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Misha Brukmanc5402402004-01-15 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 Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]10
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]11<div class="doc_title">
12 Writing an LLVM Pass
13</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]14
15<ol>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]16 <li><a href="#introduction">Introduction - What is a pass?</a></li>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]17 <li><a href="#quickstart">Quick Start - Writing hello world</a>
18 <ul>
Misha Brukmanc5402402004-01-15 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 Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]21 <li><a href="#running">Running a pass with <tt>opt</tt>
Chris Lattner8fdb2462004-09-18 06:39:35 +0000[diff] [blame]22 or <tt>analyze</tt></a></li>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]23 </ul></li>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]24 <li><a href="#passtype">Pass classes and requirements</a>
25 <ul>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]26 <li><a href="#ImmutablePass">The <tt>ImmutablePass</tt> class</a></li>
Chris Lattnerf6278922004-09-20 04:36:29 +0000[diff] [blame]27 <li><a href="#ModulePass">The <tt>ModulePass</tt> class</a>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]28 <ul>
Chris Lattnerf6278922004-09-20 04:36:29 +0000[diff] [blame]29 <li><a href="#runOnModule">The <tt>runOnModule</tt> method</a></li>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]30 </ul></li>
Chris Lattner8fdb2462004-09-18 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 &amp;)</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 &amp;)</tt> method</a></li>
38 </ul></li>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]39 <li><a href="#FunctionPass">The <tt>FunctionPass</tt> class</a>
40 <ul>
Chris Lattnerd0713f92002-09-12 17:06:43 +0000[diff] [blame]41 <li><a href="#doInitialization_mod">The <tt>doInitialization(Module
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]42 &amp;)</tt> method</a></li>
43 <li><a href="#runOnFunction">The <tt>runOnFunction</tt> method</a></li>
Chris Lattnerd0713f92002-09-12 17:06:43 +0000[diff] [blame]44 <li><a href="#doFinalization_mod">The <tt>doFinalization(Module
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]45 &amp;)</tt> method</a></li>
46 </ul></li>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]47 <li><a href="#BasicBlockPass">The <tt>BasicBlockPass</tt> class</a>
48 <ul>
Chris Lattnerd0713f92002-09-12 17:06:43 +0000[diff] [blame]49 <li><a href="#doInitialization_fn">The <tt>doInitialization(Function
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]50 &amp;)</tt> method</a></li>
51 <li><a href="#runOnBasicBlock">The <tt>runOnBasicBlock</tt>
52 method</a></li>
Chris Lattnerd0713f92002-09-12 17:06:43 +0000[diff] [blame]53 <li><a href="#doFinalization_fn">The <tt>doFinalization(Function
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]54 &amp;)</tt> method</a></li>
55 </ul></li>
Brian Gaekecab8b6f2003-07-17 18:53:20 +0000[diff] [blame]56 <li><a href="#MachineFunctionPass">The <tt>MachineFunctionPass</tt>
57 class</a>
Brian Gaeke6a33f362003-07-22 20:53:20 +0000[diff] [blame]58 <ul>
59 <li><a href="#runOnMachineFunction">The
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]60 <tt>runOnMachineFunction(MachineFunction &amp;)</tt> method</a></li>
61 </ul></li>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]62 </ul>
63 <li><a href="#registration">Pass Registration</a>
64 <ul>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]65 <li><a href="#print">The <tt>print</tt> method</a></li>
66 </ul></li>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]67 <li><a href="#interaction">Specifying interactions between passes</a>
68 <ul>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]69 <li><a href="#getAnalysisUsage">The <tt>getAnalysisUsage</tt>
70 method</a></li>
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]71 <li><a href="#AU::addRequired">The <tt>AnalysisUsage::addRequired&lt;&gt;</tt> and <tt>AnalysisUsage::addRequiredTransitive&lt;&gt;</tt> methods</a></li>
72 <li><a href="#AU::addPreserved">The <tt>AnalysisUsage::addPreserved&lt;&gt;</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&lt;&gt;</tt> and <tt>getAnalysisToUpdate&lt;&gt;</tt> methods</a></li>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]75 </ul></li>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]76 <li><a href="#analysisgroup">Implementing Analysis Groups</a>
77 <ul>
Misha Brukmanc5402402004-01-15 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 Lattnerd5383652004-11-19 01:25:14 +0000[diff] [blame]81 <li><a href="#passStatistics">Pass Statistics</a>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]82 <li><a href="#passmanager">What PassManager does</a>
83 <ul>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]84 <li><a href="#releaseMemory">The <tt>releaseMemory</tt> method</a></li>
85 </ul></li>
Jim Laskey5fa8fff2006-08-04 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 Lattner480e2ef2002-09-06 02:02:58 +0000[diff] [blame]91 <li><a href="#debughints">Using GDB with dynamically loaded passes</a>
92 <ul>
Misha Brukmanc5402402004-01-15 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 Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]96 <li><a href="#future">Future extensions planned</a>
97 <ul>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]98 <li><a href="#SMP">Multithreaded LLVM</a></li>
Chris Lattnerf6278922004-09-20 04:36:29 +0000[diff] [blame]99 <li><a href="#PassFunctionPass"><tt>ModulePass</tt>es requiring
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]100 <tt>FunctionPass</tt>es</a></li>
101 </ul></li>
102</ol>
Chris Lattner38c633d2002-08-08 20:23:41 +0000[diff] [blame]103
Chris Lattner7911ce22004-05-23 21:07:27 +0000[diff] [blame]104<div class="doc_author">
Jim Laskey5fa8fff2006-08-04 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 Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]107</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]108
109<!-- *********************************************************************** -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]110<div class="doc_section">
111 <a name="introduction">Introduction - What is a pass?</a>
112</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]113<!-- *********************************************************************** -->
114
Misha Brukmanc5402402004-01-15 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 Lattner8fdb2462004-09-18 06:39:35 +0000[diff] [blame]118passes are where most of the interesting parts of the compiler exist. Passes
119perform the transformations and optimizations that make up the compiler, they
120build the analysis results that are used by these transformations, and they are,
121above all, a structuring technique for compiler code.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]122
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]123<p>All LLVM passes are subclasses of the <tt><a
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]124href="http://llvm.org/doxygen/classllvm_1_1Pass.html">Pass</a></tt>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]125class, which implement functionality by overriding virtual methods inherited
Chris Lattnerf6278922004-09-20 04:36:29 +0000[diff] [blame]126from <tt>Pass</tt>. Depending on how your pass works, you should inherit from
127the <tt><a href="#ModulePass">ModulePass</a></tt>, <tt><a
128href="#CallGraphSCCPass">CallGraphSCCPass</a></tt>, <tt><a
129href="#FunctionPass">FunctionPass</a></tt>, or <tt><a
Chris Lattner8fdb2462004-09-18 06:39:35 +0000[diff] [blame]130href="#BasicBlockPass">BasicBlockPass</a></tt> classes, which gives the system
131more information about what your pass does, and how it can be combined with
132other passes. One of the main features of the LLVM Pass Framework is that it
133schedules passes to run in an efficient way based on the constraints that your
134pass meets (which are indicated by which class they derive from).</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]135
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]136<p>We start by showing you how to construct a pass, everything from setting up
137the code, to compiling, loading, and executing it. After the basics are down,
138more advanced features are discussed.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]139
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]140</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]141
142<!-- *********************************************************************** -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]143<div class="doc_section">
144 <a name="quickstart">Quick Start - Writing hello world</a>
145</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]146<!-- *********************************************************************** -->
147
Misha Brukmanc5402402004-01-15 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
151is designed to simply print out the name of non-external functions that exist in
Chris Lattner8fdb2462004-09-18 06:39:35 +0000[diff] [blame]152the program being compiled. It does not modify the program at all, it just
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]153inspects it. The source code and files for this pass are available in the LLVM
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]154source tree in the <tt>lib/Transforms/Hello</tt> directory.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]155
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]156</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]157
158<!-- ======================================================================= -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]159<div class="doc_subsection">
160 <a name="makefile">Setting up the build environment</a>
161</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]162
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]163<div class="doc_text">
164
Reid Spencer1bc19342004-12-11 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 Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]171
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]172<div class="doc_code"><pre>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]173# Makefile for hello pass
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]174
Chris Lattner17a4c3e2002-08-14 20:06:13 +0000[diff] [blame]175# Path to top level of LLVM heirarchy
Chris Lattner7ce83e52002-08-14 20:07:01 +0000[diff] [blame]176LEVEL = ../../..
Chris Lattner17a4c3e2002-08-14 20:06:13 +0000[diff] [blame]177
178# Name of the library to build
Reid Spencer7fa6d522005-01-11 05:16:23 +0000[diff] [blame]179LIBRARYNAME = Hello
Chris Lattner17a4c3e2002-08-14 20:06:13 +0000[diff] [blame]180
Reid Spencer7fa6d522005-01-11 05:16:23 +0000[diff] [blame]181# Make the shared library become a loadable module so the tools can
182# dlopen/dlsym on the resulting library.
Robert Bocchino3cf817d2006-01-06 22:49:23 +0000[diff] [blame]183LOADABLE_MODULE = 1
Reid Spencer7fa6d522005-01-11 05:16:23 +0000[diff] [blame]184
Reid Spencerebfe07f2006-08-08 01:48:17 +0000[diff] [blame^]185# Tell the build system which LLVM libraries your pass needs. You'll probably
186# need at least LLVMSystem.a, LLVMSupport.a, LLVMCore.a but possibly several
187# others too.
188LLVMLIBS = LLVMCore.a LLVMSupport.a LLVMSystem.a
189
Chris Lattner17a4c3e2002-08-14 20:06:13 +0000[diff] [blame]190# Include the makefile implementation stuff
191include $(LEVEL)/Makefile.common
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]192</pre></div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]193
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]194<p>This makefile specifies that all of the <tt>.cpp</tt> files in the current
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]195directory are to be compiled and linked together into a
Reid Spencer7fa6d522005-01-11 05:16:23 +0000[diff] [blame]196<tt>Debug/lib/Hello.so</tt> shared object that can be dynamically loaded by
197the <tt>opt</tt> or <tt>analyze</tt> tools via their <tt>-load</tt> options.
198If your operating system uses a suffix other than .so (such as windows or
199Mac OS/X), the appropriate extension will be used.</p>
John Criswellf9c78652004-01-26 21:26:54 +0000[diff] [blame]200
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]201<p>Now that we have the build scripts set up, we just need to write the code for
202the pass itself.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]203
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]204</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]205
206<!-- ======================================================================= -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]207<div class="doc_subsection">
208 <a name="basiccode">Basic code required</a>
209</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]210
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]211<div class="doc_text">
212
213<p>Now that we have a way to compile our new pass, we just have to write it.
214Start out with:</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]215
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]216<div class="doc_code"><pre>
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]217<b>#include</b> "<a href="http://llvm.org/doxygen/Pass_8h-source.html">llvm/Pass.h</a>"
218<b>#include</b> "<a href="http://llvm.org/doxygen/Function_8h-source.html">llvm/Function.h</a>"
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]219</pre></div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]220
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]221<p>Which are needed because we are writing a <tt><a
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]222href="http://llvm.org/doxygen/classllvm_1_1Pass.html">Pass</a></tt>, and
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]223we are operating on <tt><a
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]224href="http://llvm.org/doxygen/classllvm_1_1Function.html">Function</a></tt>'s.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]225
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]226<p>Next we have:</p>
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]227<div class="doc_code"><pre>
Jonathan Manton65acb302004-06-30 18:10:30 +0000[diff] [blame]228<b>using namespace llvm;</b>
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]229</pre></div>
Jonathan Manton65acb302004-06-30 18:10:30 +0000[diff] [blame]230<p>... which is required because the functions from the include files
231live in the llvm namespace.
232</p>
233
234<p>Next we have:</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]235
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]236<div class="doc_code"><pre>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]237<b>namespace</b> {
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]238</pre></div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]239
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]240<p>... which starts out an anonymous namespace. Anonymous namespaces are to C++
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]241what the "<tt>static</tt>" keyword is to C (at global scope). It makes the
242things declared inside of the anonymous namespace only visible to the current
243file. If you're not familiar with them, consult a decent C++ book for more
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]244information.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]245
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]246<p>Next, we declare our pass itself:</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]247
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]248<div class="doc_code"><pre>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]249 <b>struct</b> Hello : <b>public</b> <a href="#FunctionPass">FunctionPass</a> {
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]250</pre></div><p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]251
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]252<p>This declares a "<tt>Hello</tt>" class that is a subclass of <tt><a
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]253href="http://llvm.org/doxygen/classllvm_1_1FunctionPass.html">FunctionPass</a></tt>.
Chris Lattnerd6ea9262002-09-09 03:48:46 +0000[diff] [blame]254The different builtin pass subclasses are described in detail <a
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]255href="#passtype">later</a>, but for now, know that <a
256href="#FunctionPass"><tt>FunctionPass</tt></a>'s operate a function at a
257time.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]258
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]259<div class="doc_code"><pre>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]260 <b>virtual bool</b> <a href="#runOnFunction">runOnFunction</a>(Function &amp;F) {
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]261 std::cerr &lt;&lt; "<i>Hello: </i>" &lt;&lt; F.getName() &lt;&lt; "\n";
262 <b>return false</b>;
263 }
264 }; <i>// end of struct Hello</i>
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]265</pre></div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]266
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]267<p>We declare a "<a href="#runOnFunction"><tt>runOnFunction</tt></a>" method,
268which overloads an abstract virtual method inherited from <a
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]269href="#FunctionPass"><tt>FunctionPass</tt></a>. This is where we are supposed
270to do our thing, so we just print out our message with the name of each
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]271function.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]272
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]273<div class="doc_code"><pre>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]274 RegisterOpt&lt;Hello&gt; X("<i>hello</i>", "<i>Hello World Pass</i>");
275} <i>// end of anonymous namespace</i>
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]276</pre></div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]277
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]278<p>Lastly, we register our class <tt>Hello</tt>, giving it a command line
279argument "<tt>hello</tt>", and a name "<tt>Hello World Pass</tt>". There are
280several different ways of <a href="#registration">registering your pass</a>,
281depending on what it is to be used for. For "optimizations" we use the
282<tt>RegisterOpt</tt> template.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]283
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]284<p>As a whole, the <tt>.cpp</tt> file looks like:</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]285
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]286<div class="doc_code"><pre>
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]287<b>#include</b> "<a href="http://llvm.org/doxygen/Pass_8h-source.html">llvm/Pass.h</a>"
288<b>#include</b> "<a href="http://llvm.org/doxygen/Function_8h-source.html">llvm/Function.h</a>"
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]289
Jonathan Manton65acb302004-06-30 18:10:30 +0000[diff] [blame]290<b>using namespace llvm;</b>
291
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]292<b>namespace</b> {
293 <b>struct Hello</b> : <b>public</b> <a href="#FunctionPass">FunctionPass</a> {
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]294 <b>virtual bool</b> <a href="#runOnFunction">runOnFunction</a>(Function &amp;F) {
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]295 std::cerr &lt;&lt; "<i>Hello: </i>" &lt;&lt; F.getName() &lt;&lt; "\n";
296 <b>return false</b>;
297 }
298 };
299
300 RegisterOpt&lt;Hello&gt; X("<i>hello</i>", "<i>Hello World Pass</i>");
301}
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]302</pre></div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]303
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]304<p>Now that it's all together, compile the file with a simple "<tt>gmake</tt>"
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]305command in the local directory and you should get a new
Reid Spencer7fa6d522005-01-11 05:16:23 +0000[diff] [blame]306"<tt>Debug/lib/Hello.so</tt> file. Note that everything in this file is
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]307contained in an anonymous namespace: this reflects the fact that passes are self
308contained units that do not need external interfaces (although they can have
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]309them) to be useful.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]310
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]311</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]312
313<!-- ======================================================================= -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]314<div class="doc_subsection">
315 <a name="running">Running a pass with <tt>opt</tt> or <tt>analyze</tt></a>
316</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]317
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]318<div class="doc_text">
319
John Criswellf9c78652004-01-26 21:26:54 +0000[diff] [blame]320<p>Now that you have a brand new shiny shared object file, we can use the
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]321<tt>opt</tt> command to run an LLVM program through your pass. Because you
322registered your pass with the <tt>RegisterOpt</tt> template, you will be able to
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]323use the <tt>opt</tt> tool to access it, once loaded.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]324
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]325<p>To test it, follow the example at the end of the <a
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]326href="GettingStarted.html">Getting Started Guide</a> to compile "Hello World" to
327LLVM. We can now run the bytecode file (<tt>hello.bc</tt>) for the program
328through our transformation like this (or course, any bytecode file will
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]329work):</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]330
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]331<div class="doc_code"><pre>
Reid Spencer7fa6d522005-01-11 05:16:23 +0000[diff] [blame]332$ opt -load ../../../Debug/lib/Hello.so -hello &lt; hello.bc &gt; /dev/null
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]333Hello: __main
334Hello: puts
335Hello: main
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]336</pre></div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]337
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]338<p>The '<tt>-load</tt>' option specifies that '<tt>opt</tt>' should load your
339pass as a shared object, which makes '<tt>-hello</tt>' a valid command line
340argument (which is one reason you need to <a href="#registration">register your
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]341pass</a>). Because the hello pass does not modify the program in any
342interesting way, we just throw away the result of <tt>opt</tt> (sending it to
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]343<tt>/dev/null</tt>).</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]344
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]345<p>To see what happened to the other string you registered, try running
346<tt>opt</tt> with the <tt>--help</tt> option:</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]347
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]348<div class="doc_code"><pre>
Reid Spencer7fa6d522005-01-11 05:16:23 +0000[diff] [blame]349$ opt -load ../../../Debug/lib/Hello.so --help
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]350OVERVIEW: llvm .bc -&gt; .bc modular optimizer
351
352USAGE: opt [options] &lt;input bytecode&gt;
353
354OPTIONS:
355 Optimizations available:
356...
357 -funcresolve - Resolve Functions
358 -gcse - Global Common Subexpression Elimination
359 -globaldce - Dead Global Elimination
360 <b>-hello - Hello World Pass</b>
Chris Lattner065a6162003-09-10 05:29:43 +0000[diff] [blame]361 -indvars - Canonicalize Induction Variables
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]362 -inline - Function Integration/Inlining
363 -instcombine - Combine redundant instructions
364...
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]365</pre></div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]366
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]367<p>The pass name get added as the information string for your pass, giving some
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]368documentation to users of <tt>opt</tt>. Now that you have a working pass, you
369would go ahead and make it do the cool transformations you want. Once you get
370it all working and tested, it may become useful to find out how fast your pass
371is. The <a href="#passManager"><tt>PassManager</tt></a> provides a nice command
372line option (<tt>--time-passes</tt>) that allows you to get information about
373the execution time of your pass along with the other passes you queue up. For
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]374example:</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]375
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]376<div class="doc_code"><pre>
Reid Spencer7fa6d522005-01-11 05:16:23 +0000[diff] [blame]377$ opt -load ../../../Debug/lib/Hello.so -hello -time-passes &lt; hello.bc &gt; /dev/null
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]378Hello: __main
379Hello: puts
380Hello: main
381===============================================================================
382 ... Pass execution timing report ...
383===============================================================================
384 Total Execution Time: 0.02 seconds (0.0479059 wall clock)
385
386 ---User Time--- --System Time-- --User+System-- ---Wall Time--- --- Pass Name ---
387 0.0100 (100.0%) 0.0000 ( 0.0%) 0.0100 ( 50.0%) 0.0402 ( 84.0%) Bytecode Writer
388 0.0000 ( 0.0%) 0.0100 (100.0%) 0.0100 ( 50.0%) 0.0031 ( 6.4%) Dominator Set Construction
389 0.0000 ( 0.0%) 0.0000 ( 0.0%) 0.0000 ( 0.0%) 0.0013 ( 2.7%) Module Verifier
390 <b> 0.0000 ( 0.0%) 0.0000 ( 0.0%) 0.0000 ( 0.0%) 0.0033 ( 6.9%) Hello World Pass</b>
391 0.0100 (100.0%) 0.0100 (100.0%) 0.0200 (100.0%) 0.0479 (100.0%) TOTAL
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]392</pre></div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]393
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]394<p>As you can see, our implementation above is pretty fast :). The additional
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]395passes listed are automatically inserted by the '<tt>opt</tt>' tool to verify
396that the LLVM emitted by your pass is still valid and well formed LLVM, which
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]397hasn't been broken somehow.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]398
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]399<p>Now that you have seen the basics of the mechanics behind passes, we can talk
400about some more details of how they work and how to use them.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]401
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]402</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]403
404<!-- *********************************************************************** -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]405<div class="doc_section">
406 <a name="passtype">Pass classes and requirements</a>
407</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]408<!-- *********************************************************************** -->
409
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]410<div class="doc_text">
411
412<p>One of the first things that you should do when designing a new pass is to
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]413decide what class you should subclass for your pass. The <a
414href="#basiccode">Hello World</a> example uses the <tt><a
415href="#FunctionPass">FunctionPass</a></tt> class for its implementation, but we
416did not discuss why or when this should occur. Here we talk about the classes
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]417available, from the most general to the most specific.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]418
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]419<p>When choosing a superclass for your Pass, you should choose the <b>most
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]420specific</b> class possible, while still being able to meet the requirements
Misha Brukman5560c9d2003-08-18 14:43:39 +0000[diff] [blame]421listed. This gives the LLVM Pass Infrastructure information necessary to
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]422optimize how passes are run, so that the resultant compiler isn't unneccesarily
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]423slow.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]424
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]425</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]426
Chris Lattnerf004f9a2002-09-25 22:31:38 +0000[diff] [blame]427<!-- ======================================================================= -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]428<div class="doc_subsection">
429 <a name="ImmutablePass">The <tt>ImmutablePass</tt> class</a>
430</div>
Chris Lattnerf004f9a2002-09-25 22:31:38 +0000[diff] [blame]431
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]432<div class="doc_text">
433
434<p>The most plain and boring type of pass is the "<tt><a
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]435href="http://llvm.org/doxygen/classllvm_1_1ImmutablePass.html">ImmutablePass</a></tt>"
Chris Lattnerf004f9a2002-09-25 22:31:38 +0000[diff] [blame]436class. This pass type is used for passes that do not have to be run, do not
437change state, and never need to be updated. This is not a normal type of
438transformation or analysis, but can provide information about the current
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]439compiler configuration.</p>
Chris Lattnerf004f9a2002-09-25 22:31:38 +0000[diff] [blame]440
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]441<p>Although this pass class is very infrequently used, it is important for
Chris Lattnerf004f9a2002-09-25 22:31:38 +0000[diff] [blame]442providing information about the current target machine being compiled for, and
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]443other static information that can affect the various transformations.</p>
Chris Lattnerf004f9a2002-09-25 22:31:38 +0000[diff] [blame]444
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]445<p><tt>ImmutablePass</tt>es never invalidate other transformations, are never
446invalidated, and are never "run".</p>
Chris Lattnerf004f9a2002-09-25 22:31:38 +0000[diff] [blame]447
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]448</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]449
450<!-- ======================================================================= -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]451<div class="doc_subsection">
Chris Lattnerf6278922004-09-20 04:36:29 +0000[diff] [blame]452 <a name="ModulePass">The <tt>ModulePass</tt> class</a>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]453</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]454
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]455<div class="doc_text">
456
457<p>The "<tt><a
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]458href="http://llvm.org/doxygen/classllvm_1_1ModulePass.html">ModulePass</a></tt>"
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]459class is the most general of all superclasses that you can use. Deriving from
Chris Lattnerf6278922004-09-20 04:36:29 +0000[diff] [blame]460<tt>ModulePass</tt> indicates that your pass uses the entire program as a unit,
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]461refering to function bodies in no predictable order, or adding and removing
Chris Lattnerf6278922004-09-20 04:36:29 +0000[diff] [blame]462functions. Because nothing is known about the behavior of <tt>ModulePass</tt>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]463subclasses, no optimization can be done for their execution.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]464
Chris Lattnerf6278922004-09-20 04:36:29 +0000[diff] [blame]465<p>To write a correct <tt>ModulePass</tt> subclass, derive from
466<tt>ModulePass</tt> and overload the <tt>runOnModule</tt> method with the
467following signature:</p>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]468
469</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]470
471<!-- _______________________________________________________________________ -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]472<div class="doc_subsubsection">
Chris Lattnerf6278922004-09-20 04:36:29 +0000[diff] [blame]473 <a name="runOnModule">The <tt>runOnModule</tt> method</a>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]474</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]475
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]476<div class="doc_text">
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]477
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]478<div class="doc_code"><pre>
Chris Lattnerf6278922004-09-20 04:36:29 +0000[diff] [blame]479 <b>virtual bool</b> runOnModule(Module &amp;M) = 0;
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]480</pre></div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]481
John Criswell2382ff72005-07-15 19:25:12 +0000[diff] [blame]482<p>The <tt>runOnModule</tt> method performs the interesting work of the pass.
483It should return true if the module was modified by the transformation and
484false otherwise.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]485
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]486</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]487
488<!-- ======================================================================= -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]489<div class="doc_subsection">
Chris Lattner8fdb2462004-09-18 06:39:35 +0000[diff] [blame]490 <a name="CallGraphSCCPass">The <tt>CallGraphSCCPass</tt> class</a>
491</div>
492
493<div class="doc_text">
494
495<p>The "<tt><a
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]496href="http://llvm.org/doxygen/classllvm_1_1CallGraphSCCPass.html">CallGraphSCCPass</a></tt>"
Chris Lattner8fdb2462004-09-18 06:39:35 +0000[diff] [blame]497is used by passes that need to traverse the program bottom-up on the call graph
498(callees before callers). Deriving from CallGraphSCCPass provides some
499mechanics for building and traversing the CallGraph, but also allows the system
500to optimize execution of CallGraphSCCPass's. If your pass meets the
501requirements outlined below, and doesn't meet the requirements of a <tt><a
502href="#FunctionPass">FunctionPass</a></tt> or <tt><a
503href="#BasicBlockPass">BasicBlockPass</a></tt>, you should derive from
504<tt>CallGraphSCCPass</tt>.</p>
505
506<p><b>TODO</b>: explain briefly what SCC, Tarjan's algo, and B-U mean.</p>
507
508<p>To be explicit, <tt>CallGraphSCCPass</tt> subclasses are:</p>
509
510<ol>
511
512<li>... <em>not allowed</em> to modify any <tt>Function</tt>s that are not in
513the current SCC.</li>
514
515<li>... <em>allowed</em> to inspect any Function's other than those in the
516current SCC and the direct callees of the SCC.</li>
517
518<li>... <em>required</em> to preserve the current CallGraph object, updating it
519to reflect any changes made to the program.</li>
520
521<li>... <em>not allowed</em> to add or remove SCC's from the current Module,
522though they may change the contents of an SCC.</li>
523
524<li>... <em>allowed</em> to add or remove global variables from the current
525Module.</li>
526
527<li>... <em>allowed</em> to maintain state across invocations of
528 <a href="#runOnSCC"><tt>runOnSCC</tt></a> (including global data).</li>
529</ol>
530
531<p>Implementing a <tt>CallGraphSCCPass</tt> is slightly tricky in some cases
532because it has to handle SCCs with more than one node in it. All of the virtual
533methods described below should return true if they modified the program, or
534false if they didn't.</p>
535
536</div>
537
538<!-- _______________________________________________________________________ -->
539<div class="doc_subsubsection">
540 <a name="doInitialization_scc">The <tt>doInitialization(Module &amp;)</tt>
541 method</a>
542</div>
543
544<div class="doc_text">
545
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]546<div class="doc_code"><pre>
Chris Lattner8fdb2462004-09-18 06:39:35 +0000[diff] [blame]547 <b>virtual bool</b> doInitialization(Module &amp;M);
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]548</pre></div>
Chris Lattner8fdb2462004-09-18 06:39:35 +0000[diff] [blame]549
550<p>The <tt>doIninitialize</tt> method is allowed to do most of the things that
551<tt>CallGraphSCCPass</tt>'s are not allowed to do. They can add and remove
552functions, get pointers to functions, etc. The <tt>doInitialization</tt> method
553is designed to do simple initialization type of stuff that does not depend on
554the SCCs being processed. The <tt>doInitialization</tt> method call is not
555scheduled to overlap with any other pass executions (thus it should be very
556fast).</p>
557
558</div>
559
560<!-- _______________________________________________________________________ -->
561<div class="doc_subsubsection">
562 <a name="runOnSCC">The <tt>runOnSCC</tt> method</a>
563</div>
564
565<div class="doc_text">
566
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]567<div class="doc_code"><pre>
Chris Lattner8fdb2462004-09-18 06:39:35 +0000[diff] [blame]568 <b>virtual bool</b> runOnSCC(const std::vector&lt;CallGraphNode *&gt; &amp;SCCM) = 0;
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]569</pre></div>
Chris Lattner8fdb2462004-09-18 06:39:35 +0000[diff] [blame]570
571<p>The <tt>runOnSCC</tt> method performs the interesting work of the pass, and
572should return true if the module was modified by the transformation, false
573otherwise.</p>
574
575</div>
576
577<!-- _______________________________________________________________________ -->
578<div class="doc_subsubsection">
579 <a name="doFinalization_scc">The <tt>doFinalization(Module
580 &amp;)</tt> method</a>
581</div>
582
583<div class="doc_text">
584
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]585<div class="doc_code"><pre>
Chris Lattner8fdb2462004-09-18 06:39:35 +0000[diff] [blame]586 <b>virtual bool</b> doFinalization(Module &amp;M);
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]587</pre></div>
Chris Lattner8fdb2462004-09-18 06:39:35 +0000[diff] [blame]588
589<p>The <tt>doFinalization</tt> method is an infrequently used method that is
590called when the pass framework has finished calling <a
591href="#runOnFunction"><tt>runOnFunction</tt></a> for every function in the
592program being compiled.</p>
593
594</div>
595
596<!-- ======================================================================= -->
597<div class="doc_subsection">
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]598 <a name="FunctionPass">The <tt>FunctionPass</tt> class</a>
599</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]600
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]601<div class="doc_text">
602
Chris Lattnerf6278922004-09-20 04:36:29 +0000[diff] [blame]603<p>In contrast to <tt>ModulePass</tt> subclasses, <tt><a
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]604href="http://llvm.org/doxygen/classllvm_1_1Pass.html">FunctionPass</a></tt>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]605subclasses do have a predictable, local behavior that can be expected by the
606system. All <tt>FunctionPass</tt> execute on each function in the program
Misha Brukmanef6a6a62003-08-21 22:14:26 +0000[diff] [blame]607independent of all of the other functions in the program.
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]608<tt>FunctionPass</tt>'s do not require that they are executed in a particular
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]609order, and <tt>FunctionPass</tt>'s do not modify external functions.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]610
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]611<p>To be explicit, <tt>FunctionPass</tt> subclasses are not allowed to:</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]612
613<ol>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]614<li>Modify a Function other than the one currently being processed.</li>
615<li>Add or remove Function's from the current Module.</li>
616<li>Add or remove global variables from the current Module.</li>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]617<li>Maintain state across invocations of
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]618 <a href="#runOnFunction"><tt>runOnFunction</tt></a> (including global data)</li>
619</ol>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]620
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]621<p>Implementing a <tt>FunctionPass</tt> is usually straightforward (See the <a
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]622href="#basiccode">Hello World</a> pass for example). <tt>FunctionPass</tt>'s
623may overload three virtual methods to do their work. All of these methods
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]624should return true if they modified the program, or false if they didn't.</p>
625
626</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]627
628<!-- _______________________________________________________________________ -->
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]629<div class="doc_subsubsection">
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]630 <a name="doInitialization_mod">The <tt>doInitialization(Module &amp;)</tt>
631 method</a>
632</div>
633
634<div class="doc_text">
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]635
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]636<div class="doc_code"><pre>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]637 <b>virtual bool</b> doInitialization(Module &amp;M);
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]638</pre></div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]639
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]640<p>The <tt>doIninitialize</tt> method is allowed to do most of the things that
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]641<tt>FunctionPass</tt>'s are not allowed to do. They can add and remove
Chris Lattnerd0713f92002-09-12 17:06:43 +0000[diff] [blame]642functions, get pointers to functions, etc. The <tt>doInitialization</tt> method
643is designed to do simple initialization type of stuff that does not depend on
644the functions being processed. The <tt>doInitialization</tt> method call is not
645scheduled to overlap with any other pass executions (thus it should be very
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]646fast).</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]647
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]648<p>A good example of how this method should be used is the <a
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]649href="http://llvm.org/doxygen/LowerAllocations_8cpp-source.html">LowerAllocations</a>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]650pass. This pass converts <tt>malloc</tt> and <tt>free</tt> instructions into
Misha Brukmanef6a6a62003-08-21 22:14:26 +0000[diff] [blame]651platform dependent <tt>malloc()</tt> and <tt>free()</tt> function calls. It
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]652uses the <tt>doInitialization</tt> method to get a reference to the malloc and
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]653free functions that it needs, adding prototypes to the module if necessary.</p>
654
655</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]656
657<!-- _______________________________________________________________________ -->
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]658<div class="doc_subsubsection">
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]659 <a name="runOnFunction">The <tt>runOnFunction</tt> method</a>
660</div>
661
662<div class="doc_text">
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]663
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]664<div class="doc_code"><pre>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]665 <b>virtual bool</b> runOnFunction(Function &amp;F) = 0;
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]666</pre></div><p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]667
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]668<p>The <tt>runOnFunction</tt> method must be implemented by your subclass to do
669the transformation or analysis work of your pass. As usual, a true value should
670be returned if the function is modified.</p>
671
672</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]673
674<!-- _______________________________________________________________________ -->
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]675<div class="doc_subsubsection">
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]676 <a name="doFinalization_mod">The <tt>doFinalization(Module
677 &amp;)</tt> method</a>
678</div>
679
680<div class="doc_text">
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]681
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]682<div class="doc_code"><pre>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]683 <b>virtual bool</b> doFinalization(Module &amp;M);
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]684</pre></div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]685
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]686<p>The <tt>doFinalization</tt> method is an infrequently used method that is
687called when the pass framework has finished calling <a
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]688href="#runOnFunction"><tt>runOnFunction</tt></a> for every function in the
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]689program being compiled.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]690
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]691</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]692
693<!-- ======================================================================= -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]694<div class="doc_subsection">
695 <a name="BasicBlockPass">The <tt>BasicBlockPass</tt> class</a>
696</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]697
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]698<div class="doc_text">
699
700<p><tt>BasicBlockPass</tt>'s are just like <a
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]701href="#FunctionPass"><tt>FunctionPass</tt></a>'s, except that they must limit
702their scope of inspection and modification to a single basic block at a time.
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]703As such, they are <b>not</b> allowed to do any of the following:</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]704
705<ol>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]706<li>Modify or inspect any basic blocks outside of the current one</li>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]707<li>Maintain state across invocations of
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]708 <a href="#runOnBasicBlock"><tt>runOnBasicBlock</tt></a></li>
Reid Spencer1bc19342004-12-11 05:12:57 +0000[diff] [blame]709<li>Modify the control flow graph (by altering terminator instructions)</li>
710<li>Any of the things forbidden for
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]711 <a href="#FunctionPass"><tt>FunctionPass</tt></a>es.</li>
712</ol>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]713
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]714<p><tt>BasicBlockPass</tt>es are useful for traditional local and "peephole"
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]715optimizations. They may override the same <a
Chris Lattnerd0713f92002-09-12 17:06:43 +0000[diff] [blame]716href="#doInitialization_mod"><tt>doInitialization(Module &amp;)</tt></a> and <a
717href="#doFinalization_mod"><tt>doFinalization(Module &amp;)</tt></a> methods that <a
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]718href="#FunctionPass"><tt>FunctionPass</tt></a>'s have, but also have the following virtual methods that may also be implemented:</p>
719
720</div>
Chris Lattnerd0713f92002-09-12 17:06:43 +0000[diff] [blame]721
722<!-- _______________________________________________________________________ -->
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]723<div class="doc_subsubsection">
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]724 <a name="doInitialization_fn">The <tt>doInitialization(Function
725 &amp;)</tt> method</a>
726</div>
727
728<div class="doc_text">
Chris Lattnerd0713f92002-09-12 17:06:43 +0000[diff] [blame]729
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]730<div class="doc_code"><pre>
Chris Lattnerd0713f92002-09-12 17:06:43 +0000[diff] [blame]731 <b>virtual bool</b> doInitialization(Function &amp;F);
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]732</pre></div>
Chris Lattnerd0713f92002-09-12 17:06:43 +0000[diff] [blame]733
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]734<p>The <tt>doIninitialize</tt> method is allowed to do most of the things that
Chris Lattnerd0713f92002-09-12 17:06:43 +0000[diff] [blame]735<tt>BasicBlockPass</tt>'s are not allowed to do, but that
736<tt>FunctionPass</tt>'s can. The <tt>doInitialization</tt> method is designed
Reid Spencer1bc19342004-12-11 05:12:57 +0000[diff] [blame]737to do simple initialization that does not depend on the
Chris Lattnerd0713f92002-09-12 17:06:43 +0000[diff] [blame]738BasicBlocks being processed. The <tt>doInitialization</tt> method call is not
739scheduled to overlap with any other pass executions (thus it should be very
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]740fast).</p>
Chris Lattnerd0713f92002-09-12 17:06:43 +0000[diff] [blame]741
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]742</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]743
744<!-- _______________________________________________________________________ -->
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]745<div class="doc_subsubsection">
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]746 <a name="runOnBasicBlock">The <tt>runOnBasicBlock</tt> method</a>
747</div>
748
749<div class="doc_text">
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]750
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]751<div class="doc_code"><pre>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]752 <b>virtual bool</b> runOnBasicBlock(BasicBlock &amp;BB) = 0;
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]753</pre></div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]754
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]755<p>Override this function to do the work of the <tt>BasicBlockPass</tt>. This
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]756function is not allowed to inspect or modify basic blocks other than the
757parameter, and are not allowed to modify the CFG. A true value must be returned
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]758if the basic block is modified.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]759
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]760</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]761
Chris Lattnerd0713f92002-09-12 17:06:43 +0000[diff] [blame]762<!-- _______________________________________________________________________ -->
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]763<div class="doc_subsubsection">
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]764 <a name="doFinalization_fn">The <tt>doFinalization(Function &amp;)</tt>
765 method</a>
766</div>
767
768<div class="doc_text">
Chris Lattnerd0713f92002-09-12 17:06:43 +0000[diff] [blame]769
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]770<div class="doc_code"><pre>
Chris Lattnerd0713f92002-09-12 17:06:43 +0000[diff] [blame]771 <b>virtual bool</b> doFinalization(Function &amp;F);
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]772</pre></div>
Chris Lattnerd0713f92002-09-12 17:06:43 +0000[diff] [blame]773
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]774<p>The <tt>doFinalization</tt> method is an infrequently used method that is
775called when the pass framework has finished calling <a
Chris Lattnerd0713f92002-09-12 17:06:43 +0000[diff] [blame]776href="#runOnBasicBlock"><tt>runOnBasicBlock</tt></a> for every BasicBlock in the
777program being compiled. This can be used to perform per-function
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]778finalization.</p>
Chris Lattnerd0713f92002-09-12 17:06:43 +0000[diff] [blame]779
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]780</div>
Chris Lattnerd0713f92002-09-12 17:06:43 +0000[diff] [blame]781
Brian Gaekecab8b6f2003-07-17 18:53:20 +0000[diff] [blame]782<!-- ======================================================================= -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]783<div class="doc_subsection">
784 <a name="MachineFunctionPass">The <tt>MachineFunctionPass</tt> class</a>
785</div>
Brian Gaekecab8b6f2003-07-17 18:53:20 +0000[diff] [blame]786
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]787<div class="doc_text">
788
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]789<p>A <tt>MachineFunctionPass</tt> is a part of the LLVM code generator that
790executes on the machine-dependent representation of each LLVM function in the
791program. A <tt>MachineFunctionPass</tt> is also a <tt>FunctionPass</tt>, so all
Brian Gaekecab8b6f2003-07-17 18:53:20 +0000[diff] [blame]792the restrictions that apply to a <tt>FunctionPass</tt> also apply to it.
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]793<tt>MachineFunctionPass</tt>es also have additional restrictions. In particular,
794<tt>MachineFunctionPass</tt>es are not allowed to do any of the following:</p>
Brian Gaekecab8b6f2003-07-17 18:53:20 +0000[diff] [blame]795
796<ol>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]797<li>Modify any LLVM Instructions, BasicBlocks or Functions.</li>
798<li>Modify a MachineFunction other than the one currently being processed.</li>
799<li>Add or remove MachineFunctions from the current Module.</li>
800<li>Add or remove global variables from the current Module.</li>
801<li>Maintain state across invocations of <a
802href="#runOnMachineFunction"><tt>runOnMachineFunction</tt></a> (including global
803data)</li>
804</ol>
Brian Gaekecab8b6f2003-07-17 18:53:20 +0000[diff] [blame]805
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]806</div>
Chris Lattnerd0713f92002-09-12 17:06:43 +0000[diff] [blame]807
Brian Gaeke6a33f362003-07-22 20:53:20 +0000[diff] [blame]808<!-- _______________________________________________________________________ -->
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]809<div class="doc_subsubsection">
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]810 <a name="runOnMachineFunction">The <tt>runOnMachineFunction(MachineFunction
811 &amp;MF)</tt> method</a>
812</div>
813
814<div class="doc_text">
Brian Gaeke6a33f362003-07-22 20:53:20 +0000[diff] [blame]815
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]816<div class="doc_code"><pre>
Brian Gaeke6a33f362003-07-22 20:53:20 +0000[diff] [blame]817 <b>virtual bool</b> runOnMachineFunction(MachineFunction &amp;MF) = 0;
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]818</pre></div>
Brian Gaeke6a33f362003-07-22 20:53:20 +0000[diff] [blame]819
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]820<p><tt>runOnMachineFunction</tt> can be considered the main entry point of a
821<tt>MachineFunctionPass</tt>; that is, you should override this method to do the
822work of your <tt>MachineFunctionPass</tt>.</p>
Brian Gaeke6a33f362003-07-22 20:53:20 +0000[diff] [blame]823
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]824<p>The <tt>runOnMachineFunction</tt> method is called on every
Brian Gaeke6a33f362003-07-22 20:53:20 +0000[diff] [blame]825<tt>MachineFunction</tt> in a <tt>Module</tt>, so that the
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]826<tt>MachineFunctionPass</tt> may perform optimizations on the machine-dependent
827representation of the function. If you want to get at the LLVM <tt>Function</tt>
828for the <tt>MachineFunction</tt> you're working on, use
829<tt>MachineFunction</tt>'s <tt>getFunction()</tt> accessor method -- but
830remember, you may not modify the LLVM <tt>Function</tt> or its contents from a
831<tt>MachineFunctionPass</tt>.</p>
832
833</div>
Brian Gaeke6a33f362003-07-22 20:53:20 +0000[diff] [blame]834
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]835<!-- *********************************************************************** -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]836<div class="doc_section">
837 <a name="registration">Pass registration</a>
838</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]839<!-- *********************************************************************** -->
840
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]841<div class="doc_text">
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]842
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]843<p>In the <a href="#basiccode">Hello World</a> example pass we illustrated how
844pass registration works, and discussed some of the reasons that it is used and
845what it does. Here we discuss how and why passes are registered.</p>
846
847<p>Passes can be registered in several different ways. Depending on the general
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]848classification of the pass, you should use one of the following templates to
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]849register the pass:</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]850
851<ul>
852<li><b><tt>RegisterOpt</tt></b> - This template should be used when you are
853registering a pass that logically should be available for use in the
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]854'<tt>opt</tt>' utility.</li>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]855
856<li><b><tt>RegisterAnalysis</tt></b> - This template should be used when you are
857registering a pass that logically should be available for use in the
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]858'<tt>analyze</tt>' utility.</li>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]859
860<li><b><tt>RegisterPass</tt></b> - This is the generic form of the
861<tt>Register*</tt> templates that should be used if you want your pass listed by
862multiple or no utilities. This template takes an extra third argument that
863specifies which tools it should be listed in. See the <a
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]864href="http://llvm.org/doxygen/PassSupport_8h-source.html">PassSupport.h</a>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]865file for more information.</li>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]866
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]867</ul>
868
869<p>Regardless of how you register your pass, you must specify at least two
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]870parameters. The first parameter is the name of the pass that is to be used on
871the command line to specify that the pass should be added to a program (for
872example <tt>opt</tt> or <tt>analyze</tt>). The second argument is the name of
873the pass, which is to be used for the <tt>--help</tt> output of programs, as
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]874well as for debug output generated by the <tt>--debug-pass</tt> option.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]875
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]876<p>If a pass is registered to be used by the <tt>analyze</tt> utility, you
877should implement the virtual <tt>print</tt> method:</p>
878
879</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]880
881<!-- _______________________________________________________________________ -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]882<div class="doc_subsubsection">
883 <a name="print">The <tt>print</tt> method</a>
884</div>
885
886<div class="doc_text">
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]887
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]888<div class="doc_code"><pre>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]889 <b>virtual void</b> print(std::ostream &amp;O, <b>const</b> Module *M) <b>const</b>;
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]890</pre></div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]891
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]892<p>The <tt>print</tt> method must be implemented by "analyses" in order to print
893a human readable version of the analysis results. This is useful for debugging
894an analysis itself, as well as for other people to figure out how an analysis
895works. The <tt>analyze</tt> tool uses this method to generate its output.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]896
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]897<p>The <tt>ostream</tt> parameter specifies the stream to write the results on,
898and the <tt>Module</tt> parameter gives a pointer to the top level module of the
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]899program that has been analyzed. Note however that this pointer may be null in
900certain circumstances (such as calling the <tt>Pass::dump()</tt> from a
901debugger), so it should only be used to enhance debug output, it should not be
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]902depended on.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]903
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]904</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]905
906<!-- *********************************************************************** -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]907<div class="doc_section">
908 <a name="interaction">Specifying interactions between passes</a>
909</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]910<!-- *********************************************************************** -->
911
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]912<div class="doc_text">
913
914<p>One of the main responsibilities of the <tt>PassManager</tt> is the make sure
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]915that passes interact with each other correctly. Because <tt>PassManager</tt>
916tries to <a href="#passmanager">optimize the execution of passes</a> it must
917know how the passes interact with each other and what dependencies exist between
918the various passes. To track this, each pass can declare the set of passes that
919are required to be executed before the current pass, and the passes which are
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]920invalidated by the current pass.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]921
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]922<p>Typically this functionality is used to require that analysis results are
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]923computed before your pass is run. Running arbitrary transformation passes can
924invalidate the computed analysis results, which is what the invalidation set
925specifies. If a pass does not implement the <tt><a
926href="#getAnalysisUsage">getAnalysisUsage</a></tt> method, it defaults to not
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]927having any prerequisite passes, and invalidating <b>all</b> other passes.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]928
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]929</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]930
931<!-- _______________________________________________________________________ -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]932<div class="doc_subsubsection">
933 <a name="getAnalysisUsage">The <tt>getAnalysisUsage</tt> method</a>
934</div>
935
936<div class="doc_text">
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]937
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]938<div class="doc_code"><pre>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]939 <b>virtual void</b> getAnalysisUsage(AnalysisUsage &amp;Info) <b>const</b>;
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]940</pre></div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]941
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]942<p>By implementing the <tt>getAnalysisUsage</tt> method, the required and
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]943invalidated sets may be specified for your transformation. The implementation
944should fill in the <tt><a
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]945href="http://llvm.org/doxygen/classllvm_1_1AnalysisUsage.html">AnalysisUsage</a></tt>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]946object with information about which passes are required and not invalidated. To
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]947do this, a pass may call any of the following methods on the AnalysisUsage
948object:</p>
949</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]950
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]951<!-- _______________________________________________________________________ -->
952<div class="doc_subsubsection">
953 <a name="AU::addRequired">The <tt>AnalysisUsage::addRequired&lt;&gt;</tt> and <tt>AnalysisUsage::addRequiredTransitive&lt;&gt;</tt> methods</a>
954</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]955
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]956<div class="doc_text">
957<p>
Reid Spencer1bc19342004-12-11 05:12:57 +0000[diff] [blame]958If your pass requires a previous pass to be executed (an analysis for example),
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]959it can use one of these methods to arrange for it to be run before your pass.
960LLVM has many different types of analyses and passes that can be required,
Reid Spencer1bc19342004-12-11 05:12:57 +0000[diff] [blame]961spanning the range from <tt>DominatorSet</tt> to <tt>BreakCriticalEdges</tt>.
962Requiring <tt>BreakCriticalEdges</tt>, for example, guarantees that there will
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]963be no critical edges in the CFG when your pass has been run.
964</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]965
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]966<p>
967Some analyses chain to other analyses to do their job. For example, an <a
968href="AliasAnalysis.html">AliasAnalysis</a> implementation is required to <a
969href="AliasAnalysis.html#chaining">chain</a> to other alias analysis passes. In
970cases where analyses chain, the <tt>addRequiredTransitive</tt> method should be
971used instead of the <tt>addRequired</tt> method. This informs the PassManager
972that the transitively required pass should be alive as long as the requiring
973pass is.
974</p>
975</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]976
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]977<!-- _______________________________________________________________________ -->
978<div class="doc_subsubsection">
979 <a name="AU::addPreserved">The <tt>AnalysisUsage::addPreserved&lt;&gt;</tt> method</a>
980</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]981
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]982<div class="doc_text">
983<p>
984One of the jobs of the PassManager is to optimize how and when analyses are run.
985In particular, it attempts to avoid recomputing data unless it needs to. For
986this reason, passes are allowed to declare that they preserve (i.e., they don't
987invalidate) an existing analysis if it's available. For example, a simple
Reid Spencer1bc19342004-12-11 05:12:57 +0000[diff] [blame]988constant folding pass would not modify the CFG, so it can't possibly affect the
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]989results of dominator analysis. By default, all passes are assumed to invalidate
990all others.
991</p>
992
993<p>
994The <tt>AnalysisUsage</tt> class provides several methods which are useful in
995certain circumstances that are related to <tt>addPreserved</tt>. In particular,
996the <tt>setPreservesAll</tt> method can be called to indicate that the pass does
997not modify the LLVM program at all (which is true for analyses), and the
998<tt>setPreservesCFG</tt> method can be used by transformations that change
999instructions in the program but do not modify the CFG or terminator instructions
1000(note that this property is implicitly set for <a
1001href="#BasicBlockPass">BasicBlockPass</a>'s).
1002</p>
1003
1004<p>
1005<tt>addPreserved</tt> is particularly useful for transformations like
1006<tt>BreakCriticalEdges</tt>. This pass knows how to update a small set of loop
1007and dominator related analyses if they exist, so it can preserve them, despite
1008the fact that it hacks on the CFG.
1009</p>
1010</div>
1011
1012<!-- _______________________________________________________________________ -->
1013<div class="doc_subsubsection">
1014 <a name="AU::examples">Example implementations of <tt>getAnalysisUsage</tt></a>
1015</div>
1016
1017<div class="doc_text">
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1018
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1019<div class="doc_code"><pre>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1020 <i>// This is an example implementation from an analysis, which does not modify
1021 // the program at all, yet has a prerequisite.</i>
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]1022 <b>void</b> <a href="http://llvm.org/doxygen/classllvm_1_1PostDominanceFrontier.html">PostDominanceFrontier</a>::getAnalysisUsage(AnalysisUsage &amp;AU) <b>const</b> {
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1023 AU.setPreservesAll();
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]1024 AU.addRequired&lt;<a href="http://llvm.org/doxygen/classllvm_1_1PostDominatorTree.html">PostDominatorTree</a>&gt;();
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1025 }
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1026</pre></div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1027
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1028<p>and:</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1029
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1030<div class="doc_code"><pre>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1031 <i>// This example modifies the program, but does not modify the CFG</i>
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]1032 <b>void</b> <a href="http://llvm.org/doxygen/structLICM.html">LICM</a>::getAnalysisUsage(AnalysisUsage &amp;AU) <b>const</b> {
Chris Lattner8291e042002-10-21 19:57:59 +0000[diff] [blame]1033 AU.setPreservesCFG();
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]1034 AU.addRequired&lt;<a href="http://llvm.org/doxygen/classllvm_1_1LoopInfo.html">LoopInfo</a>&gt;();
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1035 }
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1036</pre></div>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1037
1038</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1039
1040<!-- _______________________________________________________________________ -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1041<div class="doc_subsubsection">
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]1042 <a name="getAnalysis">The <tt>getAnalysis&lt;&gt;</tt> and <tt>getAnalysisToUpdate&lt;&gt;</tt> methods</a>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1043</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1044
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1045<div class="doc_text">
1046
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]1047<p>The <tt>Pass::getAnalysis&lt;&gt;</tt> method is automatically inherited by
1048your class, providing you with access to the passes that you declared that you
1049required with the <a href="#getAnalysisUsage"><tt>getAnalysisUsage</tt></a>
1050method. It takes a single template argument that specifies which pass class you
1051want, and returns a reference to that pass. For example:</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1052
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1053<div class="doc_code"><pre>
Chris Lattnera5776302004-03-17 21:33:32 +0000[diff] [blame]1054 bool LICM::runOnFunction(Function &amp;F) {
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]1055 LoopInfo &amp;LI = getAnalysis&lt;LoopInfo&gt;();
1056 ...
1057 }
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1058</pre></div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1059
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1060<p>This method call returns a reference to the pass desired. You may get a
1061runtime assertion failure if you attempt to get an analysis that you did not
1062declare as required in your <a
1063href="#getAnalysisUsage"><tt>getAnalysisUsage</tt></a> implementation. This
1064method can be called by your <tt>run*</tt> method implementation, or by any
1065other local method invoked by your <tt>run*</tt> method.</p>
1066
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]1067<p>
1068If your pass is capable of updating analyses if they exist (e.g.,
1069<tt>BreakCriticalEdges</tt>, as described above), you can use the
1070<tt>getAnalysisToUpdate</tt> method, which returns a pointer to the analysis if
1071it is active. For example:</p>
1072
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1073<div class="doc_code"><pre>
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]1074 ...
1075 if (DominatorSet *DS = getAnalysisToUpdate&lt;DominatorSet&gt;()) {
1076 <i>// A DominatorSet is active. This code will update it.</i>
1077 }
1078 ...
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1079</pre></div>
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]1080
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1081</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1082
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1083<!-- *********************************************************************** -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1084<div class="doc_section">
1085 <a name="analysisgroup">Implementing Analysis Groups</a>
1086</div>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1087<!-- *********************************************************************** -->
1088
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1089<div class="doc_text">
1090
1091<p>Now that we understand the basics of how passes are defined, how the are
1092used, and how they are required from other passes, it's time to get a little bit
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1093fancier. All of the pass relationships that we have seen so far are very
1094simple: one pass depends on one other specific pass to be run before it can run.
1095For many applications, this is great, for others, more flexibility is
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1096required.</p>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1097
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1098<p>In particular, some analyses are defined such that there is a single simple
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1099interface to the analysis results, but multiple ways of calculating them.
1100Consider alias analysis for example. The most trivial alias analysis returns
1101"may alias" for any alias query. The most sophisticated analysis a
1102flow-sensitive, context-sensitive interprocedural analysis that can take a
1103significant amount of time to execute (and obviously, there is a lot of room
1104between these two extremes for other implementations). To cleanly support
1105situations like this, the LLVM Pass Infrastructure supports the notion of
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1106Analysis Groups.</p>
1107
1108</div>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1109
1110<!-- _______________________________________________________________________ -->
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]1111<div class="doc_subsubsection">
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1112 <a name="agconcepts">Analysis Group Concepts</a>
1113</div>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1114
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1115<div class="doc_text">
1116
1117<p>An Analysis Group is a single simple interface that may be implemented by
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1118multiple different passes. Analysis Groups can be given human readable names
1119just like passes, but unlike passes, they need not derive from the <tt>Pass</tt>
1120class. An analysis group may have one or more implementations, one of which is
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1121the "default" implementation.</p>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1122
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1123<p>Analysis groups are used by client passes just like other passes are: the
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1124<tt>AnalysisUsage::addRequired()</tt> and <tt>Pass::getAnalysis()</tt> methods.
1125In order to resolve this requirement, the <a href="#passmanager">PassManager</a>
1126scans the available passes to see if any implementations of the analysis group
1127are available. If none is available, the default implementation is created for
1128the pass to use. All standard rules for <A href="#interaction">interaction
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1129between passes</a> still apply.</p>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1130
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1131<p>Although <a href="#registration">Pass Registration</a> is optional for normal
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1132passes, all analysis group implementations must be registered, and must use the
1133<A href="#registerag"><tt>RegisterAnalysisGroup</tt></a> template to join the
1134implementation pool. Also, a default implementation of the interface
1135<b>must</b> be registered with <A
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1136href="#registerag"><tt>RegisterAnalysisGroup</tt></a>.</p>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1137
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1138<p>As a concrete example of an Analysis Group in action, consider the <a
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]1139href="http://llvm.org/doxygen/classllvm_1_1AliasAnalysis.html">AliasAnalysis</a>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1140analysis group. The default implementation of the alias analysis interface (the
1141<tt><a
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]1142href="http://llvm.org/doxygen/structBasicAliasAnalysis.html">basicaa</a></tt>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1143pass) just does a few simple checks that don't require significant analysis to
1144compute (such as: two different globals can never alias each other, etc).
1145Passes that use the <tt><a
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]1146href="http://llvm.org/doxygen/classllvm_1_1AliasAnalysis.html">AliasAnalysis</a></tt>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1147interface (for example the <tt><a
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]1148href="http://llvm.org/doxygen/structGCSE.html">gcse</a></tt> pass), do
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1149not care which implementation of alias analysis is actually provided, they just
1150use the designated interface.</p>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1151
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1152<p>From the user's perspective, commands work just like normal. Issuing the
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1153command '<tt>opt -gcse ...</tt>' will cause the <tt>basicaa</tt> class to be
1154instantiated and added to the pass sequence. Issuing the command '<tt>opt
1155-somefancyaa -gcse ...</tt>' will cause the <tt>gcse</tt> pass to use the
1156<tt>somefancyaa</tt> alias analysis (which doesn't actually exist, it's just a
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1157hypothetical example) instead.</p>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1158
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1159</div>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1160
1161<!-- _______________________________________________________________________ -->
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]1162<div class="doc_subsubsection">
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1163 <a name="registerag">Using <tt>RegisterAnalysisGroup</tt></a>
1164</div>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1165
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1166<div class="doc_text">
1167
1168<p>The <tt>RegisterAnalysisGroup</tt> template is used to register the analysis
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1169group itself as well as add pass implementations to the analysis group. First,
1170an analysis should be registered, with a human readable name provided for it.
1171Unlike registration of passes, there is no command line argument to be specified
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1172for the Analysis Group Interface itself, because it is "abstract":</p>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1173
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1174<div class="doc_code"><pre>
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]1175 <b>static</b> RegisterAnalysisGroup&lt;<a href="http://llvm.org/doxygen/classllvm_1_1AliasAnalysis.html">AliasAnalysis</a>&gt; A("<i>Alias Analysis</i>");
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1176</pre></div>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1177
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1178<p>Once the analysis is registered, passes can declare that they are valid
1179implementations of the interface by using the following code:</p>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1180
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1181<div class="doc_code"><pre>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1182<b>namespace</b> {
1183 //<i> Analysis Group implementations <b>must</b> be registered normally...</i>
1184 RegisterOpt&lt;FancyAA&gt;
1185 B("<i>somefancyaa</i>", "<i>A more complex alias analysis implementation</i>");
1186
1187 //<i> Declare that we implement the AliasAnalysis interface</i>
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]1188 RegisterAnalysisGroup&lt;<a href="http://llvm.org/doxygen/classllvm_1_1AliasAnalysis.html">AliasAnalysis</a>, FancyAA&gt; C;
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1189}
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1190</pre></div>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1191
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1192<p>This just shows a class <tt>FancyAA</tt> that is registered normally, then
1193uses the <tt>RegisterAnalysisGroup</tt> template to "join" the <tt><a
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]1194href="http://llvm.org/doxygen/classllvm_1_1AliasAnalysis.html">AliasAnalysis</a></tt>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1195analysis group. Every implementation of an analysis group should join using
1196this template. A single pass may join multiple different analysis groups with
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1197no problem.</p>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1198
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1199<div class="doc_code"><pre>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1200<b>namespace</b> {
1201 //<i> Analysis Group implementations <b>must</b> be registered normally...</i>
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]1202 RegisterOpt&lt;<a href="http://llvm.org/doxygen/structBasicAliasAnalysis.html">BasicAliasAnalysis</a>&gt;
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1203 D("<i>basicaa</i>", "<i>Basic Alias Analysis (default AA impl)</i>");
1204
1205 //<i> Declare that we implement the AliasAnalysis interface</i>
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]1206 RegisterAnalysisGroup&lt;<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>&gt; E;
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1207}
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1208</pre></div>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1209
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1210<p>Here we show how the default implementation is specified (using the extra
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1211argument to the <tt>RegisterAnalysisGroup</tt> template). There must be exactly
1212one default implementation available at all times for an Analysis Group to be
1213used. Here we declare that the <tt><a
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]1214href="http://llvm.org/doxygen/structBasicAliasAnalysis.html">BasicAliasAnalysis</a></tt>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1215pass is the default implementation for the interface.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1216
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1217</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1218
1219<!-- *********************************************************************** -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1220<div class="doc_section">
Tanya Lattnerd5383652004-11-19 01:25:14 +0000[diff] [blame]1221 <a name="passStatistics">Pass Statistics</a>
1222</div>
1223<!-- *********************************************************************** -->
1224
1225<div class="doc_text">
Tanya Lattner05f8d5f2004-11-19 01:26:37 +0000[diff] [blame]1226<p>The <a
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]1227href="http://llvm.org/doxygen/Statistic_8h-source.html"><tt>Statistic</tt></a>
John Criswell0b1010e2005-11-28 23:25:41 +0000[diff] [blame]1228class is designed to be an easy way to expose various success
Tanya Lattnerd5383652004-11-19 01:25:14 +0000[diff] [blame]1229metrics from passes. These statistics are printed at the end of a
1230run, when the -stats command line option is enabled on the command
Tanya Lattner05f8d5f2004-11-19 01:26:37 +0000[diff] [blame]1231line. See the <a href="http://llvm.org/docs/ProgrammersManual.html#Statistic">Statistics section</a> in the Programmer's Manual for details.
Tanya Lattnerd5383652004-11-19 01:25:14 +0000[diff] [blame]1232
1233</div>
1234
1235
1236<!-- *********************************************************************** -->
1237<div class="doc_section">
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1238 <a name="passmanager">What PassManager does</a>
1239</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1240<!-- *********************************************************************** -->
1241
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1242<div class="doc_text">
1243
1244<p>The <a
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]1245href="http://llvm.org/doxygen/PassManager_8h-source.html"><tt>PassManager</tt></a>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1246<a
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]1247href="http://llvm.org/doxygen/classllvm_1_1PassManager.html">class</a>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1248takes a list of passes, ensures their <a href="#interaction">prerequisites</a>
1249are set up correctly, and then schedules passes to run efficiently. All of the
1250LLVM tools that run passes use the <tt>PassManager</tt> for execution of these
1251passes.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1252
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1253<p>The <tt>PassManager</tt> does two main things to try to reduce the execution
1254time of a series of passes:</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1255
1256<ol>
1257<li><b>Share analysis results</b> - The PassManager attempts to avoid
1258recomputing analysis results as much as possible. This means keeping track of
1259which analyses are available already, which analyses get invalidated, and which
1260analyses are needed to be run for a pass. An important part of work is that the
1261<tt>PassManager</tt> tracks the exact lifetime of all analysis results, allowing
1262it to <a href="#releaseMemory">free memory</a> allocated to holding analysis
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1263results as soon as they are no longer needed.</li>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1264
1265<li><b>Pipeline the execution of passes on the program</b> - The
1266<tt>PassManager</tt> attempts to get better cache and memory usage behavior out
1267of a series of passes by pipelining the passes together. This means that, given
1268a series of consequtive <a href="#FunctionPass"><tt>FunctionPass</tt></a>'s, it
1269will execute all of the <a href="#FunctionPass"><tt>FunctionPass</tt></a>'s on
1270the first function, then all of the <a
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1271href="#FunctionPass"><tt>FunctionPass</tt></a>es on the second function,
1272etc... until the entire program has been run through the passes.
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1273
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1274<p>This improves the cache behavior of the compiler, because it is only touching
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1275the LLVM program representation for a single function at a time, instead of
1276traversing the entire program. It reduces the memory consumption of compiler,
1277because, for example, only one <a
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]1278href="http://llvm.org/doxygen/classllvm_1_1DominatorSet.html"><tt>DominatorSet</tt></a>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1279needs to be calculated at a time. This also makes it possible some <a
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1280href="#SMP">interesting enhancements</a> in the future.</p></li>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1281
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1282</ol>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1283
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1284<p>The effectiveness of the <tt>PassManager</tt> is influenced directly by how
1285much information it has about the behaviors of the passes it is scheduling. For
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1286example, the "preserved" set is intentionally conservative in the face of an
1287unimplemented <a href="#getAnalysisUsage"><tt>getAnalysisUsage</tt></a> method.
1288Not implementing when it should be implemented will have the effect of not
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1289allowing any analysis results to live across the execution of your pass.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1290
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1291<p>The <tt>PassManager</tt> class exposes a <tt>--debug-pass</tt> command line
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1292options that is useful for debugging pass execution, seeing how things work, and
1293diagnosing when you should be preserving more analyses than you currently are
1294(To get information about all of the variants of the <tt>--debug-pass</tt>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1295option, just type '<tt>opt --help-hidden</tt>').</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1296
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1297<p>By using the <tt>--debug-pass=Structure</tt> option, for example, we can see
1298how our <a href="#basiccode">Hello World</a> pass interacts with other passes.
1299Lets try it out with the <tt>gcse</tt> and <tt>licm</tt> passes:</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1300
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1301<div class="doc_code"><pre>
Reid Spencer7fa6d522005-01-11 05:16:23 +0000[diff] [blame]1302$ opt -load ../../../Debug/lib/Hello.so -gcse -licm --debug-pass=Structure &lt; hello.bc &gt; /dev/null
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1303Module Pass Manager
1304 Function Pass Manager
1305 Dominator Set Construction
1306 Immediate Dominators Construction
1307 Global Common Subexpression Elimination
1308-- Immediate Dominators Construction
1309-- Global Common Subexpression Elimination
1310 Natural Loop Construction
1311 Loop Invariant Code Motion
1312-- Natural Loop Construction
1313-- Loop Invariant Code Motion
1314 Module Verifier
1315-- Dominator Set Construction
1316-- Module Verifier
1317 Bytecode Writer
1318--Bytecode Writer
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1319</pre></div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1320
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1321<p>This output shows us when passes are constructed and when the analysis
1322results are known to be dead (prefixed with '<tt>--</tt>'). Here we see that
1323GCSE uses dominator and immediate dominator information to do its job. The LICM
1324pass uses natural loop information, which uses dominator sets, but not immediate
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1325dominators. Because immediate dominators are no longer useful after the GCSE
1326pass, it is immediately destroyed. The dominator sets are then reused to
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1327compute natural loop information, which is then used by the LICM pass.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1328
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1329<p>After the LICM pass, the module verifier runs (which is automatically added
1330by the '<tt>opt</tt>' tool), which uses the dominator set to check that the
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1331resultant LLVM code is well formed. After it finishes, the dominator set
1332information is destroyed, after being computed once, and shared by three
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1333passes.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1334
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1335<p>Lets see how this changes when we run the <a href="#basiccode">Hello
1336World</a> pass in between the two passes:</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1337
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1338<div class="doc_code"><pre>
Reid Spencer7fa6d522005-01-11 05:16:23 +0000[diff] [blame]1339$ opt -load ../../../Debug/lib/Hello.so -gcse -hello -licm --debug-pass=Structure &lt; hello.bc &gt; /dev/null
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1340Module Pass Manager
1341 Function Pass Manager
1342 Dominator Set Construction
1343 Immediate Dominators Construction
1344 Global Common Subexpression Elimination
1345<b>-- Dominator Set Construction</b>
1346-- Immediate Dominators Construction
1347-- Global Common Subexpression Elimination
1348<b> Hello World Pass
1349-- Hello World Pass
1350 Dominator Set Construction</b>
1351 Natural Loop Construction
1352 Loop Invariant Code Motion
1353-- Natural Loop Construction
1354-- Loop Invariant Code Motion
1355 Module Verifier
1356-- Dominator Set Construction
1357-- Module Verifier
1358 Bytecode Writer
1359--Bytecode Writer
1360Hello: __main
1361Hello: puts
1362Hello: main
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1363</pre></div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1364
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1365<p>Here we see that the <a href="#basiccode">Hello World</a> pass has killed the
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1366Dominator Set pass, even though it doesn't modify the code at all! To fix this,
1367we need to add the following <a
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1368href="#getAnalysisUsage"><tt>getAnalysisUsage</tt></a> method to our pass:</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1369
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1370<div class="doc_code"><pre>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1371 <i>// We don't modify the program, so we preserve all analyses</i>
1372 <b>virtual void</b> getAnalysisUsage(AnalysisUsage &amp;AU) <b>const</b> {
1373 AU.setPreservesAll();
1374 }
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1375</pre></div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1376
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1377<p>Now when we run our pass, we get this output:</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1378
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1379<div class="doc_code"><pre>
Reid Spencer7fa6d522005-01-11 05:16:23 +0000[diff] [blame]1380$ opt -load ../../../Debug/lib/Hello.so -gcse -hello -licm --debug-pass=Structure &lt; hello.bc &gt; /dev/null
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1381Pass Arguments: -gcse -hello -licm
1382Module Pass Manager
1383 Function Pass Manager
1384 Dominator Set Construction
1385 Immediate Dominators Construction
1386 Global Common Subexpression Elimination
1387-- Immediate Dominators Construction
1388-- Global Common Subexpression Elimination
1389 Hello World Pass
1390-- Hello World Pass
1391 Natural Loop Construction
1392 Loop Invariant Code Motion
1393-- Loop Invariant Code Motion
1394-- Natural Loop Construction
1395 Module Verifier
1396-- Dominator Set Construction
1397-- Module Verifier
1398 Bytecode Writer
1399--Bytecode Writer
1400Hello: __main
1401Hello: puts
1402Hello: main
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1403</pre></div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1404
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1405<p>Which shows that we don't accidentally invalidate dominator information
1406anymore, and therefore do not have to compute it twice.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1407
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1408</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1409
1410<!-- _______________________________________________________________________ -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1411<div class="doc_subsubsection">
1412 <a name="releaseMemory">The <tt>releaseMemory</tt> method</a>
1413</div>
1414
1415<div class="doc_text">
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1416
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1417<div class="doc_code"><pre>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1418 <b>virtual void</b> releaseMemory();
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1419</pre></div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1420
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1421<p>The <tt>PassManager</tt> automatically determines when to compute analysis
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1422results, and how long to keep them around for. Because the lifetime of the pass
1423object itself is effectively the entire duration of the compilation process, we
1424need some way to free analysis results when they are no longer useful. The
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1425<tt>releaseMemory</tt> virtual method is the way to do this.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1426
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1427<p>If you are writing an analysis or any other pass that retains a significant
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1428amount of state (for use by another pass which "requires" your pass and uses the
1429<a href="#getAnalysis">getAnalysis</a> method) you should implement
1430<tt>releaseMEmory</tt> to, well, release the memory allocated to maintain this
1431internal state. This method is called after the <tt>run*</tt> method for the
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1432class, before the next call of <tt>run*</tt> in your pass.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1433
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1434</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1435
1436<!-- *********************************************************************** -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1437<div class="doc_section">
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1438 <a name="registering">Registering dynamically loaded passes</a>
1439</div>
1440<!-- *********************************************************************** -->
1441
1442<div class="doc_text">
1443
1444<p><i>Size matters</i> when constructing production quality tools using llvm,
1445both for the purposes of distribution, and for regulating the resident code size
1446when running on the target system. Therefore, it becomes desirable to
1447selectively use some passes, while omitting others and maintain the flexibility
1448to change configurations later on. You want to be able to do all this, and,
1449provide feedback to the user. This is where pass registration comes into
1450play.</p>
1451
1452<p>The fundamental mechanisms for pass registration are the
1453<tt>MachinePassRegistry</tt> class and subclasses of
1454<tt>MachinePassRegistryNode</tt>.</p>
1455
1456<p>An instance of <tt>MachinePassRegistry</tt> is used to maintain a list of
1457<tt>MachinePassRegistryNode</tt> objects. This instance maintains the list and
1458communicates additions and deletions to the command line interface.</p>
1459
1460<p>An instance of <tt>MachinePassRegistryNode</tt> subclass is used to maintain
1461information provided about a particular pass. This information includes the
1462command line name, the command help string and the address of the function used
1463to create an instance of the pass. A global static constructor of one of these
1464instances <i>registers</i> with a corresponding <tt>MachinePassRegistry</tt>,
1465the static destructor <i>unregisters</i>. Thus a pass that is statically linked
1466in the tool will be registered at start up. A dynamically loaded pass will
1467register on load and unregister at unload.</p>
1468
1469</div>
1470
1471<!-- _______________________________________________________________________ -->
1472<div class="doc_subsection">
1473 <a name="registering_existing">Using existing registries</a>
1474</div>
1475
1476<div class="doc_text">
1477
1478<p>There are predefined registries to track instruction scheduling
1479(<tt>RegisterScheduler</tt>) and register allocation (<tt>RegisterRegAlloc</tt>)
1480machine passes. Here we will describe how to <i>register</i> a register
1481allocator machine pass.</p>
1482
1483<p>Implement your register allocator machine pass. In your register allocator
1484.cpp file add the following include;</p>
1485
1486<div class="doc_code"><pre>
1487 #include ""llvm/CodeGen/RegAllocRegistry.h""
1488</pre></div>
1489
1490<p>Also in your register allocator .cpp file, define a creator function in the
1491form; </p>
1492
1493<div class="doc_code"><pre>
1494 FunctionPass *createMyRegisterAllocator() {
1495 return new MyRegisterAllocator();
1496 }
1497</pre></div>
1498
1499<p>Note that the signature of this function should match the type of
1500<tt>RegisterRegAlloc::FunctionPassCtor</tt>. In the same file add the
1501"installing" declaration, in the form;</p>
1502
1503<div class="doc_code"><pre>
1504 static RegisterRegAlloc myRegAlloc("myregalloc",
1505 " my register allocator help string",
1506 createMyRegisterAllocator);
1507</pre></div>
1508
1509<p>Note the two spaces prior to the help string produces a tidy result on the
1510--help query.</p>
1511
1512<div class="doc_code"><pre>
1513$ llc --help
1514 ...
1515 -regalloc - Register allocator to use: (default = linearscan)
1516 =linearscan - linear scan register allocator
1517 =local - local register allocator
1518 =simple - simple register allocator
1519 =myregalloc - my register allocator help string
1520 ...
1521</pre></div>
1522
1523<p>And that's it. The user is now free to use <tt>-regalloc=myregalloc</tt> as
1524an option. Registering instruction schedulers is similar except use the
1525<tt>RegisterRegAlloc</tt> class. Note that the
1526<tt>RegisterRegAlloc::FunctionPassCtor</tt> is significantly different from
1527<tt>RegisterRegAlloc::FunctionPassCtor</tt>.</p>
1528
1529<p>To force the load/linking of your register allocator into the llc/lli tools,
1530add your creator function's global declaration to "Passes.h" and add a "pseudo"
1531call line to <tt>llvm/Codegen/LinkAllCodegenComponents.h</tt>.</p>
1532
1533</div>
1534
1535
1536<!-- _______________________________________________________________________ -->
1537<div class="doc_subsection">
1538 <a name="registering_new">Creating new registries</a>
1539</div>
1540
1541<div class="doc_text">
1542
1543<p>The easiest way to get started is to clone one of the existing registries; we
1544recommend <tt>llvm/CodeGen/RegAllocRegistry.h</tt>. The key things to modify
1545are the class name and the <tt>FunctionPassCtor</tt> type.</p>
1546
1547<p>Then you need to declare the registry. Example: if your pass registry is
1548<tt>RegisterMyPasses</tt> then define;</p>
1549
1550<div class="doc_code"><pre>
1551MachinePassRegistry RegisterMyPasses::Registry;
1552</pre></div>
1553
1554<p>And finally, declare the command line option for your passes. Example:</p>
1555
1556<div class="doc_code"><pre>
1557 cl::opt&lt;RegisterMyPasses::FunctionPassCtor, false,
1558 RegisterPassParser&lt;RegisterMyPasses&gt &gt
1559 MyPassOpt("mypass",
1560 cl::init(&amp;createDefaultMyPass),
1561 cl::desc("my pass option help"));
1562</pre></div>
1563
1564<p>Here the command option is "mypass", with createDefaultMyPass as the default
1565creator.</p>
1566
1567</div>
1568
1569<!-- *********************************************************************** -->
1570<div class="doc_section">
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1571 <a name="debughints">Using GDB with dynamically loaded passes</a>
1572</div>
Chris Lattner480e2ef2002-09-06 02:02:58 +0000[diff] [blame]1573<!-- *********************************************************************** -->
1574
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1575<div class="doc_text">
1576
1577<p>Unfortunately, using GDB with dynamically loaded passes is not as easy as it
Chris Lattner480e2ef2002-09-06 02:02:58 +0000[diff] [blame]1578should be. First of all, you can't set a breakpoint in a shared object that has
1579not been loaded yet, and second of all there are problems with inlined functions
1580in shared objects. Here are some suggestions to debugging your pass with
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1581GDB.</p>
Chris Lattner480e2ef2002-09-06 02:02:58 +0000[diff] [blame]1582
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1583<p>For sake of discussion, I'm going to assume that you are debugging a
Chris Lattner480e2ef2002-09-06 02:02:58 +0000[diff] [blame]1584transformation invoked by <tt>opt</tt>, although nothing described here depends
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1585on that.</p>
1586
1587</div>
Chris Lattner480e2ef2002-09-06 02:02:58 +0000[diff] [blame]1588
1589<!-- _______________________________________________________________________ -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1590<div class="doc_subsubsection">
1591 <a name="breakpoint">Setting a breakpoint in your pass</a>
1592</div>
Chris Lattner480e2ef2002-09-06 02:02:58 +0000[diff] [blame]1593
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1594<div class="doc_text">
1595
1596<p>First thing you do is start <tt>gdb</tt> on the <tt>opt</tt> process:</p>
Chris Lattner480e2ef2002-09-06 02:02:58 +0000[diff] [blame]1597
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1598<div class="doc_code"><pre>
Chris Lattner480e2ef2002-09-06 02:02:58 +0000[diff] [blame]1599$ <b>gdb opt</b>
1600GNU gdb 5.0
1601Copyright 2000 Free Software Foundation, Inc.
1602GDB is free software, covered by the GNU General Public License, and you are
1603welcome to change it and/or distribute copies of it under certain conditions.
1604Type "show copying" to see the conditions.
1605There is absolutely no warranty for GDB. Type "show warranty" for details.
1606This GDB was configured as "sparc-sun-solaris2.6"...
1607(gdb)
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1608</pre></div>
Chris Lattner480e2ef2002-09-06 02:02:58 +0000[diff] [blame]1609
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1610<p>Note that <tt>opt</tt> has a lot of debugging information in it, so it takes
Chris Lattner480e2ef2002-09-06 02:02:58 +0000[diff] [blame]1611time to load. Be patient. Since we cannot set a breakpoint in our pass yet
1612(the shared object isn't loaded until runtime), we must execute the process, and
1613have it stop before it invokes our pass, but after it has loaded the shared
1614object. The most foolproof way of doing this is to set a breakpoint in
1615<tt>PassManager::run</tt> and then run the process with the arguments you
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1616want:</p>
Chris Lattner480e2ef2002-09-06 02:02:58 +0000[diff] [blame]1617
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1618<div class="doc_code"><pre>
Chris Lattner480e2ef2002-09-06 02:02:58 +0000[diff] [blame]1619(gdb) <b>break PassManager::run</b>
1620Breakpoint 1 at 0x2413bc: file Pass.cpp, line 70.
Chris Lattner4c376ea2005-04-21 04:52:37 +0000[diff] [blame]1621(gdb) <b>run test.bc -load $(LLVMTOP)/llvm/Debug/lib/[libname].so -[passoption]</b>
1622Starting program: opt test.bc -load $(LLVMTOP)/llvm/Debug/lib/[libname].so -[passoption]
Chris Lattner480e2ef2002-09-06 02:02:58 +0000[diff] [blame]1623Breakpoint 1, PassManager::run (this=0xffbef174, M=@0x70b298) at Pass.cpp:70
162470 bool PassManager::run(Module &amp;M) { return PM-&gt;run(M); }
1625(gdb)
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1626</pre></div>
Chris Lattner480e2ef2002-09-06 02:02:58 +0000[diff] [blame]1627
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1628<p>Once the <tt>opt</tt> stops in the <tt>PassManager::run</tt> method you are
1629now free to set breakpoints in your pass so that you can trace through execution
1630or do other standard debugging stuff.</p>
Chris Lattner480e2ef2002-09-06 02:02:58 +0000[diff] [blame]1631
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1632</div>
Chris Lattner480e2ef2002-09-06 02:02:58 +0000[diff] [blame]1633
1634<!-- _______________________________________________________________________ -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1635<div class="doc_subsubsection">
1636 <a name="debugmisc">Miscellaneous Problems</a>
1637</div>
Chris Lattner480e2ef2002-09-06 02:02:58 +0000[diff] [blame]1638
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1639<div class="doc_text">
1640
1641<p>Once you have the basics down, there are a couple of problems that GDB has,
1642some with solutions, some without.</p>
Chris Lattner480e2ef2002-09-06 02:02:58 +0000[diff] [blame]1643
1644<ul>
1645<li>Inline functions have bogus stack information. In general, GDB does a
1646pretty good job getting stack traces and stepping through inline functions.
1647When a pass is dynamically loaded however, it somehow completely loses this
1648capability. The only solution I know of is to de-inline a function (move it
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1649from the body of a class to a .cpp file).</li>
Chris Lattner480e2ef2002-09-06 02:02:58 +0000[diff] [blame]1650
1651<li>Restarting the program breaks breakpoints. After following the information
1652above, you have succeeded in getting some breakpoints planted in your pass. Nex
1653thing you know, you restart the program (i.e., you type '<tt>run</tt>' again),
1654and you start getting errors about breakpoints being unsettable. The only way I
1655have found to "fix" this problem is to <tt>delete</tt> the breakpoints that are
1656already set in your pass, run the program, and re-set the breakpoints once
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1657execution stops in <tt>PassManager::run</tt>.</li>
Chris Lattner480e2ef2002-09-06 02:02:58 +0000[diff] [blame]1658
1659</ul>
1660
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1661<p>Hopefully these tips will help with common case debugging situations. If
1662you'd like to contribute some tips of your own, just contact <a
1663href="mailto:sabre@nondot.org">Chris</a>.</p>
Chris Lattner480e2ef2002-09-06 02:02:58 +0000[diff] [blame]1664
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1665</div>
Chris Lattner480e2ef2002-09-06 02:02:58 +0000[diff] [blame]1666
1667<!-- *********************************************************************** -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1668<div class="doc_section">
1669 <a name="future">Future extensions planned</a>
1670</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1671<!-- *********************************************************************** -->
1672
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1673<div class="doc_text">
1674
1675<p>Although the LLVM Pass Infrastructure is very capable as it stands, and does
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1676some nifty stuff, there are things we'd like to add in the future. Here is
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1677where we are going:</p>
1678
1679</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1680
1681<!-- _______________________________________________________________________ -->
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]1682<div class="doc_subsubsection">
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1683 <a name="SMP">Multithreaded LLVM</a>
1684</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1685
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1686<div class="doc_text">
1687
1688<p>Multiple CPU machines are becoming more common and compilation can never be
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1689fast enough: obviously we should allow for a multithreaded compiler. Because of
1690the semantics defined for passes above (specifically they cannot maintain state
1691across invocations of their <tt>run*</tt> methods), a nice clean way to
1692implement a multithreaded compiler would be for the <tt>PassManager</tt> class
Misha Brukmanbc0e9982003-07-14 17:20:40 +0000[diff] [blame]1693to create multiple instances of each pass object, and allow the separate
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1694instances to be hacking on different parts of the program at the same time.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1695
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1696<p>This implementation would prevent each of the passes from having to implement
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1697multithreaded constructs, requiring only the LLVM core to have locking in a few
1698places (for global resources). Although this is a simple extension, we simply
1699haven't had time (or multiprocessor machines, thus a reason) to implement this.
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1700Despite that, we have kept the LLVM passes SMP ready, and you should too.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1701
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1702</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1703
1704<!-- _______________________________________________________________________ -->
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]1705<div class="doc_subsubsection">
Chris Lattnerf6278922004-09-20 04:36:29 +0000[diff] [blame]1706<a name="PassFunctionPass"><tt>ModulePass</tt>es requiring <tt>FunctionPass</tt>es</a>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1707</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1708
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1709<div class="doc_text">
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1710
Chris Lattnerf6278922004-09-20 04:36:29 +0000[diff] [blame]1711<p>Currently it is illegal for a <a href="#ModulePass"><tt>ModulePass</tt></a>
1712to require a <a href="#FunctionPass"><tt>FunctionPass</tt></a>. This is because
1713there is only one instance of the <a
1714href="#FunctionPass"><tt>FunctionPass</tt></a> object ever created, thus nowhere
1715to store information for all of the functions in the program at the same time.
1716Although this has come up a couple of times before, this has always been worked
1717around by factoring one big complicated pass into a global and an
1718interprocedural part, both of which are distinct. In the future, it would be
1719nice to have this though.</p>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1720
1721<p>Note that it is no problem for a <a
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1722href="#FunctionPass"><tt>FunctionPass</tt></a> to require the results of a <a
Chris Lattnerf6278922004-09-20 04:36:29 +0000[diff] [blame]1723href="#ModulePass"><tt>ModulePass</tt></a>, only the other way around.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1724
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1725</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1726
1727<!-- *********************************************************************** -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1728<hr>
1729<address>
1730 <a href="http://jigsaw.w3.org/css-validator/check/referer"><img
1731 src="http://jigsaw.w3.org/css-validator/images/vcss" alt="Valid CSS!"></a>
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Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1734
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1735 <a href="mailto:sabre@nondot.org">Chris Lattner</a><br>
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]1736 <a href="http://llvm.org">The LLVM Compiler Infrastructure</a><br>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1737 Last modified: $Date$
1738</address>
1739
1740</body>
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