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gerrit-public.fairphone.software / fp2-dev / platform / external / llvm / 8de9f23fda43d2fceab37aff018f7b54d7abf7e8 / . / docs / WritingAnLLVMPass.html
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4<head>
5 <title>Writing an LLVM Pass</title>
6 <link rel="stylesheet" href="llvm.css" type="text/css">
7</head>
8<body>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]9
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]10<div class="doc_title">
11 Writing an LLVM Pass
12</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]13
14<ol>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]15 <li><a href="#introduction">Introduction - What is a pass?</a></li>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]16 <li><a href="#quickstart">Quick Start - Writing hello world</a>
17 <ul>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]18 <li><a href="#makefile">Setting up the build environment</a></li>
19 <li><a href="#basiccode">Basic code required</a></li>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]20 <li><a href="#running">Running a pass with <tt>opt</tt>
Chris Lattner8fdb2462004-09-18 06:39:35 +0000[diff] [blame]21 or <tt>analyze</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>
32 <li><a href="#doInitialization_scc">The <tt>doInitialization(Module
33 &amp;)</tt> method</a></li>
34 <li><a href="#runOnSCC">The <tt>runOnSCC</tt> method</a></li>
35 <li><a href="#doFinalization_scc">The <tt>doFinalization(Module
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>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]46 <li><a href="#BasicBlockPass">The <tt>BasicBlockPass</tt> class</a>
47 <ul>
Chris Lattnerd0713f92002-09-12 17:06:43 +0000[diff] [blame]48 <li><a href="#doInitialization_fn">The <tt>doInitialization(Function
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]49 &amp;)</tt> method</a></li>
50 <li><a href="#runOnBasicBlock">The <tt>runOnBasicBlock</tt>
51 method</a></li>
Chris Lattnerd0713f92002-09-12 17:06:43 +0000[diff] [blame]52 <li><a href="#doFinalization_fn">The <tt>doFinalization(Function
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]53 &amp;)</tt> method</a></li>
54 </ul></li>
Brian Gaekecab8b6f2003-07-17 18:53:20 +0000[diff] [blame]55 <li><a href="#MachineFunctionPass">The <tt>MachineFunctionPass</tt>
56 class</a>
Brian Gaeke6a33f362003-07-22 20:53:20 +0000[diff] [blame]57 <ul>
58 <li><a href="#runOnMachineFunction">The
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]59 <tt>runOnMachineFunction(MachineFunction &amp;)</tt> method</a></li>
60 </ul></li>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]61 </ul>
62 <li><a href="#registration">Pass Registration</a>
63 <ul>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]64 <li><a href="#print">The <tt>print</tt> method</a></li>
65 </ul></li>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]66 <li><a href="#interaction">Specifying interactions between passes</a>
67 <ul>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]68 <li><a href="#getAnalysisUsage">The <tt>getAnalysisUsage</tt>
69 method</a></li>
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]70 <li><a href="#AU::addRequired">The <tt>AnalysisUsage::addRequired&lt;&gt;</tt> and <tt>AnalysisUsage::addRequiredTransitive&lt;&gt;</tt> methods</a></li>
71 <li><a href="#AU::addPreserved">The <tt>AnalysisUsage::addPreserved&lt;&gt;</tt> method</a></li>
72 <li><a href="#AU::examples">Example implementations of <tt>getAnalysisUsage</tt></a></li>
73 <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]74 </ul></li>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]75 <li><a href="#analysisgroup">Implementing Analysis Groups</a>
76 <ul>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]77 <li><a href="#agconcepts">Analysis Group Concepts</a></li>
78 <li><a href="#registerag">Using <tt>RegisterAnalysisGroup</tt></a></li>
79 </ul></li>
Tanya Lattnerd5383652004-11-19 01:25:14 +0000[diff] [blame]80 <li><a href="#passStatistics">Pass Statistics</a>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]81 <li><a href="#passmanager">What PassManager does</a>
82 <ul>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]83 <li><a href="#releaseMemory">The <tt>releaseMemory</tt> method</a></li>
84 </ul></li>
Chris Lattner480e2ef2002-09-06 02:02:58 +0000[diff] [blame]85 <li><a href="#debughints">Using GDB with dynamically loaded passes</a>
86 <ul>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]87 <li><a href="#breakpoint">Setting a breakpoint in your pass</a></li>
88 <li><a href="#debugmisc">Miscellaneous Problems</a></li>
89 </ul></li>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]90 <li><a href="#future">Future extensions planned</a>
91 <ul>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]92 <li><a href="#SMP">Multithreaded LLVM</a></li>
Chris Lattnerf6278922004-09-20 04:36:29 +0000[diff] [blame]93 <li><a href="#PassFunctionPass"><tt>ModulePass</tt>es requiring
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]94 <tt>FunctionPass</tt>es</a></li>
95 </ul></li>
96</ol>
Chris Lattner38c633d2002-08-08 20:23:41 +0000[diff] [blame]97
Chris Lattner7911ce22004-05-23 21:07:27 +0000[diff] [blame]98<div class="doc_author">
99 <p>Written by <a href="mailto:sabre@nondot.org">Chris Lattner</a></p>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]100</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]101
102<!-- *********************************************************************** -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]103<div class="doc_section">
104 <a name="introduction">Introduction - What is a pass?</a>
105</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]106<!-- *********************************************************************** -->
107
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]108<div class="doc_text">
109
110<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]111passes are where most of the interesting parts of the compiler exist. Passes
112perform the transformations and optimizations that make up the compiler, they
113build the analysis results that are used by these transformations, and they are,
114above all, a structuring technique for compiler code.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]115
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]116<p>All LLVM passes are subclasses of the <tt><a
117href="http://llvm.cs.uiuc.edu/doxygen/classllvm_1_1Pass.html">Pass</a></tt>
118class, which implement functionality by overriding virtual methods inherited
Chris Lattnerf6278922004-09-20 04:36:29 +0000[diff] [blame]119from <tt>Pass</tt>. Depending on how your pass works, you should inherit from
120the <tt><a href="#ModulePass">ModulePass</a></tt>, <tt><a
121href="#CallGraphSCCPass">CallGraphSCCPass</a></tt>, <tt><a
122href="#FunctionPass">FunctionPass</a></tt>, or <tt><a
Chris Lattner8fdb2462004-09-18 06:39:35 +0000[diff] [blame]123href="#BasicBlockPass">BasicBlockPass</a></tt> classes, which gives the system
124more information about what your pass does, and how it can be combined with
125other passes. One of the main features of the LLVM Pass Framework is that it
126schedules passes to run in an efficient way based on the constraints that your
127pass meets (which are indicated by which class they derive from).</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]128
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]129<p>We start by showing you how to construct a pass, everything from setting up
130the code, to compiling, loading, and executing it. After the basics are down,
131more advanced features are discussed.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]132
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]133</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]134
135<!-- *********************************************************************** -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]136<div class="doc_section">
137 <a name="quickstart">Quick Start - Writing hello world</a>
138</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]139<!-- *********************************************************************** -->
140
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]141<div class="doc_text">
142
143<p>Here we describe how to write the "hello world" of passes. The "Hello" pass
144is designed to simply print out the name of non-external functions that exist in
Chris Lattner8fdb2462004-09-18 06:39:35 +0000[diff] [blame]145the program being compiled. It does not modify the program at all, it just
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]146inspects it. The source code and files for this pass are available in the LLVM
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]147source tree in the <tt>lib/Transforms/Hello</tt> directory.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]148
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]149</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]150
151<!-- ======================================================================= -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]152<div class="doc_subsection">
153 <a name="makefile">Setting up the build environment</a>
154</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]155
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]156<div class="doc_text">
157
Reid Spencer1bc19342004-12-11 05:12:57 +0000[diff] [blame]158 <p>First, you need to create a new directory somewhere in the LLVM source
159 base. For this example, we'll assume that you made
160 <tt>lib/Transforms/Hello</tt>. Next, you must set up a build script
161 (Makefile) that will compile the source code for the new pass. To do this,
162 copy the following into <tt>Makefile</tt>:</p>
163 <hr/>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]164
165<pre>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]166# Makefile for hello pass
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]167
Chris Lattner17a4c3e2002-08-14 20:06:13 +0000[diff] [blame]168# Path to top level of LLVM heirarchy
Chris Lattner7ce83e52002-08-14 20:07:01 +0000[diff] [blame]169LEVEL = ../../..
Chris Lattner17a4c3e2002-08-14 20:06:13 +0000[diff] [blame]170
171# Name of the library to build
Chris Lattner7ce83e52002-08-14 20:07:01 +0000[diff] [blame]172LIBRARYNAME = hello
Chris Lattner17a4c3e2002-08-14 20:06:13 +0000[diff] [blame]173
174# Build a dynamically loadable shared object
175SHARED_LIBRARY = 1
176
177# Include the makefile implementation stuff
178include $(LEVEL)/Makefile.common
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]179</pre>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]180
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]181<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]182directory are to be compiled and linked together into a
183<tt>lib/Debug/libhello.so</tt> shared object that can be dynamically loaded by
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]184the <tt>opt</tt> or <tt>analyze</tt> tools. If your operating system uses a
Chris Lattner8fdb2462004-09-18 06:39:35 +0000[diff] [blame]185suffix other than .so (such as windows or Mac OS/X), the appropriate extension
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]186will be used.</p>
John Criswellf9c78652004-01-26 21:26:54 +0000[diff] [blame]187
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]188<p>Now that we have the build scripts set up, we just need to write the code for
189the pass itself.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]190
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]191</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]192
193<!-- ======================================================================= -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]194<div class="doc_subsection">
195 <a name="basiccode">Basic code required</a>
196</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]197
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]198<div class="doc_text">
199
200<p>Now that we have a way to compile our new pass, we just have to write it.
201Start out with:</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]202
203<pre>
204<b>#include</b> "<a href="http://llvm.cs.uiuc.edu/doxygen/Pass_8h-source.html">llvm/Pass.h</a>"
205<b>#include</b> "<a href="http://llvm.cs.uiuc.edu/doxygen/Function_8h-source.html">llvm/Function.h</a>"
206</pre>
207
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]208<p>Which are needed because we are writing a <tt><a
209href="http://llvm.cs.uiuc.edu/doxygen/classllvm_1_1Pass.html">Pass</a></tt>, and
210we are operating on <tt><a
211href="http://llvm.cs.uiuc.edu/doxygen/classllvm_1_1Function.html">Function</a></tt>'s.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]212
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]213<p>Next we have:</p>
Jonathan Manton65acb302004-06-30 18:10:30 +0000[diff] [blame]214<pre>
215<b>using namespace llvm;</b>
216</pre>
217<p>... which is required because the functions from the include files
218live in the llvm namespace.
219</p>
220
221<p>Next we have:</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]222
223<pre>
224<b>namespace</b> {
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]225</pre>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]226
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]227<p>... which starts out an anonymous namespace. Anonymous namespaces are to C++
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]228what the "<tt>static</tt>" keyword is to C (at global scope). It makes the
229things declared inside of the anonymous namespace only visible to the current
230file. If you're not familiar with them, consult a decent C++ book for more
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]231information.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]232
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]233<p>Next, we declare our pass itself:</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]234
235<pre>
236 <b>struct</b> Hello : <b>public</b> <a href="#FunctionPass">FunctionPass</a> {
237</pre><p>
238
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]239<p>This declares a "<tt>Hello</tt>" class that is a subclass of <tt><a
240href="http://llvm.cs.uiuc.edu/doxygen/structllvm_1_1FunctionPass.html">FunctionPass</a></tt>.
Chris Lattnerd6ea9262002-09-09 03:48:46 +0000[diff] [blame]241The different builtin pass subclasses are described in detail <a
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]242href="#passtype">later</a>, but for now, know that <a
243href="#FunctionPass"><tt>FunctionPass</tt></a>'s operate a function at a
244time.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]245
246<pre>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]247 <b>virtual bool</b> <a href="#runOnFunction">runOnFunction</a>(Function &amp;F) {
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]248 std::cerr &lt;&lt; "<i>Hello: </i>" &lt;&lt; F.getName() &lt;&lt; "\n";
249 <b>return false</b>;
250 }
251 }; <i>// end of struct Hello</i>
252</pre>
253
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]254<p>We declare a "<a href="#runOnFunction"><tt>runOnFunction</tt></a>" method,
255which overloads an abstract virtual method inherited from <a
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]256href="#FunctionPass"><tt>FunctionPass</tt></a>. This is where we are supposed
257to 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]258function.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]259
260<pre>
261 RegisterOpt&lt;Hello&gt; X("<i>hello</i>", "<i>Hello World Pass</i>");
262} <i>// end of anonymous namespace</i>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]263</pre>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]264
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]265<p>Lastly, we register our class <tt>Hello</tt>, giving it a command line
266argument "<tt>hello</tt>", and a name "<tt>Hello World Pass</tt>". There are
267several different ways of <a href="#registration">registering your pass</a>,
268depending on what it is to be used for. For "optimizations" we use the
269<tt>RegisterOpt</tt> template.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]270
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]271<p>As a whole, the <tt>.cpp</tt> file looks like:</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]272
273<pre>
274<b>#include</b> "<a href="http://llvm.cs.uiuc.edu/doxygen/Pass_8h-source.html">llvm/Pass.h</a>"
275<b>#include</b> "<a href="http://llvm.cs.uiuc.edu/doxygen/Function_8h-source.html">llvm/Function.h</a>"
276
Jonathan Manton65acb302004-06-30 18:10:30 +0000[diff] [blame]277<b>using namespace llvm;</b>
278
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]279<b>namespace</b> {
280 <b>struct Hello</b> : <b>public</b> <a href="#FunctionPass">FunctionPass</a> {
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]281 <b>virtual bool</b> <a href="#runOnFunction">runOnFunction</a>(Function &amp;F) {
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]282 std::cerr &lt;&lt; "<i>Hello: </i>" &lt;&lt; F.getName() &lt;&lt; "\n";
283 <b>return false</b>;
284 }
285 };
286
287 RegisterOpt&lt;Hello&gt; X("<i>hello</i>", "<i>Hello World Pass</i>");
288}
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]289</pre>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]290
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]291<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]292command in the local directory and you should get a new
293"<tt>lib/Debug/libhello.so</tt> file. Note that everything in this file is
294contained in an anonymous namespace: this reflects the fact that passes are self
295contained units that do not need external interfaces (although they can have
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]296them) to be useful.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]297
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]298</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]299
300<!-- ======================================================================= -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]301<div class="doc_subsection">
302 <a name="running">Running a pass with <tt>opt</tt> or <tt>analyze</tt></a>
303</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]304
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]305<div class="doc_text">
306
John Criswellf9c78652004-01-26 21:26:54 +0000[diff] [blame]307<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]308<tt>opt</tt> command to run an LLVM program through your pass. Because you
309registered your pass with the <tt>RegisterOpt</tt> template, you will be able to
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]310use the <tt>opt</tt> tool to access it, once loaded.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]311
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]312<p>To test it, follow the example at the end of the <a
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]313href="GettingStarted.html">Getting Started Guide</a> to compile "Hello World" to
314LLVM. We can now run the bytecode file (<tt>hello.bc</tt>) for the program
315through our transformation like this (or course, any bytecode file will
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]316work):</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]317
318<pre>
319$ opt -load ../../../lib/Debug/libhello.so -hello &lt; hello.bc &gt; /dev/null
320Hello: __main
321Hello: puts
322Hello: main
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]323</pre>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]324
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]325<p>The '<tt>-load</tt>' option specifies that '<tt>opt</tt>' should load your
326pass as a shared object, which makes '<tt>-hello</tt>' a valid command line
327argument (which is one reason you need to <a href="#registration">register your
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]328pass</a>). Because the hello pass does not modify the program in any
329interesting way, we just throw away the result of <tt>opt</tt> (sending it to
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]330<tt>/dev/null</tt>).</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]331
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]332<p>To see what happened to the other string you registered, try running
333<tt>opt</tt> with the <tt>--help</tt> option:</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]334
335<pre>
336$ opt -load ../../../lib/Debug/libhello.so --help
337OVERVIEW: llvm .bc -&gt; .bc modular optimizer
338
339USAGE: opt [options] &lt;input bytecode&gt;
340
341OPTIONS:
342 Optimizations available:
343...
344 -funcresolve - Resolve Functions
345 -gcse - Global Common Subexpression Elimination
346 -globaldce - Dead Global Elimination
347 <b>-hello - Hello World Pass</b>
Chris Lattner065a6162003-09-10 05:29:43 +0000[diff] [blame]348 -indvars - Canonicalize Induction Variables
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]349 -inline - Function Integration/Inlining
350 -instcombine - Combine redundant instructions
351...
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]352</pre>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]353
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]354<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]355documentation to users of <tt>opt</tt>. Now that you have a working pass, you
356would go ahead and make it do the cool transformations you want. Once you get
357it all working and tested, it may become useful to find out how fast your pass
358is. The <a href="#passManager"><tt>PassManager</tt></a> provides a nice command
359line option (<tt>--time-passes</tt>) that allows you to get information about
360the execution time of your pass along with the other passes you queue up. For
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]361example:</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]362
363<pre>
364$ opt -load ../../../lib/Debug/libhello.so -hello -time-passes &lt; hello.bc &gt; /dev/null
365Hello: __main
366Hello: puts
367Hello: main
368===============================================================================
369 ... Pass execution timing report ...
370===============================================================================
371 Total Execution Time: 0.02 seconds (0.0479059 wall clock)
372
373 ---User Time--- --System Time-- --User+System-- ---Wall Time--- --- Pass Name ---
374 0.0100 (100.0%) 0.0000 ( 0.0%) 0.0100 ( 50.0%) 0.0402 ( 84.0%) Bytecode Writer
375 0.0000 ( 0.0%) 0.0100 (100.0%) 0.0100 ( 50.0%) 0.0031 ( 6.4%) Dominator Set Construction
376 0.0000 ( 0.0%) 0.0000 ( 0.0%) 0.0000 ( 0.0%) 0.0013 ( 2.7%) Module Verifier
377 <b> 0.0000 ( 0.0%) 0.0000 ( 0.0%) 0.0000 ( 0.0%) 0.0033 ( 6.9%) Hello World Pass</b>
378 0.0100 (100.0%) 0.0100 (100.0%) 0.0200 (100.0%) 0.0479 (100.0%) TOTAL
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]379</pre>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]380
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]381<p>As you can see, our implementation above is pretty fast :). The additional
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]382passes listed are automatically inserted by the '<tt>opt</tt>' tool to verify
383that the LLVM emitted by your pass is still valid and well formed LLVM, which
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]384hasn't been broken somehow.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]385
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]386<p>Now that you have seen the basics of the mechanics behind passes, we can talk
387about some more details of how they work and how to use them.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]388
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]389</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]390
391<!-- *********************************************************************** -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]392<div class="doc_section">
393 <a name="passtype">Pass classes and requirements</a>
394</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]395<!-- *********************************************************************** -->
396
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]397<div class="doc_text">
398
399<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]400decide what class you should subclass for your pass. The <a
401href="#basiccode">Hello World</a> example uses the <tt><a
402href="#FunctionPass">FunctionPass</a></tt> class for its implementation, but we
403did not discuss why or when this should occur. Here we talk about the classes
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]404available, from the most general to the most specific.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]405
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]406<p>When choosing a superclass for your Pass, you should choose the <b>most
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]407specific</b> class possible, while still being able to meet the requirements
Misha Brukman5560c9d2003-08-18 14:43:39 +0000[diff] [blame]408listed. This gives the LLVM Pass Infrastructure information necessary to
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]409optimize how passes are run, so that the resultant compiler isn't unneccesarily
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]410slow.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]411
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]412</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]413
Chris Lattnerf004f9a2002-09-25 22:31:38 +0000[diff] [blame]414<!-- ======================================================================= -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]415<div class="doc_subsection">
416 <a name="ImmutablePass">The <tt>ImmutablePass</tt> class</a>
417</div>
Chris Lattnerf004f9a2002-09-25 22:31:38 +0000[diff] [blame]418
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]419<div class="doc_text">
420
421<p>The most plain and boring type of pass is the "<tt><a
422href="http://llvm.cs.uiuc.edu/doxygen/structllvm_1_1ImmutablePass.html">ImmutablePass</a></tt>"
Chris Lattnerf004f9a2002-09-25 22:31:38 +0000[diff] [blame]423class. This pass type is used for passes that do not have to be run, do not
424change state, and never need to be updated. This is not a normal type of
425transformation or analysis, but can provide information about the current
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]426compiler configuration.</p>
Chris Lattnerf004f9a2002-09-25 22:31:38 +0000[diff] [blame]427
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]428<p>Although this pass class is very infrequently used, it is important for
Chris Lattnerf004f9a2002-09-25 22:31:38 +0000[diff] [blame]429providing information about the current target machine being compiled for, and
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]430other static information that can affect the various transformations.</p>
Chris Lattnerf004f9a2002-09-25 22:31:38 +0000[diff] [blame]431
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]432<p><tt>ImmutablePass</tt>es never invalidate other transformations, are never
433invalidated, and are never "run".</p>
Chris Lattnerf004f9a2002-09-25 22:31:38 +0000[diff] [blame]434
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]435</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]436
437<!-- ======================================================================= -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]438<div class="doc_subsection">
Chris Lattnerf6278922004-09-20 04:36:29 +0000[diff] [blame]439 <a name="ModulePass">The <tt>ModulePass</tt> class</a>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]440</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]441
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]442<div class="doc_text">
443
444<p>The "<tt><a
Chris Lattnerf6278922004-09-20 04:36:29 +0000[diff] [blame]445href="http://llvm.cs.uiuc.edu/doxygen/classllvm_1_1ModulePass.html">ModulePass</a></tt>"
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]446class is the most general of all superclasses that you can use. Deriving from
Chris Lattnerf6278922004-09-20 04:36:29 +0000[diff] [blame]447<tt>ModulePass</tt> indicates that your pass uses the entire program as a unit,
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]448refering to function bodies in no predictable order, or adding and removing
Chris Lattnerf6278922004-09-20 04:36:29 +0000[diff] [blame]449functions. Because nothing is known about the behavior of <tt>ModulePass</tt>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]450subclasses, no optimization can be done for their execution.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]451
Chris Lattnerf6278922004-09-20 04:36:29 +0000[diff] [blame]452<p>To write a correct <tt>ModulePass</tt> subclass, derive from
453<tt>ModulePass</tt> and overload the <tt>runOnModule</tt> method with the
454following signature:</p>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]455
456</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]457
458<!-- _______________________________________________________________________ -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]459<div class="doc_subsubsection">
Chris Lattnerf6278922004-09-20 04:36:29 +0000[diff] [blame]460 <a name="runOnModule">The <tt>runOnModule</tt> method</a>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]461</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]462
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]463<div class="doc_text">
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]464
465<pre>
Chris Lattnerf6278922004-09-20 04:36:29 +0000[diff] [blame]466 <b>virtual bool</b> runOnModule(Module &amp;M) = 0;
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]467</pre>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]468
Chris Lattnerf6278922004-09-20 04:36:29 +0000[diff] [blame]469<p>The <tt>runOnModule</tt> method performs the interesting work of the pass,
470and should return true if the module was modified by the transformation, false
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]471otherwise.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]472
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]473</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]474
475<!-- ======================================================================= -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]476<div class="doc_subsection">
Chris Lattner8fdb2462004-09-18 06:39:35 +0000[diff] [blame]477 <a name="CallGraphSCCPass">The <tt>CallGraphSCCPass</tt> class</a>
478</div>
479
480<div class="doc_text">
481
482<p>The "<tt><a
483href="http://llvm.cs.uiuc.edu/doxygen/structllvm_1_1CallGraphSCCPass.html">CallGraphSCCPass</a></tt>"
484is used by passes that need to traverse the program bottom-up on the call graph
485(callees before callers). Deriving from CallGraphSCCPass provides some
486mechanics for building and traversing the CallGraph, but also allows the system
487to optimize execution of CallGraphSCCPass's. If your pass meets the
488requirements outlined below, and doesn't meet the requirements of a <tt><a
489href="#FunctionPass">FunctionPass</a></tt> or <tt><a
490href="#BasicBlockPass">BasicBlockPass</a></tt>, you should derive from
491<tt>CallGraphSCCPass</tt>.</p>
492
493<p><b>TODO</b>: explain briefly what SCC, Tarjan's algo, and B-U mean.</p>
494
495<p>To be explicit, <tt>CallGraphSCCPass</tt> subclasses are:</p>
496
497<ol>
498
499<li>... <em>not allowed</em> to modify any <tt>Function</tt>s that are not in
500the current SCC.</li>
501
502<li>... <em>allowed</em> to inspect any Function's other than those in the
503current SCC and the direct callees of the SCC.</li>
504
505<li>... <em>required</em> to preserve the current CallGraph object, updating it
506to reflect any changes made to the program.</li>
507
508<li>... <em>not allowed</em> to add or remove SCC's from the current Module,
509though they may change the contents of an SCC.</li>
510
511<li>... <em>allowed</em> to add or remove global variables from the current
512Module.</li>
513
514<li>... <em>allowed</em> to maintain state across invocations of
515 <a href="#runOnSCC"><tt>runOnSCC</tt></a> (including global data).</li>
516</ol>
517
518<p>Implementing a <tt>CallGraphSCCPass</tt> is slightly tricky in some cases
519because it has to handle SCCs with more than one node in it. All of the virtual
520methods described below should return true if they modified the program, or
521false if they didn't.</p>
522
523</div>
524
525<!-- _______________________________________________________________________ -->
526<div class="doc_subsubsection">
527 <a name="doInitialization_scc">The <tt>doInitialization(Module &amp;)</tt>
528 method</a>
529</div>
530
531<div class="doc_text">
532
533<pre>
534 <b>virtual bool</b> doInitialization(Module &amp;M);
535</pre>
536
537<p>The <tt>doIninitialize</tt> method is allowed to do most of the things that
538<tt>CallGraphSCCPass</tt>'s are not allowed to do. They can add and remove
539functions, get pointers to functions, etc. The <tt>doInitialization</tt> method
540is designed to do simple initialization type of stuff that does not depend on
541the SCCs being processed. The <tt>doInitialization</tt> method call is not
542scheduled to overlap with any other pass executions (thus it should be very
543fast).</p>
544
545</div>
546
547<!-- _______________________________________________________________________ -->
548<div class="doc_subsubsection">
549 <a name="runOnSCC">The <tt>runOnSCC</tt> method</a>
550</div>
551
552<div class="doc_text">
553
554<pre>
555 <b>virtual bool</b> runOnSCC(const std::vector&lt;CallGraphNode *&gt; &amp;SCCM) = 0;
556</pre>
557
558<p>The <tt>runOnSCC</tt> method performs the interesting work of the pass, and
559should return true if the module was modified by the transformation, false
560otherwise.</p>
561
562</div>
563
564<!-- _______________________________________________________________________ -->
565<div class="doc_subsubsection">
566 <a name="doFinalization_scc">The <tt>doFinalization(Module
567 &amp;)</tt> method</a>
568</div>
569
570<div class="doc_text">
571
572<pre>
573 <b>virtual bool</b> doFinalization(Module &amp;M);
574</pre>
575
576<p>The <tt>doFinalization</tt> method is an infrequently used method that is
577called when the pass framework has finished calling <a
578href="#runOnFunction"><tt>runOnFunction</tt></a> for every function in the
579program being compiled.</p>
580
581</div>
582
583<!-- ======================================================================= -->
584<div class="doc_subsection">
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]585 <a name="FunctionPass">The <tt>FunctionPass</tt> class</a>
586</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]587
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]588<div class="doc_text">
589
Chris Lattnerf6278922004-09-20 04:36:29 +0000[diff] [blame]590<p>In contrast to <tt>ModulePass</tt> subclasses, <tt><a
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]591href="http://llvm.cs.uiuc.edu/doxygen/classllvm_1_1Pass.html">FunctionPass</a></tt>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]592subclasses do have a predictable, local behavior that can be expected by the
593system. All <tt>FunctionPass</tt> execute on each function in the program
Misha Brukmanef6a6a62003-08-21 22:14:26 +0000[diff] [blame]594independent of all of the other functions in the program.
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]595<tt>FunctionPass</tt>'s do not require that they are executed in a particular
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]596order, and <tt>FunctionPass</tt>'s do not modify external functions.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]597
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]598<p>To be explicit, <tt>FunctionPass</tt> subclasses are not allowed to:</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]599
600<ol>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]601<li>Modify a Function other than the one currently being processed.</li>
602<li>Add or remove Function's from the current Module.</li>
603<li>Add or remove global variables from the current Module.</li>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]604<li>Maintain state across invocations of
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]605 <a href="#runOnFunction"><tt>runOnFunction</tt></a> (including global data)</li>
606</ol>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]607
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]608<p>Implementing a <tt>FunctionPass</tt> is usually straightforward (See the <a
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]609href="#basiccode">Hello World</a> pass for example). <tt>FunctionPass</tt>'s
610may overload three virtual methods to do their work. All of these methods
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]611should return true if they modified the program, or false if they didn't.</p>
612
613</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]614
615<!-- _______________________________________________________________________ -->
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]616<div class="doc_subsubsection">
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]617 <a name="doInitialization_mod">The <tt>doInitialization(Module &amp;)</tt>
618 method</a>
619</div>
620
621<div class="doc_text">
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]622
623<pre>
624 <b>virtual bool</b> doInitialization(Module &amp;M);
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]625</pre>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]626
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]627<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]628<tt>FunctionPass</tt>'s are not allowed to do. They can add and remove
Chris Lattnerd0713f92002-09-12 17:06:43 +0000[diff] [blame]629functions, get pointers to functions, etc. The <tt>doInitialization</tt> method
630is designed to do simple initialization type of stuff that does not depend on
631the functions being processed. The <tt>doInitialization</tt> method call is not
632scheduled to overlap with any other pass executions (thus it should be very
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]633fast).</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]634
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]635<p>A good example of how this method should be used is the <a
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]636href="http://llvm.cs.uiuc.edu/doxygen/LowerAllocations_8cpp-source.html">LowerAllocations</a>
637pass. This pass converts <tt>malloc</tt> and <tt>free</tt> instructions into
Misha Brukmanef6a6a62003-08-21 22:14:26 +0000[diff] [blame]638platform dependent <tt>malloc()</tt> and <tt>free()</tt> function calls. It
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]639uses the <tt>doInitialization</tt> method to get a reference to the malloc and
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]640free functions that it needs, adding prototypes to the module if necessary.</p>
641
642</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]643
644<!-- _______________________________________________________________________ -->
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]645<div class="doc_subsubsection">
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]646 <a name="runOnFunction">The <tt>runOnFunction</tt> method</a>
647</div>
648
649<div class="doc_text">
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]650
651<pre>
652 <b>virtual bool</b> runOnFunction(Function &amp;F) = 0;
653</pre><p>
654
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]655<p>The <tt>runOnFunction</tt> method must be implemented by your subclass to do
656the transformation or analysis work of your pass. As usual, a true value should
657be returned if the function is modified.</p>
658
659</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]660
661<!-- _______________________________________________________________________ -->
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]662<div class="doc_subsubsection">
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]663 <a name="doFinalization_mod">The <tt>doFinalization(Module
664 &amp;)</tt> method</a>
665</div>
666
667<div class="doc_text">
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]668
669<pre>
670 <b>virtual bool</b> doFinalization(Module &amp;M);
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]671</pre>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]672
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]673<p>The <tt>doFinalization</tt> method is an infrequently used method that is
674called when the pass framework has finished calling <a
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]675href="#runOnFunction"><tt>runOnFunction</tt></a> for every function in the
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]676program being compiled.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]677
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]678</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]679
680<!-- ======================================================================= -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]681<div class="doc_subsection">
682 <a name="BasicBlockPass">The <tt>BasicBlockPass</tt> class</a>
683</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]684
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]685<div class="doc_text">
686
687<p><tt>BasicBlockPass</tt>'s are just like <a
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]688href="#FunctionPass"><tt>FunctionPass</tt></a>'s, except that they must limit
689their scope of inspection and modification to a single basic block at a time.
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]690As such, they are <b>not</b> allowed to do any of the following:</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]691
692<ol>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]693<li>Modify or inspect any basic blocks outside of the current one</li>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]694<li>Maintain state across invocations of
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]695 <a href="#runOnBasicBlock"><tt>runOnBasicBlock</tt></a></li>
Reid Spencer1bc19342004-12-11 05:12:57 +0000[diff] [blame]696<li>Modify the control flow graph (by altering terminator instructions)</li>
697<li>Any of the things forbidden for
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]698 <a href="#FunctionPass"><tt>FunctionPass</tt></a>es.</li>
699</ol>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]700
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]701<p><tt>BasicBlockPass</tt>es are useful for traditional local and "peephole"
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]702optimizations. They may override the same <a
Chris Lattnerd0713f92002-09-12 17:06:43 +0000[diff] [blame]703href="#doInitialization_mod"><tt>doInitialization(Module &amp;)</tt></a> and <a
704href="#doFinalization_mod"><tt>doFinalization(Module &amp;)</tt></a> methods that <a
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]705href="#FunctionPass"><tt>FunctionPass</tt></a>'s have, but also have the following virtual methods that may also be implemented:</p>
706
707</div>
Chris Lattnerd0713f92002-09-12 17:06:43 +0000[diff] [blame]708
709<!-- _______________________________________________________________________ -->
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]710<div class="doc_subsubsection">
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]711 <a name="doInitialization_fn">The <tt>doInitialization(Function
712 &amp;)</tt> method</a>
713</div>
714
715<div class="doc_text">
Chris Lattnerd0713f92002-09-12 17:06:43 +0000[diff] [blame]716
717<pre>
718 <b>virtual bool</b> doInitialization(Function &amp;F);
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]719</pre>
Chris Lattnerd0713f92002-09-12 17:06:43 +0000[diff] [blame]720
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]721<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]722<tt>BasicBlockPass</tt>'s are not allowed to do, but that
723<tt>FunctionPass</tt>'s can. The <tt>doInitialization</tt> method is designed
Reid Spencer1bc19342004-12-11 05:12:57 +0000[diff] [blame]724to do simple initialization that does not depend on the
Chris Lattnerd0713f92002-09-12 17:06:43 +0000[diff] [blame]725BasicBlocks being processed. The <tt>doInitialization</tt> method call is not
726scheduled to overlap with any other pass executions (thus it should be very
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]727fast).</p>
Chris Lattnerd0713f92002-09-12 17:06:43 +0000[diff] [blame]728
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]729</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]730
731<!-- _______________________________________________________________________ -->
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]732<div class="doc_subsubsection">
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]733 <a name="runOnBasicBlock">The <tt>runOnBasicBlock</tt> method</a>
734</div>
735
736<div class="doc_text">
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]737
738<pre>
739 <b>virtual bool</b> runOnBasicBlock(BasicBlock &amp;BB) = 0;
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]740</pre>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]741
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]742<p>Override this function to do the work of the <tt>BasicBlockPass</tt>. This
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]743function is not allowed to inspect or modify basic blocks other than the
744parameter, and are not allowed to modify the CFG. A true value must be returned
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]745if the basic block is modified.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]746
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]747</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]748
Chris Lattnerd0713f92002-09-12 17:06:43 +0000[diff] [blame]749<!-- _______________________________________________________________________ -->
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]750<div class="doc_subsubsection">
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]751 <a name="doFinalization_fn">The <tt>doFinalization(Function &amp;)</tt>
752 method</a>
753</div>
754
755<div class="doc_text">
Chris Lattnerd0713f92002-09-12 17:06:43 +0000[diff] [blame]756
757<pre>
758 <b>virtual bool</b> doFinalization(Function &amp;F);
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]759</pre>
Chris Lattnerd0713f92002-09-12 17:06:43 +0000[diff] [blame]760
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]761<p>The <tt>doFinalization</tt> method is an infrequently used method that is
762called when the pass framework has finished calling <a
Chris Lattnerd0713f92002-09-12 17:06:43 +0000[diff] [blame]763href="#runOnBasicBlock"><tt>runOnBasicBlock</tt></a> for every BasicBlock in the
764program being compiled. This can be used to perform per-function
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]765finalization.</p>
Chris Lattnerd0713f92002-09-12 17:06:43 +0000[diff] [blame]766
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]767</div>
Chris Lattnerd0713f92002-09-12 17:06:43 +0000[diff] [blame]768
Brian Gaekecab8b6f2003-07-17 18:53:20 +0000[diff] [blame]769<!-- ======================================================================= -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]770<div class="doc_subsection">
771 <a name="MachineFunctionPass">The <tt>MachineFunctionPass</tt> class</a>
772</div>
Brian Gaekecab8b6f2003-07-17 18:53:20 +0000[diff] [blame]773
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]774<div class="doc_text">
775
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]776<p>A <tt>MachineFunctionPass</tt> is a part of the LLVM code generator that
777executes on the machine-dependent representation of each LLVM function in the
778program. A <tt>MachineFunctionPass</tt> is also a <tt>FunctionPass</tt>, so all
Brian Gaekecab8b6f2003-07-17 18:53:20 +0000[diff] [blame]779the restrictions that apply to a <tt>FunctionPass</tt> also apply to it.
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]780<tt>MachineFunctionPass</tt>es also have additional restrictions. In particular,
781<tt>MachineFunctionPass</tt>es are not allowed to do any of the following:</p>
Brian Gaekecab8b6f2003-07-17 18:53:20 +0000[diff] [blame]782
783<ol>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]784<li>Modify any LLVM Instructions, BasicBlocks or Functions.</li>
785<li>Modify a MachineFunction other than the one currently being processed.</li>
786<li>Add or remove MachineFunctions from the current Module.</li>
787<li>Add or remove global variables from the current Module.</li>
788<li>Maintain state across invocations of <a
789href="#runOnMachineFunction"><tt>runOnMachineFunction</tt></a> (including global
790data)</li>
791</ol>
Brian Gaekecab8b6f2003-07-17 18:53:20 +0000[diff] [blame]792
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]793</div>
Chris Lattnerd0713f92002-09-12 17:06:43 +0000[diff] [blame]794
Brian Gaeke6a33f362003-07-22 20:53:20 +0000[diff] [blame]795<!-- _______________________________________________________________________ -->
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]796<div class="doc_subsubsection">
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]797 <a name="runOnMachineFunction">The <tt>runOnMachineFunction(MachineFunction
798 &amp;MF)</tt> method</a>
799</div>
800
801<div class="doc_text">
Brian Gaeke6a33f362003-07-22 20:53:20 +0000[diff] [blame]802
803<pre>
804 <b>virtual bool</b> runOnMachineFunction(MachineFunction &amp;MF) = 0;
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]805</pre>
Brian Gaeke6a33f362003-07-22 20:53:20 +0000[diff] [blame]806
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]807<p><tt>runOnMachineFunction</tt> can be considered the main entry point of a
808<tt>MachineFunctionPass</tt>; that is, you should override this method to do the
809work of your <tt>MachineFunctionPass</tt>.</p>
Brian Gaeke6a33f362003-07-22 20:53:20 +0000[diff] [blame]810
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]811<p>The <tt>runOnMachineFunction</tt> method is called on every
Brian Gaeke6a33f362003-07-22 20:53:20 +0000[diff] [blame]812<tt>MachineFunction</tt> in a <tt>Module</tt>, so that the
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]813<tt>MachineFunctionPass</tt> may perform optimizations on the machine-dependent
814representation of the function. If you want to get at the LLVM <tt>Function</tt>
815for the <tt>MachineFunction</tt> you're working on, use
816<tt>MachineFunction</tt>'s <tt>getFunction()</tt> accessor method -- but
817remember, you may not modify the LLVM <tt>Function</tt> or its contents from a
818<tt>MachineFunctionPass</tt>.</p>
819
820</div>
Brian Gaeke6a33f362003-07-22 20:53:20 +0000[diff] [blame]821
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]822<!-- *********************************************************************** -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]823<div class="doc_section">
824 <a name="registration">Pass registration</a>
825</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]826<!-- *********************************************************************** -->
827
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]828<div class="doc_text">
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]829
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]830<p>In the <a href="#basiccode">Hello World</a> example pass we illustrated how
831pass registration works, and discussed some of the reasons that it is used and
832what it does. Here we discuss how and why passes are registered.</p>
833
834<p>Passes can be registered in several different ways. Depending on the general
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]835classification of the pass, you should use one of the following templates to
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]836register the pass:</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]837
838<ul>
839<li><b><tt>RegisterOpt</tt></b> - This template should be used when you are
840registering a pass that logically should be available for use in the
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]841'<tt>opt</tt>' utility.</li>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]842
843<li><b><tt>RegisterAnalysis</tt></b> - This template should be used when you are
844registering a pass that logically should be available for use in the
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]845'<tt>analyze</tt>' utility.</li>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]846
847<li><b><tt>RegisterPass</tt></b> - This is the generic form of the
848<tt>Register*</tt> templates that should be used if you want your pass listed by
849multiple or no utilities. This template takes an extra third argument that
850specifies which tools it should be listed in. See the <a
851href="http://llvm.cs.uiuc.edu/doxygen/PassSupport_8h-source.html">PassSupport.h</a>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]852file for more information.</li>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]853
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]854</ul>
855
856<p>Regardless of how you register your pass, you must specify at least two
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]857parameters. The first parameter is the name of the pass that is to be used on
858the command line to specify that the pass should be added to a program (for
859example <tt>opt</tt> or <tt>analyze</tt>). The second argument is the name of
860the pass, which is to be used for the <tt>--help</tt> output of programs, as
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]861well as for debug output generated by the <tt>--debug-pass</tt> option.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]862
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]863<p>If a pass is registered to be used by the <tt>analyze</tt> utility, you
864should implement the virtual <tt>print</tt> method:</p>
865
866</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]867
868<!-- _______________________________________________________________________ -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]869<div class="doc_subsubsection">
870 <a name="print">The <tt>print</tt> method</a>
871</div>
872
873<div class="doc_text">
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]874
875<pre>
876 <b>virtual void</b> print(std::ostream &amp;O, <b>const</b> Module *M) <b>const</b>;
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]877</pre>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]878
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]879<p>The <tt>print</tt> method must be implemented by "analyses" in order to print
880a human readable version of the analysis results. This is useful for debugging
881an analysis itself, as well as for other people to figure out how an analysis
882works. The <tt>analyze</tt> tool uses this method to generate its output.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]883
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]884<p>The <tt>ostream</tt> parameter specifies the stream to write the results on,
885and 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]886program that has been analyzed. Note however that this pointer may be null in
887certain circumstances (such as calling the <tt>Pass::dump()</tt> from a
888debugger), so it should only be used to enhance debug output, it should not be
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]889depended on.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]890
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]891</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]892
893<!-- *********************************************************************** -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]894<div class="doc_section">
895 <a name="interaction">Specifying interactions between passes</a>
896</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]897<!-- *********************************************************************** -->
898
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]899<div class="doc_text">
900
901<p>One of the main responsibilities of the <tt>PassManager</tt> is the make sure
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]902that passes interact with each other correctly. Because <tt>PassManager</tt>
903tries to <a href="#passmanager">optimize the execution of passes</a> it must
904know how the passes interact with each other and what dependencies exist between
905the various passes. To track this, each pass can declare the set of passes that
906are required to be executed before the current pass, and the passes which are
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]907invalidated by the current pass.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]908
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]909<p>Typically this functionality is used to require that analysis results are
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]910computed before your pass is run. Running arbitrary transformation passes can
911invalidate the computed analysis results, which is what the invalidation set
912specifies. If a pass does not implement the <tt><a
913href="#getAnalysisUsage">getAnalysisUsage</a></tt> method, it defaults to not
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]914having any prerequisite passes, and invalidating <b>all</b> other passes.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]915
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]916</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]917
918<!-- _______________________________________________________________________ -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]919<div class="doc_subsubsection">
920 <a name="getAnalysisUsage">The <tt>getAnalysisUsage</tt> method</a>
921</div>
922
923<div class="doc_text">
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]924
925<pre>
926 <b>virtual void</b> getAnalysisUsage(AnalysisUsage &amp;Info) <b>const</b>;
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]927</pre>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]928
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]929<p>By implementing the <tt>getAnalysisUsage</tt> method, the required and
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]930invalidated sets may be specified for your transformation. The implementation
931should fill in the <tt><a
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]932href="http://llvm.cs.uiuc.edu/doxygen/classllvm_1_1AnalysisUsage.html">AnalysisUsage</a></tt>
933object with information about which passes are required and not invalidated. To
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]934do this, a pass may call any of the following methods on the AnalysisUsage
935object:</p>
936</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]937
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]938<!-- _______________________________________________________________________ -->
939<div class="doc_subsubsection">
940 <a name="AU::addRequired">The <tt>AnalysisUsage::addRequired&lt;&gt;</tt> and <tt>AnalysisUsage::addRequiredTransitive&lt;&gt;</tt> methods</a>
941</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]942
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]943<div class="doc_text">
944<p>
Reid Spencer1bc19342004-12-11 05:12:57 +0000[diff] [blame]945If your pass requires a previous pass to be executed (an analysis for example),
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]946it can use one of these methods to arrange for it to be run before your pass.
947LLVM has many different types of analyses and passes that can be required,
Reid Spencer1bc19342004-12-11 05:12:57 +0000[diff] [blame]948spanning the range from <tt>DominatorSet</tt> to <tt>BreakCriticalEdges</tt>.
949Requiring <tt>BreakCriticalEdges</tt>, for example, guarantees that there will
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]950be no critical edges in the CFG when your pass has been run.
951</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]952
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]953<p>
954Some analyses chain to other analyses to do their job. For example, an <a
955href="AliasAnalysis.html">AliasAnalysis</a> implementation is required to <a
956href="AliasAnalysis.html#chaining">chain</a> to other alias analysis passes. In
957cases where analyses chain, the <tt>addRequiredTransitive</tt> method should be
958used instead of the <tt>addRequired</tt> method. This informs the PassManager
959that the transitively required pass should be alive as long as the requiring
960pass is.
961</p>
962</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]963
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]964<!-- _______________________________________________________________________ -->
965<div class="doc_subsubsection">
966 <a name="AU::addPreserved">The <tt>AnalysisUsage::addPreserved&lt;&gt;</tt> method</a>
967</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]968
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]969<div class="doc_text">
970<p>
971One of the jobs of the PassManager is to optimize how and when analyses are run.
972In particular, it attempts to avoid recomputing data unless it needs to. For
973this reason, passes are allowed to declare that they preserve (i.e., they don't
974invalidate) an existing analysis if it's available. For example, a simple
Reid Spencer1bc19342004-12-11 05:12:57 +0000[diff] [blame]975constant folding pass would not modify the CFG, so it can't possibly affect the
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]976results of dominator analysis. By default, all passes are assumed to invalidate
977all others.
978</p>
979
980<p>
981The <tt>AnalysisUsage</tt> class provides several methods which are useful in
982certain circumstances that are related to <tt>addPreserved</tt>. In particular,
983the <tt>setPreservesAll</tt> method can be called to indicate that the pass does
984not modify the LLVM program at all (which is true for analyses), and the
985<tt>setPreservesCFG</tt> method can be used by transformations that change
986instructions in the program but do not modify the CFG or terminator instructions
987(note that this property is implicitly set for <a
988href="#BasicBlockPass">BasicBlockPass</a>'s).
989</p>
990
991<p>
992<tt>addPreserved</tt> is particularly useful for transformations like
993<tt>BreakCriticalEdges</tt>. This pass knows how to update a small set of loop
994and dominator related analyses if they exist, so it can preserve them, despite
995the fact that it hacks on the CFG.
996</p>
997</div>
998
999<!-- _______________________________________________________________________ -->
1000<div class="doc_subsubsection">
1001 <a name="AU::examples">Example implementations of <tt>getAnalysisUsage</tt></a>
1002</div>
1003
1004<div class="doc_text">
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1005
1006<pre>
1007 <i>// This is an example implementation from an analysis, which does not modify
1008 // the program at all, yet has a prerequisite.</i>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1009 <b>void</b> <a href="http://llvm.cs.uiuc.edu/doxygen/structllvm_1_1PostDominanceFrontier.html">PostDominanceFrontier</a>::getAnalysisUsage(AnalysisUsage &amp;AU) <b>const</b> {
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1010 AU.setPreservesAll();
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1011 AU.addRequired&lt;<a href="http://llvm.cs.uiuc.edu/doxygen/structllvm_1_1PostDominatorTree.html">PostDominatorTree</a>&gt;();
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1012 }
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1013</pre>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1014
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1015<p>and:</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1016
1017<pre>
1018 <i>// This example modifies the program, but does not modify the CFG</i>
1019 <b>void</b> <a href="http://llvm.cs.uiuc.edu/doxygen/structLICM.html">LICM</a>::getAnalysisUsage(AnalysisUsage &amp;AU) <b>const</b> {
Chris Lattner8291e042002-10-21 19:57:59 +0000[diff] [blame]1020 AU.setPreservesCFG();
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1021 AU.addRequired&lt;<a href="http://llvm.cs.uiuc.edu/doxygen/classllvm_1_1LoopInfo.html">LoopInfo</a>&gt;();
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1022 }
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1023</pre>
1024
1025</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1026
1027<!-- _______________________________________________________________________ -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1028<div class="doc_subsubsection">
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]1029 <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]1030</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1031
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1032<div class="doc_text">
1033
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]1034<p>The <tt>Pass::getAnalysis&lt;&gt;</tt> method is automatically inherited by
1035your class, providing you with access to the passes that you declared that you
1036required with the <a href="#getAnalysisUsage"><tt>getAnalysisUsage</tt></a>
1037method. It takes a single template argument that specifies which pass class you
1038want, and returns a reference to that pass. For example:</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1039
1040<pre>
Chris Lattnera5776302004-03-17 21:33:32 +0000[diff] [blame]1041 bool LICM::runOnFunction(Function &amp;F) {
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]1042 LoopInfo &amp;LI = getAnalysis&lt;LoopInfo&gt;();
1043 ...
1044 }
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1045</pre>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1046
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1047<p>This method call returns a reference to the pass desired. You may get a
1048runtime assertion failure if you attempt to get an analysis that you did not
1049declare as required in your <a
1050href="#getAnalysisUsage"><tt>getAnalysisUsage</tt></a> implementation. This
1051method can be called by your <tt>run*</tt> method implementation, or by any
1052other local method invoked by your <tt>run*</tt> method.</p>
1053
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]1054<p>
1055If your pass is capable of updating analyses if they exist (e.g.,
1056<tt>BreakCriticalEdges</tt>, as described above), you can use the
1057<tt>getAnalysisToUpdate</tt> method, which returns a pointer to the analysis if
1058it is active. For example:</p>
1059
1060<pre>
1061 ...
1062 if (DominatorSet *DS = getAnalysisToUpdate&lt;DominatorSet&gt;()) {
1063 <i>// A DominatorSet is active. This code will update it.</i>
1064 }
1065 ...
1066</pre>
1067
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1068</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1069
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1070<!-- *********************************************************************** -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1071<div class="doc_section">
1072 <a name="analysisgroup">Implementing Analysis Groups</a>
1073</div>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1074<!-- *********************************************************************** -->
1075
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1076<div class="doc_text">
1077
1078<p>Now that we understand the basics of how passes are defined, how the are
1079used, 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]1080fancier. All of the pass relationships that we have seen so far are very
1081simple: one pass depends on one other specific pass to be run before it can run.
1082For many applications, this is great, for others, more flexibility is
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1083required.</p>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1084
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1085<p>In particular, some analyses are defined such that there is a single simple
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1086interface to the analysis results, but multiple ways of calculating them.
1087Consider alias analysis for example. The most trivial alias analysis returns
1088"may alias" for any alias query. The most sophisticated analysis a
1089flow-sensitive, context-sensitive interprocedural analysis that can take a
1090significant amount of time to execute (and obviously, there is a lot of room
1091between these two extremes for other implementations). To cleanly support
1092situations like this, the LLVM Pass Infrastructure supports the notion of
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1093Analysis Groups.</p>
1094
1095</div>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1096
1097<!-- _______________________________________________________________________ -->
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]1098<div class="doc_subsubsection">
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1099 <a name="agconcepts">Analysis Group Concepts</a>
1100</div>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1101
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1102<div class="doc_text">
1103
1104<p>An Analysis Group is a single simple interface that may be implemented by
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1105multiple different passes. Analysis Groups can be given human readable names
1106just like passes, but unlike passes, they need not derive from the <tt>Pass</tt>
1107class. An analysis group may have one or more implementations, one of which is
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1108the "default" implementation.</p>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1109
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1110<p>Analysis groups are used by client passes just like other passes are: the
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1111<tt>AnalysisUsage::addRequired()</tt> and <tt>Pass::getAnalysis()</tt> methods.
1112In order to resolve this requirement, the <a href="#passmanager">PassManager</a>
1113scans the available passes to see if any implementations of the analysis group
1114are available. If none is available, the default implementation is created for
1115the pass to use. All standard rules for <A href="#interaction">interaction
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1116between passes</a> still apply.</p>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1117
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1118<p>Although <a href="#registration">Pass Registration</a> is optional for normal
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1119passes, all analysis group implementations must be registered, and must use the
1120<A href="#registerag"><tt>RegisterAnalysisGroup</tt></a> template to join the
1121implementation pool. Also, a default implementation of the interface
1122<b>must</b> be registered with <A
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1123href="#registerag"><tt>RegisterAnalysisGroup</tt></a>.</p>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1124
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1125<p>As a concrete example of an Analysis Group in action, consider the <a
1126href="http://llvm.cs.uiuc.edu/doxygen/classllvm_1_1AliasAnalysis.html">AliasAnalysis</a>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1127analysis group. The default implementation of the alias analysis interface (the
1128<tt><a
1129href="http://llvm.cs.uiuc.edu/doxygen/structBasicAliasAnalysis.html">basicaa</a></tt>
1130pass) just does a few simple checks that don't require significant analysis to
1131compute (such as: two different globals can never alias each other, etc).
1132Passes that use the <tt><a
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1133href="http://llvm.cs.uiuc.edu/doxygen/classllvm_1_1AliasAnalysis.html">AliasAnalysis</a></tt>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1134interface (for example the <tt><a
Misha Brukmand15516e2004-06-03 23:39:36 +0000[diff] [blame]1135href="http://llvm.cs.uiuc.edu/doxygen/structGCSE.html">gcse</a></tt> pass), do
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1136not care which implementation of alias analysis is actually provided, they just
1137use the designated interface.</p>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1138
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1139<p>From the user's perspective, commands work just like normal. Issuing the
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1140command '<tt>opt -gcse ...</tt>' will cause the <tt>basicaa</tt> class to be
1141instantiated and added to the pass sequence. Issuing the command '<tt>opt
1142-somefancyaa -gcse ...</tt>' will cause the <tt>gcse</tt> pass to use the
1143<tt>somefancyaa</tt> alias analysis (which doesn't actually exist, it's just a
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1144hypothetical example) instead.</p>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1145
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1146</div>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1147
1148<!-- _______________________________________________________________________ -->
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]1149<div class="doc_subsubsection">
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1150 <a name="registerag">Using <tt>RegisterAnalysisGroup</tt></a>
1151</div>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1152
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1153<div class="doc_text">
1154
1155<p>The <tt>RegisterAnalysisGroup</tt> template is used to register the analysis
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1156group itself as well as add pass implementations to the analysis group. First,
1157an analysis should be registered, with a human readable name provided for it.
1158Unlike registration of passes, there is no command line argument to be specified
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1159for the Analysis Group Interface itself, because it is "abstract":</p>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1160
1161<pre>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1162 <b>static</b> RegisterAnalysisGroup&lt;<a href="http://llvm.cs.uiuc.edu/doxygen/classllvm_1_1AliasAnalysis.html">AliasAnalysis</a>&gt; A("<i>Alias Analysis</i>");
1163</pre>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1164
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1165<p>Once the analysis is registered, passes can declare that they are valid
1166implementations of the interface by using the following code:</p>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1167
1168<pre>
1169<b>namespace</b> {
1170 //<i> Analysis Group implementations <b>must</b> be registered normally...</i>
1171 RegisterOpt&lt;FancyAA&gt;
1172 B("<i>somefancyaa</i>", "<i>A more complex alias analysis implementation</i>");
1173
1174 //<i> Declare that we implement the AliasAnalysis interface</i>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1175 RegisterAnalysisGroup&lt;<a href="http://llvm.cs.uiuc.edu/doxygen/classllvm_1_1AliasAnalysis.html">AliasAnalysis</a>, FancyAA&gt; C;
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1176}
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1177</pre>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1178
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1179<p>This just shows a class <tt>FancyAA</tt> that is registered normally, then
1180uses the <tt>RegisterAnalysisGroup</tt> template to "join" the <tt><a
1181href="http://llvm.cs.uiuc.edu/doxygen/classllvm_1_1AliasAnalysis.html">AliasAnalysis</a></tt>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1182analysis group. Every implementation of an analysis group should join using
1183this template. A single pass may join multiple different analysis groups with
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1184no problem.</p>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1185
1186<pre>
1187<b>namespace</b> {
1188 //<i> Analysis Group implementations <b>must</b> be registered normally...</i>
1189 RegisterOpt&lt;<a href="http://llvm.cs.uiuc.edu/doxygen/structBasicAliasAnalysis.html">BasicAliasAnalysis</a>&gt;
1190 D("<i>basicaa</i>", "<i>Basic Alias Analysis (default AA impl)</i>");
1191
1192 //<i> Declare that we implement the AliasAnalysis interface</i>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1193 RegisterAnalysisGroup&lt;<a href="http://llvm.cs.uiuc.edu/doxygen/classllvm_1_1AliasAnalysis.html">AliasAnalysis</a>, <a href="http://llvm.cs.uiuc.edu/doxygen/structBasicAliasAnalysis.html">BasicAliasAnalysis</a>, <b>true</b>&gt; E;
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1194}
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1195</pre>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1196
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1197<p>Here we show how the default implementation is specified (using the extra
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1198argument to the <tt>RegisterAnalysisGroup</tt> template). There must be exactly
1199one default implementation available at all times for an Analysis Group to be
1200used. Here we declare that the <tt><a
1201href="http://llvm.cs.uiuc.edu/doxygen/structBasicAliasAnalysis.html">BasicAliasAnalysis</a></tt>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1202pass is the default implementation for the interface.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1203
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1204</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1205
1206<!-- *********************************************************************** -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1207<div class="doc_section">
Tanya Lattnerd5383652004-11-19 01:25:14 +0000[diff] [blame]1208 <a name="passStatistics">Pass Statistics</a>
1209</div>
1210<!-- *********************************************************************** -->
1211
1212<div class="doc_text">
Tanya Lattner05f8d5f2004-11-19 01:26:37 +0000[diff] [blame]1213<p>The <a
Tanya Lattner54dc8b22004-12-08 18:13:51 +0000[diff] [blame]1214href="http://llvm.cs.uiuc.edu/doxygen/Statistic_8h-source.html"><tt>Statistic</tt></a>
Tanya Lattnerd5383652004-11-19 01:25:14 +0000[diff] [blame]1215class, is designed to be an easy way to expose various success
1216metrics from passes. These statistics are printed at the end of a
1217run, when the -stats command line option is enabled on the command
Tanya Lattner05f8d5f2004-11-19 01:26:37 +0000[diff] [blame]1218line. 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]1219
1220</div>
1221
1222
1223<!-- *********************************************************************** -->
1224<div class="doc_section">
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1225 <a name="passmanager">What PassManager does</a>
1226</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1227<!-- *********************************************************************** -->
1228
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1229<div class="doc_text">
1230
1231<p>The <a
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1232href="http://llvm.cs.uiuc.edu/doxygen/PassManager_8h-source.html"><tt>PassManager</tt></a>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1233<a
1234href="http://llvm.cs.uiuc.edu/doxygen/classllvm_1_1PassManager.html">class</a>
1235takes a list of passes, ensures their <a href="#interaction">prerequisites</a>
1236are set up correctly, and then schedules passes to run efficiently. All of the
1237LLVM tools that run passes use the <tt>PassManager</tt> for execution of these
1238passes.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1239
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1240<p>The <tt>PassManager</tt> does two main things to try to reduce the execution
1241time of a series of passes:</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1242
1243<ol>
1244<li><b>Share analysis results</b> - The PassManager attempts to avoid
1245recomputing analysis results as much as possible. This means keeping track of
1246which analyses are available already, which analyses get invalidated, and which
1247analyses are needed to be run for a pass. An important part of work is that the
1248<tt>PassManager</tt> tracks the exact lifetime of all analysis results, allowing
1249it to <a href="#releaseMemory">free memory</a> allocated to holding analysis
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1250results as soon as they are no longer needed.</li>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1251
1252<li><b>Pipeline the execution of passes on the program</b> - The
1253<tt>PassManager</tt> attempts to get better cache and memory usage behavior out
1254of a series of passes by pipelining the passes together. This means that, given
1255a series of consequtive <a href="#FunctionPass"><tt>FunctionPass</tt></a>'s, it
1256will execute all of the <a href="#FunctionPass"><tt>FunctionPass</tt></a>'s on
1257the first function, then all of the <a
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1258href="#FunctionPass"><tt>FunctionPass</tt></a>es on the second function,
1259etc... until the entire program has been run through the passes.
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1260
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1261<p>This improves the cache behavior of the compiler, because it is only touching
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1262the LLVM program representation for a single function at a time, instead of
1263traversing the entire program. It reduces the memory consumption of compiler,
1264because, for example, only one <a
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1265href="http://llvm.cs.uiuc.edu/doxygen/structllvm_1_1DominatorSet.html"><tt>DominatorSet</tt></a>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1266needs to be calculated at a time. This also makes it possible some <a
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1267href="#SMP">interesting enhancements</a> in the future.</p></li>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1268
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1269</ol>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1270
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1271<p>The effectiveness of the <tt>PassManager</tt> is influenced directly by how
1272much information it has about the behaviors of the passes it is scheduling. For
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1273example, the "preserved" set is intentionally conservative in the face of an
1274unimplemented <a href="#getAnalysisUsage"><tt>getAnalysisUsage</tt></a> method.
1275Not implementing when it should be implemented will have the effect of not
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1276allowing any analysis results to live across the execution of your pass.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1277
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1278<p>The <tt>PassManager</tt> class exposes a <tt>--debug-pass</tt> command line
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1279options that is useful for debugging pass execution, seeing how things work, and
1280diagnosing when you should be preserving more analyses than you currently are
1281(To get information about all of the variants of the <tt>--debug-pass</tt>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1282option, just type '<tt>opt --help-hidden</tt>').</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1283
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1284<p>By using the <tt>--debug-pass=Structure</tt> option, for example, we can see
1285how our <a href="#basiccode">Hello World</a> pass interacts with other passes.
1286Lets try it out with the <tt>gcse</tt> and <tt>licm</tt> passes:</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1287
1288<pre>
1289$ opt -load ../../../lib/Debug/libhello.so -gcse -licm --debug-pass=Structure &lt; hello.bc &gt; /dev/null
1290Module Pass Manager
1291 Function Pass Manager
1292 Dominator Set Construction
1293 Immediate Dominators Construction
1294 Global Common Subexpression Elimination
1295-- Immediate Dominators Construction
1296-- Global Common Subexpression Elimination
1297 Natural Loop Construction
1298 Loop Invariant Code Motion
1299-- Natural Loop Construction
1300-- Loop Invariant Code Motion
1301 Module Verifier
1302-- Dominator Set Construction
1303-- Module Verifier
1304 Bytecode Writer
1305--Bytecode Writer
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1306</pre>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1307
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1308<p>This output shows us when passes are constructed and when the analysis
1309results are known to be dead (prefixed with '<tt>--</tt>'). Here we see that
1310GCSE uses dominator and immediate dominator information to do its job. The LICM
1311pass uses natural loop information, which uses dominator sets, but not immediate
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1312dominators. Because immediate dominators are no longer useful after the GCSE
1313pass, it is immediately destroyed. The dominator sets are then reused to
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1314compute natural loop information, which is then used by the LICM pass.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1315
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1316<p>After the LICM pass, the module verifier runs (which is automatically added
1317by the '<tt>opt</tt>' tool), which uses the dominator set to check that the
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1318resultant LLVM code is well formed. After it finishes, the dominator set
1319information is destroyed, after being computed once, and shared by three
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1320passes.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1321
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1322<p>Lets see how this changes when we run the <a href="#basiccode">Hello
1323World</a> pass in between the two passes:</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1324
1325<pre>
1326$ opt -load ../../../lib/Debug/libhello.so -gcse -hello -licm --debug-pass=Structure &lt; hello.bc &gt; /dev/null
1327Module Pass Manager
1328 Function Pass Manager
1329 Dominator Set Construction
1330 Immediate Dominators Construction
1331 Global Common Subexpression Elimination
1332<b>-- Dominator Set Construction</b>
1333-- Immediate Dominators Construction
1334-- Global Common Subexpression Elimination
1335<b> Hello World Pass
1336-- Hello World Pass
1337 Dominator Set Construction</b>
1338 Natural Loop Construction
1339 Loop Invariant Code Motion
1340-- Natural Loop Construction
1341-- Loop Invariant Code Motion
1342 Module Verifier
1343-- Dominator Set Construction
1344-- Module Verifier
1345 Bytecode Writer
1346--Bytecode Writer
1347Hello: __main
1348Hello: puts
1349Hello: main
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1350</pre>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1351
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1352<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]1353Dominator Set pass, even though it doesn't modify the code at all! To fix this,
1354we need to add the following <a
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1355href="#getAnalysisUsage"><tt>getAnalysisUsage</tt></a> method to our pass:</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1356
1357<pre>
1358 <i>// We don't modify the program, so we preserve all analyses</i>
1359 <b>virtual void</b> getAnalysisUsage(AnalysisUsage &amp;AU) <b>const</b> {
1360 AU.setPreservesAll();
1361 }
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1362</pre>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1363
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1364<p>Now when we run our pass, we get this output:</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1365
1366<pre>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1367$ opt -load ../../../lib/Debug/libhello.so -gcse -hello -licm --debug-pass=Structure &lt; hello.bc &gt; /dev/null
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1368Pass Arguments: -gcse -hello -licm
1369Module Pass Manager
1370 Function Pass Manager
1371 Dominator Set Construction
1372 Immediate Dominators Construction
1373 Global Common Subexpression Elimination
1374-- Immediate Dominators Construction
1375-- Global Common Subexpression Elimination
1376 Hello World Pass
1377-- Hello World Pass
1378 Natural Loop Construction
1379 Loop Invariant Code Motion
1380-- Loop Invariant Code Motion
1381-- Natural Loop Construction
1382 Module Verifier
1383-- Dominator Set Construction
1384-- Module Verifier
1385 Bytecode Writer
1386--Bytecode Writer
1387Hello: __main
1388Hello: puts
1389Hello: main
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1390</pre>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1391
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1392<p>Which shows that we don't accidentally invalidate dominator information
1393anymore, and therefore do not have to compute it twice.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1394
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1395</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1396
1397<!-- _______________________________________________________________________ -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1398<div class="doc_subsubsection">
1399 <a name="releaseMemory">The <tt>releaseMemory</tt> method</a>
1400</div>
1401
1402<div class="doc_text">
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1403
1404<pre>
1405 <b>virtual void</b> releaseMemory();
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1406</pre>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1407
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1408<p>The <tt>PassManager</tt> automatically determines when to compute analysis
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1409results, and how long to keep them around for. Because the lifetime of the pass
1410object itself is effectively the entire duration of the compilation process, we
1411need some way to free analysis results when they are no longer useful. The
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1412<tt>releaseMemory</tt> virtual method is the way to do this.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1413
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1414<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]1415amount of state (for use by another pass which "requires" your pass and uses the
1416<a href="#getAnalysis">getAnalysis</a> method) you should implement
1417<tt>releaseMEmory</tt> to, well, release the memory allocated to maintain this
1418internal state. This method is called after the <tt>run*</tt> method for the
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1419class, before the next call of <tt>run*</tt> in your pass.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1420
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1421</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1422
1423<!-- *********************************************************************** -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1424<div class="doc_section">
1425 <a name="debughints">Using GDB with dynamically loaded passes</a>
1426</div>
Chris Lattner480e2ef2002-09-06 02:02:58 +0000[diff] [blame]1427<!-- *********************************************************************** -->
1428
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1429<div class="doc_text">
1430
1431<p>Unfortunately, using GDB with dynamically loaded passes is not as easy as it
Chris Lattner480e2ef2002-09-06 02:02:58 +0000[diff] [blame]1432should be. First of all, you can't set a breakpoint in a shared object that has
1433not been loaded yet, and second of all there are problems with inlined functions
1434in shared objects. Here are some suggestions to debugging your pass with
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1435GDB.</p>
Chris Lattner480e2ef2002-09-06 02:02:58 +0000[diff] [blame]1436
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1437<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]1438transformation invoked by <tt>opt</tt>, although nothing described here depends
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1439on that.</p>
1440
1441</div>
Chris Lattner480e2ef2002-09-06 02:02:58 +0000[diff] [blame]1442
1443<!-- _______________________________________________________________________ -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1444<div class="doc_subsubsection">
1445 <a name="breakpoint">Setting a breakpoint in your pass</a>
1446</div>
Chris Lattner480e2ef2002-09-06 02:02:58 +0000[diff] [blame]1447
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1448<div class="doc_text">
1449
1450<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]1451
1452<pre>
1453$ <b>gdb opt</b>
1454GNU gdb 5.0
1455Copyright 2000 Free Software Foundation, Inc.
1456GDB is free software, covered by the GNU General Public License, and you are
1457welcome to change it and/or distribute copies of it under certain conditions.
1458Type "show copying" to see the conditions.
1459There is absolutely no warranty for GDB. Type "show warranty" for details.
1460This GDB was configured as "sparc-sun-solaris2.6"...
1461(gdb)
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1462</pre>
Chris Lattner480e2ef2002-09-06 02:02:58 +0000[diff] [blame]1463
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1464<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]1465time to load. Be patient. Since we cannot set a breakpoint in our pass yet
1466(the shared object isn't loaded until runtime), we must execute the process, and
1467have it stop before it invokes our pass, but after it has loaded the shared
1468object. The most foolproof way of doing this is to set a breakpoint in
1469<tt>PassManager::run</tt> and then run the process with the arguments you
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1470want:</p>
Chris Lattner480e2ef2002-09-06 02:02:58 +0000[diff] [blame]1471
1472<pre>
1473(gdb) <b>break PassManager::run</b>
1474Breakpoint 1 at 0x2413bc: file Pass.cpp, line 70.
Chris Lattnerfafe6302003-10-23 19:48:11 +0000[diff] [blame]1475(gdb) <b>run test.bc -load $(LLVMTOP)/llvm/lib/Debug/[libname].so -[passoption]</b>
1476Starting program: opt test.bc -load $(LLVMTOP)/llvm/lib/Debug/[libname].so -[passoption]
Chris Lattner480e2ef2002-09-06 02:02:58 +0000[diff] [blame]1477Breakpoint 1, PassManager::run (this=0xffbef174, M=@0x70b298) at Pass.cpp:70
147870 bool PassManager::run(Module &amp;M) { return PM-&gt;run(M); }
1479(gdb)
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1480</pre>
Chris Lattner480e2ef2002-09-06 02:02:58 +0000[diff] [blame]1481
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1482<p>Once the <tt>opt</tt> stops in the <tt>PassManager::run</tt> method you are
1483now free to set breakpoints in your pass so that you can trace through execution
1484or do other standard debugging stuff.</p>
Chris Lattner480e2ef2002-09-06 02:02:58 +0000[diff] [blame]1485
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1486</div>
Chris Lattner480e2ef2002-09-06 02:02:58 +0000[diff] [blame]1487
1488<!-- _______________________________________________________________________ -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1489<div class="doc_subsubsection">
1490 <a name="debugmisc">Miscellaneous Problems</a>
1491</div>
Chris Lattner480e2ef2002-09-06 02:02:58 +0000[diff] [blame]1492
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1493<div class="doc_text">
1494
1495<p>Once you have the basics down, there are a couple of problems that GDB has,
1496some with solutions, some without.</p>
Chris Lattner480e2ef2002-09-06 02:02:58 +0000[diff] [blame]1497
1498<ul>
1499<li>Inline functions have bogus stack information. In general, GDB does a
1500pretty good job getting stack traces and stepping through inline functions.
1501When a pass is dynamically loaded however, it somehow completely loses this
1502capability. The only solution I know of is to de-inline a function (move it
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1503from the body of a class to a .cpp file).</li>
Chris Lattner480e2ef2002-09-06 02:02:58 +0000[diff] [blame]1504
1505<li>Restarting the program breaks breakpoints. After following the information
1506above, you have succeeded in getting some breakpoints planted in your pass. Nex
1507thing you know, you restart the program (i.e., you type '<tt>run</tt>' again),
1508and you start getting errors about breakpoints being unsettable. The only way I
1509have found to "fix" this problem is to <tt>delete</tt> the breakpoints that are
1510already set in your pass, run the program, and re-set the breakpoints once
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1511execution stops in <tt>PassManager::run</tt>.</li>
Chris Lattner480e2ef2002-09-06 02:02:58 +0000[diff] [blame]1512
1513</ul>
1514
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1515<p>Hopefully these tips will help with common case debugging situations. If
1516you'd like to contribute some tips of your own, just contact <a
1517href="mailto:sabre@nondot.org">Chris</a>.</p>
Chris Lattner480e2ef2002-09-06 02:02:58 +0000[diff] [blame]1518
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1519</div>
Chris Lattner480e2ef2002-09-06 02:02:58 +0000[diff] [blame]1520
1521<!-- *********************************************************************** -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1522<div class="doc_section">
1523 <a name="future">Future extensions planned</a>
1524</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1525<!-- *********************************************************************** -->
1526
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1527<div class="doc_text">
1528
1529<p>Although the LLVM Pass Infrastructure is very capable as it stands, and does
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1530some 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]1531where we are going:</p>
1532
1533</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1534
1535<!-- _______________________________________________________________________ -->
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]1536<div class="doc_subsubsection">
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1537 <a name="SMP">Multithreaded LLVM</a>
1538</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1539
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1540<div class="doc_text">
1541
1542<p>Multiple CPU machines are becoming more common and compilation can never be
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1543fast enough: obviously we should allow for a multithreaded compiler. Because of
1544the semantics defined for passes above (specifically they cannot maintain state
1545across invocations of their <tt>run*</tt> methods), a nice clean way to
1546implement a multithreaded compiler would be for the <tt>PassManager</tt> class
Misha Brukmanbc0e9982003-07-14 17:20:40 +0000[diff] [blame]1547to create multiple instances of each pass object, and allow the separate
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1548instances to be hacking on different parts of the program at the same time.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1549
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1550<p>This implementation would prevent each of the passes from having to implement
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1551multithreaded constructs, requiring only the LLVM core to have locking in a few
1552places (for global resources). Although this is a simple extension, we simply
1553haven't had time (or multiprocessor machines, thus a reason) to implement this.
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1554Despite that, we have kept the LLVM passes SMP ready, and you should too.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1555
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1556</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1557
1558<!-- _______________________________________________________________________ -->
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]1559<div class="doc_subsubsection">
Chris Lattnerf6278922004-09-20 04:36:29 +0000[diff] [blame]1560<a name="PassFunctionPass"><tt>ModulePass</tt>es requiring <tt>FunctionPass</tt>es</a>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1561</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1562
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1563<div class="doc_text">
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1564
Chris Lattnerf6278922004-09-20 04:36:29 +0000[diff] [blame]1565<p>Currently it is illegal for a <a href="#ModulePass"><tt>ModulePass</tt></a>
1566to require a <a href="#FunctionPass"><tt>FunctionPass</tt></a>. This is because
1567there is only one instance of the <a
1568href="#FunctionPass"><tt>FunctionPass</tt></a> object ever created, thus nowhere
1569to store information for all of the functions in the program at the same time.
1570Although this has come up a couple of times before, this has always been worked
1571around by factoring one big complicated pass into a global and an
1572interprocedural part, both of which are distinct. In the future, it would be
1573nice to have this though.</p>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1574
1575<p>Note that it is no problem for a <a
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1576href="#FunctionPass"><tt>FunctionPass</tt></a> to require the results of a <a
Chris Lattnerf6278922004-09-20 04:36:29 +0000[diff] [blame]1577href="#ModulePass"><tt>ModulePass</tt></a>, only the other way around.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1578
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1579</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1580
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Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1582<hr>
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Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1589 <a href="mailto:sabre@nondot.org">Chris Lattner</a><br>
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