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gerrit-public.fairphone.software / fp2-dev / platform / external / llvm / 2d5e3acd2a69070c4e3550e014a54626e18bf12c / . / docs / WritingAnLLVMPass.html
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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
Chris Lattner17a4c3e2002-08-14 20:06:13 +0000[diff] [blame]182# Path to top level of LLVM heirarchy
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
Reid Spencerebfe07f2006-08-08 01:48:17 +0000[diff] [blame]192# Tell the build system which LLVM libraries your pass needs. You'll probably
193# need at least LLVMSystem.a, LLVMSupport.a, LLVMCore.a but possibly several
194# others too.
195LLVMLIBS = LLVMCore.a LLVMSupport.a LLVMSystem.a
196
Chris Lattner17a4c3e2002-08-14 20:06:13 +0000[diff] [blame]197# Include the makefile implementation stuff
198include $(LEVEL)/Makefile.common
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]199</pre></div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]200
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]201<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]202directory are to be compiled and linked together into a
Reid Spencer7fa6d522005-01-11 05:16:23 +0000[diff] [blame]203<tt>Debug/lib/Hello.so</tt> shared object that can be dynamically loaded by
Chris Lattnerc8603c22006-08-27 23:18:52 +0000[diff] [blame]204the <tt>opt</tt> or <tt>bugpoint</tt> tools via their <tt>-load</tt> options.
Reid Spencer7fa6d522005-01-11 05:16:23 +0000[diff] [blame]205If your operating system uses a suffix other than .so (such as windows or
206Mac OS/X), the appropriate extension will be used.</p>
John Criswellf9c78652004-01-26 21:26:54 +0000[diff] [blame]207
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]208<p>Now that we have the build scripts set up, we just need to write the code for
209the pass itself.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]210
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]211</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]212
213<!-- ======================================================================= -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]214<div class="doc_subsection">
215 <a name="basiccode">Basic code required</a>
216</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]217
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]218<div class="doc_text">
219
220<p>Now that we have a way to compile our new pass, we just have to write it.
221Start out with:</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]222
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]223<div class="doc_code"><pre>
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]224<b>#include</b> "<a href="http://llvm.org/doxygen/Pass_8h-source.html">llvm/Pass.h</a>"
225<b>#include</b> "<a href="http://llvm.org/doxygen/Function_8h-source.html">llvm/Function.h</a>"
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]226</pre></div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]227
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]228<p>Which are needed because we are writing a <tt><a
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]229href="http://llvm.org/doxygen/classllvm_1_1Pass.html">Pass</a></tt>, and
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]230we are operating on <tt><a
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]231href="http://llvm.org/doxygen/classllvm_1_1Function.html">Function</a></tt>'s.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]232
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]233<p>Next we have:</p>
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]234<div class="doc_code"><pre>
Jonathan Manton65acb302004-06-30 18:10:30 +0000[diff] [blame]235<b>using namespace llvm;</b>
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]236</pre></div>
Jonathan Manton65acb302004-06-30 18:10:30 +0000[diff] [blame]237<p>... which is required because the functions from the include files
238live in the llvm namespace.
239</p>
240
241<p>Next we have:</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]242
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]243<div class="doc_code"><pre>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]244<b>namespace</b> {
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]245</pre></div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]246
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]247<p>... which starts out an anonymous namespace. Anonymous namespaces are to C++
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]248what the "<tt>static</tt>" keyword is to C (at global scope). It makes the
249things declared inside of the anonymous namespace only visible to the current
250file. If you're not familiar with them, consult a decent C++ book for more
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]251information.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]252
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]253<p>Next, we declare our pass itself:</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]254
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]255<div class="doc_code"><pre>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]256 <b>struct</b> Hello : <b>public</b> <a href="#FunctionPass">FunctionPass</a> {
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]257</pre></div><p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]258
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]259<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]260href="http://llvm.org/doxygen/classllvm_1_1FunctionPass.html">FunctionPass</a></tt>.
Chris Lattnerd6ea9262002-09-09 03:48:46 +0000[diff] [blame]261The different builtin pass subclasses are described in detail <a
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]262href="#passtype">later</a>, but for now, know that <a
263href="#FunctionPass"><tt>FunctionPass</tt></a>'s operate a function at a
264time.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]265
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]266<div class="doc_code"><pre>
Devang Patel19974732007-05-03 01:11:54 +0000[diff] [blame]267 static char ID;
Dan Gohman865f0062009-02-18 05:09:16 +0000[diff] [blame]268 Hello() : FunctionPass(&amp;ID) {}
Devang Patele50fb9a2007-05-01 20:55:38 +0000[diff] [blame]269</pre></div><p>
270
271<p> This declares pass identifier used by LLVM to identify pass. This allows LLVM to
272avoid using expensive C++ runtime information.</p>
273
274<div class="doc_code"><pre>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]275 <b>virtual bool</b> <a href="#runOnFunction">runOnFunction</a>(Function &amp;F) {
Bill Wendling832171c2006-12-07 20:04:42 +0000[diff] [blame]276 llvm::cerr &lt;&lt; "<i>Hello: </i>" &lt;&lt; F.getName() &lt;&lt; "\n";
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]277 <b>return false</b>;
278 }
279 }; <i>// end of struct Hello</i>
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]280</pre></div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]281
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]282<p>We declare a "<a href="#runOnFunction"><tt>runOnFunction</tt></a>" method,
283which overloads an abstract virtual method inherited from <a
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]284href="#FunctionPass"><tt>FunctionPass</tt></a>. This is where we are supposed
285to 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]286function.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]287
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]288<div class="doc_code"><pre>
Devang Patel19974732007-05-03 01:11:54 +0000[diff] [blame]289 char Hello::ID = 0;
Devang Patele50fb9a2007-05-01 20:55:38 +0000[diff] [blame]290</pre></div>
291
292<p> We initialize pass ID here. LLVM uses ID's address to identify pass so
293initialization value is not important.</p>
294
295<div class="doc_code"><pre>
Devang Patelc7582092008-03-19 21:56:59 +0000[diff] [blame]296 RegisterPass&lt;Hello&gt; X("<i>hello</i>", "<i>Hello World Pass</i>",
297 false /* Only looks at CFG */,
298 false /* Analysis Pass */);
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]299} <i>// end of anonymous namespace</i>
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]300</pre></div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]301
Chris Lattnerc8603c22006-08-27 23:18:52 +0000[diff] [blame]302<p>Lastly, we <a href="#registration">register our class</a> <tt>Hello</tt>,
303giving it a command line
Devang Patelc7582092008-03-19 21:56:59 +0000[diff] [blame]304argument "<tt>hello</tt>", and a name "<tt>Hello World Pass</tt>".
305Last two RegisterPass arguments are optional. Their default value is false.
306If a pass walks CFG without modifying it then third argument is set to true.
307If a pass is an analysis pass, for example dominator tree pass, then true
308is supplied as fourth argument. </p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]309
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]310<p>As a whole, the <tt>.cpp</tt> file looks like:</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]311
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]312<div class="doc_code"><pre>
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]313<b>#include</b> "<a href="http://llvm.org/doxygen/Pass_8h-source.html">llvm/Pass.h</a>"
314<b>#include</b> "<a href="http://llvm.org/doxygen/Function_8h-source.html">llvm/Function.h</a>"
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]315
Jonathan Manton65acb302004-06-30 18:10:30 +0000[diff] [blame]316<b>using namespace llvm;</b>
317
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]318<b>namespace</b> {
319 <b>struct Hello</b> : <b>public</b> <a href="#FunctionPass">FunctionPass</a> {
Devang Patele50fb9a2007-05-01 20:55:38 +0000[diff] [blame]320
Devang Patel19974732007-05-03 01:11:54 +0000[diff] [blame]321 static char ID;
Dan Gohman865f0062009-02-18 05:09:16 +0000[diff] [blame]322 Hello() : FunctionPass(&amp;ID) {}
Devang Patele50fb9a2007-05-01 20:55:38 +0000[diff] [blame]323
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]324 <b>virtual bool</b> <a href="#runOnFunction">runOnFunction</a>(Function &amp;F) {
Bill Wendling832171c2006-12-07 20:04:42 +0000[diff] [blame]325 llvm::cerr &lt;&lt; "<i>Hello: </i>" &lt;&lt; F.getName() &lt;&lt; "\n";
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]326 <b>return false</b>;
327 }
328 };
329
Devang Patel26e5a302007-07-25 21:05:39 +0000[diff] [blame]330 char Hello::ID = 0;
Chris Lattnerc8603c22006-08-27 23:18:52 +0000[diff] [blame]331 RegisterPass&lt;Hello&gt; X("<i>hello</i>", "<i>Hello World Pass</i>");
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]332}
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]333</pre></div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]334
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]335<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]336command in the local directory and you should get a new
Reid Spencer7fa6d522005-01-11 05:16:23 +0000[diff] [blame]337"<tt>Debug/lib/Hello.so</tt> file. Note that everything in this file is
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]338contained in an anonymous namespace: this reflects the fact that passes are self
339contained units that do not need external interfaces (although they can have
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]340them) to be useful.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]341
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]342</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]343
344<!-- ======================================================================= -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]345<div class="doc_subsection">
Chris Lattnerc8603c22006-08-27 23:18:52 +0000[diff] [blame]346 <a name="running">Running a pass with <tt>opt</tt></a>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]347</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]348
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]349<div class="doc_text">
350
John Criswellf9c78652004-01-26 21:26:54 +0000[diff] [blame]351<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]352<tt>opt</tt> command to run an LLVM program through your pass. Because you
Chris Lattnerc8603c22006-08-27 23:18:52 +0000[diff] [blame]353registered your pass with the <tt>RegisterPass</tt> template, you will be able to
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]354use the <tt>opt</tt> tool to access it, once loaded.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]355
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]356<p>To test it, follow the example at the end of the <a
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]357href="GettingStarted.html">Getting Started Guide</a> to compile "Hello World" to
Gabor Greif04367bf2007-07-06 22:07:22 +0000[diff] [blame]358LLVM. We can now run the bitcode file (<tt>hello.bc</tt>) for the program
359through our transformation like this (or course, any bitcode file will
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]360work):</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]361
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]362<div class="doc_code"><pre>
Reid Spencer7fa6d522005-01-11 05:16:23 +0000[diff] [blame]363$ opt -load ../../../Debug/lib/Hello.so -hello &lt; hello.bc &gt; /dev/null
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]364Hello: __main
365Hello: puts
366Hello: main
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]367</pre></div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]368
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]369<p>The '<tt>-load</tt>' option specifies that '<tt>opt</tt>' should load your
370pass as a shared object, which makes '<tt>-hello</tt>' a valid command line
371argument (which is one reason you need to <a href="#registration">register your
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]372pass</a>). Because the hello pass does not modify the program in any
373interesting way, we just throw away the result of <tt>opt</tt> (sending it to
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]374<tt>/dev/null</tt>).</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]375
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]376<p>To see what happened to the other string you registered, try running
377<tt>opt</tt> with the <tt>--help</tt> option:</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]378
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]379<div class="doc_code"><pre>
Reid Spencer7fa6d522005-01-11 05:16:23 +0000[diff] [blame]380$ opt -load ../../../Debug/lib/Hello.so --help
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]381OVERVIEW: llvm .bc -&gt; .bc modular optimizer
382
Gabor Greif04367bf2007-07-06 22:07:22 +0000[diff] [blame]383USAGE: opt [options] &lt;input bitcode&gt;
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]384
385OPTIONS:
386 Optimizations available:
387...
388 -funcresolve - Resolve Functions
389 -gcse - Global Common Subexpression Elimination
390 -globaldce - Dead Global Elimination
391 <b>-hello - Hello World Pass</b>
Chris Lattner065a6162003-09-10 05:29:43 +0000[diff] [blame]392 -indvars - Canonicalize Induction Variables
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]393 -inline - Function Integration/Inlining
394 -instcombine - Combine redundant instructions
395...
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]396</pre></div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]397
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]398<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]399documentation to users of <tt>opt</tt>. Now that you have a working pass, you
400would go ahead and make it do the cool transformations you want. Once you get
401it all working and tested, it may become useful to find out how fast your pass
402is. The <a href="#passManager"><tt>PassManager</tt></a> provides a nice command
403line option (<tt>--time-passes</tt>) that allows you to get information about
404the execution time of your pass along with the other passes you queue up. For
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]405example:</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]406
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]407<div class="doc_code"><pre>
Reid Spencer7fa6d522005-01-11 05:16:23 +0000[diff] [blame]408$ opt -load ../../../Debug/lib/Hello.so -hello -time-passes &lt; hello.bc &gt; /dev/null
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]409Hello: __main
410Hello: puts
411Hello: main
412===============================================================================
413 ... Pass execution timing report ...
414===============================================================================
415 Total Execution Time: 0.02 seconds (0.0479059 wall clock)
416
417 ---User Time--- --System Time-- --User+System-- ---Wall Time--- --- Pass Name ---
Gabor Greif04367bf2007-07-06 22:07:22 +0000[diff] [blame]418 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]419 0.0000 ( 0.0%) 0.0100 (100.0%) 0.0100 ( 50.0%) 0.0031 ( 6.4%) Dominator Set Construction
420 0.0000 ( 0.0%) 0.0000 ( 0.0%) 0.0000 ( 0.0%) 0.0013 ( 2.7%) Module Verifier
421 <b> 0.0000 ( 0.0%) 0.0000 ( 0.0%) 0.0000 ( 0.0%) 0.0033 ( 6.9%) Hello World Pass</b>
422 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]423</pre></div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]424
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]425<p>As you can see, our implementation above is pretty fast :). The additional
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]426passes listed are automatically inserted by the '<tt>opt</tt>' tool to verify
427that the LLVM emitted by your pass is still valid and well formed LLVM, which
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]428hasn't been broken somehow.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]429
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]430<p>Now that you have seen the basics of the mechanics behind passes, we can talk
431about some more details of how they work and how to use them.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]432
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]433</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]434
435<!-- *********************************************************************** -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]436<div class="doc_section">
437 <a name="passtype">Pass classes and requirements</a>
438</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]439<!-- *********************************************************************** -->
440
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]441<div class="doc_text">
442
443<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]444decide what class you should subclass for your pass. The <a
445href="#basiccode">Hello World</a> example uses the <tt><a
446href="#FunctionPass">FunctionPass</a></tt> class for its implementation, but we
447did not discuss why or when this should occur. Here we talk about the classes
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]448available, from the most general to the most specific.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]449
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]450<p>When choosing a superclass for your Pass, you should choose the <b>most
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]451specific</b> class possible, while still being able to meet the requirements
Misha Brukman5560c9d2003-08-18 14:43:39 +0000[diff] [blame]452listed. This gives the LLVM Pass Infrastructure information necessary to
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]453optimize how passes are run, so that the resultant compiler isn't unneccesarily
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]454slow.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]455
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]456</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]457
Chris Lattnerf004f9a2002-09-25 22:31:38 +0000[diff] [blame]458<!-- ======================================================================= -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]459<div class="doc_subsection">
460 <a name="ImmutablePass">The <tt>ImmutablePass</tt> class</a>
461</div>
Chris Lattnerf004f9a2002-09-25 22:31:38 +0000[diff] [blame]462
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]463<div class="doc_text">
464
465<p>The most plain and boring type of pass is the "<tt><a
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]466href="http://llvm.org/doxygen/classllvm_1_1ImmutablePass.html">ImmutablePass</a></tt>"
Chris Lattnerf004f9a2002-09-25 22:31:38 +0000[diff] [blame]467class. This pass type is used for passes that do not have to be run, do not
468change state, and never need to be updated. This is not a normal type of
469transformation or analysis, but can provide information about the current
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]470compiler configuration.</p>
Chris Lattnerf004f9a2002-09-25 22:31:38 +0000[diff] [blame]471
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]472<p>Although this pass class is very infrequently used, it is important for
Chris Lattnerf004f9a2002-09-25 22:31:38 +0000[diff] [blame]473providing information about the current target machine being compiled for, and
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]474other static information that can affect the various transformations.</p>
Chris Lattnerf004f9a2002-09-25 22:31:38 +0000[diff] [blame]475
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]476<p><tt>ImmutablePass</tt>es never invalidate other transformations, are never
477invalidated, and are never "run".</p>
Chris Lattnerf004f9a2002-09-25 22:31:38 +0000[diff] [blame]478
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]479</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]480
481<!-- ======================================================================= -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]482<div class="doc_subsection">
Chris Lattnerf6278922004-09-20 04:36:29 +0000[diff] [blame]483 <a name="ModulePass">The <tt>ModulePass</tt> class</a>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]484</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]485
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]486<div class="doc_text">
487
488<p>The "<tt><a
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]489href="http://llvm.org/doxygen/classllvm_1_1ModulePass.html">ModulePass</a></tt>"
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]490class is the most general of all superclasses that you can use. Deriving from
Chris Lattnerf6278922004-09-20 04:36:29 +0000[diff] [blame]491<tt>ModulePass</tt> indicates that your pass uses the entire program as a unit,
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]492refering to function bodies in no predictable order, or adding and removing
Chris Lattnerf6278922004-09-20 04:36:29 +0000[diff] [blame]493functions. Because nothing is known about the behavior of <tt>ModulePass</tt>
Daniel Dunbarb71725b2009-07-01 23:38:44 +0000[diff] [blame]494subclasses, no optimization can be done for their execution.</p>
495
496<p>A module pass can use function level passes (e.g. dominators) using
497the getAnalysis interface
498<tt>getAnalysis&lt;DominatorTree&gt;(llvm::Function *)</tt> to provide the
499function to retrieve analysis result for, if the function pass does not require
Devang Patel468857f2009-08-10 16:37:29 +0000[diff] [blame]500any 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]501analysis ran, e.g. in the case of dominators you should only ask for the
502DominatorTree for function definitions, not declarations.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]503
Chris Lattnerf6278922004-09-20 04:36:29 +0000[diff] [blame]504<p>To write a correct <tt>ModulePass</tt> subclass, derive from
505<tt>ModulePass</tt> and overload the <tt>runOnModule</tt> method with the
506following signature:</p>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]507
508</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]509
510<!-- _______________________________________________________________________ -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]511<div class="doc_subsubsection">
Chris Lattnerf6278922004-09-20 04:36:29 +0000[diff] [blame]512 <a name="runOnModule">The <tt>runOnModule</tt> method</a>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]513</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]514
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]515<div class="doc_text">
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]516
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]517<div class="doc_code"><pre>
Chris Lattnerf6278922004-09-20 04:36:29 +0000[diff] [blame]518 <b>virtual bool</b> runOnModule(Module &amp;M) = 0;
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]519</pre></div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]520
John Criswell2382ff72005-07-15 19:25:12 +0000[diff] [blame]521<p>The <tt>runOnModule</tt> method performs the interesting work of the pass.
522It should return true if the module was modified by the transformation and
523false otherwise.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]524
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]525</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]526
527<!-- ======================================================================= -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]528<div class="doc_subsection">
Chris Lattner8fdb2462004-09-18 06:39:35 +0000[diff] [blame]529 <a name="CallGraphSCCPass">The <tt>CallGraphSCCPass</tt> class</a>
530</div>
531
532<div class="doc_text">
533
534<p>The "<tt><a
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]535href="http://llvm.org/doxygen/classllvm_1_1CallGraphSCCPass.html">CallGraphSCCPass</a></tt>"
Chris Lattner8fdb2462004-09-18 06:39:35 +0000[diff] [blame]536is used by passes that need to traverse the program bottom-up on the call graph
537(callees before callers). Deriving from CallGraphSCCPass provides some
538mechanics for building and traversing the CallGraph, but also allows the system
539to optimize execution of CallGraphSCCPass's. If your pass meets the
540requirements outlined below, and doesn't meet the requirements of a <tt><a
541href="#FunctionPass">FunctionPass</a></tt> or <tt><a
542href="#BasicBlockPass">BasicBlockPass</a></tt>, you should derive from
543<tt>CallGraphSCCPass</tt>.</p>
544
545<p><b>TODO</b>: explain briefly what SCC, Tarjan's algo, and B-U mean.</p>
546
547<p>To be explicit, <tt>CallGraphSCCPass</tt> subclasses are:</p>
548
549<ol>
550
551<li>... <em>not allowed</em> to modify any <tt>Function</tt>s that are not in
552the current SCC.</li>
553
Tanya Lattner18aad232007-06-07 16:44:52 +0000[diff] [blame]554<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]555current SCC and the direct callees of the SCC.</li>
556
557<li>... <em>required</em> to preserve the current CallGraph object, updating it
558to reflect any changes made to the program.</li>
559
560<li>... <em>not allowed</em> to add or remove SCC's from the current Module,
561though they may change the contents of an SCC.</li>
562
563<li>... <em>allowed</em> to add or remove global variables from the current
564Module.</li>
565
566<li>... <em>allowed</em> to maintain state across invocations of
567 <a href="#runOnSCC"><tt>runOnSCC</tt></a> (including global data).</li>
568</ol>
569
570<p>Implementing a <tt>CallGraphSCCPass</tt> is slightly tricky in some cases
571because it has to handle SCCs with more than one node in it. All of the virtual
572methods described below should return true if they modified the program, or
573false if they didn't.</p>
574
575</div>
576
577<!-- _______________________________________________________________________ -->
578<div class="doc_subsubsection">
Devang Patelc20048d2007-01-23 22:56:28 +0000[diff] [blame]579 <a name="doInitialization_scc">The <tt>doInitialization(CallGraph &amp;)</tt>
Chris Lattner8fdb2462004-09-18 06:39:35 +0000[diff] [blame]580 method</a>
581</div>
582
583<div class="doc_text">
584
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]585<div class="doc_code"><pre>
Devang Patelc20048d2007-01-23 22:56:28 +0000[diff] [blame]586 <b>virtual bool</b> doInitialization(CallGraph &amp;CG);
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]587</pre></div>
Chris Lattner8fdb2462004-09-18 06:39:35 +0000[diff] [blame]588
589<p>The <tt>doIninitialize</tt> method is allowed to do most of the things that
590<tt>CallGraphSCCPass</tt>'s are not allowed to do. They can add and remove
591functions, get pointers to functions, etc. The <tt>doInitialization</tt> method
592is designed to do simple initialization type of stuff that does not depend on
593the SCCs being processed. The <tt>doInitialization</tt> method call is not
594scheduled to overlap with any other pass executions (thus it should be very
595fast).</p>
596
597</div>
598
599<!-- _______________________________________________________________________ -->
600<div class="doc_subsubsection">
601 <a name="runOnSCC">The <tt>runOnSCC</tt> method</a>
602</div>
603
604<div class="doc_text">
605
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]606<div class="doc_code"><pre>
Chris Lattner8fdb2462004-09-18 06:39:35 +0000[diff] [blame]607 <b>virtual bool</b> runOnSCC(const std::vector&lt;CallGraphNode *&gt; &amp;SCCM) = 0;
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]608</pre></div>
Chris Lattner8fdb2462004-09-18 06:39:35 +0000[diff] [blame]609
610<p>The <tt>runOnSCC</tt> method performs the interesting work of the pass, and
611should return true if the module was modified by the transformation, false
612otherwise.</p>
613
614</div>
615
616<!-- _______________________________________________________________________ -->
617<div class="doc_subsubsection">
Devang Patelc20048d2007-01-23 22:56:28 +0000[diff] [blame]618 <a name="doFinalization_scc">The <tt>doFinalization(CallGraph
Chris Lattner8fdb2462004-09-18 06:39:35 +0000[diff] [blame]619 &amp;)</tt> method</a>
620</div>
621
622<div class="doc_text">
623
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]624<div class="doc_code"><pre>
Devang Patelc20048d2007-01-23 22:56:28 +0000[diff] [blame]625 <b>virtual bool</b> doFinalization(CallGraph &amp;CG);
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]626</pre></div>
Chris Lattner8fdb2462004-09-18 06:39:35 +0000[diff] [blame]627
628<p>The <tt>doFinalization</tt> method is an infrequently used method that is
629called when the pass framework has finished calling <a
630href="#runOnFunction"><tt>runOnFunction</tt></a> for every function in the
631program being compiled.</p>
632
633</div>
634
635<!-- ======================================================================= -->
636<div class="doc_subsection">
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]637 <a name="FunctionPass">The <tt>FunctionPass</tt> class</a>
638</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]639
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]640<div class="doc_text">
641
Chris Lattnerf6278922004-09-20 04:36:29 +0000[diff] [blame]642<p>In contrast to <tt>ModulePass</tt> subclasses, <tt><a
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]643href="http://llvm.org/doxygen/classllvm_1_1Pass.html">FunctionPass</a></tt>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]644subclasses do have a predictable, local behavior that can be expected by the
645system. All <tt>FunctionPass</tt> execute on each function in the program
Misha Brukmanef6a6a62003-08-21 22:14:26 +0000[diff] [blame]646independent of all of the other functions in the program.
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]647<tt>FunctionPass</tt>'s do not require that they are executed in a particular
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]648order, and <tt>FunctionPass</tt>'s do not modify external functions.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]649
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]650<p>To be explicit, <tt>FunctionPass</tt> subclasses are not allowed to:</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]651
652<ol>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]653<li>Modify a Function other than the one currently being processed.</li>
654<li>Add or remove Function's from the current Module.</li>
655<li>Add or remove global variables from the current Module.</li>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]656<li>Maintain state across invocations of
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]657 <a href="#runOnFunction"><tt>runOnFunction</tt></a> (including global data)</li>
658</ol>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]659
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]660<p>Implementing a <tt>FunctionPass</tt> is usually straightforward (See the <a
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]661href="#basiccode">Hello World</a> pass for example). <tt>FunctionPass</tt>'s
662may overload three virtual methods to do their work. All of these methods
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]663should return true if they modified the program, or false if they didn't.</p>
664
665</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]666
667<!-- _______________________________________________________________________ -->
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]668<div class="doc_subsubsection">
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]669 <a name="doInitialization_mod">The <tt>doInitialization(Module &amp;)</tt>
670 method</a>
671</div>
672
673<div class="doc_text">
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]674
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]675<div class="doc_code"><pre>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]676 <b>virtual bool</b> doInitialization(Module &amp;M);
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]677</pre></div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]678
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]679<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]680<tt>FunctionPass</tt>'s are not allowed to do. They can add and remove
Chris Lattnerd0713f92002-09-12 17:06:43 +0000[diff] [blame]681functions, get pointers to functions, etc. The <tt>doInitialization</tt> method
682is designed to do simple initialization type of stuff that does not depend on
683the functions being processed. The <tt>doInitialization</tt> method call is not
684scheduled to overlap with any other pass executions (thus it should be very
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]685fast).</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]686
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]687<p>A good example of how this method should be used is the <a
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]688href="http://llvm.org/doxygen/LowerAllocations_8cpp-source.html">LowerAllocations</a>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]689pass. This pass converts <tt>malloc</tt> and <tt>free</tt> instructions into
Misha Brukmanef6a6a62003-08-21 22:14:26 +0000[diff] [blame]690platform dependent <tt>malloc()</tt> and <tt>free()</tt> function calls. It
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]691uses the <tt>doInitialization</tt> method to get a reference to the malloc and
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]692free functions that it needs, adding prototypes to the module if necessary.</p>
693
694</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]695
696<!-- _______________________________________________________________________ -->
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]697<div class="doc_subsubsection">
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]698 <a name="runOnFunction">The <tt>runOnFunction</tt> method</a>
699</div>
700
701<div class="doc_text">
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]702
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]703<div class="doc_code"><pre>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]704 <b>virtual bool</b> runOnFunction(Function &amp;F) = 0;
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]705</pre></div><p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]706
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]707<p>The <tt>runOnFunction</tt> method must be implemented by your subclass to do
708the transformation or analysis work of your pass. As usual, a true value should
709be returned if the function is modified.</p>
710
711</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]712
713<!-- _______________________________________________________________________ -->
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]714<div class="doc_subsubsection">
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]715 <a name="doFinalization_mod">The <tt>doFinalization(Module
716 &amp;)</tt> method</a>
717</div>
718
719<div class="doc_text">
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]720
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]721<div class="doc_code"><pre>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]722 <b>virtual bool</b> doFinalization(Module &amp;M);
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]723</pre></div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]724
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]725<p>The <tt>doFinalization</tt> method is an infrequently used method that is
726called when the pass framework has finished calling <a
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]727href="#runOnFunction"><tt>runOnFunction</tt></a> for every function in the
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]728program being compiled.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]729
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]730</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]731
732<!-- ======================================================================= -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]733<div class="doc_subsection">
Devang Patel2e8f27d2007-03-19 22:21:25 +0000[diff] [blame]734 <a name="LoopPass">The <tt>LoopPass</tt> class </a>
735</div>
736
737<div class="doc_text">
738
739<p> All <tt>LoopPass</tt> execute on each loop in the function independent of
740all of the other loops in the function. <tt>LoopPass</tt> processes loops in
741loop nest order such that outer most loop is processed last. </p>
742
743<p> <tt>LoopPass</tt> subclasses are allowed to update loop nest using
744<tt>LPPassManager</tt> interface. Implementing a loop pass is usually
745straightforward. <tt>Looppass</tt>'s may overload three virtual methods to
746do their work. All these methods should return true if they modified the
747program, or false if they didn't. </p>
748</div>
749
750<!-- _______________________________________________________________________ -->
751<div class="doc_subsubsection">
752 <a name="doInitialization_loop">The <tt>doInitialization(Loop *,
753 LPPassManager &amp;)</tt>
754 method</a>
755</div>
756
757<div class="doc_text">
758
759<div class="doc_code"><pre>
760 <b>virtual bool</b> doInitialization(Loop *, LPPassManager &amp;LPM);
761</pre></div>
762
Chris Lattnerb5c87f62007-05-18 05:36:14 +0000[diff] [blame]763<p>The <tt>doInitialization</tt> method is designed to do simple initialization
Devang Patel2e8f27d2007-03-19 22:21:25 +0000[diff] [blame]764type of stuff that does not depend on the functions being processed. The
765<tt>doInitialization</tt> method call is not scheduled to overlap with any
766other pass executions (thus it should be very fast). LPPassManager
767interface should be used to access Function or Module level analysis
768information.</p>
769
770</div>
771
772
773<!-- _______________________________________________________________________ -->
774<div class="doc_subsubsection">
775 <a name="runOnLoop">The <tt>runOnLoop</tt> method</a>
776</div>
777
778<div class="doc_text">
779
780<div class="doc_code"><pre>
781 <b>virtual bool</b> runOnLoop(Loop *, LPPassManager &amp;LPM) = 0;
782</pre></div><p>
783
784<p>The <tt>runOnLoop</tt> method must be implemented by your subclass to do
785the transformation or analysis work of your pass. As usual, a true value should
786be returned if the function is modified. <tt>LPPassManager</tt> interface
787should be used to update loop nest.</p>
788
789</div>
790
791<!-- _______________________________________________________________________ -->
792<div class="doc_subsubsection">
793 <a name="doFinalization_loop">The <tt>doFinalization()</tt> method</a>
794</div>
795
796<div class="doc_text">
797
798<div class="doc_code"><pre>
799 <b>virtual bool</b> doFinalization();
800</pre></div>
801
802<p>The <tt>doFinalization</tt> method is an infrequently used method that is
803called when the pass framework has finished calling <a
804href="#runOnLoop"><tt>runOnLoop</tt></a> for every loop in the
805program being compiled. </p>
806
807</div>
808
809
810
811<!-- ======================================================================= -->
812<div class="doc_subsection">
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]813 <a name="BasicBlockPass">The <tt>BasicBlockPass</tt> class</a>
814</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]815
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]816<div class="doc_text">
817
818<p><tt>BasicBlockPass</tt>'s are just like <a
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]819href="#FunctionPass"><tt>FunctionPass</tt></a>'s, except that they must limit
820their scope of inspection and modification to a single basic block at a time.
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]821As such, they are <b>not</b> allowed to do any of the following:</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]822
823<ol>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]824<li>Modify or inspect any basic blocks outside of the current one</li>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]825<li>Maintain state across invocations of
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]826 <a href="#runOnBasicBlock"><tt>runOnBasicBlock</tt></a></li>
Reid Spencer1bc19342004-12-11 05:12:57 +0000[diff] [blame]827<li>Modify the control flow graph (by altering terminator instructions)</li>
828<li>Any of the things forbidden for
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]829 <a href="#FunctionPass"><tt>FunctionPass</tt></a>es.</li>
830</ol>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]831
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]832<p><tt>BasicBlockPass</tt>es are useful for traditional local and "peephole"
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]833optimizations. They may override the same <a
Chris Lattnerd0713f92002-09-12 17:06:43 +0000[diff] [blame]834href="#doInitialization_mod"><tt>doInitialization(Module &amp;)</tt></a> and <a
835href="#doFinalization_mod"><tt>doFinalization(Module &amp;)</tt></a> methods that <a
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]836href="#FunctionPass"><tt>FunctionPass</tt></a>'s have, but also have the following virtual methods that may also be implemented:</p>
837
838</div>
Chris Lattnerd0713f92002-09-12 17:06:43 +0000[diff] [blame]839
840<!-- _______________________________________________________________________ -->
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]841<div class="doc_subsubsection">
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]842 <a name="doInitialization_fn">The <tt>doInitialization(Function
843 &amp;)</tt> method</a>
844</div>
845
846<div class="doc_text">
Chris Lattnerd0713f92002-09-12 17:06:43 +0000[diff] [blame]847
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]848<div class="doc_code"><pre>
Chris Lattnerd0713f92002-09-12 17:06:43 +0000[diff] [blame]849 <b>virtual bool</b> doInitialization(Function &amp;F);
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]850</pre></div>
Chris Lattnerd0713f92002-09-12 17:06:43 +0000[diff] [blame]851
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]852<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]853<tt>BasicBlockPass</tt>'s are not allowed to do, but that
854<tt>FunctionPass</tt>'s can. The <tt>doInitialization</tt> method is designed
Reid Spencer1bc19342004-12-11 05:12:57 +0000[diff] [blame]855to do simple initialization that does not depend on the
Chris Lattnerd0713f92002-09-12 17:06:43 +0000[diff] [blame]856BasicBlocks being processed. The <tt>doInitialization</tt> method call is not
857scheduled to overlap with any other pass executions (thus it should be very
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]858fast).</p>
Chris Lattnerd0713f92002-09-12 17:06:43 +0000[diff] [blame]859
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]860</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]861
862<!-- _______________________________________________________________________ -->
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]863<div class="doc_subsubsection">
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]864 <a name="runOnBasicBlock">The <tt>runOnBasicBlock</tt> method</a>
865</div>
866
867<div class="doc_text">
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]868
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]869<div class="doc_code"><pre>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]870 <b>virtual bool</b> runOnBasicBlock(BasicBlock &amp;BB) = 0;
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]871</pre></div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]872
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]873<p>Override this function to do the work of the <tt>BasicBlockPass</tt>. This
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]874function is not allowed to inspect or modify basic blocks other than the
875parameter, and are not allowed to modify the CFG. A true value must be returned
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]876if the basic block is modified.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]877
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]878</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]879
Chris Lattnerd0713f92002-09-12 17:06:43 +0000[diff] [blame]880<!-- _______________________________________________________________________ -->
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]881<div class="doc_subsubsection">
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]882 <a name="doFinalization_fn">The <tt>doFinalization(Function &amp;)</tt>
883 method</a>
884</div>
885
886<div class="doc_text">
Chris Lattnerd0713f92002-09-12 17:06:43 +0000[diff] [blame]887
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]888<div class="doc_code"><pre>
Chris Lattnerd0713f92002-09-12 17:06:43 +0000[diff] [blame]889 <b>virtual bool</b> doFinalization(Function &amp;F);
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]890</pre></div>
Chris Lattnerd0713f92002-09-12 17:06:43 +0000[diff] [blame]891
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]892<p>The <tt>doFinalization</tt> method is an infrequently used method that is
893called when the pass framework has finished calling <a
Chris Lattnerd0713f92002-09-12 17:06:43 +0000[diff] [blame]894href="#runOnBasicBlock"><tt>runOnBasicBlock</tt></a> for every BasicBlock in the
895program being compiled. This can be used to perform per-function
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]896finalization.</p>
Chris Lattnerd0713f92002-09-12 17:06:43 +0000[diff] [blame]897
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]898</div>
Chris Lattnerd0713f92002-09-12 17:06:43 +0000[diff] [blame]899
Brian Gaekecab8b6f2003-07-17 18:53:20 +0000[diff] [blame]900<!-- ======================================================================= -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]901<div class="doc_subsection">
902 <a name="MachineFunctionPass">The <tt>MachineFunctionPass</tt> class</a>
903</div>
Brian Gaekecab8b6f2003-07-17 18:53:20 +0000[diff] [blame]904
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]905<div class="doc_text">
906
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]907<p>A <tt>MachineFunctionPass</tt> is a part of the LLVM code generator that
908executes on the machine-dependent representation of each LLVM function in the
909program. A <tt>MachineFunctionPass</tt> is also a <tt>FunctionPass</tt>, so all
Brian Gaekecab8b6f2003-07-17 18:53:20 +0000[diff] [blame]910the restrictions that apply to a <tt>FunctionPass</tt> also apply to it.
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]911<tt>MachineFunctionPass</tt>es also have additional restrictions. In particular,
912<tt>MachineFunctionPass</tt>es are not allowed to do any of the following:</p>
Brian Gaekecab8b6f2003-07-17 18:53:20 +0000[diff] [blame]913
914<ol>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]915<li>Modify any LLVM Instructions, BasicBlocks or Functions.</li>
916<li>Modify a MachineFunction other than the one currently being processed.</li>
917<li>Add or remove MachineFunctions from the current Module.</li>
918<li>Add or remove global variables from the current Module.</li>
919<li>Maintain state across invocations of <a
920href="#runOnMachineFunction"><tt>runOnMachineFunction</tt></a> (including global
921data)</li>
922</ol>
Brian Gaekecab8b6f2003-07-17 18:53:20 +0000[diff] [blame]923
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]924</div>
Chris Lattnerd0713f92002-09-12 17:06:43 +0000[diff] [blame]925
Brian Gaeke6a33f362003-07-22 20:53:20 +0000[diff] [blame]926<!-- _______________________________________________________________________ -->
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]927<div class="doc_subsubsection">
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]928 <a name="runOnMachineFunction">The <tt>runOnMachineFunction(MachineFunction
929 &amp;MF)</tt> method</a>
930</div>
931
932<div class="doc_text">
Brian Gaeke6a33f362003-07-22 20:53:20 +0000[diff] [blame]933
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]934<div class="doc_code"><pre>
Brian Gaeke6a33f362003-07-22 20:53:20 +0000[diff] [blame]935 <b>virtual bool</b> runOnMachineFunction(MachineFunction &amp;MF) = 0;
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]936</pre></div>
Brian Gaeke6a33f362003-07-22 20:53:20 +0000[diff] [blame]937
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]938<p><tt>runOnMachineFunction</tt> can be considered the main entry point of a
939<tt>MachineFunctionPass</tt>; that is, you should override this method to do the
940work of your <tt>MachineFunctionPass</tt>.</p>
Brian Gaeke6a33f362003-07-22 20:53:20 +0000[diff] [blame]941
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]942<p>The <tt>runOnMachineFunction</tt> method is called on every
Brian Gaeke6a33f362003-07-22 20:53:20 +0000[diff] [blame]943<tt>MachineFunction</tt> in a <tt>Module</tt>, so that the
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]944<tt>MachineFunctionPass</tt> may perform optimizations on the machine-dependent
945representation of the function. If you want to get at the LLVM <tt>Function</tt>
946for the <tt>MachineFunction</tt> you're working on, use
947<tt>MachineFunction</tt>'s <tt>getFunction()</tt> accessor method -- but
948remember, you may not modify the LLVM <tt>Function</tt> or its contents from a
949<tt>MachineFunctionPass</tt>.</p>
950
951</div>
Brian Gaeke6a33f362003-07-22 20:53:20 +0000[diff] [blame]952
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]953<!-- *********************************************************************** -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]954<div class="doc_section">
955 <a name="registration">Pass registration</a>
956</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]957<!-- *********************************************************************** -->
958
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]959<div class="doc_text">
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]960
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]961<p>In the <a href="#basiccode">Hello World</a> example pass we illustrated how
962pass registration works, and discussed some of the reasons that it is used and
963what it does. Here we discuss how and why passes are registered.</p>
964
Chris Lattnerc8603c22006-08-27 23:18:52 +0000[diff] [blame]965<p>As we saw above, passes are registered with the <b><tt>RegisterPass</tt></b>
966template, which requires you to pass at least two
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]967parameters. The first parameter is the name of the pass that is to be used on
968the command line to specify that the pass should be added to a program (for
Chris Lattnerc8603c22006-08-27 23:18:52 +0000[diff] [blame]969example, with <tt>opt</tt> or <tt>bugpoint</tt>). The second argument is the
970name of the pass, which is to be used for the <tt>--help</tt> output of
971programs, as
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]972well as for debug output generated by the <tt>--debug-pass</tt> option.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]973
Chris Lattnerc8603c22006-08-27 23:18:52 +0000[diff] [blame]974<p>If you want your pass to be easily dumpable, you should
975implement the virtual <tt>print</tt> method:</p>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]976
977</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]978
979<!-- _______________________________________________________________________ -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]980<div class="doc_subsubsection">
981 <a name="print">The <tt>print</tt> method</a>
982</div>
983
984<div class="doc_text">
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]985
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]986<div class="doc_code"><pre>
Torok Edwin52790e52008-10-28 17:29:23 +0000[diff] [blame]987 <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]988</pre></div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]989
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]990<p>The <tt>print</tt> method must be implemented by "analyses" in order to print
991a human readable version of the analysis results. This is useful for debugging
992an analysis itself, as well as for other people to figure out how an analysis
Chris Lattnerc8603c22006-08-27 23:18:52 +0000[diff] [blame]993works. Use the <tt>opt -analyze</tt> argument to invoke this method.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]994
Bill Wendling832171c2006-12-07 20:04:42 +0000[diff] [blame]995<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]996and 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]997program that has been analyzed. Note however that this pointer may be null in
998certain circumstances (such as calling the <tt>Pass::dump()</tt> from a
999debugger), so it should only be used to enhance debug output, it should not be
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1000depended on.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1001
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1002</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1003
1004<!-- *********************************************************************** -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1005<div class="doc_section">
1006 <a name="interaction">Specifying interactions between passes</a>
1007</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1008<!-- *********************************************************************** -->
1009
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1010<div class="doc_text">
1011
John Criswell8528e782007-12-03 19:34:25 +0000[diff] [blame]1012<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]1013that passes interact with each other correctly. Because <tt>PassManager</tt>
1014tries to <a href="#passmanager">optimize the execution of passes</a> it must
1015know how the passes interact with each other and what dependencies exist between
1016the various passes. To track this, each pass can declare the set of passes that
1017are required to be executed before the current pass, and the passes which are
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1018invalidated by the current pass.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1019
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1020<p>Typically this functionality is used to require that analysis results are
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1021computed before your pass is run. Running arbitrary transformation passes can
1022invalidate the computed analysis results, which is what the invalidation set
1023specifies. If a pass does not implement the <tt><a
1024href="#getAnalysisUsage">getAnalysisUsage</a></tt> method, it defaults to not
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1025having any prerequisite passes, and invalidating <b>all</b> other passes.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1026
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1027</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1028
1029<!-- _______________________________________________________________________ -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1030<div class="doc_subsubsection">
1031 <a name="getAnalysisUsage">The <tt>getAnalysisUsage</tt> method</a>
1032</div>
1033
1034<div class="doc_text">
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1035
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1036<div class="doc_code"><pre>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1037 <b>virtual void</b> getAnalysisUsage(AnalysisUsage &amp;Info) <b>const</b>;
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1038</pre></div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1039
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1040<p>By implementing the <tt>getAnalysisUsage</tt> method, the required and
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1041invalidated sets may be specified for your transformation. The implementation
1042should fill in the <tt><a
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]1043href="http://llvm.org/doxygen/classllvm_1_1AnalysisUsage.html">AnalysisUsage</a></tt>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1044object with information about which passes are required and not invalidated. To
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]1045do this, a pass may call any of the following methods on the AnalysisUsage
1046object:</p>
1047</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1048
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]1049<!-- _______________________________________________________________________ -->
1050<div class="doc_subsubsection">
1051 <a name="AU::addRequired">The <tt>AnalysisUsage::addRequired&lt;&gt;</tt> and <tt>AnalysisUsage::addRequiredTransitive&lt;&gt;</tt> methods</a>
1052</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1053
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]1054<div class="doc_text">
1055<p>
Reid Spencer1bc19342004-12-11 05:12:57 +0000[diff] [blame]1056If your pass requires a previous pass to be executed (an analysis for example),
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]1057it can use one of these methods to arrange for it to be run before your pass.
1058LLVM has many different types of analyses and passes that can be required,
Reid Spencer1bc19342004-12-11 05:12:57 +0000[diff] [blame]1059spanning the range from <tt>DominatorSet</tt> to <tt>BreakCriticalEdges</tt>.
1060Requiring <tt>BreakCriticalEdges</tt>, for example, guarantees that there will
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]1061be no critical edges in the CFG when your pass has been run.
1062</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1063
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]1064<p>
1065Some analyses chain to other analyses to do their job. For example, an <a
1066href="AliasAnalysis.html">AliasAnalysis</a> implementation is required to <a
1067href="AliasAnalysis.html#chaining">chain</a> to other alias analysis passes. In
1068cases where analyses chain, the <tt>addRequiredTransitive</tt> method should be
1069used instead of the <tt>addRequired</tt> method. This informs the PassManager
1070that the transitively required pass should be alive as long as the requiring
1071pass is.
1072</p>
1073</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1074
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]1075<!-- _______________________________________________________________________ -->
1076<div class="doc_subsubsection">
1077 <a name="AU::addPreserved">The <tt>AnalysisUsage::addPreserved&lt;&gt;</tt> method</a>
1078</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1079
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]1080<div class="doc_text">
1081<p>
1082One of the jobs of the PassManager is to optimize how and when analyses are run.
1083In particular, it attempts to avoid recomputing data unless it needs to. For
1084this reason, passes are allowed to declare that they preserve (i.e., they don't
1085invalidate) an existing analysis if it's available. For example, a simple
Reid Spencer1bc19342004-12-11 05:12:57 +0000[diff] [blame]1086constant folding pass would not modify the CFG, so it can't possibly affect the
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]1087results of dominator analysis. By default, all passes are assumed to invalidate
1088all others.
1089</p>
1090
1091<p>
1092The <tt>AnalysisUsage</tt> class provides several methods which are useful in
1093certain circumstances that are related to <tt>addPreserved</tt>. In particular,
1094the <tt>setPreservesAll</tt> method can be called to indicate that the pass does
1095not modify the LLVM program at all (which is true for analyses), and the
1096<tt>setPreservesCFG</tt> method can be used by transformations that change
1097instructions in the program but do not modify the CFG or terminator instructions
1098(note that this property is implicitly set for <a
1099href="#BasicBlockPass">BasicBlockPass</a>'s).
1100</p>
1101
1102<p>
1103<tt>addPreserved</tt> is particularly useful for transformations like
1104<tt>BreakCriticalEdges</tt>. This pass knows how to update a small set of loop
1105and dominator related analyses if they exist, so it can preserve them, despite
1106the fact that it hacks on the CFG.
1107</p>
1108</div>
1109
1110<!-- _______________________________________________________________________ -->
1111<div class="doc_subsubsection">
1112 <a name="AU::examples">Example implementations of <tt>getAnalysisUsage</tt></a>
1113</div>
1114
1115<div class="doc_text">
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1116
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1117<div class="doc_code"><pre>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1118 <i>// This is an example implementation from an analysis, which does not modify
1119 // the program at all, yet has a prerequisite.</i>
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]1120 <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]1121 AU.setPreservesAll();
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]1122 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]1123 }
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1124</pre></div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1125
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1126<p>and:</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1127
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1128<div class="doc_code"><pre>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1129 <i>// This example modifies the program, but does not modify the CFG</i>
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]1130 <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]1131 AU.setPreservesCFG();
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]1132 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]1133 }
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1134</pre></div>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1135
1136</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1137
1138<!-- _______________________________________________________________________ -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1139<div class="doc_subsubsection">
Duncan Sands1465d612009-01-28 13:14:17 +0000[diff] [blame]1140 <a name="getAnalysis">The <tt>getAnalysis&lt;&gt;</tt> and
1141<tt>getAnalysisIfAvailable&lt;&gt;</tt> methods</a>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1142</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1143
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1144<div class="doc_text">
1145
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]1146<p>The <tt>Pass::getAnalysis&lt;&gt;</tt> method is automatically inherited by
1147your class, providing you with access to the passes that you declared that you
1148required with the <a href="#getAnalysisUsage"><tt>getAnalysisUsage</tt></a>
1149method. It takes a single template argument that specifies which pass class you
1150want, and returns a reference to that pass. For example:</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1151
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1152<div class="doc_code"><pre>
Chris Lattnera5776302004-03-17 21:33:32 +0000[diff] [blame]1153 bool LICM::runOnFunction(Function &amp;F) {
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]1154 LoopInfo &amp;LI = getAnalysis&lt;LoopInfo&gt;();
1155 ...
1156 }
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1157</pre></div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1158
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1159<p>This method call returns a reference to the pass desired. You may get a
1160runtime assertion failure if you attempt to get an analysis that you did not
1161declare as required in your <a
1162href="#getAnalysisUsage"><tt>getAnalysisUsage</tt></a> implementation. This
1163method can be called by your <tt>run*</tt> method implementation, or by any
Devang Patel3c1ca0b2007-04-16 21:28:14 +0000[diff] [blame]1164other local method invoked by your <tt>run*</tt> method.
1165
1166A module level pass can use function level analysis info using this interface.
1167For example:</p>
1168
1169<div class="doc_code"><pre>
1170 bool ModuleLevelPass::runOnModule(Module &amp;M) {
1171 ...
Devang Patelf23de112007-04-17 00:17:11 +0000[diff] [blame]1172 DominatorTree &amp;DT = getAnalysis&lt;DominatorTree&gt;(Func);
Devang Patel3c1ca0b2007-04-16 21:28:14 +0000[diff] [blame]1173 ...
1174 }
1175</pre></div>
1176
Chris Lattnerb5c87f62007-05-18 05:36:14 +0000[diff] [blame]1177<p>In above example, runOnFunction for DominatorTree is called by pass manager
Devang Patel3c1ca0b2007-04-16 21:28:14 +0000[diff] [blame]1178before returning a reference to the desired pass.</p>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1179
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]1180<p>
1181If your pass is capable of updating analyses if they exist (e.g.,
1182<tt>BreakCriticalEdges</tt>, as described above), you can use the
Duncan Sands1465d612009-01-28 13:14:17 +0000[diff] [blame]1183<tt>getAnalysisIfAvailable</tt> method, which returns a pointer to the analysis
1184if it is active. For example:</p>
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]1185
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1186<div class="doc_code"><pre>
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]1187 ...
Duncan Sands1465d612009-01-28 13:14:17 +0000[diff] [blame]1188 if (DominatorSet *DS = getAnalysisIfAvailable&lt;DominatorSet&gt;()) {
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]1189 <i>// A DominatorSet is active. This code will update it.</i>
1190 }
1191 ...
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1192</pre></div>
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]1193
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1194</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1195
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1196<!-- *********************************************************************** -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1197<div class="doc_section">
1198 <a name="analysisgroup">Implementing Analysis Groups</a>
1199</div>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1200<!-- *********************************************************************** -->
1201
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1202<div class="doc_text">
1203
Chris Lattnerb7632282007-11-16 05:32:05 +0000[diff] [blame]1204<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]1205used, 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]1206fancier. All of the pass relationships that we have seen so far are very
1207simple: one pass depends on one other specific pass to be run before it can run.
1208For many applications, this is great, for others, more flexibility is
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1209required.</p>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1210
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1211<p>In particular, some analyses are defined such that there is a single simple
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1212interface to the analysis results, but multiple ways of calculating them.
1213Consider alias analysis for example. The most trivial alias analysis returns
1214"may alias" for any alias query. The most sophisticated analysis a
1215flow-sensitive, context-sensitive interprocedural analysis that can take a
1216significant amount of time to execute (and obviously, there is a lot of room
1217between these two extremes for other implementations). To cleanly support
1218situations like this, the LLVM Pass Infrastructure supports the notion of
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1219Analysis Groups.</p>
1220
1221</div>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1222
1223<!-- _______________________________________________________________________ -->
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]1224<div class="doc_subsubsection">
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1225 <a name="agconcepts">Analysis Group Concepts</a>
1226</div>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1227
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1228<div class="doc_text">
1229
1230<p>An Analysis Group is a single simple interface that may be implemented by
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1231multiple different passes. Analysis Groups can be given human readable names
1232just like passes, but unlike passes, they need not derive from the <tt>Pass</tt>
1233class. An analysis group may have one or more implementations, one of which is
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1234the "default" implementation.</p>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1235
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1236<p>Analysis groups are used by client passes just like other passes are: the
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1237<tt>AnalysisUsage::addRequired()</tt> and <tt>Pass::getAnalysis()</tt> methods.
1238In order to resolve this requirement, the <a href="#passmanager">PassManager</a>
1239scans the available passes to see if any implementations of the analysis group
1240are available. If none is available, the default implementation is created for
1241the pass to use. All standard rules for <A href="#interaction">interaction
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1242between passes</a> still apply.</p>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1243
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1244<p>Although <a href="#registration">Pass Registration</a> is optional for normal
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1245passes, all analysis group implementations must be registered, and must use the
1246<A href="#registerag"><tt>RegisterAnalysisGroup</tt></a> template to join the
1247implementation pool. Also, a default implementation of the interface
1248<b>must</b> be registered with <A
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1249href="#registerag"><tt>RegisterAnalysisGroup</tt></a>.</p>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1250
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1251<p>As a concrete example of an Analysis Group in action, consider the <a
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]1252href="http://llvm.org/doxygen/classllvm_1_1AliasAnalysis.html">AliasAnalysis</a>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1253analysis group. The default implementation of the alias analysis interface (the
1254<tt><a
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]1255href="http://llvm.org/doxygen/structBasicAliasAnalysis.html">basicaa</a></tt>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1256pass) just does a few simple checks that don't require significant analysis to
1257compute (such as: two different globals can never alias each other, etc).
1258Passes that use the <tt><a
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]1259href="http://llvm.org/doxygen/classllvm_1_1AliasAnalysis.html">AliasAnalysis</a></tt>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1260interface (for example the <tt><a
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]1261href="http://llvm.org/doxygen/structGCSE.html">gcse</a></tt> pass), do
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1262not care which implementation of alias analysis is actually provided, they just
1263use the designated interface.</p>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1264
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1265<p>From the user's perspective, commands work just like normal. Issuing the
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1266command '<tt>opt -gcse ...</tt>' will cause the <tt>basicaa</tt> class to be
1267instantiated and added to the pass sequence. Issuing the command '<tt>opt
1268-somefancyaa -gcse ...</tt>' will cause the <tt>gcse</tt> pass to use the
1269<tt>somefancyaa</tt> alias analysis (which doesn't actually exist, it's just a
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1270hypothetical example) instead.</p>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1271
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1272</div>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1273
1274<!-- _______________________________________________________________________ -->
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]1275<div class="doc_subsubsection">
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1276 <a name="registerag">Using <tt>RegisterAnalysisGroup</tt></a>
1277</div>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1278
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1279<div class="doc_text">
1280
1281<p>The <tt>RegisterAnalysisGroup</tt> template is used to register the analysis
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1282group itself as well as add pass implementations to the analysis group. First,
1283an analysis should be registered, with a human readable name provided for it.
1284Unlike registration of passes, there is no command line argument to be specified
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1285for the Analysis Group Interface itself, because it is "abstract":</p>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1286
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1287<div class="doc_code"><pre>
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]1288 <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]1289</pre></div>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1290
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1291<p>Once the analysis is registered, passes can declare that they are valid
1292implementations of the interface by using the following code:</p>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1293
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1294<div class="doc_code"><pre>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1295<b>namespace</b> {
1296 //<i> Analysis Group implementations <b>must</b> be registered normally...</i>
Chris Lattnerc8603c22006-08-27 23:18:52 +0000[diff] [blame]1297 RegisterPass&lt;FancyAA&gt;
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1298 B("<i>somefancyaa</i>", "<i>A more complex alias analysis implementation</i>");
1299
1300 //<i> Declare that we implement the AliasAnalysis interface</i>
Chris Lattnerdc877252006-08-28 00:45:38 +0000[diff] [blame]1301 RegisterAnalysisGroup&lt;<a href="http://llvm.org/doxygen/classllvm_1_1AliasAnalysis.html">AliasAnalysis</a>&gt; C(B);
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1302}
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1303</pre></div>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1304
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1305<p>This just shows a class <tt>FancyAA</tt> that is registered normally, then
1306uses the <tt>RegisterAnalysisGroup</tt> template to "join" the <tt><a
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]1307href="http://llvm.org/doxygen/classllvm_1_1AliasAnalysis.html">AliasAnalysis</a></tt>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1308analysis group. Every implementation of an analysis group should join using
1309this template. A single pass may join multiple different analysis groups with
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1310no problem.</p>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1311
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1312<div class="doc_code"><pre>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1313<b>namespace</b> {
1314 //<i> Analysis Group implementations <b>must</b> be registered normally...</i>
Chris Lattnerc8603c22006-08-27 23:18:52 +0000[diff] [blame]1315 RegisterPass&lt;<a href="http://llvm.org/doxygen/structBasicAliasAnalysis.html">BasicAliasAnalysis</a>&gt;
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1316 D("<i>basicaa</i>", "<i>Basic Alias Analysis (default AA impl)</i>");
1317
1318 //<i> Declare that we implement the AliasAnalysis interface</i>
Chris Lattnerdc877252006-08-28 00:45:38 +0000[diff] [blame]1319 RegisterAnalysisGroup&lt;<a href="http://llvm.org/doxygen/classllvm_1_1AliasAnalysis.html">AliasAnalysis</a>, <b>true</b>&gt; E(D);
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1320}
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1321</pre></div>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1322
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1323<p>Here we show how the default implementation is specified (using the extra
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1324argument to the <tt>RegisterAnalysisGroup</tt> template). There must be exactly
1325one default implementation available at all times for an Analysis Group to be
Devang Patel2397f8d2007-06-20 18:51:14 +0000[diff] [blame]1326used. Only default implementation can derive from <tt>ImmutablePass</tt>.
1327Here we declare that the
1328 <tt><a href="http://llvm.org/doxygen/structBasicAliasAnalysis.html">BasicAliasAnalysis</a></tt>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1329pass is the default implementation for the interface.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1330
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1331</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1332
1333<!-- *********************************************************************** -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1334<div class="doc_section">
Tanya Lattnerd5383652004-11-19 01:25:14 +0000[diff] [blame]1335 <a name="passStatistics">Pass Statistics</a>
1336</div>
1337<!-- *********************************************************************** -->
1338
1339<div class="doc_text">
Tanya Lattner05f8d5f2004-11-19 01:26:37 +0000[diff] [blame]1340<p>The <a
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]1341href="http://llvm.org/doxygen/Statistic_8h-source.html"><tt>Statistic</tt></a>
John Criswell0b1010e2005-11-28 23:25:41 +0000[diff] [blame]1342class is designed to be an easy way to expose various success
Tanya Lattnerd5383652004-11-19 01:25:14 +0000[diff] [blame]1343metrics from passes. These statistics are printed at the end of a
1344run, when the -stats command line option is enabled on the command
Tanya Lattner05f8d5f2004-11-19 01:26:37 +0000[diff] [blame]1345line. 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]1346
1347</div>
1348
1349
1350<!-- *********************************************************************** -->
1351<div class="doc_section">
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1352 <a name="passmanager">What PassManager does</a>
1353</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1354<!-- *********************************************************************** -->
1355
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1356<div class="doc_text">
1357
1358<p>The <a
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]1359href="http://llvm.org/doxygen/PassManager_8h-source.html"><tt>PassManager</tt></a>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1360<a
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]1361href="http://llvm.org/doxygen/classllvm_1_1PassManager.html">class</a>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1362takes a list of passes, ensures their <a href="#interaction">prerequisites</a>
1363are set up correctly, and then schedules passes to run efficiently. All of the
1364LLVM tools that run passes use the <tt>PassManager</tt> for execution of these
1365passes.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1366
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1367<p>The <tt>PassManager</tt> does two main things to try to reduce the execution
1368time of a series of passes:</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1369
1370<ol>
1371<li><b>Share analysis results</b> - The PassManager attempts to avoid
1372recomputing analysis results as much as possible. This means keeping track of
1373which analyses are available already, which analyses get invalidated, and which
1374analyses are needed to be run for a pass. An important part of work is that the
1375<tt>PassManager</tt> tracks the exact lifetime of all analysis results, allowing
1376it to <a href="#releaseMemory">free memory</a> allocated to holding analysis
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1377results as soon as they are no longer needed.</li>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1378
1379<li><b>Pipeline the execution of passes on the program</b> - The
1380<tt>PassManager</tt> attempts to get better cache and memory usage behavior out
1381of a series of passes by pipelining the passes together. This means that, given
1382a series of consequtive <a href="#FunctionPass"><tt>FunctionPass</tt></a>'s, it
1383will execute all of the <a href="#FunctionPass"><tt>FunctionPass</tt></a>'s on
1384the first function, then all of the <a
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1385href="#FunctionPass"><tt>FunctionPass</tt></a>es on the second function,
1386etc... until the entire program has been run through the passes.
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1387
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1388<p>This improves the cache behavior of the compiler, because it is only touching
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1389the LLVM program representation for a single function at a time, instead of
1390traversing the entire program. It reduces the memory consumption of compiler,
1391because, for example, only one <a
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]1392href="http://llvm.org/doxygen/classllvm_1_1DominatorSet.html"><tt>DominatorSet</tt></a>
John Criswell9795bb82007-12-10 20:26:29 +0000[diff] [blame]1393needs to be calculated at a time. This also makes it possible to implement
1394some <a
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1395href="#SMP">interesting enhancements</a> in the future.</p></li>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1396
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1397</ol>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1398
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1399<p>The effectiveness of the <tt>PassManager</tt> is influenced directly by how
1400much information it has about the behaviors of the passes it is scheduling. For
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1401example, the "preserved" set is intentionally conservative in the face of an
1402unimplemented <a href="#getAnalysisUsage"><tt>getAnalysisUsage</tt></a> method.
1403Not implementing when it should be implemented will have the effect of not
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1404allowing any analysis results to live across the execution of your pass.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1405
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1406<p>The <tt>PassManager</tt> class exposes a <tt>--debug-pass</tt> command line
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1407options that is useful for debugging pass execution, seeing how things work, and
1408diagnosing when you should be preserving more analyses than you currently are
1409(To get information about all of the variants of the <tt>--debug-pass</tt>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1410option, just type '<tt>opt --help-hidden</tt>').</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1411
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1412<p>By using the <tt>--debug-pass=Structure</tt> option, for example, we can see
1413how our <a href="#basiccode">Hello World</a> pass interacts with other passes.
1414Lets try it out with the <tt>gcse</tt> and <tt>licm</tt> passes:</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1415
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1416<div class="doc_code"><pre>
Reid Spencer7fa6d522005-01-11 05:16:23 +0000[diff] [blame]1417$ opt -load ../../../Debug/lib/Hello.so -gcse -licm --debug-pass=Structure &lt; hello.bc &gt; /dev/null
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1418Module Pass Manager
1419 Function Pass Manager
1420 Dominator Set Construction
1421 Immediate Dominators Construction
1422 Global Common Subexpression Elimination
1423-- Immediate Dominators Construction
1424-- Global Common Subexpression Elimination
1425 Natural Loop Construction
1426 Loop Invariant Code Motion
1427-- Natural Loop Construction
1428-- Loop Invariant Code Motion
1429 Module Verifier
1430-- Dominator Set Construction
1431-- Module Verifier
Gabor Greif04367bf2007-07-06 22:07:22 +0000[diff] [blame]1432 Bitcode Writer
1433--Bitcode Writer
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1434</pre></div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1435
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1436<p>This output shows us when passes are constructed and when the analysis
1437results are known to be dead (prefixed with '<tt>--</tt>'). Here we see that
1438GCSE uses dominator and immediate dominator information to do its job. The LICM
1439pass uses natural loop information, which uses dominator sets, but not immediate
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1440dominators. Because immediate dominators are no longer useful after the GCSE
1441pass, it is immediately destroyed. The dominator sets are then reused to
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1442compute natural loop information, which is then used by the LICM pass.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1443
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1444<p>After the LICM pass, the module verifier runs (which is automatically added
1445by the '<tt>opt</tt>' tool), which uses the dominator set to check that the
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1446resultant LLVM code is well formed. After it finishes, the dominator set
1447information is destroyed, after being computed once, and shared by three
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1448passes.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1449
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1450<p>Lets see how this changes when we run the <a href="#basiccode">Hello
1451World</a> pass in between the two passes:</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1452
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1453<div class="doc_code"><pre>
Reid Spencer7fa6d522005-01-11 05:16:23 +0000[diff] [blame]1454$ opt -load ../../../Debug/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]1455Module Pass Manager
1456 Function Pass Manager
1457 Dominator Set Construction
1458 Immediate Dominators Construction
1459 Global Common Subexpression Elimination
1460<b>-- Dominator Set Construction</b>
1461-- Immediate Dominators Construction
1462-- Global Common Subexpression Elimination
1463<b> Hello World Pass
1464-- Hello World Pass
1465 Dominator Set Construction</b>
1466 Natural Loop Construction
1467 Loop Invariant Code Motion
1468-- Natural Loop Construction
1469-- Loop Invariant Code Motion
1470 Module Verifier
1471-- Dominator Set Construction
1472-- Module Verifier
Gabor Greif04367bf2007-07-06 22:07:22 +0000[diff] [blame]1473 Bitcode Writer
1474--Bitcode Writer
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1475Hello: __main
1476Hello: puts
1477Hello: main
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1478</pre></div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1479
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1480<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]1481Dominator Set pass, even though it doesn't modify the code at all! To fix this,
1482we need to add the following <a
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1483href="#getAnalysisUsage"><tt>getAnalysisUsage</tt></a> method to our pass:</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1484
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1485<div class="doc_code"><pre>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1486 <i>// We don't modify the program, so we preserve all analyses</i>
1487 <b>virtual void</b> getAnalysisUsage(AnalysisUsage &amp;AU) <b>const</b> {
1488 AU.setPreservesAll();
1489 }
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1490</pre></div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1491
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1492<p>Now when we run our pass, we get this output:</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1493
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1494<div class="doc_code"><pre>
Reid Spencer7fa6d522005-01-11 05:16:23 +0000[diff] [blame]1495$ opt -load ../../../Debug/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]1496Pass Arguments: -gcse -hello -licm
1497Module Pass Manager
1498 Function Pass Manager
1499 Dominator Set Construction
1500 Immediate Dominators Construction
1501 Global Common Subexpression Elimination
1502-- Immediate Dominators Construction
1503-- Global Common Subexpression Elimination
1504 Hello World Pass
1505-- Hello World Pass
1506 Natural Loop Construction
1507 Loop Invariant Code Motion
1508-- Loop Invariant Code Motion
1509-- Natural Loop Construction
1510 Module Verifier
1511-- Dominator Set Construction
1512-- Module Verifier
Gabor Greif04367bf2007-07-06 22:07:22 +0000[diff] [blame]1513 Bitcode Writer
1514--Bitcode Writer
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1515Hello: __main
1516Hello: puts
1517Hello: main
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1518</pre></div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1519
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1520<p>Which shows that we don't accidentally invalidate dominator information
1521anymore, and therefore do not have to compute it twice.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1522
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1523</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1524
1525<!-- _______________________________________________________________________ -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1526<div class="doc_subsubsection">
1527 <a name="releaseMemory">The <tt>releaseMemory</tt> method</a>
1528</div>
1529
1530<div class="doc_text">
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1531
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1532<div class="doc_code"><pre>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1533 <b>virtual void</b> releaseMemory();
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1534</pre></div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1535
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1536<p>The <tt>PassManager</tt> automatically determines when to compute analysis
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1537results, and how long to keep them around for. Because the lifetime of the pass
1538object itself is effectively the entire duration of the compilation process, we
1539need some way to free analysis results when they are no longer useful. The
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1540<tt>releaseMemory</tt> virtual method is the way to do this.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1541
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1542<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]1543amount of state (for use by another pass which "requires" your pass and uses the
1544<a href="#getAnalysis">getAnalysis</a> method) you should implement
Dan Gohmand87c9e32009-06-15 18:22:49 +0000[diff] [blame]1545<tt>releaseMemory</tt> to, well, release the memory allocated to maintain this
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1546internal state. This method is called after the <tt>run*</tt> method for the
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1547class, before the next call of <tt>run*</tt> in your pass.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1548
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1549</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1550
1551<!-- *********************************************************************** -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1552<div class="doc_section">
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1553 <a name="registering">Registering dynamically loaded passes</a>
1554</div>
1555<!-- *********************************************************************** -->
1556
1557<div class="doc_text">
1558
1559<p><i>Size matters</i> when constructing production quality tools using llvm,
1560both for the purposes of distribution, and for regulating the resident code size
1561when running on the target system. Therefore, it becomes desirable to
1562selectively use some passes, while omitting others and maintain the flexibility
1563to change configurations later on. You want to be able to do all this, and,
1564provide feedback to the user. This is where pass registration comes into
1565play.</p>
1566
1567<p>The fundamental mechanisms for pass registration are the
1568<tt>MachinePassRegistry</tt> class and subclasses of
1569<tt>MachinePassRegistryNode</tt>.</p>
1570
1571<p>An instance of <tt>MachinePassRegistry</tt> is used to maintain a list of
1572<tt>MachinePassRegistryNode</tt> objects. This instance maintains the list and
1573communicates additions and deletions to the command line interface.</p>
1574
1575<p>An instance of <tt>MachinePassRegistryNode</tt> subclass is used to maintain
1576information provided about a particular pass. This information includes the
1577command line name, the command help string and the address of the function used
1578to create an instance of the pass. A global static constructor of one of these
1579instances <i>registers</i> with a corresponding <tt>MachinePassRegistry</tt>,
1580the static destructor <i>unregisters</i>. Thus a pass that is statically linked
1581in the tool will be registered at start up. A dynamically loaded pass will
1582register on load and unregister at unload.</p>
1583
1584</div>
1585
1586<!-- _______________________________________________________________________ -->
1587<div class="doc_subsection">
1588 <a name="registering_existing">Using existing registries</a>
1589</div>
1590
1591<div class="doc_text">
1592
1593<p>There are predefined registries to track instruction scheduling
1594(<tt>RegisterScheduler</tt>) and register allocation (<tt>RegisterRegAlloc</tt>)
1595machine passes. Here we will describe how to <i>register</i> a register
1596allocator machine pass.</p>
1597
1598<p>Implement your register allocator machine pass. In your register allocator
1599.cpp file add the following include;</p>
1600
1601<div class="doc_code"><pre>
Chris Lattner8f652eb2006-08-11 16:37:02 +0000[diff] [blame]1602 #include "llvm/CodeGen/RegAllocRegistry.h"
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1603</pre></div>
1604
1605<p>Also in your register allocator .cpp file, define a creator function in the
1606form; </p>
1607
1608<div class="doc_code"><pre>
1609 FunctionPass *createMyRegisterAllocator() {
1610 return new MyRegisterAllocator();
1611 }
1612</pre></div>
1613
1614<p>Note that the signature of this function should match the type of
1615<tt>RegisterRegAlloc::FunctionPassCtor</tt>. In the same file add the
1616"installing" declaration, in the form;</p>
1617
1618<div class="doc_code"><pre>
1619 static RegisterRegAlloc myRegAlloc("myregalloc",
1620 " my register allocator help string",
1621 createMyRegisterAllocator);
1622</pre></div>
1623
1624<p>Note the two spaces prior to the help string produces a tidy result on the
1625--help query.</p>
1626
1627<div class="doc_code"><pre>
1628$ llc --help
1629 ...
1630 -regalloc - Register allocator to use: (default = linearscan)
1631 =linearscan - linear scan register allocator
1632 =local - local register allocator
1633 =simple - simple register allocator
1634 =myregalloc - my register allocator help string
1635 ...
1636</pre></div>
1637
1638<p>And that's it. The user is now free to use <tt>-regalloc=myregalloc</tt> as
1639an option. Registering instruction schedulers is similar except use the
Chris Lattner8f652eb2006-08-11 16:37:02 +0000[diff] [blame]1640<tt>RegisterScheduler</tt> class. Note that the
1641<tt>RegisterScheduler::FunctionPassCtor</tt> is significantly different from
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1642<tt>RegisterRegAlloc::FunctionPassCtor</tt>.</p>
1643
1644<p>To force the load/linking of your register allocator into the llc/lli tools,
1645add your creator function's global declaration to "Passes.h" and add a "pseudo"
1646call line to <tt>llvm/Codegen/LinkAllCodegenComponents.h</tt>.</p>
1647
1648</div>
1649
1650
1651<!-- _______________________________________________________________________ -->
1652<div class="doc_subsection">
1653 <a name="registering_new">Creating new registries</a>
1654</div>
1655
1656<div class="doc_text">
1657
1658<p>The easiest way to get started is to clone one of the existing registries; we
1659recommend <tt>llvm/CodeGen/RegAllocRegistry.h</tt>. The key things to modify
1660are the class name and the <tt>FunctionPassCtor</tt> type.</p>
1661
1662<p>Then you need to declare the registry. Example: if your pass registry is
1663<tt>RegisterMyPasses</tt> then define;</p>
1664
1665<div class="doc_code"><pre>
1666MachinePassRegistry RegisterMyPasses::Registry;
1667</pre></div>
1668
1669<p>And finally, declare the command line option for your passes. Example:</p>
1670
1671<div class="doc_code"><pre>
1672 cl::opt&lt;RegisterMyPasses::FunctionPassCtor, false,
Dan Gohman364a39f2008-10-14 17:00:38 +0000[diff] [blame]1673 RegisterPassParser&lt;RegisterMyPasses&gt; &gt;
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1674 MyPassOpt("mypass",
1675 cl::init(&amp;createDefaultMyPass),
1676 cl::desc("my pass option help"));
1677</pre></div>
1678
1679<p>Here the command option is "mypass", with createDefaultMyPass as the default
1680creator.</p>
1681
1682</div>
1683
1684<!-- *********************************************************************** -->
1685<div class="doc_section">
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1686 <a name="debughints">Using GDB with dynamically loaded passes</a>
1687</div>
Chris Lattner480e2ef2002-09-06 02:02:58 +0000[diff] [blame]1688<!-- *********************************************************************** -->
1689
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1690<div class="doc_text">
1691
1692<p>Unfortunately, using GDB with dynamically loaded passes is not as easy as it
Chris Lattner480e2ef2002-09-06 02:02:58 +0000[diff] [blame]1693should be. First of all, you can't set a breakpoint in a shared object that has
1694not been loaded yet, and second of all there are problems with inlined functions
1695in shared objects. Here are some suggestions to debugging your pass with
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1696GDB.</p>
Chris Lattner480e2ef2002-09-06 02:02:58 +0000[diff] [blame]1697
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1698<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]1699transformation invoked by <tt>opt</tt>, although nothing described here depends
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1700on that.</p>
1701
1702</div>
Chris Lattner480e2ef2002-09-06 02:02:58 +0000[diff] [blame]1703
1704<!-- _______________________________________________________________________ -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1705<div class="doc_subsubsection">
1706 <a name="breakpoint">Setting a breakpoint in your pass</a>
1707</div>
Chris Lattner480e2ef2002-09-06 02:02:58 +0000[diff] [blame]1708
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1709<div class="doc_text">
1710
1711<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]1712
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1713<div class="doc_code"><pre>
Chris Lattner480e2ef2002-09-06 02:02:58 +0000[diff] [blame]1714$ <b>gdb opt</b>
1715GNU gdb 5.0
1716Copyright 2000 Free Software Foundation, Inc.
1717GDB is free software, covered by the GNU General Public License, and you are
1718welcome to change it and/or distribute copies of it under certain conditions.
1719Type "show copying" to see the conditions.
1720There is absolutely no warranty for GDB. Type "show warranty" for details.
1721This GDB was configured as "sparc-sun-solaris2.6"...
1722(gdb)
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1723</pre></div>
Chris Lattner480e2ef2002-09-06 02:02:58 +0000[diff] [blame]1724
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1725<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]1726time to load. Be patient. Since we cannot set a breakpoint in our pass yet
1727(the shared object isn't loaded until runtime), we must execute the process, and
1728have it stop before it invokes our pass, but after it has loaded the shared
1729object. The most foolproof way of doing this is to set a breakpoint in
1730<tt>PassManager::run</tt> and then run the process with the arguments you
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1731want:</p>
Chris Lattner480e2ef2002-09-06 02:02:58 +0000[diff] [blame]1732
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1733<div class="doc_code"><pre>
Reid Spencer22a9e5b2006-09-28 16:53:47 +0000[diff] [blame]1734(gdb) <b>break llvm::PassManager::run</b>
Chris Lattner480e2ef2002-09-06 02:02:58 +0000[diff] [blame]1735Breakpoint 1 at 0x2413bc: file Pass.cpp, line 70.
Chris Lattner4c376ea2005-04-21 04:52:37 +0000[diff] [blame]1736(gdb) <b>run test.bc -load $(LLVMTOP)/llvm/Debug/lib/[libname].so -[passoption]</b>
1737Starting program: opt test.bc -load $(LLVMTOP)/llvm/Debug/lib/[libname].so -[passoption]
Chris Lattner480e2ef2002-09-06 02:02:58 +0000[diff] [blame]1738Breakpoint 1, PassManager::run (this=0xffbef174, M=@0x70b298) at Pass.cpp:70
173970 bool PassManager::run(Module &amp;M) { return PM-&gt;run(M); }
1740(gdb)
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1741</pre></div>
Chris Lattner480e2ef2002-09-06 02:02:58 +0000[diff] [blame]1742
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1743<p>Once the <tt>opt</tt> stops in the <tt>PassManager::run</tt> method you are
1744now free to set breakpoints in your pass so that you can trace through execution
1745or do other standard debugging stuff.</p>
Chris Lattner480e2ef2002-09-06 02:02:58 +0000[diff] [blame]1746
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1747</div>
Chris Lattner480e2ef2002-09-06 02:02:58 +0000[diff] [blame]1748
1749<!-- _______________________________________________________________________ -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1750<div class="doc_subsubsection">
1751 <a name="debugmisc">Miscellaneous Problems</a>
1752</div>
Chris Lattner480e2ef2002-09-06 02:02:58 +0000[diff] [blame]1753
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1754<div class="doc_text">
1755
1756<p>Once you have the basics down, there are a couple of problems that GDB has,
1757some with solutions, some without.</p>
Chris Lattner480e2ef2002-09-06 02:02:58 +0000[diff] [blame]1758
1759<ul>
1760<li>Inline functions have bogus stack information. In general, GDB does a
1761pretty good job getting stack traces and stepping through inline functions.
1762When a pass is dynamically loaded however, it somehow completely loses this
1763capability. The only solution I know of is to de-inline a function (move it
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1764from the body of a class to a .cpp file).</li>
Chris Lattner480e2ef2002-09-06 02:02:58 +0000[diff] [blame]1765
1766<li>Restarting the program breaks breakpoints. After following the information
1767above, you have succeeded in getting some breakpoints planted in your pass. Nex
1768thing you know, you restart the program (i.e., you type '<tt>run</tt>' again),
1769and you start getting errors about breakpoints being unsettable. The only way I
1770have found to "fix" this problem is to <tt>delete</tt> the breakpoints that are
1771already set in your pass, run the program, and re-set the breakpoints once
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1772execution stops in <tt>PassManager::run</tt>.</li>
Chris Lattner480e2ef2002-09-06 02:02:58 +0000[diff] [blame]1773
1774</ul>
1775
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1776<p>Hopefully these tips will help with common case debugging situations. If
1777you'd like to contribute some tips of your own, just contact <a
1778href="mailto:sabre@nondot.org">Chris</a>.</p>
Chris Lattner480e2ef2002-09-06 02:02:58 +0000[diff] [blame]1779
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1780</div>
Chris Lattner480e2ef2002-09-06 02:02:58 +0000[diff] [blame]1781
1782<!-- *********************************************************************** -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1783<div class="doc_section">
1784 <a name="future">Future extensions planned</a>
1785</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1786<!-- *********************************************************************** -->
1787
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1788<div class="doc_text">
1789
1790<p>Although the LLVM Pass Infrastructure is very capable as it stands, and does
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1791some 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]1792where we are going:</p>
1793
1794</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1795
1796<!-- _______________________________________________________________________ -->
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]1797<div class="doc_subsubsection">
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1798 <a name="SMP">Multithreaded LLVM</a>
1799</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1800
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1801<div class="doc_text">
1802
1803<p>Multiple CPU machines are becoming more common and compilation can never be
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1804fast enough: obviously we should allow for a multithreaded compiler. Because of
1805the semantics defined for passes above (specifically they cannot maintain state
1806across invocations of their <tt>run*</tt> methods), a nice clean way to
1807implement a multithreaded compiler would be for the <tt>PassManager</tt> class
Misha Brukmanbc0e9982003-07-14 17:20:40 +0000[diff] [blame]1808to create multiple instances of each pass object, and allow the separate
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1809instances to be hacking on different parts of the program at the same time.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1810
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1811<p>This implementation would prevent each of the passes from having to implement
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1812multithreaded constructs, requiring only the LLVM core to have locking in a few
1813places (for global resources). Although this is a simple extension, we simply
1814haven't had time (or multiprocessor machines, thus a reason) to implement this.
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1815Despite that, we have kept the LLVM passes SMP ready, and you should too.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1816
Chris Lattnerb5c87f62007-05-18 05:36:14 +0000[diff] [blame]1817</div>
1818
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1819<!-- *********************************************************************** -->
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