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gerrit-public.fairphone.software / fp2-dev / platform / external / llvm / 9f116aa3b1ece85b863099ffa7ea1cab88ef46a8 / . / 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
Torok Edwin87469292009-10-12 13:37:29 +0000[diff] [blame]182# Path to top level of LLVM hierarchy
Chris Lattner7ce83e52002-08-14 20:07:01 +0000[diff] [blame]183LEVEL = ../../..
Chris Lattner17a4c3e2002-08-14 20:06:13 +0000[diff] [blame]184
185# Name of the library to build
Reid Spencer7fa6d522005-01-11 05:16:23 +0000[diff] [blame]186LIBRARYNAME = Hello
Chris Lattner17a4c3e2002-08-14 20:06:13 +0000[diff] [blame]187
Reid Spencer7fa6d522005-01-11 05:16:23 +0000[diff] [blame]188# Make the shared library become a loadable module so the tools can
189# dlopen/dlsym on the resulting library.
Robert Bocchino3cf817d2006-01-06 22:49:23 +0000[diff] [blame]190LOADABLE_MODULE = 1
Reid Spencer7fa6d522005-01-11 05:16:23 +0000[diff] [blame]191
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>"
Chris Lattner0ce6f932009-09-08 05:14:44 +0000[diff] [blame]226<b>#include</b> "<a href="http://llvm.org/doxygen/raw__ostream_8h.html">llvm/Support/raw_ostream.h</a>"
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]227</pre></div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]228
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]229<p>Which are needed because we are writing a <tt><a
Chris Lattner0ce6f932009-09-08 05:14:44 +0000[diff] [blame]230href="http://llvm.org/doxygen/classllvm_1_1Pass.html">Pass</a></tt>,
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]231we are operating on <tt><a
Chris Lattner0ce6f932009-09-08 05:14:44 +0000[diff] [blame]232href="http://llvm.org/doxygen/classllvm_1_1Function.html">Function</a></tt>'s,
233and we will be doing some printing.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]234
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]235<p>Next we have:</p>
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]236<div class="doc_code"><pre>
Jonathan Manton65acb302004-06-30 18:10:30 +0000[diff] [blame]237<b>using namespace llvm;</b>
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]238</pre></div>
Jonathan Manton65acb302004-06-30 18:10:30 +0000[diff] [blame]239<p>... which is required because the functions from the include files
240live in the llvm namespace.
241</p>
242
243<p>Next we have:</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]244
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]245<div class="doc_code"><pre>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]246<b>namespace</b> {
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]247</pre></div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]248
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]249<p>... which starts out an anonymous namespace. Anonymous namespaces are to C++
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]250what the "<tt>static</tt>" keyword is to C (at global scope). It makes the
251things declared inside of the anonymous namespace only visible to the current
252file. If you're not familiar with them, consult a decent C++ book for more
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]253information.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]254
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]255<p>Next, we declare our pass itself:</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]256
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]257<div class="doc_code"><pre>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]258 <b>struct</b> Hello : <b>public</b> <a href="#FunctionPass">FunctionPass</a> {
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]259</pre></div><p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]260
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]261<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]262href="http://llvm.org/doxygen/classllvm_1_1FunctionPass.html">FunctionPass</a></tt>.
Chris Lattnerd6ea9262002-09-09 03:48:46 +0000[diff] [blame]263The different builtin pass subclasses are described in detail <a
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]264href="#passtype">later</a>, but for now, know that <a
265href="#FunctionPass"><tt>FunctionPass</tt></a>'s operate a function at a
266time.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]267
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]268<div class="doc_code"><pre>
Devang Patel19974732007-05-03 01:11:54 +0000[diff] [blame]269 static char ID;
Dan Gohman865f0062009-02-18 05:09:16 +0000[diff] [blame]270 Hello() : FunctionPass(&amp;ID) {}
Devang Patele50fb9a2007-05-01 20:55:38 +0000[diff] [blame]271</pre></div><p>
272
273<p> This declares pass identifier used by LLVM to identify pass. This allows LLVM to
274avoid using expensive C++ runtime information.</p>
275
276<div class="doc_code"><pre>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]277 <b>virtual bool</b> <a href="#runOnFunction">runOnFunction</a>(Function &amp;F) {
Chris Lattner0ce6f932009-09-08 05:14:44 +0000[diff] [blame]278 errs() &lt;&lt; "<i>Hello: </i>" &lt;&lt; F.getName() &lt;&lt; "\n";
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]279 <b>return false</b>;
280 }
281 }; <i>// end of struct Hello</i>
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]282</pre></div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]283
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]284<p>We declare a "<a href="#runOnFunction"><tt>runOnFunction</tt></a>" method,
285which overloads an abstract virtual method inherited from <a
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]286href="#FunctionPass"><tt>FunctionPass</tt></a>. This is where we are supposed
287to 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]288function.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]289
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]290<div class="doc_code"><pre>
Devang Patel19974732007-05-03 01:11:54 +0000[diff] [blame]291 char Hello::ID = 0;
Devang Patele50fb9a2007-05-01 20:55:38 +0000[diff] [blame]292</pre></div>
293
294<p> We initialize pass ID here. LLVM uses ID's address to identify pass so
295initialization value is not important.</p>
296
297<div class="doc_code"><pre>
Devang Patelc7582092008-03-19 21:56:59 +0000[diff] [blame]298 RegisterPass&lt;Hello&gt; X("<i>hello</i>", "<i>Hello World Pass</i>",
299 false /* Only looks at CFG */,
300 false /* Analysis Pass */);
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]301} <i>// end of anonymous namespace</i>
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]302</pre></div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]303
Chris Lattnerc8603c22006-08-27 23:18:52 +0000[diff] [blame]304<p>Lastly, we <a href="#registration">register our class</a> <tt>Hello</tt>,
305giving it a command line
Devang Patelc7582092008-03-19 21:56:59 +0000[diff] [blame]306argument "<tt>hello</tt>", and a name "<tt>Hello World Pass</tt>".
307Last two RegisterPass arguments are optional. Their default value is false.
308If a pass walks CFG without modifying it then third argument is set to true.
309If a pass is an analysis pass, for example dominator tree pass, then true
310is supplied as fourth argument. </p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]311
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]312<p>As a whole, the <tt>.cpp</tt> file looks like:</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]313
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]314<div class="doc_code"><pre>
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]315<b>#include</b> "<a href="http://llvm.org/doxygen/Pass_8h-source.html">llvm/Pass.h</a>"
316<b>#include</b> "<a href="http://llvm.org/doxygen/Function_8h-source.html">llvm/Function.h</a>"
Chris Lattner0ce6f932009-09-08 05:14:44 +0000[diff] [blame]317<b>#include</b> "<a href="http://llvm.org/doxygen/raw__ostream_8h.html">llvm/Support/raw_ostream.h</a>"
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]318
Jonathan Manton65acb302004-06-30 18:10:30 +0000[diff] [blame]319<b>using namespace llvm;</b>
320
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]321<b>namespace</b> {
322 <b>struct Hello</b> : <b>public</b> <a href="#FunctionPass">FunctionPass</a> {
Devang Patele50fb9a2007-05-01 20:55:38 +0000[diff] [blame]323
Devang Patel19974732007-05-03 01:11:54 +0000[diff] [blame]324 static char ID;
Dan Gohman865f0062009-02-18 05:09:16 +0000[diff] [blame]325 Hello() : FunctionPass(&amp;ID) {}
Devang Patele50fb9a2007-05-01 20:55:38 +0000[diff] [blame]326
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]327 <b>virtual bool</b> <a href="#runOnFunction">runOnFunction</a>(Function &amp;F) {
Chris Lattner0ce6f932009-09-08 05:14:44 +0000[diff] [blame]328 errs() &lt;&lt; "<i>Hello: </i>" &lt;&lt; F.getName() &lt;&lt; "\n";
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]329 <b>return false</b>;
330 }
331 };
332
Devang Patel26e5a302007-07-25 21:05:39 +0000[diff] [blame]333 char Hello::ID = 0;
Chris Lattnerc8603c22006-08-27 23:18:52 +0000[diff] [blame]334 RegisterPass&lt;Hello&gt; X("<i>hello</i>", "<i>Hello World Pass</i>");
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]335}
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]336</pre></div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]337
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]338<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]339command in the local directory and you should get a new
Reid Spencer7fa6d522005-01-11 05:16:23 +0000[diff] [blame]340"<tt>Debug/lib/Hello.so</tt> file. Note that everything in this file is
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]341contained in an anonymous namespace: this reflects the fact that passes are self
342contained units that do not need external interfaces (although they can have
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]343them) to be useful.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]344
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]345</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]346
347<!-- ======================================================================= -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]348<div class="doc_subsection">
Chris Lattnerc8603c22006-08-27 23:18:52 +0000[diff] [blame]349 <a name="running">Running a pass with <tt>opt</tt></a>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]350</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]351
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]352<div class="doc_text">
353
John Criswellf9c78652004-01-26 21:26:54 +0000[diff] [blame]354<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]355<tt>opt</tt> command to run an LLVM program through your pass. Because you
Chris Lattnerc8603c22006-08-27 23:18:52 +0000[diff] [blame]356registered your pass with the <tt>RegisterPass</tt> template, you will be able to
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]357use the <tt>opt</tt> tool to access it, once loaded.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]358
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]359<p>To test it, follow the example at the end of the <a
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]360href="GettingStarted.html">Getting Started Guide</a> to compile "Hello World" to
Gabor Greif04367bf2007-07-06 22:07:22 +0000[diff] [blame]361LLVM. We can now run the bitcode file (<tt>hello.bc</tt>) for the program
362through our transformation like this (or course, any bitcode file will
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]363work):</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]364
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]365<div class="doc_code"><pre>
Reid Spencer7fa6d522005-01-11 05:16:23 +0000[diff] [blame]366$ opt -load ../../../Debug/lib/Hello.so -hello &lt; hello.bc &gt; /dev/null
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]367Hello: __main
368Hello: puts
369Hello: main
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]370</pre></div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]371
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]372<p>The '<tt>-load</tt>' option specifies that '<tt>opt</tt>' should load your
373pass as a shared object, which makes '<tt>-hello</tt>' a valid command line
374argument (which is one reason you need to <a href="#registration">register your
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]375pass</a>). Because the hello pass does not modify the program in any
376interesting way, we just throw away the result of <tt>opt</tt> (sending it to
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]377<tt>/dev/null</tt>).</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]378
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]379<p>To see what happened to the other string you registered, try running
Duncan Sands7e7ae5a2010-02-18 14:08:13 +0000[diff] [blame]380<tt>opt</tt> with the <tt>-help</tt> option:</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]381
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]382<div class="doc_code"><pre>
Duncan Sands7e7ae5a2010-02-18 14:08:13 +0000[diff] [blame]383$ opt -load ../../../Debug/lib/Hello.so -help
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]384OVERVIEW: llvm .bc -&gt; .bc modular optimizer
385
Gabor Greif04367bf2007-07-06 22:07:22 +0000[diff] [blame]386USAGE: opt [options] &lt;input bitcode&gt;
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]387
388OPTIONS:
389 Optimizations available:
390...
391 -funcresolve - Resolve Functions
392 -gcse - Global Common Subexpression Elimination
393 -globaldce - Dead Global Elimination
394 <b>-hello - Hello World Pass</b>
Chris Lattner065a6162003-09-10 05:29:43 +0000[diff] [blame]395 -indvars - Canonicalize Induction Variables
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]396 -inline - Function Integration/Inlining
397 -instcombine - Combine redundant instructions
398...
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]399</pre></div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]400
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]401<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]402documentation to users of <tt>opt</tt>. Now that you have a working pass, you
403would go ahead and make it do the cool transformations you want. Once you get
404it all working and tested, it may become useful to find out how fast your pass
405is. The <a href="#passManager"><tt>PassManager</tt></a> provides a nice command
406line option (<tt>--time-passes</tt>) that allows you to get information about
407the execution time of your pass along with the other passes you queue up. For
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]408example:</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]409
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]410<div class="doc_code"><pre>
Reid Spencer7fa6d522005-01-11 05:16:23 +0000[diff] [blame]411$ 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]412Hello: __main
413Hello: puts
414Hello: main
415===============================================================================
416 ... Pass execution timing report ...
417===============================================================================
418 Total Execution Time: 0.02 seconds (0.0479059 wall clock)
419
420 ---User Time--- --System Time-- --User+System-- ---Wall Time--- --- Pass Name ---
Gabor Greif04367bf2007-07-06 22:07:22 +0000[diff] [blame]421 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]422 0.0000 ( 0.0%) 0.0100 (100.0%) 0.0100 ( 50.0%) 0.0031 ( 6.4%) Dominator Set Construction
423 0.0000 ( 0.0%) 0.0000 ( 0.0%) 0.0000 ( 0.0%) 0.0013 ( 2.7%) Module Verifier
424 <b> 0.0000 ( 0.0%) 0.0000 ( 0.0%) 0.0000 ( 0.0%) 0.0033 ( 6.9%) Hello World Pass</b>
425 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]426</pre></div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]427
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]428<p>As you can see, our implementation above is pretty fast :). The additional
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]429passes listed are automatically inserted by the '<tt>opt</tt>' tool to verify
430that the LLVM emitted by your pass is still valid and well formed LLVM, which
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]431hasn't been broken somehow.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]432
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]433<p>Now that you have seen the basics of the mechanics behind passes, we can talk
434about some more details of how they work and how to use them.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]435
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]436</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]437
438<!-- *********************************************************************** -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]439<div class="doc_section">
440 <a name="passtype">Pass classes and requirements</a>
441</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]442<!-- *********************************************************************** -->
443
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]444<div class="doc_text">
445
446<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]447decide what class you should subclass for your pass. The <a
448href="#basiccode">Hello World</a> example uses the <tt><a
449href="#FunctionPass">FunctionPass</a></tt> class for its implementation, but we
450did not discuss why or when this should occur. Here we talk about the classes
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]451available, from the most general to the most specific.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]452
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]453<p>When choosing a superclass for your Pass, you should choose the <b>most
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]454specific</b> class possible, while still being able to meet the requirements
Misha Brukman5560c9d2003-08-18 14:43:39 +0000[diff] [blame]455listed. This gives the LLVM Pass Infrastructure information necessary to
Benjamin Kramer8040cd32009-10-12 14:46:08 +0000[diff] [blame]456optimize how passes are run, so that the resultant compiler isn't unnecessarily
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]457slow.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]458
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]459</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]460
Chris Lattnerf004f9a2002-09-25 22:31:38 +0000[diff] [blame]461<!-- ======================================================================= -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]462<div class="doc_subsection">
463 <a name="ImmutablePass">The <tt>ImmutablePass</tt> class</a>
464</div>
Chris Lattnerf004f9a2002-09-25 22:31:38 +0000[diff] [blame]465
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]466<div class="doc_text">
467
468<p>The most plain and boring type of pass is the "<tt><a
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]469href="http://llvm.org/doxygen/classllvm_1_1ImmutablePass.html">ImmutablePass</a></tt>"
Chris Lattnerf004f9a2002-09-25 22:31:38 +0000[diff] [blame]470class. This pass type is used for passes that do not have to be run, do not
471change state, and never need to be updated. This is not a normal type of
472transformation or analysis, but can provide information about the current
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]473compiler configuration.</p>
Chris Lattnerf004f9a2002-09-25 22:31:38 +0000[diff] [blame]474
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]475<p>Although this pass class is very infrequently used, it is important for
Chris Lattnerf004f9a2002-09-25 22:31:38 +0000[diff] [blame]476providing information about the current target machine being compiled for, and
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]477other static information that can affect the various transformations.</p>
Chris Lattnerf004f9a2002-09-25 22:31:38 +0000[diff] [blame]478
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]479<p><tt>ImmutablePass</tt>es never invalidate other transformations, are never
480invalidated, and are never "run".</p>
Chris Lattnerf004f9a2002-09-25 22:31:38 +0000[diff] [blame]481
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]482</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]483
484<!-- ======================================================================= -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]485<div class="doc_subsection">
Chris Lattnerf6278922004-09-20 04:36:29 +0000[diff] [blame]486 <a name="ModulePass">The <tt>ModulePass</tt> class</a>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]487</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]488
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]489<div class="doc_text">
490
491<p>The "<tt><a
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]492href="http://llvm.org/doxygen/classllvm_1_1ModulePass.html">ModulePass</a></tt>"
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]493class is the most general of all superclasses that you can use. Deriving from
Chris Lattnerf6278922004-09-20 04:36:29 +0000[diff] [blame]494<tt>ModulePass</tt> indicates that your pass uses the entire program as a unit,
Benjamin Kramer8040cd32009-10-12 14:46:08 +0000[diff] [blame]495referring to function bodies in no predictable order, or adding and removing
Chris Lattnerf6278922004-09-20 04:36:29 +0000[diff] [blame]496functions. Because nothing is known about the behavior of <tt>ModulePass</tt>
Daniel Dunbarb71725b2009-07-01 23:38:44 +0000[diff] [blame]497subclasses, no optimization can be done for their execution.</p>
498
499<p>A module pass can use function level passes (e.g. dominators) using
500the getAnalysis interface
501<tt>getAnalysis&lt;DominatorTree&gt;(llvm::Function *)</tt> to provide the
502function to retrieve analysis result for, if the function pass does not require
Devang Patel468857f2009-08-10 16:37:29 +0000[diff] [blame]503any module or immutable passes. Note that this can only be done for functions for which the
Daniel Dunbarb71725b2009-07-01 23:38:44 +0000[diff] [blame]504analysis ran, e.g. in the case of dominators you should only ask for the
505DominatorTree for function definitions, not declarations.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]506
Chris Lattnerf6278922004-09-20 04:36:29 +0000[diff] [blame]507<p>To write a correct <tt>ModulePass</tt> subclass, derive from
508<tt>ModulePass</tt> and overload the <tt>runOnModule</tt> method with the
509following signature:</p>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]510
511</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]512
513<!-- _______________________________________________________________________ -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]514<div class="doc_subsubsection">
Chris Lattnerf6278922004-09-20 04:36:29 +0000[diff] [blame]515 <a name="runOnModule">The <tt>runOnModule</tt> method</a>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]516</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]517
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]518<div class="doc_text">
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]519
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]520<div class="doc_code"><pre>
Chris Lattnerf6278922004-09-20 04:36:29 +0000[diff] [blame]521 <b>virtual bool</b> runOnModule(Module &amp;M) = 0;
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]522</pre></div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]523
John Criswell2382ff72005-07-15 19:25:12 +0000[diff] [blame]524<p>The <tt>runOnModule</tt> method performs the interesting work of the pass.
525It should return true if the module was modified by the transformation and
526false otherwise.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]527
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]528</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]529
530<!-- ======================================================================= -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]531<div class="doc_subsection">
Chris Lattner8fdb2462004-09-18 06:39:35 +0000[diff] [blame]532 <a name="CallGraphSCCPass">The <tt>CallGraphSCCPass</tt> class</a>
533</div>
534
535<div class="doc_text">
536
537<p>The "<tt><a
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]538href="http://llvm.org/doxygen/classllvm_1_1CallGraphSCCPass.html">CallGraphSCCPass</a></tt>"
Chris Lattner8fdb2462004-09-18 06:39:35 +0000[diff] [blame]539is used by passes that need to traverse the program bottom-up on the call graph
540(callees before callers). Deriving from CallGraphSCCPass provides some
541mechanics for building and traversing the CallGraph, but also allows the system
542to optimize execution of CallGraphSCCPass's. If your pass meets the
543requirements outlined below, and doesn't meet the requirements of a <tt><a
544href="#FunctionPass">FunctionPass</a></tt> or <tt><a
545href="#BasicBlockPass">BasicBlockPass</a></tt>, you should derive from
546<tt>CallGraphSCCPass</tt>.</p>
547
548<p><b>TODO</b>: explain briefly what SCC, Tarjan's algo, and B-U mean.</p>
549
550<p>To be explicit, <tt>CallGraphSCCPass</tt> subclasses are:</p>
551
552<ol>
553
554<li>... <em>not allowed</em> to modify any <tt>Function</tt>s that are not in
555the current SCC.</li>
556
Tanya Lattner18aad232007-06-07 16:44:52 +0000[diff] [blame]557<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]558current SCC and the direct callees of the SCC.</li>
559
560<li>... <em>required</em> to preserve the current CallGraph object, updating it
561to reflect any changes made to the program.</li>
562
563<li>... <em>not allowed</em> to add or remove SCC's from the current Module,
564though they may change the contents of an SCC.</li>
565
566<li>... <em>allowed</em> to add or remove global variables from the current
567Module.</li>
568
569<li>... <em>allowed</em> to maintain state across invocations of
570 <a href="#runOnSCC"><tt>runOnSCC</tt></a> (including global data).</li>
571</ol>
572
573<p>Implementing a <tt>CallGraphSCCPass</tt> is slightly tricky in some cases
574because it has to handle SCCs with more than one node in it. All of the virtual
575methods described below should return true if they modified the program, or
576false if they didn't.</p>
577
578</div>
579
580<!-- _______________________________________________________________________ -->
581<div class="doc_subsubsection">
Devang Patelc20048d2007-01-23 22:56:28 +0000[diff] [blame]582 <a name="doInitialization_scc">The <tt>doInitialization(CallGraph &amp;)</tt>
Chris Lattner8fdb2462004-09-18 06:39:35 +0000[diff] [blame]583 method</a>
584</div>
585
586<div class="doc_text">
587
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]588<div class="doc_code"><pre>
Devang Patelc20048d2007-01-23 22:56:28 +0000[diff] [blame]589 <b>virtual bool</b> doInitialization(CallGraph &amp;CG);
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]590</pre></div>
Chris Lattner8fdb2462004-09-18 06:39:35 +0000[diff] [blame]591
592<p>The <tt>doIninitialize</tt> method is allowed to do most of the things that
593<tt>CallGraphSCCPass</tt>'s are not allowed to do. They can add and remove
594functions, get pointers to functions, etc. The <tt>doInitialization</tt> method
595is designed to do simple initialization type of stuff that does not depend on
596the SCCs being processed. The <tt>doInitialization</tt> method call is not
597scheduled to overlap with any other pass executions (thus it should be very
598fast).</p>
599
600</div>
601
602<!-- _______________________________________________________________________ -->
603<div class="doc_subsubsection">
604 <a name="runOnSCC">The <tt>runOnSCC</tt> method</a>
605</div>
606
607<div class="doc_text">
608
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]609<div class="doc_code"><pre>
Chris Lattner8fdb2462004-09-18 06:39:35 +0000[diff] [blame]610 <b>virtual bool</b> runOnSCC(const std::vector&lt;CallGraphNode *&gt; &amp;SCCM) = 0;
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]611</pre></div>
Chris Lattner8fdb2462004-09-18 06:39:35 +0000[diff] [blame]612
613<p>The <tt>runOnSCC</tt> method performs the interesting work of the pass, and
614should return true if the module was modified by the transformation, false
615otherwise.</p>
616
617</div>
618
619<!-- _______________________________________________________________________ -->
620<div class="doc_subsubsection">
Devang Patelc20048d2007-01-23 22:56:28 +0000[diff] [blame]621 <a name="doFinalization_scc">The <tt>doFinalization(CallGraph
Chris Lattner8fdb2462004-09-18 06:39:35 +0000[diff] [blame]622 &amp;)</tt> method</a>
623</div>
624
625<div class="doc_text">
626
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]627<div class="doc_code"><pre>
Devang Patelc20048d2007-01-23 22:56:28 +0000[diff] [blame]628 <b>virtual bool</b> doFinalization(CallGraph &amp;CG);
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]629</pre></div>
Chris Lattner8fdb2462004-09-18 06:39:35 +0000[diff] [blame]630
631<p>The <tt>doFinalization</tt> method is an infrequently used method that is
632called when the pass framework has finished calling <a
633href="#runOnFunction"><tt>runOnFunction</tt></a> for every function in the
634program being compiled.</p>
635
636</div>
637
638<!-- ======================================================================= -->
639<div class="doc_subsection">
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]640 <a name="FunctionPass">The <tt>FunctionPass</tt> class</a>
641</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]642
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]643<div class="doc_text">
644
Chris Lattnerf6278922004-09-20 04:36:29 +0000[diff] [blame]645<p>In contrast to <tt>ModulePass</tt> subclasses, <tt><a
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]646href="http://llvm.org/doxygen/classllvm_1_1Pass.html">FunctionPass</a></tt>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]647subclasses do have a predictable, local behavior that can be expected by the
648system. All <tt>FunctionPass</tt> execute on each function in the program
Misha Brukmanef6a6a62003-08-21 22:14:26 +0000[diff] [blame]649independent of all of the other functions in the program.
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]650<tt>FunctionPass</tt>'s do not require that they are executed in a particular
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]651order, and <tt>FunctionPass</tt>'s do not modify external functions.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]652
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]653<p>To be explicit, <tt>FunctionPass</tt> subclasses are not allowed to:</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]654
655<ol>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]656<li>Modify a Function other than the one currently being processed.</li>
657<li>Add or remove Function's from the current Module.</li>
658<li>Add or remove global variables from the current Module.</li>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]659<li>Maintain state across invocations of
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]660 <a href="#runOnFunction"><tt>runOnFunction</tt></a> (including global data)</li>
661</ol>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]662
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]663<p>Implementing a <tt>FunctionPass</tt> is usually straightforward (See the <a
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]664href="#basiccode">Hello World</a> pass for example). <tt>FunctionPass</tt>'s
665may overload three virtual methods to do their work. All of these methods
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]666should return true if they modified the program, or false if they didn't.</p>
667
668</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]669
670<!-- _______________________________________________________________________ -->
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]671<div class="doc_subsubsection">
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]672 <a name="doInitialization_mod">The <tt>doInitialization(Module &amp;)</tt>
673 method</a>
674</div>
675
676<div class="doc_text">
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]677
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]678<div class="doc_code"><pre>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]679 <b>virtual bool</b> doInitialization(Module &amp;M);
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]680</pre></div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]681
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]682<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]683<tt>FunctionPass</tt>'s are not allowed to do. They can add and remove
Chris Lattnerd0713f92002-09-12 17:06:43 +0000[diff] [blame]684functions, get pointers to functions, etc. The <tt>doInitialization</tt> method
685is designed to do simple initialization type of stuff that does not depend on
686the functions being processed. The <tt>doInitialization</tt> method call is not
687scheduled to overlap with any other pass executions (thus it should be very
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]688fast).</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]689
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]690<p>A good example of how this method should be used is the <a
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]691href="http://llvm.org/doxygen/LowerAllocations_8cpp-source.html">LowerAllocations</a>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]692pass. This pass converts <tt>malloc</tt> and <tt>free</tt> instructions into
Misha Brukmanef6a6a62003-08-21 22:14:26 +0000[diff] [blame]693platform dependent <tt>malloc()</tt> and <tt>free()</tt> function calls. It
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]694uses the <tt>doInitialization</tt> method to get a reference to the malloc and
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]695free functions that it needs, adding prototypes to the module if necessary.</p>
696
697</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]698
699<!-- _______________________________________________________________________ -->
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]700<div class="doc_subsubsection">
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]701 <a name="runOnFunction">The <tt>runOnFunction</tt> method</a>
702</div>
703
704<div class="doc_text">
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]705
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]706<div class="doc_code"><pre>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]707 <b>virtual bool</b> runOnFunction(Function &amp;F) = 0;
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]708</pre></div><p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]709
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]710<p>The <tt>runOnFunction</tt> method must be implemented by your subclass to do
711the transformation or analysis work of your pass. As usual, a true value should
712be returned if the function is modified.</p>
713
714</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]715
716<!-- _______________________________________________________________________ -->
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]717<div class="doc_subsubsection">
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]718 <a name="doFinalization_mod">The <tt>doFinalization(Module
719 &amp;)</tt> method</a>
720</div>
721
722<div class="doc_text">
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]723
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]724<div class="doc_code"><pre>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]725 <b>virtual bool</b> doFinalization(Module &amp;M);
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]726</pre></div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]727
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]728<p>The <tt>doFinalization</tt> method is an infrequently used method that is
729called when the pass framework has finished calling <a
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]730href="#runOnFunction"><tt>runOnFunction</tt></a> for every function in the
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]731program being compiled.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]732
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]733</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]734
735<!-- ======================================================================= -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]736<div class="doc_subsection">
Devang Patel2e8f27d2007-03-19 22:21:25 +0000[diff] [blame]737 <a name="LoopPass">The <tt>LoopPass</tt> class </a>
738</div>
739
740<div class="doc_text">
741
742<p> All <tt>LoopPass</tt> execute on each loop in the function independent of
743all of the other loops in the function. <tt>LoopPass</tt> processes loops in
744loop nest order such that outer most loop is processed last. </p>
745
746<p> <tt>LoopPass</tt> subclasses are allowed to update loop nest using
747<tt>LPPassManager</tt> interface. Implementing a loop pass is usually
748straightforward. <tt>Looppass</tt>'s may overload three virtual methods to
749do their work. All these methods should return true if they modified the
750program, or false if they didn't. </p>
751</div>
752
753<!-- _______________________________________________________________________ -->
754<div class="doc_subsubsection">
755 <a name="doInitialization_loop">The <tt>doInitialization(Loop *,
756 LPPassManager &amp;)</tt>
757 method</a>
758</div>
759
760<div class="doc_text">
761
762<div class="doc_code"><pre>
763 <b>virtual bool</b> doInitialization(Loop *, LPPassManager &amp;LPM);
764</pre></div>
765
Chris Lattnerb5c87f62007-05-18 05:36:14 +0000[diff] [blame]766<p>The <tt>doInitialization</tt> method is designed to do simple initialization
Devang Patel2e8f27d2007-03-19 22:21:25 +0000[diff] [blame]767type of stuff that does not depend on the functions being processed. The
768<tt>doInitialization</tt> method call is not scheduled to overlap with any
769other pass executions (thus it should be very fast). LPPassManager
770interface should be used to access Function or Module level analysis
771information.</p>
772
773</div>
774
775
776<!-- _______________________________________________________________________ -->
777<div class="doc_subsubsection">
778 <a name="runOnLoop">The <tt>runOnLoop</tt> method</a>
779</div>
780
781<div class="doc_text">
782
783<div class="doc_code"><pre>
784 <b>virtual bool</b> runOnLoop(Loop *, LPPassManager &amp;LPM) = 0;
785</pre></div><p>
786
787<p>The <tt>runOnLoop</tt> method must be implemented by your subclass to do
788the transformation or analysis work of your pass. As usual, a true value should
789be returned if the function is modified. <tt>LPPassManager</tt> interface
790should be used to update loop nest.</p>
791
792</div>
793
794<!-- _______________________________________________________________________ -->
795<div class="doc_subsubsection">
796 <a name="doFinalization_loop">The <tt>doFinalization()</tt> method</a>
797</div>
798
799<div class="doc_text">
800
801<div class="doc_code"><pre>
802 <b>virtual bool</b> doFinalization();
803</pre></div>
804
805<p>The <tt>doFinalization</tt> method is an infrequently used method that is
806called when the pass framework has finished calling <a
807href="#runOnLoop"><tt>runOnLoop</tt></a> for every loop in the
808program being compiled. </p>
809
810</div>
811
812
813
814<!-- ======================================================================= -->
815<div class="doc_subsection">
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]816 <a name="BasicBlockPass">The <tt>BasicBlockPass</tt> class</a>
817</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]818
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]819<div class="doc_text">
820
821<p><tt>BasicBlockPass</tt>'s are just like <a
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]822href="#FunctionPass"><tt>FunctionPass</tt></a>'s, except that they must limit
823their scope of inspection and modification to a single basic block at a time.
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]824As such, they are <b>not</b> allowed to do any of the following:</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]825
826<ol>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]827<li>Modify or inspect any basic blocks outside of the current one</li>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]828<li>Maintain state across invocations of
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]829 <a href="#runOnBasicBlock"><tt>runOnBasicBlock</tt></a></li>
Reid Spencer1bc19342004-12-11 05:12:57 +0000[diff] [blame]830<li>Modify the control flow graph (by altering terminator instructions)</li>
831<li>Any of the things forbidden for
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]832 <a href="#FunctionPass"><tt>FunctionPass</tt></a>es.</li>
833</ol>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]834
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]835<p><tt>BasicBlockPass</tt>es are useful for traditional local and "peephole"
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]836optimizations. They may override the same <a
Chris Lattnerd0713f92002-09-12 17:06:43 +0000[diff] [blame]837href="#doInitialization_mod"><tt>doInitialization(Module &amp;)</tt></a> and <a
838href="#doFinalization_mod"><tt>doFinalization(Module &amp;)</tt></a> methods that <a
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]839href="#FunctionPass"><tt>FunctionPass</tt></a>'s have, but also have the following virtual methods that may also be implemented:</p>
840
841</div>
Chris Lattnerd0713f92002-09-12 17:06:43 +0000[diff] [blame]842
843<!-- _______________________________________________________________________ -->
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]844<div class="doc_subsubsection">
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]845 <a name="doInitialization_fn">The <tt>doInitialization(Function
846 &amp;)</tt> method</a>
847</div>
848
849<div class="doc_text">
Chris Lattnerd0713f92002-09-12 17:06:43 +0000[diff] [blame]850
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]851<div class="doc_code"><pre>
Chris Lattnerd0713f92002-09-12 17:06:43 +0000[diff] [blame]852 <b>virtual bool</b> doInitialization(Function &amp;F);
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]853</pre></div>
Chris Lattnerd0713f92002-09-12 17:06:43 +0000[diff] [blame]854
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]855<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]856<tt>BasicBlockPass</tt>'s are not allowed to do, but that
857<tt>FunctionPass</tt>'s can. The <tt>doInitialization</tt> method is designed
Reid Spencer1bc19342004-12-11 05:12:57 +0000[diff] [blame]858to do simple initialization that does not depend on the
Chris Lattnerd0713f92002-09-12 17:06:43 +0000[diff] [blame]859BasicBlocks being processed. The <tt>doInitialization</tt> method call is not
860scheduled to overlap with any other pass executions (thus it should be very
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]861fast).</p>
Chris Lattnerd0713f92002-09-12 17:06:43 +0000[diff] [blame]862
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]863</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]864
865<!-- _______________________________________________________________________ -->
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]866<div class="doc_subsubsection">
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]867 <a name="runOnBasicBlock">The <tt>runOnBasicBlock</tt> method</a>
868</div>
869
870<div class="doc_text">
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]871
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]872<div class="doc_code"><pre>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]873 <b>virtual bool</b> runOnBasicBlock(BasicBlock &amp;BB) = 0;
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]874</pre></div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]875
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]876<p>Override this function to do the work of the <tt>BasicBlockPass</tt>. This
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]877function is not allowed to inspect or modify basic blocks other than the
878parameter, and are not allowed to modify the CFG. A true value must be returned
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]879if the basic block is modified.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]880
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]881</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]882
Chris Lattnerd0713f92002-09-12 17:06:43 +0000[diff] [blame]883<!-- _______________________________________________________________________ -->
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]884<div class="doc_subsubsection">
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]885 <a name="doFinalization_fn">The <tt>doFinalization(Function &amp;)</tt>
886 method</a>
887</div>
888
889<div class="doc_text">
Chris Lattnerd0713f92002-09-12 17:06:43 +0000[diff] [blame]890
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]891<div class="doc_code"><pre>
Chris Lattnerd0713f92002-09-12 17:06:43 +0000[diff] [blame]892 <b>virtual bool</b> doFinalization(Function &amp;F);
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]893</pre></div>
Chris Lattnerd0713f92002-09-12 17:06:43 +0000[diff] [blame]894
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]895<p>The <tt>doFinalization</tt> method is an infrequently used method that is
896called when the pass framework has finished calling <a
Chris Lattnerd0713f92002-09-12 17:06:43 +0000[diff] [blame]897href="#runOnBasicBlock"><tt>runOnBasicBlock</tt></a> for every BasicBlock in the
898program being compiled. This can be used to perform per-function
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]899finalization.</p>
Chris Lattnerd0713f92002-09-12 17:06:43 +0000[diff] [blame]900
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]901</div>
Chris Lattnerd0713f92002-09-12 17:06:43 +0000[diff] [blame]902
Brian Gaekecab8b6f2003-07-17 18:53:20 +0000[diff] [blame]903<!-- ======================================================================= -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]904<div class="doc_subsection">
905 <a name="MachineFunctionPass">The <tt>MachineFunctionPass</tt> class</a>
906</div>
Brian Gaekecab8b6f2003-07-17 18:53:20 +0000[diff] [blame]907
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]908<div class="doc_text">
909
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]910<p>A <tt>MachineFunctionPass</tt> is a part of the LLVM code generator that
911executes on the machine-dependent representation of each LLVM function in the
Dan Gohman9f116aa2010-03-10 01:29:39 +0000[diff] [blame^]912program.</p>
913
914<p>Code generator passes are registered and initialized specially by
915<tt>TargetMachine::addPassesToEmitFile</tt> and similar routines, so they
916cannot generally be run from the <tt>opt</tt> or <tt>bugpoint</tt>
917commands.</p>
918
919<p>A <tt>MachineFunctionPass</tt> is also a <tt>FunctionPass</tt>, so all
Brian Gaekecab8b6f2003-07-17 18:53:20 +0000[diff] [blame]920the restrictions that apply to a <tt>FunctionPass</tt> also apply to it.
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]921<tt>MachineFunctionPass</tt>es also have additional restrictions. In particular,
922<tt>MachineFunctionPass</tt>es are not allowed to do any of the following:</p>
Brian Gaekecab8b6f2003-07-17 18:53:20 +0000[diff] [blame]923
924<ol>
Dan Gohman9f116aa2010-03-10 01:29:39 +0000[diff] [blame^]925<li>Modify or create any LLVM IR Instructions, BasicBlocks, Arguments,
926 Functions, GlobalVariables, GlobalAliases, or Modules.</li>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]927<li>Modify a MachineFunction other than the one currently being processed.</li>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]928<li>Maintain state across invocations of <a
929href="#runOnMachineFunction"><tt>runOnMachineFunction</tt></a> (including global
930data)</li>
931</ol>
Brian Gaekecab8b6f2003-07-17 18:53:20 +0000[diff] [blame]932
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]933</div>
Chris Lattnerd0713f92002-09-12 17:06:43 +0000[diff] [blame]934
Brian Gaeke6a33f362003-07-22 20:53:20 +0000[diff] [blame]935<!-- _______________________________________________________________________ -->
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]936<div class="doc_subsubsection">
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]937 <a name="runOnMachineFunction">The <tt>runOnMachineFunction(MachineFunction
938 &amp;MF)</tt> method</a>
939</div>
940
941<div class="doc_text">
Brian Gaeke6a33f362003-07-22 20:53:20 +0000[diff] [blame]942
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]943<div class="doc_code"><pre>
Brian Gaeke6a33f362003-07-22 20:53:20 +0000[diff] [blame]944 <b>virtual bool</b> runOnMachineFunction(MachineFunction &amp;MF) = 0;
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]945</pre></div>
Brian Gaeke6a33f362003-07-22 20:53:20 +0000[diff] [blame]946
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]947<p><tt>runOnMachineFunction</tt> can be considered the main entry point of a
948<tt>MachineFunctionPass</tt>; that is, you should override this method to do the
949work of your <tt>MachineFunctionPass</tt>.</p>
Brian Gaeke6a33f362003-07-22 20:53:20 +0000[diff] [blame]950
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]951<p>The <tt>runOnMachineFunction</tt> method is called on every
Brian Gaeke6a33f362003-07-22 20:53:20 +0000[diff] [blame]952<tt>MachineFunction</tt> in a <tt>Module</tt>, so that the
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]953<tt>MachineFunctionPass</tt> may perform optimizations on the machine-dependent
954representation of the function. If you want to get at the LLVM <tt>Function</tt>
955for the <tt>MachineFunction</tt> you're working on, use
956<tt>MachineFunction</tt>'s <tt>getFunction()</tt> accessor method -- but
957remember, you may not modify the LLVM <tt>Function</tt> or its contents from a
958<tt>MachineFunctionPass</tt>.</p>
959
960</div>
Brian Gaeke6a33f362003-07-22 20:53:20 +0000[diff] [blame]961
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]962<!-- *********************************************************************** -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]963<div class="doc_section">
964 <a name="registration">Pass registration</a>
965</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]966<!-- *********************************************************************** -->
967
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]968<div class="doc_text">
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]969
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]970<p>In the <a href="#basiccode">Hello World</a> example pass we illustrated how
971pass registration works, and discussed some of the reasons that it is used and
972what it does. Here we discuss how and why passes are registered.</p>
973
Chris Lattnerc8603c22006-08-27 23:18:52 +0000[diff] [blame]974<p>As we saw above, passes are registered with the <b><tt>RegisterPass</tt></b>
975template, which requires you to pass at least two
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]976parameters. The first parameter is the name of the pass that is to be used on
977the command line to specify that the pass should be added to a program (for
Chris Lattnerc8603c22006-08-27 23:18:52 +0000[diff] [blame]978example, with <tt>opt</tt> or <tt>bugpoint</tt>). The second argument is the
Duncan Sands7e7ae5a2010-02-18 14:08:13 +0000[diff] [blame]979name of the pass, which is to be used for the <tt>-help</tt> output of
Chris Lattnerc8603c22006-08-27 23:18:52 +0000[diff] [blame]980programs, as
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]981well as for debug output generated by the <tt>--debug-pass</tt> option.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]982
Chris Lattnerc8603c22006-08-27 23:18:52 +0000[diff] [blame]983<p>If you want your pass to be easily dumpable, you should
984implement the virtual <tt>print</tt> method:</p>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]985
986</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]987
988<!-- _______________________________________________________________________ -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]989<div class="doc_subsubsection">
990 <a name="print">The <tt>print</tt> method</a>
991</div>
992
993<div class="doc_text">
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]994
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]995<div class="doc_code"><pre>
Torok Edwin52790e52008-10-28 17:29:23 +0000[diff] [blame]996 <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]997</pre></div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]998
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]999<p>The <tt>print</tt> method must be implemented by "analyses" in order to print
1000a human readable version of the analysis results. This is useful for debugging
1001an analysis itself, as well as for other people to figure out how an analysis
Chris Lattnerc8603c22006-08-27 23:18:52 +0000[diff] [blame]1002works. Use the <tt>opt -analyze</tt> argument to invoke this method.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1003
Bill Wendling832171c2006-12-07 20:04:42 +0000[diff] [blame]1004<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]1005and 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]1006program that has been analyzed. Note however that this pointer may be null in
1007certain circumstances (such as calling the <tt>Pass::dump()</tt> from a
1008debugger), so it should only be used to enhance debug output, it should not be
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1009depended on.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1010
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1011</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1012
1013<!-- *********************************************************************** -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1014<div class="doc_section">
1015 <a name="interaction">Specifying interactions between passes</a>
1016</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1017<!-- *********************************************************************** -->
1018
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1019<div class="doc_text">
1020
John Criswell8528e782007-12-03 19:34:25 +0000[diff] [blame]1021<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]1022that passes interact with each other correctly. Because <tt>PassManager</tt>
1023tries to <a href="#passmanager">optimize the execution of passes</a> it must
1024know how the passes interact with each other and what dependencies exist between
1025the various passes. To track this, each pass can declare the set of passes that
1026are required to be executed before the current pass, and the passes which are
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1027invalidated by the current pass.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1028
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1029<p>Typically this functionality is used to require that analysis results are
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1030computed before your pass is run. Running arbitrary transformation passes can
1031invalidate the computed analysis results, which is what the invalidation set
1032specifies. If a pass does not implement the <tt><a
1033href="#getAnalysisUsage">getAnalysisUsage</a></tt> method, it defaults to not
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1034having any prerequisite passes, and invalidating <b>all</b> other passes.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1035
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1036</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1037
1038<!-- _______________________________________________________________________ -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1039<div class="doc_subsubsection">
1040 <a name="getAnalysisUsage">The <tt>getAnalysisUsage</tt> method</a>
1041</div>
1042
1043<div class="doc_text">
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1044
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1045<div class="doc_code"><pre>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1046 <b>virtual void</b> getAnalysisUsage(AnalysisUsage &amp;Info) <b>const</b>;
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1047</pre></div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1048
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1049<p>By implementing the <tt>getAnalysisUsage</tt> method, the required and
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1050invalidated sets may be specified for your transformation. The implementation
1051should fill in the <tt><a
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]1052href="http://llvm.org/doxygen/classllvm_1_1AnalysisUsage.html">AnalysisUsage</a></tt>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1053object with information about which passes are required and not invalidated. To
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]1054do this, a pass may call any of the following methods on the AnalysisUsage
1055object:</p>
1056</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1057
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]1058<!-- _______________________________________________________________________ -->
1059<div class="doc_subsubsection">
1060 <a name="AU::addRequired">The <tt>AnalysisUsage::addRequired&lt;&gt;</tt> and <tt>AnalysisUsage::addRequiredTransitive&lt;&gt;</tt> methods</a>
1061</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1062
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]1063<div class="doc_text">
1064<p>
Reid Spencer1bc19342004-12-11 05:12:57 +0000[diff] [blame]1065If your pass requires a previous pass to be executed (an analysis for example),
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]1066it can use one of these methods to arrange for it to be run before your pass.
1067LLVM has many different types of analyses and passes that can be required,
Reid Spencer1bc19342004-12-11 05:12:57 +0000[diff] [blame]1068spanning the range from <tt>DominatorSet</tt> to <tt>BreakCriticalEdges</tt>.
1069Requiring <tt>BreakCriticalEdges</tt>, for example, guarantees that there will
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]1070be no critical edges in the CFG when your pass has been run.
1071</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1072
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]1073<p>
1074Some analyses chain to other analyses to do their job. For example, an <a
1075href="AliasAnalysis.html">AliasAnalysis</a> implementation is required to <a
1076href="AliasAnalysis.html#chaining">chain</a> to other alias analysis passes. In
1077cases where analyses chain, the <tt>addRequiredTransitive</tt> method should be
1078used instead of the <tt>addRequired</tt> method. This informs the PassManager
1079that the transitively required pass should be alive as long as the requiring
1080pass is.
1081</p>
1082</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1083
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]1084<!-- _______________________________________________________________________ -->
1085<div class="doc_subsubsection">
1086 <a name="AU::addPreserved">The <tt>AnalysisUsage::addPreserved&lt;&gt;</tt> method</a>
1087</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1088
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]1089<div class="doc_text">
1090<p>
1091One of the jobs of the PassManager is to optimize how and when analyses are run.
1092In particular, it attempts to avoid recomputing data unless it needs to. For
1093this reason, passes are allowed to declare that they preserve (i.e., they don't
1094invalidate) an existing analysis if it's available. For example, a simple
Reid Spencer1bc19342004-12-11 05:12:57 +0000[diff] [blame]1095constant folding pass would not modify the CFG, so it can't possibly affect the
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]1096results of dominator analysis. By default, all passes are assumed to invalidate
1097all others.
1098</p>
1099
1100<p>
1101The <tt>AnalysisUsage</tt> class provides several methods which are useful in
1102certain circumstances that are related to <tt>addPreserved</tt>. In particular,
1103the <tt>setPreservesAll</tt> method can be called to indicate that the pass does
1104not modify the LLVM program at all (which is true for analyses), and the
1105<tt>setPreservesCFG</tt> method can be used by transformations that change
1106instructions in the program but do not modify the CFG or terminator instructions
1107(note that this property is implicitly set for <a
1108href="#BasicBlockPass">BasicBlockPass</a>'s).
1109</p>
1110
1111<p>
1112<tt>addPreserved</tt> is particularly useful for transformations like
1113<tt>BreakCriticalEdges</tt>. This pass knows how to update a small set of loop
1114and dominator related analyses if they exist, so it can preserve them, despite
1115the fact that it hacks on the CFG.
1116</p>
1117</div>
1118
1119<!-- _______________________________________________________________________ -->
1120<div class="doc_subsubsection">
1121 <a name="AU::examples">Example implementations of <tt>getAnalysisUsage</tt></a>
1122</div>
1123
1124<div class="doc_text">
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1125
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1126<div class="doc_code"><pre>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1127 <i>// This is an example implementation from an analysis, which does not modify
1128 // the program at all, yet has a prerequisite.</i>
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]1129 <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]1130 AU.setPreservesAll();
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]1131 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]1132 }
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1133</pre></div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1134
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1135<p>and:</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1136
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1137<div class="doc_code"><pre>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1138 <i>// This example modifies the program, but does not modify the CFG</i>
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]1139 <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]1140 AU.setPreservesCFG();
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]1141 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]1142 }
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1143</pre></div>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1144
1145</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1146
1147<!-- _______________________________________________________________________ -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1148<div class="doc_subsubsection">
Duncan Sands1465d612009-01-28 13:14:17 +0000[diff] [blame]1149 <a name="getAnalysis">The <tt>getAnalysis&lt;&gt;</tt> and
1150<tt>getAnalysisIfAvailable&lt;&gt;</tt> methods</a>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1151</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1152
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1153<div class="doc_text">
1154
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]1155<p>The <tt>Pass::getAnalysis&lt;&gt;</tt> method is automatically inherited by
1156your class, providing you with access to the passes that you declared that you
1157required with the <a href="#getAnalysisUsage"><tt>getAnalysisUsage</tt></a>
1158method. It takes a single template argument that specifies which pass class you
1159want, and returns a reference to that pass. For example:</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1160
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1161<div class="doc_code"><pre>
Chris Lattnera5776302004-03-17 21:33:32 +0000[diff] [blame]1162 bool LICM::runOnFunction(Function &amp;F) {
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]1163 LoopInfo &amp;LI = getAnalysis&lt;LoopInfo&gt;();
1164 ...
1165 }
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1166</pre></div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1167
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1168<p>This method call returns a reference to the pass desired. You may get a
1169runtime assertion failure if you attempt to get an analysis that you did not
1170declare as required in your <a
1171href="#getAnalysisUsage"><tt>getAnalysisUsage</tt></a> implementation. This
1172method can be called by your <tt>run*</tt> method implementation, or by any
Devang Patel3c1ca0b2007-04-16 21:28:14 +0000[diff] [blame]1173other local method invoked by your <tt>run*</tt> method.
1174
1175A module level pass can use function level analysis info using this interface.
1176For example:</p>
1177
1178<div class="doc_code"><pre>
1179 bool ModuleLevelPass::runOnModule(Module &amp;M) {
1180 ...
Devang Patelf23de112007-04-17 00:17:11 +0000[diff] [blame]1181 DominatorTree &amp;DT = getAnalysis&lt;DominatorTree&gt;(Func);
Devang Patel3c1ca0b2007-04-16 21:28:14 +0000[diff] [blame]1182 ...
1183 }
1184</pre></div>
1185
Chris Lattnerb5c87f62007-05-18 05:36:14 +0000[diff] [blame]1186<p>In above example, runOnFunction for DominatorTree is called by pass manager
Devang Patel3c1ca0b2007-04-16 21:28:14 +0000[diff] [blame]1187before returning a reference to the desired pass.</p>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1188
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]1189<p>
1190If your pass is capable of updating analyses if they exist (e.g.,
1191<tt>BreakCriticalEdges</tt>, as described above), you can use the
Duncan Sands1465d612009-01-28 13:14:17 +0000[diff] [blame]1192<tt>getAnalysisIfAvailable</tt> method, which returns a pointer to the analysis
1193if it is active. For example:</p>
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]1194
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1195<div class="doc_code"><pre>
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]1196 ...
Duncan Sands1465d612009-01-28 13:14:17 +0000[diff] [blame]1197 if (DominatorSet *DS = getAnalysisIfAvailable&lt;DominatorSet&gt;()) {
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]1198 <i>// A DominatorSet is active. This code will update it.</i>
1199 }
1200 ...
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1201</pre></div>
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]1202
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1203</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1204
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1205<!-- *********************************************************************** -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1206<div class="doc_section">
1207 <a name="analysisgroup">Implementing Analysis Groups</a>
1208</div>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1209<!-- *********************************************************************** -->
1210
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1211<div class="doc_text">
1212
Chris Lattnerb7632282007-11-16 05:32:05 +0000[diff] [blame]1213<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]1214used, 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]1215fancier. All of the pass relationships that we have seen so far are very
1216simple: one pass depends on one other specific pass to be run before it can run.
1217For many applications, this is great, for others, more flexibility is
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1218required.</p>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1219
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1220<p>In particular, some analyses are defined such that there is a single simple
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1221interface to the analysis results, but multiple ways of calculating them.
1222Consider alias analysis for example. The most trivial alias analysis returns
1223"may alias" for any alias query. The most sophisticated analysis a
1224flow-sensitive, context-sensitive interprocedural analysis that can take a
1225significant amount of time to execute (and obviously, there is a lot of room
1226between these two extremes for other implementations). To cleanly support
1227situations like this, the LLVM Pass Infrastructure supports the notion of
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1228Analysis Groups.</p>
1229
1230</div>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1231
1232<!-- _______________________________________________________________________ -->
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]1233<div class="doc_subsubsection">
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1234 <a name="agconcepts">Analysis Group Concepts</a>
1235</div>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1236
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1237<div class="doc_text">
1238
1239<p>An Analysis Group is a single simple interface that may be implemented by
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1240multiple different passes. Analysis Groups can be given human readable names
1241just like passes, but unlike passes, they need not derive from the <tt>Pass</tt>
1242class. An analysis group may have one or more implementations, one of which is
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1243the "default" implementation.</p>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1244
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1245<p>Analysis groups are used by client passes just like other passes are: the
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1246<tt>AnalysisUsage::addRequired()</tt> and <tt>Pass::getAnalysis()</tt> methods.
1247In order to resolve this requirement, the <a href="#passmanager">PassManager</a>
1248scans the available passes to see if any implementations of the analysis group
1249are available. If none is available, the default implementation is created for
1250the pass to use. All standard rules for <A href="#interaction">interaction
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1251between passes</a> still apply.</p>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1252
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1253<p>Although <a href="#registration">Pass Registration</a> is optional for normal
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1254passes, all analysis group implementations must be registered, and must use the
1255<A href="#registerag"><tt>RegisterAnalysisGroup</tt></a> template to join the
1256implementation pool. Also, a default implementation of the interface
1257<b>must</b> be registered with <A
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1258href="#registerag"><tt>RegisterAnalysisGroup</tt></a>.</p>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1259
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1260<p>As a concrete example of an Analysis Group in action, consider the <a
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]1261href="http://llvm.org/doxygen/classllvm_1_1AliasAnalysis.html">AliasAnalysis</a>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1262analysis group. The default implementation of the alias analysis interface (the
1263<tt><a
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]1264href="http://llvm.org/doxygen/structBasicAliasAnalysis.html">basicaa</a></tt>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1265pass) just does a few simple checks that don't require significant analysis to
1266compute (such as: two different globals can never alias each other, etc).
1267Passes that use the <tt><a
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]1268href="http://llvm.org/doxygen/classllvm_1_1AliasAnalysis.html">AliasAnalysis</a></tt>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1269interface (for example the <tt><a
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]1270href="http://llvm.org/doxygen/structGCSE.html">gcse</a></tt> pass), do
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1271not care which implementation of alias analysis is actually provided, they just
1272use the designated interface.</p>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1273
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1274<p>From the user's perspective, commands work just like normal. Issuing the
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1275command '<tt>opt -gcse ...</tt>' will cause the <tt>basicaa</tt> class to be
1276instantiated and added to the pass sequence. Issuing the command '<tt>opt
1277-somefancyaa -gcse ...</tt>' will cause the <tt>gcse</tt> pass to use the
1278<tt>somefancyaa</tt> alias analysis (which doesn't actually exist, it's just a
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1279hypothetical example) instead.</p>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1280
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1281</div>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1282
1283<!-- _______________________________________________________________________ -->
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]1284<div class="doc_subsubsection">
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1285 <a name="registerag">Using <tt>RegisterAnalysisGroup</tt></a>
1286</div>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1287
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1288<div class="doc_text">
1289
1290<p>The <tt>RegisterAnalysisGroup</tt> template is used to register the analysis
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1291group itself as well as add pass implementations to the analysis group. First,
1292an analysis should be registered, with a human readable name provided for it.
1293Unlike registration of passes, there is no command line argument to be specified
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1294for the Analysis Group Interface itself, because it is "abstract":</p>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1295
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1296<div class="doc_code"><pre>
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]1297 <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]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>Once the analysis is registered, passes can declare that they are valid
1301implementations of the interface by using the following code:</p>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1302
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1303<div class="doc_code"><pre>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1304<b>namespace</b> {
1305 //<i> Analysis Group implementations <b>must</b> be registered normally...</i>
Chris Lattnerc8603c22006-08-27 23:18:52 +0000[diff] [blame]1306 RegisterPass&lt;FancyAA&gt;
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1307 B("<i>somefancyaa</i>", "<i>A more complex alias analysis implementation</i>");
1308
1309 //<i> Declare that we implement the AliasAnalysis interface</i>
Chris Lattnerdc877252006-08-28 00:45:38 +0000[diff] [blame]1310 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]1311}
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1312</pre></div>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1313
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1314<p>This just shows a class <tt>FancyAA</tt> that is registered normally, then
1315uses the <tt>RegisterAnalysisGroup</tt> template to "join" the <tt><a
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]1316href="http://llvm.org/doxygen/classllvm_1_1AliasAnalysis.html">AliasAnalysis</a></tt>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1317analysis group. Every implementation of an analysis group should join using
1318this template. A single pass may join multiple different analysis groups with
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1319no problem.</p>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1320
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1321<div class="doc_code"><pre>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1322<b>namespace</b> {
1323 //<i> Analysis Group implementations <b>must</b> be registered normally...</i>
Chris Lattnerc8603c22006-08-27 23:18:52 +0000[diff] [blame]1324 RegisterPass&lt;<a href="http://llvm.org/doxygen/structBasicAliasAnalysis.html">BasicAliasAnalysis</a>&gt;
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1325 D("<i>basicaa</i>", "<i>Basic Alias Analysis (default AA impl)</i>");
1326
1327 //<i> Declare that we implement the AliasAnalysis interface</i>
Chris Lattnerdc877252006-08-28 00:45:38 +0000[diff] [blame]1328 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]1329}
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1330</pre></div>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1331
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1332<p>Here we show how the default implementation is specified (using the extra
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1333argument to the <tt>RegisterAnalysisGroup</tt> template). There must be exactly
1334one default implementation available at all times for an Analysis Group to be
Devang Patel2397f8d2007-06-20 18:51:14 +0000[diff] [blame]1335used. Only default implementation can derive from <tt>ImmutablePass</tt>.
1336Here we declare that the
1337 <tt><a href="http://llvm.org/doxygen/structBasicAliasAnalysis.html">BasicAliasAnalysis</a></tt>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1338pass is the default implementation for the interface.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1339
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1340</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1341
1342<!-- *********************************************************************** -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1343<div class="doc_section">
Tanya Lattnerd5383652004-11-19 01:25:14 +0000[diff] [blame]1344 <a name="passStatistics">Pass Statistics</a>
1345</div>
1346<!-- *********************************************************************** -->
1347
1348<div class="doc_text">
Tanya Lattner05f8d5f2004-11-19 01:26:37 +0000[diff] [blame]1349<p>The <a
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]1350href="http://llvm.org/doxygen/Statistic_8h-source.html"><tt>Statistic</tt></a>
John Criswell0b1010e2005-11-28 23:25:41 +0000[diff] [blame]1351class is designed to be an easy way to expose various success
Tanya Lattnerd5383652004-11-19 01:25:14 +0000[diff] [blame]1352metrics from passes. These statistics are printed at the end of a
1353run, when the -stats command line option is enabled on the command
Tanya Lattner05f8d5f2004-11-19 01:26:37 +0000[diff] [blame]1354line. 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]1355
1356</div>
1357
1358
1359<!-- *********************************************************************** -->
1360<div class="doc_section">
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1361 <a name="passmanager">What PassManager does</a>
1362</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1363<!-- *********************************************************************** -->
1364
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1365<div class="doc_text">
1366
1367<p>The <a
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]1368href="http://llvm.org/doxygen/PassManager_8h-source.html"><tt>PassManager</tt></a>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1369<a
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]1370href="http://llvm.org/doxygen/classllvm_1_1PassManager.html">class</a>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1371takes a list of passes, ensures their <a href="#interaction">prerequisites</a>
1372are set up correctly, and then schedules passes to run efficiently. All of the
1373LLVM tools that run passes use the <tt>PassManager</tt> for execution of these
1374passes.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1375
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1376<p>The <tt>PassManager</tt> does two main things to try to reduce the execution
1377time of a series of passes:</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1378
1379<ol>
1380<li><b>Share analysis results</b> - The PassManager attempts to avoid
1381recomputing analysis results as much as possible. This means keeping track of
1382which analyses are available already, which analyses get invalidated, and which
1383analyses are needed to be run for a pass. An important part of work is that the
1384<tt>PassManager</tt> tracks the exact lifetime of all analysis results, allowing
1385it to <a href="#releaseMemory">free memory</a> allocated to holding analysis
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1386results as soon as they are no longer needed.</li>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1387
1388<li><b>Pipeline the execution of passes on the program</b> - The
1389<tt>PassManager</tt> attempts to get better cache and memory usage behavior out
1390of a series of passes by pipelining the passes together. This means that, given
1391a series of consequtive <a href="#FunctionPass"><tt>FunctionPass</tt></a>'s, it
1392will execute all of the <a href="#FunctionPass"><tt>FunctionPass</tt></a>'s on
1393the first function, then all of the <a
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1394href="#FunctionPass"><tt>FunctionPass</tt></a>es on the second function,
1395etc... until the entire program has been run through the passes.
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1396
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1397<p>This improves the cache behavior of the compiler, because it is only touching
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1398the LLVM program representation for a single function at a time, instead of
1399traversing the entire program. It reduces the memory consumption of compiler,
1400because, for example, only one <a
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]1401href="http://llvm.org/doxygen/classllvm_1_1DominatorSet.html"><tt>DominatorSet</tt></a>
John Criswell9795bb82007-12-10 20:26:29 +0000[diff] [blame]1402needs to be calculated at a time. This also makes it possible to implement
1403some <a
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1404href="#SMP">interesting enhancements</a> in the future.</p></li>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1405
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1406</ol>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1407
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1408<p>The effectiveness of the <tt>PassManager</tt> is influenced directly by how
1409much information it has about the behaviors of the passes it is scheduling. For
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1410example, the "preserved" set is intentionally conservative in the face of an
1411unimplemented <a href="#getAnalysisUsage"><tt>getAnalysisUsage</tt></a> method.
1412Not implementing when it should be implemented will have the effect of not
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1413allowing any analysis results to live across the execution of your pass.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1414
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1415<p>The <tt>PassManager</tt> class exposes a <tt>--debug-pass</tt> command line
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1416options that is useful for debugging pass execution, seeing how things work, and
1417diagnosing when you should be preserving more analyses than you currently are
1418(To get information about all of the variants of the <tt>--debug-pass</tt>
Duncan Sands7e7ae5a2010-02-18 14:08:13 +0000[diff] [blame]1419option, just type '<tt>opt -help-hidden</tt>').</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1420
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1421<p>By using the <tt>--debug-pass=Structure</tt> option, for example, we can see
1422how our <a href="#basiccode">Hello World</a> pass interacts with other passes.
1423Lets try it out with the <tt>gcse</tt> and <tt>licm</tt> passes:</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1424
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1425<div class="doc_code"><pre>
Reid Spencer7fa6d522005-01-11 05:16:23 +0000[diff] [blame]1426$ 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]1427Module Pass Manager
1428 Function Pass Manager
1429 Dominator Set Construction
1430 Immediate Dominators Construction
1431 Global Common Subexpression Elimination
1432-- Immediate Dominators Construction
1433-- Global Common Subexpression Elimination
1434 Natural Loop Construction
1435 Loop Invariant Code Motion
1436-- Natural Loop Construction
1437-- Loop Invariant Code Motion
1438 Module Verifier
1439-- Dominator Set Construction
1440-- Module Verifier
Gabor Greif04367bf2007-07-06 22:07:22 +0000[diff] [blame]1441 Bitcode Writer
1442--Bitcode Writer
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1443</pre></div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1444
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1445<p>This output shows us when passes are constructed and when the analysis
1446results are known to be dead (prefixed with '<tt>--</tt>'). Here we see that
1447GCSE uses dominator and immediate dominator information to do its job. The LICM
1448pass uses natural loop information, which uses dominator sets, but not immediate
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1449dominators. Because immediate dominators are no longer useful after the GCSE
1450pass, it is immediately destroyed. The dominator sets are then reused to
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1451compute natural loop information, which is then used by the LICM pass.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1452
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1453<p>After the LICM pass, the module verifier runs (which is automatically added
1454by the '<tt>opt</tt>' tool), which uses the dominator set to check that the
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1455resultant LLVM code is well formed. After it finishes, the dominator set
1456information is destroyed, after being computed once, and shared by three
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1457passes.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1458
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1459<p>Lets see how this changes when we run the <a href="#basiccode">Hello
1460World</a> pass in between the two passes:</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1461
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1462<div class="doc_code"><pre>
Reid Spencer7fa6d522005-01-11 05:16:23 +0000[diff] [blame]1463$ 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]1464Module Pass Manager
1465 Function Pass Manager
1466 Dominator Set Construction
1467 Immediate Dominators Construction
1468 Global Common Subexpression Elimination
1469<b>-- Dominator Set Construction</b>
1470-- Immediate Dominators Construction
1471-- Global Common Subexpression Elimination
1472<b> Hello World Pass
1473-- Hello World Pass
1474 Dominator Set Construction</b>
1475 Natural Loop Construction
1476 Loop Invariant Code Motion
1477-- Natural Loop Construction
1478-- Loop Invariant Code Motion
1479 Module Verifier
1480-- Dominator Set Construction
1481-- Module Verifier
Gabor Greif04367bf2007-07-06 22:07:22 +0000[diff] [blame]1482 Bitcode Writer
1483--Bitcode Writer
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1484Hello: __main
1485Hello: puts
1486Hello: main
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1487</pre></div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1488
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1489<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]1490Dominator Set pass, even though it doesn't modify the code at all! To fix this,
1491we need to add the following <a
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1492href="#getAnalysisUsage"><tt>getAnalysisUsage</tt></a> method to our pass:</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1493
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1494<div class="doc_code"><pre>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1495 <i>// We don't modify the program, so we preserve all analyses</i>
1496 <b>virtual void</b> getAnalysisUsage(AnalysisUsage &amp;AU) <b>const</b> {
1497 AU.setPreservesAll();
1498 }
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1499</pre></div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1500
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1501<p>Now when we run our pass, we get this output:</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1502
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1503<div class="doc_code"><pre>
Reid Spencer7fa6d522005-01-11 05:16:23 +0000[diff] [blame]1504$ 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]1505Pass Arguments: -gcse -hello -licm
1506Module Pass Manager
1507 Function Pass Manager
1508 Dominator Set Construction
1509 Immediate Dominators Construction
1510 Global Common Subexpression Elimination
1511-- Immediate Dominators Construction
1512-- Global Common Subexpression Elimination
1513 Hello World Pass
1514-- Hello World Pass
1515 Natural Loop Construction
1516 Loop Invariant Code Motion
1517-- Loop Invariant Code Motion
1518-- Natural Loop Construction
1519 Module Verifier
1520-- Dominator Set Construction
1521-- Module Verifier
Gabor Greif04367bf2007-07-06 22:07:22 +0000[diff] [blame]1522 Bitcode Writer
1523--Bitcode Writer
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1524Hello: __main
1525Hello: puts
1526Hello: main
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1527</pre></div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1528
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1529<p>Which shows that we don't accidentally invalidate dominator information
1530anymore, and therefore do not have to compute it twice.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1531
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1532</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1533
1534<!-- _______________________________________________________________________ -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1535<div class="doc_subsubsection">
1536 <a name="releaseMemory">The <tt>releaseMemory</tt> method</a>
1537</div>
1538
1539<div class="doc_text">
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1540
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1541<div class="doc_code"><pre>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1542 <b>virtual void</b> releaseMemory();
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1543</pre></div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1544
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1545<p>The <tt>PassManager</tt> automatically determines when to compute analysis
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1546results, and how long to keep them around for. Because the lifetime of the pass
1547object itself is effectively the entire duration of the compilation process, we
1548need some way to free analysis results when they are no longer useful. The
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1549<tt>releaseMemory</tt> virtual method is the way to do this.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1550
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1551<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]1552amount of state (for use by another pass which "requires" your pass and uses the
1553<a href="#getAnalysis">getAnalysis</a> method) you should implement
Dan Gohmand87c9e32009-06-15 18:22:49 +0000[diff] [blame]1554<tt>releaseMemory</tt> to, well, release the memory allocated to maintain this
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1555internal state. This method is called after the <tt>run*</tt> method for the
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1556class, before the next call of <tt>run*</tt> in your pass.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1557
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1558</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1559
1560<!-- *********************************************************************** -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1561<div class="doc_section">
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1562 <a name="registering">Registering dynamically loaded passes</a>
1563</div>
1564<!-- *********************************************************************** -->
1565
1566<div class="doc_text">
1567
1568<p><i>Size matters</i> when constructing production quality tools using llvm,
1569both for the purposes of distribution, and for regulating the resident code size
1570when running on the target system. Therefore, it becomes desirable to
1571selectively use some passes, while omitting others and maintain the flexibility
1572to change configurations later on. You want to be able to do all this, and,
1573provide feedback to the user. This is where pass registration comes into
1574play.</p>
1575
1576<p>The fundamental mechanisms for pass registration are the
1577<tt>MachinePassRegistry</tt> class and subclasses of
1578<tt>MachinePassRegistryNode</tt>.</p>
1579
1580<p>An instance of <tt>MachinePassRegistry</tt> is used to maintain a list of
1581<tt>MachinePassRegistryNode</tt> objects. This instance maintains the list and
1582communicates additions and deletions to the command line interface.</p>
1583
1584<p>An instance of <tt>MachinePassRegistryNode</tt> subclass is used to maintain
1585information provided about a particular pass. This information includes the
1586command line name, the command help string and the address of the function used
1587to create an instance of the pass. A global static constructor of one of these
1588instances <i>registers</i> with a corresponding <tt>MachinePassRegistry</tt>,
1589the static destructor <i>unregisters</i>. Thus a pass that is statically linked
1590in the tool will be registered at start up. A dynamically loaded pass will
1591register on load and unregister at unload.</p>
1592
1593</div>
1594
1595<!-- _______________________________________________________________________ -->
1596<div class="doc_subsection">
1597 <a name="registering_existing">Using existing registries</a>
1598</div>
1599
1600<div class="doc_text">
1601
1602<p>There are predefined registries to track instruction scheduling
1603(<tt>RegisterScheduler</tt>) and register allocation (<tt>RegisterRegAlloc</tt>)
1604machine passes. Here we will describe how to <i>register</i> a register
1605allocator machine pass.</p>
1606
1607<p>Implement your register allocator machine pass. In your register allocator
1608.cpp file add the following include;</p>
1609
1610<div class="doc_code"><pre>
Chris Lattner8f652eb2006-08-11 16:37:02 +0000[diff] [blame]1611 #include "llvm/CodeGen/RegAllocRegistry.h"
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1612</pre></div>
1613
1614<p>Also in your register allocator .cpp file, define a creator function in the
1615form; </p>
1616
1617<div class="doc_code"><pre>
1618 FunctionPass *createMyRegisterAllocator() {
1619 return new MyRegisterAllocator();
1620 }
1621</pre></div>
1622
1623<p>Note that the signature of this function should match the type of
1624<tt>RegisterRegAlloc::FunctionPassCtor</tt>. In the same file add the
1625"installing" declaration, in the form;</p>
1626
1627<div class="doc_code"><pre>
1628 static RegisterRegAlloc myRegAlloc("myregalloc",
1629 " my register allocator help string",
1630 createMyRegisterAllocator);
1631</pre></div>
1632
1633<p>Note the two spaces prior to the help string produces a tidy result on the
Duncan Sands7e7ae5a2010-02-18 14:08:13 +0000[diff] [blame]1634-help query.</p>
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1635
1636<div class="doc_code"><pre>
Duncan Sands7e7ae5a2010-02-18 14:08:13 +0000[diff] [blame]1637$ llc -help
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1638 ...
Duncan Sands18619b22010-02-18 14:37:52 +0000[diff] [blame]1639 -regalloc - Register allocator to use (default=linearscan)
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1640 =linearscan - linear scan register allocator
1641 =local - local register allocator
1642 =simple - simple register allocator
1643 =myregalloc - my register allocator help string
1644 ...
1645</pre></div>
1646
1647<p>And that's it. The user is now free to use <tt>-regalloc=myregalloc</tt> as
1648an option. Registering instruction schedulers is similar except use the
Chris Lattner8f652eb2006-08-11 16:37:02 +0000[diff] [blame]1649<tt>RegisterScheduler</tt> class. Note that the
1650<tt>RegisterScheduler::FunctionPassCtor</tt> is significantly different from
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1651<tt>RegisterRegAlloc::FunctionPassCtor</tt>.</p>
1652
1653<p>To force the load/linking of your register allocator into the llc/lli tools,
1654add your creator function's global declaration to "Passes.h" and add a "pseudo"
1655call line to <tt>llvm/Codegen/LinkAllCodegenComponents.h</tt>.</p>
1656
1657</div>
1658
1659
1660<!-- _______________________________________________________________________ -->
1661<div class="doc_subsection">
1662 <a name="registering_new">Creating new registries</a>
1663</div>
1664
1665<div class="doc_text">
1666
1667<p>The easiest way to get started is to clone one of the existing registries; we
1668recommend <tt>llvm/CodeGen/RegAllocRegistry.h</tt>. The key things to modify
1669are the class name and the <tt>FunctionPassCtor</tt> type.</p>
1670
1671<p>Then you need to declare the registry. Example: if your pass registry is
1672<tt>RegisterMyPasses</tt> then define;</p>
1673
1674<div class="doc_code"><pre>
1675MachinePassRegistry RegisterMyPasses::Registry;
1676</pre></div>
1677
1678<p>And finally, declare the command line option for your passes. Example:</p>
1679
1680<div class="doc_code"><pre>
1681 cl::opt&lt;RegisterMyPasses::FunctionPassCtor, false,
Dan Gohman364a39f2008-10-14 17:00:38 +0000[diff] [blame]1682 RegisterPassParser&lt;RegisterMyPasses&gt; &gt;
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1683 MyPassOpt("mypass",
1684 cl::init(&amp;createDefaultMyPass),
1685 cl::desc("my pass option help"));
1686</pre></div>
1687
1688<p>Here the command option is "mypass", with createDefaultMyPass as the default
1689creator.</p>
1690
1691</div>
1692
1693<!-- *********************************************************************** -->
1694<div class="doc_section">
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1695 <a name="debughints">Using GDB with dynamically loaded passes</a>
1696</div>
Chris Lattner480e2ef2002-09-06 02:02:58 +0000[diff] [blame]1697<!-- *********************************************************************** -->
1698
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1699<div class="doc_text">
1700
1701<p>Unfortunately, using GDB with dynamically loaded passes is not as easy as it
Chris Lattner480e2ef2002-09-06 02:02:58 +0000[diff] [blame]1702should be. First of all, you can't set a breakpoint in a shared object that has
1703not been loaded yet, and second of all there are problems with inlined functions
1704in shared objects. Here are some suggestions to debugging your pass with
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1705GDB.</p>
Chris Lattner480e2ef2002-09-06 02:02:58 +0000[diff] [blame]1706
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1707<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]1708transformation invoked by <tt>opt</tt>, although nothing described here depends
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1709on that.</p>
1710
1711</div>
Chris Lattner480e2ef2002-09-06 02:02:58 +0000[diff] [blame]1712
1713<!-- _______________________________________________________________________ -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1714<div class="doc_subsubsection">
1715 <a name="breakpoint">Setting a breakpoint in your pass</a>
1716</div>
Chris Lattner480e2ef2002-09-06 02:02:58 +0000[diff] [blame]1717
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1718<div class="doc_text">
1719
1720<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]1721
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1722<div class="doc_code"><pre>
Chris Lattner480e2ef2002-09-06 02:02:58 +0000[diff] [blame]1723$ <b>gdb opt</b>
1724GNU gdb 5.0
1725Copyright 2000 Free Software Foundation, Inc.
1726GDB is free software, covered by the GNU General Public License, and you are
1727welcome to change it and/or distribute copies of it under certain conditions.
1728Type "show copying" to see the conditions.
1729There is absolutely no warranty for GDB. Type "show warranty" for details.
1730This GDB was configured as "sparc-sun-solaris2.6"...
1731(gdb)
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1732</pre></div>
Chris Lattner480e2ef2002-09-06 02:02:58 +0000[diff] [blame]1733
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1734<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]1735time to load. Be patient. Since we cannot set a breakpoint in our pass yet
1736(the shared object isn't loaded until runtime), we must execute the process, and
1737have it stop before it invokes our pass, but after it has loaded the shared
1738object. The most foolproof way of doing this is to set a breakpoint in
1739<tt>PassManager::run</tt> and then run the process with the arguments you
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1740want:</p>
Chris Lattner480e2ef2002-09-06 02:02:58 +0000[diff] [blame]1741
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1742<div class="doc_code"><pre>
Reid Spencer22a9e5b2006-09-28 16:53:47 +0000[diff] [blame]1743(gdb) <b>break llvm::PassManager::run</b>
Chris Lattner480e2ef2002-09-06 02:02:58 +0000[diff] [blame]1744Breakpoint 1 at 0x2413bc: file Pass.cpp, line 70.
Chris Lattner4c376ea2005-04-21 04:52:37 +0000[diff] [blame]1745(gdb) <b>run test.bc -load $(LLVMTOP)/llvm/Debug/lib/[libname].so -[passoption]</b>
1746Starting program: opt test.bc -load $(LLVMTOP)/llvm/Debug/lib/[libname].so -[passoption]
Chris Lattner480e2ef2002-09-06 02:02:58 +0000[diff] [blame]1747Breakpoint 1, PassManager::run (this=0xffbef174, M=@0x70b298) at Pass.cpp:70
174870 bool PassManager::run(Module &amp;M) { return PM-&gt;run(M); }
1749(gdb)
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1750</pre></div>
Chris Lattner480e2ef2002-09-06 02:02:58 +0000[diff] [blame]1751
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1752<p>Once the <tt>opt</tt> stops in the <tt>PassManager::run</tt> method you are
1753now free to set breakpoints in your pass so that you can trace through execution
1754or do other standard debugging stuff.</p>
Chris Lattner480e2ef2002-09-06 02:02:58 +0000[diff] [blame]1755
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1756</div>
Chris Lattner480e2ef2002-09-06 02:02:58 +0000[diff] [blame]1757
1758<!-- _______________________________________________________________________ -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1759<div class="doc_subsubsection">
1760 <a name="debugmisc">Miscellaneous Problems</a>
1761</div>
Chris Lattner480e2ef2002-09-06 02:02:58 +0000[diff] [blame]1762
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1763<div class="doc_text">
1764
1765<p>Once you have the basics down, there are a couple of problems that GDB has,
1766some with solutions, some without.</p>
Chris Lattner480e2ef2002-09-06 02:02:58 +0000[diff] [blame]1767
1768<ul>
1769<li>Inline functions have bogus stack information. In general, GDB does a
1770pretty good job getting stack traces and stepping through inline functions.
1771When a pass is dynamically loaded however, it somehow completely loses this
1772capability. The only solution I know of is to de-inline a function (move it
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1773from the body of a class to a .cpp file).</li>
Chris Lattner480e2ef2002-09-06 02:02:58 +0000[diff] [blame]1774
1775<li>Restarting the program breaks breakpoints. After following the information
1776above, you have succeeded in getting some breakpoints planted in your pass. Nex
1777thing you know, you restart the program (i.e., you type '<tt>run</tt>' again),
1778and you start getting errors about breakpoints being unsettable. The only way I
1779have found to "fix" this problem is to <tt>delete</tt> the breakpoints that are
1780already set in your pass, run the program, and re-set the breakpoints once
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1781execution stops in <tt>PassManager::run</tt>.</li>
Chris Lattner480e2ef2002-09-06 02:02:58 +0000[diff] [blame]1782
1783</ul>
1784
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1785<p>Hopefully these tips will help with common case debugging situations. If
1786you'd like to contribute some tips of your own, just contact <a
1787href="mailto:sabre@nondot.org">Chris</a>.</p>
Chris Lattner480e2ef2002-09-06 02:02:58 +0000[diff] [blame]1788
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1789</div>
Chris Lattner480e2ef2002-09-06 02:02:58 +0000[diff] [blame]1790
1791<!-- *********************************************************************** -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1792<div class="doc_section">
1793 <a name="future">Future extensions planned</a>
1794</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1795<!-- *********************************************************************** -->
1796
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1797<div class="doc_text">
1798
1799<p>Although the LLVM Pass Infrastructure is very capable as it stands, and does
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1800some 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]1801where we are going:</p>
1802
1803</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1804
1805<!-- _______________________________________________________________________ -->
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]1806<div class="doc_subsubsection">
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1807 <a name="SMP">Multithreaded LLVM</a>
1808</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1809
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1810<div class="doc_text">
1811
1812<p>Multiple CPU machines are becoming more common and compilation can never be
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1813fast enough: obviously we should allow for a multithreaded compiler. Because of
1814the semantics defined for passes above (specifically they cannot maintain state
1815across invocations of their <tt>run*</tt> methods), a nice clean way to
1816implement a multithreaded compiler would be for the <tt>PassManager</tt> class
Misha Brukmanbc0e9982003-07-14 17:20:40 +0000[diff] [blame]1817to create multiple instances of each pass object, and allow the separate
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1818instances to be hacking on different parts of the program at the same time.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1819
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1820<p>This implementation would prevent each of the passes from having to implement
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1821multithreaded constructs, requiring only the LLVM core to have locking in a few
1822places (for global resources). Although this is a simple extension, we simply
1823haven't had time (or multiprocessor machines, thus a reason) to implement this.
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1824Despite that, we have kept the LLVM passes SMP ready, and you should too.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1825
Chris Lattnerb5c87f62007-05-18 05:36:14 +0000[diff] [blame]1826</div>
1827
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1828<!-- *********************************************************************** -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1829<hr>
1830<address>
1831 <a href="http://jigsaw.w3.org/css-validator/check/referer"><img
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Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1833 <a href="http://validator.w3.org/check/referer"><img
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Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1835
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1836 <a href="mailto:sabre@nondot.org">Chris Lattner</a><br>
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]1837 <a href="http://llvm.org">The LLVM Compiler Infrastructure</a><br>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1838 Last modified: $Date$
1839</address>
1840
1841</body>
1842</html>