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gerrit-public.fairphone.software / toolchain / llvm-project / f5edf1e931ca33400a1ec0b4eee060a0d58b3681 / . / llvm / docs / WritingAnLLVMPass.html
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3<html>
4<head>
5 <title>Writing an LLVM Pass</title>
6 <link rel="stylesheet" href="llvm.css" type="text/css">
7</head>
8<body>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]9
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame^]10<div class="doc_title">
11 Writing an LLVM Pass
12</div>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]13
14<ol>
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame^]15 <li><a href="#introduction">Introduction - What is a pass?</a></li>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]16 <li><a href="#quickstart">Quick Start - Writing hello world</a>
17 <ul>
Misha Brukmanf5edf1e2004-01-15 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 Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]20 <li><a href="#running">Running a pass with <tt>opt</tt>
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame^]21 or <tt>analyze</tt></a></li>
22 </ul></li>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]23 <li><a href="#passtype">Pass classes and requirements</a>
24 <ul>
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame^]25 <li><a href="#ImmutablePass">The <tt>ImmutablePass</tt> class</a></li>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]26 <li><a href="#Pass">The <tt>Pass</tt> class</a>
27 <ul>
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame^]28 <li><a href="#run">The <tt>run</tt> method</a></li>
29 </ul></li>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]30 <li><a href="#FunctionPass">The <tt>FunctionPass</tt> class</a>
31 <ul>
Chris Lattner5e08e70f2002-09-12 17:06:43 +0000[diff] [blame]32 <li><a href="#doInitialization_mod">The <tt>doInitialization(Module
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame^]33 &amp;)</tt> method</a></li>
34 <li><a href="#runOnFunction">The <tt>runOnFunction</tt> method</a></li>
Chris Lattner5e08e70f2002-09-12 17:06:43 +0000[diff] [blame]35 <li><a href="#doFinalization_mod">The <tt>doFinalization(Module
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame^]36 &amp;)</tt> method</a></li>
37 </ul></li>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]38 <li><a href="#BasicBlockPass">The <tt>BasicBlockPass</tt> class</a>
39 <ul>
Chris Lattner5e08e70f2002-09-12 17:06:43 +0000[diff] [blame]40 <li><a href="#doInitialization_fn">The <tt>doInitialization(Function
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame^]41 &amp;)</tt> method</a></li>
42 <li><a href="#runOnBasicBlock">The <tt>runOnBasicBlock</tt>
43 method</a></li>
Chris Lattner5e08e70f2002-09-12 17:06:43 +0000[diff] [blame]44 <li><a href="#doFinalization_fn">The <tt>doFinalization(Function
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame^]45 &amp;)</tt> method</a></li>
46 </ul></li>
Brian Gaeke110f07b2003-07-17 18:53:20 +0000[diff] [blame]47 <li><a href="#MachineFunctionPass">The <tt>MachineFunctionPass</tt>
48 class</a>
Brian Gaeke673ef4d2003-07-22 20:53:20 +0000[diff] [blame]49 <ul>
50 <li><a href="#runOnMachineFunction">The
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame^]51 <tt>runOnMachineFunction(MachineFunction &amp;)</tt> method</a></li>
52 </ul></li>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]53 </ul>
54 <li><a href="#registration">Pass Registration</a>
55 <ul>
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame^]56 <li><a href="#print">The <tt>print</tt> method</a></li>
57 </ul></li>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]58 <li><a href="#interaction">Specifying interactions between passes</a>
59 <ul>
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame^]60 <li><a href="#getAnalysisUsage">The <tt>getAnalysisUsage</tt>
61 method</a></li>
62 <li><a href="#getAnalysis">The <tt>getAnalysis</tt> method</a></li>
63 </ul></li>
Chris Lattner8d8a9282002-08-22 19:21:04 +0000[diff] [blame]64 <li><a href="#analysisgroup">Implementing Analysis Groups</a>
65 <ul>
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame^]66 <li><a href="#agconcepts">Analysis Group Concepts</a></li>
67 <li><a href="#registerag">Using <tt>RegisterAnalysisGroup</tt></a></li>
68 </ul></li>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]69 <li><a href="#passmanager">What PassManager does</a>
70 <ul>
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame^]71 <li><a href="#releaseMemory">The <tt>releaseMemory</tt> method</a></li>
72 </ul></li>
Chris Lattner8a97c8a2002-09-06 02:02:58 +0000[diff] [blame]73 <li><a href="#debughints">Using GDB with dynamically loaded passes</a>
74 <ul>
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame^]75 <li><a href="#breakpoint">Setting a breakpoint in your pass</a></li>
76 <li><a href="#debugmisc">Miscellaneous Problems</a></li>
77 </ul></li>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]78 <li><a href="#future">Future extensions planned</a>
79 <ul>
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame^]80 <li><a href="#SMP">Multithreaded LLVM</a></li>
81 <li><a href="#ModuleSource">A new <tt>ModuleSource</tt> interface</a></li>
82 <li><a href="#PassFunctionPass"><tt>Pass</tt>es requiring
83 <tt>FunctionPass</tt>es</a></li>
84 </ul></li>
85</ol>
Chris Lattner56d9e222002-08-08 20:23:41 +0000[diff] [blame]86
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame^]87<div class="doc_text">
Chris Lattner56d9e222002-08-08 20:23:41 +0000[diff] [blame]88 <p><b>Written by <a href="mailto:sabre@nondot.org">Chris Lattner</a></b><p>
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame^]89</div>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]90
91<!-- *********************************************************************** -->
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame^]92<div class="doc_section">
93 <a name="introduction">Introduction - What is a pass?</a>
94</div>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]95<!-- *********************************************************************** -->
96
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame^]97<div class="doc_text">
98
99<p>The LLVM Pass Framework is an important part of the LLVM system, because LLVM
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]100passes are where the interesting parts of the compiler exist. Passes perform
101the transformations and optimizations that make up the compiler, they build
102the analysis results that are used by these transformations, and they are, above
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame^]103all, a structuring technique for compiler code.</p>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]104
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame^]105<p>All LLVM passes are subclasses of the <tt><a
106href="http://llvm.cs.uiuc.edu/doxygen/classllvm_1_1Pass.html">Pass</a></tt>
107class, which implement functionality by overriding virtual methods inherited
108from <tt>Pass</tt>. Depending on how your pass works, you may be able to
109inherit from the <tt><a
110href="http://llvm.cs.uiuc.edu/doxygen/structllvm_1_1FunctionPass.html">FunctionPass</a></tt>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]111or <tt><a
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame^]112href="http://llvm.cs.uiuc.edu/doxygen/structllvm_1_1BasicBlockPass.html">BasicBlockPass</a></tt>,
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]113which gives the system more information about what your pass does, and how it
114can be combined with other passes. One of the main features of the LLVM Pass
115Framework is that it schedules passes to run in an efficient way based on the
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame^]116constraints that your pass has.</p>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]117
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame^]118<p>We start by showing you how to construct a pass, everything from setting up
119the code, to compiling, loading, and executing it. After the basics are down,
120more advanced features are discussed.</p>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]121
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame^]122</div>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]123
124<!-- *********************************************************************** -->
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame^]125<div class="doc_section">
126 <a name="quickstart">Quick Start - Writing hello world</a>
127</div>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]128<!-- *********************************************************************** -->
129
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame^]130<div class="doc_text">
131
132<p>Here we describe how to write the "hello world" of passes. The "Hello" pass
133is designed to simply print out the name of non-external functions that exist in
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]134the program being compiled. It does not modify the program at all, just
135inspects it. The source code and files for this pass are available in the LLVM
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame^]136source tree in the <tt>lib/Transforms/Hello</tt> directory.</p>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]137
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame^]138</div>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]139
140<!-- ======================================================================= -->
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame^]141<div class="doc_subsection">
142 <a name="makefile">Setting up the build environment</a>
143</div>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]144
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame^]145<div class="doc_text">
146
147<p>First thing you need to do is create a new directory somewhere in the LLVM
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]148source base. For this example, we'll assume that you made
149"<tt>lib/Transforms/Hello</tt>". The first thing you must do is set up a build
150script (Makefile) that will compile the source code for the new pass. To do
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame^]151this, copy this into "<tt>Makefile</tt>":</p>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]152
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame^]153<hr>
154
155<pre>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]156# Makefile for hello pass
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]157
Chris Lattnereb4ba3c2002-08-14 20:06:13 +0000[diff] [blame]158# Path to top level of LLVM heirarchy
Chris Lattner0c5e2932002-08-14 20:07:01 +0000[diff] [blame]159LEVEL = ../../..
Chris Lattnereb4ba3c2002-08-14 20:06:13 +0000[diff] [blame]160
161# Name of the library to build
Chris Lattner0c5e2932002-08-14 20:07:01 +0000[diff] [blame]162LIBRARYNAME = hello
Chris Lattnereb4ba3c2002-08-14 20:06:13 +0000[diff] [blame]163
164# Build a dynamically loadable shared object
165SHARED_LIBRARY = 1
166
167# Include the makefile implementation stuff
168include $(LEVEL)/Makefile.common
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame^]169</pre>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]170
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame^]171<p>This makefile specifies that all of the <tt>.cpp</tt> files in the current
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]172directory are to be compiled and linked together into a
173<tt>lib/Debug/libhello.so</tt> shared object that can be dynamically loaded by
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame^]174the <tt>opt</tt> or <tt>analyze</tt> tools.</p>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]175
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame^]176<p>Now that we have the build scripts set up, we just need to write the code for
177the pass itself.</p>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]178
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame^]179</div>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]180
181<!-- ======================================================================= -->
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame^]182<div class="doc_subsection">
183 <a name="basiccode">Basic code required</a>
184</div>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]185
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame^]186<div class="doc_text">
187
188<p>Now that we have a way to compile our new pass, we just have to write it.
189Start out with:</p>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]190
191<pre>
192<b>#include</b> "<a href="http://llvm.cs.uiuc.edu/doxygen/Pass_8h-source.html">llvm/Pass.h</a>"
193<b>#include</b> "<a href="http://llvm.cs.uiuc.edu/doxygen/Function_8h-source.html">llvm/Function.h</a>"
194</pre>
195
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame^]196<p>Which are needed because we are writing a <tt><a
197href="http://llvm.cs.uiuc.edu/doxygen/classllvm_1_1Pass.html">Pass</a></tt>, and
198we are operating on <tt><a
199href="http://llvm.cs.uiuc.edu/doxygen/classllvm_1_1Function.html">Function</a></tt>'s.</p>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]200
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame^]201<p>Next we have:</p>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]202
203<pre>
204<b>namespace</b> {
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame^]205</pre>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]206
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame^]207<p>... which starts out an anonymous namespace. Anonymous namespaces are to C++
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]208what the "<tt>static</tt>" keyword is to C (at global scope). It makes the
209things declared inside of the anonymous namespace only visible to the current
210file. If you're not familiar with them, consult a decent C++ book for more
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame^]211information.</p>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]212
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame^]213<p>Next, we declare our pass itself:</p>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]214
215<pre>
216 <b>struct</b> Hello : <b>public</b> <a href="#FunctionPass">FunctionPass</a> {
217</pre><p>
218
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame^]219<p>This declares a "<tt>Hello</tt>" class that is a subclass of <tt><a
220href="http://llvm.cs.uiuc.edu/doxygen/structllvm_1_1FunctionPass.html">FunctionPass</a></tt>.
Chris Lattnera818d922002-09-09 03:48:46 +0000[diff] [blame]221The different builtin pass subclasses are described in detail <a
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame^]222href="#passtype">later</a>, but for now, know that <a
223href="#FunctionPass"><tt>FunctionPass</tt></a>'s operate a function at a
224time.</p>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]225
226<pre>
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame^]227 <b>virtual bool</b> <a href="#runOnFunction">runOnFunction</a>(Function &amp;F) {
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]228 std::cerr &lt;&lt; "<i>Hello: </i>" &lt;&lt; F.getName() &lt;&lt; "\n";
229 <b>return false</b>;
230 }
231 }; <i>// end of struct Hello</i>
232</pre>
233
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame^]234<p>We declare a "<a href="#runOnFunction"><tt>runOnFunction</tt></a>" method,
235which overloads an abstract virtual method inherited from <a
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]236href="#FunctionPass"><tt>FunctionPass</tt></a>. This is where we are supposed
237to do our thing, so we just print out our message with the name of each
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame^]238function.</p>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]239
240<pre>
241 RegisterOpt&lt;Hello&gt; X("<i>hello</i>", "<i>Hello World Pass</i>");
242} <i>// end of anonymous namespace</i>
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame^]243</pre>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]244
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame^]245<p>Lastly, we register our class <tt>Hello</tt>, giving it a command line
246argument "<tt>hello</tt>", and a name "<tt>Hello World Pass</tt>". There are
247several different ways of <a href="#registration">registering your pass</a>,
248depending on what it is to be used for. For "optimizations" we use the
249<tt>RegisterOpt</tt> template.</p>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]250
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame^]251<p>As a whole, the <tt>.cpp</tt> file looks like:</p>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]252
253<pre>
254<b>#include</b> "<a href="http://llvm.cs.uiuc.edu/doxygen/Pass_8h-source.html">llvm/Pass.h</a>"
255<b>#include</b> "<a href="http://llvm.cs.uiuc.edu/doxygen/Function_8h-source.html">llvm/Function.h</a>"
256
257<b>namespace</b> {
258 <b>struct Hello</b> : <b>public</b> <a href="#FunctionPass">FunctionPass</a> {
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame^]259 <b>virtual bool</b> <a href="#runOnFunction">runOnFunction</a>(Function &amp;F) {
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]260 std::cerr &lt;&lt; "<i>Hello: </i>" &lt;&lt; F.getName() &lt;&lt; "\n";
261 <b>return false</b>;
262 }
263 };
264
265 RegisterOpt&lt;Hello&gt; X("<i>hello</i>", "<i>Hello World Pass</i>");
266}
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame^]267</pre>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]268
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame^]269<p>Now that it's all together, compile the file with a simple "<tt>gmake</tt>"
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]270command in the local directory and you should get a new
271"<tt>lib/Debug/libhello.so</tt> file. Note that everything in this file is
272contained in an anonymous namespace: this reflects the fact that passes are self
273contained units that do not need external interfaces (although they can have
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame^]274them) to be useful.</p>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]275
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame^]276</div>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]277
278<!-- ======================================================================= -->
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame^]279<div class="doc_subsection">
280 <a name="running">Running a pass with <tt>opt</tt> or <tt>analyze</tt></a>
281</div>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]282
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame^]283<div class="doc_text">
284
285<p>Now that you have a brand new shiny <tt>.so</tt> file, we can use the
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]286<tt>opt</tt> command to run an LLVM program through your pass. Because you
287registered your pass with the <tt>RegisterOpt</tt> template, you will be able to
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame^]288use the <tt>opt</tt> tool to access it, once loaded.</p>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]289
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame^]290<p>To test it, follow the example at the end of the <a
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]291href="GettingStarted.html">Getting Started Guide</a> to compile "Hello World" to
292LLVM. We can now run the bytecode file (<tt>hello.bc</tt>) for the program
293through our transformation like this (or course, any bytecode file will
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame^]294work):</p>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]295
296<pre>
297$ opt -load ../../../lib/Debug/libhello.so -hello &lt; hello.bc &gt; /dev/null
298Hello: __main
299Hello: puts
300Hello: main
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame^]301</pre>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]302
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame^]303<p>The '<tt>-load</tt>' option specifies that '<tt>opt</tt>' should load your
304pass as a shared object, which makes '<tt>-hello</tt>' a valid command line
305argument (which is one reason you need to <a href="#registration">register your
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]306pass</a>). Because the hello pass does not modify the program in any
307interesting way, we just throw away the result of <tt>opt</tt> (sending it to
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame^]308<tt>/dev/null</tt>).</p>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]309
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame^]310<p>To see what happened to the other string you registered, try running
311<tt>opt</tt> with the <tt>--help</tt> option:</p>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]312
313<pre>
314$ opt -load ../../../lib/Debug/libhello.so --help
315OVERVIEW: llvm .bc -&gt; .bc modular optimizer
316
317USAGE: opt [options] &lt;input bytecode&gt;
318
319OPTIONS:
320 Optimizations available:
321...
322 -funcresolve - Resolve Functions
323 -gcse - Global Common Subexpression Elimination
324 -globaldce - Dead Global Elimination
325 <b>-hello - Hello World Pass</b>
Chris Lattner216c7b82003-09-10 05:29:43 +0000[diff] [blame]326 -indvars - Canonicalize Induction Variables
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]327 -inline - Function Integration/Inlining
328 -instcombine - Combine redundant instructions
329...
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame^]330</pre>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]331
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame^]332<p>The pass name get added as the information string for your pass, giving some
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]333documentation to users of <tt>opt</tt>. Now that you have a working pass, you
334would go ahead and make it do the cool transformations you want. Once you get
335it all working and tested, it may become useful to find out how fast your pass
336is. The <a href="#passManager"><tt>PassManager</tt></a> provides a nice command
337line option (<tt>--time-passes</tt>) that allows you to get information about
338the execution time of your pass along with the other passes you queue up. For
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame^]339example:</p>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]340
341<pre>
342$ opt -load ../../../lib/Debug/libhello.so -hello -time-passes &lt; hello.bc &gt; /dev/null
343Hello: __main
344Hello: puts
345Hello: main
346===============================================================================
347 ... Pass execution timing report ...
348===============================================================================
349 Total Execution Time: 0.02 seconds (0.0479059 wall clock)
350
351 ---User Time--- --System Time-- --User+System-- ---Wall Time--- --- Pass Name ---
352 0.0100 (100.0%) 0.0000 ( 0.0%) 0.0100 ( 50.0%) 0.0402 ( 84.0%) Bytecode Writer
353 0.0000 ( 0.0%) 0.0100 (100.0%) 0.0100 ( 50.0%) 0.0031 ( 6.4%) Dominator Set Construction
354 0.0000 ( 0.0%) 0.0000 ( 0.0%) 0.0000 ( 0.0%) 0.0013 ( 2.7%) Module Verifier
355 <b> 0.0000 ( 0.0%) 0.0000 ( 0.0%) 0.0000 ( 0.0%) 0.0033 ( 6.9%) Hello World Pass</b>
356 0.0100 (100.0%) 0.0100 (100.0%) 0.0200 (100.0%) 0.0479 (100.0%) TOTAL
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame^]357</pre>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]358
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame^]359<p>As you can see, our implementation above is pretty fast :). The additional
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]360passes listed are automatically inserted by the '<tt>opt</tt>' tool to verify
361that the LLVM emitted by your pass is still valid and well formed LLVM, which
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame^]362hasn't been broken somehow.</p>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]363
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame^]364<p>Now that you have seen the basics of the mechanics behind passes, we can talk
365about some more details of how they work and how to use them.</p>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]366
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame^]367</div>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]368
369<!-- *********************************************************************** -->
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame^]370<div class="doc_section">
371 <a name="passtype">Pass classes and requirements</a>
372</div>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]373<!-- *********************************************************************** -->
374
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame^]375<div class="doc_text">
376
377<p>One of the first things that you should do when designing a new pass is to
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]378decide what class you should subclass for your pass. The <a
379href="#basiccode">Hello World</a> example uses the <tt><a
380href="#FunctionPass">FunctionPass</a></tt> class for its implementation, but we
381did not discuss why or when this should occur. Here we talk about the classes
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame^]382available, from the most general to the most specific.</p>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]383
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame^]384<p>When choosing a superclass for your Pass, you should choose the <b>most
Chris Lattner8d8a9282002-08-22 19:21:04 +0000[diff] [blame]385specific</b> class possible, while still being able to meet the requirements
Misha Brukman7eb05a12003-08-18 14:43:39 +0000[diff] [blame]386listed. This gives the LLVM Pass Infrastructure information necessary to
Chris Lattner8d8a9282002-08-22 19:21:04 +0000[diff] [blame]387optimize how passes are run, so that the resultant compiler isn't unneccesarily
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame^]388slow.</p>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]389
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame^]390</div>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]391
Chris Lattner9720dda2002-09-25 22:31:38 +0000[diff] [blame]392<!-- ======================================================================= -->
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame^]393<div class="doc_subsection">
394 <a name="ImmutablePass">The <tt>ImmutablePass</tt> class</a>
395</div>
Chris Lattner9720dda2002-09-25 22:31:38 +0000[diff] [blame]396
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame^]397<div class="doc_text">
398
399<p>The most plain and boring type of pass is the "<tt><a
400href="http://llvm.cs.uiuc.edu/doxygen/structllvm_1_1ImmutablePass.html">ImmutablePass</a></tt>"
Chris Lattner9720dda2002-09-25 22:31:38 +0000[diff] [blame]401class. This pass type is used for passes that do not have to be run, do not
402change state, and never need to be updated. This is not a normal type of
403transformation or analysis, but can provide information about the current
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame^]404compiler configuration.</p>
Chris Lattner9720dda2002-09-25 22:31:38 +0000[diff] [blame]405
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame^]406<p>Although this pass class is very infrequently used, it is important for
Chris Lattner9720dda2002-09-25 22:31:38 +0000[diff] [blame]407providing information about the current target machine being compiled for, and
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame^]408other static information that can affect the various transformations.</p>
Chris Lattner9720dda2002-09-25 22:31:38 +0000[diff] [blame]409
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame^]410<p><tt>ImmutablePass</tt>es never invalidate other transformations, are never
411invalidated, and are never "run".</p>
Chris Lattner9720dda2002-09-25 22:31:38 +0000[diff] [blame]412
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame^]413</div>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]414
415<!-- ======================================================================= -->
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame^]416<div class="doc_subsection">
417 <a name="Pass">The <tt>Pass</tt> class</a>
418</div>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]419
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame^]420<div class="doc_text">
421
422<p>The "<tt><a
423href="http://llvm.cs.uiuc.edu/doxygen/classllvm_1_1Pass.html">Pass</a></tt>"
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]424class is the most general of all superclasses that you can use. Deriving from
425<tt>Pass</tt> indicates that your pass uses the entire program as a unit,
426refering to function bodies in no predictable order, or adding and removing
427functions. Because nothing is known about the behavior of direct <tt>Pass</tt>
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame^]428subclasses, no optimization can be done for their execution.</p>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]429
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame^]430<p>To write a correct <tt>Pass</tt> subclass, derive from <tt>Pass</tt> and
431overload the <tt>run</tt> method with the following signature:</p>
432
433</div>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]434
435<!-- _______________________________________________________________________ -->
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame^]436<div class="doc_subsubsection">
437 <a name="run">The <tt>run</tt> method</a>
438</div>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]439
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame^]440<div class="doc_text">
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]441
442<pre>
443 <b>virtual bool</b> run(Module &amp;M) = 0;
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame^]444</pre>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]445
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame^]446<p>The <tt>run</tt> method performs the interesting work of the pass, and should
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]447return true if the module was modified by the transformation, false
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame^]448otherwise.</p>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]449
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame^]450</div>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]451
452<!-- ======================================================================= -->
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame^]453<div class="doc_subsection">
454 <a name="FunctionPass">The <tt>FunctionPass</tt> class</a>
455</div>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]456
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame^]457<div class="doc_text">
458
459<p>In contrast to direct <tt>Pass</tt> subclasses, direct <tt><a
460href="http://llvm.cs.uiuc.edu/doxygen/classllvm_1_1Pass.html">FunctionPass</a></tt>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]461subclasses do have a predictable, local behavior that can be expected by the
462system. All <tt>FunctionPass</tt> execute on each function in the program
Misha Brukmanbe372b92003-08-21 22:14:26 +0000[diff] [blame]463independent of all of the other functions in the program.
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]464<tt>FunctionPass</tt>'s do not require that they are executed in a particular
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame^]465order, and <tt>FunctionPass</tt>'s do not modify external functions.</p>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]466
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame^]467<p>To be explicit, <tt>FunctionPass</tt> subclasses are not allowed to:</p>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]468
469<ol>
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame^]470<li>Modify a Function other than the one currently being processed.</li>
471<li>Add or remove Function's from the current Module.</li>
472<li>Add or remove global variables from the current Module.</li>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]473<li>Maintain state across invocations of
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame^]474 <a href="#runOnFunction"><tt>runOnFunction</tt></a> (including global data)</li>
475</ol>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]476
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame^]477<p>Implementing a <tt>FunctionPass</tt> is usually straightforward (See the <a
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]478href="#basiccode">Hello World</a> pass for example). <tt>FunctionPass</tt>'s
479may overload three virtual methods to do their work. All of these methods
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame^]480should return true if they modified the program, or false if they didn't.</p>
481
482</div>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]483
484<!-- _______________________________________________________________________ -->
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame^]485<div class="subsubsection">
486 <a name="doInitialization_mod">The <tt>doInitialization(Module &amp;)</tt>
487 method</a>
488</div>
489
490<div class="doc_text">
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]491
492<pre>
493 <b>virtual bool</b> doInitialization(Module &amp;M);
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame^]494</pre>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]495
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame^]496<p>The <tt>doIninitialize</tt> method is allowed to do most of the things that
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]497<tt>FunctionPass</tt>'s are not allowed to do. They can add and remove
Chris Lattner5e08e70f2002-09-12 17:06:43 +0000[diff] [blame]498functions, get pointers to functions, etc. The <tt>doInitialization</tt> method
499is designed to do simple initialization type of stuff that does not depend on
500the functions being processed. The <tt>doInitialization</tt> method call is not
501scheduled to overlap with any other pass executions (thus it should be very
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame^]502fast).</p>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]503
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame^]504<p>A good example of how this method should be used is the <a
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]505href="http://llvm.cs.uiuc.edu/doxygen/LowerAllocations_8cpp-source.html">LowerAllocations</a>
506pass. This pass converts <tt>malloc</tt> and <tt>free</tt> instructions into
Misha Brukmanbe372b92003-08-21 22:14:26 +0000[diff] [blame]507platform dependent <tt>malloc()</tt> and <tt>free()</tt> function calls. It
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]508uses the <tt>doInitialization</tt> method to get a reference to the malloc and
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame^]509free functions that it needs, adding prototypes to the module if necessary.</p>
510
511</div>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]512
513<!-- _______________________________________________________________________ -->
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame^]514<div class="subsubsection">
515 <a name="runOnFunction">The <tt>runOnFunction</tt> method</a>
516</div>
517
518<div class="doc_text">
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]519
520<pre>
521 <b>virtual bool</b> runOnFunction(Function &amp;F) = 0;
522</pre><p>
523
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame^]524<p>The <tt>runOnFunction</tt> method must be implemented by your subclass to do
525the transformation or analysis work of your pass. As usual, a true value should
526be returned if the function is modified.</p>
527
528</div>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]529
530<!-- _______________________________________________________________________ -->
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame^]531<div class="subsubsection">
532 <a name="doFinalization_mod">The <tt>doFinalization(Module
533 &amp;)</tt> method</a>
534</div>
535
536<div class="doc_text">
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]537
538<pre>
539 <b>virtual bool</b> doFinalization(Module &amp;M);
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame^]540</pre>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]541
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame^]542<p>The <tt>doFinalization</tt> method is an infrequently used method that is
543called when the pass framework has finished calling <a
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]544href="#runOnFunction"><tt>runOnFunction</tt></a> for every function in the
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame^]545program being compiled.</p>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]546
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame^]547</div>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]548
549<!-- ======================================================================= -->
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame^]550<div class="doc_subsection">
551 <a name="BasicBlockPass">The <tt>BasicBlockPass</tt> class</a>
552</div>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]553
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame^]554<div class="doc_text">
555
556<p><tt>BasicBlockPass</tt>'s are just like <a
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]557href="#FunctionPass"><tt>FunctionPass</tt></a>'s, except that they must limit
558their scope of inspection and modification to a single basic block at a time.
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame^]559As such, they are <b>not</b> allowed to do any of the following:</p>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]560
561<ol>
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame^]562<li>Modify or inspect any basic blocks outside of the current one</li>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]563<li>Maintain state across invocations of
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame^]564 <a href="#runOnBasicBlock"><tt>runOnBasicBlock</tt></a></li>
565<li>Modify the constrol flow graph (by altering terminator instructions)</li>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]566<li>Any of the things verboten for
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame^]567 <a href="#FunctionPass"><tt>FunctionPass</tt></a>es.</li>
568</ol>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]569
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame^]570<p><tt>BasicBlockPass</tt>es are useful for traditional local and "peephole"
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]571optimizations. They may override the same <a
Chris Lattner5e08e70f2002-09-12 17:06:43 +0000[diff] [blame]572href="#doInitialization_mod"><tt>doInitialization(Module &amp;)</tt></a> and <a
573href="#doFinalization_mod"><tt>doFinalization(Module &amp;)</tt></a> methods that <a
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame^]574href="#FunctionPass"><tt>FunctionPass</tt></a>'s have, but also have the following virtual methods that may also be implemented:</p>
575
576</div>
Chris Lattner5e08e70f2002-09-12 17:06:43 +0000[diff] [blame]577
578<!-- _______________________________________________________________________ -->
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame^]579<div class="subsubsection">
580 <a name="doInitialization_fn">The <tt>doInitialization(Function
581 &amp;)</tt> method</a>
582</div>
583
584<div class="doc_text">
Chris Lattner5e08e70f2002-09-12 17:06:43 +0000[diff] [blame]585
586<pre>
587 <b>virtual bool</b> doInitialization(Function &amp;F);
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame^]588</pre>
Chris Lattner5e08e70f2002-09-12 17:06:43 +0000[diff] [blame]589
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame^]590<p>The <tt>doIninitialize</tt> method is allowed to do most of the things that
Chris Lattner5e08e70f2002-09-12 17:06:43 +0000[diff] [blame]591<tt>BasicBlockPass</tt>'s are not allowed to do, but that
592<tt>FunctionPass</tt>'s can. The <tt>doInitialization</tt> method is designed
593to do simple initialization type of stuff that does not depend on the
594BasicBlocks being processed. The <tt>doInitialization</tt> method call is not
595scheduled to overlap with any other pass executions (thus it should be very
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame^]596fast).</p>
Chris Lattner5e08e70f2002-09-12 17:06:43 +0000[diff] [blame]597
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame^]598</div>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]599
600<!-- _______________________________________________________________________ -->
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame^]601<div class="subsubsection">
602 <a name="runOnBasicBlock">The <tt>runOnBasicBlock</tt> method</a>
603</div>
604
605<div class="doc_text">
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]606
607<pre>
608 <b>virtual bool</b> runOnBasicBlock(BasicBlock &amp;BB) = 0;
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame^]609</pre>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]610
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame^]611<p>Override this function to do the work of the <tt>BasicBlockPass</tt>. This
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]612function is not allowed to inspect or modify basic blocks other than the
613parameter, and are not allowed to modify the CFG. A true value must be returned
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame^]614if the basic block is modified.</p>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]615
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame^]616</div>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]617
Chris Lattner5e08e70f2002-09-12 17:06:43 +0000[diff] [blame]618<!-- _______________________________________________________________________ -->
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame^]619<div class="subsubsection">
620 <a name="doFinalization_fn">The <tt>doFinalization(Function &amp;)</tt>
621 method</a>
622</div>
623
624<div class="doc_text">
Chris Lattner5e08e70f2002-09-12 17:06:43 +0000[diff] [blame]625
626<pre>
627 <b>virtual bool</b> doFinalization(Function &amp;F);
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame^]628</pre>
Chris Lattner5e08e70f2002-09-12 17:06:43 +0000[diff] [blame]629
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame^]630<p>The <tt>doFinalization</tt> method is an infrequently used method that is
631called when the pass framework has finished calling <a
Chris Lattner5e08e70f2002-09-12 17:06:43 +0000[diff] [blame]632href="#runOnBasicBlock"><tt>runOnBasicBlock</tt></a> for every BasicBlock in the
633program being compiled. This can be used to perform per-function
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame^]634finalization.</p>
Chris Lattner5e08e70f2002-09-12 17:06:43 +0000[diff] [blame]635
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame^]636</div>
Chris Lattner5e08e70f2002-09-12 17:06:43 +0000[diff] [blame]637
Brian Gaeke110f07b2003-07-17 18:53:20 +0000[diff] [blame]638<!-- ======================================================================= -->
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame^]639<div class="doc_subsection">
640 <a name="MachineFunctionPass">The <tt>MachineFunctionPass</tt> class</a>
641</div>
Brian Gaeke110f07b2003-07-17 18:53:20 +0000[diff] [blame]642
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame^]643<div class="doc_text">
644
645<p>A <tt>MachineFunctionPass</tt> executes on the machine-dependent
Brian Gaeke110f07b2003-07-17 18:53:20 +0000[diff] [blame]646representation of each LLVM function in the program,
647independent of all of the other functions in the program.
648A <tt>MachineFunctionPass</tt> is also a <tt>FunctionPass</tt>, so all
649the restrictions that apply to a <tt>FunctionPass</tt> also apply to it.
650<tt>MachineFunctionPass</tt>es also have additional restrictions. In
651particular, <tt>MachineFunctionPass</tt>es are not allowed to do any of
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame^]652the following:</p>
Brian Gaeke110f07b2003-07-17 18:53:20 +0000[diff] [blame]653
654<ol>
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame^]655<li>Modify any LLVM Instructions, BasicBlocks or Functions.</li>
656<li>Modify a MachineFunction other than the one currently being processed.</li>
657<li>Add or remove MachineFunctions from the current Module.</li>
658<li>Add or remove global variables from the current Module.</li>
659<li>Maintain state across invocations of <a
660href="#runOnMachineFunction"><tt>runOnMachineFunction</tt></a> (including global
661data)</li>
662</ol>
Brian Gaeke110f07b2003-07-17 18:53:20 +0000[diff] [blame]663
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame^]664</div>
Chris Lattner5e08e70f2002-09-12 17:06:43 +0000[diff] [blame]665
Brian Gaeke673ef4d2003-07-22 20:53:20 +0000[diff] [blame]666<!-- _______________________________________________________________________ -->
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame^]667<div class="subsubsection">
668 <a name="runOnMachineFunction">The <tt>runOnMachineFunction(MachineFunction
669 &amp;MF)</tt> method</a>
670</div>
671
672<div class="doc_text">
Brian Gaeke673ef4d2003-07-22 20:53:20 +0000[diff] [blame]673
674<pre>
675 <b>virtual bool</b> runOnMachineFunction(MachineFunction &amp;MF) = 0;
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame^]676</pre>
Brian Gaeke673ef4d2003-07-22 20:53:20 +0000[diff] [blame]677
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame^]678<p><tt>runOnMachineFunction</tt> can be considered the main entry point of a
679<tt>MachineFunctionPass</tt>; that is, you should override this method to do the
680work of your <tt>MachineFunctionPass</tt>.</p>
Brian Gaeke673ef4d2003-07-22 20:53:20 +0000[diff] [blame]681
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame^]682<p>The <tt>runOnMachineFunction</tt> method is called on every
Brian Gaeke673ef4d2003-07-22 20:53:20 +0000[diff] [blame]683<tt>MachineFunction</tt> in a <tt>Module</tt>, so that the
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame^]684<tt>MachineFunctionPass</tt> may perform optimizations on the machine-dependent
685representation of the function. If you want to get at the LLVM <tt>Function</tt>
686for the <tt>MachineFunction</tt> you're working on, use
687<tt>MachineFunction</tt>'s <tt>getFunction()</tt> accessor method -- but
688remember, you may not modify the LLVM <tt>Function</tt> or its contents from a
689<tt>MachineFunctionPass</tt>.</p>
690
691</div>
Brian Gaeke673ef4d2003-07-22 20:53:20 +0000[diff] [blame]692
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]693<!-- *********************************************************************** -->
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame^]694<div class="doc_section">
695 <a name="registration">Pass registration</a>
696</div>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]697<!-- *********************************************************************** -->
698
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame^]699<div class="doc_text">
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]700
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame^]701<p>In the <a href="#basiccode">Hello World</a> example pass we illustrated how
702pass registration works, and discussed some of the reasons that it is used and
703what it does. Here we discuss how and why passes are registered.</p>
704
705<p>Passes can be registered in several different ways. Depending on the general
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]706classification of the pass, you should use one of the following templates to
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame^]707register the pass:</p>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]708
709<ul>
710<li><b><tt>RegisterOpt</tt></b> - This template should be used when you are
711registering a pass that logically should be available for use in the
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame^]712'<tt>opt</tt>' utility.</li>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]713
714<li><b><tt>RegisterAnalysis</tt></b> - This template should be used when you are
715registering a pass that logically should be available for use in the
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame^]716'<tt>analysis</tt>' utility.</li>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]717
718<li><b><tt>RegisterLLC</tt></b> - This template should be used when you are
719registering a pass that logically should be available for use in the
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame^]720'<tt>llc</tt>' utility.</li>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]721
722<li><b><tt>RegisterPass</tt></b> - This is the generic form of the
723<tt>Register*</tt> templates that should be used if you want your pass listed by
724multiple or no utilities. This template takes an extra third argument that
725specifies which tools it should be listed in. See the <a
726href="http://llvm.cs.uiuc.edu/doxygen/PassSupport_8h-source.html">PassSupport.h</a>
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame^]727file for more information.</li>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]728
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame^]729</ul>
730
731<p>Regardless of how you register your pass, you must specify at least two
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]732parameters. The first parameter is the name of the pass that is to be used on
733the command line to specify that the pass should be added to a program (for
734example <tt>opt</tt> or <tt>analyze</tt>). The second argument is the name of
735the pass, which is to be used for the <tt>--help</tt> output of programs, as
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame^]736well as for debug output generated by the <tt>--debug-pass</tt> option.</p>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]737
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame^]738<p>If you pass is constructed by its default constructor, you only ever have to
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]739pass these two arguments. If, on the other hand, you require other information
740(like target specific information), you must pass an additional argument. This
741argument is a pointer to a function used to create the pass. For an example of
742how this works, look at the <a
743href="http://llvm.cs.uiuc.edu/doxygen/LowerAllocations_8cpp-source.html">LowerAllocations.cpp</a>
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame^]744file.</p>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]745
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame^]746<p>If a pass is registered to be used by the <tt>analyze</tt> utility, you
747should implement the virtual <tt>print</tt> method:</p>
748
749</div>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]750
751<!-- _______________________________________________________________________ -->
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame^]752<div class="doc_subsubsection">
753 <a name="print">The <tt>print</tt> method</a>
754</div>
755
756<div class="doc_text">
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]757
758<pre>
759 <b>virtual void</b> print(std::ostream &amp;O, <b>const</b> Module *M) <b>const</b>;
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame^]760</pre>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]761
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame^]762<p>The <tt>print</tt> method must be implemented by "analyses" in order to print
763a human readable version of the analysis results. This is useful for debugging
764an analysis itself, as well as for other people to figure out how an analysis
765works. The <tt>analyze</tt> tool uses this method to generate its output.</p>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]766
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame^]767<p>The <tt>ostream</tt> parameter specifies the stream to write the results on,
768and the <tt>Module</tt> parameter gives a pointer to the top level module of the
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]769program that has been analyzed. Note however that this pointer may be null in
770certain circumstances (such as calling the <tt>Pass::dump()</tt> from a
771debugger), so it should only be used to enhance debug output, it should not be
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame^]772depended on.</p>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]773
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame^]774</div>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]775
776<!-- *********************************************************************** -->
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame^]777<div class="doc_section">
778 <a name="interaction">Specifying interactions between passes</a>
779</div>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]780<!-- *********************************************************************** -->
781
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame^]782<div class="doc_text">
783
784<p>One of the main responsibilities of the <tt>PassManager</tt> is the make sure
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]785that passes interact with each other correctly. Because <tt>PassManager</tt>
786tries to <a href="#passmanager">optimize the execution of passes</a> it must
787know how the passes interact with each other and what dependencies exist between
788the various passes. To track this, each pass can declare the set of passes that
789are required to be executed before the current pass, and the passes which are
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame^]790invalidated by the current pass.</p>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]791
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame^]792<p>Typically this functionality is used to require that analysis results are
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]793computed before your pass is run. Running arbitrary transformation passes can
794invalidate the computed analysis results, which is what the invalidation set
795specifies. If a pass does not implement the <tt><a
796href="#getAnalysisUsage">getAnalysisUsage</a></tt> method, it defaults to not
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame^]797having any prerequisite passes, and invalidating <b>all</b> other passes.</p>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]798
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame^]799</div>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]800
801<!-- _______________________________________________________________________ -->
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame^]802<div class="doc_subsubsection">
803 <a name="getAnalysisUsage">The <tt>getAnalysisUsage</tt> method</a>
804</div>
805
806<div class="doc_text">
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]807
808<pre>
809 <b>virtual void</b> getAnalysisUsage(AnalysisUsage &amp;Info) <b>const</b>;
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame^]810</pre>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]811
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame^]812<p>By implementing the <tt>getAnalysisUsage</tt> method, the required and
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]813invalidated sets may be specified for your transformation. The implementation
814should fill in the <tt><a
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame^]815href="http://llvm.cs.uiuc.edu/doxygen/classllvm_1_1AnalysisUsage.html">AnalysisUsage</a></tt>
816object with information about which passes are required and not invalidated. To
817do this, the following set methods are provided by the <tt><a
818href="http://llvm.cs.uiuc.edu/doxygen/classllvm_1_1AnalysisUsage.html">AnalysisUsage</a></tt>
819class:</p>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]820
821<pre>
822 <i>// addRequires - Add the specified pass to the required set for your pass.</i>
823 <b>template</b>&lt;<b>class</b> PassClass&gt;
824 AnalysisUsage &amp;AnalysisUsage::addRequired();
825
826 <i>// addPreserved - Add the specified pass to the set of analyses preserved by
827 // this pass</i>
828 <b>template</b>&lt;<b>class</b> PassClass&gt;
829 AnalysisUsage &amp;AnalysisUsage::addPreserved();
830
831 <i>// setPreservesAll - Call this if the pass does not modify its input at all</i>
832 <b>void</b> AnalysisUsage::setPreservesAll();
833
Chris Lattnera8c82c22002-10-21 19:57:59 +0000[diff] [blame]834 <i>// setPreservesCFG - This function should be called by the pass, iff they do not:
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]835 //
836 // 1. Add or remove basic blocks from the function
837 // 2. Modify terminator instructions in any way.
838 //
839 // This is automatically implied for <a href="#BasicBlockPass">BasicBlockPass</a>'s
840 //</i>
Chris Lattnera8c82c22002-10-21 19:57:59 +0000[diff] [blame]841 <b>void</b> AnalysisUsage::setPreservesCFG();
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame^]842</pre>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]843
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame^]844<p>Some examples of how to use these methods are:</p>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]845
846<pre>
847 <i>// This is an example implementation from an analysis, which does not modify
848 // the program at all, yet has a prerequisite.</i>
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame^]849 <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 Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]850 AU.setPreservesAll();
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame^]851 AU.addRequired&lt;<a href="http://llvm.cs.uiuc.edu/doxygen/structllvm_1_1PostDominatorTree.html">PostDominatorTree</a>&gt;();
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]852 }
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame^]853</pre>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]854
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame^]855<p>and:</p>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]856
857<pre>
858 <i>// This example modifies the program, but does not modify the CFG</i>
859 <b>void</b> <a href="http://llvm.cs.uiuc.edu/doxygen/structLICM.html">LICM</a>::getAnalysisUsage(AnalysisUsage &amp;AU) <b>const</b> {
Chris Lattnera8c82c22002-10-21 19:57:59 +0000[diff] [blame]860 AU.setPreservesCFG();
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame^]861 AU.addRequired&lt;<a href="http://llvm.cs.uiuc.edu/doxygen/classllvm_1_1LoopInfo.html">LoopInfo</a>&gt;();
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]862 }
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame^]863</pre>
864
865</div>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]866
867<!-- _______________________________________________________________________ -->
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame^]868<div class="doc_subsubsection">
869 <a name="getAnalysis">The <tt>getAnalysis&lt;&gt;</tt> method</a>
870</div>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]871
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame^]872<div class="doc_text">
873
874<p>The <tt>Pass::getAnalysis&lt;&gt;</tt> method is inherited by your class,
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]875providing you with access to the passes that you declared that you required with
876the <a href="#getAnalysisUsage"><tt>getAnalysisUsage</tt></a> method. It takes
877a single template argument that specifies which pass class you want, and returns
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame^]878a reference to that pass.</p>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]879
880<pre>
881 <b>template</b>&lt;<b>typename</b> PassClass&gt;
882 AnalysisType &amp;getAnalysis();
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame^]883</pre>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]884
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame^]885<p>This method call returns a reference to the pass desired. You may get a
886runtime assertion failure if you attempt to get an analysis that you did not
887declare as required in your <a
888href="#getAnalysisUsage"><tt>getAnalysisUsage</tt></a> implementation. This
889method can be called by your <tt>run*</tt> method implementation, or by any
890other local method invoked by your <tt>run*</tt> method.</p>
891
892</div>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]893
Chris Lattner8d8a9282002-08-22 19:21:04 +0000[diff] [blame]894<!-- *********************************************************************** -->
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame^]895<div class="doc_section">
896 <a name="analysisgroup">Implementing Analysis Groups</a>
897</div>
Chris Lattner8d8a9282002-08-22 19:21:04 +0000[diff] [blame]898<!-- *********************************************************************** -->
899
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame^]900<div class="doc_text">
901
902<p>Now that we understand the basics of how passes are defined, how the are
903used, and how they are required from other passes, it's time to get a little bit
Chris Lattner8d8a9282002-08-22 19:21:04 +0000[diff] [blame]904fancier. All of the pass relationships that we have seen so far are very
905simple: one pass depends on one other specific pass to be run before it can run.
906For many applications, this is great, for others, more flexibility is
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame^]907required.</p>
Chris Lattner8d8a9282002-08-22 19:21:04 +0000[diff] [blame]908
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame^]909<p>In particular, some analyses are defined such that there is a single simple
Chris Lattner8d8a9282002-08-22 19:21:04 +0000[diff] [blame]910interface to the analysis results, but multiple ways of calculating them.
911Consider alias analysis for example. The most trivial alias analysis returns
912"may alias" for any alias query. The most sophisticated analysis a
913flow-sensitive, context-sensitive interprocedural analysis that can take a
914significant amount of time to execute (and obviously, there is a lot of room
915between these two extremes for other implementations). To cleanly support
916situations like this, the LLVM Pass Infrastructure supports the notion of
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame^]917Analysis Groups.</p>
918
919</div>
Chris Lattner8d8a9282002-08-22 19:21:04 +0000[diff] [blame]920
921<!-- _______________________________________________________________________ -->
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame^]922<div class="subsubsection">
923 <a name="agconcepts">Analysis Group Concepts</a>
924</div>
Chris Lattner8d8a9282002-08-22 19:21:04 +0000[diff] [blame]925
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame^]926<div class="doc_text">
927
928<p>An Analysis Group is a single simple interface that may be implemented by
Chris Lattner8d8a9282002-08-22 19:21:04 +0000[diff] [blame]929multiple different passes. Analysis Groups can be given human readable names
930just like passes, but unlike passes, they need not derive from the <tt>Pass</tt>
931class. An analysis group may have one or more implementations, one of which is
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame^]932the "default" implementation.</p>
Chris Lattner8d8a9282002-08-22 19:21:04 +0000[diff] [blame]933
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame^]934<p>Analysis groups are used by client passes just like other passes are: the
Chris Lattner8d8a9282002-08-22 19:21:04 +0000[diff] [blame]935<tt>AnalysisUsage::addRequired()</tt> and <tt>Pass::getAnalysis()</tt> methods.
936In order to resolve this requirement, the <a href="#passmanager">PassManager</a>
937scans the available passes to see if any implementations of the analysis group
938are available. If none is available, the default implementation is created for
939the pass to use. All standard rules for <A href="#interaction">interaction
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame^]940between passes</a> still apply.</p>
Chris Lattner8d8a9282002-08-22 19:21:04 +0000[diff] [blame]941
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame^]942<p>Although <a href="#registration">Pass Registration</a> is optional for normal
Chris Lattner8d8a9282002-08-22 19:21:04 +0000[diff] [blame]943passes, all analysis group implementations must be registered, and must use the
944<A href="#registerag"><tt>RegisterAnalysisGroup</tt></a> template to join the
945implementation pool. Also, a default implementation of the interface
946<b>must</b> be registered with <A
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame^]947href="#registerag"><tt>RegisterAnalysisGroup</tt></a>.</p>
Chris Lattner8d8a9282002-08-22 19:21:04 +0000[diff] [blame]948
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame^]949<p>As a concrete example of an Analysis Group in action, consider the <a
950href="http://llvm.cs.uiuc.edu/doxygen/classllvm_1_1AliasAnalysis.html">AliasAnalysis</a>
Chris Lattner8d8a9282002-08-22 19:21:04 +0000[diff] [blame]951analysis group. The default implementation of the alias analysis interface (the
952<tt><a
953href="http://llvm.cs.uiuc.edu/doxygen/structBasicAliasAnalysis.html">basicaa</a></tt>
954pass) just does a few simple checks that don't require significant analysis to
955compute (such as: two different globals can never alias each other, etc).
956Passes that use the <tt><a
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame^]957href="http://llvm.cs.uiuc.edu/doxygen/classllvm_1_1AliasAnalysis.html">AliasAnalysis</a></tt>
Chris Lattner8d8a9282002-08-22 19:21:04 +0000[diff] [blame]958interface (for example the <tt><a
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame^]959href="http://llvm.cs.uiuc.edu/doxygen/classGCSE.html">gcse</a></tt> pass), do
960not care which implementation of alias analysis is actually provided, they just
961use the designated interface.</p>
Chris Lattner8d8a9282002-08-22 19:21:04 +0000[diff] [blame]962
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame^]963<p>From the user's perspective, commands work just like normal. Issuing the
Chris Lattner8d8a9282002-08-22 19:21:04 +0000[diff] [blame]964command '<tt>opt -gcse ...</tt>' will cause the <tt>basicaa</tt> class to be
965instantiated and added to the pass sequence. Issuing the command '<tt>opt
966-somefancyaa -gcse ...</tt>' will cause the <tt>gcse</tt> pass to use the
967<tt>somefancyaa</tt> alias analysis (which doesn't actually exist, it's just a
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame^]968hypothetical example) instead.</p>
Chris Lattner8d8a9282002-08-22 19:21:04 +0000[diff] [blame]969
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame^]970</div>
Chris Lattner8d8a9282002-08-22 19:21:04 +0000[diff] [blame]971
972<!-- _______________________________________________________________________ -->
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame^]973<div class="subsubsection">
974 <a name="registerag">Using <tt>RegisterAnalysisGroup</tt></a>
975</div>
Chris Lattner8d8a9282002-08-22 19:21:04 +0000[diff] [blame]976
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame^]977<div class="doc_text">
978
979<p>The <tt>RegisterAnalysisGroup</tt> template is used to register the analysis
Chris Lattner8d8a9282002-08-22 19:21:04 +0000[diff] [blame]980group itself as well as add pass implementations to the analysis group. First,
981an analysis should be registered, with a human readable name provided for it.
982Unlike registration of passes, there is no command line argument to be specified
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame^]983for the Analysis Group Interface itself, because it is "abstract":</p>
Chris Lattner8d8a9282002-08-22 19:21:04 +0000[diff] [blame]984
985<pre>
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame^]986 <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>");
987</pre>
Chris Lattner8d8a9282002-08-22 19:21:04 +0000[diff] [blame]988
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame^]989<p>Once the analysis is registered, passes can declare that they are valid
990implementations of the interface by using the following code:</p>
Chris Lattner8d8a9282002-08-22 19:21:04 +0000[diff] [blame]991
992<pre>
993<b>namespace</b> {
994 //<i> Analysis Group implementations <b>must</b> be registered normally...</i>
995 RegisterOpt&lt;FancyAA&gt;
996 B("<i>somefancyaa</i>", "<i>A more complex alias analysis implementation</i>");
997
998 //<i> Declare that we implement the AliasAnalysis interface</i>
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame^]999 RegisterAnalysisGroup&lt;<a href="http://llvm.cs.uiuc.edu/doxygen/classllvm_1_1AliasAnalysis.html">AliasAnalysis</a>, FancyAA&gt; C;
Chris Lattner8d8a9282002-08-22 19:21:04 +0000[diff] [blame]1000}
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame^]1001</pre>
Chris Lattner8d8a9282002-08-22 19:21:04 +0000[diff] [blame]1002
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame^]1003<p>This just shows a class <tt>FancyAA</tt> that is registered normally, then
1004uses the <tt>RegisterAnalysisGroup</tt> template to "join" the <tt><a
1005href="http://llvm.cs.uiuc.edu/doxygen/classllvm_1_1AliasAnalysis.html">AliasAnalysis</a></tt>
Chris Lattner8d8a9282002-08-22 19:21:04 +0000[diff] [blame]1006analysis group. Every implementation of an analysis group should join using
1007this template. A single pass may join multiple different analysis groups with
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame^]1008no problem.</p>
Chris Lattner8d8a9282002-08-22 19:21:04 +0000[diff] [blame]1009
1010<pre>
1011<b>namespace</b> {
1012 //<i> Analysis Group implementations <b>must</b> be registered normally...</i>
1013 RegisterOpt&lt;<a href="http://llvm.cs.uiuc.edu/doxygen/structBasicAliasAnalysis.html">BasicAliasAnalysis</a>&gt;
1014 D("<i>basicaa</i>", "<i>Basic Alias Analysis (default AA impl)</i>");
1015
1016 //<i> Declare that we implement the AliasAnalysis interface</i>
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame^]1017 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 Lattner8d8a9282002-08-22 19:21:04 +0000[diff] [blame]1018}
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame^]1019</pre>
Chris Lattner8d8a9282002-08-22 19:21:04 +0000[diff] [blame]1020
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame^]1021<p>Here we show how the default implementation is specified (using the extra
Chris Lattner8d8a9282002-08-22 19:21:04 +0000[diff] [blame]1022argument to the <tt>RegisterAnalysisGroup</tt> template). There must be exactly
1023one default implementation available at all times for an Analysis Group to be
1024used. Here we declare that the <tt><a
1025href="http://llvm.cs.uiuc.edu/doxygen/structBasicAliasAnalysis.html">BasicAliasAnalysis</a></tt>
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame^]1026pass is the default implementation for the interface.</p>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]1027
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame^]1028</div>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]1029
1030<!-- *********************************************************************** -->
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame^]1031<div class="doc_section">
1032 <a name="passmanager">What PassManager does</a>
1033</div>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]1034<!-- *********************************************************************** -->
1035
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame^]1036<div class="doc_text">
1037
1038<p>The <a
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]1039href="http://llvm.cs.uiuc.edu/doxygen/PassManager_8h-source.html"><tt>PassManager</tt></a>
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame^]1040<a
1041href="http://llvm.cs.uiuc.edu/doxygen/classllvm_1_1PassManager.html">class</a>
1042takes a list of passes, ensures their <a href="#interaction">prerequisites</a>
1043are set up correctly, and then schedules passes to run efficiently. All of the
1044LLVM tools that run passes use the <tt>PassManager</tt> for execution of these
1045passes.</p>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]1046
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame^]1047<p>The <tt>PassManager</tt> does two main things to try to reduce the execution
1048time of a series of passes:</p>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]1049
1050<ol>
1051<li><b>Share analysis results</b> - The PassManager attempts to avoid
1052recomputing analysis results as much as possible. This means keeping track of
1053which analyses are available already, which analyses get invalidated, and which
1054analyses are needed to be run for a pass. An important part of work is that the
1055<tt>PassManager</tt> tracks the exact lifetime of all analysis results, allowing
1056it to <a href="#releaseMemory">free memory</a> allocated to holding analysis
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame^]1057results as soon as they are no longer needed.</li>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]1058
1059<li><b>Pipeline the execution of passes on the program</b> - The
1060<tt>PassManager</tt> attempts to get better cache and memory usage behavior out
1061of a series of passes by pipelining the passes together. This means that, given
1062a series of consequtive <a href="#FunctionPass"><tt>FunctionPass</tt></a>'s, it
1063will execute all of the <a href="#FunctionPass"><tt>FunctionPass</tt></a>'s on
1064the first function, then all of the <a
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame^]1065href="#FunctionPass"><tt>FunctionPass</tt></a>es on the second function,
1066etc... until the entire program has been run through the passes.
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]1067
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame^]1068<p>This improves the cache behavior of the compiler, because it is only touching
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]1069the LLVM program representation for a single function at a time, instead of
1070traversing the entire program. It reduces the memory consumption of compiler,
1071because, for example, only one <a
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame^]1072href="http://llvm.cs.uiuc.edu/doxygen/structllvm_1_1DominatorSet.html"><tt>DominatorSet</tt></a>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]1073needs to be calculated at a time. This also makes it possible some <a
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame^]1074href="#SMP">interesting enhancements</a> in the future.</p></li>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]1075
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame^]1076</ol>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]1077
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame^]1078<p>The effectiveness of the <tt>PassManager</tt> is influenced directly by how
1079much information it has about the behaviors of the passes it is scheduling. For
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]1080example, the "preserved" set is intentionally conservative in the face of an
1081unimplemented <a href="#getAnalysisUsage"><tt>getAnalysisUsage</tt></a> method.
1082Not implementing when it should be implemented will have the effect of not
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame^]1083allowing any analysis results to live across the execution of your pass.</p>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]1084
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame^]1085<p>The <tt>PassManager</tt> class exposes a <tt>--debug-pass</tt> command line
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]1086options that is useful for debugging pass execution, seeing how things work, and
1087diagnosing when you should be preserving more analyses than you currently are
1088(To get information about all of the variants of the <tt>--debug-pass</tt>
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame^]1089option, just type '<tt>opt --help-hidden</tt>').</p>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]1090
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame^]1091<p>By using the <tt>--debug-pass=Structure</tt> option, for example, we can see
1092how our <a href="#basiccode">Hello World</a> pass interacts with other passes.
1093Lets try it out with the <tt>gcse</tt> and <tt>licm</tt> passes:</p>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]1094
1095<pre>
1096$ opt -load ../../../lib/Debug/libhello.so -gcse -licm --debug-pass=Structure &lt; hello.bc &gt; /dev/null
1097Module Pass Manager
1098 Function Pass Manager
1099 Dominator Set Construction
1100 Immediate Dominators Construction
1101 Global Common Subexpression Elimination
1102-- Immediate Dominators Construction
1103-- Global Common Subexpression Elimination
1104 Natural Loop Construction
1105 Loop Invariant Code Motion
1106-- Natural Loop Construction
1107-- Loop Invariant Code Motion
1108 Module Verifier
1109-- Dominator Set Construction
1110-- Module Verifier
1111 Bytecode Writer
1112--Bytecode Writer
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame^]1113</pre>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]1114
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame^]1115<p>This output shows us when passes are constructed and when the analysis
1116results are known to be dead (prefixed with '<tt>--</tt>'). Here we see that
1117GCSE uses dominator and immediate dominator information to do its job. The LICM
1118pass uses natural loop information, which uses dominator sets, but not immediate
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]1119dominators. Because immediate dominators are no longer useful after the GCSE
1120pass, it is immediately destroyed. The dominator sets are then reused to
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame^]1121compute natural loop information, which is then used by the LICM pass.</p>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]1122
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame^]1123<p>After the LICM pass, the module verifier runs (which is automatically added
1124by the '<tt>opt</tt>' tool), which uses the dominator set to check that the
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]1125resultant LLVM code is well formed. After it finishes, the dominator set
1126information is destroyed, after being computed once, and shared by three
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame^]1127passes.</p>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]1128
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame^]1129<p>Lets see how this changes when we run the <a href="#basiccode">Hello
1130World</a> pass in between the two passes:</p>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]1131
1132<pre>
1133$ opt -load ../../../lib/Debug/libhello.so -gcse -hello -licm --debug-pass=Structure &lt; hello.bc &gt; /dev/null
1134Module Pass Manager
1135 Function Pass Manager
1136 Dominator Set Construction
1137 Immediate Dominators Construction
1138 Global Common Subexpression Elimination
1139<b>-- Dominator Set Construction</b>
1140-- Immediate Dominators Construction
1141-- Global Common Subexpression Elimination
1142<b> Hello World Pass
1143-- Hello World Pass
1144 Dominator Set Construction</b>
1145 Natural Loop Construction
1146 Loop Invariant Code Motion
1147-- Natural Loop Construction
1148-- Loop Invariant Code Motion
1149 Module Verifier
1150-- Dominator Set Construction
1151-- Module Verifier
1152 Bytecode Writer
1153--Bytecode Writer
1154Hello: __main
1155Hello: puts
1156Hello: main
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame^]1157</pre>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]1158
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame^]1159<p>Here we see that the <a href="#basiccode">Hello World</a> pass has killed the
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]1160Dominator Set pass, even though it doesn't modify the code at all! To fix this,
1161we need to add the following <a
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame^]1162href="#getAnalysisUsage"><tt>getAnalysisUsage</tt></a> method to our pass:</p>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]1163
1164<pre>
1165 <i>// We don't modify the program, so we preserve all analyses</i>
1166 <b>virtual void</b> getAnalysisUsage(AnalysisUsage &amp;AU) <b>const</b> {
1167 AU.setPreservesAll();
1168 }
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame^]1169</pre>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]1170
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame^]1171<p>Now when we run our pass, we get this output:</p>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]1172
1173<pre>
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame^]1174$ opt -load ../../../lib/Debug/libhello.so -gcse -hello -licm --debug-pass=Structure &lt; hello.bc &gt; /dev/null
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]1175Pass Arguments: -gcse -hello -licm
1176Module Pass Manager
1177 Function Pass Manager
1178 Dominator Set Construction
1179 Immediate Dominators Construction
1180 Global Common Subexpression Elimination
1181-- Immediate Dominators Construction
1182-- Global Common Subexpression Elimination
1183 Hello World Pass
1184-- Hello World Pass
1185 Natural Loop Construction
1186 Loop Invariant Code Motion
1187-- Loop Invariant Code Motion
1188-- Natural Loop Construction
1189 Module Verifier
1190-- Dominator Set Construction
1191-- Module Verifier
1192 Bytecode Writer
1193--Bytecode Writer
1194Hello: __main
1195Hello: puts
1196Hello: main
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame^]1197</pre>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]1198
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame^]1199<p>Which shows that we don't accidentally invalidate dominator information
1200anymore, and therefore do not have to compute it twice.</p>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]1201
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame^]1202</div>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]1203
1204<!-- _______________________________________________________________________ -->
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame^]1205<div class="doc_subsubsection">
1206 <a name="releaseMemory">The <tt>releaseMemory</tt> method</a>
1207</div>
1208
1209<div class="doc_text">
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]1210
1211<pre>
1212 <b>virtual void</b> releaseMemory();
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame^]1213</pre>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]1214
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame^]1215<p>The <tt>PassManager</tt> automatically determines when to compute analysis
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]1216results, and how long to keep them around for. Because the lifetime of the pass
1217object itself is effectively the entire duration of the compilation process, we
1218need some way to free analysis results when they are no longer useful. The
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame^]1219<tt>releaseMemory</tt> virtual method is the way to do this.</p>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]1220
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame^]1221<p>If you are writing an analysis or any other pass that retains a significant
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]1222amount of state (for use by another pass which "requires" your pass and uses the
1223<a href="#getAnalysis">getAnalysis</a> method) you should implement
1224<tt>releaseMEmory</tt> to, well, release the memory allocated to maintain this
1225internal state. This method is called after the <tt>run*</tt> method for the
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame^]1226class, before the next call of <tt>run*</tt> in your pass.</p>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]1227
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame^]1228</div>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]1229
1230<!-- *********************************************************************** -->
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame^]1231<div class="doc_section">
1232 <a name="debughints">Using GDB with dynamically loaded passes</a>
1233</div>
Chris Lattner8a97c8a2002-09-06 02:02:58 +0000[diff] [blame]1234<!-- *********************************************************************** -->
1235
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame^]1236<div class="doc_text">
1237
1238<p>Unfortunately, using GDB with dynamically loaded passes is not as easy as it
Chris Lattner8a97c8a2002-09-06 02:02:58 +0000[diff] [blame]1239should be. First of all, you can't set a breakpoint in a shared object that has
1240not been loaded yet, and second of all there are problems with inlined functions
1241in shared objects. Here are some suggestions to debugging your pass with
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame^]1242GDB.</p>
Chris Lattner8a97c8a2002-09-06 02:02:58 +0000[diff] [blame]1243
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame^]1244<p>For sake of discussion, I'm going to assume that you are debugging a
Chris Lattner8a97c8a2002-09-06 02:02:58 +0000[diff] [blame]1245transformation invoked by <tt>opt</tt>, although nothing described here depends
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame^]1246on that.</p>
1247
1248</div>
Chris Lattner8a97c8a2002-09-06 02:02:58 +0000[diff] [blame]1249
1250<!-- _______________________________________________________________________ -->
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame^]1251<div class="doc_subsubsection">
1252 <a name="breakpoint">Setting a breakpoint in your pass</a>
1253</div>
Chris Lattner8a97c8a2002-09-06 02:02:58 +0000[diff] [blame]1254
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame^]1255<div class="doc_text">
1256
1257<p>First thing you do is start <tt>gdb</tt> on the <tt>opt</tt> process:</p>
Chris Lattner8a97c8a2002-09-06 02:02:58 +0000[diff] [blame]1258
1259<pre>
1260$ <b>gdb opt</b>
1261GNU gdb 5.0
1262Copyright 2000 Free Software Foundation, Inc.
1263GDB is free software, covered by the GNU General Public License, and you are
1264welcome to change it and/or distribute copies of it under certain conditions.
1265Type "show copying" to see the conditions.
1266There is absolutely no warranty for GDB. Type "show warranty" for details.
1267This GDB was configured as "sparc-sun-solaris2.6"...
1268(gdb)
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame^]1269</pre>
Chris Lattner8a97c8a2002-09-06 02:02:58 +0000[diff] [blame]1270
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame^]1271<p>Note that <tt>opt</tt> has a lot of debugging information in it, so it takes
Chris Lattner8a97c8a2002-09-06 02:02:58 +0000[diff] [blame]1272time to load. Be patient. Since we cannot set a breakpoint in our pass yet
1273(the shared object isn't loaded until runtime), we must execute the process, and
1274have it stop before it invokes our pass, but after it has loaded the shared
1275object. The most foolproof way of doing this is to set a breakpoint in
1276<tt>PassManager::run</tt> and then run the process with the arguments you
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame^]1277want:</p>
Chris Lattner8a97c8a2002-09-06 02:02:58 +0000[diff] [blame]1278
1279<pre>
1280(gdb) <b>break PassManager::run</b>
1281Breakpoint 1 at 0x2413bc: file Pass.cpp, line 70.
Chris Lattner4541bf72003-10-23 19:48:11 +0000[diff] [blame]1282(gdb) <b>run test.bc -load $(LLVMTOP)/llvm/lib/Debug/[libname].so -[passoption]</b>
1283Starting program: opt test.bc -load $(LLVMTOP)/llvm/lib/Debug/[libname].so -[passoption]
Chris Lattner8a97c8a2002-09-06 02:02:58 +0000[diff] [blame]1284Breakpoint 1, PassManager::run (this=0xffbef174, M=@0x70b298) at Pass.cpp:70
128570 bool PassManager::run(Module &amp;M) { return PM-&gt;run(M); }
1286(gdb)
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame^]1287</pre>
Chris Lattner8a97c8a2002-09-06 02:02:58 +0000[diff] [blame]1288
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame^]1289<p>Once the <tt>opt</tt> stops in the <tt>PassManager::run</tt> method you are
1290now free to set breakpoints in your pass so that you can trace through execution
1291or do other standard debugging stuff.</p>
Chris Lattner8a97c8a2002-09-06 02:02:58 +0000[diff] [blame]1292
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame^]1293</div>
Chris Lattner8a97c8a2002-09-06 02:02:58 +0000[diff] [blame]1294
1295<!-- _______________________________________________________________________ -->
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame^]1296<div class="doc_subsubsection">
1297 <a name="debugmisc">Miscellaneous Problems</a>
1298</div>
Chris Lattner8a97c8a2002-09-06 02:02:58 +0000[diff] [blame]1299
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame^]1300<div class="doc_text">
1301
1302<p>Once you have the basics down, there are a couple of problems that GDB has,
1303some with solutions, some without.</p>
Chris Lattner8a97c8a2002-09-06 02:02:58 +0000[diff] [blame]1304
1305<ul>
1306<li>Inline functions have bogus stack information. In general, GDB does a
1307pretty good job getting stack traces and stepping through inline functions.
1308When a pass is dynamically loaded however, it somehow completely loses this
1309capability. The only solution I know of is to de-inline a function (move it
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame^]1310from the body of a class to a .cpp file).</li>
Chris Lattner8a97c8a2002-09-06 02:02:58 +0000[diff] [blame]1311
1312<li>Restarting the program breaks breakpoints. After following the information
1313above, you have succeeded in getting some breakpoints planted in your pass. Nex
1314thing you know, you restart the program (i.e., you type '<tt>run</tt>' again),
1315and you start getting errors about breakpoints being unsettable. The only way I
1316have found to "fix" this problem is to <tt>delete</tt> the breakpoints that are
1317already set in your pass, run the program, and re-set the breakpoints once
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame^]1318execution stops in <tt>PassManager::run</tt>.</li>
Chris Lattner8a97c8a2002-09-06 02:02:58 +0000[diff] [blame]1319
1320</ul>
1321
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame^]1322<p>Hopefully these tips will help with common case debugging situations. If
1323you'd like to contribute some tips of your own, just contact <a
1324href="mailto:sabre@nondot.org">Chris</a>.</p>
Chris Lattner8a97c8a2002-09-06 02:02:58 +0000[diff] [blame]1325
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame^]1326</div>
Chris Lattner8a97c8a2002-09-06 02:02:58 +0000[diff] [blame]1327
1328<!-- *********************************************************************** -->
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame^]1329<div class="doc_section">
1330 <a name="future">Future extensions planned</a>
1331</div>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]1332<!-- *********************************************************************** -->
1333
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame^]1334<div class="doc_text">
1335
1336<p>Although the LLVM Pass Infrastructure is very capable as it stands, and does
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]1337some nifty stuff, there are things we'd like to add in the future. Here is
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame^]1338where we are going:</p>
1339
1340</div>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]1341
1342<!-- _______________________________________________________________________ -->
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame^]1343<div class="subsubsection">
1344 <a name="SMP">Multithreaded LLVM</a>
1345</div>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]1346
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame^]1347<div class="doc_text">
1348
1349<p>Multiple CPU machines are becoming more common and compilation can never be
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]1350fast enough: obviously we should allow for a multithreaded compiler. Because of
1351the semantics defined for passes above (specifically they cannot maintain state
1352across invocations of their <tt>run*</tt> methods), a nice clean way to
1353implement a multithreaded compiler would be for the <tt>PassManager</tt> class
Misha Brukman7fdaab42003-07-14 17:20:40 +0000[diff] [blame]1354to create multiple instances of each pass object, and allow the separate
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame^]1355instances to be hacking on different parts of the program at the same time.</p>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]1356
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame^]1357<p>This implementation would prevent each of the passes from having to implement
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]1358multithreaded constructs, requiring only the LLVM core to have locking in a few
1359places (for global resources). Although this is a simple extension, we simply
1360haven't had time (or multiprocessor machines, thus a reason) to implement this.
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame^]1361Despite that, we have kept the LLVM passes SMP ready, and you should too.</p>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]1362
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame^]1363</div>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]1364
1365<!-- _______________________________________________________________________ -->
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame^]1366<div class="subsubsection">
1367 <a name="ModuleSource">A new <tt>ModuleSource</tt> interface</a>
1368</div>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]1369
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame^]1370<div class="doc_text">
1371
1372<p>Currently, the <tt>PassManager</tt>'s <tt>run</tt> method takes a <tt><a
1373href="http://llvm.cs.uiuc.edu/doxygen/structllvm_1_1Module.html">Module</a></tt>
1374as input, and runs all of the passes on this module. The problem with this
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]1375approach is that none of the <tt>PassManager</tt> features can be used for
1376timing and debugging the actual <b>loading</b> of the module from disk or
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame^]1377standard input.</p>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]1378
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame^]1379<p>To solve this problem, eventually the <tt>PassManger</tt> class will accept a
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]1380<tt>ModuleSource</tt> object instead of a Module itself. When complete, this
1381will also allow for streaming of functions out of the bytecode representation,
1382allowing us to avoid holding the entire program in memory at once if we only are
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame^]1383dealing with <a href="#FunctionPass">FunctionPass</a>es.</p>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]1384
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame^]1385<p>As part of a different issue, eventually the bytecode loader will be extended
1386to allow on-demand loading of functions from the bytecode representation, in
1387order to better support the runtime reoptimizer. The bytecode format is already
1388capable of this, the loader just needs to be reworked a bit.</p>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]1389
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame^]1390</div>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]1391
1392<!-- _______________________________________________________________________ -->
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame^]1393<div class="subsubsection">
1394<a name="PassFunctionPass"><tt>Pass</tt>'s requiring <tt>FunctionPass</tt>'s</a>
1395</div>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]1396
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame^]1397<div class="doc_text">
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]1398
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame^]1399<p>Currently it is illegal for a <a href="#Pass"><tt>Pass</tt></a> to require a
1400<a href="#FunctionPass"><tt>FunctionPass</tt></a>. This is because there is
1401only one instance of the <a href="#FunctionPass"><tt>FunctionPass</tt></a>
1402object ever created, thus nowhere to store information for all of the functions
1403in the program at the same time. Although this has come up a couple of times
1404before, this has always been worked around by factoring one big complicated pass
1405into a global and an interprocedural part, both of which are distinct. In the
1406future, it would be nice to have this though.</p>
1407
1408<p>Note that it is no problem for a <a
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]1409href="#FunctionPass"><tt>FunctionPass</tt></a> to require the results of a <a
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame^]1410href="#Pass"><tt>Pass</tt></a>, only the other way around.</p>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]1411
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame^]1412</div>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]1413
1414<!-- *********************************************************************** -->
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame^]1415<hr>
1416<address>
1417 <a href="http://jigsaw.w3.org/css-validator/check/referer"><img
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Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]1421
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame^]1422 <a href="mailto:sabre@nondot.org">Chris Lattner</a><br>
1423 <a href="http://llvm.cs.uiuc.edu">The LLVM Compiler Infrastructure</a><br>
1424 Last modified: $Date$
1425</address>
1426
1427</body>
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