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gerrit-public.fairphone.software / platform / external / llvm / 52790e5865202f3805cf9b1e9145ce19653c0add / . / docs / WritingAnLLVMPass.html
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Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]6 <title>Writing an LLVM Pass</title>
7 <link rel="stylesheet" href="llvm.css" type="text/css">
8</head>
9<body>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]10
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]11<div class="doc_title">
12 Writing an LLVM Pass
13</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]14
15<ol>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]16 <li><a href="#introduction">Introduction - What is a pass?</a></li>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]17 <li><a href="#quickstart">Quick Start - Writing hello world</a>
18 <ul>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]19 <li><a href="#makefile">Setting up the build environment</a></li>
20 <li><a href="#basiccode">Basic code required</a></li>
Chris Lattnerc8603c22006-08-27 23:18:52 +0000[diff] [blame]21 <li><a href="#running">Running a pass with <tt>opt</tt></a></li>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]22 </ul></li>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]23 <li><a href="#passtype">Pass classes and requirements</a>
24 <ul>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]25 <li><a href="#ImmutablePass">The <tt>ImmutablePass</tt> class</a></li>
Chris Lattnerf6278922004-09-20 04:36:29 +0000[diff] [blame]26 <li><a href="#ModulePass">The <tt>ModulePass</tt> class</a>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]27 <ul>
Chris Lattnerf6278922004-09-20 04:36:29 +0000[diff] [blame]28 <li><a href="#runOnModule">The <tt>runOnModule</tt> method</a></li>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]29 </ul></li>
Chris Lattner8fdb2462004-09-18 06:39:35 +0000[diff] [blame]30 <li><a href="#CallGraphSCCPass">The <tt>CallGraphSCCPass</tt> class</a>
31 <ul>
Devang Patelc20048d2007-01-23 22:56:28 +0000[diff] [blame]32 <li><a href="#doInitialization_scc">The <tt>doInitialization(CallGraph
Chris Lattner8fdb2462004-09-18 06:39:35 +0000[diff] [blame]33 &amp;)</tt> method</a></li>
34 <li><a href="#runOnSCC">The <tt>runOnSCC</tt> method</a></li>
Devang Patelc20048d2007-01-23 22:56:28 +0000[diff] [blame]35 <li><a href="#doFinalization_scc">The <tt>doFinalization(CallGraph
Chris Lattner8fdb2462004-09-18 06:39:35 +0000[diff] [blame]36 &amp;)</tt> method</a></li>
37 </ul></li>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]38 <li><a href="#FunctionPass">The <tt>FunctionPass</tt> class</a>
39 <ul>
Chris Lattnerd0713f92002-09-12 17:06:43 +0000[diff] [blame]40 <li><a href="#doInitialization_mod">The <tt>doInitialization(Module
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]41 &amp;)</tt> method</a></li>
42 <li><a href="#runOnFunction">The <tt>runOnFunction</tt> method</a></li>
Chris Lattnerd0713f92002-09-12 17:06:43 +0000[diff] [blame]43 <li><a href="#doFinalization_mod">The <tt>doFinalization(Module
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]44 &amp;)</tt> method</a></li>
45 </ul></li>
Devang Patel2e8f27d2007-03-19 22:21:25 +0000[diff] [blame]46 <li><a href="#LoopPass">The <tt>LoopPass</tt> class</a>
47 <ul>
48 <li><a href="#doInitialization_loop">The <tt>doInitialization(Loop *,
49 LPPassManager &amp;)</tt> method</a></li>
50 <li><a href="#runOnLoop">The <tt>runOnLoop</tt> method</a></li>
51 <li><a href="#doFinalization_loop">The <tt>doFinalization()
52 </tt> method</a></li>
53 </ul></li>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]54 <li><a href="#BasicBlockPass">The <tt>BasicBlockPass</tt> class</a>
55 <ul>
Chris Lattnerd0713f92002-09-12 17:06:43 +0000[diff] [blame]56 <li><a href="#doInitialization_fn">The <tt>doInitialization(Function
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]57 &amp;)</tt> method</a></li>
58 <li><a href="#runOnBasicBlock">The <tt>runOnBasicBlock</tt>
59 method</a></li>
Chris Lattnerd0713f92002-09-12 17:06:43 +0000[diff] [blame]60 <li><a href="#doFinalization_fn">The <tt>doFinalization(Function
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]61 &amp;)</tt> method</a></li>
62 </ul></li>
Brian Gaekecab8b6f2003-07-17 18:53:20 +0000[diff] [blame]63 <li><a href="#MachineFunctionPass">The <tt>MachineFunctionPass</tt>
64 class</a>
Brian Gaeke6a33f362003-07-22 20:53:20 +0000[diff] [blame]65 <ul>
66 <li><a href="#runOnMachineFunction">The
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]67 <tt>runOnMachineFunction(MachineFunction &amp;)</tt> method</a></li>
68 </ul></li>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]69 </ul>
70 <li><a href="#registration">Pass Registration</a>
71 <ul>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]72 <li><a href="#print">The <tt>print</tt> method</a></li>
73 </ul></li>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]74 <li><a href="#interaction">Specifying interactions between passes</a>
75 <ul>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]76 <li><a href="#getAnalysisUsage">The <tt>getAnalysisUsage</tt>
77 method</a></li>
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]78 <li><a href="#AU::addRequired">The <tt>AnalysisUsage::addRequired&lt;&gt;</tt> and <tt>AnalysisUsage::addRequiredTransitive&lt;&gt;</tt> methods</a></li>
79 <li><a href="#AU::addPreserved">The <tt>AnalysisUsage::addPreserved&lt;&gt;</tt> method</a></li>
80 <li><a href="#AU::examples">Example implementations of <tt>getAnalysisUsage</tt></a></li>
81 <li><a href="#getAnalysis">The <tt>getAnalysis&lt;&gt;</tt> and <tt>getAnalysisToUpdate&lt;&gt;</tt> methods</a></li>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]82 </ul></li>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]83 <li><a href="#analysisgroup">Implementing Analysis Groups</a>
84 <ul>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]85 <li><a href="#agconcepts">Analysis Group Concepts</a></li>
86 <li><a href="#registerag">Using <tt>RegisterAnalysisGroup</tt></a></li>
87 </ul></li>
Tanya Lattnerd5383652004-11-19 01:25:14 +0000[diff] [blame]88 <li><a href="#passStatistics">Pass Statistics</a>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]89 <li><a href="#passmanager">What PassManager does</a>
90 <ul>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]91 <li><a href="#releaseMemory">The <tt>releaseMemory</tt> method</a></li>
92 </ul></li>
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]93 <li><a href="#registering">Registering dynamically loaded passes</a>
94 <ul>
95 <li><a href="#registering_existing">Using existing registries</a></li>
96 <li><a href="#registering_new">Creating new registries</a></li>
97 </ul></li>
Chris Lattner480e2ef2002-09-06 02:02:58 +0000[diff] [blame]98 <li><a href="#debughints">Using GDB with dynamically loaded passes</a>
99 <ul>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]100 <li><a href="#breakpoint">Setting a breakpoint in your pass</a></li>
101 <li><a href="#debugmisc">Miscellaneous Problems</a></li>
102 </ul></li>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]103 <li><a href="#future">Future extensions planned</a>
104 <ul>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]105 <li><a href="#SMP">Multithreaded LLVM</a></li>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]106 </ul></li>
107</ol>
Chris Lattner38c633d2002-08-08 20:23:41 +0000[diff] [blame]108
Chris Lattner7911ce22004-05-23 21:07:27 +0000[diff] [blame]109<div class="doc_author">
Chris Lattner8f652eb2006-08-11 16:37:02 +0000[diff] [blame]110 <p>Written by <a href="mailto:sabre@nondot.org">Chris Lattner</a> and
Jim Laskeyc760a922007-03-14 19:32:21 +0000[diff] [blame]111 <a href="mailto:jlaskey@mac.com">Jim Laskey</a></p>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]112</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]113
114<!-- *********************************************************************** -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]115<div class="doc_section">
116 <a name="introduction">Introduction - What is a pass?</a>
117</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]118<!-- *********************************************************************** -->
119
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]120<div class="doc_text">
121
122<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]123passes are where most of the interesting parts of the compiler exist. Passes
124perform the transformations and optimizations that make up the compiler, they
125build the analysis results that are used by these transformations, and they are,
126above all, a structuring technique for compiler code.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]127
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]128<p>All LLVM passes are subclasses of the <tt><a
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]129href="http://llvm.org/doxygen/classllvm_1_1Pass.html">Pass</a></tt>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]130class, which implement functionality by overriding virtual methods inherited
Chris Lattnerf6278922004-09-20 04:36:29 +0000[diff] [blame]131from <tt>Pass</tt>. Depending on how your pass works, you should inherit from
132the <tt><a href="#ModulePass">ModulePass</a></tt>, <tt><a
133href="#CallGraphSCCPass">CallGraphSCCPass</a></tt>, <tt><a
134href="#FunctionPass">FunctionPass</a></tt>, or <tt><a
Devang Patel2e8f27d2007-03-19 22:21:25 +0000[diff] [blame]135href="#LoopPass">LoopPass</a></tt>, or <tt><a
Chris Lattner8fdb2462004-09-18 06:39:35 +0000[diff] [blame]136href="#BasicBlockPass">BasicBlockPass</a></tt> classes, which gives the system
137more information about what your pass does, and how it can be combined with
138other passes. One of the main features of the LLVM Pass Framework is that it
139schedules passes to run in an efficient way based on the constraints that your
140pass meets (which are indicated by which class they derive from).</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]141
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]142<p>We start by showing you how to construct a pass, everything from setting up
143the code, to compiling, loading, and executing it. After the basics are down,
144more advanced features are discussed.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]145
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]146</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]147
148<!-- *********************************************************************** -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]149<div class="doc_section">
150 <a name="quickstart">Quick Start - Writing hello world</a>
151</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]152<!-- *********************************************************************** -->
153
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]154<div class="doc_text">
155
156<p>Here we describe how to write the "hello world" of passes. The "Hello" pass
157is designed to simply print out the name of non-external functions that exist in
Chris Lattner8fdb2462004-09-18 06:39:35 +0000[diff] [blame]158the program being compiled. It does not modify the program at all, it just
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]159inspects it. The source code and files for this pass are available in the LLVM
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]160source tree in the <tt>lib/Transforms/Hello</tt> directory.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]161
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]162</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]163
164<!-- ======================================================================= -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]165<div class="doc_subsection">
166 <a name="makefile">Setting up the build environment</a>
167</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]168
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]169<div class="doc_text">
170
Reid Spencer1bc19342004-12-11 05:12:57 +0000[diff] [blame]171 <p>First, you need to create a new directory somewhere in the LLVM source
172 base. For this example, we'll assume that you made
173 <tt>lib/Transforms/Hello</tt>. Next, you must set up a build script
174 (Makefile) that will compile the source code for the new pass. To do this,
175 copy the following into <tt>Makefile</tt>:</p>
176 <hr/>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]177
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]178<div class="doc_code"><pre>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]179# Makefile for hello pass
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]180
Chris Lattner17a4c3e2002-08-14 20:06:13 +0000[diff] [blame]181# Path to top level of LLVM heirarchy
Chris Lattner7ce83e52002-08-14 20:07:01 +0000[diff] [blame]182LEVEL = ../../..
Chris Lattner17a4c3e2002-08-14 20:06:13 +0000[diff] [blame]183
184# Name of the library to build
Reid Spencer7fa6d522005-01-11 05:16:23 +0000[diff] [blame]185LIBRARYNAME = Hello
Chris Lattner17a4c3e2002-08-14 20:06:13 +0000[diff] [blame]186
Reid Spencer7fa6d522005-01-11 05:16:23 +0000[diff] [blame]187# Make the shared library become a loadable module so the tools can
188# dlopen/dlsym on the resulting library.
Robert Bocchino3cf817d2006-01-06 22:49:23 +0000[diff] [blame]189LOADABLE_MODULE = 1
Reid Spencer7fa6d522005-01-11 05:16:23 +0000[diff] [blame]190
Reid Spencerebfe07f2006-08-08 01:48:17 +0000[diff] [blame]191# Tell the build system which LLVM libraries your pass needs. You'll probably
192# need at least LLVMSystem.a, LLVMSupport.a, LLVMCore.a but possibly several
193# others too.
194LLVMLIBS = LLVMCore.a LLVMSupport.a LLVMSystem.a
195
Chris Lattner17a4c3e2002-08-14 20:06:13 +0000[diff] [blame]196# Include the makefile implementation stuff
197include $(LEVEL)/Makefile.common
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]198</pre></div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]199
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]200<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]201directory are to be compiled and linked together into a
Reid Spencer7fa6d522005-01-11 05:16:23 +0000[diff] [blame]202<tt>Debug/lib/Hello.so</tt> shared object that can be dynamically loaded by
Chris Lattnerc8603c22006-08-27 23:18:52 +0000[diff] [blame]203the <tt>opt</tt> or <tt>bugpoint</tt> tools via their <tt>-load</tt> options.
Reid Spencer7fa6d522005-01-11 05:16:23 +0000[diff] [blame]204If your operating system uses a suffix other than .so (such as windows or
205Mac OS/X), the appropriate extension will be used.</p>
John Criswellf9c78652004-01-26 21:26:54 +0000[diff] [blame]206
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]207<p>Now that we have the build scripts set up, we just need to write the code for
208the pass itself.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]209
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]210</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]211
212<!-- ======================================================================= -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]213<div class="doc_subsection">
214 <a name="basiccode">Basic code required</a>
215</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]216
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]217<div class="doc_text">
218
219<p>Now that we have a way to compile our new pass, we just have to write it.
220Start out with:</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]221
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]222<div class="doc_code"><pre>
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]223<b>#include</b> "<a href="http://llvm.org/doxygen/Pass_8h-source.html">llvm/Pass.h</a>"
224<b>#include</b> "<a href="http://llvm.org/doxygen/Function_8h-source.html">llvm/Function.h</a>"
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]225</pre></div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]226
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]227<p>Which are needed because we are writing a <tt><a
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]228href="http://llvm.org/doxygen/classllvm_1_1Pass.html">Pass</a></tt>, and
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]229we are operating on <tt><a
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]230href="http://llvm.org/doxygen/classllvm_1_1Function.html">Function</a></tt>'s.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]231
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]232<p>Next we have:</p>
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]233<div class="doc_code"><pre>
Jonathan Manton65acb302004-06-30 18:10:30 +0000[diff] [blame]234<b>using namespace llvm;</b>
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]235</pre></div>
Jonathan Manton65acb302004-06-30 18:10:30 +0000[diff] [blame]236<p>... which is required because the functions from the include files
237live in the llvm namespace.
238</p>
239
240<p>Next we have:</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]241
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]242<div class="doc_code"><pre>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]243<b>namespace</b> {
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]244</pre></div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]245
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]246<p>... which starts out an anonymous namespace. Anonymous namespaces are to C++
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]247what the "<tt>static</tt>" keyword is to C (at global scope). It makes the
248things declared inside of the anonymous namespace only visible to the current
249file. If you're not familiar with them, consult a decent C++ book for more
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]250information.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]251
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]252<p>Next, we declare our pass itself:</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]253
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]254<div class="doc_code"><pre>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]255 <b>struct</b> Hello : <b>public</b> <a href="#FunctionPass">FunctionPass</a> {
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]256</pre></div><p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]257
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]258<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]259href="http://llvm.org/doxygen/classllvm_1_1FunctionPass.html">FunctionPass</a></tt>.
Chris Lattnerd6ea9262002-09-09 03:48:46 +0000[diff] [blame]260The different builtin pass subclasses are described in detail <a
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]261href="#passtype">later</a>, but for now, know that <a
262href="#FunctionPass"><tt>FunctionPass</tt></a>'s operate a function at a
263time.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]264
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]265<div class="doc_code"><pre>
Devang Patel19974732007-05-03 01:11:54 +0000[diff] [blame]266 static char ID;
Chris Lattnerb5c87f62007-05-18 05:36:14 +0000[diff] [blame]267 Hello() : FunctionPass((intptr_t)&amp;ID) {}
Devang Patele50fb9a2007-05-01 20:55:38 +0000[diff] [blame]268</pre></div><p>
269
270<p> This declares pass identifier used by LLVM to identify pass. This allows LLVM to
271avoid using expensive C++ runtime information.</p>
272
273<div class="doc_code"><pre>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]274 <b>virtual bool</b> <a href="#runOnFunction">runOnFunction</a>(Function &amp;F) {
Bill Wendling832171c2006-12-07 20:04:42 +0000[diff] [blame]275 llvm::cerr &lt;&lt; "<i>Hello: </i>" &lt;&lt; F.getName() &lt;&lt; "\n";
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]276 <b>return false</b>;
277 }
278 }; <i>// end of struct Hello</i>
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]279</pre></div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]280
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]281<p>We declare a "<a href="#runOnFunction"><tt>runOnFunction</tt></a>" method,
282which overloads an abstract virtual method inherited from <a
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]283href="#FunctionPass"><tt>FunctionPass</tt></a>. This is where we are supposed
284to 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]285function.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]286
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]287<div class="doc_code"><pre>
Devang Patel19974732007-05-03 01:11:54 +0000[diff] [blame]288 char Hello::ID = 0;
Devang Patele50fb9a2007-05-01 20:55:38 +0000[diff] [blame]289</pre></div>
290
291<p> We initialize pass ID here. LLVM uses ID's address to identify pass so
292initialization value is not important.</p>
293
294<div class="doc_code"><pre>
Devang Patelc7582092008-03-19 21:56:59 +0000[diff] [blame]295 RegisterPass&lt;Hello&gt; X("<i>hello</i>", "<i>Hello World Pass</i>",
296 false /* Only looks at CFG */,
297 false /* Analysis Pass */);
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]298} <i>// end of anonymous namespace</i>
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]299</pre></div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]300
Chris Lattnerc8603c22006-08-27 23:18:52 +0000[diff] [blame]301<p>Lastly, we <a href="#registration">register our class</a> <tt>Hello</tt>,
302giving it a command line
Devang Patelc7582092008-03-19 21:56:59 +0000[diff] [blame]303argument "<tt>hello</tt>", and a name "<tt>Hello World Pass</tt>".
304Last two RegisterPass arguments are optional. Their default value is false.
305If a pass walks CFG without modifying it then third argument is set to true.
306If a pass is an analysis pass, for example dominator tree pass, then true
307is supplied as fourth argument. </p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]308
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]309<p>As a whole, the <tt>.cpp</tt> file looks like:</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]310
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]311<div class="doc_code"><pre>
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]312<b>#include</b> "<a href="http://llvm.org/doxygen/Pass_8h-source.html">llvm/Pass.h</a>"
313<b>#include</b> "<a href="http://llvm.org/doxygen/Function_8h-source.html">llvm/Function.h</a>"
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]314
Jonathan Manton65acb302004-06-30 18:10:30 +0000[diff] [blame]315<b>using namespace llvm;</b>
316
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]317<b>namespace</b> {
318 <b>struct Hello</b> : <b>public</b> <a href="#FunctionPass">FunctionPass</a> {
Devang Patele50fb9a2007-05-01 20:55:38 +0000[diff] [blame]319
Devang Patel19974732007-05-03 01:11:54 +0000[diff] [blame]320 static char ID;
Chris Lattner55021172007-05-18 05:38:44 +0000[diff] [blame]321 Hello() : FunctionPass((intptr_t)&amp;ID) {}
Devang Patele50fb9a2007-05-01 20:55:38 +0000[diff] [blame]322
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]323 <b>virtual bool</b> <a href="#runOnFunction">runOnFunction</a>(Function &amp;F) {
Bill Wendling832171c2006-12-07 20:04:42 +0000[diff] [blame]324 llvm::cerr &lt;&lt; "<i>Hello: </i>" &lt;&lt; F.getName() &lt;&lt; "\n";
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]325 <b>return false</b>;
326 }
327 };
328
Devang Patel26e5a302007-07-25 21:05:39 +0000[diff] [blame]329 char Hello::ID = 0;
Chris Lattnerc8603c22006-08-27 23:18:52 +0000[diff] [blame]330 RegisterPass&lt;Hello&gt; X("<i>hello</i>", "<i>Hello World Pass</i>");
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]331}
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]332</pre></div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]333
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]334<p>Now that it's all together, compile the file with a simple "<tt>gmake</tt>"
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]335command in the local directory and you should get a new
Reid Spencer7fa6d522005-01-11 05:16:23 +0000[diff] [blame]336"<tt>Debug/lib/Hello.so</tt> file. Note that everything in this file is
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]337contained in an anonymous namespace: this reflects the fact that passes are self
338contained units that do not need external interfaces (although they can have
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]339them) to be useful.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]340
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]341</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]342
343<!-- ======================================================================= -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]344<div class="doc_subsection">
Chris Lattnerc8603c22006-08-27 23:18:52 +0000[diff] [blame]345 <a name="running">Running a pass with <tt>opt</tt></a>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]346</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]347
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]348<div class="doc_text">
349
John Criswellf9c78652004-01-26 21:26:54 +0000[diff] [blame]350<p>Now that you have a brand new shiny shared object file, we can use the
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]351<tt>opt</tt> command to run an LLVM program through your pass. Because you
Chris Lattnerc8603c22006-08-27 23:18:52 +0000[diff] [blame]352registered your pass with the <tt>RegisterPass</tt> template, you will be able to
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]353use the <tt>opt</tt> tool to access it, once loaded.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]354
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]355<p>To test it, follow the example at the end of the <a
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]356href="GettingStarted.html">Getting Started Guide</a> to compile "Hello World" to
Gabor Greif04367bf2007-07-06 22:07:22 +0000[diff] [blame]357LLVM. We can now run the bitcode file (<tt>hello.bc</tt>) for the program
358through our transformation like this (or course, any bitcode file will
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]359work):</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]360
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]361<div class="doc_code"><pre>
Reid Spencer7fa6d522005-01-11 05:16:23 +0000[diff] [blame]362$ opt -load ../../../Debug/lib/Hello.so -hello &lt; hello.bc &gt; /dev/null
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]363Hello: __main
364Hello: puts
365Hello: main
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]366</pre></div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]367
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]368<p>The '<tt>-load</tt>' option specifies that '<tt>opt</tt>' should load your
369pass as a shared object, which makes '<tt>-hello</tt>' a valid command line
370argument (which is one reason you need to <a href="#registration">register your
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]371pass</a>). Because the hello pass does not modify the program in any
372interesting way, we just throw away the result of <tt>opt</tt> (sending it to
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]373<tt>/dev/null</tt>).</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]374
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]375<p>To see what happened to the other string you registered, try running
376<tt>opt</tt> with the <tt>--help</tt> option:</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]377
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]378<div class="doc_code"><pre>
Reid Spencer7fa6d522005-01-11 05:16:23 +0000[diff] [blame]379$ opt -load ../../../Debug/lib/Hello.so --help
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]380OVERVIEW: llvm .bc -&gt; .bc modular optimizer
381
Gabor Greif04367bf2007-07-06 22:07:22 +0000[diff] [blame]382USAGE: opt [options] &lt;input bitcode&gt;
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]383
384OPTIONS:
385 Optimizations available:
386...
387 -funcresolve - Resolve Functions
388 -gcse - Global Common Subexpression Elimination
389 -globaldce - Dead Global Elimination
390 <b>-hello - Hello World Pass</b>
Chris Lattner065a6162003-09-10 05:29:43 +0000[diff] [blame]391 -indvars - Canonicalize Induction Variables
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]392 -inline - Function Integration/Inlining
393 -instcombine - Combine redundant instructions
394...
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]395</pre></div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]396
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]397<p>The pass name get added as the information string for your pass, giving some
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]398documentation to users of <tt>opt</tt>. Now that you have a working pass, you
399would go ahead and make it do the cool transformations you want. Once you get
400it all working and tested, it may become useful to find out how fast your pass
401is. The <a href="#passManager"><tt>PassManager</tt></a> provides a nice command
402line option (<tt>--time-passes</tt>) that allows you to get information about
403the execution time of your pass along with the other passes you queue up. For
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]404example:</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]405
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]406<div class="doc_code"><pre>
Reid Spencer7fa6d522005-01-11 05:16:23 +0000[diff] [blame]407$ 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]408Hello: __main
409Hello: puts
410Hello: main
411===============================================================================
412 ... Pass execution timing report ...
413===============================================================================
414 Total Execution Time: 0.02 seconds (0.0479059 wall clock)
415
416 ---User Time--- --System Time-- --User+System-- ---Wall Time--- --- Pass Name ---
Gabor Greif04367bf2007-07-06 22:07:22 +0000[diff] [blame]417 0.0100 (100.0%) 0.0000 ( 0.0%) 0.0100 ( 50.0%) 0.0402 ( 84.0%) Bitcode Writer
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]418 0.0000 ( 0.0%) 0.0100 (100.0%) 0.0100 ( 50.0%) 0.0031 ( 6.4%) Dominator Set Construction
419 0.0000 ( 0.0%) 0.0000 ( 0.0%) 0.0000 ( 0.0%) 0.0013 ( 2.7%) Module Verifier
420 <b> 0.0000 ( 0.0%) 0.0000 ( 0.0%) 0.0000 ( 0.0%) 0.0033 ( 6.9%) Hello World Pass</b>
421 0.0100 (100.0%) 0.0100 (100.0%) 0.0200 (100.0%) 0.0479 (100.0%) TOTAL
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]422</pre></div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]423
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]424<p>As you can see, our implementation above is pretty fast :). The additional
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]425passes listed are automatically inserted by the '<tt>opt</tt>' tool to verify
426that the LLVM emitted by your pass is still valid and well formed LLVM, which
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]427hasn't been broken somehow.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]428
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]429<p>Now that you have seen the basics of the mechanics behind passes, we can talk
430about some more details of how they work and how to use them.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]431
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]432</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]433
434<!-- *********************************************************************** -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]435<div class="doc_section">
436 <a name="passtype">Pass classes and requirements</a>
437</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]438<!-- *********************************************************************** -->
439
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]440<div class="doc_text">
441
442<p>One of the first things that you should do when designing a new pass is to
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]443decide what class you should subclass for your pass. The <a
444href="#basiccode">Hello World</a> example uses the <tt><a
445href="#FunctionPass">FunctionPass</a></tt> class for its implementation, but we
446did not discuss why or when this should occur. Here we talk about the classes
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]447available, from the most general to the most specific.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]448
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]449<p>When choosing a superclass for your Pass, you should choose the <b>most
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]450specific</b> class possible, while still being able to meet the requirements
Misha Brukman5560c9d2003-08-18 14:43:39 +0000[diff] [blame]451listed. This gives the LLVM Pass Infrastructure information necessary to
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]452optimize how passes are run, so that the resultant compiler isn't unneccesarily
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]453slow.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]454
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]455</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]456
Chris Lattnerf004f9a2002-09-25 22:31:38 +0000[diff] [blame]457<!-- ======================================================================= -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]458<div class="doc_subsection">
459 <a name="ImmutablePass">The <tt>ImmutablePass</tt> class</a>
460</div>
Chris Lattnerf004f9a2002-09-25 22:31:38 +0000[diff] [blame]461
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]462<div class="doc_text">
463
464<p>The most plain and boring type of pass is the "<tt><a
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]465href="http://llvm.org/doxygen/classllvm_1_1ImmutablePass.html">ImmutablePass</a></tt>"
Chris Lattnerf004f9a2002-09-25 22:31:38 +0000[diff] [blame]466class. This pass type is used for passes that do not have to be run, do not
467change state, and never need to be updated. This is not a normal type of
468transformation or analysis, but can provide information about the current
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]469compiler configuration.</p>
Chris Lattnerf004f9a2002-09-25 22:31:38 +0000[diff] [blame]470
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]471<p>Although this pass class is very infrequently used, it is important for
Chris Lattnerf004f9a2002-09-25 22:31:38 +0000[diff] [blame]472providing information about the current target machine being compiled for, and
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]473other static information that can affect the various transformations.</p>
Chris Lattnerf004f9a2002-09-25 22:31:38 +0000[diff] [blame]474
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]475<p><tt>ImmutablePass</tt>es never invalidate other transformations, are never
476invalidated, and are never "run".</p>
Chris Lattnerf004f9a2002-09-25 22:31:38 +0000[diff] [blame]477
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]478</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]479
480<!-- ======================================================================= -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]481<div class="doc_subsection">
Chris Lattnerf6278922004-09-20 04:36:29 +0000[diff] [blame]482 <a name="ModulePass">The <tt>ModulePass</tt> class</a>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]483</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]484
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]485<div class="doc_text">
486
487<p>The "<tt><a
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]488href="http://llvm.org/doxygen/classllvm_1_1ModulePass.html">ModulePass</a></tt>"
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]489class is the most general of all superclasses that you can use. Deriving from
Chris Lattnerf6278922004-09-20 04:36:29 +0000[diff] [blame]490<tt>ModulePass</tt> indicates that your pass uses the entire program as a unit,
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]491refering to function bodies in no predictable order, or adding and removing
Chris Lattnerf6278922004-09-20 04:36:29 +0000[diff] [blame]492functions. Because nothing is known about the behavior of <tt>ModulePass</tt>
Devang Patel3c1ca0b2007-04-16 21:28:14 +0000[diff] [blame]493subclasses, no optimization can be done for their execution. A module pass
494can use function level passes (e.g. dominators) using getAnalysis interface
Chris Lattnerb5c87f62007-05-18 05:36:14 +0000[diff] [blame]495<tt> getAnalysis&lt;DominatorTree&gt;(Function)</tt>. </p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]496
Chris Lattnerf6278922004-09-20 04:36:29 +0000[diff] [blame]497<p>To write a correct <tt>ModulePass</tt> subclass, derive from
498<tt>ModulePass</tt> and overload the <tt>runOnModule</tt> method with the
499following signature:</p>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]500
501</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]502
503<!-- _______________________________________________________________________ -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]504<div class="doc_subsubsection">
Chris Lattnerf6278922004-09-20 04:36:29 +0000[diff] [blame]505 <a name="runOnModule">The <tt>runOnModule</tt> method</a>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]506</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]507
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]508<div class="doc_text">
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]509
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]510<div class="doc_code"><pre>
Chris Lattnerf6278922004-09-20 04:36:29 +0000[diff] [blame]511 <b>virtual bool</b> runOnModule(Module &amp;M) = 0;
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]512</pre></div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]513
John Criswell2382ff72005-07-15 19:25:12 +0000[diff] [blame]514<p>The <tt>runOnModule</tt> method performs the interesting work of the pass.
515It should return true if the module was modified by the transformation and
516false otherwise.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]517
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]518</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]519
520<!-- ======================================================================= -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]521<div class="doc_subsection">
Chris Lattner8fdb2462004-09-18 06:39:35 +0000[diff] [blame]522 <a name="CallGraphSCCPass">The <tt>CallGraphSCCPass</tt> class</a>
523</div>
524
525<div class="doc_text">
526
527<p>The "<tt><a
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]528href="http://llvm.org/doxygen/classllvm_1_1CallGraphSCCPass.html">CallGraphSCCPass</a></tt>"
Chris Lattner8fdb2462004-09-18 06:39:35 +0000[diff] [blame]529is used by passes that need to traverse the program bottom-up on the call graph
530(callees before callers). Deriving from CallGraphSCCPass provides some
531mechanics for building and traversing the CallGraph, but also allows the system
532to optimize execution of CallGraphSCCPass's. If your pass meets the
533requirements outlined below, and doesn't meet the requirements of a <tt><a
534href="#FunctionPass">FunctionPass</a></tt> or <tt><a
535href="#BasicBlockPass">BasicBlockPass</a></tt>, you should derive from
536<tt>CallGraphSCCPass</tt>.</p>
537
538<p><b>TODO</b>: explain briefly what SCC, Tarjan's algo, and B-U mean.</p>
539
540<p>To be explicit, <tt>CallGraphSCCPass</tt> subclasses are:</p>
541
542<ol>
543
544<li>... <em>not allowed</em> to modify any <tt>Function</tt>s that are not in
545the current SCC.</li>
546
Tanya Lattner18aad232007-06-07 16:44:52 +0000[diff] [blame]547<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]548current SCC and the direct callees of the SCC.</li>
549
550<li>... <em>required</em> to preserve the current CallGraph object, updating it
551to reflect any changes made to the program.</li>
552
553<li>... <em>not allowed</em> to add or remove SCC's from the current Module,
554though they may change the contents of an SCC.</li>
555
556<li>... <em>allowed</em> to add or remove global variables from the current
557Module.</li>
558
559<li>... <em>allowed</em> to maintain state across invocations of
560 <a href="#runOnSCC"><tt>runOnSCC</tt></a> (including global data).</li>
561</ol>
562
563<p>Implementing a <tt>CallGraphSCCPass</tt> is slightly tricky in some cases
564because it has to handle SCCs with more than one node in it. All of the virtual
565methods described below should return true if they modified the program, or
566false if they didn't.</p>
567
568</div>
569
570<!-- _______________________________________________________________________ -->
571<div class="doc_subsubsection">
Devang Patelc20048d2007-01-23 22:56:28 +0000[diff] [blame]572 <a name="doInitialization_scc">The <tt>doInitialization(CallGraph &amp;)</tt>
Chris Lattner8fdb2462004-09-18 06:39:35 +0000[diff] [blame]573 method</a>
574</div>
575
576<div class="doc_text">
577
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]578<div class="doc_code"><pre>
Devang Patelc20048d2007-01-23 22:56:28 +0000[diff] [blame]579 <b>virtual bool</b> doInitialization(CallGraph &amp;CG);
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]580</pre></div>
Chris Lattner8fdb2462004-09-18 06:39:35 +0000[diff] [blame]581
582<p>The <tt>doIninitialize</tt> method is allowed to do most of the things that
583<tt>CallGraphSCCPass</tt>'s are not allowed to do. They can add and remove
584functions, get pointers to functions, etc. The <tt>doInitialization</tt> method
585is designed to do simple initialization type of stuff that does not depend on
586the SCCs being processed. The <tt>doInitialization</tt> method call is not
587scheduled to overlap with any other pass executions (thus it should be very
588fast).</p>
589
590</div>
591
592<!-- _______________________________________________________________________ -->
593<div class="doc_subsubsection">
594 <a name="runOnSCC">The <tt>runOnSCC</tt> method</a>
595</div>
596
597<div class="doc_text">
598
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]599<div class="doc_code"><pre>
Chris Lattner8fdb2462004-09-18 06:39:35 +0000[diff] [blame]600 <b>virtual bool</b> runOnSCC(const std::vector&lt;CallGraphNode *&gt; &amp;SCCM) = 0;
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]601</pre></div>
Chris Lattner8fdb2462004-09-18 06:39:35 +0000[diff] [blame]602
603<p>The <tt>runOnSCC</tt> method performs the interesting work of the pass, and
604should return true if the module was modified by the transformation, false
605otherwise.</p>
606
607</div>
608
609<!-- _______________________________________________________________________ -->
610<div class="doc_subsubsection">
Devang Patelc20048d2007-01-23 22:56:28 +0000[diff] [blame]611 <a name="doFinalization_scc">The <tt>doFinalization(CallGraph
Chris Lattner8fdb2462004-09-18 06:39:35 +0000[diff] [blame]612 &amp;)</tt> method</a>
613</div>
614
615<div class="doc_text">
616
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]617<div class="doc_code"><pre>
Devang Patelc20048d2007-01-23 22:56:28 +0000[diff] [blame]618 <b>virtual bool</b> doFinalization(CallGraph &amp;CG);
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]619</pre></div>
Chris Lattner8fdb2462004-09-18 06:39:35 +0000[diff] [blame]620
621<p>The <tt>doFinalization</tt> method is an infrequently used method that is
622called when the pass framework has finished calling <a
623href="#runOnFunction"><tt>runOnFunction</tt></a> for every function in the
624program being compiled.</p>
625
626</div>
627
628<!-- ======================================================================= -->
629<div class="doc_subsection">
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]630 <a name="FunctionPass">The <tt>FunctionPass</tt> class</a>
631</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]632
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]633<div class="doc_text">
634
Chris Lattnerf6278922004-09-20 04:36:29 +0000[diff] [blame]635<p>In contrast to <tt>ModulePass</tt> subclasses, <tt><a
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]636href="http://llvm.org/doxygen/classllvm_1_1Pass.html">FunctionPass</a></tt>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]637subclasses do have a predictable, local behavior that can be expected by the
638system. All <tt>FunctionPass</tt> execute on each function in the program
Misha Brukmanef6a6a62003-08-21 22:14:26 +0000[diff] [blame]639independent of all of the other functions in the program.
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]640<tt>FunctionPass</tt>'s do not require that they are executed in a particular
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]641order, and <tt>FunctionPass</tt>'s do not modify external functions.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]642
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]643<p>To be explicit, <tt>FunctionPass</tt> subclasses are not allowed to:</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]644
645<ol>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]646<li>Modify a Function other than the one currently being processed.</li>
647<li>Add or remove Function's from the current Module.</li>
648<li>Add or remove global variables from the current Module.</li>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]649<li>Maintain state across invocations of
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]650 <a href="#runOnFunction"><tt>runOnFunction</tt></a> (including global data)</li>
651</ol>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]652
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]653<p>Implementing a <tt>FunctionPass</tt> is usually straightforward (See the <a
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]654href="#basiccode">Hello World</a> pass for example). <tt>FunctionPass</tt>'s
655may overload three virtual methods to do their work. All of these methods
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]656should return true if they modified the program, or false if they didn't.</p>
657
658</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]659
660<!-- _______________________________________________________________________ -->
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]661<div class="doc_subsubsection">
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]662 <a name="doInitialization_mod">The <tt>doInitialization(Module &amp;)</tt>
663 method</a>
664</div>
665
666<div class="doc_text">
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]667
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]668<div class="doc_code"><pre>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]669 <b>virtual bool</b> doInitialization(Module &amp;M);
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]670</pre></div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]671
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]672<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]673<tt>FunctionPass</tt>'s are not allowed to do. They can add and remove
Chris Lattnerd0713f92002-09-12 17:06:43 +0000[diff] [blame]674functions, get pointers to functions, etc. The <tt>doInitialization</tt> method
675is designed to do simple initialization type of stuff that does not depend on
676the functions being processed. The <tt>doInitialization</tt> method call is not
677scheduled to overlap with any other pass executions (thus it should be very
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]678fast).</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]679
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]680<p>A good example of how this method should be used is the <a
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]681href="http://llvm.org/doxygen/LowerAllocations_8cpp-source.html">LowerAllocations</a>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]682pass. This pass converts <tt>malloc</tt> and <tt>free</tt> instructions into
Misha Brukmanef6a6a62003-08-21 22:14:26 +0000[diff] [blame]683platform dependent <tt>malloc()</tt> and <tt>free()</tt> function calls. It
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]684uses the <tt>doInitialization</tt> method to get a reference to the malloc and
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]685free functions that it needs, adding prototypes to the module if necessary.</p>
686
687</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]688
689<!-- _______________________________________________________________________ -->
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]690<div class="doc_subsubsection">
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]691 <a name="runOnFunction">The <tt>runOnFunction</tt> method</a>
692</div>
693
694<div class="doc_text">
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]695
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]696<div class="doc_code"><pre>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]697 <b>virtual bool</b> runOnFunction(Function &amp;F) = 0;
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]698</pre></div><p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]699
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]700<p>The <tt>runOnFunction</tt> method must be implemented by your subclass to do
701the transformation or analysis work of your pass. As usual, a true value should
702be returned if the function is modified.</p>
703
704</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]705
706<!-- _______________________________________________________________________ -->
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]707<div class="doc_subsubsection">
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]708 <a name="doFinalization_mod">The <tt>doFinalization(Module
709 &amp;)</tt> method</a>
710</div>
711
712<div class="doc_text">
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]713
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]714<div class="doc_code"><pre>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]715 <b>virtual bool</b> doFinalization(Module &amp;M);
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]716</pre></div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]717
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]718<p>The <tt>doFinalization</tt> method is an infrequently used method that is
719called when the pass framework has finished calling <a
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]720href="#runOnFunction"><tt>runOnFunction</tt></a> for every function in the
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]721program being compiled.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]722
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]723</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]724
725<!-- ======================================================================= -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]726<div class="doc_subsection">
Devang Patel2e8f27d2007-03-19 22:21:25 +0000[diff] [blame]727 <a name="LoopPass">The <tt>LoopPass</tt> class </a>
728</div>
729
730<div class="doc_text">
731
732<p> All <tt>LoopPass</tt> execute on each loop in the function independent of
733all of the other loops in the function. <tt>LoopPass</tt> processes loops in
734loop nest order such that outer most loop is processed last. </p>
735
736<p> <tt>LoopPass</tt> subclasses are allowed to update loop nest using
737<tt>LPPassManager</tt> interface. Implementing a loop pass is usually
738straightforward. <tt>Looppass</tt>'s may overload three virtual methods to
739do their work. All these methods should return true if they modified the
740program, or false if they didn't. </p>
741</div>
742
743<!-- _______________________________________________________________________ -->
744<div class="doc_subsubsection">
745 <a name="doInitialization_loop">The <tt>doInitialization(Loop *,
746 LPPassManager &amp;)</tt>
747 method</a>
748</div>
749
750<div class="doc_text">
751
752<div class="doc_code"><pre>
753 <b>virtual bool</b> doInitialization(Loop *, LPPassManager &amp;LPM);
754</pre></div>
755
Chris Lattnerb5c87f62007-05-18 05:36:14 +0000[diff] [blame]756<p>The <tt>doInitialization</tt> method is designed to do simple initialization
Devang Patel2e8f27d2007-03-19 22:21:25 +0000[diff] [blame]757type of stuff that does not depend on the functions being processed. The
758<tt>doInitialization</tt> method call is not scheduled to overlap with any
759other pass executions (thus it should be very fast). LPPassManager
760interface should be used to access Function or Module level analysis
761information.</p>
762
763</div>
764
765
766<!-- _______________________________________________________________________ -->
767<div class="doc_subsubsection">
768 <a name="runOnLoop">The <tt>runOnLoop</tt> method</a>
769</div>
770
771<div class="doc_text">
772
773<div class="doc_code"><pre>
774 <b>virtual bool</b> runOnLoop(Loop *, LPPassManager &amp;LPM) = 0;
775</pre></div><p>
776
777<p>The <tt>runOnLoop</tt> method must be implemented by your subclass to do
778the transformation or analysis work of your pass. As usual, a true value should
779be returned if the function is modified. <tt>LPPassManager</tt> interface
780should be used to update loop nest.</p>
781
782</div>
783
784<!-- _______________________________________________________________________ -->
785<div class="doc_subsubsection">
786 <a name="doFinalization_loop">The <tt>doFinalization()</tt> method</a>
787</div>
788
789<div class="doc_text">
790
791<div class="doc_code"><pre>
792 <b>virtual bool</b> doFinalization();
793</pre></div>
794
795<p>The <tt>doFinalization</tt> method is an infrequently used method that is
796called when the pass framework has finished calling <a
797href="#runOnLoop"><tt>runOnLoop</tt></a> for every loop in the
798program being compiled. </p>
799
800</div>
801
802
803
804<!-- ======================================================================= -->
805<div class="doc_subsection">
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]806 <a name="BasicBlockPass">The <tt>BasicBlockPass</tt> class</a>
807</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]808
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]809<div class="doc_text">
810
811<p><tt>BasicBlockPass</tt>'s are just like <a
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]812href="#FunctionPass"><tt>FunctionPass</tt></a>'s, except that they must limit
813their scope of inspection and modification to a single basic block at a time.
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]814As such, they are <b>not</b> allowed to do any of the following:</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]815
816<ol>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]817<li>Modify or inspect any basic blocks outside of the current one</li>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]818<li>Maintain state across invocations of
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]819 <a href="#runOnBasicBlock"><tt>runOnBasicBlock</tt></a></li>
Reid Spencer1bc19342004-12-11 05:12:57 +0000[diff] [blame]820<li>Modify the control flow graph (by altering terminator instructions)</li>
821<li>Any of the things forbidden for
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]822 <a href="#FunctionPass"><tt>FunctionPass</tt></a>es.</li>
823</ol>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]824
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]825<p><tt>BasicBlockPass</tt>es are useful for traditional local and "peephole"
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]826optimizations. They may override the same <a
Chris Lattnerd0713f92002-09-12 17:06:43 +0000[diff] [blame]827href="#doInitialization_mod"><tt>doInitialization(Module &amp;)</tt></a> and <a
828href="#doFinalization_mod"><tt>doFinalization(Module &amp;)</tt></a> methods that <a
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]829href="#FunctionPass"><tt>FunctionPass</tt></a>'s have, but also have the following virtual methods that may also be implemented:</p>
830
831</div>
Chris Lattnerd0713f92002-09-12 17:06:43 +0000[diff] [blame]832
833<!-- _______________________________________________________________________ -->
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]834<div class="doc_subsubsection">
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]835 <a name="doInitialization_fn">The <tt>doInitialization(Function
836 &amp;)</tt> method</a>
837</div>
838
839<div class="doc_text">
Chris Lattnerd0713f92002-09-12 17:06:43 +0000[diff] [blame]840
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]841<div class="doc_code"><pre>
Chris Lattnerd0713f92002-09-12 17:06:43 +0000[diff] [blame]842 <b>virtual bool</b> doInitialization(Function &amp;F);
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]843</pre></div>
Chris Lattnerd0713f92002-09-12 17:06:43 +0000[diff] [blame]844
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]845<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]846<tt>BasicBlockPass</tt>'s are not allowed to do, but that
847<tt>FunctionPass</tt>'s can. The <tt>doInitialization</tt> method is designed
Reid Spencer1bc19342004-12-11 05:12:57 +0000[diff] [blame]848to do simple initialization that does not depend on the
Chris Lattnerd0713f92002-09-12 17:06:43 +0000[diff] [blame]849BasicBlocks being processed. The <tt>doInitialization</tt> method call is not
850scheduled to overlap with any other pass executions (thus it should be very
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]851fast).</p>
Chris Lattnerd0713f92002-09-12 17:06:43 +0000[diff] [blame]852
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]853</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]854
855<!-- _______________________________________________________________________ -->
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]856<div class="doc_subsubsection">
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]857 <a name="runOnBasicBlock">The <tt>runOnBasicBlock</tt> method</a>
858</div>
859
860<div class="doc_text">
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]861
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]862<div class="doc_code"><pre>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]863 <b>virtual bool</b> runOnBasicBlock(BasicBlock &amp;BB) = 0;
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]864</pre></div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]865
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]866<p>Override this function to do the work of the <tt>BasicBlockPass</tt>. This
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]867function is not allowed to inspect or modify basic blocks other than the
868parameter, and are not allowed to modify the CFG. A true value must be returned
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]869if the basic block is modified.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]870
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]871</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]872
Chris Lattnerd0713f92002-09-12 17:06:43 +0000[diff] [blame]873<!-- _______________________________________________________________________ -->
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]874<div class="doc_subsubsection">
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]875 <a name="doFinalization_fn">The <tt>doFinalization(Function &amp;)</tt>
876 method</a>
877</div>
878
879<div class="doc_text">
Chris Lattnerd0713f92002-09-12 17:06:43 +0000[diff] [blame]880
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]881<div class="doc_code"><pre>
Chris Lattnerd0713f92002-09-12 17:06:43 +0000[diff] [blame]882 <b>virtual bool</b> doFinalization(Function &amp;F);
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]883</pre></div>
Chris Lattnerd0713f92002-09-12 17:06:43 +0000[diff] [blame]884
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]885<p>The <tt>doFinalization</tt> method is an infrequently used method that is
886called when the pass framework has finished calling <a
Chris Lattnerd0713f92002-09-12 17:06:43 +0000[diff] [blame]887href="#runOnBasicBlock"><tt>runOnBasicBlock</tt></a> for every BasicBlock in the
888program being compiled. This can be used to perform per-function
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]889finalization.</p>
Chris Lattnerd0713f92002-09-12 17:06:43 +0000[diff] [blame]890
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]891</div>
Chris Lattnerd0713f92002-09-12 17:06:43 +0000[diff] [blame]892
Brian Gaekecab8b6f2003-07-17 18:53:20 +0000[diff] [blame]893<!-- ======================================================================= -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]894<div class="doc_subsection">
895 <a name="MachineFunctionPass">The <tt>MachineFunctionPass</tt> class</a>
896</div>
Brian Gaekecab8b6f2003-07-17 18:53:20 +0000[diff] [blame]897
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]898<div class="doc_text">
899
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]900<p>A <tt>MachineFunctionPass</tt> is a part of the LLVM code generator that
901executes on the machine-dependent representation of each LLVM function in the
902program. A <tt>MachineFunctionPass</tt> is also a <tt>FunctionPass</tt>, so all
Brian Gaekecab8b6f2003-07-17 18:53:20 +0000[diff] [blame]903the restrictions that apply to a <tt>FunctionPass</tt> also apply to it.
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]904<tt>MachineFunctionPass</tt>es also have additional restrictions. In particular,
905<tt>MachineFunctionPass</tt>es are not allowed to do any of the following:</p>
Brian Gaekecab8b6f2003-07-17 18:53:20 +0000[diff] [blame]906
907<ol>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]908<li>Modify any LLVM Instructions, BasicBlocks or Functions.</li>
909<li>Modify a MachineFunction other than the one currently being processed.</li>
910<li>Add or remove MachineFunctions from the current Module.</li>
911<li>Add or remove global variables from the current Module.</li>
912<li>Maintain state across invocations of <a
913href="#runOnMachineFunction"><tt>runOnMachineFunction</tt></a> (including global
914data)</li>
915</ol>
Brian Gaekecab8b6f2003-07-17 18:53:20 +0000[diff] [blame]916
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]917</div>
Chris Lattnerd0713f92002-09-12 17:06:43 +0000[diff] [blame]918
Brian Gaeke6a33f362003-07-22 20:53:20 +0000[diff] [blame]919<!-- _______________________________________________________________________ -->
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]920<div class="doc_subsubsection">
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]921 <a name="runOnMachineFunction">The <tt>runOnMachineFunction(MachineFunction
922 &amp;MF)</tt> method</a>
923</div>
924
925<div class="doc_text">
Brian Gaeke6a33f362003-07-22 20:53:20 +0000[diff] [blame]926
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]927<div class="doc_code"><pre>
Brian Gaeke6a33f362003-07-22 20:53:20 +0000[diff] [blame]928 <b>virtual bool</b> runOnMachineFunction(MachineFunction &amp;MF) = 0;
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]929</pre></div>
Brian Gaeke6a33f362003-07-22 20:53:20 +0000[diff] [blame]930
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]931<p><tt>runOnMachineFunction</tt> can be considered the main entry point of a
932<tt>MachineFunctionPass</tt>; that is, you should override this method to do the
933work of your <tt>MachineFunctionPass</tt>.</p>
Brian Gaeke6a33f362003-07-22 20:53:20 +0000[diff] [blame]934
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]935<p>The <tt>runOnMachineFunction</tt> method is called on every
Brian Gaeke6a33f362003-07-22 20:53:20 +0000[diff] [blame]936<tt>MachineFunction</tt> in a <tt>Module</tt>, so that the
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]937<tt>MachineFunctionPass</tt> may perform optimizations on the machine-dependent
938representation of the function. If you want to get at the LLVM <tt>Function</tt>
939for the <tt>MachineFunction</tt> you're working on, use
940<tt>MachineFunction</tt>'s <tt>getFunction()</tt> accessor method -- but
941remember, you may not modify the LLVM <tt>Function</tt> or its contents from a
942<tt>MachineFunctionPass</tt>.</p>
943
944</div>
Brian Gaeke6a33f362003-07-22 20:53:20 +0000[diff] [blame]945
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]946<!-- *********************************************************************** -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]947<div class="doc_section">
948 <a name="registration">Pass registration</a>
949</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]950<!-- *********************************************************************** -->
951
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]952<div class="doc_text">
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]953
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]954<p>In the <a href="#basiccode">Hello World</a> example pass we illustrated how
955pass registration works, and discussed some of the reasons that it is used and
956what it does. Here we discuss how and why passes are registered.</p>
957
Chris Lattnerc8603c22006-08-27 23:18:52 +0000[diff] [blame]958<p>As we saw above, passes are registered with the <b><tt>RegisterPass</tt></b>
959template, which requires you to pass at least two
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]960parameters. The first parameter is the name of the pass that is to be used on
961the command line to specify that the pass should be added to a program (for
Chris Lattnerc8603c22006-08-27 23:18:52 +0000[diff] [blame]962example, with <tt>opt</tt> or <tt>bugpoint</tt>). The second argument is the
963name of the pass, which is to be used for the <tt>--help</tt> output of
964programs, as
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]965well as for debug output generated by the <tt>--debug-pass</tt> option.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]966
Chris Lattnerc8603c22006-08-27 23:18:52 +0000[diff] [blame]967<p>If you want your pass to be easily dumpable, you should
968implement the virtual <tt>print</tt> method:</p>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]969
970</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]971
972<!-- _______________________________________________________________________ -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]973<div class="doc_subsubsection">
974 <a name="print">The <tt>print</tt> method</a>
975</div>
976
977<div class="doc_text">
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]978
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]979<div class="doc_code"><pre>
Torok Edwin52790e52008-10-28 17:29:23 +0000[diff] [blame^]980 <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]981</pre></div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]982
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]983<p>The <tt>print</tt> method must be implemented by "analyses" in order to print
984a human readable version of the analysis results. This is useful for debugging
985an analysis itself, as well as for other people to figure out how an analysis
Chris Lattnerc8603c22006-08-27 23:18:52 +0000[diff] [blame]986works. Use the <tt>opt -analyze</tt> argument to invoke this method.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]987
Bill Wendling832171c2006-12-07 20:04:42 +0000[diff] [blame]988<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]989and 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]990program that has been analyzed. Note however that this pointer may be null in
991certain circumstances (such as calling the <tt>Pass::dump()</tt> from a
992debugger), so it should only be used to enhance debug output, it should not be
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]993depended on.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]994
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]995</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]996
997<!-- *********************************************************************** -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]998<div class="doc_section">
999 <a name="interaction">Specifying interactions between passes</a>
1000</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1001<!-- *********************************************************************** -->
1002
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1003<div class="doc_text">
1004
John Criswell8528e782007-12-03 19:34:25 +0000[diff] [blame]1005<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]1006that passes interact with each other correctly. Because <tt>PassManager</tt>
1007tries to <a href="#passmanager">optimize the execution of passes</a> it must
1008know how the passes interact with each other and what dependencies exist between
1009the various passes. To track this, each pass can declare the set of passes that
1010are required to be executed before the current pass, and the passes which are
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1011invalidated by the current pass.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1012
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1013<p>Typically this functionality is used to require that analysis results are
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1014computed before your pass is run. Running arbitrary transformation passes can
1015invalidate the computed analysis results, which is what the invalidation set
1016specifies. If a pass does not implement the <tt><a
1017href="#getAnalysisUsage">getAnalysisUsage</a></tt> method, it defaults to not
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1018having any prerequisite passes, and invalidating <b>all</b> other passes.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1019
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1020</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1021
1022<!-- _______________________________________________________________________ -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1023<div class="doc_subsubsection">
1024 <a name="getAnalysisUsage">The <tt>getAnalysisUsage</tt> method</a>
1025</div>
1026
1027<div class="doc_text">
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1028
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1029<div class="doc_code"><pre>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1030 <b>virtual void</b> getAnalysisUsage(AnalysisUsage &amp;Info) <b>const</b>;
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1031</pre></div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1032
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1033<p>By implementing the <tt>getAnalysisUsage</tt> method, the required and
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1034invalidated sets may be specified for your transformation. The implementation
1035should fill in the <tt><a
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]1036href="http://llvm.org/doxygen/classllvm_1_1AnalysisUsage.html">AnalysisUsage</a></tt>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1037object with information about which passes are required and not invalidated. To
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]1038do this, a pass may call any of the following methods on the AnalysisUsage
1039object:</p>
1040</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1041
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]1042<!-- _______________________________________________________________________ -->
1043<div class="doc_subsubsection">
1044 <a name="AU::addRequired">The <tt>AnalysisUsage::addRequired&lt;&gt;</tt> and <tt>AnalysisUsage::addRequiredTransitive&lt;&gt;</tt> methods</a>
1045</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1046
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]1047<div class="doc_text">
1048<p>
Reid Spencer1bc19342004-12-11 05:12:57 +0000[diff] [blame]1049If your pass requires a previous pass to be executed (an analysis for example),
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]1050it can use one of these methods to arrange for it to be run before your pass.
1051LLVM has many different types of analyses and passes that can be required,
Reid Spencer1bc19342004-12-11 05:12:57 +0000[diff] [blame]1052spanning the range from <tt>DominatorSet</tt> to <tt>BreakCriticalEdges</tt>.
1053Requiring <tt>BreakCriticalEdges</tt>, for example, guarantees that there will
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]1054be no critical edges in the CFG when your pass has been run.
1055</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1056
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]1057<p>
1058Some analyses chain to other analyses to do their job. For example, an <a
1059href="AliasAnalysis.html">AliasAnalysis</a> implementation is required to <a
1060href="AliasAnalysis.html#chaining">chain</a> to other alias analysis passes. In
1061cases where analyses chain, the <tt>addRequiredTransitive</tt> method should be
1062used instead of the <tt>addRequired</tt> method. This informs the PassManager
1063that the transitively required pass should be alive as long as the requiring
1064pass is.
1065</p>
1066</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1067
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]1068<!-- _______________________________________________________________________ -->
1069<div class="doc_subsubsection">
1070 <a name="AU::addPreserved">The <tt>AnalysisUsage::addPreserved&lt;&gt;</tt> method</a>
1071</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1072
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]1073<div class="doc_text">
1074<p>
1075One of the jobs of the PassManager is to optimize how and when analyses are run.
1076In particular, it attempts to avoid recomputing data unless it needs to. For
1077this reason, passes are allowed to declare that they preserve (i.e., they don't
1078invalidate) an existing analysis if it's available. For example, a simple
Reid Spencer1bc19342004-12-11 05:12:57 +0000[diff] [blame]1079constant folding pass would not modify the CFG, so it can't possibly affect the
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]1080results of dominator analysis. By default, all passes are assumed to invalidate
1081all others.
1082</p>
1083
1084<p>
1085The <tt>AnalysisUsage</tt> class provides several methods which are useful in
1086certain circumstances that are related to <tt>addPreserved</tt>. In particular,
1087the <tt>setPreservesAll</tt> method can be called to indicate that the pass does
1088not modify the LLVM program at all (which is true for analyses), and the
1089<tt>setPreservesCFG</tt> method can be used by transformations that change
1090instructions in the program but do not modify the CFG or terminator instructions
1091(note that this property is implicitly set for <a
1092href="#BasicBlockPass">BasicBlockPass</a>'s).
1093</p>
1094
1095<p>
1096<tt>addPreserved</tt> is particularly useful for transformations like
1097<tt>BreakCriticalEdges</tt>. This pass knows how to update a small set of loop
1098and dominator related analyses if they exist, so it can preserve them, despite
1099the fact that it hacks on the CFG.
1100</p>
1101</div>
1102
1103<!-- _______________________________________________________________________ -->
1104<div class="doc_subsubsection">
1105 <a name="AU::examples">Example implementations of <tt>getAnalysisUsage</tt></a>
1106</div>
1107
1108<div class="doc_text">
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1109
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1110<div class="doc_code"><pre>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1111 <i>// This is an example implementation from an analysis, which does not modify
1112 // the program at all, yet has a prerequisite.</i>
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]1113 <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]1114 AU.setPreservesAll();
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]1115 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]1116 }
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1117</pre></div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1118
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1119<p>and:</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1120
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1121<div class="doc_code"><pre>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1122 <i>// This example modifies the program, but does not modify the CFG</i>
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]1123 <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]1124 AU.setPreservesCFG();
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]1125 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]1126 }
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1127</pre></div>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1128
1129</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1130
1131<!-- _______________________________________________________________________ -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1132<div class="doc_subsubsection">
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]1133 <a name="getAnalysis">The <tt>getAnalysis&lt;&gt;</tt> and <tt>getAnalysisToUpdate&lt;&gt;</tt> methods</a>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1134</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1135
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1136<div class="doc_text">
1137
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]1138<p>The <tt>Pass::getAnalysis&lt;&gt;</tt> method is automatically inherited by
1139your class, providing you with access to the passes that you declared that you
1140required with the <a href="#getAnalysisUsage"><tt>getAnalysisUsage</tt></a>
1141method. It takes a single template argument that specifies which pass class you
1142want, and returns a reference to that pass. For example:</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1143
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1144<div class="doc_code"><pre>
Chris Lattnera5776302004-03-17 21:33:32 +0000[diff] [blame]1145 bool LICM::runOnFunction(Function &amp;F) {
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]1146 LoopInfo &amp;LI = getAnalysis&lt;LoopInfo&gt;();
1147 ...
1148 }
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1149</pre></div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1150
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1151<p>This method call returns a reference to the pass desired. You may get a
1152runtime assertion failure if you attempt to get an analysis that you did not
1153declare as required in your <a
1154href="#getAnalysisUsage"><tt>getAnalysisUsage</tt></a> implementation. This
1155method can be called by your <tt>run*</tt> method implementation, or by any
Devang Patel3c1ca0b2007-04-16 21:28:14 +0000[diff] [blame]1156other local method invoked by your <tt>run*</tt> method.
1157
1158A module level pass can use function level analysis info using this interface.
1159For example:</p>
1160
1161<div class="doc_code"><pre>
1162 bool ModuleLevelPass::runOnModule(Module &amp;M) {
1163 ...
Devang Patelf23de112007-04-17 00:17:11 +0000[diff] [blame]1164 DominatorTree &amp;DT = getAnalysis&lt;DominatorTree&gt;(Func);
Devang Patel3c1ca0b2007-04-16 21:28:14 +0000[diff] [blame]1165 ...
1166 }
1167</pre></div>
1168
Chris Lattnerb5c87f62007-05-18 05:36:14 +0000[diff] [blame]1169<p>In above example, runOnFunction for DominatorTree is called by pass manager
Devang Patel3c1ca0b2007-04-16 21:28:14 +0000[diff] [blame]1170before returning a reference to the desired pass.</p>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1171
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]1172<p>
1173If your pass is capable of updating analyses if they exist (e.g.,
1174<tt>BreakCriticalEdges</tt>, as described above), you can use the
1175<tt>getAnalysisToUpdate</tt> method, which returns a pointer to the analysis if
1176it is active. For example:</p>
1177
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1178<div class="doc_code"><pre>
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]1179 ...
1180 if (DominatorSet *DS = getAnalysisToUpdate&lt;DominatorSet&gt;()) {
1181 <i>// A DominatorSet is active. This code will update it.</i>
1182 }
1183 ...
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1184</pre></div>
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]1185
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1186</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1187
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1188<!-- *********************************************************************** -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1189<div class="doc_section">
1190 <a name="analysisgroup">Implementing Analysis Groups</a>
1191</div>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1192<!-- *********************************************************************** -->
1193
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1194<div class="doc_text">
1195
Chris Lattnerb7632282007-11-16 05:32:05 +0000[diff] [blame]1196<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]1197used, 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]1198fancier. All of the pass relationships that we have seen so far are very
1199simple: one pass depends on one other specific pass to be run before it can run.
1200For many applications, this is great, for others, more flexibility is
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1201required.</p>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1202
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1203<p>In particular, some analyses are defined such that there is a single simple
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1204interface to the analysis results, but multiple ways of calculating them.
1205Consider alias analysis for example. The most trivial alias analysis returns
1206"may alias" for any alias query. The most sophisticated analysis a
1207flow-sensitive, context-sensitive interprocedural analysis that can take a
1208significant amount of time to execute (and obviously, there is a lot of room
1209between these two extremes for other implementations). To cleanly support
1210situations like this, the LLVM Pass Infrastructure supports the notion of
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1211Analysis Groups.</p>
1212
1213</div>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1214
1215<!-- _______________________________________________________________________ -->
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]1216<div class="doc_subsubsection">
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1217 <a name="agconcepts">Analysis Group Concepts</a>
1218</div>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1219
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1220<div class="doc_text">
1221
1222<p>An Analysis Group is a single simple interface that may be implemented by
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1223multiple different passes. Analysis Groups can be given human readable names
1224just like passes, but unlike passes, they need not derive from the <tt>Pass</tt>
1225class. An analysis group may have one or more implementations, one of which is
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1226the "default" implementation.</p>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1227
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1228<p>Analysis groups are used by client passes just like other passes are: the
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1229<tt>AnalysisUsage::addRequired()</tt> and <tt>Pass::getAnalysis()</tt> methods.
1230In order to resolve this requirement, the <a href="#passmanager">PassManager</a>
1231scans the available passes to see if any implementations of the analysis group
1232are available. If none is available, the default implementation is created for
1233the pass to use. All standard rules for <A href="#interaction">interaction
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1234between passes</a> still apply.</p>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1235
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1236<p>Although <a href="#registration">Pass Registration</a> is optional for normal
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1237passes, all analysis group implementations must be registered, and must use the
1238<A href="#registerag"><tt>RegisterAnalysisGroup</tt></a> template to join the
1239implementation pool. Also, a default implementation of the interface
1240<b>must</b> be registered with <A
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1241href="#registerag"><tt>RegisterAnalysisGroup</tt></a>.</p>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1242
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1243<p>As a concrete example of an Analysis Group in action, consider the <a
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]1244href="http://llvm.org/doxygen/classllvm_1_1AliasAnalysis.html">AliasAnalysis</a>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1245analysis group. The default implementation of the alias analysis interface (the
1246<tt><a
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]1247href="http://llvm.org/doxygen/structBasicAliasAnalysis.html">basicaa</a></tt>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1248pass) just does a few simple checks that don't require significant analysis to
1249compute (such as: two different globals can never alias each other, etc).
1250Passes that use the <tt><a
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]1251href="http://llvm.org/doxygen/classllvm_1_1AliasAnalysis.html">AliasAnalysis</a></tt>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1252interface (for example the <tt><a
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]1253href="http://llvm.org/doxygen/structGCSE.html">gcse</a></tt> pass), do
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1254not care which implementation of alias analysis is actually provided, they just
1255use the designated interface.</p>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1256
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1257<p>From the user's perspective, commands work just like normal. Issuing the
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1258command '<tt>opt -gcse ...</tt>' will cause the <tt>basicaa</tt> class to be
1259instantiated and added to the pass sequence. Issuing the command '<tt>opt
1260-somefancyaa -gcse ...</tt>' will cause the <tt>gcse</tt> pass to use the
1261<tt>somefancyaa</tt> alias analysis (which doesn't actually exist, it's just a
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1262hypothetical example) instead.</p>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1263
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1264</div>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1265
1266<!-- _______________________________________________________________________ -->
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]1267<div class="doc_subsubsection">
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1268 <a name="registerag">Using <tt>RegisterAnalysisGroup</tt></a>
1269</div>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1270
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1271<div class="doc_text">
1272
1273<p>The <tt>RegisterAnalysisGroup</tt> template is used to register the analysis
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1274group itself as well as add pass implementations to the analysis group. First,
1275an analysis should be registered, with a human readable name provided for it.
1276Unlike registration of passes, there is no command line argument to be specified
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1277for the Analysis Group Interface itself, because it is "abstract":</p>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1278
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1279<div class="doc_code"><pre>
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]1280 <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]1281</pre></div>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1282
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1283<p>Once the analysis is registered, passes can declare that they are valid
1284implementations of the interface by using the following code:</p>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1285
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1286<div class="doc_code"><pre>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1287<b>namespace</b> {
1288 //<i> Analysis Group implementations <b>must</b> be registered normally...</i>
Chris Lattnerc8603c22006-08-27 23:18:52 +0000[diff] [blame]1289 RegisterPass&lt;FancyAA&gt;
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1290 B("<i>somefancyaa</i>", "<i>A more complex alias analysis implementation</i>");
1291
1292 //<i> Declare that we implement the AliasAnalysis interface</i>
Chris Lattnerdc877252006-08-28 00:45:38 +0000[diff] [blame]1293 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]1294}
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1295</pre></div>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1296
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1297<p>This just shows a class <tt>FancyAA</tt> that is registered normally, then
1298uses the <tt>RegisterAnalysisGroup</tt> template to "join" the <tt><a
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]1299href="http://llvm.org/doxygen/classllvm_1_1AliasAnalysis.html">AliasAnalysis</a></tt>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1300analysis group. Every implementation of an analysis group should join using
1301this template. A single pass may join multiple different analysis groups with
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1302no problem.</p>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1303
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1304<div class="doc_code"><pre>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1305<b>namespace</b> {
1306 //<i> Analysis Group implementations <b>must</b> be registered normally...</i>
Chris Lattnerc8603c22006-08-27 23:18:52 +0000[diff] [blame]1307 RegisterPass&lt;<a href="http://llvm.org/doxygen/structBasicAliasAnalysis.html">BasicAliasAnalysis</a>&gt;
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1308 D("<i>basicaa</i>", "<i>Basic Alias Analysis (default AA impl)</i>");
1309
1310 //<i> Declare that we implement the AliasAnalysis interface</i>
Chris Lattnerdc877252006-08-28 00:45:38 +0000[diff] [blame]1311 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]1312}
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1313</pre></div>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1314
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1315<p>Here we show how the default implementation is specified (using the extra
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1316argument to the <tt>RegisterAnalysisGroup</tt> template). There must be exactly
1317one default implementation available at all times for an Analysis Group to be
Devang Patel2397f8d2007-06-20 18:51:14 +0000[diff] [blame]1318used. Only default implementation can derive from <tt>ImmutablePass</tt>.
1319Here we declare that the
1320 <tt><a href="http://llvm.org/doxygen/structBasicAliasAnalysis.html">BasicAliasAnalysis</a></tt>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1321pass is the default implementation for the interface.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1322
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1323</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1324
1325<!-- *********************************************************************** -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1326<div class="doc_section">
Tanya Lattnerd5383652004-11-19 01:25:14 +0000[diff] [blame]1327 <a name="passStatistics">Pass Statistics</a>
1328</div>
1329<!-- *********************************************************************** -->
1330
1331<div class="doc_text">
Tanya Lattner05f8d5f2004-11-19 01:26:37 +0000[diff] [blame]1332<p>The <a
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]1333href="http://llvm.org/doxygen/Statistic_8h-source.html"><tt>Statistic</tt></a>
John Criswell0b1010e2005-11-28 23:25:41 +0000[diff] [blame]1334class is designed to be an easy way to expose various success
Tanya Lattnerd5383652004-11-19 01:25:14 +0000[diff] [blame]1335metrics from passes. These statistics are printed at the end of a
1336run, when the -stats command line option is enabled on the command
Tanya Lattner05f8d5f2004-11-19 01:26:37 +0000[diff] [blame]1337line. 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]1338
1339</div>
1340
1341
1342<!-- *********************************************************************** -->
1343<div class="doc_section">
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1344 <a name="passmanager">What PassManager does</a>
1345</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1346<!-- *********************************************************************** -->
1347
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1348<div class="doc_text">
1349
1350<p>The <a
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]1351href="http://llvm.org/doxygen/PassManager_8h-source.html"><tt>PassManager</tt></a>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1352<a
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]1353href="http://llvm.org/doxygen/classllvm_1_1PassManager.html">class</a>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1354takes a list of passes, ensures their <a href="#interaction">prerequisites</a>
1355are set up correctly, and then schedules passes to run efficiently. All of the
1356LLVM tools that run passes use the <tt>PassManager</tt> for execution of these
1357passes.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1358
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1359<p>The <tt>PassManager</tt> does two main things to try to reduce the execution
1360time of a series of passes:</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1361
1362<ol>
1363<li><b>Share analysis results</b> - The PassManager attempts to avoid
1364recomputing analysis results as much as possible. This means keeping track of
1365which analyses are available already, which analyses get invalidated, and which
1366analyses are needed to be run for a pass. An important part of work is that the
1367<tt>PassManager</tt> tracks the exact lifetime of all analysis results, allowing
1368it to <a href="#releaseMemory">free memory</a> allocated to holding analysis
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1369results as soon as they are no longer needed.</li>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1370
1371<li><b>Pipeline the execution of passes on the program</b> - The
1372<tt>PassManager</tt> attempts to get better cache and memory usage behavior out
1373of a series of passes by pipelining the passes together. This means that, given
1374a series of consequtive <a href="#FunctionPass"><tt>FunctionPass</tt></a>'s, it
1375will execute all of the <a href="#FunctionPass"><tt>FunctionPass</tt></a>'s on
1376the first function, then all of the <a
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1377href="#FunctionPass"><tt>FunctionPass</tt></a>es on the second function,
1378etc... until the entire program has been run through the passes.
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1379
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1380<p>This improves the cache behavior of the compiler, because it is only touching
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1381the LLVM program representation for a single function at a time, instead of
1382traversing the entire program. It reduces the memory consumption of compiler,
1383because, for example, only one <a
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]1384href="http://llvm.org/doxygen/classllvm_1_1DominatorSet.html"><tt>DominatorSet</tt></a>
John Criswell9795bb82007-12-10 20:26:29 +0000[diff] [blame]1385needs to be calculated at a time. This also makes it possible to implement
1386some <a
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1387href="#SMP">interesting enhancements</a> in the future.</p></li>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1388
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1389</ol>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1390
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1391<p>The effectiveness of the <tt>PassManager</tt> is influenced directly by how
1392much information it has about the behaviors of the passes it is scheduling. For
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1393example, the "preserved" set is intentionally conservative in the face of an
1394unimplemented <a href="#getAnalysisUsage"><tt>getAnalysisUsage</tt></a> method.
1395Not implementing when it should be implemented will have the effect of not
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1396allowing any analysis results to live across the execution of your pass.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1397
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1398<p>The <tt>PassManager</tt> class exposes a <tt>--debug-pass</tt> command line
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1399options that is useful for debugging pass execution, seeing how things work, and
1400diagnosing when you should be preserving more analyses than you currently are
1401(To get information about all of the variants of the <tt>--debug-pass</tt>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1402option, just type '<tt>opt --help-hidden</tt>').</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1403
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1404<p>By using the <tt>--debug-pass=Structure</tt> option, for example, we can see
1405how our <a href="#basiccode">Hello World</a> pass interacts with other passes.
1406Lets try it out with the <tt>gcse</tt> and <tt>licm</tt> passes:</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1407
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1408<div class="doc_code"><pre>
Reid Spencer7fa6d522005-01-11 05:16:23 +0000[diff] [blame]1409$ 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]1410Module Pass Manager
1411 Function Pass Manager
1412 Dominator Set Construction
1413 Immediate Dominators Construction
1414 Global Common Subexpression Elimination
1415-- Immediate Dominators Construction
1416-- Global Common Subexpression Elimination
1417 Natural Loop Construction
1418 Loop Invariant Code Motion
1419-- Natural Loop Construction
1420-- Loop Invariant Code Motion
1421 Module Verifier
1422-- Dominator Set Construction
1423-- Module Verifier
Gabor Greif04367bf2007-07-06 22:07:22 +0000[diff] [blame]1424 Bitcode Writer
1425--Bitcode Writer
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1426</pre></div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1427
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1428<p>This output shows us when passes are constructed and when the analysis
1429results are known to be dead (prefixed with '<tt>--</tt>'). Here we see that
1430GCSE uses dominator and immediate dominator information to do its job. The LICM
1431pass uses natural loop information, which uses dominator sets, but not immediate
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1432dominators. Because immediate dominators are no longer useful after the GCSE
1433pass, it is immediately destroyed. The dominator sets are then reused to
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1434compute natural loop information, which is then used by the LICM pass.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1435
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1436<p>After the LICM pass, the module verifier runs (which is automatically added
1437by the '<tt>opt</tt>' tool), which uses the dominator set to check that the
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1438resultant LLVM code is well formed. After it finishes, the dominator set
1439information is destroyed, after being computed once, and shared by three
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1440passes.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1441
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1442<p>Lets see how this changes when we run the <a href="#basiccode">Hello
1443World</a> pass in between the two passes:</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1444
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1445<div class="doc_code"><pre>
Reid Spencer7fa6d522005-01-11 05:16:23 +0000[diff] [blame]1446$ 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]1447Module Pass Manager
1448 Function Pass Manager
1449 Dominator Set Construction
1450 Immediate Dominators Construction
1451 Global Common Subexpression Elimination
1452<b>-- Dominator Set Construction</b>
1453-- Immediate Dominators Construction
1454-- Global Common Subexpression Elimination
1455<b> Hello World Pass
1456-- Hello World Pass
1457 Dominator Set Construction</b>
1458 Natural Loop Construction
1459 Loop Invariant Code Motion
1460-- Natural Loop Construction
1461-- Loop Invariant Code Motion
1462 Module Verifier
1463-- Dominator Set Construction
1464-- Module Verifier
Gabor Greif04367bf2007-07-06 22:07:22 +0000[diff] [blame]1465 Bitcode Writer
1466--Bitcode Writer
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1467Hello: __main
1468Hello: puts
1469Hello: main
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1470</pre></div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1471
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1472<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]1473Dominator Set pass, even though it doesn't modify the code at all! To fix this,
1474we need to add the following <a
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1475href="#getAnalysisUsage"><tt>getAnalysisUsage</tt></a> method to our pass:</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1476
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1477<div class="doc_code"><pre>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1478 <i>// We don't modify the program, so we preserve all analyses</i>
1479 <b>virtual void</b> getAnalysisUsage(AnalysisUsage &amp;AU) <b>const</b> {
1480 AU.setPreservesAll();
1481 }
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1482</pre></div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1483
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1484<p>Now when we run our pass, we get this output:</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1485
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1486<div class="doc_code"><pre>
Reid Spencer7fa6d522005-01-11 05:16:23 +0000[diff] [blame]1487$ 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]1488Pass Arguments: -gcse -hello -licm
1489Module Pass Manager
1490 Function Pass Manager
1491 Dominator Set Construction
1492 Immediate Dominators Construction
1493 Global Common Subexpression Elimination
1494-- Immediate Dominators Construction
1495-- Global Common Subexpression Elimination
1496 Hello World Pass
1497-- Hello World Pass
1498 Natural Loop Construction
1499 Loop Invariant Code Motion
1500-- Loop Invariant Code Motion
1501-- Natural Loop Construction
1502 Module Verifier
1503-- Dominator Set Construction
1504-- Module Verifier
Gabor Greif04367bf2007-07-06 22:07:22 +0000[diff] [blame]1505 Bitcode Writer
1506--Bitcode Writer
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1507Hello: __main
1508Hello: puts
1509Hello: main
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1510</pre></div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1511
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1512<p>Which shows that we don't accidentally invalidate dominator information
1513anymore, and therefore do not have to compute it twice.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1514
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1515</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1516
1517<!-- _______________________________________________________________________ -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1518<div class="doc_subsubsection">
1519 <a name="releaseMemory">The <tt>releaseMemory</tt> method</a>
1520</div>
1521
1522<div class="doc_text">
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1523
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1524<div class="doc_code"><pre>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1525 <b>virtual void</b> releaseMemory();
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1526</pre></div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1527
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1528<p>The <tt>PassManager</tt> automatically determines when to compute analysis
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1529results, and how long to keep them around for. Because the lifetime of the pass
1530object itself is effectively the entire duration of the compilation process, we
1531need some way to free analysis results when they are no longer useful. The
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1532<tt>releaseMemory</tt> virtual method is the way to do this.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1533
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1534<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]1535amount of state (for use by another pass which "requires" your pass and uses the
1536<a href="#getAnalysis">getAnalysis</a> method) you should implement
1537<tt>releaseMEmory</tt> to, well, release the memory allocated to maintain this
1538internal state. This method is called after the <tt>run*</tt> method for the
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1539class, before the next call of <tt>run*</tt> in your pass.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1540
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1541</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1542
1543<!-- *********************************************************************** -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1544<div class="doc_section">
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1545 <a name="registering">Registering dynamically loaded passes</a>
1546</div>
1547<!-- *********************************************************************** -->
1548
1549<div class="doc_text">
1550
1551<p><i>Size matters</i> when constructing production quality tools using llvm,
1552both for the purposes of distribution, and for regulating the resident code size
1553when running on the target system. Therefore, it becomes desirable to
1554selectively use some passes, while omitting others and maintain the flexibility
1555to change configurations later on. You want to be able to do all this, and,
1556provide feedback to the user. This is where pass registration comes into
1557play.</p>
1558
1559<p>The fundamental mechanisms for pass registration are the
1560<tt>MachinePassRegistry</tt> class and subclasses of
1561<tt>MachinePassRegistryNode</tt>.</p>
1562
1563<p>An instance of <tt>MachinePassRegistry</tt> is used to maintain a list of
1564<tt>MachinePassRegistryNode</tt> objects. This instance maintains the list and
1565communicates additions and deletions to the command line interface.</p>
1566
1567<p>An instance of <tt>MachinePassRegistryNode</tt> subclass is used to maintain
1568information provided about a particular pass. This information includes the
1569command line name, the command help string and the address of the function used
1570to create an instance of the pass. A global static constructor of one of these
1571instances <i>registers</i> with a corresponding <tt>MachinePassRegistry</tt>,
1572the static destructor <i>unregisters</i>. Thus a pass that is statically linked
1573in the tool will be registered at start up. A dynamically loaded pass will
1574register on load and unregister at unload.</p>
1575
1576</div>
1577
1578<!-- _______________________________________________________________________ -->
1579<div class="doc_subsection">
1580 <a name="registering_existing">Using existing registries</a>
1581</div>
1582
1583<div class="doc_text">
1584
1585<p>There are predefined registries to track instruction scheduling
1586(<tt>RegisterScheduler</tt>) and register allocation (<tt>RegisterRegAlloc</tt>)
1587machine passes. Here we will describe how to <i>register</i> a register
1588allocator machine pass.</p>
1589
1590<p>Implement your register allocator machine pass. In your register allocator
1591.cpp file add the following include;</p>
1592
1593<div class="doc_code"><pre>
Chris Lattner8f652eb2006-08-11 16:37:02 +0000[diff] [blame]1594 #include "llvm/CodeGen/RegAllocRegistry.h"
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1595</pre></div>
1596
1597<p>Also in your register allocator .cpp file, define a creator function in the
1598form; </p>
1599
1600<div class="doc_code"><pre>
1601 FunctionPass *createMyRegisterAllocator() {
1602 return new MyRegisterAllocator();
1603 }
1604</pre></div>
1605
1606<p>Note that the signature of this function should match the type of
1607<tt>RegisterRegAlloc::FunctionPassCtor</tt>. In the same file add the
1608"installing" declaration, in the form;</p>
1609
1610<div class="doc_code"><pre>
1611 static RegisterRegAlloc myRegAlloc("myregalloc",
1612 " my register allocator help string",
1613 createMyRegisterAllocator);
1614</pre></div>
1615
1616<p>Note the two spaces prior to the help string produces a tidy result on the
1617--help query.</p>
1618
1619<div class="doc_code"><pre>
1620$ llc --help
1621 ...
1622 -regalloc - Register allocator to use: (default = linearscan)
1623 =linearscan - linear scan register allocator
1624 =local - local register allocator
1625 =simple - simple register allocator
1626 =myregalloc - my register allocator help string
1627 ...
1628</pre></div>
1629
1630<p>And that's it. The user is now free to use <tt>-regalloc=myregalloc</tt> as
1631an option. Registering instruction schedulers is similar except use the
Chris Lattner8f652eb2006-08-11 16:37:02 +0000[diff] [blame]1632<tt>RegisterScheduler</tt> class. Note that the
1633<tt>RegisterScheduler::FunctionPassCtor</tt> is significantly different from
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1634<tt>RegisterRegAlloc::FunctionPassCtor</tt>.</p>
1635
1636<p>To force the load/linking of your register allocator into the llc/lli tools,
1637add your creator function's global declaration to "Passes.h" and add a "pseudo"
1638call line to <tt>llvm/Codegen/LinkAllCodegenComponents.h</tt>.</p>
1639
1640</div>
1641
1642
1643<!-- _______________________________________________________________________ -->
1644<div class="doc_subsection">
1645 <a name="registering_new">Creating new registries</a>
1646</div>
1647
1648<div class="doc_text">
1649
1650<p>The easiest way to get started is to clone one of the existing registries; we
1651recommend <tt>llvm/CodeGen/RegAllocRegistry.h</tt>. The key things to modify
1652are the class name and the <tt>FunctionPassCtor</tt> type.</p>
1653
1654<p>Then you need to declare the registry. Example: if your pass registry is
1655<tt>RegisterMyPasses</tt> then define;</p>
1656
1657<div class="doc_code"><pre>
1658MachinePassRegistry RegisterMyPasses::Registry;
1659</pre></div>
1660
1661<p>And finally, declare the command line option for your passes. Example:</p>
1662
1663<div class="doc_code"><pre>
1664 cl::opt&lt;RegisterMyPasses::FunctionPassCtor, false,
Dan Gohman364a39f2008-10-14 17:00:38 +0000[diff] [blame]1665 RegisterPassParser&lt;RegisterMyPasses&gt; &gt;
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1666 MyPassOpt("mypass",
1667 cl::init(&amp;createDefaultMyPass),
1668 cl::desc("my pass option help"));
1669</pre></div>
1670
1671<p>Here the command option is "mypass", with createDefaultMyPass as the default
1672creator.</p>
1673
1674</div>
1675
1676<!-- *********************************************************************** -->
1677<div class="doc_section">
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1678 <a name="debughints">Using GDB with dynamically loaded passes</a>
1679</div>
Chris Lattner480e2ef2002-09-06 02:02:58 +0000[diff] [blame]1680<!-- *********************************************************************** -->
1681
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1682<div class="doc_text">
1683
1684<p>Unfortunately, using GDB with dynamically loaded passes is not as easy as it
Chris Lattner480e2ef2002-09-06 02:02:58 +0000[diff] [blame]1685should be. First of all, you can't set a breakpoint in a shared object that has
1686not been loaded yet, and second of all there are problems with inlined functions
1687in shared objects. Here are some suggestions to debugging your pass with
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1688GDB.</p>
Chris Lattner480e2ef2002-09-06 02:02:58 +0000[diff] [blame]1689
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1690<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]1691transformation invoked by <tt>opt</tt>, although nothing described here depends
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1692on that.</p>
1693
1694</div>
Chris Lattner480e2ef2002-09-06 02:02:58 +0000[diff] [blame]1695
1696<!-- _______________________________________________________________________ -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1697<div class="doc_subsubsection">
1698 <a name="breakpoint">Setting a breakpoint in your pass</a>
1699</div>
Chris Lattner480e2ef2002-09-06 02:02:58 +0000[diff] [blame]1700
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1701<div class="doc_text">
1702
1703<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]1704
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1705<div class="doc_code"><pre>
Chris Lattner480e2ef2002-09-06 02:02:58 +0000[diff] [blame]1706$ <b>gdb opt</b>
1707GNU gdb 5.0
1708Copyright 2000 Free Software Foundation, Inc.
1709GDB is free software, covered by the GNU General Public License, and you are
1710welcome to change it and/or distribute copies of it under certain conditions.
1711Type "show copying" to see the conditions.
1712There is absolutely no warranty for GDB. Type "show warranty" for details.
1713This GDB was configured as "sparc-sun-solaris2.6"...
1714(gdb)
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1715</pre></div>
Chris Lattner480e2ef2002-09-06 02:02:58 +0000[diff] [blame]1716
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1717<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]1718time to load. Be patient. Since we cannot set a breakpoint in our pass yet
1719(the shared object isn't loaded until runtime), we must execute the process, and
1720have it stop before it invokes our pass, but after it has loaded the shared
1721object. The most foolproof way of doing this is to set a breakpoint in
1722<tt>PassManager::run</tt> and then run the process with the arguments you
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1723want:</p>
Chris Lattner480e2ef2002-09-06 02:02:58 +0000[diff] [blame]1724
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1725<div class="doc_code"><pre>
Reid Spencer22a9e5b2006-09-28 16:53:47 +0000[diff] [blame]1726(gdb) <b>break llvm::PassManager::run</b>
Chris Lattner480e2ef2002-09-06 02:02:58 +0000[diff] [blame]1727Breakpoint 1 at 0x2413bc: file Pass.cpp, line 70.
Chris Lattner4c376ea2005-04-21 04:52:37 +0000[diff] [blame]1728(gdb) <b>run test.bc -load $(LLVMTOP)/llvm/Debug/lib/[libname].so -[passoption]</b>
1729Starting program: opt test.bc -load $(LLVMTOP)/llvm/Debug/lib/[libname].so -[passoption]
Chris Lattner480e2ef2002-09-06 02:02:58 +0000[diff] [blame]1730Breakpoint 1, PassManager::run (this=0xffbef174, M=@0x70b298) at Pass.cpp:70
173170 bool PassManager::run(Module &amp;M) { return PM-&gt;run(M); }
1732(gdb)
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000[diff] [blame]1733</pre></div>
Chris Lattner480e2ef2002-09-06 02:02:58 +0000[diff] [blame]1734
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1735<p>Once the <tt>opt</tt> stops in the <tt>PassManager::run</tt> method you are
1736now free to set breakpoints in your pass so that you can trace through execution
1737or do other standard debugging stuff.</p>
Chris Lattner480e2ef2002-09-06 02:02:58 +0000[diff] [blame]1738
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1739</div>
Chris Lattner480e2ef2002-09-06 02:02:58 +0000[diff] [blame]1740
1741<!-- _______________________________________________________________________ -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1742<div class="doc_subsubsection">
1743 <a name="debugmisc">Miscellaneous Problems</a>
1744</div>
Chris Lattner480e2ef2002-09-06 02:02:58 +0000[diff] [blame]1745
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1746<div class="doc_text">
1747
1748<p>Once you have the basics down, there are a couple of problems that GDB has,
1749some with solutions, some without.</p>
Chris Lattner480e2ef2002-09-06 02:02:58 +0000[diff] [blame]1750
1751<ul>
1752<li>Inline functions have bogus stack information. In general, GDB does a
1753pretty good job getting stack traces and stepping through inline functions.
1754When a pass is dynamically loaded however, it somehow completely loses this
1755capability. The only solution I know of is to de-inline a function (move it
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1756from the body of a class to a .cpp file).</li>
Chris Lattner480e2ef2002-09-06 02:02:58 +0000[diff] [blame]1757
1758<li>Restarting the program breaks breakpoints. After following the information
1759above, you have succeeded in getting some breakpoints planted in your pass. Nex
1760thing you know, you restart the program (i.e., you type '<tt>run</tt>' again),
1761and you start getting errors about breakpoints being unsettable. The only way I
1762have found to "fix" this problem is to <tt>delete</tt> the breakpoints that are
1763already set in your pass, run the program, and re-set the breakpoints once
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1764execution stops in <tt>PassManager::run</tt>.</li>
Chris Lattner480e2ef2002-09-06 02:02:58 +0000[diff] [blame]1765
1766</ul>
1767
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1768<p>Hopefully these tips will help with common case debugging situations. If
1769you'd like to contribute some tips of your own, just contact <a
1770href="mailto:sabre@nondot.org">Chris</a>.</p>
Chris Lattner480e2ef2002-09-06 02:02:58 +0000[diff] [blame]1771
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1772</div>
Chris Lattner480e2ef2002-09-06 02:02:58 +0000[diff] [blame]1773
1774<!-- *********************************************************************** -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1775<div class="doc_section">
1776 <a name="future">Future extensions planned</a>
1777</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1778<!-- *********************************************************************** -->
1779
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1780<div class="doc_text">
1781
1782<p>Although the LLVM Pass Infrastructure is very capable as it stands, and does
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1783some 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]1784where we are going:</p>
1785
1786</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1787
1788<!-- _______________________________________________________________________ -->
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]1789<div class="doc_subsubsection">
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1790 <a name="SMP">Multithreaded LLVM</a>
1791</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1792
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1793<div class="doc_text">
1794
1795<p>Multiple CPU machines are becoming more common and compilation can never be
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1796fast enough: obviously we should allow for a multithreaded compiler. Because of
1797the semantics defined for passes above (specifically they cannot maintain state
1798across invocations of their <tt>run*</tt> methods), a nice clean way to
1799implement a multithreaded compiler would be for the <tt>PassManager</tt> class
Misha Brukmanbc0e9982003-07-14 17:20:40 +0000[diff] [blame]1800to create multiple instances of each pass object, and allow the separate
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1801instances to be hacking on different parts of the program at the same time.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1802
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1803<p>This implementation would prevent each of the passes from having to implement
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1804multithreaded constructs, requiring only the LLVM core to have locking in a few
1805places (for global resources). Although this is a simple extension, we simply
1806haven't had time (or multiprocessor machines, thus a reason) to implement this.
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1807Despite that, we have kept the LLVM passes SMP ready, and you should too.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1808
Chris Lattnerb5c87f62007-05-18 05:36:14 +0000[diff] [blame]1809</div>
1810
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1811<!-- *********************************************************************** -->
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Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1818
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1819 <a href="mailto:sabre@nondot.org">Chris Lattner</a><br>
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