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Owen Anderson	60f8757	2009-06-16 17:40:28 +0000	[diff] [blame]	5	<meta http-equiv="Content-type" content="text/html;charset=UTF-8">
Dan Gohman	f17a25c	2007-07-18 16:29:46 +0000	[diff] [blame]	6	<title>LLVM Programmer's Manual</title>
				7	<link rel="stylesheet" href="llvm.css" type="text/css">
				8	</head>
				9	<body>
				10
				11	<div class="doc_title">
				12	LLVM Programmer's Manual
				13	</div>
				14
				15	<ol>
				16	<li><a href="#introduction">Introduction</a></li>
				17	<li><a href="#general">General Information</a>
				18	<ul>
				19	<li><a href="#stl">The C++ Standard Template Library</a></li>
				20	<!--
				21	<li>The <tt>-time-passes</tt> option</li>
				22	<li>How to use the LLVM Makefile system</li>
				23	<li>How to write a regression test</li>
				24
				25	-->
				26	</ul>
				27	</li>
				28	<li><a href="#apis">Important and useful LLVM APIs</a>
				29	<ul>
				30	<li><a href="#isa">The <tt>isa<></tt>, <tt>cast<></tt>
				31	and <tt>dyn_cast<></tt> templates</a> </li>
Daniel Dunbar	e3572ba	2009-07-25 04:41:11 +0000	[diff] [blame]	32	<li><a href="#string_apis">Passing strings (the <tt>StringRef</tt>
				33	and <tt>Twine</tt> classes)</li>
				34	<ul>
				35	<li><a href="#StringRef">The <tt>StringRef</tt> class</a> </li>
				36	<li><a href="#Twine">The <tt>Twine</tt> class</a> </li>
				37	</ul>
Dan Gohman	f17a25c	2007-07-18 16:29:46 +0000	[diff] [blame]	38	<li><a href="#DEBUG">The <tt>DEBUG()</tt> macro and <tt>-debug</tt>
				39	option</a>
				40	<ul>
				41	<li><a href="#DEBUG_TYPE">Fine grained debug info with <tt>DEBUG_TYPE</tt>
				42	and the <tt>-debug-only</tt> option</a> </li>
				43	</ul>
				44	</li>
				45	<li><a href="#Statistic">The <tt>Statistic</tt> class & <tt>-stats</tt>
				46	option</a></li>
				47	<!--
				48	<li>The <tt>InstVisitor</tt> template
				49	<li>The general graph API
				50	-->
				51	<li><a href="#ViewGraph">Viewing graphs while debugging code</a></li>
				52	</ul>
				53	</li>
				54	<li><a href="#datastructure">Picking the Right Data Structure for a Task</a>
				55	<ul>
				56	<li><a href="#ds_sequential">Sequential Containers (std::vector, std::list, etc)</a>
				57	<ul>
				58	<li><a href="#dss_fixedarrays">Fixed Size Arrays</a></li>
				59	<li><a href="#dss_heaparrays">Heap Allocated Arrays</a></li>
				60	<li><a href="#dss_smallvector">"llvm/ADT/SmallVector.h"</a></li>
				61	<li><a href="#dss_vector"><vector></a></li>
				62	<li><a href="#dss_deque"><deque></a></li>
				63	<li><a href="#dss_list"><list></a></li>
Gabor Greif	bb17f65	2009-02-27 11:37:41 +0000	[diff] [blame]	64	<li><a href="#dss_ilist">llvm/ADT/ilist.h</a></li>
Dan Gohman	f17a25c	2007-07-18 16:29:46 +0000	[diff] [blame]	65	<li><a href="#dss_other">Other Sequential Container Options</a></li>
				66	</ul></li>
				67	<li><a href="#ds_set">Set-Like Containers (std::set, SmallSet, SetVector, etc)</a>
				68	<ul>
				69	<li><a href="#dss_sortedvectorset">A sorted 'vector'</a></li>
				70	<li><a href="#dss_smallset">"llvm/ADT/SmallSet.h"</a></li>
				71	<li><a href="#dss_smallptrset">"llvm/ADT/SmallPtrSet.h"</a></li>
Chris Lattner	77ab46d	2007-09-30 00:58:59 +0000	[diff] [blame]	72	<li><a href="#dss_denseset">"llvm/ADT/DenseSet.h"</a></li>
Dan Gohman	f17a25c	2007-07-18 16:29:46 +0000	[diff] [blame]	73	<li><a href="#dss_FoldingSet">"llvm/ADT/FoldingSet.h"</a></li>
				74	<li><a href="#dss_set"><set></a></li>
				75	<li><a href="#dss_setvector">"llvm/ADT/SetVector.h"</a></li>
				76	<li><a href="#dss_uniquevector">"llvm/ADT/UniqueVector.h"</a></li>
				77	<li><a href="#dss_otherset">Other Set-Like ContainerOptions</a></li>
				78	</ul></li>
				79	<li><a href="#ds_map">Map-Like Containers (std::map, DenseMap, etc)</a>
				80	<ul>
				81	<li><a href="#dss_sortedvectormap">A sorted 'vector'</a></li>
				82	<li><a href="#dss_stringmap">"llvm/ADT/StringMap.h"</a></li>
				83	<li><a href="#dss_indexedmap">"llvm/ADT/IndexedMap.h"</a></li>
				84	<li><a href="#dss_densemap">"llvm/ADT/DenseMap.h"</a></li>
				85	<li><a href="#dss_map"><map></a></li>
				86	<li><a href="#dss_othermap">Other Map-Like Container Options</a></li>
				87	</ul></li>
Chris Lattner	d8b95b7	2009-07-25 07:22:20 +0000	[diff] [blame^]	88	<li><a href="#ds_string">String-like containers</a>
				89	<ul>
				90	<!-- todo -->
				91	</ul></li>
Daniel Berlin	7ea44dc	2007-09-24 17:52:25 +0000	[diff] [blame]	92	<li><a href="#ds_bit">BitVector-like containers</a>
				93	<ul>
				94	<li><a href="#dss_bitvector">A dense bitvector</a></li>
				95	<li><a href="#dss_sparsebitvector">A sparse bitvector</a></li>
				96	</ul></li>
Dan Gohman	f17a25c	2007-07-18 16:29:46 +0000	[diff] [blame]	97	</ul>
				98	</li>
				99	<li><a href="#common">Helpful Hints for Common Operations</a>
				100	<ul>
				101	<li><a href="#inspection">Basic Inspection and Traversal Routines</a>
				102	<ul>
				103	<li><a href="#iterate_function">Iterating over the <tt>BasicBlock</tt>s
				104	in a <tt>Function</tt></a> </li>
				105	<li><a href="#iterate_basicblock">Iterating over the <tt>Instruction</tt>s
				106	in a <tt>BasicBlock</tt></a> </li>
				107	<li><a href="#iterate_institer">Iterating over the <tt>Instruction</tt>s
				108	in a <tt>Function</tt></a> </li>
				109	<li><a href="#iterate_convert">Turning an iterator into a
				110	class pointer</a> </li>
				111	<li><a href="#iterate_complex">Finding call sites: a more
				112	complex example</a> </li>
				113	<li><a href="#calls_and_invokes">Treating calls and invokes
				114	the same way</a> </li>
				115	<li><a href="#iterate_chains">Iterating over def-use &
				116	use-def chains</a> </li>
Chris Lattner	0665e1f	2008-01-03 16:56:04 +0000	[diff] [blame]	117	<li><a href="#iterate_preds">Iterating over predecessors &
				118	successors of blocks</a></li>
Dan Gohman	f17a25c	2007-07-18 16:29:46 +0000	[diff] [blame]	119	</ul>
				120	</li>
				121	<li><a href="#simplechanges">Making simple changes</a>
				122	<ul>
				123	<li><a href="#schanges_creating">Creating and inserting new
				124	<tt>Instruction</tt>s</a> </li>
				125	<li><a href="#schanges_deleting">Deleting <tt>Instruction</tt>s</a> </li>
				126	<li><a href="#schanges_replacing">Replacing an <tt>Instruction</tt>
				127	with another <tt>Value</tt></a> </li>
				128	<li><a href="#schanges_deletingGV">Deleting <tt>GlobalVariable</tt>s</a> </li>
				129	</ul>
				130	</li>
Jeffrey Yasskin	7ebb6ac	2009-04-30 22:33:41 +0000	[diff] [blame]	131	<li><a href="#create_types">How to Create Types</a></li>
Dan Gohman	f17a25c	2007-07-18 16:29:46 +0000	[diff] [blame]	132	<!--
				133	<li>Working with the Control Flow Graph
				134	<ul>
				135	<li>Accessing predecessors and successors of a <tt>BasicBlock</tt>
				136	<li>
				137	<li>
				138	</ul>
				139	-->
				140	</ul>
				141	</li>
				142
Owen Anderson	e8370c0	2009-06-16 01:17:16 +0000	[diff] [blame]	143	<li><a href="#threading">Threads and LLVM</a>
				144	<ul>
Owen Anderson	b418690	2009-06-16 18:04:19 +0000	[diff] [blame]	145	<li><a href="#startmultithreaded">Entering and Exiting Multithreaded Mode
				146	</a></li>
Owen Anderson	e8370c0	2009-06-16 01:17:16 +0000	[diff] [blame]	147	<li><a href="#shutdown">Ending execution with <tt>llvm_shutdown()</tt></a></li>
				148	<li><a href="#managedstatic">Lazy initialization with <tt>ManagedStatic</tt></a></li>
				149	</ul>
				150	</li>
				151
Dan Gohman	f17a25c	2007-07-18 16:29:46 +0000	[diff] [blame]	152	<li><a href="#advanced">Advanced Topics</a>
				153	<ul>
				154	<li><a href="#TypeResolve">LLVM Type Resolution</a>
				155	<ul>
				156	<li><a href="#BuildRecType">Basic Recursive Type Construction</a></li>
				157	<li><a href="#refineAbstractTypeTo">The <tt>refineAbstractTypeTo</tt> method</a></li>
				158	<li><a href="#PATypeHolder">The PATypeHolder Class</a></li>
				159	<li><a href="#AbstractTypeUser">The AbstractTypeUser Class</a></li>
				160	</ul></li>
				161
Gabor Greif	92e8776	2008-06-16 21:06:12 +0000	[diff] [blame]	162	<li><a href="#SymbolTable">The <tt>ValueSymbolTable</tt> and <tt>TypeSymbolTable</tt> classes</a></li>
				163	<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]	164	</ul></li>
				165
				166	<li><a href="#coreclasses">The Core LLVM Class Hierarchy Reference</a>
				167	<ul>
				168	<li><a href="#Type">The <tt>Type</tt> class</a> </li>
				169	<li><a href="#Module">The <tt>Module</tt> class</a></li>
				170	<li><a href="#Value">The <tt>Value</tt> class</a>
				171	<ul>
				172	<li><a href="#User">The <tt>User</tt> class</a>
				173	<ul>
				174	<li><a href="#Instruction">The <tt>Instruction</tt> class</a></li>
				175	<li><a href="#Constant">The <tt>Constant</tt> class</a>
				176	<ul>
				177	<li><a href="#GlobalValue">The <tt>GlobalValue</tt> class</a>
				178	<ul>
				179	<li><a href="#Function">The <tt>Function</tt> class</a></li>
				180	<li><a href="#GlobalVariable">The <tt>GlobalVariable</tt> class</a></li>
				181	</ul>
				182	</li>
				183	</ul>
				184	</li>
				185	</ul>
				186	</li>
				187	<li><a href="#BasicBlock">The <tt>BasicBlock</tt> class</a></li>
				188	<li><a href="#Argument">The <tt>Argument</tt> class</a></li>
				189	</ul>
				190	</li>
				191	</ul>
				192	</li>
				193	</ol>
				194
				195	<div class="doc_author">
				196	<p>Written by <a href="mailto:sabre@nondot.org">Chris Lattner</a>,
				197	<a href="mailto:dhurjati@cs.uiuc.edu">Dinakar Dhurjati</a>,
Gabor Greif	92e8776	2008-06-16 21:06:12 +0000	[diff] [blame]	198	<a href="mailto:ggreif@gmail.com">Gabor Greif</a>,
Owen Anderson	e8370c0	2009-06-16 01:17:16 +0000	[diff] [blame]	199	<a href="mailto:jstanley@cs.uiuc.edu">Joel Stanley</a>,
				200	<a href="mailto:rspencer@x10sys.com">Reid Spencer</a> and
				201	<a href="mailto:owen@apple.com">Owen Anderson</a></p>
Dan Gohman	f17a25c	2007-07-18 16:29:46 +0000	[diff] [blame]	202	</div>
				203
				204	<!-- *********************************************************************** -->
				205	<div class="doc_section">
				206	<a name="introduction">Introduction </a>
				207	</div>
				208	<!-- *********************************************************************** -->
				209
				210	<div class="doc_text">
				211
				212	<p>This document is meant to highlight some of the important classes and
				213	interfaces available in the LLVM source-base. This manual is not
				214	intended to explain what LLVM is, how it works, and what LLVM code looks
				215	like. It assumes that you know the basics of LLVM and are interested
				216	in writing transformations or otherwise analyzing or manipulating the
				217	code.</p>
				218
				219	<p>This document should get you oriented so that you can find your
				220	way in the continuously growing source code that makes up the LLVM
				221	infrastructure. Note that this manual is not intended to serve as a
				222	replacement for reading the source code, so if you think there should be
				223	a method in one of these classes to do something, but it's not listed,
				224	check the source. Links to the <a href="/doxygen/">doxygen</a> sources
				225	are provided to make this as easy as possible.</p>
				226
				227	<p>The first section of this document describes general information that is
				228	useful to know when working in the LLVM infrastructure, and the second describes
				229	the Core LLVM classes. In the future this manual will be extended with
				230	information describing how to use extension libraries, such as dominator
				231	information, CFG traversal routines, and useful utilities like the <tt><a
				232	href="/doxygen/InstVisitor_8h-source.html">InstVisitor</a></tt> template.</p>
				233
				234	</div>
				235
				236	<!-- *********************************************************************** -->
				237	<div class="doc_section">
				238	<a name="general">General Information</a>
				239	</div>
				240	<!-- *********************************************************************** -->
				241
				242	<div class="doc_text">
				243
				244	<p>This section contains general information that is useful if you are working
				245	in the LLVM source-base, but that isn't specific to any particular API.</p>
				246
				247	</div>
				248
				249	<!-- ======================================================================= -->
				250	<div class="doc_subsection">
				251	<a name="stl">The C++ Standard Template Library</a>
				252	</div>
				253
				254	<div class="doc_text">
				255
				256	<p>LLVM makes heavy use of the C++ Standard Template Library (STL),
				257	perhaps much more than you are used to, or have seen before. Because of
				258	this, you might want to do a little background reading in the
				259	techniques used and capabilities of the library. There are many good
				260	pages that discuss the STL, and several books on the subject that you
				261	can get, so it will not be discussed in this document.</p>
				262
				263	<p>Here are some useful links:</p>
				264
				265	<ol>
				266
				267	<li><a href="http://www.dinkumware.com/refxcpp.html">Dinkumware C++ Library
				268	reference</a> - an excellent reference for the STL and other parts of the
				269	standard C++ library.</li>
				270
				271	<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]	272	O'Reilly book in the making. It has a decent Standard Library
				273	Reference that rivals Dinkumware's, and is unfortunately no longer free since the
				274	book has been published.</li>
Dan Gohman	f17a25c	2007-07-18 16:29:46 +0000	[diff] [blame]	275
				276	<li><a href="http://www.parashift.com/c++-faq-lite/">C++ Frequently Asked
				277	Questions</a></li>
				278
				279	<li><a href="http://www.sgi.com/tech/stl/">SGI's STL Programmer's Guide</a> -
				280	Contains a useful <a
				281	href="http://www.sgi.com/tech/stl/stl_introduction.html">Introduction to the
				282	STL</a>.</li>
				283
				284	<li><a href="http://www.research.att.com/%7Ebs/C++.html">Bjarne Stroustrup's C++
				285	Page</a></li>
				286
				287	<li><a href="http://64.78.49.204/">
				288	Bruce Eckel's Thinking in C++, 2nd ed. Volume 2 Revision 4.0 (even better, get
				289	the book).</a></li>
				290
				291	</ol>
				292
				293	<p>You are also encouraged to take a look at the <a
				294	href="CodingStandards.html">LLVM Coding Standards</a> guide which focuses on how
				295	to write maintainable code more than where to put your curly braces.</p>
				296
				297	</div>
				298
				299	<!-- ======================================================================= -->
				300	<div class="doc_subsection">
				301	<a name="stl">Other useful references</a>
				302	</div>
				303
				304	<div class="doc_text">
				305
				306	<ol>
				307	<li><a href="http://www.psc.edu/%7Esemke/cvs_branches.html">CVS
				308	Branch and Tag Primer</a></li>
				309	<li><a href="http://www.fortran-2000.com/ArnaudRecipes/sharedlib.html">Using
				310	static and shared libraries across platforms</a></li>
				311	</ol>
				312
				313	</div>
				314
				315	<!-- *********************************************************************** -->
				316	<div class="doc_section">
				317	<a name="apis">Important and useful LLVM APIs</a>
				318	</div>
				319	<!-- *********************************************************************** -->
				320
				321	<div class="doc_text">
				322
				323	<p>Here we highlight some LLVM APIs that are generally useful and good to
				324	know about when writing transformations.</p>
				325
				326	</div>
				327
				328	<!-- ======================================================================= -->
				329	<div class="doc_subsection">
				330	<a name="isa">The <tt>isa<></tt>, <tt>cast<></tt> and
				331	<tt>dyn_cast<></tt> templates</a>
				332	</div>
				333
				334	<div class="doc_text">
				335
				336	<p>The LLVM source-base makes extensive use of a custom form of RTTI.
				337	These templates have many similarities to the C++ <tt>dynamic_cast<></tt>
				338	operator, but they don't have some drawbacks (primarily stemming from
				339	the fact that <tt>dynamic_cast<></tt> only works on classes that
				340	have a v-table). Because they are used so often, you must know what they
				341	do and how they work. All of these templates are defined in the <a
				342	href="/doxygen/Casting_8h-source.html"><tt>llvm/Support/Casting.h</tt></a>
				343	file (note that you very rarely have to include this file directly).</p>
				344
				345	<dl>
				346	<dt><tt>isa<></tt>: </dt>
				347
				348	<dd><p>The <tt>isa<></tt> operator works exactly like the Java
				349	"<tt>instanceof</tt>" operator. It returns true or false depending on whether
				350	a reference or pointer points to an instance of the specified class. This can
				351	be very useful for constraint checking of various sorts (example below).</p>
				352	</dd>
				353
				354	<dt><tt>cast<></tt>: </dt>
				355
				356	<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]	357	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]	358	an assertion failure if it is not really an instance of the right type. This
				359	should be used in cases where you have some information that makes you believe
				360	that something is of the right type. An example of the <tt>isa<></tt>
				361	and <tt>cast<></tt> template is:</p>
				362
				363	<div class="doc_code">
				364	<pre>
				365	static bool isLoopInvariant(const <a href="#Value">Value</a> V, const Loop L) {
				366	if (isa<<a href="#Constant">Constant</a>>(V) \|\| isa<<a href="#Argument">Argument</a>>(V) \|\| isa<<a href="#GlobalValue">GlobalValue</a>>(V))
				367	return true;
				368
				369	// <i>Otherwise, it must be an instruction...</i>
				370	return !L->contains(cast<<a href="#Instruction">Instruction</a>>(V)->getParent());
				371	}
				372	</pre>
				373	</div>
				374
				375	<p>Note that you should <b>not</b> use an <tt>isa<></tt> test followed
				376	by a <tt>cast<></tt>, for that use the <tt>dyn_cast<></tt>
				377	operator.</p>
				378
				379	</dd>
				380
				381	<dt><tt>dyn_cast<></tt>:</dt>
				382
				383	<dd><p>The <tt>dyn_cast<></tt> operator is a "checking cast" operation.
				384	It checks to see if the operand is of the specified type, and if so, returns a
				385	pointer to it (this operator does not work with references). If the operand is
				386	not of the correct type, a null pointer is returned. Thus, this works very
				387	much like the <tt>dynamic_cast<></tt> operator in C++, and should be
				388	used in the same circumstances. Typically, the <tt>dyn_cast<></tt>
				389	operator is used in an <tt>if</tt> statement or some other flow control
				390	statement like this:</p>
				391
				392	<div class="doc_code">
				393	<pre>
				394	if (<a href="#AllocationInst">AllocationInst</a> *AI = dyn_cast<<a href="#AllocationInst">AllocationInst</a>>(Val)) {
				395	// <i>...</i>
				396	}
				397	</pre>
				398	</div>
				399
				400	<p>This form of the <tt>if</tt> statement effectively combines together a call
				401	to <tt>isa<></tt> and a call to <tt>cast<></tt> into one
				402	statement, which is very convenient.</p>
				403
				404	<p>Note that the <tt>dyn_cast<></tt> operator, like C++'s
				405	<tt>dynamic_cast<></tt> or Java's <tt>instanceof</tt> operator, can be
				406	abused. In particular, you should not use big chained <tt>if/then/else</tt>
				407	blocks to check for lots of different variants of classes. If you find
				408	yourself wanting to do this, it is much cleaner and more efficient to use the
				409	<tt>InstVisitor</tt> class to dispatch over the instruction type directly.</p>
				410
				411	</dd>
				412
				413	<dt><tt>cast_or_null<></tt>: </dt>
				414
				415	<dd><p>The <tt>cast_or_null<></tt> operator works just like the
				416	<tt>cast<></tt> operator, except that it allows for a null pointer as an
				417	argument (which it then propagates). This can sometimes be useful, allowing
				418	you to combine several null checks into one.</p></dd>
				419
				420	<dt><tt>dyn_cast_or_null<></tt>: </dt>
				421
				422	<dd><p>The <tt>dyn_cast_or_null<></tt> operator works just like the
				423	<tt>dyn_cast<></tt> operator, except that it allows for a null pointer
				424	as an argument (which it then propagates). This can sometimes be useful,
				425	allowing you to combine several null checks into one.</p></dd>
				426
				427	</dl>
				428
				429	<p>These five templates can be used with any classes, whether they have a
				430	v-table or not. To add support for these templates, you simply need to add
				431	<tt>classof</tt> static methods to the class you are interested casting
				432	to. Describing this is currently outside the scope of this document, but there
				433	are lots of examples in the LLVM source base.</p>
				434
				435	</div>
				436
Daniel Dunbar	e3572ba	2009-07-25 04:41:11 +0000	[diff] [blame]	437
				438	<!-- ======================================================================= -->
				439	<div class="doc_subsection">
				440	<a name="string_apis">Passing strings (the <tt>StringRef</tt>
				441	and <tt>Twine</tt> classes)</a>
				442	</div>
				443
				444	<div class="doc_text">
				445
				446	<p>Although LLVM generally does not do much string manipulation, we do have
Chris Lattner	c00114f	2009-07-25 07:16:59 +0000	[diff] [blame]	447	several important APIs which take strings. Two important examples are the
Daniel Dunbar	e3572ba	2009-07-25 04:41:11 +0000	[diff] [blame]	448	Value class -- which has names for instructions, functions, etc. -- and the
				449	StringMap class which is used extensively in LLVM and Clang.</p>
				450
				451	<p>These are generic classes, and they need to be able to accept strings which
				452	may have embedded null characters. Therefore, they cannot simply take
Chris Lattner	c00114f	2009-07-25 07:16:59 +0000	[diff] [blame]	453	a <tt>const char *</tt>, and taking a <tt>const std::string&</tt> requires
Daniel Dunbar	e3572ba	2009-07-25 04:41:11 +0000	[diff] [blame]	454	clients to perform a heap allocation which is usually unnecessary. Instead,
Chris Lattner	c00114f	2009-07-25 07:16:59 +0000	[diff] [blame]	455	many LLVM APIs use a <tt>const StringRef&</tt> or a <tt>const
				456	Twine&</tt> for passing strings efficiently.</p>
Daniel Dunbar	e3572ba	2009-07-25 04:41:11 +0000	[diff] [blame]	457
				458	</div>
				459
				460	<!-- _______________________________________________________________________ -->
				461	<div class="doc_subsubsection">
				462	<a name="StringRef">The <tt>StringRef</tt> class</a>
				463	</div>
				464
				465	<div class="doc_text">
				466
				467	<p>The <tt>StringRef</tt> data type represents a reference to a constant string
				468	(a character array and a length) and supports the common operations available
				469	on <tt>std:string</tt>, but does not require heap allocation.</p>
				470
Chris Lattner	c00114f	2009-07-25 07:16:59 +0000	[diff] [blame]	471	<p>It can be implicitly constructed using a C style null-terminated string,
				472	an <tt>std::string</tt>, or explicitly with a character pointer and length.
Daniel Dunbar	e3572ba	2009-07-25 04:41:11 +0000	[diff] [blame]	473	For example, the <tt>StringRef</tt> find function is declared as:</p>
Chris Lattner	c00114f	2009-07-25 07:16:59 +0000	[diff] [blame]	474
Daniel Dunbar	e3572ba	2009-07-25 04:41:11 +0000	[diff] [blame]	475	<div class="doc_code">
Chris Lattner	c00114f	2009-07-25 07:16:59 +0000	[diff] [blame]	476	iterator find(const StringRef &Key);
Daniel Dunbar	e3572ba	2009-07-25 04:41:11 +0000	[diff] [blame]	477	</div>
				478
				479	<p>and clients can call it using any one of:</p>
				480
				481	<div class="doc_code">
				482	<pre>
				483	Map.find("foo"); <i>// Lookup "foo"</i>
				484	Map.find(std::string("bar")); <i>// Lookup "bar"</i>
				485	Map.find(StringRef("\0baz", 4)); <i>// Lookup "\0baz"</i>
				486	</pre>
				487	</div>
				488
				489	<p>Similarly, APIs which need to return a string may return a <tt>StringRef</tt>
				490	instance, which can be used directly or converted to an <tt>std::string</tt>
				491	using the <tt>str</tt> member function. See
				492	"<tt><a href="/doxygen/classllvm_1_1StringRef_8h-source.html">llvm/ADT/StringRef.h</a></tt>"
				493	for more information.</p>
				494
				495	<p>You should rarely use the <tt>StringRef</tt> class directly, because it contains
				496	pointers to external memory it is not generally safe to store an instance of the
Chris Lattner	c00114f	2009-07-25 07:16:59 +0000	[diff] [blame]	497	class (unless you know that the external storage will not be freed).</p>
Daniel Dunbar	e3572ba	2009-07-25 04:41:11 +0000	[diff] [blame]	498
				499	</div>
				500
				501	<!-- _______________________________________________________________________ -->
				502	<div class="doc_subsubsection">
				503	<a name="Twine">The <tt>Twine</tt> class</a>
				504	</div>
				505
				506	<div class="doc_text">
				507
				508	<p>The <tt>Twine</tt> class is an efficient way for APIs to accept concatenated
				509	strings. For example, a common LLVM paradigm is to name one instruction based on
				510	the name of another instruction with a suffix, for example:</p>
				511
				512	<div class="doc_code">
				513	<pre>
				514	New = CmpInst::Create(<i>...</i>, SO->getName() + ".cmp");
				515	</pre>
				516	</div>
				517
				518	<p>The <tt>Twine</tt> class is effectively a
				519	lightweight <a href="http://en.wikipedia.org/wiki/Rope_(computer_science)">rope</a>
				520	which points to temporary (stack allocated) objects. Twines can be implicitly
				521	constructed as the result of the plus operator applied to strings (i.e., a C
				522	strings, an <tt>std::string</tt>, or a <tt>StringRef</tt>). The twine delays the
				523	actual concatentation of strings until it is actually required, at which point
				524	it can be efficiently rendered directly into a character array. This avoids
				525	unnecessary heap allocation involved in constructing the temporary results of
				526	string concatenation. See
				527	"<tt><a href="/doxygen/classllvm_1_1Twine_8h-source.html">llvm/ADT/Twine.h</a></tt>"
				528	for more information.</p></tt>
				529
				530	<p>As with a <tt>StringRef</tt>, <tt>Twine</tt> objects point to external memory
				531	and should almost never be stored or mentioned directly. They are intended
				532	solely for use when defining a function which should be able to efficiently
				533	accept concatenated strings.</p>
				534
				535	</div>
				536
				537
Dan Gohman	f17a25c	2007-07-18 16:29:46 +0000	[diff] [blame]	538	<!-- ======================================================================= -->
				539	<div class="doc_subsection">
				540	<a name="DEBUG">The <tt>DEBUG()</tt> macro and <tt>-debug</tt> option</a>
				541	</div>
				542
				543	<div class="doc_text">
				544
				545	<p>Often when working on your pass you will put a bunch of debugging printouts
				546	and other code into your pass. After you get it working, you want to remove
				547	it, but you may need it again in the future (to work out new bugs that you run
				548	across).</p>
				549
				550	<p> Naturally, because of this, you don't want to delete the debug printouts,
				551	but you don't want them to always be noisy. A standard compromise is to comment
				552	them out, allowing you to enable them if you need them in the future.</p>
				553
				554	<p>The "<tt><a href="/doxygen/Debug_8h-source.html">llvm/Support/Debug.h</a></tt>"
				555	file provides a macro named <tt>DEBUG()</tt> that is a much nicer solution to
				556	this problem. Basically, you can put arbitrary code into the argument of the
				557	<tt>DEBUG</tt> macro, and it is only executed if '<tt>opt</tt>' (or any other
				558	tool) is run with the '<tt>-debug</tt>' command line argument:</p>
				559
				560	<div class="doc_code">
				561	<pre>
Daniel Dunbar	e32f9b2	2009-07-25 01:55:32 +0000	[diff] [blame]	562	DEBUG(errs() << "I am here!\n");
Dan Gohman	f17a25c	2007-07-18 16:29:46 +0000	[diff] [blame]	563	</pre>
				564	</div>
				565
				566	<p>Then you can run your pass like this:</p>
				567
				568	<div class="doc_code">
				569	<pre>
				570	$ opt < a.bc > /dev/null -mypass
				571	<i><no output></i>
				572	$ opt < a.bc > /dev/null -mypass -debug
				573	I am here!
				574	</pre>
				575	</div>
				576
				577	<p>Using the <tt>DEBUG()</tt> macro instead of a home-brewed solution allows you
				578	to not have to create "yet another" command line option for the debug output for
				579	your pass. Note that <tt>DEBUG()</tt> macros are disabled for optimized builds,
				580	so they do not cause a performance impact at all (for the same reason, they
				581	should also not contain side-effects!).</p>
				582
				583	<p>One additional nice thing about the <tt>DEBUG()</tt> macro is that you can
				584	enable or disable it directly in gdb. Just use "<tt>set DebugFlag=0</tt>" or
				585	"<tt>set DebugFlag=1</tt>" from the gdb if the program is running. If the
				586	program hasn't been started yet, you can always just run it with
				587	<tt>-debug</tt>.</p>
				588
				589	</div>
				590
				591	<!-- _______________________________________________________________________ -->
				592	<div class="doc_subsubsection">
				593	<a name="DEBUG_TYPE">Fine grained debug info with <tt>DEBUG_TYPE</tt> and
				594	the <tt>-debug-only</tt> option</a>
				595	</div>
				596
				597	<div class="doc_text">
				598
				599	<p>Sometimes you may find yourself in a situation where enabling <tt>-debug</tt>
				600	just turns on <b>too much</b> information (such as when working on the code
				601	generator). If you want to enable debug information with more fine-grained
				602	control, you define the <tt>DEBUG_TYPE</tt> macro and the <tt>-debug</tt> only
				603	option as follows:</p>
				604
				605	<div class="doc_code">
				606	<pre>
Dan Gohman	f17a25c	2007-07-18 16:29:46 +0000	[diff] [blame]	607	#undef DEBUG_TYPE
Daniel Dunbar	e32f9b2	2009-07-25 01:55:32 +0000	[diff] [blame]	608	DEBUG(errs() << "No debug type\n");
Dan Gohman	f17a25c	2007-07-18 16:29:46 +0000	[diff] [blame]	609	#define DEBUG_TYPE "foo"
Daniel Dunbar	e32f9b2	2009-07-25 01:55:32 +0000	[diff] [blame]	610	DEBUG(errs() << "'foo' debug type\n");
Dan Gohman	f17a25c	2007-07-18 16:29:46 +0000	[diff] [blame]	611	#undef DEBUG_TYPE
				612	#define DEBUG_TYPE "bar"
Daniel Dunbar	e32f9b2	2009-07-25 01:55:32 +0000	[diff] [blame]	613	DEBUG(errs() << "'bar' debug type\n"));
Dan Gohman	f17a25c	2007-07-18 16:29:46 +0000	[diff] [blame]	614	#undef DEBUG_TYPE
				615	#define DEBUG_TYPE ""
Daniel Dunbar	e32f9b2	2009-07-25 01:55:32 +0000	[diff] [blame]	616	DEBUG(errs() << "No debug type (2)\n");
Dan Gohman	f17a25c	2007-07-18 16:29:46 +0000	[diff] [blame]	617	</pre>
				618	</div>
				619
				620	<p>Then you can run your pass like this:</p>
				621
				622	<div class="doc_code">
				623	<pre>
				624	$ opt < a.bc > /dev/null -mypass
				625	<i><no output></i>
				626	$ opt < a.bc > /dev/null -mypass -debug
				627	No debug type
				628	'foo' debug type
				629	'bar' debug type
				630	No debug type (2)
				631	$ opt < a.bc > /dev/null -mypass -debug-only=foo
				632	'foo' debug type
				633	$ opt < a.bc > /dev/null -mypass -debug-only=bar
				634	'bar' debug type
				635	</pre>
				636	</div>
				637
				638	<p>Of course, in practice, you should only set <tt>DEBUG_TYPE</tt> at the top of
				639	a file, to specify the debug type for the entire module (if you do this before
				640	you <tt>#include "llvm/Support/Debug.h"</tt>, you don't have to insert the ugly
				641	<tt>#undef</tt>'s). Also, you should use names more meaningful than "foo" and
				642	"bar", because there is no system in place to ensure that names do not
				643	conflict. If two different modules use the same string, they will all be turned
				644	on when the name is specified. This allows, for example, all debug information
				645	for instruction scheduling to be enabled with <tt>-debug-type=InstrSched</tt>,
				646	even if the source lives in multiple files.</p>
				647
				648	</div>
				649
				650	<!-- ======================================================================= -->
				651	<div class="doc_subsection">
				652	<a name="Statistic">The <tt>Statistic</tt> class & <tt>-stats</tt>
				653	option</a>
				654	</div>
				655
				656	<div class="doc_text">
				657
				658	<p>The "<tt><a
				659	href="/doxygen/Statistic_8h-source.html">llvm/ADT/Statistic.h</a></tt>" file
				660	provides a class named <tt>Statistic</tt> that is used as a unified way to
				661	keep track of what the LLVM compiler is doing and how effective various
				662	optimizations are. It is useful to see what optimizations are contributing to
				663	making a particular program run faster.</p>
				664
				665	<p>Often you may run your pass on some big program, and you're interested to see
				666	how many times it makes a certain transformation. Although you can do this with
				667	hand inspection, or some ad-hoc method, this is a real pain and not very useful
				668	for big programs. Using the <tt>Statistic</tt> class makes it very easy to
				669	keep track of this information, and the calculated information is presented in a
				670	uniform manner with the rest of the passes being executed.</p>
				671
				672	<p>There are many examples of <tt>Statistic</tt> uses, but the basics of using
				673	it are as follows:</p>
				674
				675	<ol>
				676	<li><p>Define your statistic like this:</p>
				677
				678	<div class="doc_code">
				679	<pre>
				680	#define <a href="#DEBUG_TYPE">DEBUG_TYPE</a> "mypassname" <i>// This goes before any #includes.</i>
				681	STATISTIC(NumXForms, "The # of times I did stuff");
				682	</pre>
				683	</div>
				684
				685	<p>The <tt>STATISTIC</tt> macro defines a static variable, whose name is
				686	specified by the first argument. The pass name is taken from the DEBUG_TYPE
				687	macro, and the description is taken from the second argument. The variable
				688	defined ("NumXForms" in this case) acts like an unsigned integer.</p></li>
				689
				690	<li><p>Whenever you make a transformation, bump the counter:</p>
				691
				692	<div class="doc_code">
				693	<pre>
				694	++NumXForms; // <i>I did stuff!</i>
				695	</pre>
				696	</div>
				697
				698	</li>
				699	</ol>
				700
				701	<p>That's all you have to do. To get '<tt>opt</tt>' to print out the
				702	statistics gathered, use the '<tt>-stats</tt>' option:</p>
				703
				704	<div class="doc_code">
				705	<pre>
				706	$ opt -stats -mypassname < program.bc > /dev/null
				707	<i>... statistics output ...</i>
				708	</pre>
				709	</div>
				710
				711	<p> When running <tt>opt</tt> on a C file from the SPEC benchmark
				712	suite, it gives a report that looks like this:</p>
				713
				714	<div class="doc_code">
				715	<pre>
				716	7646 bitcodewriter - Number of normal instructions
				717	725 bitcodewriter - Number of oversized instructions
				718	129996 bitcodewriter - Number of bitcode bytes written
				719	2817 raise - Number of insts DCEd or constprop'd
				720	3213 raise - Number of cast-of-self removed
				721	5046 raise - Number of expression trees converted
				722	75 raise - Number of other getelementptr's formed
				723	138 raise - Number of load/store peepholes
				724	42 deadtypeelim - Number of unused typenames removed from symtab
				725	392 funcresolve - Number of varargs functions resolved
				726	27 globaldce - Number of global variables removed
				727	2 adce - Number of basic blocks removed
				728	134 cee - Number of branches revectored
				729	49 cee - Number of setcc instruction eliminated
				730	532 gcse - Number of loads removed
				731	2919 gcse - Number of instructions removed
				732	86 indvars - Number of canonical indvars added
				733	87 indvars - Number of aux indvars removed
				734	25 instcombine - Number of dead inst eliminate
				735	434 instcombine - Number of insts combined
				736	248 licm - Number of load insts hoisted
				737	1298 licm - Number of insts hoisted to a loop pre-header
				738	3 licm - Number of insts hoisted to multiple loop preds (bad, no loop pre-header)
				739	75 mem2reg - Number of alloca's promoted
				740	1444 cfgsimplify - Number of blocks simplified
				741	</pre>
				742	</div>
				743
				744	<p>Obviously, with so many optimizations, having a unified framework for this
				745	stuff is very nice. Making your pass fit well into the framework makes it more
				746	maintainable and useful.</p>
				747
				748	</div>
				749
				750	<!-- ======================================================================= -->
				751	<div class="doc_subsection">
				752	<a name="ViewGraph">Viewing graphs while debugging code</a>
				753	</div>
				754
				755	<div class="doc_text">
				756
				757	<p>Several of the important data structures in LLVM are graphs: for example
				758	CFGs made out of LLVM <a href="#BasicBlock">BasicBlock</a>s, CFGs made out of
				759	LLVM <a href="CodeGenerator.html#machinebasicblock">MachineBasicBlock</a>s, and
				760	<a href="CodeGenerator.html#selectiondag_intro">Instruction Selection
				761	DAGs</a>. In many cases, while debugging various parts of the compiler, it is
				762	nice to instantly visualize these graphs.</p>
				763
				764	<p>LLVM provides several callbacks that are available in a debug build to do
				765	exactly that. If you call the <tt>Function::viewCFG()</tt> method, for example,
				766	the current LLVM tool will pop up a window containing the CFG for the function
				767	where each basic block is a node in the graph, and each node contains the
				768	instructions in the block. Similarly, there also exists
				769	<tt>Function::viewCFGOnly()</tt> (does not include the instructions), the
				770	<tt>MachineFunction::viewCFG()</tt> and <tt>MachineFunction::viewCFGOnly()</tt>,
				771	and the <tt>SelectionDAG::viewGraph()</tt> methods. Within GDB, for example,
				772	you can usually use something like <tt>call DAG.viewGraph()</tt> to pop
				773	up a window. Alternatively, you can sprinkle calls to these functions in your
				774	code in places you want to debug.</p>
				775
				776	<p>Getting this to work requires a small amount of configuration. On Unix
				777	systems with X11, install the <a href="http://www.graphviz.org">graphviz</a>
				778	toolkit, and make sure 'dot' and 'gv' are in your path. If you are running on
				779	Mac OS/X, download and install the Mac OS/X <a
				780	href="http://www.pixelglow.com/graphviz/">Graphviz program</a>, and add
				781	<tt>/Applications/Graphviz.app/Contents/MacOS/</tt> (or wherever you install
				782	it) to your path. Once in your system and path are set up, rerun the LLVM
				783	configure script and rebuild LLVM to enable this functionality.</p>
				784
				785	<p><tt>SelectionDAG</tt> has been extended to make it easier to locate
				786	<i>interesting</i> nodes in large complex graphs. From gdb, if you
				787	<tt>call DAG.setGraphColor(<i>node</i>, "<i>color</i>")</tt>, then the
				788	next <tt>call DAG.viewGraph()</tt> would highlight the node in the
				789	specified color (choices of colors can be found at <a
				790	href="http://www.graphviz.org/doc/info/colors.html">colors</a>.) More
				791	complex node attributes can be provided with <tt>call
				792	DAG.setGraphAttrs(<i>node</i>, "<i>attributes</i>")</tt> (choices can be
				793	found at <a href="http://www.graphviz.org/doc/info/attrs.html">Graph
				794	Attributes</a>.) If you want to restart and clear all the current graph
				795	attributes, then you can <tt>call DAG.clearGraphAttrs()</tt>. </p>
				796
				797	</div>
				798
				799	<!-- *********************************************************************** -->
				800	<div class="doc_section">
				801	<a name="datastructure">Picking the Right Data Structure for a Task</a>
				802	</div>
				803	<!-- *********************************************************************** -->
				804
				805	<div class="doc_text">
				806
				807	<p>LLVM has a plethora of data structures in the <tt>llvm/ADT/</tt> directory,
				808	and we commonly use STL data structures. This section describes the trade-offs
				809	you should consider when you pick one.</p>
				810
				811	<p>
				812	The first step is a choose your own adventure: do you want a sequential
				813	container, a set-like container, or a map-like container? The most important
				814	thing when choosing a container is the algorithmic properties of how you plan to
				815	access the container. Based on that, you should use:</p>
				816
				817	<ul>
				818	<li>a <a href="#ds_map">map-like</a> container if you need efficient look-up
				819	of an value based on another value. Map-like containers also support
				820	efficient queries for containment (whether a key is in the map). Map-like
				821	containers generally do not support efficient reverse mapping (values to
				822	keys). If you need that, use two maps. Some map-like containers also
				823	support efficient iteration through the keys in sorted order. Map-like
				824	containers are the most expensive sort, only use them if you need one of
				825	these capabilities.</li>
				826
				827	<li>a <a href="#ds_set">set-like</a> container if you need to put a bunch of
				828	stuff into a container that automatically eliminates duplicates. Some
				829	set-like containers support efficient iteration through the elements in
				830	sorted order. Set-like containers are more expensive than sequential
				831	containers.
				832	</li>
				833
				834	<li>a <a href="#ds_sequential">sequential</a> container provides
				835	the most efficient way to add elements and keeps track of the order they are
				836	added to the collection. They permit duplicates and support efficient
				837	iteration, but do not support efficient look-up based on a key.
				838	</li>
				839
Chris Lattner	d8b95b7	2009-07-25 07:22:20 +0000	[diff] [blame^]	840	<li>a <a href="#ds_string">string</a> container is a specialized sequential
				841	container or reference structure that is used for character or byte
				842	arrays.</li>
				843
Daniel Berlin	7ea44dc	2007-09-24 17:52:25 +0000	[diff] [blame]	844	<li>a <a href="#ds_bit">bit</a> container provides an efficient way to store and
				845	perform set operations on sets of numeric id's, while automatically
				846	eliminating duplicates. Bit containers require a maximum of 1 bit for each
				847	identifier you want to store.
				848	</li>
Dan Gohman	f17a25c	2007-07-18 16:29:46 +0000	[diff] [blame]	849	</ul>
				850
				851	<p>
				852	Once the proper category of container is determined, you can fine tune the
				853	memory use, constant factors, and cache behaviors of access by intelligently
				854	picking a member of the category. Note that constant factors and cache behavior
				855	can be a big deal. If you have a vector that usually only contains a few
				856	elements (but could contain many), for example, it's much better to use
				857	<a href="#dss_smallvector">SmallVector</a> than <a href="#dss_vector">vector</a>
				858	. Doing so avoids (relatively) expensive malloc/free calls, which dwarf the
				859	cost of adding the elements to the container. </p>
				860
				861	</div>
				862
				863	<!-- ======================================================================= -->
				864	<div class="doc_subsection">
				865	<a name="ds_sequential">Sequential Containers (std::vector, std::list, etc)</a>
				866	</div>
				867
				868	<div class="doc_text">
				869	There are a variety of sequential containers available for you, based on your
				870	needs. Pick the first in this section that will do what you want.
				871	</div>
				872
				873	<!-- _______________________________________________________________________ -->
				874	<div class="doc_subsubsection">
				875	<a name="dss_fixedarrays">Fixed Size Arrays</a>
				876	</div>
				877
				878	<div class="doc_text">
				879	<p>Fixed size arrays are very simple and very fast. They are good if you know
				880	exactly how many elements you have, or you have a (low) upper bound on how many
				881	you have.</p>
				882	</div>
				883
				884	<!-- _______________________________________________________________________ -->
				885	<div class="doc_subsubsection">
				886	<a name="dss_heaparrays">Heap Allocated Arrays</a>
				887	</div>
				888
				889	<div class="doc_text">
				890	<p>Heap allocated arrays (new[] + delete[]) are also simple. They are good if
				891	the number of elements is variable, if you know how many elements you will need
				892	before the array is allocated, and if the array is usually large (if not,
				893	consider a <a href="#dss_smallvector">SmallVector</a>). The cost of a heap
				894	allocated array is the cost of the new/delete (aka malloc/free). Also note that
				895	if you are allocating an array of a type with a constructor, the constructor and
				896	destructors will be run for every element in the array (re-sizable vectors only
				897	construct those elements actually used).</p>
				898	</div>
				899
				900	<!-- _______________________________________________________________________ -->
				901	<div class="doc_subsubsection">
				902	<a name="dss_smallvector">"llvm/ADT/SmallVector.h"</a>
				903	</div>
				904
				905	<div class="doc_text">
				906	<p><tt>SmallVector<Type, N></tt> is a simple class that looks and smells
				907	just like <tt>vector<Type></tt>:
				908	it supports efficient iteration, lays out elements in memory order (so you can
				909	do pointer arithmetic between elements), supports efficient push_back/pop_back
				910	operations, supports efficient random access to its elements, etc.</p>
				911
				912	<p>The advantage of SmallVector is that it allocates space for
				913	some number of elements (N) <b>in the object itself</b>. Because of this, if
				914	the SmallVector is dynamically smaller than N, no malloc is performed. This can
				915	be a big win in cases where the malloc/free call is far more expensive than the
				916	code that fiddles around with the elements.</p>
				917
				918	<p>This is good for vectors that are "usually small" (e.g. the number of
				919	predecessors/successors of a block is usually less than 8). On the other hand,
				920	this makes the size of the SmallVector itself large, so you don't want to
				921	allocate lots of them (doing so will waste a lot of space). As such,
				922	SmallVectors are most useful when on the stack.</p>
				923
				924	<p>SmallVector also provides a nice portable and efficient replacement for
				925	<tt>alloca</tt>.</p>
				926
				927	</div>
				928
				929	<!-- _______________________________________________________________________ -->
				930	<div class="doc_subsubsection">
				931	<a name="dss_vector"><vector></a>
				932	</div>
				933
				934	<div class="doc_text">
				935	<p>
				936	std::vector is well loved and respected. It is useful when SmallVector isn't:
				937	when the size of the vector is often large (thus the small optimization will
				938	rarely be a benefit) or if you will be allocating many instances of the vector
				939	itself (which would waste space for elements that aren't in the container).
				940	vector is also useful when interfacing with code that expects vectors :).
				941	</p>
				942
				943	<p>One worthwhile note about std::vector: avoid code like this:</p>
				944
				945	<div class="doc_code">
				946	<pre>
				947	for ( ... ) {
				948	std::vector<foo> V;
				949	use V;
				950	}
				951	</pre>
				952	</div>
				953
				954	<p>Instead, write this as:</p>
				955
				956	<div class="doc_code">
				957	<pre>
				958	std::vector<foo> V;
				959	for ( ... ) {
				960	use V;
				961	V.clear();
				962	}
				963	</pre>
				964	</div>
				965
				966	<p>Doing so will save (at least) one heap allocation and free per iteration of
				967	the loop.</p>
				968
				969	</div>
				970
				971	<!-- _______________________________________________________________________ -->
				972	<div class="doc_subsubsection">
				973	<a name="dss_deque"><deque></a>
				974	</div>
				975
				976	<div class="doc_text">
				977	<p>std::deque is, in some senses, a generalized version of std::vector. Like
				978	std::vector, it provides constant time random access and other similar
				979	properties, but it also provides efficient access to the front of the list. It
				980	does not guarantee continuity of elements within memory.</p>
				981
				982	<p>In exchange for this extra flexibility, std::deque has significantly higher
				983	constant factor costs than std::vector. If possible, use std::vector or
				984	something cheaper.</p>
				985	</div>
				986
				987	<!-- _______________________________________________________________________ -->
				988	<div class="doc_subsubsection">
				989	<a name="dss_list"><list></a>
				990	</div>
				991
				992	<div class="doc_text">
				993	<p>std::list is an extremely inefficient class that is rarely useful.
				994	It performs a heap allocation for every element inserted into it, thus having an
				995	extremely high constant factor, particularly for small data types. std::list
				996	also only supports bidirectional iteration, not random access iteration.</p>
				997
				998	<p>In exchange for this high cost, std::list supports efficient access to both
				999	ends of the list (like std::deque, but unlike std::vector or SmallVector). In
				1000	addition, the iterator invalidation characteristics of std::list are stronger
				1001	than that of a vector class: inserting or removing an element into the list does
				1002	not invalidate iterator or pointers to other elements in the list.</p>
				1003	</div>
				1004
				1005	<!-- _______________________________________________________________________ -->
				1006	<div class="doc_subsubsection">
Gabor Greif	bb17f65	2009-02-27 11:37:41 +0000	[diff] [blame]	1007	<a name="dss_ilist">llvm/ADT/ilist.h</a>
Dan Gohman	f17a25c	2007-07-18 16:29:46 +0000	[diff] [blame]	1008	</div>
				1009
				1010	<div class="doc_text">
				1011	<p><tt>ilist<T></tt> implements an 'intrusive' doubly-linked list. It is
				1012	intrusive, because it requires the element to store and provide access to the
				1013	prev/next pointers for the list.</p>
				1014
Gabor Greif	b6b21ec	2009-02-27 12:02:19 +0000	[diff] [blame]	1015	<p><tt>ilist</tt> has the same drawbacks as <tt>std::list</tt>, and additionally
				1016	requires an <tt>ilist_traits</tt> implementation for the element type, but it
				1017	provides some novel characteristics. In particular, it can efficiently store
				1018	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]	1019	removed from the list, and <tt>ilist</tt>s are guaranteed to support a
				1020	constant-time splice operation.</p>
Dan Gohman	f17a25c	2007-07-18 16:29:46 +0000	[diff] [blame]	1021
Gabor Greif	e39f0e7	2009-03-12 09:47:03 +0000	[diff] [blame]	1022	<p>These properties are exactly what we want for things like
				1023	<tt>Instruction</tt>s and basic blocks, which is why these are implemented with
				1024	<tt>ilist</tt>s.</p>
Gabor Greif	bb17f65	2009-02-27 11:37:41 +0000	[diff] [blame]	1025
				1026	Related classes of interest are explained in the following subsections:
				1027	<ul>
Gabor Greif	a17abe1	2009-02-27 13:28:07 +0000	[diff] [blame]	1028	<li><a href="#dss_ilist_traits">ilist_traits</a></li>
Gabor Greif	b6b21ec	2009-02-27 12:02:19 +0000	[diff] [blame]	1029	<li><a href="#dss_iplist">iplist</a></li>
Gabor Greif	bb17f65	2009-02-27 11:37:41 +0000	[diff] [blame]	1030	<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]	1031	<li><a href="#dss_ilist_sentinel">Sentinels</a></li>
Gabor Greif	bb17f65	2009-02-27 11:37:41 +0000	[diff] [blame]	1032	</ul>
				1033	</div>
				1034
				1035	<!-- _______________________________________________________________________ -->
				1036	<div class="doc_subsubsection">
Gabor Greif	a17abe1	2009-02-27 13:28:07 +0000	[diff] [blame]	1037	<a name="dss_ilist_traits">ilist_traits</a>
				1038	</div>
				1039
				1040	<div class="doc_text">
				1041	<p><tt>ilist_traits<T></tt> is <tt>ilist<T></tt>'s customization
				1042	mechanism. <tt>iplist<T></tt> (and consequently <tt>ilist<T></tt>)
				1043	publicly derive from this traits class.</p>
				1044	</div>
				1045
				1046	<!-- _______________________________________________________________________ -->
				1047	<div class="doc_subsubsection">
Gabor Greif	b6b21ec	2009-02-27 12:02:19 +0000	[diff] [blame]	1048	<a name="dss_iplist">iplist</a>
				1049	</div>
				1050
				1051	<div class="doc_text">
				1052	<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]	1053	supports a slightly narrower interface. Notably, inserters from
				1054	<tt>T&</tt> are absent.</p>
Gabor Greif	a17abe1	2009-02-27 13:28:07 +0000	[diff] [blame]	1055
				1056	<p><tt>ilist_traits<T></tt> is a public base of this class and can be
				1057	used for a wide variety of customizations.</p>
Gabor Greif	b6b21ec	2009-02-27 12:02:19 +0000	[diff] [blame]	1058	</div>
				1059
				1060	<!-- _______________________________________________________________________ -->
				1061	<div class="doc_subsubsection">
Gabor Greif	bb17f65	2009-02-27 11:37:41 +0000	[diff] [blame]	1062	<a name="dss_ilist_node">llvm/ADT/ilist_node.h</a>
				1063	</div>
				1064
				1065	<div class="doc_text">
				1066	<p><tt>ilist_node<T></tt> implements a the forward and backward links
				1067	that are expected by the <tt>ilist<T></tt> (and analogous containers)
				1068	in the default manner.</p>
				1069
				1070	<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]	1071	<tt>T</tt>, usually <tt>T</tt> publicly derives from
				1072	<tt>ilist_node<T></tt>.</p>
Dan Gohman	f17a25c	2007-07-18 16:29:46 +0000	[diff] [blame]	1073	</div>
				1074
				1075	<!-- _______________________________________________________________________ -->
				1076	<div class="doc_subsubsection">
Gabor Greif	d970d69	2009-03-12 10:30:31 +0000	[diff] [blame]	1077	<a name="dss_ilist_sentinel">Sentinels</a>
				1078	</div>
				1079
				1080	<div class="doc_text">
				1081	<p><tt>ilist</tt>s have another speciality that must be considered. To be a good
				1082	citizen in the C++ ecosystem, it needs to support the standard container
				1083	operations, such as <tt>begin</tt> and <tt>end</tt> iterators, etc. Also, the
				1084	<tt>operator--</tt> must work correctly on the <tt>end</tt> iterator in the
				1085	case of non-empty <tt>ilist</tt>s.</p>
				1086
				1087	<p>The only sensible solution to this problem is to allocate a so-called
				1088	<i>sentinel</i> along with the intrusive list, which serves as the <tt>end</tt>
				1089	iterator, providing the back-link to the last element. However conforming to the
				1090	C++ convention it is illegal to <tt>operator++</tt> beyond the sentinel and it
				1091	also must not be dereferenced.</p>
				1092
				1093	<p>These constraints allow for some implementation freedom to the <tt>ilist</tt>
				1094	how to allocate and store the sentinel. The corresponding policy is dictated
				1095	by <tt>ilist_traits<T></tt>. By default a <tt>T</tt> gets heap-allocated
				1096	whenever the need for a sentinel arises.</p>
				1097
				1098	<p>While the default policy is sufficient in most cases, it may break down when
				1099	<tt>T</tt> does not provide a default constructor. Also, in the case of many
				1100	instances of <tt>ilist</tt>s, the memory overhead of the associated sentinels
				1101	is wasted. To alleviate the situation with numerous and voluminous
				1102	<tt>T</tt>-sentinels, sometimes a trick is employed, leading to <i>ghostly
				1103	sentinels</i>.</p>
				1104
				1105	<p>Ghostly sentinels are obtained by specially-crafted <tt>ilist_traits<T></tt>
				1106	which superpose the sentinel with the <tt>ilist</tt> instance in memory. Pointer
				1107	arithmetic is used to obtain the sentinel, which is relative to the
				1108	<tt>ilist</tt>'s <tt>this</tt> pointer. The <tt>ilist</tt> is augmented by an
				1109	extra pointer, which serves as the back-link of the sentinel. This is the only
				1110	field in the ghostly sentinel which can be legally accessed.</p>
				1111	</div>
				1112
				1113	<!-- _______________________________________________________________________ -->
				1114	<div class="doc_subsubsection">
Dan Gohman	f17a25c	2007-07-18 16:29:46 +0000	[diff] [blame]	1115	<a name="dss_other">Other Sequential Container options</a>
				1116	</div>
				1117
				1118	<div class="doc_text">
				1119	<p>Other STL containers are available, such as std::string.</p>
				1120
				1121	<p>There are also various STL adapter classes such as std::queue,
				1122	std::priority_queue, std::stack, etc. These provide simplified access to an
				1123	underlying container but don't affect the cost of the container itself.</p>
				1124
				1125	</div>
				1126
				1127
				1128	<!-- ======================================================================= -->
				1129	<div class="doc_subsection">
				1130	<a name="ds_set">Set-Like Containers (std::set, SmallSet, SetVector, etc)</a>
				1131	</div>
				1132
				1133	<div class="doc_text">
				1134
				1135	<p>Set-like containers are useful when you need to canonicalize multiple values
				1136	into a single representation. There are several different choices for how to do
				1137	this, providing various trade-offs.</p>
				1138
				1139	</div>
				1140
				1141
				1142	<!-- _______________________________________________________________________ -->
				1143	<div class="doc_subsubsection">
				1144	<a name="dss_sortedvectorset">A sorted 'vector'</a>
				1145	</div>
				1146
				1147	<div class="doc_text">
				1148
				1149	<p>If you intend to insert a lot of elements, then do a lot of queries, a
				1150	great approach is to use a vector (or other sequential container) with
				1151	std::sort+std::unique to remove duplicates. This approach works really well if
				1152	your usage pattern has these two distinct phases (insert then query), and can be
				1153	coupled with a good choice of <a href="#ds_sequential">sequential container</a>.
				1154	</p>
				1155
				1156	<p>
				1157	This combination provides the several nice properties: the result data is
				1158	contiguous in memory (good for cache locality), has few allocations, is easy to
				1159	address (iterators in the final vector are just indices or pointers), and can be
				1160	efficiently queried with a standard binary or radix search.</p>
				1161
				1162	</div>
				1163
				1164	<!-- _______________________________________________________________________ -->
				1165	<div class="doc_subsubsection">
				1166	<a name="dss_smallset">"llvm/ADT/SmallSet.h"</a>
				1167	</div>
				1168
				1169	<div class="doc_text">
				1170
				1171	<p>If you have a set-like data structure that is usually small and whose elements
				1172	are reasonably small, a <tt>SmallSet<Type, N></tt> is a good choice. This set
				1173	has space for N elements in place (thus, if the set is dynamically smaller than
				1174	N, no malloc traffic is required) and accesses them with a simple linear search.
				1175	When the set grows beyond 'N' elements, it allocates a more expensive representation that
				1176	guarantees efficient access (for most types, it falls back to std::set, but for
				1177	pointers it uses something far better, <a
				1178	href="#dss_smallptrset">SmallPtrSet</a>).</p>
				1179
				1180	<p>The magic of this class is that it handles small sets extremely efficiently,
				1181	but gracefully handles extremely large sets without loss of efficiency. The
				1182	drawback is that the interface is quite small: it supports insertion, queries
				1183	and erasing, but does not support iteration.</p>
				1184
				1185	</div>
				1186
				1187	<!-- _______________________________________________________________________ -->
				1188	<div class="doc_subsubsection">
				1189	<a name="dss_smallptrset">"llvm/ADT/SmallPtrSet.h"</a>
				1190	</div>
				1191
				1192	<div class="doc_text">
				1193
				1194	<p>SmallPtrSet has all the advantages of SmallSet (and a SmallSet of pointers is
				1195	transparently implemented with a SmallPtrSet), but also supports iterators. If
				1196	more than 'N' insertions are performed, a single quadratically
				1197	probed hash table is allocated and grows as needed, providing extremely
				1198	efficient access (constant time insertion/deleting/queries with low constant
				1199	factors) and is very stingy with malloc traffic.</p>
				1200
				1201	<p>Note that, unlike std::set, the iterators of SmallPtrSet are invalidated
				1202	whenever an insertion occurs. Also, the values visited by the iterators are not
				1203	visited in sorted order.</p>
				1204
				1205	</div>
				1206
				1207	<!-- _______________________________________________________________________ -->
				1208	<div class="doc_subsubsection">
Chris Lattner	77ab46d	2007-09-30 00:58:59 +0000	[diff] [blame]	1209	<a name="dss_denseset">"llvm/ADT/DenseSet.h"</a>
				1210	</div>
				1211
				1212	<div class="doc_text">
				1213
				1214	<p>
				1215	DenseSet is a simple quadratically probed hash table. It excels at supporting
				1216	small values: it uses a single allocation to hold all of the pairs that
				1217	are currently inserted in the set. DenseSet is a great way to unique small
				1218	values that are not simple pointers (use <a
				1219	href="#dss_smallptrset">SmallPtrSet</a> for pointers). Note that DenseSet has
				1220	the same requirements for the value type that <a
				1221	href="#dss_densemap">DenseMap</a> has.
				1222	</p>
				1223
				1224	</div>
				1225
				1226	<!-- _______________________________________________________________________ -->
				1227	<div class="doc_subsubsection">
Dan Gohman	f17a25c	2007-07-18 16:29:46 +0000	[diff] [blame]	1228	<a name="dss_FoldingSet">"llvm/ADT/FoldingSet.h"</a>
				1229	</div>
				1230
				1231	<div class="doc_text">
				1232
				1233	<p>
				1234	FoldingSet is an aggregate class that is really good at uniquing
				1235	expensive-to-create or polymorphic objects. It is a combination of a chained
				1236	hash table with intrusive links (uniqued objects are required to inherit from
				1237	FoldingSetNode) that uses <a href="#dss_smallvector">SmallVector</a> as part of
				1238	its ID process.</p>
				1239
				1240	<p>Consider a case where you want to implement a "getOrCreateFoo" method for
				1241	a complex object (for example, a node in the code generator). The client has a
				1242	description of what it wants to generate (it knows the opcode and all the
				1243	operands), but we don't want to 'new' a node, then try inserting it into a set
				1244	only to find out it already exists, at which point we would have to delete it
				1245	and return the node that already exists.
				1246	</p>
				1247
				1248	<p>To support this style of client, FoldingSet perform a query with a
				1249	FoldingSetNodeID (which wraps SmallVector) that can be used to describe the
				1250	element that we want to query for. The query either returns the element
				1251	matching the ID or it returns an opaque ID that indicates where insertion should
				1252	take place. Construction of the ID usually does not require heap traffic.</p>
				1253
				1254	<p>Because FoldingSet uses intrusive links, it can support polymorphic objects
				1255	in the set (for example, you can have SDNode instances mixed with LoadSDNodes).
				1256	Because the elements are individually allocated, pointers to the elements are
				1257	stable: inserting or removing elements does not invalidate any pointers to other
				1258	elements.
				1259	</p>
				1260
				1261	</div>
				1262
				1263	<!-- _______________________________________________________________________ -->
				1264	<div class="doc_subsubsection">
				1265	<a name="dss_set"><set></a>
				1266	</div>
				1267
				1268	<div class="doc_text">
				1269
				1270	<p><tt>std::set</tt> is a reasonable all-around set class, which is decent at
				1271	many things but great at nothing. std::set allocates memory for each element
				1272	inserted (thus it is very malloc intensive) and typically stores three pointers
				1273	per element in the set (thus adding a large amount of per-element space
				1274	overhead). It offers guaranteed log(n) performance, which is not particularly
				1275	fast from a complexity standpoint (particularly if the elements of the set are
				1276	expensive to compare, like strings), and has extremely high constant factors for
				1277	lookup, insertion and removal.</p>
				1278
				1279	<p>The advantages of std::set are that its iterators are stable (deleting or
				1280	inserting an element from the set does not affect iterators or pointers to other
				1281	elements) and that iteration over the set is guaranteed to be in sorted order.
				1282	If the elements in the set are large, then the relative overhead of the pointers
				1283	and malloc traffic is not a big deal, but if the elements of the set are small,
				1284	std::set is almost never a good choice.</p>
				1285
				1286	</div>
				1287
				1288	<!-- _______________________________________________________________________ -->
				1289	<div class="doc_subsubsection">
				1290	<a name="dss_setvector">"llvm/ADT/SetVector.h"</a>
				1291	</div>
				1292
				1293	<div class="doc_text">
				1294	<p>LLVM's SetVector<Type> is an adapter class that combines your choice of
				1295	a set-like container along with a <a href="#ds_sequential">Sequential
				1296	Container</a>. The important property
				1297	that this provides is efficient insertion with uniquing (duplicate elements are
				1298	ignored) with iteration support. It implements this by inserting elements into
				1299	both a set-like container and the sequential container, using the set-like
				1300	container for uniquing and the sequential container for iteration.
				1301	</p>
				1302
				1303	<p>The difference between SetVector and other sets is that the order of
				1304	iteration is guaranteed to match the order of insertion into the SetVector.
				1305	This property is really important for things like sets of pointers. Because
				1306	pointer values are non-deterministic (e.g. vary across runs of the program on
				1307	different machines), iterating over the pointers in the set will
				1308	not be in a well-defined order.</p>
				1309
				1310	<p>
				1311	The drawback of SetVector is that it requires twice as much space as a normal
				1312	set and has the sum of constant factors from the set-like container and the
				1313	sequential container that it uses. Use it only if you need to iterate over
				1314	the elements in a deterministic order. SetVector is also expensive to delete
				1315	elements out of (linear time), unless you use it's "pop_back" method, which is
				1316	faster.
				1317	</p>
				1318
				1319	<p>SetVector is an adapter class that defaults to using std::vector and std::set
				1320	for the underlying containers, so it is quite expensive. However,
				1321	<tt>"llvm/ADT/SetVector.h"</tt> also provides a SmallSetVector class, which
				1322	defaults to using a SmallVector and SmallSet of a specified size. If you use
				1323	this, and if your sets are dynamically smaller than N, you will save a lot of
				1324	heap traffic.</p>
				1325
				1326	</div>
				1327
				1328	<!-- _______________________________________________________________________ -->
				1329	<div class="doc_subsubsection">
				1330	<a name="dss_uniquevector">"llvm/ADT/UniqueVector.h"</a>
				1331	</div>
				1332
				1333	<div class="doc_text">
				1334
				1335	<p>
				1336	UniqueVector is similar to <a href="#dss_setvector">SetVector</a>, but it
				1337	retains a unique ID for each element inserted into the set. It internally
				1338	contains a map and a vector, and it assigns a unique ID for each value inserted
				1339	into the set.</p>
				1340
				1341	<p>UniqueVector is very expensive: its cost is the sum of the cost of
				1342	maintaining both the map and vector, it has high complexity, high constant
				1343	factors, and produces a lot of malloc traffic. It should be avoided.</p>
				1344
				1345	</div>
				1346
				1347
				1348	<!-- _______________________________________________________________________ -->
				1349	<div class="doc_subsubsection">
				1350	<a name="dss_otherset">Other Set-Like Container Options</a>
				1351	</div>
				1352
				1353	<div class="doc_text">
				1354
				1355	<p>
				1356	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]	1357	"hash_set" like containers (whether from C++ TR1 or from the SGI library). We
				1358	never use hash_set and unordered_set because they are generally very expensive
				1359	(each insertion requires a malloc) and very non-portable.
				1360	</p>
Dan Gohman	f17a25c	2007-07-18 16:29:46 +0000	[diff] [blame]	1361
				1362	<p>std::multiset is useful if you're not interested in elimination of
				1363	duplicates, but has all the drawbacks of std::set. A sorted vector (where you
				1364	don't delete duplicate entries) or some other approach is almost always
				1365	better.</p>
				1366
Dan Gohman	f17a25c	2007-07-18 16:29:46 +0000	[diff] [blame]	1367	</div>
				1368
				1369	<!-- ======================================================================= -->
				1370	<div class="doc_subsection">
				1371	<a name="ds_map">Map-Like Containers (std::map, DenseMap, etc)</a>
				1372	</div>
				1373
				1374	<div class="doc_text">
				1375	Map-like containers are useful when you want to associate data to a key. As
				1376	usual, there are a lot of different ways to do this. :)
				1377	</div>
				1378
				1379	<!-- _______________________________________________________________________ -->
				1380	<div class="doc_subsubsection">
				1381	<a name="dss_sortedvectormap">A sorted 'vector'</a>
				1382	</div>
				1383
				1384	<div class="doc_text">
				1385
				1386	<p>
				1387	If your usage pattern follows a strict insert-then-query approach, you can
				1388	trivially use the same approach as <a href="#dss_sortedvectorset">sorted vectors
				1389	for set-like containers</a>. The only difference is that your query function
				1390	(which uses std::lower_bound to get efficient log(n) lookup) should only compare
				1391	the key, not both the key and value. This yields the same advantages as sorted
				1392	vectors for sets.
				1393	</p>
				1394	</div>
				1395
				1396	<!-- _______________________________________________________________________ -->
				1397	<div class="doc_subsubsection">
				1398	<a name="dss_stringmap">"llvm/ADT/StringMap.h"</a>
				1399	</div>
				1400
				1401	<div class="doc_text">
				1402
				1403	<p>
				1404	Strings are commonly used as keys in maps, and they are difficult to support
				1405	efficiently: they are variable length, inefficient to hash and compare when
				1406	long, expensive to copy, etc. StringMap is a specialized container designed to
				1407	cope with these issues. It supports mapping an arbitrary range of bytes to an
				1408	arbitrary other object.</p>
				1409
				1410	<p>The StringMap implementation uses a quadratically-probed hash table, where
				1411	the buckets store a pointer to the heap allocated entries (and some other
				1412	stuff). The entries in the map must be heap allocated because the strings are
				1413	variable length. The string data (key) and the element object (value) are
				1414	stored in the same allocation with the string data immediately after the element
				1415	object. This container guarantees the "<tt>(char*)(&Value+1)</tt>" points
				1416	to the key string for a value.</p>
				1417
				1418	<p>The StringMap is very fast for several reasons: quadratic probing is very
				1419	cache efficient for lookups, the hash value of strings in buckets is not
				1420	recomputed when lookup up an element, StringMap rarely has to touch the
				1421	memory for unrelated objects when looking up a value (even when hash collisions
				1422	happen), hash table growth does not recompute the hash values for strings
				1423	already in the table, and each pair in the map is store in a single allocation
				1424	(the string data is stored in the same allocation as the Value of a pair).</p>
				1425
				1426	<p>StringMap also provides query methods that take byte ranges, so it only ever
				1427	copies a string if a value is inserted into the table.</p>
				1428	</div>
				1429
				1430	<!-- _______________________________________________________________________ -->
				1431	<div class="doc_subsubsection">
				1432	<a name="dss_indexedmap">"llvm/ADT/IndexedMap.h"</a>
				1433	</div>
				1434
				1435	<div class="doc_text">
				1436	<p>
				1437	IndexedMap is a specialized container for mapping small dense integers (or
				1438	values that can be mapped to small dense integers) to some other type. It is
				1439	internally implemented as a vector with a mapping function that maps the keys to
				1440	the dense integer range.
				1441	</p>
				1442
				1443	<p>
				1444	This is useful for cases like virtual registers in the LLVM code generator: they
				1445	have a dense mapping that is offset by a compile-time constant (the first
				1446	virtual register ID).</p>
				1447
				1448	</div>
				1449
				1450	<!-- _______________________________________________________________________ -->
				1451	<div class="doc_subsubsection">
				1452	<a name="dss_densemap">"llvm/ADT/DenseMap.h"</a>
				1453	</div>
				1454
				1455	<div class="doc_text">
				1456
				1457	<p>
				1458	DenseMap is a simple quadratically probed hash table. It excels at supporting
				1459	small keys and values: it uses a single allocation to hold all of the pairs that
				1460	are currently inserted in the map. DenseMap is a great way to map pointers to
				1461	pointers, or map other small types to each other.
				1462	</p>
				1463
				1464	<p>
				1465	There are several aspects of DenseMap that you should be aware of, however. The
				1466	iterators in a densemap are invalidated whenever an insertion occurs, unlike
				1467	map. Also, because DenseMap allocates space for a large number of key/value
				1468	pairs (it starts with 64 by default), it will waste a lot of space if your keys
				1469	or values are large. Finally, you must implement a partial specialization of
Chris Lattner	92eea07	2007-09-17 18:34:04 +0000	[diff] [blame]	1470	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]	1471	is required to tell DenseMap about two special marker values (which can never be
				1472	inserted into the map) that it needs internally.</p>
				1473
				1474	</div>
				1475
				1476	<!-- _______________________________________________________________________ -->
				1477	<div class="doc_subsubsection">
				1478	<a name="dss_map"><map></a>
				1479	</div>
				1480
				1481	<div class="doc_text">
				1482
				1483	<p>
				1484	std::map has similar characteristics to <a href="#dss_set">std::set</a>: it uses
				1485	a single allocation per pair inserted into the map, it offers log(n) lookup with
				1486	an extremely large constant factor, imposes a space penalty of 3 pointers per
				1487	pair in the map, etc.</p>
				1488
				1489	<p>std::map is most useful when your keys or values are very large, if you need
				1490	to iterate over the collection in sorted order, or if you need stable iterators
				1491	into the map (i.e. they don't get invalidated if an insertion or deletion of
				1492	another element takes place).</p>
				1493
				1494	</div>
				1495
				1496	<!-- _______________________________________________________________________ -->
				1497	<div class="doc_subsubsection">
				1498	<a name="dss_othermap">Other Map-Like Container Options</a>
				1499	</div>
				1500
				1501	<div class="doc_text">
				1502
				1503	<p>
				1504	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]	1505	"hash_map" like containers (whether from C++ TR1 or from the SGI library). We
				1506	never use hash_set and unordered_set because they are generally very expensive
				1507	(each insertion requires a malloc) and very non-portable.</p>
Dan Gohman	f17a25c	2007-07-18 16:29:46 +0000	[diff] [blame]	1508
				1509	<p>std::multimap is useful if you want to map a key to multiple values, but has
				1510	all the drawbacks of std::map. A sorted vector or some other approach is almost
				1511	always better.</p>
				1512
Dan Gohman	f17a25c	2007-07-18 16:29:46 +0000	[diff] [blame]	1513	</div>
				1514
Daniel Berlin	7ea44dc	2007-09-24 17:52:25 +0000	[diff] [blame]	1515	<!-- ======================================================================= -->
				1516	<div class="doc_subsection">
Chris Lattner	d8b95b7	2009-07-25 07:22:20 +0000	[diff] [blame^]	1517	<a name="ds_string">String-like containers</a>
				1518	</div>
				1519
				1520	<div class="doc_text">
				1521
				1522	<p>
				1523	TODO: const char* vs stringref vs smallstring vs std::string. Describe twine,
				1524	xref to #string_apis.
				1525	</p>
				1526
				1527	</div>
				1528
				1529	<!-- ======================================================================= -->
				1530	<div class="doc_subsection">
Daniel Berlin	7ea44dc	2007-09-24 17:52:25 +0000	[diff] [blame]	1531	<a name="ds_bit">Bit storage containers (BitVector, SparseBitVector)</a>
				1532	</div>
				1533
				1534	<div class="doc_text">
Chris Lattner	62a4eae	2007-09-25 22:37:50 +0000	[diff] [blame]	1535	<p>Unlike the other containers, there are only two bit storage containers, and
				1536	choosing when to use each is relatively straightforward.</p>
				1537
				1538	<p>One additional option is
				1539	<tt>std::vector<bool></tt>: we discourage its use for two reasons 1) the
				1540	implementation in many common compilers (e.g. commonly available versions of
				1541	GCC) is extremely inefficient and 2) the C++ standards committee is likely to
				1542	deprecate this container and/or change it significantly somehow. In any case,
				1543	please don't use it.</p>
Daniel Berlin	7ea44dc	2007-09-24 17:52:25 +0000	[diff] [blame]	1544	</div>
				1545
				1546	<!-- _______________________________________________________________________ -->
				1547	<div class="doc_subsubsection">
				1548	<a name="dss_bitvector">BitVector</a>
				1549	</div>
				1550
				1551	<div class="doc_text">
				1552	<p> The BitVector container provides a fixed size set of bits for manipulation.
				1553	It supports individual bit setting/testing, as well as set operations. The set
				1554	operations take time O(size of bitvector), but operations are performed one word
				1555	at a time, instead of one bit at a time. This makes the BitVector very fast for
				1556	set operations compared to other containers. Use the BitVector when you expect
				1557	the number of set bits to be high (IE a dense set).
				1558	</p>
				1559	</div>
				1560
				1561	<!-- _______________________________________________________________________ -->
				1562	<div class="doc_subsubsection">
				1563	<a name="dss_sparsebitvector">SparseBitVector</a>
				1564	</div>
				1565
				1566	<div class="doc_text">
				1567	<p> The SparseBitVector container is much like BitVector, with one major
				1568	difference: Only the bits that are set, are stored. This makes the
				1569	SparseBitVector much more space efficient than BitVector when the set is sparse,
				1570	as well as making set operations O(number of set bits) instead of O(size of
				1571	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
				1572	(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).
				1573	</p>
				1574	</div>
Dan Gohman	f17a25c	2007-07-18 16:29:46 +0000	[diff] [blame]	1575
				1576	<!-- *********************************************************************** -->
				1577	<div class="doc_section">
				1578	<a name="common">Helpful Hints for Common Operations</a>
				1579	</div>
				1580	<!-- *********************************************************************** -->
				1581
				1582	<div class="doc_text">
				1583
				1584	<p>This section describes how to perform some very simple transformations of
				1585	LLVM code. This is meant to give examples of common idioms used, showing the
				1586	practical side of LLVM transformations. <p> Because this is a "how-to" section,
				1587	you should also read about the main classes that you will be working with. The
				1588	<a href="#coreclasses">Core LLVM Class Hierarchy Reference</a> contains details
				1589	and descriptions of the main classes that you should know about.</p>
				1590
				1591	</div>
				1592
				1593	<!-- NOTE: this section should be heavy on example code -->
				1594	<!-- ======================================================================= -->
				1595	<div class="doc_subsection">
				1596	<a name="inspection">Basic Inspection and Traversal Routines</a>
				1597	</div>
				1598
				1599	<div class="doc_text">
				1600
				1601	<p>The LLVM compiler infrastructure have many different data structures that may
				1602	be traversed. Following the example of the C++ standard template library, the
				1603	techniques used to traverse these various data structures are all basically the
				1604	same. For a enumerable sequence of values, the <tt>XXXbegin()</tt> function (or
				1605	method) returns an iterator to the start of the sequence, the <tt>XXXend()</tt>
				1606	function returns an iterator pointing to one past the last valid element of the
				1607	sequence, and there is some <tt>XXXiterator</tt> data type that is common
				1608	between the two operations.</p>
				1609
				1610	<p>Because the pattern for iteration is common across many different aspects of
				1611	the program representation, the standard template library algorithms may be used
				1612	on them, and it is easier to remember how to iterate. First we show a few common
				1613	examples of the data structures that need to be traversed. Other data
				1614	structures are traversed in very similar ways.</p>
				1615
				1616	</div>
				1617
				1618	<!-- _______________________________________________________________________ -->
				1619	<div class="doc_subsubsection">
				1620	<a name="iterate_function">Iterating over the </a><a
				1621	href="#BasicBlock"><tt>BasicBlock</tt></a>s in a <a
				1622	href="#Function"><tt>Function</tt></a>
				1623	</div>
				1624
				1625	<div class="doc_text">
				1626
				1627	<p>It's quite common to have a <tt>Function</tt> instance that you'd like to
				1628	transform in some way; in particular, you'd like to manipulate its
				1629	<tt>BasicBlock</tt>s. To facilitate this, you'll need to iterate over all of
				1630	the <tt>BasicBlock</tt>s that constitute the <tt>Function</tt>. The following is
				1631	an example that prints the name of a <tt>BasicBlock</tt> and the number of
				1632	<tt>Instruction</tt>s it contains:</p>
				1633
				1634	<div class="doc_code">
				1635	<pre>
				1636	// <i>func is a pointer to a Function instance</i>
				1637	for (Function::iterator i = func->begin(), e = func->end(); i != e; ++i)
				1638	// <i>Print out the name of the basic block if it has one, and then the</i>
				1639	// <i>number of instructions that it contains</i>
				1640	llvm::cerr << "Basic block (name=" << i->getName() << ") has "
				1641	<< i->size() << " instructions.\n";
				1642	</pre>
				1643	</div>
				1644
				1645	<p>Note that i can be used as if it were a pointer for the purposes of
				1646	invoking member functions of the <tt>Instruction</tt> class. This is
				1647	because the indirection operator is overloaded for the iterator
				1648	classes. In the above code, the expression <tt>i->size()</tt> is
				1649	exactly equivalent to <tt>(*i).size()</tt> just like you'd expect.</p>
				1650
				1651	</div>
				1652
				1653	<!-- _______________________________________________________________________ -->
				1654	<div class="doc_subsubsection">
				1655	<a name="iterate_basicblock">Iterating over the </a><a
				1656	href="#Instruction"><tt>Instruction</tt></a>s in a <a
				1657	href="#BasicBlock"><tt>BasicBlock</tt></a>
				1658	</div>
				1659
				1660	<div class="doc_text">
				1661
				1662	<p>Just like when dealing with <tt>BasicBlock</tt>s in <tt>Function</tt>s, it's
				1663	easy to iterate over the individual instructions that make up
				1664	<tt>BasicBlock</tt>s. Here's a code snippet that prints out each instruction in
				1665	a <tt>BasicBlock</tt>:</p>
				1666
				1667	<div class="doc_code">
				1668	<pre>
				1669	// <i>blk is a pointer to a BasicBlock instance</i>
				1670	for (BasicBlock::iterator i = blk->begin(), e = blk->end(); i != e; ++i)
				1671	// <i>The next statement works since operator<<(ostream&,...)</i>
				1672	// <i>is overloaded for Instruction&</i>
				1673	llvm::cerr << *i << "\n";
				1674	</pre>
				1675	</div>
				1676
				1677	<p>However, this isn't really the best way to print out the contents of a
				1678	<tt>BasicBlock</tt>! Since the ostream operators are overloaded for virtually
				1679	anything you'll care about, you could have just invoked the print routine on the
				1680	basic block itself: <tt>llvm::cerr << *blk << "\n";</tt>.</p>
				1681
				1682	</div>
				1683
				1684	<!-- _______________________________________________________________________ -->
				1685	<div class="doc_subsubsection">
				1686	<a name="iterate_institer">Iterating over the </a><a
				1687	href="#Instruction"><tt>Instruction</tt></a>s in a <a
				1688	href="#Function"><tt>Function</tt></a>
				1689	</div>
				1690
				1691	<div class="doc_text">
				1692
				1693	<p>If you're finding that you commonly iterate over a <tt>Function</tt>'s
				1694	<tt>BasicBlock</tt>s and then that <tt>BasicBlock</tt>'s <tt>Instruction</tt>s,
				1695	<tt>InstIterator</tt> should be used instead. You'll need to include <a
				1696	href="/doxygen/InstIterator_8h-source.html"><tt>llvm/Support/InstIterator.h</tt></a>,
				1697	and then instantiate <tt>InstIterator</tt>s explicitly in your code. Here's a
				1698	small example that shows how to dump all instructions in a function to the standard error stream:<p>
				1699
				1700	<div class="doc_code">
				1701	<pre>
				1702	#include "<a href="/doxygen/InstIterator_8h-source.html">llvm/Support/InstIterator.h</a>"
				1703
				1704	// <i>F is a pointer to a Function instance</i>
Chris Lattner	fd62ee7	2008-06-04 18:20:42 +0000	[diff] [blame]	1705	for (inst_iterator I = inst_begin(F), E = inst_end(F); I != E; ++I)
				1706	llvm::cerr << *I << "\n";
Dan Gohman	f17a25c	2007-07-18 16:29:46 +0000	[diff] [blame]	1707	</pre>
				1708	</div>
				1709
				1710	<p>Easy, isn't it? You can also use <tt>InstIterator</tt>s to fill a
				1711	work list with its initial contents. For example, if you wanted to
				1712	initialize a work list to contain all instructions in a <tt>Function</tt>
				1713	F, all you would need to do is something like:</p>
				1714
				1715	<div class="doc_code">
				1716	<pre>
				1717	std::set<Instruction*> worklist;
Chris Lattner	fd62ee7	2008-06-04 18:20:42 +0000	[diff] [blame]	1718	// or better yet, SmallPtrSet<Instruction*, 64> worklist;
				1719
				1720	for (inst_iterator I = inst_begin(F), E = inst_end(F); I != E; ++I)
				1721	worklist.insert(&*I);
Dan Gohman	f17a25c	2007-07-18 16:29:46 +0000	[diff] [blame]	1722	</pre>
				1723	</div>
				1724
				1725	<p>The STL set <tt>worklist</tt> would now contain all instructions in the
				1726	<tt>Function</tt> pointed to by F.</p>
				1727
				1728	</div>
				1729
				1730	<!-- _______________________________________________________________________ -->
				1731	<div class="doc_subsubsection">
				1732	<a name="iterate_convert">Turning an iterator into a class pointer (and
				1733	vice-versa)</a>
				1734	</div>
				1735
				1736	<div class="doc_text">
				1737
				1738	<p>Sometimes, it'll be useful to grab a reference (or pointer) to a class
				1739	instance when all you've got at hand is an iterator. Well, extracting
				1740	a reference or a pointer from an iterator is very straight-forward.
				1741	Assuming that <tt>i</tt> is a <tt>BasicBlock::iterator</tt> and <tt>j</tt>
				1742	is a <tt>BasicBlock::const_iterator</tt>:</p>
				1743
				1744	<div class="doc_code">
				1745	<pre>
				1746	Instruction& inst = *i; // <i>Grab reference to instruction reference</i>
				1747	Instruction* pinst = &*i; // <i>Grab pointer to instruction reference</i>
				1748	const Instruction& inst = *j;
				1749	</pre>
				1750	</div>
				1751
				1752	<p>However, the iterators you'll be working with in the LLVM framework are
				1753	special: they will automatically convert to a ptr-to-instance type whenever they
				1754	need to. Instead of dereferencing the iterator and then taking the address of
				1755	the result, you can simply assign the iterator to the proper pointer type and
				1756	you get the dereference and address-of operation as a result of the assignment
				1757	(behind the scenes, this is a result of overloading casting mechanisms). Thus
				1758	the last line of the last example,</p>
				1759
				1760	<div class="doc_code">
				1761	<pre>
Chris Lattner	0665e1f	2008-01-03 16:56:04 +0000	[diff] [blame]	1762	Instruction pinst = &i;
Dan Gohman	f17a25c	2007-07-18 16:29:46 +0000	[diff] [blame]	1763	</pre>
				1764	</div>
				1765
				1766	<p>is semantically equivalent to</p>
				1767
				1768	<div class="doc_code">
				1769	<pre>
Chris Lattner	0665e1f	2008-01-03 16:56:04 +0000	[diff] [blame]	1770	Instruction *pinst = i;
Dan Gohman	f17a25c	2007-07-18 16:29:46 +0000	[diff] [blame]	1771	</pre>
				1772	</div>
				1773
				1774	<p>It's also possible to turn a class pointer into the corresponding iterator,
				1775	and this is a constant time operation (very efficient). The following code
				1776	snippet illustrates use of the conversion constructors provided by LLVM
				1777	iterators. By using these, you can explicitly grab the iterator of something
				1778	without actually obtaining it via iteration over some structure:</p>
				1779
				1780	<div class="doc_code">
				1781	<pre>
				1782	void printNextInstruction(Instruction* inst) {
				1783	BasicBlock::iterator it(inst);
				1784	++it; // <i>After this line, it refers to the instruction after *inst</i>
				1785	if (it != inst->getParent()->end()) llvm::cerr << *it << "\n";
				1786	}
				1787	</pre>
				1788	</div>
				1789
				1790	</div>
				1791
				1792	<!--_______________________________________________________________________-->
				1793	<div class="doc_subsubsection">
				1794	<a name="iterate_complex">Finding call sites: a slightly more complex
				1795	example</a>
				1796	</div>
				1797
				1798	<div class="doc_text">
				1799
				1800	<p>Say that you're writing a FunctionPass and would like to count all the
				1801	locations in the entire module (that is, across every <tt>Function</tt>) where a
				1802	certain function (i.e., some <tt>Function</tt>*) is already in scope. As you'll
				1803	learn later, you may want to use an <tt>InstVisitor</tt> to accomplish this in a
				1804	much more straight-forward manner, but this example will allow us to explore how
				1805	you'd do it if you didn't have <tt>InstVisitor</tt> around. In pseudo-code, this
				1806	is what we want to do:</p>
				1807
				1808	<div class="doc_code">
				1809	<pre>
				1810	initialize callCounter to zero
				1811	for each Function f in the Module
				1812	for each BasicBlock b in f
				1813	for each Instruction i in b
				1814	if (i is a CallInst and calls the given function)
				1815	increment callCounter
				1816	</pre>
				1817	</div>
				1818
				1819	<p>And the actual code is (remember, because we're writing a
				1820	<tt>FunctionPass</tt>, our <tt>FunctionPass</tt>-derived class simply has to
				1821	override the <tt>runOnFunction</tt> method):</p>
				1822
				1823	<div class="doc_code">
				1824	<pre>
				1825	Function* targetFunc = ...;
				1826
				1827	class OurFunctionPass : public FunctionPass {
				1828	public:
				1829	OurFunctionPass(): callCounter(0) { }
				1830
				1831	virtual runOnFunction(Function& F) {
				1832	for (Function::iterator b = F.begin(), be = F.end(); b != be; ++b) {
Eric Christopher	5fbecf7	2008-11-08 08:20:49 +0000	[diff] [blame]	1833	for (BasicBlock::iterator i = b->begin(), ie = b->end(); i != ie; ++i) {
Dan Gohman	f17a25c	2007-07-18 16:29:46 +0000	[diff] [blame]	1834	if (<a href="#CallInst">CallInst</a>* callInst = <a href="#isa">dyn_cast</a><<a
				1835	href="#CallInst">CallInst</a>>(&*i)) {
				1836	// <i>We know we've encountered a call instruction, so we</i>
				1837	// <i>need to determine if it's a call to the</i>
Chris Lattner	0665e1f	2008-01-03 16:56:04 +0000	[diff] [blame]	1838	// <i>function pointed to by m_func or not.</i>
Dan Gohman	f17a25c	2007-07-18 16:29:46 +0000	[diff] [blame]	1839	if (callInst->getCalledFunction() == targetFunc)
				1840	++callCounter;
				1841	}
				1842	}
				1843	}
				1844	}
				1845
				1846	private:
Chris Lattner	0665e1f	2008-01-03 16:56:04 +0000	[diff] [blame]	1847	unsigned callCounter;
Dan Gohman	f17a25c	2007-07-18 16:29:46 +0000	[diff] [blame]	1848	};
				1849	</pre>
				1850	</div>
				1851
				1852	</div>
				1853
				1854	<!--_______________________________________________________________________-->
				1855	<div class="doc_subsubsection">
				1856	<a name="calls_and_invokes">Treating calls and invokes the same way</a>
				1857	</div>
				1858
				1859	<div class="doc_text">
				1860
				1861	<p>You may have noticed that the previous example was a bit oversimplified in
				1862	that it did not deal with call sites generated by 'invoke' instructions. In
				1863	this, and in other situations, you may find that you want to treat
				1864	<tt>CallInst</tt>s and <tt>InvokeInst</tt>s the same way, even though their
				1865	most-specific common base class is <tt>Instruction</tt>, which includes lots of
				1866	less closely-related things. For these cases, LLVM provides a handy wrapper
				1867	class called <a
				1868	href="http://llvm.org/doxygen/classllvm_1_1CallSite.html"><tt>CallSite</tt></a>.
				1869	It is essentially a wrapper around an <tt>Instruction</tt> pointer, with some
				1870	methods that provide functionality common to <tt>CallInst</tt>s and
				1871	<tt>InvokeInst</tt>s.</p>
				1872
				1873	<p>This class has "value semantics": it should be passed by value, not by
				1874	reference and it should not be dynamically allocated or deallocated using
				1875	<tt>operator new</tt> or <tt>operator delete</tt>. It is efficiently copyable,
				1876	assignable and constructable, with costs equivalents to that of a bare pointer.
				1877	If you look at its definition, it has only a single pointer member.</p>
				1878
				1879	</div>
				1880
				1881	<!--_______________________________________________________________________-->
				1882	<div class="doc_subsubsection">
				1883	<a name="iterate_chains">Iterating over def-use & use-def chains</a>
				1884	</div>
				1885
				1886	<div class="doc_text">
				1887
				1888	<p>Frequently, we might have an instance of the <a
				1889	href="/doxygen/classllvm_1_1Value.html">Value Class</a> and we want to
				1890	determine which <tt>User</tt>s use the <tt>Value</tt>. The list of all
				1891	<tt>User</tt>s of a particular <tt>Value</tt> is called a <i>def-use</i> chain.
				1892	For example, let's say we have a <tt>Function*</tt> named <tt>F</tt> to a
				1893	particular function <tt>foo</tt>. Finding all of the instructions that
				1894	<i>use</i> <tt>foo</tt> is as simple as iterating over the <i>def-use</i> chain
				1895	of <tt>F</tt>:</p>
				1896
				1897	<div class="doc_code">
				1898	<pre>
Chris Lattner	0665e1f	2008-01-03 16:56:04 +0000	[diff] [blame]	1899	Function *F = ...;
Dan Gohman	f17a25c	2007-07-18 16:29:46 +0000	[diff] [blame]	1900
				1901	for (Value::use_iterator i = F->use_begin(), e = F->use_end(); i != e; ++i)
				1902	if (Instruction Inst = dyn_cast<Instruction>(i)) {
				1903	llvm::cerr << "F is used in instruction:\n";
				1904	llvm::cerr << *Inst << "\n";
				1905	}
				1906	</pre>
				1907	</div>
				1908
				1909	<p>Alternately, it's common to have an instance of the <a
				1910	href="/doxygen/classllvm_1_1User.html">User Class</a> and need to know what
				1911	<tt>Value</tt>s are used by it. The list of all <tt>Value</tt>s used by a
				1912	<tt>User</tt> is known as a <i>use-def</i> chain. Instances of class
				1913	<tt>Instruction</tt> are common <tt>User</tt>s, so we might want to iterate over
				1914	all of the values that a particular instruction uses (that is, the operands of
				1915	the particular <tt>Instruction</tt>):</p>
				1916
				1917	<div class="doc_code">
				1918	<pre>
Chris Lattner	0665e1f	2008-01-03 16:56:04 +0000	[diff] [blame]	1919	Instruction *pi = ...;
Dan Gohman	f17a25c	2007-07-18 16:29:46 +0000	[diff] [blame]	1920
				1921	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]	1922	Value v = i;
Dan Gohman	f17a25c	2007-07-18 16:29:46 +0000	[diff] [blame]	1923	// <i>...</i>
				1924	}
				1925	</pre>
				1926	</div>
				1927
				1928	<!--
				1929	def-use chains ("finding all users of"): Value::use_begin/use_end
				1930	use-def chains ("finding all values used"): User::op_begin/op_end [op=operand]
				1931	-->
				1932
				1933	</div>
				1934
Chris Lattner	0665e1f	2008-01-03 16:56:04 +0000	[diff] [blame]	1935	<!--_______________________________________________________________________-->
				1936	<div class="doc_subsubsection">
				1937	<a name="iterate_preds">Iterating over predecessors &
				1938	successors of blocks</a>
				1939	</div>
				1940
				1941	<div class="doc_text">
				1942
				1943	<p>Iterating over the predecessors and successors of a block is quite easy
				1944	with the routines defined in <tt>"llvm/Support/CFG.h"</tt>. Just use code like
				1945	this to iterate over all predecessors of BB:</p>
				1946
				1947	<div class="doc_code">
				1948	<pre>
				1949	#include "llvm/Support/CFG.h"
				1950	BasicBlock *BB = ...;
				1951
				1952	for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI) {
				1953	BasicBlock Pred = PI;
				1954	// <i>...</i>
				1955	}
				1956	</pre>
				1957	</div>
				1958
				1959	<p>Similarly, to iterate over successors use
				1960	succ_iterator/succ_begin/succ_end.</p>
				1961
				1962	</div>
				1963
				1964
Dan Gohman	f17a25c	2007-07-18 16:29:46 +0000	[diff] [blame]	1965	<!-- ======================================================================= -->
				1966	<div class="doc_subsection">
				1967	<a name="simplechanges">Making simple changes</a>
				1968	</div>
				1969
				1970	<div class="doc_text">
				1971
				1972	<p>There are some primitive transformation operations present in the LLVM
				1973	infrastructure that are worth knowing about. When performing
				1974	transformations, it's fairly common to manipulate the contents of basic
				1975	blocks. This section describes some of the common methods for doing so
				1976	and gives example code.</p>
				1977
				1978	</div>
				1979
				1980	<!--_______________________________________________________________________-->
				1981	<div class="doc_subsubsection">
				1982	<a name="schanges_creating">Creating and inserting new
				1983	<tt>Instruction</tt>s</a>
				1984	</div>
				1985
				1986	<div class="doc_text">
				1987
				1988	<p><i>Instantiating Instructions</i></p>
				1989
				1990	<p>Creation of <tt>Instruction</tt>s is straight-forward: simply call the
				1991	constructor for the kind of instruction to instantiate and provide the necessary
				1992	parameters. For example, an <tt>AllocaInst</tt> only <i>requires</i> a
				1993	(const-ptr-to) <tt>Type</tt>. Thus:</p>
				1994
				1995	<div class="doc_code">
				1996	<pre>
Nick Lewycky	c004e5b	2007-12-03 01:52:52 +0000	[diff] [blame]	1997	AllocaInst* ai = new AllocaInst(Type::Int32Ty);
Dan Gohman	f17a25c	2007-07-18 16:29:46 +0000	[diff] [blame]	1998	</pre>
				1999	</div>
				2000
				2001	<p>will create an <tt>AllocaInst</tt> instance that represents the allocation of
				2002	one integer in the current stack frame, at run time. Each <tt>Instruction</tt>
				2003	subclass is likely to have varying default parameters which change the semantics
				2004	of the instruction, so refer to the <a
				2005	href="/doxygen/classllvm_1_1Instruction.html">doxygen documentation for the subclass of
				2006	Instruction</a> that you're interested in instantiating.</p>
				2007
				2008	<p><i>Naming values</i></p>
				2009
				2010	<p>It is very useful to name the values of instructions when you're able to, as
				2011	this facilitates the debugging of your transformations. If you end up looking
				2012	at generated LLVM machine code, you definitely want to have logical names
				2013	associated with the results of instructions! By supplying a value for the
				2014	<tt>Name</tt> (default) parameter of the <tt>Instruction</tt> constructor, you
				2015	associate a logical name with the result of the instruction's execution at
				2016	run time. For example, say that I'm writing a transformation that dynamically
				2017	allocates space for an integer on the stack, and that integer is going to be
				2018	used as some kind of index by some other code. To accomplish this, I place an
				2019	<tt>AllocaInst</tt> at the first point in the first <tt>BasicBlock</tt> of some
				2020	<tt>Function</tt>, and I'm intending to use it within the same
				2021	<tt>Function</tt>. I might do:</p>
				2022
				2023	<div class="doc_code">
				2024	<pre>
Nick Lewycky	c004e5b	2007-12-03 01:52:52 +0000	[diff] [blame]	2025	AllocaInst* pa = new AllocaInst(Type::Int32Ty, 0, "indexLoc");
Dan Gohman	f17a25c	2007-07-18 16:29:46 +0000	[diff] [blame]	2026	</pre>
				2027	</div>
				2028
				2029	<p>where <tt>indexLoc</tt> is now the logical name of the instruction's
				2030	execution value, which is a pointer to an integer on the run time stack.</p>
				2031
				2032	<p><i>Inserting instructions</i></p>
				2033
				2034	<p>There are essentially two ways to insert an <tt>Instruction</tt>
				2035	into an existing sequence of instructions that form a <tt>BasicBlock</tt>:</p>
				2036
				2037	<ul>
				2038	<li>Insertion into an explicit instruction list
				2039
				2040	<p>Given a <tt>BasicBlock* pb</tt>, an <tt>Instruction* pi</tt> within that
				2041	<tt>BasicBlock</tt>, and a newly-created instruction we wish to insert
				2042	before <tt>*pi</tt>, we do the following: </p>
				2043
				2044	<div class="doc_code">
				2045	<pre>
				2046	BasicBlock *pb = ...;
				2047	Instruction *pi = ...;
				2048	Instruction *newInst = new Instruction(...);
				2049
				2050	pb->getInstList().insert(pi, newInst); // <i>Inserts newInst before pi in pb</i>
				2051	</pre>
				2052	</div>
				2053
				2054	<p>Appending to the end of a <tt>BasicBlock</tt> is so common that
				2055	the <tt>Instruction</tt> class and <tt>Instruction</tt>-derived
				2056	classes provide constructors which take a pointer to a
				2057	<tt>BasicBlock</tt> to be appended to. For example code that
				2058	looked like: </p>
				2059
				2060	<div class="doc_code">
				2061	<pre>
				2062	BasicBlock *pb = ...;
				2063	Instruction *newInst = new Instruction(...);
				2064
				2065	pb->getInstList().push_back(newInst); // <i>Appends newInst to pb</i>
				2066	</pre>
				2067	</div>
				2068
				2069	<p>becomes: </p>
				2070
				2071	<div class="doc_code">
				2072	<pre>
				2073	BasicBlock *pb = ...;
				2074	Instruction *newInst = new Instruction(..., pb);
				2075	</pre>
				2076	</div>
				2077
				2078	<p>which is much cleaner, especially if you are creating
				2079	long instruction streams.</p></li>
				2080
				2081	<li>Insertion into an implicit instruction list
				2082
				2083	<p><tt>Instruction</tt> instances that are already in <tt>BasicBlock</tt>s
				2084	are implicitly associated with an existing instruction list: the instruction
				2085	list of the enclosing basic block. Thus, we could have accomplished the same
				2086	thing as the above code without being given a <tt>BasicBlock</tt> by doing:
				2087	</p>
				2088
				2089	<div class="doc_code">
				2090	<pre>
				2091	Instruction *pi = ...;
				2092	Instruction *newInst = new Instruction(...);
				2093
				2094	pi->getParent()->getInstList().insert(pi, newInst);
				2095	</pre>
				2096	</div>
				2097
				2098	<p>In fact, this sequence of steps occurs so frequently that the
				2099	<tt>Instruction</tt> class and <tt>Instruction</tt>-derived classes provide
				2100	constructors which take (as a default parameter) a pointer to an
				2101	<tt>Instruction</tt> which the newly-created <tt>Instruction</tt> should
				2102	precede. That is, <tt>Instruction</tt> constructors are capable of
				2103	inserting the newly-created instance into the <tt>BasicBlock</tt> of a
				2104	provided instruction, immediately before that instruction. Using an
				2105	<tt>Instruction</tt> constructor with a <tt>insertBefore</tt> (default)
				2106	parameter, the above code becomes:</p>
				2107
				2108	<div class="doc_code">
				2109	<pre>
				2110	Instruction* pi = ...;
				2111	Instruction* newInst = new Instruction(..., pi);
				2112	</pre>
				2113	</div>
				2114
				2115	<p>which is much cleaner, especially if you're creating a lot of
				2116	instructions and adding them to <tt>BasicBlock</tt>s.</p></li>
				2117	</ul>
				2118
				2119	</div>
				2120
				2121	<!--_______________________________________________________________________-->
				2122	<div class="doc_subsubsection">
				2123	<a name="schanges_deleting">Deleting <tt>Instruction</tt>s</a>
				2124	</div>
				2125
				2126	<div class="doc_text">
				2127
				2128	<p>Deleting an instruction from an existing sequence of instructions that form a
				2129	<a href="#BasicBlock"><tt>BasicBlock</tt></a> is very straight-forward. First,
				2130	you must have a pointer to the instruction that you wish to delete. Second, you
				2131	need to obtain the pointer to that instruction's basic block. You use the
				2132	pointer to the basic block to get its list of instructions and then use the
				2133	erase function to remove your instruction. For example:</p>
				2134
				2135	<div class="doc_code">
				2136	<pre>
				2137	<a href="#Instruction">Instruction</a> *I = .. ;
Chris Lattner	3db8f77	2008-02-15 22:57:17 +0000	[diff] [blame]	2138	I->eraseFromParent();
Dan Gohman	f17a25c	2007-07-18 16:29:46 +0000	[diff] [blame]	2139	</pre>
				2140	</div>
				2141
				2142	</div>
				2143
				2144	<!--_______________________________________________________________________-->
				2145	<div class="doc_subsubsection">
				2146	<a name="schanges_replacing">Replacing an <tt>Instruction</tt> with another
				2147	<tt>Value</tt></a>
				2148	</div>
				2149
				2150	<div class="doc_text">
				2151
				2152	<p><i>Replacing individual instructions</i></p>
				2153
				2154	<p>Including "<a href="/doxygen/BasicBlockUtils_8h-source.html">llvm/Transforms/Utils/BasicBlockUtils.h</a>"
				2155	permits use of two very useful replace functions: <tt>ReplaceInstWithValue</tt>
				2156	and <tt>ReplaceInstWithInst</tt>.</p>
				2157
				2158	<h4><a name="schanges_deleting">Deleting <tt>Instruction</tt>s</a></h4>
				2159
				2160	<ul>
				2161	<li><tt>ReplaceInstWithValue</tt>
				2162
Nick Lewycky	48d4b03	2008-09-15 06:31:52 +0000	[diff] [blame]	2163	<p>This function replaces all uses of a given instruction with a value,
				2164	and then removes the original instruction. The following example
				2165	illustrates the replacement of the result of a particular
Dan Gohman	f17a25c	2007-07-18 16:29:46 +0000	[diff] [blame]	2166	<tt>AllocaInst</tt> that allocates memory for a single integer with a null
				2167	pointer to an integer.</p>
				2168
				2169	<div class="doc_code">
				2170	<pre>
				2171	AllocaInst* instToReplace = ...;
				2172	BasicBlock::iterator ii(instToReplace);
				2173
				2174	ReplaceInstWithValue(instToReplace->getParent()->getInstList(), ii,
Daniel Dunbar	8ce7962	2008-10-03 22:17:25 +0000	[diff] [blame]	2175	Constant::getNullValue(PointerType::getUnqual(Type::Int32Ty)));
Dan Gohman	f17a25c	2007-07-18 16:29:46 +0000	[diff] [blame]	2176	</pre></div></li>
				2177
				2178	<li><tt>ReplaceInstWithInst</tt>
				2179
				2180	<p>This function replaces a particular instruction with another
Nick Lewycky	48d4b03	2008-09-15 06:31:52 +0000	[diff] [blame]	2181	instruction, inserting the new instruction into the basic block at the
				2182	location where the old instruction was, and replacing any uses of the old
				2183	instruction with the new instruction. The following example illustrates
				2184	the replacement of one <tt>AllocaInst</tt> with another.</p>
Dan Gohman	f17a25c	2007-07-18 16:29:46 +0000	[diff] [blame]	2185
				2186	<div class="doc_code">
				2187	<pre>
				2188	AllocaInst* instToReplace = ...;
				2189	BasicBlock::iterator ii(instToReplace);
				2190
				2191	ReplaceInstWithInst(instToReplace->getParent()->getInstList(), ii,
Nick Lewycky	c004e5b	2007-12-03 01:52:52 +0000	[diff] [blame]	2192	new AllocaInst(Type::Int32Ty, 0, "ptrToReplacedInt"));
Dan Gohman	f17a25c	2007-07-18 16:29:46 +0000	[diff] [blame]	2193	</pre></div></li>
				2194	</ul>
				2195
				2196	<p><i>Replacing multiple uses of <tt>User</tt>s and <tt>Value</tt>s</i></p>
				2197
				2198	<p>You can use <tt>Value::replaceAllUsesWith</tt> and
				2199	<tt>User::replaceUsesOfWith</tt> to change more than one use at a time. See the
				2200	doxygen documentation for the <a href="/doxygen/classllvm_1_1Value.html">Value Class</a>
				2201	and <a href="/doxygen/classllvm_1_1User.html">User Class</a>, respectively, for more
				2202	information.</p>
				2203
				2204	<!-- Value::replaceAllUsesWith User::replaceUsesOfWith Point out:
				2205	include/llvm/Transforms/Utils/ especially BasicBlockUtils.h with:
				2206	ReplaceInstWithValue, ReplaceInstWithInst -->
				2207
				2208	</div>
				2209
				2210	<!--_______________________________________________________________________-->
				2211	<div class="doc_subsubsection">
				2212	<a name="schanges_deletingGV">Deleting <tt>GlobalVariable</tt>s</a>
				2213	</div>
				2214
				2215	<div class="doc_text">
				2216
				2217	<p>Deleting a global variable from a module is just as easy as deleting an
				2218	Instruction. First, you must have a pointer to the global variable that you wish
				2219	to delete. You use this pointer to erase it from its parent, the module.
				2220	For example:</p>
				2221
				2222	<div class="doc_code">
				2223	<pre>
				2224	<a href="#GlobalVariable">GlobalVariable</a> *GV = .. ;
				2225
				2226	GV->eraseFromParent();
				2227	</pre>
				2228	</div>
				2229
				2230	</div>
				2231
Jeffrey Yasskin	7ebb6ac	2009-04-30 22:33:41 +0000	[diff] [blame]	2232	<!-- ======================================================================= -->
				2233	<div class="doc_subsection">
				2234	<a name="create_types">How to Create Types</a>
				2235	</div>
				2236
				2237	<div class="doc_text">
				2238
				2239	<p>In generating IR, you may need some complex types. If you know these types
Misha Brukman	0672513	2009-05-01 20:40:51 +0000	[diff] [blame]	2240	statically, you can use <tt>TypeBuilder<...>::get()</tt>, defined
Jeffrey Yasskin	7ebb6ac	2009-04-30 22:33:41 +0000	[diff] [blame]	2241	in <tt>llvm/Support/TypeBuilder.h</tt>, to retrieve them. <tt>TypeBuilder</tt>
				2242	has two forms depending on whether you're building types for cross-compilation
Misha Brukman	0672513	2009-05-01 20:40:51 +0000	[diff] [blame]	2243	or native library use. <tt>TypeBuilder<T, true></tt> requires
Jeffrey Yasskin	7ebb6ac	2009-04-30 22:33:41 +0000	[diff] [blame]	2244	that <tt>T</tt> be independent of the host environment, meaning that it's built
				2245	out of types from
				2246	the <a href="/doxygen/namespacellvm_1_1types.html"><tt>llvm::types</tt></a>
				2247	namespace and pointers, functions, arrays, etc. built of
Misha Brukman	0672513	2009-05-01 20:40:51 +0000	[diff] [blame]	2248	those. <tt>TypeBuilder<T, false></tt> additionally allows native C types
Jeffrey Yasskin	7ebb6ac	2009-04-30 22:33:41 +0000	[diff] [blame]	2249	whose size may depend on the host compiler. For example,</p>
				2250
				2251	<div class="doc_code">
				2252	<pre>
Misha Brukman	0672513	2009-05-01 20:40:51 +0000	[diff] [blame]	2253	FunctionType ft = TypeBuilder<types::i<8>(types::i<32>), true>::get();
Jeffrey Yasskin	7ebb6ac	2009-04-30 22:33:41 +0000	[diff] [blame]	2254	</pre>
				2255	</div>
				2256
				2257	<p>is easier to read and write than the equivalent</p>
				2258
				2259	<div class="doc_code">
				2260	<pre>
Owen Anderson	60f8757	2009-06-16 17:40:28 +0000	[diff] [blame]	2261	std::vector<const Type*> params;
Jeffrey Yasskin	7ebb6ac	2009-04-30 22:33:41 +0000	[diff] [blame]	2262	params.push_back(PointerType::getUnqual(Type::Int32Ty));
				2263	FunctionType *ft = FunctionType::get(Type::Int8Ty, params, false);
				2264	</pre>
				2265	</div>
				2266
				2267	<p>See the <a href="/doxygen/TypeBuilder_8h-source.html#l00001">class
				2268	comment</a> for more details.</p>
				2269
				2270	</div>
				2271
Dan Gohman	f17a25c	2007-07-18 16:29:46 +0000	[diff] [blame]	2272	<!-- *********************************************************************** -->
				2273	<div class="doc_section">
Owen Anderson	e8370c0	2009-06-16 01:17:16 +0000	[diff] [blame]	2274	<a name="threading">Threads and LLVM</a>
				2275	</div>
				2276	<!-- *********************************************************************** -->
				2277
				2278	<div class="doc_text">
				2279	<p>
				2280	This section describes the interaction of the LLVM APIs with multithreading,
				2281	both on the part of client applications, and in the JIT, in the hosted
				2282	application.
				2283	</p>
				2284
				2285	<p>
				2286	Note that LLVM's support for multithreading is still relatively young. Up
				2287	through version 2.5, the execution of threaded hosted applications was
				2288	supported, but not threaded client access to the APIs. While this use case is
				2289	now supported, clients <em>must</em> adhere to the guidelines specified below to
				2290	ensure proper operation in multithreaded mode.
				2291	</p>
				2292
				2293	<p>
				2294	Note that, on Unix-like platforms, LLVM requires the presence of GCC's atomic
				2295	intrinsics in order to support threaded operation. If you need a
				2296	multhreading-capable LLVM on a platform without a suitably modern system
				2297	compiler, consider compiling LLVM and LLVM-GCC in single-threaded mode, and
				2298	using the resultant compiler to build a copy of LLVM with multithreading
				2299	support.
				2300	</p>
				2301	</div>
				2302
				2303	<!-- ======================================================================= -->
				2304	<div class="doc_subsection">
Owen Anderson	b418690	2009-06-16 18:04:19 +0000	[diff] [blame]	2305	<a name="startmultithreaded">Entering and Exiting Multithreaded Mode</a>
Owen Anderson	e8370c0	2009-06-16 01:17:16 +0000	[diff] [blame]	2306	</div>
				2307
				2308	<div class="doc_text">
				2309
				2310	<p>
				2311	In order to properly protect its internal data structures while avoiding
Owen Anderson	b418690	2009-06-16 18:04:19 +0000	[diff] [blame]	2312	excessive locking overhead in the single-threaded case, the LLVM must intialize
				2313	certain data structures necessary to provide guards around its internals. To do
				2314	so, the client program must invoke <tt>llvm_start_multithreaded()</tt> before
				2315	making any concurrent LLVM API calls. To subsequently tear down these
				2316	structures, use the <tt>llvm_stop_multithreaded()</tt> call. You can also use
				2317	the <tt>llvm_is_multithreaded()</tt> call to check the status of multithreaded
				2318	mode.
Owen Anderson	e8370c0	2009-06-16 01:17:16 +0000	[diff] [blame]	2319	</p>
				2320
				2321	<p>
Owen Anderson	b418690	2009-06-16 18:04:19 +0000	[diff] [blame]	2322	Note that both of these calls must be made <em>in isolation</em>. That is to
				2323	say that no other LLVM API calls may be executing at any time during the
				2324	execution of <tt>llvm_start_multithreaded()</tt> or <tt>llvm_stop_multithreaded
				2325	</tt>. It's is the client's responsibility to enforce this isolation.
				2326	</p>
				2327
				2328	<p>
				2329	The return value of <tt>llvm_start_multithreaded()</tt> indicates the success or
				2330	failure of the initialization. Failure typically indicates that your copy of
				2331	LLVM was built without multithreading support, typically because GCC atomic
				2332	intrinsics were not found in your system compiler. In this case, the LLVM API
				2333	will not be safe for concurrent calls. However, it <em>will</em> be safe for
				2334	hosting threaded applications in the JIT, though care must be taken to ensure
				2335	that side exits and the like do not accidentally result in concurrent LLVM API
				2336	calls.
Owen Anderson	e8370c0	2009-06-16 01:17:16 +0000	[diff] [blame]	2337	</p>
				2338	</div>
				2339
				2340	<!-- ======================================================================= -->
				2341	<div class="doc_subsection">
				2342	<a name="shutdown">Ending Execution with <tt>llvm_shutdown()</tt></a>
				2343	</div>
				2344
				2345	<div class="doc_text">
				2346	<p>
				2347	When you are done using the LLVM APIs, you should call <tt>llvm_shutdown()</tt>
Owen Anderson	b418690	2009-06-16 18:04:19 +0000	[diff] [blame]	2348	to deallocate memory used for internal structures. This will also invoke
				2349	<tt>llvm_stop_multithreaded()</tt> if LLVM is operating in multithreaded mode.
				2350	As such, <tt>llvm_shutdown()</tt> requires the same isolation guarantees as
				2351	<tt>llvm_stop_multithreaded()</tt>.
Owen Anderson	e8370c0	2009-06-16 01:17:16 +0000	[diff] [blame]	2352	</p>
				2353
				2354	<p>
				2355	Note that, if you use scope-based shutdown, you can use the
				2356	<tt>llvm_shutdown_obj</tt> class, which calls <tt>llvm_shutdown()</tt> in its
				2357	destructor.
				2358	</div>
				2359
				2360	<!-- ======================================================================= -->
				2361	<div class="doc_subsection">
				2362	<a name="managedstatic">Lazy Initialization with <tt>ManagedStatic</tt></a>
				2363	</div>
				2364
				2365	<div class="doc_text">
				2366	<p>
				2367	<tt>ManagedStatic</tt> is a utility class in LLVM used to implement static
				2368	initialization of static resources, such as the global type tables. Before the
				2369	invocation of <tt>llvm_shutdown()</tt>, it implements a simple lazy
				2370	initialization scheme. Once <tt>llvm_start_multithreaded()</tt> returns,
				2371	however, it uses double-checked locking to implement thread-safe lazy
				2372	initialization.
				2373	</p>
				2374
				2375	<p>
				2376	Note that, because no other threads are allowed to issue LLVM API calls before
				2377	<tt>llvm_start_multithreaded()</tt> returns, it is possible to have
				2378	<tt>ManagedStatic</tt>s of <tt>llvm::sys::Mutex</tt>s.
				2379	</p>
Owen Anderson	b418690	2009-06-16 18:04:19 +0000	[diff] [blame]	2380
				2381	<p>
				2382	The <tt>llvm_acquire_global_lock()</tt> and <tt>llvm_release_global_lock</tt>
				2383	APIs provide access to the global lock used to implement the double-checked
				2384	locking for lazy initialization. These should only be used internally to LLVM,
				2385	and only if you know what you're doing!
				2386	</p>
Owen Anderson	e8370c0	2009-06-16 01:17:16 +0000	[diff] [blame]	2387	</div>
				2388
				2389	<!-- *********************************************************************** -->
				2390	<div class="doc_section">
Dan Gohman	f17a25c	2007-07-18 16:29:46 +0000	[diff] [blame]	2391	<a name="advanced">Advanced Topics</a>
				2392	</div>
				2393	<!-- *********************************************************************** -->
				2394
				2395	<div class="doc_text">
				2396	<p>
				2397	This section describes some of the advanced or obscure API's that most clients
				2398	do not need to be aware of. These API's tend manage the inner workings of the
				2399	LLVM system, and only need to be accessed in unusual circumstances.
				2400	</p>
				2401	</div>
				2402
				2403	<!-- ======================================================================= -->
				2404	<div class="doc_subsection">
				2405	<a name="TypeResolve">LLVM Type Resolution</a>
				2406	</div>
				2407
				2408	<div class="doc_text">
				2409
				2410	<p>
				2411	The LLVM type system has a very simple goal: allow clients to compare types for
				2412	structural equality with a simple pointer comparison (aka a shallow compare).
				2413	This goal makes clients much simpler and faster, and is used throughout the LLVM
				2414	system.
				2415	</p>
				2416
				2417	<p>
				2418	Unfortunately achieving this goal is not a simple matter. In particular,
				2419	recursive types and late resolution of opaque types makes the situation very
				2420	difficult to handle. Fortunately, for the most part, our implementation makes
				2421	most clients able to be completely unaware of the nasty internal details. The
				2422	primary case where clients are exposed to the inner workings of it are when
				2423	building a recursive type. In addition to this case, the LLVM bitcode reader,
				2424	assembly parser, and linker also have to be aware of the inner workings of this
				2425	system.
				2426	</p>
				2427
				2428	<p>
				2429	For our purposes below, we need three concepts. First, an "Opaque Type" is
				2430	exactly as defined in the <a href="LangRef.html#t_opaque">language
				2431	reference</a>. Second an "Abstract Type" is any type which includes an
				2432	opaque type as part of its type graph (for example "<tt>{ opaque, i32 }</tt>").
				2433	Third, a concrete type is a type that is not an abstract type (e.g. "<tt>{ i32,
				2434	float }</tt>").
				2435	</p>
				2436
				2437	</div>
				2438
				2439	<!-- ______________________________________________________________________ -->
				2440	<div class="doc_subsubsection">
				2441	<a name="BuildRecType">Basic Recursive Type Construction</a>
				2442	</div>
				2443
				2444	<div class="doc_text">
				2445
				2446	<p>
				2447	Because the most common question is "how do I build a recursive type with LLVM",
				2448	we answer it now and explain it as we go. Here we include enough to cause this
				2449	to be emitted to an output .ll file:
				2450	</p>
				2451
				2452	<div class="doc_code">
				2453	<pre>
				2454	%mylist = type { %mylist*, i32 }
				2455	</pre>
				2456	</div>
				2457
				2458	<p>
				2459	To build this, use the following LLVM APIs:
				2460	</p>
				2461
				2462	<div class="doc_code">
				2463	<pre>
				2464	// <i>Create the initial outer struct</i>
				2465	<a href="#PATypeHolder">PATypeHolder</a> StructTy = OpaqueType::get();
				2466	std::vector<const Type*> Elts;
Daniel Dunbar	8ce7962	2008-10-03 22:17:25 +0000	[diff] [blame]	2467	Elts.push_back(PointerType::getUnqual(StructTy));
Nick Lewycky	c004e5b	2007-12-03 01:52:52 +0000	[diff] [blame]	2468	Elts.push_back(Type::Int32Ty);
Dan Gohman	f17a25c	2007-07-18 16:29:46 +0000	[diff] [blame]	2469	StructType *NewSTy = StructType::get(Elts);
				2470
				2471	// <i>At this point, NewSTy = "{ opaque*, i32 }". Tell VMCore that</i>
				2472	// <i>the struct and the opaque type are actually the same.</i>
				2473	cast<OpaqueType>(StructTy.get())-><a href="#refineAbstractTypeTo">refineAbstractTypeTo</a>(NewSTy);
				2474
				2475	// <i>NewSTy is potentially invalidated, but StructTy (a <a href="#PATypeHolder">PATypeHolder</a>) is</i>
				2476	// <i>kept up-to-date</i>
				2477	NewSTy = cast<StructType>(StructTy.get());
				2478
				2479	// <i>Add a name for the type to the module symbol table (optional)</i>
				2480	MyModule->addTypeName("mylist", NewSTy);
				2481	</pre>
				2482	</div>
				2483
				2484	<p>
				2485	This code shows the basic approach used to build recursive types: build a
				2486	non-recursive type using 'opaque', then use type unification to close the cycle.
				2487	The type unification step is performed by the <tt><a
				2488	href="#refineAbstractTypeTo">refineAbstractTypeTo</a></tt> method, which is
				2489	described next. After that, we describe the <a
				2490	href="#PATypeHolder">PATypeHolder class</a>.
				2491	</p>
				2492
				2493	</div>
				2494
				2495	<!-- ______________________________________________________________________ -->
				2496	<div class="doc_subsubsection">
				2497	<a name="refineAbstractTypeTo">The <tt>refineAbstractTypeTo</tt> method</a>
				2498	</div>
				2499
				2500	<div class="doc_text">
				2501	<p>
				2502	The <tt>refineAbstractTypeTo</tt> method starts the type unification process.
				2503	While this method is actually a member of the DerivedType class, it is most
				2504	often used on OpaqueType instances. Type unification is actually a recursive
				2505	process. After unification, types can become structurally isomorphic to
				2506	existing types, and all duplicates are deleted (to preserve pointer equality).
				2507	</p>
				2508
				2509	<p>
				2510	In the example above, the OpaqueType object is definitely deleted.
				2511	Additionally, if there is an "{ \2*, i32}" type already created in the system,
				2512	the pointer and struct type created are <b>also</b> deleted. Obviously whenever
				2513	a type is deleted, any "Type*" pointers in the program are invalidated. As
				2514	such, it is safest to avoid having <i>any</i> "Type*" pointers to abstract types
				2515	live across a call to <tt>refineAbstractTypeTo</tt> (note that non-abstract
				2516	types can never move or be deleted). To deal with this, the <a
				2517	href="#PATypeHolder">PATypeHolder</a> class is used to maintain a stable
				2518	reference to a possibly refined type, and the <a
				2519	href="#AbstractTypeUser">AbstractTypeUser</a> class is used to update more
				2520	complex datastructures.
				2521	</p>
				2522
				2523	</div>
				2524
				2525	<!-- ______________________________________________________________________ -->
				2526	<div class="doc_subsubsection">
				2527	<a name="PATypeHolder">The PATypeHolder Class</a>
				2528	</div>
				2529
				2530	<div class="doc_text">
				2531	<p>
				2532	PATypeHolder is a form of a "smart pointer" for Type objects. When VMCore
				2533	happily goes about nuking types that become isomorphic to existing types, it
				2534	automatically updates all PATypeHolder objects to point to the new type. In the
				2535	example above, this allows the code to maintain a pointer to the resultant
				2536	resolved recursive type, even though the Type*'s are potentially invalidated.
				2537	</p>
				2538
				2539	<p>
				2540	PATypeHolder is an extremely light-weight object that uses a lazy union-find
				2541	implementation to update pointers. For example the pointer from a Value to its
				2542	Type is maintained by PATypeHolder objects.
				2543	</p>
				2544
				2545	</div>
				2546
				2547	<!-- ______________________________________________________________________ -->
				2548	<div class="doc_subsubsection">
				2549	<a name="AbstractTypeUser">The AbstractTypeUser Class</a>
				2550	</div>
				2551
				2552	<div class="doc_text">
				2553
				2554	<p>
				2555	Some data structures need more to perform more complex updates when types get
				2556	resolved. To support this, a class can derive from the AbstractTypeUser class.
				2557	This class
				2558	allows it to get callbacks when certain types are resolved. To register to get
				2559	callbacks for a particular type, the DerivedType::{add/remove}AbstractTypeUser
				2560	methods can be called on a type. Note that these methods only work for <i>
				2561	abstract</i> types. Concrete types (those that do not include any opaque
				2562	objects) can never be refined.
				2563	</p>
				2564	</div>
				2565
				2566
				2567	<!-- ======================================================================= -->
				2568	<div class="doc_subsection">
				2569	<a name="SymbolTable">The <tt>ValueSymbolTable</tt> and
				2570	<tt>TypeSymbolTable</tt> classes</a>
				2571	</div>
				2572
				2573	<div class="doc_text">
				2574	<p>The <tt><a href="http://llvm.org/doxygen/classllvm_1_1ValueSymbolTable.html">
				2575	ValueSymbolTable</a></tt> class provides a symbol table that the <a
				2576	href="#Function"><tt>Function</tt></a> and <a href="#Module">
				2577	<tt>Module</tt></a> classes use for naming value definitions. The symbol table
				2578	can provide a name for any <a href="#Value"><tt>Value</tt></a>.
				2579	The <tt><a href="http://llvm.org/doxygen/classllvm_1_1TypeSymbolTable.html">
				2580	TypeSymbolTable</a></tt> class is used by the <tt>Module</tt> class to store
				2581	names for types.</p>
				2582
				2583	<p>Note that the <tt>SymbolTable</tt> class should not be directly accessed
				2584	by most clients. It should only be used when iteration over the symbol table
				2585	names themselves are required, which is very special purpose. Note that not
				2586	all LLVM
Gabor Greif	92e8776	2008-06-16 21:06:12 +0000	[diff] [blame]	2587	<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]	2588	an empty name) do not exist in the symbol table.
				2589	</p>
				2590
				2591	<p>These symbol tables support iteration over the values/types in the symbol
				2592	table with <tt>begin/end/iterator</tt> and supports querying to see if a
				2593	specific name is in the symbol table (with <tt>lookup</tt>). The
				2594	<tt>ValueSymbolTable</tt> class exposes no public mutator methods, instead,
				2595	simply call <tt>setName</tt> on a value, which will autoinsert it into the
				2596	appropriate symbol table. For types, use the Module::addTypeName method to
				2597	insert entries into the symbol table.</p>
				2598
				2599	</div>
				2600
				2601
				2602
Gabor Greif	92e8776	2008-06-16 21:06:12 +0000	[diff] [blame]	2603	<!-- ======================================================================= -->
				2604	<div class="doc_subsection">
				2605	<a name="UserLayout">The <tt>User</tt> and owned <tt>Use</tt> classes' memory layout</a>
				2606	</div>
				2607
				2608	<div class="doc_text">
				2609	<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]	2610	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]	2611	towards other <tt><a href="http://llvm.org/doxygen/classllvm_1_1Value.html">
				2612	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]	2613	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]	2614	addition and removal.</p>
				2615
Gabor Greif	93b462b	2008-06-18 13:44:57 +0000	[diff] [blame]	2616	<!-- ______________________________________________________________________ -->
				2617	<div class="doc_subsubsection">
Gabor Greif	50626fc	2009-01-05 16:05:32 +0000	[diff] [blame]	2618	<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]	2619	</div>
Gabor Greif	92e8776	2008-06-16 21:06:12 +0000	[diff] [blame]	2620
Gabor Greif	93b462b	2008-06-18 13:44:57 +0000	[diff] [blame]	2621	<div class="doc_text">
				2622	<p>
				2623	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]	2624	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]	2625	(some <tt>Use</tt>s inline others hung off) is impractical and breaks the invariant
				2626	that the <tt>Use</tt> objects belonging to the same <tt>User</tt> form a contiguous array.
				2627	</p>
				2628	</div>
Gabor Greif	92e8776	2008-06-16 21:06:12 +0000	[diff] [blame]	2629
Gabor Greif	93b462b	2008-06-18 13:44:57 +0000	[diff] [blame]	2630	<p>
				2631	We have 2 different layouts in the <tt>User</tt> (sub)classes:
				2632	<ul>
				2633	<li><p>Layout a)
				2634	The <tt>Use</tt> object(s) are inside (resp. at fixed offset) of the <tt>User</tt>
				2635	object and there are a fixed number of them.</p>
Gabor Greif	92e8776	2008-06-16 21:06:12 +0000	[diff] [blame]	2636
Gabor Greif	93b462b	2008-06-18 13:44:57 +0000	[diff] [blame]	2637	<li><p>Layout b)
				2638	The <tt>Use</tt> object(s) are referenced by a pointer to an
				2639	array from the <tt>User</tt> object and there may be a variable
				2640	number of them.</p>
				2641	</ul>
				2642	<p>
Gabor Greif	e247e36	2008-06-25 00:10:22 +0000	[diff] [blame]	2643	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]	2644	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]	2645	we stick to this redundancy for the sake of simplicity.
Gabor Greif	e247e36	2008-06-25 00:10:22 +0000	[diff] [blame]	2646	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]	2647	has. (Theoretically this information can also be calculated
Gabor Greif	93b462b	2008-06-18 13:44:57 +0000	[diff] [blame]	2648	given the scheme presented below.)</p>
				2649	<p>
				2650	Special forms of allocation operators (<tt>operator new</tt>)
Gabor Greif	e247e36	2008-06-25 00:10:22 +0000	[diff] [blame]	2651	enforce the following memory layouts:</p>
Gabor Greif	92e8776	2008-06-16 21:06:12 +0000	[diff] [blame]	2652
Gabor Greif	93b462b	2008-06-18 13:44:57 +0000	[diff] [blame]	2653	<ul>
Gabor Greif	e247e36	2008-06-25 00:10:22 +0000	[diff] [blame]	2654	<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]	2655
Gabor Greif	93b462b	2008-06-18 13:44:57 +0000	[diff] [blame]	2656	<pre>
				2657	...---.---.---.---.-------...
				2658	\| P \| P \| P \| P \| User
				2659	'''---'---'---'---'-------'''
				2660	</pre>
Gabor Greif	92e8776	2008-06-16 21:06:12 +0000	[diff] [blame]	2661
Gabor Greif	e247e36	2008-06-25 00:10:22 +0000	[diff] [blame]	2662	<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]	2663	<pre>
				2664	.-------...
				2665	\| User
				2666	'-------'''
				2667	\|
				2668	v
				2669	.---.---.---.---...
				2670	\| P \| P \| P \| P \|
				2671	'---'---'---'---'''
				2672	</pre>
				2673	</ul>
				2674	<i>(In the above figures '<tt>P</tt>' stands for the <tt>Use**</tt> that
				2675	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]	2676
Gabor Greif	93b462b	2008-06-18 13:44:57 +0000	[diff] [blame]	2677	<!-- ______________________________________________________________________ -->
				2678	<div class="doc_subsubsection">
Gabor Greif	50626fc	2009-01-05 16:05:32 +0000	[diff] [blame]	2679	<a name="Waymarking">The waymarking algorithm</a>
Gabor Greif	93b462b	2008-06-18 13:44:57 +0000	[diff] [blame]	2680	</div>
Gabor Greif	92e8776	2008-06-16 21:06:12 +0000	[diff] [blame]	2681
Gabor Greif	93b462b	2008-06-18 13:44:57 +0000	[diff] [blame]	2682	<div class="doc_text">
				2683	<p>
Gabor Greif	e247e36	2008-06-25 00:10:22 +0000	[diff] [blame]	2684	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]	2685	their <tt>User</tt> objects, there must be a fast and exact method to
				2686	recover it. This is accomplished by the following scheme:</p>
				2687	</div>
Gabor Greif	92e8776	2008-06-16 21:06:12 +0000	[diff] [blame]	2688
Gabor Greif	e247e36	2008-06-25 00:10:22 +0000	[diff] [blame]	2689	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]	2690	start of the <tt>User</tt> object:
				2691	<ul>
				2692	<li><tt>00</tt> —> binary digit 0</li>
				2693	<li><tt>01</tt> —> binary digit 1</li>
				2694	<li><tt>10</tt> —> stop and calculate (<tt>s</tt>)</li>
				2695	<li><tt>11</tt> —> full stop (<tt>S</tt>)</li>
				2696	</ul>
				2697	<p>
				2698	Given a <tt>Use*</tt>, all we have to do is to walk till we get
				2699	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]	2700	we have to walk to the next stop picking up digits
Gabor Greif	93b462b	2008-06-18 13:44:57 +0000	[diff] [blame]	2701	and calculating the offset:</p>
				2702	<pre>
Gabor Greif	92e8776	2008-06-16 21:06:12 +0000	[diff] [blame]	2703	.---.---.---.---.---.---.---.---.---.---.---.---.---.---.---.---.----------------
				2704	\| 1 \| s \| 1 \| 0 \| 1 \| 0 \| s \| 1 \| 1 \| 0 \| s \| 1 \| 1 \| s \| 1 \| S \| User (or User*)
				2705	'---'---'---'---'---'---'---'---'---'---'---'---'---'---'---'---'----------------
				2706	\|+15 \|+10 \|+6 \|+3 \|+1
				2707	\| \| \| \| \|__>
				2708	\| \| \| \|__________>
				2709	\| \| \|______________________>
				2710	\| \|______________________________________>
				2711	\|__________________________________________________________>
Gabor Greif	93b462b	2008-06-18 13:44:57 +0000	[diff] [blame]	2712	</pre>
				2713	<p>
Gabor Greif	92e8776	2008-06-16 21:06:12 +0000	[diff] [blame]	2714	Only the significant number of bits need to be stored between the
Gabor Greif	93b462b	2008-06-18 13:44:57 +0000	[diff] [blame]	2715	stops, so that the <i>worst case is 20 memory accesses</i> when there are
				2716	1000 <tt>Use</tt> objects associated with a <tt>User</tt>.</p>
Gabor Greif	92e8776	2008-06-16 21:06:12 +0000	[diff] [blame]	2717
Gabor Greif	93b462b	2008-06-18 13:44:57 +0000	[diff] [blame]	2718	<!-- ______________________________________________________________________ -->
				2719	<div class="doc_subsubsection">
Gabor Greif	50626fc	2009-01-05 16:05:32 +0000	[diff] [blame]	2720	<a name="ReferenceImpl">Reference implementation</a>
Gabor Greif	93b462b	2008-06-18 13:44:57 +0000	[diff] [blame]	2721	</div>
Gabor Greif	92e8776	2008-06-16 21:06:12 +0000	[diff] [blame]	2722
Gabor Greif	93b462b	2008-06-18 13:44:57 +0000	[diff] [blame]	2723	<div class="doc_text">
				2724	<p>
				2725	The following literate Haskell fragment demonstrates the concept:</p>
				2726	</div>
				2727
				2728	<div class="doc_code">
				2729	<pre>
Gabor Greif	92e8776	2008-06-16 21:06:12 +0000	[diff] [blame]	2730	> import Test.QuickCheck
				2731	>
				2732	> digits :: Int -> [Char] -> [Char]
				2733	> digits 0 acc = '0' : acc
				2734	> digits 1 acc = '1' : acc
				2735	> digits n acc = digits (n `div` 2) $ digits (n `mod` 2) acc
				2736	>
				2737	> dist :: Int -> [Char] -> [Char]
				2738	> dist 0 [] = ['S']
				2739	> dist 0 acc = acc
				2740	> dist 1 acc = let r = dist 0 acc in 's' : digits (length r) r
				2741	> dist n acc = dist (n - 1) $ dist 1 acc
				2742	>
				2743	> takeLast n ss = reverse $ take n $ reverse ss
				2744	>
				2745	> test = takeLast 40 $ dist 20 []
				2746	>
Gabor Greif	93b462b	2008-06-18 13:44:57 +0000	[diff] [blame]	2747	</pre>
				2748	</div>
				2749	<p>
				2750	Printing <test> gives: <tt>"1s100000s11010s10100s1111s1010s110s11s1S"</tt></p>
				2751	<p>
				2752	The reverse algorithm computes the length of the string just by examining
				2753	a certain prefix:</p>
Gabor Greif	92e8776	2008-06-16 21:06:12 +0000	[diff] [blame]	2754
Gabor Greif	93b462b	2008-06-18 13:44:57 +0000	[diff] [blame]	2755	<div class="doc_code">
				2756	<pre>
Gabor Greif	92e8776	2008-06-16 21:06:12 +0000	[diff] [blame]	2757	> pref :: [Char] -> Int
				2758	> pref "S" = 1
				2759	> pref ('s':'1':rest) = decode 2 1 rest
				2760	> pref (_:rest) = 1 + pref rest
				2761	>
				2762	> decode walk acc ('0':rest) = decode (walk + 1) (acc * 2) rest
				2763	> decode walk acc ('1':rest) = decode (walk + 1) (acc * 2 + 1) rest
				2764	> decode walk acc _ = walk + acc
				2765	>
Gabor Greif	93b462b	2008-06-18 13:44:57 +0000	[diff] [blame]	2766	</pre>
				2767	</div>
				2768	<p>
				2769	Now, as expected, printing <pref test> gives <tt>40</tt>.</p>
				2770	<p>
				2771	We can <i>quickCheck</i> this with following property:</p>
Gabor Greif	92e8776	2008-06-16 21:06:12 +0000	[diff] [blame]	2772
Gabor Greif	93b462b	2008-06-18 13:44:57 +0000	[diff] [blame]	2773	<div class="doc_code">
				2774	<pre>
Gabor Greif	92e8776	2008-06-16 21:06:12 +0000	[diff] [blame]	2775	> testcase = dist 2000 []
				2776	> testcaseLength = length testcase
				2777	>
				2778	> identityProp n = n > 0 && n <= testcaseLength ==> length arr == pref arr
				2779	> where arr = takeLast n testcase
Gabor Greif	93b462b	2008-06-18 13:44:57 +0000	[diff] [blame]	2780	>
				2781	</pre>
				2782	</div>
				2783	<p>
				2784	As expected <quickCheck identityProp> gives:</p>
Gabor Greif	92e8776	2008-06-16 21:06:12 +0000	[diff] [blame]	2785
Gabor Greif	93b462b	2008-06-18 13:44:57 +0000	[diff] [blame]	2786	<pre>
Gabor Greif	92e8776	2008-06-16 21:06:12 +0000	[diff] [blame]	2787	*Main> quickCheck identityProp
				2788	OK, passed 100 tests.
Gabor Greif	93b462b	2008-06-18 13:44:57 +0000	[diff] [blame]	2789	</pre>
				2790	<p>
				2791	Let's be a bit more exhaustive:</p>
Gabor Greif	92e8776	2008-06-16 21:06:12 +0000	[diff] [blame]	2792
Gabor Greif	93b462b	2008-06-18 13:44:57 +0000	[diff] [blame]	2793	<div class="doc_code">
				2794	<pre>
Gabor Greif	92e8776	2008-06-16 21:06:12 +0000	[diff] [blame]	2795	>
				2796	> deepCheck p = check (defaultConfig { configMaxTest = 500 }) p
				2797	>
Gabor Greif	93b462b	2008-06-18 13:44:57 +0000	[diff] [blame]	2798	</pre>
				2799	</div>
				2800	<p>
				2801	And here is the result of <deepCheck identityProp>:</p>
Gabor Greif	92e8776	2008-06-16 21:06:12 +0000	[diff] [blame]	2802
Gabor Greif	93b462b	2008-06-18 13:44:57 +0000	[diff] [blame]	2803	<pre>
Gabor Greif	92e8776	2008-06-16 21:06:12 +0000	[diff] [blame]	2804	*Main> deepCheck identityProp
				2805	OK, passed 500 tests.
Gabor Greif	92e8776	2008-06-16 21:06:12 +0000	[diff] [blame]	2806	</pre>
				2807
Gabor Greif	93b462b	2008-06-18 13:44:57 +0000	[diff] [blame]	2808	<!-- ______________________________________________________________________ -->
				2809	<div class="doc_subsubsection">
Gabor Greif	50626fc	2009-01-05 16:05:32 +0000	[diff] [blame]	2810	<a name="Tagging">Tagging considerations</a>
Gabor Greif	93b462b	2008-06-18 13:44:57 +0000	[diff] [blame]	2811	</div>
				2812
				2813	<p>
				2814	To maintain the invariant that the 2 LSBits of each <tt>Use**</tt> in <tt>Use</tt>
				2815	never change after being set up, setters of <tt>Use::Prev</tt> must re-tag the
				2816	new <tt>Use**</tt> on every modification. Accordingly getters must strip the
				2817	tag bits.</p>
				2818	<p>
Gabor Greif	e247e36	2008-06-25 00:10:22 +0000	[diff] [blame]	2819	For layout b) instead of the <tt>User</tt> we find a pointer (<tt>User*</tt> with LSBit set).
				2820	Following this pointer brings us to the <tt>User</tt>. A portable trick ensures
				2821	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]	2822	the LSBit set. (Portability is relying on the fact that all known compilers place the
				2823	<tt>vptr</tt> in the first word of the instances.)</p>
Gabor Greif	93b462b	2008-06-18 13:44:57 +0000	[diff] [blame]	2824
Gabor Greif	92e8776	2008-06-16 21:06:12 +0000	[diff] [blame]	2825	</div>
				2826
				2827	<!-- *********************************************************************** -->
Dan Gohman	f17a25c	2007-07-18 16:29:46 +0000	[diff] [blame]	2828	<div class="doc_section">
				2829	<a name="coreclasses">The Core LLVM Class Hierarchy Reference </a>
				2830	</div>
				2831	<!-- *********************************************************************** -->
				2832
				2833	<div class="doc_text">
				2834	<p><tt>#include "<a href="/doxygen/Type_8h-source.html">llvm/Type.h</a>"</tt>
				2835	<br>doxygen info: <a href="/doxygen/classllvm_1_1Type.html">Type Class</a></p>
				2836
				2837	<p>The Core LLVM classes are the primary means of representing the program
				2838	being inspected or transformed. The core LLVM classes are defined in
				2839	header files in the <tt>include/llvm/</tt> directory, and implemented in
				2840	the <tt>lib/VMCore</tt> directory.</p>
				2841
				2842	</div>
				2843
				2844	<!-- ======================================================================= -->
				2845	<div class="doc_subsection">
				2846	<a name="Type">The <tt>Type</tt> class and Derived Types</a>
				2847	</div>
				2848
				2849	<div class="doc_text">
				2850
				2851	<p><tt>Type</tt> is a superclass of all type classes. Every <tt>Value</tt> has
				2852	a <tt>Type</tt>. <tt>Type</tt> cannot be instantiated directly but only
				2853	through its subclasses. Certain primitive types (<tt>VoidType</tt>,
				2854	<tt>LabelType</tt>, <tt>FloatType</tt> and <tt>DoubleType</tt>) have hidden
				2855	subclasses. They are hidden because they offer no useful functionality beyond
				2856	what the <tt>Type</tt> class offers except to distinguish themselves from
				2857	other subclasses of <tt>Type</tt>.</p>
				2858	<p>All other types are subclasses of <tt>DerivedType</tt>. Types can be
				2859	named, but this is not a requirement. There exists exactly
				2860	one instance of a given shape at any one time. This allows type equality to
				2861	be performed with address equality of the Type Instance. That is, given two
				2862	<tt>Type*</tt> values, the types are identical if the pointers are identical.
				2863	</p>
				2864	</div>
				2865
				2866	<!-- _______________________________________________________________________ -->
				2867	<div class="doc_subsubsection">
Gabor Greif	50626fc	2009-01-05 16:05:32 +0000	[diff] [blame]	2868	<a name="m_Type">Important Public Methods</a>
Dan Gohman	f17a25c	2007-07-18 16:29:46 +0000	[diff] [blame]	2869	</div>
				2870
				2871	<div class="doc_text">
				2872
				2873	<ul>
				2874	<li><tt>bool isInteger() const</tt>: Returns true for any integer type.</li>
				2875
				2876	<li><tt>bool isFloatingPoint()</tt>: Return true if this is one of the two
				2877	floating point types.</li>
				2878
				2879	<li><tt>bool isAbstract()</tt>: Return true if the type is abstract (contains
				2880	an OpaqueType anywhere in its definition).</li>
				2881
				2882	<li><tt>bool isSized()</tt>: Return true if the type has known size. Things
				2883	that don't have a size are abstract types, labels and void.</li>
				2884
				2885	</ul>
				2886	</div>
				2887
				2888	<!-- _______________________________________________________________________ -->
				2889	<div class="doc_subsubsection">
Gabor Greif	50626fc	2009-01-05 16:05:32 +0000	[diff] [blame]	2890	<a name="derivedtypes">Important Derived Types</a>
Dan Gohman	f17a25c	2007-07-18 16:29:46 +0000	[diff] [blame]	2891	</div>
				2892	<div class="doc_text">
				2893	<dl>
				2894	<dt><tt>IntegerType</tt></dt>
				2895	<dd>Subclass of DerivedType that represents integer types of any bit width.
				2896	Any bit width between <tt>IntegerType::MIN_INT_BITS</tt> (1) and
				2897	<tt>IntegerType::MAX_INT_BITS</tt> (~8 million) can be represented.
				2898	<ul>
				2899	<li><tt>static const IntegerType* get(unsigned NumBits)</tt>: get an integer
				2900	type of a specific bit width.</li>
				2901	<li><tt>unsigned getBitWidth() const</tt>: Get the bit width of an integer
				2902	type.</li>
				2903	</ul>
				2904	</dd>
				2905	<dt><tt>SequentialType</tt></dt>
				2906	<dd>This is subclassed by ArrayType and PointerType
				2907	<ul>
				2908	<li><tt>const Type * getElementType() const</tt>: Returns the type of each
				2909	of the elements in the sequential type. </li>
				2910	</ul>
				2911	</dd>
				2912	<dt><tt>ArrayType</tt></dt>
				2913	<dd>This is a subclass of SequentialType and defines the interface for array
				2914	types.
				2915	<ul>
				2916	<li><tt>unsigned getNumElements() const</tt>: Returns the number of
				2917	elements in the array. </li>
				2918	</ul>
				2919	</dd>
				2920	<dt><tt>PointerType</tt></dt>
				2921	<dd>Subclass of SequentialType for pointer types.</dd>
				2922	<dt><tt>VectorType</tt></dt>
				2923	<dd>Subclass of SequentialType for vector types. A
				2924	vector type is similar to an ArrayType but is distinguished because it is
				2925	a first class type wherease ArrayType is not. Vector types are used for
				2926	vector operations and are usually small vectors of of an integer or floating
				2927	point type.</dd>
				2928	<dt><tt>StructType</tt></dt>
				2929	<dd>Subclass of DerivedTypes for struct types.</dd>
				2930	<dt><tt><a name="FunctionType">FunctionType</a></tt></dt>
				2931	<dd>Subclass of DerivedTypes for function types.
				2932	<ul>
				2933	<li><tt>bool isVarArg() const</tt>: Returns true if its a vararg
				2934	function</li>
				2935	<li><tt> const Type * getReturnType() const</tt>: Returns the
				2936	return type of the function.</li>
				2937	<li><tt>const Type * getParamType (unsigned i)</tt>: Returns
				2938	the type of the ith parameter.</li>
				2939	<li><tt> const unsigned getNumParams() const</tt>: Returns the
				2940	number of formal parameters.</li>
				2941	</ul>
				2942	</dd>
				2943	<dt><tt>OpaqueType</tt></dt>
				2944	<dd>Sublcass of DerivedType for abstract types. This class
				2945	defines no content and is used as a placeholder for some other type. Note
				2946	that OpaqueType is used (temporarily) during type resolution for forward
				2947	references of types. Once the referenced type is resolved, the OpaqueType
				2948	is replaced with the actual type. OpaqueType can also be used for data
				2949	abstraction. At link time opaque types can be resolved to actual types
				2950	of the same name.</dd>
				2951	</dl>
				2952	</div>
				2953
				2954
				2955
				2956	<!-- ======================================================================= -->
				2957	<div class="doc_subsection">
				2958	<a name="Module">The <tt>Module</tt> class</a>
				2959	</div>
				2960
				2961	<div class="doc_text">
				2962
				2963	<p><tt>#include "<a
				2964	href="/doxygen/Module_8h-source.html">llvm/Module.h</a>"</tt><br> doxygen info:
				2965	<a href="/doxygen/classllvm_1_1Module.html">Module Class</a></p>
				2966
				2967	<p>The <tt>Module</tt> class represents the top level structure present in LLVM
				2968	programs. An LLVM module is effectively either a translation unit of the
				2969	original program or a combination of several translation units merged by the
				2970	linker. The <tt>Module</tt> class keeps track of a list of <a
				2971	href="#Function"><tt>Function</tt></a>s, a list of <a
				2972	href="#GlobalVariable"><tt>GlobalVariable</tt></a>s, and a <a
				2973	href="#SymbolTable"><tt>SymbolTable</tt></a>. Additionally, it contains a few
				2974	helpful member functions that try to make common operations easy.</p>
				2975
				2976	</div>
				2977
				2978	<!-- _______________________________________________________________________ -->
				2979	<div class="doc_subsubsection">
				2980	<a name="m_Module">Important Public Members of the <tt>Module</tt> class</a>
				2981	</div>
				2982
				2983	<div class="doc_text">
				2984
				2985	<ul>
				2986	<li><tt>Module::Module(std::string name = "")</tt></li>
				2987	</ul>
				2988
				2989	<p>Constructing a <a href="#Module">Module</a> is easy. You can optionally
				2990	provide a name for it (probably based on the name of the translation unit).</p>
				2991
				2992	<ul>
				2993	<li><tt>Module::iterator</tt> - Typedef for function list iterator<br>
				2994	<tt>Module::const_iterator</tt> - Typedef for const_iterator.<br>
				2995
				2996	<tt>begin()</tt>, <tt>end()</tt>
				2997	<tt>size()</tt>, <tt>empty()</tt>
				2998
				2999	<p>These are forwarding methods that make it easy to access the contents of
				3000	a <tt>Module</tt> object's <a href="#Function"><tt>Function</tt></a>
				3001	list.</p></li>
				3002
				3003	<li><tt>Module::FunctionListType &getFunctionList()</tt>
				3004
				3005	<p> Returns the list of <a href="#Function"><tt>Function</tt></a>s. This is
				3006	necessary to use when you need to update the list or perform a complex
				3007	action that doesn't have a forwarding method.</p>
				3008
				3009	<p><!-- Global Variable --></p></li>
				3010	</ul>
				3011
				3012	<hr>
				3013
				3014	<ul>
				3015	<li><tt>Module::global_iterator</tt> - Typedef for global variable list iterator<br>
				3016
				3017	<tt>Module::const_global_iterator</tt> - Typedef for const_iterator.<br>
				3018
				3019	<tt>global_begin()</tt>, <tt>global_end()</tt>
				3020	<tt>global_size()</tt>, <tt>global_empty()</tt>
				3021
				3022	<p> These are forwarding methods that make it easy to access the contents of
				3023	a <tt>Module</tt> object's <a
				3024	href="#GlobalVariable"><tt>GlobalVariable</tt></a> list.</p></li>
				3025
				3026	<li><tt>Module::GlobalListType &getGlobalList()</tt>
				3027
				3028	<p>Returns the list of <a
				3029	href="#GlobalVariable"><tt>GlobalVariable</tt></a>s. This is necessary to
				3030	use when you need to update the list or perform a complex action that
				3031	doesn't have a forwarding method.</p>
				3032
				3033	<p><!-- Symbol table stuff --> </p></li>
				3034	</ul>
				3035
				3036	<hr>
				3037
				3038	<ul>
				3039	<li><tt><a href="#SymbolTable">SymbolTable</a> *getSymbolTable()</tt>
				3040
				3041	<p>Return a reference to the <a href="#SymbolTable"><tt>SymbolTable</tt></a>
				3042	for this <tt>Module</tt>.</p>
				3043
				3044	<p><!-- Convenience methods --></p></li>
				3045	</ul>
				3046
				3047	<hr>
				3048
				3049	<ul>
				3050	<li><tt><a href="#Function">Function</a> *getFunction(const std::string
				3051	&Name, const <a href="#FunctionType">FunctionType</a> *Ty)</tt>
				3052
				3053	<p>Look up the specified function in the <tt>Module</tt> <a
				3054	href="#SymbolTable"><tt>SymbolTable</tt></a>. If it does not exist, return
				3055	<tt>null</tt>.</p></li>
				3056
				3057	<li><tt><a href="#Function">Function</a> *getOrInsertFunction(const
				3058	std::string &Name, const <a href="#FunctionType">FunctionType</a> *T)</tt>
				3059
				3060	<p>Look up the specified function in the <tt>Module</tt> <a
				3061	href="#SymbolTable"><tt>SymbolTable</tt></a>. If it does not exist, add an
				3062	external declaration for the function and return it.</p></li>
				3063
				3064	<li><tt>std::string getTypeName(const <a href="#Type">Type</a> *Ty)</tt>
				3065
				3066	<p>If there is at least one entry in the <a
				3067	href="#SymbolTable"><tt>SymbolTable</tt></a> for the specified <a
				3068	href="#Type"><tt>Type</tt></a>, return it. Otherwise return the empty
				3069	string.</p></li>
				3070
				3071	<li><tt>bool addTypeName(const std::string &Name, const <a
				3072	href="#Type">Type</a> *Ty)</tt>
				3073
				3074	<p>Insert an entry in the <a href="#SymbolTable"><tt>SymbolTable</tt></a>
				3075	mapping <tt>Name</tt> to <tt>Ty</tt>. If there is already an entry for this
				3076	name, true is returned and the <a
				3077	href="#SymbolTable"><tt>SymbolTable</tt></a> is not modified.</p></li>
				3078	</ul>
				3079
				3080	</div>
				3081
				3082
				3083	<!-- ======================================================================= -->
				3084	<div class="doc_subsection">
				3085	<a name="Value">The <tt>Value</tt> class</a>
				3086	</div>
				3087
				3088	<div class="doc_text">
				3089
				3090	<p><tt>#include "<a href="/doxygen/Value_8h-source.html">llvm/Value.h</a>"</tt>
				3091	<br>
				3092	doxygen info: <a href="/doxygen/classllvm_1_1Value.html">Value Class</a></p>
				3093
				3094	<p>The <tt>Value</tt> class is the most important class in the LLVM Source
				3095	base. It represents a typed value that may be used (among other things) as an
				3096	operand to an instruction. There are many different types of <tt>Value</tt>s,
				3097	such as <a href="#Constant"><tt>Constant</tt></a>s,<a
				3098	href="#Argument"><tt>Argument</tt></a>s. Even <a
				3099	href="#Instruction"><tt>Instruction</tt></a>s and <a
				3100	href="#Function"><tt>Function</tt></a>s are <tt>Value</tt>s.</p>
				3101
				3102	<p>A particular <tt>Value</tt> may be used many times in the LLVM representation
				3103	for a program. For example, an incoming argument to a function (represented
				3104	with an instance of the <a href="#Argument">Argument</a> class) is "used" by
				3105	every instruction in the function that references the argument. To keep track
				3106	of this relationship, the <tt>Value</tt> class keeps a list of all of the <a
				3107	href="#User"><tt>User</tt></a>s that is using it (the <a
				3108	href="#User"><tt>User</tt></a> class is a base class for all nodes in the LLVM
				3109	graph that can refer to <tt>Value</tt>s). This use list is how LLVM represents
				3110	def-use information in the program, and is accessible through the <tt>use_</tt>*
				3111	methods, shown below.</p>
				3112
				3113	<p>Because LLVM is a typed representation, every LLVM <tt>Value</tt> is typed,
				3114	and this <a href="#Type">Type</a> is available through the <tt>getType()</tt>
				3115	method. In addition, all LLVM values can be named. The "name" of the
				3116	<tt>Value</tt> is a symbolic string printed in the LLVM code:</p>
				3117
				3118	<div class="doc_code">
				3119	<pre>
				3120	%<b>foo</b> = add i32 1, 2
				3121	</pre>
				3122	</div>
				3123
				3124	<p><a name="nameWarning">The name of this instruction is "foo".</a> <b>NOTE</b>
				3125	that the name of any value may be missing (an empty string), so names should
				3126	<b>ONLY</b> be used for debugging (making the source code easier to read,
				3127	debugging printouts), they should not be used to keep track of values or map
				3128	between them. For this purpose, use a <tt>std::map</tt> of pointers to the
				3129	<tt>Value</tt> itself instead.</p>
				3130
				3131	<p>One important aspect of LLVM is that there is no distinction between an SSA
				3132	variable and the operation that produces it. Because of this, any reference to
				3133	the value produced by an instruction (or the value available as an incoming
				3134	argument, for example) is represented as a direct pointer to the instance of
				3135	the class that
				3136	represents this value. Although this may take some getting used to, it
				3137	simplifies the representation and makes it easier to manipulate.</p>
				3138
				3139	</div>
				3140
				3141	<!-- _______________________________________________________________________ -->
				3142	<div class="doc_subsubsection">
				3143	<a name="m_Value">Important Public Members of the <tt>Value</tt> class</a>
				3144	</div>
				3145
				3146	<div class="doc_text">
				3147
				3148	<ul>
				3149	<li><tt>Value::use_iterator</tt> - Typedef for iterator over the
				3150	use-list<br>
				3151	<tt>Value::use_const_iterator</tt> - Typedef for const_iterator over
				3152	the use-list<br>
				3153	<tt>unsigned use_size()</tt> - Returns the number of users of the
				3154	value.<br>
				3155	<tt>bool use_empty()</tt> - Returns true if there are no users.<br>
				3156	<tt>use_iterator use_begin()</tt> - Get an iterator to the start of
				3157	the use-list.<br>
				3158	<tt>use_iterator use_end()</tt> - Get an iterator to the end of the
				3159	use-list.<br>
				3160	<tt><a href="#User">User</a> *use_back()</tt> - Returns the last
				3161	element in the list.
				3162	<p> These methods are the interface to access the def-use
				3163	information in LLVM. As with all other iterators in LLVM, the naming
				3164	conventions follow the conventions defined by the <a href="#stl">STL</a>.</p>
				3165	</li>
				3166	<li><tt><a href="#Type">Type</a> *getType() const</tt>
				3167	<p>This method returns the Type of the Value.</p>
				3168	</li>
				3169	<li><tt>bool hasName() const</tt><br>
				3170	<tt>std::string getName() const</tt><br>
				3171	<tt>void setName(const std::string &Name)</tt>
				3172	<p> This family of methods is used to access and assign a name to a <tt>Value</tt>,
				3173	be aware of the <a href="#nameWarning">precaution above</a>.</p>
				3174	</li>
				3175	<li><tt>void replaceAllUsesWith(Value *V)</tt>
				3176
				3177	<p>This method traverses the use list of a <tt>Value</tt> changing all <a
				3178	href="#User"><tt>User</tt>s</a> of the current value to refer to
				3179	"<tt>V</tt>" instead. For example, if you detect that an instruction always
				3180	produces a constant value (for example through constant folding), you can
				3181	replace all uses of the instruction with the constant like this:</p>
				3182
				3183	<div class="doc_code">
				3184	<pre>
				3185	Inst->replaceAllUsesWith(ConstVal);
				3186	</pre>
				3187	</div>
				3188
				3189	</ul>
				3190
				3191	</div>
				3192
				3193	<!-- ======================================================================= -->
				3194	<div class="doc_subsection">
				3195	<a name="User">The <tt>User</tt> class</a>
				3196	</div>
				3197
				3198	<div class="doc_text">
				3199
				3200	<p>
				3201	<tt>#include "<a href="/doxygen/User_8h-source.html">llvm/User.h</a>"</tt><br>
				3202	doxygen info: <a href="/doxygen/classllvm_1_1User.html">User Class</a><br>
				3203	Superclass: <a href="#Value"><tt>Value</tt></a></p>
				3204
				3205	<p>The <tt>User</tt> class is the common base class of all LLVM nodes that may
				3206	refer to <a href="#Value"><tt>Value</tt></a>s. It exposes a list of "Operands"
				3207	that are all of the <a href="#Value"><tt>Value</tt></a>s that the User is
				3208	referring to. The <tt>User</tt> class itself is a subclass of
				3209	<tt>Value</tt>.</p>
				3210
				3211	<p>The operands of a <tt>User</tt> point directly to the LLVM <a
				3212	href="#Value"><tt>Value</tt></a> that it refers to. Because LLVM uses Static
				3213	Single Assignment (SSA) form, there can only be one definition referred to,
				3214	allowing this direct connection. This connection provides the use-def
				3215	information in LLVM.</p>
				3216
				3217	</div>
				3218
				3219	<!-- _______________________________________________________________________ -->
				3220	<div class="doc_subsubsection">
				3221	<a name="m_User">Important Public Members of the <tt>User</tt> class</a>
				3222	</div>
				3223
				3224	<div class="doc_text">
				3225
				3226	<p>The <tt>User</tt> class exposes the operand list in two ways: through
				3227	an index access interface and through an iterator based interface.</p>
				3228
				3229	<ul>
				3230	<li><tt>Value *getOperand(unsigned i)</tt><br>
				3231	<tt>unsigned getNumOperands()</tt>
				3232	<p> These two methods expose the operands of the <tt>User</tt> in a
				3233	convenient form for direct access.</p></li>
				3234
				3235	<li><tt>User::op_iterator</tt> - Typedef for iterator over the operand
				3236	list<br>
				3237	<tt>op_iterator op_begin()</tt> - Get an iterator to the start of
				3238	the operand list.<br>
				3239	<tt>op_iterator op_end()</tt> - Get an iterator to the end of the
				3240	operand list.
				3241	<p> Together, these methods make up the iterator based interface to
				3242	the operands of a <tt>User</tt>.</p></li>
				3243	</ul>
				3244
				3245	</div>
				3246
				3247	<!-- ======================================================================= -->
				3248	<div class="doc_subsection">
				3249	<a name="Instruction">The <tt>Instruction</tt> class</a>
				3250	</div>
				3251
				3252	<div class="doc_text">
				3253
				3254	<p><tt>#include "</tt><tt><a
				3255	href="/doxygen/Instruction_8h-source.html">llvm/Instruction.h</a>"</tt><br>
				3256	doxygen info: <a href="/doxygen/classllvm_1_1Instruction.html">Instruction Class</a><br>
				3257	Superclasses: <a href="#User"><tt>User</tt></a>, <a
				3258	href="#Value"><tt>Value</tt></a></p>
				3259
				3260	<p>The <tt>Instruction</tt> class is the common base class for all LLVM
				3261	instructions. It provides only a few methods, but is a very commonly used
				3262	class. The primary data tracked by the <tt>Instruction</tt> class itself is the
				3263	opcode (instruction type) and the parent <a
				3264	href="#BasicBlock"><tt>BasicBlock</tt></a> the <tt>Instruction</tt> is embedded
				3265	into. To represent a specific type of instruction, one of many subclasses of
				3266	<tt>Instruction</tt> are used.</p>
				3267
				3268	<p> Because the <tt>Instruction</tt> class subclasses the <a
				3269	href="#User"><tt>User</tt></a> class, its operands can be accessed in the same
				3270	way as for other <a href="#User"><tt>User</tt></a>s (with the
				3271	<tt>getOperand()</tt>/<tt>getNumOperands()</tt> and
				3272	<tt>op_begin()</tt>/<tt>op_end()</tt> methods).</p> <p> An important file for
				3273	the <tt>Instruction</tt> class is the <tt>llvm/Instruction.def</tt> file. This
				3274	file contains some meta-data about the various different types of instructions
				3275	in LLVM. It describes the enum values that are used as opcodes (for example
				3276	<tt>Instruction::Add</tt> and <tt>Instruction::ICmp</tt>), as well as the
				3277	concrete sub-classes of <tt>Instruction</tt> that implement the instruction (for
				3278	example <tt><a href="#BinaryOperator">BinaryOperator</a></tt> and <tt><a
				3279	href="#CmpInst">CmpInst</a></tt>). Unfortunately, the use of macros in
				3280	this file confuses doxygen, so these enum values don't show up correctly in the
				3281	<a href="/doxygen/classllvm_1_1Instruction.html">doxygen output</a>.</p>
				3282
				3283	</div>
				3284
				3285	<!-- _______________________________________________________________________ -->
				3286	<div class="doc_subsubsection">
				3287	<a name="s_Instruction">Important Subclasses of the <tt>Instruction</tt>
				3288	class</a>
				3289	</div>
				3290	<div class="doc_text">
				3291	<ul>
				3292	<li><tt><a name="BinaryOperator">BinaryOperator</a></tt>
				3293	<p>This subclasses represents all two operand instructions whose operands
				3294	must be the same type, except for the comparison instructions.</p></li>
				3295	<li><tt><a name="CastInst">CastInst</a></tt>
				3296	<p>This subclass is the parent of the 12 casting instructions. It provides
				3297	common operations on cast instructions.</p>
				3298	<li><tt><a name="CmpInst">CmpInst</a></tt>
				3299	<p>This subclass respresents the two comparison instructions,
				3300	<a href="LangRef.html#i_icmp">ICmpInst</a> (integer opreands), and
				3301	<a href="LangRef.html#i_fcmp">FCmpInst</a> (floating point operands).</p>
				3302	<li><tt><a name="TerminatorInst">TerminatorInst</a></tt>
				3303	<p>This subclass is the parent of all terminator instructions (those which
				3304	can terminate a block).</p>
				3305	</ul>
				3306	</div>
				3307
				3308	<!-- _______________________________________________________________________ -->
				3309	<div class="doc_subsubsection">
				3310	<a name="m_Instruction">Important Public Members of the <tt>Instruction</tt>
				3311	class</a>
				3312	</div>
				3313
				3314	<div class="doc_text">
				3315
				3316	<ul>
				3317	<li><tt><a href="#BasicBlock">BasicBlock</a> *getParent()</tt>
				3318	<p>Returns the <a href="#BasicBlock"><tt>BasicBlock</tt></a> that
				3319	this <tt>Instruction</tt> is embedded into.</p></li>
				3320	<li><tt>bool mayWriteToMemory()</tt>
				3321	<p>Returns true if the instruction writes to memory, i.e. it is a
				3322	<tt>call</tt>,<tt>free</tt>,<tt>invoke</tt>, or <tt>store</tt>.</p></li>
				3323	<li><tt>unsigned getOpcode()</tt>
				3324	<p>Returns the opcode for the <tt>Instruction</tt>.</p></li>
				3325	<li><tt><a href="#Instruction">Instruction</a> *clone() const</tt>
				3326	<p>Returns another instance of the specified instruction, identical
				3327	in all ways to the original except that the instruction has no parent
				3328	(ie it's not embedded into a <a href="#BasicBlock"><tt>BasicBlock</tt></a>),
				3329	and it has no name</p></li>
				3330	</ul>
				3331
				3332	</div>
				3333
				3334	<!-- ======================================================================= -->
				3335	<div class="doc_subsection">
				3336	<a name="Constant">The <tt>Constant</tt> class and subclasses</a>
				3337	</div>
				3338
				3339	<div class="doc_text">
				3340
				3341	<p>Constant represents a base class for different types of constants. It
				3342	is subclassed by ConstantInt, ConstantArray, etc. for representing
				3343	the various types of Constants. <a href="#GlobalValue">GlobalValue</a> is also
				3344	a subclass, which represents the address of a global variable or function.
				3345	</p>
				3346
				3347	</div>
				3348
				3349	<!-- _______________________________________________________________________ -->
				3350	<div class="doc_subsubsection">Important Subclasses of Constant </div>
				3351	<div class="doc_text">
				3352	<ul>
				3353	<li>ConstantInt : This subclass of Constant represents an integer constant of
				3354	any width.
				3355	<ul>
				3356	<li><tt>const APInt& getValue() const</tt>: Returns the underlying
				3357	value of this constant, an APInt value.</li>
				3358	<li><tt>int64_t getSExtValue() const</tt>: Converts the underlying APInt
				3359	value to an int64_t via sign extension. If the value (not the bit width)
				3360	of the APInt is too large to fit in an int64_t, an assertion will result.
				3361	For this reason, use of this method is discouraged.</li>
				3362	<li><tt>uint64_t getZExtValue() const</tt>: Converts the underlying APInt
				3363	value to a uint64_t via zero extension. IF the value (not the bit width)
				3364	of the APInt is too large to fit in a uint64_t, an assertion will result.
				3365	For this reason, use of this method is discouraged.</li>
				3366	<li><tt>static ConstantInt* get(const APInt& Val)</tt>: Returns the
				3367	ConstantInt object that represents the value provided by <tt>Val</tt>.
				3368	The type is implied as the IntegerType that corresponds to the bit width
				3369	of <tt>Val</tt>.</li>
				3370	<li><tt>static ConstantInt* get(const Type *Ty, uint64_t Val)</tt>:
				3371	Returns the ConstantInt object that represents the value provided by
				3372	<tt>Val</tt> for integer type <tt>Ty</tt>.</li>
				3373	</ul>
				3374	</li>
				3375	<li>ConstantFP : This class represents a floating point constant.
				3376	<ul>
				3377	<li><tt>double getValue() const</tt>: Returns the underlying value of
				3378	this constant. </li>
				3379	</ul>
				3380	</li>
				3381	<li>ConstantArray : This represents a constant array.
				3382	<ul>
				3383	<li><tt>const std::vector<Use> &getValues() const</tt>: Returns
				3384	a vector of component constants that makeup this array. </li>
				3385	</ul>
				3386	</li>
				3387	<li>ConstantStruct : This represents a constant struct.
				3388	<ul>
				3389	<li><tt>const std::vector<Use> &getValues() const</tt>: Returns
				3390	a vector of component constants that makeup this array. </li>
				3391	</ul>
				3392	</li>
				3393	<li>GlobalValue : This represents either a global variable or a function. In
				3394	either case, the value is a constant fixed address (after linking).
				3395	</li>
				3396	</ul>
				3397	</div>
				3398
				3399
				3400	<!-- ======================================================================= -->
				3401	<div class="doc_subsection">
				3402	<a name="GlobalValue">The <tt>GlobalValue</tt> class</a>
				3403	</div>
				3404
				3405	<div class="doc_text">
				3406
				3407	<p><tt>#include "<a
				3408	href="/doxygen/GlobalValue_8h-source.html">llvm/GlobalValue.h</a>"</tt><br>
				3409	doxygen info: <a href="/doxygen/classllvm_1_1GlobalValue.html">GlobalValue
				3410	Class</a><br>
				3411	Superclasses: <a href="#Constant"><tt>Constant</tt></a>,
				3412	<a href="#User"><tt>User</tt></a>, <a href="#Value"><tt>Value</tt></a></p>
				3413
				3414	<p>Global values (<a href="#GlobalVariable"><tt>GlobalVariable</tt></a>s or <a
				3415	href="#Function"><tt>Function</tt></a>s) are the only LLVM values that are
				3416	visible in the bodies of all <a href="#Function"><tt>Function</tt></a>s.
				3417	Because they are visible at global scope, they are also subject to linking with
				3418	other globals defined in different translation units. To control the linking
				3419	process, <tt>GlobalValue</tt>s know their linkage rules. Specifically,
				3420	<tt>GlobalValue</tt>s know whether they have internal or external linkage, as
				3421	defined by the <tt>LinkageTypes</tt> enumeration.</p>
				3422
				3423	<p>If a <tt>GlobalValue</tt> has internal linkage (equivalent to being
				3424	<tt>static</tt> in C), it is not visible to code outside the current translation
				3425	unit, and does not participate in linking. If it has external linkage, it is
				3426	visible to external code, and does participate in linking. In addition to
				3427	linkage information, <tt>GlobalValue</tt>s keep track of which <a
				3428	href="#Module"><tt>Module</tt></a> they are currently part of.</p>
				3429
				3430	<p>Because <tt>GlobalValue</tt>s are memory objects, they are always referred to
				3431	by their <b>address</b>. As such, the <a href="#Type"><tt>Type</tt></a> of a
				3432	global is always a pointer to its contents. It is important to remember this
				3433	when using the <tt>GetElementPtrInst</tt> instruction because this pointer must
				3434	be dereferenced first. For example, if you have a <tt>GlobalVariable</tt> (a
				3435	subclass of <tt>GlobalValue)</tt> that is an array of 24 ints, type <tt>[24 x
				3436	i32]</tt>, then the <tt>GlobalVariable</tt> is a pointer to that array. Although
				3437	the address of the first element of this array and the value of the
				3438	<tt>GlobalVariable</tt> are the same, they have different types. The
				3439	<tt>GlobalVariable</tt>'s type is <tt>[24 x i32]</tt>. The first element's type
				3440	is <tt>i32.</tt> Because of this, accessing a global value requires you to
				3441	dereference the pointer with <tt>GetElementPtrInst</tt> first, then its elements
				3442	can be accessed. This is explained in the <a href="LangRef.html#globalvars">LLVM
				3443	Language Reference Manual</a>.</p>
				3444
				3445	</div>
				3446
				3447	<!-- _______________________________________________________________________ -->
				3448	<div class="doc_subsubsection">
				3449	<a name="m_GlobalValue">Important Public Members of the <tt>GlobalValue</tt>
				3450	class</a>
				3451	</div>
				3452
				3453	<div class="doc_text">
				3454
				3455	<ul>
				3456	<li><tt>bool hasInternalLinkage() const</tt><br>
				3457	<tt>bool hasExternalLinkage() const</tt><br>
				3458	<tt>void setInternalLinkage(bool HasInternalLinkage)</tt>
				3459	<p> These methods manipulate the linkage characteristics of the <tt>GlobalValue</tt>.</p>
				3460	<p> </p>
				3461	</li>
				3462	<li><tt><a href="#Module">Module</a> *getParent()</tt>
				3463	<p> This returns the <a href="#Module"><tt>Module</tt></a> that the
				3464	GlobalValue is currently embedded into.</p></li>
				3465	</ul>
				3466
				3467	</div>
				3468
				3469	<!-- ======================================================================= -->
				3470	<div class="doc_subsection">
				3471	<a name="Function">The <tt>Function</tt> class</a>
				3472	</div>
				3473
				3474	<div class="doc_text">
				3475
				3476	<p><tt>#include "<a
				3477	href="/doxygen/Function_8h-source.html">llvm/Function.h</a>"</tt><br> doxygen
				3478	info: <a href="/doxygen/classllvm_1_1Function.html">Function Class</a><br>
				3479	Superclasses: <a href="#GlobalValue"><tt>GlobalValue</tt></a>,
				3480	<a href="#Constant"><tt>Constant</tt></a>,
				3481	<a href="#User"><tt>User</tt></a>,
				3482	<a href="#Value"><tt>Value</tt></a></p>
				3483
				3484	<p>The <tt>Function</tt> class represents a single procedure in LLVM. It is
				3485	actually one of the more complex classes in the LLVM heirarchy because it must
				3486	keep track of a large amount of data. The <tt>Function</tt> class keeps track
				3487	of a list of <a href="#BasicBlock"><tt>BasicBlock</tt></a>s, a list of formal
				3488	<a href="#Argument"><tt>Argument</tt></a>s, and a
				3489	<a href="#SymbolTable"><tt>SymbolTable</tt></a>.</p>
				3490
				3491	<p>The list of <a href="#BasicBlock"><tt>BasicBlock</tt></a>s is the most
				3492	commonly used part of <tt>Function</tt> objects. The list imposes an implicit
				3493	ordering of the blocks in the function, which indicate how the code will be
				3494	layed out by the backend. Additionally, the first <a
				3495	href="#BasicBlock"><tt>BasicBlock</tt></a> is the implicit entry node for the
				3496	<tt>Function</tt>. It is not legal in LLVM to explicitly branch to this initial
				3497	block. There are no implicit exit nodes, and in fact there may be multiple exit
				3498	nodes from a single <tt>Function</tt>. If the <a
				3499	href="#BasicBlock"><tt>BasicBlock</tt></a> list is empty, this indicates that
				3500	the <tt>Function</tt> is actually a function declaration: the actual body of the
				3501	function hasn't been linked in yet.</p>
				3502
				3503	<p>In addition to a list of <a href="#BasicBlock"><tt>BasicBlock</tt></a>s, the
				3504	<tt>Function</tt> class also keeps track of the list of formal <a
				3505	href="#Argument"><tt>Argument</tt></a>s that the function receives. This
				3506	container manages the lifetime of the <a href="#Argument"><tt>Argument</tt></a>
				3507	nodes, just like the <a href="#BasicBlock"><tt>BasicBlock</tt></a> list does for
				3508	the <a href="#BasicBlock"><tt>BasicBlock</tt></a>s.</p>
				3509
				3510	<p>The <a href="#SymbolTable"><tt>SymbolTable</tt></a> is a very rarely used
				3511	LLVM feature that is only used when you have to look up a value by name. Aside
				3512	from that, the <a href="#SymbolTable"><tt>SymbolTable</tt></a> is used
				3513	internally to make sure that there are not conflicts between the names of <a
				3514	href="#Instruction"><tt>Instruction</tt></a>s, <a
				3515	href="#BasicBlock"><tt>BasicBlock</tt></a>s, or <a
				3516	href="#Argument"><tt>Argument</tt></a>s in the function body.</p>
				3517
				3518	<p>Note that <tt>Function</tt> is a <a href="#GlobalValue">GlobalValue</a>
				3519	and therefore also a <a href="#Constant">Constant</a>. The value of the function
				3520	is its address (after linking) which is guaranteed to be constant.</p>
				3521	</div>
				3522
				3523	<!-- _______________________________________________________________________ -->
				3524	<div class="doc_subsubsection">
				3525	<a name="m_Function">Important Public Members of the <tt>Function</tt>
				3526	class</a>
				3527	</div>
				3528
				3529	<div class="doc_text">
				3530
				3531	<ul>
				3532	<li><tt>Function(const </tt><tt><a href="#FunctionType">FunctionType</a>
				3533	Ty, LinkageTypes Linkage, const std::string &N = "", Module Parent = 0)</tt>
				3534
				3535	<p>Constructor used when you need to create new <tt>Function</tt>s to add
				3536	the the program. The constructor must specify the type of the function to
				3537	create and what type of linkage the function should have. The <a
				3538	href="#FunctionType"><tt>FunctionType</tt></a> argument
				3539	specifies the formal arguments and return value for the function. The same
				3540	<a href="#FunctionType"><tt>FunctionType</tt></a> value can be used to
				3541	create multiple functions. The <tt>Parent</tt> argument specifies the Module
				3542	in which the function is defined. If this argument is provided, the function
				3543	will automatically be inserted into that module's list of
				3544	functions.</p></li>
				3545
Chris Lattner	5e70957	2008-11-25 18:34:50 +0000	[diff] [blame]	3546	<li><tt>bool isDeclaration()</tt>
Dan Gohman	f17a25c	2007-07-18 16:29:46 +0000	[diff] [blame]	3547
				3548	<p>Return whether or not the <tt>Function</tt> has a body defined. If the
				3549	function is "external", it does not have a body, and thus must be resolved
				3550	by linking with a function defined in a different translation unit.</p></li>
				3551
				3552	<li><tt>Function::iterator</tt> - Typedef for basic block list iterator<br>
				3553	<tt>Function::const_iterator</tt> - Typedef for const_iterator.<br>
				3554
				3555	<tt>begin()</tt>, <tt>end()</tt>
				3556	<tt>size()</tt>, <tt>empty()</tt>
				3557
				3558	<p>These are forwarding methods that make it easy to access the contents of
				3559	a <tt>Function</tt> object's <a href="#BasicBlock"><tt>BasicBlock</tt></a>
				3560	list.</p></li>
				3561
				3562	<li><tt>Function::BasicBlockListType &getBasicBlockList()</tt>
				3563
				3564	<p>Returns the list of <a href="#BasicBlock"><tt>BasicBlock</tt></a>s. This
				3565	is necessary to use when you need to update the list or perform a complex
				3566	action that doesn't have a forwarding method.</p></li>
				3567
				3568	<li><tt>Function::arg_iterator</tt> - Typedef for the argument list
				3569	iterator<br>
				3570	<tt>Function::const_arg_iterator</tt> - Typedef for const_iterator.<br>
				3571
				3572	<tt>arg_begin()</tt>, <tt>arg_end()</tt>
				3573	<tt>arg_size()</tt>, <tt>arg_empty()</tt>
				3574
				3575	<p>These are forwarding methods that make it easy to access the contents of
				3576	a <tt>Function</tt> object's <a href="#Argument"><tt>Argument</tt></a>
				3577	list.</p></li>
				3578
				3579	<li><tt>Function::ArgumentListType &getArgumentList()</tt>
				3580
				3581	<p>Returns the list of <a href="#Argument"><tt>Argument</tt></a>s. This is
				3582	necessary to use when you need to update the list or perform a complex
				3583	action that doesn't have a forwarding method.</p></li>
				3584
				3585	<li><tt><a href="#BasicBlock">BasicBlock</a> &getEntryBlock()</tt>
				3586
				3587	<p>Returns the entry <a href="#BasicBlock"><tt>BasicBlock</tt></a> for the
				3588	function. Because the entry block for the function is always the first
				3589	block, this returns the first block of the <tt>Function</tt>.</p></li>
				3590
				3591	<li><tt><a href="#Type">Type</a> *getReturnType()</tt><br>
				3592	<tt><a href="#FunctionType">FunctionType</a> *getFunctionType()</tt>
				3593
				3594	<p>This traverses the <a href="#Type"><tt>Type</tt></a> of the
				3595	<tt>Function</tt> and returns the return type of the function, or the <a
				3596	href="#FunctionType"><tt>FunctionType</tt></a> of the actual
				3597	function.</p></li>
				3598
				3599	<li><tt><a href="#SymbolTable">SymbolTable</a> *getSymbolTable()</tt>
				3600
				3601	<p> Return a pointer to the <a href="#SymbolTable"><tt>SymbolTable</tt></a>
				3602	for this <tt>Function</tt>.</p></li>
				3603	</ul>
				3604
				3605	</div>
				3606
				3607	<!-- ======================================================================= -->
				3608	<div class="doc_subsection">
				3609	<a name="GlobalVariable">The <tt>GlobalVariable</tt> class</a>
				3610	</div>
				3611
				3612	<div class="doc_text">
				3613
				3614	<p><tt>#include "<a
				3615	href="/doxygen/GlobalVariable_8h-source.html">llvm/GlobalVariable.h</a>"</tt>
				3616	<br>
				3617	doxygen info: <a href="/doxygen/classllvm_1_1GlobalVariable.html">GlobalVariable
				3618	Class</a><br>
				3619	Superclasses: <a href="#GlobalValue"><tt>GlobalValue</tt></a>,
				3620	<a href="#Constant"><tt>Constant</tt></a>,
				3621	<a href="#User"><tt>User</tt></a>,
				3622	<a href="#Value"><tt>Value</tt></a></p>
				3623
				3624	<p>Global variables are represented with the (suprise suprise)
				3625	<tt>GlobalVariable</tt> class. Like functions, <tt>GlobalVariable</tt>s are also
				3626	subclasses of <a href="#GlobalValue"><tt>GlobalValue</tt></a>, and as such are
				3627	always referenced by their address (global values must live in memory, so their
				3628	"name" refers to their constant address). See
				3629	<a href="#GlobalValue"><tt>GlobalValue</tt></a> for more on this. Global
				3630	variables may have an initial value (which must be a
				3631	<a href="#Constant"><tt>Constant</tt></a>), and if they have an initializer,
				3632	they may be marked as "constant" themselves (indicating that their contents
				3633	never change at runtime).</p>
				3634	</div>
				3635
				3636	<!-- _______________________________________________________________________ -->
				3637	<div class="doc_subsubsection">
				3638	<a name="m_GlobalVariable">Important Public Members of the
				3639	<tt>GlobalVariable</tt> class</a>
				3640	</div>
				3641
				3642	<div class="doc_text">
				3643
				3644	<ul>
				3645	<li><tt>GlobalVariable(const </tt><tt><a href="#Type">Type</a> *Ty, bool
				3646	isConstant, LinkageTypes& Linkage, <a href="#Constant">Constant</a>
				3647	Initializer = 0, const std::string &Name = "", Module Parent = 0)</tt>
				3648
				3649	<p>Create a new global variable of the specified type. If
				3650	<tt>isConstant</tt> is true then the global variable will be marked as
				3651	unchanging for the program. The Linkage parameter specifies the type of
Duncan Sands	19d161f	2009-03-07 15:45:40 +0000	[diff] [blame]	3652	linkage (internal, external, weak, linkonce, appending) for the variable.
				3653	If the linkage is InternalLinkage, WeakAnyLinkage, WeakODRLinkage,
				3654	LinkOnceAnyLinkage or LinkOnceODRLinkage,  then the resultant
				3655	global variable will have internal linkage. AppendingLinkage concatenates
				3656	together all instances (in different translation units) of the variable
				3657	into a single variable but is only applicable to arrays.  See
Dan Gohman	f17a25c	2007-07-18 16:29:46 +0000	[diff] [blame]	3658	the <a href="LangRef.html#modulestructure">LLVM Language Reference</a> for
				3659	further details on linkage types. Optionally an initializer, a name, and the
				3660	module to put the variable into may be specified for the global variable as
				3661	well.</p></li>
				3662
				3663	<li><tt>bool isConstant() const</tt>
				3664
				3665	<p>Returns true if this is a global variable that is known not to
				3666	be modified at runtime.</p></li>
				3667
				3668	<li><tt>bool hasInitializer()</tt>
				3669
				3670	<p>Returns true if this <tt>GlobalVariable</tt> has an intializer.</p></li>
				3671
				3672	<li><tt><a href="#Constant">Constant</a> *getInitializer()</tt>
				3673
				3674	<p>Returns the intial value for a <tt>GlobalVariable</tt>. It is not legal
				3675	to call this method if there is no initializer.</p></li>
				3676	</ul>
				3677
				3678	</div>
				3679
				3680
				3681	<!-- ======================================================================= -->
				3682	<div class="doc_subsection">
				3683	<a name="BasicBlock">The <tt>BasicBlock</tt> class</a>
				3684	</div>
				3685
				3686	<div class="doc_text">
				3687
				3688	<p><tt>#include "<a
				3689	href="/doxygen/BasicBlock_8h-source.html">llvm/BasicBlock.h</a>"</tt><br>
Stefanus Du Toit	f017c85	2009-06-17 21:12:26 +0000	[diff] [blame]	3690	doxygen info: <a href="/doxygen/classllvm_1_1BasicBlock.html">BasicBlock
Dan Gohman	f17a25c	2007-07-18 16:29:46 +0000	[diff] [blame]	3691	Class</a><br>
				3692	Superclass: <a href="#Value"><tt>Value</tt></a></p>
				3693
				3694	<p>This class represents a single entry multiple exit section of the code,
				3695	commonly known as a basic block by the compiler community. The
				3696	<tt>BasicBlock</tt> class maintains a list of <a
				3697	href="#Instruction"><tt>Instruction</tt></a>s, which form the body of the block.
				3698	Matching the language definition, the last element of this list of instructions
				3699	is always a terminator instruction (a subclass of the <a
				3700	href="#TerminatorInst"><tt>TerminatorInst</tt></a> class).</p>
				3701
				3702	<p>In addition to tracking the list of instructions that make up the block, the
				3703	<tt>BasicBlock</tt> class also keeps track of the <a
				3704	href="#Function"><tt>Function</tt></a> that it is embedded into.</p>
				3705
				3706	<p>Note that <tt>BasicBlock</tt>s themselves are <a
				3707	href="#Value"><tt>Value</tt></a>s, because they are referenced by instructions
				3708	like branches and can go in the switch tables. <tt>BasicBlock</tt>s have type
				3709	<tt>label</tt>.</p>
				3710
				3711	</div>
				3712
				3713	<!-- _______________________________________________________________________ -->
				3714	<div class="doc_subsubsection">
				3715	<a name="m_BasicBlock">Important Public Members of the <tt>BasicBlock</tt>
				3716	class</a>
				3717	</div>
				3718
				3719	<div class="doc_text">
				3720	<ul>
				3721
				3722	<li><tt>BasicBlock(const std::string &Name = "", </tt><tt><a
				3723	href="#Function">Function</a> *Parent = 0)</tt>
				3724
				3725	<p>The <tt>BasicBlock</tt> constructor is used to create new basic blocks for
				3726	insertion into a function. The constructor optionally takes a name for the new
				3727	block, and a <a href="#Function"><tt>Function</tt></a> to insert it into. If
				3728	the <tt>Parent</tt> parameter is specified, the new <tt>BasicBlock</tt> is
				3729	automatically inserted at the end of the specified <a
				3730	href="#Function"><tt>Function</tt></a>, if not specified, the BasicBlock must be
				3731	manually inserted into the <a href="#Function"><tt>Function</tt></a>.</p></li>
				3732
				3733	<li><tt>BasicBlock::iterator</tt> - Typedef for instruction list iterator<br>
				3734	<tt>BasicBlock::const_iterator</tt> - Typedef for const_iterator.<br>
				3735	<tt>begin()</tt>, <tt>end()</tt>, <tt>front()</tt>, <tt>back()</tt>,
				3736	<tt>size()</tt>, <tt>empty()</tt>
				3737	STL-style functions for accessing the instruction list.
				3738
				3739	<p>These methods and typedefs are forwarding functions that have the same
				3740	semantics as the standard library methods of the same names. These methods
				3741	expose the underlying instruction list of a basic block in a way that is easy to
				3742	manipulate. To get the full complement of container operations (including
				3743	operations to update the list), you must use the <tt>getInstList()</tt>
				3744	method.</p></li>
				3745
				3746	<li><tt>BasicBlock::InstListType &getInstList()</tt>
				3747
				3748	<p>This method is used to get access to the underlying container that actually
				3749	holds the Instructions. This method must be used when there isn't a forwarding
				3750	function in the <tt>BasicBlock</tt> class for the operation that you would like
				3751	to perform. Because there are no forwarding functions for "updating"
				3752	operations, you need to use this if you want to update the contents of a
				3753	<tt>BasicBlock</tt>.</p></li>
				3754
				3755	<li><tt><a href="#Function">Function</a> *getParent()</tt>
				3756
				3757	<p> Returns a pointer to <a href="#Function"><tt>Function</tt></a> the block is
				3758	embedded into, or a null pointer if it is homeless.</p></li>
				3759
				3760	<li><tt><a href="#TerminatorInst">TerminatorInst</a> *getTerminator()</tt>
				3761
				3762	<p> Returns a pointer to the terminator instruction that appears at the end of
				3763	the <tt>BasicBlock</tt>. If there is no terminator instruction, or if the last
				3764	instruction in the block is not a terminator, then a null pointer is
				3765	returned.</p></li>
				3766
				3767	</ul>
				3768
				3769	</div>
				3770
				3771
				3772	<!-- ======================================================================= -->
				3773	<div class="doc_subsection">
				3774	<a name="Argument">The <tt>Argument</tt> class</a>
				3775	</div>
				3776
				3777	<div class="doc_text">
				3778
				3779	<p>This subclass of Value defines the interface for incoming formal
				3780	arguments to a function. A Function maintains a list of its formal
				3781	arguments. An argument has a pointer to the parent Function.</p>
				3782
				3783	</div>
				3784
				3785	<!-- *********************************************************************** -->
				3786	<hr>
				3787	<address>
				3788	<a href="http://jigsaw.w3.org/css-validator/check/referer"><img
Misha Brukman	947321d	2008-12-11 17:34:48 +0000	[diff] [blame]	3789	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]	3790	<a href="http://validator.w3.org/check/referer"><img
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Dan Gohman	f17a25c	2007-07-18 16:29:46 +0000	[diff] [blame]	3792
				3793	<a href="mailto:dhurjati@cs.uiuc.edu">Dinakar Dhurjati</a> and
				3794	<a href="mailto:sabre@nondot.org">Chris Lattner</a><br>
				3795	<a href="http://llvm.org">The LLVM Compiler Infrastructure</a><br>
				3796	Last modified: $Date$
				3797	</address>
				3798
				3799	</body>
				3800	</html>