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gerrit-public.fairphone.software / fp2-dev / platform / external / llvm / 8fdb246fb1eaa2f94ea9aecb06a7e1f210d1cd26 / . / docs / WritingAnLLVMPass.html
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4<head>
5 <title>Writing an LLVM Pass</title>
6 <link rel="stylesheet" href="llvm.css" type="text/css">
7</head>
8<body>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]9
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]10<div class="doc_title">
11 Writing an LLVM Pass
12</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]13
14<ol>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]15 <li><a href="#introduction">Introduction - What is a pass?</a></li>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]16 <li><a href="#quickstart">Quick Start - Writing hello world</a>
17 <ul>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]18 <li><a href="#makefile">Setting up the build environment</a></li>
19 <li><a href="#basiccode">Basic code required</a></li>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]20 <li><a href="#running">Running a pass with <tt>opt</tt>
Chris Lattner8fdb2462004-09-18 06:39:35 +0000[diff] [blame^]21 or <tt>analyze</tt></a></li>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]22 </ul></li>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]23 <li><a href="#passtype">Pass classes and requirements</a>
24 <ul>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]25 <li><a href="#ImmutablePass">The <tt>ImmutablePass</tt> class</a></li>
Chris 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 Lattner8fdb2462004-09-18 06:39:35 +0000[diff] [blame^]30 <li><a href="#CallGraphSCCPass">The <tt>CallGraphSCCPass</tt> class</a>
31 <ul>
32 <li><a href="#doInitialization_scc">The <tt>doInitialization(Module
33 &amp;)</tt> method</a></li>
34 <li><a href="#runOnSCC">The <tt>runOnSCC</tt> method</a></li>
35 <li><a href="#doFinalization_scc">The <tt>doFinalization(Module
36 &amp;)</tt> method</a></li>
37 </ul></li>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]38 <li><a href="#FunctionPass">The <tt>FunctionPass</tt> class</a>
39 <ul>
Chris Lattnerd0713f92002-09-12 17:06:43 +0000[diff] [blame]40 <li><a href="#doInitialization_mod">The <tt>doInitialization(Module
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]41 &amp;)</tt> method</a></li>
42 <li><a href="#runOnFunction">The <tt>runOnFunction</tt> method</a></li>
Chris Lattnerd0713f92002-09-12 17:06:43 +0000[diff] [blame]43 <li><a href="#doFinalization_mod">The <tt>doFinalization(Module
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]44 &amp;)</tt> method</a></li>
45 </ul></li>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]46 <li><a href="#BasicBlockPass">The <tt>BasicBlockPass</tt> class</a>
47 <ul>
Chris Lattnerd0713f92002-09-12 17:06:43 +0000[diff] [blame]48 <li><a href="#doInitialization_fn">The <tt>doInitialization(Function
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]49 &amp;)</tt> method</a></li>
50 <li><a href="#runOnBasicBlock">The <tt>runOnBasicBlock</tt>
51 method</a></li>
Chris Lattnerd0713f92002-09-12 17:06:43 +0000[diff] [blame]52 <li><a href="#doFinalization_fn">The <tt>doFinalization(Function
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]53 &amp;)</tt> method</a></li>
54 </ul></li>
Brian Gaekecab8b6f2003-07-17 18:53:20 +0000[diff] [blame]55 <li><a href="#MachineFunctionPass">The <tt>MachineFunctionPass</tt>
56 class</a>
Brian Gaeke6a33f362003-07-22 20:53:20 +0000[diff] [blame]57 <ul>
58 <li><a href="#runOnMachineFunction">The
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]59 <tt>runOnMachineFunction(MachineFunction &amp;)</tt> method</a></li>
60 </ul></li>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]61 </ul>
62 <li><a href="#registration">Pass Registration</a>
63 <ul>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]64 <li><a href="#print">The <tt>print</tt> method</a></li>
65 </ul></li>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]66 <li><a href="#interaction">Specifying interactions between passes</a>
67 <ul>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]68 <li><a href="#getAnalysisUsage">The <tt>getAnalysisUsage</tt>
69 method</a></li>
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]70 <li><a href="#AU::addRequired">The <tt>AnalysisUsage::addRequired&lt;&gt;</tt> and <tt>AnalysisUsage::addRequiredTransitive&lt;&gt;</tt> methods</a></li>
71 <li><a href="#AU::addPreserved">The <tt>AnalysisUsage::addPreserved&lt;&gt;</tt> method</a></li>
72 <li><a href="#AU::examples">Example implementations of <tt>getAnalysisUsage</tt></a></li>
73 <li><a href="#getAnalysis">The <tt>getAnalysis&lt;&gt;</tt> and <tt>getAnalysisToUpdate&lt;&gt;</tt> methods</a></li>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]74 </ul></li>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]75 <li><a href="#analysisgroup">Implementing Analysis Groups</a>
76 <ul>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]77 <li><a href="#agconcepts">Analysis Group Concepts</a></li>
78 <li><a href="#registerag">Using <tt>RegisterAnalysisGroup</tt></a></li>
79 </ul></li>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]80 <li><a href="#passmanager">What PassManager does</a>
81 <ul>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]82 <li><a href="#releaseMemory">The <tt>releaseMemory</tt> method</a></li>
83 </ul></li>
Chris Lattner480e2ef2002-09-06 02:02:58 +0000[diff] [blame]84 <li><a href="#debughints">Using GDB with dynamically loaded passes</a>
85 <ul>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]86 <li><a href="#breakpoint">Setting a breakpoint in your pass</a></li>
87 <li><a href="#debugmisc">Miscellaneous Problems</a></li>
88 </ul></li>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]89 <li><a href="#future">Future extensions planned</a>
90 <ul>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]91 <li><a href="#SMP">Multithreaded LLVM</a></li>
92 <li><a href="#ModuleSource">A new <tt>ModuleSource</tt> interface</a></li>
93 <li><a href="#PassFunctionPass"><tt>Pass</tt>es requiring
94 <tt>FunctionPass</tt>es</a></li>
95 </ul></li>
96</ol>
Chris Lattner38c633d2002-08-08 20:23:41 +0000[diff] [blame]97
Chris Lattner7911ce22004-05-23 21:07:27 +0000[diff] [blame]98<div class="doc_author">
99 <p>Written by <a href="mailto:sabre@nondot.org">Chris Lattner</a></p>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]100</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]101
102<!-- *********************************************************************** -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]103<div class="doc_section">
104 <a name="introduction">Introduction - What is a pass?</a>
105</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]106<!-- *********************************************************************** -->
107
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]108<div class="doc_text">
109
110<p>The LLVM Pass Framework is an important part of the LLVM system, because LLVM
Chris Lattner8fdb2462004-09-18 06:39:35 +0000[diff] [blame^]111passes are where most of the interesting parts of the compiler exist. Passes
112perform the transformations and optimizations that make up the compiler, they
113build the analysis results that are used by these transformations, and they are,
114above all, a structuring technique for compiler code.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]115
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]116<p>All LLVM passes are subclasses of the <tt><a
117href="http://llvm.cs.uiuc.edu/doxygen/classllvm_1_1Pass.html">Pass</a></tt>
118class, which implement functionality by overriding virtual methods inherited
119from <tt>Pass</tt>. Depending on how your pass works, you may be able to
Chris Lattner8fdb2462004-09-18 06:39:35 +0000[diff] [blame^]120inherit from the <tt><a href="#CallGraphSCCPass">CallGraphSCCPass</a></tt>,
121<tt><a href="#FunctionPass">FunctionPass</a></tt>, or <tt><a
122href="#BasicBlockPass">BasicBlockPass</a></tt> classes, which gives the system
123more information about what your pass does, and how it can be combined with
124other passes. One of the main features of the LLVM Pass Framework is that it
125schedules passes to run in an efficient way based on the constraints that your
126pass meets (which are indicated by which class they derive from).</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]127
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]128<p>We start by showing you how to construct a pass, everything from setting up
129the code, to compiling, loading, and executing it. After the basics are down,
130more advanced features are discussed.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]131
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]132</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]133
134<!-- *********************************************************************** -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]135<div class="doc_section">
136 <a name="quickstart">Quick Start - Writing hello world</a>
137</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]138<!-- *********************************************************************** -->
139
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]140<div class="doc_text">
141
142<p>Here we describe how to write the "hello world" of passes. The "Hello" pass
143is designed to simply print out the name of non-external functions that exist in
Chris Lattner8fdb2462004-09-18 06:39:35 +0000[diff] [blame^]144the program being compiled. It does not modify the program at all, it just
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]145inspects it. The source code and files for this pass are available in the LLVM
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]146source tree in the <tt>lib/Transforms/Hello</tt> directory.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]147
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]148</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]149
150<!-- ======================================================================= -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]151<div class="doc_subsection">
152 <a name="makefile">Setting up the build environment</a>
153</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]154
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]155<div class="doc_text">
156
157<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]158source base. For this example, we'll assume that you made
159"<tt>lib/Transforms/Hello</tt>". The first thing you must do is set up a build
160script (Makefile) that will compile the source code for the new pass. To do
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]161this, copy this into "<tt>Makefile</tt>":</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]162
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]163<hr>
164
165<pre>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]166# Makefile for hello pass
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]167
Chris Lattner17a4c3e2002-08-14 20:06:13 +0000[diff] [blame]168# Path to top level of LLVM heirarchy
Chris Lattner7ce83e52002-08-14 20:07:01 +0000[diff] [blame]169LEVEL = ../../..
Chris Lattner17a4c3e2002-08-14 20:06:13 +0000[diff] [blame]170
171# Name of the library to build
Chris Lattner7ce83e52002-08-14 20:07:01 +0000[diff] [blame]172LIBRARYNAME = hello
Chris Lattner17a4c3e2002-08-14 20:06:13 +0000[diff] [blame]173
174# Build a dynamically loadable shared object
175SHARED_LIBRARY = 1
176
177# Include the makefile implementation stuff
178include $(LEVEL)/Makefile.common
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]179</pre>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]180
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]181<p>This makefile specifies that all of the <tt>.cpp</tt> files in the current
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]182directory are to be compiled and linked together into a
183<tt>lib/Debug/libhello.so</tt> shared object that can be dynamically loaded by
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]184the <tt>opt</tt> or <tt>analyze</tt> tools. If your operating system uses a
Chris Lattner8fdb2462004-09-18 06:39:35 +0000[diff] [blame^]185suffix other than .so (such as windows or Mac OS/X), the appropriate extension
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]186will be used.</p>
John Criswellf9c78652004-01-26 21:26:54 +0000[diff] [blame]187
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]188<p>Now that we have the build scripts set up, we just need to write the code for
189the pass itself.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]190
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]191</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]192
193<!-- ======================================================================= -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]194<div class="doc_subsection">
195 <a name="basiccode">Basic code required</a>
196</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]197
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]198<div class="doc_text">
199
200<p>Now that we have a way to compile our new pass, we just have to write it.
201Start out with:</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]202
203<pre>
204<b>#include</b> "<a href="http://llvm.cs.uiuc.edu/doxygen/Pass_8h-source.html">llvm/Pass.h</a>"
205<b>#include</b> "<a href="http://llvm.cs.uiuc.edu/doxygen/Function_8h-source.html">llvm/Function.h</a>"
206</pre>
207
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]208<p>Which are needed because we are writing a <tt><a
209href="http://llvm.cs.uiuc.edu/doxygen/classllvm_1_1Pass.html">Pass</a></tt>, and
210we are operating on <tt><a
211href="http://llvm.cs.uiuc.edu/doxygen/classllvm_1_1Function.html">Function</a></tt>'s.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]212
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]213<p>Next we have:</p>
Jonathan Manton65acb302004-06-30 18:10:30 +0000[diff] [blame]214<pre>
215<b>using namespace llvm;</b>
216</pre>
217<p>... which is required because the functions from the include files
218live in the llvm namespace.
219</p>
220
221<p>Next we have:</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]222
223<pre>
224<b>namespace</b> {
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]225</pre>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]226
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]227<p>... which starts out an anonymous namespace. Anonymous namespaces are to C++
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]228what the "<tt>static</tt>" keyword is to C (at global scope). It makes the
229things declared inside of the anonymous namespace only visible to the current
230file. If you're not familiar with them, consult a decent C++ book for more
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]231information.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]232
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]233<p>Next, we declare our pass itself:</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]234
235<pre>
236 <b>struct</b> Hello : <b>public</b> <a href="#FunctionPass">FunctionPass</a> {
237</pre><p>
238
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]239<p>This declares a "<tt>Hello</tt>" class that is a subclass of <tt><a
240href="http://llvm.cs.uiuc.edu/doxygen/structllvm_1_1FunctionPass.html">FunctionPass</a></tt>.
Chris Lattnerd6ea9262002-09-09 03:48:46 +0000[diff] [blame]241The different builtin pass subclasses are described in detail <a
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]242href="#passtype">later</a>, but for now, know that <a
243href="#FunctionPass"><tt>FunctionPass</tt></a>'s operate a function at a
244time.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]245
246<pre>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]247 <b>virtual bool</b> <a href="#runOnFunction">runOnFunction</a>(Function &amp;F) {
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]248 std::cerr &lt;&lt; "<i>Hello: </i>" &lt;&lt; F.getName() &lt;&lt; "\n";
249 <b>return false</b>;
250 }
251 }; <i>// end of struct Hello</i>
252</pre>
253
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]254<p>We declare a "<a href="#runOnFunction"><tt>runOnFunction</tt></a>" method,
255which overloads an abstract virtual method inherited from <a
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]256href="#FunctionPass"><tt>FunctionPass</tt></a>. This is where we are supposed
257to do our thing, so we just print out our message with the name of each
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]258function.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]259
260<pre>
261 RegisterOpt&lt;Hello&gt; X("<i>hello</i>", "<i>Hello World Pass</i>");
262} <i>// end of anonymous namespace</i>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]263</pre>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]264
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]265<p>Lastly, we register our class <tt>Hello</tt>, giving it a command line
266argument "<tt>hello</tt>", and a name "<tt>Hello World Pass</tt>". There are
267several different ways of <a href="#registration">registering your pass</a>,
268depending on what it is to be used for. For "optimizations" we use the
269<tt>RegisterOpt</tt> template.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]270
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]271<p>As a whole, the <tt>.cpp</tt> file looks like:</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]272
273<pre>
274<b>#include</b> "<a href="http://llvm.cs.uiuc.edu/doxygen/Pass_8h-source.html">llvm/Pass.h</a>"
275<b>#include</b> "<a href="http://llvm.cs.uiuc.edu/doxygen/Function_8h-source.html">llvm/Function.h</a>"
276
Jonathan Manton65acb302004-06-30 18:10:30 +0000[diff] [blame]277<b>using namespace llvm;</b>
278
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]279<b>namespace</b> {
280 <b>struct Hello</b> : <b>public</b> <a href="#FunctionPass">FunctionPass</a> {
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]281 <b>virtual bool</b> <a href="#runOnFunction">runOnFunction</a>(Function &amp;F) {
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]282 std::cerr &lt;&lt; "<i>Hello: </i>" &lt;&lt; F.getName() &lt;&lt; "\n";
283 <b>return false</b>;
284 }
285 };
286
287 RegisterOpt&lt;Hello&gt; X("<i>hello</i>", "<i>Hello World Pass</i>");
288}
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]289</pre>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]290
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]291<p>Now that it's all together, compile the file with a simple "<tt>gmake</tt>"
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]292command in the local directory and you should get a new
293"<tt>lib/Debug/libhello.so</tt> file. Note that everything in this file is
294contained in an anonymous namespace: this reflects the fact that passes are self
295contained units that do not need external interfaces (although they can have
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]296them) to be useful.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]297
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]298</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]299
300<!-- ======================================================================= -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]301<div class="doc_subsection">
302 <a name="running">Running a pass with <tt>opt</tt> or <tt>analyze</tt></a>
303</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]304
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]305<div class="doc_text">
306
John Criswellf9c78652004-01-26 21:26:54 +0000[diff] [blame]307<p>Now that you have a brand new shiny shared object file, we can use the
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]308<tt>opt</tt> command to run an LLVM program through your pass. Because you
309registered your pass with the <tt>RegisterOpt</tt> template, you will be able to
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]310use the <tt>opt</tt> tool to access it, once loaded.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]311
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]312<p>To test it, follow the example at the end of the <a
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]313href="GettingStarted.html">Getting Started Guide</a> to compile "Hello World" to
314LLVM. We can now run the bytecode file (<tt>hello.bc</tt>) for the program
315through our transformation like this (or course, any bytecode file will
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]316work):</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]317
318<pre>
319$ opt -load ../../../lib/Debug/libhello.so -hello &lt; hello.bc &gt; /dev/null
320Hello: __main
321Hello: puts
322Hello: main
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]323</pre>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]324
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]325<p>The '<tt>-load</tt>' option specifies that '<tt>opt</tt>' should load your
326pass as a shared object, which makes '<tt>-hello</tt>' a valid command line
327argument (which is one reason you need to <a href="#registration">register your
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]328pass</a>). Because the hello pass does not modify the program in any
329interesting way, we just throw away the result of <tt>opt</tt> (sending it to
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]330<tt>/dev/null</tt>).</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]331
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]332<p>To see what happened to the other string you registered, try running
333<tt>opt</tt> with the <tt>--help</tt> option:</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]334
335<pre>
336$ opt -load ../../../lib/Debug/libhello.so --help
337OVERVIEW: llvm .bc -&gt; .bc modular optimizer
338
339USAGE: opt [options] &lt;input bytecode&gt;
340
341OPTIONS:
342 Optimizations available:
343...
344 -funcresolve - Resolve Functions
345 -gcse - Global Common Subexpression Elimination
346 -globaldce - Dead Global Elimination
347 <b>-hello - Hello World Pass</b>
Chris Lattner065a6162003-09-10 05:29:43 +0000[diff] [blame]348 -indvars - Canonicalize Induction Variables
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]349 -inline - Function Integration/Inlining
350 -instcombine - Combine redundant instructions
351...
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]352</pre>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]353
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]354<p>The pass name get added as the information string for your pass, giving some
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]355documentation to users of <tt>opt</tt>. Now that you have a working pass, you
356would go ahead and make it do the cool transformations you want. Once you get
357it all working and tested, it may become useful to find out how fast your pass
358is. The <a href="#passManager"><tt>PassManager</tt></a> provides a nice command
359line option (<tt>--time-passes</tt>) that allows you to get information about
360the execution time of your pass along with the other passes you queue up. For
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]361example:</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]362
363<pre>
364$ opt -load ../../../lib/Debug/libhello.so -hello -time-passes &lt; hello.bc &gt; /dev/null
365Hello: __main
366Hello: puts
367Hello: main
368===============================================================================
369 ... Pass execution timing report ...
370===============================================================================
371 Total Execution Time: 0.02 seconds (0.0479059 wall clock)
372
373 ---User Time--- --System Time-- --User+System-- ---Wall Time--- --- Pass Name ---
374 0.0100 (100.0%) 0.0000 ( 0.0%) 0.0100 ( 50.0%) 0.0402 ( 84.0%) Bytecode Writer
375 0.0000 ( 0.0%) 0.0100 (100.0%) 0.0100 ( 50.0%) 0.0031 ( 6.4%) Dominator Set Construction
376 0.0000 ( 0.0%) 0.0000 ( 0.0%) 0.0000 ( 0.0%) 0.0013 ( 2.7%) Module Verifier
377 <b> 0.0000 ( 0.0%) 0.0000 ( 0.0%) 0.0000 ( 0.0%) 0.0033 ( 6.9%) Hello World Pass</b>
378 0.0100 (100.0%) 0.0100 (100.0%) 0.0200 (100.0%) 0.0479 (100.0%) TOTAL
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]379</pre>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]380
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]381<p>As you can see, our implementation above is pretty fast :). The additional
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]382passes listed are automatically inserted by the '<tt>opt</tt>' tool to verify
383that the LLVM emitted by your pass is still valid and well formed LLVM, which
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]384hasn't been broken somehow.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]385
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]386<p>Now that you have seen the basics of the mechanics behind passes, we can talk
387about some more details of how they work and how to use them.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]388
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]389</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]390
391<!-- *********************************************************************** -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]392<div class="doc_section">
393 <a name="passtype">Pass classes and requirements</a>
394</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]395<!-- *********************************************************************** -->
396
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]397<div class="doc_text">
398
399<p>One of the first things that you should do when designing a new pass is to
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]400decide what class you should subclass for your pass. The <a
401href="#basiccode">Hello World</a> example uses the <tt><a
402href="#FunctionPass">FunctionPass</a></tt> class for its implementation, but we
403did not discuss why or when this should occur. Here we talk about the classes
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]404available, from the most general to the most specific.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]405
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]406<p>When choosing a superclass for your Pass, you should choose the <b>most
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]407specific</b> class possible, while still being able to meet the requirements
Misha Brukman5560c9d2003-08-18 14:43:39 +0000[diff] [blame]408listed. This gives the LLVM Pass Infrastructure information necessary to
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]409optimize how passes are run, so that the resultant compiler isn't unneccesarily
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]410slow.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]411
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]412</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]413
Chris Lattnerf004f9a2002-09-25 22:31:38 +0000[diff] [blame]414<!-- ======================================================================= -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]415<div class="doc_subsection">
416 <a name="ImmutablePass">The <tt>ImmutablePass</tt> class</a>
417</div>
Chris Lattnerf004f9a2002-09-25 22:31:38 +0000[diff] [blame]418
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]419<div class="doc_text">
420
421<p>The most plain and boring type of pass is the "<tt><a
422href="http://llvm.cs.uiuc.edu/doxygen/structllvm_1_1ImmutablePass.html">ImmutablePass</a></tt>"
Chris Lattnerf004f9a2002-09-25 22:31:38 +0000[diff] [blame]423class. This pass type is used for passes that do not have to be run, do not
424change state, and never need to be updated. This is not a normal type of
425transformation or analysis, but can provide information about the current
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]426compiler configuration.</p>
Chris Lattnerf004f9a2002-09-25 22:31:38 +0000[diff] [blame]427
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]428<p>Although this pass class is very infrequently used, it is important for
Chris Lattnerf004f9a2002-09-25 22:31:38 +0000[diff] [blame]429providing information about the current target machine being compiled for, and
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]430other static information that can affect the various transformations.</p>
Chris Lattnerf004f9a2002-09-25 22:31:38 +0000[diff] [blame]431
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]432<p><tt>ImmutablePass</tt>es never invalidate other transformations, are never
433invalidated, and are never "run".</p>
Chris Lattnerf004f9a2002-09-25 22:31:38 +0000[diff] [blame]434
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]435</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]436
437<!-- ======================================================================= -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]438<div class="doc_subsection">
439 <a name="Pass">The <tt>Pass</tt> class</a>
440</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]441
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]442<div class="doc_text">
443
444<p>The "<tt><a
445href="http://llvm.cs.uiuc.edu/doxygen/classllvm_1_1Pass.html">Pass</a></tt>"
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]446class is the most general of all superclasses that you can use. Deriving from
447<tt>Pass</tt> indicates that your pass uses the entire program as a unit,
448refering to function bodies in no predictable order, or adding and removing
449functions. Because nothing is known about the behavior of direct <tt>Pass</tt>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]450subclasses, no optimization can be done for their execution.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]451
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]452<p>To write a correct <tt>Pass</tt> subclass, derive from <tt>Pass</tt> and
453overload the <tt>run</tt> method with the following signature:</p>
454
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_subsubsection">
459 <a name="run">The <tt>run</tt> method</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">
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]463
464<pre>
465 <b>virtual bool</b> run(Module &amp;M) = 0;
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]466</pre>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]467
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]468<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]469return true if the module was modified by the transformation, false
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]470otherwise.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]471
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]472</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]473
474<!-- ======================================================================= -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]475<div class="doc_subsection">
Chris Lattner8fdb2462004-09-18 06:39:35 +0000[diff] [blame^]476 <a name="CallGraphSCCPass">The <tt>CallGraphSCCPass</tt> class</a>
477</div>
478
479<div class="doc_text">
480
481<p>The "<tt><a
482href="http://llvm.cs.uiuc.edu/doxygen/structllvm_1_1CallGraphSCCPass.html">CallGraphSCCPass</a></tt>"
483is used by passes that need to traverse the program bottom-up on the call graph
484(callees before callers). Deriving from CallGraphSCCPass provides some
485mechanics for building and traversing the CallGraph, but also allows the system
486to optimize execution of CallGraphSCCPass's. If your pass meets the
487requirements outlined below, and doesn't meet the requirements of a <tt><a
488href="#FunctionPass">FunctionPass</a></tt> or <tt><a
489href="#BasicBlockPass">BasicBlockPass</a></tt>, you should derive from
490<tt>CallGraphSCCPass</tt>.</p>
491
492<p><b>TODO</b>: explain briefly what SCC, Tarjan's algo, and B-U mean.</p>
493
494<p>To be explicit, <tt>CallGraphSCCPass</tt> subclasses are:</p>
495
496<ol>
497
498<li>... <em>not allowed</em> to modify any <tt>Function</tt>s that are not in
499the current SCC.</li>
500
501<li>... <em>allowed</em> to inspect any Function's other than those in the
502current SCC and the direct callees of the SCC.</li>
503
504<li>... <em>required</em> to preserve the current CallGraph object, updating it
505to reflect any changes made to the program.</li>
506
507<li>... <em>not allowed</em> to add or remove SCC's from the current Module,
508though they may change the contents of an SCC.</li>
509
510<li>... <em>allowed</em> to add or remove global variables from the current
511Module.</li>
512
513<li>... <em>allowed</em> to maintain state across invocations of
514 <a href="#runOnSCC"><tt>runOnSCC</tt></a> (including global data).</li>
515</ol>
516
517<p>Implementing a <tt>CallGraphSCCPass</tt> is slightly tricky in some cases
518because it has to handle SCCs with more than one node in it. All of the virtual
519methods described below should return true if they modified the program, or
520false if they didn't.</p>
521
522</div>
523
524<!-- _______________________________________________________________________ -->
525<div class="doc_subsubsection">
526 <a name="doInitialization_scc">The <tt>doInitialization(Module &amp;)</tt>
527 method</a>
528</div>
529
530<div class="doc_text">
531
532<pre>
533 <b>virtual bool</b> doInitialization(Module &amp;M);
534</pre>
535
536<p>The <tt>doIninitialize</tt> method is allowed to do most of the things that
537<tt>CallGraphSCCPass</tt>'s are not allowed to do. They can add and remove
538functions, get pointers to functions, etc. The <tt>doInitialization</tt> method
539is designed to do simple initialization type of stuff that does not depend on
540the SCCs being processed. The <tt>doInitialization</tt> method call is not
541scheduled to overlap with any other pass executions (thus it should be very
542fast).</p>
543
544</div>
545
546<!-- _______________________________________________________________________ -->
547<div class="doc_subsubsection">
548 <a name="runOnSCC">The <tt>runOnSCC</tt> method</a>
549</div>
550
551<div class="doc_text">
552
553<pre>
554 <b>virtual bool</b> runOnSCC(const std::vector&lt;CallGraphNode *&gt; &amp;SCCM) = 0;
555</pre>
556
557<p>The <tt>runOnSCC</tt> method performs the interesting work of the pass, and
558should return true if the module was modified by the transformation, false
559otherwise.</p>
560
561</div>
562
563<!-- _______________________________________________________________________ -->
564<div class="doc_subsubsection">
565 <a name="doFinalization_scc">The <tt>doFinalization(Module
566 &amp;)</tt> method</a>
567</div>
568
569<div class="doc_text">
570
571<pre>
572 <b>virtual bool</b> doFinalization(Module &amp;M);
573</pre>
574
575<p>The <tt>doFinalization</tt> method is an infrequently used method that is
576called when the pass framework has finished calling <a
577href="#runOnFunction"><tt>runOnFunction</tt></a> for every function in the
578program being compiled.</p>
579
580</div>
581
582<!-- ======================================================================= -->
583<div class="doc_subsection">
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]584 <a name="FunctionPass">The <tt>FunctionPass</tt> class</a>
585</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]586
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]587<div class="doc_text">
588
589<p>In contrast to direct <tt>Pass</tt> subclasses, direct <tt><a
590href="http://llvm.cs.uiuc.edu/doxygen/classllvm_1_1Pass.html">FunctionPass</a></tt>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]591subclasses do have a predictable, local behavior that can be expected by the
592system. All <tt>FunctionPass</tt> execute on each function in the program
Misha Brukmanef6a6a62003-08-21 22:14:26 +0000[diff] [blame]593independent of all of the other functions in the program.
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]594<tt>FunctionPass</tt>'s do not require that they are executed in a particular
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]595order, and <tt>FunctionPass</tt>'s do not modify external functions.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]596
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]597<p>To be explicit, <tt>FunctionPass</tt> subclasses are not allowed to:</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]598
599<ol>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]600<li>Modify a Function other than the one currently being processed.</li>
601<li>Add or remove Function's from the current Module.</li>
602<li>Add or remove global variables from the current Module.</li>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]603<li>Maintain state across invocations of
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]604 <a href="#runOnFunction"><tt>runOnFunction</tt></a> (including global data)</li>
605</ol>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]606
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]607<p>Implementing a <tt>FunctionPass</tt> is usually straightforward (See the <a
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]608href="#basiccode">Hello World</a> pass for example). <tt>FunctionPass</tt>'s
609may overload three virtual methods to do their work. All of these methods
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]610should return true if they modified the program, or false if they didn't.</p>
611
612</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]613
614<!-- _______________________________________________________________________ -->
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]615<div class="doc_subsubsection">
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]616 <a name="doInitialization_mod">The <tt>doInitialization(Module &amp;)</tt>
617 method</a>
618</div>
619
620<div class="doc_text">
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]621
622<pre>
623 <b>virtual bool</b> doInitialization(Module &amp;M);
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]624</pre>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]625
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]626<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]627<tt>FunctionPass</tt>'s are not allowed to do. They can add and remove
Chris Lattnerd0713f92002-09-12 17:06:43 +0000[diff] [blame]628functions, get pointers to functions, etc. The <tt>doInitialization</tt> method
629is designed to do simple initialization type of stuff that does not depend on
630the functions being processed. The <tt>doInitialization</tt> method call is not
631scheduled to overlap with any other pass executions (thus it should be very
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]632fast).</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]633
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]634<p>A good example of how this method should be used is the <a
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]635href="http://llvm.cs.uiuc.edu/doxygen/LowerAllocations_8cpp-source.html">LowerAllocations</a>
636pass. This pass converts <tt>malloc</tt> and <tt>free</tt> instructions into
Misha Brukmanef6a6a62003-08-21 22:14:26 +0000[diff] [blame]637platform dependent <tt>malloc()</tt> and <tt>free()</tt> function calls. It
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]638uses the <tt>doInitialization</tt> method to get a reference to the malloc and
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]639free functions that it needs, adding prototypes to the module if necessary.</p>
640
641</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]642
643<!-- _______________________________________________________________________ -->
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]644<div class="doc_subsubsection">
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]645 <a name="runOnFunction">The <tt>runOnFunction</tt> method</a>
646</div>
647
648<div class="doc_text">
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]649
650<pre>
651 <b>virtual bool</b> runOnFunction(Function &amp;F) = 0;
652</pre><p>
653
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]654<p>The <tt>runOnFunction</tt> method must be implemented by your subclass to do
655the transformation or analysis work of your pass. As usual, a true value should
656be returned if the function is modified.</p>
657
658</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]659
660<!-- _______________________________________________________________________ -->
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]661<div class="doc_subsubsection">
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]662 <a name="doFinalization_mod">The <tt>doFinalization(Module
663 &amp;)</tt> method</a>
664</div>
665
666<div class="doc_text">
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]667
668<pre>
669 <b>virtual bool</b> doFinalization(Module &amp;M);
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]670</pre>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]671
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]672<p>The <tt>doFinalization</tt> method is an infrequently used method that is
673called when the pass framework has finished calling <a
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]674href="#runOnFunction"><tt>runOnFunction</tt></a> for every function in the
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]675program being compiled.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]676
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]677</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]678
679<!-- ======================================================================= -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]680<div class="doc_subsection">
681 <a name="BasicBlockPass">The <tt>BasicBlockPass</tt> class</a>
682</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]683
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]684<div class="doc_text">
685
686<p><tt>BasicBlockPass</tt>'s are just like <a
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]687href="#FunctionPass"><tt>FunctionPass</tt></a>'s, except that they must limit
688their scope of inspection and modification to a single basic block at a time.
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]689As such, they are <b>not</b> allowed to do any of the following:</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]690
691<ol>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]692<li>Modify or inspect any basic blocks outside of the current one</li>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]693<li>Maintain state across invocations of
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]694 <a href="#runOnBasicBlock"><tt>runOnBasicBlock</tt></a></li>
695<li>Modify the constrol flow graph (by altering terminator instructions)</li>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]696<li>Any of the things verboten for
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]697 <a href="#FunctionPass"><tt>FunctionPass</tt></a>es.</li>
698</ol>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]699
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]700<p><tt>BasicBlockPass</tt>es are useful for traditional local and "peephole"
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]701optimizations. They may override the same <a
Chris Lattnerd0713f92002-09-12 17:06:43 +0000[diff] [blame]702href="#doInitialization_mod"><tt>doInitialization(Module &amp;)</tt></a> and <a
703href="#doFinalization_mod"><tt>doFinalization(Module &amp;)</tt></a> methods that <a
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]704href="#FunctionPass"><tt>FunctionPass</tt></a>'s have, but also have the following virtual methods that may also be implemented:</p>
705
706</div>
Chris Lattnerd0713f92002-09-12 17:06:43 +0000[diff] [blame]707
708<!-- _______________________________________________________________________ -->
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]709<div class="doc_subsubsection">
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]710 <a name="doInitialization_fn">The <tt>doInitialization(Function
711 &amp;)</tt> method</a>
712</div>
713
714<div class="doc_text">
Chris Lattnerd0713f92002-09-12 17:06:43 +0000[diff] [blame]715
716<pre>
717 <b>virtual bool</b> doInitialization(Function &amp;F);
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]718</pre>
Chris Lattnerd0713f92002-09-12 17:06:43 +0000[diff] [blame]719
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]720<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]721<tt>BasicBlockPass</tt>'s are not allowed to do, but that
722<tt>FunctionPass</tt>'s can. The <tt>doInitialization</tt> method is designed
723to do simple initialization type of stuff that does not depend on the
724BasicBlocks being processed. The <tt>doInitialization</tt> method call is not
725scheduled to overlap with any other pass executions (thus it should be very
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]726fast).</p>
Chris Lattnerd0713f92002-09-12 17:06:43 +0000[diff] [blame]727
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]728</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]729
730<!-- _______________________________________________________________________ -->
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]731<div class="doc_subsubsection">
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]732 <a name="runOnBasicBlock">The <tt>runOnBasicBlock</tt> method</a>
733</div>
734
735<div class="doc_text">
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]736
737<pre>
738 <b>virtual bool</b> runOnBasicBlock(BasicBlock &amp;BB) = 0;
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]739</pre>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]740
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]741<p>Override this function to do the work of the <tt>BasicBlockPass</tt>. This
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]742function is not allowed to inspect or modify basic blocks other than the
743parameter, and are not allowed to modify the CFG. A true value must be returned
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]744if the basic block is modified.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]745
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]746</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]747
Chris Lattnerd0713f92002-09-12 17:06:43 +0000[diff] [blame]748<!-- _______________________________________________________________________ -->
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]749<div class="doc_subsubsection">
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]750 <a name="doFinalization_fn">The <tt>doFinalization(Function &amp;)</tt>
751 method</a>
752</div>
753
754<div class="doc_text">
Chris Lattnerd0713f92002-09-12 17:06:43 +0000[diff] [blame]755
756<pre>
757 <b>virtual bool</b> doFinalization(Function &amp;F);
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]758</pre>
Chris Lattnerd0713f92002-09-12 17:06:43 +0000[diff] [blame]759
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]760<p>The <tt>doFinalization</tt> method is an infrequently used method that is
761called when the pass framework has finished calling <a
Chris Lattnerd0713f92002-09-12 17:06:43 +0000[diff] [blame]762href="#runOnBasicBlock"><tt>runOnBasicBlock</tt></a> for every BasicBlock in the
763program being compiled. This can be used to perform per-function
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]764finalization.</p>
Chris Lattnerd0713f92002-09-12 17:06:43 +0000[diff] [blame]765
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]766</div>
Chris Lattnerd0713f92002-09-12 17:06:43 +0000[diff] [blame]767
Brian Gaekecab8b6f2003-07-17 18:53:20 +0000[diff] [blame]768<!-- ======================================================================= -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]769<div class="doc_subsection">
770 <a name="MachineFunctionPass">The <tt>MachineFunctionPass</tt> class</a>
771</div>
Brian Gaekecab8b6f2003-07-17 18:53:20 +0000[diff] [blame]772
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]773<div class="doc_text">
774
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]775<p>A <tt>MachineFunctionPass</tt> is a part of the LLVM code generator that
776executes on the machine-dependent representation of each LLVM function in the
777program. A <tt>MachineFunctionPass</tt> is also a <tt>FunctionPass</tt>, so all
Brian Gaekecab8b6f2003-07-17 18:53:20 +0000[diff] [blame]778the restrictions that apply to a <tt>FunctionPass</tt> also apply to it.
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]779<tt>MachineFunctionPass</tt>es also have additional restrictions. In particular,
780<tt>MachineFunctionPass</tt>es are not allowed to do any of the following:</p>
Brian Gaekecab8b6f2003-07-17 18:53:20 +0000[diff] [blame]781
782<ol>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]783<li>Modify any LLVM Instructions, BasicBlocks or Functions.</li>
784<li>Modify a MachineFunction other than the one currently being processed.</li>
785<li>Add or remove MachineFunctions from the current Module.</li>
786<li>Add or remove global variables from the current Module.</li>
787<li>Maintain state across invocations of <a
788href="#runOnMachineFunction"><tt>runOnMachineFunction</tt></a> (including global
789data)</li>
790</ol>
Brian Gaekecab8b6f2003-07-17 18:53:20 +0000[diff] [blame]791
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]792</div>
Chris Lattnerd0713f92002-09-12 17:06:43 +0000[diff] [blame]793
Brian Gaeke6a33f362003-07-22 20:53:20 +0000[diff] [blame]794<!-- _______________________________________________________________________ -->
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]795<div class="doc_subsubsection">
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]796 <a name="runOnMachineFunction">The <tt>runOnMachineFunction(MachineFunction
797 &amp;MF)</tt> method</a>
798</div>
799
800<div class="doc_text">
Brian Gaeke6a33f362003-07-22 20:53:20 +0000[diff] [blame]801
802<pre>
803 <b>virtual bool</b> runOnMachineFunction(MachineFunction &amp;MF) = 0;
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]804</pre>
Brian Gaeke6a33f362003-07-22 20:53:20 +0000[diff] [blame]805
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]806<p><tt>runOnMachineFunction</tt> can be considered the main entry point of a
807<tt>MachineFunctionPass</tt>; that is, you should override this method to do the
808work of your <tt>MachineFunctionPass</tt>.</p>
Brian Gaeke6a33f362003-07-22 20:53:20 +0000[diff] [blame]809
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]810<p>The <tt>runOnMachineFunction</tt> method is called on every
Brian Gaeke6a33f362003-07-22 20:53:20 +0000[diff] [blame]811<tt>MachineFunction</tt> in a <tt>Module</tt>, so that the
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]812<tt>MachineFunctionPass</tt> may perform optimizations on the machine-dependent
813representation of the function. If you want to get at the LLVM <tt>Function</tt>
814for the <tt>MachineFunction</tt> you're working on, use
815<tt>MachineFunction</tt>'s <tt>getFunction()</tt> accessor method -- but
816remember, you may not modify the LLVM <tt>Function</tt> or its contents from a
817<tt>MachineFunctionPass</tt>.</p>
818
819</div>
Brian Gaeke6a33f362003-07-22 20:53:20 +0000[diff] [blame]820
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]821<!-- *********************************************************************** -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]822<div class="doc_section">
823 <a name="registration">Pass registration</a>
824</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]825<!-- *********************************************************************** -->
826
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]827<div class="doc_text">
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]828
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]829<p>In the <a href="#basiccode">Hello World</a> example pass we illustrated how
830pass registration works, and discussed some of the reasons that it is used and
831what it does. Here we discuss how and why passes are registered.</p>
832
833<p>Passes can be registered in several different ways. Depending on the general
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]834classification of the pass, you should use one of the following templates to
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]835register the pass:</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]836
837<ul>
838<li><b><tt>RegisterOpt</tt></b> - This template should be used when you are
839registering a pass that logically should be available for use in the
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]840'<tt>opt</tt>' utility.</li>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]841
842<li><b><tt>RegisterAnalysis</tt></b> - This template should be used when you are
843registering a pass that logically should be available for use in the
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]844'<tt>analyze</tt>' utility.</li>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]845
846<li><b><tt>RegisterPass</tt></b> - This is the generic form of the
847<tt>Register*</tt> templates that should be used if you want your pass listed by
848multiple or no utilities. This template takes an extra third argument that
849specifies which tools it should be listed in. See the <a
850href="http://llvm.cs.uiuc.edu/doxygen/PassSupport_8h-source.html">PassSupport.h</a>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]851file for more information.</li>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]852
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]853</ul>
854
855<p>Regardless of how you register your pass, you must specify at least two
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]856parameters. The first parameter is the name of the pass that is to be used on
857the command line to specify that the pass should be added to a program (for
858example <tt>opt</tt> or <tt>analyze</tt>). The second argument is the name of
859the 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]860well as for debug output generated by the <tt>--debug-pass</tt> option.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]861
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]862<p>If a pass is registered to be used by the <tt>analyze</tt> utility, you
863should implement the virtual <tt>print</tt> method:</p>
864
865</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]866
867<!-- _______________________________________________________________________ -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]868<div class="doc_subsubsection">
869 <a name="print">The <tt>print</tt> method</a>
870</div>
871
872<div class="doc_text">
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]873
874<pre>
875 <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]876</pre>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]877
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]878<p>The <tt>print</tt> method must be implemented by "analyses" in order to print
879a human readable version of the analysis results. This is useful for debugging
880an analysis itself, as well as for other people to figure out how an analysis
881works. The <tt>analyze</tt> tool uses this method to generate its output.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]882
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]883<p>The <tt>ostream</tt> parameter specifies the stream to write the results on,
884and 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]885program that has been analyzed. Note however that this pointer may be null in
886certain circumstances (such as calling the <tt>Pass::dump()</tt> from a
887debugger), so it should only be used to enhance debug output, it should not be
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]888depended on.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]889
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]890</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]891
892<!-- *********************************************************************** -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]893<div class="doc_section">
894 <a name="interaction">Specifying interactions between passes</a>
895</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]896<!-- *********************************************************************** -->
897
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]898<div class="doc_text">
899
900<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]901that passes interact with each other correctly. Because <tt>PassManager</tt>
902tries to <a href="#passmanager">optimize the execution of passes</a> it must
903know how the passes interact with each other and what dependencies exist between
904the various passes. To track this, each pass can declare the set of passes that
905are required to be executed before the current pass, and the passes which are
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]906invalidated by the current pass.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]907
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]908<p>Typically this functionality is used to require that analysis results are
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]909computed before your pass is run. Running arbitrary transformation passes can
910invalidate the computed analysis results, which is what the invalidation set
911specifies. If a pass does not implement the <tt><a
912href="#getAnalysisUsage">getAnalysisUsage</a></tt> method, it defaults to not
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]913having any prerequisite passes, and invalidating <b>all</b> other passes.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]914
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]915</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]916
917<!-- _______________________________________________________________________ -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]918<div class="doc_subsubsection">
919 <a name="getAnalysisUsage">The <tt>getAnalysisUsage</tt> method</a>
920</div>
921
922<div class="doc_text">
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]923
924<pre>
925 <b>virtual void</b> getAnalysisUsage(AnalysisUsage &amp;Info) <b>const</b>;
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]926</pre>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]927
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]928<p>By implementing the <tt>getAnalysisUsage</tt> method, the required and
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]929invalidated sets may be specified for your transformation. The implementation
930should fill in the <tt><a
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]931href="http://llvm.cs.uiuc.edu/doxygen/classllvm_1_1AnalysisUsage.html">AnalysisUsage</a></tt>
932object with information about which passes are required and not invalidated. To
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]933do this, a pass may call any of the following methods on the AnalysisUsage
934object:</p>
935</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]936
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]937<!-- _______________________________________________________________________ -->
938<div class="doc_subsubsection">
939 <a name="AU::addRequired">The <tt>AnalysisUsage::addRequired&lt;&gt;</tt> and <tt>AnalysisUsage::addRequiredTransitive&lt;&gt;</tt> methods</a>
940</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]941
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]942<div class="doc_text">
943<p>
944If you pass requires a previous pass to be executed (an analysis for example),
945it can use one of these methods to arrange for it to be run before your pass.
946LLVM has many different types of analyses and passes that can be required,
947spaning the range from <tt>DominatorSet</tt> to <tt>BreakCriticalEdges</tt>.
948requiring <tt>BreakCriticalEdges</tt>, for example, guarantees that there will
949be no critical edges in the CFG when your pass has been run.
950</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]951
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]952<p>
953Some analyses chain to other analyses to do their job. For example, an <a
954href="AliasAnalysis.html">AliasAnalysis</a> implementation is required to <a
955href="AliasAnalysis.html#chaining">chain</a> to other alias analysis passes. In
956cases where analyses chain, the <tt>addRequiredTransitive</tt> method should be
957used instead of the <tt>addRequired</tt> method. This informs the PassManager
958that the transitively required pass should be alive as long as the requiring
959pass is.
960</p>
961</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]962
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]963<!-- _______________________________________________________________________ -->
964<div class="doc_subsubsection">
965 <a name="AU::addPreserved">The <tt>AnalysisUsage::addPreserved&lt;&gt;</tt> method</a>
966</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]967
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]968<div class="doc_text">
969<p>
970One of the jobs of the PassManager is to optimize how and when analyses are run.
971In particular, it attempts to avoid recomputing data unless it needs to. For
972this reason, passes are allowed to declare that they preserve (i.e., they don't
973invalidate) an existing analysis if it's available. For example, a simple
974constant folding pass would not modify the CFG, so it can't possible effect the
975results of dominator analysis. By default, all passes are assumed to invalidate
976all others.
977</p>
978
979<p>
980The <tt>AnalysisUsage</tt> class provides several methods which are useful in
981certain circumstances that are related to <tt>addPreserved</tt>. In particular,
982the <tt>setPreservesAll</tt> method can be called to indicate that the pass does
983not modify the LLVM program at all (which is true for analyses), and the
984<tt>setPreservesCFG</tt> method can be used by transformations that change
985instructions in the program but do not modify the CFG or terminator instructions
986(note that this property is implicitly set for <a
987href="#BasicBlockPass">BasicBlockPass</a>'s).
988</p>
989
990<p>
991<tt>addPreserved</tt> is particularly useful for transformations like
992<tt>BreakCriticalEdges</tt>. This pass knows how to update a small set of loop
993and dominator related analyses if they exist, so it can preserve them, despite
994the fact that it hacks on the CFG.
995</p>
996</div>
997
998<!-- _______________________________________________________________________ -->
999<div class="doc_subsubsection">
1000 <a name="AU::examples">Example implementations of <tt>getAnalysisUsage</tt></a>
1001</div>
1002
1003<div class="doc_text">
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1004
1005<pre>
1006 <i>// This is an example implementation from an analysis, which does not modify
1007 // the program at all, yet has a prerequisite.</i>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1008 <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]1009 AU.setPreservesAll();
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1010 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]1011 }
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1012</pre>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1013
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1014<p>and:</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1015
1016<pre>
1017 <i>// This example modifies the program, but does not modify the CFG</i>
1018 <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]1019 AU.setPreservesCFG();
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1020 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]1021 }
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1022</pre>
1023
1024</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1025
1026<!-- _______________________________________________________________________ -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1027<div class="doc_subsubsection">
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]1028 <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]1029</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1030
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1031<div class="doc_text">
1032
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]1033<p>The <tt>Pass::getAnalysis&lt;&gt;</tt> method is automatically inherited by
1034your class, providing you with access to the passes that you declared that you
1035required with the <a href="#getAnalysisUsage"><tt>getAnalysisUsage</tt></a>
1036method. It takes a single template argument that specifies which pass class you
1037want, and returns a reference to that pass. For example:</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1038
1039<pre>
Chris Lattnera5776302004-03-17 21:33:32 +0000[diff] [blame]1040 bool LICM::runOnFunction(Function &amp;F) {
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]1041 LoopInfo &amp;LI = getAnalysis&lt;LoopInfo&gt;();
1042 ...
1043 }
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1044</pre>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1045
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1046<p>This method call returns a reference to the pass desired. You may get a
1047runtime assertion failure if you attempt to get an analysis that you did not
1048declare as required in your <a
1049href="#getAnalysisUsage"><tt>getAnalysisUsage</tt></a> implementation. This
1050method can be called by your <tt>run*</tt> method implementation, or by any
1051other local method invoked by your <tt>run*</tt> method.</p>
1052
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]1053<p>
1054If your pass is capable of updating analyses if they exist (e.g.,
1055<tt>BreakCriticalEdges</tt>, as described above), you can use the
1056<tt>getAnalysisToUpdate</tt> method, which returns a pointer to the analysis if
1057it is active. For example:</p>
1058
1059<pre>
1060 ...
1061 if (DominatorSet *DS = getAnalysisToUpdate&lt;DominatorSet&gt;()) {
1062 <i>// A DominatorSet is active. This code will update it.</i>
1063 }
1064 ...
1065</pre>
1066
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1067</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1068
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1069<!-- *********************************************************************** -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1070<div class="doc_section">
1071 <a name="analysisgroup">Implementing Analysis Groups</a>
1072</div>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1073<!-- *********************************************************************** -->
1074
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1075<div class="doc_text">
1076
1077<p>Now that we understand the basics of how passes are defined, how the are
1078used, 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]1079fancier. All of the pass relationships that we have seen so far are very
1080simple: one pass depends on one other specific pass to be run before it can run.
1081For many applications, this is great, for others, more flexibility is
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1082required.</p>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1083
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1084<p>In particular, some analyses are defined such that there is a single simple
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1085interface to the analysis results, but multiple ways of calculating them.
1086Consider alias analysis for example. The most trivial alias analysis returns
1087"may alias" for any alias query. The most sophisticated analysis a
1088flow-sensitive, context-sensitive interprocedural analysis that can take a
1089significant amount of time to execute (and obviously, there is a lot of room
1090between these two extremes for other implementations). To cleanly support
1091situations like this, the LLVM Pass Infrastructure supports the notion of
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1092Analysis Groups.</p>
1093
1094</div>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1095
1096<!-- _______________________________________________________________________ -->
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]1097<div class="doc_subsubsection">
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1098 <a name="agconcepts">Analysis Group Concepts</a>
1099</div>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1100
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1101<div class="doc_text">
1102
1103<p>An Analysis Group is a single simple interface that may be implemented by
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1104multiple different passes. Analysis Groups can be given human readable names
1105just like passes, but unlike passes, they need not derive from the <tt>Pass</tt>
1106class. An analysis group may have one or more implementations, one of which is
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1107the "default" implementation.</p>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1108
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1109<p>Analysis groups are used by client passes just like other passes are: the
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1110<tt>AnalysisUsage::addRequired()</tt> and <tt>Pass::getAnalysis()</tt> methods.
1111In order to resolve this requirement, the <a href="#passmanager">PassManager</a>
1112scans the available passes to see if any implementations of the analysis group
1113are available. If none is available, the default implementation is created for
1114the pass to use. All standard rules for <A href="#interaction">interaction
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1115between passes</a> still apply.</p>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1116
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1117<p>Although <a href="#registration">Pass Registration</a> is optional for normal
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1118passes, all analysis group implementations must be registered, and must use the
1119<A href="#registerag"><tt>RegisterAnalysisGroup</tt></a> template to join the
1120implementation pool. Also, a default implementation of the interface
1121<b>must</b> be registered with <A
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1122href="#registerag"><tt>RegisterAnalysisGroup</tt></a>.</p>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1123
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1124<p>As a concrete example of an Analysis Group in action, consider the <a
1125href="http://llvm.cs.uiuc.edu/doxygen/classllvm_1_1AliasAnalysis.html">AliasAnalysis</a>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1126analysis group. The default implementation of the alias analysis interface (the
1127<tt><a
1128href="http://llvm.cs.uiuc.edu/doxygen/structBasicAliasAnalysis.html">basicaa</a></tt>
1129pass) just does a few simple checks that don't require significant analysis to
1130compute (such as: two different globals can never alias each other, etc).
1131Passes that use the <tt><a
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1132href="http://llvm.cs.uiuc.edu/doxygen/classllvm_1_1AliasAnalysis.html">AliasAnalysis</a></tt>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1133interface (for example the <tt><a
Misha Brukmand15516e2004-06-03 23:39:36 +0000[diff] [blame]1134href="http://llvm.cs.uiuc.edu/doxygen/structGCSE.html">gcse</a></tt> pass), do
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1135not care which implementation of alias analysis is actually provided, they just
1136use the designated interface.</p>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1137
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1138<p>From the user's perspective, commands work just like normal. Issuing the
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1139command '<tt>opt -gcse ...</tt>' will cause the <tt>basicaa</tt> class to be
1140instantiated and added to the pass sequence. Issuing the command '<tt>opt
1141-somefancyaa -gcse ...</tt>' will cause the <tt>gcse</tt> pass to use the
1142<tt>somefancyaa</tt> alias analysis (which doesn't actually exist, it's just a
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1143hypothetical example) instead.</p>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1144
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1145</div>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1146
1147<!-- _______________________________________________________________________ -->
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]1148<div class="doc_subsubsection">
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1149 <a name="registerag">Using <tt>RegisterAnalysisGroup</tt></a>
1150</div>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1151
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1152<div class="doc_text">
1153
1154<p>The <tt>RegisterAnalysisGroup</tt> template is used to register the analysis
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1155group itself as well as add pass implementations to the analysis group. First,
1156an analysis should be registered, with a human readable name provided for it.
1157Unlike registration of passes, there is no command line argument to be specified
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1158for the Analysis Group Interface itself, because it is "abstract":</p>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1159
1160<pre>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1161 <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>");
1162</pre>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1163
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1164<p>Once the analysis is registered, passes can declare that they are valid
1165implementations of the interface by using the following code:</p>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1166
1167<pre>
1168<b>namespace</b> {
1169 //<i> Analysis Group implementations <b>must</b> be registered normally...</i>
1170 RegisterOpt&lt;FancyAA&gt;
1171 B("<i>somefancyaa</i>", "<i>A more complex alias analysis implementation</i>");
1172
1173 //<i> Declare that we implement the AliasAnalysis interface</i>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1174 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]1175}
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1176</pre>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1177
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1178<p>This just shows a class <tt>FancyAA</tt> that is registered normally, then
1179uses the <tt>RegisterAnalysisGroup</tt> template to "join" the <tt><a
1180href="http://llvm.cs.uiuc.edu/doxygen/classllvm_1_1AliasAnalysis.html">AliasAnalysis</a></tt>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1181analysis group. Every implementation of an analysis group should join using
1182this template. A single pass may join multiple different analysis groups with
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1183no problem.</p>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1184
1185<pre>
1186<b>namespace</b> {
1187 //<i> Analysis Group implementations <b>must</b> be registered normally...</i>
1188 RegisterOpt&lt;<a href="http://llvm.cs.uiuc.edu/doxygen/structBasicAliasAnalysis.html">BasicAliasAnalysis</a>&gt;
1189 D("<i>basicaa</i>", "<i>Basic Alias Analysis (default AA impl)</i>");
1190
1191 //<i> Declare that we implement the AliasAnalysis interface</i>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1192 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]1193}
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1194</pre>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1195
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1196<p>Here we show how the default implementation is specified (using the extra
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1197argument to the <tt>RegisterAnalysisGroup</tt> template). There must be exactly
1198one default implementation available at all times for an Analysis Group to be
1199used. Here we declare that the <tt><a
1200href="http://llvm.cs.uiuc.edu/doxygen/structBasicAliasAnalysis.html">BasicAliasAnalysis</a></tt>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1201pass is the default implementation for the interface.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1202
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1203</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1204
1205<!-- *********************************************************************** -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1206<div class="doc_section">
1207 <a name="passmanager">What PassManager does</a>
1208</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1209<!-- *********************************************************************** -->
1210
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1211<div class="doc_text">
1212
1213<p>The <a
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1214href="http://llvm.cs.uiuc.edu/doxygen/PassManager_8h-source.html"><tt>PassManager</tt></a>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1215<a
1216href="http://llvm.cs.uiuc.edu/doxygen/classllvm_1_1PassManager.html">class</a>
1217takes a list of passes, ensures their <a href="#interaction">prerequisites</a>
1218are set up correctly, and then schedules passes to run efficiently. All of the
1219LLVM tools that run passes use the <tt>PassManager</tt> for execution of these
1220passes.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1221
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1222<p>The <tt>PassManager</tt> does two main things to try to reduce the execution
1223time of a series of passes:</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1224
1225<ol>
1226<li><b>Share analysis results</b> - The PassManager attempts to avoid
1227recomputing analysis results as much as possible. This means keeping track of
1228which analyses are available already, which analyses get invalidated, and which
1229analyses are needed to be run for a pass. An important part of work is that the
1230<tt>PassManager</tt> tracks the exact lifetime of all analysis results, allowing
1231it to <a href="#releaseMemory">free memory</a> allocated to holding analysis
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1232results as soon as they are no longer needed.</li>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1233
1234<li><b>Pipeline the execution of passes on the program</b> - The
1235<tt>PassManager</tt> attempts to get better cache and memory usage behavior out
1236of a series of passes by pipelining the passes together. This means that, given
1237a series of consequtive <a href="#FunctionPass"><tt>FunctionPass</tt></a>'s, it
1238will execute all of the <a href="#FunctionPass"><tt>FunctionPass</tt></a>'s on
1239the first function, then all of the <a
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1240href="#FunctionPass"><tt>FunctionPass</tt></a>es on the second function,
1241etc... until the entire program has been run through the passes.
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1242
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1243<p>This improves the cache behavior of the compiler, because it is only touching
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1244the LLVM program representation for a single function at a time, instead of
1245traversing the entire program. It reduces the memory consumption of compiler,
1246because, for example, only one <a
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1247href="http://llvm.cs.uiuc.edu/doxygen/structllvm_1_1DominatorSet.html"><tt>DominatorSet</tt></a>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1248needs to be calculated at a time. This also makes it possible some <a
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1249href="#SMP">interesting enhancements</a> in the future.</p></li>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1250
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1251</ol>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1252
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1253<p>The effectiveness of the <tt>PassManager</tt> is influenced directly by how
1254much information it has about the behaviors of the passes it is scheduling. For
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1255example, the "preserved" set is intentionally conservative in the face of an
1256unimplemented <a href="#getAnalysisUsage"><tt>getAnalysisUsage</tt></a> method.
1257Not implementing when it should be implemented will have the effect of not
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1258allowing any analysis results to live across the execution of your pass.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1259
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1260<p>The <tt>PassManager</tt> class exposes a <tt>--debug-pass</tt> command line
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1261options that is useful for debugging pass execution, seeing how things work, and
1262diagnosing when you should be preserving more analyses than you currently are
1263(To get information about all of the variants of the <tt>--debug-pass</tt>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1264option, just type '<tt>opt --help-hidden</tt>').</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1265
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1266<p>By using the <tt>--debug-pass=Structure</tt> option, for example, we can see
1267how our <a href="#basiccode">Hello World</a> pass interacts with other passes.
1268Lets try it out with the <tt>gcse</tt> and <tt>licm</tt> passes:</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1269
1270<pre>
1271$ opt -load ../../../lib/Debug/libhello.so -gcse -licm --debug-pass=Structure &lt; hello.bc &gt; /dev/null
1272Module Pass Manager
1273 Function Pass Manager
1274 Dominator Set Construction
1275 Immediate Dominators Construction
1276 Global Common Subexpression Elimination
1277-- Immediate Dominators Construction
1278-- Global Common Subexpression Elimination
1279 Natural Loop Construction
1280 Loop Invariant Code Motion
1281-- Natural Loop Construction
1282-- Loop Invariant Code Motion
1283 Module Verifier
1284-- Dominator Set Construction
1285-- Module Verifier
1286 Bytecode Writer
1287--Bytecode Writer
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1288</pre>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1289
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1290<p>This output shows us when passes are constructed and when the analysis
1291results are known to be dead (prefixed with '<tt>--</tt>'). Here we see that
1292GCSE uses dominator and immediate dominator information to do its job. The LICM
1293pass uses natural loop information, which uses dominator sets, but not immediate
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1294dominators. Because immediate dominators are no longer useful after the GCSE
1295pass, it is immediately destroyed. The dominator sets are then reused to
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1296compute natural loop information, which is then used by the LICM pass.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1297
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1298<p>After the LICM pass, the module verifier runs (which is automatically added
1299by the '<tt>opt</tt>' tool), which uses the dominator set to check that the
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1300resultant LLVM code is well formed. After it finishes, the dominator set
1301information is destroyed, after being computed once, and shared by three
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1302passes.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1303
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1304<p>Lets see how this changes when we run the <a href="#basiccode">Hello
1305World</a> pass in between the two passes:</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1306
1307<pre>
1308$ opt -load ../../../lib/Debug/libhello.so -gcse -hello -licm --debug-pass=Structure &lt; hello.bc &gt; /dev/null
1309Module Pass Manager
1310 Function Pass Manager
1311 Dominator Set Construction
1312 Immediate Dominators Construction
1313 Global Common Subexpression Elimination
1314<b>-- Dominator Set Construction</b>
1315-- Immediate Dominators Construction
1316-- Global Common Subexpression Elimination
1317<b> Hello World Pass
1318-- Hello World Pass
1319 Dominator Set Construction</b>
1320 Natural Loop Construction
1321 Loop Invariant Code Motion
1322-- Natural Loop Construction
1323-- Loop Invariant Code Motion
1324 Module Verifier
1325-- Dominator Set Construction
1326-- Module Verifier
1327 Bytecode Writer
1328--Bytecode Writer
1329Hello: __main
1330Hello: puts
1331Hello: main
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1332</pre>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1333
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1334<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]1335Dominator Set pass, even though it doesn't modify the code at all! To fix this,
1336we need to add the following <a
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1337href="#getAnalysisUsage"><tt>getAnalysisUsage</tt></a> method to our pass:</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1338
1339<pre>
1340 <i>// We don't modify the program, so we preserve all analyses</i>
1341 <b>virtual void</b> getAnalysisUsage(AnalysisUsage &amp;AU) <b>const</b> {
1342 AU.setPreservesAll();
1343 }
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1344</pre>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1345
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1346<p>Now when we run our pass, we get this output:</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1347
1348<pre>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1349$ 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]1350Pass Arguments: -gcse -hello -licm
1351Module Pass Manager
1352 Function Pass Manager
1353 Dominator Set Construction
1354 Immediate Dominators Construction
1355 Global Common Subexpression Elimination
1356-- Immediate Dominators Construction
1357-- Global Common Subexpression Elimination
1358 Hello World Pass
1359-- Hello World Pass
1360 Natural Loop Construction
1361 Loop Invariant Code Motion
1362-- Loop Invariant Code Motion
1363-- Natural Loop Construction
1364 Module Verifier
1365-- Dominator Set Construction
1366-- Module Verifier
1367 Bytecode Writer
1368--Bytecode Writer
1369Hello: __main
1370Hello: puts
1371Hello: main
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1372</pre>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1373
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1374<p>Which shows that we don't accidentally invalidate dominator information
1375anymore, and therefore do not have to compute it twice.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1376
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1377</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1378
1379<!-- _______________________________________________________________________ -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1380<div class="doc_subsubsection">
1381 <a name="releaseMemory">The <tt>releaseMemory</tt> method</a>
1382</div>
1383
1384<div class="doc_text">
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1385
1386<pre>
1387 <b>virtual void</b> releaseMemory();
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1388</pre>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1389
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1390<p>The <tt>PassManager</tt> automatically determines when to compute analysis
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1391results, and how long to keep them around for. Because the lifetime of the pass
1392object itself is effectively the entire duration of the compilation process, we
1393need some way to free analysis results when they are no longer useful. The
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1394<tt>releaseMemory</tt> virtual method is the way to do this.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1395
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1396<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]1397amount of state (for use by another pass which "requires" your pass and uses the
1398<a href="#getAnalysis">getAnalysis</a> method) you should implement
1399<tt>releaseMEmory</tt> to, well, release the memory allocated to maintain this
1400internal state. This method is called after the <tt>run*</tt> method for the
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1401class, before the next call of <tt>run*</tt> in your pass.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1402
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1403</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1404
1405<!-- *********************************************************************** -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1406<div class="doc_section">
1407 <a name="debughints">Using GDB with dynamically loaded passes</a>
1408</div>
Chris Lattner480e2ef2002-09-06 02:02:58 +0000[diff] [blame]1409<!-- *********************************************************************** -->
1410
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1411<div class="doc_text">
1412
1413<p>Unfortunately, using GDB with dynamically loaded passes is not as easy as it
Chris Lattner480e2ef2002-09-06 02:02:58 +0000[diff] [blame]1414should be. First of all, you can't set a breakpoint in a shared object that has
1415not been loaded yet, and second of all there are problems with inlined functions
1416in shared objects. Here are some suggestions to debugging your pass with
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1417GDB.</p>
Chris Lattner480e2ef2002-09-06 02:02:58 +0000[diff] [blame]1418
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1419<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]1420transformation invoked by <tt>opt</tt>, although nothing described here depends
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1421on that.</p>
1422
1423</div>
Chris Lattner480e2ef2002-09-06 02:02:58 +0000[diff] [blame]1424
1425<!-- _______________________________________________________________________ -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1426<div class="doc_subsubsection">
1427 <a name="breakpoint">Setting a breakpoint in your pass</a>
1428</div>
Chris Lattner480e2ef2002-09-06 02:02:58 +0000[diff] [blame]1429
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1430<div class="doc_text">
1431
1432<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]1433
1434<pre>
1435$ <b>gdb opt</b>
1436GNU gdb 5.0
1437Copyright 2000 Free Software Foundation, Inc.
1438GDB is free software, covered by the GNU General Public License, and you are
1439welcome to change it and/or distribute copies of it under certain conditions.
1440Type "show copying" to see the conditions.
1441There is absolutely no warranty for GDB. Type "show warranty" for details.
1442This GDB was configured as "sparc-sun-solaris2.6"...
1443(gdb)
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1444</pre>
Chris Lattner480e2ef2002-09-06 02:02:58 +0000[diff] [blame]1445
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1446<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]1447time to load. Be patient. Since we cannot set a breakpoint in our pass yet
1448(the shared object isn't loaded until runtime), we must execute the process, and
1449have it stop before it invokes our pass, but after it has loaded the shared
1450object. The most foolproof way of doing this is to set a breakpoint in
1451<tt>PassManager::run</tt> and then run the process with the arguments you
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1452want:</p>
Chris Lattner480e2ef2002-09-06 02:02:58 +0000[diff] [blame]1453
1454<pre>
1455(gdb) <b>break PassManager::run</b>
1456Breakpoint 1 at 0x2413bc: file Pass.cpp, line 70.
Chris Lattnerfafe6302003-10-23 19:48:11 +0000[diff] [blame]1457(gdb) <b>run test.bc -load $(LLVMTOP)/llvm/lib/Debug/[libname].so -[passoption]</b>
1458Starting program: opt test.bc -load $(LLVMTOP)/llvm/lib/Debug/[libname].so -[passoption]
Chris Lattner480e2ef2002-09-06 02:02:58 +0000[diff] [blame]1459Breakpoint 1, PassManager::run (this=0xffbef174, M=@0x70b298) at Pass.cpp:70
146070 bool PassManager::run(Module &amp;M) { return PM-&gt;run(M); }
1461(gdb)
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1462</pre>
Chris Lattner480e2ef2002-09-06 02:02:58 +0000[diff] [blame]1463
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1464<p>Once the <tt>opt</tt> stops in the <tt>PassManager::run</tt> method you are
1465now free to set breakpoints in your pass so that you can trace through execution
1466or do other standard debugging stuff.</p>
Chris Lattner480e2ef2002-09-06 02:02:58 +0000[diff] [blame]1467
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1468</div>
Chris Lattner480e2ef2002-09-06 02:02:58 +0000[diff] [blame]1469
1470<!-- _______________________________________________________________________ -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1471<div class="doc_subsubsection">
1472 <a name="debugmisc">Miscellaneous Problems</a>
1473</div>
Chris Lattner480e2ef2002-09-06 02:02:58 +0000[diff] [blame]1474
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1475<div class="doc_text">
1476
1477<p>Once you have the basics down, there are a couple of problems that GDB has,
1478some with solutions, some without.</p>
Chris Lattner480e2ef2002-09-06 02:02:58 +0000[diff] [blame]1479
1480<ul>
1481<li>Inline functions have bogus stack information. In general, GDB does a
1482pretty good job getting stack traces and stepping through inline functions.
1483When a pass is dynamically loaded however, it somehow completely loses this
1484capability. The only solution I know of is to de-inline a function (move it
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1485from the body of a class to a .cpp file).</li>
Chris Lattner480e2ef2002-09-06 02:02:58 +0000[diff] [blame]1486
1487<li>Restarting the program breaks breakpoints. After following the information
1488above, you have succeeded in getting some breakpoints planted in your pass. Nex
1489thing you know, you restart the program (i.e., you type '<tt>run</tt>' again),
1490and you start getting errors about breakpoints being unsettable. The only way I
1491have found to "fix" this problem is to <tt>delete</tt> the breakpoints that are
1492already set in your pass, run the program, and re-set the breakpoints once
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1493execution stops in <tt>PassManager::run</tt>.</li>
Chris Lattner480e2ef2002-09-06 02:02:58 +0000[diff] [blame]1494
1495</ul>
1496
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1497<p>Hopefully these tips will help with common case debugging situations. If
1498you'd like to contribute some tips of your own, just contact <a
1499href="mailto:sabre@nondot.org">Chris</a>.</p>
Chris Lattner480e2ef2002-09-06 02:02:58 +0000[diff] [blame]1500
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1501</div>
Chris Lattner480e2ef2002-09-06 02:02:58 +0000[diff] [blame]1502
1503<!-- *********************************************************************** -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1504<div class="doc_section">
1505 <a name="future">Future extensions planned</a>
1506</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1507<!-- *********************************************************************** -->
1508
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1509<div class="doc_text">
1510
1511<p>Although the LLVM Pass Infrastructure is very capable as it stands, and does
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1512some 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]1513where we are going:</p>
1514
1515</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1516
1517<!-- _______________________________________________________________________ -->
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]1518<div class="doc_subsubsection">
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1519 <a name="SMP">Multithreaded LLVM</a>
1520</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1521
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1522<div class="doc_text">
1523
1524<p>Multiple CPU machines are becoming more common and compilation can never be
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1525fast enough: obviously we should allow for a multithreaded compiler. Because of
1526the semantics defined for passes above (specifically they cannot maintain state
1527across invocations of their <tt>run*</tt> methods), a nice clean way to
1528implement a multithreaded compiler would be for the <tt>PassManager</tt> class
Misha Brukmanbc0e9982003-07-14 17:20:40 +0000[diff] [blame]1529to create multiple instances of each pass object, and allow the separate
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1530instances to be hacking on different parts of the program at the same time.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1531
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1532<p>This implementation would prevent each of the passes from having to implement
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1533multithreaded constructs, requiring only the LLVM core to have locking in a few
1534places (for global resources). Although this is a simple extension, we simply
1535haven't had time (or multiprocessor machines, thus a reason) to implement this.
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1536Despite that, we have kept the LLVM passes SMP ready, and you should too.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1537
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1538</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1539
1540<!-- _______________________________________________________________________ -->
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]1541<div class="doc_subsubsection">
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1542 <a name="ModuleSource">A new <tt>ModuleSource</tt> interface</a>
1543</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1544
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1545<div class="doc_text">
1546
1547<p>Currently, the <tt>PassManager</tt>'s <tt>run</tt> method takes a <tt><a
Tanya Lattnera3da7772004-06-22 08:02:25 +0000[diff] [blame]1548href="http://llvm.cs.uiuc.edu/doxygen/classllvm_1_1Module.html">Module</a></tt>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1549as input, and runs all of the passes on this module. The problem with this
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1550approach is that none of the <tt>PassManager</tt> features can be used for
1551timing and debugging the actual <b>loading</b> of the module from disk or
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1552standard input.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1553
Misha Brukmanefc182e2004-03-08 23:06:46 +0000[diff] [blame]1554<p>To solve this problem, eventually the <tt>PassManager</tt> class will accept
1555a <tt>ModuleSource</tt> object instead of a Module itself. When complete, this
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1556will also allow for streaming of functions out of the bytecode representation,
1557allowing 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]1558dealing with <a href="#FunctionPass">FunctionPass</a>es.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1559
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1560<p>As part of a different issue, eventually the bytecode loader will be extended
1561to allow on-demand loading of functions from the bytecode representation, in
1562order to better support the runtime reoptimizer. The bytecode format is already
1563capable of this, the loader just needs to be reworked a bit.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1564
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1565</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1566
1567<!-- _______________________________________________________________________ -->
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]1568<div class="doc_subsubsection">
Misha Brukmanefc182e2004-03-08 23:06:46 +0000[diff] [blame]1569<a name="PassFunctionPass"><tt>Pass</tt>es requiring <tt>FunctionPass</tt>es</a>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1570</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1571
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1572<div class="doc_text">
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1573
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1574<p>Currently it is illegal for a <a href="#Pass"><tt>Pass</tt></a> to require a
1575<a href="#FunctionPass"><tt>FunctionPass</tt></a>. This is because there is
1576only one instance of the <a href="#FunctionPass"><tt>FunctionPass</tt></a>
1577object ever created, thus nowhere to store information for all of the functions
1578in the program at the same time. Although this has come up a couple of times
1579before, this has always been worked around by factoring one big complicated pass
1580into a global and an interprocedural part, both of which are distinct. In the
1581future, it would be nice to have this though.</p>
1582
1583<p>Note that it is no problem for a <a
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1584href="#FunctionPass"><tt>FunctionPass</tt></a> to require the results of a <a
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1585href="#Pass"><tt>Pass</tt></a>, only the other way around.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1586
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1587</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1588
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