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gerrit-public.fairphone.software / fp2-dev / platform / external / llvm / d87c9e35d10d0b7b01bcd618f2cf083ce838d1d8 / . / 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>
Devang Patel3c1ca0b2007-04-16 21:28:14 +0000[diff] [blame]494subclasses, no optimization can be done for their execution. A module pass
495can use function level passes (e.g. dominators) using getAnalysis interface
Devang Patel00f1c402008-11-06 19:47:49 +0000[diff] [blame]496<tt> getAnalysis&lt;DominatorTree&gt;(Function)</tt>, if the function pass
497does not require any module passes. </p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]498
Chris Lattnerf6278922004-09-20 04:36:29 +0000[diff] [blame]499<p>To write a correct <tt>ModulePass</tt> subclass, derive from
500<tt>ModulePass</tt> and overload the <tt>runOnModule</tt> method with the
501following signature:</p>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]502
503</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]504
505<!-- _______________________________________________________________________ -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]506<div class="doc_subsubsection">
Chris Lattnerf6278922004-09-20 04:36:29 +0000[diff] [blame]507 <a name="runOnModule">The <tt>runOnModule</tt> method</a>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]508</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]509
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]510<div class="doc_text">
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]511
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]512<div class="doc_code"><pre>
Chris Lattnerf6278922004-09-20 04:36:29 +0000[diff] [blame]513 <b>virtual bool</b> runOnModule(Module &amp;M) = 0;
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]514</pre></div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]515
John Criswell2382ff72005-07-15 19:25:12 +0000[diff] [blame]516<p>The <tt>runOnModule</tt> method performs the interesting work of the pass.
517It should return true if the module was modified by the transformation and
518false otherwise.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]519
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]520</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]521
522<!-- ======================================================================= -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]523<div class="doc_subsection">
Chris Lattner8fdb2462004-09-18 06:39:35 +0000[diff] [blame]524 <a name="CallGraphSCCPass">The <tt>CallGraphSCCPass</tt> class</a>
525</div>
526
527<div class="doc_text">
528
529<p>The "<tt><a
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]530href="http://llvm.org/doxygen/classllvm_1_1CallGraphSCCPass.html">CallGraphSCCPass</a></tt>"
Chris Lattner8fdb2462004-09-18 06:39:35 +0000[diff] [blame]531is used by passes that need to traverse the program bottom-up on the call graph
532(callees before callers). Deriving from CallGraphSCCPass provides some
533mechanics for building and traversing the CallGraph, but also allows the system
534to optimize execution of CallGraphSCCPass's. If your pass meets the
535requirements outlined below, and doesn't meet the requirements of a <tt><a
536href="#FunctionPass">FunctionPass</a></tt> or <tt><a
537href="#BasicBlockPass">BasicBlockPass</a></tt>, you should derive from
538<tt>CallGraphSCCPass</tt>.</p>
539
540<p><b>TODO</b>: explain briefly what SCC, Tarjan's algo, and B-U mean.</p>
541
542<p>To be explicit, <tt>CallGraphSCCPass</tt> subclasses are:</p>
543
544<ol>
545
546<li>... <em>not allowed</em> to modify any <tt>Function</tt>s that are not in
547the current SCC.</li>
548
Tanya Lattner18aad232007-06-07 16:44:52 +0000[diff] [blame]549<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]550current SCC and the direct callees of the SCC.</li>
551
552<li>... <em>required</em> to preserve the current CallGraph object, updating it
553to reflect any changes made to the program.</li>
554
555<li>... <em>not allowed</em> to add or remove SCC's from the current Module,
556though they may change the contents of an SCC.</li>
557
558<li>... <em>allowed</em> to add or remove global variables from the current
559Module.</li>
560
561<li>... <em>allowed</em> to maintain state across invocations of
562 <a href="#runOnSCC"><tt>runOnSCC</tt></a> (including global data).</li>
563</ol>
564
565<p>Implementing a <tt>CallGraphSCCPass</tt> is slightly tricky in some cases
566because it has to handle SCCs with more than one node in it. All of the virtual
567methods described below should return true if they modified the program, or
568false if they didn't.</p>
569
570</div>
571
572<!-- _______________________________________________________________________ -->
573<div class="doc_subsubsection">
Devang Patelc20048d2007-01-23 22:56:28 +0000[diff] [blame]574 <a name="doInitialization_scc">The <tt>doInitialization(CallGraph &amp;)</tt>
Chris Lattner8fdb2462004-09-18 06:39:35 +0000[diff] [blame]575 method</a>
576</div>
577
578<div class="doc_text">
579
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]580<div class="doc_code"><pre>
Devang Patelc20048d2007-01-23 22:56:28 +0000[diff] [blame]581 <b>virtual bool</b> doInitialization(CallGraph &amp;CG);
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]582</pre></div>
Chris Lattner8fdb2462004-09-18 06:39:35 +0000[diff] [blame]583
584<p>The <tt>doIninitialize</tt> method is allowed to do most of the things that
585<tt>CallGraphSCCPass</tt>'s are not allowed to do. They can add and remove
586functions, get pointers to functions, etc. The <tt>doInitialization</tt> method
587is designed to do simple initialization type of stuff that does not depend on
588the SCCs being processed. The <tt>doInitialization</tt> method call is not
589scheduled to overlap with any other pass executions (thus it should be very
590fast).</p>
591
592</div>
593
594<!-- _______________________________________________________________________ -->
595<div class="doc_subsubsection">
596 <a name="runOnSCC">The <tt>runOnSCC</tt> method</a>
597</div>
598
599<div class="doc_text">
600
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]601<div class="doc_code"><pre>
Chris Lattner8fdb2462004-09-18 06:39:35 +0000[diff] [blame]602 <b>virtual bool</b> runOnSCC(const std::vector&lt;CallGraphNode *&gt; &amp;SCCM) = 0;
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]603</pre></div>
Chris Lattner8fdb2462004-09-18 06:39:35 +0000[diff] [blame]604
605<p>The <tt>runOnSCC</tt> method performs the interesting work of the pass, and
606should return true if the module was modified by the transformation, false
607otherwise.</p>
608
609</div>
610
611<!-- _______________________________________________________________________ -->
612<div class="doc_subsubsection">
Devang Patelc20048d2007-01-23 22:56:28 +0000[diff] [blame]613 <a name="doFinalization_scc">The <tt>doFinalization(CallGraph
Chris Lattner8fdb2462004-09-18 06:39:35 +0000[diff] [blame]614 &amp;)</tt> method</a>
615</div>
616
617<div class="doc_text">
618
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]619<div class="doc_code"><pre>
Devang Patelc20048d2007-01-23 22:56:28 +0000[diff] [blame]620 <b>virtual bool</b> doFinalization(CallGraph &amp;CG);
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]621</pre></div>
Chris Lattner8fdb2462004-09-18 06:39:35 +0000[diff] [blame]622
623<p>The <tt>doFinalization</tt> method is an infrequently used method that is
624called when the pass framework has finished calling <a
625href="#runOnFunction"><tt>runOnFunction</tt></a> for every function in the
626program being compiled.</p>
627
628</div>
629
630<!-- ======================================================================= -->
631<div class="doc_subsection">
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]632 <a name="FunctionPass">The <tt>FunctionPass</tt> class</a>
633</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]634
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]635<div class="doc_text">
636
Chris Lattnerf6278922004-09-20 04:36:29 +0000[diff] [blame]637<p>In contrast to <tt>ModulePass</tt> subclasses, <tt><a
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]638href="http://llvm.org/doxygen/classllvm_1_1Pass.html">FunctionPass</a></tt>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]639subclasses do have a predictable, local behavior that can be expected by the
640system. All <tt>FunctionPass</tt> execute on each function in the program
Misha Brukmanef6a6a62003-08-21 22:14:26 +0000[diff] [blame]641independent of all of the other functions in the program.
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]642<tt>FunctionPass</tt>'s do not require that they are executed in a particular
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]643order, and <tt>FunctionPass</tt>'s do not modify external functions.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]644
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]645<p>To be explicit, <tt>FunctionPass</tt> subclasses are not allowed to:</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]646
647<ol>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]648<li>Modify a Function other than the one currently being processed.</li>
649<li>Add or remove Function's from the current Module.</li>
650<li>Add or remove global variables from the current Module.</li>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]651<li>Maintain state across invocations of
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]652 <a href="#runOnFunction"><tt>runOnFunction</tt></a> (including global data)</li>
653</ol>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]654
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]655<p>Implementing a <tt>FunctionPass</tt> is usually straightforward (See the <a
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]656href="#basiccode">Hello World</a> pass for example). <tt>FunctionPass</tt>'s
657may overload three virtual methods to do their work. All of these methods
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]658should return true if they modified the program, or false if they didn't.</p>
659
660</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]661
662<!-- _______________________________________________________________________ -->
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]663<div class="doc_subsubsection">
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]664 <a name="doInitialization_mod">The <tt>doInitialization(Module &amp;)</tt>
665 method</a>
666</div>
667
668<div class="doc_text">
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]669
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]670<div class="doc_code"><pre>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]671 <b>virtual bool</b> doInitialization(Module &amp;M);
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]672</pre></div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]673
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]674<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]675<tt>FunctionPass</tt>'s are not allowed to do. They can add and remove
Chris Lattnerd0713f92002-09-12 17:06:43 +0000[diff] [blame]676functions, get pointers to functions, etc. The <tt>doInitialization</tt> method
677is designed to do simple initialization type of stuff that does not depend on
678the functions being processed. The <tt>doInitialization</tt> method call is not
679scheduled to overlap with any other pass executions (thus it should be very
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]680fast).</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]681
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]682<p>A good example of how this method should be used is the <a
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]683href="http://llvm.org/doxygen/LowerAllocations_8cpp-source.html">LowerAllocations</a>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]684pass. This pass converts <tt>malloc</tt> and <tt>free</tt> instructions into
Misha Brukmanef6a6a62003-08-21 22:14:26 +0000[diff] [blame]685platform dependent <tt>malloc()</tt> and <tt>free()</tt> function calls. It
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]686uses the <tt>doInitialization</tt> method to get a reference to the malloc and
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]687free functions that it needs, adding prototypes to the module if necessary.</p>
688
689</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]690
691<!-- _______________________________________________________________________ -->
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]692<div class="doc_subsubsection">
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]693 <a name="runOnFunction">The <tt>runOnFunction</tt> method</a>
694</div>
695
696<div class="doc_text">
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]697
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]698<div class="doc_code"><pre>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]699 <b>virtual bool</b> runOnFunction(Function &amp;F) = 0;
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]700</pre></div><p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]701
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]702<p>The <tt>runOnFunction</tt> method must be implemented by your subclass to do
703the transformation or analysis work of your pass. As usual, a true value should
704be returned if the function is modified.</p>
705
706</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]707
708<!-- _______________________________________________________________________ -->
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]709<div class="doc_subsubsection">
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]710 <a name="doFinalization_mod">The <tt>doFinalization(Module
711 &amp;)</tt> method</a>
712</div>
713
714<div class="doc_text">
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]715
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]716<div class="doc_code"><pre>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]717 <b>virtual bool</b> doFinalization(Module &amp;M);
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]718</pre></div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]719
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]720<p>The <tt>doFinalization</tt> method is an infrequently used method that is
721called when the pass framework has finished calling <a
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]722href="#runOnFunction"><tt>runOnFunction</tt></a> for every function in the
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]723program being compiled.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]724
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]725</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]726
727<!-- ======================================================================= -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]728<div class="doc_subsection">
Devang Patel2e8f27d2007-03-19 22:21:25 +0000[diff] [blame]729 <a name="LoopPass">The <tt>LoopPass</tt> class </a>
730</div>
731
732<div class="doc_text">
733
734<p> All <tt>LoopPass</tt> execute on each loop in the function independent of
735all of the other loops in the function. <tt>LoopPass</tt> processes loops in
736loop nest order such that outer most loop is processed last. </p>
737
738<p> <tt>LoopPass</tt> subclasses are allowed to update loop nest using
739<tt>LPPassManager</tt> interface. Implementing a loop pass is usually
740straightforward. <tt>Looppass</tt>'s may overload three virtual methods to
741do their work. All these methods should return true if they modified the
742program, or false if they didn't. </p>
743</div>
744
745<!-- _______________________________________________________________________ -->
746<div class="doc_subsubsection">
747 <a name="doInitialization_loop">The <tt>doInitialization(Loop *,
748 LPPassManager &amp;)</tt>
749 method</a>
750</div>
751
752<div class="doc_text">
753
754<div class="doc_code"><pre>
755 <b>virtual bool</b> doInitialization(Loop *, LPPassManager &amp;LPM);
756</pre></div>
757
Chris Lattnerb5c87f62007-05-18 05:36:14 +0000[diff] [blame]758<p>The <tt>doInitialization</tt> method is designed to do simple initialization
Devang Patel2e8f27d2007-03-19 22:21:25 +0000[diff] [blame]759type of stuff that does not depend on the functions being processed. The
760<tt>doInitialization</tt> method call is not scheduled to overlap with any
761other pass executions (thus it should be very fast). LPPassManager
762interface should be used to access Function or Module level analysis
763information.</p>
764
765</div>
766
767
768<!-- _______________________________________________________________________ -->
769<div class="doc_subsubsection">
770 <a name="runOnLoop">The <tt>runOnLoop</tt> method</a>
771</div>
772
773<div class="doc_text">
774
775<div class="doc_code"><pre>
776 <b>virtual bool</b> runOnLoop(Loop *, LPPassManager &amp;LPM) = 0;
777</pre></div><p>
778
779<p>The <tt>runOnLoop</tt> method must be implemented by your subclass to do
780the transformation or analysis work of your pass. As usual, a true value should
781be returned if the function is modified. <tt>LPPassManager</tt> interface
782should be used to update loop nest.</p>
783
784</div>
785
786<!-- _______________________________________________________________________ -->
787<div class="doc_subsubsection">
788 <a name="doFinalization_loop">The <tt>doFinalization()</tt> method</a>
789</div>
790
791<div class="doc_text">
792
793<div class="doc_code"><pre>
794 <b>virtual bool</b> doFinalization();
795</pre></div>
796
797<p>The <tt>doFinalization</tt> method is an infrequently used method that is
798called when the pass framework has finished calling <a
799href="#runOnLoop"><tt>runOnLoop</tt></a> for every loop in the
800program being compiled. </p>
801
802</div>
803
804
805
806<!-- ======================================================================= -->
807<div class="doc_subsection">
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]808 <a name="BasicBlockPass">The <tt>BasicBlockPass</tt> class</a>
809</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]810
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]811<div class="doc_text">
812
813<p><tt>BasicBlockPass</tt>'s are just like <a
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]814href="#FunctionPass"><tt>FunctionPass</tt></a>'s, except that they must limit
815their scope of inspection and modification to a single basic block at a time.
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]816As such, they are <b>not</b> allowed to do any of the following:</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]817
818<ol>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]819<li>Modify or inspect any basic blocks outside of the current one</li>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]820<li>Maintain state across invocations of
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]821 <a href="#runOnBasicBlock"><tt>runOnBasicBlock</tt></a></li>
Reid Spencer1bc19342004-12-11 05:12:57 +0000[diff] [blame]822<li>Modify the control flow graph (by altering terminator instructions)</li>
823<li>Any of the things forbidden for
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]824 <a href="#FunctionPass"><tt>FunctionPass</tt></a>es.</li>
825</ol>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]826
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]827<p><tt>BasicBlockPass</tt>es are useful for traditional local and "peephole"
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]828optimizations. They may override the same <a
Chris Lattnerd0713f92002-09-12 17:06:43 +0000[diff] [blame]829href="#doInitialization_mod"><tt>doInitialization(Module &amp;)</tt></a> and <a
830href="#doFinalization_mod"><tt>doFinalization(Module &amp;)</tt></a> methods that <a
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]831href="#FunctionPass"><tt>FunctionPass</tt></a>'s have, but also have the following virtual methods that may also be implemented:</p>
832
833</div>
Chris Lattnerd0713f92002-09-12 17:06:43 +0000[diff] [blame]834
835<!-- _______________________________________________________________________ -->
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]836<div class="doc_subsubsection">
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]837 <a name="doInitialization_fn">The <tt>doInitialization(Function
838 &amp;)</tt> method</a>
839</div>
840
841<div class="doc_text">
Chris Lattnerd0713f92002-09-12 17:06:43 +0000[diff] [blame]842
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]843<div class="doc_code"><pre>
Chris Lattnerd0713f92002-09-12 17:06:43 +0000[diff] [blame]844 <b>virtual bool</b> doInitialization(Function &amp;F);
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]845</pre></div>
Chris Lattnerd0713f92002-09-12 17:06:43 +0000[diff] [blame]846
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]847<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]848<tt>BasicBlockPass</tt>'s are not allowed to do, but that
849<tt>FunctionPass</tt>'s can. The <tt>doInitialization</tt> method is designed
Reid Spencer1bc19342004-12-11 05:12:57 +0000[diff] [blame]850to do simple initialization that does not depend on the
Chris Lattnerd0713f92002-09-12 17:06:43 +0000[diff] [blame]851BasicBlocks being processed. The <tt>doInitialization</tt> method call is not
852scheduled to overlap with any other pass executions (thus it should be very
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]853fast).</p>
Chris Lattnerd0713f92002-09-12 17:06:43 +0000[diff] [blame]854
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]855</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]856
857<!-- _______________________________________________________________________ -->
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]858<div class="doc_subsubsection">
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]859 <a name="runOnBasicBlock">The <tt>runOnBasicBlock</tt> method</a>
860</div>
861
862<div class="doc_text">
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]863
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]864<div class="doc_code"><pre>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]865 <b>virtual bool</b> runOnBasicBlock(BasicBlock &amp;BB) = 0;
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]866</pre></div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]867
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]868<p>Override this function to do the work of the <tt>BasicBlockPass</tt>. This
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]869function is not allowed to inspect or modify basic blocks other than the
870parameter, and are not allowed to modify the CFG. A true value must be returned
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]871if the basic block is modified.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]872
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]873</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]874
Chris Lattnerd0713f92002-09-12 17:06:43 +0000[diff] [blame]875<!-- _______________________________________________________________________ -->
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]876<div class="doc_subsubsection">
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]877 <a name="doFinalization_fn">The <tt>doFinalization(Function &amp;)</tt>
878 method</a>
879</div>
880
881<div class="doc_text">
Chris Lattnerd0713f92002-09-12 17:06:43 +0000[diff] [blame]882
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]883<div class="doc_code"><pre>
Chris Lattnerd0713f92002-09-12 17:06:43 +0000[diff] [blame]884 <b>virtual bool</b> doFinalization(Function &amp;F);
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]885</pre></div>
Chris Lattnerd0713f92002-09-12 17:06:43 +0000[diff] [blame]886
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]887<p>The <tt>doFinalization</tt> method is an infrequently used method that is
888called when the pass framework has finished calling <a
Chris Lattnerd0713f92002-09-12 17:06:43 +0000[diff] [blame]889href="#runOnBasicBlock"><tt>runOnBasicBlock</tt></a> for every BasicBlock in the
890program being compiled. This can be used to perform per-function
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]891finalization.</p>
Chris Lattnerd0713f92002-09-12 17:06:43 +0000[diff] [blame]892
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]893</div>
Chris Lattnerd0713f92002-09-12 17:06:43 +0000[diff] [blame]894
Brian Gaekecab8b6f2003-07-17 18:53:20 +0000[diff] [blame]895<!-- ======================================================================= -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]896<div class="doc_subsection">
897 <a name="MachineFunctionPass">The <tt>MachineFunctionPass</tt> class</a>
898</div>
Brian Gaekecab8b6f2003-07-17 18:53:20 +0000[diff] [blame]899
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]900<div class="doc_text">
901
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]902<p>A <tt>MachineFunctionPass</tt> is a part of the LLVM code generator that
903executes on the machine-dependent representation of each LLVM function in the
904program. A <tt>MachineFunctionPass</tt> is also a <tt>FunctionPass</tt>, so all
Brian Gaekecab8b6f2003-07-17 18:53:20 +0000[diff] [blame]905the restrictions that apply to a <tt>FunctionPass</tt> also apply to it.
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]906<tt>MachineFunctionPass</tt>es also have additional restrictions. In particular,
907<tt>MachineFunctionPass</tt>es are not allowed to do any of the following:</p>
Brian Gaekecab8b6f2003-07-17 18:53:20 +0000[diff] [blame]908
909<ol>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]910<li>Modify any LLVM Instructions, BasicBlocks or Functions.</li>
911<li>Modify a MachineFunction other than the one currently being processed.</li>
912<li>Add or remove MachineFunctions from the current Module.</li>
913<li>Add or remove global variables from the current Module.</li>
914<li>Maintain state across invocations of <a
915href="#runOnMachineFunction"><tt>runOnMachineFunction</tt></a> (including global
916data)</li>
917</ol>
Brian Gaekecab8b6f2003-07-17 18:53:20 +0000[diff] [blame]918
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]919</div>
Chris Lattnerd0713f92002-09-12 17:06:43 +0000[diff] [blame]920
Brian Gaeke6a33f362003-07-22 20:53:20 +0000[diff] [blame]921<!-- _______________________________________________________________________ -->
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]922<div class="doc_subsubsection">
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]923 <a name="runOnMachineFunction">The <tt>runOnMachineFunction(MachineFunction
924 &amp;MF)</tt> method</a>
925</div>
926
927<div class="doc_text">
Brian Gaeke6a33f362003-07-22 20:53:20 +0000[diff] [blame]928
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]929<div class="doc_code"><pre>
Brian Gaeke6a33f362003-07-22 20:53:20 +0000[diff] [blame]930 <b>virtual bool</b> runOnMachineFunction(MachineFunction &amp;MF) = 0;
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]931</pre></div>
Brian Gaeke6a33f362003-07-22 20:53:20 +0000[diff] [blame]932
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]933<p><tt>runOnMachineFunction</tt> can be considered the main entry point of a
934<tt>MachineFunctionPass</tt>; that is, you should override this method to do the
935work of your <tt>MachineFunctionPass</tt>.</p>
Brian Gaeke6a33f362003-07-22 20:53:20 +0000[diff] [blame]936
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]937<p>The <tt>runOnMachineFunction</tt> method is called on every
Brian Gaeke6a33f362003-07-22 20:53:20 +0000[diff] [blame]938<tt>MachineFunction</tt> in a <tt>Module</tt>, so that the
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]939<tt>MachineFunctionPass</tt> may perform optimizations on the machine-dependent
940representation of the function. If you want to get at the LLVM <tt>Function</tt>
941for the <tt>MachineFunction</tt> you're working on, use
942<tt>MachineFunction</tt>'s <tt>getFunction()</tt> accessor method -- but
943remember, you may not modify the LLVM <tt>Function</tt> or its contents from a
944<tt>MachineFunctionPass</tt>.</p>
945
946</div>
Brian Gaeke6a33f362003-07-22 20:53:20 +0000[diff] [blame]947
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]948<!-- *********************************************************************** -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]949<div class="doc_section">
950 <a name="registration">Pass registration</a>
951</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]952<!-- *********************************************************************** -->
953
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]954<div class="doc_text">
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]955
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]956<p>In the <a href="#basiccode">Hello World</a> example pass we illustrated how
957pass registration works, and discussed some of the reasons that it is used and
958what it does. Here we discuss how and why passes are registered.</p>
959
Chris Lattnerc8603c22006-08-27 23:18:52 +0000[diff] [blame]960<p>As we saw above, passes are registered with the <b><tt>RegisterPass</tt></b>
961template, which requires you to pass at least two
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]962parameters. The first parameter is the name of the pass that is to be used on
963the command line to specify that the pass should be added to a program (for
Chris Lattnerc8603c22006-08-27 23:18:52 +0000[diff] [blame]964example, with <tt>opt</tt> or <tt>bugpoint</tt>). The second argument is the
965name of the pass, which is to be used for the <tt>--help</tt> output of
966programs, as
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]967well as for debug output generated by the <tt>--debug-pass</tt> option.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]968
Chris Lattnerc8603c22006-08-27 23:18:52 +0000[diff] [blame]969<p>If you want your pass to be easily dumpable, you should
970implement the virtual <tt>print</tt> method:</p>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]971
972</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]973
974<!-- _______________________________________________________________________ -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]975<div class="doc_subsubsection">
976 <a name="print">The <tt>print</tt> method</a>
977</div>
978
979<div class="doc_text">
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]980
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]981<div class="doc_code"><pre>
Torok Edwin52790e52008-10-28 17:29:23 +0000[diff] [blame]982 <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]983</pre></div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]984
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]985<p>The <tt>print</tt> method must be implemented by "analyses" in order to print
986a human readable version of the analysis results. This is useful for debugging
987an analysis itself, as well as for other people to figure out how an analysis
Chris Lattnerc8603c22006-08-27 23:18:52 +0000[diff] [blame]988works. Use the <tt>opt -analyze</tt> argument to invoke this method.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]989
Bill Wendling832171c2006-12-07 20:04:42 +0000[diff] [blame]990<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]991and 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]992program that has been analyzed. Note however that this pointer may be null in
993certain circumstances (such as calling the <tt>Pass::dump()</tt> from a
994debugger), so it should only be used to enhance debug output, it should not be
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]995depended on.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]996
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]997</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]998
999<!-- *********************************************************************** -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1000<div class="doc_section">
1001 <a name="interaction">Specifying interactions between passes</a>
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_text">
1006
John Criswell8528e782007-12-03 19:34:25 +0000[diff] [blame]1007<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]1008that passes interact with each other correctly. Because <tt>PassManager</tt>
1009tries to <a href="#passmanager">optimize the execution of passes</a> it must
1010know how the passes interact with each other and what dependencies exist between
1011the various passes. To track this, each pass can declare the set of passes that
1012are required to be executed before the current pass, and the passes which are
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1013invalidated by the current pass.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1014
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1015<p>Typically this functionality is used to require that analysis results are
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1016computed before your pass is run. Running arbitrary transformation passes can
1017invalidate the computed analysis results, which is what the invalidation set
1018specifies. If a pass does not implement the <tt><a
1019href="#getAnalysisUsage">getAnalysisUsage</a></tt> method, it defaults to not
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1020having any prerequisite passes, and invalidating <b>all</b> other passes.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1021
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1022</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1023
1024<!-- _______________________________________________________________________ -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1025<div class="doc_subsubsection">
1026 <a name="getAnalysisUsage">The <tt>getAnalysisUsage</tt> method</a>
1027</div>
1028
1029<div class="doc_text">
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1030
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1031<div class="doc_code"><pre>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1032 <b>virtual void</b> getAnalysisUsage(AnalysisUsage &amp;Info) <b>const</b>;
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1033</pre></div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1034
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1035<p>By implementing the <tt>getAnalysisUsage</tt> method, the required and
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1036invalidated sets may be specified for your transformation. The implementation
1037should fill in the <tt><a
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]1038href="http://llvm.org/doxygen/classllvm_1_1AnalysisUsage.html">AnalysisUsage</a></tt>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1039object with information about which passes are required and not invalidated. To
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]1040do this, a pass may call any of the following methods on the AnalysisUsage
1041object:</p>
1042</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1043
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]1044<!-- _______________________________________________________________________ -->
1045<div class="doc_subsubsection">
1046 <a name="AU::addRequired">The <tt>AnalysisUsage::addRequired&lt;&gt;</tt> and <tt>AnalysisUsage::addRequiredTransitive&lt;&gt;</tt> methods</a>
1047</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1048
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]1049<div class="doc_text">
1050<p>
Reid Spencer1bc19342004-12-11 05:12:57 +0000[diff] [blame]1051If your pass requires a previous pass to be executed (an analysis for example),
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]1052it can use one of these methods to arrange for it to be run before your pass.
1053LLVM has many different types of analyses and passes that can be required,
Reid Spencer1bc19342004-12-11 05:12:57 +0000[diff] [blame]1054spanning the range from <tt>DominatorSet</tt> to <tt>BreakCriticalEdges</tt>.
1055Requiring <tt>BreakCriticalEdges</tt>, for example, guarantees that there will
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]1056be no critical edges in the CFG when your pass has been run.
1057</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1058
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]1059<p>
1060Some analyses chain to other analyses to do their job. For example, an <a
1061href="AliasAnalysis.html">AliasAnalysis</a> implementation is required to <a
1062href="AliasAnalysis.html#chaining">chain</a> to other alias analysis passes. In
1063cases where analyses chain, the <tt>addRequiredTransitive</tt> method should be
1064used instead of the <tt>addRequired</tt> method. This informs the PassManager
1065that the transitively required pass should be alive as long as the requiring
1066pass is.
1067</p>
1068</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1069
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]1070<!-- _______________________________________________________________________ -->
1071<div class="doc_subsubsection">
1072 <a name="AU::addPreserved">The <tt>AnalysisUsage::addPreserved&lt;&gt;</tt> method</a>
1073</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1074
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]1075<div class="doc_text">
1076<p>
1077One of the jobs of the PassManager is to optimize how and when analyses are run.
1078In particular, it attempts to avoid recomputing data unless it needs to. For
1079this reason, passes are allowed to declare that they preserve (i.e., they don't
1080invalidate) an existing analysis if it's available. For example, a simple
Reid Spencer1bc19342004-12-11 05:12:57 +0000[diff] [blame]1081constant folding pass would not modify the CFG, so it can't possibly affect the
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]1082results of dominator analysis. By default, all passes are assumed to invalidate
1083all others.
1084</p>
1085
1086<p>
1087The <tt>AnalysisUsage</tt> class provides several methods which are useful in
1088certain circumstances that are related to <tt>addPreserved</tt>. In particular,
1089the <tt>setPreservesAll</tt> method can be called to indicate that the pass does
1090not modify the LLVM program at all (which is true for analyses), and the
1091<tt>setPreservesCFG</tt> method can be used by transformations that change
1092instructions in the program but do not modify the CFG or terminator instructions
1093(note that this property is implicitly set for <a
1094href="#BasicBlockPass">BasicBlockPass</a>'s).
1095</p>
1096
1097<p>
1098<tt>addPreserved</tt> is particularly useful for transformations like
1099<tt>BreakCriticalEdges</tt>. This pass knows how to update a small set of loop
1100and dominator related analyses if they exist, so it can preserve them, despite
1101the fact that it hacks on the CFG.
1102</p>
1103</div>
1104
1105<!-- _______________________________________________________________________ -->
1106<div class="doc_subsubsection">
1107 <a name="AU::examples">Example implementations of <tt>getAnalysisUsage</tt></a>
1108</div>
1109
1110<div class="doc_text">
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1111
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1112<div class="doc_code"><pre>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1113 <i>// This is an example implementation from an analysis, which does not modify
1114 // the program at all, yet has a prerequisite.</i>
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]1115 <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]1116 AU.setPreservesAll();
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]1117 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]1118 }
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1119</pre></div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1120
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1121<p>and:</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1122
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1123<div class="doc_code"><pre>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1124 <i>// This example modifies the program, but does not modify the CFG</i>
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]1125 <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]1126 AU.setPreservesCFG();
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]1127 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]1128 }
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1129</pre></div>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1130
1131</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1132
1133<!-- _______________________________________________________________________ -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1134<div class="doc_subsubsection">
Duncan Sands1465d612009-01-28 13:14:17 +0000[diff] [blame]1135 <a name="getAnalysis">The <tt>getAnalysis&lt;&gt;</tt> and
1136<tt>getAnalysisIfAvailable&lt;&gt;</tt> methods</a>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1137</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1138
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1139<div class="doc_text">
1140
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]1141<p>The <tt>Pass::getAnalysis&lt;&gt;</tt> method is automatically inherited by
1142your class, providing you with access to the passes that you declared that you
1143required with the <a href="#getAnalysisUsage"><tt>getAnalysisUsage</tt></a>
1144method. It takes a single template argument that specifies which pass class you
1145want, and returns a reference to that pass. For example:</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1146
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1147<div class="doc_code"><pre>
Chris Lattnera5776302004-03-17 21:33:32 +0000[diff] [blame]1148 bool LICM::runOnFunction(Function &amp;F) {
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]1149 LoopInfo &amp;LI = getAnalysis&lt;LoopInfo&gt;();
1150 ...
1151 }
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1152</pre></div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1153
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1154<p>This method call returns a reference to the pass desired. You may get a
1155runtime assertion failure if you attempt to get an analysis that you did not
1156declare as required in your <a
1157href="#getAnalysisUsage"><tt>getAnalysisUsage</tt></a> implementation. This
1158method can be called by your <tt>run*</tt> method implementation, or by any
Devang Patel3c1ca0b2007-04-16 21:28:14 +0000[diff] [blame]1159other local method invoked by your <tt>run*</tt> method.
1160
1161A module level pass can use function level analysis info using this interface.
1162For example:</p>
1163
1164<div class="doc_code"><pre>
1165 bool ModuleLevelPass::runOnModule(Module &amp;M) {
1166 ...
Devang Patelf23de112007-04-17 00:17:11 +0000[diff] [blame]1167 DominatorTree &amp;DT = getAnalysis&lt;DominatorTree&gt;(Func);
Devang Patel3c1ca0b2007-04-16 21:28:14 +0000[diff] [blame]1168 ...
1169 }
1170</pre></div>
1171
Chris Lattnerb5c87f62007-05-18 05:36:14 +0000[diff] [blame]1172<p>In above example, runOnFunction for DominatorTree is called by pass manager
Devang Patel3c1ca0b2007-04-16 21:28:14 +0000[diff] [blame]1173before returning a reference to the desired pass.</p>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1174
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]1175<p>
1176If your pass is capable of updating analyses if they exist (e.g.,
1177<tt>BreakCriticalEdges</tt>, as described above), you can use the
Duncan Sands1465d612009-01-28 13:14:17 +0000[diff] [blame]1178<tt>getAnalysisIfAvailable</tt> method, which returns a pointer to the analysis
1179if it is active. For example:</p>
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]1180
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1181<div class="doc_code"><pre>
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]1182 ...
Duncan Sands1465d612009-01-28 13:14:17 +0000[diff] [blame]1183 if (DominatorSet *DS = getAnalysisIfAvailable&lt;DominatorSet&gt;()) {
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]1184 <i>// A DominatorSet is active. This code will update it.</i>
1185 }
1186 ...
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1187</pre></div>
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]1188
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1189</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1190
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1191<!-- *********************************************************************** -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1192<div class="doc_section">
1193 <a name="analysisgroup">Implementing Analysis Groups</a>
1194</div>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1195<!-- *********************************************************************** -->
1196
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1197<div class="doc_text">
1198
Chris Lattnerb7632282007-11-16 05:32:05 +0000[diff] [blame]1199<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]1200used, 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]1201fancier. All of the pass relationships that we have seen so far are very
1202simple: one pass depends on one other specific pass to be run before it can run.
1203For many applications, this is great, for others, more flexibility is
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1204required.</p>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1205
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1206<p>In particular, some analyses are defined such that there is a single simple
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1207interface to the analysis results, but multiple ways of calculating them.
1208Consider alias analysis for example. The most trivial alias analysis returns
1209"may alias" for any alias query. The most sophisticated analysis a
1210flow-sensitive, context-sensitive interprocedural analysis that can take a
1211significant amount of time to execute (and obviously, there is a lot of room
1212between these two extremes for other implementations). To cleanly support
1213situations like this, the LLVM Pass Infrastructure supports the notion of
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1214Analysis Groups.</p>
1215
1216</div>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1217
1218<!-- _______________________________________________________________________ -->
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]1219<div class="doc_subsubsection">
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1220 <a name="agconcepts">Analysis Group Concepts</a>
1221</div>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1222
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1223<div class="doc_text">
1224
1225<p>An Analysis Group is a single simple interface that may be implemented by
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1226multiple different passes. Analysis Groups can be given human readable names
1227just like passes, but unlike passes, they need not derive from the <tt>Pass</tt>
1228class. An analysis group may have one or more implementations, one of which is
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1229the "default" implementation.</p>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1230
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1231<p>Analysis groups are used by client passes just like other passes are: the
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1232<tt>AnalysisUsage::addRequired()</tt> and <tt>Pass::getAnalysis()</tt> methods.
1233In order to resolve this requirement, the <a href="#passmanager">PassManager</a>
1234scans the available passes to see if any implementations of the analysis group
1235are available. If none is available, the default implementation is created for
1236the pass to use. All standard rules for <A href="#interaction">interaction
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1237between passes</a> still apply.</p>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1238
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1239<p>Although <a href="#registration">Pass Registration</a> is optional for normal
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1240passes, all analysis group implementations must be registered, and must use the
1241<A href="#registerag"><tt>RegisterAnalysisGroup</tt></a> template to join the
1242implementation pool. Also, a default implementation of the interface
1243<b>must</b> be registered with <A
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1244href="#registerag"><tt>RegisterAnalysisGroup</tt></a>.</p>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1245
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1246<p>As a concrete example of an Analysis Group in action, consider the <a
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]1247href="http://llvm.org/doxygen/classllvm_1_1AliasAnalysis.html">AliasAnalysis</a>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1248analysis group. The default implementation of the alias analysis interface (the
1249<tt><a
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]1250href="http://llvm.org/doxygen/structBasicAliasAnalysis.html">basicaa</a></tt>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1251pass) just does a few simple checks that don't require significant analysis to
1252compute (such as: two different globals can never alias each other, etc).
1253Passes that use the <tt><a
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]1254href="http://llvm.org/doxygen/classllvm_1_1AliasAnalysis.html">AliasAnalysis</a></tt>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1255interface (for example the <tt><a
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]1256href="http://llvm.org/doxygen/structGCSE.html">gcse</a></tt> pass), do
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1257not care which implementation of alias analysis is actually provided, they just
1258use the designated interface.</p>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1259
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1260<p>From the user's perspective, commands work just like normal. Issuing the
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1261command '<tt>opt -gcse ...</tt>' will cause the <tt>basicaa</tt> class to be
1262instantiated and added to the pass sequence. Issuing the command '<tt>opt
1263-somefancyaa -gcse ...</tt>' will cause the <tt>gcse</tt> pass to use the
1264<tt>somefancyaa</tt> alias analysis (which doesn't actually exist, it's just a
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1265hypothetical example) instead.</p>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1266
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1267</div>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1268
1269<!-- _______________________________________________________________________ -->
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]1270<div class="doc_subsubsection">
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1271 <a name="registerag">Using <tt>RegisterAnalysisGroup</tt></a>
1272</div>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1273
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1274<div class="doc_text">
1275
1276<p>The <tt>RegisterAnalysisGroup</tt> template is used to register the analysis
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1277group itself as well as add pass implementations to the analysis group. First,
1278an analysis should be registered, with a human readable name provided for it.
1279Unlike registration of passes, there is no command line argument to be specified
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1280for the Analysis Group Interface itself, because it is "abstract":</p>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1281
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1282<div class="doc_code"><pre>
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]1283 <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]1284</pre></div>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1285
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1286<p>Once the analysis is registered, passes can declare that they are valid
1287implementations of the interface by using the following code:</p>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1288
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1289<div class="doc_code"><pre>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1290<b>namespace</b> {
1291 //<i> Analysis Group implementations <b>must</b> be registered normally...</i>
Chris Lattnerc8603c22006-08-27 23:18:52 +0000[diff] [blame]1292 RegisterPass&lt;FancyAA&gt;
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1293 B("<i>somefancyaa</i>", "<i>A more complex alias analysis implementation</i>");
1294
1295 //<i> Declare that we implement the AliasAnalysis interface</i>
Chris Lattnerdc877252006-08-28 00:45:38 +0000[diff] [blame]1296 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]1297}
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1298</pre></div>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1299
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1300<p>This just shows a class <tt>FancyAA</tt> that is registered normally, then
1301uses the <tt>RegisterAnalysisGroup</tt> template to "join" the <tt><a
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]1302href="http://llvm.org/doxygen/classllvm_1_1AliasAnalysis.html">AliasAnalysis</a></tt>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1303analysis group. Every implementation of an analysis group should join using
1304this template. A single pass may join multiple different analysis groups with
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1305no problem.</p>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1306
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1307<div class="doc_code"><pre>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1308<b>namespace</b> {
1309 //<i> Analysis Group implementations <b>must</b> be registered normally...</i>
Chris Lattnerc8603c22006-08-27 23:18:52 +0000[diff] [blame]1310 RegisterPass&lt;<a href="http://llvm.org/doxygen/structBasicAliasAnalysis.html">BasicAliasAnalysis</a>&gt;
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1311 D("<i>basicaa</i>", "<i>Basic Alias Analysis (default AA impl)</i>");
1312
1313 //<i> Declare that we implement the AliasAnalysis interface</i>
Chris Lattnerdc877252006-08-28 00:45:38 +0000[diff] [blame]1314 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]1315}
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1316</pre></div>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1317
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1318<p>Here we show how the default implementation is specified (using the extra
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1319argument to the <tt>RegisterAnalysisGroup</tt> template). There must be exactly
1320one default implementation available at all times for an Analysis Group to be
Devang Patel2397f8d2007-06-20 18:51:14 +0000[diff] [blame]1321used. Only default implementation can derive from <tt>ImmutablePass</tt>.
1322Here we declare that the
1323 <tt><a href="http://llvm.org/doxygen/structBasicAliasAnalysis.html">BasicAliasAnalysis</a></tt>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1324pass is the default implementation for the interface.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1325
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1326</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1327
1328<!-- *********************************************************************** -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1329<div class="doc_section">
Tanya Lattnerd5383652004-11-19 01:25:14 +0000[diff] [blame]1330 <a name="passStatistics">Pass Statistics</a>
1331</div>
1332<!-- *********************************************************************** -->
1333
1334<div class="doc_text">
Tanya Lattner05f8d5f2004-11-19 01:26:37 +0000[diff] [blame]1335<p>The <a
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]1336href="http://llvm.org/doxygen/Statistic_8h-source.html"><tt>Statistic</tt></a>
John Criswell0b1010e2005-11-28 23:25:41 +0000[diff] [blame]1337class is designed to be an easy way to expose various success
Tanya Lattnerd5383652004-11-19 01:25:14 +0000[diff] [blame]1338metrics from passes. These statistics are printed at the end of a
1339run, when the -stats command line option is enabled on the command
Tanya Lattner05f8d5f2004-11-19 01:26:37 +0000[diff] [blame]1340line. 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]1341
1342</div>
1343
1344
1345<!-- *********************************************************************** -->
1346<div class="doc_section">
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1347 <a name="passmanager">What PassManager does</a>
1348</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1349<!-- *********************************************************************** -->
1350
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1351<div class="doc_text">
1352
1353<p>The <a
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]1354href="http://llvm.org/doxygen/PassManager_8h-source.html"><tt>PassManager</tt></a>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1355<a
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]1356href="http://llvm.org/doxygen/classllvm_1_1PassManager.html">class</a>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1357takes a list of passes, ensures their <a href="#interaction">prerequisites</a>
1358are set up correctly, and then schedules passes to run efficiently. All of the
1359LLVM tools that run passes use the <tt>PassManager</tt> for execution of these
1360passes.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1361
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1362<p>The <tt>PassManager</tt> does two main things to try to reduce the execution
1363time of a series of passes:</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1364
1365<ol>
1366<li><b>Share analysis results</b> - The PassManager attempts to avoid
1367recomputing analysis results as much as possible. This means keeping track of
1368which analyses are available already, which analyses get invalidated, and which
1369analyses are needed to be run for a pass. An important part of work is that the
1370<tt>PassManager</tt> tracks the exact lifetime of all analysis results, allowing
1371it to <a href="#releaseMemory">free memory</a> allocated to holding analysis
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1372results as soon as they are no longer needed.</li>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1373
1374<li><b>Pipeline the execution of passes on the program</b> - The
1375<tt>PassManager</tt> attempts to get better cache and memory usage behavior out
1376of a series of passes by pipelining the passes together. This means that, given
1377a series of consequtive <a href="#FunctionPass"><tt>FunctionPass</tt></a>'s, it
1378will execute all of the <a href="#FunctionPass"><tt>FunctionPass</tt></a>'s on
1379the first function, then all of the <a
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1380href="#FunctionPass"><tt>FunctionPass</tt></a>es on the second function,
1381etc... until the entire program has been run through the passes.
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1382
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1383<p>This improves the cache behavior of the compiler, because it is only touching
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1384the LLVM program representation for a single function at a time, instead of
1385traversing the entire program. It reduces the memory consumption of compiler,
1386because, for example, only one <a
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]1387href="http://llvm.org/doxygen/classllvm_1_1DominatorSet.html"><tt>DominatorSet</tt></a>
John Criswell9795bb82007-12-10 20:26:29 +0000[diff] [blame]1388needs to be calculated at a time. This also makes it possible to implement
1389some <a
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1390href="#SMP">interesting enhancements</a> in the future.</p></li>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1391
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1392</ol>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1393
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1394<p>The effectiveness of the <tt>PassManager</tt> is influenced directly by how
1395much information it has about the behaviors of the passes it is scheduling. For
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1396example, the "preserved" set is intentionally conservative in the face of an
1397unimplemented <a href="#getAnalysisUsage"><tt>getAnalysisUsage</tt></a> method.
1398Not implementing when it should be implemented will have the effect of not
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1399allowing any analysis results to live across the execution of your pass.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1400
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1401<p>The <tt>PassManager</tt> class exposes a <tt>--debug-pass</tt> command line
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1402options that is useful for debugging pass execution, seeing how things work, and
1403diagnosing when you should be preserving more analyses than you currently are
1404(To get information about all of the variants of the <tt>--debug-pass</tt>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1405option, just type '<tt>opt --help-hidden</tt>').</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1406
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1407<p>By using the <tt>--debug-pass=Structure</tt> option, for example, we can see
1408how our <a href="#basiccode">Hello World</a> pass interacts with other passes.
1409Lets try it out with the <tt>gcse</tt> and <tt>licm</tt> passes:</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1410
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1411<div class="doc_code"><pre>
Reid Spencer7fa6d522005-01-11 05:16:23 +0000[diff] [blame]1412$ 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]1413Module Pass Manager
1414 Function Pass Manager
1415 Dominator Set Construction
1416 Immediate Dominators Construction
1417 Global Common Subexpression Elimination
1418-- Immediate Dominators Construction
1419-- Global Common Subexpression Elimination
1420 Natural Loop Construction
1421 Loop Invariant Code Motion
1422-- Natural Loop Construction
1423-- Loop Invariant Code Motion
1424 Module Verifier
1425-- Dominator Set Construction
1426-- Module Verifier
Gabor Greif04367bf2007-07-06 22:07:22 +0000[diff] [blame]1427 Bitcode Writer
1428--Bitcode Writer
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1429</pre></div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1430
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1431<p>This output shows us when passes are constructed and when the analysis
1432results are known to be dead (prefixed with '<tt>--</tt>'). Here we see that
1433GCSE uses dominator and immediate dominator information to do its job. The LICM
1434pass uses natural loop information, which uses dominator sets, but not immediate
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1435dominators. Because immediate dominators are no longer useful after the GCSE
1436pass, it is immediately destroyed. The dominator sets are then reused to
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1437compute natural loop information, which is then used by the LICM pass.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1438
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1439<p>After the LICM pass, the module verifier runs (which is automatically added
1440by the '<tt>opt</tt>' tool), which uses the dominator set to check that the
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1441resultant LLVM code is well formed. After it finishes, the dominator set
1442information is destroyed, after being computed once, and shared by three
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1443passes.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1444
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1445<p>Lets see how this changes when we run the <a href="#basiccode">Hello
1446World</a> pass in between the two passes:</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1447
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1448<div class="doc_code"><pre>
Reid Spencer7fa6d522005-01-11 05:16:23 +0000[diff] [blame]1449$ 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]1450Module Pass Manager
1451 Function Pass Manager
1452 Dominator Set Construction
1453 Immediate Dominators Construction
1454 Global Common Subexpression Elimination
1455<b>-- Dominator Set Construction</b>
1456-- Immediate Dominators Construction
1457-- Global Common Subexpression Elimination
1458<b> Hello World Pass
1459-- Hello World Pass
1460 Dominator Set Construction</b>
1461 Natural Loop Construction
1462 Loop Invariant Code Motion
1463-- Natural Loop Construction
1464-- Loop Invariant Code Motion
1465 Module Verifier
1466-- Dominator Set Construction
1467-- Module Verifier
Gabor Greif04367bf2007-07-06 22:07:22 +0000[diff] [blame]1468 Bitcode Writer
1469--Bitcode Writer
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1470Hello: __main
1471Hello: puts
1472Hello: main
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1473</pre></div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1474
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1475<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]1476Dominator Set pass, even though it doesn't modify the code at all! To fix this,
1477we need to add the following <a
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1478href="#getAnalysisUsage"><tt>getAnalysisUsage</tt></a> method to our pass:</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1479
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1480<div class="doc_code"><pre>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1481 <i>// We don't modify the program, so we preserve all analyses</i>
1482 <b>virtual void</b> getAnalysisUsage(AnalysisUsage &amp;AU) <b>const</b> {
1483 AU.setPreservesAll();
1484 }
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1485</pre></div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1486
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1487<p>Now when we run our pass, we get this output:</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1488
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1489<div class="doc_code"><pre>
Reid Spencer7fa6d522005-01-11 05:16:23 +0000[diff] [blame]1490$ 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]1491Pass Arguments: -gcse -hello -licm
1492Module Pass Manager
1493 Function Pass Manager
1494 Dominator Set Construction
1495 Immediate Dominators Construction
1496 Global Common Subexpression Elimination
1497-- Immediate Dominators Construction
1498-- Global Common Subexpression Elimination
1499 Hello World Pass
1500-- Hello World Pass
1501 Natural Loop Construction
1502 Loop Invariant Code Motion
1503-- Loop Invariant Code Motion
1504-- Natural Loop Construction
1505 Module Verifier
1506-- Dominator Set Construction
1507-- Module Verifier
Gabor Greif04367bf2007-07-06 22:07:22 +0000[diff] [blame]1508 Bitcode Writer
1509--Bitcode Writer
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1510Hello: __main
1511Hello: puts
1512Hello: main
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1513</pre></div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1514
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1515<p>Which shows that we don't accidentally invalidate dominator information
1516anymore, and therefore do not have to compute it twice.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1517
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1518</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1519
1520<!-- _______________________________________________________________________ -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1521<div class="doc_subsubsection">
1522 <a name="releaseMemory">The <tt>releaseMemory</tt> method</a>
1523</div>
1524
1525<div class="doc_text">
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1526
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1527<div class="doc_code"><pre>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1528 <b>virtual void</b> releaseMemory();
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1529</pre></div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1530
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1531<p>The <tt>PassManager</tt> automatically determines when to compute analysis
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1532results, and how long to keep them around for. Because the lifetime of the pass
1533object itself is effectively the entire duration of the compilation process, we
1534need some way to free analysis results when they are no longer useful. The
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1535<tt>releaseMemory</tt> virtual method is the way to do this.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1536
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1537<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]1538amount of state (for use by another pass which "requires" your pass and uses the
1539<a href="#getAnalysis">getAnalysis</a> method) you should implement
Dan Gohmand87c9e32009-06-15 18:22:49 +0000[diff] [blame^]1540<tt>releaseMemory</tt> to, well, release the memory allocated to maintain this
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1541internal state. This method is called after the <tt>run*</tt> method for the
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1542class, before the next call of <tt>run*</tt> in your pass.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1543
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1544</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1545
1546<!-- *********************************************************************** -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1547<div class="doc_section">
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1548 <a name="registering">Registering dynamically loaded passes</a>
1549</div>
1550<!-- *********************************************************************** -->
1551
1552<div class="doc_text">
1553
1554<p><i>Size matters</i> when constructing production quality tools using llvm,
1555both for the purposes of distribution, and for regulating the resident code size
1556when running on the target system. Therefore, it becomes desirable to
1557selectively use some passes, while omitting others and maintain the flexibility
1558to change configurations later on. You want to be able to do all this, and,
1559provide feedback to the user. This is where pass registration comes into
1560play.</p>
1561
1562<p>The fundamental mechanisms for pass registration are the
1563<tt>MachinePassRegistry</tt> class and subclasses of
1564<tt>MachinePassRegistryNode</tt>.</p>
1565
1566<p>An instance of <tt>MachinePassRegistry</tt> is used to maintain a list of
1567<tt>MachinePassRegistryNode</tt> objects. This instance maintains the list and
1568communicates additions and deletions to the command line interface.</p>
1569
1570<p>An instance of <tt>MachinePassRegistryNode</tt> subclass is used to maintain
1571information provided about a particular pass. This information includes the
1572command line name, the command help string and the address of the function used
1573to create an instance of the pass. A global static constructor of one of these
1574instances <i>registers</i> with a corresponding <tt>MachinePassRegistry</tt>,
1575the static destructor <i>unregisters</i>. Thus a pass that is statically linked
1576in the tool will be registered at start up. A dynamically loaded pass will
1577register on load and unregister at unload.</p>
1578
1579</div>
1580
1581<!-- _______________________________________________________________________ -->
1582<div class="doc_subsection">
1583 <a name="registering_existing">Using existing registries</a>
1584</div>
1585
1586<div class="doc_text">
1587
1588<p>There are predefined registries to track instruction scheduling
1589(<tt>RegisterScheduler</tt>) and register allocation (<tt>RegisterRegAlloc</tt>)
1590machine passes. Here we will describe how to <i>register</i> a register
1591allocator machine pass.</p>
1592
1593<p>Implement your register allocator machine pass. In your register allocator
1594.cpp file add the following include;</p>
1595
1596<div class="doc_code"><pre>
Chris Lattner8f652eb2006-08-11 16:37:02 +0000[diff] [blame]1597 #include "llvm/CodeGen/RegAllocRegistry.h"
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1598</pre></div>
1599
1600<p>Also in your register allocator .cpp file, define a creator function in the
1601form; </p>
1602
1603<div class="doc_code"><pre>
1604 FunctionPass *createMyRegisterAllocator() {
1605 return new MyRegisterAllocator();
1606 }
1607</pre></div>
1608
1609<p>Note that the signature of this function should match the type of
1610<tt>RegisterRegAlloc::FunctionPassCtor</tt>. In the same file add the
1611"installing" declaration, in the form;</p>
1612
1613<div class="doc_code"><pre>
1614 static RegisterRegAlloc myRegAlloc("myregalloc",
1615 " my register allocator help string",
1616 createMyRegisterAllocator);
1617</pre></div>
1618
1619<p>Note the two spaces prior to the help string produces a tidy result on the
1620--help query.</p>
1621
1622<div class="doc_code"><pre>
1623$ llc --help
1624 ...
1625 -regalloc - Register allocator to use: (default = linearscan)
1626 =linearscan - linear scan register allocator
1627 =local - local register allocator
1628 =simple - simple register allocator
1629 =myregalloc - my register allocator help string
1630 ...
1631</pre></div>
1632
1633<p>And that's it. The user is now free to use <tt>-regalloc=myregalloc</tt> as
1634an option. Registering instruction schedulers is similar except use the
Chris Lattner8f652eb2006-08-11 16:37:02 +0000[diff] [blame]1635<tt>RegisterScheduler</tt> class. Note that the
1636<tt>RegisterScheduler::FunctionPassCtor</tt> is significantly different from
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1637<tt>RegisterRegAlloc::FunctionPassCtor</tt>.</p>
1638
1639<p>To force the load/linking of your register allocator into the llc/lli tools,
1640add your creator function's global declaration to "Passes.h" and add a "pseudo"
1641call line to <tt>llvm/Codegen/LinkAllCodegenComponents.h</tt>.</p>
1642
1643</div>
1644
1645
1646<!-- _______________________________________________________________________ -->
1647<div class="doc_subsection">
1648 <a name="registering_new">Creating new registries</a>
1649</div>
1650
1651<div class="doc_text">
1652
1653<p>The easiest way to get started is to clone one of the existing registries; we
1654recommend <tt>llvm/CodeGen/RegAllocRegistry.h</tt>. The key things to modify
1655are the class name and the <tt>FunctionPassCtor</tt> type.</p>
1656
1657<p>Then you need to declare the registry. Example: if your pass registry is
1658<tt>RegisterMyPasses</tt> then define;</p>
1659
1660<div class="doc_code"><pre>
1661MachinePassRegistry RegisterMyPasses::Registry;
1662</pre></div>
1663
1664<p>And finally, declare the command line option for your passes. Example:</p>
1665
1666<div class="doc_code"><pre>
1667 cl::opt&lt;RegisterMyPasses::FunctionPassCtor, false,
Dan Gohman364a39f2008-10-14 17:00:38 +0000[diff] [blame]1668 RegisterPassParser&lt;RegisterMyPasses&gt; &gt;
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1669 MyPassOpt("mypass",
1670 cl::init(&amp;createDefaultMyPass),
1671 cl::desc("my pass option help"));
1672</pre></div>
1673
1674<p>Here the command option is "mypass", with createDefaultMyPass as the default
1675creator.</p>
1676
1677</div>
1678
1679<!-- *********************************************************************** -->
1680<div class="doc_section">
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1681 <a name="debughints">Using GDB with dynamically loaded passes</a>
1682</div>
Chris Lattner480e2ef2002-09-06 02:02:58 +0000[diff] [blame]1683<!-- *********************************************************************** -->
1684
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1685<div class="doc_text">
1686
1687<p>Unfortunately, using GDB with dynamically loaded passes is not as easy as it
Chris Lattner480e2ef2002-09-06 02:02:58 +0000[diff] [blame]1688should be. First of all, you can't set a breakpoint in a shared object that has
1689not been loaded yet, and second of all there are problems with inlined functions
1690in shared objects. Here are some suggestions to debugging your pass with
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1691GDB.</p>
Chris Lattner480e2ef2002-09-06 02:02:58 +0000[diff] [blame]1692
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1693<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]1694transformation invoked by <tt>opt</tt>, although nothing described here depends
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1695on that.</p>
1696
1697</div>
Chris Lattner480e2ef2002-09-06 02:02:58 +0000[diff] [blame]1698
1699<!-- _______________________________________________________________________ -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1700<div class="doc_subsubsection">
1701 <a name="breakpoint">Setting a breakpoint in your pass</a>
1702</div>
Chris Lattner480e2ef2002-09-06 02:02:58 +0000[diff] [blame]1703
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1704<div class="doc_text">
1705
1706<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]1707
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1708<div class="doc_code"><pre>
Chris Lattner480e2ef2002-09-06 02:02:58 +0000[diff] [blame]1709$ <b>gdb opt</b>
1710GNU gdb 5.0
1711Copyright 2000 Free Software Foundation, Inc.
1712GDB is free software, covered by the GNU General Public License, and you are
1713welcome to change it and/or distribute copies of it under certain conditions.
1714Type "show copying" to see the conditions.
1715There is absolutely no warranty for GDB. Type "show warranty" for details.
1716This GDB was configured as "sparc-sun-solaris2.6"...
1717(gdb)
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1718</pre></div>
Chris Lattner480e2ef2002-09-06 02:02:58 +0000[diff] [blame]1719
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1720<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]1721time to load. Be patient. Since we cannot set a breakpoint in our pass yet
1722(the shared object isn't loaded until runtime), we must execute the process, and
1723have it stop before it invokes our pass, but after it has loaded the shared
1724object. The most foolproof way of doing this is to set a breakpoint in
1725<tt>PassManager::run</tt> and then run the process with the arguments you
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1726want:</p>
Chris Lattner480e2ef2002-09-06 02:02:58 +0000[diff] [blame]1727
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1728<div class="doc_code"><pre>
Reid Spencer22a9e5b2006-09-28 16:53:47 +0000[diff] [blame]1729(gdb) <b>break llvm::PassManager::run</b>
Chris Lattner480e2ef2002-09-06 02:02:58 +0000[diff] [blame]1730Breakpoint 1 at 0x2413bc: file Pass.cpp, line 70.
Chris Lattner4c376ea2005-04-21 04:52:37 +0000[diff] [blame]1731(gdb) <b>run test.bc -load $(LLVMTOP)/llvm/Debug/lib/[libname].so -[passoption]</b>
1732Starting program: opt test.bc -load $(LLVMTOP)/llvm/Debug/lib/[libname].so -[passoption]
Chris Lattner480e2ef2002-09-06 02:02:58 +0000[diff] [blame]1733Breakpoint 1, PassManager::run (this=0xffbef174, M=@0x70b298) at Pass.cpp:70
173470 bool PassManager::run(Module &amp;M) { return PM-&gt;run(M); }
1735(gdb)
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1736</pre></div>
Chris Lattner480e2ef2002-09-06 02:02:58 +0000[diff] [blame]1737
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1738<p>Once the <tt>opt</tt> stops in the <tt>PassManager::run</tt> method you are
1739now free to set breakpoints in your pass so that you can trace through execution
1740or do other standard debugging stuff.</p>
Chris Lattner480e2ef2002-09-06 02:02:58 +0000[diff] [blame]1741
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1742</div>
Chris Lattner480e2ef2002-09-06 02:02:58 +0000[diff] [blame]1743
1744<!-- _______________________________________________________________________ -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1745<div class="doc_subsubsection">
1746 <a name="debugmisc">Miscellaneous Problems</a>
1747</div>
Chris Lattner480e2ef2002-09-06 02:02:58 +0000[diff] [blame]1748
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1749<div class="doc_text">
1750
1751<p>Once you have the basics down, there are a couple of problems that GDB has,
1752some with solutions, some without.</p>
Chris Lattner480e2ef2002-09-06 02:02:58 +0000[diff] [blame]1753
1754<ul>
1755<li>Inline functions have bogus stack information. In general, GDB does a
1756pretty good job getting stack traces and stepping through inline functions.
1757When a pass is dynamically loaded however, it somehow completely loses this
1758capability. The only solution I know of is to de-inline a function (move it
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1759from the body of a class to a .cpp file).</li>
Chris Lattner480e2ef2002-09-06 02:02:58 +0000[diff] [blame]1760
1761<li>Restarting the program breaks breakpoints. After following the information
1762above, you have succeeded in getting some breakpoints planted in your pass. Nex
1763thing you know, you restart the program (i.e., you type '<tt>run</tt>' again),
1764and you start getting errors about breakpoints being unsettable. The only way I
1765have found to "fix" this problem is to <tt>delete</tt> the breakpoints that are
1766already set in your pass, run the program, and re-set the breakpoints once
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1767execution stops in <tt>PassManager::run</tt>.</li>
Chris Lattner480e2ef2002-09-06 02:02:58 +0000[diff] [blame]1768
1769</ul>
1770
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1771<p>Hopefully these tips will help with common case debugging situations. If
1772you'd like to contribute some tips of your own, just contact <a
1773href="mailto:sabre@nondot.org">Chris</a>.</p>
Chris Lattner480e2ef2002-09-06 02:02:58 +0000[diff] [blame]1774
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1775</div>
Chris Lattner480e2ef2002-09-06 02:02:58 +0000[diff] [blame]1776
1777<!-- *********************************************************************** -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1778<div class="doc_section">
1779 <a name="future">Future extensions planned</a>
1780</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1781<!-- *********************************************************************** -->
1782
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1783<div class="doc_text">
1784
1785<p>Although the LLVM Pass Infrastructure is very capable as it stands, and does
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1786some 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]1787where we are going:</p>
1788
1789</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1790
1791<!-- _______________________________________________________________________ -->
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]1792<div class="doc_subsubsection">
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1793 <a name="SMP">Multithreaded LLVM</a>
1794</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1795
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1796<div class="doc_text">
1797
1798<p>Multiple CPU machines are becoming more common and compilation can never be
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1799fast enough: obviously we should allow for a multithreaded compiler. Because of
1800the semantics defined for passes above (specifically they cannot maintain state
1801across invocations of their <tt>run*</tt> methods), a nice clean way to
1802implement a multithreaded compiler would be for the <tt>PassManager</tt> class
Misha Brukmanbc0e9982003-07-14 17:20:40 +0000[diff] [blame]1803to create multiple instances of each pass object, and allow the separate
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1804instances to be hacking on different parts of the program at the same time.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1805
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1806<p>This implementation would prevent each of the passes from having to implement
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1807multithreaded constructs, requiring only the LLVM core to have locking in a few
1808places (for global resources). Although this is a simple extension, we simply
1809haven't had time (or multiprocessor machines, thus a reason) to implement this.
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1810Despite that, we have kept the LLVM passes SMP ready, and you should too.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1811
Chris Lattnerb5c87f62007-05-18 05:36:14 +0000[diff] [blame]1812</div>
1813
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1814<!-- *********************************************************************** -->
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