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gerrit-public.fairphone.software / fp2-dev / platform / external / llvm / 444087057ad0592f3e0bb2e434e0b610aa7914f6 / . / docs / WritingAnLLVMPass.html
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Reid Spencer7fa6d522005-01-11 05:16:23 +0000[diff] [blame]5 <meta http-equiv="Content-Type" content="text/html; charset=utf-8">
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]6 <title>Writing an LLVM Pass</title>
7 <link rel="stylesheet" href="llvm.css" type="text/css">
8</head>
9<body>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]10
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]11<div class="doc_title">
12 Writing an LLVM Pass
13</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]14
15<ol>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]16 <li><a href="#introduction">Introduction - What is a pass?</a></li>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]17 <li><a href="#quickstart">Quick Start - Writing hello world</a>
18 <ul>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]19 <li><a href="#makefile">Setting up the build environment</a></li>
20 <li><a href="#basiccode">Basic code required</a></li>
Chris Lattnerc8603c22006-08-27 23:18:52 +0000[diff] [blame]21 <li><a href="#running">Running a pass with <tt>opt</tt></a></li>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]22 </ul></li>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]23 <li><a href="#passtype">Pass classes and requirements</a>
24 <ul>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]25 <li><a href="#ImmutablePass">The <tt>ImmutablePass</tt> class</a></li>
Chris Lattnerf6278922004-09-20 04:36:29 +0000[diff] [blame]26 <li><a href="#ModulePass">The <tt>ModulePass</tt> class</a>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]27 <ul>
Chris Lattnerf6278922004-09-20 04:36:29 +0000[diff] [blame]28 <li><a href="#runOnModule">The <tt>runOnModule</tt> method</a></li>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]29 </ul></li>
Chris Lattner8fdb2462004-09-18 06:39:35 +0000[diff] [blame]30 <li><a href="#CallGraphSCCPass">The <tt>CallGraphSCCPass</tt> class</a>
31 <ul>
Devang Patelc20048d2007-01-23 22:56:28 +0000[diff] [blame]32 <li><a href="#doInitialization_scc">The <tt>doInitialization(CallGraph
Chris Lattner8fdb2462004-09-18 06:39:35 +0000[diff] [blame]33 &amp;)</tt> method</a></li>
34 <li><a href="#runOnSCC">The <tt>runOnSCC</tt> method</a></li>
Devang Patelc20048d2007-01-23 22:56:28 +0000[diff] [blame]35 <li><a href="#doFinalization_scc">The <tt>doFinalization(CallGraph
Chris Lattner8fdb2462004-09-18 06:39:35 +0000[diff] [blame]36 &amp;)</tt> method</a></li>
37 </ul></li>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]38 <li><a href="#FunctionPass">The <tt>FunctionPass</tt> class</a>
39 <ul>
Chris Lattnerd0713f92002-09-12 17:06:43 +0000[diff] [blame]40 <li><a href="#doInitialization_mod">The <tt>doInitialization(Module
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]41 &amp;)</tt> method</a></li>
42 <li><a href="#runOnFunction">The <tt>runOnFunction</tt> method</a></li>
Chris Lattnerd0713f92002-09-12 17:06:43 +0000[diff] [blame]43 <li><a href="#doFinalization_mod">The <tt>doFinalization(Module
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]44 &amp;)</tt> method</a></li>
45 </ul></li>
Devang Patel2e8f27d2007-03-19 22:21:25 +0000[diff] [blame]46 <li><a href="#LoopPass">The <tt>LoopPass</tt> class</a>
47 <ul>
48 <li><a href="#doInitialization_loop">The <tt>doInitialization(Loop *,
49 LPPassManager &amp;)</tt> method</a></li>
50 <li><a href="#runOnLoop">The <tt>runOnLoop</tt> method</a></li>
51 <li><a href="#doFinalization_loop">The <tt>doFinalization()
52 </tt> method</a></li>
53 </ul></li>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]54 <li><a href="#BasicBlockPass">The <tt>BasicBlockPass</tt> class</a>
55 <ul>
Chris Lattnerd0713f92002-09-12 17:06:43 +0000[diff] [blame]56 <li><a href="#doInitialization_fn">The <tt>doInitialization(Function
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]57 &amp;)</tt> method</a></li>
58 <li><a href="#runOnBasicBlock">The <tt>runOnBasicBlock</tt>
59 method</a></li>
Chris Lattnerd0713f92002-09-12 17:06:43 +0000[diff] [blame]60 <li><a href="#doFinalization_fn">The <tt>doFinalization(Function
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]61 &amp;)</tt> method</a></li>
62 </ul></li>
Brian Gaekecab8b6f2003-07-17 18:53:20 +0000[diff] [blame]63 <li><a href="#MachineFunctionPass">The <tt>MachineFunctionPass</tt>
64 class</a>
Brian Gaeke6a33f362003-07-22 20:53:20 +0000[diff] [blame]65 <ul>
66 <li><a href="#runOnMachineFunction">The
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]67 <tt>runOnMachineFunction(MachineFunction &amp;)</tt> method</a></li>
68 </ul></li>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]69 </ul>
70 <li><a href="#registration">Pass Registration</a>
71 <ul>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]72 <li><a href="#print">The <tt>print</tt> method</a></li>
73 </ul></li>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]74 <li><a href="#interaction">Specifying interactions between passes</a>
75 <ul>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]76 <li><a href="#getAnalysisUsage">The <tt>getAnalysisUsage</tt>
77 method</a></li>
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]78 <li><a href="#AU::addRequired">The <tt>AnalysisUsage::addRequired&lt;&gt;</tt> and <tt>AnalysisUsage::addRequiredTransitive&lt;&gt;</tt> methods</a></li>
79 <li><a href="#AU::addPreserved">The <tt>AnalysisUsage::addPreserved&lt;&gt;</tt> method</a></li>
80 <li><a href="#AU::examples">Example implementations of <tt>getAnalysisUsage</tt></a></li>
81 <li><a href="#getAnalysis">The <tt>getAnalysis&lt;&gt;</tt> and <tt>getAnalysisToUpdate&lt;&gt;</tt> methods</a></li>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]82 </ul></li>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]83 <li><a href="#analysisgroup">Implementing Analysis Groups</a>
84 <ul>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]85 <li><a href="#agconcepts">Analysis Group Concepts</a></li>
86 <li><a href="#registerag">Using <tt>RegisterAnalysisGroup</tt></a></li>
87 </ul></li>
Tanya Lattnerd5383652004-11-19 01:25:14 +0000[diff] [blame]88 <li><a href="#passStatistics">Pass Statistics</a>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]89 <li><a href="#passmanager">What PassManager does</a>
90 <ul>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]91 <li><a href="#releaseMemory">The <tt>releaseMemory</tt> method</a></li>
92 </ul></li>
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]93 <li><a href="#registering">Registering dynamically loaded passes</a>
94 <ul>
95 <li><a href="#registering_existing">Using existing registries</a></li>
96 <li><a href="#registering_new">Creating new registries</a></li>
97 </ul></li>
Chris Lattner480e2ef2002-09-06 02:02:58 +0000[diff] [blame]98 <li><a href="#debughints">Using GDB with dynamically loaded passes</a>
99 <ul>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]100 <li><a href="#breakpoint">Setting a breakpoint in your pass</a></li>
101 <li><a href="#debugmisc">Miscellaneous Problems</a></li>
102 </ul></li>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]103 <li><a href="#future">Future extensions planned</a>
104 <ul>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]105 <li><a href="#SMP">Multithreaded LLVM</a></li>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]106 </ul></li>
107</ol>
Chris Lattner38c633d2002-08-08 20:23:41 +0000[diff] [blame]108
Chris Lattner7911ce22004-05-23 21:07:27 +0000[diff] [blame]109<div class="doc_author">
Chris Lattner8f652eb2006-08-11 16:37:02 +0000[diff] [blame]110 <p>Written by <a href="mailto:sabre@nondot.org">Chris Lattner</a> and
Jim Laskeyc760a922007-03-14 19:32:21 +0000[diff] [blame]111 <a href="mailto:jlaskey@mac.com">Jim Laskey</a></p>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]112</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]113
114<!-- *********************************************************************** -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]115<div class="doc_section">
116 <a name="introduction">Introduction - What is a pass?</a>
117</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]118<!-- *********************************************************************** -->
119
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]120<div class="doc_text">
121
122<p>The LLVM Pass Framework is an important part of the LLVM system, because LLVM
Chris Lattner8fdb2462004-09-18 06:39:35 +0000[diff] [blame]123passes are where most of the interesting parts of the compiler exist. Passes
124perform the transformations and optimizations that make up the compiler, they
125build the analysis results that are used by these transformations, and they are,
126above all, a structuring technique for compiler code.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]127
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]128<p>All LLVM passes are subclasses of the <tt><a
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]129href="http://llvm.org/doxygen/classllvm_1_1Pass.html">Pass</a></tt>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]130class, which implement functionality by overriding virtual methods inherited
Chris Lattnerf6278922004-09-20 04:36:29 +0000[diff] [blame]131from <tt>Pass</tt>. Depending on how your pass works, you should inherit from
132the <tt><a href="#ModulePass">ModulePass</a></tt>, <tt><a
133href="#CallGraphSCCPass">CallGraphSCCPass</a></tt>, <tt><a
134href="#FunctionPass">FunctionPass</a></tt>, or <tt><a
Devang Patel2e8f27d2007-03-19 22:21:25 +0000[diff] [blame]135href="#LoopPass">LoopPass</a></tt>, or <tt><a
Chris Lattner8fdb2462004-09-18 06:39:35 +0000[diff] [blame]136href="#BasicBlockPass">BasicBlockPass</a></tt> classes, which gives the system
137more information about what your pass does, and how it can be combined with
138other passes. One of the main features of the LLVM Pass Framework is that it
139schedules passes to run in an efficient way based on the constraints that your
140pass meets (which are indicated by which class they derive from).</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]141
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]142<p>We start by showing you how to construct a pass, everything from setting up
143the code, to compiling, loading, and executing it. After the basics are down,
144more advanced features are discussed.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]145
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]146</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]147
148<!-- *********************************************************************** -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]149<div class="doc_section">
150 <a name="quickstart">Quick Start - Writing hello world</a>
151</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]152<!-- *********************************************************************** -->
153
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]154<div class="doc_text">
155
156<p>Here we describe how to write the "hello world" of passes. The "Hello" pass
157is designed to simply print out the name of non-external functions that exist in
Chris Lattner8fdb2462004-09-18 06:39:35 +0000[diff] [blame]158the program being compiled. It does not modify the program at all, it just
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]159inspects it. The source code and files for this pass are available in the LLVM
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]160source tree in the <tt>lib/Transforms/Hello</tt> directory.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]161
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]162</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]163
164<!-- ======================================================================= -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]165<div class="doc_subsection">
166 <a name="makefile">Setting up the build environment</a>
167</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]168
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]169<div class="doc_text">
170
Reid Spencer1bc19342004-12-11 05:12:57 +0000[diff] [blame]171 <p>First, you need to create a new directory somewhere in the LLVM source
172 base. For this example, we'll assume that you made
173 <tt>lib/Transforms/Hello</tt>. Next, you must set up a build script
174 (Makefile) that will compile the source code for the new pass. To do this,
175 copy the following into <tt>Makefile</tt>:</p>
176 <hr/>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]177
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]178<div class="doc_code"><pre>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]179# Makefile for hello pass
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]180
Chris Lattner17a4c3e2002-08-14 20:06:13 +0000[diff] [blame]181# Path to top level of LLVM heirarchy
Chris Lattner7ce83e52002-08-14 20:07:01 +0000[diff] [blame]182LEVEL = ../../..
Chris Lattner17a4c3e2002-08-14 20:06:13 +0000[diff] [blame]183
184# Name of the library to build
Reid Spencer7fa6d522005-01-11 05:16:23 +0000[diff] [blame]185LIBRARYNAME = Hello
Chris Lattner17a4c3e2002-08-14 20:06:13 +0000[diff] [blame]186
Reid Spencer7fa6d522005-01-11 05:16:23 +0000[diff] [blame]187# Make the shared library become a loadable module so the tools can
188# dlopen/dlsym on the resulting library.
Robert Bocchino3cf817d2006-01-06 22:49:23 +0000[diff] [blame]189LOADABLE_MODULE = 1
Reid Spencer7fa6d522005-01-11 05:16:23 +0000[diff] [blame]190
Reid Spencerebfe07f2006-08-08 01:48:17 +0000[diff] [blame]191# Tell the build system which LLVM libraries your pass needs. You'll probably
192# need at least LLVMSystem.a, LLVMSupport.a, LLVMCore.a but possibly several
193# others too.
194LLVMLIBS = LLVMCore.a LLVMSupport.a LLVMSystem.a
195
Chris Lattner17a4c3e2002-08-14 20:06:13 +0000[diff] [blame]196# Include the makefile implementation stuff
197include $(LEVEL)/Makefile.common
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]198</pre></div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]199
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]200<p>This makefile specifies that all of the <tt>.cpp</tt> files in the current
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]201directory are to be compiled and linked together into a
Reid Spencer7fa6d522005-01-11 05:16:23 +0000[diff] [blame]202<tt>Debug/lib/Hello.so</tt> shared object that can be dynamically loaded by
Chris Lattnerc8603c22006-08-27 23:18:52 +0000[diff] [blame]203the <tt>opt</tt> or <tt>bugpoint</tt> tools via their <tt>-load</tt> options.
Reid Spencer7fa6d522005-01-11 05:16:23 +0000[diff] [blame]204If your operating system uses a suffix other than .so (such as windows or
205Mac OS/X), the appropriate extension will be used.</p>
John Criswellf9c78652004-01-26 21:26:54 +0000[diff] [blame]206
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]207<p>Now that we have the build scripts set up, we just need to write the code for
208the pass itself.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]209
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]210</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]211
212<!-- ======================================================================= -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]213<div class="doc_subsection">
214 <a name="basiccode">Basic code required</a>
215</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]216
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]217<div class="doc_text">
218
219<p>Now that we have a way to compile our new pass, we just have to write it.
220Start out with:</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]221
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]222<div class="doc_code"><pre>
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]223<b>#include</b> "<a href="http://llvm.org/doxygen/Pass_8h-source.html">llvm/Pass.h</a>"
224<b>#include</b> "<a href="http://llvm.org/doxygen/Function_8h-source.html">llvm/Function.h</a>"
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]225</pre></div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]226
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]227<p>Which are needed because we are writing a <tt><a
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]228href="http://llvm.org/doxygen/classllvm_1_1Pass.html">Pass</a></tt>, and
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]229we are operating on <tt><a
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]230href="http://llvm.org/doxygen/classllvm_1_1Function.html">Function</a></tt>'s.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]231
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]232<p>Next we have:</p>
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]233<div class="doc_code"><pre>
Jonathan Manton65acb302004-06-30 18:10:30 +0000[diff] [blame]234<b>using namespace llvm;</b>
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]235</pre></div>
Jonathan Manton65acb302004-06-30 18:10:30 +0000[diff] [blame]236<p>... which is required because the functions from the include files
237live in the llvm namespace.
238</p>
239
240<p>Next we have:</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]241
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]242<div class="doc_code"><pre>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]243<b>namespace</b> {
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]244</pre></div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]245
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]246<p>... which starts out an anonymous namespace. Anonymous namespaces are to C++
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]247what the "<tt>static</tt>" keyword is to C (at global scope). It makes the
248things declared inside of the anonymous namespace only visible to the current
249file. If you're not familiar with them, consult a decent C++ book for more
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]250information.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]251
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]252<p>Next, we declare our pass itself:</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]253
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]254<div class="doc_code"><pre>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]255 <b>struct</b> Hello : <b>public</b> <a href="#FunctionPass">FunctionPass</a> {
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]256</pre></div><p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]257
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]258<p>This declares a "<tt>Hello</tt>" class that is a subclass of <tt><a
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]259href="http://llvm.org/doxygen/classllvm_1_1FunctionPass.html">FunctionPass</a></tt>.
Chris Lattnerd6ea9262002-09-09 03:48:46 +0000[diff] [blame]260The different builtin pass subclasses are described in detail <a
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]261href="#passtype">later</a>, but for now, know that <a
262href="#FunctionPass"><tt>FunctionPass</tt></a>'s operate a function at a
263time.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]264
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]265<div class="doc_code"><pre>
Devang Patel19974732007-05-03 01:11:54 +0000[diff] [blame]266 static char ID;
Chris Lattnerb5c87f62007-05-18 05:36:14 +0000[diff] [blame]267 Hello() : FunctionPass((intptr_t)&amp;ID) {}
Devang Patele50fb9a2007-05-01 20:55:38 +0000[diff] [blame]268</pre></div><p>
269
270<p> This declares pass identifier used by LLVM to identify pass. This allows LLVM to
271avoid using expensive C++ runtime information.</p>
272
273<div class="doc_code"><pre>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]274 <b>virtual bool</b> <a href="#runOnFunction">runOnFunction</a>(Function &amp;F) {
Bill Wendling832171c2006-12-07 20:04:42 +0000[diff] [blame]275 llvm::cerr &lt;&lt; "<i>Hello: </i>" &lt;&lt; F.getName() &lt;&lt; "\n";
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]276 <b>return false</b>;
277 }
278 }; <i>// end of struct Hello</i>
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]279</pre></div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]280
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]281<p>We declare a "<a href="#runOnFunction"><tt>runOnFunction</tt></a>" method,
282which overloads an abstract virtual method inherited from <a
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]283href="#FunctionPass"><tt>FunctionPass</tt></a>. This is where we are supposed
284to do our thing, so we just print out our message with the name of each
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]285function.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]286
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]287<div class="doc_code"><pre>
Devang Patel19974732007-05-03 01:11:54 +0000[diff] [blame]288 char Hello::ID = 0;
Devang Patele50fb9a2007-05-01 20:55:38 +0000[diff] [blame]289</pre></div>
290
291<p> We initialize pass ID here. LLVM uses ID's address to identify pass so
292initialization value is not important.</p>
293
294<div class="doc_code"><pre>
Devang Patelc7582092008-03-19 21:56:59 +0000[diff] [blame]295 RegisterPass&lt;Hello&gt; X("<i>hello</i>", "<i>Hello World Pass</i>",
296 false /* Only looks at CFG */,
297 false /* Analysis Pass */);
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]298} <i>// end of anonymous namespace</i>
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]299</pre></div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]300
Chris Lattnerc8603c22006-08-27 23:18:52 +0000[diff] [blame]301<p>Lastly, we <a href="#registration">register our class</a> <tt>Hello</tt>,
302giving it a command line
Devang Patelc7582092008-03-19 21:56:59 +0000[diff] [blame]303argument "<tt>hello</tt>", and a name "<tt>Hello World Pass</tt>".
304Last two RegisterPass arguments are optional. Their default value is false.
305If a pass walks CFG without modifying it then third argument is set to true.
306If a pass is an analysis pass, for example dominator tree pass, then true
307is supplied as fourth argument. </p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]308
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]309<p>As a whole, the <tt>.cpp</tt> file looks like:</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]310
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]311<div class="doc_code"><pre>
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]312<b>#include</b> "<a href="http://llvm.org/doxygen/Pass_8h-source.html">llvm/Pass.h</a>"
313<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]314
Jonathan Manton65acb302004-06-30 18:10:30 +0000[diff] [blame]315<b>using namespace llvm;</b>
316
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]317<b>namespace</b> {
318 <b>struct Hello</b> : <b>public</b> <a href="#FunctionPass">FunctionPass</a> {
Devang Patele50fb9a2007-05-01 20:55:38 +0000[diff] [blame]319
Devang Patel19974732007-05-03 01:11:54 +0000[diff] [blame]320 static char ID;
Chris Lattner55021172007-05-18 05:38:44 +0000[diff] [blame]321 Hello() : FunctionPass((intptr_t)&amp;ID) {}
Devang Patele50fb9a2007-05-01 20:55:38 +0000[diff] [blame]322
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]323 <b>virtual bool</b> <a href="#runOnFunction">runOnFunction</a>(Function &amp;F) {
Bill Wendling832171c2006-12-07 20:04:42 +0000[diff] [blame]324 llvm::cerr &lt;&lt; "<i>Hello: </i>" &lt;&lt; F.getName() &lt;&lt; "\n";
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]325 <b>return false</b>;
326 }
327 };
328
Devang Patel26e5a302007-07-25 21:05:39 +0000[diff] [blame]329 char Hello::ID = 0;
Chris Lattnerc8603c22006-08-27 23:18:52 +0000[diff] [blame]330 RegisterPass&lt;Hello&gt; X("<i>hello</i>", "<i>Hello World Pass</i>");
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]331}
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]332</pre></div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]333
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]334<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]335command in the local directory and you should get a new
Reid Spencer7fa6d522005-01-11 05:16:23 +0000[diff] [blame]336"<tt>Debug/lib/Hello.so</tt> file. Note that everything in this file is
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]337contained in an anonymous namespace: this reflects the fact that passes are self
338contained units that do not need external interfaces (although they can have
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]339them) to be useful.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]340
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]341</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]342
343<!-- ======================================================================= -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]344<div class="doc_subsection">
Chris Lattnerc8603c22006-08-27 23:18:52 +0000[diff] [blame]345 <a name="running">Running a pass with <tt>opt</tt></a>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]346</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]347
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]348<div class="doc_text">
349
John Criswellf9c78652004-01-26 21:26:54 +0000[diff] [blame]350<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]351<tt>opt</tt> command to run an LLVM program through your pass. Because you
Chris Lattnerc8603c22006-08-27 23:18:52 +0000[diff] [blame]352registered your pass with the <tt>RegisterPass</tt> template, you will be able to
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]353use the <tt>opt</tt> tool to access it, once loaded.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]354
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]355<p>To test it, follow the example at the end of the <a
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]356href="GettingStarted.html">Getting Started Guide</a> to compile "Hello World" to
Gabor Greif04367bf2007-07-06 22:07:22 +0000[diff] [blame]357LLVM. We can now run the bitcode file (<tt>hello.bc</tt>) for the program
358through our transformation like this (or course, any bitcode file will
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]359work):</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]360
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]361<div class="doc_code"><pre>
Reid Spencer7fa6d522005-01-11 05:16:23 +0000[diff] [blame]362$ opt -load ../../../Debug/lib/Hello.so -hello &lt; hello.bc &gt; /dev/null
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]363Hello: __main
364Hello: puts
365Hello: main
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]366</pre></div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]367
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]368<p>The '<tt>-load</tt>' option specifies that '<tt>opt</tt>' should load your
369pass as a shared object, which makes '<tt>-hello</tt>' a valid command line
370argument (which is one reason you need to <a href="#registration">register your
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]371pass</a>). Because the hello pass does not modify the program in any
372interesting way, we just throw away the result of <tt>opt</tt> (sending it to
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]373<tt>/dev/null</tt>).</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]374
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]375<p>To see what happened to the other string you registered, try running
376<tt>opt</tt> with the <tt>--help</tt> option:</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]377
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]378<div class="doc_code"><pre>
Reid Spencer7fa6d522005-01-11 05:16:23 +0000[diff] [blame]379$ opt -load ../../../Debug/lib/Hello.so --help
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]380OVERVIEW: llvm .bc -&gt; .bc modular optimizer
381
Gabor Greif04367bf2007-07-06 22:07:22 +0000[diff] [blame]382USAGE: opt [options] &lt;input bitcode&gt;
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]383
384OPTIONS:
385 Optimizations available:
386...
387 -funcresolve - Resolve Functions
388 -gcse - Global Common Subexpression Elimination
389 -globaldce - Dead Global Elimination
390 <b>-hello - Hello World Pass</b>
Chris Lattner065a6162003-09-10 05:29:43 +0000[diff] [blame]391 -indvars - Canonicalize Induction Variables
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]392 -inline - Function Integration/Inlining
393 -instcombine - Combine redundant instructions
394...
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]395</pre></div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]396
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]397<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]398documentation to users of <tt>opt</tt>. Now that you have a working pass, you
399would go ahead and make it do the cool transformations you want. Once you get
400it all working and tested, it may become useful to find out how fast your pass
401is. The <a href="#passManager"><tt>PassManager</tt></a> provides a nice command
402line option (<tt>--time-passes</tt>) that allows you to get information about
403the execution time of your pass along with the other passes you queue up. For
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]404example:</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]405
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]406<div class="doc_code"><pre>
Reid Spencer7fa6d522005-01-11 05:16:23 +0000[diff] [blame]407$ 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]408Hello: __main
409Hello: puts
410Hello: main
411===============================================================================
412 ... Pass execution timing report ...
413===============================================================================
414 Total Execution Time: 0.02 seconds (0.0479059 wall clock)
415
416 ---User Time--- --System Time-- --User+System-- ---Wall Time--- --- Pass Name ---
Gabor Greif04367bf2007-07-06 22:07:22 +0000[diff] [blame]417 0.0100 (100.0%) 0.0000 ( 0.0%) 0.0100 ( 50.0%) 0.0402 ( 84.0%) Bitcode Writer
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]418 0.0000 ( 0.0%) 0.0100 (100.0%) 0.0100 ( 50.0%) 0.0031 ( 6.4%) Dominator Set Construction
419 0.0000 ( 0.0%) 0.0000 ( 0.0%) 0.0000 ( 0.0%) 0.0013 ( 2.7%) Module Verifier
420 <b> 0.0000 ( 0.0%) 0.0000 ( 0.0%) 0.0000 ( 0.0%) 0.0033 ( 6.9%) Hello World Pass</b>
421 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]422</pre></div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]423
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]424<p>As you can see, our implementation above is pretty fast :). The additional
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]425passes listed are automatically inserted by the '<tt>opt</tt>' tool to verify
426that the LLVM emitted by your pass is still valid and well formed LLVM, which
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]427hasn't been broken somehow.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]428
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]429<p>Now that you have seen the basics of the mechanics behind passes, we can talk
430about some more details of how they work and how to use them.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]431
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]432</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]433
434<!-- *********************************************************************** -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]435<div class="doc_section">
436 <a name="passtype">Pass classes and requirements</a>
437</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]438<!-- *********************************************************************** -->
439
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]440<div class="doc_text">
441
442<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]443decide what class you should subclass for your pass. The <a
444href="#basiccode">Hello World</a> example uses the <tt><a
445href="#FunctionPass">FunctionPass</a></tt> class for its implementation, but we
446did not discuss why or when this should occur. Here we talk about the classes
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]447available, from the most general to the most specific.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]448
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]449<p>When choosing a superclass for your Pass, you should choose the <b>most
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]450specific</b> class possible, while still being able to meet the requirements
Misha Brukman5560c9d2003-08-18 14:43:39 +0000[diff] [blame]451listed. This gives the LLVM Pass Infrastructure information necessary to
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]452optimize how passes are run, so that the resultant compiler isn't unneccesarily
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]453slow.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]454
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]455</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]456
Chris Lattnerf004f9a2002-09-25 22:31:38 +0000[diff] [blame]457<!-- ======================================================================= -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]458<div class="doc_subsection">
459 <a name="ImmutablePass">The <tt>ImmutablePass</tt> class</a>
460</div>
Chris Lattnerf004f9a2002-09-25 22:31:38 +0000[diff] [blame]461
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]462<div class="doc_text">
463
464<p>The most plain and boring type of pass is the "<tt><a
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]465href="http://llvm.org/doxygen/classllvm_1_1ImmutablePass.html">ImmutablePass</a></tt>"
Chris Lattnerf004f9a2002-09-25 22:31:38 +0000[diff] [blame]466class. This pass type is used for passes that do not have to be run, do not
467change state, and never need to be updated. This is not a normal type of
468transformation or analysis, but can provide information about the current
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]469compiler configuration.</p>
Chris Lattnerf004f9a2002-09-25 22:31:38 +0000[diff] [blame]470
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]471<p>Although this pass class is very infrequently used, it is important for
Chris Lattnerf004f9a2002-09-25 22:31:38 +0000[diff] [blame]472providing information about the current target machine being compiled for, and
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]473other static information that can affect the various transformations.</p>
Chris Lattnerf004f9a2002-09-25 22:31:38 +0000[diff] [blame]474
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]475<p><tt>ImmutablePass</tt>es never invalidate other transformations, are never
476invalidated, and are never "run".</p>
Chris Lattnerf004f9a2002-09-25 22:31:38 +0000[diff] [blame]477
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]478</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]479
480<!-- ======================================================================= -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]481<div class="doc_subsection">
Chris Lattnerf6278922004-09-20 04:36:29 +0000[diff] [blame]482 <a name="ModulePass">The <tt>ModulePass</tt> class</a>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]483</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]484
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]485<div class="doc_text">
486
487<p>The "<tt><a
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]488href="http://llvm.org/doxygen/classllvm_1_1ModulePass.html">ModulePass</a></tt>"
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]489class is the most general of all superclasses that you can use. Deriving from
Chris Lattnerf6278922004-09-20 04:36:29 +0000[diff] [blame]490<tt>ModulePass</tt> indicates that your pass uses the entire program as a unit,
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]491refering to function bodies in no predictable order, or adding and removing
Chris Lattnerf6278922004-09-20 04:36:29 +0000[diff] [blame]492functions. Because nothing is known about the behavior of <tt>ModulePass</tt>
Devang Patel3c1ca0b2007-04-16 21:28:14 +0000[diff] [blame]493subclasses, no optimization can be done for their execution. A module pass
494can use function level passes (e.g. dominators) using getAnalysis interface
Devang Patel00f1c402008-11-06 19:47:49 +0000[diff] [blame]495<tt> getAnalysis&lt;DominatorTree&gt;(Function)</tt>, if the function pass
496does not require any module passes. </p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]497
Chris Lattnerf6278922004-09-20 04:36:29 +0000[diff] [blame]498<p>To write a correct <tt>ModulePass</tt> subclass, derive from
499<tt>ModulePass</tt> and overload the <tt>runOnModule</tt> method with the
500following signature:</p>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]501
502</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]503
504<!-- _______________________________________________________________________ -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]505<div class="doc_subsubsection">
Chris Lattnerf6278922004-09-20 04:36:29 +0000[diff] [blame]506 <a name="runOnModule">The <tt>runOnModule</tt> method</a>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]507</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]508
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]509<div class="doc_text">
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]510
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]511<div class="doc_code"><pre>
Chris Lattnerf6278922004-09-20 04:36:29 +0000[diff] [blame]512 <b>virtual bool</b> runOnModule(Module &amp;M) = 0;
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]513</pre></div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]514
John Criswell2382ff72005-07-15 19:25:12 +0000[diff] [blame]515<p>The <tt>runOnModule</tt> method performs the interesting work of the pass.
516It should return true if the module was modified by the transformation and
517false otherwise.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]518
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]519</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]520
521<!-- ======================================================================= -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]522<div class="doc_subsection">
Chris Lattner8fdb2462004-09-18 06:39:35 +0000[diff] [blame]523 <a name="CallGraphSCCPass">The <tt>CallGraphSCCPass</tt> class</a>
524</div>
525
526<div class="doc_text">
527
528<p>The "<tt><a
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]529href="http://llvm.org/doxygen/classllvm_1_1CallGraphSCCPass.html">CallGraphSCCPass</a></tt>"
Chris Lattner8fdb2462004-09-18 06:39:35 +0000[diff] [blame]530is used by passes that need to traverse the program bottom-up on the call graph
531(callees before callers). Deriving from CallGraphSCCPass provides some
532mechanics for building and traversing the CallGraph, but also allows the system
533to optimize execution of CallGraphSCCPass's. If your pass meets the
534requirements outlined below, and doesn't meet the requirements of a <tt><a
535href="#FunctionPass">FunctionPass</a></tt> or <tt><a
536href="#BasicBlockPass">BasicBlockPass</a></tt>, you should derive from
537<tt>CallGraphSCCPass</tt>.</p>
538
539<p><b>TODO</b>: explain briefly what SCC, Tarjan's algo, and B-U mean.</p>
540
541<p>To be explicit, <tt>CallGraphSCCPass</tt> subclasses are:</p>
542
543<ol>
544
545<li>... <em>not allowed</em> to modify any <tt>Function</tt>s that are not in
546the current SCC.</li>
547
Tanya Lattner18aad232007-06-07 16:44:52 +0000[diff] [blame]548<li>... <em>not allowed</em> to inspect any Function's other than those in the
Chris Lattner8fdb2462004-09-18 06:39:35 +0000[diff] [blame]549current SCC and the direct callees of the SCC.</li>
550
551<li>... <em>required</em> to preserve the current CallGraph object, updating it
552to reflect any changes made to the program.</li>
553
554<li>... <em>not allowed</em> to add or remove SCC's from the current Module,
555though they may change the contents of an SCC.</li>
556
557<li>... <em>allowed</em> to add or remove global variables from the current
558Module.</li>
559
560<li>... <em>allowed</em> to maintain state across invocations of
561 <a href="#runOnSCC"><tt>runOnSCC</tt></a> (including global data).</li>
562</ol>
563
564<p>Implementing a <tt>CallGraphSCCPass</tt> is slightly tricky in some cases
565because it has to handle SCCs with more than one node in it. All of the virtual
566methods described below should return true if they modified the program, or
567false if they didn't.</p>
568
569</div>
570
571<!-- _______________________________________________________________________ -->
572<div class="doc_subsubsection">
Devang Patelc20048d2007-01-23 22:56:28 +0000[diff] [blame]573 <a name="doInitialization_scc">The <tt>doInitialization(CallGraph &amp;)</tt>
Chris Lattner8fdb2462004-09-18 06:39:35 +0000[diff] [blame]574 method</a>
575</div>
576
577<div class="doc_text">
578
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]579<div class="doc_code"><pre>
Devang Patelc20048d2007-01-23 22:56:28 +0000[diff] [blame]580 <b>virtual bool</b> doInitialization(CallGraph &amp;CG);
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]581</pre></div>
Chris Lattner8fdb2462004-09-18 06:39:35 +0000[diff] [blame]582
583<p>The <tt>doIninitialize</tt> method is allowed to do most of the things that
584<tt>CallGraphSCCPass</tt>'s are not allowed to do. They can add and remove
585functions, get pointers to functions, etc. The <tt>doInitialization</tt> method
586is designed to do simple initialization type of stuff that does not depend on
587the SCCs being processed. The <tt>doInitialization</tt> method call is not
588scheduled to overlap with any other pass executions (thus it should be very
589fast).</p>
590
591</div>
592
593<!-- _______________________________________________________________________ -->
594<div class="doc_subsubsection">
595 <a name="runOnSCC">The <tt>runOnSCC</tt> method</a>
596</div>
597
598<div class="doc_text">
599
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]600<div class="doc_code"><pre>
Chris Lattner8fdb2462004-09-18 06:39:35 +0000[diff] [blame]601 <b>virtual bool</b> runOnSCC(const std::vector&lt;CallGraphNode *&gt; &amp;SCCM) = 0;
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]602</pre></div>
Chris Lattner8fdb2462004-09-18 06:39:35 +0000[diff] [blame]603
604<p>The <tt>runOnSCC</tt> method performs the interesting work of the pass, and
605should return true if the module was modified by the transformation, false
606otherwise.</p>
607
608</div>
609
610<!-- _______________________________________________________________________ -->
611<div class="doc_subsubsection">
Devang Patelc20048d2007-01-23 22:56:28 +0000[diff] [blame]612 <a name="doFinalization_scc">The <tt>doFinalization(CallGraph
Chris Lattner8fdb2462004-09-18 06:39:35 +0000[diff] [blame]613 &amp;)</tt> method</a>
614</div>
615
616<div class="doc_text">
617
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]618<div class="doc_code"><pre>
Devang Patelc20048d2007-01-23 22:56:28 +0000[diff] [blame]619 <b>virtual bool</b> doFinalization(CallGraph &amp;CG);
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]620</pre></div>
Chris Lattner8fdb2462004-09-18 06:39:35 +0000[diff] [blame]621
622<p>The <tt>doFinalization</tt> method is an infrequently used method that is
623called when the pass framework has finished calling <a
624href="#runOnFunction"><tt>runOnFunction</tt></a> for every function in the
625program being compiled.</p>
626
627</div>
628
629<!-- ======================================================================= -->
630<div class="doc_subsection">
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]631 <a name="FunctionPass">The <tt>FunctionPass</tt> class</a>
632</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]633
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]634<div class="doc_text">
635
Chris Lattnerf6278922004-09-20 04:36:29 +0000[diff] [blame]636<p>In contrast to <tt>ModulePass</tt> subclasses, <tt><a
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]637href="http://llvm.org/doxygen/classllvm_1_1Pass.html">FunctionPass</a></tt>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]638subclasses do have a predictable, local behavior that can be expected by the
639system. All <tt>FunctionPass</tt> execute on each function in the program
Misha Brukmanef6a6a62003-08-21 22:14:26 +0000[diff] [blame]640independent of all of the other functions in the program.
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]641<tt>FunctionPass</tt>'s do not require that they are executed in a particular
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]642order, and <tt>FunctionPass</tt>'s do not modify external functions.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]643
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]644<p>To be explicit, <tt>FunctionPass</tt> subclasses are not allowed to:</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]645
646<ol>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]647<li>Modify a Function other than the one currently being processed.</li>
648<li>Add or remove Function's from the current Module.</li>
649<li>Add or remove global variables from the current Module.</li>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]650<li>Maintain state across invocations of
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]651 <a href="#runOnFunction"><tt>runOnFunction</tt></a> (including global data)</li>
652</ol>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]653
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]654<p>Implementing a <tt>FunctionPass</tt> is usually straightforward (See the <a
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]655href="#basiccode">Hello World</a> pass for example). <tt>FunctionPass</tt>'s
656may overload three virtual methods to do their work. All of these methods
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]657should return true if they modified the program, or false if they didn't.</p>
658
659</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]660
661<!-- _______________________________________________________________________ -->
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]662<div class="doc_subsubsection">
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]663 <a name="doInitialization_mod">The <tt>doInitialization(Module &amp;)</tt>
664 method</a>
665</div>
666
667<div class="doc_text">
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]668
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]669<div class="doc_code"><pre>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]670 <b>virtual bool</b> doInitialization(Module &amp;M);
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]671</pre></div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]672
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]673<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]674<tt>FunctionPass</tt>'s are not allowed to do. They can add and remove
Chris Lattnerd0713f92002-09-12 17:06:43 +0000[diff] [blame]675functions, get pointers to functions, etc. The <tt>doInitialization</tt> method
676is designed to do simple initialization type of stuff that does not depend on
677the functions being processed. The <tt>doInitialization</tt> method call is not
678scheduled to overlap with any other pass executions (thus it should be very
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]679fast).</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]680
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]681<p>A good example of how this method should be used is the <a
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]682href="http://llvm.org/doxygen/LowerAllocations_8cpp-source.html">LowerAllocations</a>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]683pass. This pass converts <tt>malloc</tt> and <tt>free</tt> instructions into
Misha Brukmanef6a6a62003-08-21 22:14:26 +0000[diff] [blame]684platform dependent <tt>malloc()</tt> and <tt>free()</tt> function calls. It
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]685uses the <tt>doInitialization</tt> method to get a reference to the malloc and
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]686free functions that it needs, adding prototypes to the module if necessary.</p>
687
688</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]689
690<!-- _______________________________________________________________________ -->
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]691<div class="doc_subsubsection">
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]692 <a name="runOnFunction">The <tt>runOnFunction</tt> method</a>
693</div>
694
695<div class="doc_text">
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]696
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]697<div class="doc_code"><pre>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]698 <b>virtual bool</b> runOnFunction(Function &amp;F) = 0;
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]699</pre></div><p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]700
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]701<p>The <tt>runOnFunction</tt> method must be implemented by your subclass to do
702the transformation or analysis work of your pass. As usual, a true value should
703be returned if the function is modified.</p>
704
705</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]706
707<!-- _______________________________________________________________________ -->
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]708<div class="doc_subsubsection">
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]709 <a name="doFinalization_mod">The <tt>doFinalization(Module
710 &amp;)</tt> method</a>
711</div>
712
713<div class="doc_text">
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]714
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]715<div class="doc_code"><pre>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]716 <b>virtual bool</b> doFinalization(Module &amp;M);
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]717</pre></div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]718
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]719<p>The <tt>doFinalization</tt> method is an infrequently used method that is
720called when the pass framework has finished calling <a
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]721href="#runOnFunction"><tt>runOnFunction</tt></a> for every function in the
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]722program being compiled.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]723
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]724</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]725
726<!-- ======================================================================= -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]727<div class="doc_subsection">
Devang Patel2e8f27d2007-03-19 22:21:25 +0000[diff] [blame]728 <a name="LoopPass">The <tt>LoopPass</tt> class </a>
729</div>
730
731<div class="doc_text">
732
733<p> All <tt>LoopPass</tt> execute on each loop in the function independent of
734all of the other loops in the function. <tt>LoopPass</tt> processes loops in
735loop nest order such that outer most loop is processed last. </p>
736
737<p> <tt>LoopPass</tt> subclasses are allowed to update loop nest using
738<tt>LPPassManager</tt> interface. Implementing a loop pass is usually
739straightforward. <tt>Looppass</tt>'s may overload three virtual methods to
740do their work. All these methods should return true if they modified the
741program, or false if they didn't. </p>
742</div>
743
744<!-- _______________________________________________________________________ -->
745<div class="doc_subsubsection">
746 <a name="doInitialization_loop">The <tt>doInitialization(Loop *,
747 LPPassManager &amp;)</tt>
748 method</a>
749</div>
750
751<div class="doc_text">
752
753<div class="doc_code"><pre>
754 <b>virtual bool</b> doInitialization(Loop *, LPPassManager &amp;LPM);
755</pre></div>
756
Chris Lattnerb5c87f62007-05-18 05:36:14 +0000[diff] [blame]757<p>The <tt>doInitialization</tt> method is designed to do simple initialization
Devang Patel2e8f27d2007-03-19 22:21:25 +0000[diff] [blame]758type of stuff that does not depend on the functions being processed. The
759<tt>doInitialization</tt> method call is not scheduled to overlap with any
760other pass executions (thus it should be very fast). LPPassManager
761interface should be used to access Function or Module level analysis
762information.</p>
763
764</div>
765
766
767<!-- _______________________________________________________________________ -->
768<div class="doc_subsubsection">
769 <a name="runOnLoop">The <tt>runOnLoop</tt> method</a>
770</div>
771
772<div class="doc_text">
773
774<div class="doc_code"><pre>
775 <b>virtual bool</b> runOnLoop(Loop *, LPPassManager &amp;LPM) = 0;
776</pre></div><p>
777
778<p>The <tt>runOnLoop</tt> method must be implemented by your subclass to do
779the transformation or analysis work of your pass. As usual, a true value should
780be returned if the function is modified. <tt>LPPassManager</tt> interface
781should be used to update loop nest.</p>
782
783</div>
784
785<!-- _______________________________________________________________________ -->
786<div class="doc_subsubsection">
787 <a name="doFinalization_loop">The <tt>doFinalization()</tt> method</a>
788</div>
789
790<div class="doc_text">
791
792<div class="doc_code"><pre>
793 <b>virtual bool</b> doFinalization();
794</pre></div>
795
796<p>The <tt>doFinalization</tt> method is an infrequently used method that is
797called when the pass framework has finished calling <a
798href="#runOnLoop"><tt>runOnLoop</tt></a> for every loop in the
799program being compiled. </p>
800
801</div>
802
803
804
805<!-- ======================================================================= -->
806<div class="doc_subsection">
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]807 <a name="BasicBlockPass">The <tt>BasicBlockPass</tt> class</a>
808</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]809
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]810<div class="doc_text">
811
812<p><tt>BasicBlockPass</tt>'s are just like <a
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]813href="#FunctionPass"><tt>FunctionPass</tt></a>'s, except that they must limit
814their scope of inspection and modification to a single basic block at a time.
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]815As such, they are <b>not</b> allowed to do any of the following:</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]816
817<ol>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]818<li>Modify or inspect any basic blocks outside of the current one</li>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]819<li>Maintain state across invocations of
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]820 <a href="#runOnBasicBlock"><tt>runOnBasicBlock</tt></a></li>
Reid Spencer1bc19342004-12-11 05:12:57 +0000[diff] [blame]821<li>Modify the control flow graph (by altering terminator instructions)</li>
822<li>Any of the things forbidden for
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]823 <a href="#FunctionPass"><tt>FunctionPass</tt></a>es.</li>
824</ol>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]825
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]826<p><tt>BasicBlockPass</tt>es are useful for traditional local and "peephole"
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]827optimizations. They may override the same <a
Chris Lattnerd0713f92002-09-12 17:06:43 +0000[diff] [blame]828href="#doInitialization_mod"><tt>doInitialization(Module &amp;)</tt></a> and <a
829href="#doFinalization_mod"><tt>doFinalization(Module &amp;)</tt></a> methods that <a
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]830href="#FunctionPass"><tt>FunctionPass</tt></a>'s have, but also have the following virtual methods that may also be implemented:</p>
831
832</div>
Chris Lattnerd0713f92002-09-12 17:06:43 +0000[diff] [blame]833
834<!-- _______________________________________________________________________ -->
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]835<div class="doc_subsubsection">
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]836 <a name="doInitialization_fn">The <tt>doInitialization(Function
837 &amp;)</tt> method</a>
838</div>
839
840<div class="doc_text">
Chris Lattnerd0713f92002-09-12 17:06:43 +0000[diff] [blame]841
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]842<div class="doc_code"><pre>
Chris Lattnerd0713f92002-09-12 17:06:43 +0000[diff] [blame]843 <b>virtual bool</b> doInitialization(Function &amp;F);
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]844</pre></div>
Chris Lattnerd0713f92002-09-12 17:06:43 +0000[diff] [blame]845
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]846<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]847<tt>BasicBlockPass</tt>'s are not allowed to do, but that
848<tt>FunctionPass</tt>'s can. The <tt>doInitialization</tt> method is designed
Reid Spencer1bc19342004-12-11 05:12:57 +0000[diff] [blame]849to do simple initialization that does not depend on the
Chris Lattnerd0713f92002-09-12 17:06:43 +0000[diff] [blame]850BasicBlocks being processed. The <tt>doInitialization</tt> method call is not
851scheduled to overlap with any other pass executions (thus it should be very
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]852fast).</p>
Chris Lattnerd0713f92002-09-12 17:06:43 +0000[diff] [blame]853
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]854</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]855
856<!-- _______________________________________________________________________ -->
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]857<div class="doc_subsubsection">
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]858 <a name="runOnBasicBlock">The <tt>runOnBasicBlock</tt> method</a>
859</div>
860
861<div class="doc_text">
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]862
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]863<div class="doc_code"><pre>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]864 <b>virtual bool</b> runOnBasicBlock(BasicBlock &amp;BB) = 0;
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]865</pre></div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]866
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]867<p>Override this function to do the work of the <tt>BasicBlockPass</tt>. This
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]868function is not allowed to inspect or modify basic blocks other than the
869parameter, and are not allowed to modify the CFG. A true value must be returned
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]870if the basic block is modified.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]871
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]872</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]873
Chris Lattnerd0713f92002-09-12 17:06:43 +0000[diff] [blame]874<!-- _______________________________________________________________________ -->
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]875<div class="doc_subsubsection">
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]876 <a name="doFinalization_fn">The <tt>doFinalization(Function &amp;)</tt>
877 method</a>
878</div>
879
880<div class="doc_text">
Chris Lattnerd0713f92002-09-12 17:06:43 +0000[diff] [blame]881
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]882<div class="doc_code"><pre>
Chris Lattnerd0713f92002-09-12 17:06:43 +0000[diff] [blame]883 <b>virtual bool</b> doFinalization(Function &amp;F);
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]884</pre></div>
Chris Lattnerd0713f92002-09-12 17:06:43 +0000[diff] [blame]885
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]886<p>The <tt>doFinalization</tt> method is an infrequently used method that is
887called when the pass framework has finished calling <a
Chris Lattnerd0713f92002-09-12 17:06:43 +0000[diff] [blame]888href="#runOnBasicBlock"><tt>runOnBasicBlock</tt></a> for every BasicBlock in the
889program being compiled. This can be used to perform per-function
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]890finalization.</p>
Chris Lattnerd0713f92002-09-12 17:06:43 +0000[diff] [blame]891
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]892</div>
Chris Lattnerd0713f92002-09-12 17:06:43 +0000[diff] [blame]893
Brian Gaekecab8b6f2003-07-17 18:53:20 +0000[diff] [blame]894<!-- ======================================================================= -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]895<div class="doc_subsection">
896 <a name="MachineFunctionPass">The <tt>MachineFunctionPass</tt> class</a>
897</div>
Brian Gaekecab8b6f2003-07-17 18:53:20 +0000[diff] [blame]898
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]899<div class="doc_text">
900
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]901<p>A <tt>MachineFunctionPass</tt> is a part of the LLVM code generator that
902executes on the machine-dependent representation of each LLVM function in the
903program. A <tt>MachineFunctionPass</tt> is also a <tt>FunctionPass</tt>, so all
Brian Gaekecab8b6f2003-07-17 18:53:20 +0000[diff] [blame]904the restrictions that apply to a <tt>FunctionPass</tt> also apply to it.
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]905<tt>MachineFunctionPass</tt>es also have additional restrictions. In particular,
906<tt>MachineFunctionPass</tt>es are not allowed to do any of the following:</p>
Brian Gaekecab8b6f2003-07-17 18:53:20 +0000[diff] [blame]907
908<ol>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]909<li>Modify any LLVM Instructions, BasicBlocks or Functions.</li>
910<li>Modify a MachineFunction other than the one currently being processed.</li>
911<li>Add or remove MachineFunctions from the current Module.</li>
912<li>Add or remove global variables from the current Module.</li>
913<li>Maintain state across invocations of <a
914href="#runOnMachineFunction"><tt>runOnMachineFunction</tt></a> (including global
915data)</li>
916</ol>
Brian Gaekecab8b6f2003-07-17 18:53:20 +0000[diff] [blame]917
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]918</div>
Chris Lattnerd0713f92002-09-12 17:06:43 +0000[diff] [blame]919
Brian Gaeke6a33f362003-07-22 20:53:20 +0000[diff] [blame]920<!-- _______________________________________________________________________ -->
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]921<div class="doc_subsubsection">
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]922 <a name="runOnMachineFunction">The <tt>runOnMachineFunction(MachineFunction
923 &amp;MF)</tt> method</a>
924</div>
925
926<div class="doc_text">
Brian Gaeke6a33f362003-07-22 20:53:20 +0000[diff] [blame]927
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]928<div class="doc_code"><pre>
Brian Gaeke6a33f362003-07-22 20:53:20 +0000[diff] [blame]929 <b>virtual bool</b> runOnMachineFunction(MachineFunction &amp;MF) = 0;
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]930</pre></div>
Brian Gaeke6a33f362003-07-22 20:53:20 +0000[diff] [blame]931
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]932<p><tt>runOnMachineFunction</tt> can be considered the main entry point of a
933<tt>MachineFunctionPass</tt>; that is, you should override this method to do the
934work of your <tt>MachineFunctionPass</tt>.</p>
Brian Gaeke6a33f362003-07-22 20:53:20 +0000[diff] [blame]935
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]936<p>The <tt>runOnMachineFunction</tt> method is called on every
Brian Gaeke6a33f362003-07-22 20:53:20 +0000[diff] [blame]937<tt>MachineFunction</tt> in a <tt>Module</tt>, so that the
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]938<tt>MachineFunctionPass</tt> may perform optimizations on the machine-dependent
939representation of the function. If you want to get at the LLVM <tt>Function</tt>
940for the <tt>MachineFunction</tt> you're working on, use
941<tt>MachineFunction</tt>'s <tt>getFunction()</tt> accessor method -- but
942remember, you may not modify the LLVM <tt>Function</tt> or its contents from a
943<tt>MachineFunctionPass</tt>.</p>
944
945</div>
Brian Gaeke6a33f362003-07-22 20:53:20 +0000[diff] [blame]946
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]947<!-- *********************************************************************** -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]948<div class="doc_section">
949 <a name="registration">Pass registration</a>
950</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]951<!-- *********************************************************************** -->
952
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]953<div class="doc_text">
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]954
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]955<p>In the <a href="#basiccode">Hello World</a> example pass we illustrated how
956pass registration works, and discussed some of the reasons that it is used and
957what it does. Here we discuss how and why passes are registered.</p>
958
Chris Lattnerc8603c22006-08-27 23:18:52 +0000[diff] [blame]959<p>As we saw above, passes are registered with the <b><tt>RegisterPass</tt></b>
960template, which requires you to pass at least two
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]961parameters. The first parameter is the name of the pass that is to be used on
962the command line to specify that the pass should be added to a program (for
Chris Lattnerc8603c22006-08-27 23:18:52 +0000[diff] [blame]963example, with <tt>opt</tt> or <tt>bugpoint</tt>). The second argument is the
964name of the pass, which is to be used for the <tt>--help</tt> output of
965programs, as
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]966well as for debug output generated by the <tt>--debug-pass</tt> option.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]967
Chris Lattnerc8603c22006-08-27 23:18:52 +0000[diff] [blame]968<p>If you want your pass to be easily dumpable, you should
969implement the virtual <tt>print</tt> method:</p>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]970
971</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]972
973<!-- _______________________________________________________________________ -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]974<div class="doc_subsubsection">
975 <a name="print">The <tt>print</tt> method</a>
976</div>
977
978<div class="doc_text">
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]979
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]980<div class="doc_code"><pre>
Torok Edwin52790e52008-10-28 17:29:23 +0000[diff] [blame]981 <b>virtual void</b> print(std::ostream &amp;O, <b>const</b> Module *M) <b>const</b>;
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]982</pre></div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]983
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]984<p>The <tt>print</tt> method must be implemented by "analyses" in order to print
985a human readable version of the analysis results. This is useful for debugging
986an analysis itself, as well as for other people to figure out how an analysis
Chris Lattnerc8603c22006-08-27 23:18:52 +0000[diff] [blame]987works. Use the <tt>opt -analyze</tt> argument to invoke this method.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]988
Bill Wendling832171c2006-12-07 20:04:42 +0000[diff] [blame]989<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]990and 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]991program that has been analyzed. Note however that this pointer may be null in
992certain circumstances (such as calling the <tt>Pass::dump()</tt> from a
993debugger), so it should only be used to enhance debug output, it should not be
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]994depended on.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]995
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]996</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]997
998<!-- *********************************************************************** -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]999<div class="doc_section">
1000 <a name="interaction">Specifying interactions between passes</a>
1001</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1002<!-- *********************************************************************** -->
1003
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1004<div class="doc_text">
1005
John Criswell8528e782007-12-03 19:34:25 +0000[diff] [blame]1006<p>One of the main responsibilities of the <tt>PassManager</tt> is to make sure
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1007that passes interact with each other correctly. Because <tt>PassManager</tt>
1008tries to <a href="#passmanager">optimize the execution of passes</a> it must
1009know how the passes interact with each other and what dependencies exist between
1010the various passes. To track this, each pass can declare the set of passes that
1011are required to be executed before the current pass, and the passes which are
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1012invalidated by the current pass.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1013
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1014<p>Typically this functionality is used to require that analysis results are
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1015computed before your pass is run. Running arbitrary transformation passes can
1016invalidate the computed analysis results, which is what the invalidation set
1017specifies. If a pass does not implement the <tt><a
1018href="#getAnalysisUsage">getAnalysisUsage</a></tt> method, it defaults to not
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1019having any prerequisite passes, and invalidating <b>all</b> other passes.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1020
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1021</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1022
1023<!-- _______________________________________________________________________ -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1024<div class="doc_subsubsection">
1025 <a name="getAnalysisUsage">The <tt>getAnalysisUsage</tt> method</a>
1026</div>
1027
1028<div class="doc_text">
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1029
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1030<div class="doc_code"><pre>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1031 <b>virtual void</b> getAnalysisUsage(AnalysisUsage &amp;Info) <b>const</b>;
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1032</pre></div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1033
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1034<p>By implementing the <tt>getAnalysisUsage</tt> method, the required and
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1035invalidated sets may be specified for your transformation. The implementation
1036should fill in the <tt><a
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]1037href="http://llvm.org/doxygen/classllvm_1_1AnalysisUsage.html">AnalysisUsage</a></tt>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1038object with information about which passes are required and not invalidated. To
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]1039do this, a pass may call any of the following methods on the AnalysisUsage
1040object:</p>
1041</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1042
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]1043<!-- _______________________________________________________________________ -->
1044<div class="doc_subsubsection">
1045 <a name="AU::addRequired">The <tt>AnalysisUsage::addRequired&lt;&gt;</tt> and <tt>AnalysisUsage::addRequiredTransitive&lt;&gt;</tt> methods</a>
1046</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1047
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]1048<div class="doc_text">
1049<p>
Reid Spencer1bc19342004-12-11 05:12:57 +0000[diff] [blame]1050If your pass requires a previous pass to be executed (an analysis for example),
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]1051it can use one of these methods to arrange for it to be run before your pass.
1052LLVM has many different types of analyses and passes that can be required,
Reid Spencer1bc19342004-12-11 05:12:57 +0000[diff] [blame]1053spanning the range from <tt>DominatorSet</tt> to <tt>BreakCriticalEdges</tt>.
1054Requiring <tt>BreakCriticalEdges</tt>, for example, guarantees that there will
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]1055be no critical edges in the CFG when your pass has been run.
1056</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1057
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]1058<p>
1059Some analyses chain to other analyses to do their job. For example, an <a
1060href="AliasAnalysis.html">AliasAnalysis</a> implementation is required to <a
1061href="AliasAnalysis.html#chaining">chain</a> to other alias analysis passes. In
1062cases where analyses chain, the <tt>addRequiredTransitive</tt> method should be
1063used instead of the <tt>addRequired</tt> method. This informs the PassManager
1064that the transitively required pass should be alive as long as the requiring
1065pass is.
1066</p>
1067</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1068
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]1069<!-- _______________________________________________________________________ -->
1070<div class="doc_subsubsection">
1071 <a name="AU::addPreserved">The <tt>AnalysisUsage::addPreserved&lt;&gt;</tt> method</a>
1072</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1073
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]1074<div class="doc_text">
1075<p>
1076One of the jobs of the PassManager is to optimize how and when analyses are run.
1077In particular, it attempts to avoid recomputing data unless it needs to. For
1078this reason, passes are allowed to declare that they preserve (i.e., they don't
1079invalidate) an existing analysis if it's available. For example, a simple
Reid Spencer1bc19342004-12-11 05:12:57 +0000[diff] [blame]1080constant folding pass would not modify the CFG, so it can't possibly affect the
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]1081results of dominator analysis. By default, all passes are assumed to invalidate
1082all others.
1083</p>
1084
1085<p>
1086The <tt>AnalysisUsage</tt> class provides several methods which are useful in
1087certain circumstances that are related to <tt>addPreserved</tt>. In particular,
1088the <tt>setPreservesAll</tt> method can be called to indicate that the pass does
1089not modify the LLVM program at all (which is true for analyses), and the
1090<tt>setPreservesCFG</tt> method can be used by transformations that change
1091instructions in the program but do not modify the CFG or terminator instructions
1092(note that this property is implicitly set for <a
1093href="#BasicBlockPass">BasicBlockPass</a>'s).
1094</p>
1095
1096<p>
1097<tt>addPreserved</tt> is particularly useful for transformations like
1098<tt>BreakCriticalEdges</tt>. This pass knows how to update a small set of loop
1099and dominator related analyses if they exist, so it can preserve them, despite
1100the fact that it hacks on the CFG.
1101</p>
1102</div>
1103
1104<!-- _______________________________________________________________________ -->
1105<div class="doc_subsubsection">
1106 <a name="AU::examples">Example implementations of <tt>getAnalysisUsage</tt></a>
1107</div>
1108
1109<div class="doc_text">
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1110
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1111<div class="doc_code"><pre>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1112 <i>// This is an example implementation from an analysis, which does not modify
1113 // the program at all, yet has a prerequisite.</i>
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]1114 <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]1115 AU.setPreservesAll();
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]1116 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]1117 }
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1118</pre></div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1119
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1120<p>and:</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1121
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1122<div class="doc_code"><pre>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1123 <i>// This example modifies the program, but does not modify the CFG</i>
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]1124 <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]1125 AU.setPreservesCFG();
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]1126 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]1127 }
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1128</pre></div>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1129
1130</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1131
1132<!-- _______________________________________________________________________ -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1133<div class="doc_subsubsection">
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]1134 <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]1135</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1136
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1137<div class="doc_text">
1138
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]1139<p>The <tt>Pass::getAnalysis&lt;&gt;</tt> method is automatically inherited by
1140your class, providing you with access to the passes that you declared that you
1141required with the <a href="#getAnalysisUsage"><tt>getAnalysisUsage</tt></a>
1142method. It takes a single template argument that specifies which pass class you
1143want, and returns a reference to that pass. For example:</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1144
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1145<div class="doc_code"><pre>
Chris Lattnera5776302004-03-17 21:33:32 +0000[diff] [blame]1146 bool LICM::runOnFunction(Function &amp;F) {
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]1147 LoopInfo &amp;LI = getAnalysis&lt;LoopInfo&gt;();
1148 ...
1149 }
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1150</pre></div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1151
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1152<p>This method call returns a reference to the pass desired. You may get a
1153runtime assertion failure if you attempt to get an analysis that you did not
1154declare as required in your <a
1155href="#getAnalysisUsage"><tt>getAnalysisUsage</tt></a> implementation. This
1156method can be called by your <tt>run*</tt> method implementation, or by any
Devang Patel3c1ca0b2007-04-16 21:28:14 +0000[diff] [blame]1157other local method invoked by your <tt>run*</tt> method.
1158
1159A module level pass can use function level analysis info using this interface.
1160For example:</p>
1161
1162<div class="doc_code"><pre>
1163 bool ModuleLevelPass::runOnModule(Module &amp;M) {
1164 ...
Devang Patelf23de112007-04-17 00:17:11 +0000[diff] [blame]1165 DominatorTree &amp;DT = getAnalysis&lt;DominatorTree&gt;(Func);
Devang Patel3c1ca0b2007-04-16 21:28:14 +0000[diff] [blame]1166 ...
1167 }
1168</pre></div>
1169
Chris Lattnerb5c87f62007-05-18 05:36:14 +0000[diff] [blame]1170<p>In above example, runOnFunction for DominatorTree is called by pass manager
Devang Patel3c1ca0b2007-04-16 21:28:14 +0000[diff] [blame]1171before returning a reference to the desired pass.</p>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1172
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]1173<p>
1174If your pass is capable of updating analyses if they exist (e.g.,
1175<tt>BreakCriticalEdges</tt>, as described above), you can use the
1176<tt>getAnalysisToUpdate</tt> method, which returns a pointer to the analysis if
1177it is active. For example:</p>
1178
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1179<div class="doc_code"><pre>
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]1180 ...
1181 if (DominatorSet *DS = getAnalysisToUpdate&lt;DominatorSet&gt;()) {
1182 <i>// A DominatorSet is active. This code will update it.</i>
1183 }
1184 ...
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1185</pre></div>
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]1186
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1187</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1188
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1189<!-- *********************************************************************** -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1190<div class="doc_section">
1191 <a name="analysisgroup">Implementing Analysis Groups</a>
1192</div>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1193<!-- *********************************************************************** -->
1194
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1195<div class="doc_text">
1196
Chris Lattnerb7632282007-11-16 05:32:05 +0000[diff] [blame]1197<p>Now that we understand the basics of how passes are defined, how they are
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1198used, 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]1199fancier. All of the pass relationships that we have seen so far are very
1200simple: one pass depends on one other specific pass to be run before it can run.
1201For many applications, this is great, for others, more flexibility is
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1202required.</p>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1203
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1204<p>In particular, some analyses are defined such that there is a single simple
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1205interface to the analysis results, but multiple ways of calculating them.
1206Consider alias analysis for example. The most trivial alias analysis returns
1207"may alias" for any alias query. The most sophisticated analysis a
1208flow-sensitive, context-sensitive interprocedural analysis that can take a
1209significant amount of time to execute (and obviously, there is a lot of room
1210between these two extremes for other implementations). To cleanly support
1211situations like this, the LLVM Pass Infrastructure supports the notion of
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1212Analysis Groups.</p>
1213
1214</div>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1215
1216<!-- _______________________________________________________________________ -->
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]1217<div class="doc_subsubsection">
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1218 <a name="agconcepts">Analysis Group Concepts</a>
1219</div>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1220
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1221<div class="doc_text">
1222
1223<p>An Analysis Group is a single simple interface that may be implemented by
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1224multiple different passes. Analysis Groups can be given human readable names
1225just like passes, but unlike passes, they need not derive from the <tt>Pass</tt>
1226class. An analysis group may have one or more implementations, one of which is
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1227the "default" implementation.</p>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1228
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1229<p>Analysis groups are used by client passes just like other passes are: the
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1230<tt>AnalysisUsage::addRequired()</tt> and <tt>Pass::getAnalysis()</tt> methods.
1231In order to resolve this requirement, the <a href="#passmanager">PassManager</a>
1232scans the available passes to see if any implementations of the analysis group
1233are available. If none is available, the default implementation is created for
1234the pass to use. All standard rules for <A href="#interaction">interaction
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1235between passes</a> still apply.</p>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1236
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1237<p>Although <a href="#registration">Pass Registration</a> is optional for normal
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1238passes, all analysis group implementations must be registered, and must use the
1239<A href="#registerag"><tt>RegisterAnalysisGroup</tt></a> template to join the
1240implementation pool. Also, a default implementation of the interface
1241<b>must</b> be registered with <A
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1242href="#registerag"><tt>RegisterAnalysisGroup</tt></a>.</p>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1243
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1244<p>As a concrete example of an Analysis Group in action, consider the <a
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]1245href="http://llvm.org/doxygen/classllvm_1_1AliasAnalysis.html">AliasAnalysis</a>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1246analysis group. The default implementation of the alias analysis interface (the
1247<tt><a
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]1248href="http://llvm.org/doxygen/structBasicAliasAnalysis.html">basicaa</a></tt>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1249pass) just does a few simple checks that don't require significant analysis to
1250compute (such as: two different globals can never alias each other, etc).
1251Passes that use the <tt><a
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]1252href="http://llvm.org/doxygen/classllvm_1_1AliasAnalysis.html">AliasAnalysis</a></tt>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1253interface (for example the <tt><a
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]1254href="http://llvm.org/doxygen/structGCSE.html">gcse</a></tt> pass), do
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1255not care which implementation of alias analysis is actually provided, they just
1256use the designated interface.</p>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1257
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1258<p>From the user's perspective, commands work just like normal. Issuing the
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1259command '<tt>opt -gcse ...</tt>' will cause the <tt>basicaa</tt> class to be
1260instantiated and added to the pass sequence. Issuing the command '<tt>opt
1261-somefancyaa -gcse ...</tt>' will cause the <tt>gcse</tt> pass to use the
1262<tt>somefancyaa</tt> alias analysis (which doesn't actually exist, it's just a
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1263hypothetical example) instead.</p>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1264
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1265</div>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1266
1267<!-- _______________________________________________________________________ -->
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]1268<div class="doc_subsubsection">
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1269 <a name="registerag">Using <tt>RegisterAnalysisGroup</tt></a>
1270</div>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1271
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1272<div class="doc_text">
1273
1274<p>The <tt>RegisterAnalysisGroup</tt> template is used to register the analysis
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1275group itself as well as add pass implementations to the analysis group. First,
1276an analysis should be registered, with a human readable name provided for it.
1277Unlike registration of passes, there is no command line argument to be specified
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1278for the Analysis Group Interface itself, because it is "abstract":</p>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1279
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1280<div class="doc_code"><pre>
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]1281 <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]1282</pre></div>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1283
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1284<p>Once the analysis is registered, passes can declare that they are valid
1285implementations of the interface by using the following code:</p>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1286
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1287<div class="doc_code"><pre>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1288<b>namespace</b> {
1289 //<i> Analysis Group implementations <b>must</b> be registered normally...</i>
Chris Lattnerc8603c22006-08-27 23:18:52 +0000[diff] [blame]1290 RegisterPass&lt;FancyAA&gt;
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1291 B("<i>somefancyaa</i>", "<i>A more complex alias analysis implementation</i>");
1292
1293 //<i> Declare that we implement the AliasAnalysis interface</i>
Chris Lattnerdc877252006-08-28 00:45:38 +0000[diff] [blame]1294 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]1295}
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1296</pre></div>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1297
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1298<p>This just shows a class <tt>FancyAA</tt> that is registered normally, then
1299uses the <tt>RegisterAnalysisGroup</tt> template to "join" the <tt><a
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]1300href="http://llvm.org/doxygen/classllvm_1_1AliasAnalysis.html">AliasAnalysis</a></tt>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1301analysis group. Every implementation of an analysis group should join using
1302this template. A single pass may join multiple different analysis groups with
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1303no problem.</p>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1304
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1305<div class="doc_code"><pre>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1306<b>namespace</b> {
1307 //<i> Analysis Group implementations <b>must</b> be registered normally...</i>
Chris Lattnerc8603c22006-08-27 23:18:52 +0000[diff] [blame]1308 RegisterPass&lt;<a href="http://llvm.org/doxygen/structBasicAliasAnalysis.html">BasicAliasAnalysis</a>&gt;
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1309 D("<i>basicaa</i>", "<i>Basic Alias Analysis (default AA impl)</i>");
1310
1311 //<i> Declare that we implement the AliasAnalysis interface</i>
Chris Lattnerdc877252006-08-28 00:45:38 +0000[diff] [blame]1312 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]1313}
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1314</pre></div>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1315
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1316<p>Here we show how the default implementation is specified (using the extra
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1317argument to the <tt>RegisterAnalysisGroup</tt> template). There must be exactly
1318one default implementation available at all times for an Analysis Group to be
Devang Patel2397f8d2007-06-20 18:51:14 +0000[diff] [blame]1319used. Only default implementation can derive from <tt>ImmutablePass</tt>.
1320Here we declare that the
1321 <tt><a href="http://llvm.org/doxygen/structBasicAliasAnalysis.html">BasicAliasAnalysis</a></tt>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1322pass is the default implementation for the interface.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1323
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1324</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1325
1326<!-- *********************************************************************** -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1327<div class="doc_section">
Tanya Lattnerd5383652004-11-19 01:25:14 +0000[diff] [blame]1328 <a name="passStatistics">Pass Statistics</a>
1329</div>
1330<!-- *********************************************************************** -->
1331
1332<div class="doc_text">
Tanya Lattner05f8d5f2004-11-19 01:26:37 +0000[diff] [blame]1333<p>The <a
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]1334href="http://llvm.org/doxygen/Statistic_8h-source.html"><tt>Statistic</tt></a>
John Criswell0b1010e2005-11-28 23:25:41 +0000[diff] [blame]1335class is designed to be an easy way to expose various success
Tanya Lattnerd5383652004-11-19 01:25:14 +0000[diff] [blame]1336metrics from passes. These statistics are printed at the end of a
1337run, when the -stats command line option is enabled on the command
Tanya Lattner05f8d5f2004-11-19 01:26:37 +0000[diff] [blame]1338line. 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]1339
1340</div>
1341
1342
1343<!-- *********************************************************************** -->
1344<div class="doc_section">
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1345 <a name="passmanager">What PassManager does</a>
1346</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1347<!-- *********************************************************************** -->
1348
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1349<div class="doc_text">
1350
1351<p>The <a
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]1352href="http://llvm.org/doxygen/PassManager_8h-source.html"><tt>PassManager</tt></a>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1353<a
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]1354href="http://llvm.org/doxygen/classllvm_1_1PassManager.html">class</a>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1355takes a list of passes, ensures their <a href="#interaction">prerequisites</a>
1356are set up correctly, and then schedules passes to run efficiently. All of the
1357LLVM tools that run passes use the <tt>PassManager</tt> for execution of these
1358passes.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1359
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1360<p>The <tt>PassManager</tt> does two main things to try to reduce the execution
1361time of a series of passes:</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1362
1363<ol>
1364<li><b>Share analysis results</b> - The PassManager attempts to avoid
1365recomputing analysis results as much as possible. This means keeping track of
1366which analyses are available already, which analyses get invalidated, and which
1367analyses are needed to be run for a pass. An important part of work is that the
1368<tt>PassManager</tt> tracks the exact lifetime of all analysis results, allowing
1369it to <a href="#releaseMemory">free memory</a> allocated to holding analysis
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1370results as soon as they are no longer needed.</li>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1371
1372<li><b>Pipeline the execution of passes on the program</b> - The
1373<tt>PassManager</tt> attempts to get better cache and memory usage behavior out
1374of a series of passes by pipelining the passes together. This means that, given
1375a series of consequtive <a href="#FunctionPass"><tt>FunctionPass</tt></a>'s, it
1376will execute all of the <a href="#FunctionPass"><tt>FunctionPass</tt></a>'s on
1377the first function, then all of the <a
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1378href="#FunctionPass"><tt>FunctionPass</tt></a>es on the second function,
1379etc... until the entire program has been run through the passes.
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1380
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1381<p>This improves the cache behavior of the compiler, because it is only touching
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1382the LLVM program representation for a single function at a time, instead of
1383traversing the entire program. It reduces the memory consumption of compiler,
1384because, for example, only one <a
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]1385href="http://llvm.org/doxygen/classllvm_1_1DominatorSet.html"><tt>DominatorSet</tt></a>
John Criswell9795bb82007-12-10 20:26:29 +0000[diff] [blame]1386needs to be calculated at a time. This also makes it possible to implement
1387some <a
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1388href="#SMP">interesting enhancements</a> in the future.</p></li>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1389
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1390</ol>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1391
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1392<p>The effectiveness of the <tt>PassManager</tt> is influenced directly by how
1393much information it has about the behaviors of the passes it is scheduling. For
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1394example, the "preserved" set is intentionally conservative in the face of an
1395unimplemented <a href="#getAnalysisUsage"><tt>getAnalysisUsage</tt></a> method.
1396Not implementing when it should be implemented will have the effect of not
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1397allowing any analysis results to live across the execution of your pass.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1398
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1399<p>The <tt>PassManager</tt> class exposes a <tt>--debug-pass</tt> command line
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1400options that is useful for debugging pass execution, seeing how things work, and
1401diagnosing when you should be preserving more analyses than you currently are
1402(To get information about all of the variants of the <tt>--debug-pass</tt>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1403option, just type '<tt>opt --help-hidden</tt>').</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1404
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1405<p>By using the <tt>--debug-pass=Structure</tt> option, for example, we can see
1406how our <a href="#basiccode">Hello World</a> pass interacts with other passes.
1407Lets try it out with the <tt>gcse</tt> and <tt>licm</tt> passes:</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1408
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1409<div class="doc_code"><pre>
Reid Spencer7fa6d522005-01-11 05:16:23 +0000[diff] [blame]1410$ 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]1411Module Pass Manager
1412 Function Pass Manager
1413 Dominator Set Construction
1414 Immediate Dominators Construction
1415 Global Common Subexpression Elimination
1416-- Immediate Dominators Construction
1417-- Global Common Subexpression Elimination
1418 Natural Loop Construction
1419 Loop Invariant Code Motion
1420-- Natural Loop Construction
1421-- Loop Invariant Code Motion
1422 Module Verifier
1423-- Dominator Set Construction
1424-- Module Verifier
Gabor Greif04367bf2007-07-06 22:07:22 +0000[diff] [blame]1425 Bitcode Writer
1426--Bitcode Writer
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1427</pre></div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1428
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1429<p>This output shows us when passes are constructed and when the analysis
1430results are known to be dead (prefixed with '<tt>--</tt>'). Here we see that
1431GCSE uses dominator and immediate dominator information to do its job. The LICM
1432pass uses natural loop information, which uses dominator sets, but not immediate
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1433dominators. Because immediate dominators are no longer useful after the GCSE
1434pass, it is immediately destroyed. The dominator sets are then reused to
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1435compute natural loop information, which is then used by the LICM pass.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1436
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1437<p>After the LICM pass, the module verifier runs (which is automatically added
1438by the '<tt>opt</tt>' tool), which uses the dominator set to check that the
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1439resultant LLVM code is well formed. After it finishes, the dominator set
1440information is destroyed, after being computed once, and shared by three
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1441passes.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1442
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1443<p>Lets see how this changes when we run the <a href="#basiccode">Hello
1444World</a> pass in between the two passes:</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1445
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1446<div class="doc_code"><pre>
Reid Spencer7fa6d522005-01-11 05:16:23 +0000[diff] [blame]1447$ 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]1448Module Pass Manager
1449 Function Pass Manager
1450 Dominator Set Construction
1451 Immediate Dominators Construction
1452 Global Common Subexpression Elimination
1453<b>-- Dominator Set Construction</b>
1454-- Immediate Dominators Construction
1455-- Global Common Subexpression Elimination
1456<b> Hello World Pass
1457-- Hello World Pass
1458 Dominator Set Construction</b>
1459 Natural Loop Construction
1460 Loop Invariant Code Motion
1461-- Natural Loop Construction
1462-- Loop Invariant Code Motion
1463 Module Verifier
1464-- Dominator Set Construction
1465-- Module Verifier
Gabor Greif04367bf2007-07-06 22:07:22 +0000[diff] [blame]1466 Bitcode Writer
1467--Bitcode Writer
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1468Hello: __main
1469Hello: puts
1470Hello: main
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1471</pre></div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1472
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1473<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]1474Dominator Set pass, even though it doesn't modify the code at all! To fix this,
1475we need to add the following <a
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1476href="#getAnalysisUsage"><tt>getAnalysisUsage</tt></a> method to our pass:</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1477
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1478<div class="doc_code"><pre>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1479 <i>// We don't modify the program, so we preserve all analyses</i>
1480 <b>virtual void</b> getAnalysisUsage(AnalysisUsage &amp;AU) <b>const</b> {
1481 AU.setPreservesAll();
1482 }
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1483</pre></div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1484
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1485<p>Now when we run our pass, we get this output:</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1486
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1487<div class="doc_code"><pre>
Reid Spencer7fa6d522005-01-11 05:16:23 +0000[diff] [blame]1488$ 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]1489Pass Arguments: -gcse -hello -licm
1490Module Pass Manager
1491 Function Pass Manager
1492 Dominator Set Construction
1493 Immediate Dominators Construction
1494 Global Common Subexpression Elimination
1495-- Immediate Dominators Construction
1496-- Global Common Subexpression Elimination
1497 Hello World Pass
1498-- Hello World Pass
1499 Natural Loop Construction
1500 Loop Invariant Code Motion
1501-- Loop Invariant Code Motion
1502-- Natural Loop Construction
1503 Module Verifier
1504-- Dominator Set Construction
1505-- Module Verifier
Gabor Greif04367bf2007-07-06 22:07:22 +0000[diff] [blame]1506 Bitcode Writer
1507--Bitcode Writer
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1508Hello: __main
1509Hello: puts
1510Hello: main
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1511</pre></div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1512
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1513<p>Which shows that we don't accidentally invalidate dominator information
1514anymore, and therefore do not have to compute it twice.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1515
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1516</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1517
1518<!-- _______________________________________________________________________ -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1519<div class="doc_subsubsection">
1520 <a name="releaseMemory">The <tt>releaseMemory</tt> method</a>
1521</div>
1522
1523<div class="doc_text">
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1524
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1525<div class="doc_code"><pre>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1526 <b>virtual void</b> releaseMemory();
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1527</pre></div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1528
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1529<p>The <tt>PassManager</tt> automatically determines when to compute analysis
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1530results, and how long to keep them around for. Because the lifetime of the pass
1531object itself is effectively the entire duration of the compilation process, we
1532need some way to free analysis results when they are no longer useful. The
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1533<tt>releaseMemory</tt> virtual method is the way to do this.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1534
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1535<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]1536amount of state (for use by another pass which "requires" your pass and uses the
1537<a href="#getAnalysis">getAnalysis</a> method) you should implement
1538<tt>releaseMEmory</tt> to, well, release the memory allocated to maintain this
1539internal state. This method is called after the <tt>run*</tt> method for the
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1540class, before the next call of <tt>run*</tt> in your pass.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1541
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1542</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1543
1544<!-- *********************************************************************** -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1545<div class="doc_section">
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1546 <a name="registering">Registering dynamically loaded passes</a>
1547</div>
1548<!-- *********************************************************************** -->
1549
1550<div class="doc_text">
1551
1552<p><i>Size matters</i> when constructing production quality tools using llvm,
1553both for the purposes of distribution, and for regulating the resident code size
1554when running on the target system. Therefore, it becomes desirable to
1555selectively use some passes, while omitting others and maintain the flexibility
1556to change configurations later on. You want to be able to do all this, and,
1557provide feedback to the user. This is where pass registration comes into
1558play.</p>
1559
1560<p>The fundamental mechanisms for pass registration are the
1561<tt>MachinePassRegistry</tt> class and subclasses of
1562<tt>MachinePassRegistryNode</tt>.</p>
1563
1564<p>An instance of <tt>MachinePassRegistry</tt> is used to maintain a list of
1565<tt>MachinePassRegistryNode</tt> objects. This instance maintains the list and
1566communicates additions and deletions to the command line interface.</p>
1567
1568<p>An instance of <tt>MachinePassRegistryNode</tt> subclass is used to maintain
1569information provided about a particular pass. This information includes the
1570command line name, the command help string and the address of the function used
1571to create an instance of the pass. A global static constructor of one of these
1572instances <i>registers</i> with a corresponding <tt>MachinePassRegistry</tt>,
1573the static destructor <i>unregisters</i>. Thus a pass that is statically linked
1574in the tool will be registered at start up. A dynamically loaded pass will
1575register on load and unregister at unload.</p>
1576
1577</div>
1578
1579<!-- _______________________________________________________________________ -->
1580<div class="doc_subsection">
1581 <a name="registering_existing">Using existing registries</a>
1582</div>
1583
1584<div class="doc_text">
1585
1586<p>There are predefined registries to track instruction scheduling
1587(<tt>RegisterScheduler</tt>) and register allocation (<tt>RegisterRegAlloc</tt>)
1588machine passes. Here we will describe how to <i>register</i> a register
1589allocator machine pass.</p>
1590
1591<p>Implement your register allocator machine pass. In your register allocator
1592.cpp file add the following include;</p>
1593
1594<div class="doc_code"><pre>
Chris Lattner8f652eb2006-08-11 16:37:02 +0000[diff] [blame]1595 #include "llvm/CodeGen/RegAllocRegistry.h"
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1596</pre></div>
1597
1598<p>Also in your register allocator .cpp file, define a creator function in the
1599form; </p>
1600
1601<div class="doc_code"><pre>
1602 FunctionPass *createMyRegisterAllocator() {
1603 return new MyRegisterAllocator();
1604 }
1605</pre></div>
1606
1607<p>Note that the signature of this function should match the type of
1608<tt>RegisterRegAlloc::FunctionPassCtor</tt>. In the same file add the
1609"installing" declaration, in the form;</p>
1610
1611<div class="doc_code"><pre>
1612 static RegisterRegAlloc myRegAlloc("myregalloc",
1613 " my register allocator help string",
1614 createMyRegisterAllocator);
1615</pre></div>
1616
1617<p>Note the two spaces prior to the help string produces a tidy result on the
1618--help query.</p>
1619
1620<div class="doc_code"><pre>
1621$ llc --help
1622 ...
1623 -regalloc - Register allocator to use: (default = linearscan)
1624 =linearscan - linear scan register allocator
1625 =local - local register allocator
1626 =simple - simple register allocator
1627 =myregalloc - my register allocator help string
1628 ...
1629</pre></div>
1630
1631<p>And that's it. The user is now free to use <tt>-regalloc=myregalloc</tt> as
1632an option. Registering instruction schedulers is similar except use the
Chris Lattner8f652eb2006-08-11 16:37:02 +0000[diff] [blame]1633<tt>RegisterScheduler</tt> class. Note that the
1634<tt>RegisterScheduler::FunctionPassCtor</tt> is significantly different from
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1635<tt>RegisterRegAlloc::FunctionPassCtor</tt>.</p>
1636
1637<p>To force the load/linking of your register allocator into the llc/lli tools,
1638add your creator function's global declaration to "Passes.h" and add a "pseudo"
1639call line to <tt>llvm/Codegen/LinkAllCodegenComponents.h</tt>.</p>
1640
1641</div>
1642
1643
1644<!-- _______________________________________________________________________ -->
1645<div class="doc_subsection">
1646 <a name="registering_new">Creating new registries</a>
1647</div>
1648
1649<div class="doc_text">
1650
1651<p>The easiest way to get started is to clone one of the existing registries; we
1652recommend <tt>llvm/CodeGen/RegAllocRegistry.h</tt>. The key things to modify
1653are the class name and the <tt>FunctionPassCtor</tt> type.</p>
1654
1655<p>Then you need to declare the registry. Example: if your pass registry is
1656<tt>RegisterMyPasses</tt> then define;</p>
1657
1658<div class="doc_code"><pre>
1659MachinePassRegistry RegisterMyPasses::Registry;
1660</pre></div>
1661
1662<p>And finally, declare the command line option for your passes. Example:</p>
1663
1664<div class="doc_code"><pre>
1665 cl::opt&lt;RegisterMyPasses::FunctionPassCtor, false,
Dan Gohman364a39f2008-10-14 17:00:38 +0000[diff] [blame]1666 RegisterPassParser&lt;RegisterMyPasses&gt; &gt;
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1667 MyPassOpt("mypass",
1668 cl::init(&amp;createDefaultMyPass),
1669 cl::desc("my pass option help"));
1670</pre></div>
1671
1672<p>Here the command option is "mypass", with createDefaultMyPass as the default
1673creator.</p>
1674
1675</div>
1676
1677<!-- *********************************************************************** -->
1678<div class="doc_section">
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1679 <a name="debughints">Using GDB with dynamically loaded passes</a>
1680</div>
Chris Lattner480e2ef2002-09-06 02:02:58 +0000[diff] [blame]1681<!-- *********************************************************************** -->
1682
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1683<div class="doc_text">
1684
1685<p>Unfortunately, using GDB with dynamically loaded passes is not as easy as it
Chris Lattner480e2ef2002-09-06 02:02:58 +0000[diff] [blame]1686should be. First of all, you can't set a breakpoint in a shared object that has
1687not been loaded yet, and second of all there are problems with inlined functions
1688in shared objects. Here are some suggestions to debugging your pass with
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1689GDB.</p>
Chris Lattner480e2ef2002-09-06 02:02:58 +0000[diff] [blame]1690
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1691<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]1692transformation invoked by <tt>opt</tt>, although nothing described here depends
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1693on that.</p>
1694
1695</div>
Chris Lattner480e2ef2002-09-06 02:02:58 +0000[diff] [blame]1696
1697<!-- _______________________________________________________________________ -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1698<div class="doc_subsubsection">
1699 <a name="breakpoint">Setting a breakpoint in your pass</a>
1700</div>
Chris Lattner480e2ef2002-09-06 02:02:58 +0000[diff] [blame]1701
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1702<div class="doc_text">
1703
1704<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]1705
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1706<div class="doc_code"><pre>
Chris Lattner480e2ef2002-09-06 02:02:58 +0000[diff] [blame]1707$ <b>gdb opt</b>
1708GNU gdb 5.0
1709Copyright 2000 Free Software Foundation, Inc.
1710GDB is free software, covered by the GNU General Public License, and you are
1711welcome to change it and/or distribute copies of it under certain conditions.
1712Type "show copying" to see the conditions.
1713There is absolutely no warranty for GDB. Type "show warranty" for details.
1714This GDB was configured as "sparc-sun-solaris2.6"...
1715(gdb)
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1716</pre></div>
Chris Lattner480e2ef2002-09-06 02:02:58 +0000[diff] [blame]1717
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1718<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]1719time to load. Be patient. Since we cannot set a breakpoint in our pass yet
1720(the shared object isn't loaded until runtime), we must execute the process, and
1721have it stop before it invokes our pass, but after it has loaded the shared
1722object. The most foolproof way of doing this is to set a breakpoint in
1723<tt>PassManager::run</tt> and then run the process with the arguments you
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1724want:</p>
Chris Lattner480e2ef2002-09-06 02:02:58 +0000[diff] [blame]1725
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1726<div class="doc_code"><pre>
Reid Spencer22a9e5b2006-09-28 16:53:47 +0000[diff] [blame]1727(gdb) <b>break llvm::PassManager::run</b>
Chris Lattner480e2ef2002-09-06 02:02:58 +0000[diff] [blame]1728Breakpoint 1 at 0x2413bc: file Pass.cpp, line 70.
Chris Lattner4c376ea2005-04-21 04:52:37 +0000[diff] [blame]1729(gdb) <b>run test.bc -load $(LLVMTOP)/llvm/Debug/lib/[libname].so -[passoption]</b>
1730Starting program: opt test.bc -load $(LLVMTOP)/llvm/Debug/lib/[libname].so -[passoption]
Chris Lattner480e2ef2002-09-06 02:02:58 +0000[diff] [blame]1731Breakpoint 1, PassManager::run (this=0xffbef174, M=@0x70b298) at Pass.cpp:70
173270 bool PassManager::run(Module &amp;M) { return PM-&gt;run(M); }
1733(gdb)
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1734</pre></div>
Chris Lattner480e2ef2002-09-06 02:02:58 +0000[diff] [blame]1735
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1736<p>Once the <tt>opt</tt> stops in the <tt>PassManager::run</tt> method you are
1737now free to set breakpoints in your pass so that you can trace through execution
1738or do other standard debugging stuff.</p>
Chris Lattner480e2ef2002-09-06 02:02:58 +0000[diff] [blame]1739
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1740</div>
Chris Lattner480e2ef2002-09-06 02:02:58 +0000[diff] [blame]1741
1742<!-- _______________________________________________________________________ -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1743<div class="doc_subsubsection">
1744 <a name="debugmisc">Miscellaneous Problems</a>
1745</div>
Chris Lattner480e2ef2002-09-06 02:02:58 +0000[diff] [blame]1746
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1747<div class="doc_text">
1748
1749<p>Once you have the basics down, there are a couple of problems that GDB has,
1750some with solutions, some without.</p>
Chris Lattner480e2ef2002-09-06 02:02:58 +0000[diff] [blame]1751
1752<ul>
1753<li>Inline functions have bogus stack information. In general, GDB does a
1754pretty good job getting stack traces and stepping through inline functions.
1755When a pass is dynamically loaded however, it somehow completely loses this
1756capability. The only solution I know of is to de-inline a function (move it
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1757from the body of a class to a .cpp file).</li>
Chris Lattner480e2ef2002-09-06 02:02:58 +0000[diff] [blame]1758
1759<li>Restarting the program breaks breakpoints. After following the information
1760above, you have succeeded in getting some breakpoints planted in your pass. Nex
1761thing you know, you restart the program (i.e., you type '<tt>run</tt>' again),
1762and you start getting errors about breakpoints being unsettable. The only way I
1763have found to "fix" this problem is to <tt>delete</tt> the breakpoints that are
1764already set in your pass, run the program, and re-set the breakpoints once
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1765execution stops in <tt>PassManager::run</tt>.</li>
Chris Lattner480e2ef2002-09-06 02:02:58 +0000[diff] [blame]1766
1767</ul>
1768
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1769<p>Hopefully these tips will help with common case debugging situations. If
1770you'd like to contribute some tips of your own, just contact <a
1771href="mailto:sabre@nondot.org">Chris</a>.</p>
Chris Lattner480e2ef2002-09-06 02:02:58 +0000[diff] [blame]1772
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1773</div>
Chris Lattner480e2ef2002-09-06 02:02:58 +0000[diff] [blame]1774
1775<!-- *********************************************************************** -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1776<div class="doc_section">
1777 <a name="future">Future extensions planned</a>
1778</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1779<!-- *********************************************************************** -->
1780
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1781<div class="doc_text">
1782
1783<p>Although the LLVM Pass Infrastructure is very capable as it stands, and does
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1784some 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]1785where we are going:</p>
1786
1787</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1788
1789<!-- _______________________________________________________________________ -->
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]1790<div class="doc_subsubsection">
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1791 <a name="SMP">Multithreaded LLVM</a>
1792</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1793
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1794<div class="doc_text">
1795
1796<p>Multiple CPU machines are becoming more common and compilation can never be
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1797fast enough: obviously we should allow for a multithreaded compiler. Because of
1798the semantics defined for passes above (specifically they cannot maintain state
1799across invocations of their <tt>run*</tt> methods), a nice clean way to
1800implement a multithreaded compiler would be for the <tt>PassManager</tt> class
Misha Brukmanbc0e9982003-07-14 17:20:40 +0000[diff] [blame]1801to create multiple instances of each pass object, and allow the separate
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1802instances to be hacking on different parts of the program at the same time.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1803
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1804<p>This implementation would prevent each of the passes from having to implement
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1805multithreaded constructs, requiring only the LLVM core to have locking in a few
1806places (for global resources). Although this is a simple extension, we simply
1807haven't had time (or multiprocessor machines, thus a reason) to implement this.
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1808Despite that, we have kept the LLVM passes SMP ready, and you should too.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1809
Chris Lattnerb5c87f62007-05-18 05:36:14 +0000[diff] [blame]1810</div>
1811
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1812<!-- *********************************************************************** -->
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Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1820 <a href="mailto:sabre@nondot.org">Chris Lattner</a><br>
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