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gerrit-public.fairphone.software / platform / external / llvm / 7070387f08f7dc797b554ed8013cba9f8b74121a / . / 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>
Owen Anderson20813e02010-07-21 22:58:07 +0000[diff] [blame]293 INITIALIZE_PASS(Hello, "<i>hello</i>", "<i>Hello World Pass</i>",
Devang Patelc7582092008-03-19 21:56:59 +0000[diff] [blame]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>".
Owen Anderson20813e02010-07-21 22:58:07 +0000[diff] [blame]302Last two arguments describe its behavior.
Devang Patelc7582092008-03-19 21:56:59 +0000[diff] [blame]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;
Owen Anderson20813e02010-07-21 22:58:07 +0000[diff] [blame]329 INITIALIZE_PASS(Hello, "<i>Hello</i>", "<i>Hello World Pass</i>", false, false);
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]330}
Owen Anderson20813e02010-07-21 22:58:07 +0000[diff] [blame]331
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]332</pre></div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]333
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]334<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]335command in the local directory and you should get a new
Duncan Sands67f8a7b2010-07-08 08:27:18 +0000[diff] [blame]336"<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]337contained in an anonymous namespace: this reflects the fact that passes are self
338contained units that do not need external interfaces (although they can have
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]339them) to be useful.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]340
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]341</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]342
343<!-- ======================================================================= -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]344<div class="doc_subsection">
Chris Lattnerc8603c22006-08-27 23:18:52 +0000[diff] [blame]345 <a name="running">Running a pass with <tt>opt</tt></a>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]346</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]347
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]348<div class="doc_text">
349
John Criswellf9c78652004-01-26 21:26:54 +0000[diff] [blame]350<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]351<tt>opt</tt> command to run an LLVM program through your pass. Because you
Owen Anderson20813e02010-07-21 22:58:07 +0000[diff] [blame]352registered your pass with the <tt>INITIALIZE_PASS</tt> macro, you will be able to
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]353use the <tt>opt</tt> tool to access it, once loaded.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]354
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]355<p>To test it, follow the example at the end of the <a
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]356href="GettingStarted.html">Getting Started Guide</a> to compile "Hello World" to
Gabor Greif04367bf2007-07-06 22:07:22 +0000[diff] [blame]357LLVM. We can now run the bitcode file (<tt>hello.bc</tt>) for the program
358through our transformation like this (or course, any bitcode file will
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]359work):</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]360
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]361<div class="doc_code"><pre>
Duncan Sands67f8a7b2010-07-08 08:27:18 +0000[diff] [blame]362$ opt -load ../../../Debug+Asserts/lib/Hello.so -hello &lt; hello.bc &gt; /dev/null
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]363Hello: __main
364Hello: puts
365Hello: main
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]366</pre></div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]367
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]368<p>The '<tt>-load</tt>' option specifies that '<tt>opt</tt>' should load your
369pass as a shared object, which makes '<tt>-hello</tt>' a valid command line
370argument (which is one reason you need to <a href="#registration">register your
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]371pass</a>). Because the hello pass does not modify the program in any
372interesting way, we just throw away the result of <tt>opt</tt> (sending it to
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]373<tt>/dev/null</tt>).</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]374
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]375<p>To see what happened to the other string you registered, try running
Duncan Sands7e7ae5a2010-02-18 14:08:13 +0000[diff] [blame]376<tt>opt</tt> with the <tt>-help</tt> option:</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]377
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]378<div class="doc_code"><pre>
Duncan Sands67f8a7b2010-07-08 08:27:18 +0000[diff] [blame]379$ opt -load ../../../Debug+Asserts/lib/Hello.so -help
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]380OVERVIEW: llvm .bc -&gt; .bc modular optimizer
381
Gabor Greif04367bf2007-07-06 22:07:22 +0000[diff] [blame]382USAGE: opt [options] &lt;input bitcode&gt;
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]383
384OPTIONS:
385 Optimizations available:
386...
387 -funcresolve - Resolve Functions
388 -gcse - Global Common Subexpression Elimination
389 -globaldce - Dead Global Elimination
390 <b>-hello - Hello World Pass</b>
Chris Lattner065a6162003-09-10 05:29:43 +0000[diff] [blame]391 -indvars - Canonicalize Induction Variables
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]392 -inline - Function Integration/Inlining
393 -instcombine - Combine redundant instructions
394...
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]395</pre></div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]396
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]397<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]398documentation to users of <tt>opt</tt>. Now that you have a working pass, you
399would go ahead and make it do the cool transformations you want. Once you get
400it all working and tested, it may become useful to find out how fast your pass
401is. The <a href="#passManager"><tt>PassManager</tt></a> provides a nice command
402line option (<tt>--time-passes</tt>) that allows you to get information about
403the execution time of your pass along with the other passes you queue up. For
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]404example:</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]405
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]406<div class="doc_code"><pre>
Duncan Sands67f8a7b2010-07-08 08:27:18 +0000[diff] [blame]407$ 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]408Hello: __main
409Hello: puts
410Hello: main
411===============================================================================
412 ... Pass execution timing report ...
413===============================================================================
414 Total Execution Time: 0.02 seconds (0.0479059 wall clock)
415
416 ---User Time--- --System Time-- --User+System-- ---Wall Time--- --- Pass Name ---
Gabor Greif04367bf2007-07-06 22:07:22 +0000[diff] [blame]417 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]418 0.0000 ( 0.0%) 0.0100 (100.0%) 0.0100 ( 50.0%) 0.0031 ( 6.4%) Dominator Set Construction
419 0.0000 ( 0.0%) 0.0000 ( 0.0%) 0.0000 ( 0.0%) 0.0013 ( 2.7%) Module Verifier
420 <b> 0.0000 ( 0.0%) 0.0000 ( 0.0%) 0.0000 ( 0.0%) 0.0033 ( 6.9%) Hello World Pass</b>
421 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]422</pre></div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]423
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]424<p>As you can see, our implementation above is pretty fast :). The additional
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]425passes listed are automatically inserted by the '<tt>opt</tt>' tool to verify
426that the LLVM emitted by your pass is still valid and well formed LLVM, which
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]427hasn't been broken somehow.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]428
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]429<p>Now that you have seen the basics of the mechanics behind passes, we can talk
430about some more details of how they work and how to use them.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]431
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]432</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]433
434<!-- *********************************************************************** -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]435<div class="doc_section">
436 <a name="passtype">Pass classes and requirements</a>
437</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]438<!-- *********************************************************************** -->
439
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]440<div class="doc_text">
441
442<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]443decide what class you should subclass for your pass. The <a
444href="#basiccode">Hello World</a> example uses the <tt><a
445href="#FunctionPass">FunctionPass</a></tt> class for its implementation, but we
446did not discuss why or when this should occur. Here we talk about the classes
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]447available, from the most general to the most specific.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]448
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]449<p>When choosing a superclass for your Pass, you should choose the <b>most
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]450specific</b> class possible, while still being able to meet the requirements
Misha Brukman5560c9d2003-08-18 14:43:39 +0000[diff] [blame]451listed. This gives the LLVM Pass Infrastructure information necessary to
Benjamin Kramer8040cd32009-10-12 14:46:08 +0000[diff] [blame]452optimize how passes are run, so that the resultant compiler isn't unnecessarily
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]453slow.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]454
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]455</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]456
Chris Lattnerf004f9a2002-09-25 22:31:38 +0000[diff] [blame]457<!-- ======================================================================= -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]458<div class="doc_subsection">
459 <a name="ImmutablePass">The <tt>ImmutablePass</tt> class</a>
460</div>
Chris Lattnerf004f9a2002-09-25 22:31:38 +0000[diff] [blame]461
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]462<div class="doc_text">
463
464<p>The most plain and boring type of pass is the "<tt><a
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]465href="http://llvm.org/doxygen/classllvm_1_1ImmutablePass.html">ImmutablePass</a></tt>"
Chris Lattnerf004f9a2002-09-25 22:31:38 +0000[diff] [blame]466class. This pass type is used for passes that do not have to be run, do not
467change state, and never need to be updated. This is not a normal type of
468transformation or analysis, but can provide information about the current
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]469compiler configuration.</p>
Chris Lattnerf004f9a2002-09-25 22:31:38 +0000[diff] [blame]470
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]471<p>Although this pass class is very infrequently used, it is important for
Chris Lattnerf004f9a2002-09-25 22:31:38 +0000[diff] [blame]472providing information about the current target machine being compiled for, and
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]473other static information that can affect the various transformations.</p>
Chris Lattnerf004f9a2002-09-25 22:31:38 +0000[diff] [blame]474
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]475<p><tt>ImmutablePass</tt>es never invalidate other transformations, are never
476invalidated, and are never "run".</p>
Chris Lattnerf004f9a2002-09-25 22:31:38 +0000[diff] [blame]477
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]478</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]479
480<!-- ======================================================================= -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]481<div class="doc_subsection">
Chris Lattnerf6278922004-09-20 04:36:29 +0000[diff] [blame]482 <a name="ModulePass">The <tt>ModulePass</tt> class</a>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]483</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]484
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]485<div class="doc_text">
486
487<p>The "<tt><a
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]488href="http://llvm.org/doxygen/classllvm_1_1ModulePass.html">ModulePass</a></tt>"
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]489class is the most general of all superclasses that you can use. Deriving from
Chris Lattnerf6278922004-09-20 04:36:29 +0000[diff] [blame]490<tt>ModulePass</tt> indicates that your pass uses the entire program as a unit,
Benjamin Kramer8040cd32009-10-12 14:46:08 +0000[diff] [blame]491referring to function bodies in no predictable order, or adding and removing
Chris Lattnerf6278922004-09-20 04:36:29 +0000[diff] [blame]492functions. Because nothing is known about the behavior of <tt>ModulePass</tt>
Daniel Dunbarb71725b2009-07-01 23:38:44 +0000[diff] [blame]493subclasses, no optimization can be done for their execution.</p>
494
495<p>A module pass can use function level passes (e.g. dominators) using
496the getAnalysis interface
497<tt>getAnalysis&lt;DominatorTree&gt;(llvm::Function *)</tt> to provide the
498function to retrieve analysis result for, if the function pass does not require
Devang Patel468857f2009-08-10 16:37:29 +0000[diff] [blame]499any 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]500analysis ran, e.g. in the case of dominators you should only ask for the
501DominatorTree for function definitions, not declarations.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]502
Chris Lattnerf6278922004-09-20 04:36:29 +0000[diff] [blame]503<p>To write a correct <tt>ModulePass</tt> subclass, derive from
504<tt>ModulePass</tt> and overload the <tt>runOnModule</tt> method with the
505following signature:</p>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]506
507</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]508
509<!-- _______________________________________________________________________ -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]510<div class="doc_subsubsection">
Chris Lattnerf6278922004-09-20 04:36:29 +0000[diff] [blame]511 <a name="runOnModule">The <tt>runOnModule</tt> method</a>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]512</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]513
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]514<div class="doc_text">
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]515
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]516<div class="doc_code"><pre>
Chris Lattnerf6278922004-09-20 04:36:29 +0000[diff] [blame]517 <b>virtual bool</b> runOnModule(Module &amp;M) = 0;
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]518</pre></div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]519
John Criswell2382ff72005-07-15 19:25:12 +0000[diff] [blame]520<p>The <tt>runOnModule</tt> method performs the interesting work of the pass.
521It should return true if the module was modified by the transformation and
522false otherwise.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]523
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]524</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]525
526<!-- ======================================================================= -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]527<div class="doc_subsection">
Chris Lattner8fdb2462004-09-18 06:39:35 +0000[diff] [blame]528 <a name="CallGraphSCCPass">The <tt>CallGraphSCCPass</tt> class</a>
529</div>
530
531<div class="doc_text">
532
533<p>The "<tt><a
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]534href="http://llvm.org/doxygen/classllvm_1_1CallGraphSCCPass.html">CallGraphSCCPass</a></tt>"
Chris Lattner8fdb2462004-09-18 06:39:35 +0000[diff] [blame]535is used by passes that need to traverse the program bottom-up on the call graph
536(callees before callers). Deriving from CallGraphSCCPass provides some
537mechanics for building and traversing the CallGraph, but also allows the system
538to optimize execution of CallGraphSCCPass's. If your pass meets the
539requirements outlined below, and doesn't meet the requirements of a <tt><a
540href="#FunctionPass">FunctionPass</a></tt> or <tt><a
541href="#BasicBlockPass">BasicBlockPass</a></tt>, you should derive from
542<tt>CallGraphSCCPass</tt>.</p>
543
544<p><b>TODO</b>: explain briefly what SCC, Tarjan's algo, and B-U mean.</p>
545
546<p>To be explicit, <tt>CallGraphSCCPass</tt> subclasses are:</p>
547
548<ol>
549
550<li>... <em>not allowed</em> to modify any <tt>Function</tt>s that are not in
551the current SCC.</li>
552
Tanya Lattner18aad232007-06-07 16:44:52 +0000[diff] [blame]553<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]554current SCC and the direct callees of the SCC.</li>
555
556<li>... <em>required</em> to preserve the current CallGraph object, updating it
557to reflect any changes made to the program.</li>
558
559<li>... <em>not allowed</em> to add or remove SCC's from the current Module,
560though they may change the contents of an SCC.</li>
561
562<li>... <em>allowed</em> to add or remove global variables from the current
563Module.</li>
564
565<li>... <em>allowed</em> to maintain state across invocations of
566 <a href="#runOnSCC"><tt>runOnSCC</tt></a> (including global data).</li>
567</ol>
568
569<p>Implementing a <tt>CallGraphSCCPass</tt> is slightly tricky in some cases
570because it has to handle SCCs with more than one node in it. All of the virtual
571methods described below should return true if they modified the program, or
572false if they didn't.</p>
573
574</div>
575
576<!-- _______________________________________________________________________ -->
577<div class="doc_subsubsection">
Devang Patelc20048d2007-01-23 22:56:28 +0000[diff] [blame]578 <a name="doInitialization_scc">The <tt>doInitialization(CallGraph &amp;)</tt>
Chris Lattner8fdb2462004-09-18 06:39:35 +0000[diff] [blame]579 method</a>
580</div>
581
582<div class="doc_text">
583
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]584<div class="doc_code"><pre>
Devang Patelc20048d2007-01-23 22:56:28 +0000[diff] [blame]585 <b>virtual bool</b> doInitialization(CallGraph &amp;CG);
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]586</pre></div>
Chris Lattner8fdb2462004-09-18 06:39:35 +0000[diff] [blame]587
588<p>The <tt>doIninitialize</tt> method is allowed to do most of the things that
589<tt>CallGraphSCCPass</tt>'s are not allowed to do. They can add and remove
590functions, get pointers to functions, etc. The <tt>doInitialization</tt> method
591is designed to do simple initialization type of stuff that does not depend on
592the SCCs being processed. The <tt>doInitialization</tt> method call is not
593scheduled to overlap with any other pass executions (thus it should be very
594fast).</p>
595
596</div>
597
598<!-- _______________________________________________________________________ -->
599<div class="doc_subsubsection">
600 <a name="runOnSCC">The <tt>runOnSCC</tt> method</a>
601</div>
602
603<div class="doc_text">
604
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]605<div class="doc_code"><pre>
Chris Lattner6f25d9f2010-04-16 23:07:44 +0000[diff] [blame]606 <b>virtual bool</b> runOnSCC(CallGraphSCC &amp;SCC) = 0;
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]607</pre></div>
Chris Lattner8fdb2462004-09-18 06:39:35 +0000[diff] [blame]608
609<p>The <tt>runOnSCC</tt> method performs the interesting work of the pass, and
610should return true if the module was modified by the transformation, false
611otherwise.</p>
612
613</div>
614
615<!-- _______________________________________________________________________ -->
616<div class="doc_subsubsection">
Devang Patelc20048d2007-01-23 22:56:28 +0000[diff] [blame]617 <a name="doFinalization_scc">The <tt>doFinalization(CallGraph
Chris Lattner8fdb2462004-09-18 06:39:35 +0000[diff] [blame]618 &amp;)</tt> method</a>
619</div>
620
621<div class="doc_text">
622
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]623<div class="doc_code"><pre>
Devang Patelc20048d2007-01-23 22:56:28 +0000[diff] [blame]624 <b>virtual bool</b> doFinalization(CallGraph &amp;CG);
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]625</pre></div>
Chris Lattner8fdb2462004-09-18 06:39:35 +0000[diff] [blame]626
627<p>The <tt>doFinalization</tt> method is an infrequently used method that is
628called when the pass framework has finished calling <a
629href="#runOnFunction"><tt>runOnFunction</tt></a> for every function in the
630program being compiled.</p>
631
632</div>
633
634<!-- ======================================================================= -->
635<div class="doc_subsection">
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]636 <a name="FunctionPass">The <tt>FunctionPass</tt> class</a>
637</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]638
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]639<div class="doc_text">
640
Chris Lattnerf6278922004-09-20 04:36:29 +0000[diff] [blame]641<p>In contrast to <tt>ModulePass</tt> subclasses, <tt><a
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]642href="http://llvm.org/doxygen/classllvm_1_1Pass.html">FunctionPass</a></tt>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]643subclasses do have a predictable, local behavior that can be expected by the
644system. All <tt>FunctionPass</tt> execute on each function in the program
Misha Brukmanef6a6a62003-08-21 22:14:26 +0000[diff] [blame]645independent of all of the other functions in the program.
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]646<tt>FunctionPass</tt>'s do not require that they are executed in a particular
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]647order, and <tt>FunctionPass</tt>'s do not modify external functions.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]648
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]649<p>To be explicit, <tt>FunctionPass</tt> subclasses are not allowed to:</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]650
651<ol>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]652<li>Modify a Function other than the one currently being processed.</li>
653<li>Add or remove Function's from the current Module.</li>
654<li>Add or remove global variables from the current Module.</li>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]655<li>Maintain state across invocations of
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]656 <a href="#runOnFunction"><tt>runOnFunction</tt></a> (including global data)</li>
657</ol>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]658
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]659<p>Implementing a <tt>FunctionPass</tt> is usually straightforward (See the <a
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]660href="#basiccode">Hello World</a> pass for example). <tt>FunctionPass</tt>'s
661may overload three virtual methods to do their work. All of these methods
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]662should return true if they modified the program, or false if they didn't.</p>
663
664</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]665
666<!-- _______________________________________________________________________ -->
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]667<div class="doc_subsubsection">
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]668 <a name="doInitialization_mod">The <tt>doInitialization(Module &amp;)</tt>
669 method</a>
670</div>
671
672<div class="doc_text">
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]673
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]674<div class="doc_code"><pre>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]675 <b>virtual bool</b> doInitialization(Module &amp;M);
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]676</pre></div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]677
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]678<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]679<tt>FunctionPass</tt>'s are not allowed to do. They can add and remove
Chris Lattnerd0713f92002-09-12 17:06:43 +0000[diff] [blame]680functions, get pointers to functions, etc. The <tt>doInitialization</tt> method
681is designed to do simple initialization type of stuff that does not depend on
682the functions being processed. The <tt>doInitialization</tt> method call is not
683scheduled to overlap with any other pass executions (thus it should be very
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]684fast).</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]685
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]686<p>A good example of how this method should be used is the <a
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]687href="http://llvm.org/doxygen/LowerAllocations_8cpp-source.html">LowerAllocations</a>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]688pass. This pass converts <tt>malloc</tt> and <tt>free</tt> instructions into
Misha Brukmanef6a6a62003-08-21 22:14:26 +0000[diff] [blame]689platform dependent <tt>malloc()</tt> and <tt>free()</tt> function calls. It
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]690uses the <tt>doInitialization</tt> method to get a reference to the malloc and
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]691free functions that it needs, adding prototypes to the module if necessary.</p>
692
693</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]694
695<!-- _______________________________________________________________________ -->
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]696<div class="doc_subsubsection">
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]697 <a name="runOnFunction">The <tt>runOnFunction</tt> method</a>
698</div>
699
700<div class="doc_text">
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]701
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]702<div class="doc_code"><pre>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]703 <b>virtual bool</b> runOnFunction(Function &amp;F) = 0;
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]704</pre></div><p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]705
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]706<p>The <tt>runOnFunction</tt> method must be implemented by your subclass to do
707the transformation or analysis work of your pass. As usual, a true value should
708be returned if the function is modified.</p>
709
710</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]711
712<!-- _______________________________________________________________________ -->
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]713<div class="doc_subsubsection">
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]714 <a name="doFinalization_mod">The <tt>doFinalization(Module
715 &amp;)</tt> method</a>
716</div>
717
718<div class="doc_text">
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]719
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]720<div class="doc_code"><pre>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]721 <b>virtual bool</b> doFinalization(Module &amp;M);
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]722</pre></div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]723
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]724<p>The <tt>doFinalization</tt> method is an infrequently used method that is
725called when the pass framework has finished calling <a
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]726href="#runOnFunction"><tt>runOnFunction</tt></a> for every function in the
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]727program being compiled.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]728
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]729</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]730
731<!-- ======================================================================= -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]732<div class="doc_subsection">
Devang Patel2e8f27d2007-03-19 22:21:25 +0000[diff] [blame]733 <a name="LoopPass">The <tt>LoopPass</tt> class </a>
734</div>
735
736<div class="doc_text">
737
738<p> All <tt>LoopPass</tt> execute on each loop in the function independent of
739all of the other loops in the function. <tt>LoopPass</tt> processes loops in
740loop nest order such that outer most loop is processed last. </p>
741
742<p> <tt>LoopPass</tt> subclasses are allowed to update loop nest using
743<tt>LPPassManager</tt> interface. Implementing a loop pass is usually
744straightforward. <tt>Looppass</tt>'s may overload three virtual methods to
745do their work. All these methods should return true if they modified the
746program, or false if they didn't. </p>
747</div>
748
749<!-- _______________________________________________________________________ -->
750<div class="doc_subsubsection">
751 <a name="doInitialization_loop">The <tt>doInitialization(Loop *,
752 LPPassManager &amp;)</tt>
753 method</a>
754</div>
755
756<div class="doc_text">
757
758<div class="doc_code"><pre>
759 <b>virtual bool</b> doInitialization(Loop *, LPPassManager &amp;LPM);
760</pre></div>
761
Chris Lattnerb5c87f62007-05-18 05:36:14 +0000[diff] [blame]762<p>The <tt>doInitialization</tt> method is designed to do simple initialization
Devang Patel2e8f27d2007-03-19 22:21:25 +0000[diff] [blame]763type of stuff that does not depend on the functions being processed. The
764<tt>doInitialization</tt> method call is not scheduled to overlap with any
765other pass executions (thus it should be very fast). LPPassManager
766interface should be used to access Function or Module level analysis
767information.</p>
768
769</div>
770
771
772<!-- _______________________________________________________________________ -->
773<div class="doc_subsubsection">
774 <a name="runOnLoop">The <tt>runOnLoop</tt> method</a>
775</div>
776
777<div class="doc_text">
778
779<div class="doc_code"><pre>
780 <b>virtual bool</b> runOnLoop(Loop *, LPPassManager &amp;LPM) = 0;
781</pre></div><p>
782
783<p>The <tt>runOnLoop</tt> method must be implemented by your subclass to do
784the transformation or analysis work of your pass. As usual, a true value should
785be returned if the function is modified. <tt>LPPassManager</tt> interface
786should be used to update loop nest.</p>
787
788</div>
789
790<!-- _______________________________________________________________________ -->
791<div class="doc_subsubsection">
792 <a name="doFinalization_loop">The <tt>doFinalization()</tt> method</a>
793</div>
794
795<div class="doc_text">
796
797<div class="doc_code"><pre>
798 <b>virtual bool</b> doFinalization();
799</pre></div>
800
801<p>The <tt>doFinalization</tt> method is an infrequently used method that is
802called when the pass framework has finished calling <a
803href="#runOnLoop"><tt>runOnLoop</tt></a> for every loop in the
804program being compiled. </p>
805
806</div>
807
808
809
810<!-- ======================================================================= -->
811<div class="doc_subsection">
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]812 <a name="BasicBlockPass">The <tt>BasicBlockPass</tt> class</a>
813</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]814
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]815<div class="doc_text">
816
817<p><tt>BasicBlockPass</tt>'s are just like <a
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]818href="#FunctionPass"><tt>FunctionPass</tt></a>'s, except that they must limit
819their scope of inspection and modification to a single basic block at a time.
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]820As such, they are <b>not</b> allowed to do any of the following:</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]821
822<ol>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]823<li>Modify or inspect any basic blocks outside of the current one</li>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]824<li>Maintain state across invocations of
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]825 <a href="#runOnBasicBlock"><tt>runOnBasicBlock</tt></a></li>
Reid Spencer1bc19342004-12-11 05:12:57 +0000[diff] [blame]826<li>Modify the control flow graph (by altering terminator instructions)</li>
827<li>Any of the things forbidden for
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]828 <a href="#FunctionPass"><tt>FunctionPass</tt></a>es.</li>
829</ol>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]830
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]831<p><tt>BasicBlockPass</tt>es are useful for traditional local and "peephole"
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]832optimizations. They may override the same <a
Chris Lattnerd0713f92002-09-12 17:06:43 +0000[diff] [blame]833href="#doInitialization_mod"><tt>doInitialization(Module &amp;)</tt></a> and <a
834href="#doFinalization_mod"><tt>doFinalization(Module &amp;)</tt></a> methods that <a
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]835href="#FunctionPass"><tt>FunctionPass</tt></a>'s have, but also have the following virtual methods that may also be implemented:</p>
836
837</div>
Chris Lattnerd0713f92002-09-12 17:06:43 +0000[diff] [blame]838
839<!-- _______________________________________________________________________ -->
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]840<div class="doc_subsubsection">
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]841 <a name="doInitialization_fn">The <tt>doInitialization(Function
842 &amp;)</tt> method</a>
843</div>
844
845<div class="doc_text">
Chris Lattnerd0713f92002-09-12 17:06:43 +0000[diff] [blame]846
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]847<div class="doc_code"><pre>
Chris Lattnerd0713f92002-09-12 17:06:43 +0000[diff] [blame]848 <b>virtual bool</b> doInitialization(Function &amp;F);
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]849</pre></div>
Chris Lattnerd0713f92002-09-12 17:06:43 +0000[diff] [blame]850
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]851<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]852<tt>BasicBlockPass</tt>'s are not allowed to do, but that
853<tt>FunctionPass</tt>'s can. The <tt>doInitialization</tt> method is designed
Reid Spencer1bc19342004-12-11 05:12:57 +0000[diff] [blame]854to do simple initialization that does not depend on the
Chris Lattnerd0713f92002-09-12 17:06:43 +0000[diff] [blame]855BasicBlocks being processed. The <tt>doInitialization</tt> method call is not
856scheduled to overlap with any other pass executions (thus it should be very
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]857fast).</p>
Chris Lattnerd0713f92002-09-12 17:06:43 +0000[diff] [blame]858
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]859</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]860
861<!-- _______________________________________________________________________ -->
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]862<div class="doc_subsubsection">
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]863 <a name="runOnBasicBlock">The <tt>runOnBasicBlock</tt> method</a>
864</div>
865
866<div class="doc_text">
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]867
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]868<div class="doc_code"><pre>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]869 <b>virtual bool</b> runOnBasicBlock(BasicBlock &amp;BB) = 0;
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]870</pre></div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]871
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]872<p>Override this function to do the work of the <tt>BasicBlockPass</tt>. This
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]873function is not allowed to inspect or modify basic blocks other than the
874parameter, and are not allowed to modify the CFG. A true value must be returned
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]875if the basic block is modified.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]876
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]877</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]878
Chris Lattnerd0713f92002-09-12 17:06:43 +0000[diff] [blame]879<!-- _______________________________________________________________________ -->
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]880<div class="doc_subsubsection">
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]881 <a name="doFinalization_fn">The <tt>doFinalization(Function &amp;)</tt>
882 method</a>
883</div>
884
885<div class="doc_text">
Chris Lattnerd0713f92002-09-12 17:06:43 +0000[diff] [blame]886
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]887<div class="doc_code"><pre>
Chris Lattnerd0713f92002-09-12 17:06:43 +0000[diff] [blame]888 <b>virtual bool</b> doFinalization(Function &amp;F);
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]889</pre></div>
Chris Lattnerd0713f92002-09-12 17:06:43 +0000[diff] [blame]890
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]891<p>The <tt>doFinalization</tt> method is an infrequently used method that is
892called when the pass framework has finished calling <a
Chris Lattnerd0713f92002-09-12 17:06:43 +0000[diff] [blame]893href="#runOnBasicBlock"><tt>runOnBasicBlock</tt></a> for every BasicBlock in the
894program being compiled. This can be used to perform per-function
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]895finalization.</p>
Chris Lattnerd0713f92002-09-12 17:06:43 +0000[diff] [blame]896
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]897</div>
Chris Lattnerd0713f92002-09-12 17:06:43 +0000[diff] [blame]898
Brian Gaekecab8b6f2003-07-17 18:53:20 +0000[diff] [blame]899<!-- ======================================================================= -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]900<div class="doc_subsection">
901 <a name="MachineFunctionPass">The <tt>MachineFunctionPass</tt> class</a>
902</div>
Brian Gaekecab8b6f2003-07-17 18:53:20 +0000[diff] [blame]903
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]904<div class="doc_text">
905
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]906<p>A <tt>MachineFunctionPass</tt> is a part of the LLVM code generator that
907executes on the machine-dependent representation of each LLVM function in the
Dan Gohman9f116aa2010-03-10 01:29:39 +0000[diff] [blame]908program.</p>
909
910<p>Code generator passes are registered and initialized specially by
911<tt>TargetMachine::addPassesToEmitFile</tt> and similar routines, so they
912cannot generally be run from the <tt>opt</tt> or <tt>bugpoint</tt>
913commands.</p>
914
915<p>A <tt>MachineFunctionPass</tt> is also a <tt>FunctionPass</tt>, so all
Brian Gaekecab8b6f2003-07-17 18:53:20 +0000[diff] [blame]916the restrictions that apply to a <tt>FunctionPass</tt> also apply to it.
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]917<tt>MachineFunctionPass</tt>es also have additional restrictions. In particular,
918<tt>MachineFunctionPass</tt>es are not allowed to do any of the following:</p>
Brian Gaekecab8b6f2003-07-17 18:53:20 +0000[diff] [blame]919
920<ol>
Dan Gohman9f116aa2010-03-10 01:29:39 +0000[diff] [blame]921<li>Modify or create any LLVM IR Instructions, BasicBlocks, Arguments,
922 Functions, GlobalVariables, GlobalAliases, or Modules.</li>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]923<li>Modify a MachineFunction other than the one currently being processed.</li>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]924<li>Maintain state across invocations of <a
925href="#runOnMachineFunction"><tt>runOnMachineFunction</tt></a> (including global
926data)</li>
927</ol>
Brian Gaekecab8b6f2003-07-17 18:53:20 +0000[diff] [blame]928
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]929</div>
Chris Lattnerd0713f92002-09-12 17:06:43 +0000[diff] [blame]930
Brian Gaeke6a33f362003-07-22 20:53:20 +0000[diff] [blame]931<!-- _______________________________________________________________________ -->
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]932<div class="doc_subsubsection">
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]933 <a name="runOnMachineFunction">The <tt>runOnMachineFunction(MachineFunction
934 &amp;MF)</tt> method</a>
935</div>
936
937<div class="doc_text">
Brian Gaeke6a33f362003-07-22 20:53:20 +0000[diff] [blame]938
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]939<div class="doc_code"><pre>
Brian Gaeke6a33f362003-07-22 20:53:20 +0000[diff] [blame]940 <b>virtual bool</b> runOnMachineFunction(MachineFunction &amp;MF) = 0;
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]941</pre></div>
Brian Gaeke6a33f362003-07-22 20:53:20 +0000[diff] [blame]942
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]943<p><tt>runOnMachineFunction</tt> can be considered the main entry point of a
944<tt>MachineFunctionPass</tt>; that is, you should override this method to do the
945work of your <tt>MachineFunctionPass</tt>.</p>
Brian Gaeke6a33f362003-07-22 20:53:20 +0000[diff] [blame]946
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]947<p>The <tt>runOnMachineFunction</tt> method is called on every
Brian Gaeke6a33f362003-07-22 20:53:20 +0000[diff] [blame]948<tt>MachineFunction</tt> in a <tt>Module</tt>, so that the
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]949<tt>MachineFunctionPass</tt> may perform optimizations on the machine-dependent
950representation of the function. If you want to get at the LLVM <tt>Function</tt>
951for the <tt>MachineFunction</tt> you're working on, use
952<tt>MachineFunction</tt>'s <tt>getFunction()</tt> accessor method -- but
953remember, you may not modify the LLVM <tt>Function</tt> or its contents from a
954<tt>MachineFunctionPass</tt>.</p>
955
956</div>
Brian Gaeke6a33f362003-07-22 20:53:20 +0000[diff] [blame]957
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]958<!-- *********************************************************************** -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]959<div class="doc_section">
960 <a name="registration">Pass registration</a>
961</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]962<!-- *********************************************************************** -->
963
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]964<div class="doc_text">
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]965
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]966<p>In the <a href="#basiccode">Hello World</a> example pass we illustrated how
967pass registration works, and discussed some of the reasons that it is used and
968what it does. Here we discuss how and why passes are registered.</p>
969
Owen Anderson20813e02010-07-21 22:58:07 +0000[diff] [blame]970<p>As we saw above, passes are registered with the <b><tt>INITIALIZE_PASS</tt></b>
971macro. The first parameter is the name of the pass that is to be used on
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]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
Owen Andersond8cc7be2010-07-21 23:07:00 +0000[diff] [blame]1250<A href="#registerag"><tt>INITIALIZE_AG_PASS</tt></a> template to join the
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]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
Owen Andersond8cc7be2010-07-21 23:07:00 +0000[diff] [blame]1286group itself, while the <tt>INITIALIZE_AG_PASS</tt> is used to add pass
1287implementations to the analysis group. First,
1288an analysis group should be registered, with a human readable name
1289provided for it.
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1290Unlike registration of passes, there is no command line argument to be specified
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1291for the Analysis Group Interface itself, because it is "abstract":</p>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1292
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1293<div class="doc_code"><pre>
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]1294 <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]1295</pre></div>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1296
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1297<p>Once the analysis is registered, passes can declare that they are valid
1298implementations of the interface by using the following code:</p>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1299
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1300<div class="doc_code"><pre>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1301<b>namespace</b> {
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1302 //<i> Declare that we implement the AliasAnalysis interface</i>
Owen Andersond8cc7be2010-07-21 23:07:00 +0000[diff] [blame]1303 INITIALIZE_AG_PASS(FancyAA, <a href="http://llvm.org/doxygen/classllvm_1_1AliasAnalysis.html">AliasAnalysis</a>, "<i>somefancyaa</i>",
1304 "<i>A more complex alias analysis implementation</i>",
1305 false, // <i>Is CFG Only?</i>
1306 true, // <i>Is Analysis?</i>
1307 false, // <i>Is default Analysis Group implementation?</i>
1308 );
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1309}
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1310</pre></div>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1311
Owen Andersond8cc7be2010-07-21 23:07:00 +0000[diff] [blame]1312<p>This just shows a class <tt>FancyAA</tt> that
1313uses the <tt>INITIALIZE_AG_PASS</tt> macro both to register and
1314to "join" the <tt><a href="http://llvm.org/doxygen/classllvm_1_1AliasAnalysis.html">AliasAnalysis</a></tt>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1315analysis group. Every implementation of an analysis group should join using
Owen Andersond8cc7be2010-07-21 23:07:00 +0000[diff] [blame]1316this macro.</p>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1317
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1318<div class="doc_code"><pre>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1319<b>namespace</b> {
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1320 //<i> Declare that we implement the AliasAnalysis interface</i>
Owen Andersond8cc7be2010-07-21 23:07:00 +0000[diff] [blame]1321 INITIALIZE_AG_PASS(BasicAA, <a href="http://llvm.org/doxygen/classllvm_1_1AliasAnalysis.html">AliasAnalysis</a>, "<i>basicaa</i>",
1322 "<i>Basic Alias Analysis (default AA impl)</i>",
1323 false, // <i>Is CFG Only?</i>
1324 true, // <i>Is Analysis?</i>
1325 true, // <i>Is default Analysis Group implementation?</i>
1326 );
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1327}
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1328</pre></div>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1329
Owen Andersond8cc7be2010-07-21 23:07:00 +0000[diff] [blame]1330<p>Here we show how the default implementation is specified (using the final
1331argument to the <tt>INITIALIZE_AG_PASS</tt> template). There must be exactly
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1332one default implementation available at all times for an Analysis Group to be
Devang Patel2397f8d2007-06-20 18:51:14 +0000[diff] [blame]1333used. Only default implementation can derive from <tt>ImmutablePass</tt>.
1334Here we declare that the
1335 <tt><a href="http://llvm.org/doxygen/structBasicAliasAnalysis.html">BasicAliasAnalysis</a></tt>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1336pass is the default implementation for the interface.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1337
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1338</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1339
1340<!-- *********************************************************************** -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1341<div class="doc_section">
Tanya Lattnerd5383652004-11-19 01:25:14 +0000[diff] [blame]1342 <a name="passStatistics">Pass Statistics</a>
1343</div>
1344<!-- *********************************************************************** -->
1345
1346<div class="doc_text">
Tanya Lattner05f8d5f2004-11-19 01:26:37 +0000[diff] [blame]1347<p>The <a
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]1348href="http://llvm.org/doxygen/Statistic_8h-source.html"><tt>Statistic</tt></a>
John Criswell0b1010e2005-11-28 23:25:41 +0000[diff] [blame]1349class is designed to be an easy way to expose various success
Tanya Lattnerd5383652004-11-19 01:25:14 +0000[diff] [blame]1350metrics from passes. These statistics are printed at the end of a
1351run, when the -stats command line option is enabled on the command
Tanya Lattner05f8d5f2004-11-19 01:26:37 +0000[diff] [blame]1352line. 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]1353
1354</div>
1355
1356
1357<!-- *********************************************************************** -->
1358<div class="doc_section">
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1359 <a name="passmanager">What PassManager does</a>
1360</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1361<!-- *********************************************************************** -->
1362
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1363<div class="doc_text">
1364
1365<p>The <a
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]1366href="http://llvm.org/doxygen/PassManager_8h-source.html"><tt>PassManager</tt></a>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1367<a
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]1368href="http://llvm.org/doxygen/classllvm_1_1PassManager.html">class</a>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1369takes a list of passes, ensures their <a href="#interaction">prerequisites</a>
1370are set up correctly, and then schedules passes to run efficiently. All of the
1371LLVM tools that run passes use the <tt>PassManager</tt> for execution of these
1372passes.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1373
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1374<p>The <tt>PassManager</tt> does two main things to try to reduce the execution
1375time of a series of passes:</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1376
1377<ol>
1378<li><b>Share analysis results</b> - The PassManager attempts to avoid
1379recomputing analysis results as much as possible. This means keeping track of
1380which analyses are available already, which analyses get invalidated, and which
1381analyses are needed to be run for a pass. An important part of work is that the
1382<tt>PassManager</tt> tracks the exact lifetime of all analysis results, allowing
1383it to <a href="#releaseMemory">free memory</a> allocated to holding analysis
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1384results as soon as they are no longer needed.</li>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1385
1386<li><b>Pipeline the execution of passes on the program</b> - The
1387<tt>PassManager</tt> attempts to get better cache and memory usage behavior out
1388of a series of passes by pipelining the passes together. This means that, given
1389a series of consequtive <a href="#FunctionPass"><tt>FunctionPass</tt></a>'s, it
1390will execute all of the <a href="#FunctionPass"><tt>FunctionPass</tt></a>'s on
1391the first function, then all of the <a
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1392href="#FunctionPass"><tt>FunctionPass</tt></a>es on the second function,
1393etc... until the entire program has been run through the passes.
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1394
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1395<p>This improves the cache behavior of the compiler, because it is only touching
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1396the LLVM program representation for a single function at a time, instead of
1397traversing the entire program. It reduces the memory consumption of compiler,
1398because, for example, only one <a
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]1399href="http://llvm.org/doxygen/classllvm_1_1DominatorSet.html"><tt>DominatorSet</tt></a>
John Criswell9795bb82007-12-10 20:26:29 +0000[diff] [blame]1400needs to be calculated at a time. This also makes it possible to implement
1401some <a
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1402href="#SMP">interesting enhancements</a> in the future.</p></li>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1403
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1404</ol>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1405
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1406<p>The effectiveness of the <tt>PassManager</tt> is influenced directly by how
1407much information it has about the behaviors of the passes it is scheduling. For
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1408example, the "preserved" set is intentionally conservative in the face of an
1409unimplemented <a href="#getAnalysisUsage"><tt>getAnalysisUsage</tt></a> method.
1410Not implementing when it should be implemented will have the effect of not
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1411allowing any analysis results to live across the execution of your pass.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1412
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1413<p>The <tt>PassManager</tt> class exposes a <tt>--debug-pass</tt> command line
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1414options that is useful for debugging pass execution, seeing how things work, and
1415diagnosing when you should be preserving more analyses than you currently are
1416(To get information about all of the variants of the <tt>--debug-pass</tt>
Duncan Sands7e7ae5a2010-02-18 14:08:13 +0000[diff] [blame]1417option, just type '<tt>opt -help-hidden</tt>').</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1418
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1419<p>By using the <tt>--debug-pass=Structure</tt> option, for example, we can see
1420how our <a href="#basiccode">Hello World</a> pass interacts with other passes.
1421Lets try it out with the <tt>gcse</tt> and <tt>licm</tt> passes:</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1422
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1423<div class="doc_code"><pre>
Duncan Sands67f8a7b2010-07-08 08:27:18 +0000[diff] [blame]1424$ 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]1425Module Pass Manager
1426 Function Pass Manager
1427 Dominator Set Construction
1428 Immediate Dominators Construction
1429 Global Common Subexpression Elimination
1430-- Immediate Dominators Construction
1431-- Global Common Subexpression Elimination
1432 Natural Loop Construction
1433 Loop Invariant Code Motion
1434-- Natural Loop Construction
1435-- Loop Invariant Code Motion
1436 Module Verifier
1437-- Dominator Set Construction
1438-- Module Verifier
Gabor Greif04367bf2007-07-06 22:07:22 +0000[diff] [blame]1439 Bitcode Writer
1440--Bitcode Writer
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1441</pre></div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1442
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1443<p>This output shows us when passes are constructed and when the analysis
1444results are known to be dead (prefixed with '<tt>--</tt>'). Here we see that
1445GCSE uses dominator and immediate dominator information to do its job. The LICM
1446pass uses natural loop information, which uses dominator sets, but not immediate
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1447dominators. Because immediate dominators are no longer useful after the GCSE
1448pass, it is immediately destroyed. The dominator sets are then reused to
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1449compute natural loop information, which is then used by the LICM pass.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1450
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1451<p>After the LICM pass, the module verifier runs (which is automatically added
1452by the '<tt>opt</tt>' tool), which uses the dominator set to check that the
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1453resultant LLVM code is well formed. After it finishes, the dominator set
1454information is destroyed, after being computed once, and shared by three
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1455passes.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1456
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1457<p>Lets see how this changes when we run the <a href="#basiccode">Hello
1458World</a> pass in between the two passes:</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1459
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1460<div class="doc_code"><pre>
Duncan Sands67f8a7b2010-07-08 08:27:18 +0000[diff] [blame]1461$ 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]1462Module Pass Manager
1463 Function Pass Manager
1464 Dominator Set Construction
1465 Immediate Dominators Construction
1466 Global Common Subexpression Elimination
1467<b>-- Dominator Set Construction</b>
1468-- Immediate Dominators Construction
1469-- Global Common Subexpression Elimination
1470<b> Hello World Pass
1471-- Hello World Pass
1472 Dominator Set Construction</b>
1473 Natural Loop Construction
1474 Loop Invariant Code Motion
1475-- Natural Loop Construction
1476-- Loop Invariant Code Motion
1477 Module Verifier
1478-- Dominator Set Construction
1479-- Module Verifier
Gabor Greif04367bf2007-07-06 22:07:22 +0000[diff] [blame]1480 Bitcode Writer
1481--Bitcode Writer
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1482Hello: __main
1483Hello: puts
1484Hello: main
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1485</pre></div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1486
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1487<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]1488Dominator Set pass, even though it doesn't modify the code at all! To fix this,
1489we need to add the following <a
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1490href="#getAnalysisUsage"><tt>getAnalysisUsage</tt></a> method to our pass:</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1491
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1492<div class="doc_code"><pre>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1493 <i>// We don't modify the program, so we preserve all analyses</i>
1494 <b>virtual void</b> getAnalysisUsage(AnalysisUsage &amp;AU) <b>const</b> {
1495 AU.setPreservesAll();
1496 }
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1497</pre></div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1498
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1499<p>Now when we run our pass, we get this output:</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1500
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1501<div class="doc_code"><pre>
Duncan Sands67f8a7b2010-07-08 08:27:18 +0000[diff] [blame]1502$ 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]1503Pass Arguments: -gcse -hello -licm
1504Module Pass Manager
1505 Function Pass Manager
1506 Dominator Set Construction
1507 Immediate Dominators Construction
1508 Global Common Subexpression Elimination
1509-- Immediate Dominators Construction
1510-- Global Common Subexpression Elimination
1511 Hello World Pass
1512-- Hello World Pass
1513 Natural Loop Construction
1514 Loop Invariant Code Motion
1515-- Loop Invariant Code Motion
1516-- Natural Loop Construction
1517 Module Verifier
1518-- Dominator Set Construction
1519-- Module Verifier
Gabor Greif04367bf2007-07-06 22:07:22 +0000[diff] [blame]1520 Bitcode Writer
1521--Bitcode Writer
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1522Hello: __main
1523Hello: puts
1524Hello: main
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1525</pre></div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1526
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1527<p>Which shows that we don't accidentally invalidate dominator information
1528anymore, and therefore do not have to compute it twice.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1529
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1530</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1531
1532<!-- _______________________________________________________________________ -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1533<div class="doc_subsubsection">
1534 <a name="releaseMemory">The <tt>releaseMemory</tt> method</a>
1535</div>
1536
1537<div class="doc_text">
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1538
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1539<div class="doc_code"><pre>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1540 <b>virtual void</b> releaseMemory();
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1541</pre></div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1542
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1543<p>The <tt>PassManager</tt> automatically determines when to compute analysis
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1544results, and how long to keep them around for. Because the lifetime of the pass
1545object itself is effectively the entire duration of the compilation process, we
1546need some way to free analysis results when they are no longer useful. The
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1547<tt>releaseMemory</tt> virtual method is the way to do this.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1548
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1549<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]1550amount of state (for use by another pass which "requires" your pass and uses the
1551<a href="#getAnalysis">getAnalysis</a> method) you should implement
Dan Gohmand87c9e32009-06-15 18:22:49 +0000[diff] [blame]1552<tt>releaseMemory</tt> to, well, release the memory allocated to maintain this
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1553internal state. This method is called after the <tt>run*</tt> method for the
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1554class, before the next call of <tt>run*</tt> in your pass.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1555
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1556</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1557
1558<!-- *********************************************************************** -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1559<div class="doc_section">
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1560 <a name="registering">Registering dynamically loaded passes</a>
1561</div>
1562<!-- *********************************************************************** -->
1563
1564<div class="doc_text">
1565
1566<p><i>Size matters</i> when constructing production quality tools using llvm,
1567both for the purposes of distribution, and for regulating the resident code size
1568when running on the target system. Therefore, it becomes desirable to
1569selectively use some passes, while omitting others and maintain the flexibility
1570to change configurations later on. You want to be able to do all this, and,
1571provide feedback to the user. This is where pass registration comes into
1572play.</p>
1573
1574<p>The fundamental mechanisms for pass registration are the
1575<tt>MachinePassRegistry</tt> class and subclasses of
1576<tt>MachinePassRegistryNode</tt>.</p>
1577
1578<p>An instance of <tt>MachinePassRegistry</tt> is used to maintain a list of
1579<tt>MachinePassRegistryNode</tt> objects. This instance maintains the list and
1580communicates additions and deletions to the command line interface.</p>
1581
1582<p>An instance of <tt>MachinePassRegistryNode</tt> subclass is used to maintain
1583information provided about a particular pass. This information includes the
1584command line name, the command help string and the address of the function used
1585to create an instance of the pass. A global static constructor of one of these
1586instances <i>registers</i> with a corresponding <tt>MachinePassRegistry</tt>,
1587the static destructor <i>unregisters</i>. Thus a pass that is statically linked
1588in the tool will be registered at start up. A dynamically loaded pass will
1589register on load and unregister at unload.</p>
1590
1591</div>
1592
1593<!-- _______________________________________________________________________ -->
1594<div class="doc_subsection">
1595 <a name="registering_existing">Using existing registries</a>
1596</div>
1597
1598<div class="doc_text">
1599
1600<p>There are predefined registries to track instruction scheduling
1601(<tt>RegisterScheduler</tt>) and register allocation (<tt>RegisterRegAlloc</tt>)
1602machine passes. Here we will describe how to <i>register</i> a register
1603allocator machine pass.</p>
1604
1605<p>Implement your register allocator machine pass. In your register allocator
1606.cpp file add the following include;</p>
1607
1608<div class="doc_code"><pre>
Chris Lattner8f652eb2006-08-11 16:37:02 +0000[diff] [blame]1609 #include "llvm/CodeGen/RegAllocRegistry.h"
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1610</pre></div>
1611
1612<p>Also in your register allocator .cpp file, define a creator function in the
1613form; </p>
1614
1615<div class="doc_code"><pre>
1616 FunctionPass *createMyRegisterAllocator() {
1617 return new MyRegisterAllocator();
1618 }
1619</pre></div>
1620
1621<p>Note that the signature of this function should match the type of
1622<tt>RegisterRegAlloc::FunctionPassCtor</tt>. In the same file add the
1623"installing" declaration, in the form;</p>
1624
1625<div class="doc_code"><pre>
1626 static RegisterRegAlloc myRegAlloc("myregalloc",
1627 " my register allocator help string",
1628 createMyRegisterAllocator);
1629</pre></div>
1630
1631<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]1632-help query.</p>
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1633
1634<div class="doc_code"><pre>
Duncan Sands7e7ae5a2010-02-18 14:08:13 +0000[diff] [blame]1635$ llc -help
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1636 ...
Duncan Sands18619b22010-02-18 14:37:52 +0000[diff] [blame]1637 -regalloc - Register allocator to use (default=linearscan)
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1638 =linearscan - linear scan register allocator
1639 =local - local register allocator
1640 =simple - simple register allocator
1641 =myregalloc - my register allocator help string
1642 ...
1643</pre></div>
1644
1645<p>And that's it. The user is now free to use <tt>-regalloc=myregalloc</tt> as
1646an option. Registering instruction schedulers is similar except use the
Chris Lattner8f652eb2006-08-11 16:37:02 +0000[diff] [blame]1647<tt>RegisterScheduler</tt> class. Note that the
1648<tt>RegisterScheduler::FunctionPassCtor</tt> is significantly different from
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1649<tt>RegisterRegAlloc::FunctionPassCtor</tt>.</p>
1650
1651<p>To force the load/linking of your register allocator into the llc/lli tools,
1652add your creator function's global declaration to "Passes.h" and add a "pseudo"
1653call line to <tt>llvm/Codegen/LinkAllCodegenComponents.h</tt>.</p>
1654
1655</div>
1656
1657
1658<!-- _______________________________________________________________________ -->
1659<div class="doc_subsection">
1660 <a name="registering_new">Creating new registries</a>
1661</div>
1662
1663<div class="doc_text">
1664
1665<p>The easiest way to get started is to clone one of the existing registries; we
1666recommend <tt>llvm/CodeGen/RegAllocRegistry.h</tt>. The key things to modify
1667are the class name and the <tt>FunctionPassCtor</tt> type.</p>
1668
1669<p>Then you need to declare the registry. Example: if your pass registry is
1670<tt>RegisterMyPasses</tt> then define;</p>
1671
1672<div class="doc_code"><pre>
1673MachinePassRegistry RegisterMyPasses::Registry;
1674</pre></div>
1675
1676<p>And finally, declare the command line option for your passes. Example:</p>
1677
1678<div class="doc_code"><pre>
1679 cl::opt&lt;RegisterMyPasses::FunctionPassCtor, false,
Dan Gohman364a39f2008-10-14 17:00:38 +0000[diff] [blame]1680 RegisterPassParser&lt;RegisterMyPasses&gt; &gt;
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1681 MyPassOpt("mypass",
1682 cl::init(&amp;createDefaultMyPass),
1683 cl::desc("my pass option help"));
1684</pre></div>
1685
1686<p>Here the command option is "mypass", with createDefaultMyPass as the default
1687creator.</p>
1688
1689</div>
1690
1691<!-- *********************************************************************** -->
1692<div class="doc_section">
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1693 <a name="debughints">Using GDB with dynamically loaded passes</a>
1694</div>
Chris Lattner480e2ef2002-09-06 02:02:58 +0000[diff] [blame]1695<!-- *********************************************************************** -->
1696
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1697<div class="doc_text">
1698
1699<p>Unfortunately, using GDB with dynamically loaded passes is not as easy as it
Chris Lattner480e2ef2002-09-06 02:02:58 +0000[diff] [blame]1700should be. First of all, you can't set a breakpoint in a shared object that has
1701not been loaded yet, and second of all there are problems with inlined functions
1702in shared objects. Here are some suggestions to debugging your pass with
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1703GDB.</p>
Chris Lattner480e2ef2002-09-06 02:02:58 +0000[diff] [blame]1704
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1705<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]1706transformation invoked by <tt>opt</tt>, although nothing described here depends
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1707on that.</p>
1708
1709</div>
Chris Lattner480e2ef2002-09-06 02:02:58 +0000[diff] [blame]1710
1711<!-- _______________________________________________________________________ -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1712<div class="doc_subsubsection">
1713 <a name="breakpoint">Setting a breakpoint in your pass</a>
1714</div>
Chris Lattner480e2ef2002-09-06 02:02:58 +0000[diff] [blame]1715
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1716<div class="doc_text">
1717
1718<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]1719
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1720<div class="doc_code"><pre>
Chris Lattner480e2ef2002-09-06 02:02:58 +0000[diff] [blame]1721$ <b>gdb opt</b>
1722GNU gdb 5.0
1723Copyright 2000 Free Software Foundation, Inc.
1724GDB is free software, covered by the GNU General Public License, and you are
1725welcome to change it and/or distribute copies of it under certain conditions.
1726Type "show copying" to see the conditions.
1727There is absolutely no warranty for GDB. Type "show warranty" for details.
1728This GDB was configured as "sparc-sun-solaris2.6"...
1729(gdb)
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1730</pre></div>
Chris Lattner480e2ef2002-09-06 02:02:58 +0000[diff] [blame]1731
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1732<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]1733time to load. Be patient. Since we cannot set a breakpoint in our pass yet
1734(the shared object isn't loaded until runtime), we must execute the process, and
1735have it stop before it invokes our pass, but after it has loaded the shared
1736object. The most foolproof way of doing this is to set a breakpoint in
1737<tt>PassManager::run</tt> and then run the process with the arguments you
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1738want:</p>
Chris Lattner480e2ef2002-09-06 02:02:58 +0000[diff] [blame]1739
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1740<div class="doc_code"><pre>
Reid Spencer22a9e5b2006-09-28 16:53:47 +0000[diff] [blame]1741(gdb) <b>break llvm::PassManager::run</b>
Chris Lattner480e2ef2002-09-06 02:02:58 +0000[diff] [blame]1742Breakpoint 1 at 0x2413bc: file Pass.cpp, line 70.
Duncan Sands67f8a7b2010-07-08 08:27:18 +0000[diff] [blame]1743(gdb) <b>run test.bc -load $(LLVMTOP)/llvm/Debug+Asserts/lib/[libname].so -[passoption]</b>
1744Starting program: opt test.bc -load $(LLVMTOP)/llvm/Debug+Asserts/lib/[libname].so -[passoption]
Chris Lattner480e2ef2002-09-06 02:02:58 +0000[diff] [blame]1745Breakpoint 1, PassManager::run (this=0xffbef174, M=@0x70b298) at Pass.cpp:70
174670 bool PassManager::run(Module &amp;M) { return PM-&gt;run(M); }
1747(gdb)
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1748</pre></div>
Chris Lattner480e2ef2002-09-06 02:02:58 +0000[diff] [blame]1749
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1750<p>Once the <tt>opt</tt> stops in the <tt>PassManager::run</tt> method you are
1751now free to set breakpoints in your pass so that you can trace through execution
1752or do other standard debugging stuff.</p>
Chris Lattner480e2ef2002-09-06 02:02:58 +0000[diff] [blame]1753
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1754</div>
Chris Lattner480e2ef2002-09-06 02:02:58 +0000[diff] [blame]1755
1756<!-- _______________________________________________________________________ -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1757<div class="doc_subsubsection">
1758 <a name="debugmisc">Miscellaneous Problems</a>
1759</div>
Chris Lattner480e2ef2002-09-06 02:02:58 +0000[diff] [blame]1760
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1761<div class="doc_text">
1762
1763<p>Once you have the basics down, there are a couple of problems that GDB has,
1764some with solutions, some without.</p>
Chris Lattner480e2ef2002-09-06 02:02:58 +0000[diff] [blame]1765
1766<ul>
1767<li>Inline functions have bogus stack information. In general, GDB does a
1768pretty good job getting stack traces and stepping through inline functions.
1769When a pass is dynamically loaded however, it somehow completely loses this
1770capability. The only solution I know of is to de-inline a function (move it
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1771from the body of a class to a .cpp file).</li>
Chris Lattner480e2ef2002-09-06 02:02:58 +0000[diff] [blame]1772
1773<li>Restarting the program breaks breakpoints. After following the information
1774above, you have succeeded in getting some breakpoints planted in your pass. Nex
1775thing you know, you restart the program (i.e., you type '<tt>run</tt>' again),
1776and you start getting errors about breakpoints being unsettable. The only way I
1777have found to "fix" this problem is to <tt>delete</tt> the breakpoints that are
1778already set in your pass, run the program, and re-set the breakpoints once
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1779execution stops in <tt>PassManager::run</tt>.</li>
Chris Lattner480e2ef2002-09-06 02:02:58 +0000[diff] [blame]1780
1781</ul>
1782
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1783<p>Hopefully these tips will help with common case debugging situations. If
1784you'd like to contribute some tips of your own, just contact <a
1785href="mailto:sabre@nondot.org">Chris</a>.</p>
Chris Lattner480e2ef2002-09-06 02:02:58 +0000[diff] [blame]1786
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1787</div>
Chris Lattner480e2ef2002-09-06 02:02:58 +0000[diff] [blame]1788
1789<!-- *********************************************************************** -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1790<div class="doc_section">
1791 <a name="future">Future extensions planned</a>
1792</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1793<!-- *********************************************************************** -->
1794
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1795<div class="doc_text">
1796
1797<p>Although the LLVM Pass Infrastructure is very capable as it stands, and does
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1798some 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]1799where we are going:</p>
1800
1801</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1802
1803<!-- _______________________________________________________________________ -->
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]1804<div class="doc_subsubsection">
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1805 <a name="SMP">Multithreaded LLVM</a>
1806</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1807
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1808<div class="doc_text">
1809
1810<p>Multiple CPU machines are becoming more common and compilation can never be
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1811fast enough: obviously we should allow for a multithreaded compiler. Because of
1812the semantics defined for passes above (specifically they cannot maintain state
1813across invocations of their <tt>run*</tt> methods), a nice clean way to
1814implement a multithreaded compiler would be for the <tt>PassManager</tt> class
Misha Brukmanbc0e9982003-07-14 17:20:40 +0000[diff] [blame]1815to create multiple instances of each pass object, and allow the separate
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1816instances to be hacking on different parts of the program at the same time.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1817
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1818<p>This implementation would prevent each of the passes from having to implement
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1819multithreaded constructs, requiring only the LLVM core to have locking in a few
1820places (for global resources). Although this is a simple extension, we simply
1821haven't had time (or multiprocessor machines, thus a reason) to implement this.
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1822Despite that, we have kept the LLVM passes SMP ready, and you should too.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1823
Chris Lattnerb5c87f62007-05-18 05:36:14 +0000[diff] [blame]1824</div>
1825
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1826<!-- *********************************************************************** -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1827<hr>
1828<address>
1829 <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]1831 <a href="http://validator.w3.org/check/referer"><img
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Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1833
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1834 <a href="mailto:sabre@nondot.org">Chris Lattner</a><br>
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]1835 <a href="http://llvm.org">The LLVM Compiler Infrastructure</a><br>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1836 Last modified: $Date$
1837</address>
1838
1839</body>
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