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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>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]21 or <tt>analyze</tt></a></li>
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 Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]26 <li><a href="#Pass">The <tt>Pass</tt> class</a>
27 <ul>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]28 <li><a href="#run">The <tt>run</tt> method</a></li>
29 </ul></li>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]30 <li><a href="#FunctionPass">The <tt>FunctionPass</tt> class</a>
31 <ul>
Chris Lattnerd0713f92002-09-12 17:06:43 +0000[diff] [blame]32 <li><a href="#doInitialization_mod">The <tt>doInitialization(Module
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]33 &amp;)</tt> method</a></li>
34 <li><a href="#runOnFunction">The <tt>runOnFunction</tt> method</a></li>
Chris Lattnerd0713f92002-09-12 17:06:43 +0000[diff] [blame]35 <li><a href="#doFinalization_mod">The <tt>doFinalization(Module
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]36 &amp;)</tt> method</a></li>
37 </ul></li>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]38 <li><a href="#BasicBlockPass">The <tt>BasicBlockPass</tt> class</a>
39 <ul>
Chris Lattnerd0713f92002-09-12 17:06:43 +0000[diff] [blame]40 <li><a href="#doInitialization_fn">The <tt>doInitialization(Function
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]41 &amp;)</tt> method</a></li>
42 <li><a href="#runOnBasicBlock">The <tt>runOnBasicBlock</tt>
43 method</a></li>
Chris Lattnerd0713f92002-09-12 17:06:43 +0000[diff] [blame]44 <li><a href="#doFinalization_fn">The <tt>doFinalization(Function
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]45 &amp;)</tt> method</a></li>
46 </ul></li>
Brian Gaekecab8b6f2003-07-17 18:53:20 +0000[diff] [blame]47 <li><a href="#MachineFunctionPass">The <tt>MachineFunctionPass</tt>
48 class</a>
Brian Gaeke6a33f362003-07-22 20:53:20 +0000[diff] [blame]49 <ul>
50 <li><a href="#runOnMachineFunction">The
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]51 <tt>runOnMachineFunction(MachineFunction &amp;)</tt> method</a></li>
52 </ul></li>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]53 </ul>
54 <li><a href="#registration">Pass Registration</a>
55 <ul>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]56 <li><a href="#print">The <tt>print</tt> method</a></li>
57 </ul></li>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]58 <li><a href="#interaction">Specifying interactions between passes</a>
59 <ul>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]60 <li><a href="#getAnalysisUsage">The <tt>getAnalysisUsage</tt>
61 method</a></li>
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]62 <li><a href="#AU::addRequired">The <tt>AnalysisUsage::addRequired&lt;&gt;</tt> and <tt>AnalysisUsage::addRequiredTransitive&lt;&gt;</tt> methods</a></li>
63 <li><a href="#AU::addPreserved">The <tt>AnalysisUsage::addPreserved&lt;&gt;</tt> method</a></li>
64 <li><a href="#AU::examples">Example implementations of <tt>getAnalysisUsage</tt></a></li>
65 <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]66 </ul></li>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]67 <li><a href="#analysisgroup">Implementing Analysis Groups</a>
68 <ul>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]69 <li><a href="#agconcepts">Analysis Group Concepts</a></li>
70 <li><a href="#registerag">Using <tt>RegisterAnalysisGroup</tt></a></li>
71 </ul></li>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]72 <li><a href="#passmanager">What PassManager does</a>
73 <ul>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]74 <li><a href="#releaseMemory">The <tt>releaseMemory</tt> method</a></li>
75 </ul></li>
Chris Lattner480e2ef2002-09-06 02:02:58 +0000[diff] [blame]76 <li><a href="#debughints">Using GDB with dynamically loaded passes</a>
77 <ul>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]78 <li><a href="#breakpoint">Setting a breakpoint in your pass</a></li>
79 <li><a href="#debugmisc">Miscellaneous Problems</a></li>
80 </ul></li>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]81 <li><a href="#future">Future extensions planned</a>
82 <ul>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]83 <li><a href="#SMP">Multithreaded LLVM</a></li>
84 <li><a href="#ModuleSource">A new <tt>ModuleSource</tt> interface</a></li>
85 <li><a href="#PassFunctionPass"><tt>Pass</tt>es requiring
86 <tt>FunctionPass</tt>es</a></li>
87 </ul></li>
88</ol>
Chris Lattner38c633d2002-08-08 20:23:41 +0000[diff] [blame]89
Chris Lattner7911ce22004-05-23 21:07:27 +0000[diff] [blame]90<div class="doc_author">
91 <p>Written by <a href="mailto:sabre@nondot.org">Chris Lattner</a></p>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]92</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]93
94<!-- *********************************************************************** -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]95<div class="doc_section">
96 <a name="introduction">Introduction - What is a pass?</a>
97</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]98<!-- *********************************************************************** -->
99
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]100<div class="doc_text">
101
102<p>The LLVM Pass Framework is an important part of the LLVM system, because LLVM
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]103passes are where the interesting parts of the compiler exist. Passes perform
104the transformations and optimizations that make up the compiler, they build
105the analysis results that are used by these transformations, and they are, above
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]106all, a structuring technique for compiler code.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]107
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]108<p>All LLVM passes are subclasses of the <tt><a
109href="http://llvm.cs.uiuc.edu/doxygen/classllvm_1_1Pass.html">Pass</a></tt>
110class, which implement functionality by overriding virtual methods inherited
111from <tt>Pass</tt>. Depending on how your pass works, you may be able to
112inherit from the <tt><a
113href="http://llvm.cs.uiuc.edu/doxygen/structllvm_1_1FunctionPass.html">FunctionPass</a></tt>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]114or <tt><a
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]115href="http://llvm.cs.uiuc.edu/doxygen/structllvm_1_1BasicBlockPass.html">BasicBlockPass</a></tt>,
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]116which gives the system more information about what your pass does, and how it
117can be combined with other passes. One of the main features of the LLVM Pass
118Framework is that it schedules passes to run in an efficient way based on the
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]119constraints that your pass has.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]120
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]121<p>We start by showing you how to construct a pass, everything from setting up
122the code, to compiling, loading, and executing it. After the basics are down,
123more advanced features are discussed.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]124
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]125</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]126
127<!-- *********************************************************************** -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]128<div class="doc_section">
129 <a name="quickstart">Quick Start - Writing hello world</a>
130</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]131<!-- *********************************************************************** -->
132
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]133<div class="doc_text">
134
135<p>Here we describe how to write the "hello world" of passes. The "Hello" pass
136is designed to simply print out the name of non-external functions that exist in
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]137the program being compiled. It does not modify the program at all, just
138inspects it. The source code and files for this pass are available in the LLVM
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]139source tree in the <tt>lib/Transforms/Hello</tt> directory.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]140
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]141</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]142
143<!-- ======================================================================= -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]144<div class="doc_subsection">
145 <a name="makefile">Setting up the build environment</a>
146</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]147
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]148<div class="doc_text">
149
150<p>First thing you need to do is create a new directory somewhere in the LLVM
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]151source base. For this example, we'll assume that you made
152"<tt>lib/Transforms/Hello</tt>". The first thing you must do is set up a build
153script (Makefile) that will compile the source code for the new pass. To do
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]154this, copy this into "<tt>Makefile</tt>":</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]155
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]156<hr>
157
158<pre>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]159# Makefile for hello pass
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]160
Chris Lattner17a4c3e2002-08-14 20:06:13 +0000[diff] [blame]161# Path to top level of LLVM heirarchy
Chris Lattner7ce83e52002-08-14 20:07:01 +0000[diff] [blame]162LEVEL = ../../..
Chris Lattner17a4c3e2002-08-14 20:06:13 +0000[diff] [blame]163
164# Name of the library to build
Chris Lattner7ce83e52002-08-14 20:07:01 +0000[diff] [blame]165LIBRARYNAME = hello
Chris Lattner17a4c3e2002-08-14 20:06:13 +0000[diff] [blame]166
167# Build a dynamically loadable shared object
168SHARED_LIBRARY = 1
169
170# Include the makefile implementation stuff
171include $(LEVEL)/Makefile.common
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]172</pre>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]173
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]174<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]175directory are to be compiled and linked together into a
176<tt>lib/Debug/libhello.so</tt> shared object that can be dynamically loaded by
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]177the <tt>opt</tt> or <tt>analyze</tt> tools. If your operating system uses a
178suffix other than .so (such as windows of Mac OS/X), the appropriate extension
179will be used.</p>
John Criswellf9c78652004-01-26 21:26:54 +0000[diff] [blame]180
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]181<p>Now that we have the build scripts set up, we just need to write the code for
182the pass itself.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]183
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]184</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]185
186<!-- ======================================================================= -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]187<div class="doc_subsection">
188 <a name="basiccode">Basic code required</a>
189</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]190
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]191<div class="doc_text">
192
193<p>Now that we have a way to compile our new pass, we just have to write it.
194Start out with:</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]195
196<pre>
197<b>#include</b> "<a href="http://llvm.cs.uiuc.edu/doxygen/Pass_8h-source.html">llvm/Pass.h</a>"
198<b>#include</b> "<a href="http://llvm.cs.uiuc.edu/doxygen/Function_8h-source.html">llvm/Function.h</a>"
199</pre>
200
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]201<p>Which are needed because we are writing a <tt><a
202href="http://llvm.cs.uiuc.edu/doxygen/classllvm_1_1Pass.html">Pass</a></tt>, and
203we are operating on <tt><a
204href="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]205
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]206<p>Next we have:</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]207
208<pre>
209<b>namespace</b> {
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]210</pre>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]211
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]212<p>... which starts out an anonymous namespace. Anonymous namespaces are to C++
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]213what the "<tt>static</tt>" keyword is to C (at global scope). It makes the
214things declared inside of the anonymous namespace only visible to the current
215file. If you're not familiar with them, consult a decent C++ book for more
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]216information.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]217
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]218<p>Next, we declare our pass itself:</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]219
220<pre>
221 <b>struct</b> Hello : <b>public</b> <a href="#FunctionPass">FunctionPass</a> {
222</pre><p>
223
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]224<p>This declares a "<tt>Hello</tt>" class that is a subclass of <tt><a
225href="http://llvm.cs.uiuc.edu/doxygen/structllvm_1_1FunctionPass.html">FunctionPass</a></tt>.
Chris Lattnerd6ea9262002-09-09 03:48:46 +0000[diff] [blame]226The different builtin pass subclasses are described in detail <a
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]227href="#passtype">later</a>, but for now, know that <a
228href="#FunctionPass"><tt>FunctionPass</tt></a>'s operate a function at a
229time.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]230
231<pre>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]232 <b>virtual bool</b> <a href="#runOnFunction">runOnFunction</a>(Function &amp;F) {
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]233 std::cerr &lt;&lt; "<i>Hello: </i>" &lt;&lt; F.getName() &lt;&lt; "\n";
234 <b>return false</b>;
235 }
236 }; <i>// end of struct Hello</i>
237</pre>
238
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]239<p>We declare a "<a href="#runOnFunction"><tt>runOnFunction</tt></a>" method,
240which overloads an abstract virtual method inherited from <a
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]241href="#FunctionPass"><tt>FunctionPass</tt></a>. This is where we are supposed
242to 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]243function.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]244
245<pre>
246 RegisterOpt&lt;Hello&gt; X("<i>hello</i>", "<i>Hello World Pass</i>");
247} <i>// end of anonymous namespace</i>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]248</pre>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]249
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]250<p>Lastly, we register our class <tt>Hello</tt>, giving it a command line
251argument "<tt>hello</tt>", and a name "<tt>Hello World Pass</tt>". There are
252several different ways of <a href="#registration">registering your pass</a>,
253depending on what it is to be used for. For "optimizations" we use the
254<tt>RegisterOpt</tt> template.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]255
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]256<p>As a whole, the <tt>.cpp</tt> file looks like:</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]257
258<pre>
259<b>#include</b> "<a href="http://llvm.cs.uiuc.edu/doxygen/Pass_8h-source.html">llvm/Pass.h</a>"
260<b>#include</b> "<a href="http://llvm.cs.uiuc.edu/doxygen/Function_8h-source.html">llvm/Function.h</a>"
261
262<b>namespace</b> {
263 <b>struct Hello</b> : <b>public</b> <a href="#FunctionPass">FunctionPass</a> {
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]264 <b>virtual bool</b> <a href="#runOnFunction">runOnFunction</a>(Function &amp;F) {
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]265 std::cerr &lt;&lt; "<i>Hello: </i>" &lt;&lt; F.getName() &lt;&lt; "\n";
266 <b>return false</b>;
267 }
268 };
269
270 RegisterOpt&lt;Hello&gt; X("<i>hello</i>", "<i>Hello World Pass</i>");
271}
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]272</pre>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]273
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]274<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]275command in the local directory and you should get a new
276"<tt>lib/Debug/libhello.so</tt> file. Note that everything in this file is
277contained in an anonymous namespace: this reflects the fact that passes are self
278contained units that do not need external interfaces (although they can have
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]279them) to be useful.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]280
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]281</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]282
283<!-- ======================================================================= -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]284<div class="doc_subsection">
285 <a name="running">Running a pass with <tt>opt</tt> or <tt>analyze</tt></a>
286</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]287
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]288<div class="doc_text">
289
John Criswellf9c78652004-01-26 21:26:54 +0000[diff] [blame]290<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]291<tt>opt</tt> command to run an LLVM program through your pass. Because you
292registered your pass with the <tt>RegisterOpt</tt> template, you will be able to
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]293use the <tt>opt</tt> tool to access it, once loaded.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]294
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]295<p>To test it, follow the example at the end of the <a
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]296href="GettingStarted.html">Getting Started Guide</a> to compile "Hello World" to
297LLVM. We can now run the bytecode file (<tt>hello.bc</tt>) for the program
298through our transformation like this (or course, any bytecode file will
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]299work):</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]300
301<pre>
302$ opt -load ../../../lib/Debug/libhello.so -hello &lt; hello.bc &gt; /dev/null
303Hello: __main
304Hello: puts
305Hello: main
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]306</pre>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]307
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]308<p>The '<tt>-load</tt>' option specifies that '<tt>opt</tt>' should load your
309pass as a shared object, which makes '<tt>-hello</tt>' a valid command line
310argument (which is one reason you need to <a href="#registration">register your
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]311pass</a>). Because the hello pass does not modify the program in any
312interesting way, we just throw away the result of <tt>opt</tt> (sending it to
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]313<tt>/dev/null</tt>).</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]314
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]315<p>To see what happened to the other string you registered, try running
316<tt>opt</tt> with the <tt>--help</tt> option:</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]317
318<pre>
319$ opt -load ../../../lib/Debug/libhello.so --help
320OVERVIEW: llvm .bc -&gt; .bc modular optimizer
321
322USAGE: opt [options] &lt;input bytecode&gt;
323
324OPTIONS:
325 Optimizations available:
326...
327 -funcresolve - Resolve Functions
328 -gcse - Global Common Subexpression Elimination
329 -globaldce - Dead Global Elimination
330 <b>-hello - Hello World Pass</b>
Chris Lattner065a6162003-09-10 05:29:43 +0000[diff] [blame]331 -indvars - Canonicalize Induction Variables
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]332 -inline - Function Integration/Inlining
333 -instcombine - Combine redundant instructions
334...
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]335</pre>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]336
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]337<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]338documentation to users of <tt>opt</tt>. Now that you have a working pass, you
339would go ahead and make it do the cool transformations you want. Once you get
340it all working and tested, it may become useful to find out how fast your pass
341is. The <a href="#passManager"><tt>PassManager</tt></a> provides a nice command
342line option (<tt>--time-passes</tt>) that allows you to get information about
343the execution time of your pass along with the other passes you queue up. For
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]344example:</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]345
346<pre>
347$ opt -load ../../../lib/Debug/libhello.so -hello -time-passes &lt; hello.bc &gt; /dev/null
348Hello: __main
349Hello: puts
350Hello: main
351===============================================================================
352 ... Pass execution timing report ...
353===============================================================================
354 Total Execution Time: 0.02 seconds (0.0479059 wall clock)
355
356 ---User Time--- --System Time-- --User+System-- ---Wall Time--- --- Pass Name ---
357 0.0100 (100.0%) 0.0000 ( 0.0%) 0.0100 ( 50.0%) 0.0402 ( 84.0%) Bytecode Writer
358 0.0000 ( 0.0%) 0.0100 (100.0%) 0.0100 ( 50.0%) 0.0031 ( 6.4%) Dominator Set Construction
359 0.0000 ( 0.0%) 0.0000 ( 0.0%) 0.0000 ( 0.0%) 0.0013 ( 2.7%) Module Verifier
360 <b> 0.0000 ( 0.0%) 0.0000 ( 0.0%) 0.0000 ( 0.0%) 0.0033 ( 6.9%) Hello World Pass</b>
361 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]362</pre>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]363
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]364<p>As you can see, our implementation above is pretty fast :). The additional
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]365passes listed are automatically inserted by the '<tt>opt</tt>' tool to verify
366that the LLVM emitted by your pass is still valid and well formed LLVM, which
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]367hasn't been broken somehow.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]368
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]369<p>Now that you have seen the basics of the mechanics behind passes, we can talk
370about some more details of how they work and how to use them.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]371
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]372</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]373
374<!-- *********************************************************************** -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]375<div class="doc_section">
376 <a name="passtype">Pass classes and requirements</a>
377</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]378<!-- *********************************************************************** -->
379
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]380<div class="doc_text">
381
382<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]383decide what class you should subclass for your pass. The <a
384href="#basiccode">Hello World</a> example uses the <tt><a
385href="#FunctionPass">FunctionPass</a></tt> class for its implementation, but we
386did not discuss why or when this should occur. Here we talk about the classes
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]387available, from the most general to the most specific.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]388
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]389<p>When choosing a superclass for your Pass, you should choose the <b>most
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]390specific</b> class possible, while still being able to meet the requirements
Misha Brukman5560c9d2003-08-18 14:43:39 +0000[diff] [blame]391listed. This gives the LLVM Pass Infrastructure information necessary to
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]392optimize how passes are run, so that the resultant compiler isn't unneccesarily
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]393slow.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]394
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]395</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]396
Chris Lattnerf004f9a2002-09-25 22:31:38 +0000[diff] [blame]397<!-- ======================================================================= -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]398<div class="doc_subsection">
399 <a name="ImmutablePass">The <tt>ImmutablePass</tt> class</a>
400</div>
Chris Lattnerf004f9a2002-09-25 22:31:38 +0000[diff] [blame]401
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]402<div class="doc_text">
403
404<p>The most plain and boring type of pass is the "<tt><a
405href="http://llvm.cs.uiuc.edu/doxygen/structllvm_1_1ImmutablePass.html">ImmutablePass</a></tt>"
Chris Lattnerf004f9a2002-09-25 22:31:38 +0000[diff] [blame]406class. This pass type is used for passes that do not have to be run, do not
407change state, and never need to be updated. This is not a normal type of
408transformation or analysis, but can provide information about the current
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]409compiler configuration.</p>
Chris Lattnerf004f9a2002-09-25 22:31:38 +0000[diff] [blame]410
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]411<p>Although this pass class is very infrequently used, it is important for
Chris Lattnerf004f9a2002-09-25 22:31:38 +0000[diff] [blame]412providing information about the current target machine being compiled for, and
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]413other static information that can affect the various transformations.</p>
Chris Lattnerf004f9a2002-09-25 22:31:38 +0000[diff] [blame]414
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]415<p><tt>ImmutablePass</tt>es never invalidate other transformations, are never
416invalidated, and are never "run".</p>
Chris Lattnerf004f9a2002-09-25 22:31:38 +0000[diff] [blame]417
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]418</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]419
420<!-- ======================================================================= -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]421<div class="doc_subsection">
422 <a name="Pass">The <tt>Pass</tt> class</a>
423</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]424
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]425<div class="doc_text">
426
427<p>The "<tt><a
428href="http://llvm.cs.uiuc.edu/doxygen/classllvm_1_1Pass.html">Pass</a></tt>"
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]429class is the most general of all superclasses that you can use. Deriving from
430<tt>Pass</tt> indicates that your pass uses the entire program as a unit,
431refering to function bodies in no predictable order, or adding and removing
432functions. Because nothing is known about the behavior of direct <tt>Pass</tt>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]433subclasses, no optimization can be done for their execution.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]434
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]435<p>To write a correct <tt>Pass</tt> subclass, derive from <tt>Pass</tt> and
436overload the <tt>run</tt> method with the following signature:</p>
437
438</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]439
440<!-- _______________________________________________________________________ -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]441<div class="doc_subsubsection">
442 <a name="run">The <tt>run</tt> method</a>
443</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]444
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]445<div class="doc_text">
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]446
447<pre>
448 <b>virtual bool</b> run(Module &amp;M) = 0;
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]449</pre>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]450
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]451<p>The <tt>run</tt> method performs the interesting work of the pass, and should
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]452return true if the module was modified by the transformation, false
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]453otherwise.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]454
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]455</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]456
457<!-- ======================================================================= -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]458<div class="doc_subsection">
459 <a name="FunctionPass">The <tt>FunctionPass</tt> class</a>
460</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]461
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]462<div class="doc_text">
463
464<p>In contrast to direct <tt>Pass</tt> subclasses, direct <tt><a
465href="http://llvm.cs.uiuc.edu/doxygen/classllvm_1_1Pass.html">FunctionPass</a></tt>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]466subclasses do have a predictable, local behavior that can be expected by the
467system. All <tt>FunctionPass</tt> execute on each function in the program
Misha Brukmanef6a6a62003-08-21 22:14:26 +0000[diff] [blame]468independent of all of the other functions in the program.
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]469<tt>FunctionPass</tt>'s do not require that they are executed in a particular
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]470order, and <tt>FunctionPass</tt>'s do not modify external functions.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]471
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]472<p>To be explicit, <tt>FunctionPass</tt> subclasses are not allowed to:</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]473
474<ol>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]475<li>Modify a Function other than the one currently being processed.</li>
476<li>Add or remove Function's from the current Module.</li>
477<li>Add or remove global variables from the current Module.</li>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]478<li>Maintain state across invocations of
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]479 <a href="#runOnFunction"><tt>runOnFunction</tt></a> (including global data)</li>
480</ol>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]481
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]482<p>Implementing a <tt>FunctionPass</tt> is usually straightforward (See the <a
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]483href="#basiccode">Hello World</a> pass for example). <tt>FunctionPass</tt>'s
484may overload three virtual methods to do their work. All of these methods
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]485should return true if they modified the program, or false if they didn't.</p>
486
487</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]488
489<!-- _______________________________________________________________________ -->
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]490<div class="doc_subsubsection">
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]491 <a name="doInitialization_mod">The <tt>doInitialization(Module &amp;)</tt>
492 method</a>
493</div>
494
495<div class="doc_text">
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]496
497<pre>
498 <b>virtual bool</b> doInitialization(Module &amp;M);
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]499</pre>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]500
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]501<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]502<tt>FunctionPass</tt>'s are not allowed to do. They can add and remove
Chris Lattnerd0713f92002-09-12 17:06:43 +0000[diff] [blame]503functions, get pointers to functions, etc. The <tt>doInitialization</tt> method
504is designed to do simple initialization type of stuff that does not depend on
505the functions being processed. The <tt>doInitialization</tt> method call is not
506scheduled to overlap with any other pass executions (thus it should be very
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]507fast).</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]508
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]509<p>A good example of how this method should be used is the <a
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]510href="http://llvm.cs.uiuc.edu/doxygen/LowerAllocations_8cpp-source.html">LowerAllocations</a>
511pass. This pass converts <tt>malloc</tt> and <tt>free</tt> instructions into
Misha Brukmanef6a6a62003-08-21 22:14:26 +0000[diff] [blame]512platform dependent <tt>malloc()</tt> and <tt>free()</tt> function calls. It
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]513uses the <tt>doInitialization</tt> method to get a reference to the malloc and
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]514free functions that it needs, adding prototypes to the module if necessary.</p>
515
516</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]517
518<!-- _______________________________________________________________________ -->
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]519<div class="doc_subsubsection">
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]520 <a name="runOnFunction">The <tt>runOnFunction</tt> method</a>
521</div>
522
523<div class="doc_text">
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]524
525<pre>
526 <b>virtual bool</b> runOnFunction(Function &amp;F) = 0;
527</pre><p>
528
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]529<p>The <tt>runOnFunction</tt> method must be implemented by your subclass to do
530the transformation or analysis work of your pass. As usual, a true value should
531be returned if the function is modified.</p>
532
533</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]534
535<!-- _______________________________________________________________________ -->
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]536<div class="doc_subsubsection">
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]537 <a name="doFinalization_mod">The <tt>doFinalization(Module
538 &amp;)</tt> method</a>
539</div>
540
541<div class="doc_text">
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]542
543<pre>
544 <b>virtual bool</b> doFinalization(Module &amp;M);
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]545</pre>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]546
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]547<p>The <tt>doFinalization</tt> method is an infrequently used method that is
548called when the pass framework has finished calling <a
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]549href="#runOnFunction"><tt>runOnFunction</tt></a> for every function in the
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]550program being compiled.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]551
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]552</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]553
554<!-- ======================================================================= -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]555<div class="doc_subsection">
556 <a name="BasicBlockPass">The <tt>BasicBlockPass</tt> class</a>
557</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]558
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]559<div class="doc_text">
560
561<p><tt>BasicBlockPass</tt>'s are just like <a
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]562href="#FunctionPass"><tt>FunctionPass</tt></a>'s, except that they must limit
563their scope of inspection and modification to a single basic block at a time.
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]564As such, they are <b>not</b> allowed to do any of the following:</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]565
566<ol>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]567<li>Modify or inspect any basic blocks outside of the current one</li>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]568<li>Maintain state across invocations of
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]569 <a href="#runOnBasicBlock"><tt>runOnBasicBlock</tt></a></li>
570<li>Modify the constrol flow graph (by altering terminator instructions)</li>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]571<li>Any of the things verboten for
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]572 <a href="#FunctionPass"><tt>FunctionPass</tt></a>es.</li>
573</ol>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]574
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]575<p><tt>BasicBlockPass</tt>es are useful for traditional local and "peephole"
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]576optimizations. They may override the same <a
Chris Lattnerd0713f92002-09-12 17:06:43 +0000[diff] [blame]577href="#doInitialization_mod"><tt>doInitialization(Module &amp;)</tt></a> and <a
578href="#doFinalization_mod"><tt>doFinalization(Module &amp;)</tt></a> methods that <a
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]579href="#FunctionPass"><tt>FunctionPass</tt></a>'s have, but also have the following virtual methods that may also be implemented:</p>
580
581</div>
Chris Lattnerd0713f92002-09-12 17:06:43 +0000[diff] [blame]582
583<!-- _______________________________________________________________________ -->
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]584<div class="doc_subsubsection">
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]585 <a name="doInitialization_fn">The <tt>doInitialization(Function
586 &amp;)</tt> method</a>
587</div>
588
589<div class="doc_text">
Chris Lattnerd0713f92002-09-12 17:06:43 +0000[diff] [blame]590
591<pre>
592 <b>virtual bool</b> doInitialization(Function &amp;F);
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]593</pre>
Chris Lattnerd0713f92002-09-12 17:06:43 +0000[diff] [blame]594
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]595<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]596<tt>BasicBlockPass</tt>'s are not allowed to do, but that
597<tt>FunctionPass</tt>'s can. The <tt>doInitialization</tt> method is designed
598to do simple initialization type of stuff that does not depend on the
599BasicBlocks being processed. The <tt>doInitialization</tt> method call is not
600scheduled to overlap with any other pass executions (thus it should be very
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]601fast).</p>
Chris Lattnerd0713f92002-09-12 17:06:43 +0000[diff] [blame]602
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]603</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]604
605<!-- _______________________________________________________________________ -->
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]606<div class="doc_subsubsection">
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]607 <a name="runOnBasicBlock">The <tt>runOnBasicBlock</tt> method</a>
608</div>
609
610<div class="doc_text">
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]611
612<pre>
613 <b>virtual bool</b> runOnBasicBlock(BasicBlock &amp;BB) = 0;
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]614</pre>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]615
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]616<p>Override this function to do the work of the <tt>BasicBlockPass</tt>. This
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]617function is not allowed to inspect or modify basic blocks other than the
618parameter, and are not allowed to modify the CFG. A true value must be returned
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]619if the basic block is modified.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]620
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]621</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]622
Chris Lattnerd0713f92002-09-12 17:06:43 +0000[diff] [blame]623<!-- _______________________________________________________________________ -->
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]624<div class="doc_subsubsection">
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]625 <a name="doFinalization_fn">The <tt>doFinalization(Function &amp;)</tt>
626 method</a>
627</div>
628
629<div class="doc_text">
Chris Lattnerd0713f92002-09-12 17:06:43 +0000[diff] [blame]630
631<pre>
632 <b>virtual bool</b> doFinalization(Function &amp;F);
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]633</pre>
Chris Lattnerd0713f92002-09-12 17:06:43 +0000[diff] [blame]634
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]635<p>The <tt>doFinalization</tt> method is an infrequently used method that is
636called when the pass framework has finished calling <a
Chris Lattnerd0713f92002-09-12 17:06:43 +0000[diff] [blame]637href="#runOnBasicBlock"><tt>runOnBasicBlock</tt></a> for every BasicBlock in the
638program being compiled. This can be used to perform per-function
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]639finalization.</p>
Chris Lattnerd0713f92002-09-12 17:06:43 +0000[diff] [blame]640
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]641</div>
Chris Lattnerd0713f92002-09-12 17:06:43 +0000[diff] [blame]642
Brian Gaekecab8b6f2003-07-17 18:53:20 +0000[diff] [blame]643<!-- ======================================================================= -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]644<div class="doc_subsection">
645 <a name="MachineFunctionPass">The <tt>MachineFunctionPass</tt> class</a>
646</div>
Brian Gaekecab8b6f2003-07-17 18:53:20 +0000[diff] [blame]647
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]648<div class="doc_text">
649
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]650<p>A <tt>MachineFunctionPass</tt> is a part of the LLVM code generator that
651executes on the machine-dependent representation of each LLVM function in the
652program. A <tt>MachineFunctionPass</tt> is also a <tt>FunctionPass</tt>, so all
Brian Gaekecab8b6f2003-07-17 18:53:20 +0000[diff] [blame]653the restrictions that apply to a <tt>FunctionPass</tt> also apply to it.
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]654<tt>MachineFunctionPass</tt>es also have additional restrictions. In particular,
655<tt>MachineFunctionPass</tt>es are not allowed to do any of the following:</p>
Brian Gaekecab8b6f2003-07-17 18:53:20 +0000[diff] [blame]656
657<ol>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]658<li>Modify any LLVM Instructions, BasicBlocks or Functions.</li>
659<li>Modify a MachineFunction other than the one currently being processed.</li>
660<li>Add or remove MachineFunctions from the current Module.</li>
661<li>Add or remove global variables from the current Module.</li>
662<li>Maintain state across invocations of <a
663href="#runOnMachineFunction"><tt>runOnMachineFunction</tt></a> (including global
664data)</li>
665</ol>
Brian Gaekecab8b6f2003-07-17 18:53:20 +0000[diff] [blame]666
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]667</div>
Chris Lattnerd0713f92002-09-12 17:06:43 +0000[diff] [blame]668
Brian Gaeke6a33f362003-07-22 20:53:20 +0000[diff] [blame]669<!-- _______________________________________________________________________ -->
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]670<div class="doc_subsubsection">
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]671 <a name="runOnMachineFunction">The <tt>runOnMachineFunction(MachineFunction
672 &amp;MF)</tt> method</a>
673</div>
674
675<div class="doc_text">
Brian Gaeke6a33f362003-07-22 20:53:20 +0000[diff] [blame]676
677<pre>
678 <b>virtual bool</b> runOnMachineFunction(MachineFunction &amp;MF) = 0;
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]679</pre>
Brian Gaeke6a33f362003-07-22 20:53:20 +0000[diff] [blame]680
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]681<p><tt>runOnMachineFunction</tt> can be considered the main entry point of a
682<tt>MachineFunctionPass</tt>; that is, you should override this method to do the
683work of your <tt>MachineFunctionPass</tt>.</p>
Brian Gaeke6a33f362003-07-22 20:53:20 +0000[diff] [blame]684
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]685<p>The <tt>runOnMachineFunction</tt> method is called on every
Brian Gaeke6a33f362003-07-22 20:53:20 +0000[diff] [blame]686<tt>MachineFunction</tt> in a <tt>Module</tt>, so that the
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]687<tt>MachineFunctionPass</tt> may perform optimizations on the machine-dependent
688representation of the function. If you want to get at the LLVM <tt>Function</tt>
689for the <tt>MachineFunction</tt> you're working on, use
690<tt>MachineFunction</tt>'s <tt>getFunction()</tt> accessor method -- but
691remember, you may not modify the LLVM <tt>Function</tt> or its contents from a
692<tt>MachineFunctionPass</tt>.</p>
693
694</div>
Brian Gaeke6a33f362003-07-22 20:53:20 +0000[diff] [blame]695
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]696<!-- *********************************************************************** -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]697<div class="doc_section">
698 <a name="registration">Pass registration</a>
699</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]700<!-- *********************************************************************** -->
701
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]702<div class="doc_text">
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]703
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]704<p>In the <a href="#basiccode">Hello World</a> example pass we illustrated how
705pass registration works, and discussed some of the reasons that it is used and
706what it does. Here we discuss how and why passes are registered.</p>
707
708<p>Passes can be registered in several different ways. Depending on the general
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]709classification of the pass, you should use one of the following templates to
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]710register the pass:</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]711
712<ul>
713<li><b><tt>RegisterOpt</tt></b> - This template should be used when you are
714registering a pass that logically should be available for use in the
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]715'<tt>opt</tt>' utility.</li>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]716
717<li><b><tt>RegisterAnalysis</tt></b> - This template should be used when you are
718registering a pass that logically should be available for use in the
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]719'<tt>analyze</tt>' utility.</li>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]720
721<li><b><tt>RegisterPass</tt></b> - This is the generic form of the
722<tt>Register*</tt> templates that should be used if you want your pass listed by
723multiple or no utilities. This template takes an extra third argument that
724specifies which tools it should be listed in. See the <a
725href="http://llvm.cs.uiuc.edu/doxygen/PassSupport_8h-source.html">PassSupport.h</a>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]726file for more information.</li>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]727
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]728</ul>
729
730<p>Regardless of how you register your pass, you must specify at least two
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]731parameters. The first parameter is the name of the pass that is to be used on
732the command line to specify that the pass should be added to a program (for
733example <tt>opt</tt> or <tt>analyze</tt>). The second argument is the name of
734the 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]735well as for debug output generated by the <tt>--debug-pass</tt> option.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]736
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]737<p>If a pass is registered to be used by the <tt>analyze</tt> utility, you
738should implement the virtual <tt>print</tt> method:</p>
739
740</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]741
742<!-- _______________________________________________________________________ -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]743<div class="doc_subsubsection">
744 <a name="print">The <tt>print</tt> method</a>
745</div>
746
747<div class="doc_text">
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]748
749<pre>
750 <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]751</pre>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]752
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]753<p>The <tt>print</tt> method must be implemented by "analyses" in order to print
754a human readable version of the analysis results. This is useful for debugging
755an analysis itself, as well as for other people to figure out how an analysis
756works. The <tt>analyze</tt> tool uses this method to generate its output.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]757
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]758<p>The <tt>ostream</tt> parameter specifies the stream to write the results on,
759and 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]760program that has been analyzed. Note however that this pointer may be null in
761certain circumstances (such as calling the <tt>Pass::dump()</tt> from a
762debugger), so it should only be used to enhance debug output, it should not be
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]763depended on.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]764
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]765</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]766
767<!-- *********************************************************************** -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]768<div class="doc_section">
769 <a name="interaction">Specifying interactions between passes</a>
770</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]771<!-- *********************************************************************** -->
772
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]773<div class="doc_text">
774
775<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]776that passes interact with each other correctly. Because <tt>PassManager</tt>
777tries to <a href="#passmanager">optimize the execution of passes</a> it must
778know how the passes interact with each other and what dependencies exist between
779the various passes. To track this, each pass can declare the set of passes that
780are required to be executed before the current pass, and the passes which are
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]781invalidated by the current pass.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]782
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]783<p>Typically this functionality is used to require that analysis results are
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]784computed before your pass is run. Running arbitrary transformation passes can
785invalidate the computed analysis results, which is what the invalidation set
786specifies. If a pass does not implement the <tt><a
787href="#getAnalysisUsage">getAnalysisUsage</a></tt> method, it defaults to not
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]788having any prerequisite passes, and invalidating <b>all</b> other passes.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]789
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]790</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]791
792<!-- _______________________________________________________________________ -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]793<div class="doc_subsubsection">
794 <a name="getAnalysisUsage">The <tt>getAnalysisUsage</tt> method</a>
795</div>
796
797<div class="doc_text">
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]798
799<pre>
800 <b>virtual void</b> getAnalysisUsage(AnalysisUsage &amp;Info) <b>const</b>;
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]801</pre>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]802
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]803<p>By implementing the <tt>getAnalysisUsage</tt> method, the required and
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]804invalidated sets may be specified for your transformation. The implementation
805should fill in the <tt><a
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]806href="http://llvm.cs.uiuc.edu/doxygen/classllvm_1_1AnalysisUsage.html">AnalysisUsage</a></tt>
807object with information about which passes are required and not invalidated. To
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]808do this, a pass may call any of the following methods on the AnalysisUsage
809object:</p>
810</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]811
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]812<!-- _______________________________________________________________________ -->
813<div class="doc_subsubsection">
814 <a name="AU::addRequired">The <tt>AnalysisUsage::addRequired&lt;&gt;</tt> and <tt>AnalysisUsage::addRequiredTransitive&lt;&gt;</tt> methods</a>
815</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]816
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]817<div class="doc_text">
818<p>
819If you pass requires a previous pass to be executed (an analysis for example),
820it can use one of these methods to arrange for it to be run before your pass.
821LLVM has many different types of analyses and passes that can be required,
822spaning the range from <tt>DominatorSet</tt> to <tt>BreakCriticalEdges</tt>.
823requiring <tt>BreakCriticalEdges</tt>, for example, guarantees that there will
824be no critical edges in the CFG when your pass has been run.
825</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]826
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]827<p>
828Some analyses chain to other analyses to do their job. For example, an <a
829href="AliasAnalysis.html">AliasAnalysis</a> implementation is required to <a
830href="AliasAnalysis.html#chaining">chain</a> to other alias analysis passes. In
831cases where analyses chain, the <tt>addRequiredTransitive</tt> method should be
832used instead of the <tt>addRequired</tt> method. This informs the PassManager
833that the transitively required pass should be alive as long as the requiring
834pass is.
835</p>
836</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]837
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]838<!-- _______________________________________________________________________ -->
839<div class="doc_subsubsection">
840 <a name="AU::addPreserved">The <tt>AnalysisUsage::addPreserved&lt;&gt;</tt> method</a>
841</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]842
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]843<div class="doc_text">
844<p>
845One of the jobs of the PassManager is to optimize how and when analyses are run.
846In particular, it attempts to avoid recomputing data unless it needs to. For
847this reason, passes are allowed to declare that they preserve (i.e., they don't
848invalidate) an existing analysis if it's available. For example, a simple
849constant folding pass would not modify the CFG, so it can't possible effect the
850results of dominator analysis. By default, all passes are assumed to invalidate
851all others.
852</p>
853
854<p>
855The <tt>AnalysisUsage</tt> class provides several methods which are useful in
856certain circumstances that are related to <tt>addPreserved</tt>. In particular,
857the <tt>setPreservesAll</tt> method can be called to indicate that the pass does
858not modify the LLVM program at all (which is true for analyses), and the
859<tt>setPreservesCFG</tt> method can be used by transformations that change
860instructions in the program but do not modify the CFG or terminator instructions
861(note that this property is implicitly set for <a
862href="#BasicBlockPass">BasicBlockPass</a>'s).
863</p>
864
865<p>
866<tt>addPreserved</tt> is particularly useful for transformations like
867<tt>BreakCriticalEdges</tt>. This pass knows how to update a small set of loop
868and dominator related analyses if they exist, so it can preserve them, despite
869the fact that it hacks on the CFG.
870</p>
871</div>
872
873<!-- _______________________________________________________________________ -->
874<div class="doc_subsubsection">
875 <a name="AU::examples">Example implementations of <tt>getAnalysisUsage</tt></a>
876</div>
877
878<div class="doc_text">
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]879
880<pre>
881 <i>// This is an example implementation from an analysis, which does not modify
882 // the program at all, yet has a prerequisite.</i>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]883 <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]884 AU.setPreservesAll();
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]885 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]886 }
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]887</pre>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]888
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]889<p>and:</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]890
891<pre>
892 <i>// This example modifies the program, but does not modify the CFG</i>
893 <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]894 AU.setPreservesCFG();
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]895 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]896 }
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]897</pre>
898
899</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]900
901<!-- _______________________________________________________________________ -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]902<div class="doc_subsubsection">
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]903 <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]904</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]905
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]906<div class="doc_text">
907
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]908<p>The <tt>Pass::getAnalysis&lt;&gt;</tt> method is automatically inherited by
909your class, providing you with access to the passes that you declared that you
910required with the <a href="#getAnalysisUsage"><tt>getAnalysisUsage</tt></a>
911method. It takes a single template argument that specifies which pass class you
912want, and returns a reference to that pass. For example:</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]913
914<pre>
Chris Lattnera5776302004-03-17 21:33:32 +0000[diff] [blame]915 bool LICM::runOnFunction(Function &amp;F) {
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]916 LoopInfo &amp;LI = getAnalysis&lt;LoopInfo&gt;();
917 ...
918 }
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]919</pre>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]920
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]921<p>This method call returns a reference to the pass desired. You may get a
922runtime assertion failure if you attempt to get an analysis that you did not
923declare as required in your <a
924href="#getAnalysisUsage"><tt>getAnalysisUsage</tt></a> implementation. This
925method can be called by your <tt>run*</tt> method implementation, or by any
926other local method invoked by your <tt>run*</tt> method.</p>
927
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]928<p>
929If your pass is capable of updating analyses if they exist (e.g.,
930<tt>BreakCriticalEdges</tt>, as described above), you can use the
931<tt>getAnalysisToUpdate</tt> method, which returns a pointer to the analysis if
932it is active. For example:</p>
933
934<pre>
935 ...
936 if (DominatorSet *DS = getAnalysisToUpdate&lt;DominatorSet&gt;()) {
937 <i>// A DominatorSet is active. This code will update it.</i>
938 }
939 ...
940</pre>
941
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]942</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]943
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]944<!-- *********************************************************************** -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]945<div class="doc_section">
946 <a name="analysisgroup">Implementing Analysis Groups</a>
947</div>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]948<!-- *********************************************************************** -->
949
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]950<div class="doc_text">
951
952<p>Now that we understand the basics of how passes are defined, how the are
953used, 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]954fancier. All of the pass relationships that we have seen so far are very
955simple: one pass depends on one other specific pass to be run before it can run.
956For many applications, this is great, for others, more flexibility is
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]957required.</p>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]958
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]959<p>In particular, some analyses are defined such that there is a single simple
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]960interface to the analysis results, but multiple ways of calculating them.
961Consider alias analysis for example. The most trivial alias analysis returns
962"may alias" for any alias query. The most sophisticated analysis a
963flow-sensitive, context-sensitive interprocedural analysis that can take a
964significant amount of time to execute (and obviously, there is a lot of room
965between these two extremes for other implementations). To cleanly support
966situations like this, the LLVM Pass Infrastructure supports the notion of
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]967Analysis Groups.</p>
968
969</div>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]970
971<!-- _______________________________________________________________________ -->
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]972<div class="doc_subsubsection">
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]973 <a name="agconcepts">Analysis Group Concepts</a>
974</div>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]975
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]976<div class="doc_text">
977
978<p>An Analysis Group is a single simple interface that may be implemented by
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]979multiple different passes. Analysis Groups can be given human readable names
980just like passes, but unlike passes, they need not derive from the <tt>Pass</tt>
981class. An analysis group may have one or more implementations, one of which is
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]982the "default" implementation.</p>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]983
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]984<p>Analysis groups are used by client passes just like other passes are: the
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]985<tt>AnalysisUsage::addRequired()</tt> and <tt>Pass::getAnalysis()</tt> methods.
986In order to resolve this requirement, the <a href="#passmanager">PassManager</a>
987scans the available passes to see if any implementations of the analysis group
988are available. If none is available, the default implementation is created for
989the pass to use. All standard rules for <A href="#interaction">interaction
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]990between passes</a> still apply.</p>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]991
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]992<p>Although <a href="#registration">Pass Registration</a> is optional for normal
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]993passes, all analysis group implementations must be registered, and must use the
994<A href="#registerag"><tt>RegisterAnalysisGroup</tt></a> template to join the
995implementation pool. Also, a default implementation of the interface
996<b>must</b> be registered with <A
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]997href="#registerag"><tt>RegisterAnalysisGroup</tt></a>.</p>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]998
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]999<p>As a concrete example of an Analysis Group in action, consider the <a
1000href="http://llvm.cs.uiuc.edu/doxygen/classllvm_1_1AliasAnalysis.html">AliasAnalysis</a>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1001analysis group. The default implementation of the alias analysis interface (the
1002<tt><a
1003href="http://llvm.cs.uiuc.edu/doxygen/structBasicAliasAnalysis.html">basicaa</a></tt>
1004pass) just does a few simple checks that don't require significant analysis to
1005compute (such as: two different globals can never alias each other, etc).
1006Passes that use the <tt><a
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1007href="http://llvm.cs.uiuc.edu/doxygen/classllvm_1_1AliasAnalysis.html">AliasAnalysis</a></tt>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1008interface (for example the <tt><a
Misha Brukmand15516e2004-06-03 23:39:36 +0000[diff] [blame^]1009href="http://llvm.cs.uiuc.edu/doxygen/structGCSE.html">gcse</a></tt> pass), do
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1010not care which implementation of alias analysis is actually provided, they just
1011use the designated interface.</p>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1012
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1013<p>From the user's perspective, commands work just like normal. Issuing the
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1014command '<tt>opt -gcse ...</tt>' will cause the <tt>basicaa</tt> class to be
1015instantiated and added to the pass sequence. Issuing the command '<tt>opt
1016-somefancyaa -gcse ...</tt>' will cause the <tt>gcse</tt> pass to use the
1017<tt>somefancyaa</tt> alias analysis (which doesn't actually exist, it's just a
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1018hypothetical example) instead.</p>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1019
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1020</div>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1021
1022<!-- _______________________________________________________________________ -->
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]1023<div class="doc_subsubsection">
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1024 <a name="registerag">Using <tt>RegisterAnalysisGroup</tt></a>
1025</div>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1026
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1027<div class="doc_text">
1028
1029<p>The <tt>RegisterAnalysisGroup</tt> template is used to register the analysis
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1030group itself as well as add pass implementations to the analysis group. First,
1031an analysis should be registered, with a human readable name provided for it.
1032Unlike registration of passes, there is no command line argument to be specified
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1033for the Analysis Group Interface itself, because it is "abstract":</p>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1034
1035<pre>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1036 <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>");
1037</pre>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1038
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1039<p>Once the analysis is registered, passes can declare that they are valid
1040implementations of the interface by using the following code:</p>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1041
1042<pre>
1043<b>namespace</b> {
1044 //<i> Analysis Group implementations <b>must</b> be registered normally...</i>
1045 RegisterOpt&lt;FancyAA&gt;
1046 B("<i>somefancyaa</i>", "<i>A more complex alias analysis implementation</i>");
1047
1048 //<i> Declare that we implement the AliasAnalysis interface</i>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1049 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]1050}
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1051</pre>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1052
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1053<p>This just shows a class <tt>FancyAA</tt> that is registered normally, then
1054uses the <tt>RegisterAnalysisGroup</tt> template to "join" the <tt><a
1055href="http://llvm.cs.uiuc.edu/doxygen/classllvm_1_1AliasAnalysis.html">AliasAnalysis</a></tt>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1056analysis group. Every implementation of an analysis group should join using
1057this template. A single pass may join multiple different analysis groups with
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1058no problem.</p>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1059
1060<pre>
1061<b>namespace</b> {
1062 //<i> Analysis Group implementations <b>must</b> be registered normally...</i>
1063 RegisterOpt&lt;<a href="http://llvm.cs.uiuc.edu/doxygen/structBasicAliasAnalysis.html">BasicAliasAnalysis</a>&gt;
1064 D("<i>basicaa</i>", "<i>Basic Alias Analysis (default AA impl)</i>");
1065
1066 //<i> Declare that we implement the AliasAnalysis interface</i>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1067 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]1068}
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1069</pre>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1070
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1071<p>Here we show how the default implementation is specified (using the extra
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1072argument to the <tt>RegisterAnalysisGroup</tt> template). There must be exactly
1073one default implementation available at all times for an Analysis Group to be
1074used. Here we declare that the <tt><a
1075href="http://llvm.cs.uiuc.edu/doxygen/structBasicAliasAnalysis.html">BasicAliasAnalysis</a></tt>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1076pass is the default implementation for the interface.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1077
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1078</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1079
1080<!-- *********************************************************************** -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1081<div class="doc_section">
1082 <a name="passmanager">What PassManager does</a>
1083</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1084<!-- *********************************************************************** -->
1085
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1086<div class="doc_text">
1087
1088<p>The <a
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1089href="http://llvm.cs.uiuc.edu/doxygen/PassManager_8h-source.html"><tt>PassManager</tt></a>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1090<a
1091href="http://llvm.cs.uiuc.edu/doxygen/classllvm_1_1PassManager.html">class</a>
1092takes a list of passes, ensures their <a href="#interaction">prerequisites</a>
1093are set up correctly, and then schedules passes to run efficiently. All of the
1094LLVM tools that run passes use the <tt>PassManager</tt> for execution of these
1095passes.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1096
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1097<p>The <tt>PassManager</tt> does two main things to try to reduce the execution
1098time of a series of passes:</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1099
1100<ol>
1101<li><b>Share analysis results</b> - The PassManager attempts to avoid
1102recomputing analysis results as much as possible. This means keeping track of
1103which analyses are available already, which analyses get invalidated, and which
1104analyses are needed to be run for a pass. An important part of work is that the
1105<tt>PassManager</tt> tracks the exact lifetime of all analysis results, allowing
1106it to <a href="#releaseMemory">free memory</a> allocated to holding analysis
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1107results as soon as they are no longer needed.</li>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1108
1109<li><b>Pipeline the execution of passes on the program</b> - The
1110<tt>PassManager</tt> attempts to get better cache and memory usage behavior out
1111of a series of passes by pipelining the passes together. This means that, given
1112a series of consequtive <a href="#FunctionPass"><tt>FunctionPass</tt></a>'s, it
1113will execute all of the <a href="#FunctionPass"><tt>FunctionPass</tt></a>'s on
1114the first function, then all of the <a
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1115href="#FunctionPass"><tt>FunctionPass</tt></a>es on the second function,
1116etc... until the entire program has been run through the passes.
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1117
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1118<p>This improves the cache behavior of the compiler, because it is only touching
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1119the LLVM program representation for a single function at a time, instead of
1120traversing the entire program. It reduces the memory consumption of compiler,
1121because, for example, only one <a
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1122href="http://llvm.cs.uiuc.edu/doxygen/structllvm_1_1DominatorSet.html"><tt>DominatorSet</tt></a>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1123needs to be calculated at a time. This also makes it possible some <a
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1124href="#SMP">interesting enhancements</a> in the future.</p></li>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1125
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1126</ol>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1127
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1128<p>The effectiveness of the <tt>PassManager</tt> is influenced directly by how
1129much information it has about the behaviors of the passes it is scheduling. For
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1130example, the "preserved" set is intentionally conservative in the face of an
1131unimplemented <a href="#getAnalysisUsage"><tt>getAnalysisUsage</tt></a> method.
1132Not implementing when it should be implemented will have the effect of not
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1133allowing any analysis results to live across the execution of your pass.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1134
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1135<p>The <tt>PassManager</tt> class exposes a <tt>--debug-pass</tt> command line
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1136options that is useful for debugging pass execution, seeing how things work, and
1137diagnosing when you should be preserving more analyses than you currently are
1138(To get information about all of the variants of the <tt>--debug-pass</tt>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1139option, just type '<tt>opt --help-hidden</tt>').</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1140
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1141<p>By using the <tt>--debug-pass=Structure</tt> option, for example, we can see
1142how our <a href="#basiccode">Hello World</a> pass interacts with other passes.
1143Lets try it out with the <tt>gcse</tt> and <tt>licm</tt> passes:</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1144
1145<pre>
1146$ opt -load ../../../lib/Debug/libhello.so -gcse -licm --debug-pass=Structure &lt; hello.bc &gt; /dev/null
1147Module Pass Manager
1148 Function Pass Manager
1149 Dominator Set Construction
1150 Immediate Dominators Construction
1151 Global Common Subexpression Elimination
1152-- Immediate Dominators Construction
1153-- Global Common Subexpression Elimination
1154 Natural Loop Construction
1155 Loop Invariant Code Motion
1156-- Natural Loop Construction
1157-- Loop Invariant Code Motion
1158 Module Verifier
1159-- Dominator Set Construction
1160-- Module Verifier
1161 Bytecode Writer
1162--Bytecode Writer
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1163</pre>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1164
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1165<p>This output shows us when passes are constructed and when the analysis
1166results are known to be dead (prefixed with '<tt>--</tt>'). Here we see that
1167GCSE uses dominator and immediate dominator information to do its job. The LICM
1168pass uses natural loop information, which uses dominator sets, but not immediate
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1169dominators. Because immediate dominators are no longer useful after the GCSE
1170pass, it is immediately destroyed. The dominator sets are then reused to
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1171compute natural loop information, which is then used by the LICM pass.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1172
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1173<p>After the LICM pass, the module verifier runs (which is automatically added
1174by the '<tt>opt</tt>' tool), which uses the dominator set to check that the
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1175resultant LLVM code is well formed. After it finishes, the dominator set
1176information is destroyed, after being computed once, and shared by three
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1177passes.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1178
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1179<p>Lets see how this changes when we run the <a href="#basiccode">Hello
1180World</a> pass in between the two passes:</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1181
1182<pre>
1183$ opt -load ../../../lib/Debug/libhello.so -gcse -hello -licm --debug-pass=Structure &lt; hello.bc &gt; /dev/null
1184Module Pass Manager
1185 Function Pass Manager
1186 Dominator Set Construction
1187 Immediate Dominators Construction
1188 Global Common Subexpression Elimination
1189<b>-- Dominator Set Construction</b>
1190-- Immediate Dominators Construction
1191-- Global Common Subexpression Elimination
1192<b> Hello World Pass
1193-- Hello World Pass
1194 Dominator Set Construction</b>
1195 Natural Loop Construction
1196 Loop Invariant Code Motion
1197-- Natural Loop Construction
1198-- Loop Invariant Code Motion
1199 Module Verifier
1200-- Dominator Set Construction
1201-- Module Verifier
1202 Bytecode Writer
1203--Bytecode Writer
1204Hello: __main
1205Hello: puts
1206Hello: main
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1207</pre>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1208
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1209<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]1210Dominator Set pass, even though it doesn't modify the code at all! To fix this,
1211we need to add the following <a
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1212href="#getAnalysisUsage"><tt>getAnalysisUsage</tt></a> method to our pass:</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1213
1214<pre>
1215 <i>// We don't modify the program, so we preserve all analyses</i>
1216 <b>virtual void</b> getAnalysisUsage(AnalysisUsage &amp;AU) <b>const</b> {
1217 AU.setPreservesAll();
1218 }
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1219</pre>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1220
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1221<p>Now when we run our pass, we get this output:</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1222
1223<pre>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1224$ 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]1225Pass Arguments: -gcse -hello -licm
1226Module Pass Manager
1227 Function Pass Manager
1228 Dominator Set Construction
1229 Immediate Dominators Construction
1230 Global Common Subexpression Elimination
1231-- Immediate Dominators Construction
1232-- Global Common Subexpression Elimination
1233 Hello World Pass
1234-- Hello World Pass
1235 Natural Loop Construction
1236 Loop Invariant Code Motion
1237-- Loop Invariant Code Motion
1238-- Natural Loop Construction
1239 Module Verifier
1240-- Dominator Set Construction
1241-- Module Verifier
1242 Bytecode Writer
1243--Bytecode Writer
1244Hello: __main
1245Hello: puts
1246Hello: main
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1247</pre>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1248
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1249<p>Which shows that we don't accidentally invalidate dominator information
1250anymore, and therefore do not have to compute it twice.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1251
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1252</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1253
1254<!-- _______________________________________________________________________ -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1255<div class="doc_subsubsection">
1256 <a name="releaseMemory">The <tt>releaseMemory</tt> method</a>
1257</div>
1258
1259<div class="doc_text">
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1260
1261<pre>
1262 <b>virtual void</b> releaseMemory();
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1263</pre>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1264
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1265<p>The <tt>PassManager</tt> automatically determines when to compute analysis
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1266results, and how long to keep them around for. Because the lifetime of the pass
1267object itself is effectively the entire duration of the compilation process, we
1268need some way to free analysis results when they are no longer useful. The
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1269<tt>releaseMemory</tt> virtual method is the way to do this.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1270
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1271<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]1272amount of state (for use by another pass which "requires" your pass and uses the
1273<a href="#getAnalysis">getAnalysis</a> method) you should implement
1274<tt>releaseMEmory</tt> to, well, release the memory allocated to maintain this
1275internal state. This method is called after the <tt>run*</tt> method for the
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1276class, before the next call of <tt>run*</tt> in 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</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1279
1280<!-- *********************************************************************** -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1281<div class="doc_section">
1282 <a name="debughints">Using GDB with dynamically loaded passes</a>
1283</div>
Chris Lattner480e2ef2002-09-06 02:02:58 +0000[diff] [blame]1284<!-- *********************************************************************** -->
1285
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1286<div class="doc_text">
1287
1288<p>Unfortunately, using GDB with dynamically loaded passes is not as easy as it
Chris Lattner480e2ef2002-09-06 02:02:58 +0000[diff] [blame]1289should be. First of all, you can't set a breakpoint in a shared object that has
1290not been loaded yet, and second of all there are problems with inlined functions
1291in shared objects. Here are some suggestions to debugging your pass with
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1292GDB.</p>
Chris Lattner480e2ef2002-09-06 02:02:58 +0000[diff] [blame]1293
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1294<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]1295transformation invoked by <tt>opt</tt>, although nothing described here depends
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1296on that.</p>
1297
1298</div>
Chris Lattner480e2ef2002-09-06 02:02:58 +0000[diff] [blame]1299
1300<!-- _______________________________________________________________________ -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1301<div class="doc_subsubsection">
1302 <a name="breakpoint">Setting a breakpoint in your pass</a>
1303</div>
Chris Lattner480e2ef2002-09-06 02:02:58 +0000[diff] [blame]1304
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1305<div class="doc_text">
1306
1307<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]1308
1309<pre>
1310$ <b>gdb opt</b>
1311GNU gdb 5.0
1312Copyright 2000 Free Software Foundation, Inc.
1313GDB is free software, covered by the GNU General Public License, and you are
1314welcome to change it and/or distribute copies of it under certain conditions.
1315Type "show copying" to see the conditions.
1316There is absolutely no warranty for GDB. Type "show warranty" for details.
1317This GDB was configured as "sparc-sun-solaris2.6"...
1318(gdb)
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1319</pre>
Chris Lattner480e2ef2002-09-06 02:02:58 +0000[diff] [blame]1320
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1321<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]1322time to load. Be patient. Since we cannot set a breakpoint in our pass yet
1323(the shared object isn't loaded until runtime), we must execute the process, and
1324have it stop before it invokes our pass, but after it has loaded the shared
1325object. The most foolproof way of doing this is to set a breakpoint in
1326<tt>PassManager::run</tt> and then run the process with the arguments you
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1327want:</p>
Chris Lattner480e2ef2002-09-06 02:02:58 +0000[diff] [blame]1328
1329<pre>
1330(gdb) <b>break PassManager::run</b>
1331Breakpoint 1 at 0x2413bc: file Pass.cpp, line 70.
Chris Lattnerfafe6302003-10-23 19:48:11 +0000[diff] [blame]1332(gdb) <b>run test.bc -load $(LLVMTOP)/llvm/lib/Debug/[libname].so -[passoption]</b>
1333Starting program: opt test.bc -load $(LLVMTOP)/llvm/lib/Debug/[libname].so -[passoption]
Chris Lattner480e2ef2002-09-06 02:02:58 +0000[diff] [blame]1334Breakpoint 1, PassManager::run (this=0xffbef174, M=@0x70b298) at Pass.cpp:70
133570 bool PassManager::run(Module &amp;M) { return PM-&gt;run(M); }
1336(gdb)
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1337</pre>
Chris Lattner480e2ef2002-09-06 02:02:58 +0000[diff] [blame]1338
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1339<p>Once the <tt>opt</tt> stops in the <tt>PassManager::run</tt> method you are
1340now free to set breakpoints in your pass so that you can trace through execution
1341or do other standard debugging stuff.</p>
Chris Lattner480e2ef2002-09-06 02:02:58 +0000[diff] [blame]1342
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1343</div>
Chris Lattner480e2ef2002-09-06 02:02:58 +0000[diff] [blame]1344
1345<!-- _______________________________________________________________________ -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1346<div class="doc_subsubsection">
1347 <a name="debugmisc">Miscellaneous Problems</a>
1348</div>
Chris Lattner480e2ef2002-09-06 02:02:58 +0000[diff] [blame]1349
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1350<div class="doc_text">
1351
1352<p>Once you have the basics down, there are a couple of problems that GDB has,
1353some with solutions, some without.</p>
Chris Lattner480e2ef2002-09-06 02:02:58 +0000[diff] [blame]1354
1355<ul>
1356<li>Inline functions have bogus stack information. In general, GDB does a
1357pretty good job getting stack traces and stepping through inline functions.
1358When a pass is dynamically loaded however, it somehow completely loses this
1359capability. The only solution I know of is to de-inline a function (move it
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1360from the body of a class to a .cpp file).</li>
Chris Lattner480e2ef2002-09-06 02:02:58 +0000[diff] [blame]1361
1362<li>Restarting the program breaks breakpoints. After following the information
1363above, you have succeeded in getting some breakpoints planted in your pass. Nex
1364thing you know, you restart the program (i.e., you type '<tt>run</tt>' again),
1365and you start getting errors about breakpoints being unsettable. The only way I
1366have found to "fix" this problem is to <tt>delete</tt> the breakpoints that are
1367already set in your pass, run the program, and re-set the breakpoints once
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1368execution stops in <tt>PassManager::run</tt>.</li>
Chris Lattner480e2ef2002-09-06 02:02:58 +0000[diff] [blame]1369
1370</ul>
1371
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1372<p>Hopefully these tips will help with common case debugging situations. If
1373you'd like to contribute some tips of your own, just contact <a
1374href="mailto:sabre@nondot.org">Chris</a>.</p>
Chris Lattner480e2ef2002-09-06 02:02:58 +0000[diff] [blame]1375
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1376</div>
Chris Lattner480e2ef2002-09-06 02:02:58 +0000[diff] [blame]1377
1378<!-- *********************************************************************** -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1379<div class="doc_section">
1380 <a name="future">Future extensions planned</a>
1381</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1382<!-- *********************************************************************** -->
1383
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1384<div class="doc_text">
1385
1386<p>Although the LLVM Pass Infrastructure is very capable as it stands, and does
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1387some 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]1388where we are going:</p>
1389
1390</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1391
1392<!-- _______________________________________________________________________ -->
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]1393<div class="doc_subsubsection">
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1394 <a name="SMP">Multithreaded LLVM</a>
1395</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1396
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1397<div class="doc_text">
1398
1399<p>Multiple CPU machines are becoming more common and compilation can never be
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1400fast enough: obviously we should allow for a multithreaded compiler. Because of
1401the semantics defined for passes above (specifically they cannot maintain state
1402across invocations of their <tt>run*</tt> methods), a nice clean way to
1403implement a multithreaded compiler would be for the <tt>PassManager</tt> class
Misha Brukmanbc0e9982003-07-14 17:20:40 +0000[diff] [blame]1404to create multiple instances of each pass object, and allow the separate
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1405instances to be hacking on different parts of the program at the same time.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1406
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1407<p>This implementation would prevent each of the passes from having to implement
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1408multithreaded constructs, requiring only the LLVM core to have locking in a few
1409places (for global resources). Although this is a simple extension, we simply
1410haven't had time (or multiprocessor machines, thus a reason) to implement this.
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1411Despite that, we have kept the LLVM passes SMP ready, and you should too.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1412
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1413</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1414
1415<!-- _______________________________________________________________________ -->
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]1416<div class="doc_subsubsection">
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1417 <a name="ModuleSource">A new <tt>ModuleSource</tt> interface</a>
1418</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1419
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1420<div class="doc_text">
1421
1422<p>Currently, the <tt>PassManager</tt>'s <tt>run</tt> method takes a <tt><a
1423href="http://llvm.cs.uiuc.edu/doxygen/structllvm_1_1Module.html">Module</a></tt>
1424as input, and runs all of the passes on this module. The problem with this
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1425approach is that none of the <tt>PassManager</tt> features can be used for
1426timing and debugging the actual <b>loading</b> of the module from disk or
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1427standard input.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1428
Misha Brukmanefc182e2004-03-08 23:06:46 +0000[diff] [blame]1429<p>To solve this problem, eventually the <tt>PassManager</tt> class will accept
1430a <tt>ModuleSource</tt> object instead of a Module itself. When complete, this
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1431will also allow for streaming of functions out of the bytecode representation,
1432allowing us to avoid holding the entire program in memory at once if we only are
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1433dealing with <a href="#FunctionPass">FunctionPass</a>es.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1434
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1435<p>As part of a different issue, eventually the bytecode loader will be extended
1436to allow on-demand loading of functions from the bytecode representation, in
1437order to better support the runtime reoptimizer. The bytecode format is already
1438capable of this, the loader just needs to be reworked a bit.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1439
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1440</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1441
1442<!-- _______________________________________________________________________ -->
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]1443<div class="doc_subsubsection">
Misha Brukmanefc182e2004-03-08 23:06:46 +0000[diff] [blame]1444<a name="PassFunctionPass"><tt>Pass</tt>es requiring <tt>FunctionPass</tt>es</a>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1445</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1446
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1447<div class="doc_text">
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1448
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1449<p>Currently it is illegal for a <a href="#Pass"><tt>Pass</tt></a> to require a
1450<a href="#FunctionPass"><tt>FunctionPass</tt></a>. This is because there is
1451only one instance of the <a href="#FunctionPass"><tt>FunctionPass</tt></a>
1452object ever created, thus nowhere to store information for all of the functions
1453in the program at the same time. Although this has come up a couple of times
1454before, this has always been worked around by factoring one big complicated pass
1455into a global and an interprocedural part, both of which are distinct. In the
1456future, it would be nice to have this though.</p>
1457
1458<p>Note that it is no problem for a <a
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1459href="#FunctionPass"><tt>FunctionPass</tt></a> to require the results of a <a
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1460href="#Pass"><tt>Pass</tt></a>, only the other way around.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1461
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1462</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1463
1464<!-- *********************************************************************** -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1465<hr>
1466<address>
1467 <a href="http://jigsaw.w3.org/css-validator/check/referer"><img
1468 src="http://jigsaw.w3.org/css-validator/images/vcss" alt="Valid CSS!"></a>
1469 <a href="http://validator.w3.org/check/referer"><img
1470 src="http://www.w3.org/Icons/valid-html401" alt="Valid HTML 4.01!" /></a>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1471
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1472 <a href="mailto:sabre@nondot.org">Chris Lattner</a><br>
1473 <a href="http://llvm.cs.uiuc.edu">The LLVM Compiler Infrastructure</a><br>
1474 Last modified: $Date$
1475</address>
1476
1477</body>
1478</html>