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gerrit-public.fairphone.software / fp2-dev / platform / external / llvm / 2e8f27d0bdb2b20ac6582b53e2ddf2bfc5c28411 / . / docs / WritingAnLLVMPass.html
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Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]6 <title>Writing an LLVM Pass</title>
7 <link rel="stylesheet" href="llvm.css" type="text/css">
8</head>
9<body>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]10
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]11<div class="doc_title">
12 Writing an LLVM Pass
13</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]14
15<ol>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]16 <li><a href="#introduction">Introduction - What is a pass?</a></li>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]17 <li><a href="#quickstart">Quick Start - Writing hello world</a>
18 <ul>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]19 <li><a href="#makefile">Setting up the build environment</a></li>
20 <li><a href="#basiccode">Basic code required</a></li>
Chris 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>
Chris Lattnerf6278922004-09-20 04:36:29 +0000[diff] [blame]106 <li><a href="#PassFunctionPass"><tt>ModulePass</tt>es requiring
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]107 <tt>FunctionPass</tt>es</a></li>
108 </ul></li>
109</ol>
Chris Lattner38c633d2002-08-08 20:23:41 +0000[diff] [blame]110
Chris Lattner7911ce22004-05-23 21:07:27 +0000[diff] [blame]111<div class="doc_author">
Chris Lattner8f652eb2006-08-11 16:37:02 +0000[diff] [blame]112 <p>Written by <a href="mailto:sabre@nondot.org">Chris Lattner</a> and
Jim Laskeyc760a922007-03-14 19:32:21 +0000[diff] [blame]113 <a href="mailto:jlaskey@mac.com">Jim Laskey</a></p>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]114</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]115
116<!-- *********************************************************************** -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]117<div class="doc_section">
118 <a name="introduction">Introduction - What is a pass?</a>
119</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]120<!-- *********************************************************************** -->
121
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]122<div class="doc_text">
123
124<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]125passes are where most of the interesting parts of the compiler exist. Passes
126perform the transformations and optimizations that make up the compiler, they
127build the analysis results that are used by these transformations, and they are,
128above all, a structuring technique for compiler code.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]129
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]130<p>All LLVM passes are subclasses of the <tt><a
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]131href="http://llvm.org/doxygen/classllvm_1_1Pass.html">Pass</a></tt>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]132class, which implement functionality by overriding virtual methods inherited
Chris Lattnerf6278922004-09-20 04:36:29 +0000[diff] [blame]133from <tt>Pass</tt>. Depending on how your pass works, you should inherit from
134the <tt><a href="#ModulePass">ModulePass</a></tt>, <tt><a
135href="#CallGraphSCCPass">CallGraphSCCPass</a></tt>, <tt><a
136href="#FunctionPass">FunctionPass</a></tt>, or <tt><a
Devang Patel2e8f27d2007-03-19 22:21:25 +0000[diff] [blame^]137href="#LoopPass">LoopPass</a></tt>, or <tt><a
Chris Lattner8fdb2462004-09-18 06:39:35 +0000[diff] [blame]138href="#BasicBlockPass">BasicBlockPass</a></tt> classes, which gives the system
139more information about what your pass does, and how it can be combined with
140other passes. One of the main features of the LLVM Pass Framework is that it
141schedules passes to run in an efficient way based on the constraints that your
142pass meets (which are indicated by which class they derive from).</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]143
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]144<p>We start by showing you how to construct a pass, everything from setting up
145the code, to compiling, loading, and executing it. After the basics are down,
146more advanced features are discussed.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]147
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]148</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]149
150<!-- *********************************************************************** -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]151<div class="doc_section">
152 <a name="quickstart">Quick Start - Writing hello world</a>
153</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]154<!-- *********************************************************************** -->
155
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]156<div class="doc_text">
157
158<p>Here we describe how to write the "hello world" of passes. The "Hello" pass
159is designed to simply print out the name of non-external functions that exist in
Chris Lattner8fdb2462004-09-18 06:39:35 +0000[diff] [blame]160the program being compiled. It does not modify the program at all, it just
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]161inspects it. The source code and files for this pass are available in the LLVM
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]162source tree in the <tt>lib/Transforms/Hello</tt> directory.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]163
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]164</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]165
166<!-- ======================================================================= -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]167<div class="doc_subsection">
168 <a name="makefile">Setting up the build environment</a>
169</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]170
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]171<div class="doc_text">
172
Reid Spencer1bc19342004-12-11 05:12:57 +0000[diff] [blame]173 <p>First, you need to create a new directory somewhere in the LLVM source
174 base. For this example, we'll assume that you made
175 <tt>lib/Transforms/Hello</tt>. Next, you must set up a build script
176 (Makefile) that will compile the source code for the new pass. To do this,
177 copy the following into <tt>Makefile</tt>:</p>
178 <hr/>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]179
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]180<div class="doc_code"><pre>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]181# Makefile for hello pass
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]182
Chris Lattner17a4c3e2002-08-14 20:06:13 +0000[diff] [blame]183# Path to top level of LLVM heirarchy
Chris Lattner7ce83e52002-08-14 20:07:01 +0000[diff] [blame]184LEVEL = ../../..
Chris Lattner17a4c3e2002-08-14 20:06:13 +0000[diff] [blame]185
186# Name of the library to build
Reid Spencer7fa6d522005-01-11 05:16:23 +0000[diff] [blame]187LIBRARYNAME = Hello
Chris Lattner17a4c3e2002-08-14 20:06:13 +0000[diff] [blame]188
Reid Spencer7fa6d522005-01-11 05:16:23 +0000[diff] [blame]189# Make the shared library become a loadable module so the tools can
190# dlopen/dlsym on the resulting library.
Robert Bocchino3cf817d2006-01-06 22:49:23 +0000[diff] [blame]191LOADABLE_MODULE = 1
Reid Spencer7fa6d522005-01-11 05:16:23 +0000[diff] [blame]192
Reid Spencerebfe07f2006-08-08 01:48:17 +0000[diff] [blame]193# Tell the build system which LLVM libraries your pass needs. You'll probably
194# need at least LLVMSystem.a, LLVMSupport.a, LLVMCore.a but possibly several
195# others too.
196LLVMLIBS = LLVMCore.a LLVMSupport.a LLVMSystem.a
197
Chris Lattner17a4c3e2002-08-14 20:06:13 +0000[diff] [blame]198# Include the makefile implementation stuff
199include $(LEVEL)/Makefile.common
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]200</pre></div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]201
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]202<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]203directory are to be compiled and linked together into a
Reid Spencer7fa6d522005-01-11 05:16:23 +0000[diff] [blame]204<tt>Debug/lib/Hello.so</tt> shared object that can be dynamically loaded by
Chris Lattnerc8603c22006-08-27 23:18:52 +0000[diff] [blame]205the <tt>opt</tt> or <tt>bugpoint</tt> tools via their <tt>-load</tt> options.
Reid Spencer7fa6d522005-01-11 05:16:23 +0000[diff] [blame]206If your operating system uses a suffix other than .so (such as windows or
207Mac OS/X), the appropriate extension will be used.</p>
John Criswellf9c78652004-01-26 21:26:54 +0000[diff] [blame]208
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]209<p>Now that we have the build scripts set up, we just need to write the code for
210the pass itself.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]211
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]212</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]213
214<!-- ======================================================================= -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]215<div class="doc_subsection">
216 <a name="basiccode">Basic code required</a>
217</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]218
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]219<div class="doc_text">
220
221<p>Now that we have a way to compile our new pass, we just have to write it.
222Start out with:</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]223
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]224<div class="doc_code"><pre>
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]225<b>#include</b> "<a href="http://llvm.org/doxygen/Pass_8h-source.html">llvm/Pass.h</a>"
226<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]227</pre></div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]228
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]229<p>Which are needed because we are writing a <tt><a
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]230href="http://llvm.org/doxygen/classllvm_1_1Pass.html">Pass</a></tt>, and
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]231we are operating on <tt><a
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]232href="http://llvm.org/doxygen/classllvm_1_1Function.html">Function</a></tt>'s.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]233
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]234<p>Next we have:</p>
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]235<div class="doc_code"><pre>
Jonathan Manton65acb302004-06-30 18:10:30 +0000[diff] [blame]236<b>using namespace llvm;</b>
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]237</pre></div>
Jonathan Manton65acb302004-06-30 18:10:30 +0000[diff] [blame]238<p>... which is required because the functions from the include files
239live in the llvm namespace.
240</p>
241
242<p>Next we have:</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]243
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]244<div class="doc_code"><pre>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]245<b>namespace</b> {
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]246</pre></div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]247
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]248<p>... which starts out an anonymous namespace. Anonymous namespaces are to C++
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]249what the "<tt>static</tt>" keyword is to C (at global scope). It makes the
250things declared inside of the anonymous namespace only visible to the current
251file. If you're not familiar with them, consult a decent C++ book for more
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]252information.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]253
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]254<p>Next, we declare our pass itself:</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]255
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]256<div class="doc_code"><pre>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]257 <b>struct</b> Hello : <b>public</b> <a href="#FunctionPass">FunctionPass</a> {
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]258</pre></div><p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]259
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]260<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]261href="http://llvm.org/doxygen/classllvm_1_1FunctionPass.html">FunctionPass</a></tt>.
Chris Lattnerd6ea9262002-09-09 03:48:46 +0000[diff] [blame]262The different builtin pass subclasses are described in detail <a
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]263href="#passtype">later</a>, but for now, know that <a
264href="#FunctionPass"><tt>FunctionPass</tt></a>'s operate a function at a
265time.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]266
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]267<div class="doc_code"><pre>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]268 <b>virtual bool</b> <a href="#runOnFunction">runOnFunction</a>(Function &amp;F) {
Bill Wendling832171c2006-12-07 20:04:42 +0000[diff] [blame]269 llvm::cerr &lt;&lt; "<i>Hello: </i>" &lt;&lt; F.getName() &lt;&lt; "\n";
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]270 <b>return false</b>;
271 }
272 }; <i>// end of struct Hello</i>
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]273</pre></div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]274
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]275<p>We declare a "<a href="#runOnFunction"><tt>runOnFunction</tt></a>" method,
276which overloads an abstract virtual method inherited from <a
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]277href="#FunctionPass"><tt>FunctionPass</tt></a>. This is where we are supposed
278to 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]279function.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]280
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]281<div class="doc_code"><pre>
Chris Lattnerc8603c22006-08-27 23:18:52 +0000[diff] [blame]282 RegisterPass&lt;Hello&gt; X("<i>hello</i>", "<i>Hello World Pass</i>");
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]283} <i>// end of anonymous namespace</i>
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]284</pre></div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]285
Chris Lattnerc8603c22006-08-27 23:18:52 +0000[diff] [blame]286<p>Lastly, we <a href="#registration">register our class</a> <tt>Hello</tt>,
287giving it a command line
288argument "<tt>hello</tt>", and a name "<tt>Hello World Pass</tt>".</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]289
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]290<p>As a whole, the <tt>.cpp</tt> file looks like:</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]291
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]292<div class="doc_code"><pre>
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]293<b>#include</b> "<a href="http://llvm.org/doxygen/Pass_8h-source.html">llvm/Pass.h</a>"
294<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]295
Jonathan Manton65acb302004-06-30 18:10:30 +0000[diff] [blame]296<b>using namespace llvm;</b>
297
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]298<b>namespace</b> {
299 <b>struct Hello</b> : <b>public</b> <a href="#FunctionPass">FunctionPass</a> {
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]300 <b>virtual bool</b> <a href="#runOnFunction">runOnFunction</a>(Function &amp;F) {
Bill Wendling832171c2006-12-07 20:04:42 +0000[diff] [blame]301 llvm::cerr &lt;&lt; "<i>Hello: </i>" &lt;&lt; F.getName() &lt;&lt; "\n";
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]302 <b>return false</b>;
303 }
304 };
305
Chris Lattnerc8603c22006-08-27 23:18:52 +0000[diff] [blame]306 RegisterPass&lt;Hello&gt; X("<i>hello</i>", "<i>Hello World Pass</i>");
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]307}
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]308</pre></div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]309
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]310<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]311command in the local directory and you should get a new
Reid Spencer7fa6d522005-01-11 05:16:23 +0000[diff] [blame]312"<tt>Debug/lib/Hello.so</tt> file. Note that everything in this file is
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]313contained in an anonymous namespace: this reflects the fact that passes are self
314contained units that do not need external interfaces (although they can have
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]315them) to be useful.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]316
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]317</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]318
319<!-- ======================================================================= -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]320<div class="doc_subsection">
Chris Lattnerc8603c22006-08-27 23:18:52 +0000[diff] [blame]321 <a name="running">Running a pass with <tt>opt</tt></a>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]322</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]323
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]324<div class="doc_text">
325
John Criswellf9c78652004-01-26 21:26:54 +0000[diff] [blame]326<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]327<tt>opt</tt> command to run an LLVM program through your pass. Because you
Chris Lattnerc8603c22006-08-27 23:18:52 +0000[diff] [blame]328registered your pass with the <tt>RegisterPass</tt> template, you will be able to
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]329use the <tt>opt</tt> tool to access it, once loaded.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]330
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]331<p>To test it, follow the example at the end of the <a
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]332href="GettingStarted.html">Getting Started Guide</a> to compile "Hello World" to
333LLVM. We can now run the bytecode file (<tt>hello.bc</tt>) for the program
334through our transformation like this (or course, any bytecode file will
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]335work):</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]336
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]337<div class="doc_code"><pre>
Reid Spencer7fa6d522005-01-11 05:16:23 +0000[diff] [blame]338$ opt -load ../../../Debug/lib/Hello.so -hello &lt; hello.bc &gt; /dev/null
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]339Hello: __main
340Hello: puts
341Hello: main
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]342</pre></div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]343
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]344<p>The '<tt>-load</tt>' option specifies that '<tt>opt</tt>' should load your
345pass as a shared object, which makes '<tt>-hello</tt>' a valid command line
346argument (which is one reason you need to <a href="#registration">register your
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]347pass</a>). Because the hello pass does not modify the program in any
348interesting way, we just throw away the result of <tt>opt</tt> (sending it to
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]349<tt>/dev/null</tt>).</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]350
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]351<p>To see what happened to the other string you registered, try running
352<tt>opt</tt> with the <tt>--help</tt> option:</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 --help
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]356OVERVIEW: llvm .bc -&gt; .bc modular optimizer
357
358USAGE: opt [options] &lt;input bytecode&gt;
359
360OPTIONS:
361 Optimizations available:
362...
363 -funcresolve - Resolve Functions
364 -gcse - Global Common Subexpression Elimination
365 -globaldce - Dead Global Elimination
366 <b>-hello - Hello World Pass</b>
Chris Lattner065a6162003-09-10 05:29:43 +0000[diff] [blame]367 -indvars - Canonicalize Induction Variables
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]368 -inline - Function Integration/Inlining
369 -instcombine - Combine redundant instructions
370...
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]371</pre></div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]372
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]373<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]374documentation to users of <tt>opt</tt>. Now that you have a working pass, you
375would go ahead and make it do the cool transformations you want. Once you get
376it all working and tested, it may become useful to find out how fast your pass
377is. The <a href="#passManager"><tt>PassManager</tt></a> provides a nice command
378line option (<tt>--time-passes</tt>) that allows you to get information about
379the execution time of your pass along with the other passes you queue up. For
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]380example:</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]381
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]382<div class="doc_code"><pre>
Reid Spencer7fa6d522005-01-11 05:16:23 +0000[diff] [blame]383$ 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]384Hello: __main
385Hello: puts
386Hello: main
387===============================================================================
388 ... Pass execution timing report ...
389===============================================================================
390 Total Execution Time: 0.02 seconds (0.0479059 wall clock)
391
392 ---User Time--- --System Time-- --User+System-- ---Wall Time--- --- Pass Name ---
393 0.0100 (100.0%) 0.0000 ( 0.0%) 0.0100 ( 50.0%) 0.0402 ( 84.0%) Bytecode Writer
394 0.0000 ( 0.0%) 0.0100 (100.0%) 0.0100 ( 50.0%) 0.0031 ( 6.4%) Dominator Set Construction
395 0.0000 ( 0.0%) 0.0000 ( 0.0%) 0.0000 ( 0.0%) 0.0013 ( 2.7%) Module Verifier
396 <b> 0.0000 ( 0.0%) 0.0000 ( 0.0%) 0.0000 ( 0.0%) 0.0033 ( 6.9%) Hello World Pass</b>
397 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]398</pre></div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]399
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]400<p>As you can see, our implementation above is pretty fast :). The additional
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]401passes listed are automatically inserted by the '<tt>opt</tt>' tool to verify
402that the LLVM emitted by your pass is still valid and well formed LLVM, which
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]403hasn't been broken somehow.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]404
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]405<p>Now that you have seen the basics of the mechanics behind passes, we can talk
406about some more details of how they work and how to use them.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]407
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]408</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]409
410<!-- *********************************************************************** -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]411<div class="doc_section">
412 <a name="passtype">Pass classes and requirements</a>
413</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]414<!-- *********************************************************************** -->
415
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]416<div class="doc_text">
417
418<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]419decide what class you should subclass for your pass. The <a
420href="#basiccode">Hello World</a> example uses the <tt><a
421href="#FunctionPass">FunctionPass</a></tt> class for its implementation, but we
422did not discuss why or when this should occur. Here we talk about the classes
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]423available, from the most general to the most specific.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]424
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]425<p>When choosing a superclass for your Pass, you should choose the <b>most
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]426specific</b> class possible, while still being able to meet the requirements
Misha Brukman5560c9d2003-08-18 14:43:39 +0000[diff] [blame]427listed. This gives the LLVM Pass Infrastructure information necessary to
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]428optimize how passes are run, so that the resultant compiler isn't unneccesarily
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]429slow.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]430
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]431</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]432
Chris Lattnerf004f9a2002-09-25 22:31:38 +0000[diff] [blame]433<!-- ======================================================================= -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]434<div class="doc_subsection">
435 <a name="ImmutablePass">The <tt>ImmutablePass</tt> class</a>
436</div>
Chris Lattnerf004f9a2002-09-25 22:31:38 +0000[diff] [blame]437
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]438<div class="doc_text">
439
440<p>The most plain and boring type of pass is the "<tt><a
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]441href="http://llvm.org/doxygen/classllvm_1_1ImmutablePass.html">ImmutablePass</a></tt>"
Chris Lattnerf004f9a2002-09-25 22:31:38 +0000[diff] [blame]442class. This pass type is used for passes that do not have to be run, do not
443change state, and never need to be updated. This is not a normal type of
444transformation or analysis, but can provide information about the current
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]445compiler configuration.</p>
Chris Lattnerf004f9a2002-09-25 22:31:38 +0000[diff] [blame]446
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]447<p>Although this pass class is very infrequently used, it is important for
Chris Lattnerf004f9a2002-09-25 22:31:38 +0000[diff] [blame]448providing information about the current target machine being compiled for, and
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]449other static information that can affect the various transformations.</p>
Chris Lattnerf004f9a2002-09-25 22:31:38 +0000[diff] [blame]450
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]451<p><tt>ImmutablePass</tt>es never invalidate other transformations, are never
452invalidated, and are never "run".</p>
Chris Lattnerf004f9a2002-09-25 22:31:38 +0000[diff] [blame]453
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]454</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]455
456<!-- ======================================================================= -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]457<div class="doc_subsection">
Chris Lattnerf6278922004-09-20 04:36:29 +0000[diff] [blame]458 <a name="ModulePass">The <tt>ModulePass</tt> class</a>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]459</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]460
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]461<div class="doc_text">
462
463<p>The "<tt><a
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]464href="http://llvm.org/doxygen/classllvm_1_1ModulePass.html">ModulePass</a></tt>"
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]465class is the most general of all superclasses that you can use. Deriving from
Chris Lattnerf6278922004-09-20 04:36:29 +0000[diff] [blame]466<tt>ModulePass</tt> indicates that your pass uses the entire program as a unit,
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]467refering to function bodies in no predictable order, or adding and removing
Chris Lattnerf6278922004-09-20 04:36:29 +0000[diff] [blame]468functions. Because nothing is known about the behavior of <tt>ModulePass</tt>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]469subclasses, no optimization can be done for their execution.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]470
Chris Lattnerf6278922004-09-20 04:36:29 +0000[diff] [blame]471<p>To write a correct <tt>ModulePass</tt> subclass, derive from
472<tt>ModulePass</tt> and overload the <tt>runOnModule</tt> method with the
473following signature:</p>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]474
475</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]476
477<!-- _______________________________________________________________________ -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]478<div class="doc_subsubsection">
Chris Lattnerf6278922004-09-20 04:36:29 +0000[diff] [blame]479 <a name="runOnModule">The <tt>runOnModule</tt> method</a>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]480</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]481
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]482<div class="doc_text">
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]483
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]484<div class="doc_code"><pre>
Chris Lattnerf6278922004-09-20 04:36:29 +0000[diff] [blame]485 <b>virtual bool</b> runOnModule(Module &amp;M) = 0;
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]486</pre></div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]487
John Criswell2382ff72005-07-15 19:25:12 +0000[diff] [blame]488<p>The <tt>runOnModule</tt> method performs the interesting work of the pass.
489It should return true if the module was modified by the transformation and
490false otherwise.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]491
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]492</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]493
494<!-- ======================================================================= -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]495<div class="doc_subsection">
Chris Lattner8fdb2462004-09-18 06:39:35 +0000[diff] [blame]496 <a name="CallGraphSCCPass">The <tt>CallGraphSCCPass</tt> class</a>
497</div>
498
499<div class="doc_text">
500
501<p>The "<tt><a
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]502href="http://llvm.org/doxygen/classllvm_1_1CallGraphSCCPass.html">CallGraphSCCPass</a></tt>"
Chris Lattner8fdb2462004-09-18 06:39:35 +0000[diff] [blame]503is used by passes that need to traverse the program bottom-up on the call graph
504(callees before callers). Deriving from CallGraphSCCPass provides some
505mechanics for building and traversing the CallGraph, but also allows the system
506to optimize execution of CallGraphSCCPass's. If your pass meets the
507requirements outlined below, and doesn't meet the requirements of a <tt><a
508href="#FunctionPass">FunctionPass</a></tt> or <tt><a
509href="#BasicBlockPass">BasicBlockPass</a></tt>, you should derive from
510<tt>CallGraphSCCPass</tt>.</p>
511
512<p><b>TODO</b>: explain briefly what SCC, Tarjan's algo, and B-U mean.</p>
513
514<p>To be explicit, <tt>CallGraphSCCPass</tt> subclasses are:</p>
515
516<ol>
517
518<li>... <em>not allowed</em> to modify any <tt>Function</tt>s that are not in
519the current SCC.</li>
520
521<li>... <em>allowed</em> to inspect any Function's other than those in the
522current SCC and the direct callees of the SCC.</li>
523
524<li>... <em>required</em> to preserve the current CallGraph object, updating it
525to reflect any changes made to the program.</li>
526
527<li>... <em>not allowed</em> to add or remove SCC's from the current Module,
528though they may change the contents of an SCC.</li>
529
530<li>... <em>allowed</em> to add or remove global variables from the current
531Module.</li>
532
533<li>... <em>allowed</em> to maintain state across invocations of
534 <a href="#runOnSCC"><tt>runOnSCC</tt></a> (including global data).</li>
535</ol>
536
537<p>Implementing a <tt>CallGraphSCCPass</tt> is slightly tricky in some cases
538because it has to handle SCCs with more than one node in it. All of the virtual
539methods described below should return true if they modified the program, or
540false if they didn't.</p>
541
542</div>
543
544<!-- _______________________________________________________________________ -->
545<div class="doc_subsubsection">
Devang Patelc20048d2007-01-23 22:56:28 +0000[diff] [blame]546 <a name="doInitialization_scc">The <tt>doInitialization(CallGraph &amp;)</tt>
Chris Lattner8fdb2462004-09-18 06:39:35 +0000[diff] [blame]547 method</a>
548</div>
549
550<div class="doc_text">
551
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]552<div class="doc_code"><pre>
Devang Patelc20048d2007-01-23 22:56:28 +0000[diff] [blame]553 <b>virtual bool</b> doInitialization(CallGraph &amp;CG);
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]554</pre></div>
Chris Lattner8fdb2462004-09-18 06:39:35 +0000[diff] [blame]555
556<p>The <tt>doIninitialize</tt> method is allowed to do most of the things that
557<tt>CallGraphSCCPass</tt>'s are not allowed to do. They can add and remove
558functions, get pointers to functions, etc. The <tt>doInitialization</tt> method
559is designed to do simple initialization type of stuff that does not depend on
560the SCCs being processed. The <tt>doInitialization</tt> method call is not
561scheduled to overlap with any other pass executions (thus it should be very
562fast).</p>
563
564</div>
565
566<!-- _______________________________________________________________________ -->
567<div class="doc_subsubsection">
568 <a name="runOnSCC">The <tt>runOnSCC</tt> method</a>
569</div>
570
571<div class="doc_text">
572
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]573<div class="doc_code"><pre>
Chris Lattner8fdb2462004-09-18 06:39:35 +0000[diff] [blame]574 <b>virtual bool</b> runOnSCC(const std::vector&lt;CallGraphNode *&gt; &amp;SCCM) = 0;
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]575</pre></div>
Chris Lattner8fdb2462004-09-18 06:39:35 +0000[diff] [blame]576
577<p>The <tt>runOnSCC</tt> method performs the interesting work of the pass, and
578should return true if the module was modified by the transformation, false
579otherwise.</p>
580
581</div>
582
583<!-- _______________________________________________________________________ -->
584<div class="doc_subsubsection">
Devang Patelc20048d2007-01-23 22:56:28 +0000[diff] [blame]585 <a name="doFinalization_scc">The <tt>doFinalization(CallGraph
Chris Lattner8fdb2462004-09-18 06:39:35 +0000[diff] [blame]586 &amp;)</tt> method</a>
587</div>
588
589<div class="doc_text">
590
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]591<div class="doc_code"><pre>
Devang Patelc20048d2007-01-23 22:56:28 +0000[diff] [blame]592 <b>virtual bool</b> doFinalization(CallGraph &amp;CG);
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]593</pre></div>
Chris Lattner8fdb2462004-09-18 06:39:35 +0000[diff] [blame]594
595<p>The <tt>doFinalization</tt> method is an infrequently used method that is
596called when the pass framework has finished calling <a
597href="#runOnFunction"><tt>runOnFunction</tt></a> for every function in the
598program being compiled.</p>
599
600</div>
601
602<!-- ======================================================================= -->
603<div class="doc_subsection">
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]604 <a name="FunctionPass">The <tt>FunctionPass</tt> class</a>
605</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]606
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]607<div class="doc_text">
608
Chris Lattnerf6278922004-09-20 04:36:29 +0000[diff] [blame]609<p>In contrast to <tt>ModulePass</tt> subclasses, <tt><a
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]610href="http://llvm.org/doxygen/classllvm_1_1Pass.html">FunctionPass</a></tt>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]611subclasses do have a predictable, local behavior that can be expected by the
612system. All <tt>FunctionPass</tt> execute on each function in the program
Misha Brukmanef6a6a62003-08-21 22:14:26 +0000[diff] [blame]613independent of all of the other functions in the program.
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]614<tt>FunctionPass</tt>'s do not require that they are executed in a particular
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]615order, and <tt>FunctionPass</tt>'s do not modify external functions.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]616
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]617<p>To be explicit, <tt>FunctionPass</tt> subclasses are not allowed to:</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]618
619<ol>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]620<li>Modify a Function other than the one currently being processed.</li>
621<li>Add or remove Function's from the current Module.</li>
622<li>Add or remove global variables from the current Module.</li>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]623<li>Maintain state across invocations of
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]624 <a href="#runOnFunction"><tt>runOnFunction</tt></a> (including global data)</li>
625</ol>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]626
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]627<p>Implementing a <tt>FunctionPass</tt> is usually straightforward (See the <a
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]628href="#basiccode">Hello World</a> pass for example). <tt>FunctionPass</tt>'s
629may overload three virtual methods to do their work. All of these methods
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]630should return true if they modified the program, or false if they didn't.</p>
631
632</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]633
634<!-- _______________________________________________________________________ -->
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]635<div class="doc_subsubsection">
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]636 <a name="doInitialization_mod">The <tt>doInitialization(Module &amp;)</tt>
637 method</a>
638</div>
639
640<div class="doc_text">
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]641
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]642<div class="doc_code"><pre>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]643 <b>virtual bool</b> doInitialization(Module &amp;M);
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]644</pre></div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]645
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]646<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]647<tt>FunctionPass</tt>'s are not allowed to do. They can add and remove
Chris Lattnerd0713f92002-09-12 17:06:43 +0000[diff] [blame]648functions, get pointers to functions, etc. The <tt>doInitialization</tt> method
649is designed to do simple initialization type of stuff that does not depend on
650the functions being processed. The <tt>doInitialization</tt> method call is not
651scheduled to overlap with any other pass executions (thus it should be very
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]652fast).</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]653
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]654<p>A good example of how this method should be used is the <a
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]655href="http://llvm.org/doxygen/LowerAllocations_8cpp-source.html">LowerAllocations</a>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]656pass. This pass converts <tt>malloc</tt> and <tt>free</tt> instructions into
Misha Brukmanef6a6a62003-08-21 22:14:26 +0000[diff] [blame]657platform dependent <tt>malloc()</tt> and <tt>free()</tt> function calls. It
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]658uses the <tt>doInitialization</tt> method to get a reference to the malloc and
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]659free functions that it needs, adding prototypes to the module if necessary.</p>
660
661</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]662
663<!-- _______________________________________________________________________ -->
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]664<div class="doc_subsubsection">
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]665 <a name="runOnFunction">The <tt>runOnFunction</tt> method</a>
666</div>
667
668<div class="doc_text">
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]669
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]670<div class="doc_code"><pre>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]671 <b>virtual bool</b> runOnFunction(Function &amp;F) = 0;
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]672</pre></div><p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]673
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]674<p>The <tt>runOnFunction</tt> method must be implemented by your subclass to do
675the transformation or analysis work of your pass. As usual, a true value should
676be returned if the function is modified.</p>
677
678</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]679
680<!-- _______________________________________________________________________ -->
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]681<div class="doc_subsubsection">
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]682 <a name="doFinalization_mod">The <tt>doFinalization(Module
683 &amp;)</tt> method</a>
684</div>
685
686<div class="doc_text">
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]687
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]688<div class="doc_code"><pre>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]689 <b>virtual bool</b> doFinalization(Module &amp;M);
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]690</pre></div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]691
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]692<p>The <tt>doFinalization</tt> method is an infrequently used method that is
693called when the pass framework has finished calling <a
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]694href="#runOnFunction"><tt>runOnFunction</tt></a> for every function in the
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]695program being compiled.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]696
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]697</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]698
699<!-- ======================================================================= -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]700<div class="doc_subsection">
Devang Patel2e8f27d2007-03-19 22:21:25 +0000[diff] [blame^]701 <a name="LoopPass">The <tt>LoopPass</tt> class </a>
702</div>
703
704<div class="doc_text">
705
706<p> All <tt>LoopPass</tt> execute on each loop in the function independent of
707all of the other loops in the function. <tt>LoopPass</tt> processes loops in
708loop nest order such that outer most loop is processed last. </p>
709
710<p> <tt>LoopPass</tt> subclasses are allowed to update loop nest using
711<tt>LPPassManager</tt> interface. Implementing a loop pass is usually
712straightforward. <tt>Looppass</tt>'s may overload three virtual methods to
713do their work. All these methods should return true if they modified the
714program, or false if they didn't. </p>
715</div>
716
717<!-- _______________________________________________________________________ -->
718<div class="doc_subsubsection">
719 <a name="doInitialization_loop">The <tt>doInitialization(Loop *,
720 LPPassManager &amp;)</tt>
721 method</a>
722</div>
723
724<div class="doc_text">
725
726<div class="doc_code"><pre>
727 <b>virtual bool</b> doInitialization(Loop *, LPPassManager &amp;LPM);
728</pre></div>
729
730The <tt>doInitialization</tt> method is designed to do simple initialization
731type of stuff that does not depend on the functions being processed. The
732<tt>doInitialization</tt> method call is not scheduled to overlap with any
733other pass executions (thus it should be very fast). LPPassManager
734interface should be used to access Function or Module level analysis
735information.</p>
736
737</div>
738
739
740<!-- _______________________________________________________________________ -->
741<div class="doc_subsubsection">
742 <a name="runOnLoop">The <tt>runOnLoop</tt> method</a>
743</div>
744
745<div class="doc_text">
746
747<div class="doc_code"><pre>
748 <b>virtual bool</b> runOnLoop(Loop *, LPPassManager &amp;LPM) = 0;
749</pre></div><p>
750
751<p>The <tt>runOnLoop</tt> method must be implemented by your subclass to do
752the transformation or analysis work of your pass. As usual, a true value should
753be returned if the function is modified. <tt>LPPassManager</tt> interface
754should be used to update loop nest.</p>
755
756</div>
757
758<!-- _______________________________________________________________________ -->
759<div class="doc_subsubsection">
760 <a name="doFinalization_loop">The <tt>doFinalization()</tt> method</a>
761</div>
762
763<div class="doc_text">
764
765<div class="doc_code"><pre>
766 <b>virtual bool</b> doFinalization();
767</pre></div>
768
769<p>The <tt>doFinalization</tt> method is an infrequently used method that is
770called when the pass framework has finished calling <a
771href="#runOnLoop"><tt>runOnLoop</tt></a> for every loop in the
772program being compiled. </p>
773
774</div>
775
776
777
778<!-- ======================================================================= -->
779<div class="doc_subsection">
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]780 <a name="BasicBlockPass">The <tt>BasicBlockPass</tt> class</a>
781</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]782
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]783<div class="doc_text">
784
785<p><tt>BasicBlockPass</tt>'s are just like <a
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]786href="#FunctionPass"><tt>FunctionPass</tt></a>'s, except that they must limit
787their scope of inspection and modification to a single basic block at a time.
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]788As such, they are <b>not</b> allowed to do any of the following:</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]789
790<ol>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]791<li>Modify or inspect any basic blocks outside of the current one</li>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]792<li>Maintain state across invocations of
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]793 <a href="#runOnBasicBlock"><tt>runOnBasicBlock</tt></a></li>
Reid Spencer1bc19342004-12-11 05:12:57 +0000[diff] [blame]794<li>Modify the control flow graph (by altering terminator instructions)</li>
795<li>Any of the things forbidden for
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]796 <a href="#FunctionPass"><tt>FunctionPass</tt></a>es.</li>
797</ol>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]798
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]799<p><tt>BasicBlockPass</tt>es are useful for traditional local and "peephole"
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]800optimizations. They may override the same <a
Chris Lattnerd0713f92002-09-12 17:06:43 +0000[diff] [blame]801href="#doInitialization_mod"><tt>doInitialization(Module &amp;)</tt></a> and <a
802href="#doFinalization_mod"><tt>doFinalization(Module &amp;)</tt></a> methods that <a
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]803href="#FunctionPass"><tt>FunctionPass</tt></a>'s have, but also have the following virtual methods that may also be implemented:</p>
804
805</div>
Chris Lattnerd0713f92002-09-12 17:06:43 +0000[diff] [blame]806
807<!-- _______________________________________________________________________ -->
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]808<div class="doc_subsubsection">
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]809 <a name="doInitialization_fn">The <tt>doInitialization(Function
810 &amp;)</tt> method</a>
811</div>
812
813<div class="doc_text">
Chris Lattnerd0713f92002-09-12 17:06:43 +0000[diff] [blame]814
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]815<div class="doc_code"><pre>
Chris Lattnerd0713f92002-09-12 17:06:43 +0000[diff] [blame]816 <b>virtual bool</b> doInitialization(Function &amp;F);
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]817</pre></div>
Chris Lattnerd0713f92002-09-12 17:06:43 +0000[diff] [blame]818
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]819<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]820<tt>BasicBlockPass</tt>'s are not allowed to do, but that
821<tt>FunctionPass</tt>'s can. The <tt>doInitialization</tt> method is designed
Reid Spencer1bc19342004-12-11 05:12:57 +0000[diff] [blame]822to do simple initialization that does not depend on the
Chris Lattnerd0713f92002-09-12 17:06:43 +0000[diff] [blame]823BasicBlocks being processed. The <tt>doInitialization</tt> method call is not
824scheduled to overlap with any other pass executions (thus it should be very
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]825fast).</p>
Chris Lattnerd0713f92002-09-12 17:06:43 +0000[diff] [blame]826
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]827</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]828
829<!-- _______________________________________________________________________ -->
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]830<div class="doc_subsubsection">
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]831 <a name="runOnBasicBlock">The <tt>runOnBasicBlock</tt> method</a>
832</div>
833
834<div class="doc_text">
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]835
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]836<div class="doc_code"><pre>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]837 <b>virtual bool</b> runOnBasicBlock(BasicBlock &amp;BB) = 0;
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]838</pre></div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]839
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]840<p>Override this function to do the work of the <tt>BasicBlockPass</tt>. This
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]841function is not allowed to inspect or modify basic blocks other than the
842parameter, and are not allowed to modify the CFG. A true value must be returned
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]843if the basic block is modified.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]844
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]845</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]846
Chris Lattnerd0713f92002-09-12 17:06:43 +0000[diff] [blame]847<!-- _______________________________________________________________________ -->
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]848<div class="doc_subsubsection">
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]849 <a name="doFinalization_fn">The <tt>doFinalization(Function &amp;)</tt>
850 method</a>
851</div>
852
853<div class="doc_text">
Chris Lattnerd0713f92002-09-12 17:06:43 +0000[diff] [blame]854
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]855<div class="doc_code"><pre>
Chris Lattnerd0713f92002-09-12 17:06:43 +0000[diff] [blame]856 <b>virtual bool</b> doFinalization(Function &amp;F);
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]857</pre></div>
Chris Lattnerd0713f92002-09-12 17:06:43 +0000[diff] [blame]858
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]859<p>The <tt>doFinalization</tt> method is an infrequently used method that is
860called when the pass framework has finished calling <a
Chris Lattnerd0713f92002-09-12 17:06:43 +0000[diff] [blame]861href="#runOnBasicBlock"><tt>runOnBasicBlock</tt></a> for every BasicBlock in the
862program being compiled. This can be used to perform per-function
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]863finalization.</p>
Chris Lattnerd0713f92002-09-12 17:06:43 +0000[diff] [blame]864
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]865</div>
Chris Lattnerd0713f92002-09-12 17:06:43 +0000[diff] [blame]866
Brian Gaekecab8b6f2003-07-17 18:53:20 +0000[diff] [blame]867<!-- ======================================================================= -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]868<div class="doc_subsection">
869 <a name="MachineFunctionPass">The <tt>MachineFunctionPass</tt> class</a>
870</div>
Brian Gaekecab8b6f2003-07-17 18:53:20 +0000[diff] [blame]871
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]872<div class="doc_text">
873
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]874<p>A <tt>MachineFunctionPass</tt> is a part of the LLVM code generator that
875executes on the machine-dependent representation of each LLVM function in the
876program. A <tt>MachineFunctionPass</tt> is also a <tt>FunctionPass</tt>, so all
Brian Gaekecab8b6f2003-07-17 18:53:20 +0000[diff] [blame]877the restrictions that apply to a <tt>FunctionPass</tt> also apply to it.
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]878<tt>MachineFunctionPass</tt>es also have additional restrictions. In particular,
879<tt>MachineFunctionPass</tt>es are not allowed to do any of the following:</p>
Brian Gaekecab8b6f2003-07-17 18:53:20 +0000[diff] [blame]880
881<ol>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]882<li>Modify any LLVM Instructions, BasicBlocks or Functions.</li>
883<li>Modify a MachineFunction other than the one currently being processed.</li>
884<li>Add or remove MachineFunctions from the current Module.</li>
885<li>Add or remove global variables from the current Module.</li>
886<li>Maintain state across invocations of <a
887href="#runOnMachineFunction"><tt>runOnMachineFunction</tt></a> (including global
888data)</li>
889</ol>
Brian Gaekecab8b6f2003-07-17 18:53:20 +0000[diff] [blame]890
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]891</div>
Chris Lattnerd0713f92002-09-12 17:06:43 +0000[diff] [blame]892
Brian Gaeke6a33f362003-07-22 20:53:20 +0000[diff] [blame]893<!-- _______________________________________________________________________ -->
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]894<div class="doc_subsubsection">
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]895 <a name="runOnMachineFunction">The <tt>runOnMachineFunction(MachineFunction
896 &amp;MF)</tt> method</a>
897</div>
898
899<div class="doc_text">
Brian Gaeke6a33f362003-07-22 20:53:20 +0000[diff] [blame]900
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]901<div class="doc_code"><pre>
Brian Gaeke6a33f362003-07-22 20:53:20 +0000[diff] [blame]902 <b>virtual bool</b> runOnMachineFunction(MachineFunction &amp;MF) = 0;
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]903</pre></div>
Brian Gaeke6a33f362003-07-22 20:53:20 +0000[diff] [blame]904
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]905<p><tt>runOnMachineFunction</tt> can be considered the main entry point of a
906<tt>MachineFunctionPass</tt>; that is, you should override this method to do the
907work of your <tt>MachineFunctionPass</tt>.</p>
Brian Gaeke6a33f362003-07-22 20:53:20 +0000[diff] [blame]908
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]909<p>The <tt>runOnMachineFunction</tt> method is called on every
Brian Gaeke6a33f362003-07-22 20:53:20 +0000[diff] [blame]910<tt>MachineFunction</tt> in a <tt>Module</tt>, so that the
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]911<tt>MachineFunctionPass</tt> may perform optimizations on the machine-dependent
912representation of the function. If you want to get at the LLVM <tt>Function</tt>
913for the <tt>MachineFunction</tt> you're working on, use
914<tt>MachineFunction</tt>'s <tt>getFunction()</tt> accessor method -- but
915remember, you may not modify the LLVM <tt>Function</tt> or its contents from a
916<tt>MachineFunctionPass</tt>.</p>
917
918</div>
Brian Gaeke6a33f362003-07-22 20:53:20 +0000[diff] [blame]919
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]920<!-- *********************************************************************** -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]921<div class="doc_section">
922 <a name="registration">Pass registration</a>
923</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]924<!-- *********************************************************************** -->
925
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]926<div class="doc_text">
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]927
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]928<p>In the <a href="#basiccode">Hello World</a> example pass we illustrated how
929pass registration works, and discussed some of the reasons that it is used and
930what it does. Here we discuss how and why passes are registered.</p>
931
Chris Lattnerc8603c22006-08-27 23:18:52 +0000[diff] [blame]932<p>As we saw above, passes are registered with the <b><tt>RegisterPass</tt></b>
933template, which requires you to pass at least two
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]934parameters. The first parameter is the name of the pass that is to be used on
935the command line to specify that the pass should be added to a program (for
Chris Lattnerc8603c22006-08-27 23:18:52 +0000[diff] [blame]936example, with <tt>opt</tt> or <tt>bugpoint</tt>). The second argument is the
937name of the pass, which is to be used for the <tt>--help</tt> output of
938programs, as
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]939well as for debug output generated by the <tt>--debug-pass</tt> option.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]940
Chris Lattnerc8603c22006-08-27 23:18:52 +0000[diff] [blame]941<p>If you want your pass to be easily dumpable, you should
942implement the virtual <tt>print</tt> method:</p>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]943
944</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]945
946<!-- _______________________________________________________________________ -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]947<div class="doc_subsubsection">
948 <a name="print">The <tt>print</tt> method</a>
949</div>
950
951<div class="doc_text">
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]952
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]953<div class="doc_code"><pre>
Bill Wendling832171c2006-12-07 20:04:42 +0000[diff] [blame]954 <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]955</pre></div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]956
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]957<p>The <tt>print</tt> method must be implemented by "analyses" in order to print
958a human readable version of the analysis results. This is useful for debugging
959an analysis itself, as well as for other people to figure out how an analysis
Chris Lattnerc8603c22006-08-27 23:18:52 +0000[diff] [blame]960works. Use the <tt>opt -analyze</tt> argument to invoke this method.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]961
Bill Wendling832171c2006-12-07 20:04:42 +0000[diff] [blame]962<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]963and 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]964program that has been analyzed. Note however that this pointer may be null in
965certain circumstances (such as calling the <tt>Pass::dump()</tt> from a
966debugger), so it should only be used to enhance debug output, it should not be
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]967depended on.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]968
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]969</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]970
971<!-- *********************************************************************** -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]972<div class="doc_section">
973 <a name="interaction">Specifying interactions between passes</a>
974</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]975<!-- *********************************************************************** -->
976
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]977<div class="doc_text">
978
979<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]980that passes interact with each other correctly. Because <tt>PassManager</tt>
981tries to <a href="#passmanager">optimize the execution of passes</a> it must
982know how the passes interact with each other and what dependencies exist between
983the various passes. To track this, each pass can declare the set of passes that
984are required to be executed before the current pass, and the passes which are
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]985invalidated by the current pass.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]986
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]987<p>Typically this functionality is used to require that analysis results are
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]988computed before your pass is run. Running arbitrary transformation passes can
989invalidate the computed analysis results, which is what the invalidation set
990specifies. If a pass does not implement the <tt><a
991href="#getAnalysisUsage">getAnalysisUsage</a></tt> method, it defaults to not
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]992having any prerequisite passes, and invalidating <b>all</b> other passes.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]993
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]994</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]995
996<!-- _______________________________________________________________________ -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]997<div class="doc_subsubsection">
998 <a name="getAnalysisUsage">The <tt>getAnalysisUsage</tt> method</a>
999</div>
1000
1001<div class="doc_text">
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1002
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1003<div class="doc_code"><pre>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1004 <b>virtual void</b> getAnalysisUsage(AnalysisUsage &amp;Info) <b>const</b>;
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1005</pre></div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1006
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1007<p>By implementing the <tt>getAnalysisUsage</tt> method, the required and
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1008invalidated sets may be specified for your transformation. The implementation
1009should fill in the <tt><a
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]1010href="http://llvm.org/doxygen/classllvm_1_1AnalysisUsage.html">AnalysisUsage</a></tt>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1011object with information about which passes are required and not invalidated. To
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]1012do this, a pass may call any of the following methods on the AnalysisUsage
1013object:</p>
1014</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1015
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]1016<!-- _______________________________________________________________________ -->
1017<div class="doc_subsubsection">
1018 <a name="AU::addRequired">The <tt>AnalysisUsage::addRequired&lt;&gt;</tt> and <tt>AnalysisUsage::addRequiredTransitive&lt;&gt;</tt> methods</a>
1019</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1020
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]1021<div class="doc_text">
1022<p>
Reid Spencer1bc19342004-12-11 05:12:57 +0000[diff] [blame]1023If your pass requires a previous pass to be executed (an analysis for example),
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]1024it can use one of these methods to arrange for it to be run before your pass.
1025LLVM has many different types of analyses and passes that can be required,
Reid Spencer1bc19342004-12-11 05:12:57 +0000[diff] [blame]1026spanning the range from <tt>DominatorSet</tt> to <tt>BreakCriticalEdges</tt>.
1027Requiring <tt>BreakCriticalEdges</tt>, for example, guarantees that there will
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]1028be no critical edges in the CFG when your pass has been run.
1029</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1030
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]1031<p>
1032Some analyses chain to other analyses to do their job. For example, an <a
1033href="AliasAnalysis.html">AliasAnalysis</a> implementation is required to <a
1034href="AliasAnalysis.html#chaining">chain</a> to other alias analysis passes. In
1035cases where analyses chain, the <tt>addRequiredTransitive</tt> method should be
1036used instead of the <tt>addRequired</tt> method. This informs the PassManager
1037that the transitively required pass should be alive as long as the requiring
1038pass is.
1039</p>
1040</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1041
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]1042<!-- _______________________________________________________________________ -->
1043<div class="doc_subsubsection">
1044 <a name="AU::addPreserved">The <tt>AnalysisUsage::addPreserved&lt;&gt;</tt> method</a>
1045</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1046
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]1047<div class="doc_text">
1048<p>
1049One of the jobs of the PassManager is to optimize how and when analyses are run.
1050In particular, it attempts to avoid recomputing data unless it needs to. For
1051this reason, passes are allowed to declare that they preserve (i.e., they don't
1052invalidate) an existing analysis if it's available. For example, a simple
Reid Spencer1bc19342004-12-11 05:12:57 +0000[diff] [blame]1053constant folding pass would not modify the CFG, so it can't possibly affect the
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]1054results of dominator analysis. By default, all passes are assumed to invalidate
1055all others.
1056</p>
1057
1058<p>
1059The <tt>AnalysisUsage</tt> class provides several methods which are useful in
1060certain circumstances that are related to <tt>addPreserved</tt>. In particular,
1061the <tt>setPreservesAll</tt> method can be called to indicate that the pass does
1062not modify the LLVM program at all (which is true for analyses), and the
1063<tt>setPreservesCFG</tt> method can be used by transformations that change
1064instructions in the program but do not modify the CFG or terminator instructions
1065(note that this property is implicitly set for <a
1066href="#BasicBlockPass">BasicBlockPass</a>'s).
1067</p>
1068
1069<p>
1070<tt>addPreserved</tt> is particularly useful for transformations like
1071<tt>BreakCriticalEdges</tt>. This pass knows how to update a small set of loop
1072and dominator related analyses if they exist, so it can preserve them, despite
1073the fact that it hacks on the CFG.
1074</p>
1075</div>
1076
1077<!-- _______________________________________________________________________ -->
1078<div class="doc_subsubsection">
1079 <a name="AU::examples">Example implementations of <tt>getAnalysisUsage</tt></a>
1080</div>
1081
1082<div class="doc_text">
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1083
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1084<div class="doc_code"><pre>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1085 <i>// This is an example implementation from an analysis, which does not modify
1086 // the program at all, yet has a prerequisite.</i>
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]1087 <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]1088 AU.setPreservesAll();
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]1089 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]1090 }
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1091</pre></div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1092
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1093<p>and:</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1094
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1095<div class="doc_code"><pre>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1096 <i>// This example modifies the program, but does not modify the CFG</i>
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]1097 <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]1098 AU.setPreservesCFG();
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]1099 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]1100 }
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1101</pre></div>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1102
1103</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1104
1105<!-- _______________________________________________________________________ -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1106<div class="doc_subsubsection">
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]1107 <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]1108</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1109
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1110<div class="doc_text">
1111
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]1112<p>The <tt>Pass::getAnalysis&lt;&gt;</tt> method is automatically inherited by
1113your class, providing you with access to the passes that you declared that you
1114required with the <a href="#getAnalysisUsage"><tt>getAnalysisUsage</tt></a>
1115method. It takes a single template argument that specifies which pass class you
1116want, and returns a reference to that pass. For example:</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1117
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1118<div class="doc_code"><pre>
Chris Lattnera5776302004-03-17 21:33:32 +0000[diff] [blame]1119 bool LICM::runOnFunction(Function &amp;F) {
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]1120 LoopInfo &amp;LI = getAnalysis&lt;LoopInfo&gt;();
1121 ...
1122 }
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1123</pre></div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1124
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1125<p>This method call returns a reference to the pass desired. You may get a
1126runtime assertion failure if you attempt to get an analysis that you did not
1127declare as required in your <a
1128href="#getAnalysisUsage"><tt>getAnalysisUsage</tt></a> implementation. This
1129method can be called by your <tt>run*</tt> method implementation, or by any
1130other local method invoked by your <tt>run*</tt> method.</p>
1131
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]1132<p>
1133If your pass is capable of updating analyses if they exist (e.g.,
1134<tt>BreakCriticalEdges</tt>, as described above), you can use the
1135<tt>getAnalysisToUpdate</tt> method, which returns a pointer to the analysis if
1136it is active. For example:</p>
1137
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1138<div class="doc_code"><pre>
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]1139 ...
1140 if (DominatorSet *DS = getAnalysisToUpdate&lt;DominatorSet&gt;()) {
1141 <i>// A DominatorSet is active. This code will update it.</i>
1142 }
1143 ...
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1144</pre></div>
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]1145
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1146</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1147
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1148<!-- *********************************************************************** -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1149<div class="doc_section">
1150 <a name="analysisgroup">Implementing Analysis Groups</a>
1151</div>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1152<!-- *********************************************************************** -->
1153
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1154<div class="doc_text">
1155
1156<p>Now that we understand the basics of how passes are defined, how the are
1157used, 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]1158fancier. All of the pass relationships that we have seen so far are very
1159simple: one pass depends on one other specific pass to be run before it can run.
1160For many applications, this is great, for others, more flexibility is
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1161required.</p>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1162
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1163<p>In particular, some analyses are defined such that there is a single simple
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1164interface to the analysis results, but multiple ways of calculating them.
1165Consider alias analysis for example. The most trivial alias analysis returns
1166"may alias" for any alias query. The most sophisticated analysis a
1167flow-sensitive, context-sensitive interprocedural analysis that can take a
1168significant amount of time to execute (and obviously, there is a lot of room
1169between these two extremes for other implementations). To cleanly support
1170situations like this, the LLVM Pass Infrastructure supports the notion of
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1171Analysis Groups.</p>
1172
1173</div>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1174
1175<!-- _______________________________________________________________________ -->
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]1176<div class="doc_subsubsection">
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1177 <a name="agconcepts">Analysis Group Concepts</a>
1178</div>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1179
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1180<div class="doc_text">
1181
1182<p>An Analysis Group is a single simple interface that may be implemented by
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1183multiple different passes. Analysis Groups can be given human readable names
1184just like passes, but unlike passes, they need not derive from the <tt>Pass</tt>
1185class. An analysis group may have one or more implementations, one of which is
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1186the "default" implementation.</p>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1187
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1188<p>Analysis groups are used by client passes just like other passes are: the
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1189<tt>AnalysisUsage::addRequired()</tt> and <tt>Pass::getAnalysis()</tt> methods.
1190In order to resolve this requirement, the <a href="#passmanager">PassManager</a>
1191scans the available passes to see if any implementations of the analysis group
1192are available. If none is available, the default implementation is created for
1193the pass to use. All standard rules for <A href="#interaction">interaction
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1194between passes</a> still apply.</p>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1195
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1196<p>Although <a href="#registration">Pass Registration</a> is optional for normal
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1197passes, all analysis group implementations must be registered, and must use the
1198<A href="#registerag"><tt>RegisterAnalysisGroup</tt></a> template to join the
1199implementation pool. Also, a default implementation of the interface
1200<b>must</b> be registered with <A
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1201href="#registerag"><tt>RegisterAnalysisGroup</tt></a>.</p>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1202
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1203<p>As a concrete example of an Analysis Group in action, consider the <a
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]1204href="http://llvm.org/doxygen/classllvm_1_1AliasAnalysis.html">AliasAnalysis</a>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1205analysis group. The default implementation of the alias analysis interface (the
1206<tt><a
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]1207href="http://llvm.org/doxygen/structBasicAliasAnalysis.html">basicaa</a></tt>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1208pass) just does a few simple checks that don't require significant analysis to
1209compute (such as: two different globals can never alias each other, etc).
1210Passes that use the <tt><a
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]1211href="http://llvm.org/doxygen/classllvm_1_1AliasAnalysis.html">AliasAnalysis</a></tt>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1212interface (for example the <tt><a
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]1213href="http://llvm.org/doxygen/structGCSE.html">gcse</a></tt> pass), do
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1214not care which implementation of alias analysis is actually provided, they just
1215use the designated interface.</p>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1216
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1217<p>From the user's perspective, commands work just like normal. Issuing the
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1218command '<tt>opt -gcse ...</tt>' will cause the <tt>basicaa</tt> class to be
1219instantiated and added to the pass sequence. Issuing the command '<tt>opt
1220-somefancyaa -gcse ...</tt>' will cause the <tt>gcse</tt> pass to use the
1221<tt>somefancyaa</tt> alias analysis (which doesn't actually exist, it's just a
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1222hypothetical example) instead.</p>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1223
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1224</div>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1225
1226<!-- _______________________________________________________________________ -->
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]1227<div class="doc_subsubsection">
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1228 <a name="registerag">Using <tt>RegisterAnalysisGroup</tt></a>
1229</div>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1230
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1231<div class="doc_text">
1232
1233<p>The <tt>RegisterAnalysisGroup</tt> template is used to register the analysis
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1234group itself as well as add pass implementations to the analysis group. First,
1235an analysis should be registered, with a human readable name provided for it.
1236Unlike registration of passes, there is no command line argument to be specified
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1237for the Analysis Group Interface itself, because it is "abstract":</p>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1238
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1239<div class="doc_code"><pre>
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]1240 <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]1241</pre></div>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1242
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1243<p>Once the analysis is registered, passes can declare that they are valid
1244implementations of the interface by using the following code:</p>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1245
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1246<div class="doc_code"><pre>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1247<b>namespace</b> {
1248 //<i> Analysis Group implementations <b>must</b> be registered normally...</i>
Chris Lattnerc8603c22006-08-27 23:18:52 +0000[diff] [blame]1249 RegisterPass&lt;FancyAA&gt;
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1250 B("<i>somefancyaa</i>", "<i>A more complex alias analysis implementation</i>");
1251
1252 //<i> Declare that we implement the AliasAnalysis interface</i>
Chris Lattnerdc877252006-08-28 00:45:38 +0000[diff] [blame]1253 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]1254}
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1255</pre></div>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1256
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1257<p>This just shows a class <tt>FancyAA</tt> that is registered normally, then
1258uses the <tt>RegisterAnalysisGroup</tt> template to "join" the <tt><a
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]1259href="http://llvm.org/doxygen/classllvm_1_1AliasAnalysis.html">AliasAnalysis</a></tt>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1260analysis group. Every implementation of an analysis group should join using
1261this template. A single pass may join multiple different analysis groups with
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1262no problem.</p>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1263
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1264<div class="doc_code"><pre>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1265<b>namespace</b> {
1266 //<i> Analysis Group implementations <b>must</b> be registered normally...</i>
Chris Lattnerc8603c22006-08-27 23:18:52 +0000[diff] [blame]1267 RegisterPass&lt;<a href="http://llvm.org/doxygen/structBasicAliasAnalysis.html">BasicAliasAnalysis</a>&gt;
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1268 D("<i>basicaa</i>", "<i>Basic Alias Analysis (default AA impl)</i>");
1269
1270 //<i> Declare that we implement the AliasAnalysis interface</i>
Chris Lattnerdc877252006-08-28 00:45:38 +0000[diff] [blame]1271 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]1272}
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1273</pre></div>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1274
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1275<p>Here we show how the default implementation is specified (using the extra
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1276argument to the <tt>RegisterAnalysisGroup</tt> template). There must be exactly
1277one default implementation available at all times for an Analysis Group to be
1278used. Here we declare that the <tt><a
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]1279href="http://llvm.org/doxygen/structBasicAliasAnalysis.html">BasicAliasAnalysis</a></tt>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1280pass is the default implementation for the interface.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1281
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1282</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1283
1284<!-- *********************************************************************** -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1285<div class="doc_section">
Tanya Lattnerd5383652004-11-19 01:25:14 +0000[diff] [blame]1286 <a name="passStatistics">Pass Statistics</a>
1287</div>
1288<!-- *********************************************************************** -->
1289
1290<div class="doc_text">
Tanya Lattner05f8d5f2004-11-19 01:26:37 +0000[diff] [blame]1291<p>The <a
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]1292href="http://llvm.org/doxygen/Statistic_8h-source.html"><tt>Statistic</tt></a>
John Criswell0b1010e2005-11-28 23:25:41 +0000[diff] [blame]1293class is designed to be an easy way to expose various success
Tanya Lattnerd5383652004-11-19 01:25:14 +0000[diff] [blame]1294metrics from passes. These statistics are printed at the end of a
1295run, when the -stats command line option is enabled on the command
Tanya Lattner05f8d5f2004-11-19 01:26:37 +0000[diff] [blame]1296line. 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]1297
1298</div>
1299
1300
1301<!-- *********************************************************************** -->
1302<div class="doc_section">
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1303 <a name="passmanager">What PassManager does</a>
1304</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1305<!-- *********************************************************************** -->
1306
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1307<div class="doc_text">
1308
1309<p>The <a
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]1310href="http://llvm.org/doxygen/PassManager_8h-source.html"><tt>PassManager</tt></a>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1311<a
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]1312href="http://llvm.org/doxygen/classllvm_1_1PassManager.html">class</a>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1313takes a list of passes, ensures their <a href="#interaction">prerequisites</a>
1314are set up correctly, and then schedules passes to run efficiently. All of the
1315LLVM tools that run passes use the <tt>PassManager</tt> for execution of these
1316passes.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1317
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1318<p>The <tt>PassManager</tt> does two main things to try to reduce the execution
1319time of a series of passes:</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1320
1321<ol>
1322<li><b>Share analysis results</b> - The PassManager attempts to avoid
1323recomputing analysis results as much as possible. This means keeping track of
1324which analyses are available already, which analyses get invalidated, and which
1325analyses are needed to be run for a pass. An important part of work is that the
1326<tt>PassManager</tt> tracks the exact lifetime of all analysis results, allowing
1327it to <a href="#releaseMemory">free memory</a> allocated to holding analysis
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1328results as soon as they are no longer needed.</li>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1329
1330<li><b>Pipeline the execution of passes on the program</b> - The
1331<tt>PassManager</tt> attempts to get better cache and memory usage behavior out
1332of a series of passes by pipelining the passes together. This means that, given
1333a series of consequtive <a href="#FunctionPass"><tt>FunctionPass</tt></a>'s, it
1334will execute all of the <a href="#FunctionPass"><tt>FunctionPass</tt></a>'s on
1335the first function, then all of the <a
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1336href="#FunctionPass"><tt>FunctionPass</tt></a>es on the second function,
1337etc... until the entire program has been run through the passes.
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1338
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1339<p>This improves the cache behavior of the compiler, because it is only touching
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1340the LLVM program representation for a single function at a time, instead of
1341traversing the entire program. It reduces the memory consumption of compiler,
1342because, for example, only one <a
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]1343href="http://llvm.org/doxygen/classllvm_1_1DominatorSet.html"><tt>DominatorSet</tt></a>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1344needs to be calculated at a time. This also makes it possible some <a
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1345href="#SMP">interesting enhancements</a> in the future.</p></li>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1346
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1347</ol>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1348
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1349<p>The effectiveness of the <tt>PassManager</tt> is influenced directly by how
1350much information it has about the behaviors of the passes it is scheduling. For
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1351example, the "preserved" set is intentionally conservative in the face of an
1352unimplemented <a href="#getAnalysisUsage"><tt>getAnalysisUsage</tt></a> method.
1353Not implementing when it should be implemented will have the effect of not
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1354allowing any analysis results to live across the execution of your pass.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1355
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1356<p>The <tt>PassManager</tt> class exposes a <tt>--debug-pass</tt> command line
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1357options that is useful for debugging pass execution, seeing how things work, and
1358diagnosing when you should be preserving more analyses than you currently are
1359(To get information about all of the variants of the <tt>--debug-pass</tt>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1360option, just type '<tt>opt --help-hidden</tt>').</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1361
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1362<p>By using the <tt>--debug-pass=Structure</tt> option, for example, we can see
1363how our <a href="#basiccode">Hello World</a> pass interacts with other passes.
1364Lets try it out with the <tt>gcse</tt> and <tt>licm</tt> passes:</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1365
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1366<div class="doc_code"><pre>
Reid Spencer7fa6d522005-01-11 05:16:23 +0000[diff] [blame]1367$ 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]1368Module Pass Manager
1369 Function Pass Manager
1370 Dominator Set Construction
1371 Immediate Dominators Construction
1372 Global Common Subexpression Elimination
1373-- Immediate Dominators Construction
1374-- Global Common Subexpression Elimination
1375 Natural Loop Construction
1376 Loop Invariant Code Motion
1377-- Natural Loop Construction
1378-- Loop Invariant Code Motion
1379 Module Verifier
1380-- Dominator Set Construction
1381-- Module Verifier
1382 Bytecode Writer
1383--Bytecode Writer
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1384</pre></div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1385
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1386<p>This output shows us when passes are constructed and when the analysis
1387results are known to be dead (prefixed with '<tt>--</tt>'). Here we see that
1388GCSE uses dominator and immediate dominator information to do its job. The LICM
1389pass uses natural loop information, which uses dominator sets, but not immediate
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1390dominators. Because immediate dominators are no longer useful after the GCSE
1391pass, it is immediately destroyed. The dominator sets are then reused to
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1392compute natural loop information, which is then used by the LICM pass.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1393
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1394<p>After the LICM pass, the module verifier runs (which is automatically added
1395by the '<tt>opt</tt>' tool), which uses the dominator set to check that the
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1396resultant LLVM code is well formed. After it finishes, the dominator set
1397information is destroyed, after being computed once, and shared by three
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1398passes.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1399
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1400<p>Lets see how this changes when we run the <a href="#basiccode">Hello
1401World</a> pass in between the two passes:</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1402
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1403<div class="doc_code"><pre>
Reid Spencer7fa6d522005-01-11 05:16:23 +0000[diff] [blame]1404$ 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]1405Module Pass Manager
1406 Function Pass Manager
1407 Dominator Set Construction
1408 Immediate Dominators Construction
1409 Global Common Subexpression Elimination
1410<b>-- Dominator Set Construction</b>
1411-- Immediate Dominators Construction
1412-- Global Common Subexpression Elimination
1413<b> Hello World Pass
1414-- Hello World Pass
1415 Dominator Set Construction</b>
1416 Natural Loop Construction
1417 Loop Invariant Code Motion
1418-- Natural Loop Construction
1419-- Loop Invariant Code Motion
1420 Module Verifier
1421-- Dominator Set Construction
1422-- Module Verifier
1423 Bytecode Writer
1424--Bytecode Writer
1425Hello: __main
1426Hello: puts
1427Hello: main
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1428</pre></div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1429
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1430<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]1431Dominator Set pass, even though it doesn't modify the code at all! To fix this,
1432we need to add the following <a
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1433href="#getAnalysisUsage"><tt>getAnalysisUsage</tt></a> method to our pass:</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1434
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1435<div class="doc_code"><pre>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1436 <i>// We don't modify the program, so we preserve all analyses</i>
1437 <b>virtual void</b> getAnalysisUsage(AnalysisUsage &amp;AU) <b>const</b> {
1438 AU.setPreservesAll();
1439 }
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1440</pre></div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1441
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1442<p>Now when we run our pass, we get this output:</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1443
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1444<div class="doc_code"><pre>
Reid Spencer7fa6d522005-01-11 05:16:23 +0000[diff] [blame]1445$ 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]1446Pass Arguments: -gcse -hello -licm
1447Module Pass Manager
1448 Function Pass Manager
1449 Dominator Set Construction
1450 Immediate Dominators Construction
1451 Global Common Subexpression Elimination
1452-- Immediate Dominators Construction
1453-- Global Common Subexpression Elimination
1454 Hello World Pass
1455-- Hello World Pass
1456 Natural Loop Construction
1457 Loop Invariant Code Motion
1458-- Loop Invariant Code Motion
1459-- Natural Loop Construction
1460 Module Verifier
1461-- Dominator Set Construction
1462-- Module Verifier
1463 Bytecode Writer
1464--Bytecode Writer
1465Hello: __main
1466Hello: puts
1467Hello: main
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1468</pre></div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1469
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1470<p>Which shows that we don't accidentally invalidate dominator information
1471anymore, and therefore do not have to compute it twice.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1472
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1473</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1474
1475<!-- _______________________________________________________________________ -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1476<div class="doc_subsubsection">
1477 <a name="releaseMemory">The <tt>releaseMemory</tt> method</a>
1478</div>
1479
1480<div class="doc_text">
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1481
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1482<div class="doc_code"><pre>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1483 <b>virtual void</b> releaseMemory();
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1484</pre></div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1485
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1486<p>The <tt>PassManager</tt> automatically determines when to compute analysis
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1487results, and how long to keep them around for. Because the lifetime of the pass
1488object itself is effectively the entire duration of the compilation process, we
1489need some way to free analysis results when they are no longer useful. The
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1490<tt>releaseMemory</tt> virtual method is the way to do this.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1491
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1492<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]1493amount of state (for use by another pass which "requires" your pass and uses the
1494<a href="#getAnalysis">getAnalysis</a> method) you should implement
1495<tt>releaseMEmory</tt> to, well, release the memory allocated to maintain this
1496internal state. This method is called after the <tt>run*</tt> method for the
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1497class, before the next call of <tt>run*</tt> in your pass.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1498
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1499</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1500
1501<!-- *********************************************************************** -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1502<div class="doc_section">
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1503 <a name="registering">Registering dynamically loaded passes</a>
1504</div>
1505<!-- *********************************************************************** -->
1506
1507<div class="doc_text">
1508
1509<p><i>Size matters</i> when constructing production quality tools using llvm,
1510both for the purposes of distribution, and for regulating the resident code size
1511when running on the target system. Therefore, it becomes desirable to
1512selectively use some passes, while omitting others and maintain the flexibility
1513to change configurations later on. You want to be able to do all this, and,
1514provide feedback to the user. This is where pass registration comes into
1515play.</p>
1516
1517<p>The fundamental mechanisms for pass registration are the
1518<tt>MachinePassRegistry</tt> class and subclasses of
1519<tt>MachinePassRegistryNode</tt>.</p>
1520
1521<p>An instance of <tt>MachinePassRegistry</tt> is used to maintain a list of
1522<tt>MachinePassRegistryNode</tt> objects. This instance maintains the list and
1523communicates additions and deletions to the command line interface.</p>
1524
1525<p>An instance of <tt>MachinePassRegistryNode</tt> subclass is used to maintain
1526information provided about a particular pass. This information includes the
1527command line name, the command help string and the address of the function used
1528to create an instance of the pass. A global static constructor of one of these
1529instances <i>registers</i> with a corresponding <tt>MachinePassRegistry</tt>,
1530the static destructor <i>unregisters</i>. Thus a pass that is statically linked
1531in the tool will be registered at start up. A dynamically loaded pass will
1532register on load and unregister at unload.</p>
1533
1534</div>
1535
1536<!-- _______________________________________________________________________ -->
1537<div class="doc_subsection">
1538 <a name="registering_existing">Using existing registries</a>
1539</div>
1540
1541<div class="doc_text">
1542
1543<p>There are predefined registries to track instruction scheduling
1544(<tt>RegisterScheduler</tt>) and register allocation (<tt>RegisterRegAlloc</tt>)
1545machine passes. Here we will describe how to <i>register</i> a register
1546allocator machine pass.</p>
1547
1548<p>Implement your register allocator machine pass. In your register allocator
1549.cpp file add the following include;</p>
1550
1551<div class="doc_code"><pre>
Chris Lattner8f652eb2006-08-11 16:37:02 +0000[diff] [blame]1552 #include "llvm/CodeGen/RegAllocRegistry.h"
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1553</pre></div>
1554
1555<p>Also in your register allocator .cpp file, define a creator function in the
1556form; </p>
1557
1558<div class="doc_code"><pre>
1559 FunctionPass *createMyRegisterAllocator() {
1560 return new MyRegisterAllocator();
1561 }
1562</pre></div>
1563
1564<p>Note that the signature of this function should match the type of
1565<tt>RegisterRegAlloc::FunctionPassCtor</tt>. In the same file add the
1566"installing" declaration, in the form;</p>
1567
1568<div class="doc_code"><pre>
1569 static RegisterRegAlloc myRegAlloc("myregalloc",
1570 " my register allocator help string",
1571 createMyRegisterAllocator);
1572</pre></div>
1573
1574<p>Note the two spaces prior to the help string produces a tidy result on the
1575--help query.</p>
1576
1577<div class="doc_code"><pre>
1578$ llc --help
1579 ...
1580 -regalloc - Register allocator to use: (default = linearscan)
1581 =linearscan - linear scan register allocator
1582 =local - local register allocator
1583 =simple - simple register allocator
1584 =myregalloc - my register allocator help string
1585 ...
1586</pre></div>
1587
1588<p>And that's it. The user is now free to use <tt>-regalloc=myregalloc</tt> as
1589an option. Registering instruction schedulers is similar except use the
Chris Lattner8f652eb2006-08-11 16:37:02 +0000[diff] [blame]1590<tt>RegisterScheduler</tt> class. Note that the
1591<tt>RegisterScheduler::FunctionPassCtor</tt> is significantly different from
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1592<tt>RegisterRegAlloc::FunctionPassCtor</tt>.</p>
1593
1594<p>To force the load/linking of your register allocator into the llc/lli tools,
1595add your creator function's global declaration to "Passes.h" and add a "pseudo"
1596call line to <tt>llvm/Codegen/LinkAllCodegenComponents.h</tt>.</p>
1597
1598</div>
1599
1600
1601<!-- _______________________________________________________________________ -->
1602<div class="doc_subsection">
1603 <a name="registering_new">Creating new registries</a>
1604</div>
1605
1606<div class="doc_text">
1607
1608<p>The easiest way to get started is to clone one of the existing registries; we
1609recommend <tt>llvm/CodeGen/RegAllocRegistry.h</tt>. The key things to modify
1610are the class name and the <tt>FunctionPassCtor</tt> type.</p>
1611
1612<p>Then you need to declare the registry. Example: if your pass registry is
1613<tt>RegisterMyPasses</tt> then define;</p>
1614
1615<div class="doc_code"><pre>
1616MachinePassRegistry RegisterMyPasses::Registry;
1617</pre></div>
1618
1619<p>And finally, declare the command line option for your passes. Example:</p>
1620
1621<div class="doc_code"><pre>
1622 cl::opt&lt;RegisterMyPasses::FunctionPassCtor, false,
1623 RegisterPassParser&lt;RegisterMyPasses&gt &gt
1624 MyPassOpt("mypass",
1625 cl::init(&amp;createDefaultMyPass),
1626 cl::desc("my pass option help"));
1627</pre></div>
1628
1629<p>Here the command option is "mypass", with createDefaultMyPass as the default
1630creator.</p>
1631
1632</div>
1633
1634<!-- *********************************************************************** -->
1635<div class="doc_section">
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1636 <a name="debughints">Using GDB with dynamically loaded passes</a>
1637</div>
Chris Lattner480e2ef2002-09-06 02:02:58 +0000[diff] [blame]1638<!-- *********************************************************************** -->
1639
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1640<div class="doc_text">
1641
1642<p>Unfortunately, using GDB with dynamically loaded passes is not as easy as it
Chris Lattner480e2ef2002-09-06 02:02:58 +0000[diff] [blame]1643should be. First of all, you can't set a breakpoint in a shared object that has
1644not been loaded yet, and second of all there are problems with inlined functions
1645in shared objects. Here are some suggestions to debugging your pass with
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1646GDB.</p>
Chris Lattner480e2ef2002-09-06 02:02:58 +0000[diff] [blame]1647
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1648<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]1649transformation invoked by <tt>opt</tt>, although nothing described here depends
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1650on that.</p>
1651
1652</div>
Chris Lattner480e2ef2002-09-06 02:02:58 +0000[diff] [blame]1653
1654<!-- _______________________________________________________________________ -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1655<div class="doc_subsubsection">
1656 <a name="breakpoint">Setting a breakpoint in your pass</a>
1657</div>
Chris Lattner480e2ef2002-09-06 02:02:58 +0000[diff] [blame]1658
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1659<div class="doc_text">
1660
1661<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]1662
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1663<div class="doc_code"><pre>
Chris Lattner480e2ef2002-09-06 02:02:58 +0000[diff] [blame]1664$ <b>gdb opt</b>
1665GNU gdb 5.0
1666Copyright 2000 Free Software Foundation, Inc.
1667GDB is free software, covered by the GNU General Public License, and you are
1668welcome to change it and/or distribute copies of it under certain conditions.
1669Type "show copying" to see the conditions.
1670There is absolutely no warranty for GDB. Type "show warranty" for details.
1671This GDB was configured as "sparc-sun-solaris2.6"...
1672(gdb)
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1673</pre></div>
Chris Lattner480e2ef2002-09-06 02:02:58 +0000[diff] [blame]1674
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1675<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]1676time to load. Be patient. Since we cannot set a breakpoint in our pass yet
1677(the shared object isn't loaded until runtime), we must execute the process, and
1678have it stop before it invokes our pass, but after it has loaded the shared
1679object. The most foolproof way of doing this is to set a breakpoint in
1680<tt>PassManager::run</tt> and then run the process with the arguments you
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1681want:</p>
Chris Lattner480e2ef2002-09-06 02:02:58 +0000[diff] [blame]1682
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1683<div class="doc_code"><pre>
Reid Spencer22a9e5b2006-09-28 16:53:47 +0000[diff] [blame]1684(gdb) <b>break llvm::PassManager::run</b>
Chris Lattner480e2ef2002-09-06 02:02:58 +0000[diff] [blame]1685Breakpoint 1 at 0x2413bc: file Pass.cpp, line 70.
Chris Lattner4c376ea2005-04-21 04:52:37 +0000[diff] [blame]1686(gdb) <b>run test.bc -load $(LLVMTOP)/llvm/Debug/lib/[libname].so -[passoption]</b>
1687Starting program: opt test.bc -load $(LLVMTOP)/llvm/Debug/lib/[libname].so -[passoption]
Chris Lattner480e2ef2002-09-06 02:02:58 +0000[diff] [blame]1688Breakpoint 1, PassManager::run (this=0xffbef174, M=@0x70b298) at Pass.cpp:70
168970 bool PassManager::run(Module &amp;M) { return PM-&gt;run(M); }
1690(gdb)
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1691</pre></div>
Chris Lattner480e2ef2002-09-06 02:02:58 +0000[diff] [blame]1692
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1693<p>Once the <tt>opt</tt> stops in the <tt>PassManager::run</tt> method you are
1694now free to set breakpoints in your pass so that you can trace through execution
1695or do other standard debugging stuff.</p>
Chris Lattner480e2ef2002-09-06 02:02:58 +0000[diff] [blame]1696
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1697</div>
Chris Lattner480e2ef2002-09-06 02:02:58 +0000[diff] [blame]1698
1699<!-- _______________________________________________________________________ -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1700<div class="doc_subsubsection">
1701 <a name="debugmisc">Miscellaneous Problems</a>
1702</div>
Chris Lattner480e2ef2002-09-06 02:02:58 +0000[diff] [blame]1703
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1704<div class="doc_text">
1705
1706<p>Once you have the basics down, there are a couple of problems that GDB has,
1707some with solutions, some without.</p>
Chris Lattner480e2ef2002-09-06 02:02:58 +0000[diff] [blame]1708
1709<ul>
1710<li>Inline functions have bogus stack information. In general, GDB does a
1711pretty good job getting stack traces and stepping through inline functions.
1712When a pass is dynamically loaded however, it somehow completely loses this
1713capability. The only solution I know of is to de-inline a function (move it
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1714from the body of a class to a .cpp file).</li>
Chris Lattner480e2ef2002-09-06 02:02:58 +0000[diff] [blame]1715
1716<li>Restarting the program breaks breakpoints. After following the information
1717above, you have succeeded in getting some breakpoints planted in your pass. Nex
1718thing you know, you restart the program (i.e., you type '<tt>run</tt>' again),
1719and you start getting errors about breakpoints being unsettable. The only way I
1720have found to "fix" this problem is to <tt>delete</tt> the breakpoints that are
1721already set in your pass, run the program, and re-set the breakpoints once
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1722execution stops in <tt>PassManager::run</tt>.</li>
Chris Lattner480e2ef2002-09-06 02:02:58 +0000[diff] [blame]1723
1724</ul>
1725
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1726<p>Hopefully these tips will help with common case debugging situations. If
1727you'd like to contribute some tips of your own, just contact <a
1728href="mailto:sabre@nondot.org">Chris</a>.</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_section">
1734 <a name="future">Future extensions planned</a>
1735</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1736<!-- *********************************************************************** -->
1737
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1738<div class="doc_text">
1739
1740<p>Although the LLVM Pass Infrastructure is very capable as it stands, and does
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1741some 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]1742where we are going:</p>
1743
1744</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1745
1746<!-- _______________________________________________________________________ -->
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]1747<div class="doc_subsubsection">
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1748 <a name="SMP">Multithreaded LLVM</a>
1749</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1750
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1751<div class="doc_text">
1752
1753<p>Multiple CPU machines are becoming more common and compilation can never be
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1754fast enough: obviously we should allow for a multithreaded compiler. Because of
1755the semantics defined for passes above (specifically they cannot maintain state
1756across invocations of their <tt>run*</tt> methods), a nice clean way to
1757implement a multithreaded compiler would be for the <tt>PassManager</tt> class
Misha Brukmanbc0e9982003-07-14 17:20:40 +0000[diff] [blame]1758to create multiple instances of each pass object, and allow the separate
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1759instances to be hacking on different parts of the program at the same time.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1760
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1761<p>This implementation would prevent each of the passes from having to implement
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1762multithreaded constructs, requiring only the LLVM core to have locking in a few
1763places (for global resources). Although this is a simple extension, we simply
1764haven't had time (or multiprocessor machines, thus a reason) to implement this.
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1765Despite that, we have kept the LLVM passes SMP ready, and you should too.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1766
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1767</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1768
1769<!-- _______________________________________________________________________ -->
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]1770<div class="doc_subsubsection">
Chris Lattnerf6278922004-09-20 04:36:29 +0000[diff] [blame]1771<a name="PassFunctionPass"><tt>ModulePass</tt>es requiring <tt>FunctionPass</tt>es</a>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1772</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1773
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1774<div class="doc_text">
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1775
Chris Lattnerf6278922004-09-20 04:36:29 +0000[diff] [blame]1776<p>Currently it is illegal for a <a href="#ModulePass"><tt>ModulePass</tt></a>
1777to require a <a href="#FunctionPass"><tt>FunctionPass</tt></a>. This is because
1778there is only one instance of the <a
1779href="#FunctionPass"><tt>FunctionPass</tt></a> object ever created, thus nowhere
1780to store information for all of the functions in the program at the same time.
1781Although this has come up a couple of times before, this has always been worked
1782around by factoring one big complicated pass into a global and an
1783interprocedural part, both of which are distinct. In the future, it would be
1784nice to have this though.</p>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1785
1786<p>Note that it is no problem for a <a
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1787href="#FunctionPass"><tt>FunctionPass</tt></a> to require the results of a <a
Chris Lattnerf6278922004-09-20 04:36:29 +0000[diff] [blame]1788href="#ModulePass"><tt>ModulePass</tt></a>, only the other way around.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1789
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1790</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1791
1792<!-- *********************************************************************** -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1793<hr>
1794<address>
1795 <a href="http://jigsaw.w3.org/css-validator/check/referer"><img
1796 src="http://jigsaw.w3.org/css-validator/images/vcss" alt="Valid CSS!"></a>
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1798 src="http://www.w3.org/Icons/valid-html401" alt="Valid HTML 4.01!" /></a>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1799
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1800 <a href="mailto:sabre@nondot.org">Chris Lattner</a><br>
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]1801 <a href="http://llvm.org">The LLVM Compiler Infrastructure</a><br>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1802 Last modified: $Date$
1803</address>
1804
1805</body>
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