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gerrit-public.fairphone.software / toolchain / llvm-project / 9b5e8e5c32b68e2f7c337f9a7e59de04c7fd5737 / . / llvm / docs / WritingAnLLVMPass.html
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Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]6 <title>Writing an LLVM Pass</title>
7 <link rel="stylesheet" href="llvm.css" type="text/css">
8</head>
9<body>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]10
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]11<div class="doc_title">
12 Writing an LLVM Pass
13</div>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]14
15<ol>
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]16 <li><a href="#introduction">Introduction - What is a pass?</a></li>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]17 <li><a href="#quickstart">Quick Start - Writing hello world</a>
18 <ul>
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]19 <li><a href="#makefile">Setting up the build environment</a></li>
20 <li><a href="#basiccode">Basic code required</a></li>
Chris Lattnerb693cb02006-08-27 23:18:52 +0000[diff] [blame]21 <li><a href="#running">Running a pass with <tt>opt</tt></a></li>
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]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 Lattner3c11c042004-09-20 04:36:29 +0000[diff] [blame]26 <li><a href="#ModulePass">The <tt>ModulePass</tt> class</a>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]27 <ul>
Chris Lattner3c11c042004-09-20 04:36:29 +0000[diff] [blame]28 <li><a href="#runOnModule">The <tt>runOnModule</tt> method</a></li>
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]29 </ul></li>
Chris Lattner9e4be6f2004-09-18 06:39:35 +0000[diff] [blame]30 <li><a href="#CallGraphSCCPass">The <tt>CallGraphSCCPass</tt> class</a>
31 <ul>
Devang Patel40ec0802007-01-23 22:56:28 +0000[diff] [blame]32 <li><a href="#doInitialization_scc">The <tt>doInitialization(CallGraph
Chris Lattner9e4be6f2004-09-18 06:39:35 +0000[diff] [blame]33 &amp;)</tt> method</a></li>
34 <li><a href="#runOnSCC">The <tt>runOnSCC</tt> method</a></li>
Devang Patel40ec0802007-01-23 22:56:28 +0000[diff] [blame]35 <li><a href="#doFinalization_scc">The <tt>doFinalization(CallGraph
Chris Lattner9e4be6f2004-09-18 06:39:35 +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="#FunctionPass">The <tt>FunctionPass</tt> class</a>
39 <ul>
Chris Lattner5e08e70f2002-09-12 17:06:43 +0000[diff] [blame]40 <li><a href="#doInitialization_mod">The <tt>doInitialization(Module
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]41 &amp;)</tt> method</a></li>
42 <li><a href="#runOnFunction">The <tt>runOnFunction</tt> method</a></li>
Chris Lattner5e08e70f2002-09-12 17:06:43 +0000[diff] [blame]43 <li><a href="#doFinalization_mod">The <tt>doFinalization(Module
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]44 &amp;)</tt> method</a></li>
45 </ul></li>
Devang Patel1d3bb032007-03-19 22:21:25 +0000[diff] [blame]46 <li><a href="#LoopPass">The <tt>LoopPass</tt> class</a>
47 <ul>
48 <li><a href="#doInitialization_loop">The <tt>doInitialization(Loop *,
49 LPPassManager &amp;)</tt> method</a></li>
50 <li><a href="#runOnLoop">The <tt>runOnLoop</tt> method</a></li>
51 <li><a href="#doFinalization_loop">The <tt>doFinalization()
52 </tt> method</a></li>
53 </ul></li>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]54 <li><a href="#BasicBlockPass">The <tt>BasicBlockPass</tt> class</a>
55 <ul>
Chris Lattner5e08e70f2002-09-12 17:06:43 +0000[diff] [blame]56 <li><a href="#doInitialization_fn">The <tt>doInitialization(Function
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]57 &amp;)</tt> method</a></li>
58 <li><a href="#runOnBasicBlock">The <tt>runOnBasicBlock</tt>
59 method</a></li>
Chris Lattner5e08e70f2002-09-12 17:06:43 +0000[diff] [blame]60 <li><a href="#doFinalization_fn">The <tt>doFinalization(Function
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]61 &amp;)</tt> method</a></li>
62 </ul></li>
Brian Gaeke110f07b2003-07-17 18:53:20 +0000[diff] [blame]63 <li><a href="#MachineFunctionPass">The <tt>MachineFunctionPass</tt>
64 class</a>
Brian Gaeke673ef4d2003-07-22 20:53:20 +0000[diff] [blame]65 <ul>
66 <li><a href="#runOnMachineFunction">The
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]67 <tt>runOnMachineFunction(MachineFunction &amp;)</tt> method</a></li>
68 </ul></li>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]69 </ul>
70 <li><a href="#registration">Pass Registration</a>
71 <ul>
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]72 <li><a href="#print">The <tt>print</tt> method</a></li>
73 </ul></li>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]74 <li><a href="#interaction">Specifying interactions between passes</a>
75 <ul>
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]76 <li><a href="#getAnalysisUsage">The <tt>getAnalysisUsage</tt>
77 method</a></li>
Chris Lattner8e871652004-03-17 21:09:55 +0000[diff] [blame]78 <li><a href="#AU::addRequired">The <tt>AnalysisUsage::addRequired&lt;&gt;</tt> and <tt>AnalysisUsage::addRequiredTransitive&lt;&gt;</tt> methods</a></li>
79 <li><a href="#AU::addPreserved">The <tt>AnalysisUsage::addPreserved&lt;&gt;</tt> method</a></li>
80 <li><a href="#AU::examples">Example implementations of <tt>getAnalysisUsage</tt></a></li>
81 <li><a href="#getAnalysis">The <tt>getAnalysis&lt;&gt;</tt> and <tt>getAnalysisToUpdate&lt;&gt;</tt> methods</a></li>
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]82 </ul></li>
Chris Lattner8d8a9282002-08-22 19:21:04 +0000[diff] [blame]83 <li><a href="#analysisgroup">Implementing Analysis Groups</a>
84 <ul>
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]85 <li><a href="#agconcepts">Analysis Group Concepts</a></li>
86 <li><a href="#registerag">Using <tt>RegisterAnalysisGroup</tt></a></li>
87 </ul></li>
Tanya Lattnerfb966ba2004-11-19 01:25:14 +0000[diff] [blame]88 <li><a href="#passStatistics">Pass Statistics</a>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]89 <li><a href="#passmanager">What PassManager does</a>
90 <ul>
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]91 <li><a href="#releaseMemory">The <tt>releaseMemory</tt> method</a></li>
92 </ul></li>
Jim Laskey575df8b2006-08-04 18:10:12 +0000[diff] [blame]93 <li><a href="#registering">Registering dynamically loaded passes</a>
94 <ul>
95 <li><a href="#registering_existing">Using existing registries</a></li>
96 <li><a href="#registering_new">Creating new registries</a></li>
97 </ul></li>
Chris Lattner8a97c8a2002-09-06 02:02:58 +0000[diff] [blame]98 <li><a href="#debughints">Using GDB with dynamically loaded passes</a>
99 <ul>
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]100 <li><a href="#breakpoint">Setting a breakpoint in your pass</a></li>
101 <li><a href="#debugmisc">Miscellaneous Problems</a></li>
102 </ul></li>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]103 <li><a href="#future">Future extensions planned</a>
104 <ul>
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]105 <li><a href="#SMP">Multithreaded LLVM</a></li>
Chris Lattner3c11c042004-09-20 04:36:29 +0000[diff] [blame]106 <li><a href="#PassFunctionPass"><tt>ModulePass</tt>es requiring
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]107 <tt>FunctionPass</tt>es</a></li>
108 </ul></li>
109</ol>
Chris Lattner56d9e222002-08-08 20:23:41 +0000[diff] [blame]110
Chris Lattner020e1fc2004-05-23 21:07:27 +0000[diff] [blame]111<div class="doc_author">
Chris Lattner4bde9fb2006-08-11 16:37:02 +0000[diff] [blame]112 <p>Written by <a href="mailto:sabre@nondot.org">Chris Lattner</a> and
Jim Laskey6e8a2f42007-03-14 19:32:21 +0000[diff] [blame]113 <a href="mailto:jlaskey@mac.com">Jim Laskey</a></p>
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]114</div>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]115
116<!-- *********************************************************************** -->
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]117<div class="doc_section">
118 <a name="introduction">Introduction - What is a pass?</a>
119</div>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]120<!-- *********************************************************************** -->
121
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]122<div class="doc_text">
123
124<p>The LLVM Pass Framework is an important part of the LLVM system, because LLVM
Chris Lattner9e4be6f2004-09-18 06:39:35 +0000[diff] [blame]125passes are where most of the interesting parts of the compiler exist. Passes
126perform the transformations and optimizations that make up the compiler, they
127build the analysis results that are used by these transformations, and they are,
128above all, a structuring technique for compiler code.</p>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]129
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]130<p>All LLVM passes are subclasses of the <tt><a
Reid Spencerca058542006-03-14 05:39:39 +0000[diff] [blame]131href="http://llvm.org/doxygen/classllvm_1_1Pass.html">Pass</a></tt>
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]132class, which implement functionality by overriding virtual methods inherited
Chris Lattner3c11c042004-09-20 04:36:29 +0000[diff] [blame]133from <tt>Pass</tt>. Depending on how your pass works, you should inherit from
134the <tt><a href="#ModulePass">ModulePass</a></tt>, <tt><a
135href="#CallGraphSCCPass">CallGraphSCCPass</a></tt>, <tt><a
136href="#FunctionPass">FunctionPass</a></tt>, or <tt><a
Devang Patel1d3bb032007-03-19 22:21:25 +0000[diff] [blame]137href="#LoopPass">LoopPass</a></tt>, or <tt><a
Chris Lattner9e4be6f2004-09-18 06:39:35 +0000[diff] [blame]138href="#BasicBlockPass">BasicBlockPass</a></tt> classes, which gives the system
139more information about what your pass does, and how it can be combined with
140other passes. One of the main features of the LLVM Pass Framework is that it
141schedules passes to run in an efficient way based on the constraints that your
142pass meets (which are indicated by which class they derive from).</p>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]143
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]144<p>We start by showing you how to construct a pass, everything from setting up
145the code, to compiling, loading, and executing it. After the basics are down,
146more advanced features are discussed.</p>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]147
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]148</div>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]149
150<!-- *********************************************************************** -->
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]151<div class="doc_section">
152 <a name="quickstart">Quick Start - Writing hello world</a>
153</div>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]154<!-- *********************************************************************** -->
155
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]156<div class="doc_text">
157
158<p>Here we describe how to write the "hello world" of passes. The "Hello" pass
159is designed to simply print out the name of non-external functions that exist in
Chris Lattner9e4be6f2004-09-18 06:39:35 +0000[diff] [blame]160the program being compiled. It does not modify the program at all, it just
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]161inspects it. The source code and files for this pass are available in the LLVM
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]162source tree in the <tt>lib/Transforms/Hello</tt> directory.</p>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]163
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]164</div>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]165
166<!-- ======================================================================= -->
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]167<div class="doc_subsection">
168 <a name="makefile">Setting up the build environment</a>
169</div>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]170
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]171<div class="doc_text">
172
Reid Spencera1799682004-12-11 05:12:57 +0000[diff] [blame]173 <p>First, you need to create a new directory somewhere in the LLVM source
174 base. For this example, we'll assume that you made
175 <tt>lib/Transforms/Hello</tt>. Next, you must set up a build script
176 (Makefile) that will compile the source code for the new pass. To do this,
177 copy the following into <tt>Makefile</tt>:</p>
178 <hr/>
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]179
Jim Laskey575df8b2006-08-04 18:10:12 +0000[diff] [blame]180<div class="doc_code"><pre>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]181# Makefile for hello pass
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]182
Chris Lattnereb4ba3c2002-08-14 20:06:13 +0000[diff] [blame]183# Path to top level of LLVM heirarchy
Chris Lattner0c5e2932002-08-14 20:07:01 +0000[diff] [blame]184LEVEL = ../../..
Chris Lattnereb4ba3c2002-08-14 20:06:13 +0000[diff] [blame]185
186# Name of the library to build
Reid Spencer4a1ab182005-01-11 05:16:23 +0000[diff] [blame]187LIBRARYNAME = Hello
Chris Lattnereb4ba3c2002-08-14 20:06:13 +0000[diff] [blame]188
Reid Spencer4a1ab182005-01-11 05:16:23 +0000[diff] [blame]189# Make the shared library become a loadable module so the tools can
190# dlopen/dlsym on the resulting library.
Robert Bocchino19cbea12006-01-06 22:49:23 +0000[diff] [blame]191LOADABLE_MODULE = 1
Reid Spencer4a1ab182005-01-11 05:16:23 +0000[diff] [blame]192
Reid Spencer197d7bf2006-08-08 01:48:17 +0000[diff] [blame]193# Tell the build system which LLVM libraries your pass needs. You'll probably
194# need at least LLVMSystem.a, LLVMSupport.a, LLVMCore.a but possibly several
195# others too.
196LLVMLIBS = LLVMCore.a LLVMSupport.a LLVMSystem.a
197
Chris Lattnereb4ba3c2002-08-14 20:06:13 +0000[diff] [blame]198# Include the makefile implementation stuff
199include $(LEVEL)/Makefile.common
Jim Laskey575df8b2006-08-04 18:10:12 +0000[diff] [blame]200</pre></div>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]201
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]202<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]203directory are to be compiled and linked together into a
Reid Spencer4a1ab182005-01-11 05:16:23 +0000[diff] [blame]204<tt>Debug/lib/Hello.so</tt> shared object that can be dynamically loaded by
Chris Lattnerb693cb02006-08-27 23:18:52 +0000[diff] [blame]205the <tt>opt</tt> or <tt>bugpoint</tt> tools via their <tt>-load</tt> options.
Reid Spencer4a1ab182005-01-11 05:16:23 +0000[diff] [blame]206If your operating system uses a suffix other than .so (such as windows or
207Mac OS/X), the appropriate extension will be used.</p>
John Criswell2edea842004-01-26 21:26:54 +0000[diff] [blame]208
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]209<p>Now that we have the build scripts set up, we just need to write the code for
210the pass itself.</p>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]211
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]212</div>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]213
214<!-- ======================================================================= -->
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]215<div class="doc_subsection">
216 <a name="basiccode">Basic code required</a>
217</div>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]218
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]219<div class="doc_text">
220
221<p>Now that we have a way to compile our new pass, we just have to write it.
222Start out with:</p>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]223
Jim Laskey575df8b2006-08-04 18:10:12 +0000[diff] [blame]224<div class="doc_code"><pre>
Reid Spencerca058542006-03-14 05:39:39 +0000[diff] [blame]225<b>#include</b> "<a href="http://llvm.org/doxygen/Pass_8h-source.html">llvm/Pass.h</a>"
226<b>#include</b> "<a href="http://llvm.org/doxygen/Function_8h-source.html">llvm/Function.h</a>"
Jim Laskey575df8b2006-08-04 18:10:12 +0000[diff] [blame]227</pre></div>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]228
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]229<p>Which are needed because we are writing a <tt><a
Reid Spencerca058542006-03-14 05:39:39 +0000[diff] [blame]230href="http://llvm.org/doxygen/classllvm_1_1Pass.html">Pass</a></tt>, and
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]231we are operating on <tt><a
Reid Spencerca058542006-03-14 05:39:39 +0000[diff] [blame]232href="http://llvm.org/doxygen/classllvm_1_1Function.html">Function</a></tt>'s.</p>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]233
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]234<p>Next we have:</p>
Jim Laskey575df8b2006-08-04 18:10:12 +0000[diff] [blame]235<div class="doc_code"><pre>
Jonathan Mantonaff4a6a2004-06-30 18:10:30 +0000[diff] [blame]236<b>using namespace llvm;</b>
Jim Laskey575df8b2006-08-04 18:10:12 +0000[diff] [blame]237</pre></div>
Jonathan Mantonaff4a6a2004-06-30 18:10:30 +0000[diff] [blame]238<p>... which is required because the functions from the include files
239live in the llvm namespace.
240</p>
241
242<p>Next we have:</p>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]243
Jim Laskey575df8b2006-08-04 18:10:12 +0000[diff] [blame]244<div class="doc_code"><pre>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]245<b>namespace</b> {
Jim Laskey575df8b2006-08-04 18:10:12 +0000[diff] [blame]246</pre></div>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]247
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]248<p>... which starts out an anonymous namespace. Anonymous namespaces are to C++
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]249what the "<tt>static</tt>" keyword is to C (at global scope). It makes the
250things declared inside of the anonymous namespace only visible to the current
251file. If you're not familiar with them, consult a decent C++ book for more
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]252information.</p>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]253
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]254<p>Next, we declare our pass itself:</p>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]255
Jim Laskey575df8b2006-08-04 18:10:12 +0000[diff] [blame]256<div class="doc_code"><pre>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]257 <b>struct</b> Hello : <b>public</b> <a href="#FunctionPass">FunctionPass</a> {
Jim Laskey575df8b2006-08-04 18:10:12 +0000[diff] [blame]258</pre></div><p>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]259
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]260<p>This declares a "<tt>Hello</tt>" class that is a subclass of <tt><a
Reid Spencerca058542006-03-14 05:39:39 +0000[diff] [blame]261href="http://llvm.org/doxygen/classllvm_1_1FunctionPass.html">FunctionPass</a></tt>.
Chris Lattnera818d922002-09-09 03:48:46 +0000[diff] [blame]262The different builtin pass subclasses are described in detail <a
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]263href="#passtype">later</a>, but for now, know that <a
264href="#FunctionPass"><tt>FunctionPass</tt></a>'s operate a function at a
265time.</p>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]266
Jim Laskey575df8b2006-08-04 18:10:12 +0000[diff] [blame]267<div class="doc_code"><pre>
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]268 <b>virtual bool</b> <a href="#runOnFunction">runOnFunction</a>(Function &amp;F) {
Bill Wendling22e978a2006-12-07 20:04:42 +0000[diff] [blame]269 llvm::cerr &lt;&lt; "<i>Hello: </i>" &lt;&lt; F.getName() &lt;&lt; "\n";
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]270 <b>return false</b>;
271 }
272 }; <i>// end of struct Hello</i>
Jim Laskey575df8b2006-08-04 18:10:12 +0000[diff] [blame]273</pre></div>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]274
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]275<p>We declare a "<a href="#runOnFunction"><tt>runOnFunction</tt></a>" method,
276which overloads an abstract virtual method inherited from <a
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]277href="#FunctionPass"><tt>FunctionPass</tt></a>. This is where we are supposed
278to 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]279function.</p>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]280
Jim Laskey575df8b2006-08-04 18:10:12 +0000[diff] [blame]281<div class="doc_code"><pre>
Chris Lattnerb693cb02006-08-27 23:18:52 +0000[diff] [blame]282 RegisterPass&lt;Hello&gt; X("<i>hello</i>", "<i>Hello World Pass</i>");
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]283} <i>// end of anonymous namespace</i>
Jim Laskey575df8b2006-08-04 18:10:12 +0000[diff] [blame]284</pre></div>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]285
Chris Lattnerb693cb02006-08-27 23:18:52 +0000[diff] [blame]286<p>Lastly, we <a href="#registration">register our class</a> <tt>Hello</tt>,
287giving it a command line
288argument "<tt>hello</tt>", and a name "<tt>Hello World Pass</tt>".</p>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]289
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]290<p>As a whole, the <tt>.cpp</tt> file looks like:</p>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]291
Jim Laskey575df8b2006-08-04 18:10:12 +0000[diff] [blame]292<div class="doc_code"><pre>
Reid Spencerca058542006-03-14 05:39:39 +0000[diff] [blame]293<b>#include</b> "<a href="http://llvm.org/doxygen/Pass_8h-source.html">llvm/Pass.h</a>"
294<b>#include</b> "<a href="http://llvm.org/doxygen/Function_8h-source.html">llvm/Function.h</a>"
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]295
Jonathan Mantonaff4a6a2004-06-30 18:10:30 +0000[diff] [blame]296<b>using namespace llvm;</b>
297
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]298<b>namespace</b> {
299 <b>struct Hello</b> : <b>public</b> <a href="#FunctionPass">FunctionPass</a> {
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]300 <b>virtual bool</b> <a href="#runOnFunction">runOnFunction</a>(Function &amp;F) {
Bill Wendling22e978a2006-12-07 20:04:42 +0000[diff] [blame]301 llvm::cerr &lt;&lt; "<i>Hello: </i>" &lt;&lt; F.getName() &lt;&lt; "\n";
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]302 <b>return false</b>;
303 }
304 };
305
Chris Lattnerb693cb02006-08-27 23:18:52 +0000[diff] [blame]306 RegisterPass&lt;Hello&gt; X("<i>hello</i>", "<i>Hello World Pass</i>");
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]307}
Jim Laskey575df8b2006-08-04 18:10:12 +0000[diff] [blame]308</pre></div>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]309
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]310<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]311command in the local directory and you should get a new
Reid Spencer4a1ab182005-01-11 05:16:23 +0000[diff] [blame]312"<tt>Debug/lib/Hello.so</tt> file. Note that everything in this file is
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]313contained in an anonymous namespace: this reflects the fact that passes are self
314contained units that do not need external interfaces (although they can have
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]315them) to be useful.</p>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]316
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]317</div>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]318
319<!-- ======================================================================= -->
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]320<div class="doc_subsection">
Chris Lattnerb693cb02006-08-27 23:18:52 +0000[diff] [blame]321 <a name="running">Running a pass with <tt>opt</tt></a>
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]322</div>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]323
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]324<div class="doc_text">
325
John Criswell2edea842004-01-26 21:26:54 +0000[diff] [blame]326<p>Now that you have a brand new shiny shared object file, we can use the
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]327<tt>opt</tt> command to run an LLVM program through your pass. Because you
Chris Lattnerb693cb02006-08-27 23:18:52 +0000[diff] [blame]328registered your pass with the <tt>RegisterPass</tt> template, you will be able to
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]329use the <tt>opt</tt> tool to access it, once loaded.</p>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]330
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]331<p>To test it, follow the example at the end of the <a
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]332href="GettingStarted.html">Getting Started Guide</a> to compile "Hello World" to
333LLVM. We can now run the bytecode file (<tt>hello.bc</tt>) for the program
334through our transformation like this (or course, any bytecode file will
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]335work):</p>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]336
Jim Laskey575df8b2006-08-04 18:10:12 +0000[diff] [blame]337<div class="doc_code"><pre>
Reid Spencer4a1ab182005-01-11 05:16:23 +0000[diff] [blame]338$ opt -load ../../../Debug/lib/Hello.so -hello &lt; hello.bc &gt; /dev/null
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]339Hello: __main
340Hello: puts
341Hello: main
Jim Laskey575df8b2006-08-04 18:10:12 +0000[diff] [blame]342</pre></div>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]343
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]344<p>The '<tt>-load</tt>' option specifies that '<tt>opt</tt>' should load your
345pass as a shared object, which makes '<tt>-hello</tt>' a valid command line
346argument (which is one reason you need to <a href="#registration">register your
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]347pass</a>). Because the hello pass does not modify the program in any
348interesting way, we just throw away the result of <tt>opt</tt> (sending it to
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]349<tt>/dev/null</tt>).</p>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]350
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]351<p>To see what happened to the other string you registered, try running
352<tt>opt</tt> with the <tt>--help</tt> option:</p>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]353
Jim Laskey575df8b2006-08-04 18:10:12 +0000[diff] [blame]354<div class="doc_code"><pre>
Reid Spencer4a1ab182005-01-11 05:16:23 +0000[diff] [blame]355$ opt -load ../../../Debug/lib/Hello.so --help
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]356OVERVIEW: llvm .bc -&gt; .bc modular optimizer
357
358USAGE: opt [options] &lt;input bytecode&gt;
359
360OPTIONS:
361 Optimizations available:
362...
363 -funcresolve - Resolve Functions
364 -gcse - Global Common Subexpression Elimination
365 -globaldce - Dead Global Elimination
366 <b>-hello - Hello World Pass</b>
Chris Lattner216c7b82003-09-10 05:29:43 +0000[diff] [blame]367 -indvars - Canonicalize Induction Variables
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]368 -inline - Function Integration/Inlining
369 -instcombine - Combine redundant instructions
370...
Jim Laskey575df8b2006-08-04 18:10:12 +0000[diff] [blame]371</pre></div>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]372
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]373<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]374documentation to users of <tt>opt</tt>. Now that you have a working pass, you
375would go ahead and make it do the cool transformations you want. Once you get
376it all working and tested, it may become useful to find out how fast your pass
377is. The <a href="#passManager"><tt>PassManager</tt></a> provides a nice command
378line option (<tt>--time-passes</tt>) that allows you to get information about
379the execution time of your pass along with the other passes you queue up. For
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]380example:</p>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]381
Jim Laskey575df8b2006-08-04 18:10:12 +0000[diff] [blame]382<div class="doc_code"><pre>
Reid Spencer4a1ab182005-01-11 05:16:23 +0000[diff] [blame]383$ opt -load ../../../Debug/lib/Hello.so -hello -time-passes &lt; hello.bc &gt; /dev/null
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]384Hello: __main
385Hello: puts
386Hello: main
387===============================================================================
388 ... Pass execution timing report ...
389===============================================================================
390 Total Execution Time: 0.02 seconds (0.0479059 wall clock)
391
392 ---User Time--- --System Time-- --User+System-- ---Wall Time--- --- Pass Name ---
393 0.0100 (100.0%) 0.0000 ( 0.0%) 0.0100 ( 50.0%) 0.0402 ( 84.0%) Bytecode Writer
394 0.0000 ( 0.0%) 0.0100 (100.0%) 0.0100 ( 50.0%) 0.0031 ( 6.4%) Dominator Set Construction
395 0.0000 ( 0.0%) 0.0000 ( 0.0%) 0.0000 ( 0.0%) 0.0013 ( 2.7%) Module Verifier
396 <b> 0.0000 ( 0.0%) 0.0000 ( 0.0%) 0.0000 ( 0.0%) 0.0033 ( 6.9%) Hello World Pass</b>
397 0.0100 (100.0%) 0.0100 (100.0%) 0.0200 (100.0%) 0.0479 (100.0%) TOTAL
Jim Laskey575df8b2006-08-04 18:10:12 +0000[diff] [blame]398</pre></div>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]399
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]400<p>As you can see, our implementation above is pretty fast :). The additional
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]401passes listed are automatically inserted by the '<tt>opt</tt>' tool to verify
402that the LLVM emitted by your pass is still valid and well formed LLVM, which
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]403hasn't been broken somehow.</p>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]404
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]405<p>Now that you have seen the basics of the mechanics behind passes, we can talk
406about some more details of how they work and how to use them.</p>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]407
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]408</div>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]409
410<!-- *********************************************************************** -->
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]411<div class="doc_section">
412 <a name="passtype">Pass classes and requirements</a>
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_text">
417
418<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]419decide what class you should subclass for your pass. The <a
420href="#basiccode">Hello World</a> example uses the <tt><a
421href="#FunctionPass">FunctionPass</a></tt> class for its implementation, but we
422did not discuss why or when this should occur. Here we talk about the classes
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]423available, from the most general to the most specific.</p>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]424
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]425<p>When choosing a superclass for your Pass, you should choose the <b>most
Chris Lattner8d8a9282002-08-22 19:21:04 +0000[diff] [blame]426specific</b> class possible, while still being able to meet the requirements
Misha Brukman7eb05a12003-08-18 14:43:39 +0000[diff] [blame]427listed. This gives the LLVM Pass Infrastructure information necessary to
Chris Lattner8d8a9282002-08-22 19:21:04 +0000[diff] [blame]428optimize how passes are run, so that the resultant compiler isn't unneccesarily
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]429slow.</p>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]430
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]431</div>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]432
Chris Lattner9720dda2002-09-25 22:31:38 +0000[diff] [blame]433<!-- ======================================================================= -->
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]434<div class="doc_subsection">
435 <a name="ImmutablePass">The <tt>ImmutablePass</tt> class</a>
436</div>
Chris Lattner9720dda2002-09-25 22:31:38 +0000[diff] [blame]437
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]438<div class="doc_text">
439
440<p>The most plain and boring type of pass is the "<tt><a
Reid Spencerca058542006-03-14 05:39:39 +0000[diff] [blame]441href="http://llvm.org/doxygen/classllvm_1_1ImmutablePass.html">ImmutablePass</a></tt>"
Chris Lattner9720dda2002-09-25 22:31:38 +0000[diff] [blame]442class. This pass type is used for passes that do not have to be run, do not
443change state, and never need to be updated. This is not a normal type of
444transformation or analysis, but can provide information about the current
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]445compiler configuration.</p>
Chris Lattner9720dda2002-09-25 22:31:38 +0000[diff] [blame]446
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]447<p>Although this pass class is very infrequently used, it is important for
Chris Lattner9720dda2002-09-25 22:31:38 +0000[diff] [blame]448providing information about the current target machine being compiled for, and
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]449other static information that can affect the various transformations.</p>
Chris Lattner9720dda2002-09-25 22:31:38 +0000[diff] [blame]450
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]451<p><tt>ImmutablePass</tt>es never invalidate other transformations, are never
452invalidated, and are never "run".</p>
Chris Lattner9720dda2002-09-25 22:31:38 +0000[diff] [blame]453
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]454</div>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]455
456<!-- ======================================================================= -->
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]457<div class="doc_subsection">
Chris Lattner3c11c042004-09-20 04:36:29 +0000[diff] [blame]458 <a name="ModulePass">The <tt>ModulePass</tt> class</a>
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]459</div>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]460
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]461<div class="doc_text">
462
463<p>The "<tt><a
Reid Spencerca058542006-03-14 05:39:39 +0000[diff] [blame]464href="http://llvm.org/doxygen/classllvm_1_1ModulePass.html">ModulePass</a></tt>"
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]465class is the most general of all superclasses that you can use. Deriving from
Chris Lattner3c11c042004-09-20 04:36:29 +0000[diff] [blame]466<tt>ModulePass</tt> indicates that your pass uses the entire program as a unit,
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]467refering to function bodies in no predictable order, or adding and removing
Chris Lattner3c11c042004-09-20 04:36:29 +0000[diff] [blame]468functions. Because nothing is known about the behavior of <tt>ModulePass</tt>
Devang Patel9b5e8e52007-04-16 21:28:14 +0000[diff] [blame^]469subclasses, no optimization can be done for their execution. A module pass
470can use function level passes (e.g. dominators) using getAnalysis interface
471<tt> getAnalysis<DominatorTree>(Function)</tt>. </p>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]472
Chris Lattner3c11c042004-09-20 04:36:29 +0000[diff] [blame]473<p>To write a correct <tt>ModulePass</tt> subclass, derive from
474<tt>ModulePass</tt> and overload the <tt>runOnModule</tt> method with the
475following signature:</p>
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]476
477</div>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]478
479<!-- _______________________________________________________________________ -->
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]480<div class="doc_subsubsection">
Chris Lattner3c11c042004-09-20 04:36:29 +0000[diff] [blame]481 <a name="runOnModule">The <tt>runOnModule</tt> method</a>
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]482</div>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]483
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]484<div class="doc_text">
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]485
Jim Laskey575df8b2006-08-04 18:10:12 +0000[diff] [blame]486<div class="doc_code"><pre>
Chris Lattner3c11c042004-09-20 04:36:29 +0000[diff] [blame]487 <b>virtual bool</b> runOnModule(Module &amp;M) = 0;
Jim Laskey575df8b2006-08-04 18:10:12 +0000[diff] [blame]488</pre></div>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]489
John Criswella3f51102005-07-15 19:25:12 +0000[diff] [blame]490<p>The <tt>runOnModule</tt> method performs the interesting work of the pass.
491It should return true if the module was modified by the transformation and
492false otherwise.</p>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]493
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]494</div>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]495
496<!-- ======================================================================= -->
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]497<div class="doc_subsection">
Chris Lattner9e4be6f2004-09-18 06:39:35 +0000[diff] [blame]498 <a name="CallGraphSCCPass">The <tt>CallGraphSCCPass</tt> class</a>
499</div>
500
501<div class="doc_text">
502
503<p>The "<tt><a
Reid Spencerca058542006-03-14 05:39:39 +0000[diff] [blame]504href="http://llvm.org/doxygen/classllvm_1_1CallGraphSCCPass.html">CallGraphSCCPass</a></tt>"
Chris Lattner9e4be6f2004-09-18 06:39:35 +0000[diff] [blame]505is used by passes that need to traverse the program bottom-up on the call graph
506(callees before callers). Deriving from CallGraphSCCPass provides some
507mechanics for building and traversing the CallGraph, but also allows the system
508to optimize execution of CallGraphSCCPass's. If your pass meets the
509requirements outlined below, and doesn't meet the requirements of a <tt><a
510href="#FunctionPass">FunctionPass</a></tt> or <tt><a
511href="#BasicBlockPass">BasicBlockPass</a></tt>, you should derive from
512<tt>CallGraphSCCPass</tt>.</p>
513
514<p><b>TODO</b>: explain briefly what SCC, Tarjan's algo, and B-U mean.</p>
515
516<p>To be explicit, <tt>CallGraphSCCPass</tt> subclasses are:</p>
517
518<ol>
519
520<li>... <em>not allowed</em> to modify any <tt>Function</tt>s that are not in
521the current SCC.</li>
522
523<li>... <em>allowed</em> to inspect any Function's other than those in the
524current SCC and the direct callees of the SCC.</li>
525
526<li>... <em>required</em> to preserve the current CallGraph object, updating it
527to reflect any changes made to the program.</li>
528
529<li>... <em>not allowed</em> to add or remove SCC's from the current Module,
530though they may change the contents of an SCC.</li>
531
532<li>... <em>allowed</em> to add or remove global variables from the current
533Module.</li>
534
535<li>... <em>allowed</em> to maintain state across invocations of
536 <a href="#runOnSCC"><tt>runOnSCC</tt></a> (including global data).</li>
537</ol>
538
539<p>Implementing a <tt>CallGraphSCCPass</tt> is slightly tricky in some cases
540because it has to handle SCCs with more than one node in it. All of the virtual
541methods described below should return true if they modified the program, or
542false if they didn't.</p>
543
544</div>
545
546<!-- _______________________________________________________________________ -->
547<div class="doc_subsubsection">
Devang Patel40ec0802007-01-23 22:56:28 +0000[diff] [blame]548 <a name="doInitialization_scc">The <tt>doInitialization(CallGraph &amp;)</tt>
Chris Lattner9e4be6f2004-09-18 06:39:35 +0000[diff] [blame]549 method</a>
550</div>
551
552<div class="doc_text">
553
Jim Laskey575df8b2006-08-04 18:10:12 +0000[diff] [blame]554<div class="doc_code"><pre>
Devang Patel40ec0802007-01-23 22:56:28 +0000[diff] [blame]555 <b>virtual bool</b> doInitialization(CallGraph &amp;CG);
Jim Laskey575df8b2006-08-04 18:10:12 +0000[diff] [blame]556</pre></div>
Chris Lattner9e4be6f2004-09-18 06:39:35 +0000[diff] [blame]557
558<p>The <tt>doIninitialize</tt> method is allowed to do most of the things that
559<tt>CallGraphSCCPass</tt>'s are not allowed to do. They can add and remove
560functions, get pointers to functions, etc. The <tt>doInitialization</tt> method
561is designed to do simple initialization type of stuff that does not depend on
562the SCCs being processed. The <tt>doInitialization</tt> method call is not
563scheduled to overlap with any other pass executions (thus it should be very
564fast).</p>
565
566</div>
567
568<!-- _______________________________________________________________________ -->
569<div class="doc_subsubsection">
570 <a name="runOnSCC">The <tt>runOnSCC</tt> method</a>
571</div>
572
573<div class="doc_text">
574
Jim Laskey575df8b2006-08-04 18:10:12 +0000[diff] [blame]575<div class="doc_code"><pre>
Chris Lattner9e4be6f2004-09-18 06:39:35 +0000[diff] [blame]576 <b>virtual bool</b> runOnSCC(const std::vector&lt;CallGraphNode *&gt; &amp;SCCM) = 0;
Jim Laskey575df8b2006-08-04 18:10:12 +0000[diff] [blame]577</pre></div>
Chris Lattner9e4be6f2004-09-18 06:39:35 +0000[diff] [blame]578
579<p>The <tt>runOnSCC</tt> method performs the interesting work of the pass, and
580should return true if the module was modified by the transformation, false
581otherwise.</p>
582
583</div>
584
585<!-- _______________________________________________________________________ -->
586<div class="doc_subsubsection">
Devang Patel40ec0802007-01-23 22:56:28 +0000[diff] [blame]587 <a name="doFinalization_scc">The <tt>doFinalization(CallGraph
Chris Lattner9e4be6f2004-09-18 06:39:35 +0000[diff] [blame]588 &amp;)</tt> method</a>
589</div>
590
591<div class="doc_text">
592
Jim Laskey575df8b2006-08-04 18:10:12 +0000[diff] [blame]593<div class="doc_code"><pre>
Devang Patel40ec0802007-01-23 22:56:28 +0000[diff] [blame]594 <b>virtual bool</b> doFinalization(CallGraph &amp;CG);
Jim Laskey575df8b2006-08-04 18:10:12 +0000[diff] [blame]595</pre></div>
Chris Lattner9e4be6f2004-09-18 06:39:35 +0000[diff] [blame]596
597<p>The <tt>doFinalization</tt> method is an infrequently used method that is
598called when the pass framework has finished calling <a
599href="#runOnFunction"><tt>runOnFunction</tt></a> for every function in the
600program being compiled.</p>
601
602</div>
603
604<!-- ======================================================================= -->
605<div class="doc_subsection">
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]606 <a name="FunctionPass">The <tt>FunctionPass</tt> class</a>
607</div>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]608
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]609<div class="doc_text">
610
Chris Lattner3c11c042004-09-20 04:36:29 +0000[diff] [blame]611<p>In contrast to <tt>ModulePass</tt> subclasses, <tt><a
Reid Spencerca058542006-03-14 05:39:39 +0000[diff] [blame]612href="http://llvm.org/doxygen/classllvm_1_1Pass.html">FunctionPass</a></tt>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]613subclasses do have a predictable, local behavior that can be expected by the
614system. All <tt>FunctionPass</tt> execute on each function in the program
Misha Brukmanbe372b92003-08-21 22:14:26 +0000[diff] [blame]615independent of all of the other functions in the program.
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]616<tt>FunctionPass</tt>'s do not require that they are executed in a particular
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]617order, and <tt>FunctionPass</tt>'s do not modify external functions.</p>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]618
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]619<p>To be explicit, <tt>FunctionPass</tt> subclasses are not allowed to:</p>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]620
621<ol>
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]622<li>Modify a Function other than the one currently being processed.</li>
623<li>Add or remove Function's from the current Module.</li>
624<li>Add or remove global variables from the current Module.</li>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]625<li>Maintain state across invocations of
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]626 <a href="#runOnFunction"><tt>runOnFunction</tt></a> (including global data)</li>
627</ol>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]628
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]629<p>Implementing a <tt>FunctionPass</tt> is usually straightforward (See the <a
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]630href="#basiccode">Hello World</a> pass for example). <tt>FunctionPass</tt>'s
631may overload three virtual methods to do their work. All of these methods
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]632should return true if they modified the program, or false if they didn't.</p>
633
634</div>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]635
636<!-- _______________________________________________________________________ -->
Chris Lattner8e871652004-03-17 21:09:55 +0000[diff] [blame]637<div class="doc_subsubsection">
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]638 <a name="doInitialization_mod">The <tt>doInitialization(Module &amp;)</tt>
639 method</a>
640</div>
641
642<div class="doc_text">
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]643
Jim Laskey575df8b2006-08-04 18:10:12 +0000[diff] [blame]644<div class="doc_code"><pre>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]645 <b>virtual bool</b> doInitialization(Module &amp;M);
Jim Laskey575df8b2006-08-04 18:10:12 +0000[diff] [blame]646</pre></div>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]647
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]648<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]649<tt>FunctionPass</tt>'s are not allowed to do. They can add and remove
Chris Lattner5e08e70f2002-09-12 17:06:43 +0000[diff] [blame]650functions, get pointers to functions, etc. The <tt>doInitialization</tt> method
651is designed to do simple initialization type of stuff that does not depend on
652the functions being processed. The <tt>doInitialization</tt> method call is not
653scheduled to overlap with any other pass executions (thus it should be very
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]654fast).</p>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]655
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]656<p>A good example of how this method should be used is the <a
Reid Spencerca058542006-03-14 05:39:39 +0000[diff] [blame]657href="http://llvm.org/doxygen/LowerAllocations_8cpp-source.html">LowerAllocations</a>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]658pass. This pass converts <tt>malloc</tt> and <tt>free</tt> instructions into
Misha Brukmanbe372b92003-08-21 22:14:26 +0000[diff] [blame]659platform dependent <tt>malloc()</tt> and <tt>free()</tt> function calls. It
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]660uses the <tt>doInitialization</tt> method to get a reference to the malloc and
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]661free functions that it needs, adding prototypes to the module if necessary.</p>
662
663</div>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]664
665<!-- _______________________________________________________________________ -->
Chris Lattner8e871652004-03-17 21:09:55 +0000[diff] [blame]666<div class="doc_subsubsection">
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]667 <a name="runOnFunction">The <tt>runOnFunction</tt> method</a>
668</div>
669
670<div class="doc_text">
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]671
Jim Laskey575df8b2006-08-04 18:10:12 +0000[diff] [blame]672<div class="doc_code"><pre>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]673 <b>virtual bool</b> runOnFunction(Function &amp;F) = 0;
Jim Laskey575df8b2006-08-04 18:10:12 +0000[diff] [blame]674</pre></div><p>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]675
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]676<p>The <tt>runOnFunction</tt> method must be implemented by your subclass to do
677the transformation or analysis work of your pass. As usual, a true value should
678be returned if the function is modified.</p>
679
680</div>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]681
682<!-- _______________________________________________________________________ -->
Chris Lattner8e871652004-03-17 21:09:55 +0000[diff] [blame]683<div class="doc_subsubsection">
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]684 <a name="doFinalization_mod">The <tt>doFinalization(Module
685 &amp;)</tt> method</a>
686</div>
687
688<div class="doc_text">
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]689
Jim Laskey575df8b2006-08-04 18:10:12 +0000[diff] [blame]690<div class="doc_code"><pre>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]691 <b>virtual bool</b> doFinalization(Module &amp;M);
Jim Laskey575df8b2006-08-04 18:10:12 +0000[diff] [blame]692</pre></div>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]693
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]694<p>The <tt>doFinalization</tt> method is an infrequently used method that is
695called when the pass framework has finished calling <a
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]696href="#runOnFunction"><tt>runOnFunction</tt></a> for every function in the
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]697program being compiled.</p>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]698
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]699</div>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]700
701<!-- ======================================================================= -->
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]702<div class="doc_subsection">
Devang Patel1d3bb032007-03-19 22:21:25 +0000[diff] [blame]703 <a name="LoopPass">The <tt>LoopPass</tt> class </a>
704</div>
705
706<div class="doc_text">
707
708<p> All <tt>LoopPass</tt> execute on each loop in the function independent of
709all of the other loops in the function. <tt>LoopPass</tt> processes loops in
710loop nest order such that outer most loop is processed last. </p>
711
712<p> <tt>LoopPass</tt> subclasses are allowed to update loop nest using
713<tt>LPPassManager</tt> interface. Implementing a loop pass is usually
714straightforward. <tt>Looppass</tt>'s may overload three virtual methods to
715do their work. All these methods should return true if they modified the
716program, or false if they didn't. </p>
717</div>
718
719<!-- _______________________________________________________________________ -->
720<div class="doc_subsubsection">
721 <a name="doInitialization_loop">The <tt>doInitialization(Loop *,
722 LPPassManager &amp;)</tt>
723 method</a>
724</div>
725
726<div class="doc_text">
727
728<div class="doc_code"><pre>
729 <b>virtual bool</b> doInitialization(Loop *, LPPassManager &amp;LPM);
730</pre></div>
731
732The <tt>doInitialization</tt> method is designed to do simple initialization
733type of stuff that does not depend on the functions being processed. The
734<tt>doInitialization</tt> method call is not scheduled to overlap with any
735other pass executions (thus it should be very fast). LPPassManager
736interface should be used to access Function or Module level analysis
737information.</p>
738
739</div>
740
741
742<!-- _______________________________________________________________________ -->
743<div class="doc_subsubsection">
744 <a name="runOnLoop">The <tt>runOnLoop</tt> method</a>
745</div>
746
747<div class="doc_text">
748
749<div class="doc_code"><pre>
750 <b>virtual bool</b> runOnLoop(Loop *, LPPassManager &amp;LPM) = 0;
751</pre></div><p>
752
753<p>The <tt>runOnLoop</tt> method must be implemented by your subclass to do
754the transformation or analysis work of your pass. As usual, a true value should
755be returned if the function is modified. <tt>LPPassManager</tt> interface
756should be used to update loop nest.</p>
757
758</div>
759
760<!-- _______________________________________________________________________ -->
761<div class="doc_subsubsection">
762 <a name="doFinalization_loop">The <tt>doFinalization()</tt> method</a>
763</div>
764
765<div class="doc_text">
766
767<div class="doc_code"><pre>
768 <b>virtual bool</b> doFinalization();
769</pre></div>
770
771<p>The <tt>doFinalization</tt> method is an infrequently used method that is
772called when the pass framework has finished calling <a
773href="#runOnLoop"><tt>runOnLoop</tt></a> for every loop in the
774program being compiled. </p>
775
776</div>
777
778
779
780<!-- ======================================================================= -->
781<div class="doc_subsection">
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]782 <a name="BasicBlockPass">The <tt>BasicBlockPass</tt> class</a>
783</div>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]784
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]785<div class="doc_text">
786
787<p><tt>BasicBlockPass</tt>'s are just like <a
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]788href="#FunctionPass"><tt>FunctionPass</tt></a>'s, except that they must limit
789their scope of inspection and modification to a single basic block at a time.
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]790As such, they are <b>not</b> allowed to do any of the following:</p>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]791
792<ol>
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]793<li>Modify or inspect any basic blocks outside of the current one</li>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]794<li>Maintain state across invocations of
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]795 <a href="#runOnBasicBlock"><tt>runOnBasicBlock</tt></a></li>
Reid Spencera1799682004-12-11 05:12:57 +0000[diff] [blame]796<li>Modify the control flow graph (by altering terminator instructions)</li>
797<li>Any of the things forbidden for
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]798 <a href="#FunctionPass"><tt>FunctionPass</tt></a>es.</li>
799</ol>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]800
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]801<p><tt>BasicBlockPass</tt>es are useful for traditional local and "peephole"
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]802optimizations. They may override the same <a
Chris Lattner5e08e70f2002-09-12 17:06:43 +0000[diff] [blame]803href="#doInitialization_mod"><tt>doInitialization(Module &amp;)</tt></a> and <a
804href="#doFinalization_mod"><tt>doFinalization(Module &amp;)</tt></a> methods that <a
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]805href="#FunctionPass"><tt>FunctionPass</tt></a>'s have, but also have the following virtual methods that may also be implemented:</p>
806
807</div>
Chris Lattner5e08e70f2002-09-12 17:06:43 +0000[diff] [blame]808
809<!-- _______________________________________________________________________ -->
Chris Lattner8e871652004-03-17 21:09:55 +0000[diff] [blame]810<div class="doc_subsubsection">
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]811 <a name="doInitialization_fn">The <tt>doInitialization(Function
812 &amp;)</tt> method</a>
813</div>
814
815<div class="doc_text">
Chris Lattner5e08e70f2002-09-12 17:06:43 +0000[diff] [blame]816
Jim Laskey575df8b2006-08-04 18:10:12 +0000[diff] [blame]817<div class="doc_code"><pre>
Chris Lattner5e08e70f2002-09-12 17:06:43 +0000[diff] [blame]818 <b>virtual bool</b> doInitialization(Function &amp;F);
Jim Laskey575df8b2006-08-04 18:10:12 +0000[diff] [blame]819</pre></div>
Chris Lattner5e08e70f2002-09-12 17:06:43 +0000[diff] [blame]820
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]821<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]822<tt>BasicBlockPass</tt>'s are not allowed to do, but that
823<tt>FunctionPass</tt>'s can. The <tt>doInitialization</tt> method is designed
Reid Spencera1799682004-12-11 05:12:57 +0000[diff] [blame]824to do simple initialization that does not depend on the
Chris Lattner5e08e70f2002-09-12 17:06:43 +0000[diff] [blame]825BasicBlocks being processed. The <tt>doInitialization</tt> method call is not
826scheduled to overlap with any other pass executions (thus it should be very
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]827fast).</p>
Chris Lattner5e08e70f2002-09-12 17:06:43 +0000[diff] [blame]828
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]829</div>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]830
831<!-- _______________________________________________________________________ -->
Chris Lattner8e871652004-03-17 21:09:55 +0000[diff] [blame]832<div class="doc_subsubsection">
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]833 <a name="runOnBasicBlock">The <tt>runOnBasicBlock</tt> method</a>
834</div>
835
836<div class="doc_text">
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]837
Jim Laskey575df8b2006-08-04 18:10:12 +0000[diff] [blame]838<div class="doc_code"><pre>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]839 <b>virtual bool</b> runOnBasicBlock(BasicBlock &amp;BB) = 0;
Jim Laskey575df8b2006-08-04 18:10:12 +0000[diff] [blame]840</pre></div>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]841
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]842<p>Override this function to do the work of the <tt>BasicBlockPass</tt>. This
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]843function is not allowed to inspect or modify basic blocks other than the
844parameter, and are not allowed to modify the CFG. A true value must be returned
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]845if the basic block is modified.</p>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]846
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]847</div>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]848
Chris Lattner5e08e70f2002-09-12 17:06:43 +0000[diff] [blame]849<!-- _______________________________________________________________________ -->
Chris Lattner8e871652004-03-17 21:09:55 +0000[diff] [blame]850<div class="doc_subsubsection">
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]851 <a name="doFinalization_fn">The <tt>doFinalization(Function &amp;)</tt>
852 method</a>
853</div>
854
855<div class="doc_text">
Chris Lattner5e08e70f2002-09-12 17:06:43 +0000[diff] [blame]856
Jim Laskey575df8b2006-08-04 18:10:12 +0000[diff] [blame]857<div class="doc_code"><pre>
Chris Lattner5e08e70f2002-09-12 17:06:43 +0000[diff] [blame]858 <b>virtual bool</b> doFinalization(Function &amp;F);
Jim Laskey575df8b2006-08-04 18:10:12 +0000[diff] [blame]859</pre></div>
Chris Lattner5e08e70f2002-09-12 17:06:43 +0000[diff] [blame]860
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]861<p>The <tt>doFinalization</tt> method is an infrequently used method that is
862called when the pass framework has finished calling <a
Chris Lattner5e08e70f2002-09-12 17:06:43 +0000[diff] [blame]863href="#runOnBasicBlock"><tt>runOnBasicBlock</tt></a> for every BasicBlock in the
864program being compiled. This can be used to perform per-function
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]865finalization.</p>
Chris Lattner5e08e70f2002-09-12 17:06:43 +0000[diff] [blame]866
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]867</div>
Chris Lattner5e08e70f2002-09-12 17:06:43 +0000[diff] [blame]868
Brian Gaeke110f07b2003-07-17 18:53:20 +0000[diff] [blame]869<!-- ======================================================================= -->
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]870<div class="doc_subsection">
871 <a name="MachineFunctionPass">The <tt>MachineFunctionPass</tt> class</a>
872</div>
Brian Gaeke110f07b2003-07-17 18:53:20 +0000[diff] [blame]873
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]874<div class="doc_text">
875
Chris Lattner8e871652004-03-17 21:09:55 +0000[diff] [blame]876<p>A <tt>MachineFunctionPass</tt> is a part of the LLVM code generator that
877executes on the machine-dependent representation of each LLVM function in the
878program. A <tt>MachineFunctionPass</tt> is also a <tt>FunctionPass</tt>, so all
Brian Gaeke110f07b2003-07-17 18:53:20 +0000[diff] [blame]879the restrictions that apply to a <tt>FunctionPass</tt> also apply to it.
Chris Lattner8e871652004-03-17 21:09:55 +0000[diff] [blame]880<tt>MachineFunctionPass</tt>es also have additional restrictions. In particular,
881<tt>MachineFunctionPass</tt>es are not allowed to do any of the following:</p>
Brian Gaeke110f07b2003-07-17 18:53:20 +0000[diff] [blame]882
883<ol>
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]884<li>Modify any LLVM Instructions, BasicBlocks or Functions.</li>
885<li>Modify a MachineFunction other than the one currently being processed.</li>
886<li>Add or remove MachineFunctions from the current Module.</li>
887<li>Add or remove global variables from the current Module.</li>
888<li>Maintain state across invocations of <a
889href="#runOnMachineFunction"><tt>runOnMachineFunction</tt></a> (including global
890data)</li>
891</ol>
Brian Gaeke110f07b2003-07-17 18:53:20 +0000[diff] [blame]892
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]893</div>
Chris Lattner5e08e70f2002-09-12 17:06:43 +0000[diff] [blame]894
Brian Gaeke673ef4d2003-07-22 20:53:20 +0000[diff] [blame]895<!-- _______________________________________________________________________ -->
Chris Lattner8e871652004-03-17 21:09:55 +0000[diff] [blame]896<div class="doc_subsubsection">
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]897 <a name="runOnMachineFunction">The <tt>runOnMachineFunction(MachineFunction
898 &amp;MF)</tt> method</a>
899</div>
900
901<div class="doc_text">
Brian Gaeke673ef4d2003-07-22 20:53:20 +0000[diff] [blame]902
Jim Laskey575df8b2006-08-04 18:10:12 +0000[diff] [blame]903<div class="doc_code"><pre>
Brian Gaeke673ef4d2003-07-22 20:53:20 +0000[diff] [blame]904 <b>virtual bool</b> runOnMachineFunction(MachineFunction &amp;MF) = 0;
Jim Laskey575df8b2006-08-04 18:10:12 +0000[diff] [blame]905</pre></div>
Brian Gaeke673ef4d2003-07-22 20:53:20 +0000[diff] [blame]906
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]907<p><tt>runOnMachineFunction</tt> can be considered the main entry point of a
908<tt>MachineFunctionPass</tt>; that is, you should override this method to do the
909work of your <tt>MachineFunctionPass</tt>.</p>
Brian Gaeke673ef4d2003-07-22 20:53:20 +0000[diff] [blame]910
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]911<p>The <tt>runOnMachineFunction</tt> method is called on every
Brian Gaeke673ef4d2003-07-22 20:53:20 +0000[diff] [blame]912<tt>MachineFunction</tt> in a <tt>Module</tt>, so that the
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]913<tt>MachineFunctionPass</tt> may perform optimizations on the machine-dependent
914representation of the function. If you want to get at the LLVM <tt>Function</tt>
915for the <tt>MachineFunction</tt> you're working on, use
916<tt>MachineFunction</tt>'s <tt>getFunction()</tt> accessor method -- but
917remember, you may not modify the LLVM <tt>Function</tt> or its contents from a
918<tt>MachineFunctionPass</tt>.</p>
919
920</div>
Brian Gaeke673ef4d2003-07-22 20:53:20 +0000[diff] [blame]921
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]922<!-- *********************************************************************** -->
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]923<div class="doc_section">
924 <a name="registration">Pass registration</a>
925</div>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]926<!-- *********************************************************************** -->
927
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]928<div class="doc_text">
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]929
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]930<p>In the <a href="#basiccode">Hello World</a> example pass we illustrated how
931pass registration works, and discussed some of the reasons that it is used and
932what it does. Here we discuss how and why passes are registered.</p>
933
Chris Lattnerb693cb02006-08-27 23:18:52 +0000[diff] [blame]934<p>As we saw above, passes are registered with the <b><tt>RegisterPass</tt></b>
935template, which requires you to pass at least two
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]936parameters. The first parameter is the name of the pass that is to be used on
937the command line to specify that the pass should be added to a program (for
Chris Lattnerb693cb02006-08-27 23:18:52 +0000[diff] [blame]938example, with <tt>opt</tt> or <tt>bugpoint</tt>). The second argument is the
939name of the pass, which is to be used for the <tt>--help</tt> output of
940programs, as
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]941well as for debug output generated by the <tt>--debug-pass</tt> option.</p>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]942
Chris Lattnerb693cb02006-08-27 23:18:52 +0000[diff] [blame]943<p>If you want your pass to be easily dumpable, you should
944implement the virtual <tt>print</tt> method:</p>
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]945
946</div>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]947
948<!-- _______________________________________________________________________ -->
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]949<div class="doc_subsubsection">
950 <a name="print">The <tt>print</tt> method</a>
951</div>
952
953<div class="doc_text">
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]954
Jim Laskey575df8b2006-08-04 18:10:12 +0000[diff] [blame]955<div class="doc_code"><pre>
Bill Wendling22e978a2006-12-07 20:04:42 +0000[diff] [blame]956 <b>virtual void</b> print(llvm::OStream &amp;O, <b>const</b> Module *M) <b>const</b>;
Jim Laskey575df8b2006-08-04 18:10:12 +0000[diff] [blame]957</pre></div>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]958
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]959<p>The <tt>print</tt> method must be implemented by "analyses" in order to print
960a human readable version of the analysis results. This is useful for debugging
961an analysis itself, as well as for other people to figure out how an analysis
Chris Lattnerb693cb02006-08-27 23:18:52 +0000[diff] [blame]962works. Use the <tt>opt -analyze</tt> argument to invoke this method.</p>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]963
Bill Wendling22e978a2006-12-07 20:04:42 +0000[diff] [blame]964<p>The <tt>llvm::OStream</tt> parameter specifies the stream to write the results on,
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]965and 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]966program that has been analyzed. Note however that this pointer may be null in
967certain circumstances (such as calling the <tt>Pass::dump()</tt> from a
968debugger), so it should only be used to enhance debug output, it should not be
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]969depended on.</p>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]970
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]971</div>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]972
973<!-- *********************************************************************** -->
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]974<div class="doc_section">
975 <a name="interaction">Specifying interactions between passes</a>
976</div>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]977<!-- *********************************************************************** -->
978
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]979<div class="doc_text">
980
981<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]982that passes interact with each other correctly. Because <tt>PassManager</tt>
983tries to <a href="#passmanager">optimize the execution of passes</a> it must
984know how the passes interact with each other and what dependencies exist between
985the various passes. To track this, each pass can declare the set of passes that
986are required to be executed before the current pass, and the passes which are
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]987invalidated by the current pass.</p>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]988
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]989<p>Typically this functionality is used to require that analysis results are
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]990computed before your pass is run. Running arbitrary transformation passes can
991invalidate the computed analysis results, which is what the invalidation set
992specifies. If a pass does not implement the <tt><a
993href="#getAnalysisUsage">getAnalysisUsage</a></tt> method, it defaults to not
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]994having any prerequisite passes, and invalidating <b>all</b> other passes.</p>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]995
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]996</div>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]997
998<!-- _______________________________________________________________________ -->
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]999<div class="doc_subsubsection">
1000 <a name="getAnalysisUsage">The <tt>getAnalysisUsage</tt> method</a>
1001</div>
1002
1003<div class="doc_text">
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]1004
Jim Laskey575df8b2006-08-04 18:10:12 +0000[diff] [blame]1005<div class="doc_code"><pre>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]1006 <b>virtual void</b> getAnalysisUsage(AnalysisUsage &amp;Info) <b>const</b>;
Jim Laskey575df8b2006-08-04 18:10:12 +0000[diff] [blame]1007</pre></div>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]1008
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]1009<p>By implementing the <tt>getAnalysisUsage</tt> method, the required and
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]1010invalidated sets may be specified for your transformation. The implementation
1011should fill in the <tt><a
Reid Spencerca058542006-03-14 05:39:39 +0000[diff] [blame]1012href="http://llvm.org/doxygen/classllvm_1_1AnalysisUsage.html">AnalysisUsage</a></tt>
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]1013object with information about which passes are required and not invalidated. To
Chris Lattner8e871652004-03-17 21:09:55 +0000[diff] [blame]1014do this, a pass may call any of the following methods on the AnalysisUsage
1015object:</p>
1016</div>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]1017
Chris Lattner8e871652004-03-17 21:09:55 +0000[diff] [blame]1018<!-- _______________________________________________________________________ -->
1019<div class="doc_subsubsection">
1020 <a name="AU::addRequired">The <tt>AnalysisUsage::addRequired&lt;&gt;</tt> and <tt>AnalysisUsage::addRequiredTransitive&lt;&gt;</tt> methods</a>
1021</div>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]1022
Chris Lattner8e871652004-03-17 21:09:55 +0000[diff] [blame]1023<div class="doc_text">
1024<p>
Reid Spencera1799682004-12-11 05:12:57 +0000[diff] [blame]1025If your pass requires a previous pass to be executed (an analysis for example),
Chris Lattner8e871652004-03-17 21:09:55 +0000[diff] [blame]1026it can use one of these methods to arrange for it to be run before your pass.
1027LLVM has many different types of analyses and passes that can be required,
Reid Spencera1799682004-12-11 05:12:57 +0000[diff] [blame]1028spanning the range from <tt>DominatorSet</tt> to <tt>BreakCriticalEdges</tt>.
1029Requiring <tt>BreakCriticalEdges</tt>, for example, guarantees that there will
Chris Lattner8e871652004-03-17 21:09:55 +0000[diff] [blame]1030be no critical edges in the CFG when your pass has been run.
1031</p>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]1032
Chris Lattner8e871652004-03-17 21:09:55 +0000[diff] [blame]1033<p>
1034Some analyses chain to other analyses to do their job. For example, an <a
1035href="AliasAnalysis.html">AliasAnalysis</a> implementation is required to <a
1036href="AliasAnalysis.html#chaining">chain</a> to other alias analysis passes. In
1037cases where analyses chain, the <tt>addRequiredTransitive</tt> method should be
1038used instead of the <tt>addRequired</tt> method. This informs the PassManager
1039that the transitively required pass should be alive as long as the requiring
1040pass is.
1041</p>
1042</div>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]1043
Chris Lattner8e871652004-03-17 21:09:55 +0000[diff] [blame]1044<!-- _______________________________________________________________________ -->
1045<div class="doc_subsubsection">
1046 <a name="AU::addPreserved">The <tt>AnalysisUsage::addPreserved&lt;&gt;</tt> method</a>
1047</div>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]1048
Chris Lattner8e871652004-03-17 21:09:55 +0000[diff] [blame]1049<div class="doc_text">
1050<p>
1051One of the jobs of the PassManager is to optimize how and when analyses are run.
1052In particular, it attempts to avoid recomputing data unless it needs to. For
1053this reason, passes are allowed to declare that they preserve (i.e., they don't
1054invalidate) an existing analysis if it's available. For example, a simple
Reid Spencera1799682004-12-11 05:12:57 +0000[diff] [blame]1055constant folding pass would not modify the CFG, so it can't possibly affect the
Chris Lattner8e871652004-03-17 21:09:55 +0000[diff] [blame]1056results of dominator analysis. By default, all passes are assumed to invalidate
1057all others.
1058</p>
1059
1060<p>
1061The <tt>AnalysisUsage</tt> class provides several methods which are useful in
1062certain circumstances that are related to <tt>addPreserved</tt>. In particular,
1063the <tt>setPreservesAll</tt> method can be called to indicate that the pass does
1064not modify the LLVM program at all (which is true for analyses), and the
1065<tt>setPreservesCFG</tt> method can be used by transformations that change
1066instructions in the program but do not modify the CFG or terminator instructions
1067(note that this property is implicitly set for <a
1068href="#BasicBlockPass">BasicBlockPass</a>'s).
1069</p>
1070
1071<p>
1072<tt>addPreserved</tt> is particularly useful for transformations like
1073<tt>BreakCriticalEdges</tt>. This pass knows how to update a small set of loop
1074and dominator related analyses if they exist, so it can preserve them, despite
1075the fact that it hacks on the CFG.
1076</p>
1077</div>
1078
1079<!-- _______________________________________________________________________ -->
1080<div class="doc_subsubsection">
1081 <a name="AU::examples">Example implementations of <tt>getAnalysisUsage</tt></a>
1082</div>
1083
1084<div class="doc_text">
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]1085
Jim Laskey575df8b2006-08-04 18:10:12 +0000[diff] [blame]1086<div class="doc_code"><pre>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]1087 <i>// This is an example implementation from an analysis, which does not modify
1088 // the program at all, yet has a prerequisite.</i>
Reid Spencerca058542006-03-14 05:39:39 +0000[diff] [blame]1089 <b>void</b> <a href="http://llvm.org/doxygen/classllvm_1_1PostDominanceFrontier.html">PostDominanceFrontier</a>::getAnalysisUsage(AnalysisUsage &amp;AU) <b>const</b> {
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]1090 AU.setPreservesAll();
Reid Spencerca058542006-03-14 05:39:39 +0000[diff] [blame]1091 AU.addRequired&lt;<a href="http://llvm.org/doxygen/classllvm_1_1PostDominatorTree.html">PostDominatorTree</a>&gt;();
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]1092 }
Jim Laskey575df8b2006-08-04 18:10:12 +0000[diff] [blame]1093</pre></div>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]1094
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]1095<p>and:</p>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]1096
Jim Laskey575df8b2006-08-04 18:10:12 +0000[diff] [blame]1097<div class="doc_code"><pre>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]1098 <i>// This example modifies the program, but does not modify the CFG</i>
Reid Spencerca058542006-03-14 05:39:39 +0000[diff] [blame]1099 <b>void</b> <a href="http://llvm.org/doxygen/structLICM.html">LICM</a>::getAnalysisUsage(AnalysisUsage &amp;AU) <b>const</b> {
Chris Lattnera8c82c22002-10-21 19:57:59 +0000[diff] [blame]1100 AU.setPreservesCFG();
Reid Spencerca058542006-03-14 05:39:39 +0000[diff] [blame]1101 AU.addRequired&lt;<a href="http://llvm.org/doxygen/classllvm_1_1LoopInfo.html">LoopInfo</a>&gt;();
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]1102 }
Jim Laskey575df8b2006-08-04 18:10:12 +0000[diff] [blame]1103</pre></div>
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]1104
1105</div>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]1106
1107<!-- _______________________________________________________________________ -->
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]1108<div class="doc_subsubsection">
Chris Lattner8e871652004-03-17 21:09:55 +0000[diff] [blame]1109 <a name="getAnalysis">The <tt>getAnalysis&lt;&gt;</tt> and <tt>getAnalysisToUpdate&lt;&gt;</tt> methods</a>
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]1110</div>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]1111
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]1112<div class="doc_text">
1113
Chris Lattner8e871652004-03-17 21:09:55 +0000[diff] [blame]1114<p>The <tt>Pass::getAnalysis&lt;&gt;</tt> method is automatically inherited by
1115your class, providing you with access to the passes that you declared that you
1116required with the <a href="#getAnalysisUsage"><tt>getAnalysisUsage</tt></a>
1117method. It takes a single template argument that specifies which pass class you
1118want, and returns a reference to that pass. For example:</p>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]1119
Jim Laskey575df8b2006-08-04 18:10:12 +0000[diff] [blame]1120<div class="doc_code"><pre>
Chris Lattnerbaf3f622004-03-17 21:33:32 +0000[diff] [blame]1121 bool LICM::runOnFunction(Function &amp;F) {
Chris Lattner8e871652004-03-17 21:09:55 +0000[diff] [blame]1122 LoopInfo &amp;LI = getAnalysis&lt;LoopInfo&gt;();
1123 ...
1124 }
Jim Laskey575df8b2006-08-04 18:10:12 +0000[diff] [blame]1125</pre></div>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]1126
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]1127<p>This method call returns a reference to the pass desired. You may get a
1128runtime assertion failure if you attempt to get an analysis that you did not
1129declare as required in your <a
1130href="#getAnalysisUsage"><tt>getAnalysisUsage</tt></a> implementation. This
1131method can be called by your <tt>run*</tt> method implementation, or by any
Devang Patel9b5e8e52007-04-16 21:28:14 +0000[diff] [blame^]1132other local method invoked by your <tt>run*</tt> method.
1133
1134A module level pass can use function level analysis info using this interface.
1135For example:</p>
1136
1137<div class="doc_code"><pre>
1138 bool ModuleLevelPass::runOnModule(Module &amp;M) {
1139 ...
1140 DominatorTree &amp;DT = getAnalysis&lt;DominatorTree&gt;(Function &amp;F);
1141 ...
1142 }
1143</pre></div>
1144
1145In above example, runOnFunction for DominatorTree is called by pass manager
1146before returning a reference to the desired pass.</p>
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]1147
Chris Lattner8e871652004-03-17 21:09:55 +0000[diff] [blame]1148<p>
1149If your pass is capable of updating analyses if they exist (e.g.,
1150<tt>BreakCriticalEdges</tt>, as described above), you can use the
1151<tt>getAnalysisToUpdate</tt> method, which returns a pointer to the analysis if
1152it is active. For example:</p>
1153
Jim Laskey575df8b2006-08-04 18:10:12 +0000[diff] [blame]1154<div class="doc_code"><pre>
Chris Lattner8e871652004-03-17 21:09:55 +0000[diff] [blame]1155 ...
1156 if (DominatorSet *DS = getAnalysisToUpdate&lt;DominatorSet&gt;()) {
1157 <i>// A DominatorSet is active. This code will update it.</i>
1158 }
1159 ...
Jim Laskey575df8b2006-08-04 18:10:12 +0000[diff] [blame]1160</pre></div>
Chris Lattner8e871652004-03-17 21:09:55 +0000[diff] [blame]1161
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]1162</div>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]1163
Chris Lattner8d8a9282002-08-22 19:21:04 +0000[diff] [blame]1164<!-- *********************************************************************** -->
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]1165<div class="doc_section">
1166 <a name="analysisgroup">Implementing Analysis Groups</a>
1167</div>
Chris Lattner8d8a9282002-08-22 19:21:04 +0000[diff] [blame]1168<!-- *********************************************************************** -->
1169
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]1170<div class="doc_text">
1171
1172<p>Now that we understand the basics of how passes are defined, how the are
1173used, 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]1174fancier. All of the pass relationships that we have seen so far are very
1175simple: one pass depends on one other specific pass to be run before it can run.
1176For many applications, this is great, for others, more flexibility is
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]1177required.</p>
Chris Lattner8d8a9282002-08-22 19:21:04 +0000[diff] [blame]1178
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]1179<p>In particular, some analyses are defined such that there is a single simple
Chris Lattner8d8a9282002-08-22 19:21:04 +0000[diff] [blame]1180interface to the analysis results, but multiple ways of calculating them.
1181Consider alias analysis for example. The most trivial alias analysis returns
1182"may alias" for any alias query. The most sophisticated analysis a
1183flow-sensitive, context-sensitive interprocedural analysis that can take a
1184significant amount of time to execute (and obviously, there is a lot of room
1185between these two extremes for other implementations). To cleanly support
1186situations like this, the LLVM Pass Infrastructure supports the notion of
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]1187Analysis Groups.</p>
1188
1189</div>
Chris Lattner8d8a9282002-08-22 19:21:04 +0000[diff] [blame]1190
1191<!-- _______________________________________________________________________ -->
Chris Lattner8e871652004-03-17 21:09:55 +0000[diff] [blame]1192<div class="doc_subsubsection">
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]1193 <a name="agconcepts">Analysis Group Concepts</a>
1194</div>
Chris Lattner8d8a9282002-08-22 19:21:04 +0000[diff] [blame]1195
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]1196<div class="doc_text">
1197
1198<p>An Analysis Group is a single simple interface that may be implemented by
Chris Lattner8d8a9282002-08-22 19:21:04 +0000[diff] [blame]1199multiple different passes. Analysis Groups can be given human readable names
1200just like passes, but unlike passes, they need not derive from the <tt>Pass</tt>
1201class. An analysis group may have one or more implementations, one of which is
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]1202the "default" implementation.</p>
Chris Lattner8d8a9282002-08-22 19:21:04 +0000[diff] [blame]1203
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]1204<p>Analysis groups are used by client passes just like other passes are: the
Chris Lattner8d8a9282002-08-22 19:21:04 +0000[diff] [blame]1205<tt>AnalysisUsage::addRequired()</tt> and <tt>Pass::getAnalysis()</tt> methods.
1206In order to resolve this requirement, the <a href="#passmanager">PassManager</a>
1207scans the available passes to see if any implementations of the analysis group
1208are available. If none is available, the default implementation is created for
1209the pass to use. All standard rules for <A href="#interaction">interaction
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]1210between passes</a> still apply.</p>
Chris Lattner8d8a9282002-08-22 19:21:04 +0000[diff] [blame]1211
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]1212<p>Although <a href="#registration">Pass Registration</a> is optional for normal
Chris Lattner8d8a9282002-08-22 19:21:04 +0000[diff] [blame]1213passes, all analysis group implementations must be registered, and must use the
1214<A href="#registerag"><tt>RegisterAnalysisGroup</tt></a> template to join the
1215implementation pool. Also, a default implementation of the interface
1216<b>must</b> be registered with <A
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]1217href="#registerag"><tt>RegisterAnalysisGroup</tt></a>.</p>
Chris Lattner8d8a9282002-08-22 19:21:04 +0000[diff] [blame]1218
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]1219<p>As a concrete example of an Analysis Group in action, consider the <a
Reid Spencerca058542006-03-14 05:39:39 +0000[diff] [blame]1220href="http://llvm.org/doxygen/classllvm_1_1AliasAnalysis.html">AliasAnalysis</a>
Chris Lattner8d8a9282002-08-22 19:21:04 +0000[diff] [blame]1221analysis group. The default implementation of the alias analysis interface (the
1222<tt><a
Reid Spencerca058542006-03-14 05:39:39 +0000[diff] [blame]1223href="http://llvm.org/doxygen/structBasicAliasAnalysis.html">basicaa</a></tt>
Chris Lattner8d8a9282002-08-22 19:21:04 +0000[diff] [blame]1224pass) just does a few simple checks that don't require significant analysis to
1225compute (such as: two different globals can never alias each other, etc).
1226Passes that use the <tt><a
Reid Spencerca058542006-03-14 05:39:39 +0000[diff] [blame]1227href="http://llvm.org/doxygen/classllvm_1_1AliasAnalysis.html">AliasAnalysis</a></tt>
Chris Lattner8d8a9282002-08-22 19:21:04 +0000[diff] [blame]1228interface (for example the <tt><a
Reid Spencerca058542006-03-14 05:39:39 +0000[diff] [blame]1229href="http://llvm.org/doxygen/structGCSE.html">gcse</a></tt> pass), do
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]1230not care which implementation of alias analysis is actually provided, they just
1231use the designated interface.</p>
Chris Lattner8d8a9282002-08-22 19:21:04 +0000[diff] [blame]1232
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]1233<p>From the user's perspective, commands work just like normal. Issuing the
Chris Lattner8d8a9282002-08-22 19:21:04 +0000[diff] [blame]1234command '<tt>opt -gcse ...</tt>' will cause the <tt>basicaa</tt> class to be
1235instantiated and added to the pass sequence. Issuing the command '<tt>opt
1236-somefancyaa -gcse ...</tt>' will cause the <tt>gcse</tt> pass to use the
1237<tt>somefancyaa</tt> alias analysis (which doesn't actually exist, it's just a
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]1238hypothetical example) instead.</p>
Chris Lattner8d8a9282002-08-22 19:21:04 +0000[diff] [blame]1239
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]1240</div>
Chris Lattner8d8a9282002-08-22 19:21:04 +0000[diff] [blame]1241
1242<!-- _______________________________________________________________________ -->
Chris Lattner8e871652004-03-17 21:09:55 +0000[diff] [blame]1243<div class="doc_subsubsection">
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]1244 <a name="registerag">Using <tt>RegisterAnalysisGroup</tt></a>
1245</div>
Chris Lattner8d8a9282002-08-22 19:21:04 +0000[diff] [blame]1246
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]1247<div class="doc_text">
1248
1249<p>The <tt>RegisterAnalysisGroup</tt> template is used to register the analysis
Chris Lattner8d8a9282002-08-22 19:21:04 +0000[diff] [blame]1250group itself as well as add pass implementations to the analysis group. First,
1251an analysis should be registered, with a human readable name provided for it.
1252Unlike registration of passes, there is no command line argument to be specified
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]1253for the Analysis Group Interface itself, because it is "abstract":</p>
Chris Lattner8d8a9282002-08-22 19:21:04 +0000[diff] [blame]1254
Jim Laskey575df8b2006-08-04 18:10:12 +0000[diff] [blame]1255<div class="doc_code"><pre>
Reid Spencerca058542006-03-14 05:39:39 +0000[diff] [blame]1256 <b>static</b> RegisterAnalysisGroup&lt;<a href="http://llvm.org/doxygen/classllvm_1_1AliasAnalysis.html">AliasAnalysis</a>&gt; A("<i>Alias Analysis</i>");
Jim Laskey575df8b2006-08-04 18:10:12 +0000[diff] [blame]1257</pre></div>
Chris Lattner8d8a9282002-08-22 19:21:04 +0000[diff] [blame]1258
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]1259<p>Once the analysis is registered, passes can declare that they are valid
1260implementations of the interface by using the following code:</p>
Chris Lattner8d8a9282002-08-22 19:21:04 +0000[diff] [blame]1261
Jim Laskey575df8b2006-08-04 18:10:12 +0000[diff] [blame]1262<div class="doc_code"><pre>
Chris Lattner8d8a9282002-08-22 19:21:04 +0000[diff] [blame]1263<b>namespace</b> {
1264 //<i> Analysis Group implementations <b>must</b> be registered normally...</i>
Chris Lattnerb693cb02006-08-27 23:18:52 +0000[diff] [blame]1265 RegisterPass&lt;FancyAA&gt;
Chris Lattner8d8a9282002-08-22 19:21:04 +0000[diff] [blame]1266 B("<i>somefancyaa</i>", "<i>A more complex alias analysis implementation</i>");
1267
1268 //<i> Declare that we implement the AliasAnalysis interface</i>
Chris Lattnerea3c2b22006-08-28 00:45:38 +0000[diff] [blame]1269 RegisterAnalysisGroup&lt;<a href="http://llvm.org/doxygen/classllvm_1_1AliasAnalysis.html">AliasAnalysis</a>&gt; C(B);
Chris Lattner8d8a9282002-08-22 19:21:04 +0000[diff] [blame]1270}
Jim Laskey575df8b2006-08-04 18:10:12 +0000[diff] [blame]1271</pre></div>
Chris Lattner8d8a9282002-08-22 19:21:04 +0000[diff] [blame]1272
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]1273<p>This just shows a class <tt>FancyAA</tt> that is registered normally, then
1274uses the <tt>RegisterAnalysisGroup</tt> template to "join" the <tt><a
Reid Spencerca058542006-03-14 05:39:39 +0000[diff] [blame]1275href="http://llvm.org/doxygen/classllvm_1_1AliasAnalysis.html">AliasAnalysis</a></tt>
Chris Lattner8d8a9282002-08-22 19:21:04 +0000[diff] [blame]1276analysis group. Every implementation of an analysis group should join using
1277this template. A single pass may join multiple different analysis groups with
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]1278no problem.</p>
Chris Lattner8d8a9282002-08-22 19:21:04 +0000[diff] [blame]1279
Jim Laskey575df8b2006-08-04 18:10:12 +0000[diff] [blame]1280<div class="doc_code"><pre>
Chris Lattner8d8a9282002-08-22 19:21:04 +0000[diff] [blame]1281<b>namespace</b> {
1282 //<i> Analysis Group implementations <b>must</b> be registered normally...</i>
Chris Lattnerb693cb02006-08-27 23:18:52 +0000[diff] [blame]1283 RegisterPass&lt;<a href="http://llvm.org/doxygen/structBasicAliasAnalysis.html">BasicAliasAnalysis</a>&gt;
Chris Lattner8d8a9282002-08-22 19:21:04 +0000[diff] [blame]1284 D("<i>basicaa</i>", "<i>Basic Alias Analysis (default AA impl)</i>");
1285
1286 //<i> Declare that we implement the AliasAnalysis interface</i>
Chris Lattnerea3c2b22006-08-28 00:45:38 +0000[diff] [blame]1287 RegisterAnalysisGroup&lt;<a href="http://llvm.org/doxygen/classllvm_1_1AliasAnalysis.html">AliasAnalysis</a>, <b>true</b>&gt; E(D);
Chris Lattner8d8a9282002-08-22 19:21:04 +0000[diff] [blame]1288}
Jim Laskey575df8b2006-08-04 18:10:12 +0000[diff] [blame]1289</pre></div>
Chris Lattner8d8a9282002-08-22 19:21:04 +0000[diff] [blame]1290
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]1291<p>Here we show how the default implementation is specified (using the extra
Chris Lattner8d8a9282002-08-22 19:21:04 +0000[diff] [blame]1292argument to the <tt>RegisterAnalysisGroup</tt> template). There must be exactly
1293one default implementation available at all times for an Analysis Group to be
1294used. Here we declare that the <tt><a
Reid Spencerca058542006-03-14 05:39:39 +0000[diff] [blame]1295href="http://llvm.org/doxygen/structBasicAliasAnalysis.html">BasicAliasAnalysis</a></tt>
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]1296pass is the default implementation for the interface.</p>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]1297
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]1298</div>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]1299
1300<!-- *********************************************************************** -->
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]1301<div class="doc_section">
Tanya Lattnerfb966ba2004-11-19 01:25:14 +0000[diff] [blame]1302 <a name="passStatistics">Pass Statistics</a>
1303</div>
1304<!-- *********************************************************************** -->
1305
1306<div class="doc_text">
Tanya Lattner0b40ee62004-11-19 01:26:37 +0000[diff] [blame]1307<p>The <a
Reid Spencerca058542006-03-14 05:39:39 +0000[diff] [blame]1308href="http://llvm.org/doxygen/Statistic_8h-source.html"><tt>Statistic</tt></a>
John Criswell3e149a22005-11-28 23:25:41 +0000[diff] [blame]1309class is designed to be an easy way to expose various success
Tanya Lattnerfb966ba2004-11-19 01:25:14 +0000[diff] [blame]1310metrics from passes. These statistics are printed at the end of a
1311run, when the -stats command line option is enabled on the command
Tanya Lattner0b40ee62004-11-19 01:26:37 +0000[diff] [blame]1312line. See the <a href="http://llvm.org/docs/ProgrammersManual.html#Statistic">Statistics section</a> in the Programmer's Manual for details.
Tanya Lattnerfb966ba2004-11-19 01:25:14 +0000[diff] [blame]1313
1314</div>
1315
1316
1317<!-- *********************************************************************** -->
1318<div class="doc_section">
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]1319 <a name="passmanager">What PassManager does</a>
1320</div>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]1321<!-- *********************************************************************** -->
1322
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]1323<div class="doc_text">
1324
1325<p>The <a
Reid Spencerca058542006-03-14 05:39:39 +0000[diff] [blame]1326href="http://llvm.org/doxygen/PassManager_8h-source.html"><tt>PassManager</tt></a>
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]1327<a
Reid Spencerca058542006-03-14 05:39:39 +0000[diff] [blame]1328href="http://llvm.org/doxygen/classllvm_1_1PassManager.html">class</a>
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]1329takes a list of passes, ensures their <a href="#interaction">prerequisites</a>
1330are set up correctly, and then schedules passes to run efficiently. All of the
1331LLVM tools that run passes use the <tt>PassManager</tt> for execution of these
1332passes.</p>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]1333
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]1334<p>The <tt>PassManager</tt> does two main things to try to reduce the execution
1335time of a series of passes:</p>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]1336
1337<ol>
1338<li><b>Share analysis results</b> - The PassManager attempts to avoid
1339recomputing analysis results as much as possible. This means keeping track of
1340which analyses are available already, which analyses get invalidated, and which
1341analyses are needed to be run for a pass. An important part of work is that the
1342<tt>PassManager</tt> tracks the exact lifetime of all analysis results, allowing
1343it to <a href="#releaseMemory">free memory</a> allocated to holding analysis
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]1344results as soon as they are no longer needed.</li>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]1345
1346<li><b>Pipeline the execution of passes on the program</b> - The
1347<tt>PassManager</tt> attempts to get better cache and memory usage behavior out
1348of a series of passes by pipelining the passes together. This means that, given
1349a series of consequtive <a href="#FunctionPass"><tt>FunctionPass</tt></a>'s, it
1350will execute all of the <a href="#FunctionPass"><tt>FunctionPass</tt></a>'s on
1351the first function, then all of the <a
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]1352href="#FunctionPass"><tt>FunctionPass</tt></a>es on the second function,
1353etc... until the entire program has been run through the passes.
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]1354
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]1355<p>This improves the cache behavior of the compiler, because it is only touching
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]1356the LLVM program representation for a single function at a time, instead of
1357traversing the entire program. It reduces the memory consumption of compiler,
1358because, for example, only one <a
Reid Spencerca058542006-03-14 05:39:39 +0000[diff] [blame]1359href="http://llvm.org/doxygen/classllvm_1_1DominatorSet.html"><tt>DominatorSet</tt></a>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]1360needs to be calculated at a time. This also makes it possible some <a
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]1361href="#SMP">interesting enhancements</a> in the future.</p></li>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]1362
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]1363</ol>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]1364
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]1365<p>The effectiveness of the <tt>PassManager</tt> is influenced directly by how
1366much information it has about the behaviors of the passes it is scheduling. For
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]1367example, the "preserved" set is intentionally conservative in the face of an
1368unimplemented <a href="#getAnalysisUsage"><tt>getAnalysisUsage</tt></a> method.
1369Not implementing when it should be implemented will have the effect of not
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]1370allowing any analysis results to live across the execution of your pass.</p>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]1371
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]1372<p>The <tt>PassManager</tt> class exposes a <tt>--debug-pass</tt> command line
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]1373options that is useful for debugging pass execution, seeing how things work, and
1374diagnosing when you should be preserving more analyses than you currently are
1375(To get information about all of the variants of the <tt>--debug-pass</tt>
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]1376option, just type '<tt>opt --help-hidden</tt>').</p>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]1377
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]1378<p>By using the <tt>--debug-pass=Structure</tt> option, for example, we can see
1379how our <a href="#basiccode">Hello World</a> pass interacts with other passes.
1380Lets try it out with the <tt>gcse</tt> and <tt>licm</tt> passes:</p>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]1381
Jim Laskey575df8b2006-08-04 18:10:12 +0000[diff] [blame]1382<div class="doc_code"><pre>
Reid Spencer4a1ab182005-01-11 05:16:23 +0000[diff] [blame]1383$ opt -load ../../../Debug/lib/Hello.so -gcse -licm --debug-pass=Structure &lt; hello.bc &gt; /dev/null
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]1384Module Pass Manager
1385 Function Pass Manager
1386 Dominator Set Construction
1387 Immediate Dominators Construction
1388 Global Common Subexpression Elimination
1389-- Immediate Dominators Construction
1390-- Global Common Subexpression Elimination
1391 Natural Loop Construction
1392 Loop Invariant Code Motion
1393-- Natural Loop Construction
1394-- Loop Invariant Code Motion
1395 Module Verifier
1396-- Dominator Set Construction
1397-- Module Verifier
1398 Bytecode Writer
1399--Bytecode Writer
Jim Laskey575df8b2006-08-04 18:10:12 +0000[diff] [blame]1400</pre></div>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]1401
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]1402<p>This output shows us when passes are constructed and when the analysis
1403results are known to be dead (prefixed with '<tt>--</tt>'). Here we see that
1404GCSE uses dominator and immediate dominator information to do its job. The LICM
1405pass uses natural loop information, which uses dominator sets, but not immediate
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]1406dominators. Because immediate dominators are no longer useful after the GCSE
1407pass, it is immediately destroyed. The dominator sets are then reused to
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]1408compute natural loop information, which is then used by the LICM pass.</p>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]1409
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]1410<p>After the LICM pass, the module verifier runs (which is automatically added
1411by the '<tt>opt</tt>' tool), which uses the dominator set to check that the
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]1412resultant LLVM code is well formed. After it finishes, the dominator set
1413information is destroyed, after being computed once, and shared by three
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]1414passes.</p>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]1415
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]1416<p>Lets see how this changes when we run the <a href="#basiccode">Hello
1417World</a> pass in between the two passes:</p>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]1418
Jim Laskey575df8b2006-08-04 18:10:12 +0000[diff] [blame]1419<div class="doc_code"><pre>
Reid Spencer4a1ab182005-01-11 05:16:23 +0000[diff] [blame]1420$ opt -load ../../../Debug/lib/Hello.so -gcse -hello -licm --debug-pass=Structure &lt; hello.bc &gt; /dev/null
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]1421Module Pass Manager
1422 Function Pass Manager
1423 Dominator Set Construction
1424 Immediate Dominators Construction
1425 Global Common Subexpression Elimination
1426<b>-- Dominator Set Construction</b>
1427-- Immediate Dominators Construction
1428-- Global Common Subexpression Elimination
1429<b> Hello World Pass
1430-- Hello World Pass
1431 Dominator Set Construction</b>
1432 Natural Loop Construction
1433 Loop Invariant Code Motion
1434-- Natural Loop Construction
1435-- Loop Invariant Code Motion
1436 Module Verifier
1437-- Dominator Set Construction
1438-- Module Verifier
1439 Bytecode Writer
1440--Bytecode Writer
1441Hello: __main
1442Hello: puts
1443Hello: main
Jim Laskey575df8b2006-08-04 18:10:12 +0000[diff] [blame]1444</pre></div>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]1445
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]1446<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]1447Dominator Set pass, even though it doesn't modify the code at all! To fix this,
1448we need to add the following <a
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]1449href="#getAnalysisUsage"><tt>getAnalysisUsage</tt></a> method to our pass:</p>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]1450
Jim Laskey575df8b2006-08-04 18:10:12 +0000[diff] [blame]1451<div class="doc_code"><pre>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]1452 <i>// We don't modify the program, so we preserve all analyses</i>
1453 <b>virtual void</b> getAnalysisUsage(AnalysisUsage &amp;AU) <b>const</b> {
1454 AU.setPreservesAll();
1455 }
Jim Laskey575df8b2006-08-04 18:10:12 +0000[diff] [blame]1456</pre></div>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]1457
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]1458<p>Now when we run our pass, we get this output:</p>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]1459
Jim Laskey575df8b2006-08-04 18:10:12 +0000[diff] [blame]1460<div class="doc_code"><pre>
Reid Spencer4a1ab182005-01-11 05:16:23 +0000[diff] [blame]1461$ opt -load ../../../Debug/lib/Hello.so -gcse -hello -licm --debug-pass=Structure &lt; hello.bc &gt; /dev/null
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]1462Pass Arguments: -gcse -hello -licm
1463Module Pass Manager
1464 Function Pass Manager
1465 Dominator Set Construction
1466 Immediate Dominators Construction
1467 Global Common Subexpression Elimination
1468-- Immediate Dominators Construction
1469-- Global Common Subexpression Elimination
1470 Hello World Pass
1471-- Hello World Pass
1472 Natural Loop Construction
1473 Loop Invariant Code Motion
1474-- Loop Invariant Code Motion
1475-- Natural Loop Construction
1476 Module Verifier
1477-- Dominator Set Construction
1478-- Module Verifier
1479 Bytecode Writer
1480--Bytecode Writer
1481Hello: __main
1482Hello: puts
1483Hello: main
Jim Laskey575df8b2006-08-04 18:10:12 +0000[diff] [blame]1484</pre></div>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]1485
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]1486<p>Which shows that we don't accidentally invalidate dominator information
1487anymore, and therefore do not have to compute it twice.</p>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]1488
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]1489</div>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]1490
1491<!-- _______________________________________________________________________ -->
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]1492<div class="doc_subsubsection">
1493 <a name="releaseMemory">The <tt>releaseMemory</tt> method</a>
1494</div>
1495
1496<div class="doc_text">
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]1497
Jim Laskey575df8b2006-08-04 18:10:12 +0000[diff] [blame]1498<div class="doc_code"><pre>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]1499 <b>virtual void</b> releaseMemory();
Jim Laskey575df8b2006-08-04 18:10:12 +0000[diff] [blame]1500</pre></div>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]1501
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]1502<p>The <tt>PassManager</tt> automatically determines when to compute analysis
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]1503results, and how long to keep them around for. Because the lifetime of the pass
1504object itself is effectively the entire duration of the compilation process, we
1505need some way to free analysis results when they are no longer useful. The
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]1506<tt>releaseMemory</tt> virtual method is the way to do this.</p>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]1507
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]1508<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]1509amount of state (for use by another pass which "requires" your pass and uses the
1510<a href="#getAnalysis">getAnalysis</a> method) you should implement
1511<tt>releaseMEmory</tt> to, well, release the memory allocated to maintain this
1512internal state. This method is called after the <tt>run*</tt> method for the
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]1513class, before the next call of <tt>run*</tt> in your pass.</p>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]1514
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]1515</div>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]1516
1517<!-- *********************************************************************** -->
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]1518<div class="doc_section">
Jim Laskey575df8b2006-08-04 18:10:12 +0000[diff] [blame]1519 <a name="registering">Registering dynamically loaded passes</a>
1520</div>
1521<!-- *********************************************************************** -->
1522
1523<div class="doc_text">
1524
1525<p><i>Size matters</i> when constructing production quality tools using llvm,
1526both for the purposes of distribution, and for regulating the resident code size
1527when running on the target system. Therefore, it becomes desirable to
1528selectively use some passes, while omitting others and maintain the flexibility
1529to change configurations later on. You want to be able to do all this, and,
1530provide feedback to the user. This is where pass registration comes into
1531play.</p>
1532
1533<p>The fundamental mechanisms for pass registration are the
1534<tt>MachinePassRegistry</tt> class and subclasses of
1535<tt>MachinePassRegistryNode</tt>.</p>
1536
1537<p>An instance of <tt>MachinePassRegistry</tt> is used to maintain a list of
1538<tt>MachinePassRegistryNode</tt> objects. This instance maintains the list and
1539communicates additions and deletions to the command line interface.</p>
1540
1541<p>An instance of <tt>MachinePassRegistryNode</tt> subclass is used to maintain
1542information provided about a particular pass. This information includes the
1543command line name, the command help string and the address of the function used
1544to create an instance of the pass. A global static constructor of one of these
1545instances <i>registers</i> with a corresponding <tt>MachinePassRegistry</tt>,
1546the static destructor <i>unregisters</i>. Thus a pass that is statically linked
1547in the tool will be registered at start up. A dynamically loaded pass will
1548register on load and unregister at unload.</p>
1549
1550</div>
1551
1552<!-- _______________________________________________________________________ -->
1553<div class="doc_subsection">
1554 <a name="registering_existing">Using existing registries</a>
1555</div>
1556
1557<div class="doc_text">
1558
1559<p>There are predefined registries to track instruction scheduling
1560(<tt>RegisterScheduler</tt>) and register allocation (<tt>RegisterRegAlloc</tt>)
1561machine passes. Here we will describe how to <i>register</i> a register
1562allocator machine pass.</p>
1563
1564<p>Implement your register allocator machine pass. In your register allocator
1565.cpp file add the following include;</p>
1566
1567<div class="doc_code"><pre>
Chris Lattner4bde9fb2006-08-11 16:37:02 +0000[diff] [blame]1568 #include "llvm/CodeGen/RegAllocRegistry.h"
Jim Laskey575df8b2006-08-04 18:10:12 +0000[diff] [blame]1569</pre></div>
1570
1571<p>Also in your register allocator .cpp file, define a creator function in the
1572form; </p>
1573
1574<div class="doc_code"><pre>
1575 FunctionPass *createMyRegisterAllocator() {
1576 return new MyRegisterAllocator();
1577 }
1578</pre></div>
1579
1580<p>Note that the signature of this function should match the type of
1581<tt>RegisterRegAlloc::FunctionPassCtor</tt>. In the same file add the
1582"installing" declaration, in the form;</p>
1583
1584<div class="doc_code"><pre>
1585 static RegisterRegAlloc myRegAlloc("myregalloc",
1586 " my register allocator help string",
1587 createMyRegisterAllocator);
1588</pre></div>
1589
1590<p>Note the two spaces prior to the help string produces a tidy result on the
1591--help query.</p>
1592
1593<div class="doc_code"><pre>
1594$ llc --help
1595 ...
1596 -regalloc - Register allocator to use: (default = linearscan)
1597 =linearscan - linear scan register allocator
1598 =local - local register allocator
1599 =simple - simple register allocator
1600 =myregalloc - my register allocator help string
1601 ...
1602</pre></div>
1603
1604<p>And that's it. The user is now free to use <tt>-regalloc=myregalloc</tt> as
1605an option. Registering instruction schedulers is similar except use the
Chris Lattner4bde9fb2006-08-11 16:37:02 +0000[diff] [blame]1606<tt>RegisterScheduler</tt> class. Note that the
1607<tt>RegisterScheduler::FunctionPassCtor</tt> is significantly different from
Jim Laskey575df8b2006-08-04 18:10:12 +0000[diff] [blame]1608<tt>RegisterRegAlloc::FunctionPassCtor</tt>.</p>
1609
1610<p>To force the load/linking of your register allocator into the llc/lli tools,
1611add your creator function's global declaration to "Passes.h" and add a "pseudo"
1612call line to <tt>llvm/Codegen/LinkAllCodegenComponents.h</tt>.</p>
1613
1614</div>
1615
1616
1617<!-- _______________________________________________________________________ -->
1618<div class="doc_subsection">
1619 <a name="registering_new">Creating new registries</a>
1620</div>
1621
1622<div class="doc_text">
1623
1624<p>The easiest way to get started is to clone one of the existing registries; we
1625recommend <tt>llvm/CodeGen/RegAllocRegistry.h</tt>. The key things to modify
1626are the class name and the <tt>FunctionPassCtor</tt> type.</p>
1627
1628<p>Then you need to declare the registry. Example: if your pass registry is
1629<tt>RegisterMyPasses</tt> then define;</p>
1630
1631<div class="doc_code"><pre>
1632MachinePassRegistry RegisterMyPasses::Registry;
1633</pre></div>
1634
1635<p>And finally, declare the command line option for your passes. Example:</p>
1636
1637<div class="doc_code"><pre>
1638 cl::opt&lt;RegisterMyPasses::FunctionPassCtor, false,
1639 RegisterPassParser&lt;RegisterMyPasses&gt &gt
1640 MyPassOpt("mypass",
1641 cl::init(&amp;createDefaultMyPass),
1642 cl::desc("my pass option help"));
1643</pre></div>
1644
1645<p>Here the command option is "mypass", with createDefaultMyPass as the default
1646creator.</p>
1647
1648</div>
1649
1650<!-- *********************************************************************** -->
1651<div class="doc_section">
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]1652 <a name="debughints">Using GDB with dynamically loaded passes</a>
1653</div>
Chris Lattner8a97c8a2002-09-06 02:02:58 +0000[diff] [blame]1654<!-- *********************************************************************** -->
1655
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]1656<div class="doc_text">
1657
1658<p>Unfortunately, using GDB with dynamically loaded passes is not as easy as it
Chris Lattner8a97c8a2002-09-06 02:02:58 +0000[diff] [blame]1659should be. First of all, you can't set a breakpoint in a shared object that has
1660not been loaded yet, and second of all there are problems with inlined functions
1661in shared objects. Here are some suggestions to debugging your pass with
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]1662GDB.</p>
Chris Lattner8a97c8a2002-09-06 02:02:58 +0000[diff] [blame]1663
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]1664<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]1665transformation invoked by <tt>opt</tt>, although nothing described here depends
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]1666on that.</p>
1667
1668</div>
Chris Lattner8a97c8a2002-09-06 02:02:58 +0000[diff] [blame]1669
1670<!-- _______________________________________________________________________ -->
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]1671<div class="doc_subsubsection">
1672 <a name="breakpoint">Setting a breakpoint in your pass</a>
1673</div>
Chris Lattner8a97c8a2002-09-06 02:02:58 +0000[diff] [blame]1674
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]1675<div class="doc_text">
1676
1677<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]1678
Jim Laskey575df8b2006-08-04 18:10:12 +0000[diff] [blame]1679<div class="doc_code"><pre>
Chris Lattner8a97c8a2002-09-06 02:02:58 +0000[diff] [blame]1680$ <b>gdb opt</b>
1681GNU gdb 5.0
1682Copyright 2000 Free Software Foundation, Inc.
1683GDB is free software, covered by the GNU General Public License, and you are
1684welcome to change it and/or distribute copies of it under certain conditions.
1685Type "show copying" to see the conditions.
1686There is absolutely no warranty for GDB. Type "show warranty" for details.
1687This GDB was configured as "sparc-sun-solaris2.6"...
1688(gdb)
Jim Laskey575df8b2006-08-04 18:10:12 +0000[diff] [blame]1689</pre></div>
Chris Lattner8a97c8a2002-09-06 02:02:58 +0000[diff] [blame]1690
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]1691<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]1692time to load. Be patient. Since we cannot set a breakpoint in our pass yet
1693(the shared object isn't loaded until runtime), we must execute the process, and
1694have it stop before it invokes our pass, but after it has loaded the shared
1695object. The most foolproof way of doing this is to set a breakpoint in
1696<tt>PassManager::run</tt> and then run the process with the arguments you
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]1697want:</p>
Chris Lattner8a97c8a2002-09-06 02:02:58 +0000[diff] [blame]1698
Jim Laskey575df8b2006-08-04 18:10:12 +0000[diff] [blame]1699<div class="doc_code"><pre>
Reid Spencer48cf6a62006-09-28 16:53:47 +0000[diff] [blame]1700(gdb) <b>break llvm::PassManager::run</b>
Chris Lattner8a97c8a2002-09-06 02:02:58 +0000[diff] [blame]1701Breakpoint 1 at 0x2413bc: file Pass.cpp, line 70.
Chris Lattner07275182005-04-21 04:52:37 +0000[diff] [blame]1702(gdb) <b>run test.bc -load $(LLVMTOP)/llvm/Debug/lib/[libname].so -[passoption]</b>
1703Starting program: opt test.bc -load $(LLVMTOP)/llvm/Debug/lib/[libname].so -[passoption]
Chris Lattner8a97c8a2002-09-06 02:02:58 +0000[diff] [blame]1704Breakpoint 1, PassManager::run (this=0xffbef174, M=@0x70b298) at Pass.cpp:70
170570 bool PassManager::run(Module &amp;M) { return PM-&gt;run(M); }
1706(gdb)
Jim Laskey575df8b2006-08-04 18:10:12 +0000[diff] [blame]1707</pre></div>
Chris Lattner8a97c8a2002-09-06 02:02:58 +0000[diff] [blame]1708
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]1709<p>Once the <tt>opt</tt> stops in the <tt>PassManager::run</tt> method you are
1710now free to set breakpoints in your pass so that you can trace through execution
1711or do other standard debugging stuff.</p>
Chris Lattner8a97c8a2002-09-06 02:02:58 +0000[diff] [blame]1712
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]1713</div>
Chris Lattner8a97c8a2002-09-06 02:02:58 +0000[diff] [blame]1714
1715<!-- _______________________________________________________________________ -->
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]1716<div class="doc_subsubsection">
1717 <a name="debugmisc">Miscellaneous Problems</a>
1718</div>
Chris Lattner8a97c8a2002-09-06 02:02:58 +0000[diff] [blame]1719
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]1720<div class="doc_text">
1721
1722<p>Once you have the basics down, there are a couple of problems that GDB has,
1723some with solutions, some without.</p>
Chris Lattner8a97c8a2002-09-06 02:02:58 +0000[diff] [blame]1724
1725<ul>
1726<li>Inline functions have bogus stack information. In general, GDB does a
1727pretty good job getting stack traces and stepping through inline functions.
1728When a pass is dynamically loaded however, it somehow completely loses this
1729capability. The only solution I know of is to de-inline a function (move it
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]1730from the body of a class to a .cpp file).</li>
Chris Lattner8a97c8a2002-09-06 02:02:58 +0000[diff] [blame]1731
1732<li>Restarting the program breaks breakpoints. After following the information
1733above, you have succeeded in getting some breakpoints planted in your pass. Nex
1734thing you know, you restart the program (i.e., you type '<tt>run</tt>' again),
1735and you start getting errors about breakpoints being unsettable. The only way I
1736have found to "fix" this problem is to <tt>delete</tt> the breakpoints that are
1737already set in your pass, run the program, and re-set the breakpoints once
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]1738execution stops in <tt>PassManager::run</tt>.</li>
Chris Lattner8a97c8a2002-09-06 02:02:58 +0000[diff] [blame]1739
1740</ul>
1741
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]1742<p>Hopefully these tips will help with common case debugging situations. If
1743you'd like to contribute some tips of your own, just contact <a
1744href="mailto:sabre@nondot.org">Chris</a>.</p>
Chris Lattner8a97c8a2002-09-06 02:02:58 +0000[diff] [blame]1745
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]1746</div>
Chris Lattner8a97c8a2002-09-06 02:02:58 +0000[diff] [blame]1747
1748<!-- *********************************************************************** -->
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]1749<div class="doc_section">
1750 <a name="future">Future extensions planned</a>
1751</div>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]1752<!-- *********************************************************************** -->
1753
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]1754<div class="doc_text">
1755
1756<p>Although the LLVM Pass Infrastructure is very capable as it stands, and does
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]1757some 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]1758where we are going:</p>
1759
1760</div>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]1761
1762<!-- _______________________________________________________________________ -->
Chris Lattner8e871652004-03-17 21:09:55 +0000[diff] [blame]1763<div class="doc_subsubsection">
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]1764 <a name="SMP">Multithreaded LLVM</a>
1765</div>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]1766
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]1767<div class="doc_text">
1768
1769<p>Multiple CPU machines are becoming more common and compilation can never be
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]1770fast enough: obviously we should allow for a multithreaded compiler. Because of
1771the semantics defined for passes above (specifically they cannot maintain state
1772across invocations of their <tt>run*</tt> methods), a nice clean way to
1773implement a multithreaded compiler would be for the <tt>PassManager</tt> class
Misha Brukman7fdaab42003-07-14 17:20:40 +0000[diff] [blame]1774to create multiple instances of each pass object, and allow the separate
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]1775instances to be hacking on different parts of the program at the same time.</p>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]1776
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]1777<p>This implementation would prevent each of the passes from having to implement
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]1778multithreaded constructs, requiring only the LLVM core to have locking in a few
1779places (for global resources). Although this is a simple extension, we simply
1780haven't had time (or multiprocessor machines, thus a reason) to implement this.
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]1781Despite that, we have kept the LLVM passes SMP ready, and you should too.</p>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]1782
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]1783</div>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]1784
1785<!-- _______________________________________________________________________ -->
Chris Lattner8e871652004-03-17 21:09:55 +0000[diff] [blame]1786<div class="doc_subsubsection">
Chris Lattner3c11c042004-09-20 04:36:29 +0000[diff] [blame]1787<a name="PassFunctionPass"><tt>ModulePass</tt>es requiring <tt>FunctionPass</tt>es</a>
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]1788</div>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]1789
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]1790<div class="doc_text">
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]1791
Chris Lattner3c11c042004-09-20 04:36:29 +0000[diff] [blame]1792<p>Currently it is illegal for a <a href="#ModulePass"><tt>ModulePass</tt></a>
1793to require a <a href="#FunctionPass"><tt>FunctionPass</tt></a>. This is because
1794there is only one instance of the <a
1795href="#FunctionPass"><tt>FunctionPass</tt></a> object ever created, thus nowhere
1796to store information for all of the functions in the program at the same time.
1797Although this has come up a couple of times before, this has always been worked
1798around by factoring one big complicated pass into a global and an
1799interprocedural part, both of which are distinct. In the future, it would be
1800nice to have this though.</p>
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]1801
1802<p>Note that it is no problem for a <a
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]1803href="#FunctionPass"><tt>FunctionPass</tt></a> to require the results of a <a
Chris Lattner3c11c042004-09-20 04:36:29 +0000[diff] [blame]1804href="#ModulePass"><tt>ModulePass</tt></a>, only the other way around.</p>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]1805
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