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gerrit-public.fairphone.software / fp2-dev / platform / external / llvm / 18aad23ce36f9c1dc14c818a10d69448137ebe07 / . / docs / WritingAnLLVMPass.html
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Reid Spencer7fa6d522005-01-11 05:16:23 +0000[diff] [blame]5 <meta http-equiv="Content-Type" content="text/html; charset=utf-8">
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 Lattnerc8603c22006-08-27 23:18:52 +0000[diff] [blame]21 <li><a href="#running">Running a pass with <tt>opt</tt></a></li>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]22 </ul></li>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]23 <li><a href="#passtype">Pass classes and requirements</a>
24 <ul>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]25 <li><a href="#ImmutablePass">The <tt>ImmutablePass</tt> class</a></li>
Chris Lattnerf6278922004-09-20 04:36:29 +0000[diff] [blame]26 <li><a href="#ModulePass">The <tt>ModulePass</tt> class</a>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]27 <ul>
Chris Lattnerf6278922004-09-20 04:36:29 +0000[diff] [blame]28 <li><a href="#runOnModule">The <tt>runOnModule</tt> method</a></li>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]29 </ul></li>
Chris Lattner8fdb2462004-09-18 06:39:35 +0000[diff] [blame]30 <li><a href="#CallGraphSCCPass">The <tt>CallGraphSCCPass</tt> class</a>
31 <ul>
Devang Patelc20048d2007-01-23 22:56:28 +0000[diff] [blame]32 <li><a href="#doInitialization_scc">The <tt>doInitialization(CallGraph
Chris Lattner8fdb2462004-09-18 06:39:35 +0000[diff] [blame]33 &amp;)</tt> method</a></li>
34 <li><a href="#runOnSCC">The <tt>runOnSCC</tt> method</a></li>
Devang Patelc20048d2007-01-23 22:56:28 +0000[diff] [blame]35 <li><a href="#doFinalization_scc">The <tt>doFinalization(CallGraph
Chris Lattner8fdb2462004-09-18 06:39:35 +0000[diff] [blame]36 &amp;)</tt> method</a></li>
37 </ul></li>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]38 <li><a href="#FunctionPass">The <tt>FunctionPass</tt> class</a>
39 <ul>
Chris Lattnerd0713f92002-09-12 17:06:43 +0000[diff] [blame]40 <li><a href="#doInitialization_mod">The <tt>doInitialization(Module
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]41 &amp;)</tt> method</a></li>
42 <li><a href="#runOnFunction">The <tt>runOnFunction</tt> method</a></li>
Chris Lattnerd0713f92002-09-12 17:06:43 +0000[diff] [blame]43 <li><a href="#doFinalization_mod">The <tt>doFinalization(Module
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]44 &amp;)</tt> method</a></li>
45 </ul></li>
Devang Patel2e8f27d2007-03-19 22:21:25 +0000[diff] [blame]46 <li><a href="#LoopPass">The <tt>LoopPass</tt> class</a>
47 <ul>
48 <li><a href="#doInitialization_loop">The <tt>doInitialization(Loop *,
49 LPPassManager &amp;)</tt> method</a></li>
50 <li><a href="#runOnLoop">The <tt>runOnLoop</tt> method</a></li>
51 <li><a href="#doFinalization_loop">The <tt>doFinalization()
52 </tt> method</a></li>
53 </ul></li>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]54 <li><a href="#BasicBlockPass">The <tt>BasicBlockPass</tt> class</a>
55 <ul>
Chris Lattnerd0713f92002-09-12 17:06:43 +0000[diff] [blame]56 <li><a href="#doInitialization_fn">The <tt>doInitialization(Function
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]57 &amp;)</tt> method</a></li>
58 <li><a href="#runOnBasicBlock">The <tt>runOnBasicBlock</tt>
59 method</a></li>
Chris Lattnerd0713f92002-09-12 17:06:43 +0000[diff] [blame]60 <li><a href="#doFinalization_fn">The <tt>doFinalization(Function
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]61 &amp;)</tt> method</a></li>
62 </ul></li>
Brian Gaekecab8b6f2003-07-17 18:53:20 +0000[diff] [blame]63 <li><a href="#MachineFunctionPass">The <tt>MachineFunctionPass</tt>
64 class</a>
Brian Gaeke6a33f362003-07-22 20:53:20 +0000[diff] [blame]65 <ul>
66 <li><a href="#runOnMachineFunction">The
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]67 <tt>runOnMachineFunction(MachineFunction &amp;)</tt> method</a></li>
68 </ul></li>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]69 </ul>
70 <li><a href="#registration">Pass Registration</a>
71 <ul>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]72 <li><a href="#print">The <tt>print</tt> method</a></li>
73 </ul></li>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]74 <li><a href="#interaction">Specifying interactions between passes</a>
75 <ul>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]76 <li><a href="#getAnalysisUsage">The <tt>getAnalysisUsage</tt>
77 method</a></li>
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]78 <li><a href="#AU::addRequired">The <tt>AnalysisUsage::addRequired&lt;&gt;</tt> and <tt>AnalysisUsage::addRequiredTransitive&lt;&gt;</tt> methods</a></li>
79 <li><a href="#AU::addPreserved">The <tt>AnalysisUsage::addPreserved&lt;&gt;</tt> method</a></li>
80 <li><a href="#AU::examples">Example implementations of <tt>getAnalysisUsage</tt></a></li>
81 <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]82 </ul></li>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]83 <li><a href="#analysisgroup">Implementing Analysis Groups</a>
84 <ul>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]85 <li><a href="#agconcepts">Analysis Group Concepts</a></li>
86 <li><a href="#registerag">Using <tt>RegisterAnalysisGroup</tt></a></li>
87 </ul></li>
Tanya Lattnerd5383652004-11-19 01:25:14 +0000[diff] [blame]88 <li><a href="#passStatistics">Pass Statistics</a>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]89 <li><a href="#passmanager">What PassManager does</a>
90 <ul>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]91 <li><a href="#releaseMemory">The <tt>releaseMemory</tt> method</a></li>
92 </ul></li>
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]93 <li><a href="#registering">Registering dynamically loaded passes</a>
94 <ul>
95 <li><a href="#registering_existing">Using existing registries</a></li>
96 <li><a href="#registering_new">Creating new registries</a></li>
97 </ul></li>
Chris Lattner480e2ef2002-09-06 02:02:58 +0000[diff] [blame]98 <li><a href="#debughints">Using GDB with dynamically loaded passes</a>
99 <ul>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]100 <li><a href="#breakpoint">Setting a breakpoint in your pass</a></li>
101 <li><a href="#debugmisc">Miscellaneous Problems</a></li>
102 </ul></li>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]103 <li><a href="#future">Future extensions planned</a>
104 <ul>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]105 <li><a href="#SMP">Multithreaded LLVM</a></li>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]106 </ul></li>
107</ol>
Chris Lattner38c633d2002-08-08 20:23:41 +0000[diff] [blame]108
Chris Lattner7911ce22004-05-23 21:07:27 +0000[diff] [blame]109<div class="doc_author">
Chris Lattner8f652eb2006-08-11 16:37:02 +0000[diff] [blame]110 <p>Written by <a href="mailto:sabre@nondot.org">Chris Lattner</a> and
Jim Laskeyc760a922007-03-14 19:32:21 +0000[diff] [blame]111 <a href="mailto:jlaskey@mac.com">Jim Laskey</a></p>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]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_section">
116 <a name="introduction">Introduction - What is a pass?</a>
117</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]118<!-- *********************************************************************** -->
119
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]120<div class="doc_text">
121
122<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]123passes are where most of the interesting parts of the compiler exist. Passes
124perform the transformations and optimizations that make up the compiler, they
125build the analysis results that are used by these transformations, and they are,
126above all, a structuring technique for compiler code.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]127
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]128<p>All LLVM passes are subclasses of the <tt><a
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]129href="http://llvm.org/doxygen/classllvm_1_1Pass.html">Pass</a></tt>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]130class, which implement functionality by overriding virtual methods inherited
Chris Lattnerf6278922004-09-20 04:36:29 +0000[diff] [blame]131from <tt>Pass</tt>. Depending on how your pass works, you should inherit from
132the <tt><a href="#ModulePass">ModulePass</a></tt>, <tt><a
133href="#CallGraphSCCPass">CallGraphSCCPass</a></tt>, <tt><a
134href="#FunctionPass">FunctionPass</a></tt>, or <tt><a
Devang Patel2e8f27d2007-03-19 22:21:25 +0000[diff] [blame]135href="#LoopPass">LoopPass</a></tt>, or <tt><a
Chris Lattner8fdb2462004-09-18 06:39:35 +0000[diff] [blame]136href="#BasicBlockPass">BasicBlockPass</a></tt> classes, which gives the system
137more information about what your pass does, and how it can be combined with
138other passes. One of the main features of the LLVM Pass Framework is that it
139schedules passes to run in an efficient way based on the constraints that your
140pass meets (which are indicated by which class they derive from).</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]141
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]142<p>We start by showing you how to construct a pass, everything from setting up
143the code, to compiling, loading, and executing it. After the basics are down,
144more advanced features are discussed.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]145
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]146</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]147
148<!-- *********************************************************************** -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]149<div class="doc_section">
150 <a name="quickstart">Quick Start - Writing hello world</a>
151</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]152<!-- *********************************************************************** -->
153
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]154<div class="doc_text">
155
156<p>Here we describe how to write the "hello world" of passes. The "Hello" pass
157is designed to simply print out the name of non-external functions that exist in
Chris Lattner8fdb2462004-09-18 06:39:35 +0000[diff] [blame]158the program being compiled. It does not modify the program at all, it just
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]159inspects it. The source code and files for this pass are available in the LLVM
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]160source tree in the <tt>lib/Transforms/Hello</tt> directory.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]161
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]162</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]163
164<!-- ======================================================================= -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]165<div class="doc_subsection">
166 <a name="makefile">Setting up the build environment</a>
167</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]168
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]169<div class="doc_text">
170
Reid Spencer1bc19342004-12-11 05:12:57 +0000[diff] [blame]171 <p>First, you need to create a new directory somewhere in the LLVM source
172 base. For this example, we'll assume that you made
173 <tt>lib/Transforms/Hello</tt>. Next, you must set up a build script
174 (Makefile) that will compile the source code for the new pass. To do this,
175 copy the following into <tt>Makefile</tt>:</p>
176 <hr/>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]177
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]178<div class="doc_code"><pre>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]179# Makefile for hello pass
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]180
Chris Lattner17a4c3e2002-08-14 20:06:13 +0000[diff] [blame]181# Path to top level of LLVM heirarchy
Chris Lattner7ce83e52002-08-14 20:07:01 +0000[diff] [blame]182LEVEL = ../../..
Chris Lattner17a4c3e2002-08-14 20:06:13 +0000[diff] [blame]183
184# Name of the library to build
Reid Spencer7fa6d522005-01-11 05:16:23 +0000[diff] [blame]185LIBRARYNAME = Hello
Chris Lattner17a4c3e2002-08-14 20:06:13 +0000[diff] [blame]186
Reid Spencer7fa6d522005-01-11 05:16:23 +0000[diff] [blame]187# Make the shared library become a loadable module so the tools can
188# dlopen/dlsym on the resulting library.
Robert Bocchino3cf817d2006-01-06 22:49:23 +0000[diff] [blame]189LOADABLE_MODULE = 1
Reid Spencer7fa6d522005-01-11 05:16:23 +0000[diff] [blame]190
Reid Spencerebfe07f2006-08-08 01:48:17 +0000[diff] [blame]191# Tell the build system which LLVM libraries your pass needs. You'll probably
192# need at least LLVMSystem.a, LLVMSupport.a, LLVMCore.a but possibly several
193# others too.
194LLVMLIBS = LLVMCore.a LLVMSupport.a LLVMSystem.a
195
Chris Lattner17a4c3e2002-08-14 20:06:13 +0000[diff] [blame]196# Include the makefile implementation stuff
197include $(LEVEL)/Makefile.common
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]198</pre></div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]199
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]200<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]201directory are to be compiled and linked together into a
Reid Spencer7fa6d522005-01-11 05:16:23 +0000[diff] [blame]202<tt>Debug/lib/Hello.so</tt> shared object that can be dynamically loaded by
Chris Lattnerc8603c22006-08-27 23:18:52 +0000[diff] [blame]203the <tt>opt</tt> or <tt>bugpoint</tt> tools via their <tt>-load</tt> options.
Reid Spencer7fa6d522005-01-11 05:16:23 +0000[diff] [blame]204If your operating system uses a suffix other than .so (such as windows or
205Mac OS/X), the appropriate extension will be used.</p>
John Criswellf9c78652004-01-26 21:26:54 +0000[diff] [blame]206
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]207<p>Now that we have the build scripts set up, we just need to write the code for
208the pass itself.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]209
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]210</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]211
212<!-- ======================================================================= -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]213<div class="doc_subsection">
214 <a name="basiccode">Basic code required</a>
215</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]216
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]217<div class="doc_text">
218
219<p>Now that we have a way to compile our new pass, we just have to write it.
220Start out with:</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]221
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]222<div class="doc_code"><pre>
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]223<b>#include</b> "<a href="http://llvm.org/doxygen/Pass_8h-source.html">llvm/Pass.h</a>"
224<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]225</pre></div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]226
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]227<p>Which are needed because we are writing a <tt><a
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]228href="http://llvm.org/doxygen/classllvm_1_1Pass.html">Pass</a></tt>, and
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]229we are operating on <tt><a
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]230href="http://llvm.org/doxygen/classllvm_1_1Function.html">Function</a></tt>'s.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]231
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]232<p>Next we have:</p>
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]233<div class="doc_code"><pre>
Jonathan Manton65acb302004-06-30 18:10:30 +0000[diff] [blame]234<b>using namespace llvm;</b>
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]235</pre></div>
Jonathan Manton65acb302004-06-30 18:10:30 +0000[diff] [blame]236<p>... which is required because the functions from the include files
237live in the llvm namespace.
238</p>
239
240<p>Next we have:</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]241
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]242<div class="doc_code"><pre>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]243<b>namespace</b> {
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]244</pre></div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]245
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]246<p>... which starts out an anonymous namespace. Anonymous namespaces are to C++
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]247what the "<tt>static</tt>" keyword is to C (at global scope). It makes the
248things declared inside of the anonymous namespace only visible to the current
249file. If you're not familiar with them, consult a decent C++ book for more
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]250information.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]251
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]252<p>Next, we declare our pass itself:</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]253
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]254<div class="doc_code"><pre>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]255 <b>struct</b> Hello : <b>public</b> <a href="#FunctionPass">FunctionPass</a> {
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]256</pre></div><p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]257
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]258<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]259href="http://llvm.org/doxygen/classllvm_1_1FunctionPass.html">FunctionPass</a></tt>.
Chris Lattnerd6ea9262002-09-09 03:48:46 +0000[diff] [blame]260The different builtin pass subclasses are described in detail <a
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]261href="#passtype">later</a>, but for now, know that <a
262href="#FunctionPass"><tt>FunctionPass</tt></a>'s operate a function at a
263time.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]264
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]265<div class="doc_code"><pre>
Devang Patel19974732007-05-03 01:11:54 +0000[diff] [blame]266 static char ID;
Chris Lattnerb5c87f62007-05-18 05:36:14 +0000[diff] [blame]267 Hello() : FunctionPass((intptr_t)&amp;ID) {}
Devang Patele50fb9a2007-05-01 20:55:38 +0000[diff] [blame]268</pre></div><p>
269
270<p> This declares pass identifier used by LLVM to identify pass. This allows LLVM to
271avoid using expensive C++ runtime information.</p>
272
273<div class="doc_code"><pre>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]274 <b>virtual bool</b> <a href="#runOnFunction">runOnFunction</a>(Function &amp;F) {
Bill Wendling832171c2006-12-07 20:04:42 +0000[diff] [blame]275 llvm::cerr &lt;&lt; "<i>Hello: </i>" &lt;&lt; F.getName() &lt;&lt; "\n";
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]276 <b>return false</b>;
277 }
278 }; <i>// end of struct Hello</i>
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]279</pre></div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]280
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]281<p>We declare a "<a href="#runOnFunction"><tt>runOnFunction</tt></a>" method,
282which overloads an abstract virtual method inherited from <a
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]283href="#FunctionPass"><tt>FunctionPass</tt></a>. This is where we are supposed
284to 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]285function.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]286
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]287<div class="doc_code"><pre>
Devang Patel19974732007-05-03 01:11:54 +0000[diff] [blame]288 char Hello::ID = 0;
Devang Patele50fb9a2007-05-01 20:55:38 +0000[diff] [blame]289</pre></div>
290
291<p> We initialize pass ID here. LLVM uses ID's address to identify pass so
292initialization value is not important.</p>
293
294<div class="doc_code"><pre>
Chris Lattnerc8603c22006-08-27 23:18:52 +0000[diff] [blame]295 RegisterPass&lt;Hello&gt; X("<i>hello</i>", "<i>Hello World Pass</i>");
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]296} <i>// end of anonymous namespace</i>
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]297</pre></div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]298
Chris Lattnerc8603c22006-08-27 23:18:52 +0000[diff] [blame]299<p>Lastly, we <a href="#registration">register our class</a> <tt>Hello</tt>,
300giving it a command line
301argument "<tt>hello</tt>", and a name "<tt>Hello World Pass</tt>".</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]302
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]303<p>As a whole, the <tt>.cpp</tt> file looks like:</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]304
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]305<div class="doc_code"><pre>
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]306<b>#include</b> "<a href="http://llvm.org/doxygen/Pass_8h-source.html">llvm/Pass.h</a>"
307<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]308
Jonathan Manton65acb302004-06-30 18:10:30 +0000[diff] [blame]309<b>using namespace llvm;</b>
310
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]311<b>namespace</b> {
312 <b>struct Hello</b> : <b>public</b> <a href="#FunctionPass">FunctionPass</a> {
Devang Patele50fb9a2007-05-01 20:55:38 +0000[diff] [blame]313
Devang Patel19974732007-05-03 01:11:54 +0000[diff] [blame]314 static char ID;
Chris Lattner55021172007-05-18 05:38:44 +0000[diff] [blame]315 Hello() : FunctionPass((intptr_t)&amp;ID) {}
Devang Patele50fb9a2007-05-01 20:55:38 +0000[diff] [blame]316
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]317 <b>virtual bool</b> <a href="#runOnFunction">runOnFunction</a>(Function &amp;F) {
Bill Wendling832171c2006-12-07 20:04:42 +0000[diff] [blame]318 llvm::cerr &lt;&lt; "<i>Hello: </i>" &lt;&lt; F.getName() &lt;&lt; "\n";
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]319 <b>return false</b>;
320 }
321 };
322
Chris Lattnerc8603c22006-08-27 23:18:52 +0000[diff] [blame]323 RegisterPass&lt;Hello&gt; X("<i>hello</i>", "<i>Hello World Pass</i>");
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]324}
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]325</pre></div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]326
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]327<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]328command in the local directory and you should get a new
Reid Spencer7fa6d522005-01-11 05:16:23 +0000[diff] [blame]329"<tt>Debug/lib/Hello.so</tt> file. Note that everything in this file is
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]330contained in an anonymous namespace: this reflects the fact that passes are self
331contained units that do not need external interfaces (although they can have
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]332them) to be useful.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]333
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]334</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]335
336<!-- ======================================================================= -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]337<div class="doc_subsection">
Chris Lattnerc8603c22006-08-27 23:18:52 +0000[diff] [blame]338 <a name="running">Running a pass with <tt>opt</tt></a>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]339</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]340
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]341<div class="doc_text">
342
John Criswellf9c78652004-01-26 21:26:54 +0000[diff] [blame]343<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]344<tt>opt</tt> command to run an LLVM program through your pass. Because you
Chris Lattnerc8603c22006-08-27 23:18:52 +0000[diff] [blame]345registered your pass with the <tt>RegisterPass</tt> template, you will be able to
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]346use the <tt>opt</tt> tool to access it, once loaded.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]347
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]348<p>To test it, follow the example at the end of the <a
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]349href="GettingStarted.html">Getting Started Guide</a> to compile "Hello World" to
350LLVM. We can now run the bytecode file (<tt>hello.bc</tt>) for the program
351through our transformation like this (or course, any bytecode file will
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]352work):</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]353
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]354<div class="doc_code"><pre>
Reid Spencer7fa6d522005-01-11 05:16:23 +0000[diff] [blame]355$ opt -load ../../../Debug/lib/Hello.so -hello &lt; hello.bc &gt; /dev/null
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]356Hello: __main
357Hello: puts
358Hello: main
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]359</pre></div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]360
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]361<p>The '<tt>-load</tt>' option specifies that '<tt>opt</tt>' should load your
362pass as a shared object, which makes '<tt>-hello</tt>' a valid command line
363argument (which is one reason you need to <a href="#registration">register your
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]364pass</a>). Because the hello pass does not modify the program in any
365interesting way, we just throw away the result of <tt>opt</tt> (sending it to
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]366<tt>/dev/null</tt>).</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]367
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]368<p>To see what happened to the other string you registered, try running
369<tt>opt</tt> with the <tt>--help</tt> option:</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]370
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]371<div class="doc_code"><pre>
Reid Spencer7fa6d522005-01-11 05:16:23 +0000[diff] [blame]372$ opt -load ../../../Debug/lib/Hello.so --help
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]373OVERVIEW: llvm .bc -&gt; .bc modular optimizer
374
375USAGE: opt [options] &lt;input bytecode&gt;
376
377OPTIONS:
378 Optimizations available:
379...
380 -funcresolve - Resolve Functions
381 -gcse - Global Common Subexpression Elimination
382 -globaldce - Dead Global Elimination
383 <b>-hello - Hello World Pass</b>
Chris Lattner065a6162003-09-10 05:29:43 +0000[diff] [blame]384 -indvars - Canonicalize Induction Variables
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]385 -inline - Function Integration/Inlining
386 -instcombine - Combine redundant instructions
387...
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]388</pre></div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]389
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]390<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]391documentation to users of <tt>opt</tt>. Now that you have a working pass, you
392would go ahead and make it do the cool transformations you want. Once you get
393it all working and tested, it may become useful to find out how fast your pass
394is. The <a href="#passManager"><tt>PassManager</tt></a> provides a nice command
395line option (<tt>--time-passes</tt>) that allows you to get information about
396the execution time of your pass along with the other passes you queue up. For
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]397example:</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]398
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]399<div class="doc_code"><pre>
Reid Spencer7fa6d522005-01-11 05:16:23 +0000[diff] [blame]400$ 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]401Hello: __main
402Hello: puts
403Hello: main
404===============================================================================
405 ... Pass execution timing report ...
406===============================================================================
407 Total Execution Time: 0.02 seconds (0.0479059 wall clock)
408
409 ---User Time--- --System Time-- --User+System-- ---Wall Time--- --- Pass Name ---
410 0.0100 (100.0%) 0.0000 ( 0.0%) 0.0100 ( 50.0%) 0.0402 ( 84.0%) Bytecode Writer
411 0.0000 ( 0.0%) 0.0100 (100.0%) 0.0100 ( 50.0%) 0.0031 ( 6.4%) Dominator Set Construction
412 0.0000 ( 0.0%) 0.0000 ( 0.0%) 0.0000 ( 0.0%) 0.0013 ( 2.7%) Module Verifier
413 <b> 0.0000 ( 0.0%) 0.0000 ( 0.0%) 0.0000 ( 0.0%) 0.0033 ( 6.9%) Hello World Pass</b>
414 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]415</pre></div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]416
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]417<p>As you can see, our implementation above is pretty fast :). The additional
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]418passes listed are automatically inserted by the '<tt>opt</tt>' tool to verify
419that the LLVM emitted by your pass is still valid and well formed LLVM, which
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]420hasn't been broken somehow.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]421
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]422<p>Now that you have seen the basics of the mechanics behind passes, we can talk
423about some more details of how they work and how to use them.</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
427<!-- *********************************************************************** -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]428<div class="doc_section">
429 <a name="passtype">Pass classes and requirements</a>
430</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]431<!-- *********************************************************************** -->
432
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]433<div class="doc_text">
434
435<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]436decide what class you should subclass for your pass. The <a
437href="#basiccode">Hello World</a> example uses the <tt><a
438href="#FunctionPass">FunctionPass</a></tt> class for its implementation, but we
439did not discuss why or when this should occur. Here we talk about the classes
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]440available, from the most general to the most specific.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]441
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]442<p>When choosing a superclass for your Pass, you should choose the <b>most
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]443specific</b> class possible, while still being able to meet the requirements
Misha Brukman5560c9d2003-08-18 14:43:39 +0000[diff] [blame]444listed. This gives the LLVM Pass Infrastructure information necessary to
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]445optimize how passes are run, so that the resultant compiler isn't unneccesarily
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]446slow.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +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
Chris Lattnerf004f9a2002-09-25 22:31:38 +0000[diff] [blame]450<!-- ======================================================================= -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]451<div class="doc_subsection">
452 <a name="ImmutablePass">The <tt>ImmutablePass</tt> class</a>
453</div>
Chris Lattnerf004f9a2002-09-25 22:31:38 +0000[diff] [blame]454
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]455<div class="doc_text">
456
457<p>The most plain and boring type of pass is the "<tt><a
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]458href="http://llvm.org/doxygen/classllvm_1_1ImmutablePass.html">ImmutablePass</a></tt>"
Chris Lattnerf004f9a2002-09-25 22:31:38 +0000[diff] [blame]459class. This pass type is used for passes that do not have to be run, do not
460change state, and never need to be updated. This is not a normal type of
461transformation or analysis, but can provide information about the current
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]462compiler configuration.</p>
Chris Lattnerf004f9a2002-09-25 22:31:38 +0000[diff] [blame]463
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]464<p>Although this pass class is very infrequently used, it is important for
Chris Lattnerf004f9a2002-09-25 22:31:38 +0000[diff] [blame]465providing information about the current target machine being compiled for, and
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]466other static information that can affect the various transformations.</p>
Chris Lattnerf004f9a2002-09-25 22:31:38 +0000[diff] [blame]467
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]468<p><tt>ImmutablePass</tt>es never invalidate other transformations, are never
469invalidated, and are never "run".</p>
Chris Lattnerf004f9a2002-09-25 22:31:38 +0000[diff] [blame]470
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]471</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]472
473<!-- ======================================================================= -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]474<div class="doc_subsection">
Chris Lattnerf6278922004-09-20 04:36:29 +0000[diff] [blame]475 <a name="ModulePass">The <tt>ModulePass</tt> class</a>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]476</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]477
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]478<div class="doc_text">
479
480<p>The "<tt><a
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]481href="http://llvm.org/doxygen/classllvm_1_1ModulePass.html">ModulePass</a></tt>"
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]482class is the most general of all superclasses that you can use. Deriving from
Chris Lattnerf6278922004-09-20 04:36:29 +0000[diff] [blame]483<tt>ModulePass</tt> indicates that your pass uses the entire program as a unit,
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]484refering to function bodies in no predictable order, or adding and removing
Chris Lattnerf6278922004-09-20 04:36:29 +0000[diff] [blame]485functions. Because nothing is known about the behavior of <tt>ModulePass</tt>
Devang Patel3c1ca0b2007-04-16 21:28:14 +0000[diff] [blame]486subclasses, no optimization can be done for their execution. A module pass
487can use function level passes (e.g. dominators) using getAnalysis interface
Chris Lattnerb5c87f62007-05-18 05:36:14 +0000[diff] [blame]488<tt> getAnalysis&lt;DominatorTree&gt;(Function)</tt>. </p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]489
Chris Lattnerf6278922004-09-20 04:36:29 +0000[diff] [blame]490<p>To write a correct <tt>ModulePass</tt> subclass, derive from
491<tt>ModulePass</tt> and overload the <tt>runOnModule</tt> method with the
492following signature:</p>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]493
494</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]495
496<!-- _______________________________________________________________________ -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]497<div class="doc_subsubsection">
Chris Lattnerf6278922004-09-20 04:36:29 +0000[diff] [blame]498 <a name="runOnModule">The <tt>runOnModule</tt> method</a>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]499</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]500
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]501<div class="doc_text">
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]502
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]503<div class="doc_code"><pre>
Chris Lattnerf6278922004-09-20 04:36:29 +0000[diff] [blame]504 <b>virtual bool</b> runOnModule(Module &amp;M) = 0;
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]505</pre></div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]506
John Criswell2382ff72005-07-15 19:25:12 +0000[diff] [blame]507<p>The <tt>runOnModule</tt> method performs the interesting work of the pass.
508It should return true if the module was modified by the transformation and
509false otherwise.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]510
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]511</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]512
513<!-- ======================================================================= -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]514<div class="doc_subsection">
Chris Lattner8fdb2462004-09-18 06:39:35 +0000[diff] [blame]515 <a name="CallGraphSCCPass">The <tt>CallGraphSCCPass</tt> class</a>
516</div>
517
518<div class="doc_text">
519
520<p>The "<tt><a
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]521href="http://llvm.org/doxygen/classllvm_1_1CallGraphSCCPass.html">CallGraphSCCPass</a></tt>"
Chris Lattner8fdb2462004-09-18 06:39:35 +0000[diff] [blame]522is used by passes that need to traverse the program bottom-up on the call graph
523(callees before callers). Deriving from CallGraphSCCPass provides some
524mechanics for building and traversing the CallGraph, but also allows the system
525to optimize execution of CallGraphSCCPass's. If your pass meets the
526requirements outlined below, and doesn't meet the requirements of a <tt><a
527href="#FunctionPass">FunctionPass</a></tt> or <tt><a
528href="#BasicBlockPass">BasicBlockPass</a></tt>, you should derive from
529<tt>CallGraphSCCPass</tt>.</p>
530
531<p><b>TODO</b>: explain briefly what SCC, Tarjan's algo, and B-U mean.</p>
532
533<p>To be explicit, <tt>CallGraphSCCPass</tt> subclasses are:</p>
534
535<ol>
536
537<li>... <em>not allowed</em> to modify any <tt>Function</tt>s that are not in
538the current SCC.</li>
539
Tanya Lattner18aad232007-06-07 16:44:52 +0000[diff] [blame^]540<li>... <em>not allowed</em> to inspect any Function's other than those in the
Chris Lattner8fdb2462004-09-18 06:39:35 +0000[diff] [blame]541current SCC and the direct callees of the SCC.</li>
542
543<li>... <em>required</em> to preserve the current CallGraph object, updating it
544to reflect any changes made to the program.</li>
545
546<li>... <em>not allowed</em> to add or remove SCC's from the current Module,
547though they may change the contents of an SCC.</li>
548
549<li>... <em>allowed</em> to add or remove global variables from the current
550Module.</li>
551
552<li>... <em>allowed</em> to maintain state across invocations of
553 <a href="#runOnSCC"><tt>runOnSCC</tt></a> (including global data).</li>
554</ol>
555
556<p>Implementing a <tt>CallGraphSCCPass</tt> is slightly tricky in some cases
557because it has to handle SCCs with more than one node in it. All of the virtual
558methods described below should return true if they modified the program, or
559false if they didn't.</p>
560
561</div>
562
563<!-- _______________________________________________________________________ -->
564<div class="doc_subsubsection">
Devang Patelc20048d2007-01-23 22:56:28 +0000[diff] [blame]565 <a name="doInitialization_scc">The <tt>doInitialization(CallGraph &amp;)</tt>
Chris Lattner8fdb2462004-09-18 06:39:35 +0000[diff] [blame]566 method</a>
567</div>
568
569<div class="doc_text">
570
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]571<div class="doc_code"><pre>
Devang Patelc20048d2007-01-23 22:56:28 +0000[diff] [blame]572 <b>virtual bool</b> doInitialization(CallGraph &amp;CG);
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]573</pre></div>
Chris Lattner8fdb2462004-09-18 06:39:35 +0000[diff] [blame]574
575<p>The <tt>doIninitialize</tt> method is allowed to do most of the things that
576<tt>CallGraphSCCPass</tt>'s are not allowed to do. They can add and remove
577functions, get pointers to functions, etc. The <tt>doInitialization</tt> method
578is designed to do simple initialization type of stuff that does not depend on
579the SCCs being processed. The <tt>doInitialization</tt> method call is not
580scheduled to overlap with any other pass executions (thus it should be very
581fast).</p>
582
583</div>
584
585<!-- _______________________________________________________________________ -->
586<div class="doc_subsubsection">
587 <a name="runOnSCC">The <tt>runOnSCC</tt> method</a>
588</div>
589
590<div class="doc_text">
591
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]592<div class="doc_code"><pre>
Chris Lattner8fdb2462004-09-18 06:39:35 +0000[diff] [blame]593 <b>virtual bool</b> runOnSCC(const std::vector&lt;CallGraphNode *&gt; &amp;SCCM) = 0;
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]594</pre></div>
Chris Lattner8fdb2462004-09-18 06:39:35 +0000[diff] [blame]595
596<p>The <tt>runOnSCC</tt> method performs the interesting work of the pass, and
597should return true if the module was modified by the transformation, false
598otherwise.</p>
599
600</div>
601
602<!-- _______________________________________________________________________ -->
603<div class="doc_subsubsection">
Devang Patelc20048d2007-01-23 22:56:28 +0000[diff] [blame]604 <a name="doFinalization_scc">The <tt>doFinalization(CallGraph
Chris Lattner8fdb2462004-09-18 06:39:35 +0000[diff] [blame]605 &amp;)</tt> method</a>
606</div>
607
608<div class="doc_text">
609
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]610<div class="doc_code"><pre>
Devang Patelc20048d2007-01-23 22:56:28 +0000[diff] [blame]611 <b>virtual bool</b> doFinalization(CallGraph &amp;CG);
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]612</pre></div>
Chris Lattner8fdb2462004-09-18 06:39:35 +0000[diff] [blame]613
614<p>The <tt>doFinalization</tt> method is an infrequently used method that is
615called when the pass framework has finished calling <a
616href="#runOnFunction"><tt>runOnFunction</tt></a> for every function in the
617program being compiled.</p>
618
619</div>
620
621<!-- ======================================================================= -->
622<div class="doc_subsection">
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]623 <a name="FunctionPass">The <tt>FunctionPass</tt> class</a>
624</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]625
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]626<div class="doc_text">
627
Chris Lattnerf6278922004-09-20 04:36:29 +0000[diff] [blame]628<p>In contrast to <tt>ModulePass</tt> subclasses, <tt><a
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]629href="http://llvm.org/doxygen/classllvm_1_1Pass.html">FunctionPass</a></tt>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]630subclasses do have a predictable, local behavior that can be expected by the
631system. All <tt>FunctionPass</tt> execute on each function in the program
Misha Brukmanef6a6a62003-08-21 22:14:26 +0000[diff] [blame]632independent of all of the other functions in the program.
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]633<tt>FunctionPass</tt>'s do not require that they are executed in a particular
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]634order, and <tt>FunctionPass</tt>'s do not modify external functions.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]635
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]636<p>To be explicit, <tt>FunctionPass</tt> subclasses are not allowed to:</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]637
638<ol>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]639<li>Modify a Function other than the one currently being processed.</li>
640<li>Add or remove Function's from the current Module.</li>
641<li>Add or remove global variables from the current Module.</li>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]642<li>Maintain state across invocations of
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]643 <a href="#runOnFunction"><tt>runOnFunction</tt></a> (including global data)</li>
644</ol>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]645
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]646<p>Implementing a <tt>FunctionPass</tt> is usually straightforward (See the <a
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]647href="#basiccode">Hello World</a> pass for example). <tt>FunctionPass</tt>'s
648may overload three virtual methods to do their work. All of these methods
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]649should return true if they modified the program, or false if they didn't.</p>
650
651</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]652
653<!-- _______________________________________________________________________ -->
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]654<div class="doc_subsubsection">
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]655 <a name="doInitialization_mod">The <tt>doInitialization(Module &amp;)</tt>
656 method</a>
657</div>
658
659<div class="doc_text">
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]660
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]661<div class="doc_code"><pre>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]662 <b>virtual bool</b> doInitialization(Module &amp;M);
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]663</pre></div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]664
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]665<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]666<tt>FunctionPass</tt>'s are not allowed to do. They can add and remove
Chris Lattnerd0713f92002-09-12 17:06:43 +0000[diff] [blame]667functions, get pointers to functions, etc. The <tt>doInitialization</tt> method
668is designed to do simple initialization type of stuff that does not depend on
669the functions being processed. The <tt>doInitialization</tt> method call is not
670scheduled to overlap with any other pass executions (thus it should be very
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]671fast).</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]672
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]673<p>A good example of how this method should be used is the <a
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]674href="http://llvm.org/doxygen/LowerAllocations_8cpp-source.html">LowerAllocations</a>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]675pass. This pass converts <tt>malloc</tt> and <tt>free</tt> instructions into
Misha Brukmanef6a6a62003-08-21 22:14:26 +0000[diff] [blame]676platform dependent <tt>malloc()</tt> and <tt>free()</tt> function calls. It
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]677uses the <tt>doInitialization</tt> method to get a reference to the malloc and
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]678free functions that it needs, adding prototypes to the module if necessary.</p>
679
680</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]681
682<!-- _______________________________________________________________________ -->
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]683<div class="doc_subsubsection">
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]684 <a name="runOnFunction">The <tt>runOnFunction</tt> method</a>
685</div>
686
687<div class="doc_text">
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]688
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]689<div class="doc_code"><pre>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]690 <b>virtual bool</b> runOnFunction(Function &amp;F) = 0;
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]691</pre></div><p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]692
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]693<p>The <tt>runOnFunction</tt> method must be implemented by your subclass to do
694the transformation or analysis work of your pass. As usual, a true value should
695be returned if the function is modified.</p>
696
697</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]698
699<!-- _______________________________________________________________________ -->
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]700<div class="doc_subsubsection">
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]701 <a name="doFinalization_mod">The <tt>doFinalization(Module
702 &amp;)</tt> method</a>
703</div>
704
705<div class="doc_text">
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]706
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]707<div class="doc_code"><pre>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]708 <b>virtual bool</b> doFinalization(Module &amp;M);
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]709</pre></div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]710
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]711<p>The <tt>doFinalization</tt> method is an infrequently used method that is
712called when the pass framework has finished calling <a
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]713href="#runOnFunction"><tt>runOnFunction</tt></a> for every function in the
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]714program being compiled.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]715
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]716</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]717
718<!-- ======================================================================= -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]719<div class="doc_subsection">
Devang Patel2e8f27d2007-03-19 22:21:25 +0000[diff] [blame]720 <a name="LoopPass">The <tt>LoopPass</tt> class </a>
721</div>
722
723<div class="doc_text">
724
725<p> All <tt>LoopPass</tt> execute on each loop in the function independent of
726all of the other loops in the function. <tt>LoopPass</tt> processes loops in
727loop nest order such that outer most loop is processed last. </p>
728
729<p> <tt>LoopPass</tt> subclasses are allowed to update loop nest using
730<tt>LPPassManager</tt> interface. Implementing a loop pass is usually
731straightforward. <tt>Looppass</tt>'s may overload three virtual methods to
732do their work. All these methods should return true if they modified the
733program, or false if they didn't. </p>
734</div>
735
736<!-- _______________________________________________________________________ -->
737<div class="doc_subsubsection">
738 <a name="doInitialization_loop">The <tt>doInitialization(Loop *,
739 LPPassManager &amp;)</tt>
740 method</a>
741</div>
742
743<div class="doc_text">
744
745<div class="doc_code"><pre>
746 <b>virtual bool</b> doInitialization(Loop *, LPPassManager &amp;LPM);
747</pre></div>
748
Chris Lattnerb5c87f62007-05-18 05:36:14 +0000[diff] [blame]749<p>The <tt>doInitialization</tt> method is designed to do simple initialization
Devang Patel2e8f27d2007-03-19 22:21:25 +0000[diff] [blame]750type of stuff that does not depend on the functions being processed. The
751<tt>doInitialization</tt> method call is not scheduled to overlap with any
752other pass executions (thus it should be very fast). LPPassManager
753interface should be used to access Function or Module level analysis
754information.</p>
755
756</div>
757
758
759<!-- _______________________________________________________________________ -->
760<div class="doc_subsubsection">
761 <a name="runOnLoop">The <tt>runOnLoop</tt> method</a>
762</div>
763
764<div class="doc_text">
765
766<div class="doc_code"><pre>
767 <b>virtual bool</b> runOnLoop(Loop *, LPPassManager &amp;LPM) = 0;
768</pre></div><p>
769
770<p>The <tt>runOnLoop</tt> method must be implemented by your subclass to do
771the transformation or analysis work of your pass. As usual, a true value should
772be returned if the function is modified. <tt>LPPassManager</tt> interface
773should be used to update loop nest.</p>
774
775</div>
776
777<!-- _______________________________________________________________________ -->
778<div class="doc_subsubsection">
779 <a name="doFinalization_loop">The <tt>doFinalization()</tt> method</a>
780</div>
781
782<div class="doc_text">
783
784<div class="doc_code"><pre>
785 <b>virtual bool</b> doFinalization();
786</pre></div>
787
788<p>The <tt>doFinalization</tt> method is an infrequently used method that is
789called when the pass framework has finished calling <a
790href="#runOnLoop"><tt>runOnLoop</tt></a> for every loop in the
791program being compiled. </p>
792
793</div>
794
795
796
797<!-- ======================================================================= -->
798<div class="doc_subsection">
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]799 <a name="BasicBlockPass">The <tt>BasicBlockPass</tt> class</a>
800</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]801
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]802<div class="doc_text">
803
804<p><tt>BasicBlockPass</tt>'s are just like <a
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]805href="#FunctionPass"><tt>FunctionPass</tt></a>'s, except that they must limit
806their scope of inspection and modification to a single basic block at a time.
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]807As such, they are <b>not</b> allowed to do any of the following:</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]808
809<ol>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]810<li>Modify or inspect any basic blocks outside of the current one</li>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]811<li>Maintain state across invocations of
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]812 <a href="#runOnBasicBlock"><tt>runOnBasicBlock</tt></a></li>
Reid Spencer1bc19342004-12-11 05:12:57 +0000[diff] [blame]813<li>Modify the control flow graph (by altering terminator instructions)</li>
814<li>Any of the things forbidden for
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]815 <a href="#FunctionPass"><tt>FunctionPass</tt></a>es.</li>
816</ol>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]817
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]818<p><tt>BasicBlockPass</tt>es are useful for traditional local and "peephole"
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]819optimizations. They may override the same <a
Chris Lattnerd0713f92002-09-12 17:06:43 +0000[diff] [blame]820href="#doInitialization_mod"><tt>doInitialization(Module &amp;)</tt></a> and <a
821href="#doFinalization_mod"><tt>doFinalization(Module &amp;)</tt></a> methods that <a
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]822href="#FunctionPass"><tt>FunctionPass</tt></a>'s have, but also have the following virtual methods that may also be implemented:</p>
823
824</div>
Chris Lattnerd0713f92002-09-12 17:06:43 +0000[diff] [blame]825
826<!-- _______________________________________________________________________ -->
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]827<div class="doc_subsubsection">
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]828 <a name="doInitialization_fn">The <tt>doInitialization(Function
829 &amp;)</tt> method</a>
830</div>
831
832<div class="doc_text">
Chris Lattnerd0713f92002-09-12 17:06:43 +0000[diff] [blame]833
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]834<div class="doc_code"><pre>
Chris Lattnerd0713f92002-09-12 17:06:43 +0000[diff] [blame]835 <b>virtual bool</b> doInitialization(Function &amp;F);
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]836</pre></div>
Chris Lattnerd0713f92002-09-12 17:06:43 +0000[diff] [blame]837
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]838<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]839<tt>BasicBlockPass</tt>'s are not allowed to do, but that
840<tt>FunctionPass</tt>'s can. The <tt>doInitialization</tt> method is designed
Reid Spencer1bc19342004-12-11 05:12:57 +0000[diff] [blame]841to do simple initialization that does not depend on the
Chris Lattnerd0713f92002-09-12 17:06:43 +0000[diff] [blame]842BasicBlocks being processed. The <tt>doInitialization</tt> method call is not
843scheduled to overlap with any other pass executions (thus it should be very
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]844fast).</p>
Chris Lattnerd0713f92002-09-12 17:06:43 +0000[diff] [blame]845
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]846</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]847
848<!-- _______________________________________________________________________ -->
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]849<div class="doc_subsubsection">
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]850 <a name="runOnBasicBlock">The <tt>runOnBasicBlock</tt> method</a>
851</div>
852
853<div class="doc_text">
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]854
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]855<div class="doc_code"><pre>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]856 <b>virtual bool</b> runOnBasicBlock(BasicBlock &amp;BB) = 0;
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]857</pre></div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]858
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]859<p>Override this function to do the work of the <tt>BasicBlockPass</tt>. This
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]860function is not allowed to inspect or modify basic blocks other than the
861parameter, and are not allowed to modify the CFG. A true value must be returned
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]862if the basic block is modified.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]863
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]864</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]865
Chris Lattnerd0713f92002-09-12 17:06:43 +0000[diff] [blame]866<!-- _______________________________________________________________________ -->
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]867<div class="doc_subsubsection">
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]868 <a name="doFinalization_fn">The <tt>doFinalization(Function &amp;)</tt>
869 method</a>
870</div>
871
872<div class="doc_text">
Chris Lattnerd0713f92002-09-12 17:06:43 +0000[diff] [blame]873
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]874<div class="doc_code"><pre>
Chris Lattnerd0713f92002-09-12 17:06:43 +0000[diff] [blame]875 <b>virtual bool</b> doFinalization(Function &amp;F);
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]876</pre></div>
Chris Lattnerd0713f92002-09-12 17:06:43 +0000[diff] [blame]877
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]878<p>The <tt>doFinalization</tt> method is an infrequently used method that is
879called when the pass framework has finished calling <a
Chris Lattnerd0713f92002-09-12 17:06:43 +0000[diff] [blame]880href="#runOnBasicBlock"><tt>runOnBasicBlock</tt></a> for every BasicBlock in the
881program being compiled. This can be used to perform per-function
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]882finalization.</p>
Chris Lattnerd0713f92002-09-12 17:06:43 +0000[diff] [blame]883
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]884</div>
Chris Lattnerd0713f92002-09-12 17:06:43 +0000[diff] [blame]885
Brian Gaekecab8b6f2003-07-17 18:53:20 +0000[diff] [blame]886<!-- ======================================================================= -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]887<div class="doc_subsection">
888 <a name="MachineFunctionPass">The <tt>MachineFunctionPass</tt> class</a>
889</div>
Brian Gaekecab8b6f2003-07-17 18:53:20 +0000[diff] [blame]890
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]891<div class="doc_text">
892
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]893<p>A <tt>MachineFunctionPass</tt> is a part of the LLVM code generator that
894executes on the machine-dependent representation of each LLVM function in the
895program. A <tt>MachineFunctionPass</tt> is also a <tt>FunctionPass</tt>, so all
Brian Gaekecab8b6f2003-07-17 18:53:20 +0000[diff] [blame]896the restrictions that apply to a <tt>FunctionPass</tt> also apply to it.
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]897<tt>MachineFunctionPass</tt>es also have additional restrictions. In particular,
898<tt>MachineFunctionPass</tt>es are not allowed to do any of the following:</p>
Brian Gaekecab8b6f2003-07-17 18:53:20 +0000[diff] [blame]899
900<ol>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]901<li>Modify any LLVM Instructions, BasicBlocks or Functions.</li>
902<li>Modify a MachineFunction other than the one currently being processed.</li>
903<li>Add or remove MachineFunctions from the current Module.</li>
904<li>Add or remove global variables from the current Module.</li>
905<li>Maintain state across invocations of <a
906href="#runOnMachineFunction"><tt>runOnMachineFunction</tt></a> (including global
907data)</li>
908</ol>
Brian Gaekecab8b6f2003-07-17 18:53:20 +0000[diff] [blame]909
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]910</div>
Chris Lattnerd0713f92002-09-12 17:06:43 +0000[diff] [blame]911
Brian Gaeke6a33f362003-07-22 20:53:20 +0000[diff] [blame]912<!-- _______________________________________________________________________ -->
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]913<div class="doc_subsubsection">
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]914 <a name="runOnMachineFunction">The <tt>runOnMachineFunction(MachineFunction
915 &amp;MF)</tt> method</a>
916</div>
917
918<div class="doc_text">
Brian Gaeke6a33f362003-07-22 20:53:20 +0000[diff] [blame]919
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]920<div class="doc_code"><pre>
Brian Gaeke6a33f362003-07-22 20:53:20 +0000[diff] [blame]921 <b>virtual bool</b> runOnMachineFunction(MachineFunction &amp;MF) = 0;
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]922</pre></div>
Brian Gaeke6a33f362003-07-22 20:53:20 +0000[diff] [blame]923
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]924<p><tt>runOnMachineFunction</tt> can be considered the main entry point of a
925<tt>MachineFunctionPass</tt>; that is, you should override this method to do the
926work of your <tt>MachineFunctionPass</tt>.</p>
Brian Gaeke6a33f362003-07-22 20:53:20 +0000[diff] [blame]927
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]928<p>The <tt>runOnMachineFunction</tt> method is called on every
Brian Gaeke6a33f362003-07-22 20:53:20 +0000[diff] [blame]929<tt>MachineFunction</tt> in a <tt>Module</tt>, so that the
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]930<tt>MachineFunctionPass</tt> may perform optimizations on the machine-dependent
931representation of the function. If you want to get at the LLVM <tt>Function</tt>
932for the <tt>MachineFunction</tt> you're working on, use
933<tt>MachineFunction</tt>'s <tt>getFunction()</tt> accessor method -- but
934remember, you may not modify the LLVM <tt>Function</tt> or its contents from a
935<tt>MachineFunctionPass</tt>.</p>
936
937</div>
Brian Gaeke6a33f362003-07-22 20:53:20 +0000[diff] [blame]938
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]939<!-- *********************************************************************** -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]940<div class="doc_section">
941 <a name="registration">Pass registration</a>
942</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]943<!-- *********************************************************************** -->
944
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]945<div class="doc_text">
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]946
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]947<p>In the <a href="#basiccode">Hello World</a> example pass we illustrated how
948pass registration works, and discussed some of the reasons that it is used and
949what it does. Here we discuss how and why passes are registered.</p>
950
Chris Lattnerc8603c22006-08-27 23:18:52 +0000[diff] [blame]951<p>As we saw above, passes are registered with the <b><tt>RegisterPass</tt></b>
952template, which requires you to pass at least two
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]953parameters. The first parameter is the name of the pass that is to be used on
954the command line to specify that the pass should be added to a program (for
Chris Lattnerc8603c22006-08-27 23:18:52 +0000[diff] [blame]955example, with <tt>opt</tt> or <tt>bugpoint</tt>). The second argument is the
956name of the pass, which is to be used for the <tt>--help</tt> output of
957programs, as
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]958well as for debug output generated by the <tt>--debug-pass</tt> option.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]959
Chris Lattnerc8603c22006-08-27 23:18:52 +0000[diff] [blame]960<p>If you want your pass to be easily dumpable, you should
961implement the virtual <tt>print</tt> method:</p>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]962
963</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]964
965<!-- _______________________________________________________________________ -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]966<div class="doc_subsubsection">
967 <a name="print">The <tt>print</tt> method</a>
968</div>
969
970<div class="doc_text">
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]971
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]972<div class="doc_code"><pre>
Bill Wendling832171c2006-12-07 20:04:42 +0000[diff] [blame]973 <b>virtual void</b> print(llvm::OStream &amp;O, <b>const</b> Module *M) <b>const</b>;
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]974</pre></div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]975
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]976<p>The <tt>print</tt> method must be implemented by "analyses" in order to print
977a human readable version of the analysis results. This is useful for debugging
978an analysis itself, as well as for other people to figure out how an analysis
Chris Lattnerc8603c22006-08-27 23:18:52 +0000[diff] [blame]979works. Use the <tt>opt -analyze</tt> argument to invoke this method.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]980
Bill Wendling832171c2006-12-07 20:04:42 +0000[diff] [blame]981<p>The <tt>llvm::OStream</tt> parameter specifies the stream to write the results on,
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]982and 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]983program that has been analyzed. Note however that this pointer may be null in
984certain circumstances (such as calling the <tt>Pass::dump()</tt> from a
985debugger), so it should only be used to enhance debug output, it should not be
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]986depended on.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]987
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]988</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]989
990<!-- *********************************************************************** -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]991<div class="doc_section">
992 <a name="interaction">Specifying interactions between passes</a>
993</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]994<!-- *********************************************************************** -->
995
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]996<div class="doc_text">
997
998<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]999that passes interact with each other correctly. Because <tt>PassManager</tt>
1000tries to <a href="#passmanager">optimize the execution of passes</a> it must
1001know how the passes interact with each other and what dependencies exist between
1002the various passes. To track this, each pass can declare the set of passes that
1003are required to be executed before the current pass, and the passes which are
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1004invalidated by the current pass.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1005
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1006<p>Typically this functionality is used to require that analysis results are
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1007computed before your pass is run. Running arbitrary transformation passes can
1008invalidate the computed analysis results, which is what the invalidation set
1009specifies. If a pass does not implement the <tt><a
1010href="#getAnalysisUsage">getAnalysisUsage</a></tt> method, it defaults to not
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1011having any prerequisite passes, and invalidating <b>all</b> other passes.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1012
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1013</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1014
1015<!-- _______________________________________________________________________ -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1016<div class="doc_subsubsection">
1017 <a name="getAnalysisUsage">The <tt>getAnalysisUsage</tt> method</a>
1018</div>
1019
1020<div class="doc_text">
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1021
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1022<div class="doc_code"><pre>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1023 <b>virtual void</b> getAnalysisUsage(AnalysisUsage &amp;Info) <b>const</b>;
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1024</pre></div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1025
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1026<p>By implementing the <tt>getAnalysisUsage</tt> method, the required and
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1027invalidated sets may be specified for your transformation. The implementation
1028should fill in the <tt><a
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]1029href="http://llvm.org/doxygen/classllvm_1_1AnalysisUsage.html">AnalysisUsage</a></tt>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1030object with information about which passes are required and not invalidated. To
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]1031do this, a pass may call any of the following methods on the AnalysisUsage
1032object:</p>
1033</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1034
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]1035<!-- _______________________________________________________________________ -->
1036<div class="doc_subsubsection">
1037 <a name="AU::addRequired">The <tt>AnalysisUsage::addRequired&lt;&gt;</tt> and <tt>AnalysisUsage::addRequiredTransitive&lt;&gt;</tt> methods</a>
1038</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1039
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]1040<div class="doc_text">
1041<p>
Reid Spencer1bc19342004-12-11 05:12:57 +0000[diff] [blame]1042If your pass requires a previous pass to be executed (an analysis for example),
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]1043it can use one of these methods to arrange for it to be run before your pass.
1044LLVM has many different types of analyses and passes that can be required,
Reid Spencer1bc19342004-12-11 05:12:57 +0000[diff] [blame]1045spanning the range from <tt>DominatorSet</tt> to <tt>BreakCriticalEdges</tt>.
1046Requiring <tt>BreakCriticalEdges</tt>, for example, guarantees that there will
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]1047be no critical edges in the CFG when your pass has been run.
1048</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1049
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]1050<p>
1051Some analyses chain to other analyses to do their job. For example, an <a
1052href="AliasAnalysis.html">AliasAnalysis</a> implementation is required to <a
1053href="AliasAnalysis.html#chaining">chain</a> to other alias analysis passes. In
1054cases where analyses chain, the <tt>addRequiredTransitive</tt> method should be
1055used instead of the <tt>addRequired</tt> method. This informs the PassManager
1056that the transitively required pass should be alive as long as the requiring
1057pass is.
1058</p>
1059</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1060
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]1061<!-- _______________________________________________________________________ -->
1062<div class="doc_subsubsection">
1063 <a name="AU::addPreserved">The <tt>AnalysisUsage::addPreserved&lt;&gt;</tt> method</a>
1064</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1065
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]1066<div class="doc_text">
1067<p>
1068One of the jobs of the PassManager is to optimize how and when analyses are run.
1069In particular, it attempts to avoid recomputing data unless it needs to. For
1070this reason, passes are allowed to declare that they preserve (i.e., they don't
1071invalidate) an existing analysis if it's available. For example, a simple
Reid Spencer1bc19342004-12-11 05:12:57 +0000[diff] [blame]1072constant folding pass would not modify the CFG, so it can't possibly affect the
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]1073results of dominator analysis. By default, all passes are assumed to invalidate
1074all others.
1075</p>
1076
1077<p>
1078The <tt>AnalysisUsage</tt> class provides several methods which are useful in
1079certain circumstances that are related to <tt>addPreserved</tt>. In particular,
1080the <tt>setPreservesAll</tt> method can be called to indicate that the pass does
1081not modify the LLVM program at all (which is true for analyses), and the
1082<tt>setPreservesCFG</tt> method can be used by transformations that change
1083instructions in the program but do not modify the CFG or terminator instructions
1084(note that this property is implicitly set for <a
1085href="#BasicBlockPass">BasicBlockPass</a>'s).
1086</p>
1087
1088<p>
1089<tt>addPreserved</tt> is particularly useful for transformations like
1090<tt>BreakCriticalEdges</tt>. This pass knows how to update a small set of loop
1091and dominator related analyses if they exist, so it can preserve them, despite
1092the fact that it hacks on the CFG.
1093</p>
1094</div>
1095
1096<!-- _______________________________________________________________________ -->
1097<div class="doc_subsubsection">
1098 <a name="AU::examples">Example implementations of <tt>getAnalysisUsage</tt></a>
1099</div>
1100
1101<div class="doc_text">
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1102
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1103<div class="doc_code"><pre>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1104 <i>// This is an example implementation from an analysis, which does not modify
1105 // the program at all, yet has a prerequisite.</i>
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]1106 <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]1107 AU.setPreservesAll();
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]1108 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]1109 }
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1110</pre></div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1111
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1112<p>and:</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1113
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1114<div class="doc_code"><pre>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1115 <i>// This example modifies the program, but does not modify the CFG</i>
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]1116 <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]1117 AU.setPreservesCFG();
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]1118 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]1119 }
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1120</pre></div>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1121
1122</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1123
1124<!-- _______________________________________________________________________ -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1125<div class="doc_subsubsection">
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]1126 <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]1127</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1128
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1129<div class="doc_text">
1130
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]1131<p>The <tt>Pass::getAnalysis&lt;&gt;</tt> method is automatically inherited by
1132your class, providing you with access to the passes that you declared that you
1133required with the <a href="#getAnalysisUsage"><tt>getAnalysisUsage</tt></a>
1134method. It takes a single template argument that specifies which pass class you
1135want, and returns a reference to that pass. For example:</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1136
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1137<div class="doc_code"><pre>
Chris Lattnera5776302004-03-17 21:33:32 +0000[diff] [blame]1138 bool LICM::runOnFunction(Function &amp;F) {
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]1139 LoopInfo &amp;LI = getAnalysis&lt;LoopInfo&gt;();
1140 ...
1141 }
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1142</pre></div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1143
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1144<p>This method call returns a reference to the pass desired. You may get a
1145runtime assertion failure if you attempt to get an analysis that you did not
1146declare as required in your <a
1147href="#getAnalysisUsage"><tt>getAnalysisUsage</tt></a> implementation. This
1148method can be called by your <tt>run*</tt> method implementation, or by any
Devang Patel3c1ca0b2007-04-16 21:28:14 +0000[diff] [blame]1149other local method invoked by your <tt>run*</tt> method.
1150
1151A module level pass can use function level analysis info using this interface.
1152For example:</p>
1153
1154<div class="doc_code"><pre>
1155 bool ModuleLevelPass::runOnModule(Module &amp;M) {
1156 ...
Devang Patelf23de112007-04-17 00:17:11 +0000[diff] [blame]1157 DominatorTree &amp;DT = getAnalysis&lt;DominatorTree&gt;(Func);
Devang Patel3c1ca0b2007-04-16 21:28:14 +0000[diff] [blame]1158 ...
1159 }
1160</pre></div>
1161
Chris Lattnerb5c87f62007-05-18 05:36:14 +0000[diff] [blame]1162<p>In above example, runOnFunction for DominatorTree is called by pass manager
Devang Patel3c1ca0b2007-04-16 21:28:14 +0000[diff] [blame]1163before returning a reference to the desired pass.</p>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1164
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]1165<p>
1166If your pass is capable of updating analyses if they exist (e.g.,
1167<tt>BreakCriticalEdges</tt>, as described above), you can use the
1168<tt>getAnalysisToUpdate</tt> method, which returns a pointer to the analysis if
1169it is active. For example:</p>
1170
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1171<div class="doc_code"><pre>
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]1172 ...
1173 if (DominatorSet *DS = getAnalysisToUpdate&lt;DominatorSet&gt;()) {
1174 <i>// A DominatorSet is active. This code will update it.</i>
1175 }
1176 ...
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1177</pre></div>
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]1178
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1179</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1180
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1181<!-- *********************************************************************** -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1182<div class="doc_section">
1183 <a name="analysisgroup">Implementing Analysis Groups</a>
1184</div>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1185<!-- *********************************************************************** -->
1186
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1187<div class="doc_text">
1188
1189<p>Now that we understand the basics of how passes are defined, how the are
1190used, 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]1191fancier. All of the pass relationships that we have seen so far are very
1192simple: one pass depends on one other specific pass to be run before it can run.
1193For many applications, this is great, for others, more flexibility is
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1194required.</p>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1195
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1196<p>In particular, some analyses are defined such that there is a single simple
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1197interface to the analysis results, but multiple ways of calculating them.
1198Consider alias analysis for example. The most trivial alias analysis returns
1199"may alias" for any alias query. The most sophisticated analysis a
1200flow-sensitive, context-sensitive interprocedural analysis that can take a
1201significant amount of time to execute (and obviously, there is a lot of room
1202between these two extremes for other implementations). To cleanly support
1203situations like this, the LLVM Pass Infrastructure supports the notion of
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1204Analysis Groups.</p>
1205
1206</div>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1207
1208<!-- _______________________________________________________________________ -->
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]1209<div class="doc_subsubsection">
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1210 <a name="agconcepts">Analysis Group Concepts</a>
1211</div>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1212
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1213<div class="doc_text">
1214
1215<p>An Analysis Group is a single simple interface that may be implemented by
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1216multiple different passes. Analysis Groups can be given human readable names
1217just like passes, but unlike passes, they need not derive from the <tt>Pass</tt>
1218class. An analysis group may have one or more implementations, one of which is
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1219the "default" implementation.</p>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1220
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1221<p>Analysis groups are used by client passes just like other passes are: the
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1222<tt>AnalysisUsage::addRequired()</tt> and <tt>Pass::getAnalysis()</tt> methods.
1223In order to resolve this requirement, the <a href="#passmanager">PassManager</a>
1224scans the available passes to see if any implementations of the analysis group
1225are available. If none is available, the default implementation is created for
1226the pass to use. All standard rules for <A href="#interaction">interaction
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1227between passes</a> still apply.</p>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1228
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1229<p>Although <a href="#registration">Pass Registration</a> is optional for normal
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1230passes, all analysis group implementations must be registered, and must use the
1231<A href="#registerag"><tt>RegisterAnalysisGroup</tt></a> template to join the
1232implementation pool. Also, a default implementation of the interface
1233<b>must</b> be registered with <A
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1234href="#registerag"><tt>RegisterAnalysisGroup</tt></a>.</p>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1235
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1236<p>As a concrete example of an Analysis Group in action, consider the <a
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]1237href="http://llvm.org/doxygen/classllvm_1_1AliasAnalysis.html">AliasAnalysis</a>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1238analysis group. The default implementation of the alias analysis interface (the
1239<tt><a
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]1240href="http://llvm.org/doxygen/structBasicAliasAnalysis.html">basicaa</a></tt>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1241pass) just does a few simple checks that don't require significant analysis to
1242compute (such as: two different globals can never alias each other, etc).
1243Passes that use the <tt><a
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]1244href="http://llvm.org/doxygen/classllvm_1_1AliasAnalysis.html">AliasAnalysis</a></tt>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1245interface (for example the <tt><a
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]1246href="http://llvm.org/doxygen/structGCSE.html">gcse</a></tt> pass), do
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1247not care which implementation of alias analysis is actually provided, they just
1248use the designated interface.</p>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1249
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1250<p>From the user's perspective, commands work just like normal. Issuing the
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1251command '<tt>opt -gcse ...</tt>' will cause the <tt>basicaa</tt> class to be
1252instantiated and added to the pass sequence. Issuing the command '<tt>opt
1253-somefancyaa -gcse ...</tt>' will cause the <tt>gcse</tt> pass to use the
1254<tt>somefancyaa</tt> alias analysis (which doesn't actually exist, it's just a
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1255hypothetical example) instead.</p>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1256
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1257</div>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1258
1259<!-- _______________________________________________________________________ -->
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]1260<div class="doc_subsubsection">
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1261 <a name="registerag">Using <tt>RegisterAnalysisGroup</tt></a>
1262</div>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1263
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1264<div class="doc_text">
1265
1266<p>The <tt>RegisterAnalysisGroup</tt> template is used to register the analysis
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1267group itself as well as add pass implementations to the analysis group. First,
1268an analysis should be registered, with a human readable name provided for it.
1269Unlike registration of passes, there is no command line argument to be specified
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1270for the Analysis Group Interface itself, because it is "abstract":</p>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1271
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1272<div class="doc_code"><pre>
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]1273 <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]1274</pre></div>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1275
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1276<p>Once the analysis is registered, passes can declare that they are valid
1277implementations of the interface by using the following code:</p>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1278
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1279<div class="doc_code"><pre>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1280<b>namespace</b> {
1281 //<i> Analysis Group implementations <b>must</b> be registered normally...</i>
Chris Lattnerc8603c22006-08-27 23:18:52 +0000[diff] [blame]1282 RegisterPass&lt;FancyAA&gt;
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1283 B("<i>somefancyaa</i>", "<i>A more complex alias analysis implementation</i>");
1284
1285 //<i> Declare that we implement the AliasAnalysis interface</i>
Chris Lattnerdc877252006-08-28 00:45:38 +0000[diff] [blame]1286 RegisterAnalysisGroup&lt;<a href="http://llvm.org/doxygen/classllvm_1_1AliasAnalysis.html">AliasAnalysis</a>&gt; C(B);
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1287}
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1288</pre></div>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1289
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1290<p>This just shows a class <tt>FancyAA</tt> that is registered normally, then
1291uses the <tt>RegisterAnalysisGroup</tt> template to "join" the <tt><a
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]1292href="http://llvm.org/doxygen/classllvm_1_1AliasAnalysis.html">AliasAnalysis</a></tt>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1293analysis group. Every implementation of an analysis group should join using
1294this template. A single pass may join multiple different analysis groups with
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1295no problem.</p>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1296
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1297<div class="doc_code"><pre>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1298<b>namespace</b> {
1299 //<i> Analysis Group implementations <b>must</b> be registered normally...</i>
Chris Lattnerc8603c22006-08-27 23:18:52 +0000[diff] [blame]1300 RegisterPass&lt;<a href="http://llvm.org/doxygen/structBasicAliasAnalysis.html">BasicAliasAnalysis</a>&gt;
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1301 D("<i>basicaa</i>", "<i>Basic Alias Analysis (default AA impl)</i>");
1302
1303 //<i> Declare that we implement the AliasAnalysis interface</i>
Chris Lattnerdc877252006-08-28 00:45:38 +0000[diff] [blame]1304 RegisterAnalysisGroup&lt;<a href="http://llvm.org/doxygen/classllvm_1_1AliasAnalysis.html">AliasAnalysis</a>, <b>true</b>&gt; E(D);
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1305}
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1306</pre></div>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1307
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1308<p>Here we show how the default implementation is specified (using the extra
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1309argument to the <tt>RegisterAnalysisGroup</tt> template). There must be exactly
1310one default implementation available at all times for an Analysis Group to be
1311used. Here we declare that the <tt><a
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]1312href="http://llvm.org/doxygen/structBasicAliasAnalysis.html">BasicAliasAnalysis</a></tt>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1313pass is the default implementation for the interface.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1314
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1315</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1316
1317<!-- *********************************************************************** -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1318<div class="doc_section">
Tanya Lattnerd5383652004-11-19 01:25:14 +0000[diff] [blame]1319 <a name="passStatistics">Pass Statistics</a>
1320</div>
1321<!-- *********************************************************************** -->
1322
1323<div class="doc_text">
Tanya Lattner05f8d5f2004-11-19 01:26:37 +0000[diff] [blame]1324<p>The <a
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]1325href="http://llvm.org/doxygen/Statistic_8h-source.html"><tt>Statistic</tt></a>
John Criswell0b1010e2005-11-28 23:25:41 +0000[diff] [blame]1326class is designed to be an easy way to expose various success
Tanya Lattnerd5383652004-11-19 01:25:14 +0000[diff] [blame]1327metrics from passes. These statistics are printed at the end of a
1328run, when the -stats command line option is enabled on the command
Tanya Lattner05f8d5f2004-11-19 01:26:37 +0000[diff] [blame]1329line. 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]1330
1331</div>
1332
1333
1334<!-- *********************************************************************** -->
1335<div class="doc_section">
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1336 <a name="passmanager">What PassManager does</a>
1337</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1338<!-- *********************************************************************** -->
1339
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1340<div class="doc_text">
1341
1342<p>The <a
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]1343href="http://llvm.org/doxygen/PassManager_8h-source.html"><tt>PassManager</tt></a>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1344<a
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]1345href="http://llvm.org/doxygen/classllvm_1_1PassManager.html">class</a>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1346takes a list of passes, ensures their <a href="#interaction">prerequisites</a>
1347are set up correctly, and then schedules passes to run efficiently. All of the
1348LLVM tools that run passes use the <tt>PassManager</tt> for execution of these
1349passes.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1350
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1351<p>The <tt>PassManager</tt> does two main things to try to reduce the execution
1352time of a series of passes:</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1353
1354<ol>
1355<li><b>Share analysis results</b> - The PassManager attempts to avoid
1356recomputing analysis results as much as possible. This means keeping track of
1357which analyses are available already, which analyses get invalidated, and which
1358analyses are needed to be run for a pass. An important part of work is that the
1359<tt>PassManager</tt> tracks the exact lifetime of all analysis results, allowing
1360it to <a href="#releaseMemory">free memory</a> allocated to holding analysis
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1361results as soon as they are no longer needed.</li>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1362
1363<li><b>Pipeline the execution of passes on the program</b> - The
1364<tt>PassManager</tt> attempts to get better cache and memory usage behavior out
1365of a series of passes by pipelining the passes together. This means that, given
1366a series of consequtive <a href="#FunctionPass"><tt>FunctionPass</tt></a>'s, it
1367will execute all of the <a href="#FunctionPass"><tt>FunctionPass</tt></a>'s on
1368the first function, then all of the <a
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1369href="#FunctionPass"><tt>FunctionPass</tt></a>es on the second function,
1370etc... until the entire program has been run through the passes.
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1371
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1372<p>This improves the cache behavior of the compiler, because it is only touching
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1373the LLVM program representation for a single function at a time, instead of
1374traversing the entire program. It reduces the memory consumption of compiler,
1375because, for example, only one <a
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]1376href="http://llvm.org/doxygen/classllvm_1_1DominatorSet.html"><tt>DominatorSet</tt></a>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1377needs to be calculated at a time. This also makes it possible some <a
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1378href="#SMP">interesting enhancements</a> in the future.</p></li>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1379
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1380</ol>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1381
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1382<p>The effectiveness of the <tt>PassManager</tt> is influenced directly by how
1383much information it has about the behaviors of the passes it is scheduling. For
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1384example, the "preserved" set is intentionally conservative in the face of an
1385unimplemented <a href="#getAnalysisUsage"><tt>getAnalysisUsage</tt></a> method.
1386Not implementing when it should be implemented will have the effect of not
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1387allowing any analysis results to live across the execution of your pass.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1388
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1389<p>The <tt>PassManager</tt> class exposes a <tt>--debug-pass</tt> command line
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1390options that is useful for debugging pass execution, seeing how things work, and
1391diagnosing when you should be preserving more analyses than you currently are
1392(To get information about all of the variants of the <tt>--debug-pass</tt>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1393option, just type '<tt>opt --help-hidden</tt>').</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1394
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1395<p>By using the <tt>--debug-pass=Structure</tt> option, for example, we can see
1396how our <a href="#basiccode">Hello World</a> pass interacts with other passes.
1397Lets try it out with the <tt>gcse</tt> and <tt>licm</tt> passes:</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1398
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1399<div class="doc_code"><pre>
Reid Spencer7fa6d522005-01-11 05:16:23 +0000[diff] [blame]1400$ 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]1401Module Pass Manager
1402 Function Pass Manager
1403 Dominator Set Construction
1404 Immediate Dominators Construction
1405 Global Common Subexpression Elimination
1406-- Immediate Dominators Construction
1407-- Global Common Subexpression Elimination
1408 Natural Loop Construction
1409 Loop Invariant Code Motion
1410-- Natural Loop Construction
1411-- Loop Invariant Code Motion
1412 Module Verifier
1413-- Dominator Set Construction
1414-- Module Verifier
1415 Bytecode Writer
1416--Bytecode Writer
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1417</pre></div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1418
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1419<p>This output shows us when passes are constructed and when the analysis
1420results are known to be dead (prefixed with '<tt>--</tt>'). Here we see that
1421GCSE uses dominator and immediate dominator information to do its job. The LICM
1422pass uses natural loop information, which uses dominator sets, but not immediate
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1423dominators. Because immediate dominators are no longer useful after the GCSE
1424pass, it is immediately destroyed. The dominator sets are then reused to
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1425compute natural loop information, which is then used by the LICM pass.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1426
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1427<p>After the LICM pass, the module verifier runs (which is automatically added
1428by the '<tt>opt</tt>' tool), which uses the dominator set to check that the
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1429resultant LLVM code is well formed. After it finishes, the dominator set
1430information is destroyed, after being computed once, and shared by three
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1431passes.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1432
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1433<p>Lets see how this changes when we run the <a href="#basiccode">Hello
1434World</a> pass in between the two passes:</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1435
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1436<div class="doc_code"><pre>
Reid Spencer7fa6d522005-01-11 05:16:23 +0000[diff] [blame]1437$ 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]1438Module Pass Manager
1439 Function Pass Manager
1440 Dominator Set Construction
1441 Immediate Dominators Construction
1442 Global Common Subexpression Elimination
1443<b>-- Dominator Set Construction</b>
1444-- Immediate Dominators Construction
1445-- Global Common Subexpression Elimination
1446<b> Hello World Pass
1447-- Hello World Pass
1448 Dominator Set Construction</b>
1449 Natural Loop Construction
1450 Loop Invariant Code Motion
1451-- Natural Loop Construction
1452-- Loop Invariant Code Motion
1453 Module Verifier
1454-- Dominator Set Construction
1455-- Module Verifier
1456 Bytecode Writer
1457--Bytecode Writer
1458Hello: __main
1459Hello: puts
1460Hello: main
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1461</pre></div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1462
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1463<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]1464Dominator Set pass, even though it doesn't modify the code at all! To fix this,
1465we need to add the following <a
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1466href="#getAnalysisUsage"><tt>getAnalysisUsage</tt></a> method to our pass:</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1467
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1468<div class="doc_code"><pre>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1469 <i>// We don't modify the program, so we preserve all analyses</i>
1470 <b>virtual void</b> getAnalysisUsage(AnalysisUsage &amp;AU) <b>const</b> {
1471 AU.setPreservesAll();
1472 }
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1473</pre></div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1474
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1475<p>Now when we run our pass, we get this output:</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1476
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1477<div class="doc_code"><pre>
Reid Spencer7fa6d522005-01-11 05:16:23 +0000[diff] [blame]1478$ 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]1479Pass Arguments: -gcse -hello -licm
1480Module Pass Manager
1481 Function Pass Manager
1482 Dominator Set Construction
1483 Immediate Dominators Construction
1484 Global Common Subexpression Elimination
1485-- Immediate Dominators Construction
1486-- Global Common Subexpression Elimination
1487 Hello World Pass
1488-- Hello World Pass
1489 Natural Loop Construction
1490 Loop Invariant Code Motion
1491-- Loop Invariant Code Motion
1492-- Natural Loop Construction
1493 Module Verifier
1494-- Dominator Set Construction
1495-- Module Verifier
1496 Bytecode Writer
1497--Bytecode Writer
1498Hello: __main
1499Hello: puts
1500Hello: main
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1501</pre></div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1502
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1503<p>Which shows that we don't accidentally invalidate dominator information
1504anymore, and therefore do not have to compute it twice.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1505
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1506</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1507
1508<!-- _______________________________________________________________________ -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1509<div class="doc_subsubsection">
1510 <a name="releaseMemory">The <tt>releaseMemory</tt> method</a>
1511</div>
1512
1513<div class="doc_text">
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1514
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1515<div class="doc_code"><pre>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1516 <b>virtual void</b> releaseMemory();
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1517</pre></div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1518
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1519<p>The <tt>PassManager</tt> automatically determines when to compute analysis
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1520results, and how long to keep them around for. Because the lifetime of the pass
1521object itself is effectively the entire duration of the compilation process, we
1522need some way to free analysis results when they are no longer useful. The
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1523<tt>releaseMemory</tt> virtual method is the way to do this.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1524
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1525<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]1526amount of state (for use by another pass which "requires" your pass and uses the
1527<a href="#getAnalysis">getAnalysis</a> method) you should implement
1528<tt>releaseMEmory</tt> to, well, release the memory allocated to maintain this
1529internal state. This method is called after the <tt>run*</tt> method for the
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1530class, before the next call of <tt>run*</tt> in your pass.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1531
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1532</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1533
1534<!-- *********************************************************************** -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1535<div class="doc_section">
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1536 <a name="registering">Registering dynamically loaded passes</a>
1537</div>
1538<!-- *********************************************************************** -->
1539
1540<div class="doc_text">
1541
1542<p><i>Size matters</i> when constructing production quality tools using llvm,
1543both for the purposes of distribution, and for regulating the resident code size
1544when running on the target system. Therefore, it becomes desirable to
1545selectively use some passes, while omitting others and maintain the flexibility
1546to change configurations later on. You want to be able to do all this, and,
1547provide feedback to the user. This is where pass registration comes into
1548play.</p>
1549
1550<p>The fundamental mechanisms for pass registration are the
1551<tt>MachinePassRegistry</tt> class and subclasses of
1552<tt>MachinePassRegistryNode</tt>.</p>
1553
1554<p>An instance of <tt>MachinePassRegistry</tt> is used to maintain a list of
1555<tt>MachinePassRegistryNode</tt> objects. This instance maintains the list and
1556communicates additions and deletions to the command line interface.</p>
1557
1558<p>An instance of <tt>MachinePassRegistryNode</tt> subclass is used to maintain
1559information provided about a particular pass. This information includes the
1560command line name, the command help string and the address of the function used
1561to create an instance of the pass. A global static constructor of one of these
1562instances <i>registers</i> with a corresponding <tt>MachinePassRegistry</tt>,
1563the static destructor <i>unregisters</i>. Thus a pass that is statically linked
1564in the tool will be registered at start up. A dynamically loaded pass will
1565register on load and unregister at unload.</p>
1566
1567</div>
1568
1569<!-- _______________________________________________________________________ -->
1570<div class="doc_subsection">
1571 <a name="registering_existing">Using existing registries</a>
1572</div>
1573
1574<div class="doc_text">
1575
1576<p>There are predefined registries to track instruction scheduling
1577(<tt>RegisterScheduler</tt>) and register allocation (<tt>RegisterRegAlloc</tt>)
1578machine passes. Here we will describe how to <i>register</i> a register
1579allocator machine pass.</p>
1580
1581<p>Implement your register allocator machine pass. In your register allocator
1582.cpp file add the following include;</p>
1583
1584<div class="doc_code"><pre>
Chris Lattner8f652eb2006-08-11 16:37:02 +0000[diff] [blame]1585 #include "llvm/CodeGen/RegAllocRegistry.h"
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1586</pre></div>
1587
1588<p>Also in your register allocator .cpp file, define a creator function in the
1589form; </p>
1590
1591<div class="doc_code"><pre>
1592 FunctionPass *createMyRegisterAllocator() {
1593 return new MyRegisterAllocator();
1594 }
1595</pre></div>
1596
1597<p>Note that the signature of this function should match the type of
1598<tt>RegisterRegAlloc::FunctionPassCtor</tt>. In the same file add the
1599"installing" declaration, in the form;</p>
1600
1601<div class="doc_code"><pre>
1602 static RegisterRegAlloc myRegAlloc("myregalloc",
1603 " my register allocator help string",
1604 createMyRegisterAllocator);
1605</pre></div>
1606
1607<p>Note the two spaces prior to the help string produces a tidy result on the
1608--help query.</p>
1609
1610<div class="doc_code"><pre>
1611$ llc --help
1612 ...
1613 -regalloc - Register allocator to use: (default = linearscan)
1614 =linearscan - linear scan register allocator
1615 =local - local register allocator
1616 =simple - simple register allocator
1617 =myregalloc - my register allocator help string
1618 ...
1619</pre></div>
1620
1621<p>And that's it. The user is now free to use <tt>-regalloc=myregalloc</tt> as
1622an option. Registering instruction schedulers is similar except use the
Chris Lattner8f652eb2006-08-11 16:37:02 +0000[diff] [blame]1623<tt>RegisterScheduler</tt> class. Note that the
1624<tt>RegisterScheduler::FunctionPassCtor</tt> is significantly different from
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1625<tt>RegisterRegAlloc::FunctionPassCtor</tt>.</p>
1626
1627<p>To force the load/linking of your register allocator into the llc/lli tools,
1628add your creator function's global declaration to "Passes.h" and add a "pseudo"
1629call line to <tt>llvm/Codegen/LinkAllCodegenComponents.h</tt>.</p>
1630
1631</div>
1632
1633
1634<!-- _______________________________________________________________________ -->
1635<div class="doc_subsection">
1636 <a name="registering_new">Creating new registries</a>
1637</div>
1638
1639<div class="doc_text">
1640
1641<p>The easiest way to get started is to clone one of the existing registries; we
1642recommend <tt>llvm/CodeGen/RegAllocRegistry.h</tt>. The key things to modify
1643are the class name and the <tt>FunctionPassCtor</tt> type.</p>
1644
1645<p>Then you need to declare the registry. Example: if your pass registry is
1646<tt>RegisterMyPasses</tt> then define;</p>
1647
1648<div class="doc_code"><pre>
1649MachinePassRegistry RegisterMyPasses::Registry;
1650</pre></div>
1651
1652<p>And finally, declare the command line option for your passes. Example:</p>
1653
1654<div class="doc_code"><pre>
1655 cl::opt&lt;RegisterMyPasses::FunctionPassCtor, false,
1656 RegisterPassParser&lt;RegisterMyPasses&gt &gt
1657 MyPassOpt("mypass",
1658 cl::init(&amp;createDefaultMyPass),
1659 cl::desc("my pass option help"));
1660</pre></div>
1661
1662<p>Here the command option is "mypass", with createDefaultMyPass as the default
1663creator.</p>
1664
1665</div>
1666
1667<!-- *********************************************************************** -->
1668<div class="doc_section">
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1669 <a name="debughints">Using GDB with dynamically loaded passes</a>
1670</div>
Chris Lattner480e2ef2002-09-06 02:02:58 +0000[diff] [blame]1671<!-- *********************************************************************** -->
1672
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1673<div class="doc_text">
1674
1675<p>Unfortunately, using GDB with dynamically loaded passes is not as easy as it
Chris Lattner480e2ef2002-09-06 02:02:58 +0000[diff] [blame]1676should be. First of all, you can't set a breakpoint in a shared object that has
1677not been loaded yet, and second of all there are problems with inlined functions
1678in shared objects. Here are some suggestions to debugging your pass with
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1679GDB.</p>
Chris Lattner480e2ef2002-09-06 02:02:58 +0000[diff] [blame]1680
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1681<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]1682transformation invoked by <tt>opt</tt>, although nothing described here depends
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1683on that.</p>
1684
1685</div>
Chris Lattner480e2ef2002-09-06 02:02:58 +0000[diff] [blame]1686
1687<!-- _______________________________________________________________________ -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1688<div class="doc_subsubsection">
1689 <a name="breakpoint">Setting a breakpoint in your pass</a>
1690</div>
Chris Lattner480e2ef2002-09-06 02:02:58 +0000[diff] [blame]1691
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1692<div class="doc_text">
1693
1694<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]1695
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1696<div class="doc_code"><pre>
Chris Lattner480e2ef2002-09-06 02:02:58 +0000[diff] [blame]1697$ <b>gdb opt</b>
1698GNU gdb 5.0
1699Copyright 2000 Free Software Foundation, Inc.
1700GDB is free software, covered by the GNU General Public License, and you are
1701welcome to change it and/or distribute copies of it under certain conditions.
1702Type "show copying" to see the conditions.
1703There is absolutely no warranty for GDB. Type "show warranty" for details.
1704This GDB was configured as "sparc-sun-solaris2.6"...
1705(gdb)
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1706</pre></div>
Chris Lattner480e2ef2002-09-06 02:02:58 +0000[diff] [blame]1707
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1708<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]1709time to load. Be patient. Since we cannot set a breakpoint in our pass yet
1710(the shared object isn't loaded until runtime), we must execute the process, and
1711have it stop before it invokes our pass, but after it has loaded the shared
1712object. The most foolproof way of doing this is to set a breakpoint in
1713<tt>PassManager::run</tt> and then run the process with the arguments you
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1714want:</p>
Chris Lattner480e2ef2002-09-06 02:02:58 +0000[diff] [blame]1715
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1716<div class="doc_code"><pre>
Reid Spencer22a9e5b2006-09-28 16:53:47 +0000[diff] [blame]1717(gdb) <b>break llvm::PassManager::run</b>
Chris Lattner480e2ef2002-09-06 02:02:58 +0000[diff] [blame]1718Breakpoint 1 at 0x2413bc: file Pass.cpp, line 70.
Chris Lattner4c376ea2005-04-21 04:52:37 +0000[diff] [blame]1719(gdb) <b>run test.bc -load $(LLVMTOP)/llvm/Debug/lib/[libname].so -[passoption]</b>
1720Starting program: opt test.bc -load $(LLVMTOP)/llvm/Debug/lib/[libname].so -[passoption]
Chris Lattner480e2ef2002-09-06 02:02:58 +0000[diff] [blame]1721Breakpoint 1, PassManager::run (this=0xffbef174, M=@0x70b298) at Pass.cpp:70
172270 bool PassManager::run(Module &amp;M) { return PM-&gt;run(M); }
1723(gdb)
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1724</pre></div>
Chris Lattner480e2ef2002-09-06 02:02:58 +0000[diff] [blame]1725
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1726<p>Once the <tt>opt</tt> stops in the <tt>PassManager::run</tt> method you are
1727now free to set breakpoints in your pass so that you can trace through execution
1728or do other standard debugging stuff.</p>
Chris Lattner480e2ef2002-09-06 02:02:58 +0000[diff] [blame]1729
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1730</div>
Chris Lattner480e2ef2002-09-06 02:02:58 +0000[diff] [blame]1731
1732<!-- _______________________________________________________________________ -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1733<div class="doc_subsubsection">
1734 <a name="debugmisc">Miscellaneous Problems</a>
1735</div>
Chris Lattner480e2ef2002-09-06 02:02:58 +0000[diff] [blame]1736
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1737<div class="doc_text">
1738
1739<p>Once you have the basics down, there are a couple of problems that GDB has,
1740some with solutions, some without.</p>
Chris Lattner480e2ef2002-09-06 02:02:58 +0000[diff] [blame]1741
1742<ul>
1743<li>Inline functions have bogus stack information. In general, GDB does a
1744pretty good job getting stack traces and stepping through inline functions.
1745When a pass is dynamically loaded however, it somehow completely loses this
1746capability. The only solution I know of is to de-inline a function (move it
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1747from the body of a class to a .cpp file).</li>
Chris Lattner480e2ef2002-09-06 02:02:58 +0000[diff] [blame]1748
1749<li>Restarting the program breaks breakpoints. After following the information
1750above, you have succeeded in getting some breakpoints planted in your pass. Nex
1751thing you know, you restart the program (i.e., you type '<tt>run</tt>' again),
1752and you start getting errors about breakpoints being unsettable. The only way I
1753have found to "fix" this problem is to <tt>delete</tt> the breakpoints that are
1754already set in your pass, run the program, and re-set the breakpoints once
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1755execution stops in <tt>PassManager::run</tt>.</li>
Chris Lattner480e2ef2002-09-06 02:02:58 +0000[diff] [blame]1756
1757</ul>
1758
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1759<p>Hopefully these tips will help with common case debugging situations. If
1760you'd like to contribute some tips of your own, just contact <a
1761href="mailto:sabre@nondot.org">Chris</a>.</p>
Chris Lattner480e2ef2002-09-06 02:02:58 +0000[diff] [blame]1762
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1763</div>
Chris Lattner480e2ef2002-09-06 02:02:58 +0000[diff] [blame]1764
1765<!-- *********************************************************************** -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1766<div class="doc_section">
1767 <a name="future">Future extensions planned</a>
1768</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1769<!-- *********************************************************************** -->
1770
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1771<div class="doc_text">
1772
1773<p>Although the LLVM Pass Infrastructure is very capable as it stands, and does
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1774some 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]1775where we are going:</p>
1776
1777</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1778
1779<!-- _______________________________________________________________________ -->
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]1780<div class="doc_subsubsection">
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1781 <a name="SMP">Multithreaded LLVM</a>
1782</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1783
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1784<div class="doc_text">
1785
1786<p>Multiple CPU machines are becoming more common and compilation can never be
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1787fast enough: obviously we should allow for a multithreaded compiler. Because of
1788the semantics defined for passes above (specifically they cannot maintain state
1789across invocations of their <tt>run*</tt> methods), a nice clean way to
1790implement a multithreaded compiler would be for the <tt>PassManager</tt> class
Misha Brukmanbc0e9982003-07-14 17:20:40 +0000[diff] [blame]1791to create multiple instances of each pass object, and allow the separate
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1792instances to be hacking on different parts of the program at the same time.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1793
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1794<p>This implementation would prevent each of the passes from having to implement
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1795multithreaded constructs, requiring only the LLVM core to have locking in a few
1796places (for global resources). Although this is a simple extension, we simply
1797haven't had time (or multiprocessor machines, thus a reason) to implement this.
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1798Despite that, we have kept the LLVM passes SMP ready, and you should too.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1799
Chris Lattnerb5c87f62007-05-18 05:36:14 +0000[diff] [blame]1800</div>
1801
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1802<!-- *********************************************************************** -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1803<hr>
1804<address>
1805 <a href="http://jigsaw.w3.org/css-validator/check/referer"><img
1806 src="http://jigsaw.w3.org/css-validator/images/vcss" alt="Valid CSS!"></a>
1807 <a href="http://validator.w3.org/check/referer"><img
1808 src="http://www.w3.org/Icons/valid-html401" alt="Valid HTML 4.01!" /></a>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1809
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1810 <a href="mailto:sabre@nondot.org">Chris Lattner</a><br>
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]1811 <a href="http://llvm.org">The LLVM Compiler Infrastructure</a><br>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1812 Last modified: $Date$
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