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Chris Lattner	261efe9	2003-11-25 01:02:51 +0000	[diff] [blame]	6	<title>LLVM Programmer's Manual</title>
Misha Brukman	13fd15c	2004-01-15 00:14:41 +0000	[diff] [blame]	7	<link rel="stylesheet" href="llvm.css" type="text/css">
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Misha Brukman	13fd15c	2004-01-15 00:14:41 +0000	[diff] [blame]	9	<body>
				10
NAKAMURA Takumi	05d0265	2011-04-18 23:59:50 +0000	[diff] [blame]	11	<h1>
Misha Brukman	13fd15c	2004-01-15 00:14:41 +0000	[diff] [blame]	12	LLVM Programmer's Manual
NAKAMURA Takumi	05d0265	2011-04-18 23:59:50 +0000	[diff] [blame]	13	</h1>
Misha Brukman	13fd15c	2004-01-15 00:14:41 +0000	[diff] [blame]	14
Chris Lattner	9355b47	2002-09-06 02:50:58 +0000	[diff] [blame]	15	<ol>
Misha Brukman	13fd15c	2004-01-15 00:14:41 +0000	[diff] [blame]	16	<li><a href="#introduction">Introduction</a></li>
Chris Lattner	9355b47	2002-09-06 02:50:58 +0000	[diff] [blame]	17	<li><a href="#general">General Information</a>
Chris Lattner	261efe9	2003-11-25 01:02:51 +0000	[diff] [blame]	18	<ul>
Reid Spencer	fe8f4ff	2004-11-01 09:02:53 +0000	[diff] [blame]	19	<li><a href="#stl">The C++ Standard Template Library</a></li>
				20	<!--
				21	<li>The <tt>-time-passes</tt> option</li>
				22	<li>How to use the LLVM Makefile system</li>
				23	<li>How to write a regression test</li>
Chris Lattner	61db465	2004-12-08 19:05:44 +0000	[diff] [blame]	24
Reid Spencer	fe8f4ff	2004-11-01 09:02:53 +0000	[diff] [blame]	25	-->
Chris Lattner	84b7f8d	2003-08-01 22:20:59 +0000	[diff] [blame]	26	</ul>
Chris Lattner	261efe9	2003-11-25 01:02:51 +0000	[diff] [blame]	27	</li>
				28	<li><a href="#apis">Important and useful LLVM APIs</a>
				29	<ul>
				30	<li><a href="#isa">The <tt>isa<></tt>, <tt>cast<></tt>
				31	and <tt>dyn_cast<></tt> templates</a> </li>
Daniel Dunbar	6e0d1cb	2009-07-25 04:41:11 +0000	[diff] [blame]	32	<li><a href="#string_apis">Passing strings (the <tt>StringRef</tt>
Benjamin Kramer	e15192b	2009-08-05 15:42:44 +0000	[diff] [blame]	33	and <tt>Twine</tt> classes)</a>
Daniel Dunbar	6e0d1cb	2009-07-25 04:41:11 +0000	[diff] [blame]	34	<ul>
				35	<li><a href="#StringRef">The <tt>StringRef</tt> class</a> </li>
				36	<li><a href="#Twine">The <tt>Twine</tt> class</a> </li>
				37	</ul>
Benjamin Kramer	e15192b	2009-08-05 15:42:44 +0000	[diff] [blame]	38	</li>
Misha Brukman	2c122ce	2005-11-01 21:12:49 +0000	[diff] [blame]	39	<li><a href="#DEBUG">The <tt>DEBUG()</tt> macro and <tt>-debug</tt>
Chris Lattner	261efe9	2003-11-25 01:02:51 +0000	[diff] [blame]	40	option</a>
				41	<ul>
				42	<li><a href="#DEBUG_TYPE">Fine grained debug info with <tt>DEBUG_TYPE</tt>
				43	and the <tt>-debug-only</tt> option</a> </li>
				44	</ul>
				45	</li>
Chris Lattner	0be6fdf	2006-12-19 21:46:21 +0000	[diff] [blame]	46	<li><a href="#Statistic">The <tt>Statistic</tt> class & <tt>-stats</tt>
Reid Spencer	fe8f4ff	2004-11-01 09:02:53 +0000	[diff] [blame]	47	option</a></li>
				48	<!--
				49	<li>The <tt>InstVisitor</tt> template
				50	<li>The general graph API
				51	-->
Chris Lattner	f623a08	2005-10-17 01:36:23 +0000	[diff] [blame]	52	<li><a href="#ViewGraph">Viewing graphs while debugging code</a></li>
Chris Lattner	261efe9	2003-11-25 01:02:51 +0000	[diff] [blame]	53	</ul>
				54	</li>
Chris Lattner	098129a	2007-02-03 03:04:03 +0000	[diff] [blame]	55	<li><a href="#datastructure">Picking the Right Data Structure for a Task</a>
				56	<ul>
Chris Lattner	74c4ca1	2007-02-03 07:59:07 +0000	[diff] [blame]	57	<li><a href="#ds_sequential">Sequential Containers (std::vector, std::list, etc)</a>
				58	<ul>
Chris Lattner	8ae4261	2011-04-05 23:18:20 +0000	[diff] [blame]	59	<li><a href="#dss_arrayref">llvm/ADT/ArrayRef.h</a></li>
Chris Lattner	74c4ca1	2007-02-03 07:59:07 +0000	[diff] [blame]	60	<li><a href="#dss_fixedarrays">Fixed Size Arrays</a></li>
				61	<li><a href="#dss_heaparrays">Heap Allocated Arrays</a></li>
Chris Lattner	9d69d4a	2011-07-18 01:40:02 +0000	[diff] [blame]	62	<li><a href="#dss_tinyptrvector">"llvm/ADT/TinyPtrVector.h"</a></li>
Chris Lattner	74c4ca1	2007-02-03 07:59:07 +0000	[diff] [blame]	63	<li><a href="#dss_smallvector">"llvm/ADT/SmallVector.h"</a></li>
				64	<li><a href="#dss_vector"><vector></a></li>
				65	<li><a href="#dss_deque"><deque></a></li>
				66	<li><a href="#dss_list"><list></a></li>
Gabor Greif	3899e49	2009-02-27 11:37:41 +0000	[diff] [blame]	67	<li><a href="#dss_ilist">llvm/ADT/ilist.h</a></li>
Argyrios Kyrtzidis	81df089	2011-06-15 19:56:01 +0000	[diff] [blame]	68	<li><a href="#dss_packedvector">llvm/ADT/PackedVector.h</a></li>
Chris Lattner	c572243	2007-02-03 19:49:31 +0000	[diff] [blame]	69	<li><a href="#dss_other">Other Sequential Container Options</a></li>
Chris Lattner	098129a	2007-02-03 03:04:03 +0000	[diff] [blame]	70	</ul></li>
Chris Lattner	7314a20	2011-07-22 20:46:49 +0000	[diff] [blame]	71	<li><a href="#ds_string">String-like containers</a>
Chris Lattner	6682746	2011-07-22 21:36:29 +0000	[diff] [blame]	72	<ul>
				73	<li><a href="#dss_stringref">llvm/ADT/StringRef.h</a></li>
				74	<li><a href="#dss_twine">llvm/ADT/Twine.h</a></li>
				75	<li><a href="#dss_smallstring">llvm/ADT/SmallString.h</a></li>
				76	<li><a href="#dss_stdstring">std::string</a></li>
				77	</ul></li>
Chris Lattner	74c4ca1	2007-02-03 07:59:07 +0000	[diff] [blame]	78	<li><a href="#ds_set">Set-Like Containers (std::set, SmallSet, SetVector, etc)</a>
				79	<ul>
				80	<li><a href="#dss_sortedvectorset">A sorted 'vector'</a></li>
				81	<li><a href="#dss_smallset">"llvm/ADT/SmallSet.h"</a></li>
				82	<li><a href="#dss_smallptrset">"llvm/ADT/SmallPtrSet.h"</a></li>
Chris Lattner	c28476f	2007-09-30 00:58:59 +0000	[diff] [blame]	83	<li><a href="#dss_denseset">"llvm/ADT/DenseSet.h"</a></li>
Chris Lattner	74c4ca1	2007-02-03 07:59:07 +0000	[diff] [blame]	84	<li><a href="#dss_FoldingSet">"llvm/ADT/FoldingSet.h"</a></li>
				85	<li><a href="#dss_set"><set></a></li>
				86	<li><a href="#dss_setvector">"llvm/ADT/SetVector.h"</a></li>
Chris Lattner	c572243	2007-02-03 19:49:31 +0000	[diff] [blame]	87	<li><a href="#dss_uniquevector">"llvm/ADT/UniqueVector.h"</a></li>
				88	<li><a href="#dss_otherset">Other Set-Like ContainerOptions</a></li>
Chris Lattner	74c4ca1	2007-02-03 07:59:07 +0000	[diff] [blame]	89	</ul></li>
Chris Lattner	f369252	2007-02-03 19:51:56 +0000	[diff] [blame]	90	<li><a href="#ds_map">Map-Like Containers (std::map, DenseMap, etc)</a>
				91	<ul>
				92	<li><a href="#dss_sortedvectormap">A sorted 'vector'</a></li>
Chris Lattner	796f9fa	2007-02-08 19:14:21 +0000	[diff] [blame]	93	<li><a href="#dss_stringmap">"llvm/ADT/StringMap.h"</a></li>
Chris Lattner	f369252	2007-02-03 19:51:56 +0000	[diff] [blame]	94	<li><a href="#dss_indexedmap">"llvm/ADT/IndexedMap.h"</a></li>
				95	<li><a href="#dss_densemap">"llvm/ADT/DenseMap.h"</a></li>
Jeffrey Yasskin	71a5c22	2009-10-22 22:11:22 +0000	[diff] [blame]	96	<li><a href="#dss_valuemap">"llvm/ADT/ValueMap.h"</a></li>
Jakob Stoklund Olesen	aca0da6	2010-12-14 00:55:51 +0000	[diff] [blame]	97	<li><a href="#dss_intervalmap">"llvm/ADT/IntervalMap.h"</a></li>
Chris Lattner	f369252	2007-02-03 19:51:56 +0000	[diff] [blame]	98	<li><a href="#dss_map"><map></a></li>
Jakob Stoklund Olesen	4359e5e	2011-04-05 20:56:08 +0000	[diff] [blame]	99	<li><a href="#dss_inteqclasses">"llvm/ADT/IntEqClasses.h"</a></li>
Chris Lattner	f369252	2007-02-03 19:51:56 +0000	[diff] [blame]	100	<li><a href="#dss_othermap">Other Map-Like Container Options</a></li>
				101	</ul></li>
Daniel Berlin	1939ace	2007-09-24 17:52:25 +0000	[diff] [blame]	102	<li><a href="#ds_bit">BitVector-like containers</a>
				103	<ul>
				104	<li><a href="#dss_bitvector">A dense bitvector</a></li>
Dan Gohman	5f7775c	2010-01-05 18:24:00 +0000	[diff] [blame]	105	<li><a href="#dss_smallbitvector">A "small" dense bitvector</a></li>
Daniel Berlin	1939ace	2007-09-24 17:52:25 +0000	[diff] [blame]	106	<li><a href="#dss_sparsebitvector">A sparse bitvector</a></li>
				107	</ul></li>
Chris Lattner	74c4ca1	2007-02-03 07:59:07 +0000	[diff] [blame]	108	</ul>
Chris Lattner	098129a	2007-02-03 03:04:03 +0000	[diff] [blame]	109	</li>
Chris Lattner	ae7f759	2002-09-06 18:31:18 +0000	[diff] [blame]	110	<li><a href="#common">Helpful Hints for Common Operations</a>
Chris Lattner	ae7f759	2002-09-06 18:31:18 +0000	[diff] [blame]	111	<ul>
Chris Lattner	261efe9	2003-11-25 01:02:51 +0000	[diff] [blame]	112	<li><a href="#inspection">Basic Inspection and Traversal Routines</a>
				113	<ul>
				114	<li><a href="#iterate_function">Iterating over the <tt>BasicBlock</tt>s
				115	in a <tt>Function</tt></a> </li>
				116	<li><a href="#iterate_basicblock">Iterating over the <tt>Instruction</tt>s
				117	in a <tt>BasicBlock</tt></a> </li>
				118	<li><a href="#iterate_institer">Iterating over the <tt>Instruction</tt>s
				119	in a <tt>Function</tt></a> </li>
				120	<li><a href="#iterate_convert">Turning an iterator into a
				121	class pointer</a> </li>
				122	<li><a href="#iterate_complex">Finding call sites: a more
				123	complex example</a> </li>
				124	<li><a href="#calls_and_invokes">Treating calls and invokes
				125	the same way</a> </li>
				126	<li><a href="#iterate_chains">Iterating over def-use &
				127	use-def chains</a> </li>
Chris Lattner	2e438ca	2008-01-03 16:56:04 +0000	[diff] [blame]	128	<li><a href="#iterate_preds">Iterating over predecessors &
				129	successors of blocks</a></li>
Chris Lattner	261efe9	2003-11-25 01:02:51 +0000	[diff] [blame]	130	</ul>
				131	</li>
				132	<li><a href="#simplechanges">Making simple changes</a>
				133	<ul>
				134	<li><a href="#schanges_creating">Creating and inserting new
				135	<tt>Instruction</tt>s</a> </li>
				136	<li><a href="#schanges_deleting">Deleting <tt>Instruction</tt>s</a> </li>
				137	<li><a href="#schanges_replacing">Replacing an <tt>Instruction</tt>
				138	with another <tt>Value</tt></a> </li>
Tanya Lattner	b011c66	2007-06-20 18:33:15 +0000	[diff] [blame]	139	<li><a href="#schanges_deletingGV">Deleting <tt>GlobalVariable</tt>s</a> </li>
Chris Lattner	261efe9	2003-11-25 01:02:51 +0000	[diff] [blame]	140	</ul>
Reid Spencer	fe8f4ff	2004-11-01 09:02:53 +0000	[diff] [blame]	141	</li>
Jeffrey Yasskin	714257f	2009-04-30 22:33:41 +0000	[diff] [blame]	142	<li><a href="#create_types">How to Create Types</a></li>
Chris Lattner	ae7f759	2002-09-06 18:31:18 +0000	[diff] [blame]	143	<!--
				144	<li>Working with the Control Flow Graph
				145	<ul>
				146	<li>Accessing predecessors and successors of a <tt>BasicBlock</tt>
				147	<li>
				148	<li>
				149	</ul>
Reid Spencer	fe8f4ff	2004-11-01 09:02:53 +0000	[diff] [blame]	150	-->
Chris Lattner	261efe9	2003-11-25 01:02:51 +0000	[diff] [blame]	151	</ul>
				152	</li>
Chris Lattner	d9d6e10	2005-04-23 16:10:52 +0000	[diff] [blame]	153
Owen Anderson	8bc1b3b	2009-06-16 01:17:16 +0000	[diff] [blame]	154	<li><a href="#threading">Threads and LLVM</a>
				155	<ul>
Owen Anderson	1ad70e3	2009-06-16 18:04:19 +0000	[diff] [blame]	156	<li><a href="#startmultithreaded">Entering and Exiting Multithreaded Mode
				157	</a></li>
Owen Anderson	8bc1b3b	2009-06-16 01:17:16 +0000	[diff] [blame]	158	<li><a href="#shutdown">Ending execution with <tt>llvm_shutdown()</tt></a></li>
				159	<li><a href="#managedstatic">Lazy initialization with <tt>ManagedStatic</tt></a></li>
Owen Anderson	e0c951a	2009-08-19 17:58:52 +0000	[diff] [blame]	160	<li><a href="#llvmcontext">Achieving Isolation with <tt>LLVMContext</tt></a></li>
Jeffrey Yasskin	01eba39	2010-01-29 19:10:38 +0000	[diff] [blame]	161	<li><a href="#jitthreading">Threads and the JIT</a></li>
Owen Anderson	8bc1b3b	2009-06-16 01:17:16 +0000	[diff] [blame]	162	</ul>
				163	</li>
				164
Chris Lattner	d9d6e10	2005-04-23 16:10:52 +0000	[diff] [blame]	165	<li><a href="#advanced">Advanced Topics</a>
				166	<ul>
Chris Lattner	f1b200b	2005-04-23 17:27:36 +0000	[diff] [blame]	167
Chris Lattner	1afcace	2011-07-09 17:41:24 +0000	[diff] [blame]	168	<li><a href="#SymbolTable">The <tt>ValueSymbolTable</tt> class</a></li>
Gabor Greif	e98fc27	2008-06-16 21:06:12 +0000	[diff] [blame]	169	<li><a href="#UserLayout">The <tt>User</tt> and owned <tt>Use</tt> classes' memory layout</a></li>
Chris Lattner	d9d6e10	2005-04-23 16:10:52 +0000	[diff] [blame]	170	</ul></li>
				171
Joel Stanley	9b96c44	2002-09-06 21:55:13 +0000	[diff] [blame]	172	<li><a href="#coreclasses">The Core LLVM Class Hierarchy Reference</a>
Chris Lattner	9355b47	2002-09-06 02:50:58 +0000	[diff] [blame]	173	<ul>
Reid Spencer	303c4b4	2007-01-12 17:26:25 +0000	[diff] [blame]	174	<li><a href="#Type">The <tt>Type</tt> class</a> </li>
Chris Lattner	2b78d96	2007-02-03 20:02:25 +0000	[diff] [blame]	175	<li><a href="#Module">The <tt>Module</tt> class</a></li>
Reid Spencer	fe8f4ff	2004-11-01 09:02:53 +0000	[diff] [blame]	176	<li><a href="#Value">The <tt>Value</tt> class</a>
Chris Lattner	2b78d96	2007-02-03 20:02:25 +0000	[diff] [blame]	177	<ul>
				178	<li><a href="#User">The <tt>User</tt> class</a>
Chris Lattner	9355b47	2002-09-06 02:50:58 +0000	[diff] [blame]	179	<ul>
Chris Lattner	2b78d96	2007-02-03 20:02:25 +0000	[diff] [blame]	180	<li><a href="#Instruction">The <tt>Instruction</tt> class</a></li>
				181	<li><a href="#Constant">The <tt>Constant</tt> class</a>
				182	<ul>
				183	<li><a href="#GlobalValue">The <tt>GlobalValue</tt> class</a>
Chris Lattner	261efe9	2003-11-25 01:02:51 +0000	[diff] [blame]	184	<ul>
Chris Lattner	2b78d96	2007-02-03 20:02:25 +0000	[diff] [blame]	185	<li><a href="#Function">The <tt>Function</tt> class</a></li>
				186	<li><a href="#GlobalVariable">The <tt>GlobalVariable</tt> class</a></li>
				187	</ul>
				188	</li>
				189	</ul>
				190	</li>
Reid Spencer	fe8f4ff	2004-11-01 09:02:53 +0000	[diff] [blame]	191	</ul>
Chris Lattner	2b78d96	2007-02-03 20:02:25 +0000	[diff] [blame]	192	</li>
				193	<li><a href="#BasicBlock">The <tt>BasicBlock</tt> class</a></li>
				194	<li><a href="#Argument">The <tt>Argument</tt> class</a></li>
				195	</ul>
Reid Spencer	fe8f4ff	2004-11-01 09:02:53 +0000	[diff] [blame]	196	</li>
				197	</ul>
Chris Lattner	261efe9	2003-11-25 01:02:51 +0000	[diff] [blame]	198	</li>
Chris Lattner	9355b47	2002-09-06 02:50:58 +0000	[diff] [blame]	199	</ol>
Misha Brukman	13fd15c	2004-01-15 00:14:41 +0000	[diff] [blame]	200
Chris Lattner	69bf8a9	2004-05-23 21:06:58 +0000	[diff] [blame]	201	<div class="doc_author">
				202	<p>Written by <a href="mailto:sabre@nondot.org">Chris Lattner</a>,
Chris Lattner	94c4359	2004-05-26 16:52:55 +0000	[diff] [blame]	203	<a href="mailto:dhurjati@cs.uiuc.edu">Dinakar Dhurjati</a>,
Gabor Greif	e98fc27	2008-06-16 21:06:12 +0000	[diff] [blame]	204	<a href="mailto:ggreif@gmail.com">Gabor Greif</a>,
Owen Anderson	8bc1b3b	2009-06-16 01:17:16 +0000	[diff] [blame]	205	<a href="mailto:jstanley@cs.uiuc.edu">Joel Stanley</a>,
				206	<a href="mailto:rspencer@x10sys.com">Reid Spencer</a> and
				207	<a href="mailto:owen@apple.com">Owen Anderson</a></p>
Misha Brukman	13fd15c	2004-01-15 00:14:41 +0000	[diff] [blame]	208	</div>
				209
Chris Lattner	9355b47	2002-09-06 02:50:58 +0000	[diff] [blame]	210	<!-- *********************************************************************** -->
NAKAMURA Takumi	05d0265	2011-04-18 23:59:50 +0000	[diff] [blame]	211	<h2>
Misha Brukman	13fd15c	2004-01-15 00:14:41 +0000	[diff] [blame]	212	<a name="introduction">Introduction </a>
NAKAMURA Takumi	05d0265	2011-04-18 23:59:50 +0000	[diff] [blame]	213	</h2>
Chris Lattner	9355b47	2002-09-06 02:50:58 +0000	[diff] [blame]	214	<!-- *********************************************************************** -->
Misha Brukman	13fd15c	2004-01-15 00:14:41 +0000	[diff] [blame]	215
NAKAMURA Takumi	f5af6ad	2011-04-23 00:30:22 +0000	[diff] [blame]	216	<div>
Misha Brukman	13fd15c	2004-01-15 00:14:41 +0000	[diff] [blame]	217
				218	<p>This document is meant to highlight some of the important classes and
Chris Lattner	261efe9	2003-11-25 01:02:51 +0000	[diff] [blame]	219	interfaces available in the LLVM source-base. This manual is not
				220	intended to explain what LLVM is, how it works, and what LLVM code looks
				221	like. It assumes that you know the basics of LLVM and are interested
				222	in writing transformations or otherwise analyzing or manipulating the
Misha Brukman	13fd15c	2004-01-15 00:14:41 +0000	[diff] [blame]	223	code.</p>
				224
				225	<p>This document should get you oriented so that you can find your
Chris Lattner	261efe9	2003-11-25 01:02:51 +0000	[diff] [blame]	226	way in the continuously growing source code that makes up the LLVM
				227	infrastructure. Note that this manual is not intended to serve as a
				228	replacement for reading the source code, so if you think there should be
				229	a method in one of these classes to do something, but it's not listed,
				230	check the source. Links to the <a href="/doxygen/">doxygen</a> sources
				231	are provided to make this as easy as possible.</p>
Misha Brukman	13fd15c	2004-01-15 00:14:41 +0000	[diff] [blame]	232
				233	<p>The first section of this document describes general information that is
				234	useful to know when working in the LLVM infrastructure, and the second describes
				235	the Core LLVM classes. In the future this manual will be extended with
				236	information describing how to use extension libraries, such as dominator
				237	information, CFG traversal routines, and useful utilities like the <tt><a
				238	href="/doxygen/InstVisitor_8h-source.html">InstVisitor</a></tt> template.</p>
				239
				240	</div>
				241
Chris Lattner	9355b47	2002-09-06 02:50:58 +0000	[diff] [blame]	242	<!-- *********************************************************************** -->
NAKAMURA Takumi	05d0265	2011-04-18 23:59:50 +0000	[diff] [blame]	243	<h2>
Misha Brukman	13fd15c	2004-01-15 00:14:41 +0000	[diff] [blame]	244	<a name="general">General Information</a>
NAKAMURA Takumi	05d0265	2011-04-18 23:59:50 +0000	[diff] [blame]	245	</h2>
Misha Brukman	13fd15c	2004-01-15 00:14:41 +0000	[diff] [blame]	246	<!-- *********************************************************************** -->
				247
NAKAMURA Takumi	f5af6ad	2011-04-23 00:30:22 +0000	[diff] [blame]	248	<div>
Misha Brukman	13fd15c	2004-01-15 00:14:41 +0000	[diff] [blame]	249
				250	<p>This section contains general information that is useful if you are working
				251	in the LLVM source-base, but that isn't specific to any particular API.</p>
				252
Misha Brukman	13fd15c	2004-01-15 00:14:41 +0000	[diff] [blame]	253	<!-- ======================================================================= -->
NAKAMURA Takumi	05d0265	2011-04-18 23:59:50 +0000	[diff] [blame]	254	<h3>
Misha Brukman	13fd15c	2004-01-15 00:14:41 +0000	[diff] [blame]	255	<a name="stl">The C++ Standard Template Library</a>
NAKAMURA Takumi	05d0265	2011-04-18 23:59:50 +0000	[diff] [blame]	256	</h3>
Misha Brukman	13fd15c	2004-01-15 00:14:41 +0000	[diff] [blame]	257
NAKAMURA Takumi	f5af6ad	2011-04-23 00:30:22 +0000	[diff] [blame]	258	<div>
Misha Brukman	13fd15c	2004-01-15 00:14:41 +0000	[diff] [blame]	259
				260	<p>LLVM makes heavy use of the C++ Standard Template Library (STL),
Chris Lattner	261efe9	2003-11-25 01:02:51 +0000	[diff] [blame]	261	perhaps much more than you are used to, or have seen before. Because of
				262	this, you might want to do a little background reading in the
				263	techniques used and capabilities of the library. There are many good
				264	pages that discuss the STL, and several books on the subject that you
Misha Brukman	13fd15c	2004-01-15 00:14:41 +0000	[diff] [blame]	265	can get, so it will not be discussed in this document.</p>
				266
				267	<p>Here are some useful links:</p>
				268
				269	<ol>
				270
Nick Lewycky	ea1fe2c	2010-10-09 21:12:29 +0000	[diff] [blame]	271	<li><a href="http://www.dinkumware.com/manuals/#Standard C++ Library">Dinkumware
				272	C++ Library reference</a> - an excellent reference for the STL and other parts
				273	of the standard C++ library.</li>
Misha Brukman	13fd15c	2004-01-15 00:14:41 +0000	[diff] [blame]	274
				275	<li><a href="http://www.tempest-sw.com/cpp/">C++ In a Nutshell</a> - This is an
Gabor Greif	0cbcabe	2009-03-12 09:47:03 +0000	[diff] [blame]	276	O'Reilly book in the making. It has a decent Standard Library
				277	Reference that rivals Dinkumware's, and is unfortunately no longer free since the
				278	book has been published.</li>
Misha Brukman	13fd15c	2004-01-15 00:14:41 +0000	[diff] [blame]	279
				280	<li><a href="http://www.parashift.com/c++-faq-lite/">C++ Frequently Asked
				281	Questions</a></li>
				282
				283	<li><a href="http://www.sgi.com/tech/stl/">SGI's STL Programmer's Guide</a> -
				284	Contains a useful <a
				285	href="http://www.sgi.com/tech/stl/stl_introduction.html">Introduction to the
				286	STL</a>.</li>
				287
				288	<li><a href="http://www.research.att.com/%7Ebs/C++.html">Bjarne Stroustrup's C++
				289	Page</a></li>
				290
Tanya Lattner	79445ba	2004-12-08 18:34:56 +0000	[diff] [blame]	291	<li><a href="http://64.78.49.204/">
Reid Spencer	096603a	2004-05-26 08:41:35 +0000	[diff] [blame]	292	Bruce Eckel's Thinking in C++, 2nd ed. Volume 2 Revision 4.0 (even better, get
				293	the book).</a></li>
				294
Misha Brukman	13fd15c	2004-01-15 00:14:41 +0000	[diff] [blame]	295	</ol>
				296
				297	<p>You are also encouraged to take a look at the <a
				298	href="CodingStandards.html">LLVM Coding Standards</a> guide which focuses on how
				299	to write maintainable code more than where to put your curly braces.</p>
				300
				301	</div>
				302
				303	<!-- ======================================================================= -->
NAKAMURA Takumi	05d0265	2011-04-18 23:59:50 +0000	[diff] [blame]	304	<h3>
Misha Brukman	13fd15c	2004-01-15 00:14:41 +0000	[diff] [blame]	305	<a name="stl">Other useful references</a>
NAKAMURA Takumi	05d0265	2011-04-18 23:59:50 +0000	[diff] [blame]	306	</h3>
Misha Brukman	13fd15c	2004-01-15 00:14:41 +0000	[diff] [blame]	307
NAKAMURA Takumi	f5af6ad	2011-04-23 00:30:22 +0000	[diff] [blame]	308	<div>
Misha Brukman	13fd15c	2004-01-15 00:14:41 +0000	[diff] [blame]	309
Misha Brukman	13fd15c	2004-01-15 00:14:41 +0000	[diff] [blame]	310	<ol>
Misha Brukman	a0f71e4	2004-06-18 18:39:00 +0000	[diff] [blame]	311	<li><a href="http://www.fortran-2000.com/ArnaudRecipes/sharedlib.html">Using
				312	static and shared libraries across platforms</a></li>
Misha Brukman	13fd15c	2004-01-15 00:14:41 +0000	[diff] [blame]	313	</ol>
				314
				315	</div>
				316
NAKAMURA Takumi	f5af6ad	2011-04-23 00:30:22 +0000	[diff] [blame]	317	</div>
				318
Chris Lattner	9355b47	2002-09-06 02:50:58 +0000	[diff] [blame]	319	<!-- *********************************************************************** -->
NAKAMURA Takumi	05d0265	2011-04-18 23:59:50 +0000	[diff] [blame]	320	<h2>
Misha Brukman	13fd15c	2004-01-15 00:14:41 +0000	[diff] [blame]	321	<a name="apis">Important and useful LLVM APIs</a>
NAKAMURA Takumi	05d0265	2011-04-18 23:59:50 +0000	[diff] [blame]	322	</h2>
Misha Brukman	13fd15c	2004-01-15 00:14:41 +0000	[diff] [blame]	323	<!-- *********************************************************************** -->
				324
NAKAMURA Takumi	f5af6ad	2011-04-23 00:30:22 +0000	[diff] [blame]	325	<div>
Misha Brukman	13fd15c	2004-01-15 00:14:41 +0000	[diff] [blame]	326
				327	<p>Here we highlight some LLVM APIs that are generally useful and good to
				328	know about when writing transformations.</p>
				329
Misha Brukman	13fd15c	2004-01-15 00:14:41 +0000	[diff] [blame]	330	<!-- ======================================================================= -->
NAKAMURA Takumi	05d0265	2011-04-18 23:59:50 +0000	[diff] [blame]	331	<h3>
Misha Brukman	2c122ce	2005-11-01 21:12:49 +0000	[diff] [blame]	332	<a name="isa">The <tt>isa<></tt>, <tt>cast<></tt> and
				333	<tt>dyn_cast<></tt> templates</a>
NAKAMURA Takumi	05d0265	2011-04-18 23:59:50 +0000	[diff] [blame]	334	</h3>
Misha Brukman	13fd15c	2004-01-15 00:14:41 +0000	[diff] [blame]	335
NAKAMURA Takumi	f5af6ad	2011-04-23 00:30:22 +0000	[diff] [blame]	336	<div>
Misha Brukman	13fd15c	2004-01-15 00:14:41 +0000	[diff] [blame]	337
				338	<p>The LLVM source-base makes extensive use of a custom form of RTTI.
Chris Lattner	261efe9	2003-11-25 01:02:51 +0000	[diff] [blame]	339	These templates have many similarities to the C++ <tt>dynamic_cast<></tt>
				340	operator, but they don't have some drawbacks (primarily stemming from
				341	the fact that <tt>dynamic_cast<></tt> only works on classes that
				342	have a v-table). Because they are used so often, you must know what they
				343	do and how they work. All of these templates are defined in the <a
Chris Lattner	695b78b	2005-04-26 22:56:16 +0000	[diff] [blame]	344	href="/doxygen/Casting_8h-source.html"><tt>llvm/Support/Casting.h</tt></a>
Misha Brukman	13fd15c	2004-01-15 00:14:41 +0000	[diff] [blame]	345	file (note that you very rarely have to include this file directly).</p>
				346
				347	<dl>
				348	<dt><tt>isa<></tt>: </dt>
				349
Bill Wendling	3cd5ca6	2006-10-11 06:30:10 +0000	[diff] [blame]	350	<dd><p>The <tt>isa<></tt> operator works exactly like the Java
Misha Brukman	13fd15c	2004-01-15 00:14:41 +0000	[diff] [blame]	351	"<tt>instanceof</tt>" operator. It returns true or false depending on whether
				352	a reference or pointer points to an instance of the specified class. This can
Bill Wendling	3cd5ca6	2006-10-11 06:30:10 +0000	[diff] [blame]	353	be very useful for constraint checking of various sorts (example below).</p>
				354	</dd>
Misha Brukman	13fd15c	2004-01-15 00:14:41 +0000	[diff] [blame]	355
				356	<dt><tt>cast<></tt>: </dt>
				357
Bill Wendling	3cd5ca6	2006-10-11 06:30:10 +0000	[diff] [blame]	358	<dd><p>The <tt>cast<></tt> operator is a "checked cast" operation. It
Chris Lattner	28e6ff5	2008-06-20 05:03:17 +0000	[diff] [blame]	359	converts a pointer or reference from a base class to a derived class, causing
Misha Brukman	13fd15c	2004-01-15 00:14:41 +0000	[diff] [blame]	360	an assertion failure if it is not really an instance of the right type. This
				361	should be used in cases where you have some information that makes you believe
				362	that something is of the right type. An example of the <tt>isa<></tt>
Bill Wendling	3cd5ca6	2006-10-11 06:30:10 +0000	[diff] [blame]	363	and <tt>cast<></tt> template is:</p>
Misha Brukman	13fd15c	2004-01-15 00:14:41 +0000	[diff] [blame]	364
Bill Wendling	3cd5ca6	2006-10-11 06:30:10 +0000	[diff] [blame]	365	<div class="doc_code">
				366	<pre>
				367	static bool isLoopInvariant(const <a href="#Value">Value</a> V, const Loop L) {
				368	if (isa<<a href="#Constant">Constant</a>>(V) \|\| isa<<a href="#Argument">Argument</a>>(V) \|\| isa<<a href="#GlobalValue">GlobalValue</a>>(V))
				369	return true;
Chris Lattner	69bf8a9	2004-05-23 21:06:58 +0000	[diff] [blame]	370
Bill Wendling	82e2eea	2006-10-11 18:00:22 +0000	[diff] [blame]	371	// <i>Otherwise, it must be an instruction...</i>
Bill Wendling	3cd5ca6	2006-10-11 06:30:10 +0000	[diff] [blame]	372	return !L->contains(cast<<a href="#Instruction">Instruction</a>>(V)->getParent());
				373	}
				374	</pre>
				375	</div>
Misha Brukman	13fd15c	2004-01-15 00:14:41 +0000	[diff] [blame]	376
				377	<p>Note that you should <b>not</b> use an <tt>isa<></tt> test followed
				378	by a <tt>cast<></tt>, for that use the <tt>dyn_cast<></tt>
				379	operator.</p>
				380
				381	</dd>
				382
				383	<dt><tt>dyn_cast<></tt>:</dt>
				384
Bill Wendling	3cd5ca6	2006-10-11 06:30:10 +0000	[diff] [blame]	385	<dd><p>The <tt>dyn_cast<></tt> operator is a "checking cast" operation.
				386	It checks to see if the operand is of the specified type, and if so, returns a
Misha Brukman	13fd15c	2004-01-15 00:14:41 +0000	[diff] [blame]	387	pointer to it (this operator does not work with references). If the operand is
				388	not of the correct type, a null pointer is returned. Thus, this works very
Misha Brukman	2c122ce	2005-11-01 21:12:49 +0000	[diff] [blame]	389	much like the <tt>dynamic_cast<></tt> operator in C++, and should be
				390	used in the same circumstances. Typically, the <tt>dyn_cast<></tt>
				391	operator is used in an <tt>if</tt> statement or some other flow control
Bill Wendling	3cd5ca6	2006-10-11 06:30:10 +0000	[diff] [blame]	392	statement like this:</p>
Misha Brukman	13fd15c	2004-01-15 00:14:41 +0000	[diff] [blame]	393
Bill Wendling	3cd5ca6	2006-10-11 06:30:10 +0000	[diff] [blame]	394	<div class="doc_code">
				395	<pre>
				396	if (<a href="#AllocationInst">AllocationInst</a> *AI = dyn_cast<<a href="#AllocationInst">AllocationInst</a>>(Val)) {
Bill Wendling	82e2eea	2006-10-11 18:00:22 +0000	[diff] [blame]	397	// <i>...</i>
Bill Wendling	3cd5ca6	2006-10-11 06:30:10 +0000	[diff] [blame]	398	}
				399	</pre>
				400	</div>
Misha Brukman	13fd15c	2004-01-15 00:14:41 +0000	[diff] [blame]	401
Misha Brukman	2c122ce	2005-11-01 21:12:49 +0000	[diff] [blame]	402	<p>This form of the <tt>if</tt> statement effectively combines together a call
				403	to <tt>isa<></tt> and a call to <tt>cast<></tt> into one
				404	statement, which is very convenient.</p>
Misha Brukman	13fd15c	2004-01-15 00:14:41 +0000	[diff] [blame]	405
Misha Brukman	2c122ce	2005-11-01 21:12:49 +0000	[diff] [blame]	406	<p>Note that the <tt>dyn_cast<></tt> operator, like C++'s
				407	<tt>dynamic_cast<></tt> or Java's <tt>instanceof</tt> operator, can be
				408	abused. In particular, you should not use big chained <tt>if/then/else</tt>
				409	blocks to check for lots of different variants of classes. If you find
				410	yourself wanting to do this, it is much cleaner and more efficient to use the
				411	<tt>InstVisitor</tt> class to dispatch over the instruction type directly.</p>
Misha Brukman	13fd15c	2004-01-15 00:14:41 +0000	[diff] [blame]	412
Misha Brukman	2c122ce	2005-11-01 21:12:49 +0000	[diff] [blame]	413	</dd>
Misha Brukman	13fd15c	2004-01-15 00:14:41 +0000	[diff] [blame]	414
Misha Brukman	2c122ce	2005-11-01 21:12:49 +0000	[diff] [blame]	415	<dt><tt>cast_or_null<></tt>: </dt>
				416
Bill Wendling	3cd5ca6	2006-10-11 06:30:10 +0000	[diff] [blame]	417	<dd><p>The <tt>cast_or_null<></tt> operator works just like the
Misha Brukman	2c122ce	2005-11-01 21:12:49 +0000	[diff] [blame]	418	<tt>cast<></tt> operator, except that it allows for a null pointer as an
				419	argument (which it then propagates). This can sometimes be useful, allowing
Bill Wendling	3cd5ca6	2006-10-11 06:30:10 +0000	[diff] [blame]	420	you to combine several null checks into one.</p></dd>
Misha Brukman	13fd15c	2004-01-15 00:14:41 +0000	[diff] [blame]	421
Misha Brukman	2c122ce	2005-11-01 21:12:49 +0000	[diff] [blame]	422	<dt><tt>dyn_cast_or_null<></tt>: </dt>
Misha Brukman	13fd15c	2004-01-15 00:14:41 +0000	[diff] [blame]	423
Bill Wendling	3cd5ca6	2006-10-11 06:30:10 +0000	[diff] [blame]	424	<dd><p>The <tt>dyn_cast_or_null<></tt> operator works just like the
Misha Brukman	2c122ce	2005-11-01 21:12:49 +0000	[diff] [blame]	425	<tt>dyn_cast<></tt> operator, except that it allows for a null pointer
				426	as an argument (which it then propagates). This can sometimes be useful,
Bill Wendling	3cd5ca6	2006-10-11 06:30:10 +0000	[diff] [blame]	427	allowing you to combine several null checks into one.</p></dd>
Misha Brukman	13fd15c	2004-01-15 00:14:41 +0000	[diff] [blame]	428
Misha Brukman	2c122ce	2005-11-01 21:12:49 +0000	[diff] [blame]	429	</dl>
Misha Brukman	13fd15c	2004-01-15 00:14:41 +0000	[diff] [blame]	430
				431	<p>These five templates can be used with any classes, whether they have a
				432	v-table or not. To add support for these templates, you simply need to add
				433	<tt>classof</tt> static methods to the class you are interested casting
				434	to. Describing this is currently outside the scope of this document, but there
				435	are lots of examples in the LLVM source base.</p>
				436
				437	</div>
				438
Daniel Dunbar	6e0d1cb	2009-07-25 04:41:11 +0000	[diff] [blame]	439
				440	<!-- ======================================================================= -->
NAKAMURA Takumi	05d0265	2011-04-18 23:59:50 +0000	[diff] [blame]	441	<h3>
Daniel Dunbar	6e0d1cb	2009-07-25 04:41:11 +0000	[diff] [blame]	442	<a name="string_apis">Passing strings (the <tt>StringRef</tt>
				443	and <tt>Twine</tt> classes)</a>
NAKAMURA Takumi	05d0265	2011-04-18 23:59:50 +0000	[diff] [blame]	444	</h3>
Daniel Dunbar	6e0d1cb	2009-07-25 04:41:11 +0000	[diff] [blame]	445
NAKAMURA Takumi	f5af6ad	2011-04-23 00:30:22 +0000	[diff] [blame]	446	<div>
Daniel Dunbar	6e0d1cb	2009-07-25 04:41:11 +0000	[diff] [blame]	447
				448	<p>Although LLVM generally does not do much string manipulation, we do have
Chris Lattner	81187ae	2009-07-25 07:16:59 +0000	[diff] [blame]	449	several important APIs which take strings. Two important examples are the
Daniel Dunbar	6e0d1cb	2009-07-25 04:41:11 +0000	[diff] [blame]	450	Value class -- which has names for instructions, functions, etc. -- and the
				451	StringMap class which is used extensively in LLVM and Clang.</p>
				452
				453	<p>These are generic classes, and they need to be able to accept strings which
				454	may have embedded null characters. Therefore, they cannot simply take
Chris Lattner	81187ae	2009-07-25 07:16:59 +0000	[diff] [blame]	455	a <tt>const char *</tt>, and taking a <tt>const std::string&</tt> requires
Daniel Dunbar	6e0d1cb	2009-07-25 04:41:11 +0000	[diff] [blame]	456	clients to perform a heap allocation which is usually unnecessary. Instead,
Benjamin Kramer	38e5989	2010-07-14 22:38:02 +0000	[diff] [blame]	457	many LLVM APIs use a <tt>StringRef</tt> or a <tt>const Twine&</tt> for
				458	passing strings efficiently.</p>
Daniel Dunbar	6e0d1cb	2009-07-25 04:41:11 +0000	[diff] [blame]	459
Daniel Dunbar	6e0d1cb	2009-07-25 04:41:11 +0000	[diff] [blame]	460	<!-- _______________________________________________________________________ -->
NAKAMURA Takumi	05d0265	2011-04-18 23:59:50 +0000	[diff] [blame]	461	<h4>
Daniel Dunbar	6e0d1cb	2009-07-25 04:41:11 +0000	[diff] [blame]	462	<a name="StringRef">The <tt>StringRef</tt> class</a>
NAKAMURA Takumi	05d0265	2011-04-18 23:59:50 +0000	[diff] [blame]	463	</h4>
Daniel Dunbar	6e0d1cb	2009-07-25 04:41:11 +0000	[diff] [blame]	464
NAKAMURA Takumi	f5af6ad	2011-04-23 00:30:22 +0000	[diff] [blame]	465	<div>
Daniel Dunbar	6e0d1cb	2009-07-25 04:41:11 +0000	[diff] [blame]	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	81187ae	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	6e0d1cb	2009-07-25 04:41:11 +0000	[diff] [blame]	473	For example, the <tt>StringRef</tt> find function is declared as:</p>
Chris Lattner	81187ae	2009-07-25 07:16:59 +0000	[diff] [blame]	474
Benjamin Kramer	38e5989	2010-07-14 22:38:02 +0000	[diff] [blame]	475	<pre class="doc_code">
				476	iterator find(StringRef Key);
				477	</pre>
Daniel Dunbar	6e0d1cb	2009-07-25 04:41:11 +0000	[diff] [blame]	478
				479	<p>and clients can call it using any one of:</p>
				480
Benjamin Kramer	38e5989	2010-07-14 22:38:02 +0000	[diff] [blame]	481	<pre class="doc_code">
Daniel Dunbar	6e0d1cb	2009-07-25 04:41:11 +0000	[diff] [blame]	482	Map.find("foo"); <i>// Lookup "foo"</i>
				483	Map.find(std::string("bar")); <i>// Lookup "bar"</i>
				484	Map.find(StringRef("\0baz", 4)); <i>// Lookup "\0baz"</i>
				485	</pre>
Daniel Dunbar	6e0d1cb	2009-07-25 04:41:11 +0000	[diff] [blame]	486
				487	<p>Similarly, APIs which need to return a string may return a <tt>StringRef</tt>
				488	instance, which can be used directly or converted to an <tt>std::string</tt>
				489	using the <tt>str</tt> member function. See
				490	"<tt><a href="/doxygen/classllvm_1_1StringRef_8h-source.html">llvm/ADT/StringRef.h</a></tt>"
				491	for more information.</p>
				492
				493	<p>You should rarely use the <tt>StringRef</tt> class directly, because it contains
				494	pointers to external memory it is not generally safe to store an instance of the
Benjamin Kramer	38e5989	2010-07-14 22:38:02 +0000	[diff] [blame]	495	class (unless you know that the external storage will not be freed). StringRef is
				496	small and pervasive enough in LLVM that it should always be passed by value.</p>
Daniel Dunbar	6e0d1cb	2009-07-25 04:41:11 +0000	[diff] [blame]	497
				498	</div>
				499
				500	<!-- _______________________________________________________________________ -->
NAKAMURA Takumi	05d0265	2011-04-18 23:59:50 +0000	[diff] [blame]	501	<h4>
Daniel Dunbar	6e0d1cb	2009-07-25 04:41:11 +0000	[diff] [blame]	502	<a name="Twine">The <tt>Twine</tt> class</a>
NAKAMURA Takumi	05d0265	2011-04-18 23:59:50 +0000	[diff] [blame]	503	</h4>
Daniel Dunbar	6e0d1cb	2009-07-25 04:41:11 +0000	[diff] [blame]	504
NAKAMURA Takumi	f5af6ad	2011-04-23 00:30:22 +0000	[diff] [blame]	505	<div>
Daniel Dunbar	6e0d1cb	2009-07-25 04:41:11 +0000	[diff] [blame]	506
				507	<p>The <tt>Twine</tt> class is an efficient way for APIs to accept concatenated
				508	strings. For example, a common LLVM paradigm is to name one instruction based on
				509	the name of another instruction with a suffix, for example:</p>
				510
				511	<div class="doc_code">
				512	<pre>
				513	New = CmpInst::Create(<i>...</i>, SO->getName() + ".cmp");
				514	</pre>
				515	</div>
				516
				517	<p>The <tt>Twine</tt> class is effectively a
				518	lightweight <a href="http://en.wikipedia.org/wiki/Rope_(computer_science)">rope</a>
				519	which points to temporary (stack allocated) objects. Twines can be implicitly
				520	constructed as the result of the plus operator applied to strings (i.e., a C
				521	strings, an <tt>std::string</tt>, or a <tt>StringRef</tt>). The twine delays the
Dan Gohman	cf0c9bc	2010-02-25 23:51:27 +0000	[diff] [blame]	522	actual concatenation of strings until it is actually required, at which point
Daniel Dunbar	6e0d1cb	2009-07-25 04:41:11 +0000	[diff] [blame]	523	it can be efficiently rendered directly into a character array. This avoids
				524	unnecessary heap allocation involved in constructing the temporary results of
				525	string concatenation. See
				526	"<tt><a href="/doxygen/classllvm_1_1Twine_8h-source.html">llvm/ADT/Twine.h</a></tt>"
Benjamin Kramer	e15192b	2009-08-05 15:42:44 +0000	[diff] [blame]	527	for more information.</p>
Daniel Dunbar	6e0d1cb	2009-07-25 04:41:11 +0000	[diff] [blame]	528
				529	<p>As with a <tt>StringRef</tt>, <tt>Twine</tt> objects point to external memory
				530	and should almost never be stored or mentioned directly. They are intended
				531	solely for use when defining a function which should be able to efficiently
				532	accept concatenated strings.</p>
				533
				534	</div>
				535
NAKAMURA Takumi	f5af6ad	2011-04-23 00:30:22 +0000	[diff] [blame]	536	</div>
Daniel Dunbar	6e0d1cb	2009-07-25 04:41:11 +0000	[diff] [blame]	537
Misha Brukman	13fd15c	2004-01-15 00:14:41 +0000	[diff] [blame]	538	<!-- ======================================================================= -->
NAKAMURA Takumi	05d0265	2011-04-18 23:59:50 +0000	[diff] [blame]	539	<h3>
Misha Brukman	2c122ce	2005-11-01 21:12:49 +0000	[diff] [blame]	540	<a name="DEBUG">The <tt>DEBUG()</tt> macro and <tt>-debug</tt> option</a>
NAKAMURA Takumi	05d0265	2011-04-18 23:59:50 +0000	[diff] [blame]	541	</h3>
Misha Brukman	13fd15c	2004-01-15 00:14:41 +0000	[diff] [blame]	542
NAKAMURA Takumi	f5af6ad	2011-04-23 00:30:22 +0000	[diff] [blame]	543	<div>
Misha Brukman	13fd15c	2004-01-15 00:14:41 +0000	[diff] [blame]	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
Bill Wendling	3cd5ca6	2006-10-11 06:30:10 +0000	[diff] [blame]	547	it, but you may need it again in the future (to work out new bugs that you run
Misha Brukman	13fd15c	2004-01-15 00:14:41 +0000	[diff] [blame]	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
Chris Lattner	695b78b	2005-04-26 22:56:16 +0000	[diff] [blame]	554	<p>The "<tt><a href="/doxygen/Debug_8h-source.html">llvm/Support/Debug.h</a></tt>"
Misha Brukman	13fd15c	2004-01-15 00:14:41 +0000	[diff] [blame]	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
Bill Wendling	3cd5ca6	2006-10-11 06:30:10 +0000	[diff] [blame]	560	<div class="doc_code">
				561	<pre>
Daniel Dunbar	06388ae	2009-07-25 01:55:32 +0000	[diff] [blame]	562	DEBUG(errs() << "I am here!\n");
Bill Wendling	3cd5ca6	2006-10-11 06:30:10 +0000	[diff] [blame]	563	</pre>
				564	</div>
Misha Brukman	13fd15c	2004-01-15 00:14:41 +0000	[diff] [blame]	565
				566	<p>Then you can run your pass like this:</p>
				567
Bill Wendling	3cd5ca6	2006-10-11 06:30:10 +0000	[diff] [blame]	568	<div class="doc_code">
				569	<pre>
				570	$ opt < a.bc > /dev/null -mypass
Bill Wendling	82e2eea	2006-10-11 18:00:22 +0000	[diff] [blame]	571	<i><no output></i>
Bill Wendling	3cd5ca6	2006-10-11 06:30:10 +0000	[diff] [blame]	572	$ opt < a.bc > /dev/null -mypass -debug
				573	I am here!
				574	</pre>
				575	</div>
Misha Brukman	13fd15c	2004-01-15 00:14:41 +0000	[diff] [blame]	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
Misha Brukman	13fd15c	2004-01-15 00:14:41 +0000	[diff] [blame]	589	<!-- _______________________________________________________________________ -->
NAKAMURA Takumi	05d0265	2011-04-18 23:59:50 +0000	[diff] [blame]	590	<h4>
Chris Lattner	c915108	2005-04-26 22:57:07 +0000	[diff] [blame]	591	<a name="DEBUG_TYPE">Fine grained debug info with <tt>DEBUG_TYPE</tt> and
Misha Brukman	13fd15c	2004-01-15 00:14:41 +0000	[diff] [blame]	592	the <tt>-debug-only</tt> option</a>
NAKAMURA Takumi	05d0265	2011-04-18 23:59:50 +0000	[diff] [blame]	593	</h4>
Misha Brukman	13fd15c	2004-01-15 00:14:41 +0000	[diff] [blame]	594
NAKAMURA Takumi	f5af6ad	2011-04-23 00:30:22 +0000	[diff] [blame]	595	<div>
Misha Brukman	13fd15c	2004-01-15 00:14:41 +0000	[diff] [blame]	596
				597	<p>Sometimes you may find yourself in a situation where enabling <tt>-debug</tt>
				598	just turns on <b>too much</b> information (such as when working on the code
				599	generator). If you want to enable debug information with more fine-grained
				600	control, you define the <tt>DEBUG_TYPE</tt> macro and the <tt>-debug</tt> only
				601	option as follows:</p>
				602
Bill Wendling	3cd5ca6	2006-10-11 06:30:10 +0000	[diff] [blame]	603	<div class="doc_code">
				604	<pre>
Bill Wendling	3cd5ca6	2006-10-11 06:30:10 +0000	[diff] [blame]	605	#undef DEBUG_TYPE
Daniel Dunbar	06388ae	2009-07-25 01:55:32 +0000	[diff] [blame]	606	DEBUG(errs() << "No debug type\n");
Bill Wendling	3cd5ca6	2006-10-11 06:30:10 +0000	[diff] [blame]	607	#define DEBUG_TYPE "foo"
Daniel Dunbar	06388ae	2009-07-25 01:55:32 +0000	[diff] [blame]	608	DEBUG(errs() << "'foo' debug type\n");
Bill Wendling	3cd5ca6	2006-10-11 06:30:10 +0000	[diff] [blame]	609	#undef DEBUG_TYPE
				610	#define DEBUG_TYPE "bar"
Daniel Dunbar	06388ae	2009-07-25 01:55:32 +0000	[diff] [blame]	611	DEBUG(errs() << "'bar' debug type\n"));
Bill Wendling	3cd5ca6	2006-10-11 06:30:10 +0000	[diff] [blame]	612	#undef DEBUG_TYPE
				613	#define DEBUG_TYPE ""
Daniel Dunbar	06388ae	2009-07-25 01:55:32 +0000	[diff] [blame]	614	DEBUG(errs() << "No debug type (2)\n");
Bill Wendling	3cd5ca6	2006-10-11 06:30:10 +0000	[diff] [blame]	615	</pre>
				616	</div>
Misha Brukman	13fd15c	2004-01-15 00:14:41 +0000	[diff] [blame]	617
				618	<p>Then you can run your pass like this:</p>
				619
Bill Wendling	3cd5ca6	2006-10-11 06:30:10 +0000	[diff] [blame]	620	<div class="doc_code">
				621	<pre>
				622	$ opt < a.bc > /dev/null -mypass
Bill Wendling	82e2eea	2006-10-11 18:00:22 +0000	[diff] [blame]	623	<i><no output></i>
Bill Wendling	3cd5ca6	2006-10-11 06:30:10 +0000	[diff] [blame]	624	$ opt < a.bc > /dev/null -mypass -debug
				625	No debug type
				626	'foo' debug type
				627	'bar' debug type
				628	No debug type (2)
				629	$ opt < a.bc > /dev/null -mypass -debug-only=foo
				630	'foo' debug type
				631	$ opt < a.bc > /dev/null -mypass -debug-only=bar
				632	'bar' debug type
				633	</pre>
				634	</div>
Misha Brukman	13fd15c	2004-01-15 00:14:41 +0000	[diff] [blame]	635
				636	<p>Of course, in practice, you should only set <tt>DEBUG_TYPE</tt> at the top of
				637	a file, to specify the debug type for the entire module (if you do this before
Chris Lattner	695b78b	2005-04-26 22:56:16 +0000	[diff] [blame]	638	you <tt>#include "llvm/Support/Debug.h"</tt>, you don't have to insert the ugly
Misha Brukman	13fd15c	2004-01-15 00:14:41 +0000	[diff] [blame]	639	<tt>#undef</tt>'s). Also, you should use names more meaningful than "foo" and
				640	"bar", because there is no system in place to ensure that names do not
				641	conflict. If two different modules use the same string, they will all be turned
				642	on when the name is specified. This allows, for example, all debug information
				643	for instruction scheduling to be enabled with <tt>-debug-type=InstrSched</tt>,
Chris Lattner	261efe9	2003-11-25 01:02:51 +0000	[diff] [blame]	644	even if the source lives in multiple files.</p>
Misha Brukman	13fd15c	2004-01-15 00:14:41 +0000	[diff] [blame]	645
Daniel Dunbar	c3c9239	2009-08-07 23:48:59 +0000	[diff] [blame]	646	<p>The <tt>DEBUG_WITH_TYPE</tt> macro is also available for situations where you
				647	would like to set <tt>DEBUG_TYPE</tt>, but only for one specific <tt>DEBUG</tt>
				648	statement. It takes an additional first parameter, which is the type to use. For
Benjamin Kramer	8040cd3	2009-10-12 14:46:08 +0000	[diff] [blame]	649	example, the preceding example could be written as:</p>
Daniel Dunbar	c3c9239	2009-08-07 23:48:59 +0000	[diff] [blame]	650
				651
				652	<div class="doc_code">
				653	<pre>
				654	DEBUG_WITH_TYPE("", errs() << "No debug type\n");
				655	DEBUG_WITH_TYPE("foo", errs() << "'foo' debug type\n");
				656	DEBUG_WITH_TYPE("bar", errs() << "'bar' debug type\n"));
				657	DEBUG_WITH_TYPE("", errs() << "No debug type (2)\n");
				658	</pre>
				659	</div>
				660
Misha Brukman	13fd15c	2004-01-15 00:14:41 +0000	[diff] [blame]	661	</div>
				662
NAKAMURA Takumi	f5af6ad	2011-04-23 00:30:22 +0000	[diff] [blame]	663	</div>
				664
Misha Brukman	13fd15c	2004-01-15 00:14:41 +0000	[diff] [blame]	665	<!-- ======================================================================= -->
NAKAMURA Takumi	05d0265	2011-04-18 23:59:50 +0000	[diff] [blame]	666	<h3>
Chris Lattner	0be6fdf	2006-12-19 21:46:21 +0000	[diff] [blame]	667	<a name="Statistic">The <tt>Statistic</tt> class & <tt>-stats</tt>
Misha Brukman	13fd15c	2004-01-15 00:14:41 +0000	[diff] [blame]	668	option</a>
NAKAMURA Takumi	05d0265	2011-04-18 23:59:50 +0000	[diff] [blame]	669	</h3>
Misha Brukman	13fd15c	2004-01-15 00:14:41 +0000	[diff] [blame]	670
NAKAMURA Takumi	f5af6ad	2011-04-23 00:30:22 +0000	[diff] [blame]	671	<div>
Misha Brukman	13fd15c	2004-01-15 00:14:41 +0000	[diff] [blame]	672
				673	<p>The "<tt><a
Chris Lattner	695b78b	2005-04-26 22:56:16 +0000	[diff] [blame]	674	href="/doxygen/Statistic_8h-source.html">llvm/ADT/Statistic.h</a></tt>" file
Chris Lattner	0be6fdf	2006-12-19 21:46:21 +0000	[diff] [blame]	675	provides a class named <tt>Statistic</tt> that is used as a unified way to
Misha Brukman	13fd15c	2004-01-15 00:14:41 +0000	[diff] [blame]	676	keep track of what the LLVM compiler is doing and how effective various
				677	optimizations are. It is useful to see what optimizations are contributing to
				678	making a particular program run faster.</p>
				679
				680	<p>Often you may run your pass on some big program, and you're interested to see
				681	how many times it makes a certain transformation. Although you can do this with
				682	hand inspection, or some ad-hoc method, this is a real pain and not very useful
Chris Lattner	0be6fdf	2006-12-19 21:46:21 +0000	[diff] [blame]	683	for big programs. Using the <tt>Statistic</tt> class makes it very easy to
Misha Brukman	13fd15c	2004-01-15 00:14:41 +0000	[diff] [blame]	684	keep track of this information, and the calculated information is presented in a
				685	uniform manner with the rest of the passes being executed.</p>
				686
				687	<p>There are many examples of <tt>Statistic</tt> uses, but the basics of using
				688	it are as follows:</p>
				689
				690	<ol>
Bill Wendling	3cd5ca6	2006-10-11 06:30:10 +0000	[diff] [blame]	691	<li><p>Define your statistic like this:</p>
				692
				693	<div class="doc_code">
				694	<pre>
Chris Lattner	0be6fdf	2006-12-19 21:46:21 +0000	[diff] [blame]	695	#define <a href="#DEBUG_TYPE">DEBUG_TYPE</a> "mypassname" <i>// This goes before any #includes.</i>
				696	STATISTIC(NumXForms, "The # of times I did stuff");
Bill Wendling	3cd5ca6	2006-10-11 06:30:10 +0000	[diff] [blame]	697	</pre>
				698	</div>
Misha Brukman	13fd15c	2004-01-15 00:14:41 +0000	[diff] [blame]	699
Chris Lattner	0be6fdf	2006-12-19 21:46:21 +0000	[diff] [blame]	700	<p>The <tt>STATISTIC</tt> macro defines a static variable, whose name is
				701	specified by the first argument. The pass name is taken from the DEBUG_TYPE
				702	macro, and the description is taken from the second argument. The variable
Reid Spencer	06565dc	2007-01-12 17:11:23 +0000	[diff] [blame]	703	defined ("NumXForms" in this case) acts like an unsigned integer.</p></li>
Misha Brukman	13fd15c	2004-01-15 00:14:41 +0000	[diff] [blame]	704
Bill Wendling	3cd5ca6	2006-10-11 06:30:10 +0000	[diff] [blame]	705	<li><p>Whenever you make a transformation, bump the counter:</p>
				706
				707	<div class="doc_code">
				708	<pre>
Bill Wendling	82e2eea	2006-10-11 18:00:22 +0000	[diff] [blame]	709	++NumXForms; // <i>I did stuff!</i>
Bill Wendling	3cd5ca6	2006-10-11 06:30:10 +0000	[diff] [blame]	710	</pre>
				711	</div>
				712
Chris Lattner	261efe9	2003-11-25 01:02:51 +0000	[diff] [blame]	713	</li>
				714	</ol>
Misha Brukman	13fd15c	2004-01-15 00:14:41 +0000	[diff] [blame]	715
				716	<p>That's all you have to do. To get '<tt>opt</tt>' to print out the
				717	statistics gathered, use the '<tt>-stats</tt>' option:</p>
				718
Bill Wendling	3cd5ca6	2006-10-11 06:30:10 +0000	[diff] [blame]	719	<div class="doc_code">
				720	<pre>
				721	$ opt -stats -mypassname < program.bc > /dev/null
Bill Wendling	82e2eea	2006-10-11 18:00:22 +0000	[diff] [blame]	722	<i>... statistics output ...</i>
Bill Wendling	3cd5ca6	2006-10-11 06:30:10 +0000	[diff] [blame]	723	</pre>
				724	</div>
Misha Brukman	13fd15c	2004-01-15 00:14:41 +0000	[diff] [blame]	725
Reid Spencer	6b6c73e	2007-02-09 16:00:28 +0000	[diff] [blame]	726	<p> When running <tt>opt</tt> on a C file from the SPEC benchmark
Chris Lattner	261efe9	2003-11-25 01:02:51 +0000	[diff] [blame]	727	suite, it gives a report that looks like this:</p>
Misha Brukman	13fd15c	2004-01-15 00:14:41 +0000	[diff] [blame]	728
Bill Wendling	3cd5ca6	2006-10-11 06:30:10 +0000	[diff] [blame]	729	<div class="doc_code">
				730	<pre>
Gabor Greif	04367bf	2007-07-06 22:07:22 +0000	[diff] [blame]	731	7646 bitcodewriter - Number of normal instructions
				732	725 bitcodewriter - Number of oversized instructions
				733	129996 bitcodewriter - Number of bitcode bytes written
Bill Wendling	3cd5ca6	2006-10-11 06:30:10 +0000	[diff] [blame]	734	2817 raise - Number of insts DCEd or constprop'd
				735	3213 raise - Number of cast-of-self removed
				736	5046 raise - Number of expression trees converted
				737	75 raise - Number of other getelementptr's formed
				738	138 raise - Number of load/store peepholes
				739	42 deadtypeelim - Number of unused typenames removed from symtab
				740	392 funcresolve - Number of varargs functions resolved
				741	27 globaldce - Number of global variables removed
				742	2 adce - Number of basic blocks removed
				743	134 cee - Number of branches revectored
				744	49 cee - Number of setcc instruction eliminated
				745	532 gcse - Number of loads removed
				746	2919 gcse - Number of instructions removed
				747	86 indvars - Number of canonical indvars added
				748	87 indvars - Number of aux indvars removed
				749	25 instcombine - Number of dead inst eliminate
				750	434 instcombine - Number of insts combined
				751	248 licm - Number of load insts hoisted
				752	1298 licm - Number of insts hoisted to a loop pre-header
				753	3 licm - Number of insts hoisted to multiple loop preds (bad, no loop pre-header)
				754	75 mem2reg - Number of alloca's promoted
				755	1444 cfgsimplify - Number of blocks simplified
				756	</pre>
				757	</div>
Misha Brukman	13fd15c	2004-01-15 00:14:41 +0000	[diff] [blame]	758
				759	<p>Obviously, with so many optimizations, having a unified framework for this
				760	stuff is very nice. Making your pass fit well into the framework makes it more
				761	maintainable and useful.</p>
				762
				763	</div>
				764
Chris Lattner	f623a08	2005-10-17 01:36:23 +0000	[diff] [blame]	765	<!-- ======================================================================= -->
NAKAMURA Takumi	05d0265	2011-04-18 23:59:50 +0000	[diff] [blame]	766	<h3>
Chris Lattner	f623a08	2005-10-17 01:36:23 +0000	[diff] [blame]	767	<a name="ViewGraph">Viewing graphs while debugging code</a>
NAKAMURA Takumi	05d0265	2011-04-18 23:59:50 +0000	[diff] [blame]	768	</h3>
Chris Lattner	f623a08	2005-10-17 01:36:23 +0000	[diff] [blame]	769
NAKAMURA Takumi	f5af6ad	2011-04-23 00:30:22 +0000	[diff] [blame]	770	<div>
Chris Lattner	f623a08	2005-10-17 01:36:23 +0000	[diff] [blame]	771
				772	<p>Several of the important data structures in LLVM are graphs: for example
				773	CFGs made out of LLVM <a href="#BasicBlock">BasicBlock</a>s, CFGs made out of
				774	LLVM <a href="CodeGenerator.html#machinebasicblock">MachineBasicBlock</a>s, and
				775	<a href="CodeGenerator.html#selectiondag_intro">Instruction Selection
				776	DAGs</a>. In many cases, while debugging various parts of the compiler, it is
				777	nice to instantly visualize these graphs.</p>
				778
				779	<p>LLVM provides several callbacks that are available in a debug build to do
				780	exactly that. If you call the <tt>Function::viewCFG()</tt> method, for example,
				781	the current LLVM tool will pop up a window containing the CFG for the function
				782	where each basic block is a node in the graph, and each node contains the
				783	instructions in the block. Similarly, there also exists
				784	<tt>Function::viewCFGOnly()</tt> (does not include the instructions), the
				785	<tt>MachineFunction::viewCFG()</tt> and <tt>MachineFunction::viewCFGOnly()</tt>,
				786	and the <tt>SelectionDAG::viewGraph()</tt> methods. Within GDB, for example,
Jim Laskey	543a0ee	2006-10-02 12:28:07 +0000	[diff] [blame]	787	you can usually use something like <tt>call DAG.viewGraph()</tt> to pop
Chris Lattner	f623a08	2005-10-17 01:36:23 +0000	[diff] [blame]	788	up a window. Alternatively, you can sprinkle calls to these functions in your
				789	code in places you want to debug.</p>
				790
				791	<p>Getting this to work requires a small amount of configuration. On Unix
				792	systems with X11, install the <a href="http://www.graphviz.org">graphviz</a>
				793	toolkit, and make sure 'dot' and 'gv' are in your path. If you are running on
				794	Mac OS/X, download and install the Mac OS/X <a
				795	href="http://www.pixelglow.com/graphviz/">Graphviz program</a>, and add
Reid Spencer	128a7a7	2007-02-03 21:06:43 +0000	[diff] [blame]	796	<tt>/Applications/Graphviz.app/Contents/MacOS/</tt> (or wherever you install
Chris Lattner	f623a08	2005-10-17 01:36:23 +0000	[diff] [blame]	797	it) to your path. Once in your system and path are set up, rerun the LLVM
				798	configure script and rebuild LLVM to enable this functionality.</p>
				799
Jim Laskey	543a0ee	2006-10-02 12:28:07 +0000	[diff] [blame]	800	<p><tt>SelectionDAG</tt> has been extended to make it easier to locate
				801	<i>interesting</i> nodes in large complex graphs. From gdb, if you
				802	<tt>call DAG.setGraphColor(<i>node</i>, "<i>color</i>")</tt>, then the
Reid Spencer	128a7a7	2007-02-03 21:06:43 +0000	[diff] [blame]	803	next <tt>call DAG.viewGraph()</tt> would highlight the node in the
Jim Laskey	543a0ee	2006-10-02 12:28:07 +0000	[diff] [blame]	804	specified color (choices of colors can be found at <a
Chris Lattner	302da1e	2007-02-03 03:05:57 +0000	[diff] [blame]	805	href="http://www.graphviz.org/doc/info/colors.html">colors</a>.) More
Jim Laskey	543a0ee	2006-10-02 12:28:07 +0000	[diff] [blame]	806	complex node attributes can be provided with <tt>call
				807	DAG.setGraphAttrs(<i>node</i>, "<i>attributes</i>")</tt> (choices can be
				808	found at <a href="http://www.graphviz.org/doc/info/attrs.html">Graph
				809	Attributes</a>.) If you want to restart and clear all the current graph
				810	attributes, then you can <tt>call DAG.clearGraphAttrs()</tt>. </p>
				811
Chris Lattner	83f9467	2011-06-13 15:59:35 +0000	[diff] [blame]	812	<p>Note that graph visualization features are compiled out of Release builds
				813	to reduce file size. This means that you need a Debug+Asserts or
				814	Release+Asserts build to use these features.</p>
				815
Chris Lattner	f623a08	2005-10-17 01:36:23 +0000	[diff] [blame]	816	</div>
				817
NAKAMURA Takumi	f5af6ad	2011-04-23 00:30:22 +0000	[diff] [blame]	818	</div>
				819
Chris Lattner	098129a	2007-02-03 03:04:03 +0000	[diff] [blame]	820	<!-- *********************************************************************** -->
NAKAMURA Takumi	05d0265	2011-04-18 23:59:50 +0000	[diff] [blame]	821	<h2>
Chris Lattner	098129a	2007-02-03 03:04:03 +0000	[diff] [blame]	822	<a name="datastructure">Picking the Right Data Structure for a Task</a>
NAKAMURA Takumi	05d0265	2011-04-18 23:59:50 +0000	[diff] [blame]	823	</h2>
Chris Lattner	098129a	2007-02-03 03:04:03 +0000	[diff] [blame]	824	<!-- *********************************************************************** -->
				825
NAKAMURA Takumi	f5af6ad	2011-04-23 00:30:22 +0000	[diff] [blame]	826	<div>
Chris Lattner	098129a	2007-02-03 03:04:03 +0000	[diff] [blame]	827
Reid Spencer	128a7a7	2007-02-03 21:06:43 +0000	[diff] [blame]	828	<p>LLVM has a plethora of data structures in the <tt>llvm/ADT/</tt> directory,
				829	and we commonly use STL data structures. This section describes the trade-offs
Chris Lattner	098129a	2007-02-03 03:04:03 +0000	[diff] [blame]	830	you should consider when you pick one.</p>
				831
				832	<p>
				833	The first step is a choose your own adventure: do you want a sequential
				834	container, a set-like container, or a map-like container? The most important
				835	thing when choosing a container is the algorithmic properties of how you plan to
				836	access the container. Based on that, you should use:</p>
				837
				838	<ul>
Reid Spencer	128a7a7	2007-02-03 21:06:43 +0000	[diff] [blame]	839	<li>a <a href="#ds_map">map-like</a> container if you need efficient look-up
Chris Lattner	098129a	2007-02-03 03:04:03 +0000	[diff] [blame]	840	of an value based on another value. Map-like containers also support
				841	efficient queries for containment (whether a key is in the map). Map-like
				842	containers generally do not support efficient reverse mapping (values to
				843	keys). If you need that, use two maps. Some map-like containers also
				844	support efficient iteration through the keys in sorted order. Map-like
				845	containers are the most expensive sort, only use them if you need one of
				846	these capabilities.</li>
				847
				848	<li>a <a href="#ds_set">set-like</a> container if you need to put a bunch of
				849	stuff into a container that automatically eliminates duplicates. Some
				850	set-like containers support efficient iteration through the elements in
				851	sorted order. Set-like containers are more expensive than sequential
				852	containers.
				853	</li>
				854
				855	<li>a <a href="#ds_sequential">sequential</a> container provides
				856	the most efficient way to add elements and keeps track of the order they are
				857	added to the collection. They permit duplicates and support efficient
Reid Spencer	128a7a7	2007-02-03 21:06:43 +0000	[diff] [blame]	858	iteration, but do not support efficient look-up based on a key.
Chris Lattner	098129a	2007-02-03 03:04:03 +0000	[diff] [blame]	859	</li>
				860
Chris Lattner	dced9fb	2009-07-25 07:22:20 +0000	[diff] [blame]	861	<li>a <a href="#ds_string">string</a> container is a specialized sequential
				862	container or reference structure that is used for character or byte
				863	arrays.</li>
				864
Daniel Berlin	1939ace	2007-09-24 17:52:25 +0000	[diff] [blame]	865	<li>a <a href="#ds_bit">bit</a> container provides an efficient way to store and
				866	perform set operations on sets of numeric id's, while automatically
				867	eliminating duplicates. Bit containers require a maximum of 1 bit for each
				868	identifier you want to store.
				869	</li>
Chris Lattner	098129a	2007-02-03 03:04:03 +0000	[diff] [blame]	870	</ul>
				871
				872	<p>
Reid Spencer	128a7a7	2007-02-03 21:06:43 +0000	[diff] [blame]	873	Once the proper category of container is determined, you can fine tune the
Chris Lattner	098129a	2007-02-03 03:04:03 +0000	[diff] [blame]	874	memory use, constant factors, and cache behaviors of access by intelligently
Reid Spencer	128a7a7	2007-02-03 21:06:43 +0000	[diff] [blame]	875	picking a member of the category. Note that constant factors and cache behavior
Chris Lattner	098129a	2007-02-03 03:04:03 +0000	[diff] [blame]	876	can be a big deal. If you have a vector that usually only contains a few
				877	elements (but could contain many), for example, it's much better to use
				878	<a href="#dss_smallvector">SmallVector</a> than <a href="#dss_vector">vector</a>
				879	. Doing so avoids (relatively) expensive malloc/free calls, which dwarf the
				880	cost of adding the elements to the container. </p>
				881
Chris Lattner	098129a	2007-02-03 03:04:03 +0000	[diff] [blame]	882	<!-- ======================================================================= -->
NAKAMURA Takumi	05d0265	2011-04-18 23:59:50 +0000	[diff] [blame]	883	<h3>
Chris Lattner	098129a	2007-02-03 03:04:03 +0000	[diff] [blame]	884	<a name="ds_sequential">Sequential Containers (std::vector, std::list, etc)</a>
NAKAMURA Takumi	05d0265	2011-04-18 23:59:50 +0000	[diff] [blame]	885	</h3>
Chris Lattner	098129a	2007-02-03 03:04:03 +0000	[diff] [blame]	886
NAKAMURA Takumi	f5af6ad	2011-04-23 00:30:22 +0000	[diff] [blame]	887	<div>
Chris Lattner	098129a	2007-02-03 03:04:03 +0000	[diff] [blame]	888	There are a variety of sequential containers available for you, based on your
				889	needs. Pick the first in this section that will do what you want.
Chris Lattner	3b4f417	2011-07-22 21:34:12 +0000	[diff] [blame]	890
Chris Lattner	098129a	2007-02-03 03:04:03 +0000	[diff] [blame]	891	<!-- _______________________________________________________________________ -->
NAKAMURA Takumi	05d0265	2011-04-18 23:59:50 +0000	[diff] [blame]	892	<h4>
Chris Lattner	8ae4261	2011-04-05 23:18:20 +0000	[diff] [blame]	893	<a name="dss_arrayref">llvm/ADT/ArrayRef.h</a>
NAKAMURA Takumi	05d0265	2011-04-18 23:59:50 +0000	[diff] [blame]	894	</h4>
Chris Lattner	8ae4261	2011-04-05 23:18:20 +0000	[diff] [blame]	895
NAKAMURA Takumi	f5af6ad	2011-04-23 00:30:22 +0000	[diff] [blame]	896	<div>
Chris Lattner	8ae4261	2011-04-05 23:18:20 +0000	[diff] [blame]	897	<p>The llvm::ArrayRef class is the preferred class to use in an interface that
				898	accepts a sequential list of elements in memory and just reads from them. By
				899	taking an ArrayRef, the API can be passed a fixed size array, an std::vector,
				900	an llvm::SmallVector and anything else that is contiguous in memory.
				901	</p>
				902	</div>
				903
				904
				905
				906	<!-- _______________________________________________________________________ -->
NAKAMURA Takumi	05d0265	2011-04-18 23:59:50 +0000	[diff] [blame]	907	<h4>
Chris Lattner	098129a	2007-02-03 03:04:03 +0000	[diff] [blame]	908	<a name="dss_fixedarrays">Fixed Size Arrays</a>
NAKAMURA Takumi	05d0265	2011-04-18 23:59:50 +0000	[diff] [blame]	909	</h4>
Chris Lattner	098129a	2007-02-03 03:04:03 +0000	[diff] [blame]	910
NAKAMURA Takumi	f5af6ad	2011-04-23 00:30:22 +0000	[diff] [blame]	911	<div>
Chris Lattner	098129a	2007-02-03 03:04:03 +0000	[diff] [blame]	912	<p>Fixed size arrays are very simple and very fast. They are good if you know
				913	exactly how many elements you have, or you have a (low) upper bound on how many
				914	you have.</p>
				915	</div>
				916
				917	<!-- _______________________________________________________________________ -->
NAKAMURA Takumi	05d0265	2011-04-18 23:59:50 +0000	[diff] [blame]	918	<h4>
Chris Lattner	098129a	2007-02-03 03:04:03 +0000	[diff] [blame]	919	<a name="dss_heaparrays">Heap Allocated Arrays</a>
NAKAMURA Takumi	05d0265	2011-04-18 23:59:50 +0000	[diff] [blame]	920	</h4>
Chris Lattner	098129a	2007-02-03 03:04:03 +0000	[diff] [blame]	921
NAKAMURA Takumi	f5af6ad	2011-04-23 00:30:22 +0000	[diff] [blame]	922	<div>
Chris Lattner	098129a	2007-02-03 03:04:03 +0000	[diff] [blame]	923	<p>Heap allocated arrays (new[] + delete[]) are also simple. They are good if
				924	the number of elements is variable, if you know how many elements you will need
				925	before the array is allocated, and if the array is usually large (if not,
				926	consider a <a href="#dss_smallvector">SmallVector</a>). The cost of a heap
				927	allocated array is the cost of the new/delete (aka malloc/free). Also note that
				928	if you are allocating an array of a type with a constructor, the constructor and
Reid Spencer	128a7a7	2007-02-03 21:06:43 +0000	[diff] [blame]	929	destructors will be run for every element in the array (re-sizable vectors only
Chris Lattner	098129a	2007-02-03 03:04:03 +0000	[diff] [blame]	930	construct those elements actually used).</p>
				931	</div>
				932
				933	<!-- _______________________________________________________________________ -->
NAKAMURA Takumi	05d0265	2011-04-18 23:59:50 +0000	[diff] [blame]	934	<h4>
Chris Lattner	9d69d4a	2011-07-18 01:40:02 +0000	[diff] [blame]	935	<a name="dss_tinyptrvector">"llvm/ADT/TinyPtrVector.h"</a>
				936	</h4>
				937
				938
				939	<div>
				940	<p><tt>TinyPtrVector<Type></tt> is a highly specialized collection class
				941	that is optimized to avoid allocation in the case when a vector has zero or one
				942	elements. It has two major restrictions: 1) it can only hold values of pointer
				943	type, and 2) it cannot hold a null pointer.</p>
				944
				945	<p>Since this container is highly specialized, it is rarely used.</p>
				946
				947	</div>
				948
Chris Lattner	9d69d4a	2011-07-18 01:40:02 +0000	[diff] [blame]	949	<!-- _______________________________________________________________________ -->
				950	<h4>
Chris Lattner	098129a	2007-02-03 03:04:03 +0000	[diff] [blame]	951	<a name="dss_smallvector">"llvm/ADT/SmallVector.h"</a>
NAKAMURA Takumi	05d0265	2011-04-18 23:59:50 +0000	[diff] [blame]	952	</h4>
Chris Lattner	098129a	2007-02-03 03:04:03 +0000	[diff] [blame]	953
NAKAMURA Takumi	f5af6ad	2011-04-23 00:30:22 +0000	[diff] [blame]	954	<div>
Chris Lattner	098129a	2007-02-03 03:04:03 +0000	[diff] [blame]	955	<p><tt>SmallVector<Type, N></tt> is a simple class that looks and smells
				956	just like <tt>vector<Type></tt>:
				957	it supports efficient iteration, lays out elements in memory order (so you can
				958	do pointer arithmetic between elements), supports efficient push_back/pop_back
				959	operations, supports efficient random access to its elements, etc.</p>
				960
				961	<p>The advantage of SmallVector is that it allocates space for
				962	some number of elements (N) <b>in the object itself</b>. Because of this, if
				963	the SmallVector is dynamically smaller than N, no malloc is performed. This can
				964	be a big win in cases where the malloc/free call is far more expensive than the
				965	code that fiddles around with the elements.</p>
				966
				967	<p>This is good for vectors that are "usually small" (e.g. the number of
				968	predecessors/successors of a block is usually less than 8). On the other hand,
				969	this makes the size of the SmallVector itself large, so you don't want to
				970	allocate lots of them (doing so will waste a lot of space). As such,
				971	SmallVectors are most useful when on the stack.</p>
				972
				973	<p>SmallVector also provides a nice portable and efficient replacement for
				974	<tt>alloca</tt>.</p>
				975
				976	</div>
				977
				978	<!-- _______________________________________________________________________ -->
NAKAMURA Takumi	05d0265	2011-04-18 23:59:50 +0000	[diff] [blame]	979	<h4>
Chris Lattner	098129a	2007-02-03 03:04:03 +0000	[diff] [blame]	980	<a name="dss_vector"><vector></a>
NAKAMURA Takumi	05d0265	2011-04-18 23:59:50 +0000	[diff] [blame]	981	</h4>
Chris Lattner	098129a	2007-02-03 03:04:03 +0000	[diff] [blame]	982
NAKAMURA Takumi	f5af6ad	2011-04-23 00:30:22 +0000	[diff] [blame]	983	<div>
Chris Lattner	098129a	2007-02-03 03:04:03 +0000	[diff] [blame]	984	<p>
				985	std::vector is well loved and respected. It is useful when SmallVector isn't:
				986	when the size of the vector is often large (thus the small optimization will
				987	rarely be a benefit) or if you will be allocating many instances of the vector
				988	itself (which would waste space for elements that aren't in the container).
				989	vector is also useful when interfacing with code that expects vectors :).
				990	</p>
Chris Lattner	32d8476	2007-02-05 06:30:51 +0000	[diff] [blame]	991
				992	<p>One worthwhile note about std::vector: avoid code like this:</p>
				993
				994	<div class="doc_code">
				995	<pre>
				996	for ( ... ) {
Chris Lattner	9bb3dbb	2007-03-28 18:27:57 +0000	[diff] [blame]	997	std::vector<foo> V;
Jim Grosbach	087f050	2011-10-28 20:52:20 +0000	[diff] [blame]	998	// make use of V.
Chris Lattner	32d8476	2007-02-05 06:30:51 +0000	[diff] [blame]	999	}
				1000	</pre>
				1001	</div>
				1002
				1003	<p>Instead, write this as:</p>
				1004
				1005	<div class="doc_code">
				1006	<pre>
Chris Lattner	9bb3dbb	2007-03-28 18:27:57 +0000	[diff] [blame]	1007	std::vector<foo> V;
Chris Lattner	32d8476	2007-02-05 06:30:51 +0000	[diff] [blame]	1008	for ( ... ) {
Jim Grosbach	087f050	2011-10-28 20:52:20 +0000	[diff] [blame]	1009	// make use of V.
Chris Lattner	32d8476	2007-02-05 06:30:51 +0000	[diff] [blame]	1010	V.clear();
				1011	}
				1012	</pre>
				1013	</div>
				1014
				1015	<p>Doing so will save (at least) one heap allocation and free per iteration of
				1016	the loop.</p>
				1017
Chris Lattner	098129a	2007-02-03 03:04:03 +0000	[diff] [blame]	1018	</div>
				1019
				1020	<!-- _______________________________________________________________________ -->
NAKAMURA Takumi	05d0265	2011-04-18 23:59:50 +0000	[diff] [blame]	1021	<h4>
Chris Lattner	74c4ca1	2007-02-03 07:59:07 +0000	[diff] [blame]	1022	<a name="dss_deque"><deque></a>
NAKAMURA Takumi	05d0265	2011-04-18 23:59:50 +0000	[diff] [blame]	1023	</h4>
Chris Lattner	74c4ca1	2007-02-03 07:59:07 +0000	[diff] [blame]	1024
NAKAMURA Takumi	f5af6ad	2011-04-23 00:30:22 +0000	[diff] [blame]	1025	<div>
Chris Lattner	74c4ca1	2007-02-03 07:59:07 +0000	[diff] [blame]	1026	<p>std::deque is, in some senses, a generalized version of std::vector. Like
				1027	std::vector, it provides constant time random access and other similar
				1028	properties, but it also provides efficient access to the front of the list. It
				1029	does not guarantee continuity of elements within memory.</p>
				1030
				1031	<p>In exchange for this extra flexibility, std::deque has significantly higher
				1032	constant factor costs than std::vector. If possible, use std::vector or
				1033	something cheaper.</p>
				1034	</div>
				1035
				1036	<!-- _______________________________________________________________________ -->
NAKAMURA Takumi	05d0265	2011-04-18 23:59:50 +0000	[diff] [blame]	1037	<h4>
Chris Lattner	098129a	2007-02-03 03:04:03 +0000	[diff] [blame]	1038	<a name="dss_list"><list></a>
NAKAMURA Takumi	05d0265	2011-04-18 23:59:50 +0000	[diff] [blame]	1039	</h4>
Chris Lattner	098129a	2007-02-03 03:04:03 +0000	[diff] [blame]	1040
NAKAMURA Takumi	f5af6ad	2011-04-23 00:30:22 +0000	[diff] [blame]	1041	<div>
Chris Lattner	098129a	2007-02-03 03:04:03 +0000	[diff] [blame]	1042	<p>std::list is an extremely inefficient class that is rarely useful.
				1043	It performs a heap allocation for every element inserted into it, thus having an
				1044	extremely high constant factor, particularly for small data types. std::list
				1045	also only supports bidirectional iteration, not random access iteration.</p>
				1046
				1047	<p>In exchange for this high cost, std::list supports efficient access to both
				1048	ends of the list (like std::deque, but unlike std::vector or SmallVector). In
				1049	addition, the iterator invalidation characteristics of std::list are stronger
				1050	than that of a vector class: inserting or removing an element into the list does
				1051	not invalidate iterator or pointers to other elements in the list.</p>
				1052	</div>
				1053
				1054	<!-- _______________________________________________________________________ -->
NAKAMURA Takumi	05d0265	2011-04-18 23:59:50 +0000	[diff] [blame]	1055	<h4>
Gabor Greif	3899e49	2009-02-27 11:37:41 +0000	[diff] [blame]	1056	<a name="dss_ilist">llvm/ADT/ilist.h</a>
NAKAMURA Takumi	05d0265	2011-04-18 23:59:50 +0000	[diff] [blame]	1057	</h4>
Chris Lattner	098129a	2007-02-03 03:04:03 +0000	[diff] [blame]	1058
NAKAMURA Takumi	f5af6ad	2011-04-23 00:30:22 +0000	[diff] [blame]	1059	<div>
Chris Lattner	098129a	2007-02-03 03:04:03 +0000	[diff] [blame]	1060	<p><tt>ilist<T></tt> implements an 'intrusive' doubly-linked list. It is
				1061	intrusive, because it requires the element to store and provide access to the
				1062	prev/next pointers for the list.</p>
				1063
Gabor Greif	2946d1c	2009-02-27 12:02:19 +0000	[diff] [blame]	1064	<p><tt>ilist</tt> has the same drawbacks as <tt>std::list</tt>, and additionally
				1065	requires an <tt>ilist_traits</tt> implementation for the element type, but it
				1066	provides some novel characteristics. In particular, it can efficiently store
				1067	polymorphic objects, the traits class is informed when an element is inserted or
Gabor Greif	0cbcabe	2009-03-12 09:47:03 +0000	[diff] [blame]	1068	removed from the list, and <tt>ilist</tt>s are guaranteed to support a
				1069	constant-time splice operation.</p>
Chris Lattner	098129a	2007-02-03 03:04:03 +0000	[diff] [blame]	1070
Gabor Greif	0cbcabe	2009-03-12 09:47:03 +0000	[diff] [blame]	1071	<p>These properties are exactly what we want for things like
				1072	<tt>Instruction</tt>s and basic blocks, which is why these are implemented with
				1073	<tt>ilist</tt>s.</p>
Gabor Greif	3899e49	2009-02-27 11:37:41 +0000	[diff] [blame]	1074
				1075	Related classes of interest are explained in the following subsections:
				1076	<ul>
Gabor Greif	0186250	2009-02-27 13:28:07 +0000	[diff] [blame]	1077	<li><a href="#dss_ilist_traits">ilist_traits</a></li>
Gabor Greif	2946d1c	2009-02-27 12:02:19 +0000	[diff] [blame]	1078	<li><a href="#dss_iplist">iplist</a></li>
Gabor Greif	3899e49	2009-02-27 11:37:41 +0000	[diff] [blame]	1079	<li><a href="#dss_ilist_node">llvm/ADT/ilist_node.h</a></li>
Gabor Greif	6a65f42	2009-03-12 10:30:31 +0000	[diff] [blame]	1080	<li><a href="#dss_ilist_sentinel">Sentinels</a></li>
Gabor Greif	3899e49	2009-02-27 11:37:41 +0000	[diff] [blame]	1081	</ul>
				1082	</div>
				1083
				1084	<!-- _______________________________________________________________________ -->
NAKAMURA Takumi	05d0265	2011-04-18 23:59:50 +0000	[diff] [blame]	1085	<h4>
Argyrios Kyrtzidis	81df089	2011-06-15 19:56:01 +0000	[diff] [blame]	1086	<a name="dss_packedvector">llvm/ADT/PackedVector.h</a>
				1087	</h4>
				1088
				1089	<div>
				1090	<p>
				1091	Useful for storing a vector of values using only a few number of bits for each
				1092	value. Apart from the standard operations of a vector-like container, it can
				1093	also perform an 'or' set operation.
				1094	</p>
				1095
				1096	<p>For example:</p>
				1097
				1098	<div class="doc_code">
				1099	<pre>
				1100	enum State {
				1101	None = 0x0,
				1102	FirstCondition = 0x1,
				1103	SecondCondition = 0x2,
				1104	Both = 0x3
				1105	};
				1106
				1107	State get() {
				1108	PackedVector<State, 2> Vec1;
				1109	Vec1.push_back(FirstCondition);
				1110
				1111	PackedVector<State, 2> Vec2;
				1112	Vec2.push_back(SecondCondition);
				1113
				1114	Vec1 \|= Vec2;
				1115	return Vec1[0]; // returns 'Both'.
				1116	}
				1117	</pre>
				1118	</div>
				1119
				1120	</div>
				1121
				1122	<!-- _______________________________________________________________________ -->
				1123	<h4>
Gabor Greif	0186250	2009-02-27 13:28:07 +0000	[diff] [blame]	1124	<a name="dss_ilist_traits">ilist_traits</a>
NAKAMURA Takumi	05d0265	2011-04-18 23:59:50 +0000	[diff] [blame]	1125	</h4>
Gabor Greif	0186250	2009-02-27 13:28:07 +0000	[diff] [blame]	1126
NAKAMURA Takumi	f5af6ad	2011-04-23 00:30:22 +0000	[diff] [blame]	1127	<div>
Gabor Greif	0186250	2009-02-27 13:28:07 +0000	[diff] [blame]	1128	<p><tt>ilist_traits<T></tt> is <tt>ilist<T></tt>'s customization
				1129	mechanism. <tt>iplist<T></tt> (and consequently <tt>ilist<T></tt>)
				1130	publicly derive from this traits class.</p>
				1131	</div>
				1132
				1133	<!-- _______________________________________________________________________ -->
NAKAMURA Takumi	05d0265	2011-04-18 23:59:50 +0000	[diff] [blame]	1134	<h4>
Gabor Greif	2946d1c	2009-02-27 12:02:19 +0000	[diff] [blame]	1135	<a name="dss_iplist">iplist</a>
NAKAMURA Takumi	05d0265	2011-04-18 23:59:50 +0000	[diff] [blame]	1136	</h4>
Gabor Greif	2946d1c	2009-02-27 12:02:19 +0000	[diff] [blame]	1137
NAKAMURA Takumi	f5af6ad	2011-04-23 00:30:22 +0000	[diff] [blame]	1138	<div>
Gabor Greif	2946d1c	2009-02-27 12:02:19 +0000	[diff] [blame]	1139	<p><tt>iplist<T></tt> is <tt>ilist<T></tt>'s base and as such
Gabor Greif	0cbcabe	2009-03-12 09:47:03 +0000	[diff] [blame]	1140	supports a slightly narrower interface. Notably, inserters from
				1141	<tt>T&</tt> are absent.</p>
Gabor Greif	0186250	2009-02-27 13:28:07 +0000	[diff] [blame]	1142
				1143	<p><tt>ilist_traits<T></tt> is a public base of this class and can be
				1144	used for a wide variety of customizations.</p>
Gabor Greif	2946d1c	2009-02-27 12:02:19 +0000	[diff] [blame]	1145	</div>
				1146
				1147	<!-- _______________________________________________________________________ -->
NAKAMURA Takumi	05d0265	2011-04-18 23:59:50 +0000	[diff] [blame]	1148	<h4>
Gabor Greif	3899e49	2009-02-27 11:37:41 +0000	[diff] [blame]	1149	<a name="dss_ilist_node">llvm/ADT/ilist_node.h</a>
NAKAMURA Takumi	05d0265	2011-04-18 23:59:50 +0000	[diff] [blame]	1150	</h4>
Gabor Greif	3899e49	2009-02-27 11:37:41 +0000	[diff] [blame]	1151
NAKAMURA Takumi	f5af6ad	2011-04-23 00:30:22 +0000	[diff] [blame]	1152	<div>
Gabor Greif	3899e49	2009-02-27 11:37:41 +0000	[diff] [blame]	1153	<p><tt>ilist_node<T></tt> implements a the forward and backward links
				1154	that are expected by the <tt>ilist<T></tt> (and analogous containers)
				1155	in the default manner.</p>
				1156
				1157	<p><tt>ilist_node<T></tt>s are meant to be embedded in the node type
Gabor Greif	0cbcabe	2009-03-12 09:47:03 +0000	[diff] [blame]	1158	<tt>T</tt>, usually <tt>T</tt> publicly derives from
				1159	<tt>ilist_node<T></tt>.</p>
Chris Lattner	098129a	2007-02-03 03:04:03 +0000	[diff] [blame]	1160	</div>
				1161
				1162	<!-- _______________________________________________________________________ -->
NAKAMURA Takumi	05d0265	2011-04-18 23:59:50 +0000	[diff] [blame]	1163	<h4>
Gabor Greif	6a65f42	2009-03-12 10:30:31 +0000	[diff] [blame]	1164	<a name="dss_ilist_sentinel">Sentinels</a>
NAKAMURA Takumi	05d0265	2011-04-18 23:59:50 +0000	[diff] [blame]	1165	</h4>
Gabor Greif	6a65f42	2009-03-12 10:30:31 +0000	[diff] [blame]	1166
NAKAMURA Takumi	f5af6ad	2011-04-23 00:30:22 +0000	[diff] [blame]	1167	<div>
Dan Gohman	cf0c9bc	2010-02-25 23:51:27 +0000	[diff] [blame]	1168	<p><tt>ilist</tt>s have another specialty that must be considered. To be a good
Gabor Greif	6a65f42	2009-03-12 10:30:31 +0000	[diff] [blame]	1169	citizen in the C++ ecosystem, it needs to support the standard container
				1170	operations, such as <tt>begin</tt> and <tt>end</tt> iterators, etc. Also, the
				1171	<tt>operator--</tt> must work correctly on the <tt>end</tt> iterator in the
				1172	case of non-empty <tt>ilist</tt>s.</p>
				1173
				1174	<p>The only sensible solution to this problem is to allocate a so-called
				1175	<i>sentinel</i> along with the intrusive list, which serves as the <tt>end</tt>
				1176	iterator, providing the back-link to the last element. However conforming to the
				1177	C++ convention it is illegal to <tt>operator++</tt> beyond the sentinel and it
				1178	also must not be dereferenced.</p>
				1179
				1180	<p>These constraints allow for some implementation freedom to the <tt>ilist</tt>
				1181	how to allocate and store the sentinel. The corresponding policy is dictated
				1182	by <tt>ilist_traits<T></tt>. By default a <tt>T</tt> gets heap-allocated
				1183	whenever the need for a sentinel arises.</p>
				1184
				1185	<p>While the default policy is sufficient in most cases, it may break down when
				1186	<tt>T</tt> does not provide a default constructor. Also, in the case of many
				1187	instances of <tt>ilist</tt>s, the memory overhead of the associated sentinels
				1188	is wasted. To alleviate the situation with numerous and voluminous
				1189	<tt>T</tt>-sentinels, sometimes a trick is employed, leading to <i>ghostly
				1190	sentinels</i>.</p>
				1191
				1192	<p>Ghostly sentinels are obtained by specially-crafted <tt>ilist_traits<T></tt>
				1193	which superpose the sentinel with the <tt>ilist</tt> instance in memory. Pointer
				1194	arithmetic is used to obtain the sentinel, which is relative to the
				1195	<tt>ilist</tt>'s <tt>this</tt> pointer. The <tt>ilist</tt> is augmented by an
				1196	extra pointer, which serves as the back-link of the sentinel. This is the only
				1197	field in the ghostly sentinel which can be legally accessed.</p>
				1198	</div>
				1199
				1200	<!-- _______________________________________________________________________ -->
NAKAMURA Takumi	05d0265	2011-04-18 23:59:50 +0000	[diff] [blame]	1201	<h4>
Chris Lattner	c572243	2007-02-03 19:49:31 +0000	[diff] [blame]	1202	<a name="dss_other">Other Sequential Container options</a>
NAKAMURA Takumi	05d0265	2011-04-18 23:59:50 +0000	[diff] [blame]	1203	</h4>
Chris Lattner	098129a	2007-02-03 03:04:03 +0000	[diff] [blame]	1204
NAKAMURA Takumi	f5af6ad	2011-04-23 00:30:22 +0000	[diff] [blame]	1205	<div>
Chris Lattner	74c4ca1	2007-02-03 07:59:07 +0000	[diff] [blame]	1206	<p>Other STL containers are available, such as std::string.</p>
Chris Lattner	098129a	2007-02-03 03:04:03 +0000	[diff] [blame]	1207
				1208	<p>There are also various STL adapter classes such as std::queue,
				1209	std::priority_queue, std::stack, etc. These provide simplified access to an
				1210	underlying container but don't affect the cost of the container itself.</p>
				1211
				1212	</div>
NAKAMURA Takumi	f5af6ad	2011-04-23 00:30:22 +0000	[diff] [blame]	1213	</div>
Chris Lattner	098129a	2007-02-03 03:04:03 +0000	[diff] [blame]	1214
				1215	<!-- ======================================================================= -->
NAKAMURA Takumi	05d0265	2011-04-18 23:59:50 +0000	[diff] [blame]	1216	<h3>
Chris Lattner	7314a20	2011-07-22 20:46:49 +0000	[diff] [blame]	1217	<a name="ds_string">String-like containers</a>
				1218	</h3>
				1219
				1220	<div>
				1221
				1222	<p>
Chris Lattner	3b4f417	2011-07-22 21:34:12 +0000	[diff] [blame]	1223	There are a variety of ways to pass around and use strings in C and C++, and
				1224	LLVM adds a few new options to choose from. Pick the first option on this list
				1225	that will do what you need, they are ordered according to their relative cost.
				1226	</p>
				1227	<p>
				1228	Note that is is generally preferred to <em>not</em> pass strings around as
				1229	"<tt>const char*</tt>"'s. These have a number of problems, including the fact
				1230	that they cannot represent embedded nul ("\0") characters, and do not have a
				1231	length available efficiently. The general replacement for '<tt>const
				1232	char*</tt>' is StringRef.
				1233	</p>
				1234
				1235	<p>For more information on choosing string containers for APIs, please see
				1236	<a href="#string_apis">Passing strings</a>.</p>
				1237
				1238
				1239	<!-- _______________________________________________________________________ -->
				1240	<h4>
				1241	<a name="dss_stringref">llvm/ADT/StringRef.h</a>
				1242	</h4>
				1243
				1244	<div>
				1245	<p>
				1246	The StringRef class is a simple value class that contains a pointer to a
				1247	character and a length, and is quite related to the <a
				1248	href="#dss_arrayref">ArrayRef</a> class (but specialized for arrays of
				1249	characters). Because StringRef carries a length with it, it safely handles
				1250	strings with embedded nul characters in it, getting the length does not require
				1251	a strlen call, and it even has very convenient APIs for slicing and dicing the
				1252	character range that it represents.
				1253	</p>
				1254
				1255	<p>
				1256	StringRef is ideal for passing simple strings around that are known to be live,
				1257	either because they are C string literals, std::string, a C array, or a
				1258	SmallVector. Each of these cases has an efficient implicit conversion to
				1259	StringRef, which doesn't result in a dynamic strlen being executed.
				1260	</p>
				1261
				1262	<p>StringRef has a few major limitations which make more powerful string
				1263	containers useful:</p>
				1264
				1265	<ol>
				1266	<li>You cannot directly convert a StringRef to a 'const char*' because there is
				1267	no way to add a trailing nul (unlike the .c_str() method on various stronger
				1268	classes).</li>
				1269
				1270
				1271	<li>StringRef doesn't own or keep alive the underlying string bytes.
				1272	As such it can easily lead to dangling pointers, and is not suitable for
				1273	embedding in datastructures in most cases (instead, use an std::string or
				1274	something like that).</li>
				1275
				1276	<li>For the same reason, StringRef cannot be used as the return value of a
				1277	method if the method "computes" the result string. Instead, use
				1278	std::string.</li>
				1279
Chris Lattner	ec8f1ea	2011-07-23 17:18:57 +0000	[diff] [blame]	1280	<li>StringRef's do not allow you to mutate the pointed-to string bytes and it
				1281	doesn't allow you to insert or remove bytes from the range. For editing
				1282	operations like this, it interoperates with the <a
				1283	href="#dss_twine">Twine</a> class.</li>
Chris Lattner	3b4f417	2011-07-22 21:34:12 +0000	[diff] [blame]	1284	</ol>
				1285
				1286	<p>Because of its strengths and limitations, it is very common for a function to
				1287	take a StringRef and for a method on an object to return a StringRef that
				1288	points into some string that it owns.</p>
				1289
				1290	</div>
				1291
				1292	<!-- _______________________________________________________________________ -->
				1293	<h4>
				1294	<a name="dss_twine">llvm/ADT/Twine.h</a>
				1295	</h4>
				1296
				1297	<div>
				1298	<p>
				1299	The Twine class is used as an intermediary datatype for APIs that want to take
				1300	a string that can be constructed inline with a series of concatenations.
				1301	Twine works by forming recursive instances of the Twine datatype (a simple
				1302	value object) on the stack as temporary objects, linking them together into a
				1303	tree which is then linearized when the Twine is consumed. Twine is only safe
				1304	to use as the argument to a function, and should always be a const reference,
				1305	e.g.:
				1306	</p>
				1307
				1308	<pre>
				1309	void foo(const Twine &T);
				1310	...
				1311	StringRef X = ...
				1312	unsigned i = ...
				1313	foo(X + "." + Twine(i));
				1314	</pre>
				1315
				1316	<p>This example forms a string like "blarg.42" by concatenating the values
				1317	together, and does not form intermediate strings containing "blarg" or
				1318	"blarg.".
				1319	</p>
				1320
				1321	<p>Because Twine is constructed with temporary objects on the stack, and
				1322	because these instances are destroyed at the end of the current statement,
				1323	it is an inherently dangerous API. For example, this simple variant contains
				1324	undefined behavior and will probably crash:</p>
				1325
				1326	<pre>
				1327	void foo(const Twine &T);
				1328	...
				1329	StringRef X = ...
				1330	unsigned i = ...
				1331	const Twine &Tmp = X + "." + Twine(i);
				1332	foo(Tmp);
				1333	</pre>
				1334
				1335	<p>... because the temporaries are destroyed before the call. That said,
				1336	Twine's are much more efficient than intermediate std::string temporaries, and
				1337	they work really well with StringRef. Just be aware of their limitations.</p>
				1338
				1339	</div>
				1340
				1341
				1342	<!-- _______________________________________________________________________ -->
				1343	<h4>
				1344	<a name="dss_smallstring">llvm/ADT/SmallString.h</a>
				1345	</h4>
				1346
				1347	<div>
				1348
				1349	<p>SmallString is a subclass of <a href="#dss_smallvector">SmallVector</a> that
				1350	adds some convenience APIs like += that takes StringRef's. SmallString avoids
				1351	allocating memory in the case when the preallocated space is enough to hold its
				1352	data, and it calls back to general heap allocation when required. Since it owns
				1353	its data, it is very safe to use and supports full mutation of the string.</p>
				1354
				1355	<p>Like SmallVector's, the big downside to SmallString is their sizeof. While
				1356	they are optimized for small strings, they themselves are not particularly
				1357	small. This means that they work great for temporary scratch buffers on the
				1358	stack, but should not generally be put into the heap: it is very rare to
				1359	see a SmallString as the member of a frequently-allocated heap data structure
				1360	or returned by-value.
Chris Lattner	7314a20	2011-07-22 20:46:49 +0000	[diff] [blame]	1361	</p>
				1362
				1363	</div>
Chris Lattner	3b4f417	2011-07-22 21:34:12 +0000	[diff] [blame]	1364
				1365	<!-- _______________________________________________________________________ -->
				1366	<h4>
				1367	<a name="dss_stdstring">std::string</a>
				1368	</h4>
				1369
				1370	<div>
				1371
				1372	<p>The standard C++ std::string class is a very general class that (like
				1373	SmallString) owns its underlying data. sizeof(std::string) is very reasonable
				1374	so it can be embedded into heap data structures and returned by-value.
				1375	On the other hand, std::string is highly inefficient for inline editing (e.g.
				1376	concatenating a bunch of stuff together) and because it is provided by the
				1377	standard library, its performance characteristics depend a lot of the host
				1378	standard library (e.g. libc++ and MSVC provide a highly optimized string
				1379	class, GCC contains a really slow implementation).
				1380	</p>
				1381
				1382	<p>The major disadvantage of std::string is that almost every operation that
				1383	makes them larger can allocate memory, which is slow. As such, it is better
				1384	to use SmallVector or Twine as a scratch buffer, but then use std::string to
				1385	persist the result.</p>
				1386
				1387
				1388	</div>
				1389
				1390	<!-- end of strings -->
				1391	</div>
				1392
Chris Lattner	7314a20	2011-07-22 20:46:49 +0000	[diff] [blame]	1393
				1394	<!-- ======================================================================= -->
				1395	<h3>
Chris Lattner	098129a	2007-02-03 03:04:03 +0000	[diff] [blame]	1396	<a name="ds_set">Set-Like Containers (std::set, SmallSet, SetVector, etc)</a>
NAKAMURA Takumi	05d0265	2011-04-18 23:59:50 +0000	[diff] [blame]	1397	</h3>
Chris Lattner	098129a	2007-02-03 03:04:03 +0000	[diff] [blame]	1398
NAKAMURA Takumi	f5af6ad	2011-04-23 00:30:22 +0000	[diff] [blame]	1399	<div>
Chris Lattner	098129a	2007-02-03 03:04:03 +0000	[diff] [blame]	1400
Chris Lattner	74c4ca1	2007-02-03 07:59:07 +0000	[diff] [blame]	1401	<p>Set-like containers are useful when you need to canonicalize multiple values
				1402	into a single representation. There are several different choices for how to do
				1403	this, providing various trade-offs.</p>
				1404
Chris Lattner	74c4ca1	2007-02-03 07:59:07 +0000	[diff] [blame]	1405	<!-- _______________________________________________________________________ -->
NAKAMURA Takumi	05d0265	2011-04-18 23:59:50 +0000	[diff] [blame]	1406	<h4>
Chris Lattner	74c4ca1	2007-02-03 07:59:07 +0000	[diff] [blame]	1407	<a name="dss_sortedvectorset">A sorted 'vector'</a>
NAKAMURA Takumi	05d0265	2011-04-18 23:59:50 +0000	[diff] [blame]	1408	</h4>
Chris Lattner	74c4ca1	2007-02-03 07:59:07 +0000	[diff] [blame]	1409
NAKAMURA Takumi	f5af6ad	2011-04-23 00:30:22 +0000	[diff] [blame]	1410	<div>
Chris Lattner	74c4ca1	2007-02-03 07:59:07 +0000	[diff] [blame]	1411
Chris Lattner	3b23a8c	2007-02-03 08:10:45 +0000	[diff] [blame]	1412	<p>If you intend to insert a lot of elements, then do a lot of queries, a
				1413	great approach is to use a vector (or other sequential container) with
Chris Lattner	74c4ca1	2007-02-03 07:59:07 +0000	[diff] [blame]	1414	std::sort+std::unique to remove duplicates. This approach works really well if
Chris Lattner	3b23a8c	2007-02-03 08:10:45 +0000	[diff] [blame]	1415	your usage pattern has these two distinct phases (insert then query), and can be
				1416	coupled with a good choice of <a href="#ds_sequential">sequential container</a>.
				1417	</p>
				1418
				1419	<p>
				1420	This combination provides the several nice properties: the result data is
				1421	contiguous in memory (good for cache locality), has few allocations, is easy to
				1422	address (iterators in the final vector are just indices or pointers), and can be
				1423	efficiently queried with a standard binary or radix search.</p>
Chris Lattner	74c4ca1	2007-02-03 07:59:07 +0000	[diff] [blame]	1424
				1425	</div>
				1426
				1427	<!-- _______________________________________________________________________ -->
NAKAMURA Takumi	05d0265	2011-04-18 23:59:50 +0000	[diff] [blame]	1428	<h4>
Chris Lattner	74c4ca1	2007-02-03 07:59:07 +0000	[diff] [blame]	1429	<a name="dss_smallset">"llvm/ADT/SmallSet.h"</a>
NAKAMURA Takumi	05d0265	2011-04-18 23:59:50 +0000	[diff] [blame]	1430	</h4>
Chris Lattner	74c4ca1	2007-02-03 07:59:07 +0000	[diff] [blame]	1431
NAKAMURA Takumi	f5af6ad	2011-04-23 00:30:22 +0000	[diff] [blame]	1432	<div>
Chris Lattner	74c4ca1	2007-02-03 07:59:07 +0000	[diff] [blame]	1433
Reid Spencer	128a7a7	2007-02-03 21:06:43 +0000	[diff] [blame]	1434	<p>If you have a set-like data structure that is usually small and whose elements
Chris Lattner	4ddfac1	2007-02-03 07:59:51 +0000	[diff] [blame]	1435	are reasonably small, a <tt>SmallSet<Type, N></tt> is a good choice. This set
Chris Lattner	74c4ca1	2007-02-03 07:59:07 +0000	[diff] [blame]	1436	has space for N elements in place (thus, if the set is dynamically smaller than
Chris Lattner	14868db	2007-02-03 08:20:15 +0000	[diff] [blame]	1437	N, no malloc traffic is required) and accesses them with a simple linear search.
				1438	When the set grows beyond 'N' elements, it allocates a more expensive representation that
Chris Lattner	74c4ca1	2007-02-03 07:59:07 +0000	[diff] [blame]	1439	guarantees efficient access (for most types, it falls back to std::set, but for
Chris Lattner	14868db	2007-02-03 08:20:15 +0000	[diff] [blame]	1440	pointers it uses something far better, <a
Chris Lattner	74c4ca1	2007-02-03 07:59:07 +0000	[diff] [blame]	1441	href="#dss_smallptrset">SmallPtrSet</a>).</p>
				1442
				1443	<p>The magic of this class is that it handles small sets extremely efficiently,
				1444	but gracefully handles extremely large sets without loss of efficiency. The
				1445	drawback is that the interface is quite small: it supports insertion, queries
				1446	and erasing, but does not support iteration.</p>
				1447
				1448	</div>
				1449
				1450	<!-- _______________________________________________________________________ -->
NAKAMURA Takumi	05d0265	2011-04-18 23:59:50 +0000	[diff] [blame]	1451	<h4>
Chris Lattner	74c4ca1	2007-02-03 07:59:07 +0000	[diff] [blame]	1452	<a name="dss_smallptrset">"llvm/ADT/SmallPtrSet.h"</a>
NAKAMURA Takumi	05d0265	2011-04-18 23:59:50 +0000	[diff] [blame]	1453	</h4>
Chris Lattner	74c4ca1	2007-02-03 07:59:07 +0000	[diff] [blame]	1454
NAKAMURA Takumi	f5af6ad	2011-04-23 00:30:22 +0000	[diff] [blame]	1455	<div>
Chris Lattner	74c4ca1	2007-02-03 07:59:07 +0000	[diff] [blame]	1456
Gabor Greif	4de7368	2010-03-26 19:30:47 +0000	[diff] [blame]	1457	<p>SmallPtrSet has all the advantages of <tt>SmallSet</tt> (and a <tt>SmallSet</tt> of pointers is
				1458	transparently implemented with a <tt>SmallPtrSet</tt>), but also supports iterators. If
Chris Lattner	14868db	2007-02-03 08:20:15 +0000	[diff] [blame]	1459	more than 'N' insertions are performed, a single quadratically
Chris Lattner	74c4ca1	2007-02-03 07:59:07 +0000	[diff] [blame]	1460	probed hash table is allocated and grows as needed, providing extremely
				1461	efficient access (constant time insertion/deleting/queries with low constant
				1462	factors) and is very stingy with malloc traffic.</p>
				1463
Gabor Greif	4de7368	2010-03-26 19:30:47 +0000	[diff] [blame]	1464	<p>Note that, unlike <tt>std::set</tt>, the iterators of <tt>SmallPtrSet</tt> are invalidated
Chris Lattner	74c4ca1	2007-02-03 07:59:07 +0000	[diff] [blame]	1465	whenever an insertion occurs. Also, the values visited by the iterators are not
				1466	visited in sorted order.</p>
				1467
				1468	</div>
				1469
				1470	<!-- _______________________________________________________________________ -->
NAKAMURA Takumi	05d0265	2011-04-18 23:59:50 +0000	[diff] [blame]	1471	<h4>
Chris Lattner	c28476f	2007-09-30 00:58:59 +0000	[diff] [blame]	1472	<a name="dss_denseset">"llvm/ADT/DenseSet.h"</a>
NAKAMURA Takumi	05d0265	2011-04-18 23:59:50 +0000	[diff] [blame]	1473	</h4>
Chris Lattner	c28476f	2007-09-30 00:58:59 +0000	[diff] [blame]	1474
NAKAMURA Takumi	f5af6ad	2011-04-23 00:30:22 +0000	[diff] [blame]	1475	<div>
Chris Lattner	c28476f	2007-09-30 00:58:59 +0000	[diff] [blame]	1476
				1477	<p>
				1478	DenseSet is a simple quadratically probed hash table. It excels at supporting
				1479	small values: it uses a single allocation to hold all of the pairs that
				1480	are currently inserted in the set. DenseSet is a great way to unique small
				1481	values that are not simple pointers (use <a
				1482	href="#dss_smallptrset">SmallPtrSet</a> for pointers). Note that DenseSet has
				1483	the same requirements for the value type that <a
				1484	href="#dss_densemap">DenseMap</a> has.
				1485	</p>
				1486
				1487	</div>
				1488
				1489	<!-- _______________________________________________________________________ -->
NAKAMURA Takumi	05d0265	2011-04-18 23:59:50 +0000	[diff] [blame]	1490	<h4>
Chris Lattner	74c4ca1	2007-02-03 07:59:07 +0000	[diff] [blame]	1491	<a name="dss_FoldingSet">"llvm/ADT/FoldingSet.h"</a>
NAKAMURA Takumi	05d0265	2011-04-18 23:59:50 +0000	[diff] [blame]	1492	</h4>
Chris Lattner	74c4ca1	2007-02-03 07:59:07 +0000	[diff] [blame]	1493
NAKAMURA Takumi	f5af6ad	2011-04-23 00:30:22 +0000	[diff] [blame]	1494	<div>
Chris Lattner	74c4ca1	2007-02-03 07:59:07 +0000	[diff] [blame]	1495
Chris Lattner	098129a	2007-02-03 03:04:03 +0000	[diff] [blame]	1496	<p>
Chris Lattner	74c4ca1	2007-02-03 07:59:07 +0000	[diff] [blame]	1497	FoldingSet is an aggregate class that is really good at uniquing
				1498	expensive-to-create or polymorphic objects. It is a combination of a chained
				1499	hash table with intrusive links (uniqued objects are required to inherit from
Chris Lattner	14868db	2007-02-03 08:20:15 +0000	[diff] [blame]	1500	FoldingSetNode) that uses <a href="#dss_smallvector">SmallVector</a> as part of
				1501	its ID process.</p>
Chris Lattner	74c4ca1	2007-02-03 07:59:07 +0000	[diff] [blame]	1502
Chris Lattner	14868db	2007-02-03 08:20:15 +0000	[diff] [blame]	1503	<p>Consider a case where you want to implement a "getOrCreateFoo" method for
Chris Lattner	74c4ca1	2007-02-03 07:59:07 +0000	[diff] [blame]	1504	a complex object (for example, a node in the code generator). The client has a
				1505	description of what it wants to generate (it knows the opcode and all the
				1506	operands), but we don't want to 'new' a node, then try inserting it into a set
Chris Lattner	14868db	2007-02-03 08:20:15 +0000	[diff] [blame]	1507	only to find out it already exists, at which point we would have to delete it
				1508	and return the node that already exists.
Chris Lattner	098129a	2007-02-03 03:04:03 +0000	[diff] [blame]	1509	</p>
				1510
Chris Lattner	74c4ca1	2007-02-03 07:59:07 +0000	[diff] [blame]	1511	<p>To support this style of client, FoldingSet perform a query with a
				1512	FoldingSetNodeID (which wraps SmallVector) that can be used to describe the
				1513	element that we want to query for. The query either returns the element
				1514	matching the ID or it returns an opaque ID that indicates where insertion should
Chris Lattner	14868db	2007-02-03 08:20:15 +0000	[diff] [blame]	1515	take place. Construction of the ID usually does not require heap traffic.</p>
Chris Lattner	74c4ca1	2007-02-03 07:59:07 +0000	[diff] [blame]	1516
				1517	<p>Because FoldingSet uses intrusive links, it can support polymorphic objects
				1518	in the set (for example, you can have SDNode instances mixed with LoadSDNodes).
				1519	Because the elements are individually allocated, pointers to the elements are
				1520	stable: inserting or removing elements does not invalidate any pointers to other
				1521	elements.
				1522	</p>
				1523
				1524	</div>
				1525
				1526	<!-- _______________________________________________________________________ -->
NAKAMURA Takumi	05d0265	2011-04-18 23:59:50 +0000	[diff] [blame]	1527	<h4>
Chris Lattner	74c4ca1	2007-02-03 07:59:07 +0000	[diff] [blame]	1528	<a name="dss_set"><set></a>
NAKAMURA Takumi	05d0265	2011-04-18 23:59:50 +0000	[diff] [blame]	1529	</h4>
Chris Lattner	74c4ca1	2007-02-03 07:59:07 +0000	[diff] [blame]	1530
NAKAMURA Takumi	f5af6ad	2011-04-23 00:30:22 +0000	[diff] [blame]	1531	<div>
Chris Lattner	74c4ca1	2007-02-03 07:59:07 +0000	[diff] [blame]	1532
Chris Lattner	c572243	2007-02-03 19:49:31 +0000	[diff] [blame]	1533	<p><tt>std::set</tt> is a reasonable all-around set class, which is decent at
				1534	many things but great at nothing. std::set allocates memory for each element
Chris Lattner	74c4ca1	2007-02-03 07:59:07 +0000	[diff] [blame]	1535	inserted (thus it is very malloc intensive) and typically stores three pointers
Chris Lattner	14868db	2007-02-03 08:20:15 +0000	[diff] [blame]	1536	per element in the set (thus adding a large amount of per-element space
				1537	overhead). It offers guaranteed log(n) performance, which is not particularly
Chris Lattner	c572243	2007-02-03 19:49:31 +0000	[diff] [blame]	1538	fast from a complexity standpoint (particularly if the elements of the set are
				1539	expensive to compare, like strings), and has extremely high constant factors for
				1540	lookup, insertion and removal.</p>
Chris Lattner	74c4ca1	2007-02-03 07:59:07 +0000	[diff] [blame]	1541
Chris Lattner	14868db	2007-02-03 08:20:15 +0000	[diff] [blame]	1542	<p>The advantages of std::set are that its iterators are stable (deleting or
Chris Lattner	74c4ca1	2007-02-03 07:59:07 +0000	[diff] [blame]	1543	inserting an element from the set does not affect iterators or pointers to other
				1544	elements) and that iteration over the set is guaranteed to be in sorted order.
				1545	If the elements in the set are large, then the relative overhead of the pointers
				1546	and malloc traffic is not a big deal, but if the elements of the set are small,
				1547	std::set is almost never a good choice.</p>
				1548
				1549	</div>
				1550
				1551	<!-- _______________________________________________________________________ -->
NAKAMURA Takumi	05d0265	2011-04-18 23:59:50 +0000	[diff] [blame]	1552	<h4>
Chris Lattner	74c4ca1	2007-02-03 07:59:07 +0000	[diff] [blame]	1553	<a name="dss_setvector">"llvm/ADT/SetVector.h"</a>
NAKAMURA Takumi	05d0265	2011-04-18 23:59:50 +0000	[diff] [blame]	1554	</h4>
Chris Lattner	74c4ca1	2007-02-03 07:59:07 +0000	[diff] [blame]	1555
NAKAMURA Takumi	f5af6ad	2011-04-23 00:30:22 +0000	[diff] [blame]	1556	<div>
Chris Lattner	edca3c5	2007-02-04 00:00:26 +0000	[diff] [blame]	1557	<p>LLVM's SetVector<Type> is an adapter class that combines your choice of
				1558	a set-like container along with a <a href="#ds_sequential">Sequential
				1559	Container</a>. The important property
Chris Lattner	74c4ca1	2007-02-03 07:59:07 +0000	[diff] [blame]	1560	that this provides is efficient insertion with uniquing (duplicate elements are
				1561	ignored) with iteration support. It implements this by inserting elements into
				1562	both a set-like container and the sequential container, using the set-like
				1563	container for uniquing and the sequential container for iteration.
				1564	</p>
				1565
				1566	<p>The difference between SetVector and other sets is that the order of
				1567	iteration is guaranteed to match the order of insertion into the SetVector.
				1568	This property is really important for things like sets of pointers. Because
				1569	pointer values are non-deterministic (e.g. vary across runs of the program on
Chris Lattner	edca3c5	2007-02-04 00:00:26 +0000	[diff] [blame]	1570	different machines), iterating over the pointers in the set will
Chris Lattner	74c4ca1	2007-02-03 07:59:07 +0000	[diff] [blame]	1571	not be in a well-defined order.</p>
				1572
				1573	<p>
				1574	The drawback of SetVector is that it requires twice as much space as a normal
				1575	set and has the sum of constant factors from the set-like container and the
				1576	sequential container that it uses. Use it only if you need to iterate over
				1577	the elements in a deterministic order. SetVector is also expensive to delete
Chris Lattner	edca3c5	2007-02-04 00:00:26 +0000	[diff] [blame]	1578	elements out of (linear time), unless you use it's "pop_back" method, which is
				1579	faster.
Chris Lattner	74c4ca1	2007-02-03 07:59:07 +0000	[diff] [blame]	1580	</p>
				1581
Bill Wendling	3478173	2011-10-11 06:33:56 +0000	[diff] [blame]	1582	<p><tt>SetVector</tt> is an adapter class that defaults to
				1583	using <tt>std::vector</tt> and a size 16 <tt>SmallSet</tt> for the underlying
				1584	containers, so it is quite expensive. However,
				1585	<tt>"llvm/ADT/SetVector.h"</tt> also provides a <tt>SmallSetVector</tt>
				1586	class, which defaults to using a <tt>SmallVector</tt> and <tt>SmallSet</tt>
				1587	of a specified size. If you use this, and if your sets are dynamically
				1588	smaller than <tt>N</tt>, you will save a lot of heap traffic.</p>
Chris Lattner	edca3c5	2007-02-04 00:00:26 +0000	[diff] [blame]	1589
Chris Lattner	74c4ca1	2007-02-03 07:59:07 +0000	[diff] [blame]	1590	</div>
				1591
				1592	<!-- _______________________________________________________________________ -->
NAKAMURA Takumi	05d0265	2011-04-18 23:59:50 +0000	[diff] [blame]	1593	<h4>
Chris Lattner	c572243	2007-02-03 19:49:31 +0000	[diff] [blame]	1594	<a name="dss_uniquevector">"llvm/ADT/UniqueVector.h"</a>
NAKAMURA Takumi	05d0265	2011-04-18 23:59:50 +0000	[diff] [blame]	1595	</h4>
Chris Lattner	c572243	2007-02-03 19:49:31 +0000	[diff] [blame]	1596
NAKAMURA Takumi	f5af6ad	2011-04-23 00:30:22 +0000	[diff] [blame]	1597	<div>
Chris Lattner	c572243	2007-02-03 19:49:31 +0000	[diff] [blame]	1598
				1599	<p>
				1600	UniqueVector is similar to <a href="#dss_setvector">SetVector</a>, but it
				1601	retains a unique ID for each element inserted into the set. It internally
				1602	contains a map and a vector, and it assigns a unique ID for each value inserted
				1603	into the set.</p>
				1604
				1605	<p>UniqueVector is very expensive: its cost is the sum of the cost of
				1606	maintaining both the map and vector, it has high complexity, high constant
				1607	factors, and produces a lot of malloc traffic. It should be avoided.</p>
				1608
				1609	</div>
				1610
				1611
				1612	<!-- _______________________________________________________________________ -->
NAKAMURA Takumi	05d0265	2011-04-18 23:59:50 +0000	[diff] [blame]	1613	<h4>
Chris Lattner	c572243	2007-02-03 19:49:31 +0000	[diff] [blame]	1614	<a name="dss_otherset">Other Set-Like Container Options</a>
NAKAMURA Takumi	05d0265	2011-04-18 23:59:50 +0000	[diff] [blame]	1615	</h4>
Chris Lattner	74c4ca1	2007-02-03 07:59:07 +0000	[diff] [blame]	1616
NAKAMURA Takumi	f5af6ad	2011-04-23 00:30:22 +0000	[diff] [blame]	1617	<div>
Chris Lattner	74c4ca1	2007-02-03 07:59:07 +0000	[diff] [blame]	1618
				1619	<p>
				1620	The STL provides several other options, such as std::multiset and the various
Chris Lattner	f1a3082	2009-03-09 05:20:45 +0000	[diff] [blame]	1621	"hash_set" like containers (whether from C++ TR1 or from the SGI library). We
				1622	never use hash_set and unordered_set because they are generally very expensive
				1623	(each insertion requires a malloc) and very non-portable.
				1624	</p>
Chris Lattner	74c4ca1	2007-02-03 07:59:07 +0000	[diff] [blame]	1625
				1626	<p>std::multiset is useful if you're not interested in elimination of
Chris Lattner	14868db	2007-02-03 08:20:15 +0000	[diff] [blame]	1627	duplicates, but has all the drawbacks of std::set. A sorted vector (where you
				1628	don't delete duplicate entries) or some other approach is almost always
				1629	better.</p>
Chris Lattner	74c4ca1	2007-02-03 07:59:07 +0000	[diff] [blame]	1630
Chris Lattner	098129a	2007-02-03 03:04:03 +0000	[diff] [blame]	1631	</div>
				1632
NAKAMURA Takumi	f5af6ad	2011-04-23 00:30:22 +0000	[diff] [blame]	1633	</div>
				1634
Chris Lattner	098129a	2007-02-03 03:04:03 +0000	[diff] [blame]	1635	<!-- ======================================================================= -->
NAKAMURA Takumi	05d0265	2011-04-18 23:59:50 +0000	[diff] [blame]	1636	<h3>
Chris Lattner	098129a	2007-02-03 03:04:03 +0000	[diff] [blame]	1637	<a name="ds_map">Map-Like Containers (std::map, DenseMap, etc)</a>
NAKAMURA Takumi	05d0265	2011-04-18 23:59:50 +0000	[diff] [blame]	1638	</h3>
Chris Lattner	098129a	2007-02-03 03:04:03 +0000	[diff] [blame]	1639
NAKAMURA Takumi	f5af6ad	2011-04-23 00:30:22 +0000	[diff] [blame]	1640	<div>
Chris Lattner	c572243	2007-02-03 19:49:31 +0000	[diff] [blame]	1641	Map-like containers are useful when you want to associate data to a key. As
				1642	usual, there are a lot of different ways to do this. :)
Chris Lattner	c572243	2007-02-03 19:49:31 +0000	[diff] [blame]	1643
				1644	<!-- _______________________________________________________________________ -->
NAKAMURA Takumi	05d0265	2011-04-18 23:59:50 +0000	[diff] [blame]	1645	<h4>
Chris Lattner	c572243	2007-02-03 19:49:31 +0000	[diff] [blame]	1646	<a name="dss_sortedvectormap">A sorted 'vector'</a>
NAKAMURA Takumi	05d0265	2011-04-18 23:59:50 +0000	[diff] [blame]	1647	</h4>
Chris Lattner	c572243	2007-02-03 19:49:31 +0000	[diff] [blame]	1648
NAKAMURA Takumi	f5af6ad	2011-04-23 00:30:22 +0000	[diff] [blame]	1649	<div>
Chris Lattner	c572243	2007-02-03 19:49:31 +0000	[diff] [blame]	1650
				1651	<p>
				1652	If your usage pattern follows a strict insert-then-query approach, you can
				1653	trivially use the same approach as <a href="#dss_sortedvectorset">sorted vectors
				1654	for set-like containers</a>. The only difference is that your query function
				1655	(which uses std::lower_bound to get efficient log(n) lookup) should only compare
				1656	the key, not both the key and value. This yields the same advantages as sorted
				1657	vectors for sets.
				1658	</p>
				1659	</div>
				1660
				1661	<!-- _______________________________________________________________________ -->
NAKAMURA Takumi	05d0265	2011-04-18 23:59:50 +0000	[diff] [blame]	1662	<h4>
Chris Lattner	796f9fa	2007-02-08 19:14:21 +0000	[diff] [blame]	1663	<a name="dss_stringmap">"llvm/ADT/StringMap.h"</a>
NAKAMURA Takumi	05d0265	2011-04-18 23:59:50 +0000	[diff] [blame]	1664	</h4>
Chris Lattner	c572243	2007-02-03 19:49:31 +0000	[diff] [blame]	1665
NAKAMURA Takumi	f5af6ad	2011-04-23 00:30:22 +0000	[diff] [blame]	1666	<div>
Chris Lattner	c572243	2007-02-03 19:49:31 +0000	[diff] [blame]	1667
				1668	<p>
				1669	Strings are commonly used as keys in maps, and they are difficult to support
				1670	efficiently: they are variable length, inefficient to hash and compare when
Chris Lattner	796f9fa	2007-02-08 19:14:21 +0000	[diff] [blame]	1671	long, expensive to copy, etc. StringMap is a specialized container designed to
				1672	cope with these issues. It supports mapping an arbitrary range of bytes to an
				1673	arbitrary other object.</p>
Chris Lattner	c572243	2007-02-03 19:49:31 +0000	[diff] [blame]	1674
Chris Lattner	796f9fa	2007-02-08 19:14:21 +0000	[diff] [blame]	1675	<p>The StringMap implementation uses a quadratically-probed hash table, where
Chris Lattner	c572243	2007-02-03 19:49:31 +0000	[diff] [blame]	1676	the buckets store a pointer to the heap allocated entries (and some other
				1677	stuff). The entries in the map must be heap allocated because the strings are
				1678	variable length. The string data (key) and the element object (value) are
				1679	stored in the same allocation with the string data immediately after the element
				1680	object. This container guarantees the "<tt>(char*)(&Value+1)</tt>" points
				1681	to the key string for a value.</p>
				1682
Chris Lattner	796f9fa	2007-02-08 19:14:21 +0000	[diff] [blame]	1683	<p>The StringMap is very fast for several reasons: quadratic probing is very
Chris Lattner	c572243	2007-02-03 19:49:31 +0000	[diff] [blame]	1684	cache efficient for lookups, the hash value of strings in buckets is not
Nick Lewycky	2a80aca	2010-08-01 23:18:45 +0000	[diff] [blame]	1685	recomputed when looking up an element, StringMap rarely has to touch the
Chris Lattner	c572243	2007-02-03 19:49:31 +0000	[diff] [blame]	1686	memory for unrelated objects when looking up a value (even when hash collisions
				1687	happen), hash table growth does not recompute the hash values for strings
				1688	already in the table, and each pair in the map is store in a single allocation
				1689	(the string data is stored in the same allocation as the Value of a pair).</p>
				1690
Chris Lattner	796f9fa	2007-02-08 19:14:21 +0000	[diff] [blame]	1691	<p>StringMap also provides query methods that take byte ranges, so it only ever
Chris Lattner	c572243	2007-02-03 19:49:31 +0000	[diff] [blame]	1692	copies a string if a value is inserted into the table.</p>
				1693	</div>
				1694
				1695	<!-- _______________________________________________________________________ -->
NAKAMURA Takumi	05d0265	2011-04-18 23:59:50 +0000	[diff] [blame]	1696	<h4>
Chris Lattner	c572243	2007-02-03 19:49:31 +0000	[diff] [blame]	1697	<a name="dss_indexedmap">"llvm/ADT/IndexedMap.h"</a>
NAKAMURA Takumi	05d0265	2011-04-18 23:59:50 +0000	[diff] [blame]	1698	</h4>
Chris Lattner	c572243	2007-02-03 19:49:31 +0000	[diff] [blame]	1699
NAKAMURA Takumi	f5af6ad	2011-04-23 00:30:22 +0000	[diff] [blame]	1700	<div>
Chris Lattner	c572243	2007-02-03 19:49:31 +0000	[diff] [blame]	1701	<p>
				1702	IndexedMap is a specialized container for mapping small dense integers (or
				1703	values that can be mapped to small dense integers) to some other type. It is
				1704	internally implemented as a vector with a mapping function that maps the keys to
				1705	the dense integer range.
				1706	</p>
				1707
				1708	<p>
				1709	This is useful for cases like virtual registers in the LLVM code generator: they
				1710	have a dense mapping that is offset by a compile-time constant (the first
				1711	virtual register ID).</p>
				1712
				1713	</div>
				1714
				1715	<!-- _______________________________________________________________________ -->
NAKAMURA Takumi	05d0265	2011-04-18 23:59:50 +0000	[diff] [blame]	1716	<h4>
Chris Lattner	c572243	2007-02-03 19:49:31 +0000	[diff] [blame]	1717	<a name="dss_densemap">"llvm/ADT/DenseMap.h"</a>
NAKAMURA Takumi	05d0265	2011-04-18 23:59:50 +0000	[diff] [blame]	1718	</h4>
Chris Lattner	c572243	2007-02-03 19:49:31 +0000	[diff] [blame]	1719
NAKAMURA Takumi	f5af6ad	2011-04-23 00:30:22 +0000	[diff] [blame]	1720	<div>
Chris Lattner	c572243	2007-02-03 19:49:31 +0000	[diff] [blame]	1721
				1722	<p>
				1723	DenseMap is a simple quadratically probed hash table. It excels at supporting
				1724	small keys and values: it uses a single allocation to hold all of the pairs that
				1725	are currently inserted in the map. DenseMap is a great way to map pointers to
				1726	pointers, or map other small types to each other.
				1727	</p>
				1728
				1729	<p>
				1730	There are several aspects of DenseMap that you should be aware of, however. The
				1731	iterators in a densemap are invalidated whenever an insertion occurs, unlike
				1732	map. Also, because DenseMap allocates space for a large number of key/value
Chris Lattner	a4a264d	2007-02-03 20:17:53 +0000	[diff] [blame]	1733	pairs (it starts with 64 by default), it will waste a lot of space if your keys
				1734	or values are large. Finally, you must implement a partial specialization of
Chris Lattner	76c1b97	2007-09-17 18:34:04 +0000	[diff] [blame]	1735	DenseMapInfo for the key that you want, if it isn't already supported. This
Chris Lattner	c572243	2007-02-03 19:49:31 +0000	[diff] [blame]	1736	is required to tell DenseMap about two special marker values (which can never be
Chris Lattner	a4a264d	2007-02-03 20:17:53 +0000	[diff] [blame]	1737	inserted into the map) that it needs internally.</p>
Chris Lattner	c572243	2007-02-03 19:49:31 +0000	[diff] [blame]	1738
				1739	</div>
				1740
				1741	<!-- _______________________________________________________________________ -->
NAKAMURA Takumi	05d0265	2011-04-18 23:59:50 +0000	[diff] [blame]	1742	<h4>
Jeffrey Yasskin	71a5c22	2009-10-22 22:11:22 +0000	[diff] [blame]	1743	<a name="dss_valuemap">"llvm/ADT/ValueMap.h"</a>
NAKAMURA Takumi	05d0265	2011-04-18 23:59:50 +0000	[diff] [blame]	1744	</h4>
Jeffrey Yasskin	71a5c22	2009-10-22 22:11:22 +0000	[diff] [blame]	1745
NAKAMURA Takumi	f5af6ad	2011-04-23 00:30:22 +0000	[diff] [blame]	1746	<div>
Jeffrey Yasskin	71a5c22	2009-10-22 22:11:22 +0000	[diff] [blame]	1747
				1748	<p>
				1749	ValueMap is a wrapper around a <a href="#dss_densemap">DenseMap</a> mapping
				1750	Value*s (or subclasses) to another type. When a Value is deleted or RAUW'ed,
				1751	ValueMap will update itself so the new version of the key is mapped to the same
				1752	value, just as if the key were a WeakVH. You can configure exactly how this
				1753	happens, and what else happens on these two events, by passing
				1754	a <code>Config</code> parameter to the ValueMap template.</p>
				1755
				1756	</div>
				1757
				1758	<!-- _______________________________________________________________________ -->
NAKAMURA Takumi	05d0265	2011-04-18 23:59:50 +0000	[diff] [blame]	1759	<h4>
Jakob Stoklund Olesen	aca0da6	2010-12-14 00:55:51 +0000	[diff] [blame]	1760	<a name="dss_intervalmap">"llvm/ADT/IntervalMap.h"</a>
NAKAMURA Takumi	05d0265	2011-04-18 23:59:50 +0000	[diff] [blame]	1761	</h4>
Jakob Stoklund Olesen	aca0da6	2010-12-14 00:55:51 +0000	[diff] [blame]	1762
NAKAMURA Takumi	f5af6ad	2011-04-23 00:30:22 +0000	[diff] [blame]	1763	<div>
Jakob Stoklund Olesen	aca0da6	2010-12-14 00:55:51 +0000	[diff] [blame]	1764
				1765	<p> IntervalMap is a compact map for small keys and values. It maps key
				1766	intervals instead of single keys, and it will automatically coalesce adjacent
				1767	intervals. When then map only contains a few intervals, they are stored in the
				1768	map object itself to avoid allocations.</p>
				1769
				1770	<p> The IntervalMap iterators are quite big, so they should not be passed around
				1771	as STL iterators. The heavyweight iterators allow a smaller data structure.</p>
				1772
				1773	</div>
				1774
				1775	<!-- _______________________________________________________________________ -->
NAKAMURA Takumi	05d0265	2011-04-18 23:59:50 +0000	[diff] [blame]	1776	<h4>
Chris Lattner	c572243	2007-02-03 19:49:31 +0000	[diff] [blame]	1777	<a name="dss_map"><map></a>
NAKAMURA Takumi	05d0265	2011-04-18 23:59:50 +0000	[diff] [blame]	1778	</h4>
Chris Lattner	c572243	2007-02-03 19:49:31 +0000	[diff] [blame]	1779
NAKAMURA Takumi	f5af6ad	2011-04-23 00:30:22 +0000	[diff] [blame]	1780	<div>
Chris Lattner	c572243	2007-02-03 19:49:31 +0000	[diff] [blame]	1781
				1782	<p>
				1783	std::map has similar characteristics to <a href="#dss_set">std::set</a>: it uses
				1784	a single allocation per pair inserted into the map, it offers log(n) lookup with
				1785	an extremely large constant factor, imposes a space penalty of 3 pointers per
				1786	pair in the map, etc.</p>
				1787
				1788	<p>std::map is most useful when your keys or values are very large, if you need
				1789	to iterate over the collection in sorted order, or if you need stable iterators
				1790	into the map (i.e. they don't get invalidated if an insertion or deletion of
				1791	another element takes place).</p>
				1792
				1793	</div>
				1794
				1795	<!-- _______________________________________________________________________ -->
NAKAMURA Takumi	05d0265	2011-04-18 23:59:50 +0000	[diff] [blame]	1796	<h4>
Jakob Stoklund Olesen	4359e5e	2011-04-05 20:56:08 +0000	[diff] [blame]	1797	<a name="dss_inteqclasses">"llvm/ADT/IntEqClasses.h"</a>
NAKAMURA Takumi	05d0265	2011-04-18 23:59:50 +0000	[diff] [blame]	1798	</h4>
Jakob Stoklund Olesen	4359e5e	2011-04-05 20:56:08 +0000	[diff] [blame]	1799
NAKAMURA Takumi	f5af6ad	2011-04-23 00:30:22 +0000	[diff] [blame]	1800	<div>
Jakob Stoklund Olesen	4359e5e	2011-04-05 20:56:08 +0000	[diff] [blame]	1801
				1802	<p>IntEqClasses provides a compact representation of equivalence classes of
				1803	small integers. Initially, each integer in the range 0..n-1 has its own
				1804	equivalence class. Classes can be joined by passing two class representatives to
				1805	the join(a, b) method. Two integers are in the same class when findLeader()
				1806	returns the same representative.</p>
				1807
				1808	<p>Once all equivalence classes are formed, the map can be compressed so each
				1809	integer 0..n-1 maps to an equivalence class number in the range 0..m-1, where m
				1810	is the total number of equivalence classes. The map must be uncompressed before
				1811	it can be edited again.</p>
				1812
				1813	</div>
				1814
				1815	<!-- _______________________________________________________________________ -->
NAKAMURA Takumi	05d0265	2011-04-18 23:59:50 +0000	[diff] [blame]	1816	<h4>
Chris Lattner	c572243	2007-02-03 19:49:31 +0000	[diff] [blame]	1817	<a name="dss_othermap">Other Map-Like Container Options</a>
NAKAMURA Takumi	05d0265	2011-04-18 23:59:50 +0000	[diff] [blame]	1818	</h4>
Chris Lattner	c572243	2007-02-03 19:49:31 +0000	[diff] [blame]	1819
NAKAMURA Takumi	f5af6ad	2011-04-23 00:30:22 +0000	[diff] [blame]	1820	<div>
Chris Lattner	c572243	2007-02-03 19:49:31 +0000	[diff] [blame]	1821
				1822	<p>
				1823	The STL provides several other options, such as std::multimap and the various
Chris Lattner	f1a3082	2009-03-09 05:20:45 +0000	[diff] [blame]	1824	"hash_map" like containers (whether from C++ TR1 or from the SGI library). We
				1825	never use hash_set and unordered_set because they are generally very expensive
				1826	(each insertion requires a malloc) and very non-portable.</p>
Chris Lattner	c572243	2007-02-03 19:49:31 +0000	[diff] [blame]	1827
				1828	<p>std::multimap is useful if you want to map a key to multiple values, but has
				1829	all the drawbacks of std::map. A sorted vector or some other approach is almost
				1830	always better.</p>
				1831
Chris Lattner	098129a	2007-02-03 03:04:03 +0000	[diff] [blame]	1832	</div>
				1833
NAKAMURA Takumi	f5af6ad	2011-04-23 00:30:22 +0000	[diff] [blame]	1834	</div>
				1835
Daniel Berlin	1939ace	2007-09-24 17:52:25 +0000	[diff] [blame]	1836	<!-- ======================================================================= -->
NAKAMURA Takumi	05d0265	2011-04-18 23:59:50 +0000	[diff] [blame]	1837	<h3>
Daniel Berlin	1939ace	2007-09-24 17:52:25 +0000	[diff] [blame]	1838	<a name="ds_bit">Bit storage containers (BitVector, SparseBitVector)</a>
NAKAMURA Takumi	05d0265	2011-04-18 23:59:50 +0000	[diff] [blame]	1839	</h3>
Daniel Berlin	1939ace	2007-09-24 17:52:25 +0000	[diff] [blame]	1840
NAKAMURA Takumi	f5af6ad	2011-04-23 00:30:22 +0000	[diff] [blame]	1841	<div>
Chris Lattner	7086ce7	2007-09-25 22:37:50 +0000	[diff] [blame]	1842	<p>Unlike the other containers, there are only two bit storage containers, and
				1843	choosing when to use each is relatively straightforward.</p>
				1844
				1845	<p>One additional option is
				1846	<tt>std::vector<bool></tt>: we discourage its use for two reasons 1) the
				1847	implementation in many common compilers (e.g. commonly available versions of
				1848	GCC) is extremely inefficient and 2) the C++ standards committee is likely to
				1849	deprecate this container and/or change it significantly somehow. In any case,
				1850	please don't use it.</p>
Daniel Berlin	1939ace	2007-09-24 17:52:25 +0000	[diff] [blame]	1851
				1852	<!-- _______________________________________________________________________ -->
NAKAMURA Takumi	05d0265	2011-04-18 23:59:50 +0000	[diff] [blame]	1853	<h4>
Daniel Berlin	1939ace	2007-09-24 17:52:25 +0000	[diff] [blame]	1854	<a name="dss_bitvector">BitVector</a>
NAKAMURA Takumi	05d0265	2011-04-18 23:59:50 +0000	[diff] [blame]	1855	</h4>
Daniel Berlin	1939ace	2007-09-24 17:52:25 +0000	[diff] [blame]	1856
NAKAMURA Takumi	f5af6ad	2011-04-23 00:30:22 +0000	[diff] [blame]	1857	<div>
Dan Gohman	5f7775c	2010-01-05 18:24:00 +0000	[diff] [blame]	1858	<p> The BitVector container provides a dynamic size set of bits for manipulation.
Daniel Berlin	1939ace	2007-09-24 17:52:25 +0000	[diff] [blame]	1859	It supports individual bit setting/testing, as well as set operations. The set
				1860	operations take time O(size of bitvector), but operations are performed one word
				1861	at a time, instead of one bit at a time. This makes the BitVector very fast for
				1862	set operations compared to other containers. Use the BitVector when you expect
				1863	the number of set bits to be high (IE a dense set).
				1864	</p>
				1865	</div>
				1866
				1867	<!-- _______________________________________________________________________ -->
NAKAMURA Takumi	05d0265	2011-04-18 23:59:50 +0000	[diff] [blame]	1868	<h4>
Dan Gohman	5f7775c	2010-01-05 18:24:00 +0000	[diff] [blame]	1869	<a name="dss_smallbitvector">SmallBitVector</a>
NAKAMURA Takumi	05d0265	2011-04-18 23:59:50 +0000	[diff] [blame]	1870	</h4>
Dan Gohman	5f7775c	2010-01-05 18:24:00 +0000	[diff] [blame]	1871
NAKAMURA Takumi	f5af6ad	2011-04-23 00:30:22 +0000	[diff] [blame]	1872	<div>
Dan Gohman	5f7775c	2010-01-05 18:24:00 +0000	[diff] [blame]	1873	<p> The SmallBitVector container provides the same interface as BitVector, but
				1874	it is optimized for the case where only a small number of bits, less than
				1875	25 or so, are needed. It also transparently supports larger bit counts, but
				1876	slightly less efficiently than a plain BitVector, so SmallBitVector should
				1877	only be used when larger counts are rare.
				1878	</p>
				1879
				1880	<p>
				1881	At this time, SmallBitVector does not support set operations (and, or, xor),
				1882	and its operator[] does not provide an assignable lvalue.
				1883	</p>
				1884	</div>
				1885
				1886	<!-- _______________________________________________________________________ -->
NAKAMURA Takumi	05d0265	2011-04-18 23:59:50 +0000	[diff] [blame]	1887	<h4>
Daniel Berlin	1939ace	2007-09-24 17:52:25 +0000	[diff] [blame]	1888	<a name="dss_sparsebitvector">SparseBitVector</a>
NAKAMURA Takumi	05d0265	2011-04-18 23:59:50 +0000	[diff] [blame]	1889	</h4>
Daniel Berlin	1939ace	2007-09-24 17:52:25 +0000	[diff] [blame]	1890
NAKAMURA Takumi	f5af6ad	2011-04-23 00:30:22 +0000	[diff] [blame]	1891	<div>
Daniel Berlin	1939ace	2007-09-24 17:52:25 +0000	[diff] [blame]	1892	<p> The SparseBitVector container is much like BitVector, with one major
				1893	difference: Only the bits that are set, are stored. This makes the
				1894	SparseBitVector much more space efficient than BitVector when the set is sparse,
				1895	as well as making set operations O(number of set bits) instead of O(size of
				1896	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
				1897	(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).
				1898	</p>
				1899	</div>
Chris Lattner	f623a08	2005-10-17 01:36:23 +0000	[diff] [blame]	1900
NAKAMURA Takumi	f5af6ad	2011-04-23 00:30:22 +0000	[diff] [blame]	1901	</div>
				1902
				1903	</div>
				1904
Misha Brukman	13fd15c	2004-01-15 00:14:41 +0000	[diff] [blame]	1905	<!-- *********************************************************************** -->
NAKAMURA Takumi	05d0265	2011-04-18 23:59:50 +0000	[diff] [blame]	1906	<h2>
Misha Brukman	13fd15c	2004-01-15 00:14:41 +0000	[diff] [blame]	1907	<a name="common">Helpful Hints for Common Operations</a>
NAKAMURA Takumi	05d0265	2011-04-18 23:59:50 +0000	[diff] [blame]	1908	</h2>
Misha Brukman	13fd15c	2004-01-15 00:14:41 +0000	[diff] [blame]	1909	<!-- *********************************************************************** -->
				1910
NAKAMURA Takumi	f5af6ad	2011-04-23 00:30:22 +0000	[diff] [blame]	1911	<div>
Misha Brukman	13fd15c	2004-01-15 00:14:41 +0000	[diff] [blame]	1912
				1913	<p>This section describes how to perform some very simple transformations of
				1914	LLVM code. This is meant to give examples of common idioms used, showing the
				1915	practical side of LLVM transformations. <p> Because this is a "how-to" section,
				1916	you should also read about the main classes that you will be working with. The
				1917	<a href="#coreclasses">Core LLVM Class Hierarchy Reference</a> contains details
				1918	and descriptions of the main classes that you should know about.</p>
				1919
Misha Brukman	13fd15c	2004-01-15 00:14:41 +0000	[diff] [blame]	1920	<!-- NOTE: this section should be heavy on example code -->
				1921	<!-- ======================================================================= -->
NAKAMURA Takumi	05d0265	2011-04-18 23:59:50 +0000	[diff] [blame]	1922	<h3>
Misha Brukman	13fd15c	2004-01-15 00:14:41 +0000	[diff] [blame]	1923	<a name="inspection">Basic Inspection and Traversal Routines</a>
NAKAMURA Takumi	05d0265	2011-04-18 23:59:50 +0000	[diff] [blame]	1924	</h3>
Misha Brukman	13fd15c	2004-01-15 00:14:41 +0000	[diff] [blame]	1925
NAKAMURA Takumi	f5af6ad	2011-04-23 00:30:22 +0000	[diff] [blame]	1926	<div>
Misha Brukman	13fd15c	2004-01-15 00:14:41 +0000	[diff] [blame]	1927
				1928	<p>The LLVM compiler infrastructure have many different data structures that may
				1929	be traversed. Following the example of the C++ standard template library, the
				1930	techniques used to traverse these various data structures are all basically the
				1931	same. For a enumerable sequence of values, the <tt>XXXbegin()</tt> function (or
				1932	method) returns an iterator to the start of the sequence, the <tt>XXXend()</tt>
				1933	function returns an iterator pointing to one past the last valid element of the
				1934	sequence, and there is some <tt>XXXiterator</tt> data type that is common
				1935	between the two operations.</p>
				1936
				1937	<p>Because the pattern for iteration is common across many different aspects of
				1938	the program representation, the standard template library algorithms may be used
				1939	on them, and it is easier to remember how to iterate. First we show a few common
				1940	examples of the data structures that need to be traversed. Other data
				1941	structures are traversed in very similar ways.</p>
				1942
Misha Brukman	13fd15c	2004-01-15 00:14:41 +0000	[diff] [blame]	1943	<!-- _______________________________________________________________________ -->
NAKAMURA Takumi	05d0265	2011-04-18 23:59:50 +0000	[diff] [blame]	1944	<h4>
Misha Brukman	13fd15c	2004-01-15 00:14:41 +0000	[diff] [blame]	1945	<a name="iterate_function">Iterating over the </a><a
				1946	href="#BasicBlock"><tt>BasicBlock</tt></a>s in a <a
				1947	href="#Function"><tt>Function</tt></a>
NAKAMURA Takumi	05d0265	2011-04-18 23:59:50 +0000	[diff] [blame]	1948	</h4>
Misha Brukman	13fd15c	2004-01-15 00:14:41 +0000	[diff] [blame]	1949
NAKAMURA Takumi	f5af6ad	2011-04-23 00:30:22 +0000	[diff] [blame]	1950	<div>
Misha Brukman	13fd15c	2004-01-15 00:14:41 +0000	[diff] [blame]	1951
				1952	<p>It's quite common to have a <tt>Function</tt> instance that you'd like to
				1953	transform in some way; in particular, you'd like to manipulate its
				1954	<tt>BasicBlock</tt>s. To facilitate this, you'll need to iterate over all of
				1955	the <tt>BasicBlock</tt>s that constitute the <tt>Function</tt>. The following is
				1956	an example that prints the name of a <tt>BasicBlock</tt> and the number of
				1957	<tt>Instruction</tt>s it contains:</p>
				1958
Bill Wendling	3cd5ca6	2006-10-11 06:30:10 +0000	[diff] [blame]	1959	<div class="doc_code">
				1960	<pre>
Bill Wendling	82e2eea	2006-10-11 18:00:22 +0000	[diff] [blame]	1961	// <i>func is a pointer to a Function instance</i>
				1962	for (Function::iterator i = func->begin(), e = func->end(); i != e; ++i)
				1963	// <i>Print out the name of the basic block if it has one, and then the</i>
				1964	// <i>number of instructions that it contains</i>
Chris Lattner	3fee6ed	2009-09-08 05:15:50 +0000	[diff] [blame]	1965	errs() << "Basic block (name=" << i->getName() << ") has "
Bill Wendling	832171c	2006-12-07 20:04:42 +0000	[diff] [blame]	1966	<< i->size() << " instructions.\n";
Bill Wendling	3cd5ca6	2006-10-11 06:30:10 +0000	[diff] [blame]	1967	</pre>
				1968	</div>
Misha Brukman	13fd15c	2004-01-15 00:14:41 +0000	[diff] [blame]	1969
				1970	<p>Note that i can be used as if it were a pointer for the purposes of
Joel Stanley	9b96c44	2002-09-06 21:55:13 +0000	[diff] [blame]	1971	invoking member functions of the <tt>Instruction</tt> class. This is
				1972	because the indirection operator is overloaded for the iterator
Chris Lattner	7496ec5	2003-08-05 22:54:23 +0000	[diff] [blame]	1973	classes. In the above code, the expression <tt>i->size()</tt> is
Misha Brukman	13fd15c	2004-01-15 00:14:41 +0000	[diff] [blame]	1974	exactly equivalent to <tt>(*i).size()</tt> just like you'd expect.</p>
				1975
				1976	</div>
				1977
				1978	<!-- _______________________________________________________________________ -->
NAKAMURA Takumi	05d0265	2011-04-18 23:59:50 +0000	[diff] [blame]	1979	<h4>
Misha Brukman	13fd15c	2004-01-15 00:14:41 +0000	[diff] [blame]	1980	<a name="iterate_basicblock">Iterating over the </a><a
				1981	href="#Instruction"><tt>Instruction</tt></a>s in a <a
				1982	href="#BasicBlock"><tt>BasicBlock</tt></a>
NAKAMURA Takumi	05d0265	2011-04-18 23:59:50 +0000	[diff] [blame]	1983	</h4>
Misha Brukman	13fd15c	2004-01-15 00:14:41 +0000	[diff] [blame]	1984
NAKAMURA Takumi	f5af6ad	2011-04-23 00:30:22 +0000	[diff] [blame]	1985	<div>
Misha Brukman	13fd15c	2004-01-15 00:14:41 +0000	[diff] [blame]	1986
				1987	<p>Just like when dealing with <tt>BasicBlock</tt>s in <tt>Function</tt>s, it's
				1988	easy to iterate over the individual instructions that make up
				1989	<tt>BasicBlock</tt>s. Here's a code snippet that prints out each instruction in
				1990	a <tt>BasicBlock</tt>:</p>
				1991
Bill Wendling	3cd5ca6	2006-10-11 06:30:10 +0000	[diff] [blame]	1992	<div class="doc_code">
Chris Lattner	55c0461	2005-03-06 06:00:13 +0000	[diff] [blame]	1993	<pre>
Bill Wendling	82e2eea	2006-10-11 18:00:22 +0000	[diff] [blame]	1994	// <i>blk is a pointer to a BasicBlock instance</i>
Bill Wendling	3cd5ca6	2006-10-11 06:30:10 +0000	[diff] [blame]	1995	for (BasicBlock::iterator i = blk->begin(), e = blk->end(); i != e; ++i)
Bill Wendling	82e2eea	2006-10-11 18:00:22 +0000	[diff] [blame]	1996	// <i>The next statement works since operator<<(ostream&,...)</i>
				1997	// <i>is overloaded for Instruction&</i>
Chris Lattner	3fee6ed	2009-09-08 05:15:50 +0000	[diff] [blame]	1998	errs() << *i << "\n";
Chris Lattner	55c0461	2005-03-06 06:00:13 +0000	[diff] [blame]	1999	</pre>
Bill Wendling	3cd5ca6	2006-10-11 06:30:10 +0000	[diff] [blame]	2000	</div>
Misha Brukman	13fd15c	2004-01-15 00:14:41 +0000	[diff] [blame]	2001
				2002	<p>However, this isn't really the best way to print out the contents of a
				2003	<tt>BasicBlock</tt>! Since the ostream operators are overloaded for virtually
				2004	anything you'll care about, you could have just invoked the print routine on the
Chris Lattner	3fee6ed	2009-09-08 05:15:50 +0000	[diff] [blame]	2005	basic block itself: <tt>errs() << *blk << "\n";</tt>.</p>
Misha Brukman	13fd15c	2004-01-15 00:14:41 +0000	[diff] [blame]	2006
				2007	</div>
				2008
				2009	<!-- _______________________________________________________________________ -->
NAKAMURA Takumi	05d0265	2011-04-18 23:59:50 +0000	[diff] [blame]	2010	<h4>
Misha Brukman	13fd15c	2004-01-15 00:14:41 +0000	[diff] [blame]	2011	<a name="iterate_institer">Iterating over the </a><a
				2012	href="#Instruction"><tt>Instruction</tt></a>s in a <a
				2013	href="#Function"><tt>Function</tt></a>
NAKAMURA Takumi	05d0265	2011-04-18 23:59:50 +0000	[diff] [blame]	2014	</h4>
Misha Brukman	13fd15c	2004-01-15 00:14:41 +0000	[diff] [blame]	2015
NAKAMURA Takumi	f5af6ad	2011-04-23 00:30:22 +0000	[diff] [blame]	2016	<div>
Misha Brukman	13fd15c	2004-01-15 00:14:41 +0000	[diff] [blame]	2017
				2018	<p>If you're finding that you commonly iterate over a <tt>Function</tt>'s
				2019	<tt>BasicBlock</tt>s and then that <tt>BasicBlock</tt>'s <tt>Instruction</tt>s,
				2020	<tt>InstIterator</tt> should be used instead. You'll need to include <a
				2021	href="/doxygen/InstIterator_8h-source.html"><tt>llvm/Support/InstIterator.h</tt></a>,
				2022	and then instantiate <tt>InstIterator</tt>s explicitly in your code. Here's a
Chris Lattner	69bf8a9	2004-05-23 21:06:58 +0000	[diff] [blame]	2023	small example that shows how to dump all instructions in a function to the standard error stream:<p>
Misha Brukman	13fd15c	2004-01-15 00:14:41 +0000	[diff] [blame]	2024
Bill Wendling	3cd5ca6	2006-10-11 06:30:10 +0000	[diff] [blame]	2025	<div class="doc_code">
				2026	<pre>
				2027	#include "<a href="/doxygen/InstIterator_8h-source.html">llvm/Support/InstIterator.h</a>"
				2028
Reid Spencer	128a7a7	2007-02-03 21:06:43 +0000	[diff] [blame]	2029	// <i>F is a pointer to a Function instance</i>
Chris Lattner	da021aa	2008-06-04 18:20:42 +0000	[diff] [blame]	2030	for (inst_iterator I = inst_begin(F), E = inst_end(F); I != E; ++I)
Chris Lattner	3fee6ed	2009-09-08 05:15:50 +0000	[diff] [blame]	2031	errs() << *I << "\n";
Bill Wendling	3cd5ca6	2006-10-11 06:30:10 +0000	[diff] [blame]	2032	</pre>
				2033	</div>
				2034
				2035	<p>Easy, isn't it? You can also use <tt>InstIterator</tt>s to fill a
Reid Spencer	128a7a7	2007-02-03 21:06:43 +0000	[diff] [blame]	2036	work list with its initial contents. For example, if you wanted to
				2037	initialize a work list to contain all instructions in a <tt>Function</tt>
Bill Wendling	3cd5ca6	2006-10-11 06:30:10 +0000	[diff] [blame]	2038	F, all you would need to do is something like:</p>
				2039
				2040	<div class="doc_code">
				2041	<pre>
				2042	std::set<Instruction*> worklist;
Chris Lattner	da021aa	2008-06-04 18:20:42 +0000	[diff] [blame]	2043	// or better yet, SmallPtrSet<Instruction*, 64> worklist;
				2044
				2045	for (inst_iterator I = inst_begin(F), E = inst_end(F); I != E; ++I)
				2046	worklist.insert(&*I);
Bill Wendling	3cd5ca6	2006-10-11 06:30:10 +0000	[diff] [blame]	2047	</pre>
				2048	</div>
Misha Brukman	13fd15c	2004-01-15 00:14:41 +0000	[diff] [blame]	2049
				2050	<p>The STL set <tt>worklist</tt> would now contain all instructions in the
				2051	<tt>Function</tt> pointed to by F.</p>
				2052
				2053	</div>
				2054
				2055	<!-- _______________________________________________________________________ -->
NAKAMURA Takumi	05d0265	2011-04-18 23:59:50 +0000	[diff] [blame]	2056	<h4>
Misha Brukman	13fd15c	2004-01-15 00:14:41 +0000	[diff] [blame]	2057	<a name="iterate_convert">Turning an iterator into a class pointer (and
				2058	vice-versa)</a>
NAKAMURA Takumi	05d0265	2011-04-18 23:59:50 +0000	[diff] [blame]	2059	</h4>
Misha Brukman	13fd15c	2004-01-15 00:14:41 +0000	[diff] [blame]	2060
NAKAMURA Takumi	f5af6ad	2011-04-23 00:30:22 +0000	[diff] [blame]	2061	<div>
Misha Brukman	13fd15c	2004-01-15 00:14:41 +0000	[diff] [blame]	2062
				2063	<p>Sometimes, it'll be useful to grab a reference (or pointer) to a class
Joel Stanley	9b96c44	2002-09-06 21:55:13 +0000	[diff] [blame]	2064	instance when all you've got at hand is an iterator. Well, extracting
Chris Lattner	69bf8a9	2004-05-23 21:06:58 +0000	[diff] [blame]	2065	a reference or a pointer from an iterator is very straight-forward.
Chris Lattner	261efe9	2003-11-25 01:02:51 +0000	[diff] [blame]	2066	Assuming that <tt>i</tt> is a <tt>BasicBlock::iterator</tt> and <tt>j</tt>
Misha Brukman	13fd15c	2004-01-15 00:14:41 +0000	[diff] [blame]	2067	is a <tt>BasicBlock::const_iterator</tt>:</p>
				2068
Bill Wendling	3cd5ca6	2006-10-11 06:30:10 +0000	[diff] [blame]	2069	<div class="doc_code">
				2070	<pre>
Bill Wendling	82e2eea	2006-10-11 18:00:22 +0000	[diff] [blame]	2071	Instruction& inst = *i; // <i>Grab reference to instruction reference</i>
				2072	Instruction* pinst = &*i; // <i>Grab pointer to instruction reference</i>
Bill Wendling	3cd5ca6	2006-10-11 06:30:10 +0000	[diff] [blame]	2073	const Instruction& inst = *j;
				2074	</pre>
				2075	</div>
Misha Brukman	13fd15c	2004-01-15 00:14:41 +0000	[diff] [blame]	2076
				2077	<p>However, the iterators you'll be working with in the LLVM framework are
				2078	special: they will automatically convert to a ptr-to-instance type whenever they
				2079	need to. Instead of dereferencing the iterator and then taking the address of
				2080	the result, you can simply assign the iterator to the proper pointer type and
				2081	you get the dereference and address-of operation as a result of the assignment
				2082	(behind the scenes, this is a result of overloading casting mechanisms). Thus
				2083	the last line of the last example,</p>
				2084
Bill Wendling	3cd5ca6	2006-10-11 06:30:10 +0000	[diff] [blame]	2085	<div class="doc_code">
				2086	<pre>
Chris Lattner	2e438ca	2008-01-03 16:56:04 +0000	[diff] [blame]	2087	Instruction pinst = &i;
Bill Wendling	3cd5ca6	2006-10-11 06:30:10 +0000	[diff] [blame]	2088	</pre>
				2089	</div>
Misha Brukman	13fd15c	2004-01-15 00:14:41 +0000	[diff] [blame]	2090
				2091	<p>is semantically equivalent to</p>
				2092
Bill Wendling	3cd5ca6	2006-10-11 06:30:10 +0000	[diff] [blame]	2093	<div class="doc_code">
				2094	<pre>
Chris Lattner	2e438ca	2008-01-03 16:56:04 +0000	[diff] [blame]	2095	Instruction *pinst = i;
Bill Wendling	3cd5ca6	2006-10-11 06:30:10 +0000	[diff] [blame]	2096	</pre>
				2097	</div>
Misha Brukman	13fd15c	2004-01-15 00:14:41 +0000	[diff] [blame]	2098
Chris Lattner	69bf8a9	2004-05-23 21:06:58 +0000	[diff] [blame]	2099	<p>It's also possible to turn a class pointer into the corresponding iterator,
				2100	and this is a constant time operation (very efficient). The following code
				2101	snippet illustrates use of the conversion constructors provided by LLVM
				2102	iterators. By using these, you can explicitly grab the iterator of something
				2103	without actually obtaining it via iteration over some structure:</p>
Misha Brukman	13fd15c	2004-01-15 00:14:41 +0000	[diff] [blame]	2104
Bill Wendling	3cd5ca6	2006-10-11 06:30:10 +0000	[diff] [blame]	2105	<div class="doc_code">
				2106	<pre>
				2107	void printNextInstruction(Instruction* inst) {
				2108	BasicBlock::iterator it(inst);
Bill Wendling	82e2eea	2006-10-11 18:00:22 +0000	[diff] [blame]	2109	++it; // <i>After this line, it refers to the instruction after *inst</i>
Chris Lattner	3fee6ed	2009-09-08 05:15:50 +0000	[diff] [blame]	2110	if (it != inst->getParent()->end()) errs() << *it << "\n";
Bill Wendling	3cd5ca6	2006-10-11 06:30:10 +0000	[diff] [blame]	2111	}
				2112	</pre>
				2113	</div>
Misha Brukman	13fd15c	2004-01-15 00:14:41 +0000	[diff] [blame]	2114
Dan Gohman	525bf8e	2010-03-26 19:39:05 +0000	[diff] [blame]	2115	<p>Unfortunately, these implicit conversions come at a cost; they prevent
				2116	these iterators from conforming to standard iterator conventions, and thus
Dan Gohman	0d91c11	2010-03-26 19:51:14 +0000	[diff] [blame]	2117	from being usable with standard algorithms and containers. For example, they
				2118	prevent the following code, where <tt>B</tt> is a <tt>BasicBlock</tt>,
Dan Gohman	525bf8e	2010-03-26 19:39:05 +0000	[diff] [blame]	2119	from compiling:</p>
				2120
				2121	<div class="doc_code">
				2122	<pre>
				2123	llvm::SmallVector<llvm::Instruction *, 16>(B->begin(), B->end());
				2124	</pre>
				2125	</div>
				2126
				2127	<p>Because of this, these implicit conversions may be removed some day,
Dan Gohman	0d91c11	2010-03-26 19:51:14 +0000	[diff] [blame]	2128	and <tt>operator*</tt> changed to return a pointer instead of a reference.</p>
Dan Gohman	525bf8e	2010-03-26 19:39:05 +0000	[diff] [blame]	2129
Misha Brukman	13fd15c	2004-01-15 00:14:41 +0000	[diff] [blame]	2130	</div>
				2131
				2132	<!--_______________________________________________________________________-->
NAKAMURA Takumi	05d0265	2011-04-18 23:59:50 +0000	[diff] [blame]	2133	<h4>
Misha Brukman	13fd15c	2004-01-15 00:14:41 +0000	[diff] [blame]	2134	<a name="iterate_complex">Finding call sites: a slightly more complex
				2135	example</a>
NAKAMURA Takumi	05d0265	2011-04-18 23:59:50 +0000	[diff] [blame]	2136	</h4>
Misha Brukman	13fd15c	2004-01-15 00:14:41 +0000	[diff] [blame]	2137
NAKAMURA Takumi	f5af6ad	2011-04-23 00:30:22 +0000	[diff] [blame]	2138	<div>
Misha Brukman	13fd15c	2004-01-15 00:14:41 +0000	[diff] [blame]	2139
				2140	<p>Say that you're writing a FunctionPass and would like to count all the
				2141	locations in the entire module (that is, across every <tt>Function</tt>) where a
				2142	certain function (i.e., some <tt>Function</tt>*) is already in scope. As you'll
				2143	learn later, you may want to use an <tt>InstVisitor</tt> to accomplish this in a
Chris Lattner	69bf8a9	2004-05-23 21:06:58 +0000	[diff] [blame]	2144	much more straight-forward manner, but this example will allow us to explore how
Reid Spencer	128a7a7	2007-02-03 21:06:43 +0000	[diff] [blame]	2145	you'd do it if you didn't have <tt>InstVisitor</tt> around. In pseudo-code, this
Misha Brukman	13fd15c	2004-01-15 00:14:41 +0000	[diff] [blame]	2146	is what we want to do:</p>
				2147
Bill Wendling	3cd5ca6	2006-10-11 06:30:10 +0000	[diff] [blame]	2148	<div class="doc_code">
				2149	<pre>
				2150	initialize callCounter to zero
				2151	for each Function f in the Module
				2152	for each BasicBlock b in f
				2153	for each Instruction i in b
				2154	if (i is a CallInst and calls the given function)
				2155	increment callCounter
				2156	</pre>
				2157	</div>
Misha Brukman	13fd15c	2004-01-15 00:14:41 +0000	[diff] [blame]	2158
Bill Wendling	3cd5ca6	2006-10-11 06:30:10 +0000	[diff] [blame]	2159	<p>And the actual code is (remember, because we're writing a
Misha Brukman	13fd15c	2004-01-15 00:14:41 +0000	[diff] [blame]	2160	<tt>FunctionPass</tt>, our <tt>FunctionPass</tt>-derived class simply has to
Bill Wendling	3cd5ca6	2006-10-11 06:30:10 +0000	[diff] [blame]	2161	override the <tt>runOnFunction</tt> method):</p>
Misha Brukman	13fd15c	2004-01-15 00:14:41 +0000	[diff] [blame]	2162
Bill Wendling	3cd5ca6	2006-10-11 06:30:10 +0000	[diff] [blame]	2163	<div class="doc_code">
				2164	<pre>
				2165	Function* targetFunc = ...;
				2166
				2167	class OurFunctionPass : public FunctionPass {
				2168	public:
				2169	OurFunctionPass(): callCounter(0) { }
				2170
				2171	virtual runOnFunction(Function& F) {
				2172	for (Function::iterator b = F.begin(), be = F.end(); b != be; ++b) {
Eric Christopher	203e71d	2008-11-08 08:20:49 +0000	[diff] [blame]	2173	for (BasicBlock::iterator i = b->begin(), ie = b->end(); i != ie; ++i) {
Bill Wendling	3cd5ca6	2006-10-11 06:30:10 +0000	[diff] [blame]	2174	if (<a href="#CallInst">CallInst</a>* callInst = <a href="#isa">dyn_cast</a><<a
				2175	href="#CallInst">CallInst</a>>(&*i)) {
Bill Wendling	82e2eea	2006-10-11 18:00:22 +0000	[diff] [blame]	2176	// <i>We know we've encountered a call instruction, so we</i>
				2177	// <i>need to determine if it's a call to the</i>
Chris Lattner	2e438ca	2008-01-03 16:56:04 +0000	[diff] [blame]	2178	// <i>function pointed to by m_func or not.</i>
Bill Wendling	3cd5ca6	2006-10-11 06:30:10 +0000	[diff] [blame]	2179	if (callInst->getCalledFunction() == targetFunc)
				2180	++callCounter;
				2181	}
				2182	}
				2183	}
Bill Wendling	82e2eea	2006-10-11 18:00:22 +0000	[diff] [blame]	2184	}
Bill Wendling	3cd5ca6	2006-10-11 06:30:10 +0000	[diff] [blame]	2185
				2186	private:
Chris Lattner	2e438ca	2008-01-03 16:56:04 +0000	[diff] [blame]	2187	unsigned callCounter;
Bill Wendling	3cd5ca6	2006-10-11 06:30:10 +0000	[diff] [blame]	2188	};
				2189	</pre>
				2190	</div>
Misha Brukman	13fd15c	2004-01-15 00:14:41 +0000	[diff] [blame]	2191
				2192	</div>
				2193
Brian Gaeke	f1972c6	2003-11-07 19:25:45 +0000	[diff] [blame]	2194	<!--_______________________________________________________________________-->
NAKAMURA Takumi	05d0265	2011-04-18 23:59:50 +0000	[diff] [blame]	2195	<h4>
Misha Brukman	13fd15c	2004-01-15 00:14:41 +0000	[diff] [blame]	2196	<a name="calls_and_invokes">Treating calls and invokes the same way</a>
NAKAMURA Takumi	05d0265	2011-04-18 23:59:50 +0000	[diff] [blame]	2197	</h4>
Misha Brukman	13fd15c	2004-01-15 00:14:41 +0000	[diff] [blame]	2198
NAKAMURA Takumi	f5af6ad	2011-04-23 00:30:22 +0000	[diff] [blame]	2199	<div>
Misha Brukman	13fd15c	2004-01-15 00:14:41 +0000	[diff] [blame]	2200
				2201	<p>You may have noticed that the previous example was a bit oversimplified in
				2202	that it did not deal with call sites generated by 'invoke' instructions. In
				2203	this, and in other situations, you may find that you want to treat
				2204	<tt>CallInst</tt>s and <tt>InvokeInst</tt>s the same way, even though their
				2205	most-specific common base class is <tt>Instruction</tt>, which includes lots of
				2206	less closely-related things. For these cases, LLVM provides a handy wrapper
				2207	class called <a
Reid Spencer	05fe4b0	2006-03-14 05:39:39 +0000	[diff] [blame]	2208	href="http://llvm.org/doxygen/classllvm_1_1CallSite.html"><tt>CallSite</tt></a>.
Chris Lattner	69bf8a9	2004-05-23 21:06:58 +0000	[diff] [blame]	2209	It is essentially a wrapper around an <tt>Instruction</tt> pointer, with some
				2210	methods that provide functionality common to <tt>CallInst</tt>s and
Misha Brukman	13fd15c	2004-01-15 00:14:41 +0000	[diff] [blame]	2211	<tt>InvokeInst</tt>s.</p>
				2212
Chris Lattner	69bf8a9	2004-05-23 21:06:58 +0000	[diff] [blame]	2213	<p>This class has "value semantics": it should be passed by value, not by
				2214	reference and it should not be dynamically allocated or deallocated using
				2215	<tt>operator new</tt> or <tt>operator delete</tt>. It is efficiently copyable,
				2216	assignable and constructable, with costs equivalents to that of a bare pointer.
				2217	If you look at its definition, it has only a single pointer member.</p>
Misha Brukman	13fd15c	2004-01-15 00:14:41 +0000	[diff] [blame]	2218
				2219	</div>
				2220
Chris Lattner	1a3105b	2002-09-09 05:49:39 +0000	[diff] [blame]	2221	<!--_______________________________________________________________________-->
NAKAMURA Takumi	05d0265	2011-04-18 23:59:50 +0000	[diff] [blame]	2222	<h4>
Misha Brukman	13fd15c	2004-01-15 00:14:41 +0000	[diff] [blame]	2223	<a name="iterate_chains">Iterating over def-use & use-def chains</a>
NAKAMURA Takumi	05d0265	2011-04-18 23:59:50 +0000	[diff] [blame]	2224	</h4>
Misha Brukman	13fd15c	2004-01-15 00:14:41 +0000	[diff] [blame]	2225
NAKAMURA Takumi	f5af6ad	2011-04-23 00:30:22 +0000	[diff] [blame]	2226	<div>
Misha Brukman	13fd15c	2004-01-15 00:14:41 +0000	[diff] [blame]	2227
				2228	<p>Frequently, we might have an instance of the <a
Chris Lattner	0081517	2007-01-04 22:01:45 +0000	[diff] [blame]	2229	href="/doxygen/classllvm_1_1Value.html">Value Class</a> and we want to
Misha Brukman	384047f	2004-06-03 23:29:12 +0000	[diff] [blame]	2230	determine which <tt>User</tt>s use the <tt>Value</tt>. The list of all
				2231	<tt>User</tt>s of a particular <tt>Value</tt> is called a <i>def-use</i> chain.
				2232	For example, let's say we have a <tt>Function*</tt> named <tt>F</tt> to a
				2233	particular function <tt>foo</tt>. Finding all of the instructions that
				2234	<i>use</i> <tt>foo</tt> is as simple as iterating over the <i>def-use</i> chain
				2235	of <tt>F</tt>:</p>
Misha Brukman	13fd15c	2004-01-15 00:14:41 +0000	[diff] [blame]	2236
Bill Wendling	3cd5ca6	2006-10-11 06:30:10 +0000	[diff] [blame]	2237	<div class="doc_code">
				2238	<pre>
Chris Lattner	2e438ca	2008-01-03 16:56:04 +0000	[diff] [blame]	2239	Function *F = ...;
Bill Wendling	3cd5ca6	2006-10-11 06:30:10 +0000	[diff] [blame]	2240
Bill Wendling	82e2eea	2006-10-11 18:00:22 +0000	[diff] [blame]	2241	for (Value::use_iterator i = F->use_begin(), e = F->use_end(); i != e; ++i)
Bill Wendling	3cd5ca6	2006-10-11 06:30:10 +0000	[diff] [blame]	2242	if (Instruction Inst = dyn_cast<Instruction>(i)) {
Chris Lattner	3fee6ed	2009-09-08 05:15:50 +0000	[diff] [blame]	2243	errs() << "F is used in instruction:\n";
				2244	errs() << *Inst << "\n";
Bill Wendling	3cd5ca6	2006-10-11 06:30:10 +0000	[diff] [blame]	2245	}
Bill Wendling	3cd5ca6	2006-10-11 06:30:10 +0000	[diff] [blame]	2246	</pre>
Gabor Greif	394fdfb	2010-03-26 19:35:48 +0000	[diff] [blame]	2247	</div>
				2248
Gabor Greif	ce9431953	2010-03-26 19:40:38 +0000	[diff] [blame]	2249	<p>Note that dereferencing a <tt>Value::use_iterator</tt> is not a very cheap
Gabor Greif	4de7368	2010-03-26 19:30:47 +0000	[diff] [blame]	2250	operation. Instead of performing <tt>*i</tt> above several times, consider
Gabor Greif	ce9431953	2010-03-26 19:40:38 +0000	[diff] [blame]	2251	doing it only once in the loop body and reusing its result.</p>
Gabor Greif	4de7368	2010-03-26 19:30:47 +0000	[diff] [blame]	2252
Gabor Greif	6091ff3	2010-03-26 19:04:42 +0000	[diff] [blame]	2253	<p>Alternatively, it's common to have an instance of the <a
Misha Brukman	384047f	2004-06-03 23:29:12 +0000	[diff] [blame]	2254	href="/doxygen/classllvm_1_1User.html">User Class</a> and need to know what
Misha Brukman	13fd15c	2004-01-15 00:14:41 +0000	[diff] [blame]	2255	<tt>Value</tt>s are used by it. The list of all <tt>Value</tt>s used by a
				2256	<tt>User</tt> is known as a <i>use-def</i> chain. Instances of class
				2257	<tt>Instruction</tt> are common <tt>User</tt>s, so we might want to iterate over
				2258	all of the values that a particular instruction uses (that is, the operands of
				2259	the particular <tt>Instruction</tt>):</p>
				2260
Bill Wendling	3cd5ca6	2006-10-11 06:30:10 +0000	[diff] [blame]	2261	<div class="doc_code">
				2262	<pre>
Chris Lattner	2e438ca	2008-01-03 16:56:04 +0000	[diff] [blame]	2263	Instruction *pi = ...;
Bill Wendling	3cd5ca6	2006-10-11 06:30:10 +0000	[diff] [blame]	2264
				2265	for (User::op_iterator i = pi->op_begin(), e = pi->op_end(); i != e; ++i) {
Chris Lattner	2e438ca	2008-01-03 16:56:04 +0000	[diff] [blame]	2266	Value v = i;
Bill Wendling	82e2eea	2006-10-11 18:00:22 +0000	[diff] [blame]	2267	// <i>...</i>
Bill Wendling	3cd5ca6	2006-10-11 06:30:10 +0000	[diff] [blame]	2268	}
				2269	</pre>
				2270	</div>
Misha Brukman	13fd15c	2004-01-15 00:14:41 +0000	[diff] [blame]	2271
Gabor Greif	4de7368	2010-03-26 19:30:47 +0000	[diff] [blame]	2272	<p>Declaring objects as <tt>const</tt> is an important tool of enforcing
Gabor Greif	ce9431953	2010-03-26 19:40:38 +0000	[diff] [blame]	2273	mutation free algorithms (such as analyses, etc.). For this purpose above
Gabor Greif	4de7368	2010-03-26 19:30:47 +0000	[diff] [blame]	2274	iterators come in constant flavors as <tt>Value::const_use_iterator</tt>
				2275	and <tt>Value::const_op_iterator</tt>. They automatically arise when
				2276	calling <tt>use/op_begin()</tt> on <tt>const Value*</tt>s or
				2277	<tt>const User*</tt>s respectively. Upon dereferencing, they return
Gabor Greif	ce9431953	2010-03-26 19:40:38 +0000	[diff] [blame]	2278	<tt>const Use*</tt>s. Otherwise the above patterns remain unchanged.</p>
				2279
Misha Brukman	13fd15c	2004-01-15 00:14:41 +0000	[diff] [blame]	2280	</div>
				2281
Chris Lattner	2e438ca	2008-01-03 16:56:04 +0000	[diff] [blame]	2282	<!--_______________________________________________________________________-->
NAKAMURA Takumi	05d0265	2011-04-18 23:59:50 +0000	[diff] [blame]	2283	<h4>
Chris Lattner	2e438ca	2008-01-03 16:56:04 +0000	[diff] [blame]	2284	<a name="iterate_preds">Iterating over predecessors &
				2285	successors of blocks</a>
NAKAMURA Takumi	05d0265	2011-04-18 23:59:50 +0000	[diff] [blame]	2286	</h4>
Chris Lattner	2e438ca	2008-01-03 16:56:04 +0000	[diff] [blame]	2287
NAKAMURA Takumi	f5af6ad	2011-04-23 00:30:22 +0000	[diff] [blame]	2288	<div>
Chris Lattner	2e438ca	2008-01-03 16:56:04 +0000	[diff] [blame]	2289
				2290	<p>Iterating over the predecessors and successors of a block is quite easy
				2291	with the routines defined in <tt>"llvm/Support/CFG.h"</tt>. Just use code like
				2292	this to iterate over all predecessors of BB:</p>
				2293
				2294	<div class="doc_code">
				2295	<pre>
				2296	#include "llvm/Support/CFG.h"
				2297	BasicBlock *BB = ...;
				2298
				2299	for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI) {
				2300	BasicBlock Pred = PI;
				2301	// <i>...</i>
				2302	}
				2303	</pre>
				2304	</div>
				2305
				2306	<p>Similarly, to iterate over successors use
				2307	succ_iterator/succ_begin/succ_end.</p>
				2308
				2309	</div>
				2310
NAKAMURA Takumi	f5af6ad	2011-04-23 00:30:22 +0000	[diff] [blame]	2311	</div>
Chris Lattner	2e438ca	2008-01-03 16:56:04 +0000	[diff] [blame]	2312
Misha Brukman	13fd15c	2004-01-15 00:14:41 +0000	[diff] [blame]	2313	<!-- ======================================================================= -->
NAKAMURA Takumi	05d0265	2011-04-18 23:59:50 +0000	[diff] [blame]	2314	<h3>
Misha Brukman	13fd15c	2004-01-15 00:14:41 +0000	[diff] [blame]	2315	<a name="simplechanges">Making simple changes</a>
NAKAMURA Takumi	05d0265	2011-04-18 23:59:50 +0000	[diff] [blame]	2316	</h3>
Misha Brukman	13fd15c	2004-01-15 00:14:41 +0000	[diff] [blame]	2317
NAKAMURA Takumi	f5af6ad	2011-04-23 00:30:22 +0000	[diff] [blame]	2318	<div>
Misha Brukman	13fd15c	2004-01-15 00:14:41 +0000	[diff] [blame]	2319
				2320	<p>There are some primitive transformation operations present in the LLVM
Joel Stanley	753eb71	2002-09-11 22:32:24 +0000	[diff] [blame]	2321	infrastructure that are worth knowing about. When performing
Chris Lattner	261efe9	2003-11-25 01:02:51 +0000	[diff] [blame]	2322	transformations, it's fairly common to manipulate the contents of basic
				2323	blocks. This section describes some of the common methods for doing so
Misha Brukman	13fd15c	2004-01-15 00:14:41 +0000	[diff] [blame]	2324	and gives example code.</p>
				2325
Chris Lattner	261efe9	2003-11-25 01:02:51 +0000	[diff] [blame]	2326	<!--_______________________________________________________________________-->
NAKAMURA Takumi	05d0265	2011-04-18 23:59:50 +0000	[diff] [blame]	2327	<h4>
Misha Brukman	13fd15c	2004-01-15 00:14:41 +0000	[diff] [blame]	2328	<a name="schanges_creating">Creating and inserting new
				2329	<tt>Instruction</tt>s</a>
NAKAMURA Takumi	05d0265	2011-04-18 23:59:50 +0000	[diff] [blame]	2330	</h4>
Misha Brukman	13fd15c	2004-01-15 00:14:41 +0000	[diff] [blame]	2331
NAKAMURA Takumi	f5af6ad	2011-04-23 00:30:22 +0000	[diff] [blame]	2332	<div>
Misha Brukman	13fd15c	2004-01-15 00:14:41 +0000	[diff] [blame]	2333
				2334	<p><i>Instantiating Instructions</i></p>
				2335
Chris Lattner	69bf8a9	2004-05-23 21:06:58 +0000	[diff] [blame]	2336	<p>Creation of <tt>Instruction</tt>s is straight-forward: simply call the
Misha Brukman	13fd15c	2004-01-15 00:14:41 +0000	[diff] [blame]	2337	constructor for the kind of instruction to instantiate and provide the necessary
				2338	parameters. For example, an <tt>AllocaInst</tt> only <i>requires</i> a
				2339	(const-ptr-to) <tt>Type</tt>. Thus:</p>
				2340
Bill Wendling	3cd5ca6	2006-10-11 06:30:10 +0000	[diff] [blame]	2341	<div class="doc_code">
				2342	<pre>
Nick Lewycky	10d64b9	2007-12-03 01:52:52 +0000	[diff] [blame]	2343	AllocaInst* ai = new AllocaInst(Type::Int32Ty);
Bill Wendling	3cd5ca6	2006-10-11 06:30:10 +0000	[diff] [blame]	2344	</pre>
				2345	</div>
Misha Brukman	13fd15c	2004-01-15 00:14:41 +0000	[diff] [blame]	2346
				2347	<p>will create an <tt>AllocaInst</tt> instance that represents the allocation of
Reid Spencer	128a7a7	2007-02-03 21:06:43 +0000	[diff] [blame]	2348	one integer in the current stack frame, at run time. Each <tt>Instruction</tt>
Misha Brukman	13fd15c	2004-01-15 00:14:41 +0000	[diff] [blame]	2349	subclass is likely to have varying default parameters which change the semantics
				2350	of the instruction, so refer to the <a
Misha Brukman	31ca1de	2004-06-03 23:35:54 +0000	[diff] [blame]	2351	href="/doxygen/classllvm_1_1Instruction.html">doxygen documentation for the subclass of
Misha Brukman	13fd15c	2004-01-15 00:14:41 +0000	[diff] [blame]	2352	Instruction</a> that you're interested in instantiating.</p>
				2353
				2354	<p><i>Naming values</i></p>
				2355
				2356	<p>It is very useful to name the values of instructions when you're able to, as
				2357	this facilitates the debugging of your transformations. If you end up looking
				2358	at generated LLVM machine code, you definitely want to have logical names
				2359	associated with the results of instructions! By supplying a value for the
				2360	<tt>Name</tt> (default) parameter of the <tt>Instruction</tt> constructor, you
				2361	associate a logical name with the result of the instruction's execution at
Reid Spencer	128a7a7	2007-02-03 21:06:43 +0000	[diff] [blame]	2362	run time. For example, say that I'm writing a transformation that dynamically
Misha Brukman	13fd15c	2004-01-15 00:14:41 +0000	[diff] [blame]	2363	allocates space for an integer on the stack, and that integer is going to be
				2364	used as some kind of index by some other code. To accomplish this, I place an
				2365	<tt>AllocaInst</tt> at the first point in the first <tt>BasicBlock</tt> of some
				2366	<tt>Function</tt>, and I'm intending to use it within the same
				2367	<tt>Function</tt>. I might do:</p>
				2368
Bill Wendling	3cd5ca6	2006-10-11 06:30:10 +0000	[diff] [blame]	2369	<div class="doc_code">
				2370	<pre>
Nick Lewycky	10d64b9	2007-12-03 01:52:52 +0000	[diff] [blame]	2371	AllocaInst* pa = new AllocaInst(Type::Int32Ty, 0, "indexLoc");
Bill Wendling	3cd5ca6	2006-10-11 06:30:10 +0000	[diff] [blame]	2372	</pre>
				2373	</div>
Misha Brukman	13fd15c	2004-01-15 00:14:41 +0000	[diff] [blame]	2374
				2375	<p>where <tt>indexLoc</tt> is now the logical name of the instruction's
Reid Spencer	128a7a7	2007-02-03 21:06:43 +0000	[diff] [blame]	2376	execution value, which is a pointer to an integer on the run time stack.</p>
Misha Brukman	13fd15c	2004-01-15 00:14:41 +0000	[diff] [blame]	2377
				2378	<p><i>Inserting instructions</i></p>
				2379
				2380	<p>There are essentially two ways to insert an <tt>Instruction</tt>
				2381	into an existing sequence of instructions that form a <tt>BasicBlock</tt>:</p>
				2382
Joel Stanley	9dd1ad6	2002-09-18 03:17:23 +0000	[diff] [blame]	2383	<ul>
Misha Brukman	13fd15c	2004-01-15 00:14:41 +0000	[diff] [blame]	2384	<li>Insertion into an explicit instruction list
				2385
				2386	<p>Given a <tt>BasicBlock* pb</tt>, an <tt>Instruction* pi</tt> within that
				2387	<tt>BasicBlock</tt>, and a newly-created instruction we wish to insert
				2388	before <tt>*pi</tt>, we do the following: </p>
				2389
Bill Wendling	3cd5ca6	2006-10-11 06:30:10 +0000	[diff] [blame]	2390	<div class="doc_code">
				2391	<pre>
				2392	BasicBlock *pb = ...;
				2393	Instruction *pi = ...;
				2394	Instruction *newInst = new Instruction(...);
				2395
Bill Wendling	82e2eea	2006-10-11 18:00:22 +0000	[diff] [blame]	2396	pb->getInstList().insert(pi, newInst); // <i>Inserts newInst before pi in pb</i>
Bill Wendling	3cd5ca6	2006-10-11 06:30:10 +0000	[diff] [blame]	2397	</pre>
				2398	</div>
Alkis Evlogimenos	9a5dc4f	2004-05-27 00:57:51 +0000	[diff] [blame]	2399
				2400	<p>Appending to the end of a <tt>BasicBlock</tt> is so common that
				2401	the <tt>Instruction</tt> class and <tt>Instruction</tt>-derived
				2402	classes provide constructors which take a pointer to a
				2403	<tt>BasicBlock</tt> to be appended to. For example code that
				2404	looked like: </p>
				2405
Bill Wendling	3cd5ca6	2006-10-11 06:30:10 +0000	[diff] [blame]	2406	<div class="doc_code">
				2407	<pre>
				2408	BasicBlock *pb = ...;
				2409	Instruction *newInst = new Instruction(...);
				2410
Bill Wendling	82e2eea	2006-10-11 18:00:22 +0000	[diff] [blame]	2411	pb->getInstList().push_back(newInst); // <i>Appends newInst to pb</i>
Bill Wendling	3cd5ca6	2006-10-11 06:30:10 +0000	[diff] [blame]	2412	</pre>
				2413	</div>
Alkis Evlogimenos	9a5dc4f	2004-05-27 00:57:51 +0000	[diff] [blame]	2414
				2415	<p>becomes: </p>
				2416
Bill Wendling	3cd5ca6	2006-10-11 06:30:10 +0000	[diff] [blame]	2417	<div class="doc_code">
				2418	<pre>
				2419	BasicBlock *pb = ...;
				2420	Instruction *newInst = new Instruction(..., pb);
				2421	</pre>
				2422	</div>
Alkis Evlogimenos	9a5dc4f	2004-05-27 00:57:51 +0000	[diff] [blame]	2423
				2424	<p>which is much cleaner, especially if you are creating
				2425	long instruction streams.</p></li>
Misha Brukman	13fd15c	2004-01-15 00:14:41 +0000	[diff] [blame]	2426
				2427	<li>Insertion into an implicit instruction list
				2428
				2429	<p><tt>Instruction</tt> instances that are already in <tt>BasicBlock</tt>s
				2430	are implicitly associated with an existing instruction list: the instruction
				2431	list of the enclosing basic block. Thus, we could have accomplished the same
				2432	thing as the above code without being given a <tt>BasicBlock</tt> by doing:
				2433	</p>
				2434
Bill Wendling	3cd5ca6	2006-10-11 06:30:10 +0000	[diff] [blame]	2435	<div class="doc_code">
				2436	<pre>
				2437	Instruction *pi = ...;
				2438	Instruction *newInst = new Instruction(...);
				2439
				2440	pi->getParent()->getInstList().insert(pi, newInst);
				2441	</pre>
				2442	</div>
Misha Brukman	13fd15c	2004-01-15 00:14:41 +0000	[diff] [blame]	2443
				2444	<p>In fact, this sequence of steps occurs so frequently that the
				2445	<tt>Instruction</tt> class and <tt>Instruction</tt>-derived classes provide
				2446	constructors which take (as a default parameter) a pointer to an
				2447	<tt>Instruction</tt> which the newly-created <tt>Instruction</tt> should
				2448	precede. That is, <tt>Instruction</tt> constructors are capable of
				2449	inserting the newly-created instance into the <tt>BasicBlock</tt> of a
				2450	provided instruction, immediately before that instruction. Using an
				2451	<tt>Instruction</tt> constructor with a <tt>insertBefore</tt> (default)
				2452	parameter, the above code becomes:</p>
				2453
Bill Wendling	3cd5ca6	2006-10-11 06:30:10 +0000	[diff] [blame]	2454	<div class="doc_code">
				2455	<pre>
				2456	Instruction* pi = ...;
				2457	Instruction* newInst = new Instruction(..., pi);
				2458	</pre>
				2459	</div>
Misha Brukman	13fd15c	2004-01-15 00:14:41 +0000	[diff] [blame]	2460
				2461	<p>which is much cleaner, especially if you're creating a lot of
Bill Wendling	3cd5ca6	2006-10-11 06:30:10 +0000	[diff] [blame]	2462	instructions and adding them to <tt>BasicBlock</tt>s.</p></li>
Misha Brukman	13fd15c	2004-01-15 00:14:41 +0000	[diff] [blame]	2463	</ul>
				2464
				2465	</div>
				2466
				2467	<!--_______________________________________________________________________-->
NAKAMURA Takumi	05d0265	2011-04-18 23:59:50 +0000	[diff] [blame]	2468	<h4>
Misha Brukman	13fd15c	2004-01-15 00:14:41 +0000	[diff] [blame]	2469	<a name="schanges_deleting">Deleting <tt>Instruction</tt>s</a>
NAKAMURA Takumi	05d0265	2011-04-18 23:59:50 +0000	[diff] [blame]	2470	</h4>
Misha Brukman	13fd15c	2004-01-15 00:14:41 +0000	[diff] [blame]	2471
NAKAMURA Takumi	f5af6ad	2011-04-23 00:30:22 +0000	[diff] [blame]	2472	<div>
Misha Brukman	13fd15c	2004-01-15 00:14:41 +0000	[diff] [blame]	2473
				2474	<p>Deleting an instruction from an existing sequence of instructions that form a
Chris Lattner	49e0ccf	2011-03-24 16:13:31 +0000	[diff] [blame]	2475	<a href="#BasicBlock"><tt>BasicBlock</tt></a> is very straight-forward: just
				2476	call the instruction's eraseFromParent() method. For example:</p>
Misha Brukman	13fd15c	2004-01-15 00:14:41 +0000	[diff] [blame]	2477
Bill Wendling	3cd5ca6	2006-10-11 06:30:10 +0000	[diff] [blame]	2478	<div class="doc_code">
				2479	<pre>
				2480	<a href="#Instruction">Instruction</a> *I = .. ;
Chris Lattner	9f8ec25	2008-02-15 22:57:17 +0000	[diff] [blame]	2481	I->eraseFromParent();
Bill Wendling	3cd5ca6	2006-10-11 06:30:10 +0000	[diff] [blame]	2482	</pre>
				2483	</div>
Misha Brukman	13fd15c	2004-01-15 00:14:41 +0000	[diff] [blame]	2484
Chris Lattner	49e0ccf	2011-03-24 16:13:31 +0000	[diff] [blame]	2485	<p>This unlinks the instruction from its containing basic block and deletes
				2486	it. If you'd just like to unlink the instruction from its containing basic
				2487	block but not delete it, you can use the <tt>removeFromParent()</tt> method.</p>
				2488
Misha Brukman	13fd15c	2004-01-15 00:14:41 +0000	[diff] [blame]	2489	</div>
				2490
				2491	<!--_______________________________________________________________________-->
NAKAMURA Takumi	05d0265	2011-04-18 23:59:50 +0000	[diff] [blame]	2492	<h4>
Misha Brukman	13fd15c	2004-01-15 00:14:41 +0000	[diff] [blame]	2493	<a name="schanges_replacing">Replacing an <tt>Instruction</tt> with another
				2494	<tt>Value</tt></a>
NAKAMURA Takumi	05d0265	2011-04-18 23:59:50 +0000	[diff] [blame]	2495	</h4>
Misha Brukman	13fd15c	2004-01-15 00:14:41 +0000	[diff] [blame]	2496
NAKAMURA Takumi	f5af6ad	2011-04-23 00:30:22 +0000	[diff] [blame]	2497	<div>
Misha Brukman	13fd15c	2004-01-15 00:14:41 +0000	[diff] [blame]	2498
				2499	<p><i>Replacing individual instructions</i></p>
				2500
				2501	<p>Including "<a href="/doxygen/BasicBlockUtils_8h-source.html">llvm/Transforms/Utils/BasicBlockUtils.h</a>"
Chris Lattner	261efe9	2003-11-25 01:02:51 +0000	[diff] [blame]	2502	permits use of two very useful replace functions: <tt>ReplaceInstWithValue</tt>
Misha Brukman	13fd15c	2004-01-15 00:14:41 +0000	[diff] [blame]	2503	and <tt>ReplaceInstWithInst</tt>.</p>
				2504
NAKAMURA Takumi	06c6d9a	2011-04-18 01:17:51 +0000	[diff] [blame]	2505	<h5><a name="schanges_deleting">Deleting <tt>Instruction</tt>s</a></h5>
Misha Brukman	13fd15c	2004-01-15 00:14:41 +0000	[diff] [blame]	2506
Chris Lattner	261efe9	2003-11-25 01:02:51 +0000	[diff] [blame]	2507	<ul>
Misha Brukman	13fd15c	2004-01-15 00:14:41 +0000	[diff] [blame]	2508	<li><tt>ReplaceInstWithValue</tt>
				2509
Nick Lewycky	b6d1f39	2008-09-15 06:31:52 +0000	[diff] [blame]	2510	<p>This function replaces all uses of a given instruction with a value,
				2511	and then removes the original instruction. The following example
				2512	illustrates the replacement of the result of a particular
Chris Lattner	5836082	2005-01-17 00:12:04 +0000	[diff] [blame]	2513	<tt>AllocaInst</tt> that allocates memory for a single integer with a null
Misha Brukman	13fd15c	2004-01-15 00:14:41 +0000	[diff] [blame]	2514	pointer to an integer.</p>
				2515
Bill Wendling	3cd5ca6	2006-10-11 06:30:10 +0000	[diff] [blame]	2516	<div class="doc_code">
				2517	<pre>
				2518	AllocaInst* instToReplace = ...;
				2519	BasicBlock::iterator ii(instToReplace);
				2520
				2521	ReplaceInstWithValue(instToReplace->getParent()->getInstList(), ii,
Daniel Dunbar	58c2ac0	2008-10-03 22:17:25 +0000	[diff] [blame]	2522	Constant::getNullValue(PointerType::getUnqual(Type::Int32Ty)));
Bill Wendling	3cd5ca6	2006-10-11 06:30:10 +0000	[diff] [blame]	2523	</pre></div></li>
Misha Brukman	13fd15c	2004-01-15 00:14:41 +0000	[diff] [blame]	2524
				2525	<li><tt>ReplaceInstWithInst</tt>
				2526
				2527	<p>This function replaces a particular instruction with another
Nick Lewycky	b6d1f39	2008-09-15 06:31:52 +0000	[diff] [blame]	2528	instruction, inserting the new instruction into the basic block at the
				2529	location where the old instruction was, and replacing any uses of the old
				2530	instruction with the new instruction. The following example illustrates
				2531	the replacement of one <tt>AllocaInst</tt> with another.</p>
Misha Brukman	13fd15c	2004-01-15 00:14:41 +0000	[diff] [blame]	2532
Bill Wendling	3cd5ca6	2006-10-11 06:30:10 +0000	[diff] [blame]	2533	<div class="doc_code">
				2534	<pre>
				2535	AllocaInst* instToReplace = ...;
				2536	BasicBlock::iterator ii(instToReplace);
				2537
				2538	ReplaceInstWithInst(instToReplace->getParent()->getInstList(), ii,
Nick Lewycky	10d64b9	2007-12-03 01:52:52 +0000	[diff] [blame]	2539	new AllocaInst(Type::Int32Ty, 0, "ptrToReplacedInt"));
Bill Wendling	3cd5ca6	2006-10-11 06:30:10 +0000	[diff] [blame]	2540	</pre></div></li>
Chris Lattner	261efe9	2003-11-25 01:02:51 +0000	[diff] [blame]	2541	</ul>
Misha Brukman	13fd15c	2004-01-15 00:14:41 +0000	[diff] [blame]	2542
				2543	<p><i>Replacing multiple uses of <tt>User</tt>s and <tt>Value</tt>s</i></p>
				2544
				2545	<p>You can use <tt>Value::replaceAllUsesWith</tt> and
				2546	<tt>User::replaceUsesOfWith</tt> to change more than one use at a time. See the
Chris Lattner	0081517	2007-01-04 22:01:45 +0000	[diff] [blame]	2547	doxygen documentation for the <a href="/doxygen/classllvm_1_1Value.html">Value Class</a>
Misha Brukman	384047f	2004-06-03 23:29:12 +0000	[diff] [blame]	2548	and <a href="/doxygen/classllvm_1_1User.html">User Class</a>, respectively, for more
Misha Brukman	13fd15c	2004-01-15 00:14:41 +0000	[diff] [blame]	2549	information.</p>
				2550
				2551	<!-- Value::replaceAllUsesWith User::replaceUsesOfWith Point out:
				2552	include/llvm/Transforms/Utils/ especially BasicBlockUtils.h with:
				2553	ReplaceInstWithValue, ReplaceInstWithInst -->
				2554
				2555	</div>
				2556
Tanya Lattner	b011c66	2007-06-20 18:33:15 +0000	[diff] [blame]	2557	<!--_______________________________________________________________________-->
NAKAMURA Takumi	05d0265	2011-04-18 23:59:50 +0000	[diff] [blame]	2558	<h4>
Tanya Lattner	b011c66	2007-06-20 18:33:15 +0000	[diff] [blame]	2559	<a name="schanges_deletingGV">Deleting <tt>GlobalVariable</tt>s</a>
NAKAMURA Takumi	05d0265	2011-04-18 23:59:50 +0000	[diff] [blame]	2560	</h4>
Tanya Lattner	b011c66	2007-06-20 18:33:15 +0000	[diff] [blame]	2561
NAKAMURA Takumi	f5af6ad	2011-04-23 00:30:22 +0000	[diff] [blame]	2562	<div>
Tanya Lattner	b011c66	2007-06-20 18:33:15 +0000	[diff] [blame]	2563
Tanya Lattner	c5dfcdb	2007-06-20 20:46:37 +0000	[diff] [blame]	2564	<p>Deleting a global variable from a module is just as easy as deleting an
				2565	Instruction. First, you must have a pointer to the global variable that you wish
				2566	to delete. You use this pointer to erase it from its parent, the module.
Tanya Lattner	b011c66	2007-06-20 18:33:15 +0000	[diff] [blame]	2567	For example:</p>
				2568
				2569	<div class="doc_code">
				2570	<pre>
				2571	<a href="#GlobalVariable">GlobalVariable</a> *GV = .. ;
Tanya Lattner	b011c66	2007-06-20 18:33:15 +0000	[diff] [blame]	2572
Tanya Lattner	c5dfcdb	2007-06-20 20:46:37 +0000	[diff] [blame]	2573	GV->eraseFromParent();
Tanya Lattner	b011c66	2007-06-20 18:33:15 +0000	[diff] [blame]	2574	</pre>
				2575	</div>
				2576
				2577	</div>
				2578
NAKAMURA Takumi	f5af6ad	2011-04-23 00:30:22 +0000	[diff] [blame]	2579	</div>
				2580
Jeffrey Yasskin	714257f	2009-04-30 22:33:41 +0000	[diff] [blame]	2581	<!-- ======================================================================= -->
NAKAMURA Takumi	05d0265	2011-04-18 23:59:50 +0000	[diff] [blame]	2582	<h3>
Jeffrey Yasskin	714257f	2009-04-30 22:33:41 +0000	[diff] [blame]	2583	<a name="create_types">How to Create Types</a>
NAKAMURA Takumi	05d0265	2011-04-18 23:59:50 +0000	[diff] [blame]	2584	</h3>
Jeffrey Yasskin	714257f	2009-04-30 22:33:41 +0000	[diff] [blame]	2585
NAKAMURA Takumi	f5af6ad	2011-04-23 00:30:22 +0000	[diff] [blame]	2586	<div>
Jeffrey Yasskin	714257f	2009-04-30 22:33:41 +0000	[diff] [blame]	2587
				2588	<p>In generating IR, you may need some complex types. If you know these types
Misha Brukman	1af789f	2009-05-01 20:40:51 +0000	[diff] [blame]	2589	statically, you can use <tt>TypeBuilder<...>::get()</tt>, defined
Jeffrey Yasskin	714257f	2009-04-30 22:33:41 +0000	[diff] [blame]	2590	in <tt>llvm/Support/TypeBuilder.h</tt>, to retrieve them. <tt>TypeBuilder</tt>
				2591	has two forms depending on whether you're building types for cross-compilation
Misha Brukman	1af789f	2009-05-01 20:40:51 +0000	[diff] [blame]	2592	or native library use. <tt>TypeBuilder<T, true></tt> requires
Jeffrey Yasskin	714257f	2009-04-30 22:33:41 +0000	[diff] [blame]	2593	that <tt>T</tt> be independent of the host environment, meaning that it's built
				2594	out of types from
				2595	the <a href="/doxygen/namespacellvm_1_1types.html"><tt>llvm::types</tt></a>
				2596	namespace and pointers, functions, arrays, etc. built of
Misha Brukman	1af789f	2009-05-01 20:40:51 +0000	[diff] [blame]	2597	those. <tt>TypeBuilder<T, false></tt> additionally allows native C types
Jeffrey Yasskin	714257f	2009-04-30 22:33:41 +0000	[diff] [blame]	2598	whose size may depend on the host compiler. For example,</p>
				2599
				2600	<div class="doc_code">
				2601	<pre>
Misha Brukman	1af789f	2009-05-01 20:40:51 +0000	[diff] [blame]	2602	FunctionType ft = TypeBuilder<types::i<8>(types::i<32>), true>::get();
Jeffrey Yasskin	714257f	2009-04-30 22:33:41 +0000	[diff] [blame]	2603	</pre>
				2604	</div>
				2605
				2606	<p>is easier to read and write than the equivalent</p>
				2607
				2608	<div class="doc_code">
				2609	<pre>
Owen Anderson	5e8c50e	2009-06-16 17:40:28 +0000	[diff] [blame]	2610	std::vector<const Type*> params;
Jeffrey Yasskin	714257f	2009-04-30 22:33:41 +0000	[diff] [blame]	2611	params.push_back(PointerType::getUnqual(Type::Int32Ty));
				2612	FunctionType *ft = FunctionType::get(Type::Int8Ty, params, false);
				2613	</pre>
				2614	</div>
				2615
				2616	<p>See the <a href="/doxygen/TypeBuilder_8h-source.html#l00001">class
				2617	comment</a> for more details.</p>
				2618
				2619	</div>
				2620
NAKAMURA Takumi	f5af6ad	2011-04-23 00:30:22 +0000	[diff] [blame]	2621	</div>
				2622
Chris Lattner	9355b47	2002-09-06 02:50:58 +0000	[diff] [blame]	2623	<!-- *********************************************************************** -->
NAKAMURA Takumi	05d0265	2011-04-18 23:59:50 +0000	[diff] [blame]	2624	<h2>
Owen Anderson	8bc1b3b	2009-06-16 01:17:16 +0000	[diff] [blame]	2625	<a name="threading">Threads and LLVM</a>
NAKAMURA Takumi	05d0265	2011-04-18 23:59:50 +0000	[diff] [blame]	2626	</h2>
Owen Anderson	8bc1b3b	2009-06-16 01:17:16 +0000	[diff] [blame]	2627	<!-- *********************************************************************** -->
				2628
NAKAMURA Takumi	f5af6ad	2011-04-23 00:30:22 +0000	[diff] [blame]	2629	<div>
Owen Anderson	8bc1b3b	2009-06-16 01:17:16 +0000	[diff] [blame]	2630	<p>
				2631	This section describes the interaction of the LLVM APIs with multithreading,
				2632	both on the part of client applications, and in the JIT, in the hosted
				2633	application.
				2634	</p>
				2635
				2636	<p>
				2637	Note that LLVM's support for multithreading is still relatively young. Up
				2638	through version 2.5, the execution of threaded hosted applications was
				2639	supported, but not threaded client access to the APIs. While this use case is
				2640	now supported, clients <em>must</em> adhere to the guidelines specified below to
				2641	ensure proper operation in multithreaded mode.
				2642	</p>
				2643
				2644	<p>
				2645	Note that, on Unix-like platforms, LLVM requires the presence of GCC's atomic
				2646	intrinsics in order to support threaded operation. If you need a
				2647	multhreading-capable LLVM on a platform without a suitably modern system
				2648	compiler, consider compiling LLVM and LLVM-GCC in single-threaded mode, and
				2649	using the resultant compiler to build a copy of LLVM with multithreading
				2650	support.
				2651	</p>
Owen Anderson	8bc1b3b	2009-06-16 01:17:16 +0000	[diff] [blame]	2652
				2653	<!-- ======================================================================= -->
NAKAMURA Takumi	05d0265	2011-04-18 23:59:50 +0000	[diff] [blame]	2654	<h3>
Owen Anderson	1ad70e3	2009-06-16 18:04:19 +0000	[diff] [blame]	2655	<a name="startmultithreaded">Entering and Exiting Multithreaded Mode</a>
NAKAMURA Takumi	05d0265	2011-04-18 23:59:50 +0000	[diff] [blame]	2656	</h3>
Owen Anderson	8bc1b3b	2009-06-16 01:17:16 +0000	[diff] [blame]	2657
NAKAMURA Takumi	f5af6ad	2011-04-23 00:30:22 +0000	[diff] [blame]	2658	<div>
Owen Anderson	8bc1b3b	2009-06-16 01:17:16 +0000	[diff] [blame]	2659
				2660	<p>
				2661	In order to properly protect its internal data structures while avoiding
Owen Anderson	1ad70e3	2009-06-16 18:04:19 +0000	[diff] [blame]	2662	excessive locking overhead in the single-threaded case, the LLVM must intialize
				2663	certain data structures necessary to provide guards around its internals. To do
				2664	so, the client program must invoke <tt>llvm_start_multithreaded()</tt> before
				2665	making any concurrent LLVM API calls. To subsequently tear down these
				2666	structures, use the <tt>llvm_stop_multithreaded()</tt> call. You can also use
				2667	the <tt>llvm_is_multithreaded()</tt> call to check the status of multithreaded
				2668	mode.
Owen Anderson	8bc1b3b	2009-06-16 01:17:16 +0000	[diff] [blame]	2669	</p>
				2670
				2671	<p>
Owen Anderson	1ad70e3	2009-06-16 18:04:19 +0000	[diff] [blame]	2672	Note that both of these calls must be made <em>in isolation</em>. That is to
				2673	say that no other LLVM API calls may be executing at any time during the
				2674	execution of <tt>llvm_start_multithreaded()</tt> or <tt>llvm_stop_multithreaded
				2675	</tt>. It's is the client's responsibility to enforce this isolation.
				2676	</p>
				2677
				2678	<p>
				2679	The return value of <tt>llvm_start_multithreaded()</tt> indicates the success or
				2680	failure of the initialization. Failure typically indicates that your copy of
				2681	LLVM was built without multithreading support, typically because GCC atomic
				2682	intrinsics were not found in your system compiler. In this case, the LLVM API
				2683	will not be safe for concurrent calls. However, it <em>will</em> be safe for
Jeffrey Yasskin	01eba39	2010-01-29 19:10:38 +0000	[diff] [blame]	2684	hosting threaded applications in the JIT, though <a href="#jitthreading">care
				2685	must be taken</a> to ensure that side exits and the like do not accidentally
				2686	result in concurrent LLVM API calls.
Owen Anderson	8bc1b3b	2009-06-16 01:17:16 +0000	[diff] [blame]	2687	</p>
				2688	</div>
				2689
				2690	<!-- ======================================================================= -->
NAKAMURA Takumi	05d0265	2011-04-18 23:59:50 +0000	[diff] [blame]	2691	<h3>
Owen Anderson	8bc1b3b	2009-06-16 01:17:16 +0000	[diff] [blame]	2692	<a name="shutdown">Ending Execution with <tt>llvm_shutdown()</tt></a>
NAKAMURA Takumi	05d0265	2011-04-18 23:59:50 +0000	[diff] [blame]	2693	</h3>
Owen Anderson	8bc1b3b	2009-06-16 01:17:16 +0000	[diff] [blame]	2694
NAKAMURA Takumi	f5af6ad	2011-04-23 00:30:22 +0000	[diff] [blame]	2695	<div>
Owen Anderson	8bc1b3b	2009-06-16 01:17:16 +0000	[diff] [blame]	2696	<p>
				2697	When you are done using the LLVM APIs, you should call <tt>llvm_shutdown()</tt>
Owen Anderson	1ad70e3	2009-06-16 18:04:19 +0000	[diff] [blame]	2698	to deallocate memory used for internal structures. This will also invoke
				2699	<tt>llvm_stop_multithreaded()</tt> if LLVM is operating in multithreaded mode.
				2700	As such, <tt>llvm_shutdown()</tt> requires the same isolation guarantees as
				2701	<tt>llvm_stop_multithreaded()</tt>.
Owen Anderson	8bc1b3b	2009-06-16 01:17:16 +0000	[diff] [blame]	2702	</p>
				2703
				2704	<p>
				2705	Note that, if you use scope-based shutdown, you can use the
				2706	<tt>llvm_shutdown_obj</tt> class, which calls <tt>llvm_shutdown()</tt> in its
				2707	destructor.
				2708	</div>
				2709
				2710	<!-- ======================================================================= -->
NAKAMURA Takumi	05d0265	2011-04-18 23:59:50 +0000	[diff] [blame]	2711	<h3>
Owen Anderson	8bc1b3b	2009-06-16 01:17:16 +0000	[diff] [blame]	2712	<a name="managedstatic">Lazy Initialization with <tt>ManagedStatic</tt></a>
NAKAMURA Takumi	05d0265	2011-04-18 23:59:50 +0000	[diff] [blame]	2713	</h3>
Owen Anderson	8bc1b3b	2009-06-16 01:17:16 +0000	[diff] [blame]	2714
NAKAMURA Takumi	f5af6ad	2011-04-23 00:30:22 +0000	[diff] [blame]	2715	<div>
Owen Anderson	8bc1b3b	2009-06-16 01:17:16 +0000	[diff] [blame]	2716	<p>
				2717	<tt>ManagedStatic</tt> is a utility class in LLVM used to implement static
				2718	initialization of static resources, such as the global type tables. Before the
				2719	invocation of <tt>llvm_shutdown()</tt>, it implements a simple lazy
				2720	initialization scheme. Once <tt>llvm_start_multithreaded()</tt> returns,
				2721	however, it uses double-checked locking to implement thread-safe lazy
				2722	initialization.
				2723	</p>
				2724
				2725	<p>
				2726	Note that, because no other threads are allowed to issue LLVM API calls before
				2727	<tt>llvm_start_multithreaded()</tt> returns, it is possible to have
				2728	<tt>ManagedStatic</tt>s of <tt>llvm::sys::Mutex</tt>s.
				2729	</p>
Owen Anderson	1ad70e3	2009-06-16 18:04:19 +0000	[diff] [blame]	2730
				2731	<p>
				2732	The <tt>llvm_acquire_global_lock()</tt> and <tt>llvm_release_global_lock</tt>
				2733	APIs provide access to the global lock used to implement the double-checked
				2734	locking for lazy initialization. These should only be used internally to LLVM,
				2735	and only if you know what you're doing!
				2736	</p>
Owen Anderson	8bc1b3b	2009-06-16 01:17:16 +0000	[diff] [blame]	2737	</div>
				2738
Owen Anderson	e0c951a	2009-08-19 17:58:52 +0000	[diff] [blame]	2739	<!-- ======================================================================= -->
NAKAMURA Takumi	05d0265	2011-04-18 23:59:50 +0000	[diff] [blame]	2740	<h3>
Owen Anderson	e0c951a	2009-08-19 17:58:52 +0000	[diff] [blame]	2741	<a name="llvmcontext">Achieving Isolation with <tt>LLVMContext</tt></a>
NAKAMURA Takumi	05d0265	2011-04-18 23:59:50 +0000	[diff] [blame]	2742	</h3>
Owen Anderson	e0c951a	2009-08-19 17:58:52 +0000	[diff] [blame]	2743
NAKAMURA Takumi	f5af6ad	2011-04-23 00:30:22 +0000	[diff] [blame]	2744	<div>
Owen Anderson	e0c951a	2009-08-19 17:58:52 +0000	[diff] [blame]	2745	<p>
				2746	<tt>LLVMContext</tt> is an opaque class in the LLVM API which clients can use
				2747	to operate multiple, isolated instances of LLVM concurrently within the same
				2748	address space. For instance, in a hypothetical compile-server, the compilation
				2749	of an individual translation unit is conceptually independent from all the
				2750	others, and it would be desirable to be able to compile incoming translation
				2751	units concurrently on independent server threads. Fortunately,
				2752	<tt>LLVMContext</tt> exists to enable just this kind of scenario!
				2753	</p>
				2754
				2755	<p>
				2756	Conceptually, <tt>LLVMContext</tt> provides isolation. Every LLVM entity
				2757	(<tt>Module</tt>s, <tt>Value</tt>s, <tt>Type</tt>s, <tt>Constant</tt>s, etc.)
Chris Lattner	38eee3c	2009-08-20 03:10:14 +0000	[diff] [blame]	2758	in LLVM's in-memory IR belongs to an <tt>LLVMContext</tt>. Entities in
Owen Anderson	e0c951a	2009-08-19 17:58:52 +0000	[diff] [blame]	2759	different contexts <em>cannot</em> interact with each other: <tt>Module</tt>s in
				2760	different contexts cannot be linked together, <tt>Function</tt>s cannot be added
				2761	to <tt>Module</tt>s in different contexts, etc. What this means is that is is
				2762	safe to compile on multiple threads simultaneously, as long as no two threads
				2763	operate on entities within the same context.
				2764	</p>
				2765
				2766	<p>
				2767	In practice, very few places in the API require the explicit specification of a
				2768	<tt>LLVMContext</tt>, other than the <tt>Type</tt> creation/lookup APIs.
				2769	Because every <tt>Type</tt> carries a reference to its owning context, most
				2770	other entities can determine what context they belong to by looking at their
				2771	own <tt>Type</tt>. If you are adding new entities to LLVM IR, please try to
				2772	maintain this interface design.
				2773	</p>
				2774
				2775	<p>
				2776	For clients that do <em>not</em> require the benefits of isolation, LLVM
				2777	provides a convenience API <tt>getGlobalContext()</tt>. This returns a global,
				2778	lazily initialized <tt>LLVMContext</tt> that may be used in situations where
				2779	isolation is not a concern.
				2780	</p>
				2781	</div>
				2782
Jeffrey Yasskin	01eba39	2010-01-29 19:10:38 +0000	[diff] [blame]	2783	<!-- ======================================================================= -->
NAKAMURA Takumi	05d0265	2011-04-18 23:59:50 +0000	[diff] [blame]	2784	<h3>
Jeffrey Yasskin	01eba39	2010-01-29 19:10:38 +0000	[diff] [blame]	2785	<a name="jitthreading">Threads and the JIT</a>
NAKAMURA Takumi	05d0265	2011-04-18 23:59:50 +0000	[diff] [blame]	2786	</h3>
Jeffrey Yasskin	01eba39	2010-01-29 19:10:38 +0000	[diff] [blame]	2787
NAKAMURA Takumi	f5af6ad	2011-04-23 00:30:22 +0000	[diff] [blame]	2788	<div>
Jeffrey Yasskin	01eba39	2010-01-29 19:10:38 +0000	[diff] [blame]	2789	<p>
				2790	LLVM's "eager" JIT compiler is safe to use in threaded programs. Multiple
				2791	threads can call <tt>ExecutionEngine::getPointerToFunction()</tt> or
				2792	<tt>ExecutionEngine::runFunction()</tt> concurrently, and multiple threads can
				2793	run code output by the JIT concurrently. The user must still ensure that only
				2794	one thread accesses IR in a given <tt>LLVMContext</tt> while another thread
				2795	might be modifying it. One way to do that is to always hold the JIT lock while
				2796	accessing IR outside the JIT (the JIT <em>modifies</em> the IR by adding
				2797	<tt>CallbackVH</tt>s). Another way is to only
				2798	call <tt>getPointerToFunction()</tt> from the <tt>LLVMContext</tt>'s thread.
				2799	</p>
				2800
				2801	<p>When the JIT is configured to compile lazily (using
				2802	<tt>ExecutionEngine::DisableLazyCompilation(false)</tt>), there is currently a
				2803	<a href="http://llvm.org/bugs/show_bug.cgi?id=5184">race condition</a> in
				2804	updating call sites after a function is lazily-jitted. It's still possible to
				2805	use the lazy JIT in a threaded program if you ensure that only one thread at a
				2806	time can call any particular lazy stub and that the JIT lock guards any IR
				2807	access, but we suggest using only the eager JIT in threaded programs.
				2808	</p>
				2809	</div>
				2810
NAKAMURA Takumi	f5af6ad	2011-04-23 00:30:22 +0000	[diff] [blame]	2811	</div>
				2812
Owen Anderson	8bc1b3b	2009-06-16 01:17:16 +0000	[diff] [blame]	2813	<!-- *********************************************************************** -->
NAKAMURA Takumi	05d0265	2011-04-18 23:59:50 +0000	[diff] [blame]	2814	<h2>
Chris Lattner	d9d6e10	2005-04-23 16:10:52 +0000	[diff] [blame]	2815	<a name="advanced">Advanced Topics</a>
NAKAMURA Takumi	05d0265	2011-04-18 23:59:50 +0000	[diff] [blame]	2816	</h2>
Chris Lattner	d9d6e10	2005-04-23 16:10:52 +0000	[diff] [blame]	2817	<!-- *********************************************************************** -->
				2818
NAKAMURA Takumi	f5af6ad	2011-04-23 00:30:22 +0000	[diff] [blame]	2819	<div>
Chris Lattner	f1b200b	2005-04-23 17:27:36 +0000	[diff] [blame]	2820	<p>
				2821	This section describes some of the advanced or obscure API's that most clients
				2822	do not need to be aware of. These API's tend manage the inner workings of the
				2823	LLVM system, and only need to be accessed in unusual circumstances.
				2824	</p>
Chris Lattner	d9d6e10	2005-04-23 16:10:52 +0000	[diff] [blame]	2825
Chris Lattner	1afcace	2011-07-09 17:41:24 +0000	[diff] [blame]	2826
Chris Lattner	f1b200b	2005-04-23 17:27:36 +0000	[diff] [blame]	2827	<!-- ======================================================================= -->
NAKAMURA Takumi	05d0265	2011-04-18 23:59:50 +0000	[diff] [blame]	2828	<h3>
Chris Lattner	1afcace	2011-07-09 17:41:24 +0000	[diff] [blame]	2829	<a name="SymbolTable">The <tt>ValueSymbolTable</tt> class</a>
NAKAMURA Takumi	05d0265	2011-04-18 23:59:50 +0000	[diff] [blame]	2830	</h3>
Chris Lattner	f1b200b	2005-04-23 17:27:36 +0000	[diff] [blame]	2831
NAKAMURA Takumi	f5af6ad	2011-04-23 00:30:22 +0000	[diff] [blame]	2832	<div>
Chris Lattner	263a98e	2007-02-16 04:37:31 +0000	[diff] [blame]	2833	<p>The <tt><a href="http://llvm.org/doxygen/classllvm_1_1ValueSymbolTable.html">
				2834	ValueSymbolTable</a></tt> class provides a symbol table that the <a
Chris Lattner	d9d6e10	2005-04-23 16:10:52 +0000	[diff] [blame]	2835	href="#Function"><tt>Function</tt></a> and <a href="#Module">
Chris Lattner	263a98e	2007-02-16 04:37:31 +0000	[diff] [blame]	2836	<tt>Module</tt></a> classes use for naming value definitions. The symbol table
				2837	can provide a name for any <a href="#Value"><tt>Value</tt></a>.
Chris Lattner	1afcace	2011-07-09 17:41:24 +0000	[diff] [blame]	2838	</p>
Chris Lattner	d9d6e10	2005-04-23 16:10:52 +0000	[diff] [blame]	2839
Reid Spencer	a636224	2007-01-07 00:41:39 +0000	[diff] [blame]	2840	<p>Note that the <tt>SymbolTable</tt> class should not be directly accessed
				2841	by most clients. It should only be used when iteration over the symbol table
				2842	names themselves are required, which is very special purpose. Note that not
				2843	all LLVM
Gabor Greif	e98fc27	2008-06-16 21:06:12 +0000	[diff] [blame]	2844	<tt><a href="#Value">Value</a></tt>s have names, and those without names (i.e. they have
Chris Lattner	d9d6e10	2005-04-23 16:10:52 +0000	[diff] [blame]	2845	an empty name) do not exist in the symbol table.
				2846	</p>
				2847
Chris Lattner	1afcace	2011-07-09 17:41:24 +0000	[diff] [blame]	2848	<p>Symbol tables support iteration over the values in the symbol
Chris Lattner	263a98e	2007-02-16 04:37:31 +0000	[diff] [blame]	2849	table with <tt>begin/end/iterator</tt> and supports querying to see if a
				2850	specific name is in the symbol table (with <tt>lookup</tt>). The
				2851	<tt>ValueSymbolTable</tt> class exposes no public mutator methods, instead,
				2852	simply call <tt>setName</tt> on a value, which will autoinsert it into the
Chris Lattner	1afcace	2011-07-09 17:41:24 +0000	[diff] [blame]	2853	appropriate symbol table.</p>
Chris Lattner	d9d6e10	2005-04-23 16:10:52 +0000	[diff] [blame]	2854
Chris Lattner	d9d6e10	2005-04-23 16:10:52 +0000	[diff] [blame]	2855	</div>
				2856
				2857
				2858
Gabor Greif	e98fc27	2008-06-16 21:06:12 +0000	[diff] [blame]	2859	<!-- ======================================================================= -->
NAKAMURA Takumi	05d0265	2011-04-18 23:59:50 +0000	[diff] [blame]	2860	<h3>
Gabor Greif	e98fc27	2008-06-16 21:06:12 +0000	[diff] [blame]	2861	<a name="UserLayout">The <tt>User</tt> and owned <tt>Use</tt> classes' memory layout</a>
NAKAMURA Takumi	05d0265	2011-04-18 23:59:50 +0000	[diff] [blame]	2862	</h3>
Gabor Greif	e98fc27	2008-06-16 21:06:12 +0000	[diff] [blame]	2863
NAKAMURA Takumi	f5af6ad	2011-04-23 00:30:22 +0000	[diff] [blame]	2864	<div>
Gabor Greif	e98fc27	2008-06-16 21:06:12 +0000	[diff] [blame]	2865	<p>The <tt><a href="http://llvm.org/doxygen/classllvm_1_1User.html">
Gabor Greif	fd095b6	2009-01-05 16:05:32 +0000	[diff] [blame]	2866	User</a></tt> class provides a basis for expressing the ownership of <tt>User</tt>
Gabor Greif	e98fc27	2008-06-16 21:06:12 +0000	[diff] [blame]	2867	towards other <tt><a href="http://llvm.org/doxygen/classllvm_1_1Value.html">
				2868	Value</a></tt>s. The <tt><a href="http://llvm.org/doxygen/classllvm_1_1Use.html">
Gabor Greif	dfed118	2008-06-18 13:44:57 +0000	[diff] [blame]	2869	Use</a></tt> helper class is employed to do the bookkeeping and to facilitate <i>O(1)</i>
Gabor Greif	e98fc27	2008-06-16 21:06:12 +0000	[diff] [blame]	2870	addition and removal.</p>
				2871
Gabor Greif	dfed118	2008-06-18 13:44:57 +0000	[diff] [blame]	2872	<!-- ______________________________________________________________________ -->
NAKAMURA Takumi	05d0265	2011-04-18 23:59:50 +0000	[diff] [blame]	2873	<h4>
				2874	<a name="Use2User">
				2875	Interaction and relationship between <tt>User</tt> and <tt>Use</tt> objects
				2876	</a>
				2877	</h4>
Gabor Greif	e98fc27	2008-06-16 21:06:12 +0000	[diff] [blame]	2878
NAKAMURA Takumi	f5af6ad	2011-04-23 00:30:22 +0000	[diff] [blame]	2879	<div>
Gabor Greif	dfed118	2008-06-18 13:44:57 +0000	[diff] [blame]	2880	<p>
				2881	A subclass of <tt>User</tt> can choose between incorporating its <tt>Use</tt> objects
Gabor Greif	e98fc27	2008-06-16 21:06:12 +0000	[diff] [blame]	2882	or refer to them out-of-line by means of a pointer. A mixed variant
Gabor Greif	dfed118	2008-06-18 13:44:57 +0000	[diff] [blame]	2883	(some <tt>Use</tt>s inline others hung off) is impractical and breaks the invariant
				2884	that the <tt>Use</tt> objects belonging to the same <tt>User</tt> form a contiguous array.
				2885	</p>
Gabor Greif	e98fc27	2008-06-16 21:06:12 +0000	[diff] [blame]	2886
Gabor Greif	dfed118	2008-06-18 13:44:57 +0000	[diff] [blame]	2887	<p>
				2888	We have 2 different layouts in the <tt>User</tt> (sub)classes:
				2889	<ul>
				2890	<li><p>Layout a)
				2891	The <tt>Use</tt> object(s) are inside (resp. at fixed offset) of the <tt>User</tt>
				2892	object and there are a fixed number of them.</p>
Gabor Greif	e98fc27	2008-06-16 21:06:12 +0000	[diff] [blame]	2893
Gabor Greif	dfed118	2008-06-18 13:44:57 +0000	[diff] [blame]	2894	<li><p>Layout b)
				2895	The <tt>Use</tt> object(s) are referenced by a pointer to an
				2896	array from the <tt>User</tt> object and there may be a variable
				2897	number of them.</p>
				2898	</ul>
				2899	<p>
Gabor Greif	d41720a	2008-06-25 00:10:22 +0000	[diff] [blame]	2900	As of v2.4 each layout still possesses a direct pointer to the
Gabor Greif	dfed118	2008-06-18 13:44:57 +0000	[diff] [blame]	2901	start of the array of <tt>Use</tt>s. Though not mandatory for layout a),
Gabor Greif	e98fc27	2008-06-16 21:06:12 +0000	[diff] [blame]	2902	we stick to this redundancy for the sake of simplicity.
Gabor Greif	d41720a	2008-06-25 00:10:22 +0000	[diff] [blame]	2903	The <tt>User</tt> object also stores the number of <tt>Use</tt> objects it
Gabor Greif	e98fc27	2008-06-16 21:06:12 +0000	[diff] [blame]	2904	has. (Theoretically this information can also be calculated
Gabor Greif	dfed118	2008-06-18 13:44:57 +0000	[diff] [blame]	2905	given the scheme presented below.)</p>
				2906	<p>
				2907	Special forms of allocation operators (<tt>operator new</tt>)
Gabor Greif	d41720a	2008-06-25 00:10:22 +0000	[diff] [blame]	2908	enforce the following memory layouts:</p>
Gabor Greif	e98fc27	2008-06-16 21:06:12 +0000	[diff] [blame]	2909
Gabor Greif	dfed118	2008-06-18 13:44:57 +0000	[diff] [blame]	2910	<ul>
Gabor Greif	d41720a	2008-06-25 00:10:22 +0000	[diff] [blame]	2911	<li><p>Layout a) is modelled by prepending the <tt>User</tt> object by the <tt>Use[]</tt> array.</p>
Gabor Greif	e98fc27	2008-06-16 21:06:12 +0000	[diff] [blame]	2912
Gabor Greif	dfed118	2008-06-18 13:44:57 +0000	[diff] [blame]	2913	<pre>
				2914	...---.---.---.---.-------...
				2915	\| P \| P \| P \| P \| User
				2916	'''---'---'---'---'-------'''
				2917	</pre>
Gabor Greif	e98fc27	2008-06-16 21:06:12 +0000	[diff] [blame]	2918
Gabor Greif	d41720a	2008-06-25 00:10:22 +0000	[diff] [blame]	2919	<li><p>Layout b) is modelled by pointing at the <tt>Use[]</tt> array.</p>
Gabor Greif	dfed118	2008-06-18 13:44:57 +0000	[diff] [blame]	2920	<pre>
				2921	.-------...
				2922	\| User
				2923	'-------'''
				2924	\|
				2925	v
				2926	.---.---.---.---...
				2927	\| P \| P \| P \| P \|
				2928	'---'---'---'---'''
				2929	</pre>
				2930	</ul>
				2931	<i>(In the above figures '<tt>P</tt>' stands for the <tt>Use**</tt> that
				2932	is stored in each <tt>Use</tt> object in the member <tt>Use::Prev</tt>)</i>
Gabor Greif	e98fc27	2008-06-16 21:06:12 +0000	[diff] [blame]	2933
NAKAMURA Takumi	f5af6ad	2011-04-23 00:30:22 +0000	[diff] [blame]	2934	</div>
				2935
Gabor Greif	dfed118	2008-06-18 13:44:57 +0000	[diff] [blame]	2936	<!-- ______________________________________________________________________ -->
NAKAMURA Takumi	05d0265	2011-04-18 23:59:50 +0000	[diff] [blame]	2937	<h4>
Gabor Greif	fd095b6	2009-01-05 16:05:32 +0000	[diff] [blame]	2938	<a name="Waymarking">The waymarking algorithm</a>
NAKAMURA Takumi	05d0265	2011-04-18 23:59:50 +0000	[diff] [blame]	2939	</h4>
Gabor Greif	e98fc27	2008-06-16 21:06:12 +0000	[diff] [blame]	2940
NAKAMURA Takumi	f5af6ad	2011-04-23 00:30:22 +0000	[diff] [blame]	2941	<div>
Gabor Greif	dfed118	2008-06-18 13:44:57 +0000	[diff] [blame]	2942	<p>
Gabor Greif	d41720a	2008-06-25 00:10:22 +0000	[diff] [blame]	2943	Since the <tt>Use</tt> objects are deprived of the direct (back)pointer to
Gabor Greif	dfed118	2008-06-18 13:44:57 +0000	[diff] [blame]	2944	their <tt>User</tt> objects, there must be a fast and exact method to
				2945	recover it. This is accomplished by the following scheme:</p>
Gabor Greif	e98fc27	2008-06-16 21:06:12 +0000	[diff] [blame]	2946
Gabor Greif	d41720a	2008-06-25 00:10:22 +0000	[diff] [blame]	2947	A bit-encoding in the 2 LSBits (least significant bits) of the <tt>Use::Prev</tt> allows to find the
Gabor Greif	dfed118	2008-06-18 13:44:57 +0000	[diff] [blame]	2948	start of the <tt>User</tt> object:
				2949	<ul>
				2950	<li><tt>00</tt> —> binary digit 0</li>
				2951	<li><tt>01</tt> —> binary digit 1</li>
				2952	<li><tt>10</tt> —> stop and calculate (<tt>s</tt>)</li>
				2953	<li><tt>11</tt> —> full stop (<tt>S</tt>)</li>
				2954	</ul>
				2955	<p>
				2956	Given a <tt>Use*</tt>, all we have to do is to walk till we get
				2957	a stop and we either have a <tt>User</tt> immediately behind or
Gabor Greif	e98fc27	2008-06-16 21:06:12 +0000	[diff] [blame]	2958	we have to walk to the next stop picking up digits
Gabor Greif	dfed118	2008-06-18 13:44:57 +0000	[diff] [blame]	2959	and calculating the offset:</p>
				2960	<pre>
Gabor Greif	e98fc27	2008-06-16 21:06:12 +0000	[diff] [blame]	2961	.---.---.---.---.---.---.---.---.---.---.---.---.---.---.---.---.----------------
				2962	\| 1 \| s \| 1 \| 0 \| 1 \| 0 \| s \| 1 \| 1 \| 0 \| s \| 1 \| 1 \| s \| 1 \| S \| User (or User*)
				2963	'---'---'---'---'---'---'---'---'---'---'---'---'---'---'---'---'----------------
				2964	\|+15 \|+10 \|+6 \|+3 \|+1
				2965	\| \| \| \| \|__>
				2966	\| \| \| \|__________>
				2967	\| \| \|______________________>
				2968	\| \|______________________________________>
				2969	\|__________________________________________________________>
Gabor Greif	dfed118	2008-06-18 13:44:57 +0000	[diff] [blame]	2970	</pre>
				2971	<p>
Gabor Greif	e98fc27	2008-06-16 21:06:12 +0000	[diff] [blame]	2972	Only the significant number of bits need to be stored between the
Gabor Greif	dfed118	2008-06-18 13:44:57 +0000	[diff] [blame]	2973	stops, so that the <i>worst case is 20 memory accesses</i> when there are
				2974	1000 <tt>Use</tt> objects associated with a <tt>User</tt>.</p>
Gabor Greif	e98fc27	2008-06-16 21:06:12 +0000	[diff] [blame]	2975
NAKAMURA Takumi	f5af6ad	2011-04-23 00:30:22 +0000	[diff] [blame]	2976	</div>
				2977
Gabor Greif	dfed118	2008-06-18 13:44:57 +0000	[diff] [blame]	2978	<!-- ______________________________________________________________________ -->
NAKAMURA Takumi	05d0265	2011-04-18 23:59:50 +0000	[diff] [blame]	2979	<h4>
Gabor Greif	fd095b6	2009-01-05 16:05:32 +0000	[diff] [blame]	2980	<a name="ReferenceImpl">Reference implementation</a>
NAKAMURA Takumi	05d0265	2011-04-18 23:59:50 +0000	[diff] [blame]	2981	</h4>
Gabor Greif	e98fc27	2008-06-16 21:06:12 +0000	[diff] [blame]	2982
NAKAMURA Takumi	f5af6ad	2011-04-23 00:30:22 +0000	[diff] [blame]	2983	<div>
Gabor Greif	dfed118	2008-06-18 13:44:57 +0000	[diff] [blame]	2984	<p>
				2985	The following literate Haskell fragment demonstrates the concept:</p>
Gabor Greif	dfed118	2008-06-18 13:44:57 +0000	[diff] [blame]	2986
				2987	<div class="doc_code">
				2988	<pre>
Gabor Greif	e98fc27	2008-06-16 21:06:12 +0000	[diff] [blame]	2989	> import Test.QuickCheck
				2990	>
				2991	> digits :: Int -> [Char] -> [Char]
				2992	> digits 0 acc = '0' : acc
				2993	> digits 1 acc = '1' : acc
				2994	> digits n acc = digits (n `div` 2) $ digits (n `mod` 2) acc
				2995	>
				2996	> dist :: Int -> [Char] -> [Char]
				2997	> dist 0 [] = ['S']
				2998	> dist 0 acc = acc
				2999	> dist 1 acc = let r = dist 0 acc in 's' : digits (length r) r
				3000	> dist n acc = dist (n - 1) $ dist 1 acc
				3001	>
				3002	> takeLast n ss = reverse $ take n $ reverse ss
				3003	>
				3004	> test = takeLast 40 $ dist 20 []
				3005	>
Gabor Greif	dfed118	2008-06-18 13:44:57 +0000	[diff] [blame]	3006	</pre>
				3007	</div>
				3008	<p>
				3009	Printing <test> gives: <tt>"1s100000s11010s10100s1111s1010s110s11s1S"</tt></p>
				3010	<p>
				3011	The reverse algorithm computes the length of the string just by examining
				3012	a certain prefix:</p>
Gabor Greif	e98fc27	2008-06-16 21:06:12 +0000	[diff] [blame]	3013
Gabor Greif	dfed118	2008-06-18 13:44:57 +0000	[diff] [blame]	3014	<div class="doc_code">
				3015	<pre>
Gabor Greif	e98fc27	2008-06-16 21:06:12 +0000	[diff] [blame]	3016	> pref :: [Char] -> Int
				3017	> pref "S" = 1
				3018	> pref ('s':'1':rest) = decode 2 1 rest
				3019	> pref (_:rest) = 1 + pref rest
				3020	>
				3021	> decode walk acc ('0':rest) = decode (walk + 1) (acc * 2) rest
				3022	> decode walk acc ('1':rest) = decode (walk + 1) (acc * 2 + 1) rest
				3023	> decode walk acc _ = walk + acc
				3024	>
Gabor Greif	dfed118	2008-06-18 13:44:57 +0000	[diff] [blame]	3025	</pre>
				3026	</div>
				3027	<p>
				3028	Now, as expected, printing <pref test> gives <tt>40</tt>.</p>
				3029	<p>
				3030	We can <i>quickCheck</i> this with following property:</p>
Gabor Greif	e98fc27	2008-06-16 21:06:12 +0000	[diff] [blame]	3031
Gabor Greif	dfed118	2008-06-18 13:44:57 +0000	[diff] [blame]	3032	<div class="doc_code">
				3033	<pre>
Gabor Greif	e98fc27	2008-06-16 21:06:12 +0000	[diff] [blame]	3034	> testcase = dist 2000 []
				3035	> testcaseLength = length testcase
				3036	>
				3037	> identityProp n = n > 0 && n <= testcaseLength ==> length arr == pref arr
				3038	> where arr = takeLast n testcase
Gabor Greif	dfed118	2008-06-18 13:44:57 +0000	[diff] [blame]	3039	>
				3040	</pre>
				3041	</div>
				3042	<p>
				3043	As expected <quickCheck identityProp> gives:</p>
Gabor Greif	e98fc27	2008-06-16 21:06:12 +0000	[diff] [blame]	3044
Gabor Greif	dfed118	2008-06-18 13:44:57 +0000	[diff] [blame]	3045	<pre>
Gabor Greif	e98fc27	2008-06-16 21:06:12 +0000	[diff] [blame]	3046	*Main> quickCheck identityProp
				3047	OK, passed 100 tests.
Gabor Greif	dfed118	2008-06-18 13:44:57 +0000	[diff] [blame]	3048	</pre>
				3049	<p>
				3050	Let's be a bit more exhaustive:</p>
Gabor Greif	e98fc27	2008-06-16 21:06:12 +0000	[diff] [blame]	3051
Gabor Greif	dfed118	2008-06-18 13:44:57 +0000	[diff] [blame]	3052	<div class="doc_code">
				3053	<pre>
Gabor Greif	e98fc27	2008-06-16 21:06:12 +0000	[diff] [blame]	3054	>
				3055	> deepCheck p = check (defaultConfig { configMaxTest = 500 }) p
				3056	>
Gabor Greif	dfed118	2008-06-18 13:44:57 +0000	[diff] [blame]	3057	</pre>
				3058	</div>
				3059	<p>
				3060	And here is the result of <deepCheck identityProp>:</p>
Gabor Greif	e98fc27	2008-06-16 21:06:12 +0000	[diff] [blame]	3061
Gabor Greif	dfed118	2008-06-18 13:44:57 +0000	[diff] [blame]	3062	<pre>
Gabor Greif	e98fc27	2008-06-16 21:06:12 +0000	[diff] [blame]	3063	*Main> deepCheck identityProp
				3064	OK, passed 500 tests.
Gabor Greif	e98fc27	2008-06-16 21:06:12 +0000	[diff] [blame]	3065	</pre>
				3066
NAKAMURA Takumi	f5af6ad	2011-04-23 00:30:22 +0000	[diff] [blame]	3067	</div>
				3068
Gabor Greif	dfed118	2008-06-18 13:44:57 +0000	[diff] [blame]	3069	<!-- ______________________________________________________________________ -->
NAKAMURA Takumi	05d0265	2011-04-18 23:59:50 +0000	[diff] [blame]	3070	<h4>
Gabor Greif	fd095b6	2009-01-05 16:05:32 +0000	[diff] [blame]	3071	<a name="Tagging">Tagging considerations</a>
NAKAMURA Takumi	05d0265	2011-04-18 23:59:50 +0000	[diff] [blame]	3072	</h4>
Gabor Greif	dfed118	2008-06-18 13:44:57 +0000	[diff] [blame]	3073
NAKAMURA Takumi	f5af6ad	2011-04-23 00:30:22 +0000	[diff] [blame]	3074	<div>
				3075
Gabor Greif	dfed118	2008-06-18 13:44:57 +0000	[diff] [blame]	3076	<p>
				3077	To maintain the invariant that the 2 LSBits of each <tt>Use**</tt> in <tt>Use</tt>
				3078	never change after being set up, setters of <tt>Use::Prev</tt> must re-tag the
				3079	new <tt>Use**</tt> on every modification. Accordingly getters must strip the
				3080	tag bits.</p>
				3081	<p>
Gabor Greif	d41720a	2008-06-25 00:10:22 +0000	[diff] [blame]	3082	For layout b) instead of the <tt>User</tt> we find a pointer (<tt>User*</tt> with LSBit set).
				3083	Following this pointer brings us to the <tt>User</tt>. A portable trick ensures
				3084	that the first bytes of <tt>User</tt> (if interpreted as a pointer) never has
Gabor Greif	fd095b6	2009-01-05 16:05:32 +0000	[diff] [blame]	3085	the LSBit set. (Portability is relying on the fact that all known compilers place the
				3086	<tt>vptr</tt> in the first word of the instances.)</p>
Gabor Greif	dfed118	2008-06-18 13:44:57 +0000	[diff] [blame]	3087
Gabor Greif	e98fc27	2008-06-16 21:06:12 +0000	[diff] [blame]	3088	</div>
				3089
NAKAMURA Takumi	f5af6ad	2011-04-23 00:30:22 +0000	[diff] [blame]	3090	</div>
				3091
				3092	</div>
				3093
				3094	<!-- *********************************************************************** -->
NAKAMURA Takumi	05d0265	2011-04-18 23:59:50 +0000	[diff] [blame]	3095	<h2>
Misha Brukman	13fd15c	2004-01-15 00:14:41 +0000	[diff] [blame]	3096	<a name="coreclasses">The Core LLVM Class Hierarchy Reference </a>
NAKAMURA Takumi	05d0265	2011-04-18 23:59:50 +0000	[diff] [blame]	3097	</h2>
Misha Brukman	13fd15c	2004-01-15 00:14:41 +0000	[diff] [blame]	3098	<!-- *********************************************************************** -->
				3099
NAKAMURA Takumi	f5af6ad	2011-04-23 00:30:22 +0000	[diff] [blame]	3100	<div>
Reid Spencer	303c4b4	2007-01-12 17:26:25 +0000	[diff] [blame]	3101	<p><tt>#include "<a href="/doxygen/Type_8h-source.html">llvm/Type.h</a>"</tt>
				3102	<br>doxygen info: <a href="/doxygen/classllvm_1_1Type.html">Type Class</a></p>
Misha Brukman	13fd15c	2004-01-15 00:14:41 +0000	[diff] [blame]	3103
				3104	<p>The Core LLVM classes are the primary means of representing the program
Chris Lattner	261efe9	2003-11-25 01:02:51 +0000	[diff] [blame]	3105	being inspected or transformed. The core LLVM classes are defined in
				3106	header files in the <tt>include/llvm/</tt> directory, and implemented in
Misha Brukman	13fd15c	2004-01-15 00:14:41 +0000	[diff] [blame]	3107	the <tt>lib/VMCore</tt> directory.</p>
				3108
Misha Brukman	13fd15c	2004-01-15 00:14:41 +0000	[diff] [blame]	3109	<!-- ======================================================================= -->
NAKAMURA Takumi	05d0265	2011-04-18 23:59:50 +0000	[diff] [blame]	3110	<h3>
Reid Spencer	303c4b4	2007-01-12 17:26:25 +0000	[diff] [blame]	3111	<a name="Type">The <tt>Type</tt> class and Derived Types</a>
NAKAMURA Takumi	05d0265	2011-04-18 23:59:50 +0000	[diff] [blame]	3112	</h3>
Reid Spencer	303c4b4	2007-01-12 17:26:25 +0000	[diff] [blame]	3113
NAKAMURA Takumi	f5af6ad	2011-04-23 00:30:22 +0000	[diff] [blame]	3114	<div>
Reid Spencer	303c4b4	2007-01-12 17:26:25 +0000	[diff] [blame]	3115
				3116	<p><tt>Type</tt> is a superclass of all type classes. Every <tt>Value</tt> has
				3117	a <tt>Type</tt>. <tt>Type</tt> cannot be instantiated directly but only
				3118	through its subclasses. Certain primitive types (<tt>VoidType</tt>,
				3119	<tt>LabelType</tt>, <tt>FloatType</tt> and <tt>DoubleType</tt>) have hidden
				3120	subclasses. They are hidden because they offer no useful functionality beyond
				3121	what the <tt>Type</tt> class offers except to distinguish themselves from
				3122	other subclasses of <tt>Type</tt>.</p>
				3123	<p>All other types are subclasses of <tt>DerivedType</tt>. Types can be
				3124	named, but this is not a requirement. There exists exactly
				3125	one instance of a given shape at any one time. This allows type equality to
				3126	be performed with address equality of the Type Instance. That is, given two
				3127	<tt>Type*</tt> values, the types are identical if the pointers are identical.
				3128	</p>
Reid Spencer	303c4b4	2007-01-12 17:26:25 +0000	[diff] [blame]	3129
				3130	<!-- _______________________________________________________________________ -->
NAKAMURA Takumi	05d0265	2011-04-18 23:59:50 +0000	[diff] [blame]	3131	<h4>
Gabor Greif	fd095b6	2009-01-05 16:05:32 +0000	[diff] [blame]	3132	<a name="m_Type">Important Public Methods</a>
NAKAMURA Takumi	05d0265	2011-04-18 23:59:50 +0000	[diff] [blame]	3133	</h4>
Reid Spencer	303c4b4	2007-01-12 17:26:25 +0000	[diff] [blame]	3134
NAKAMURA Takumi	f5af6ad	2011-04-23 00:30:22 +0000	[diff] [blame]	3135	<div>
Reid Spencer	303c4b4	2007-01-12 17:26:25 +0000	[diff] [blame]	3136
				3137	<ul>
Duncan Sands	b0bc6c3	2010-02-15 16:12:20 +0000	[diff] [blame]	3138	<li><tt>bool isIntegerTy() const</tt>: Returns true for any integer type.</li>
Reid Spencer	303c4b4	2007-01-12 17:26:25 +0000	[diff] [blame]	3139
Duncan Sands	b0bc6c3	2010-02-15 16:12:20 +0000	[diff] [blame]	3140	<li><tt>bool isFloatingPointTy()</tt>: Return true if this is one of the five
Reid Spencer	303c4b4	2007-01-12 17:26:25 +0000	[diff] [blame]	3141	floating point types.</li>
				3142
Reid Spencer	303c4b4	2007-01-12 17:26:25 +0000	[diff] [blame]	3143	<li><tt>bool isSized()</tt>: Return true if the type has known size. Things
				3144	that don't have a size are abstract types, labels and void.</li>
				3145
				3146	</ul>
				3147	</div>
				3148
				3149	<!-- _______________________________________________________________________ -->
NAKAMURA Takumi	05d0265	2011-04-18 23:59:50 +0000	[diff] [blame]	3150	<h4>
Gabor Greif	fd095b6	2009-01-05 16:05:32 +0000	[diff] [blame]	3151	<a name="derivedtypes">Important Derived Types</a>
NAKAMURA Takumi	05d0265	2011-04-18 23:59:50 +0000	[diff] [blame]	3152	</h4>
NAKAMURA Takumi	f5af6ad	2011-04-23 00:30:22 +0000	[diff] [blame]	3153	<div>
Reid Spencer	303c4b4	2007-01-12 17:26:25 +0000	[diff] [blame]	3154	<dl>
				3155	<dt><tt>IntegerType</tt></dt>
				3156	<dd>Subclass of DerivedType that represents integer types of any bit width.
				3157	Any bit width between <tt>IntegerType::MIN_INT_BITS</tt> (1) and
				3158	<tt>IntegerType::MAX_INT_BITS</tt> (~8 million) can be represented.
				3159	<ul>
				3160	<li><tt>static const IntegerType* get(unsigned NumBits)</tt>: get an integer
				3161	type of a specific bit width.</li>
				3162	<li><tt>unsigned getBitWidth() const</tt>: Get the bit width of an integer
				3163	type.</li>
				3164	</ul>
				3165	</dd>
				3166	<dt><tt>SequentialType</tt></dt>
Tobias Grosser	d475c10	2011-07-12 11:37:02 +0000	[diff] [blame]	3167	<dd>This is subclassed by ArrayType, PointerType and VectorType.
Reid Spencer	303c4b4	2007-01-12 17:26:25 +0000	[diff] [blame]	3168	<ul>
				3169	<li><tt>const Type * getElementType() const</tt>: Returns the type of each
				3170	of the elements in the sequential type. </li>
				3171	</ul>
				3172	</dd>
				3173	<dt><tt>ArrayType</tt></dt>
				3174	<dd>This is a subclass of SequentialType and defines the interface for array
				3175	types.
				3176	<ul>
				3177	<li><tt>unsigned getNumElements() const</tt>: Returns the number of
				3178	elements in the array. </li>
				3179	</ul>
				3180	</dd>
				3181	<dt><tt>PointerType</tt></dt>
Chris Lattner	302da1e	2007-02-03 03:05:57 +0000	[diff] [blame]	3182	<dd>Subclass of SequentialType for pointer types.</dd>
Reid Spencer	9d6565a	2007-02-15 02:26:10 +0000	[diff] [blame]	3183	<dt><tt>VectorType</tt></dt>
Reid Spencer	485bad1	2007-02-15 03:07:05 +0000	[diff] [blame]	3184	<dd>Subclass of SequentialType for vector types. A
				3185	vector type is similar to an ArrayType but is distinguished because it is
Benjamin Kramer	8040cd3	2009-10-12 14:46:08 +0000	[diff] [blame]	3186	a first class type whereas ArrayType is not. Vector types are used for
Reid Spencer	303c4b4	2007-01-12 17:26:25 +0000	[diff] [blame]	3187	vector operations and are usually small vectors of of an integer or floating
				3188	point type.</dd>
				3189	<dt><tt>StructType</tt></dt>
				3190	<dd>Subclass of DerivedTypes for struct types.</dd>
Duncan Sands	8036ca4	2007-03-30 12:22:09 +0000	[diff] [blame]	3191	<dt><tt><a name="FunctionType">FunctionType</a></tt></dt>
Reid Spencer	303c4b4	2007-01-12 17:26:25 +0000	[diff] [blame]	3192	<dd>Subclass of DerivedTypes for function types.
				3193	<ul>
Dan Gohman	4bb31bf	2010-03-30 20:04:57 +0000	[diff] [blame]	3194	<li><tt>bool isVarArg() const</tt>: Returns true if it's a vararg
Reid Spencer	303c4b4	2007-01-12 17:26:25 +0000	[diff] [blame]	3195	function</li>
				3196	<li><tt> const Type * getReturnType() const</tt>: Returns the
				3197	return type of the function.</li>
				3198	<li><tt>const Type * getParamType (unsigned i)</tt>: Returns
				3199	the type of the ith parameter.</li>
				3200	<li><tt> const unsigned getNumParams() const</tt>: Returns the
				3201	number of formal parameters.</li>
				3202	</ul>
				3203	</dd>
Reid Spencer	303c4b4	2007-01-12 17:26:25 +0000	[diff] [blame]	3204	</dl>
				3205	</div>
				3206
NAKAMURA Takumi	f5af6ad	2011-04-23 00:30:22 +0000	[diff] [blame]	3207	</div>
Chris Lattner	2b78d96	2007-02-03 20:02:25 +0000	[diff] [blame]	3208
				3209	<!-- ======================================================================= -->
NAKAMURA Takumi	05d0265	2011-04-18 23:59:50 +0000	[diff] [blame]	3210	<h3>
Chris Lattner	2b78d96	2007-02-03 20:02:25 +0000	[diff] [blame]	3211	<a name="Module">The <tt>Module</tt> class</a>
NAKAMURA Takumi	05d0265	2011-04-18 23:59:50 +0000	[diff] [blame]	3212	</h3>
Chris Lattner	2b78d96	2007-02-03 20:02:25 +0000	[diff] [blame]	3213
NAKAMURA Takumi	f5af6ad	2011-04-23 00:30:22 +0000	[diff] [blame]	3214	<div>
Chris Lattner	2b78d96	2007-02-03 20:02:25 +0000	[diff] [blame]	3215
				3216	<p><tt>#include "<a
				3217	href="/doxygen/Module_8h-source.html">llvm/Module.h</a>"</tt><br> doxygen info:
				3218	<a href="/doxygen/classllvm_1_1Module.html">Module Class</a></p>
				3219
				3220	<p>The <tt>Module</tt> class represents the top level structure present in LLVM
				3221	programs. An LLVM module is effectively either a translation unit of the
				3222	original program or a combination of several translation units merged by the
				3223	linker. The <tt>Module</tt> class keeps track of a list of <a
				3224	href="#Function"><tt>Function</tt></a>s, a list of <a
				3225	href="#GlobalVariable"><tt>GlobalVariable</tt></a>s, and a <a
				3226	href="#SymbolTable"><tt>SymbolTable</tt></a>. Additionally, it contains a few
				3227	helpful member functions that try to make common operations easy.</p>
				3228
Chris Lattner	2b78d96	2007-02-03 20:02:25 +0000	[diff] [blame]	3229	<!-- _______________________________________________________________________ -->
NAKAMURA Takumi	05d0265	2011-04-18 23:59:50 +0000	[diff] [blame]	3230	<h4>
Chris Lattner	2b78d96	2007-02-03 20:02:25 +0000	[diff] [blame]	3231	<a name="m_Module">Important Public Members of the <tt>Module</tt> class</a>
NAKAMURA Takumi	05d0265	2011-04-18 23:59:50 +0000	[diff] [blame]	3232	</h4>
Chris Lattner	2b78d96	2007-02-03 20:02:25 +0000	[diff] [blame]	3233
NAKAMURA Takumi	f5af6ad	2011-04-23 00:30:22 +0000	[diff] [blame]	3234	<div>
Chris Lattner	2b78d96	2007-02-03 20:02:25 +0000	[diff] [blame]	3235
				3236	<ul>
				3237	<li><tt>Module::Module(std::string name = "")</tt></li>
				3238	</ul>
				3239
				3240	<p>Constructing a <a href="#Module">Module</a> is easy. You can optionally
				3241	provide a name for it (probably based on the name of the translation unit).</p>
				3242
				3243	<ul>
				3244	<li><tt>Module::iterator</tt> - Typedef for function list iterator<br>
				3245	<tt>Module::const_iterator</tt> - Typedef for const_iterator.<br>
				3246
				3247	<tt>begin()</tt>, <tt>end()</tt>
				3248	<tt>size()</tt>, <tt>empty()</tt>
				3249
				3250	<p>These are forwarding methods that make it easy to access the contents of
				3251	a <tt>Module</tt> object's <a href="#Function"><tt>Function</tt></a>
				3252	list.</p></li>
				3253
				3254	<li><tt>Module::FunctionListType &getFunctionList()</tt>
				3255
				3256	<p> Returns the list of <a href="#Function"><tt>Function</tt></a>s. This is
				3257	necessary to use when you need to update the list or perform a complex
				3258	action that doesn't have a forwarding method.</p>
				3259
				3260	<p><!-- Global Variable --></p></li>
				3261	</ul>
				3262
				3263	<hr>
				3264
				3265	<ul>
				3266	<li><tt>Module::global_iterator</tt> - Typedef for global variable list iterator<br>
				3267
				3268	<tt>Module::const_global_iterator</tt> - Typedef for const_iterator.<br>
				3269
				3270	<tt>global_begin()</tt>, <tt>global_end()</tt>
				3271	<tt>global_size()</tt>, <tt>global_empty()</tt>
				3272
				3273	<p> These are forwarding methods that make it easy to access the contents of
				3274	a <tt>Module</tt> object's <a
				3275	href="#GlobalVariable"><tt>GlobalVariable</tt></a> list.</p></li>
				3276
				3277	<li><tt>Module::GlobalListType &getGlobalList()</tt>
				3278
				3279	<p>Returns the list of <a
				3280	href="#GlobalVariable"><tt>GlobalVariable</tt></a>s. This is necessary to
				3281	use when you need to update the list or perform a complex action that
				3282	doesn't have a forwarding method.</p>
				3283
				3284	<p><!-- Symbol table stuff --> </p></li>
				3285	</ul>
				3286
				3287	<hr>
				3288
				3289	<ul>
				3290	<li><tt><a href="#SymbolTable">SymbolTable</a> *getSymbolTable()</tt>
				3291
				3292	<p>Return a reference to the <a href="#SymbolTable"><tt>SymbolTable</tt></a>
				3293	for this <tt>Module</tt>.</p>
				3294
				3295	<p><!-- Convenience methods --></p></li>
				3296	</ul>
				3297
				3298	<hr>
				3299
				3300	<ul>
				3301	<li><tt><a href="#Function">Function</a> *getFunction(const std::string
				3302	&Name, const <a href="#FunctionType">FunctionType</a> *Ty)</tt>
				3303
				3304	<p>Look up the specified function in the <tt>Module</tt> <a
				3305	href="#SymbolTable"><tt>SymbolTable</tt></a>. If it does not exist, return
				3306	<tt>null</tt>.</p></li>
				3307
				3308	<li><tt><a href="#Function">Function</a> *getOrInsertFunction(const
				3309	std::string &Name, const <a href="#FunctionType">FunctionType</a> *T)</tt>
				3310
				3311	<p>Look up the specified function in the <tt>Module</tt> <a
				3312	href="#SymbolTable"><tt>SymbolTable</tt></a>. If it does not exist, add an
				3313	external declaration for the function and return it.</p></li>
				3314
				3315	<li><tt>std::string getTypeName(const <a href="#Type">Type</a> *Ty)</tt>
				3316
				3317	<p>If there is at least one entry in the <a
				3318	href="#SymbolTable"><tt>SymbolTable</tt></a> for the specified <a
				3319	href="#Type"><tt>Type</tt></a>, return it. Otherwise return the empty
				3320	string.</p></li>
				3321
				3322	<li><tt>bool addTypeName(const std::string &Name, const <a
				3323	href="#Type">Type</a> *Ty)</tt>
				3324
				3325	<p>Insert an entry in the <a href="#SymbolTable"><tt>SymbolTable</tt></a>
				3326	mapping <tt>Name</tt> to <tt>Ty</tt>. If there is already an entry for this
				3327	name, true is returned and the <a
				3328	href="#SymbolTable"><tt>SymbolTable</tt></a> is not modified.</p></li>
				3329	</ul>
				3330
				3331	</div>
				3332
NAKAMURA Takumi	f5af6ad	2011-04-23 00:30:22 +0000	[diff] [blame]	3333	</div>
Chris Lattner	2b78d96	2007-02-03 20:02:25 +0000	[diff] [blame]	3334
Reid Spencer	303c4b4	2007-01-12 17:26:25 +0000	[diff] [blame]	3335	<!-- ======================================================================= -->
NAKAMURA Takumi	05d0265	2011-04-18 23:59:50 +0000	[diff] [blame]	3336	<h3>
Misha Brukman	13fd15c	2004-01-15 00:14:41 +0000	[diff] [blame]	3337	<a name="Value">The <tt>Value</tt> class</a>
NAKAMURA Takumi	05d0265	2011-04-18 23:59:50 +0000	[diff] [blame]	3338	</h3>
Misha Brukman	13fd15c	2004-01-15 00:14:41 +0000	[diff] [blame]	3339
NAKAMURA Takumi	f5af6ad	2011-04-23 00:30:22 +0000	[diff] [blame]	3340	<div>
Misha Brukman	13fd15c	2004-01-15 00:14:41 +0000	[diff] [blame]	3341
				3342	<p><tt>#include "<a href="/doxygen/Value_8h-source.html">llvm/Value.h</a>"</tt>
				3343	<br>
Chris Lattner	0081517	2007-01-04 22:01:45 +0000	[diff] [blame]	3344	doxygen info: <a href="/doxygen/classllvm_1_1Value.html">Value Class</a></p>
Misha Brukman	13fd15c	2004-01-15 00:14:41 +0000	[diff] [blame]	3345
				3346	<p>The <tt>Value</tt> class is the most important class in the LLVM Source
				3347	base. It represents a typed value that may be used (among other things) as an
				3348	operand to an instruction. There are many different types of <tt>Value</tt>s,
				3349	such as <a href="#Constant"><tt>Constant</tt></a>s,<a
				3350	href="#Argument"><tt>Argument</tt></a>s. Even <a
				3351	href="#Instruction"><tt>Instruction</tt></a>s and <a
				3352	href="#Function"><tt>Function</tt></a>s are <tt>Value</tt>s.</p>
				3353
				3354	<p>A particular <tt>Value</tt> may be used many times in the LLVM representation
				3355	for a program. For example, an incoming argument to a function (represented
				3356	with an instance of the <a href="#Argument">Argument</a> class) is "used" by
				3357	every instruction in the function that references the argument. To keep track
				3358	of this relationship, the <tt>Value</tt> class keeps a list of all of the <a
				3359	href="#User"><tt>User</tt></a>s that is using it (the <a
				3360	href="#User"><tt>User</tt></a> class is a base class for all nodes in the LLVM
				3361	graph that can refer to <tt>Value</tt>s). This use list is how LLVM represents
				3362	def-use information in the program, and is accessible through the <tt>use_</tt>*
				3363	methods, shown below.</p>
				3364
				3365	<p>Because LLVM is a typed representation, every LLVM <tt>Value</tt> is typed,
				3366	and this <a href="#Type">Type</a> is available through the <tt>getType()</tt>
				3367	method. In addition, all LLVM values can be named. The "name" of the
				3368	<tt>Value</tt> is a symbolic string printed in the LLVM code:</p>
				3369
Bill Wendling	3cd5ca6	2006-10-11 06:30:10 +0000	[diff] [blame]	3370	<div class="doc_code">
				3371	<pre>
Reid Spencer	06565dc	2007-01-12 17:11:23 +0000	[diff] [blame]	3372	%<b>foo</b> = add i32 1, 2
Bill Wendling	3cd5ca6	2006-10-11 06:30:10 +0000	[diff] [blame]	3373	</pre>
				3374	</div>
Misha Brukman	13fd15c	2004-01-15 00:14:41 +0000	[diff] [blame]	3375
Duncan Sands	8036ca4	2007-03-30 12:22:09 +0000	[diff] [blame]	3376	<p><a name="nameWarning">The name of this instruction is "foo".</a> <b>NOTE</b>
Misha Brukman	13fd15c	2004-01-15 00:14:41 +0000	[diff] [blame]	3377	that the name of any value may be missing (an empty string), so names should
				3378	<b>ONLY</b> be used for debugging (making the source code easier to read,
				3379	debugging printouts), they should not be used to keep track of values or map
				3380	between them. For this purpose, use a <tt>std::map</tt> of pointers to the
				3381	<tt>Value</tt> itself instead.</p>
				3382
				3383	<p>One important aspect of LLVM is that there is no distinction between an SSA
				3384	variable and the operation that produces it. Because of this, any reference to
				3385	the value produced by an instruction (or the value available as an incoming
Chris Lattner	d5fc4fc	2004-03-18 14:58:55 +0000	[diff] [blame]	3386	argument, for example) is represented as a direct pointer to the instance of
				3387	the class that
Misha Brukman	13fd15c	2004-01-15 00:14:41 +0000	[diff] [blame]	3388	represents this value. Although this may take some getting used to, it
				3389	simplifies the representation and makes it easier to manipulate.</p>
				3390
Misha Brukman	13fd15c	2004-01-15 00:14:41 +0000	[diff] [blame]	3391	<!-- _______________________________________________________________________ -->
NAKAMURA Takumi	05d0265	2011-04-18 23:59:50 +0000	[diff] [blame]	3392	<h4>
Misha Brukman	13fd15c	2004-01-15 00:14:41 +0000	[diff] [blame]	3393	<a name="m_Value">Important Public Members of the <tt>Value</tt> class</a>
NAKAMURA Takumi	05d0265	2011-04-18 23:59:50 +0000	[diff] [blame]	3394	</h4>
Misha Brukman	13fd15c	2004-01-15 00:14:41 +0000	[diff] [blame]	3395
NAKAMURA Takumi	f5af6ad	2011-04-23 00:30:22 +0000	[diff] [blame]	3396	<div>
Misha Brukman	13fd15c	2004-01-15 00:14:41 +0000	[diff] [blame]	3397
Chris Lattner	261efe9	2003-11-25 01:02:51 +0000	[diff] [blame]	3398	<ul>
				3399	<li><tt>Value::use_iterator</tt> - Typedef for iterator over the
				3400	use-list<br>
Gabor Greif	bbbf9a2	2010-03-26 19:59:25 +0000	[diff] [blame]	3401	<tt>Value::const_use_iterator</tt> - Typedef for const_iterator over
Chris Lattner	261efe9	2003-11-25 01:02:51 +0000	[diff] [blame]	3402	the use-list<br>
				3403	<tt>unsigned use_size()</tt> - Returns the number of users of the
				3404	value.<br>
Chris Lattner	9355b47	2002-09-06 02:50:58 +0000	[diff] [blame]	3405	<tt>bool use_empty()</tt> - Returns true if there are no users.<br>
Chris Lattner	261efe9	2003-11-25 01:02:51 +0000	[diff] [blame]	3406	<tt>use_iterator use_begin()</tt> - Get an iterator to the start of
				3407	the use-list.<br>
				3408	<tt>use_iterator use_end()</tt> - Get an iterator to the end of the
				3409	use-list.<br>
				3410	<tt><a href="#User">User</a> *use_back()</tt> - Returns the last
				3411	element in the list.
				3412	<p> These methods are the interface to access the def-use
				3413	information in LLVM. As with all other iterators in LLVM, the naming
				3414	conventions follow the conventions defined by the <a href="#stl">STL</a>.</p>
Chris Lattner	261efe9	2003-11-25 01:02:51 +0000	[diff] [blame]	3415	</li>
				3416	<li><tt><a href="#Type">Type</a> *getType() const</tt>
Misha Brukman	13fd15c	2004-01-15 00:14:41 +0000	[diff] [blame]	3417	<p>This method returns the Type of the Value.</p>
Chris Lattner	261efe9	2003-11-25 01:02:51 +0000	[diff] [blame]	3418	</li>
				3419	<li><tt>bool hasName() const</tt><br>
Chris Lattner	9355b47	2002-09-06 02:50:58 +0000	[diff] [blame]	3420	<tt>std::string getName() const</tt><br>
Chris Lattner	261efe9	2003-11-25 01:02:51 +0000	[diff] [blame]	3421	<tt>void setName(const std::string &Name)</tt>
				3422	<p> This family of methods is used to access and assign a name to a <tt>Value</tt>,
				3423	be aware of the <a href="#nameWarning">precaution above</a>.</p>
Chris Lattner	261efe9	2003-11-25 01:02:51 +0000	[diff] [blame]	3424	</li>
				3425	<li><tt>void replaceAllUsesWith(Value *V)</tt>
Misha Brukman	13fd15c	2004-01-15 00:14:41 +0000	[diff] [blame]	3426
				3427	<p>This method traverses the use list of a <tt>Value</tt> changing all <a
				3428	href="#User"><tt>User</tt>s</a> of the current value to refer to
				3429	"<tt>V</tt>" instead. For example, if you detect that an instruction always
				3430	produces a constant value (for example through constant folding), you can
				3431	replace all uses of the instruction with the constant like this:</p>
				3432
Bill Wendling	3cd5ca6	2006-10-11 06:30:10 +0000	[diff] [blame]	3433	<div class="doc_code">
				3434	<pre>
				3435	Inst->replaceAllUsesWith(ConstVal);
				3436	</pre>
				3437	</div>
				3438
Chris Lattner	261efe9	2003-11-25 01:02:51 +0000	[diff] [blame]	3439	</ul>
Misha Brukman	13fd15c	2004-01-15 00:14:41 +0000	[diff] [blame]	3440
				3441	</div>
				3442
NAKAMURA Takumi	f5af6ad	2011-04-23 00:30:22 +0000	[diff] [blame]	3443	</div>
				3444
Misha Brukman	13fd15c	2004-01-15 00:14:41 +0000	[diff] [blame]	3445	<!-- ======================================================================= -->
NAKAMURA Takumi	05d0265	2011-04-18 23:59:50 +0000	[diff] [blame]	3446	<h3>
Misha Brukman	13fd15c	2004-01-15 00:14:41 +0000	[diff] [blame]	3447	<a name="User">The <tt>User</tt> class</a>
NAKAMURA Takumi	05d0265	2011-04-18 23:59:50 +0000	[diff] [blame]	3448	</h3>
Misha Brukman	13fd15c	2004-01-15 00:14:41 +0000	[diff] [blame]	3449
NAKAMURA Takumi	f5af6ad	2011-04-23 00:30:22 +0000	[diff] [blame]	3450	<div>
Misha Brukman	13fd15c	2004-01-15 00:14:41 +0000	[diff] [blame]	3451
				3452	<p>
				3453	<tt>#include "<a href="/doxygen/User_8h-source.html">llvm/User.h</a>"</tt><br>
Misha Brukman	384047f	2004-06-03 23:29:12 +0000	[diff] [blame]	3454	doxygen info: <a href="/doxygen/classllvm_1_1User.html">User Class</a><br>
Misha Brukman	13fd15c	2004-01-15 00:14:41 +0000	[diff] [blame]	3455	Superclass: <a href="#Value"><tt>Value</tt></a></p>
				3456
				3457	<p>The <tt>User</tt> class is the common base class of all LLVM nodes that may
				3458	refer to <a href="#Value"><tt>Value</tt></a>s. It exposes a list of "Operands"
				3459	that are all of the <a href="#Value"><tt>Value</tt></a>s that the User is
				3460	referring to. The <tt>User</tt> class itself is a subclass of
				3461	<tt>Value</tt>.</p>
				3462
				3463	<p>The operands of a <tt>User</tt> point directly to the LLVM <a
				3464	href="#Value"><tt>Value</tt></a> that it refers to. Because LLVM uses Static
				3465	Single Assignment (SSA) form, there can only be one definition referred to,
				3466	allowing this direct connection. This connection provides the use-def
				3467	information in LLVM.</p>
				3468
Misha Brukman	13fd15c	2004-01-15 00:14:41 +0000	[diff] [blame]	3469	<!-- _______________________________________________________________________ -->
NAKAMURA Takumi	05d0265	2011-04-18 23:59:50 +0000	[diff] [blame]	3470	<h4>
Misha Brukman	13fd15c	2004-01-15 00:14:41 +0000	[diff] [blame]	3471	<a name="m_User">Important Public Members of the <tt>User</tt> class</a>
NAKAMURA Takumi	05d0265	2011-04-18 23:59:50 +0000	[diff] [blame]	3472	</h4>
Misha Brukman	13fd15c	2004-01-15 00:14:41 +0000	[diff] [blame]	3473
NAKAMURA Takumi	f5af6ad	2011-04-23 00:30:22 +0000	[diff] [blame]	3474	<div>
Misha Brukman	13fd15c	2004-01-15 00:14:41 +0000	[diff] [blame]	3475
				3476	<p>The <tt>User</tt> class exposes the operand list in two ways: through
				3477	an index access interface and through an iterator based interface.</p>
				3478
Chris Lattner	261efe9	2003-11-25 01:02:51 +0000	[diff] [blame]	3479	<ul>
Chris Lattner	261efe9	2003-11-25 01:02:51 +0000	[diff] [blame]	3480	<li><tt>Value *getOperand(unsigned i)</tt><br>
				3481	<tt>unsigned getNumOperands()</tt>
				3482	<p> These two methods expose the operands of the <tt>User</tt> in a
Misha Brukman	13fd15c	2004-01-15 00:14:41 +0000	[diff] [blame]	3483	convenient form for direct access.</p></li>
				3484
Chris Lattner	261efe9	2003-11-25 01:02:51 +0000	[diff] [blame]	3485	<li><tt>User::op_iterator</tt> - Typedef for iterator over the operand
				3486	list<br>
Chris Lattner	5836082	2005-01-17 00:12:04 +0000	[diff] [blame]	3487	<tt>op_iterator op_begin()</tt> - Get an iterator to the start of
				3488	the operand list.<br>
				3489	<tt>op_iterator op_end()</tt> - Get an iterator to the end of the
Chris Lattner	261efe9	2003-11-25 01:02:51 +0000	[diff] [blame]	3490	operand list.
				3491	<p> Together, these methods make up the iterator based interface to
Misha Brukman	13fd15c	2004-01-15 00:14:41 +0000	[diff] [blame]	3492	the operands of a <tt>User</tt>.</p></li>
Chris Lattner	261efe9	2003-11-25 01:02:51 +0000	[diff] [blame]	3493	</ul>
Misha Brukman	13fd15c	2004-01-15 00:14:41 +0000	[diff] [blame]	3494
				3495	</div>
				3496
NAKAMURA Takumi	f5af6ad	2011-04-23 00:30:22 +0000	[diff] [blame]	3497	</div>
				3498
Misha Brukman	13fd15c	2004-01-15 00:14:41 +0000	[diff] [blame]	3499	<!-- ======================================================================= -->
NAKAMURA Takumi	05d0265	2011-04-18 23:59:50 +0000	[diff] [blame]	3500	<h3>
Misha Brukman	13fd15c	2004-01-15 00:14:41 +0000	[diff] [blame]	3501	<a name="Instruction">The <tt>Instruction</tt> class</a>
NAKAMURA Takumi	05d0265	2011-04-18 23:59:50 +0000	[diff] [blame]	3502	</h3>
Misha Brukman	13fd15c	2004-01-15 00:14:41 +0000	[diff] [blame]	3503
NAKAMURA Takumi	f5af6ad	2011-04-23 00:30:22 +0000	[diff] [blame]	3504	<div>
Misha Brukman	13fd15c	2004-01-15 00:14:41 +0000	[diff] [blame]	3505
				3506	<p><tt>#include "</tt><tt><a
				3507	href="/doxygen/Instruction_8h-source.html">llvm/Instruction.h</a>"</tt><br>
Misha Brukman	31ca1de	2004-06-03 23:35:54 +0000	[diff] [blame]	3508	doxygen info: <a href="/doxygen/classllvm_1_1Instruction.html">Instruction Class</a><br>
Misha Brukman	13fd15c	2004-01-15 00:14:41 +0000	[diff] [blame]	3509	Superclasses: <a href="#User"><tt>User</tt></a>, <a
				3510	href="#Value"><tt>Value</tt></a></p>
				3511
				3512	<p>The <tt>Instruction</tt> class is the common base class for all LLVM
				3513	instructions. It provides only a few methods, but is a very commonly used
				3514	class. The primary data tracked by the <tt>Instruction</tt> class itself is the
				3515	opcode (instruction type) and the parent <a
				3516	href="#BasicBlock"><tt>BasicBlock</tt></a> the <tt>Instruction</tt> is embedded
				3517	into. To represent a specific type of instruction, one of many subclasses of
				3518	<tt>Instruction</tt> are used.</p>
				3519
				3520	<p> Because the <tt>Instruction</tt> class subclasses the <a
				3521	href="#User"><tt>User</tt></a> class, its operands can be accessed in the same
				3522	way as for other <a href="#User"><tt>User</tt></a>s (with the
				3523	<tt>getOperand()</tt>/<tt>getNumOperands()</tt> and
				3524	<tt>op_begin()</tt>/<tt>op_end()</tt> methods).</p> <p> An important file for
				3525	the <tt>Instruction</tt> class is the <tt>llvm/Instruction.def</tt> file. This
				3526	file contains some meta-data about the various different types of instructions
				3527	in LLVM. It describes the enum values that are used as opcodes (for example
Reid Spencer	c92d25d	2006-12-19 19:47:19 +0000	[diff] [blame]	3528	<tt>Instruction::Add</tt> and <tt>Instruction::ICmp</tt>), as well as the
Misha Brukman	13fd15c	2004-01-15 00:14:41 +0000	[diff] [blame]	3529	concrete sub-classes of <tt>Instruction</tt> that implement the instruction (for
				3530	example <tt><a href="#BinaryOperator">BinaryOperator</a></tt> and <tt><a
Reid Spencer	c92d25d	2006-12-19 19:47:19 +0000	[diff] [blame]	3531	href="#CmpInst">CmpInst</a></tt>). Unfortunately, the use of macros in
Misha Brukman	13fd15c	2004-01-15 00:14:41 +0000	[diff] [blame]	3532	this file confuses doxygen, so these enum values don't show up correctly in the
Misha Brukman	31ca1de	2004-06-03 23:35:54 +0000	[diff] [blame]	3533	<a href="/doxygen/classllvm_1_1Instruction.html">doxygen output</a>.</p>
Misha Brukman	13fd15c	2004-01-15 00:14:41 +0000	[diff] [blame]	3534
Misha Brukman	13fd15c	2004-01-15 00:14:41 +0000	[diff] [blame]	3535	<!-- _______________________________________________________________________ -->
NAKAMURA Takumi	05d0265	2011-04-18 23:59:50 +0000	[diff] [blame]	3536	<h4>
				3537	<a name="s_Instruction">
				3538	Important Subclasses of the <tt>Instruction</tt> class
				3539	</a>
				3540	</h4>
NAKAMURA Takumi	f5af6ad	2011-04-23 00:30:22 +0000	[diff] [blame]	3541	<div>
Reid Spencer	c92d25d	2006-12-19 19:47:19 +0000	[diff] [blame]	3542	<ul>
				3543	<li><tt><a name="BinaryOperator">BinaryOperator</a></tt>
				3544	<p>This subclasses represents all two operand instructions whose operands
				3545	must be the same type, except for the comparison instructions.</p></li>
				3546	<li><tt><a name="CastInst">CastInst</a></tt>
				3547	<p>This subclass is the parent of the 12 casting instructions. It provides
				3548	common operations on cast instructions.</p>
				3549	<li><tt><a name="CmpInst">CmpInst</a></tt>
				3550	<p>This subclass respresents the two comparison instructions,
				3551	<a href="LangRef.html#i_icmp">ICmpInst</a> (integer opreands), and
				3552	<a href="LangRef.html#i_fcmp">FCmpInst</a> (floating point operands).</p>
				3553	<li><tt><a name="TerminatorInst">TerminatorInst</a></tt>
				3554	<p>This subclass is the parent of all terminator instructions (those which
				3555	can terminate a block).</p>
				3556	</ul>
				3557	</div>
				3558
				3559	<!-- _______________________________________________________________________ -->
NAKAMURA Takumi	05d0265	2011-04-18 23:59:50 +0000	[diff] [blame]	3560	<h4>
				3561	<a name="m_Instruction">
				3562	Important Public Members of the <tt>Instruction</tt> class
				3563	</a>
				3564	</h4>
Misha Brukman	13fd15c	2004-01-15 00:14:41 +0000	[diff] [blame]	3565
NAKAMURA Takumi	f5af6ad	2011-04-23 00:30:22 +0000	[diff] [blame]	3566	<div>
Misha Brukman	13fd15c	2004-01-15 00:14:41 +0000	[diff] [blame]	3567
Chris Lattner	261efe9	2003-11-25 01:02:51 +0000	[diff] [blame]	3568	<ul>
				3569	<li><tt><a href="#BasicBlock">BasicBlock</a> *getParent()</tt>
Misha Brukman	13fd15c	2004-01-15 00:14:41 +0000	[diff] [blame]	3570	<p>Returns the <a href="#BasicBlock"><tt>BasicBlock</tt></a> that
				3571	this <tt>Instruction</tt> is embedded into.</p></li>
Chris Lattner	261efe9	2003-11-25 01:02:51 +0000	[diff] [blame]	3572	<li><tt>bool mayWriteToMemory()</tt>
Misha Brukman	13fd15c	2004-01-15 00:14:41 +0000	[diff] [blame]	3573	<p>Returns true if the instruction writes to memory, i.e. it is a
				3574	<tt>call</tt>,<tt>free</tt>,<tt>invoke</tt>, or <tt>store</tt>.</p></li>
Chris Lattner	261efe9	2003-11-25 01:02:51 +0000	[diff] [blame]	3575	<li><tt>unsigned getOpcode()</tt>
Misha Brukman	13fd15c	2004-01-15 00:14:41 +0000	[diff] [blame]	3576	<p>Returns the opcode for the <tt>Instruction</tt>.</p></li>
Chris Lattner	261efe9	2003-11-25 01:02:51 +0000	[diff] [blame]	3577	<li><tt><a href="#Instruction">Instruction</a> *clone() const</tt>
Misha Brukman	13fd15c	2004-01-15 00:14:41 +0000	[diff] [blame]	3578	<p>Returns another instance of the specified instruction, identical
Chris Lattner	261efe9	2003-11-25 01:02:51 +0000	[diff] [blame]	3579	in all ways to the original except that the instruction has no parent
				3580	(ie it's not embedded into a <a href="#BasicBlock"><tt>BasicBlock</tt></a>),
Misha Brukman	13fd15c	2004-01-15 00:14:41 +0000	[diff] [blame]	3581	and it has no name</p></li>
Chris Lattner	261efe9	2003-11-25 01:02:51 +0000	[diff] [blame]	3582	</ul>
Misha Brukman	13fd15c	2004-01-15 00:14:41 +0000	[diff] [blame]	3583
				3584	</div>
				3585
NAKAMURA Takumi	f5af6ad	2011-04-23 00:30:22 +0000	[diff] [blame]	3586	</div>
				3587
Misha Brukman	13fd15c	2004-01-15 00:14:41 +0000	[diff] [blame]	3588	<!-- ======================================================================= -->
NAKAMURA Takumi	05d0265	2011-04-18 23:59:50 +0000	[diff] [blame]	3589	<h3>
Chris Lattner	2b78d96	2007-02-03 20:02:25 +0000	[diff] [blame]	3590	<a name="Constant">The <tt>Constant</tt> class and subclasses</a>
NAKAMURA Takumi	05d0265	2011-04-18 23:59:50 +0000	[diff] [blame]	3591	</h3>
Misha Brukman	13fd15c	2004-01-15 00:14:41 +0000	[diff] [blame]	3592
NAKAMURA Takumi	f5af6ad	2011-04-23 00:30:22 +0000	[diff] [blame]	3593	<div>
Misha Brukman	13fd15c	2004-01-15 00:14:41 +0000	[diff] [blame]	3594
Chris Lattner	2b78d96	2007-02-03 20:02:25 +0000	[diff] [blame]	3595	<p>Constant represents a base class for different types of constants. It
				3596	is subclassed by ConstantInt, ConstantArray, etc. for representing
				3597	the various types of Constants. <a href="#GlobalValue">GlobalValue</a> is also
				3598	a subclass, which represents the address of a global variable or function.
				3599	</p>
Misha Brukman	13fd15c	2004-01-15 00:14:41 +0000	[diff] [blame]	3600
Misha Brukman	13fd15c	2004-01-15 00:14:41 +0000	[diff] [blame]	3601	<!-- _______________________________________________________________________ -->
NAKAMURA Takumi	05d0265	2011-04-18 23:59:50 +0000	[diff] [blame]	3602	<h4>Important Subclasses of Constant</h4>
NAKAMURA Takumi	f5af6ad	2011-04-23 00:30:22 +0000	[diff] [blame]	3603	<div>
Chris Lattner	261efe9	2003-11-25 01:02:51 +0000	[diff] [blame]	3604	<ul>
Chris Lattner	2b78d96	2007-02-03 20:02:25 +0000	[diff] [blame]	3605	<li>ConstantInt : This subclass of Constant represents an integer constant of
				3606	any width.
				3607	<ul>
Reid Spencer	97b4ee3	2007-03-01 21:05:33 +0000	[diff] [blame]	3608	<li><tt>const APInt& getValue() const</tt>: Returns the underlying
				3609	value of this constant, an APInt value.</li>
				3610	<li><tt>int64_t getSExtValue() const</tt>: Converts the underlying APInt
				3611	value to an int64_t via sign extension. If the value (not the bit width)
				3612	of the APInt is too large to fit in an int64_t, an assertion will result.
				3613	For this reason, use of this method is discouraged.</li>
				3614	<li><tt>uint64_t getZExtValue() const</tt>: Converts the underlying APInt
				3615	value to a uint64_t via zero extension. IF the value (not the bit width)
				3616	of the APInt is too large to fit in a uint64_t, an assertion will result.
Reid Spencer	4474d87	2007-03-02 01:31:31 +0000	[diff] [blame]	3617	For this reason, use of this method is discouraged.</li>
Reid Spencer	97b4ee3	2007-03-01 21:05:33 +0000	[diff] [blame]	3618	<li><tt>static ConstantInt* get(const APInt& Val)</tt>: Returns the
				3619	ConstantInt object that represents the value provided by <tt>Val</tt>.
				3620	The type is implied as the IntegerType that corresponds to the bit width
				3621	of <tt>Val</tt>.</li>
Chris Lattner	2b78d96	2007-02-03 20:02:25 +0000	[diff] [blame]	3622	<li><tt>static ConstantInt* get(const Type *Ty, uint64_t Val)</tt>:
				3623	Returns the ConstantInt object that represents the value provided by
				3624	<tt>Val</tt> for integer type <tt>Ty</tt>.</li>
				3625	</ul>
				3626	</li>
				3627	<li>ConstantFP : This class represents a floating point constant.
				3628	<ul>
				3629	<li><tt>double getValue() const</tt>: Returns the underlying value of
				3630	this constant. </li>
				3631	</ul>
				3632	</li>
				3633	<li>ConstantArray : This represents a constant array.
				3634	<ul>
				3635	<li><tt>const std::vector<Use> &getValues() const</tt>: Returns
				3636	a vector of component constants that makeup this array. </li>
				3637	</ul>
				3638	</li>
				3639	<li>ConstantStruct : This represents a constant struct.
				3640	<ul>
				3641	<li><tt>const std::vector<Use> &getValues() const</tt>: Returns
				3642	a vector of component constants that makeup this array. </li>
				3643	</ul>
				3644	</li>
				3645	<li>GlobalValue : This represents either a global variable or a function. In
				3646	either case, the value is a constant fixed address (after linking).
				3647	</li>
Chris Lattner	261efe9	2003-11-25 01:02:51 +0000	[diff] [blame]	3648	</ul>
Misha Brukman	13fd15c	2004-01-15 00:14:41 +0000	[diff] [blame]	3649	</div>
				3650
NAKAMURA Takumi	f5af6ad	2011-04-23 00:30:22 +0000	[diff] [blame]	3651	</div>
Chris Lattner	2b78d96	2007-02-03 20:02:25 +0000	[diff] [blame]	3652
Misha Brukman	13fd15c	2004-01-15 00:14:41 +0000	[diff] [blame]	3653	<!-- ======================================================================= -->
NAKAMURA Takumi	05d0265	2011-04-18 23:59:50 +0000	[diff] [blame]	3654	<h3>
Misha Brukman	13fd15c	2004-01-15 00:14:41 +0000	[diff] [blame]	3655	<a name="GlobalValue">The <tt>GlobalValue</tt> class</a>
NAKAMURA Takumi	05d0265	2011-04-18 23:59:50 +0000	[diff] [blame]	3656	</h3>
Misha Brukman	13fd15c	2004-01-15 00:14:41 +0000	[diff] [blame]	3657
NAKAMURA Takumi	f5af6ad	2011-04-23 00:30:22 +0000	[diff] [blame]	3658	<div>
Misha Brukman	13fd15c	2004-01-15 00:14:41 +0000	[diff] [blame]	3659
				3660	<p><tt>#include "<a
				3661	href="/doxygen/GlobalValue_8h-source.html">llvm/GlobalValue.h</a>"</tt><br>
Misha Brukman	384047f	2004-06-03 23:29:12 +0000	[diff] [blame]	3662	doxygen info: <a href="/doxygen/classllvm_1_1GlobalValue.html">GlobalValue
				3663	Class</a><br>
Reid Spencer	be5e85e	2006-04-14 14:11:48 +0000	[diff] [blame]	3664	Superclasses: <a href="#Constant"><tt>Constant</tt></a>,
				3665	<a href="#User"><tt>User</tt></a>, <a href="#Value"><tt>Value</tt></a></p>
Misha Brukman	13fd15c	2004-01-15 00:14:41 +0000	[diff] [blame]	3666
				3667	<p>Global values (<a href="#GlobalVariable"><tt>GlobalVariable</tt></a>s or <a
				3668	href="#Function"><tt>Function</tt></a>s) are the only LLVM values that are
				3669	visible in the bodies of all <a href="#Function"><tt>Function</tt></a>s.
				3670	Because they are visible at global scope, they are also subject to linking with
				3671	other globals defined in different translation units. To control the linking
				3672	process, <tt>GlobalValue</tt>s know their linkage rules. Specifically,
				3673	<tt>GlobalValue</tt>s know whether they have internal or external linkage, as
Reid Spencer	8b2da7a	2004-07-18 13:10:31 +0000	[diff] [blame]	3674	defined by the <tt>LinkageTypes</tt> enumeration.</p>
Misha Brukman	13fd15c	2004-01-15 00:14:41 +0000	[diff] [blame]	3675
				3676	<p>If a <tt>GlobalValue</tt> has internal linkage (equivalent to being
				3677	<tt>static</tt> in C), it is not visible to code outside the current translation
				3678	unit, and does not participate in linking. If it has external linkage, it is
				3679	visible to external code, and does participate in linking. In addition to
				3680	linkage information, <tt>GlobalValue</tt>s keep track of which <a
				3681	href="#Module"><tt>Module</tt></a> they are currently part of.</p>
				3682
				3683	<p>Because <tt>GlobalValue</tt>s are memory objects, they are always referred to
				3684	by their <b>address</b>. As such, the <a href="#Type"><tt>Type</tt></a> of a
				3685	global is always a pointer to its contents. It is important to remember this
				3686	when using the <tt>GetElementPtrInst</tt> instruction because this pointer must
				3687	be dereferenced first. For example, if you have a <tt>GlobalVariable</tt> (a
				3688	subclass of <tt>GlobalValue)</tt> that is an array of 24 ints, type <tt>[24 x
Reid Spencer	06565dc	2007-01-12 17:11:23 +0000	[diff] [blame]	3689	i32]</tt>, then the <tt>GlobalVariable</tt> is a pointer to that array. Although
Misha Brukman	13fd15c	2004-01-15 00:14:41 +0000	[diff] [blame]	3690	the address of the first element of this array and the value of the
				3691	<tt>GlobalVariable</tt> are the same, they have different types. The
Reid Spencer	06565dc	2007-01-12 17:11:23 +0000	[diff] [blame]	3692	<tt>GlobalVariable</tt>'s type is <tt>[24 x i32]</tt>. The first element's type
				3693	is <tt>i32.</tt> Because of this, accessing a global value requires you to
Misha Brukman	13fd15c	2004-01-15 00:14:41 +0000	[diff] [blame]	3694	dereference the pointer with <tt>GetElementPtrInst</tt> first, then its elements
				3695	can be accessed. This is explained in the <a href="LangRef.html#globalvars">LLVM
				3696	Language Reference Manual</a>.</p>
				3697
Misha Brukman	13fd15c	2004-01-15 00:14:41 +0000	[diff] [blame]	3698	<!-- _______________________________________________________________________ -->
NAKAMURA Takumi	05d0265	2011-04-18 23:59:50 +0000	[diff] [blame]	3699	<h4>
				3700	<a name="m_GlobalValue">
				3701	Important Public Members of the <tt>GlobalValue</tt> class
				3702	</a>
				3703	</h4>
Misha Brukman	13fd15c	2004-01-15 00:14:41 +0000	[diff] [blame]	3704
NAKAMURA Takumi	f5af6ad	2011-04-23 00:30:22 +0000	[diff] [blame]	3705	<div>
Misha Brukman	13fd15c	2004-01-15 00:14:41 +0000	[diff] [blame]	3706
Chris Lattner	261efe9	2003-11-25 01:02:51 +0000	[diff] [blame]	3707	<ul>
				3708	<li><tt>bool hasInternalLinkage() const</tt><br>
Chris Lattner	9355b47	2002-09-06 02:50:58 +0000	[diff] [blame]	3709	<tt>bool hasExternalLinkage() const</tt><br>
Chris Lattner	261efe9	2003-11-25 01:02:51 +0000	[diff] [blame]	3710	<tt>void setInternalLinkage(bool HasInternalLinkage)</tt>
				3711	<p> These methods manipulate the linkage characteristics of the <tt>GlobalValue</tt>.</p>
				3712	<p> </p>
				3713	</li>
				3714	<li><tt><a href="#Module">Module</a> *getParent()</tt>
				3715	<p> This returns the <a href="#Module"><tt>Module</tt></a> that the
Misha Brukman	13fd15c	2004-01-15 00:14:41 +0000	[diff] [blame]	3716	GlobalValue is currently embedded into.</p></li>
Chris Lattner	261efe9	2003-11-25 01:02:51 +0000	[diff] [blame]	3717	</ul>
Misha Brukman	13fd15c	2004-01-15 00:14:41 +0000	[diff] [blame]	3718
				3719	</div>
				3720
NAKAMURA Takumi	f5af6ad	2011-04-23 00:30:22 +0000	[diff] [blame]	3721	</div>
				3722
Misha Brukman	13fd15c	2004-01-15 00:14:41 +0000	[diff] [blame]	3723	<!-- ======================================================================= -->
NAKAMURA Takumi	05d0265	2011-04-18 23:59:50 +0000	[diff] [blame]	3724	<h3>
Misha Brukman	13fd15c	2004-01-15 00:14:41 +0000	[diff] [blame]	3725	<a name="Function">The <tt>Function</tt> class</a>
NAKAMURA Takumi	05d0265	2011-04-18 23:59:50 +0000	[diff] [blame]	3726	</h3>
Misha Brukman	13fd15c	2004-01-15 00:14:41 +0000	[diff] [blame]	3727
NAKAMURA Takumi	f5af6ad	2011-04-23 00:30:22 +0000	[diff] [blame]	3728	<div>
Misha Brukman	13fd15c	2004-01-15 00:14:41 +0000	[diff] [blame]	3729
				3730	<p><tt>#include "<a
				3731	href="/doxygen/Function_8h-source.html">llvm/Function.h</a>"</tt><br> doxygen
Misha Brukman	31ca1de	2004-06-03 23:35:54 +0000	[diff] [blame]	3732	info: <a href="/doxygen/classllvm_1_1Function.html">Function Class</a><br>
Reid Spencer	be5e85e	2006-04-14 14:11:48 +0000	[diff] [blame]	3733	Superclasses: <a href="#GlobalValue"><tt>GlobalValue</tt></a>,
				3734	<a href="#Constant"><tt>Constant</tt></a>,
				3735	<a href="#User"><tt>User</tt></a>,
				3736	<a href="#Value"><tt>Value</tt></a></p>
Misha Brukman	13fd15c	2004-01-15 00:14:41 +0000	[diff] [blame]	3737
				3738	<p>The <tt>Function</tt> class represents a single procedure in LLVM. It is
Torok Edwin	8746929	2009-10-12 13:37:29 +0000	[diff] [blame]	3739	actually one of the more complex classes in the LLVM hierarchy because it must
Misha Brukman	13fd15c	2004-01-15 00:14:41 +0000	[diff] [blame]	3740	keep track of a large amount of data. The <tt>Function</tt> class keeps track
Reid Spencer	be5e85e	2006-04-14 14:11:48 +0000	[diff] [blame]	3741	of a list of <a href="#BasicBlock"><tt>BasicBlock</tt></a>s, a list of formal
				3742	<a href="#Argument"><tt>Argument</tt></a>s, and a
				3743	<a href="#SymbolTable"><tt>SymbolTable</tt></a>.</p>
Misha Brukman	13fd15c	2004-01-15 00:14:41 +0000	[diff] [blame]	3744
				3745	<p>The list of <a href="#BasicBlock"><tt>BasicBlock</tt></a>s is the most
				3746	commonly used part of <tt>Function</tt> objects. The list imposes an implicit
				3747	ordering of the blocks in the function, which indicate how the code will be
Benjamin Kramer	8040cd3	2009-10-12 14:46:08 +0000	[diff] [blame]	3748	laid out by the backend. Additionally, the first <a
Misha Brukman	13fd15c	2004-01-15 00:14:41 +0000	[diff] [blame]	3749	href="#BasicBlock"><tt>BasicBlock</tt></a> is the implicit entry node for the
				3750	<tt>Function</tt>. It is not legal in LLVM to explicitly branch to this initial
				3751	block. There are no implicit exit nodes, and in fact there may be multiple exit
				3752	nodes from a single <tt>Function</tt>. If the <a
				3753	href="#BasicBlock"><tt>BasicBlock</tt></a> list is empty, this indicates that
				3754	the <tt>Function</tt> is actually a function declaration: the actual body of the
				3755	function hasn't been linked in yet.</p>
				3756
				3757	<p>In addition to a list of <a href="#BasicBlock"><tt>BasicBlock</tt></a>s, the
				3758	<tt>Function</tt> class also keeps track of the list of formal <a
				3759	href="#Argument"><tt>Argument</tt></a>s that the function receives. This
				3760	container manages the lifetime of the <a href="#Argument"><tt>Argument</tt></a>
				3761	nodes, just like the <a href="#BasicBlock"><tt>BasicBlock</tt></a> list does for
				3762	the <a href="#BasicBlock"><tt>BasicBlock</tt></a>s.</p>
				3763
				3764	<p>The <a href="#SymbolTable"><tt>SymbolTable</tt></a> is a very rarely used
				3765	LLVM feature that is only used when you have to look up a value by name. Aside
				3766	from that, the <a href="#SymbolTable"><tt>SymbolTable</tt></a> is used
				3767	internally to make sure that there are not conflicts between the names of <a
				3768	href="#Instruction"><tt>Instruction</tt></a>s, <a
				3769	href="#BasicBlock"><tt>BasicBlock</tt></a>s, or <a
				3770	href="#Argument"><tt>Argument</tt></a>s in the function body.</p>
				3771
Reid Spencer	8b2da7a	2004-07-18 13:10:31 +0000	[diff] [blame]	3772	<p>Note that <tt>Function</tt> is a <a href="#GlobalValue">GlobalValue</a>
				3773	and therefore also a <a href="#Constant">Constant</a>. The value of the function
				3774	is its address (after linking) which is guaranteed to be constant.</p>
Misha Brukman	13fd15c	2004-01-15 00:14:41 +0000	[diff] [blame]	3775
				3776	<!-- _______________________________________________________________________ -->
NAKAMURA Takumi	05d0265	2011-04-18 23:59:50 +0000	[diff] [blame]	3777	<h4>
				3778	<a name="m_Function">
				3779	Important Public Members of the <tt>Function</tt> class
				3780	</a>
				3781	</h4>
Misha Brukman	13fd15c	2004-01-15 00:14:41 +0000	[diff] [blame]	3782
NAKAMURA Takumi	f5af6ad	2011-04-23 00:30:22 +0000	[diff] [blame]	3783	<div>
Misha Brukman	13fd15c	2004-01-15 00:14:41 +0000	[diff] [blame]	3784
Chris Lattner	261efe9	2003-11-25 01:02:51 +0000	[diff] [blame]	3785	<ul>
				3786	<li><tt>Function(const </tt><tt><a href="#FunctionType">FunctionType</a>
Chris Lattner	ac479e5	2004-08-04 05:10:48 +0000	[diff] [blame]	3787	Ty, LinkageTypes Linkage, const std::string &N = "", Module Parent = 0)</tt>
Misha Brukman	13fd15c	2004-01-15 00:14:41 +0000	[diff] [blame]	3788
				3789	<p>Constructor used when you need to create new <tt>Function</tt>s to add
				3790	the the program. The constructor must specify the type of the function to
Chris Lattner	ac479e5	2004-08-04 05:10:48 +0000	[diff] [blame]	3791	create and what type of linkage the function should have. The <a
				3792	href="#FunctionType"><tt>FunctionType</tt></a> argument
Misha Brukman	13fd15c	2004-01-15 00:14:41 +0000	[diff] [blame]	3793	specifies the formal arguments and return value for the function. The same
Duncan Sands	8036ca4	2007-03-30 12:22:09 +0000	[diff] [blame]	3794	<a href="#FunctionType"><tt>FunctionType</tt></a> value can be used to
Misha Brukman	13fd15c	2004-01-15 00:14:41 +0000	[diff] [blame]	3795	create multiple functions. The <tt>Parent</tt> argument specifies the Module
				3796	in which the function is defined. If this argument is provided, the function
				3797	will automatically be inserted into that module's list of
				3798	functions.</p></li>
				3799
Chris Lattner	62810e3	2008-11-25 18:34:50 +0000	[diff] [blame]	3800	<li><tt>bool isDeclaration()</tt>
Misha Brukman	13fd15c	2004-01-15 00:14:41 +0000	[diff] [blame]	3801
				3802	<p>Return whether or not the <tt>Function</tt> has a body defined. If the
				3803	function is "external", it does not have a body, and thus must be resolved
				3804	by linking with a function defined in a different translation unit.</p></li>
				3805
Chris Lattner	261efe9	2003-11-25 01:02:51 +0000	[diff] [blame]	3806	<li><tt>Function::iterator</tt> - Typedef for basic block list iterator<br>
Chris Lattner	9355b47	2002-09-06 02:50:58 +0000	[diff] [blame]	3807	<tt>Function::const_iterator</tt> - Typedef for const_iterator.<br>
Misha Brukman	13fd15c	2004-01-15 00:14:41 +0000	[diff] [blame]	3808
Chris Lattner	77d6924	2005-03-15 05:19:20 +0000	[diff] [blame]	3809	<tt>begin()</tt>, <tt>end()</tt>
				3810	<tt>size()</tt>, <tt>empty()</tt>
Misha Brukman	13fd15c	2004-01-15 00:14:41 +0000	[diff] [blame]	3811
				3812	<p>These are forwarding methods that make it easy to access the contents of
				3813	a <tt>Function</tt> object's <a href="#BasicBlock"><tt>BasicBlock</tt></a>
				3814	list.</p></li>
				3815
Chris Lattner	261efe9	2003-11-25 01:02:51 +0000	[diff] [blame]	3816	<li><tt>Function::BasicBlockListType &getBasicBlockList()</tt>
Misha Brukman	13fd15c	2004-01-15 00:14:41 +0000	[diff] [blame]	3817
				3818	<p>Returns the list of <a href="#BasicBlock"><tt>BasicBlock</tt></a>s. This
				3819	is necessary to use when you need to update the list or perform a complex
				3820	action that doesn't have a forwarding method.</p></li>
				3821
Chris Lattner	89cc265	2005-03-15 04:48:32 +0000	[diff] [blame]	3822	<li><tt>Function::arg_iterator</tt> - Typedef for the argument list
Chris Lattner	261efe9	2003-11-25 01:02:51 +0000	[diff] [blame]	3823	iterator<br>
Chris Lattner	89cc265	2005-03-15 04:48:32 +0000	[diff] [blame]	3824	<tt>Function::const_arg_iterator</tt> - Typedef for const_iterator.<br>
Misha Brukman	13fd15c	2004-01-15 00:14:41 +0000	[diff] [blame]	3825
Chris Lattner	77d6924	2005-03-15 05:19:20 +0000	[diff] [blame]	3826	<tt>arg_begin()</tt>, <tt>arg_end()</tt>
Chris Lattner	89cc265	2005-03-15 04:48:32 +0000	[diff] [blame]	3827	<tt>arg_size()</tt>, <tt>arg_empty()</tt>
Misha Brukman	13fd15c	2004-01-15 00:14:41 +0000	[diff] [blame]	3828
				3829	<p>These are forwarding methods that make it easy to access the contents of
				3830	a <tt>Function</tt> object's <a href="#Argument"><tt>Argument</tt></a>
				3831	list.</p></li>
				3832
Chris Lattner	261efe9	2003-11-25 01:02:51 +0000	[diff] [blame]	3833	<li><tt>Function::ArgumentListType &getArgumentList()</tt>
Misha Brukman	13fd15c	2004-01-15 00:14:41 +0000	[diff] [blame]	3834
				3835	<p>Returns the list of <a href="#Argument"><tt>Argument</tt></a>s. This is
				3836	necessary to use when you need to update the list or perform a complex
				3837	action that doesn't have a forwarding method.</p></li>
				3838
Chris Lattner	261efe9	2003-11-25 01:02:51 +0000	[diff] [blame]	3839	<li><tt><a href="#BasicBlock">BasicBlock</a> &getEntryBlock()</tt>
Misha Brukman	13fd15c	2004-01-15 00:14:41 +0000	[diff] [blame]	3840
				3841	<p>Returns the entry <a href="#BasicBlock"><tt>BasicBlock</tt></a> for the
				3842	function. Because the entry block for the function is always the first
				3843	block, this returns the first block of the <tt>Function</tt>.</p></li>
				3844
Chris Lattner	261efe9	2003-11-25 01:02:51 +0000	[diff] [blame]	3845	<li><tt><a href="#Type">Type</a> *getReturnType()</tt><br>
				3846	<tt><a href="#FunctionType">FunctionType</a> *getFunctionType()</tt>
Misha Brukman	13fd15c	2004-01-15 00:14:41 +0000	[diff] [blame]	3847
				3848	<p>This traverses the <a href="#Type"><tt>Type</tt></a> of the
				3849	<tt>Function</tt> and returns the return type of the function, or the <a
				3850	href="#FunctionType"><tt>FunctionType</tt></a> of the actual
				3851	function.</p></li>
				3852
Chris Lattner	261efe9	2003-11-25 01:02:51 +0000	[diff] [blame]	3853	<li><tt><a href="#SymbolTable">SymbolTable</a> *getSymbolTable()</tt>
Misha Brukman	13fd15c	2004-01-15 00:14:41 +0000	[diff] [blame]	3854
Chris Lattner	261efe9	2003-11-25 01:02:51 +0000	[diff] [blame]	3855	<p> Return a pointer to the <a href="#SymbolTable"><tt>SymbolTable</tt></a>
Misha Brukman	13fd15c	2004-01-15 00:14:41 +0000	[diff] [blame]	3856	for this <tt>Function</tt>.</p></li>
Chris Lattner	261efe9	2003-11-25 01:02:51 +0000	[diff] [blame]	3857	</ul>
Misha Brukman	13fd15c	2004-01-15 00:14:41 +0000	[diff] [blame]	3858
				3859	</div>
				3860
NAKAMURA Takumi	f5af6ad	2011-04-23 00:30:22 +0000	[diff] [blame]	3861	</div>
				3862
Misha Brukman	13fd15c	2004-01-15 00:14:41 +0000	[diff] [blame]	3863	<!-- ======================================================================= -->
NAKAMURA Takumi	05d0265	2011-04-18 23:59:50 +0000	[diff] [blame]	3864	<h3>
Misha Brukman	13fd15c	2004-01-15 00:14:41 +0000	[diff] [blame]	3865	<a name="GlobalVariable">The <tt>GlobalVariable</tt> class</a>
NAKAMURA Takumi	05d0265	2011-04-18 23:59:50 +0000	[diff] [blame]	3866	</h3>
Misha Brukman	13fd15c	2004-01-15 00:14:41 +0000	[diff] [blame]	3867
NAKAMURA Takumi	f5af6ad	2011-04-23 00:30:22 +0000	[diff] [blame]	3868	<div>
Misha Brukman	13fd15c	2004-01-15 00:14:41 +0000	[diff] [blame]	3869
				3870	<p><tt>#include "<a
				3871	href="/doxygen/GlobalVariable_8h-source.html">llvm/GlobalVariable.h</a>"</tt>
				3872	<br>
Tanya Lattner	a3da777	2004-06-22 08:02:25 +0000	[diff] [blame]	3873	doxygen info: <a href="/doxygen/classllvm_1_1GlobalVariable.html">GlobalVariable
Reid Spencer	be5e85e	2006-04-14 14:11:48 +0000	[diff] [blame]	3874	Class</a><br>
				3875	Superclasses: <a href="#GlobalValue"><tt>GlobalValue</tt></a>,
				3876	<a href="#Constant"><tt>Constant</tt></a>,
				3877	<a href="#User"><tt>User</tt></a>,
				3878	<a href="#Value"><tt>Value</tt></a></p>
Misha Brukman	13fd15c	2004-01-15 00:14:41 +0000	[diff] [blame]	3879
Benjamin Kramer	8040cd3	2009-10-12 14:46:08 +0000	[diff] [blame]	3880	<p>Global variables are represented with the (surprise surprise)
Misha Brukman	13fd15c	2004-01-15 00:14:41 +0000	[diff] [blame]	3881	<tt>GlobalVariable</tt> class. Like functions, <tt>GlobalVariable</tt>s are also
				3882	subclasses of <a href="#GlobalValue"><tt>GlobalValue</tt></a>, and as such are
				3883	always referenced by their address (global values must live in memory, so their
Reid Spencer	be5e85e	2006-04-14 14:11:48 +0000	[diff] [blame]	3884	"name" refers to their constant address). See
				3885	<a href="#GlobalValue"><tt>GlobalValue</tt></a> for more on this. Global
				3886	variables may have an initial value (which must be a
				3887	<a href="#Constant"><tt>Constant</tt></a>), and if they have an initializer,
				3888	they may be marked as "constant" themselves (indicating that their contents
				3889	never change at runtime).</p>
Misha Brukman	13fd15c	2004-01-15 00:14:41 +0000	[diff] [blame]	3890
				3891	<!-- _______________________________________________________________________ -->
NAKAMURA Takumi	05d0265	2011-04-18 23:59:50 +0000	[diff] [blame]	3892	<h4>
				3893	<a name="m_GlobalVariable">
				3894	Important Public Members of the <tt>GlobalVariable</tt> class
				3895	</a>
				3896	</h4>
Misha Brukman	13fd15c	2004-01-15 00:14:41 +0000	[diff] [blame]	3897
NAKAMURA Takumi	f5af6ad	2011-04-23 00:30:22 +0000	[diff] [blame]	3898	<div>
Misha Brukman	13fd15c	2004-01-15 00:14:41 +0000	[diff] [blame]	3899
Chris Lattner	261efe9	2003-11-25 01:02:51 +0000	[diff] [blame]	3900	<ul>
Misha Brukman	13fd15c	2004-01-15 00:14:41 +0000	[diff] [blame]	3901	<li><tt>GlobalVariable(const </tt><tt><a href="#Type">Type</a> *Ty, bool
				3902	isConstant, LinkageTypes& Linkage, <a href="#Constant">Constant</a>
				3903	Initializer = 0, const std::string &Name = "", Module Parent = 0)</tt>
				3904
				3905	<p>Create a new global variable of the specified type. If
				3906	<tt>isConstant</tt> is true then the global variable will be marked as
				3907	unchanging for the program. The Linkage parameter specifies the type of
Duncan Sands	667d4b8	2009-03-07 15:45:40 +0000	[diff] [blame]	3908	linkage (internal, external, weak, linkonce, appending) for the variable.
				3909	If the linkage is InternalLinkage, WeakAnyLinkage, WeakODRLinkage,
				3910	LinkOnceAnyLinkage or LinkOnceODRLinkage,  then the resultant
				3911	global variable will have internal linkage. AppendingLinkage concatenates
				3912	together all instances (in different translation units) of the variable
				3913	into a single variable but is only applicable to arrays.  See
Misha Brukman	13fd15c	2004-01-15 00:14:41 +0000	[diff] [blame]	3914	the <a href="LangRef.html#modulestructure">LLVM Language Reference</a> for
				3915	further details on linkage types. Optionally an initializer, a name, and the
				3916	module to put the variable into may be specified for the global variable as
				3917	well.</p></li>
				3918
Chris Lattner	261efe9	2003-11-25 01:02:51 +0000	[diff] [blame]	3919	<li><tt>bool isConstant() const</tt>
Misha Brukman	13fd15c	2004-01-15 00:14:41 +0000	[diff] [blame]	3920
				3921	<p>Returns true if this is a global variable that is known not to
				3922	be modified at runtime.</p></li>
				3923
Chris Lattner	261efe9	2003-11-25 01:02:51 +0000	[diff] [blame]	3924	<li><tt>bool hasInitializer()</tt>
Misha Brukman	13fd15c	2004-01-15 00:14:41 +0000	[diff] [blame]	3925
				3926	<p>Returns true if this <tt>GlobalVariable</tt> has an intializer.</p></li>
				3927
Chris Lattner	261efe9	2003-11-25 01:02:51 +0000	[diff] [blame]	3928	<li><tt><a href="#Constant">Constant</a> *getInitializer()</tt>
Misha Brukman	13fd15c	2004-01-15 00:14:41 +0000	[diff] [blame]	3929
Benjamin Kramer	8040cd3	2009-10-12 14:46:08 +0000	[diff] [blame]	3930	<p>Returns the initial value for a <tt>GlobalVariable</tt>. It is not legal
Misha Brukman	13fd15c	2004-01-15 00:14:41 +0000	[diff] [blame]	3931	to call this method if there is no initializer.</p></li>
Chris Lattner	261efe9	2003-11-25 01:02:51 +0000	[diff] [blame]	3932	</ul>
Misha Brukman	13fd15c	2004-01-15 00:14:41 +0000	[diff] [blame]	3933
				3934	</div>
				3935
NAKAMURA Takumi	f5af6ad	2011-04-23 00:30:22 +0000	[diff] [blame]	3936	</div>
Chris Lattner	2b78d96	2007-02-03 20:02:25 +0000	[diff] [blame]	3937
Misha Brukman	13fd15c	2004-01-15 00:14:41 +0000	[diff] [blame]	3938	<!-- ======================================================================= -->
NAKAMURA Takumi	05d0265	2011-04-18 23:59:50 +0000	[diff] [blame]	3939	<h3>
Chris Lattner	2b78d96	2007-02-03 20:02:25 +0000	[diff] [blame]	3940	<a name="BasicBlock">The <tt>BasicBlock</tt> class</a>
NAKAMURA Takumi	05d0265	2011-04-18 23:59:50 +0000	[diff] [blame]	3941	</h3>
Misha Brukman	13fd15c	2004-01-15 00:14:41 +0000	[diff] [blame]	3942
NAKAMURA Takumi	f5af6ad	2011-04-23 00:30:22 +0000	[diff] [blame]	3943	<div>
Misha Brukman	13fd15c	2004-01-15 00:14:41 +0000	[diff] [blame]	3944
				3945	<p><tt>#include "<a
Chris Lattner	2b78d96	2007-02-03 20:02:25 +0000	[diff] [blame]	3946	href="/doxygen/BasicBlock_8h-source.html">llvm/BasicBlock.h</a>"</tt><br>
Stefanus Du Toit	24e0411	2009-06-17 21:12:26 +0000	[diff] [blame]	3947	doxygen info: <a href="/doxygen/classllvm_1_1BasicBlock.html">BasicBlock
Chris Lattner	2b78d96	2007-02-03 20:02:25 +0000	[diff] [blame]	3948	Class</a><br>
				3949	Superclass: <a href="#Value"><tt>Value</tt></a></p>
Misha Brukman	13fd15c	2004-01-15 00:14:41 +0000	[diff] [blame]	3950
Nick Lewycky	ccd279d	2011-02-17 02:19:22 +0000	[diff] [blame]	3951	<p>This class represents a single entry single exit section of the code,
Chris Lattner	2b78d96	2007-02-03 20:02:25 +0000	[diff] [blame]	3952	commonly known as a basic block by the compiler community. The
				3953	<tt>BasicBlock</tt> class maintains a list of <a
				3954	href="#Instruction"><tt>Instruction</tt></a>s, which form the body of the block.
				3955	Matching the language definition, the last element of this list of instructions
				3956	is always a terminator instruction (a subclass of the <a
				3957	href="#TerminatorInst"><tt>TerminatorInst</tt></a> class).</p>
				3958
				3959	<p>In addition to tracking the list of instructions that make up the block, the
				3960	<tt>BasicBlock</tt> class also keeps track of the <a
				3961	href="#Function"><tt>Function</tt></a> that it is embedded into.</p>
				3962
				3963	<p>Note that <tt>BasicBlock</tt>s themselves are <a
				3964	href="#Value"><tt>Value</tt></a>s, because they are referenced by instructions
				3965	like branches and can go in the switch tables. <tt>BasicBlock</tt>s have type
				3966	<tt>label</tt>.</p>
Misha Brukman	13fd15c	2004-01-15 00:14:41 +0000	[diff] [blame]	3967
Misha Brukman	13fd15c	2004-01-15 00:14:41 +0000	[diff] [blame]	3968	<!-- _______________________________________________________________________ -->
NAKAMURA Takumi	05d0265	2011-04-18 23:59:50 +0000	[diff] [blame]	3969	<h4>
				3970	<a name="m_BasicBlock">
				3971	Important Public Members of the <tt>BasicBlock</tt> class
				3972	</a>
				3973	</h4>
Misha Brukman	13fd15c	2004-01-15 00:14:41 +0000	[diff] [blame]	3974
NAKAMURA Takumi	f5af6ad	2011-04-23 00:30:22 +0000	[diff] [blame]	3975	<div>
Chris Lattner	261efe9	2003-11-25 01:02:51 +0000	[diff] [blame]	3976	<ul>
Misha Brukman	13fd15c	2004-01-15 00:14:41 +0000	[diff] [blame]	3977
Chris Lattner	2b78d96	2007-02-03 20:02:25 +0000	[diff] [blame]	3978	<li><tt>BasicBlock(const std::string &Name = "", </tt><tt><a
				3979	href="#Function">Function</a> *Parent = 0)</tt>
Misha Brukman	13fd15c	2004-01-15 00:14:41 +0000	[diff] [blame]	3980
Chris Lattner	2b78d96	2007-02-03 20:02:25 +0000	[diff] [blame]	3981	<p>The <tt>BasicBlock</tt> constructor is used to create new basic blocks for
				3982	insertion into a function. The constructor optionally takes a name for the new
				3983	block, and a <a href="#Function"><tt>Function</tt></a> to insert it into. If
				3984	the <tt>Parent</tt> parameter is specified, the new <tt>BasicBlock</tt> is
				3985	automatically inserted at the end of the specified <a
				3986	href="#Function"><tt>Function</tt></a>, if not specified, the BasicBlock must be
				3987	manually inserted into the <a href="#Function"><tt>Function</tt></a>.</p></li>
Misha Brukman	13fd15c	2004-01-15 00:14:41 +0000	[diff] [blame]	3988
Chris Lattner	2b78d96	2007-02-03 20:02:25 +0000	[diff] [blame]	3989	<li><tt>BasicBlock::iterator</tt> - Typedef for instruction list iterator<br>
				3990	<tt>BasicBlock::const_iterator</tt> - Typedef for const_iterator.<br>
				3991	<tt>begin()</tt>, <tt>end()</tt>, <tt>front()</tt>, <tt>back()</tt>,
				3992	<tt>size()</tt>, <tt>empty()</tt>
				3993	STL-style functions for accessing the instruction list.
Misha Brukman	13fd15c	2004-01-15 00:14:41 +0000	[diff] [blame]	3994
Chris Lattner	2b78d96	2007-02-03 20:02:25 +0000	[diff] [blame]	3995	<p>These methods and typedefs are forwarding functions that have the same
				3996	semantics as the standard library methods of the same names. These methods
				3997	expose the underlying instruction list of a basic block in a way that is easy to
				3998	manipulate. To get the full complement of container operations (including
				3999	operations to update the list), you must use the <tt>getInstList()</tt>
				4000	method.</p></li>
Misha Brukman	13fd15c	2004-01-15 00:14:41 +0000	[diff] [blame]	4001
Chris Lattner	2b78d96	2007-02-03 20:02:25 +0000	[diff] [blame]	4002	<li><tt>BasicBlock::InstListType &getInstList()</tt>
Misha Brukman	13fd15c	2004-01-15 00:14:41 +0000	[diff] [blame]	4003
Chris Lattner	2b78d96	2007-02-03 20:02:25 +0000	[diff] [blame]	4004	<p>This method is used to get access to the underlying container that actually
				4005	holds the Instructions. This method must be used when there isn't a forwarding
				4006	function in the <tt>BasicBlock</tt> class for the operation that you would like
				4007	to perform. Because there are no forwarding functions for "updating"
				4008	operations, you need to use this if you want to update the contents of a
				4009	<tt>BasicBlock</tt>.</p></li>
Misha Brukman	13fd15c	2004-01-15 00:14:41 +0000	[diff] [blame]	4010
Chris Lattner	2b78d96	2007-02-03 20:02:25 +0000	[diff] [blame]	4011	<li><tt><a href="#Function">Function</a> *getParent()</tt>
Misha Brukman	13fd15c	2004-01-15 00:14:41 +0000	[diff] [blame]	4012
Chris Lattner	2b78d96	2007-02-03 20:02:25 +0000	[diff] [blame]	4013	<p> Returns a pointer to <a href="#Function"><tt>Function</tt></a> the block is
				4014	embedded into, or a null pointer if it is homeless.</p></li>
Misha Brukman	13fd15c	2004-01-15 00:14:41 +0000	[diff] [blame]	4015
Chris Lattner	2b78d96	2007-02-03 20:02:25 +0000	[diff] [blame]	4016	<li><tt><a href="#TerminatorInst">TerminatorInst</a> *getTerminator()</tt>
Misha Brukman	13fd15c	2004-01-15 00:14:41 +0000	[diff] [blame]	4017
Chris Lattner	2b78d96	2007-02-03 20:02:25 +0000	[diff] [blame]	4018	<p> Returns a pointer to the terminator instruction that appears at the end of
				4019	the <tt>BasicBlock</tt>. If there is no terminator instruction, or if the last
				4020	instruction in the block is not a terminator, then a null pointer is
				4021	returned.</p></li>
Misha Brukman	13fd15c	2004-01-15 00:14:41 +0000	[diff] [blame]	4022
Misha Brukman	13fd15c	2004-01-15 00:14:41 +0000	[diff] [blame]	4023	</ul>
				4024
				4025	</div>
				4026
NAKAMURA Takumi	f5af6ad	2011-04-23 00:30:22 +0000	[diff] [blame]	4027	</div>
Misha Brukman	13fd15c	2004-01-15 00:14:41 +0000	[diff] [blame]	4028
Misha Brukman	13fd15c	2004-01-15 00:14:41 +0000	[diff] [blame]	4029	<!-- ======================================================================= -->
NAKAMURA Takumi	05d0265	2011-04-18 23:59:50 +0000	[diff] [blame]	4030	<h3>
Misha Brukman	13fd15c	2004-01-15 00:14:41 +0000	[diff] [blame]	4031	<a name="Argument">The <tt>Argument</tt> class</a>
NAKAMURA Takumi	05d0265	2011-04-18 23:59:50 +0000	[diff] [blame]	4032	</h3>
Misha Brukman	13fd15c	2004-01-15 00:14:41 +0000	[diff] [blame]	4033
NAKAMURA Takumi	f5af6ad	2011-04-23 00:30:22 +0000	[diff] [blame]	4034	<div>
Misha Brukman	13fd15c	2004-01-15 00:14:41 +0000	[diff] [blame]	4035
				4036	<p>This subclass of Value defines the interface for incoming formal
Chris Lattner	5836082	2005-01-17 00:12:04 +0000	[diff] [blame]	4037	arguments to a function. A Function maintains a list of its formal
Misha Brukman	13fd15c	2004-01-15 00:14:41 +0000	[diff] [blame]	4038	arguments. An argument has a pointer to the parent Function.</p>
				4039
				4040	</div>
				4041
NAKAMURA Takumi	f5af6ad	2011-04-23 00:30:22 +0000	[diff] [blame]	4042	</div>
				4043
Chris Lattner	9355b47	2002-09-06 02:50:58 +0000	[diff] [blame]	4044	<!-- *********************************************************************** -->
Misha Brukman	13fd15c	2004-01-15 00:14:41 +0000	[diff] [blame]	4045	<hr>
				4046	<address>
				4047	<a href="http://jigsaw.w3.org/css-validator/check/referer"><img
Misha Brukman	4440870	2008-12-11 17:34:48 +0000	[diff] [blame]	4048	src="http://jigsaw.w3.org/css-validator/images/vcss-blue" alt="Valid CSS"></a>
Misha Brukman	13fd15c	2004-01-15 00:14:41 +0000	[diff] [blame]	4049	<a href="http://validator.w3.org/check/referer"><img
Gabor Greif	a9c0f2b	2008-06-18 14:05:31 +0000	[diff] [blame]	4050	src="http://www.w3.org/Icons/valid-html401" alt="Valid HTML 4.01 Strict"></a>
Misha Brukman	13fd15c	2004-01-15 00:14:41 +0000	[diff] [blame]	4051
				4052	<a href="mailto:dhurjati@cs.uiuc.edu">Dinakar Dhurjati</a> and
				4053	<a href="mailto:sabre@nondot.org">Chris Lattner</a><br>
NAKAMURA Takumi	b9a3363	2011-04-09 02:13:37 +0000	[diff] [blame]	4054	<a href="http://llvm.org/">The LLVM Compiler Infrastructure</a><br>
Misha Brukman	13fd15c	2004-01-15 00:14:41 +0000	[diff] [blame]	4055	Last modified: $Date$
				4056	</address>
				4057
Chris Lattner	261efe9	2003-11-25 01:02:51 +0000	[diff] [blame]	4058	</body>
				4059	</html>