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gerrit-public.fairphone.software / fp2-dev / platform / external / llvm / 1f48a95ccbff731a8bcf4890204e5eef09eb99d1 / . / docs / WritingAnLLVMPass.html
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4<head>
Reid Spencer7fa6d522005-01-11 05:16:23 +0000[diff] [blame]5 <meta http-equiv="Content-Type" content="text/html; charset=utf-8">
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]6 <title>Writing an LLVM Pass</title>
7 <link rel="stylesheet" href="llvm.css" type="text/css">
8</head>
9<body>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]10
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]11<div class="doc_title">
12 Writing an LLVM Pass
13</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]14
15<ol>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]16 <li><a href="#introduction">Introduction - What is a pass?</a></li>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]17 <li><a href="#quickstart">Quick Start - Writing hello world</a>
18 <ul>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]19 <li><a href="#makefile">Setting up the build environment</a></li>
20 <li><a href="#basiccode">Basic code required</a></li>
Chris Lattnerc8603c22006-08-27 23:18:52 +0000[diff] [blame]21 <li><a href="#running">Running a pass with <tt>opt</tt></a></li>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]22 </ul></li>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]23 <li><a href="#passtype">Pass classes and requirements</a>
24 <ul>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]25 <li><a href="#ImmutablePass">The <tt>ImmutablePass</tt> class</a></li>
Chris Lattnerf6278922004-09-20 04:36:29 +0000[diff] [blame]26 <li><a href="#ModulePass">The <tt>ModulePass</tt> class</a>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]27 <ul>
Chris Lattnerf6278922004-09-20 04:36:29 +0000[diff] [blame]28 <li><a href="#runOnModule">The <tt>runOnModule</tt> method</a></li>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]29 </ul></li>
Chris Lattner8fdb2462004-09-18 06:39:35 +0000[diff] [blame]30 <li><a href="#CallGraphSCCPass">The <tt>CallGraphSCCPass</tt> class</a>
31 <ul>
Devang Patelc20048d2007-01-23 22:56:28 +0000[diff] [blame]32 <li><a href="#doInitialization_scc">The <tt>doInitialization(CallGraph
Chris Lattner8fdb2462004-09-18 06:39:35 +0000[diff] [blame]33 &amp;)</tt> method</a></li>
34 <li><a href="#runOnSCC">The <tt>runOnSCC</tt> method</a></li>
Devang Patelc20048d2007-01-23 22:56:28 +0000[diff] [blame]35 <li><a href="#doFinalization_scc">The <tt>doFinalization(CallGraph
Chris Lattner8fdb2462004-09-18 06:39:35 +0000[diff] [blame]36 &amp;)</tt> method</a></li>
37 </ul></li>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]38 <li><a href="#FunctionPass">The <tt>FunctionPass</tt> class</a>
39 <ul>
Chris Lattnerd0713f92002-09-12 17:06:43 +0000[diff] [blame]40 <li><a href="#doInitialization_mod">The <tt>doInitialization(Module
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]41 &amp;)</tt> method</a></li>
42 <li><a href="#runOnFunction">The <tt>runOnFunction</tt> method</a></li>
Chris Lattnerd0713f92002-09-12 17:06:43 +0000[diff] [blame]43 <li><a href="#doFinalization_mod">The <tt>doFinalization(Module
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]44 &amp;)</tt> method</a></li>
45 </ul></li>
Devang Patel2e8f27d2007-03-19 22:21:25 +0000[diff] [blame]46 <li><a href="#LoopPass">The <tt>LoopPass</tt> class</a>
47 <ul>
48 <li><a href="#doInitialization_loop">The <tt>doInitialization(Loop *,
49 LPPassManager &amp;)</tt> method</a></li>
50 <li><a href="#runOnLoop">The <tt>runOnLoop</tt> method</a></li>
51 <li><a href="#doFinalization_loop">The <tt>doFinalization()
52 </tt> method</a></li>
53 </ul></li>
Tobias Grosser65513602010-10-20 01:54:44 +0000[diff] [blame]54 <li><a href="#RegionPass">The <tt>RegionPass</tt> class</a>
55 <ul>
56 <li><a href="#doInitialization_region">The <tt>doInitialization(Region *,
57 RGPassManager &amp;)</tt> method</a></li>
58 <li><a href="#runOnRegion">The <tt>runOnRegion</tt> method</a></li>
59 <li><a href="#doFinalization_region">The <tt>doFinalization()
60 </tt> method</a></li>
61 </ul></li>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]62 <li><a href="#BasicBlockPass">The <tt>BasicBlockPass</tt> class</a>
63 <ul>
Chris Lattnerd0713f92002-09-12 17:06:43 +0000[diff] [blame]64 <li><a href="#doInitialization_fn">The <tt>doInitialization(Function
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]65 &amp;)</tt> method</a></li>
66 <li><a href="#runOnBasicBlock">The <tt>runOnBasicBlock</tt>
67 method</a></li>
Chris Lattnerd0713f92002-09-12 17:06:43 +0000[diff] [blame]68 <li><a href="#doFinalization_fn">The <tt>doFinalization(Function
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]69 &amp;)</tt> method</a></li>
70 </ul></li>
Brian Gaekecab8b6f2003-07-17 18:53:20 +0000[diff] [blame]71 <li><a href="#MachineFunctionPass">The <tt>MachineFunctionPass</tt>
72 class</a>
Brian Gaeke6a33f362003-07-22 20:53:20 +0000[diff] [blame]73 <ul>
74 <li><a href="#runOnMachineFunction">The
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]75 <tt>runOnMachineFunction(MachineFunction &amp;)</tt> method</a></li>
76 </ul></li>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]77 </ul>
78 <li><a href="#registration">Pass Registration</a>
79 <ul>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]80 <li><a href="#print">The <tt>print</tt> method</a></li>
81 </ul></li>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]82 <li><a href="#interaction">Specifying interactions between passes</a>
83 <ul>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]84 <li><a href="#getAnalysisUsage">The <tt>getAnalysisUsage</tt>
85 method</a></li>
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]86 <li><a href="#AU::addRequired">The <tt>AnalysisUsage::addRequired&lt;&gt;</tt> and <tt>AnalysisUsage::addRequiredTransitive&lt;&gt;</tt> methods</a></li>
87 <li><a href="#AU::addPreserved">The <tt>AnalysisUsage::addPreserved&lt;&gt;</tt> method</a></li>
88 <li><a href="#AU::examples">Example implementations of <tt>getAnalysisUsage</tt></a></li>
Duncan Sands1465d612009-01-28 13:14:17 +0000[diff] [blame]89 <li><a href="#getAnalysis">The <tt>getAnalysis&lt;&gt;</tt> and
90<tt>getAnalysisIfAvailable&lt;&gt;</tt> methods</a></li>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]91 </ul></li>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]92 <li><a href="#analysisgroup">Implementing Analysis Groups</a>
93 <ul>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]94 <li><a href="#agconcepts">Analysis Group Concepts</a></li>
95 <li><a href="#registerag">Using <tt>RegisterAnalysisGroup</tt></a></li>
96 </ul></li>
Tanya Lattnerd5383652004-11-19 01:25:14 +0000[diff] [blame]97 <li><a href="#passStatistics">Pass Statistics</a>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]98 <li><a href="#passmanager">What PassManager does</a>
99 <ul>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]100 <li><a href="#releaseMemory">The <tt>releaseMemory</tt> method</a></li>
101 </ul></li>
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]102 <li><a href="#registering">Registering dynamically loaded passes</a>
103 <ul>
104 <li><a href="#registering_existing">Using existing registries</a></li>
105 <li><a href="#registering_new">Creating new registries</a></li>
106 </ul></li>
Chris Lattner480e2ef2002-09-06 02:02:58 +0000[diff] [blame]107 <li><a href="#debughints">Using GDB with dynamically loaded passes</a>
108 <ul>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]109 <li><a href="#breakpoint">Setting a breakpoint in your pass</a></li>
110 <li><a href="#debugmisc">Miscellaneous Problems</a></li>
111 </ul></li>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]112 <li><a href="#future">Future extensions planned</a>
113 <ul>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]114 <li><a href="#SMP">Multithreaded LLVM</a></li>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]115 </ul></li>
116</ol>
Chris Lattner38c633d2002-08-08 20:23:41 +0000[diff] [blame]117
Chris Lattner7911ce22004-05-23 21:07:27 +0000[diff] [blame]118<div class="doc_author">
Chris Lattner8f652eb2006-08-11 16:37:02 +0000[diff] [blame]119 <p>Written by <a href="mailto:sabre@nondot.org">Chris Lattner</a> and
Jim Laskeyc760a922007-03-14 19:32:21 +0000[diff] [blame]120 <a href="mailto:jlaskey@mac.com">Jim Laskey</a></p>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]121</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]122
123<!-- *********************************************************************** -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]124<div class="doc_section">
125 <a name="introduction">Introduction - What is a pass?</a>
126</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]127<!-- *********************************************************************** -->
128
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]129<div class="doc_text">
130
131<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]132passes are where most of the interesting parts of the compiler exist. Passes
133perform the transformations and optimizations that make up the compiler, they
134build the analysis results that are used by these transformations, and they are,
135above all, a structuring technique for compiler code.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]136
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]137<p>All LLVM passes are subclasses of the <tt><a
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]138href="http://llvm.org/doxygen/classllvm_1_1Pass.html">Pass</a></tt>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]139class, which implement functionality by overriding virtual methods inherited
Chris Lattnerf6278922004-09-20 04:36:29 +0000[diff] [blame]140from <tt>Pass</tt>. Depending on how your pass works, you should inherit from
141the <tt><a href="#ModulePass">ModulePass</a></tt>, <tt><a
142href="#CallGraphSCCPass">CallGraphSCCPass</a></tt>, <tt><a
143href="#FunctionPass">FunctionPass</a></tt>, or <tt><a
Devang Patel2e8f27d2007-03-19 22:21:25 +0000[diff] [blame]144href="#LoopPass">LoopPass</a></tt>, or <tt><a
Tobias Grosser65513602010-10-20 01:54:44 +0000[diff] [blame]145href="#RegionPass">RegionPass</a></tt>, or <tt><a
Chris Lattner8fdb2462004-09-18 06:39:35 +0000[diff] [blame]146href="#BasicBlockPass">BasicBlockPass</a></tt> classes, which gives the system
147more information about what your pass does, and how it can be combined with
148other passes. One of the main features of the LLVM Pass Framework is that it
149schedules passes to run in an efficient way based on the constraints that your
150pass meets (which are indicated by which class they derive from).</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]151
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]152<p>We start by showing you how to construct a pass, everything from setting up
153the code, to compiling, loading, and executing it. After the basics are down,
154more advanced features are discussed.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]155
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]156</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]157
158<!-- *********************************************************************** -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]159<div class="doc_section">
160 <a name="quickstart">Quick Start - Writing hello world</a>
161</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]162<!-- *********************************************************************** -->
163
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]164<div class="doc_text">
165
166<p>Here we describe how to write the "hello world" of passes. The "Hello" pass
167is designed to simply print out the name of non-external functions that exist in
Chris Lattner8fdb2462004-09-18 06:39:35 +0000[diff] [blame]168the program being compiled. It does not modify the program at all, it just
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]169inspects it. The source code and files for this pass are available in the LLVM
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]170source tree in the <tt>lib/Transforms/Hello</tt> directory.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]171
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]172</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]173
174<!-- ======================================================================= -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]175<div class="doc_subsection">
176 <a name="makefile">Setting up the build environment</a>
177</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]178
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]179<div class="doc_text">
180
Duncan Sandsdc97c0b2011-01-01 17:28:49 +0000[diff] [blame]181 <p>First, configure and build LLVM. This needs to be done directly inside the
182 LLVM source tree rather than in a separate objects directory.
183 Next, you need to create a new directory somewhere in the LLVM source
Reid Spencer1bc19342004-12-11 05:12:57 +0000[diff] [blame]184 base. For this example, we'll assume that you made
Duncan Sandsdc97c0b2011-01-01 17:28:49 +0000[diff] [blame]185 <tt>lib/Transforms/Hello</tt>. Finally, you must set up a build script
Reid Spencer1bc19342004-12-11 05:12:57 +0000[diff] [blame]186 (Makefile) that will compile the source code for the new pass. To do this,
187 copy the following into <tt>Makefile</tt>:</p>
NAKAMURA Takumi4d6deb02011-04-09 09:51:57 +0000[diff] [blame]188 <hr>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]189
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]190<div class="doc_code"><pre>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]191# Makefile for hello pass
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]192
Torok Edwin87469292009-10-12 13:37:29 +0000[diff] [blame]193# Path to top level of LLVM hierarchy
Chris Lattner7ce83e52002-08-14 20:07:01 +0000[diff] [blame]194LEVEL = ../../..
Chris Lattner17a4c3e2002-08-14 20:06:13 +0000[diff] [blame]195
196# Name of the library to build
Reid Spencer7fa6d522005-01-11 05:16:23 +0000[diff] [blame]197LIBRARYNAME = Hello
Chris Lattner17a4c3e2002-08-14 20:06:13 +0000[diff] [blame]198
Reid Spencer7fa6d522005-01-11 05:16:23 +0000[diff] [blame]199# Make the shared library become a loadable module so the tools can
200# dlopen/dlsym on the resulting library.
Robert Bocchino3cf817d2006-01-06 22:49:23 +0000[diff] [blame]201LOADABLE_MODULE = 1
Reid Spencer7fa6d522005-01-11 05:16:23 +0000[diff] [blame]202
Chris Lattner17a4c3e2002-08-14 20:06:13 +0000[diff] [blame]203# Include the makefile implementation stuff
204include $(LEVEL)/Makefile.common
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]205</pre></div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]206
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]207<p>This makefile specifies that all of the <tt>.cpp</tt> files in the current
Duncan Sands779ff7f2011-01-01 17:21:58 +0000[diff] [blame]208directory are to be compiled and linked together into a shared object
209<tt>$(LEVEL)/Debug+Asserts/lib/Hello.so</tt> that can be dynamically loaded by
Chris Lattnerc8603c22006-08-27 23:18:52 +0000[diff] [blame]210the <tt>opt</tt> or <tt>bugpoint</tt> tools via their <tt>-load</tt> options.
Reid Spencer7fa6d522005-01-11 05:16:23 +0000[diff] [blame]211If your operating system uses a suffix other than .so (such as windows or
212Mac OS/X), the appropriate extension will be used.</p>
John Criswellf9c78652004-01-26 21:26:54 +0000[diff] [blame]213
Oscar Fuentes23ba1e42011-04-12 19:40:35 +0000[diff] [blame]214<p>If you are used CMake to build LLVM, see
215<a href="CMake.html#passdev">Developing an LLVM pass with CMake</a>.</p>
216
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]217<p>Now that we have the build scripts set up, we just need to write the code for
218the pass itself.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]219
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]220</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]221
222<!-- ======================================================================= -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]223<div class="doc_subsection">
224 <a name="basiccode">Basic code required</a>
225</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]226
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]227<div class="doc_text">
228
229<p>Now that we have a way to compile our new pass, we just have to write it.
230Start out with:</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]231
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]232<div class="doc_code"><pre>
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]233<b>#include</b> "<a href="http://llvm.org/doxygen/Pass_8h-source.html">llvm/Pass.h</a>"
234<b>#include</b> "<a href="http://llvm.org/doxygen/Function_8h-source.html">llvm/Function.h</a>"
Chris Lattner0ce6f932009-09-08 05:14:44 +0000[diff] [blame]235<b>#include</b> "<a href="http://llvm.org/doxygen/raw__ostream_8h.html">llvm/Support/raw_ostream.h</a>"
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]236</pre></div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]237
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]238<p>Which are needed because we are writing a <tt><a
Chris Lattner0ce6f932009-09-08 05:14:44 +0000[diff] [blame]239href="http://llvm.org/doxygen/classllvm_1_1Pass.html">Pass</a></tt>,
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]240we are operating on <tt><a
Chris Lattner0ce6f932009-09-08 05:14:44 +0000[diff] [blame]241href="http://llvm.org/doxygen/classllvm_1_1Function.html">Function</a></tt>'s,
242and we will be doing some printing.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]243
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]244<p>Next we have:</p>
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]245<div class="doc_code"><pre>
Jonathan Manton65acb302004-06-30 18:10:30 +0000[diff] [blame]246<b>using namespace llvm;</b>
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]247</pre></div>
Jonathan Manton65acb302004-06-30 18:10:30 +0000[diff] [blame]248<p>... which is required because the functions from the include files
249live in the llvm namespace.
250</p>
251
252<p>Next we have:</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>namespace</b> {
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]256</pre></div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]257
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]258<p>... which starts out an anonymous namespace. Anonymous namespaces are to C++
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]259what the "<tt>static</tt>" keyword is to C (at global scope). It makes the
260things declared inside of the anonymous namespace only visible to the current
261file. If you're not familiar with them, consult a decent C++ book for more
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]262information.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]263
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]264<p>Next, we declare our pass itself:</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]265
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]266<div class="doc_code"><pre>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]267 <b>struct</b> Hello : <b>public</b> <a href="#FunctionPass">FunctionPass</a> {
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]268</pre></div><p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]269
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]270<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]271href="http://llvm.org/doxygen/classllvm_1_1FunctionPass.html">FunctionPass</a></tt>.
Chris Lattnerd6ea9262002-09-09 03:48:46 +0000[diff] [blame]272The different builtin pass subclasses are described in detail <a
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]273href="#passtype">later</a>, but for now, know that <a
274href="#FunctionPass"><tt>FunctionPass</tt></a>'s operate a function at a
275time.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]276
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]277<div class="doc_code"><pre>
Devang Patel19974732007-05-03 01:11:54 +0000[diff] [blame]278 static char ID;
Duncan Sands5e09eef2011-01-01 17:37:07 +0000[diff] [blame]279 Hello() : FunctionPass(ID) {}
Devang Patele50fb9a2007-05-01 20:55:38 +0000[diff] [blame]280</pre></div><p>
281
282<p> This declares pass identifier used by LLVM to identify pass. This allows LLVM to
283avoid using expensive C++ runtime information.</p>
284
285<div class="doc_code"><pre>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]286 <b>virtual bool</b> <a href="#runOnFunction">runOnFunction</a>(Function &amp;F) {
Chris Lattner0ce6f932009-09-08 05:14:44 +0000[diff] [blame]287 errs() &lt;&lt; "<i>Hello: </i>" &lt;&lt; F.getName() &lt;&lt; "\n";
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]288 <b>return false</b>;
289 }
290 }; <i>// end of struct Hello</i>
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]291</pre></div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]292
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]293<p>We declare a "<a href="#runOnFunction"><tt>runOnFunction</tt></a>" method,
294which overloads an abstract virtual method inherited from <a
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]295href="#FunctionPass"><tt>FunctionPass</tt></a>. This is where we are supposed
296to 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]297function.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]298
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]299<div class="doc_code"><pre>
Devang Patel19974732007-05-03 01:11:54 +0000[diff] [blame]300 char Hello::ID = 0;
Devang Patele50fb9a2007-05-01 20:55:38 +0000[diff] [blame]301</pre></div>
302
303<p> We initialize pass ID here. LLVM uses ID's address to identify pass so
304initialization value is not important.</p>
305
306<div class="doc_code"><pre>
NAKAMURA Takumi4d6deb02011-04-09 09:51:57 +0000[diff] [blame]307 static RegisterPass&lt;Hello&gt; X("<i>hello</i>", "<i>Hello World Pass</i>",
Devang Patelc7582092008-03-19 21:56:59 +0000[diff] [blame]308 false /* Only looks at CFG */,
309 false /* Analysis Pass */);
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]310} <i>// end of anonymous namespace</i>
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]311</pre></div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]312
Chris Lattnerc8603c22006-08-27 23:18:52 +0000[diff] [blame]313<p>Lastly, we <a href="#registration">register our class</a> <tt>Hello</tt>,
314giving it a command line
Devang Patelc7582092008-03-19 21:56:59 +0000[diff] [blame]315argument "<tt>hello</tt>", and a name "<tt>Hello World Pass</tt>".
Owen Anderson20813e02010-07-21 22:58:07 +0000[diff] [blame]316Last two arguments describe its behavior.
Devang Patelc7582092008-03-19 21:56:59 +0000[diff] [blame]317If a pass walks CFG without modifying it then third argument is set to true.
318If a pass is an analysis pass, for example dominator tree pass, then true
319is supplied as fourth argument. </p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]320
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]321<p>As a whole, the <tt>.cpp</tt> file looks like:</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]322
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]323<div class="doc_code"><pre>
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]324<b>#include</b> "<a href="http://llvm.org/doxygen/Pass_8h-source.html">llvm/Pass.h</a>"
325<b>#include</b> "<a href="http://llvm.org/doxygen/Function_8h-source.html">llvm/Function.h</a>"
Chris Lattner0ce6f932009-09-08 05:14:44 +0000[diff] [blame]326<b>#include</b> "<a href="http://llvm.org/doxygen/raw__ostream_8h.html">llvm/Support/raw_ostream.h</a>"
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]327
Jonathan Manton65acb302004-06-30 18:10:30 +0000[diff] [blame]328<b>using namespace llvm;</b>
329
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]330<b>namespace</b> {
331 <b>struct Hello</b> : <b>public</b> <a href="#FunctionPass">FunctionPass</a> {
Devang Patele50fb9a2007-05-01 20:55:38 +0000[diff] [blame]332
Devang Patel19974732007-05-03 01:11:54 +0000[diff] [blame]333 static char ID;
Duncan Sands5e09eef2011-01-01 17:37:07 +0000[diff] [blame]334 Hello() : FunctionPass(ID) {}
Devang Patele50fb9a2007-05-01 20:55:38 +0000[diff] [blame]335
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]336 <b>virtual bool</b> <a href="#runOnFunction">runOnFunction</a>(Function &amp;F) {
Chris Lattner0ce6f932009-09-08 05:14:44 +0000[diff] [blame]337 errs() &lt;&lt; "<i>Hello: </i>" &lt;&lt; F.getName() &lt;&lt; "\n";
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]338 <b>return false</b>;
339 }
340 };
341
Devang Patel26e5a302007-07-25 21:05:39 +0000[diff] [blame]342 char Hello::ID = 0;
NAKAMURA Takumi4d6deb02011-04-09 09:51:57 +0000[diff] [blame]343 static RegisterPass&lt;Hello&gt; X("hello", "Hello World Pass", false, false);
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]344}
Owen Anderson20813e02010-07-21 22:58:07 +0000[diff] [blame]345
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]346</pre></div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]347
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]348<p>Now that it's all together, compile the file with a simple "<tt>gmake</tt>"
Duncan Sands779ff7f2011-01-01 17:21:58 +0000[diff] [blame]349command in the local directory and you should get a new file
350"<tt>Debug+Asserts/lib/Hello.so</tt>" under the top level directory of the LLVM
351source tree (not in the local directory). Note that everything in this file is
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]352contained in an anonymous namespace: this reflects the fact that passes are self
353contained units that do not need external interfaces (although they can have
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]354them) to be useful.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]355
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]356</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]357
358<!-- ======================================================================= -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]359<div class="doc_subsection">
Chris Lattnerc8603c22006-08-27 23:18:52 +0000[diff] [blame]360 <a name="running">Running a pass with <tt>opt</tt></a>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]361</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]362
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]363<div class="doc_text">
364
John Criswellf9c78652004-01-26 21:26:54 +0000[diff] [blame]365<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]366<tt>opt</tt> command to run an LLVM program through your pass. Because you
Duncan Sands5e09eef2011-01-01 17:37:07 +0000[diff] [blame]367registered your pass with <tt>RegisterPass</tt>, you will be able to
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]368use the <tt>opt</tt> tool to access it, once loaded.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]369
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]370<p>To test it, follow the example at the end of the <a
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]371href="GettingStarted.html">Getting Started Guide</a> to compile "Hello World" to
Gabor Greif04367bf2007-07-06 22:07:22 +0000[diff] [blame]372LLVM. We can now run the bitcode file (<tt>hello.bc</tt>) for the program
373through our transformation like this (or course, any bitcode file will
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]374work):</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]375
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]376<div class="doc_code"><pre>
Duncan Sands67f8a7b2010-07-08 08:27:18 +0000[diff] [blame]377$ opt -load ../../../Debug+Asserts/lib/Hello.so -hello &lt; hello.bc &gt; /dev/null
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]378Hello: __main
379Hello: puts
380Hello: main
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]381</pre></div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]382
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]383<p>The '<tt>-load</tt>' option specifies that '<tt>opt</tt>' should load your
384pass as a shared object, which makes '<tt>-hello</tt>' a valid command line
385argument (which is one reason you need to <a href="#registration">register your
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]386pass</a>). Because the hello pass does not modify the program in any
387interesting way, we just throw away the result of <tt>opt</tt> (sending it to
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]388<tt>/dev/null</tt>).</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]389
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]390<p>To see what happened to the other string you registered, try running
Duncan Sands7e7ae5a2010-02-18 14:08:13 +0000[diff] [blame]391<tt>opt</tt> with the <tt>-help</tt> option:</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]392
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]393<div class="doc_code"><pre>
Duncan Sands67f8a7b2010-07-08 08:27:18 +0000[diff] [blame]394$ opt -load ../../../Debug+Asserts/lib/Hello.so -help
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]395OVERVIEW: llvm .bc -&gt; .bc modular optimizer
396
Gabor Greif04367bf2007-07-06 22:07:22 +0000[diff] [blame]397USAGE: opt [options] &lt;input bitcode&gt;
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]398
399OPTIONS:
400 Optimizations available:
401...
402 -funcresolve - Resolve Functions
403 -gcse - Global Common Subexpression Elimination
404 -globaldce - Dead Global Elimination
405 <b>-hello - Hello World Pass</b>
Chris Lattner065a6162003-09-10 05:29:43 +0000[diff] [blame]406 -indvars - Canonicalize Induction Variables
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]407 -inline - Function Integration/Inlining
408 -instcombine - Combine redundant instructions
409...
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]410</pre></div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]411
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]412<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]413documentation to users of <tt>opt</tt>. Now that you have a working pass, you
414would go ahead and make it do the cool transformations you want. Once you get
415it all working and tested, it may become useful to find out how fast your pass
416is. The <a href="#passManager"><tt>PassManager</tt></a> provides a nice command
417line option (<tt>--time-passes</tt>) that allows you to get information about
418the execution time of your pass along with the other passes you queue up. For
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]419example:</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]420
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]421<div class="doc_code"><pre>
Duncan Sands67f8a7b2010-07-08 08:27:18 +0000[diff] [blame]422$ opt -load ../../../Debug+Asserts/lib/Hello.so -hello -time-passes &lt; hello.bc &gt; /dev/null
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]423Hello: __main
424Hello: puts
425Hello: main
426===============================================================================
427 ... Pass execution timing report ...
428===============================================================================
429 Total Execution Time: 0.02 seconds (0.0479059 wall clock)
430
431 ---User Time--- --System Time-- --User+System-- ---Wall Time--- --- Pass Name ---
Gabor Greif04367bf2007-07-06 22:07:22 +0000[diff] [blame]432 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]433 0.0000 ( 0.0%) 0.0100 (100.0%) 0.0100 ( 50.0%) 0.0031 ( 6.4%) Dominator Set Construction
434 0.0000 ( 0.0%) 0.0000 ( 0.0%) 0.0000 ( 0.0%) 0.0013 ( 2.7%) Module Verifier
435 <b> 0.0000 ( 0.0%) 0.0000 ( 0.0%) 0.0000 ( 0.0%) 0.0033 ( 6.9%) Hello World Pass</b>
436 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]437</pre></div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]438
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]439<p>As you can see, our implementation above is pretty fast :). The additional
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]440passes listed are automatically inserted by the '<tt>opt</tt>' tool to verify
441that the LLVM emitted by your pass is still valid and well formed LLVM, which
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]442hasn't been broken somehow.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]443
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]444<p>Now that you have seen the basics of the mechanics behind passes, we can talk
445about some more details of how they work and how to use them.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]446
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]447</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]448
449<!-- *********************************************************************** -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]450<div class="doc_section">
451 <a name="passtype">Pass classes and requirements</a>
452</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]453<!-- *********************************************************************** -->
454
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]455<div class="doc_text">
456
457<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]458decide what class you should subclass for your pass. The <a
459href="#basiccode">Hello World</a> example uses the <tt><a
460href="#FunctionPass">FunctionPass</a></tt> class for its implementation, but we
461did not discuss why or when this should occur. Here we talk about the classes
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]462available, from the most general to the most specific.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]463
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]464<p>When choosing a superclass for your Pass, you should choose the <b>most
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]465specific</b> class possible, while still being able to meet the requirements
Misha Brukman5560c9d2003-08-18 14:43:39 +0000[diff] [blame]466listed. This gives the LLVM Pass Infrastructure information necessary to
Benjamin Kramer8040cd32009-10-12 14:46:08 +0000[diff] [blame]467optimize how passes are run, so that the resultant compiler isn't unnecessarily
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]468slow.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]469
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]470</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]471
Chris Lattnerf004f9a2002-09-25 22:31:38 +0000[diff] [blame]472<!-- ======================================================================= -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]473<div class="doc_subsection">
474 <a name="ImmutablePass">The <tt>ImmutablePass</tt> class</a>
475</div>
Chris Lattnerf004f9a2002-09-25 22:31:38 +0000[diff] [blame]476
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]477<div class="doc_text">
478
479<p>The most plain and boring type of pass is the "<tt><a
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]480href="http://llvm.org/doxygen/classllvm_1_1ImmutablePass.html">ImmutablePass</a></tt>"
Chris Lattnerf004f9a2002-09-25 22:31:38 +0000[diff] [blame]481class. This pass type is used for passes that do not have to be run, do not
482change state, and never need to be updated. This is not a normal type of
483transformation or analysis, but can provide information about the current
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]484compiler configuration.</p>
Chris Lattnerf004f9a2002-09-25 22:31:38 +0000[diff] [blame]485
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]486<p>Although this pass class is very infrequently used, it is important for
Chris Lattnerf004f9a2002-09-25 22:31:38 +0000[diff] [blame]487providing information about the current target machine being compiled for, and
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]488other static information that can affect the various transformations.</p>
Chris Lattnerf004f9a2002-09-25 22:31:38 +0000[diff] [blame]489
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]490<p><tt>ImmutablePass</tt>es never invalidate other transformations, are never
491invalidated, and are never "run".</p>
Chris Lattnerf004f9a2002-09-25 22:31:38 +0000[diff] [blame]492
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]493</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]494
495<!-- ======================================================================= -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]496<div class="doc_subsection">
Chris Lattnerf6278922004-09-20 04:36:29 +0000[diff] [blame]497 <a name="ModulePass">The <tt>ModulePass</tt> class</a>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]498</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]499
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]500<div class="doc_text">
501
502<p>The "<tt><a
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]503href="http://llvm.org/doxygen/classllvm_1_1ModulePass.html">ModulePass</a></tt>"
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]504class is the most general of all superclasses that you can use. Deriving from
Chris Lattnerf6278922004-09-20 04:36:29 +0000[diff] [blame]505<tt>ModulePass</tt> indicates that your pass uses the entire program as a unit,
Benjamin Kramer8040cd32009-10-12 14:46:08 +0000[diff] [blame]506referring to function bodies in no predictable order, or adding and removing
Chris Lattnerf6278922004-09-20 04:36:29 +0000[diff] [blame]507functions. Because nothing is known about the behavior of <tt>ModulePass</tt>
Daniel Dunbarb71725b2009-07-01 23:38:44 +0000[diff] [blame]508subclasses, no optimization can be done for their execution.</p>
509
510<p>A module pass can use function level passes (e.g. dominators) using
511the getAnalysis interface
512<tt>getAnalysis&lt;DominatorTree&gt;(llvm::Function *)</tt> to provide the
513function to retrieve analysis result for, if the function pass does not require
Devang Patel468857f2009-08-10 16:37:29 +0000[diff] [blame]514any module or immutable passes. Note that this can only be done for functions for which the
Daniel Dunbarb71725b2009-07-01 23:38:44 +0000[diff] [blame]515analysis ran, e.g. in the case of dominators you should only ask for the
516DominatorTree for function definitions, not declarations.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]517
Chris Lattnerf6278922004-09-20 04:36:29 +0000[diff] [blame]518<p>To write a correct <tt>ModulePass</tt> subclass, derive from
519<tt>ModulePass</tt> and overload the <tt>runOnModule</tt> method with the
520following signature:</p>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]521
522</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]523
524<!-- _______________________________________________________________________ -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]525<div class="doc_subsubsection">
Chris Lattnerf6278922004-09-20 04:36:29 +0000[diff] [blame]526 <a name="runOnModule">The <tt>runOnModule</tt> method</a>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]527</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]528
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]529<div class="doc_text">
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]530
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]531<div class="doc_code"><pre>
Chris Lattnerf6278922004-09-20 04:36:29 +0000[diff] [blame]532 <b>virtual bool</b> runOnModule(Module &amp;M) = 0;
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]533</pre></div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]534
John Criswell2382ff72005-07-15 19:25:12 +0000[diff] [blame]535<p>The <tt>runOnModule</tt> method performs the interesting work of the pass.
536It should return true if the module was modified by the transformation and
537false otherwise.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]538
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]539</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]540
541<!-- ======================================================================= -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]542<div class="doc_subsection">
Chris Lattner8fdb2462004-09-18 06:39:35 +0000[diff] [blame]543 <a name="CallGraphSCCPass">The <tt>CallGraphSCCPass</tt> class</a>
544</div>
545
546<div class="doc_text">
547
548<p>The "<tt><a
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]549href="http://llvm.org/doxygen/classllvm_1_1CallGraphSCCPass.html">CallGraphSCCPass</a></tt>"
Chris Lattner8fdb2462004-09-18 06:39:35 +0000[diff] [blame]550is used by passes that need to traverse the program bottom-up on the call graph
551(callees before callers). Deriving from CallGraphSCCPass provides some
552mechanics for building and traversing the CallGraph, but also allows the system
553to optimize execution of CallGraphSCCPass's. If your pass meets the
554requirements outlined below, and doesn't meet the requirements of a <tt><a
555href="#FunctionPass">FunctionPass</a></tt> or <tt><a
556href="#BasicBlockPass">BasicBlockPass</a></tt>, you should derive from
557<tt>CallGraphSCCPass</tt>.</p>
558
559<p><b>TODO</b>: explain briefly what SCC, Tarjan's algo, and B-U mean.</p>
560
561<p>To be explicit, <tt>CallGraphSCCPass</tt> subclasses are:</p>
562
563<ol>
564
Nick Lewycky99597062011-01-03 06:16:07 +0000[diff] [blame]565<li>... <em>not allowed</em> to inspect or modify any <tt>Function</tt>s other
566than those in the current SCC and the direct callers and direct callees of the
567SCC.</li>
Chris Lattner8fdb2462004-09-18 06:39:35 +0000[diff] [blame]568
569<li>... <em>required</em> to preserve the current CallGraph object, updating it
570to reflect any changes made to the program.</li>
571
572<li>... <em>not allowed</em> to add or remove SCC's from the current Module,
573though they may change the contents of an SCC.</li>
574
575<li>... <em>allowed</em> to add or remove global variables from the current
576Module.</li>
577
578<li>... <em>allowed</em> to maintain state across invocations of
579 <a href="#runOnSCC"><tt>runOnSCC</tt></a> (including global data).</li>
580</ol>
581
582<p>Implementing a <tt>CallGraphSCCPass</tt> is slightly tricky in some cases
583because it has to handle SCCs with more than one node in it. All of the virtual
584methods described below should return true if they modified the program, or
585false if they didn't.</p>
586
587</div>
588
589<!-- _______________________________________________________________________ -->
590<div class="doc_subsubsection">
Devang Patelc20048d2007-01-23 22:56:28 +0000[diff] [blame]591 <a name="doInitialization_scc">The <tt>doInitialization(CallGraph &amp;)</tt>
Chris Lattner8fdb2462004-09-18 06:39:35 +0000[diff] [blame]592 method</a>
593</div>
594
595<div class="doc_text">
596
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]597<div class="doc_code"><pre>
Devang Patelc20048d2007-01-23 22:56:28 +0000[diff] [blame]598 <b>virtual bool</b> doInitialization(CallGraph &amp;CG);
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]599</pre></div>
Chris Lattner8fdb2462004-09-18 06:39:35 +0000[diff] [blame]600
601<p>The <tt>doIninitialize</tt> method is allowed to do most of the things that
602<tt>CallGraphSCCPass</tt>'s are not allowed to do. They can add and remove
603functions, get pointers to functions, etc. The <tt>doInitialization</tt> method
604is designed to do simple initialization type of stuff that does not depend on
605the SCCs being processed. The <tt>doInitialization</tt> method call is not
606scheduled to overlap with any other pass executions (thus it should be very
607fast).</p>
608
609</div>
610
611<!-- _______________________________________________________________________ -->
612<div class="doc_subsubsection">
613 <a name="runOnSCC">The <tt>runOnSCC</tt> method</a>
614</div>
615
616<div class="doc_text">
617
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]618<div class="doc_code"><pre>
Chris Lattner6f25d9f2010-04-16 23:07:44 +0000[diff] [blame]619 <b>virtual bool</b> runOnSCC(CallGraphSCC &amp;SCC) = 0;
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]620</pre></div>
Chris Lattner8fdb2462004-09-18 06:39:35 +0000[diff] [blame]621
622<p>The <tt>runOnSCC</tt> method performs the interesting work of the pass, and
623should return true if the module was modified by the transformation, false
624otherwise.</p>
625
626</div>
627
628<!-- _______________________________________________________________________ -->
629<div class="doc_subsubsection">
Devang Patelc20048d2007-01-23 22:56:28 +0000[diff] [blame]630 <a name="doFinalization_scc">The <tt>doFinalization(CallGraph
Chris Lattner8fdb2462004-09-18 06:39:35 +0000[diff] [blame]631 &amp;)</tt> method</a>
632</div>
633
634<div class="doc_text">
635
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]636<div class="doc_code"><pre>
Devang Patelc20048d2007-01-23 22:56:28 +0000[diff] [blame]637 <b>virtual bool</b> doFinalization(CallGraph &amp;CG);
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]638</pre></div>
Chris Lattner8fdb2462004-09-18 06:39:35 +0000[diff] [blame]639
640<p>The <tt>doFinalization</tt> method is an infrequently used method that is
641called when the pass framework has finished calling <a
642href="#runOnFunction"><tt>runOnFunction</tt></a> for every function in the
643program being compiled.</p>
644
645</div>
646
647<!-- ======================================================================= -->
648<div class="doc_subsection">
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]649 <a name="FunctionPass">The <tt>FunctionPass</tt> class</a>
650</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]651
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]652<div class="doc_text">
653
Chris Lattnerf6278922004-09-20 04:36:29 +0000[diff] [blame]654<p>In contrast to <tt>ModulePass</tt> subclasses, <tt><a
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]655href="http://llvm.org/doxygen/classllvm_1_1Pass.html">FunctionPass</a></tt>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]656subclasses do have a predictable, local behavior that can be expected by the
657system. All <tt>FunctionPass</tt> execute on each function in the program
Misha Brukmanef6a6a62003-08-21 22:14:26 +0000[diff] [blame]658independent of all of the other functions in the program.
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]659<tt>FunctionPass</tt>'s do not require that they are executed in a particular
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]660order, and <tt>FunctionPass</tt>'s do not modify external functions.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]661
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]662<p>To be explicit, <tt>FunctionPass</tt> subclasses are not allowed to:</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]663
664<ol>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]665<li>Modify a Function other than the one currently being processed.</li>
666<li>Add or remove Function's from the current Module.</li>
667<li>Add or remove global variables from the current Module.</li>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]668<li>Maintain state across invocations of
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]669 <a href="#runOnFunction"><tt>runOnFunction</tt></a> (including global data)</li>
670</ol>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]671
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]672<p>Implementing a <tt>FunctionPass</tt> is usually straightforward (See the <a
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]673href="#basiccode">Hello World</a> pass for example). <tt>FunctionPass</tt>'s
674may overload three virtual methods to do their work. All of these methods
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]675should return true if they modified the program, or false if they didn't.</p>
676
677</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]678
679<!-- _______________________________________________________________________ -->
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]680<div class="doc_subsubsection">
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]681 <a name="doInitialization_mod">The <tt>doInitialization(Module &amp;)</tt>
682 method</a>
683</div>
684
685<div class="doc_text">
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]686
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]687<div class="doc_code"><pre>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]688 <b>virtual bool</b> doInitialization(Module &amp;M);
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]689</pre></div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]690
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]691<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]692<tt>FunctionPass</tt>'s are not allowed to do. They can add and remove
Chris Lattnerd0713f92002-09-12 17:06:43 +0000[diff] [blame]693functions, get pointers to functions, etc. The <tt>doInitialization</tt> method
694is designed to do simple initialization type of stuff that does not depend on
695the functions being processed. The <tt>doInitialization</tt> method call is not
696scheduled to overlap with any other pass executions (thus it should be very
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]697fast).</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]698
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]699<p>A good example of how this method should be used is the <a
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]700href="http://llvm.org/doxygen/LowerAllocations_8cpp-source.html">LowerAllocations</a>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]701pass. This pass converts <tt>malloc</tt> and <tt>free</tt> instructions into
Misha Brukmanef6a6a62003-08-21 22:14:26 +0000[diff] [blame]702platform dependent <tt>malloc()</tt> and <tt>free()</tt> function calls. It
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]703uses the <tt>doInitialization</tt> method to get a reference to the malloc and
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]704free functions that it needs, adding prototypes to the module if necessary.</p>
705
706</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]707
708<!-- _______________________________________________________________________ -->
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]709<div class="doc_subsubsection">
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]710 <a name="runOnFunction">The <tt>runOnFunction</tt> method</a>
711</div>
712
713<div class="doc_text">
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]714
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]715<div class="doc_code"><pre>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]716 <b>virtual bool</b> runOnFunction(Function &amp;F) = 0;
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]717</pre></div><p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]718
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]719<p>The <tt>runOnFunction</tt> method must be implemented by your subclass to do
720the transformation or analysis work of your pass. As usual, a true value should
721be returned if the function is modified.</p>
722
723</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]724
725<!-- _______________________________________________________________________ -->
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]726<div class="doc_subsubsection">
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]727 <a name="doFinalization_mod">The <tt>doFinalization(Module
728 &amp;)</tt> method</a>
729</div>
730
731<div class="doc_text">
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]732
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]733<div class="doc_code"><pre>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]734 <b>virtual bool</b> doFinalization(Module &amp;M);
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]735</pre></div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]736
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]737<p>The <tt>doFinalization</tt> method is an infrequently used method that is
738called when the pass framework has finished calling <a
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]739href="#runOnFunction"><tt>runOnFunction</tt></a> for every function in the
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]740program being compiled.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]741
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]742</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]743
744<!-- ======================================================================= -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]745<div class="doc_subsection">
Devang Patel2e8f27d2007-03-19 22:21:25 +0000[diff] [blame]746 <a name="LoopPass">The <tt>LoopPass</tt> class </a>
747</div>
748
749<div class="doc_text">
750
751<p> All <tt>LoopPass</tt> execute on each loop in the function independent of
752all of the other loops in the function. <tt>LoopPass</tt> processes loops in
753loop nest order such that outer most loop is processed last. </p>
754
755<p> <tt>LoopPass</tt> subclasses are allowed to update loop nest using
756<tt>LPPassManager</tt> interface. Implementing a loop pass is usually
Jay Foad71001c92011-04-07 12:41:09 +0000[diff] [blame]757straightforward. <tt>LoopPass</tt>'s may overload three virtual methods to
Devang Patel2e8f27d2007-03-19 22:21:25 +0000[diff] [blame]758do their work. All these methods should return true if they modified the
759program, or false if they didn't. </p>
760</div>
761
762<!-- _______________________________________________________________________ -->
763<div class="doc_subsubsection">
764 <a name="doInitialization_loop">The <tt>doInitialization(Loop *,
765 LPPassManager &amp;)</tt>
766 method</a>
767</div>
768
769<div class="doc_text">
770
771<div class="doc_code"><pre>
772 <b>virtual bool</b> doInitialization(Loop *, LPPassManager &amp;LPM);
773</pre></div>
774
Chris Lattnerb5c87f62007-05-18 05:36:14 +0000[diff] [blame]775<p>The <tt>doInitialization</tt> method is designed to do simple initialization
Devang Patel2e8f27d2007-03-19 22:21:25 +0000[diff] [blame]776type of stuff that does not depend on the functions being processed. The
777<tt>doInitialization</tt> method call is not scheduled to overlap with any
778other pass executions (thus it should be very fast). LPPassManager
779interface should be used to access Function or Module level analysis
780information.</p>
781
782</div>
783
784
785<!-- _______________________________________________________________________ -->
786<div class="doc_subsubsection">
787 <a name="runOnLoop">The <tt>runOnLoop</tt> method</a>
788</div>
789
790<div class="doc_text">
791
792<div class="doc_code"><pre>
793 <b>virtual bool</b> runOnLoop(Loop *, LPPassManager &amp;LPM) = 0;
794</pre></div><p>
795
796<p>The <tt>runOnLoop</tt> method must be implemented by your subclass to do
797the transformation or analysis work of your pass. As usual, a true value should
798be returned if the function is modified. <tt>LPPassManager</tt> interface
799should be used to update loop nest.</p>
800
801</div>
802
803<!-- _______________________________________________________________________ -->
804<div class="doc_subsubsection">
805 <a name="doFinalization_loop">The <tt>doFinalization()</tt> method</a>
806</div>
807
808<div class="doc_text">
809
810<div class="doc_code"><pre>
811 <b>virtual bool</b> doFinalization();
812</pre></div>
813
814<p>The <tt>doFinalization</tt> method is an infrequently used method that is
815called when the pass framework has finished calling <a
816href="#runOnLoop"><tt>runOnLoop</tt></a> for every loop in the
817program being compiled. </p>
818
819</div>
820
Tobias Grosser65513602010-10-20 01:54:44 +0000[diff] [blame]821<!-- ======================================================================= -->
822<div class="doc_subsection">
823 <a name="RegionPass">The <tt>RegionPass</tt> class </a>
824</div>
825
826<div class="doc_text">
827
828<p> <tt>RegionPass</tt> is similar to <a href="#LoopPass"><tt>LoopPass</tt></a>,
829but executes on each single entry single exit region in the function.
830<tt>RegionPass</tt> processes regions in nested order such that the outer most
831region is processed last. </p>
832
833<p> <tt>RegionPass</tt> subclasses are allowed to update the region tree by using
834the <tt>RGPassManager</tt> interface. You may overload three virtual methods of
Jay Foad71001c92011-04-07 12:41:09 +0000[diff] [blame]835<tt>RegionPass</tt> to implement your own region pass. All these
Tobias Grosser65513602010-10-20 01:54:44 +0000[diff] [blame]836methods should return true if they modified the program, or false if they didn not.
837</p>
838</div>
839
840<!-- _______________________________________________________________________ -->
841<div class="doc_subsubsection">
842 <a name="doInitialization_region">The <tt>doInitialization(Region *,
843 RGPassManager &amp;)</tt>
844 method</a>
845</div>
846
847<div class="doc_text">
848
849<div class="doc_code"><pre>
850 <b>virtual bool</b> doInitialization(Region *, RGPassManager &amp;RGM);
851</pre></div>
852
853<p>The <tt>doInitialization</tt> method is designed to do simple initialization
854type of stuff that does not depend on the functions being processed. The
855<tt>doInitialization</tt> method call is not scheduled to overlap with any
856other pass executions (thus it should be very fast). RPPassManager
857interface should be used to access Function or Module level analysis
858information.</p>
859
860</div>
861
862
863<!-- _______________________________________________________________________ -->
864<div class="doc_subsubsection">
865 <a name="runOnRegion">The <tt>runOnRegion</tt> method</a>
866</div>
867
868<div class="doc_text">
869
870<div class="doc_code"><pre>
871 <b>virtual bool</b> runOnRegion(Region *, RGPassManager &amp;RGM) = 0;
872</pre></div><p>
873
874<p>The <tt>runOnRegion</tt> method must be implemented by your subclass to do
875the transformation or analysis work of your pass. As usual, a true value should
876be returned if the region is modified. <tt>RGPassManager</tt> interface
877should be used to update region tree.</p>
878
879</div>
880
881<!-- _______________________________________________________________________ -->
882<div class="doc_subsubsection">
883 <a name="doFinalization_region">The <tt>doFinalization()</tt> method</a>
884</div>
885
886<div class="doc_text">
887
888<div class="doc_code"><pre>
889 <b>virtual bool</b> doFinalization();
890</pre></div>
891
892<p>The <tt>doFinalization</tt> method is an infrequently used method that is
893called when the pass framework has finished calling <a
894href="#runOnRegion"><tt>runOnRegion</tt></a> for every region in the
895program being compiled. </p>
896
897</div>
898
Devang Patel2e8f27d2007-03-19 22:21:25 +0000[diff] [blame]899
900
901<!-- ======================================================================= -->
902<div class="doc_subsection">
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]903 <a name="BasicBlockPass">The <tt>BasicBlockPass</tt> class</a>
904</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]905
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]906<div class="doc_text">
907
908<p><tt>BasicBlockPass</tt>'s are just like <a
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]909href="#FunctionPass"><tt>FunctionPass</tt></a>'s, except that they must limit
910their scope of inspection and modification to a single basic block at a time.
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]911As such, they are <b>not</b> allowed to do any of the following:</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]912
913<ol>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]914<li>Modify or inspect any basic blocks outside of the current one</li>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]915<li>Maintain state across invocations of
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]916 <a href="#runOnBasicBlock"><tt>runOnBasicBlock</tt></a></li>
Reid Spencer1bc19342004-12-11 05:12:57 +0000[diff] [blame]917<li>Modify the control flow graph (by altering terminator instructions)</li>
918<li>Any of the things forbidden for
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]919 <a href="#FunctionPass"><tt>FunctionPass</tt></a>es.</li>
920</ol>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]921
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]922<p><tt>BasicBlockPass</tt>es are useful for traditional local and "peephole"
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]923optimizations. They may override the same <a
Chris Lattnerd0713f92002-09-12 17:06:43 +0000[diff] [blame]924href="#doInitialization_mod"><tt>doInitialization(Module &amp;)</tt></a> and <a
925href="#doFinalization_mod"><tt>doFinalization(Module &amp;)</tt></a> methods that <a
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]926href="#FunctionPass"><tt>FunctionPass</tt></a>'s have, but also have the following virtual methods that may also be implemented:</p>
927
928</div>
Chris Lattnerd0713f92002-09-12 17:06:43 +0000[diff] [blame]929
930<!-- _______________________________________________________________________ -->
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]931<div class="doc_subsubsection">
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]932 <a name="doInitialization_fn">The <tt>doInitialization(Function
933 &amp;)</tt> method</a>
934</div>
935
936<div class="doc_text">
Chris Lattnerd0713f92002-09-12 17:06:43 +0000[diff] [blame]937
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]938<div class="doc_code"><pre>
Chris Lattnerd0713f92002-09-12 17:06:43 +0000[diff] [blame]939 <b>virtual bool</b> doInitialization(Function &amp;F);
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]940</pre></div>
Chris Lattnerd0713f92002-09-12 17:06:43 +0000[diff] [blame]941
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]942<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]943<tt>BasicBlockPass</tt>'s are not allowed to do, but that
944<tt>FunctionPass</tt>'s can. The <tt>doInitialization</tt> method is designed
Reid Spencer1bc19342004-12-11 05:12:57 +0000[diff] [blame]945to do simple initialization that does not depend on the
Chris Lattnerd0713f92002-09-12 17:06:43 +0000[diff] [blame]946BasicBlocks being processed. The <tt>doInitialization</tt> method call is not
947scheduled to overlap with any other pass executions (thus it should be very
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]948fast).</p>
Chris Lattnerd0713f92002-09-12 17:06:43 +0000[diff] [blame]949
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]950</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]951
952<!-- _______________________________________________________________________ -->
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]953<div class="doc_subsubsection">
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]954 <a name="runOnBasicBlock">The <tt>runOnBasicBlock</tt> method</a>
955</div>
956
957<div class="doc_text">
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]958
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]959<div class="doc_code"><pre>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]960 <b>virtual bool</b> runOnBasicBlock(BasicBlock &amp;BB) = 0;
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]961</pre></div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]962
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]963<p>Override this function to do the work of the <tt>BasicBlockPass</tt>. This
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]964function is not allowed to inspect or modify basic blocks other than the
965parameter, and are not allowed to modify the CFG. A true value must be returned
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]966if the basic block is modified.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]967
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]968</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]969
Chris Lattnerd0713f92002-09-12 17:06:43 +0000[diff] [blame]970<!-- _______________________________________________________________________ -->
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]971<div class="doc_subsubsection">
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]972 <a name="doFinalization_fn">The <tt>doFinalization(Function &amp;)</tt>
973 method</a>
974</div>
975
976<div class="doc_text">
Chris Lattnerd0713f92002-09-12 17:06:43 +0000[diff] [blame]977
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]978<div class="doc_code"><pre>
Chris Lattnerd0713f92002-09-12 17:06:43 +0000[diff] [blame]979 <b>virtual bool</b> doFinalization(Function &amp;F);
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]980</pre></div>
Chris Lattnerd0713f92002-09-12 17:06:43 +0000[diff] [blame]981
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]982<p>The <tt>doFinalization</tt> method is an infrequently used method that is
983called when the pass framework has finished calling <a
Chris Lattnerd0713f92002-09-12 17:06:43 +0000[diff] [blame]984href="#runOnBasicBlock"><tt>runOnBasicBlock</tt></a> for every BasicBlock in the
985program being compiled. This can be used to perform per-function
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]986finalization.</p>
Chris Lattnerd0713f92002-09-12 17:06:43 +0000[diff] [blame]987
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]988</div>
Chris Lattnerd0713f92002-09-12 17:06:43 +0000[diff] [blame]989
Brian Gaekecab8b6f2003-07-17 18:53:20 +0000[diff] [blame]990<!-- ======================================================================= -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]991<div class="doc_subsection">
992 <a name="MachineFunctionPass">The <tt>MachineFunctionPass</tt> class</a>
993</div>
Brian Gaekecab8b6f2003-07-17 18:53:20 +0000[diff] [blame]994
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]995<div class="doc_text">
996
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]997<p>A <tt>MachineFunctionPass</tt> is a part of the LLVM code generator that
998executes on the machine-dependent representation of each LLVM function in the
Dan Gohman9f116aa2010-03-10 01:29:39 +0000[diff] [blame]999program.</p>
1000
1001<p>Code generator passes are registered and initialized specially by
1002<tt>TargetMachine::addPassesToEmitFile</tt> and similar routines, so they
1003cannot generally be run from the <tt>opt</tt> or <tt>bugpoint</tt>
1004commands.</p>
1005
1006<p>A <tt>MachineFunctionPass</tt> is also a <tt>FunctionPass</tt>, so all
Brian Gaekecab8b6f2003-07-17 18:53:20 +0000[diff] [blame]1007the restrictions that apply to a <tt>FunctionPass</tt> also apply to it.
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]1008<tt>MachineFunctionPass</tt>es also have additional restrictions. In particular,
1009<tt>MachineFunctionPass</tt>es are not allowed to do any of the following:</p>
Brian Gaekecab8b6f2003-07-17 18:53:20 +0000[diff] [blame]1010
1011<ol>
Dan Gohman9f116aa2010-03-10 01:29:39 +0000[diff] [blame]1012<li>Modify or create any LLVM IR Instructions, BasicBlocks, Arguments,
1013 Functions, GlobalVariables, GlobalAliases, or Modules.</li>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1014<li>Modify a MachineFunction other than the one currently being processed.</li>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1015<li>Maintain state across invocations of <a
1016href="#runOnMachineFunction"><tt>runOnMachineFunction</tt></a> (including global
1017data)</li>
1018</ol>
Brian Gaekecab8b6f2003-07-17 18:53:20 +0000[diff] [blame]1019
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1020</div>
Chris Lattnerd0713f92002-09-12 17:06:43 +0000[diff] [blame]1021
Brian Gaeke6a33f362003-07-22 20:53:20 +0000[diff] [blame]1022<!-- _______________________________________________________________________ -->
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]1023<div class="doc_subsubsection">
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1024 <a name="runOnMachineFunction">The <tt>runOnMachineFunction(MachineFunction
1025 &amp;MF)</tt> method</a>
1026</div>
1027
1028<div class="doc_text">
Brian Gaeke6a33f362003-07-22 20:53:20 +0000[diff] [blame]1029
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1030<div class="doc_code"><pre>
Brian Gaeke6a33f362003-07-22 20:53:20 +0000[diff] [blame]1031 <b>virtual bool</b> runOnMachineFunction(MachineFunction &amp;MF) = 0;
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1032</pre></div>
Brian Gaeke6a33f362003-07-22 20:53:20 +0000[diff] [blame]1033
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1034<p><tt>runOnMachineFunction</tt> can be considered the main entry point of a
1035<tt>MachineFunctionPass</tt>; that is, you should override this method to do the
1036work of your <tt>MachineFunctionPass</tt>.</p>
Brian Gaeke6a33f362003-07-22 20:53:20 +0000[diff] [blame]1037
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1038<p>The <tt>runOnMachineFunction</tt> method is called on every
Brian Gaeke6a33f362003-07-22 20:53:20 +0000[diff] [blame]1039<tt>MachineFunction</tt> in a <tt>Module</tt>, so that the
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1040<tt>MachineFunctionPass</tt> may perform optimizations on the machine-dependent
1041representation of the function. If you want to get at the LLVM <tt>Function</tt>
1042for the <tt>MachineFunction</tt> you're working on, use
1043<tt>MachineFunction</tt>'s <tt>getFunction()</tt> accessor method -- but
1044remember, you may not modify the LLVM <tt>Function</tt> or its contents from a
1045<tt>MachineFunctionPass</tt>.</p>
1046
1047</div>
Brian Gaeke6a33f362003-07-22 20:53:20 +0000[diff] [blame]1048
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1049<!-- *********************************************************************** -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1050<div class="doc_section">
1051 <a name="registration">Pass registration</a>
1052</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1053<!-- *********************************************************************** -->
1054
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1055<div class="doc_text">
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1056
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1057<p>In the <a href="#basiccode">Hello World</a> example pass we illustrated how
1058pass registration works, and discussed some of the reasons that it is used and
1059what it does. Here we discuss how and why passes are registered.</p>
1060
Duncan Sands5e09eef2011-01-01 17:37:07 +0000[diff] [blame]1061<p>As we saw above, passes are registered with the <b><tt>RegisterPass</tt></b>
1062template. The template parameter is the name of the pass that is to be used on
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1063the command line to specify that the pass should be added to a program (for
Duncan Sands5e09eef2011-01-01 17:37:07 +0000[diff] [blame]1064example, with <tt>opt</tt> or <tt>bugpoint</tt>). The first argument is the
Duncan Sands7e7ae5a2010-02-18 14:08:13 +0000[diff] [blame]1065name of the pass, which is to be used for the <tt>-help</tt> output of
Chris Lattnerc8603c22006-08-27 23:18:52 +0000[diff] [blame]1066programs, as
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1067well as for debug output generated by the <tt>--debug-pass</tt> option.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1068
Chris Lattnerc8603c22006-08-27 23:18:52 +0000[diff] [blame]1069<p>If you want your pass to be easily dumpable, you should
1070implement the virtual <tt>print</tt> method:</p>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1071
1072</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1073
1074<!-- _______________________________________________________________________ -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1075<div class="doc_subsubsection">
1076 <a name="print">The <tt>print</tt> method</a>
1077</div>
1078
1079<div class="doc_text">
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1080
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1081<div class="doc_code"><pre>
Torok Edwin52790e52008-10-28 17:29:23 +0000[diff] [blame]1082 <b>virtual void</b> print(std::ostream &amp;O, <b>const</b> Module *M) <b>const</b>;
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1083</pre></div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1084
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1085<p>The <tt>print</tt> method must be implemented by "analyses" in order to print
1086a human readable version of the analysis results. This is useful for debugging
1087an analysis itself, as well as for other people to figure out how an analysis
Chris Lattnerc8603c22006-08-27 23:18:52 +0000[diff] [blame]1088works. Use the <tt>opt -analyze</tt> argument to invoke this method.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1089
Bill Wendling832171c2006-12-07 20:04:42 +0000[diff] [blame]1090<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]1091and 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]1092program that has been analyzed. Note however that this pointer may be null in
1093certain circumstances (such as calling the <tt>Pass::dump()</tt> from a
1094debugger), so it should only be used to enhance debug output, it should not be
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1095depended on.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1096
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1097</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1098
1099<!-- *********************************************************************** -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1100<div class="doc_section">
1101 <a name="interaction">Specifying interactions between passes</a>
1102</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1103<!-- *********************************************************************** -->
1104
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1105<div class="doc_text">
1106
John Criswell8528e782007-12-03 19:34:25 +0000[diff] [blame]1107<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]1108that passes interact with each other correctly. Because <tt>PassManager</tt>
1109tries to <a href="#passmanager">optimize the execution of passes</a> it must
1110know how the passes interact with each other and what dependencies exist between
1111the various passes. To track this, each pass can declare the set of passes that
1112are required to be executed before the current pass, and the passes which are
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1113invalidated by the current pass.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1114
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1115<p>Typically this functionality is used to require that analysis results are
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1116computed before your pass is run. Running arbitrary transformation passes can
1117invalidate the computed analysis results, which is what the invalidation set
1118specifies. If a pass does not implement the <tt><a
1119href="#getAnalysisUsage">getAnalysisUsage</a></tt> method, it defaults to not
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1120having any prerequisite passes, and invalidating <b>all</b> other passes.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1121
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1122</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1123
1124<!-- _______________________________________________________________________ -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1125<div class="doc_subsubsection">
1126 <a name="getAnalysisUsage">The <tt>getAnalysisUsage</tt> method</a>
1127</div>
1128
1129<div class="doc_text">
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1130
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1131<div class="doc_code"><pre>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1132 <b>virtual void</b> getAnalysisUsage(AnalysisUsage &amp;Info) <b>const</b>;
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1133</pre></div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1134
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1135<p>By implementing the <tt>getAnalysisUsage</tt> method, the required and
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1136invalidated sets may be specified for your transformation. The implementation
1137should fill in the <tt><a
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]1138href="http://llvm.org/doxygen/classllvm_1_1AnalysisUsage.html">AnalysisUsage</a></tt>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1139object with information about which passes are required and not invalidated. To
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]1140do this, a pass may call any of the following methods on the AnalysisUsage
1141object:</p>
1142</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1143
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]1144<!-- _______________________________________________________________________ -->
1145<div class="doc_subsubsection">
1146 <a name="AU::addRequired">The <tt>AnalysisUsage::addRequired&lt;&gt;</tt> and <tt>AnalysisUsage::addRequiredTransitive&lt;&gt;</tt> methods</a>
1147</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1148
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]1149<div class="doc_text">
1150<p>
Reid Spencer1bc19342004-12-11 05:12:57 +0000[diff] [blame]1151If your pass requires a previous pass to be executed (an analysis for example),
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]1152it can use one of these methods to arrange for it to be run before your pass.
1153LLVM has many different types of analyses and passes that can be required,
Reid Spencer1bc19342004-12-11 05:12:57 +0000[diff] [blame]1154spanning the range from <tt>DominatorSet</tt> to <tt>BreakCriticalEdges</tt>.
1155Requiring <tt>BreakCriticalEdges</tt>, for example, guarantees that there will
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]1156be no critical edges in the CFG when your pass has been run.
1157</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1158
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]1159<p>
1160Some analyses chain to other analyses to do their job. For example, an <a
1161href="AliasAnalysis.html">AliasAnalysis</a> implementation is required to <a
1162href="AliasAnalysis.html#chaining">chain</a> to other alias analysis passes. In
1163cases where analyses chain, the <tt>addRequiredTransitive</tt> method should be
1164used instead of the <tt>addRequired</tt> method. This informs the PassManager
1165that the transitively required pass should be alive as long as the requiring
1166pass is.
1167</p>
1168</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1169
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]1170<!-- _______________________________________________________________________ -->
1171<div class="doc_subsubsection">
1172 <a name="AU::addPreserved">The <tt>AnalysisUsage::addPreserved&lt;&gt;</tt> method</a>
1173</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1174
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]1175<div class="doc_text">
1176<p>
1177One of the jobs of the PassManager is to optimize how and when analyses are run.
1178In particular, it attempts to avoid recomputing data unless it needs to. For
1179this reason, passes are allowed to declare that they preserve (i.e., they don't
1180invalidate) an existing analysis if it's available. For example, a simple
Reid Spencer1bc19342004-12-11 05:12:57 +0000[diff] [blame]1181constant folding pass would not modify the CFG, so it can't possibly affect the
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]1182results of dominator analysis. By default, all passes are assumed to invalidate
1183all others.
1184</p>
1185
1186<p>
1187The <tt>AnalysisUsage</tt> class provides several methods which are useful in
1188certain circumstances that are related to <tt>addPreserved</tt>. In particular,
1189the <tt>setPreservesAll</tt> method can be called to indicate that the pass does
1190not modify the LLVM program at all (which is true for analyses), and the
1191<tt>setPreservesCFG</tt> method can be used by transformations that change
1192instructions in the program but do not modify the CFG or terminator instructions
1193(note that this property is implicitly set for <a
1194href="#BasicBlockPass">BasicBlockPass</a>'s).
1195</p>
1196
1197<p>
1198<tt>addPreserved</tt> is particularly useful for transformations like
1199<tt>BreakCriticalEdges</tt>. This pass knows how to update a small set of loop
1200and dominator related analyses if they exist, so it can preserve them, despite
1201the fact that it hacks on the CFG.
1202</p>
1203</div>
1204
1205<!-- _______________________________________________________________________ -->
1206<div class="doc_subsubsection">
1207 <a name="AU::examples">Example implementations of <tt>getAnalysisUsage</tt></a>
1208</div>
1209
1210<div class="doc_text">
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1211
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1212<div class="doc_code"><pre>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1213 <i>// This example modifies the program, but does not modify the CFG</i>
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]1214 <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]1215 AU.setPreservesCFG();
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]1216 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]1217 }
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1218</pre></div>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1219
1220</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1221
1222<!-- _______________________________________________________________________ -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1223<div class="doc_subsubsection">
Duncan Sands1465d612009-01-28 13:14:17 +0000[diff] [blame]1224 <a name="getAnalysis">The <tt>getAnalysis&lt;&gt;</tt> and
1225<tt>getAnalysisIfAvailable&lt;&gt;</tt> methods</a>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1226</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1227
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1228<div class="doc_text">
1229
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]1230<p>The <tt>Pass::getAnalysis&lt;&gt;</tt> method is automatically inherited by
1231your class, providing you with access to the passes that you declared that you
1232required with the <a href="#getAnalysisUsage"><tt>getAnalysisUsage</tt></a>
1233method. It takes a single template argument that specifies which pass class you
1234want, and returns a reference to that pass. For example:</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1235
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1236<div class="doc_code"><pre>
Chris Lattnera5776302004-03-17 21:33:32 +0000[diff] [blame]1237 bool LICM::runOnFunction(Function &amp;F) {
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]1238 LoopInfo &amp;LI = getAnalysis&lt;LoopInfo&gt;();
1239 ...
1240 }
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1241</pre></div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1242
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1243<p>This method call returns a reference to the pass desired. You may get a
1244runtime assertion failure if you attempt to get an analysis that you did not
1245declare as required in your <a
1246href="#getAnalysisUsage"><tt>getAnalysisUsage</tt></a> implementation. This
1247method can be called by your <tt>run*</tt> method implementation, or by any
Devang Patel3c1ca0b2007-04-16 21:28:14 +0000[diff] [blame]1248other local method invoked by your <tt>run*</tt> method.
1249
1250A module level pass can use function level analysis info using this interface.
1251For example:</p>
1252
1253<div class="doc_code"><pre>
1254 bool ModuleLevelPass::runOnModule(Module &amp;M) {
1255 ...
Devang Patelf23de112007-04-17 00:17:11 +0000[diff] [blame]1256 DominatorTree &amp;DT = getAnalysis&lt;DominatorTree&gt;(Func);
Devang Patel3c1ca0b2007-04-16 21:28:14 +0000[diff] [blame]1257 ...
1258 }
1259</pre></div>
1260
Chris Lattnerb5c87f62007-05-18 05:36:14 +0000[diff] [blame]1261<p>In above example, runOnFunction for DominatorTree is called by pass manager
Devang Patel3c1ca0b2007-04-16 21:28:14 +0000[diff] [blame]1262before returning a reference to the desired pass.</p>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1263
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]1264<p>
1265If your pass is capable of updating analyses if they exist (e.g.,
1266<tt>BreakCriticalEdges</tt>, as described above), you can use the
Duncan Sands1465d612009-01-28 13:14:17 +0000[diff] [blame]1267<tt>getAnalysisIfAvailable</tt> method, which returns a pointer to the analysis
1268if it is active. For example:</p>
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]1269
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1270<div class="doc_code"><pre>
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]1271 ...
Duncan Sands1465d612009-01-28 13:14:17 +0000[diff] [blame]1272 if (DominatorSet *DS = getAnalysisIfAvailable&lt;DominatorSet&gt;()) {
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]1273 <i>// A DominatorSet is active. This code will update it.</i>
1274 }
1275 ...
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1276</pre></div>
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]1277
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1278</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1279
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1280<!-- *********************************************************************** -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1281<div class="doc_section">
1282 <a name="analysisgroup">Implementing Analysis Groups</a>
1283</div>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1284<!-- *********************************************************************** -->
1285
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1286<div class="doc_text">
1287
Chris Lattnerb7632282007-11-16 05:32:05 +0000[diff] [blame]1288<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]1289used, 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]1290fancier. All of the pass relationships that we have seen so far are very
1291simple: one pass depends on one other specific pass to be run before it can run.
1292For many applications, this is great, for others, more flexibility is
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1293required.</p>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1294
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1295<p>In particular, some analyses are defined such that there is a single simple
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1296interface to the analysis results, but multiple ways of calculating them.
1297Consider alias analysis for example. The most trivial alias analysis returns
1298"may alias" for any alias query. The most sophisticated analysis a
1299flow-sensitive, context-sensitive interprocedural analysis that can take a
1300significant amount of time to execute (and obviously, there is a lot of room
1301between these two extremes for other implementations). To cleanly support
1302situations like this, the LLVM Pass Infrastructure supports the notion of
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1303Analysis Groups.</p>
1304
1305</div>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1306
1307<!-- _______________________________________________________________________ -->
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]1308<div class="doc_subsubsection">
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1309 <a name="agconcepts">Analysis Group Concepts</a>
1310</div>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1311
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1312<div class="doc_text">
1313
1314<p>An Analysis Group is a single simple interface that may be implemented by
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1315multiple different passes. Analysis Groups can be given human readable names
1316just like passes, but unlike passes, they need not derive from the <tt>Pass</tt>
1317class. An analysis group may have one or more implementations, one of which is
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1318the "default" implementation.</p>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1319
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1320<p>Analysis groups are used by client passes just like other passes are: the
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1321<tt>AnalysisUsage::addRequired()</tt> and <tt>Pass::getAnalysis()</tt> methods.
1322In order to resolve this requirement, the <a href="#passmanager">PassManager</a>
1323scans the available passes to see if any implementations of the analysis group
1324are available. If none is available, the default implementation is created for
1325the pass to use. All standard rules for <A href="#interaction">interaction
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1326between passes</a> still apply.</p>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1327
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1328<p>Although <a href="#registration">Pass Registration</a> is optional for normal
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1329passes, all analysis group implementations must be registered, and must use the
Owen Andersond8cc7be2010-07-21 23:07:00 +0000[diff] [blame]1330<A href="#registerag"><tt>INITIALIZE_AG_PASS</tt></a> template to join the
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1331implementation pool. Also, a default implementation of the interface
1332<b>must</b> be registered with <A
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1333href="#registerag"><tt>RegisterAnalysisGroup</tt></a>.</p>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1334
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1335<p>As a concrete example of an Analysis Group in action, consider the <a
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]1336href="http://llvm.org/doxygen/classllvm_1_1AliasAnalysis.html">AliasAnalysis</a>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1337analysis group. The default implementation of the alias analysis interface (the
1338<tt><a
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]1339href="http://llvm.org/doxygen/structBasicAliasAnalysis.html">basicaa</a></tt>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1340pass) just does a few simple checks that don't require significant analysis to
1341compute (such as: two different globals can never alias each other, etc).
1342Passes that use the <tt><a
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]1343href="http://llvm.org/doxygen/classllvm_1_1AliasAnalysis.html">AliasAnalysis</a></tt>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1344interface (for example the <tt><a
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]1345href="http://llvm.org/doxygen/structGCSE.html">gcse</a></tt> pass), do
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1346not care which implementation of alias analysis is actually provided, they just
1347use the designated interface.</p>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1348
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1349<p>From the user's perspective, commands work just like normal. Issuing the
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1350command '<tt>opt -gcse ...</tt>' will cause the <tt>basicaa</tt> class to be
1351instantiated and added to the pass sequence. Issuing the command '<tt>opt
1352-somefancyaa -gcse ...</tt>' will cause the <tt>gcse</tt> pass to use the
1353<tt>somefancyaa</tt> alias analysis (which doesn't actually exist, it's just a
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1354hypothetical example) instead.</p>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1355
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1356</div>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1357
1358<!-- _______________________________________________________________________ -->
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]1359<div class="doc_subsubsection">
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1360 <a name="registerag">Using <tt>RegisterAnalysisGroup</tt></a>
1361</div>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1362
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1363<div class="doc_text">
1364
1365<p>The <tt>RegisterAnalysisGroup</tt> template is used to register the analysis
Owen Andersond8cc7be2010-07-21 23:07:00 +0000[diff] [blame]1366group itself, while the <tt>INITIALIZE_AG_PASS</tt> is used to add pass
1367implementations to the analysis group. First,
1368an analysis group should be registered, with a human readable name
1369provided for it.
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1370Unlike registration of passes, there is no command line argument to be specified
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1371for the Analysis Group Interface itself, because it is "abstract":</p>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1372
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1373<div class="doc_code"><pre>
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]1374 <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]1375</pre></div>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1376
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1377<p>Once the analysis is registered, passes can declare that they are valid
1378implementations of the interface by using the following code:</p>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1379
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1380<div class="doc_code"><pre>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1381<b>namespace</b> {
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1382 //<i> Declare that we implement the AliasAnalysis interface</i>
Owen Andersond8cc7be2010-07-21 23:07:00 +0000[diff] [blame]1383 INITIALIZE_AG_PASS(FancyAA, <a href="http://llvm.org/doxygen/classllvm_1_1AliasAnalysis.html">AliasAnalysis</a>, "<i>somefancyaa</i>",
1384 "<i>A more complex alias analysis implementation</i>",
1385 false, // <i>Is CFG Only?</i>
1386 true, // <i>Is Analysis?</i>
1387 false, // <i>Is default Analysis Group implementation?</i>
1388 );
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1389}
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1390</pre></div>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1391
Owen Andersond8cc7be2010-07-21 23:07:00 +0000[diff] [blame]1392<p>This just shows a class <tt>FancyAA</tt> that
1393uses the <tt>INITIALIZE_AG_PASS</tt> macro both to register and
1394to "join" the <tt><a href="http://llvm.org/doxygen/classllvm_1_1AliasAnalysis.html">AliasAnalysis</a></tt>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1395analysis group. Every implementation of an analysis group should join using
Owen Andersond8cc7be2010-07-21 23:07:00 +0000[diff] [blame]1396this macro.</p>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1397
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1398<div class="doc_code"><pre>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1399<b>namespace</b> {
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1400 //<i> Declare that we implement the AliasAnalysis interface</i>
Owen Andersond8cc7be2010-07-21 23:07:00 +0000[diff] [blame]1401 INITIALIZE_AG_PASS(BasicAA, <a href="http://llvm.org/doxygen/classllvm_1_1AliasAnalysis.html">AliasAnalysis</a>, "<i>basicaa</i>",
1402 "<i>Basic Alias Analysis (default AA impl)</i>",
1403 false, // <i>Is CFG Only?</i>
1404 true, // <i>Is Analysis?</i>
1405 true, // <i>Is default Analysis Group implementation?</i>
1406 );
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1407}
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1408</pre></div>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1409
Owen Andersond8cc7be2010-07-21 23:07:00 +0000[diff] [blame]1410<p>Here we show how the default implementation is specified (using the final
1411argument to the <tt>INITIALIZE_AG_PASS</tt> template). There must be exactly
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1412one default implementation available at all times for an Analysis Group to be
Devang Patel2397f8d2007-06-20 18:51:14 +0000[diff] [blame]1413used. Only default implementation can derive from <tt>ImmutablePass</tt>.
1414Here we declare that the
1415 <tt><a href="http://llvm.org/doxygen/structBasicAliasAnalysis.html">BasicAliasAnalysis</a></tt>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1416pass is the default implementation for the interface.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1417
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1418</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1419
1420<!-- *********************************************************************** -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1421<div class="doc_section">
Tanya Lattnerd5383652004-11-19 01:25:14 +0000[diff] [blame]1422 <a name="passStatistics">Pass Statistics</a>
1423</div>
1424<!-- *********************************************************************** -->
1425
1426<div class="doc_text">
Tanya Lattner05f8d5f2004-11-19 01:26:37 +0000[diff] [blame]1427<p>The <a
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]1428href="http://llvm.org/doxygen/Statistic_8h-source.html"><tt>Statistic</tt></a>
John Criswell0b1010e2005-11-28 23:25:41 +0000[diff] [blame]1429class is designed to be an easy way to expose various success
Tanya Lattnerd5383652004-11-19 01:25:14 +0000[diff] [blame]1430metrics from passes. These statistics are printed at the end of a
1431run, when the -stats command line option is enabled on the command
Tanya Lattner05f8d5f2004-11-19 01:26:37 +0000[diff] [blame]1432line. 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]1433
1434</div>
1435
1436
1437<!-- *********************************************************************** -->
1438<div class="doc_section">
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1439 <a name="passmanager">What PassManager does</a>
1440</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1441<!-- *********************************************************************** -->
1442
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1443<div class="doc_text">
1444
1445<p>The <a
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]1446href="http://llvm.org/doxygen/PassManager_8h-source.html"><tt>PassManager</tt></a>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1447<a
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]1448href="http://llvm.org/doxygen/classllvm_1_1PassManager.html">class</a>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1449takes a list of passes, ensures their <a href="#interaction">prerequisites</a>
1450are set up correctly, and then schedules passes to run efficiently. All of the
1451LLVM tools that run passes use the <tt>PassManager</tt> for execution of these
1452passes.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1453
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1454<p>The <tt>PassManager</tt> does two main things to try to reduce the execution
1455time of a series of passes:</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1456
1457<ol>
1458<li><b>Share analysis results</b> - The PassManager attempts to avoid
1459recomputing analysis results as much as possible. This means keeping track of
1460which analyses are available already, which analyses get invalidated, and which
1461analyses are needed to be run for a pass. An important part of work is that the
1462<tt>PassManager</tt> tracks the exact lifetime of all analysis results, allowing
1463it to <a href="#releaseMemory">free memory</a> allocated to holding analysis
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1464results as soon as they are no longer needed.</li>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1465
1466<li><b>Pipeline the execution of passes on the program</b> - The
1467<tt>PassManager</tt> attempts to get better cache and memory usage behavior out
1468of a series of passes by pipelining the passes together. This means that, given
Duncan Sandsab4c3662011-02-15 09:23:02 +0000[diff] [blame]1469a series of consecutive <a href="#FunctionPass"><tt>FunctionPass</tt></a>'s, it
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1470will execute all of the <a href="#FunctionPass"><tt>FunctionPass</tt></a>'s on
1471the first function, then all of the <a
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1472href="#FunctionPass"><tt>FunctionPass</tt></a>es on the second function,
1473etc... until the entire program has been run through the passes.
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1474
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1475<p>This improves the cache behavior of the compiler, because it is only touching
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1476the LLVM program representation for a single function at a time, instead of
1477traversing the entire program. It reduces the memory consumption of compiler,
1478because, for example, only one <a
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]1479href="http://llvm.org/doxygen/classllvm_1_1DominatorSet.html"><tt>DominatorSet</tt></a>
John Criswell9795bb82007-12-10 20:26:29 +0000[diff] [blame]1480needs to be calculated at a time. This also makes it possible to implement
1481some <a
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1482href="#SMP">interesting enhancements</a> in the future.</p></li>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1483
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1484</ol>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1485
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1486<p>The effectiveness of the <tt>PassManager</tt> is influenced directly by how
1487much information it has about the behaviors of the passes it is scheduling. For
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1488example, the "preserved" set is intentionally conservative in the face of an
1489unimplemented <a href="#getAnalysisUsage"><tt>getAnalysisUsage</tt></a> method.
1490Not implementing when it should be implemented will have the effect of not
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1491allowing any analysis results to live across the execution of your pass.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1492
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1493<p>The <tt>PassManager</tt> class exposes a <tt>--debug-pass</tt> command line
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1494options that is useful for debugging pass execution, seeing how things work, and
1495diagnosing when you should be preserving more analyses than you currently are
1496(To get information about all of the variants of the <tt>--debug-pass</tt>
Duncan Sands7e7ae5a2010-02-18 14:08:13 +0000[diff] [blame]1497option, just type '<tt>opt -help-hidden</tt>').</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1498
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1499<p>By using the <tt>--debug-pass=Structure</tt> option, for example, we can see
1500how our <a href="#basiccode">Hello World</a> pass interacts with other passes.
1501Lets try it out with the <tt>gcse</tt> and <tt>licm</tt> passes:</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1502
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1503<div class="doc_code"><pre>
Duncan Sands67f8a7b2010-07-08 08:27:18 +0000[diff] [blame]1504$ opt -load ../../../Debug+Asserts/lib/Hello.so -gcse -licm --debug-pass=Structure &lt; hello.bc &gt; /dev/null
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1505Module Pass Manager
1506 Function Pass Manager
1507 Dominator Set Construction
1508 Immediate Dominators Construction
1509 Global Common Subexpression Elimination
1510-- Immediate Dominators Construction
1511-- Global Common Subexpression Elimination
1512 Natural Loop Construction
1513 Loop Invariant Code Motion
1514-- Natural Loop Construction
1515-- Loop Invariant Code Motion
1516 Module Verifier
1517-- Dominator Set Construction
1518-- Module Verifier
Gabor Greif04367bf2007-07-06 22:07:22 +0000[diff] [blame]1519 Bitcode Writer
1520--Bitcode Writer
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1521</pre></div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1522
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1523<p>This output shows us when passes are constructed and when the analysis
1524results are known to be dead (prefixed with '<tt>--</tt>'). Here we see that
1525GCSE uses dominator and immediate dominator information to do its job. The LICM
1526pass uses natural loop information, which uses dominator sets, but not immediate
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1527dominators. Because immediate dominators are no longer useful after the GCSE
1528pass, it is immediately destroyed. The dominator sets are then reused to
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1529compute natural loop information, which is then used by the LICM pass.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1530
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1531<p>After the LICM pass, the module verifier runs (which is automatically added
1532by the '<tt>opt</tt>' tool), which uses the dominator set to check that the
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1533resultant LLVM code is well formed. After it finishes, the dominator set
1534information is destroyed, after being computed once, and shared by three
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1535passes.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1536
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1537<p>Lets see how this changes when we run the <a href="#basiccode">Hello
1538World</a> pass in between the two passes:</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1539
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1540<div class="doc_code"><pre>
Duncan Sands67f8a7b2010-07-08 08:27:18 +0000[diff] [blame]1541$ opt -load ../../../Debug+Asserts/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]1542Module Pass Manager
1543 Function Pass Manager
1544 Dominator Set Construction
1545 Immediate Dominators Construction
1546 Global Common Subexpression Elimination
1547<b>-- Dominator Set Construction</b>
1548-- Immediate Dominators Construction
1549-- Global Common Subexpression Elimination
1550<b> Hello World Pass
1551-- Hello World Pass
1552 Dominator Set Construction</b>
1553 Natural Loop Construction
1554 Loop Invariant Code Motion
1555-- Natural Loop Construction
1556-- Loop Invariant Code Motion
1557 Module Verifier
1558-- Dominator Set Construction
1559-- Module Verifier
Gabor Greif04367bf2007-07-06 22:07:22 +0000[diff] [blame]1560 Bitcode Writer
1561--Bitcode Writer
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1562Hello: __main
1563Hello: puts
1564Hello: main
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1565</pre></div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1566
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1567<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]1568Dominator Set pass, even though it doesn't modify the code at all! To fix this,
1569we need to add the following <a
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1570href="#getAnalysisUsage"><tt>getAnalysisUsage</tt></a> method to our pass:</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1571
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1572<div class="doc_code"><pre>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1573 <i>// We don't modify the program, so we preserve all analyses</i>
1574 <b>virtual void</b> getAnalysisUsage(AnalysisUsage &amp;AU) <b>const</b> {
1575 AU.setPreservesAll();
1576 }
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1577</pre></div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1578
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1579<p>Now when we run our pass, we get this output:</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1580
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1581<div class="doc_code"><pre>
Duncan Sands67f8a7b2010-07-08 08:27:18 +0000[diff] [blame]1582$ opt -load ../../../Debug+Asserts/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]1583Pass Arguments: -gcse -hello -licm
1584Module Pass Manager
1585 Function Pass Manager
1586 Dominator Set Construction
1587 Immediate Dominators Construction
1588 Global Common Subexpression Elimination
1589-- Immediate Dominators Construction
1590-- Global Common Subexpression Elimination
1591 Hello World Pass
1592-- Hello World Pass
1593 Natural Loop Construction
1594 Loop Invariant Code Motion
1595-- Loop Invariant Code Motion
1596-- Natural Loop Construction
1597 Module Verifier
1598-- Dominator Set Construction
1599-- Module Verifier
Gabor Greif04367bf2007-07-06 22:07:22 +0000[diff] [blame]1600 Bitcode Writer
1601--Bitcode Writer
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1602Hello: __main
1603Hello: puts
1604Hello: main
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1605</pre></div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1606
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1607<p>Which shows that we don't accidentally invalidate dominator information
1608anymore, and therefore do not have to compute it twice.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1609
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1610</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1611
1612<!-- _______________________________________________________________________ -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1613<div class="doc_subsubsection">
1614 <a name="releaseMemory">The <tt>releaseMemory</tt> method</a>
1615</div>
1616
1617<div class="doc_text">
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1618
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1619<div class="doc_code"><pre>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1620 <b>virtual void</b> releaseMemory();
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1621</pre></div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1622
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1623<p>The <tt>PassManager</tt> automatically determines when to compute analysis
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1624results, and how long to keep them around for. Because the lifetime of the pass
1625object itself is effectively the entire duration of the compilation process, we
1626need some way to free analysis results when they are no longer useful. The
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1627<tt>releaseMemory</tt> virtual method is the way to do this.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1628
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1629<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]1630amount of state (for use by another pass which "requires" your pass and uses the
1631<a href="#getAnalysis">getAnalysis</a> method) you should implement
Dan Gohmand87c9e32009-06-15 18:22:49 +0000[diff] [blame]1632<tt>releaseMemory</tt> to, well, release the memory allocated to maintain this
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1633internal state. This method is called after the <tt>run*</tt> method for the
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1634class, before the next call of <tt>run*</tt> in your pass.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1635
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1636</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1637
1638<!-- *********************************************************************** -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1639<div class="doc_section">
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1640 <a name="registering">Registering dynamically loaded passes</a>
1641</div>
1642<!-- *********************************************************************** -->
1643
1644<div class="doc_text">
1645
1646<p><i>Size matters</i> when constructing production quality tools using llvm,
1647both for the purposes of distribution, and for regulating the resident code size
1648when running on the target system. Therefore, it becomes desirable to
1649selectively use some passes, while omitting others and maintain the flexibility
1650to change configurations later on. You want to be able to do all this, and,
1651provide feedback to the user. This is where pass registration comes into
1652play.</p>
1653
1654<p>The fundamental mechanisms for pass registration are the
1655<tt>MachinePassRegistry</tt> class and subclasses of
1656<tt>MachinePassRegistryNode</tt>.</p>
1657
1658<p>An instance of <tt>MachinePassRegistry</tt> is used to maintain a list of
1659<tt>MachinePassRegistryNode</tt> objects. This instance maintains the list and
1660communicates additions and deletions to the command line interface.</p>
1661
1662<p>An instance of <tt>MachinePassRegistryNode</tt> subclass is used to maintain
1663information provided about a particular pass. This information includes the
1664command line name, the command help string and the address of the function used
1665to create an instance of the pass. A global static constructor of one of these
1666instances <i>registers</i> with a corresponding <tt>MachinePassRegistry</tt>,
1667the static destructor <i>unregisters</i>. Thus a pass that is statically linked
1668in the tool will be registered at start up. A dynamically loaded pass will
1669register on load and unregister at unload.</p>
1670
1671</div>
1672
1673<!-- _______________________________________________________________________ -->
1674<div class="doc_subsection">
1675 <a name="registering_existing">Using existing registries</a>
1676</div>
1677
1678<div class="doc_text">
1679
1680<p>There are predefined registries to track instruction scheduling
1681(<tt>RegisterScheduler</tt>) and register allocation (<tt>RegisterRegAlloc</tt>)
1682machine passes. Here we will describe how to <i>register</i> a register
1683allocator machine pass.</p>
1684
1685<p>Implement your register allocator machine pass. In your register allocator
1686.cpp file add the following include;</p>
1687
1688<div class="doc_code"><pre>
Chris Lattner8f652eb2006-08-11 16:37:02 +0000[diff] [blame]1689 #include "llvm/CodeGen/RegAllocRegistry.h"
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1690</pre></div>
1691
1692<p>Also in your register allocator .cpp file, define a creator function in the
1693form; </p>
1694
1695<div class="doc_code"><pre>
1696 FunctionPass *createMyRegisterAllocator() {
1697 return new MyRegisterAllocator();
1698 }
1699</pre></div>
1700
1701<p>Note that the signature of this function should match the type of
1702<tt>RegisterRegAlloc::FunctionPassCtor</tt>. In the same file add the
1703"installing" declaration, in the form;</p>
1704
1705<div class="doc_code"><pre>
1706 static RegisterRegAlloc myRegAlloc("myregalloc",
1707 " my register allocator help string",
1708 createMyRegisterAllocator);
1709</pre></div>
1710
1711<p>Note the two spaces prior to the help string produces a tidy result on the
Duncan Sands7e7ae5a2010-02-18 14:08:13 +0000[diff] [blame]1712-help query.</p>
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1713
1714<div class="doc_code"><pre>
Duncan Sands7e7ae5a2010-02-18 14:08:13 +0000[diff] [blame]1715$ llc -help
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1716 ...
Duncan Sands18619b22010-02-18 14:37:52 +0000[diff] [blame]1717 -regalloc - Register allocator to use (default=linearscan)
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1718 =linearscan - linear scan register allocator
1719 =local - local register allocator
1720 =simple - simple register allocator
1721 =myregalloc - my register allocator help string
1722 ...
1723</pre></div>
1724
1725<p>And that's it. The user is now free to use <tt>-regalloc=myregalloc</tt> as
1726an option. Registering instruction schedulers is similar except use the
Chris Lattner8f652eb2006-08-11 16:37:02 +0000[diff] [blame]1727<tt>RegisterScheduler</tt> class. Note that the
1728<tt>RegisterScheduler::FunctionPassCtor</tt> is significantly different from
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1729<tt>RegisterRegAlloc::FunctionPassCtor</tt>.</p>
1730
1731<p>To force the load/linking of your register allocator into the llc/lli tools,
1732add your creator function's global declaration to "Passes.h" and add a "pseudo"
1733call line to <tt>llvm/Codegen/LinkAllCodegenComponents.h</tt>.</p>
1734
1735</div>
1736
1737
1738<!-- _______________________________________________________________________ -->
1739<div class="doc_subsection">
1740 <a name="registering_new">Creating new registries</a>
1741</div>
1742
1743<div class="doc_text">
1744
1745<p>The easiest way to get started is to clone one of the existing registries; we
1746recommend <tt>llvm/CodeGen/RegAllocRegistry.h</tt>. The key things to modify
1747are the class name and the <tt>FunctionPassCtor</tt> type.</p>
1748
1749<p>Then you need to declare the registry. Example: if your pass registry is
1750<tt>RegisterMyPasses</tt> then define;</p>
1751
1752<div class="doc_code"><pre>
1753MachinePassRegistry RegisterMyPasses::Registry;
1754</pre></div>
1755
1756<p>And finally, declare the command line option for your passes. Example:</p>
1757
1758<div class="doc_code"><pre>
1759 cl::opt&lt;RegisterMyPasses::FunctionPassCtor, false,
Dan Gohman364a39f2008-10-14 17:00:38 +0000[diff] [blame]1760 RegisterPassParser&lt;RegisterMyPasses&gt; &gt;
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1761 MyPassOpt("mypass",
1762 cl::init(&amp;createDefaultMyPass),
1763 cl::desc("my pass option help"));
1764</pre></div>
1765
1766<p>Here the command option is "mypass", with createDefaultMyPass as the default
1767creator.</p>
1768
1769</div>
1770
1771<!-- *********************************************************************** -->
1772<div class="doc_section">
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1773 <a name="debughints">Using GDB with dynamically loaded passes</a>
1774</div>
Chris Lattner480e2ef2002-09-06 02:02:58 +0000[diff] [blame]1775<!-- *********************************************************************** -->
1776
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1777<div class="doc_text">
1778
1779<p>Unfortunately, using GDB with dynamically loaded passes is not as easy as it
Chris Lattner480e2ef2002-09-06 02:02:58 +0000[diff] [blame]1780should be. First of all, you can't set a breakpoint in a shared object that has
1781not been loaded yet, and second of all there are problems with inlined functions
1782in shared objects. Here are some suggestions to debugging your pass with
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1783GDB.</p>
Chris Lattner480e2ef2002-09-06 02:02:58 +0000[diff] [blame]1784
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1785<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]1786transformation invoked by <tt>opt</tt>, although nothing described here depends
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1787on that.</p>
1788
1789</div>
Chris Lattner480e2ef2002-09-06 02:02:58 +0000[diff] [blame]1790
1791<!-- _______________________________________________________________________ -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1792<div class="doc_subsubsection">
1793 <a name="breakpoint">Setting a breakpoint in your pass</a>
1794</div>
Chris Lattner480e2ef2002-09-06 02:02:58 +0000[diff] [blame]1795
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1796<div class="doc_text">
1797
1798<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]1799
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1800<div class="doc_code"><pre>
Chris Lattner480e2ef2002-09-06 02:02:58 +0000[diff] [blame]1801$ <b>gdb opt</b>
1802GNU gdb 5.0
1803Copyright 2000 Free Software Foundation, Inc.
1804GDB is free software, covered by the GNU General Public License, and you are
1805welcome to change it and/or distribute copies of it under certain conditions.
1806Type "show copying" to see the conditions.
1807There is absolutely no warranty for GDB. Type "show warranty" for details.
1808This GDB was configured as "sparc-sun-solaris2.6"...
1809(gdb)
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1810</pre></div>
Chris Lattner480e2ef2002-09-06 02:02:58 +0000[diff] [blame]1811
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1812<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]1813time to load. Be patient. Since we cannot set a breakpoint in our pass yet
1814(the shared object isn't loaded until runtime), we must execute the process, and
1815have it stop before it invokes our pass, but after it has loaded the shared
1816object. The most foolproof way of doing this is to set a breakpoint in
1817<tt>PassManager::run</tt> and then run the process with the arguments you
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1818want:</p>
Chris Lattner480e2ef2002-09-06 02:02:58 +0000[diff] [blame]1819
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1820<div class="doc_code"><pre>
Reid Spencer22a9e5b2006-09-28 16:53:47 +0000[diff] [blame]1821(gdb) <b>break llvm::PassManager::run</b>
Chris Lattner480e2ef2002-09-06 02:02:58 +0000[diff] [blame]1822Breakpoint 1 at 0x2413bc: file Pass.cpp, line 70.
Duncan Sands67f8a7b2010-07-08 08:27:18 +0000[diff] [blame]1823(gdb) <b>run test.bc -load $(LLVMTOP)/llvm/Debug+Asserts/lib/[libname].so -[passoption]</b>
1824Starting program: opt test.bc -load $(LLVMTOP)/llvm/Debug+Asserts/lib/[libname].so -[passoption]
Chris Lattner480e2ef2002-09-06 02:02:58 +0000[diff] [blame]1825Breakpoint 1, PassManager::run (this=0xffbef174, M=@0x70b298) at Pass.cpp:70
182670 bool PassManager::run(Module &amp;M) { return PM-&gt;run(M); }
1827(gdb)
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1828</pre></div>
Chris Lattner480e2ef2002-09-06 02:02:58 +0000[diff] [blame]1829
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1830<p>Once the <tt>opt</tt> stops in the <tt>PassManager::run</tt> method you are
1831now free to set breakpoints in your pass so that you can trace through execution
1832or do other standard debugging stuff.</p>
Chris Lattner480e2ef2002-09-06 02:02:58 +0000[diff] [blame]1833
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1834</div>
Chris Lattner480e2ef2002-09-06 02:02:58 +0000[diff] [blame]1835
1836<!-- _______________________________________________________________________ -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1837<div class="doc_subsubsection">
1838 <a name="debugmisc">Miscellaneous Problems</a>
1839</div>
Chris Lattner480e2ef2002-09-06 02:02:58 +0000[diff] [blame]1840
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1841<div class="doc_text">
1842
1843<p>Once you have the basics down, there are a couple of problems that GDB has,
1844some with solutions, some without.</p>
Chris Lattner480e2ef2002-09-06 02:02:58 +0000[diff] [blame]1845
1846<ul>
1847<li>Inline functions have bogus stack information. In general, GDB does a
1848pretty good job getting stack traces and stepping through inline functions.
1849When a pass is dynamically loaded however, it somehow completely loses this
1850capability. The only solution I know of is to de-inline a function (move it
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1851from the body of a class to a .cpp file).</li>
Chris Lattner480e2ef2002-09-06 02:02:58 +0000[diff] [blame]1852
1853<li>Restarting the program breaks breakpoints. After following the information
1854above, you have succeeded in getting some breakpoints planted in your pass. Nex
1855thing you know, you restart the program (i.e., you type '<tt>run</tt>' again),
1856and you start getting errors about breakpoints being unsettable. The only way I
1857have found to "fix" this problem is to <tt>delete</tt> the breakpoints that are
1858already set in your pass, run the program, and re-set the breakpoints once
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1859execution stops in <tt>PassManager::run</tt>.</li>
Chris Lattner480e2ef2002-09-06 02:02:58 +0000[diff] [blame]1860
1861</ul>
1862
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1863<p>Hopefully these tips will help with common case debugging situations. If
1864you'd like to contribute some tips of your own, just contact <a
1865href="mailto:sabre@nondot.org">Chris</a>.</p>
Chris Lattner480e2ef2002-09-06 02:02:58 +0000[diff] [blame]1866
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1867</div>
Chris Lattner480e2ef2002-09-06 02:02:58 +0000[diff] [blame]1868
1869<!-- *********************************************************************** -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1870<div class="doc_section">
1871 <a name="future">Future extensions planned</a>
1872</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1873<!-- *********************************************************************** -->
1874
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1875<div class="doc_text">
1876
1877<p>Although the LLVM Pass Infrastructure is very capable as it stands, and does
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1878some 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]1879where we are going:</p>
1880
1881</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1882
1883<!-- _______________________________________________________________________ -->
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]1884<div class="doc_subsubsection">
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1885 <a name="SMP">Multithreaded LLVM</a>
1886</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1887
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1888<div class="doc_text">
1889
1890<p>Multiple CPU machines are becoming more common and compilation can never be
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1891fast enough: obviously we should allow for a multithreaded compiler. Because of
1892the semantics defined for passes above (specifically they cannot maintain state
1893across invocations of their <tt>run*</tt> methods), a nice clean way to
1894implement a multithreaded compiler would be for the <tt>PassManager</tt> class
Misha Brukmanbc0e9982003-07-14 17:20:40 +0000[diff] [blame]1895to create multiple instances of each pass object, and allow the separate
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1896instances to be hacking on different parts of the program at the same time.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1897
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1898<p>This implementation would prevent each of the passes from having to implement
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1899multithreaded constructs, requiring only the LLVM core to have locking in a few
1900places (for global resources). Although this is a simple extension, we simply
1901haven't had time (or multiprocessor machines, thus a reason) to implement this.
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1902Despite that, we have kept the LLVM passes SMP ready, and you should too.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1903
Chris Lattnerb5c87f62007-05-18 05:36:14 +0000[diff] [blame]1904</div>
1905
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1906<!-- *********************************************************************** -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1907<hr>
1908<address>
1909 <a href="http://jigsaw.w3.org/css-validator/check/referer"><img
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Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1911 <a href="http://validator.w3.org/check/referer"><img
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Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1913
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1914 <a href="mailto:sabre@nondot.org">Chris Lattner</a><br>
NAKAMURA Takumib9a33632011-04-09 02:13:37 +0000[diff] [blame]1915 <a href="http://llvm.org/">The LLVM Compiler Infrastructure</a><br>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1916 Last modified: $Date$
1917</address>
1918
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