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gerrit-public.fairphone.software / platform / external / llvm / 18619b2aeba5468512d6684c4fd96d0ad280e01d / . / docs / WritingAnLLVMPass.html
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Reid Spencer7fa6d522005-01-11 05:16:23 +0000[diff] [blame]5 <meta http-equiv="Content-Type" content="text/html; charset=utf-8">
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]6 <title>Writing an LLVM Pass</title>
7 <link rel="stylesheet" href="llvm.css" type="text/css">
8</head>
9<body>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]10
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]11<div class="doc_title">
12 Writing an LLVM Pass
13</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]14
15<ol>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]16 <li><a href="#introduction">Introduction - What is a pass?</a></li>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]17 <li><a href="#quickstart">Quick Start - Writing hello world</a>
18 <ul>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]19 <li><a href="#makefile">Setting up the build environment</a></li>
20 <li><a href="#basiccode">Basic code required</a></li>
Chris Lattnerc8603c22006-08-27 23:18:52 +0000[diff] [blame]21 <li><a href="#running">Running a pass with <tt>opt</tt></a></li>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]22 </ul></li>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]23 <li><a href="#passtype">Pass classes and requirements</a>
24 <ul>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]25 <li><a href="#ImmutablePass">The <tt>ImmutablePass</tt> class</a></li>
Chris Lattnerf6278922004-09-20 04:36:29 +0000[diff] [blame]26 <li><a href="#ModulePass">The <tt>ModulePass</tt> class</a>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]27 <ul>
Chris Lattnerf6278922004-09-20 04:36:29 +0000[diff] [blame]28 <li><a href="#runOnModule">The <tt>runOnModule</tt> method</a></li>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]29 </ul></li>
Chris Lattner8fdb2462004-09-18 06:39:35 +0000[diff] [blame]30 <li><a href="#CallGraphSCCPass">The <tt>CallGraphSCCPass</tt> class</a>
31 <ul>
Devang Patelc20048d2007-01-23 22:56:28 +0000[diff] [blame]32 <li><a href="#doInitialization_scc">The <tt>doInitialization(CallGraph
Chris Lattner8fdb2462004-09-18 06:39:35 +0000[diff] [blame]33 &amp;)</tt> method</a></li>
34 <li><a href="#runOnSCC">The <tt>runOnSCC</tt> method</a></li>
Devang Patelc20048d2007-01-23 22:56:28 +0000[diff] [blame]35 <li><a href="#doFinalization_scc">The <tt>doFinalization(CallGraph
Chris Lattner8fdb2462004-09-18 06:39:35 +0000[diff] [blame]36 &amp;)</tt> method</a></li>
37 </ul></li>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]38 <li><a href="#FunctionPass">The <tt>FunctionPass</tt> class</a>
39 <ul>
Chris Lattnerd0713f92002-09-12 17:06:43 +0000[diff] [blame]40 <li><a href="#doInitialization_mod">The <tt>doInitialization(Module
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]41 &amp;)</tt> method</a></li>
42 <li><a href="#runOnFunction">The <tt>runOnFunction</tt> method</a></li>
Chris Lattnerd0713f92002-09-12 17:06:43 +0000[diff] [blame]43 <li><a href="#doFinalization_mod">The <tt>doFinalization(Module
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]44 &amp;)</tt> method</a></li>
45 </ul></li>
Devang Patel2e8f27d2007-03-19 22:21:25 +0000[diff] [blame]46 <li><a href="#LoopPass">The <tt>LoopPass</tt> class</a>
47 <ul>
48 <li><a href="#doInitialization_loop">The <tt>doInitialization(Loop *,
49 LPPassManager &amp;)</tt> method</a></li>
50 <li><a href="#runOnLoop">The <tt>runOnLoop</tt> method</a></li>
51 <li><a href="#doFinalization_loop">The <tt>doFinalization()
52 </tt> method</a></li>
53 </ul></li>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]54 <li><a href="#BasicBlockPass">The <tt>BasicBlockPass</tt> class</a>
55 <ul>
Chris Lattnerd0713f92002-09-12 17:06:43 +0000[diff] [blame]56 <li><a href="#doInitialization_fn">The <tt>doInitialization(Function
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]57 &amp;)</tt> method</a></li>
58 <li><a href="#runOnBasicBlock">The <tt>runOnBasicBlock</tt>
59 method</a></li>
Chris Lattnerd0713f92002-09-12 17:06:43 +0000[diff] [blame]60 <li><a href="#doFinalization_fn">The <tt>doFinalization(Function
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]61 &amp;)</tt> method</a></li>
62 </ul></li>
Brian Gaekecab8b6f2003-07-17 18:53:20 +0000[diff] [blame]63 <li><a href="#MachineFunctionPass">The <tt>MachineFunctionPass</tt>
64 class</a>
Brian Gaeke6a33f362003-07-22 20:53:20 +0000[diff] [blame]65 <ul>
66 <li><a href="#runOnMachineFunction">The
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]67 <tt>runOnMachineFunction(MachineFunction &amp;)</tt> method</a></li>
68 </ul></li>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]69 </ul>
70 <li><a href="#registration">Pass Registration</a>
71 <ul>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]72 <li><a href="#print">The <tt>print</tt> method</a></li>
73 </ul></li>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]74 <li><a href="#interaction">Specifying interactions between passes</a>
75 <ul>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]76 <li><a href="#getAnalysisUsage">The <tt>getAnalysisUsage</tt>
77 method</a></li>
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]78 <li><a href="#AU::addRequired">The <tt>AnalysisUsage::addRequired&lt;&gt;</tt> and <tt>AnalysisUsage::addRequiredTransitive&lt;&gt;</tt> methods</a></li>
79 <li><a href="#AU::addPreserved">The <tt>AnalysisUsage::addPreserved&lt;&gt;</tt> method</a></li>
80 <li><a href="#AU::examples">Example implementations of <tt>getAnalysisUsage</tt></a></li>
Duncan Sands1465d612009-01-28 13:14:17 +0000[diff] [blame]81 <li><a href="#getAnalysis">The <tt>getAnalysis&lt;&gt;</tt> and
82<tt>getAnalysisIfAvailable&lt;&gt;</tt> methods</a></li>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]83 </ul></li>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]84 <li><a href="#analysisgroup">Implementing Analysis Groups</a>
85 <ul>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]86 <li><a href="#agconcepts">Analysis Group Concepts</a></li>
87 <li><a href="#registerag">Using <tt>RegisterAnalysisGroup</tt></a></li>
88 </ul></li>
Tanya Lattnerd5383652004-11-19 01:25:14 +0000[diff] [blame]89 <li><a href="#passStatistics">Pass Statistics</a>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]90 <li><a href="#passmanager">What PassManager does</a>
91 <ul>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]92 <li><a href="#releaseMemory">The <tt>releaseMemory</tt> method</a></li>
93 </ul></li>
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]94 <li><a href="#registering">Registering dynamically loaded passes</a>
95 <ul>
96 <li><a href="#registering_existing">Using existing registries</a></li>
97 <li><a href="#registering_new">Creating new registries</a></li>
98 </ul></li>
Chris Lattner480e2ef2002-09-06 02:02:58 +0000[diff] [blame]99 <li><a href="#debughints">Using GDB with dynamically loaded passes</a>
100 <ul>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]101 <li><a href="#breakpoint">Setting a breakpoint in your pass</a></li>
102 <li><a href="#debugmisc">Miscellaneous Problems</a></li>
103 </ul></li>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]104 <li><a href="#future">Future extensions planned</a>
105 <ul>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]106 <li><a href="#SMP">Multithreaded LLVM</a></li>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]107 </ul></li>
108</ol>
Chris Lattner38c633d2002-08-08 20:23:41 +0000[diff] [blame]109
Chris Lattner7911ce22004-05-23 21:07:27 +0000[diff] [blame]110<div class="doc_author">
Chris Lattner8f652eb2006-08-11 16:37:02 +0000[diff] [blame]111 <p>Written by <a href="mailto:sabre@nondot.org">Chris Lattner</a> and
Jim Laskeyc760a922007-03-14 19:32:21 +0000[diff] [blame]112 <a href="mailto:jlaskey@mac.com">Jim Laskey</a></p>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]113</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]114
115<!-- *********************************************************************** -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]116<div class="doc_section">
117 <a name="introduction">Introduction - What is a pass?</a>
118</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]119<!-- *********************************************************************** -->
120
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]121<div class="doc_text">
122
123<p>The LLVM Pass Framework is an important part of the LLVM system, because LLVM
Chris Lattner8fdb2462004-09-18 06:39:35 +0000[diff] [blame]124passes are where most of the interesting parts of the compiler exist. Passes
125perform the transformations and optimizations that make up the compiler, they
126build the analysis results that are used by these transformations, and they are,
127above all, a structuring technique for compiler code.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]128
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]129<p>All LLVM passes are subclasses of the <tt><a
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]130href="http://llvm.org/doxygen/classllvm_1_1Pass.html">Pass</a></tt>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]131class, which implement functionality by overriding virtual methods inherited
Chris Lattnerf6278922004-09-20 04:36:29 +0000[diff] [blame]132from <tt>Pass</tt>. Depending on how your pass works, you should inherit from
133the <tt><a href="#ModulePass">ModulePass</a></tt>, <tt><a
134href="#CallGraphSCCPass">CallGraphSCCPass</a></tt>, <tt><a
135href="#FunctionPass">FunctionPass</a></tt>, or <tt><a
Devang Patel2e8f27d2007-03-19 22:21:25 +0000[diff] [blame]136href="#LoopPass">LoopPass</a></tt>, or <tt><a
Chris Lattner8fdb2462004-09-18 06:39:35 +0000[diff] [blame]137href="#BasicBlockPass">BasicBlockPass</a></tt> classes, which gives the system
138more information about what your pass does, and how it can be combined with
139other passes. One of the main features of the LLVM Pass Framework is that it
140schedules passes to run in an efficient way based on the constraints that your
141pass meets (which are indicated by which class they derive from).</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]142
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]143<p>We start by showing you how to construct a pass, everything from setting up
144the code, to compiling, loading, and executing it. After the basics are down,
145more advanced features are discussed.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]146
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]147</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]148
149<!-- *********************************************************************** -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]150<div class="doc_section">
151 <a name="quickstart">Quick Start - Writing hello world</a>
152</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]153<!-- *********************************************************************** -->
154
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]155<div class="doc_text">
156
157<p>Here we describe how to write the "hello world" of passes. The "Hello" pass
158is designed to simply print out the name of non-external functions that exist in
Chris Lattner8fdb2462004-09-18 06:39:35 +0000[diff] [blame]159the program being compiled. It does not modify the program at all, it just
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]160inspects it. The source code and files for this pass are available in the LLVM
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]161source tree in the <tt>lib/Transforms/Hello</tt> directory.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]162
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]163</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]164
165<!-- ======================================================================= -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]166<div class="doc_subsection">
167 <a name="makefile">Setting up the build environment</a>
168</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]169
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]170<div class="doc_text">
171
Reid Spencer1bc19342004-12-11 05:12:57 +0000[diff] [blame]172 <p>First, you need to create a new directory somewhere in the LLVM source
173 base. For this example, we'll assume that you made
174 <tt>lib/Transforms/Hello</tt>. Next, you must set up a build script
175 (Makefile) that will compile the source code for the new pass. To do this,
176 copy the following into <tt>Makefile</tt>:</p>
177 <hr/>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]178
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]179<div class="doc_code"><pre>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]180# Makefile for hello pass
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]181
Torok Edwin87469292009-10-12 13:37:29 +0000[diff] [blame]182# Path to top level of LLVM hierarchy
Chris Lattner7ce83e52002-08-14 20:07:01 +0000[diff] [blame]183LEVEL = ../../..
Chris Lattner17a4c3e2002-08-14 20:06:13 +0000[diff] [blame]184
185# Name of the library to build
Reid Spencer7fa6d522005-01-11 05:16:23 +0000[diff] [blame]186LIBRARYNAME = Hello
Chris Lattner17a4c3e2002-08-14 20:06:13 +0000[diff] [blame]187
Reid Spencer7fa6d522005-01-11 05:16:23 +0000[diff] [blame]188# Make the shared library become a loadable module so the tools can
189# dlopen/dlsym on the resulting library.
Robert Bocchino3cf817d2006-01-06 22:49:23 +0000[diff] [blame]190LOADABLE_MODULE = 1
Reid Spencer7fa6d522005-01-11 05:16:23 +0000[diff] [blame]191
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
912program. A <tt>MachineFunctionPass</tt> is also a <tt>FunctionPass</tt>, so all
Brian Gaekecab8b6f2003-07-17 18:53:20 +0000[diff] [blame]913the restrictions that apply to a <tt>FunctionPass</tt> also apply to it.
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]914<tt>MachineFunctionPass</tt>es also have additional restrictions. In particular,
915<tt>MachineFunctionPass</tt>es are not allowed to do any of the following:</p>
Brian Gaekecab8b6f2003-07-17 18:53:20 +0000[diff] [blame]916
917<ol>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]918<li>Modify any LLVM Instructions, BasicBlocks or Functions.</li>
919<li>Modify a MachineFunction other than the one currently being processed.</li>
920<li>Add or remove MachineFunctions from the current Module.</li>
921<li>Add or remove global variables from the current Module.</li>
922<li>Maintain state across invocations of <a
923href="#runOnMachineFunction"><tt>runOnMachineFunction</tt></a> (including global
924data)</li>
925</ol>
Brian Gaekecab8b6f2003-07-17 18:53:20 +0000[diff] [blame]926
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]927</div>
Chris Lattnerd0713f92002-09-12 17:06:43 +0000[diff] [blame]928
Brian Gaeke6a33f362003-07-22 20:53:20 +0000[diff] [blame]929<!-- _______________________________________________________________________ -->
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]930<div class="doc_subsubsection">
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]931 <a name="runOnMachineFunction">The <tt>runOnMachineFunction(MachineFunction
932 &amp;MF)</tt> method</a>
933</div>
934
935<div class="doc_text">
Brian Gaeke6a33f362003-07-22 20:53:20 +0000[diff] [blame]936
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]937<div class="doc_code"><pre>
Brian Gaeke6a33f362003-07-22 20:53:20 +0000[diff] [blame]938 <b>virtual bool</b> runOnMachineFunction(MachineFunction &amp;MF) = 0;
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]939</pre></div>
Brian Gaeke6a33f362003-07-22 20:53:20 +0000[diff] [blame]940
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]941<p><tt>runOnMachineFunction</tt> can be considered the main entry point of a
942<tt>MachineFunctionPass</tt>; that is, you should override this method to do the
943work of your <tt>MachineFunctionPass</tt>.</p>
Brian Gaeke6a33f362003-07-22 20:53:20 +0000[diff] [blame]944
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]945<p>The <tt>runOnMachineFunction</tt> method is called on every
Brian Gaeke6a33f362003-07-22 20:53:20 +0000[diff] [blame]946<tt>MachineFunction</tt> in a <tt>Module</tt>, so that the
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]947<tt>MachineFunctionPass</tt> may perform optimizations on the machine-dependent
948representation of the function. If you want to get at the LLVM <tt>Function</tt>
949for the <tt>MachineFunction</tt> you're working on, use
950<tt>MachineFunction</tt>'s <tt>getFunction()</tt> accessor method -- but
951remember, you may not modify the LLVM <tt>Function</tt> or its contents from a
952<tt>MachineFunctionPass</tt>.</p>
953
954</div>
Brian Gaeke6a33f362003-07-22 20:53:20 +0000[diff] [blame]955
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]956<!-- *********************************************************************** -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]957<div class="doc_section">
958 <a name="registration">Pass registration</a>
959</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]960<!-- *********************************************************************** -->
961
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]962<div class="doc_text">
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]963
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]964<p>In the <a href="#basiccode">Hello World</a> example pass we illustrated how
965pass registration works, and discussed some of the reasons that it is used and
966what it does. Here we discuss how and why passes are registered.</p>
967
Chris Lattnerc8603c22006-08-27 23:18:52 +0000[diff] [blame]968<p>As we saw above, passes are registered with the <b><tt>RegisterPass</tt></b>
969template, which requires you to pass at least two
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]970parameters. The first parameter is the name of the pass that is to be used on
971the command line to specify that the pass should be added to a program (for
Chris Lattnerc8603c22006-08-27 23:18:52 +0000[diff] [blame]972example, with <tt>opt</tt> or <tt>bugpoint</tt>). The second argument is the
Duncan Sands7e7ae5a2010-02-18 14:08:13 +0000[diff] [blame]973name 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]974programs, as
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]975well as for debug output generated by the <tt>--debug-pass</tt> option.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]976
Chris Lattnerc8603c22006-08-27 23:18:52 +0000[diff] [blame]977<p>If you want your pass to be easily dumpable, you should
978implement the virtual <tt>print</tt> method:</p>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]979
980</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]981
982<!-- _______________________________________________________________________ -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]983<div class="doc_subsubsection">
984 <a name="print">The <tt>print</tt> method</a>
985</div>
986
987<div class="doc_text">
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]988
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]989<div class="doc_code"><pre>
Torok Edwin52790e52008-10-28 17:29:23 +0000[diff] [blame]990 <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]991</pre></div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]992
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]993<p>The <tt>print</tt> method must be implemented by "analyses" in order to print
994a human readable version of the analysis results. This is useful for debugging
995an analysis itself, as well as for other people to figure out how an analysis
Chris Lattnerc8603c22006-08-27 23:18:52 +0000[diff] [blame]996works. Use the <tt>opt -analyze</tt> argument to invoke this method.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]997
Bill Wendling832171c2006-12-07 20:04:42 +0000[diff] [blame]998<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]999and 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]1000program that has been analyzed. Note however that this pointer may be null in
1001certain circumstances (such as calling the <tt>Pass::dump()</tt> from a
1002debugger), so it should only be used to enhance debug output, it should not be
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1003depended on.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1004
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1005</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1006
1007<!-- *********************************************************************** -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1008<div class="doc_section">
1009 <a name="interaction">Specifying interactions between passes</a>
1010</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1011<!-- *********************************************************************** -->
1012
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1013<div class="doc_text">
1014
John Criswell8528e782007-12-03 19:34:25 +0000[diff] [blame]1015<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]1016that passes interact with each other correctly. Because <tt>PassManager</tt>
1017tries to <a href="#passmanager">optimize the execution of passes</a> it must
1018know how the passes interact with each other and what dependencies exist between
1019the various passes. To track this, each pass can declare the set of passes that
1020are required to be executed before the current pass, and the passes which are
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1021invalidated by the current pass.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1022
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1023<p>Typically this functionality is used to require that analysis results are
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1024computed before your pass is run. Running arbitrary transformation passes can
1025invalidate the computed analysis results, which is what the invalidation set
1026specifies. If a pass does not implement the <tt><a
1027href="#getAnalysisUsage">getAnalysisUsage</a></tt> method, it defaults to not
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1028having any prerequisite passes, and invalidating <b>all</b> other passes.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1029
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1030</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1031
1032<!-- _______________________________________________________________________ -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1033<div class="doc_subsubsection">
1034 <a name="getAnalysisUsage">The <tt>getAnalysisUsage</tt> method</a>
1035</div>
1036
1037<div class="doc_text">
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1038
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1039<div class="doc_code"><pre>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1040 <b>virtual void</b> getAnalysisUsage(AnalysisUsage &amp;Info) <b>const</b>;
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1041</pre></div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1042
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1043<p>By implementing the <tt>getAnalysisUsage</tt> method, the required and
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1044invalidated sets may be specified for your transformation. The implementation
1045should fill in the <tt><a
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]1046href="http://llvm.org/doxygen/classllvm_1_1AnalysisUsage.html">AnalysisUsage</a></tt>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1047object with information about which passes are required and not invalidated. To
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]1048do this, a pass may call any of the following methods on the AnalysisUsage
1049object:</p>
1050</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1051
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]1052<!-- _______________________________________________________________________ -->
1053<div class="doc_subsubsection">
1054 <a name="AU::addRequired">The <tt>AnalysisUsage::addRequired&lt;&gt;</tt> and <tt>AnalysisUsage::addRequiredTransitive&lt;&gt;</tt> methods</a>
1055</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1056
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]1057<div class="doc_text">
1058<p>
Reid Spencer1bc19342004-12-11 05:12:57 +0000[diff] [blame]1059If your pass requires a previous pass to be executed (an analysis for example),
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]1060it can use one of these methods to arrange for it to be run before your pass.
1061LLVM has many different types of analyses and passes that can be required,
Reid Spencer1bc19342004-12-11 05:12:57 +0000[diff] [blame]1062spanning the range from <tt>DominatorSet</tt> to <tt>BreakCriticalEdges</tt>.
1063Requiring <tt>BreakCriticalEdges</tt>, for example, guarantees that there will
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]1064be no critical edges in the CFG when your pass has been run.
1065</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1066
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]1067<p>
1068Some analyses chain to other analyses to do their job. For example, an <a
1069href="AliasAnalysis.html">AliasAnalysis</a> implementation is required to <a
1070href="AliasAnalysis.html#chaining">chain</a> to other alias analysis passes. In
1071cases where analyses chain, the <tt>addRequiredTransitive</tt> method should be
1072used instead of the <tt>addRequired</tt> method. This informs the PassManager
1073that the transitively required pass should be alive as long as the requiring
1074pass is.
1075</p>
1076</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1077
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]1078<!-- _______________________________________________________________________ -->
1079<div class="doc_subsubsection">
1080 <a name="AU::addPreserved">The <tt>AnalysisUsage::addPreserved&lt;&gt;</tt> method</a>
1081</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1082
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]1083<div class="doc_text">
1084<p>
1085One of the jobs of the PassManager is to optimize how and when analyses are run.
1086In particular, it attempts to avoid recomputing data unless it needs to. For
1087this reason, passes are allowed to declare that they preserve (i.e., they don't
1088invalidate) an existing analysis if it's available. For example, a simple
Reid Spencer1bc19342004-12-11 05:12:57 +0000[diff] [blame]1089constant folding pass would not modify the CFG, so it can't possibly affect the
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]1090results of dominator analysis. By default, all passes are assumed to invalidate
1091all others.
1092</p>
1093
1094<p>
1095The <tt>AnalysisUsage</tt> class provides several methods which are useful in
1096certain circumstances that are related to <tt>addPreserved</tt>. In particular,
1097the <tt>setPreservesAll</tt> method can be called to indicate that the pass does
1098not modify the LLVM program at all (which is true for analyses), and the
1099<tt>setPreservesCFG</tt> method can be used by transformations that change
1100instructions in the program but do not modify the CFG or terminator instructions
1101(note that this property is implicitly set for <a
1102href="#BasicBlockPass">BasicBlockPass</a>'s).
1103</p>
1104
1105<p>
1106<tt>addPreserved</tt> is particularly useful for transformations like
1107<tt>BreakCriticalEdges</tt>. This pass knows how to update a small set of loop
1108and dominator related analyses if they exist, so it can preserve them, despite
1109the fact that it hacks on the CFG.
1110</p>
1111</div>
1112
1113<!-- _______________________________________________________________________ -->
1114<div class="doc_subsubsection">
1115 <a name="AU::examples">Example implementations of <tt>getAnalysisUsage</tt></a>
1116</div>
1117
1118<div class="doc_text">
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1119
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1120<div class="doc_code"><pre>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1121 <i>// This is an example implementation from an analysis, which does not modify
1122 // the program at all, yet has a prerequisite.</i>
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]1123 <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]1124 AU.setPreservesAll();
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]1125 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]1126 }
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1127</pre></div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1128
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1129<p>and:</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1130
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1131<div class="doc_code"><pre>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1132 <i>// This example modifies the program, but does not modify the CFG</i>
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]1133 <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]1134 AU.setPreservesCFG();
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]1135 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]1136 }
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1137</pre></div>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1138
1139</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1140
1141<!-- _______________________________________________________________________ -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1142<div class="doc_subsubsection">
Duncan Sands1465d612009-01-28 13:14:17 +0000[diff] [blame]1143 <a name="getAnalysis">The <tt>getAnalysis&lt;&gt;</tt> and
1144<tt>getAnalysisIfAvailable&lt;&gt;</tt> methods</a>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1145</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1146
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1147<div class="doc_text">
1148
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]1149<p>The <tt>Pass::getAnalysis&lt;&gt;</tt> method is automatically inherited by
1150your class, providing you with access to the passes that you declared that you
1151required with the <a href="#getAnalysisUsage"><tt>getAnalysisUsage</tt></a>
1152method. It takes a single template argument that specifies which pass class you
1153want, and returns a reference to that pass. For example:</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1154
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1155<div class="doc_code"><pre>
Chris Lattnera5776302004-03-17 21:33:32 +0000[diff] [blame]1156 bool LICM::runOnFunction(Function &amp;F) {
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]1157 LoopInfo &amp;LI = getAnalysis&lt;LoopInfo&gt;();
1158 ...
1159 }
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1160</pre></div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1161
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1162<p>This method call returns a reference to the pass desired. You may get a
1163runtime assertion failure if you attempt to get an analysis that you did not
1164declare as required in your <a
1165href="#getAnalysisUsage"><tt>getAnalysisUsage</tt></a> implementation. This
1166method can be called by your <tt>run*</tt> method implementation, or by any
Devang Patel3c1ca0b2007-04-16 21:28:14 +0000[diff] [blame]1167other local method invoked by your <tt>run*</tt> method.
1168
1169A module level pass can use function level analysis info using this interface.
1170For example:</p>
1171
1172<div class="doc_code"><pre>
1173 bool ModuleLevelPass::runOnModule(Module &amp;M) {
1174 ...
Devang Patelf23de112007-04-17 00:17:11 +0000[diff] [blame]1175 DominatorTree &amp;DT = getAnalysis&lt;DominatorTree&gt;(Func);
Devang Patel3c1ca0b2007-04-16 21:28:14 +0000[diff] [blame]1176 ...
1177 }
1178</pre></div>
1179
Chris Lattnerb5c87f62007-05-18 05:36:14 +0000[diff] [blame]1180<p>In above example, runOnFunction for DominatorTree is called by pass manager
Devang Patel3c1ca0b2007-04-16 21:28:14 +0000[diff] [blame]1181before returning a reference to the desired pass.</p>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1182
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]1183<p>
1184If your pass is capable of updating analyses if they exist (e.g.,
1185<tt>BreakCriticalEdges</tt>, as described above), you can use the
Duncan Sands1465d612009-01-28 13:14:17 +0000[diff] [blame]1186<tt>getAnalysisIfAvailable</tt> method, which returns a pointer to the analysis
1187if it is active. For example:</p>
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]1188
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1189<div class="doc_code"><pre>
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]1190 ...
Duncan Sands1465d612009-01-28 13:14:17 +0000[diff] [blame]1191 if (DominatorSet *DS = getAnalysisIfAvailable&lt;DominatorSet&gt;()) {
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]1192 <i>// A DominatorSet is active. This code will update it.</i>
1193 }
1194 ...
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1195</pre></div>
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]1196
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1197</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1198
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1199<!-- *********************************************************************** -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1200<div class="doc_section">
1201 <a name="analysisgroup">Implementing Analysis Groups</a>
1202</div>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1203<!-- *********************************************************************** -->
1204
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1205<div class="doc_text">
1206
Chris Lattnerb7632282007-11-16 05:32:05 +0000[diff] [blame]1207<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]1208used, 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]1209fancier. All of the pass relationships that we have seen so far are very
1210simple: one pass depends on one other specific pass to be run before it can run.
1211For many applications, this is great, for others, more flexibility is
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1212required.</p>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1213
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1214<p>In particular, some analyses are defined such that there is a single simple
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1215interface to the analysis results, but multiple ways of calculating them.
1216Consider alias analysis for example. The most trivial alias analysis returns
1217"may alias" for any alias query. The most sophisticated analysis a
1218flow-sensitive, context-sensitive interprocedural analysis that can take a
1219significant amount of time to execute (and obviously, there is a lot of room
1220between these two extremes for other implementations). To cleanly support
1221situations like this, the LLVM Pass Infrastructure supports the notion of
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1222Analysis Groups.</p>
1223
1224</div>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1225
1226<!-- _______________________________________________________________________ -->
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]1227<div class="doc_subsubsection">
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1228 <a name="agconcepts">Analysis Group Concepts</a>
1229</div>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1230
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1231<div class="doc_text">
1232
1233<p>An Analysis Group is a single simple interface that may be implemented by
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1234multiple different passes. Analysis Groups can be given human readable names
1235just like passes, but unlike passes, they need not derive from the <tt>Pass</tt>
1236class. An analysis group may have one or more implementations, one of which is
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1237the "default" implementation.</p>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1238
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1239<p>Analysis groups are used by client passes just like other passes are: the
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1240<tt>AnalysisUsage::addRequired()</tt> and <tt>Pass::getAnalysis()</tt> methods.
1241In order to resolve this requirement, the <a href="#passmanager">PassManager</a>
1242scans the available passes to see if any implementations of the analysis group
1243are available. If none is available, the default implementation is created for
1244the pass to use. All standard rules for <A href="#interaction">interaction
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1245between passes</a> still apply.</p>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1246
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1247<p>Although <a href="#registration">Pass Registration</a> is optional for normal
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1248passes, all analysis group implementations must be registered, and must use the
1249<A href="#registerag"><tt>RegisterAnalysisGroup</tt></a> template to join the
1250implementation pool. Also, a default implementation of the interface
1251<b>must</b> be registered with <A
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1252href="#registerag"><tt>RegisterAnalysisGroup</tt></a>.</p>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1253
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1254<p>As a concrete example of an Analysis Group in action, consider the <a
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]1255href="http://llvm.org/doxygen/classllvm_1_1AliasAnalysis.html">AliasAnalysis</a>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1256analysis group. The default implementation of the alias analysis interface (the
1257<tt><a
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]1258href="http://llvm.org/doxygen/structBasicAliasAnalysis.html">basicaa</a></tt>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1259pass) just does a few simple checks that don't require significant analysis to
1260compute (such as: two different globals can never alias each other, etc).
1261Passes that use the <tt><a
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]1262href="http://llvm.org/doxygen/classllvm_1_1AliasAnalysis.html">AliasAnalysis</a></tt>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1263interface (for example the <tt><a
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]1264href="http://llvm.org/doxygen/structGCSE.html">gcse</a></tt> pass), do
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1265not care which implementation of alias analysis is actually provided, they just
1266use the designated interface.</p>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1267
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1268<p>From the user's perspective, commands work just like normal. Issuing the
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1269command '<tt>opt -gcse ...</tt>' will cause the <tt>basicaa</tt> class to be
1270instantiated and added to the pass sequence. Issuing the command '<tt>opt
1271-somefancyaa -gcse ...</tt>' will cause the <tt>gcse</tt> pass to use the
1272<tt>somefancyaa</tt> alias analysis (which doesn't actually exist, it's just a
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1273hypothetical example) instead.</p>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1274
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1275</div>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1276
1277<!-- _______________________________________________________________________ -->
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]1278<div class="doc_subsubsection">
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1279 <a name="registerag">Using <tt>RegisterAnalysisGroup</tt></a>
1280</div>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1281
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1282<div class="doc_text">
1283
1284<p>The <tt>RegisterAnalysisGroup</tt> template is used to register the analysis
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1285group itself as well as add pass implementations to the analysis group. First,
1286an analysis should be registered, with a human readable name provided for it.
1287Unlike registration of passes, there is no command line argument to be specified
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1288for the Analysis Group Interface itself, because it is "abstract":</p>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1289
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1290<div class="doc_code"><pre>
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]1291 <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]1292</pre></div>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1293
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1294<p>Once the analysis is registered, passes can declare that they are valid
1295implementations of the interface by using the following code:</p>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1296
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1297<div class="doc_code"><pre>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1298<b>namespace</b> {
1299 //<i> Analysis Group implementations <b>must</b> be registered normally...</i>
Chris Lattnerc8603c22006-08-27 23:18:52 +0000[diff] [blame]1300 RegisterPass&lt;FancyAA&gt;
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1301 B("<i>somefancyaa</i>", "<i>A more complex alias analysis implementation</i>");
1302
1303 //<i> Declare that we implement the AliasAnalysis interface</i>
Chris Lattnerdc877252006-08-28 00:45:38 +0000[diff] [blame]1304 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]1305}
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1306</pre></div>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1307
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1308<p>This just shows a class <tt>FancyAA</tt> that is registered normally, then
1309uses the <tt>RegisterAnalysisGroup</tt> template to "join" the <tt><a
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]1310href="http://llvm.org/doxygen/classllvm_1_1AliasAnalysis.html">AliasAnalysis</a></tt>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1311analysis group. Every implementation of an analysis group should join using
1312this template. A single pass may join multiple different analysis groups with
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1313no problem.</p>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1314
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1315<div class="doc_code"><pre>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1316<b>namespace</b> {
1317 //<i> Analysis Group implementations <b>must</b> be registered normally...</i>
Chris Lattnerc8603c22006-08-27 23:18:52 +0000[diff] [blame]1318 RegisterPass&lt;<a href="http://llvm.org/doxygen/structBasicAliasAnalysis.html">BasicAliasAnalysis</a>&gt;
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1319 D("<i>basicaa</i>", "<i>Basic Alias Analysis (default AA impl)</i>");
1320
1321 //<i> Declare that we implement the AliasAnalysis interface</i>
Chris Lattnerdc877252006-08-28 00:45:38 +0000[diff] [blame]1322 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]1323}
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1324</pre></div>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1325
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1326<p>Here we show how the default implementation is specified (using the extra
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1327argument to the <tt>RegisterAnalysisGroup</tt> template). There must be exactly
1328one default implementation available at all times for an Analysis Group to be
Devang Patel2397f8d2007-06-20 18:51:14 +0000[diff] [blame]1329used. Only default implementation can derive from <tt>ImmutablePass</tt>.
1330Here we declare that the
1331 <tt><a href="http://llvm.org/doxygen/structBasicAliasAnalysis.html">BasicAliasAnalysis</a></tt>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1332pass is the default implementation for the interface.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1333
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1334</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1335
1336<!-- *********************************************************************** -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1337<div class="doc_section">
Tanya Lattnerd5383652004-11-19 01:25:14 +0000[diff] [blame]1338 <a name="passStatistics">Pass Statistics</a>
1339</div>
1340<!-- *********************************************************************** -->
1341
1342<div class="doc_text">
Tanya Lattner05f8d5f2004-11-19 01:26:37 +0000[diff] [blame]1343<p>The <a
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]1344href="http://llvm.org/doxygen/Statistic_8h-source.html"><tt>Statistic</tt></a>
John Criswell0b1010e2005-11-28 23:25:41 +0000[diff] [blame]1345class is designed to be an easy way to expose various success
Tanya Lattnerd5383652004-11-19 01:25:14 +0000[diff] [blame]1346metrics from passes. These statistics are printed at the end of a
1347run, when the -stats command line option is enabled on the command
Tanya Lattner05f8d5f2004-11-19 01:26:37 +0000[diff] [blame]1348line. 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]1349
1350</div>
1351
1352
1353<!-- *********************************************************************** -->
1354<div class="doc_section">
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1355 <a name="passmanager">What PassManager does</a>
1356</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1357<!-- *********************************************************************** -->
1358
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1359<div class="doc_text">
1360
1361<p>The <a
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]1362href="http://llvm.org/doxygen/PassManager_8h-source.html"><tt>PassManager</tt></a>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1363<a
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]1364href="http://llvm.org/doxygen/classllvm_1_1PassManager.html">class</a>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1365takes a list of passes, ensures their <a href="#interaction">prerequisites</a>
1366are set up correctly, and then schedules passes to run efficiently. All of the
1367LLVM tools that run passes use the <tt>PassManager</tt> for execution of these
1368passes.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1369
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1370<p>The <tt>PassManager</tt> does two main things to try to reduce the execution
1371time of a series of passes:</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1372
1373<ol>
1374<li><b>Share analysis results</b> - The PassManager attempts to avoid
1375recomputing analysis results as much as possible. This means keeping track of
1376which analyses are available already, which analyses get invalidated, and which
1377analyses are needed to be run for a pass. An important part of work is that the
1378<tt>PassManager</tt> tracks the exact lifetime of all analysis results, allowing
1379it to <a href="#releaseMemory">free memory</a> allocated to holding analysis
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1380results as soon as they are no longer needed.</li>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1381
1382<li><b>Pipeline the execution of passes on the program</b> - The
1383<tt>PassManager</tt> attempts to get better cache and memory usage behavior out
1384of a series of passes by pipelining the passes together. This means that, given
1385a series of consequtive <a href="#FunctionPass"><tt>FunctionPass</tt></a>'s, it
1386will execute all of the <a href="#FunctionPass"><tt>FunctionPass</tt></a>'s on
1387the first function, then all of the <a
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1388href="#FunctionPass"><tt>FunctionPass</tt></a>es on the second function,
1389etc... until the entire program has been run through the passes.
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1390
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1391<p>This improves the cache behavior of the compiler, because it is only touching
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1392the LLVM program representation for a single function at a time, instead of
1393traversing the entire program. It reduces the memory consumption of compiler,
1394because, for example, only one <a
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]1395href="http://llvm.org/doxygen/classllvm_1_1DominatorSet.html"><tt>DominatorSet</tt></a>
John Criswell9795bb82007-12-10 20:26:29 +0000[diff] [blame]1396needs to be calculated at a time. This also makes it possible to implement
1397some <a
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1398href="#SMP">interesting enhancements</a> in the future.</p></li>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1399
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1400</ol>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1401
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1402<p>The effectiveness of the <tt>PassManager</tt> is influenced directly by how
1403much information it has about the behaviors of the passes it is scheduling. For
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1404example, the "preserved" set is intentionally conservative in the face of an
1405unimplemented <a href="#getAnalysisUsage"><tt>getAnalysisUsage</tt></a> method.
1406Not implementing when it should be implemented will have the effect of not
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1407allowing any analysis results to live across the execution of your pass.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1408
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1409<p>The <tt>PassManager</tt> class exposes a <tt>--debug-pass</tt> command line
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1410options that is useful for debugging pass execution, seeing how things work, and
1411diagnosing when you should be preserving more analyses than you currently are
1412(To get information about all of the variants of the <tt>--debug-pass</tt>
Duncan Sands7e7ae5a2010-02-18 14:08:13 +0000[diff] [blame]1413option, just type '<tt>opt -help-hidden</tt>').</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1414
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1415<p>By using the <tt>--debug-pass=Structure</tt> option, for example, we can see
1416how our <a href="#basiccode">Hello World</a> pass interacts with other passes.
1417Lets try it out with the <tt>gcse</tt> and <tt>licm</tt> passes:</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1418
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1419<div class="doc_code"><pre>
Reid Spencer7fa6d522005-01-11 05:16:23 +0000[diff] [blame]1420$ 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]1421Module Pass Manager
1422 Function Pass Manager
1423 Dominator Set Construction
1424 Immediate Dominators Construction
1425 Global Common Subexpression Elimination
1426-- Immediate Dominators Construction
1427-- Global Common Subexpression Elimination
1428 Natural Loop Construction
1429 Loop Invariant Code Motion
1430-- Natural Loop Construction
1431-- Loop Invariant Code Motion
1432 Module Verifier
1433-- Dominator Set Construction
1434-- Module Verifier
Gabor Greif04367bf2007-07-06 22:07:22 +0000[diff] [blame]1435 Bitcode Writer
1436--Bitcode Writer
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1437</pre></div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1438
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1439<p>This output shows us when passes are constructed and when the analysis
1440results are known to be dead (prefixed with '<tt>--</tt>'). Here we see that
1441GCSE uses dominator and immediate dominator information to do its job. The LICM
1442pass uses natural loop information, which uses dominator sets, but not immediate
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1443dominators. Because immediate dominators are no longer useful after the GCSE
1444pass, it is immediately destroyed. The dominator sets are then reused to
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1445compute natural loop information, which is then used by the LICM pass.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1446
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1447<p>After the LICM pass, the module verifier runs (which is automatically added
1448by the '<tt>opt</tt>' tool), which uses the dominator set to check that the
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1449resultant LLVM code is well formed. After it finishes, the dominator set
1450information is destroyed, after being computed once, and shared by three
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1451passes.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1452
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1453<p>Lets see how this changes when we run the <a href="#basiccode">Hello
1454World</a> pass in between the two passes:</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1455
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1456<div class="doc_code"><pre>
Reid Spencer7fa6d522005-01-11 05:16:23 +0000[diff] [blame]1457$ 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]1458Module Pass Manager
1459 Function Pass Manager
1460 Dominator Set Construction
1461 Immediate Dominators Construction
1462 Global Common Subexpression Elimination
1463<b>-- Dominator Set Construction</b>
1464-- Immediate Dominators Construction
1465-- Global Common Subexpression Elimination
1466<b> Hello World Pass
1467-- Hello World Pass
1468 Dominator Set Construction</b>
1469 Natural Loop Construction
1470 Loop Invariant Code Motion
1471-- Natural Loop Construction
1472-- Loop Invariant Code Motion
1473 Module Verifier
1474-- Dominator Set Construction
1475-- Module Verifier
Gabor Greif04367bf2007-07-06 22:07:22 +0000[diff] [blame]1476 Bitcode Writer
1477--Bitcode Writer
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1478Hello: __main
1479Hello: puts
1480Hello: main
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1481</pre></div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1482
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1483<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]1484Dominator Set pass, even though it doesn't modify the code at all! To fix this,
1485we need to add the following <a
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1486href="#getAnalysisUsage"><tt>getAnalysisUsage</tt></a> method to our pass:</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1487
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1488<div class="doc_code"><pre>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1489 <i>// We don't modify the program, so we preserve all analyses</i>
1490 <b>virtual void</b> getAnalysisUsage(AnalysisUsage &amp;AU) <b>const</b> {
1491 AU.setPreservesAll();
1492 }
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1493</pre></div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1494
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1495<p>Now when we run our pass, we get this output:</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1496
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1497<div class="doc_code"><pre>
Reid Spencer7fa6d522005-01-11 05:16:23 +0000[diff] [blame]1498$ 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]1499Pass Arguments: -gcse -hello -licm
1500Module Pass Manager
1501 Function Pass Manager
1502 Dominator Set Construction
1503 Immediate Dominators Construction
1504 Global Common Subexpression Elimination
1505-- Immediate Dominators Construction
1506-- Global Common Subexpression Elimination
1507 Hello World Pass
1508-- Hello World Pass
1509 Natural Loop Construction
1510 Loop Invariant Code Motion
1511-- Loop Invariant Code Motion
1512-- Natural Loop Construction
1513 Module Verifier
1514-- Dominator Set Construction
1515-- Module Verifier
Gabor Greif04367bf2007-07-06 22:07:22 +0000[diff] [blame]1516 Bitcode Writer
1517--Bitcode Writer
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1518Hello: __main
1519Hello: puts
1520Hello: main
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1521</pre></div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1522
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1523<p>Which shows that we don't accidentally invalidate dominator information
1524anymore, and therefore do not have to compute it twice.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1525
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1526</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1527
1528<!-- _______________________________________________________________________ -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1529<div class="doc_subsubsection">
1530 <a name="releaseMemory">The <tt>releaseMemory</tt> method</a>
1531</div>
1532
1533<div class="doc_text">
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1534
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1535<div class="doc_code"><pre>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1536 <b>virtual void</b> releaseMemory();
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1537</pre></div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1538
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1539<p>The <tt>PassManager</tt> automatically determines when to compute analysis
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1540results, and how long to keep them around for. Because the lifetime of the pass
1541object itself is effectively the entire duration of the compilation process, we
1542need some way to free analysis results when they are no longer useful. The
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1543<tt>releaseMemory</tt> virtual method is the way to do this.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1544
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1545<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]1546amount of state (for use by another pass which "requires" your pass and uses the
1547<a href="#getAnalysis">getAnalysis</a> method) you should implement
Dan Gohmand87c9e32009-06-15 18:22:49 +0000[diff] [blame]1548<tt>releaseMemory</tt> to, well, release the memory allocated to maintain this
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1549internal state. This method is called after the <tt>run*</tt> method for the
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1550class, before the next call of <tt>run*</tt> in your pass.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1551
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1552</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1553
1554<!-- *********************************************************************** -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1555<div class="doc_section">
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1556 <a name="registering">Registering dynamically loaded passes</a>
1557</div>
1558<!-- *********************************************************************** -->
1559
1560<div class="doc_text">
1561
1562<p><i>Size matters</i> when constructing production quality tools using llvm,
1563both for the purposes of distribution, and for regulating the resident code size
1564when running on the target system. Therefore, it becomes desirable to
1565selectively use some passes, while omitting others and maintain the flexibility
1566to change configurations later on. You want to be able to do all this, and,
1567provide feedback to the user. This is where pass registration comes into
1568play.</p>
1569
1570<p>The fundamental mechanisms for pass registration are the
1571<tt>MachinePassRegistry</tt> class and subclasses of
1572<tt>MachinePassRegistryNode</tt>.</p>
1573
1574<p>An instance of <tt>MachinePassRegistry</tt> is used to maintain a list of
1575<tt>MachinePassRegistryNode</tt> objects. This instance maintains the list and
1576communicates additions and deletions to the command line interface.</p>
1577
1578<p>An instance of <tt>MachinePassRegistryNode</tt> subclass is used to maintain
1579information provided about a particular pass. This information includes the
1580command line name, the command help string and the address of the function used
1581to create an instance of the pass. A global static constructor of one of these
1582instances <i>registers</i> with a corresponding <tt>MachinePassRegistry</tt>,
1583the static destructor <i>unregisters</i>. Thus a pass that is statically linked
1584in the tool will be registered at start up. A dynamically loaded pass will
1585register on load and unregister at unload.</p>
1586
1587</div>
1588
1589<!-- _______________________________________________________________________ -->
1590<div class="doc_subsection">
1591 <a name="registering_existing">Using existing registries</a>
1592</div>
1593
1594<div class="doc_text">
1595
1596<p>There are predefined registries to track instruction scheduling
1597(<tt>RegisterScheduler</tt>) and register allocation (<tt>RegisterRegAlloc</tt>)
1598machine passes. Here we will describe how to <i>register</i> a register
1599allocator machine pass.</p>
1600
1601<p>Implement your register allocator machine pass. In your register allocator
1602.cpp file add the following include;</p>
1603
1604<div class="doc_code"><pre>
Chris Lattner8f652eb2006-08-11 16:37:02 +0000[diff] [blame]1605 #include "llvm/CodeGen/RegAllocRegistry.h"
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1606</pre></div>
1607
1608<p>Also in your register allocator .cpp file, define a creator function in the
1609form; </p>
1610
1611<div class="doc_code"><pre>
1612 FunctionPass *createMyRegisterAllocator() {
1613 return new MyRegisterAllocator();
1614 }
1615</pre></div>
1616
1617<p>Note that the signature of this function should match the type of
1618<tt>RegisterRegAlloc::FunctionPassCtor</tt>. In the same file add the
1619"installing" declaration, in the form;</p>
1620
1621<div class="doc_code"><pre>
1622 static RegisterRegAlloc myRegAlloc("myregalloc",
1623 " my register allocator help string",
1624 createMyRegisterAllocator);
1625</pre></div>
1626
1627<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]1628-help query.</p>
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1629
1630<div class="doc_code"><pre>
Duncan Sands7e7ae5a2010-02-18 14:08:13 +0000[diff] [blame]1631$ llc -help
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1632 ...
Duncan Sands18619b22010-02-18 14:37:52 +0000[diff] [blame^]1633 -regalloc - Register allocator to use (default=linearscan)
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1634 =linearscan - linear scan register allocator
1635 =local - local register allocator
1636 =simple - simple register allocator
1637 =myregalloc - my register allocator help string
1638 ...
1639</pre></div>
1640
1641<p>And that's it. The user is now free to use <tt>-regalloc=myregalloc</tt> as
1642an option. Registering instruction schedulers is similar except use the
Chris Lattner8f652eb2006-08-11 16:37:02 +0000[diff] [blame]1643<tt>RegisterScheduler</tt> class. Note that the
1644<tt>RegisterScheduler::FunctionPassCtor</tt> is significantly different from
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1645<tt>RegisterRegAlloc::FunctionPassCtor</tt>.</p>
1646
1647<p>To force the load/linking of your register allocator into the llc/lli tools,
1648add your creator function's global declaration to "Passes.h" and add a "pseudo"
1649call line to <tt>llvm/Codegen/LinkAllCodegenComponents.h</tt>.</p>
1650
1651</div>
1652
1653
1654<!-- _______________________________________________________________________ -->
1655<div class="doc_subsection">
1656 <a name="registering_new">Creating new registries</a>
1657</div>
1658
1659<div class="doc_text">
1660
1661<p>The easiest way to get started is to clone one of the existing registries; we
1662recommend <tt>llvm/CodeGen/RegAllocRegistry.h</tt>. The key things to modify
1663are the class name and the <tt>FunctionPassCtor</tt> type.</p>
1664
1665<p>Then you need to declare the registry. Example: if your pass registry is
1666<tt>RegisterMyPasses</tt> then define;</p>
1667
1668<div class="doc_code"><pre>
1669MachinePassRegistry RegisterMyPasses::Registry;
1670</pre></div>
1671
1672<p>And finally, declare the command line option for your passes. Example:</p>
1673
1674<div class="doc_code"><pre>
1675 cl::opt&lt;RegisterMyPasses::FunctionPassCtor, false,
Dan Gohman364a39f2008-10-14 17:00:38 +0000[diff] [blame]1676 RegisterPassParser&lt;RegisterMyPasses&gt; &gt;
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1677 MyPassOpt("mypass",
1678 cl::init(&amp;createDefaultMyPass),
1679 cl::desc("my pass option help"));
1680</pre></div>
1681
1682<p>Here the command option is "mypass", with createDefaultMyPass as the default
1683creator.</p>
1684
1685</div>
1686
1687<!-- *********************************************************************** -->
1688<div class="doc_section">
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1689 <a name="debughints">Using GDB with dynamically loaded passes</a>
1690</div>
Chris Lattner480e2ef2002-09-06 02:02:58 +0000[diff] [blame]1691<!-- *********************************************************************** -->
1692
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1693<div class="doc_text">
1694
1695<p>Unfortunately, using GDB with dynamically loaded passes is not as easy as it
Chris Lattner480e2ef2002-09-06 02:02:58 +0000[diff] [blame]1696should be. First of all, you can't set a breakpoint in a shared object that has
1697not been loaded yet, and second of all there are problems with inlined functions
1698in shared objects. Here are some suggestions to debugging your pass with
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1699GDB.</p>
Chris Lattner480e2ef2002-09-06 02:02:58 +0000[diff] [blame]1700
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1701<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]1702transformation invoked by <tt>opt</tt>, although nothing described here depends
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1703on that.</p>
1704
1705</div>
Chris Lattner480e2ef2002-09-06 02:02:58 +0000[diff] [blame]1706
1707<!-- _______________________________________________________________________ -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1708<div class="doc_subsubsection">
1709 <a name="breakpoint">Setting a breakpoint in your pass</a>
1710</div>
Chris Lattner480e2ef2002-09-06 02:02:58 +0000[diff] [blame]1711
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1712<div class="doc_text">
1713
1714<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]1715
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1716<div class="doc_code"><pre>
Chris Lattner480e2ef2002-09-06 02:02:58 +0000[diff] [blame]1717$ <b>gdb opt</b>
1718GNU gdb 5.0
1719Copyright 2000 Free Software Foundation, Inc.
1720GDB is free software, covered by the GNU General Public License, and you are
1721welcome to change it and/or distribute copies of it under certain conditions.
1722Type "show copying" to see the conditions.
1723There is absolutely no warranty for GDB. Type "show warranty" for details.
1724This GDB was configured as "sparc-sun-solaris2.6"...
1725(gdb)
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1726</pre></div>
Chris Lattner480e2ef2002-09-06 02:02:58 +0000[diff] [blame]1727
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1728<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]1729time to load. Be patient. Since we cannot set a breakpoint in our pass yet
1730(the shared object isn't loaded until runtime), we must execute the process, and
1731have it stop before it invokes our pass, but after it has loaded the shared
1732object. The most foolproof way of doing this is to set a breakpoint in
1733<tt>PassManager::run</tt> and then run the process with the arguments you
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1734want:</p>
Chris Lattner480e2ef2002-09-06 02:02:58 +0000[diff] [blame]1735
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1736<div class="doc_code"><pre>
Reid Spencer22a9e5b2006-09-28 16:53:47 +0000[diff] [blame]1737(gdb) <b>break llvm::PassManager::run</b>
Chris Lattner480e2ef2002-09-06 02:02:58 +0000[diff] [blame]1738Breakpoint 1 at 0x2413bc: file Pass.cpp, line 70.
Chris Lattner4c376ea2005-04-21 04:52:37 +0000[diff] [blame]1739(gdb) <b>run test.bc -load $(LLVMTOP)/llvm/Debug/lib/[libname].so -[passoption]</b>
1740Starting program: opt test.bc -load $(LLVMTOP)/llvm/Debug/lib/[libname].so -[passoption]
Chris Lattner480e2ef2002-09-06 02:02:58 +0000[diff] [blame]1741Breakpoint 1, PassManager::run (this=0xffbef174, M=@0x70b298) at Pass.cpp:70
174270 bool PassManager::run(Module &amp;M) { return PM-&gt;run(M); }
1743(gdb)
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1744</pre></div>
Chris Lattner480e2ef2002-09-06 02:02:58 +0000[diff] [blame]1745
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1746<p>Once the <tt>opt</tt> stops in the <tt>PassManager::run</tt> method you are
1747now free to set breakpoints in your pass so that you can trace through execution
1748or do other standard debugging stuff.</p>
Chris Lattner480e2ef2002-09-06 02:02:58 +0000[diff] [blame]1749
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1750</div>
Chris Lattner480e2ef2002-09-06 02:02:58 +0000[diff] [blame]1751
1752<!-- _______________________________________________________________________ -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1753<div class="doc_subsubsection">
1754 <a name="debugmisc">Miscellaneous Problems</a>
1755</div>
Chris Lattner480e2ef2002-09-06 02:02:58 +0000[diff] [blame]1756
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1757<div class="doc_text">
1758
1759<p>Once you have the basics down, there are a couple of problems that GDB has,
1760some with solutions, some without.</p>
Chris Lattner480e2ef2002-09-06 02:02:58 +0000[diff] [blame]1761
1762<ul>
1763<li>Inline functions have bogus stack information. In general, GDB does a
1764pretty good job getting stack traces and stepping through inline functions.
1765When a pass is dynamically loaded however, it somehow completely loses this
1766capability. The only solution I know of is to de-inline a function (move it
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1767from the body of a class to a .cpp file).</li>
Chris Lattner480e2ef2002-09-06 02:02:58 +0000[diff] [blame]1768
1769<li>Restarting the program breaks breakpoints. After following the information
1770above, you have succeeded in getting some breakpoints planted in your pass. Nex
1771thing you know, you restart the program (i.e., you type '<tt>run</tt>' again),
1772and you start getting errors about breakpoints being unsettable. The only way I
1773have found to "fix" this problem is to <tt>delete</tt> the breakpoints that are
1774already set in your pass, run the program, and re-set the breakpoints once
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1775execution stops in <tt>PassManager::run</tt>.</li>
Chris Lattner480e2ef2002-09-06 02:02:58 +0000[diff] [blame]1776
1777</ul>
1778
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1779<p>Hopefully these tips will help with common case debugging situations. If
1780you'd like to contribute some tips of your own, just contact <a
1781href="mailto:sabre@nondot.org">Chris</a>.</p>
Chris Lattner480e2ef2002-09-06 02:02:58 +0000[diff] [blame]1782
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1783</div>
Chris Lattner480e2ef2002-09-06 02:02:58 +0000[diff] [blame]1784
1785<!-- *********************************************************************** -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1786<div class="doc_section">
1787 <a name="future">Future extensions planned</a>
1788</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1789<!-- *********************************************************************** -->
1790
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1791<div class="doc_text">
1792
1793<p>Although the LLVM Pass Infrastructure is very capable as it stands, and does
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1794some 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]1795where we are going:</p>
1796
1797</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1798
1799<!-- _______________________________________________________________________ -->
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]1800<div class="doc_subsubsection">
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1801 <a name="SMP">Multithreaded LLVM</a>
1802</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1803
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1804<div class="doc_text">
1805
1806<p>Multiple CPU machines are becoming more common and compilation can never be
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1807fast enough: obviously we should allow for a multithreaded compiler. Because of
1808the semantics defined for passes above (specifically they cannot maintain state
1809across invocations of their <tt>run*</tt> methods), a nice clean way to
1810implement a multithreaded compiler would be for the <tt>PassManager</tt> class
Misha Brukmanbc0e9982003-07-14 17:20:40 +0000[diff] [blame]1811to create multiple instances of each pass object, and allow the separate
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1812instances to be hacking on different parts of the program at the same time.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1813
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1814<p>This implementation would prevent each of the passes from having to implement
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1815multithreaded constructs, requiring only the LLVM core to have locking in a few
1816places (for global resources). Although this is a simple extension, we simply
1817haven't had time (or multiprocessor machines, thus a reason) to implement this.
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1818Despite that, we have kept the LLVM passes SMP ready, and you should too.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1819
Chris Lattnerb5c87f62007-05-18 05:36:14 +0000[diff] [blame]1820</div>
1821
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1822<!-- *********************************************************************** -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1823<hr>
1824<address>
1825 <a href="http://jigsaw.w3.org/css-validator/check/referer"><img
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Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1829
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1830 <a href="mailto:sabre@nondot.org">Chris Lattner</a><br>
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]1831 <a href="http://llvm.org">The LLVM Compiler Infrastructure</a><br>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1832 Last modified: $Date$
1833</address>
1834
1835</body>
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