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gerrit-public.fairphone.software / fp2-dev / platform / external / llvm / 65513605353c7e3ee8be6fc92892f257ad399d92 / . / docs / WritingAnLLVMPass.html
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Reid Spencer7fa6d522005-01-11 05:16:23 +0000[diff] [blame]5 <meta http-equiv="Content-Type" content="text/html; charset=utf-8">
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]6 <title>Writing an LLVM Pass</title>
7 <link rel="stylesheet" href="llvm.css" type="text/css">
8</head>
9<body>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]10
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]11<div class="doc_title">
12 Writing an LLVM Pass
13</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]14
15<ol>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]16 <li><a href="#introduction">Introduction - What is a pass?</a></li>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]17 <li><a href="#quickstart">Quick Start - Writing hello world</a>
18 <ul>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]19 <li><a href="#makefile">Setting up the build environment</a></li>
20 <li><a href="#basiccode">Basic code required</a></li>
Chris Lattnerc8603c22006-08-27 23:18:52 +0000[diff] [blame]21 <li><a href="#running">Running a pass with <tt>opt</tt></a></li>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]22 </ul></li>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]23 <li><a href="#passtype">Pass classes and requirements</a>
24 <ul>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]25 <li><a href="#ImmutablePass">The <tt>ImmutablePass</tt> class</a></li>
Chris Lattnerf6278922004-09-20 04:36:29 +0000[diff] [blame]26 <li><a href="#ModulePass">The <tt>ModulePass</tt> class</a>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]27 <ul>
Chris Lattnerf6278922004-09-20 04:36:29 +0000[diff] [blame]28 <li><a href="#runOnModule">The <tt>runOnModule</tt> method</a></li>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]29 </ul></li>
Chris Lattner8fdb2462004-09-18 06:39:35 +0000[diff] [blame]30 <li><a href="#CallGraphSCCPass">The <tt>CallGraphSCCPass</tt> class</a>
31 <ul>
Devang Patelc20048d2007-01-23 22:56:28 +0000[diff] [blame]32 <li><a href="#doInitialization_scc">The <tt>doInitialization(CallGraph
Chris Lattner8fdb2462004-09-18 06:39:35 +0000[diff] [blame]33 &amp;)</tt> method</a></li>
34 <li><a href="#runOnSCC">The <tt>runOnSCC</tt> method</a></li>
Devang Patelc20048d2007-01-23 22:56:28 +0000[diff] [blame]35 <li><a href="#doFinalization_scc">The <tt>doFinalization(CallGraph
Chris Lattner8fdb2462004-09-18 06:39:35 +0000[diff] [blame]36 &amp;)</tt> method</a></li>
37 </ul></li>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]38 <li><a href="#FunctionPass">The <tt>FunctionPass</tt> class</a>
39 <ul>
Chris Lattnerd0713f92002-09-12 17:06:43 +0000[diff] [blame]40 <li><a href="#doInitialization_mod">The <tt>doInitialization(Module
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]41 &amp;)</tt> method</a></li>
42 <li><a href="#runOnFunction">The <tt>runOnFunction</tt> method</a></li>
Chris Lattnerd0713f92002-09-12 17:06:43 +0000[diff] [blame]43 <li><a href="#doFinalization_mod">The <tt>doFinalization(Module
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]44 &amp;)</tt> method</a></li>
45 </ul></li>
Devang Patel2e8f27d2007-03-19 22:21:25 +0000[diff] [blame]46 <li><a href="#LoopPass">The <tt>LoopPass</tt> class</a>
47 <ul>
48 <li><a href="#doInitialization_loop">The <tt>doInitialization(Loop *,
49 LPPassManager &amp;)</tt> method</a></li>
50 <li><a href="#runOnLoop">The <tt>runOnLoop</tt> method</a></li>
51 <li><a href="#doFinalization_loop">The <tt>doFinalization()
52 </tt> method</a></li>
53 </ul></li>
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
Reid Spencer1bc19342004-12-11 05:12:57 +0000[diff] [blame]181 <p>First, you need to create a new directory somewhere in the LLVM source
182 base. For this example, we'll assume that you made
183 <tt>lib/Transforms/Hello</tt>. Next, you must set up a build script
184 (Makefile) that will compile the source code for the new pass. To do this,
185 copy the following into <tt>Makefile</tt>:</p>
186 <hr/>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]187
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]188<div class="doc_code"><pre>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]189# Makefile for hello pass
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]190
Torok Edwin87469292009-10-12 13:37:29 +0000[diff] [blame]191# Path to top level of LLVM hierarchy
Chris Lattner7ce83e52002-08-14 20:07:01 +0000[diff] [blame]192LEVEL = ../../..
Chris Lattner17a4c3e2002-08-14 20:06:13 +0000[diff] [blame]193
194# Name of the library to build
Reid Spencer7fa6d522005-01-11 05:16:23 +0000[diff] [blame]195LIBRARYNAME = Hello
Chris Lattner17a4c3e2002-08-14 20:06:13 +0000[diff] [blame]196
Reid Spencer7fa6d522005-01-11 05:16:23 +0000[diff] [blame]197# Make the shared library become a loadable module so the tools can
198# dlopen/dlsym on the resulting library.
Robert Bocchino3cf817d2006-01-06 22:49:23 +0000[diff] [blame]199LOADABLE_MODULE = 1
Reid Spencer7fa6d522005-01-11 05:16:23 +0000[diff] [blame]200
Chris Lattner17a4c3e2002-08-14 20:06:13 +0000[diff] [blame]201# Include the makefile implementation stuff
202include $(LEVEL)/Makefile.common
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]203</pre></div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]204
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]205<p>This makefile specifies that all of the <tt>.cpp</tt> files in the current
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]206directory are to be compiled and linked together into a
Duncan Sands67f8a7b2010-07-08 08:27:18 +0000[diff] [blame]207<tt>Debug+Asserts/lib/Hello.so</tt> shared object that can be dynamically loaded by
Chris Lattnerc8603c22006-08-27 23:18:52 +0000[diff] [blame]208the <tt>opt</tt> or <tt>bugpoint</tt> tools via their <tt>-load</tt> options.
Reid Spencer7fa6d522005-01-11 05:16:23 +0000[diff] [blame]209If your operating system uses a suffix other than .so (such as windows or
210Mac OS/X), the appropriate extension will be used.</p>
John Criswellf9c78652004-01-26 21:26:54 +0000[diff] [blame]211
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]212<p>Now that we have the build scripts set up, we just need to write the code for
213the pass itself.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]214
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]215</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]216
217<!-- ======================================================================= -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]218<div class="doc_subsection">
219 <a name="basiccode">Basic code required</a>
220</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]221
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]222<div class="doc_text">
223
224<p>Now that we have a way to compile our new pass, we just have to write it.
225Start out with:</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]226
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]227<div class="doc_code"><pre>
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]228<b>#include</b> "<a href="http://llvm.org/doxygen/Pass_8h-source.html">llvm/Pass.h</a>"
229<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]230<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]231</pre></div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]232
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]233<p>Which are needed because we are writing a <tt><a
Chris Lattner0ce6f932009-09-08 05:14:44 +0000[diff] [blame]234href="http://llvm.org/doxygen/classllvm_1_1Pass.html">Pass</a></tt>,
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]235we are operating on <tt><a
Chris Lattner0ce6f932009-09-08 05:14:44 +0000[diff] [blame]236href="http://llvm.org/doxygen/classllvm_1_1Function.html">Function</a></tt>'s,
237and we will be doing some printing.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]238
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]239<p>Next we have:</p>
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]240<div class="doc_code"><pre>
Jonathan Manton65acb302004-06-30 18:10:30 +0000[diff] [blame]241<b>using namespace llvm;</b>
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]242</pre></div>
Jonathan Manton65acb302004-06-30 18:10:30 +0000[diff] [blame]243<p>... which is required because the functions from the include files
244live in the llvm namespace.
245</p>
246
247<p>Next we have:</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]248
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]249<div class="doc_code"><pre>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]250<b>namespace</b> {
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]251</pre></div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]252
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]253<p>... which starts out an anonymous namespace. Anonymous namespaces are to C++
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]254what the "<tt>static</tt>" keyword is to C (at global scope). It makes the
255things declared inside of the anonymous namespace only visible to the current
256file. If you're not familiar with them, consult a decent C++ book for more
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]257information.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]258
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]259<p>Next, we declare our pass itself:</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]260
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]261<div class="doc_code"><pre>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]262 <b>struct</b> Hello : <b>public</b> <a href="#FunctionPass">FunctionPass</a> {
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]263</pre></div><p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]264
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]265<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]266href="http://llvm.org/doxygen/classllvm_1_1FunctionPass.html">FunctionPass</a></tt>.
Chris Lattnerd6ea9262002-09-09 03:48:46 +0000[diff] [blame]267The different builtin pass subclasses are described in detail <a
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]268href="#passtype">later</a>, but for now, know that <a
269href="#FunctionPass"><tt>FunctionPass</tt></a>'s operate a function at a
270time.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]271
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]272<div class="doc_code"><pre>
Devang Patel19974732007-05-03 01:11:54 +0000[diff] [blame]273 static char ID;
Dan Gohman865f0062009-02-18 05:09:16 +0000[diff] [blame]274 Hello() : FunctionPass(&amp;ID) {}
Devang Patele50fb9a2007-05-01 20:55:38 +0000[diff] [blame]275</pre></div><p>
276
277<p> This declares pass identifier used by LLVM to identify pass. This allows LLVM to
278avoid using expensive C++ runtime information.</p>
279
280<div class="doc_code"><pre>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]281 <b>virtual bool</b> <a href="#runOnFunction">runOnFunction</a>(Function &amp;F) {
Chris Lattner0ce6f932009-09-08 05:14:44 +0000[diff] [blame]282 errs() &lt;&lt; "<i>Hello: </i>" &lt;&lt; F.getName() &lt;&lt; "\n";
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]283 <b>return false</b>;
284 }
285 }; <i>// end of struct Hello</i>
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]286</pre></div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]287
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]288<p>We declare a "<a href="#runOnFunction"><tt>runOnFunction</tt></a>" method,
289which overloads an abstract virtual method inherited from <a
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]290href="#FunctionPass"><tt>FunctionPass</tt></a>. This is where we are supposed
291to 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]292function.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]293
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]294<div class="doc_code"><pre>
Devang Patel19974732007-05-03 01:11:54 +0000[diff] [blame]295 char Hello::ID = 0;
Devang Patele50fb9a2007-05-01 20:55:38 +0000[diff] [blame]296</pre></div>
297
298<p> We initialize pass ID here. LLVM uses ID's address to identify pass so
299initialization value is not important.</p>
300
301<div class="doc_code"><pre>
Owen Anderson20813e02010-07-21 22:58:07 +0000[diff] [blame]302 INITIALIZE_PASS(Hello, "<i>hello</i>", "<i>Hello World Pass</i>",
Devang Patelc7582092008-03-19 21:56:59 +0000[diff] [blame]303 false /* Only looks at CFG */,
304 false /* Analysis Pass */);
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]305} <i>// end of anonymous namespace</i>
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]306</pre></div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]307
Chris Lattnerc8603c22006-08-27 23:18:52 +0000[diff] [blame]308<p>Lastly, we <a href="#registration">register our class</a> <tt>Hello</tt>,
309giving it a command line
Devang Patelc7582092008-03-19 21:56:59 +0000[diff] [blame]310argument "<tt>hello</tt>", and a name "<tt>Hello World Pass</tt>".
Owen Anderson20813e02010-07-21 22:58:07 +0000[diff] [blame]311Last two arguments describe its behavior.
Devang Patelc7582092008-03-19 21:56:59 +0000[diff] [blame]312If a pass walks CFG without modifying it then third argument is set to true.
313If a pass is an analysis pass, for example dominator tree pass, then true
314is supplied as fourth argument. </p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]315
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]316<p>As a whole, the <tt>.cpp</tt> file looks like:</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]317
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]318<div class="doc_code"><pre>
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]319<b>#include</b> "<a href="http://llvm.org/doxygen/Pass_8h-source.html">llvm/Pass.h</a>"
320<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]321<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]322
Jonathan Manton65acb302004-06-30 18:10:30 +0000[diff] [blame]323<b>using namespace llvm;</b>
324
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]325<b>namespace</b> {
326 <b>struct Hello</b> : <b>public</b> <a href="#FunctionPass">FunctionPass</a> {
Devang Patele50fb9a2007-05-01 20:55:38 +0000[diff] [blame]327
Devang Patel19974732007-05-03 01:11:54 +0000[diff] [blame]328 static char ID;
Dan Gohman865f0062009-02-18 05:09:16 +0000[diff] [blame]329 Hello() : FunctionPass(&amp;ID) {}
Devang Patele50fb9a2007-05-01 20:55:38 +0000[diff] [blame]330
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]331 <b>virtual bool</b> <a href="#runOnFunction">runOnFunction</a>(Function &amp;F) {
Chris Lattner0ce6f932009-09-08 05:14:44 +0000[diff] [blame]332 errs() &lt;&lt; "<i>Hello: </i>" &lt;&lt; F.getName() &lt;&lt; "\n";
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]333 <b>return false</b>;
334 }
335 };
336
Devang Patel26e5a302007-07-25 21:05:39 +0000[diff] [blame]337 char Hello::ID = 0;
Owen Anderson20813e02010-07-21 22:58:07 +0000[diff] [blame]338 INITIALIZE_PASS(Hello, "<i>Hello</i>", "<i>Hello World Pass</i>", false, false);
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]339}
Owen Anderson20813e02010-07-21 22:58:07 +0000[diff] [blame]340
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]341</pre></div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]342
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]343<p>Now that it's all together, compile the file with a simple "<tt>gmake</tt>"
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]344command in the local directory and you should get a new
Duncan Sands67f8a7b2010-07-08 08:27:18 +0000[diff] [blame]345"<tt>Debug+Asserts/lib/Hello.so</tt> file. Note that everything in this file is
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]346contained in an anonymous namespace: this reflects the fact that passes are self
347contained units that do not need external interfaces (although they can have
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]348them) to be useful.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]349
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]350</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]351
352<!-- ======================================================================= -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]353<div class="doc_subsection">
Chris Lattnerc8603c22006-08-27 23:18:52 +0000[diff] [blame]354 <a name="running">Running a pass with <tt>opt</tt></a>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]355</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]356
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]357<div class="doc_text">
358
John Criswellf9c78652004-01-26 21:26:54 +0000[diff] [blame]359<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]360<tt>opt</tt> command to run an LLVM program through your pass. Because you
Owen Anderson20813e02010-07-21 22:58:07 +0000[diff] [blame]361registered your pass with the <tt>INITIALIZE_PASS</tt> macro, you will be able to
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]362use the <tt>opt</tt> tool to access it, once loaded.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]363
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]364<p>To test it, follow the example at the end of the <a
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]365href="GettingStarted.html">Getting Started Guide</a> to compile "Hello World" to
Gabor Greif04367bf2007-07-06 22:07:22 +0000[diff] [blame]366LLVM. We can now run the bitcode file (<tt>hello.bc</tt>) for the program
367through our transformation like this (or course, any bitcode file will
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]368work):</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]369
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]370<div class="doc_code"><pre>
Duncan Sands67f8a7b2010-07-08 08:27:18 +0000[diff] [blame]371$ opt -load ../../../Debug+Asserts/lib/Hello.so -hello &lt; hello.bc &gt; /dev/null
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]372Hello: __main
373Hello: puts
374Hello: main
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]375</pre></div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]376
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]377<p>The '<tt>-load</tt>' option specifies that '<tt>opt</tt>' should load your
378pass as a shared object, which makes '<tt>-hello</tt>' a valid command line
379argument (which is one reason you need to <a href="#registration">register your
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]380pass</a>). Because the hello pass does not modify the program in any
381interesting way, we just throw away the result of <tt>opt</tt> (sending it to
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]382<tt>/dev/null</tt>).</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]383
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]384<p>To see what happened to the other string you registered, try running
Duncan Sands7e7ae5a2010-02-18 14:08:13 +0000[diff] [blame]385<tt>opt</tt> with the <tt>-help</tt> option:</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]386
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]387<div class="doc_code"><pre>
Duncan Sands67f8a7b2010-07-08 08:27:18 +0000[diff] [blame]388$ opt -load ../../../Debug+Asserts/lib/Hello.so -help
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]389OVERVIEW: llvm .bc -&gt; .bc modular optimizer
390
Gabor Greif04367bf2007-07-06 22:07:22 +0000[diff] [blame]391USAGE: opt [options] &lt;input bitcode&gt;
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]392
393OPTIONS:
394 Optimizations available:
395...
396 -funcresolve - Resolve Functions
397 -gcse - Global Common Subexpression Elimination
398 -globaldce - Dead Global Elimination
399 <b>-hello - Hello World Pass</b>
Chris Lattner065a6162003-09-10 05:29:43 +0000[diff] [blame]400 -indvars - Canonicalize Induction Variables
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]401 -inline - Function Integration/Inlining
402 -instcombine - Combine redundant instructions
403...
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]404</pre></div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]405
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]406<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]407documentation to users of <tt>opt</tt>. Now that you have a working pass, you
408would go ahead and make it do the cool transformations you want. Once you get
409it all working and tested, it may become useful to find out how fast your pass
410is. The <a href="#passManager"><tt>PassManager</tt></a> provides a nice command
411line option (<tt>--time-passes</tt>) that allows you to get information about
412the execution time of your pass along with the other passes you queue up. For
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]413example:</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]414
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]415<div class="doc_code"><pre>
Duncan Sands67f8a7b2010-07-08 08:27:18 +0000[diff] [blame]416$ 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]417Hello: __main
418Hello: puts
419Hello: main
420===============================================================================
421 ... Pass execution timing report ...
422===============================================================================
423 Total Execution Time: 0.02 seconds (0.0479059 wall clock)
424
425 ---User Time--- --System Time-- --User+System-- ---Wall Time--- --- Pass Name ---
Gabor Greif04367bf2007-07-06 22:07:22 +0000[diff] [blame]426 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]427 0.0000 ( 0.0%) 0.0100 (100.0%) 0.0100 ( 50.0%) 0.0031 ( 6.4%) Dominator Set Construction
428 0.0000 ( 0.0%) 0.0000 ( 0.0%) 0.0000 ( 0.0%) 0.0013 ( 2.7%) Module Verifier
429 <b> 0.0000 ( 0.0%) 0.0000 ( 0.0%) 0.0000 ( 0.0%) 0.0033 ( 6.9%) Hello World Pass</b>
430 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]431</pre></div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]432
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]433<p>As you can see, our implementation above is pretty fast :). The additional
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]434passes listed are automatically inserted by the '<tt>opt</tt>' tool to verify
435that the LLVM emitted by your pass is still valid and well formed LLVM, which
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]436hasn't been broken somehow.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]437
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]438<p>Now that you have seen the basics of the mechanics behind passes, we can talk
439about some more details of how they work and how to use them.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]440
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]441</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]442
443<!-- *********************************************************************** -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]444<div class="doc_section">
445 <a name="passtype">Pass classes and requirements</a>
446</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]447<!-- *********************************************************************** -->
448
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]449<div class="doc_text">
450
451<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]452decide what class you should subclass for your pass. The <a
453href="#basiccode">Hello World</a> example uses the <tt><a
454href="#FunctionPass">FunctionPass</a></tt> class for its implementation, but we
455did not discuss why or when this should occur. Here we talk about the classes
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]456available, from the most general to the most specific.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]457
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]458<p>When choosing a superclass for your Pass, you should choose the <b>most
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]459specific</b> class possible, while still being able to meet the requirements
Misha Brukman5560c9d2003-08-18 14:43:39 +0000[diff] [blame]460listed. This gives the LLVM Pass Infrastructure information necessary to
Benjamin Kramer8040cd32009-10-12 14:46:08 +0000[diff] [blame]461optimize how passes are run, so that the resultant compiler isn't unnecessarily
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]462slow.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]463
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]464</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]465
Chris Lattnerf004f9a2002-09-25 22:31:38 +0000[diff] [blame]466<!-- ======================================================================= -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]467<div class="doc_subsection">
468 <a name="ImmutablePass">The <tt>ImmutablePass</tt> class</a>
469</div>
Chris Lattnerf004f9a2002-09-25 22:31:38 +0000[diff] [blame]470
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]471<div class="doc_text">
472
473<p>The most plain and boring type of pass is the "<tt><a
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]474href="http://llvm.org/doxygen/classllvm_1_1ImmutablePass.html">ImmutablePass</a></tt>"
Chris Lattnerf004f9a2002-09-25 22:31:38 +0000[diff] [blame]475class. This pass type is used for passes that do not have to be run, do not
476change state, and never need to be updated. This is not a normal type of
477transformation or analysis, but can provide information about the current
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]478compiler configuration.</p>
Chris Lattnerf004f9a2002-09-25 22:31:38 +0000[diff] [blame]479
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]480<p>Although this pass class is very infrequently used, it is important for
Chris Lattnerf004f9a2002-09-25 22:31:38 +0000[diff] [blame]481providing information about the current target machine being compiled for, and
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]482other static information that can affect the various transformations.</p>
Chris Lattnerf004f9a2002-09-25 22:31:38 +0000[diff] [blame]483
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]484<p><tt>ImmutablePass</tt>es never invalidate other transformations, are never
485invalidated, and are never "run".</p>
Chris Lattnerf004f9a2002-09-25 22:31:38 +0000[diff] [blame]486
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]487</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]488
489<!-- ======================================================================= -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]490<div class="doc_subsection">
Chris Lattnerf6278922004-09-20 04:36:29 +0000[diff] [blame]491 <a name="ModulePass">The <tt>ModulePass</tt> class</a>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]492</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]493
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]494<div class="doc_text">
495
496<p>The "<tt><a
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]497href="http://llvm.org/doxygen/classllvm_1_1ModulePass.html">ModulePass</a></tt>"
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]498class is the most general of all superclasses that you can use. Deriving from
Chris Lattnerf6278922004-09-20 04:36:29 +0000[diff] [blame]499<tt>ModulePass</tt> indicates that your pass uses the entire program as a unit,
Benjamin Kramer8040cd32009-10-12 14:46:08 +0000[diff] [blame]500referring to function bodies in no predictable order, or adding and removing
Chris Lattnerf6278922004-09-20 04:36:29 +0000[diff] [blame]501functions. Because nothing is known about the behavior of <tt>ModulePass</tt>
Daniel Dunbarb71725b2009-07-01 23:38:44 +0000[diff] [blame]502subclasses, no optimization can be done for their execution.</p>
503
504<p>A module pass can use function level passes (e.g. dominators) using
505the getAnalysis interface
506<tt>getAnalysis&lt;DominatorTree&gt;(llvm::Function *)</tt> to provide the
507function to retrieve analysis result for, if the function pass does not require
Devang Patel468857f2009-08-10 16:37:29 +0000[diff] [blame]508any 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]509analysis ran, e.g. in the case of dominators you should only ask for the
510DominatorTree for function definitions, not declarations.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]511
Chris Lattnerf6278922004-09-20 04:36:29 +0000[diff] [blame]512<p>To write a correct <tt>ModulePass</tt> subclass, derive from
513<tt>ModulePass</tt> and overload the <tt>runOnModule</tt> method with the
514following signature:</p>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]515
516</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]517
518<!-- _______________________________________________________________________ -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]519<div class="doc_subsubsection">
Chris Lattnerf6278922004-09-20 04:36:29 +0000[diff] [blame]520 <a name="runOnModule">The <tt>runOnModule</tt> method</a>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]521</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]522
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]523<div class="doc_text">
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]524
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]525<div class="doc_code"><pre>
Chris Lattnerf6278922004-09-20 04:36:29 +0000[diff] [blame]526 <b>virtual bool</b> runOnModule(Module &amp;M) = 0;
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]527</pre></div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]528
John Criswell2382ff72005-07-15 19:25:12 +0000[diff] [blame]529<p>The <tt>runOnModule</tt> method performs the interesting work of the pass.
530It should return true if the module was modified by the transformation and
531false otherwise.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]532
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]533</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]534
535<!-- ======================================================================= -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]536<div class="doc_subsection">
Chris Lattner8fdb2462004-09-18 06:39:35 +0000[diff] [blame]537 <a name="CallGraphSCCPass">The <tt>CallGraphSCCPass</tt> class</a>
538</div>
539
540<div class="doc_text">
541
542<p>The "<tt><a
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]543href="http://llvm.org/doxygen/classllvm_1_1CallGraphSCCPass.html">CallGraphSCCPass</a></tt>"
Chris Lattner8fdb2462004-09-18 06:39:35 +0000[diff] [blame]544is used by passes that need to traverse the program bottom-up on the call graph
545(callees before callers). Deriving from CallGraphSCCPass provides some
546mechanics for building and traversing the CallGraph, but also allows the system
547to optimize execution of CallGraphSCCPass's. If your pass meets the
548requirements outlined below, and doesn't meet the requirements of a <tt><a
549href="#FunctionPass">FunctionPass</a></tt> or <tt><a
550href="#BasicBlockPass">BasicBlockPass</a></tt>, you should derive from
551<tt>CallGraphSCCPass</tt>.</p>
552
553<p><b>TODO</b>: explain briefly what SCC, Tarjan's algo, and B-U mean.</p>
554
555<p>To be explicit, <tt>CallGraphSCCPass</tt> subclasses are:</p>
556
557<ol>
558
559<li>... <em>not allowed</em> to modify any <tt>Function</tt>s that are not in
560the current SCC.</li>
561
Tanya Lattner18aad232007-06-07 16:44:52 +0000[diff] [blame]562<li>... <em>not allowed</em> to inspect any Function's other than those in the
Chris Lattner8fdb2462004-09-18 06:39:35 +0000[diff] [blame]563current SCC and the direct callees of the SCC.</li>
564
565<li>... <em>required</em> to preserve the current CallGraph object, updating it
566to reflect any changes made to the program.</li>
567
568<li>... <em>not allowed</em> to add or remove SCC's from the current Module,
569though they may change the contents of an SCC.</li>
570
571<li>... <em>allowed</em> to add or remove global variables from the current
572Module.</li>
573
574<li>... <em>allowed</em> to maintain state across invocations of
575 <a href="#runOnSCC"><tt>runOnSCC</tt></a> (including global data).</li>
576</ol>
577
578<p>Implementing a <tt>CallGraphSCCPass</tt> is slightly tricky in some cases
579because it has to handle SCCs with more than one node in it. All of the virtual
580methods described below should return true if they modified the program, or
581false if they didn't.</p>
582
583</div>
584
585<!-- _______________________________________________________________________ -->
586<div class="doc_subsubsection">
Devang Patelc20048d2007-01-23 22:56:28 +0000[diff] [blame]587 <a name="doInitialization_scc">The <tt>doInitialization(CallGraph &amp;)</tt>
Chris Lattner8fdb2462004-09-18 06:39:35 +0000[diff] [blame]588 method</a>
589</div>
590
591<div class="doc_text">
592
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]593<div class="doc_code"><pre>
Devang Patelc20048d2007-01-23 22:56:28 +0000[diff] [blame]594 <b>virtual bool</b> doInitialization(CallGraph &amp;CG);
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]595</pre></div>
Chris Lattner8fdb2462004-09-18 06:39:35 +0000[diff] [blame]596
597<p>The <tt>doIninitialize</tt> method is allowed to do most of the things that
598<tt>CallGraphSCCPass</tt>'s are not allowed to do. They can add and remove
599functions, get pointers to functions, etc. The <tt>doInitialization</tt> method
600is designed to do simple initialization type of stuff that does not depend on
601the SCCs being processed. The <tt>doInitialization</tt> method call is not
602scheduled to overlap with any other pass executions (thus it should be very
603fast).</p>
604
605</div>
606
607<!-- _______________________________________________________________________ -->
608<div class="doc_subsubsection">
609 <a name="runOnSCC">The <tt>runOnSCC</tt> method</a>
610</div>
611
612<div class="doc_text">
613
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]614<div class="doc_code"><pre>
Chris Lattner6f25d9f2010-04-16 23:07:44 +0000[diff] [blame]615 <b>virtual bool</b> runOnSCC(CallGraphSCC &amp;SCC) = 0;
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]616</pre></div>
Chris Lattner8fdb2462004-09-18 06:39:35 +0000[diff] [blame]617
618<p>The <tt>runOnSCC</tt> method performs the interesting work of the pass, and
619should return true if the module was modified by the transformation, false
620otherwise.</p>
621
622</div>
623
624<!-- _______________________________________________________________________ -->
625<div class="doc_subsubsection">
Devang Patelc20048d2007-01-23 22:56:28 +0000[diff] [blame]626 <a name="doFinalization_scc">The <tt>doFinalization(CallGraph
Chris Lattner8fdb2462004-09-18 06:39:35 +0000[diff] [blame]627 &amp;)</tt> method</a>
628</div>
629
630<div class="doc_text">
631
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]632<div class="doc_code"><pre>
Devang Patelc20048d2007-01-23 22:56:28 +0000[diff] [blame]633 <b>virtual bool</b> doFinalization(CallGraph &amp;CG);
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]634</pre></div>
Chris Lattner8fdb2462004-09-18 06:39:35 +0000[diff] [blame]635
636<p>The <tt>doFinalization</tt> method is an infrequently used method that is
637called when the pass framework has finished calling <a
638href="#runOnFunction"><tt>runOnFunction</tt></a> for every function in the
639program being compiled.</p>
640
641</div>
642
643<!-- ======================================================================= -->
644<div class="doc_subsection">
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]645 <a name="FunctionPass">The <tt>FunctionPass</tt> class</a>
646</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]647
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]648<div class="doc_text">
649
Chris Lattnerf6278922004-09-20 04:36:29 +0000[diff] [blame]650<p>In contrast to <tt>ModulePass</tt> subclasses, <tt><a
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]651href="http://llvm.org/doxygen/classllvm_1_1Pass.html">FunctionPass</a></tt>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]652subclasses do have a predictable, local behavior that can be expected by the
653system. All <tt>FunctionPass</tt> execute on each function in the program
Misha Brukmanef6a6a62003-08-21 22:14:26 +0000[diff] [blame]654independent of all of the other functions in the program.
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]655<tt>FunctionPass</tt>'s do not require that they are executed in a particular
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]656order, and <tt>FunctionPass</tt>'s do not modify external functions.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]657
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]658<p>To be explicit, <tt>FunctionPass</tt> subclasses are not allowed to:</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]659
660<ol>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]661<li>Modify a Function other than the one currently being processed.</li>
662<li>Add or remove Function's from the current Module.</li>
663<li>Add or remove global variables from the current Module.</li>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]664<li>Maintain state across invocations of
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]665 <a href="#runOnFunction"><tt>runOnFunction</tt></a> (including global data)</li>
666</ol>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]667
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]668<p>Implementing a <tt>FunctionPass</tt> is usually straightforward (See the <a
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]669href="#basiccode">Hello World</a> pass for example). <tt>FunctionPass</tt>'s
670may overload three virtual methods to do their work. All of these methods
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]671should return true if they modified the program, or false if they didn't.</p>
672
673</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]674
675<!-- _______________________________________________________________________ -->
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]676<div class="doc_subsubsection">
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]677 <a name="doInitialization_mod">The <tt>doInitialization(Module &amp;)</tt>
678 method</a>
679</div>
680
681<div class="doc_text">
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]682
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]683<div class="doc_code"><pre>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]684 <b>virtual bool</b> doInitialization(Module &amp;M);
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]685</pre></div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]686
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]687<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]688<tt>FunctionPass</tt>'s are not allowed to do. They can add and remove
Chris Lattnerd0713f92002-09-12 17:06:43 +0000[diff] [blame]689functions, get pointers to functions, etc. The <tt>doInitialization</tt> method
690is designed to do simple initialization type of stuff that does not depend on
691the functions being processed. The <tt>doInitialization</tt> method call is not
692scheduled to overlap with any other pass executions (thus it should be very
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]693fast).</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]694
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]695<p>A good example of how this method should be used is the <a
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]696href="http://llvm.org/doxygen/LowerAllocations_8cpp-source.html">LowerAllocations</a>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]697pass. This pass converts <tt>malloc</tt> and <tt>free</tt> instructions into
Misha Brukmanef6a6a62003-08-21 22:14:26 +0000[diff] [blame]698platform dependent <tt>malloc()</tt> and <tt>free()</tt> function calls. It
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]699uses the <tt>doInitialization</tt> method to get a reference to the malloc and
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]700free functions that it needs, adding prototypes to the module if necessary.</p>
701
702</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]703
704<!-- _______________________________________________________________________ -->
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]705<div class="doc_subsubsection">
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]706 <a name="runOnFunction">The <tt>runOnFunction</tt> method</a>
707</div>
708
709<div class="doc_text">
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]710
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]711<div class="doc_code"><pre>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]712 <b>virtual bool</b> runOnFunction(Function &amp;F) = 0;
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]713</pre></div><p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]714
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]715<p>The <tt>runOnFunction</tt> method must be implemented by your subclass to do
716the transformation or analysis work of your pass. As usual, a true value should
717be returned if the function is modified.</p>
718
719</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]720
721<!-- _______________________________________________________________________ -->
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]722<div class="doc_subsubsection">
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]723 <a name="doFinalization_mod">The <tt>doFinalization(Module
724 &amp;)</tt> method</a>
725</div>
726
727<div class="doc_text">
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]728
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]729<div class="doc_code"><pre>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]730 <b>virtual bool</b> doFinalization(Module &amp;M);
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]731</pre></div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]732
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]733<p>The <tt>doFinalization</tt> method is an infrequently used method that is
734called when the pass framework has finished calling <a
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]735href="#runOnFunction"><tt>runOnFunction</tt></a> for every function in the
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]736program being compiled.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]737
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]738</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]739
740<!-- ======================================================================= -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]741<div class="doc_subsection">
Devang Patel2e8f27d2007-03-19 22:21:25 +0000[diff] [blame]742 <a name="LoopPass">The <tt>LoopPass</tt> class </a>
743</div>
744
745<div class="doc_text">
746
747<p> All <tt>LoopPass</tt> execute on each loop in the function independent of
748all of the other loops in the function. <tt>LoopPass</tt> processes loops in
749loop nest order such that outer most loop is processed last. </p>
750
751<p> <tt>LoopPass</tt> subclasses are allowed to update loop nest using
752<tt>LPPassManager</tt> interface. Implementing a loop pass is usually
753straightforward. <tt>Looppass</tt>'s may overload three virtual methods to
754do their work. All these methods should return true if they modified the
755program, or false if they didn't. </p>
756</div>
757
758<!-- _______________________________________________________________________ -->
759<div class="doc_subsubsection">
760 <a name="doInitialization_loop">The <tt>doInitialization(Loop *,
761 LPPassManager &amp;)</tt>
762 method</a>
763</div>
764
765<div class="doc_text">
766
767<div class="doc_code"><pre>
768 <b>virtual bool</b> doInitialization(Loop *, LPPassManager &amp;LPM);
769</pre></div>
770
Chris Lattnerb5c87f62007-05-18 05:36:14 +0000[diff] [blame]771<p>The <tt>doInitialization</tt> method is designed to do simple initialization
Devang Patel2e8f27d2007-03-19 22:21:25 +0000[diff] [blame]772type of stuff that does not depend on the functions being processed. The
773<tt>doInitialization</tt> method call is not scheduled to overlap with any
774other pass executions (thus it should be very fast). LPPassManager
775interface should be used to access Function or Module level analysis
776information.</p>
777
778</div>
779
780
781<!-- _______________________________________________________________________ -->
782<div class="doc_subsubsection">
783 <a name="runOnLoop">The <tt>runOnLoop</tt> method</a>
784</div>
785
786<div class="doc_text">
787
788<div class="doc_code"><pre>
789 <b>virtual bool</b> runOnLoop(Loop *, LPPassManager &amp;LPM) = 0;
790</pre></div><p>
791
792<p>The <tt>runOnLoop</tt> method must be implemented by your subclass to do
793the transformation or analysis work of your pass. As usual, a true value should
794be returned if the function is modified. <tt>LPPassManager</tt> interface
795should be used to update loop nest.</p>
796
797</div>
798
799<!-- _______________________________________________________________________ -->
800<div class="doc_subsubsection">
801 <a name="doFinalization_loop">The <tt>doFinalization()</tt> method</a>
802</div>
803
804<div class="doc_text">
805
806<div class="doc_code"><pre>
807 <b>virtual bool</b> doFinalization();
808</pre></div>
809
810<p>The <tt>doFinalization</tt> method is an infrequently used method that is
811called when the pass framework has finished calling <a
812href="#runOnLoop"><tt>runOnLoop</tt></a> for every loop in the
813program being compiled. </p>
814
815</div>
816
Tobias Grosser65513602010-10-20 01:54:44 +0000[diff] [blame^]817<!-- ======================================================================= -->
818<div class="doc_subsection">
819 <a name="RegionPass">The <tt>RegionPass</tt> class </a>
820</div>
821
822<div class="doc_text">
823
824<p> <tt>RegionPass</tt> is similar to <a href="#LoopPass"><tt>LoopPass</tt></a>,
825but executes on each single entry single exit region in the function.
826<tt>RegionPass</tt> processes regions in nested order such that the outer most
827region is processed last. </p>
828
829<p> <tt>RegionPass</tt> subclasses are allowed to update the region tree by using
830the <tt>RGPassManager</tt> interface. You may overload three virtual methods of
831<tt>RegionPass</tt> to implementing your own region pass is usually. All these
832methods should return true if they modified the program, or false if they didn not.
833</p>
834</div>
835
836<!-- _______________________________________________________________________ -->
837<div class="doc_subsubsection">
838 <a name="doInitialization_region">The <tt>doInitialization(Region *,
839 RGPassManager &amp;)</tt>
840 method</a>
841</div>
842
843<div class="doc_text">
844
845<div class="doc_code"><pre>
846 <b>virtual bool</b> doInitialization(Region *, RGPassManager &amp;RGM);
847</pre></div>
848
849<p>The <tt>doInitialization</tt> method is designed to do simple initialization
850type of stuff that does not depend on the functions being processed. The
851<tt>doInitialization</tt> method call is not scheduled to overlap with any
852other pass executions (thus it should be very fast). RPPassManager
853interface should be used to access Function or Module level analysis
854information.</p>
855
856</div>
857
858
859<!-- _______________________________________________________________________ -->
860<div class="doc_subsubsection">
861 <a name="runOnRegion">The <tt>runOnRegion</tt> method</a>
862</div>
863
864<div class="doc_text">
865
866<div class="doc_code"><pre>
867 <b>virtual bool</b> runOnRegion(Region *, RGPassManager &amp;RGM) = 0;
868</pre></div><p>
869
870<p>The <tt>runOnRegion</tt> method must be implemented by your subclass to do
871the transformation or analysis work of your pass. As usual, a true value should
872be returned if the region is modified. <tt>RGPassManager</tt> interface
873should be used to update region tree.</p>
874
875</div>
876
877<!-- _______________________________________________________________________ -->
878<div class="doc_subsubsection">
879 <a name="doFinalization_region">The <tt>doFinalization()</tt> method</a>
880</div>
881
882<div class="doc_text">
883
884<div class="doc_code"><pre>
885 <b>virtual bool</b> doFinalization();
886</pre></div>
887
888<p>The <tt>doFinalization</tt> method is an infrequently used method that is
889called when the pass framework has finished calling <a
890href="#runOnRegion"><tt>runOnRegion</tt></a> for every region in the
891program being compiled. </p>
892
893</div>
894
Devang Patel2e8f27d2007-03-19 22:21:25 +0000[diff] [blame]895
896
897<!-- ======================================================================= -->
898<div class="doc_subsection">
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]899 <a name="BasicBlockPass">The <tt>BasicBlockPass</tt> class</a>
900</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]901
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]902<div class="doc_text">
903
904<p><tt>BasicBlockPass</tt>'s are just like <a
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]905href="#FunctionPass"><tt>FunctionPass</tt></a>'s, except that they must limit
906their scope of inspection and modification to a single basic block at a time.
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]907As such, they are <b>not</b> allowed to do any of the following:</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]908
909<ol>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]910<li>Modify or inspect any basic blocks outside of the current one</li>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]911<li>Maintain state across invocations of
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]912 <a href="#runOnBasicBlock"><tt>runOnBasicBlock</tt></a></li>
Reid Spencer1bc19342004-12-11 05:12:57 +0000[diff] [blame]913<li>Modify the control flow graph (by altering terminator instructions)</li>
914<li>Any of the things forbidden for
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]915 <a href="#FunctionPass"><tt>FunctionPass</tt></a>es.</li>
916</ol>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]917
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]918<p><tt>BasicBlockPass</tt>es are useful for traditional local and "peephole"
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]919optimizations. They may override the same <a
Chris Lattnerd0713f92002-09-12 17:06:43 +0000[diff] [blame]920href="#doInitialization_mod"><tt>doInitialization(Module &amp;)</tt></a> and <a
921href="#doFinalization_mod"><tt>doFinalization(Module &amp;)</tt></a> methods that <a
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]922href="#FunctionPass"><tt>FunctionPass</tt></a>'s have, but also have the following virtual methods that may also be implemented:</p>
923
924</div>
Chris Lattnerd0713f92002-09-12 17:06:43 +0000[diff] [blame]925
926<!-- _______________________________________________________________________ -->
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]927<div class="doc_subsubsection">
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]928 <a name="doInitialization_fn">The <tt>doInitialization(Function
929 &amp;)</tt> method</a>
930</div>
931
932<div class="doc_text">
Chris Lattnerd0713f92002-09-12 17:06:43 +0000[diff] [blame]933
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]934<div class="doc_code"><pre>
Chris Lattnerd0713f92002-09-12 17:06:43 +0000[diff] [blame]935 <b>virtual bool</b> doInitialization(Function &amp;F);
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]936</pre></div>
Chris Lattnerd0713f92002-09-12 17:06:43 +0000[diff] [blame]937
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]938<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]939<tt>BasicBlockPass</tt>'s are not allowed to do, but that
940<tt>FunctionPass</tt>'s can. The <tt>doInitialization</tt> method is designed
Reid Spencer1bc19342004-12-11 05:12:57 +0000[diff] [blame]941to do simple initialization that does not depend on the
Chris Lattnerd0713f92002-09-12 17:06:43 +0000[diff] [blame]942BasicBlocks being processed. The <tt>doInitialization</tt> method call is not
943scheduled to overlap with any other pass executions (thus it should be very
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]944fast).</p>
Chris Lattnerd0713f92002-09-12 17:06:43 +0000[diff] [blame]945
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]946</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]947
948<!-- _______________________________________________________________________ -->
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]949<div class="doc_subsubsection">
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]950 <a name="runOnBasicBlock">The <tt>runOnBasicBlock</tt> method</a>
951</div>
952
953<div class="doc_text">
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]954
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]955<div class="doc_code"><pre>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]956 <b>virtual bool</b> runOnBasicBlock(BasicBlock &amp;BB) = 0;
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]957</pre></div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]958
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]959<p>Override this function to do the work of the <tt>BasicBlockPass</tt>. This
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]960function is not allowed to inspect or modify basic blocks other than the
961parameter, and are not allowed to modify the CFG. A true value must be returned
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]962if the basic block is modified.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]963
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]964</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]965
Chris Lattnerd0713f92002-09-12 17:06:43 +0000[diff] [blame]966<!-- _______________________________________________________________________ -->
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]967<div class="doc_subsubsection">
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]968 <a name="doFinalization_fn">The <tt>doFinalization(Function &amp;)</tt>
969 method</a>
970</div>
971
972<div class="doc_text">
Chris Lattnerd0713f92002-09-12 17:06:43 +0000[diff] [blame]973
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]974<div class="doc_code"><pre>
Chris Lattnerd0713f92002-09-12 17:06:43 +0000[diff] [blame]975 <b>virtual bool</b> doFinalization(Function &amp;F);
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]976</pre></div>
Chris Lattnerd0713f92002-09-12 17:06:43 +0000[diff] [blame]977
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]978<p>The <tt>doFinalization</tt> method is an infrequently used method that is
979called when the pass framework has finished calling <a
Chris Lattnerd0713f92002-09-12 17:06:43 +0000[diff] [blame]980href="#runOnBasicBlock"><tt>runOnBasicBlock</tt></a> for every BasicBlock in the
981program being compiled. This can be used to perform per-function
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]982finalization.</p>
Chris Lattnerd0713f92002-09-12 17:06:43 +0000[diff] [blame]983
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]984</div>
Chris Lattnerd0713f92002-09-12 17:06:43 +0000[diff] [blame]985
Brian Gaekecab8b6f2003-07-17 18:53:20 +0000[diff] [blame]986<!-- ======================================================================= -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]987<div class="doc_subsection">
988 <a name="MachineFunctionPass">The <tt>MachineFunctionPass</tt> class</a>
989</div>
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_text">
992
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]993<p>A <tt>MachineFunctionPass</tt> is a part of the LLVM code generator that
994executes on the machine-dependent representation of each LLVM function in the
Dan Gohman9f116aa2010-03-10 01:29:39 +0000[diff] [blame]995program.</p>
996
997<p>Code generator passes are registered and initialized specially by
998<tt>TargetMachine::addPassesToEmitFile</tt> and similar routines, so they
999cannot generally be run from the <tt>opt</tt> or <tt>bugpoint</tt>
1000commands.</p>
1001
1002<p>A <tt>MachineFunctionPass</tt> is also a <tt>FunctionPass</tt>, so all
Brian Gaekecab8b6f2003-07-17 18:53:20 +0000[diff] [blame]1003the restrictions that apply to a <tt>FunctionPass</tt> also apply to it.
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]1004<tt>MachineFunctionPass</tt>es also have additional restrictions. In particular,
1005<tt>MachineFunctionPass</tt>es are not allowed to do any of the following:</p>
Brian Gaekecab8b6f2003-07-17 18:53:20 +0000[diff] [blame]1006
1007<ol>
Dan Gohman9f116aa2010-03-10 01:29:39 +0000[diff] [blame]1008<li>Modify or create any LLVM IR Instructions, BasicBlocks, Arguments,
1009 Functions, GlobalVariables, GlobalAliases, or Modules.</li>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1010<li>Modify a MachineFunction other than the one currently being processed.</li>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1011<li>Maintain state across invocations of <a
1012href="#runOnMachineFunction"><tt>runOnMachineFunction</tt></a> (including global
1013data)</li>
1014</ol>
Brian Gaekecab8b6f2003-07-17 18:53:20 +0000[diff] [blame]1015
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1016</div>
Chris Lattnerd0713f92002-09-12 17:06:43 +0000[diff] [blame]1017
Brian Gaeke6a33f362003-07-22 20:53:20 +0000[diff] [blame]1018<!-- _______________________________________________________________________ -->
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]1019<div class="doc_subsubsection">
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1020 <a name="runOnMachineFunction">The <tt>runOnMachineFunction(MachineFunction
1021 &amp;MF)</tt> method</a>
1022</div>
1023
1024<div class="doc_text">
Brian Gaeke6a33f362003-07-22 20:53:20 +0000[diff] [blame]1025
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1026<div class="doc_code"><pre>
Brian Gaeke6a33f362003-07-22 20:53:20 +0000[diff] [blame]1027 <b>virtual bool</b> runOnMachineFunction(MachineFunction &amp;MF) = 0;
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1028</pre></div>
Brian Gaeke6a33f362003-07-22 20:53:20 +0000[diff] [blame]1029
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1030<p><tt>runOnMachineFunction</tt> can be considered the main entry point of a
1031<tt>MachineFunctionPass</tt>; that is, you should override this method to do the
1032work of your <tt>MachineFunctionPass</tt>.</p>
Brian Gaeke6a33f362003-07-22 20:53:20 +0000[diff] [blame]1033
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1034<p>The <tt>runOnMachineFunction</tt> method is called on every
Brian Gaeke6a33f362003-07-22 20:53:20 +0000[diff] [blame]1035<tt>MachineFunction</tt> in a <tt>Module</tt>, so that the
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1036<tt>MachineFunctionPass</tt> may perform optimizations on the machine-dependent
1037representation of the function. If you want to get at the LLVM <tt>Function</tt>
1038for the <tt>MachineFunction</tt> you're working on, use
1039<tt>MachineFunction</tt>'s <tt>getFunction()</tt> accessor method -- but
1040remember, you may not modify the LLVM <tt>Function</tt> or its contents from a
1041<tt>MachineFunctionPass</tt>.</p>
1042
1043</div>
Brian Gaeke6a33f362003-07-22 20:53:20 +0000[diff] [blame]1044
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1045<!-- *********************************************************************** -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1046<div class="doc_section">
1047 <a name="registration">Pass registration</a>
1048</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1049<!-- *********************************************************************** -->
1050
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1051<div class="doc_text">
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1052
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1053<p>In the <a href="#basiccode">Hello World</a> example pass we illustrated how
1054pass registration works, and discussed some of the reasons that it is used and
1055what it does. Here we discuss how and why passes are registered.</p>
1056
Owen Anderson20813e02010-07-21 22:58:07 +0000[diff] [blame]1057<p>As we saw above, passes are registered with the <b><tt>INITIALIZE_PASS</tt></b>
1058macro. The first parameter is the name of the pass that is to be used on
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1059the command line to specify that the pass should be added to a program (for
Chris Lattnerc8603c22006-08-27 23:18:52 +0000[diff] [blame]1060example, with <tt>opt</tt> or <tt>bugpoint</tt>). The second argument is the
Duncan Sands7e7ae5a2010-02-18 14:08:13 +0000[diff] [blame]1061name 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]1062programs, as
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1063well as for debug output generated by the <tt>--debug-pass</tt> option.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1064
Chris Lattnerc8603c22006-08-27 23:18:52 +0000[diff] [blame]1065<p>If you want your pass to be easily dumpable, you should
1066implement the virtual <tt>print</tt> method:</p>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1067
1068</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1069
1070<!-- _______________________________________________________________________ -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1071<div class="doc_subsubsection">
1072 <a name="print">The <tt>print</tt> method</a>
1073</div>
1074
1075<div class="doc_text">
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1076
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1077<div class="doc_code"><pre>
Torok Edwin52790e52008-10-28 17:29:23 +0000[diff] [blame]1078 <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]1079</pre></div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1080
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1081<p>The <tt>print</tt> method must be implemented by "analyses" in order to print
1082a human readable version of the analysis results. This is useful for debugging
1083an analysis itself, as well as for other people to figure out how an analysis
Chris Lattnerc8603c22006-08-27 23:18:52 +0000[diff] [blame]1084works. Use the <tt>opt -analyze</tt> argument to invoke this method.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1085
Bill Wendling832171c2006-12-07 20:04:42 +0000[diff] [blame]1086<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]1087and 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]1088program that has been analyzed. Note however that this pointer may be null in
1089certain circumstances (such as calling the <tt>Pass::dump()</tt> from a
1090debugger), so it should only be used to enhance debug output, it should not be
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1091depended on.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1092
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1093</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1094
1095<!-- *********************************************************************** -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1096<div class="doc_section">
1097 <a name="interaction">Specifying interactions between passes</a>
1098</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1099<!-- *********************************************************************** -->
1100
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1101<div class="doc_text">
1102
John Criswell8528e782007-12-03 19:34:25 +0000[diff] [blame]1103<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]1104that passes interact with each other correctly. Because <tt>PassManager</tt>
1105tries to <a href="#passmanager">optimize the execution of passes</a> it must
1106know how the passes interact with each other and what dependencies exist between
1107the various passes. To track this, each pass can declare the set of passes that
1108are required to be executed before the current pass, and the passes which are
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1109invalidated by the current pass.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1110
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1111<p>Typically this functionality is used to require that analysis results are
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1112computed before your pass is run. Running arbitrary transformation passes can
1113invalidate the computed analysis results, which is what the invalidation set
1114specifies. If a pass does not implement the <tt><a
1115href="#getAnalysisUsage">getAnalysisUsage</a></tt> method, it defaults to not
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1116having any prerequisite passes, and invalidating <b>all</b> other passes.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1117
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1118</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1119
1120<!-- _______________________________________________________________________ -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1121<div class="doc_subsubsection">
1122 <a name="getAnalysisUsage">The <tt>getAnalysisUsage</tt> method</a>
1123</div>
1124
1125<div class="doc_text">
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1126
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1127<div class="doc_code"><pre>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1128 <b>virtual void</b> getAnalysisUsage(AnalysisUsage &amp;Info) <b>const</b>;
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1129</pre></div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1130
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1131<p>By implementing the <tt>getAnalysisUsage</tt> method, the required and
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1132invalidated sets may be specified for your transformation. The implementation
1133should fill in the <tt><a
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]1134href="http://llvm.org/doxygen/classllvm_1_1AnalysisUsage.html">AnalysisUsage</a></tt>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1135object with information about which passes are required and not invalidated. To
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]1136do this, a pass may call any of the following methods on the AnalysisUsage
1137object:</p>
1138</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1139
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]1140<!-- _______________________________________________________________________ -->
1141<div class="doc_subsubsection">
1142 <a name="AU::addRequired">The <tt>AnalysisUsage::addRequired&lt;&gt;</tt> and <tt>AnalysisUsage::addRequiredTransitive&lt;&gt;</tt> methods</a>
1143</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1144
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]1145<div class="doc_text">
1146<p>
Reid Spencer1bc19342004-12-11 05:12:57 +0000[diff] [blame]1147If your pass requires a previous pass to be executed (an analysis for example),
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]1148it can use one of these methods to arrange for it to be run before your pass.
1149LLVM has many different types of analyses and passes that can be required,
Reid Spencer1bc19342004-12-11 05:12:57 +0000[diff] [blame]1150spanning the range from <tt>DominatorSet</tt> to <tt>BreakCriticalEdges</tt>.
1151Requiring <tt>BreakCriticalEdges</tt>, for example, guarantees that there will
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]1152be no critical edges in the CFG when your pass has been run.
1153</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1154
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]1155<p>
1156Some analyses chain to other analyses to do their job. For example, an <a
1157href="AliasAnalysis.html">AliasAnalysis</a> implementation is required to <a
1158href="AliasAnalysis.html#chaining">chain</a> to other alias analysis passes. In
1159cases where analyses chain, the <tt>addRequiredTransitive</tt> method should be
1160used instead of the <tt>addRequired</tt> method. This informs the PassManager
1161that the transitively required pass should be alive as long as the requiring
1162pass is.
1163</p>
1164</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1165
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]1166<!-- _______________________________________________________________________ -->
1167<div class="doc_subsubsection">
1168 <a name="AU::addPreserved">The <tt>AnalysisUsage::addPreserved&lt;&gt;</tt> method</a>
1169</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1170
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]1171<div class="doc_text">
1172<p>
1173One of the jobs of the PassManager is to optimize how and when analyses are run.
1174In particular, it attempts to avoid recomputing data unless it needs to. For
1175this reason, passes are allowed to declare that they preserve (i.e., they don't
1176invalidate) an existing analysis if it's available. For example, a simple
Reid Spencer1bc19342004-12-11 05:12:57 +0000[diff] [blame]1177constant folding pass would not modify the CFG, so it can't possibly affect the
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]1178results of dominator analysis. By default, all passes are assumed to invalidate
1179all others.
1180</p>
1181
1182<p>
1183The <tt>AnalysisUsage</tt> class provides several methods which are useful in
1184certain circumstances that are related to <tt>addPreserved</tt>. In particular,
1185the <tt>setPreservesAll</tt> method can be called to indicate that the pass does
1186not modify the LLVM program at all (which is true for analyses), and the
1187<tt>setPreservesCFG</tt> method can be used by transformations that change
1188instructions in the program but do not modify the CFG or terminator instructions
1189(note that this property is implicitly set for <a
1190href="#BasicBlockPass">BasicBlockPass</a>'s).
1191</p>
1192
1193<p>
1194<tt>addPreserved</tt> is particularly useful for transformations like
1195<tt>BreakCriticalEdges</tt>. This pass knows how to update a small set of loop
1196and dominator related analyses if they exist, so it can preserve them, despite
1197the fact that it hacks on the CFG.
1198</p>
1199</div>
1200
1201<!-- _______________________________________________________________________ -->
1202<div class="doc_subsubsection">
1203 <a name="AU::examples">Example implementations of <tt>getAnalysisUsage</tt></a>
1204</div>
1205
1206<div class="doc_text">
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1207
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1208<div class="doc_code"><pre>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1209 <i>// This is an example implementation from an analysis, which does not modify
1210 // the program at all, yet has a prerequisite.</i>
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]1211 <b>void</b> <a href="http://llvm.org/doxygen/classllvm_1_1PostDominanceFrontier.html">PostDominanceFrontier</a>::getAnalysisUsage(AnalysisUsage &amp;AU) <b>const</b> {
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1212 AU.setPreservesAll();
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]1213 AU.addRequired&lt;<a href="http://llvm.org/doxygen/classllvm_1_1PostDominatorTree.html">PostDominatorTree</a>&gt;();
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1214 }
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1215</pre></div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1216
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1217<p>and:</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1218
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1219<div class="doc_code"><pre>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1220 <i>// This example modifies the program, but does not modify the CFG</i>
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]1221 <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]1222 AU.setPreservesCFG();
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]1223 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]1224 }
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1225</pre></div>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1226
1227</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1228
1229<!-- _______________________________________________________________________ -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1230<div class="doc_subsubsection">
Duncan Sands1465d612009-01-28 13:14:17 +0000[diff] [blame]1231 <a name="getAnalysis">The <tt>getAnalysis&lt;&gt;</tt> and
1232<tt>getAnalysisIfAvailable&lt;&gt;</tt> methods</a>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1233</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1234
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1235<div class="doc_text">
1236
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]1237<p>The <tt>Pass::getAnalysis&lt;&gt;</tt> method is automatically inherited by
1238your class, providing you with access to the passes that you declared that you
1239required with the <a href="#getAnalysisUsage"><tt>getAnalysisUsage</tt></a>
1240method. It takes a single template argument that specifies which pass class you
1241want, and returns a reference to that pass. For example:</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1242
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1243<div class="doc_code"><pre>
Chris Lattnera5776302004-03-17 21:33:32 +0000[diff] [blame]1244 bool LICM::runOnFunction(Function &amp;F) {
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]1245 LoopInfo &amp;LI = getAnalysis&lt;LoopInfo&gt;();
1246 ...
1247 }
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1248</pre></div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1249
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1250<p>This method call returns a reference to the pass desired. You may get a
1251runtime assertion failure if you attempt to get an analysis that you did not
1252declare as required in your <a
1253href="#getAnalysisUsage"><tt>getAnalysisUsage</tt></a> implementation. This
1254method can be called by your <tt>run*</tt> method implementation, or by any
Devang Patel3c1ca0b2007-04-16 21:28:14 +0000[diff] [blame]1255other local method invoked by your <tt>run*</tt> method.
1256
1257A module level pass can use function level analysis info using this interface.
1258For example:</p>
1259
1260<div class="doc_code"><pre>
1261 bool ModuleLevelPass::runOnModule(Module &amp;M) {
1262 ...
Devang Patelf23de112007-04-17 00:17:11 +0000[diff] [blame]1263 DominatorTree &amp;DT = getAnalysis&lt;DominatorTree&gt;(Func);
Devang Patel3c1ca0b2007-04-16 21:28:14 +0000[diff] [blame]1264 ...
1265 }
1266</pre></div>
1267
Chris Lattnerb5c87f62007-05-18 05:36:14 +0000[diff] [blame]1268<p>In above example, runOnFunction for DominatorTree is called by pass manager
Devang Patel3c1ca0b2007-04-16 21:28:14 +0000[diff] [blame]1269before returning a reference to the desired pass.</p>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1270
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]1271<p>
1272If your pass is capable of updating analyses if they exist (e.g.,
1273<tt>BreakCriticalEdges</tt>, as described above), you can use the
Duncan Sands1465d612009-01-28 13:14:17 +0000[diff] [blame]1274<tt>getAnalysisIfAvailable</tt> method, which returns a pointer to the analysis
1275if it is active. For example:</p>
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]1276
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1277<div class="doc_code"><pre>
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]1278 ...
Duncan Sands1465d612009-01-28 13:14:17 +0000[diff] [blame]1279 if (DominatorSet *DS = getAnalysisIfAvailable&lt;DominatorSet&gt;()) {
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]1280 <i>// A DominatorSet is active. This code will update it.</i>
1281 }
1282 ...
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1283</pre></div>
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]1284
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1285</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1286
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1287<!-- *********************************************************************** -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1288<div class="doc_section">
1289 <a name="analysisgroup">Implementing Analysis Groups</a>
1290</div>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1291<!-- *********************************************************************** -->
1292
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1293<div class="doc_text">
1294
Chris Lattnerb7632282007-11-16 05:32:05 +0000[diff] [blame]1295<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]1296used, 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]1297fancier. All of the pass relationships that we have seen so far are very
1298simple: one pass depends on one other specific pass to be run before it can run.
1299For many applications, this is great, for others, more flexibility is
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1300required.</p>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1301
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1302<p>In particular, some analyses are defined such that there is a single simple
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1303interface to the analysis results, but multiple ways of calculating them.
1304Consider alias analysis for example. The most trivial alias analysis returns
1305"may alias" for any alias query. The most sophisticated analysis a
1306flow-sensitive, context-sensitive interprocedural analysis that can take a
1307significant amount of time to execute (and obviously, there is a lot of room
1308between these two extremes for other implementations). To cleanly support
1309situations like this, the LLVM Pass Infrastructure supports the notion of
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1310Analysis Groups.</p>
1311
1312</div>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1313
1314<!-- _______________________________________________________________________ -->
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]1315<div class="doc_subsubsection">
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1316 <a name="agconcepts">Analysis Group Concepts</a>
1317</div>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1318
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1319<div class="doc_text">
1320
1321<p>An Analysis Group is a single simple interface that may be implemented by
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1322multiple different passes. Analysis Groups can be given human readable names
1323just like passes, but unlike passes, they need not derive from the <tt>Pass</tt>
1324class. An analysis group may have one or more implementations, one of which is
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1325the "default" implementation.</p>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1326
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1327<p>Analysis groups are used by client passes just like other passes are: the
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1328<tt>AnalysisUsage::addRequired()</tt> and <tt>Pass::getAnalysis()</tt> methods.
1329In order to resolve this requirement, the <a href="#passmanager">PassManager</a>
1330scans the available passes to see if any implementations of the analysis group
1331are available. If none is available, the default implementation is created for
1332the pass to use. All standard rules for <A href="#interaction">interaction
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1333between passes</a> still apply.</p>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1334
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1335<p>Although <a href="#registration">Pass Registration</a> is optional for normal
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1336passes, all analysis group implementations must be registered, and must use the
Owen Andersond8cc7be2010-07-21 23:07:00 +0000[diff] [blame]1337<A href="#registerag"><tt>INITIALIZE_AG_PASS</tt></a> template to join the
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1338implementation pool. Also, a default implementation of the interface
1339<b>must</b> be registered with <A
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1340href="#registerag"><tt>RegisterAnalysisGroup</tt></a>.</p>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1341
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1342<p>As a concrete example of an Analysis Group in action, consider the <a
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]1343href="http://llvm.org/doxygen/classllvm_1_1AliasAnalysis.html">AliasAnalysis</a>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1344analysis group. The default implementation of the alias analysis interface (the
1345<tt><a
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]1346href="http://llvm.org/doxygen/structBasicAliasAnalysis.html">basicaa</a></tt>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1347pass) just does a few simple checks that don't require significant analysis to
1348compute (such as: two different globals can never alias each other, etc).
1349Passes that use the <tt><a
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]1350href="http://llvm.org/doxygen/classllvm_1_1AliasAnalysis.html">AliasAnalysis</a></tt>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1351interface (for example the <tt><a
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]1352href="http://llvm.org/doxygen/structGCSE.html">gcse</a></tt> pass), do
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1353not care which implementation of alias analysis is actually provided, they just
1354use the designated interface.</p>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1355
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1356<p>From the user's perspective, commands work just like normal. Issuing the
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1357command '<tt>opt -gcse ...</tt>' will cause the <tt>basicaa</tt> class to be
1358instantiated and added to the pass sequence. Issuing the command '<tt>opt
1359-somefancyaa -gcse ...</tt>' will cause the <tt>gcse</tt> pass to use the
1360<tt>somefancyaa</tt> alias analysis (which doesn't actually exist, it's just a
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1361hypothetical example) instead.</p>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1362
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1363</div>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1364
1365<!-- _______________________________________________________________________ -->
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]1366<div class="doc_subsubsection">
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1367 <a name="registerag">Using <tt>RegisterAnalysisGroup</tt></a>
1368</div>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1369
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1370<div class="doc_text">
1371
1372<p>The <tt>RegisterAnalysisGroup</tt> template is used to register the analysis
Owen Andersond8cc7be2010-07-21 23:07:00 +0000[diff] [blame]1373group itself, while the <tt>INITIALIZE_AG_PASS</tt> is used to add pass
1374implementations to the analysis group. First,
1375an analysis group should be registered, with a human readable name
1376provided for it.
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1377Unlike registration of passes, there is no command line argument to be specified
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1378for the Analysis Group Interface itself, because it is "abstract":</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>
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]1381 <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]1382</pre></div>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1383
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1384<p>Once the analysis is registered, passes can declare that they are valid
1385implementations of the interface by using the following code:</p>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1386
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1387<div class="doc_code"><pre>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1388<b>namespace</b> {
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1389 //<i> Declare that we implement the AliasAnalysis interface</i>
Owen Andersond8cc7be2010-07-21 23:07:00 +0000[diff] [blame]1390 INITIALIZE_AG_PASS(FancyAA, <a href="http://llvm.org/doxygen/classllvm_1_1AliasAnalysis.html">AliasAnalysis</a>, "<i>somefancyaa</i>",
1391 "<i>A more complex alias analysis implementation</i>",
1392 false, // <i>Is CFG Only?</i>
1393 true, // <i>Is Analysis?</i>
1394 false, // <i>Is default Analysis Group implementation?</i>
1395 );
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1396}
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1397</pre></div>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1398
Owen Andersond8cc7be2010-07-21 23:07:00 +0000[diff] [blame]1399<p>This just shows a class <tt>FancyAA</tt> that
1400uses the <tt>INITIALIZE_AG_PASS</tt> macro both to register and
1401to "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]1402analysis group. Every implementation of an analysis group should join using
Owen Andersond8cc7be2010-07-21 23:07:00 +0000[diff] [blame]1403this macro.</p>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1404
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1405<div class="doc_code"><pre>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1406<b>namespace</b> {
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1407 //<i> Declare that we implement the AliasAnalysis interface</i>
Owen Andersond8cc7be2010-07-21 23:07:00 +0000[diff] [blame]1408 INITIALIZE_AG_PASS(BasicAA, <a href="http://llvm.org/doxygen/classllvm_1_1AliasAnalysis.html">AliasAnalysis</a>, "<i>basicaa</i>",
1409 "<i>Basic Alias Analysis (default AA impl)</i>",
1410 false, // <i>Is CFG Only?</i>
1411 true, // <i>Is Analysis?</i>
1412 true, // <i>Is default Analysis Group implementation?</i>
1413 );
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1414}
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1415</pre></div>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1416
Owen Andersond8cc7be2010-07-21 23:07:00 +0000[diff] [blame]1417<p>Here we show how the default implementation is specified (using the final
1418argument to the <tt>INITIALIZE_AG_PASS</tt> template). There must be exactly
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1419one default implementation available at all times for an Analysis Group to be
Devang Patel2397f8d2007-06-20 18:51:14 +0000[diff] [blame]1420used. Only default implementation can derive from <tt>ImmutablePass</tt>.
1421Here we declare that the
1422 <tt><a href="http://llvm.org/doxygen/structBasicAliasAnalysis.html">BasicAliasAnalysis</a></tt>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1423pass is the default implementation for the interface.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1424
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1425</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1426
1427<!-- *********************************************************************** -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1428<div class="doc_section">
Tanya Lattnerd5383652004-11-19 01:25:14 +0000[diff] [blame]1429 <a name="passStatistics">Pass Statistics</a>
1430</div>
1431<!-- *********************************************************************** -->
1432
1433<div class="doc_text">
Tanya Lattner05f8d5f2004-11-19 01:26:37 +0000[diff] [blame]1434<p>The <a
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]1435href="http://llvm.org/doxygen/Statistic_8h-source.html"><tt>Statistic</tt></a>
John Criswell0b1010e2005-11-28 23:25:41 +0000[diff] [blame]1436class is designed to be an easy way to expose various success
Tanya Lattnerd5383652004-11-19 01:25:14 +0000[diff] [blame]1437metrics from passes. These statistics are printed at the end of a
1438run, when the -stats command line option is enabled on the command
Tanya Lattner05f8d5f2004-11-19 01:26:37 +0000[diff] [blame]1439line. 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]1440
1441</div>
1442
1443
1444<!-- *********************************************************************** -->
1445<div class="doc_section">
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1446 <a name="passmanager">What PassManager does</a>
1447</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1448<!-- *********************************************************************** -->
1449
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1450<div class="doc_text">
1451
1452<p>The <a
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]1453href="http://llvm.org/doxygen/PassManager_8h-source.html"><tt>PassManager</tt></a>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1454<a
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]1455href="http://llvm.org/doxygen/classllvm_1_1PassManager.html">class</a>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1456takes a list of passes, ensures their <a href="#interaction">prerequisites</a>
1457are set up correctly, and then schedules passes to run efficiently. All of the
1458LLVM tools that run passes use the <tt>PassManager</tt> for execution of these
1459passes.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1460
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1461<p>The <tt>PassManager</tt> does two main things to try to reduce the execution
1462time of a series of passes:</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1463
1464<ol>
1465<li><b>Share analysis results</b> - The PassManager attempts to avoid
1466recomputing analysis results as much as possible. This means keeping track of
1467which analyses are available already, which analyses get invalidated, and which
1468analyses are needed to be run for a pass. An important part of work is that the
1469<tt>PassManager</tt> tracks the exact lifetime of all analysis results, allowing
1470it to <a href="#releaseMemory">free memory</a> allocated to holding analysis
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1471results as soon as they are no longer needed.</li>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1472
1473<li><b>Pipeline the execution of passes on the program</b> - The
1474<tt>PassManager</tt> attempts to get better cache and memory usage behavior out
1475of a series of passes by pipelining the passes together. This means that, given
1476a series of consequtive <a href="#FunctionPass"><tt>FunctionPass</tt></a>'s, it
1477will execute all of the <a href="#FunctionPass"><tt>FunctionPass</tt></a>'s on
1478the first function, then all of the <a
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1479href="#FunctionPass"><tt>FunctionPass</tt></a>es on the second function,
1480etc... until the entire program has been run through the passes.
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1481
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1482<p>This improves the cache behavior of the compiler, because it is only touching
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1483the LLVM program representation for a single function at a time, instead of
1484traversing the entire program. It reduces the memory consumption of compiler,
1485because, for example, only one <a
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]1486href="http://llvm.org/doxygen/classllvm_1_1DominatorSet.html"><tt>DominatorSet</tt></a>
John Criswell9795bb82007-12-10 20:26:29 +0000[diff] [blame]1487needs to be calculated at a time. This also makes it possible to implement
1488some <a
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1489href="#SMP">interesting enhancements</a> in the future.</p></li>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1490
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1491</ol>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1492
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1493<p>The effectiveness of the <tt>PassManager</tt> is influenced directly by how
1494much information it has about the behaviors of the passes it is scheduling. For
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1495example, the "preserved" set is intentionally conservative in the face of an
1496unimplemented <a href="#getAnalysisUsage"><tt>getAnalysisUsage</tt></a> method.
1497Not implementing when it should be implemented will have the effect of not
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1498allowing any analysis results to live across the execution of your pass.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1499
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1500<p>The <tt>PassManager</tt> class exposes a <tt>--debug-pass</tt> command line
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1501options that is useful for debugging pass execution, seeing how things work, and
1502diagnosing when you should be preserving more analyses than you currently are
1503(To get information about all of the variants of the <tt>--debug-pass</tt>
Duncan Sands7e7ae5a2010-02-18 14:08:13 +0000[diff] [blame]1504option, just type '<tt>opt -help-hidden</tt>').</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1505
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1506<p>By using the <tt>--debug-pass=Structure</tt> option, for example, we can see
1507how our <a href="#basiccode">Hello World</a> pass interacts with other passes.
1508Lets try it out with the <tt>gcse</tt> and <tt>licm</tt> passes:</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1509
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1510<div class="doc_code"><pre>
Duncan Sands67f8a7b2010-07-08 08:27:18 +0000[diff] [blame]1511$ 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]1512Module Pass Manager
1513 Function Pass Manager
1514 Dominator Set Construction
1515 Immediate Dominators Construction
1516 Global Common Subexpression Elimination
1517-- Immediate Dominators Construction
1518-- Global Common Subexpression Elimination
1519 Natural Loop Construction
1520 Loop Invariant Code Motion
1521-- Natural Loop Construction
1522-- Loop Invariant Code Motion
1523 Module Verifier
1524-- Dominator Set Construction
1525-- Module Verifier
Gabor Greif04367bf2007-07-06 22:07:22 +0000[diff] [blame]1526 Bitcode Writer
1527--Bitcode Writer
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1528</pre></div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1529
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1530<p>This output shows us when passes are constructed and when the analysis
1531results are known to be dead (prefixed with '<tt>--</tt>'). Here we see that
1532GCSE uses dominator and immediate dominator information to do its job. The LICM
1533pass uses natural loop information, which uses dominator sets, but not immediate
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1534dominators. Because immediate dominators are no longer useful after the GCSE
1535pass, it is immediately destroyed. The dominator sets are then reused to
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1536compute natural loop information, which is then used by the LICM pass.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1537
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1538<p>After the LICM pass, the module verifier runs (which is automatically added
1539by the '<tt>opt</tt>' tool), which uses the dominator set to check that the
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1540resultant LLVM code is well formed. After it finishes, the dominator set
1541information is destroyed, after being computed once, and shared by three
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1542passes.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1543
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1544<p>Lets see how this changes when we run the <a href="#basiccode">Hello
1545World</a> pass in between the two passes:</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1546
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1547<div class="doc_code"><pre>
Duncan Sands67f8a7b2010-07-08 08:27:18 +0000[diff] [blame]1548$ 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]1549Module Pass Manager
1550 Function Pass Manager
1551 Dominator Set Construction
1552 Immediate Dominators Construction
1553 Global Common Subexpression Elimination
1554<b>-- Dominator Set Construction</b>
1555-- Immediate Dominators Construction
1556-- Global Common Subexpression Elimination
1557<b> Hello World Pass
1558-- Hello World Pass
1559 Dominator Set Construction</b>
1560 Natural Loop Construction
1561 Loop Invariant Code Motion
1562-- Natural Loop Construction
1563-- Loop Invariant Code Motion
1564 Module Verifier
1565-- Dominator Set Construction
1566-- Module Verifier
Gabor Greif04367bf2007-07-06 22:07:22 +0000[diff] [blame]1567 Bitcode Writer
1568--Bitcode Writer
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1569Hello: __main
1570Hello: puts
1571Hello: main
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1572</pre></div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1573
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1574<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]1575Dominator Set pass, even though it doesn't modify the code at all! To fix this,
1576we need to add the following <a
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1577href="#getAnalysisUsage"><tt>getAnalysisUsage</tt></a> method to our pass:</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1578
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1579<div class="doc_code"><pre>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1580 <i>// We don't modify the program, so we preserve all analyses</i>
1581 <b>virtual void</b> getAnalysisUsage(AnalysisUsage &amp;AU) <b>const</b> {
1582 AU.setPreservesAll();
1583 }
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1584</pre></div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1585
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1586<p>Now when we run our pass, we get this output:</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1587
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1588<div class="doc_code"><pre>
Duncan Sands67f8a7b2010-07-08 08:27:18 +0000[diff] [blame]1589$ 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]1590Pass Arguments: -gcse -hello -licm
1591Module Pass Manager
1592 Function Pass Manager
1593 Dominator Set Construction
1594 Immediate Dominators Construction
1595 Global Common Subexpression Elimination
1596-- Immediate Dominators Construction
1597-- Global Common Subexpression Elimination
1598 Hello World Pass
1599-- Hello World Pass
1600 Natural Loop Construction
1601 Loop Invariant Code Motion
1602-- Loop Invariant Code Motion
1603-- Natural Loop Construction
1604 Module Verifier
1605-- Dominator Set Construction
1606-- Module Verifier
Gabor Greif04367bf2007-07-06 22:07:22 +0000[diff] [blame]1607 Bitcode Writer
1608--Bitcode Writer
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1609Hello: __main
1610Hello: puts
1611Hello: main
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1612</pre></div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1613
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1614<p>Which shows that we don't accidentally invalidate dominator information
1615anymore, and therefore do not have to compute it twice.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1616
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1617</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1618
1619<!-- _______________________________________________________________________ -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1620<div class="doc_subsubsection">
1621 <a name="releaseMemory">The <tt>releaseMemory</tt> method</a>
1622</div>
1623
1624<div class="doc_text">
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1625
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1626<div class="doc_code"><pre>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1627 <b>virtual void</b> releaseMemory();
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1628</pre></div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1629
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1630<p>The <tt>PassManager</tt> automatically determines when to compute analysis
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1631results, and how long to keep them around for. Because the lifetime of the pass
1632object itself is effectively the entire duration of the compilation process, we
1633need some way to free analysis results when they are no longer useful. The
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1634<tt>releaseMemory</tt> virtual method is the way to do this.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1635
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1636<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]1637amount of state (for use by another pass which "requires" your pass and uses the
1638<a href="#getAnalysis">getAnalysis</a> method) you should implement
Dan Gohmand87c9e32009-06-15 18:22:49 +0000[diff] [blame]1639<tt>releaseMemory</tt> to, well, release the memory allocated to maintain this
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1640internal state. This method is called after the <tt>run*</tt> method for the
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1641class, before the next call of <tt>run*</tt> in your pass.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1642
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1643</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1644
1645<!-- *********************************************************************** -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1646<div class="doc_section">
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1647 <a name="registering">Registering dynamically loaded passes</a>
1648</div>
1649<!-- *********************************************************************** -->
1650
1651<div class="doc_text">
1652
1653<p><i>Size matters</i> when constructing production quality tools using llvm,
1654both for the purposes of distribution, and for regulating the resident code size
1655when running on the target system. Therefore, it becomes desirable to
1656selectively use some passes, while omitting others and maintain the flexibility
1657to change configurations later on. You want to be able to do all this, and,
1658provide feedback to the user. This is where pass registration comes into
1659play.</p>
1660
1661<p>The fundamental mechanisms for pass registration are the
1662<tt>MachinePassRegistry</tt> class and subclasses of
1663<tt>MachinePassRegistryNode</tt>.</p>
1664
1665<p>An instance of <tt>MachinePassRegistry</tt> is used to maintain a list of
1666<tt>MachinePassRegistryNode</tt> objects. This instance maintains the list and
1667communicates additions and deletions to the command line interface.</p>
1668
1669<p>An instance of <tt>MachinePassRegistryNode</tt> subclass is used to maintain
1670information provided about a particular pass. This information includes the
1671command line name, the command help string and the address of the function used
1672to create an instance of the pass. A global static constructor of one of these
1673instances <i>registers</i> with a corresponding <tt>MachinePassRegistry</tt>,
1674the static destructor <i>unregisters</i>. Thus a pass that is statically linked
1675in the tool will be registered at start up. A dynamically loaded pass will
1676register on load and unregister at unload.</p>
1677
1678</div>
1679
1680<!-- _______________________________________________________________________ -->
1681<div class="doc_subsection">
1682 <a name="registering_existing">Using existing registries</a>
1683</div>
1684
1685<div class="doc_text">
1686
1687<p>There are predefined registries to track instruction scheduling
1688(<tt>RegisterScheduler</tt>) and register allocation (<tt>RegisterRegAlloc</tt>)
1689machine passes. Here we will describe how to <i>register</i> a register
1690allocator machine pass.</p>
1691
1692<p>Implement your register allocator machine pass. In your register allocator
1693.cpp file add the following include;</p>
1694
1695<div class="doc_code"><pre>
Chris Lattner8f652eb2006-08-11 16:37:02 +0000[diff] [blame]1696 #include "llvm/CodeGen/RegAllocRegistry.h"
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1697</pre></div>
1698
1699<p>Also in your register allocator .cpp file, define a creator function in the
1700form; </p>
1701
1702<div class="doc_code"><pre>
1703 FunctionPass *createMyRegisterAllocator() {
1704 return new MyRegisterAllocator();
1705 }
1706</pre></div>
1707
1708<p>Note that the signature of this function should match the type of
1709<tt>RegisterRegAlloc::FunctionPassCtor</tt>. In the same file add the
1710"installing" declaration, in the form;</p>
1711
1712<div class="doc_code"><pre>
1713 static RegisterRegAlloc myRegAlloc("myregalloc",
1714 " my register allocator help string",
1715 createMyRegisterAllocator);
1716</pre></div>
1717
1718<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]1719-help query.</p>
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1720
1721<div class="doc_code"><pre>
Duncan Sands7e7ae5a2010-02-18 14:08:13 +0000[diff] [blame]1722$ llc -help
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1723 ...
Duncan Sands18619b22010-02-18 14:37:52 +0000[diff] [blame]1724 -regalloc - Register allocator to use (default=linearscan)
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1725 =linearscan - linear scan register allocator
1726 =local - local register allocator
1727 =simple - simple register allocator
1728 =myregalloc - my register allocator help string
1729 ...
1730</pre></div>
1731
1732<p>And that's it. The user is now free to use <tt>-regalloc=myregalloc</tt> as
1733an option. Registering instruction schedulers is similar except use the
Chris Lattner8f652eb2006-08-11 16:37:02 +0000[diff] [blame]1734<tt>RegisterScheduler</tt> class. Note that the
1735<tt>RegisterScheduler::FunctionPassCtor</tt> is significantly different from
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1736<tt>RegisterRegAlloc::FunctionPassCtor</tt>.</p>
1737
1738<p>To force the load/linking of your register allocator into the llc/lli tools,
1739add your creator function's global declaration to "Passes.h" and add a "pseudo"
1740call line to <tt>llvm/Codegen/LinkAllCodegenComponents.h</tt>.</p>
1741
1742</div>
1743
1744
1745<!-- _______________________________________________________________________ -->
1746<div class="doc_subsection">
1747 <a name="registering_new">Creating new registries</a>
1748</div>
1749
1750<div class="doc_text">
1751
1752<p>The easiest way to get started is to clone one of the existing registries; we
1753recommend <tt>llvm/CodeGen/RegAllocRegistry.h</tt>. The key things to modify
1754are the class name and the <tt>FunctionPassCtor</tt> type.</p>
1755
1756<p>Then you need to declare the registry. Example: if your pass registry is
1757<tt>RegisterMyPasses</tt> then define;</p>
1758
1759<div class="doc_code"><pre>
1760MachinePassRegistry RegisterMyPasses::Registry;
1761</pre></div>
1762
1763<p>And finally, declare the command line option for your passes. Example:</p>
1764
1765<div class="doc_code"><pre>
1766 cl::opt&lt;RegisterMyPasses::FunctionPassCtor, false,
Dan Gohman364a39f2008-10-14 17:00:38 +0000[diff] [blame]1767 RegisterPassParser&lt;RegisterMyPasses&gt; &gt;
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1768 MyPassOpt("mypass",
1769 cl::init(&amp;createDefaultMyPass),
1770 cl::desc("my pass option help"));
1771</pre></div>
1772
1773<p>Here the command option is "mypass", with createDefaultMyPass as the default
1774creator.</p>
1775
1776</div>
1777
1778<!-- *********************************************************************** -->
1779<div class="doc_section">
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1780 <a name="debughints">Using GDB with dynamically loaded passes</a>
1781</div>
Chris Lattner480e2ef2002-09-06 02:02:58 +0000[diff] [blame]1782<!-- *********************************************************************** -->
1783
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1784<div class="doc_text">
1785
1786<p>Unfortunately, using GDB with dynamically loaded passes is not as easy as it
Chris Lattner480e2ef2002-09-06 02:02:58 +0000[diff] [blame]1787should be. First of all, you can't set a breakpoint in a shared object that has
1788not been loaded yet, and second of all there are problems with inlined functions
1789in shared objects. Here are some suggestions to debugging your pass with
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1790GDB.</p>
Chris Lattner480e2ef2002-09-06 02:02:58 +0000[diff] [blame]1791
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1792<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]1793transformation invoked by <tt>opt</tt>, although nothing described here depends
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1794on that.</p>
1795
1796</div>
Chris Lattner480e2ef2002-09-06 02:02:58 +0000[diff] [blame]1797
1798<!-- _______________________________________________________________________ -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1799<div class="doc_subsubsection">
1800 <a name="breakpoint">Setting a breakpoint in your pass</a>
1801</div>
Chris Lattner480e2ef2002-09-06 02:02:58 +0000[diff] [blame]1802
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1803<div class="doc_text">
1804
1805<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]1806
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1807<div class="doc_code"><pre>
Chris Lattner480e2ef2002-09-06 02:02:58 +0000[diff] [blame]1808$ <b>gdb opt</b>
1809GNU gdb 5.0
1810Copyright 2000 Free Software Foundation, Inc.
1811GDB is free software, covered by the GNU General Public License, and you are
1812welcome to change it and/or distribute copies of it under certain conditions.
1813Type "show copying" to see the conditions.
1814There is absolutely no warranty for GDB. Type "show warranty" for details.
1815This GDB was configured as "sparc-sun-solaris2.6"...
1816(gdb)
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1817</pre></div>
Chris Lattner480e2ef2002-09-06 02:02:58 +0000[diff] [blame]1818
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1819<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]1820time to load. Be patient. Since we cannot set a breakpoint in our pass yet
1821(the shared object isn't loaded until runtime), we must execute the process, and
1822have it stop before it invokes our pass, but after it has loaded the shared
1823object. The most foolproof way of doing this is to set a breakpoint in
1824<tt>PassManager::run</tt> and then run the process with the arguments you
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1825want:</p>
Chris Lattner480e2ef2002-09-06 02:02:58 +0000[diff] [blame]1826
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1827<div class="doc_code"><pre>
Reid Spencer22a9e5b2006-09-28 16:53:47 +0000[diff] [blame]1828(gdb) <b>break llvm::PassManager::run</b>
Chris Lattner480e2ef2002-09-06 02:02:58 +0000[diff] [blame]1829Breakpoint 1 at 0x2413bc: file Pass.cpp, line 70.
Duncan Sands67f8a7b2010-07-08 08:27:18 +0000[diff] [blame]1830(gdb) <b>run test.bc -load $(LLVMTOP)/llvm/Debug+Asserts/lib/[libname].so -[passoption]</b>
1831Starting program: opt test.bc -load $(LLVMTOP)/llvm/Debug+Asserts/lib/[libname].so -[passoption]
Chris Lattner480e2ef2002-09-06 02:02:58 +0000[diff] [blame]1832Breakpoint 1, PassManager::run (this=0xffbef174, M=@0x70b298) at Pass.cpp:70
183370 bool PassManager::run(Module &amp;M) { return PM-&gt;run(M); }
1834(gdb)
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1835</pre></div>
Chris Lattner480e2ef2002-09-06 02:02:58 +0000[diff] [blame]1836
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1837<p>Once the <tt>opt</tt> stops in the <tt>PassManager::run</tt> method you are
1838now free to set breakpoints in your pass so that you can trace through execution
1839or do other standard debugging stuff.</p>
Chris Lattner480e2ef2002-09-06 02:02:58 +0000[diff] [blame]1840
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1841</div>
Chris Lattner480e2ef2002-09-06 02:02:58 +0000[diff] [blame]1842
1843<!-- _______________________________________________________________________ -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1844<div class="doc_subsubsection">
1845 <a name="debugmisc">Miscellaneous Problems</a>
1846</div>
Chris Lattner480e2ef2002-09-06 02:02:58 +0000[diff] [blame]1847
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1848<div class="doc_text">
1849
1850<p>Once you have the basics down, there are a couple of problems that GDB has,
1851some with solutions, some without.</p>
Chris Lattner480e2ef2002-09-06 02:02:58 +0000[diff] [blame]1852
1853<ul>
1854<li>Inline functions have bogus stack information. In general, GDB does a
1855pretty good job getting stack traces and stepping through inline functions.
1856When a pass is dynamically loaded however, it somehow completely loses this
1857capability. The only solution I know of is to de-inline a function (move it
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1858from the body of a class to a .cpp file).</li>
Chris Lattner480e2ef2002-09-06 02:02:58 +0000[diff] [blame]1859
1860<li>Restarting the program breaks breakpoints. After following the information
1861above, you have succeeded in getting some breakpoints planted in your pass. Nex
1862thing you know, you restart the program (i.e., you type '<tt>run</tt>' again),
1863and you start getting errors about breakpoints being unsettable. The only way I
1864have found to "fix" this problem is to <tt>delete</tt> the breakpoints that are
1865already set in your pass, run the program, and re-set the breakpoints once
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1866execution stops in <tt>PassManager::run</tt>.</li>
Chris Lattner480e2ef2002-09-06 02:02:58 +0000[diff] [blame]1867
1868</ul>
1869
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1870<p>Hopefully these tips will help with common case debugging situations. If
1871you'd like to contribute some tips of your own, just contact <a
1872href="mailto:sabre@nondot.org">Chris</a>.</p>
Chris Lattner480e2ef2002-09-06 02:02:58 +0000[diff] [blame]1873
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1874</div>
Chris Lattner480e2ef2002-09-06 02:02:58 +0000[diff] [blame]1875
1876<!-- *********************************************************************** -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1877<div class="doc_section">
1878 <a name="future">Future extensions planned</a>
1879</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1880<!-- *********************************************************************** -->
1881
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1882<div class="doc_text">
1883
1884<p>Although the LLVM Pass Infrastructure is very capable as it stands, and does
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1885some 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]1886where we are going:</p>
1887
1888</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1889
1890<!-- _______________________________________________________________________ -->
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]1891<div class="doc_subsubsection">
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1892 <a name="SMP">Multithreaded LLVM</a>
1893</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1894
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1895<div class="doc_text">
1896
1897<p>Multiple CPU machines are becoming more common and compilation can never be
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1898fast enough: obviously we should allow for a multithreaded compiler. Because of
1899the semantics defined for passes above (specifically they cannot maintain state
1900across invocations of their <tt>run*</tt> methods), a nice clean way to
1901implement a multithreaded compiler would be for the <tt>PassManager</tt> class
Misha Brukmanbc0e9982003-07-14 17:20:40 +0000[diff] [blame]1902to create multiple instances of each pass object, and allow the separate
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1903instances to be hacking on different parts of the program at the same time.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1904
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1905<p>This implementation would prevent each of the passes from having to implement
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1906multithreaded constructs, requiring only the LLVM core to have locking in a few
1907places (for global resources). Although this is a simple extension, we simply
1908haven't had time (or multiprocessor machines, thus a reason) to implement this.
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1909Despite that, we have kept the LLVM passes SMP ready, and you should too.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1910
Chris Lattnerb5c87f62007-05-18 05:36:14 +0000[diff] [blame]1911</div>
1912
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1913<!-- *********************************************************************** -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1914<hr>
1915<address>
1916 <a href="http://jigsaw.w3.org/css-validator/check/referer"><img
Misha Brukman44408702008-12-11 17:34:48 +0000[diff] [blame]1917 src="http://jigsaw.w3.org/css-validator/images/vcss-blue" alt="Valid CSS"></a>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1918 <a href="http://validator.w3.org/check/referer"><img
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Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1920
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1921 <a href="mailto:sabre@nondot.org">Chris Lattner</a><br>
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]1922 <a href="http://llvm.org">The LLVM Compiler Infrastructure</a><br>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1923 Last modified: $Date$
1924</address>
1925
1926</body>
1927</html>