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gerrit-public.fairphone.software / fp2-dev / platform / external / llvm / 67f8a7bc26c2993854a7e9ab43af362bc4477e3f / . / docs / WritingAnLLVMPass.html
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Reid Spencer7fa6d522005-01-11 05:16:23 +0000[diff] [blame]5 <meta http-equiv="Content-Type" content="text/html; charset=utf-8">
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]6 <title>Writing an LLVM Pass</title>
7 <link rel="stylesheet" href="llvm.css" type="text/css">
8</head>
9<body>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]10
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]11<div class="doc_title">
12 Writing an LLVM Pass
13</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]14
15<ol>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]16 <li><a href="#introduction">Introduction - What is a pass?</a></li>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]17 <li><a href="#quickstart">Quick Start - Writing hello world</a>
18 <ul>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]19 <li><a href="#makefile">Setting up the build environment</a></li>
20 <li><a href="#basiccode">Basic code required</a></li>
Chris Lattnerc8603c22006-08-27 23:18:52 +0000[diff] [blame]21 <li><a href="#running">Running a pass with <tt>opt</tt></a></li>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]22 </ul></li>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]23 <li><a href="#passtype">Pass classes and requirements</a>
24 <ul>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]25 <li><a href="#ImmutablePass">The <tt>ImmutablePass</tt> class</a></li>
Chris Lattnerf6278922004-09-20 04:36:29 +0000[diff] [blame]26 <li><a href="#ModulePass">The <tt>ModulePass</tt> class</a>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]27 <ul>
Chris Lattnerf6278922004-09-20 04:36:29 +0000[diff] [blame]28 <li><a href="#runOnModule">The <tt>runOnModule</tt> method</a></li>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]29 </ul></li>
Chris Lattner8fdb2462004-09-18 06:39:35 +0000[diff] [blame]30 <li><a href="#CallGraphSCCPass">The <tt>CallGraphSCCPass</tt> class</a>
31 <ul>
Devang Patelc20048d2007-01-23 22:56:28 +0000[diff] [blame]32 <li><a href="#doInitialization_scc">The <tt>doInitialization(CallGraph
Chris Lattner8fdb2462004-09-18 06:39:35 +0000[diff] [blame]33 &amp;)</tt> method</a></li>
34 <li><a href="#runOnSCC">The <tt>runOnSCC</tt> method</a></li>
Devang Patelc20048d2007-01-23 22:56:28 +0000[diff] [blame]35 <li><a href="#doFinalization_scc">The <tt>doFinalization(CallGraph
Chris Lattner8fdb2462004-09-18 06:39:35 +0000[diff] [blame]36 &amp;)</tt> method</a></li>
37 </ul></li>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]38 <li><a href="#FunctionPass">The <tt>FunctionPass</tt> class</a>
39 <ul>
Chris Lattnerd0713f92002-09-12 17:06:43 +0000[diff] [blame]40 <li><a href="#doInitialization_mod">The <tt>doInitialization(Module
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]41 &amp;)</tt> method</a></li>
42 <li><a href="#runOnFunction">The <tt>runOnFunction</tt> method</a></li>
Chris Lattnerd0713f92002-09-12 17:06:43 +0000[diff] [blame]43 <li><a href="#doFinalization_mod">The <tt>doFinalization(Module
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]44 &amp;)</tt> method</a></li>
45 </ul></li>
Devang Patel2e8f27d2007-03-19 22:21:25 +0000[diff] [blame]46 <li><a href="#LoopPass">The <tt>LoopPass</tt> class</a>
47 <ul>
48 <li><a href="#doInitialization_loop">The <tt>doInitialization(Loop *,
49 LPPassManager &amp;)</tt> method</a></li>
50 <li><a href="#runOnLoop">The <tt>runOnLoop</tt> method</a></li>
51 <li><a href="#doFinalization_loop">The <tt>doFinalization()
52 </tt> method</a></li>
53 </ul></li>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]54 <li><a href="#BasicBlockPass">The <tt>BasicBlockPass</tt> class</a>
55 <ul>
Chris Lattnerd0713f92002-09-12 17:06:43 +0000[diff] [blame]56 <li><a href="#doInitialization_fn">The <tt>doInitialization(Function
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]57 &amp;)</tt> method</a></li>
58 <li><a href="#runOnBasicBlock">The <tt>runOnBasicBlock</tt>
59 method</a></li>
Chris Lattnerd0713f92002-09-12 17:06:43 +0000[diff] [blame]60 <li><a href="#doFinalization_fn">The <tt>doFinalization(Function
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]61 &amp;)</tt> method</a></li>
62 </ul></li>
Brian Gaekecab8b6f2003-07-17 18:53:20 +0000[diff] [blame]63 <li><a href="#MachineFunctionPass">The <tt>MachineFunctionPass</tt>
64 class</a>
Brian Gaeke6a33f362003-07-22 20:53:20 +0000[diff] [blame]65 <ul>
66 <li><a href="#runOnMachineFunction">The
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]67 <tt>runOnMachineFunction(MachineFunction &amp;)</tt> method</a></li>
68 </ul></li>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]69 </ul>
70 <li><a href="#registration">Pass Registration</a>
71 <ul>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]72 <li><a href="#print">The <tt>print</tt> method</a></li>
73 </ul></li>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]74 <li><a href="#interaction">Specifying interactions between passes</a>
75 <ul>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]76 <li><a href="#getAnalysisUsage">The <tt>getAnalysisUsage</tt>
77 method</a></li>
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]78 <li><a href="#AU::addRequired">The <tt>AnalysisUsage::addRequired&lt;&gt;</tt> and <tt>AnalysisUsage::addRequiredTransitive&lt;&gt;</tt> methods</a></li>
79 <li><a href="#AU::addPreserved">The <tt>AnalysisUsage::addPreserved&lt;&gt;</tt> method</a></li>
80 <li><a href="#AU::examples">Example implementations of <tt>getAnalysisUsage</tt></a></li>
Duncan Sands1465d612009-01-28 13:14:17 +0000[diff] [blame]81 <li><a href="#getAnalysis">The <tt>getAnalysis&lt;&gt;</tt> and
82<tt>getAnalysisIfAvailable&lt;&gt;</tt> methods</a></li>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]83 </ul></li>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]84 <li><a href="#analysisgroup">Implementing Analysis Groups</a>
85 <ul>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]86 <li><a href="#agconcepts">Analysis Group Concepts</a></li>
87 <li><a href="#registerag">Using <tt>RegisterAnalysisGroup</tt></a></li>
88 </ul></li>
Tanya Lattnerd5383652004-11-19 01:25:14 +0000[diff] [blame]89 <li><a href="#passStatistics">Pass Statistics</a>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]90 <li><a href="#passmanager">What PassManager does</a>
91 <ul>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]92 <li><a href="#releaseMemory">The <tt>releaseMemory</tt> method</a></li>
93 </ul></li>
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]94 <li><a href="#registering">Registering dynamically loaded passes</a>
95 <ul>
96 <li><a href="#registering_existing">Using existing registries</a></li>
97 <li><a href="#registering_new">Creating new registries</a></li>
98 </ul></li>
Chris Lattner480e2ef2002-09-06 02:02:58 +0000[diff] [blame]99 <li><a href="#debughints">Using GDB with dynamically loaded passes</a>
100 <ul>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]101 <li><a href="#breakpoint">Setting a breakpoint in your pass</a></li>
102 <li><a href="#debugmisc">Miscellaneous Problems</a></li>
103 </ul></li>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]104 <li><a href="#future">Future extensions planned</a>
105 <ul>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]106 <li><a href="#SMP">Multithreaded LLVM</a></li>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]107 </ul></li>
108</ol>
Chris Lattner38c633d2002-08-08 20:23:41 +0000[diff] [blame]109
Chris Lattner7911ce22004-05-23 21:07:27 +0000[diff] [blame]110<div class="doc_author">
Chris Lattner8f652eb2006-08-11 16:37:02 +0000[diff] [blame]111 <p>Written by <a href="mailto:sabre@nondot.org">Chris Lattner</a> and
Jim Laskeyc760a922007-03-14 19:32:21 +0000[diff] [blame]112 <a href="mailto:jlaskey@mac.com">Jim Laskey</a></p>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]113</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]114
115<!-- *********************************************************************** -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]116<div class="doc_section">
117 <a name="introduction">Introduction - What is a pass?</a>
118</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]119<!-- *********************************************************************** -->
120
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]121<div class="doc_text">
122
123<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]124passes are where most of the interesting parts of the compiler exist. Passes
125perform the transformations and optimizations that make up the compiler, they
126build the analysis results that are used by these transformations, and they are,
127above all, a structuring technique for compiler code.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]128
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]129<p>All LLVM passes are subclasses of the <tt><a
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]130href="http://llvm.org/doxygen/classllvm_1_1Pass.html">Pass</a></tt>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]131class, which implement functionality by overriding virtual methods inherited
Chris Lattnerf6278922004-09-20 04:36:29 +0000[diff] [blame]132from <tt>Pass</tt>. Depending on how your pass works, you should inherit from
133the <tt><a href="#ModulePass">ModulePass</a></tt>, <tt><a
134href="#CallGraphSCCPass">CallGraphSCCPass</a></tt>, <tt><a
135href="#FunctionPass">FunctionPass</a></tt>, or <tt><a
Devang Patel2e8f27d2007-03-19 22:21:25 +0000[diff] [blame]136href="#LoopPass">LoopPass</a></tt>, or <tt><a
Chris Lattner8fdb2462004-09-18 06:39:35 +0000[diff] [blame]137href="#BasicBlockPass">BasicBlockPass</a></tt> classes, which gives the system
138more information about what your pass does, and how it can be combined with
139other passes. One of the main features of the LLVM Pass Framework is that it
140schedules passes to run in an efficient way based on the constraints that your
141pass meets (which are indicated by which class they derive from).</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]142
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]143<p>We start by showing you how to construct a pass, everything from setting up
144the code, to compiling, loading, and executing it. After the basics are down,
145more advanced features are discussed.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]146
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]147</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]148
149<!-- *********************************************************************** -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]150<div class="doc_section">
151 <a name="quickstart">Quick Start - Writing hello world</a>
152</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]153<!-- *********************************************************************** -->
154
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]155<div class="doc_text">
156
157<p>Here we describe how to write the "hello world" of passes. The "Hello" pass
158is designed to simply print out the name of non-external functions that exist in
Chris Lattner8fdb2462004-09-18 06:39:35 +0000[diff] [blame]159the program being compiled. It does not modify the program at all, it just
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]160inspects it. The source code and files for this pass are available in the LLVM
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]161source tree in the <tt>lib/Transforms/Hello</tt> directory.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]162
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]163</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]164
165<!-- ======================================================================= -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]166<div class="doc_subsection">
167 <a name="makefile">Setting up the build environment</a>
168</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]169
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]170<div class="doc_text">
171
Reid Spencer1bc19342004-12-11 05:12:57 +0000[diff] [blame]172 <p>First, you need to create a new directory somewhere in the LLVM source
173 base. For this example, we'll assume that you made
174 <tt>lib/Transforms/Hello</tt>. Next, you must set up a build script
175 (Makefile) that will compile the source code for the new pass. To do this,
176 copy the following into <tt>Makefile</tt>:</p>
177 <hr/>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]178
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]179<div class="doc_code"><pre>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]180# Makefile for hello pass
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]181
Torok Edwin87469292009-10-12 13:37:29 +0000[diff] [blame]182# Path to top level of LLVM hierarchy
Chris Lattner7ce83e52002-08-14 20:07:01 +0000[diff] [blame]183LEVEL = ../../..
Chris Lattner17a4c3e2002-08-14 20:06:13 +0000[diff] [blame]184
185# Name of the library to build
Reid Spencer7fa6d522005-01-11 05:16:23 +0000[diff] [blame]186LIBRARYNAME = Hello
Chris Lattner17a4c3e2002-08-14 20:06:13 +0000[diff] [blame]187
Reid Spencer7fa6d522005-01-11 05:16:23 +0000[diff] [blame]188# Make the shared library become a loadable module so the tools can
189# dlopen/dlsym on the resulting library.
Robert Bocchino3cf817d2006-01-06 22:49:23 +0000[diff] [blame]190LOADABLE_MODULE = 1
Reid Spencer7fa6d522005-01-11 05:16:23 +0000[diff] [blame]191
Chris Lattner17a4c3e2002-08-14 20:06:13 +0000[diff] [blame]192# Include the makefile implementation stuff
193include $(LEVEL)/Makefile.common
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]194</pre></div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]195
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]196<p>This makefile specifies that all of the <tt>.cpp</tt> files in the current
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]197directory are to be compiled and linked together into a
Duncan Sands67f8a7b2010-07-08 08:27:18 +0000[diff] [blame^]198<tt>Debug+Asserts/lib/Hello.so</tt> shared object that can be dynamically loaded by
Chris Lattnerc8603c22006-08-27 23:18:52 +0000[diff] [blame]199the <tt>opt</tt> or <tt>bugpoint</tt> tools via their <tt>-load</tt> options.
Reid Spencer7fa6d522005-01-11 05:16:23 +0000[diff] [blame]200If your operating system uses a suffix other than .so (such as windows or
201Mac OS/X), the appropriate extension will be used.</p>
John Criswellf9c78652004-01-26 21:26:54 +0000[diff] [blame]202
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]203<p>Now that we have the build scripts set up, we just need to write the code for
204the pass itself.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]205
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]206</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]207
208<!-- ======================================================================= -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]209<div class="doc_subsection">
210 <a name="basiccode">Basic code required</a>
211</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]212
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]213<div class="doc_text">
214
215<p>Now that we have a way to compile our new pass, we just have to write it.
216Start out with:</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]217
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]218<div class="doc_code"><pre>
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]219<b>#include</b> "<a href="http://llvm.org/doxygen/Pass_8h-source.html">llvm/Pass.h</a>"
220<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]221<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]222</pre></div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]223
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]224<p>Which are needed because we are writing a <tt><a
Chris Lattner0ce6f932009-09-08 05:14:44 +0000[diff] [blame]225href="http://llvm.org/doxygen/classllvm_1_1Pass.html">Pass</a></tt>,
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]226we are operating on <tt><a
Chris Lattner0ce6f932009-09-08 05:14:44 +0000[diff] [blame]227href="http://llvm.org/doxygen/classllvm_1_1Function.html">Function</a></tt>'s,
228and we will be doing some printing.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]229
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]230<p>Next we have:</p>
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]231<div class="doc_code"><pre>
Jonathan Manton65acb302004-06-30 18:10:30 +0000[diff] [blame]232<b>using namespace llvm;</b>
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]233</pre></div>
Jonathan Manton65acb302004-06-30 18:10:30 +0000[diff] [blame]234<p>... which is required because the functions from the include files
235live in the llvm namespace.
236</p>
237
238<p>Next we have:</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]239
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]240<div class="doc_code"><pre>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]241<b>namespace</b> {
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]242</pre></div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]243
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]244<p>... which starts out an anonymous namespace. Anonymous namespaces are to C++
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]245what the "<tt>static</tt>" keyword is to C (at global scope). It makes the
246things declared inside of the anonymous namespace only visible to the current
247file. If you're not familiar with them, consult a decent C++ book for more
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]248information.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]249
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]250<p>Next, we declare our pass itself:</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]251
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]252<div class="doc_code"><pre>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]253 <b>struct</b> Hello : <b>public</b> <a href="#FunctionPass">FunctionPass</a> {
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]254</pre></div><p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]255
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]256<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]257href="http://llvm.org/doxygen/classllvm_1_1FunctionPass.html">FunctionPass</a></tt>.
Chris Lattnerd6ea9262002-09-09 03:48:46 +0000[diff] [blame]258The different builtin pass subclasses are described in detail <a
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]259href="#passtype">later</a>, but for now, know that <a
260href="#FunctionPass"><tt>FunctionPass</tt></a>'s operate a function at a
261time.</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>
Devang Patel19974732007-05-03 01:11:54 +0000[diff] [blame]264 static char ID;
Dan Gohman865f0062009-02-18 05:09:16 +0000[diff] [blame]265 Hello() : FunctionPass(&amp;ID) {}
Devang Patele50fb9a2007-05-01 20:55:38 +0000[diff] [blame]266</pre></div><p>
267
268<p> This declares pass identifier used by LLVM to identify pass. This allows LLVM to
269avoid using expensive C++ runtime information.</p>
270
271<div class="doc_code"><pre>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]272 <b>virtual bool</b> <a href="#runOnFunction">runOnFunction</a>(Function &amp;F) {
Chris Lattner0ce6f932009-09-08 05:14:44 +0000[diff] [blame]273 errs() &lt;&lt; "<i>Hello: </i>" &lt;&lt; F.getName() &lt;&lt; "\n";
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]274 <b>return false</b>;
275 }
276 }; <i>// end of struct Hello</i>
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]277</pre></div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]278
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]279<p>We declare a "<a href="#runOnFunction"><tt>runOnFunction</tt></a>" method,
280which overloads an abstract virtual method inherited from <a
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]281href="#FunctionPass"><tt>FunctionPass</tt></a>. This is where we are supposed
282to 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]283function.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]284
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]285<div class="doc_code"><pre>
Devang Patel19974732007-05-03 01:11:54 +0000[diff] [blame]286 char Hello::ID = 0;
Devang Patele50fb9a2007-05-01 20:55:38 +0000[diff] [blame]287</pre></div>
288
289<p> We initialize pass ID here. LLVM uses ID's address to identify pass so
290initialization value is not important.</p>
291
292<div class="doc_code"><pre>
Devang Patelc7582092008-03-19 21:56:59 +0000[diff] [blame]293 RegisterPass&lt;Hello&gt; X("<i>hello</i>", "<i>Hello World Pass</i>",
294 false /* Only looks at CFG */,
295 false /* Analysis Pass */);
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]296} <i>// end of anonymous namespace</i>
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]297</pre></div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]298
Chris Lattnerc8603c22006-08-27 23:18:52 +0000[diff] [blame]299<p>Lastly, we <a href="#registration">register our class</a> <tt>Hello</tt>,
300giving it a command line
Devang Patelc7582092008-03-19 21:56:59 +0000[diff] [blame]301argument "<tt>hello</tt>", and a name "<tt>Hello World Pass</tt>".
302Last two RegisterPass arguments are optional. Their default value is false.
303If a pass walks CFG without modifying it then third argument is set to true.
304If a pass is an analysis pass, for example dominator tree pass, then true
305is supplied as fourth argument. </p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]306
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]307<p>As a whole, the <tt>.cpp</tt> file looks like:</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]308
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]309<div class="doc_code"><pre>
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]310<b>#include</b> "<a href="http://llvm.org/doxygen/Pass_8h-source.html">llvm/Pass.h</a>"
311<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]312<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]313
Jonathan Manton65acb302004-06-30 18:10:30 +0000[diff] [blame]314<b>using namespace llvm;</b>
315
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]316<b>namespace</b> {
317 <b>struct Hello</b> : <b>public</b> <a href="#FunctionPass">FunctionPass</a> {
Devang Patele50fb9a2007-05-01 20:55:38 +0000[diff] [blame]318
Devang Patel19974732007-05-03 01:11:54 +0000[diff] [blame]319 static char ID;
Dan Gohman865f0062009-02-18 05:09:16 +0000[diff] [blame]320 Hello() : FunctionPass(&amp;ID) {}
Devang Patele50fb9a2007-05-01 20:55:38 +0000[diff] [blame]321
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]322 <b>virtual bool</b> <a href="#runOnFunction">runOnFunction</a>(Function &amp;F) {
Chris Lattner0ce6f932009-09-08 05:14:44 +0000[diff] [blame]323 errs() &lt;&lt; "<i>Hello: </i>" &lt;&lt; F.getName() &lt;&lt; "\n";
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]324 <b>return false</b>;
325 }
326 };
327
Devang Patel26e5a302007-07-25 21:05:39 +0000[diff] [blame]328 char Hello::ID = 0;
Chris Lattnerc8603c22006-08-27 23:18:52 +0000[diff] [blame]329 RegisterPass&lt;Hello&gt; X("<i>hello</i>", "<i>Hello World Pass</i>");
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]330}
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]331</pre></div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]332
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]333<p>Now that it's all together, compile the file with a simple "<tt>gmake</tt>"
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]334command in the local directory and you should get a new
Duncan Sands67f8a7b2010-07-08 08:27:18 +0000[diff] [blame^]335"<tt>Debug+Asserts/lib/Hello.so</tt> file. Note that everything in this file is
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]336contained in an anonymous namespace: this reflects the fact that passes are self
337contained units that do not need external interfaces (although they can have
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]338them) to be useful.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]339
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]340</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]341
342<!-- ======================================================================= -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]343<div class="doc_subsection">
Chris Lattnerc8603c22006-08-27 23:18:52 +0000[diff] [blame]344 <a name="running">Running a pass with <tt>opt</tt></a>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]345</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]346
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]347<div class="doc_text">
348
John Criswellf9c78652004-01-26 21:26:54 +0000[diff] [blame]349<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]350<tt>opt</tt> command to run an LLVM program through your pass. Because you
Chris Lattnerc8603c22006-08-27 23:18:52 +0000[diff] [blame]351registered your pass with the <tt>RegisterPass</tt> template, you will be able to
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]352use the <tt>opt</tt> tool to access it, once loaded.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]353
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]354<p>To test it, follow the example at the end of the <a
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]355href="GettingStarted.html">Getting Started Guide</a> to compile "Hello World" to
Gabor Greif04367bf2007-07-06 22:07:22 +0000[diff] [blame]356LLVM. We can now run the bitcode file (<tt>hello.bc</tt>) for the program
357through our transformation like this (or course, any bitcode file will
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]358work):</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]359
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]360<div class="doc_code"><pre>
Duncan Sands67f8a7b2010-07-08 08:27:18 +0000[diff] [blame^]361$ opt -load ../../../Debug+Asserts/lib/Hello.so -hello &lt; hello.bc &gt; /dev/null
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]362Hello: __main
363Hello: puts
364Hello: main
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]365</pre></div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]366
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]367<p>The '<tt>-load</tt>' option specifies that '<tt>opt</tt>' should load your
368pass as a shared object, which makes '<tt>-hello</tt>' a valid command line
369argument (which is one reason you need to <a href="#registration">register your
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]370pass</a>). Because the hello pass does not modify the program in any
371interesting way, we just throw away the result of <tt>opt</tt> (sending it to
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]372<tt>/dev/null</tt>).</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]373
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]374<p>To see what happened to the other string you registered, try running
Duncan Sands7e7ae5a2010-02-18 14:08:13 +0000[diff] [blame]375<tt>opt</tt> with the <tt>-help</tt> option:</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]376
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]377<div class="doc_code"><pre>
Duncan Sands67f8a7b2010-07-08 08:27:18 +0000[diff] [blame^]378$ opt -load ../../../Debug+Asserts/lib/Hello.so -help
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]379OVERVIEW: llvm .bc -&gt; .bc modular optimizer
380
Gabor Greif04367bf2007-07-06 22:07:22 +0000[diff] [blame]381USAGE: opt [options] &lt;input bitcode&gt;
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]382
383OPTIONS:
384 Optimizations available:
385...
386 -funcresolve - Resolve Functions
387 -gcse - Global Common Subexpression Elimination
388 -globaldce - Dead Global Elimination
389 <b>-hello - Hello World Pass</b>
Chris Lattner065a6162003-09-10 05:29:43 +0000[diff] [blame]390 -indvars - Canonicalize Induction Variables
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]391 -inline - Function Integration/Inlining
392 -instcombine - Combine redundant instructions
393...
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]394</pre></div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]395
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]396<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]397documentation to users of <tt>opt</tt>. Now that you have a working pass, you
398would go ahead and make it do the cool transformations you want. Once you get
399it all working and tested, it may become useful to find out how fast your pass
400is. The <a href="#passManager"><tt>PassManager</tt></a> provides a nice command
401line option (<tt>--time-passes</tt>) that allows you to get information about
402the execution time of your pass along with the other passes you queue up. For
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]403example:</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]404
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]405<div class="doc_code"><pre>
Duncan Sands67f8a7b2010-07-08 08:27:18 +0000[diff] [blame^]406$ 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]407Hello: __main
408Hello: puts
409Hello: main
410===============================================================================
411 ... Pass execution timing report ...
412===============================================================================
413 Total Execution Time: 0.02 seconds (0.0479059 wall clock)
414
415 ---User Time--- --System Time-- --User+System-- ---Wall Time--- --- Pass Name ---
Gabor Greif04367bf2007-07-06 22:07:22 +0000[diff] [blame]416 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]417 0.0000 ( 0.0%) 0.0100 (100.0%) 0.0100 ( 50.0%) 0.0031 ( 6.4%) Dominator Set Construction
418 0.0000 ( 0.0%) 0.0000 ( 0.0%) 0.0000 ( 0.0%) 0.0013 ( 2.7%) Module Verifier
419 <b> 0.0000 ( 0.0%) 0.0000 ( 0.0%) 0.0000 ( 0.0%) 0.0033 ( 6.9%) Hello World Pass</b>
420 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]421</pre></div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]422
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]423<p>As you can see, our implementation above is pretty fast :). The additional
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]424passes listed are automatically inserted by the '<tt>opt</tt>' tool to verify
425that the LLVM emitted by your pass is still valid and well formed LLVM, which
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]426hasn't been broken somehow.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]427
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]428<p>Now that you have seen the basics of the mechanics behind passes, we can talk
429about some more details of how they work and how to use them.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]430
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]431</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]432
433<!-- *********************************************************************** -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]434<div class="doc_section">
435 <a name="passtype">Pass classes and requirements</a>
436</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]437<!-- *********************************************************************** -->
438
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]439<div class="doc_text">
440
441<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]442decide what class you should subclass for your pass. The <a
443href="#basiccode">Hello World</a> example uses the <tt><a
444href="#FunctionPass">FunctionPass</a></tt> class for its implementation, but we
445did not discuss why or when this should occur. Here we talk about the classes
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]446available, from the most general to the most specific.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]447
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]448<p>When choosing a superclass for your Pass, you should choose the <b>most
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]449specific</b> class possible, while still being able to meet the requirements
Misha Brukman5560c9d2003-08-18 14:43:39 +0000[diff] [blame]450listed. This gives the LLVM Pass Infrastructure information necessary to
Benjamin Kramer8040cd32009-10-12 14:46:08 +0000[diff] [blame]451optimize how passes are run, so that the resultant compiler isn't unnecessarily
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]452slow.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]453
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]454</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]455
Chris Lattnerf004f9a2002-09-25 22:31:38 +0000[diff] [blame]456<!-- ======================================================================= -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]457<div class="doc_subsection">
458 <a name="ImmutablePass">The <tt>ImmutablePass</tt> class</a>
459</div>
Chris Lattnerf004f9a2002-09-25 22:31:38 +0000[diff] [blame]460
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]461<div class="doc_text">
462
463<p>The most plain and boring type of pass is the "<tt><a
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]464href="http://llvm.org/doxygen/classllvm_1_1ImmutablePass.html">ImmutablePass</a></tt>"
Chris Lattnerf004f9a2002-09-25 22:31:38 +0000[diff] [blame]465class. This pass type is used for passes that do not have to be run, do not
466change state, and never need to be updated. This is not a normal type of
467transformation or analysis, but can provide information about the current
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]468compiler configuration.</p>
Chris Lattnerf004f9a2002-09-25 22:31:38 +0000[diff] [blame]469
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]470<p>Although this pass class is very infrequently used, it is important for
Chris Lattnerf004f9a2002-09-25 22:31:38 +0000[diff] [blame]471providing information about the current target machine being compiled for, and
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]472other static information that can affect the various transformations.</p>
Chris Lattnerf004f9a2002-09-25 22:31:38 +0000[diff] [blame]473
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]474<p><tt>ImmutablePass</tt>es never invalidate other transformations, are never
475invalidated, and are never "run".</p>
Chris Lattnerf004f9a2002-09-25 22:31:38 +0000[diff] [blame]476
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]477</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]478
479<!-- ======================================================================= -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]480<div class="doc_subsection">
Chris Lattnerf6278922004-09-20 04:36:29 +0000[diff] [blame]481 <a name="ModulePass">The <tt>ModulePass</tt> class</a>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]482</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]483
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]484<div class="doc_text">
485
486<p>The "<tt><a
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]487href="http://llvm.org/doxygen/classllvm_1_1ModulePass.html">ModulePass</a></tt>"
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]488class is the most general of all superclasses that you can use. Deriving from
Chris Lattnerf6278922004-09-20 04:36:29 +0000[diff] [blame]489<tt>ModulePass</tt> indicates that your pass uses the entire program as a unit,
Benjamin Kramer8040cd32009-10-12 14:46:08 +0000[diff] [blame]490referring to function bodies in no predictable order, or adding and removing
Chris Lattnerf6278922004-09-20 04:36:29 +0000[diff] [blame]491functions. Because nothing is known about the behavior of <tt>ModulePass</tt>
Daniel Dunbarb71725b2009-07-01 23:38:44 +0000[diff] [blame]492subclasses, no optimization can be done for their execution.</p>
493
494<p>A module pass can use function level passes (e.g. dominators) using
495the getAnalysis interface
496<tt>getAnalysis&lt;DominatorTree&gt;(llvm::Function *)</tt> to provide the
497function to retrieve analysis result for, if the function pass does not require
Devang Patel468857f2009-08-10 16:37:29 +0000[diff] [blame]498any 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]499analysis ran, e.g. in the case of dominators you should only ask for the
500DominatorTree for function definitions, not declarations.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]501
Chris Lattnerf6278922004-09-20 04:36:29 +0000[diff] [blame]502<p>To write a correct <tt>ModulePass</tt> subclass, derive from
503<tt>ModulePass</tt> and overload the <tt>runOnModule</tt> method with the
504following signature:</p>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]505
506</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]507
508<!-- _______________________________________________________________________ -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]509<div class="doc_subsubsection">
Chris Lattnerf6278922004-09-20 04:36:29 +0000[diff] [blame]510 <a name="runOnModule">The <tt>runOnModule</tt> method</a>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]511</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]512
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]513<div class="doc_text">
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]514
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]515<div class="doc_code"><pre>
Chris Lattnerf6278922004-09-20 04:36:29 +0000[diff] [blame]516 <b>virtual bool</b> runOnModule(Module &amp;M) = 0;
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]517</pre></div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]518
John Criswell2382ff72005-07-15 19:25:12 +0000[diff] [blame]519<p>The <tt>runOnModule</tt> method performs the interesting work of the pass.
520It should return true if the module was modified by the transformation and
521false otherwise.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]522
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]523</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]524
525<!-- ======================================================================= -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]526<div class="doc_subsection">
Chris Lattner8fdb2462004-09-18 06:39:35 +0000[diff] [blame]527 <a name="CallGraphSCCPass">The <tt>CallGraphSCCPass</tt> class</a>
528</div>
529
530<div class="doc_text">
531
532<p>The "<tt><a
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]533href="http://llvm.org/doxygen/classllvm_1_1CallGraphSCCPass.html">CallGraphSCCPass</a></tt>"
Chris Lattner8fdb2462004-09-18 06:39:35 +0000[diff] [blame]534is used by passes that need to traverse the program bottom-up on the call graph
535(callees before callers). Deriving from CallGraphSCCPass provides some
536mechanics for building and traversing the CallGraph, but also allows the system
537to optimize execution of CallGraphSCCPass's. If your pass meets the
538requirements outlined below, and doesn't meet the requirements of a <tt><a
539href="#FunctionPass">FunctionPass</a></tt> or <tt><a
540href="#BasicBlockPass">BasicBlockPass</a></tt>, you should derive from
541<tt>CallGraphSCCPass</tt>.</p>
542
543<p><b>TODO</b>: explain briefly what SCC, Tarjan's algo, and B-U mean.</p>
544
545<p>To be explicit, <tt>CallGraphSCCPass</tt> subclasses are:</p>
546
547<ol>
548
549<li>... <em>not allowed</em> to modify any <tt>Function</tt>s that are not in
550the current SCC.</li>
551
Tanya Lattner18aad232007-06-07 16:44:52 +0000[diff] [blame]552<li>... <em>not allowed</em> to inspect any Function's other than those in the
Chris Lattner8fdb2462004-09-18 06:39:35 +0000[diff] [blame]553current SCC and the direct callees of the SCC.</li>
554
555<li>... <em>required</em> to preserve the current CallGraph object, updating it
556to reflect any changes made to the program.</li>
557
558<li>... <em>not allowed</em> to add or remove SCC's from the current Module,
559though they may change the contents of an SCC.</li>
560
561<li>... <em>allowed</em> to add or remove global variables from the current
562Module.</li>
563
564<li>... <em>allowed</em> to maintain state across invocations of
565 <a href="#runOnSCC"><tt>runOnSCC</tt></a> (including global data).</li>
566</ol>
567
568<p>Implementing a <tt>CallGraphSCCPass</tt> is slightly tricky in some cases
569because it has to handle SCCs with more than one node in it. All of the virtual
570methods described below should return true if they modified the program, or
571false if they didn't.</p>
572
573</div>
574
575<!-- _______________________________________________________________________ -->
576<div class="doc_subsubsection">
Devang Patelc20048d2007-01-23 22:56:28 +0000[diff] [blame]577 <a name="doInitialization_scc">The <tt>doInitialization(CallGraph &amp;)</tt>
Chris Lattner8fdb2462004-09-18 06:39:35 +0000[diff] [blame]578 method</a>
579</div>
580
581<div class="doc_text">
582
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]583<div class="doc_code"><pre>
Devang Patelc20048d2007-01-23 22:56:28 +0000[diff] [blame]584 <b>virtual bool</b> doInitialization(CallGraph &amp;CG);
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]585</pre></div>
Chris Lattner8fdb2462004-09-18 06:39:35 +0000[diff] [blame]586
587<p>The <tt>doIninitialize</tt> method is allowed to do most of the things that
588<tt>CallGraphSCCPass</tt>'s are not allowed to do. They can add and remove
589functions, get pointers to functions, etc. The <tt>doInitialization</tt> method
590is designed to do simple initialization type of stuff that does not depend on
591the SCCs being processed. The <tt>doInitialization</tt> method call is not
592scheduled to overlap with any other pass executions (thus it should be very
593fast).</p>
594
595</div>
596
597<!-- _______________________________________________________________________ -->
598<div class="doc_subsubsection">
599 <a name="runOnSCC">The <tt>runOnSCC</tt> method</a>
600</div>
601
602<div class="doc_text">
603
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]604<div class="doc_code"><pre>
Chris Lattner6f25d9f2010-04-16 23:07:44 +0000[diff] [blame]605 <b>virtual bool</b> runOnSCC(CallGraphSCC &amp;SCC) = 0;
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]606</pre></div>
Chris Lattner8fdb2462004-09-18 06:39:35 +0000[diff] [blame]607
608<p>The <tt>runOnSCC</tt> method performs the interesting work of the pass, and
609should return true if the module was modified by the transformation, false
610otherwise.</p>
611
612</div>
613
614<!-- _______________________________________________________________________ -->
615<div class="doc_subsubsection">
Devang Patelc20048d2007-01-23 22:56:28 +0000[diff] [blame]616 <a name="doFinalization_scc">The <tt>doFinalization(CallGraph
Chris Lattner8fdb2462004-09-18 06:39:35 +0000[diff] [blame]617 &amp;)</tt> method</a>
618</div>
619
620<div class="doc_text">
621
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]622<div class="doc_code"><pre>
Devang Patelc20048d2007-01-23 22:56:28 +0000[diff] [blame]623 <b>virtual bool</b> doFinalization(CallGraph &amp;CG);
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]624</pre></div>
Chris Lattner8fdb2462004-09-18 06:39:35 +0000[diff] [blame]625
626<p>The <tt>doFinalization</tt> method is an infrequently used method that is
627called when the pass framework has finished calling <a
628href="#runOnFunction"><tt>runOnFunction</tt></a> for every function in the
629program being compiled.</p>
630
631</div>
632
633<!-- ======================================================================= -->
634<div class="doc_subsection">
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]635 <a name="FunctionPass">The <tt>FunctionPass</tt> class</a>
636</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]637
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]638<div class="doc_text">
639
Chris Lattnerf6278922004-09-20 04:36:29 +0000[diff] [blame]640<p>In contrast to <tt>ModulePass</tt> subclasses, <tt><a
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]641href="http://llvm.org/doxygen/classllvm_1_1Pass.html">FunctionPass</a></tt>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]642subclasses do have a predictable, local behavior that can be expected by the
643system. All <tt>FunctionPass</tt> execute on each function in the program
Misha Brukmanef6a6a62003-08-21 22:14:26 +0000[diff] [blame]644independent of all of the other functions in the program.
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]645<tt>FunctionPass</tt>'s do not require that they are executed in a particular
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]646order, and <tt>FunctionPass</tt>'s do not modify external functions.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]647
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]648<p>To be explicit, <tt>FunctionPass</tt> subclasses are not allowed to:</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]649
650<ol>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]651<li>Modify a Function other than the one currently being processed.</li>
652<li>Add or remove Function's from the current Module.</li>
653<li>Add or remove global variables from the current Module.</li>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]654<li>Maintain state across invocations of
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]655 <a href="#runOnFunction"><tt>runOnFunction</tt></a> (including global data)</li>
656</ol>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]657
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]658<p>Implementing a <tt>FunctionPass</tt> is usually straightforward (See the <a
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]659href="#basiccode">Hello World</a> pass for example). <tt>FunctionPass</tt>'s
660may overload three virtual methods to do their work. All of these methods
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]661should return true if they modified the program, or false if they didn't.</p>
662
663</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]664
665<!-- _______________________________________________________________________ -->
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]666<div class="doc_subsubsection">
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]667 <a name="doInitialization_mod">The <tt>doInitialization(Module &amp;)</tt>
668 method</a>
669</div>
670
671<div class="doc_text">
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]672
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]673<div class="doc_code"><pre>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]674 <b>virtual bool</b> doInitialization(Module &amp;M);
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]675</pre></div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]676
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]677<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]678<tt>FunctionPass</tt>'s are not allowed to do. They can add and remove
Chris Lattnerd0713f92002-09-12 17:06:43 +0000[diff] [blame]679functions, get pointers to functions, etc. The <tt>doInitialization</tt> method
680is designed to do simple initialization type of stuff that does not depend on
681the functions being processed. The <tt>doInitialization</tt> method call is not
682scheduled to overlap with any other pass executions (thus it should be very
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]683fast).</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]684
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]685<p>A good example of how this method should be used is the <a
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]686href="http://llvm.org/doxygen/LowerAllocations_8cpp-source.html">LowerAllocations</a>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]687pass. This pass converts <tt>malloc</tt> and <tt>free</tt> instructions into
Misha Brukmanef6a6a62003-08-21 22:14:26 +0000[diff] [blame]688platform dependent <tt>malloc()</tt> and <tt>free()</tt> function calls. It
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]689uses the <tt>doInitialization</tt> method to get a reference to the malloc and
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]690free functions that it needs, adding prototypes to the module if necessary.</p>
691
692</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]693
694<!-- _______________________________________________________________________ -->
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]695<div class="doc_subsubsection">
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]696 <a name="runOnFunction">The <tt>runOnFunction</tt> method</a>
697</div>
698
699<div class="doc_text">
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]700
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]701<div class="doc_code"><pre>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]702 <b>virtual bool</b> runOnFunction(Function &amp;F) = 0;
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]703</pre></div><p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]704
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]705<p>The <tt>runOnFunction</tt> method must be implemented by your subclass to do
706the transformation or analysis work of your pass. As usual, a true value should
707be returned if the function is modified.</p>
708
709</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]710
711<!-- _______________________________________________________________________ -->
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]712<div class="doc_subsubsection">
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]713 <a name="doFinalization_mod">The <tt>doFinalization(Module
714 &amp;)</tt> method</a>
715</div>
716
717<div class="doc_text">
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]718
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]719<div class="doc_code"><pre>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]720 <b>virtual bool</b> doFinalization(Module &amp;M);
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]721</pre></div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]722
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]723<p>The <tt>doFinalization</tt> method is an infrequently used method that is
724called when the pass framework has finished calling <a
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]725href="#runOnFunction"><tt>runOnFunction</tt></a> for every function in the
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]726program being compiled.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]727
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]728</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]729
730<!-- ======================================================================= -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]731<div class="doc_subsection">
Devang Patel2e8f27d2007-03-19 22:21:25 +0000[diff] [blame]732 <a name="LoopPass">The <tt>LoopPass</tt> class </a>
733</div>
734
735<div class="doc_text">
736
737<p> All <tt>LoopPass</tt> execute on each loop in the function independent of
738all of the other loops in the function. <tt>LoopPass</tt> processes loops in
739loop nest order such that outer most loop is processed last. </p>
740
741<p> <tt>LoopPass</tt> subclasses are allowed to update loop nest using
742<tt>LPPassManager</tt> interface. Implementing a loop pass is usually
743straightforward. <tt>Looppass</tt>'s may overload three virtual methods to
744do their work. All these methods should return true if they modified the
745program, or false if they didn't. </p>
746</div>
747
748<!-- _______________________________________________________________________ -->
749<div class="doc_subsubsection">
750 <a name="doInitialization_loop">The <tt>doInitialization(Loop *,
751 LPPassManager &amp;)</tt>
752 method</a>
753</div>
754
755<div class="doc_text">
756
757<div class="doc_code"><pre>
758 <b>virtual bool</b> doInitialization(Loop *, LPPassManager &amp;LPM);
759</pre></div>
760
Chris Lattnerb5c87f62007-05-18 05:36:14 +0000[diff] [blame]761<p>The <tt>doInitialization</tt> method is designed to do simple initialization
Devang Patel2e8f27d2007-03-19 22:21:25 +0000[diff] [blame]762type of stuff that does not depend on the functions being processed. The
763<tt>doInitialization</tt> method call is not scheduled to overlap with any
764other pass executions (thus it should be very fast). LPPassManager
765interface should be used to access Function or Module level analysis
766information.</p>
767
768</div>
769
770
771<!-- _______________________________________________________________________ -->
772<div class="doc_subsubsection">
773 <a name="runOnLoop">The <tt>runOnLoop</tt> method</a>
774</div>
775
776<div class="doc_text">
777
778<div class="doc_code"><pre>
779 <b>virtual bool</b> runOnLoop(Loop *, LPPassManager &amp;LPM) = 0;
780</pre></div><p>
781
782<p>The <tt>runOnLoop</tt> method must be implemented by your subclass to do
783the transformation or analysis work of your pass. As usual, a true value should
784be returned if the function is modified. <tt>LPPassManager</tt> interface
785should be used to update loop nest.</p>
786
787</div>
788
789<!-- _______________________________________________________________________ -->
790<div class="doc_subsubsection">
791 <a name="doFinalization_loop">The <tt>doFinalization()</tt> method</a>
792</div>
793
794<div class="doc_text">
795
796<div class="doc_code"><pre>
797 <b>virtual bool</b> doFinalization();
798</pre></div>
799
800<p>The <tt>doFinalization</tt> method is an infrequently used method that is
801called when the pass framework has finished calling <a
802href="#runOnLoop"><tt>runOnLoop</tt></a> for every loop in the
803program being compiled. </p>
804
805</div>
806
807
808
809<!-- ======================================================================= -->
810<div class="doc_subsection">
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]811 <a name="BasicBlockPass">The <tt>BasicBlockPass</tt> class</a>
812</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]813
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]814<div class="doc_text">
815
816<p><tt>BasicBlockPass</tt>'s are just like <a
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]817href="#FunctionPass"><tt>FunctionPass</tt></a>'s, except that they must limit
818their scope of inspection and modification to a single basic block at a time.
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]819As such, they are <b>not</b> allowed to do any of the following:</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]820
821<ol>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]822<li>Modify or inspect any basic blocks outside of the current one</li>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]823<li>Maintain state across invocations of
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]824 <a href="#runOnBasicBlock"><tt>runOnBasicBlock</tt></a></li>
Reid Spencer1bc19342004-12-11 05:12:57 +0000[diff] [blame]825<li>Modify the control flow graph (by altering terminator instructions)</li>
826<li>Any of the things forbidden for
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]827 <a href="#FunctionPass"><tt>FunctionPass</tt></a>es.</li>
828</ol>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]829
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]830<p><tt>BasicBlockPass</tt>es are useful for traditional local and "peephole"
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]831optimizations. They may override the same <a
Chris Lattnerd0713f92002-09-12 17:06:43 +0000[diff] [blame]832href="#doInitialization_mod"><tt>doInitialization(Module &amp;)</tt></a> and <a
833href="#doFinalization_mod"><tt>doFinalization(Module &amp;)</tt></a> methods that <a
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]834href="#FunctionPass"><tt>FunctionPass</tt></a>'s have, but also have the following virtual methods that may also be implemented:</p>
835
836</div>
Chris Lattnerd0713f92002-09-12 17:06:43 +0000[diff] [blame]837
838<!-- _______________________________________________________________________ -->
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]839<div class="doc_subsubsection">
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]840 <a name="doInitialization_fn">The <tt>doInitialization(Function
841 &amp;)</tt> method</a>
842</div>
843
844<div class="doc_text">
Chris Lattnerd0713f92002-09-12 17:06:43 +0000[diff] [blame]845
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]846<div class="doc_code"><pre>
Chris Lattnerd0713f92002-09-12 17:06:43 +0000[diff] [blame]847 <b>virtual bool</b> doInitialization(Function &amp;F);
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]848</pre></div>
Chris Lattnerd0713f92002-09-12 17:06:43 +0000[diff] [blame]849
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]850<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]851<tt>BasicBlockPass</tt>'s are not allowed to do, but that
852<tt>FunctionPass</tt>'s can. The <tt>doInitialization</tt> method is designed
Reid Spencer1bc19342004-12-11 05:12:57 +0000[diff] [blame]853to do simple initialization that does not depend on the
Chris Lattnerd0713f92002-09-12 17:06:43 +0000[diff] [blame]854BasicBlocks being processed. The <tt>doInitialization</tt> method call is not
855scheduled to overlap with any other pass executions (thus it should be very
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]856fast).</p>
Chris Lattnerd0713f92002-09-12 17:06:43 +0000[diff] [blame]857
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]858</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]859
860<!-- _______________________________________________________________________ -->
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]861<div class="doc_subsubsection">
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]862 <a name="runOnBasicBlock">The <tt>runOnBasicBlock</tt> method</a>
863</div>
864
865<div class="doc_text">
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]866
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]867<div class="doc_code"><pre>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]868 <b>virtual bool</b> runOnBasicBlock(BasicBlock &amp;BB) = 0;
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]869</pre></div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]870
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]871<p>Override this function to do the work of the <tt>BasicBlockPass</tt>. This
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]872function is not allowed to inspect or modify basic blocks other than the
873parameter, and are not allowed to modify the CFG. A true value must be returned
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]874if the basic block is modified.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]875
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]876</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]877
Chris Lattnerd0713f92002-09-12 17:06:43 +0000[diff] [blame]878<!-- _______________________________________________________________________ -->
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]879<div class="doc_subsubsection">
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]880 <a name="doFinalization_fn">The <tt>doFinalization(Function &amp;)</tt>
881 method</a>
882</div>
883
884<div class="doc_text">
Chris Lattnerd0713f92002-09-12 17:06:43 +0000[diff] [blame]885
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]886<div class="doc_code"><pre>
Chris Lattnerd0713f92002-09-12 17:06:43 +0000[diff] [blame]887 <b>virtual bool</b> doFinalization(Function &amp;F);
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]888</pre></div>
Chris Lattnerd0713f92002-09-12 17:06:43 +0000[diff] [blame]889
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]890<p>The <tt>doFinalization</tt> method is an infrequently used method that is
891called when the pass framework has finished calling <a
Chris Lattnerd0713f92002-09-12 17:06:43 +0000[diff] [blame]892href="#runOnBasicBlock"><tt>runOnBasicBlock</tt></a> for every BasicBlock in the
893program being compiled. This can be used to perform per-function
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]894finalization.</p>
Chris Lattnerd0713f92002-09-12 17:06:43 +0000[diff] [blame]895
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]896</div>
Chris Lattnerd0713f92002-09-12 17:06:43 +0000[diff] [blame]897
Brian Gaekecab8b6f2003-07-17 18:53:20 +0000[diff] [blame]898<!-- ======================================================================= -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]899<div class="doc_subsection">
900 <a name="MachineFunctionPass">The <tt>MachineFunctionPass</tt> class</a>
901</div>
Brian Gaekecab8b6f2003-07-17 18:53:20 +0000[diff] [blame]902
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]903<div class="doc_text">
904
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]905<p>A <tt>MachineFunctionPass</tt> is a part of the LLVM code generator that
906executes on the machine-dependent representation of each LLVM function in the
Dan Gohman9f116aa2010-03-10 01:29:39 +0000[diff] [blame]907program.</p>
908
909<p>Code generator passes are registered and initialized specially by
910<tt>TargetMachine::addPassesToEmitFile</tt> and similar routines, so they
911cannot generally be run from the <tt>opt</tt> or <tt>bugpoint</tt>
912commands.</p>
913
914<p>A <tt>MachineFunctionPass</tt> is also a <tt>FunctionPass</tt>, so all
Brian Gaekecab8b6f2003-07-17 18:53:20 +0000[diff] [blame]915the restrictions that apply to a <tt>FunctionPass</tt> also apply to it.
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]916<tt>MachineFunctionPass</tt>es also have additional restrictions. In particular,
917<tt>MachineFunctionPass</tt>es are not allowed to do any of the following:</p>
Brian Gaekecab8b6f2003-07-17 18:53:20 +0000[diff] [blame]918
919<ol>
Dan Gohman9f116aa2010-03-10 01:29:39 +0000[diff] [blame]920<li>Modify or create any LLVM IR Instructions, BasicBlocks, Arguments,
921 Functions, GlobalVariables, GlobalAliases, or Modules.</li>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]922<li>Modify a MachineFunction other than the one currently being processed.</li>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]923<li>Maintain state across invocations of <a
924href="#runOnMachineFunction"><tt>runOnMachineFunction</tt></a> (including global
925data)</li>
926</ol>
Brian Gaekecab8b6f2003-07-17 18:53:20 +0000[diff] [blame]927
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]928</div>
Chris Lattnerd0713f92002-09-12 17:06:43 +0000[diff] [blame]929
Brian Gaeke6a33f362003-07-22 20:53:20 +0000[diff] [blame]930<!-- _______________________________________________________________________ -->
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]931<div class="doc_subsubsection">
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]932 <a name="runOnMachineFunction">The <tt>runOnMachineFunction(MachineFunction
933 &amp;MF)</tt> method</a>
934</div>
935
936<div class="doc_text">
Brian Gaeke6a33f362003-07-22 20:53:20 +0000[diff] [blame]937
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]938<div class="doc_code"><pre>
Brian Gaeke6a33f362003-07-22 20:53:20 +0000[diff] [blame]939 <b>virtual bool</b> runOnMachineFunction(MachineFunction &amp;MF) = 0;
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]940</pre></div>
Brian Gaeke6a33f362003-07-22 20:53:20 +0000[diff] [blame]941
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]942<p><tt>runOnMachineFunction</tt> can be considered the main entry point of a
943<tt>MachineFunctionPass</tt>; that is, you should override this method to do the
944work of your <tt>MachineFunctionPass</tt>.</p>
Brian Gaeke6a33f362003-07-22 20:53:20 +0000[diff] [blame]945
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]946<p>The <tt>runOnMachineFunction</tt> method is called on every
Brian Gaeke6a33f362003-07-22 20:53:20 +0000[diff] [blame]947<tt>MachineFunction</tt> in a <tt>Module</tt>, so that the
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]948<tt>MachineFunctionPass</tt> may perform optimizations on the machine-dependent
949representation of the function. If you want to get at the LLVM <tt>Function</tt>
950for the <tt>MachineFunction</tt> you're working on, use
951<tt>MachineFunction</tt>'s <tt>getFunction()</tt> accessor method -- but
952remember, you may not modify the LLVM <tt>Function</tt> or its contents from a
953<tt>MachineFunctionPass</tt>.</p>
954
955</div>
Brian Gaeke6a33f362003-07-22 20:53:20 +0000[diff] [blame]956
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]957<!-- *********************************************************************** -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]958<div class="doc_section">
959 <a name="registration">Pass registration</a>
960</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]961<!-- *********************************************************************** -->
962
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]963<div class="doc_text">
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]964
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]965<p>In the <a href="#basiccode">Hello World</a> example pass we illustrated how
966pass registration works, and discussed some of the reasons that it is used and
967what it does. Here we discuss how and why passes are registered.</p>
968
Chris Lattnerc8603c22006-08-27 23:18:52 +0000[diff] [blame]969<p>As we saw above, passes are registered with the <b><tt>RegisterPass</tt></b>
970template, which requires you to pass at least two
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]971parameters. The first parameter is the name of the pass that is to be used on
972the command line to specify that the pass should be added to a program (for
Chris Lattnerc8603c22006-08-27 23:18:52 +0000[diff] [blame]973example, with <tt>opt</tt> or <tt>bugpoint</tt>). The second argument is the
Duncan Sands7e7ae5a2010-02-18 14:08:13 +0000[diff] [blame]974name 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]975programs, as
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]976well as for debug output generated by the <tt>--debug-pass</tt> option.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]977
Chris Lattnerc8603c22006-08-27 23:18:52 +0000[diff] [blame]978<p>If you want your pass to be easily dumpable, you should
979implement the virtual <tt>print</tt> method:</p>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]980
981</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]982
983<!-- _______________________________________________________________________ -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]984<div class="doc_subsubsection">
985 <a name="print">The <tt>print</tt> method</a>
986</div>
987
988<div class="doc_text">
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]989
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]990<div class="doc_code"><pre>
Torok Edwin52790e52008-10-28 17:29:23 +0000[diff] [blame]991 <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]992</pre></div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]993
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]994<p>The <tt>print</tt> method must be implemented by "analyses" in order to print
995a human readable version of the analysis results. This is useful for debugging
996an analysis itself, as well as for other people to figure out how an analysis
Chris Lattnerc8603c22006-08-27 23:18:52 +0000[diff] [blame]997works. Use the <tt>opt -analyze</tt> argument to invoke this method.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]998
Bill Wendling832171c2006-12-07 20:04:42 +0000[diff] [blame]999<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]1000and 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]1001program that has been analyzed. Note however that this pointer may be null in
1002certain circumstances (such as calling the <tt>Pass::dump()</tt> from a
1003debugger), so it should only be used to enhance debug output, it should not be
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1004depended on.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1005
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1006</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1007
1008<!-- *********************************************************************** -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1009<div class="doc_section">
1010 <a name="interaction">Specifying interactions between passes</a>
1011</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1012<!-- *********************************************************************** -->
1013
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1014<div class="doc_text">
1015
John Criswell8528e782007-12-03 19:34:25 +0000[diff] [blame]1016<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]1017that passes interact with each other correctly. Because <tt>PassManager</tt>
1018tries to <a href="#passmanager">optimize the execution of passes</a> it must
1019know how the passes interact with each other and what dependencies exist between
1020the various passes. To track this, each pass can declare the set of passes that
1021are required to be executed before the current pass, and the passes which are
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1022invalidated by the current pass.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1023
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1024<p>Typically this functionality is used to require that analysis results are
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1025computed before your pass is run. Running arbitrary transformation passes can
1026invalidate the computed analysis results, which is what the invalidation set
1027specifies. If a pass does not implement the <tt><a
1028href="#getAnalysisUsage">getAnalysisUsage</a></tt> method, it defaults to not
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1029having any prerequisite passes, and invalidating <b>all</b> other passes.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1030
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1031</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1032
1033<!-- _______________________________________________________________________ -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1034<div class="doc_subsubsection">
1035 <a name="getAnalysisUsage">The <tt>getAnalysisUsage</tt> method</a>
1036</div>
1037
1038<div class="doc_text">
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1039
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1040<div class="doc_code"><pre>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1041 <b>virtual void</b> getAnalysisUsage(AnalysisUsage &amp;Info) <b>const</b>;
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1042</pre></div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1043
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1044<p>By implementing the <tt>getAnalysisUsage</tt> method, the required and
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1045invalidated sets may be specified for your transformation. The implementation
1046should fill in the <tt><a
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]1047href="http://llvm.org/doxygen/classllvm_1_1AnalysisUsage.html">AnalysisUsage</a></tt>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1048object with information about which passes are required and not invalidated. To
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]1049do this, a pass may call any of the following methods on the AnalysisUsage
1050object:</p>
1051</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1052
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]1053<!-- _______________________________________________________________________ -->
1054<div class="doc_subsubsection">
1055 <a name="AU::addRequired">The <tt>AnalysisUsage::addRequired&lt;&gt;</tt> and <tt>AnalysisUsage::addRequiredTransitive&lt;&gt;</tt> methods</a>
1056</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1057
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]1058<div class="doc_text">
1059<p>
Reid Spencer1bc19342004-12-11 05:12:57 +0000[diff] [blame]1060If your pass requires a previous pass to be executed (an analysis for example),
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]1061it can use one of these methods to arrange for it to be run before your pass.
1062LLVM has many different types of analyses and passes that can be required,
Reid Spencer1bc19342004-12-11 05:12:57 +0000[diff] [blame]1063spanning the range from <tt>DominatorSet</tt> to <tt>BreakCriticalEdges</tt>.
1064Requiring <tt>BreakCriticalEdges</tt>, for example, guarantees that there will
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]1065be no critical edges in the CFG when your pass has been run.
1066</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1067
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]1068<p>
1069Some analyses chain to other analyses to do their job. For example, an <a
1070href="AliasAnalysis.html">AliasAnalysis</a> implementation is required to <a
1071href="AliasAnalysis.html#chaining">chain</a> to other alias analysis passes. In
1072cases where analyses chain, the <tt>addRequiredTransitive</tt> method should be
1073used instead of the <tt>addRequired</tt> method. This informs the PassManager
1074that the transitively required pass should be alive as long as the requiring
1075pass is.
1076</p>
1077</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1078
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]1079<!-- _______________________________________________________________________ -->
1080<div class="doc_subsubsection">
1081 <a name="AU::addPreserved">The <tt>AnalysisUsage::addPreserved&lt;&gt;</tt> method</a>
1082</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1083
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]1084<div class="doc_text">
1085<p>
1086One of the jobs of the PassManager is to optimize how and when analyses are run.
1087In particular, it attempts to avoid recomputing data unless it needs to. For
1088this reason, passes are allowed to declare that they preserve (i.e., they don't
1089invalidate) an existing analysis if it's available. For example, a simple
Reid Spencer1bc19342004-12-11 05:12:57 +0000[diff] [blame]1090constant folding pass would not modify the CFG, so it can't possibly affect the
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]1091results of dominator analysis. By default, all passes are assumed to invalidate
1092all others.
1093</p>
1094
1095<p>
1096The <tt>AnalysisUsage</tt> class provides several methods which are useful in
1097certain circumstances that are related to <tt>addPreserved</tt>. In particular,
1098the <tt>setPreservesAll</tt> method can be called to indicate that the pass does
1099not modify the LLVM program at all (which is true for analyses), and the
1100<tt>setPreservesCFG</tt> method can be used by transformations that change
1101instructions in the program but do not modify the CFG or terminator instructions
1102(note that this property is implicitly set for <a
1103href="#BasicBlockPass">BasicBlockPass</a>'s).
1104</p>
1105
1106<p>
1107<tt>addPreserved</tt> is particularly useful for transformations like
1108<tt>BreakCriticalEdges</tt>. This pass knows how to update a small set of loop
1109and dominator related analyses if they exist, so it can preserve them, despite
1110the fact that it hacks on the CFG.
1111</p>
1112</div>
1113
1114<!-- _______________________________________________________________________ -->
1115<div class="doc_subsubsection">
1116 <a name="AU::examples">Example implementations of <tt>getAnalysisUsage</tt></a>
1117</div>
1118
1119<div class="doc_text">
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1120
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1121<div class="doc_code"><pre>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1122 <i>// This is an example implementation from an analysis, which does not modify
1123 // the program at all, yet has a prerequisite.</i>
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]1124 <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]1125 AU.setPreservesAll();
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]1126 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]1127 }
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1128</pre></div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1129
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1130<p>and:</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1131
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1132<div class="doc_code"><pre>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1133 <i>// This example modifies the program, but does not modify the CFG</i>
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]1134 <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]1135 AU.setPreservesCFG();
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]1136 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]1137 }
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1138</pre></div>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1139
1140</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1141
1142<!-- _______________________________________________________________________ -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1143<div class="doc_subsubsection">
Duncan Sands1465d612009-01-28 13:14:17 +0000[diff] [blame]1144 <a name="getAnalysis">The <tt>getAnalysis&lt;&gt;</tt> and
1145<tt>getAnalysisIfAvailable&lt;&gt;</tt> methods</a>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1146</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1147
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1148<div class="doc_text">
1149
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]1150<p>The <tt>Pass::getAnalysis&lt;&gt;</tt> method is automatically inherited by
1151your class, providing you with access to the passes that you declared that you
1152required with the <a href="#getAnalysisUsage"><tt>getAnalysisUsage</tt></a>
1153method. It takes a single template argument that specifies which pass class you
1154want, and returns a reference to that pass. For example:</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1155
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1156<div class="doc_code"><pre>
Chris Lattnera5776302004-03-17 21:33:32 +0000[diff] [blame]1157 bool LICM::runOnFunction(Function &amp;F) {
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]1158 LoopInfo &amp;LI = getAnalysis&lt;LoopInfo&gt;();
1159 ...
1160 }
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1161</pre></div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1162
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1163<p>This method call returns a reference to the pass desired. You may get a
1164runtime assertion failure if you attempt to get an analysis that you did not
1165declare as required in your <a
1166href="#getAnalysisUsage"><tt>getAnalysisUsage</tt></a> implementation. This
1167method can be called by your <tt>run*</tt> method implementation, or by any
Devang Patel3c1ca0b2007-04-16 21:28:14 +0000[diff] [blame]1168other local method invoked by your <tt>run*</tt> method.
1169
1170A module level pass can use function level analysis info using this interface.
1171For example:</p>
1172
1173<div class="doc_code"><pre>
1174 bool ModuleLevelPass::runOnModule(Module &amp;M) {
1175 ...
Devang Patelf23de112007-04-17 00:17:11 +0000[diff] [blame]1176 DominatorTree &amp;DT = getAnalysis&lt;DominatorTree&gt;(Func);
Devang Patel3c1ca0b2007-04-16 21:28:14 +0000[diff] [blame]1177 ...
1178 }
1179</pre></div>
1180
Chris Lattnerb5c87f62007-05-18 05:36:14 +0000[diff] [blame]1181<p>In above example, runOnFunction for DominatorTree is called by pass manager
Devang Patel3c1ca0b2007-04-16 21:28:14 +0000[diff] [blame]1182before returning a reference to the desired pass.</p>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1183
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]1184<p>
1185If your pass is capable of updating analyses if they exist (e.g.,
1186<tt>BreakCriticalEdges</tt>, as described above), you can use the
Duncan Sands1465d612009-01-28 13:14:17 +0000[diff] [blame]1187<tt>getAnalysisIfAvailable</tt> method, which returns a pointer to the analysis
1188if it is active. For example:</p>
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]1189
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1190<div class="doc_code"><pre>
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]1191 ...
Duncan Sands1465d612009-01-28 13:14:17 +0000[diff] [blame]1192 if (DominatorSet *DS = getAnalysisIfAvailable&lt;DominatorSet&gt;()) {
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]1193 <i>// A DominatorSet is active. This code will update it.</i>
1194 }
1195 ...
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1196</pre></div>
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]1197
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1198</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1199
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1200<!-- *********************************************************************** -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1201<div class="doc_section">
1202 <a name="analysisgroup">Implementing Analysis Groups</a>
1203</div>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1204<!-- *********************************************************************** -->
1205
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1206<div class="doc_text">
1207
Chris Lattnerb7632282007-11-16 05:32:05 +0000[diff] [blame]1208<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]1209used, 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]1210fancier. All of the pass relationships that we have seen so far are very
1211simple: one pass depends on one other specific pass to be run before it can run.
1212For many applications, this is great, for others, more flexibility is
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1213required.</p>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1214
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1215<p>In particular, some analyses are defined such that there is a single simple
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1216interface to the analysis results, but multiple ways of calculating them.
1217Consider alias analysis for example. The most trivial alias analysis returns
1218"may alias" for any alias query. The most sophisticated analysis a
1219flow-sensitive, context-sensitive interprocedural analysis that can take a
1220significant amount of time to execute (and obviously, there is a lot of room
1221between these two extremes for other implementations). To cleanly support
1222situations like this, the LLVM Pass Infrastructure supports the notion of
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1223Analysis Groups.</p>
1224
1225</div>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1226
1227<!-- _______________________________________________________________________ -->
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]1228<div class="doc_subsubsection">
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1229 <a name="agconcepts">Analysis Group Concepts</a>
1230</div>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1231
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1232<div class="doc_text">
1233
1234<p>An Analysis Group is a single simple interface that may be implemented by
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1235multiple different passes. Analysis Groups can be given human readable names
1236just like passes, but unlike passes, they need not derive from the <tt>Pass</tt>
1237class. An analysis group may have one or more implementations, one of which is
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1238the "default" implementation.</p>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1239
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1240<p>Analysis groups are used by client passes just like other passes are: the
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1241<tt>AnalysisUsage::addRequired()</tt> and <tt>Pass::getAnalysis()</tt> methods.
1242In order to resolve this requirement, the <a href="#passmanager">PassManager</a>
1243scans the available passes to see if any implementations of the analysis group
1244are available. If none is available, the default implementation is created for
1245the pass to use. All standard rules for <A href="#interaction">interaction
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1246between passes</a> still apply.</p>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1247
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1248<p>Although <a href="#registration">Pass Registration</a> is optional for normal
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1249passes, all analysis group implementations must be registered, and must use the
1250<A href="#registerag"><tt>RegisterAnalysisGroup</tt></a> template to join the
1251implementation pool. Also, a default implementation of the interface
1252<b>must</b> be registered with <A
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1253href="#registerag"><tt>RegisterAnalysisGroup</tt></a>.</p>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1254
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1255<p>As a concrete example of an Analysis Group in action, consider the <a
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]1256href="http://llvm.org/doxygen/classllvm_1_1AliasAnalysis.html">AliasAnalysis</a>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1257analysis group. The default implementation of the alias analysis interface (the
1258<tt><a
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]1259href="http://llvm.org/doxygen/structBasicAliasAnalysis.html">basicaa</a></tt>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1260pass) just does a few simple checks that don't require significant analysis to
1261compute (such as: two different globals can never alias each other, etc).
1262Passes that use the <tt><a
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]1263href="http://llvm.org/doxygen/classllvm_1_1AliasAnalysis.html">AliasAnalysis</a></tt>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1264interface (for example the <tt><a
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]1265href="http://llvm.org/doxygen/structGCSE.html">gcse</a></tt> pass), do
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1266not care which implementation of alias analysis is actually provided, they just
1267use the designated interface.</p>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1268
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1269<p>From the user's perspective, commands work just like normal. Issuing the
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1270command '<tt>opt -gcse ...</tt>' will cause the <tt>basicaa</tt> class to be
1271instantiated and added to the pass sequence. Issuing the command '<tt>opt
1272-somefancyaa -gcse ...</tt>' will cause the <tt>gcse</tt> pass to use the
1273<tt>somefancyaa</tt> alias analysis (which doesn't actually exist, it's just a
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1274hypothetical example) instead.</p>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1275
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1276</div>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1277
1278<!-- _______________________________________________________________________ -->
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]1279<div class="doc_subsubsection">
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1280 <a name="registerag">Using <tt>RegisterAnalysisGroup</tt></a>
1281</div>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1282
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1283<div class="doc_text">
1284
1285<p>The <tt>RegisterAnalysisGroup</tt> template is used to register the analysis
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1286group itself as well as add pass implementations to the analysis group. First,
1287an analysis should be registered, with a human readable name provided for it.
1288Unlike registration of passes, there is no command line argument to be specified
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1289for the Analysis Group Interface itself, because it is "abstract":</p>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1290
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1291<div class="doc_code"><pre>
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]1292 <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]1293</pre></div>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1294
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1295<p>Once the analysis is registered, passes can declare that they are valid
1296implementations of the interface by using the following code:</p>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1297
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1298<div class="doc_code"><pre>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1299<b>namespace</b> {
1300 //<i> Analysis Group implementations <b>must</b> be registered normally...</i>
Chris Lattnerc8603c22006-08-27 23:18:52 +0000[diff] [blame]1301 RegisterPass&lt;FancyAA&gt;
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1302 B("<i>somefancyaa</i>", "<i>A more complex alias analysis implementation</i>");
1303
1304 //<i> Declare that we implement the AliasAnalysis interface</i>
Chris Lattnerdc877252006-08-28 00:45:38 +0000[diff] [blame]1305 RegisterAnalysisGroup&lt;<a href="http://llvm.org/doxygen/classllvm_1_1AliasAnalysis.html">AliasAnalysis</a>&gt; C(B);
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1306}
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1307</pre></div>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1308
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1309<p>This just shows a class <tt>FancyAA</tt> that is registered normally, then
1310uses the <tt>RegisterAnalysisGroup</tt> template to "join" the <tt><a
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]1311href="http://llvm.org/doxygen/classllvm_1_1AliasAnalysis.html">AliasAnalysis</a></tt>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1312analysis group. Every implementation of an analysis group should join using
1313this template. A single pass may join multiple different analysis groups with
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1314no problem.</p>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1315
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1316<div class="doc_code"><pre>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1317<b>namespace</b> {
1318 //<i> Analysis Group implementations <b>must</b> be registered normally...</i>
Chris Lattnerc8603c22006-08-27 23:18:52 +0000[diff] [blame]1319 RegisterPass&lt;<a href="http://llvm.org/doxygen/structBasicAliasAnalysis.html">BasicAliasAnalysis</a>&gt;
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1320 D("<i>basicaa</i>", "<i>Basic Alias Analysis (default AA impl)</i>");
1321
1322 //<i> Declare that we implement the AliasAnalysis interface</i>
Chris Lattnerdc877252006-08-28 00:45:38 +0000[diff] [blame]1323 RegisterAnalysisGroup&lt;<a href="http://llvm.org/doxygen/classllvm_1_1AliasAnalysis.html">AliasAnalysis</a>, <b>true</b>&gt; E(D);
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1324}
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1325</pre></div>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1326
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1327<p>Here we show how the default implementation is specified (using the extra
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1328argument to the <tt>RegisterAnalysisGroup</tt> template). There must be exactly
1329one default implementation available at all times for an Analysis Group to be
Devang Patel2397f8d2007-06-20 18:51:14 +0000[diff] [blame]1330used. Only default implementation can derive from <tt>ImmutablePass</tt>.
1331Here we declare that the
1332 <tt><a href="http://llvm.org/doxygen/structBasicAliasAnalysis.html">BasicAliasAnalysis</a></tt>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1333pass is the default implementation for the interface.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1334
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1335</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1336
1337<!-- *********************************************************************** -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1338<div class="doc_section">
Tanya Lattnerd5383652004-11-19 01:25:14 +0000[diff] [blame]1339 <a name="passStatistics">Pass Statistics</a>
1340</div>
1341<!-- *********************************************************************** -->
1342
1343<div class="doc_text">
Tanya Lattner05f8d5f2004-11-19 01:26:37 +0000[diff] [blame]1344<p>The <a
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]1345href="http://llvm.org/doxygen/Statistic_8h-source.html"><tt>Statistic</tt></a>
John Criswell0b1010e2005-11-28 23:25:41 +0000[diff] [blame]1346class is designed to be an easy way to expose various success
Tanya Lattnerd5383652004-11-19 01:25:14 +0000[diff] [blame]1347metrics from passes. These statistics are printed at the end of a
1348run, when the -stats command line option is enabled on the command
Tanya Lattner05f8d5f2004-11-19 01:26:37 +0000[diff] [blame]1349line. 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]1350
1351</div>
1352
1353
1354<!-- *********************************************************************** -->
1355<div class="doc_section">
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1356 <a name="passmanager">What PassManager does</a>
1357</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1358<!-- *********************************************************************** -->
1359
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1360<div class="doc_text">
1361
1362<p>The <a
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]1363href="http://llvm.org/doxygen/PassManager_8h-source.html"><tt>PassManager</tt></a>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1364<a
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]1365href="http://llvm.org/doxygen/classllvm_1_1PassManager.html">class</a>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1366takes a list of passes, ensures their <a href="#interaction">prerequisites</a>
1367are set up correctly, and then schedules passes to run efficiently. All of the
1368LLVM tools that run passes use the <tt>PassManager</tt> for execution of these
1369passes.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1370
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1371<p>The <tt>PassManager</tt> does two main things to try to reduce the execution
1372time of a series of passes:</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1373
1374<ol>
1375<li><b>Share analysis results</b> - The PassManager attempts to avoid
1376recomputing analysis results as much as possible. This means keeping track of
1377which analyses are available already, which analyses get invalidated, and which
1378analyses are needed to be run for a pass. An important part of work is that the
1379<tt>PassManager</tt> tracks the exact lifetime of all analysis results, allowing
1380it to <a href="#releaseMemory">free memory</a> allocated to holding analysis
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1381results as soon as they are no longer needed.</li>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1382
1383<li><b>Pipeline the execution of passes on the program</b> - The
1384<tt>PassManager</tt> attempts to get better cache and memory usage behavior out
1385of a series of passes by pipelining the passes together. This means that, given
1386a series of consequtive <a href="#FunctionPass"><tt>FunctionPass</tt></a>'s, it
1387will execute all of the <a href="#FunctionPass"><tt>FunctionPass</tt></a>'s on
1388the first function, then all of the <a
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1389href="#FunctionPass"><tt>FunctionPass</tt></a>es on the second function,
1390etc... until the entire program has been run through the passes.
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1391
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1392<p>This improves the cache behavior of the compiler, because it is only touching
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1393the LLVM program representation for a single function at a time, instead of
1394traversing the entire program. It reduces the memory consumption of compiler,
1395because, for example, only one <a
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]1396href="http://llvm.org/doxygen/classllvm_1_1DominatorSet.html"><tt>DominatorSet</tt></a>
John Criswell9795bb82007-12-10 20:26:29 +0000[diff] [blame]1397needs to be calculated at a time. This also makes it possible to implement
1398some <a
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1399href="#SMP">interesting enhancements</a> in the future.</p></li>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1400
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1401</ol>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1402
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1403<p>The effectiveness of the <tt>PassManager</tt> is influenced directly by how
1404much information it has about the behaviors of the passes it is scheduling. For
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1405example, the "preserved" set is intentionally conservative in the face of an
1406unimplemented <a href="#getAnalysisUsage"><tt>getAnalysisUsage</tt></a> method.
1407Not implementing when it should be implemented will have the effect of not
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1408allowing any analysis results to live across the execution of your pass.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1409
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1410<p>The <tt>PassManager</tt> class exposes a <tt>--debug-pass</tt> command line
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1411options that is useful for debugging pass execution, seeing how things work, and
1412diagnosing when you should be preserving more analyses than you currently are
1413(To get information about all of the variants of the <tt>--debug-pass</tt>
Duncan Sands7e7ae5a2010-02-18 14:08:13 +0000[diff] [blame]1414option, just type '<tt>opt -help-hidden</tt>').</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1415
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1416<p>By using the <tt>--debug-pass=Structure</tt> option, for example, we can see
1417how our <a href="#basiccode">Hello World</a> pass interacts with other passes.
1418Lets try it out with the <tt>gcse</tt> and <tt>licm</tt> passes:</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1419
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1420<div class="doc_code"><pre>
Duncan Sands67f8a7b2010-07-08 08:27:18 +0000[diff] [blame^]1421$ 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]1422Module Pass Manager
1423 Function Pass Manager
1424 Dominator Set Construction
1425 Immediate Dominators Construction
1426 Global Common Subexpression Elimination
1427-- Immediate Dominators Construction
1428-- Global Common Subexpression Elimination
1429 Natural Loop Construction
1430 Loop Invariant Code Motion
1431-- Natural Loop Construction
1432-- Loop Invariant Code Motion
1433 Module Verifier
1434-- Dominator Set Construction
1435-- Module Verifier
Gabor Greif04367bf2007-07-06 22:07:22 +0000[diff] [blame]1436 Bitcode Writer
1437--Bitcode Writer
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1438</pre></div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1439
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1440<p>This output shows us when passes are constructed and when the analysis
1441results are known to be dead (prefixed with '<tt>--</tt>'). Here we see that
1442GCSE uses dominator and immediate dominator information to do its job. The LICM
1443pass uses natural loop information, which uses dominator sets, but not immediate
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1444dominators. Because immediate dominators are no longer useful after the GCSE
1445pass, it is immediately destroyed. The dominator sets are then reused to
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1446compute natural loop information, which is then used by the LICM pass.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1447
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1448<p>After the LICM pass, the module verifier runs (which is automatically added
1449by the '<tt>opt</tt>' tool), which uses the dominator set to check that the
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1450resultant LLVM code is well formed. After it finishes, the dominator set
1451information is destroyed, after being computed once, and shared by three
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1452passes.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1453
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1454<p>Lets see how this changes when we run the <a href="#basiccode">Hello
1455World</a> pass in between the two passes:</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1456
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1457<div class="doc_code"><pre>
Duncan Sands67f8a7b2010-07-08 08:27:18 +0000[diff] [blame^]1458$ 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]1459Module Pass Manager
1460 Function Pass Manager
1461 Dominator Set Construction
1462 Immediate Dominators Construction
1463 Global Common Subexpression Elimination
1464<b>-- Dominator Set Construction</b>
1465-- Immediate Dominators Construction
1466-- Global Common Subexpression Elimination
1467<b> Hello World Pass
1468-- Hello World Pass
1469 Dominator Set Construction</b>
1470 Natural Loop Construction
1471 Loop Invariant Code Motion
1472-- Natural Loop Construction
1473-- Loop Invariant Code Motion
1474 Module Verifier
1475-- Dominator Set Construction
1476-- Module Verifier
Gabor Greif04367bf2007-07-06 22:07:22 +0000[diff] [blame]1477 Bitcode Writer
1478--Bitcode Writer
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1479Hello: __main
1480Hello: puts
1481Hello: main
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1482</pre></div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1483
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1484<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]1485Dominator Set pass, even though it doesn't modify the code at all! To fix this,
1486we need to add the following <a
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1487href="#getAnalysisUsage"><tt>getAnalysisUsage</tt></a> method to our pass:</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1488
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1489<div class="doc_code"><pre>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1490 <i>// We don't modify the program, so we preserve all analyses</i>
1491 <b>virtual void</b> getAnalysisUsage(AnalysisUsage &amp;AU) <b>const</b> {
1492 AU.setPreservesAll();
1493 }
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1494</pre></div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1495
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1496<p>Now when we run our pass, we get this output:</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1497
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1498<div class="doc_code"><pre>
Duncan Sands67f8a7b2010-07-08 08:27:18 +0000[diff] [blame^]1499$ 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]1500Pass Arguments: -gcse -hello -licm
1501Module Pass Manager
1502 Function Pass Manager
1503 Dominator Set Construction
1504 Immediate Dominators Construction
1505 Global Common Subexpression Elimination
1506-- Immediate Dominators Construction
1507-- Global Common Subexpression Elimination
1508 Hello World Pass
1509-- Hello World Pass
1510 Natural Loop Construction
1511 Loop Invariant Code Motion
1512-- Loop Invariant Code Motion
1513-- Natural Loop Construction
1514 Module Verifier
1515-- Dominator Set Construction
1516-- Module Verifier
Gabor Greif04367bf2007-07-06 22:07:22 +0000[diff] [blame]1517 Bitcode Writer
1518--Bitcode Writer
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1519Hello: __main
1520Hello: puts
1521Hello: main
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1522</pre></div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1523
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1524<p>Which shows that we don't accidentally invalidate dominator information
1525anymore, and therefore do not have to compute it twice.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1526
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1527</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1528
1529<!-- _______________________________________________________________________ -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1530<div class="doc_subsubsection">
1531 <a name="releaseMemory">The <tt>releaseMemory</tt> method</a>
1532</div>
1533
1534<div class="doc_text">
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1535
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1536<div class="doc_code"><pre>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1537 <b>virtual void</b> releaseMemory();
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1538</pre></div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1539
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1540<p>The <tt>PassManager</tt> automatically determines when to compute analysis
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1541results, and how long to keep them around for. Because the lifetime of the pass
1542object itself is effectively the entire duration of the compilation process, we
1543need some way to free analysis results when they are no longer useful. The
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1544<tt>releaseMemory</tt> virtual method is the way to do this.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1545
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1546<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]1547amount of state (for use by another pass which "requires" your pass and uses the
1548<a href="#getAnalysis">getAnalysis</a> method) you should implement
Dan Gohmand87c9e32009-06-15 18:22:49 +0000[diff] [blame]1549<tt>releaseMemory</tt> to, well, release the memory allocated to maintain this
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1550internal state. This method is called after the <tt>run*</tt> method for the
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1551class, before the next call of <tt>run*</tt> in your pass.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1552
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1553</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1554
1555<!-- *********************************************************************** -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1556<div class="doc_section">
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1557 <a name="registering">Registering dynamically loaded passes</a>
1558</div>
1559<!-- *********************************************************************** -->
1560
1561<div class="doc_text">
1562
1563<p><i>Size matters</i> when constructing production quality tools using llvm,
1564both for the purposes of distribution, and for regulating the resident code size
1565when running on the target system. Therefore, it becomes desirable to
1566selectively use some passes, while omitting others and maintain the flexibility
1567to change configurations later on. You want to be able to do all this, and,
1568provide feedback to the user. This is where pass registration comes into
1569play.</p>
1570
1571<p>The fundamental mechanisms for pass registration are the
1572<tt>MachinePassRegistry</tt> class and subclasses of
1573<tt>MachinePassRegistryNode</tt>.</p>
1574
1575<p>An instance of <tt>MachinePassRegistry</tt> is used to maintain a list of
1576<tt>MachinePassRegistryNode</tt> objects. This instance maintains the list and
1577communicates additions and deletions to the command line interface.</p>
1578
1579<p>An instance of <tt>MachinePassRegistryNode</tt> subclass is used to maintain
1580information provided about a particular pass. This information includes the
1581command line name, the command help string and the address of the function used
1582to create an instance of the pass. A global static constructor of one of these
1583instances <i>registers</i> with a corresponding <tt>MachinePassRegistry</tt>,
1584the static destructor <i>unregisters</i>. Thus a pass that is statically linked
1585in the tool will be registered at start up. A dynamically loaded pass will
1586register on load and unregister at unload.</p>
1587
1588</div>
1589
1590<!-- _______________________________________________________________________ -->
1591<div class="doc_subsection">
1592 <a name="registering_existing">Using existing registries</a>
1593</div>
1594
1595<div class="doc_text">
1596
1597<p>There are predefined registries to track instruction scheduling
1598(<tt>RegisterScheduler</tt>) and register allocation (<tt>RegisterRegAlloc</tt>)
1599machine passes. Here we will describe how to <i>register</i> a register
1600allocator machine pass.</p>
1601
1602<p>Implement your register allocator machine pass. In your register allocator
1603.cpp file add the following include;</p>
1604
1605<div class="doc_code"><pre>
Chris Lattner8f652eb2006-08-11 16:37:02 +0000[diff] [blame]1606 #include "llvm/CodeGen/RegAllocRegistry.h"
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1607</pre></div>
1608
1609<p>Also in your register allocator .cpp file, define a creator function in the
1610form; </p>
1611
1612<div class="doc_code"><pre>
1613 FunctionPass *createMyRegisterAllocator() {
1614 return new MyRegisterAllocator();
1615 }
1616</pre></div>
1617
1618<p>Note that the signature of this function should match the type of
1619<tt>RegisterRegAlloc::FunctionPassCtor</tt>. In the same file add the
1620"installing" declaration, in the form;</p>
1621
1622<div class="doc_code"><pre>
1623 static RegisterRegAlloc myRegAlloc("myregalloc",
1624 " my register allocator help string",
1625 createMyRegisterAllocator);
1626</pre></div>
1627
1628<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]1629-help query.</p>
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1630
1631<div class="doc_code"><pre>
Duncan Sands7e7ae5a2010-02-18 14:08:13 +0000[diff] [blame]1632$ llc -help
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1633 ...
Duncan Sands18619b22010-02-18 14:37:52 +0000[diff] [blame]1634 -regalloc - Register allocator to use (default=linearscan)
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1635 =linearscan - linear scan register allocator
1636 =local - local register allocator
1637 =simple - simple register allocator
1638 =myregalloc - my register allocator help string
1639 ...
1640</pre></div>
1641
1642<p>And that's it. The user is now free to use <tt>-regalloc=myregalloc</tt> as
1643an option. Registering instruction schedulers is similar except use the
Chris Lattner8f652eb2006-08-11 16:37:02 +0000[diff] [blame]1644<tt>RegisterScheduler</tt> class. Note that the
1645<tt>RegisterScheduler::FunctionPassCtor</tt> is significantly different from
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1646<tt>RegisterRegAlloc::FunctionPassCtor</tt>.</p>
1647
1648<p>To force the load/linking of your register allocator into the llc/lli tools,
1649add your creator function's global declaration to "Passes.h" and add a "pseudo"
1650call line to <tt>llvm/Codegen/LinkAllCodegenComponents.h</tt>.</p>
1651
1652</div>
1653
1654
1655<!-- _______________________________________________________________________ -->
1656<div class="doc_subsection">
1657 <a name="registering_new">Creating new registries</a>
1658</div>
1659
1660<div class="doc_text">
1661
1662<p>The easiest way to get started is to clone one of the existing registries; we
1663recommend <tt>llvm/CodeGen/RegAllocRegistry.h</tt>. The key things to modify
1664are the class name and the <tt>FunctionPassCtor</tt> type.</p>
1665
1666<p>Then you need to declare the registry. Example: if your pass registry is
1667<tt>RegisterMyPasses</tt> then define;</p>
1668
1669<div class="doc_code"><pre>
1670MachinePassRegistry RegisterMyPasses::Registry;
1671</pre></div>
1672
1673<p>And finally, declare the command line option for your passes. Example:</p>
1674
1675<div class="doc_code"><pre>
1676 cl::opt&lt;RegisterMyPasses::FunctionPassCtor, false,
Dan Gohman364a39f2008-10-14 17:00:38 +0000[diff] [blame]1677 RegisterPassParser&lt;RegisterMyPasses&gt; &gt;
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1678 MyPassOpt("mypass",
1679 cl::init(&amp;createDefaultMyPass),
1680 cl::desc("my pass option help"));
1681</pre></div>
1682
1683<p>Here the command option is "mypass", with createDefaultMyPass as the default
1684creator.</p>
1685
1686</div>
1687
1688<!-- *********************************************************************** -->
1689<div class="doc_section">
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1690 <a name="debughints">Using GDB with dynamically loaded passes</a>
1691</div>
Chris Lattner480e2ef2002-09-06 02:02:58 +0000[diff] [blame]1692<!-- *********************************************************************** -->
1693
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1694<div class="doc_text">
1695
1696<p>Unfortunately, using GDB with dynamically loaded passes is not as easy as it
Chris Lattner480e2ef2002-09-06 02:02:58 +0000[diff] [blame]1697should be. First of all, you can't set a breakpoint in a shared object that has
1698not been loaded yet, and second of all there are problems with inlined functions
1699in shared objects. Here are some suggestions to debugging your pass with
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1700GDB.</p>
Chris Lattner480e2ef2002-09-06 02:02:58 +0000[diff] [blame]1701
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1702<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]1703transformation invoked by <tt>opt</tt>, although nothing described here depends
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1704on that.</p>
1705
1706</div>
Chris Lattner480e2ef2002-09-06 02:02:58 +0000[diff] [blame]1707
1708<!-- _______________________________________________________________________ -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1709<div class="doc_subsubsection">
1710 <a name="breakpoint">Setting a breakpoint in your pass</a>
1711</div>
Chris Lattner480e2ef2002-09-06 02:02:58 +0000[diff] [blame]1712
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1713<div class="doc_text">
1714
1715<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]1716
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1717<div class="doc_code"><pre>
Chris Lattner480e2ef2002-09-06 02:02:58 +0000[diff] [blame]1718$ <b>gdb opt</b>
1719GNU gdb 5.0
1720Copyright 2000 Free Software Foundation, Inc.
1721GDB is free software, covered by the GNU General Public License, and you are
1722welcome to change it and/or distribute copies of it under certain conditions.
1723Type "show copying" to see the conditions.
1724There is absolutely no warranty for GDB. Type "show warranty" for details.
1725This GDB was configured as "sparc-sun-solaris2.6"...
1726(gdb)
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1727</pre></div>
Chris Lattner480e2ef2002-09-06 02:02:58 +0000[diff] [blame]1728
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1729<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]1730time to load. Be patient. Since we cannot set a breakpoint in our pass yet
1731(the shared object isn't loaded until runtime), we must execute the process, and
1732have it stop before it invokes our pass, but after it has loaded the shared
1733object. The most foolproof way of doing this is to set a breakpoint in
1734<tt>PassManager::run</tt> and then run the process with the arguments you
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1735want:</p>
Chris Lattner480e2ef2002-09-06 02:02:58 +0000[diff] [blame]1736
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1737<div class="doc_code"><pre>
Reid Spencer22a9e5b2006-09-28 16:53:47 +0000[diff] [blame]1738(gdb) <b>break llvm::PassManager::run</b>
Chris Lattner480e2ef2002-09-06 02:02:58 +0000[diff] [blame]1739Breakpoint 1 at 0x2413bc: file Pass.cpp, line 70.
Duncan Sands67f8a7b2010-07-08 08:27:18 +0000[diff] [blame^]1740(gdb) <b>run test.bc -load $(LLVMTOP)/llvm/Debug+Asserts/lib/[libname].so -[passoption]</b>
1741Starting program: opt test.bc -load $(LLVMTOP)/llvm/Debug+Asserts/lib/[libname].so -[passoption]
Chris Lattner480e2ef2002-09-06 02:02:58 +0000[diff] [blame]1742Breakpoint 1, PassManager::run (this=0xffbef174, M=@0x70b298) at Pass.cpp:70
174370 bool PassManager::run(Module &amp;M) { return PM-&gt;run(M); }
1744(gdb)
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1745</pre></div>
Chris Lattner480e2ef2002-09-06 02:02:58 +0000[diff] [blame]1746
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1747<p>Once the <tt>opt</tt> stops in the <tt>PassManager::run</tt> method you are
1748now free to set breakpoints in your pass so that you can trace through execution
1749or do other standard debugging stuff.</p>
Chris Lattner480e2ef2002-09-06 02:02:58 +0000[diff] [blame]1750
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1751</div>
Chris Lattner480e2ef2002-09-06 02:02:58 +0000[diff] [blame]1752
1753<!-- _______________________________________________________________________ -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1754<div class="doc_subsubsection">
1755 <a name="debugmisc">Miscellaneous Problems</a>
1756</div>
Chris Lattner480e2ef2002-09-06 02:02:58 +0000[diff] [blame]1757
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1758<div class="doc_text">
1759
1760<p>Once you have the basics down, there are a couple of problems that GDB has,
1761some with solutions, some without.</p>
Chris Lattner480e2ef2002-09-06 02:02:58 +0000[diff] [blame]1762
1763<ul>
1764<li>Inline functions have bogus stack information. In general, GDB does a
1765pretty good job getting stack traces and stepping through inline functions.
1766When a pass is dynamically loaded however, it somehow completely loses this
1767capability. The only solution I know of is to de-inline a function (move it
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1768from the body of a class to a .cpp file).</li>
Chris Lattner480e2ef2002-09-06 02:02:58 +0000[diff] [blame]1769
1770<li>Restarting the program breaks breakpoints. After following the information
1771above, you have succeeded in getting some breakpoints planted in your pass. Nex
1772thing you know, you restart the program (i.e., you type '<tt>run</tt>' again),
1773and you start getting errors about breakpoints being unsettable. The only way I
1774have found to "fix" this problem is to <tt>delete</tt> the breakpoints that are
1775already set in your pass, run the program, and re-set the breakpoints once
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1776execution stops in <tt>PassManager::run</tt>.</li>
Chris Lattner480e2ef2002-09-06 02:02:58 +0000[diff] [blame]1777
1778</ul>
1779
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1780<p>Hopefully these tips will help with common case debugging situations. If
1781you'd like to contribute some tips of your own, just contact <a
1782href="mailto:sabre@nondot.org">Chris</a>.</p>
Chris Lattner480e2ef2002-09-06 02:02:58 +0000[diff] [blame]1783
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1784</div>
Chris Lattner480e2ef2002-09-06 02:02:58 +0000[diff] [blame]1785
1786<!-- *********************************************************************** -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1787<div class="doc_section">
1788 <a name="future">Future extensions planned</a>
1789</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1790<!-- *********************************************************************** -->
1791
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1792<div class="doc_text">
1793
1794<p>Although the LLVM Pass Infrastructure is very capable as it stands, and does
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1795some 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]1796where we are going:</p>
1797
1798</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1799
1800<!-- _______________________________________________________________________ -->
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]1801<div class="doc_subsubsection">
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1802 <a name="SMP">Multithreaded LLVM</a>
1803</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1804
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1805<div class="doc_text">
1806
1807<p>Multiple CPU machines are becoming more common and compilation can never be
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1808fast enough: obviously we should allow for a multithreaded compiler. Because of
1809the semantics defined for passes above (specifically they cannot maintain state
1810across invocations of their <tt>run*</tt> methods), a nice clean way to
1811implement a multithreaded compiler would be for the <tt>PassManager</tt> class
Misha Brukmanbc0e9982003-07-14 17:20:40 +0000[diff] [blame]1812to create multiple instances of each pass object, and allow the separate
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1813instances to be hacking on different parts of the program at the same time.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1814
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1815<p>This implementation would prevent each of the passes from having to implement
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1816multithreaded constructs, requiring only the LLVM core to have locking in a few
1817places (for global resources). Although this is a simple extension, we simply
1818haven't had time (or multiprocessor machines, thus a reason) to implement this.
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1819Despite that, we have kept the LLVM passes SMP ready, and you should too.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1820
Chris Lattnerb5c87f62007-05-18 05:36:14 +0000[diff] [blame]1821</div>
1822
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1823<!-- *********************************************************************** -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1824<hr>
1825<address>
1826 <a href="http://jigsaw.w3.org/css-validator/check/referer"><img
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Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1828 <a href="http://validator.w3.org/check/referer"><img
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Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1830
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1831 <a href="mailto:sabre@nondot.org">Chris Lattner</a><br>
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]1832 <a href="http://llvm.org">The LLVM Compiler Infrastructure</a><br>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1833 Last modified: $Date$
1834</address>
1835
1836</body>
1837</html>