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gerrit-public.fairphone.software / toolchain / llvm-project / f96c3625c2cc9c580882b4914b293d9e64099022 / . / 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>
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]106 </ul></li>
107</ol>
Chris Lattner56d9e222002-08-08 20:23:41 +0000[diff] [blame]108
Chris Lattner020e1fc2004-05-23 21:07:27 +0000[diff] [blame]109<div class="doc_author">
Chris Lattner4bde9fb2006-08-11 16:37:02 +0000[diff] [blame]110 <p>Written by <a href="mailto:sabre@nondot.org">Chris Lattner</a> and
Jim Laskey6e8a2f42007-03-14 19:32:21 +0000[diff] [blame]111 <a href="mailto:jlaskey@mac.com">Jim Laskey</a></p>
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]112</div>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]113
114<!-- *********************************************************************** -->
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]115<div class="doc_section">
116 <a name="introduction">Introduction - What is a pass?</a>
117</div>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]118<!-- *********************************************************************** -->
119
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]120<div class="doc_text">
121
122<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]123passes are where most of the interesting parts of the compiler exist. Passes
124perform the transformations and optimizations that make up the compiler, they
125build the analysis results that are used by these transformations, and they are,
126above all, a structuring technique for compiler code.</p>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]127
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]128<p>All LLVM passes are subclasses of the <tt><a
Reid Spencerca058542006-03-14 05:39:39 +0000[diff] [blame]129href="http://llvm.org/doxygen/classllvm_1_1Pass.html">Pass</a></tt>
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]130class, which implement functionality by overriding virtual methods inherited
Chris Lattner3c11c042004-09-20 04:36:29 +0000[diff] [blame]131from <tt>Pass</tt>. Depending on how your pass works, you should inherit from
132the <tt><a href="#ModulePass">ModulePass</a></tt>, <tt><a
133href="#CallGraphSCCPass">CallGraphSCCPass</a></tt>, <tt><a
134href="#FunctionPass">FunctionPass</a></tt>, or <tt><a
Devang Patel1d3bb032007-03-19 22:21:25 +0000[diff] [blame]135href="#LoopPass">LoopPass</a></tt>, or <tt><a
Chris Lattner9e4be6f2004-09-18 06:39:35 +0000[diff] [blame]136href="#BasicBlockPass">BasicBlockPass</a></tt> classes, which gives the system
137more information about what your pass does, and how it can be combined with
138other passes. One of the main features of the LLVM Pass Framework is that it
139schedules passes to run in an efficient way based on the constraints that your
140pass meets (which are indicated by which class they derive from).</p>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]141
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]142<p>We start by showing you how to construct a pass, everything from setting up
143the code, to compiling, loading, and executing it. After the basics are down,
144more advanced features are discussed.</p>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]145
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]146</div>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]147
148<!-- *********************************************************************** -->
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]149<div class="doc_section">
150 <a name="quickstart">Quick Start - Writing hello world</a>
151</div>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]152<!-- *********************************************************************** -->
153
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]154<div class="doc_text">
155
156<p>Here we describe how to write the "hello world" of passes. The "Hello" pass
157is designed to simply print out the name of non-external functions that exist in
Chris Lattner9e4be6f2004-09-18 06:39:35 +0000[diff] [blame]158the program being compiled. It does not modify the program at all, it just
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]159inspects it. The source code and files for this pass are available in the LLVM
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]160source tree in the <tt>lib/Transforms/Hello</tt> directory.</p>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]161
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]162</div>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]163
164<!-- ======================================================================= -->
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]165<div class="doc_subsection">
166 <a name="makefile">Setting up the build environment</a>
167</div>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]168
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]169<div class="doc_text">
170
Reid Spencera1799682004-12-11 05:12:57 +0000[diff] [blame]171 <p>First, you need to create a new directory somewhere in the LLVM source
172 base. For this example, we'll assume that you made
173 <tt>lib/Transforms/Hello</tt>. Next, you must set up a build script
174 (Makefile) that will compile the source code for the new pass. To do this,
175 copy the following into <tt>Makefile</tt>:</p>
176 <hr/>
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]177
Jim Laskey575df8b2006-08-04 18:10:12 +0000[diff] [blame]178<div class="doc_code"><pre>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]179# Makefile for hello pass
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]180
Chris Lattnereb4ba3c2002-08-14 20:06:13 +0000[diff] [blame]181# Path to top level of LLVM heirarchy
Chris Lattner0c5e2932002-08-14 20:07:01 +0000[diff] [blame]182LEVEL = ../../..
Chris Lattnereb4ba3c2002-08-14 20:06:13 +0000[diff] [blame]183
184# Name of the library to build
Reid Spencer4a1ab182005-01-11 05:16:23 +0000[diff] [blame]185LIBRARYNAME = Hello
Chris Lattnereb4ba3c2002-08-14 20:06:13 +0000[diff] [blame]186
Reid Spencer4a1ab182005-01-11 05:16:23 +0000[diff] [blame]187# Make the shared library become a loadable module so the tools can
188# dlopen/dlsym on the resulting library.
Robert Bocchino19cbea12006-01-06 22:49:23 +0000[diff] [blame]189LOADABLE_MODULE = 1
Reid Spencer4a1ab182005-01-11 05:16:23 +0000[diff] [blame]190
Reid Spencer197d7bf2006-08-08 01:48:17 +0000[diff] [blame]191# Tell the build system which LLVM libraries your pass needs. You'll probably
192# need at least LLVMSystem.a, LLVMSupport.a, LLVMCore.a but possibly several
193# others too.
194LLVMLIBS = LLVMCore.a LLVMSupport.a LLVMSystem.a
195
Chris Lattnereb4ba3c2002-08-14 20:06:13 +0000[diff] [blame]196# Include the makefile implementation stuff
197include $(LEVEL)/Makefile.common
Jim Laskey575df8b2006-08-04 18:10:12 +0000[diff] [blame]198</pre></div>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]199
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]200<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]201directory are to be compiled and linked together into a
Reid Spencer4a1ab182005-01-11 05:16:23 +0000[diff] [blame]202<tt>Debug/lib/Hello.so</tt> shared object that can be dynamically loaded by
Chris Lattnerb693cb02006-08-27 23:18:52 +0000[diff] [blame]203the <tt>opt</tt> or <tt>bugpoint</tt> tools via their <tt>-load</tt> options.
Reid Spencer4a1ab182005-01-11 05:16:23 +0000[diff] [blame]204If your operating system uses a suffix other than .so (such as windows or
205Mac OS/X), the appropriate extension will be used.</p>
John Criswell2edea842004-01-26 21:26:54 +0000[diff] [blame]206
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]207<p>Now that we have the build scripts set up, we just need to write the code for
208the pass itself.</p>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]209
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]210</div>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]211
212<!-- ======================================================================= -->
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]213<div class="doc_subsection">
214 <a name="basiccode">Basic code required</a>
215</div>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]216
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]217<div class="doc_text">
218
219<p>Now that we have a way to compile our new pass, we just have to write it.
220Start out with:</p>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]221
Jim Laskey575df8b2006-08-04 18:10:12 +0000[diff] [blame]222<div class="doc_code"><pre>
Reid Spencerca058542006-03-14 05:39:39 +0000[diff] [blame]223<b>#include</b> "<a href="http://llvm.org/doxygen/Pass_8h-source.html">llvm/Pass.h</a>"
224<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]225</pre></div>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]226
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]227<p>Which are needed because we are writing a <tt><a
Reid Spencerca058542006-03-14 05:39:39 +0000[diff] [blame]228href="http://llvm.org/doxygen/classllvm_1_1Pass.html">Pass</a></tt>, and
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]229we are operating on <tt><a
Reid Spencerca058542006-03-14 05:39:39 +0000[diff] [blame]230href="http://llvm.org/doxygen/classllvm_1_1Function.html">Function</a></tt>'s.</p>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]231
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]232<p>Next we have:</p>
Jim Laskey575df8b2006-08-04 18:10:12 +0000[diff] [blame]233<div class="doc_code"><pre>
Jonathan Mantonaff4a6a2004-06-30 18:10:30 +0000[diff] [blame]234<b>using namespace llvm;</b>
Jim Laskey575df8b2006-08-04 18:10:12 +0000[diff] [blame]235</pre></div>
Jonathan Mantonaff4a6a2004-06-30 18:10:30 +0000[diff] [blame]236<p>... which is required because the functions from the include files
237live in the llvm namespace.
238</p>
239
240<p>Next we have:</p>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]241
Jim Laskey575df8b2006-08-04 18:10:12 +0000[diff] [blame]242<div class="doc_code"><pre>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]243<b>namespace</b> {
Jim Laskey575df8b2006-08-04 18:10:12 +0000[diff] [blame]244</pre></div>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]245
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]246<p>... which starts out an anonymous namespace. Anonymous namespaces are to C++
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]247what the "<tt>static</tt>" keyword is to C (at global scope). It makes the
248things declared inside of the anonymous namespace only visible to the current
249file. If you're not familiar with them, consult a decent C++ book for more
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]250information.</p>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]251
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]252<p>Next, we declare our pass itself:</p>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]253
Jim Laskey575df8b2006-08-04 18:10:12 +0000[diff] [blame]254<div class="doc_code"><pre>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]255 <b>struct</b> Hello : <b>public</b> <a href="#FunctionPass">FunctionPass</a> {
Jim Laskey575df8b2006-08-04 18:10:12 +0000[diff] [blame]256</pre></div><p>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]257
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]258<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]259href="http://llvm.org/doxygen/classllvm_1_1FunctionPass.html">FunctionPass</a></tt>.
Chris Lattnera818d922002-09-09 03:48:46 +0000[diff] [blame]260The different builtin pass subclasses are described in detail <a
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]261href="#passtype">later</a>, but for now, know that <a
262href="#FunctionPass"><tt>FunctionPass</tt></a>'s operate a function at a
263time.</p>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]264
Jim Laskey575df8b2006-08-04 18:10:12 +0000[diff] [blame]265<div class="doc_code"><pre>
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]266 <b>virtual bool</b> <a href="#runOnFunction">runOnFunction</a>(Function &amp;F) {
Bill Wendling22e978a2006-12-07 20:04:42 +0000[diff] [blame]267 llvm::cerr &lt;&lt; "<i>Hello: </i>" &lt;&lt; F.getName() &lt;&lt; "\n";
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]268 <b>return false</b>;
269 }
270 }; <i>// end of struct Hello</i>
Jim Laskey575df8b2006-08-04 18:10:12 +0000[diff] [blame]271</pre></div>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]272
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]273<p>We declare a "<a href="#runOnFunction"><tt>runOnFunction</tt></a>" method,
274which overloads an abstract virtual method inherited from <a
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]275href="#FunctionPass"><tt>FunctionPass</tt></a>. This is where we are supposed
276to 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]277function.</p>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]278
Jim Laskey575df8b2006-08-04 18:10:12 +0000[diff] [blame]279<div class="doc_code"><pre>
Chris Lattnerb693cb02006-08-27 23:18:52 +0000[diff] [blame]280 RegisterPass&lt;Hello&gt; X("<i>hello</i>", "<i>Hello World Pass</i>");
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]281} <i>// end of anonymous namespace</i>
Jim Laskey575df8b2006-08-04 18:10:12 +0000[diff] [blame]282</pre></div>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]283
Chris Lattnerb693cb02006-08-27 23:18:52 +0000[diff] [blame]284<p>Lastly, we <a href="#registration">register our class</a> <tt>Hello</tt>,
285giving it a command line
286argument "<tt>hello</tt>", and a name "<tt>Hello World Pass</tt>".</p>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]287
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]288<p>As a whole, the <tt>.cpp</tt> file looks like:</p>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]289
Jim Laskey575df8b2006-08-04 18:10:12 +0000[diff] [blame]290<div class="doc_code"><pre>
Reid Spencerca058542006-03-14 05:39:39 +0000[diff] [blame]291<b>#include</b> "<a href="http://llvm.org/doxygen/Pass_8h-source.html">llvm/Pass.h</a>"
292<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]293
Jonathan Mantonaff4a6a2004-06-30 18:10:30 +0000[diff] [blame]294<b>using namespace llvm;</b>
295
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]296<b>namespace</b> {
297 <b>struct Hello</b> : <b>public</b> <a href="#FunctionPass">FunctionPass</a> {
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]298 <b>virtual bool</b> <a href="#runOnFunction">runOnFunction</a>(Function &amp;F) {
Bill Wendling22e978a2006-12-07 20:04:42 +0000[diff] [blame]299 llvm::cerr &lt;&lt; "<i>Hello: </i>" &lt;&lt; F.getName() &lt;&lt; "\n";
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]300 <b>return false</b>;
301 }
302 };
303
Chris Lattnerb693cb02006-08-27 23:18:52 +0000[diff] [blame]304 RegisterPass&lt;Hello&gt; X("<i>hello</i>", "<i>Hello World Pass</i>");
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]305}
Jim Laskey575df8b2006-08-04 18:10:12 +0000[diff] [blame]306</pre></div>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]307
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]308<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]309command in the local directory and you should get a new
Reid Spencer4a1ab182005-01-11 05:16:23 +0000[diff] [blame]310"<tt>Debug/lib/Hello.so</tt> file. Note that everything in this file is
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]311contained in an anonymous namespace: this reflects the fact that passes are self
312contained units that do not need external interfaces (although they can have
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]313them) to be useful.</p>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]314
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]315</div>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]316
317<!-- ======================================================================= -->
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]318<div class="doc_subsection">
Chris Lattnerb693cb02006-08-27 23:18:52 +0000[diff] [blame]319 <a name="running">Running a pass with <tt>opt</tt></a>
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]320</div>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]321
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]322<div class="doc_text">
323
John Criswell2edea842004-01-26 21:26:54 +0000[diff] [blame]324<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]325<tt>opt</tt> command to run an LLVM program through your pass. Because you
Chris Lattnerb693cb02006-08-27 23:18:52 +0000[diff] [blame]326registered your pass with the <tt>RegisterPass</tt> template, you will be able to
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]327use the <tt>opt</tt> tool to access it, once loaded.</p>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]328
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]329<p>To test it, follow the example at the end of the <a
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]330href="GettingStarted.html">Getting Started Guide</a> to compile "Hello World" to
331LLVM. We can now run the bytecode file (<tt>hello.bc</tt>) for the program
332through our transformation like this (or course, any bytecode file will
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]333work):</p>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]334
Jim Laskey575df8b2006-08-04 18:10:12 +0000[diff] [blame]335<div class="doc_code"><pre>
Reid Spencer4a1ab182005-01-11 05:16:23 +0000[diff] [blame]336$ opt -load ../../../Debug/lib/Hello.so -hello &lt; hello.bc &gt; /dev/null
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]337Hello: __main
338Hello: puts
339Hello: main
Jim Laskey575df8b2006-08-04 18:10:12 +0000[diff] [blame]340</pre></div>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]341
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]342<p>The '<tt>-load</tt>' option specifies that '<tt>opt</tt>' should load your
343pass as a shared object, which makes '<tt>-hello</tt>' a valid command line
344argument (which is one reason you need to <a href="#registration">register your
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]345pass</a>). Because the hello pass does not modify the program in any
346interesting way, we just throw away the result of <tt>opt</tt> (sending it to
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]347<tt>/dev/null</tt>).</p>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]348
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]349<p>To see what happened to the other string you registered, try running
350<tt>opt</tt> with the <tt>--help</tt> option:</p>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]351
Jim Laskey575df8b2006-08-04 18:10:12 +0000[diff] [blame]352<div class="doc_code"><pre>
Reid Spencer4a1ab182005-01-11 05:16:23 +0000[diff] [blame]353$ opt -load ../../../Debug/lib/Hello.so --help
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]354OVERVIEW: llvm .bc -&gt; .bc modular optimizer
355
356USAGE: opt [options] &lt;input bytecode&gt;
357
358OPTIONS:
359 Optimizations available:
360...
361 -funcresolve - Resolve Functions
362 -gcse - Global Common Subexpression Elimination
363 -globaldce - Dead Global Elimination
364 <b>-hello - Hello World Pass</b>
Chris Lattner216c7b82003-09-10 05:29:43 +0000[diff] [blame]365 -indvars - Canonicalize Induction Variables
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]366 -inline - Function Integration/Inlining
367 -instcombine - Combine redundant instructions
368...
Jim Laskey575df8b2006-08-04 18:10:12 +0000[diff] [blame]369</pre></div>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]370
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]371<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]372documentation to users of <tt>opt</tt>. Now that you have a working pass, you
373would go ahead and make it do the cool transformations you want. Once you get
374it all working and tested, it may become useful to find out how fast your pass
375is. The <a href="#passManager"><tt>PassManager</tt></a> provides a nice command
376line option (<tt>--time-passes</tt>) that allows you to get information about
377the execution time of your pass along with the other passes you queue up. For
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]378example:</p>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]379
Jim Laskey575df8b2006-08-04 18:10:12 +0000[diff] [blame]380<div class="doc_code"><pre>
Reid Spencer4a1ab182005-01-11 05:16:23 +0000[diff] [blame]381$ 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]382Hello: __main
383Hello: puts
384Hello: main
385===============================================================================
386 ... Pass execution timing report ...
387===============================================================================
388 Total Execution Time: 0.02 seconds (0.0479059 wall clock)
389
390 ---User Time--- --System Time-- --User+System-- ---Wall Time--- --- Pass Name ---
391 0.0100 (100.0%) 0.0000 ( 0.0%) 0.0100 ( 50.0%) 0.0402 ( 84.0%) Bytecode Writer
392 0.0000 ( 0.0%) 0.0100 (100.0%) 0.0100 ( 50.0%) 0.0031 ( 6.4%) Dominator Set Construction
393 0.0000 ( 0.0%) 0.0000 ( 0.0%) 0.0000 ( 0.0%) 0.0013 ( 2.7%) Module Verifier
394 <b> 0.0000 ( 0.0%) 0.0000 ( 0.0%) 0.0000 ( 0.0%) 0.0033 ( 6.9%) Hello World Pass</b>
395 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]396</pre></div>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]397
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]398<p>As you can see, our implementation above is pretty fast :). The additional
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]399passes listed are automatically inserted by the '<tt>opt</tt>' tool to verify
400that the LLVM emitted by your pass is still valid and well formed LLVM, which
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]401hasn't been broken somehow.</p>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]402
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]403<p>Now that you have seen the basics of the mechanics behind passes, we can talk
404about some more details of how they work and how to use them.</p>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]405
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]406</div>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]407
408<!-- *********************************************************************** -->
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]409<div class="doc_section">
410 <a name="passtype">Pass classes and requirements</a>
411</div>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]412<!-- *********************************************************************** -->
413
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]414<div class="doc_text">
415
416<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]417decide what class you should subclass for your pass. The <a
418href="#basiccode">Hello World</a> example uses the <tt><a
419href="#FunctionPass">FunctionPass</a></tt> class for its implementation, but we
420did not discuss why or when this should occur. Here we talk about the classes
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]421available, from the most general to the most specific.</p>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]422
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]423<p>When choosing a superclass for your Pass, you should choose the <b>most
Chris Lattner8d8a9282002-08-22 19:21:04 +0000[diff] [blame]424specific</b> class possible, while still being able to meet the requirements
Misha Brukman7eb05a12003-08-18 14:43:39 +0000[diff] [blame]425listed. This gives the LLVM Pass Infrastructure information necessary to
Chris Lattner8d8a9282002-08-22 19:21:04 +0000[diff] [blame]426optimize how passes are run, so that the resultant compiler isn't unneccesarily
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]427slow.</p>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]428
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]429</div>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]430
Chris Lattner9720dda2002-09-25 22:31:38 +0000[diff] [blame]431<!-- ======================================================================= -->
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]432<div class="doc_subsection">
433 <a name="ImmutablePass">The <tt>ImmutablePass</tt> class</a>
434</div>
Chris Lattner9720dda2002-09-25 22:31:38 +0000[diff] [blame]435
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]436<div class="doc_text">
437
438<p>The most plain and boring type of pass is the "<tt><a
Reid Spencerca058542006-03-14 05:39:39 +0000[diff] [blame]439href="http://llvm.org/doxygen/classllvm_1_1ImmutablePass.html">ImmutablePass</a></tt>"
Chris Lattner9720dda2002-09-25 22:31:38 +0000[diff] [blame]440class. This pass type is used for passes that do not have to be run, do not
441change state, and never need to be updated. This is not a normal type of
442transformation or analysis, but can provide information about the current
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]443compiler configuration.</p>
Chris Lattner9720dda2002-09-25 22:31:38 +0000[diff] [blame]444
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]445<p>Although this pass class is very infrequently used, it is important for
Chris Lattner9720dda2002-09-25 22:31:38 +0000[diff] [blame]446providing information about the current target machine being compiled for, and
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]447other static information that can affect the various transformations.</p>
Chris Lattner9720dda2002-09-25 22:31:38 +0000[diff] [blame]448
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]449<p><tt>ImmutablePass</tt>es never invalidate other transformations, are never
450invalidated, and are never "run".</p>
Chris Lattner9720dda2002-09-25 22:31:38 +0000[diff] [blame]451
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]452</div>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]453
454<!-- ======================================================================= -->
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]455<div class="doc_subsection">
Chris Lattner3c11c042004-09-20 04:36:29 +0000[diff] [blame]456 <a name="ModulePass">The <tt>ModulePass</tt> class</a>
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]457</div>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]458
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]459<div class="doc_text">
460
461<p>The "<tt><a
Reid Spencerca058542006-03-14 05:39:39 +0000[diff] [blame]462href="http://llvm.org/doxygen/classllvm_1_1ModulePass.html">ModulePass</a></tt>"
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]463class is the most general of all superclasses that you can use. Deriving from
Chris Lattner3c11c042004-09-20 04:36:29 +0000[diff] [blame]464<tt>ModulePass</tt> indicates that your pass uses the entire program as a unit,
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]465refering to function bodies in no predictable order, or adding and removing
Chris Lattner3c11c042004-09-20 04:36:29 +0000[diff] [blame]466functions. Because nothing is known about the behavior of <tt>ModulePass</tt>
Devang Patel9b5e8e52007-04-16 21:28:14 +0000[diff] [blame]467subclasses, no optimization can be done for their execution. A module pass
468can use function level passes (e.g. dominators) using getAnalysis interface
469<tt> getAnalysis<DominatorTree>(Function)</tt>. </p>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]470
Chris Lattner3c11c042004-09-20 04:36:29 +0000[diff] [blame]471<p>To write a correct <tt>ModulePass</tt> subclass, derive from
472<tt>ModulePass</tt> and overload the <tt>runOnModule</tt> method with the
473following signature:</p>
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]474
475</div>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]476
477<!-- _______________________________________________________________________ -->
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]478<div class="doc_subsubsection">
Chris Lattner3c11c042004-09-20 04:36:29 +0000[diff] [blame]479 <a name="runOnModule">The <tt>runOnModule</tt> method</a>
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]480</div>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]481
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]482<div class="doc_text">
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]483
Jim Laskey575df8b2006-08-04 18:10:12 +0000[diff] [blame]484<div class="doc_code"><pre>
Chris Lattner3c11c042004-09-20 04:36:29 +0000[diff] [blame]485 <b>virtual bool</b> runOnModule(Module &amp;M) = 0;
Jim Laskey575df8b2006-08-04 18:10:12 +0000[diff] [blame]486</pre></div>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]487
John Criswella3f51102005-07-15 19:25:12 +0000[diff] [blame]488<p>The <tt>runOnModule</tt> method performs the interesting work of the pass.
489It should return true if the module was modified by the transformation and
490false otherwise.</p>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]491
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]492</div>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]493
494<!-- ======================================================================= -->
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]495<div class="doc_subsection">
Chris Lattner9e4be6f2004-09-18 06:39:35 +0000[diff] [blame]496 <a name="CallGraphSCCPass">The <tt>CallGraphSCCPass</tt> class</a>
497</div>
498
499<div class="doc_text">
500
501<p>The "<tt><a
Reid Spencerca058542006-03-14 05:39:39 +0000[diff] [blame]502href="http://llvm.org/doxygen/classllvm_1_1CallGraphSCCPass.html">CallGraphSCCPass</a></tt>"
Chris Lattner9e4be6f2004-09-18 06:39:35 +0000[diff] [blame]503is used by passes that need to traverse the program bottom-up on the call graph
504(callees before callers). Deriving from CallGraphSCCPass provides some
505mechanics for building and traversing the CallGraph, but also allows the system
506to optimize execution of CallGraphSCCPass's. If your pass meets the
507requirements outlined below, and doesn't meet the requirements of a <tt><a
508href="#FunctionPass">FunctionPass</a></tt> or <tt><a
509href="#BasicBlockPass">BasicBlockPass</a></tt>, you should derive from
510<tt>CallGraphSCCPass</tt>.</p>
511
512<p><b>TODO</b>: explain briefly what SCC, Tarjan's algo, and B-U mean.</p>
513
514<p>To be explicit, <tt>CallGraphSCCPass</tt> subclasses are:</p>
515
516<ol>
517
518<li>... <em>not allowed</em> to modify any <tt>Function</tt>s that are not in
519the current SCC.</li>
520
521<li>... <em>allowed</em> to inspect any Function's other than those in the
522current SCC and the direct callees of the SCC.</li>
523
524<li>... <em>required</em> to preserve the current CallGraph object, updating it
525to reflect any changes made to the program.</li>
526
527<li>... <em>not allowed</em> to add or remove SCC's from the current Module,
528though they may change the contents of an SCC.</li>
529
530<li>... <em>allowed</em> to add or remove global variables from the current
531Module.</li>
532
533<li>... <em>allowed</em> to maintain state across invocations of
534 <a href="#runOnSCC"><tt>runOnSCC</tt></a> (including global data).</li>
535</ol>
536
537<p>Implementing a <tt>CallGraphSCCPass</tt> is slightly tricky in some cases
538because it has to handle SCCs with more than one node in it. All of the virtual
539methods described below should return true if they modified the program, or
540false if they didn't.</p>
541
542</div>
543
544<!-- _______________________________________________________________________ -->
545<div class="doc_subsubsection">
Devang Patel40ec0802007-01-23 22:56:28 +0000[diff] [blame]546 <a name="doInitialization_scc">The <tt>doInitialization(CallGraph &amp;)</tt>
Chris Lattner9e4be6f2004-09-18 06:39:35 +0000[diff] [blame]547 method</a>
548</div>
549
550<div class="doc_text">
551
Jim Laskey575df8b2006-08-04 18:10:12 +0000[diff] [blame]552<div class="doc_code"><pre>
Devang Patel40ec0802007-01-23 22:56:28 +0000[diff] [blame]553 <b>virtual bool</b> doInitialization(CallGraph &amp;CG);
Jim Laskey575df8b2006-08-04 18:10:12 +0000[diff] [blame]554</pre></div>
Chris Lattner9e4be6f2004-09-18 06:39:35 +0000[diff] [blame]555
556<p>The <tt>doIninitialize</tt> method is allowed to do most of the things that
557<tt>CallGraphSCCPass</tt>'s are not allowed to do. They can add and remove
558functions, get pointers to functions, etc. The <tt>doInitialization</tt> method
559is designed to do simple initialization type of stuff that does not depend on
560the SCCs being processed. The <tt>doInitialization</tt> method call is not
561scheduled to overlap with any other pass executions (thus it should be very
562fast).</p>
563
564</div>
565
566<!-- _______________________________________________________________________ -->
567<div class="doc_subsubsection">
568 <a name="runOnSCC">The <tt>runOnSCC</tt> method</a>
569</div>
570
571<div class="doc_text">
572
Jim Laskey575df8b2006-08-04 18:10:12 +0000[diff] [blame]573<div class="doc_code"><pre>
Chris Lattner9e4be6f2004-09-18 06:39:35 +0000[diff] [blame]574 <b>virtual bool</b> runOnSCC(const std::vector&lt;CallGraphNode *&gt; &amp;SCCM) = 0;
Jim Laskey575df8b2006-08-04 18:10:12 +0000[diff] [blame]575</pre></div>
Chris Lattner9e4be6f2004-09-18 06:39:35 +0000[diff] [blame]576
577<p>The <tt>runOnSCC</tt> method performs the interesting work of the pass, and
578should return true if the module was modified by the transformation, false
579otherwise.</p>
580
581</div>
582
583<!-- _______________________________________________________________________ -->
584<div class="doc_subsubsection">
Devang Patel40ec0802007-01-23 22:56:28 +0000[diff] [blame]585 <a name="doFinalization_scc">The <tt>doFinalization(CallGraph
Chris Lattner9e4be6f2004-09-18 06:39:35 +0000[diff] [blame]586 &amp;)</tt> method</a>
587</div>
588
589<div class="doc_text">
590
Jim Laskey575df8b2006-08-04 18:10:12 +0000[diff] [blame]591<div class="doc_code"><pre>
Devang Patel40ec0802007-01-23 22:56:28 +0000[diff] [blame]592 <b>virtual bool</b> doFinalization(CallGraph &amp;CG);
Jim Laskey575df8b2006-08-04 18:10:12 +0000[diff] [blame]593</pre></div>
Chris Lattner9e4be6f2004-09-18 06:39:35 +0000[diff] [blame]594
595<p>The <tt>doFinalization</tt> method is an infrequently used method that is
596called when the pass framework has finished calling <a
597href="#runOnFunction"><tt>runOnFunction</tt></a> for every function in the
598program being compiled.</p>
599
600</div>
601
602<!-- ======================================================================= -->
603<div class="doc_subsection">
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]604 <a name="FunctionPass">The <tt>FunctionPass</tt> class</a>
605</div>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]606
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]607<div class="doc_text">
608
Chris Lattner3c11c042004-09-20 04:36:29 +0000[diff] [blame]609<p>In contrast to <tt>ModulePass</tt> subclasses, <tt><a
Reid Spencerca058542006-03-14 05:39:39 +0000[diff] [blame]610href="http://llvm.org/doxygen/classllvm_1_1Pass.html">FunctionPass</a></tt>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]611subclasses do have a predictable, local behavior that can be expected by the
612system. All <tt>FunctionPass</tt> execute on each function in the program
Misha Brukmanbe372b92003-08-21 22:14:26 +0000[diff] [blame]613independent of all of the other functions in the program.
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]614<tt>FunctionPass</tt>'s do not require that they are executed in a particular
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]615order, and <tt>FunctionPass</tt>'s do not modify external functions.</p>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]616
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]617<p>To be explicit, <tt>FunctionPass</tt> subclasses are not allowed to:</p>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]618
619<ol>
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]620<li>Modify a Function other than the one currently being processed.</li>
621<li>Add or remove Function's from the current Module.</li>
622<li>Add or remove global variables from the current Module.</li>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]623<li>Maintain state across invocations of
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]624 <a href="#runOnFunction"><tt>runOnFunction</tt></a> (including global data)</li>
625</ol>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]626
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]627<p>Implementing a <tt>FunctionPass</tt> is usually straightforward (See the <a
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]628href="#basiccode">Hello World</a> pass for example). <tt>FunctionPass</tt>'s
629may overload three virtual methods to do their work. All of these methods
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]630should return true if they modified the program, or false if they didn't.</p>
631
632</div>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]633
634<!-- _______________________________________________________________________ -->
Chris Lattner8e871652004-03-17 21:09:55 +0000[diff] [blame]635<div class="doc_subsubsection">
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]636 <a name="doInitialization_mod">The <tt>doInitialization(Module &amp;)</tt>
637 method</a>
638</div>
639
640<div class="doc_text">
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]641
Jim Laskey575df8b2006-08-04 18:10:12 +0000[diff] [blame]642<div class="doc_code"><pre>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]643 <b>virtual bool</b> doInitialization(Module &amp;M);
Jim Laskey575df8b2006-08-04 18:10:12 +0000[diff] [blame]644</pre></div>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]645
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]646<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]647<tt>FunctionPass</tt>'s are not allowed to do. They can add and remove
Chris Lattner5e08e70f2002-09-12 17:06:43 +0000[diff] [blame]648functions, get pointers to functions, etc. The <tt>doInitialization</tt> method
649is designed to do simple initialization type of stuff that does not depend on
650the functions being processed. The <tt>doInitialization</tt> method call is not
651scheduled to overlap with any other pass executions (thus it should be very
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]652fast).</p>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]653
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]654<p>A good example of how this method should be used is the <a
Reid Spencerca058542006-03-14 05:39:39 +0000[diff] [blame]655href="http://llvm.org/doxygen/LowerAllocations_8cpp-source.html">LowerAllocations</a>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]656pass. This pass converts <tt>malloc</tt> and <tt>free</tt> instructions into
Misha Brukmanbe372b92003-08-21 22:14:26 +0000[diff] [blame]657platform dependent <tt>malloc()</tt> and <tt>free()</tt> function calls. It
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]658uses the <tt>doInitialization</tt> method to get a reference to the malloc and
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]659free functions that it needs, adding prototypes to the module if necessary.</p>
660
661</div>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]662
663<!-- _______________________________________________________________________ -->
Chris Lattner8e871652004-03-17 21:09:55 +0000[diff] [blame]664<div class="doc_subsubsection">
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]665 <a name="runOnFunction">The <tt>runOnFunction</tt> method</a>
666</div>
667
668<div class="doc_text">
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]669
Jim Laskey575df8b2006-08-04 18:10:12 +0000[diff] [blame]670<div class="doc_code"><pre>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]671 <b>virtual bool</b> runOnFunction(Function &amp;F) = 0;
Jim Laskey575df8b2006-08-04 18:10:12 +0000[diff] [blame]672</pre></div><p>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]673
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]674<p>The <tt>runOnFunction</tt> method must be implemented by your subclass to do
675the transformation or analysis work of your pass. As usual, a true value should
676be returned if the function is modified.</p>
677
678</div>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]679
680<!-- _______________________________________________________________________ -->
Chris Lattner8e871652004-03-17 21:09:55 +0000[diff] [blame]681<div class="doc_subsubsection">
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]682 <a name="doFinalization_mod">The <tt>doFinalization(Module
683 &amp;)</tt> method</a>
684</div>
685
686<div class="doc_text">
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]687
Jim Laskey575df8b2006-08-04 18:10:12 +0000[diff] [blame]688<div class="doc_code"><pre>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]689 <b>virtual bool</b> doFinalization(Module &amp;M);
Jim Laskey575df8b2006-08-04 18:10:12 +0000[diff] [blame]690</pre></div>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]691
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]692<p>The <tt>doFinalization</tt> method is an infrequently used method that is
693called when the pass framework has finished calling <a
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]694href="#runOnFunction"><tt>runOnFunction</tt></a> for every function in the
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]695program being compiled.</p>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]696
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]697</div>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]698
699<!-- ======================================================================= -->
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]700<div class="doc_subsection">
Devang Patel1d3bb032007-03-19 22:21:25 +0000[diff] [blame]701 <a name="LoopPass">The <tt>LoopPass</tt> class </a>
702</div>
703
704<div class="doc_text">
705
706<p> All <tt>LoopPass</tt> execute on each loop in the function independent of
707all of the other loops in the function. <tt>LoopPass</tt> processes loops in
708loop nest order such that outer most loop is processed last. </p>
709
710<p> <tt>LoopPass</tt> subclasses are allowed to update loop nest using
711<tt>LPPassManager</tt> interface. Implementing a loop pass is usually
712straightforward. <tt>Looppass</tt>'s may overload three virtual methods to
713do their work. All these methods should return true if they modified the
714program, or false if they didn't. </p>
715</div>
716
717<!-- _______________________________________________________________________ -->
718<div class="doc_subsubsection">
719 <a name="doInitialization_loop">The <tt>doInitialization(Loop *,
720 LPPassManager &amp;)</tt>
721 method</a>
722</div>
723
724<div class="doc_text">
725
726<div class="doc_code"><pre>
727 <b>virtual bool</b> doInitialization(Loop *, LPPassManager &amp;LPM);
728</pre></div>
729
730The <tt>doInitialization</tt> method is designed to do simple initialization
731type of stuff that does not depend on the functions being processed. The
732<tt>doInitialization</tt> method call is not scheduled to overlap with any
733other pass executions (thus it should be very fast). LPPassManager
734interface should be used to access Function or Module level analysis
735information.</p>
736
737</div>
738
739
740<!-- _______________________________________________________________________ -->
741<div class="doc_subsubsection">
742 <a name="runOnLoop">The <tt>runOnLoop</tt> method</a>
743</div>
744
745<div class="doc_text">
746
747<div class="doc_code"><pre>
748 <b>virtual bool</b> runOnLoop(Loop *, LPPassManager &amp;LPM) = 0;
749</pre></div><p>
750
751<p>The <tt>runOnLoop</tt> method must be implemented by your subclass to do
752the transformation or analysis work of your pass. As usual, a true value should
753be returned if the function is modified. <tt>LPPassManager</tt> interface
754should be used to update loop nest.</p>
755
756</div>
757
758<!-- _______________________________________________________________________ -->
759<div class="doc_subsubsection">
760 <a name="doFinalization_loop">The <tt>doFinalization()</tt> method</a>
761</div>
762
763<div class="doc_text">
764
765<div class="doc_code"><pre>
766 <b>virtual bool</b> doFinalization();
767</pre></div>
768
769<p>The <tt>doFinalization</tt> method is an infrequently used method that is
770called when the pass framework has finished calling <a
771href="#runOnLoop"><tt>runOnLoop</tt></a> for every loop in the
772program being compiled. </p>
773
774</div>
775
776
777
778<!-- ======================================================================= -->
779<div class="doc_subsection">
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]780 <a name="BasicBlockPass">The <tt>BasicBlockPass</tt> class</a>
781</div>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]782
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]783<div class="doc_text">
784
785<p><tt>BasicBlockPass</tt>'s are just like <a
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]786href="#FunctionPass"><tt>FunctionPass</tt></a>'s, except that they must limit
787their scope of inspection and modification to a single basic block at a time.
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]788As such, they are <b>not</b> allowed to do any of the following:</p>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]789
790<ol>
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]791<li>Modify or inspect any basic blocks outside of the current one</li>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]792<li>Maintain state across invocations of
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]793 <a href="#runOnBasicBlock"><tt>runOnBasicBlock</tt></a></li>
Reid Spencera1799682004-12-11 05:12:57 +0000[diff] [blame]794<li>Modify the control flow graph (by altering terminator instructions)</li>
795<li>Any of the things forbidden for
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]796 <a href="#FunctionPass"><tt>FunctionPass</tt></a>es.</li>
797</ol>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]798
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]799<p><tt>BasicBlockPass</tt>es are useful for traditional local and "peephole"
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]800optimizations. They may override the same <a
Chris Lattner5e08e70f2002-09-12 17:06:43 +0000[diff] [blame]801href="#doInitialization_mod"><tt>doInitialization(Module &amp;)</tt></a> and <a
802href="#doFinalization_mod"><tt>doFinalization(Module &amp;)</tt></a> methods that <a
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]803href="#FunctionPass"><tt>FunctionPass</tt></a>'s have, but also have the following virtual methods that may also be implemented:</p>
804
805</div>
Chris Lattner5e08e70f2002-09-12 17:06:43 +0000[diff] [blame]806
807<!-- _______________________________________________________________________ -->
Chris Lattner8e871652004-03-17 21:09:55 +0000[diff] [blame]808<div class="doc_subsubsection">
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]809 <a name="doInitialization_fn">The <tt>doInitialization(Function
810 &amp;)</tt> method</a>
811</div>
812
813<div class="doc_text">
Chris Lattner5e08e70f2002-09-12 17:06:43 +0000[diff] [blame]814
Jim Laskey575df8b2006-08-04 18:10:12 +0000[diff] [blame]815<div class="doc_code"><pre>
Chris Lattner5e08e70f2002-09-12 17:06:43 +0000[diff] [blame]816 <b>virtual bool</b> doInitialization(Function &amp;F);
Jim Laskey575df8b2006-08-04 18:10:12 +0000[diff] [blame]817</pre></div>
Chris Lattner5e08e70f2002-09-12 17:06:43 +0000[diff] [blame]818
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]819<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]820<tt>BasicBlockPass</tt>'s are not allowed to do, but that
821<tt>FunctionPass</tt>'s can. The <tt>doInitialization</tt> method is designed
Reid Spencera1799682004-12-11 05:12:57 +0000[diff] [blame]822to do simple initialization that does not depend on the
Chris Lattner5e08e70f2002-09-12 17:06:43 +0000[diff] [blame]823BasicBlocks being processed. The <tt>doInitialization</tt> method call is not
824scheduled to overlap with any other pass executions (thus it should be very
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]825fast).</p>
Chris Lattner5e08e70f2002-09-12 17:06:43 +0000[diff] [blame]826
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]827</div>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]828
829<!-- _______________________________________________________________________ -->
Chris Lattner8e871652004-03-17 21:09:55 +0000[diff] [blame]830<div class="doc_subsubsection">
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]831 <a name="runOnBasicBlock">The <tt>runOnBasicBlock</tt> method</a>
832</div>
833
834<div class="doc_text">
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]835
Jim Laskey575df8b2006-08-04 18:10:12 +0000[diff] [blame]836<div class="doc_code"><pre>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]837 <b>virtual bool</b> runOnBasicBlock(BasicBlock &amp;BB) = 0;
Jim Laskey575df8b2006-08-04 18:10:12 +0000[diff] [blame]838</pre></div>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]839
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]840<p>Override this function to do the work of the <tt>BasicBlockPass</tt>. This
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]841function is not allowed to inspect or modify basic blocks other than the
842parameter, and are not allowed to modify the CFG. A true value must be returned
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]843if the basic block is modified.</p>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]844
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]845</div>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]846
Chris Lattner5e08e70f2002-09-12 17:06:43 +0000[diff] [blame]847<!-- _______________________________________________________________________ -->
Chris Lattner8e871652004-03-17 21:09:55 +0000[diff] [blame]848<div class="doc_subsubsection">
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]849 <a name="doFinalization_fn">The <tt>doFinalization(Function &amp;)</tt>
850 method</a>
851</div>
852
853<div class="doc_text">
Chris Lattner5e08e70f2002-09-12 17:06:43 +0000[diff] [blame]854
Jim Laskey575df8b2006-08-04 18:10:12 +0000[diff] [blame]855<div class="doc_code"><pre>
Chris Lattner5e08e70f2002-09-12 17:06:43 +0000[diff] [blame]856 <b>virtual bool</b> doFinalization(Function &amp;F);
Jim Laskey575df8b2006-08-04 18:10:12 +0000[diff] [blame]857</pre></div>
Chris Lattner5e08e70f2002-09-12 17:06:43 +0000[diff] [blame]858
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]859<p>The <tt>doFinalization</tt> method is an infrequently used method that is
860called when the pass framework has finished calling <a
Chris Lattner5e08e70f2002-09-12 17:06:43 +0000[diff] [blame]861href="#runOnBasicBlock"><tt>runOnBasicBlock</tt></a> for every BasicBlock in the
862program being compiled. This can be used to perform per-function
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]863finalization.</p>
Chris Lattner5e08e70f2002-09-12 17:06:43 +0000[diff] [blame]864
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]865</div>
Chris Lattner5e08e70f2002-09-12 17:06:43 +0000[diff] [blame]866
Brian Gaeke110f07b2003-07-17 18:53:20 +0000[diff] [blame]867<!-- ======================================================================= -->
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]868<div class="doc_subsection">
869 <a name="MachineFunctionPass">The <tt>MachineFunctionPass</tt> class</a>
870</div>
Brian Gaeke110f07b2003-07-17 18:53:20 +0000[diff] [blame]871
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]872<div class="doc_text">
873
Chris Lattner8e871652004-03-17 21:09:55 +0000[diff] [blame]874<p>A <tt>MachineFunctionPass</tt> is a part of the LLVM code generator that
875executes on the machine-dependent representation of each LLVM function in the
876program. A <tt>MachineFunctionPass</tt> is also a <tt>FunctionPass</tt>, so all
Brian Gaeke110f07b2003-07-17 18:53:20 +0000[diff] [blame]877the restrictions that apply to a <tt>FunctionPass</tt> also apply to it.
Chris Lattner8e871652004-03-17 21:09:55 +0000[diff] [blame]878<tt>MachineFunctionPass</tt>es also have additional restrictions. In particular,
879<tt>MachineFunctionPass</tt>es are not allowed to do any of the following:</p>
Brian Gaeke110f07b2003-07-17 18:53:20 +0000[diff] [blame]880
881<ol>
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]882<li>Modify any LLVM Instructions, BasicBlocks or Functions.</li>
883<li>Modify a MachineFunction other than the one currently being processed.</li>
884<li>Add or remove MachineFunctions from the current Module.</li>
885<li>Add or remove global variables from the current Module.</li>
886<li>Maintain state across invocations of <a
887href="#runOnMachineFunction"><tt>runOnMachineFunction</tt></a> (including global
888data)</li>
889</ol>
Brian Gaeke110f07b2003-07-17 18:53:20 +0000[diff] [blame]890
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]891</div>
Chris Lattner5e08e70f2002-09-12 17:06:43 +0000[diff] [blame]892
Brian Gaeke673ef4d2003-07-22 20:53:20 +0000[diff] [blame]893<!-- _______________________________________________________________________ -->
Chris Lattner8e871652004-03-17 21:09:55 +0000[diff] [blame]894<div class="doc_subsubsection">
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]895 <a name="runOnMachineFunction">The <tt>runOnMachineFunction(MachineFunction
896 &amp;MF)</tt> method</a>
897</div>
898
899<div class="doc_text">
Brian Gaeke673ef4d2003-07-22 20:53:20 +0000[diff] [blame]900
Jim Laskey575df8b2006-08-04 18:10:12 +0000[diff] [blame]901<div class="doc_code"><pre>
Brian Gaeke673ef4d2003-07-22 20:53:20 +0000[diff] [blame]902 <b>virtual bool</b> runOnMachineFunction(MachineFunction &amp;MF) = 0;
Jim Laskey575df8b2006-08-04 18:10:12 +0000[diff] [blame]903</pre></div>
Brian Gaeke673ef4d2003-07-22 20:53:20 +0000[diff] [blame]904
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]905<p><tt>runOnMachineFunction</tt> can be considered the main entry point of a
906<tt>MachineFunctionPass</tt>; that is, you should override this method to do the
907work of your <tt>MachineFunctionPass</tt>.</p>
Brian Gaeke673ef4d2003-07-22 20:53:20 +0000[diff] [blame]908
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]909<p>The <tt>runOnMachineFunction</tt> method is called on every
Brian Gaeke673ef4d2003-07-22 20:53:20 +0000[diff] [blame]910<tt>MachineFunction</tt> in a <tt>Module</tt>, so that the
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]911<tt>MachineFunctionPass</tt> may perform optimizations on the machine-dependent
912representation of the function. If you want to get at the LLVM <tt>Function</tt>
913for the <tt>MachineFunction</tt> you're working on, use
914<tt>MachineFunction</tt>'s <tt>getFunction()</tt> accessor method -- but
915remember, you may not modify the LLVM <tt>Function</tt> or its contents from a
916<tt>MachineFunctionPass</tt>.</p>
917
918</div>
Brian Gaeke673ef4d2003-07-22 20:53:20 +0000[diff] [blame]919
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]920<!-- *********************************************************************** -->
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]921<div class="doc_section">
922 <a name="registration">Pass registration</a>
923</div>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]924<!-- *********************************************************************** -->
925
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]926<div class="doc_text">
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]927
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]928<p>In the <a href="#basiccode">Hello World</a> example pass we illustrated how
929pass registration works, and discussed some of the reasons that it is used and
930what it does. Here we discuss how and why passes are registered.</p>
931
Chris Lattnerb693cb02006-08-27 23:18:52 +0000[diff] [blame]932<p>As we saw above, passes are registered with the <b><tt>RegisterPass</tt></b>
933template, which requires you to pass at least two
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]934parameters. The first parameter is the name of the pass that is to be used on
935the command line to specify that the pass should be added to a program (for
Chris Lattnerb693cb02006-08-27 23:18:52 +0000[diff] [blame]936example, with <tt>opt</tt> or <tt>bugpoint</tt>). The second argument is the
937name of the pass, which is to be used for the <tt>--help</tt> output of
938programs, as
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]939well as for debug output generated by the <tt>--debug-pass</tt> option.</p>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]940
Chris Lattnerb693cb02006-08-27 23:18:52 +0000[diff] [blame]941<p>If you want your pass to be easily dumpable, you should
942implement the virtual <tt>print</tt> method:</p>
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]943
944</div>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]945
946<!-- _______________________________________________________________________ -->
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]947<div class="doc_subsubsection">
948 <a name="print">The <tt>print</tt> method</a>
949</div>
950
951<div class="doc_text">
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]952
Jim Laskey575df8b2006-08-04 18:10:12 +0000[diff] [blame]953<div class="doc_code"><pre>
Bill Wendling22e978a2006-12-07 20:04:42 +0000[diff] [blame]954 <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]955</pre></div>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]956
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]957<p>The <tt>print</tt> method must be implemented by "analyses" in order to print
958a human readable version of the analysis results. This is useful for debugging
959an analysis itself, as well as for other people to figure out how an analysis
Chris Lattnerb693cb02006-08-27 23:18:52 +0000[diff] [blame]960works. Use the <tt>opt -analyze</tt> argument to invoke this method.</p>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]961
Bill Wendling22e978a2006-12-07 20:04:42 +0000[diff] [blame]962<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]963and 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]964program that has been analyzed. Note however that this pointer may be null in
965certain circumstances (such as calling the <tt>Pass::dump()</tt> from a
966debugger), so it should only be used to enhance debug output, it should not be
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]967depended on.</p>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]968
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]969</div>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]970
971<!-- *********************************************************************** -->
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]972<div class="doc_section">
973 <a name="interaction">Specifying interactions between passes</a>
974</div>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]975<!-- *********************************************************************** -->
976
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]977<div class="doc_text">
978
979<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]980that passes interact with each other correctly. Because <tt>PassManager</tt>
981tries to <a href="#passmanager">optimize the execution of passes</a> it must
982know how the passes interact with each other and what dependencies exist between
983the various passes. To track this, each pass can declare the set of passes that
984are required to be executed before the current pass, and the passes which are
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]985invalidated by the current pass.</p>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]986
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]987<p>Typically this functionality is used to require that analysis results are
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]988computed before your pass is run. Running arbitrary transformation passes can
989invalidate the computed analysis results, which is what the invalidation set
990specifies. If a pass does not implement the <tt><a
991href="#getAnalysisUsage">getAnalysisUsage</a></tt> method, it defaults to not
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]992having any prerequisite passes, and invalidating <b>all</b> other passes.</p>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]993
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]994</div>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]995
996<!-- _______________________________________________________________________ -->
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]997<div class="doc_subsubsection">
998 <a name="getAnalysisUsage">The <tt>getAnalysisUsage</tt> method</a>
999</div>
1000
1001<div class="doc_text">
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]1002
Jim Laskey575df8b2006-08-04 18:10:12 +0000[diff] [blame]1003<div class="doc_code"><pre>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]1004 <b>virtual void</b> getAnalysisUsage(AnalysisUsage &amp;Info) <b>const</b>;
Jim Laskey575df8b2006-08-04 18:10:12 +0000[diff] [blame]1005</pre></div>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]1006
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]1007<p>By implementing the <tt>getAnalysisUsage</tt> method, the required and
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]1008invalidated sets may be specified for your transformation. The implementation
1009should fill in the <tt><a
Reid Spencerca058542006-03-14 05:39:39 +0000[diff] [blame]1010href="http://llvm.org/doxygen/classllvm_1_1AnalysisUsage.html">AnalysisUsage</a></tt>
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]1011object with information about which passes are required and not invalidated. To
Chris Lattner8e871652004-03-17 21:09:55 +0000[diff] [blame]1012do this, a pass may call any of the following methods on the AnalysisUsage
1013object:</p>
1014</div>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]1015
Chris Lattner8e871652004-03-17 21:09:55 +0000[diff] [blame]1016<!-- _______________________________________________________________________ -->
1017<div class="doc_subsubsection">
1018 <a name="AU::addRequired">The <tt>AnalysisUsage::addRequired&lt;&gt;</tt> and <tt>AnalysisUsage::addRequiredTransitive&lt;&gt;</tt> methods</a>
1019</div>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]1020
Chris Lattner8e871652004-03-17 21:09:55 +0000[diff] [blame]1021<div class="doc_text">
1022<p>
Reid Spencera1799682004-12-11 05:12:57 +0000[diff] [blame]1023If your pass requires a previous pass to be executed (an analysis for example),
Chris Lattner8e871652004-03-17 21:09:55 +0000[diff] [blame]1024it can use one of these methods to arrange for it to be run before your pass.
1025LLVM has many different types of analyses and passes that can be required,
Reid Spencera1799682004-12-11 05:12:57 +0000[diff] [blame]1026spanning the range from <tt>DominatorSet</tt> to <tt>BreakCriticalEdges</tt>.
1027Requiring <tt>BreakCriticalEdges</tt>, for example, guarantees that there will
Chris Lattner8e871652004-03-17 21:09:55 +0000[diff] [blame]1028be no critical edges in the CFG when your pass has been run.
1029</p>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]1030
Chris Lattner8e871652004-03-17 21:09:55 +0000[diff] [blame]1031<p>
1032Some analyses chain to other analyses to do their job. For example, an <a
1033href="AliasAnalysis.html">AliasAnalysis</a> implementation is required to <a
1034href="AliasAnalysis.html#chaining">chain</a> to other alias analysis passes. In
1035cases where analyses chain, the <tt>addRequiredTransitive</tt> method should be
1036used instead of the <tt>addRequired</tt> method. This informs the PassManager
1037that the transitively required pass should be alive as long as the requiring
1038pass is.
1039</p>
1040</div>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]1041
Chris Lattner8e871652004-03-17 21:09:55 +0000[diff] [blame]1042<!-- _______________________________________________________________________ -->
1043<div class="doc_subsubsection">
1044 <a name="AU::addPreserved">The <tt>AnalysisUsage::addPreserved&lt;&gt;</tt> method</a>
1045</div>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]1046
Chris Lattner8e871652004-03-17 21:09:55 +0000[diff] [blame]1047<div class="doc_text">
1048<p>
1049One of the jobs of the PassManager is to optimize how and when analyses are run.
1050In particular, it attempts to avoid recomputing data unless it needs to. For
1051this reason, passes are allowed to declare that they preserve (i.e., they don't
1052invalidate) an existing analysis if it's available. For example, a simple
Reid Spencera1799682004-12-11 05:12:57 +0000[diff] [blame]1053constant folding pass would not modify the CFG, so it can't possibly affect the
Chris Lattner8e871652004-03-17 21:09:55 +0000[diff] [blame]1054results of dominator analysis. By default, all passes are assumed to invalidate
1055all others.
1056</p>
1057
1058<p>
1059The <tt>AnalysisUsage</tt> class provides several methods which are useful in
1060certain circumstances that are related to <tt>addPreserved</tt>. In particular,
1061the <tt>setPreservesAll</tt> method can be called to indicate that the pass does
1062not modify the LLVM program at all (which is true for analyses), and the
1063<tt>setPreservesCFG</tt> method can be used by transformations that change
1064instructions in the program but do not modify the CFG or terminator instructions
1065(note that this property is implicitly set for <a
1066href="#BasicBlockPass">BasicBlockPass</a>'s).
1067</p>
1068
1069<p>
1070<tt>addPreserved</tt> is particularly useful for transformations like
1071<tt>BreakCriticalEdges</tt>. This pass knows how to update a small set of loop
1072and dominator related analyses if they exist, so it can preserve them, despite
1073the fact that it hacks on the CFG.
1074</p>
1075</div>
1076
1077<!-- _______________________________________________________________________ -->
1078<div class="doc_subsubsection">
1079 <a name="AU::examples">Example implementations of <tt>getAnalysisUsage</tt></a>
1080</div>
1081
1082<div class="doc_text">
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]1083
Jim Laskey575df8b2006-08-04 18:10:12 +0000[diff] [blame]1084<div class="doc_code"><pre>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]1085 <i>// This is an example implementation from an analysis, which does not modify
1086 // the program at all, yet has a prerequisite.</i>
Reid Spencerca058542006-03-14 05:39:39 +0000[diff] [blame]1087 <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]1088 AU.setPreservesAll();
Reid Spencerca058542006-03-14 05:39:39 +0000[diff] [blame]1089 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]1090 }
Jim Laskey575df8b2006-08-04 18:10:12 +0000[diff] [blame]1091</pre></div>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]1092
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]1093<p>and:</p>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]1094
Jim Laskey575df8b2006-08-04 18:10:12 +0000[diff] [blame]1095<div class="doc_code"><pre>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]1096 <i>// This example modifies the program, but does not modify the CFG</i>
Reid Spencerca058542006-03-14 05:39:39 +0000[diff] [blame]1097 <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]1098 AU.setPreservesCFG();
Reid Spencerca058542006-03-14 05:39:39 +0000[diff] [blame]1099 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]1100 }
Jim Laskey575df8b2006-08-04 18:10:12 +0000[diff] [blame]1101</pre></div>
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]1102
1103</div>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]1104
1105<!-- _______________________________________________________________________ -->
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]1106<div class="doc_subsubsection">
Chris Lattner8e871652004-03-17 21:09:55 +0000[diff] [blame]1107 <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]1108</div>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]1109
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]1110<div class="doc_text">
1111
Chris Lattner8e871652004-03-17 21:09:55 +0000[diff] [blame]1112<p>The <tt>Pass::getAnalysis&lt;&gt;</tt> method is automatically inherited by
1113your class, providing you with access to the passes that you declared that you
1114required with the <a href="#getAnalysisUsage"><tt>getAnalysisUsage</tt></a>
1115method. It takes a single template argument that specifies which pass class you
1116want, and returns a reference to that pass. For example:</p>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]1117
Jim Laskey575df8b2006-08-04 18:10:12 +0000[diff] [blame]1118<div class="doc_code"><pre>
Chris Lattnerbaf3f622004-03-17 21:33:32 +0000[diff] [blame]1119 bool LICM::runOnFunction(Function &amp;F) {
Chris Lattner8e871652004-03-17 21:09:55 +0000[diff] [blame]1120 LoopInfo &amp;LI = getAnalysis&lt;LoopInfo&gt;();
1121 ...
1122 }
Jim Laskey575df8b2006-08-04 18:10:12 +0000[diff] [blame]1123</pre></div>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]1124
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]1125<p>This method call returns a reference to the pass desired. You may get a
1126runtime assertion failure if you attempt to get an analysis that you did not
1127declare as required in your <a
1128href="#getAnalysisUsage"><tt>getAnalysisUsage</tt></a> implementation. This
1129method can be called by your <tt>run*</tt> method implementation, or by any
Devang Patel9b5e8e52007-04-16 21:28:14 +0000[diff] [blame]1130other local method invoked by your <tt>run*</tt> method.
1131
1132A module level pass can use function level analysis info using this interface.
1133For example:</p>
1134
1135<div class="doc_code"><pre>
1136 bool ModuleLevelPass::runOnModule(Module &amp;M) {
1137 ...
Devang Patelf96c3622007-04-17 00:17:11 +0000[diff] [blame^]1138 DominatorTree &amp;DT = getAnalysis&lt;DominatorTree&gt;(Func);
Devang Patel9b5e8e52007-04-16 21:28:14 +0000[diff] [blame]1139 ...
1140 }
1141</pre></div>
1142
1143In above example, runOnFunction for DominatorTree is called by pass manager
1144before returning a reference to the desired pass.</p>
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]1145
Chris Lattner8e871652004-03-17 21:09:55 +0000[diff] [blame]1146<p>
1147If your pass is capable of updating analyses if they exist (e.g.,
1148<tt>BreakCriticalEdges</tt>, as described above), you can use the
1149<tt>getAnalysisToUpdate</tt> method, which returns a pointer to the analysis if
1150it is active. For example:</p>
1151
Jim Laskey575df8b2006-08-04 18:10:12 +0000[diff] [blame]1152<div class="doc_code"><pre>
Chris Lattner8e871652004-03-17 21:09:55 +0000[diff] [blame]1153 ...
1154 if (DominatorSet *DS = getAnalysisToUpdate&lt;DominatorSet&gt;()) {
1155 <i>// A DominatorSet is active. This code will update it.</i>
1156 }
1157 ...
Jim Laskey575df8b2006-08-04 18:10:12 +0000[diff] [blame]1158</pre></div>
Chris Lattner8e871652004-03-17 21:09:55 +0000[diff] [blame]1159
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]1160</div>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]1161
Chris Lattner8d8a9282002-08-22 19:21:04 +0000[diff] [blame]1162<!-- *********************************************************************** -->
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]1163<div class="doc_section">
1164 <a name="analysisgroup">Implementing Analysis Groups</a>
1165</div>
Chris Lattner8d8a9282002-08-22 19:21:04 +0000[diff] [blame]1166<!-- *********************************************************************** -->
1167
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]1168<div class="doc_text">
1169
1170<p>Now that we understand the basics of how passes are defined, how the are
1171used, 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]1172fancier. All of the pass relationships that we have seen so far are very
1173simple: one pass depends on one other specific pass to be run before it can run.
1174For many applications, this is great, for others, more flexibility is
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]1175required.</p>
Chris Lattner8d8a9282002-08-22 19:21:04 +0000[diff] [blame]1176
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]1177<p>In particular, some analyses are defined such that there is a single simple
Chris Lattner8d8a9282002-08-22 19:21:04 +0000[diff] [blame]1178interface to the analysis results, but multiple ways of calculating them.
1179Consider alias analysis for example. The most trivial alias analysis returns
1180"may alias" for any alias query. The most sophisticated analysis a
1181flow-sensitive, context-sensitive interprocedural analysis that can take a
1182significant amount of time to execute (and obviously, there is a lot of room
1183between these two extremes for other implementations). To cleanly support
1184situations like this, the LLVM Pass Infrastructure supports the notion of
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]1185Analysis Groups.</p>
1186
1187</div>
Chris Lattner8d8a9282002-08-22 19:21:04 +0000[diff] [blame]1188
1189<!-- _______________________________________________________________________ -->
Chris Lattner8e871652004-03-17 21:09:55 +0000[diff] [blame]1190<div class="doc_subsubsection">
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]1191 <a name="agconcepts">Analysis Group Concepts</a>
1192</div>
Chris Lattner8d8a9282002-08-22 19:21:04 +0000[diff] [blame]1193
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]1194<div class="doc_text">
1195
1196<p>An Analysis Group is a single simple interface that may be implemented by
Chris Lattner8d8a9282002-08-22 19:21:04 +0000[diff] [blame]1197multiple different passes. Analysis Groups can be given human readable names
1198just like passes, but unlike passes, they need not derive from the <tt>Pass</tt>
1199class. An analysis group may have one or more implementations, one of which is
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]1200the "default" implementation.</p>
Chris Lattner8d8a9282002-08-22 19:21:04 +0000[diff] [blame]1201
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]1202<p>Analysis groups are used by client passes just like other passes are: the
Chris Lattner8d8a9282002-08-22 19:21:04 +0000[diff] [blame]1203<tt>AnalysisUsage::addRequired()</tt> and <tt>Pass::getAnalysis()</tt> methods.
1204In order to resolve this requirement, the <a href="#passmanager">PassManager</a>
1205scans the available passes to see if any implementations of the analysis group
1206are available. If none is available, the default implementation is created for
1207the pass to use. All standard rules for <A href="#interaction">interaction
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]1208between passes</a> still apply.</p>
Chris Lattner8d8a9282002-08-22 19:21:04 +0000[diff] [blame]1209
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]1210<p>Although <a href="#registration">Pass Registration</a> is optional for normal
Chris Lattner8d8a9282002-08-22 19:21:04 +0000[diff] [blame]1211passes, all analysis group implementations must be registered, and must use the
1212<A href="#registerag"><tt>RegisterAnalysisGroup</tt></a> template to join the
1213implementation pool. Also, a default implementation of the interface
1214<b>must</b> be registered with <A
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]1215href="#registerag"><tt>RegisterAnalysisGroup</tt></a>.</p>
Chris Lattner8d8a9282002-08-22 19:21:04 +0000[diff] [blame]1216
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]1217<p>As a concrete example of an Analysis Group in action, consider the <a
Reid Spencerca058542006-03-14 05:39:39 +0000[diff] [blame]1218href="http://llvm.org/doxygen/classllvm_1_1AliasAnalysis.html">AliasAnalysis</a>
Chris Lattner8d8a9282002-08-22 19:21:04 +0000[diff] [blame]1219analysis group. The default implementation of the alias analysis interface (the
1220<tt><a
Reid Spencerca058542006-03-14 05:39:39 +0000[diff] [blame]1221href="http://llvm.org/doxygen/structBasicAliasAnalysis.html">basicaa</a></tt>
Chris Lattner8d8a9282002-08-22 19:21:04 +0000[diff] [blame]1222pass) just does a few simple checks that don't require significant analysis to
1223compute (such as: two different globals can never alias each other, etc).
1224Passes that use the <tt><a
Reid Spencerca058542006-03-14 05:39:39 +0000[diff] [blame]1225href="http://llvm.org/doxygen/classllvm_1_1AliasAnalysis.html">AliasAnalysis</a></tt>
Chris Lattner8d8a9282002-08-22 19:21:04 +0000[diff] [blame]1226interface (for example the <tt><a
Reid Spencerca058542006-03-14 05:39:39 +0000[diff] [blame]1227href="http://llvm.org/doxygen/structGCSE.html">gcse</a></tt> pass), do
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]1228not care which implementation of alias analysis is actually provided, they just
1229use the designated interface.</p>
Chris Lattner8d8a9282002-08-22 19:21:04 +0000[diff] [blame]1230
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]1231<p>From the user's perspective, commands work just like normal. Issuing the
Chris Lattner8d8a9282002-08-22 19:21:04 +0000[diff] [blame]1232command '<tt>opt -gcse ...</tt>' will cause the <tt>basicaa</tt> class to be
1233instantiated and added to the pass sequence. Issuing the command '<tt>opt
1234-somefancyaa -gcse ...</tt>' will cause the <tt>gcse</tt> pass to use the
1235<tt>somefancyaa</tt> alias analysis (which doesn't actually exist, it's just a
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]1236hypothetical example) instead.</p>
Chris Lattner8d8a9282002-08-22 19:21:04 +0000[diff] [blame]1237
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]1238</div>
Chris Lattner8d8a9282002-08-22 19:21:04 +0000[diff] [blame]1239
1240<!-- _______________________________________________________________________ -->
Chris Lattner8e871652004-03-17 21:09:55 +0000[diff] [blame]1241<div class="doc_subsubsection">
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]1242 <a name="registerag">Using <tt>RegisterAnalysisGroup</tt></a>
1243</div>
Chris Lattner8d8a9282002-08-22 19:21:04 +0000[diff] [blame]1244
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]1245<div class="doc_text">
1246
1247<p>The <tt>RegisterAnalysisGroup</tt> template is used to register the analysis
Chris Lattner8d8a9282002-08-22 19:21:04 +0000[diff] [blame]1248group itself as well as add pass implementations to the analysis group. First,
1249an analysis should be registered, with a human readable name provided for it.
1250Unlike registration of passes, there is no command line argument to be specified
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]1251for the Analysis Group Interface itself, because it is "abstract":</p>
Chris Lattner8d8a9282002-08-22 19:21:04 +0000[diff] [blame]1252
Jim Laskey575df8b2006-08-04 18:10:12 +0000[diff] [blame]1253<div class="doc_code"><pre>
Reid Spencerca058542006-03-14 05:39:39 +0000[diff] [blame]1254 <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]1255</pre></div>
Chris Lattner8d8a9282002-08-22 19:21:04 +0000[diff] [blame]1256
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]1257<p>Once the analysis is registered, passes can declare that they are valid
1258implementations of the interface by using the following code:</p>
Chris Lattner8d8a9282002-08-22 19:21:04 +0000[diff] [blame]1259
Jim Laskey575df8b2006-08-04 18:10:12 +0000[diff] [blame]1260<div class="doc_code"><pre>
Chris Lattner8d8a9282002-08-22 19:21:04 +0000[diff] [blame]1261<b>namespace</b> {
1262 //<i> Analysis Group implementations <b>must</b> be registered normally...</i>
Chris Lattnerb693cb02006-08-27 23:18:52 +0000[diff] [blame]1263 RegisterPass&lt;FancyAA&gt;
Chris Lattner8d8a9282002-08-22 19:21:04 +0000[diff] [blame]1264 B("<i>somefancyaa</i>", "<i>A more complex alias analysis implementation</i>");
1265
1266 //<i> Declare that we implement the AliasAnalysis interface</i>
Chris Lattnerea3c2b22006-08-28 00:45:38 +0000[diff] [blame]1267 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]1268}
Jim Laskey575df8b2006-08-04 18:10:12 +0000[diff] [blame]1269</pre></div>
Chris Lattner8d8a9282002-08-22 19:21:04 +0000[diff] [blame]1270
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]1271<p>This just shows a class <tt>FancyAA</tt> that is registered normally, then
1272uses the <tt>RegisterAnalysisGroup</tt> template to "join" the <tt><a
Reid Spencerca058542006-03-14 05:39:39 +0000[diff] [blame]1273href="http://llvm.org/doxygen/classllvm_1_1AliasAnalysis.html">AliasAnalysis</a></tt>
Chris Lattner8d8a9282002-08-22 19:21:04 +0000[diff] [blame]1274analysis group. Every implementation of an analysis group should join using
1275this template. A single pass may join multiple different analysis groups with
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]1276no problem.</p>
Chris Lattner8d8a9282002-08-22 19:21:04 +0000[diff] [blame]1277
Jim Laskey575df8b2006-08-04 18:10:12 +0000[diff] [blame]1278<div class="doc_code"><pre>
Chris Lattner8d8a9282002-08-22 19:21:04 +0000[diff] [blame]1279<b>namespace</b> {
1280 //<i> Analysis Group implementations <b>must</b> be registered normally...</i>
Chris Lattnerb693cb02006-08-27 23:18:52 +0000[diff] [blame]1281 RegisterPass&lt;<a href="http://llvm.org/doxygen/structBasicAliasAnalysis.html">BasicAliasAnalysis</a>&gt;
Chris Lattner8d8a9282002-08-22 19:21:04 +0000[diff] [blame]1282 D("<i>basicaa</i>", "<i>Basic Alias Analysis (default AA impl)</i>");
1283
1284 //<i> Declare that we implement the AliasAnalysis interface</i>
Chris Lattnerea3c2b22006-08-28 00:45:38 +0000[diff] [blame]1285 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]1286}
Jim Laskey575df8b2006-08-04 18:10:12 +0000[diff] [blame]1287</pre></div>
Chris Lattner8d8a9282002-08-22 19:21:04 +0000[diff] [blame]1288
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]1289<p>Here we show how the default implementation is specified (using the extra
Chris Lattner8d8a9282002-08-22 19:21:04 +0000[diff] [blame]1290argument to the <tt>RegisterAnalysisGroup</tt> template). There must be exactly
1291one default implementation available at all times for an Analysis Group to be
1292used. Here we declare that the <tt><a
Reid Spencerca058542006-03-14 05:39:39 +0000[diff] [blame]1293href="http://llvm.org/doxygen/structBasicAliasAnalysis.html">BasicAliasAnalysis</a></tt>
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]1294pass is the default implementation for the interface.</p>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]1295
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]1296</div>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]1297
1298<!-- *********************************************************************** -->
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]1299<div class="doc_section">
Tanya Lattnerfb966ba2004-11-19 01:25:14 +0000[diff] [blame]1300 <a name="passStatistics">Pass Statistics</a>
1301</div>
1302<!-- *********************************************************************** -->
1303
1304<div class="doc_text">
Tanya Lattner0b40ee62004-11-19 01:26:37 +0000[diff] [blame]1305<p>The <a
Reid Spencerca058542006-03-14 05:39:39 +0000[diff] [blame]1306href="http://llvm.org/doxygen/Statistic_8h-source.html"><tt>Statistic</tt></a>
John Criswell3e149a22005-11-28 23:25:41 +0000[diff] [blame]1307class is designed to be an easy way to expose various success
Tanya Lattnerfb966ba2004-11-19 01:25:14 +0000[diff] [blame]1308metrics from passes. These statistics are printed at the end of a
1309run, when the -stats command line option is enabled on the command
Tanya Lattner0b40ee62004-11-19 01:26:37 +0000[diff] [blame]1310line. 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]1311
1312</div>
1313
1314
1315<!-- *********************************************************************** -->
1316<div class="doc_section">
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]1317 <a name="passmanager">What PassManager does</a>
1318</div>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]1319<!-- *********************************************************************** -->
1320
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]1321<div class="doc_text">
1322
1323<p>The <a
Reid Spencerca058542006-03-14 05:39:39 +0000[diff] [blame]1324href="http://llvm.org/doxygen/PassManager_8h-source.html"><tt>PassManager</tt></a>
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]1325<a
Reid Spencerca058542006-03-14 05:39:39 +0000[diff] [blame]1326href="http://llvm.org/doxygen/classllvm_1_1PassManager.html">class</a>
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]1327takes a list of passes, ensures their <a href="#interaction">prerequisites</a>
1328are set up correctly, and then schedules passes to run efficiently. All of the
1329LLVM tools that run passes use the <tt>PassManager</tt> for execution of these
1330passes.</p>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]1331
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]1332<p>The <tt>PassManager</tt> does two main things to try to reduce the execution
1333time of a series of passes:</p>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]1334
1335<ol>
1336<li><b>Share analysis results</b> - The PassManager attempts to avoid
1337recomputing analysis results as much as possible. This means keeping track of
1338which analyses are available already, which analyses get invalidated, and which
1339analyses are needed to be run for a pass. An important part of work is that the
1340<tt>PassManager</tt> tracks the exact lifetime of all analysis results, allowing
1341it to <a href="#releaseMemory">free memory</a> allocated to holding analysis
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]1342results as soon as they are no longer needed.</li>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]1343
1344<li><b>Pipeline the execution of passes on the program</b> - The
1345<tt>PassManager</tt> attempts to get better cache and memory usage behavior out
1346of a series of passes by pipelining the passes together. This means that, given
1347a series of consequtive <a href="#FunctionPass"><tt>FunctionPass</tt></a>'s, it
1348will execute all of the <a href="#FunctionPass"><tt>FunctionPass</tt></a>'s on
1349the first function, then all of the <a
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]1350href="#FunctionPass"><tt>FunctionPass</tt></a>es on the second function,
1351etc... until the entire program has been run through the passes.
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]1352
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]1353<p>This improves the cache behavior of the compiler, because it is only touching
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]1354the LLVM program representation for a single function at a time, instead of
1355traversing the entire program. It reduces the memory consumption of compiler,
1356because, for example, only one <a
Reid Spencerca058542006-03-14 05:39:39 +0000[diff] [blame]1357href="http://llvm.org/doxygen/classllvm_1_1DominatorSet.html"><tt>DominatorSet</tt></a>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]1358needs to be calculated at a time. This also makes it possible some <a
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]1359href="#SMP">interesting enhancements</a> in the future.</p></li>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]1360
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]1361</ol>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]1362
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]1363<p>The effectiveness of the <tt>PassManager</tt> is influenced directly by how
1364much information it has about the behaviors of the passes it is scheduling. For
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]1365example, the "preserved" set is intentionally conservative in the face of an
1366unimplemented <a href="#getAnalysisUsage"><tt>getAnalysisUsage</tt></a> method.
1367Not implementing when it should be implemented will have the effect of not
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]1368allowing any analysis results to live across the execution of your pass.</p>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]1369
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]1370<p>The <tt>PassManager</tt> class exposes a <tt>--debug-pass</tt> command line
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]1371options that is useful for debugging pass execution, seeing how things work, and
1372diagnosing when you should be preserving more analyses than you currently are
1373(To get information about all of the variants of the <tt>--debug-pass</tt>
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]1374option, just type '<tt>opt --help-hidden</tt>').</p>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]1375
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]1376<p>By using the <tt>--debug-pass=Structure</tt> option, for example, we can see
1377how our <a href="#basiccode">Hello World</a> pass interacts with other passes.
1378Lets try it out with the <tt>gcse</tt> and <tt>licm</tt> passes:</p>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]1379
Jim Laskey575df8b2006-08-04 18:10:12 +0000[diff] [blame]1380<div class="doc_code"><pre>
Reid Spencer4a1ab182005-01-11 05:16:23 +0000[diff] [blame]1381$ 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]1382Module Pass Manager
1383 Function Pass Manager
1384 Dominator Set Construction
1385 Immediate Dominators Construction
1386 Global Common Subexpression Elimination
1387-- Immediate Dominators Construction
1388-- Global Common Subexpression Elimination
1389 Natural Loop Construction
1390 Loop Invariant Code Motion
1391-- Natural Loop Construction
1392-- Loop Invariant Code Motion
1393 Module Verifier
1394-- Dominator Set Construction
1395-- Module Verifier
1396 Bytecode Writer
1397--Bytecode Writer
Jim Laskey575df8b2006-08-04 18:10:12 +0000[diff] [blame]1398</pre></div>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]1399
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]1400<p>This output shows us when passes are constructed and when the analysis
1401results are known to be dead (prefixed with '<tt>--</tt>'). Here we see that
1402GCSE uses dominator and immediate dominator information to do its job. The LICM
1403pass uses natural loop information, which uses dominator sets, but not immediate
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]1404dominators. Because immediate dominators are no longer useful after the GCSE
1405pass, it is immediately destroyed. The dominator sets are then reused to
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]1406compute natural loop information, which is then used by the LICM pass.</p>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]1407
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]1408<p>After the LICM pass, the module verifier runs (which is automatically added
1409by the '<tt>opt</tt>' tool), which uses the dominator set to check that the
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]1410resultant LLVM code is well formed. After it finishes, the dominator set
1411information is destroyed, after being computed once, and shared by three
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]1412passes.</p>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]1413
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]1414<p>Lets see how this changes when we run the <a href="#basiccode">Hello
1415World</a> pass in between the two passes:</p>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]1416
Jim Laskey575df8b2006-08-04 18:10:12 +0000[diff] [blame]1417<div class="doc_code"><pre>
Reid Spencer4a1ab182005-01-11 05:16:23 +0000[diff] [blame]1418$ 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]1419Module Pass Manager
1420 Function Pass Manager
1421 Dominator Set Construction
1422 Immediate Dominators Construction
1423 Global Common Subexpression Elimination
1424<b>-- Dominator Set Construction</b>
1425-- Immediate Dominators Construction
1426-- Global Common Subexpression Elimination
1427<b> Hello World Pass
1428-- Hello World Pass
1429 Dominator Set Construction</b>
1430 Natural Loop Construction
1431 Loop Invariant Code Motion
1432-- Natural Loop Construction
1433-- Loop Invariant Code Motion
1434 Module Verifier
1435-- Dominator Set Construction
1436-- Module Verifier
1437 Bytecode Writer
1438--Bytecode Writer
1439Hello: __main
1440Hello: puts
1441Hello: main
Jim Laskey575df8b2006-08-04 18:10:12 +0000[diff] [blame]1442</pre></div>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]1443
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]1444<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]1445Dominator Set pass, even though it doesn't modify the code at all! To fix this,
1446we need to add the following <a
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]1447href="#getAnalysisUsage"><tt>getAnalysisUsage</tt></a> method to our pass:</p>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]1448
Jim Laskey575df8b2006-08-04 18:10:12 +0000[diff] [blame]1449<div class="doc_code"><pre>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]1450 <i>// We don't modify the program, so we preserve all analyses</i>
1451 <b>virtual void</b> getAnalysisUsage(AnalysisUsage &amp;AU) <b>const</b> {
1452 AU.setPreservesAll();
1453 }
Jim Laskey575df8b2006-08-04 18:10:12 +0000[diff] [blame]1454</pre></div>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]1455
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]1456<p>Now when we run our pass, we get this output:</p>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]1457
Jim Laskey575df8b2006-08-04 18:10:12 +0000[diff] [blame]1458<div class="doc_code"><pre>
Reid Spencer4a1ab182005-01-11 05:16:23 +0000[diff] [blame]1459$ 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]1460Pass Arguments: -gcse -hello -licm
1461Module Pass Manager
1462 Function Pass Manager
1463 Dominator Set Construction
1464 Immediate Dominators Construction
1465 Global Common Subexpression Elimination
1466-- Immediate Dominators Construction
1467-- Global Common Subexpression Elimination
1468 Hello World Pass
1469-- Hello World Pass
1470 Natural Loop Construction
1471 Loop Invariant Code Motion
1472-- Loop Invariant Code Motion
1473-- Natural Loop Construction
1474 Module Verifier
1475-- Dominator Set Construction
1476-- Module Verifier
1477 Bytecode Writer
1478--Bytecode Writer
1479Hello: __main
1480Hello: puts
1481Hello: main
Jim Laskey575df8b2006-08-04 18:10:12 +0000[diff] [blame]1482</pre></div>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]1483
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]1484<p>Which shows that we don't accidentally invalidate dominator information
1485anymore, and therefore do not have to compute it twice.</p>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]1486
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]1487</div>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]1488
1489<!-- _______________________________________________________________________ -->
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]1490<div class="doc_subsubsection">
1491 <a name="releaseMemory">The <tt>releaseMemory</tt> method</a>
1492</div>
1493
1494<div class="doc_text">
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]1495
Jim Laskey575df8b2006-08-04 18:10:12 +0000[diff] [blame]1496<div class="doc_code"><pre>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]1497 <b>virtual void</b> releaseMemory();
Jim Laskey575df8b2006-08-04 18:10:12 +0000[diff] [blame]1498</pre></div>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]1499
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]1500<p>The <tt>PassManager</tt> automatically determines when to compute analysis
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]1501results, and how long to keep them around for. Because the lifetime of the pass
1502object itself is effectively the entire duration of the compilation process, we
1503need some way to free analysis results when they are no longer useful. The
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]1504<tt>releaseMemory</tt> virtual method is the way to do this.</p>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]1505
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]1506<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]1507amount of state (for use by another pass which "requires" your pass and uses the
1508<a href="#getAnalysis">getAnalysis</a> method) you should implement
1509<tt>releaseMEmory</tt> to, well, release the memory allocated to maintain this
1510internal state. This method is called after the <tt>run*</tt> method for the
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]1511class, before the next call of <tt>run*</tt> in your pass.</p>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]1512
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]1513</div>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]1514
1515<!-- *********************************************************************** -->
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]1516<div class="doc_section">
Jim Laskey575df8b2006-08-04 18:10:12 +0000[diff] [blame]1517 <a name="registering">Registering dynamically loaded passes</a>
1518</div>
1519<!-- *********************************************************************** -->
1520
1521<div class="doc_text">
1522
1523<p><i>Size matters</i> when constructing production quality tools using llvm,
1524both for the purposes of distribution, and for regulating the resident code size
1525when running on the target system. Therefore, it becomes desirable to
1526selectively use some passes, while omitting others and maintain the flexibility
1527to change configurations later on. You want to be able to do all this, and,
1528provide feedback to the user. This is where pass registration comes into
1529play.</p>
1530
1531<p>The fundamental mechanisms for pass registration are the
1532<tt>MachinePassRegistry</tt> class and subclasses of
1533<tt>MachinePassRegistryNode</tt>.</p>
1534
1535<p>An instance of <tt>MachinePassRegistry</tt> is used to maintain a list of
1536<tt>MachinePassRegistryNode</tt> objects. This instance maintains the list and
1537communicates additions and deletions to the command line interface.</p>
1538
1539<p>An instance of <tt>MachinePassRegistryNode</tt> subclass is used to maintain
1540information provided about a particular pass. This information includes the
1541command line name, the command help string and the address of the function used
1542to create an instance of the pass. A global static constructor of one of these
1543instances <i>registers</i> with a corresponding <tt>MachinePassRegistry</tt>,
1544the static destructor <i>unregisters</i>. Thus a pass that is statically linked
1545in the tool will be registered at start up. A dynamically loaded pass will
1546register on load and unregister at unload.</p>
1547
1548</div>
1549
1550<!-- _______________________________________________________________________ -->
1551<div class="doc_subsection">
1552 <a name="registering_existing">Using existing registries</a>
1553</div>
1554
1555<div class="doc_text">
1556
1557<p>There are predefined registries to track instruction scheduling
1558(<tt>RegisterScheduler</tt>) and register allocation (<tt>RegisterRegAlloc</tt>)
1559machine passes. Here we will describe how to <i>register</i> a register
1560allocator machine pass.</p>
1561
1562<p>Implement your register allocator machine pass. In your register allocator
1563.cpp file add the following include;</p>
1564
1565<div class="doc_code"><pre>
Chris Lattner4bde9fb2006-08-11 16:37:02 +0000[diff] [blame]1566 #include "llvm/CodeGen/RegAllocRegistry.h"
Jim Laskey575df8b2006-08-04 18:10:12 +0000[diff] [blame]1567</pre></div>
1568
1569<p>Also in your register allocator .cpp file, define a creator function in the
1570form; </p>
1571
1572<div class="doc_code"><pre>
1573 FunctionPass *createMyRegisterAllocator() {
1574 return new MyRegisterAllocator();
1575 }
1576</pre></div>
1577
1578<p>Note that the signature of this function should match the type of
1579<tt>RegisterRegAlloc::FunctionPassCtor</tt>. In the same file add the
1580"installing" declaration, in the form;</p>
1581
1582<div class="doc_code"><pre>
1583 static RegisterRegAlloc myRegAlloc("myregalloc",
1584 " my register allocator help string",
1585 createMyRegisterAllocator);
1586</pre></div>
1587
1588<p>Note the two spaces prior to the help string produces a tidy result on the
1589--help query.</p>
1590
1591<div class="doc_code"><pre>
1592$ llc --help
1593 ...
1594 -regalloc - Register allocator to use: (default = linearscan)
1595 =linearscan - linear scan register allocator
1596 =local - local register allocator
1597 =simple - simple register allocator
1598 =myregalloc - my register allocator help string
1599 ...
1600</pre></div>
1601
1602<p>And that's it. The user is now free to use <tt>-regalloc=myregalloc</tt> as
1603an option. Registering instruction schedulers is similar except use the
Chris Lattner4bde9fb2006-08-11 16:37:02 +0000[diff] [blame]1604<tt>RegisterScheduler</tt> class. Note that the
1605<tt>RegisterScheduler::FunctionPassCtor</tt> is significantly different from
Jim Laskey575df8b2006-08-04 18:10:12 +0000[diff] [blame]1606<tt>RegisterRegAlloc::FunctionPassCtor</tt>.</p>
1607
1608<p>To force the load/linking of your register allocator into the llc/lli tools,
1609add your creator function's global declaration to "Passes.h" and add a "pseudo"
1610call line to <tt>llvm/Codegen/LinkAllCodegenComponents.h</tt>.</p>
1611
1612</div>
1613
1614
1615<!-- _______________________________________________________________________ -->
1616<div class="doc_subsection">
1617 <a name="registering_new">Creating new registries</a>
1618</div>
1619
1620<div class="doc_text">
1621
1622<p>The easiest way to get started is to clone one of the existing registries; we
1623recommend <tt>llvm/CodeGen/RegAllocRegistry.h</tt>. The key things to modify
1624are the class name and the <tt>FunctionPassCtor</tt> type.</p>
1625
1626<p>Then you need to declare the registry. Example: if your pass registry is
1627<tt>RegisterMyPasses</tt> then define;</p>
1628
1629<div class="doc_code"><pre>
1630MachinePassRegistry RegisterMyPasses::Registry;
1631</pre></div>
1632
1633<p>And finally, declare the command line option for your passes. Example:</p>
1634
1635<div class="doc_code"><pre>
1636 cl::opt&lt;RegisterMyPasses::FunctionPassCtor, false,
1637 RegisterPassParser&lt;RegisterMyPasses&gt &gt
1638 MyPassOpt("mypass",
1639 cl::init(&amp;createDefaultMyPass),
1640 cl::desc("my pass option help"));
1641</pre></div>
1642
1643<p>Here the command option is "mypass", with createDefaultMyPass as the default
1644creator.</p>
1645
1646</div>
1647
1648<!-- *********************************************************************** -->
1649<div class="doc_section">
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]1650 <a name="debughints">Using GDB with dynamically loaded passes</a>
1651</div>
Chris Lattner8a97c8a2002-09-06 02:02:58 +0000[diff] [blame]1652<!-- *********************************************************************** -->
1653
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]1654<div class="doc_text">
1655
1656<p>Unfortunately, using GDB with dynamically loaded passes is not as easy as it
Chris Lattner8a97c8a2002-09-06 02:02:58 +0000[diff] [blame]1657should be. First of all, you can't set a breakpoint in a shared object that has
1658not been loaded yet, and second of all there are problems with inlined functions
1659in shared objects. Here are some suggestions to debugging your pass with
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]1660GDB.</p>
Chris Lattner8a97c8a2002-09-06 02:02:58 +0000[diff] [blame]1661
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]1662<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]1663transformation invoked by <tt>opt</tt>, although nothing described here depends
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]1664on that.</p>
1665
1666</div>
Chris Lattner8a97c8a2002-09-06 02:02:58 +0000[diff] [blame]1667
1668<!-- _______________________________________________________________________ -->
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]1669<div class="doc_subsubsection">
1670 <a name="breakpoint">Setting a breakpoint in your pass</a>
1671</div>
Chris Lattner8a97c8a2002-09-06 02:02:58 +0000[diff] [blame]1672
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]1673<div class="doc_text">
1674
1675<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]1676
Jim Laskey575df8b2006-08-04 18:10:12 +0000[diff] [blame]1677<div class="doc_code"><pre>
Chris Lattner8a97c8a2002-09-06 02:02:58 +0000[diff] [blame]1678$ <b>gdb opt</b>
1679GNU gdb 5.0
1680Copyright 2000 Free Software Foundation, Inc.
1681GDB is free software, covered by the GNU General Public License, and you are
1682welcome to change it and/or distribute copies of it under certain conditions.
1683Type "show copying" to see the conditions.
1684There is absolutely no warranty for GDB. Type "show warranty" for details.
1685This GDB was configured as "sparc-sun-solaris2.6"...
1686(gdb)
Jim Laskey575df8b2006-08-04 18:10:12 +0000[diff] [blame]1687</pre></div>
Chris Lattner8a97c8a2002-09-06 02:02:58 +0000[diff] [blame]1688
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]1689<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]1690time to load. Be patient. Since we cannot set a breakpoint in our pass yet
1691(the shared object isn't loaded until runtime), we must execute the process, and
1692have it stop before it invokes our pass, but after it has loaded the shared
1693object. The most foolproof way of doing this is to set a breakpoint in
1694<tt>PassManager::run</tt> and then run the process with the arguments you
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]1695want:</p>
Chris Lattner8a97c8a2002-09-06 02:02:58 +0000[diff] [blame]1696
Jim Laskey575df8b2006-08-04 18:10:12 +0000[diff] [blame]1697<div class="doc_code"><pre>
Reid Spencer48cf6a62006-09-28 16:53:47 +0000[diff] [blame]1698(gdb) <b>break llvm::PassManager::run</b>
Chris Lattner8a97c8a2002-09-06 02:02:58 +0000[diff] [blame]1699Breakpoint 1 at 0x2413bc: file Pass.cpp, line 70.
Chris Lattner07275182005-04-21 04:52:37 +0000[diff] [blame]1700(gdb) <b>run test.bc -load $(LLVMTOP)/llvm/Debug/lib/[libname].so -[passoption]</b>
1701Starting program: opt test.bc -load $(LLVMTOP)/llvm/Debug/lib/[libname].so -[passoption]
Chris Lattner8a97c8a2002-09-06 02:02:58 +0000[diff] [blame]1702Breakpoint 1, PassManager::run (this=0xffbef174, M=@0x70b298) at Pass.cpp:70
170370 bool PassManager::run(Module &amp;M) { return PM-&gt;run(M); }
1704(gdb)
Jim Laskey575df8b2006-08-04 18:10:12 +0000[diff] [blame]1705</pre></div>
Chris Lattner8a97c8a2002-09-06 02:02:58 +0000[diff] [blame]1706
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]1707<p>Once the <tt>opt</tt> stops in the <tt>PassManager::run</tt> method you are
1708now free to set breakpoints in your pass so that you can trace through execution
1709or do other standard debugging stuff.</p>
Chris Lattner8a97c8a2002-09-06 02:02:58 +0000[diff] [blame]1710
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]1711</div>
Chris Lattner8a97c8a2002-09-06 02:02:58 +0000[diff] [blame]1712
1713<!-- _______________________________________________________________________ -->
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]1714<div class="doc_subsubsection">
1715 <a name="debugmisc">Miscellaneous Problems</a>
1716</div>
Chris Lattner8a97c8a2002-09-06 02:02:58 +0000[diff] [blame]1717
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]1718<div class="doc_text">
1719
1720<p>Once you have the basics down, there are a couple of problems that GDB has,
1721some with solutions, some without.</p>
Chris Lattner8a97c8a2002-09-06 02:02:58 +0000[diff] [blame]1722
1723<ul>
1724<li>Inline functions have bogus stack information. In general, GDB does a
1725pretty good job getting stack traces and stepping through inline functions.
1726When a pass is dynamically loaded however, it somehow completely loses this
1727capability. The only solution I know of is to de-inline a function (move it
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]1728from the body of a class to a .cpp file).</li>
Chris Lattner8a97c8a2002-09-06 02:02:58 +0000[diff] [blame]1729
1730<li>Restarting the program breaks breakpoints. After following the information
1731above, you have succeeded in getting some breakpoints planted in your pass. Nex
1732thing you know, you restart the program (i.e., you type '<tt>run</tt>' again),
1733and you start getting errors about breakpoints being unsettable. The only way I
1734have found to "fix" this problem is to <tt>delete</tt> the breakpoints that are
1735already set in your pass, run the program, and re-set the breakpoints once
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]1736execution stops in <tt>PassManager::run</tt>.</li>
Chris Lattner8a97c8a2002-09-06 02:02:58 +0000[diff] [blame]1737
1738</ul>
1739
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]1740<p>Hopefully these tips will help with common case debugging situations. If
1741you'd like to contribute some tips of your own, just contact <a
1742href="mailto:sabre@nondot.org">Chris</a>.</p>
Chris Lattner8a97c8a2002-09-06 02:02:58 +0000[diff] [blame]1743
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]1744</div>
Chris Lattner8a97c8a2002-09-06 02:02:58 +0000[diff] [blame]1745
1746<!-- *********************************************************************** -->
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]1747<div class="doc_section">
1748 <a name="future">Future extensions planned</a>
1749</div>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]1750<!-- *********************************************************************** -->
1751
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]1752<div class="doc_text">
1753
1754<p>Although the LLVM Pass Infrastructure is very capable as it stands, and does
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]1755some 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]1756where we are going:</p>
1757
1758</div>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]1759
1760<!-- _______________________________________________________________________ -->
Chris Lattner8e871652004-03-17 21:09:55 +0000[diff] [blame]1761<div class="doc_subsubsection">
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]1762 <a name="SMP">Multithreaded LLVM</a>
1763</div>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]1764
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]1765<div class="doc_text">
1766
1767<p>Multiple CPU machines are becoming more common and compilation can never be
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]1768fast enough: obviously we should allow for a multithreaded compiler. Because of
1769the semantics defined for passes above (specifically they cannot maintain state
1770across invocations of their <tt>run*</tt> methods), a nice clean way to
1771implement a multithreaded compiler would be for the <tt>PassManager</tt> class
Misha Brukman7fdaab42003-07-14 17:20:40 +0000[diff] [blame]1772to create multiple instances of each pass object, and allow the separate
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]1773instances to be hacking on different parts of the program at the same time.</p>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]1774
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]1775<p>This implementation would prevent each of the passes from having to implement
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]1776multithreaded constructs, requiring only the LLVM core to have locking in a few
1777places (for global resources). Although this is a simple extension, we simply
1778haven't had time (or multiprocessor machines, thus a reason) to implement this.
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]1779Despite that, we have kept the LLVM passes SMP ready, and you should too.</p>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]1780
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]1781<!-- *********************************************************************** -->
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]1782<hr>
1783<address>
1784 <a href="http://jigsaw.w3.org/css-validator/check/referer"><img
1785 src="http://jigsaw.w3.org/css-validator/images/vcss" alt="Valid CSS!"></a>
1786 <a href="http://validator.w3.org/check/referer"><img
1787 src="http://www.w3.org/Icons/valid-html401" alt="Valid HTML 4.01!" /></a>
Chris Lattner34ceebe2002-08-08 20:11:18 +0000[diff] [blame]1788
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]1789 <a href="mailto:sabre@nondot.org">Chris Lattner</a><br>
Reid Spencerca058542006-03-14 05:39:39 +0000[diff] [blame]1790 <a href="http://llvm.org">The LLVM Compiler Infrastructure</a><br>
Misha Brukmanf5edf1e2004-01-15 18:34:11 +0000[diff] [blame]1791 Last modified: $Date$
1792</address>
1793
1794</body>
1795</html>