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gerrit-public.fairphone.software / fp2-dev / platform / external / llvm / 8528e78f0d281de4d683de4e1b93b6ff9bed7f5c / . / docs / WritingAnLLVMPass.html
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Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]6 <title>Writing an LLVM Pass</title>
7 <link rel="stylesheet" href="llvm.css" type="text/css">
8</head>
9<body>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]10
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]11<div class="doc_title">
12 Writing an LLVM Pass
13</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]14
15<ol>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]16 <li><a href="#introduction">Introduction - What is a pass?</a></li>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]17 <li><a href="#quickstart">Quick Start - Writing hello world</a>
18 <ul>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]19 <li><a href="#makefile">Setting up the build environment</a></li>
20 <li><a href="#basiccode">Basic code required</a></li>
Chris Lattnerc8603c22006-08-27 23:18:52 +0000[diff] [blame]21 <li><a href="#running">Running a pass with <tt>opt</tt></a></li>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]22 </ul></li>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]23 <li><a href="#passtype">Pass classes and requirements</a>
24 <ul>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]25 <li><a href="#ImmutablePass">The <tt>ImmutablePass</tt> class</a></li>
Chris Lattnerf6278922004-09-20 04:36:29 +0000[diff] [blame]26 <li><a href="#ModulePass">The <tt>ModulePass</tt> class</a>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]27 <ul>
Chris Lattnerf6278922004-09-20 04:36:29 +0000[diff] [blame]28 <li><a href="#runOnModule">The <tt>runOnModule</tt> method</a></li>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]29 </ul></li>
Chris Lattner8fdb2462004-09-18 06:39:35 +0000[diff] [blame]30 <li><a href="#CallGraphSCCPass">The <tt>CallGraphSCCPass</tt> class</a>
31 <ul>
Devang Patelc20048d2007-01-23 22:56:28 +0000[diff] [blame]32 <li><a href="#doInitialization_scc">The <tt>doInitialization(CallGraph
Chris Lattner8fdb2462004-09-18 06:39:35 +0000[diff] [blame]33 &amp;)</tt> method</a></li>
34 <li><a href="#runOnSCC">The <tt>runOnSCC</tt> method</a></li>
Devang Patelc20048d2007-01-23 22:56:28 +0000[diff] [blame]35 <li><a href="#doFinalization_scc">The <tt>doFinalization(CallGraph
Chris Lattner8fdb2462004-09-18 06:39:35 +0000[diff] [blame]36 &amp;)</tt> method</a></li>
37 </ul></li>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]38 <li><a href="#FunctionPass">The <tt>FunctionPass</tt> class</a>
39 <ul>
Chris Lattnerd0713f92002-09-12 17:06:43 +0000[diff] [blame]40 <li><a href="#doInitialization_mod">The <tt>doInitialization(Module
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]41 &amp;)</tt> method</a></li>
42 <li><a href="#runOnFunction">The <tt>runOnFunction</tt> method</a></li>
Chris Lattnerd0713f92002-09-12 17:06:43 +0000[diff] [blame]43 <li><a href="#doFinalization_mod">The <tt>doFinalization(Module
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]44 &amp;)</tt> method</a></li>
45 </ul></li>
Devang Patel2e8f27d2007-03-19 22:21:25 +0000[diff] [blame]46 <li><a href="#LoopPass">The <tt>LoopPass</tt> class</a>
47 <ul>
48 <li><a href="#doInitialization_loop">The <tt>doInitialization(Loop *,
49 LPPassManager &amp;)</tt> method</a></li>
50 <li><a href="#runOnLoop">The <tt>runOnLoop</tt> method</a></li>
51 <li><a href="#doFinalization_loop">The <tt>doFinalization()
52 </tt> method</a></li>
53 </ul></li>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]54 <li><a href="#BasicBlockPass">The <tt>BasicBlockPass</tt> class</a>
55 <ul>
Chris Lattnerd0713f92002-09-12 17:06:43 +0000[diff] [blame]56 <li><a href="#doInitialization_fn">The <tt>doInitialization(Function
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]57 &amp;)</tt> method</a></li>
58 <li><a href="#runOnBasicBlock">The <tt>runOnBasicBlock</tt>
59 method</a></li>
Chris Lattnerd0713f92002-09-12 17:06:43 +0000[diff] [blame]60 <li><a href="#doFinalization_fn">The <tt>doFinalization(Function
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]61 &amp;)</tt> method</a></li>
62 </ul></li>
Brian Gaekecab8b6f2003-07-17 18:53:20 +0000[diff] [blame]63 <li><a href="#MachineFunctionPass">The <tt>MachineFunctionPass</tt>
64 class</a>
Brian Gaeke6a33f362003-07-22 20:53:20 +0000[diff] [blame]65 <ul>
66 <li><a href="#runOnMachineFunction">The
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]67 <tt>runOnMachineFunction(MachineFunction &amp;)</tt> method</a></li>
68 </ul></li>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]69 </ul>
70 <li><a href="#registration">Pass Registration</a>
71 <ul>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]72 <li><a href="#print">The <tt>print</tt> method</a></li>
73 </ul></li>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]74 <li><a href="#interaction">Specifying interactions between passes</a>
75 <ul>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]76 <li><a href="#getAnalysisUsage">The <tt>getAnalysisUsage</tt>
77 method</a></li>
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]78 <li><a href="#AU::addRequired">The <tt>AnalysisUsage::addRequired&lt;&gt;</tt> and <tt>AnalysisUsage::addRequiredTransitive&lt;&gt;</tt> methods</a></li>
79 <li><a href="#AU::addPreserved">The <tt>AnalysisUsage::addPreserved&lt;&gt;</tt> method</a></li>
80 <li><a href="#AU::examples">Example implementations of <tt>getAnalysisUsage</tt></a></li>
81 <li><a href="#getAnalysis">The <tt>getAnalysis&lt;&gt;</tt> and <tt>getAnalysisToUpdate&lt;&gt;</tt> methods</a></li>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]82 </ul></li>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]83 <li><a href="#analysisgroup">Implementing Analysis Groups</a>
84 <ul>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]85 <li><a href="#agconcepts">Analysis Group Concepts</a></li>
86 <li><a href="#registerag">Using <tt>RegisterAnalysisGroup</tt></a></li>
87 </ul></li>
Tanya Lattnerd5383652004-11-19 01:25:14 +0000[diff] [blame]88 <li><a href="#passStatistics">Pass Statistics</a>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]89 <li><a href="#passmanager">What PassManager does</a>
90 <ul>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]91 <li><a href="#releaseMemory">The <tt>releaseMemory</tt> method</a></li>
92 </ul></li>
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]93 <li><a href="#registering">Registering dynamically loaded passes</a>
94 <ul>
95 <li><a href="#registering_existing">Using existing registries</a></li>
96 <li><a href="#registering_new">Creating new registries</a></li>
97 </ul></li>
Chris Lattner480e2ef2002-09-06 02:02:58 +0000[diff] [blame]98 <li><a href="#debughints">Using GDB with dynamically loaded passes</a>
99 <ul>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]100 <li><a href="#breakpoint">Setting a breakpoint in your pass</a></li>
101 <li><a href="#debugmisc">Miscellaneous Problems</a></li>
102 </ul></li>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]103 <li><a href="#future">Future extensions planned</a>
104 <ul>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]105 <li><a href="#SMP">Multithreaded LLVM</a></li>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]106 </ul></li>
107</ol>
Chris Lattner38c633d2002-08-08 20:23:41 +0000[diff] [blame]108
Chris Lattner7911ce22004-05-23 21:07:27 +0000[diff] [blame]109<div class="doc_author">
Chris Lattner8f652eb2006-08-11 16:37:02 +0000[diff] [blame]110 <p>Written by <a href="mailto:sabre@nondot.org">Chris Lattner</a> and
Jim Laskeyc760a922007-03-14 19:32:21 +0000[diff] [blame]111 <a href="mailto:jlaskey@mac.com">Jim Laskey</a></p>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]112</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]113
114<!-- *********************************************************************** -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]115<div class="doc_section">
116 <a name="introduction">Introduction - What is a pass?</a>
117</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]118<!-- *********************************************************************** -->
119
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]120<div class="doc_text">
121
122<p>The LLVM Pass Framework is an important part of the LLVM system, because LLVM
Chris Lattner8fdb2462004-09-18 06:39:35 +0000[diff] [blame]123passes are where most of the interesting parts of the compiler exist. Passes
124perform the transformations and optimizations that make up the compiler, they
125build the analysis results that are used by these transformations, and they are,
126above all, a structuring technique for compiler code.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]127
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]128<p>All LLVM passes are subclasses of the <tt><a
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]129href="http://llvm.org/doxygen/classllvm_1_1Pass.html">Pass</a></tt>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]130class, which implement functionality by overriding virtual methods inherited
Chris Lattnerf6278922004-09-20 04:36:29 +0000[diff] [blame]131from <tt>Pass</tt>. Depending on how your pass works, you should inherit from
132the <tt><a href="#ModulePass">ModulePass</a></tt>, <tt><a
133href="#CallGraphSCCPass">CallGraphSCCPass</a></tt>, <tt><a
134href="#FunctionPass">FunctionPass</a></tt>, or <tt><a
Devang Patel2e8f27d2007-03-19 22:21:25 +0000[diff] [blame]135href="#LoopPass">LoopPass</a></tt>, or <tt><a
Chris Lattner8fdb2462004-09-18 06:39:35 +0000[diff] [blame]136href="#BasicBlockPass">BasicBlockPass</a></tt> classes, which gives the system
137more information about what your pass does, and how it can be combined with
138other passes. One of the main features of the LLVM Pass Framework is that it
139schedules passes to run in an efficient way based on the constraints that your
140pass meets (which are indicated by which class they derive from).</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]141
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]142<p>We start by showing you how to construct a pass, everything from setting up
143the code, to compiling, loading, and executing it. After the basics are down,
144more advanced features are discussed.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]145
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]146</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]147
148<!-- *********************************************************************** -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]149<div class="doc_section">
150 <a name="quickstart">Quick Start - Writing hello world</a>
151</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]152<!-- *********************************************************************** -->
153
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]154<div class="doc_text">
155
156<p>Here we describe how to write the "hello world" of passes. The "Hello" pass
157is designed to simply print out the name of non-external functions that exist in
Chris Lattner8fdb2462004-09-18 06:39:35 +0000[diff] [blame]158the program being compiled. It does not modify the program at all, it just
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]159inspects it. The source code and files for this pass are available in the LLVM
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]160source tree in the <tt>lib/Transforms/Hello</tt> directory.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]161
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]162</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]163
164<!-- ======================================================================= -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]165<div class="doc_subsection">
166 <a name="makefile">Setting up the build environment</a>
167</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]168
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]169<div class="doc_text">
170
Reid Spencer1bc19342004-12-11 05:12:57 +0000[diff] [blame]171 <p>First, you need to create a new directory somewhere in the LLVM source
172 base. For this example, we'll assume that you made
173 <tt>lib/Transforms/Hello</tt>. Next, you must set up a build script
174 (Makefile) that will compile the source code for the new pass. To do this,
175 copy the following into <tt>Makefile</tt>:</p>
176 <hr/>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]177
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]178<div class="doc_code"><pre>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]179# Makefile for hello pass
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]180
Chris Lattner17a4c3e2002-08-14 20:06:13 +0000[diff] [blame]181# Path to top level of LLVM heirarchy
Chris Lattner7ce83e52002-08-14 20:07:01 +0000[diff] [blame]182LEVEL = ../../..
Chris Lattner17a4c3e2002-08-14 20:06:13 +0000[diff] [blame]183
184# Name of the library to build
Reid Spencer7fa6d522005-01-11 05:16:23 +0000[diff] [blame]185LIBRARYNAME = Hello
Chris Lattner17a4c3e2002-08-14 20:06:13 +0000[diff] [blame]186
Reid Spencer7fa6d522005-01-11 05:16:23 +0000[diff] [blame]187# Make the shared library become a loadable module so the tools can
188# dlopen/dlsym on the resulting library.
Robert Bocchino3cf817d2006-01-06 22:49:23 +0000[diff] [blame]189LOADABLE_MODULE = 1
Reid Spencer7fa6d522005-01-11 05:16:23 +0000[diff] [blame]190
Reid Spencerebfe07f2006-08-08 01:48:17 +0000[diff] [blame]191# Tell the build system which LLVM libraries your pass needs. You'll probably
192# need at least LLVMSystem.a, LLVMSupport.a, LLVMCore.a but possibly several
193# others too.
194LLVMLIBS = LLVMCore.a LLVMSupport.a LLVMSystem.a
195
Chris Lattner17a4c3e2002-08-14 20:06:13 +0000[diff] [blame]196# Include the makefile implementation stuff
197include $(LEVEL)/Makefile.common
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]198</pre></div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]199
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]200<p>This makefile specifies that all of the <tt>.cpp</tt> files in the current
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]201directory are to be compiled and linked together into a
Reid Spencer7fa6d522005-01-11 05:16:23 +0000[diff] [blame]202<tt>Debug/lib/Hello.so</tt> shared object that can be dynamically loaded by
Chris Lattnerc8603c22006-08-27 23:18:52 +0000[diff] [blame]203the <tt>opt</tt> or <tt>bugpoint</tt> tools via their <tt>-load</tt> options.
Reid Spencer7fa6d522005-01-11 05:16:23 +0000[diff] [blame]204If your operating system uses a suffix other than .so (such as windows or
205Mac OS/X), the appropriate extension will be used.</p>
John Criswellf9c78652004-01-26 21:26:54 +0000[diff] [blame]206
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]207<p>Now that we have the build scripts set up, we just need to write the code for
208the pass itself.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]209
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]210</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]211
212<!-- ======================================================================= -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]213<div class="doc_subsection">
214 <a name="basiccode">Basic code required</a>
215</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]216
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]217<div class="doc_text">
218
219<p>Now that we have a way to compile our new pass, we just have to write it.
220Start out with:</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]221
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]222<div class="doc_code"><pre>
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]223<b>#include</b> "<a href="http://llvm.org/doxygen/Pass_8h-source.html">llvm/Pass.h</a>"
224<b>#include</b> "<a href="http://llvm.org/doxygen/Function_8h-source.html">llvm/Function.h</a>"
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]225</pre></div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]226
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]227<p>Which are needed because we are writing a <tt><a
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]228href="http://llvm.org/doxygen/classllvm_1_1Pass.html">Pass</a></tt>, and
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]229we are operating on <tt><a
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]230href="http://llvm.org/doxygen/classllvm_1_1Function.html">Function</a></tt>'s.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]231
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]232<p>Next we have:</p>
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]233<div class="doc_code"><pre>
Jonathan Manton65acb302004-06-30 18:10:30 +0000[diff] [blame]234<b>using namespace llvm;</b>
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]235</pre></div>
Jonathan Manton65acb302004-06-30 18:10:30 +0000[diff] [blame]236<p>... which is required because the functions from the include files
237live in the llvm namespace.
238</p>
239
240<p>Next we have:</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]241
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]242<div class="doc_code"><pre>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]243<b>namespace</b> {
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]244</pre></div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]245
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]246<p>... which starts out an anonymous namespace. Anonymous namespaces are to C++
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]247what the "<tt>static</tt>" keyword is to C (at global scope). It makes the
248things declared inside of the anonymous namespace only visible to the current
249file. If you're not familiar with them, consult a decent C++ book for more
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]250information.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]251
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]252<p>Next, we declare our pass itself:</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]253
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]254<div class="doc_code"><pre>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]255 <b>struct</b> Hello : <b>public</b> <a href="#FunctionPass">FunctionPass</a> {
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]256</pre></div><p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]257
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]258<p>This declares a "<tt>Hello</tt>" class that is a subclass of <tt><a
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]259href="http://llvm.org/doxygen/classllvm_1_1FunctionPass.html">FunctionPass</a></tt>.
Chris Lattnerd6ea9262002-09-09 03:48:46 +0000[diff] [blame]260The different builtin pass subclasses are described in detail <a
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]261href="#passtype">later</a>, but for now, know that <a
262href="#FunctionPass"><tt>FunctionPass</tt></a>'s operate a function at a
263time.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]264
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]265<div class="doc_code"><pre>
Devang Patel19974732007-05-03 01:11:54 +0000[diff] [blame]266 static char ID;
Chris Lattnerb5c87f62007-05-18 05:36:14 +0000[diff] [blame]267 Hello() : FunctionPass((intptr_t)&amp;ID) {}
Devang Patele50fb9a2007-05-01 20:55:38 +0000[diff] [blame]268</pre></div><p>
269
270<p> This declares pass identifier used by LLVM to identify pass. This allows LLVM to
271avoid using expensive C++ runtime information.</p>
272
273<div class="doc_code"><pre>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]274 <b>virtual bool</b> <a href="#runOnFunction">runOnFunction</a>(Function &amp;F) {
Bill Wendling832171c2006-12-07 20:04:42 +0000[diff] [blame]275 llvm::cerr &lt;&lt; "<i>Hello: </i>" &lt;&lt; F.getName() &lt;&lt; "\n";
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]276 <b>return false</b>;
277 }
278 }; <i>// end of struct Hello</i>
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]279</pre></div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]280
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]281<p>We declare a "<a href="#runOnFunction"><tt>runOnFunction</tt></a>" method,
282which overloads an abstract virtual method inherited from <a
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]283href="#FunctionPass"><tt>FunctionPass</tt></a>. This is where we are supposed
284to do our thing, so we just print out our message with the name of each
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]285function.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]286
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]287<div class="doc_code"><pre>
Devang Patel19974732007-05-03 01:11:54 +0000[diff] [blame]288 char Hello::ID = 0;
Devang Patele50fb9a2007-05-01 20:55:38 +0000[diff] [blame]289</pre></div>
290
291<p> We initialize pass ID here. LLVM uses ID's address to identify pass so
292initialization value is not important.</p>
293
294<div class="doc_code"><pre>
Chris Lattnerc8603c22006-08-27 23:18:52 +0000[diff] [blame]295 RegisterPass&lt;Hello&gt; X("<i>hello</i>", "<i>Hello World Pass</i>");
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]296} <i>// end of anonymous namespace</i>
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]297</pre></div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]298
Chris Lattnerc8603c22006-08-27 23:18:52 +0000[diff] [blame]299<p>Lastly, we <a href="#registration">register our class</a> <tt>Hello</tt>,
300giving it a command line
301argument "<tt>hello</tt>", and a name "<tt>Hello World Pass</tt>".</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]302
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]303<p>As a whole, the <tt>.cpp</tt> file looks like:</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]304
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]305<div class="doc_code"><pre>
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]306<b>#include</b> "<a href="http://llvm.org/doxygen/Pass_8h-source.html">llvm/Pass.h</a>"
307<b>#include</b> "<a href="http://llvm.org/doxygen/Function_8h-source.html">llvm/Function.h</a>"
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]308
Jonathan Manton65acb302004-06-30 18:10:30 +0000[diff] [blame]309<b>using namespace llvm;</b>
310
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]311<b>namespace</b> {
312 <b>struct Hello</b> : <b>public</b> <a href="#FunctionPass">FunctionPass</a> {
Devang Patele50fb9a2007-05-01 20:55:38 +0000[diff] [blame]313
Devang Patel19974732007-05-03 01:11:54 +0000[diff] [blame]314 static char ID;
Chris Lattner55021172007-05-18 05:38:44 +0000[diff] [blame]315 Hello() : FunctionPass((intptr_t)&amp;ID) {}
Devang Patele50fb9a2007-05-01 20:55:38 +0000[diff] [blame]316
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]317 <b>virtual bool</b> <a href="#runOnFunction">runOnFunction</a>(Function &amp;F) {
Bill Wendling832171c2006-12-07 20:04:42 +0000[diff] [blame]318 llvm::cerr &lt;&lt; "<i>Hello: </i>" &lt;&lt; F.getName() &lt;&lt; "\n";
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]319 <b>return false</b>;
320 }
321 };
322
Devang Patel26e5a302007-07-25 21:05:39 +0000[diff] [blame]323 char Hello::ID = 0;
Chris Lattnerc8603c22006-08-27 23:18:52 +0000[diff] [blame]324 RegisterPass&lt;Hello&gt; X("<i>hello</i>", "<i>Hello World Pass</i>");
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]325}
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]326</pre></div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]327
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]328<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]329command in the local directory and you should get a new
Reid Spencer7fa6d522005-01-11 05:16:23 +0000[diff] [blame]330"<tt>Debug/lib/Hello.so</tt> file. Note that everything in this file is
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]331contained in an anonymous namespace: this reflects the fact that passes are self
332contained units that do not need external interfaces (although they can have
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]333them) to be useful.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]334
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]335</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]336
337<!-- ======================================================================= -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]338<div class="doc_subsection">
Chris Lattnerc8603c22006-08-27 23:18:52 +0000[diff] [blame]339 <a name="running">Running a pass with <tt>opt</tt></a>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]340</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]341
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]342<div class="doc_text">
343
John Criswellf9c78652004-01-26 21:26:54 +0000[diff] [blame]344<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]345<tt>opt</tt> command to run an LLVM program through your pass. Because you
Chris Lattnerc8603c22006-08-27 23:18:52 +0000[diff] [blame]346registered your pass with the <tt>RegisterPass</tt> template, you will be able to
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]347use the <tt>opt</tt> tool to access it, once loaded.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]348
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]349<p>To test it, follow the example at the end of the <a
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]350href="GettingStarted.html">Getting Started Guide</a> to compile "Hello World" to
Gabor Greif04367bf2007-07-06 22:07:22 +0000[diff] [blame]351LLVM. We can now run the bitcode file (<tt>hello.bc</tt>) for the program
352through our transformation like this (or course, any bitcode file will
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]353work):</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]354
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]355<div class="doc_code"><pre>
Reid Spencer7fa6d522005-01-11 05:16:23 +0000[diff] [blame]356$ opt -load ../../../Debug/lib/Hello.so -hello &lt; hello.bc &gt; /dev/null
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]357Hello: __main
358Hello: puts
359Hello: main
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]360</pre></div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]361
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]362<p>The '<tt>-load</tt>' option specifies that '<tt>opt</tt>' should load your
363pass as a shared object, which makes '<tt>-hello</tt>' a valid command line
364argument (which is one reason you need to <a href="#registration">register your
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]365pass</a>). Because the hello pass does not modify the program in any
366interesting way, we just throw away the result of <tt>opt</tt> (sending it to
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]367<tt>/dev/null</tt>).</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]368
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]369<p>To see what happened to the other string you registered, try running
370<tt>opt</tt> with the <tt>--help</tt> option:</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]371
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]372<div class="doc_code"><pre>
Reid Spencer7fa6d522005-01-11 05:16:23 +0000[diff] [blame]373$ opt -load ../../../Debug/lib/Hello.so --help
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]374OVERVIEW: llvm .bc -&gt; .bc modular optimizer
375
Gabor Greif04367bf2007-07-06 22:07:22 +0000[diff] [blame]376USAGE: opt [options] &lt;input bitcode&gt;
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]377
378OPTIONS:
379 Optimizations available:
380...
381 -funcresolve - Resolve Functions
382 -gcse - Global Common Subexpression Elimination
383 -globaldce - Dead Global Elimination
384 <b>-hello - Hello World Pass</b>
Chris Lattner065a6162003-09-10 05:29:43 +0000[diff] [blame]385 -indvars - Canonicalize Induction Variables
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]386 -inline - Function Integration/Inlining
387 -instcombine - Combine redundant instructions
388...
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]389</pre></div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]390
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]391<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]392documentation to users of <tt>opt</tt>. Now that you have a working pass, you
393would go ahead and make it do the cool transformations you want. Once you get
394it all working and tested, it may become useful to find out how fast your pass
395is. The <a href="#passManager"><tt>PassManager</tt></a> provides a nice command
396line option (<tt>--time-passes</tt>) that allows you to get information about
397the execution time of your pass along with the other passes you queue up. For
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]398example:</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]399
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]400<div class="doc_code"><pre>
Reid Spencer7fa6d522005-01-11 05:16:23 +0000[diff] [blame]401$ 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]402Hello: __main
403Hello: puts
404Hello: main
405===============================================================================
406 ... Pass execution timing report ...
407===============================================================================
408 Total Execution Time: 0.02 seconds (0.0479059 wall clock)
409
410 ---User Time--- --System Time-- --User+System-- ---Wall Time--- --- Pass Name ---
Gabor Greif04367bf2007-07-06 22:07:22 +0000[diff] [blame]411 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]412 0.0000 ( 0.0%) 0.0100 (100.0%) 0.0100 ( 50.0%) 0.0031 ( 6.4%) Dominator Set Construction
413 0.0000 ( 0.0%) 0.0000 ( 0.0%) 0.0000 ( 0.0%) 0.0013 ( 2.7%) Module Verifier
414 <b> 0.0000 ( 0.0%) 0.0000 ( 0.0%) 0.0000 ( 0.0%) 0.0033 ( 6.9%) Hello World Pass</b>
415 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]416</pre></div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]417
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]418<p>As you can see, our implementation above is pretty fast :). The additional
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]419passes listed are automatically inserted by the '<tt>opt</tt>' tool to verify
420that the LLVM emitted by your pass is still valid and well formed LLVM, which
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]421hasn't been broken somehow.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]422
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]423<p>Now that you have seen the basics of the mechanics behind passes, we can talk
424about some more details of how they work and how to use them.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]425
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]426</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]427
428<!-- *********************************************************************** -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]429<div class="doc_section">
430 <a name="passtype">Pass classes and requirements</a>
431</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]432<!-- *********************************************************************** -->
433
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]434<div class="doc_text">
435
436<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]437decide what class you should subclass for your pass. The <a
438href="#basiccode">Hello World</a> example uses the <tt><a
439href="#FunctionPass">FunctionPass</a></tt> class for its implementation, but we
440did not discuss why or when this should occur. Here we talk about the classes
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]441available, from the most general to the most specific.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]442
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]443<p>When choosing a superclass for your Pass, you should choose the <b>most
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]444specific</b> class possible, while still being able to meet the requirements
Misha Brukman5560c9d2003-08-18 14:43:39 +0000[diff] [blame]445listed. This gives the LLVM Pass Infrastructure information necessary to
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]446optimize how passes are run, so that the resultant compiler isn't unneccesarily
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]447slow.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]448
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]449</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]450
Chris Lattnerf004f9a2002-09-25 22:31:38 +0000[diff] [blame]451<!-- ======================================================================= -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]452<div class="doc_subsection">
453 <a name="ImmutablePass">The <tt>ImmutablePass</tt> class</a>
454</div>
Chris Lattnerf004f9a2002-09-25 22:31:38 +0000[diff] [blame]455
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]456<div class="doc_text">
457
458<p>The most plain and boring type of pass is the "<tt><a
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]459href="http://llvm.org/doxygen/classllvm_1_1ImmutablePass.html">ImmutablePass</a></tt>"
Chris Lattnerf004f9a2002-09-25 22:31:38 +0000[diff] [blame]460class. This pass type is used for passes that do not have to be run, do not
461change state, and never need to be updated. This is not a normal type of
462transformation or analysis, but can provide information about the current
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]463compiler configuration.</p>
Chris Lattnerf004f9a2002-09-25 22:31:38 +0000[diff] [blame]464
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]465<p>Although this pass class is very infrequently used, it is important for
Chris Lattnerf004f9a2002-09-25 22:31:38 +0000[diff] [blame]466providing information about the current target machine being compiled for, and
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]467other static information that can affect the various transformations.</p>
Chris Lattnerf004f9a2002-09-25 22:31:38 +0000[diff] [blame]468
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]469<p><tt>ImmutablePass</tt>es never invalidate other transformations, are never
470invalidated, and are never "run".</p>
Chris Lattnerf004f9a2002-09-25 22:31:38 +0000[diff] [blame]471
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]472</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]473
474<!-- ======================================================================= -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]475<div class="doc_subsection">
Chris Lattnerf6278922004-09-20 04:36:29 +0000[diff] [blame]476 <a name="ModulePass">The <tt>ModulePass</tt> class</a>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]477</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]478
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]479<div class="doc_text">
480
481<p>The "<tt><a
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]482href="http://llvm.org/doxygen/classllvm_1_1ModulePass.html">ModulePass</a></tt>"
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]483class is the most general of all superclasses that you can use. Deriving from
Chris Lattnerf6278922004-09-20 04:36:29 +0000[diff] [blame]484<tt>ModulePass</tt> indicates that your pass uses the entire program as a unit,
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]485refering to function bodies in no predictable order, or adding and removing
Chris Lattnerf6278922004-09-20 04:36:29 +0000[diff] [blame]486functions. Because nothing is known about the behavior of <tt>ModulePass</tt>
Devang Patel3c1ca0b2007-04-16 21:28:14 +0000[diff] [blame]487subclasses, no optimization can be done for their execution. A module pass
488can use function level passes (e.g. dominators) using getAnalysis interface
Chris Lattnerb5c87f62007-05-18 05:36:14 +0000[diff] [blame]489<tt> getAnalysis&lt;DominatorTree&gt;(Function)</tt>. </p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]490
Chris Lattnerf6278922004-09-20 04:36:29 +0000[diff] [blame]491<p>To write a correct <tt>ModulePass</tt> subclass, derive from
492<tt>ModulePass</tt> and overload the <tt>runOnModule</tt> method with the
493following signature:</p>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]494
495</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]496
497<!-- _______________________________________________________________________ -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]498<div class="doc_subsubsection">
Chris Lattnerf6278922004-09-20 04:36:29 +0000[diff] [blame]499 <a name="runOnModule">The <tt>runOnModule</tt> method</a>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]500</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]501
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]502<div class="doc_text">
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]503
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]504<div class="doc_code"><pre>
Chris Lattnerf6278922004-09-20 04:36:29 +0000[diff] [blame]505 <b>virtual bool</b> runOnModule(Module &amp;M) = 0;
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]506</pre></div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]507
John Criswell2382ff72005-07-15 19:25:12 +0000[diff] [blame]508<p>The <tt>runOnModule</tt> method performs the interesting work of the pass.
509It should return true if the module was modified by the transformation and
510false otherwise.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]511
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]512</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]513
514<!-- ======================================================================= -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]515<div class="doc_subsection">
Chris Lattner8fdb2462004-09-18 06:39:35 +0000[diff] [blame]516 <a name="CallGraphSCCPass">The <tt>CallGraphSCCPass</tt> class</a>
517</div>
518
519<div class="doc_text">
520
521<p>The "<tt><a
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]522href="http://llvm.org/doxygen/classllvm_1_1CallGraphSCCPass.html">CallGraphSCCPass</a></tt>"
Chris Lattner8fdb2462004-09-18 06:39:35 +0000[diff] [blame]523is used by passes that need to traverse the program bottom-up on the call graph
524(callees before callers). Deriving from CallGraphSCCPass provides some
525mechanics for building and traversing the CallGraph, but also allows the system
526to optimize execution of CallGraphSCCPass's. If your pass meets the
527requirements outlined below, and doesn't meet the requirements of a <tt><a
528href="#FunctionPass">FunctionPass</a></tt> or <tt><a
529href="#BasicBlockPass">BasicBlockPass</a></tt>, you should derive from
530<tt>CallGraphSCCPass</tt>.</p>
531
532<p><b>TODO</b>: explain briefly what SCC, Tarjan's algo, and B-U mean.</p>
533
534<p>To be explicit, <tt>CallGraphSCCPass</tt> subclasses are:</p>
535
536<ol>
537
538<li>... <em>not allowed</em> to modify any <tt>Function</tt>s that are not in
539the current SCC.</li>
540
Tanya Lattner18aad232007-06-07 16:44:52 +0000[diff] [blame]541<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]542current SCC and the direct callees of the SCC.</li>
543
544<li>... <em>required</em> to preserve the current CallGraph object, updating it
545to reflect any changes made to the program.</li>
546
547<li>... <em>not allowed</em> to add or remove SCC's from the current Module,
548though they may change the contents of an SCC.</li>
549
550<li>... <em>allowed</em> to add or remove global variables from the current
551Module.</li>
552
553<li>... <em>allowed</em> to maintain state across invocations of
554 <a href="#runOnSCC"><tt>runOnSCC</tt></a> (including global data).</li>
555</ol>
556
557<p>Implementing a <tt>CallGraphSCCPass</tt> is slightly tricky in some cases
558because it has to handle SCCs with more than one node in it. All of the virtual
559methods described below should return true if they modified the program, or
560false if they didn't.</p>
561
562</div>
563
564<!-- _______________________________________________________________________ -->
565<div class="doc_subsubsection">
Devang Patelc20048d2007-01-23 22:56:28 +0000[diff] [blame]566 <a name="doInitialization_scc">The <tt>doInitialization(CallGraph &amp;)</tt>
Chris Lattner8fdb2462004-09-18 06:39:35 +0000[diff] [blame]567 method</a>
568</div>
569
570<div class="doc_text">
571
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]572<div class="doc_code"><pre>
Devang Patelc20048d2007-01-23 22:56:28 +0000[diff] [blame]573 <b>virtual bool</b> doInitialization(CallGraph &amp;CG);
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]574</pre></div>
Chris Lattner8fdb2462004-09-18 06:39:35 +0000[diff] [blame]575
576<p>The <tt>doIninitialize</tt> method is allowed to do most of the things that
577<tt>CallGraphSCCPass</tt>'s are not allowed to do. They can add and remove
578functions, get pointers to functions, etc. The <tt>doInitialization</tt> method
579is designed to do simple initialization type of stuff that does not depend on
580the SCCs being processed. The <tt>doInitialization</tt> method call is not
581scheduled to overlap with any other pass executions (thus it should be very
582fast).</p>
583
584</div>
585
586<!-- _______________________________________________________________________ -->
587<div class="doc_subsubsection">
588 <a name="runOnSCC">The <tt>runOnSCC</tt> method</a>
589</div>
590
591<div class="doc_text">
592
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]593<div class="doc_code"><pre>
Chris Lattner8fdb2462004-09-18 06:39:35 +0000[diff] [blame]594 <b>virtual bool</b> runOnSCC(const std::vector&lt;CallGraphNode *&gt; &amp;SCCM) = 0;
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]595</pre></div>
Chris Lattner8fdb2462004-09-18 06:39:35 +0000[diff] [blame]596
597<p>The <tt>runOnSCC</tt> method performs the interesting work of the pass, and
598should return true if the module was modified by the transformation, false
599otherwise.</p>
600
601</div>
602
603<!-- _______________________________________________________________________ -->
604<div class="doc_subsubsection">
Devang Patelc20048d2007-01-23 22:56:28 +0000[diff] [blame]605 <a name="doFinalization_scc">The <tt>doFinalization(CallGraph
Chris Lattner8fdb2462004-09-18 06:39:35 +0000[diff] [blame]606 &amp;)</tt> method</a>
607</div>
608
609<div class="doc_text">
610
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]611<div class="doc_code"><pre>
Devang Patelc20048d2007-01-23 22:56:28 +0000[diff] [blame]612 <b>virtual bool</b> doFinalization(CallGraph &amp;CG);
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]613</pre></div>
Chris Lattner8fdb2462004-09-18 06:39:35 +0000[diff] [blame]614
615<p>The <tt>doFinalization</tt> method is an infrequently used method that is
616called when the pass framework has finished calling <a
617href="#runOnFunction"><tt>runOnFunction</tt></a> for every function in the
618program being compiled.</p>
619
620</div>
621
622<!-- ======================================================================= -->
623<div class="doc_subsection">
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]624 <a name="FunctionPass">The <tt>FunctionPass</tt> class</a>
625</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]626
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]627<div class="doc_text">
628
Chris Lattnerf6278922004-09-20 04:36:29 +0000[diff] [blame]629<p>In contrast to <tt>ModulePass</tt> subclasses, <tt><a
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]630href="http://llvm.org/doxygen/classllvm_1_1Pass.html">FunctionPass</a></tt>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]631subclasses do have a predictable, local behavior that can be expected by the
632system. All <tt>FunctionPass</tt> execute on each function in the program
Misha Brukmanef6a6a62003-08-21 22:14:26 +0000[diff] [blame]633independent of all of the other functions in the program.
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]634<tt>FunctionPass</tt>'s do not require that they are executed in a particular
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]635order, and <tt>FunctionPass</tt>'s do not modify external functions.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]636
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]637<p>To be explicit, <tt>FunctionPass</tt> subclasses are not allowed to:</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]638
639<ol>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]640<li>Modify a Function other than the one currently being processed.</li>
641<li>Add or remove Function's from the current Module.</li>
642<li>Add or remove global variables from the current Module.</li>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]643<li>Maintain state across invocations of
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]644 <a href="#runOnFunction"><tt>runOnFunction</tt></a> (including global data)</li>
645</ol>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]646
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]647<p>Implementing a <tt>FunctionPass</tt> is usually straightforward (See the <a
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]648href="#basiccode">Hello World</a> pass for example). <tt>FunctionPass</tt>'s
649may overload three virtual methods to do their work. All of these methods
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]650should return true if they modified the program, or false if they didn't.</p>
651
652</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]653
654<!-- _______________________________________________________________________ -->
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]655<div class="doc_subsubsection">
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]656 <a name="doInitialization_mod">The <tt>doInitialization(Module &amp;)</tt>
657 method</a>
658</div>
659
660<div class="doc_text">
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]661
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]662<div class="doc_code"><pre>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]663 <b>virtual bool</b> doInitialization(Module &amp;M);
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]664</pre></div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]665
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]666<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]667<tt>FunctionPass</tt>'s are not allowed to do. They can add and remove
Chris Lattnerd0713f92002-09-12 17:06:43 +0000[diff] [blame]668functions, get pointers to functions, etc. The <tt>doInitialization</tt> method
669is designed to do simple initialization type of stuff that does not depend on
670the functions being processed. The <tt>doInitialization</tt> method call is not
671scheduled to overlap with any other pass executions (thus it should be very
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]672fast).</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]673
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]674<p>A good example of how this method should be used is the <a
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]675href="http://llvm.org/doxygen/LowerAllocations_8cpp-source.html">LowerAllocations</a>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]676pass. This pass converts <tt>malloc</tt> and <tt>free</tt> instructions into
Misha Brukmanef6a6a62003-08-21 22:14:26 +0000[diff] [blame]677platform dependent <tt>malloc()</tt> and <tt>free()</tt> function calls. It
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]678uses the <tt>doInitialization</tt> method to get a reference to the malloc and
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]679free functions that it needs, adding prototypes to the module if necessary.</p>
680
681</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]682
683<!-- _______________________________________________________________________ -->
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]684<div class="doc_subsubsection">
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]685 <a name="runOnFunction">The <tt>runOnFunction</tt> method</a>
686</div>
687
688<div class="doc_text">
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]689
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]690<div class="doc_code"><pre>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]691 <b>virtual bool</b> runOnFunction(Function &amp;F) = 0;
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]692</pre></div><p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]693
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]694<p>The <tt>runOnFunction</tt> method must be implemented by your subclass to do
695the transformation or analysis work of your pass. As usual, a true value should
696be returned if the function is modified.</p>
697
698</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]699
700<!-- _______________________________________________________________________ -->
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]701<div class="doc_subsubsection">
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]702 <a name="doFinalization_mod">The <tt>doFinalization(Module
703 &amp;)</tt> method</a>
704</div>
705
706<div class="doc_text">
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]707
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]708<div class="doc_code"><pre>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]709 <b>virtual bool</b> doFinalization(Module &amp;M);
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]710</pre></div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]711
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]712<p>The <tt>doFinalization</tt> method is an infrequently used method that is
713called when the pass framework has finished calling <a
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]714href="#runOnFunction"><tt>runOnFunction</tt></a> for every function in the
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]715program being compiled.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]716
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]717</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]718
719<!-- ======================================================================= -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]720<div class="doc_subsection">
Devang Patel2e8f27d2007-03-19 22:21:25 +0000[diff] [blame]721 <a name="LoopPass">The <tt>LoopPass</tt> class </a>
722</div>
723
724<div class="doc_text">
725
726<p> All <tt>LoopPass</tt> execute on each loop in the function independent of
727all of the other loops in the function. <tt>LoopPass</tt> processes loops in
728loop nest order such that outer most loop is processed last. </p>
729
730<p> <tt>LoopPass</tt> subclasses are allowed to update loop nest using
731<tt>LPPassManager</tt> interface. Implementing a loop pass is usually
732straightforward. <tt>Looppass</tt>'s may overload three virtual methods to
733do their work. All these methods should return true if they modified the
734program, or false if they didn't. </p>
735</div>
736
737<!-- _______________________________________________________________________ -->
738<div class="doc_subsubsection">
739 <a name="doInitialization_loop">The <tt>doInitialization(Loop *,
740 LPPassManager &amp;)</tt>
741 method</a>
742</div>
743
744<div class="doc_text">
745
746<div class="doc_code"><pre>
747 <b>virtual bool</b> doInitialization(Loop *, LPPassManager &amp;LPM);
748</pre></div>
749
Chris Lattnerb5c87f62007-05-18 05:36:14 +0000[diff] [blame]750<p>The <tt>doInitialization</tt> method is designed to do simple initialization
Devang Patel2e8f27d2007-03-19 22:21:25 +0000[diff] [blame]751type of stuff that does not depend on the functions being processed. The
752<tt>doInitialization</tt> method call is not scheduled to overlap with any
753other pass executions (thus it should be very fast). LPPassManager
754interface should be used to access Function or Module level analysis
755information.</p>
756
757</div>
758
759
760<!-- _______________________________________________________________________ -->
761<div class="doc_subsubsection">
762 <a name="runOnLoop">The <tt>runOnLoop</tt> method</a>
763</div>
764
765<div class="doc_text">
766
767<div class="doc_code"><pre>
768 <b>virtual bool</b> runOnLoop(Loop *, LPPassManager &amp;LPM) = 0;
769</pre></div><p>
770
771<p>The <tt>runOnLoop</tt> method must be implemented by your subclass to do
772the transformation or analysis work of your pass. As usual, a true value should
773be returned if the function is modified. <tt>LPPassManager</tt> interface
774should be used to update loop nest.</p>
775
776</div>
777
778<!-- _______________________________________________________________________ -->
779<div class="doc_subsubsection">
780 <a name="doFinalization_loop">The <tt>doFinalization()</tt> method</a>
781</div>
782
783<div class="doc_text">
784
785<div class="doc_code"><pre>
786 <b>virtual bool</b> doFinalization();
787</pre></div>
788
789<p>The <tt>doFinalization</tt> method is an infrequently used method that is
790called when the pass framework has finished calling <a
791href="#runOnLoop"><tt>runOnLoop</tt></a> for every loop in the
792program being compiled. </p>
793
794</div>
795
796
797
798<!-- ======================================================================= -->
799<div class="doc_subsection">
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]800 <a name="BasicBlockPass">The <tt>BasicBlockPass</tt> class</a>
801</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]802
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]803<div class="doc_text">
804
805<p><tt>BasicBlockPass</tt>'s are just like <a
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]806href="#FunctionPass"><tt>FunctionPass</tt></a>'s, except that they must limit
807their scope of inspection and modification to a single basic block at a time.
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]808As such, they are <b>not</b> allowed to do any of the following:</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]809
810<ol>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]811<li>Modify or inspect any basic blocks outside of the current one</li>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]812<li>Maintain state across invocations of
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]813 <a href="#runOnBasicBlock"><tt>runOnBasicBlock</tt></a></li>
Reid Spencer1bc19342004-12-11 05:12:57 +0000[diff] [blame]814<li>Modify the control flow graph (by altering terminator instructions)</li>
815<li>Any of the things forbidden for
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]816 <a href="#FunctionPass"><tt>FunctionPass</tt></a>es.</li>
817</ol>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]818
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]819<p><tt>BasicBlockPass</tt>es are useful for traditional local and "peephole"
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]820optimizations. They may override the same <a
Chris Lattnerd0713f92002-09-12 17:06:43 +0000[diff] [blame]821href="#doInitialization_mod"><tt>doInitialization(Module &amp;)</tt></a> and <a
822href="#doFinalization_mod"><tt>doFinalization(Module &amp;)</tt></a> methods that <a
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]823href="#FunctionPass"><tt>FunctionPass</tt></a>'s have, but also have the following virtual methods that may also be implemented:</p>
824
825</div>
Chris Lattnerd0713f92002-09-12 17:06:43 +0000[diff] [blame]826
827<!-- _______________________________________________________________________ -->
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]828<div class="doc_subsubsection">
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]829 <a name="doInitialization_fn">The <tt>doInitialization(Function
830 &amp;)</tt> method</a>
831</div>
832
833<div class="doc_text">
Chris Lattnerd0713f92002-09-12 17:06:43 +0000[diff] [blame]834
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]835<div class="doc_code"><pre>
Chris Lattnerd0713f92002-09-12 17:06:43 +0000[diff] [blame]836 <b>virtual bool</b> doInitialization(Function &amp;F);
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]837</pre></div>
Chris Lattnerd0713f92002-09-12 17:06:43 +0000[diff] [blame]838
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]839<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]840<tt>BasicBlockPass</tt>'s are not allowed to do, but that
841<tt>FunctionPass</tt>'s can. The <tt>doInitialization</tt> method is designed
Reid Spencer1bc19342004-12-11 05:12:57 +0000[diff] [blame]842to do simple initialization that does not depend on the
Chris Lattnerd0713f92002-09-12 17:06:43 +0000[diff] [blame]843BasicBlocks being processed. The <tt>doInitialization</tt> method call is not
844scheduled to overlap with any other pass executions (thus it should be very
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]845fast).</p>
Chris Lattnerd0713f92002-09-12 17:06:43 +0000[diff] [blame]846
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]847</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]848
849<!-- _______________________________________________________________________ -->
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]850<div class="doc_subsubsection">
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]851 <a name="runOnBasicBlock">The <tt>runOnBasicBlock</tt> method</a>
852</div>
853
854<div class="doc_text">
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]855
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]856<div class="doc_code"><pre>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]857 <b>virtual bool</b> runOnBasicBlock(BasicBlock &amp;BB) = 0;
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]858</pre></div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]859
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]860<p>Override this function to do the work of the <tt>BasicBlockPass</tt>. This
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]861function is not allowed to inspect or modify basic blocks other than the
862parameter, and are not allowed to modify the CFG. A true value must be returned
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]863if the basic block is modified.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]864
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]865</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]866
Chris Lattnerd0713f92002-09-12 17:06:43 +0000[diff] [blame]867<!-- _______________________________________________________________________ -->
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]868<div class="doc_subsubsection">
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]869 <a name="doFinalization_fn">The <tt>doFinalization(Function &amp;)</tt>
870 method</a>
871</div>
872
873<div class="doc_text">
Chris Lattnerd0713f92002-09-12 17:06:43 +0000[diff] [blame]874
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]875<div class="doc_code"><pre>
Chris Lattnerd0713f92002-09-12 17:06:43 +0000[diff] [blame]876 <b>virtual bool</b> doFinalization(Function &amp;F);
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]877</pre></div>
Chris Lattnerd0713f92002-09-12 17:06:43 +0000[diff] [blame]878
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]879<p>The <tt>doFinalization</tt> method is an infrequently used method that is
880called when the pass framework has finished calling <a
Chris Lattnerd0713f92002-09-12 17:06:43 +0000[diff] [blame]881href="#runOnBasicBlock"><tt>runOnBasicBlock</tt></a> for every BasicBlock in the
882program being compiled. This can be used to perform per-function
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]883finalization.</p>
Chris Lattnerd0713f92002-09-12 17:06:43 +0000[diff] [blame]884
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]885</div>
Chris Lattnerd0713f92002-09-12 17:06:43 +0000[diff] [blame]886
Brian Gaekecab8b6f2003-07-17 18:53:20 +0000[diff] [blame]887<!-- ======================================================================= -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]888<div class="doc_subsection">
889 <a name="MachineFunctionPass">The <tt>MachineFunctionPass</tt> class</a>
890</div>
Brian Gaekecab8b6f2003-07-17 18:53:20 +0000[diff] [blame]891
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]892<div class="doc_text">
893
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]894<p>A <tt>MachineFunctionPass</tt> is a part of the LLVM code generator that
895executes on the machine-dependent representation of each LLVM function in the
896program. A <tt>MachineFunctionPass</tt> is also a <tt>FunctionPass</tt>, so all
Brian Gaekecab8b6f2003-07-17 18:53:20 +0000[diff] [blame]897the restrictions that apply to a <tt>FunctionPass</tt> also apply to it.
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]898<tt>MachineFunctionPass</tt>es also have additional restrictions. In particular,
899<tt>MachineFunctionPass</tt>es are not allowed to do any of the following:</p>
Brian Gaekecab8b6f2003-07-17 18:53:20 +0000[diff] [blame]900
901<ol>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]902<li>Modify any LLVM Instructions, BasicBlocks or Functions.</li>
903<li>Modify a MachineFunction other than the one currently being processed.</li>
904<li>Add or remove MachineFunctions from the current Module.</li>
905<li>Add or remove global variables from the current Module.</li>
906<li>Maintain state across invocations of <a
907href="#runOnMachineFunction"><tt>runOnMachineFunction</tt></a> (including global
908data)</li>
909</ol>
Brian Gaekecab8b6f2003-07-17 18:53:20 +0000[diff] [blame]910
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]911</div>
Chris Lattnerd0713f92002-09-12 17:06:43 +0000[diff] [blame]912
Brian Gaeke6a33f362003-07-22 20:53:20 +0000[diff] [blame]913<!-- _______________________________________________________________________ -->
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]914<div class="doc_subsubsection">
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]915 <a name="runOnMachineFunction">The <tt>runOnMachineFunction(MachineFunction
916 &amp;MF)</tt> method</a>
917</div>
918
919<div class="doc_text">
Brian Gaeke6a33f362003-07-22 20:53:20 +0000[diff] [blame]920
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]921<div class="doc_code"><pre>
Brian Gaeke6a33f362003-07-22 20:53:20 +0000[diff] [blame]922 <b>virtual bool</b> runOnMachineFunction(MachineFunction &amp;MF) = 0;
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]923</pre></div>
Brian Gaeke6a33f362003-07-22 20:53:20 +0000[diff] [blame]924
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]925<p><tt>runOnMachineFunction</tt> can be considered the main entry point of a
926<tt>MachineFunctionPass</tt>; that is, you should override this method to do the
927work of your <tt>MachineFunctionPass</tt>.</p>
Brian Gaeke6a33f362003-07-22 20:53:20 +0000[diff] [blame]928
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]929<p>The <tt>runOnMachineFunction</tt> method is called on every
Brian Gaeke6a33f362003-07-22 20:53:20 +0000[diff] [blame]930<tt>MachineFunction</tt> in a <tt>Module</tt>, so that the
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]931<tt>MachineFunctionPass</tt> may perform optimizations on the machine-dependent
932representation of the function. If you want to get at the LLVM <tt>Function</tt>
933for the <tt>MachineFunction</tt> you're working on, use
934<tt>MachineFunction</tt>'s <tt>getFunction()</tt> accessor method -- but
935remember, you may not modify the LLVM <tt>Function</tt> or its contents from a
936<tt>MachineFunctionPass</tt>.</p>
937
938</div>
Brian Gaeke6a33f362003-07-22 20:53:20 +0000[diff] [blame]939
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]940<!-- *********************************************************************** -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]941<div class="doc_section">
942 <a name="registration">Pass registration</a>
943</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]944<!-- *********************************************************************** -->
945
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]946<div class="doc_text">
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]947
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]948<p>In the <a href="#basiccode">Hello World</a> example pass we illustrated how
949pass registration works, and discussed some of the reasons that it is used and
950what it does. Here we discuss how and why passes are registered.</p>
951
Chris Lattnerc8603c22006-08-27 23:18:52 +0000[diff] [blame]952<p>As we saw above, passes are registered with the <b><tt>RegisterPass</tt></b>
953template, which requires you to pass at least two
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]954parameters. The first parameter is the name of the pass that is to be used on
955the command line to specify that the pass should be added to a program (for
Chris Lattnerc8603c22006-08-27 23:18:52 +0000[diff] [blame]956example, with <tt>opt</tt> or <tt>bugpoint</tt>). The second argument is the
957name of the pass, which is to be used for the <tt>--help</tt> output of
958programs, as
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]959well as for debug output generated by the <tt>--debug-pass</tt> option.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]960
Chris Lattnerc8603c22006-08-27 23:18:52 +0000[diff] [blame]961<p>If you want your pass to be easily dumpable, you should
962implement the virtual <tt>print</tt> method:</p>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]963
964</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]965
966<!-- _______________________________________________________________________ -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]967<div class="doc_subsubsection">
968 <a name="print">The <tt>print</tt> method</a>
969</div>
970
971<div class="doc_text">
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]972
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]973<div class="doc_code"><pre>
Bill Wendling832171c2006-12-07 20:04:42 +0000[diff] [blame]974 <b>virtual void</b> print(llvm::OStream &amp;O, <b>const</b> Module *M) <b>const</b>;
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]975</pre></div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]976
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]977<p>The <tt>print</tt> method must be implemented by "analyses" in order to print
978a human readable version of the analysis results. This is useful for debugging
979an analysis itself, as well as for other people to figure out how an analysis
Chris Lattnerc8603c22006-08-27 23:18:52 +0000[diff] [blame]980works. Use the <tt>opt -analyze</tt> argument to invoke this method.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]981
Bill Wendling832171c2006-12-07 20:04:42 +0000[diff] [blame]982<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]983and 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]984program that has been analyzed. Note however that this pointer may be null in
985certain circumstances (such as calling the <tt>Pass::dump()</tt> from a
986debugger), so it should only be used to enhance debug output, it should not be
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]987depended on.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]988
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]989</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]990
991<!-- *********************************************************************** -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]992<div class="doc_section">
993 <a name="interaction">Specifying interactions between passes</a>
994</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]995<!-- *********************************************************************** -->
996
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]997<div class="doc_text">
998
John Criswell8528e782007-12-03 19:34:25 +0000[diff] [blame^]999<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]1000that passes interact with each other correctly. Because <tt>PassManager</tt>
1001tries to <a href="#passmanager">optimize the execution of passes</a> it must
1002know how the passes interact with each other and what dependencies exist between
1003the various passes. To track this, each pass can declare the set of passes that
1004are required to be executed before the current pass, and the passes which are
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1005invalidated by the current pass.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1006
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1007<p>Typically this functionality is used to require that analysis results are
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1008computed before your pass is run. Running arbitrary transformation passes can
1009invalidate the computed analysis results, which is what the invalidation set
1010specifies. If a pass does not implement the <tt><a
1011href="#getAnalysisUsage">getAnalysisUsage</a></tt> method, it defaults to not
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1012having any prerequisite passes, and invalidating <b>all</b> other passes.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1013
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1014</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1015
1016<!-- _______________________________________________________________________ -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1017<div class="doc_subsubsection">
1018 <a name="getAnalysisUsage">The <tt>getAnalysisUsage</tt> method</a>
1019</div>
1020
1021<div class="doc_text">
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1022
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1023<div class="doc_code"><pre>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1024 <b>virtual void</b> getAnalysisUsage(AnalysisUsage &amp;Info) <b>const</b>;
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1025</pre></div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1026
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1027<p>By implementing the <tt>getAnalysisUsage</tt> method, the required and
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1028invalidated sets may be specified for your transformation. The implementation
1029should fill in the <tt><a
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]1030href="http://llvm.org/doxygen/classllvm_1_1AnalysisUsage.html">AnalysisUsage</a></tt>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1031object with information about which passes are required and not invalidated. To
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]1032do this, a pass may call any of the following methods on the AnalysisUsage
1033object:</p>
1034</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1035
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]1036<!-- _______________________________________________________________________ -->
1037<div class="doc_subsubsection">
1038 <a name="AU::addRequired">The <tt>AnalysisUsage::addRequired&lt;&gt;</tt> and <tt>AnalysisUsage::addRequiredTransitive&lt;&gt;</tt> methods</a>
1039</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1040
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]1041<div class="doc_text">
1042<p>
Reid Spencer1bc19342004-12-11 05:12:57 +0000[diff] [blame]1043If your pass requires a previous pass to be executed (an analysis for example),
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]1044it can use one of these methods to arrange for it to be run before your pass.
1045LLVM has many different types of analyses and passes that can be required,
Reid Spencer1bc19342004-12-11 05:12:57 +0000[diff] [blame]1046spanning the range from <tt>DominatorSet</tt> to <tt>BreakCriticalEdges</tt>.
1047Requiring <tt>BreakCriticalEdges</tt>, for example, guarantees that there will
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]1048be no critical edges in the CFG when your pass has been run.
1049</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1050
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]1051<p>
1052Some analyses chain to other analyses to do their job. For example, an <a
1053href="AliasAnalysis.html">AliasAnalysis</a> implementation is required to <a
1054href="AliasAnalysis.html#chaining">chain</a> to other alias analysis passes. In
1055cases where analyses chain, the <tt>addRequiredTransitive</tt> method should be
1056used instead of the <tt>addRequired</tt> method. This informs the PassManager
1057that the transitively required pass should be alive as long as the requiring
1058pass is.
1059</p>
1060</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1061
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]1062<!-- _______________________________________________________________________ -->
1063<div class="doc_subsubsection">
1064 <a name="AU::addPreserved">The <tt>AnalysisUsage::addPreserved&lt;&gt;</tt> method</a>
1065</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1066
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]1067<div class="doc_text">
1068<p>
1069One of the jobs of the PassManager is to optimize how and when analyses are run.
1070In particular, it attempts to avoid recomputing data unless it needs to. For
1071this reason, passes are allowed to declare that they preserve (i.e., they don't
1072invalidate) an existing analysis if it's available. For example, a simple
Reid Spencer1bc19342004-12-11 05:12:57 +0000[diff] [blame]1073constant folding pass would not modify the CFG, so it can't possibly affect the
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]1074results of dominator analysis. By default, all passes are assumed to invalidate
1075all others.
1076</p>
1077
1078<p>
1079The <tt>AnalysisUsage</tt> class provides several methods which are useful in
1080certain circumstances that are related to <tt>addPreserved</tt>. In particular,
1081the <tt>setPreservesAll</tt> method can be called to indicate that the pass does
1082not modify the LLVM program at all (which is true for analyses), and the
1083<tt>setPreservesCFG</tt> method can be used by transformations that change
1084instructions in the program but do not modify the CFG or terminator instructions
1085(note that this property is implicitly set for <a
1086href="#BasicBlockPass">BasicBlockPass</a>'s).
1087</p>
1088
1089<p>
1090<tt>addPreserved</tt> is particularly useful for transformations like
1091<tt>BreakCriticalEdges</tt>. This pass knows how to update a small set of loop
1092and dominator related analyses if they exist, so it can preserve them, despite
1093the fact that it hacks on the CFG.
1094</p>
1095</div>
1096
1097<!-- _______________________________________________________________________ -->
1098<div class="doc_subsubsection">
1099 <a name="AU::examples">Example implementations of <tt>getAnalysisUsage</tt></a>
1100</div>
1101
1102<div class="doc_text">
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1103
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1104<div class="doc_code"><pre>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1105 <i>// This is an example implementation from an analysis, which does not modify
1106 // the program at all, yet has a prerequisite.</i>
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]1107 <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]1108 AU.setPreservesAll();
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]1109 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]1110 }
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1111</pre></div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1112
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1113<p>and:</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1114
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1115<div class="doc_code"><pre>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1116 <i>// This example modifies the program, but does not modify the CFG</i>
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]1117 <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]1118 AU.setPreservesCFG();
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]1119 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]1120 }
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1121</pre></div>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1122
1123</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1124
1125<!-- _______________________________________________________________________ -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1126<div class="doc_subsubsection">
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]1127 <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]1128</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1129
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1130<div class="doc_text">
1131
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]1132<p>The <tt>Pass::getAnalysis&lt;&gt;</tt> method is automatically inherited by
1133your class, providing you with access to the passes that you declared that you
1134required with the <a href="#getAnalysisUsage"><tt>getAnalysisUsage</tt></a>
1135method. It takes a single template argument that specifies which pass class you
1136want, and returns a reference to that pass. For example:</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1137
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1138<div class="doc_code"><pre>
Chris Lattnera5776302004-03-17 21:33:32 +0000[diff] [blame]1139 bool LICM::runOnFunction(Function &amp;F) {
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]1140 LoopInfo &amp;LI = getAnalysis&lt;LoopInfo&gt;();
1141 ...
1142 }
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1143</pre></div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1144
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1145<p>This method call returns a reference to the pass desired. You may get a
1146runtime assertion failure if you attempt to get an analysis that you did not
1147declare as required in your <a
1148href="#getAnalysisUsage"><tt>getAnalysisUsage</tt></a> implementation. This
1149method can be called by your <tt>run*</tt> method implementation, or by any
Devang Patel3c1ca0b2007-04-16 21:28:14 +0000[diff] [blame]1150other local method invoked by your <tt>run*</tt> method.
1151
1152A module level pass can use function level analysis info using this interface.
1153For example:</p>
1154
1155<div class="doc_code"><pre>
1156 bool ModuleLevelPass::runOnModule(Module &amp;M) {
1157 ...
Devang Patelf23de112007-04-17 00:17:11 +0000[diff] [blame]1158 DominatorTree &amp;DT = getAnalysis&lt;DominatorTree&gt;(Func);
Devang Patel3c1ca0b2007-04-16 21:28:14 +0000[diff] [blame]1159 ...
1160 }
1161</pre></div>
1162
Chris Lattnerb5c87f62007-05-18 05:36:14 +0000[diff] [blame]1163<p>In above example, runOnFunction for DominatorTree is called by pass manager
Devang Patel3c1ca0b2007-04-16 21:28:14 +0000[diff] [blame]1164before returning a reference to the desired pass.</p>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1165
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]1166<p>
1167If your pass is capable of updating analyses if they exist (e.g.,
1168<tt>BreakCriticalEdges</tt>, as described above), you can use the
1169<tt>getAnalysisToUpdate</tt> method, which returns a pointer to the analysis if
1170it is active. For example:</p>
1171
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1172<div class="doc_code"><pre>
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]1173 ...
1174 if (DominatorSet *DS = getAnalysisToUpdate&lt;DominatorSet&gt;()) {
1175 <i>// A DominatorSet is active. This code will update it.</i>
1176 }
1177 ...
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1178</pre></div>
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]1179
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1180</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1181
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1182<!-- *********************************************************************** -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1183<div class="doc_section">
1184 <a name="analysisgroup">Implementing Analysis Groups</a>
1185</div>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1186<!-- *********************************************************************** -->
1187
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1188<div class="doc_text">
1189
Chris Lattnerb7632282007-11-16 05:32:05 +0000[diff] [blame]1190<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]1191used, 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]1192fancier. All of the pass relationships that we have seen so far are very
1193simple: one pass depends on one other specific pass to be run before it can run.
1194For many applications, this is great, for others, more flexibility is
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1195required.</p>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1196
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1197<p>In particular, some analyses are defined such that there is a single simple
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1198interface to the analysis results, but multiple ways of calculating them.
1199Consider alias analysis for example. The most trivial alias analysis returns
1200"may alias" for any alias query. The most sophisticated analysis a
1201flow-sensitive, context-sensitive interprocedural analysis that can take a
1202significant amount of time to execute (and obviously, there is a lot of room
1203between these two extremes for other implementations). To cleanly support
1204situations like this, the LLVM Pass Infrastructure supports the notion of
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1205Analysis Groups.</p>
1206
1207</div>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1208
1209<!-- _______________________________________________________________________ -->
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]1210<div class="doc_subsubsection">
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1211 <a name="agconcepts">Analysis Group Concepts</a>
1212</div>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1213
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1214<div class="doc_text">
1215
1216<p>An Analysis Group is a single simple interface that may be implemented by
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1217multiple different passes. Analysis Groups can be given human readable names
1218just like passes, but unlike passes, they need not derive from the <tt>Pass</tt>
1219class. An analysis group may have one or more implementations, one of which is
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1220the "default" implementation.</p>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1221
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1222<p>Analysis groups are used by client passes just like other passes are: the
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1223<tt>AnalysisUsage::addRequired()</tt> and <tt>Pass::getAnalysis()</tt> methods.
1224In order to resolve this requirement, the <a href="#passmanager">PassManager</a>
1225scans the available passes to see if any implementations of the analysis group
1226are available. If none is available, the default implementation is created for
1227the pass to use. All standard rules for <A href="#interaction">interaction
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1228between passes</a> still apply.</p>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1229
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1230<p>Although <a href="#registration">Pass Registration</a> is optional for normal
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1231passes, all analysis group implementations must be registered, and must use the
1232<A href="#registerag"><tt>RegisterAnalysisGroup</tt></a> template to join the
1233implementation pool. Also, a default implementation of the interface
1234<b>must</b> be registered with <A
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1235href="#registerag"><tt>RegisterAnalysisGroup</tt></a>.</p>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1236
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1237<p>As a concrete example of an Analysis Group in action, consider the <a
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]1238href="http://llvm.org/doxygen/classllvm_1_1AliasAnalysis.html">AliasAnalysis</a>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1239analysis group. The default implementation of the alias analysis interface (the
1240<tt><a
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]1241href="http://llvm.org/doxygen/structBasicAliasAnalysis.html">basicaa</a></tt>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1242pass) just does a few simple checks that don't require significant analysis to
1243compute (such as: two different globals can never alias each other, etc).
1244Passes that use the <tt><a
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]1245href="http://llvm.org/doxygen/classllvm_1_1AliasAnalysis.html">AliasAnalysis</a></tt>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1246interface (for example the <tt><a
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]1247href="http://llvm.org/doxygen/structGCSE.html">gcse</a></tt> pass), do
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1248not care which implementation of alias analysis is actually provided, they just
1249use the designated interface.</p>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1250
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1251<p>From the user's perspective, commands work just like normal. Issuing the
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1252command '<tt>opt -gcse ...</tt>' will cause the <tt>basicaa</tt> class to be
1253instantiated and added to the pass sequence. Issuing the command '<tt>opt
1254-somefancyaa -gcse ...</tt>' will cause the <tt>gcse</tt> pass to use the
1255<tt>somefancyaa</tt> alias analysis (which doesn't actually exist, it's just a
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1256hypothetical example) instead.</p>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1257
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1258</div>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1259
1260<!-- _______________________________________________________________________ -->
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]1261<div class="doc_subsubsection">
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1262 <a name="registerag">Using <tt>RegisterAnalysisGroup</tt></a>
1263</div>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1264
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1265<div class="doc_text">
1266
1267<p>The <tt>RegisterAnalysisGroup</tt> template is used to register the analysis
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1268group itself as well as add pass implementations to the analysis group. First,
1269an analysis should be registered, with a human readable name provided for it.
1270Unlike registration of passes, there is no command line argument to be specified
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1271for the Analysis Group Interface itself, because it is "abstract":</p>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1272
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1273<div class="doc_code"><pre>
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]1274 <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]1275</pre></div>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1276
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1277<p>Once the analysis is registered, passes can declare that they are valid
1278implementations of the interface by using the following code:</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>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1281<b>namespace</b> {
1282 //<i> Analysis Group implementations <b>must</b> be registered normally...</i>
Chris Lattnerc8603c22006-08-27 23:18:52 +0000[diff] [blame]1283 RegisterPass&lt;FancyAA&gt;
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1284 B("<i>somefancyaa</i>", "<i>A more complex alias analysis implementation</i>");
1285
1286 //<i> Declare that we implement the AliasAnalysis interface</i>
Chris Lattnerdc877252006-08-28 00:45:38 +0000[diff] [blame]1287 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]1288}
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1289</pre></div>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1290
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1291<p>This just shows a class <tt>FancyAA</tt> that is registered normally, then
1292uses the <tt>RegisterAnalysisGroup</tt> template to "join" the <tt><a
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]1293href="http://llvm.org/doxygen/classllvm_1_1AliasAnalysis.html">AliasAnalysis</a></tt>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1294analysis group. Every implementation of an analysis group should join using
1295this template. A single pass may join multiple different analysis groups with
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1296no problem.</p>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1297
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1298<div class="doc_code"><pre>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1299<b>namespace</b> {
1300 //<i> Analysis Group implementations <b>must</b> be registered normally...</i>
Chris Lattnerc8603c22006-08-27 23:18:52 +0000[diff] [blame]1301 RegisterPass&lt;<a href="http://llvm.org/doxygen/structBasicAliasAnalysis.html">BasicAliasAnalysis</a>&gt;
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1302 D("<i>basicaa</i>", "<i>Basic Alias Analysis (default AA impl)</i>");
1303
1304 //<i> Declare that we implement the AliasAnalysis interface</i>
Chris Lattnerdc877252006-08-28 00:45:38 +0000[diff] [blame]1305 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]1306}
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1307</pre></div>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1308
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1309<p>Here we show how the default implementation is specified (using the extra
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1310argument to the <tt>RegisterAnalysisGroup</tt> template). There must be exactly
1311one default implementation available at all times for an Analysis Group to be
Devang Patel2397f8d2007-06-20 18:51:14 +0000[diff] [blame]1312used. Only default implementation can derive from <tt>ImmutablePass</tt>.
1313Here we declare that the
1314 <tt><a href="http://llvm.org/doxygen/structBasicAliasAnalysis.html">BasicAliasAnalysis</a></tt>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1315pass is the default implementation for the interface.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1316
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1317</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1318
1319<!-- *********************************************************************** -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1320<div class="doc_section">
Tanya Lattnerd5383652004-11-19 01:25:14 +0000[diff] [blame]1321 <a name="passStatistics">Pass Statistics</a>
1322</div>
1323<!-- *********************************************************************** -->
1324
1325<div class="doc_text">
Tanya Lattner05f8d5f2004-11-19 01:26:37 +0000[diff] [blame]1326<p>The <a
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]1327href="http://llvm.org/doxygen/Statistic_8h-source.html"><tt>Statistic</tt></a>
John Criswell0b1010e2005-11-28 23:25:41 +0000[diff] [blame]1328class is designed to be an easy way to expose various success
Tanya Lattnerd5383652004-11-19 01:25:14 +0000[diff] [blame]1329metrics from passes. These statistics are printed at the end of a
1330run, when the -stats command line option is enabled on the command
Tanya Lattner05f8d5f2004-11-19 01:26:37 +0000[diff] [blame]1331line. 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]1332
1333</div>
1334
1335
1336<!-- *********************************************************************** -->
1337<div class="doc_section">
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1338 <a name="passmanager">What PassManager does</a>
1339</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1340<!-- *********************************************************************** -->
1341
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1342<div class="doc_text">
1343
1344<p>The <a
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]1345href="http://llvm.org/doxygen/PassManager_8h-source.html"><tt>PassManager</tt></a>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1346<a
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]1347href="http://llvm.org/doxygen/classllvm_1_1PassManager.html">class</a>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1348takes a list of passes, ensures their <a href="#interaction">prerequisites</a>
1349are set up correctly, and then schedules passes to run efficiently. All of the
1350LLVM tools that run passes use the <tt>PassManager</tt> for execution of these
1351passes.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1352
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1353<p>The <tt>PassManager</tt> does two main things to try to reduce the execution
1354time of a series of passes:</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1355
1356<ol>
1357<li><b>Share analysis results</b> - The PassManager attempts to avoid
1358recomputing analysis results as much as possible. This means keeping track of
1359which analyses are available already, which analyses get invalidated, and which
1360analyses are needed to be run for a pass. An important part of work is that the
1361<tt>PassManager</tt> tracks the exact lifetime of all analysis results, allowing
1362it to <a href="#releaseMemory">free memory</a> allocated to holding analysis
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1363results as soon as they are no longer needed.</li>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1364
1365<li><b>Pipeline the execution of passes on the program</b> - The
1366<tt>PassManager</tt> attempts to get better cache and memory usage behavior out
1367of a series of passes by pipelining the passes together. This means that, given
1368a series of consequtive <a href="#FunctionPass"><tt>FunctionPass</tt></a>'s, it
1369will execute all of the <a href="#FunctionPass"><tt>FunctionPass</tt></a>'s on
1370the first function, then all of the <a
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1371href="#FunctionPass"><tt>FunctionPass</tt></a>es on the second function,
1372etc... until the entire program has been run through the passes.
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1373
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1374<p>This improves the cache behavior of the compiler, because it is only touching
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1375the LLVM program representation for a single function at a time, instead of
1376traversing the entire program. It reduces the memory consumption of compiler,
1377because, for example, only one <a
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]1378href="http://llvm.org/doxygen/classllvm_1_1DominatorSet.html"><tt>DominatorSet</tt></a>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1379needs to be calculated at a time. This also makes it possible some <a
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1380href="#SMP">interesting enhancements</a> in the future.</p></li>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1381
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1382</ol>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1383
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1384<p>The effectiveness of the <tt>PassManager</tt> is influenced directly by how
1385much information it has about the behaviors of the passes it is scheduling. For
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1386example, the "preserved" set is intentionally conservative in the face of an
1387unimplemented <a href="#getAnalysisUsage"><tt>getAnalysisUsage</tt></a> method.
1388Not implementing when it should be implemented will have the effect of not
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1389allowing any analysis results to live across the execution of your pass.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1390
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1391<p>The <tt>PassManager</tt> class exposes a <tt>--debug-pass</tt> command line
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1392options that is useful for debugging pass execution, seeing how things work, and
1393diagnosing when you should be preserving more analyses than you currently are
1394(To get information about all of the variants of the <tt>--debug-pass</tt>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1395option, just type '<tt>opt --help-hidden</tt>').</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1396
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1397<p>By using the <tt>--debug-pass=Structure</tt> option, for example, we can see
1398how our <a href="#basiccode">Hello World</a> pass interacts with other passes.
1399Lets try it out with the <tt>gcse</tt> and <tt>licm</tt> passes:</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1400
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1401<div class="doc_code"><pre>
Reid Spencer7fa6d522005-01-11 05:16:23 +0000[diff] [blame]1402$ 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]1403Module Pass Manager
1404 Function Pass Manager
1405 Dominator Set Construction
1406 Immediate Dominators Construction
1407 Global Common Subexpression Elimination
1408-- Immediate Dominators Construction
1409-- Global Common Subexpression Elimination
1410 Natural Loop Construction
1411 Loop Invariant Code Motion
1412-- Natural Loop Construction
1413-- Loop Invariant Code Motion
1414 Module Verifier
1415-- Dominator Set Construction
1416-- Module Verifier
Gabor Greif04367bf2007-07-06 22:07:22 +0000[diff] [blame]1417 Bitcode Writer
1418--Bitcode Writer
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1419</pre></div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1420
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1421<p>This output shows us when passes are constructed and when the analysis
1422results are known to be dead (prefixed with '<tt>--</tt>'). Here we see that
1423GCSE uses dominator and immediate dominator information to do its job. The LICM
1424pass uses natural loop information, which uses dominator sets, but not immediate
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1425dominators. Because immediate dominators are no longer useful after the GCSE
1426pass, it is immediately destroyed. The dominator sets are then reused to
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1427compute natural loop information, which is then used by the LICM pass.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1428
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1429<p>After the LICM pass, the module verifier runs (which is automatically added
1430by the '<tt>opt</tt>' tool), which uses the dominator set to check that the
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1431resultant LLVM code is well formed. After it finishes, the dominator set
1432information is destroyed, after being computed once, and shared by three
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1433passes.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1434
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1435<p>Lets see how this changes when we run the <a href="#basiccode">Hello
1436World</a> pass in between the two passes:</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1437
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1438<div class="doc_code"><pre>
Reid Spencer7fa6d522005-01-11 05:16:23 +0000[diff] [blame]1439$ 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]1440Module Pass Manager
1441 Function Pass Manager
1442 Dominator Set Construction
1443 Immediate Dominators Construction
1444 Global Common Subexpression Elimination
1445<b>-- Dominator Set Construction</b>
1446-- Immediate Dominators Construction
1447-- Global Common Subexpression Elimination
1448<b> Hello World Pass
1449-- Hello World Pass
1450 Dominator Set Construction</b>
1451 Natural Loop Construction
1452 Loop Invariant Code Motion
1453-- Natural Loop Construction
1454-- Loop Invariant Code Motion
1455 Module Verifier
1456-- Dominator Set Construction
1457-- Module Verifier
Gabor Greif04367bf2007-07-06 22:07:22 +0000[diff] [blame]1458 Bitcode Writer
1459--Bitcode Writer
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1460Hello: __main
1461Hello: puts
1462Hello: main
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1463</pre></div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1464
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1465<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]1466Dominator Set pass, even though it doesn't modify the code at all! To fix this,
1467we need to add the following <a
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1468href="#getAnalysisUsage"><tt>getAnalysisUsage</tt></a> method to our pass:</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1469
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1470<div class="doc_code"><pre>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1471 <i>// We don't modify the program, so we preserve all analyses</i>
1472 <b>virtual void</b> getAnalysisUsage(AnalysisUsage &amp;AU) <b>const</b> {
1473 AU.setPreservesAll();
1474 }
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1475</pre></div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1476
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1477<p>Now when we run our pass, we get this output:</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1478
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1479<div class="doc_code"><pre>
Reid Spencer7fa6d522005-01-11 05:16:23 +0000[diff] [blame]1480$ 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]1481Pass Arguments: -gcse -hello -licm
1482Module Pass Manager
1483 Function Pass Manager
1484 Dominator Set Construction
1485 Immediate Dominators Construction
1486 Global Common Subexpression Elimination
1487-- Immediate Dominators Construction
1488-- Global Common Subexpression Elimination
1489 Hello World Pass
1490-- Hello World Pass
1491 Natural Loop Construction
1492 Loop Invariant Code Motion
1493-- Loop Invariant Code Motion
1494-- Natural Loop Construction
1495 Module Verifier
1496-- Dominator Set Construction
1497-- Module Verifier
Gabor Greif04367bf2007-07-06 22:07:22 +0000[diff] [blame]1498 Bitcode Writer
1499--Bitcode Writer
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1500Hello: __main
1501Hello: puts
1502Hello: main
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1503</pre></div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1504
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1505<p>Which shows that we don't accidentally invalidate dominator information
1506anymore, and therefore do not have to compute it twice.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1507
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1508</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1509
1510<!-- _______________________________________________________________________ -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1511<div class="doc_subsubsection">
1512 <a name="releaseMemory">The <tt>releaseMemory</tt> method</a>
1513</div>
1514
1515<div class="doc_text">
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1516
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1517<div class="doc_code"><pre>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1518 <b>virtual void</b> releaseMemory();
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1519</pre></div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1520
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1521<p>The <tt>PassManager</tt> automatically determines when to compute analysis
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1522results, and how long to keep them around for. Because the lifetime of the pass
1523object itself is effectively the entire duration of the compilation process, we
1524need some way to free analysis results when they are no longer useful. The
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1525<tt>releaseMemory</tt> virtual method is the way to do this.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1526
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1527<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]1528amount of state (for use by another pass which "requires" your pass and uses the
1529<a href="#getAnalysis">getAnalysis</a> method) you should implement
1530<tt>releaseMEmory</tt> to, well, release the memory allocated to maintain this
1531internal state. This method is called after the <tt>run*</tt> method for the
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1532class, before the next call of <tt>run*</tt> in your pass.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1533
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1534</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1535
1536<!-- *********************************************************************** -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1537<div class="doc_section">
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1538 <a name="registering">Registering dynamically loaded passes</a>
1539</div>
1540<!-- *********************************************************************** -->
1541
1542<div class="doc_text">
1543
1544<p><i>Size matters</i> when constructing production quality tools using llvm,
1545both for the purposes of distribution, and for regulating the resident code size
1546when running on the target system. Therefore, it becomes desirable to
1547selectively use some passes, while omitting others and maintain the flexibility
1548to change configurations later on. You want to be able to do all this, and,
1549provide feedback to the user. This is where pass registration comes into
1550play.</p>
1551
1552<p>The fundamental mechanisms for pass registration are the
1553<tt>MachinePassRegistry</tt> class and subclasses of
1554<tt>MachinePassRegistryNode</tt>.</p>
1555
1556<p>An instance of <tt>MachinePassRegistry</tt> is used to maintain a list of
1557<tt>MachinePassRegistryNode</tt> objects. This instance maintains the list and
1558communicates additions and deletions to the command line interface.</p>
1559
1560<p>An instance of <tt>MachinePassRegistryNode</tt> subclass is used to maintain
1561information provided about a particular pass. This information includes the
1562command line name, the command help string and the address of the function used
1563to create an instance of the pass. A global static constructor of one of these
1564instances <i>registers</i> with a corresponding <tt>MachinePassRegistry</tt>,
1565the static destructor <i>unregisters</i>. Thus a pass that is statically linked
1566in the tool will be registered at start up. A dynamically loaded pass will
1567register on load and unregister at unload.</p>
1568
1569</div>
1570
1571<!-- _______________________________________________________________________ -->
1572<div class="doc_subsection">
1573 <a name="registering_existing">Using existing registries</a>
1574</div>
1575
1576<div class="doc_text">
1577
1578<p>There are predefined registries to track instruction scheduling
1579(<tt>RegisterScheduler</tt>) and register allocation (<tt>RegisterRegAlloc</tt>)
1580machine passes. Here we will describe how to <i>register</i> a register
1581allocator machine pass.</p>
1582
1583<p>Implement your register allocator machine pass. In your register allocator
1584.cpp file add the following include;</p>
1585
1586<div class="doc_code"><pre>
Chris Lattner8f652eb2006-08-11 16:37:02 +0000[diff] [blame]1587 #include "llvm/CodeGen/RegAllocRegistry.h"
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1588</pre></div>
1589
1590<p>Also in your register allocator .cpp file, define a creator function in the
1591form; </p>
1592
1593<div class="doc_code"><pre>
1594 FunctionPass *createMyRegisterAllocator() {
1595 return new MyRegisterAllocator();
1596 }
1597</pre></div>
1598
1599<p>Note that the signature of this function should match the type of
1600<tt>RegisterRegAlloc::FunctionPassCtor</tt>. In the same file add the
1601"installing" declaration, in the form;</p>
1602
1603<div class="doc_code"><pre>
1604 static RegisterRegAlloc myRegAlloc("myregalloc",
1605 " my register allocator help string",
1606 createMyRegisterAllocator);
1607</pre></div>
1608
1609<p>Note the two spaces prior to the help string produces a tidy result on the
1610--help query.</p>
1611
1612<div class="doc_code"><pre>
1613$ llc --help
1614 ...
1615 -regalloc - Register allocator to use: (default = linearscan)
1616 =linearscan - linear scan register allocator
1617 =local - local register allocator
1618 =simple - simple register allocator
1619 =myregalloc - my register allocator help string
1620 ...
1621</pre></div>
1622
1623<p>And that's it. The user is now free to use <tt>-regalloc=myregalloc</tt> as
1624an option. Registering instruction schedulers is similar except use the
Chris Lattner8f652eb2006-08-11 16:37:02 +0000[diff] [blame]1625<tt>RegisterScheduler</tt> class. Note that the
1626<tt>RegisterScheduler::FunctionPassCtor</tt> is significantly different from
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1627<tt>RegisterRegAlloc::FunctionPassCtor</tt>.</p>
1628
1629<p>To force the load/linking of your register allocator into the llc/lli tools,
1630add your creator function's global declaration to "Passes.h" and add a "pseudo"
1631call line to <tt>llvm/Codegen/LinkAllCodegenComponents.h</tt>.</p>
1632
1633</div>
1634
1635
1636<!-- _______________________________________________________________________ -->
1637<div class="doc_subsection">
1638 <a name="registering_new">Creating new registries</a>
1639</div>
1640
1641<div class="doc_text">
1642
1643<p>The easiest way to get started is to clone one of the existing registries; we
1644recommend <tt>llvm/CodeGen/RegAllocRegistry.h</tt>. The key things to modify
1645are the class name and the <tt>FunctionPassCtor</tt> type.</p>
1646
1647<p>Then you need to declare the registry. Example: if your pass registry is
1648<tt>RegisterMyPasses</tt> then define;</p>
1649
1650<div class="doc_code"><pre>
1651MachinePassRegistry RegisterMyPasses::Registry;
1652</pre></div>
1653
1654<p>And finally, declare the command line option for your passes. Example:</p>
1655
1656<div class="doc_code"><pre>
1657 cl::opt&lt;RegisterMyPasses::FunctionPassCtor, false,
1658 RegisterPassParser&lt;RegisterMyPasses&gt &gt
1659 MyPassOpt("mypass",
1660 cl::init(&amp;createDefaultMyPass),
1661 cl::desc("my pass option help"));
1662</pre></div>
1663
1664<p>Here the command option is "mypass", with createDefaultMyPass as the default
1665creator.</p>
1666
1667</div>
1668
1669<!-- *********************************************************************** -->
1670<div class="doc_section">
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1671 <a name="debughints">Using GDB with dynamically loaded passes</a>
1672</div>
Chris Lattner480e2ef2002-09-06 02:02:58 +0000[diff] [blame]1673<!-- *********************************************************************** -->
1674
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1675<div class="doc_text">
1676
1677<p>Unfortunately, using GDB with dynamically loaded passes is not as easy as it
Chris Lattner480e2ef2002-09-06 02:02:58 +0000[diff] [blame]1678should be. First of all, you can't set a breakpoint in a shared object that has
1679not been loaded yet, and second of all there are problems with inlined functions
1680in shared objects. Here are some suggestions to debugging your pass with
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1681GDB.</p>
Chris Lattner480e2ef2002-09-06 02:02:58 +0000[diff] [blame]1682
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1683<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]1684transformation invoked by <tt>opt</tt>, although nothing described here depends
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1685on that.</p>
1686
1687</div>
Chris Lattner480e2ef2002-09-06 02:02:58 +0000[diff] [blame]1688
1689<!-- _______________________________________________________________________ -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1690<div class="doc_subsubsection">
1691 <a name="breakpoint">Setting a breakpoint in your pass</a>
1692</div>
Chris Lattner480e2ef2002-09-06 02:02:58 +0000[diff] [blame]1693
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1694<div class="doc_text">
1695
1696<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]1697
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1698<div class="doc_code"><pre>
Chris Lattner480e2ef2002-09-06 02:02:58 +0000[diff] [blame]1699$ <b>gdb opt</b>
1700GNU gdb 5.0
1701Copyright 2000 Free Software Foundation, Inc.
1702GDB is free software, covered by the GNU General Public License, and you are
1703welcome to change it and/or distribute copies of it under certain conditions.
1704Type "show copying" to see the conditions.
1705There is absolutely no warranty for GDB. Type "show warranty" for details.
1706This GDB was configured as "sparc-sun-solaris2.6"...
1707(gdb)
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1708</pre></div>
Chris Lattner480e2ef2002-09-06 02:02:58 +0000[diff] [blame]1709
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1710<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]1711time to load. Be patient. Since we cannot set a breakpoint in our pass yet
1712(the shared object isn't loaded until runtime), we must execute the process, and
1713have it stop before it invokes our pass, but after it has loaded the shared
1714object. The most foolproof way of doing this is to set a breakpoint in
1715<tt>PassManager::run</tt> and then run the process with the arguments you
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1716want:</p>
Chris Lattner480e2ef2002-09-06 02:02:58 +0000[diff] [blame]1717
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1718<div class="doc_code"><pre>
Reid Spencer22a9e5b2006-09-28 16:53:47 +0000[diff] [blame]1719(gdb) <b>break llvm::PassManager::run</b>
Chris Lattner480e2ef2002-09-06 02:02:58 +0000[diff] [blame]1720Breakpoint 1 at 0x2413bc: file Pass.cpp, line 70.
Chris Lattner4c376ea2005-04-21 04:52:37 +0000[diff] [blame]1721(gdb) <b>run test.bc -load $(LLVMTOP)/llvm/Debug/lib/[libname].so -[passoption]</b>
1722Starting program: opt test.bc -load $(LLVMTOP)/llvm/Debug/lib/[libname].so -[passoption]
Chris Lattner480e2ef2002-09-06 02:02:58 +0000[diff] [blame]1723Breakpoint 1, PassManager::run (this=0xffbef174, M=@0x70b298) at Pass.cpp:70
172470 bool PassManager::run(Module &amp;M) { return PM-&gt;run(M); }
1725(gdb)
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1726</pre></div>
Chris Lattner480e2ef2002-09-06 02:02:58 +0000[diff] [blame]1727
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1728<p>Once the <tt>opt</tt> stops in the <tt>PassManager::run</tt> method you are
1729now free to set breakpoints in your pass so that you can trace through execution
1730or do other standard debugging stuff.</p>
Chris Lattner480e2ef2002-09-06 02:02:58 +0000[diff] [blame]1731
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1732</div>
Chris Lattner480e2ef2002-09-06 02:02:58 +0000[diff] [blame]1733
1734<!-- _______________________________________________________________________ -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1735<div class="doc_subsubsection">
1736 <a name="debugmisc">Miscellaneous Problems</a>
1737</div>
Chris Lattner480e2ef2002-09-06 02:02:58 +0000[diff] [blame]1738
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1739<div class="doc_text">
1740
1741<p>Once you have the basics down, there are a couple of problems that GDB has,
1742some with solutions, some without.</p>
Chris Lattner480e2ef2002-09-06 02:02:58 +0000[diff] [blame]1743
1744<ul>
1745<li>Inline functions have bogus stack information. In general, GDB does a
1746pretty good job getting stack traces and stepping through inline functions.
1747When a pass is dynamically loaded however, it somehow completely loses this
1748capability. The only solution I know of is to de-inline a function (move it
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1749from the body of a class to a .cpp file).</li>
Chris Lattner480e2ef2002-09-06 02:02:58 +0000[diff] [blame]1750
1751<li>Restarting the program breaks breakpoints. After following the information
1752above, you have succeeded in getting some breakpoints planted in your pass. Nex
1753thing you know, you restart the program (i.e., you type '<tt>run</tt>' again),
1754and you start getting errors about breakpoints being unsettable. The only way I
1755have found to "fix" this problem is to <tt>delete</tt> the breakpoints that are
1756already set in your pass, run the program, and re-set the breakpoints once
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1757execution stops in <tt>PassManager::run</tt>.</li>
Chris Lattner480e2ef2002-09-06 02:02:58 +0000[diff] [blame]1758
1759</ul>
1760
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1761<p>Hopefully these tips will help with common case debugging situations. If
1762you'd like to contribute some tips of your own, just contact <a
1763href="mailto:sabre@nondot.org">Chris</a>.</p>
Chris Lattner480e2ef2002-09-06 02:02:58 +0000[diff] [blame]1764
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1765</div>
Chris Lattner480e2ef2002-09-06 02:02:58 +0000[diff] [blame]1766
1767<!-- *********************************************************************** -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1768<div class="doc_section">
1769 <a name="future">Future extensions planned</a>
1770</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1771<!-- *********************************************************************** -->
1772
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1773<div class="doc_text">
1774
1775<p>Although the LLVM Pass Infrastructure is very capable as it stands, and does
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1776some 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]1777where we are going:</p>
1778
1779</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1780
1781<!-- _______________________________________________________________________ -->
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]1782<div class="doc_subsubsection">
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1783 <a name="SMP">Multithreaded LLVM</a>
1784</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1785
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1786<div class="doc_text">
1787
1788<p>Multiple CPU machines are becoming more common and compilation can never be
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1789fast enough: obviously we should allow for a multithreaded compiler. Because of
1790the semantics defined for passes above (specifically they cannot maintain state
1791across invocations of their <tt>run*</tt> methods), a nice clean way to
1792implement a multithreaded compiler would be for the <tt>PassManager</tt> class
Misha Brukmanbc0e9982003-07-14 17:20:40 +0000[diff] [blame]1793to create multiple instances of each pass object, and allow the separate
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1794instances to be hacking on different parts of the program at the same time.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1795
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1796<p>This implementation would prevent each of the passes from having to implement
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1797multithreaded constructs, requiring only the LLVM core to have locking in a few
1798places (for global resources). Although this is a simple extension, we simply
1799haven't had time (or multiprocessor machines, thus a reason) to implement this.
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1800Despite that, we have kept the LLVM passes SMP ready, and you should too.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1801
Chris Lattnerb5c87f62007-05-18 05:36:14 +0000[diff] [blame]1802</div>
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