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gerrit-public.fairphone.software / fp2-dev / platform / external / llvm / 05f8d5fed6b966b2a5854cdc564bd7f362765779 / . / docs / WritingAnLLVMPass.html
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4<head>
5 <title>Writing an LLVM Pass</title>
6 <link rel="stylesheet" href="llvm.css" type="text/css">
7</head>
8<body>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]9
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]10<div class="doc_title">
11 Writing an LLVM Pass
12</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]13
14<ol>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]15 <li><a href="#introduction">Introduction - What is a pass?</a></li>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]16 <li><a href="#quickstart">Quick Start - Writing hello world</a>
17 <ul>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]18 <li><a href="#makefile">Setting up the build environment</a></li>
19 <li><a href="#basiccode">Basic code required</a></li>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]20 <li><a href="#running">Running a pass with <tt>opt</tt>
Chris Lattner8fdb2462004-09-18 06:39:35 +0000[diff] [blame]21 or <tt>analyze</tt></a></li>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]22 </ul></li>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]23 <li><a href="#passtype">Pass classes and requirements</a>
24 <ul>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]25 <li><a href="#ImmutablePass">The <tt>ImmutablePass</tt> class</a></li>
Chris Lattnerf6278922004-09-20 04:36:29 +0000[diff] [blame]26 <li><a href="#ModulePass">The <tt>ModulePass</tt> class</a>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]27 <ul>
Chris Lattnerf6278922004-09-20 04:36:29 +0000[diff] [blame]28 <li><a href="#runOnModule">The <tt>runOnModule</tt> method</a></li>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]29 </ul></li>
Chris Lattner8fdb2462004-09-18 06:39:35 +0000[diff] [blame]30 <li><a href="#CallGraphSCCPass">The <tt>CallGraphSCCPass</tt> class</a>
31 <ul>
32 <li><a href="#doInitialization_scc">The <tt>doInitialization(Module
33 &amp;)</tt> method</a></li>
34 <li><a href="#runOnSCC">The <tt>runOnSCC</tt> method</a></li>
35 <li><a href="#doFinalization_scc">The <tt>doFinalization(Module
36 &amp;)</tt> method</a></li>
37 </ul></li>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]38 <li><a href="#FunctionPass">The <tt>FunctionPass</tt> class</a>
39 <ul>
Chris Lattnerd0713f92002-09-12 17:06:43 +0000[diff] [blame]40 <li><a href="#doInitialization_mod">The <tt>doInitialization(Module
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]41 &amp;)</tt> method</a></li>
42 <li><a href="#runOnFunction">The <tt>runOnFunction</tt> method</a></li>
Chris Lattnerd0713f92002-09-12 17:06:43 +0000[diff] [blame]43 <li><a href="#doFinalization_mod">The <tt>doFinalization(Module
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]44 &amp;)</tt> method</a></li>
45 </ul></li>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]46 <li><a href="#BasicBlockPass">The <tt>BasicBlockPass</tt> class</a>
47 <ul>
Chris Lattnerd0713f92002-09-12 17:06:43 +0000[diff] [blame]48 <li><a href="#doInitialization_fn">The <tt>doInitialization(Function
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]49 &amp;)</tt> method</a></li>
50 <li><a href="#runOnBasicBlock">The <tt>runOnBasicBlock</tt>
51 method</a></li>
Chris Lattnerd0713f92002-09-12 17:06:43 +0000[diff] [blame]52 <li><a href="#doFinalization_fn">The <tt>doFinalization(Function
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]53 &amp;)</tt> method</a></li>
54 </ul></li>
Brian Gaekecab8b6f2003-07-17 18:53:20 +0000[diff] [blame]55 <li><a href="#MachineFunctionPass">The <tt>MachineFunctionPass</tt>
56 class</a>
Brian Gaeke6a33f362003-07-22 20:53:20 +0000[diff] [blame]57 <ul>
58 <li><a href="#runOnMachineFunction">The
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]59 <tt>runOnMachineFunction(MachineFunction &amp;)</tt> method</a></li>
60 </ul></li>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]61 </ul>
62 <li><a href="#registration">Pass Registration</a>
63 <ul>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]64 <li><a href="#print">The <tt>print</tt> method</a></li>
65 </ul></li>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]66 <li><a href="#interaction">Specifying interactions between passes</a>
67 <ul>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]68 <li><a href="#getAnalysisUsage">The <tt>getAnalysisUsage</tt>
69 method</a></li>
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]70 <li><a href="#AU::addRequired">The <tt>AnalysisUsage::addRequired&lt;&gt;</tt> and <tt>AnalysisUsage::addRequiredTransitive&lt;&gt;</tt> methods</a></li>
71 <li><a href="#AU::addPreserved">The <tt>AnalysisUsage::addPreserved&lt;&gt;</tt> method</a></li>
72 <li><a href="#AU::examples">Example implementations of <tt>getAnalysisUsage</tt></a></li>
73 <li><a href="#getAnalysis">The <tt>getAnalysis&lt;&gt;</tt> and <tt>getAnalysisToUpdate&lt;&gt;</tt> methods</a></li>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]74 </ul></li>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]75 <li><a href="#analysisgroup">Implementing Analysis Groups</a>
76 <ul>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]77 <li><a href="#agconcepts">Analysis Group Concepts</a></li>
78 <li><a href="#registerag">Using <tt>RegisterAnalysisGroup</tt></a></li>
79 </ul></li>
Tanya Lattnerd5383652004-11-19 01:25:14 +0000[diff] [blame]80 <li><a href="#passStatistics">Pass Statistics</a>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]81 <li><a href="#passmanager">What PassManager does</a>
82 <ul>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]83 <li><a href="#releaseMemory">The <tt>releaseMemory</tt> method</a></li>
84 </ul></li>
Chris Lattner480e2ef2002-09-06 02:02:58 +0000[diff] [blame]85 <li><a href="#debughints">Using GDB with dynamically loaded passes</a>
86 <ul>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]87 <li><a href="#breakpoint">Setting a breakpoint in your pass</a></li>
88 <li><a href="#debugmisc">Miscellaneous Problems</a></li>
89 </ul></li>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]90 <li><a href="#future">Future extensions planned</a>
91 <ul>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]92 <li><a href="#SMP">Multithreaded LLVM</a></li>
Chris Lattnerf6278922004-09-20 04:36:29 +0000[diff] [blame]93 <li><a href="#PassFunctionPass"><tt>ModulePass</tt>es requiring
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]94 <tt>FunctionPass</tt>es</a></li>
95 </ul></li>
96</ol>
Chris Lattner38c633d2002-08-08 20:23:41 +0000[diff] [blame]97
Chris Lattner7911ce22004-05-23 21:07:27 +0000[diff] [blame]98<div class="doc_author">
99 <p>Written by <a href="mailto:sabre@nondot.org">Chris Lattner</a></p>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]100</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]101
102<!-- *********************************************************************** -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]103<div class="doc_section">
104 <a name="introduction">Introduction - What is a pass?</a>
105</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]106<!-- *********************************************************************** -->
107
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]108<div class="doc_text">
109
110<p>The LLVM Pass Framework is an important part of the LLVM system, because LLVM
Chris Lattner8fdb2462004-09-18 06:39:35 +0000[diff] [blame]111passes are where most of the interesting parts of the compiler exist. Passes
112perform the transformations and optimizations that make up the compiler, they
113build the analysis results that are used by these transformations, and they are,
114above all, a structuring technique for compiler code.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]115
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]116<p>All LLVM passes are subclasses of the <tt><a
117href="http://llvm.cs.uiuc.edu/doxygen/classllvm_1_1Pass.html">Pass</a></tt>
118class, which implement functionality by overriding virtual methods inherited
Chris Lattnerf6278922004-09-20 04:36:29 +0000[diff] [blame]119from <tt>Pass</tt>. Depending on how your pass works, you should inherit from
120the <tt><a href="#ModulePass">ModulePass</a></tt>, <tt><a
121href="#CallGraphSCCPass">CallGraphSCCPass</a></tt>, <tt><a
122href="#FunctionPass">FunctionPass</a></tt>, or <tt><a
Chris Lattner8fdb2462004-09-18 06:39:35 +0000[diff] [blame]123href="#BasicBlockPass">BasicBlockPass</a></tt> classes, which gives the system
124more information about what your pass does, and how it can be combined with
125other passes. One of the main features of the LLVM Pass Framework is that it
126schedules passes to run in an efficient way based on the constraints that your
127pass meets (which are indicated by which class they derive from).</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]128
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]129<p>We start by showing you how to construct a pass, everything from setting up
130the code, to compiling, loading, and executing it. After the basics are down,
131more advanced features are discussed.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]132
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]133</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]134
135<!-- *********************************************************************** -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]136<div class="doc_section">
137 <a name="quickstart">Quick Start - Writing hello world</a>
138</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]139<!-- *********************************************************************** -->
140
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]141<div class="doc_text">
142
143<p>Here we describe how to write the "hello world" of passes. The "Hello" pass
144is designed to simply print out the name of non-external functions that exist in
Chris Lattner8fdb2462004-09-18 06:39:35 +0000[diff] [blame]145the program being compiled. It does not modify the program at all, it just
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]146inspects it. The source code and files for this pass are available in the LLVM
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]147source tree in the <tt>lib/Transforms/Hello</tt> directory.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]148
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]149</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]150
151<!-- ======================================================================= -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]152<div class="doc_subsection">
153 <a name="makefile">Setting up the build environment</a>
154</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]155
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]156<div class="doc_text">
157
158<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]159source base. For this example, we'll assume that you made
160"<tt>lib/Transforms/Hello</tt>". The first thing you must do is set up a build
161script (Makefile) that will compile the source code for the new pass. To do
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]162this, copy this into "<tt>Makefile</tt>":</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]163
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]164<hr>
165
166<pre>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]167# Makefile for hello pass
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]168
Chris Lattner17a4c3e2002-08-14 20:06:13 +0000[diff] [blame]169# Path to top level of LLVM heirarchy
Chris Lattner7ce83e52002-08-14 20:07:01 +0000[diff] [blame]170LEVEL = ../../..
Chris Lattner17a4c3e2002-08-14 20:06:13 +0000[diff] [blame]171
172# Name of the library to build
Chris Lattner7ce83e52002-08-14 20:07:01 +0000[diff] [blame]173LIBRARYNAME = hello
Chris Lattner17a4c3e2002-08-14 20:06:13 +0000[diff] [blame]174
175# Build a dynamically loadable shared object
176SHARED_LIBRARY = 1
177
178# Include the makefile implementation stuff
179include $(LEVEL)/Makefile.common
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]180</pre>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]181
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]182<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]183directory are to be compiled and linked together into a
184<tt>lib/Debug/libhello.so</tt> shared object that can be dynamically loaded by
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]185the <tt>opt</tt> or <tt>analyze</tt> tools. If your operating system uses a
Chris Lattner8fdb2462004-09-18 06:39:35 +0000[diff] [blame]186suffix other than .so (such as windows or Mac OS/X), the appropriate extension
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]187will be used.</p>
John Criswellf9c78652004-01-26 21:26:54 +0000[diff] [blame]188
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]189<p>Now that we have the build scripts set up, we just need to write the code for
190the pass itself.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]191
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]192</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]193
194<!-- ======================================================================= -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]195<div class="doc_subsection">
196 <a name="basiccode">Basic code required</a>
197</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]198
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]199<div class="doc_text">
200
201<p>Now that we have a way to compile our new pass, we just have to write it.
202Start out with:</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]203
204<pre>
205<b>#include</b> "<a href="http://llvm.cs.uiuc.edu/doxygen/Pass_8h-source.html">llvm/Pass.h</a>"
206<b>#include</b> "<a href="http://llvm.cs.uiuc.edu/doxygen/Function_8h-source.html">llvm/Function.h</a>"
207</pre>
208
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]209<p>Which are needed because we are writing a <tt><a
210href="http://llvm.cs.uiuc.edu/doxygen/classllvm_1_1Pass.html">Pass</a></tt>, and
211we are operating on <tt><a
212href="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]213
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]214<p>Next we have:</p>
Jonathan Manton65acb302004-06-30 18:10:30 +0000[diff] [blame]215<pre>
216<b>using namespace llvm;</b>
217</pre>
218<p>... which is required because the functions from the include files
219live in the llvm namespace.
220</p>
221
222<p>Next we have:</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]223
224<pre>
225<b>namespace</b> {
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]226</pre>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]227
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]228<p>... which starts out an anonymous namespace. Anonymous namespaces are to C++
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]229what the "<tt>static</tt>" keyword is to C (at global scope). It makes the
230things declared inside of the anonymous namespace only visible to the current
231file. If you're not familiar with them, consult a decent C++ book for more
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]232information.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]233
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]234<p>Next, we declare our pass itself:</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]235
236<pre>
237 <b>struct</b> Hello : <b>public</b> <a href="#FunctionPass">FunctionPass</a> {
238</pre><p>
239
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]240<p>This declares a "<tt>Hello</tt>" class that is a subclass of <tt><a
241href="http://llvm.cs.uiuc.edu/doxygen/structllvm_1_1FunctionPass.html">FunctionPass</a></tt>.
Chris Lattnerd6ea9262002-09-09 03:48:46 +0000[diff] [blame]242The different builtin pass subclasses are described in detail <a
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]243href="#passtype">later</a>, but for now, know that <a
244href="#FunctionPass"><tt>FunctionPass</tt></a>'s operate a function at a
245time.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]246
247<pre>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]248 <b>virtual bool</b> <a href="#runOnFunction">runOnFunction</a>(Function &amp;F) {
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]249 std::cerr &lt;&lt; "<i>Hello: </i>" &lt;&lt; F.getName() &lt;&lt; "\n";
250 <b>return false</b>;
251 }
252 }; <i>// end of struct Hello</i>
253</pre>
254
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]255<p>We declare a "<a href="#runOnFunction"><tt>runOnFunction</tt></a>" method,
256which overloads an abstract virtual method inherited from <a
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]257href="#FunctionPass"><tt>FunctionPass</tt></a>. This is where we are supposed
258to 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]259function.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]260
261<pre>
262 RegisterOpt&lt;Hello&gt; X("<i>hello</i>", "<i>Hello World Pass</i>");
263} <i>// end of anonymous namespace</i>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]264</pre>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]265
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]266<p>Lastly, we register our class <tt>Hello</tt>, giving it a command line
267argument "<tt>hello</tt>", and a name "<tt>Hello World Pass</tt>". There are
268several different ways of <a href="#registration">registering your pass</a>,
269depending on what it is to be used for. For "optimizations" we use the
270<tt>RegisterOpt</tt> template.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]271
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]272<p>As a whole, the <tt>.cpp</tt> file looks like:</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]273
274<pre>
275<b>#include</b> "<a href="http://llvm.cs.uiuc.edu/doxygen/Pass_8h-source.html">llvm/Pass.h</a>"
276<b>#include</b> "<a href="http://llvm.cs.uiuc.edu/doxygen/Function_8h-source.html">llvm/Function.h</a>"
277
Jonathan Manton65acb302004-06-30 18:10:30 +0000[diff] [blame]278<b>using namespace llvm;</b>
279
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]280<b>namespace</b> {
281 <b>struct Hello</b> : <b>public</b> <a href="#FunctionPass">FunctionPass</a> {
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]282 <b>virtual bool</b> <a href="#runOnFunction">runOnFunction</a>(Function &amp;F) {
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]283 std::cerr &lt;&lt; "<i>Hello: </i>" &lt;&lt; F.getName() &lt;&lt; "\n";
284 <b>return false</b>;
285 }
286 };
287
288 RegisterOpt&lt;Hello&gt; X("<i>hello</i>", "<i>Hello World Pass</i>");
289}
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]290</pre>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]291
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]292<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]293command in the local directory and you should get a new
294"<tt>lib/Debug/libhello.so</tt> file. Note that everything in this file is
295contained in an anonymous namespace: this reflects the fact that passes are self
296contained units that do not need external interfaces (although they can have
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]297them) to be useful.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]298
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]299</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]300
301<!-- ======================================================================= -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]302<div class="doc_subsection">
303 <a name="running">Running a pass with <tt>opt</tt> or <tt>analyze</tt></a>
304</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]305
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]306<div class="doc_text">
307
John Criswellf9c78652004-01-26 21:26:54 +0000[diff] [blame]308<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]309<tt>opt</tt> command to run an LLVM program through your pass. Because you
310registered your pass with the <tt>RegisterOpt</tt> template, you will be able to
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]311use the <tt>opt</tt> tool to access it, once loaded.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]312
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]313<p>To test it, follow the example at the end of the <a
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]314href="GettingStarted.html">Getting Started Guide</a> to compile "Hello World" to
315LLVM. We can now run the bytecode file (<tt>hello.bc</tt>) for the program
316through our transformation like this (or course, any bytecode file will
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]317work):</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]318
319<pre>
320$ opt -load ../../../lib/Debug/libhello.so -hello &lt; hello.bc &gt; /dev/null
321Hello: __main
322Hello: puts
323Hello: main
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]324</pre>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]325
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]326<p>The '<tt>-load</tt>' option specifies that '<tt>opt</tt>' should load your
327pass as a shared object, which makes '<tt>-hello</tt>' a valid command line
328argument (which is one reason you need to <a href="#registration">register your
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]329pass</a>). Because the hello pass does not modify the program in any
330interesting way, we just throw away the result of <tt>opt</tt> (sending it to
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]331<tt>/dev/null</tt>).</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]332
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]333<p>To see what happened to the other string you registered, try running
334<tt>opt</tt> with the <tt>--help</tt> option:</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]335
336<pre>
337$ opt -load ../../../lib/Debug/libhello.so --help
338OVERVIEW: llvm .bc -&gt; .bc modular optimizer
339
340USAGE: opt [options] &lt;input bytecode&gt;
341
342OPTIONS:
343 Optimizations available:
344...
345 -funcresolve - Resolve Functions
346 -gcse - Global Common Subexpression Elimination
347 -globaldce - Dead Global Elimination
348 <b>-hello - Hello World Pass</b>
Chris Lattner065a6162003-09-10 05:29:43 +0000[diff] [blame]349 -indvars - Canonicalize Induction Variables
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]350 -inline - Function Integration/Inlining
351 -instcombine - Combine redundant instructions
352...
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]353</pre>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]354
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]355<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]356documentation to users of <tt>opt</tt>. Now that you have a working pass, you
357would go ahead and make it do the cool transformations you want. Once you get
358it all working and tested, it may become useful to find out how fast your pass
359is. The <a href="#passManager"><tt>PassManager</tt></a> provides a nice command
360line option (<tt>--time-passes</tt>) that allows you to get information about
361the execution time of your pass along with the other passes you queue up. For
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]362example:</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]363
364<pre>
365$ opt -load ../../../lib/Debug/libhello.so -hello -time-passes &lt; hello.bc &gt; /dev/null
366Hello: __main
367Hello: puts
368Hello: main
369===============================================================================
370 ... Pass execution timing report ...
371===============================================================================
372 Total Execution Time: 0.02 seconds (0.0479059 wall clock)
373
374 ---User Time--- --System Time-- --User+System-- ---Wall Time--- --- Pass Name ---
375 0.0100 (100.0%) 0.0000 ( 0.0%) 0.0100 ( 50.0%) 0.0402 ( 84.0%) Bytecode Writer
376 0.0000 ( 0.0%) 0.0100 (100.0%) 0.0100 ( 50.0%) 0.0031 ( 6.4%) Dominator Set Construction
377 0.0000 ( 0.0%) 0.0000 ( 0.0%) 0.0000 ( 0.0%) 0.0013 ( 2.7%) Module Verifier
378 <b> 0.0000 ( 0.0%) 0.0000 ( 0.0%) 0.0000 ( 0.0%) 0.0033 ( 6.9%) Hello World Pass</b>
379 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]380</pre>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]381
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]382<p>As you can see, our implementation above is pretty fast :). The additional
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]383passes listed are automatically inserted by the '<tt>opt</tt>' tool to verify
384that the LLVM emitted by your pass is still valid and well formed LLVM, which
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]385hasn't been broken somehow.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]386
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]387<p>Now that you have seen the basics of the mechanics behind passes, we can talk
388about some more details of how they work and how to use them.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]389
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]390</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]391
392<!-- *********************************************************************** -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]393<div class="doc_section">
394 <a name="passtype">Pass classes and requirements</a>
395</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]396<!-- *********************************************************************** -->
397
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]398<div class="doc_text">
399
400<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]401decide what class you should subclass for your pass. The <a
402href="#basiccode">Hello World</a> example uses the <tt><a
403href="#FunctionPass">FunctionPass</a></tt> class for its implementation, but we
404did not discuss why or when this should occur. Here we talk about the classes
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]405available, from the most general to the most specific.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]406
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]407<p>When choosing a superclass for your Pass, you should choose the <b>most
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]408specific</b> class possible, while still being able to meet the requirements
Misha Brukman5560c9d2003-08-18 14:43:39 +0000[diff] [blame]409listed. This gives the LLVM Pass Infrastructure information necessary to
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]410optimize how passes are run, so that the resultant compiler isn't unneccesarily
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]411slow.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]412
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]413</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]414
Chris Lattnerf004f9a2002-09-25 22:31:38 +0000[diff] [blame]415<!-- ======================================================================= -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]416<div class="doc_subsection">
417 <a name="ImmutablePass">The <tt>ImmutablePass</tt> class</a>
418</div>
Chris Lattnerf004f9a2002-09-25 22:31:38 +0000[diff] [blame]419
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]420<div class="doc_text">
421
422<p>The most plain and boring type of pass is the "<tt><a
423href="http://llvm.cs.uiuc.edu/doxygen/structllvm_1_1ImmutablePass.html">ImmutablePass</a></tt>"
Chris Lattnerf004f9a2002-09-25 22:31:38 +0000[diff] [blame]424class. This pass type is used for passes that do not have to be run, do not
425change state, and never need to be updated. This is not a normal type of
426transformation or analysis, but can provide information about the current
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]427compiler configuration.</p>
Chris Lattnerf004f9a2002-09-25 22:31:38 +0000[diff] [blame]428
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]429<p>Although this pass class is very infrequently used, it is important for
Chris Lattnerf004f9a2002-09-25 22:31:38 +0000[diff] [blame]430providing information about the current target machine being compiled for, and
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]431other static information that can affect the various transformations.</p>
Chris Lattnerf004f9a2002-09-25 22:31:38 +0000[diff] [blame]432
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]433<p><tt>ImmutablePass</tt>es never invalidate other transformations, are never
434invalidated, and are never "run".</p>
Chris Lattnerf004f9a2002-09-25 22:31:38 +0000[diff] [blame]435
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]436</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]437
438<!-- ======================================================================= -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]439<div class="doc_subsection">
Chris Lattnerf6278922004-09-20 04:36:29 +0000[diff] [blame]440 <a name="ModulePass">The <tt>ModulePass</tt> class</a>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]441</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]442
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]443<div class="doc_text">
444
445<p>The "<tt><a
Chris Lattnerf6278922004-09-20 04:36:29 +0000[diff] [blame]446href="http://llvm.cs.uiuc.edu/doxygen/classllvm_1_1ModulePass.html">ModulePass</a></tt>"
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]447class is the most general of all superclasses that you can use. Deriving from
Chris Lattnerf6278922004-09-20 04:36:29 +0000[diff] [blame]448<tt>ModulePass</tt> indicates that your pass uses the entire program as a unit,
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]449refering to function bodies in no predictable order, or adding and removing
Chris Lattnerf6278922004-09-20 04:36:29 +0000[diff] [blame]450functions. Because nothing is known about the behavior of <tt>ModulePass</tt>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]451subclasses, no optimization can be done for their execution.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]452
Chris Lattnerf6278922004-09-20 04:36:29 +0000[diff] [blame]453<p>To write a correct <tt>ModulePass</tt> subclass, derive from
454<tt>ModulePass</tt> and overload the <tt>runOnModule</tt> method with the
455following signature:</p>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]456
457</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]458
459<!-- _______________________________________________________________________ -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]460<div class="doc_subsubsection">
Chris Lattnerf6278922004-09-20 04:36:29 +0000[diff] [blame]461 <a name="runOnModule">The <tt>runOnModule</tt> method</a>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]462</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]463
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]464<div class="doc_text">
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]465
466<pre>
Chris Lattnerf6278922004-09-20 04:36:29 +0000[diff] [blame]467 <b>virtual bool</b> runOnModule(Module &amp;M) = 0;
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]468</pre>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]469
Chris Lattnerf6278922004-09-20 04:36:29 +0000[diff] [blame]470<p>The <tt>runOnModule</tt> method performs the interesting work of the pass,
471and should return true if the module was modified by the transformation, false
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]472otherwise.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]473
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]474</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]475
476<!-- ======================================================================= -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]477<div class="doc_subsection">
Chris Lattner8fdb2462004-09-18 06:39:35 +0000[diff] [blame]478 <a name="CallGraphSCCPass">The <tt>CallGraphSCCPass</tt> class</a>
479</div>
480
481<div class="doc_text">
482
483<p>The "<tt><a
484href="http://llvm.cs.uiuc.edu/doxygen/structllvm_1_1CallGraphSCCPass.html">CallGraphSCCPass</a></tt>"
485is used by passes that need to traverse the program bottom-up on the call graph
486(callees before callers). Deriving from CallGraphSCCPass provides some
487mechanics for building and traversing the CallGraph, but also allows the system
488to optimize execution of CallGraphSCCPass's. If your pass meets the
489requirements outlined below, and doesn't meet the requirements of a <tt><a
490href="#FunctionPass">FunctionPass</a></tt> or <tt><a
491href="#BasicBlockPass">BasicBlockPass</a></tt>, you should derive from
492<tt>CallGraphSCCPass</tt>.</p>
493
494<p><b>TODO</b>: explain briefly what SCC, Tarjan's algo, and B-U mean.</p>
495
496<p>To be explicit, <tt>CallGraphSCCPass</tt> subclasses are:</p>
497
498<ol>
499
500<li>... <em>not allowed</em> to modify any <tt>Function</tt>s that are not in
501the current SCC.</li>
502
503<li>... <em>allowed</em> to inspect any Function's other than those in the
504current SCC and the direct callees of the SCC.</li>
505
506<li>... <em>required</em> to preserve the current CallGraph object, updating it
507to reflect any changes made to the program.</li>
508
509<li>... <em>not allowed</em> to add or remove SCC's from the current Module,
510though they may change the contents of an SCC.</li>
511
512<li>... <em>allowed</em> to add or remove global variables from the current
513Module.</li>
514
515<li>... <em>allowed</em> to maintain state across invocations of
516 <a href="#runOnSCC"><tt>runOnSCC</tt></a> (including global data).</li>
517</ol>
518
519<p>Implementing a <tt>CallGraphSCCPass</tt> is slightly tricky in some cases
520because it has to handle SCCs with more than one node in it. All of the virtual
521methods described below should return true if they modified the program, or
522false if they didn't.</p>
523
524</div>
525
526<!-- _______________________________________________________________________ -->
527<div class="doc_subsubsection">
528 <a name="doInitialization_scc">The <tt>doInitialization(Module &amp;)</tt>
529 method</a>
530</div>
531
532<div class="doc_text">
533
534<pre>
535 <b>virtual bool</b> doInitialization(Module &amp;M);
536</pre>
537
538<p>The <tt>doIninitialize</tt> method is allowed to do most of the things that
539<tt>CallGraphSCCPass</tt>'s are not allowed to do. They can add and remove
540functions, get pointers to functions, etc. The <tt>doInitialization</tt> method
541is designed to do simple initialization type of stuff that does not depend on
542the SCCs being processed. The <tt>doInitialization</tt> method call is not
543scheduled to overlap with any other pass executions (thus it should be very
544fast).</p>
545
546</div>
547
548<!-- _______________________________________________________________________ -->
549<div class="doc_subsubsection">
550 <a name="runOnSCC">The <tt>runOnSCC</tt> method</a>
551</div>
552
553<div class="doc_text">
554
555<pre>
556 <b>virtual bool</b> runOnSCC(const std::vector&lt;CallGraphNode *&gt; &amp;SCCM) = 0;
557</pre>
558
559<p>The <tt>runOnSCC</tt> method performs the interesting work of the pass, and
560should return true if the module was modified by the transformation, false
561otherwise.</p>
562
563</div>
564
565<!-- _______________________________________________________________________ -->
566<div class="doc_subsubsection">
567 <a name="doFinalization_scc">The <tt>doFinalization(Module
568 &amp;)</tt> method</a>
569</div>
570
571<div class="doc_text">
572
573<pre>
574 <b>virtual bool</b> doFinalization(Module &amp;M);
575</pre>
576
577<p>The <tt>doFinalization</tt> method is an infrequently used method that is
578called when the pass framework has finished calling <a
579href="#runOnFunction"><tt>runOnFunction</tt></a> for every function in the
580program being compiled.</p>
581
582</div>
583
584<!-- ======================================================================= -->
585<div class="doc_subsection">
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]586 <a name="FunctionPass">The <tt>FunctionPass</tt> class</a>
587</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]588
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]589<div class="doc_text">
590
Chris Lattnerf6278922004-09-20 04:36:29 +0000[diff] [blame]591<p>In contrast to <tt>ModulePass</tt> subclasses, <tt><a
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]592href="http://llvm.cs.uiuc.edu/doxygen/classllvm_1_1Pass.html">FunctionPass</a></tt>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]593subclasses do have a predictable, local behavior that can be expected by the
594system. All <tt>FunctionPass</tt> execute on each function in the program
Misha Brukmanef6a6a62003-08-21 22:14:26 +0000[diff] [blame]595independent of all of the other functions in the program.
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]596<tt>FunctionPass</tt>'s do not require that they are executed in a particular
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]597order, and <tt>FunctionPass</tt>'s do not modify external functions.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]598
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]599<p>To be explicit, <tt>FunctionPass</tt> subclasses are not allowed to:</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]600
601<ol>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]602<li>Modify a Function other than the one currently being processed.</li>
603<li>Add or remove Function's from the current Module.</li>
604<li>Add or remove global variables from the current Module.</li>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]605<li>Maintain state across invocations of
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]606 <a href="#runOnFunction"><tt>runOnFunction</tt></a> (including global data)</li>
607</ol>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]608
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]609<p>Implementing a <tt>FunctionPass</tt> is usually straightforward (See the <a
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]610href="#basiccode">Hello World</a> pass for example). <tt>FunctionPass</tt>'s
611may overload three virtual methods to do their work. All of these methods
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]612should return true if they modified the program, or false if they didn't.</p>
613
614</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]615
616<!-- _______________________________________________________________________ -->
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]617<div class="doc_subsubsection">
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]618 <a name="doInitialization_mod">The <tt>doInitialization(Module &amp;)</tt>
619 method</a>
620</div>
621
622<div class="doc_text">
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]623
624<pre>
625 <b>virtual bool</b> doInitialization(Module &amp;M);
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]626</pre>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]627
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]628<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]629<tt>FunctionPass</tt>'s are not allowed to do. They can add and remove
Chris Lattnerd0713f92002-09-12 17:06:43 +0000[diff] [blame]630functions, get pointers to functions, etc. The <tt>doInitialization</tt> method
631is designed to do simple initialization type of stuff that does not depend on
632the functions being processed. The <tt>doInitialization</tt> method call is not
633scheduled to overlap with any other pass executions (thus it should be very
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]634fast).</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]635
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]636<p>A good example of how this method should be used is the <a
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]637href="http://llvm.cs.uiuc.edu/doxygen/LowerAllocations_8cpp-source.html">LowerAllocations</a>
638pass. This pass converts <tt>malloc</tt> and <tt>free</tt> instructions into
Misha Brukmanef6a6a62003-08-21 22:14:26 +0000[diff] [blame]639platform dependent <tt>malloc()</tt> and <tt>free()</tt> function calls. It
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]640uses the <tt>doInitialization</tt> method to get a reference to the malloc and
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]641free functions that it needs, adding prototypes to the module if necessary.</p>
642
643</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]644
645<!-- _______________________________________________________________________ -->
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]646<div class="doc_subsubsection">
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]647 <a name="runOnFunction">The <tt>runOnFunction</tt> method</a>
648</div>
649
650<div class="doc_text">
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]651
652<pre>
653 <b>virtual bool</b> runOnFunction(Function &amp;F) = 0;
654</pre><p>
655
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]656<p>The <tt>runOnFunction</tt> method must be implemented by your subclass to do
657the transformation or analysis work of your pass. As usual, a true value should
658be returned if the function is modified.</p>
659
660</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]661
662<!-- _______________________________________________________________________ -->
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]663<div class="doc_subsubsection">
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]664 <a name="doFinalization_mod">The <tt>doFinalization(Module
665 &amp;)</tt> method</a>
666</div>
667
668<div class="doc_text">
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]669
670<pre>
671 <b>virtual bool</b> doFinalization(Module &amp;M);
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]672</pre>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]673
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]674<p>The <tt>doFinalization</tt> method is an infrequently used method that is
675called when the pass framework has finished calling <a
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]676href="#runOnFunction"><tt>runOnFunction</tt></a> for every function in the
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]677program being compiled.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]678
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]679</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]680
681<!-- ======================================================================= -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]682<div class="doc_subsection">
683 <a name="BasicBlockPass">The <tt>BasicBlockPass</tt> class</a>
684</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]685
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]686<div class="doc_text">
687
688<p><tt>BasicBlockPass</tt>'s are just like <a
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]689href="#FunctionPass"><tt>FunctionPass</tt></a>'s, except that they must limit
690their scope of inspection and modification to a single basic block at a time.
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]691As such, they are <b>not</b> allowed to do any of the following:</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]692
693<ol>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]694<li>Modify or inspect any basic blocks outside of the current one</li>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]695<li>Maintain state across invocations of
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]696 <a href="#runOnBasicBlock"><tt>runOnBasicBlock</tt></a></li>
697<li>Modify the constrol flow graph (by altering terminator instructions)</li>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]698<li>Any of the things verboten for
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]699 <a href="#FunctionPass"><tt>FunctionPass</tt></a>es.</li>
700</ol>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]701
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]702<p><tt>BasicBlockPass</tt>es are useful for traditional local and "peephole"
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]703optimizations. They may override the same <a
Chris Lattnerd0713f92002-09-12 17:06:43 +0000[diff] [blame]704href="#doInitialization_mod"><tt>doInitialization(Module &amp;)</tt></a> and <a
705href="#doFinalization_mod"><tt>doFinalization(Module &amp;)</tt></a> methods that <a
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]706href="#FunctionPass"><tt>FunctionPass</tt></a>'s have, but also have the following virtual methods that may also be implemented:</p>
707
708</div>
Chris Lattnerd0713f92002-09-12 17:06:43 +0000[diff] [blame]709
710<!-- _______________________________________________________________________ -->
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]711<div class="doc_subsubsection">
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]712 <a name="doInitialization_fn">The <tt>doInitialization(Function
713 &amp;)</tt> method</a>
714</div>
715
716<div class="doc_text">
Chris Lattnerd0713f92002-09-12 17:06:43 +0000[diff] [blame]717
718<pre>
719 <b>virtual bool</b> doInitialization(Function &amp;F);
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]720</pre>
Chris Lattnerd0713f92002-09-12 17:06:43 +0000[diff] [blame]721
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]722<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]723<tt>BasicBlockPass</tt>'s are not allowed to do, but that
724<tt>FunctionPass</tt>'s can. The <tt>doInitialization</tt> method is designed
725to do simple initialization type of stuff that does not depend on the
726BasicBlocks being processed. The <tt>doInitialization</tt> method call is not
727scheduled to overlap with any other pass executions (thus it should be very
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]728fast).</p>
Chris Lattnerd0713f92002-09-12 17:06:43 +0000[diff] [blame]729
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]730</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]731
732<!-- _______________________________________________________________________ -->
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]733<div class="doc_subsubsection">
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]734 <a name="runOnBasicBlock">The <tt>runOnBasicBlock</tt> method</a>
735</div>
736
737<div class="doc_text">
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]738
739<pre>
740 <b>virtual bool</b> runOnBasicBlock(BasicBlock &amp;BB) = 0;
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]741</pre>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]742
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]743<p>Override this function to do the work of the <tt>BasicBlockPass</tt>. This
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]744function is not allowed to inspect or modify basic blocks other than the
745parameter, and are not allowed to modify the CFG. A true value must be returned
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]746if the basic block is modified.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]747
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]748</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]749
Chris Lattnerd0713f92002-09-12 17:06:43 +0000[diff] [blame]750<!-- _______________________________________________________________________ -->
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]751<div class="doc_subsubsection">
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]752 <a name="doFinalization_fn">The <tt>doFinalization(Function &amp;)</tt>
753 method</a>
754</div>
755
756<div class="doc_text">
Chris Lattnerd0713f92002-09-12 17:06:43 +0000[diff] [blame]757
758<pre>
759 <b>virtual bool</b> doFinalization(Function &amp;F);
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]760</pre>
Chris Lattnerd0713f92002-09-12 17:06:43 +0000[diff] [blame]761
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]762<p>The <tt>doFinalization</tt> method is an infrequently used method that is
763called when the pass framework has finished calling <a
Chris Lattnerd0713f92002-09-12 17:06:43 +0000[diff] [blame]764href="#runOnBasicBlock"><tt>runOnBasicBlock</tt></a> for every BasicBlock in the
765program being compiled. This can be used to perform per-function
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]766finalization.</p>
Chris Lattnerd0713f92002-09-12 17:06:43 +0000[diff] [blame]767
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]768</div>
Chris Lattnerd0713f92002-09-12 17:06:43 +0000[diff] [blame]769
Brian Gaekecab8b6f2003-07-17 18:53:20 +0000[diff] [blame]770<!-- ======================================================================= -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]771<div class="doc_subsection">
772 <a name="MachineFunctionPass">The <tt>MachineFunctionPass</tt> class</a>
773</div>
Brian Gaekecab8b6f2003-07-17 18:53:20 +0000[diff] [blame]774
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]775<div class="doc_text">
776
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]777<p>A <tt>MachineFunctionPass</tt> is a part of the LLVM code generator that
778executes on the machine-dependent representation of each LLVM function in the
779program. A <tt>MachineFunctionPass</tt> is also a <tt>FunctionPass</tt>, so all
Brian Gaekecab8b6f2003-07-17 18:53:20 +0000[diff] [blame]780the restrictions that apply to a <tt>FunctionPass</tt> also apply to it.
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]781<tt>MachineFunctionPass</tt>es also have additional restrictions. In particular,
782<tt>MachineFunctionPass</tt>es are not allowed to do any of the following:</p>
Brian Gaekecab8b6f2003-07-17 18:53:20 +0000[diff] [blame]783
784<ol>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]785<li>Modify any LLVM Instructions, BasicBlocks or Functions.</li>
786<li>Modify a MachineFunction other than the one currently being processed.</li>
787<li>Add or remove MachineFunctions from the current Module.</li>
788<li>Add or remove global variables from the current Module.</li>
789<li>Maintain state across invocations of <a
790href="#runOnMachineFunction"><tt>runOnMachineFunction</tt></a> (including global
791data)</li>
792</ol>
Brian Gaekecab8b6f2003-07-17 18:53:20 +0000[diff] [blame]793
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]794</div>
Chris Lattnerd0713f92002-09-12 17:06:43 +0000[diff] [blame]795
Brian Gaeke6a33f362003-07-22 20:53:20 +0000[diff] [blame]796<!-- _______________________________________________________________________ -->
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]797<div class="doc_subsubsection">
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]798 <a name="runOnMachineFunction">The <tt>runOnMachineFunction(MachineFunction
799 &amp;MF)</tt> method</a>
800</div>
801
802<div class="doc_text">
Brian Gaeke6a33f362003-07-22 20:53:20 +0000[diff] [blame]803
804<pre>
805 <b>virtual bool</b> runOnMachineFunction(MachineFunction &amp;MF) = 0;
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]806</pre>
Brian Gaeke6a33f362003-07-22 20:53:20 +0000[diff] [blame]807
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]808<p><tt>runOnMachineFunction</tt> can be considered the main entry point of a
809<tt>MachineFunctionPass</tt>; that is, you should override this method to do the
810work of your <tt>MachineFunctionPass</tt>.</p>
Brian Gaeke6a33f362003-07-22 20:53:20 +0000[diff] [blame]811
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]812<p>The <tt>runOnMachineFunction</tt> method is called on every
Brian Gaeke6a33f362003-07-22 20:53:20 +0000[diff] [blame]813<tt>MachineFunction</tt> in a <tt>Module</tt>, so that the
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]814<tt>MachineFunctionPass</tt> may perform optimizations on the machine-dependent
815representation of the function. If you want to get at the LLVM <tt>Function</tt>
816for the <tt>MachineFunction</tt> you're working on, use
817<tt>MachineFunction</tt>'s <tt>getFunction()</tt> accessor method -- but
818remember, you may not modify the LLVM <tt>Function</tt> or its contents from a
819<tt>MachineFunctionPass</tt>.</p>
820
821</div>
Brian Gaeke6a33f362003-07-22 20:53:20 +0000[diff] [blame]822
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]823<!-- *********************************************************************** -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]824<div class="doc_section">
825 <a name="registration">Pass registration</a>
826</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]827<!-- *********************************************************************** -->
828
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]829<div class="doc_text">
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]830
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]831<p>In the <a href="#basiccode">Hello World</a> example pass we illustrated how
832pass registration works, and discussed some of the reasons that it is used and
833what it does. Here we discuss how and why passes are registered.</p>
834
835<p>Passes can be registered in several different ways. Depending on the general
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]836classification of the pass, you should use one of the following templates to
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]837register the pass:</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]838
839<ul>
840<li><b><tt>RegisterOpt</tt></b> - This template should be used when you are
841registering a pass that logically should be available for use in the
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]842'<tt>opt</tt>' utility.</li>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]843
844<li><b><tt>RegisterAnalysis</tt></b> - This template should be used when you are
845registering a pass that logically should be available for use in the
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]846'<tt>analyze</tt>' utility.</li>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]847
848<li><b><tt>RegisterPass</tt></b> - This is the generic form of the
849<tt>Register*</tt> templates that should be used if you want your pass listed by
850multiple or no utilities. This template takes an extra third argument that
851specifies which tools it should be listed in. See the <a
852href="http://llvm.cs.uiuc.edu/doxygen/PassSupport_8h-source.html">PassSupport.h</a>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]853file for more information.</li>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]854
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]855</ul>
856
857<p>Regardless of how you register your pass, you must specify at least two
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]858parameters. The first parameter is the name of the pass that is to be used on
859the command line to specify that the pass should be added to a program (for
860example <tt>opt</tt> or <tt>analyze</tt>). The second argument is the name of
861the 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]862well as for debug output generated by the <tt>--debug-pass</tt> option.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]863
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]864<p>If a pass is registered to be used by the <tt>analyze</tt> utility, you
865should implement the virtual <tt>print</tt> method:</p>
866
867</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]868
869<!-- _______________________________________________________________________ -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]870<div class="doc_subsubsection">
871 <a name="print">The <tt>print</tt> method</a>
872</div>
873
874<div class="doc_text">
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]875
876<pre>
877 <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]878</pre>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]879
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]880<p>The <tt>print</tt> method must be implemented by "analyses" in order to print
881a human readable version of the analysis results. This is useful for debugging
882an analysis itself, as well as for other people to figure out how an analysis
883works. The <tt>analyze</tt> tool uses this method to generate its output.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]884
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]885<p>The <tt>ostream</tt> parameter specifies the stream to write the results on,
886and 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]887program that has been analyzed. Note however that this pointer may be null in
888certain circumstances (such as calling the <tt>Pass::dump()</tt> from a
889debugger), so it should only be used to enhance debug output, it should not be
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]890depended on.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]891
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]892</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]893
894<!-- *********************************************************************** -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]895<div class="doc_section">
896 <a name="interaction">Specifying interactions between passes</a>
897</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]898<!-- *********************************************************************** -->
899
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]900<div class="doc_text">
901
902<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]903that passes interact with each other correctly. Because <tt>PassManager</tt>
904tries to <a href="#passmanager">optimize the execution of passes</a> it must
905know how the passes interact with each other and what dependencies exist between
906the various passes. To track this, each pass can declare the set of passes that
907are required to be executed before the current pass, and the passes which are
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]908invalidated by the current pass.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]909
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]910<p>Typically this functionality is used to require that analysis results are
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]911computed before your pass is run. Running arbitrary transformation passes can
912invalidate the computed analysis results, which is what the invalidation set
913specifies. If a pass does not implement the <tt><a
914href="#getAnalysisUsage">getAnalysisUsage</a></tt> method, it defaults to not
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]915having any prerequisite passes, and invalidating <b>all</b> other passes.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]916
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]917</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]918
919<!-- _______________________________________________________________________ -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]920<div class="doc_subsubsection">
921 <a name="getAnalysisUsage">The <tt>getAnalysisUsage</tt> method</a>
922</div>
923
924<div class="doc_text">
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]925
926<pre>
927 <b>virtual void</b> getAnalysisUsage(AnalysisUsage &amp;Info) <b>const</b>;
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]928</pre>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]929
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]930<p>By implementing the <tt>getAnalysisUsage</tt> method, the required and
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]931invalidated sets may be specified for your transformation. The implementation
932should fill in the <tt><a
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]933href="http://llvm.cs.uiuc.edu/doxygen/classllvm_1_1AnalysisUsage.html">AnalysisUsage</a></tt>
934object with information about which passes are required and not invalidated. To
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]935do this, a pass may call any of the following methods on the AnalysisUsage
936object:</p>
937</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]938
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]939<!-- _______________________________________________________________________ -->
940<div class="doc_subsubsection">
941 <a name="AU::addRequired">The <tt>AnalysisUsage::addRequired&lt;&gt;</tt> and <tt>AnalysisUsage::addRequiredTransitive&lt;&gt;</tt> methods</a>
942</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]943
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]944<div class="doc_text">
945<p>
946If you pass requires a previous pass to be executed (an analysis for example),
947it can use one of these methods to arrange for it to be run before your pass.
948LLVM has many different types of analyses and passes that can be required,
949spaning the range from <tt>DominatorSet</tt> to <tt>BreakCriticalEdges</tt>.
950requiring <tt>BreakCriticalEdges</tt>, for example, guarantees that there will
951be no critical edges in the CFG when your pass has been run.
952</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]953
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]954<p>
955Some analyses chain to other analyses to do their job. For example, an <a
956href="AliasAnalysis.html">AliasAnalysis</a> implementation is required to <a
957href="AliasAnalysis.html#chaining">chain</a> to other alias analysis passes. In
958cases where analyses chain, the <tt>addRequiredTransitive</tt> method should be
959used instead of the <tt>addRequired</tt> method. This informs the PassManager
960that the transitively required pass should be alive as long as the requiring
961pass is.
962</p>
963</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]964
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]965<!-- _______________________________________________________________________ -->
966<div class="doc_subsubsection">
967 <a name="AU::addPreserved">The <tt>AnalysisUsage::addPreserved&lt;&gt;</tt> method</a>
968</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]969
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]970<div class="doc_text">
971<p>
972One of the jobs of the PassManager is to optimize how and when analyses are run.
973In particular, it attempts to avoid recomputing data unless it needs to. For
974this reason, passes are allowed to declare that they preserve (i.e., they don't
975invalidate) an existing analysis if it's available. For example, a simple
976constant folding pass would not modify the CFG, so it can't possible effect the
977results of dominator analysis. By default, all passes are assumed to invalidate
978all others.
979</p>
980
981<p>
982The <tt>AnalysisUsage</tt> class provides several methods which are useful in
983certain circumstances that are related to <tt>addPreserved</tt>. In particular,
984the <tt>setPreservesAll</tt> method can be called to indicate that the pass does
985not modify the LLVM program at all (which is true for analyses), and the
986<tt>setPreservesCFG</tt> method can be used by transformations that change
987instructions in the program but do not modify the CFG or terminator instructions
988(note that this property is implicitly set for <a
989href="#BasicBlockPass">BasicBlockPass</a>'s).
990</p>
991
992<p>
993<tt>addPreserved</tt> is particularly useful for transformations like
994<tt>BreakCriticalEdges</tt>. This pass knows how to update a small set of loop
995and dominator related analyses if they exist, so it can preserve them, despite
996the fact that it hacks on the CFG.
997</p>
998</div>
999
1000<!-- _______________________________________________________________________ -->
1001<div class="doc_subsubsection">
1002 <a name="AU::examples">Example implementations of <tt>getAnalysisUsage</tt></a>
1003</div>
1004
1005<div class="doc_text">
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1006
1007<pre>
1008 <i>// This is an example implementation from an analysis, which does not modify
1009 // the program at all, yet has a prerequisite.</i>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1010 <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]1011 AU.setPreservesAll();
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1012 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]1013 }
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1014</pre>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1015
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1016<p>and:</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1017
1018<pre>
1019 <i>// This example modifies the program, but does not modify the CFG</i>
1020 <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]1021 AU.setPreservesCFG();
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1022 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]1023 }
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1024</pre>
1025
1026</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1027
1028<!-- _______________________________________________________________________ -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1029<div class="doc_subsubsection">
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]1030 <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]1031</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1032
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1033<div class="doc_text">
1034
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]1035<p>The <tt>Pass::getAnalysis&lt;&gt;</tt> method is automatically inherited by
1036your class, providing you with access to the passes that you declared that you
1037required with the <a href="#getAnalysisUsage"><tt>getAnalysisUsage</tt></a>
1038method. It takes a single template argument that specifies which pass class you
1039want, and returns a reference to that pass. For example:</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1040
1041<pre>
Chris Lattnera5776302004-03-17 21:33:32 +0000[diff] [blame]1042 bool LICM::runOnFunction(Function &amp;F) {
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]1043 LoopInfo &amp;LI = getAnalysis&lt;LoopInfo&gt;();
1044 ...
1045 }
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1046</pre>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1047
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1048<p>This method call returns a reference to the pass desired. You may get a
1049runtime assertion failure if you attempt to get an analysis that you did not
1050declare as required in your <a
1051href="#getAnalysisUsage"><tt>getAnalysisUsage</tt></a> implementation. This
1052method can be called by your <tt>run*</tt> method implementation, or by any
1053other local method invoked by your <tt>run*</tt> method.</p>
1054
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]1055<p>
1056If your pass is capable of updating analyses if they exist (e.g.,
1057<tt>BreakCriticalEdges</tt>, as described above), you can use the
1058<tt>getAnalysisToUpdate</tt> method, which returns a pointer to the analysis if
1059it is active. For example:</p>
1060
1061<pre>
1062 ...
1063 if (DominatorSet *DS = getAnalysisToUpdate&lt;DominatorSet&gt;()) {
1064 <i>// A DominatorSet is active. This code will update it.</i>
1065 }
1066 ...
1067</pre>
1068
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1069</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1070
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1071<!-- *********************************************************************** -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1072<div class="doc_section">
1073 <a name="analysisgroup">Implementing Analysis Groups</a>
1074</div>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1075<!-- *********************************************************************** -->
1076
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1077<div class="doc_text">
1078
1079<p>Now that we understand the basics of how passes are defined, how the are
1080used, 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]1081fancier. All of the pass relationships that we have seen so far are very
1082simple: one pass depends on one other specific pass to be run before it can run.
1083For many applications, this is great, for others, more flexibility is
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1084required.</p>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1085
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1086<p>In particular, some analyses are defined such that there is a single simple
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1087interface to the analysis results, but multiple ways of calculating them.
1088Consider alias analysis for example. The most trivial alias analysis returns
1089"may alias" for any alias query. The most sophisticated analysis a
1090flow-sensitive, context-sensitive interprocedural analysis that can take a
1091significant amount of time to execute (and obviously, there is a lot of room
1092between these two extremes for other implementations). To cleanly support
1093situations like this, the LLVM Pass Infrastructure supports the notion of
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1094Analysis Groups.</p>
1095
1096</div>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1097
1098<!-- _______________________________________________________________________ -->
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]1099<div class="doc_subsubsection">
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1100 <a name="agconcepts">Analysis Group Concepts</a>
1101</div>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1102
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1103<div class="doc_text">
1104
1105<p>An Analysis Group is a single simple interface that may be implemented by
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1106multiple different passes. Analysis Groups can be given human readable names
1107just like passes, but unlike passes, they need not derive from the <tt>Pass</tt>
1108class. An analysis group may have one or more implementations, one of which is
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1109the "default" implementation.</p>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1110
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1111<p>Analysis groups are used by client passes just like other passes are: the
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1112<tt>AnalysisUsage::addRequired()</tt> and <tt>Pass::getAnalysis()</tt> methods.
1113In order to resolve this requirement, the <a href="#passmanager">PassManager</a>
1114scans the available passes to see if any implementations of the analysis group
1115are available. If none is available, the default implementation is created for
1116the pass to use. All standard rules for <A href="#interaction">interaction
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1117between passes</a> still apply.</p>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1118
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1119<p>Although <a href="#registration">Pass Registration</a> is optional for normal
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1120passes, all analysis group implementations must be registered, and must use the
1121<A href="#registerag"><tt>RegisterAnalysisGroup</tt></a> template to join the
1122implementation pool. Also, a default implementation of the interface
1123<b>must</b> be registered with <A
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1124href="#registerag"><tt>RegisterAnalysisGroup</tt></a>.</p>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1125
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1126<p>As a concrete example of an Analysis Group in action, consider the <a
1127href="http://llvm.cs.uiuc.edu/doxygen/classllvm_1_1AliasAnalysis.html">AliasAnalysis</a>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1128analysis group. The default implementation of the alias analysis interface (the
1129<tt><a
1130href="http://llvm.cs.uiuc.edu/doxygen/structBasicAliasAnalysis.html">basicaa</a></tt>
1131pass) just does a few simple checks that don't require significant analysis to
1132compute (such as: two different globals can never alias each other, etc).
1133Passes that use the <tt><a
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1134href="http://llvm.cs.uiuc.edu/doxygen/classllvm_1_1AliasAnalysis.html">AliasAnalysis</a></tt>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1135interface (for example the <tt><a
Misha Brukmand15516e2004-06-03 23:39:36 +0000[diff] [blame]1136href="http://llvm.cs.uiuc.edu/doxygen/structGCSE.html">gcse</a></tt> pass), do
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1137not care which implementation of alias analysis is actually provided, they just
1138use the designated interface.</p>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1139
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1140<p>From the user's perspective, commands work just like normal. Issuing the
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1141command '<tt>opt -gcse ...</tt>' will cause the <tt>basicaa</tt> class to be
1142instantiated and added to the pass sequence. Issuing the command '<tt>opt
1143-somefancyaa -gcse ...</tt>' will cause the <tt>gcse</tt> pass to use the
1144<tt>somefancyaa</tt> alias analysis (which doesn't actually exist, it's just a
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1145hypothetical example) instead.</p>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1146
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1147</div>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1148
1149<!-- _______________________________________________________________________ -->
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]1150<div class="doc_subsubsection">
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1151 <a name="registerag">Using <tt>RegisterAnalysisGroup</tt></a>
1152</div>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1153
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1154<div class="doc_text">
1155
1156<p>The <tt>RegisterAnalysisGroup</tt> template is used to register the analysis
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1157group itself as well as add pass implementations to the analysis group. First,
1158an analysis should be registered, with a human readable name provided for it.
1159Unlike registration of passes, there is no command line argument to be specified
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1160for the Analysis Group Interface itself, because it is "abstract":</p>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1161
1162<pre>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1163 <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>");
1164</pre>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1165
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1166<p>Once the analysis is registered, passes can declare that they are valid
1167implementations of the interface by using the following code:</p>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1168
1169<pre>
1170<b>namespace</b> {
1171 //<i> Analysis Group implementations <b>must</b> be registered normally...</i>
1172 RegisterOpt&lt;FancyAA&gt;
1173 B("<i>somefancyaa</i>", "<i>A more complex alias analysis implementation</i>");
1174
1175 //<i> Declare that we implement the AliasAnalysis interface</i>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1176 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]1177}
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1178</pre>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1179
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1180<p>This just shows a class <tt>FancyAA</tt> that is registered normally, then
1181uses the <tt>RegisterAnalysisGroup</tt> template to "join" the <tt><a
1182href="http://llvm.cs.uiuc.edu/doxygen/classllvm_1_1AliasAnalysis.html">AliasAnalysis</a></tt>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1183analysis group. Every implementation of an analysis group should join using
1184this template. A single pass may join multiple different analysis groups with
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1185no problem.</p>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1186
1187<pre>
1188<b>namespace</b> {
1189 //<i> Analysis Group implementations <b>must</b> be registered normally...</i>
1190 RegisterOpt&lt;<a href="http://llvm.cs.uiuc.edu/doxygen/structBasicAliasAnalysis.html">BasicAliasAnalysis</a>&gt;
1191 D("<i>basicaa</i>", "<i>Basic Alias Analysis (default AA impl)</i>");
1192
1193 //<i> Declare that we implement the AliasAnalysis interface</i>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1194 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]1195}
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1196</pre>
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1197
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1198<p>Here we show how the default implementation is specified (using the extra
Chris Lattner79910702002-08-22 19:21:04 +0000[diff] [blame]1199argument to the <tt>RegisterAnalysisGroup</tt> template). There must be exactly
1200one default implementation available at all times for an Analysis Group to be
1201used. Here we declare that the <tt><a
1202href="http://llvm.cs.uiuc.edu/doxygen/structBasicAliasAnalysis.html">BasicAliasAnalysis</a></tt>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1203pass is the default implementation for the interface.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1204
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1205</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1206
1207<!-- *********************************************************************** -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1208<div class="doc_section">
Tanya Lattnerd5383652004-11-19 01:25:14 +0000[diff] [blame]1209 <a name="passStatistics">Pass Statistics</a>
1210</div>
1211<!-- *********************************************************************** -->
1212
1213<div class="doc_text">
Tanya Lattner05f8d5f2004-11-19 01:26:37 +0000[diff] [blame^]1214<p>The <a
Tanya Lattnerd5383652004-11-19 01:25:14 +0000[diff] [blame]1215href="http:://llvm.cs.uiuc.edu/doxygen/Statistic_8h-source.html"><tt>Statistic</tt></a>
1216class, is designed to be an easy way to expose various success
1217metrics from passes. These statistics are printed at the end of a
1218run, when the -stats command line option is enabled on the command
Tanya Lattner05f8d5f2004-11-19 01:26:37 +0000[diff] [blame^]1219line. See the <a href="http://llvm.org/docs/ProgrammersManual.html#Statistic">Statistics section</a> in the Programmer's Manual for details.
Tanya Lattnerd5383652004-11-19 01:25:14 +0000[diff] [blame]1220
1221</div>
1222
1223
1224<!-- *********************************************************************** -->
1225<div class="doc_section">
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1226 <a name="passmanager">What PassManager does</a>
1227</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1228<!-- *********************************************************************** -->
1229
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1230<div class="doc_text">
1231
1232<p>The <a
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1233href="http://llvm.cs.uiuc.edu/doxygen/PassManager_8h-source.html"><tt>PassManager</tt></a>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1234<a
1235href="http://llvm.cs.uiuc.edu/doxygen/classllvm_1_1PassManager.html">class</a>
1236takes a list of passes, ensures their <a href="#interaction">prerequisites</a>
1237are set up correctly, and then schedules passes to run efficiently. All of the
1238LLVM tools that run passes use the <tt>PassManager</tt> for execution of these
1239passes.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1240
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1241<p>The <tt>PassManager</tt> does two main things to try to reduce the execution
1242time of a series of passes:</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1243
1244<ol>
1245<li><b>Share analysis results</b> - The PassManager attempts to avoid
1246recomputing analysis results as much as possible. This means keeping track of
1247which analyses are available already, which analyses get invalidated, and which
1248analyses are needed to be run for a pass. An important part of work is that the
1249<tt>PassManager</tt> tracks the exact lifetime of all analysis results, allowing
1250it to <a href="#releaseMemory">free memory</a> allocated to holding analysis
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1251results as soon as they are no longer needed.</li>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1252
1253<li><b>Pipeline the execution of passes on the program</b> - The
1254<tt>PassManager</tt> attempts to get better cache and memory usage behavior out
1255of a series of passes by pipelining the passes together. This means that, given
1256a series of consequtive <a href="#FunctionPass"><tt>FunctionPass</tt></a>'s, it
1257will execute all of the <a href="#FunctionPass"><tt>FunctionPass</tt></a>'s on
1258the first function, then all of the <a
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1259href="#FunctionPass"><tt>FunctionPass</tt></a>es on the second function,
1260etc... until the entire program has been run through the passes.
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1261
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1262<p>This improves the cache behavior of the compiler, because it is only touching
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1263the LLVM program representation for a single function at a time, instead of
1264traversing the entire program. It reduces the memory consumption of compiler,
1265because, for example, only one <a
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1266href="http://llvm.cs.uiuc.edu/doxygen/structllvm_1_1DominatorSet.html"><tt>DominatorSet</tt></a>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1267needs to be calculated at a time. This also makes it possible some <a
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1268href="#SMP">interesting enhancements</a> in the future.</p></li>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1269
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1270</ol>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1271
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1272<p>The effectiveness of the <tt>PassManager</tt> is influenced directly by how
1273much information it has about the behaviors of the passes it is scheduling. For
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1274example, the "preserved" set is intentionally conservative in the face of an
1275unimplemented <a href="#getAnalysisUsage"><tt>getAnalysisUsage</tt></a> method.
1276Not implementing when it should be implemented will have the effect of not
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1277allowing any analysis results to live across the execution of your pass.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1278
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1279<p>The <tt>PassManager</tt> class exposes a <tt>--debug-pass</tt> command line
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1280options that is useful for debugging pass execution, seeing how things work, and
1281diagnosing when you should be preserving more analyses than you currently are
1282(To get information about all of the variants of the <tt>--debug-pass</tt>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1283option, just type '<tt>opt --help-hidden</tt>').</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1284
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1285<p>By using the <tt>--debug-pass=Structure</tt> option, for example, we can see
1286how our <a href="#basiccode">Hello World</a> pass interacts with other passes.
1287Lets try it out with the <tt>gcse</tt> and <tt>licm</tt> passes:</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1288
1289<pre>
1290$ opt -load ../../../lib/Debug/libhello.so -gcse -licm --debug-pass=Structure &lt; hello.bc &gt; /dev/null
1291Module Pass Manager
1292 Function Pass Manager
1293 Dominator Set Construction
1294 Immediate Dominators Construction
1295 Global Common Subexpression Elimination
1296-- Immediate Dominators Construction
1297-- Global Common Subexpression Elimination
1298 Natural Loop Construction
1299 Loop Invariant Code Motion
1300-- Natural Loop Construction
1301-- Loop Invariant Code Motion
1302 Module Verifier
1303-- Dominator Set Construction
1304-- Module Verifier
1305 Bytecode Writer
1306--Bytecode Writer
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1307</pre>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1308
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1309<p>This output shows us when passes are constructed and when the analysis
1310results are known to be dead (prefixed with '<tt>--</tt>'). Here we see that
1311GCSE uses dominator and immediate dominator information to do its job. The LICM
1312pass uses natural loop information, which uses dominator sets, but not immediate
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1313dominators. Because immediate dominators are no longer useful after the GCSE
1314pass, it is immediately destroyed. The dominator sets are then reused to
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1315compute natural loop information, which is then used by the LICM pass.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1316
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1317<p>After the LICM pass, the module verifier runs (which is automatically added
1318by the '<tt>opt</tt>' tool), which uses the dominator set to check that the
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1319resultant LLVM code is well formed. After it finishes, the dominator set
1320information is destroyed, after being computed once, and shared by three
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1321passes.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1322
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1323<p>Lets see how this changes when we run the <a href="#basiccode">Hello
1324World</a> pass in between the two passes:</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1325
1326<pre>
1327$ opt -load ../../../lib/Debug/libhello.so -gcse -hello -licm --debug-pass=Structure &lt; hello.bc &gt; /dev/null
1328Module Pass Manager
1329 Function Pass Manager
1330 Dominator Set Construction
1331 Immediate Dominators Construction
1332 Global Common Subexpression Elimination
1333<b>-- Dominator Set Construction</b>
1334-- Immediate Dominators Construction
1335-- Global Common Subexpression Elimination
1336<b> Hello World Pass
1337-- Hello World Pass
1338 Dominator Set Construction</b>
1339 Natural Loop Construction
1340 Loop Invariant Code Motion
1341-- Natural Loop Construction
1342-- Loop Invariant Code Motion
1343 Module Verifier
1344-- Dominator Set Construction
1345-- Module Verifier
1346 Bytecode Writer
1347--Bytecode Writer
1348Hello: __main
1349Hello: puts
1350Hello: main
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1351</pre>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1352
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1353<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]1354Dominator Set pass, even though it doesn't modify the code at all! To fix this,
1355we need to add the following <a
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1356href="#getAnalysisUsage"><tt>getAnalysisUsage</tt></a> method to our pass:</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1357
1358<pre>
1359 <i>// We don't modify the program, so we preserve all analyses</i>
1360 <b>virtual void</b> getAnalysisUsage(AnalysisUsage &amp;AU) <b>const</b> {
1361 AU.setPreservesAll();
1362 }
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1363</pre>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1364
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1365<p>Now when we run our pass, we get this output:</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1366
1367<pre>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1368$ 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]1369Pass Arguments: -gcse -hello -licm
1370Module Pass Manager
1371 Function Pass Manager
1372 Dominator Set Construction
1373 Immediate Dominators Construction
1374 Global Common Subexpression Elimination
1375-- Immediate Dominators Construction
1376-- Global Common Subexpression Elimination
1377 Hello World Pass
1378-- Hello World Pass
1379 Natural Loop Construction
1380 Loop Invariant Code Motion
1381-- Loop Invariant Code Motion
1382-- Natural Loop Construction
1383 Module Verifier
1384-- Dominator Set Construction
1385-- Module Verifier
1386 Bytecode Writer
1387--Bytecode Writer
1388Hello: __main
1389Hello: puts
1390Hello: main
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1391</pre>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1392
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1393<p>Which shows that we don't accidentally invalidate dominator information
1394anymore, and therefore do not have to compute it twice.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1395
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1396</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1397
1398<!-- _______________________________________________________________________ -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1399<div class="doc_subsubsection">
1400 <a name="releaseMemory">The <tt>releaseMemory</tt> method</a>
1401</div>
1402
1403<div class="doc_text">
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1404
1405<pre>
1406 <b>virtual void</b> releaseMemory();
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1407</pre>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1408
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1409<p>The <tt>PassManager</tt> automatically determines when to compute analysis
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1410results, and how long to keep them around for. Because the lifetime of the pass
1411object itself is effectively the entire duration of the compilation process, we
1412need some way to free analysis results when they are no longer useful. The
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1413<tt>releaseMemory</tt> virtual method is the way to do this.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1414
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1415<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]1416amount of state (for use by another pass which "requires" your pass and uses the
1417<a href="#getAnalysis">getAnalysis</a> method) you should implement
1418<tt>releaseMEmory</tt> to, well, release the memory allocated to maintain this
1419internal state. This method is called after the <tt>run*</tt> method for the
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1420class, before the next call of <tt>run*</tt> in your pass.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1421
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1422</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1423
1424<!-- *********************************************************************** -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1425<div class="doc_section">
1426 <a name="debughints">Using GDB with dynamically loaded passes</a>
1427</div>
Chris Lattner480e2ef2002-09-06 02:02:58 +0000[diff] [blame]1428<!-- *********************************************************************** -->
1429
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1430<div class="doc_text">
1431
1432<p>Unfortunately, using GDB with dynamically loaded passes is not as easy as it
Chris Lattner480e2ef2002-09-06 02:02:58 +0000[diff] [blame]1433should be. First of all, you can't set a breakpoint in a shared object that has
1434not been loaded yet, and second of all there are problems with inlined functions
1435in shared objects. Here are some suggestions to debugging your pass with
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1436GDB.</p>
Chris Lattner480e2ef2002-09-06 02:02:58 +0000[diff] [blame]1437
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1438<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]1439transformation invoked by <tt>opt</tt>, although nothing described here depends
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1440on that.</p>
1441
1442</div>
Chris Lattner480e2ef2002-09-06 02:02:58 +0000[diff] [blame]1443
1444<!-- _______________________________________________________________________ -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1445<div class="doc_subsubsection">
1446 <a name="breakpoint">Setting a breakpoint in your pass</a>
1447</div>
Chris Lattner480e2ef2002-09-06 02:02:58 +0000[diff] [blame]1448
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1449<div class="doc_text">
1450
1451<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]1452
1453<pre>
1454$ <b>gdb opt</b>
1455GNU gdb 5.0
1456Copyright 2000 Free Software Foundation, Inc.
1457GDB is free software, covered by the GNU General Public License, and you are
1458welcome to change it and/or distribute copies of it under certain conditions.
1459Type "show copying" to see the conditions.
1460There is absolutely no warranty for GDB. Type "show warranty" for details.
1461This GDB was configured as "sparc-sun-solaris2.6"...
1462(gdb)
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1463</pre>
Chris Lattner480e2ef2002-09-06 02:02:58 +0000[diff] [blame]1464
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1465<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]1466time to load. Be patient. Since we cannot set a breakpoint in our pass yet
1467(the shared object isn't loaded until runtime), we must execute the process, and
1468have it stop before it invokes our pass, but after it has loaded the shared
1469object. The most foolproof way of doing this is to set a breakpoint in
1470<tt>PassManager::run</tt> and then run the process with the arguments you
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1471want:</p>
Chris Lattner480e2ef2002-09-06 02:02:58 +0000[diff] [blame]1472
1473<pre>
1474(gdb) <b>break PassManager::run</b>
1475Breakpoint 1 at 0x2413bc: file Pass.cpp, line 70.
Chris Lattnerfafe6302003-10-23 19:48:11 +0000[diff] [blame]1476(gdb) <b>run test.bc -load $(LLVMTOP)/llvm/lib/Debug/[libname].so -[passoption]</b>
1477Starting program: opt test.bc -load $(LLVMTOP)/llvm/lib/Debug/[libname].so -[passoption]
Chris Lattner480e2ef2002-09-06 02:02:58 +0000[diff] [blame]1478Breakpoint 1, PassManager::run (this=0xffbef174, M=@0x70b298) at Pass.cpp:70
147970 bool PassManager::run(Module &amp;M) { return PM-&gt;run(M); }
1480(gdb)
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1481</pre>
Chris Lattner480e2ef2002-09-06 02:02:58 +0000[diff] [blame]1482
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1483<p>Once the <tt>opt</tt> stops in the <tt>PassManager::run</tt> method you are
1484now free to set breakpoints in your pass so that you can trace through execution
1485or do other standard debugging stuff.</p>
Chris Lattner480e2ef2002-09-06 02:02:58 +0000[diff] [blame]1486
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1487</div>
Chris Lattner480e2ef2002-09-06 02:02:58 +0000[diff] [blame]1488
1489<!-- _______________________________________________________________________ -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1490<div class="doc_subsubsection">
1491 <a name="debugmisc">Miscellaneous Problems</a>
1492</div>
Chris Lattner480e2ef2002-09-06 02:02:58 +0000[diff] [blame]1493
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1494<div class="doc_text">
1495
1496<p>Once you have the basics down, there are a couple of problems that GDB has,
1497some with solutions, some without.</p>
Chris Lattner480e2ef2002-09-06 02:02:58 +0000[diff] [blame]1498
1499<ul>
1500<li>Inline functions have bogus stack information. In general, GDB does a
1501pretty good job getting stack traces and stepping through inline functions.
1502When a pass is dynamically loaded however, it somehow completely loses this
1503capability. The only solution I know of is to de-inline a function (move it
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1504from the body of a class to a .cpp file).</li>
Chris Lattner480e2ef2002-09-06 02:02:58 +0000[diff] [blame]1505
1506<li>Restarting the program breaks breakpoints. After following the information
1507above, you have succeeded in getting some breakpoints planted in your pass. Nex
1508thing you know, you restart the program (i.e., you type '<tt>run</tt>' again),
1509and you start getting errors about breakpoints being unsettable. The only way I
1510have found to "fix" this problem is to <tt>delete</tt> the breakpoints that are
1511already set in your pass, run the program, and re-set the breakpoints once
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1512execution stops in <tt>PassManager::run</tt>.</li>
Chris Lattner480e2ef2002-09-06 02:02:58 +0000[diff] [blame]1513
1514</ul>
1515
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1516<p>Hopefully these tips will help with common case debugging situations. If
1517you'd like to contribute some tips of your own, just contact <a
1518href="mailto:sabre@nondot.org">Chris</a>.</p>
Chris Lattner480e2ef2002-09-06 02:02:58 +0000[diff] [blame]1519
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1520</div>
Chris Lattner480e2ef2002-09-06 02:02:58 +0000[diff] [blame]1521
1522<!-- *********************************************************************** -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1523<div class="doc_section">
1524 <a name="future">Future extensions planned</a>
1525</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1526<!-- *********************************************************************** -->
1527
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1528<div class="doc_text">
1529
1530<p>Although the LLVM Pass Infrastructure is very capable as it stands, and does
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1531some 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]1532where we are going:</p>
1533
1534</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1535
1536<!-- _______________________________________________________________________ -->
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]1537<div class="doc_subsubsection">
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1538 <a name="SMP">Multithreaded LLVM</a>
1539</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1540
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1541<div class="doc_text">
1542
1543<p>Multiple CPU machines are becoming more common and compilation can never be
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1544fast enough: obviously we should allow for a multithreaded compiler. Because of
1545the semantics defined for passes above (specifically they cannot maintain state
1546across invocations of their <tt>run*</tt> methods), a nice clean way to
1547implement a multithreaded compiler would be for the <tt>PassManager</tt> class
Misha Brukmanbc0e9982003-07-14 17:20:40 +0000[diff] [blame]1548to create multiple instances of each pass object, and allow the separate
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1549instances to be hacking on different parts of the program at the same time.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1550
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1551<p>This implementation would prevent each of the passes from having to implement
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1552multithreaded constructs, requiring only the LLVM core to have locking in a few
1553places (for global resources). Although this is a simple extension, we simply
1554haven't had time (or multiprocessor machines, thus a reason) to implement this.
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1555Despite that, we have kept the LLVM passes SMP ready, and you should too.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1556
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1557</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1558
1559<!-- _______________________________________________________________________ -->
Chris Lattner89256272004-03-17 21:09:55 +0000[diff] [blame]1560<div class="doc_subsubsection">
Chris Lattnerf6278922004-09-20 04:36:29 +0000[diff] [blame]1561<a name="PassFunctionPass"><tt>ModulePass</tt>es requiring <tt>FunctionPass</tt>es</a>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1562</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1563
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1564<div class="doc_text">
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1565
Chris Lattnerf6278922004-09-20 04:36:29 +0000[diff] [blame]1566<p>Currently it is illegal for a <a href="#ModulePass"><tt>ModulePass</tt></a>
1567to require a <a href="#FunctionPass"><tt>FunctionPass</tt></a>. This is because
1568there is only one instance of the <a
1569href="#FunctionPass"><tt>FunctionPass</tt></a> object ever created, thus nowhere
1570to store information for all of the functions in the program at the same time.
1571Although this has come up a couple of times before, this has always been worked
1572around by factoring one big complicated pass into a global and an
1573interprocedural part, both of which are distinct. In the future, it would be
1574nice to have this though.</p>
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1575
1576<p>Note that it is no problem for a <a
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1577href="#FunctionPass"><tt>FunctionPass</tt></a> to require the results of a <a
Chris Lattnerf6278922004-09-20 04:36:29 +0000[diff] [blame]1578href="#ModulePass"><tt>ModulePass</tt></a>, only the other way around.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1579
Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1580</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000[diff] [blame]1581
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Misha Brukmanc5402402004-01-15 18:34:11 +0000[diff] [blame]1590 <a href="mailto:sabre@nondot.org">Chris Lattner</a><br>
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