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| author | Misha Brukman <brukman+llvm@gmail.com> | 2004-01-15 18:34:11 +0000 |
|---|---|---|
| committer | Misha Brukman <brukman+llvm@gmail.com> | 2004-01-15 18:34:11 +0000 |
| commit | c5402408576898449c5545bac7e111faa7546647 (patch) | |
| tree | 5834f362933b04b1e9fb3f3b5fd707d0ef1cab87 /docs/WritingAnLLVMPass.html | |
| parent | d011a027e0f60d9b6d20097ef94e09f51af897c5 (diff) | |
| download | external_llvm-c5402408576898449c5545bac7e111faa7546647.zip external_llvm-c5402408576898449c5545bac7e111faa7546647.tar.gz external_llvm-c5402408576898449c5545bac7e111faa7546647.tar.bz2 | |
* HTML 4.01 Strict DTD compliance
* Use stylesheets instead of adhoc formatting
* Fix broken links in doxygen due to llvm namespace
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@10881 91177308-0d34-0410-b5e6-96231b3b80d8
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diff --git a/docs/WritingAnLLVMPass.html b/docs/WritingAnLLVMPass.html index dc70d03..3570717 100644 --- a/docs/WritingAnLLVMPass.html +++ b/docs/WritingAnLLVMPass.html @@ -1,146 +1,158 @@ -<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"> -<html><head><title>Writing an LLVM Pass</title></head> - -<body bgcolor=white> - -<table width="100%" bgcolor="#330077" border=0 cellpadding=4 cellspacing=0> -<tr><td> <font size=+3 color="#EEEEFF" face="Georgia,Palatino,Times,Roman"><b>Writing an LLVM Pass</b></font></td> -</tr></table> - +<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN" + "http://www.w3.org/TR/html4/strict.dtd"> +<html> +<head> + <title>Writing an LLVM Pass</title> + <link rel="stylesheet" href="llvm.css" type="text/css"> +</head> +<body> + +<div class="doc_title"> + Writing an LLVM Pass +</div> <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="#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> - or <tt>analyze</tt></a> - </ul> + or <tt>analyze</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="#ImmutablePass">The <tt>ImmutablePass</tt> class</a></li> <li><a href="#Pass">The <tt>Pass</tt> class</a> <ul> - <li><a href="#run">The <tt>run</tt> method</a> - </ul> + <li><a href="#run">The <tt>run</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="#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> - </ul> + <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="#getAnalysis">The <tt>getAnalysis</tt> method</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="#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="#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> - + <li><a href="#SMP">Multithreaded LLVM</a></li> + <li><a href="#ModuleSource">A new <tt>ModuleSource</tt> interface</a></li> + <li><a href="#PassFunctionPass"><tt>Pass</tt>es requiring + <tt>FunctionPass</tt>es</a></li> + </ul></li> +</ol> + +<div class="doc_text"> <p><b>Written by <a href="mailto:sabre@nondot.org">Chris Lattner</a></b><p> -</ol><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> +<div class="doc_section"> + <a name="introduction">Introduction - What is a pass?</a> +</div> <!-- *********************************************************************** --> -The LLVM Pass Framework is an important part of the LLVM system, because LLVM +<div class="doc_text"> + +<p>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> +all, a structuring technique for compiler code.</p> + +<p>All LLVM passes are subclasses of the <tt><a +href="http://llvm.cs.uiuc.edu/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 may be able to +inherit from the <tt><a +href="http://llvm.cs.uiuc.edu/doxygen/structllvm_1_1FunctionPass.html">FunctionPass</a></tt> or <tt><a -href="http://llvm.cs.uiuc.edu/doxygen/structBasicBlockPass.html">BasicBlockPass</a></tt>, +href="http://llvm.cs.uiuc.edu/doxygen/structllvm_1_1BasicBlockPass.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> +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> +<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> +<div class="doc_section"> + <a name="quickstart">Quick Start - Writing hello world</a> +</div> <!-- *********************************************************************** --> -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 +<div class="doc_text"> + +<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, 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> +source tree in the <tt>lib/Transforms/Hello</tt> directory.</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="makefile">Setting up the build environment -</b></font></td></tr></table><ul> +<div class="doc_subsection"> + <a name="makefile">Setting up the build environment</a> +</div> + +<div class="doc_text"> -First thing you need to do is create a new directory somewhere in the LLVM +<p>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> +this, copy this into "<tt>Makefile</tt>":</p> -</ul><hr><ul><pre> +<hr> + +<pre> # Makefile for hello pass # Path to top level of LLVM heirarchy @@ -154,87 +166,89 @@ SHARED_LIBRARY = 1 # Include the makefile implementation stuff include $(LEVEL)/Makefile.common -</pre></ul><hr><ul><p> +</pre> -This makefile specifies that all of the <tt>.cpp</tt> files in the current +<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> +the <tt>opt</tt> or <tt>analyze</tt> tools.</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> +<div class="doc_subsection"> + <a name="basiccode">Basic code required</a> +</div> + +<div class="doc_text"> -Now that we have a way to compile our new pass, we just have to write it. Start -out with:<p> +<p>Now that we have a way to compile our new pass, we just have to write it. +Start out with:</p> <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>" </pre> -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.cs.uiuc.edu/doxygen/classllvm_1_1Pass.html">Pass</a></tt>, and +we are operating on <tt><a +href="http://llvm.cs.uiuc.edu/doxygen/classllvm_1_1Function.html">Function</a></tt>'s.</p> -Next we have:<p> +<p>Next we have:</p> <pre> <b>namespace</b> { -</pre><p> +</pre> -... 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 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> <pre> <b>struct</b> Hello : <b>public</b> <a href="#FunctionPass">FunctionPass</a> { </pre><p> -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.cs.uiuc.edu/doxygen/structllvm_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 a function at a +time.</p> <pre> - <b>virtual bool</b> <a href="#runOnFunction">runOnFunction</a>(Function &F) { + <b>virtual bool</b> <a href="#runOnFunction">runOnFunction</a>(Function &F) { std::cerr << "<i>Hello: </i>" << F.getName() << "\n"; <b>return false</b>; } }; <i>// end of struct Hello</i> </pre> -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> <pre> RegisterOpt<Hello> X("<i>hello</i>", "<i>Hello World Pass</i>"); } <i>// end of anonymous namespace</i> -</pre><p> +</pre> -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 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> -As a whole, the <tt>.cpp</tt> file looks like:<p> +<p>As a whole, the <tt>.cpp</tt> file looks like:</p> <pre> <b>#include</b> "<a href="http://llvm.cs.uiuc.edu/doxygen/Pass_8h-source.html">llvm/Pass.h</a>" @@ -242,7 +256,7 @@ As a whole, the <tt>.cpp</tt> file looks like:<p> <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) { + <b>virtual bool</b> <a href="#runOnFunction">runOnFunction</a>(Function &F) { std::cerr << "<i>Hello: </i>" << F.getName() << "\n"; <b>return false</b>; } @@ -250,50 +264,51 @@ As a whole, the <tt>.cpp</tt> file looks like:<p> RegisterOpt<Hello> X("<i>hello</i>", "<i>Hello World Pass</i>"); } -</pre><p> +</pre> -Now that it's all together, compile the file with a simple "<tt>gmake</tt>" +<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 "<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> +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> +<div class="doc_subsection"> + <a name="running">Running a pass with <tt>opt</tt> or <tt>analyze</tt></a> +</div> -Now that you have a brand new shiny <tt>.so</tt> file, we can use the +<div class="doc_text"> + +<p>Now that you have a brand new shiny <tt>.so</tt> 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> +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> +work):</p> <pre> $ opt -load ../../../lib/Debug/libhello.so -hello < hello.bc > /dev/null Hello: __main Hello: puts Hello: main -</pre><p> +</pre> -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 @@ -312,16 +327,16 @@ OPTIONS: -inline - Function Integration/Inlining -instcombine - Combine redundant instructions ... -</pre><p> +</pre> -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 @@ -339,400 +354,469 @@ Hello: main 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> -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. - -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> +hasn't been broken somehow.</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> <!-- *********************************************************************** --> -</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> +<div class="doc_section"> + <a name="passtype">Pass classes and requirements</a> +</div> <!-- *********************************************************************** --> -One of the first things that you should do when designing a new pass is to +<div class="doc_text"> + +<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 necessary to optimize how passes are run, so that the resultant compiler isn't unneccesarily -slow.<p> +slow.</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="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>" +<div class="doc_subsection"> + <a name="ImmutablePass">The <tt>ImmutablePass</tt> class</a> +</div> + +<div class="doc_text"> + +<p>The most plain and boring type of pass is the "<tt><a +href="http://llvm.cs.uiuc.edu/doxygen/structllvm_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> +<div class="doc_subsection"> + <a name="Pass">The <tt>Pass</tt> class</a> +</div> -The "<tt><a href="http://llvm.cs.uiuc.edu/doxygen/classPass.html">Pass</a></tt>" +<div class="doc_text"> + +<p>The "<tt><a +href="http://llvm.cs.uiuc.edu/doxygen/classllvm_1_1Pass.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> +subclasses, no optimization can be done for their execution.</p> + +<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> -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> +</div> <!-- _______________________________________________________________________ --> -</ul><h4><a name="run"><hr size=0>The <tt>run</tt> method</h4><ul> +<div class="doc_subsubsection"> + <a name="run">The <tt>run</tt> method</a> +</div> +<div class="doc_text"> <pre> <b>virtual bool</b> run(Module &M) = 0; -</pre><p> +</pre> -The <tt>run</tt> method performs the interesting work of the pass, and should +<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> - +otherwise.</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="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> +<div class="doc_subsection"> + <a name="FunctionPass">The <tt>FunctionPass</tt> class</a> +</div> + +<div class="doc_text"> + +<p>In contrast to direct <tt>Pass</tt> subclasses, direct <tt><a +href="http://llvm.cs.uiuc.edu/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 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> + +</div> <!-- _______________________________________________________________________ --> -</ul><h4><a name="doInitialization_mod"><hr size=0>The -<tt>doInitialization(Module &)</tt> method</h4><ul> +<div class="subsubsection"> + <a name="doInitialization_mod">The <tt>doInitialization(Module &)</tt> + method</a> +</div> + +<div class="doc_text"> <pre> <b>virtual bool</b> doInitialization(Module &M); -</pre><p> +</pre> -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 +<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> pass. This pass converts <tt>malloc</tt> and <tt>free</tt> instructions into 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 necessary.<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> +<div class="subsubsection"> + <a name="runOnFunction">The <tt>runOnFunction</tt> method</a> +</div> + +<div class="doc_text"> <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> +<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> +<div class="subsubsection"> + <a name="doFinalization_mod">The <tt>doFinalization(Module + &)</tt> method</a> +</div> + +<div class="doc_text"> <pre> <b>virtual bool</b> doFinalization(Module &M); -</pre></p> +</pre> -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> <!-- ======================================================================= --> -</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> +<div class="doc_subsection"> + <a name="BasicBlockPass">The <tt>BasicBlockPass</tt> class</a> +</div> + +<div class="doc_text"> -<tt>BasicBlockPass</tt>'s are just like <a +<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) + <a href="#runOnBasicBlock"><tt>runOnBasicBlock</tt></a></li> +<li>Modify the constrol flow graph (by altering terminator instructions)</li> <li>Any of the things verboten for - <a href="#FunctionPass"><tt>FunctionPass</tt></a>'s. -</ol><p> + <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> + +</div> <!-- _______________________________________________________________________ --> -</ul><h4><a name="doInitialization_fn"><hr size=0>The -<tt>doInitialization(Function &)</tt> method</h4><ul> +<div class="subsubsection"> + <a name="doInitialization_fn">The <tt>doInitialization(Function + &)</tt> method</a> +</div> + +<div class="doc_text"> <pre> <b>virtual bool</b> doInitialization(Function &F); -</pre><p> +</pre> -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 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> +<div class="subsubsection"> + <a name="runOnBasicBlock">The <tt>runOnBasicBlock</tt> method</a> +</div> + +<div class="doc_text"> <pre> <b>virtual bool</b> runOnBasicBlock(BasicBlock &BB) = 0; -</pre><p> +</pre> -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> +<div class="subsubsection"> + <a name="doFinalization_fn">The <tt>doFinalization(Function &)</tt> + method</a> +</div> + +<div class="doc_text"> <pre> <b>virtual bool</b> doFinalization(Function &F); -</pre></p> +</pre> -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> <!-- ======================================================================= --> -</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="MachineFunctionPass">The <tt>MachineFunctionPass</tt> class -</b></font></td></tr></table><ul> +<div class="doc_subsection"> + <a name="MachineFunctionPass">The <tt>MachineFunctionPass</tt> class</a> +</div> + +<div class="doc_text"> -A <tt>MachineFunctionPass</tt> executes on the machine-dependent +<p>A <tt>MachineFunctionPass</tt> executes on the machine-dependent representation of each LLVM function in the program, independent of all of the other functions in the program. 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: +the following:</p> <ol> -<li>Modify any LLVM Instructions, BasicBlocks or Functions. -<li>Modify a MachineFunction other than the one currently being processed. -<li>Add or remove MachineFunctions from the current Module. -<li>Add or remove global variables from the current Module. -<li>Maintain state across invocations of - <a href="#runOnMachineFunction"><tt>runOnMachineFunction</tt></a> (including global data) -</ol><p> +<li>Modify any LLVM Instructions, BasicBlocks or Functions.</li> +<li>Modify a MachineFunction other than the one currently being processed.</li> +<li>Add or remove MachineFunctions from the current Module.</li> +<li>Add or remove global variables from the current Module.</li> +<li>Maintain state across invocations of <a +href="#runOnMachineFunction"><tt>runOnMachineFunction</tt></a> (including global +data)</li> +</ol> +</div> <!-- _______________________________________________________________________ --> -</ul><h4><a name="runOnMachineFunction"><hr size=0>The -<tt>runOnMachineFunction(MachineFunction &MF)</tt> method</h4><ul> +<div class="subsubsection"> + <a name="runOnMachineFunction">The <tt>runOnMachineFunction(MachineFunction + &MF)</tt> method</a> +</div> + +<div class="doc_text"> <pre> <b>virtual bool</b> runOnMachineFunction(MachineFunction &MF) = 0; -</pre></p> +</pre> -<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><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> -The <tt>runOnMachineFunction</tt> method is called on every +<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> +<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> <!-- *********************************************************************** --> -</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> +<div class="doc_section"> + <a name="registration">Pass registration</a> +</div> <!-- *********************************************************************** --> -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 class="doc_text"> + +<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> -Passes can be registered in several different ways. Depending on the general +<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> +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> +'<tt>opt</tt>' utility.</li> <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> +'<tt>analysis</tt>' utility.</li> <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> +'<tt>llc</tt>' utility.</li> <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> +file for more information.</li> -Regardless of how you register your pass, you must specify at least two +</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> +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 +<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> +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> +<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> + +</div> <!-- _______________________________________________________________________ --> -</ul><h4><a name="print"><hr size=0>The <tt>print</tt> method</h4><ul> +<div class="doc_subsubsection"> + <a name="print">The <tt>print</tt> method</a> +</div> + +<div class="doc_text"> <pre> <b>virtual void</b> print(std::ostream &O, <b>const</b> Module *M) <b>const</b>; -</pre><p> +</pre> -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. 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 +<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> +depended on.</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="interaction">Specifying interactions between passes -</b></font></td></tr></table><ul> +<div class="doc_section"> + <a name="interaction">Specifying interactions between passes</a> +</div> <!-- *********************************************************************** --> -One of the main responsibilities of the <tt>PassManager</tt> is the make sure +<div class="doc_text"> + +<p>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> +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> +</div> <!-- _______________________________________________________________________ --> -</ul><h4><a name="getAnalysisUsage"><hr size=0>The <tt>getAnalysisUsage</tt> method</h4><ul> +<div class="doc_subsubsection"> + <a name="getAnalysisUsage">The <tt>getAnalysisUsage</tt> method</a> +</div> + +<div class="doc_text"> <pre> <b>virtual void</b> getAnalysisUsage(AnalysisUsage &Info) <b>const</b>; -</pre><p> +</pre> -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.cs.uiuc.edu/doxygen/classllvm_1_1AnalysisUsage.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/classllvm_1_1AnalysisUsage.html">AnalysisUsage</a></tt> +class:</p> <pre> <i>// addRequires - Add the specified pass to the required set for your pass.</i> @@ -755,65 +839,74 @@ href="http://llvm.cs.uiuc.edu/doxygen/classAnalysisUsage.html">AnalysisUsage</a> // This is automatically implied for <a href="#BasicBlockPass">BasicBlockPass</a>'s //</i> <b>void</b> AnalysisUsage::setPreservesCFG(); -</pre><p> +</pre> -Some examples of how to use these methods are:<p> +<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> { + <b>void</b> <a href="http://llvm.cs.uiuc.edu/doxygen/structllvm_1_1PostDominanceFrontier.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>>(); + AU.addRequired<<a href="http://llvm.cs.uiuc.edu/doxygen/structllvm_1_1PostDominatorTree.html">PostDominatorTree</a>>(); } -</pre><p> +</pre> -and:<p> +<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.setPreservesCFG(); - AU.addRequired<<a href="http://llvm.cs.uiuc.edu/doxygen/classLoopInfo.html">LoopInfo</a>>(); + AU.addRequired<<a href="http://llvm.cs.uiuc.edu/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 class="doc_subsubsection"> + <a name="getAnalysis">The <tt>getAnalysis<></tt> method</a> +</div> + +<div class="doc_text"> -The <tt>Pass::getAnalysis<></tt> method is inherited by your class, +<p>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> +a reference to that pass.</p> <pre> <b>template</b><<b>typename</b> PassClass> AnalysisType &getAnalysis(); -</pre><p> +</pre> -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> +<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> + +</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> +<div class="doc_section"> + <a name="analysisgroup">Implementing Analysis Groups</a> +</div> <!-- *********************************************************************** --> -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 class="doc_text"> + +<p>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> +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 @@ -821,69 +914,80 @@ 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> +Analysis Groups.</p> + +</div> <!-- _______________________________________________________________________ --> -</ul><h4><a name="agconcepts"><hr size=0>Analysis Group Concepts</h4><ul> +<div class="subsubsection"> + <a name="agconcepts">Analysis Group Concepts</a> +</div> + +<div class="doc_text"> -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 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.cs.uiuc.edu/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> 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.cs.uiuc.edu/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.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 +<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> +<div class="subsubsection"> + <a name="registerag">Using <tt>RegisterAnalysisGroup</tt></a> +</div> -The <tt>RegisterAnalysisGroup</tt> template is used to register the analysis +<div class="doc_text"> + +<p>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> +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> + <b>static</b> RegisterAnalysisGroup<<a href="http://llvm.cs.uiuc.edu/doxygen/classllvm_1_1AliasAnalysis.html">AliasAnalysis</a>> A("<i>Alias Analysis</i>"); +</pre> -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> <b>namespace</b> { @@ -892,16 +996,16 @@ implementations of the interface by using the following code:<p> 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; + RegisterAnalysisGroup<<a href="http://llvm.cs.uiuc.edu/doxygen/classllvm_1_1AliasAnalysis.html">AliasAnalysis</a>, FancyAA> C; } -</pre><p> +</pre> -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 is registered normally, then +uses the <tt>RegisterAnalysisGroup</tt> template to "join" the <tt><a +href="http://llvm.cs.uiuc.edu/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> +no problem.</p> <pre> <b>namespace</b> { @@ -910,35 +1014,38 @@ no problem.<p> 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; + RegisterAnalysisGroup<<a href="http://llvm.cs.uiuc.edu/doxygen/classllvm_1_1AliasAnalysis.html">AliasAnalysis</a>, <a href="http://llvm.cs.uiuc.edu/doxygen/structBasicAliasAnalysis.html">BasicAliasAnalysis</a>, <b>true</b>> E; } -</pre><p> +</pre> -Here we show how the default implementation is specified (using the extra +<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> +pass is the default implementation for the interface.</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="passmanager">What PassManager does -</b></font></td></tr></table><ul> +<div class="doc_section"> + <a name="passmanager">What PassManager does</a> +</div> <!-- *********************************************************************** --> -The <a +<div class="doc_text"> + +<p>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> +<a +href="http://llvm.cs.uiuc.edu/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> -The <tt>PassManager</tt> does two main things to try to reduce the execution -time of a series of 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 @@ -947,7 +1054,7 @@ 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> +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 @@ -955,35 +1062,35 @@ 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> +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> +href="http://llvm.cs.uiuc.edu/doxygen/structllvm_1_1DominatorSet.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="#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 @@ -1003,24 +1110,24 @@ Module Pass Manager -- Module Verifier Bytecode Writer --Bytecode Writer -</pre><p> +</pre> -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 +<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 @@ -1047,24 +1154,24 @@ Module Pass Manager Hello: __main Hello: puts Hello: main -</pre><p> +</pre> -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> <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> -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 +$ 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 @@ -1087,54 +1194,67 @@ Module Pass Manager Hello: __main Hello: puts Hello: main -</pre><p> +</pre> -Which shows that we don't accidentally invalidate dominator information -anymore, and therefore do not have to compute it twice.<p> +<p>Which shows that we don't accidentally invalidate dominator information +anymore, and therefore do not have to compute it twice.</p> +</div> <!-- _______________________________________________________________________ --> -</ul><h4><a name="releaseMemory"><hr size=0>The <tt>releaseMemory</tt> method</h4><ul> +<div class="doc_subsubsection"> + <a name="releaseMemory">The <tt>releaseMemory</tt> method</a> +</div> + +<div class="doc_text"> <pre> <b>virtual void</b> releaseMemory(); -</pre><p> +</pre> -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 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> <!-- *********************************************************************** --> -</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> +<div class="doc_section"> + <a name="debughints">Using GDB with dynamically loaded passes</a> +</div> <!-- *********************************************************************** --> -Unfortunately, using GDB with dynamically loaded passes is not as easy as it +<div class="doc_text"> + +<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> + +</div> <!-- _______________________________________________________________________ --> -</ul><h4><a name="breakpoint"><hr size=0>Setting a breakpoint in your pass</h4><ul> +<div class="doc_subsubsection"> + <a name="breakpoint">Setting a breakpoint in your pass</a> +</div> + +<div class="doc_text"> -First thing you do is start <tt>gdb</tt> on the <tt>opt</tt> process:<p> +<p>First thing you do is start <tt>gdb</tt> on the <tt>opt</tt> process:</p> <pre> $ <b>gdb opt</b> @@ -1146,15 +1266,15 @@ 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> +</pre> -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> @@ -1164,25 +1284,30 @@ Starting program: opt test.bc -load $(LLVMTOP)/llvm/lib/Debug/[libname].so -[pas 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> -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> +<div class="doc_subsubsection"> + <a name="debugmisc">Miscellaneous Problems</a> +</div> + +<div class="doc_text"> -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 @@ -1190,93 +1315,114 @@ 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> +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> <!-- *********************************************************************** --> -</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> +<div class="doc_section"> + <a name="future">Future extensions planned</a> +</div> <!-- *********************************************************************** --> -Although the LLVM Pass Infrastructure is very capable as it stands, and does +<div class="doc_text"> + +<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> + +</div> <!-- _______________________________________________________________________ --> -</ul><h4><a name="SMP"><hr size=0>Multithreaded LLVM</h4><ul> +<div class="subsubsection"> + <a name="SMP">Multithreaded LLVM</a> +</div> -Multiple CPU machines are becoming more common and compilation can never be +<div class="doc_text"> + +<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 separate -instances to be hacking on different parts of the program at the same time.<p> +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> +Despite that, we have kept the LLVM passes SMP ready, and you should too.</p> +</div> <!-- _______________________________________________________________________ --> -</ul><h4><a name="ModuleSource"><hr size=0>A new <tt>ModuleSource</tt> interface</h4><ul> +<div class="subsubsection"> + <a name="ModuleSource">A new <tt>ModuleSource</tt> interface</a> +</div> + +<div class="doc_text"> -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 +<p>Currently, the <tt>PassManager</tt>'s <tt>run</tt> method takes a <tt><a +href="http://llvm.cs.uiuc.edu/doxygen/structllvm_1_1Module.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> +standard input.</p> -To solve this problem, eventually the <tt>PassManger</tt> class will accept a +<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> +dealing with <a href="#FunctionPass">FunctionPass</a>es.</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> +<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> <!-- _______________________________________________________________________ --> -</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 +<div class="subsubsection"> +<a name="PassFunctionPass"><tt>Pass</tt>'s requiring <tt>FunctionPass</tt>'s</a> +</div> + +<div class="doc_text"> + +<p>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> + +<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> +href="#Pass"><tt>Pass</tt></a>, only the other way around.</p> +</div> <!-- *********************************************************************** --> -</ul> -<!-- *********************************************************************** --> - -<hr><font size-1> -<address><a href="mailto:sabre@nondot.org">Chris Lattner</a></address> -<a href="http://llvm.cs.uiuc.edu">The LLVM Compiler Infrastructure</a> -<br> -<!-- Created: Tue Aug 6 15:00:33 CDT 2002 --> -<!-- hhmts start --> -Last modified: Mon Oct 27 12:00:00 CDT 2003 -<!-- 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" alt="Valid CSS!"></a> + <a href="http://validator.w3.org/check/referer"><img + src="http://www.w3.org/Icons/valid-html401" alt="Valid HTML 4.01!" /></a> + + <a href="mailto:sabre@nondot.org">Chris Lattner</a><br> + <a href="http://llvm.cs.uiuc.edu">The LLVM Compiler Infrastructure</a><br> + Last modified: $Date$ +</address> + +</body> +</html> |