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-</tr></table>
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+ <title>Writing an LLVM Pass</title>
+ <link rel="stylesheet" href="llvm.css" type="text/css">
+</head>
+<body>
+
+<h1>
+ Writing an LLVM Pass
+</h1>
<ol>
- <li><a href="#introduction">Introduction - What is a pass?</a>
+ <li><a href="#introduction">Introduction - What is a pass?</a></li>
<li><a href="#quickstart">Quick Start - Writing hello world</a>
<ul>
- <li><a href="#makefile">Setting up the build environment</a>
- <li><a href="#basiccode">Basic code required</a>
- <li><a href="#running">Running a pass with <tt>opt</tt>
- or <tt>analyze</tt></a>
- </ul>
+ <li><a href="#makefile">Setting up the build environment</a></li>
+ <li><a href="#basiccode">Basic code required</a></li>
+ <li><a href="#running">Running a pass with <tt>opt</tt></a></li>
+ </ul></li>
<li><a href="#passtype">Pass classes and requirements</a>
<ul>
- <li><a href="#ImmutablePass">The <tt>ImmutablePass</tt> class</a>
- <li><a href="#Pass">The <tt>Pass</tt> class</a>
+ <li><a href="#ImmutablePass">The <tt>ImmutablePass</tt> class</a></li>
+ <li><a href="#ModulePass">The <tt>ModulePass</tt> class</a>
<ul>
- <li><a href="#run">The <tt>run</tt> method</a>
- </ul>
+ <li><a href="#runOnModule">The <tt>runOnModule</tt> method</a></li>
+ </ul></li>
+ <li><a href="#CallGraphSCCPass">The <tt>CallGraphSCCPass</tt> class</a>
+ <ul>
+ <li><a href="#doInitialization_scc">The <tt>doInitialization(CallGraph
+ &)</tt> method</a></li>
+ <li><a href="#runOnSCC">The <tt>runOnSCC</tt> method</a></li>
+ <li><a href="#doFinalization_scc">The <tt>doFinalization(CallGraph
+ &)</tt> method</a></li>
+ </ul></li>
<li><a href="#FunctionPass">The <tt>FunctionPass</tt> class</a>
<ul>
<li><a href="#doInitialization_mod">The <tt>doInitialization(Module
- &)</tt> method</a>
- <li><a href="#runOnFunction">The <tt>runOnFunction</tt> method</a>
+ &)</tt> method</a></li>
+ <li><a href="#runOnFunction">The <tt>runOnFunction</tt> method</a></li>
<li><a href="#doFinalization_mod">The <tt>doFinalization(Module
- &)</tt> method</a>
- </ul>
+ &)</tt> method</a></li>
+ </ul></li>
+ <li><a href="#LoopPass">The <tt>LoopPass</tt> class</a>
+ <ul>
+ <li><a href="#doInitialization_loop">The <tt>doInitialization(Loop *,
+ LPPassManager &)</tt> method</a></li>
+ <li><a href="#runOnLoop">The <tt>runOnLoop</tt> method</a></li>
+ <li><a href="#doFinalization_loop">The <tt>doFinalization()
+ </tt> method</a></li>
+ </ul></li>
+ <li><a href="#RegionPass">The <tt>RegionPass</tt> class</a>
+ <ul>
+ <li><a href="#doInitialization_region">The <tt>doInitialization(Region *,
+ RGPassManager &)</tt> method</a></li>
+ <li><a href="#runOnRegion">The <tt>runOnRegion</tt> method</a></li>
+ <li><a href="#doFinalization_region">The <tt>doFinalization()
+ </tt> method</a></li>
+ </ul></li>
<li><a href="#BasicBlockPass">The <tt>BasicBlockPass</tt> class</a>
<ul>
<li><a href="#doInitialization_fn">The <tt>doInitialization(Function
- &)</tt> method</a>
- <li><a href="#runOnBasicBlock">The <tt>runOnBasicBlock</tt> method</a>
+ &)</tt> method</a></li>
+ <li><a href="#runOnBasicBlock">The <tt>runOnBasicBlock</tt>
+ method</a></li>
<li><a href="#doFinalization_fn">The <tt>doFinalization(Function
- &)</tt> method</a>
- </ul>
+ &)</tt> method</a></li>
+ </ul></li>
+ <li><a href="#MachineFunctionPass">The <tt>MachineFunctionPass</tt>
+ class</a>
+ <ul>
+ <li><a href="#runOnMachineFunction">The
+ <tt>runOnMachineFunction(MachineFunction &)</tt> method</a></li>
+ </ul></li>
</ul>
<li><a href="#registration">Pass Registration</a>
<ul>
- <li><a href="#print">The <tt>print</tt> method</a>
- </ul>
+ <li><a href="#print">The <tt>print</tt> method</a></li>
+ </ul></li>
<li><a href="#interaction">Specifying interactions between passes</a>
<ul>
- <li><a href="#getAnalysisUsage">The <tt>getAnalysisUsage</tt> method</a>
- <li><a href="#getAnalysis">The <tt>getAnalysis</tt> method</a>
- </ul>
+ <li><a href="#getAnalysisUsage">The <tt>getAnalysisUsage</tt>
+ method</a></li>
+ <li><a href="#AU::addRequired">The <tt>AnalysisUsage::addRequired<></tt> and <tt>AnalysisUsage::addRequiredTransitive<></tt> methods</a></li>
+ <li><a href="#AU::addPreserved">The <tt>AnalysisUsage::addPreserved<></tt> method</a></li>
+ <li><a href="#AU::examples">Example implementations of <tt>getAnalysisUsage</tt></a></li>
+ <li><a href="#getAnalysis">The <tt>getAnalysis<></tt> and
+<tt>getAnalysisIfAvailable<></tt> methods</a></li>
+ </ul></li>
<li><a href="#analysisgroup">Implementing Analysis Groups</a>
<ul>
- <li><a href="#agconcepts">Analysis Group Concepts</a>
- <li><a href="#registerag">Using <tt>RegisterAnalysisGroup</tt></a>
- </ul>
+ <li><a href="#agconcepts">Analysis Group Concepts</a></li>
+ <li><a href="#registerag">Using <tt>RegisterAnalysisGroup</tt></a></li>
+ </ul></li>
+ <li><a href="#passStatistics">Pass Statistics</a>
<li><a href="#passmanager">What PassManager does</a>
<ul>
- <li><a href="#releaseMemory">The <tt>releaseMemory</tt> method</a>
- </ul>
+ <li><a href="#releaseMemory">The <tt>releaseMemory</tt> method</a></li>
+ </ul></li>
+ <li><a href="#registering">Registering dynamically loaded passes</a>
+ <ul>
+ <li><a href="#registering_existing">Using existing registries</a></li>
+ <li><a href="#registering_new">Creating new registries</a></li>
+ </ul></li>
<li><a href="#debughints">Using GDB with dynamically loaded passes</a>
<ul>
- <li><a href="#breakpoint">Setting a breakpoint in your pass
- <li><a href="#debugmisc">Miscellaneous Problems
- </ul>
+ <li><a href="#breakpoint">Setting a breakpoint in your pass</a></li>
+ <li><a href="#debugmisc">Miscellaneous Problems</a></li>
+ </ul></li>
<li><a href="#future">Future extensions planned</a>
<ul>
- <li><a href="#SMP">Multithreaded LLVM</a>
- <li><a href="#ModuleSource">A new <tt>ModuleSource</tt> interface</a>
- <li><a href="#PassFunctionPass"><tt>Pass</tt>'s requiring <tt>FunctionPass</tt>'s</a>
- </ul>
-
- <p><b>Written by <a href="mailto:sabre@nondot.org">Chris Lattner</a></b><p>
-</ol><p>
-
+ <li><a href="#SMP">Multithreaded LLVM</a></li>
+ </ul></li>
+</ol>
+<div class="doc_author">
+ <p>Written by <a href="mailto:sabre@nondot.org">Chris Lattner</a> and
+ <a href="mailto:jlaskey@mac.com">Jim Laskey</a></p>
+</div>
<!-- *********************************************************************** -->
-<table width="100%" bgcolor="#330077" border=0 cellpadding=4 cellspacing=0>
-<tr><td align=center><font color="#EEEEFF" size=+2 face="Georgia,Palatino"><b>
-<a name="introduction">Introduction - What is a pass?
-</b></font></td></tr></table><ul>
+<h2>
+ <a name="introduction">Introduction - What is a pass?</a>
+</h2>
<!-- *********************************************************************** -->
-The LLVM Pass Framework is an important part of the LLVM system, because LLVM
-passes are where the interesting parts of the compiler exist. Passes perform
-the transformations and optimizations that make up the compiler, they build
-the analysis results that are used by these transformations, and they are, above
-all, a structuring technique for compiler code.<p>
-
-All LLVM passes are subclasses of the <tt><a
-href="http://llvm.cs.uiuc.edu/doxygen/classPass.html">Pass</a></tt> class, which
-implement functionality by overriding virtual methods inherited from
-<tt>Pass</tt>. Depending on how your pass works, you may be able to inherit
-from the <tt><a
-href="http://llvm.cs.uiuc.edu/doxygen/structFunctionPass.html">FunctionPass</a></tt>
-or <tt><a
-href="http://llvm.cs.uiuc.edu/doxygen/structBasicBlockPass.html">BasicBlockPass</a></tt>,
-which gives the system more information about what your pass does, and how it
-can be combined with other passes. One of the main features of the LLVM Pass
-Framework is that it schedules passes to run in an efficient way based on the
-constraints that your pass has.<p>
-
-We start by showing you how to construct a pass, everything from setting up the
-code, to compiling, loading, and executing it. After the basics are down, more
-advanced features are discussed.<p>
-
+<div>
+
+<p>The LLVM Pass Framework is an important part of the LLVM system, because LLVM
+passes are where most of the interesting parts of the compiler exist. Passes
+perform the transformations and optimizations that make up the compiler, they
+build the analysis results that are used by these transformations, and they are,
+above all, a structuring technique for compiler code.</p>
+
+<p>All LLVM passes are subclasses of the <tt><a
+href="http://llvm.org/doxygen/classllvm_1_1Pass.html">Pass</a></tt>
+class, which implement functionality by overriding virtual methods inherited
+from <tt>Pass</tt>. Depending on how your pass works, you should inherit from
+the <tt><a href="#ModulePass">ModulePass</a></tt>, <tt><a
+href="#CallGraphSCCPass">CallGraphSCCPass</a></tt>, <tt><a
+href="#FunctionPass">FunctionPass</a></tt>, or <tt><a
+href="#LoopPass">LoopPass</a></tt>, or <tt><a
+href="#RegionPass">RegionPass</a></tt>, or <tt><a
+href="#BasicBlockPass">BasicBlockPass</a></tt> classes, which gives the system
+more information about what your pass does, and how it can be combined with
+other passes. One of the main features of the LLVM Pass Framework is that it
+schedules passes to run in an efficient way based on the constraints that your
+pass meets (which are indicated by which class they derive from).</p>
+
+<p>We start by showing you how to construct a pass, everything from setting up
+the code, to compiling, loading, and executing it. After the basics are down,
+more advanced features are discussed.</p>
+
+</div>
<!-- *********************************************************************** -->
-</ul><table width="100%" bgcolor="#330077" border=0 cellpadding=4 cellspacing=0>
-<tr><td align=center><font color="#EEEEFF" size=+2 face="Georgia,Palatino"><b>
-<a name="quickstart">Quick Start - Writing hello world
-</b></font></td></tr></table><ul>
+<h2>
+ <a name="quickstart">Quick Start - Writing hello world</a>
+</h2>
<!-- *********************************************************************** -->
-Here we describe how to write the "hello world" of passes. The "Hello" pass is
-designed to simply print out the name of non-external functions that exist in
-the program being compiled. It does not modify the program at all, just
-inspects it. The source code and files for this pass are available in the LLVM
-source tree in the <tt>lib/Transforms/Hello</tt> directory.<p>
+<div>
+<p>Here we describe how to write the "hello world" of passes. The "Hello" pass
+is designed to simply print out the name of non-external functions that exist in
+the program being compiled. It does not modify the program at all, it just
+inspects it. The source code and files for this pass are available in the LLVM
+source tree in the <tt>lib/Transforms/Hello</tt> directory.</p>
<!-- ======================================================================= -->
-</ul><table width="100%" bgcolor="#441188" border=0 cellpadding=4 cellspacing=0>
-<tr><td> </td><td width="100%">
-<font color="#EEEEFF" face="Georgia,Palatino"><b>
-<a name="makefile">Setting up the build environment
-</b></font></td></tr></table><ul>
-
-First thing you need to do is create a new directory somewhere in the LLVM
-source base. For this example, we'll assume that you made
-"<tt>lib/Transforms/Hello</tt>". The first thing you must do is set up a build
-script (Makefile) that will compile the source code for the new pass. To do
-this, copy this into "<tt>Makefile</tt>":<p>
-
-</ul><hr><ul><pre>
+<h3>
+ <a name="makefile">Setting up the build environment</a>
+</h3>
+
+<div>
+
+ <p>First, configure and build LLVM. This needs to be done directly inside the
+ LLVM source tree rather than in a separate objects directory.
+ Next, you need to create a new directory somewhere in the LLVM source
+ base. For this example, we'll assume that you made
+ <tt>lib/Transforms/Hello</tt>. Finally, you must set up a build script
+ (Makefile) that will compile the source code for the new pass. To do this,
+ copy the following into <tt>Makefile</tt>:</p>
+ <hr>
+
+<div class="doc_code"><pre>
# Makefile for hello pass
-# Path to top level of LLVM heirarchy
+# Path to top level of LLVM hierarchy
LEVEL = ../../..
# Name of the library to build
-LIBRARYNAME = hello
+LIBRARYNAME = Hello
-# Build a dynamically loadable shared object
-SHARED_LIBRARY = 1
+# Make the shared library become a loadable module so the tools can
+# dlopen/dlsym on the resulting library.
+LOADABLE_MODULE = 1
# Include the makefile implementation stuff
include $(LEVEL)/Makefile.common
-</pre></ul><hr><ul><p>
+</pre></div>
+
+<p>This makefile specifies that all of the <tt>.cpp</tt> files in the current
+directory are to be compiled and linked together into a shared object
+<tt>$(LEVEL)/Debug+Asserts/lib/Hello.so</tt> that can be dynamically loaded by
+the <tt>opt</tt> or <tt>bugpoint</tt> tools via their <tt>-load</tt> options.
+If your operating system uses a suffix other than .so (such as windows or
+Mac OS/X), the appropriate extension will be used.</p>
-This makefile specifies that all of the <tt>.cpp</tt> files in the current
-directory are to be compiled and linked together into a
-<tt>lib/Debug/libhello.so</tt> shared object that can be dynamically loaded by
-the <tt>opt</tt> or <tt>analyze</tt> tools.<p>
+<p>If you are used CMake to build LLVM, see
+<a href="CMake.html#passdev">Developing an LLVM pass with CMake</a>.</p>
-Now that we have the build scripts set up, we just need to write the code for
-the pass itself.<p>
+<p>Now that we have the build scripts set up, we just need to write the code for
+the pass itself.</p>
+</div>
<!-- ======================================================================= -->
-</ul><table width="100%" bgcolor="#441188" border=0 cellpadding=4 cellspacing=0>
-<tr><td> </td><td width="100%">
-<font color="#EEEEFF" face="Georgia,Palatino"><b>
-<a name="basiccode">Basic code required
-</b></font></td></tr></table><ul>
+<h3>
+ <a name="basiccode">Basic code required</a>
+</h3>
-Now that we have a way to compile our new pass, we just have to write it. Start
-out with:<p>
+<div>
+<p>Now that we have a way to compile our new pass, we just have to write it.
+Start out with:</p>
+
+<div class="doc_code">
<pre>
-<b>#include</b> "<a href="http://llvm.cs.uiuc.edu/doxygen/Pass_8h-source.html">llvm/Pass.h</a>"
-<b>#include</b> "<a href="http://llvm.cs.uiuc.edu/doxygen/Function_8h-source.html">llvm/Function.h</a>"
+<b>#include</b> "<a href="http://llvm.org/doxygen/Pass_8h-source.html">llvm/Pass.h</a>"
+<b>#include</b> "<a href="http://llvm.org/doxygen/Function_8h-source.html">llvm/Function.h</a>"
+<b>#include</b> "<a href="http://llvm.org/doxygen/raw__ostream_8h.html">llvm/Support/raw_ostream.h</a>"
</pre>
+</div>
-Which are needed because we are writing a <tt><a
-href="http://llvm.cs.uiuc.edu/doxygen/classPass.html">Pass</a></tt>, and we are
-operating on <tt><a
-href="http://llvm.cs.uiuc.edu/doxygen/classFunction.html">Function</a></tt>'s.<p>
+<p>Which are needed because we are writing a <tt><a
+href="http://llvm.org/doxygen/classllvm_1_1Pass.html">Pass</a></tt>,
+we are operating on <tt><a
+href="http://llvm.org/doxygen/classllvm_1_1Function.html">Function</a></tt>'s,
+and we will be doing some printing.</p>
-Next we have:<p>
+<p>Next we have:</p>
+<div class="doc_code">
+<pre>
+<b>using namespace llvm;</b>
+</pre>
+</div>
+
+<p>... which is required because the functions from the include files
+live in the llvm namespace.</p>
+
+<p>Next we have:</p>
+
+<div class="doc_code">
<pre>
<b>namespace</b> {
-</pre><p>
+</pre>
+</div>
-... which starts out an anonymous namespace. Anonymous namespaces are to C++
+<p>... which starts out an anonymous namespace. Anonymous namespaces are to C++
what the "<tt>static</tt>" keyword is to C (at global scope). It makes the
-things declared inside of the anonymous namespace only visible to the current
+things declared inside of the anonymous namespace visible only to the current
file. If you're not familiar with them, consult a decent C++ book for more
-information.<p>
+information.</p>
-Next, we declare our pass itself:<p>
+<p>Next, we declare our pass itself:</p>
+<div class="doc_code">
<pre>
<b>struct</b> Hello : <b>public</b> <a href="#FunctionPass">FunctionPass</a> {
-</pre><p>
+</pre>
+</div>
-This declares a "<tt>Hello</tt>" class that is a subclass of <tt><a
-href="http://llvm.cs.uiuc.edu/doxygen/structFunctionPass.html">FunctionPass</a></tt>.
+
<p>This declares a "<tt>Hello</tt>" class that is a subclass of <tt><a
+href="http://llvm.org/doxygen/classllvm_1_1FunctionPass.html">FunctionPass</a></tt>.
The different builtin pass subclasses are described in detail <a
-href="#passtype">later</a>, but for now, know that <a href="#FunctionPass"><tt>FunctionPass</tt></a>'s
-operate a function at a time.<p>
+href="#passtype">later</a>, but for now, know that <a
+href="#FunctionPass"><tt>FunctionPass</tt></a>'s operate on a function at a
+time.</p>
+<div class="doc_code">
<pre>
- <b>virtual bool</b> <a href="#runOnFunction">runOnFunction</a>(Function &F) {
- std::cerr << "<i>Hello: </i>" << F.getName() << "\n";
+ static char ID;
+ Hello() : FunctionPass(ID) {}
+</pre>
+</div>
+
+<p>This declares pass identifier used by LLVM to identify pass. This allows LLVM
+to avoid using expensive C++ runtime information.</p>
+
+<div class="doc_code">
+<pre>
+ <b>virtual bool</b> <a href="#runOnFunction">runOnFunction</a>(Function &F) {
+ errs() << "<i>Hello: </i>";
+ errs().write_escaped(F.getName()) << "\n";
<b>return false</b>;
}
}; <i>// end of struct Hello</i>
+} <i>// end of anonymous namespace</i>
</pre>
+</div>
-We declare a "<a href="#runOnFunction"><tt>runOnFunction</tt></a>" method, which
-overloads an abstract virtual method inherited from <a
+<p>We declare a "<a href="#runOnFunction"><tt>runOnFunction</tt></a>" method,
+
which overloads an abstract virtual method inherited from <a
href="#FunctionPass"><tt>FunctionPass</tt></a>. This is where we are supposed
to do our thing, so we just print out our message with the name of each
-function.<p>
+function.</p>
+<div class="doc_code">
<pre>
- RegisterOpt<Hello> X("<i>hello</i>", "<i>Hello World Pass</i>");
-} <i>// end of anonymous namespace</i>
-</pre><p>
+char Hello::ID = 0;
+</pre>
+</div>
+
+<p>We initialize pass ID here. LLVM uses ID's address to identify a pass, so
+initialization value is not important.</p>
+
+<div class="doc_code">
+<pre>
+static RegisterPass<Hello> X("<i>hello</i>", "<i>Hello World Pass</i>",
+ false /* Only looks at CFG */,
+ false /* Analysis Pass */);
+</pre>
+</div>
-Lastly, we register our class <tt>Hello</tt>, giving it a command line argument
-"<tt>hello</tt>", and a name "<tt>Hello World Pass</tt>". There are several
-different ways of <a href="#registration">registering your pass</a>, depending
-on what it is to be used for. For "optimizations" we use the
-<tt>RegisterOpt</tt> template.<p>
+<p>Lastly, we <a href="#registration">register our class</a> <tt>Hello</tt>,
+giving it a command line argument "<tt>hello</tt>", and a name "<tt>Hello World
+Pass</tt>". The last two arguments describe its behavior: if a pass walks CFG
+without modifying it then the third argument is set to <tt>true</tt>; if a pass
+is an analysis pass, for example dominator tree pass, then <tt>true</tt> is
+supplied as the fourth argument.</p>
-As a whole, the <tt>.cpp</tt> file looks like:<p>
+<p>As a whole, the <tt>.cpp</tt> file looks like:</p>
+<div class="doc_code">
<pre>
-<b>#include</b> "<a href="http://llvm.cs.uiuc.edu/doxygen/Pass_8h-source.html">llvm/Pass.h</a>"
-<b>#include</b> "<a href="http://llvm.cs.uiuc.edu/doxygen/Function_8h-source.html">llvm/Function.h</a>"
+<b>#include</b> "<a href="http://llvm.org/doxygen/Pass_8h-source.html">llvm/Pass.h</a>"
+<b>#include</b> "<a href="http://llvm.org/doxygen/Function_8h-source.html">llvm/Function.h</a>"
+<b>#include</b> "<a href="http://llvm.org/doxygen/raw__ostream_8h.html">llvm/Support/raw_ostream.h</a>"
+
+<b>using namespace llvm;</b>
<b>namespace</b> {
<b>struct Hello</b> : <b>public</b> <a href="#FunctionPass">FunctionPass</a> {
- <b>virtual bool</b> <a href="#runOnFunction">runOnFunction</a>(Function &F) {
- std::cerr << "<i>Hello: </i>" << F.getName() << "\n";
+
+ static char ID;
+ Hello() : FunctionPass(ID) {}
+
+ <b>virtual bool</b> <a href="#runOnFunction">runOnFunction</a>(Function &F) {
+ errs() << "<i>Hello: </i>";
+ errs().write_escaped(F.getName()) << '\n';
<b>return false</b>;
}
+
};
-
- RegisterOpt<Hello> X("<i>hello</i>", "<i>Hello World Pass</i>");
}
-</pre><p>
+
+char Hello::ID = 0;
+static RegisterPass<Hello> X("hello", "Hello World Pass", false, false);
+</pre>
+</div>
-Now that it's all together, compile the file with a simple "<tt>gmake</tt>"
-command in the local directory and you should get a new
-"<tt>lib/Debug/libhello.so</tt> file. Note that everything in this file is
-contained in an anonymous namespace: this reflects the fact that passes are self
-contained units that do not need external interfaces (although they can have
-them) to be useful.<p>
+<p>Now that it's all together, compile the file with a simple "<tt>gmake</tt>"
+command in the local directory and you should get a new file
+"<tt>Debug+Asserts/lib/Hello.so</tt>" under the top level directory of the LLVM
+source tree (not in the local directory). Note that everything in this file is
+contained in an anonymous namespace — this reflects the fact that passes
+are self contained units that do not need external interfaces (although they can
+have them) to be useful.</p>
+</div>
<!-- ======================================================================= -->
-</ul><table width="100%" bgcolor="#441188" border=0 cellpadding=4 cellspacing=0>
-<tr><td> </td><td width="100%">
-<font color="#EEEEFF" face="Georgia,Palatino"><b>
-<a name="running">Running a pass with <tt>opt</tt> or <tt>analyze</tt>
-</b></font></td></tr></table><ul>
+<h3>
+ <a name="running">Running a pass with <tt>opt</tt></a>
+</h3>
+
+<div>
-Now that you have a brand new shiny <tt>.so</tt> file, we can use the
+<p>Now that you have a brand new shiny shared object file, we can use the
<tt>opt</tt> command to run an LLVM program through your pass. Because you
-registered your pass with the <tt>RegisterOpt</tt> template, you will be able to
-use the <tt>opt</tt> tool to access it, once loaded.<p>
+registered your pass with <tt>RegisterPass</tt>, you will be able to
+use the <tt>opt</tt> tool to access it, once loaded.</p>
-To test it, follow the example at the end of the <a
+
<p>To test it, follow the example at the end of the <a
href="GettingStarted.html">Getting Started Guide</a> to compile "Hello World" to
-LLVM. We can now run the bytecode file (<tt>hello.bc</tt>) for the program
-through our transformation like this (or course, any bytecode file will
-work):<p>
+LLVM. We can now run the bitcode file (<tt>hello.bc</tt>) for the program
+through our transformation like this (or course, any bitcode file will
+work):</p>
-<pre>
-$ opt -load ../../../lib/Debug/libhello.so -hello < hello.bc > /dev/null
+<div class="doc_code"><pre>
+$ opt -load ../../../Debug+Asserts/lib/Hello.so -hello < hello.bc > /dev/null
Hello: __main
Hello: puts
Hello: main
-</pre><p>
+</pre></div>
-The '<tt>-load</tt>' option specifies that '<tt>opt</tt>' should load your pass
-as a shared object, which makes '<tt>-hello</tt>' a valid command line argument
-(which is one reason you need to <a href="#registration">register your
+<p>The '<tt>-load</tt>' option specifies that '<tt>opt</tt>' should load your
+pass as a shared object, which makes '<tt>-hello</tt>' a valid command line
+
argument (which is one reason you need to <a href="#registration">register your
pass</a>). Because the hello pass does not modify the program in any
interesting way, we just throw away the result of <tt>opt</tt> (sending it to
-<tt>/dev/null</tt>).<p>
+<tt>/dev/null</tt>).</p>
-To see what happened to the other string you registered, try running
-<tt>opt</tt> with the <tt>--help</tt> option:<p>
+<p>To see what happened to the other string you registered, try running
+<tt>opt</tt> with the <tt>-help</tt> option:</p>
-<pre>
-$ opt -load ../../../lib/Debug/libhello.so --help
+<div class="doc_code"><pre>
+$ opt -load ../../../Debug+Asserts/lib/Hello.so -help
OVERVIEW: llvm .bc -> .bc modular optimizer
-USAGE: opt [options] <input bytecode>
+USAGE: opt [options] <input bitcode>
OPTIONS:
Optimizations available:
-gcse - Global Common Subexpression Elimination
-globaldce - Dead Global Elimination
<b>-hello - Hello World Pass</b>
- -indvars - Cannonicalize Induction Variables
+ -indvars - Canonicalize Induction Variables
-inline - Function Integration/Inlining
-instcombine - Combine redundant instructions
...
-</pre><p>
+</pre></div>
-The pass name get added as the information string for your pass, giving some
+<p>The pass name get added as the information string for your pass, giving some
documentation to users of <tt>opt</tt>. Now that you have a working pass, you
would go ahead and make it do the cool transformations you want. Once you get
it all working and tested, it may become useful to find out how fast your pass
is. The <a href="#passManager"><tt>PassManager</tt></a> provides a nice command
line option (<tt>--time-passes</tt>) that allows you to get information about
the execution time of your pass along with the other passes you queue up. For
-example:<p>
+example:</p>
-<pre>
-$ opt -load ../../../lib/Debug/libhello.so -hello -time-passes < hello.bc > /dev/null
+<div class="doc_code"><pre>
+$ opt -load ../../../Debug+Asserts/lib/Hello.so -hello -time-passes < hello.bc > /dev/null
Hello: __main
Hello: puts
Hello: main
Total Execution Time: 0.02 seconds (0.0479059 wall clock)
---User Time--- --System Time-- --User+System-- ---Wall Time--- --- Pass Name ---
- 0.0100 (100.0%) 0.0000 ( 0.0%) 0.0100 ( 50.0%) 0.0402 ( 84.0%) Bytecode Writer
+ 0.0100 (100.0%) 0.0000 ( 0.0%) 0.0100 ( 50.0%) 0.0402 ( 84.0%) Bitcode Writer
0.0000 ( 0.0%) 0.0100 (100.0%) 0.0100 ( 50.0%) 0.0031 ( 6.4%) Dominator Set Construction
0.0000 ( 0.0%) 0.0000 ( 0.0%) 0.0000 ( 0.0%) 0.0013 ( 2.7%) Module Verifier
<b> 0.0000 ( 0.0%) 0.0000 ( 0.0%) 0.0000 ( 0.0%) 0.0033 ( 6.9%) Hello World Pass</b>
0.0100 (100.0%) 0.0100 (100.0%) 0.0200 (100.0%) 0.0479 (100.0%) TOTAL
-</pre><p>
+</pre></div>
-As you can see, our implementation above is pretty fast :). The additional
+<p>As you can see, our implementation above is pretty fast :). The additional
passes listed are automatically inserted by the '<tt>opt</tt>' tool to verify
that the LLVM emitted by your pass is still valid and well formed LLVM, which
-hasn't been broken somehow.
+hasn't been broken somehow.</p>
-Now that you have seen the basics of the mechanics behind passes, we can talk
-about some more details of how they work and how to use them.<p>
+<p>Now that you have seen the basics of the mechanics behind passes, we can talk
+about some more details of how they work and how to use them.</p>
+</div>
+</div>
<!-- *********************************************************************** -->
-</ul><table width="100%" bgcolor="#330077" border=0 cellpadding=4 cellspacing=0>
-<tr><td align=center><font color="#EEEEFF" size=+2 face="Georgia,Palatino"><b>
-<a name="passtype">Pass classes and requirements
-</b></font></td></tr></table><ul>
+<h2>
+ <a name="passtype">Pass classes and requirements</a>
+</h2>
<!-- *********************************************************************** -->
-One of the first things that you should do when designing a new pass is to
+<div>
+
+<p>One of the first things that you should do when designing a new pass is to
decide what class you should subclass for your pass. The <a
href="#basiccode">Hello World</a> example uses the <tt><a
href="#FunctionPass">FunctionPass</a></tt> class for its implementation, but we
did not discuss why or when this should occur. Here we talk about the classes
-available, from the most general to the most specific.<p>
+available, from the most general to the most specific.</p>
-When choosing a superclass for your Pass, you should choose the <b>most
+<p>When choosing a superclass for your Pass, you should choose the <b>most
specific</b> class possible, while still being able to meet the requirements
-listed. This gives the LLVM Pass Infrastructure information neccesary to
-optimize how passes are run, so that the resultant compiler isn't unneccesarily
-slow.<p>
-
+listed. This gives the LLVM Pass Infrastructure information necessary to
+optimize how passes are run, so that the resultant compiler isn't unnecessarily
+slow.</p>
<!-- ======================================================================= -->
-</ul><table width="100%" bgcolor="#441188" border=0 cellpadding=4 cellspacing=0>
-<tr><td> </td><td width="100%">
-<font color="#EEEEFF" face="Georgia,Palatino"><b>
-<a name="ImmutablePass">The <tt>ImmutablePass</tt> class
-</b></font></td></tr></table><ul>
-
-The most plain and boring type of pass is the "<tt><a
-href="http://llvm.cs.uiuc.edu/doxygen/structImmutablePass.html">ImmutablePass</a></tt>"
+<h3>
+ <a name="ImmutablePass">The <tt>ImmutablePass</tt> class</a>
+</h3>
+
+<div>
+
+
<p>The most plain and boring type of pass is the "<tt><a
+href="http://llvm.org/doxygen/classllvm_1_1ImmutablePass.html">ImmutablePass</a></tt>"
class. This pass type is used for passes that do not have to be run, do not
change state, and never need to be updated. This is not a normal type of
transformation or analysis, but can provide information about the current
-compiler configuration.<p>
+compiler configuration.</p>
-Although this pass class is very infrequently used, it is important for
+<p>Although this pass class is very infrequently used, it is important for
providing information about the current target machine being compiled for, and
-other static information that can affect the various transformations.<p>
+other static information that can affect the various transformations.</p>
-<tt>ImmutablePass</tt>'s never invalidate other transformations, are never
-invalidated, and are never "run".<p>
+<p><tt>ImmutablePass</tt>es never invalidate other transformations, are never
+invalidated, and are never "run".</p>
+</div>
<!-- ======================================================================= -->
-</ul><table width="100%" bgcolor="#441188" border=0 cellpadding=4 cellspacing=0>
-<tr><td> </td><td width="100%">
-<font color="#EEEEFF" face="Georgia,Palatino"><b>
-<a name="Pass">The <tt>Pass</tt> class
-</b></font></td></tr></table><ul>
+<h3>
+ <a name="ModulePass">The <tt>ModulePass</tt> class</a>
+</h3>
+
+<div>
-The "<tt><a href="http://llvm.cs.uiuc.edu/doxygen/classPass.html">Pass</a></tt>"
+<p>The "<tt><a
+href="http://llvm.org/doxygen/classllvm_1_1ModulePass.html">ModulePass</a></tt>"
class is the most general of all superclasses that you can use. Deriving from
-<tt>Pass</tt> indicates that your pass uses the entire program as a unit,
-refering to function bodies in no predictable order, or adding and removing
-functions. Because nothing is known about the behavior of direct <tt>Pass</tt>
-subclasses, no optimization can be done for their execution.<p>
+<tt>ModulePass</tt> indicates that your pass uses the entire program as a unit,
+referring to function bodies in no predictable order, or adding and removing
+functions. Because nothing is known about the behavior of <tt>ModulePass</tt>
+subclasses, no optimization can be done for their execution.</p>
+
+<p>A module pass can use function level passes (e.g. dominators) using
+the getAnalysis interface
+<tt>getAnalysis<DominatorTree>(llvm::Function *)</tt> to provide the
+function to retrieve analysis result for, if the function pass does not require
+any module or immutable passes. Note that this can only be done for functions for which the
+analysis ran, e.g. in the case of dominators you should only ask for the
+DominatorTree for function definitions, not declarations.</p>
+
+<p>To write a correct <tt>ModulePass</tt> subclass, derive from
+<tt>ModulePass</tt> and overload the <tt>runOnModule</tt> method with the
+following signature:</p>
+
+<!-- _______________________________________________________________________ -->
+<h4>
+ <a name="runOnModule">The <tt>runOnModule</tt> method</a>
+</h4>
+
+<div>
+
+<div class="doc_code"><pre>
+ <b>virtual bool</b> runOnModule(Module &M) = 0;
+</pre></div>
+
+<p>The <tt>runOnModule</tt> method performs the interesting work of the pass.
+It should return true if the module was modified by the transformation and
+false otherwise.</p>
+
+</div>
+
+</div>
+
+<!-- ======================================================================= -->
+<h3>
+ <a name="CallGraphSCCPass">The <tt>CallGraphSCCPass</tt> class</a>
+</h3>
+
+<div>
+
+<p>The "<tt><a
+href="http://llvm.org/doxygen/classllvm_1_1CallGraphSCCPass.html">CallGraphSCCPass</a></tt>"
+is used by passes that need to traverse the program bottom-up on the call graph
+(callees before callers). Deriving from CallGraphSCCPass provides some
+mechanics for building and traversing the CallGraph, but also allows the system
+to optimize execution of CallGraphSCCPass's. If your pass meets the
+requirements outlined below, and doesn't meet the requirements of a <tt><a
+href="#FunctionPass">FunctionPass</a></tt> or <tt><a
+href="#BasicBlockPass">BasicBlockPass</a></tt>, you should derive from
+<tt>CallGraphSCCPass</tt>.</p>
+
+<p><b>TODO</b>: explain briefly what SCC, Tarjan's algo, and B-U mean.</p>
+
+<p>To be explicit, <tt>CallGraphSCCPass</tt> subclasses are:</p>
+
+<ol>
+
+<li>... <em>not allowed</em> to inspect or modify any <tt>Function</tt>s other
+than those in the current SCC and the direct callers and direct callees of the
+SCC.</li>
+
+<li>... <em>required</em> to preserve the current CallGraph object, updating it
+to reflect any changes made to the program.</li>
-To write a correct <tt>Pass</tt> subclass, derive from <tt>Pass</tt> and
-overload the <tt>run</tt> method with the following signature:<p>
+<li>... <em>not allowed</em> to add or remove SCC's from the current Module,
+though they may change the contents of an SCC.</li>
+
+<li>... <em>allowed</em> to add or remove global variables from the current
+Module.</li>
+
+<li>... <em>allowed</em> to maintain state across invocations of
+ <a href="#runOnSCC"><tt>runOnSCC</tt></a> (including global data).</li>
+</ol>
+
+<p>Implementing a <tt>CallGraphSCCPass</tt> is slightly tricky in some cases
+because it has to handle SCCs with more than one node in it. All of the virtual
+methods described below should return true if they modified the program, or
+false if they didn't.</p>
<!-- _______________________________________________________________________ -->
-</ul><h4><a name="run"><hr size=0>The <tt>run</tt> method</h4><ul>
+<h4>
+ <a name="doInitialization_scc">
+ The <tt>doInitialization(CallGraph &)</tt> method
+ </a>
+</h4>
+<div>
-<pre>
- <b>virtual bool</b> run(Module &M) = 0;
-</pre><p>
+<div class="doc_code"><pre>
+ <b>virtual bool</b> doInitialization(CallGraph &CG);
+</pre></div>
+
+<p>The <tt>doIninitialize</tt> method is allowed to do most of the things that
+<tt>CallGraphSCCPass</tt>'s are not allowed to do. They can add and remove
+functions, get pointers to functions, etc. The <tt>doInitialization</tt> method
+is designed to do simple initialization type of stuff that does not depend on
+the SCCs being processed. The <tt>doInitialization</tt> method call is not
+scheduled to overlap with any other pass executions (thus it should be very
+fast).</p>
+
+</div>
+
+<!-- _______________________________________________________________________ -->
+<h4>
+ <a name="runOnSCC">The <tt>runOnSCC</tt> method</a>
+</h4>
+
+<div>
+
+<div class="doc_code"><pre>
+ <b>virtual bool</b> runOnSCC(CallGraphSCC &SCC) = 0;
+</pre></div>
+
+<p>The <tt>runOnSCC</tt> method performs the interesting work of the pass, and
+should return true if the module was modified by the transformation, false
+otherwise.</p>
+
+</div>
+
+<!-- _______________________________________________________________________ -->
+<h4>
+ <a name="doFinalization_scc">
+ The <tt>doFinalization(CallGraph &)</tt> method
+ </a>
+</h4>
-The <tt>run</tt> method performs the interesting work of the pass, and should
-return true if the module was modified by the transformation, false
-otherwise.<p>
+<div>
+<div class="doc_code"><pre>
+ <b>virtual bool</b> doFinalization(CallGraph &CG);
+</pre></div>
+<p>The <tt>doFinalization</tt> method is an infrequently used method that is
+called when the pass framework has finished calling <a
+href="#runOnFunction"><tt>runOnFunction</tt></a> for every function in the
+program being compiled.</p>
+
+</div>
+
+</div>
<!-- ======================================================================= -->
-</ul><table width="100%" bgcolor="#441188" border=0 cellpadding=4 cellspacing=0>
-<tr><td> </td><td width="100%">
-<font color="#EEEEFF" face="Georgia,Palatino"><b>
-<a name="FunctionPass">The <tt>FunctionPass</tt> class
-</b></font></td></tr></table><ul>
-
-
In contrast to direct <tt>Pass</tt> subclasses, direct <tt><a
-href="http://llvm.cs.uiuc.edu/doxygen/classPass.html">FunctionPass</a></tt>
+<h3>
+ <a name="FunctionPass">The <tt>FunctionPass</tt> class</a>
+</h3>
+
+<div>
+
+
<p>In contrast to <tt>ModulePass</tt> subclasses, <tt><a
+href="http://llvm.org/doxygen/classllvm_1_1Pass.html">FunctionPass</a></tt>
subclasses do have a predictable, local behavior that can be expected by the
system. All <tt>FunctionPass</tt> execute on each function in the program
-independant of all of the other functions in the program.
+independent of all of the other functions in the program.
<tt>FunctionPass</tt>'s do not require that they are executed in a particular
-order, and <tt>FunctionPass</tt>'s do not modify external functions.<p>
+order, and <tt>FunctionPass</tt>'s do not modify external functions.</p>
-To be explicit, <tt>FunctionPass</tt> subclasses are not allowed to:<p>
+<p>To be explicit, <tt>FunctionPass</tt> subclasses are not allowed to:</p>
<ol>
-<li>Modify a Function other than the one currently being processed.
-<li>Add or remove Function's from the current Module.
-<li>Add or remove global variables from the current Module.
+<li>Modify a Function other than the one currently being processed.</li>
+<li>Add or remove Function's from the current Module.</li>
+<li>Add or remove global variables from the current Module.</li>
<li>Maintain state across invocations of
- <a href="#runOnFunction"><tt>runOnFunction</tt></a> (including global data)
-</ol><p>
+ <a href="#runOnFunction"><tt>runOnFunction</tt></a> (including global data)</li>
+</ol>
-Implementing a <tt>FunctionPass</tt> is usually straightforward (See the <a
+
<p>Implementing a <tt>FunctionPass</tt> is usually straightforward (See the <a
href="#basiccode">Hello World</a> pass for example). <tt>FunctionPass</tt>'s
may overload three virtual methods to do their work. All of these methods
-should return true if they modified the program, or false if they didn't.<p>
+should return true if they modified the program, or false if they didn't.</p>
<!-- _______________________________________________________________________ -->
-</ul><h4><a name="doInitialization_mod"><hr size=0>The
-<tt>doInitialization(Module &)</tt> method</h4><ul>
+<h4>
+ <a name="doInitialization_mod">
+ The <tt>doInitialization(Module &)</tt> method
+ </a>
+</h4>
-<pre>
+<div>
+
+<div class="doc_code"><pre>
<b>virtual bool</b> doInitialization(Module &M);
-</pre><p>
+</pre></div>
-The <tt>doIninitialize</tt> method is allowed to do most of the things that
+<p>The <tt>doIninitialize</tt> method is allowed to do most of the things that
<tt>FunctionPass</tt>'s are not allowed to do. They can add and remove
functions, get pointers to functions, etc. The <tt>doInitialization</tt> method
is designed to do simple initialization type of stuff that does not depend on
the functions being processed. The <tt>doInitialization</tt> method call is not
scheduled to overlap with any other pass executions (thus it should be very
-fast).<p>
+fast).</p>
-A good example of how this method should be used is the <a
-href="http://llvm.cs.uiuc.edu/doxygen/LowerAllocations_8cpp-source.html">LowerAllocations</a>
+
<p>A good example of how this method should be used is the <a
+href="http://llvm.org/doxygen/LowerAllocations_8cpp-source.html">LowerAllocations</a>
pass. This pass converts <tt>malloc</tt> and <tt>free</tt> instructions into
-platform dependant <tt>malloc()</tt> and <tt>free()</tt> function calls. It
+platform dependent <tt>malloc()</tt> and <tt>free()</tt> function calls. It
uses the <tt>doInitialization</tt> method to get a reference to the malloc and
-free functions that it needs, adding prototypes to the module if neccesary.<p>
+free functions that it needs, adding prototypes to the module if necessary.</p>
+
+</div>
<!-- _______________________________________________________________________ -->
-</ul><h4><a name="runOnFunction"><hr size=0>The <tt>runOnFunction</tt> method</h4><ul>
+<h4>
+ <a name="runOnFunction">The <tt>runOnFunction</tt> method</a>
+</h4>
-<pre>
+<div>
+
+<div class="doc_code"><pre>
<b>virtual bool</b> runOnFunction(Function &F) = 0;
-</pre><p>
+</pre></div><p>
+
+<p>The <tt>runOnFunction</tt> method must be implemented by your subclass to do
+the transformation or analysis work of your pass. As usual, a true value should
+be returned if the function is modified.</p>
-The <tt>runOnFunction</tt> method must be implemented by your subclass to do the
-transformation or analysis work of your pass. As usual, a true value should be
-returned if the function is modified.<p>
+</div>
<!-- _______________________________________________________________________ -->
-</ul><h4><a name="doFinalization_mod"><hr size=0>The <tt>doFinalization(Module &)</tt> method</h4><ul>
+<h4>
+ <a name="doFinalization_mod">
+ The <tt>doFinalization(Module &)</tt> method
+ </a>
+</h4>
-<pre>
+<div>
+
+<div class="doc_code"><pre>
<b>virtual bool</b> doFinalization(Module &M);
-</pre</p>
+</pre></div>
-The <tt>doFinalization</tt> method is an infrequently used method that is called
-when the pass framework has finished calling <a
+<p>The <tt>doFinalization</tt> method is an infrequently used method that is
+
called when the pass framework has finished calling <a
href="#runOnFunction"><tt>runOnFunction</tt></a> for every function in the
-program being compiled.<p>
+program being compiled.</p>
+
+</div>
+
+</div>
+
+<!-- ======================================================================= -->
+<h3>
+ <a name="LoopPass">The <tt>LoopPass</tt> class </a>
+</h3>
+
+<div>
+
+<p> All <tt>LoopPass</tt> execute on each loop in the function independent of
+all of the other loops in the function. <tt>LoopPass</tt> processes loops in
+loop nest order such that outer most loop is processed last. </p>
+
+<p> <tt>LoopPass</tt> subclasses are allowed to update loop nest using
+<tt>LPPassManager</tt> interface. Implementing a loop pass is usually
+straightforward. <tt>LoopPass</tt>'s may overload three virtual methods to
+do their work. All these methods should return true if they modified the
+program, or false if they didn't. </p>
+
+<!-- _______________________________________________________________________ -->
+<h4>
+ <a name="doInitialization_loop">
+ The <tt>doInitialization(Loop *,LPPassManager &)</tt> method
+ </a>
+</h4>
+
+<div>
+
+<div class="doc_code"><pre>
+ <b>virtual bool</b> doInitialization(Loop *, LPPassManager &LPM);
+</pre></div>
+
+<p>The <tt>doInitialization</tt> method is designed to do simple initialization
+type of stuff that does not depend on the functions being processed. The
+<tt>doInitialization</tt> method call is not scheduled to overlap with any
+other pass executions (thus it should be very fast). LPPassManager
+interface should be used to access Function or Module level analysis
+information.</p>
+
+</div>
+
+
+<!-- _______________________________________________________________________ -->
+<h4>
+ <a name="runOnLoop">The <tt>runOnLoop</tt> method</a>
+</h4>
+
+<div>
+
+<div class="doc_code"><pre>
+ <b>virtual bool</b> runOnLoop(Loop *, LPPassManager &LPM) = 0;
+</pre></div><p>
+
+<p>The <tt>runOnLoop</tt> method must be implemented by your subclass to do
+the transformation or analysis work of your pass. As usual, a true value should
+be returned if the function is modified. <tt>LPPassManager</tt> interface
+should be used to update loop nest.</p>
+
+</div>
+
+<!-- _______________________________________________________________________ -->
+<h4>
+ <a name="doFinalization_loop">The <tt>doFinalization()</tt> method</a>
+</h4>
+
+<div>
+
+<div class="doc_code"><pre>
+ <b>virtual bool</b> doFinalization();
+</pre></div>
+
+<p>The <tt>doFinalization</tt> method is an infrequently used method that is
+called when the pass framework has finished calling <a
+href="#runOnLoop"><tt>runOnLoop</tt></a> for every loop in the
+program being compiled. </p>
+
+</div>
+
+</div>
+
+<!-- ======================================================================= -->
+<h3>
+ <a name="RegionPass">The <tt>RegionPass</tt> class </a>
+</h3>
+
+<div>
+
+<p> <tt>RegionPass</tt> is similar to <a href="#LoopPass"><tt>LoopPass</tt></a>,
+but executes on each single entry single exit region in the function.
+<tt>RegionPass</tt> processes regions in nested order such that the outer most
+region is processed last. </p>
+
+<p> <tt>RegionPass</tt> subclasses are allowed to update the region tree by using
+the <tt>RGPassManager</tt> interface. You may overload three virtual methods of
+<tt>RegionPass</tt> to implement your own region pass. All these
+methods should return true if they modified the program, or false if they didn not.
+</p>
+
+<!-- _______________________________________________________________________ -->
+<h4>
+ <a name="doInitialization_region">
+ The <tt>doInitialization(Region *, RGPassManager &)</tt> method
+ </a>
+</h4>
+
+<div>
+
+<div class="doc_code"><pre>
+ <b>virtual bool</b> doInitialization(Region *, RGPassManager &RGM);
+</pre></div>
+
+<p>The <tt>doInitialization</tt> method is designed to do simple initialization
+type of stuff that does not depend on the functions being processed. The
+<tt>doInitialization</tt> method call is not scheduled to overlap with any
+other pass executions (thus it should be very fast). RPPassManager
+interface should be used to access Function or Module level analysis
+information.</p>
+</div>
+<!-- _______________________________________________________________________ -->
+<h4>
+ <a name="runOnRegion">The <tt>runOnRegion</tt> method</a>
+</h4>
+
+<div>
+
+<div class="doc_code"><pre>
+ <b>virtual bool</b> runOnRegion(Region *, RGPassManager &RGM) = 0;
+</pre></div><p>
+
+<p>The <tt>runOnRegion</tt> method must be implemented by your subclass to do
+the transformation or analysis work of your pass. As usual, a true value should
+be returned if the region is modified. <tt>RGPassManager</tt> interface
+should be used to update region tree.</p>
+
+</div>
+
+<!-- _______________________________________________________________________ -->
+<h4>
+ <a name="doFinalization_region">The <tt>doFinalization()</tt> method</a>
+</h4>
+
+<div>
+
+<div class="doc_code"><pre>
+ <b>virtual bool</b> doFinalization();
+</pre></div>
+
+<p>The <tt>doFinalization</tt> method is an infrequently used method that is
+called when the pass framework has finished calling <a
+href="#runOnRegion"><tt>runOnRegion</tt></a> for every region in the
+program being compiled. </p>
+
+</div>
+
+</div>
+
<!-- ======================================================================= -->
-</ul><table width="100%" bgcolor="#441188" border=0 cellpadding=4 cellspacing=0>
-<tr><td> </td><td width="100%">
-<font color="#EEEEFF" face="Georgia,Palatino"><b>
-<a name="BasicBlockPass">The <tt>BasicBlockPass</tt> class</a>
-</b></font></td></tr></table><ul>
+<h3>
+ <a name="BasicBlockPass">The <tt>BasicBlockPass</tt> class</a>
+</h3>
-<tt>BasicBlockPass</tt>'s are just like <a
+<div>
+
+<p><tt>BasicBlockPass</tt>'s are just like <a
href="#FunctionPass"><tt>FunctionPass</tt></a>'s, except that they must limit
their scope of inspection and modification to a single basic block at a time.
-As such, they are <b>not</b> allowed to do any of the following:<p>
+As such, they are <b>not</b> allowed to do any of the following:</p>
<ol>
-<li>Modify or inspect any basic blocks outside of the current one
+<li>Modify or inspect any basic blocks outside of the current one</li>
<li>Maintain state across invocations of
- <a href="#runOnBasicBlock"><tt>runOnBasicBlock</tt></a>
-<li>Modify the constrol flow graph (by altering terminator instructions)
-<li>Any of the things verboten for
- <a href="#FunctionPass"><tt>FunctionPass</tt></a>'s.
-</ol><p>
+ <a href="#runOnBasicBlock"><tt>runOnBasicBlock</tt></a></li>
+<li>Modify the control flow graph (by altering terminator instructions)</li>
+<li>Any of the things forbidden for
+ <a href="#FunctionPass"><tt>FunctionPass</tt></a>es.</li>
+</ol>
-<tt>BasicBlockPass</tt>'s are useful for traditional local and "peephole"
+<p><tt>BasicBlockPass</tt>es are useful for traditional local and "peephole"
optimizations. They may override the same <a
href="#doInitialization_mod"><tt>doInitialization(Module &)</tt></a> and <a
href="#doFinalization_mod"><tt>doFinalization(Module &)</tt></a> methods that <a
-href="#FunctionPass"><tt>FunctionPass</tt></a>'s have, but also have the following virtual methods that may also be implemented:<p>
+href="#FunctionPass"><tt>FunctionPass</tt></a>'s have, but also have the following virtual methods that may also be implemented:</p>
<!-- _______________________________________________________________________ -->
-</ul><h4><a name="doInitialization_fn"><hr size=0>The
-<tt>doInitialization(Function &)</tt> method</h4><ul>
+<h4>
+ <a name="doInitialization_fn">
+ The <tt>doInitialization(Function &)</tt> method
+ </a>
+</h4>
-<pre>
+<div>
+
+<div class="doc_code"><pre>
<b>virtual bool</b> doInitialization(Function &F);
-</pre><p>
+</pre></div>
-The <tt>doIninitialize</tt> method is allowed to do most of the things that
+<p>The <tt>doIninitialize</tt> method is allowed to do most of the things that
<tt>BasicBlockPass</tt>'s are not allowed to do, but that
<tt>FunctionPass</tt>'s can. The <tt>doInitialization</tt> method is designed
-to do simple initialization type of stuff that does not depend on the
+to do simple initialization that does not depend on the
BasicBlocks being processed. The <tt>doInitialization</tt> method call is not
scheduled to overlap with any other pass executions (thus it should be very
-fast).<p>
+fast).</p>
+</div>
<!-- _______________________________________________________________________ -->
-</ul><h4><a name="runOnBasicBlock"><hr size=0>The <tt>runOnBasicBlock</tt> method</h4><ul>
+<h4>
+ <a name="runOnBasicBlock">The <tt>runOnBasicBlock</tt> method</a>
+</h4>
-<pre>
+<div>
+
+<div class="doc_code"><pre>
<b>virtual bool</b> runOnBasicBlock(BasicBlock &BB) = 0;
-</pre><p>
+</pre></div>
-Override this function to do the work of the <tt>BasicBlockPass</tt>. This
+<p>Override this function to do the work of the <tt>BasicBlockPass</tt>. This
function is not allowed to inspect or modify basic blocks other than the
parameter, and are not allowed to modify the CFG. A true value must be returned
-if the basic block is modified.<p>
+if the basic block is modified.</p>
+</div>
<!-- _______________________________________________________________________ -->
-</ul><h4><a name="doFinalization_fn"><hr size=0>The <tt>doFinalization(Function
-&)</tt> method</h4><ul>
+<h4>
+ <a name="doFinalization_fn">
+ The <tt>doFinalization(Function &)</tt> method
+ </a>
+</h4>
-<pre>
+<div>
+
+<div class="doc_code"><pre>
<b>virtual bool</b> doFinalization(Function &F);
-</pre</p>
+</pre></div>
-The <tt>doFinalization</tt> method is an infrequently used method that is called
-when the pass framework has finished calling <a
+<p>The <tt>doFinalization</tt> method is an infrequently used method that is
+
called when the pass framework has finished calling <a
href="#runOnBasicBlock"><tt>runOnBasicBlock</tt></a> for every BasicBlock in the
program being compiled. This can be used to perform per-function
-finalization.<p>
+finalization.</p>
+
+</div>
+
+</div>
+
+<!-- ======================================================================= -->
+<h3>
+ <a name="MachineFunctionPass">The <tt>MachineFunctionPass</tt> class</a>
+</h3>
+
+<div>
+
+<p>A <tt>MachineFunctionPass</tt> is a part of the LLVM code generator that
+executes on the machine-dependent representation of each LLVM function in the
+program.</p>
+
+<p>Code generator passes are registered and initialized specially by
+<tt>TargetMachine::addPassesToEmitFile</tt> and similar routines, so they
+cannot generally be run from the <tt>opt</tt> or <tt>bugpoint</tt>
+commands.</p>
+
+<p>A <tt>MachineFunctionPass</tt> is also a <tt>FunctionPass</tt>, so all
+the restrictions that apply to a <tt>FunctionPass</tt> also apply to it.
+<tt>MachineFunctionPass</tt>es also have additional restrictions. In particular,
+<tt>MachineFunctionPass</tt>es are not allowed to do any of the following:</p>
+
+<ol>
+<li>Modify or create any LLVM IR Instructions, BasicBlocks, Arguments,
+ Functions, GlobalVariables, GlobalAliases, or Modules.</li>
+<li>Modify a MachineFunction other than the one currently being processed.</li>
+<li>Maintain state across invocations of <a
+href="#runOnMachineFunction"><tt>runOnMachineFunction</tt></a> (including global
+data)</li>
+</ol>
+
+<!-- _______________________________________________________________________ -->
+<h4>
+ <a name="runOnMachineFunction">
+ The <tt>runOnMachineFunction(MachineFunction &MF)</tt> method
+ </a>
+</h4>
+
+<div>
+
+<div class="doc_code"><pre>
+ <b>virtual bool</b> runOnMachineFunction(MachineFunction &MF) = 0;
+</pre></div>
+<p><tt>runOnMachineFunction</tt> can be considered the main entry point of a
+<tt>MachineFunctionPass</tt>; that is, you should override this method to do the
+work of your <tt>MachineFunctionPass</tt>.</p>
+<p>The <tt>runOnMachineFunction</tt> method is called on every
+<tt>MachineFunction</tt> in a <tt>Module</tt>, so that the
+<tt>MachineFunctionPass</tt> may perform optimizations on the machine-dependent
+representation of the function. If you want to get at the LLVM <tt>Function</tt>
+for the <tt>MachineFunction</tt> you're working on, use
+<tt>MachineFunction</tt>'s <tt>getFunction()</tt> accessor method -- but
+remember, you may not modify the LLVM <tt>Function</tt> or its contents from a
+<tt>MachineFunctionPass</tt>.</p>
+
+</div>
+
+</div>
+
+</div>
<!-- *********************************************************************** -->
-</ul><table width="100%" bgcolor="#330077" border=0 cellpadding=4 cellspacing=0>
-<tr><td align=center><font color="#EEEEFF" size=+2 face="Georgia,Palatino"><b>
-<a name="registration">Pass registration
-</b></font></td></tr></table><ul>
+<h2>
+ <a name="registration">Pass registration</a>
+</h2>
<!-- *********************************************************************** -->
-In the <a href="#basiccode">Hello World</a> example pass we illustrated how pass
-registration works, and discussed some of the reasons that it is used and what
-it does. Here we discuss how and why passes are registered.<p>
+<div>
-Passes can be registered in several different ways. Depending on the general
-classification of the pass, you should use one of the following templates to
-register the pass:<p>
+<p>In the <a href="#basiccode">Hello World</a> example pass we illustrated how
+pass registration works, and discussed some of the reasons that it is used and
+what it does. Here we discuss how and why passes are registered.</p>
-<ul>
-<li><b><tt>RegisterOpt</tt></b> - This template should be used when you are
-registering a pass that logically should be available for use in the
-'<tt>opt</tt>' utility.<p>
-
-<li><b><tt>RegisterAnalysis</tt></b> - This template should be used when you are
-registering a pass that logically should be available for use in the
-'<tt>analysis</tt>' utility.<p>
-
-<li><b><tt>RegisterLLC</tt></b> - This template should be used when you are
-registering a pass that logically should be available for use in the
-'<tt>llc</tt>' utility.<p>
-
-<li><b><tt>RegisterPass</tt></b> - This is the generic form of the
-<tt>Register*</tt> templates that should be used if you want your pass listed by
-multiple or no utilities. This template takes an extra third argument that
-specifies which tools it should be listed in. See the <a
-href="http://llvm.cs.uiuc.edu/doxygen/PassSupport_8h-source.html">PassSupport.h</a>
-file for more information.<p>
-</ul><p>
-
-Regardless of how you register your pass, you must specify at least two
-parameters. The first parameter is the name of the pass that is to be used on
+<p>As we saw above, passes are registered with the <b><tt>RegisterPass</tt></b>
+template. The template parameter is the name of the pass that is to be used on
the command line to specify that the pass should be added to a program (for
-example <tt>opt</tt> or <tt>analyze</tt>). The second argument is the name of
-the pass, which is to be used for the <tt>--help</tt> output of programs, as
-well as for debug output generated by the <tt>--debug-pass</tt> option.<p>
-
-If you pass is constructed by its default constructor, you only ever have to
-pass these two arguments. If, on the other hand, you require other information
-(like target specific information), you must pass an additional argument. This
-argument is a pointer to a function used to create the pass. For an example of
-how this works, look at the <a
-href="http://llvm.cs.uiuc.edu/doxygen/LowerAllocations_8cpp-source.html">LowerAllocations.cpp</a>
-file.<p>
+example, with <tt>opt</tt> or <tt>bugpoint</tt>). The first argument is the
+name of the pass, which is to be used for the <tt>-help</tt> output of
+programs, as
+well as for debug output generated by the <tt>--debug-pass</tt> option.</p>
-If a pass is registered to be used by the <tt>analyze</tt> utility, you should
-implement the virtual <tt>print</tt> method:<p>
+<p>If you want your pass to be easily dumpable, you should
+implement the virtual <tt>print</tt> method:</p>
<!-- _______________________________________________________________________ -->
-</ul><h4><a name="print"><hr size=0>The <tt>print</tt> method</h4><ul>
+<h4>
+ <a name="print">The <tt>print</tt> method</a>
+</h4>
-<pre>
+<div>
+
+<div class="doc_code"><pre>
<b>virtual void</b> print(std::ostream &O, <b>const</b> Module *M) <b>const</b>;
-</pre><p>
+</pre></div>
-The <tt>print</tt> method must be implemented by "analyses" in order to print a
-human readable version of the analysis results. This is useful for debugging an
-analysis itself, as well as for other people to figure out how an analysis
-works. The <tt>analyze</tt> tool uses this method to generate its output.<p>
+<p>The <tt>print</tt> method must be implemented by "analyses" in order to print
+a human readable version of the analysis results. This is useful for debugging
+an analysis itself, as well as for other people to figure out how an analysis
+works. Use the <tt>opt -analyze</tt> argument to invoke this method.</p>
-The <tt>ostream</tt> parameter specifies the stream to write the results on, and
-the <tt>Module</tt> parameter gives a pointer to the top level module of the
+<p>The <tt>llvm::OStream</tt> parameter specifies the stream to write the results on,
+and the <tt>Module</tt> parameter gives a pointer to the top level module of the
program that has been analyzed. Note however that this pointer may be null in
certain circumstances (such as calling the <tt>Pass::dump()</tt> from a
debugger), so it should only be used to enhance debug output, it should not be
-depended on.<p>
+depended on.</p>
+</div>
+
+</div>
<!-- *********************************************************************** -->
-</ul><table width="100%" bgcolor="#330077" border=0 cellpadding=4 cellspacing=0>
-<tr><td align=center><font color="#EEEEFF" size=+2 face="Georgia,Palatino"><b>
-<a name="interaction">Specifying interactions between passes
-</b></font></td></tr></table><ul>
+<h2>
+ <a name="interaction">Specifying interactions between passes</a>
+</h2>
<!-- *********************************************************************** -->
-One of the main responsibilities of the <tt>PassManager</tt> is the make sure
+<div>
+
+<p>One of the main responsibilities of the <tt>PassManager</tt> is to make sure
that passes interact with each other correctly. Because <tt>PassManager</tt>
tries to <a href="#passmanager">optimize the execution of passes</a> it must
know how the passes interact with each other and what dependencies exist between
the various passes. To track this, each pass can declare the set of passes that
are required to be executed before the current pass, and the passes which are
-invalidated by the current pass.<p>
+invalidated by the current pass.</p>
-Typically this functionality is used to require that analysis results are
+<p>Typically this functionality is used to require that analysis results are
computed before your pass is run. Running arbitrary transformation passes can
invalidate the computed analysis results, which is what the invalidation set
specifies. If a pass does not implement the <tt><a
href="#getAnalysisUsage">getAnalysisUsage</a></tt> method, it defaults to not
-having any prerequisite passes, and invalidating <b>all</b> other passes.<p>
-
+having any prerequisite passes, and invalidating <b>all</b> other passes.</p>
<!-- _______________________________________________________________________ -->
-</ul><h4><a name="getAnalysisUsage"><hr size=0>The <tt>getAnalysisUsage</tt> method</h4><ul>
+<h4>
+ <a name="getAnalysisUsage">The <tt>getAnalysisUsage</tt> method</a>
+</h4>
-<pre>
+<div>
+
+<div class="doc_code"><pre>
<b>virtual void</b> getAnalysisUsage(AnalysisUsage &Info) <b>const</b>;
-</pre><p>
+</pre></div>
-By implementing the <tt>getAnalysisUsage</tt> method, the required and
+<p>By implementing the <tt>getAnalysisUsage</tt> method, the required and
invalidated sets may be specified for your transformation. The implementation
should fill in the <tt><a
-href="http://llvm.cs.uiuc.edu/doxygen/classAnalysisUsage.html">AnalysisUsage</a></tt>
-object with information about which passes are required and not invalidated. To do this, the following set methods are provided by the <tt><a
-href="http://llvm.cs.uiuc.edu/doxygen/classAnalysisUsage.html">AnalysisUsage</a></tt> class:<p>
+href="http://llvm.org/doxygen/classllvm_1_1AnalysisUsage.html">AnalysisUsage</a></tt>
+object with information about which passes are required and not invalidated. To
+do this, a pass may call any of the following methods on the AnalysisUsage
+object:</p>
+</div>
-<pre>
- <i>// addRequires - Add the specified pass to the required set for your pass.</i>
- <b>template</b><<b>class</b> PassClass>
- AnalysisUsage &AnalysisUsage::addRequired();
-
- <i>// addPreserved - Add the specified pass to the set of analyses preserved by
- // this pass</i>
- <b>template</b><<b>class</b> PassClass>
- AnalysisUsage &AnalysisUsage::addPreserved();
-
- <i>// setPreservesAll - Call this if the pass does not modify its input at all</i>
- <b>void</b> AnalysisUsage::setPreservesAll();
-
- <i>// setPreservesCFG - This function should be called by the pass, iff they do not:
- //
- // 1. Add or remove basic blocks from the function
- // 2. Modify terminator instructions in any way.
- //
- // This is automatically implied for <a href="#BasicBlockPass">BasicBlockPass</a>'s
- //</i>
- <b>void</b> AnalysisUsage::setPreservesCFG();
-</pre><p>
-
-Some examples of how to use these methods are:<p>
+<!-- _______________________________________________________________________ -->
+<h4>
+ <a name="AU::addRequired">
+ The <tt>AnalysisUsage::addRequired<></tt>
+ and <tt>AnalysisUsage::addRequiredTransitive<></tt> methods
+ </a>
+</h4>
+
+<div>
+<p>
+If your pass requires a previous pass to be executed (an analysis for example),
+it can use one of these methods to arrange for it to be run before your pass.
+LLVM has many different types of analyses and passes that can be required,
+spanning the range from <tt>DominatorSet</tt> to <tt>BreakCriticalEdges</tt>.
+Requiring <tt>BreakCriticalEdges</tt>, for example, guarantees that there will
+be no critical edges in the CFG when your pass has been run.
+</p>
+
+<p>
+Some analyses chain to other analyses to do their job. For example, an <a
+href="AliasAnalysis.html">AliasAnalysis</a> implementation is required to <a
+href="AliasAnalysis.html#chaining">chain</a> to other alias analysis passes. In
+cases where analyses chain, the <tt>addRequiredTransitive</tt> method should be
+used instead of the <tt>addRequired</tt> method. This informs the PassManager
+that the transitively required pass should be alive as long as the requiring
+pass is.
+</p>
+</div>
-<pre>
- <i>// This is an example implementation from an analysis, which does not modify
- // the program at all, yet has a prerequisite.</i>
- <b>void</b> <a href="http://llvm.cs.uiuc.edu/doxygen/structPostDominanceFrontier.html">PostDominanceFrontier</a>::getAnalysisUsage(AnalysisUsage &AU) <b>const</b> {
- AU.setPreservesAll();
- AU.addRequired<<a href="http://llvm.cs.uiuc.edu/doxygen/structPostDominatorTree.html">PostDominatorTree</a>>();
- }
-</pre><p>
+<!-- _______________________________________________________________________ -->
+<h4>
+ <a name="AU::addPreserved">
+ The <tt>AnalysisUsage::addPreserved<></tt> method
+ </a>
+</h4>
+
+<div>
+<p>
+One of the jobs of the PassManager is to optimize how and when analyses are run.
+In particular, it attempts to avoid recomputing data unless it needs to. For
+this reason, passes are allowed to declare that they preserve (i.e., they don't
+invalidate) an existing analysis if it's available. For example, a simple
+constant folding pass would not modify the CFG, so it can't possibly affect the
+results of dominator analysis. By default, all passes are assumed to invalidate
+all others.
+</p>
+
+<p>
+The <tt>AnalysisUsage</tt> class provides several methods which are useful in
+certain circumstances that are related to <tt>addPreserved</tt>. In particular,
+the <tt>setPreservesAll</tt> method can be called to indicate that the pass does
+not modify the LLVM program at all (which is true for analyses), and the
+<tt>setPreservesCFG</tt> method can be used by transformations that change
+instructions in the program but do not modify the CFG or terminator instructions
+(note that this property is implicitly set for <a
+href="#BasicBlockPass">BasicBlockPass</a>'s).
+</p>
+
+<p>
+<tt>addPreserved</tt> is particularly useful for transformations like
+<tt>BreakCriticalEdges</tt>. This pass knows how to update a small set of loop
+and dominator related analyses if they exist, so it can preserve them, despite
+the fact that it hacks on the CFG.
+</p>
+</div>
-and:<p>
+<!-- _______________________________________________________________________ -->
+<h4>
+ <a name="AU::examples">
+ Example implementations of <tt>getAnalysisUsage</tt>
+ </a>
+</h4>
-<pre>
+<div>
+
+<div class="doc_code"><pre>
<i>// This example modifies the program, but does not modify the CFG</i>
- <b>void</b> <a href="http://llvm.cs.uiuc.edu/doxygen/structLICM.html">LICM</a>::getAnalysisUsage(AnalysisUsage &AU) <b>const</b> {
+ <b>void</b> <a href="http://llvm.org/doxygen/structLICM.html">LICM</a>::getAnalysisUsage(AnalysisUsage &AU) <b>const</b> {
AU.setPreservesCFG();
- AU.addRequired<<a href="http://llvm.cs.uiuc.edu/doxygen/classLoopInfo.html">LoopInfo</a>>();
+ AU.addRequired<<a href="http://llvm.org/doxygen/classllvm_1_1LoopInfo.html">LoopInfo</a>>();
}
-</pre><p>
+</pre></div>
-<!-- _______________________________________________________________________ -->
-</ul><h4><a name="getAnalysis"><hr size=0>The <tt>getAnalysis<></tt> method</h4><ul>
+</div>
-The <tt>Pass::getAnalysis<></tt> method is inherited by your class,
-providing you with access to the passes that you declared that you required with
-the <a href="#getAnalysisUsage"><tt>getAnalysisUsage</tt></a> method. It takes
-a single template argument that specifies which pass class you want, and returns
-a reference to that pass.<p>
+<!-- _______________________________________________________________________ -->
+<h4>
+ <a name="getAnalysis">
+ The <tt>getAnalysis<></tt> and
+ <tt>getAnalysisIfAvailable<></tt> methods
+ </a>
+</h4>
+
+<div>
+
+<p>The <tt>Pass::getAnalysis<></tt> method is automatically inherited by
+your class, providing you with access to the passes that you declared that you
+required with the <a href="#getAnalysisUsage"><tt>getAnalysisUsage</tt></a>
+method. It takes a single template argument that specifies which pass class you
+want, and returns a reference to that pass. For example:</p>
+
+<div class="doc_code"><pre>
+ bool LICM::runOnFunction(Function &F) {
+ LoopInfo &LI = getAnalysis<LoopInfo>();
+ ...
+ }
+</pre></div>
+
+<p>This method call returns a reference to the pass desired. You may get a
+runtime assertion failure if you attempt to get an analysis that you did not
+declare as required in your <a
+href="#getAnalysisUsage"><tt>getAnalysisUsage</tt></a> implementation. This
+method can be called by your <tt>run*</tt> method implementation, or by any
+other local method invoked by your <tt>run*</tt> method.
+
+A module level pass can use function level analysis info using this interface.
+For example:</p>
+
+<div class="doc_code"><pre>
+ bool ModuleLevelPass::runOnModule(Module &M) {
+ ...
+ DominatorTree &DT = getAnalysis<DominatorTree>(Func);
+ ...
+ }
+</pre></div>
+
+<p>In above example, runOnFunction for DominatorTree is called by pass manager
+before returning a reference to the desired pass.</p>
+
+<p>
+If your pass is capable of updating analyses if they exist (e.g.,
+<tt>BreakCriticalEdges</tt>, as described above), you can use the
+<tt>getAnalysisIfAvailable</tt> method, which returns a pointer to the analysis
+if it is active. For example:</p>
+
+<div class="doc_code"><pre>
+ ...
+ if (DominatorSet *DS = getAnalysisIfAvailable<DominatorSet>()) {
+ <i>// A DominatorSet is active. This code will update it.</i>
+ }
+ ...
+</pre></div>
-<pre>
- <b>template</b><<b>typename</b> PassClass>
- AnalysisType &getAnalysis();
-</pre><p>
+</div>
-This method call returns a reference to the pass desired. You may get a runtime
-assertion failure if you attempt to get an analysis that you did not declare as
-required in your <a href="#getAnalysisUsage"><tt>getAnalysisUsage</tt></a>
-implementation. This method can be called by your <tt>run*</tt> method
-implementation, or by any other local method invoked by your <tt>run*</tt>
-method.<p>
+</div>
<!-- *********************************************************************** -->
-</ul><table width="100%" bgcolor="#330077" border=0 cellpadding=4 cellspacing=0>
-<tr><td align=center><font color="#EEEEFF" size=+2 face="Georgia,Palatino"><b>
-<a name="analysisgroup">Implementing Analysis Groups
-</b></font></td></tr></table><ul>
+<h2>
+ <a name="analysisgroup">Implementing Analysis Groups</a>
+</h2>
<!-- *********************************************************************** -->
-Now that we understand the basics of how passes are defined, how the are used,
-and how they are required from other passes, it's time to get a little bit
+<div>
+
+<p>Now that we understand the basics of how passes are defined, how they are
+used, and how they are required from other passes, it's time to get a little bit
fancier. All of the pass relationships that we have seen so far are very
simple: one pass depends on one other specific pass to be run before it can run.
For many applications, this is great, for others, more flexibility is
-required.<p>
+required.</p>
-In particular, some analyses are defined such that there is a single simple
+<p>In particular, some analyses are defined such that there is a single simple
interface to the analysis results, but multiple ways of calculating them.
Consider alias analysis for example. The most trivial alias analysis returns
"may alias" for any alias query. The most sophisticated analysis a
significant amount of time to execute (and obviously, there is a lot of room
between these two extremes for other implementations). To cleanly support
situations like this, the LLVM Pass Infrastructure supports the notion of
-Analysis Groups.<p>
+Analysis Groups.</p>
<!-- _______________________________________________________________________ -->
-</ul><h4><a name="agconcepts"><hr size=0>Analysis Group Concepts</h4><ul>
+<h4>
+ <a name="agconcepts">Analysis Group Concepts</a>
+</h4>
+
+<div>
-An Analysis Group is a single simple interface that may be implemented by
+<p>An Analysis Group is a single simple interface that may be implemented by
multiple different passes. Analysis Groups can be given human readable names
just like passes, but unlike passes, they need not derive from the <tt>Pass</tt>
class. An analysis group may have one or more implementations, one of which is
-the "default" implementation.<p>
+the "default" implementation.</p>
-Analysis groups are used by client passes just like other passes are: the
+<p>Analysis groups are used by client passes just like other passes are: the
<tt>AnalysisUsage::addRequired()</tt> and <tt>Pass::getAnalysis()</tt> methods.
In order to resolve this requirement, the <a href="#passmanager">PassManager</a>
scans the available passes to see if any implementations of the analysis group
are available. If none is available, the default implementation is created for
the pass to use. All standard rules for <A href="#interaction">interaction
-between passes</a> still apply.<p>
+between passes</a> still apply.</p>
-Although <a href="#registration">Pass Registration</a> is optional for normal
+
<p>Although <a href="#registration">Pass Registration</a> is optional for normal
passes, all analysis group implementations must be registered, and must use the
-<A href="#registerag"><tt>RegisterAnalysisGroup</tt></a> template to join the
+<A href="#registerag"><tt>INITIALIZE_AG_PASS</tt></a> template to join the
implementation pool. Also, a default implementation of the interface
<b>must</b> be registered with <A
-href="#registerag"><tt>RegisterAnalysisGroup</tt></a>.<p>
+href="#registerag"><tt>RegisterAnalysisGroup</tt></a>.</p>
-As a concrete example of an Analysis Group in action, consider the <a
-href="http://llvm.cs.uiuc.edu/doxygen/structAliasAnalysis.html">AliasAnalysis</a>
+
<p>As a concrete example of an Analysis Group in action, consider the <a
+href="http://llvm.org/doxygen/classllvm_1_1AliasAnalysis.html">AliasAnalysis</a>
analysis group. The default implementation of the alias analysis interface (the
<tt><a
-href="http://llvm.cs.uiuc.edu/doxygen/structBasicAliasAnalysis.html">basicaa</a></tt>
+href="http://llvm.org/doxygen/structBasicAliasAnalysis.html">basicaa</a></tt>
pass) just does a few simple checks that don't require significant analysis to
compute (such as: two different globals can never alias each other, etc).
Passes that use the <tt><a
-href="http://llvm.cs.uiuc.edu/doxygen/structAliasAnalysis.html">AliasAnalysis</a></tt>
+href="http://llvm.org/doxygen/classllvm_1_1AliasAnalysis.html">AliasAnalysis</a></tt>
interface (for example the <tt><a
-href="http://llvm.cs.uiuc.edu/doxygen/classGCSE.html">gcse</a></tt> pass), do not care which implementation
-of alias analysis is actually provided, they just use the designated
-interface.<p>
+href="http://llvm.org/doxygen/structGCSE.html">gcse</a></tt> pass), do
+not care which implementation of alias analysis is actually provided, they just
+use the designated interface.</p>
-From the user's perspective, commands work just like normal. Issuing the
+<p>From the user's perspective, commands work just like normal. Issuing the
command '<tt>opt -gcse ...</tt>' will cause the <tt>basicaa</tt> class to be
instantiated and added to the pass sequence. Issuing the command '<tt>opt
-somefancyaa -gcse ...</tt>' will cause the <tt>gcse</tt> pass to use the
<tt>somefancyaa</tt> alias analysis (which doesn't actually exist, it's just a
-hypothetical example) instead.<p>
+hypothetical example) instead.</p>
+</div>
<!-- _______________________________________________________________________ -->
-</ul><h4><a name="registerag"><hr size=0>Using <tt>RegisterAnalysisGroup</tt></h4><ul>
+<h4>
+ <a name="registerag">Using <tt>RegisterAnalysisGroup</tt></a>
+</h4>
-The <tt>RegisterAnalysisGroup</tt> template is used to register the analysis
-group itself as well as add pass implementations to the analysis group. First,
-an analysis should be registered, with a human readable name provided for it.
+<div>
+
+<p>The <tt>RegisterAnalysisGroup</tt> template is used to register the analysis
+group itself, while the <tt>INITIALIZE_AG_PASS</tt> is used to add pass
+implementations to the analysis group. First,
+an analysis group should be registered, with a human readable name
+provided for it.
Unlike registration of passes, there is no command line argument to be specified
-for the Analysis Group Interface itself, because it is "abstract":<p>
+for the Analysis Group Interface itself, because it is "abstract":</p>
-<pre>
- <b>static</b> RegisterAnalysisGroup<<a href="http://llvm.cs.uiuc.edu/doxygen/structAliasAnalysis.html">AliasAnalysis</a>> A("<i>Alias Analysis</i>");
-</pre><p>
+<div class="doc_code"><pre>
+ <b>static</b> RegisterAnalysisGroup<<a href="http://llvm.org/doxygen/classllvm_1_1AliasAnalysis.html">AliasAnalysis</a>> A("<i>Alias Analysis</i>");
+</pre></div>
-Once the analysis is registered, passes can declare that they are valid
-implementations of the interface by using the following code:<p>
+<p>Once the analysis is registered, passes can declare that they are valid
+implementations of the interface by using the following code:</p>
-<pre>
+<div class="doc_code"><pre>
<b>namespace</b> {
- //<i> Analysis Group implementations <b>must</b> be registered normally...</i>
- RegisterOpt<FancyAA>
- B("<i>somefancyaa</i>", "<i>A more complex alias analysis implementation</i>");
-
//<i> Declare that we implement the AliasAnalysis interface</i>
- RegisterAnalysisGroup<<a href="http://llvm.cs.uiuc.edu/doxygen/structAliasAnalysis.html">AliasAnalysis</a>, FancyAA> C;
+ INITIALIZE_AG_PASS(FancyAA, <a href="http://llvm.org/doxygen/classllvm_1_1AliasAnalysis.html">AliasAnalysis</a>, "<i>somefancyaa</i>",
+ "<i>A more complex alias analysis implementation</i>",
+ false, // <i>Is CFG Only?</i>
+ true, // <i>Is Analysis?</i>
+ false, // <i>Is default Analysis Group implementation?</i>
+ );
}
-</pre><p>
+</pre></div>
-This just shows a class <tt>FancyAA</tt> that is registered normally, then uses
-the <tt>RegisterAnalysisGroup</tt> template to "join" the <tt><a
-href="http://llvm.cs.uiuc.edu/doxygen/structAliasAnalysis.html">AliasAnalysis</a></tt>
+<p>This just shows a class <tt>FancyAA</tt> that
+uses the <tt>INITIALIZE_AG_PASS</tt> macro both to register and
+to "join" the <tt><a href="http://llvm.org/doxygen/classllvm_1_1AliasAnalysis.html">AliasAnalysis</a></tt>
analysis group. Every implementation of an analysis group should join using
-this template. A single pass may join multiple different analysis groups with
-no problem.<p>
+this macro.</p>
-<pre>
+<div class="doc_code"><pre>
<b>namespace</b> {
- //<i> Analysis Group implementations <b>must</b> be registered normally...</i>
- RegisterOpt<<a href="http://llvm.cs.uiuc.edu/doxygen/structBasicAliasAnalysis.html">BasicAliasAnalysis</a>>
- D("<i>basicaa</i>", "<i>Basic Alias Analysis (default AA impl)</i>");
-
//<i> Declare that we implement the AliasAnalysis interface</i>
- RegisterAnalysisGroup<<a href="http://llvm.cs.uiuc.edu/doxygen/structAliasAnalysis.html">AliasAnalysis</a>, <a href="http://llvm.cs.uiuc.edu/doxygen/structBasicAliasAnalysis.html">BasicAliasAnalysis</a>, <b>true</b>> E;
+ INITIALIZE_AG_PASS(BasicAA, <a href="http://llvm.org/doxygen/classllvm_1_1AliasAnalysis.html">AliasAnalysis</a>, "<i>basicaa</i>",
+ "<i>Basic Alias Analysis (default AA impl)</i>",
+ false, // <i>Is CFG Only?</i>
+ true, // <i>Is Analysis?</i>
+ true, // <i>Is default Analysis Group implementation?</i>
+ );
}
-</pre><p>
+</pre></div>
-Here we show how the default implementation is specified (using the extra
-argument to the <tt>RegisterAnalysisGroup</tt> template). There must be exactly
+<p>Here we show how the default implementation is specified (using the final
+argument to the <tt>INITIALIZE_AG_PASS</tt> template). There must be exactly
one default implementation available at all times for an Analysis Group to be
-used. Here we declare that the <tt><a
-href="http://llvm.cs.uiuc.edu/doxygen/structBasicAliasAnalysis.html">BasicAliasAnalysis</a></tt>
-pass is the default implementation for the interface.<p>
+used. Only default implementation can derive from <tt>ImmutablePass</tt>.
+Here we declare that the
+ <tt><a href="http://llvm.org/doxygen/structBasicAliasAnalysis.html">BasicAliasAnalysis</a></tt>
+pass is the default implementation for the interface.</p>
+</div>
+
+</div>
<!-- *********************************************************************** -->
-</ul><table width="100%" bgcolor="#330077" border=0 cellpadding=4 cellspacing=0>
-<tr><td align=center><font color="#EEEEFF" size=+2 face="Georgia,Palatino"><b>
-<a name="passmanager">What PassManager does
-</b></font></td></tr></table><ul>
+<h2>
+ <a name="passStatistics">Pass Statistics</a>
+</h2>
<!-- *********************************************************************** -->
-The <a
-href="http://llvm.cs.uiuc.edu/doxygen/PassManager_8h-source.html"><tt>PassManager</tt></a>
-<a href="http://llvm.cs.uiuc.edu/doxygen/classPassManager.html">class</a> takes
-a list of passes, ensures their <a href="#interaction">prerequisites</a> are set
-up correctly, and then schedules passes to run efficiently. All of the LLVM
-tools that run passes use the <tt>PassManager</tt> for execution of these
-passes.<p>
+<div>
+<p>The <a
+href="http://llvm.org/doxygen/Statistic_8h-source.html"><tt>Statistic</tt></a>
+class is designed to be an easy way to expose various success
+metrics from passes. These statistics are printed at the end of a
+run, when the -stats command line option is enabled on the command
+line. See the <a href="http://llvm.org/docs/ProgrammersManual.html#Statistic">Statistics section</a> in the Programmer's Manual for details.
+
+</div>
-The <tt>PassManager</tt> does two main things to try to reduce the execution
-time of a series of passes:<p>
+
+<!-- *********************************************************************** -->
+<h2>
+ <a name="passmanager">What PassManager does</a>
+</h2>
+<!-- *********************************************************************** -->
+
+<div>
+
+<p>The <a
+href="http://llvm.org/doxygen/PassManager_8h-source.html"><tt>PassManager</tt></a>
+<a
+href="http://llvm.org/doxygen/classllvm_1_1PassManager.html">class</a>
+takes a list of passes, ensures their <a href="#interaction">prerequisites</a>
+are set up correctly, and then schedules passes to run efficiently. All of the
+LLVM tools that run passes use the <tt>PassManager</tt> for execution of these
+passes.</p>
+
+<p>The <tt>PassManager</tt> does two main things to try to reduce the execution
+time of a series of passes:</p>
<ol>
<li><b>Share analysis results</b> - The PassManager attempts to avoid
analyses are needed to be run for a pass. An important part of work is that the
<tt>PassManager</tt> tracks the exact lifetime of all analysis results, allowing
it to <a href="#releaseMemory">free memory</a> allocated to holding analysis
-results as soon as they are no longer needed.<p>
+results as soon as they are no longer needed.</li>
<li><b>Pipeline the execution of passes on the program</b> - The
<tt>PassManager</tt> attempts to get better cache and memory usage behavior out
of a series of passes by pipelining the passes together. This means that, given
-a series of conse
qutive <a href="#FunctionPass"><tt>FunctionPass</tt></a>'s, it
+a series of conse
cutive <a href="#FunctionPass"><tt>FunctionPass</tt></a>'s, it
will execute all of the <a href="#FunctionPass"><tt>FunctionPass</tt></a>'s on
the first function, then all of the <a
-href="#FunctionPass"><tt>FunctionPass</tt></a>'s on the second function,
-etc... until the entire program has been run through the passes.<p>
+href="#FunctionPass"><tt>FunctionPass</tt></a>es on the second function,
+etc... until the entire program has been run through the passes.
-This improves the cache behavior of the compiler, because it is only touching
+<p>This improves the cache behavior of the compiler, because it is only touching
the LLVM program representation for a single function at a time, instead of
traversing the entire program. It reduces the memory consumption of compiler,
because, for example, only one <a
-href="http://llvm.cs.uiuc.edu/doxygen/structDominatorSet.html"><tt>DominatorSet</tt></a>
-needs to be calculated at a time. This also makes it possible some <a
-href="#SMP">interesting enhancements</a> in the future.<p>
+href="http://llvm.org/doxygen/classllvm_1_1DominatorSet.html"><tt>DominatorSet</tt></a>
+needs to be calculated at a time. This also makes it possible to implement
+some <a
+href="#SMP">interesting enhancements</a> in the future.</p></li>
-</ol><p>
+</ol>
-The effectiveness of the <tt>PassManager</tt> is influenced directly by how much
-information it has about the behaviors of the passes it is scheduling. For
+<p>The effectiveness of the <tt>PassManager</tt> is influenced directly by how
+much information it has about the behaviors of the passes it is scheduling. For
example, the "preserved" set is intentionally conservative in the face of an
unimplemented <a href="#getAnalysisUsage"><tt>getAnalysisUsage</tt></a> method.
Not implementing when it should be implemented will have the effect of not
-allowing any analysis results to live across the execution of your pass.<p>
+allowing any analysis results to live across the execution of your pass.</p>
-The <tt>PassManager</tt> class exposes a <tt>--debug-pass</tt> command line
+<p>The <tt>PassManager</tt> class exposes a <tt>--debug-pass</tt> command line
options that is useful for debugging pass execution, seeing how things work, and
diagnosing when you should be preserving more analyses than you currently are
(To get information about all of the variants of the <tt>--debug-pass</tt>
-option, just type '<tt>opt --help-hidden</tt>').<p>
+option, just type '<tt>opt -help-hidden</tt>').</p>
-By using the <tt>--debug-pass=Structure</tt> option, for example, we can see how
-our <a href="#basiccode">Hello World</a> pass interacts with other passes. Lets
-try it out with the <tt>gcse</tt> and <tt>licm</tt> passes:<p>
+<p>By using the <tt>--debug-pass=Structure</tt> option, for example, we can see
+how our <a href="#basiccode">Hello World</a> pass interacts with other passes.
+Lets try it out with the <tt>gcse</tt> and <tt>licm</tt> passes:</p>
-<pre>
-$ opt -load ../../../lib/Debug/libhello.so -gcse -licm --debug-pass=Structure < hello.bc > /dev/null
+<div class="doc_code"><pre>
+$ opt -load ../../../Debug+Asserts/lib/Hello.so -gcse -licm --debug-pass=Structure < hello.bc > /dev/null
Module Pass Manager
Function Pass Manager
Dominator Set Construction
Module Verifier
-- Dominator Set Construction
-- Module Verifier
- Bytecode Writer
---Bytecode Writer
-</pre><p>
-
-This output shows us when passes are constructed and when the analysis results
-are known to be dead (prefixed with '<tt>--</tt>'). Here we see that GCSE uses
-dominator and immediate dominator information to do its job. The LICM pass uses
-natural loop information, which uses dominator sets, but not immediate
+ Bitcode Writer
+--Bitcode Writer
+</pre></div>
+
+<p>This output shows us when passes are constructed and when the analysis
+results are known to be dead (prefixed with '<tt>--</tt>'). Here we see that
+GCSE uses dominator and immediate dominator information to do its job. The LICM
+pass uses natural loop information, which uses dominator sets, but not immediate
dominators. Because immediate dominators are no longer useful after the GCSE
pass, it is immediately destroyed. The dominator sets are then reused to
-compute natural loop information, which is then used by the LICM pass.<p>
+compute natural loop information, which is then used by the LICM pass.</p>
-After the LICM pass, the module verifier runs (which is automatically added by
-the '<tt>opt</tt>' tool), which uses the dominator set to check that the
+<p>After the LICM pass, the module verifier runs (which is automatically added
+by the '<tt>opt</tt>' tool), which uses the dominator set to check that the
resultant LLVM code is well formed. After it finishes, the dominator set
information is destroyed, after being computed once, and shared by three
-passes.<p>
+passes.</p>
-Lets see how this changes when we run the <a href="#basiccode">Hello World</a>
-pass in between the two passes:<p>
+<p>Lets see how this changes when we run the <a href="#basiccode">Hello
+World</a> pass in between the two passes:</p>
-<pre>
-$ opt -load ../../../lib/Debug/libhello.so -gcse -hello -licm --debug-pass=Structure < hello.bc > /dev/null
+<div class="doc_code"><pre>
+$ opt -load ../../../Debug+Asserts/lib/Hello.so -gcse -hello -licm --debug-pass=Structure < hello.bc > /dev/null
Module Pass Manager
Function Pass Manager
Dominator Set Construction
Module Verifier
-- Dominator Set Construction
-- Module Verifier
- Bytecode Writer
---Bytecode Writer
+ Bitcode Writer
+--Bitcode Writer
Hello: __main
Hello: puts
Hello: main
-</pre><p>
+</pre></div>
-Here we see that the <a href="#basiccode">Hello World</a> pass has killed the
+
<p>Here we see that the <a href="#basiccode">Hello World</a> pass has killed the
Dominator Set pass, even though it doesn't modify the code at all! To fix this,
we need to add the following <a
-href="#getAnalysisUsage"><tt>getAnalysisUsage</tt></a> method to our pass:<p>
+href="#getAnalysisUsage"><tt>getAnalysisUsage</tt></a> method to our pass:</p>
-<pre>
+<div class="doc_code"><pre>
<i>// We don't modify the program, so we preserve all analyses</i>
<b>virtual void</b> getAnalysisUsage(AnalysisUsage &AU) <b>const</b> {
AU.setPreservesAll();
}
-</pre><p>
+</pre></div>
-Now when we run our pass, we get this output:<p>
+<p>Now when we run our pass, we get this output:</p>
-<pre>
-$ opt -load ../../../lib/Debug/libhello.so -gcse -hello -licm --debug-pass=Structure < hello.bc > /dev/null
+<div class="doc_code"><pre>
+$ opt -load ../../../Debug+Asserts/lib/Hello.so -gcse -hello -licm --debug-pass=Structure < hello.bc > /dev/null
Pass Arguments: -gcse -hello -licm
Module Pass Manager
Function Pass Manager
Module Verifier
-- Dominator Set Construction
-- Module Verifier
- Bytecode Writer
---Bytecode Writer
+ Bitcode Writer
+--Bitcode Writer
Hello: __main
Hello: puts
Hello: main
-</pre><p>
-
-Which shows that we don't accidentally invalidate dominator information
-anymore, and therefore do not have to compute it twice.<p>
+</pre></div>
+<p>Which shows that we don't accidentally invalidate dominator information
+anymore, and therefore do not have to compute it twice.</p>
<!-- _______________________________________________________________________ -->
-</ul><h4><a name="releaseMemory"><hr size=0>The <tt>releaseMemory</tt> method</h4><ul>
+<h4>
+ <a name="releaseMemory">The <tt>releaseMemory</tt> method</a>
+</h4>
-<pre>
+<div>
+
+<div class="doc_code"><pre>
<b>virtual void</b> releaseMemory();
-</pre><p>
+</pre></div>
-The <tt>PassManager</tt> automatically determines when to compute analysis
+<p>The <tt>PassManager</tt> automatically determines when to compute analysis
results, and how long to keep them around for. Because the lifetime of the pass
object itself is effectively the entire duration of the compilation process, we
need some way to free analysis results when they are no longer useful. The
-<tt>releaseMemory</tt> virtual method is the way to do this.<p>
+<tt>releaseMemory</tt> virtual method is the way to do this.</p>
-If you are writing an analysis or any other pass that retains a significant
+<p>If you are writing an analysis or any other pass that retains a significant
amount of state (for use by another pass which "requires" your pass and uses the
<a href="#getAnalysis">getAnalysis</a> method) you should implement
-<tt>releaseMEmory</tt> to, well, release the memory allocated to maintain this
+<tt>releaseMemory</tt> to, well, release the memory allocated to maintain this
internal state. This method is called after the <tt>run*</tt> method for the
-class, before the next call of <tt>run*</tt> in your pass.<p>
+class, before the next call of <tt>run*</tt> in your pass.</p>
+</div>
+
+</div>
<!-- *********************************************************************** -->
-</ul><table width="100%" bgcolor="#330077" border=0 cellpadding=4 cellspacing=0>
-<tr><td align=center><font color="#EEEEFF" size=+2 face="Georgia,Palatino"><b>
-<a name="debughints">Using GDB with dynamically loaded passes
-</b></font></td></tr></table><ul>
+<h2>
+ <a name="registering">Registering dynamically loaded passes</a>
+</h2>
<!-- *********************************************************************** -->
-Unfortunately, using GDB with dynamically loaded passes is not as easy as it
+<div>
+
+<p><i>Size matters</i> when constructing production quality tools using llvm,
+both for the purposes of distribution, and for regulating the resident code size
+when running on the target system. Therefore, it becomes desirable to
+selectively use some passes, while omitting others and maintain the flexibility
+to change configurations later on. You want to be able to do all this, and,
+provide feedback to the user. This is where pass registration comes into
+play.</p>
+
+<p>The fundamental mechanisms for pass registration are the
+<tt>MachinePassRegistry</tt> class and subclasses of
+<tt>MachinePassRegistryNode</tt>.</p>
+
+<p>An instance of <tt>MachinePassRegistry</tt> is used to maintain a list of
+<tt>MachinePassRegistryNode</tt> objects. This instance maintains the list and
+communicates additions and deletions to the command line interface.</p>
+
+<p>An instance of <tt>MachinePassRegistryNode</tt> subclass is used to maintain
+information provided about a particular pass. This information includes the
+command line name, the command help string and the address of the function used
+to create an instance of the pass. A global static constructor of one of these
+instances <i>registers</i> with a corresponding <tt>MachinePassRegistry</tt>,
+the static destructor <i>unregisters</i>. Thus a pass that is statically linked
+in the tool will be registered at start up. A dynamically loaded pass will
+register on load and unregister at unload.</p>
+
+<!-- _______________________________________________________________________ -->
+<h3>
+ <a name="registering_existing">Using existing registries</a>
+</h3>
+
+<div>
+
+<p>There are predefined registries to track instruction scheduling
+(<tt>RegisterScheduler</tt>) and register allocation (<tt>RegisterRegAlloc</tt>)
+machine passes. Here we will describe how to <i>register</i> a register
+allocator machine pass.</p>
+
+<p>Implement your register allocator machine pass. In your register allocator
+.cpp file add the following include;</p>
+
+<div class="doc_code"><pre>
+ #include "llvm/CodeGen/RegAllocRegistry.h"
+</pre></div>
+
+<p>Also in your register allocator .cpp file, define a creator function in the
+form; </p>
+
+<div class="doc_code"><pre>
+ FunctionPass *createMyRegisterAllocator() {
+ return new MyRegisterAllocator();
+ }
+</pre></div>
+
+<p>Note that the signature of this function should match the type of
+<tt>RegisterRegAlloc::FunctionPassCtor</tt>. In the same file add the
+"installing" declaration, in the form;</p>
+
+<div class="doc_code"><pre>
+ static RegisterRegAlloc myRegAlloc("myregalloc",
+ " my register allocator help string",
+ createMyRegisterAllocator);
+</pre></div>
+
+<p>Note the two spaces prior to the help string produces a tidy result on the
+-help query.</p>
+
+<div class="doc_code"><pre>
+$ llc -help
+ ...
+ -regalloc - Register allocator to use (default=linearscan)
+ =linearscan - linear scan register allocator
+ =local - local register allocator
+ =simple - simple register allocator
+ =myregalloc - my register allocator help string
+ ...
+</pre></div>
+
+<p>And that's it. The user is now free to use <tt>-regalloc=myregalloc</tt> as
+an option. Registering instruction schedulers is similar except use the
+<tt>RegisterScheduler</tt> class. Note that the
+<tt>RegisterScheduler::FunctionPassCtor</tt> is significantly different from
+<tt>RegisterRegAlloc::FunctionPassCtor</tt>.</p>
+
+<p>To force the load/linking of your register allocator into the llc/lli tools,
+add your creator function's global declaration to "Passes.h" and add a "pseudo"
+call line to <tt>llvm/Codegen/LinkAllCodegenComponents.h</tt>.</p>
+
+</div>
+
+
+<!-- _______________________________________________________________________ -->
+<h3>
+ <a name="registering_new">Creating new registries</a>
+</h3>
+
+<div>
+
+<p>The easiest way to get started is to clone one of the existing registries; we
+recommend <tt>llvm/CodeGen/RegAllocRegistry.h</tt>. The key things to modify
+are the class name and the <tt>FunctionPassCtor</tt> type.</p>
+
+<p>Then you need to declare the registry. Example: if your pass registry is
+<tt>RegisterMyPasses</tt> then define;</p>
+
+<div class="doc_code"><pre>
+MachinePassRegistry RegisterMyPasses::Registry;
+</pre></div>
+
+<p>And finally, declare the command line option for your passes. Example:</p>
+
+<div class="doc_code"><pre>
+ cl::opt<RegisterMyPasses::FunctionPassCtor, false,
+ RegisterPassParser<RegisterMyPasses> >
+ MyPassOpt("mypass",
+ cl::init(&createDefaultMyPass),
+ cl::desc("my pass option help"));
+</pre></div>
+
+<p>Here the command option is "mypass", with createDefaultMyPass as the default
+creator.</p>
+
+</div>
+
+</div>
+
+<!-- *********************************************************************** -->
+<h2>
+ <a name="debughints">Using GDB with dynamically loaded passes</a>
+</h2>
+<!-- *********************************************************************** -->
+
+<div>
+
+<p>Unfortunately, using GDB with dynamically loaded passes is not as easy as it
should be. First of all, you can't set a breakpoint in a shared object that has
not been loaded yet, and second of all there are problems with inlined functions
in shared objects. Here are some suggestions to debugging your pass with
-GDB.<p>
+GDB.</p>
-For sake of discussion, I'm going to assume that you are debugging a
+<p>For sake of discussion, I'm going to assume that you are debugging a
transformation invoked by <tt>opt</tt>, although nothing described here depends
-on that.<p>
+on that.</p>
<!-- _______________________________________________________________________ -->
-</ul><h4><a name="breakpoint"><hr size=0>Setting a breakpoint in your pass</h4><ul>
+<h4>
+ <a name="breakpoint">Setting a breakpoint in your pass</a>
+</h4>
-First thing you do is start <tt>gdb</tt> on the <tt>opt</tt> process:<p>
+<div>
-<pre>
+<p>First thing you do is start <tt>gdb</tt> on the <tt>opt</tt> process:</p>
+
+<div class="doc_code"><pre>
$ <b>gdb opt</b>
GNU gdb 5.0
Copyright 2000 Free Software Foundation, Inc.
There is absolutely no warranty for GDB. Type "show warranty" for details.
This GDB was configured as "sparc-sun-solaris2.6"...
(gdb)
-</pre><p>
+</pre></div>
-Note that <tt>opt</tt> has a lot of debugging information in it, so it takes
+<p>Note that <tt>opt</tt> has a lot of debugging information in it, so it takes
time to load. Be patient. Since we cannot set a breakpoint in our pass yet
(the shared object isn't loaded until runtime), we must execute the process, and
have it stop before it invokes our pass, but after it has loaded the shared
object. The most foolproof way of doing this is to set a breakpoint in
<tt>PassManager::run</tt> and then run the process with the arguments you
-want:<p>
+want:</p>
-<pre>
-(gdb) <b>break PassManager::run</b>
+<div class="doc_code"><pre>
+(gdb) <b>break llvm::PassManager::run</b>
Breakpoint 1 at 0x2413bc: file Pass.cpp, line 70.
-(gdb) <b>run test.bc -load /shared/lattner/cvs/llvm/lib/Debug/[libname].so -[passoption]</b>
-Starting program: /shared/lattner/cvs/llvm/tools/Debug/opt test.bc
- -load /shared/lattner/cvs/llvm/lib/Debug/[libname].so -[passoption]
+(gdb) <b>run test.bc -load $(LLVMTOP)/llvm/Debug+Asserts/lib/[libname].so -[passoption]</b>
+Starting program: opt test.bc -load $(LLVMTOP)/llvm/Debug+Asserts/lib/[libname].so -[passoption]
Breakpoint 1, PassManager::run (this=0xffbef174, M=@0x70b298) at Pass.cpp:70
70 bool PassManager::run(Module &M) { return PM->run(M); }
(gdb)
-</pre></p>
+</pre></div>
-Once the <tt>opt</tt> stops in the <tt>PassManager::run</tt> method you are now
-free to set breakpoints in your pass so that you can trace through execution or
-do other standard debugging stuff.<p>
+<p>Once the <tt>opt</tt> stops in the <tt>PassManager::run</tt> method you are
+now free to set breakpoints in your pass so that you can trace through execution
+or do other standard debugging stuff.</p>
+</div>
<!-- _______________________________________________________________________ -->
-</ul><h4><a name="debugmisc"><hr size=0>Miscellaneous Problems</h4><ul>
+<h4>
+ <a name="debugmisc">Miscellaneous Problems</a>
+</h4>
+
+<div>
-Once you have the basics down, there are a couple of problems that GDB has, some
-with solutions, some without.<p>
+<p>Once you have the basics down, there are a couple of problems that GDB has,
+some with solutions, some without.</p>
<ul>
<li>Inline functions have bogus stack information. In general, GDB does a
pretty good job getting stack traces and stepping through inline functions.
When a pass is dynamically loaded however, it somehow completely loses this
capability. The only solution I know of is to de-inline a function (move it
-from the body of a class to a .cpp file).<p>
+from the body of a class to a .cpp file).</li>
<li>Restarting the program breaks breakpoints. After following the information
above, you have succeeded in getting some breakpoints planted in your pass. Nex
and you start getting errors about breakpoints being unsettable. The only way I
have found to "fix" this problem is to <tt>delete</tt> the breakpoints that are
already set in your pass, run the program, and re-set the breakpoints once
-execution stops in <tt>PassManager::run</tt>.<p>
+execution stops in <tt>PassManager::run</tt>.</li>
</ul>
-Hopefully these tips will help with common case debugging situations. If you'd
-like to contribute some tips of your own, just contact <a
-href="mailto:sabre@nondot.org">Chris</a>.<p>
+<p>Hopefully these tips will help with common case debugging situations. If
+
you'd like to contribute some tips of your own, just contact <a
+href="mailto:sabre@nondot.org">Chris</a>.</p>
+</div>
+
+</div>
<!-- *********************************************************************** -->
-</ul><table width="100%" bgcolor="#330077" border=0 cellpadding=4 cellspacing=0>
-<tr><td align=center><font color="#EEEEFF" size=+2 face="Georgia,Palatino"><b>
-<a name="future">Future extensions planned
-</b></font></td></tr></table><ul>
+<h2>
+ <a name="future">Future extensions planned</a>
+</h2>
<!-- *********************************************************************** -->
-Although the LLVM Pass Infrastructure is very capable as it stands, and does
+<div>
+
+<p>Although the LLVM Pass Infrastructure is very capable as it stands, and does
some nifty stuff, there are things we'd like to add in the future. Here is
-where we are going:<p>
+where we are going:</p>
<!-- _______________________________________________________________________ -->
-</ul><h4><a name="SMP"><hr size=0>Multithreaded LLVM</h4><ul>
+<h4>
+ <a name="SMP">Multithreaded LLVM</a>
+</h4>
-Multiple CPU machines are becoming more common and compilation can never be
+<div>
+
+<p>Multiple CPU machines are becoming more common and compilation can never be
fast enough: obviously we should allow for a multithreaded compiler. Because of
the semantics defined for passes above (specifically they cannot maintain state
across invocations of their <tt>run*</tt> methods), a nice clean way to
implement a multithreaded compiler would be for the <tt>PassManager</tt> class
-to create multiple instances of each pass object, and allow the seperate
-instances to be hacking on different parts of the program at the same time.<p>
+to create multiple instances of each pass object, and allow the separate
+instances to be hacking on different parts of the program at the same time.</p>
-This implementation would prevent each of the passes from having to implement
+<p>This implementation would prevent each of the passes from having to implement
multithreaded constructs, requiring only the LLVM core to have locking in a few
places (for global resources). Although this is a simple extension, we simply
haven't had time (or multiprocessor machines, thus a reason) to implement this.
-Despite that, we have kept the LLVM passes SMP ready, and you should too.<p>
-
-
-<!-- _______________________________________________________________________ -->
-</ul><h4><a name="ModuleSource"><hr size=0>A new <tt>ModuleSource</tt> interface</h4><ul>
-
-Currently, the <tt>PassManager</tt>'s <tt>run</tt> method takes a <tt><a
-href="http://llvm.cs.uiuc.edu/doxygen/classModule.html">Module</a></tt> as
-input, and runs all of the passes on this module. The problem with this
-approach is that none of the <tt>PassManager</tt> features can be used for
-timing and debugging the actual <b>loading</b> of the module from disk or
-standard input.<p>
-
-To solve this problem, eventually the <tt>PassManger</tt> class will accept a
-<tt>ModuleSource</tt> object instead of a Module itself. When complete, this
-will also allow for streaming of functions out of the bytecode representation,
-allowing us to avoid holding the entire program in memory at once if we only are
-dealing with <a href="#FunctionPass">FunctionPass</a>'s.<p>
+Despite that, we have kept the LLVM passes SMP ready, and you should too.</p>
-As part of a different issue, eventually the bytecode loader will be extended to
-allow on-demand loading of functions from the bytecode representation, in order
-to better support the runtime reoptimizer. The bytecode format is already
-capable of this, the loader just needs to be reworked a bit.<p>
+</div>
+</div>
-<!-- _______________________________________________________________________ -->
-</ul><h4><a name="PassFunctionPass"><hr size=0><tt>Pass</tt>'s requiring <tt>FunctionPass</tt>'s</h4><ul>
-
-Currently it is illegal for a <a href="#Pass"><tt>Pass</tt></a> to require a <a
-href="#FunctionPass"><tt>FunctionPass</tt></a>. This is because there is only
-one instance of the <a href="#FunctionPass"><tt>FunctionPass</tt></a> object
-ever created, thus nowhere to store information for all of the functions in the
-program at the same time. Although this has come up a couple of times before,
-this has always been worked around by factoring one big complicated pass into a
-global and an interprocedural part, both of which are distinct. In the future,
-it would be nice to have this though.<p>
-
-Note that it is no problem for a <a
-href="#FunctionPass"><tt>FunctionPass</tt></a> to require the results of a <a
-href="#Pass"><tt>Pass</tt></a>, only the other way around.<p>
-
-
-<!-- *********************************************************************** -->
-</ul>
<!-- *********************************************************************** -->
-
-<hr><font size-1>
-<address><a href="mailto:sabre@nondot.org">Chris Lattner</a></address>
-<!-- Created: Tue Aug 6 15:00:33 CDT 2002 -->
-<!-- hhmts start -->
-Last modified: Mon Oct 21 14:52:55 CDT 2002
-<!-- hhmts end -->
-</font></body></html>
+<hr>
+<address>
+ <a href="http://jigsaw.w3.org/css-validator/check/referer"><img
+ src="http://jigsaw.w3.org/css-validator/images/vcss-blue" alt="Valid CSS"></a>
+ <a href="http://validator.w3.org/check/referer"><img
+ src="http://www.w3.org/Icons/valid-html401-blue" alt="Valid HTML 4.01"></a>
+
+ <a href="mailto:sabre@nondot.org">Chris Lattner</a><br>
+ <a href="http://llvm.org/">The LLVM Compiler Infrastructure</a><br>
+ Last modified: $Date$
+</address>
+
+</body>
+</html>
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