285	the buckets store a pointer to the heap allocated entries (and some other
				1286	stuff). The entries in the map must be heap allocated because the strings are
				1287	variable length. The string data (key) and the element object (value) are
				1288	stored in the same allocation with the string data immediately after the element
				1289	object. This container guarantees the "<tt>(char*)(&Value+1)</tt>" points
				1290	to the key string for a value.</p>
				1291
				1292	<p>The StringMap is very fast for several reasons: quadratic probing is very
				1293	cache efficient for lookups, the hash value of strings in buckets is not
				1294	recomputed when lookup up an element, StringMap rarely has to touch the
				1295	memory for unrelated objects when looking up a value (even when hash collisions
				1296	happen), hash table growth does not recompute the hash values for strings
				1297	already in the table, and each pair in the map is store in a single allocation
				1298	(the string data is stored in the same allocation as the Value of a pair).</p>
				1299
				1300	<p>StringMap also provides query methods that take byte ranges, so it only ever
				1301	copies a string if a value is inserted into the table.</p>
				1302	</div>
				1303
				1304	<!-- _______________________________________________________________________ -->
				1305	<div class="doc_subsubsection">
				1306	<a name="dss_indexedmap">"llvm/ADT/IndexedMap.h"</a>
				1307	</div>
				1308
				1309	<div class="doc_text">
				1310	<p>
				1311	IndexedMap is a specialized container for mapping small dense integers (or
				1312	values that can be mapped to small dense integers) to some other type. It is
				1313	internally implemented as a vector with a mapping function that maps the keys to
				1314	the dense integer range.
				1315	</p>
				1316
				1317	<p>
				1318	This is useful for cases like virtual registers in the LLVM code generator: they
				1319	have a dense mapping that is offset by a compile-time constant (the first
				1320	virtual register ID).</p>
				1321
				1322	</div>
				1323
				1324	<!-- _______________________________________________________________________ -->
				1325	<div class="doc_subsubsection">
				1326	<a name="dss_densemap">"llvm/ADT/DenseMap.h"</a>
				1327	</div>
				1328
				1329	<div class="doc_text">
				1330
				1331	<p>
				1332	DenseMap is a simple quadratically probed hash table. It excels at supporting
				1333	small keys and values: it uses a single allocation to hold all of the pairs that
				1334	are currently inserted in the map. DenseMap is a great way to map pointers to
				1335	pointers, or map other small types to each other.
				1336	</p>
				1337
				1338	<p>
				1339	There are several aspects of DenseMap that you should be aware of, however. The
				1340	iterators in a densemap are invalidated whenever an insertion occurs, unlike
				1341	map. Also, because DenseMap allocates space for a large number of key/value
				1342	pairs (it starts with 64 by default), it will waste a lot of space if your keys
				1343	or values are large. Finally, you must implement a partial specialization of
Chris Lattner	92eea07	2007-09-17 18:34:04 +0000	[diff] [blame]	1344	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]	1345	is required to tell DenseMap about two special marker values (which can never be
				1346	inserted into the map) that it needs internally.</p>
				1347
				1348	</div>
				1349
				1350	<!-- _______________________________________________________________________ -->
				1351	<div class="doc_subsubsection">
				1352	<a name="dss_map"><map></a>
				1353	</div>
				1354
				1355	<div class="doc_text">
				1356
				1357	<p>
				1358	std::map has similar characteristics to <a href="#dss_set">std::set</a>: it uses
				1359	a single allocation per pair inserted into the map, it offers log(n) lookup with
				1360	an extremely large constant factor, imposes a space penalty of 3 pointers per
				1361	pair in the map, etc.</p>
				1362
				1363	<p>std::map is most useful when your keys or values are very large, if you need
				1364	to iterate over the collection in sorted order, or if you need stable iterators
				1365	into the map (i.e. they don't get invalidated if an insertion or deletion of
				1366	another element takes place).</p>
				1367
				1368	</div>
				1369
				1370	<!-- _______________________________________________________________________ -->
				1371	<div class="doc_subsubsection">
				1372	<a name="dss_othermap">Other Map-Like Container Options</a>
				1373	</div>
				1374
				1375	<div class="doc_text">
				1376
				1377	<p>
				1378	The STL provides several other options, such as std::multimap and the various
Chris Lattner	86a63d0	2009-03-09 05:20:45 +0000	[diff] [blame]	1379	"hash_map" like containers (whether from C++ TR1 or from the SGI library). We
				1380	never use hash_set and unordered_set because they are generally very expensive
				1381	(each insertion requires a malloc) and very non-portable.</p>
Dan Gohman	f17a25c	2007-07-18 16:29:46 +0000	[diff] [blame]	1382
				1383	<p>std::multimap is useful if you want to map a key to multiple values, but has
				1384	all the drawbacks of std::map. A sorted vector or some other approach is almost
				1385	always better.</p>
				1386
Dan Gohman	f17a25c	2007-07-18 16:29:46 +0000	[diff] [blame]	1387	</div>
				1388
Daniel Berlin	7ea44dc	2007-09-24 17:52:25 +0000	[diff] [blame]	1389	<!-- ======================================================================= -->
				1390	<div class="doc_subsection">
				1391	<a name="ds_bit">Bit storage containers (BitVector, SparseBitVector)</a>
				1392	</div>
				1393
				1394	<div class="doc_text">
Chris Lattner	62a4eae	2007-09-25 22:37:50 +0000	[diff] [blame]	1395	<p>Unlike the other containers, there are only two bit storage containers, and
				1396	choosing when to use each is relatively straightforward.</p>
				1397
				1398	<p>One additional option is
				1399	<tt>std::vector<bool></tt>: we discourage its use for two reasons 1) the
				1400	implementation in many common compilers (e.g. commonly available versions of
				1401	GCC) is extremely inefficient and 2) the C++ standards committee is likely to
				1402	deprecate this container and/or change it significantly somehow. In any case,
				1403	please don't use it.</p>
Daniel Berlin	7ea44dc	2007-09-24 17:52:25 +0000	[diff] [blame]	1404	</div>
				1405
				1406	<!-- _______________________________________________________________________ -->
				1407	<div class="doc_subsubsection">
				1408	<a name="dss_bitvector">BitVector</a>
				1409	</div>
				1410
				1411	<div class="doc_text">
				1412	<p> The BitVector container provides a fixed size set of bits for manipulation.
				1413	It supports individual bit setting/testing, as well as set operations. The set
				1414	operations take time O(size of bitvector), but operations are performed one word
				1415	at a time, instead of one bit at a time. This makes the BitVector very fast for
				1416	set operations compared to other containers. Use the BitVector when you expect
				1417	the number of set bits to be high (IE a dense set).
				1418	</p>
				1419	</div>
				1420
				1421	<!-- _______________________________________________________________________ -->
				1422	<div class="doc_subsubsection">
				1423	<a name="dss_sparsebitvector">SparseBitVector</a>
				1424	</div>
				1425
				1426	<div class="doc_text">
				1427	<p> The SparseBitVector container is much like BitVector, with one major
				1428	difference: Only the bits that are set, are stored. This makes the
				1429	SparseBitVector much more space efficient than BitVector when the set is sparse,
				1430	as well as making set operations O(number of set bits) instead of O(size of
				1431	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
				1432	(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).
				1433	</p>
				1434	</div>
Dan Gohman	f17a25c	2007-07-18 16:29:46 +0000	[diff] [blame]	1435
				1436	<!-- *********************************************************************** -->
				1437	<div class="doc_section">
				1438	<a name="common">Helpful Hints for Common Operations</a>
				1439	</div>
				1440	<!-- *********************************************************************** -->
				1441
				1442	<div class="doc_text">
				1443
				1444	<p>This section describes how to perform some very simple transformations of
				1445	LLVM code. This is meant to give examples of common idioms used, showing the
				1446	practical side of LLVM transformations. <p> Because this is a "how-to" section,
				1447	you should also read about the main classes that you will be working with. The
				1448	<a href="#coreclasses">Core LLVM Class Hierarchy Reference</a> contains details
				1449	and descriptions of the main classes that you should know about.</p>
				1450
				1451	</div>
				1452
				1453	<!-- NOTE: this section should be heavy on example code -->
				1454	<!-- ======================================================================= -->
				1455	<div class="doc_subsection">
				1456	<a name="inspection">Basic Inspection and Traversal Routines</a>
				1457	</div>
				1458
				1459	<div class="doc_text">
				1460
				1461	<p>The LLVM compiler infrastructure have many different data structures that may
				1462	be traversed. Following the example of the C++ standard template library, the
				1463	techniques used to traverse these various data structures are all basically the
				1464	same. For a enumerable sequence of values, the <tt>XXXbegin()</tt> function (or
				1465	method) returns an iterator to the start of the sequence, the <tt>XXXend()</tt>
				1466	function returns an iterator pointing to one past the last valid element of the
				1467	sequence, and there is some <tt>XXXiterator</tt> data type that is common
				1468	between the two operations.</p>
				1469
				1470	<p>Because the pattern for iteration is common across many different aspects of
				1471	the program representation, the standard template library algorithms may be used
				1472	on them, and it is easier to remember how to iterate. First we show a few common
				1473	examples of the data structures that need to be traversed. Other data
				1474	structures are traversed in very similar ways.</p>
				1475
				1476	</div>
				1477
				1478	<!-- _______________________________________________________________________ -->
				1479	<div class="doc_subsubsection">
				1480	<a name="iterate_function">Iterating over the </a><a
				1481	href="#BasicBlock"><tt>BasicBlock</tt></a>s in a <a
				1482	href="#Function"><tt>Function</tt></a>
				1483	</div>
				1484
				1485	<div class="doc_text">
				1486
				1487	<p>It's quite common to have a <tt>Function</tt> instance that you'd like to
				1488	transform in some way; in particular, you'd like to manipulate its
				1489	<tt>BasicBlock</tt>s. To facilitate this, you'll need to iterate over all of
				1490	the <tt>BasicBlock</tt>s that constitute the <tt>Function</tt>. The following is
				1491	an example that prints the name of a <tt>BasicBlock</tt> and the number of
				1492	<tt>Instruction</tt>s it contains:</p>
				1493
				1494	<div class="doc_code">
				1495	<pre>
				1496	// <i>func is a pointer to a Function instance</i>
				1497	for (Function::iterator i = func->begin(), e = func->end(); i != e; ++i)
				1498	// <i>Print out the name of the basic block if it has one, and then the</i>
				1499	// <i>number of instructions that it contains</i>
				1500	llvm::cerr << "Basic block (name=" << i->getName() << ") has "
				1501	<< i->size() << " instructions.\n";
				1502	</pre>
				1503	</div>
				1504
				1505	<p>Note that i can be used as if it were a pointer for the purposes of
				1506	invoking member functions of the <tt>Instruction</tt> class. This is
				1507	because the indirection operator is overloaded for the iterator
				1508	classes. In the above code, the expression <tt>i->size()</tt> is
				1509	exactly equivalent to <tt>(*i).size()</tt> just like you'd expect.</p>
				1510
				1511	</div>
				1512
				1513	<!-- _______________________________________________________________________ -->
				1514	<div class="doc_subsubsection">
				1515	<a name="iterate_basicblock">Iterating over the </a><a
				1516	href="#Instruction"><tt>Instruction</tt></a>s in a <a
				1517	href="#BasicBlock"><tt>BasicBlock</tt></a>
				1518	</div>
				1519
				1520	<div class="doc_text">
				1521
				1522	<p>Just like when dealing with <tt>BasicBlock</tt>s in <tt>Function</tt>s, it's
				1523	easy to iterate over the individual instructions that make up
				1524	<tt>BasicBlock</tt>s. Here's a code snippet that prints out each instruction in
				1525	a <tt>BasicBlock</tt>:</p>
				1526
				1527	<div class="doc_code">
				1528	<pre>
				1529	// <i>blk is a pointer to a BasicBlock instance</i>
				1530	for (BasicBlock::iterator i = blk->begin(), e = blk->end(); i != e; ++i)
				1531	// <i>The next statement works since operator<<(ostream&,...)</i>
				1532	// <i>is overloaded for Instruction&</i>
				1533	llvm::cerr << *i << "\n";
				1534	</pre>
				1535	</div>
				1536
				1537	<p>However, this isn't really the best way to print out the contents of a
				1538	<tt>BasicBlock</tt>! Since the ostream operators are overloaded for virtually
				1539	anything you'll care about, you could have just invoked the print routine on the
				1540	basic block itself: <tt>llvm::cerr << *blk << "\n";</tt>.</p>
				1541
				1542	</div>
				1543
				1544	<!-- _______________________________________________________________________ -->
				1545	<div class="doc_subsubsection">
				1546	<a name="iterate_institer">Iterating over the </a><a
				1547	href="#Instruction"><tt>Instruction</tt></a>s in a <a
				1548	href="#Function"><tt>Function</tt></a>
				1549	</div>
				1550
				1551	<div class="doc_text">
				1552
				1553	<p>If you're finding that you commonly iterate over a <tt>Function</tt>'s
				1554	<tt>BasicBlock</tt>s and then that <tt>BasicBlock</tt>'s <tt>Instruction</tt>s,
				1555	<tt>InstIterator</tt> should be used instead. You'll need to include <a
				1556	href="/doxygen/InstIterator_8h-source.html"><tt>llvm/Support/InstIterator.h</tt></a>,
				1557	and then instantiate <tt>InstIterator</tt>s explicitly in your code. Here's a
				1558	small example that shows how to dump all instructions in a function to the standard error stream:<p>
				1559
				1560	<div class="doc_code">
				1561	<pre>
				1562	#include "<a href="/doxygen/InstIterator_8h-source.html">llvm/Support/InstIterator.h</a>"
				1563
				1564	// <i>F is a pointer to a Function instance</i>
Chris Lattner	fd62ee7	2008-06-04 18:20:42 +0000	[diff] [blame]	1565	for (inst_iterator I = inst_begin(F), E = inst_end(F); I != E; ++I)
				1566	llvm::cerr << *I << "\n";
Dan Gohman	f17a25c	2007-07-18 16:29:46 +0000	[diff] [blame]	1567	</pre>
				1568	</div>
				1569
				1570	<p>Easy, isn't it? You can also use <tt>InstIterator</tt>s to fill a
				1571	work list with its initial contents. For example, if you wanted to
				1572	initialize a work list to contain all instructions in a <tt>Function</tt>
				1573	F, all you would need to do is something like:</p>
				1574
				1575	<div class="doc_code">
				1576	<pre>
				1577	std::set<Instruction*> worklist;
Chris Lattner	fd62ee7	2008-06-04 18:20:42 +0000	[diff] [blame]	1578	// or better yet, SmallPtrSet<Instruction*, 64> worklist;
				1579
				1580	for (inst_iterator I = inst_begin(F), E = inst_end(F); I != E; ++I)
				1581	worklist.insert(&*I);
Dan Gohman	f17a25c	2007-07-18 16:29:46 +0000	[diff] [blame]	1582	</pre>
				1583	</div>
				1584
				1585	<p>The STL set <tt>worklist</tt> would now contain all instructions in the
				1586	<tt>Function</tt> pointed to by F.</p>
				1587
				1588	</div>
				1589
				1590	<!-- _______________________________________________________________________ -->
				1591	<div class="doc_subsubsection">
				1592	<a name="iterate_convert">Turning an iterator into a class pointer (and
				1593	vice-versa)</a>
				1594	</div>
				1595
				1596	<div class="doc_text">
				1597
				1598	<p>Sometimes, it'll be useful to grab a reference (or pointer) to a class
				1599	instance when all you've got at hand is an iterator. Well, extracting
				1600	a reference or a pointer from an iterator is very straight-forward.
				1601	Assuming that <tt>i</tt> is a <tt>BasicBlock::iterator</tt> and <tt>j</tt>
				1602	is a <tt>BasicBlock::const_iterator</tt>:</p>
				1603
				1604	<div class="doc_code">
				1605	<pre>
				1606	Instruction& inst = *i; // <i>Grab reference to instruction reference</i>
				1607	Instruction* pinst = &*i; // <i>Grab pointer to instruction reference</i>
				1608	const Instruction& inst = *j;
				1609	</pre>
				1610	</div>
				1611
				1612	<p>However, the iterators you'll be working with in the LLVM framework are
				1613	special: they will automatically convert to a ptr-to-instance type whenever they
				1614	need to. Instead of dereferencing the iterator and then taking the address of
				1615	the result, you can simply assign the iterator to the proper pointer type and
				1616	you get the dereference and address-of operation as a result of the assignment
				1617	(behind the scenes, this is a result of overloading casting mechanisms). Thus
				1618	the last line of the last example,</p>
				1619
				1620	<div class="doc_code">
				1621	<pre>
Chris Lattner	0665e1f	2008-01-03 16:56:04 +0000	[diff] [blame]	1622	Instruction pinst = &i;
Dan Gohman	f17a25c	2007-07-18 16:29:46 +0000	[diff] [blame]	1623	</pre>
				1624	</div>
				1625
				1626	<p>is semantically equivalent to</p>
				1627
				1628	<div class="doc_code">
				1629	<pre>
Chris Lattner	0665e1f	2008-01-03 16:56:04 +0000	[diff] [blame]	1630	Instruction *pinst = i;
Dan Gohman	f17a25c	2007-07-18 16:29:46 +0000	[diff] [blame]	1631	</pre>
				1632	</div>
				1633
				1634	<p>It's also possible to turn a class pointer into the corresponding iterator,
				1635	and this is a constant time operation (very efficient). The following code
				1636	snippet illustrates use of the conversion constructors provided by LLVM
				1637	iterators. By using these, you can explicitly grab the iterator of something
				1638	without actually obtaining it via iteration over some structure:</p>
				1639
				1640	<div class="doc_code">
				1641	<pre>
				1642	void printNextInstruction(Instruction* inst) {
				1643	BasicBlock::iterator it(inst);
				1644	++it; // <i>After this line, it refers to the instruction after *inst</i>
				1645	if (it != inst->getParent()->end()) llvm::cerr << *it << "\n";
				1646	}
				1647	</pre>
				1648	</div>
				1649
				1650	</div>
				1651
				1652	<!--_______________________________________________________________________-->
				1653	<div class="doc_subsubsection">
				1654	<a name="iterate_complex">Finding call sites: a slightly more complex
				1655	example</a>
				1656	</div>
				1657
				1658	<div class="doc_text">
				1659
				1660	<p>Say that you're writing a FunctionPass and would like to count all the
				1661	locations in the entire module (that is, across every <tt>Function</tt>) where a
				1662	certain function (i.e., some <tt>Function</tt>*) is already in scope. As you'll
				1663	learn later, you may want to use an <tt>InstVisitor</tt> to accomplish this in a
				1664	much more straight-forward manner, but this example will allow us to explore how
				1665	you'd do it if you didn't have <tt>InstVisitor</tt> around. In pseudo-code, this
				1666	is what we want to do:</p>
				1667
				1668	<div class="doc_code">
				1669	<pre>
				1670	initialize callCounter to zero
				1671	for each Function f in the Module
				1672	for each BasicBlock b in f
				1673	for each Instruction i in b
				1674	if (i is a CallInst and calls the given function)
				1675	increment callCounter
				1676	</pre>
				1677	</div>
				1678
				1679	<p>And the actual code is (remember, because we're writing a
				1680	<tt>FunctionPass</tt>, our <tt>FunctionPass</tt>-derived class simply has to
				1681	override the <tt>runOnFunction</tt> method):</p>
				1682
				1683	<div class="doc_code">
				1684	<pre>
				1685	Function* targetFunc = ...;
				1686
				1687	class OurFunctionPass : public FunctionPass {
				1688	public:
				1689	OurFunctionPass(): callCounter(0) { }
				1690
				1691	virtual runOnFunction(Function& F) {
				1692	for (Function::iterator b = F.begin(), be = F.end(); b != be; ++b) {
Eric Christopher	5fbecf7	2008-11-08 08:20:49 +0000	[diff] [blame]	1693	for (BasicBlock::iterator i = b->begin(), ie = b->end(); i != ie; ++i) {
Dan Gohman	f17a25c	2007-07-18 16:29:46 +0000	[diff] [blame]	1694	if (<a href="#CallInst">CallInst</a>* callInst = <a href="#isa">dyn_cast</a><<a
				1695	href="#CallInst">CallInst</a>>(&*i)) {
				1696	// <i>We know we've encountered a call instruction, so we</i>
				1697	// <i>need to determine if it's a call to the</i>
Chris Lattner	0665e1f	2008-01-03 16:56:04 +0000	[diff] [blame]	1698	// <i>function pointed to by m_func or not.</i>
Dan Gohman	f17a25c	2007-07-18 16:29:46 +0000	[diff] [blame]	1699	if (callInst->getCalledFunction() == targetFunc)
				1700	++callCounter;
				1701	}
				1702	}
				1703	}
				1704	}
				1705
				1706	private:
Chris Lattner	0665e1f	2008-01-03 16:56:04 +0000	[diff] [blame]	1707	unsigned callCounter;
Dan Gohman	f17a25c	2007-07-18 16:29:46 +0000	[diff] [blame]	1708	};
				1709	</pre>
				1710	</div>
				1711
				1712	</div>
				1713
				1714	<!--_______________________________________________________________________-->
				1715	<div class="doc_subsubsection">
				1716	<a name="calls_and_invokes">Treating calls and invokes the same way</a>
				1717	</div>
				1718
				1719	<div class="doc_text">
				1720
				1721	<p>You may have noticed that the previous example was a bit oversimplified in
				1722	that it did not deal with call sites generated by 'invoke' instructions. In
				1723	this, and in other situations, you may find that you want to treat
				1724	<tt>CallInst</tt>s and <tt>InvokeInst</tt>s the same way, even though their
				1725	most-specific common base class is <tt>Instruction</tt>, which includes lots of
				1726	less closely-related things. For these cases, LLVM provides a handy wrapper
				1727	class called <a
				1728	href="http://llvm.org/doxygen/classllvm_1_1CallSite.html"><tt>CallSite</tt></a>.
				1729	It is essentially a wrapper around an <tt>Instruction</tt> pointer, with some
				1730	methods that provide functionality common to <tt>CallInst</tt>s and
				1731	<tt>InvokeInst</tt>s.</p>
				1732
				1733	<p>This class has "value semantics": it should be passed by value, not by
				1734	reference and it should not be dynamically allocated or deallocated using
				1735	<tt>operator new</tt> or <tt>operator delete</tt>. It is efficiently copyable,
				1736	assignable and constructable, with costs equivalents to that of a bare pointer.
				1737	If you look at its definition, it has only a single pointer member.</p>
				1738
				1739	</div>
				1740
				1741	<!--_______________________________________________________________________-->
				1742	<div class="doc_subsubsection">
				1743	<a name="iterate_chains">Iterating over def-use & use-def chains</a>
				1744	</div>
				1745
				1746	<div class="doc_text">
				1747
				1748	<p>Frequently, we might have an instance of the <a
				1749	href="/doxygen/classllvm_1_1Value.html">Value Class</a> and we want to
				1750	determine which <tt>User</tt>s use the <tt>Value</tt>. The list of all
				1751	<tt>User</tt>s of a particular <tt>Value</tt> is called a <i>def-use</i> chain.
				1752	For example, let's say we have a <tt>Function*</tt> named <tt>F</tt> to a
				1753	particular function <tt>foo</tt>. Finding all of the instructions that
				1754	<i>use</i> <tt>foo</tt> is as simple as iterating over the <i>def-use</i> chain
				1755	of <tt>F</tt>:</p>
				1756
				1757	<div class="doc_code">
				1758	<pre>
Chris Lattner	0665e1f	2008-01-03 16:56:04 +0000	[diff] [blame]	1759	Function *F = ...;
Dan Gohman	f17a25c	2007-07-18 16:29:46 +0000	[diff] [blame]	1760
				1761	for (Value::use_iterator i = F->use_begin(), e = F->use_end(); i != e; ++i)
				1762	if (Instruction Inst = dyn_cast<Instruction>(i)) {
				1763	llvm::cerr << "F is used in instruction:\n";
				1764	llvm::cerr << *Inst << "\n";
				1765	}
				1766	</pre>
				1767	</div>
				1768
				1769	<p>Alternately, it's common to have an instance of the <a
				1770	href="/doxygen/classllvm_1_1User.html">User Class</a> and need to know what
				1771	<tt>Value</tt>s are used by it. The list of all <tt>Value</tt>s used by a
				1772	<tt>User</tt> is known as a <i>use-def</i> chain. Instances of class
				1773	<tt>Instruction</tt> are common <tt>User</tt>s, so we might want to iterate over
				1774	all of the values that a particular instruction uses (that is, the operands of
				1775	the particular <tt>Instruction</tt>):</p>
				1776
				1777	<div class="doc_code">
				1778	<pre>
Chris Lattner	0665e1f	2008-01-03 16:56:04 +0000	[diff] [blame]	1779	Instruction *pi = ...;
Dan Gohman	f17a25c	2007-07-18 16:29:46 +0000	[diff] [blame]	1780
				1781	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]	1782	Value v = i;
Dan Gohman	f17a25c	2007-07-18 16:29:46 +0000	[diff] [blame]	1783	// <i>...</i>
				1784	}
				1785	</pre>
				1786	</div>
				1787
				1788	<!--
				1789	def-use chains ("finding all users of"): Value::use_begin/use_end
				1790	use-def chains ("finding all values used"): User::op_begin/op_end [op=operand]
				1791	-->
				1792
				1793	</div>
				1794
Chris Lattner	0665e1f	2008-01-03 16:56:04 +0000	[diff] [blame]	1795	<!--_______________________________________________________________________-->
				1796	<div class="doc_subsubsection">
				1797	<a name="iterate_preds">Iterating over predecessors &
				1798	successors of blocks</a>
				1799	</div>
				1800
				1801	<div class="doc_text">
				1802
				1803	<p>Iterating over the predecessors and successors of a block is quite easy
				1804	with the routines defined in <tt>"llvm/Support/CFG.h"</tt>. Just use code like
				1805	this to iterate over all predecessors of BB:</p>
				1806
				1807	<div class="doc_code">
				1808	<pre>
				1809	#include "llvm/Support/CFG.h"
				1810	BasicBlock *BB = ...;
				1811
				1812	for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI) {
				1813	BasicBlock Pred = PI;
				1814	// <i>...</i>
				1815	}
				1816	</pre>
				1817	</div>
				1818
				1819	<p>Similarly, to iterate over successors use
				1820	succ_iterator/succ_begin/succ_end.</p>
				1821
				1822	</div>
				1823
				1824
Dan Gohman	f17a25c	2007-07-18 16:29:46 +0000	[diff] [blame]	1825	<!-- ======================================================================= -->
				1826	<div class="doc_subsection">
				1827	<a name="simplechanges">Making simple changes</a>
				1828	</div>
				1829
				1830	<div class="doc_text">
				1831
				1832	<p>There are some primitive transformation operations present in the LLVM
				1833	infrastructure that are worth knowing about. When performing
				1834	transformations, it's fairly common to manipulate the contents of basic
				1835	blocks. This section describes some of the common methods for doing so
				1836	and gives example code.</p>
				1837
				1838	</div>
				1839
				1840	<!--_______________________________________________________________________-->
				1841	<div class="doc_subsubsection">
				1842	<a name="schanges_creating">Creating and inserting new
				1843	<tt>Instruction</tt>s</a>
				1844	</div>
				1845
				1846	<div class="doc_text">
				1847
				1848	<p><i>Instantiating Instructions</i></p>
				1849
				1850	<p>Creation of <tt>Instruction</tt>s is straight-forward: simply call the
				1851	constructor for the kind of instruction to instantiate and provide the necessary
				1852	parameters. For example, an <tt>AllocaInst</tt> only <i>requires</i> a
				1853	(const-ptr-to) <tt>Type</tt>. Thus:</p>
				1854
				1855	<div class="doc_code">
				1856	<pre>
Nick Lewycky	c004e5b	2007-12-03 01:52:52 +0000	[diff] [blame]	1857	AllocaInst* ai = new AllocaInst(Type::Int32Ty);
Dan Gohman	f17a25c	2007-07-18 16:29:46 +0000	[diff] [blame]	1858	</pre>
				1859	</div>
				1860
				1861	<p>will create an <tt>AllocaInst</tt> instance that represents the allocation of
				1862	one integer in the current stack frame, at run time. Each <tt>Instruction</tt>
				1863	subclass is likely to have varying default parameters which change the semantics
				1864	of the instruction, so refer to the <a
				1865	href="/doxygen/classllvm_1_1Instruction.html">doxygen documentation for the subclass of
				1866	Instruction</a> that you're interested in instantiating.</p>
				1867
				1868	<p><i>Naming values</i></p>
				1869
				1870	<p>It is very useful to name the values of instructions when you're able to, as
				1871	this facilitates the debugging of your transformations. If you end up looking
				1872	at generated LLVM machine code, you definitely want to have logical names
				1873	associated with the results of instructions! By supplying a value for the
				1874	<tt>Name</tt> (default) parameter of the <tt>Instruction</tt> constructor, you
				1875	associate a logical name with the result of the instruction's execution at
				1876	run time. For example, say that I'm writing a transformation that dynamically
				1877	allocates space for an integer on the stack, and that integer is going to be
				1878	used as some kind of index by some other code. To accomplish this, I place an
				1879	<tt>AllocaInst</tt> at the first point in the first <tt>BasicBlock</tt> of some
				1880	<tt>Function</tt>, and I'm intending to use it within the same
				1881	<tt>Function</tt>. I might do:</p>
				1882
				1883	<div class="doc_code">
				1884	<pre>
Nick Lewycky	c004e5b	2007-12-03 01:52:52 +0000	[diff] [blame]	1885	AllocaInst* pa = new AllocaInst(Type::Int32Ty, 0, "indexLoc");
Dan Gohman	f17a25c	2007-07-18 16:29:46 +0000	[diff] [blame]	1886	</pre>
				1887	</div>
				1888
				1889	<p>where <tt>indexLoc</tt> is now the logical name of the instruction's
				1890	execution value, which is a pointer to an integer on the run time stack.</p>
				1891
				1892	<p><i>Inserting instructions</i></p>
				1893
				1894	<p>There are essentially two ways to insert an <tt>Instruction</tt>
				1895	into an existing sequence of instructions that form a <tt>BasicBlock</tt>:</p>
				1896
				1897	<ul>
				1898	<li>Insertion into an explicit instruction list
				1899
				1900	<p>Given a <tt>BasicBlock* pb</tt>, an <tt>Instruction* pi</tt> within that
				1901	<tt>BasicBlock</tt>, and a newly-created instruction we wish to insert
				1902	before <tt>*pi</tt>, we do the following: </p>
				1903
				1904	<div class="doc_code">
				1905	<pre>
				1906	BasicBlock *pb = ...;
				1907	Instruction *pi = ...;
				1908	Instruction *newInst = new Instruction(...);
				1909
				1910	pb->getInstList().insert(pi, newInst); // <i>Inserts newInst before pi in pb</i>
				1911	</pre>
				1912	</div>
				1913
				1914	<p>Appending to the end of a <tt>BasicBlock</tt> is so common that
				1915	the <tt>Instruction</tt> class and <tt>Instruction</tt>-derived
				1916	classes provide constructors which take a pointer to a
				1917	<tt>BasicBlock</tt> to be appended to. For example code that
				1918	looked like: </p>
				1919
				1920	<div class="doc_code">
				1921	<pre>
				1922	BasicBlock *pb = ...;
				1923	Instruction *newInst = new Instruction(...);
				1924
				1925	pb->getInstList().push_back(newInst); // <i>Appends newInst to pb</i>
				1926	</pre>
				1927	</div>
				1928
				1929	<p>becomes: </p>
				1930
				1931	<div class="doc_code">
				1932	<pre>
				1933	BasicBlock *pb = ...;
				1934	Instruction *newInst = new Instruction(..., pb);
				1935	</pre>
				1936	</div>
				1937
				1938	<p>which is much cleaner, especially if you are creating
				1939	long instruction streams.</p></li>
				1940
				1941	<li>Insertion into an implicit instruction list
				1942
				1943	<p><tt>Instruction</tt> instances that are already in <tt>BasicBlock</tt>s
				1944	are implicitly associated with an existing instruction list: the instruction
				1945	list of the enclosing basic block. Thus, we could have accomplished the same
				1946	thing as the above code without being given a <tt>BasicBlock</tt> by doing:
				1947	</p>
				1948
				1949	<div class="doc_code">
				1950	<pre>
				1951	Instruction *pi = ...;
				1952	Instruction *newInst = new Instruction(...);
				1953
				1954	pi->getParent()->getInstList().insert(pi, newInst);
				1955	</pre>
				1956	</div>
				1957
				1958	<p>In fact, this sequence of steps occurs so frequently that the
				1959	<tt>Instruction</tt> class and <tt>Instruction</tt>-derived classes provide
				1960	constructors which take (as a default parameter) a pointer to an
				1961	<tt>Instruction</tt> which the newly-created <tt>Instruction</tt> should
				1962	precede. That is, <tt>Instruction</tt> constructors are capable of
				1963	inserting the newly-created instance into the <tt>BasicBlock</tt> of a
				1964	provided instruction, immediately before that instruction. Using an
				1965	<tt>Instruction</tt> constructor with a <tt>insertBefore</tt> (default)
				1966	parameter, the above code becomes:</p>
				1967
				1968	<div class="doc_code">
				1969	<pre>
				1970	Instruction* pi = ...;
				1971	Instruction* newInst = new Instruction(..., pi);
				1972	</pre>
				1973	</div>
				1974
				1975	<p>which is much cleaner, especially if you're creating a lot of
				1976	instructions and adding them to <tt>BasicBlock</tt>s.</p></li>
				1977	</ul>
				1978
				1979	</div>
				1980
				1981	<!--_______________________________________________________________________-->
				1982	<div class="doc_subsubsection">
				1983	<a name="schanges_deleting">Deleting <tt>Instruction</tt>s</a>
				1984	</div>
				1985
				1986	<div class="doc_text">
				1987
				1988	<p>Deleting an instruction from an existing sequence of instructions that form a
				1989	<a href="#BasicBlock"><tt>BasicBlock</tt></a> is very straight-forward. First,
				1990	you must have a pointer to the instruction that you wish to delete. Second, you
				1991	need to obtain the pointer to that instruction's basic block. You use the
				1992	pointer to the basic block to get its list of instructions and then use the
				1993	erase function to remove your instruction. For example:</p>
				1994
				1995	<div class="doc_code">
				1996	<pre>
				1997	<a href="#Instruction">Instruction</a> *I = .. ;
Chris Lattner	3db8f77	2008-02-15 22:57:17 +0000	[diff] [blame]	1998	I->eraseFromParent();
Dan Gohman	f17a25c	2007-07-18 16:29:46 +0000	[diff] [blame]	1999	</pre>
				2000	</div>
				2001
				2002	</div>
				2003
				2004	<!--_______________________________________________________________________-->
				2005	<div class="doc_subsubsection">
				2006	<a name="schanges_replacing">Replacing an <tt>Instruction</tt> with another
				2007	<tt>Value</tt></a>
				2008	</div>
				2009
				2010	<div class="doc_text">
				2011
				2012	<p><i>Replacing individual instructions</i></p>
				2013
				2014	<p>Including "<a href="/doxygen/BasicBlockUtils_8h-source.html">llvm/Transforms/Utils/BasicBlockUtils.h</a>"
				2015	permits use of two very useful replace functions: <tt>ReplaceInstWithValue</tt>
				2016	and <tt>ReplaceInstWithInst</tt>.</p>
				2017
				2018	<h4><a name="schanges_deleting">Deleting <tt>Instruction</tt>s</a></h4>
				2019
				2020	<ul>
				2021	<li><tt>ReplaceInstWithValue</tt>
				2022
Nick Lewycky	48d4b03	2008-09-15 06:31:52 +0000	[diff] [blame]	2023	<p>This function replaces all uses of a given instruction with a value,
				2024	and then removes the original instruction. The following example
				2025	illustrates the replacement of the result of a particular
Dan Gohman	f17a25c	2007-07-18 16:29:46 +0000	[diff] [blame]	2026	<tt>AllocaInst</tt> that allocates memory for a single integer with a null
				2027	pointer to an integer.</p>
				2028
				2029	<div class="doc_code">
				2030	<pre>
				2031	AllocaInst* instToReplace = ...;
				2032	BasicBlock::iterator ii(instToReplace);
				2033
				2034	ReplaceInstWithValue(instToReplace->getParent()->getInstList(), ii,
Daniel Dunbar	8ce7962	2008-10-03 22:17:25 +0000	[diff] [blame]	2035	Constant::getNullValue(PointerType::getUnqual(Type::Int32Ty)));
Dan Gohman	f17a25c	2007-07-18 16:29:46 +0000	[diff] [blame]	2036	</pre></div></li>
				2037
				2038	<li><tt>ReplaceInstWithInst</tt>
				2039
				2040	<p>This function replaces a particular instruction with another
Nick Lewycky	48d4b03	2008-09-15 06:31:52 +0000	[diff] [blame]	2041	instruction, inserting the new instruction into the basic block at the
				2042	location where the old instruction was, and replacing any uses of the old
				2043	instruction with the new instruction. The following example illustrates
				2044	the replacement of one <tt>AllocaInst</tt> with another.</p>
Dan Gohman	f17a25c	2007-07-18 16:29:46 +0000	[diff] [blame]	2045
				2046	<div class="doc_code">
				2047	<pre>
				2048	AllocaInst* instToReplace = ...;
				2049	BasicBlock::iterator ii(instToReplace);
				2050
				2051	ReplaceInstWithInst(instToReplace->getParent()->getInstList(), ii,
Nick Lewycky	c004e5b	2007-12-03 01:52:52 +0000	[diff] [blame]	2052	new AllocaInst(Type::Int32Ty, 0, "ptrToReplacedInt"));
Dan Gohman	f17a25c	2007-07-18 16:29:46 +0000	[diff] [blame]	2053	</pre></div></li>
				2054	</ul>
				2055
				2056	<p><i>Replacing multiple uses of <tt>User</tt>s and <tt>Value</tt>s</i></p>
				2057
				2058	<p>You can use <tt>Value::replaceAllUsesWith</tt> and
				2059	<tt>User::replaceUsesOfWith</tt> to change more than one use at a time. See the
				2060	doxygen documentation for the <a href="/doxygen/classllvm_1_1Value.html">Value Class</a>
				2061	and <a href="/doxygen/classllvm_1_1User.html">User Class</a>, respectively, for more
				2062	information.</p>
				2063
				2064	<!-- Value::replaceAllUsesWith User::replaceUsesOfWith Point out:
				2065	include/llvm/Transforms/Utils/ especially BasicBlockUtils.h with:
				2066	ReplaceInstWithValue, ReplaceInstWithInst -->
				2067
				2068	</div>
				2069
				2070	<!--_______________________________________________________________________-->
				2071	<div class="doc_subsubsection">
				2072	<a name="schanges_deletingGV">Deleting <tt>GlobalVariable</tt>s</a>
				2073	</div>
				2074
				2075	<div class="doc_text">
				2076
				2077	<p>Deleting a global variable from a module is just as easy as deleting an
				2078	Instruction. First, you must have a pointer to the global variable that you wish
				2079	to delete. You use this pointer to erase it from its parent, the module.
				2080	For example:</p>
				2081
				2082	<div class="doc_code">
				2083	<pre>
				2084	<a href="#GlobalVariable">GlobalVariable</a> *GV = .. ;
				2085
				2086	GV->eraseFromParent();
				2087	</pre>
				2088	</div>
				2089
				2090	</div>
				2091
Jeffrey Yasskin	7ebb6ac	2009-04-30 22:33:41 +0000	[diff] [blame^]	2092	<!-- ======================================================================= -->
				2093	<div class="doc_subsection">
				2094	<a name="create_types">How to Create Types</a>
				2095	</div>
				2096
				2097	<div class="doc_text">
				2098
				2099	<p>In generating IR, you may need some complex types. If you know these types
				2100	statically, you can use <tt>TypeBuilder<...>::get()</tt>, defined
				2101	in <tt>llvm/Support/TypeBuilder.h</tt>, to retrieve them. <tt>TypeBuilder</tt>
				2102	has two forms depending on whether you're building types for cross-compilation
				2103	or native library use. <tt>TypeBuilder<T, true></tt> requires
				2104	that <tt>T</tt> be independent of the host environment, meaning that it's built
				2105	out of types from
				2106	the <a href="/doxygen/namespacellvm_1_1types.html"><tt>llvm::types</tt></a>
				2107	namespace and pointers, functions, arrays, etc. built of
				2108	those. <tt>TypeBuilder<T, false></tt> additionally allows native C types
				2109	whose size may depend on the host compiler. For example,</p>
				2110
				2111	<div class="doc_code">
				2112	<pre>
				2113	FunctionType ft = TypeBuilder<types::i<8>(types::i<32>), true>::get();
				2114	</pre>
				2115	</div>
				2116
				2117	<p>is easier to read and write than the equivalent</p>
				2118
				2119	<div class="doc_code">
				2120	<pre>
				2121	std::vector<const Type*> params;
				2122	params.push_back(PointerType::getUnqual(Type::Int32Ty));
				2123	FunctionType *ft = FunctionType::get(Type::Int8Ty, params, false);
				2124	</pre>
				2125	</div>
				2126
				2127	<p>See the <a href="/doxygen/TypeBuilder_8h-source.html#l00001">class
				2128	comment</a> for more details.</p>
				2129
				2130	</div>
				2131
Dan Gohman	f17a25c	2007-07-18 16:29:46 +0000	[diff] [blame]	2132	<!-- *********************************************************************** -->
				2133	<div class="doc_section">
				2134	<a name="advanced">Advanced Topics</a>
				2135	</div>
				2136	<!-- *********************************************************************** -->
				2137
				2138	<div class="doc_text">
				2139	<p>
				2140	This section describes some of the advanced or obscure API's that most clients
				2141	do not need to be aware of. These API's tend manage the inner workings of the
				2142	LLVM system, and only need to be accessed in unusual circumstances.
				2143	</p>
				2144	</div>
				2145
				2146	<!-- ======================================================================= -->
				2147	<div class="doc_subsection">
				2148	<a name="TypeResolve">LLVM Type Resolution</a>
				2149	</div>
				2150
				2151	<div class="doc_text">
				2152
				2153	<p>
				2154	The LLVM type system has a very simple goal: allow clients to compare types for
				2155	structural equality with a simple pointer comparison (aka a shallow compare).
				2156	This goal makes clients much simpler and faster, and is used throughout the LLVM
				2157	system.
				2158	</p>
				2159
				2160	<p>
				2161	Unfortunately achieving this goal is not a simple matter. In particular,
				2162	recursive types and late resolution of opaque types makes the situation very
				2163	difficult to handle. Fortunately, for the most part, our implementation makes
				2164	most clients able to be completely unaware of the nasty internal details. The
				2165	primary case where clients are exposed to the inner workings of it are when
				2166	building a recursive type. In addition to this case, the LLVM bitcode reader,
				2167	assembly parser, and linker also have to be aware of the inner workings of this
				2168	system.
				2169	</p>
				2170
				2171	<p>
				2172	For our purposes below, we need three concepts. First, an "Opaque Type" is
				2173	exactly as defined in the <a href="LangRef.html#t_opaque">language
				2174	reference</a>. Second an "Abstract Type" is any type which includes an
				2175	opaque type as part of its type graph (for example "<tt>{ opaque, i32 }</tt>").
				2176	Third, a concrete type is a type that is not an abstract type (e.g. "<tt>{ i32,
				2177	float }</tt>").
				2178	</p>
				2179
				2180	</div>
				2181
				2182	<!-- ______________________________________________________________________ -->
				2183	<div class="doc_subsubsection">
				2184	<a name="BuildRecType">Basic Recursive Type Construction</a>
				2185	</div>
				2186
				2187	<div class="doc_text">
				2188
				2189	<p>
				2190	Because the most common question is "how do I build a recursive type with LLVM",
				2191	we answer it now and explain it as we go. Here we include enough to cause this
				2192	to be emitted to an output .ll file:
				2193	</p>
				2194
				2195	<div class="doc_code">
				2196	<pre>
				2197	%mylist = type { %mylist*, i32 }
				2198	</pre>
				2199	</div>
				2200
				2201	<p>
				2202	To build this, use the following LLVM APIs:
				2203	</p>
				2204
				2205	<div class="doc_code">
				2206	<pre>
				2207	// <i>Create the initial outer struct</i>
				2208	<a href="#PATypeHolder">PATypeHolder</a> StructTy = OpaqueType::get();
				2209	std::vector<const Type*> Elts;
Daniel Dunbar	8ce7962	2008-10-03 22:17:25 +0000	[diff] [blame]	2210	Elts.push_back(PointerType::getUnqual(StructTy));
Nick Lewycky	c004e5b	2007-12-03 01:52:52 +0000	[diff] [blame]	2211	Elts.push_back(Type::Int32Ty);
Dan Gohman	f17a25c	2007-07-18 16:29:46 +0000	[diff] [blame]	2212	StructType *NewSTy = StructType::get(Elts);
				2213
				2214	// <i>At this point, NewSTy = "{ opaque*, i32 }". Tell VMCore that</i>
				2215	// <i>the struct and the opaque type are actually the same.</i>
				2216	cast<OpaqueType>(StructTy.get())-><a href="#refineAbstractTypeTo">refineAbstractTypeTo</a>(NewSTy);
				2217
				2218	// <i>NewSTy is potentially invalidated, but StructTy (a <a href="#PATypeHolder">PATypeHolder</a>) is</i>
				2219	// <i>kept up-to-date</i>
				2220	NewSTy = cast<StructType>(StructTy.get());
				2221
				2222	// <i>Add a name for the type to the module symbol table (optional)</i>
				2223	MyModule->addTypeName("mylist", NewSTy);
				2224	</pre>
				2225	</div>
				2226
				2227	<p>
				2228	This code shows the basic approach used to build recursive types: build a
				2229	non-recursive type using 'opaque', then use type unification to close the cycle.
				2230	The type unification step is performed by the <tt><a
				2231	href="#refineAbstractTypeTo">refineAbstractTypeTo</a></tt> method, which is
				2232	described next. After that, we describe the <a
				2233	href="#PATypeHolder">PATypeHolder class</a>.
				2234	</p>
				2235
				2236	</div>
				2237
				2238	<!-- ______________________________________________________________________ -->
				2239	<div class="doc_subsubsection">
				2240	<a name="refineAbstractTypeTo">The <tt>refineAbstractTypeTo</tt> method</a>
				2241	</div>
				2242
				2243	<div class="doc_text">
				2244	<p>
				2245	The <tt>refineAbstractTypeTo</tt> method starts the type unification process.
				2246	While this method is actually a member of the DerivedType class, it is most
				2247	often used on OpaqueType instances. Type unification is actually a recursive
				2248	process. After unification, types can become structurally isomorphic to
				2249	existing types, and all duplicates are deleted (to preserve pointer equality).
				2250	</p>
				2251
				2252	<p>
				2253	In the example above, the OpaqueType object is definitely deleted.
				2254	Additionally, if there is an "{ \2*, i32}" type already created in the system,
				2255	the pointer and struct type created are <b>also</b> deleted. Obviously whenever
				2256	a type is deleted, any "Type*" pointers in the program are invalidated. As
				2257	such, it is safest to avoid having <i>any</i> "Type*" pointers to abstract types
				2258	live across a call to <tt>refineAbstractTypeTo</tt> (note that non-abstract
				2259	types can never move or be deleted). To deal with this, the <a
				2260	href="#PATypeHolder">PATypeHolder</a> class is used to maintain a stable
				2261	reference to a possibly refined type, and the <a
				2262	href="#AbstractTypeUser">AbstractTypeUser</a> class is used to update more
				2263	complex datastructures.
				2264	</p>
				2265
				2266	</div>
				2267
				2268	<!-- ______________________________________________________________________ -->
				2269	<div class="doc_subsubsection">
				2270	<a name="PATypeHolder">The PATypeHolder Class</a>
				2271	</div>
				2272
				2273	<div class="doc_text">
				2274	<p>
				2275	PATypeHolder is a form of a "smart pointer" for Type objects. When VMCore
				2276	happily goes about nuking types that become isomorphic to existing types, it
				2277	automatically updates all PATypeHolder objects to point to the new type. In the
				2278	example above, this allows the code to maintain a pointer to the resultant
				2279	resolved recursive type, even though the Type*'s are potentially invalidated.
				2280	</p>
				2281
				2282	<p>
				2283	PATypeHolder is an extremely light-weight object that uses a lazy union-find
				2284	implementation to update pointers. For example the pointer from a Value to its
				2285	Type is maintained by PATypeHolder objects.
				2286	</p>
				2287
				2288	</div>
				2289
				2290	<!-- ______________________________________________________________________ -->
				2291	<div class="doc_subsubsection">
				2292	<a name="AbstractTypeUser">The AbstractTypeUser Class</a>
				2293	</div>
				2294
				2295	<div class="doc_text">
				2296
				2297	<p>
				2298	Some data structures need more to perform more complex updates when types get
				2299	resolved. To support this, a class can derive from the AbstractTypeUser class.
				2300	This class
				2301	allows it to get callbacks when certain types are resolved. To register to get
				2302	callbacks for a particular type, the DerivedType::{add/remove}AbstractTypeUser
				2303	methods can be called on a type. Note that these methods only work for <i>
				2304	abstract</i> types. Concrete types (those that do not include any opaque
				2305	objects) can never be refined.
				2306	</p>
				2307	</div>
				2308
				2309
				2310	<!-- ======================================================================= -->
				2311	<div class="doc_subsection">
				2312	<a name="SymbolTable">The <tt>ValueSymbolTable</tt> and
				2313	<tt>TypeSymbolTable</tt> classes</a>
				2314	</div>
				2315
				2316	<div class="doc_text">
				2317	<p>The <tt><a href="http://llvm.org/doxygen/classllvm_1_1ValueSymbolTable.html">
				2318	ValueSymbolTable</a></tt> class provides a symbol table that the <a
				2319	href="#Function"><tt>Function</tt></a> and <a href="#Module">
				2320	<tt>Module</tt></a> classes use for naming value definitions. The symbol table
				2321	can provide a name for any <a href="#Value"><tt>Value</tt></a>.
				2322	The <tt><a href="http://llvm.org/doxygen/classllvm_1_1TypeSymbolTable.html">
				2323	TypeSymbolTable</a></tt> class is used by the <tt>Module</tt> class to store
				2324	names for types.</p>
				2325
				2326	<p>Note that the <tt>SymbolTable</tt> class should not be directly accessed
				2327	by most clients. It should only be used when iteration over the symbol table
				2328	names themselves are required, which is very special purpose. Note that not
				2329	all LLVM
Gabor Greif	92e8776	2008-06-16 21:06:12 +0000	[diff] [blame]	2330	<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]	2331	an empty name) do not exist in the symbol table.
				2332	</p>
				2333
				2334	<p>These symbol tables support iteration over the values/types in the symbol
				2335	table with <tt>begin/end/iterator</tt> and supports querying to see if a
				2336	specific name is in the symbol table (with <tt>lookup</tt>). The
				2337	<tt>ValueSymbolTable</tt> class exposes no public mutator methods, instead,
				2338	simply call <tt>setName</tt> on a value, which will autoinsert it into the
				2339	appropriate symbol table. For types, use the Module::addTypeName method to
				2340	insert entries into the symbol table.</p>
				2341
				2342	</div>
				2343
				2344
				2345
Gabor Greif	92e8776	2008-06-16 21:06:12 +0000	[diff] [blame]	2346	<!-- ======================================================================= -->
				2347	<div class="doc_subsection">
				2348	<a name="UserLayout">The <tt>User</tt> and owned <tt>Use</tt> classes' memory layout</a>
				2349	</div>
				2350
				2351	<div class="doc_text">
				2352	<p>The <tt><a href="http://llvm.org/doxygen/classllvm_1_1User.html">
Gabor Greif	50626fc	2009-01-05 16:05:32 +0000	[diff] [blame]	2353	User</a></tt> class provides a basis for expressing the ownership of <tt>User</tt>
Gabor Greif	92e8776	2008-06-16 21:06:12 +0000	[diff] [blame]	2354	towards other <tt><a href="http://llvm.org/doxygen/classllvm_1_1Value.html">
				2355	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]	2356	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]	2357	addition and removal.</p>
				2358
Gabor Greif	93b462b	2008-06-18 13:44:57 +0000	[diff] [blame]	2359	<!-- ______________________________________________________________________ -->
				2360	<div class="doc_subsubsection">
Gabor Greif	50626fc	2009-01-05 16:05:32 +0000	[diff] [blame]	2361	<a name="Use2User">Interaction and relationship between <tt>User</tt> and <tt>Use</tt> objects</a>
Gabor Greif	93b462b	2008-06-18 13:44:57 +0000	[diff] [blame]	2362	</div>
Gabor Greif	92e8776	2008-06-16 21:06:12 +0000	[diff] [blame]	2363
Gabor Greif	93b462b	2008-06-18 13:44:57 +0000	[diff] [blame]	2364	<div class="doc_text">
				2365	<p>
				2366	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]	2367	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]	2368	(some <tt>Use</tt>s inline others hung off) is impractical and breaks the invariant
				2369	that the <tt>Use</tt> objects belonging to the same <tt>User</tt> form a contiguous array.
				2370	</p>
				2371	</div>
Gabor Greif	92e8776	2008-06-16 21:06:12 +0000	[diff] [blame]	2372
Gabor Greif	93b462b	2008-06-18 13:44:57 +0000	[diff] [blame]	2373	<p>
				2374	We have 2 different layouts in the <tt>User</tt> (sub)classes:
				2375	<ul>
				2376	<li><p>Layout a)
				2377	The <tt>Use</tt> object(s) are inside (resp. at fixed offset) of the <tt>User</tt>
				2378	object and there are a fixed number of them.</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	<li><p>Layout b)
				2381	The <tt>Use</tt> object(s) are referenced by a pointer to an
				2382	array from the <tt>User</tt> object and there may be a variable
				2383	number of them.</p>
				2384	</ul>
				2385	<p>
Gabor Greif	e247e36	2008-06-25 00:10:22 +0000	[diff] [blame]	2386	As of v2.4 each layout still possesses a direct pointer to the
Gabor Greif	93b462b	2008-06-18 13:44:57 +0000	[diff] [blame]	2387	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]	2388	we stick to this redundancy for the sake of simplicity.
Gabor Greif	e247e36	2008-06-25 00:10:22 +0000	[diff] [blame]	2389	The <tt>User</tt> object also stores the number of <tt>Use</tt> objects it
Gabor Greif	92e8776	2008-06-16 21:06:12 +0000	[diff] [blame]	2390	has. (Theoretically this information can also be calculated
Gabor Greif	93b462b	2008-06-18 13:44:57 +0000	[diff] [blame]	2391	given the scheme presented below.)</p>
				2392	<p>
				2393	Special forms of allocation operators (<tt>operator new</tt>)
Gabor Greif	e247e36	2008-06-25 00:10:22 +0000	[diff] [blame]	2394	enforce the following memory layouts:</p>
Gabor Greif	92e8776	2008-06-16 21:06:12 +0000	[diff] [blame]	2395
Gabor Greif	93b462b	2008-06-18 13:44:57 +0000	[diff] [blame]	2396	<ul>
Gabor Greif	e247e36	2008-06-25 00:10:22 +0000	[diff] [blame]	2397	<li><p>Layout a) is 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]	2398
Gabor Greif	93b462b	2008-06-18 13:44:57 +0000	[diff] [blame]	2399	<pre>
				2400	...---.---.---.---.-------...
				2401	\| P \| P \| P \| P \| User
				2402	'''---'---'---'---'-------'''
				2403	</pre>
Gabor Greif	92e8776	2008-06-16 21:06:12 +0000	[diff] [blame]	2404
Gabor Greif	e247e36	2008-06-25 00:10:22 +0000	[diff] [blame]	2405	<li><p>Layout b) is modelled by pointing at the <tt>Use[]</tt> array.</p>
Gabor Greif	93b462b	2008-06-18 13:44:57 +0000	[diff] [blame]	2406	<pre>
				2407	.-------...
				2408	\| User
				2409	'-------'''
				2410	\|
				2411	v
				2412	.---.---.---.---...
				2413	\| P \| P \| P \| P \|
				2414	'---'---'---'---'''
				2415	</pre>
				2416	</ul>
				2417	<i>(In the above figures '<tt>P</tt>' stands for the <tt>Use**</tt> that
				2418	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]	2419
Gabor Greif	93b462b	2008-06-18 13:44:57 +0000	[diff] [blame]	2420	<!-- ______________________________________________________________________ -->
				2421	<div class="doc_subsubsection">
Gabor Greif	50626fc	2009-01-05 16:05:32 +0000	[diff] [blame]	2422	<a name="Waymarking">The waymarking algorithm</a>
Gabor Greif	93b462b	2008-06-18 13:44:57 +0000	[diff] [blame]	2423	</div>
Gabor Greif	92e8776	2008-06-16 21:06:12 +0000	[diff] [blame]	2424
Gabor Greif	93b462b	2008-06-18 13:44:57 +0000	[diff] [blame]	2425	<div class="doc_text">
				2426	<p>
Gabor Greif	e247e36	2008-06-25 00:10:22 +0000	[diff] [blame]	2427	Since the <tt>Use</tt> objects are deprived of the direct (back)pointer to
Gabor Greif	93b462b	2008-06-18 13:44:57 +0000	[diff] [blame]	2428	their <tt>User</tt> objects, there must be a fast and exact method to
				2429	recover it. This is accomplished by the following scheme:</p>
				2430	</div>
Gabor Greif	92e8776	2008-06-16 21:06:12 +0000	[diff] [blame]	2431
Gabor Greif	e247e36	2008-06-25 00:10:22 +0000	[diff] [blame]	2432	A bit-encoding in the 2 LSBits (least significant bits) of the <tt>Use::Prev</tt> allows to find the
Gabor Greif	93b462b	2008-06-18 13:44:57 +0000	[diff] [blame]	2433	start of the <tt>User</tt> object:
				2434	<ul>
				2435	<li><tt>00</tt> —> binary digit 0</li>
				2436	<li><tt>01</tt> —> binary digit 1</li>
				2437	<li><tt>10</tt> —> stop and calculate (<tt>s</tt>)</li>
				2438	<li><tt>11</tt> —> full stop (<tt>S</tt>)</li>
				2439	</ul>
				2440	<p>
				2441	Given a <tt>Use*</tt>, all we have to do is to walk till we get
				2442	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]	2443	we have to walk to the next stop picking up digits
Gabor Greif	93b462b	2008-06-18 13:44:57 +0000	[diff] [blame]	2444	and calculating the offset:</p>
				2445	<pre>
Gabor Greif	92e8776	2008-06-16 21:06:12 +0000	[diff] [blame]	2446	.---.---.---.---.---.---.---.---.---.---.---.---.---.---.---.---.----------------
				2447	\| 1 \| s \| 1 \| 0 \| 1 \| 0 \| s \| 1 \| 1 \| 0 \| s \| 1 \| 1 \| s \| 1 \| S \| User (or User*)
				2448	'---'---'---'---'---'---'---'---'---'---'---'---'---'---'---'---'----------------
				2449	\|+15 \|+10 \|+6 \|+3 \|+1
				2450	\| \| \| \| \|__>
				2451	\| \| \| \|__________>
				2452	\| \| \|______________________>
				2453	\| \|______________________________________>
				2454	\|__________________________________________________________>
Gabor Greif	93b462b	2008-06-18 13:44:57 +0000	[diff] [blame]	2455	</pre>
				2456	<p>
Gabor Greif	92e8776	2008-06-16 21:06:12 +0000	[diff] [blame]	2457	Only the significant number of bits need to be stored between the
Gabor Greif	93b462b	2008-06-18 13:44:57 +0000	[diff] [blame]	2458	stops, so that the <i>worst case is 20 memory accesses</i> when there are
				2459	1000 <tt>Use</tt> objects associated with a <tt>User</tt>.</p>
Gabor Greif	92e8776	2008-06-16 21:06:12 +0000	[diff] [blame]	2460
Gabor Greif	93b462b	2008-06-18 13:44:57 +0000	[diff] [blame]	2461	<!-- ______________________________________________________________________ -->
				2462	<div class="doc_subsubsection">
Gabor Greif	50626fc	2009-01-05 16:05:32 +0000	[diff] [blame]	2463	<a name="ReferenceImpl">Reference implementation</a>
Gabor Greif	93b462b	2008-06-18 13:44:57 +0000	[diff] [blame]	2464	</div>
Gabor Greif	92e8776	2008-06-16 21:06:12 +0000	[diff] [blame]	2465
Gabor Greif	93b462b	2008-06-18 13:44:57 +0000	[diff] [blame]	2466	<div class="doc_text">
				2467	<p>
				2468	The following literate Haskell fragment demonstrates the concept:</p>
				2469	</div>
				2470
				2471	<div class="doc_code">
				2472	<pre>
Gabor Greif	92e8776	2008-06-16 21:06:12 +0000	[diff] [blame]	2473	> import Test.QuickCheck
				2474	>
				2475	> digits :: Int -> [Char] -> [Char]
				2476	> digits 0 acc = '0' : acc
				2477	> digits 1 acc = '1' : acc
				2478	> digits n acc = digits (n `div` 2) $ digits (n `mod` 2) acc
				2479	>
				2480	> dist :: Int -> [Char] -> [Char]
				2481	> dist 0 [] = ['S']
				2482	> dist 0 acc = acc
				2483	> dist 1 acc = let r = dist 0 acc in 's' : digits (length r) r
				2484	> dist n acc = dist (n - 1) $ dist 1 acc
				2485	>
				2486	> takeLast n ss = reverse $ take n $ reverse ss
				2487	>
				2488	> test = takeLast 40 $ dist 20 []
				2489	>
Gabor Greif	93b462b	2008-06-18 13:44:57 +0000	[diff] [blame]	2490	</pre>
				2491	</div>
				2492	<p>
				2493	Printing <test> gives: <tt>"1s100000s11010s10100s1111s1010s110s11s1S"</tt></p>
				2494	<p>
				2495	The reverse algorithm computes the length of the string just by examining
				2496	a certain prefix:</p>
Gabor Greif	92e8776	2008-06-16 21:06:12 +0000	[diff] [blame]	2497
Gabor Greif	93b462b	2008-06-18 13:44:57 +0000	[diff] [blame]	2498	<div class="doc_code">
				2499	<pre>
Gabor Greif	92e8776	2008-06-16 21:06:12 +0000	[diff] [blame]	2500	> pref :: [Char] -> Int
				2501	> pref "S" = 1
				2502	> pref ('s':'1':rest) = decode 2 1 rest
				2503	> pref (_:rest) = 1 + pref rest
				2504	>
				2505	> decode walk acc ('0':rest) = decode (walk + 1) (acc * 2) rest
				2506	> decode walk acc ('1':rest) = decode (walk + 1) (acc * 2 + 1) rest
				2507	> decode walk acc _ = walk + acc
				2508	>
Gabor Greif	93b462b	2008-06-18 13:44:57 +0000	[diff] [blame]	2509	</pre>
				2510	</div>
				2511	<p>
				2512	Now, as expected, printing <pref test> gives <tt>40</tt>.</p>
				2513	<p>
				2514	We can <i>quickCheck</i> this with following property:</p>
Gabor Greif	92e8776	2008-06-16 21:06:12 +0000	[diff] [blame]	2515
Gabor Greif	93b462b	2008-06-18 13:44:57 +0000	[diff] [blame]	2516	<div class="doc_code">
				2517	<pre>
Gabor Greif	92e8776	2008-06-16 21:06:12 +0000	[diff] [blame]	2518	> testcase = dist 2000 []
				2519	> testcaseLength = length testcase
				2520	>
				2521	> identityProp n = n > 0 && n <= testcaseLength ==> length arr == pref arr
				2522	> where arr = takeLast n testcase
Gabor Greif	93b462b	2008-06-18 13:44:57 +0000	[diff] [blame]	2523	>
				2524	</pre>
				2525	</div>
				2526	<p>
				2527	As expected <quickCheck identityProp> gives:</p>
Gabor Greif	92e8776	2008-06-16 21:06:12 +0000	[diff] [blame]	2528
Gabor Greif	93b462b	2008-06-18 13:44:57 +0000	[diff] [blame]	2529	<pre>
Gabor Greif	92e8776	2008-06-16 21:06:12 +0000	[diff] [blame]	2530	*Main> quickCheck identityProp
				2531	OK, passed 100 tests.
Gabor Greif	93b462b	2008-06-18 13:44:57 +0000	[diff] [blame]	2532	</pre>
				2533	<p>
				2534	Let's be a bit more exhaustive:</p>
Gabor Greif	92e8776	2008-06-16 21:06:12 +0000	[diff] [blame]	2535
Gabor Greif	93b462b	2008-06-18 13:44:57 +0000	[diff] [blame]	2536	<div class="doc_code">
				2537	<pre>
Gabor Greif	92e8776	2008-06-16 21:06:12 +0000	[diff] [blame]	2538	>
				2539	> deepCheck p = check (defaultConfig { configMaxTest = 500 }) p
				2540	>
Gabor Greif	93b462b	2008-06-18 13:44:57 +0000	[diff] [blame]	2541	</pre>
				2542	</div>
				2543	<p>
				2544	And here is the result of <deepCheck identityProp>:</p>
Gabor Greif	92e8776	2008-06-16 21:06:12 +0000	[diff] [blame]	2545
Gabor Greif	93b462b	2008-06-18 13:44:57 +0000	[diff] [blame]	2546	<pre>
Gabor Greif	92e8776	2008-06-16 21:06:12 +0000	[diff] [blame]	2547	*Main> deepCheck identityProp
				2548	OK, passed 500 tests.
Gabor Greif	92e8776	2008-06-16 21:06:12 +0000	[diff] [blame]	2549	</pre>
				2550
Gabor Greif	93b462b	2008-06-18 13:44:57 +0000	[diff] [blame]	2551	<!-- ______________________________________________________________________ -->
				2552	<div class="doc_subsubsection">
Gabor Greif	50626fc	2009-01-05 16:05:32 +0000	[diff] [blame]	2553	<a name="Tagging">Tagging considerations</a>
Gabor Greif	93b462b	2008-06-18 13:44:57 +0000	[diff] [blame]	2554	</div>
				2555
				2556	<p>
				2557	To maintain the invariant that the 2 LSBits of each <tt>Use**</tt> in <tt>Use</tt>
				2558	never change after being set up, setters of <tt>Use::Prev</tt> must re-tag the
				2559	new <tt>Use**</tt> on every modification. Accordingly getters must strip the
				2560	tag bits.</p>
				2561	<p>
Gabor Greif	e247e36	2008-06-25 00:10:22 +0000	[diff] [blame]	2562	For layout b) instead of the <tt>User</tt> we find a pointer (<tt>User*</tt> with LSBit set).
				2563	Following this pointer brings us to the <tt>User</tt>. A portable trick ensures
				2564	that the first bytes of <tt>User</tt> (if interpreted as a pointer) never has
Gabor Greif	50626fc	2009-01-05 16:05:32 +0000	[diff] [blame]	2565	the LSBit set. (Portability is relying on the fact that all known compilers place the
				2566	<tt>vptr</tt> in the first word of the instances.)</p>
Gabor Greif	93b462b	2008-06-18 13:44:57 +0000	[diff] [blame]	2567
Gabor Greif	92e8776	2008-06-16 21:06:12 +0000	[diff] [blame]	2568	</div>
				2569
				2570	<!-- *********************************************************************** -->
Dan Gohman	f17a25c	2007-07-18 16:29:46 +0000	[diff] [blame]	2571	<div class="doc_section">
				2572	<a name="coreclasses">The Core LLVM Class Hierarchy Reference </a>
				2573	</div>
				2574	<!-- *********************************************************************** -->
				2575
				2576	<div class="doc_text">
				2577	<p><tt>#include "<a href="/doxygen/Type_8h-source.html">llvm/Type.h</a>"</tt>
				2578	<br>doxygen info: <a href="/doxygen/classllvm_1_1Type.html">Type Class</a></p>
				2579
				2580	<p>The Core LLVM classes are the primary means of representing the program
				2581	being inspected or transformed. The core LLVM classes are defined in
				2582	header files in the <tt>include/llvm/</tt> directory, and implemented in
				2583	the <tt>lib/VMCore</tt> directory.</p>
				2584
				2585	</div>
				2586
				2587	<!-- ======================================================================= -->
				2588	<div class="doc_subsection">
				2589	<a name="Type">The <tt>Type</tt> class and Derived Types</a>
				2590	</div>
				2591
				2592	<div class="doc_text">
				2593
				2594	<p><tt>Type</tt> is a superclass of all type classes. Every <tt>Value</tt> has
				2595	a <tt>Type</tt>. <tt>Type</tt> cannot be instantiated directly but only
				2596	through its subclasses. Certain primitive types (<tt>VoidType</tt>,
				2597	<tt>LabelType</tt>, <tt>FloatType</tt> and <tt>DoubleType</tt>) have hidden
				2598	subclasses. They are hidden because they offer no useful functionality beyond
				2599	what the <tt>Type</tt> class offers except to distinguish themselves from
				2600	other subclasses of <tt>Type</tt>.</p>
				2601	<p>All other types are subclasses of <tt>DerivedType</tt>. Types can be
				2602	named, but this is not a requirement. There exists exactly
				2603	one instance of a given shape at any one time. This allows type equality to
				2604	be performed with address equality of the Type Instance. That is, given two
				2605	<tt>Type*</tt> values, the types are identical if the pointers are identical.
				2606	</p>
				2607	</div>
				2608
				2609	<!-- _______________________________________________________________________ -->
				2610	<div class="doc_subsubsection">
Gabor Greif	50626fc	2009-01-05 16:05:32 +0000	[diff] [blame]	2611	<a name="m_Type">Important Public Methods</a>
Dan Gohman	f17a25c	2007-07-18 16:29:46 +0000	[diff] [blame]	2612	</div>
				2613
				2614	<div class="doc_text">
				2615
				2616	<ul>
				2617	<li><tt>bool isInteger() const</tt>: Returns true for any integer type.</li>
				2618
				2619	<li><tt>bool isFloatingPoint()</tt>: Return true if this is one of the two
				2620	floating point types.</li>
				2621
				2622	<li><tt>bool isAbstract()</tt>: Return true if the type is abstract (contains
				2623	an OpaqueType anywhere in its definition).</li>
				2624
				2625	<li><tt>bool isSized()</tt>: Return true if the type has known size. Things
				2626	that don't have a size are abstract types, labels and void.</li>
				2627
				2628	</ul>
				2629	</div>
				2630
				2631	<!-- _______________________________________________________________________ -->
				2632	<div class="doc_subsubsection">
Gabor Greif	50626fc	2009-01-05 16:05:32 +0000	[diff] [blame]	2633	<a name="derivedtypes">Important Derived Types</a>
Dan Gohman	f17a25c	2007-07-18 16:29:46 +0000	[diff] [blame]	2634	</div>
				2635	<div class="doc_text">
				2636	<dl>
				2637	<dt><tt>IntegerType</tt></dt>
				2638	<dd>Subclass of DerivedType that represents integer types of any bit width.
				2639	Any bit width between <tt>IntegerType::MIN_INT_BITS</tt> (1) and
				2640	<tt>IntegerType::MAX_INT_BITS</tt> (~8 million) can be represented.
				2641	<ul>
				2642	<li><tt>static const IntegerType* get(unsigned NumBits)</tt>: get an integer
				2643	type of a specific bit width.</li>
				2644	<li><tt>unsigned getBitWidth() const</tt>: Get the bit width of an integer
				2645	type.</li>
				2646	</ul>
				2647	</dd>
				2648	<dt><tt>SequentialType</tt></dt>
				2649	<dd>This is subclassed by ArrayType and PointerType
				2650	<ul>
				2651	<li><tt>const Type * getElementType() const</tt>: Returns the type of each
				2652	of the elements in the sequential type. </li>
				2653	</ul>
				2654	</dd>
				2655	<dt><tt>ArrayType</tt></dt>
				2656	<dd>This is a subclass of SequentialType and defines the interface for array
				2657	types.
				2658	<ul>
				2659	<li><tt>unsigned getNumElements() const</tt>: Returns the number of
				2660	elements in the array. </li>
				2661	</ul>
				2662	</dd>
				2663	<dt><tt>PointerType</tt></dt>
				2664	<dd>Subclass of SequentialType for pointer types.</dd>
				2665	<dt><tt>VectorType</tt></dt>
				2666	<dd>Subclass of SequentialType for vector types. A
				2667	vector type is similar to an ArrayType but is distinguished because it is
				2668	a first class type wherease ArrayType is not. Vector types are used for
				2669	vector operations and are usually small vectors of of an integer or floating
				2670	point type.</dd>
				2671	<dt><tt>StructType</tt></dt>
				2672	<dd>Subclass of DerivedTypes for struct types.</dd>
				2673	<dt><tt><a name="FunctionType">FunctionType</a></tt></dt>
				2674	<dd>Subclass of DerivedTypes for function types.
				2675	<ul>
				2676	<li><tt>bool isVarArg() const</tt>: Returns true if its a vararg
				2677	function</li>
				2678	<li><tt> const Type * getReturnType() const</tt>: Returns the
				2679	return type of the function.</li>
				2680	<li><tt>const Type * getParamType (unsigned i)</tt>: Returns
				2681	the type of the ith parameter.</li>
				2682	<li><tt> const unsigned getNumParams() const</tt>: Returns the
				2683	number of formal parameters.</li>
				2684	</ul>
				2685	</dd>
				2686	<dt><tt>OpaqueType</tt></dt>
				2687	<dd>Sublcass of DerivedType for abstract types. This class
				2688	defines no content and is used as a placeholder for some other type. Note
				2689	that OpaqueType is used (temporarily) during type resolution for forward
				2690	references of types. Once the referenced type is resolved, the OpaqueType
				2691	is replaced with the actual type. OpaqueType can also be used for data
				2692	abstraction. At link time opaque types can be resolved to actual types
				2693	of the same name.</dd>
				2694	</dl>
				2695	</div>
				2696
				2697
				2698
				2699	<!-- ======================================================================= -->
				2700	<div class="doc_subsection">
				2701	<a name="Module">The <tt>Module</tt> class</a>
				2702	</div>
				2703
				2704	<div class="doc_text">
				2705
				2706	<p><tt>#include "<a
				2707	href="/doxygen/Module_8h-source.html">llvm/Module.h</a>"</tt><br> doxygen info:
				2708	<a href="/doxygen/classllvm_1_1Module.html">Module Class</a></p>
				2709
				2710	<p>The <tt>Module</tt> class represents the top level structure present in LLVM
				2711	programs. An LLVM module is effectively either a translation unit of the
				2712	original program or a combination of several translation units merged by the
				2713	linker. The <tt>Module</tt> class keeps track of a list of <a
				2714	href="#Function"><tt>Function</tt></a>s, a list of <a
				2715	href="#GlobalVariable"><tt>GlobalVariable</tt></a>s, and a <a
				2716	href="#SymbolTable"><tt>SymbolTable</tt></a>. Additionally, it contains a few
				2717	helpful member functions that try to make common operations easy.</p>
				2718
				2719	</div>
				2720
				2721	<!-- _______________________________________________________________________ -->
				2722	<div class="doc_subsubsection">
				2723	<a name="m_Module">Important Public Members of the <tt>Module</tt> class</a>
				2724	</div>
				2725
				2726	<div class="doc_text">
				2727
				2728	<ul>
				2729	<li><tt>Module::Module(std::string name = "")</tt></li>
				2730	</ul>
				2731
				2732	<p>Constructing a <a href="#Module">Module</a> is easy. You can optionally
				2733	provide a name for it (probably based on the name of the translation unit).</p>
				2734
				2735	<ul>
				2736	<li><tt>Module::iterator</tt> - Typedef for function list iterator<br>
				2737	<tt>Module::const_iterator</tt> - Typedef for const_iterator.<br>
				2738
				2739	<tt>begin()</tt>, <tt>end()</tt>
				2740	<tt>size()</tt>, <tt>empty()</tt>
				2741
				2742	<p>These are forwarding methods that make it easy to access the contents of
				2743	a <tt>Module</tt> object's <a href="#Function"><tt>Function</tt></a>
				2744	list.</p></li>
				2745
				2746	<li><tt>Module::FunctionListType &getFunctionList()</tt>
				2747
				2748	<p> Returns the list of <a href="#Function"><tt>Function</tt></a>s. This is
				2749	necessary to use when you need to update the list or perform a complex
				2750	action that doesn't have a forwarding method.</p>
				2751
				2752	<p><!-- Global Variable --></p></li>
				2753	</ul>
				2754
				2755	<hr>
				2756
				2757	<ul>
				2758	<li><tt>Module::global_iterator</tt> - Typedef for global variable list iterator<br>
				2759
				2760	<tt>Module::const_global_iterator</tt> - Typedef for const_iterator.<br>
				2761
				2762	<tt>global_begin()</tt>, <tt>global_end()</tt>
				2763	<tt>global_size()</tt>, <tt>global_empty()</tt>
				2764
				2765	<p> These are forwarding methods that make it easy to access the contents of
				2766	a <tt>Module</tt> object's <a
				2767	href="#GlobalVariable"><tt>GlobalVariable</tt></a> list.</p></li>
				2768
				2769	<li><tt>Module::GlobalListType &getGlobalList()</tt>
				2770
				2771	<p>Returns the list of <a
				2772	href="#GlobalVariable"><tt>GlobalVariable</tt></a>s. This is necessary to
				2773	use when you need to update the list or perform a complex action that
				2774	doesn't have a forwarding method.</p>
				2775
				2776	<p><!-- Symbol table stuff --> </p></li>
				2777	</ul>
				2778
				2779	<hr>
				2780
				2781	<ul>
				2782	<li><tt><a href="#SymbolTable">SymbolTable</a> *getSymbolTable()</tt>
				2783
				2784	<p>Return a reference to the <a href="#SymbolTable"><tt>SymbolTable</tt></a>
				2785	for this <tt>Module</tt>.</p>
				2786
				2787	<p><!-- Convenience methods --></p></li>
				2788	</ul>
				2789
				2790	<hr>
				2791
				2792	<ul>
				2793	<li><tt><a href="#Function">Function</a> *getFunction(const std::string
				2794	&Name, const <a href="#FunctionType">FunctionType</a> *Ty)</tt>
				2795
				2796	<p>Look up the specified function in the <tt>Module</tt> <a
				2797	href="#SymbolTable"><tt>SymbolTable</tt></a>. If it does not exist, return
				2798	<tt>null</tt>.</p></li>
				2799
				2800	<li><tt><a href="#Function">Function</a> *getOrInsertFunction(const
				2801	std::string &Name, const <a href="#FunctionType">FunctionType</a> *T)</tt>
				2802
				2803	<p>Look up the specified function in the <tt>Module</tt> <a
				2804	href="#SymbolTable"><tt>SymbolTable</tt></a>. If it does not exist, add an
				2805	external declaration for the function and return it.</p></li>
				2806
				2807	<li><tt>std::string getTypeName(const <a href="#Type">Type</a> *Ty)</tt>
				2808
				2809	<p>If there is at least one entry in the <a
				2810	href="#SymbolTable"><tt>SymbolTable</tt></a> for the specified <a
				2811	href="#Type"><tt>Type</tt></a>, return it. Otherwise return the empty
				2812	string.</p></li>
				2813
				2814	<li><tt>bool addTypeName(const std::string &Name, const <a
				2815	href="#Type">Type</a> *Ty)</tt>
				2816
				2817	<p>Insert an entry in the <a href="#SymbolTable"><tt>SymbolTable</tt></a>
				2818	mapping <tt>Name</tt> to <tt>Ty</tt>. If there is already an entry for this
				2819	name, true is returned and the <a
				2820	href="#SymbolTable"><tt>SymbolTable</tt></a> is not modified.</p></li>
				2821	</ul>
				2822
				2823	</div>
				2824
				2825
				2826	<!-- ======================================================================= -->
				2827	<div class="doc_subsection">
				2828	<a name="Value">The <tt>Value</tt> class</a>
				2829	</div>
				2830
				2831	<div class="doc_text">
				2832
				2833	<p><tt>#include "<a href="/doxygen/Value_8h-source.html">llvm/Value.h</a>"</tt>
				2834	<br>
				2835	doxygen info: <a href="/doxygen/classllvm_1_1Value.html">Value Class</a></p>
				2836
				2837	<p>The <tt>Value</tt> class is the most important class in the LLVM Source
				2838	base. It represents a typed value that may be used (among other things) as an
				2839	operand to an instruction. There are many different types of <tt>Value</tt>s,
				2840	such as <a href="#Constant"><tt>Constant</tt></a>s,<a
				2841	href="#Argument"><tt>Argument</tt></a>s. Even <a
				2842	href="#Instruction"><tt>Instruction</tt></a>s and <a
				2843	href="#Function"><tt>Function</tt></a>s are <tt>Value</tt>s.</p>
				2844
				2845	<p>A particular <tt>Value</tt> may be used many times in the LLVM representation
				2846	for a program. For example, an incoming argument to a function (represented
				2847	with an instance of the <a href="#Argument">Argument</a> class) is "used" by
				2848	every instruction in the function that references the argument. To keep track
				2849	of this relationship, the <tt>Value</tt> class keeps a list of all of the <a
				2850	href="#User"><tt>User</tt></a>s that is using it (the <a
				2851	href="#User"><tt>User</tt></a> class is a base class for all nodes in the LLVM
				2852	graph that can refer to <tt>Value</tt>s). This use list is how LLVM represents
				2853	def-use information in the program, and is accessible through the <tt>use_</tt>*
				2854	methods, shown below.</p>
				2855
				2856	<p>Because LLVM is a typed representation, every LLVM <tt>Value</tt> is typed,
				2857	and this <a href="#Type">Type</a> is available through the <tt>getType()</tt>
				2858	method. In addition, all LLVM values can be named. The "name" of the
				2859	<tt>Value</tt> is a symbolic string printed in the LLVM code:</p>
				2860
				2861	<div class="doc_code">
				2862	<pre>
				2863	%<b>foo</b> = add i32 1, 2
				2864	</pre>
				2865	</div>
				2866
				2867	<p><a name="nameWarning">The name of this instruction is "foo".</a> <b>NOTE</b>
				2868	that the name of any value may be missing (an empty string), so names should
				2869	<b>ONLY</b> be used for debugging (making the source code easier to read,
				2870	debugging printouts), they should not be used to keep track of values or map
				2871	between them. For this purpose, use a <tt>std::map</tt> of pointers to the
				2872	<tt>Value</tt> itself instead.</p>
				2873
				2874	<p>One important aspect of LLVM is that there is no distinction between an SSA
				2875	variable and the operation that produces it. Because of this, any reference to
				2876	the value produced by an instruction (or the value available as an incoming
				2877	argument, for example) is represented as a direct pointer to the instance of
				2878	the class that
				2879	represents this value. Although this may take some getting used to, it
				2880	simplifies the representation and makes it easier to manipulate.</p>
				2881
				2882	</div>
				2883
				2884	<!-- _______________________________________________________________________ -->
				2885	<div class="doc_subsubsection">
				2886	<a name="m_Value">Important Public Members of the <tt>Value</tt> class</a>
				2887	</div>
				2888
				2889	<div class="doc_text">
				2890
				2891	<ul>
				2892	<li><tt>Value::use_iterator</tt> - Typedef for iterator over the
				2893	use-list<br>
				2894	<tt>Value::use_const_iterator</tt> - Typedef for const_iterator over
				2895	the use-list<br>
				2896	<tt>unsigned use_size()</tt> - Returns the number of users of the
				2897	value.<br>
				2898	<tt>bool use_empty()</tt> - Returns true if there are no users.<br>
				2899	<tt>use_iterator use_begin()</tt> - Get an iterator to the start of
				2900	the use-list.<br>
				2901	<tt>use_iterator use_end()</tt> - Get an iterator to the end of the
				2902	use-list.<br>
				2903	<tt><a href="#User">User</a> *use_back()</tt> - Returns the last
				2904	element in the list.
				2905	<p> These methods are the interface to access the def-use
				2906	information in LLVM. As with all other iterators in LLVM, the naming
				2907	conventions follow the conventions defined by the <a href="#stl">STL</a>.</p>
				2908	</li>
				2909	<li><tt><a href="#Type">Type</a> *getType() const</tt>
				2910	<p>This method returns the Type of the Value.</p>
				2911	</li>
				2912	<li><tt>bool hasName() const</tt><br>
				2913	<tt>std::string getName() const</tt><br>
				2914	<tt>void setName(const std::string &Name)</tt>
				2915	<p> This family of methods is used to access and assign a name to a <tt>Value</tt>,
				2916	be aware of the <a href="#nameWarning">precaution above</a>.</p>
				2917	</li>
				2918	<li><tt>void replaceAllUsesWith(Value *V)</tt>
				2919
				2920	<p>This method traverses the use list of a <tt>Value</tt> changing all <a
				2921	href="#User"><tt>User</tt>s</a> of the current value to refer to
				2922	"<tt>V</tt>" instead. For example, if you detect that an instruction always
				2923	produces a constant value (for example through constant folding), you can
				2924	replace all uses of the instruction with the constant like this:</p>
				2925
				2926	<div class="doc_code">
				2927	<pre>
				2928	Inst->replaceAllUsesWith(ConstVal);
				2929	</pre>
				2930	</div>
				2931
				2932	</ul>
				2933
				2934	</div>
				2935
				2936	<!-- ======================================================================= -->
				2937	<div class="doc_subsection">
				2938	<a name="User">The <tt>User</tt> class</a>
				2939	</div>
				2940
				2941	<div class="doc_text">
				2942
				2943	<p>
				2944	<tt>#include "<a href="/doxygen/User_8h-source.html">llvm/User.h</a>"</tt><br>
				2945	doxygen info: <a href="/doxygen/classllvm_1_1User.html">User Class</a><br>
				2946	Superclass: <a href="#Value"><tt>Value</tt></a></p>
				2947
				2948	<p>The <tt>User</tt> class is the common base class of all LLVM nodes that may
				2949	refer to <a href="#Value"><tt>Value</tt></a>s. It exposes a list of "Operands"
				2950	that are all of the <a href="#Value"><tt>Value</tt></a>s that the User is
				2951	referring to. The <tt>User</tt> class itself is a subclass of
				2952	<tt>Value</tt>.</p>
				2953
				2954	<p>The operands of a <tt>User</tt> point directly to the LLVM <a
				2955	href="#Value"><tt>Value</tt></a> that it refers to. Because LLVM uses Static
				2956	Single Assignment (SSA) form, there can only be one definition referred to,
				2957	allowing this direct connection. This connection provides the use-def
				2958	information in LLVM.</p>
				2959
				2960	</div>
				2961
				2962	<!-- _______________________________________________________________________ -->
				2963	<div class="doc_subsubsection">
				2964	<a name="m_User">Important Public Members of the <tt>User</tt> class</a>
				2965	</div>
				2966
				2967	<div class="doc_text">
				2968
				2969	<p>The <tt>User</tt> class exposes the operand list in two ways: through
				2970	an index access interface and through an iterator based interface.</p>
				2971
				2972	<ul>
				2973	<li><tt>Value *getOperand(unsigned i)</tt><br>
				2974	<tt>unsigned getNumOperands()</tt>
				2975	<p> These two methods expose the operands of the <tt>User</tt> in a
				2976	convenient form for direct access.</p></li>
				2977
				2978	<li><tt>User::op_iterator</tt> - Typedef for iterator over the operand
				2979	list<br>
				2980	<tt>op_iterator op_begin()</tt> - Get an iterator to the start of
				2981	the operand list.<br>
				2982	<tt>op_iterator op_end()</tt> - Get an iterator to the end of the
				2983	operand list.
				2984	<p> Together, these methods make up the iterator based interface to
				2985	the operands of a <tt>User</tt>.</p></li>
				2986	</ul>
				2987
				2988	</div>
				2989
				2990	<!-- ======================================================================= -->
				2991	<div class="doc_subsection">
				2992	<a name="Instruction">The <tt>Instruction</tt> class</a>
				2993	</div>
				2994
				2995	<div class="doc_text">
				2996
				2997	<p><tt>#include "</tt><tt><a
				2998	href="/doxygen/Instruction_8h-source.html">llvm/Instruction.h</a>"</tt><br>
				2999	doxygen info: <a href="/doxygen/classllvm_1_1Instruction.html">Instruction Class</a><br>
				3000	Superclasses: <a href="#User"><tt>User</tt></a>, <a
				3001	href="#Value"><tt>Value</tt></a></p>
				3002
				3003	<p>The <tt>Instruction</tt> class is the common base class for all LLVM
				3004	instructions. It provides only a few methods, but is a very commonly used
				3005	class. The primary data tracked by the <tt>Instruction</tt> class itself is the
				3006	opcode (instruction type) and the parent <a
				3007	href="#BasicBlock"><tt>BasicBlock</tt></a> the <tt>Instruction</tt> is embedded
				3008	into. To represent a specific type of instruction, one of many subclasses of
				3009	<tt>Instruction</tt> are used.</p>
				3010
				3011	<p> Because the <tt>Instruction</tt> class subclasses the <a
				3012	href="#User"><tt>User</tt></a> class, its operands can be accessed in the same
				3013	way as for other <a href="#User"><tt>User</tt></a>s (with the
				3014	<tt>getOperand()</tt>/<tt>getNumOperands()</tt> and
				3015	<tt>op_begin()</tt>/<tt>op_end()</tt> methods).</p> <p> An important file for
				3016	the <tt>Instruction</tt> class is the <tt>llvm/Instruction.def</tt> file. This
				3017	file contains some meta-data about the various different types of instructions
				3018	in LLVM. It describes the enum values that are used as opcodes (for example
				3019	<tt>Instruction::Add</tt> and <tt>Instruction::ICmp</tt>), as well as the
				3020	concrete sub-classes of <tt>Instruction</tt> that implement the instruction (for
				3021	example <tt><a href="#BinaryOperator">BinaryOperator</a></tt> and <tt><a
				3022	href="#CmpInst">CmpInst</a></tt>). Unfortunately, the use of macros in
				3023	this file confuses doxygen, so these enum values don't show up correctly in the
				3024	<a href="/doxygen/classllvm_1_1Instruction.html">doxygen output</a>.</p>
				3025
				3026	</div>
				3027
				3028	<!-- _______________________________________________________________________ -->
				3029	<div class="doc_subsubsection">
				3030	<a name="s_Instruction">Important Subclasses of the <tt>Instruction</tt>
				3031	class</a>
				3032	</div>
				3033	<div class="doc_text">
				3034	<ul>
				3035	<li><tt><a name="BinaryOperator">BinaryOperator</a></tt>
				3036	<p>This subclasses represents all two operand instructions whose operands
				3037	must be the same type, except for the comparison instructions.</p></li>
				3038	<li><tt><a name="CastInst">CastInst</a></tt>
				3039	<p>This subclass is the parent of the 12 casting instructions. It provides
				3040	common operations on cast instructions.</p>
				3041	<li><tt><a name="CmpInst">CmpInst</a></tt>
				3042	<p>This subclass respresents the two comparison instructions,
				3043	<a href="LangRef.html#i_icmp">ICmpInst</a> (integer opreands), and
				3044	<a href="LangRef.html#i_fcmp">FCmpInst</a> (floating point operands).</p>
				3045	<li><tt><a name="TerminatorInst">TerminatorInst</a></tt>
				3046	<p>This subclass is the parent of all terminator instructions (those which
				3047	can terminate a block).</p>
				3048	</ul>
				3049	</div>
				3050
				3051	<!-- _______________________________________________________________________ -->
				3052	<div class="doc_subsubsection">
				3053	<a name="m_Instruction">Important Public Members of the <tt>Instruction</tt>
				3054	class</a>
				3055	</div>
				3056
				3057	<div class="doc_text">
				3058
				3059	<ul>
				3060	<li><tt><a href="#BasicBlock">BasicBlock</a> *getParent()</tt>
				3061	<p>Returns the <a href="#BasicBlock"><tt>BasicBlock</tt></a> that
				3062	this <tt>Instruction</tt> is embedded into.</p></li>
				3063	<li><tt>bool mayWriteToMemory()</tt>
				3064	<p>Returns true if the instruction writes to memory, i.e. it is a
				3065	<tt>call</tt>,<tt>free</tt>,<tt>invoke</tt>, or <tt>store</tt>.</p></li>
				3066	<li><tt>unsigned getOpcode()</tt>
				3067	<p>Returns the opcode for the <tt>Instruction</tt>.</p></li>
				3068	<li><tt><a href="#Instruction">Instruction</a> *clone() const</tt>
				3069	<p>Returns another instance of the specified instruction, identical
				3070	in all ways to the original except that the instruction has no parent
				3071	(ie it's not embedded into a <a href="#BasicBlock"><tt>BasicBlock</tt></a>),
				3072	and it has no name</p></li>
				3073	</ul>
				3074
				3075	</div>
				3076
				3077	<!-- ======================================================================= -->
				3078	<div class="doc_subsection">
				3079	<a name="Constant">The <tt>Constant</tt> class and subclasses</a>
				3080	</div>
				3081
				3082	<div class="doc_text">
				3083
				3084	<p>Constant represents a base class for different types of constants. It
				3085	is subclassed by ConstantInt, ConstantArray, etc. for representing
				3086	the various types of Constants. <a href="#GlobalValue">GlobalValue</a> is also
				3087	a subclass, which represents the address of a global variable or function.
				3088	</p>
				3089
				3090	</div>
				3091
				3092	<!-- _______________________________________________________________________ -->
				3093	<div class="doc_subsubsection">Important Subclasses of Constant </div>
				3094	<div class="doc_text">
				3095	<ul>
				3096	<li>ConstantInt : This subclass of Constant represents an integer constant of
				3097	any width.
				3098	<ul>
				3099	<li><tt>const APInt& getValue() const</tt>: Returns the underlying
				3100	value of this constant, an APInt value.</li>
				3101	<li><tt>int64_t getSExtValue() const</tt>: Converts the underlying APInt
				3102	value to an int64_t via sign extension. If the value (not the bit width)
				3103	of the APInt is too large to fit in an int64_t, an assertion will result.
				3104	For this reason, use of this method is discouraged.</li>
				3105	<li><tt>uint64_t getZExtValue() const</tt>: Converts the underlying APInt
				3106	value to a uint64_t via zero extension. IF the value (not the bit width)
				3107	of the APInt is too large to fit in a uint64_t, an assertion will result.
				3108	For this reason, use of this method is discouraged.</li>
				3109	<li><tt>static ConstantInt* get(const APInt& Val)</tt>: Returns the
				3110	ConstantInt object that represents the value provided by <tt>Val</tt>.
				3111	The type is implied as the IntegerType that corresponds to the bit width
				3112	of <tt>Val</tt>.</li>
				3113	<li><tt>static ConstantInt* get(const Type *Ty, uint64_t Val)</tt>:
				3114	Returns the ConstantInt object that represents the value provided by
				3115	<tt>Val</tt> for integer type <tt>Ty</tt>.</li>
				3116	</ul>
				3117	</li>
				3118	<li>ConstantFP : This class represents a floating point constant.
				3119	<ul>
				3120	<li><tt>double getValue() const</tt>: Returns the underlying value of
				3121	this constant. </li>
				3122	</ul>
				3123	</li>
				3124	<li>ConstantArray : This represents a constant array.
				3125	<ul>
				3126	<li><tt>const std::vector<Use> &getValues() const</tt>: Returns
				3127	a vector of component constants that makeup this array. </li>
				3128	</ul>
				3129	</li>
				3130	<li>ConstantStruct : This represents a constant struct.
				3131	<ul>
				3132	<li><tt>const std::vector<Use> &getValues() const</tt>: Returns
				3133	a vector of component constants that makeup this array. </li>
				3134	</ul>
				3135	</li>
				3136	<li>GlobalValue : This represents either a global variable or a function. In
				3137	either case, the value is a constant fixed address (after linking).
				3138	</li>
				3139	</ul>
				3140	</div>
				3141
				3142
				3143	<!-- ======================================================================= -->
				3144	<div class="doc_subsection">
				3145	<a name="GlobalValue">The <tt>GlobalValue</tt> class</a>
				3146	</div>
				3147
				3148	<div class="doc_text">
				3149
				3150	<p><tt>#include "<a
				3151	href="/doxygen/GlobalValue_8h-source.html">llvm/GlobalValue.h</a>"</tt><br>
				3152	doxygen info: <a href="/doxygen/classllvm_1_1GlobalValue.html">GlobalValue
				3153	Class</a><br>
				3154	Superclasses: <a href="#Constant"><tt>Constant</tt></a>,
				3155	<a href="#User"><tt>User</tt></a>, <a href="#Value"><tt>Value</tt></a></p>
				3156
				3157	<p>Global values (<a href="#GlobalVariable"><tt>GlobalVariable</tt></a>s or <a
				3158	href="#Function"><tt>Function</tt></a>s) are the only LLVM values that are
				3159	visible in the bodies of all <a href="#Function"><tt>Function</tt></a>s.
				3160	Because they are visible at global scope, they are also subject to linking with
				3161	other globals defined in different translation units. To control the linking
				3162	process, <tt>GlobalValue</tt>s know their linkage rules. Specifically,
				3163	<tt>GlobalValue</tt>s know whether they have internal or external linkage, as
				3164	defined by the <tt>LinkageTypes</tt> enumeration.</p>
				3165
				3166	<p>If a <tt>GlobalValue</tt> has internal linkage (equivalent to being
				3167	<tt>static</tt> in C), it is not visible to code outside the current translation
				3168	unit, and does not participate in linking. If it has external linkage, it is
				3169	visible to external code, and does participate in linking. In addition to
				3170	linkage information, <tt>GlobalValue</tt>s keep track of which <a
				3171	href="#Module"><tt>Module</tt></a> they are currently part of.</p>
				3172
				3173	<p>Because <tt>GlobalValue</tt>s are memory objects, they are always referred to
				3174	by their <b>address</b>. As such, the <a href="#Type"><tt>Type</tt></a> of a
				3175	global is always a pointer to its contents. It is important to remember this
				3176	when using the <tt>GetElementPtrInst</tt> instruction because this pointer must
				3177	be dereferenced first. For example, if you have a <tt>GlobalVariable</tt> (a
				3178	subclass of <tt>GlobalValue)</tt> that is an array of 24 ints, type <tt>[24 x
				3179	i32]</tt>, then the <tt>GlobalVariable</tt> is a pointer to that array. Although
				3180	the address of the first element of this array and the value of the
				3181	<tt>GlobalVariable</tt> are the same, they have different types. The
				3182	<tt>GlobalVariable</tt>'s type is <tt>[24 x i32]</tt>. The first element's type
				3183	is <tt>i32.</tt> Because of this, accessing a global value requires you to
				3184	dereference the pointer with <tt>GetElementPtrInst</tt> first, then its elements
				3185	can be accessed. This is explained in the <a href="LangRef.html#globalvars">LLVM
				3186	Language Reference Manual</a>.</p>
				3187
				3188	</div>
				3189
				3190	<!-- _______________________________________________________________________ -->
				3191	<div class="doc_subsubsection">
				3192	<a name="m_GlobalValue">Important Public Members of the <tt>GlobalValue</tt>
				3193	class</a>
				3194	</div>
				3195
				3196	<div class="doc_text">
				3197
				3198	<ul>
				3199	<li><tt>bool hasInternalLinkage() const</tt><br>
				3200	<tt>bool hasExternalLinkage() const</tt><br>
				3201	<tt>void setInternalLinkage(bool HasInternalLinkage)</tt>
				3202	<p> These methods manipulate the linkage characteristics of the <tt>GlobalValue</tt>.</p>
				3203	<p> </p>
				3204	</li>
				3205	<li><tt><a href="#Module">Module</a> *getParent()</tt>
				3206	<p> This returns the <a href="#Module"><tt>Module</tt></a> that the
				3207	GlobalValue is currently embedded into.</p></li>
				3208	</ul>
				3209
				3210	</div>
				3211
				3212	<!-- ======================================================================= -->
				3213	<div class="doc_subsection">
				3214	<a name="Function">The <tt>Function</tt> class</a>
				3215	</div>
				3216
				3217	<div class="doc_text">
				3218
				3219	<p><tt>#include "<a
				3220	href="/doxygen/Function_8h-source.html">llvm/Function.h</a>"</tt><br> doxygen
				3221	info: <a href="/doxygen/classllvm_1_1Function.html">Function Class</a><br>
				3222	Superclasses: <a href="#GlobalValue"><tt>GlobalValue</tt></a>,
				3223	<a href="#Constant"><tt>Constant</tt></a>,
				3224	<a href="#User"><tt>User</tt></a>,
				3225	<a href="#Value"><tt>Value</tt></a></p>
				3226
				3227	<p>The <tt>Function</tt> class represents a single procedure in LLVM. It is
				3228	actually one of the more complex classes in the LLVM heirarchy because it must
				3229	keep track of a large amount of data. The <tt>Function</tt> class keeps track
				3230	of a list of <a href="#BasicBlock"><tt>BasicBlock</tt></a>s, a list of formal
				3231	<a href="#Argument"><tt>Argument</tt></a>s, and a
				3232	<a href="#SymbolTable"><tt>SymbolTable</tt></a>.</p>
				3233
				3234	<p>The list of <a href="#BasicBlock"><tt>BasicBlock</tt></a>s is the most
				3235	commonly used part of <tt>Function</tt> objects. The list imposes an implicit
				3236	ordering of the blocks in the function, which indicate how the code will be
				3237	layed out by the backend. Additionally, the first <a
				3238	href="#BasicBlock"><tt>BasicBlock</tt></a> is the implicit entry node for the
				3239	<tt>Function</tt>. It is not legal in LLVM to explicitly branch to this initial
				3240	block. There are no implicit exit nodes, and in fact there may be multiple exit
				3241	nodes from a single <tt>Function</tt>. If the <a
				3242	href="#BasicBlock"><tt>BasicBlock</tt></a> list is empty, this indicates that
				3243	the <tt>Function</tt> is actually a function declaration: the actual body of the
				3244	function hasn't been linked in yet.</p>
				3245
				3246	<p>In addition to a list of <a href="#BasicBlock"><tt>BasicBlock</tt></a>s, the
				3247	<tt>Function</tt> class also keeps track of the list of formal <a
				3248	href="#Argument"><tt>Argument</tt></a>s that the function receives. This
				3249	container manages the lifetime of the <a href="#Argument"><tt>Argument</tt></a>
				3250	nodes, just like the <a href="#BasicBlock"><tt>BasicBlock</tt></a> list does for
				3251	the <a href="#BasicBlock"><tt>BasicBlock</tt></a>s.</p>
				3252
				3253	<p>The <a href="#SymbolTable"><tt>SymbolTable</tt></a> is a very rarely used
				3254	LLVM feature that is only used when you have to look up a value by name. Aside
				3255	from that, the <a href="#SymbolTable"><tt>SymbolTable</tt></a> is used
				3256	internally to make sure that there are not conflicts between the names of <a
				3257	href="#Instruction"><tt>Instruction</tt></a>s, <a
				3258	href="#BasicBlock"><tt>BasicBlock</tt></a>s, or <a
				3259	href="#Argument"><tt>Argument</tt></a>s in the function body.</p>
				3260
				3261	<p>Note that <tt>Function</tt> is a <a href="#GlobalValue">GlobalValue</a>
				3262	and therefore also a <a href="#Constant">Constant</a>. The value of the function
				3263	is its address (after linking) which is guaranteed to be constant.</p>
				3264	</div>
				3265
				3266	<!-- _______________________________________________________________________ -->
				3267	<div class="doc_subsubsection">
				3268	<a name="m_Function">Important Public Members of the <tt>Function</tt>
				3269	class</a>
				3270	</div>
				3271
				3272	<div class="doc_text">
				3273
				3274	<ul>
				3275	<li><tt>Function(const </tt><tt><a href="#FunctionType">FunctionType</a>
				3276	Ty, LinkageTypes Linkage, const std::string &N = "", Module Parent = 0)</tt>
				3277
				3278	<p>Constructor used when you need to create new <tt>Function</tt>s to add
				3279	the the program. The constructor must specify the type of the function to
				3280	create and what type of linkage the function should have. The <a
				3281	href="#FunctionType"><tt>FunctionType</tt></a> argument
				3282	specifies the formal arguments and return value for the function. The same
				3283	<a href="#FunctionType"><tt>FunctionType</tt></a> value can be used to
				3284	create multiple functions. The <tt>Parent</tt> argument specifies the Module
				3285	in which the function is defined. If this argument is provided, the function
				3286	will automatically be inserted into that module's list of
				3287	functions.</p></li>
				3288
Chris Lattner	5e70957	2008-11-25 18:34:50 +0000	[diff] [blame]	3289	<li><tt>bool isDeclaration()</tt>
Dan Gohman	f17a25c	2007-07-18 16:29:46 +0000	[diff] [blame]	3290
				3291	<p>Return whether or not the <tt>Function</tt> has a body defined. If the
				3292	function is "external", it does not have a body, and thus must be resolved
				3293	by linking with a function defined in a different translation unit.</p></li>
				3294
				3295	<li><tt>Function::iterator</tt> - Typedef for basic block list iterator<br>
				3296	<tt>Function::const_iterator</tt> - Typedef for const_iterator.<br>
				3297
				3298	<tt>begin()</tt>, <tt>end()</tt>
				3299	<tt>size()</tt>, <tt>empty()</tt>
				3300
				3301	<p>These are forwarding methods that make it easy to access the contents of
				3302	a <tt>Function</tt> object's <a href="#BasicBlock"><tt>BasicBlock</tt></a>
				3303	list.</p></li>
				3304
				3305	<li><tt>Function::BasicBlockListType &getBasicBlockList()</tt>
				3306
				3307	<p>Returns the list of <a href="#BasicBlock"><tt>BasicBlock</tt></a>s. This
				3308	is necessary to use when you need to update the list or perform a complex
				3309	action that doesn't have a forwarding method.</p></li>
				3310
				3311	<li><tt>Function::arg_iterator</tt> - Typedef for the argument list
				3312	iterator<br>
				3313	<tt>Function::const_arg_iterator</tt> - Typedef for const_iterator.<br>
				3314
				3315	<tt>arg_begin()</tt>, <tt>arg_end()</tt>
				3316	<tt>arg_size()</tt>, <tt>arg_empty()</tt>
				3317
				3318	<p>These are forwarding methods that make it easy to access the contents of
				3319	a <tt>Function</tt> object's <a href="#Argument"><tt>Argument</tt></a>
				3320	list.</p></li>
				3321
				3322	<li><tt>Function::ArgumentListType &getArgumentList()</tt>
				3323
				3324	<p>Returns the list of <a href="#Argument"><tt>Argument</tt></a>s. This is
				3325	necessary to use when you need to update the list or perform a complex
				3326	action that doesn't have a forwarding method.</p></li>
				3327
				3328	<li><tt><a href="#BasicBlock">BasicBlock</a> &getEntryBlock()</tt>
				3329
				3330	<p>Returns the entry <a href="#BasicBlock"><tt>BasicBlock</tt></a> for the
				3331	function. Because the entry block for the function is always the first
				3332	block, this returns the first block of the <tt>Function</tt>.</p></li>
				3333
				3334	<li><tt><a href="#Type">Type</a> *getReturnType()</tt><br>
				3335	<tt><a href="#FunctionType">FunctionType</a> *getFunctionType()</tt>
				3336
				3337	<p>This traverses the <a href="#Type"><tt>Type</tt></a> of the
				3338	<tt>Function</tt> and returns the return type of the function, or the <a
				3339	href="#FunctionType"><tt>FunctionType</tt></a> of the actual
				3340	function.</p></li>
				3341
				3342	<li><tt><a href="#SymbolTable">SymbolTable</a> *getSymbolTable()</tt>
				3343
				3344	<p> Return a pointer to the <a href="#SymbolTable"><tt>SymbolTable</tt></a>
				3345	for this <tt>Function</tt>.</p></li>
				3346	</ul>
				3347
				3348	</div>
				3349
				3350	<!-- ======================================================================= -->
				3351	<div class="doc_subsection">
				3352	<a name="GlobalVariable">The <tt>GlobalVariable</tt> class</a>
				3353	</div>
				3354
				3355	<div class="doc_text">
				3356
				3357	<p><tt>#include "<a
				3358	href="/doxygen/GlobalVariable_8h-source.html">llvm/GlobalVariable.h</a>"</tt>
				3359	<br>
				3360	doxygen info: <a href="/doxygen/classllvm_1_1GlobalVariable.html">GlobalVariable
				3361	Class</a><br>
				3362	Superclasses: <a href="#GlobalValue"><tt>GlobalValue</tt></a>,
				3363	<a href="#Constant"><tt>Constant</tt></a>,
				3364	<a href="#User"><tt>User</tt></a>,
				3365	<a href="#Value"><tt>Value</tt></a></p>
				3366
				3367	<p>Global variables are represented with the (suprise suprise)
				3368	<tt>GlobalVariable</tt> class. Like functions, <tt>GlobalVariable</tt>s are also
				3369	subclasses of <a href="#GlobalValue"><tt>GlobalValue</tt></a>, and as such are
				3370	always referenced by their address (global values must live in memory, so their
				3371	"name" refers to their constant address). See
				3372	<a href="#GlobalValue"><tt>GlobalValue</tt></a> for more on this. Global
				3373	variables may have an initial value (which must be a
				3374	<a href="#Constant"><tt>Constant</tt></a>), and if they have an initializer,
				3375	they may be marked as "constant" themselves (indicating that their contents
				3376	never change at runtime).</p>
				3377	</div>
				3378
				3379	<!-- _______________________________________________________________________ -->
				3380	<div class="doc_subsubsection">
				3381	<a name="m_GlobalVariable">Important Public Members of the
				3382	<tt>GlobalVariable</tt> class</a>
				3383	</div>
				3384
				3385	<div class="doc_text">
				3386
				3387	<ul>
				3388	<li><tt>GlobalVariable(const </tt><tt><a href="#Type">Type</a> *Ty, bool
				3389	isConstant, LinkageTypes& Linkage, <a href="#Constant">Constant</a>
				3390	Initializer = 0, const std::string &Name = "", Module Parent = 0)</tt>
				3391
				3392	<p>Create a new global variable of the specified type. If
				3393	<tt>isConstant</tt> is true then the global variable will be marked as
				3394	unchanging for the program. The Linkage parameter specifies the type of
Duncan Sands	19d161f	2009-03-07 15:45:40 +0000	[diff] [blame]	3395	linkage (internal, external, weak, linkonce, appending) for the variable.
				3396	If the linkage is InternalLinkage, WeakAnyLinkage, WeakODRLinkage,
				3397	LinkOnceAnyLinkage or LinkOnceODRLinkage,  then the resultant
				3398	global variable will have internal linkage. AppendingLinkage concatenates
				3399	together all instances (in different translation units) of the variable
				3400	into a single variable but is only applicable to arrays.  See
Dan Gohman	f17a25c	2007-07-18 16:29:46 +0000	[diff] [blame]	3401	the <a href="LangRef.html#modulestructure">LLVM Language Reference</a> for
				3402	further details on linkage types. Optionally an initializer, a name, and the
				3403	module to put the variable into may be specified for the global variable as
				3404	well.</p></li>
				3405
				3406	<li><tt>bool isConstant() const</tt>
				3407
				3408	<p>Returns true if this is a global variable that is known not to
				3409	be modified at runtime.</p></li>
				3410
				3411	<li><tt>bool hasInitializer()</tt>
				3412
				3413	<p>Returns true if this <tt>GlobalVariable</tt> has an intializer.</p></li>
				3414
				3415	<li><tt><a href="#Constant">Constant</a> *getInitializer()</tt>
				3416
				3417	<p>Returns the intial value for a <tt>GlobalVariable</tt>. It is not legal
				3418	to call this method if there is no initializer.</p></li>
				3419	</ul>
				3420
				3421	</div>
				3422
				3423
				3424	<!-- ======================================================================= -->
				3425	<div class="doc_subsection">
				3426	<a name="BasicBlock">The <tt>BasicBlock</tt> class</a>
				3427	</div>
				3428
				3429	<div class="doc_text">
				3430
				3431	<p><tt>#include "<a
				3432	href="/doxygen/BasicBlock_8h-source.html">llvm/BasicBlock.h</a>"</tt><br>
				3433	doxygen info: <a href="/doxygen/structllvm_1_1BasicBlock.html">BasicBlock
				3434	Class</a><br>
				3435	Superclass: <a href="#Value"><tt>Value</tt></a></p>
				3436
				3437	<p>This class represents a single entry multiple exit section of the code,
				3438	commonly known as a basic block by the compiler community. The
				3439	<tt>BasicBlock</tt> class maintains a list of <a
				3440	href="#Instruction"><tt>Instruction</tt></a>s, which form the body of the block.
				3441	Matching the language definition, the last element of this list of instructions
				3442	is always a terminator instruction (a subclass of the <a
				3443	href="#TerminatorInst"><tt>TerminatorInst</tt></a> class).</p>
				3444
				3445	<p>In addition to tracking the list of instructions that make up the block, the
				3446	<tt>BasicBlock</tt> class also keeps track of the <a
				3447	href="#Function"><tt>Function</tt></a> that it is embedded into.</p>
				3448
				3449	<p>Note that <tt>BasicBlock</tt>s themselves are <a
				3450	href="#Value"><tt>Value</tt></a>s, because they are referenced by instructions
				3451	like branches and can go in the switch tables. <tt>BasicBlock</tt>s have type
				3452	<tt>label</tt>.</p>
				3453
				3454	</div>
				3455
				3456	<!-- _______________________________________________________________________ -->
				3457	<div class="doc_subsubsection">
				3458	<a name="m_BasicBlock">Important Public Members of the <tt>BasicBlock</tt>
				3459	class</a>
				3460	</div>
				3461
				3462	<div class="doc_text">
				3463	<ul>
				3464
				3465	<li><tt>BasicBlock(const std::string &Name = "", </tt><tt><a
				3466	href="#Function">Function</a> *Parent = 0)</tt>
				3467
				3468	<p>The <tt>BasicBlock</tt> constructor is used to create new basic blocks for
				3469	insertion into a function. The constructor optionally takes a name for the new
				3470	block, and a <a href="#Function"><tt>Function</tt></a> to insert it into. If
				3471	the <tt>Parent</tt> parameter is specified, the new <tt>BasicBlock</tt> is
				3472	automatically inserted at the end of the specified <a
				3473	href="#Function"><tt>Function</tt></a>, if not specified, the BasicBlock must be
				3474	manually inserted into the <a href="#Function"><tt>Function</tt></a>.</p></li>
				3475
				3476	<li><tt>BasicBlock::iterator</tt> - Typedef for instruction list iterator<br>
				3477	<tt>BasicBlock::const_iterator</tt> - Typedef for const_iterator.<br>
				3478	<tt>begin()</tt>, <tt>end()</tt>, <tt>front()</tt>, <tt>back()</tt>,
				3479	<tt>size()</tt>, <tt>empty()</tt>
				3480	STL-style functions for accessing the instruction list.
				3481
				3482	<p>These methods and typedefs are forwarding functions that have the same
				3483	semantics as the standard library methods of the same names. These methods
				3484	expose the underlying instruction list of a basic block in a way that is easy to
				3485	manipulate. To get the full complement of container operations (including
				3486	operations to update the list), you must use the <tt>getInstList()</tt>
				3487	method.</p></li>
				3488
				3489	<li><tt>BasicBlock::InstListType &getInstList()</tt>
				3490
				3491	<p>This method is used to get access to the underlying container that actually
				3492	holds the Instructions. This method must be used when there isn't a forwarding
				3493	function in the <tt>BasicBlock</tt> class for the operation that you would like
				3494	to perform. Because there are no forwarding functions for "updating"
				3495	operations, you need to use this if you want to update the contents of a
				3496	<tt>BasicBlock</tt>.</p></li>
				3497
				3498	<li><tt><a href="#Function">Function</a> *getParent()</tt>
				3499
				3500	<p> Returns a pointer to <a href="#Function"><tt>Function</tt></a> the block is
				3501	embedded into, or a null pointer if it is homeless.</p></li>
				3502
				3503	<li><tt><a href="#TerminatorInst">TerminatorInst</a> *getTerminator()</tt>
				3504
				3505	<p> Returns a pointer to the terminator instruction that appears at the end of
				3506	the <tt>BasicBlock</tt>. If there is no terminator instruction, or if the last
				3507	instruction in the block is not a terminator, then a null pointer is
				3508	returned.</p></li>
				3509
				3510	</ul>
				3511
				3512	</div>
				3513
				3514
				3515	<!-- ======================================================================= -->
				3516	<div class="doc_subsection">
				3517	<a name="Argument">The <tt>Argument</tt> class</a>
				3518	</div>
				3519
				3520	<div class="doc_text">
				3521
				3522	<p>This subclass of Value defines the interface for incoming formal
				3523	arguments to a function. A Function maintains a list of its formal
				3524	arguments. An argument has a pointer to the parent Function.</p>
				3525
				3526	</div>
				3527
				3528	<!-- *********************************************************************** -->
				3529	<hr>
				3530	<address>
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Dan Gohman	f17a25c	2007-07-18 16:29:46 +0000	[diff] [blame]	3535
				3536	<a href="mailto:dhurjati@cs.uiuc.edu">Dinakar Dhurjati</a> and
				3537	<a href="mailto:sabre@nondot.org">Chris Lattner</a><br>
				3538	<a href="http://llvm.org">The LLVM Compiler Infrastructure</a><br>
				3539	Last modified: $Date$
				3540	</address>
				3541
				3542	</body>
				3543	</html>