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gerrit-public.fairphone.software / fp2-dev / platform / external / llvm / ab4c366274a582dd8146b2820c6b999cad5fce36 / . / 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
Duncan Sandsdc97c0b2011-01-01 17:28:49 +0000[diff] [blame]181 <p>First, configure and build LLVM. This needs to be done directly inside the
182 LLVM source tree rather than in a separate objects directory.
183 Next, you need to create a new directory somewhere in the LLVM source
Reid Spencer1bc19342004-12-11 05:12:57 +0000[diff] [blame]184 base. For this example, we'll assume that you made
Duncan Sandsdc97c0b2011-01-01 17:28:49 +0000[diff] [blame]185 <tt>lib/Transforms/Hello</tt>. Finally, you must set up a build script
Reid Spencer1bc19342004-12-11 05:12:57 +0000[diff] [blame]186 (Makefile) that will compile the source code for the new pass. To do this,
187 copy the following into <tt>Makefile</tt>:</p>
188 <hr/>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]189
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]190<div class="doc_code"><pre>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]191# Makefile for hello pass
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]192
Torok Edwin87469292009-10-12 13:37:29 +0000[diff] [blame]193# Path to top level of LLVM hierarchy
Chris Lattner7ce83e52002-08-14 20:07:01 +0000[diff] [blame]194LEVEL = ../../..
Chris Lattner17a4c3e2002-08-14 20:06:13 +0000[diff] [blame]195
196# Name of the library to build
Reid Spencer7fa6d522005-01-11 05:16:23 +0000[diff] [blame]197LIBRARYNAME = Hello
Chris Lattner17a4c3e2002-08-14 20:06:13 +0000[diff] [blame]198
Reid Spencer7fa6d522005-01-11 05:16:23 +0000[diff] [blame]199# Make the shared library become a loadable module so the tools can
200# dlopen/dlsym on the resulting library.
Robert Bocchino3cf817d2006-01-06 22:49:23 +0000[diff] [blame]201LOADABLE_MODULE = 1
Reid Spencer7fa6d522005-01-11 05:16:23 +0000[diff] [blame]202
Chris Lattner17a4c3e2002-08-14 20:06:13 +0000[diff] [blame]203# Include the makefile implementation stuff
204include $(LEVEL)/Makefile.common
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]205</pre></div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]206
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]207<p>This makefile specifies that all of the <tt>.cpp</tt> files in the current
Duncan Sands779ff7f2011-01-01 17:21:58 +0000[diff] [blame]208directory are to be compiled and linked together into a shared object
209<tt>$(LEVEL)/Debug+Asserts/lib/Hello.so</tt> that can be dynamically loaded by
Chris Lattnerc8603c22006-08-27 23:18:52 +0000[diff] [blame]210the <tt>opt</tt> or <tt>bugpoint</tt> tools via their <tt>-load</tt> options.
Reid Spencer7fa6d522005-01-11 05:16:23 +0000[diff] [blame]211If your operating system uses a suffix other than .so (such as windows or
212Mac OS/X), the appropriate extension will be used.</p>
John Criswellf9c78652004-01-26 21:26:54 +0000[diff] [blame]213
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]214<p>Now that we have the build scripts set up, we just need to write the code for
215the pass itself.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]216
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]217</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]218
219<!-- ======================================================================= -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]220<div class="doc_subsection">
221 <a name="basiccode">Basic code required</a>
222</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]223
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]224<div class="doc_text">
225
226<p>Now that we have a way to compile our new pass, we just have to write it.
227Start out with:</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]228
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]229<div class="doc_code"><pre>
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]230<b>#include</b> "<a href="http://llvm.org/doxygen/Pass_8h-source.html">llvm/Pass.h</a>"
231<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]232<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]233</pre></div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]234
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]235<p>Which are needed because we are writing a <tt><a
Chris Lattner0ce6f932009-09-08 05:14:44 +0000[diff] [blame]236href="http://llvm.org/doxygen/classllvm_1_1Pass.html">Pass</a></tt>,
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]237we are operating on <tt><a
Chris Lattner0ce6f932009-09-08 05:14:44 +0000[diff] [blame]238href="http://llvm.org/doxygen/classllvm_1_1Function.html">Function</a></tt>'s,
239and we will be doing some printing.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]240
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]241<p>Next we have:</p>
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]242<div class="doc_code"><pre>
Jonathan Manton65acb302004-06-30 18:10:30 +0000[diff] [blame]243<b>using namespace llvm;</b>
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]244</pre></div>
Jonathan Manton65acb302004-06-30 18:10:30 +0000[diff] [blame]245<p>... which is required because the functions from the include files
246live in the llvm namespace.
247</p>
248
249<p>Next we have:</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]250
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]251<div class="doc_code"><pre>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]252<b>namespace</b> {
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]253</pre></div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]254
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]255<p>... which starts out an anonymous namespace. Anonymous namespaces are to C++
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]256what the "<tt>static</tt>" keyword is to C (at global scope). It makes the
257things declared inside of the anonymous namespace only visible to the current
258file. If you're not familiar with them, consult a decent C++ book for more
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]259information.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]260
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]261<p>Next, we declare our pass itself:</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]262
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]263<div class="doc_code"><pre>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]264 <b>struct</b> Hello : <b>public</b> <a href="#FunctionPass">FunctionPass</a> {
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]265</pre></div><p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]266
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]267<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]268href="http://llvm.org/doxygen/classllvm_1_1FunctionPass.html">FunctionPass</a></tt>.
Chris Lattnerd6ea9262002-09-09 03:48:46 +0000[diff] [blame]269The different builtin pass subclasses are described in detail <a
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]270href="#passtype">later</a>, but for now, know that <a
271href="#FunctionPass"><tt>FunctionPass</tt></a>'s operate a function at a
272time.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]273
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]274<div class="doc_code"><pre>
Devang Patel19974732007-05-03 01:11:54 +0000[diff] [blame]275 static char ID;
Duncan Sands5e09eef2011-01-01 17:37:07 +0000[diff] [blame]276 Hello() : FunctionPass(ID) {}
Devang Patele50fb9a2007-05-01 20:55:38 +0000[diff] [blame]277</pre></div><p>
278
279<p> This declares pass identifier used by LLVM to identify pass. This allows LLVM to
280avoid using expensive C++ runtime information.</p>
281
282<div class="doc_code"><pre>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]283 <b>virtual bool</b> <a href="#runOnFunction">runOnFunction</a>(Function &amp;F) {
Chris Lattner0ce6f932009-09-08 05:14:44 +0000[diff] [blame]284 errs() &lt;&lt; "<i>Hello: </i>" &lt;&lt; F.getName() &lt;&lt; "\n";
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]285 <b>return false</b>;
286 }
287 }; <i>// end of struct Hello</i>
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]288</pre></div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]289
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]290<p>We declare a "<a href="#runOnFunction"><tt>runOnFunction</tt></a>" method,
291which overloads an abstract virtual method inherited from <a
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]292href="#FunctionPass"><tt>FunctionPass</tt></a>. This is where we are supposed
293to 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]294function.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]295
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]296<div class="doc_code"><pre>
Devang Patel19974732007-05-03 01:11:54 +0000[diff] [blame]297 char Hello::ID = 0;
Devang Patele50fb9a2007-05-01 20:55:38 +0000[diff] [blame]298</pre></div>
299
300<p> We initialize pass ID here. LLVM uses ID's address to identify pass so
301initialization value is not important.</p>
302
303<div class="doc_code"><pre>
Duncan Sands5e09eef2011-01-01 17:37:07 +0000[diff] [blame]304 static RegisterPass<Hello> X("<i>hello</i>", "<i>Hello World Pass</i>",
Devang Patelc7582092008-03-19 21:56:59 +0000[diff] [blame]305 false /* Only looks at CFG */,
306 false /* Analysis Pass */);
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]307} <i>// end of anonymous namespace</i>
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]308</pre></div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]309
Chris Lattnerc8603c22006-08-27 23:18:52 +0000[diff] [blame]310<p>Lastly, we <a href="#registration">register our class</a> <tt>Hello</tt>,
311giving it a command line
Devang Patelc7582092008-03-19 21:56:59 +0000[diff] [blame]312argument "<tt>hello</tt>", and a name "<tt>Hello World Pass</tt>".
Owen Anderson20813e02010-07-21 22:58:07 +0000[diff] [blame]313Last two arguments describe its behavior.
Devang Patelc7582092008-03-19 21:56:59 +0000[diff] [blame]314If a pass walks CFG without modifying it then third argument is set to true.
315If a pass is an analysis pass, for example dominator tree pass, then true
316is supplied as fourth argument. </p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]317
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]318<p>As a whole, the <tt>.cpp</tt> file looks like:</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]319
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]320<div class="doc_code"><pre>
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]321<b>#include</b> "<a href="http://llvm.org/doxygen/Pass_8h-source.html">llvm/Pass.h</a>"
322<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]323<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]324
Jonathan Manton65acb302004-06-30 18:10:30 +0000[diff] [blame]325<b>using namespace llvm;</b>
326
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]327<b>namespace</b> {
328 <b>struct Hello</b> : <b>public</b> <a href="#FunctionPass">FunctionPass</a> {
Devang Patele50fb9a2007-05-01 20:55:38 +0000[diff] [blame]329
Devang Patel19974732007-05-03 01:11:54 +0000[diff] [blame]330 static char ID;
Duncan Sands5e09eef2011-01-01 17:37:07 +0000[diff] [blame]331 Hello() : FunctionPass(ID) {}
Devang Patele50fb9a2007-05-01 20:55:38 +0000[diff] [blame]332
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]333 <b>virtual bool</b> <a href="#runOnFunction">runOnFunction</a>(Function &amp;F) {
Chris Lattner0ce6f932009-09-08 05:14:44 +0000[diff] [blame]334 errs() &lt;&lt; "<i>Hello: </i>" &lt;&lt; F.getName() &lt;&lt; "\n";
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]335 <b>return false</b>;
336 }
337 };
338
Devang Patel26e5a302007-07-25 21:05:39 +0000[diff] [blame]339 char Hello::ID = 0;
Duncan Sands5e09eef2011-01-01 17:37:07 +0000[diff] [blame]340 static RegisterPass<Hello> X("hello", "Hello World Pass", false, false);
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]341}
Owen Anderson20813e02010-07-21 22:58:07 +0000[diff] [blame]342
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]343</pre></div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]344
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]345<p>Now that it's all together, compile the file with a simple "<tt>gmake</tt>"
Duncan Sands779ff7f2011-01-01 17:21:58 +0000[diff] [blame]346command in the local directory and you should get a new file
347"<tt>Debug+Asserts/lib/Hello.so</tt>" under the top level directory of the LLVM
348source tree (not in the local directory). Note that everything in this file is
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]349contained in an anonymous namespace: this reflects the fact that passes are self
350contained units that do not need external interfaces (although they can have
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]351them) to be useful.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]352
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]353</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]354
355<!-- ======================================================================= -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]356<div class="doc_subsection">
Chris Lattnerc8603c22006-08-27 23:18:52 +0000[diff] [blame]357 <a name="running">Running a pass with <tt>opt</tt></a>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]358</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]359
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]360<div class="doc_text">
361
John Criswellf9c78652004-01-26 21:26:54 +0000[diff] [blame]362<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]363<tt>opt</tt> command to run an LLVM program through your pass. Because you
Duncan Sands5e09eef2011-01-01 17:37:07 +0000[diff] [blame]364registered your pass with <tt>RegisterPass</tt>, you will be able to
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]365use the <tt>opt</tt> tool to access it, once loaded.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]366
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]367<p>To test it, follow the example at the end of the <a
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]368href="GettingStarted.html">Getting Started Guide</a> to compile "Hello World" to
Gabor Greif04367bf2007-07-06 22:07:22 +0000[diff] [blame]369LLVM. We can now run the bitcode file (<tt>hello.bc</tt>) for the program
370through our transformation like this (or course, any bitcode file will
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]371work):</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]372
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]373<div class="doc_code"><pre>
Duncan Sands67f8a7b2010-07-08 08:27:18 +0000[diff] [blame]374$ opt -load ../../../Debug+Asserts/lib/Hello.so -hello &lt; hello.bc &gt; /dev/null
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]375Hello: __main
376Hello: puts
377Hello: main
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]378</pre></div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]379
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]380<p>The '<tt>-load</tt>' option specifies that '<tt>opt</tt>' should load your
381pass as a shared object, which makes '<tt>-hello</tt>' a valid command line
382argument (which is one reason you need to <a href="#registration">register your
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]383pass</a>). Because the hello pass does not modify the program in any
384interesting way, we just throw away the result of <tt>opt</tt> (sending it to
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]385<tt>/dev/null</tt>).</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]386
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]387<p>To see what happened to the other string you registered, try running
Duncan Sands7e7ae5a2010-02-18 14:08:13 +0000[diff] [blame]388<tt>opt</tt> with the <tt>-help</tt> option:</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]389
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]390<div class="doc_code"><pre>
Duncan Sands67f8a7b2010-07-08 08:27:18 +0000[diff] [blame]391$ opt -load ../../../Debug+Asserts/lib/Hello.so -help
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]392OVERVIEW: llvm .bc -&gt; .bc modular optimizer
393
Gabor Greif04367bf2007-07-06 22:07:22 +0000[diff] [blame]394USAGE: opt [options] &lt;input bitcode&gt;
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]395
396OPTIONS:
397 Optimizations available:
398...
399 -funcresolve - Resolve Functions
400 -gcse - Global Common Subexpression Elimination
401 -globaldce - Dead Global Elimination
402 <b>-hello - Hello World Pass</b>
Chris Lattner065a6162003-09-10 05:29:43 +0000[diff] [blame]403 -indvars - Canonicalize Induction Variables
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]404 -inline - Function Integration/Inlining
405 -instcombine - Combine redundant instructions
406...
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]407</pre></div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]408
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]409<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]410documentation to users of <tt>opt</tt>. Now that you have a working pass, you
411would go ahead and make it do the cool transformations you want. Once you get
412it all working and tested, it may become useful to find out how fast your pass
413is. The <a href="#passManager"><tt>PassManager</tt></a> provides a nice command
414line option (<tt>--time-passes</tt>) that allows you to get information about
415the execution time of your pass along with the other passes you queue up. For
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]416example:</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]417
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]418<div class="doc_code"><pre>
Duncan Sands67f8a7b2010-07-08 08:27:18 +0000[diff] [blame]419$ 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]420Hello: __main
421Hello: puts
422Hello: main
423===============================================================================
424 ... Pass execution timing report ...
425===============================================================================
426 Total Execution Time: 0.02 seconds (0.0479059 wall clock)
427
428 ---User Time--- --System Time-- --User+System-- ---Wall Time--- --- Pass Name ---
Gabor Greif04367bf2007-07-06 22:07:22 +0000[diff] [blame]429 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]430 0.0000 ( 0.0%) 0.0100 (100.0%) 0.0100 ( 50.0%) 0.0031 ( 6.4%) Dominator Set Construction
431 0.0000 ( 0.0%) 0.0000 ( 0.0%) 0.0000 ( 0.0%) 0.0013 ( 2.7%) Module Verifier
432 <b> 0.0000 ( 0.0%) 0.0000 ( 0.0%) 0.0000 ( 0.0%) 0.0033 ( 6.9%) Hello World Pass</b>
433 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]434</pre></div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]435
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]436<p>As you can see, our implementation above is pretty fast :). The additional
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]437passes listed are automatically inserted by the '<tt>opt</tt>' tool to verify
438that the LLVM emitted by your pass is still valid and well formed LLVM, which
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]439hasn't been broken somehow.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]440
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]441<p>Now that you have seen the basics of the mechanics behind passes, we can talk
442about some more details of how they work and how to use them.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]443
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]444</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]445
446<!-- *********************************************************************** -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]447<div class="doc_section">
448 <a name="passtype">Pass classes and requirements</a>
449</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]450<!-- *********************************************************************** -->
451
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]452<div class="doc_text">
453
454<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]455decide what class you should subclass for your pass. The <a
456href="#basiccode">Hello World</a> example uses the <tt><a
457href="#FunctionPass">FunctionPass</a></tt> class for its implementation, but we
458did not discuss why or when this should occur. Here we talk about the classes
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]459available, from the most general to the most specific.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]460
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]461<p>When choosing a superclass for your Pass, you should choose the <b>most
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]462specific</b> class possible, while still being able to meet the requirements
Misha Brukman5560c9d2003-08-18 14:43:39 +0000[diff] [blame]463listed. This gives the LLVM Pass Infrastructure information necessary to
Benjamin Kramer8040cd32009-10-12 14:46:08 +0000[diff] [blame]464optimize how passes are run, so that the resultant compiler isn't unnecessarily
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]465slow.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]466
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]467</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]468
Chris Lattnerf004f9a2002-09-25 22:31:38 +0000[diff] [blame]469<!-- ======================================================================= -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]470<div class="doc_subsection">
471 <a name="ImmutablePass">The <tt>ImmutablePass</tt> class</a>
472</div>
Chris Lattnerf004f9a2002-09-25 22:31:38 +0000[diff] [blame]473
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]474<div class="doc_text">
475
476<p>The most plain and boring type of pass is the "<tt><a
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]477href="http://llvm.org/doxygen/classllvm_1_1ImmutablePass.html">ImmutablePass</a></tt>"
Chris Lattnerf004f9a2002-09-25 22:31:38 +0000[diff] [blame]478class. This pass type is used for passes that do not have to be run, do not
479change state, and never need to be updated. This is not a normal type of
480transformation or analysis, but can provide information about the current
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]481compiler configuration.</p>
Chris Lattnerf004f9a2002-09-25 22:31:38 +0000[diff] [blame]482
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]483<p>Although this pass class is very infrequently used, it is important for
Chris Lattnerf004f9a2002-09-25 22:31:38 +0000[diff] [blame]484providing information about the current target machine being compiled for, and
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]485other static information that can affect the various transformations.</p>
Chris Lattnerf004f9a2002-09-25 22:31:38 +0000[diff] [blame]486
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]487<p><tt>ImmutablePass</tt>es never invalidate other transformations, are never
488invalidated, and are never "run".</p>
Chris Lattnerf004f9a2002-09-25 22:31:38 +0000[diff] [blame]489
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]490</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]491
492<!-- ======================================================================= -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]493<div class="doc_subsection">
Chris Lattnerf6278922004-09-20 04:36:29 +0000[diff] [blame]494 <a name="ModulePass">The <tt>ModulePass</tt> class</a>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]495</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]496
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]497<div class="doc_text">
498
499<p>The "<tt><a
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]500href="http://llvm.org/doxygen/classllvm_1_1ModulePass.html">ModulePass</a></tt>"
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]501class is the most general of all superclasses that you can use. Deriving from
Chris Lattnerf6278922004-09-20 04:36:29 +0000[diff] [blame]502<tt>ModulePass</tt> indicates that your pass uses the entire program as a unit,
Benjamin Kramer8040cd32009-10-12 14:46:08 +0000[diff] [blame]503referring to function bodies in no predictable order, or adding and removing
Chris Lattnerf6278922004-09-20 04:36:29 +0000[diff] [blame]504functions. Because nothing is known about the behavior of <tt>ModulePass</tt>
Daniel Dunbarb71725b2009-07-01 23:38:44 +0000[diff] [blame]505subclasses, no optimization can be done for their execution.</p>
506
507<p>A module pass can use function level passes (e.g. dominators) using
508the getAnalysis interface
509<tt>getAnalysis&lt;DominatorTree&gt;(llvm::Function *)</tt> to provide the
510function to retrieve analysis result for, if the function pass does not require
Devang Patel468857f2009-08-10 16:37:29 +0000[diff] [blame]511any 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]512analysis ran, e.g. in the case of dominators you should only ask for the
513DominatorTree for function definitions, not declarations.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]514
Chris Lattnerf6278922004-09-20 04:36:29 +0000[diff] [blame]515<p>To write a correct <tt>ModulePass</tt> subclass, derive from
516<tt>ModulePass</tt> and overload the <tt>runOnModule</tt> method with the
517following signature:</p>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]518
519</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]520
521<!-- _______________________________________________________________________ -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]522<div class="doc_subsubsection">
Chris Lattnerf6278922004-09-20 04:36:29 +0000[diff] [blame]523 <a name="runOnModule">The <tt>runOnModule</tt> method</a>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]524</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]525
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]526<div class="doc_text">
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]527
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]528<div class="doc_code"><pre>
Chris Lattnerf6278922004-09-20 04:36:29 +0000[diff] [blame]529 <b>virtual bool</b> runOnModule(Module &amp;M) = 0;
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]530</pre></div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]531
John Criswell2382ff72005-07-15 19:25:12 +0000[diff] [blame]532<p>The <tt>runOnModule</tt> method performs the interesting work of the pass.
533It should return true if the module was modified by the transformation and
534false otherwise.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]535
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]536</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]537
538<!-- ======================================================================= -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]539<div class="doc_subsection">
Chris Lattner8fdb2462004-09-18 06:39:35 +0000[diff] [blame]540 <a name="CallGraphSCCPass">The <tt>CallGraphSCCPass</tt> class</a>
541</div>
542
543<div class="doc_text">
544
545<p>The "<tt><a
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]546href="http://llvm.org/doxygen/classllvm_1_1CallGraphSCCPass.html">CallGraphSCCPass</a></tt>"
Chris Lattner8fdb2462004-09-18 06:39:35 +0000[diff] [blame]547is used by passes that need to traverse the program bottom-up on the call graph
548(callees before callers). Deriving from CallGraphSCCPass provides some
549mechanics for building and traversing the CallGraph, but also allows the system
550to optimize execution of CallGraphSCCPass's. If your pass meets the
551requirements outlined below, and doesn't meet the requirements of a <tt><a
552href="#FunctionPass">FunctionPass</a></tt> or <tt><a
553href="#BasicBlockPass">BasicBlockPass</a></tt>, you should derive from
554<tt>CallGraphSCCPass</tt>.</p>
555
556<p><b>TODO</b>: explain briefly what SCC, Tarjan's algo, and B-U mean.</p>
557
558<p>To be explicit, <tt>CallGraphSCCPass</tt> subclasses are:</p>
559
560<ol>
561
Nick Lewycky99597062011-01-03 06:16:07 +0000[diff] [blame]562<li>... <em>not allowed</em> to inspect or modify any <tt>Function</tt>s other
563than those in the current SCC and the direct callers and direct callees of the
564SCC.</li>
Chris Lattner8fdb2462004-09-18 06:39:35 +0000[diff] [blame]565
566<li>... <em>required</em> to preserve the current CallGraph object, updating it
567to reflect any changes made to the program.</li>
568
569<li>... <em>not allowed</em> to add or remove SCC's from the current Module,
570though they may change the contents of an SCC.</li>
571
572<li>... <em>allowed</em> to add or remove global variables from the current
573Module.</li>
574
575<li>... <em>allowed</em> to maintain state across invocations of
576 <a href="#runOnSCC"><tt>runOnSCC</tt></a> (including global data).</li>
577</ol>
578
579<p>Implementing a <tt>CallGraphSCCPass</tt> is slightly tricky in some cases
580because it has to handle SCCs with more than one node in it. All of the virtual
581methods described below should return true if they modified the program, or
582false if they didn't.</p>
583
584</div>
585
586<!-- _______________________________________________________________________ -->
587<div class="doc_subsubsection">
Devang Patelc20048d2007-01-23 22:56:28 +0000[diff] [blame]588 <a name="doInitialization_scc">The <tt>doInitialization(CallGraph &amp;)</tt>
Chris Lattner8fdb2462004-09-18 06:39:35 +0000[diff] [blame]589 method</a>
590</div>
591
592<div class="doc_text">
593
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]594<div class="doc_code"><pre>
Devang Patelc20048d2007-01-23 22:56:28 +0000[diff] [blame]595 <b>virtual bool</b> doInitialization(CallGraph &amp;CG);
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]596</pre></div>
Chris Lattner8fdb2462004-09-18 06:39:35 +0000[diff] [blame]597
598<p>The <tt>doIninitialize</tt> method is allowed to do most of the things that
599<tt>CallGraphSCCPass</tt>'s are not allowed to do. They can add and remove
600functions, get pointers to functions, etc. The <tt>doInitialization</tt> method
601is designed to do simple initialization type of stuff that does not depend on
602the SCCs being processed. The <tt>doInitialization</tt> method call is not
603scheduled to overlap with any other pass executions (thus it should be very
604fast).</p>
605
606</div>
607
608<!-- _______________________________________________________________________ -->
609<div class="doc_subsubsection">
610 <a name="runOnSCC">The <tt>runOnSCC</tt> method</a>
611</div>
612
613<div class="doc_text">
614
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]615<div class="doc_code"><pre>
Chris Lattner6f25d9f2010-04-16 23:07:44 +0000[diff] [blame]616 <b>virtual bool</b> runOnSCC(CallGraphSCC &amp;SCC) = 0;
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]617</pre></div>
Chris Lattner8fdb2462004-09-18 06:39:35 +0000[diff] [blame]618
619<p>The <tt>runOnSCC</tt> method performs the interesting work of the pass, and
620should return true if the module was modified by the transformation, false
621otherwise.</p>
622
623</div>
624
625<!-- _______________________________________________________________________ -->
626<div class="doc_subsubsection">
Devang Patelc20048d2007-01-23 22:56:28 +0000[diff] [blame]627 <a name="doFinalization_scc">The <tt>doFinalization(CallGraph
Chris Lattner8fdb2462004-09-18 06:39:35 +0000[diff] [blame]628 &amp;)</tt> method</a>
629</div>
630
631<div class="doc_text">
632
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]633<div class="doc_code"><pre>
Devang Patelc20048d2007-01-23 22:56:28 +0000[diff] [blame]634 <b>virtual bool</b> doFinalization(CallGraph &amp;CG);
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]635</pre></div>
Chris Lattner8fdb2462004-09-18 06:39:35 +0000[diff] [blame]636
637<p>The <tt>doFinalization</tt> method is an infrequently used method that is
638called when the pass framework has finished calling <a
639href="#runOnFunction"><tt>runOnFunction</tt></a> for every function in the
640program being compiled.</p>
641
642</div>
643
644<!-- ======================================================================= -->
645<div class="doc_subsection">
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]646 <a name="FunctionPass">The <tt>FunctionPass</tt> class</a>
647</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]648
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]649<div class="doc_text">
650
Chris Lattnerf6278922004-09-20 04:36:29 +0000[diff] [blame]651<p>In contrast to <tt>ModulePass</tt> subclasses, <tt><a
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]652href="http://llvm.org/doxygen/classllvm_1_1Pass.html">FunctionPass</a></tt>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]653subclasses do have a predictable, local behavior that can be expected by the
654system. All <tt>FunctionPass</tt> execute on each function in the program
Misha Brukmanef6a6a62003-08-21 22:14:26 +0000[diff] [blame]655independent of all of the other functions in the program.
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]656<tt>FunctionPass</tt>'s do not require that they are executed in a particular
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]657order, and <tt>FunctionPass</tt>'s do not modify external functions.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]658
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]659<p>To be explicit, <tt>FunctionPass</tt> subclasses are not allowed to:</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]660
661<ol>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]662<li>Modify a Function other than the one currently being processed.</li>
663<li>Add or remove Function's from the current Module.</li>
664<li>Add or remove global variables from the current Module.</li>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]665<li>Maintain state across invocations of
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]666 <a href="#runOnFunction"><tt>runOnFunction</tt></a> (including global data)</li>
667</ol>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]668
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]669<p>Implementing a <tt>FunctionPass</tt> is usually straightforward (See the <a
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]670href="#basiccode">Hello World</a> pass for example). <tt>FunctionPass</tt>'s
671may overload three virtual methods to do their work. All of these methods
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]672should return true if they modified the program, or false if they didn't.</p>
673
674</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]675
676<!-- _______________________________________________________________________ -->
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]677<div class="doc_subsubsection">
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]678 <a name="doInitialization_mod">The <tt>doInitialization(Module &amp;)</tt>
679 method</a>
680</div>
681
682<div class="doc_text">
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]683
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]684<div class="doc_code"><pre>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]685 <b>virtual bool</b> doInitialization(Module &amp;M);
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]686</pre></div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]687
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]688<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]689<tt>FunctionPass</tt>'s are not allowed to do. They can add and remove
Chris Lattnerd0713f92002-09-12 17:06:43 +0000[diff] [blame]690functions, get pointers to functions, etc. The <tt>doInitialization</tt> method
691is designed to do simple initialization type of stuff that does not depend on
692the functions being processed. The <tt>doInitialization</tt> method call is not
693scheduled to overlap with any other pass executions (thus it should be very
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]694fast).</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]695
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]696<p>A good example of how this method should be used is the <a
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]697href="http://llvm.org/doxygen/LowerAllocations_8cpp-source.html">LowerAllocations</a>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]698pass. This pass converts <tt>malloc</tt> and <tt>free</tt> instructions into
Misha Brukmanef6a6a62003-08-21 22:14:26 +0000[diff] [blame]699platform dependent <tt>malloc()</tt> and <tt>free()</tt> function calls. It
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]700uses the <tt>doInitialization</tt> method to get a reference to the malloc and
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]701free functions that it needs, adding prototypes to the module if necessary.</p>
702
703</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]704
705<!-- _______________________________________________________________________ -->
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]706<div class="doc_subsubsection">
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]707 <a name="runOnFunction">The <tt>runOnFunction</tt> method</a>
708</div>
709
710<div class="doc_text">
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]711
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]712<div class="doc_code"><pre>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]713 <b>virtual bool</b> runOnFunction(Function &amp;F) = 0;
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]714</pre></div><p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]715
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]716<p>The <tt>runOnFunction</tt> method must be implemented by your subclass to do
717the transformation or analysis work of your pass. As usual, a true value should
718be returned if the function is modified.</p>
719
720</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]721
722<!-- _______________________________________________________________________ -->
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]723<div class="doc_subsubsection">
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]724 <a name="doFinalization_mod">The <tt>doFinalization(Module
725 &amp;)</tt> method</a>
726</div>
727
728<div class="doc_text">
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]729
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]730<div class="doc_code"><pre>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]731 <b>virtual bool</b> doFinalization(Module &amp;M);
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]732</pre></div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]733
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]734<p>The <tt>doFinalization</tt> method is an infrequently used method that is
735called when the pass framework has finished calling <a
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]736href="#runOnFunction"><tt>runOnFunction</tt></a> for every function in the
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]737program being compiled.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]738
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]739</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]740
741<!-- ======================================================================= -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]742<div class="doc_subsection">
Devang Patel2e8f27d2007-03-19 22:21:25 +0000[diff] [blame]743 <a name="LoopPass">The <tt>LoopPass</tt> class </a>
744</div>
745
746<div class="doc_text">
747
748<p> All <tt>LoopPass</tt> execute on each loop in the function independent of
749all of the other loops in the function. <tt>LoopPass</tt> processes loops in
750loop nest order such that outer most loop is processed last. </p>
751
752<p> <tt>LoopPass</tt> subclasses are allowed to update loop nest using
753<tt>LPPassManager</tt> interface. Implementing a loop pass is usually
754straightforward. <tt>Looppass</tt>'s may overload three virtual methods to
755do their work. All these methods should return true if they modified the
756program, or false if they didn't. </p>
757</div>
758
759<!-- _______________________________________________________________________ -->
760<div class="doc_subsubsection">
761 <a name="doInitialization_loop">The <tt>doInitialization(Loop *,
762 LPPassManager &amp;)</tt>
763 method</a>
764</div>
765
766<div class="doc_text">
767
768<div class="doc_code"><pre>
769 <b>virtual bool</b> doInitialization(Loop *, LPPassManager &amp;LPM);
770</pre></div>
771
Chris Lattnerb5c87f62007-05-18 05:36:14 +0000[diff] [blame]772<p>The <tt>doInitialization</tt> method is designed to do simple initialization
Devang Patel2e8f27d2007-03-19 22:21:25 +0000[diff] [blame]773type of stuff that does not depend on the functions being processed. The
774<tt>doInitialization</tt> method call is not scheduled to overlap with any
775other pass executions (thus it should be very fast). LPPassManager
776interface should be used to access Function or Module level analysis
777information.</p>
778
779</div>
780
781
782<!-- _______________________________________________________________________ -->
783<div class="doc_subsubsection">
784 <a name="runOnLoop">The <tt>runOnLoop</tt> method</a>
785</div>
786
787<div class="doc_text">
788
789<div class="doc_code"><pre>
790 <b>virtual bool</b> runOnLoop(Loop *, LPPassManager &amp;LPM) = 0;
791</pre></div><p>
792
793<p>The <tt>runOnLoop</tt> method must be implemented by your subclass to do
794the transformation or analysis work of your pass. As usual, a true value should
795be returned if the function is modified. <tt>LPPassManager</tt> interface
796should be used to update loop nest.</p>
797
798</div>
799
800<!-- _______________________________________________________________________ -->
801<div class="doc_subsubsection">
802 <a name="doFinalization_loop">The <tt>doFinalization()</tt> method</a>
803</div>
804
805<div class="doc_text">
806
807<div class="doc_code"><pre>
808 <b>virtual bool</b> doFinalization();
809</pre></div>
810
811<p>The <tt>doFinalization</tt> method is an infrequently used method that is
812called when the pass framework has finished calling <a
813href="#runOnLoop"><tt>runOnLoop</tt></a> for every loop in the
814program being compiled. </p>
815
816</div>
817
Tobias Grosser65513602010-10-20 01:54:44 +0000[diff] [blame]818<!-- ======================================================================= -->
819<div class="doc_subsection">
820 <a name="RegionPass">The <tt>RegionPass</tt> class </a>
821</div>
822
823<div class="doc_text">
824
825<p> <tt>RegionPass</tt> is similar to <a href="#LoopPass"><tt>LoopPass</tt></a>,
826but executes on each single entry single exit region in the function.
827<tt>RegionPass</tt> processes regions in nested order such that the outer most
828region is processed last. </p>
829
830<p> <tt>RegionPass</tt> subclasses are allowed to update the region tree by using
831the <tt>RGPassManager</tt> interface. You may overload three virtual methods of
832<tt>RegionPass</tt> to implementing your own region pass is usually. All these
833methods should return true if they modified the program, or false if they didn not.
834</p>
835</div>
836
837<!-- _______________________________________________________________________ -->
838<div class="doc_subsubsection">
839 <a name="doInitialization_region">The <tt>doInitialization(Region *,
840 RGPassManager &amp;)</tt>
841 method</a>
842</div>
843
844<div class="doc_text">
845
846<div class="doc_code"><pre>
847 <b>virtual bool</b> doInitialization(Region *, RGPassManager &amp;RGM);
848</pre></div>
849
850<p>The <tt>doInitialization</tt> method is designed to do simple initialization
851type of stuff that does not depend on the functions being processed. The
852<tt>doInitialization</tt> method call is not scheduled to overlap with any
853other pass executions (thus it should be very fast). RPPassManager
854interface should be used to access Function or Module level analysis
855information.</p>
856
857</div>
858
859
860<!-- _______________________________________________________________________ -->
861<div class="doc_subsubsection">
862 <a name="runOnRegion">The <tt>runOnRegion</tt> method</a>
863</div>
864
865<div class="doc_text">
866
867<div class="doc_code"><pre>
868 <b>virtual bool</b> runOnRegion(Region *, RGPassManager &amp;RGM) = 0;
869</pre></div><p>
870
871<p>The <tt>runOnRegion</tt> method must be implemented by your subclass to do
872the transformation or analysis work of your pass. As usual, a true value should
873be returned if the region is modified. <tt>RGPassManager</tt> interface
874should be used to update region tree.</p>
875
876</div>
877
878<!-- _______________________________________________________________________ -->
879<div class="doc_subsubsection">
880 <a name="doFinalization_region">The <tt>doFinalization()</tt> method</a>
881</div>
882
883<div class="doc_text">
884
885<div class="doc_code"><pre>
886 <b>virtual bool</b> doFinalization();
887</pre></div>
888
889<p>The <tt>doFinalization</tt> method is an infrequently used method that is
890called when the pass framework has finished calling <a
891href="#runOnRegion"><tt>runOnRegion</tt></a> for every region in the
892program being compiled. </p>
893
894</div>
895
Devang Patel2e8f27d2007-03-19 22:21:25 +0000[diff] [blame]896
897
898<!-- ======================================================================= -->
899<div class="doc_subsection">
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]900 <a name="BasicBlockPass">The <tt>BasicBlockPass</tt> class</a>
901</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]902
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]903<div class="doc_text">
904
905<p><tt>BasicBlockPass</tt>'s are just like <a
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]906href="#FunctionPass"><tt>FunctionPass</tt></a>'s, except that they must limit
907their scope of inspection and modification to a single basic block at a time.
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]908As such, they are <b>not</b> allowed to do any of the following:</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]909
910<ol>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]911<li>Modify or inspect any basic blocks outside of the current one</li>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]912<li>Maintain state across invocations of
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]913 <a href="#runOnBasicBlock"><tt>runOnBasicBlock</tt></a></li>
Reid Spencer1bc19342004-12-11 05:12:57 +0000[diff] [blame]914<li>Modify the control flow graph (by altering terminator instructions)</li>
915<li>Any of the things forbidden for
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]916 <a href="#FunctionPass"><tt>FunctionPass</tt></a>es.</li>
917</ol>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]918
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]919<p><tt>BasicBlockPass</tt>es are useful for traditional local and "peephole"
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]920optimizations. They may override the same <a
Chris Lattnerd0713f92002-09-12 17:06:43 +0000[diff] [blame]921href="#doInitialization_mod"><tt>doInitialization(Module &amp;)</tt></a> and <a
922href="#doFinalization_mod"><tt>doFinalization(Module &amp;)</tt></a> methods that <a
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]923href="#FunctionPass"><tt>FunctionPass</tt></a>'s have, but also have the following virtual methods that may also be implemented:</p>
924
925</div>
Chris Lattnerd0713f92002-09-12 17:06:43 +0000[diff] [blame]926
927<!-- _______________________________________________________________________ -->
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]928<div class="doc_subsubsection">
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]929 <a name="doInitialization_fn">The <tt>doInitialization(Function
930 &amp;)</tt> method</a>
931</div>
932
933<div class="doc_text">
Chris Lattnerd0713f92002-09-12 17:06:43 +0000[diff] [blame]934
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]935<div class="doc_code"><pre>
Chris Lattnerd0713f92002-09-12 17:06:43 +0000[diff] [blame]936 <b>virtual bool</b> doInitialization(Function &amp;F);
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]937</pre></div>
Chris Lattnerd0713f92002-09-12 17:06:43 +0000[diff] [blame]938
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]939<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]940<tt>BasicBlockPass</tt>'s are not allowed to do, but that
941<tt>FunctionPass</tt>'s can. The <tt>doInitialization</tt> method is designed
Reid Spencer1bc19342004-12-11 05:12:57 +0000[diff] [blame]942to do simple initialization that does not depend on the
Chris Lattnerd0713f92002-09-12 17:06:43 +0000[diff] [blame]943BasicBlocks being processed. The <tt>doInitialization</tt> method call is not
944scheduled to overlap with any other pass executions (thus it should be very
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]945fast).</p>
Chris Lattnerd0713f92002-09-12 17:06:43 +0000[diff] [blame]946
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]947</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]948
949<!-- _______________________________________________________________________ -->
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]950<div class="doc_subsubsection">
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]951 <a name="runOnBasicBlock">The <tt>runOnBasicBlock</tt> method</a>
952</div>
953
954<div class="doc_text">
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]955
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]956<div class="doc_code"><pre>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]957 <b>virtual bool</b> runOnBasicBlock(BasicBlock &amp;BB) = 0;
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]958</pre></div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]959
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]960<p>Override this function to do the work of the <tt>BasicBlockPass</tt>. This
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]961function is not allowed to inspect or modify basic blocks other than the
962parameter, and are not allowed to modify the CFG. A true value must be returned
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]963if the basic block is modified.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]964
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]965</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]966
Chris Lattnerd0713f92002-09-12 17:06:43 +0000[diff] [blame]967<!-- _______________________________________________________________________ -->
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]968<div class="doc_subsubsection">
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]969 <a name="doFinalization_fn">The <tt>doFinalization(Function &amp;)</tt>
970 method</a>
971</div>
972
973<div class="doc_text">
Chris Lattnerd0713f92002-09-12 17:06:43 +0000[diff] [blame]974
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]975<div class="doc_code"><pre>
Chris Lattnerd0713f92002-09-12 17:06:43 +0000[diff] [blame]976 <b>virtual bool</b> doFinalization(Function &amp;F);
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]977</pre></div>
Chris Lattnerd0713f92002-09-12 17:06:43 +0000[diff] [blame]978
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]979<p>The <tt>doFinalization</tt> method is an infrequently used method that is
980called when the pass framework has finished calling <a
Chris Lattnerd0713f92002-09-12 17:06:43 +0000[diff] [blame]981href="#runOnBasicBlock"><tt>runOnBasicBlock</tt></a> for every BasicBlock in the
982program being compiled. This can be used to perform per-function
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]983finalization.</p>
Chris Lattnerd0713f92002-09-12 17:06:43 +0000[diff] [blame]984
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]985</div>
Chris Lattnerd0713f92002-09-12 17:06:43 +0000[diff] [blame]986
Brian Gaekecab8b6f2003-07-17 18:53:20 +0000[diff] [blame]987<!-- ======================================================================= -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]988<div class="doc_subsection">
989 <a name="MachineFunctionPass">The <tt>MachineFunctionPass</tt> class</a>
990</div>
Brian Gaekecab8b6f2003-07-17 18:53:20 +0000[diff] [blame]991
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]992<div class="doc_text">
993
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]994<p>A <tt>MachineFunctionPass</tt> is a part of the LLVM code generator that
995executes on the machine-dependent representation of each LLVM function in the
Dan Gohman9f116aa2010-03-10 01:29:39 +0000[diff] [blame]996program.</p>
997
998<p>Code generator passes are registered and initialized specially by
999<tt>TargetMachine::addPassesToEmitFile</tt> and similar routines, so they
1000cannot generally be run from the <tt>opt</tt> or <tt>bugpoint</tt>
1001commands.</p>
1002
1003<p>A <tt>MachineFunctionPass</tt> is also a <tt>FunctionPass</tt>, so all
Brian Gaekecab8b6f2003-07-17 18:53:20 +0000[diff] [blame]1004the restrictions that apply to a <tt>FunctionPass</tt> also apply to it.
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]1005<tt>MachineFunctionPass</tt>es also have additional restrictions. In particular,
1006<tt>MachineFunctionPass</tt>es are not allowed to do any of the following:</p>
Brian Gaekecab8b6f2003-07-17 18:53:20 +0000[diff] [blame]1007
1008<ol>
Dan Gohman9f116aa2010-03-10 01:29:39 +0000[diff] [blame]1009<li>Modify or create any LLVM IR Instructions, BasicBlocks, Arguments,
1010 Functions, GlobalVariables, GlobalAliases, or Modules.</li>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1011<li>Modify a MachineFunction other than the one currently being processed.</li>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1012<li>Maintain state across invocations of <a
1013href="#runOnMachineFunction"><tt>runOnMachineFunction</tt></a> (including global
1014data)</li>
1015</ol>
Brian Gaekecab8b6f2003-07-17 18:53:20 +0000[diff] [blame]1016
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1017</div>
Chris Lattnerd0713f92002-09-12 17:06:43 +0000[diff] [blame]1018
Brian Gaeke6a33f362003-07-22 20:53:20 +0000[diff] [blame]1019<!-- _______________________________________________________________________ -->
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]1020<div class="doc_subsubsection">
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1021 <a name="runOnMachineFunction">The <tt>runOnMachineFunction(MachineFunction
1022 &amp;MF)</tt> method</a>
1023</div>
1024
1025<div class="doc_text">
Brian Gaeke6a33f362003-07-22 20:53:20 +0000[diff] [blame]1026
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1027<div class="doc_code"><pre>
Brian Gaeke6a33f362003-07-22 20:53:20 +0000[diff] [blame]1028 <b>virtual bool</b> runOnMachineFunction(MachineFunction &amp;MF) = 0;
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1029</pre></div>
Brian Gaeke6a33f362003-07-22 20:53:20 +0000[diff] [blame]1030
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1031<p><tt>runOnMachineFunction</tt> can be considered the main entry point of a
1032<tt>MachineFunctionPass</tt>; that is, you should override this method to do the
1033work of your <tt>MachineFunctionPass</tt>.</p>
Brian Gaeke6a33f362003-07-22 20:53:20 +0000[diff] [blame]1034
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1035<p>The <tt>runOnMachineFunction</tt> method is called on every
Brian Gaeke6a33f362003-07-22 20:53:20 +0000[diff] [blame]1036<tt>MachineFunction</tt> in a <tt>Module</tt>, so that the
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1037<tt>MachineFunctionPass</tt> may perform optimizations on the machine-dependent
1038representation of the function. If you want to get at the LLVM <tt>Function</tt>
1039for the <tt>MachineFunction</tt> you're working on, use
1040<tt>MachineFunction</tt>'s <tt>getFunction()</tt> accessor method -- but
1041remember, you may not modify the LLVM <tt>Function</tt> or its contents from a
1042<tt>MachineFunctionPass</tt>.</p>
1043
1044</div>
Brian Gaeke6a33f362003-07-22 20:53:20 +0000[diff] [blame]1045
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1046<!-- *********************************************************************** -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1047<div class="doc_section">
1048 <a name="registration">Pass registration</a>
1049</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1050<!-- *********************************************************************** -->
1051
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1052<div class="doc_text">
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1053
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1054<p>In the <a href="#basiccode">Hello World</a> example pass we illustrated how
1055pass registration works, and discussed some of the reasons that it is used and
1056what it does. Here we discuss how and why passes are registered.</p>
1057
Duncan Sands5e09eef2011-01-01 17:37:07 +0000[diff] [blame]1058<p>As we saw above, passes are registered with the <b><tt>RegisterPass</tt></b>
1059template. The template parameter is the name of the pass that is to be used on
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1060the command line to specify that the pass should be added to a program (for
Duncan Sands5e09eef2011-01-01 17:37:07 +0000[diff] [blame]1061example, with <tt>opt</tt> or <tt>bugpoint</tt>). The first argument is the
Duncan Sands7e7ae5a2010-02-18 14:08:13 +0000[diff] [blame]1062name 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]1063programs, as
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1064well as for debug output generated by the <tt>--debug-pass</tt> option.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1065
Chris Lattnerc8603c22006-08-27 23:18:52 +0000[diff] [blame]1066<p>If you want your pass to be easily dumpable, you should
1067implement the virtual <tt>print</tt> method:</p>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1068
1069</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1070
1071<!-- _______________________________________________________________________ -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1072<div class="doc_subsubsection">
1073 <a name="print">The <tt>print</tt> method</a>
1074</div>
1075
1076<div class="doc_text">
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1077
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1078<div class="doc_code"><pre>
Torok Edwin52790e52008-10-28 17:29:23 +0000[diff] [blame]1079 <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]1080</pre></div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1081
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1082<p>The <tt>print</tt> method must be implemented by "analyses" in order to print
1083a human readable version of the analysis results. This is useful for debugging
1084an analysis itself, as well as for other people to figure out how an analysis
Chris Lattnerc8603c22006-08-27 23:18:52 +0000[diff] [blame]1085works. Use the <tt>opt -analyze</tt> argument to invoke this method.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1086
Bill Wendling832171c2006-12-07 20:04:42 +0000[diff] [blame]1087<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]1088and 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]1089program that has been analyzed. Note however that this pointer may be null in
1090certain circumstances (such as calling the <tt>Pass::dump()</tt> from a
1091debugger), so it should only be used to enhance debug output, it should not be
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1092depended on.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1093
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1094</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1095
1096<!-- *********************************************************************** -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1097<div class="doc_section">
1098 <a name="interaction">Specifying interactions between passes</a>
1099</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1100<!-- *********************************************************************** -->
1101
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1102<div class="doc_text">
1103
John Criswell8528e782007-12-03 19:34:25 +0000[diff] [blame]1104<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]1105that passes interact with each other correctly. Because <tt>PassManager</tt>
1106tries to <a href="#passmanager">optimize the execution of passes</a> it must
1107know how the passes interact with each other and what dependencies exist between
1108the various passes. To track this, each pass can declare the set of passes that
1109are required to be executed before the current pass, and the passes which are
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1110invalidated by the current pass.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1111
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1112<p>Typically this functionality is used to require that analysis results are
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1113computed before your pass is run. Running arbitrary transformation passes can
1114invalidate the computed analysis results, which is what the invalidation set
1115specifies. If a pass does not implement the <tt><a
1116href="#getAnalysisUsage">getAnalysisUsage</a></tt> method, it defaults to not
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1117having any prerequisite passes, and invalidating <b>all</b> other passes.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1118
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1119</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1120
1121<!-- _______________________________________________________________________ -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1122<div class="doc_subsubsection">
1123 <a name="getAnalysisUsage">The <tt>getAnalysisUsage</tt> method</a>
1124</div>
1125
1126<div class="doc_text">
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1127
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1128<div class="doc_code"><pre>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1129 <b>virtual void</b> getAnalysisUsage(AnalysisUsage &amp;Info) <b>const</b>;
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1130</pre></div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1131
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1132<p>By implementing the <tt>getAnalysisUsage</tt> method, the required and
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1133invalidated sets may be specified for your transformation. The implementation
1134should fill in the <tt><a
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]1135href="http://llvm.org/doxygen/classllvm_1_1AnalysisUsage.html">AnalysisUsage</a></tt>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1136object with information about which passes are required and not invalidated. To
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]1137do this, a pass may call any of the following methods on the AnalysisUsage
1138object:</p>
1139</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1140
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]1141<!-- _______________________________________________________________________ -->
1142<div class="doc_subsubsection">
1143 <a name="AU::addRequired">The <tt>AnalysisUsage::addRequired&lt;&gt;</tt> and <tt>AnalysisUsage::addRequiredTransitive&lt;&gt;</tt> methods</a>
1144</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1145
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]1146<div class="doc_text">
1147<p>
Reid Spencer1bc19342004-12-11 05:12:57 +0000[diff] [blame]1148If your pass requires a previous pass to be executed (an analysis for example),
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]1149it can use one of these methods to arrange for it to be run before your pass.
1150LLVM has many different types of analyses and passes that can be required,
Reid Spencer1bc19342004-12-11 05:12:57 +0000[diff] [blame]1151spanning the range from <tt>DominatorSet</tt> to <tt>BreakCriticalEdges</tt>.
1152Requiring <tt>BreakCriticalEdges</tt>, for example, guarantees that there will
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]1153be no critical edges in the CFG when your pass has been run.
1154</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1155
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]1156<p>
1157Some analyses chain to other analyses to do their job. For example, an <a
1158href="AliasAnalysis.html">AliasAnalysis</a> implementation is required to <a
1159href="AliasAnalysis.html#chaining">chain</a> to other alias analysis passes. In
1160cases where analyses chain, the <tt>addRequiredTransitive</tt> method should be
1161used instead of the <tt>addRequired</tt> method. This informs the PassManager
1162that the transitively required pass should be alive as long as the requiring
1163pass is.
1164</p>
1165</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1166
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]1167<!-- _______________________________________________________________________ -->
1168<div class="doc_subsubsection">
1169 <a name="AU::addPreserved">The <tt>AnalysisUsage::addPreserved&lt;&gt;</tt> method</a>
1170</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1171
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]1172<div class="doc_text">
1173<p>
1174One of the jobs of the PassManager is to optimize how and when analyses are run.
1175In particular, it attempts to avoid recomputing data unless it needs to. For
1176this reason, passes are allowed to declare that they preserve (i.e., they don't
1177invalidate) an existing analysis if it's available. For example, a simple
Reid Spencer1bc19342004-12-11 05:12:57 +0000[diff] [blame]1178constant folding pass would not modify the CFG, so it can't possibly affect the
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]1179results of dominator analysis. By default, all passes are assumed to invalidate
1180all others.
1181</p>
1182
1183<p>
1184The <tt>AnalysisUsage</tt> class provides several methods which are useful in
1185certain circumstances that are related to <tt>addPreserved</tt>. In particular,
1186the <tt>setPreservesAll</tt> method can be called to indicate that the pass does
1187not modify the LLVM program at all (which is true for analyses), and the
1188<tt>setPreservesCFG</tt> method can be used by transformations that change
1189instructions in the program but do not modify the CFG or terminator instructions
1190(note that this property is implicitly set for <a
1191href="#BasicBlockPass">BasicBlockPass</a>'s).
1192</p>
1193
1194<p>
1195<tt>addPreserved</tt> is particularly useful for transformations like
1196<tt>BreakCriticalEdges</tt>. This pass knows how to update a small set of loop
1197and dominator related analyses if they exist, so it can preserve them, despite
1198the fact that it hacks on the CFG.
1199</p>
1200</div>
1201
1202<!-- _______________________________________________________________________ -->
1203<div class="doc_subsubsection">
1204 <a name="AU::examples">Example implementations of <tt>getAnalysisUsage</tt></a>
1205</div>
1206
1207<div class="doc_text">
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1208
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1209<div class="doc_code"><pre>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1210 <i>// This is an example implementation from an analysis, which does not modify
1211 // the program at all, yet has a prerequisite.</i>
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]1212 <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]1213 AU.setPreservesAll();
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]1214 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]1215 }
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1216</pre></div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1217
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1218<p>and:</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1219
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1220<div class="doc_code"><pre>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1221 <i>// This example modifies the program, but does not modify the CFG</i>
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]1222 <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]1223 AU.setPreservesCFG();
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]1224 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]1225 }
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1226</pre></div>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1227
1228</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1229
1230<!-- _______________________________________________________________________ -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1231<div class="doc_subsubsection">
Duncan Sands1465d612009-01-28 13:14:17 +0000[diff] [blame]1232 <a name="getAnalysis">The <tt>getAnalysis&lt;&gt;</tt> and
1233<tt>getAnalysisIfAvailable&lt;&gt;</tt> methods</a>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1234</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1235
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1236<div class="doc_text">
1237
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]1238<p>The <tt>Pass::getAnalysis&lt;&gt;</tt> method is automatically inherited by
1239your class, providing you with access to the passes that you declared that you
1240required with the <a href="#getAnalysisUsage"><tt>getAnalysisUsage</tt></a>
1241method. It takes a single template argument that specifies which pass class you
1242want, and returns a reference to that pass. For example:</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1243
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1244<div class="doc_code"><pre>
Chris Lattnera5776302004-03-17 21:33:32 +0000[diff] [blame]1245 bool LICM::runOnFunction(Function &amp;F) {
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]1246 LoopInfo &amp;LI = getAnalysis&lt;LoopInfo&gt;();
1247 ...
1248 }
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1249</pre></div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1250
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1251<p>This method call returns a reference to the pass desired. You may get a
1252runtime assertion failure if you attempt to get an analysis that you did not
1253declare as required in your <a
1254href="#getAnalysisUsage"><tt>getAnalysisUsage</tt></a> implementation. This
1255method can be called by your <tt>run*</tt> method implementation, or by any
Devang Patel3c1ca0b2007-04-16 21:28:14 +0000[diff] [blame]1256other local method invoked by your <tt>run*</tt> method.
1257
1258A module level pass can use function level analysis info using this interface.
1259For example:</p>
1260
1261<div class="doc_code"><pre>
1262 bool ModuleLevelPass::runOnModule(Module &amp;M) {
1263 ...
Devang Patelf23de112007-04-17 00:17:11 +0000[diff] [blame]1264 DominatorTree &amp;DT = getAnalysis&lt;DominatorTree&gt;(Func);
Devang Patel3c1ca0b2007-04-16 21:28:14 +0000[diff] [blame]1265 ...
1266 }
1267</pre></div>
1268
Chris Lattnerb5c87f62007-05-18 05:36:14 +0000[diff] [blame]1269<p>In above example, runOnFunction for DominatorTree is called by pass manager
Devang Patel3c1ca0b2007-04-16 21:28:14 +0000[diff] [blame]1270before returning a reference to the desired pass.</p>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1271
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]1272<p>
1273If your pass is capable of updating analyses if they exist (e.g.,
1274<tt>BreakCriticalEdges</tt>, as described above), you can use the
Duncan Sands1465d612009-01-28 13:14:17 +0000[diff] [blame]1275<tt>getAnalysisIfAvailable</tt> method, which returns a pointer to the analysis
1276if it is active. For example:</p>
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]1277
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1278<div class="doc_code"><pre>
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]1279 ...
Duncan Sands1465d612009-01-28 13:14:17 +0000[diff] [blame]1280 if (DominatorSet *DS = getAnalysisIfAvailable&lt;DominatorSet&gt;()) {
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]1281 <i>// A DominatorSet is active. This code will update it.</i>
1282 }
1283 ...
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1284</pre></div>
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]1285
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1286</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1287
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1288<!-- *********************************************************************** -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1289<div class="doc_section">
1290 <a name="analysisgroup">Implementing Analysis Groups</a>
1291</div>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1292<!-- *********************************************************************** -->
1293
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1294<div class="doc_text">
1295
Chris Lattnerb7632282007-11-16 05:32:05 +0000[diff] [blame]1296<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]1297used, 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]1298fancier. All of the pass relationships that we have seen so far are very
1299simple: one pass depends on one other specific pass to be run before it can run.
1300For many applications, this is great, for others, more flexibility is
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1301required.</p>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1302
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1303<p>In particular, some analyses are defined such that there is a single simple
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1304interface to the analysis results, but multiple ways of calculating them.
1305Consider alias analysis for example. The most trivial alias analysis returns
1306"may alias" for any alias query. The most sophisticated analysis a
1307flow-sensitive, context-sensitive interprocedural analysis that can take a
1308significant amount of time to execute (and obviously, there is a lot of room
1309between these two extremes for other implementations). To cleanly support
1310situations like this, the LLVM Pass Infrastructure supports the notion of
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1311Analysis Groups.</p>
1312
1313</div>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1314
1315<!-- _______________________________________________________________________ -->
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]1316<div class="doc_subsubsection">
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1317 <a name="agconcepts">Analysis Group Concepts</a>
1318</div>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1319
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1320<div class="doc_text">
1321
1322<p>An Analysis Group is a single simple interface that may be implemented by
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1323multiple different passes. Analysis Groups can be given human readable names
1324just like passes, but unlike passes, they need not derive from the <tt>Pass</tt>
1325class. An analysis group may have one or more implementations, one of which is
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1326the "default" implementation.</p>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1327
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1328<p>Analysis groups are used by client passes just like other passes are: the
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1329<tt>AnalysisUsage::addRequired()</tt> and <tt>Pass::getAnalysis()</tt> methods.
1330In order to resolve this requirement, the <a href="#passmanager">PassManager</a>
1331scans the available passes to see if any implementations of the analysis group
1332are available. If none is available, the default implementation is created for
1333the pass to use. All standard rules for <A href="#interaction">interaction
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1334between passes</a> still apply.</p>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1335
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1336<p>Although <a href="#registration">Pass Registration</a> is optional for normal
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1337passes, all analysis group implementations must be registered, and must use the
Owen Andersond8cc7be2010-07-21 23:07:00 +0000[diff] [blame]1338<A href="#registerag"><tt>INITIALIZE_AG_PASS</tt></a> template to join the
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1339implementation pool. Also, a default implementation of the interface
1340<b>must</b> be registered with <A
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1341href="#registerag"><tt>RegisterAnalysisGroup</tt></a>.</p>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1342
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1343<p>As a concrete example of an Analysis Group in action, consider the <a
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]1344href="http://llvm.org/doxygen/classllvm_1_1AliasAnalysis.html">AliasAnalysis</a>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1345analysis group. The default implementation of the alias analysis interface (the
1346<tt><a
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]1347href="http://llvm.org/doxygen/structBasicAliasAnalysis.html">basicaa</a></tt>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1348pass) just does a few simple checks that don't require significant analysis to
1349compute (such as: two different globals can never alias each other, etc).
1350Passes that use the <tt><a
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]1351href="http://llvm.org/doxygen/classllvm_1_1AliasAnalysis.html">AliasAnalysis</a></tt>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1352interface (for example the <tt><a
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]1353href="http://llvm.org/doxygen/structGCSE.html">gcse</a></tt> pass), do
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1354not care which implementation of alias analysis is actually provided, they just
1355use the designated interface.</p>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1356
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1357<p>From the user's perspective, commands work just like normal. Issuing the
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1358command '<tt>opt -gcse ...</tt>' will cause the <tt>basicaa</tt> class to be
1359instantiated and added to the pass sequence. Issuing the command '<tt>opt
1360-somefancyaa -gcse ...</tt>' will cause the <tt>gcse</tt> pass to use the
1361<tt>somefancyaa</tt> alias analysis (which doesn't actually exist, it's just a
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1362hypothetical example) instead.</p>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1363
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1364</div>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1365
1366<!-- _______________________________________________________________________ -->
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]1367<div class="doc_subsubsection">
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1368 <a name="registerag">Using <tt>RegisterAnalysisGroup</tt></a>
1369</div>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1370
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1371<div class="doc_text">
1372
1373<p>The <tt>RegisterAnalysisGroup</tt> template is used to register the analysis
Owen Andersond8cc7be2010-07-21 23:07:00 +0000[diff] [blame]1374group itself, while the <tt>INITIALIZE_AG_PASS</tt> is used to add pass
1375implementations to the analysis group. First,
1376an analysis group should be registered, with a human readable name
1377provided for it.
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1378Unlike registration of passes, there is no command line argument to be specified
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1379for the Analysis Group Interface itself, because it is "abstract":</p>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1380
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1381<div class="doc_code"><pre>
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]1382 <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]1383</pre></div>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1384
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1385<p>Once the analysis is registered, passes can declare that they are valid
1386implementations of the interface by using the following code:</p>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1387
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1388<div class="doc_code"><pre>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1389<b>namespace</b> {
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1390 //<i> Declare that we implement the AliasAnalysis interface</i>
Owen Andersond8cc7be2010-07-21 23:07:00 +0000[diff] [blame]1391 INITIALIZE_AG_PASS(FancyAA, <a href="http://llvm.org/doxygen/classllvm_1_1AliasAnalysis.html">AliasAnalysis</a>, "<i>somefancyaa</i>",
1392 "<i>A more complex alias analysis implementation</i>",
1393 false, // <i>Is CFG Only?</i>
1394 true, // <i>Is Analysis?</i>
1395 false, // <i>Is default Analysis Group implementation?</i>
1396 );
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1397}
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1398</pre></div>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1399
Owen Andersond8cc7be2010-07-21 23:07:00 +0000[diff] [blame]1400<p>This just shows a class <tt>FancyAA</tt> that
1401uses the <tt>INITIALIZE_AG_PASS</tt> macro both to register and
1402to "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]1403analysis group. Every implementation of an analysis group should join using
Owen Andersond8cc7be2010-07-21 23:07:00 +0000[diff] [blame]1404this macro.</p>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1405
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1406<div class="doc_code"><pre>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1407<b>namespace</b> {
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1408 //<i> Declare that we implement the AliasAnalysis interface</i>
Owen Andersond8cc7be2010-07-21 23:07:00 +0000[diff] [blame]1409 INITIALIZE_AG_PASS(BasicAA, <a href="http://llvm.org/doxygen/classllvm_1_1AliasAnalysis.html">AliasAnalysis</a>, "<i>basicaa</i>",
1410 "<i>Basic Alias Analysis (default AA impl)</i>",
1411 false, // <i>Is CFG Only?</i>
1412 true, // <i>Is Analysis?</i>
1413 true, // <i>Is default Analysis Group implementation?</i>
1414 );
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1415}
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1416</pre></div>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1417
Owen Andersond8cc7be2010-07-21 23:07:00 +0000[diff] [blame]1418<p>Here we show how the default implementation is specified (using the final
1419argument to the <tt>INITIALIZE_AG_PASS</tt> template). There must be exactly
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1420one default implementation available at all times for an Analysis Group to be
Devang Patel2397f8d2007-06-20 18:51:14 +0000[diff] [blame]1421used. Only default implementation can derive from <tt>ImmutablePass</tt>.
1422Here we declare that the
1423 <tt><a href="http://llvm.org/doxygen/structBasicAliasAnalysis.html">BasicAliasAnalysis</a></tt>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1424pass is the default implementation for the interface.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1425
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1426</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1427
1428<!-- *********************************************************************** -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1429<div class="doc_section">
Tanya Lattnerd5383652004-11-19 01:25:14 +0000[diff] [blame]1430 <a name="passStatistics">Pass Statistics</a>
1431</div>
1432<!-- *********************************************************************** -->
1433
1434<div class="doc_text">
Tanya Lattner05f8d5f2004-11-19 01:26:37 +0000[diff] [blame]1435<p>The <a
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]1436href="http://llvm.org/doxygen/Statistic_8h-source.html"><tt>Statistic</tt></a>
John Criswell0b1010e2005-11-28 23:25:41 +0000[diff] [blame]1437class is designed to be an easy way to expose various success
Tanya Lattnerd5383652004-11-19 01:25:14 +0000[diff] [blame]1438metrics from passes. These statistics are printed at the end of a
1439run, when the -stats command line option is enabled on the command
Tanya Lattner05f8d5f2004-11-19 01:26:37 +0000[diff] [blame]1440line. 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]1441
1442</div>
1443
1444
1445<!-- *********************************************************************** -->
1446<div class="doc_section">
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1447 <a name="passmanager">What PassManager does</a>
1448</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1449<!-- *********************************************************************** -->
1450
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1451<div class="doc_text">
1452
1453<p>The <a
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]1454href="http://llvm.org/doxygen/PassManager_8h-source.html"><tt>PassManager</tt></a>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1455<a
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]1456href="http://llvm.org/doxygen/classllvm_1_1PassManager.html">class</a>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1457takes a list of passes, ensures their <a href="#interaction">prerequisites</a>
1458are set up correctly, and then schedules passes to run efficiently. All of the
1459LLVM tools that run passes use the <tt>PassManager</tt> for execution of these
1460passes.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1461
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1462<p>The <tt>PassManager</tt> does two main things to try to reduce the execution
1463time of a series of passes:</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1464
1465<ol>
1466<li><b>Share analysis results</b> - The PassManager attempts to avoid
1467recomputing analysis results as much as possible. This means keeping track of
1468which analyses are available already, which analyses get invalidated, and which
1469analyses are needed to be run for a pass. An important part of work is that the
1470<tt>PassManager</tt> tracks the exact lifetime of all analysis results, allowing
1471it to <a href="#releaseMemory">free memory</a> allocated to holding analysis
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1472results as soon as they are no longer needed.</li>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1473
1474<li><b>Pipeline the execution of passes on the program</b> - The
1475<tt>PassManager</tt> attempts to get better cache and memory usage behavior out
1476of a series of passes by pipelining the passes together. This means that, given
Duncan Sandsab4c3662011-02-15 09:23:02 +0000[diff] [blame^]1477a series of consecutive <a href="#FunctionPass"><tt>FunctionPass</tt></a>'s, it
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1478will execute all of the <a href="#FunctionPass"><tt>FunctionPass</tt></a>'s on
1479the first function, then all of the <a
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1480href="#FunctionPass"><tt>FunctionPass</tt></a>es on the second function,
1481etc... until the entire program has been run through the passes.
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1482
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1483<p>This improves the cache behavior of the compiler, because it is only touching
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1484the LLVM program representation for a single function at a time, instead of
1485traversing the entire program. It reduces the memory consumption of compiler,
1486because, for example, only one <a
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]1487href="http://llvm.org/doxygen/classllvm_1_1DominatorSet.html"><tt>DominatorSet</tt></a>
John Criswell9795bb82007-12-10 20:26:29 +0000[diff] [blame]1488needs to be calculated at a time. This also makes it possible to implement
1489some <a
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1490href="#SMP">interesting enhancements</a> in the future.</p></li>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1491
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1492</ol>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1493
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1494<p>The effectiveness of the <tt>PassManager</tt> is influenced directly by how
1495much information it has about the behaviors of the passes it is scheduling. For
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1496example, the "preserved" set is intentionally conservative in the face of an
1497unimplemented <a href="#getAnalysisUsage"><tt>getAnalysisUsage</tt></a> method.
1498Not implementing when it should be implemented will have the effect of not
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1499allowing any analysis results to live across the execution of your pass.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1500
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1501<p>The <tt>PassManager</tt> class exposes a <tt>--debug-pass</tt> command line
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1502options that is useful for debugging pass execution, seeing how things work, and
1503diagnosing when you should be preserving more analyses than you currently are
1504(To get information about all of the variants of the <tt>--debug-pass</tt>
Duncan Sands7e7ae5a2010-02-18 14:08:13 +0000[diff] [blame]1505option, just type '<tt>opt -help-hidden</tt>').</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1506
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1507<p>By using the <tt>--debug-pass=Structure</tt> option, for example, we can see
1508how our <a href="#basiccode">Hello World</a> pass interacts with other passes.
1509Lets try it out with the <tt>gcse</tt> and <tt>licm</tt> passes:</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1510
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1511<div class="doc_code"><pre>
Duncan Sands67f8a7b2010-07-08 08:27:18 +0000[diff] [blame]1512$ 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]1513Module Pass Manager
1514 Function Pass Manager
1515 Dominator Set Construction
1516 Immediate Dominators Construction
1517 Global Common Subexpression Elimination
1518-- Immediate Dominators Construction
1519-- Global Common Subexpression Elimination
1520 Natural Loop Construction
1521 Loop Invariant Code Motion
1522-- Natural Loop Construction
1523-- Loop Invariant Code Motion
1524 Module Verifier
1525-- Dominator Set Construction
1526-- Module Verifier
Gabor Greif04367bf2007-07-06 22:07:22 +0000[diff] [blame]1527 Bitcode Writer
1528--Bitcode Writer
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1529</pre></div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1530
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1531<p>This output shows us when passes are constructed and when the analysis
1532results are known to be dead (prefixed with '<tt>--</tt>'). Here we see that
1533GCSE uses dominator and immediate dominator information to do its job. The LICM
1534pass uses natural loop information, which uses dominator sets, but not immediate
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1535dominators. Because immediate dominators are no longer useful after the GCSE
1536pass, it is immediately destroyed. The dominator sets are then reused to
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1537compute natural loop information, which is then used by the LICM pass.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1538
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1539<p>After the LICM pass, the module verifier runs (which is automatically added
1540by the '<tt>opt</tt>' tool), which uses the dominator set to check that the
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1541resultant LLVM code is well formed. After it finishes, the dominator set
1542information is destroyed, after being computed once, and shared by three
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1543passes.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1544
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1545<p>Lets see how this changes when we run the <a href="#basiccode">Hello
1546World</a> pass in between the two passes:</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1547
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1548<div class="doc_code"><pre>
Duncan Sands67f8a7b2010-07-08 08:27:18 +0000[diff] [blame]1549$ 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]1550Module Pass Manager
1551 Function Pass Manager
1552 Dominator Set Construction
1553 Immediate Dominators Construction
1554 Global Common Subexpression Elimination
1555<b>-- Dominator Set Construction</b>
1556-- Immediate Dominators Construction
1557-- Global Common Subexpression Elimination
1558<b> Hello World Pass
1559-- Hello World Pass
1560 Dominator Set Construction</b>
1561 Natural Loop Construction
1562 Loop Invariant Code Motion
1563-- Natural Loop Construction
1564-- Loop Invariant Code Motion
1565 Module Verifier
1566-- Dominator Set Construction
1567-- Module Verifier
Gabor Greif04367bf2007-07-06 22:07:22 +0000[diff] [blame]1568 Bitcode Writer
1569--Bitcode Writer
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1570Hello: __main
1571Hello: puts
1572Hello: main
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1573</pre></div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1574
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1575<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]1576Dominator Set pass, even though it doesn't modify the code at all! To fix this,
1577we need to add the following <a
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1578href="#getAnalysisUsage"><tt>getAnalysisUsage</tt></a> method to our pass:</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1579
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1580<div class="doc_code"><pre>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1581 <i>// We don't modify the program, so we preserve all analyses</i>
1582 <b>virtual void</b> getAnalysisUsage(AnalysisUsage &amp;AU) <b>const</b> {
1583 AU.setPreservesAll();
1584 }
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1585</pre></div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1586
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1587<p>Now when we run our pass, we get this output:</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1588
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1589<div class="doc_code"><pre>
Duncan Sands67f8a7b2010-07-08 08:27:18 +0000[diff] [blame]1590$ 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]1591Pass Arguments: -gcse -hello -licm
1592Module Pass Manager
1593 Function Pass Manager
1594 Dominator Set Construction
1595 Immediate Dominators Construction
1596 Global Common Subexpression Elimination
1597-- Immediate Dominators Construction
1598-- Global Common Subexpression Elimination
1599 Hello World Pass
1600-- Hello World Pass
1601 Natural Loop Construction
1602 Loop Invariant Code Motion
1603-- Loop Invariant Code Motion
1604-- Natural Loop Construction
1605 Module Verifier
1606-- Dominator Set Construction
1607-- Module Verifier
Gabor Greif04367bf2007-07-06 22:07:22 +0000[diff] [blame]1608 Bitcode Writer
1609--Bitcode Writer
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1610Hello: __main
1611Hello: puts
1612Hello: main
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1613</pre></div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1614
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1615<p>Which shows that we don't accidentally invalidate dominator information
1616anymore, and therefore do not have to compute it twice.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1617
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1618</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1619
1620<!-- _______________________________________________________________________ -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1621<div class="doc_subsubsection">
1622 <a name="releaseMemory">The <tt>releaseMemory</tt> method</a>
1623</div>
1624
1625<div class="doc_text">
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1626
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1627<div class="doc_code"><pre>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1628 <b>virtual void</b> releaseMemory();
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1629</pre></div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1630
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1631<p>The <tt>PassManager</tt> automatically determines when to compute analysis
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1632results, and how long to keep them around for. Because the lifetime of the pass
1633object itself is effectively the entire duration of the compilation process, we
1634need some way to free analysis results when they are no longer useful. The
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1635<tt>releaseMemory</tt> virtual method is the way to do this.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1636
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1637<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]1638amount of state (for use by another pass which "requires" your pass and uses the
1639<a href="#getAnalysis">getAnalysis</a> method) you should implement
Dan Gohmand87c9e32009-06-15 18:22:49 +0000[diff] [blame]1640<tt>releaseMemory</tt> to, well, release the memory allocated to maintain this
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1641internal state. This method is called after the <tt>run*</tt> method for the
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1642class, before the next call of <tt>run*</tt> in your pass.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1643
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1644</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1645
1646<!-- *********************************************************************** -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1647<div class="doc_section">
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1648 <a name="registering">Registering dynamically loaded passes</a>
1649</div>
1650<!-- *********************************************************************** -->
1651
1652<div class="doc_text">
1653
1654<p><i>Size matters</i> when constructing production quality tools using llvm,
1655both for the purposes of distribution, and for regulating the resident code size
1656when running on the target system. Therefore, it becomes desirable to
1657selectively use some passes, while omitting others and maintain the flexibility
1658to change configurations later on. You want to be able to do all this, and,
1659provide feedback to the user. This is where pass registration comes into
1660play.</p>
1661
1662<p>The fundamental mechanisms for pass registration are the
1663<tt>MachinePassRegistry</tt> class and subclasses of
1664<tt>MachinePassRegistryNode</tt>.</p>
1665
1666<p>An instance of <tt>MachinePassRegistry</tt> is used to maintain a list of
1667<tt>MachinePassRegistryNode</tt> objects. This instance maintains the list and
1668communicates additions and deletions to the command line interface.</p>
1669
1670<p>An instance of <tt>MachinePassRegistryNode</tt> subclass is used to maintain
1671information provided about a particular pass. This information includes the
1672command line name, the command help string and the address of the function used
1673to create an instance of the pass. A global static constructor of one of these
1674instances <i>registers</i> with a corresponding <tt>MachinePassRegistry</tt>,
1675the static destructor <i>unregisters</i>. Thus a pass that is statically linked
1676in the tool will be registered at start up. A dynamically loaded pass will
1677register on load and unregister at unload.</p>
1678
1679</div>
1680
1681<!-- _______________________________________________________________________ -->
1682<div class="doc_subsection">
1683 <a name="registering_existing">Using existing registries</a>
1684</div>
1685
1686<div class="doc_text">
1687
1688<p>There are predefined registries to track instruction scheduling
1689(<tt>RegisterScheduler</tt>) and register allocation (<tt>RegisterRegAlloc</tt>)
1690machine passes. Here we will describe how to <i>register</i> a register
1691allocator machine pass.</p>
1692
1693<p>Implement your register allocator machine pass. In your register allocator
1694.cpp file add the following include;</p>
1695
1696<div class="doc_code"><pre>
Chris Lattner8f652eb2006-08-11 16:37:02 +0000[diff] [blame]1697 #include "llvm/CodeGen/RegAllocRegistry.h"
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1698</pre></div>
1699
1700<p>Also in your register allocator .cpp file, define a creator function in the
1701form; </p>
1702
1703<div class="doc_code"><pre>
1704 FunctionPass *createMyRegisterAllocator() {
1705 return new MyRegisterAllocator();
1706 }
1707</pre></div>
1708
1709<p>Note that the signature of this function should match the type of
1710<tt>RegisterRegAlloc::FunctionPassCtor</tt>. In the same file add the
1711"installing" declaration, in the form;</p>
1712
1713<div class="doc_code"><pre>
1714 static RegisterRegAlloc myRegAlloc("myregalloc",
1715 " my register allocator help string",
1716 createMyRegisterAllocator);
1717</pre></div>
1718
1719<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]1720-help query.</p>
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1721
1722<div class="doc_code"><pre>
Duncan Sands7e7ae5a2010-02-18 14:08:13 +0000[diff] [blame]1723$ llc -help
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1724 ...
Duncan Sands18619b22010-02-18 14:37:52 +0000[diff] [blame]1725 -regalloc - Register allocator to use (default=linearscan)
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1726 =linearscan - linear scan register allocator
1727 =local - local register allocator
1728 =simple - simple register allocator
1729 =myregalloc - my register allocator help string
1730 ...
1731</pre></div>
1732
1733<p>And that's it. The user is now free to use <tt>-regalloc=myregalloc</tt> as
1734an option. Registering instruction schedulers is similar except use the
Chris Lattner8f652eb2006-08-11 16:37:02 +0000[diff] [blame]1735<tt>RegisterScheduler</tt> class. Note that the
1736<tt>RegisterScheduler::FunctionPassCtor</tt> is significantly different from
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1737<tt>RegisterRegAlloc::FunctionPassCtor</tt>.</p>
1738
1739<p>To force the load/linking of your register allocator into the llc/lli tools,
1740add your creator function's global declaration to "Passes.h" and add a "pseudo"
1741call line to <tt>llvm/Codegen/LinkAllCodegenComponents.h</tt>.</p>
1742
1743</div>
1744
1745
1746<!-- _______________________________________________________________________ -->
1747<div class="doc_subsection">
1748 <a name="registering_new">Creating new registries</a>
1749</div>
1750
1751<div class="doc_text">
1752
1753<p>The easiest way to get started is to clone one of the existing registries; we
1754recommend <tt>llvm/CodeGen/RegAllocRegistry.h</tt>. The key things to modify
1755are the class name and the <tt>FunctionPassCtor</tt> type.</p>
1756
1757<p>Then you need to declare the registry. Example: if your pass registry is
1758<tt>RegisterMyPasses</tt> then define;</p>
1759
1760<div class="doc_code"><pre>
1761MachinePassRegistry RegisterMyPasses::Registry;
1762</pre></div>
1763
1764<p>And finally, declare the command line option for your passes. Example:</p>
1765
1766<div class="doc_code"><pre>
1767 cl::opt&lt;RegisterMyPasses::FunctionPassCtor, false,
Dan Gohman364a39f2008-10-14 17:00:38 +0000[diff] [blame]1768 RegisterPassParser&lt;RegisterMyPasses&gt; &gt;
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1769 MyPassOpt("mypass",
1770 cl::init(&amp;createDefaultMyPass),
1771 cl::desc("my pass option help"));
1772</pre></div>
1773
1774<p>Here the command option is "mypass", with createDefaultMyPass as the default
1775creator.</p>
1776
1777</div>
1778
1779<!-- *********************************************************************** -->
1780<div class="doc_section">
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1781 <a name="debughints">Using GDB with dynamically loaded passes</a>
1782</div>
Chris Lattner480e2ef2002-09-06 02:02:58 +0000[diff] [blame]1783<!-- *********************************************************************** -->
1784
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1785<div class="doc_text">
1786
1787<p>Unfortunately, using GDB with dynamically loaded passes is not as easy as it
Chris Lattner480e2ef2002-09-06 02:02:58 +0000[diff] [blame]1788should be. First of all, you can't set a breakpoint in a shared object that has
1789not been loaded yet, and second of all there are problems with inlined functions
1790in shared objects. Here are some suggestions to debugging your pass with
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1791GDB.</p>
Chris Lattner480e2ef2002-09-06 02:02:58 +0000[diff] [blame]1792
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1793<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]1794transformation invoked by <tt>opt</tt>, although nothing described here depends
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1795on that.</p>
1796
1797</div>
Chris Lattner480e2ef2002-09-06 02:02:58 +0000[diff] [blame]1798
1799<!-- _______________________________________________________________________ -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1800<div class="doc_subsubsection">
1801 <a name="breakpoint">Setting a breakpoint in your pass</a>
1802</div>
Chris Lattner480e2ef2002-09-06 02:02:58 +0000[diff] [blame]1803
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1804<div class="doc_text">
1805
1806<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]1807
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1808<div class="doc_code"><pre>
Chris Lattner480e2ef2002-09-06 02:02:58 +0000[diff] [blame]1809$ <b>gdb opt</b>
1810GNU gdb 5.0
1811Copyright 2000 Free Software Foundation, Inc.
1812GDB is free software, covered by the GNU General Public License, and you are
1813welcome to change it and/or distribute copies of it under certain conditions.
1814Type "show copying" to see the conditions.
1815There is absolutely no warranty for GDB. Type "show warranty" for details.
1816This GDB was configured as "sparc-sun-solaris2.6"...
1817(gdb)
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1818</pre></div>
Chris Lattner480e2ef2002-09-06 02:02:58 +0000[diff] [blame]1819
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1820<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]1821time to load. Be patient. Since we cannot set a breakpoint in our pass yet
1822(the shared object isn't loaded until runtime), we must execute the process, and
1823have it stop before it invokes our pass, but after it has loaded the shared
1824object. The most foolproof way of doing this is to set a breakpoint in
1825<tt>PassManager::run</tt> and then run the process with the arguments you
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1826want:</p>
Chris Lattner480e2ef2002-09-06 02:02:58 +0000[diff] [blame]1827
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1828<div class="doc_code"><pre>
Reid Spencer22a9e5b2006-09-28 16:53:47 +0000[diff] [blame]1829(gdb) <b>break llvm::PassManager::run</b>
Chris Lattner480e2ef2002-09-06 02:02:58 +0000[diff] [blame]1830Breakpoint 1 at 0x2413bc: file Pass.cpp, line 70.
Duncan Sands67f8a7b2010-07-08 08:27:18 +0000[diff] [blame]1831(gdb) <b>run test.bc -load $(LLVMTOP)/llvm/Debug+Asserts/lib/[libname].so -[passoption]</b>
1832Starting program: opt test.bc -load $(LLVMTOP)/llvm/Debug+Asserts/lib/[libname].so -[passoption]
Chris Lattner480e2ef2002-09-06 02:02:58 +0000[diff] [blame]1833Breakpoint 1, PassManager::run (this=0xffbef174, M=@0x70b298) at Pass.cpp:70
183470 bool PassManager::run(Module &amp;M) { return PM-&gt;run(M); }
1835(gdb)
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1836</pre></div>
Chris Lattner480e2ef2002-09-06 02:02:58 +0000[diff] [blame]1837
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1838<p>Once the <tt>opt</tt> stops in the <tt>PassManager::run</tt> method you are
1839now free to set breakpoints in your pass so that you can trace through execution
1840or do other standard debugging stuff.</p>
Chris Lattner480e2ef2002-09-06 02:02:58 +0000[diff] [blame]1841
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1842</div>
Chris Lattner480e2ef2002-09-06 02:02:58 +0000[diff] [blame]1843
1844<!-- _______________________________________________________________________ -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1845<div class="doc_subsubsection">
1846 <a name="debugmisc">Miscellaneous Problems</a>
1847</div>
Chris Lattner480e2ef2002-09-06 02:02:58 +0000[diff] [blame]1848
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1849<div class="doc_text">
1850
1851<p>Once you have the basics down, there are a couple of problems that GDB has,
1852some with solutions, some without.</p>
Chris Lattner480e2ef2002-09-06 02:02:58 +0000[diff] [blame]1853
1854<ul>
1855<li>Inline functions have bogus stack information. In general, GDB does a
1856pretty good job getting stack traces and stepping through inline functions.
1857When a pass is dynamically loaded however, it somehow completely loses this
1858capability. The only solution I know of is to de-inline a function (move it
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1859from the body of a class to a .cpp file).</li>
Chris Lattner480e2ef2002-09-06 02:02:58 +0000[diff] [blame]1860
1861<li>Restarting the program breaks breakpoints. After following the information
1862above, you have succeeded in getting some breakpoints planted in your pass. Nex
1863thing you know, you restart the program (i.e., you type '<tt>run</tt>' again),
1864and you start getting errors about breakpoints being unsettable. The only way I
1865have found to "fix" this problem is to <tt>delete</tt> the breakpoints that are
1866already set in your pass, run the program, and re-set the breakpoints once
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1867execution stops in <tt>PassManager::run</tt>.</li>
Chris Lattner480e2ef2002-09-06 02:02:58 +0000[diff] [blame]1868
1869</ul>
1870
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1871<p>Hopefully these tips will help with common case debugging situations. If
1872you'd like to contribute some tips of your own, just contact <a
1873href="mailto:sabre@nondot.org">Chris</a>.</p>
Chris Lattner480e2ef2002-09-06 02:02:58 +0000[diff] [blame]1874
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1875</div>
Chris Lattner480e2ef2002-09-06 02:02:58 +0000[diff] [blame]1876
1877<!-- *********************************************************************** -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1878<div class="doc_section">
1879 <a name="future">Future extensions planned</a>
1880</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1881<!-- *********************************************************************** -->
1882
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1883<div class="doc_text">
1884
1885<p>Although the LLVM Pass Infrastructure is very capable as it stands, and does
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1886some 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]1887where we are going:</p>
1888
1889</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1890
1891<!-- _______________________________________________________________________ -->
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]1892<div class="doc_subsubsection">
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1893 <a name="SMP">Multithreaded LLVM</a>
1894</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1895
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1896<div class="doc_text">
1897
1898<p>Multiple CPU machines are becoming more common and compilation can never be
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1899fast enough: obviously we should allow for a multithreaded compiler. Because of
1900the semantics defined for passes above (specifically they cannot maintain state
1901across invocations of their <tt>run*</tt> methods), a nice clean way to
1902implement a multithreaded compiler would be for the <tt>PassManager</tt> class
Misha Brukmanbc0e9982003-07-14 17:20:40 +0000[diff] [blame]1903to create multiple instances of each pass object, and allow the separate
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1904instances to be hacking on different parts of the program at the same time.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1905
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1906<p>This implementation would prevent each of the passes from having to implement
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1907multithreaded constructs, requiring only the LLVM core to have locking in a few
1908places (for global resources). Although this is a simple extension, we simply
1909haven't had time (or multiprocessor machines, thus a reason) to implement this.
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1910Despite that, we have kept the LLVM passes SMP ready, and you should too.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1911
Chris Lattnerb5c87f62007-05-18 05:36:14 +0000[diff] [blame]1912</div>
1913
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1914<!-- *********************************************************************** -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1915<hr>
1916<address>
1917 <a href="http://jigsaw.w3.org/css-validator/check/referer"><img
Misha Brukman44408702008-12-11 17:34:48 +0000[diff] [blame]1918 src="http://jigsaw.w3.org/css-validator/images/vcss-blue" alt="Valid CSS"></a>
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Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1921
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1922 <a href="mailto:sabre@nondot.org">Chris Lattner</a><br>
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]1923 <a href="http://llvm.org">The LLVM Compiler Infrastructure</a><br>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1924 Last modified: $Date$
1925</address>
1926
1927</body>
1928</html>