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Misha Brukman	c540240	2004-01-15 18:34:11 +0000	[diff] [blame]	1	<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN"
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Reid Spencer	7fa6d52	2005-01-11 05:16:23 +0000	[diff] [blame]	5	<meta http-equiv="Content-Type" content="text/html; charset=utf-8">
Misha Brukman	c540240	2004-01-15 18:34:11 +0000	[diff] [blame]	6	<title>Writing an LLVM Pass</title>
				7	<link rel="stylesheet" href="llvm.css" type="text/css">
				8	</head>
				9	<body>
Chris Lattner	c6bb824	2002-08-08 20:11:18 +0000	[diff] [blame]	10
Misha Brukman	c540240	2004-01-15 18:34:11 +0000	[diff] [blame]	11	<div class="doc_title">
				12	Writing an LLVM Pass
				13	</div>
Chris Lattner	c6bb824	2002-08-08 20:11:18 +0000	[diff] [blame]	14
				15	<ol>
Misha Brukman	c540240	2004-01-15 18:34:11 +0000	[diff] [blame]	16	<li><a href="#introduction">Introduction - What is a pass?</a></li>
Chris Lattner	c6bb824	2002-08-08 20:11:18 +0000	[diff] [blame]	17	<li><a href="#quickstart">Quick Start - Writing hello world</a>
				18	<ul>
Misha Brukman	c540240	2004-01-15 18:34:11 +0000	[diff] [blame]	19	<li><a href="#makefile">Setting up the build environment</a></li>
				20	<li><a href="#basiccode">Basic code required</a></li>
Chris Lattner	c6bb824	2002-08-08 20:11:18 +0000	[diff] [blame]	21	<li><a href="#running">Running a pass with <tt>opt</tt>
Chris Lattner	8fdb246	2004-09-18 06:39:35 +0000	[diff] [blame]	22	or <tt>analyze</tt></a></li>
Misha Brukman	c540240	2004-01-15 18:34:11 +0000	[diff] [blame]	23	</ul></li>
Chris Lattner	c6bb824	2002-08-08 20:11:18 +0000	[diff] [blame]	24	<li><a href="#passtype">Pass classes and requirements</a>
				25	<ul>
Misha Brukman	c540240	2004-01-15 18:34:11 +0000	[diff] [blame]	26	<li><a href="#ImmutablePass">The <tt>ImmutablePass</tt> class</a></li>
Chris Lattner	f627892	2004-09-20 04:36:29 +0000	[diff] [blame]	27	<li><a href="#ModulePass">The <tt>ModulePass</tt> class</a>
Chris Lattner	c6bb824	2002-08-08 20:11:18 +0000	[diff] [blame]	28	<ul>
Chris Lattner	f627892	2004-09-20 04:36:29 +0000	[diff] [blame]	29	<li><a href="#runOnModule">The <tt>runOnModule</tt> method</a></li>
Misha Brukman	c540240	2004-01-15 18:34:11 +0000	[diff] [blame]	30	</ul></li>
Chris Lattner	8fdb246	2004-09-18 06:39:35 +0000	[diff] [blame]	31	<li><a href="#CallGraphSCCPass">The <tt>CallGraphSCCPass</tt> class</a>
				32	<ul>
				33	<li><a href="#doInitialization_scc">The <tt>doInitialization(Module
				34	&)</tt> method</a></li>
				35	<li><a href="#runOnSCC">The <tt>runOnSCC</tt> method</a></li>
				36	<li><a href="#doFinalization_scc">The <tt>doFinalization(Module
				37	&)</tt> method</a></li>
				38	</ul></li>
Chris Lattner	c6bb824	2002-08-08 20:11:18 +0000	[diff] [blame]	39	<li><a href="#FunctionPass">The <tt>FunctionPass</tt> class</a>
				40	<ul>
Chris Lattner	d0713f9	2002-09-12 17:06:43 +0000	[diff] [blame]	41	<li><a href="#doInitialization_mod">The <tt>doInitialization(Module
Misha Brukman	c540240	2004-01-15 18:34:11 +0000	[diff] [blame]	42	&)</tt> method</a></li>
				43	<li><a href="#runOnFunction">The <tt>runOnFunction</tt> method</a></li>
Chris Lattner	d0713f9	2002-09-12 17:06:43 +0000	[diff] [blame]	44	<li><a href="#doFinalization_mod">The <tt>doFinalization(Module
Misha Brukman	c540240	2004-01-15 18:34:11 +0000	[diff] [blame]	45	&)</tt> method</a></li>
				46	</ul></li>
Chris Lattner	c6bb824	2002-08-08 20:11:18 +0000	[diff] [blame]	47	<li><a href="#BasicBlockPass">The <tt>BasicBlockPass</tt> class</a>
				48	<ul>
Chris Lattner	d0713f9	2002-09-12 17:06:43 +0000	[diff] [blame]	49	<li><a href="#doInitialization_fn">The <tt>doInitialization(Function
Misha Brukman	c540240	2004-01-15 18:34:11 +0000	[diff] [blame]	50	&)</tt> method</a></li>
				51	<li><a href="#runOnBasicBlock">The <tt>runOnBasicBlock</tt>
				52	method</a></li>
Chris Lattner	d0713f9	2002-09-12 17:06:43 +0000	[diff] [blame]	53	<li><a href="#doFinalization_fn">The <tt>doFinalization(Function
Misha Brukman	c540240	2004-01-15 18:34:11 +0000	[diff] [blame]	54	&)</tt> method</a></li>
				55	</ul></li>
Brian Gaeke	cab8b6f	2003-07-17 18:53:20 +0000	[diff] [blame]	56	<li><a href="#MachineFunctionPass">The <tt>MachineFunctionPass</tt>
				57	class</a>
Brian Gaeke	6a33f36	2003-07-22 20:53:20 +0000	[diff] [blame]	58	<ul>
				59	<li><a href="#runOnMachineFunction">The
Misha Brukman	c540240	2004-01-15 18:34:11 +0000	[diff] [blame]	60	<tt>runOnMachineFunction(MachineFunction &)</tt> method</a></li>
				61	</ul></li>
Chris Lattner	c6bb824	2002-08-08 20:11:18 +0000	[diff] [blame]	62	</ul>
				63	<li><a href="#registration">Pass Registration</a>
				64	<ul>
Misha Brukman	c540240	2004-01-15 18:34:11 +0000	[diff] [blame]	65	<li><a href="#print">The <tt>print</tt> method</a></li>
				66	</ul></li>
Chris Lattner	c6bb824	2002-08-08 20:11:18 +0000	[diff] [blame]	67	<li><a href="#interaction">Specifying interactions between passes</a>
				68	<ul>
Misha Brukman	c540240	2004-01-15 18:34:11 +0000	[diff] [blame]	69	<li><a href="#getAnalysisUsage">The <tt>getAnalysisUsage</tt>
				70	method</a></li>
Chris Lattner	8925627	2004-03-17 21:09:55 +0000	[diff] [blame]	71	<li><a href="#AU::addRequired">The <tt>AnalysisUsage::addRequired<></tt> and <tt>AnalysisUsage::addRequiredTransitive<></tt> methods</a></li>
				72	<li><a href="#AU::addPreserved">The <tt>AnalysisUsage::addPreserved<></tt> method</a></li>
				73	<li><a href="#AU::examples">Example implementations of <tt>getAnalysisUsage</tt></a></li>
				74	<li><a href="#getAnalysis">The <tt>getAnalysis<></tt> and <tt>getAnalysisToUpdate<></tt> methods</a></li>
Misha Brukman	c540240	2004-01-15 18:34:11 +0000	[diff] [blame]	75	</ul></li>
Chris Lattner	7991070	2002-08-22 19:21:04 +0000	[diff] [blame]	76	<li><a href="#analysisgroup">Implementing Analysis Groups</a>
				77	<ul>
Misha Brukman	c540240	2004-01-15 18:34:11 +0000	[diff] [blame]	78	<li><a href="#agconcepts">Analysis Group Concepts</a></li>
				79	<li><a href="#registerag">Using <tt>RegisterAnalysisGroup</tt></a></li>
				80	</ul></li>
Tanya Lattner	d538365	2004-11-19 01:25:14 +0000	[diff] [blame]	81	<li><a href="#passStatistics">Pass Statistics</a>
Chris Lattner	c6bb824	2002-08-08 20:11:18 +0000	[diff] [blame]	82	<li><a href="#passmanager">What PassManager does</a>
				83	<ul>
Misha Brukman	c540240	2004-01-15 18:34:11 +0000	[diff] [blame]	84	<li><a href="#releaseMemory">The <tt>releaseMemory</tt> method</a></li>
				85	</ul></li>
Jim Laskey	5fa8fff	2006-08-04 18:10:12 +0000	[diff] [blame]	86	<li><a href="#registering">Registering dynamically loaded passes</a>
				87	<ul>
				88	<li><a href="#registering_existing">Using existing registries</a></li>
				89	<li><a href="#registering_new">Creating new registries</a></li>
				90	</ul></li>
Chris Lattner	480e2ef	2002-09-06 02:02:58 +0000	[diff] [blame]	91	<li><a href="#debughints">Using GDB with dynamically loaded passes</a>
				92	<ul>
Misha Brukman	c540240	2004-01-15 18:34:11 +0000	[diff] [blame]	93	<li><a href="#breakpoint">Setting a breakpoint in your pass</a></li>
				94	<li><a href="#debugmisc">Miscellaneous Problems</a></li>
				95	</ul></li>
Chris Lattner	c6bb824	2002-08-08 20:11:18 +0000	[diff] [blame]	96	<li><a href="#future">Future extensions planned</a>
				97	<ul>
Misha Brukman	c540240	2004-01-15 18:34:11 +0000	[diff] [blame]	98	<li><a href="#SMP">Multithreaded LLVM</a></li>
Chris Lattner	f627892	2004-09-20 04:36:29 +0000	[diff] [blame]	99	<li><a href="#PassFunctionPass"><tt>ModulePass</tt>es requiring
Misha Brukman	c540240	2004-01-15 18:34:11 +0000	[diff] [blame]	100	<tt>FunctionPass</tt>es</a></li>
				101	</ul></li>
				102	</ol>
Chris Lattner	38c633d	2002-08-08 20:23:41 +0000	[diff] [blame]	103
Chris Lattner	7911ce2	2004-05-23 21:07:27 +0000	[diff] [blame]	104	<div class="doc_author">
Jim Laskey	5fa8fff	2006-08-04 18:10:12 +0000	[diff] [blame]	105	<p>Written by <a href="mailto:sabre@nondot.org">Chris Lattner</a>,
				106	<a href="mailto:jlaskey@apple.com">Jim Laskey</a></p>
Misha Brukman	c540240	2004-01-15 18:34:11 +0000	[diff] [blame]	107	</div>
Chris Lattner	c6bb824	2002-08-08 20:11:18 +0000	[diff] [blame]	108
				109	<!-- *********************************************************************** -->
Misha Brukman	c540240	2004-01-15 18:34:11 +0000	[diff] [blame]	110	<div class="doc_section">
				111	<a name="introduction">Introduction - What is a pass?</a>
				112	</div>
Chris Lattner	c6bb824	2002-08-08 20:11:18 +0000	[diff] [blame]	113	<!-- *********************************************************************** -->
				114
Misha Brukman	c540240	2004-01-15 18:34:11 +0000	[diff] [blame]	115	<div class="doc_text">
				116
				117	<p>The LLVM Pass Framework is an important part of the LLVM system, because LLVM
Chris Lattner	8fdb246	2004-09-18 06:39:35 +0000	[diff] [blame]	118	passes are where most of the interesting parts of the compiler exist. Passes
				119	perform the transformations and optimizations that make up the compiler, they
				120	build the analysis results that are used by these transformations, and they are,
				121	above all, a structuring technique for compiler code.</p>
Chris Lattner	c6bb824	2002-08-08 20:11:18 +0000	[diff] [blame]	122
Misha Brukman	c540240	2004-01-15 18:34:11 +0000	[diff] [blame]	123	<p>All LLVM passes are subclasses of the <tt><a
Reid Spencer	05fe4b0	2006-03-14 05:39:39 +0000	[diff] [blame]	124	href="http://llvm.org/doxygen/classllvm_1_1Pass.html">Pass</a></tt>
Misha Brukman	c540240	2004-01-15 18:34:11 +0000	[diff] [blame]	125	class, which implement functionality by overriding virtual methods inherited
Chris Lattner	f627892	2004-09-20 04:36:29 +0000	[diff] [blame]	126	from <tt>Pass</tt>. Depending on how your pass works, you should inherit from
				127	the <tt><a href="#ModulePass">ModulePass</a></tt>, <tt><a
				128	href="#CallGraphSCCPass">CallGraphSCCPass</a></tt>, <tt><a
				129	href="#FunctionPass">FunctionPass</a></tt>, or <tt><a
Chris Lattner	8fdb246	2004-09-18 06:39:35 +0000	[diff] [blame]	130	href="#BasicBlockPass">BasicBlockPass</a></tt> classes, which gives the system
				131	more information about what your pass does, and how it can be combined with
				132	other passes. One of the main features of the LLVM Pass Framework is that it
				133	schedules passes to run in an efficient way based on the constraints that your
				134	pass meets (which are indicated by which class they derive from).</p>
Chris Lattner	c6bb824	2002-08-08 20:11:18 +0000	[diff] [blame]	135
Misha Brukman	c540240	2004-01-15 18:34:11 +0000	[diff] [blame]	136	<p>We start by showing you how to construct a pass, everything from setting up
				137	the code, to compiling, loading, and executing it. After the basics are down,
				138	more advanced features are discussed.</p>
Chris Lattner	c6bb824	2002-08-08 20:11:18 +0000	[diff] [blame]	139
Misha Brukman	c540240	2004-01-15 18:34:11 +0000	[diff] [blame]	140	</div>
Chris Lattner	c6bb824	2002-08-08 20:11:18 +0000	[diff] [blame]	141
				142	<!-- *********************************************************************** -->
Misha Brukman	c540240	2004-01-15 18:34:11 +0000	[diff] [blame]	143	<div class="doc_section">
				144	<a name="quickstart">Quick Start - Writing hello world</a>
				145	</div>
Chris Lattner	c6bb824	2002-08-08 20:11:18 +0000	[diff] [blame]	146	<!-- *********************************************************************** -->
				147
Misha Brukman	c540240	2004-01-15 18:34:11 +0000	[diff] [blame]	148	<div class="doc_text">
				149
				150	<p>Here we describe how to write the "hello world" of passes. The "Hello" pass
				151	is designed to simply print out the name of non-external functions that exist in
Chris Lattner	8fdb246	2004-09-18 06:39:35 +0000	[diff] [blame]	152	the program being compiled. It does not modify the program at all, it just
Chris Lattner	c6bb824	2002-08-08 20:11:18 +0000	[diff] [blame]	153	inspects it. The source code and files for this pass are available in the LLVM
Misha Brukman	c540240	2004-01-15 18:34:11 +0000	[diff] [blame]	154	source tree in the <tt>lib/Transforms/Hello</tt> directory.</p>
Chris Lattner	c6bb824	2002-08-08 20:11:18 +0000	[diff] [blame]	155
Misha Brukman	c540240	2004-01-15 18:34:11 +0000	[diff] [blame]	156	</div>
Chris Lattner	c6bb824	2002-08-08 20:11:18 +0000	[diff] [blame]	157
				158	<!-- ======================================================================= -->
Misha Brukman	c540240	2004-01-15 18:34:11 +0000	[diff] [blame]	159	<div class="doc_subsection">
				160	<a name="makefile">Setting up the build environment</a>
				161	</div>
Chris Lattner	c6bb824	2002-08-08 20:11:18 +0000	[diff] [blame]	162
Misha Brukman	c540240	2004-01-15 18:34:11 +0000	[diff] [blame]	163	<div class="doc_text">
				164
Reid Spencer	1bc1934	2004-12-11 05:12:57 +0000	[diff] [blame]	165	<p>First, you need to create a new directory somewhere in the LLVM source
				166	base. For this example, we'll assume that you made
				167	<tt>lib/Transforms/Hello</tt>. Next, you must set up a build script
				168	(Makefile) that will compile the source code for the new pass. To do this,
				169	copy the following into <tt>Makefile</tt>:</p>
				170	<hr/>
Misha Brukman	c540240	2004-01-15 18:34:11 +0000	[diff] [blame]	171
Jim Laskey	5fa8fff	2006-08-04 18:10:12 +0000	[diff] [blame]	172	<div class="doc_code"><pre>
Chris Lattner	c6bb824	2002-08-08 20:11:18 +0000	[diff] [blame]	173	# Makefile for hello pass
Chris Lattner	c6bb824	2002-08-08 20:11:18 +0000	[diff] [blame]	174
Chris Lattner	17a4c3e	2002-08-14 20:06:13 +0000	[diff] [blame]	175	# Path to top level of LLVM heirarchy
Chris Lattner	7ce83e5	2002-08-14 20:07:01 +0000	[diff] [blame]	176	LEVEL = ../../..
Chris Lattner	17a4c3e	2002-08-14 20:06:13 +0000	[diff] [blame]	177
				178	# Name of the library to build
Reid Spencer	7fa6d52	2005-01-11 05:16:23 +0000	[diff] [blame]	179	LIBRARYNAME = Hello
Chris Lattner	17a4c3e	2002-08-14 20:06:13 +0000	[diff] [blame]	180
Reid Spencer	7fa6d52	2005-01-11 05:16:23 +0000	[diff] [blame]	181	# Build a dynamically linkable shared object
Chris Lattner	17a4c3e	2002-08-14 20:06:13 +0000	[diff] [blame]	182	SHARED_LIBRARY = 1
				183
Reid Spencer	7fa6d52	2005-01-11 05:16:23 +0000	[diff] [blame]	184	# Make the shared library become a loadable module so the tools can
				185	# dlopen/dlsym on the resulting library.
Robert Bocchino	3cf817d	2006-01-06 22:49:23 +0000	[diff] [blame]	186	LOADABLE_MODULE = 1
Reid Spencer	7fa6d52	2005-01-11 05:16:23 +0000	[diff] [blame]	187
Chris Lattner	17a4c3e	2002-08-14 20:06:13 +0000	[diff] [blame]	188	# Include the makefile implementation stuff
				189	include $(LEVEL)/Makefile.common
Jim Laskey	5fa8fff	2006-08-04 18:10:12 +0000	[diff] [blame]	190	</pre></div>
Chris Lattner	c6bb824	2002-08-08 20:11:18 +0000	[diff] [blame]	191
Misha Brukman	c540240	2004-01-15 18:34:11 +0000	[diff] [blame]	192	<p>This makefile specifies that all of the <tt>.cpp</tt> files in the current
Chris Lattner	c6bb824	2002-08-08 20:11:18 +0000	[diff] [blame]	193	directory are to be compiled and linked together into a
Reid Spencer	7fa6d52	2005-01-11 05:16:23 +0000	[diff] [blame]	194	<tt>Debug/lib/Hello.so</tt> shared object that can be dynamically loaded by
				195	the <tt>opt</tt> or <tt>analyze</tt> tools via their <tt>-load</tt> options.
				196	If your operating system uses a suffix other than .so (such as windows or
				197	Mac OS/X), the appropriate extension will be used.</p>
John Criswell	f9c7865	2004-01-26 21:26:54 +0000	[diff] [blame]	198
Misha Brukman	c540240	2004-01-15 18:34:11 +0000	[diff] [blame]	199	<p>Now that we have the build scripts set up, we just need to write the code for
				200	the pass itself.</p>
Chris Lattner	c6bb824	2002-08-08 20:11:18 +0000	[diff] [blame]	201
Misha Brukman	c540240	2004-01-15 18:34:11 +0000	[diff] [blame]	202	</div>
Chris Lattner	c6bb824	2002-08-08 20:11:18 +0000	[diff] [blame]	203
				204	<!-- ======================================================================= -->
Misha Brukman	c540240	2004-01-15 18:34:11 +0000	[diff] [blame]	205	<div class="doc_subsection">
				206	<a name="basiccode">Basic code required</a>
				207	</div>
Chris Lattner	c6bb824	2002-08-08 20:11:18 +0000	[diff] [blame]	208
Misha Brukman	c540240	2004-01-15 18:34:11 +0000	[diff] [blame]	209	<div class="doc_text">
				210
				211	<p>Now that we have a way to compile our new pass, we just have to write it.
				212	Start out with:</p>
Chris Lattner	c6bb824	2002-08-08 20:11:18 +0000	[diff] [blame]	213
Jim Laskey	5fa8fff	2006-08-04 18:10:12 +0000	[diff] [blame]	214	<div class="doc_code"><pre>
Reid Spencer	05fe4b0	2006-03-14 05:39:39 +0000	[diff] [blame]	215	<b>#include</b> "<a href="http://llvm.org/doxygen/Pass_8h-source.html">llvm/Pass.h</a>"
				216	<b>#include</b> "<a href="http://llvm.org/doxygen/Function_8h-source.html">llvm/Function.h</a>"
Jim Laskey	5fa8fff	2006-08-04 18:10:12 +0000	[diff] [blame]	217	</pre></div>
Chris Lattner	c6bb824	2002-08-08 20:11:18 +0000	[diff] [blame]	218
Misha Brukman	c540240	2004-01-15 18:34:11 +0000	[diff] [blame]	219	<p>Which are needed because we are writing a <tt><a
Reid Spencer	05fe4b0	2006-03-14 05:39:39 +0000	[diff] [blame]	220	href="http://llvm.org/doxygen/classllvm_1_1Pass.html">Pass</a></tt>, and
Misha Brukman	c540240	2004-01-15 18:34:11 +0000	[diff] [blame]	221	we are operating on <tt><a
Reid Spencer	05fe4b0	2006-03-14 05:39:39 +0000	[diff] [blame]	222	href="http://llvm.org/doxygen/classllvm_1_1Function.html">Function</a></tt>'s.</p>
Chris Lattner	c6bb824	2002-08-08 20:11:18 +0000	[diff] [blame]	223
Misha Brukman	c540240	2004-01-15 18:34:11 +0000	[diff] [blame]	224	<p>Next we have:</p>
Jim Laskey	5fa8fff	2006-08-04 18:10:12 +0000	[diff] [blame]	225	<div class="doc_code"><pre>
Jonathan Manton	65acb30	2004-06-30 18:10:30 +0000	[diff] [blame]	226	<b>using namespace llvm;</b>
Jim Laskey	5fa8fff	2006-08-04 18:10:12 +0000	[diff] [blame]	227	</pre></div>
Jonathan Manton	65acb30	2004-06-30 18:10:30 +0000	[diff] [blame]	228	<p>... which is required because the functions from the include files
				229	live in the llvm namespace.
				230	</p>
				231
				232	<p>Next we have:</p>
Chris Lattner	c6bb824	2002-08-08 20:11:18 +0000	[diff] [blame]	233
Jim Laskey	5fa8fff	2006-08-04 18:10:12 +0000	[diff] [blame]	234	<div class="doc_code"><pre>
Chris Lattner	c6bb824	2002-08-08 20:11:18 +0000	[diff] [blame]	235	<b>namespace</b> {
Jim Laskey	5fa8fff	2006-08-04 18:10:12 +0000	[diff] [blame]	236	</pre></div>
Chris Lattner	c6bb824	2002-08-08 20:11:18 +0000	[diff] [blame]	237
Misha Brukman	c540240	2004-01-15 18:34:11 +0000	[diff] [blame]	238	<p>... which starts out an anonymous namespace. Anonymous namespaces are to C++
Chris Lattner	c6bb824	2002-08-08 20:11:18 +0000	[diff] [blame]	239	what the "<tt>static</tt>" keyword is to C (at global scope). It makes the
				240	things declared inside of the anonymous namespace only visible to the current
				241	file. If you're not familiar with them, consult a decent C++ book for more
Misha Brukman	c540240	2004-01-15 18:34:11 +0000	[diff] [blame]	242	information.</p>
Chris Lattner	c6bb824	2002-08-08 20:11:18 +0000	[diff] [blame]	243
Misha Brukman	c540240	2004-01-15 18:34:11 +0000	[diff] [blame]	244	<p>Next, we declare our pass itself:</p>
Chris Lattner	c6bb824	2002-08-08 20:11:18 +0000	[diff] [blame]	245
Jim Laskey	5fa8fff	2006-08-04 18:10:12 +0000	[diff] [blame]	246	<div class="doc_code"><pre>
Chris Lattner	c6bb824	2002-08-08 20:11:18 +0000	[diff] [blame]	247	<b>struct</b> Hello : <b>public</b> <a href="#FunctionPass">FunctionPass</a> {
Jim Laskey	5fa8fff	2006-08-04 18:10:12 +0000	[diff] [blame]	248	</pre></div><p>
Chris Lattner	c6bb824	2002-08-08 20:11:18 +0000	[diff] [blame]	249
Misha Brukman	c540240	2004-01-15 18:34:11 +0000	[diff] [blame]	250	<p>This declares a "<tt>Hello</tt>" class that is a subclass of <tt><a
Reid Spencer	05fe4b0	2006-03-14 05:39:39 +0000	[diff] [blame]	251	href="http://llvm.org/doxygen/classllvm_1_1FunctionPass.html">FunctionPass</a></tt>.
Chris Lattner	d6ea926	2002-09-09 03:48:46 +0000	[diff] [blame]	252	The different builtin pass subclasses are described in detail <a
Misha Brukman	c540240	2004-01-15 18:34:11 +0000	[diff] [blame]	253	href="#passtype">later</a>, but for now, know that <a
				254	href="#FunctionPass"><tt>FunctionPass</tt></a>'s operate a function at a
				255	time.</p>
Chris Lattner	c6bb824	2002-08-08 20:11:18 +0000	[diff] [blame]	256
Jim Laskey	5fa8fff	2006-08-04 18:10:12 +0000	[diff] [blame]	257	<div class="doc_code"><pre>
Misha Brukman	c540240	2004-01-15 18:34:11 +0000	[diff] [blame]	258	<b>virtual bool</b> <a href="#runOnFunction">runOnFunction</a>(Function &F) {
Chris Lattner	c6bb824	2002-08-08 20:11:18 +0000	[diff] [blame]	259	std::cerr << "<i>Hello: </i>" << F.getName() << "\n";
				260	<b>return false</b>;
				261	}
				262	}; <i>// end of struct Hello</i>
Jim Laskey	5fa8fff	2006-08-04 18:10:12 +0000	[diff] [blame]	263	</pre></div>
Chris Lattner	c6bb824	2002-08-08 20:11:18 +0000	[diff] [blame]	264
Misha Brukman	c540240	2004-01-15 18:34:11 +0000	[diff] [blame]	265	<p>We declare a "<a href="#runOnFunction"><tt>runOnFunction</tt></a>" method,
				266	which overloads an abstract virtual method inherited from <a
Chris Lattner	c6bb824	2002-08-08 20:11:18 +0000	[diff] [blame]	267	href="#FunctionPass"><tt>FunctionPass</tt></a>. This is where we are supposed
				268	to do our thing, so we just print out our message with the name of each
Misha Brukman	c540240	2004-01-15 18:34:11 +0000	[diff] [blame]	269	function.</p>
Chris Lattner	c6bb824	2002-08-08 20:11:18 +0000	[diff] [blame]	270
Jim Laskey	5fa8fff	2006-08-04 18:10:12 +0000	[diff] [blame]	271	<div class="doc_code"><pre>
Chris Lattner	c6bb824	2002-08-08 20:11:18 +0000	[diff] [blame]	272	RegisterOpt<Hello> X("<i>hello</i>", "<i>Hello World Pass</i>");
				273	} <i>// end of anonymous namespace</i>
Jim Laskey	5fa8fff	2006-08-04 18:10:12 +0000	[diff] [blame]	274	</pre></div>
Chris Lattner	c6bb824	2002-08-08 20:11:18 +0000	[diff] [blame]	275
Misha Brukman	c540240	2004-01-15 18:34:11 +0000	[diff] [blame]	276	<p>Lastly, we register our class <tt>Hello</tt>, giving it a command line
				277	argument "<tt>hello</tt>", and a name "<tt>Hello World Pass</tt>". There are
				278	several different ways of <a href="#registration">registering your pass</a>,
				279	depending on what it is to be used for. For "optimizations" we use the
				280	<tt>RegisterOpt</tt> template.</p>
Chris Lattner	c6bb824	2002-08-08 20:11:18 +0000	[diff] [blame]	281
Misha Brukman	c540240	2004-01-15 18:34:11 +0000	[diff] [blame]	282	<p>As a whole, the <tt>.cpp</tt> file looks like:</p>
Chris Lattner	c6bb824	2002-08-08 20:11:18 +0000	[diff] [blame]	283
Jim Laskey	5fa8fff	2006-08-04 18:10:12 +0000	[diff] [blame]	284	<div class="doc_code"><pre>
Reid Spencer	05fe4b0	2006-03-14 05:39:39 +0000	[diff] [blame]	285	<b>#include</b> "<a href="http://llvm.org/doxygen/Pass_8h-source.html">llvm/Pass.h</a>"
				286	<b>#include</b> "<a href="http://llvm.org/doxygen/Function_8h-source.html">llvm/Function.h</a>"
Chris Lattner	c6bb824	2002-08-08 20:11:18 +0000	[diff] [blame]	287
Jonathan Manton	65acb30	2004-06-30 18:10:30 +0000	[diff] [blame]	288	<b>using namespace llvm;</b>
				289
Chris Lattner	c6bb824	2002-08-08 20:11:18 +0000	[diff] [blame]	290	<b>namespace</b> {
				291	<b>struct Hello</b> : <b>public</b> <a href="#FunctionPass">FunctionPass</a> {
Misha Brukman	c540240	2004-01-15 18:34:11 +0000	[diff] [blame]	292	<b>virtual bool</b> <a href="#runOnFunction">runOnFunction</a>(Function &F) {
Chris Lattner	c6bb824	2002-08-08 20:11:18 +0000	[diff] [blame]	293	std::cerr << "<i>Hello: </i>" << F.getName() << "\n";
				294	<b>return false</b>;
				295	}
				296	};
				297
				298	RegisterOpt<Hello> X("<i>hello</i>", "<i>Hello World Pass</i>");
				299	}
Jim Laskey	5fa8fff	2006-08-04 18:10:12 +0000	[diff] [blame]	300	</pre></div>
Chris Lattner	c6bb824	2002-08-08 20:11:18 +0000	[diff] [blame]	301
Misha Brukman	c540240	2004-01-15 18:34:11 +0000	[diff] [blame]	302	<p>Now that it's all together, compile the file with a simple "<tt>gmake</tt>"
Chris Lattner	c6bb824	2002-08-08 20:11:18 +0000	[diff] [blame]	303	command in the local directory and you should get a new
Reid Spencer	7fa6d52	2005-01-11 05:16:23 +0000	[diff] [blame]	304	"<tt>Debug/lib/Hello.so</tt> file. Note that everything in this file is
Chris Lattner	c6bb824	2002-08-08 20:11:18 +0000	[diff] [blame]	305	contained in an anonymous namespace: this reflects the fact that passes are self
				306	contained units that do not need external interfaces (although they can have
Misha Brukman	c540240	2004-01-15 18:34:11 +0000	[diff] [blame]	307	them) to be useful.</p>
Chris Lattner	c6bb824	2002-08-08 20:11:18 +0000	[diff] [blame]	308
Misha Brukman	c540240	2004-01-15 18:34:11 +0000	[diff] [blame]	309	</div>
Chris Lattner	c6bb824	2002-08-08 20:11:18 +0000	[diff] [blame]	310
				311	<!-- ======================================================================= -->
Misha Brukman	c540240	2004-01-15 18:34:11 +0000	[diff] [blame]	312	<div class="doc_subsection">
				313	<a name="running">Running a pass with <tt>opt</tt> or <tt>analyze</tt></a>
				314	</div>
Chris Lattner	c6bb824	2002-08-08 20:11:18 +0000	[diff] [blame]	315
Misha Brukman	c540240	2004-01-15 18:34:11 +0000	[diff] [blame]	316	<div class="doc_text">
				317
John Criswell	f9c7865	2004-01-26 21:26:54 +0000	[diff] [blame]	318	<p>Now that you have a brand new shiny shared object file, we can use the
Chris Lattner	c6bb824	2002-08-08 20:11:18 +0000	[diff] [blame]	319	<tt>opt</tt> command to run an LLVM program through your pass. Because you
				320	registered your pass with the <tt>RegisterOpt</tt> template, you will be able to
Misha Brukman	c540240	2004-01-15 18:34:11 +0000	[diff] [blame]	321	use the <tt>opt</tt> tool to access it, once loaded.</p>
Chris Lattner	c6bb824	2002-08-08 20:11:18 +0000	[diff] [blame]	322
Misha Brukman	c540240	2004-01-15 18:34:11 +0000	[diff] [blame]	323	<p>To test it, follow the example at the end of the <a
Chris Lattner	c6bb824	2002-08-08 20:11:18 +0000	[diff] [blame]	324	href="GettingStarted.html">Getting Started Guide</a> to compile "Hello World" to
				325	LLVM. We can now run the bytecode file (<tt>hello.bc</tt>) for the program
				326	through our transformation like this (or course, any bytecode file will
Misha Brukman	c540240	2004-01-15 18:34:11 +0000	[diff] [blame]	327	work):</p>
Chris Lattner	c6bb824	2002-08-08 20:11:18 +0000	[diff] [blame]	328
Jim Laskey	5fa8fff	2006-08-04 18:10:12 +0000	[diff] [blame]	329	<div class="doc_code"><pre>
Reid Spencer	7fa6d52	2005-01-11 05:16:23 +0000	[diff] [blame]	330	$ opt -load ../../../Debug/lib/Hello.so -hello < hello.bc > /dev/null
Chris Lattner	c6bb824	2002-08-08 20:11:18 +0000	[diff] [blame]	331	Hello: __main
				332	Hello: puts
				333	Hello: main
Jim Laskey	5fa8fff	2006-08-04 18:10:12 +0000	[diff] [blame]	334	</pre></div>
Chris Lattner	c6bb824	2002-08-08 20:11:18 +0000	[diff] [blame]	335
Misha Brukman	c540240	2004-01-15 18:34:11 +0000	[diff] [blame]	336	<p>The '<tt>-load</tt>' option specifies that '<tt>opt</tt>' should load your
				337	pass as a shared object, which makes '<tt>-hello</tt>' a valid command line
				338	argument (which is one reason you need to <a href="#registration">register your
Chris Lattner	c6bb824	2002-08-08 20:11:18 +0000	[diff] [blame]	339	pass</a>). Because the hello pass does not modify the program in any
				340	interesting way, we just throw away the result of <tt>opt</tt> (sending it to
Misha Brukman	c540240	2004-01-15 18:34:11 +0000	[diff] [blame]	341	<tt>/dev/null</tt>).</p>
Chris Lattner	c6bb824	2002-08-08 20:11:18 +0000	[diff] [blame]	342
Misha Brukman	c540240	2004-01-15 18:34:11 +0000	[diff] [blame]	343	<p>To see what happened to the other string you registered, try running
				344	<tt>opt</tt> with the <tt>--help</tt> option:</p>
Chris Lattner	c6bb824	2002-08-08 20:11:18 +0000	[diff] [blame]	345
Jim Laskey	5fa8fff	2006-08-04 18:10:12 +0000	[diff] [blame]	346	<div class="doc_code"><pre>
Reid Spencer	7fa6d52	2005-01-11 05:16:23 +0000	[diff] [blame]	347	$ opt -load ../../../Debug/lib/Hello.so --help
Chris Lattner	c6bb824	2002-08-08 20:11:18 +0000	[diff] [blame]	348	OVERVIEW: llvm .bc -> .bc modular optimizer
				349
				350	USAGE: opt [options] <input bytecode>
				351
				352	OPTIONS:
				353	Optimizations available:
				354	...
				355	-funcresolve - Resolve Functions
				356	-gcse - Global Common Subexpression Elimination
				357	-globaldce - Dead Global Elimination
				358	<b>-hello - Hello World Pass</b>
Chris Lattner	065a616	2003-09-10 05:29:43 +0000	[diff] [blame]	359	-indvars - Canonicalize Induction Variables
Chris Lattner	c6bb824	2002-08-08 20:11:18 +0000	[diff] [blame]	360	-inline - Function Integration/Inlining
				361	-instcombine - Combine redundant instructions
				362	...
Jim Laskey	5fa8fff	2006-08-04 18:10:12 +0000	[diff] [blame]	363	</pre></div>
Chris Lattner	c6bb824	2002-08-08 20:11:18 +0000	[diff] [blame]	364
Misha Brukman	c540240	2004-01-15 18:34:11 +0000	[diff] [blame]	365	<p>The pass name get added as the information string for your pass, giving some
Chris Lattner	c6bb824	2002-08-08 20:11:18 +0000	[diff] [blame]	366	documentation to users of <tt>opt</tt>. Now that you have a working pass, you
				367	would go ahead and make it do the cool transformations you want. Once you get
				368	it all working and tested, it may become useful to find out how fast your pass
				369	is. The <a href="#passManager"><tt>PassManager</tt></a> provides a nice command
				370	line option (<tt>--time-passes</tt>) that allows you to get information about
				371	the execution time of your pass along with the other passes you queue up. For
Misha Brukman	c540240	2004-01-15 18:34:11 +0000	[diff] [blame]	372	example:</p>
Chris Lattner	c6bb824	2002-08-08 20:11:18 +0000	[diff] [blame]	373
Jim Laskey	5fa8fff	2006-08-04 18:10:12 +0000	[diff] [blame]	374	<div class="doc_code"><pre>
Reid Spencer	7fa6d52	2005-01-11 05:16:23 +0000	[diff] [blame]	375	$ opt -load ../../../Debug/lib/Hello.so -hello -time-passes < hello.bc > /dev/null
Chris Lattner	c6bb824	2002-08-08 20:11:18 +0000	[diff] [blame]	376	Hello: __main
				377	Hello: puts
				378	Hello: main
				379	===============================================================================
				380	... Pass execution timing report ...
				381	===============================================================================
				382	Total Execution Time: 0.02 seconds (0.0479059 wall clock)
				383
				384	---User Time--- --System Time-- --User+System-- ---Wall Time--- --- Pass Name ---
				385	0.0100 (100.0%) 0.0000 ( 0.0%) 0.0100 ( 50.0%) 0.0402 ( 84.0%) Bytecode Writer
				386	0.0000 ( 0.0%) 0.0100 (100.0%) 0.0100 ( 50.0%) 0.0031 ( 6.4%) Dominator Set Construction
				387	0.0000 ( 0.0%) 0.0000 ( 0.0%) 0.0000 ( 0.0%) 0.0013 ( 2.7%) Module Verifier
				388	<b> 0.0000 ( 0.0%) 0.0000 ( 0.0%) 0.0000 ( 0.0%) 0.0033 ( 6.9%) Hello World Pass</b>
				389	0.0100 (100.0%) 0.0100 (100.0%) 0.0200 (100.0%) 0.0479 (100.0%) TOTAL
Jim Laskey	5fa8fff	2006-08-04 18:10:12 +0000	[diff] [blame]	390	</pre></div>
Chris Lattner	c6bb824	2002-08-08 20:11:18 +0000	[diff] [blame]	391
Misha Brukman	c540240	2004-01-15 18:34:11 +0000	[diff] [blame]	392	<p>As you can see, our implementation above is pretty fast :). The additional
Chris Lattner	c6bb824	2002-08-08 20:11:18 +0000	[diff] [blame]	393	passes listed are automatically inserted by the '<tt>opt</tt>' tool to verify
				394	that the LLVM emitted by your pass is still valid and well formed LLVM, which
Misha Brukman	c540240	2004-01-15 18:34:11 +0000	[diff] [blame]	395	hasn't been broken somehow.</p>
Chris Lattner	c6bb824	2002-08-08 20:11:18 +0000	[diff] [blame]	396
Misha Brukman	c540240	2004-01-15 18:34:11 +0000	[diff] [blame]	397	<p>Now that you have seen the basics of the mechanics behind passes, we can talk
				398	about some more details of how they work and how to use them.</p>
Chris Lattner	c6bb824	2002-08-08 20:11:18 +0000	[diff] [blame]	399
Misha Brukman	c540240	2004-01-15 18:34:11 +0000	[diff] [blame]	400	</div>
Chris Lattner	c6bb824	2002-08-08 20:11:18 +0000	[diff] [blame]	401
				402	<!-- *********************************************************************** -->
Misha Brukman	c540240	2004-01-15 18:34:11 +0000	[diff] [blame]	403	<div class="doc_section">
				404	<a name="passtype">Pass classes and requirements</a>
				405	</div>
Chris Lattner	c6bb824	2002-08-08 20:11:18 +0000	[diff] [blame]	406	<!-- *********************************************************************** -->
				407
Misha Brukman	c540240	2004-01-15 18:34:11 +0000	[diff] [blame]	408	<div class="doc_text">
				409
				410	<p>One of the first things that you should do when designing a new pass is to
Chris Lattner	c6bb824	2002-08-08 20:11:18 +0000	[diff] [blame]	411	decide what class you should subclass for your pass. The <a
				412	href="#basiccode">Hello World</a> example uses the <tt><a
				413	href="#FunctionPass">FunctionPass</a></tt> class for its implementation, but we
				414	did not discuss why or when this should occur. Here we talk about the classes
Misha Brukman	c540240	2004-01-15 18:34:11 +0000	[diff] [blame]	415	available, from the most general to the most specific.</p>
Chris Lattner	c6bb824	2002-08-08 20:11:18 +0000	[diff] [blame]	416
Misha Brukman	c540240	2004-01-15 18:34:11 +0000	[diff] [blame]	417	<p>When choosing a superclass for your Pass, you should choose the <b>most
Chris Lattner	7991070	2002-08-22 19:21:04 +0000	[diff] [blame]	418	specific</b> class possible, while still being able to meet the requirements
Misha Brukman	5560c9d	2003-08-18 14:43:39 +0000	[diff] [blame]	419	listed. This gives the LLVM Pass Infrastructure information necessary to
Chris Lattner	7991070	2002-08-22 19:21:04 +0000	[diff] [blame]	420	optimize how passes are run, so that the resultant compiler isn't unneccesarily
Misha Brukman	c540240	2004-01-15 18:34:11 +0000	[diff] [blame]	421	slow.</p>
Chris Lattner	c6bb824	2002-08-08 20:11:18 +0000	[diff] [blame]	422
Misha Brukman	c540240	2004-01-15 18:34:11 +0000	[diff] [blame]	423	</div>
Chris Lattner	c6bb824	2002-08-08 20:11:18 +0000	[diff] [blame]	424
Chris Lattner	f004f9a	2002-09-25 22:31:38 +0000	[diff] [blame]	425	<!-- ======================================================================= -->
Misha Brukman	c540240	2004-01-15 18:34:11 +0000	[diff] [blame]	426	<div class="doc_subsection">
				427	<a name="ImmutablePass">The <tt>ImmutablePass</tt> class</a>
				428	</div>
Chris Lattner	f004f9a	2002-09-25 22:31:38 +0000	[diff] [blame]	429
Misha Brukman	c540240	2004-01-15 18:34:11 +0000	[diff] [blame]	430	<div class="doc_text">
				431
				432	<p>The most plain and boring type of pass is the "<tt><a
Reid Spencer	05fe4b0	2006-03-14 05:39:39 +0000	[diff] [blame]	433	href="http://llvm.org/doxygen/classllvm_1_1ImmutablePass.html">ImmutablePass</a></tt>"
Chris Lattner	f004f9a	2002-09-25 22:31:38 +0000	[diff] [blame]	434	class. This pass type is used for passes that do not have to be run, do not
				435	change state, and never need to be updated. This is not a normal type of
				436	transformation or analysis, but can provide information about the current
Misha Brukman	c540240	2004-01-15 18:34:11 +0000	[diff] [blame]	437	compiler configuration.</p>
Chris Lattner	f004f9a	2002-09-25 22:31:38 +0000	[diff] [blame]	438
Misha Brukman	c540240	2004-01-15 18:34:11 +0000	[diff] [blame]	439	<p>Although this pass class is very infrequently used, it is important for
Chris Lattner	f004f9a	2002-09-25 22:31:38 +0000	[diff] [blame]	440	providing information about the current target machine being compiled for, and
Misha Brukman	c540240	2004-01-15 18:34:11 +0000	[diff] [blame]	441	other static information that can affect the various transformations.</p>
Chris Lattner	f004f9a	2002-09-25 22:31:38 +0000	[diff] [blame]	442
Misha Brukman	c540240	2004-01-15 18:34:11 +0000	[diff] [blame]	443	<p><tt>ImmutablePass</tt>es never invalidate other transformations, are never
				444	invalidated, and are never "run".</p>
Chris Lattner	f004f9a	2002-09-25 22:31:38 +0000	[diff] [blame]	445
Misha Brukman	c540240	2004-01-15 18:34:11 +0000	[diff] [blame]	446	</div>
Chris Lattner	c6bb824	2002-08-08 20:11:18 +0000	[diff] [blame]	447
				448	<!-- ======================================================================= -->
Misha Brukman	c540240	2004-01-15 18:34:11 +0000	[diff] [blame]	449	<div class="doc_subsection">
Chris Lattner	f627892	2004-09-20 04:36:29 +0000	[diff] [blame]	450	<a name="ModulePass">The <tt>ModulePass</tt> class</a>
Misha Brukman	c540240	2004-01-15 18:34:11 +0000	[diff] [blame]	451	</div>
Chris Lattner	c6bb824	2002-08-08 20:11:18 +0000	[diff] [blame]	452
Misha Brukman	c540240	2004-01-15 18:34:11 +0000	[diff] [blame]	453	<div class="doc_text">
				454
				455	<p>The "<tt><a
Reid Spencer	05fe4b0	2006-03-14 05:39:39 +0000	[diff] [blame]	456	href="http://llvm.org/doxygen/classllvm_1_1ModulePass.html">ModulePass</a></tt>"
Chris Lattner	c6bb824	2002-08-08 20:11:18 +0000	[diff] [blame]	457	class is the most general of all superclasses that you can use. Deriving from
Chris Lattner	f627892	2004-09-20 04:36:29 +0000	[diff] [blame]	458	<tt>ModulePass</tt> indicates that your pass uses the entire program as a unit,
Chris Lattner	c6bb824	2002-08-08 20:11:18 +0000	[diff] [blame]	459	refering to function bodies in no predictable order, or adding and removing
Chris Lattner	f627892	2004-09-20 04:36:29 +0000	[diff] [blame]	460	functions. Because nothing is known about the behavior of <tt>ModulePass</tt>
Misha Brukman	c540240	2004-01-15 18:34:11 +0000	[diff] [blame]	461	subclasses, no optimization can be done for their execution.</p>
Chris Lattner	c6bb824	2002-08-08 20:11:18 +0000	[diff] [blame]	462
Chris Lattner	f627892	2004-09-20 04:36:29 +0000	[diff] [blame]	463	<p>To write a correct <tt>ModulePass</tt> subclass, derive from
				464	<tt>ModulePass</tt> and overload the <tt>runOnModule</tt> method with the
				465	following signature:</p>
Misha Brukman	c540240	2004-01-15 18:34:11 +0000	[diff] [blame]	466
				467	</div>
Chris Lattner	c6bb824	2002-08-08 20:11:18 +0000	[diff] [blame]	468
				469	<!-- _______________________________________________________________________ -->
Misha Brukman	c540240	2004-01-15 18:34:11 +0000	[diff] [blame]	470	<div class="doc_subsubsection">
Chris Lattner	f627892	2004-09-20 04:36:29 +0000	[diff] [blame]	471	<a name="runOnModule">The <tt>runOnModule</tt> method</a>
Misha Brukman	c540240	2004-01-15 18:34:11 +0000	[diff] [blame]	472	</div>
Chris Lattner	c6bb824	2002-08-08 20:11:18 +0000	[diff] [blame]	473
Misha Brukman	c540240	2004-01-15 18:34:11 +0000	[diff] [blame]	474	<div class="doc_text">
Chris Lattner	c6bb824	2002-08-08 20:11:18 +0000	[diff] [blame]	475
Jim Laskey	5fa8fff	2006-08-04 18:10:12 +0000	[diff] [blame]	476	<div class="doc_code"><pre>
Chris Lattner	f627892	2004-09-20 04:36:29 +0000	[diff] [blame]	477	<b>virtual bool</b> runOnModule(Module &M) = 0;
Jim Laskey	5fa8fff	2006-08-04 18:10:12 +0000	[diff] [blame]	478	</pre></div>
Chris Lattner	c6bb824	2002-08-08 20:11:18 +0000	[diff] [blame]	479
John Criswell	2382ff7	2005-07-15 19:25:12 +0000	[diff] [blame]	480	<p>The <tt>runOnModule</tt> method performs the interesting work of the pass.
				481	It should return true if the module was modified by the transformation and
				482	false otherwise.</p>
Chris Lattner	c6bb824	2002-08-08 20:11:18 +0000	[diff] [blame]	483
Misha Brukman	c540240	2004-01-15 18:34:11 +0000	[diff] [blame]	484	</div>
Chris Lattner	c6bb824	2002-08-08 20:11:18 +0000	[diff] [blame]	485
				486	<!-- ======================================================================= -->
Misha Brukman	c540240	2004-01-15 18:34:11 +0000	[diff] [blame]	487	<div class="doc_subsection">
Chris Lattner	8fdb246	2004-09-18 06:39:35 +0000	[diff] [blame]	488	<a name="CallGraphSCCPass">The <tt>CallGraphSCCPass</tt> class</a>
				489	</div>
				490
				491	<div class="doc_text">
				492
				493	<p>The "<tt><a
Reid Spencer	05fe4b0	2006-03-14 05:39:39 +0000	[diff] [blame]	494	href="http://llvm.org/doxygen/classllvm_1_1CallGraphSCCPass.html">CallGraphSCCPass</a></tt>"
Chris Lattner	8fdb246	2004-09-18 06:39:35 +0000	[diff] [blame]	495	is used by passes that need to traverse the program bottom-up on the call graph
				496	(callees before callers). Deriving from CallGraphSCCPass provides some
				497	mechanics for building and traversing the CallGraph, but also allows the system
				498	to optimize execution of CallGraphSCCPass's. If your pass meets the
				499	requirements outlined below, and doesn't meet the requirements of a <tt><a
				500	href="#FunctionPass">FunctionPass</a></tt> or <tt><a
				501	href="#BasicBlockPass">BasicBlockPass</a></tt>, you should derive from
				502	<tt>CallGraphSCCPass</tt>.</p>
				503
				504	<p><b>TODO</b>: explain briefly what SCC, Tarjan's algo, and B-U mean.</p>
				505
				506	<p>To be explicit, <tt>CallGraphSCCPass</tt> subclasses are:</p>
				507
				508	<ol>
				509
				510	<li>... <em>not allowed</em> to modify any <tt>Function</tt>s that are not in
				511	the current SCC.</li>
				512
				513	<li>... <em>allowed</em> to inspect any Function's other than those in the
				514	current SCC and the direct callees of the SCC.</li>
				515
				516	<li>... <em>required</em> to preserve the current CallGraph object, updating it
				517	to reflect any changes made to the program.</li>
				518
				519	<li>... <em>not allowed</em> to add or remove SCC's from the current Module,
				520	though they may change the contents of an SCC.</li>
				521
				522	<li>... <em>allowed</em> to add or remove global variables from the current
				523	Module.</li>
				524
				525	<li>... <em>allowed</em> to maintain state across invocations of
				526	<a href="#runOnSCC"><tt>runOnSCC</tt></a> (including global data).</li>
				527	</ol>
				528
				529	<p>Implementing a <tt>CallGraphSCCPass</tt> is slightly tricky in some cases
				530	because it has to handle SCCs with more than one node in it. All of the virtual
				531	methods described below should return true if they modified the program, or
				532	false if they didn't.</p>
				533
				534	</div>
				535
				536	<!-- _______________________________________________________________________ -->
				537	<div class="doc_subsubsection">
				538	<a name="doInitialization_scc">The <tt>doInitialization(Module &)</tt>
				539	method</a>
				540	</div>
				541
				542	<div class="doc_text">
				543
Jim Laskey	5fa8fff	2006-08-04 18:10:12 +0000	[diff] [blame]	544	<div class="doc_code"><pre>
Chris Lattner	8fdb246	2004-09-18 06:39:35 +0000	[diff] [blame]	545	<b>virtual bool</b> doInitialization(Module &M);
Jim Laskey	5fa8fff	2006-08-04 18:10:12 +0000	[diff] [blame]	546	</pre></div>
Chris Lattner	8fdb246	2004-09-18 06:39:35 +0000	[diff] [blame]	547
				548	<p>The <tt>doIninitialize</tt> method is allowed to do most of the things that
				549	<tt>CallGraphSCCPass</tt>'s are not allowed to do. They can add and remove
				550	functions, get pointers to functions, etc. The <tt>doInitialization</tt> method
				551	is designed to do simple initialization type of stuff that does not depend on
				552	the SCCs being processed. The <tt>doInitialization</tt> method call is not
				553	scheduled to overlap with any other pass executions (thus it should be very
				554	fast).</p>
				555
				556	</div>
				557
				558	<!-- _______________________________________________________________________ -->
				559	<div class="doc_subsubsection">
				560	<a name="runOnSCC">The <tt>runOnSCC</tt> method</a>
				561	</div>
				562
				563	<div class="doc_text">
				564
Jim Laskey	5fa8fff	2006-08-04 18:10:12 +0000	[diff] [blame]	565	<div class="doc_code"><pre>
Chris Lattner	8fdb246	2004-09-18 06:39:35 +0000	[diff] [blame]	566	<b>virtual bool</b> runOnSCC(const std::vector<CallGraphNode *> &SCCM) = 0;
Jim Laskey	5fa8fff	2006-08-04 18:10:12 +0000	[diff] [blame]	567	</pre></div>
Chris Lattner	8fdb246	2004-09-18 06:39:35 +0000	[diff] [blame]	568
				569	<p>The <tt>runOnSCC</tt> method performs the interesting work of the pass, and
				570	should return true if the module was modified by the transformation, false
				571	otherwise.</p>
				572
				573	</div>
				574
				575	<!-- _______________________________________________________________________ -->
				576	<div class="doc_subsubsection">
				577	<a name="doFinalization_scc">The <tt>doFinalization(Module
				578	&)</tt> method</a>
				579	</div>
				580
				581	<div class="doc_text">
				582
Jim Laskey	5fa8fff	2006-08-04 18:10:12 +0000	[diff] [blame]	583	<div class="doc_code"><pre>
Chris Lattner	8fdb246	2004-09-18 06:39:35 +0000	[diff] [blame]	584	<b>virtual bool</b> doFinalization(Module &M);
Jim Laskey	5fa8fff	2006-08-04 18:10:12 +0000	[diff] [blame]	585	</pre></div>
Chris Lattner	8fdb246	2004-09-18 06:39:35 +0000	[diff] [blame]	586
				587	<p>The <tt>doFinalization</tt> method is an infrequently used method that is
				588	called when the pass framework has finished calling <a
				589	href="#runOnFunction"><tt>runOnFunction</tt></a> for every function in the
				590	program being compiled.</p>
				591
				592	</div>
				593
				594	<!-- ======================================================================= -->
				595	<div class="doc_subsection">
Misha Brukman	c540240	2004-01-15 18:34:11 +0000	[diff] [blame]	596	<a name="FunctionPass">The <tt>FunctionPass</tt> class</a>
				597	</div>
Chris Lattner	c6bb824	2002-08-08 20:11:18 +0000	[diff] [blame]	598
Misha Brukman	c540240	2004-01-15 18:34:11 +0000	[diff] [blame]	599	<div class="doc_text">
				600
Chris Lattner	f627892	2004-09-20 04:36:29 +0000	[diff] [blame]	601	<p>In contrast to <tt>ModulePass</tt> subclasses, <tt><a
Reid Spencer	05fe4b0	2006-03-14 05:39:39 +0000	[diff] [blame]	602	href="http://llvm.org/doxygen/classllvm_1_1Pass.html">FunctionPass</a></tt>
Chris Lattner	c6bb824	2002-08-08 20:11:18 +0000	[diff] [blame]	603	subclasses do have a predictable, local behavior that can be expected by the
				604	system. All <tt>FunctionPass</tt> execute on each function in the program
Misha Brukman	ef6a6a6	2003-08-21 22:14:26 +0000	[diff] [blame]	605	independent of all of the other functions in the program.
Chris Lattner	c6bb824	2002-08-08 20:11:18 +0000	[diff] [blame]	606	<tt>FunctionPass</tt>'s do not require that they are executed in a particular
Misha Brukman	c540240	2004-01-15 18:34:11 +0000	[diff] [blame]	607	order, and <tt>FunctionPass</tt>'s do not modify external functions.</p>
Chris Lattner	c6bb824	2002-08-08 20:11:18 +0000	[diff] [blame]	608
Misha Brukman	c540240	2004-01-15 18:34:11 +0000	[diff] [blame]	609	<p>To be explicit, <tt>FunctionPass</tt> subclasses are not allowed to:</p>
Chris Lattner	c6bb824	2002-08-08 20:11:18 +0000	[diff] [blame]	610
				611	<ol>
Misha Brukman	c540240	2004-01-15 18:34:11 +0000	[diff] [blame]	612	<li>Modify a Function other than the one currently being processed.</li>
				613	<li>Add or remove Function's from the current Module.</li>
				614	<li>Add or remove global variables from the current Module.</li>
Chris Lattner	c6bb824	2002-08-08 20:11:18 +0000	[diff] [blame]	615	<li>Maintain state across invocations of
Misha Brukman	c540240	2004-01-15 18:34:11 +0000	[diff] [blame]	616	<a href="#runOnFunction"><tt>runOnFunction</tt></a> (including global data)</li>
				617	</ol>
Chris Lattner	c6bb824	2002-08-08 20:11:18 +0000	[diff] [blame]	618
Misha Brukman	c540240	2004-01-15 18:34:11 +0000	[diff] [blame]	619	<p>Implementing a <tt>FunctionPass</tt> is usually straightforward (See the <a
Chris Lattner	c6bb824	2002-08-08 20:11:18 +0000	[diff] [blame]	620	href="#basiccode">Hello World</a> pass for example). <tt>FunctionPass</tt>'s
				621	may overload three virtual methods to do their work. All of these methods
Misha Brukman	c540240	2004-01-15 18:34:11 +0000	[diff] [blame]	622	should return true if they modified the program, or false if they didn't.</p>
				623
				624	</div>
Chris Lattner	c6bb824	2002-08-08 20:11:18 +0000	[diff] [blame]	625
				626	<!-- _______________________________________________________________________ -->
Chris Lattner	8925627	2004-03-17 21:09:55 +0000	[diff] [blame]	627	<div class="doc_subsubsection">
Misha Brukman	c540240	2004-01-15 18:34:11 +0000	[diff] [blame]	628	<a name="doInitialization_mod">The <tt>doInitialization(Module &)</tt>
				629	method</a>
				630	</div>
				631
				632	<div class="doc_text">
Chris Lattner	c6bb824	2002-08-08 20:11:18 +0000	[diff] [blame]	633
Jim Laskey	5fa8fff	2006-08-04 18:10:12 +0000	[diff] [blame]	634	<div class="doc_code"><pre>
Chris Lattner	c6bb824	2002-08-08 20:11:18 +0000	[diff] [blame]	635	<b>virtual bool</b> doInitialization(Module &M);
Jim Laskey	5fa8fff	2006-08-04 18:10:12 +0000	[diff] [blame]	636	</pre></div>
Chris Lattner	c6bb824	2002-08-08 20:11:18 +0000	[diff] [blame]	637
Misha Brukman	c540240	2004-01-15 18:34:11 +0000	[diff] [blame]	638	<p>The <tt>doIninitialize</tt> method is allowed to do most of the things that
Chris Lattner	c6bb824	2002-08-08 20:11:18 +0000	[diff] [blame]	639	<tt>FunctionPass</tt>'s are not allowed to do. They can add and remove
Chris Lattner	d0713f9	2002-09-12 17:06:43 +0000	[diff] [blame]	640	functions, get pointers to functions, etc. The <tt>doInitialization</tt> method
				641	is designed to do simple initialization type of stuff that does not depend on
				642	the functions being processed. The <tt>doInitialization</tt> method call is not
				643	scheduled to overlap with any other pass executions (thus it should be very
Misha Brukman	c540240	2004-01-15 18:34:11 +0000	[diff] [blame]	644	fast).</p>
Chris Lattner	c6bb824	2002-08-08 20:11:18 +0000	[diff] [blame]	645
Misha Brukman	c540240	2004-01-15 18:34:11 +0000	[diff] [blame]	646	<p>A good example of how this method should be used is the <a
Reid Spencer	05fe4b0	2006-03-14 05:39:39 +0000	[diff] [blame]	647	href="http://llvm.org/doxygen/LowerAllocations_8cpp-source.html">LowerAllocations</a>
Chris Lattner	c6bb824	2002-08-08 20:11:18 +0000	[diff] [blame]	648	pass. This pass converts <tt>malloc</tt> and <tt>free</tt> instructions into
Misha Brukman	ef6a6a6	2003-08-21 22:14:26 +0000	[diff] [blame]	649	platform dependent <tt>malloc()</tt> and <tt>free()</tt> function calls. It
Chris Lattner	c6bb824	2002-08-08 20:11:18 +0000	[diff] [blame]	650	uses the <tt>doInitialization</tt> method to get a reference to the malloc and
Misha Brukman	c540240	2004-01-15 18:34:11 +0000	[diff] [blame]	651	free functions that it needs, adding prototypes to the module if necessary.</p>
				652
				653	</div>
Chris Lattner	c6bb824	2002-08-08 20:11:18 +0000	[diff] [blame]	654
				655	<!-- _______________________________________________________________________ -->
Chris Lattner	8925627	2004-03-17 21:09:55 +0000	[diff] [blame]	656	<div class="doc_subsubsection">
Misha Brukman	c540240	2004-01-15 18:34:11 +0000	[diff] [blame]	657	<a name="runOnFunction">The <tt>runOnFunction</tt> method</a>
				658	</div>
				659
				660	<div class="doc_text">
Chris Lattner	c6bb824	2002-08-08 20:11:18 +0000	[diff] [blame]	661
Jim Laskey	5fa8fff	2006-08-04 18:10:12 +0000	[diff] [blame]	662	<div class="doc_code"><pre>
Chris Lattner	c6bb824	2002-08-08 20:11:18 +0000	[diff] [blame]	663	<b>virtual bool</b> runOnFunction(Function &F) = 0;
Jim Laskey	5fa8fff	2006-08-04 18:10:12 +0000	[diff] [blame]	664	</pre></div><p>
Chris Lattner	c6bb824	2002-08-08 20:11:18 +0000	[diff] [blame]	665
Misha Brukman	c540240	2004-01-15 18:34:11 +0000	[diff] [blame]	666	<p>The <tt>runOnFunction</tt> method must be implemented by your subclass to do
				667	the transformation or analysis work of your pass. As usual, a true value should
				668	be returned if the function is modified.</p>
				669
				670	</div>
Chris Lattner	c6bb824	2002-08-08 20:11:18 +0000	[diff] [blame]	671
				672	<!-- _______________________________________________________________________ -->
Chris Lattner	8925627	2004-03-17 21:09:55 +0000	[diff] [blame]	673	<div class="doc_subsubsection">
Misha Brukman	c540240	2004-01-15 18:34:11 +0000	[diff] [blame]	674	<a name="doFinalization_mod">The <tt>doFinalization(Module
				675	&)</tt> method</a>
				676	</div>
				677
				678	<div class="doc_text">
Chris Lattner	c6bb824	2002-08-08 20:11:18 +0000	[diff] [blame]	679
Jim Laskey	5fa8fff	2006-08-04 18:10:12 +0000	[diff] [blame]	680	<div class="doc_code"><pre>
Chris Lattner	c6bb824	2002-08-08 20:11:18 +0000	[diff] [blame]	681	<b>virtual bool</b> doFinalization(Module &M);
Jim Laskey	5fa8fff	2006-08-04 18:10:12 +0000	[diff] [blame]	682	</pre></div>
Chris Lattner	c6bb824	2002-08-08 20:11:18 +0000	[diff] [blame]	683
Misha Brukman	c540240	2004-01-15 18:34:11 +0000	[diff] [blame]	684	<p>The <tt>doFinalization</tt> method is an infrequently used method that is
				685	called when the pass framework has finished calling <a
Chris Lattner	c6bb824	2002-08-08 20:11:18 +0000	[diff] [blame]	686	href="#runOnFunction"><tt>runOnFunction</tt></a> for every function in the
Misha Brukman	c540240	2004-01-15 18:34:11 +0000	[diff] [blame]	687	program being compiled.</p>
Chris Lattner	c6bb824	2002-08-08 20:11:18 +0000	[diff] [blame]	688
Misha Brukman	c540240	2004-01-15 18:34:11 +0000	[diff] [blame]	689	</div>
Chris Lattner	c6bb824	2002-08-08 20:11:18 +0000	[diff] [blame]	690
				691	<!-- ======================================================================= -->
Misha Brukman	c540240	2004-01-15 18:34:11 +0000	[diff] [blame]	692	<div class="doc_subsection">
				693	<a name="BasicBlockPass">The <tt>BasicBlockPass</tt> class</a>
				694	</div>
Chris Lattner	c6bb824	2002-08-08 20:11:18 +0000	[diff] [blame]	695
Misha Brukman	c540240	2004-01-15 18:34:11 +0000	[diff] [blame]	696	<div class="doc_text">
				697
				698	<p><tt>BasicBlockPass</tt>'s are just like <a
Chris Lattner	c6bb824	2002-08-08 20:11:18 +0000	[diff] [blame]	699	href="#FunctionPass"><tt>FunctionPass</tt></a>'s, except that they must limit
				700	their scope of inspection and modification to a single basic block at a time.
Misha Brukman	c540240	2004-01-15 18:34:11 +0000	[diff] [blame]	701	As such, they are <b>not</b> allowed to do any of the following:</p>
Chris Lattner	c6bb824	2002-08-08 20:11:18 +0000	[diff] [blame]	702
				703	<ol>
Misha Brukman	c540240	2004-01-15 18:34:11 +0000	[diff] [blame]	704	<li>Modify or inspect any basic blocks outside of the current one</li>
Chris Lattner	c6bb824	2002-08-08 20:11:18 +0000	[diff] [blame]	705	<li>Maintain state across invocations of
Misha Brukman	c540240	2004-01-15 18:34:11 +0000	[diff] [blame]	706	<a href="#runOnBasicBlock"><tt>runOnBasicBlock</tt></a></li>
Reid Spencer	1bc1934	2004-12-11 05:12:57 +0000	[diff] [blame]	707	<li>Modify the control flow graph (by altering terminator instructions)</li>
				708	<li>Any of the things forbidden for
Misha Brukman	c540240	2004-01-15 18:34:11 +0000	[diff] [blame]	709	<a href="#FunctionPass"><tt>FunctionPass</tt></a>es.</li>
				710	</ol>
Chris Lattner	c6bb824	2002-08-08 20:11:18 +0000	[diff] [blame]	711
Misha Brukman	c540240	2004-01-15 18:34:11 +0000	[diff] [blame]	712	<p><tt>BasicBlockPass</tt>es are useful for traditional local and "peephole"
Chris Lattner	c6bb824	2002-08-08 20:11:18 +0000	[diff] [blame]	713	optimizations. They may override the same <a
Chris Lattner	d0713f9	2002-09-12 17:06:43 +0000	[diff] [blame]	714	href="#doInitialization_mod"><tt>doInitialization(Module &)</tt></a> and <a
				715	href="#doFinalization_mod"><tt>doFinalization(Module &)</tt></a> methods that <a
Misha Brukman	c540240	2004-01-15 18:34:11 +0000	[diff] [blame]	716	href="#FunctionPass"><tt>FunctionPass</tt></a>'s have, but also have the following virtual methods that may also be implemented:</p>
				717
				718	</div>
Chris Lattner	d0713f9	2002-09-12 17:06:43 +0000	[diff] [blame]	719
				720	<!-- _______________________________________________________________________ -->
Chris Lattner	8925627	2004-03-17 21:09:55 +0000	[diff] [blame]	721	<div class="doc_subsubsection">
Misha Brukman	c540240	2004-01-15 18:34:11 +0000	[diff] [blame]	722	<a name="doInitialization_fn">The <tt>doInitialization(Function
				723	&)</tt> method</a>
				724	</div>
				725
				726	<div class="doc_text">
Chris Lattner	d0713f9	2002-09-12 17:06:43 +0000	[diff] [blame]	727
Jim Laskey	5fa8fff	2006-08-04 18:10:12 +0000	[diff] [blame]	728	<div class="doc_code"><pre>
Chris Lattner	d0713f9	2002-09-12 17:06:43 +0000	[diff] [blame]	729	<b>virtual bool</b> doInitialization(Function &F);
Jim Laskey	5fa8fff	2006-08-04 18:10:12 +0000	[diff] [blame]	730	</pre></div>
Chris Lattner	d0713f9	2002-09-12 17:06:43 +0000	[diff] [blame]	731
Misha Brukman	c540240	2004-01-15 18:34:11 +0000	[diff] [blame]	732	<p>The <tt>doIninitialize</tt> method is allowed to do most of the things that
Chris Lattner	d0713f9	2002-09-12 17:06:43 +0000	[diff] [blame]	733	<tt>BasicBlockPass</tt>'s are not allowed to do, but that
				734	<tt>FunctionPass</tt>'s can. The <tt>doInitialization</tt> method is designed
Reid Spencer	1bc1934	2004-12-11 05:12:57 +0000	[diff] [blame]	735	to do simple initialization that does not depend on the
Chris Lattner	d0713f9	2002-09-12 17:06:43 +0000	[diff] [blame]	736	BasicBlocks being processed. The <tt>doInitialization</tt> method call is not
				737	scheduled to overlap with any other pass executions (thus it should be very
Misha Brukman	c540240	2004-01-15 18:34:11 +0000	[diff] [blame]	738	fast).</p>
Chris Lattner	d0713f9	2002-09-12 17:06:43 +0000	[diff] [blame]	739
Misha Brukman	c540240	2004-01-15 18:34:11 +0000	[diff] [blame]	740	</div>
Chris Lattner	c6bb824	2002-08-08 20:11:18 +0000	[diff] [blame]	741
				742	<!-- _______________________________________________________________________ -->
Chris Lattner	8925627	2004-03-17 21:09:55 +0000	[diff] [blame]	743	<div class="doc_subsubsection">
Misha Brukman	c540240	2004-01-15 18:34:11 +0000	[diff] [blame]	744	<a name="runOnBasicBlock">The <tt>runOnBasicBlock</tt> method</a>
				745	</div>
				746
				747	<div class="doc_text">
Chris Lattner	c6bb824	2002-08-08 20:11:18 +0000	[diff] [blame]	748
Jim Laskey	5fa8fff	2006-08-04 18:10:12 +0000	[diff] [blame]	749	<div class="doc_code"><pre>
Chris Lattner	c6bb824	2002-08-08 20:11:18 +0000	[diff] [blame]	750	<b>virtual bool</b> runOnBasicBlock(BasicBlock &BB) = 0;
Jim Laskey	5fa8fff	2006-08-04 18:10:12 +0000	[diff] [blame]	751	</pre></div>
Chris Lattner	c6bb824	2002-08-08 20:11:18 +0000	[diff] [blame]	752
Misha Brukman	c540240	2004-01-15 18:34:11 +0000	[diff] [blame]	753	<p>Override this function to do the work of the <tt>BasicBlockPass</tt>. This
Chris Lattner	c6bb824	2002-08-08 20:11:18 +0000	[diff] [blame]	754	function is not allowed to inspect or modify basic blocks other than the
				755	parameter, and are not allowed to modify the CFG. A true value must be returned
Misha Brukman	c540240	2004-01-15 18:34:11 +0000	[diff] [blame]	756	if the basic block is modified.</p>
Chris Lattner	c6bb824	2002-08-08 20:11:18 +0000	[diff] [blame]	757
Misha Brukman	c540240	2004-01-15 18:34:11 +0000	[diff] [blame]	758	</div>
Chris Lattner	c6bb824	2002-08-08 20:11:18 +0000	[diff] [blame]	759
Chris Lattner	d0713f9	2002-09-12 17:06:43 +0000	[diff] [blame]	760	<!-- _______________________________________________________________________ -->
Chris Lattner	8925627	2004-03-17 21:09:55 +0000	[diff] [blame]	761	<div class="doc_subsubsection">
Misha Brukman	c540240	2004-01-15 18:34:11 +0000	[diff] [blame]	762	<a name="doFinalization_fn">The <tt>doFinalization(Function &)</tt>
				763	method</a>
				764	</div>
				765
				766	<div class="doc_text">
Chris Lattner	d0713f9	2002-09-12 17:06:43 +0000	[diff] [blame]	767
Jim Laskey	5fa8fff	2006-08-04 18:10:12 +0000	[diff] [blame]	768	<div class="doc_code"><pre>
Chris Lattner	d0713f9	2002-09-12 17:06:43 +0000	[diff] [blame]	769	<b>virtual bool</b> doFinalization(Function &F);
Jim Laskey	5fa8fff	2006-08-04 18:10:12 +0000	[diff] [blame]	770	</pre></div>
Chris Lattner	d0713f9	2002-09-12 17:06:43 +0000	[diff] [blame]	771
Misha Brukman	c540240	2004-01-15 18:34:11 +0000	[diff] [blame]	772	<p>The <tt>doFinalization</tt> method is an infrequently used method that is
				773	called when the pass framework has finished calling <a
Chris Lattner	d0713f9	2002-09-12 17:06:43 +0000	[diff] [blame]	774	href="#runOnBasicBlock"><tt>runOnBasicBlock</tt></a> for every BasicBlock in the
				775	program being compiled. This can be used to perform per-function
Misha Brukman	c540240	2004-01-15 18:34:11 +0000	[diff] [blame]	776	finalization.</p>
Chris Lattner	d0713f9	2002-09-12 17:06:43 +0000	[diff] [blame]	777
Misha Brukman	c540240	2004-01-15 18:34:11 +0000	[diff] [blame]	778	</div>
Chris Lattner	d0713f9	2002-09-12 17:06:43 +0000	[diff] [blame]	779
Brian Gaeke	cab8b6f	2003-07-17 18:53:20 +0000	[diff] [blame]	780	<!-- ======================================================================= -->
Misha Brukman	c540240	2004-01-15 18:34:11 +0000	[diff] [blame]	781	<div class="doc_subsection">
				782	<a name="MachineFunctionPass">The <tt>MachineFunctionPass</tt> class</a>
				783	</div>
Brian Gaeke	cab8b6f	2003-07-17 18:53:20 +0000	[diff] [blame]	784
Misha Brukman	c540240	2004-01-15 18:34:11 +0000	[diff] [blame]	785	<div class="doc_text">
				786
Chris Lattner	8925627	2004-03-17 21:09:55 +0000	[diff] [blame]	787	<p>A <tt>MachineFunctionPass</tt> is a part of the LLVM code generator that
				788	executes on the machine-dependent representation of each LLVM function in the
				789	program. A <tt>MachineFunctionPass</tt> is also a <tt>FunctionPass</tt>, so all
Brian Gaeke	cab8b6f	2003-07-17 18:53:20 +0000	[diff] [blame]	790	the restrictions that apply to a <tt>FunctionPass</tt> also apply to it.
Chris Lattner	8925627	2004-03-17 21:09:55 +0000	[diff] [blame]	791	<tt>MachineFunctionPass</tt>es also have additional restrictions. In particular,
				792	<tt>MachineFunctionPass</tt>es are not allowed to do any of the following:</p>
Brian Gaeke	cab8b6f	2003-07-17 18:53:20 +0000	[diff] [blame]	793
				794	<ol>
Misha Brukman	c540240	2004-01-15 18:34:11 +0000	[diff] [blame]	795	<li>Modify any LLVM Instructions, BasicBlocks or Functions.</li>
				796	<li>Modify a MachineFunction other than the one currently being processed.</li>
				797	<li>Add or remove MachineFunctions from the current Module.</li>
				798	<li>Add or remove global variables from the current Module.</li>
				799	<li>Maintain state across invocations of <a
				800	href="#runOnMachineFunction"><tt>runOnMachineFunction</tt></a> (including global
				801	data)</li>
				802	</ol>
Brian Gaeke	cab8b6f	2003-07-17 18:53:20 +0000	[diff] [blame]	803
Misha Brukman	c540240	2004-01-15 18:34:11 +0000	[diff] [blame]	804	</div>
Chris Lattner	d0713f9	2002-09-12 17:06:43 +0000	[diff] [blame]	805
Brian Gaeke	6a33f36	2003-07-22 20:53:20 +0000	[diff] [blame]	806	<!-- _______________________________________________________________________ -->
Chris Lattner	8925627	2004-03-17 21:09:55 +0000	[diff] [blame]	807	<div class="doc_subsubsection">
Misha Brukman	c540240	2004-01-15 18:34:11 +0000	[diff] [blame]	808	<a name="runOnMachineFunction">The <tt>runOnMachineFunction(MachineFunction
				809	&MF)</tt> method</a>
				810	</div>
				811
				812	<div class="doc_text">
Brian Gaeke	6a33f36	2003-07-22 20:53:20 +0000	[diff] [blame]	813
Jim Laskey	5fa8fff	2006-08-04 18:10:12 +0000	[diff] [blame]	814	<div class="doc_code"><pre>
Brian Gaeke	6a33f36	2003-07-22 20:53:20 +0000	[diff] [blame]	815	<b>virtual bool</b> runOnMachineFunction(MachineFunction &MF) = 0;
Jim Laskey	5fa8fff	2006-08-04 18:10:12 +0000	[diff] [blame]	816	</pre></div>
Brian Gaeke	6a33f36	2003-07-22 20:53:20 +0000	[diff] [blame]	817
Misha Brukman	c540240	2004-01-15 18:34:11 +0000	[diff] [blame]	818	<p><tt>runOnMachineFunction</tt> can be considered the main entry point of a
				819	<tt>MachineFunctionPass</tt>; that is, you should override this method to do the
				820	work of your <tt>MachineFunctionPass</tt>.</p>
Brian Gaeke	6a33f36	2003-07-22 20:53:20 +0000	[diff] [blame]	821
Misha Brukman	c540240	2004-01-15 18:34:11 +0000	[diff] [blame]	822	<p>The <tt>runOnMachineFunction</tt> method is called on every
Brian Gaeke	6a33f36	2003-07-22 20:53:20 +0000	[diff] [blame]	823	<tt>MachineFunction</tt> in a <tt>Module</tt>, so that the
Misha Brukman	c540240	2004-01-15 18:34:11 +0000	[diff] [blame]	824	<tt>MachineFunctionPass</tt> may perform optimizations on the machine-dependent
				825	representation of the function. If you want to get at the LLVM <tt>Function</tt>
				826	for the <tt>MachineFunction</tt> you're working on, use
				827	<tt>MachineFunction</tt>'s <tt>getFunction()</tt> accessor method -- but
				828	remember, you may not modify the LLVM <tt>Function</tt> or its contents from a
				829	<tt>MachineFunctionPass</tt>.</p>
				830
				831	</div>
Brian Gaeke	6a33f36	2003-07-22 20:53:20 +0000	[diff] [blame]	832
Chris Lattner	c6bb824	2002-08-08 20:11:18 +0000	[diff] [blame]	833	<!-- *********************************************************************** -->
Misha Brukman	c540240	2004-01-15 18:34:11 +0000	[diff] [blame]	834	<div class="doc_section">
				835	<a name="registration">Pass registration</a>
				836	</div>
Chris Lattner	c6bb824	2002-08-08 20:11:18 +0000	[diff] [blame]	837	<!-- *********************************************************************** -->
				838
Misha Brukman	c540240	2004-01-15 18:34:11 +0000	[diff] [blame]	839	<div class="doc_text">
Chris Lattner	c6bb824	2002-08-08 20:11:18 +0000	[diff] [blame]	840
Misha Brukman	c540240	2004-01-15 18:34:11 +0000	[diff] [blame]	841	<p>In the <a href="#basiccode">Hello World</a> example pass we illustrated how
				842	pass registration works, and discussed some of the reasons that it is used and
				843	what it does. Here we discuss how and why passes are registered.</p>
				844
				845	<p>Passes can be registered in several different ways. Depending on the general
Chris Lattner	c6bb824	2002-08-08 20:11:18 +0000	[diff] [blame]	846	classification of the pass, you should use one of the following templates to
Misha Brukman	c540240	2004-01-15 18:34:11 +0000	[diff] [blame]	847	register the pass:</p>
Chris Lattner	c6bb824	2002-08-08 20:11:18 +0000	[diff] [blame]	848
				849	<ul>
				850	<li><b><tt>RegisterOpt</tt></b> - This template should be used when you are
				851	registering a pass that logically should be available for use in the
Misha Brukman	c540240	2004-01-15 18:34:11 +0000	[diff] [blame]	852	'<tt>opt</tt>' utility.</li>
Chris Lattner	c6bb824	2002-08-08 20:11:18 +0000	[diff] [blame]	853
				854	<li><b><tt>RegisterAnalysis</tt></b> - This template should be used when you are
				855	registering a pass that logically should be available for use in the
Chris Lattner	8925627	2004-03-17 21:09:55 +0000	[diff] [blame]	856	'<tt>analyze</tt>' utility.</li>
Chris Lattner	c6bb824	2002-08-08 20:11:18 +0000	[diff] [blame]	857
				858	<li><b><tt>RegisterPass</tt></b> - This is the generic form of the
				859	<tt>Register*</tt> templates that should be used if you want your pass listed by
				860	multiple or no utilities. This template takes an extra third argument that
				861	specifies which tools it should be listed in. See the <a
Reid Spencer	05fe4b0	2006-03-14 05:39:39 +0000	[diff] [blame]	862	href="http://llvm.org/doxygen/PassSupport_8h-source.html">PassSupport.h</a>
Misha Brukman	c540240	2004-01-15 18:34:11 +0000	[diff] [blame]	863	file for more information.</li>
Chris Lattner	c6bb824	2002-08-08 20:11:18 +0000	[diff] [blame]	864
Misha Brukman	c540240	2004-01-15 18:34:11 +0000	[diff] [blame]	865	</ul>
				866
				867	<p>Regardless of how you register your pass, you must specify at least two
Chris Lattner	c6bb824	2002-08-08 20:11:18 +0000	[diff] [blame]	868	parameters. The first parameter is the name of the pass that is to be used on
				869	the command line to specify that the pass should be added to a program (for
				870	example <tt>opt</tt> or <tt>analyze</tt>). The second argument is the name of
				871	the pass, which is to be used for the <tt>--help</tt> output of programs, as
Misha Brukman	c540240	2004-01-15 18:34:11 +0000	[diff] [blame]	872	well as for debug output generated by the <tt>--debug-pass</tt> option.</p>
Chris Lattner	c6bb824	2002-08-08 20:11:18 +0000	[diff] [blame]	873
Misha Brukman	c540240	2004-01-15 18:34:11 +0000	[diff] [blame]	874	<p>If a pass is registered to be used by the <tt>analyze</tt> utility, you
				875	should implement the virtual <tt>print</tt> method:</p>
				876
				877	</div>
Chris Lattner	c6bb824	2002-08-08 20:11:18 +0000	[diff] [blame]	878
				879	<!-- _______________________________________________________________________ -->
Misha Brukman	c540240	2004-01-15 18:34:11 +0000	[diff] [blame]	880	<div class="doc_subsubsection">
				881	<a name="print">The <tt>print</tt> method</a>
				882	</div>
				883
				884	<div class="doc_text">
Chris Lattner	c6bb824	2002-08-08 20:11:18 +0000	[diff] [blame]	885
Jim Laskey	5fa8fff	2006-08-04 18:10:12 +0000	[diff] [blame]	886	<div class="doc_code"><pre>
Chris Lattner	c6bb824	2002-08-08 20:11:18 +0000	[diff] [blame]	887	<b>virtual void</b> print(std::ostream &O, <b>const</b> Module *M) <b>const</b>;
Jim Laskey	5fa8fff	2006-08-04 18:10:12 +0000	[diff] [blame]	888	</pre></div>
Chris Lattner	c6bb824	2002-08-08 20:11:18 +0000	[diff] [blame]	889
Misha Brukman	c540240	2004-01-15 18:34:11 +0000	[diff] [blame]	890	<p>The <tt>print</tt> method must be implemented by "analyses" in order to print
				891	a human readable version of the analysis results. This is useful for debugging
				892	an analysis itself, as well as for other people to figure out how an analysis
				893	works. The <tt>analyze</tt> tool uses this method to generate its output.</p>
Chris Lattner	c6bb824	2002-08-08 20:11:18 +0000	[diff] [blame]	894
Misha Brukman	c540240	2004-01-15 18:34:11 +0000	[diff] [blame]	895	<p>The <tt>ostream</tt> parameter specifies the stream to write the results on,
				896	and the <tt>Module</tt> parameter gives a pointer to the top level module of the
Chris Lattner	c6bb824	2002-08-08 20:11:18 +0000	[diff] [blame]	897	program that has been analyzed. Note however that this pointer may be null in
				898	certain circumstances (such as calling the <tt>Pass::dump()</tt> from a
				899	debugger), so it should only be used to enhance debug output, it should not be
Misha Brukman	c540240	2004-01-15 18:34:11 +0000	[diff] [blame]	900	depended on.</p>
Chris Lattner	c6bb824	2002-08-08 20:11:18 +0000	[diff] [blame]	901
Misha Brukman	c540240	2004-01-15 18:34:11 +0000	[diff] [blame]	902	</div>
Chris Lattner	c6bb824	2002-08-08 20:11:18 +0000	[diff] [blame]	903
				904	<!-- *********************************************************************** -->
Misha Brukman	c540240	2004-01-15 18:34:11 +0000	[diff] [blame]	905	<div class="doc_section">
				906	<a name="interaction">Specifying interactions between passes</a>
				907	</div>
Chris Lattner	c6bb824	2002-08-08 20:11:18 +0000	[diff] [blame]	908	<!-- *********************************************************************** -->
				909
Misha Brukman	c540240	2004-01-15 18:34:11 +0000	[diff] [blame]	910	<div class="doc_text">
				911
				912	<p>One of the main responsibilities of the <tt>PassManager</tt> is the make sure
Chris Lattner	c6bb824	2002-08-08 20:11:18 +0000	[diff] [blame]	913	that passes interact with each other correctly. Because <tt>PassManager</tt>
				914	tries to <a href="#passmanager">optimize the execution of passes</a> it must
				915	know how the passes interact with each other and what dependencies exist between
				916	the various passes. To track this, each pass can declare the set of passes that
				917	are required to be executed before the current pass, and the passes which are
Misha Brukman	c540240	2004-01-15 18:34:11 +0000	[diff] [blame]	918	invalidated by the current pass.</p>
Chris Lattner	c6bb824	2002-08-08 20:11:18 +0000	[diff] [blame]	919
Misha Brukman	c540240	2004-01-15 18:34:11 +0000	[diff] [blame]	920	<p>Typically this functionality is used to require that analysis results are
Chris Lattner	c6bb824	2002-08-08 20:11:18 +0000	[diff] [blame]	921	computed before your pass is run. Running arbitrary transformation passes can
				922	invalidate the computed analysis results, which is what the invalidation set
				923	specifies. If a pass does not implement the <tt><a
				924	href="#getAnalysisUsage">getAnalysisUsage</a></tt> method, it defaults to not
Misha Brukman	c540240	2004-01-15 18:34:11 +0000	[diff] [blame]	925	having any prerequisite passes, and invalidating <b>all</b> other passes.</p>
Chris Lattner	c6bb824	2002-08-08 20:11:18 +0000	[diff] [blame]	926
Misha Brukman	c540240	2004-01-15 18:34:11 +0000	[diff] [blame]	927	</div>
Chris Lattner	c6bb824	2002-08-08 20:11:18 +0000	[diff] [blame]	928
				929	<!-- _______________________________________________________________________ -->
Misha Brukman	c540240	2004-01-15 18:34:11 +0000	[diff] [blame]	930	<div class="doc_subsubsection">
				931	<a name="getAnalysisUsage">The <tt>getAnalysisUsage</tt> method</a>
				932	</div>
				933
				934	<div class="doc_text">
Chris Lattner	c6bb824	2002-08-08 20:11:18 +0000	[diff] [blame]	935
Jim Laskey	5fa8fff	2006-08-04 18:10:12 +0000	[diff] [blame]	936	<div class="doc_code"><pre>
Chris Lattner	c6bb824	2002-08-08 20:11:18 +0000	[diff] [blame]	937	<b>virtual void</b> getAnalysisUsage(AnalysisUsage &Info) <b>const</b>;
Jim Laskey	5fa8fff	2006-08-04 18:10:12 +0000	[diff] [blame]	938	</pre></div>
Chris Lattner	c6bb824	2002-08-08 20:11:18 +0000	[diff] [blame]	939
Misha Brukman	c540240	2004-01-15 18:34:11 +0000	[diff] [blame]	940	<p>By implementing the <tt>getAnalysisUsage</tt> method, the required and
Chris Lattner	c6bb824	2002-08-08 20:11:18 +0000	[diff] [blame]	941	invalidated sets may be specified for your transformation. The implementation
				942	should fill in the <tt><a
Reid Spencer	05fe4b0	2006-03-14 05:39:39 +0000	[diff] [blame]	943	href="http://llvm.org/doxygen/classllvm_1_1AnalysisUsage.html">AnalysisUsage</a></tt>
Misha Brukman	c540240	2004-01-15 18:34:11 +0000	[diff] [blame]	944	object with information about which passes are required and not invalidated. To
Chris Lattner	8925627	2004-03-17 21:09:55 +0000	[diff] [blame]	945	do this, a pass may call any of the following methods on the AnalysisUsage
				946	object:</p>
				947	</div>
Chris Lattner	c6bb824	2002-08-08 20:11:18 +0000	[diff] [blame]	948
Chris Lattner	8925627	2004-03-17 21:09:55 +0000	[diff] [blame]	949	<!-- _______________________________________________________________________ -->
				950	<div class="doc_subsubsection">
				951	<a name="AU::addRequired">The <tt>AnalysisUsage::addRequired<></tt> and <tt>AnalysisUsage::addRequiredTransitive<></tt> methods</a>
				952	</div>
Chris Lattner	c6bb824	2002-08-08 20:11:18 +0000	[diff] [blame]	953
Chris Lattner	8925627	2004-03-17 21:09:55 +0000	[diff] [blame]	954	<div class="doc_text">
				955	<p>
Reid Spencer	1bc1934	2004-12-11 05:12:57 +0000	[diff] [blame]	956	If your pass requires a previous pass to be executed (an analysis for example),
Chris Lattner	8925627	2004-03-17 21:09:55 +0000	[diff] [blame]	957	it can use one of these methods to arrange for it to be run before your pass.
				958	LLVM has many different types of analyses and passes that can be required,
Reid Spencer	1bc1934	2004-12-11 05:12:57 +0000	[diff] [blame]	959	spanning the range from <tt>DominatorSet</tt> to <tt>BreakCriticalEdges</tt>.
				960	Requiring <tt>BreakCriticalEdges</tt>, for example, guarantees that there will
Chris Lattner	8925627	2004-03-17 21:09:55 +0000	[diff] [blame]	961	be no critical edges in the CFG when your pass has been run.
				962	</p>
Chris Lattner	c6bb824	2002-08-08 20:11:18 +0000	[diff] [blame]	963
Chris Lattner	8925627	2004-03-17 21:09:55 +0000	[diff] [blame]	964	<p>
				965	Some analyses chain to other analyses to do their job. For example, an <a
				966	href="AliasAnalysis.html">AliasAnalysis</a> implementation is required to <a
				967	href="AliasAnalysis.html#chaining">chain</a> to other alias analysis passes. In
				968	cases where analyses chain, the <tt>addRequiredTransitive</tt> method should be
				969	used instead of the <tt>addRequired</tt> method. This informs the PassManager
				970	that the transitively required pass should be alive as long as the requiring
				971	pass is.
				972	</p>
				973	</div>
Chris Lattner	c6bb824	2002-08-08 20:11:18 +0000	[diff] [blame]	974
Chris Lattner	8925627	2004-03-17 21:09:55 +0000	[diff] [blame]	975	<!-- _______________________________________________________________________ -->
				976	<div class="doc_subsubsection">
				977	<a name="AU::addPreserved">The <tt>AnalysisUsage::addPreserved<></tt> method</a>
				978	</div>
Chris Lattner	c6bb824	2002-08-08 20:11:18 +0000	[diff] [blame]	979
Chris Lattner	8925627	2004-03-17 21:09:55 +0000	[diff] [blame]	980	<div class="doc_text">
				981	<p>
				982	One of the jobs of the PassManager is to optimize how and when analyses are run.
				983	In particular, it attempts to avoid recomputing data unless it needs to. For
				984	this reason, passes are allowed to declare that they preserve (i.e., they don't
				985	invalidate) an existing analysis if it's available. For example, a simple
Reid Spencer	1bc1934	2004-12-11 05:12:57 +0000	[diff] [blame]	986	constant folding pass would not modify the CFG, so it can't possibly affect the
Chris Lattner	8925627	2004-03-17 21:09:55 +0000	[diff] [blame]	987	results of dominator analysis. By default, all passes are assumed to invalidate
				988	all others.
				989	</p>
				990
				991	<p>
				992	The <tt>AnalysisUsage</tt> class provides several methods which are useful in
				993	certain circumstances that are related to <tt>addPreserved</tt>. In particular,
				994	the <tt>setPreservesAll</tt> method can be called to indicate that the pass does
				995	not modify the LLVM program at all (which is true for analyses), and the
				996	<tt>setPreservesCFG</tt> method can be used by transformations that change
				997	instructions in the program but do not modify the CFG or terminator instructions
				998	(note that this property is implicitly set for <a
				999	href="#BasicBlockPass">BasicBlockPass</a>'s).
				1000	</p>
				1001
				1002	<p>
				1003	<tt>addPreserved</tt> is particularly useful for transformations like
				1004	<tt>BreakCriticalEdges</tt>. This pass knows how to update a small set of loop
				1005	and dominator related analyses if they exist, so it can preserve them, despite
				1006	the fact that it hacks on the CFG.
				1007	</p>
				1008	</div>
				1009
				1010	<!-- _______________________________________________________________________ -->
				1011	<div class="doc_subsubsection">
				1012	<a name="AU::examples">Example implementations of <tt>getAnalysisUsage</tt></a>
				1013	</div>
				1014
				1015	<div class="doc_text">
Chris Lattner	c6bb824	2002-08-08 20:11:18 +0000	[diff] [blame]	1016
Jim Laskey	5fa8fff	2006-08-04 18:10:12 +0000	[diff] [blame]	1017	<div class="doc_code"><pre>
Chris Lattner	c6bb824	2002-08-08 20:11:18 +0000	[diff] [blame]	1018	<i>// This is an example implementation from an analysis, which does not modify
				1019	// the program at all, yet has a prerequisite.</i>
Reid Spencer	05fe4b0	2006-03-14 05:39:39 +0000	[diff] [blame]	1020	<b>void</b> <a href="http://llvm.org/doxygen/classllvm_1_1PostDominanceFrontier.html">PostDominanceFrontier</a>::getAnalysisUsage(AnalysisUsage &AU) <b>const</b> {
Chris Lattner	c6bb824	2002-08-08 20:11:18 +0000	[diff] [blame]	1021	AU.setPreservesAll();
Reid Spencer	05fe4b0	2006-03-14 05:39:39 +0000	[diff] [blame]	1022	AU.addRequired<<a href="http://llvm.org/doxygen/classllvm_1_1PostDominatorTree.html">PostDominatorTree</a>>();
Chris Lattner	c6bb824	2002-08-08 20:11:18 +0000	[diff] [blame]	1023	}
Jim Laskey	5fa8fff	2006-08-04 18:10:12 +0000	[diff] [blame]	1024	</pre></div>
Chris Lattner	c6bb824	2002-08-08 20:11:18 +0000	[diff] [blame]	1025
Misha Brukman	c540240	2004-01-15 18:34:11 +0000	[diff] [blame]	1026	<p>and:</p>
Chris Lattner	c6bb824	2002-08-08 20:11:18 +0000	[diff] [blame]	1027
Jim Laskey	5fa8fff	2006-08-04 18:10:12 +0000	[diff] [blame]	1028	<div class="doc_code"><pre>
Chris Lattner	c6bb824	2002-08-08 20:11:18 +0000	[diff] [blame]	1029	<i>// This example modifies the program, but does not modify the CFG</i>
Reid Spencer	05fe4b0	2006-03-14 05:39:39 +0000	[diff] [blame]	1030	<b>void</b> <a href="http://llvm.org/doxygen/structLICM.html">LICM</a>::getAnalysisUsage(AnalysisUsage &AU) <b>const</b> {
Chris Lattner	8291e04	2002-10-21 19:57:59 +0000	[diff] [blame]	1031	AU.setPreservesCFG();
Reid Spencer	05fe4b0	2006-03-14 05:39:39 +0000	[diff] [blame]	1032	AU.addRequired<<a href="http://llvm.org/doxygen/classllvm_1_1LoopInfo.html">LoopInfo</a>>();
Chris Lattner	c6bb824	2002-08-08 20:11:18 +0000	[diff] [blame]	1033	}
Jim Laskey	5fa8fff	2006-08-04 18:10:12 +0000	[diff] [blame]	1034	</pre></div>
Misha Brukman	c540240	2004-01-15 18:34:11 +0000	[diff] [blame]	1035
				1036	</div>
Chris Lattner	c6bb824	2002-08-08 20:11:18 +0000	[diff] [blame]	1037
				1038	<!-- _______________________________________________________________________ -->
Misha Brukman	c540240	2004-01-15 18:34:11 +0000	[diff] [blame]	1039	<div class="doc_subsubsection">
Chris Lattner	8925627	2004-03-17 21:09:55 +0000	[diff] [blame]	1040	<a name="getAnalysis">The <tt>getAnalysis<></tt> and <tt>getAnalysisToUpdate<></tt> methods</a>
Misha Brukman	c540240	2004-01-15 18:34:11 +0000	[diff] [blame]	1041	</div>
Chris Lattner	c6bb824	2002-08-08 20:11:18 +0000	[diff] [blame]	1042
Misha Brukman	c540240	2004-01-15 18:34:11 +0000	[diff] [blame]	1043	<div class="doc_text">
				1044
Chris Lattner	8925627	2004-03-17 21:09:55 +0000	[diff] [blame]	1045	<p>The <tt>Pass::getAnalysis<></tt> method is automatically inherited by
				1046	your class, providing you with access to the passes that you declared that you
				1047	required with the <a href="#getAnalysisUsage"><tt>getAnalysisUsage</tt></a>
				1048	method. It takes a single template argument that specifies which pass class you
				1049	want, and returns a reference to that pass. For example:</p>
Chris Lattner	c6bb824	2002-08-08 20:11:18 +0000	[diff] [blame]	1050
Jim Laskey	5fa8fff	2006-08-04 18:10:12 +0000	[diff] [blame]	1051	<div class="doc_code"><pre>
Chris Lattner	a577630	2004-03-17 21:33:32 +0000	[diff] [blame]	1052	bool LICM::runOnFunction(Function &F) {
Chris Lattner	8925627	2004-03-17 21:09:55 +0000	[diff] [blame]	1053	LoopInfo &LI = getAnalysis<LoopInfo>();
				1054	...
				1055	}
Jim Laskey	5fa8fff	2006-08-04 18:10:12 +0000	[diff] [blame]	1056	</pre></div>
Chris Lattner	c6bb824	2002-08-08 20:11:18 +0000	[diff] [blame]	1057
Misha Brukman	c540240	2004-01-15 18:34:11 +0000	[diff] [blame]	1058	<p>This method call returns a reference to the pass desired. You may get a
				1059	runtime assertion failure if you attempt to get an analysis that you did not
				1060	declare as required in your <a
				1061	href="#getAnalysisUsage"><tt>getAnalysisUsage</tt></a> implementation. This
				1062	method can be called by your <tt>run*</tt> method implementation, or by any
				1063	other local method invoked by your <tt>run*</tt> method.</p>
				1064
Chris Lattner	8925627	2004-03-17 21:09:55 +0000	[diff] [blame]	1065	<p>
				1066	If your pass is capable of updating analyses if they exist (e.g.,
				1067	<tt>BreakCriticalEdges</tt>, as described above), you can use the
				1068	<tt>getAnalysisToUpdate</tt> method, which returns a pointer to the analysis if
				1069	it is active. For example:</p>
				1070
Jim Laskey	5fa8fff	2006-08-04 18:10:12 +0000	[diff] [blame]	1071	<div class="doc_code"><pre>
Chris Lattner	8925627	2004-03-17 21:09:55 +0000	[diff] [blame]	1072	...
				1073	if (DominatorSet *DS = getAnalysisToUpdate<DominatorSet>()) {
				1074	<i>// A DominatorSet is active. This code will update it.</i>
				1075	}
				1076	...
Jim Laskey	5fa8fff	2006-08-04 18:10:12 +0000	[diff] [blame]	1077	</pre></div>
Chris Lattner	8925627	2004-03-17 21:09:55 +0000	[diff] [blame]	1078
Misha Brukman	c540240	2004-01-15 18:34:11 +0000	[diff] [blame]	1079	</div>
Chris Lattner	c6bb824	2002-08-08 20:11:18 +0000	[diff] [blame]	1080
Chris Lattner	7991070	2002-08-22 19:21:04 +0000	[diff] [blame]	1081	<!-- *********************************************************************** -->
Misha Brukman	c540240	2004-01-15 18:34:11 +0000	[diff] [blame]	1082	<div class="doc_section">
				1083	<a name="analysisgroup">Implementing Analysis Groups</a>
				1084	</div>
Chris Lattner	7991070	2002-08-22 19:21:04 +0000	[diff] [blame]	1085	<!-- *********************************************************************** -->
				1086
Misha Brukman	c540240	2004-01-15 18:34:11 +0000	[diff] [blame]	1087	<div class="doc_text">
				1088
				1089	<p>Now that we understand the basics of how passes are defined, how the are
				1090	used, and how they are required from other passes, it's time to get a little bit
Chris Lattner	7991070	2002-08-22 19:21:04 +0000	[diff] [blame]	1091	fancier. All of the pass relationships that we have seen so far are very
				1092	simple: one pass depends on one other specific pass to be run before it can run.
				1093	For many applications, this is great, for others, more flexibility is
Misha Brukman	c540240	2004-01-15 18:34:11 +0000	[diff] [blame]	1094	required.</p>
Chris Lattner	7991070	2002-08-22 19:21:04 +0000	[diff] [blame]	1095
Misha Brukman	c540240	2004-01-15 18:34:11 +0000	[diff] [blame]	1096	<p>In particular, some analyses are defined such that there is a single simple
Chris Lattner	7991070	2002-08-22 19:21:04 +0000	[diff] [blame]	1097	interface to the analysis results, but multiple ways of calculating them.
				1098	Consider alias analysis for example. The most trivial alias analysis returns
				1099	"may alias" for any alias query. The most sophisticated analysis a
				1100	flow-sensitive, context-sensitive interprocedural analysis that can take a
				1101	significant amount of time to execute (and obviously, there is a lot of room
				1102	between these two extremes for other implementations). To cleanly support
				1103	situations like this, the LLVM Pass Infrastructure supports the notion of
Misha Brukman	c540240	2004-01-15 18:34:11 +0000	[diff] [blame]	1104	Analysis Groups.</p>
				1105
				1106	</div>
Chris Lattner	7991070	2002-08-22 19:21:04 +0000	[diff] [blame]	1107
				1108	<!-- _______________________________________________________________________ -->
Chris Lattner	8925627	2004-03-17 21:09:55 +0000	[diff] [blame]	1109	<div class="doc_subsubsection">
Misha Brukman	c540240	2004-01-15 18:34:11 +0000	[diff] [blame]	1110	<a name="agconcepts">Analysis Group Concepts</a>
				1111	</div>
Chris Lattner	7991070	2002-08-22 19:21:04 +0000	[diff] [blame]	1112
Misha Brukman	c540240	2004-01-15 18:34:11 +0000	[diff] [blame]	1113	<div class="doc_text">
				1114
				1115	<p>An Analysis Group is a single simple interface that may be implemented by
Chris Lattner	7991070	2002-08-22 19:21:04 +0000	[diff] [blame]	1116	multiple different passes. Analysis Groups can be given human readable names
				1117	just like passes, but unlike passes, they need not derive from the <tt>Pass</tt>
				1118	class. An analysis group may have one or more implementations, one of which is
Misha Brukman	c540240	2004-01-15 18:34:11 +0000	[diff] [blame]	1119	the "default" implementation.</p>
Chris Lattner	7991070	2002-08-22 19:21:04 +0000	[diff] [blame]	1120
Misha Brukman	c540240	2004-01-15 18:34:11 +0000	[diff] [blame]	1121	<p>Analysis groups are used by client passes just like other passes are: the
Chris Lattner	7991070	2002-08-22 19:21:04 +0000	[diff] [blame]	1122	<tt>AnalysisUsage::addRequired()</tt> and <tt>Pass::getAnalysis()</tt> methods.
				1123	In order to resolve this requirement, the <a href="#passmanager">PassManager</a>
				1124	scans the available passes to see if any implementations of the analysis group
				1125	are available. If none is available, the default implementation is created for
				1126	the pass to use. All standard rules for <A href="#interaction">interaction
Misha Brukman	c540240	2004-01-15 18:34:11 +0000	[diff] [blame]	1127	between passes</a> still apply.</p>
Chris Lattner	7991070	2002-08-22 19:21:04 +0000	[diff] [blame]	1128
Misha Brukman	c540240	2004-01-15 18:34:11 +0000	[diff] [blame]	1129	<p>Although <a href="#registration">Pass Registration</a> is optional for normal
Chris Lattner	7991070	2002-08-22 19:21:04 +0000	[diff] [blame]	1130	passes, all analysis group implementations must be registered, and must use the
				1131	<A href="#registerag"><tt>RegisterAnalysisGroup</tt></a> template to join the
				1132	implementation pool. Also, a default implementation of the interface
				1133	<b>must</b> be registered with <A
Misha Brukman	c540240	2004-01-15 18:34:11 +0000	[diff] [blame]	1134	href="#registerag"><tt>RegisterAnalysisGroup</tt></a>.</p>
Chris Lattner	7991070	2002-08-22 19:21:04 +0000	[diff] [blame]	1135
Misha Brukman	c540240	2004-01-15 18:34:11 +0000	[diff] [blame]	1136	<p>As a concrete example of an Analysis Group in action, consider the <a
Reid Spencer	05fe4b0	2006-03-14 05:39:39 +0000	[diff] [blame]	1137	href="http://llvm.org/doxygen/classllvm_1_1AliasAnalysis.html">AliasAnalysis</a>
Chris Lattner	7991070	2002-08-22 19:21:04 +0000	[diff] [blame]	1138	analysis group. The default implementation of the alias analysis interface (the
				1139	<tt><a
Reid Spencer	05fe4b0	2006-03-14 05:39:39 +0000	[diff] [blame]	1140	href="http://llvm.org/doxygen/structBasicAliasAnalysis.html">basicaa</a></tt>
Chris Lattner	7991070	2002-08-22 19:21:04 +0000	[diff] [blame]	1141	pass) just does a few simple checks that don't require significant analysis to
				1142	compute (such as: two different globals can never alias each other, etc).
				1143	Passes that use the <tt><a
Reid Spencer	05fe4b0	2006-03-14 05:39:39 +0000	[diff] [blame]	1144	href="http://llvm.org/doxygen/classllvm_1_1AliasAnalysis.html">AliasAnalysis</a></tt>
Chris Lattner	7991070	2002-08-22 19:21:04 +0000	[diff] [blame]	1145	interface (for example the <tt><a
Reid Spencer	05fe4b0	2006-03-14 05:39:39 +0000	[diff] [blame]	1146	href="http://llvm.org/doxygen/structGCSE.html">gcse</a></tt> pass), do
Misha Brukman	c540240	2004-01-15 18:34:11 +0000	[diff] [blame]	1147	not care which implementation of alias analysis is actually provided, they just
				1148	use the designated interface.</p>
Chris Lattner	7991070	2002-08-22 19:21:04 +0000	[diff] [blame]	1149
Misha Brukman	c540240	2004-01-15 18:34:11 +0000	[diff] [blame]	1150	<p>From the user's perspective, commands work just like normal. Issuing the
Chris Lattner	7991070	2002-08-22 19:21:04 +0000	[diff] [blame]	1151	command '<tt>opt -gcse ...</tt>' will cause the <tt>basicaa</tt> class to be
				1152	instantiated and added to the pass sequence. Issuing the command '<tt>opt
				1153	-somefancyaa -gcse ...</tt>' will cause the <tt>gcse</tt> pass to use the
				1154	<tt>somefancyaa</tt> alias analysis (which doesn't actually exist, it's just a
Misha Brukman	c540240	2004-01-15 18:34:11 +0000	[diff] [blame]	1155	hypothetical example) instead.</p>
Chris Lattner	7991070	2002-08-22 19:21:04 +0000	[diff] [blame]	1156
Misha Brukman	c540240	2004-01-15 18:34:11 +0000	[diff] [blame]	1157	</div>
Chris Lattner	7991070	2002-08-22 19:21:04 +0000	[diff] [blame]	1158
				1159	<!-- _______________________________________________________________________ -->
Chris Lattner	8925627	2004-03-17 21:09:55 +0000	[diff] [blame]	1160	<div class="doc_subsubsection">
Misha Brukman	c540240	2004-01-15 18:34:11 +0000	[diff] [blame]	1161	<a name="registerag">Using <tt>RegisterAnalysisGroup</tt></a>
				1162	</div>
Chris Lattner	7991070	2002-08-22 19:21:04 +0000	[diff] [blame]	1163
Misha Brukman	c540240	2004-01-15 18:34:11 +0000	[diff] [blame]	1164	<div class="doc_text">
				1165
				1166	<p>The <tt>RegisterAnalysisGroup</tt> template is used to register the analysis
Chris Lattner	7991070	2002-08-22 19:21:04 +0000	[diff] [blame]	1167	group itself as well as add pass implementations to the analysis group. First,
				1168	an analysis should be registered, with a human readable name provided for it.
				1169	Unlike registration of passes, there is no command line argument to be specified
Misha Brukman	c540240	2004-01-15 18:34:11 +0000	[diff] [blame]	1170	for the Analysis Group Interface itself, because it is "abstract":</p>
Chris Lattner	7991070	2002-08-22 19:21:04 +0000	[diff] [blame]	1171
Jim Laskey	5fa8fff	2006-08-04 18:10:12 +0000	[diff] [blame]	1172	<div class="doc_code"><pre>
Reid Spencer	05fe4b0	2006-03-14 05:39:39 +0000	[diff] [blame]	1173	<b>static</b> RegisterAnalysisGroup<<a href="http://llvm.org/doxygen/classllvm_1_1AliasAnalysis.html">AliasAnalysis</a>> A("<i>Alias Analysis</i>");
Jim Laskey	5fa8fff	2006-08-04 18:10:12 +0000	[diff] [blame]	1174	</pre></div>
Chris Lattner	7991070	2002-08-22 19:21:04 +0000	[diff] [blame]	1175
Misha Brukman	c540240	2004-01-15 18:34:11 +0000	[diff] [blame]	1176	<p>Once the analysis is registered, passes can declare that they are valid
				1177	implementations of the interface by using the following code:</p>
Chris Lattner	7991070	2002-08-22 19:21:04 +0000	[diff] [blame]	1178
Jim Laskey	5fa8fff	2006-08-04 18:10:12 +0000	[diff] [blame]	1179	<div class="doc_code"><pre>
Chris Lattner	7991070	2002-08-22 19:21:04 +0000	[diff] [blame]	1180	<b>namespace</b> {
				1181	//<i> Analysis Group implementations <b>must</b> be registered normally...</i>
				1182	RegisterOpt<FancyAA>
				1183	B("<i>somefancyaa</i>", "<i>A more complex alias analysis implementation</i>");
				1184
				1185	//<i> Declare that we implement the AliasAnalysis interface</i>
Reid Spencer	05fe4b0	2006-03-14 05:39:39 +0000	[diff] [blame]	1186	RegisterAnalysisGroup<<a href="http://llvm.org/doxygen/classllvm_1_1AliasAnalysis.html">AliasAnalysis</a>, FancyAA> C;
Chris Lattner	7991070	2002-08-22 19:21:04 +0000	[diff] [blame]	1187	}
Jim Laskey	5fa8fff	2006-08-04 18:10:12 +0000	[diff] [blame]	1188	</pre></div>
Chris Lattner	7991070	2002-08-22 19:21:04 +0000	[diff] [blame]	1189
Misha Brukman	c540240	2004-01-15 18:34:11 +0000	[diff] [blame]	1190	<p>This just shows a class <tt>FancyAA</tt> that is registered normally, then
				1191	uses the <tt>RegisterAnalysisGroup</tt> template to "join" the <tt><a
Reid Spencer	05fe4b0	2006-03-14 05:39:39 +0000	[diff] [blame]	1192	href="http://llvm.org/doxygen/classllvm_1_1AliasAnalysis.html">AliasAnalysis</a></tt>
Chris Lattner	7991070	2002-08-22 19:21:04 +0000	[diff] [blame]	1193	analysis group. Every implementation of an analysis group should join using
				1194	this template. A single pass may join multiple different analysis groups with
Misha Brukman	c540240	2004-01-15 18:34:11 +0000	[diff] [blame]	1195	no problem.</p>
Chris Lattner	7991070	2002-08-22 19:21:04 +0000	[diff] [blame]	1196
Jim Laskey	5fa8fff	2006-08-04 18:10:12 +0000	[diff] [blame]	1197	<div class="doc_code"><pre>
Chris Lattner	7991070	2002-08-22 19:21:04 +0000	[diff] [blame]	1198	<b>namespace</b> {
				1199	//<i> Analysis Group implementations <b>must</b> be registered normally...</i>
Reid Spencer	05fe4b0	2006-03-14 05:39:39 +0000	[diff] [blame]	1200	RegisterOpt<<a href="http://llvm.org/doxygen/structBasicAliasAnalysis.html">BasicAliasAnalysis</a>>
Chris Lattner	7991070	2002-08-22 19:21:04 +0000	[diff] [blame]	1201	D("<i>basicaa</i>", "<i>Basic Alias Analysis (default AA impl)</i>");
				1202
				1203	//<i> Declare that we implement the AliasAnalysis interface</i>
Reid Spencer	05fe4b0	2006-03-14 05:39:39 +0000	[diff] [blame]	1204	RegisterAnalysisGroup<<a href="http://llvm.org/doxygen/classllvm_1_1AliasAnalysis.html">AliasAnalysis</a>, <a href="http://llvm.org/doxygen/structBasicAliasAnalysis.html">BasicAliasAnalysis</a>, <b>true</b>> E;
Chris Lattner	7991070	2002-08-22 19:21:04 +0000	[diff] [blame]	1205	}
Jim Laskey	5fa8fff	2006-08-04 18:10:12 +0000	[diff] [blame]	1206	</pre></div>
Chris Lattner	7991070	2002-08-22 19:21:04 +0000	[diff] [blame]	1207
Misha Brukman	c540240	2004-01-15 18:34:11 +0000	[diff] [blame]	1208	<p>Here we show how the default implementation is specified (using the extra
Chris Lattner	7991070	2002-08-22 19:21:04 +0000	[diff] [blame]	1209	argument to the <tt>RegisterAnalysisGroup</tt> template). There must be exactly
				1210	one default implementation available at all times for an Analysis Group to be
				1211	used. Here we declare that the <tt><a
Reid Spencer	05fe4b0	2006-03-14 05:39:39 +0000	[diff] [blame]	1212	href="http://llvm.org/doxygen/structBasicAliasAnalysis.html">BasicAliasAnalysis</a></tt>
Misha Brukman	c540240	2004-01-15 18:34:11 +0000	[diff] [blame]	1213	pass is the default implementation for the interface.</p>
Chris Lattner	c6bb824	2002-08-08 20:11:18 +0000	[diff] [blame]	1214
Misha Brukman	c540240	2004-01-15 18:34:11 +0000	[diff] [blame]	1215	</div>
Chris Lattner	c6bb824	2002-08-08 20:11:18 +0000	[diff] [blame]	1216
				1217	<!-- *********************************************************************** -->
Misha Brukman	c540240	2004-01-15 18:34:11 +0000	[diff] [blame]	1218	<div class="doc_section">
Tanya Lattner	d538365	2004-11-19 01:25:14 +0000	[diff] [blame]	1219	<a name="passStatistics">Pass Statistics</a>
				1220	</div>
				1221	<!-- *********************************************************************** -->
				1222
				1223	<div class="doc_text">
Tanya Lattner	05f8d5f	2004-11-19 01:26:37 +0000	[diff] [blame]	1224	<p>The <a
Reid Spencer	05fe4b0	2006-03-14 05:39:39 +0000	[diff] [blame]	1225	href="http://llvm.org/doxygen/Statistic_8h-source.html"><tt>Statistic</tt></a>
John Criswell	0b1010e	2005-11-28 23:25:41 +0000	[diff] [blame]	1226	class is designed to be an easy way to expose various success
Tanya Lattner	d538365	2004-11-19 01:25:14 +0000	[diff] [blame]	1227	metrics from passes. These statistics are printed at the end of a
				1228	run, when the -stats command line option is enabled on the command
Tanya Lattner	05f8d5f	2004-11-19 01:26:37 +0000	[diff] [blame]	1229	line. See the <a href="http://llvm.org/docs/ProgrammersManual.html#Statistic">Statistics section</a> in the Programmer's Manual for details.
Tanya Lattner	d538365	2004-11-19 01:25:14 +0000	[diff] [blame]	1230
				1231	</div>
				1232
				1233
				1234	<!-- *********************************************************************** -->
				1235	<div class="doc_section">
Misha Brukman	c540240	2004-01-15 18:34:11 +0000	[diff] [blame]	1236	<a name="passmanager">What PassManager does</a>
				1237	</div>
Chris Lattner	c6bb824	2002-08-08 20:11:18 +0000	[diff] [blame]	1238	<!-- *********************************************************************** -->
				1239
Misha Brukman	c540240	2004-01-15 18:34:11 +0000	[diff] [blame]	1240	<div class="doc_text">
				1241
				1242	<p>The <a
Reid Spencer	05fe4b0	2006-03-14 05:39:39 +0000	[diff] [blame]	1243	href="http://llvm.org/doxygen/PassManager_8h-source.html"><tt>PassManager</tt></a>
Misha Brukman	c540240	2004-01-15 18:34:11 +0000	[diff] [blame]	1244	<a
Reid Spencer	05fe4b0	2006-03-14 05:39:39 +0000	[diff] [blame]	1245	href="http://llvm.org/doxygen/classllvm_1_1PassManager.html">class</a>
Misha Brukman	c540240	2004-01-15 18:34:11 +0000	[diff] [blame]	1246	takes a list of passes, ensures their <a href="#interaction">prerequisites</a>
				1247	are set up correctly, and then schedules passes to run efficiently. All of the
				1248	LLVM tools that run passes use the <tt>PassManager</tt> for execution of these
				1249	passes.</p>
Chris Lattner	c6bb824	2002-08-08 20:11:18 +0000	[diff] [blame]	1250
Misha Brukman	c540240	2004-01-15 18:34:11 +0000	[diff] [blame]	1251	<p>The <tt>PassManager</tt> does two main things to try to reduce the execution
				1252	time of a series of passes:</p>
Chris Lattner	c6bb824	2002-08-08 20:11:18 +0000	[diff] [blame]	1253
				1254	<ol>
				1255	<li><b>Share analysis results</b> - The PassManager attempts to avoid
				1256	recomputing analysis results as much as possible. This means keeping track of
				1257	which analyses are available already, which analyses get invalidated, and which
				1258	analyses are needed to be run for a pass. An important part of work is that the
				1259	<tt>PassManager</tt> tracks the exact lifetime of all analysis results, allowing
				1260	it to <a href="#releaseMemory">free memory</a> allocated to holding analysis
Misha Brukman	c540240	2004-01-15 18:34:11 +0000	[diff] [blame]	1261	results as soon as they are no longer needed.</li>
Chris Lattner	c6bb824	2002-08-08 20:11:18 +0000	[diff] [blame]	1262
				1263	<li><b>Pipeline the execution of passes on the program</b> - The
				1264	<tt>PassManager</tt> attempts to get better cache and memory usage behavior out
				1265	of a series of passes by pipelining the passes together. This means that, given
				1266	a series of consequtive <a href="#FunctionPass"><tt>FunctionPass</tt></a>'s, it
				1267	will execute all of the <a href="#FunctionPass"><tt>FunctionPass</tt></a>'s on
				1268	the first function, then all of the <a
Misha Brukman	c540240	2004-01-15 18:34:11 +0000	[diff] [blame]	1269	href="#FunctionPass"><tt>FunctionPass</tt></a>es on the second function,
				1270	etc... until the entire program has been run through the passes.
Chris Lattner	c6bb824	2002-08-08 20:11:18 +0000	[diff] [blame]	1271
Misha Brukman	c540240	2004-01-15 18:34:11 +0000	[diff] [blame]	1272	<p>This improves the cache behavior of the compiler, because it is only touching
Chris Lattner	c6bb824	2002-08-08 20:11:18 +0000	[diff] [blame]	1273	the LLVM program representation for a single function at a time, instead of
				1274	traversing the entire program. It reduces the memory consumption of compiler,
				1275	because, for example, only one <a
Reid Spencer	05fe4b0	2006-03-14 05:39:39 +0000	[diff] [blame]	1276	href="http://llvm.org/doxygen/classllvm_1_1DominatorSet.html"><tt>DominatorSet</tt></a>
Chris Lattner	c6bb824	2002-08-08 20:11:18 +0000	[diff] [blame]	1277	needs to be calculated at a time. This also makes it possible some <a
Misha Brukman	c540240	2004-01-15 18:34:11 +0000	[diff] [blame]	1278	href="#SMP">interesting enhancements</a> in the future.</p></li>
Chris Lattner	c6bb824	2002-08-08 20:11:18 +0000	[diff] [blame]	1279
Misha Brukman	c540240	2004-01-15 18:34:11 +0000	[diff] [blame]	1280	</ol>
Chris Lattner	c6bb824	2002-08-08 20:11:18 +0000	[diff] [blame]	1281
Misha Brukman	c540240	2004-01-15 18:34:11 +0000	[diff] [blame]	1282	<p>The effectiveness of the <tt>PassManager</tt> is influenced directly by how
				1283	much information it has about the behaviors of the passes it is scheduling. For
Chris Lattner	c6bb824	2002-08-08 20:11:18 +0000	[diff] [blame]	1284	example, the "preserved" set is intentionally conservative in the face of an
				1285	unimplemented <a href="#getAnalysisUsage"><tt>getAnalysisUsage</tt></a> method.
				1286	Not implementing when it should be implemented will have the effect of not
Misha Brukman	c540240	2004-01-15 18:34:11 +0000	[diff] [blame]	1287	allowing any analysis results to live across the execution of your pass.</p>
Chris Lattner	c6bb824	2002-08-08 20:11:18 +0000	[diff] [blame]	1288
Misha Brukman	c540240	2004-01-15 18:34:11 +0000	[diff] [blame]	1289	<p>The <tt>PassManager</tt> class exposes a <tt>--debug-pass</tt> command line
Chris Lattner	c6bb824	2002-08-08 20:11:18 +0000	[diff] [blame]	1290	options that is useful for debugging pass execution, seeing how things work, and
				1291	diagnosing when you should be preserving more analyses than you currently are
				1292	(To get information about all of the variants of the <tt>--debug-pass</tt>
Misha Brukman	c540240	2004-01-15 18:34:11 +0000	[diff] [blame]	1293	option, just type '<tt>opt --help-hidden</tt>').</p>
Chris Lattner	c6bb824	2002-08-08 20:11:18 +0000	[diff] [blame]	1294
Misha Brukman	c540240	2004-01-15 18:34:11 +0000	[diff] [blame]	1295	<p>By using the <tt>--debug-pass=Structure</tt> option, for example, we can see
				1296	how our <a href="#basiccode">Hello World</a> pass interacts with other passes.
				1297	Lets try it out with the <tt>gcse</tt> and <tt>licm</tt> passes:</p>
Chris Lattner	c6bb824	2002-08-08 20:11:18 +0000	[diff] [blame]	1298
Jim Laskey	5fa8fff	2006-08-04 18:10:12 +0000	[diff] [blame]	1299	<div class="doc_code"><pre>
Reid Spencer	7fa6d52	2005-01-11 05:16:23 +0000	[diff] [blame]	1300	$ opt -load ../../../Debug/lib/Hello.so -gcse -licm --debug-pass=Structure < hello.bc > /dev/null
Chris Lattner	c6bb824	2002-08-08 20:11:18 +0000	[diff] [blame]	1301	Module Pass Manager
				1302	Function Pass Manager
				1303	Dominator Set Construction
				1304	Immediate Dominators Construction
				1305	Global Common Subexpression Elimination
				1306	-- Immediate Dominators Construction
				1307	-- Global Common Subexpression Elimination
				1308	Natural Loop Construction
				1309	Loop Invariant Code Motion
				1310	-- Natural Loop Construction
				1311	-- Loop Invariant Code Motion
				1312	Module Verifier
				1313	-- Dominator Set Construction
				1314	-- Module Verifier
				1315	Bytecode Writer
				1316	--Bytecode Writer
Jim Laskey	5fa8fff	2006-08-04 18:10:12 +0000	[diff] [blame]	1317	</pre></div>
Chris Lattner	c6bb824	2002-08-08 20:11:18 +0000	[diff] [blame]	1318
Misha Brukman	c540240	2004-01-15 18:34:11 +0000	[diff] [blame]	1319	<p>This output shows us when passes are constructed and when the analysis
				1320	results are known to be dead (prefixed with '<tt>--</tt>'). Here we see that
				1321	GCSE uses dominator and immediate dominator information to do its job. The LICM
				1322	pass uses natural loop information, which uses dominator sets, but not immediate
Chris Lattner	c6bb824	2002-08-08 20:11:18 +0000	[diff] [blame]	1323	dominators. Because immediate dominators are no longer useful after the GCSE
				1324	pass, it is immediately destroyed. The dominator sets are then reused to
Misha Brukman	c540240	2004-01-15 18:34:11 +0000	[diff] [blame]	1325	compute natural loop information, which is then used by the LICM pass.</p>
Chris Lattner	c6bb824	2002-08-08 20:11:18 +0000	[diff] [blame]	1326
Misha Brukman	c540240	2004-01-15 18:34:11 +0000	[diff] [blame]	1327	<p>After the LICM pass, the module verifier runs (which is automatically added
				1328	by the '<tt>opt</tt>' tool), which uses the dominator set to check that the
Chris Lattner	c6bb824	2002-08-08 20:11:18 +0000	[diff] [blame]	1329	resultant LLVM code is well formed. After it finishes, the dominator set
				1330	information is destroyed, after being computed once, and shared by three
Misha Brukman	c540240	2004-01-15 18:34:11 +0000	[diff] [blame]	1331	passes.</p>
Chris Lattner	c6bb824	2002-08-08 20:11:18 +0000	[diff] [blame]	1332
Misha Brukman	c540240	2004-01-15 18:34:11 +0000	[diff] [blame]	1333	<p>Lets see how this changes when we run the <a href="#basiccode">Hello
				1334	World</a> pass in between the two passes:</p>
Chris Lattner	c6bb824	2002-08-08 20:11:18 +0000	[diff] [blame]	1335
Jim Laskey	5fa8fff	2006-08-04 18:10:12 +0000	[diff] [blame]	1336	<div class="doc_code"><pre>
Reid Spencer	7fa6d52	2005-01-11 05:16:23 +0000	[diff] [blame]	1337	$ opt -load ../../../Debug/lib/Hello.so -gcse -hello -licm --debug-pass=Structure < hello.bc > /dev/null
Chris Lattner	c6bb824	2002-08-08 20:11:18 +0000	[diff] [blame]	1338	Module Pass Manager
				1339	Function Pass Manager
				1340	Dominator Set Construction
				1341	Immediate Dominators Construction
				1342	Global Common Subexpression Elimination
				1343	<b>-- Dominator Set Construction</b>
				1344	-- Immediate Dominators Construction
				1345	-- Global Common Subexpression Elimination
				1346	<b> Hello World Pass
				1347	-- Hello World Pass
				1348	Dominator Set Construction</b>
				1349	Natural Loop Construction
				1350	Loop Invariant Code Motion
				1351	-- Natural Loop Construction
				1352	-- Loop Invariant Code Motion
				1353	Module Verifier
				1354	-- Dominator Set Construction
				1355	-- Module Verifier
				1356	Bytecode Writer
				1357	--Bytecode Writer
				1358	Hello: __main
				1359	Hello: puts
				1360	Hello: main
Jim Laskey	5fa8fff	2006-08-04 18:10:12 +0000	[diff] [blame]	1361	</pre></div>
Chris Lattner	c6bb824	2002-08-08 20:11:18 +0000	[diff] [blame]	1362
Misha Brukman	c540240	2004-01-15 18:34:11 +0000	[diff] [blame]	1363	<p>Here we see that the <a href="#basiccode">Hello World</a> pass has killed the
Chris Lattner	c6bb824	2002-08-08 20:11:18 +0000	[diff] [blame]	1364	Dominator Set pass, even though it doesn't modify the code at all! To fix this,
				1365	we need to add the following <a
Misha Brukman	c540240	2004-01-15 18:34:11 +0000	[diff] [blame]	1366	href="#getAnalysisUsage"><tt>getAnalysisUsage</tt></a> method to our pass:</p>
Chris Lattner	c6bb824	2002-08-08 20:11:18 +0000	[diff] [blame]	1367
Jim Laskey	5fa8fff	2006-08-04 18:10:12 +0000	[diff] [blame]	1368	<div class="doc_code"><pre>
Chris Lattner	c6bb824	2002-08-08 20:11:18 +0000	[diff] [blame]	1369	<i>// We don't modify the program, so we preserve all analyses</i>
				1370	<b>virtual void</b> getAnalysisUsage(AnalysisUsage &AU) <b>const</b> {
				1371	AU.setPreservesAll();
				1372	}
Jim Laskey	5fa8fff	2006-08-04 18:10:12 +0000	[diff] [blame]	1373	</pre></div>
Chris Lattner	c6bb824	2002-08-08 20:11:18 +0000	[diff] [blame]	1374
Misha Brukman	c540240	2004-01-15 18:34:11 +0000	[diff] [blame]	1375	<p>Now when we run our pass, we get this output:</p>
Chris Lattner	c6bb824	2002-08-08 20:11:18 +0000	[diff] [blame]	1376
Jim Laskey	5fa8fff	2006-08-04 18:10:12 +0000	[diff] [blame]	1377	<div class="doc_code"><pre>
Reid Spencer	7fa6d52	2005-01-11 05:16:23 +0000	[diff] [blame]	1378	$ opt -load ../../../Debug/lib/Hello.so -gcse -hello -licm --debug-pass=Structure < hello.bc > /dev/null
Chris Lattner	c6bb824	2002-08-08 20:11:18 +0000	[diff] [blame]	1379	Pass Arguments: -gcse -hello -licm
				1380	Module Pass Manager
				1381	Function Pass Manager
				1382	Dominator Set Construction
				1383	Immediate Dominators Construction
				1384	Global Common Subexpression Elimination
				1385	-- Immediate Dominators Construction
				1386	-- Global Common Subexpression Elimination
				1387	Hello World Pass
				1388	-- Hello World Pass
				1389	Natural Loop Construction
				1390	Loop Invariant Code Motion
				1391	-- Loop Invariant Code Motion
				1392	-- Natural Loop Construction
				1393	Module Verifier
				1394	-- Dominator Set Construction
				1395	-- Module Verifier
				1396	Bytecode Writer
				1397	--Bytecode Writer
				1398	Hello: __main
				1399	Hello: puts
				1400	Hello: main
Jim Laskey	5fa8fff	2006-08-04 18:10:12 +0000	[diff] [blame]	1401	</pre></div>
Chris Lattner	c6bb824	2002-08-08 20:11:18 +0000	[diff] [blame]	1402
Misha Brukman	c540240	2004-01-15 18:34:11 +0000	[diff] [blame]	1403	<p>Which shows that we don't accidentally invalidate dominator information
				1404	anymore, and therefore do not have to compute it twice.</p>
Chris Lattner	c6bb824	2002-08-08 20:11:18 +0000	[diff] [blame]	1405
Misha Brukman	c540240	2004-01-15 18:34:11 +0000	[diff] [blame]	1406	</div>
Chris Lattner	c6bb824	2002-08-08 20:11:18 +0000	[diff] [blame]	1407
				1408	<!-- _______________________________________________________________________ -->
Misha Brukman	c540240	2004-01-15 18:34:11 +0000	[diff] [blame]	1409	<div class="doc_subsubsection">
				1410	<a name="releaseMemory">The <tt>releaseMemory</tt> method</a>
				1411	</div>
				1412
				1413	<div class="doc_text">
Chris Lattner	c6bb824	2002-08-08 20:11:18 +0000	[diff] [blame]	1414
Jim Laskey	5fa8fff	2006-08-04 18:10:12 +0000	[diff] [blame]	1415	<div class="doc_code"><pre>
Chris Lattner	c6bb824	2002-08-08 20:11:18 +0000	[diff] [blame]	1416	<b>virtual void</b> releaseMemory();
Jim Laskey	5fa8fff	2006-08-04 18:10:12 +0000	[diff] [blame]	1417	</pre></div>
Chris Lattner	c6bb824	2002-08-08 20:11:18 +0000	[diff] [blame]	1418
Misha Brukman	c540240	2004-01-15 18:34:11 +0000	[diff] [blame]	1419	<p>The <tt>PassManager</tt> automatically determines when to compute analysis
Chris Lattner	c6bb824	2002-08-08 20:11:18 +0000	[diff] [blame]	1420	results, and how long to keep them around for. Because the lifetime of the pass
				1421	object itself is effectively the entire duration of the compilation process, we
				1422	need some way to free analysis results when they are no longer useful. The
Misha Brukman	c540240	2004-01-15 18:34:11 +0000	[diff] [blame]	1423	<tt>releaseMemory</tt> virtual method is the way to do this.</p>
Chris Lattner	c6bb824	2002-08-08 20:11:18 +0000	[diff] [blame]	1424
Misha Brukman	c540240	2004-01-15 18:34:11 +0000	[diff] [blame]	1425	<p>If you are writing an analysis or any other pass that retains a significant
Chris Lattner	c6bb824	2002-08-08 20:11:18 +0000	[diff] [blame]	1426	amount of state (for use by another pass which "requires" your pass and uses the
				1427	<a href="#getAnalysis">getAnalysis</a> method) you should implement
				1428	<tt>releaseMEmory</tt> to, well, release the memory allocated to maintain this
				1429	internal state. This method is called after the <tt>run*</tt> method for the
Misha Brukman	c540240	2004-01-15 18:34:11 +0000	[diff] [blame]	1430	class, before the next call of <tt>run*</tt> in your pass.</p>
Chris Lattner	c6bb824	2002-08-08 20:11:18 +0000	[diff] [blame]	1431
Misha Brukman	c540240	2004-01-15 18:34:11 +0000	[diff] [blame]	1432	</div>
Chris Lattner	c6bb824	2002-08-08 20:11:18 +0000	[diff] [blame]	1433
				1434	<!-- *********************************************************************** -->
Misha Brukman	c540240	2004-01-15 18:34:11 +0000	[diff] [blame]	1435	<div class="doc_section">
Jim Laskey	5fa8fff	2006-08-04 18:10:12 +0000	[diff] [blame]	1436	<a name="registering">Registering dynamically loaded passes</a>
				1437	</div>
				1438	<!-- *********************************************************************** -->
				1439
				1440	<div class="doc_text">
				1441
				1442	<p><i>Size matters</i> when constructing production quality tools using llvm,
				1443	both for the purposes of distribution, and for regulating the resident code size
				1444	when running on the target system. Therefore, it becomes desirable to
				1445	selectively use some passes, while omitting others and maintain the flexibility
				1446	to change configurations later on. You want to be able to do all this, and,
				1447	provide feedback to the user. This is where pass registration comes into
				1448	play.</p>
				1449
				1450	<p>The fundamental mechanisms for pass registration are the
				1451	<tt>MachinePassRegistry</tt> class and subclasses of
				1452	<tt>MachinePassRegistryNode</tt>.</p>
				1453
				1454	<p>An instance of <tt>MachinePassRegistry</tt> is used to maintain a list of
				1455	<tt>MachinePassRegistryNode</tt> objects. This instance maintains the list and
				1456	communicates additions and deletions to the command line interface.</p>
				1457
				1458	<p>An instance of <tt>MachinePassRegistryNode</tt> subclass is used to maintain
				1459	information provided about a particular pass. This information includes the
				1460	command line name, the command help string and the address of the function used
				1461	to create an instance of the pass. A global static constructor of one of these
				1462	instances <i>registers</i> with a corresponding <tt>MachinePassRegistry</tt>,
				1463	the static destructor <i>unregisters</i>. Thus a pass that is statically linked
				1464	in the tool will be registered at start up. A dynamically loaded pass will
				1465	register on load and unregister at unload.</p>
				1466
				1467	</div>
				1468
				1469	<!-- _______________________________________________________________________ -->
				1470	<div class="doc_subsection">
				1471	<a name="registering_existing">Using existing registries</a>
				1472	</div>
				1473
				1474	<div class="doc_text">
				1475
				1476	<p>There are predefined registries to track instruction scheduling
				1477	(<tt>RegisterScheduler</tt>) and register allocation (<tt>RegisterRegAlloc</tt>)
				1478	machine passes. Here we will describe how to <i>register</i> a register
				1479	allocator machine pass.</p>
				1480
				1481	<p>Implement your register allocator machine pass. In your register allocator
				1482	.cpp file add the following include;</p>
				1483
				1484	<div class="doc_code"><pre>
				1485	#include ""llvm/CodeGen/RegAllocRegistry.h""
				1486	</pre></div>
				1487
				1488	<p>Also in your register allocator .cpp file, define a creator function in the
				1489	form; </p>
				1490
				1491	<div class="doc_code"><pre>
				1492	FunctionPass *createMyRegisterAllocator() {
				1493	return new MyRegisterAllocator();
				1494	}
				1495	</pre></div>
				1496
				1497	<p>Note that the signature of this function should match the type of
				1498	<tt>RegisterRegAlloc::FunctionPassCtor</tt>. In the same file add the
				1499	"installing" declaration, in the form;</p>
				1500
				1501	<div class="doc_code"><pre>
				1502	static RegisterRegAlloc myRegAlloc("myregalloc",
				1503	" my register allocator help string",
				1504	createMyRegisterAllocator);
				1505	</pre></div>
				1506
				1507	<p>Note the two spaces prior to the help string produces a tidy result on the
				1508	--help query.</p>
				1509
				1510	<div class="doc_code"><pre>
				1511	$ llc --help
				1512	...
				1513	-regalloc - Register allocator to use: (default = linearscan)
				1514	=linearscan - linear scan register allocator
				1515	=local - local register allocator
				1516	=simple - simple register allocator
				1517	=myregalloc - my register allocator help string
				1518	...
				1519	</pre></div>
				1520
				1521	<p>And that's it. The user is now free to use <tt>-regalloc=myregalloc</tt> as
				1522	an option. Registering instruction schedulers is similar except use the
				1523	<tt>RegisterRegAlloc</tt> class. Note that the
				1524	<tt>RegisterRegAlloc::FunctionPassCtor</tt> is significantly different from
				1525	<tt>RegisterRegAlloc::FunctionPassCtor</tt>.</p>
				1526
				1527	<p>To force the load/linking of your register allocator into the llc/lli tools,
				1528	add your creator function's global declaration to "Passes.h" and add a "pseudo"
				1529	call line to <tt>llvm/Codegen/LinkAllCodegenComponents.h</tt>.</p>
				1530
				1531	</div>
				1532
				1533
				1534	<!-- _______________________________________________________________________ -->
				1535	<div class="doc_subsection">
				1536	<a name="registering_new">Creating new registries</a>
				1537	</div>
				1538
				1539	<div class="doc_text">
				1540
				1541	<p>The easiest way to get started is to clone one of the existing registries; we
				1542	recommend <tt>llvm/CodeGen/RegAllocRegistry.h</tt>. The key things to modify
				1543	are the class name and the <tt>FunctionPassCtor</tt> type.</p>
				1544
				1545	<p>Then you need to declare the registry. Example: if your pass registry is
				1546	<tt>RegisterMyPasses</tt> then define;</p>
				1547
				1548	<div class="doc_code"><pre>
				1549	MachinePassRegistry RegisterMyPasses::Registry;
				1550	</pre></div>
				1551
				1552	<p>And finally, declare the command line option for your passes. Example:</p>
				1553
				1554	<div class="doc_code"><pre>
				1555	cl::opt<RegisterMyPasses::FunctionPassCtor, false,
				1556	RegisterPassParser<RegisterMyPasses&gt &gt
				1557	MyPassOpt("mypass",
				1558	cl::init(&createDefaultMyPass),
				1559	cl::desc("my pass option help"));
				1560	</pre></div>
				1561
				1562	<p>Here the command option is "mypass", with createDefaultMyPass as the default
				1563	creator.</p>
				1564
				1565	</div>
				1566
				1567	<!-- *********************************************************************** -->
				1568	<div class="doc_section">
Misha Brukman	c540240	2004-01-15 18:34:11 +0000	[diff] [blame]	1569	<a name="debughints">Using GDB with dynamically loaded passes</a>
				1570	</div>
Chris Lattner	480e2ef	2002-09-06 02:02:58 +0000	[diff] [blame]	1571	<!-- *********************************************************************** -->
				1572
Misha Brukman	c540240	2004-01-15 18:34:11 +0000	[diff] [blame]	1573	<div class="doc_text">
				1574
				1575	<p>Unfortunately, using GDB with dynamically loaded passes is not as easy as it
Chris Lattner	480e2ef	2002-09-06 02:02:58 +0000	[diff] [blame]	1576	should be. First of all, you can't set a breakpoint in a shared object that has
				1577	not been loaded yet, and second of all there are problems with inlined functions
				1578	in shared objects. Here are some suggestions to debugging your pass with
Misha Brukman	c540240	2004-01-15 18:34:11 +0000	[diff] [blame]	1579	GDB.</p>
Chris Lattner	480e2ef	2002-09-06 02:02:58 +0000	[diff] [blame]	1580
Misha Brukman	c540240	2004-01-15 18:34:11 +0000	[diff] [blame]	1581	<p>For sake of discussion, I'm going to assume that you are debugging a
Chris Lattner	480e2ef	2002-09-06 02:02:58 +0000	[diff] [blame]	1582	transformation invoked by <tt>opt</tt>, although nothing described here depends
Misha Brukman	c540240	2004-01-15 18:34:11 +0000	[diff] [blame]	1583	on that.</p>
				1584
				1585	</div>
Chris Lattner	480e2ef	2002-09-06 02:02:58 +0000	[diff] [blame]	1586
				1587	<!-- _______________________________________________________________________ -->
Misha Brukman	c540240	2004-01-15 18:34:11 +0000	[diff] [blame]	1588	<div class="doc_subsubsection">
				1589	<a name="breakpoint">Setting a breakpoint in your pass</a>
				1590	</div>
Chris Lattner	480e2ef	2002-09-06 02:02:58 +0000	[diff] [blame]	1591
Misha Brukman	c540240	2004-01-15 18:34:11 +0000	[diff] [blame]	1592	<div class="doc_text">
				1593
				1594	<p>First thing you do is start <tt>gdb</tt> on the <tt>opt</tt> process:</p>
Chris Lattner	480e2ef	2002-09-06 02:02:58 +0000	[diff] [blame]	1595
Jim Laskey	5fa8fff	2006-08-04 18:10:12 +0000	[diff] [blame]	1596	<div class="doc_code"><pre>
Chris Lattner	480e2ef	2002-09-06 02:02:58 +0000	[diff] [blame]	1597	$ <b>gdb opt</b>
				1598	GNU gdb 5.0
				1599	Copyright 2000 Free Software Foundation, Inc.
				1600	GDB is free software, covered by the GNU General Public License, and you are
				1601	welcome to change it and/or distribute copies of it under certain conditions.
				1602	Type "show copying" to see the conditions.
				1603	There is absolutely no warranty for GDB. Type "show warranty" for details.
				1604	This GDB was configured as "sparc-sun-solaris2.6"...
				1605	(gdb)
Jim Laskey	5fa8fff	2006-08-04 18:10:12 +0000	[diff] [blame]	1606	</pre></div>
Chris Lattner	480e2ef	2002-09-06 02:02:58 +0000	[diff] [blame]	1607
Misha Brukman	c540240	2004-01-15 18:34:11 +0000	[diff] [blame]	1608	<p>Note that <tt>opt</tt> has a lot of debugging information in it, so it takes
Chris Lattner	480e2ef	2002-09-06 02:02:58 +0000	[diff] [blame]	1609	time to load. Be patient. Since we cannot set a breakpoint in our pass yet
				1610	(the shared object isn't loaded until runtime), we must execute the process, and
				1611	have it stop before it invokes our pass, but after it has loaded the shared
				1612	object. The most foolproof way of doing this is to set a breakpoint in
				1613	<tt>PassManager::run</tt> and then run the process with the arguments you
Misha Brukman	c540240	2004-01-15 18:34:11 +0000	[diff] [blame]	1614	want:</p>
Chris Lattner	480e2ef	2002-09-06 02:02:58 +0000	[diff] [blame]	1615
Jim Laskey	5fa8fff	2006-08-04 18:10:12 +0000	[diff] [blame]	1616	<div class="doc_code"><pre>
Chris Lattner	480e2ef	2002-09-06 02:02:58 +0000	[diff] [blame]	1617	(gdb) <b>break PassManager::run</b>
				1618	Breakpoint 1 at 0x2413bc: file Pass.cpp, line 70.
Chris Lattner	4c376ea	2005-04-21 04:52:37 +0000	[diff] [blame]	1619	(gdb) <b>run test.bc -load $(LLVMTOP)/llvm/Debug/lib/[libname].so -[passoption]</b>
				1620	Starting program: opt test.bc -load $(LLVMTOP)/llvm/Debug/lib/[libname].so -[passoption]
Chris Lattner	480e2ef	2002-09-06 02:02:58 +0000	[diff] [blame]	1621	Breakpoint 1, PassManager::run (this=0xffbef174, M=@0x70b298) at Pass.cpp:70
				1622	70 bool PassManager::run(Module &M) { return PM->run(M); }
				1623	(gdb)
Jim Laskey	5fa8fff	2006-08-04 18:10:12 +0000	[diff] [blame]	1624	</pre></div>
Chris Lattner	480e2ef	2002-09-06 02:02:58 +0000	[diff] [blame]	1625
Misha Brukman	c540240	2004-01-15 18:34:11 +0000	[diff] [blame]	1626	<p>Once the <tt>opt</tt> stops in the <tt>PassManager::run</tt> method you are
				1627	now free to set breakpoints in your pass so that you can trace through execution
				1628	or do other standard debugging stuff.</p>
Chris Lattner	480e2ef	2002-09-06 02:02:58 +0000	[diff] [blame]	1629
Misha Brukman	c540240	2004-01-15 18:34:11 +0000	[diff] [blame]	1630	</div>
Chris Lattner	480e2ef	2002-09-06 02:02:58 +0000	[diff] [blame]	1631
				1632	<!-- _______________________________________________________________________ -->
Misha Brukman	c540240	2004-01-15 18:34:11 +0000	[diff] [blame]	1633	<div class="doc_subsubsection">
				1634	<a name="debugmisc">Miscellaneous Problems</a>
				1635	</div>
Chris Lattner	480e2ef	2002-09-06 02:02:58 +0000	[diff] [blame]	1636
Misha Brukman	c540240	2004-01-15 18:34:11 +0000	[diff] [blame]	1637	<div class="doc_text">
				1638
				1639	<p>Once you have the basics down, there are a couple of problems that GDB has,
				1640	some with solutions, some without.</p>
Chris Lattner	480e2ef	2002-09-06 02:02:58 +0000	[diff] [blame]	1641
				1642	<ul>
				1643	<li>Inline functions have bogus stack information. In general, GDB does a
				1644	pretty good job getting stack traces and stepping through inline functions.
				1645	When a pass is dynamically loaded however, it somehow completely loses this
				1646	capability. The only solution I know of is to de-inline a function (move it
Misha Brukman	c540240	2004-01-15 18:34:11 +0000	[diff] [blame]	1647	from the body of a class to a .cpp file).</li>
Chris Lattner	480e2ef	2002-09-06 02:02:58 +0000	[diff] [blame]	1648
				1649	<li>Restarting the program breaks breakpoints. After following the information
				1650	above, you have succeeded in getting some breakpoints planted in your pass. Nex
				1651	thing you know, you restart the program (i.e., you type '<tt>run</tt>' again),
				1652	and you start getting errors about breakpoints being unsettable. The only way I
				1653	have found to "fix" this problem is to <tt>delete</tt> the breakpoints that are
				1654	already set in your pass, run the program, and re-set the breakpoints once
Misha Brukman	c540240	2004-01-15 18:34:11 +0000	[diff] [blame]	1655	execution stops in <tt>PassManager::run</tt>.</li>
Chris Lattner	480e2ef	2002-09-06 02:02:58 +0000	[diff] [blame]	1656
				1657	</ul>
				1658
Misha Brukman	c540240	2004-01-15 18:34:11 +0000	[diff] [blame]	1659	<p>Hopefully these tips will help with common case debugging situations. If
				1660	you'd like to contribute some tips of your own, just contact <a
				1661	href="mailto:sabre@nondot.org">Chris</a>.</p>
Chris Lattner	480e2ef	2002-09-06 02:02:58 +0000	[diff] [blame]	1662
Misha Brukman	c540240	2004-01-15 18:34:11 +0000	[diff] [blame]	1663	</div>
Chris Lattner	480e2ef	2002-09-06 02:02:58 +0000	[diff] [blame]	1664
				1665	<!-- *********************************************************************** -->
Misha Brukman	c540240	2004-01-15 18:34:11 +0000	[diff] [blame]	1666	<div class="doc_section">
				1667	<a name="future">Future extensions planned</a>
				1668	</div>
Chris Lattner	c6bb824	2002-08-08 20:11:18 +0000	[diff] [blame]	1669	<!-- *********************************************************************** -->
				1670
Misha Brukman	c540240	2004-01-15 18:34:11 +0000	[diff] [blame]	1671	<div class="doc_text">
				1672
				1673	<p>Although the LLVM Pass Infrastructure is very capable as it stands, and does
Chris Lattner	c6bb824	2002-08-08 20:11:18 +0000	[diff] [blame]	1674	some nifty stuff, there are things we'd like to add in the future. Here is
Misha Brukman	c540240	2004-01-15 18:34:11 +0000	[diff] [blame]	1675	where we are going:</p>
				1676
				1677	</div>
Chris Lattner	c6bb824	2002-08-08 20:11:18 +0000	[diff] [blame]	1678
				1679	<!-- _______________________________________________________________________ -->
Chris Lattner	8925627	2004-03-17 21:09:55 +0000	[diff] [blame]	1680	<div class="doc_subsubsection">
Misha Brukman	c540240	2004-01-15 18:34:11 +0000	[diff] [blame]	1681	<a name="SMP">Multithreaded LLVM</a>
				1682	</div>
Chris Lattner	c6bb824	2002-08-08 20:11:18 +0000	[diff] [blame]	1683
Misha Brukman	c540240	2004-01-15 18:34:11 +0000	[diff] [blame]	1684	<div class="doc_text">
				1685
				1686	<p>Multiple CPU machines are becoming more common and compilation can never be
Chris Lattner	c6bb824	2002-08-08 20:11:18 +0000	[diff] [blame]	1687	fast enough: obviously we should allow for a multithreaded compiler. Because of
				1688	the semantics defined for passes above (specifically they cannot maintain state
				1689	across invocations of their <tt>run*</tt> methods), a nice clean way to
				1690	implement a multithreaded compiler would be for the <tt>PassManager</tt> class
Misha Brukman	bc0e998	2003-07-14 17:20:40 +0000	[diff] [blame]	1691	to create multiple instances of each pass object, and allow the separate
Misha Brukman	c540240	2004-01-15 18:34:11 +0000	[diff] [blame]	1692	instances to be hacking on different parts of the program at the same time.</p>
Chris Lattner	c6bb824	2002-08-08 20:11:18 +0000	[diff] [blame]	1693
Misha Brukman	c540240	2004-01-15 18:34:11 +0000	[diff] [blame]	1694	<p>This implementation would prevent each of the passes from having to implement
Chris Lattner	c6bb824	2002-08-08 20:11:18 +0000	[diff] [blame]	1695	multithreaded constructs, requiring only the LLVM core to have locking in a few
				1696	places (for global resources). Although this is a simple extension, we simply
				1697	haven't had time (or multiprocessor machines, thus a reason) to implement this.
Misha Brukman	c540240	2004-01-15 18:34:11 +0000	[diff] [blame]	1698	Despite that, we have kept the LLVM passes SMP ready, and you should too.</p>
Chris Lattner	c6bb824	2002-08-08 20:11:18 +0000	[diff] [blame]	1699
Misha Brukman	c540240	2004-01-15 18:34:11 +0000	[diff] [blame]	1700	</div>
Chris Lattner	c6bb824	2002-08-08 20:11:18 +0000	[diff] [blame]	1701
				1702	<!-- _______________________________________________________________________ -->
Chris Lattner	8925627	2004-03-17 21:09:55 +0000	[diff] [blame]	1703	<div class="doc_subsubsection">
Chris Lattner	f627892	2004-09-20 04:36:29 +0000	[diff] [blame]	1704	<a name="PassFunctionPass"><tt>ModulePass</tt>es requiring <tt>FunctionPass</tt>es</a>
Misha Brukman	c540240	2004-01-15 18:34:11 +0000	[diff] [blame]	1705	</div>
Chris Lattner	c6bb824	2002-08-08 20:11:18 +0000	[diff] [blame]	1706
Misha Brukman	c540240	2004-01-15 18:34:11 +0000	[diff] [blame]	1707	<div class="doc_text">
Chris Lattner	c6bb824	2002-08-08 20:11:18 +0000	[diff] [blame]	1708
Chris Lattner	f627892	2004-09-20 04:36:29 +0000	[diff] [blame]	1709	<p>Currently it is illegal for a <a href="#ModulePass"><tt>ModulePass</tt></a>
				1710	to require a <a href="#FunctionPass"><tt>FunctionPass</tt></a>. This is because
				1711	there is only one instance of the <a
				1712	href="#FunctionPass"><tt>FunctionPass</tt></a> object ever created, thus nowhere
				1713	to store information for all of the functions in the program at the same time.
				1714	Although this has come up a couple of times before, this has always been worked
				1715	around by factoring one big complicated pass into a global and an
				1716	interprocedural part, both of which are distinct. In the future, it would be
				1717	nice to have this though.</p>
Misha Brukman	c540240	2004-01-15 18:34:11 +0000	[diff] [blame]	1718
				1719	<p>Note that it is no problem for a <a
Chris Lattner	c6bb824	2002-08-08 20:11:18 +0000	[diff] [blame]	1720	href="#FunctionPass"><tt>FunctionPass</tt></a> to require the results of a <a
Chris Lattner	f627892	2004-09-20 04:36:29 +0000	[diff] [blame]	1721	href="#ModulePass"><tt>ModulePass</tt></a>, only the other way around.</p>
Chris Lattner	c6bb824	2002-08-08 20:11:18 +0000	[diff] [blame]	1722
Misha Brukman	c540240	2004-01-15 18:34:11 +0000	[diff] [blame]	1723	</div>
Chris Lattner	c6bb824	2002-08-08 20:11:18 +0000	[diff] [blame]	1724
				1725	<!-- *********************************************************************** -->
Misha Brukman	c540240	2004-01-15 18:34:11 +0000	[diff] [blame]	1726	<hr>
				1727	<address>
				1728	<a href="http://jigsaw.w3.org/css-validator/check/referer"><img
				1729	src="http://jigsaw.w3.org/css-validator/images/vcss" alt="Valid CSS!"></a>
				1730	<a href="http://validator.w3.org/check/referer"><img
				1731	src="http://www.w3.org/Icons/valid-html401" alt="Valid HTML 4.01!" /></a>
Chris Lattner	c6bb824	2002-08-08 20:11:18 +0000	[diff] [blame]	1732
Misha Brukman	c540240	2004-01-15 18:34:11 +0000	[diff] [blame]	1733	<a href="mailto:sabre@nondot.org">Chris Lattner</a><br>
Reid Spencer	05fe4b0	2006-03-14 05:39:39 +0000	[diff] [blame]	1734	<a href="http://llvm.org">The LLVM Compiler Infrastructure</a><br>
Misha Brukman	c540240	2004-01-15 18:34:11 +0000	[diff] [blame]	1735	Last modified: $Date$
				1736	</address>
				1737
				1738	</body>
				1739	</html>