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				5	<title>LLVM Programmer's Manual</title>
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				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>
				120	<!--
				121	<li>Working with the Control Flow Graph
				122	<ul>
				123	<li>Accessing predecessors and successors of a <tt>BasicBlock</tt>
				124	<li>
				125	<li>
				126	</ul>
				127	-->
				128	</ul>
				129	</li>
				130
				131	<li><a href="#advanced">Advanced Topics</a>
				132	<ul>
				133	<li><a href="#TypeResolve">LLVM Type Resolution</a>
				134	<ul>
				135	<li><a href="#BuildRecType">Basic Recursive Type Construction</a></li>
				136	<li><a href="#refineAbstractTypeTo">The <tt>refineAbstractTypeTo</tt> method</a></li>
				137	<li><a href="#PATypeHolder">The PATypeHolder Class</a></li>
				138	<li><a href="#AbstractTypeUser">The AbstractTypeUser Class</a></li>
				139	</ul></li>
				140
Gabor Greif	92e8776	2008-06-16 21:06:12 +0000	[diff] [blame]	141	<li><a href="#SymbolTable">The <tt>ValueSymbolTable</tt> and <tt>TypeSymbolTable</tt> classes</a></li>
				142	<li><a href="#UserLayout">The <tt>User</tt> and owned <tt>Use</tt> classes' memory layout</a></li>
Dan Gohman	f17a25c	2007-07-18 16:29:46 +0000	[diff] [blame]	143	</ul></li>
				144
				145	<li><a href="#coreclasses">The Core LLVM Class Hierarchy Reference</a>
				146	<ul>
				147	<li><a href="#Type">The <tt>Type</tt> class</a> </li>
				148	<li><a href="#Module">The <tt>Module</tt> class</a></li>
				149	<li><a href="#Value">The <tt>Value</tt> class</a>
				150	<ul>
				151	<li><a href="#User">The <tt>User</tt> class</a>
				152	<ul>
				153	<li><a href="#Instruction">The <tt>Instruction</tt> class</a></li>
				154	<li><a href="#Constant">The <tt>Constant</tt> class</a>
				155	<ul>
				156	<li><a href="#GlobalValue">The <tt>GlobalValue</tt> class</a>
				157	<ul>
				158	<li><a href="#Function">The <tt>Function</tt> class</a></li>
				159	<li><a href="#GlobalVariable">The <tt>GlobalVariable</tt> class</a></li>
				160	</ul>
				161	</li>
				162	</ul>
				163	</li>
				164	</ul>
				165	</li>
				166	<li><a href="#BasicBlock">The <tt>BasicBlock</tt> class</a></li>
				167	<li><a href="#Argument">The <tt>Argument</tt> class</a></li>
				168	</ul>
				169	</li>
				170	</ul>
				171	</li>
				172	</ol>
				173
				174	<div class="doc_author">
				175	<p>Written by <a href="mailto:sabre@nondot.org">Chris Lattner</a>,
				176	<a href="mailto:dhurjati@cs.uiuc.edu">Dinakar Dhurjati</a>,
Gabor Greif	92e8776	2008-06-16 21:06:12 +0000	[diff] [blame]	177	<a href="mailto:ggreif@gmail.com">Gabor Greif</a>,
				178	<a href="mailto:jstanley@cs.uiuc.edu">Joel Stanley</a> and
Dan Gohman	f17a25c	2007-07-18 16:29:46 +0000	[diff] [blame]	179	<a href="mailto:rspencer@x10sys.com">Reid Spencer</a></p>
				180	</div>
				181
				182	<!-- *********************************************************************** -->
				183	<div class="doc_section">
				184	<a name="introduction">Introduction </a>
				185	</div>
				186	<!-- *********************************************************************** -->
				187
				188	<div class="doc_text">
				189
				190	<p>This document is meant to highlight some of the important classes and
				191	interfaces available in the LLVM source-base. This manual is not
				192	intended to explain what LLVM is, how it works, and what LLVM code looks
				193	like. It assumes that you know the basics of LLVM and are interested
				194	in writing transformations or otherwise analyzing or manipulating the
				195	code.</p>
				196
				197	<p>This document should get you oriented so that you can find your
				198	way in the continuously growing source code that makes up the LLVM
				199	infrastructure. Note that this manual is not intended to serve as a
				200	replacement for reading the source code, so if you think there should be
				201	a method in one of these classes to do something, but it's not listed,
				202	check the source. Links to the <a href="/doxygen/">doxygen</a> sources
				203	are provided to make this as easy as possible.</p>
				204
				205	<p>The first section of this document describes general information that is
				206	useful to know when working in the LLVM infrastructure, and the second describes
				207	the Core LLVM classes. In the future this manual will be extended with
				208	information describing how to use extension libraries, such as dominator
				209	information, CFG traversal routines, and useful utilities like the <tt><a
				210	href="/doxygen/InstVisitor_8h-source.html">InstVisitor</a></tt> template.</p>
				211
				212	</div>
				213
				214	<!-- *********************************************************************** -->
				215	<div class="doc_section">
				216	<a name="general">General Information</a>
				217	</div>
				218	<!-- *********************************************************************** -->
				219
				220	<div class="doc_text">
				221
				222	<p>This section contains general information that is useful if you are working
				223	in the LLVM source-base, but that isn't specific to any particular API.</p>
				224
				225	</div>
				226
				227	<!-- ======================================================================= -->
				228	<div class="doc_subsection">
				229	<a name="stl">The C++ Standard Template Library</a>
				230	</div>
				231
				232	<div class="doc_text">
				233
				234	<p>LLVM makes heavy use of the C++ Standard Template Library (STL),
				235	perhaps much more than you are used to, or have seen before. Because of
				236	this, you might want to do a little background reading in the
				237	techniques used and capabilities of the library. There are many good
				238	pages that discuss the STL, and several books on the subject that you
				239	can get, so it will not be discussed in this document.</p>
				240
				241	<p>Here are some useful links:</p>
				242
				243	<ol>
				244
				245	<li><a href="http://www.dinkumware.com/refxcpp.html">Dinkumware C++ Library
				246	reference</a> - an excellent reference for the STL and other parts of the
				247	standard C++ library.</li>
				248
				249	<li><a href="http://www.tempest-sw.com/cpp/">C++ In a Nutshell</a> - This is an
Gabor Greif	e39f0e7	2009-03-12 09:47:03 +0000	[diff] [blame]	250	O'Reilly book in the making. It has a decent Standard Library
				251	Reference that rivals Dinkumware's, and is unfortunately no longer free since the
				252	book has been published.</li>
Dan Gohman	f17a25c	2007-07-18 16:29:46 +0000	[diff] [blame]	253
				254	<li><a href="http://www.parashift.com/c++-faq-lite/">C++ Frequently Asked
				255	Questions</a></li>
				256
				257	<li><a href="http://www.sgi.com/tech/stl/">SGI's STL Programmer's Guide</a> -
				258	Contains a useful <a
				259	href="http://www.sgi.com/tech/stl/stl_introduction.html">Introduction to the
				260	STL</a>.</li>
				261
				262	<li><a href="http://www.research.att.com/%7Ebs/C++.html">Bjarne Stroustrup's C++
				263	Page</a></li>
				264
				265	<li><a href="http://64.78.49.204/">
				266	Bruce Eckel's Thinking in C++, 2nd ed. Volume 2 Revision 4.0 (even better, get
				267	the book).</a></li>
				268
				269	</ol>
				270
				271	<p>You are also encouraged to take a look at the <a
				272	href="CodingStandards.html">LLVM Coding Standards</a> guide which focuses on how
				273	to write maintainable code more than where to put your curly braces.</p>
				274
				275	</div>
				276
				277	<!-- ======================================================================= -->
				278	<div class="doc_subsection">
				279	<a name="stl">Other useful references</a>
				280	</div>
				281
				282	<div class="doc_text">
				283
				284	<ol>
				285	<li><a href="http://www.psc.edu/%7Esemke/cvs_branches.html">CVS
				286	Branch and Tag Primer</a></li>
				287	<li><a href="http://www.fortran-2000.com/ArnaudRecipes/sharedlib.html">Using
				288	static and shared libraries across platforms</a></li>
				289	</ol>
				290
				291	</div>
				292
				293	<!-- *********************************************************************** -->
				294	<div class="doc_section">
				295	<a name="apis">Important and useful LLVM APIs</a>
				296	</div>
				297	<!-- *********************************************************************** -->
				298
				299	<div class="doc_text">
				300
				301	<p>Here we highlight some LLVM APIs that are generally useful and good to
				302	know about when writing transformations.</p>
				303
				304	</div>
				305
				306	<!-- ======================================================================= -->
				307	<div class="doc_subsection">
				308	<a name="isa">The <tt>isa<></tt>, <tt>cast<></tt> and
				309	<tt>dyn_cast<></tt> templates</a>
				310	</div>
				311
				312	<div class="doc_text">
				313
				314	<p>The LLVM source-base makes extensive use of a custom form of RTTI.
				315	These templates have many similarities to the C++ <tt>dynamic_cast<></tt>
				316	operator, but they don't have some drawbacks (primarily stemming from
				317	the fact that <tt>dynamic_cast<></tt> only works on classes that
				318	have a v-table). Because they are used so often, you must know what they
				319	do and how they work. All of these templates are defined in the <a
				320	href="/doxygen/Casting_8h-source.html"><tt>llvm/Support/Casting.h</tt></a>
				321	file (note that you very rarely have to include this file directly).</p>
				322
				323	<dl>
				324	<dt><tt>isa<></tt>: </dt>
				325
				326	<dd><p>The <tt>isa<></tt> operator works exactly like the Java
				327	"<tt>instanceof</tt>" operator. It returns true or false depending on whether
				328	a reference or pointer points to an instance of the specified class. This can
				329	be very useful for constraint checking of various sorts (example below).</p>
				330	</dd>
				331
				332	<dt><tt>cast<></tt>: </dt>
				333
				334	<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]	335	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]	336	an assertion failure if it is not really an instance of the right type. This
				337	should be used in cases where you have some information that makes you believe
				338	that something is of the right type. An example of the <tt>isa<></tt>
				339	and <tt>cast<></tt> template is:</p>
				340
				341	<div class="doc_code">
				342	<pre>
				343	static bool isLoopInvariant(const <a href="#Value">Value</a> V, const Loop L) {
				344	if (isa<<a href="#Constant">Constant</a>>(V) \|\| isa<<a href="#Argument">Argument</a>>(V) \|\| isa<<a href="#GlobalValue">GlobalValue</a>>(V))
				345	return true;
				346
				347	// <i>Otherwise, it must be an instruction...</i>
				348	return !L->contains(cast<<a href="#Instruction">Instruction</a>>(V)->getParent());
				349	}
				350	</pre>
				351	</div>
				352
				353	<p>Note that you should <b>not</b> use an <tt>isa<></tt> test followed
				354	by a <tt>cast<></tt>, for that use the <tt>dyn_cast<></tt>
				355	operator.</p>
				356
				357	</dd>
				358
				359	<dt><tt>dyn_cast<></tt>:</dt>
				360
				361	<dd><p>The <tt>dyn_cast<></tt> operator is a "checking cast" operation.
				362	It checks to see if the operand is of the specified type, and if so, returns a
				363	pointer to it (this operator does not work with references). If the operand is
				364	not of the correct type, a null pointer is returned. Thus, this works very
				365	much like the <tt>dynamic_cast<></tt> operator in C++, and should be
				366	used in the same circumstances. Typically, the <tt>dyn_cast<></tt>
				367	operator is used in an <tt>if</tt> statement or some other flow control
				368	statement like this:</p>
				369
				370	<div class="doc_code">
				371	<pre>
				372	if (<a href="#AllocationInst">AllocationInst</a> *AI = dyn_cast<<a href="#AllocationInst">AllocationInst</a>>(Val)) {
				373	// <i>...</i>
				374	}
				375	</pre>
				376	</div>
				377
				378	<p>This form of the <tt>if</tt> statement effectively combines together a call
				379	to <tt>isa<></tt> and a call to <tt>cast<></tt> into one
				380	statement, which is very convenient.</p>
				381
				382	<p>Note that the <tt>dyn_cast<></tt> operator, like C++'s
				383	<tt>dynamic_cast<></tt> or Java's <tt>instanceof</tt> operator, can be
				384	abused. In particular, you should not use big chained <tt>if/then/else</tt>
				385	blocks to check for lots of different variants of classes. If you find
				386	yourself wanting to do this, it is much cleaner and more efficient to use the
				387	<tt>InstVisitor</tt> class to dispatch over the instruction type directly.</p>
				388
				389	</dd>
				390
				391	<dt><tt>cast_or_null<></tt>: </dt>
				392
				393	<dd><p>The <tt>cast_or_null<></tt> operator works just like the
				394	<tt>cast<></tt> operator, except that it allows for a null pointer as an
				395	argument (which it then propagates). This can sometimes be useful, allowing
				396	you to combine several null checks into one.</p></dd>
				397
				398	<dt><tt>dyn_cast_or_null<></tt>: </dt>
				399
				400	<dd><p>The <tt>dyn_cast_or_null<></tt> operator works just like the
				401	<tt>dyn_cast<></tt> operator, except that it allows for a null pointer
				402	as an argument (which it then propagates). This can sometimes be useful,
				403	allowing you to combine several null checks into one.</p></dd>
				404
				405	</dl>
				406
				407	<p>These five templates can be used with any classes, whether they have a
				408	v-table or not. To add support for these templates, you simply need to add
				409	<tt>classof</tt> static methods to the class you are interested casting
				410	to. Describing this is currently outside the scope of this document, but there
				411	are lots of examples in the LLVM source base.</p>
				412
				413	</div>
				414
				415	<!-- ======================================================================= -->
				416	<div class="doc_subsection">
				417	<a name="DEBUG">The <tt>DEBUG()</tt> macro and <tt>-debug</tt> option</a>
				418	</div>
				419
				420	<div class="doc_text">
				421
				422	<p>Often when working on your pass you will put a bunch of debugging printouts
				423	and other code into your pass. After you get it working, you want to remove
				424	it, but you may need it again in the future (to work out new bugs that you run
				425	across).</p>
				426
				427	<p> Naturally, because of this, you don't want to delete the debug printouts,
				428	but you don't want them to always be noisy. A standard compromise is to comment
				429	them out, allowing you to enable them if you need them in the future.</p>
				430
				431	<p>The "<tt><a href="/doxygen/Debug_8h-source.html">llvm/Support/Debug.h</a></tt>"
				432	file provides a macro named <tt>DEBUG()</tt> that is a much nicer solution to
				433	this problem. Basically, you can put arbitrary code into the argument of the
				434	<tt>DEBUG</tt> macro, and it is only executed if '<tt>opt</tt>' (or any other
				435	tool) is run with the '<tt>-debug</tt>' command line argument:</p>
				436
				437	<div class="doc_code">
				438	<pre>
				439	DOUT << "I am here!\n";
				440	</pre>
				441	</div>
				442
				443	<p>Then you can run your pass like this:</p>
				444
				445	<div class="doc_code">
				446	<pre>
				447	$ opt < a.bc > /dev/null -mypass
				448	<i><no output></i>
				449	$ opt < a.bc > /dev/null -mypass -debug
				450	I am here!
				451	</pre>
				452	</div>
				453
				454	<p>Using the <tt>DEBUG()</tt> macro instead of a home-brewed solution allows you
				455	to not have to create "yet another" command line option for the debug output for
				456	your pass. Note that <tt>DEBUG()</tt> macros are disabled for optimized builds,
				457	so they do not cause a performance impact at all (for the same reason, they
				458	should also not contain side-effects!).</p>
				459
				460	<p>One additional nice thing about the <tt>DEBUG()</tt> macro is that you can
				461	enable or disable it directly in gdb. Just use "<tt>set DebugFlag=0</tt>" or
				462	"<tt>set DebugFlag=1</tt>" from the gdb if the program is running. If the
				463	program hasn't been started yet, you can always just run it with
				464	<tt>-debug</tt>.</p>
				465
				466	</div>
				467
				468	<!-- _______________________________________________________________________ -->
				469	<div class="doc_subsubsection">
				470	<a name="DEBUG_TYPE">Fine grained debug info with <tt>DEBUG_TYPE</tt> and
				471	the <tt>-debug-only</tt> option</a>
				472	</div>
				473
				474	<div class="doc_text">
				475
				476	<p>Sometimes you may find yourself in a situation where enabling <tt>-debug</tt>
				477	just turns on <b>too much</b> information (such as when working on the code
				478	generator). If you want to enable debug information with more fine-grained
				479	control, you define the <tt>DEBUG_TYPE</tt> macro and the <tt>-debug</tt> only
				480	option as follows:</p>
				481
				482	<div class="doc_code">
				483	<pre>
				484	DOUT << "No debug type\n";
				485	#undef DEBUG_TYPE
				486	#define DEBUG_TYPE "foo"
				487	DOUT << "'foo' debug type\n";
				488	#undef DEBUG_TYPE
				489	#define DEBUG_TYPE "bar"
				490	DOUT << "'bar' debug type\n";
				491	#undef DEBUG_TYPE
				492	#define DEBUG_TYPE ""
				493	DOUT << "No debug type (2)\n";
				494	</pre>
				495	</div>
				496
				497	<p>Then you can run your pass like this:</p>
				498
				499	<div class="doc_code">
				500	<pre>
				501	$ opt < a.bc > /dev/null -mypass
				502	<i><no output></i>
				503	$ opt < a.bc > /dev/null -mypass -debug
				504	No debug type
				505	'foo' debug type
				506	'bar' debug type
				507	No debug type (2)
				508	$ opt < a.bc > /dev/null -mypass -debug-only=foo
				509	'foo' debug type
				510	$ opt < a.bc > /dev/null -mypass -debug-only=bar
				511	'bar' debug type
				512	</pre>
				513	</div>
				514
				515	<p>Of course, in practice, you should only set <tt>DEBUG_TYPE</tt> at the top of
				516	a file, to specify the debug type for the entire module (if you do this before
				517	you <tt>#include "llvm/Support/Debug.h"</tt>, you don't have to insert the ugly
				518	<tt>#undef</tt>'s). Also, you should use names more meaningful than "foo" and
				519	"bar", because there is no system in place to ensure that names do not
				520	conflict. If two different modules use the same string, they will all be turned
				521	on when the name is specified. This allows, for example, all debug information
				522	for instruction scheduling to be enabled with <tt>-debug-type=InstrSched</tt>,
				523	even if the source lives in multiple files.</p>
				524
				525	</div>
				526
				527	<!-- ======================================================================= -->
				528	<div class="doc_subsection">
				529	<a name="Statistic">The <tt>Statistic</tt> class & <tt>-stats</tt>
				530	option</a>
				531	</div>
				532
				533	<div class="doc_text">
				534
				535	<p>The "<tt><a
				536	href="/doxygen/Statistic_8h-source.html">llvm/ADT/Statistic.h</a></tt>" file
				537	provides a class named <tt>Statistic</tt> that is used as a unified way to
				538	keep track of what the LLVM compiler is doing and how effective various
				539	optimizations are. It is useful to see what optimizations are contributing to
				540	making a particular program run faster.</p>
				541
				542	<p>Often you may run your pass on some big program, and you're interested to see
				543	how many times it makes a certain transformation. Although you can do this with
				544	hand inspection, or some ad-hoc method, this is a real pain and not very useful
				545	for big programs. Using the <tt>Statistic</tt> class makes it very easy to
				546	keep track of this information, and the calculated information is presented in a
				547	uniform manner with the rest of the passes being executed.</p>
				548
				549	<p>There are many examples of <tt>Statistic</tt> uses, but the basics of using
				550	it are as follows:</p>
				551
				552	<ol>
				553	<li><p>Define your statistic like this:</p>
				554
				555	<div class="doc_code">
				556	<pre>
				557	#define <a href="#DEBUG_TYPE">DEBUG_TYPE</a> "mypassname" <i>// This goes before any #includes.</i>
				558	STATISTIC(NumXForms, "The # of times I did stuff");
				559	</pre>
				560	</div>
				561
				562	<p>The <tt>STATISTIC</tt> macro defines a static variable, whose name is
				563	specified by the first argument. The pass name is taken from the DEBUG_TYPE
				564	macro, and the description is taken from the second argument. The variable
				565	defined ("NumXForms" in this case) acts like an unsigned integer.</p></li>
				566
				567	<li><p>Whenever you make a transformation, bump the counter:</p>
				568
				569	<div class="doc_code">
				570	<pre>
				571	++NumXForms; // <i>I did stuff!</i>
				572	</pre>
				573	</div>
				574
				575	</li>
				576	</ol>
				577
				578	<p>That's all you have to do. To get '<tt>opt</tt>' to print out the
				579	statistics gathered, use the '<tt>-stats</tt>' option:</p>
				580
				581	<div class="doc_code">
				582	<pre>
				583	$ opt -stats -mypassname < program.bc > /dev/null
				584	<i>... statistics output ...</i>
				585	</pre>
				586	</div>
				587
				588	<p> When running <tt>opt</tt> on a C file from the SPEC benchmark
				589	suite, it gives a report that looks like this:</p>
				590
				591	<div class="doc_code">
				592	<pre>
				593	7646 bitcodewriter - Number of normal instructions
				594	725 bitcodewriter - Number of oversized instructions
				595	129996 bitcodewriter - Number of bitcode bytes written
				596	2817 raise - Number of insts DCEd or constprop'd
				597	3213 raise - Number of cast-of-self removed
				598	5046 raise - Number of expression trees converted
				599	75 raise - Number of other getelementptr's formed
				600	138 raise - Number of load/store peepholes
				601	42 deadtypeelim - Number of unused typenames removed from symtab
				602	392 funcresolve - Number of varargs functions resolved
				603	27 globaldce - Number of global variables removed
				604	2 adce - Number of basic blocks removed
				605	134 cee - Number of branches revectored
				606	49 cee - Number of setcc instruction eliminated
				607	532 gcse - Number of loads removed
				608	2919 gcse - Number of instructions removed
				609	86 indvars - Number of canonical indvars added
				610	87 indvars - Number of aux indvars removed
				611	25 instcombine - Number of dead inst eliminate
				612	434 instcombine - Number of insts combined
				613	248 licm - Number of load insts hoisted
				614	1298 licm - Number of insts hoisted to a loop pre-header
				615	3 licm - Number of insts hoisted to multiple loop preds (bad, no loop pre-header)
				616	75 mem2reg - Number of alloca's promoted
				617	1444 cfgsimplify - Number of blocks simplified
				618	</pre>
				619	</div>
				620
				621	<p>Obviously, with so many optimizations, having a unified framework for this
				622	stuff is very nice. Making your pass fit well into the framework makes it more
				623	maintainable and useful.</p>
				624
				625	</div>
				626
				627	<!-- ======================================================================= -->
				628	<div class="doc_subsection">
				629	<a name="ViewGraph">Viewing graphs while debugging code</a>
				630	</div>
				631
				632	<div class="doc_text">
				633
				634	<p>Several of the important data structures in LLVM are graphs: for example
				635	CFGs made out of LLVM <a href="#BasicBlock">BasicBlock</a>s, CFGs made out of
				636	LLVM <a href="CodeGenerator.html#machinebasicblock">MachineBasicBlock</a>s, and
				637	<a href="CodeGenerator.html#selectiondag_intro">Instruction Selection
				638	DAGs</a>. In many cases, while debugging various parts of the compiler, it is
				639	nice to instantly visualize these graphs.</p>
				640
				641	<p>LLVM provides several callbacks that are available in a debug build to do
				642	exactly that. If you call the <tt>Function::viewCFG()</tt> method, for example,
				643	the current LLVM tool will pop up a window containing the CFG for the function
				644	where each basic block is a node in the graph, and each node contains the
				645	instructions in the block. Similarly, there also exists
				646	<tt>Function::viewCFGOnly()</tt> (does not include the instructions), the
				647	<tt>MachineFunction::viewCFG()</tt> and <tt>MachineFunction::viewCFGOnly()</tt>,
				648	and the <tt>SelectionDAG::viewGraph()</tt> methods. Within GDB, for example,
				649	you can usually use something like <tt>call DAG.viewGraph()</tt> to pop
				650	up a window. Alternatively, you can sprinkle calls to these functions in your
				651	code in places you want to debug.</p>
				652
				653	<p>Getting this to work requires a small amount of configuration. On Unix
				654	systems with X11, install the <a href="http://www.graphviz.org">graphviz</a>
				655	toolkit, and make sure 'dot' and 'gv' are in your path. If you are running on
				656	Mac OS/X, download and install the Mac OS/X <a
				657	href="http://www.pixelglow.com/graphviz/">Graphviz program</a>, and add
				658	<tt>/Applications/Graphviz.app/Contents/MacOS/</tt> (or wherever you install
				659	it) to your path. Once in your system and path are set up, rerun the LLVM
				660	configure script and rebuild LLVM to enable this functionality.</p>
				661
				662	<p><tt>SelectionDAG</tt> has been extended to make it easier to locate
				663	<i>interesting</i> nodes in large complex graphs. From gdb, if you
				664	<tt>call DAG.setGraphColor(<i>node</i>, "<i>color</i>")</tt>, then the
				665	next <tt>call DAG.viewGraph()</tt> would highlight the node in the
				666	specified color (choices of colors can be found at <a
				667	href="http://www.graphviz.org/doc/info/colors.html">colors</a>.) More
				668	complex node attributes can be provided with <tt>call
				669	DAG.setGraphAttrs(<i>node</i>, "<i>attributes</i>")</tt> (choices can be
				670	found at <a href="http://www.graphviz.org/doc/info/attrs.html">Graph
				671	Attributes</a>.) If you want to restart and clear all the current graph
				672	attributes, then you can <tt>call DAG.clearGraphAttrs()</tt>. </p>
				673
				674	</div>
				675
				676	<!-- *********************************************************************** -->
				677	<div class="doc_section">
				678	<a name="datastructure">Picking the Right Data Structure for a Task</a>
				679	</div>
				680	<!-- *********************************************************************** -->
				681
				682	<div class="doc_text">
				683
				684	<p>LLVM has a plethora of data structures in the <tt>llvm/ADT/</tt> directory,
				685	and we commonly use STL data structures. This section describes the trade-offs
				686	you should consider when you pick one.</p>
				687
				688	<p>
				689	The first step is a choose your own adventure: do you want a sequential
				690	container, a set-like container, or a map-like container? The most important
				691	thing when choosing a container is the algorithmic properties of how you plan to
				692	access the container. Based on that, you should use:</p>
				693
				694	<ul>
				695	<li>a <a href="#ds_map">map-like</a> container if you need efficient look-up
				696	of an value based on another value. Map-like containers also support
				697	efficient queries for containment (whether a key is in the map). Map-like
				698	containers generally do not support efficient reverse mapping (values to
				699	keys). If you need that, use two maps. Some map-like containers also
				700	support efficient iteration through the keys in sorted order. Map-like
				701	containers are the most expensive sort, only use them if you need one of
				702	these capabilities.</li>
				703
				704	<li>a <a href="#ds_set">set-like</a> container if you need to put a bunch of
				705	stuff into a container that automatically eliminates duplicates. Some
				706	set-like containers support efficient iteration through the elements in
				707	sorted order. Set-like containers are more expensive than sequential
				708	containers.
				709	</li>
				710
				711	<li>a <a href="#ds_sequential">sequential</a> container provides
				712	the most efficient way to add elements and keeps track of the order they are
				713	added to the collection. They permit duplicates and support efficient
				714	iteration, but do not support efficient look-up based on a key.
				715	</li>
				716
Daniel Berlin	7ea44dc	2007-09-24 17:52:25 +0000	[diff] [blame]	717	<li>a <a href="#ds_bit">bit</a> container provides an efficient way to store and
				718	perform set operations on sets of numeric id's, while automatically
				719	eliminating duplicates. Bit containers require a maximum of 1 bit for each
				720	identifier you want to store.
				721	</li>
Dan Gohman	f17a25c	2007-07-18 16:29:46 +0000	[diff] [blame]	722	</ul>
				723
				724	<p>
				725	Once the proper category of container is determined, you can fine tune the
				726	memory use, constant factors, and cache behaviors of access by intelligently
				727	picking a member of the category. Note that constant factors and cache behavior
				728	can be a big deal. If you have a vector that usually only contains a few
				729	elements (but could contain many), for example, it's much better to use
				730	<a href="#dss_smallvector">SmallVector</a> than <a href="#dss_vector">vector</a>
				731	. Doing so avoids (relatively) expensive malloc/free calls, which dwarf the
				732	cost of adding the elements to the container. </p>
				733
				734	</div>
				735
				736	<!-- ======================================================================= -->
				737	<div class="doc_subsection">
				738	<a name="ds_sequential">Sequential Containers (std::vector, std::list, etc)</a>
				739	</div>
				740
				741	<div class="doc_text">
				742	There are a variety of sequential containers available for you, based on your
				743	needs. Pick the first in this section that will do what you want.
				744	</div>
				745
				746	<!-- _______________________________________________________________________ -->
				747	<div class="doc_subsubsection">
				748	<a name="dss_fixedarrays">Fixed Size Arrays</a>
				749	</div>
				750
				751	<div class="doc_text">
				752	<p>Fixed size arrays are very simple and very fast. They are good if you know
				753	exactly how many elements you have, or you have a (low) upper bound on how many
				754	you have.</p>
				755	</div>
				756
				757	<!-- _______________________________________________________________________ -->
				758	<div class="doc_subsubsection">
				759	<a name="dss_heaparrays">Heap Allocated Arrays</a>
				760	</div>
				761
				762	<div class="doc_text">
				763	<p>Heap allocated arrays (new[] + delete[]) are also simple. They are good if
				764	the number of elements is variable, if you know how many elements you will need
				765	before the array is allocated, and if the array is usually large (if not,
				766	consider a <a href="#dss_smallvector">SmallVector</a>). The cost of a heap
				767	allocated array is the cost of the new/delete (aka malloc/free). Also note that
				768	if you are allocating an array of a type with a constructor, the constructor and
				769	destructors will be run for every element in the array (re-sizable vectors only
				770	construct those elements actually used).</p>
				771	</div>
				772
				773	<!-- _______________________________________________________________________ -->
				774	<div class="doc_subsubsection">
				775	<a name="dss_smallvector">"llvm/ADT/SmallVector.h"</a>
				776	</div>
				777
				778	<div class="doc_text">
				779	<p><tt>SmallVector<Type, N></tt> is a simple class that looks and smells
				780	just like <tt>vector<Type></tt>:
				781	it supports efficient iteration, lays out elements in memory order (so you can
				782	do pointer arithmetic between elements), supports efficient push_back/pop_back
				783	operations, supports efficient random access to its elements, etc.</p>
				784
				785	<p>The advantage of SmallVector is that it allocates space for
				786	some number of elements (N) <b>in the object itself</b>. Because of this, if
				787	the SmallVector is dynamically smaller than N, no malloc is performed. This can
				788	be a big win in cases where the malloc/free call is far more expensive than the
				789	code that fiddles around with the elements.</p>
				790
				791	<p>This is good for vectors that are "usually small" (e.g. the number of
				792	predecessors/successors of a block is usually less than 8). On the other hand,
				793	this makes the size of the SmallVector itself large, so you don't want to
				794	allocate lots of them (doing so will waste a lot of space). As such,
				795	SmallVectors are most useful when on the stack.</p>
				796
				797	<p>SmallVector also provides a nice portable and efficient replacement for
				798	<tt>alloca</tt>.</p>
				799
				800	</div>
				801
				802	<!-- _______________________________________________________________________ -->
				803	<div class="doc_subsubsection">
				804	<a name="dss_vector"><vector></a>
				805	</div>
				806
				807	<div class="doc_text">
				808	<p>
				809	std::vector is well loved and respected. It is useful when SmallVector isn't:
				810	when the size of the vector is often large (thus the small optimization will
				811	rarely be a benefit) or if you will be allocating many instances of the vector
				812	itself (which would waste space for elements that aren't in the container).
				813	vector is also useful when interfacing with code that expects vectors :).
				814	</p>
				815
				816	<p>One worthwhile note about std::vector: avoid code like this:</p>
				817
				818	<div class="doc_code">
				819	<pre>
				820	for ( ... ) {
				821	std::vector<foo> V;
				822	use V;
				823	}
				824	</pre>
				825	</div>
				826
				827	<p>Instead, write this as:</p>
				828
				829	<div class="doc_code">
				830	<pre>
				831	std::vector<foo> V;
				832	for ( ... ) {
				833	use V;
				834	V.clear();
				835	}
				836	</pre>
				837	</div>
				838
				839	<p>Doing so will save (at least) one heap allocation and free per iteration of
				840	the loop.</p>
				841
				842	</div>
				843
				844	<!-- _______________________________________________________________________ -->
				845	<div class="doc_subsubsection">
				846	<a name="dss_deque"><deque></a>
				847	</div>
				848
				849	<div class="doc_text">
				850	<p>std::deque is, in some senses, a generalized version of std::vector. Like
				851	std::vector, it provides constant time random access and other similar
				852	properties, but it also provides efficient access to the front of the list. It
				853	does not guarantee continuity of elements within memory.</p>
				854
				855	<p>In exchange for this extra flexibility, std::deque has significantly higher
				856	constant factor costs than std::vector. If possible, use std::vector or
				857	something cheaper.</p>
				858	</div>
				859
				860	<!-- _______________________________________________________________________ -->
				861	<div class="doc_subsubsection">
				862	<a name="dss_list"><list></a>
				863	</div>
				864
				865	<div class="doc_text">
				866	<p>std::list is an extremely inefficient class that is rarely useful.
				867	It performs a heap allocation for every element inserted into it, thus having an
				868	extremely high constant factor, particularly for small data types. std::list
				869	also only supports bidirectional iteration, not random access iteration.</p>
				870
				871	<p>In exchange for this high cost, std::list supports efficient access to both
				872	ends of the list (like std::deque, but unlike std::vector or SmallVector). In
				873	addition, the iterator invalidation characteristics of std::list are stronger
				874	than that of a vector class: inserting or removing an element into the list does
				875	not invalidate iterator or pointers to other elements in the list.</p>
				876	</div>
				877
				878	<!-- _______________________________________________________________________ -->
				879	<div class="doc_subsubsection">
Gabor Greif	bb17f65	2009-02-27 11:37:41 +0000	[diff] [blame]	880	<a name="dss_ilist">llvm/ADT/ilist.h</a>
Dan Gohman	f17a25c	2007-07-18 16:29:46 +0000	[diff] [blame]	881	</div>
				882
				883	<div class="doc_text">
				884	<p><tt>ilist<T></tt> implements an 'intrusive' doubly-linked list. It is
				885	intrusive, because it requires the element to store and provide access to the
				886	prev/next pointers for the list.</p>
				887
Gabor Greif	b6b21ec	2009-02-27 12:02:19 +0000	[diff] [blame]	888	<p><tt>ilist</tt> has the same drawbacks as <tt>std::list</tt>, and additionally
				889	requires an <tt>ilist_traits</tt> implementation for the element type, but it
				890	provides some novel characteristics. In particular, it can efficiently store
				891	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]	892	removed from the list, and <tt>ilist</tt>s are guaranteed to support a
				893	constant-time splice operation.</p>
Dan Gohman	f17a25c	2007-07-18 16:29:46 +0000	[diff] [blame]	894
Gabor Greif	e39f0e7	2009-03-12 09:47:03 +0000	[diff] [blame]	895	<p>These properties are exactly what we want for things like
				896	<tt>Instruction</tt>s and basic blocks, which is why these are implemented with
				897	<tt>ilist</tt>s.</p>
Gabor Greif	bb17f65	2009-02-27 11:37:41 +0000	[diff] [blame]	898
				899	Related classes of interest are explained in the following subsections:
				900	<ul>
Gabor Greif	a17abe1	2009-02-27 13:28:07 +0000	[diff] [blame]	901	<li><a href="#dss_ilist_traits">ilist_traits</a></li>
Gabor Greif	b6b21ec	2009-02-27 12:02:19 +0000	[diff] [blame]	902	<li><a href="#dss_iplist">iplist</a></li>
Gabor Greif	bb17f65	2009-02-27 11:37:41 +0000	[diff] [blame]	903	<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^]	904	<li><a href="#dss_ilist_sentinel">Sentinels</a></li>
Gabor Greif	bb17f65	2009-02-27 11:37:41 +0000	[diff] [blame]	905	</ul>
				906	</div>
				907
				908	<!-- _______________________________________________________________________ -->
				909	<div class="doc_subsubsection">
Gabor Greif	a17abe1	2009-02-27 13:28:07 +0000	[diff] [blame]	910	<a name="dss_ilist_traits">ilist_traits</a>
				911	</div>
				912
				913	<div class="doc_text">
				914	<p><tt>ilist_traits<T></tt> is <tt>ilist<T></tt>'s customization
				915	mechanism. <tt>iplist<T></tt> (and consequently <tt>ilist<T></tt>)
				916	publicly derive from this traits class.</p>
				917	</div>
				918
				919	<!-- _______________________________________________________________________ -->
				920	<div class="doc_subsubsection">
Gabor Greif	b6b21ec	2009-02-27 12:02:19 +0000	[diff] [blame]	921	<a name="dss_iplist">iplist</a>
				922	</div>
				923
				924	<div class="doc_text">
				925	<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]	926	supports a slightly narrower interface. Notably, inserters from
				927	<tt>T&</tt> are absent.</p>
Gabor Greif	a17abe1	2009-02-27 13:28:07 +0000	[diff] [blame]	928
				929	<p><tt>ilist_traits<T></tt> is a public base of this class and can be
				930	used for a wide variety of customizations.</p>
Gabor Greif	b6b21ec	2009-02-27 12:02:19 +0000	[diff] [blame]	931	</div>
				932
				933	<!-- _______________________________________________________________________ -->
				934	<div class="doc_subsubsection">
Gabor Greif	bb17f65	2009-02-27 11:37:41 +0000	[diff] [blame]	935	<a name="dss_ilist_node">llvm/ADT/ilist_node.h</a>
				936	</div>
				937
				938	<div class="doc_text">
				939	<p><tt>ilist_node<T></tt> implements a the forward and backward links
				940	that are expected by the <tt>ilist<T></tt> (and analogous containers)
				941	in the default manner.</p>
				942
				943	<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]	944	<tt>T</tt>, usually <tt>T</tt> publicly derives from
				945	<tt>ilist_node<T></tt>.</p>
Dan Gohman	f17a25c	2007-07-18 16:29:46 +0000	[diff] [blame]	946	</div>
				947
				948	<!-- _______________________________________________________________________ -->
				949	<div class="doc_subsubsection">
Gabor Greif	d970d69	2009-03-12 10:30:31 +0000	[diff] [blame^]	950	<a name="dss_ilist_sentinel">Sentinels</a>
				951	</div>
				952
				953	<div class="doc_text">
				954	<p><tt>ilist</tt>s have another speciality that must be considered. To be a good
				955	citizen in the C++ ecosystem, it needs to support the standard container
				956	operations, such as <tt>begin</tt> and <tt>end</tt> iterators, etc. Also, the
				957	<tt>operator--</tt> must work correctly on the <tt>end</tt> iterator in the
				958	case of non-empty <tt>ilist</tt>s.</p>
				959
				960	<p>The only sensible solution to this problem is to allocate a so-called
				961	<i>sentinel</i> along with the intrusive list, which serves as the <tt>end</tt>
				962	iterator, providing the back-link to the last element. However conforming to the
				963	C++ convention it is illegal to <tt>operator++</tt> beyond the sentinel and it
				964	also must not be dereferenced.</p>
				965
				966	<p>These constraints allow for some implementation freedom to the <tt>ilist</tt>
				967	how to allocate and store the sentinel. The corresponding policy is dictated
				968	by <tt>ilist_traits<T></tt>. By default a <tt>T</tt> gets heap-allocated
				969	whenever the need for a sentinel arises.</p>
				970
				971	<p>While the default policy is sufficient in most cases, it may break down when
				972	<tt>T</tt> does not provide a default constructor. Also, in the case of many
				973	instances of <tt>ilist</tt>s, the memory overhead of the associated sentinels
				974	is wasted. To alleviate the situation with numerous and voluminous
				975	<tt>T</tt>-sentinels, sometimes a trick is employed, leading to <i>ghostly
				976	sentinels</i>.</p>
				977
				978	<p>Ghostly sentinels are obtained by specially-crafted <tt>ilist_traits<T></tt>
				979	which superpose the sentinel with the <tt>ilist</tt> instance in memory. Pointer
				980	arithmetic is used to obtain the sentinel, which is relative to the
				981	<tt>ilist</tt>'s <tt>this</tt> pointer. The <tt>ilist</tt> is augmented by an
				982	extra pointer, which serves as the back-link of the sentinel. This is the only
				983	field in the ghostly sentinel which can be legally accessed.</p>
				984	</div>
				985
				986	<!-- _______________________________________________________________________ -->
				987	<div class="doc_subsubsection">
Dan Gohman	f17a25c	2007-07-18 16:29:46 +0000	[diff] [blame]	988	<a name="dss_other">Other Sequential Container options</a>
				989	</div>
				990
				991	<div class="doc_text">
				992	<p>Other STL containers are available, such as std::string.</p>
				993
				994	<p>There are also various STL adapter classes such as std::queue,
				995	std::priority_queue, std::stack, etc. These provide simplified access to an
				996	underlying container but don't affect the cost of the container itself.</p>
				997
				998	</div>
				999
				1000
				1001	<!-- ======================================================================= -->
				1002	<div class="doc_subsection">
				1003	<a name="ds_set">Set-Like Containers (std::set, SmallSet, SetVector, etc)</a>
				1004	</div>
				1005
				1006	<div class="doc_text">
				1007
				1008	<p>Set-like containers are useful when you need to canonicalize multiple values
				1009	into a single representation. There are several different choices for how to do
				1010	this, providing various trade-offs.</p>
				1011
				1012	</div>
				1013
				1014
				1015	<!-- _______________________________________________________________________ -->
				1016	<div class="doc_subsubsection">
				1017	<a name="dss_sortedvectorset">A sorted 'vector'</a>
				1018	</div>
				1019
				1020	<div class="doc_text">
				1021
				1022	<p>If you intend to insert a lot of elements, then do a lot of queries, a
				1023	great approach is to use a vector (or other sequential container) with
				1024	std::sort+std::unique to remove duplicates. This approach works really well if
				1025	your usage pattern has these two distinct phases (insert then query), and can be
				1026	coupled with a good choice of <a href="#ds_sequential">sequential container</a>.
				1027	</p>
				1028
				1029	<p>
				1030	This combination provides the several nice properties: the result data is
				1031	contiguous in memory (good for cache locality), has few allocations, is easy to
				1032	address (iterators in the final vector are just indices or pointers), and can be
				1033	efficiently queried with a standard binary or radix search.</p>
				1034
				1035	</div>
				1036
				1037	<!-- _______________________________________________________________________ -->
				1038	<div class="doc_subsubsection">
				1039	<a name="dss_smallset">"llvm/ADT/SmallSet.h"</a>
				1040	</div>
				1041
				1042	<div class="doc_text">
				1043
				1044	<p>If you have a set-like data structure that is usually small and whose elements
				1045	are reasonably small, a <tt>SmallSet<Type, N></tt> is a good choice. This set
				1046	has space for N elements in place (thus, if the set is dynamically smaller than
				1047	N, no malloc traffic is required) and accesses them with a simple linear search.
				1048	When the set grows beyond 'N' elements, it allocates a more expensive representation that
				1049	guarantees efficient access (for most types, it falls back to std::set, but for
				1050	pointers it uses something far better, <a
				1051	href="#dss_smallptrset">SmallPtrSet</a>).</p>
				1052
				1053	<p>The magic of this class is that it handles small sets extremely efficiently,
				1054	but gracefully handles extremely large sets without loss of efficiency. The
				1055	drawback is that the interface is quite small: it supports insertion, queries
				1056	and erasing, but does not support iteration.</p>
				1057
				1058	</div>
				1059
				1060	<!-- _______________________________________________________________________ -->
				1061	<div class="doc_subsubsection">
				1062	<a name="dss_smallptrset">"llvm/ADT/SmallPtrSet.h"</a>
				1063	</div>
				1064
				1065	<div class="doc_text">
				1066
				1067	<p>SmallPtrSet has all the advantages of SmallSet (and a SmallSet of pointers is
				1068	transparently implemented with a SmallPtrSet), but also supports iterators. If
				1069	more than 'N' insertions are performed, a single quadratically
				1070	probed hash table is allocated and grows as needed, providing extremely
				1071	efficient access (constant time insertion/deleting/queries with low constant
				1072	factors) and is very stingy with malloc traffic.</p>
				1073
				1074	<p>Note that, unlike std::set, the iterators of SmallPtrSet are invalidated
				1075	whenever an insertion occurs. Also, the values visited by the iterators are not
				1076	visited in sorted order.</p>
				1077
				1078	</div>
				1079
				1080	<!-- _______________________________________________________________________ -->
				1081	<div class="doc_subsubsection">
Chris Lattner	77ab46d	2007-09-30 00:58:59 +0000	[diff] [blame]	1082	<a name="dss_denseset">"llvm/ADT/DenseSet.h"</a>
				1083	</div>
				1084
				1085	<div class="doc_text">
				1086
				1087	<p>
				1088	DenseSet is a simple quadratically probed hash table. It excels at supporting
				1089	small values: it uses a single allocation to hold all of the pairs that
				1090	are currently inserted in the set. DenseSet is a great way to unique small
				1091	values that are not simple pointers (use <a
				1092	href="#dss_smallptrset">SmallPtrSet</a> for pointers). Note that DenseSet has
				1093	the same requirements for the value type that <a
				1094	href="#dss_densemap">DenseMap</a> has.
				1095	</p>
				1096
				1097	</div>
				1098
				1099	<!-- _______________________________________________________________________ -->
				1100	<div class="doc_subsubsection">
Dan Gohman	f17a25c	2007-07-18 16:29:46 +0000	[diff] [blame]	1101	<a name="dss_FoldingSet">"llvm/ADT/FoldingSet.h"</a>
				1102	</div>
				1103
				1104	<div class="doc_text">
				1105
				1106	<p>
				1107	FoldingSet is an aggregate class that is really good at uniquing
				1108	expensive-to-create or polymorphic objects. It is a combination of a chained
				1109	hash table with intrusive links (uniqued objects are required to inherit from
				1110	FoldingSetNode) that uses <a href="#dss_smallvector">SmallVector</a> as part of
				1111	its ID process.</p>
				1112
				1113	<p>Consider a case where you want to implement a "getOrCreateFoo" method for
				1114	a complex object (for example, a node in the code generator). The client has a
				1115	description of what it wants to generate (it knows the opcode and all the
				1116	operands), but we don't want to 'new' a node, then try inserting it into a set
				1117	only to find out it already exists, at which point we would have to delete it
				1118	and return the node that already exists.
				1119	</p>
				1120
				1121	<p>To support this style of client, FoldingSet perform a query with a
				1122	FoldingSetNodeID (which wraps SmallVector) that can be used to describe the
				1123	element that we want to query for. The query either returns the element
				1124	matching the ID or it returns an opaque ID that indicates where insertion should
				1125	take place. Construction of the ID usually does not require heap traffic.</p>
				1126
				1127	<p>Because FoldingSet uses intrusive links, it can support polymorphic objects
				1128	in the set (for example, you can have SDNode instances mixed with LoadSDNodes).
				1129	Because the elements are individually allocated, pointers to the elements are
				1130	stable: inserting or removing elements does not invalidate any pointers to other
				1131	elements.
				1132	</p>
				1133
				1134	</div>
				1135
				1136	<!-- _______________________________________________________________________ -->
				1137	<div class="doc_subsubsection">
				1138	<a name="dss_set"><set></a>
				1139	</div>
				1140
				1141	<div class="doc_text">
				1142
				1143	<p><tt>std::set</tt> is a reasonable all-around set class, which is decent at
				1144	many things but great at nothing. std::set allocates memory for each element
				1145	inserted (thus it is very malloc intensive) and typically stores three pointers
				1146	per element in the set (thus adding a large amount of per-element space
				1147	overhead). It offers guaranteed log(n) performance, which is not particularly
				1148	fast from a complexity standpoint (particularly if the elements of the set are
				1149	expensive to compare, like strings), and has extremely high constant factors for
				1150	lookup, insertion and removal.</p>
				1151
				1152	<p>The advantages of std::set are that its iterators are stable (deleting or
				1153	inserting an element from the set does not affect iterators or pointers to other
				1154	elements) and that iteration over the set is guaranteed to be in sorted order.
				1155	If the elements in the set are large, then the relative overhead of the pointers
				1156	and malloc traffic is not a big deal, but if the elements of the set are small,
				1157	std::set is almost never a good choice.</p>
				1158
				1159	</div>
				1160
				1161	<!-- _______________________________________________________________________ -->
				1162	<div class="doc_subsubsection">
				1163	<a name="dss_setvector">"llvm/ADT/SetVector.h"</a>
				1164	</div>
				1165
				1166	<div class="doc_text">
				1167	<p>LLVM's SetVector<Type> is an adapter class that combines your choice of
				1168	a set-like container along with a <a href="#ds_sequential">Sequential
				1169	Container</a>. The important property
				1170	that this provides is efficient insertion with uniquing (duplicate elements are
				1171	ignored) with iteration support. It implements this by inserting elements into
				1172	both a set-like container and the sequential container, using the set-like
				1173	container for uniquing and the sequential container for iteration.
				1174	</p>
				1175
				1176	<p>The difference between SetVector and other sets is that the order of
				1177	iteration is guaranteed to match the order of insertion into the SetVector.
				1178	This property is really important for things like sets of pointers. Because
				1179	pointer values are non-deterministic (e.g. vary across runs of the program on
				1180	different machines), iterating over the pointers in the set will
				1181	not be in a well-defined order.</p>
				1182
				1183	<p>
				1184	The drawback of SetVector is that it requires twice as much space as a normal
				1185	set and has the sum of constant factors from the set-like container and the
				1186	sequential container that it uses. Use it only if you need to iterate over
				1187	the elements in a deterministic order. SetVector is also expensive to delete
				1188	elements out of (linear time), unless you use it's "pop_back" method, which is
				1189	faster.
				1190	</p>
				1191
				1192	<p>SetVector is an adapter class that defaults to using std::vector and std::set
				1193	for the underlying containers, so it is quite expensive. However,
				1194	<tt>"llvm/ADT/SetVector.h"</tt> also provides a SmallSetVector class, which
				1195	defaults to using a SmallVector and SmallSet of a specified size. If you use
				1196	this, and if your sets are dynamically smaller than N, you will save a lot of
				1197	heap traffic.</p>
				1198
				1199	</div>
				1200
				1201	<!-- _______________________________________________________________________ -->
				1202	<div class="doc_subsubsection">
				1203	<a name="dss_uniquevector">"llvm/ADT/UniqueVector.h"</a>
				1204	</div>
				1205
				1206	<div class="doc_text">
				1207
				1208	<p>
				1209	UniqueVector is similar to <a href="#dss_setvector">SetVector</a>, but it
				1210	retains a unique ID for each element inserted into the set. It internally
				1211	contains a map and a vector, and it assigns a unique ID for each value inserted
				1212	into the set.</p>
				1213
				1214	<p>UniqueVector is very expensive: its cost is the sum of the cost of
				1215	maintaining both the map and vector, it has high complexity, high constant
				1216	factors, and produces a lot of malloc traffic. It should be avoided.</p>
				1217
				1218	</div>
				1219
				1220
				1221	<!-- _______________________________________________________________________ -->
				1222	<div class="doc_subsubsection">
				1223	<a name="dss_otherset">Other Set-Like Container Options</a>
				1224	</div>
				1225
				1226	<div class="doc_text">
				1227
				1228	<p>
				1229	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]	1230	"hash_set" like containers (whether from C++ TR1 or from the SGI library). We
				1231	never use hash_set and unordered_set because they are generally very expensive
				1232	(each insertion requires a malloc) and very non-portable.
				1233	</p>
Dan Gohman	f17a25c	2007-07-18 16:29:46 +0000	[diff] [blame]	1234
				1235	<p>std::multiset is useful if you're not interested in elimination of
				1236	duplicates, but has all the drawbacks of std::set. A sorted vector (where you
				1237	don't delete duplicate entries) or some other approach is almost always
				1238	better.</p>
				1239
Dan Gohman	f17a25c	2007-07-18 16:29:46 +0000	[diff] [blame]	1240	</div>
				1241
				1242	<!-- ======================================================================= -->
				1243	<div class="doc_subsection">
				1244	<a name="ds_map">Map-Like Containers (std::map, DenseMap, etc)</a>
				1245	</div>
				1246
				1247	<div class="doc_text">
				1248	Map-like containers are useful when you want to associate data to a key. As
				1249	usual, there are a lot of different ways to do this. :)
				1250	</div>
				1251
				1252	<!-- _______________________________________________________________________ -->
				1253	<div class="doc_subsubsection">
				1254	<a name="dss_sortedvectormap">A sorted 'vector'</a>
				1255	</div>
				1256
				1257	<div class="doc_text">
				1258
				1259	<p>
				1260	If your usage pattern follows a strict insert-then-query approach, you can
				1261	trivially use the same approach as <a href="#dss_sortedvectorset">sorted vectors
				1262	for set-like containers</a>. The only difference is that your query function
				1263	(which uses std::lower_bound to get efficient log(n) lookup) should only compare
				1264	the key, not both the key and value. This yields the same advantages as sorted
				1265	vectors for sets.
				1266	</p>
				1267	</div>
				1268
				1269	<!-- _______________________________________________________________________ -->
				1270	<div class="doc_subsubsection">
				1271	<a name="dss_stringmap">"llvm/ADT/StringMap.h"</a>
				1272	</div>
				1273
				1274	<div class="doc_text">
				1275
				1276	<p>
				1277	Strings are commonly used as keys in maps, and they are difficult to support
				1278	efficiently: they are variable length, inefficient to hash and compare when
				1279	long, expensive to copy, etc. StringMap is a specialized container designed to
				1280	cope with these issues. It supports mapping an arbitrary range of bytes to an
				1281	arbitrary other object.</p>
				1282
				1283	<p>The StringMap implementation uses a quadratically-probed hash table, where
				1284	the buckets store a pointer to the heap allocated entries (and some other
				1285	stuff). The entries in the map must be heap allocated because the strings are
				1286	variable length. The string data (key) and the element object (value) are
				1287	stored in the same allocation with the string data immediately after the element
				1288	object. This container guarantees the "<tt>(char*)(&Value+1)</tt>" points
				1289	to the key string for a value.</p>
				1290
				1291	<p>The StringMap is very fast for several reasons: quadratic probing is very
				1292	cache efficient for lookups, the hash value of strings in buckets is not
				1293	recomputed when lookup up an element, StringMap rarely has to touch the
				1294	memory for unrelated objects when looking up a value (even when hash collisions
				1295	happen), hash table growth does not recompute the hash values for strings
				1296	already in the table, and each pair in the map is store in a single allocation
				1297	(the string data is stored in the same allocation as the Value of a pair).</p>
				1298
				1299	<p>StringMap also provides query methods that take byte ranges, so it only ever
				1300	copies a string if a value is inserted into the table.</p>
				1301	</div>
				1302
				1303	<!-- _______________________________________________________________________ -->
				1304	<div class="doc_subsubsection">
				1305	<a name="dss_indexedmap">"llvm/ADT/IndexedMap.h"</a>
				1306	</div>
				1307
				1308	<div class="doc_text">
				1309	<p>
				1310	IndexedMap is a specialized container for mapping small dense integers (or
				1311	values that can be mapped to small dense integers) to some other type. It is
				1312	internally implemented as a vector with a mapping function that maps the keys to
				1313	the dense integer range.
				1314	</p>
				1315
				1316	<p>
				1317	This is useful for cases like virtual registers in the LLVM code generator: they
				1318	have a dense mapping that is offset by a compile-time constant (the first
				1319	virtual register ID).</p>
				1320
				1321	</div>
				1322
				1323	<!-- _______________________________________________________________________ -->
				1324	<div class="doc_subsubsection">
				1325	<a name="dss_densemap">"llvm/ADT/DenseMap.h"</a>
				1326	</div>
				1327
				1328	<div class="doc_text">
				1329
				1330	<p>
				1331	DenseMap is a simple quadratically probed hash table. It excels at supporting
				1332	small keys and values: it uses a single allocation to hold all of the pairs that
				1333	are currently inserted in the map. DenseMap is a great way to map pointers to
				1334	pointers, or map other small types to each other.
				1335	</p>
				1336
				1337	<p>
				1338	There are several aspects of DenseMap that you should be aware of, however. The
				1339	iterators in a densemap are invalidated whenever an insertion occurs, unlike
				1340	map. Also, because DenseMap allocates space for a large number of key/value
				1341	pairs (it starts with 64 by default), it will waste a lot of space if your keys
				1342	or values are large. Finally, you must implement a partial specialization of
Chris Lattner	92eea07	2007-09-17 18:34:04 +0000	[diff] [blame]	1343	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]	1344	is required to tell DenseMap about two special marker values (which can never be
				1345	inserted into the map) that it needs internally.</p>
				1346
				1347	</div>
				1348
				1349	<!-- _______________________________________________________________________ -->
				1350	<div class="doc_subsubsection">
				1351	<a name="dss_map"><map></a>
				1352	</div>
				1353
				1354	<div class="doc_text">
				1355
				1356	<p>
				1357	std::map has similar characteristics to <a href="#dss_set">std::set</a>: it uses
				1358	a single allocation per pair inserted into the map, it offers log(n) lookup with
				1359	an extremely large constant factor, imposes a space penalty of 3 pointers per
				1360	pair in the map, etc.</p>
				1361
				1362	<p>std::map is most useful when your keys or values are very large, if you need
				1363	to iterate over the collection in sorted order, or if you need stable iterators
				1364	into the map (i.e. they don't get invalidated if an insertion or deletion of
				1365	another element takes place).</p>
				1366
				1367	</div>
				1368
				1369	<!-- _______________________________________________________________________ -->
				1370	<div class="doc_subsubsection">
				1371	<a name="dss_othermap">Other Map-Like Container Options</a>
				1372	</div>
				1373
				1374	<div class="doc_text">
				1375
				1376	<p>
				1377	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]	1378	"hash_map" like containers (whether from C++ TR1 or from the SGI library). We
				1379	never use hash_set and unordered_set because they are generally very expensive
				1380	(each insertion requires a malloc) and very non-portable.</p>
Dan Gohman	f17a25c	2007-07-18 16:29:46 +0000	[diff] [blame]	1381
				1382	<p>std::multimap is useful if you want to map a key to multiple values, but has
				1383	all the drawbacks of std::map. A sorted vector or some other approach is almost
				1384	always better.</p>
				1385
Dan Gohman	f17a25c	2007-07-18 16:29:46 +0000	[diff] [blame]	1386	</div>
				1387
Daniel Berlin	7ea44dc	2007-09-24 17:52:25 +0000	[diff] [blame]	1388	<!-- ======================================================================= -->
				1389	<div class="doc_subsection">
				1390	<a name="ds_bit">Bit storage containers (BitVector, SparseBitVector)</a>
				1391	</div>
				1392
				1393	<div class="doc_text">
Chris Lattner	62a4eae	2007-09-25 22:37:50 +0000	[diff] [blame]	1394	<p>Unlike the other containers, there are only two bit storage containers, and
				1395	choosing when to use each is relatively straightforward.</p>
				1396
				1397	<p>One additional option is
				1398	<tt>std::vector<bool></tt>: we discourage its use for two reasons 1) the
				1399	implementation in many common compilers (e.g. commonly available versions of
				1400	GCC) is extremely inefficient and 2) the C++ standards committee is likely to
				1401	deprecate this container and/or change it significantly somehow. In any case,
				1402	please don't use it.</p>
Daniel Berlin	7ea44dc	2007-09-24 17:52:25 +0000	[diff] [blame]	1403	</div>
				1404
				1405	<!-- _______________________________________________________________________ -->
				1406	<div class="doc_subsubsection">
				1407	<a name="dss_bitvector">BitVector</a>
				1408	</div>
				1409
				1410	<div class="doc_text">
				1411	<p> The BitVector container provides a fixed size set of bits for manipulation.
				1412	It supports individual bit setting/testing, as well as set operations. The set
				1413	operations take time O(size of bitvector), but operations are performed one word
				1414	at a time, instead of one bit at a time. This makes the BitVector very fast for
				1415	set operations compared to other containers. Use the BitVector when you expect
				1416	the number of set bits to be high (IE a dense set).
				1417	</p>
				1418	</div>
				1419
				1420	<!-- _______________________________________________________________________ -->
				1421	<div class="doc_subsubsection">
				1422	<a name="dss_sparsebitvector">SparseBitVector</a>
				1423	</div>
				1424
				1425	<div class="doc_text">
				1426	<p> The SparseBitVector container is much like BitVector, with one major
				1427	difference: Only the bits that are set, are stored. This makes the
				1428	SparseBitVector much more space efficient than BitVector when the set is sparse,
				1429	as well as making set operations O(number of set bits) instead of O(size of
				1430	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
				1431	(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).
				1432	</p>
				1433	</div>
Dan Gohman	f17a25c	2007-07-18 16:29:46 +0000	[diff] [blame]	1434
				1435	<!-- *********************************************************************** -->
				1436	<div class="doc_section">
				1437	<a name="common">Helpful Hints for Common Operations</a>
				1438	</div>
				1439	<!-- *********************************************************************** -->
				1440
				1441	<div class="doc_text">
				1442
				1443	<p>This section describes how to perform some very simple transformations of
				1444	LLVM code. This is meant to give examples of common idioms used, showing the
				1445	practical side of LLVM transformations. <p> Because this is a "how-to" section,
				1446	you should also read about the main classes that you will be working with. The
				1447	<a href="#coreclasses">Core LLVM Class Hierarchy Reference</a> contains details
				1448	and descriptions of the main classes that you should know about.</p>
				1449
				1450	</div>
				1451
				1452	<!-- NOTE: this section should be heavy on example code -->
				1453	<!-- ======================================================================= -->
				1454	<div class="doc_subsection">
				1455	<a name="inspection">Basic Inspection and Traversal Routines</a>
				1456	</div>
				1457
				1458	<div class="doc_text">
				1459
				1460	<p>The LLVM compiler infrastructure have many different data structures that may
				1461	be traversed. Following the example of the C++ standard template library, the
				1462	techniques used to traverse these various data structures are all basically the
				1463	same. For a enumerable sequence of values, the <tt>XXXbegin()</tt> function (or
				1464	method) returns an iterator to the start of the sequence, the <tt>XXXend()</tt>
				1465	function returns an iterator pointing to one past the last valid element of the
				1466	sequence, and there is some <tt>XXXiterator</tt> data type that is common
				1467	between the two operations.</p>
				1468
				1469	<p>Because the pattern for iteration is common across many different aspects of
				1470	the program representation, the standard template library algorithms may be used
				1471	on them, and it is easier to remember how to iterate. First we show a few common
				1472	examples of the data structures that need to be traversed. Other data
				1473	structures are traversed in very similar ways.</p>
				1474
				1475	</div>
				1476
				1477	<!-- _______________________________________________________________________ -->
				1478	<div class="doc_subsubsection">
				1479	<a name="iterate_function">Iterating over the </a><a
				1480	href="#BasicBlock"><tt>BasicBlock</tt></a>s in a <a
				1481	href="#Function"><tt>Function</tt></a>
				1482	</div>
				1483
				1484	<div class="doc_text">
				1485
				1486	<p>It's quite common to have a <tt>Function</tt> instance that you'd like to
				1487	transform in some way; in particular, you'd like to manipulate its
				1488	<tt>BasicBlock</tt>s. To facilitate this, you'll need to iterate over all of
				1489	the <tt>BasicBlock</tt>s that constitute the <tt>Function</tt>. The following is
				1490	an example that prints the name of a <tt>BasicBlock</tt> and the number of
				1491	<tt>Instruction</tt>s it contains:</p>
				1492
				1493	<div class="doc_code">
				1494	<pre>
				1495	// <i>func is a pointer to a Function instance</i>
				1496	for (Function::iterator i = func->begin(), e = func->end(); i != e; ++i)
				1497	// <i>Print out the name of the basic block if it has one, and then the</i>
				1498	// <i>number of instructions that it contains</i>
				1499	llvm::cerr << "Basic block (name=" << i->getName() << ") has "
				1500	<< i->size() << " instructions.\n";
				1501	</pre>
				1502	</div>
				1503
				1504	<p>Note that i can be used as if it were a pointer for the purposes of
				1505	invoking member functions of the <tt>Instruction</tt> class. This is
				1506	because the indirection operator is overloaded for the iterator
				1507	classes. In the above code, the expression <tt>i->size()</tt> is
				1508	exactly equivalent to <tt>(*i).size()</tt> just like you'd expect.</p>
				1509
				1510	</div>
				1511
				1512	<!-- _______________________________________________________________________ -->
				1513	<div class="doc_subsubsection">
				1514	<a name="iterate_basicblock">Iterating over the </a><a
				1515	href="#Instruction"><tt>Instruction</tt></a>s in a <a
				1516	href="#BasicBlock"><tt>BasicBlock</tt></a>
				1517	</div>
				1518
				1519	<div class="doc_text">
				1520
				1521	<p>Just like when dealing with <tt>BasicBlock</tt>s in <tt>Function</tt>s, it's
				1522	easy to iterate over the individual instructions that make up
				1523	<tt>BasicBlock</tt>s. Here's a code snippet that prints out each instruction in
				1524	a <tt>BasicBlock</tt>:</p>
				1525
				1526	<div class="doc_code">
				1527	<pre>
				1528	// <i>blk is a pointer to a BasicBlock instance</i>
				1529	for (BasicBlock::iterator i = blk->begin(), e = blk->end(); i != e; ++i)
				1530	// <i>The next statement works since operator<<(ostream&,...)</i>
				1531	// <i>is overloaded for Instruction&</i>
				1532	llvm::cerr << *i << "\n";
				1533	</pre>
				1534	</div>
				1535
				1536	<p>However, this isn't really the best way to print out the contents of a
				1537	<tt>BasicBlock</tt>! Since the ostream operators are overloaded for virtually
				1538	anything you'll care about, you could have just invoked the print routine on the
				1539	basic block itself: <tt>llvm::cerr << *blk << "\n";</tt>.</p>
				1540
				1541	</div>
				1542
				1543	<!-- _______________________________________________________________________ -->
				1544	<div class="doc_subsubsection">
				1545	<a name="iterate_institer">Iterating over the </a><a
				1546	href="#Instruction"><tt>Instruction</tt></a>s in a <a
				1547	href="#Function"><tt>Function</tt></a>
				1548	</div>
				1549
				1550	<div class="doc_text">
				1551
				1552	<p>If you're finding that you commonly iterate over a <tt>Function</tt>'s
				1553	<tt>BasicBlock</tt>s and then that <tt>BasicBlock</tt>'s <tt>Instruction</tt>s,
				1554	<tt>InstIterator</tt> should be used instead. You'll need to include <a
				1555	href="/doxygen/InstIterator_8h-source.html"><tt>llvm/Support/InstIterator.h</tt></a>,
				1556	and then instantiate <tt>InstIterator</tt>s explicitly in your code. Here's a
				1557	small example that shows how to dump all instructions in a function to the standard error stream:<p>
				1558
				1559	<div class="doc_code">
				1560	<pre>
				1561	#include "<a href="/doxygen/InstIterator_8h-source.html">llvm/Support/InstIterator.h</a>"
				1562
				1563	// <i>F is a pointer to a Function instance</i>
Chris Lattner	fd62ee7	2008-06-04 18:20:42 +0000	[diff] [blame]	1564	for (inst_iterator I = inst_begin(F), E = inst_end(F); I != E; ++I)
				1565	llvm::cerr << *I << "\n";
Dan Gohman	f17a25c	2007-07-18 16:29:46 +0000	[diff] [blame]	1566	</pre>
				1567	</div>
				1568
				1569	<p>Easy, isn't it? You can also use <tt>InstIterator</tt>s to fill a
				1570	work list with its initial contents. For example, if you wanted to
				1571	initialize a work list to contain all instructions in a <tt>Function</tt>
				1572	F, all you would need to do is something like:</p>
				1573
				1574	<div class="doc_code">
				1575	<pre>
				1576	std::set<Instruction*> worklist;
Chris Lattner	fd62ee7	2008-06-04 18:20:42 +0000	[diff] [blame]	1577	// or better yet, SmallPtrSet<Instruction*, 64> worklist;
				1578
				1579	for (inst_iterator I = inst_begin(F), E = inst_end(F); I != E; ++I)
				1580	worklist.insert(&*I);
Dan Gohman	f17a25c	2007-07-18 16:29:46 +0000	[diff] [blame]	1581	</pre>
				1582	</div>
				1583
				1584	<p>The STL set <tt>worklist</tt> would now contain all instructions in the
				1585	<tt>Function</tt> pointed to by F.</p>
				1586
				1587	</div>
				1588
				1589	<!-- _______________________________________________________________________ -->
				1590	<div class="doc_subsubsection">
				1591	<a name="iterate_convert">Turning an iterator into a class pointer (and
				1592	vice-versa)</a>
				1593	</div>
				1594
				1595	<div class="doc_text">
				1596
				1597	<p>Sometimes, it'll be useful to grab a reference (or pointer) to a class
				1598	instance when all you've got at hand is an iterator. Well, extracting
				1599	a reference or a pointer from an iterator is very straight-forward.
				1600	Assuming that <tt>i</tt> is a <tt>BasicBlock::iterator</tt> and <tt>j</tt>
				1601	is a <tt>BasicBlock::const_iterator</tt>:</p>
				1602
				1603	<div class="doc_code">
				1604	<pre>
				1605	Instruction& inst = *i; // <i>Grab reference to instruction reference</i>
				1606	Instruction* pinst = &*i; // <i>Grab pointer to instruction reference</i>
				1607	const Instruction& inst = *j;
				1608	</pre>
				1609	</div>
				1610
				1611	<p>However, the iterators you'll be working with in the LLVM framework are
				1612	special: they will automatically convert to a ptr-to-instance type whenever they
				1613	need to. Instead of dereferencing the iterator and then taking the address of
				1614	the result, you can simply assign the iterator to the proper pointer type and
				1615	you get the dereference and address-of operation as a result of the assignment
				1616	(behind the scenes, this is a result of overloading casting mechanisms). Thus
				1617	the last line of the last example,</p>
				1618
				1619	<div class="doc_code">
				1620	<pre>
Chris Lattner	0665e1f	2008-01-03 16:56:04 +0000	[diff] [blame]	1621	Instruction pinst = &i;
Dan Gohman	f17a25c	2007-07-18 16:29:46 +0000	[diff] [blame]	1622	</pre>
				1623	</div>
				1624
				1625	<p>is semantically equivalent to</p>
				1626
				1627	<div class="doc_code">
				1628	<pre>
Chris Lattner	0665e1f	2008-01-03 16:56:04 +0000	[diff] [blame]	1629	Instruction *pinst = i;
Dan Gohman	f17a25c	2007-07-18 16:29:46 +0000	[diff] [blame]	1630	</pre>
				1631	</div>
				1632
				1633	<p>It's also possible to turn a class pointer into the corresponding iterator,
				1634	and this is a constant time operation (very efficient). The following code
				1635	snippet illustrates use of the conversion constructors provided by LLVM
				1636	iterators. By using these, you can explicitly grab the iterator of something
				1637	without actually obtaining it via iteration over some structure:</p>
				1638
				1639	<div class="doc_code">
				1640	<pre>
				1641	void printNextInstruction(Instruction* inst) {
				1642	BasicBlock::iterator it(inst);
				1643	++it; // <i>After this line, it refers to the instruction after *inst</i>
				1644	if (it != inst->getParent()->end()) llvm::cerr << *it << "\n";
				1645	}
				1646	</pre>
				1647	</div>
				1648
				1649	</div>
				1650
				1651	<!--_______________________________________________________________________-->
				1652	<div class="doc_subsubsection">
				1653	<a name="iterate_complex">Finding call sites: a slightly more complex
				1654	example</a>
				1655	</div>
				1656
				1657	<div class="doc_text">
				1658
				1659	<p>Say that you're writing a FunctionPass and would like to count all the
				1660	locations in the entire module (that is, across every <tt>Function</tt>) where a
				1661	certain function (i.e., some <tt>Function</tt>*) is already in scope. As you'll
				1662	learn later, you may want to use an <tt>InstVisitor</tt> to accomplish this in a
				1663	much more straight-forward manner, but this example will allow us to explore how
				1664	you'd do it if you didn't have <tt>InstVisitor</tt> around. In pseudo-code, this
				1665	is what we want to do:</p>
				1666
				1667	<div class="doc_code">
				1668	<pre>
				1669	initialize callCounter to zero
				1670	for each Function f in the Module
				1671	for each BasicBlock b in f
				1672	for each Instruction i in b
				1673	if (i is a CallInst and calls the given function)
				1674	increment callCounter
				1675	</pre>
				1676	</div>
				1677
				1678	<p>And the actual code is (remember, because we're writing a
				1679	<tt>FunctionPass</tt>, our <tt>FunctionPass</tt>-derived class simply has to
				1680	override the <tt>runOnFunction</tt> method):</p>
				1681
				1682	<div class="doc_code">
				1683	<pre>
				1684	Function* targetFunc = ...;
				1685
				1686	class OurFunctionPass : public FunctionPass {
				1687	public:
				1688	OurFunctionPass(): callCounter(0) { }
				1689
				1690	virtual runOnFunction(Function& F) {
				1691	for (Function::iterator b = F.begin(), be = F.end(); b != be; ++b) {
Eric Christopher	5fbecf7	2008-11-08 08:20:49 +0000	[diff] [blame]	1692	for (BasicBlock::iterator i = b->begin(), ie = b->end(); i != ie; ++i) {
Dan Gohman	f17a25c	2007-07-18 16:29:46 +0000	[diff] [blame]	1693	if (<a href="#CallInst">CallInst</a>* callInst = <a href="#isa">dyn_cast</a><<a
				1694	href="#CallInst">CallInst</a>>(&*i)) {
				1695	// <i>We know we've encountered a call instruction, so we</i>
				1696	// <i>need to determine if it's a call to the</i>
Chris Lattner	0665e1f	2008-01-03 16:56:04 +0000	[diff] [blame]	1697	// <i>function pointed to by m_func or not.</i>
Dan Gohman	f17a25c	2007-07-18 16:29:46 +0000	[diff] [blame]	1698	if (callInst->getCalledFunction() == targetFunc)
				1699	++callCounter;
				1700	}
				1701	}
				1702	}
				1703	}
				1704
				1705	private:
Chris Lattner	0665e1f	2008-01-03 16:56:04 +0000	[diff] [blame]	1706	unsigned callCounter;
Dan Gohman	f17a25c	2007-07-18 16:29:46 +0000	[diff] [blame]	1707	};
				1708	</pre>
				1709	</div>
				1710
				1711	</div>
				1712
				1713	<!--_______________________________________________________________________-->
				1714	<div class="doc_subsubsection">
				1715	<a name="calls_and_invokes">Treating calls and invokes the same way</a>
				1716	</div>
				1717
				1718	<div class="doc_text">
				1719
				1720	<p>You may have noticed that the previous example was a bit oversimplified in
				1721	that it did not deal with call sites generated by 'invoke' instructions. In
				1722	this, and in other situations, you may find that you want to treat
				1723	<tt>CallInst</tt>s and <tt>InvokeInst</tt>s the same way, even though their
				1724	most-specific common base class is <tt>Instruction</tt>, which includes lots of
				1725	less closely-related things. For these cases, LLVM provides a handy wrapper
				1726	class called <a
				1727	href="http://llvm.org/doxygen/classllvm_1_1CallSite.html"><tt>CallSite</tt></a>.
				1728	It is essentially a wrapper around an <tt>Instruction</tt> pointer, with some
				1729	methods that provide functionality common to <tt>CallInst</tt>s and
				1730	<tt>InvokeInst</tt>s.</p>
				1731
				1732	<p>This class has "value semantics": it should be passed by value, not by
				1733	reference and it should not be dynamically allocated or deallocated using
				1734	<tt>operator new</tt> or <tt>operator delete</tt>. It is efficiently copyable,
				1735	assignable and constructable, with costs equivalents to that of a bare pointer.
				1736	If you look at its definition, it has only a single pointer member.</p>
				1737
				1738	</div>
				1739
				1740	<!--_______________________________________________________________________-->
				1741	<div class="doc_subsubsection">
				1742	<a name="iterate_chains">Iterating over def-use & use-def chains</a>
				1743	</div>
				1744
				1745	<div class="doc_text">
				1746
				1747	<p>Frequently, we might have an instance of the <a
				1748	href="/doxygen/classllvm_1_1Value.html">Value Class</a> and we want to
				1749	determine which <tt>User</tt>s use the <tt>Value</tt>. The list of all
				1750	<tt>User</tt>s of a particular <tt>Value</tt> is called a <i>def-use</i> chain.
				1751	For example, let's say we have a <tt>Function*</tt> named <tt>F</tt> to a
				1752	particular function <tt>foo</tt>. Finding all of the instructions that
				1753	<i>use</i> <tt>foo</tt> is as simple as iterating over the <i>def-use</i> chain
				1754	of <tt>F</tt>:</p>
				1755
				1756	<div class="doc_code">
				1757	<pre>
Chris Lattner	0665e1f	2008-01-03 16:56:04 +0000	[diff] [blame]	1758	Function *F = ...;
Dan Gohman	f17a25c	2007-07-18 16:29:46 +0000	[diff] [blame]	1759
				1760	for (Value::use_iterator i = F->use_begin(), e = F->use_end(); i != e; ++i)
				1761	if (Instruction Inst = dyn_cast<Instruction>(i)) {
				1762	llvm::cerr << "F is used in instruction:\n";
				1763	llvm::cerr << *Inst << "\n";
				1764	}
				1765	</pre>
				1766	</div>
				1767
				1768	<p>Alternately, it's common to have an instance of the <a
				1769	href="/doxygen/classllvm_1_1User.html">User Class</a> and need to know what
				1770	<tt>Value</tt>s are used by it. The list of all <tt>Value</tt>s used by a
				1771	<tt>User</tt> is known as a <i>use-def</i> chain. Instances of class
				1772	<tt>Instruction</tt> are common <tt>User</tt>s, so we might want to iterate over
				1773	all of the values that a particular instruction uses (that is, the operands of
				1774	the particular <tt>Instruction</tt>):</p>
				1775
				1776	<div class="doc_code">
				1777	<pre>
Chris Lattner	0665e1f	2008-01-03 16:56:04 +0000	[diff] [blame]	1778	Instruction *pi = ...;
Dan Gohman	f17a25c	2007-07-18 16:29:46 +0000	[diff] [blame]	1779
				1780	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]	1781	Value v = i;
Dan Gohman	f17a25c	2007-07-18 16:29:46 +0000	[diff] [blame]	1782	// <i>...</i>
				1783	}
				1784	</pre>
				1785	</div>
				1786
				1787	<!--
				1788	def-use chains ("finding all users of"): Value::use_begin/use_end
				1789	use-def chains ("finding all values used"): User::op_begin/op_end [op=operand]
				1790	-->
				1791
				1792	</div>
				1793
Chris Lattner	0665e1f	2008-01-03 16:56:04 +0000	[diff] [blame]	1794	<!--_______________________________________________________________________-->
				1795	<div class="doc_subsubsection">
				1796	<a name="iterate_preds">Iterating over predecessors &
				1797	successors of blocks</a>
				1798	</div>
				1799
				1800	<div class="doc_text">
				1801
				1802	<p>Iterating over the predecessors and successors of a block is quite easy
				1803	with the routines defined in <tt>"llvm/Support/CFG.h"</tt>. Just use code like
				1804	this to iterate over all predecessors of BB:</p>
				1805
				1806	<div class="doc_code">
				1807	<pre>
				1808	#include "llvm/Support/CFG.h"
				1809	BasicBlock *BB = ...;
				1810
				1811	for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI) {
				1812	BasicBlock Pred = PI;
				1813	// <i>...</i>
				1814	}
				1815	</pre>
				1816	</div>
				1817
				1818	<p>Similarly, to iterate over successors use
				1819	succ_iterator/succ_begin/succ_end.</p>
				1820
				1821	</div>
				1822
				1823
Dan Gohman	f17a25c	2007-07-18 16:29:46 +0000	[diff] [blame]	1824	<!-- ======================================================================= -->
				1825	<div class="doc_subsection">
				1826	<a name="simplechanges">Making simple changes</a>
				1827	</div>
				1828
				1829	<div class="doc_text">
				1830
				1831	<p>There are some primitive transformation operations present in the LLVM
				1832	infrastructure that are worth knowing about. When performing
				1833	transformations, it's fairly common to manipulate the contents of basic
				1834	blocks. This section describes some of the common methods for doing so
				1835	and gives example code.</p>
				1836
				1837	</div>
				1838
				1839	<!--_______________________________________________________________________-->
				1840	<div class="doc_subsubsection">
				1841	<a name="schanges_creating">Creating and inserting new
				1842	<tt>Instruction</tt>s</a>
				1843	</div>
				1844
				1845	<div class="doc_text">
				1846
				1847	<p><i>Instantiating Instructions</i></p>
				1848
				1849	<p>Creation of <tt>Instruction</tt>s is straight-forward: simply call the
				1850	constructor for the kind of instruction to instantiate and provide the necessary
				1851	parameters. For example, an <tt>AllocaInst</tt> only <i>requires</i> a
				1852	(const-ptr-to) <tt>Type</tt>. Thus:</p>
				1853
				1854	<div class="doc_code">
				1855	<pre>
Nick Lewycky	c004e5b	2007-12-03 01:52:52 +0000	[diff] [blame]	1856	AllocaInst* ai = new AllocaInst(Type::Int32Ty);
Dan Gohman	f17a25c	2007-07-18 16:29:46 +0000	[diff] [blame]	1857	</pre>
				1858	</div>
				1859
				1860	<p>will create an <tt>AllocaInst</tt> instance that represents the allocation of
				1861	one integer in the current stack frame, at run time. Each <tt>Instruction</tt>
				1862	subclass is likely to have varying default parameters which change the semantics
				1863	of the instruction, so refer to the <a
				1864	href="/doxygen/classllvm_1_1Instruction.html">doxygen documentation for the subclass of
				1865	Instruction</a> that you're interested in instantiating.</p>
				1866
				1867	<p><i>Naming values</i></p>
				1868
				1869	<p>It is very useful to name the values of instructions when you're able to, as
				1870	this facilitates the debugging of your transformations. If you end up looking
				1871	at generated LLVM machine code, you definitely want to have logical names
				1872	associated with the results of instructions! By supplying a value for the
				1873	<tt>Name</tt> (default) parameter of the <tt>Instruction</tt> constructor, you
				1874	associate a logical name with the result of the instruction's execution at
				1875	run time. For example, say that I'm writing a transformation that dynamically
				1876	allocates space for an integer on the stack, and that integer is going to be
				1877	used as some kind of index by some other code. To accomplish this, I place an
				1878	<tt>AllocaInst</tt> at the first point in the first <tt>BasicBlock</tt> of some
				1879	<tt>Function</tt>, and I'm intending to use it within the same
				1880	<tt>Function</tt>. I might do:</p>
				1881
				1882	<div class="doc_code">
				1883	<pre>
Nick Lewycky	c004e5b	2007-12-03 01:52:52 +0000	[diff] [blame]	1884	AllocaInst* pa = new AllocaInst(Type::Int32Ty, 0, "indexLoc");
Dan Gohman	f17a25c	2007-07-18 16:29:46 +0000	[diff] [blame]	1885	</pre>
				1886	</div>
				1887
				1888	<p>where <tt>indexLoc</tt> is now the logical name of the instruction's
				1889	execution value, which is a pointer to an integer on the run time stack.</p>
				1890
				1891	<p><i>Inserting instructions</i></p>
				1892
				1893	<p>There are essentially two ways to insert an <tt>Instruction</tt>
				1894	into an existing sequence of instructions that form a <tt>BasicBlock</tt>:</p>
				1895
				1896	<ul>
				1897	<li>Insertion into an explicit instruction list
				1898
				1899	<p>Given a <tt>BasicBlock* pb</tt>, an <tt>Instruction* pi</tt> within that
				1900	<tt>BasicBlock</tt>, and a newly-created instruction we wish to insert
				1901	before <tt>*pi</tt>, we do the following: </p>
				1902
				1903	<div class="doc_code">
				1904	<pre>
				1905	BasicBlock *pb = ...;
				1906	Instruction *pi = ...;
				1907	Instruction *newInst = new Instruction(...);
				1908
				1909	pb->getInstList().insert(pi, newInst); // <i>Inserts newInst before pi in pb</i>
				1910	</pre>
				1911	</div>
				1912
				1913	<p>Appending to the end of a <tt>BasicBlock</tt> is so common that
				1914	the <tt>Instruction</tt> class and <tt>Instruction</tt>-derived
				1915	classes provide constructors which take a pointer to a
				1916	<tt>BasicBlock</tt> to be appended to. For example code that
				1917	looked like: </p>
				1918
				1919	<div class="doc_code">
				1920	<pre>
				1921	BasicBlock *pb = ...;
				1922	Instruction *newInst = new Instruction(...);
				1923
				1924	pb->getInstList().push_back(newInst); // <i>Appends newInst to pb</i>
				1925	</pre>
				1926	</div>
				1927
				1928	<p>becomes: </p>
				1929
				1930	<div class="doc_code">
				1931	<pre>
				1932	BasicBlock *pb = ...;
				1933	Instruction *newInst = new Instruction(..., pb);
				1934	</pre>
				1935	</div>
				1936
				1937	<p>which is much cleaner, especially if you are creating
				1938	long instruction streams.</p></li>
				1939
				1940	<li>Insertion into an implicit instruction list
				1941
				1942	<p><tt>Instruction</tt> instances that are already in <tt>BasicBlock</tt>s
				1943	are implicitly associated with an existing instruction list: the instruction
				1944	list of the enclosing basic block. Thus, we could have accomplished the same
				1945	thing as the above code without being given a <tt>BasicBlock</tt> by doing:
				1946	</p>
				1947
				1948	<div class="doc_code">
				1949	<pre>
				1950	Instruction *pi = ...;
				1951	Instruction *newInst = new Instruction(...);
				1952
				1953	pi->getParent()->getInstList().insert(pi, newInst);
				1954	</pre>
				1955	</div>
				1956
				1957	<p>In fact, this sequence of steps occurs so frequently that the
				1958	<tt>Instruction</tt> class and <tt>Instruction</tt>-derived classes provide
				1959	constructors which take (as a default parameter) a pointer to an
				1960	<tt>Instruction</tt> which the newly-created <tt>Instruction</tt> should
				1961	precede. That is, <tt>Instruction</tt> constructors are capable of
				1962	inserting the newly-created instance into the <tt>BasicBlock</tt> of a
				1963	provided instruction, immediately before that instruction. Using an
				1964	<tt>Instruction</tt> constructor with a <tt>insertBefore</tt> (default)
				1965	parameter, the above code becomes:</p>
				1966
				1967	<div class="doc_code">
				1968	<pre>
				1969	Instruction* pi = ...;
				1970	Instruction* newInst = new Instruction(..., pi);
				1971	</pre>
				1972	</div>
				1973
				1974	<p>which is much cleaner, especially if you're creating a lot of
				1975	instructions and adding them to <tt>BasicBlock</tt>s.</p></li>
				1976	</ul>
				1977
				1978	</div>
				1979
				1980	<!--_______________________________________________________________________-->
				1981	<div class="doc_subsubsection">
				1982	<a name="schanges_deleting">Deleting <tt>Instruction</tt>s</a>
				1983	</div>
				1984
				1985	<div class="doc_text">
				1986
				1987	<p>Deleting an instruction from an existing sequence of instructions that form a
				1988	<a href="#BasicBlock"><tt>BasicBlock</tt></a> is very straight-forward. First,
				1989	you must have a pointer to the instruction that you wish to delete. Second, you
				1990	need to obtain the pointer to that instruction's basic block. You use the
				1991	pointer to the basic block to get its list of instructions and then use the
				1992	erase function to remove your instruction. For example:</p>
				1993
				1994	<div class="doc_code">
				1995	<pre>
				1996	<a href="#Instruction">Instruction</a> *I = .. ;
Chris Lattner	3db8f77	2008-02-15 22:57:17 +0000	[diff] [blame]	1997	I->eraseFromParent();
Dan Gohman	f17a25c	2007-07-18 16:29:46 +0000	[diff] [blame]	1998	</pre>
				1999	</div>
				2000
				2001	</div>
				2002
				2003	<!--_______________________________________________________________________-->
				2004	<div class="doc_subsubsection">
				2005	<a name="schanges_replacing">Replacing an <tt>Instruction</tt> with another
				2006	<tt>Value</tt></a>
				2007	</div>
				2008
				2009	<div class="doc_text">
				2010
				2011	<p><i>Replacing individual instructions</i></p>
				2012
				2013	<p>Including "<a href="/doxygen/BasicBlockUtils_8h-source.html">llvm/Transforms/Utils/BasicBlockUtils.h</a>"
				2014	permits use of two very useful replace functions: <tt>ReplaceInstWithValue</tt>
				2015	and <tt>ReplaceInstWithInst</tt>.</p>
				2016
				2017	<h4><a name="schanges_deleting">Deleting <tt>Instruction</tt>s</a></h4>
				2018
				2019	<ul>
				2020	<li><tt>ReplaceInstWithValue</tt>
				2021
Nick Lewycky	48d4b03	2008-09-15 06:31:52 +0000	[diff] [blame]	2022	<p>This function replaces all uses of a given instruction with a value,
				2023	and then removes the original instruction. The following example
				2024	illustrates the replacement of the result of a particular
Dan Gohman	f17a25c	2007-07-18 16:29:46 +0000	[diff] [blame]	2025	<tt>AllocaInst</tt> that allocates memory for a single integer with a null
				2026	pointer to an integer.</p>
				2027
				2028	<div class="doc_code">
				2029	<pre>
				2030	AllocaInst* instToReplace = ...;
				2031	BasicBlock::iterator ii(instToReplace);
				2032
				2033	ReplaceInstWithValue(instToReplace->getParent()->getInstList(), ii,
Daniel Dunbar	8ce7962	2008-10-03 22:17:25 +0000	[diff] [blame]	2034	Constant::getNullValue(PointerType::getUnqual(Type::Int32Ty)));
Dan Gohman	f17a25c	2007-07-18 16:29:46 +0000	[diff] [blame]	2035	</pre></div></li>
				2036
				2037	<li><tt>ReplaceInstWithInst</tt>
				2038
				2039	<p>This function replaces a particular instruction with another
Nick Lewycky	48d4b03	2008-09-15 06:31:52 +0000	[diff] [blame]	2040	instruction, inserting the new instruction into the basic block at the
				2041	location where the old instruction was, and replacing any uses of the old
				2042	instruction with the new instruction. The following example illustrates
				2043	the replacement of one <tt>AllocaInst</tt> with another.</p>
Dan Gohman	f17a25c	2007-07-18 16:29:46 +0000	[diff] [blame]	2044
				2045	<div class="doc_code">
				2046	<pre>
				2047	AllocaInst* instToReplace = ...;
				2048	BasicBlock::iterator ii(instToReplace);
				2049
				2050	ReplaceInstWithInst(instToReplace->getParent()->getInstList(), ii,
Nick Lewycky	c004e5b	2007-12-03 01:52:52 +0000	[diff] [blame]	2051	new AllocaInst(Type::Int32Ty, 0, "ptrToReplacedInt"));
Dan Gohman	f17a25c	2007-07-18 16:29:46 +0000	[diff] [blame]	2052	</pre></div></li>
				2053	</ul>
				2054
				2055	<p><i>Replacing multiple uses of <tt>User</tt>s and <tt>Value</tt>s</i></p>
				2056
				2057	<p>You can use <tt>Value::replaceAllUsesWith</tt> and
				2058	<tt>User::replaceUsesOfWith</tt> to change more than one use at a time. See the
				2059	doxygen documentation for the <a href="/doxygen/classllvm_1_1Value.html">Value Class</a>
				2060	and <a href="/doxygen/classllvm_1_1User.html">User Class</a>, respectively, for more
				2061	information.</p>
				2062
				2063	<!-- Value::replaceAllUsesWith User::replaceUsesOfWith Point out:
				2064	include/llvm/Transforms/Utils/ especially BasicBlockUtils.h with:
				2065	ReplaceInstWithValue, ReplaceInstWithInst -->
				2066
				2067	</div>
				2068
				2069	<!--_______________________________________________________________________-->
				2070	<div class="doc_subsubsection">
				2071	<a name="schanges_deletingGV">Deleting <tt>GlobalVariable</tt>s</a>
				2072	</div>
				2073
				2074	<div class="doc_text">
				2075
				2076	<p>Deleting a global variable from a module is just as easy as deleting an
				2077	Instruction. First, you must have a pointer to the global variable that you wish
				2078	to delete. You use this pointer to erase it from its parent, the module.
				2079	For example:</p>
				2080
				2081	<div class="doc_code">
				2082	<pre>
				2083	<a href="#GlobalVariable">GlobalVariable</a> *GV = .. ;
				2084
				2085	GV->eraseFromParent();
				2086	</pre>
				2087	</div>
				2088
				2089	</div>
				2090
				2091	<!-- *********************************************************************** -->
				2092	<div class="doc_section">
				2093	<a name="advanced">Advanced Topics</a>
				2094	</div>
				2095	<!-- *********************************************************************** -->
				2096
				2097	<div class="doc_text">
				2098	<p>
				2099	This section describes some of the advanced or obscure API's that most clients
				2100	do not need to be aware of. These API's tend manage the inner workings of the
				2101	LLVM system, and only need to be accessed in unusual circumstances.
				2102	</p>
				2103	</div>
				2104
				2105	<!-- ======================================================================= -->
				2106	<div class="doc_subsection">
				2107	<a name="TypeResolve">LLVM Type Resolution</a>
				2108	</div>
				2109
				2110	<div class="doc_text">
				2111
				2112	<p>
				2113	The LLVM type system has a very simple goal: allow clients to compare types for
				2114	structural equality with a simple pointer comparison (aka a shallow compare).
				2115	This goal makes clients much simpler and faster, and is used throughout the LLVM
				2116	system.
				2117	</p>
				2118
				2119	<p>
				2120	Unfortunately achieving this goal is not a simple matter. In particular,
				2121	recursive types and late resolution of opaque types makes the situation very
				2122	difficult to handle. Fortunately, for the most part, our implementation makes
				2123	most clients able to be completely unaware of the nasty internal details. The
				2124	primary case where clients are exposed to the inner workings of it are when
				2125	building a recursive type. In addition to this case, the LLVM bitcode reader,
				2126	assembly parser, and linker also have to be aware of the inner workings of this
				2127	system.
				2128	</p>
				2129
				2130	<p>
				2131	For our purposes below, we need three concepts. First, an "Opaque Type" is
				2132	exactly as defined in the <a href="LangRef.html#t_opaque">language
				2133	reference</a>. Second an "Abstract Type" is any type which includes an
				2134	opaque type as part of its type graph (for example "<tt>{ opaque, i32 }</tt>").
				2135	Third, a concrete type is a type that is not an abstract type (e.g. "<tt>{ i32,
				2136	float }</tt>").
				2137	</p>
				2138
				2139	</div>
				2140
				2141	<!-- ______________________________________________________________________ -->
				2142	<div class="doc_subsubsection">
				2143	<a name="BuildRecType">Basic Recursive Type Construction</a>
				2144	</div>
				2145
				2146	<div class="doc_text">
				2147
				2148	<p>
				2149	Because the most common question is "how do I build a recursive type with LLVM",
				2150	we answer it now and explain it as we go. Here we include enough to cause this
				2151	to be emitted to an output .ll file:
				2152	</p>
				2153
				2154	<div class="doc_code">
				2155	<pre>
				2156	%mylist = type { %mylist*, i32 }
				2157	</pre>
				2158	</div>
				2159
				2160	<p>
				2161	To build this, use the following LLVM APIs:
				2162	</p>
				2163
				2164	<div class="doc_code">
				2165	<pre>
				2166	// <i>Create the initial outer struct</i>
				2167	<a href="#PATypeHolder">PATypeHolder</a> StructTy = OpaqueType::get();
				2168	std::vector<const Type*> Elts;
Daniel Dunbar	8ce7962	2008-10-03 22:17:25 +0000	[diff] [blame]	2169	Elts.push_back(PointerType::getUnqual(StructTy));
Nick Lewycky	c004e5b	2007-12-03 01:52:52 +0000	[diff] [blame]	2170	Elts.push_back(Type::Int32Ty);
Dan Gohman	f17a25c	2007-07-18 16:29:46 +0000	[diff] [blame]	2171	StructType *NewSTy = StructType::get(Elts);
				2172
				2173	// <i>At this point, NewSTy = "{ opaque*, i32 }". Tell VMCore that</i>
				2174	// <i>the struct and the opaque type are actually the same.</i>
				2175	cast<OpaqueType>(StructTy.get())-><a href="#refineAbstractTypeTo">refineAbstractTypeTo</a>(NewSTy);
				2176
				2177	// <i>NewSTy is potentially invalidated, but StructTy (a <a href="#PATypeHolder">PATypeHolder</a>) is</i>
				2178	// <i>kept up-to-date</i>
				2179	NewSTy = cast<StructType>(StructTy.get());
				2180
				2181	// <i>Add a name for the type to the module symbol table (optional)</i>
				2182	MyModule->addTypeName("mylist", NewSTy);
				2183	</pre>
				2184	</div>
				2185
				2186	<p>
				2187	This code shows the basic approach used to build recursive types: build a
				2188	non-recursive type using 'opaque', then use type unification to close the cycle.
				2189	The type unification step is performed by the <tt><a
				2190	href="#refineAbstractTypeTo">refineAbstractTypeTo</a></tt> method, which is
				2191	described next. After that, we describe the <a
				2192	href="#PATypeHolder">PATypeHolder class</a>.
				2193	</p>
				2194
				2195	</div>
				2196
				2197	<!-- ______________________________________________________________________ -->
				2198	<div class="doc_subsubsection">
				2199	<a name="refineAbstractTypeTo">The <tt>refineAbstractTypeTo</tt> method</a>
				2200	</div>
				2201
				2202	<div class="doc_text">
				2203	<p>
				2204	The <tt>refineAbstractTypeTo</tt> method starts the type unification process.
				2205	While this method is actually a member of the DerivedType class, it is most
				2206	often used on OpaqueType instances. Type unification is actually a recursive
				2207	process. After unification, types can become structurally isomorphic to
				2208	existing types, and all duplicates are deleted (to preserve pointer equality).
				2209	</p>
				2210
				2211	<p>
				2212	In the example above, the OpaqueType object is definitely deleted.
				2213	Additionally, if there is an "{ \2*, i32}" type already created in the system,
				2214	the pointer and struct type created are <b>also</b> deleted. Obviously whenever
				2215	a type is deleted, any "Type*" pointers in the program are invalidated. As
				2216	such, it is safest to avoid having <i>any</i> "Type*" pointers to abstract types
				2217	live across a call to <tt>refineAbstractTypeTo</tt> (note that non-abstract
				2218	types can never move or be deleted). To deal with this, the <a
				2219	href="#PATypeHolder">PATypeHolder</a> class is used to maintain a stable
				2220	reference to a possibly refined type, and the <a
				2221	href="#AbstractTypeUser">AbstractTypeUser</a> class is used to update more
				2222	complex datastructures.
				2223	</p>
				2224
				2225	</div>
				2226
				2227	<!-- ______________________________________________________________________ -->
				2228	<div class="doc_subsubsection">
				2229	<a name="PATypeHolder">The PATypeHolder Class</a>
				2230	</div>
				2231
				2232	<div class="doc_text">
				2233	<p>
				2234	PATypeHolder is a form of a "smart pointer" for Type objects. When VMCore
				2235	happily goes about nuking types that become isomorphic to existing types, it
				2236	automatically updates all PATypeHolder objects to point to the new type. In the
				2237	example above, this allows the code to maintain a pointer to the resultant
				2238	resolved recursive type, even though the Type*'s are potentially invalidated.
				2239	</p>
				2240
				2241	<p>
				2242	PATypeHolder is an extremely light-weight object that uses a lazy union-find
				2243	implementation to update pointers. For example the pointer from a Value to its
				2244	Type is maintained by PATypeHolder objects.
				2245	</p>
				2246
				2247	</div>
				2248
				2249	<!-- ______________________________________________________________________ -->
				2250	<div class="doc_subsubsection">
				2251	<a name="AbstractTypeUser">The AbstractTypeUser Class</a>
				2252	</div>
				2253
				2254	<div class="doc_text">
				2255
				2256	<p>
				2257	Some data structures need more to perform more complex updates when types get
				2258	resolved. To support this, a class can derive from the AbstractTypeUser class.
				2259	This class
				2260	allows it to get callbacks when certain types are resolved. To register to get
				2261	callbacks for a particular type, the DerivedType::{add/remove}AbstractTypeUser
				2262	methods can be called on a type. Note that these methods only work for <i>
				2263	abstract</i> types. Concrete types (those that do not include any opaque
				2264	objects) can never be refined.
				2265	</p>
				2266	</div>
				2267
				2268
				2269	<!-- ======================================================================= -->
				2270	<div class="doc_subsection">
				2271	<a name="SymbolTable">The <tt>ValueSymbolTable</tt> and
				2272	<tt>TypeSymbolTable</tt> classes</a>
				2273	</div>
				2274
				2275	<div class="doc_text">
				2276	<p>The <tt><a href="http://llvm.org/doxygen/classllvm_1_1ValueSymbolTable.html">
				2277	ValueSymbolTable</a></tt> class provides a symbol table that the <a
				2278	href="#Function"><tt>Function</tt></a> and <a href="#Module">
				2279	<tt>Module</tt></a> classes use for naming value definitions. The symbol table
				2280	can provide a name for any <a href="#Value"><tt>Value</tt></a>.
				2281	The <tt><a href="http://llvm.org/doxygen/classllvm_1_1TypeSymbolTable.html">
				2282	TypeSymbolTable</a></tt> class is used by the <tt>Module</tt> class to store
				2283	names for types.</p>
				2284
				2285	<p>Note that the <tt>SymbolTable</tt> class should not be directly accessed
				2286	by most clients. It should only be used when iteration over the symbol table
				2287	names themselves are required, which is very special purpose. Note that not
				2288	all LLVM
Gabor Greif	92e8776	2008-06-16 21:06:12 +0000	[diff] [blame]	2289	<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]	2290	an empty name) do not exist in the symbol table.
				2291	</p>
				2292
				2293	<p>These symbol tables support iteration over the values/types in the symbol
				2294	table with <tt>begin/end/iterator</tt> and supports querying to see if a
				2295	specific name is in the symbol table (with <tt>lookup</tt>). The
				2296	<tt>ValueSymbolTable</tt> class exposes no public mutator methods, instead,
				2297	simply call <tt>setName</tt> on a value, which will autoinsert it into the
				2298	appropriate symbol table. For types, use the Module::addTypeName method to
				2299	insert entries into the symbol table.</p>
				2300
				2301	</div>
				2302
				2303
				2304
Gabor Greif	92e8776	2008-06-16 21:06:12 +0000	[diff] [blame]	2305	<!-- ======================================================================= -->
				2306	<div class="doc_subsection">
				2307	<a name="UserLayout">The <tt>User</tt> and owned <tt>Use</tt> classes' memory layout</a>
				2308	</div>
				2309
				2310	<div class="doc_text">
				2311	<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]	2312	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]	2313	towards other <tt><a href="http://llvm.org/doxygen/classllvm_1_1Value.html">
				2314	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]	2315	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]	2316	addition and removal.</p>
				2317
Gabor Greif	93b462b	2008-06-18 13:44:57 +0000	[diff] [blame]	2318	<!-- ______________________________________________________________________ -->
				2319	<div class="doc_subsubsection">
Gabor Greif	50626fc	2009-01-05 16:05:32 +0000	[diff] [blame]	2320	<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]	2321	</div>
Gabor Greif	92e8776	2008-06-16 21:06:12 +0000	[diff] [blame]	2322
Gabor Greif	93b462b	2008-06-18 13:44:57 +0000	[diff] [blame]	2323	<div class="doc_text">
				2324	<p>
				2325	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]	2326	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]	2327	(some <tt>Use</tt>s inline others hung off) is impractical and breaks the invariant
				2328	that the <tt>Use</tt> objects belonging to the same <tt>User</tt> form a contiguous array.
				2329	</p>
				2330	</div>
Gabor Greif	92e8776	2008-06-16 21:06:12 +0000	[diff] [blame]	2331
Gabor Greif	93b462b	2008-06-18 13:44:57 +0000	[diff] [blame]	2332	<p>
				2333	We have 2 different layouts in the <tt>User</tt> (sub)classes:
				2334	<ul>
				2335	<li><p>Layout a)
				2336	The <tt>Use</tt> object(s) are inside (resp. at fixed offset) of the <tt>User</tt>
				2337	object and there are a fixed number of them.</p>
Gabor Greif	92e8776	2008-06-16 21:06:12 +0000	[diff] [blame]	2338
Gabor Greif	93b462b	2008-06-18 13:44:57 +0000	[diff] [blame]	2339	<li><p>Layout b)
				2340	The <tt>Use</tt> object(s) are referenced by a pointer to an
				2341	array from the <tt>User</tt> object and there may be a variable
				2342	number of them.</p>
				2343	</ul>
				2344	<p>
Gabor Greif	e247e36	2008-06-25 00:10:22 +0000	[diff] [blame]	2345	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]	2346	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]	2347	we stick to this redundancy for the sake of simplicity.
Gabor Greif	e247e36	2008-06-25 00:10:22 +0000	[diff] [blame]	2348	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]	2349	has. (Theoretically this information can also be calculated
Gabor Greif	93b462b	2008-06-18 13:44:57 +0000	[diff] [blame]	2350	given the scheme presented below.)</p>
				2351	<p>
				2352	Special forms of allocation operators (<tt>operator new</tt>)
Gabor Greif	e247e36	2008-06-25 00:10:22 +0000	[diff] [blame]	2353	enforce the following memory layouts:</p>
Gabor Greif	92e8776	2008-06-16 21:06:12 +0000	[diff] [blame]	2354
Gabor Greif	93b462b	2008-06-18 13:44:57 +0000	[diff] [blame]	2355	<ul>
Gabor Greif	e247e36	2008-06-25 00:10:22 +0000	[diff] [blame]	2356	<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]	2357
Gabor Greif	93b462b	2008-06-18 13:44:57 +0000	[diff] [blame]	2358	<pre>
				2359	...---.---.---.---.-------...
				2360	\| P \| P \| P \| P \| User
				2361	'''---'---'---'---'-------'''
				2362	</pre>
Gabor Greif	92e8776	2008-06-16 21:06:12 +0000	[diff] [blame]	2363
Gabor Greif	e247e36	2008-06-25 00:10:22 +0000	[diff] [blame]	2364	<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]	2365	<pre>
				2366	.-------...
				2367	\| User
				2368	'-------'''
				2369	\|
				2370	v
				2371	.---.---.---.---...
				2372	\| P \| P \| P \| P \|
				2373	'---'---'---'---'''
				2374	</pre>
				2375	</ul>
				2376	<i>(In the above figures '<tt>P</tt>' stands for the <tt>Use**</tt> that
				2377	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]	2378
Gabor Greif	93b462b	2008-06-18 13:44:57 +0000	[diff] [blame]	2379	<!-- ______________________________________________________________________ -->
				2380	<div class="doc_subsubsection">
Gabor Greif	50626fc	2009-01-05 16:05:32 +0000	[diff] [blame]	2381	<a name="Waymarking">The waymarking algorithm</a>
Gabor Greif	93b462b	2008-06-18 13:44:57 +0000	[diff] [blame]	2382	</div>
Gabor Greif	92e8776	2008-06-16 21:06:12 +0000	[diff] [blame]	2383
Gabor Greif	93b462b	2008-06-18 13:44:57 +0000	[diff] [blame]	2384	<div class="doc_text">
				2385	<p>
Gabor Greif	e247e36	2008-06-25 00:10:22 +0000	[diff] [blame]	2386	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]	2387	their <tt>User</tt> objects, there must be a fast and exact method to
				2388	recover it. This is accomplished by the following scheme:</p>
				2389	</div>
Gabor Greif	92e8776	2008-06-16 21:06:12 +0000	[diff] [blame]	2390
Gabor Greif	e247e36	2008-06-25 00:10:22 +0000	[diff] [blame]	2391	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]	2392	start of the <tt>User</tt> object:
				2393	<ul>
				2394	<li><tt>00</tt> —> binary digit 0</li>
				2395	<li><tt>01</tt> —> binary digit 1</li>
				2396	<li><tt>10</tt> —> stop and calculate (<tt>s</tt>)</li>
				2397	<li><tt>11</tt> —> full stop (<tt>S</tt>)</li>
				2398	</ul>
				2399	<p>
				2400	Given a <tt>Use*</tt>, all we have to do is to walk till we get
				2401	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]	2402	we have to walk to the next stop picking up digits
Gabor Greif	93b462b	2008-06-18 13:44:57 +0000	[diff] [blame]	2403	and calculating the offset:</p>
				2404	<pre>
Gabor Greif	92e8776	2008-06-16 21:06:12 +0000	[diff] [blame]	2405	.---.---.---.---.---.---.---.---.---.---.---.---.---.---.---.---.----------------
				2406	\| 1 \| s \| 1 \| 0 \| 1 \| 0 \| s \| 1 \| 1 \| 0 \| s \| 1 \| 1 \| s \| 1 \| S \| User (or User*)
				2407	'---'---'---'---'---'---'---'---'---'---'---'---'---'---'---'---'----------------
				2408	\|+15 \|+10 \|+6 \|+3 \|+1
				2409	\| \| \| \| \|__>
				2410	\| \| \| \|__________>
				2411	\| \| \|______________________>
				2412	\| \|______________________________________>
				2413	\|__________________________________________________________>
Gabor Greif	93b462b	2008-06-18 13:44:57 +0000	[diff] [blame]	2414	</pre>
				2415	<p>
Gabor Greif	92e8776	2008-06-16 21:06:12 +0000	[diff] [blame]	2416	Only the significant number of bits need to be stored between the
Gabor Greif	93b462b	2008-06-18 13:44:57 +0000	[diff] [blame]	2417	stops, so that the <i>worst case is 20 memory accesses</i> when there are
				2418	1000 <tt>Use</tt> objects associated with a <tt>User</tt>.</p>
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="ReferenceImpl">Reference implementation</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>
				2427	The following literate Haskell fragment demonstrates the concept:</p>
				2428	</div>
				2429
				2430	<div class="doc_code">
				2431	<pre>
Gabor Greif	92e8776	2008-06-16 21:06:12 +0000	[diff] [blame]	2432	> import Test.QuickCheck
				2433	>
				2434	> digits :: Int -> [Char] -> [Char]
				2435	> digits 0 acc = '0' : acc
				2436	> digits 1 acc = '1' : acc
				2437	> digits n acc = digits (n `div` 2) $ digits (n `mod` 2) acc
				2438	>
				2439	> dist :: Int -> [Char] -> [Char]
				2440	> dist 0 [] = ['S']
				2441	> dist 0 acc = acc
				2442	> dist 1 acc = let r = dist 0 acc in 's' : digits (length r) r
				2443	> dist n acc = dist (n - 1) $ dist 1 acc
				2444	>
				2445	> takeLast n ss = reverse $ take n $ reverse ss
				2446	>
				2447	> test = takeLast 40 $ dist 20 []
				2448	>
Gabor Greif	93b462b	2008-06-18 13:44:57 +0000	[diff] [blame]	2449	</pre>
				2450	</div>
				2451	<p>
				2452	Printing <test> gives: <tt>"1s100000s11010s10100s1111s1010s110s11s1S"</tt></p>
				2453	<p>
				2454	The reverse algorithm computes the length of the string just by examining
				2455	a certain prefix:</p>
Gabor Greif	92e8776	2008-06-16 21:06:12 +0000	[diff] [blame]	2456
Gabor Greif	93b462b	2008-06-18 13:44:57 +0000	[diff] [blame]	2457	<div class="doc_code">
				2458	<pre>
Gabor Greif	92e8776	2008-06-16 21:06:12 +0000	[diff] [blame]	2459	> pref :: [Char] -> Int
				2460	> pref "S" = 1
				2461	> pref ('s':'1':rest) = decode 2 1 rest
				2462	> pref (_:rest) = 1 + pref rest
				2463	>
				2464	> decode walk acc ('0':rest) = decode (walk + 1) (acc * 2) rest
				2465	> decode walk acc ('1':rest) = decode (walk + 1) (acc * 2 + 1) rest
				2466	> decode walk acc _ = walk + acc
				2467	>
Gabor Greif	93b462b	2008-06-18 13:44:57 +0000	[diff] [blame]	2468	</pre>
				2469	</div>
				2470	<p>
				2471	Now, as expected, printing <pref test> gives <tt>40</tt>.</p>
				2472	<p>
				2473	We can <i>quickCheck</i> this with following property:</p>
Gabor Greif	92e8776	2008-06-16 21:06:12 +0000	[diff] [blame]	2474
Gabor Greif	93b462b	2008-06-18 13:44:57 +0000	[diff] [blame]	2475	<div class="doc_code">
				2476	<pre>
Gabor Greif	92e8776	2008-06-16 21:06:12 +0000	[diff] [blame]	2477	> testcase = dist 2000 []
				2478	> testcaseLength = length testcase
				2479	>
				2480	> identityProp n = n > 0 && n <= testcaseLength ==> length arr == pref arr
				2481	> where arr = takeLast n testcase
Gabor Greif	93b462b	2008-06-18 13:44:57 +0000	[diff] [blame]	2482	>
				2483	</pre>
				2484	</div>
				2485	<p>
				2486	As expected <quickCheck identityProp> gives:</p>
Gabor Greif	92e8776	2008-06-16 21:06:12 +0000	[diff] [blame]	2487
Gabor Greif	93b462b	2008-06-18 13:44:57 +0000	[diff] [blame]	2488	<pre>
Gabor Greif	92e8776	2008-06-16 21:06:12 +0000	[diff] [blame]	2489	*Main> quickCheck identityProp
				2490	OK, passed 100 tests.
Gabor Greif	93b462b	2008-06-18 13:44:57 +0000	[diff] [blame]	2491	</pre>
				2492	<p>
				2493	Let's be a bit more exhaustive:</p>
Gabor Greif	92e8776	2008-06-16 21:06:12 +0000	[diff] [blame]	2494
Gabor Greif	93b462b	2008-06-18 13:44:57 +0000	[diff] [blame]	2495	<div class="doc_code">
				2496	<pre>
Gabor Greif	92e8776	2008-06-16 21:06:12 +0000	[diff] [blame]	2497	>
				2498	> deepCheck p = check (defaultConfig { configMaxTest = 500 }) p
				2499	>
Gabor Greif	93b462b	2008-06-18 13:44:57 +0000	[diff] [blame]	2500	</pre>
				2501	</div>
				2502	<p>
				2503	And here is the result of <deepCheck identityProp>:</p>
Gabor Greif	92e8776	2008-06-16 21:06:12 +0000	[diff] [blame]	2504
Gabor Greif	93b462b	2008-06-18 13:44:57 +0000	[diff] [blame]	2505	<pre>
Gabor Greif	92e8776	2008-06-16 21:06:12 +0000	[diff] [blame]	2506	*Main> deepCheck identityProp
				2507	OK, passed 500 tests.
Gabor Greif	92e8776	2008-06-16 21:06:12 +0000	[diff] [blame]	2508	</pre>
				2509
Gabor Greif	93b462b	2008-06-18 13:44:57 +0000	[diff] [blame]	2510	<!-- ______________________________________________________________________ -->
				2511	<div class="doc_subsubsection">
Gabor Greif	50626fc	2009-01-05 16:05:32 +0000	[diff] [blame]	2512	<a name="Tagging">Tagging considerations</a>
Gabor Greif	93b462b	2008-06-18 13:44:57 +0000	[diff] [blame]	2513	</div>
				2514
				2515	<p>
				2516	To maintain the invariant that the 2 LSBits of each <tt>Use**</tt> in <tt>Use</tt>
				2517	never change after being set up, setters of <tt>Use::Prev</tt> must re-tag the
				2518	new <tt>Use**</tt> on every modification. Accordingly getters must strip the
				2519	tag bits.</p>
				2520	<p>
Gabor Greif	e247e36	2008-06-25 00:10:22 +0000	[diff] [blame]	2521	For layout b) instead of the <tt>User</tt> we find a pointer (<tt>User*</tt> with LSBit set).
				2522	Following this pointer brings us to the <tt>User</tt>. A portable trick ensures
				2523	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]	2524	the LSBit set. (Portability is relying on the fact that all known compilers place the
				2525	<tt>vptr</tt> in the first word of the instances.)</p>
Gabor Greif	93b462b	2008-06-18 13:44:57 +0000	[diff] [blame]	2526
Gabor Greif	92e8776	2008-06-16 21:06:12 +0000	[diff] [blame]	2527	</div>
				2528
				2529	<!-- *********************************************************************** -->
Dan Gohman	f17a25c	2007-07-18 16:29:46 +0000	[diff] [blame]	2530	<div class="doc_section">
				2531	<a name="coreclasses">The Core LLVM Class Hierarchy Reference </a>
				2532	</div>
				2533	<!-- *********************************************************************** -->
				2534
				2535	<div class="doc_text">
				2536	<p><tt>#include "<a href="/doxygen/Type_8h-source.html">llvm/Type.h</a>"</tt>
				2537	<br>doxygen info: <a href="/doxygen/classllvm_1_1Type.html">Type Class</a></p>
				2538
				2539	<p>The Core LLVM classes are the primary means of representing the program
				2540	being inspected or transformed. The core LLVM classes are defined in
				2541	header files in the <tt>include/llvm/</tt> directory, and implemented in
				2542	the <tt>lib/VMCore</tt> directory.</p>
				2543
				2544	</div>
				2545
				2546	<!-- ======================================================================= -->
				2547	<div class="doc_subsection">
				2548	<a name="Type">The <tt>Type</tt> class and Derived Types</a>
				2549	</div>
				2550
				2551	<div class="doc_text">
				2552
				2553	<p><tt>Type</tt> is a superclass of all type classes. Every <tt>Value</tt> has
				2554	a <tt>Type</tt>. <tt>Type</tt> cannot be instantiated directly but only
				2555	through its subclasses. Certain primitive types (<tt>VoidType</tt>,
				2556	<tt>LabelType</tt>, <tt>FloatType</tt> and <tt>DoubleType</tt>) have hidden
				2557	subclasses. They are hidden because they offer no useful functionality beyond
				2558	what the <tt>Type</tt> class offers except to distinguish themselves from
				2559	other subclasses of <tt>Type</tt>.</p>
				2560	<p>All other types are subclasses of <tt>DerivedType</tt>. Types can be
				2561	named, but this is not a requirement. There exists exactly
				2562	one instance of a given shape at any one time. This allows type equality to
				2563	be performed with address equality of the Type Instance. That is, given two
				2564	<tt>Type*</tt> values, the types are identical if the pointers are identical.
				2565	</p>
				2566	</div>
				2567
				2568	<!-- _______________________________________________________________________ -->
				2569	<div class="doc_subsubsection">
Gabor Greif	50626fc	2009-01-05 16:05:32 +0000	[diff] [blame]	2570	<a name="m_Type">Important Public Methods</a>
Dan Gohman	f17a25c	2007-07-18 16:29:46 +0000	[diff] [blame]	2571	</div>
				2572
				2573	<div class="doc_text">
				2574
				2575	<ul>
				2576	<li><tt>bool isInteger() const</tt>: Returns true for any integer type.</li>
				2577
				2578	<li><tt>bool isFloatingPoint()</tt>: Return true if this is one of the two
				2579	floating point types.</li>
				2580
				2581	<li><tt>bool isAbstract()</tt>: Return true if the type is abstract (contains
				2582	an OpaqueType anywhere in its definition).</li>
				2583
				2584	<li><tt>bool isSized()</tt>: Return true if the type has known size. Things
				2585	that don't have a size are abstract types, labels and void.</li>
				2586
				2587	</ul>
				2588	</div>
				2589
				2590	<!-- _______________________________________________________________________ -->
				2591	<div class="doc_subsubsection">
Gabor Greif	50626fc	2009-01-05 16:05:32 +0000	[diff] [blame]	2592	<a name="derivedtypes">Important Derived Types</a>
Dan Gohman	f17a25c	2007-07-18 16:29:46 +0000	[diff] [blame]	2593	</div>
				2594	<div class="doc_text">
				2595	<dl>
				2596	<dt><tt>IntegerType</tt></dt>
				2597	<dd>Subclass of DerivedType that represents integer types of any bit width.
				2598	Any bit width between <tt>IntegerType::MIN_INT_BITS</tt> (1) and
				2599	<tt>IntegerType::MAX_INT_BITS</tt> (~8 million) can be represented.
				2600	<ul>
				2601	<li><tt>static const IntegerType* get(unsigned NumBits)</tt>: get an integer
				2602	type of a specific bit width.</li>
				2603	<li><tt>unsigned getBitWidth() const</tt>: Get the bit width of an integer
				2604	type.</li>
				2605	</ul>
				2606	</dd>
				2607	<dt><tt>SequentialType</tt></dt>
				2608	<dd>This is subclassed by ArrayType and PointerType
				2609	<ul>
				2610	<li><tt>const Type * getElementType() const</tt>: Returns the type of each
				2611	of the elements in the sequential type. </li>
				2612	</ul>
				2613	</dd>
				2614	<dt><tt>ArrayType</tt></dt>
				2615	<dd>This is a subclass of SequentialType and defines the interface for array
				2616	types.
				2617	<ul>
				2618	<li><tt>unsigned getNumElements() const</tt>: Returns the number of
				2619	elements in the array. </li>
				2620	</ul>
				2621	</dd>
				2622	<dt><tt>PointerType</tt></dt>
				2623	<dd>Subclass of SequentialType for pointer types.</dd>
				2624	<dt><tt>VectorType</tt></dt>
				2625	<dd>Subclass of SequentialType for vector types. A
				2626	vector type is similar to an ArrayType but is distinguished because it is
				2627	a first class type wherease ArrayType is not. Vector types are used for
				2628	vector operations and are usually small vectors of of an integer or floating
				2629	point type.</dd>
				2630	<dt><tt>StructType</tt></dt>
				2631	<dd>Subclass of DerivedTypes for struct types.</dd>
				2632	<dt><tt><a name="FunctionType">FunctionType</a></tt></dt>
				2633	<dd>Subclass of DerivedTypes for function types.
				2634	<ul>
				2635	<li><tt>bool isVarArg() const</tt>: Returns true if its a vararg
				2636	function</li>
				2637	<li><tt> const Type * getReturnType() const</tt>: Returns the
				2638	return type of the function.</li>
				2639	<li><tt>const Type * getParamType (unsigned i)</tt>: Returns
				2640	the type of the ith parameter.</li>
				2641	<li><tt> const unsigned getNumParams() const</tt>: Returns the
				2642	number of formal parameters.</li>
				2643	</ul>
				2644	</dd>
				2645	<dt><tt>OpaqueType</tt></dt>
				2646	<dd>Sublcass of DerivedType for abstract types. This class
				2647	defines no content and is used as a placeholder for some other type. Note
				2648	that OpaqueType is used (temporarily) during type resolution for forward
				2649	references of types. Once the referenced type is resolved, the OpaqueType
				2650	is replaced with the actual type. OpaqueType can also be used for data
				2651	abstraction. At link time opaque types can be resolved to actual types
				2652	of the same name.</dd>
				2653	</dl>
				2654	</div>
				2655
				2656
				2657
				2658	<!-- ======================================================================= -->
				2659	<div class="doc_subsection">
				2660	<a name="Module">The <tt>Module</tt> class</a>
				2661	</div>
				2662
				2663	<div class="doc_text">
				2664
				2665	<p><tt>#include "<a
				2666	href="/doxygen/Module_8h-source.html">llvm/Module.h</a>"</tt><br> doxygen info:
				2667	<a href="/doxygen/classllvm_1_1Module.html">Module Class</a></p>
				2668
				2669	<p>The <tt>Module</tt> class represents the top level structure present in LLVM
				2670	programs. An LLVM module is effectively either a translation unit of the
				2671	original program or a combination of several translation units merged by the
				2672	linker. The <tt>Module</tt> class keeps track of a list of <a
				2673	href="#Function"><tt>Function</tt></a>s, a list of <a
				2674	href="#GlobalVariable"><tt>GlobalVariable</tt></a>s, and a <a
				2675	href="#SymbolTable"><tt>SymbolTable</tt></a>. Additionally, it contains a few
				2676	helpful member functions that try to make common operations easy.</p>
				2677
				2678	</div>
				2679
				2680	<!-- _______________________________________________________________________ -->
				2681	<div class="doc_subsubsection">
				2682	<a name="m_Module">Important Public Members of the <tt>Module</tt> class</a>
				2683	</div>
				2684
				2685	<div class="doc_text">
				2686
				2687	<ul>
				2688	<li><tt>Module::Module(std::string name = "")</tt></li>
				2689	</ul>
				2690
				2691	<p>Constructing a <a href="#Module">Module</a> is easy. You can optionally
				2692	provide a name for it (probably based on the name of the translation unit).</p>
				2693
				2694	<ul>
				2695	<li><tt>Module::iterator</tt> - Typedef for function list iterator<br>
				2696	<tt>Module::const_iterator</tt> - Typedef for const_iterator.<br>
				2697
				2698	<tt>begin()</tt>, <tt>end()</tt>
				2699	<tt>size()</tt>, <tt>empty()</tt>
				2700
				2701	<p>These are forwarding methods that make it easy to access the contents of
				2702	a <tt>Module</tt> object's <a href="#Function"><tt>Function</tt></a>
				2703	list.</p></li>
				2704
				2705	<li><tt>Module::FunctionListType &getFunctionList()</tt>
				2706
				2707	<p> Returns the list of <a href="#Function"><tt>Function</tt></a>s. This is
				2708	necessary to use when you need to update the list or perform a complex
				2709	action that doesn't have a forwarding method.</p>
				2710
				2711	<p><!-- Global Variable --></p></li>
				2712	</ul>
				2713
				2714	<hr>
				2715
				2716	<ul>
				2717	<li><tt>Module::global_iterator</tt> - Typedef for global variable list iterator<br>
				2718
				2719	<tt>Module::const_global_iterator</tt> - Typedef for const_iterator.<br>
				2720
				2721	<tt>global_begin()</tt>, <tt>global_end()</tt>
				2722	<tt>global_size()</tt>, <tt>global_empty()</tt>
				2723
				2724	<p> These are forwarding methods that make it easy to access the contents of
				2725	a <tt>Module</tt> object's <a
				2726	href="#GlobalVariable"><tt>GlobalVariable</tt></a> list.</p></li>
				2727
				2728	<li><tt>Module::GlobalListType &getGlobalList()</tt>
				2729
				2730	<p>Returns the list of <a
				2731	href="#GlobalVariable"><tt>GlobalVariable</tt></a>s. This is necessary to
				2732	use when you need to update the list or perform a complex action that
				2733	doesn't have a forwarding method.</p>
				2734
				2735	<p><!-- Symbol table stuff --> </p></li>
				2736	</ul>
				2737
				2738	<hr>
				2739
				2740	<ul>
				2741	<li><tt><a href="#SymbolTable">SymbolTable</a> *getSymbolTable()</tt>
				2742
				2743	<p>Return a reference to the <a href="#SymbolTable"><tt>SymbolTable</tt></a>
				2744	for this <tt>Module</tt>.</p>
				2745
				2746	<p><!-- Convenience methods --></p></li>
				2747	</ul>
				2748
				2749	<hr>
				2750
				2751	<ul>
				2752	<li><tt><a href="#Function">Function</a> *getFunction(const std::string
				2753	&Name, const <a href="#FunctionType">FunctionType</a> *Ty)</tt>
				2754
				2755	<p>Look up the specified function in the <tt>Module</tt> <a
				2756	href="#SymbolTable"><tt>SymbolTable</tt></a>. If it does not exist, return
				2757	<tt>null</tt>.</p></li>
				2758
				2759	<li><tt><a href="#Function">Function</a> *getOrInsertFunction(const
				2760	std::string &Name, const <a href="#FunctionType">FunctionType</a> *T)</tt>
				2761
				2762	<p>Look up the specified function in the <tt>Module</tt> <a
				2763	href="#SymbolTable"><tt>SymbolTable</tt></a>. If it does not exist, add an
				2764	external declaration for the function and return it.</p></li>
				2765
				2766	<li><tt>std::string getTypeName(const <a href="#Type">Type</a> *Ty)</tt>
				2767
				2768	<p>If there is at least one entry in the <a
				2769	href="#SymbolTable"><tt>SymbolTable</tt></a> for the specified <a
				2770	href="#Type"><tt>Type</tt></a>, return it. Otherwise return the empty
				2771	string.</p></li>
				2772
				2773	<li><tt>bool addTypeName(const std::string &Name, const <a
				2774	href="#Type">Type</a> *Ty)</tt>
				2775
				2776	<p>Insert an entry in the <a href="#SymbolTable"><tt>SymbolTable</tt></a>
				2777	mapping <tt>Name</tt> to <tt>Ty</tt>. If there is already an entry for this
				2778	name, true is returned and the <a
				2779	href="#SymbolTable"><tt>SymbolTable</tt></a> is not modified.</p></li>
				2780	</ul>
				2781
				2782	</div>
				2783
				2784
				2785	<!-- ======================================================================= -->
				2786	<div class="doc_subsection">
				2787	<a name="Value">The <tt>Value</tt> class</a>
				2788	</div>
				2789
				2790	<div class="doc_text">
				2791
				2792	<p><tt>#include "<a href="/doxygen/Value_8h-source.html">llvm/Value.h</a>"</tt>
				2793	<br>
				2794	doxygen info: <a href="/doxygen/classllvm_1_1Value.html">Value Class</a></p>
				2795
				2796	<p>The <tt>Value</tt> class is the most important class in the LLVM Source
				2797	base. It represents a typed value that may be used (among other things) as an
				2798	operand to an instruction. There are many different types of <tt>Value</tt>s,
				2799	such as <a href="#Constant"><tt>Constant</tt></a>s,<a
				2800	href="#Argument"><tt>Argument</tt></a>s. Even <a
				2801	href="#Instruction"><tt>Instruction</tt></a>s and <a
				2802	href="#Function"><tt>Function</tt></a>s are <tt>Value</tt>s.</p>
				2803
				2804	<p>A particular <tt>Value</tt> may be used many times in the LLVM representation
				2805	for a program. For example, an incoming argument to a function (represented
				2806	with an instance of the <a href="#Argument">Argument</a> class) is "used" by
				2807	every instruction in the function that references the argument. To keep track
				2808	of this relationship, the <tt>Value</tt> class keeps a list of all of the <a
				2809	href="#User"><tt>User</tt></a>s that is using it (the <a
				2810	href="#User"><tt>User</tt></a> class is a base class for all nodes in the LLVM
				2811	graph that can refer to <tt>Value</tt>s). This use list is how LLVM represents
				2812	def-use information in the program, and is accessible through the <tt>use_</tt>*
				2813	methods, shown below.</p>
				2814
				2815	<p>Because LLVM is a typed representation, every LLVM <tt>Value</tt> is typed,
				2816	and this <a href="#Type">Type</a> is available through the <tt>getType()</tt>
				2817	method. In addition, all LLVM values can be named. The "name" of the
				2818	<tt>Value</tt> is a symbolic string printed in the LLVM code:</p>
				2819
				2820	<div class="doc_code">
				2821	<pre>
				2822	%<b>foo</b> = add i32 1, 2
				2823	</pre>
				2824	</div>
				2825
				2826	<p><a name="nameWarning">The name of this instruction is "foo".</a> <b>NOTE</b>
				2827	that the name of any value may be missing (an empty string), so names should
				2828	<b>ONLY</b> be used for debugging (making the source code easier to read,
				2829	debugging printouts), they should not be used to keep track of values or map
				2830	between them. For this purpose, use a <tt>std::map</tt> of pointers to the
				2831	<tt>Value</tt> itself instead.</p>
				2832
				2833	<p>One important aspect of LLVM is that there is no distinction between an SSA
				2834	variable and the operation that produces it. Because of this, any reference to
				2835	the value produced by an instruction (or the value available as an incoming
				2836	argument, for example) is represented as a direct pointer to the instance of
				2837	the class that
				2838	represents this value. Although this may take some getting used to, it
				2839	simplifies the representation and makes it easier to manipulate.</p>
				2840
				2841	</div>
				2842
				2843	<!-- _______________________________________________________________________ -->
				2844	<div class="doc_subsubsection">
				2845	<a name="m_Value">Important Public Members of the <tt>Value</tt> class</a>
				2846	</div>
				2847
				2848	<div class="doc_text">
				2849
				2850	<ul>
				2851	<li><tt>Value::use_iterator</tt> - Typedef for iterator over the
				2852	use-list<br>
				2853	<tt>Value::use_const_iterator</tt> - Typedef for const_iterator over
				2854	the use-list<br>
				2855	<tt>unsigned use_size()</tt> - Returns the number of users of the
				2856	value.<br>
				2857	<tt>bool use_empty()</tt> - Returns true if there are no users.<br>
				2858	<tt>use_iterator use_begin()</tt> - Get an iterator to the start of
				2859	the use-list.<br>
				2860	<tt>use_iterator use_end()</tt> - Get an iterator to the end of the
				2861	use-list.<br>
				2862	<tt><a href="#User">User</a> *use_back()</tt> - Returns the last
				2863	element in the list.
				2864	<p> These methods are the interface to access the def-use
				2865	information in LLVM. As with all other iterators in LLVM, the naming
				2866	conventions follow the conventions defined by the <a href="#stl">STL</a>.</p>
				2867	</li>
				2868	<li><tt><a href="#Type">Type</a> *getType() const</tt>
				2869	<p>This method returns the Type of the Value.</p>
				2870	</li>
				2871	<li><tt>bool hasName() const</tt><br>
				2872	<tt>std::string getName() const</tt><br>
				2873	<tt>void setName(const std::string &Name)</tt>
				2874	<p> This family of methods is used to access and assign a name to a <tt>Value</tt>,
				2875	be aware of the <a href="#nameWarning">precaution above</a>.</p>
				2876	</li>
				2877	<li><tt>void replaceAllUsesWith(Value *V)</tt>
				2878
				2879	<p>This method traverses the use list of a <tt>Value</tt> changing all <a
				2880	href="#User"><tt>User</tt>s</a> of the current value to refer to
				2881	"<tt>V</tt>" instead. For example, if you detect that an instruction always
				2882	produces a constant value (for example through constant folding), you can
				2883	replace all uses of the instruction with the constant like this:</p>
				2884
				2885	<div class="doc_code">
				2886	<pre>
				2887	Inst->replaceAllUsesWith(ConstVal);
				2888	</pre>
				2889	</div>
				2890
				2891	</ul>
				2892
				2893	</div>
				2894
				2895	<!-- ======================================================================= -->
				2896	<div class="doc_subsection">
				2897	<a name="User">The <tt>User</tt> class</a>
				2898	</div>
				2899
				2900	<div class="doc_text">
				2901
				2902	<p>
				2903	<tt>#include "<a href="/doxygen/User_8h-source.html">llvm/User.h</a>"</tt><br>
				2904	doxygen info: <a href="/doxygen/classllvm_1_1User.html">User Class</a><br>
				2905	Superclass: <a href="#Value"><tt>Value</tt></a></p>
				2906
				2907	<p>The <tt>User</tt> class is the common base class of all LLVM nodes that may
				2908	refer to <a href="#Value"><tt>Value</tt></a>s. It exposes a list of "Operands"
				2909	that are all of the <a href="#Value"><tt>Value</tt></a>s that the User is
				2910	referring to. The <tt>User</tt> class itself is a subclass of
				2911	<tt>Value</tt>.</p>
				2912
				2913	<p>The operands of a <tt>User</tt> point directly to the LLVM <a
				2914	href="#Value"><tt>Value</tt></a> that it refers to. Because LLVM uses Static
				2915	Single Assignment (SSA) form, there can only be one definition referred to,
				2916	allowing this direct connection. This connection provides the use-def
				2917	information in LLVM.</p>
				2918
				2919	</div>
				2920
				2921	<!-- _______________________________________________________________________ -->
				2922	<div class="doc_subsubsection">
				2923	<a name="m_User">Important Public Members of the <tt>User</tt> class</a>
				2924	</div>
				2925
				2926	<div class="doc_text">
				2927
				2928	<p>The <tt>User</tt> class exposes the operand list in two ways: through
				2929	an index access interface and through an iterator based interface.</p>
				2930
				2931	<ul>
				2932	<li><tt>Value *getOperand(unsigned i)</tt><br>
				2933	<tt>unsigned getNumOperands()</tt>
				2934	<p> These two methods expose the operands of the <tt>User</tt> in a
				2935	convenient form for direct access.</p></li>
				2936
				2937	<li><tt>User::op_iterator</tt> - Typedef for iterator over the operand
				2938	list<br>
				2939	<tt>op_iterator op_begin()</tt> - Get an iterator to the start of
				2940	the operand list.<br>
				2941	<tt>op_iterator op_end()</tt> - Get an iterator to the end of the
				2942	operand list.
				2943	<p> Together, these methods make up the iterator based interface to
				2944	the operands of a <tt>User</tt>.</p></li>
				2945	</ul>
				2946
				2947	</div>
				2948
				2949	<!-- ======================================================================= -->
				2950	<div class="doc_subsection">
				2951	<a name="Instruction">The <tt>Instruction</tt> class</a>
				2952	</div>
				2953
				2954	<div class="doc_text">
				2955
				2956	<p><tt>#include "</tt><tt><a
				2957	href="/doxygen/Instruction_8h-source.html">llvm/Instruction.h</a>"</tt><br>
				2958	doxygen info: <a href="/doxygen/classllvm_1_1Instruction.html">Instruction Class</a><br>
				2959	Superclasses: <a href="#User"><tt>User</tt></a>, <a
				2960	href="#Value"><tt>Value</tt></a></p>
				2961
				2962	<p>The <tt>Instruction</tt> class is the common base class for all LLVM
				2963	instructions. It provides only a few methods, but is a very commonly used
				2964	class. The primary data tracked by the <tt>Instruction</tt> class itself is the
				2965	opcode (instruction type) and the parent <a
				2966	href="#BasicBlock"><tt>BasicBlock</tt></a> the <tt>Instruction</tt> is embedded
				2967	into. To represent a specific type of instruction, one of many subclasses of
				2968	<tt>Instruction</tt> are used.</p>
				2969
				2970	<p> Because the <tt>Instruction</tt> class subclasses the <a
				2971	href="#User"><tt>User</tt></a> class, its operands can be accessed in the same
				2972	way as for other <a href="#User"><tt>User</tt></a>s (with the
				2973	<tt>getOperand()</tt>/<tt>getNumOperands()</tt> and
				2974	<tt>op_begin()</tt>/<tt>op_end()</tt> methods).</p> <p> An important file for
				2975	the <tt>Instruction</tt> class is the <tt>llvm/Instruction.def</tt> file. This
				2976	file contains some meta-data about the various different types of instructions
				2977	in LLVM. It describes the enum values that are used as opcodes (for example
				2978	<tt>Instruction::Add</tt> and <tt>Instruction::ICmp</tt>), as well as the
				2979	concrete sub-classes of <tt>Instruction</tt> that implement the instruction (for
				2980	example <tt><a href="#BinaryOperator">BinaryOperator</a></tt> and <tt><a
				2981	href="#CmpInst">CmpInst</a></tt>). Unfortunately, the use of macros in
				2982	this file confuses doxygen, so these enum values don't show up correctly in the
				2983	<a href="/doxygen/classllvm_1_1Instruction.html">doxygen output</a>.</p>
				2984
				2985	</div>
				2986
				2987	<!-- _______________________________________________________________________ -->
				2988	<div class="doc_subsubsection">
				2989	<a name="s_Instruction">Important Subclasses of the <tt>Instruction</tt>
				2990	class</a>
				2991	</div>
				2992	<div class="doc_text">
				2993	<ul>
				2994	<li><tt><a name="BinaryOperator">BinaryOperator</a></tt>
				2995	<p>This subclasses represents all two operand instructions whose operands
				2996	must be the same type, except for the comparison instructions.</p></li>
				2997	<li><tt><a name="CastInst">CastInst</a></tt>
				2998	<p>This subclass is the parent of the 12 casting instructions. It provides
				2999	common operations on cast instructions.</p>
				3000	<li><tt><a name="CmpInst">CmpInst</a></tt>
				3001	<p>This subclass respresents the two comparison instructions,
				3002	<a href="LangRef.html#i_icmp">ICmpInst</a> (integer opreands), and
				3003	<a href="LangRef.html#i_fcmp">FCmpInst</a> (floating point operands).</p>
				3004	<li><tt><a name="TerminatorInst">TerminatorInst</a></tt>
				3005	<p>This subclass is the parent of all terminator instructions (those which
				3006	can terminate a block).</p>
				3007	</ul>
				3008	</div>
				3009
				3010	<!-- _______________________________________________________________________ -->
				3011	<div class="doc_subsubsection">
				3012	<a name="m_Instruction">Important Public Members of the <tt>Instruction</tt>
				3013	class</a>
				3014	</div>
				3015
				3016	<div class="doc_text">
				3017
				3018	<ul>
				3019	<li><tt><a href="#BasicBlock">BasicBlock</a> *getParent()</tt>
				3020	<p>Returns the <a href="#BasicBlock"><tt>BasicBlock</tt></a> that
				3021	this <tt>Instruction</tt> is embedded into.</p></li>
				3022	<li><tt>bool mayWriteToMemory()</tt>
				3023	<p>Returns true if the instruction writes to memory, i.e. it is a
				3024	<tt>call</tt>,<tt>free</tt>,<tt>invoke</tt>, or <tt>store</tt>.</p></li>
				3025	<li><tt>unsigned getOpcode()</tt>
				3026	<p>Returns the opcode for the <tt>Instruction</tt>.</p></li>
				3027	<li><tt><a href="#Instruction">Instruction</a> *clone() const</tt>
				3028	<p>Returns another instance of the specified instruction, identical
				3029	in all ways to the original except that the instruction has no parent
				3030	(ie it's not embedded into a <a href="#BasicBlock"><tt>BasicBlock</tt></a>),
				3031	and it has no name</p></li>
				3032	</ul>
				3033
				3034	</div>
				3035
				3036	<!-- ======================================================================= -->
				3037	<div class="doc_subsection">
				3038	<a name="Constant">The <tt>Constant</tt> class and subclasses</a>
				3039	</div>
				3040
				3041	<div class="doc_text">
				3042
				3043	<p>Constant represents a base class for different types of constants. It
				3044	is subclassed by ConstantInt, ConstantArray, etc. for representing
				3045	the various types of Constants. <a href="#GlobalValue">GlobalValue</a> is also
				3046	a subclass, which represents the address of a global variable or function.
				3047	</p>
				3048
				3049	</div>
				3050
				3051	<!-- _______________________________________________________________________ -->
				3052	<div class="doc_subsubsection">Important Subclasses of Constant </div>
				3053	<div class="doc_text">
				3054	<ul>
				3055	<li>ConstantInt : This subclass of Constant represents an integer constant of
				3056	any width.
				3057	<ul>
				3058	<li><tt>const APInt& getValue() const</tt>: Returns the underlying
				3059	value of this constant, an APInt value.</li>
				3060	<li><tt>int64_t getSExtValue() const</tt>: Converts the underlying APInt
				3061	value to an int64_t via sign extension. If the value (not the bit width)
				3062	of the APInt is too large to fit in an int64_t, an assertion will result.
				3063	For this reason, use of this method is discouraged.</li>
				3064	<li><tt>uint64_t getZExtValue() const</tt>: Converts the underlying APInt
				3065	value to a uint64_t via zero extension. IF the value (not the bit width)
				3066	of the APInt is too large to fit in a uint64_t, an assertion will result.
				3067	For this reason, use of this method is discouraged.</li>
				3068	<li><tt>static ConstantInt* get(const APInt& Val)</tt>: Returns the
				3069	ConstantInt object that represents the value provided by <tt>Val</tt>.
				3070	The type is implied as the IntegerType that corresponds to the bit width
				3071	of <tt>Val</tt>.</li>
				3072	<li><tt>static ConstantInt* get(const Type *Ty, uint64_t Val)</tt>:
				3073	Returns the ConstantInt object that represents the value provided by
				3074	<tt>Val</tt> for integer type <tt>Ty</tt>.</li>
				3075	</ul>
				3076	</li>
				3077	<li>ConstantFP : This class represents a floating point constant.
				3078	<ul>
				3079	<li><tt>double getValue() const</tt>: Returns the underlying value of
				3080	this constant. </li>
				3081	</ul>
				3082	</li>
				3083	<li>ConstantArray : This represents a constant array.
				3084	<ul>
				3085	<li><tt>const std::vector<Use> &getValues() const</tt>: Returns
				3086	a vector of component constants that makeup this array. </li>
				3087	</ul>
				3088	</li>
				3089	<li>ConstantStruct : This represents a constant struct.
				3090	<ul>
				3091	<li><tt>const std::vector<Use> &getValues() const</tt>: Returns
				3092	a vector of component constants that makeup this array. </li>
				3093	</ul>
				3094	</li>
				3095	<li>GlobalValue : This represents either a global variable or a function. In
				3096	either case, the value is a constant fixed address (after linking).
				3097	</li>
				3098	</ul>
				3099	</div>
				3100
				3101
				3102	<!-- ======================================================================= -->
				3103	<div class="doc_subsection">
				3104	<a name="GlobalValue">The <tt>GlobalValue</tt> class</a>
				3105	</div>
				3106
				3107	<div class="doc_text">
				3108
				3109	<p><tt>#include "<a
				3110	href="/doxygen/GlobalValue_8h-source.html">llvm/GlobalValue.h</a>"</tt><br>
				3111	doxygen info: <a href="/doxygen/classllvm_1_1GlobalValue.html">GlobalValue
				3112	Class</a><br>
				3113	Superclasses: <a href="#Constant"><tt>Constant</tt></a>,
				3114	<a href="#User"><tt>User</tt></a>, <a href="#Value"><tt>Value</tt></a></p>
				3115
				3116	<p>Global values (<a href="#GlobalVariable"><tt>GlobalVariable</tt></a>s or <a
				3117	href="#Function"><tt>Function</tt></a>s) are the only LLVM values that are
				3118	visible in the bodies of all <a href="#Function"><tt>Function</tt></a>s.
				3119	Because they are visible at global scope, they are also subject to linking with
				3120	other globals defined in different translation units. To control the linking
				3121	process, <tt>GlobalValue</tt>s know their linkage rules. Specifically,
				3122	<tt>GlobalValue</tt>s know whether they have internal or external linkage, as
				3123	defined by the <tt>LinkageTypes</tt> enumeration.</p>
				3124
				3125	<p>If a <tt>GlobalValue</tt> has internal linkage (equivalent to being
				3126	<tt>static</tt> in C), it is not visible to code outside the current translation
				3127	unit, and does not participate in linking. If it has external linkage, it is
				3128	visible to external code, and does participate in linking. In addition to
				3129	linkage information, <tt>GlobalValue</tt>s keep track of which <a
				3130	href="#Module"><tt>Module</tt></a> they are currently part of.</p>
				3131
				3132	<p>Because <tt>GlobalValue</tt>s are memory objects, they are always referred to
				3133	by their <b>address</b>. As such, the <a href="#Type"><tt>Type</tt></a> of a
				3134	global is always a pointer to its contents. It is important to remember this
				3135	when using the <tt>GetElementPtrInst</tt> instruction because this pointer must
				3136	be dereferenced first. For example, if you have a <tt>GlobalVariable</tt> (a
				3137	subclass of <tt>GlobalValue)</tt> that is an array of 24 ints, type <tt>[24 x
				3138	i32]</tt>, then the <tt>GlobalVariable</tt> is a pointer to that array. Although
				3139	the address of the first element of this array and the value of the
				3140	<tt>GlobalVariable</tt> are the same, they have different types. The
				3141	<tt>GlobalVariable</tt>'s type is <tt>[24 x i32]</tt>. The first element's type
				3142	is <tt>i32.</tt> Because of this, accessing a global value requires you to
				3143	dereference the pointer with <tt>GetElementPtrInst</tt> first, then its elements
				3144	can be accessed. This is explained in the <a href="LangRef.html#globalvars">LLVM
				3145	Language Reference Manual</a>.</p>
				3146
				3147	</div>
				3148
				3149	<!-- _______________________________________________________________________ -->
				3150	<div class="doc_subsubsection">
				3151	<a name="m_GlobalValue">Important Public Members of the <tt>GlobalValue</tt>
				3152	class</a>
				3153	</div>
				3154
				3155	<div class="doc_text">
				3156
				3157	<ul>
				3158	<li><tt>bool hasInternalLinkage() const</tt><br>
				3159	<tt>bool hasExternalLinkage() const</tt><br>
				3160	<tt>void setInternalLinkage(bool HasInternalLinkage)</tt>
				3161	<p> These methods manipulate the linkage characteristics of the <tt>GlobalValue</tt>.</p>
				3162	<p> </p>
				3163	</li>
				3164	<li><tt><a href="#Module">Module</a> *getParent()</tt>
				3165	<p> This returns the <a href="#Module"><tt>Module</tt></a> that the
				3166	GlobalValue is currently embedded into.</p></li>
				3167	</ul>
				3168
				3169	</div>
				3170
				3171	<!-- ======================================================================= -->
				3172	<div class="doc_subsection">
				3173	<a name="Function">The <tt>Function</tt> class</a>
				3174	</div>
				3175
				3176	<div class="doc_text">
				3177
				3178	<p><tt>#include "<a
				3179	href="/doxygen/Function_8h-source.html">llvm/Function.h</a>"</tt><br> doxygen
				3180	info: <a href="/doxygen/classllvm_1_1Function.html">Function Class</a><br>
				3181	Superclasses: <a href="#GlobalValue"><tt>GlobalValue</tt></a>,
				3182	<a href="#Constant"><tt>Constant</tt></a>,
				3183	<a href="#User"><tt>User</tt></a>,
				3184	<a href="#Value"><tt>Value</tt></a></p>
				3185
				3186	<p>The <tt>Function</tt> class represents a single procedure in LLVM. It is
				3187	actually one of the more complex classes in the LLVM heirarchy because it must
				3188	keep track of a large amount of data. The <tt>Function</tt> class keeps track
				3189	of a list of <a href="#BasicBlock"><tt>BasicBlock</tt></a>s, a list of formal
				3190	<a href="#Argument"><tt>Argument</tt></a>s, and a
				3191	<a href="#SymbolTable"><tt>SymbolTable</tt></a>.</p>
				3192
				3193	<p>The list of <a href="#BasicBlock"><tt>BasicBlock</tt></a>s is the most
				3194	commonly used part of <tt>Function</tt> objects. The list imposes an implicit
				3195	ordering of the blocks in the function, which indicate how the code will be
				3196	layed out by the backend. Additionally, the first <a
				3197	href="#BasicBlock"><tt>BasicBlock</tt></a> is the implicit entry node for the
				3198	<tt>Function</tt>. It is not legal in LLVM to explicitly branch to this initial
				3199	block. There are no implicit exit nodes, and in fact there may be multiple exit
				3200	nodes from a single <tt>Function</tt>. If the <a
				3201	href="#BasicBlock"><tt>BasicBlock</tt></a> list is empty, this indicates that
				3202	the <tt>Function</tt> is actually a function declaration: the actual body of the
				3203	function hasn't been linked in yet.</p>
				3204
				3205	<p>In addition to a list of <a href="#BasicBlock"><tt>BasicBlock</tt></a>s, the
				3206	<tt>Function</tt> class also keeps track of the list of formal <a
				3207	href="#Argument"><tt>Argument</tt></a>s that the function receives. This
				3208	container manages the lifetime of the <a href="#Argument"><tt>Argument</tt></a>
				3209	nodes, just like the <a href="#BasicBlock"><tt>BasicBlock</tt></a> list does for
				3210	the <a href="#BasicBlock"><tt>BasicBlock</tt></a>s.</p>
				3211
				3212	<p>The <a href="#SymbolTable"><tt>SymbolTable</tt></a> is a very rarely used
				3213	LLVM feature that is only used when you have to look up a value by name. Aside
				3214	from that, the <a href="#SymbolTable"><tt>SymbolTable</tt></a> is used
				3215	internally to make sure that there are not conflicts between the names of <a
				3216	href="#Instruction"><tt>Instruction</tt></a>s, <a
				3217	href="#BasicBlock"><tt>BasicBlock</tt></a>s, or <a
				3218	href="#Argument"><tt>Argument</tt></a>s in the function body.</p>
				3219
				3220	<p>Note that <tt>Function</tt> is a <a href="#GlobalValue">GlobalValue</a>
				3221	and therefore also a <a href="#Constant">Constant</a>. The value of the function
				3222	is its address (after linking) which is guaranteed to be constant.</p>
				3223	</div>
				3224
				3225	<!-- _______________________________________________________________________ -->
				3226	<div class="doc_subsubsection">
				3227	<a name="m_Function">Important Public Members of the <tt>Function</tt>
				3228	class</a>
				3229	</div>
				3230
				3231	<div class="doc_text">
				3232
				3233	<ul>
				3234	<li><tt>Function(const </tt><tt><a href="#FunctionType">FunctionType</a>
				3235	Ty, LinkageTypes Linkage, const std::string &N = "", Module Parent = 0)</tt>
				3236
				3237	<p>Constructor used when you need to create new <tt>Function</tt>s to add
				3238	the the program. The constructor must specify the type of the function to
				3239	create and what type of linkage the function should have. The <a
				3240	href="#FunctionType"><tt>FunctionType</tt></a> argument
				3241	specifies the formal arguments and return value for the function. The same
				3242	<a href="#FunctionType"><tt>FunctionType</tt></a> value can be used to
				3243	create multiple functions. The <tt>Parent</tt> argument specifies the Module
				3244	in which the function is defined. If this argument is provided, the function
				3245	will automatically be inserted into that module's list of
				3246	functions.</p></li>
				3247
Chris Lattner	5e70957	2008-11-25 18:34:50 +0000	[diff] [blame]	3248	<li><tt>bool isDeclaration()</tt>
Dan Gohman	f17a25c	2007-07-18 16:29:46 +0000	[diff] [blame]	3249
				3250	<p>Return whether or not the <tt>Function</tt> has a body defined. If the
				3251	function is "external", it does not have a body, and thus must be resolved
				3252	by linking with a function defined in a different translation unit.</p></li>
				3253
				3254	<li><tt>Function::iterator</tt> - Typedef for basic block list iterator<br>
				3255	<tt>Function::const_iterator</tt> - Typedef for const_iterator.<br>
				3256
				3257	<tt>begin()</tt>, <tt>end()</tt>
				3258	<tt>size()</tt>, <tt>empty()</tt>
				3259
				3260	<p>These are forwarding methods that make it easy to access the contents of
				3261	a <tt>Function</tt> object's <a href="#BasicBlock"><tt>BasicBlock</tt></a>
				3262	list.</p></li>
				3263
				3264	<li><tt>Function::BasicBlockListType &getBasicBlockList()</tt>
				3265
				3266	<p>Returns the list of <a href="#BasicBlock"><tt>BasicBlock</tt></a>s. This
				3267	is necessary to use when you need to update the list or perform a complex
				3268	action that doesn't have a forwarding method.</p></li>
				3269
				3270	<li><tt>Function::arg_iterator</tt> - Typedef for the argument list
				3271	iterator<br>
				3272	<tt>Function::const_arg_iterator</tt> - Typedef for const_iterator.<br>
				3273
				3274	<tt>arg_begin()</tt>, <tt>arg_end()</tt>
				3275	<tt>arg_size()</tt>, <tt>arg_empty()</tt>
				3276
				3277	<p>These are forwarding methods that make it easy to access the contents of
				3278	a <tt>Function</tt> object's <a href="#Argument"><tt>Argument</tt></a>
				3279	list.</p></li>
				3280
				3281	<li><tt>Function::ArgumentListType &getArgumentList()</tt>
				3282
				3283	<p>Returns the list of <a href="#Argument"><tt>Argument</tt></a>s. This is
				3284	necessary to use when you need to update the list or perform a complex
				3285	action that doesn't have a forwarding method.</p></li>
				3286
				3287	<li><tt><a href="#BasicBlock">BasicBlock</a> &getEntryBlock()</tt>
				3288
				3289	<p>Returns the entry <a href="#BasicBlock"><tt>BasicBlock</tt></a> for the
				3290	function. Because the entry block for the function is always the first
				3291	block, this returns the first block of the <tt>Function</tt>.</p></li>
				3292
				3293	<li><tt><a href="#Type">Type</a> *getReturnType()</tt><br>
				3294	<tt><a href="#FunctionType">FunctionType</a> *getFunctionType()</tt>
				3295
				3296	<p>This traverses the <a href="#Type"><tt>Type</tt></a> of the
				3297	<tt>Function</tt> and returns the return type of the function, or the <a
				3298	href="#FunctionType"><tt>FunctionType</tt></a> of the actual
				3299	function.</p></li>
				3300
				3301	<li><tt><a href="#SymbolTable">SymbolTable</a> *getSymbolTable()</tt>
				3302
				3303	<p> Return a pointer to the <a href="#SymbolTable"><tt>SymbolTable</tt></a>
				3304	for this <tt>Function</tt>.</p></li>
				3305	</ul>
				3306
				3307	</div>
				3308
				3309	<!-- ======================================================================= -->
				3310	<div class="doc_subsection">
				3311	<a name="GlobalVariable">The <tt>GlobalVariable</tt> class</a>
				3312	</div>
				3313
				3314	<div class="doc_text">
				3315
				3316	<p><tt>#include "<a
				3317	href="/doxygen/GlobalVariable_8h-source.html">llvm/GlobalVariable.h</a>"</tt>
				3318	<br>
				3319	doxygen info: <a href="/doxygen/classllvm_1_1GlobalVariable.html">GlobalVariable
				3320	Class</a><br>
				3321	Superclasses: <a href="#GlobalValue"><tt>GlobalValue</tt></a>,
				3322	<a href="#Constant"><tt>Constant</tt></a>,
				3323	<a href="#User"><tt>User</tt></a>,
				3324	<a href="#Value"><tt>Value</tt></a></p>
				3325
				3326	<p>Global variables are represented with the (suprise suprise)
				3327	<tt>GlobalVariable</tt> class. Like functions, <tt>GlobalVariable</tt>s are also
				3328	subclasses of <a href="#GlobalValue"><tt>GlobalValue</tt></a>, and as such are
				3329	always referenced by their address (global values must live in memory, so their
				3330	"name" refers to their constant address). See
				3331	<a href="#GlobalValue"><tt>GlobalValue</tt></a> for more on this. Global
				3332	variables may have an initial value (which must be a
				3333	<a href="#Constant"><tt>Constant</tt></a>), and if they have an initializer,
				3334	they may be marked as "constant" themselves (indicating that their contents
				3335	never change at runtime).</p>
				3336	</div>
				3337
				3338	<!-- _______________________________________________________________________ -->
				3339	<div class="doc_subsubsection">
				3340	<a name="m_GlobalVariable">Important Public Members of the
				3341	<tt>GlobalVariable</tt> class</a>
				3342	</div>
				3343
				3344	<div class="doc_text">
				3345
				3346	<ul>
				3347	<li><tt>GlobalVariable(const </tt><tt><a href="#Type">Type</a> *Ty, bool
				3348	isConstant, LinkageTypes& Linkage, <a href="#Constant">Constant</a>
				3349	Initializer = 0, const std::string &Name = "", Module Parent = 0)</tt>
				3350
				3351	<p>Create a new global variable of the specified type. If
				3352	<tt>isConstant</tt> is true then the global variable will be marked as
				3353	unchanging for the program. The Linkage parameter specifies the type of
Duncan Sands	19d161f	2009-03-07 15:45:40 +0000	[diff] [blame]	3354	linkage (internal, external, weak, linkonce, appending) for the variable.
				3355	If the linkage is InternalLinkage, WeakAnyLinkage, WeakODRLinkage,
				3356	LinkOnceAnyLinkage or LinkOnceODRLinkage,  then the resultant
				3357	global variable will have internal linkage. AppendingLinkage concatenates
				3358	together all instances (in different translation units) of the variable
				3359	into a single variable but is only applicable to arrays.  See
Dan Gohman	f17a25c	2007-07-18 16:29:46 +0000	[diff] [blame]	3360	the <a href="LangRef.html#modulestructure">LLVM Language Reference</a> for
				3361	further details on linkage types. Optionally an initializer, a name, and the
				3362	module to put the variable into may be specified for the global variable as
				3363	well.</p></li>
				3364
				3365	<li><tt>bool isConstant() const</tt>
				3366
				3367	<p>Returns true if this is a global variable that is known not to
				3368	be modified at runtime.</p></li>
				3369
				3370	<li><tt>bool hasInitializer()</tt>
				3371
				3372	<p>Returns true if this <tt>GlobalVariable</tt> has an intializer.</p></li>
				3373
				3374	<li><tt><a href="#Constant">Constant</a> *getInitializer()</tt>
				3375
				3376	<p>Returns the intial value for a <tt>GlobalVariable</tt>. It is not legal
				3377	to call this method if there is no initializer.</p></li>
				3378	</ul>
				3379
				3380	</div>
				3381
				3382
				3383	<!-- ======================================================================= -->
				3384	<div class="doc_subsection">
				3385	<a name="BasicBlock">The <tt>BasicBlock</tt> class</a>
				3386	</div>
				3387
				3388	<div class="doc_text">
				3389
				3390	<p><tt>#include "<a
				3391	href="/doxygen/BasicBlock_8h-source.html">llvm/BasicBlock.h</a>"</tt><br>
				3392	doxygen info: <a href="/doxygen/structllvm_1_1BasicBlock.html">BasicBlock
				3393	Class</a><br>
				3394	Superclass: <a href="#Value"><tt>Value</tt></a></p>
				3395
				3396	<p>This class represents a single entry multiple exit section of the code,
				3397	commonly known as a basic block by the compiler community. The
				3398	<tt>BasicBlock</tt> class maintains a list of <a
				3399	href="#Instruction"><tt>Instruction</tt></a>s, which form the body of the block.
				3400	Matching the language definition, the last element of this list of instructions
				3401	is always a terminator instruction (a subclass of the <a
				3402	href="#TerminatorInst"><tt>TerminatorInst</tt></a> class).</p>
				3403
				3404	<p>In addition to tracking the list of instructions that make up the block, the
				3405	<tt>BasicBlock</tt> class also keeps track of the <a
				3406	href="#Function"><tt>Function</tt></a> that it is embedded into.</p>
				3407
				3408	<p>Note that <tt>BasicBlock</tt>s themselves are <a
				3409	href="#Value"><tt>Value</tt></a>s, because they are referenced by instructions
				3410	like branches and can go in the switch tables. <tt>BasicBlock</tt>s have type
				3411	<tt>label</tt>.</p>
				3412
				3413	</div>
				3414
				3415	<!-- _______________________________________________________________________ -->
				3416	<div class="doc_subsubsection">
				3417	<a name="m_BasicBlock">Important Public Members of the <tt>BasicBlock</tt>
				3418	class</a>
				3419	</div>
				3420
				3421	<div class="doc_text">
				3422	<ul>
				3423
				3424	<li><tt>BasicBlock(const std::string &Name = "", </tt><tt><a
				3425	href="#Function">Function</a> *Parent = 0)</tt>
				3426
				3427	<p>The <tt>BasicBlock</tt> constructor is used to create new basic blocks for
				3428	insertion into a function. The constructor optionally takes a name for the new
				3429	block, and a <a href="#Function"><tt>Function</tt></a> to insert it into. If
				3430	the <tt>Parent</tt> parameter is specified, the new <tt>BasicBlock</tt> is
				3431	automatically inserted at the end of the specified <a
				3432	href="#Function"><tt>Function</tt></a>, if not specified, the BasicBlock must be
				3433	manually inserted into the <a href="#Function"><tt>Function</tt></a>.</p></li>
				3434
				3435	<li><tt>BasicBlock::iterator</tt> - Typedef for instruction list iterator<br>
				3436	<tt>BasicBlock::const_iterator</tt> - Typedef for const_iterator.<br>
				3437	<tt>begin()</tt>, <tt>end()</tt>, <tt>front()</tt>, <tt>back()</tt>,
				3438	<tt>size()</tt>, <tt>empty()</tt>
				3439	STL-style functions for accessing the instruction list.
				3440
				3441	<p>These methods and typedefs are forwarding functions that have the same
				3442	semantics as the standard library methods of the same names. These methods
				3443	expose the underlying instruction list of a basic block in a way that is easy to
				3444	manipulate. To get the full complement of container operations (including
				3445	operations to update the list), you must use the <tt>getInstList()</tt>
				3446	method.</p></li>
				3447
				3448	<li><tt>BasicBlock::InstListType &getInstList()</tt>
				3449
				3450	<p>This method is used to get access to the underlying container that actually
				3451	holds the Instructions. This method must be used when there isn't a forwarding
				3452	function in the <tt>BasicBlock</tt> class for the operation that you would like
				3453	to perform. Because there are no forwarding functions for "updating"
				3454	operations, you need to use this if you want to update the contents of a
				3455	<tt>BasicBlock</tt>.</p></li>
				3456
				3457	<li><tt><a href="#Function">Function</a> *getParent()</tt>
				3458
				3459	<p> Returns a pointer to <a href="#Function"><tt>Function</tt></a> the block is
				3460	embedded into, or a null pointer if it is homeless.</p></li>
				3461
				3462	<li><tt><a href="#TerminatorInst">TerminatorInst</a> *getTerminator()</tt>
				3463
				3464	<p> Returns a pointer to the terminator instruction that appears at the end of
				3465	the <tt>BasicBlock</tt>. If there is no terminator instruction, or if the last
				3466	instruction in the block is not a terminator, then a null pointer is
				3467	returned.</p></li>
				3468
				3469	</ul>
				3470
				3471	</div>
				3472
				3473
				3474	<!-- ======================================================================= -->
				3475	<div class="doc_subsection">
				3476	<a name="Argument">The <tt>Argument</tt> class</a>
				3477	</div>
				3478
				3479	<div class="doc_text">
				3480
				3481	<p>This subclass of Value defines the interface for incoming formal
				3482	arguments to a function. A Function maintains a list of its formal
				3483	arguments. An argument has a pointer to the parent Function.</p>
				3484
				3485	</div>
				3486
				3487	<!-- *********************************************************************** -->
				3488	<hr>
				3489	<address>
				3490	<a href="http://jigsaw.w3.org/css-validator/check/referer"><img
Misha Brukman	947321d	2008-12-11 17:34:48 +0000	[diff] [blame]	3491	src="http://jigsaw.w3.org/css-validator/images/vcss-blue" alt="Valid CSS"></a>
Dan Gohman	f17a25c	2007-07-18 16:29:46 +0000	[diff] [blame]	3492	<a href="http://validator.w3.org/check/referer"><img
Gabor Greif	7dabe38	2008-06-18 14:05:31 +0000	[diff] [blame]	3493	src="http://www.w3.org/Icons/valid-html401" alt="Valid HTML 4.01 Strict"></a>
Dan Gohman	f17a25c	2007-07-18 16:29:46 +0000	[diff] [blame]	3494
				3495	<a href="mailto:dhurjati@cs.uiuc.edu">Dinakar Dhurjati</a> and
				3496	<a href="mailto:sabre@nondot.org">Chris Lattner</a><br>
				3497	<a href="http://llvm.org">The LLVM Compiler Infrastructure</a><br>
				3498	Last modified: $Date$
				3499	</address>
				3500
				3501	</body>
				3502	</html>