2002-08-08 20:11:18 +00:00
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<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
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<html><head><title>Writing an LLVM Pass</title></head>
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<body bgcolor=white>
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<table width="100%" bgcolor="#330077" border=0 cellpadding=4 cellspacing=0>
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<tr><td> <font size=+3 color="#EEEEFF" face="Georgia,Palatino,Times,Roman"><b>Writing an LLVM Pass</b></font></td>
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</tr></table>
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<ol>
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<li><a href="#introduction">Introduction - What is a pass?</a>
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<li><a href="#quickstart">Quick Start - Writing hello world</a>
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<ul>
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<li><a href="#makefile">Setting up the build environment</a>
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<li><a href="#basiccode">Basic code required</a>
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<li><a href="#running">Running a pass with <tt>opt</tt>
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or <tt>analyze</tt></a>
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</ul>
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<li><a href="#passtype">Pass classes and requirements</a>
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<ul>
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<li><a href="#Pass">The <tt>Pass</tt> class</a>
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<ul>
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<li><a href="#run">The <tt>run</tt> method</a>
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</ul>
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<li><a href="#FunctionPass">The <tt>FunctionPass</tt> class</a>
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<ul>
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<li><a href="#doInitialization_mod">The <tt>doInitialization(Module
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&)</tt> method</a>
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<li><a href="#runOnFunction">The <tt>runOnFunction</tt> method</a>
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<li><a href="#doFinalization_mod">The <tt>doFinalization(Module
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&)</tt> method</a>
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</ul>
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<li><a href="#BasicBlockPass">The <tt>BasicBlockPass</tt> class</a>
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<ul>
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<li><a href="#doInitialization_fn">The <tt>doInitialization(Function
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&)</tt> method</a>
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<li><a href="#runOnBasicBlock">The <tt>runOnBasicBlock</tt> method</a>
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<li><a href="#doFinalization_fn">The <tt>doFinalization(Function
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&)</tt> method</a>
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</ul>
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</ul>
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<li><a href="#registration">Pass Registration</a>
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<ul>
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<li><a href="#print">The <tt>print</tt> method</a>
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</ul>
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<li><a href="#interaction">Specifying interactions between passes</a>
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<ul>
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<li><a href="#getAnalysisUsage">The <tt>getAnalysisUsage</tt> method</a>
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<li><a href="#getAnalysis">The <tt>getAnalysis</tt> method</a>
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</ul>
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2002-08-22 19:21:04 +00:00
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<li><a href="#analysisgroup">Implementing Analysis Groups</a>
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<ul>
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<li><a href="#agconcepts">Analysis Group Concepts</a>
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<li><a href="#registerag">Using <tt>RegisterAnalysisGroup</tt></a>
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</ul>
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<li><a href="#passmanager">What PassManager does</a>
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<ul>
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<li><a href="#releaseMemory">The <tt>releaseMemory</tt> method</a>
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</ul>
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2002-09-06 02:02:58 +00:00
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<li><a href="#debughints">Using GDB with dynamically loaded passes</a>
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<ul>
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<li><a href="#breakpoint">Setting a breakpoint in your pass
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<li><a href="#debugmisc">Miscellaneous Problems
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</ul>
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<li><a href="#future">Future extensions planned</a>
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<ul>
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<li><a href="#SMP">Multithreaded LLVM</a>
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<li><a href="#ModuleSource">A new <tt>ModuleSource</tt> interface</a>
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<li><a href="#PassFunctionPass"><tt>Pass</tt>'s requiring <tt>FunctionPass</tt>'s</a>
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</ul>
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2002-08-08 20:23:41 +00:00
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<p><b>Written by <a href="mailto:sabre@nondot.org">Chris Lattner</a></b><p>
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2002-08-08 20:11:18 +00:00
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</ol><p>
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<!-- *********************************************************************** -->
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<table width="100%" bgcolor="#330077" border=0 cellpadding=4 cellspacing=0>
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<tr><td align=center><font color="#EEEEFF" size=+2 face="Georgia,Palatino"><b>
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<a name="introduction">Introduction - What is a pass?
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</b></font></td></tr></table><ul>
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<!-- *********************************************************************** -->
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The LLVM Pass Framework is an important part of the LLVM system, because LLVM
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passes are where the interesting parts of the compiler exist. Passes perform
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the transformations and optimizations that make up the compiler, they build
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the analysis results that are used by these transformations, and they are, above
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all, a structuring technique for compiler code.<p>
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All LLVM passes are subclasses of the <tt><a
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href="http://llvm.cs.uiuc.edu/doxygen/classPass.html">Pass</a></tt> class, which
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implement functionality by overriding virtual methods inherited from
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<tt>Pass</tt>. Depending on how your pass works, you may be able to inherit
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from the <tt><a
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href="http://llvm.cs.uiuc.edu/doxygen/structFunctionPass.html">FunctionPass</a></tt>
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or <tt><a
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href="http://llvm.cs.uiuc.edu/doxygen/structBasicBlockPass.html">BasicBlockPass</a></tt>,
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which gives the system more information about what your pass does, and how it
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can be combined with other passes. One of the main features of the LLVM Pass
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Framework is that it schedules passes to run in an efficient way based on the
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constraints that your pass has.<p>
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We start by showing you how to construct a pass, everything from setting up the
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code, to compiling, loading, and executing it. After the basics are down, more
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advanced features are discussed.<p>
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<!-- *********************************************************************** -->
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</ul><table width="100%" bgcolor="#330077" border=0 cellpadding=4 cellspacing=0>
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<tr><td align=center><font color="#EEEEFF" size=+2 face="Georgia,Palatino"><b>
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<a name="quickstart">Quick Start - Writing hello world
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</b></font></td></tr></table><ul>
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<!-- *********************************************************************** -->
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Here we describe how to write the "hello world" of passes. The "Hello" pass is
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designed to simply print out the name of non-external functions that exist in
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the program being compiled. It does not modify the program at all, just
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inspects it. The source code and files for this pass are available in the LLVM
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source tree in the <tt>lib/Transforms/Hello</tt> directory.<p>
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<!-- ======================================================================= -->
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</ul><table width="100%" bgcolor="#441188" border=0 cellpadding=4 cellspacing=0>
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<tr><td> </td><td width="100%">
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<font color="#EEEEFF" face="Georgia,Palatino"><b>
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<a name="makefile">Setting up the build environment
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</b></font></td></tr></table><ul>
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First thing you need to do is create a new directory somewhere in the LLVM
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source base. For this example, we'll assume that you made
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"<tt>lib/Transforms/Hello</tt>". The first thing you must do is set up a build
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script (Makefile) that will compile the source code for the new pass. To do
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2002-09-16 22:37:56 +00:00
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this, copy this into "<tt>Makefile</tt>":<p>
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2002-08-08 20:11:18 +00:00
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</ul><hr><ul><pre>
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# Makefile for hello pass
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2002-08-14 20:06:13 +00:00
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# Path to top level of LLVM heirarchy
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LEVEL = ../../..
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# Name of the library to build
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LIBRARYNAME = hello
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# Build a dynamically loadable shared object
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SHARED_LIBRARY = 1
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# Include the makefile implementation stuff
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include $(LEVEL)/Makefile.common
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</pre></ul><hr><ul><p>
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This makefile specifies that all of the <tt>.cpp</tt> files in the current
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directory are to be compiled and linked together into a
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<tt>lib/Debug/libhello.so</tt> shared object that can be dynamically loaded by
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the <tt>opt</tt> or <tt>analyze</tt> tools.<p>
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Now that we have the build scripts set up, we just need to write the code for
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the pass itself.<p>
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<!-- ======================================================================= -->
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</ul><table width="100%" bgcolor="#441188" border=0 cellpadding=4 cellspacing=0>
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<tr><td> </td><td width="100%">
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<font color="#EEEEFF" face="Georgia,Palatino"><b>
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<a name="basiccode">Basic code required
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</b></font></td></tr></table><ul>
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Now that we have a way to compile our new pass, we just have to write it. Start
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out with:<p>
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<pre>
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<b>#include</b> "<a href="http://llvm.cs.uiuc.edu/doxygen/Pass_8h-source.html">llvm/Pass.h</a>"
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<b>#include</b> "<a href="http://llvm.cs.uiuc.edu/doxygen/Function_8h-source.html">llvm/Function.h</a>"
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</pre>
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Which are needed because we are writing a <tt><a
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href="http://llvm.cs.uiuc.edu/doxygen/classPass.html">Pass</a></tt>, and we are
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operating on <tt><a
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href="http://llvm.cs.uiuc.edu/doxygen/classFunction.html">Function</a></tt>'s.<p>
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Next we have:<p>
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<pre>
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<b>namespace</b> {
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</pre><p>
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... which starts out an anonymous namespace. Anonymous namespaces are to C++
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what the "<tt>static</tt>" keyword is to C (at global scope). It makes the
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things declared inside of the anonymous namespace only visible to the current
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file. If you're not familiar with them, consult a decent C++ book for more
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information.<p>
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Next, we declare our pass itself:<p>
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<pre>
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<b>struct</b> Hello : <b>public</b> <a href="#FunctionPass">FunctionPass</a> {
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</pre><p>
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This declares a "<tt>Hello</tt>" class that is a subclass of <tt><a
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href="http://llvm.cs.uiuc.edu/doxygen/structFunctionPass.html">FunctionPass</a></tt>.
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2002-09-09 03:48:46 +00:00
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The different builtin pass subclasses are described in detail <a
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href="#passtype">later</a>, but for now, know that <a href="#FunctionPass"><tt>FunctionPass</tt></a>'s
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operate a function at a time.<p>
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<pre>
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<b>virtual bool</b> <a href="#runOnFunction">runOnFunction</a>(Function &F) {
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std::cerr << "<i>Hello: </i>" << F.getName() << "\n";
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<b>return false</b>;
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}
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}; <i>// end of struct Hello</i>
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</pre>
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We declare a "<a href="#runOnFunction"><tt>runOnFunction</tt></a>" method, which
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overloads an abstract virtual method inherited from <a
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href="#FunctionPass"><tt>FunctionPass</tt></a>. This is where we are supposed
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to do our thing, so we just print out our message with the name of each
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function.<p>
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<pre>
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RegisterOpt<Hello> X("<i>hello</i>", "<i>Hello World Pass</i>");
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} <i>// end of anonymous namespace</i>
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</pre><p>
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Lastly, we register our class <tt>Hello</tt>, giving it a command line argument
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"<tt>hello</tt>", and a name "<tt>Hello World Pass</tt>". There are several
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different ways of <a href="#registration">registering your pass</a>, depending
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on what it is to be used for. For "optimizations" we use the
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<tt>RegisterOpt</tt> template.<p>
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As a whole, the <tt>.cpp</tt> file looks like:<p>
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<pre>
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<b>#include</b> "<a href="http://llvm.cs.uiuc.edu/doxygen/Pass_8h-source.html">llvm/Pass.h</a>"
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<b>#include</b> "<a href="http://llvm.cs.uiuc.edu/doxygen/Function_8h-source.html">llvm/Function.h</a>"
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<b>namespace</b> {
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<b>struct Hello</b> : <b>public</b> <a href="#FunctionPass">FunctionPass</a> {
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<b>virtual bool</b> <a href="#runOnFunction">runOnFunction</a>(Function &F) {
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std::cerr << "<i>Hello: </i>" << F.getName() << "\n";
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<b>return false</b>;
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}
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};
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RegisterOpt<Hello> X("<i>hello</i>", "<i>Hello World Pass</i>");
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}
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</pre><p>
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Now that it's all together, compile the file with a simple "<tt>gmake</tt>"
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command in the local directory and you should get a new
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"<tt>lib/Debug/libhello.so</tt> file. Note that everything in this file is
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contained in an anonymous namespace: this reflects the fact that passes are self
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contained units that do not need external interfaces (although they can have
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them) to be useful.<p>
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<!-- ======================================================================= -->
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</ul><table width="100%" bgcolor="#441188" border=0 cellpadding=4 cellspacing=0>
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<tr><td> </td><td width="100%">
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<font color="#EEEEFF" face="Georgia,Palatino"><b>
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<a name="running">Running a pass with <tt>opt</tt> or <tt>analyze</tt>
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</b></font></td></tr></table><ul>
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Now that you have a brand new shiny <tt>.so</tt> file, we can use the
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<tt>opt</tt> command to run an LLVM program through your pass. Because you
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registered your pass with the <tt>RegisterOpt</tt> template, you will be able to
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use the <tt>opt</tt> tool to access it, once loaded.<p>
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To test it, follow the example at the end of the <a
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href="GettingStarted.html">Getting Started Guide</a> to compile "Hello World" to
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LLVM. We can now run the bytecode file (<tt>hello.bc</tt>) for the program
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through our transformation like this (or course, any bytecode file will
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work):<p>
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<pre>
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$ opt -load ../../../lib/Debug/libhello.so -hello < hello.bc > /dev/null
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|
Hello: __main
|
|
|
|
|
Hello: puts
|
|
|
|
|
Hello: main
|
|
|
|
|
</pre><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>
|
|
|
|
|
|
|
|
|
|
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
|
|
|
|
|
OVERVIEW: llvm .bc -> .bc modular optimizer
|
|
|
|
|
|
|
|
|
|
USAGE: opt [options] <input bytecode>
|
|
|
|
|
|
|
|
|
|
OPTIONS:
|
|
|
|
|
Optimizations available:
|
|
|
|
|
...
|
|
|
|
|
-funcresolve - Resolve Functions
|
|
|
|
|
-gcse - Global Common Subexpression Elimination
|
|
|
|
|
-globaldce - Dead Global Elimination
|
|
|
|
|
<b>-hello - Hello World Pass</b>
|
|
|
|
|
-indvars - Cannonicalize Induction Variables
|
|
|
|
|
-inline - Function Integration/Inlining
|
|
|
|
|
-instcombine - Combine redundant instructions
|
|
|
|
|
...
|
|
|
|
|
</pre><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>
|
|
|
|
|
|
|
|
|
|
<pre>
|
|
|
|
|
$ opt -load ../../../lib/Debug/libhello.so -hello -time-passes < hello.bc > /dev/null
|
|
|
|
|
Hello: __main
|
|
|
|
|
Hello: puts
|
|
|
|
|
Hello: main
|
|
|
|
|
===============================================================================
|
|
|
|
|
... Pass execution timing report ...
|
|
|
|
|
===============================================================================
|
|
|
|
|
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
|
|
|
|
|
0.0000 ( 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>
|
|
|
|
|
|
|
|
|
|
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.
|
|
|
|
|
|
|
|
|
|
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>
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
<!-- *********************************************************************** -->
|
|
|
|
|
</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>
|
|
|
|
|
<!-- *********************************************************************** -->
|
|
|
|
|
|
|
|
|
|
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>
|
|
|
|
|
|
2002-08-22 19:21:04 +00:00
|
|
|
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>
|
2002-08-08 20:11:18 +00:00
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
<!-- ======================================================================= -->
|
|
|
|
|
</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>
|
|
|
|
|
|
|
|
|
|
The "<tt><a href="http://llvm.cs.uiuc.edu/doxygen/classPass.html">Pass</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>
|
|
|
|
|
|
|
|
|
|
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>
|
|
|
|
|
|
|
|
|
|
<!-- _______________________________________________________________________ -->
|
|
|
|
|
</ul><h4><a name="run"><hr size=0>The <tt>run</tt> method</h4><ul>
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
<pre>
|
|
|
|
|
<b>virtual bool</b> run(Module &M) = 0;
|
|
|
|
|
</pre><p>
|
|
|
|
|
|
|
|
|
|
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>
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
<!-- ======================================================================= -->
|
|
|
|
|
</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>
|
|
|
|
|
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.
|
|
|
|
|
<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>
|
|
|
|
|
|
|
|
|
|
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>Maintain state across invocations of
|
|
|
|
|
<a href="#runOnFunction"><tt>runOnFunction</tt></a> (including global data)
|
|
|
|
|
</ol><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>
|
|
|
|
|
|
|
|
|
|
<!-- _______________________________________________________________________ -->
|
2002-09-12 17:06:43 +00:00
|
|
|
</ul><h4><a name="doInitialization_mod"><hr size=0>The
|
|
|
|
|
<tt>doInitialization(Module &)</tt> method</h4><ul>
|
2002-08-08 20:11:18 +00:00
|
|
|
|
|
|
|
|
<pre>
|
|
|
|
|
<b>virtual bool</b> doInitialization(Module &M);
|
|
|
|
|
</pre><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
|
2002-09-12 17:06:43 +00:00
|
|
|
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>
|
2002-08-08 20:11:18 +00:00
|
|
|
|
|
|
|
|
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>
|
|
|
|
|
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
|
|
|
|
|
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>
|
|
|
|
|
|
|
|
|
|
<!-- _______________________________________________________________________ -->
|
|
|
|
|
</ul><h4><a name="runOnFunction"><hr size=0>The <tt>runOnFunction</tt> method</h4><ul>
|
|
|
|
|
|
|
|
|
|
<pre>
|
|
|
|
|
<b>virtual bool</b> runOnFunction(Function &F) = 0;
|
|
|
|
|
</pre><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>
|
|
|
|
|
|
|
|
|
|
<!-- _______________________________________________________________________ -->
|
2002-09-12 17:06:43 +00:00
|
|
|
</ul><h4><a name="doFinalization_mod"><hr size=0>The <tt>doFinalization(Module &)</tt> method</h4><ul>
|
2002-08-08 20:11:18 +00:00
|
|
|
|
|
|
|
|
<pre>
|
|
|
|
|
<b>virtual bool</b> doFinalization(Module &M);
|
|
|
|
|
</pre</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>
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
<!-- ======================================================================= -->
|
|
|
|
|
</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>
|
|
|
|
|
|
|
|
|
|
<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>
|
|
|
|
|
|
|
|
|
|
<ol>
|
|
|
|
|
<li>Modify or inspect any basic blocks outside of the current one
|
|
|
|
|
<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>
|
|
|
|
|
|
|
|
|
|
<tt>BasicBlockPass</tt>'s are useful for traditional local and "peephole"
|
|
|
|
|
optimizations. They may override the same <a
|
2002-09-12 17:06:43 +00:00
|
|
|
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>
|
|
|
|
|
|
|
|
|
|
<!-- _______________________________________________________________________ -->
|
|
|
|
|
</ul><h4><a name="doInitialization_fn"><hr size=0>The
|
|
|
|
|
<tt>doInitialization(Function &)</tt> method</h4><ul>
|
|
|
|
|
|
|
|
|
|
<pre>
|
|
|
|
|
<b>virtual bool</b> doInitialization(Function &F);
|
|
|
|
|
</pre><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
|
|
|
|
|
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>
|
|
|
|
|
|
2002-08-08 20:11:18 +00:00
|
|
|
|
|
|
|
|
<!-- _______________________________________________________________________ -->
|
|
|
|
|
</ul><h4><a name="runOnBasicBlock"><hr size=0>The <tt>runOnBasicBlock</tt> method</h4><ul>
|
|
|
|
|
|
|
|
|
|
<pre>
|
|
|
|
|
<b>virtual bool</b> runOnBasicBlock(BasicBlock &BB) = 0;
|
|
|
|
|
</pre><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>
|
|
|
|
|
|
|
|
|
|
|
2002-09-12 17:06:43 +00:00
|
|
|
<!-- _______________________________________________________________________ -->
|
|
|
|
|
</ul><h4><a name="doFinalization_fn"><hr size=0>The <tt>doFinalization(Function
|
|
|
|
|
&)</tt> method</h4><ul>
|
|
|
|
|
|
|
|
|
|
<pre>
|
|
|
|
|
<b>virtual bool</b> doFinalization(Function &F);
|
|
|
|
|
</pre</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>
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
2002-08-08 20:11:18 +00:00
|
|
|
<!-- *********************************************************************** -->
|
|
|
|
|
</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>
|
|
|
|
|
<!-- *********************************************************************** -->
|
|
|
|
|
|
|
|
|
|
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>
|
|
|
|
|
|
|
|
|
|
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>
|
|
|
|
|
|
|
|
|
|
<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
|
|
|
|
|
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>
|
|
|
|
|
|
|
|
|
|
If a pass is registered to be used by the <tt>analyze</tt> utility, 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>
|
|
|
|
|
|
|
|
|
|
<pre>
|
|
|
|
|
<b>virtual void</b> print(std::ostream &O, <b>const</b> Module *M) <b>const</b>;
|
|
|
|
|
</pre><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. The <tt>analyze</tt> tool uses this method to generate its output.<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
|
|
|
|
|
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>
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
<!-- *********************************************************************** -->
|
|
|
|
|
</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>
|
|
|
|
|
<!-- *********************************************************************** -->
|
|
|
|
|
|
|
|
|
|
One of the main responsibilities of the <tt>PassManager</tt> is the 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>
|
|
|
|
|
|
|
|
|
|
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>
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
<!-- _______________________________________________________________________ -->
|
|
|
|
|
</ul><h4><a name="getAnalysisUsage"><hr size=0>The <tt>getAnalysisUsage</tt> method</h4><ul>
|
|
|
|
|
|
|
|
|
|
<pre>
|
|
|
|
|
<b>virtual void</b> getAnalysisUsage(AnalysisUsage &Info) <b>const</b>;
|
|
|
|
|
</pre><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>
|
|
|
|
|
|
|
|
|
|
<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>// preservesCFG - 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::preservesCFG();
|
|
|
|
|
</pre><p>
|
|
|
|
|
|
|
|
|
|
Some examples of how to use these methods are:<p>
|
|
|
|
|
|
|
|
|
|
<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>
|
|
|
|
|
|
|
|
|
|
and:<p>
|
|
|
|
|
|
|
|
|
|
<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> {
|
|
|
|
|
AU.preservesCFG();
|
|
|
|
|
AU.addRequired<<a href="http://llvm.cs.uiuc.edu/doxygen/classLoopInfo.html">LoopInfo</a>>();
|
|
|
|
|
}
|
|
|
|
|
</pre><p>
|
|
|
|
|
|
|
|
|
|
<!-- _______________________________________________________________________ -->
|
|
|
|
|
</ul><h4><a name="getAnalysis"><hr size=0>The <tt>getAnalysis<></tt> method</h4><ul>
|
|
|
|
|
|
|
|
|
|
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>
|
|
|
|
|
|
|
|
|
|
<pre>
|
|
|
|
|
<b>template</b><<b>typename</b> PassClass>
|
|
|
|
|
AnalysisType &getAnalysis();
|
|
|
|
|
</pre><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.<p>
|
|
|
|
|
|
2002-08-22 19:21:04 +00:00
|
|
|
<!-- *********************************************************************** -->
|
|
|
|
|
</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>
|
|
|
|
|
<!-- *********************************************************************** -->
|
|
|
|
|
|
|
|
|
|
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
|
|
|
|
|
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>
|
|
|
|
|
|
|
|
|
|
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
|
|
|
|
|
flow-sensitive, context-sensitive interprocedural analysis that can take 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>
|
|
|
|
|
|
|
|
|
|
<!-- _______________________________________________________________________ -->
|
|
|
|
|
</ul><h4><a name="agconcepts"><hr size=0>Analysis Group Concepts</h4><ul>
|
|
|
|
|
|
|
|
|
|
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>
|
|
|
|
|
|
|
|
|
|
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>
|
|
|
|
|
|
|
|
|
|
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
|
|
|
|
|
implementation pool. Also, a default implementation of the interface
|
|
|
|
|
<b>must</b> be registered with <A
|
|
|
|
|
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>
|
|
|
|
|
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>
|
|
|
|
|
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>
|
|
|
|
|
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>
|
|
|
|
|
|
|
|
|
|
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>
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
<!-- _______________________________________________________________________ -->
|
|
|
|
|
</ul><h4><a name="registerag"><hr size=0>Using <tt>RegisterAnalysisGroup</tt></h4><ul>
|
|
|
|
|
|
|
|
|
|
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.
|
|
|
|
|
Unlike registration of passes, there is no command line argument to be specified
|
|
|
|
|
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>
|
|
|
|
|
|
|
|
|
|
Once the analysis is registered, passes can declare that they are valid
|
|
|
|
|
implementations of the interface by using the following code:<p>
|
|
|
|
|
|
|
|
|
|
<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;
|
|
|
|
|
}
|
|
|
|
|
</pre><p>
|
|
|
|
|
|
|
|
|
|
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>
|
|
|
|
|
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>
|
|
|
|
|
|
|
|
|
|
<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;
|
|
|
|
|
}
|
|
|
|
|
</pre><p>
|
|
|
|
|
|
|
|
|
|
Here we show how the default implementation is specified (using the extra
|
|
|
|
|
argument to the <tt>RegisterAnalysisGroup</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>
|
2002-08-08 20:11:18 +00:00
|
|
|
|
|
|
|
|
|
|
|
|
|
<!-- *********************************************************************** -->
|
|
|
|
|
</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>
|
|
|
|
|
<!-- *********************************************************************** -->
|
|
|
|
|
|
|
|
|
|
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>
|
|
|
|
|
|
|
|
|
|
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
|
|
|
|
|
recomputing analysis results as much as possible. This means keeping track of
|
|
|
|
|
which analyses are available already, which analyses get invalidated, and which
|
|
|
|
|
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>
|
|
|
|
|
|
|
|
|
|
<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 consequtive <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>
|
|
|
|
|
|
|
|
|
|
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>
|
|
|
|
|
|
|
|
|
|
</ol><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>
|
|
|
|
|
|
|
|
|
|
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>
|
|
|
|
|
|
|
|
|
|
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
|
|
|
|
|
Module Pass Manager
|
|
|
|
|
Function Pass Manager
|
|
|
|
|
Dominator Set Construction
|
|
|
|
|
Immediate Dominators Construction
|
|
|
|
|
Global Common Subexpression Elimination
|
|
|
|
|
-- Immediate Dominators Construction
|
|
|
|
|
-- Global Common Subexpression Elimination
|
|
|
|
|
Natural Loop Construction
|
|
|
|
|
Loop Invariant Code Motion
|
|
|
|
|
-- Natural Loop Construction
|
|
|
|
|
-- Loop Invariant Code Motion
|
|
|
|
|
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
|
|
|
|
|
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>
|
|
|
|
|
|
|
|
|
|
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>
|
|
|
|
|
|
|
|
|
|
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
|
|
|
|
|
Module Pass Manager
|
|
|
|
|
Function Pass Manager
|
|
|
|
|
Dominator Set Construction
|
|
|
|
|
Immediate Dominators Construction
|
|
|
|
|
Global Common Subexpression Elimination
|
|
|
|
|
<b>-- Dominator Set Construction</b>
|
|
|
|
|
-- Immediate Dominators Construction
|
|
|
|
|
-- Global Common Subexpression Elimination
|
|
|
|
|
<b> Hello World Pass
|
|
|
|
|
-- Hello World Pass
|
|
|
|
|
Dominator Set Construction</b>
|
|
|
|
|
Natural Loop Construction
|
|
|
|
|
Loop Invariant Code Motion
|
|
|
|
|
-- Natural Loop Construction
|
|
|
|
|
-- Loop Invariant Code Motion
|
|
|
|
|
Module Verifier
|
|
|
|
|
-- Dominator Set Construction
|
|
|
|
|
-- Module Verifier
|
|
|
|
|
Bytecode Writer
|
|
|
|
|
--Bytecode Writer
|
|
|
|
|
Hello: __main
|
|
|
|
|
Hello: puts
|
|
|
|
|
Hello: main
|
|
|
|
|
</pre><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>
|
|
|
|
|
|
|
|
|
|
<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>
|
|
|
|
|
|
|
|
|
|
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
|
|
|
|
|
Pass Arguments: -gcse -hello -licm
|
|
|
|
|
Module Pass Manager
|
|
|
|
|
Function Pass Manager
|
|
|
|
|
Dominator Set Construction
|
|
|
|
|
Immediate Dominators Construction
|
|
|
|
|
Global Common Subexpression Elimination
|
|
|
|
|
-- Immediate Dominators Construction
|
|
|
|
|
-- Global Common Subexpression Elimination
|
|
|
|
|
Hello World Pass
|
|
|
|
|
-- Hello World Pass
|
|
|
|
|
Natural Loop Construction
|
|
|
|
|
Loop Invariant Code Motion
|
|
|
|
|
-- Loop Invariant Code Motion
|
|
|
|
|
-- Natural Loop Construction
|
|
|
|
|
Module Verifier
|
|
|
|
|
-- Dominator Set Construction
|
|
|
|
|
-- Module Verifier
|
|
|
|
|
Bytecode Writer
|
|
|
|
|
--Bytecode 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>
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
<!-- _______________________________________________________________________ -->
|
|
|
|
|
</ul><h4><a name="releaseMemory"><hr size=0>The <tt>releaseMemory</tt> method</h4><ul>
|
|
|
|
|
|
|
|
|
|
<pre>
|
|
|
|
|
<b>virtual void</b> releaseMemory();
|
|
|
|
|
</pre><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>
|
|
|
|
|
|
|
|
|
|
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
|
|
|
|
|
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>
|
|
|
|
|
|
|
|
|
|
|
2002-09-06 02:02:58 +00:00
|
|
|
<!-- *********************************************************************** -->
|
|
|
|
|
</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>
|
|
|
|
|
<!-- *********************************************************************** -->
|
|
|
|
|
|
|
|
|
|
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>
|
|
|
|
|
|
|
|
|
|
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>
|
|
|
|
|
|
|
|
|
|
<!-- _______________________________________________________________________ -->
|
|
|
|
|
</ul><h4><a name="breakpoint"><hr size=0>Setting a breakpoint in your pass</h4><ul>
|
|
|
|
|
|
|
|
|
|
First thing you do is start <tt>gdb</tt> on the <tt>opt</tt> process:<p>
|
|
|
|
|
|
|
|
|
|
<pre>
|
|
|
|
|
$ <b>gdb opt</b>
|
|
|
|
|
GNU gdb 5.0
|
|
|
|
|
Copyright 2000 Free Software Foundation, Inc.
|
|
|
|
|
GDB is free software, covered by the GNU General Public License, and you are
|
|
|
|
|
welcome to change it and/or distribute copies of it under certain conditions.
|
|
|
|
|
Type "show copying" to see the conditions.
|
|
|
|
|
There is absolutely no warranty for GDB. Type "show warranty" for details.
|
|
|
|
|
This GDB was configured as "sparc-sun-solaris2.6"...
|
|
|
|
|
(gdb)
|
|
|
|
|
</pre><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>
|
|
|
|
|
|
|
|
|
|
<pre>
|
|
|
|
|
(gdb) <b>break 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]
|
|
|
|
|
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>
|
|
|
|
|
|
|
|
|
|
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>
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
<!-- _______________________________________________________________________ -->
|
|
|
|
|
</ul><h4><a name="debugmisc"><hr size=0>Miscellaneous Problems</h4><ul>
|
|
|
|
|
|
|
|
|
|
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>
|
|
|
|
|
|
|
|
|
|
<li>Restarting the program breaks breakpoints. After following the information
|
|
|
|
|
above, you have succeeded in getting some breakpoints planted in your pass. Nex
|
|
|
|
|
thing you know, you restart the program (i.e., you type '<tt>run</tt>' again),
|
|
|
|
|
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>
|
|
|
|
|
|
|
|
|
|
</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>
|
|
|
|
|
|
|
|
|
|
|
2002-08-08 20:11:18 +00:00
|
|
|
<!-- *********************************************************************** -->
|
|
|
|
|
</ul><table width="100%" bgcolor="#330077" border=0 cellpadding=4 cellspacing=0>
|
|
|
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<tr><td align=center><font color="#EEEEFF" size=+2 face="Georgia,Palatino"><b>
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<a name="future">Future extensions planned
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</b></font></td></tr></table><ul>
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<!-- *********************************************************************** -->
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Although the LLVM Pass Infrastructure is very capable as it stands, and does
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some nifty stuff, there are things we'd like to add in the future. Here is
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where we are going:<p>
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<!-- _______________________________________________________________________ -->
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</ul><h4><a name="SMP"><hr size=0>Multithreaded LLVM</h4><ul>
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Multiple CPU machines are becoming more command and compilation can never be
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fast enough: obviously we should allow for a multithreaded compiler. Because of
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the semantics defined for passes above (specifically they cannot maintain state
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across invocations of their <tt>run*</tt> methods), a nice clean way to
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implement a multithreaded compiler would be for the <tt>PassManager</tt> class
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to create multiple instances of each pass object, and allow the seperate
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instances to be hacking on different parts of the program at the same time.<p>
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This implementation would prevent each of the passes from having to implement
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multithreaded constructs, requiring only the LLVM core to have locking in a few
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places (for global resources). Although this is a simple extension, we simply
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haven't had time (or multiprocessor machines, thus a reason) to implement this.
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Despite that, we have kept the LLVM passes SMP ready, and you should too.<p>
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<!-- _______________________________________________________________________ -->
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</ul><h4><a name="ModuleSource"><hr size=0>A new <tt>ModuleSource</tt> interface</h4><ul>
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Currently, the <tt>PassManager</tt>'s <tt>run</tt> method takes a <tt><a
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href="http://llvm.cs.uiuc.edu/doxygen/classModule.html">Module</a></tt> as
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input, and runs all of the passes on this module. The problem with this
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approach is that none of the <tt>PassManager</tt> features can be used for
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timing and debugging the actual <b>loading</b> of the module from disk or
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standard input.<p>
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To solve this problem, eventually the <tt>PassManger</tt> class will accept a
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<tt>ModuleSource</tt> object instead of a Module itself. When complete, this
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will also allow for streaming of functions out of the bytecode representation,
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allowing us to avoid holding the entire program in memory at once if we only are
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dealing with <a href="#FunctionPass">FunctionPass</a>'s.<p>
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As part of a different issue, eventually the bytecode loader will be extended to
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allow on-demand loading of functions from the bytecode representation, in order
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to better support the runtime reoptimizer. The bytecode format is already
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capable of this, the loader just needs to be reworked a bit.<p>
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<!-- _______________________________________________________________________ -->
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</ul><h4><a name="PassFunctionPass"><hr size=0><tt>Pass</tt>'s requiring <tt>FunctionPass</tt>'s</h4><ul>
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Currently it is illegal for a <a href="#Pass"><tt>Pass</tt></a> to require a <a
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href="#FunctionPass"><tt>FunctionPass</tt></a>. This is because there is only
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one instance of the <a href="#FunctionPass"><tt>FunctionPass</tt></a> object
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ever created, thus nowhere to store information for all of the functions in the
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program at the same time. Although this has come up a couple of times before,
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this has always been worked around by factoring one big complicated pass into a
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global and an interprocedural part, both of which are distinct. In the future,
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it would be nice to have this though.<p>
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Note that it is no problem for a <a
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href="#FunctionPass"><tt>FunctionPass</tt></a> to require the results of a <a
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href="#Pass"><tt>Pass</tt></a>, only the other way around.<p>
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<!-- *********************************************************************** -->
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</ul>
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<!-- *********************************************************************** -->
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<hr><font size-1>
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2002-09-06 02:02:58 +00:00
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<address><a href="mailto:sabre@nondot.org">Chris Lattner</a></address>
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2002-08-08 20:11:18 +00:00
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<!-- Created: Tue Aug 6 15:00:33 CDT 2002 -->
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<!-- hhmts start -->
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2002-09-16 22:37:56 +00:00
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Last modified: Mon Sep 16 17:37:27 CDT 2002
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2002-08-08 20:11:18 +00:00
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<!-- hhmts end -->
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</font></body></html>
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