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Misha Brukmanc5402402004-01-15 18:34:11 +00006 <title>Writing an LLVM Pass</title>
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Chris Lattnerc6bb8242002-08-08 20:11:18 +000010
Misha Brukmanc5402402004-01-15 18:34:11 +000011<div class="doc_title">
12 Writing an LLVM Pass
13</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +000014
15<ol>
Misha Brukmanc5402402004-01-15 18:34:11 +000016 <li><a href="#introduction">Introduction - What is a pass?</a></li>
Chris Lattnerc6bb8242002-08-08 20:11:18 +000017 <li><a href="#quickstart">Quick Start - Writing hello world</a>
18 <ul>
Misha Brukmanc5402402004-01-15 18:34:11 +000019 <li><a href="#makefile">Setting up the build environment</a></li>
20 <li><a href="#basiccode">Basic code required</a></li>
Chris Lattnerc8603c22006-08-27 23:18:52 +000021 <li><a href="#running">Running a pass with <tt>opt</tt></a></li>
Misha Brukmanc5402402004-01-15 18:34:11 +000022 </ul></li>
Chris Lattnerc6bb8242002-08-08 20:11:18 +000023 <li><a href="#passtype">Pass classes and requirements</a>
24 <ul>
Misha Brukmanc5402402004-01-15 18:34:11 +000025 <li><a href="#ImmutablePass">The <tt>ImmutablePass</tt> class</a></li>
Chris Lattnerf6278922004-09-20 04:36:29 +000026 <li><a href="#ModulePass">The <tt>ModulePass</tt> class</a>
Chris Lattnerc6bb8242002-08-08 20:11:18 +000027 <ul>
Chris Lattnerf6278922004-09-20 04:36:29 +000028 <li><a href="#runOnModule">The <tt>runOnModule</tt> method</a></li>
Misha Brukmanc5402402004-01-15 18:34:11 +000029 </ul></li>
Chris Lattner8fdb2462004-09-18 06:39:35 +000030 <li><a href="#CallGraphSCCPass">The <tt>CallGraphSCCPass</tt> class</a>
31 <ul>
Devang Patelc20048d2007-01-23 22:56:28 +000032 <li><a href="#doInitialization_scc">The <tt>doInitialization(CallGraph
Chris Lattner8fdb2462004-09-18 06:39:35 +000033 &amp;)</tt> method</a></li>
34 <li><a href="#runOnSCC">The <tt>runOnSCC</tt> method</a></li>
Devang Patelc20048d2007-01-23 22:56:28 +000035 <li><a href="#doFinalization_scc">The <tt>doFinalization(CallGraph
Chris Lattner8fdb2462004-09-18 06:39:35 +000036 &amp;)</tt> method</a></li>
37 </ul></li>
Chris Lattnerc6bb8242002-08-08 20:11:18 +000038 <li><a href="#FunctionPass">The <tt>FunctionPass</tt> class</a>
39 <ul>
Chris Lattnerd0713f92002-09-12 17:06:43 +000040 <li><a href="#doInitialization_mod">The <tt>doInitialization(Module
Misha Brukmanc5402402004-01-15 18:34:11 +000041 &amp;)</tt> method</a></li>
42 <li><a href="#runOnFunction">The <tt>runOnFunction</tt> method</a></li>
Chris Lattnerd0713f92002-09-12 17:06:43 +000043 <li><a href="#doFinalization_mod">The <tt>doFinalization(Module
Misha Brukmanc5402402004-01-15 18:34:11 +000044 &amp;)</tt> method</a></li>
45 </ul></li>
Devang Patel2e8f27d2007-03-19 22:21:25 +000046 <li><a href="#LoopPass">The <tt>LoopPass</tt> class</a>
47 <ul>
48 <li><a href="#doInitialization_loop">The <tt>doInitialization(Loop *,
49 LPPassManager &amp;)</tt> method</a></li>
50 <li><a href="#runOnLoop">The <tt>runOnLoop</tt> method</a></li>
51 <li><a href="#doFinalization_loop">The <tt>doFinalization()
52 </tt> method</a></li>
53 </ul></li>
Tobias Grosser65513602010-10-20 01:54:44 +000054 <li><a href="#RegionPass">The <tt>RegionPass</tt> class</a>
55 <ul>
56 <li><a href="#doInitialization_region">The <tt>doInitialization(Region *,
57 RGPassManager &amp;)</tt> method</a></li>
58 <li><a href="#runOnRegion">The <tt>runOnRegion</tt> method</a></li>
59 <li><a href="#doFinalization_region">The <tt>doFinalization()
60 </tt> method</a></li>
61 </ul></li>
Chris Lattnerc6bb8242002-08-08 20:11:18 +000062 <li><a href="#BasicBlockPass">The <tt>BasicBlockPass</tt> class</a>
63 <ul>
Chris Lattnerd0713f92002-09-12 17:06:43 +000064 <li><a href="#doInitialization_fn">The <tt>doInitialization(Function
Misha Brukmanc5402402004-01-15 18:34:11 +000065 &amp;)</tt> method</a></li>
66 <li><a href="#runOnBasicBlock">The <tt>runOnBasicBlock</tt>
67 method</a></li>
Chris Lattnerd0713f92002-09-12 17:06:43 +000068 <li><a href="#doFinalization_fn">The <tt>doFinalization(Function
Misha Brukmanc5402402004-01-15 18:34:11 +000069 &amp;)</tt> method</a></li>
70 </ul></li>
Brian Gaekecab8b6f2003-07-17 18:53:20 +000071 <li><a href="#MachineFunctionPass">The <tt>MachineFunctionPass</tt>
72 class</a>
Brian Gaeke6a33f362003-07-22 20:53:20 +000073 <ul>
74 <li><a href="#runOnMachineFunction">The
Misha Brukmanc5402402004-01-15 18:34:11 +000075 <tt>runOnMachineFunction(MachineFunction &amp;)</tt> method</a></li>
76 </ul></li>
Chris Lattnerc6bb8242002-08-08 20:11:18 +000077 </ul>
78 <li><a href="#registration">Pass Registration</a>
79 <ul>
Misha Brukmanc5402402004-01-15 18:34:11 +000080 <li><a href="#print">The <tt>print</tt> method</a></li>
81 </ul></li>
Chris Lattnerc6bb8242002-08-08 20:11:18 +000082 <li><a href="#interaction">Specifying interactions between passes</a>
83 <ul>
Misha Brukmanc5402402004-01-15 18:34:11 +000084 <li><a href="#getAnalysisUsage">The <tt>getAnalysisUsage</tt>
85 method</a></li>
Chris Lattner89256272004-03-17 21:09:55 +000086 <li><a href="#AU::addRequired">The <tt>AnalysisUsage::addRequired&lt;&gt;</tt> and <tt>AnalysisUsage::addRequiredTransitive&lt;&gt;</tt> methods</a></li>
87 <li><a href="#AU::addPreserved">The <tt>AnalysisUsage::addPreserved&lt;&gt;</tt> method</a></li>
88 <li><a href="#AU::examples">Example implementations of <tt>getAnalysisUsage</tt></a></li>
Duncan Sands1465d612009-01-28 13:14:17 +000089 <li><a href="#getAnalysis">The <tt>getAnalysis&lt;&gt;</tt> and
90<tt>getAnalysisIfAvailable&lt;&gt;</tt> methods</a></li>
Misha Brukmanc5402402004-01-15 18:34:11 +000091 </ul></li>
Chris Lattner79910702002-08-22 19:21:04 +000092 <li><a href="#analysisgroup">Implementing Analysis Groups</a>
93 <ul>
Misha Brukmanc5402402004-01-15 18:34:11 +000094 <li><a href="#agconcepts">Analysis Group Concepts</a></li>
95 <li><a href="#registerag">Using <tt>RegisterAnalysisGroup</tt></a></li>
96 </ul></li>
Tanya Lattnerd5383652004-11-19 01:25:14 +000097 <li><a href="#passStatistics">Pass Statistics</a>
Chris Lattnerc6bb8242002-08-08 20:11:18 +000098 <li><a href="#passmanager">What PassManager does</a>
99 <ul>
Misha Brukmanc5402402004-01-15 18:34:11 +0000100 <li><a href="#releaseMemory">The <tt>releaseMemory</tt> method</a></li>
101 </ul></li>
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000102 <li><a href="#registering">Registering dynamically loaded passes</a>
103 <ul>
104 <li><a href="#registering_existing">Using existing registries</a></li>
105 <li><a href="#registering_new">Creating new registries</a></li>
106 </ul></li>
Chris Lattner480e2ef2002-09-06 02:02:58 +0000107 <li><a href="#debughints">Using GDB with dynamically loaded passes</a>
108 <ul>
Misha Brukmanc5402402004-01-15 18:34:11 +0000109 <li><a href="#breakpoint">Setting a breakpoint in your pass</a></li>
110 <li><a href="#debugmisc">Miscellaneous Problems</a></li>
111 </ul></li>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000112 <li><a href="#future">Future extensions planned</a>
113 <ul>
Misha Brukmanc5402402004-01-15 18:34:11 +0000114 <li><a href="#SMP">Multithreaded LLVM</a></li>
Misha Brukmanc5402402004-01-15 18:34:11 +0000115 </ul></li>
116</ol>
Chris Lattner38c633d2002-08-08 20:23:41 +0000117
Chris Lattner7911ce22004-05-23 21:07:27 +0000118<div class="doc_author">
Chris Lattner8f652eb2006-08-11 16:37:02 +0000119 <p>Written by <a href="mailto:sabre@nondot.org">Chris Lattner</a> and
Jim Laskeyc760a922007-03-14 19:32:21 +0000120 <a href="mailto:jlaskey@mac.com">Jim Laskey</a></p>
Misha Brukmanc5402402004-01-15 18:34:11 +0000121</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000122
123<!-- *********************************************************************** -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000124<div class="doc_section">
125 <a name="introduction">Introduction - What is a pass?</a>
126</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000127<!-- *********************************************************************** -->
128
Misha Brukmanc5402402004-01-15 18:34:11 +0000129<div class="doc_text">
130
131<p>The LLVM Pass Framework is an important part of the LLVM system, because LLVM
Chris Lattner8fdb2462004-09-18 06:39:35 +0000132passes are where most of the interesting parts of the compiler exist. Passes
133perform the transformations and optimizations that make up the compiler, they
134build the analysis results that are used by these transformations, and they are,
135above all, a structuring technique for compiler code.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000136
Misha Brukmanc5402402004-01-15 18:34:11 +0000137<p>All LLVM passes are subclasses of the <tt><a
Reid Spencer05fe4b02006-03-14 05:39:39 +0000138href="http://llvm.org/doxygen/classllvm_1_1Pass.html">Pass</a></tt>
Misha Brukmanc5402402004-01-15 18:34:11 +0000139class, which implement functionality by overriding virtual methods inherited
Chris Lattnerf6278922004-09-20 04:36:29 +0000140from <tt>Pass</tt>. Depending on how your pass works, you should inherit from
141the <tt><a href="#ModulePass">ModulePass</a></tt>, <tt><a
142href="#CallGraphSCCPass">CallGraphSCCPass</a></tt>, <tt><a
143href="#FunctionPass">FunctionPass</a></tt>, or <tt><a
Devang Patel2e8f27d2007-03-19 22:21:25 +0000144href="#LoopPass">LoopPass</a></tt>, or <tt><a
Tobias Grosser65513602010-10-20 01:54:44 +0000145href="#RegionPass">RegionPass</a></tt>, or <tt><a
Chris Lattner8fdb2462004-09-18 06:39:35 +0000146href="#BasicBlockPass">BasicBlockPass</a></tt> classes, which gives the system
147more information about what your pass does, and how it can be combined with
148other passes. One of the main features of the LLVM Pass Framework is that it
149schedules passes to run in an efficient way based on the constraints that your
150pass meets (which are indicated by which class they derive from).</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000151
Misha Brukmanc5402402004-01-15 18:34:11 +0000152<p>We start by showing you how to construct a pass, everything from setting up
153the code, to compiling, loading, and executing it. After the basics are down,
154more advanced features are discussed.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000155
Misha Brukmanc5402402004-01-15 18:34:11 +0000156</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000157
158<!-- *********************************************************************** -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000159<div class="doc_section">
160 <a name="quickstart">Quick Start - Writing hello world</a>
161</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000162<!-- *********************************************************************** -->
163
Misha Brukmanc5402402004-01-15 18:34:11 +0000164<div class="doc_text">
165
166<p>Here we describe how to write the "hello world" of passes. The "Hello" pass
167is designed to simply print out the name of non-external functions that exist in
Chris Lattner8fdb2462004-09-18 06:39:35 +0000168the program being compiled. It does not modify the program at all, it just
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000169inspects it. The source code and files for this pass are available in the LLVM
Misha Brukmanc5402402004-01-15 18:34:11 +0000170source tree in the <tt>lib/Transforms/Hello</tt> directory.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000171
Misha Brukmanc5402402004-01-15 18:34:11 +0000172</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000173
174<!-- ======================================================================= -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000175<div class="doc_subsection">
176 <a name="makefile">Setting up the build environment</a>
177</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000178
Misha Brukmanc5402402004-01-15 18:34:11 +0000179<div class="doc_text">
180
Duncan Sandsdc97c0b2011-01-01 17:28:49 +0000181 <p>First, configure and build LLVM. This needs to be done directly inside the
182 LLVM source tree rather than in a separate objects directory.
183 Next, you need to create a new directory somewhere in the LLVM source
Reid Spencer1bc19342004-12-11 05:12:57 +0000184 base. For this example, we'll assume that you made
Duncan Sandsdc97c0b2011-01-01 17:28:49 +0000185 <tt>lib/Transforms/Hello</tt>. Finally, you must set up a build script
Reid Spencer1bc19342004-12-11 05:12:57 +0000186 (Makefile) that will compile the source code for the new pass. To do this,
187 copy the following into <tt>Makefile</tt>:</p>
188 <hr/>
Misha Brukmanc5402402004-01-15 18:34:11 +0000189
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000190<div class="doc_code"><pre>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000191# Makefile for hello pass
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000192
Torok Edwin87469292009-10-12 13:37:29 +0000193# Path to top level of LLVM hierarchy
Chris Lattner7ce83e52002-08-14 20:07:01 +0000194LEVEL = ../../..
Chris Lattner17a4c3e2002-08-14 20:06:13 +0000195
196# Name of the library to build
Reid Spencer7fa6d522005-01-11 05:16:23 +0000197LIBRARYNAME = Hello
Chris Lattner17a4c3e2002-08-14 20:06:13 +0000198
Reid Spencer7fa6d522005-01-11 05:16:23 +0000199# Make the shared library become a loadable module so the tools can
200# dlopen/dlsym on the resulting library.
Robert Bocchino3cf817d2006-01-06 22:49:23 +0000201LOADABLE_MODULE = 1
Reid Spencer7fa6d522005-01-11 05:16:23 +0000202
Chris Lattner17a4c3e2002-08-14 20:06:13 +0000203# Include the makefile implementation stuff
204include $(LEVEL)/Makefile.common
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000205</pre></div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000206
Misha Brukmanc5402402004-01-15 18:34:11 +0000207<p>This makefile specifies that all of the <tt>.cpp</tt> files in the current
Duncan Sands779ff7f2011-01-01 17:21:58 +0000208directory are to be compiled and linked together into a shared object
209<tt>$(LEVEL)/Debug+Asserts/lib/Hello.so</tt> that can be dynamically loaded by
Chris Lattnerc8603c22006-08-27 23:18:52 +0000210the <tt>opt</tt> or <tt>bugpoint</tt> tools via their <tt>-load</tt> options.
Reid Spencer7fa6d522005-01-11 05:16:23 +0000211If your operating system uses a suffix other than .so (such as windows or
212Mac OS/X), the appropriate extension will be used.</p>
John Criswellf9c78652004-01-26 21:26:54 +0000213
Misha Brukmanc5402402004-01-15 18:34:11 +0000214<p>Now that we have the build scripts set up, we just need to write the code for
215the pass itself.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000216
Misha Brukmanc5402402004-01-15 18:34:11 +0000217</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000218
219<!-- ======================================================================= -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000220<div class="doc_subsection">
221 <a name="basiccode">Basic code required</a>
222</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000223
Misha Brukmanc5402402004-01-15 18:34:11 +0000224<div class="doc_text">
225
226<p>Now that we have a way to compile our new pass, we just have to write it.
227Start out with:</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000228
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000229<div class="doc_code"><pre>
Reid Spencer05fe4b02006-03-14 05:39:39 +0000230<b>#include</b> "<a href="http://llvm.org/doxygen/Pass_8h-source.html">llvm/Pass.h</a>"
231<b>#include</b> "<a href="http://llvm.org/doxygen/Function_8h-source.html">llvm/Function.h</a>"
Chris Lattner0ce6f932009-09-08 05:14:44 +0000232<b>#include</b> "<a href="http://llvm.org/doxygen/raw__ostream_8h.html">llvm/Support/raw_ostream.h</a>"
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000233</pre></div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000234
Misha Brukmanc5402402004-01-15 18:34:11 +0000235<p>Which are needed because we are writing a <tt><a
Chris Lattner0ce6f932009-09-08 05:14:44 +0000236href="http://llvm.org/doxygen/classllvm_1_1Pass.html">Pass</a></tt>,
Misha Brukmanc5402402004-01-15 18:34:11 +0000237we are operating on <tt><a
Chris Lattner0ce6f932009-09-08 05:14:44 +0000238href="http://llvm.org/doxygen/classllvm_1_1Function.html">Function</a></tt>'s,
239and we will be doing some printing.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000240
Misha Brukmanc5402402004-01-15 18:34:11 +0000241<p>Next we have:</p>
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000242<div class="doc_code"><pre>
Jonathan Manton65acb302004-06-30 18:10:30 +0000243<b>using namespace llvm;</b>
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000244</pre></div>
Jonathan Manton65acb302004-06-30 18:10:30 +0000245<p>... which is required because the functions from the include files
246live in the llvm namespace.
247</p>
248
249<p>Next we have:</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000250
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000251<div class="doc_code"><pre>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000252<b>namespace</b> {
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000253</pre></div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000254
Misha Brukmanc5402402004-01-15 18:34:11 +0000255<p>... which starts out an anonymous namespace. Anonymous namespaces are to C++
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000256what the "<tt>static</tt>" keyword is to C (at global scope). It makes the
257things declared inside of the anonymous namespace only visible to the current
258file. If you're not familiar with them, consult a decent C++ book for more
Misha Brukmanc5402402004-01-15 18:34:11 +0000259information.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000260
Misha Brukmanc5402402004-01-15 18:34:11 +0000261<p>Next, we declare our pass itself:</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000262
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000263<div class="doc_code"><pre>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000264 <b>struct</b> Hello : <b>public</b> <a href="#FunctionPass">FunctionPass</a> {
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000265</pre></div><p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000266
Misha Brukmanc5402402004-01-15 18:34:11 +0000267<p>This declares a "<tt>Hello</tt>" class that is a subclass of <tt><a
Reid Spencer05fe4b02006-03-14 05:39:39 +0000268href="http://llvm.org/doxygen/classllvm_1_1FunctionPass.html">FunctionPass</a></tt>.
Chris Lattnerd6ea9262002-09-09 03:48:46 +0000269The different builtin pass subclasses are described in detail <a
Misha Brukmanc5402402004-01-15 18:34:11 +0000270href="#passtype">later</a>, but for now, know that <a
271href="#FunctionPass"><tt>FunctionPass</tt></a>'s operate a function at a
272time.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000273
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000274<div class="doc_code"><pre>
Devang Patel19974732007-05-03 01:11:54 +0000275 static char ID;
Dan Gohman865f0062009-02-18 05:09:16 +0000276 Hello() : FunctionPass(&amp;ID) {}
Devang Patele50fb9a2007-05-01 20:55:38 +0000277</pre></div><p>
278
279<p> This declares pass identifier used by LLVM to identify pass. This allows LLVM to
280avoid using expensive C++ runtime information.</p>
281
282<div class="doc_code"><pre>
Misha Brukmanc5402402004-01-15 18:34:11 +0000283 <b>virtual bool</b> <a href="#runOnFunction">runOnFunction</a>(Function &amp;F) {
Chris Lattner0ce6f932009-09-08 05:14:44 +0000284 errs() &lt;&lt; "<i>Hello: </i>" &lt;&lt; F.getName() &lt;&lt; "\n";
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000285 <b>return false</b>;
286 }
287 }; <i>// end of struct Hello</i>
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000288</pre></div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000289
Misha Brukmanc5402402004-01-15 18:34:11 +0000290<p>We declare a "<a href="#runOnFunction"><tt>runOnFunction</tt></a>" method,
291which overloads an abstract virtual method inherited from <a
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000292href="#FunctionPass"><tt>FunctionPass</tt></a>. This is where we are supposed
293to do our thing, so we just print out our message with the name of each
Misha Brukmanc5402402004-01-15 18:34:11 +0000294function.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000295
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000296<div class="doc_code"><pre>
Devang Patel19974732007-05-03 01:11:54 +0000297 char Hello::ID = 0;
Devang Patele50fb9a2007-05-01 20:55:38 +0000298</pre></div>
299
300<p> We initialize pass ID here. LLVM uses ID's address to identify pass so
301initialization value is not important.</p>
302
303<div class="doc_code"><pre>
Owen Anderson20813e02010-07-21 22:58:07 +0000304 INITIALIZE_PASS(Hello, "<i>hello</i>", "<i>Hello World Pass</i>",
Devang Patelc7582092008-03-19 21:56:59 +0000305 false /* Only looks at CFG */,
306 false /* Analysis Pass */);
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000307} <i>// end of anonymous namespace</i>
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000308</pre></div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000309
Chris Lattnerc8603c22006-08-27 23:18:52 +0000310<p>Lastly, we <a href="#registration">register our class</a> <tt>Hello</tt>,
311giving it a command line
Devang Patelc7582092008-03-19 21:56:59 +0000312argument "<tt>hello</tt>", and a name "<tt>Hello World Pass</tt>".
Owen Anderson20813e02010-07-21 22:58:07 +0000313Last two arguments describe its behavior.
Devang Patelc7582092008-03-19 21:56:59 +0000314If a pass walks CFG without modifying it then third argument is set to true.
315If a pass is an analysis pass, for example dominator tree pass, then true
316is supplied as fourth argument. </p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000317
Misha Brukmanc5402402004-01-15 18:34:11 +0000318<p>As a whole, the <tt>.cpp</tt> file looks like:</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000319
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000320<div class="doc_code"><pre>
Reid Spencer05fe4b02006-03-14 05:39:39 +0000321<b>#include</b> "<a href="http://llvm.org/doxygen/Pass_8h-source.html">llvm/Pass.h</a>"
322<b>#include</b> "<a href="http://llvm.org/doxygen/Function_8h-source.html">llvm/Function.h</a>"
Chris Lattner0ce6f932009-09-08 05:14:44 +0000323<b>#include</b> "<a href="http://llvm.org/doxygen/raw__ostream_8h.html">llvm/Support/raw_ostream.h</a>"
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000324
Jonathan Manton65acb302004-06-30 18:10:30 +0000325<b>using namespace llvm;</b>
326
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000327<b>namespace</b> {
328 <b>struct Hello</b> : <b>public</b> <a href="#FunctionPass">FunctionPass</a> {
Devang Patele50fb9a2007-05-01 20:55:38 +0000329
Devang Patel19974732007-05-03 01:11:54 +0000330 static char ID;
Dan Gohman865f0062009-02-18 05:09:16 +0000331 Hello() : FunctionPass(&amp;ID) {}
Devang Patele50fb9a2007-05-01 20:55:38 +0000332
Misha Brukmanc5402402004-01-15 18:34:11 +0000333 <b>virtual bool</b> <a href="#runOnFunction">runOnFunction</a>(Function &amp;F) {
Chris Lattner0ce6f932009-09-08 05:14:44 +0000334 errs() &lt;&lt; "<i>Hello: </i>" &lt;&lt; F.getName() &lt;&lt; "\n";
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000335 <b>return false</b>;
336 }
337 };
338
Devang Patel26e5a302007-07-25 21:05:39 +0000339 char Hello::ID = 0;
Owen Anderson20813e02010-07-21 22:58:07 +0000340 INITIALIZE_PASS(Hello, "<i>Hello</i>", "<i>Hello World Pass</i>", false, false);
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000341}
Owen Anderson20813e02010-07-21 22:58:07 +0000342
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000343</pre></div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000344
Misha Brukmanc5402402004-01-15 18:34:11 +0000345<p>Now that it's all together, compile the file with a simple "<tt>gmake</tt>"
Duncan Sands779ff7f2011-01-01 17:21:58 +0000346command in the local directory and you should get a new file
347"<tt>Debug+Asserts/lib/Hello.so</tt>" under the top level directory of the LLVM
348source tree (not in the local directory). Note that everything in this file is
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000349contained in an anonymous namespace: this reflects the fact that passes are self
350contained units that do not need external interfaces (although they can have
Misha Brukmanc5402402004-01-15 18:34:11 +0000351them) to be useful.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000352
Misha Brukmanc5402402004-01-15 18:34:11 +0000353</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000354
355<!-- ======================================================================= -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000356<div class="doc_subsection">
Chris Lattnerc8603c22006-08-27 23:18:52 +0000357 <a name="running">Running a pass with <tt>opt</tt></a>
Misha Brukmanc5402402004-01-15 18:34:11 +0000358</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000359
Misha Brukmanc5402402004-01-15 18:34:11 +0000360<div class="doc_text">
361
John Criswellf9c78652004-01-26 21:26:54 +0000362<p>Now that you have a brand new shiny shared object file, we can use the
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000363<tt>opt</tt> command to run an LLVM program through your pass. Because you
Owen Anderson20813e02010-07-21 22:58:07 +0000364registered your pass with the <tt>INITIALIZE_PASS</tt> macro, you will be able to
Misha Brukmanc5402402004-01-15 18:34:11 +0000365use the <tt>opt</tt> tool to access it, once loaded.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000366
Misha Brukmanc5402402004-01-15 18:34:11 +0000367<p>To test it, follow the example at the end of the <a
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000368href="GettingStarted.html">Getting Started Guide</a> to compile "Hello World" to
Gabor Greif04367bf2007-07-06 22:07:22 +0000369LLVM. We can now run the bitcode file (<tt>hello.bc</tt>) for the program
370through our transformation like this (or course, any bitcode file will
Misha Brukmanc5402402004-01-15 18:34:11 +0000371work):</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000372
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000373<div class="doc_code"><pre>
Duncan Sands67f8a7b2010-07-08 08:27:18 +0000374$ opt -load ../../../Debug+Asserts/lib/Hello.so -hello &lt; hello.bc &gt; /dev/null
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000375Hello: __main
376Hello: puts
377Hello: main
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000378</pre></div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000379
Misha Brukmanc5402402004-01-15 18:34:11 +0000380<p>The '<tt>-load</tt>' option specifies that '<tt>opt</tt>' should load your
381pass as a shared object, which makes '<tt>-hello</tt>' a valid command line
382argument (which is one reason you need to <a href="#registration">register your
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000383pass</a>). Because the hello pass does not modify the program in any
384interesting way, we just throw away the result of <tt>opt</tt> (sending it to
Misha Brukmanc5402402004-01-15 18:34:11 +0000385<tt>/dev/null</tt>).</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000386
Misha Brukmanc5402402004-01-15 18:34:11 +0000387<p>To see what happened to the other string you registered, try running
Duncan Sands7e7ae5a2010-02-18 14:08:13 +0000388<tt>opt</tt> with the <tt>-help</tt> option:</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000389
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000390<div class="doc_code"><pre>
Duncan Sands67f8a7b2010-07-08 08:27:18 +0000391$ opt -load ../../../Debug+Asserts/lib/Hello.so -help
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000392OVERVIEW: llvm .bc -&gt; .bc modular optimizer
393
Gabor Greif04367bf2007-07-06 22:07:22 +0000394USAGE: opt [options] &lt;input bitcode&gt;
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000395
396OPTIONS:
397 Optimizations available:
398...
399 -funcresolve - Resolve Functions
400 -gcse - Global Common Subexpression Elimination
401 -globaldce - Dead Global Elimination
402 <b>-hello - Hello World Pass</b>
Chris Lattner065a6162003-09-10 05:29:43 +0000403 -indvars - Canonicalize Induction Variables
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000404 -inline - Function Integration/Inlining
405 -instcombine - Combine redundant instructions
406...
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000407</pre></div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000408
Misha Brukmanc5402402004-01-15 18:34:11 +0000409<p>The pass name get added as the information string for your pass, giving some
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000410documentation to users of <tt>opt</tt>. Now that you have a working pass, you
411would go ahead and make it do the cool transformations you want. Once you get
412it all working and tested, it may become useful to find out how fast your pass
413is. The <a href="#passManager"><tt>PassManager</tt></a> provides a nice command
414line option (<tt>--time-passes</tt>) that allows you to get information about
415the execution time of your pass along with the other passes you queue up. For
Misha Brukmanc5402402004-01-15 18:34:11 +0000416example:</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000417
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000418<div class="doc_code"><pre>
Duncan Sands67f8a7b2010-07-08 08:27:18 +0000419$ opt -load ../../../Debug+Asserts/lib/Hello.so -hello -time-passes &lt; hello.bc &gt; /dev/null
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000420Hello: __main
421Hello: puts
422Hello: main
423===============================================================================
424 ... Pass execution timing report ...
425===============================================================================
426 Total Execution Time: 0.02 seconds (0.0479059 wall clock)
427
428 ---User Time--- --System Time-- --User+System-- ---Wall Time--- --- Pass Name ---
Gabor Greif04367bf2007-07-06 22:07:22 +0000429 0.0100 (100.0%) 0.0000 ( 0.0%) 0.0100 ( 50.0%) 0.0402 ( 84.0%) Bitcode Writer
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000430 0.0000 ( 0.0%) 0.0100 (100.0%) 0.0100 ( 50.0%) 0.0031 ( 6.4%) Dominator Set Construction
431 0.0000 ( 0.0%) 0.0000 ( 0.0%) 0.0000 ( 0.0%) 0.0013 ( 2.7%) Module Verifier
432 <b> 0.0000 ( 0.0%) 0.0000 ( 0.0%) 0.0000 ( 0.0%) 0.0033 ( 6.9%) Hello World Pass</b>
433 0.0100 (100.0%) 0.0100 (100.0%) 0.0200 (100.0%) 0.0479 (100.0%) TOTAL
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000434</pre></div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000435
Misha Brukmanc5402402004-01-15 18:34:11 +0000436<p>As you can see, our implementation above is pretty fast :). The additional
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000437passes listed are automatically inserted by the '<tt>opt</tt>' tool to verify
438that the LLVM emitted by your pass is still valid and well formed LLVM, which
Misha Brukmanc5402402004-01-15 18:34:11 +0000439hasn't been broken somehow.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000440
Misha Brukmanc5402402004-01-15 18:34:11 +0000441<p>Now that you have seen the basics of the mechanics behind passes, we can talk
442about some more details of how they work and how to use them.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000443
Misha Brukmanc5402402004-01-15 18:34:11 +0000444</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000445
446<!-- *********************************************************************** -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000447<div class="doc_section">
448 <a name="passtype">Pass classes and requirements</a>
449</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000450<!-- *********************************************************************** -->
451
Misha Brukmanc5402402004-01-15 18:34:11 +0000452<div class="doc_text">
453
454<p>One of the first things that you should do when designing a new pass is to
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000455decide what class you should subclass for your pass. The <a
456href="#basiccode">Hello World</a> example uses the <tt><a
457href="#FunctionPass">FunctionPass</a></tt> class for its implementation, but we
458did not discuss why or when this should occur. Here we talk about the classes
Misha Brukmanc5402402004-01-15 18:34:11 +0000459available, from the most general to the most specific.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000460
Misha Brukmanc5402402004-01-15 18:34:11 +0000461<p>When choosing a superclass for your Pass, you should choose the <b>most
Chris Lattner79910702002-08-22 19:21:04 +0000462specific</b> class possible, while still being able to meet the requirements
Misha Brukman5560c9d2003-08-18 14:43:39 +0000463listed. This gives the LLVM Pass Infrastructure information necessary to
Benjamin Kramer8040cd32009-10-12 14:46:08 +0000464optimize how passes are run, so that the resultant compiler isn't unnecessarily
Misha Brukmanc5402402004-01-15 18:34:11 +0000465slow.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000466
Misha Brukmanc5402402004-01-15 18:34:11 +0000467</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000468
Chris Lattnerf004f9a2002-09-25 22:31:38 +0000469<!-- ======================================================================= -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000470<div class="doc_subsection">
471 <a name="ImmutablePass">The <tt>ImmutablePass</tt> class</a>
472</div>
Chris Lattnerf004f9a2002-09-25 22:31:38 +0000473
Misha Brukmanc5402402004-01-15 18:34:11 +0000474<div class="doc_text">
475
476<p>The most plain and boring type of pass is the "<tt><a
Reid Spencer05fe4b02006-03-14 05:39:39 +0000477href="http://llvm.org/doxygen/classllvm_1_1ImmutablePass.html">ImmutablePass</a></tt>"
Chris Lattnerf004f9a2002-09-25 22:31:38 +0000478class. This pass type is used for passes that do not have to be run, do not
479change state, and never need to be updated. This is not a normal type of
480transformation or analysis, but can provide information about the current
Misha Brukmanc5402402004-01-15 18:34:11 +0000481compiler configuration.</p>
Chris Lattnerf004f9a2002-09-25 22:31:38 +0000482
Misha Brukmanc5402402004-01-15 18:34:11 +0000483<p>Although this pass class is very infrequently used, it is important for
Chris Lattnerf004f9a2002-09-25 22:31:38 +0000484providing information about the current target machine being compiled for, and
Misha Brukmanc5402402004-01-15 18:34:11 +0000485other static information that can affect the various transformations.</p>
Chris Lattnerf004f9a2002-09-25 22:31:38 +0000486
Misha Brukmanc5402402004-01-15 18:34:11 +0000487<p><tt>ImmutablePass</tt>es never invalidate other transformations, are never
488invalidated, and are never "run".</p>
Chris Lattnerf004f9a2002-09-25 22:31:38 +0000489
Misha Brukmanc5402402004-01-15 18:34:11 +0000490</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000491
492<!-- ======================================================================= -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000493<div class="doc_subsection">
Chris Lattnerf6278922004-09-20 04:36:29 +0000494 <a name="ModulePass">The <tt>ModulePass</tt> class</a>
Misha Brukmanc5402402004-01-15 18:34:11 +0000495</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000496
Misha Brukmanc5402402004-01-15 18:34:11 +0000497<div class="doc_text">
498
499<p>The "<tt><a
Reid Spencer05fe4b02006-03-14 05:39:39 +0000500href="http://llvm.org/doxygen/classllvm_1_1ModulePass.html">ModulePass</a></tt>"
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000501class is the most general of all superclasses that you can use. Deriving from
Chris Lattnerf6278922004-09-20 04:36:29 +0000502<tt>ModulePass</tt> indicates that your pass uses the entire program as a unit,
Benjamin Kramer8040cd32009-10-12 14:46:08 +0000503referring to function bodies in no predictable order, or adding and removing
Chris Lattnerf6278922004-09-20 04:36:29 +0000504functions. Because nothing is known about the behavior of <tt>ModulePass</tt>
Daniel Dunbarb71725b2009-07-01 23:38:44 +0000505subclasses, no optimization can be done for their execution.</p>
506
507<p>A module pass can use function level passes (e.g. dominators) using
508the getAnalysis interface
509<tt>getAnalysis&lt;DominatorTree&gt;(llvm::Function *)</tt> to provide the
510function to retrieve analysis result for, if the function pass does not require
Devang Patel468857f2009-08-10 16:37:29 +0000511any module or immutable passes. Note that this can only be done for functions for which the
Daniel Dunbarb71725b2009-07-01 23:38:44 +0000512analysis ran, e.g. in the case of dominators you should only ask for the
513DominatorTree for function definitions, not declarations.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000514
Chris Lattnerf6278922004-09-20 04:36:29 +0000515<p>To write a correct <tt>ModulePass</tt> subclass, derive from
516<tt>ModulePass</tt> and overload the <tt>runOnModule</tt> method with the
517following signature:</p>
Misha Brukmanc5402402004-01-15 18:34:11 +0000518
519</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000520
521<!-- _______________________________________________________________________ -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000522<div class="doc_subsubsection">
Chris Lattnerf6278922004-09-20 04:36:29 +0000523 <a name="runOnModule">The <tt>runOnModule</tt> method</a>
Misha Brukmanc5402402004-01-15 18:34:11 +0000524</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000525
Misha Brukmanc5402402004-01-15 18:34:11 +0000526<div class="doc_text">
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000527
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000528<div class="doc_code"><pre>
Chris Lattnerf6278922004-09-20 04:36:29 +0000529 <b>virtual bool</b> runOnModule(Module &amp;M) = 0;
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000530</pre></div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000531
John Criswell2382ff72005-07-15 19:25:12 +0000532<p>The <tt>runOnModule</tt> method performs the interesting work of the pass.
533It should return true if the module was modified by the transformation and
534false otherwise.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000535
Misha Brukmanc5402402004-01-15 18:34:11 +0000536</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000537
538<!-- ======================================================================= -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000539<div class="doc_subsection">
Chris Lattner8fdb2462004-09-18 06:39:35 +0000540 <a name="CallGraphSCCPass">The <tt>CallGraphSCCPass</tt> class</a>
541</div>
542
543<div class="doc_text">
544
545<p>The "<tt><a
Reid Spencer05fe4b02006-03-14 05:39:39 +0000546href="http://llvm.org/doxygen/classllvm_1_1CallGraphSCCPass.html">CallGraphSCCPass</a></tt>"
Chris Lattner8fdb2462004-09-18 06:39:35 +0000547is used by passes that need to traverse the program bottom-up on the call graph
548(callees before callers). Deriving from CallGraphSCCPass provides some
549mechanics for building and traversing the CallGraph, but also allows the system
550to optimize execution of CallGraphSCCPass's. If your pass meets the
551requirements outlined below, and doesn't meet the requirements of a <tt><a
552href="#FunctionPass">FunctionPass</a></tt> or <tt><a
553href="#BasicBlockPass">BasicBlockPass</a></tt>, you should derive from
554<tt>CallGraphSCCPass</tt>.</p>
555
556<p><b>TODO</b>: explain briefly what SCC, Tarjan's algo, and B-U mean.</p>
557
558<p>To be explicit, <tt>CallGraphSCCPass</tt> subclasses are:</p>
559
560<ol>
561
562<li>... <em>not allowed</em> to modify any <tt>Function</tt>s that are not in
563the current SCC.</li>
564
Tanya Lattner18aad232007-06-07 16:44:52 +0000565<li>... <em>not allowed</em> to inspect any Function's other than those in the
Chris Lattner8fdb2462004-09-18 06:39:35 +0000566current SCC and the direct callees of the SCC.</li>
567
568<li>... <em>required</em> to preserve the current CallGraph object, updating it
569to reflect any changes made to the program.</li>
570
571<li>... <em>not allowed</em> to add or remove SCC's from the current Module,
572though they may change the contents of an SCC.</li>
573
574<li>... <em>allowed</em> to add or remove global variables from the current
575Module.</li>
576
577<li>... <em>allowed</em> to maintain state across invocations of
578 <a href="#runOnSCC"><tt>runOnSCC</tt></a> (including global data).</li>
579</ol>
580
581<p>Implementing a <tt>CallGraphSCCPass</tt> is slightly tricky in some cases
582because it has to handle SCCs with more than one node in it. All of the virtual
583methods described below should return true if they modified the program, or
584false if they didn't.</p>
585
586</div>
587
588<!-- _______________________________________________________________________ -->
589<div class="doc_subsubsection">
Devang Patelc20048d2007-01-23 22:56:28 +0000590 <a name="doInitialization_scc">The <tt>doInitialization(CallGraph &amp;)</tt>
Chris Lattner8fdb2462004-09-18 06:39:35 +0000591 method</a>
592</div>
593
594<div class="doc_text">
595
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000596<div class="doc_code"><pre>
Devang Patelc20048d2007-01-23 22:56:28 +0000597 <b>virtual bool</b> doInitialization(CallGraph &amp;CG);
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000598</pre></div>
Chris Lattner8fdb2462004-09-18 06:39:35 +0000599
600<p>The <tt>doIninitialize</tt> method is allowed to do most of the things that
601<tt>CallGraphSCCPass</tt>'s are not allowed to do. They can add and remove
602functions, get pointers to functions, etc. The <tt>doInitialization</tt> method
603is designed to do simple initialization type of stuff that does not depend on
604the SCCs being processed. The <tt>doInitialization</tt> method call is not
605scheduled to overlap with any other pass executions (thus it should be very
606fast).</p>
607
608</div>
609
610<!-- _______________________________________________________________________ -->
611<div class="doc_subsubsection">
612 <a name="runOnSCC">The <tt>runOnSCC</tt> method</a>
613</div>
614
615<div class="doc_text">
616
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000617<div class="doc_code"><pre>
Chris Lattner6f25d9f2010-04-16 23:07:44 +0000618 <b>virtual bool</b> runOnSCC(CallGraphSCC &amp;SCC) = 0;
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000619</pre></div>
Chris Lattner8fdb2462004-09-18 06:39:35 +0000620
621<p>The <tt>runOnSCC</tt> method performs the interesting work of the pass, and
622should return true if the module was modified by the transformation, false
623otherwise.</p>
624
625</div>
626
627<!-- _______________________________________________________________________ -->
628<div class="doc_subsubsection">
Devang Patelc20048d2007-01-23 22:56:28 +0000629 <a name="doFinalization_scc">The <tt>doFinalization(CallGraph
Chris Lattner8fdb2462004-09-18 06:39:35 +0000630 &amp;)</tt> method</a>
631</div>
632
633<div class="doc_text">
634
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000635<div class="doc_code"><pre>
Devang Patelc20048d2007-01-23 22:56:28 +0000636 <b>virtual bool</b> doFinalization(CallGraph &amp;CG);
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000637</pre></div>
Chris Lattner8fdb2462004-09-18 06:39:35 +0000638
639<p>The <tt>doFinalization</tt> method is an infrequently used method that is
640called when the pass framework has finished calling <a
641href="#runOnFunction"><tt>runOnFunction</tt></a> for every function in the
642program being compiled.</p>
643
644</div>
645
646<!-- ======================================================================= -->
647<div class="doc_subsection">
Misha Brukmanc5402402004-01-15 18:34:11 +0000648 <a name="FunctionPass">The <tt>FunctionPass</tt> class</a>
649</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000650
Misha Brukmanc5402402004-01-15 18:34:11 +0000651<div class="doc_text">
652
Chris Lattnerf6278922004-09-20 04:36:29 +0000653<p>In contrast to <tt>ModulePass</tt> subclasses, <tt><a
Reid Spencer05fe4b02006-03-14 05:39:39 +0000654href="http://llvm.org/doxygen/classllvm_1_1Pass.html">FunctionPass</a></tt>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000655subclasses do have a predictable, local behavior that can be expected by the
656system. All <tt>FunctionPass</tt> execute on each function in the program
Misha Brukmanef6a6a62003-08-21 22:14:26 +0000657independent of all of the other functions in the program.
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000658<tt>FunctionPass</tt>'s do not require that they are executed in a particular
Misha Brukmanc5402402004-01-15 18:34:11 +0000659order, and <tt>FunctionPass</tt>'s do not modify external functions.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000660
Misha Brukmanc5402402004-01-15 18:34:11 +0000661<p>To be explicit, <tt>FunctionPass</tt> subclasses are not allowed to:</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000662
663<ol>
Misha Brukmanc5402402004-01-15 18:34:11 +0000664<li>Modify a Function other than the one currently being processed.</li>
665<li>Add or remove Function's from the current Module.</li>
666<li>Add or remove global variables from the current Module.</li>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000667<li>Maintain state across invocations of
Misha Brukmanc5402402004-01-15 18:34:11 +0000668 <a href="#runOnFunction"><tt>runOnFunction</tt></a> (including global data)</li>
669</ol>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000670
Misha Brukmanc5402402004-01-15 18:34:11 +0000671<p>Implementing a <tt>FunctionPass</tt> is usually straightforward (See the <a
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000672href="#basiccode">Hello World</a> pass for example). <tt>FunctionPass</tt>'s
673may overload three virtual methods to do their work. All of these methods
Misha Brukmanc5402402004-01-15 18:34:11 +0000674should return true if they modified the program, or false if they didn't.</p>
675
676</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000677
678<!-- _______________________________________________________________________ -->
Chris Lattner89256272004-03-17 21:09:55 +0000679<div class="doc_subsubsection">
Misha Brukmanc5402402004-01-15 18:34:11 +0000680 <a name="doInitialization_mod">The <tt>doInitialization(Module &amp;)</tt>
681 method</a>
682</div>
683
684<div class="doc_text">
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000685
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000686<div class="doc_code"><pre>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000687 <b>virtual bool</b> doInitialization(Module &amp;M);
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000688</pre></div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000689
Misha Brukmanc5402402004-01-15 18:34:11 +0000690<p>The <tt>doIninitialize</tt> method is allowed to do most of the things that
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000691<tt>FunctionPass</tt>'s are not allowed to do. They can add and remove
Chris Lattnerd0713f92002-09-12 17:06:43 +0000692functions, get pointers to functions, etc. The <tt>doInitialization</tt> method
693is designed to do simple initialization type of stuff that does not depend on
694the functions being processed. The <tt>doInitialization</tt> method call is not
695scheduled to overlap with any other pass executions (thus it should be very
Misha Brukmanc5402402004-01-15 18:34:11 +0000696fast).</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000697
Misha Brukmanc5402402004-01-15 18:34:11 +0000698<p>A good example of how this method should be used is the <a
Reid Spencer05fe4b02006-03-14 05:39:39 +0000699href="http://llvm.org/doxygen/LowerAllocations_8cpp-source.html">LowerAllocations</a>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000700pass. This pass converts <tt>malloc</tt> and <tt>free</tt> instructions into
Misha Brukmanef6a6a62003-08-21 22:14:26 +0000701platform dependent <tt>malloc()</tt> and <tt>free()</tt> function calls. It
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000702uses the <tt>doInitialization</tt> method to get a reference to the malloc and
Misha Brukmanc5402402004-01-15 18:34:11 +0000703free functions that it needs, adding prototypes to the module if necessary.</p>
704
705</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000706
707<!-- _______________________________________________________________________ -->
Chris Lattner89256272004-03-17 21:09:55 +0000708<div class="doc_subsubsection">
Misha Brukmanc5402402004-01-15 18:34:11 +0000709 <a name="runOnFunction">The <tt>runOnFunction</tt> method</a>
710</div>
711
712<div class="doc_text">
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000713
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000714<div class="doc_code"><pre>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000715 <b>virtual bool</b> runOnFunction(Function &amp;F) = 0;
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000716</pre></div><p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000717
Misha Brukmanc5402402004-01-15 18:34:11 +0000718<p>The <tt>runOnFunction</tt> method must be implemented by your subclass to do
719the transformation or analysis work of your pass. As usual, a true value should
720be returned if the function is modified.</p>
721
722</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000723
724<!-- _______________________________________________________________________ -->
Chris Lattner89256272004-03-17 21:09:55 +0000725<div class="doc_subsubsection">
Misha Brukmanc5402402004-01-15 18:34:11 +0000726 <a name="doFinalization_mod">The <tt>doFinalization(Module
727 &amp;)</tt> method</a>
728</div>
729
730<div class="doc_text">
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000731
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000732<div class="doc_code"><pre>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000733 <b>virtual bool</b> doFinalization(Module &amp;M);
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000734</pre></div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000735
Misha Brukmanc5402402004-01-15 18:34:11 +0000736<p>The <tt>doFinalization</tt> method is an infrequently used method that is
737called when the pass framework has finished calling <a
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000738href="#runOnFunction"><tt>runOnFunction</tt></a> for every function in the
Misha Brukmanc5402402004-01-15 18:34:11 +0000739program being compiled.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000740
Misha Brukmanc5402402004-01-15 18:34:11 +0000741</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000742
743<!-- ======================================================================= -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000744<div class="doc_subsection">
Devang Patel2e8f27d2007-03-19 22:21:25 +0000745 <a name="LoopPass">The <tt>LoopPass</tt> class </a>
746</div>
747
748<div class="doc_text">
749
750<p> All <tt>LoopPass</tt> execute on each loop in the function independent of
751all of the other loops in the function. <tt>LoopPass</tt> processes loops in
752loop nest order such that outer most loop is processed last. </p>
753
754<p> <tt>LoopPass</tt> subclasses are allowed to update loop nest using
755<tt>LPPassManager</tt> interface. Implementing a loop pass is usually
756straightforward. <tt>Looppass</tt>'s may overload three virtual methods to
757do their work. All these methods should return true if they modified the
758program, or false if they didn't. </p>
759</div>
760
761<!-- _______________________________________________________________________ -->
762<div class="doc_subsubsection">
763 <a name="doInitialization_loop">The <tt>doInitialization(Loop *,
764 LPPassManager &amp;)</tt>
765 method</a>
766</div>
767
768<div class="doc_text">
769
770<div class="doc_code"><pre>
771 <b>virtual bool</b> doInitialization(Loop *, LPPassManager &amp;LPM);
772</pre></div>
773
Chris Lattnerb5c87f62007-05-18 05:36:14 +0000774<p>The <tt>doInitialization</tt> method is designed to do simple initialization
Devang Patel2e8f27d2007-03-19 22:21:25 +0000775type of stuff that does not depend on the functions being processed. The
776<tt>doInitialization</tt> method call is not scheduled to overlap with any
777other pass executions (thus it should be very fast). LPPassManager
778interface should be used to access Function or Module level analysis
779information.</p>
780
781</div>
782
783
784<!-- _______________________________________________________________________ -->
785<div class="doc_subsubsection">
786 <a name="runOnLoop">The <tt>runOnLoop</tt> method</a>
787</div>
788
789<div class="doc_text">
790
791<div class="doc_code"><pre>
792 <b>virtual bool</b> runOnLoop(Loop *, LPPassManager &amp;LPM) = 0;
793</pre></div><p>
794
795<p>The <tt>runOnLoop</tt> method must be implemented by your subclass to do
796the transformation or analysis work of your pass. As usual, a true value should
797be returned if the function is modified. <tt>LPPassManager</tt> interface
798should be used to update loop nest.</p>
799
800</div>
801
802<!-- _______________________________________________________________________ -->
803<div class="doc_subsubsection">
804 <a name="doFinalization_loop">The <tt>doFinalization()</tt> method</a>
805</div>
806
807<div class="doc_text">
808
809<div class="doc_code"><pre>
810 <b>virtual bool</b> doFinalization();
811</pre></div>
812
813<p>The <tt>doFinalization</tt> method is an infrequently used method that is
814called when the pass framework has finished calling <a
815href="#runOnLoop"><tt>runOnLoop</tt></a> for every loop in the
816program being compiled. </p>
817
818</div>
819
Tobias Grosser65513602010-10-20 01:54:44 +0000820<!-- ======================================================================= -->
821<div class="doc_subsection">
822 <a name="RegionPass">The <tt>RegionPass</tt> class </a>
823</div>
824
825<div class="doc_text">
826
827<p> <tt>RegionPass</tt> is similar to <a href="#LoopPass"><tt>LoopPass</tt></a>,
828but executes on each single entry single exit region in the function.
829<tt>RegionPass</tt> processes regions in nested order such that the outer most
830region is processed last. </p>
831
832<p> <tt>RegionPass</tt> subclasses are allowed to update the region tree by using
833the <tt>RGPassManager</tt> interface. You may overload three virtual methods of
834<tt>RegionPass</tt> to implementing your own region pass is usually. All these
835methods should return true if they modified the program, or false if they didn not.
836</p>
837</div>
838
839<!-- _______________________________________________________________________ -->
840<div class="doc_subsubsection">
841 <a name="doInitialization_region">The <tt>doInitialization(Region *,
842 RGPassManager &amp;)</tt>
843 method</a>
844</div>
845
846<div class="doc_text">
847
848<div class="doc_code"><pre>
849 <b>virtual bool</b> doInitialization(Region *, RGPassManager &amp;RGM);
850</pre></div>
851
852<p>The <tt>doInitialization</tt> method is designed to do simple initialization
853type of stuff that does not depend on the functions being processed. The
854<tt>doInitialization</tt> method call is not scheduled to overlap with any
855other pass executions (thus it should be very fast). RPPassManager
856interface should be used to access Function or Module level analysis
857information.</p>
858
859</div>
860
861
862<!-- _______________________________________________________________________ -->
863<div class="doc_subsubsection">
864 <a name="runOnRegion">The <tt>runOnRegion</tt> method</a>
865</div>
866
867<div class="doc_text">
868
869<div class="doc_code"><pre>
870 <b>virtual bool</b> runOnRegion(Region *, RGPassManager &amp;RGM) = 0;
871</pre></div><p>
872
873<p>The <tt>runOnRegion</tt> method must be implemented by your subclass to do
874the transformation or analysis work of your pass. As usual, a true value should
875be returned if the region is modified. <tt>RGPassManager</tt> interface
876should be used to update region tree.</p>
877
878</div>
879
880<!-- _______________________________________________________________________ -->
881<div class="doc_subsubsection">
882 <a name="doFinalization_region">The <tt>doFinalization()</tt> method</a>
883</div>
884
885<div class="doc_text">
886
887<div class="doc_code"><pre>
888 <b>virtual bool</b> doFinalization();
889</pre></div>
890
891<p>The <tt>doFinalization</tt> method is an infrequently used method that is
892called when the pass framework has finished calling <a
893href="#runOnRegion"><tt>runOnRegion</tt></a> for every region in the
894program being compiled. </p>
895
896</div>
897
Devang Patel2e8f27d2007-03-19 22:21:25 +0000898
899
900<!-- ======================================================================= -->
901<div class="doc_subsection">
Misha Brukmanc5402402004-01-15 18:34:11 +0000902 <a name="BasicBlockPass">The <tt>BasicBlockPass</tt> class</a>
903</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000904
Misha Brukmanc5402402004-01-15 18:34:11 +0000905<div class="doc_text">
906
907<p><tt>BasicBlockPass</tt>'s are just like <a
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000908href="#FunctionPass"><tt>FunctionPass</tt></a>'s, except that they must limit
909their scope of inspection and modification to a single basic block at a time.
Misha Brukmanc5402402004-01-15 18:34:11 +0000910As such, they are <b>not</b> allowed to do any of the following:</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000911
912<ol>
Misha Brukmanc5402402004-01-15 18:34:11 +0000913<li>Modify or inspect any basic blocks outside of the current one</li>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000914<li>Maintain state across invocations of
Misha Brukmanc5402402004-01-15 18:34:11 +0000915 <a href="#runOnBasicBlock"><tt>runOnBasicBlock</tt></a></li>
Reid Spencer1bc19342004-12-11 05:12:57 +0000916<li>Modify the control flow graph (by altering terminator instructions)</li>
917<li>Any of the things forbidden for
Misha Brukmanc5402402004-01-15 18:34:11 +0000918 <a href="#FunctionPass"><tt>FunctionPass</tt></a>es.</li>
919</ol>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000920
Misha Brukmanc5402402004-01-15 18:34:11 +0000921<p><tt>BasicBlockPass</tt>es are useful for traditional local and "peephole"
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000922optimizations. They may override the same <a
Chris Lattnerd0713f92002-09-12 17:06:43 +0000923href="#doInitialization_mod"><tt>doInitialization(Module &amp;)</tt></a> and <a
924href="#doFinalization_mod"><tt>doFinalization(Module &amp;)</tt></a> methods that <a
Misha Brukmanc5402402004-01-15 18:34:11 +0000925href="#FunctionPass"><tt>FunctionPass</tt></a>'s have, but also have the following virtual methods that may also be implemented:</p>
926
927</div>
Chris Lattnerd0713f92002-09-12 17:06:43 +0000928
929<!-- _______________________________________________________________________ -->
Chris Lattner89256272004-03-17 21:09:55 +0000930<div class="doc_subsubsection">
Misha Brukmanc5402402004-01-15 18:34:11 +0000931 <a name="doInitialization_fn">The <tt>doInitialization(Function
932 &amp;)</tt> method</a>
933</div>
934
935<div class="doc_text">
Chris Lattnerd0713f92002-09-12 17:06:43 +0000936
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000937<div class="doc_code"><pre>
Chris Lattnerd0713f92002-09-12 17:06:43 +0000938 <b>virtual bool</b> doInitialization(Function &amp;F);
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000939</pre></div>
Chris Lattnerd0713f92002-09-12 17:06:43 +0000940
Misha Brukmanc5402402004-01-15 18:34:11 +0000941<p>The <tt>doIninitialize</tt> method is allowed to do most of the things that
Chris Lattnerd0713f92002-09-12 17:06:43 +0000942<tt>BasicBlockPass</tt>'s are not allowed to do, but that
943<tt>FunctionPass</tt>'s can. The <tt>doInitialization</tt> method is designed
Reid Spencer1bc19342004-12-11 05:12:57 +0000944to do simple initialization that does not depend on the
Chris Lattnerd0713f92002-09-12 17:06:43 +0000945BasicBlocks being processed. The <tt>doInitialization</tt> method call is not
946scheduled to overlap with any other pass executions (thus it should be very
Misha Brukmanc5402402004-01-15 18:34:11 +0000947fast).</p>
Chris Lattnerd0713f92002-09-12 17:06:43 +0000948
Misha Brukmanc5402402004-01-15 18:34:11 +0000949</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000950
951<!-- _______________________________________________________________________ -->
Chris Lattner89256272004-03-17 21:09:55 +0000952<div class="doc_subsubsection">
Misha Brukmanc5402402004-01-15 18:34:11 +0000953 <a name="runOnBasicBlock">The <tt>runOnBasicBlock</tt> method</a>
954</div>
955
956<div class="doc_text">
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000957
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000958<div class="doc_code"><pre>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000959 <b>virtual bool</b> runOnBasicBlock(BasicBlock &amp;BB) = 0;
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000960</pre></div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000961
Misha Brukmanc5402402004-01-15 18:34:11 +0000962<p>Override this function to do the work of the <tt>BasicBlockPass</tt>. This
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000963function is not allowed to inspect or modify basic blocks other than the
964parameter, and are not allowed to modify the CFG. A true value must be returned
Misha Brukmanc5402402004-01-15 18:34:11 +0000965if the basic block is modified.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000966
Misha Brukmanc5402402004-01-15 18:34:11 +0000967</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +0000968
Chris Lattnerd0713f92002-09-12 17:06:43 +0000969<!-- _______________________________________________________________________ -->
Chris Lattner89256272004-03-17 21:09:55 +0000970<div class="doc_subsubsection">
Misha Brukmanc5402402004-01-15 18:34:11 +0000971 <a name="doFinalization_fn">The <tt>doFinalization(Function &amp;)</tt>
972 method</a>
973</div>
974
975<div class="doc_text">
Chris Lattnerd0713f92002-09-12 17:06:43 +0000976
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000977<div class="doc_code"><pre>
Chris Lattnerd0713f92002-09-12 17:06:43 +0000978 <b>virtual bool</b> doFinalization(Function &amp;F);
Jim Laskey5fa8fff2006-08-04 18:10:12 +0000979</pre></div>
Chris Lattnerd0713f92002-09-12 17:06:43 +0000980
Misha Brukmanc5402402004-01-15 18:34:11 +0000981<p>The <tt>doFinalization</tt> method is an infrequently used method that is
982called when the pass framework has finished calling <a
Chris Lattnerd0713f92002-09-12 17:06:43 +0000983href="#runOnBasicBlock"><tt>runOnBasicBlock</tt></a> for every BasicBlock in the
984program being compiled. This can be used to perform per-function
Misha Brukmanc5402402004-01-15 18:34:11 +0000985finalization.</p>
Chris Lattnerd0713f92002-09-12 17:06:43 +0000986
Misha Brukmanc5402402004-01-15 18:34:11 +0000987</div>
Chris Lattnerd0713f92002-09-12 17:06:43 +0000988
Brian Gaekecab8b6f2003-07-17 18:53:20 +0000989<!-- ======================================================================= -->
Misha Brukmanc5402402004-01-15 18:34:11 +0000990<div class="doc_subsection">
991 <a name="MachineFunctionPass">The <tt>MachineFunctionPass</tt> class</a>
992</div>
Brian Gaekecab8b6f2003-07-17 18:53:20 +0000993
Misha Brukmanc5402402004-01-15 18:34:11 +0000994<div class="doc_text">
995
Chris Lattner89256272004-03-17 21:09:55 +0000996<p>A <tt>MachineFunctionPass</tt> is a part of the LLVM code generator that
997executes on the machine-dependent representation of each LLVM function in the
Dan Gohman9f116aa2010-03-10 01:29:39 +0000998program.</p>
999
1000<p>Code generator passes are registered and initialized specially by
1001<tt>TargetMachine::addPassesToEmitFile</tt> and similar routines, so they
1002cannot generally be run from the <tt>opt</tt> or <tt>bugpoint</tt>
1003commands.</p>
1004
1005<p>A <tt>MachineFunctionPass</tt> is also a <tt>FunctionPass</tt>, so all
Brian Gaekecab8b6f2003-07-17 18:53:20 +00001006the restrictions that apply to a <tt>FunctionPass</tt> also apply to it.
Chris Lattner89256272004-03-17 21:09:55 +00001007<tt>MachineFunctionPass</tt>es also have additional restrictions. In particular,
1008<tt>MachineFunctionPass</tt>es are not allowed to do any of the following:</p>
Brian Gaekecab8b6f2003-07-17 18:53:20 +00001009
1010<ol>
Dan Gohman9f116aa2010-03-10 01:29:39 +00001011<li>Modify or create any LLVM IR Instructions, BasicBlocks, Arguments,
1012 Functions, GlobalVariables, GlobalAliases, or Modules.</li>
Misha Brukmanc5402402004-01-15 18:34:11 +00001013<li>Modify a MachineFunction other than the one currently being processed.</li>
Misha Brukmanc5402402004-01-15 18:34:11 +00001014<li>Maintain state across invocations of <a
1015href="#runOnMachineFunction"><tt>runOnMachineFunction</tt></a> (including global
1016data)</li>
1017</ol>
Brian Gaekecab8b6f2003-07-17 18:53:20 +00001018
Misha Brukmanc5402402004-01-15 18:34:11 +00001019</div>
Chris Lattnerd0713f92002-09-12 17:06:43 +00001020
Brian Gaeke6a33f362003-07-22 20:53:20 +00001021<!-- _______________________________________________________________________ -->
Chris Lattner89256272004-03-17 21:09:55 +00001022<div class="doc_subsubsection">
Misha Brukmanc5402402004-01-15 18:34:11 +00001023 <a name="runOnMachineFunction">The <tt>runOnMachineFunction(MachineFunction
1024 &amp;MF)</tt> method</a>
1025</div>
1026
1027<div class="doc_text">
Brian Gaeke6a33f362003-07-22 20:53:20 +00001028
Jim Laskey5fa8fff2006-08-04 18:10:12 +00001029<div class="doc_code"><pre>
Brian Gaeke6a33f362003-07-22 20:53:20 +00001030 <b>virtual bool</b> runOnMachineFunction(MachineFunction &amp;MF) = 0;
Jim Laskey5fa8fff2006-08-04 18:10:12 +00001031</pre></div>
Brian Gaeke6a33f362003-07-22 20:53:20 +00001032
Misha Brukmanc5402402004-01-15 18:34:11 +00001033<p><tt>runOnMachineFunction</tt> can be considered the main entry point of a
1034<tt>MachineFunctionPass</tt>; that is, you should override this method to do the
1035work of your <tt>MachineFunctionPass</tt>.</p>
Brian Gaeke6a33f362003-07-22 20:53:20 +00001036
Misha Brukmanc5402402004-01-15 18:34:11 +00001037<p>The <tt>runOnMachineFunction</tt> method is called on every
Brian Gaeke6a33f362003-07-22 20:53:20 +00001038<tt>MachineFunction</tt> in a <tt>Module</tt>, so that the
Misha Brukmanc5402402004-01-15 18:34:11 +00001039<tt>MachineFunctionPass</tt> may perform optimizations on the machine-dependent
1040representation of the function. If you want to get at the LLVM <tt>Function</tt>
1041for the <tt>MachineFunction</tt> you're working on, use
1042<tt>MachineFunction</tt>'s <tt>getFunction()</tt> accessor method -- but
1043remember, you may not modify the LLVM <tt>Function</tt> or its contents from a
1044<tt>MachineFunctionPass</tt>.</p>
1045
1046</div>
Brian Gaeke6a33f362003-07-22 20:53:20 +00001047
Chris Lattnerc6bb8242002-08-08 20:11:18 +00001048<!-- *********************************************************************** -->
Misha Brukmanc5402402004-01-15 18:34:11 +00001049<div class="doc_section">
1050 <a name="registration">Pass registration</a>
1051</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +00001052<!-- *********************************************************************** -->
1053
Misha Brukmanc5402402004-01-15 18:34:11 +00001054<div class="doc_text">
Chris Lattnerc6bb8242002-08-08 20:11:18 +00001055
Misha Brukmanc5402402004-01-15 18:34:11 +00001056<p>In the <a href="#basiccode">Hello World</a> example pass we illustrated how
1057pass registration works, and discussed some of the reasons that it is used and
1058what it does. Here we discuss how and why passes are registered.</p>
1059
Owen Anderson20813e02010-07-21 22:58:07 +00001060<p>As we saw above, passes are registered with the <b><tt>INITIALIZE_PASS</tt></b>
1061macro. The first parameter is the name of the pass that is to be used on
Chris Lattnerc6bb8242002-08-08 20:11:18 +00001062the command line to specify that the pass should be added to a program (for
Chris Lattnerc8603c22006-08-27 23:18:52 +00001063example, with <tt>opt</tt> or <tt>bugpoint</tt>). The second argument is the
Duncan Sands7e7ae5a2010-02-18 14:08:13 +00001064name of the pass, which is to be used for the <tt>-help</tt> output of
Chris Lattnerc8603c22006-08-27 23:18:52 +00001065programs, as
Misha Brukmanc5402402004-01-15 18:34:11 +00001066well as for debug output generated by the <tt>--debug-pass</tt> option.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +00001067
Chris Lattnerc8603c22006-08-27 23:18:52 +00001068<p>If you want your pass to be easily dumpable, you should
1069implement the virtual <tt>print</tt> method:</p>
Misha Brukmanc5402402004-01-15 18:34:11 +00001070
1071</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +00001072
1073<!-- _______________________________________________________________________ -->
Misha Brukmanc5402402004-01-15 18:34:11 +00001074<div class="doc_subsubsection">
1075 <a name="print">The <tt>print</tt> method</a>
1076</div>
1077
1078<div class="doc_text">
Chris Lattnerc6bb8242002-08-08 20:11:18 +00001079
Jim Laskey5fa8fff2006-08-04 18:10:12 +00001080<div class="doc_code"><pre>
Torok Edwin52790e52008-10-28 17:29:23 +00001081 <b>virtual void</b> print(std::ostream &amp;O, <b>const</b> Module *M) <b>const</b>;
Jim Laskey5fa8fff2006-08-04 18:10:12 +00001082</pre></div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +00001083
Misha Brukmanc5402402004-01-15 18:34:11 +00001084<p>The <tt>print</tt> method must be implemented by "analyses" in order to print
1085a human readable version of the analysis results. This is useful for debugging
1086an analysis itself, as well as for other people to figure out how an analysis
Chris Lattnerc8603c22006-08-27 23:18:52 +00001087works. Use the <tt>opt -analyze</tt> argument to invoke this method.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +00001088
Bill Wendling832171c2006-12-07 20:04:42 +00001089<p>The <tt>llvm::OStream</tt> parameter specifies the stream to write the results on,
Misha Brukmanc5402402004-01-15 18:34:11 +00001090and the <tt>Module</tt> parameter gives a pointer to the top level module of the
Chris Lattnerc6bb8242002-08-08 20:11:18 +00001091program that has been analyzed. Note however that this pointer may be null in
1092certain circumstances (such as calling the <tt>Pass::dump()</tt> from a
1093debugger), so it should only be used to enhance debug output, it should not be
Misha Brukmanc5402402004-01-15 18:34:11 +00001094depended on.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +00001095
Misha Brukmanc5402402004-01-15 18:34:11 +00001096</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +00001097
1098<!-- *********************************************************************** -->
Misha Brukmanc5402402004-01-15 18:34:11 +00001099<div class="doc_section">
1100 <a name="interaction">Specifying interactions between passes</a>
1101</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +00001102<!-- *********************************************************************** -->
1103
Misha Brukmanc5402402004-01-15 18:34:11 +00001104<div class="doc_text">
1105
John Criswell8528e782007-12-03 19:34:25 +00001106<p>One of the main responsibilities of the <tt>PassManager</tt> is to make sure
Chris Lattnerc6bb8242002-08-08 20:11:18 +00001107that passes interact with each other correctly. Because <tt>PassManager</tt>
1108tries to <a href="#passmanager">optimize the execution of passes</a> it must
1109know how the passes interact with each other and what dependencies exist between
1110the various passes. To track this, each pass can declare the set of passes that
1111are required to be executed before the current pass, and the passes which are
Misha Brukmanc5402402004-01-15 18:34:11 +00001112invalidated by the current pass.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +00001113
Misha Brukmanc5402402004-01-15 18:34:11 +00001114<p>Typically this functionality is used to require that analysis results are
Chris Lattnerc6bb8242002-08-08 20:11:18 +00001115computed before your pass is run. Running arbitrary transformation passes can
1116invalidate the computed analysis results, which is what the invalidation set
1117specifies. If a pass does not implement the <tt><a
1118href="#getAnalysisUsage">getAnalysisUsage</a></tt> method, it defaults to not
Misha Brukmanc5402402004-01-15 18:34:11 +00001119having any prerequisite passes, and invalidating <b>all</b> other passes.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +00001120
Misha Brukmanc5402402004-01-15 18:34:11 +00001121</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +00001122
1123<!-- _______________________________________________________________________ -->
Misha Brukmanc5402402004-01-15 18:34:11 +00001124<div class="doc_subsubsection">
1125 <a name="getAnalysisUsage">The <tt>getAnalysisUsage</tt> method</a>
1126</div>
1127
1128<div class="doc_text">
Chris Lattnerc6bb8242002-08-08 20:11:18 +00001129
Jim Laskey5fa8fff2006-08-04 18:10:12 +00001130<div class="doc_code"><pre>
Chris Lattnerc6bb8242002-08-08 20:11:18 +00001131 <b>virtual void</b> getAnalysisUsage(AnalysisUsage &amp;Info) <b>const</b>;
Jim Laskey5fa8fff2006-08-04 18:10:12 +00001132</pre></div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +00001133
Misha Brukmanc5402402004-01-15 18:34:11 +00001134<p>By implementing the <tt>getAnalysisUsage</tt> method, the required and
Chris Lattnerc6bb8242002-08-08 20:11:18 +00001135invalidated sets may be specified for your transformation. The implementation
1136should fill in the <tt><a
Reid Spencer05fe4b02006-03-14 05:39:39 +00001137href="http://llvm.org/doxygen/classllvm_1_1AnalysisUsage.html">AnalysisUsage</a></tt>
Misha Brukmanc5402402004-01-15 18:34:11 +00001138object with information about which passes are required and not invalidated. To
Chris Lattner89256272004-03-17 21:09:55 +00001139do this, a pass may call any of the following methods on the AnalysisUsage
1140object:</p>
1141</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +00001142
Chris Lattner89256272004-03-17 21:09:55 +00001143<!-- _______________________________________________________________________ -->
1144<div class="doc_subsubsection">
1145 <a name="AU::addRequired">The <tt>AnalysisUsage::addRequired&lt;&gt;</tt> and <tt>AnalysisUsage::addRequiredTransitive&lt;&gt;</tt> methods</a>
1146</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +00001147
Chris Lattner89256272004-03-17 21:09:55 +00001148<div class="doc_text">
1149<p>
Reid Spencer1bc19342004-12-11 05:12:57 +00001150If your pass requires a previous pass to be executed (an analysis for example),
Chris Lattner89256272004-03-17 21:09:55 +00001151it can use one of these methods to arrange for it to be run before your pass.
1152LLVM has many different types of analyses and passes that can be required,
Reid Spencer1bc19342004-12-11 05:12:57 +00001153spanning the range from <tt>DominatorSet</tt> to <tt>BreakCriticalEdges</tt>.
1154Requiring <tt>BreakCriticalEdges</tt>, for example, guarantees that there will
Chris Lattner89256272004-03-17 21:09:55 +00001155be no critical edges in the CFG when your pass has been run.
1156</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +00001157
Chris Lattner89256272004-03-17 21:09:55 +00001158<p>
1159Some analyses chain to other analyses to do their job. For example, an <a
1160href="AliasAnalysis.html">AliasAnalysis</a> implementation is required to <a
1161href="AliasAnalysis.html#chaining">chain</a> to other alias analysis passes. In
1162cases where analyses chain, the <tt>addRequiredTransitive</tt> method should be
1163used instead of the <tt>addRequired</tt> method. This informs the PassManager
1164that the transitively required pass should be alive as long as the requiring
1165pass is.
1166</p>
1167</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +00001168
Chris Lattner89256272004-03-17 21:09:55 +00001169<!-- _______________________________________________________________________ -->
1170<div class="doc_subsubsection">
1171 <a name="AU::addPreserved">The <tt>AnalysisUsage::addPreserved&lt;&gt;</tt> method</a>
1172</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +00001173
Chris Lattner89256272004-03-17 21:09:55 +00001174<div class="doc_text">
1175<p>
1176One of the jobs of the PassManager is to optimize how and when analyses are run.
1177In particular, it attempts to avoid recomputing data unless it needs to. For
1178this reason, passes are allowed to declare that they preserve (i.e., they don't
1179invalidate) an existing analysis if it's available. For example, a simple
Reid Spencer1bc19342004-12-11 05:12:57 +00001180constant folding pass would not modify the CFG, so it can't possibly affect the
Chris Lattner89256272004-03-17 21:09:55 +00001181results of dominator analysis. By default, all passes are assumed to invalidate
1182all others.
1183</p>
1184
1185<p>
1186The <tt>AnalysisUsage</tt> class provides several methods which are useful in
1187certain circumstances that are related to <tt>addPreserved</tt>. In particular,
1188the <tt>setPreservesAll</tt> method can be called to indicate that the pass does
1189not modify the LLVM program at all (which is true for analyses), and the
1190<tt>setPreservesCFG</tt> method can be used by transformations that change
1191instructions in the program but do not modify the CFG or terminator instructions
1192(note that this property is implicitly set for <a
1193href="#BasicBlockPass">BasicBlockPass</a>'s).
1194</p>
1195
1196<p>
1197<tt>addPreserved</tt> is particularly useful for transformations like
1198<tt>BreakCriticalEdges</tt>. This pass knows how to update a small set of loop
1199and dominator related analyses if they exist, so it can preserve them, despite
1200the fact that it hacks on the CFG.
1201</p>
1202</div>
1203
1204<!-- _______________________________________________________________________ -->
1205<div class="doc_subsubsection">
1206 <a name="AU::examples">Example implementations of <tt>getAnalysisUsage</tt></a>
1207</div>
1208
1209<div class="doc_text">
Chris Lattnerc6bb8242002-08-08 20:11:18 +00001210
Jim Laskey5fa8fff2006-08-04 18:10:12 +00001211<div class="doc_code"><pre>
Chris Lattnerc6bb8242002-08-08 20:11:18 +00001212 <i>// This is an example implementation from an analysis, which does not modify
1213 // the program at all, yet has a prerequisite.</i>
Reid Spencer05fe4b02006-03-14 05:39:39 +00001214 <b>void</b> <a href="http://llvm.org/doxygen/classllvm_1_1PostDominanceFrontier.html">PostDominanceFrontier</a>::getAnalysisUsage(AnalysisUsage &amp;AU) <b>const</b> {
Chris Lattnerc6bb8242002-08-08 20:11:18 +00001215 AU.setPreservesAll();
Reid Spencer05fe4b02006-03-14 05:39:39 +00001216 AU.addRequired&lt;<a href="http://llvm.org/doxygen/classllvm_1_1PostDominatorTree.html">PostDominatorTree</a>&gt;();
Chris Lattnerc6bb8242002-08-08 20:11:18 +00001217 }
Jim Laskey5fa8fff2006-08-04 18:10:12 +00001218</pre></div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +00001219
Misha Brukmanc5402402004-01-15 18:34:11 +00001220<p>and:</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +00001221
Jim Laskey5fa8fff2006-08-04 18:10:12 +00001222<div class="doc_code"><pre>
Chris Lattnerc6bb8242002-08-08 20:11:18 +00001223 <i>// This example modifies the program, but does not modify the CFG</i>
Reid Spencer05fe4b02006-03-14 05:39:39 +00001224 <b>void</b> <a href="http://llvm.org/doxygen/structLICM.html">LICM</a>::getAnalysisUsage(AnalysisUsage &amp;AU) <b>const</b> {
Chris Lattner8291e042002-10-21 19:57:59 +00001225 AU.setPreservesCFG();
Reid Spencer05fe4b02006-03-14 05:39:39 +00001226 AU.addRequired&lt;<a href="http://llvm.org/doxygen/classllvm_1_1LoopInfo.html">LoopInfo</a>&gt;();
Chris Lattnerc6bb8242002-08-08 20:11:18 +00001227 }
Jim Laskey5fa8fff2006-08-04 18:10:12 +00001228</pre></div>
Misha Brukmanc5402402004-01-15 18:34:11 +00001229
1230</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +00001231
1232<!-- _______________________________________________________________________ -->
Misha Brukmanc5402402004-01-15 18:34:11 +00001233<div class="doc_subsubsection">
Duncan Sands1465d612009-01-28 13:14:17 +00001234 <a name="getAnalysis">The <tt>getAnalysis&lt;&gt;</tt> and
1235<tt>getAnalysisIfAvailable&lt;&gt;</tt> methods</a>
Misha Brukmanc5402402004-01-15 18:34:11 +00001236</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +00001237
Misha Brukmanc5402402004-01-15 18:34:11 +00001238<div class="doc_text">
1239
Chris Lattner89256272004-03-17 21:09:55 +00001240<p>The <tt>Pass::getAnalysis&lt;&gt;</tt> method is automatically inherited by
1241your class, providing you with access to the passes that you declared that you
1242required with the <a href="#getAnalysisUsage"><tt>getAnalysisUsage</tt></a>
1243method. It takes a single template argument that specifies which pass class you
1244want, and returns a reference to that pass. For example:</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +00001245
Jim Laskey5fa8fff2006-08-04 18:10:12 +00001246<div class="doc_code"><pre>
Chris Lattnera5776302004-03-17 21:33:32 +00001247 bool LICM::runOnFunction(Function &amp;F) {
Chris Lattner89256272004-03-17 21:09:55 +00001248 LoopInfo &amp;LI = getAnalysis&lt;LoopInfo&gt;();
1249 ...
1250 }
Jim Laskey5fa8fff2006-08-04 18:10:12 +00001251</pre></div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +00001252
Misha Brukmanc5402402004-01-15 18:34:11 +00001253<p>This method call returns a reference to the pass desired. You may get a
1254runtime assertion failure if you attempt to get an analysis that you did not
1255declare as required in your <a
1256href="#getAnalysisUsage"><tt>getAnalysisUsage</tt></a> implementation. This
1257method can be called by your <tt>run*</tt> method implementation, or by any
Devang Patel3c1ca0b2007-04-16 21:28:14 +00001258other local method invoked by your <tt>run*</tt> method.
1259
1260A module level pass can use function level analysis info using this interface.
1261For example:</p>
1262
1263<div class="doc_code"><pre>
1264 bool ModuleLevelPass::runOnModule(Module &amp;M) {
1265 ...
Devang Patelf23de112007-04-17 00:17:11 +00001266 DominatorTree &amp;DT = getAnalysis&lt;DominatorTree&gt;(Func);
Devang Patel3c1ca0b2007-04-16 21:28:14 +00001267 ...
1268 }
1269</pre></div>
1270
Chris Lattnerb5c87f62007-05-18 05:36:14 +00001271<p>In above example, runOnFunction for DominatorTree is called by pass manager
Devang Patel3c1ca0b2007-04-16 21:28:14 +00001272before returning a reference to the desired pass.</p>
Misha Brukmanc5402402004-01-15 18:34:11 +00001273
Chris Lattner89256272004-03-17 21:09:55 +00001274<p>
1275If your pass is capable of updating analyses if they exist (e.g.,
1276<tt>BreakCriticalEdges</tt>, as described above), you can use the
Duncan Sands1465d612009-01-28 13:14:17 +00001277<tt>getAnalysisIfAvailable</tt> method, which returns a pointer to the analysis
1278if it is active. For example:</p>
Chris Lattner89256272004-03-17 21:09:55 +00001279
Jim Laskey5fa8fff2006-08-04 18:10:12 +00001280<div class="doc_code"><pre>
Chris Lattner89256272004-03-17 21:09:55 +00001281 ...
Duncan Sands1465d612009-01-28 13:14:17 +00001282 if (DominatorSet *DS = getAnalysisIfAvailable&lt;DominatorSet&gt;()) {
Chris Lattner89256272004-03-17 21:09:55 +00001283 <i>// A DominatorSet is active. This code will update it.</i>
1284 }
1285 ...
Jim Laskey5fa8fff2006-08-04 18:10:12 +00001286</pre></div>
Chris Lattner89256272004-03-17 21:09:55 +00001287
Misha Brukmanc5402402004-01-15 18:34:11 +00001288</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +00001289
Chris Lattner79910702002-08-22 19:21:04 +00001290<!-- *********************************************************************** -->
Misha Brukmanc5402402004-01-15 18:34:11 +00001291<div class="doc_section">
1292 <a name="analysisgroup">Implementing Analysis Groups</a>
1293</div>
Chris Lattner79910702002-08-22 19:21:04 +00001294<!-- *********************************************************************** -->
1295
Misha Brukmanc5402402004-01-15 18:34:11 +00001296<div class="doc_text">
1297
Chris Lattnerb7632282007-11-16 05:32:05 +00001298<p>Now that we understand the basics of how passes are defined, how they are
Misha Brukmanc5402402004-01-15 18:34:11 +00001299used, and how they are required from other passes, it's time to get a little bit
Chris Lattner79910702002-08-22 19:21:04 +00001300fancier. All of the pass relationships that we have seen so far are very
1301simple: one pass depends on one other specific pass to be run before it can run.
1302For many applications, this is great, for others, more flexibility is
Misha Brukmanc5402402004-01-15 18:34:11 +00001303required.</p>
Chris Lattner79910702002-08-22 19:21:04 +00001304
Misha Brukmanc5402402004-01-15 18:34:11 +00001305<p>In particular, some analyses are defined such that there is a single simple
Chris Lattner79910702002-08-22 19:21:04 +00001306interface to the analysis results, but multiple ways of calculating them.
1307Consider alias analysis for example. The most trivial alias analysis returns
1308"may alias" for any alias query. The most sophisticated analysis a
1309flow-sensitive, context-sensitive interprocedural analysis that can take a
1310significant amount of time to execute (and obviously, there is a lot of room
1311between these two extremes for other implementations). To cleanly support
1312situations like this, the LLVM Pass Infrastructure supports the notion of
Misha Brukmanc5402402004-01-15 18:34:11 +00001313Analysis Groups.</p>
1314
1315</div>
Chris Lattner79910702002-08-22 19:21:04 +00001316
1317<!-- _______________________________________________________________________ -->
Chris Lattner89256272004-03-17 21:09:55 +00001318<div class="doc_subsubsection">
Misha Brukmanc5402402004-01-15 18:34:11 +00001319 <a name="agconcepts">Analysis Group Concepts</a>
1320</div>
Chris Lattner79910702002-08-22 19:21:04 +00001321
Misha Brukmanc5402402004-01-15 18:34:11 +00001322<div class="doc_text">
1323
1324<p>An Analysis Group is a single simple interface that may be implemented by
Chris Lattner79910702002-08-22 19:21:04 +00001325multiple different passes. Analysis Groups can be given human readable names
1326just like passes, but unlike passes, they need not derive from the <tt>Pass</tt>
1327class. An analysis group may have one or more implementations, one of which is
Misha Brukmanc5402402004-01-15 18:34:11 +00001328the "default" implementation.</p>
Chris Lattner79910702002-08-22 19:21:04 +00001329
Misha Brukmanc5402402004-01-15 18:34:11 +00001330<p>Analysis groups are used by client passes just like other passes are: the
Chris Lattner79910702002-08-22 19:21:04 +00001331<tt>AnalysisUsage::addRequired()</tt> and <tt>Pass::getAnalysis()</tt> methods.
1332In order to resolve this requirement, the <a href="#passmanager">PassManager</a>
1333scans the available passes to see if any implementations of the analysis group
1334are available. If none is available, the default implementation is created for
1335the pass to use. All standard rules for <A href="#interaction">interaction
Misha Brukmanc5402402004-01-15 18:34:11 +00001336between passes</a> still apply.</p>
Chris Lattner79910702002-08-22 19:21:04 +00001337
Misha Brukmanc5402402004-01-15 18:34:11 +00001338<p>Although <a href="#registration">Pass Registration</a> is optional for normal
Chris Lattner79910702002-08-22 19:21:04 +00001339passes, all analysis group implementations must be registered, and must use the
Owen Andersond8cc7be2010-07-21 23:07:00 +00001340<A href="#registerag"><tt>INITIALIZE_AG_PASS</tt></a> template to join the
Chris Lattner79910702002-08-22 19:21:04 +00001341implementation pool. Also, a default implementation of the interface
1342<b>must</b> be registered with <A
Misha Brukmanc5402402004-01-15 18:34:11 +00001343href="#registerag"><tt>RegisterAnalysisGroup</tt></a>.</p>
Chris Lattner79910702002-08-22 19:21:04 +00001344
Misha Brukmanc5402402004-01-15 18:34:11 +00001345<p>As a concrete example of an Analysis Group in action, consider the <a
Reid Spencer05fe4b02006-03-14 05:39:39 +00001346href="http://llvm.org/doxygen/classllvm_1_1AliasAnalysis.html">AliasAnalysis</a>
Chris Lattner79910702002-08-22 19:21:04 +00001347analysis group. The default implementation of the alias analysis interface (the
1348<tt><a
Reid Spencer05fe4b02006-03-14 05:39:39 +00001349href="http://llvm.org/doxygen/structBasicAliasAnalysis.html">basicaa</a></tt>
Chris Lattner79910702002-08-22 19:21:04 +00001350pass) just does a few simple checks that don't require significant analysis to
1351compute (such as: two different globals can never alias each other, etc).
1352Passes that use the <tt><a
Reid Spencer05fe4b02006-03-14 05:39:39 +00001353href="http://llvm.org/doxygen/classllvm_1_1AliasAnalysis.html">AliasAnalysis</a></tt>
Chris Lattner79910702002-08-22 19:21:04 +00001354interface (for example the <tt><a
Reid Spencer05fe4b02006-03-14 05:39:39 +00001355href="http://llvm.org/doxygen/structGCSE.html">gcse</a></tt> pass), do
Misha Brukmanc5402402004-01-15 18:34:11 +00001356not care which implementation of alias analysis is actually provided, they just
1357use the designated interface.</p>
Chris Lattner79910702002-08-22 19:21:04 +00001358
Misha Brukmanc5402402004-01-15 18:34:11 +00001359<p>From the user's perspective, commands work just like normal. Issuing the
Chris Lattner79910702002-08-22 19:21:04 +00001360command '<tt>opt -gcse ...</tt>' will cause the <tt>basicaa</tt> class to be
1361instantiated and added to the pass sequence. Issuing the command '<tt>opt
1362-somefancyaa -gcse ...</tt>' will cause the <tt>gcse</tt> pass to use the
1363<tt>somefancyaa</tt> alias analysis (which doesn't actually exist, it's just a
Misha Brukmanc5402402004-01-15 18:34:11 +00001364hypothetical example) instead.</p>
Chris Lattner79910702002-08-22 19:21:04 +00001365
Misha Brukmanc5402402004-01-15 18:34:11 +00001366</div>
Chris Lattner79910702002-08-22 19:21:04 +00001367
1368<!-- _______________________________________________________________________ -->
Chris Lattner89256272004-03-17 21:09:55 +00001369<div class="doc_subsubsection">
Misha Brukmanc5402402004-01-15 18:34:11 +00001370 <a name="registerag">Using <tt>RegisterAnalysisGroup</tt></a>
1371</div>
Chris Lattner79910702002-08-22 19:21:04 +00001372
Misha Brukmanc5402402004-01-15 18:34:11 +00001373<div class="doc_text">
1374
1375<p>The <tt>RegisterAnalysisGroup</tt> template is used to register the analysis
Owen Andersond8cc7be2010-07-21 23:07:00 +00001376group itself, while the <tt>INITIALIZE_AG_PASS</tt> is used to add pass
1377implementations to the analysis group. First,
1378an analysis group should be registered, with a human readable name
1379provided for it.
Chris Lattner79910702002-08-22 19:21:04 +00001380Unlike registration of passes, there is no command line argument to be specified
Misha Brukmanc5402402004-01-15 18:34:11 +00001381for the Analysis Group Interface itself, because it is "abstract":</p>
Chris Lattner79910702002-08-22 19:21:04 +00001382
Jim Laskey5fa8fff2006-08-04 18:10:12 +00001383<div class="doc_code"><pre>
Reid Spencer05fe4b02006-03-14 05:39:39 +00001384 <b>static</b> RegisterAnalysisGroup&lt;<a href="http://llvm.org/doxygen/classllvm_1_1AliasAnalysis.html">AliasAnalysis</a>&gt; A("<i>Alias Analysis</i>");
Jim Laskey5fa8fff2006-08-04 18:10:12 +00001385</pre></div>
Chris Lattner79910702002-08-22 19:21:04 +00001386
Misha Brukmanc5402402004-01-15 18:34:11 +00001387<p>Once the analysis is registered, passes can declare that they are valid
1388implementations of the interface by using the following code:</p>
Chris Lattner79910702002-08-22 19:21:04 +00001389
Jim Laskey5fa8fff2006-08-04 18:10:12 +00001390<div class="doc_code"><pre>
Chris Lattner79910702002-08-22 19:21:04 +00001391<b>namespace</b> {
Chris Lattner79910702002-08-22 19:21:04 +00001392 //<i> Declare that we implement the AliasAnalysis interface</i>
Owen Andersond8cc7be2010-07-21 23:07:00 +00001393 INITIALIZE_AG_PASS(FancyAA, <a href="http://llvm.org/doxygen/classllvm_1_1AliasAnalysis.html">AliasAnalysis</a>, "<i>somefancyaa</i>",
1394 "<i>A more complex alias analysis implementation</i>",
1395 false, // <i>Is CFG Only?</i>
1396 true, // <i>Is Analysis?</i>
1397 false, // <i>Is default Analysis Group implementation?</i>
1398 );
Chris Lattner79910702002-08-22 19:21:04 +00001399}
Jim Laskey5fa8fff2006-08-04 18:10:12 +00001400</pre></div>
Chris Lattner79910702002-08-22 19:21:04 +00001401
Owen Andersond8cc7be2010-07-21 23:07:00 +00001402<p>This just shows a class <tt>FancyAA</tt> that
1403uses the <tt>INITIALIZE_AG_PASS</tt> macro both to register and
1404to "join" the <tt><a href="http://llvm.org/doxygen/classllvm_1_1AliasAnalysis.html">AliasAnalysis</a></tt>
Chris Lattner79910702002-08-22 19:21:04 +00001405analysis group. Every implementation of an analysis group should join using
Owen Andersond8cc7be2010-07-21 23:07:00 +00001406this macro.</p>
Chris Lattner79910702002-08-22 19:21:04 +00001407
Jim Laskey5fa8fff2006-08-04 18:10:12 +00001408<div class="doc_code"><pre>
Chris Lattner79910702002-08-22 19:21:04 +00001409<b>namespace</b> {
Chris Lattner79910702002-08-22 19:21:04 +00001410 //<i> Declare that we implement the AliasAnalysis interface</i>
Owen Andersond8cc7be2010-07-21 23:07:00 +00001411 INITIALIZE_AG_PASS(BasicAA, <a href="http://llvm.org/doxygen/classllvm_1_1AliasAnalysis.html">AliasAnalysis</a>, "<i>basicaa</i>",
1412 "<i>Basic Alias Analysis (default AA impl)</i>",
1413 false, // <i>Is CFG Only?</i>
1414 true, // <i>Is Analysis?</i>
1415 true, // <i>Is default Analysis Group implementation?</i>
1416 );
Chris Lattner79910702002-08-22 19:21:04 +00001417}
Jim Laskey5fa8fff2006-08-04 18:10:12 +00001418</pre></div>
Chris Lattner79910702002-08-22 19:21:04 +00001419
Owen Andersond8cc7be2010-07-21 23:07:00 +00001420<p>Here we show how the default implementation is specified (using the final
1421argument to the <tt>INITIALIZE_AG_PASS</tt> template). There must be exactly
Chris Lattner79910702002-08-22 19:21:04 +00001422one default implementation available at all times for an Analysis Group to be
Devang Patel2397f8d2007-06-20 18:51:14 +00001423used. Only default implementation can derive from <tt>ImmutablePass</tt>.
1424Here we declare that the
1425 <tt><a href="http://llvm.org/doxygen/structBasicAliasAnalysis.html">BasicAliasAnalysis</a></tt>
Misha Brukmanc5402402004-01-15 18:34:11 +00001426pass is the default implementation for the interface.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +00001427
Misha Brukmanc5402402004-01-15 18:34:11 +00001428</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +00001429
1430<!-- *********************************************************************** -->
Misha Brukmanc5402402004-01-15 18:34:11 +00001431<div class="doc_section">
Tanya Lattnerd5383652004-11-19 01:25:14 +00001432 <a name="passStatistics">Pass Statistics</a>
1433</div>
1434<!-- *********************************************************************** -->
1435
1436<div class="doc_text">
Tanya Lattner05f8d5f2004-11-19 01:26:37 +00001437<p>The <a
Reid Spencer05fe4b02006-03-14 05:39:39 +00001438href="http://llvm.org/doxygen/Statistic_8h-source.html"><tt>Statistic</tt></a>
John Criswell0b1010e2005-11-28 23:25:41 +00001439class is designed to be an easy way to expose various success
Tanya Lattnerd5383652004-11-19 01:25:14 +00001440metrics from passes. These statistics are printed at the end of a
1441run, when the -stats command line option is enabled on the command
Tanya Lattner05f8d5f2004-11-19 01:26:37 +00001442line. See the <a href="http://llvm.org/docs/ProgrammersManual.html#Statistic">Statistics section</a> in the Programmer's Manual for details.
Tanya Lattnerd5383652004-11-19 01:25:14 +00001443
1444</div>
1445
1446
1447<!-- *********************************************************************** -->
1448<div class="doc_section">
Misha Brukmanc5402402004-01-15 18:34:11 +00001449 <a name="passmanager">What PassManager does</a>
1450</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +00001451<!-- *********************************************************************** -->
1452
Misha Brukmanc5402402004-01-15 18:34:11 +00001453<div class="doc_text">
1454
1455<p>The <a
Reid Spencer05fe4b02006-03-14 05:39:39 +00001456href="http://llvm.org/doxygen/PassManager_8h-source.html"><tt>PassManager</tt></a>
Misha Brukmanc5402402004-01-15 18:34:11 +00001457<a
Reid Spencer05fe4b02006-03-14 05:39:39 +00001458href="http://llvm.org/doxygen/classllvm_1_1PassManager.html">class</a>
Misha Brukmanc5402402004-01-15 18:34:11 +00001459takes a list of passes, ensures their <a href="#interaction">prerequisites</a>
1460are set up correctly, and then schedules passes to run efficiently. All of the
1461LLVM tools that run passes use the <tt>PassManager</tt> for execution of these
1462passes.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +00001463
Misha Brukmanc5402402004-01-15 18:34:11 +00001464<p>The <tt>PassManager</tt> does two main things to try to reduce the execution
1465time of a series of passes:</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +00001466
1467<ol>
1468<li><b>Share analysis results</b> - The PassManager attempts to avoid
1469recomputing analysis results as much as possible. This means keeping track of
1470which analyses are available already, which analyses get invalidated, and which
1471analyses are needed to be run for a pass. An important part of work is that the
1472<tt>PassManager</tt> tracks the exact lifetime of all analysis results, allowing
1473it to <a href="#releaseMemory">free memory</a> allocated to holding analysis
Misha Brukmanc5402402004-01-15 18:34:11 +00001474results as soon as they are no longer needed.</li>
Chris Lattnerc6bb8242002-08-08 20:11:18 +00001475
1476<li><b>Pipeline the execution of passes on the program</b> - The
1477<tt>PassManager</tt> attempts to get better cache and memory usage behavior out
1478of a series of passes by pipelining the passes together. This means that, given
1479a series of consequtive <a href="#FunctionPass"><tt>FunctionPass</tt></a>'s, it
1480will execute all of the <a href="#FunctionPass"><tt>FunctionPass</tt></a>'s on
1481the first function, then all of the <a
Misha Brukmanc5402402004-01-15 18:34:11 +00001482href="#FunctionPass"><tt>FunctionPass</tt></a>es on the second function,
1483etc... until the entire program has been run through the passes.
Chris Lattnerc6bb8242002-08-08 20:11:18 +00001484
Misha Brukmanc5402402004-01-15 18:34:11 +00001485<p>This improves the cache behavior of the compiler, because it is only touching
Chris Lattnerc6bb8242002-08-08 20:11:18 +00001486the LLVM program representation for a single function at a time, instead of
1487traversing the entire program. It reduces the memory consumption of compiler,
1488because, for example, only one <a
Reid Spencer05fe4b02006-03-14 05:39:39 +00001489href="http://llvm.org/doxygen/classllvm_1_1DominatorSet.html"><tt>DominatorSet</tt></a>
John Criswell9795bb82007-12-10 20:26:29 +00001490needs to be calculated at a time. This also makes it possible to implement
1491some <a
Misha Brukmanc5402402004-01-15 18:34:11 +00001492href="#SMP">interesting enhancements</a> in the future.</p></li>
Chris Lattnerc6bb8242002-08-08 20:11:18 +00001493
Misha Brukmanc5402402004-01-15 18:34:11 +00001494</ol>
Chris Lattnerc6bb8242002-08-08 20:11:18 +00001495
Misha Brukmanc5402402004-01-15 18:34:11 +00001496<p>The effectiveness of the <tt>PassManager</tt> is influenced directly by how
1497much information it has about the behaviors of the passes it is scheduling. For
Chris Lattnerc6bb8242002-08-08 20:11:18 +00001498example, the "preserved" set is intentionally conservative in the face of an
1499unimplemented <a href="#getAnalysisUsage"><tt>getAnalysisUsage</tt></a> method.
1500Not implementing when it should be implemented will have the effect of not
Misha Brukmanc5402402004-01-15 18:34:11 +00001501allowing any analysis results to live across the execution of your pass.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +00001502
Misha Brukmanc5402402004-01-15 18:34:11 +00001503<p>The <tt>PassManager</tt> class exposes a <tt>--debug-pass</tt> command line
Chris Lattnerc6bb8242002-08-08 20:11:18 +00001504options that is useful for debugging pass execution, seeing how things work, and
1505diagnosing when you should be preserving more analyses than you currently are
1506(To get information about all of the variants of the <tt>--debug-pass</tt>
Duncan Sands7e7ae5a2010-02-18 14:08:13 +00001507option, just type '<tt>opt -help-hidden</tt>').</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +00001508
Misha Brukmanc5402402004-01-15 18:34:11 +00001509<p>By using the <tt>--debug-pass=Structure</tt> option, for example, we can see
1510how our <a href="#basiccode">Hello World</a> pass interacts with other passes.
1511Lets try it out with the <tt>gcse</tt> and <tt>licm</tt> passes:</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +00001512
Jim Laskey5fa8fff2006-08-04 18:10:12 +00001513<div class="doc_code"><pre>
Duncan Sands67f8a7b2010-07-08 08:27:18 +00001514$ opt -load ../../../Debug+Asserts/lib/Hello.so -gcse -licm --debug-pass=Structure &lt; hello.bc &gt; /dev/null
Chris Lattnerc6bb8242002-08-08 20:11:18 +00001515Module Pass Manager
1516 Function Pass Manager
1517 Dominator Set Construction
1518 Immediate Dominators Construction
1519 Global Common Subexpression Elimination
1520-- Immediate Dominators Construction
1521-- Global Common Subexpression Elimination
1522 Natural Loop Construction
1523 Loop Invariant Code Motion
1524-- Natural Loop Construction
1525-- Loop Invariant Code Motion
1526 Module Verifier
1527-- Dominator Set Construction
1528-- Module Verifier
Gabor Greif04367bf2007-07-06 22:07:22 +00001529 Bitcode Writer
1530--Bitcode Writer
Jim Laskey5fa8fff2006-08-04 18:10:12 +00001531</pre></div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +00001532
Misha Brukmanc5402402004-01-15 18:34:11 +00001533<p>This output shows us when passes are constructed and when the analysis
1534results are known to be dead (prefixed with '<tt>--</tt>'). Here we see that
1535GCSE uses dominator and immediate dominator information to do its job. The LICM
1536pass uses natural loop information, which uses dominator sets, but not immediate
Chris Lattnerc6bb8242002-08-08 20:11:18 +00001537dominators. Because immediate dominators are no longer useful after the GCSE
1538pass, it is immediately destroyed. The dominator sets are then reused to
Misha Brukmanc5402402004-01-15 18:34:11 +00001539compute natural loop information, which is then used by the LICM pass.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +00001540
Misha Brukmanc5402402004-01-15 18:34:11 +00001541<p>After the LICM pass, the module verifier runs (which is automatically added
1542by the '<tt>opt</tt>' tool), which uses the dominator set to check that the
Chris Lattnerc6bb8242002-08-08 20:11:18 +00001543resultant LLVM code is well formed. After it finishes, the dominator set
1544information is destroyed, after being computed once, and shared by three
Misha Brukmanc5402402004-01-15 18:34:11 +00001545passes.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +00001546
Misha Brukmanc5402402004-01-15 18:34:11 +00001547<p>Lets see how this changes when we run the <a href="#basiccode">Hello
1548World</a> pass in between the two passes:</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +00001549
Jim Laskey5fa8fff2006-08-04 18:10:12 +00001550<div class="doc_code"><pre>
Duncan Sands67f8a7b2010-07-08 08:27:18 +00001551$ opt -load ../../../Debug+Asserts/lib/Hello.so -gcse -hello -licm --debug-pass=Structure &lt; hello.bc &gt; /dev/null
Chris Lattnerc6bb8242002-08-08 20:11:18 +00001552Module Pass Manager
1553 Function Pass Manager
1554 Dominator Set Construction
1555 Immediate Dominators Construction
1556 Global Common Subexpression Elimination
1557<b>-- Dominator Set Construction</b>
1558-- Immediate Dominators Construction
1559-- Global Common Subexpression Elimination
1560<b> Hello World Pass
1561-- Hello World Pass
1562 Dominator Set Construction</b>
1563 Natural Loop Construction
1564 Loop Invariant Code Motion
1565-- Natural Loop Construction
1566-- Loop Invariant Code Motion
1567 Module Verifier
1568-- Dominator Set Construction
1569-- Module Verifier
Gabor Greif04367bf2007-07-06 22:07:22 +00001570 Bitcode Writer
1571--Bitcode Writer
Chris Lattnerc6bb8242002-08-08 20:11:18 +00001572Hello: __main
1573Hello: puts
1574Hello: main
Jim Laskey5fa8fff2006-08-04 18:10:12 +00001575</pre></div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +00001576
Misha Brukmanc5402402004-01-15 18:34:11 +00001577<p>Here we see that the <a href="#basiccode">Hello World</a> pass has killed the
Chris Lattnerc6bb8242002-08-08 20:11:18 +00001578Dominator Set pass, even though it doesn't modify the code at all! To fix this,
1579we need to add the following <a
Misha Brukmanc5402402004-01-15 18:34:11 +00001580href="#getAnalysisUsage"><tt>getAnalysisUsage</tt></a> method to our pass:</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +00001581
Jim Laskey5fa8fff2006-08-04 18:10:12 +00001582<div class="doc_code"><pre>
Chris Lattnerc6bb8242002-08-08 20:11:18 +00001583 <i>// We don't modify the program, so we preserve all analyses</i>
1584 <b>virtual void</b> getAnalysisUsage(AnalysisUsage &amp;AU) <b>const</b> {
1585 AU.setPreservesAll();
1586 }
Jim Laskey5fa8fff2006-08-04 18:10:12 +00001587</pre></div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +00001588
Misha Brukmanc5402402004-01-15 18:34:11 +00001589<p>Now when we run our pass, we get this output:</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +00001590
Jim Laskey5fa8fff2006-08-04 18:10:12 +00001591<div class="doc_code"><pre>
Duncan Sands67f8a7b2010-07-08 08:27:18 +00001592$ opt -load ../../../Debug+Asserts/lib/Hello.so -gcse -hello -licm --debug-pass=Structure &lt; hello.bc &gt; /dev/null
Chris Lattnerc6bb8242002-08-08 20:11:18 +00001593Pass Arguments: -gcse -hello -licm
1594Module Pass Manager
1595 Function Pass Manager
1596 Dominator Set Construction
1597 Immediate Dominators Construction
1598 Global Common Subexpression Elimination
1599-- Immediate Dominators Construction
1600-- Global Common Subexpression Elimination
1601 Hello World Pass
1602-- Hello World Pass
1603 Natural Loop Construction
1604 Loop Invariant Code Motion
1605-- Loop Invariant Code Motion
1606-- Natural Loop Construction
1607 Module Verifier
1608-- Dominator Set Construction
1609-- Module Verifier
Gabor Greif04367bf2007-07-06 22:07:22 +00001610 Bitcode Writer
1611--Bitcode Writer
Chris Lattnerc6bb8242002-08-08 20:11:18 +00001612Hello: __main
1613Hello: puts
1614Hello: main
Jim Laskey5fa8fff2006-08-04 18:10:12 +00001615</pre></div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +00001616
Misha Brukmanc5402402004-01-15 18:34:11 +00001617<p>Which shows that we don't accidentally invalidate dominator information
1618anymore, and therefore do not have to compute it twice.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +00001619
Misha Brukmanc5402402004-01-15 18:34:11 +00001620</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +00001621
1622<!-- _______________________________________________________________________ -->
Misha Brukmanc5402402004-01-15 18:34:11 +00001623<div class="doc_subsubsection">
1624 <a name="releaseMemory">The <tt>releaseMemory</tt> method</a>
1625</div>
1626
1627<div class="doc_text">
Chris Lattnerc6bb8242002-08-08 20:11:18 +00001628
Jim Laskey5fa8fff2006-08-04 18:10:12 +00001629<div class="doc_code"><pre>
Chris Lattnerc6bb8242002-08-08 20:11:18 +00001630 <b>virtual void</b> releaseMemory();
Jim Laskey5fa8fff2006-08-04 18:10:12 +00001631</pre></div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +00001632
Misha Brukmanc5402402004-01-15 18:34:11 +00001633<p>The <tt>PassManager</tt> automatically determines when to compute analysis
Chris Lattnerc6bb8242002-08-08 20:11:18 +00001634results, and how long to keep them around for. Because the lifetime of the pass
1635object itself is effectively the entire duration of the compilation process, we
1636need some way to free analysis results when they are no longer useful. The
Misha Brukmanc5402402004-01-15 18:34:11 +00001637<tt>releaseMemory</tt> virtual method is the way to do this.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +00001638
Misha Brukmanc5402402004-01-15 18:34:11 +00001639<p>If you are writing an analysis or any other pass that retains a significant
Chris Lattnerc6bb8242002-08-08 20:11:18 +00001640amount of state (for use by another pass which "requires" your pass and uses the
1641<a href="#getAnalysis">getAnalysis</a> method) you should implement
Dan Gohmand87c9e32009-06-15 18:22:49 +00001642<tt>releaseMemory</tt> to, well, release the memory allocated to maintain this
Chris Lattnerc6bb8242002-08-08 20:11:18 +00001643internal state. This method is called after the <tt>run*</tt> method for the
Misha Brukmanc5402402004-01-15 18:34:11 +00001644class, before the next call of <tt>run*</tt> in your pass.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +00001645
Misha Brukmanc5402402004-01-15 18:34:11 +00001646</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +00001647
1648<!-- *********************************************************************** -->
Misha Brukmanc5402402004-01-15 18:34:11 +00001649<div class="doc_section">
Jim Laskey5fa8fff2006-08-04 18:10:12 +00001650 <a name="registering">Registering dynamically loaded passes</a>
1651</div>
1652<!-- *********************************************************************** -->
1653
1654<div class="doc_text">
1655
1656<p><i>Size matters</i> when constructing production quality tools using llvm,
1657both for the purposes of distribution, and for regulating the resident code size
1658when running on the target system. Therefore, it becomes desirable to
1659selectively use some passes, while omitting others and maintain the flexibility
1660to change configurations later on. You want to be able to do all this, and,
1661provide feedback to the user. This is where pass registration comes into
1662play.</p>
1663
1664<p>The fundamental mechanisms for pass registration are the
1665<tt>MachinePassRegistry</tt> class and subclasses of
1666<tt>MachinePassRegistryNode</tt>.</p>
1667
1668<p>An instance of <tt>MachinePassRegistry</tt> is used to maintain a list of
1669<tt>MachinePassRegistryNode</tt> objects. This instance maintains the list and
1670communicates additions and deletions to the command line interface.</p>
1671
1672<p>An instance of <tt>MachinePassRegistryNode</tt> subclass is used to maintain
1673information provided about a particular pass. This information includes the
1674command line name, the command help string and the address of the function used
1675to create an instance of the pass. A global static constructor of one of these
1676instances <i>registers</i> with a corresponding <tt>MachinePassRegistry</tt>,
1677the static destructor <i>unregisters</i>. Thus a pass that is statically linked
1678in the tool will be registered at start up. A dynamically loaded pass will
1679register on load and unregister at unload.</p>
1680
1681</div>
1682
1683<!-- _______________________________________________________________________ -->
1684<div class="doc_subsection">
1685 <a name="registering_existing">Using existing registries</a>
1686</div>
1687
1688<div class="doc_text">
1689
1690<p>There are predefined registries to track instruction scheduling
1691(<tt>RegisterScheduler</tt>) and register allocation (<tt>RegisterRegAlloc</tt>)
1692machine passes. Here we will describe how to <i>register</i> a register
1693allocator machine pass.</p>
1694
1695<p>Implement your register allocator machine pass. In your register allocator
1696.cpp file add the following include;</p>
1697
1698<div class="doc_code"><pre>
Chris Lattner8f652eb2006-08-11 16:37:02 +00001699 #include "llvm/CodeGen/RegAllocRegistry.h"
Jim Laskey5fa8fff2006-08-04 18:10:12 +00001700</pre></div>
1701
1702<p>Also in your register allocator .cpp file, define a creator function in the
1703form; </p>
1704
1705<div class="doc_code"><pre>
1706 FunctionPass *createMyRegisterAllocator() {
1707 return new MyRegisterAllocator();
1708 }
1709</pre></div>
1710
1711<p>Note that the signature of this function should match the type of
1712<tt>RegisterRegAlloc::FunctionPassCtor</tt>. In the same file add the
1713"installing" declaration, in the form;</p>
1714
1715<div class="doc_code"><pre>
1716 static RegisterRegAlloc myRegAlloc("myregalloc",
1717 " my register allocator help string",
1718 createMyRegisterAllocator);
1719</pre></div>
1720
1721<p>Note the two spaces prior to the help string produces a tidy result on the
Duncan Sands7e7ae5a2010-02-18 14:08:13 +00001722-help query.</p>
Jim Laskey5fa8fff2006-08-04 18:10:12 +00001723
1724<div class="doc_code"><pre>
Duncan Sands7e7ae5a2010-02-18 14:08:13 +00001725$ llc -help
Jim Laskey5fa8fff2006-08-04 18:10:12 +00001726 ...
Duncan Sands18619b22010-02-18 14:37:52 +00001727 -regalloc - Register allocator to use (default=linearscan)
Jim Laskey5fa8fff2006-08-04 18:10:12 +00001728 =linearscan - linear scan register allocator
1729 =local - local register allocator
1730 =simple - simple register allocator
1731 =myregalloc - my register allocator help string
1732 ...
1733</pre></div>
1734
1735<p>And that's it. The user is now free to use <tt>-regalloc=myregalloc</tt> as
1736an option. Registering instruction schedulers is similar except use the
Chris Lattner8f652eb2006-08-11 16:37:02 +00001737<tt>RegisterScheduler</tt> class. Note that the
1738<tt>RegisterScheduler::FunctionPassCtor</tt> is significantly different from
Jim Laskey5fa8fff2006-08-04 18:10:12 +00001739<tt>RegisterRegAlloc::FunctionPassCtor</tt>.</p>
1740
1741<p>To force the load/linking of your register allocator into the llc/lli tools,
1742add your creator function's global declaration to "Passes.h" and add a "pseudo"
1743call line to <tt>llvm/Codegen/LinkAllCodegenComponents.h</tt>.</p>
1744
1745</div>
1746
1747
1748<!-- _______________________________________________________________________ -->
1749<div class="doc_subsection">
1750 <a name="registering_new">Creating new registries</a>
1751</div>
1752
1753<div class="doc_text">
1754
1755<p>The easiest way to get started is to clone one of the existing registries; we
1756recommend <tt>llvm/CodeGen/RegAllocRegistry.h</tt>. The key things to modify
1757are the class name and the <tt>FunctionPassCtor</tt> type.</p>
1758
1759<p>Then you need to declare the registry. Example: if your pass registry is
1760<tt>RegisterMyPasses</tt> then define;</p>
1761
1762<div class="doc_code"><pre>
1763MachinePassRegistry RegisterMyPasses::Registry;
1764</pre></div>
1765
1766<p>And finally, declare the command line option for your passes. Example:</p>
1767
1768<div class="doc_code"><pre>
1769 cl::opt&lt;RegisterMyPasses::FunctionPassCtor, false,
Dan Gohman364a39f2008-10-14 17:00:38 +00001770 RegisterPassParser&lt;RegisterMyPasses&gt; &gt;
Jim Laskey5fa8fff2006-08-04 18:10:12 +00001771 MyPassOpt("mypass",
1772 cl::init(&amp;createDefaultMyPass),
1773 cl::desc("my pass option help"));
1774</pre></div>
1775
1776<p>Here the command option is "mypass", with createDefaultMyPass as the default
1777creator.</p>
1778
1779</div>
1780
1781<!-- *********************************************************************** -->
1782<div class="doc_section">
Misha Brukmanc5402402004-01-15 18:34:11 +00001783 <a name="debughints">Using GDB with dynamically loaded passes</a>
1784</div>
Chris Lattner480e2ef2002-09-06 02:02:58 +00001785<!-- *********************************************************************** -->
1786
Misha Brukmanc5402402004-01-15 18:34:11 +00001787<div class="doc_text">
1788
1789<p>Unfortunately, using GDB with dynamically loaded passes is not as easy as it
Chris Lattner480e2ef2002-09-06 02:02:58 +00001790should be. First of all, you can't set a breakpoint in a shared object that has
1791not been loaded yet, and second of all there are problems with inlined functions
1792in shared objects. Here are some suggestions to debugging your pass with
Misha Brukmanc5402402004-01-15 18:34:11 +00001793GDB.</p>
Chris Lattner480e2ef2002-09-06 02:02:58 +00001794
Misha Brukmanc5402402004-01-15 18:34:11 +00001795<p>For sake of discussion, I'm going to assume that you are debugging a
Chris Lattner480e2ef2002-09-06 02:02:58 +00001796transformation invoked by <tt>opt</tt>, although nothing described here depends
Misha Brukmanc5402402004-01-15 18:34:11 +00001797on that.</p>
1798
1799</div>
Chris Lattner480e2ef2002-09-06 02:02:58 +00001800
1801<!-- _______________________________________________________________________ -->
Misha Brukmanc5402402004-01-15 18:34:11 +00001802<div class="doc_subsubsection">
1803 <a name="breakpoint">Setting a breakpoint in your pass</a>
1804</div>
Chris Lattner480e2ef2002-09-06 02:02:58 +00001805
Misha Brukmanc5402402004-01-15 18:34:11 +00001806<div class="doc_text">
1807
1808<p>First thing you do is start <tt>gdb</tt> on the <tt>opt</tt> process:</p>
Chris Lattner480e2ef2002-09-06 02:02:58 +00001809
Jim Laskey5fa8fff2006-08-04 18:10:12 +00001810<div class="doc_code"><pre>
Chris Lattner480e2ef2002-09-06 02:02:58 +00001811$ <b>gdb opt</b>
1812GNU gdb 5.0
1813Copyright 2000 Free Software Foundation, Inc.
1814GDB is free software, covered by the GNU General Public License, and you are
1815welcome to change it and/or distribute copies of it under certain conditions.
1816Type "show copying" to see the conditions.
1817There is absolutely no warranty for GDB. Type "show warranty" for details.
1818This GDB was configured as "sparc-sun-solaris2.6"...
1819(gdb)
Jim Laskey5fa8fff2006-08-04 18:10:12 +00001820</pre></div>
Chris Lattner480e2ef2002-09-06 02:02:58 +00001821
Misha Brukmanc5402402004-01-15 18:34:11 +00001822<p>Note that <tt>opt</tt> has a lot of debugging information in it, so it takes
Chris Lattner480e2ef2002-09-06 02:02:58 +00001823time to load. Be patient. Since we cannot set a breakpoint in our pass yet
1824(the shared object isn't loaded until runtime), we must execute the process, and
1825have it stop before it invokes our pass, but after it has loaded the shared
1826object. The most foolproof way of doing this is to set a breakpoint in
1827<tt>PassManager::run</tt> and then run the process with the arguments you
Misha Brukmanc5402402004-01-15 18:34:11 +00001828want:</p>
Chris Lattner480e2ef2002-09-06 02:02:58 +00001829
Jim Laskey5fa8fff2006-08-04 18:10:12 +00001830<div class="doc_code"><pre>
Reid Spencer22a9e5b2006-09-28 16:53:47 +00001831(gdb) <b>break llvm::PassManager::run</b>
Chris Lattner480e2ef2002-09-06 02:02:58 +00001832Breakpoint 1 at 0x2413bc: file Pass.cpp, line 70.
Duncan Sands67f8a7b2010-07-08 08:27:18 +00001833(gdb) <b>run test.bc -load $(LLVMTOP)/llvm/Debug+Asserts/lib/[libname].so -[passoption]</b>
1834Starting program: opt test.bc -load $(LLVMTOP)/llvm/Debug+Asserts/lib/[libname].so -[passoption]
Chris Lattner480e2ef2002-09-06 02:02:58 +00001835Breakpoint 1, PassManager::run (this=0xffbef174, M=@0x70b298) at Pass.cpp:70
183670 bool PassManager::run(Module &amp;M) { return PM-&gt;run(M); }
1837(gdb)
Jim Laskey5fa8fff2006-08-04 18:10:12 +00001838</pre></div>
Chris Lattner480e2ef2002-09-06 02:02:58 +00001839
Misha Brukmanc5402402004-01-15 18:34:11 +00001840<p>Once the <tt>opt</tt> stops in the <tt>PassManager::run</tt> method you are
1841now free to set breakpoints in your pass so that you can trace through execution
1842or do other standard debugging stuff.</p>
Chris Lattner480e2ef2002-09-06 02:02:58 +00001843
Misha Brukmanc5402402004-01-15 18:34:11 +00001844</div>
Chris Lattner480e2ef2002-09-06 02:02:58 +00001845
1846<!-- _______________________________________________________________________ -->
Misha Brukmanc5402402004-01-15 18:34:11 +00001847<div class="doc_subsubsection">
1848 <a name="debugmisc">Miscellaneous Problems</a>
1849</div>
Chris Lattner480e2ef2002-09-06 02:02:58 +00001850
Misha Brukmanc5402402004-01-15 18:34:11 +00001851<div class="doc_text">
1852
1853<p>Once you have the basics down, there are a couple of problems that GDB has,
1854some with solutions, some without.</p>
Chris Lattner480e2ef2002-09-06 02:02:58 +00001855
1856<ul>
1857<li>Inline functions have bogus stack information. In general, GDB does a
1858pretty good job getting stack traces and stepping through inline functions.
1859When a pass is dynamically loaded however, it somehow completely loses this
1860capability. The only solution I know of is to de-inline a function (move it
Misha Brukmanc5402402004-01-15 18:34:11 +00001861from the body of a class to a .cpp file).</li>
Chris Lattner480e2ef2002-09-06 02:02:58 +00001862
1863<li>Restarting the program breaks breakpoints. After following the information
1864above, you have succeeded in getting some breakpoints planted in your pass. Nex
1865thing you know, you restart the program (i.e., you type '<tt>run</tt>' again),
1866and you start getting errors about breakpoints being unsettable. The only way I
1867have found to "fix" this problem is to <tt>delete</tt> the breakpoints that are
1868already set in your pass, run the program, and re-set the breakpoints once
Misha Brukmanc5402402004-01-15 18:34:11 +00001869execution stops in <tt>PassManager::run</tt>.</li>
Chris Lattner480e2ef2002-09-06 02:02:58 +00001870
1871</ul>
1872
Misha Brukmanc5402402004-01-15 18:34:11 +00001873<p>Hopefully these tips will help with common case debugging situations. If
1874you'd like to contribute some tips of your own, just contact <a
1875href="mailto:sabre@nondot.org">Chris</a>.</p>
Chris Lattner480e2ef2002-09-06 02:02:58 +00001876
Misha Brukmanc5402402004-01-15 18:34:11 +00001877</div>
Chris Lattner480e2ef2002-09-06 02:02:58 +00001878
1879<!-- *********************************************************************** -->
Misha Brukmanc5402402004-01-15 18:34:11 +00001880<div class="doc_section">
1881 <a name="future">Future extensions planned</a>
1882</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +00001883<!-- *********************************************************************** -->
1884
Misha Brukmanc5402402004-01-15 18:34:11 +00001885<div class="doc_text">
1886
1887<p>Although the LLVM Pass Infrastructure is very capable as it stands, and does
Chris Lattnerc6bb8242002-08-08 20:11:18 +00001888some nifty stuff, there are things we'd like to add in the future. Here is
Misha Brukmanc5402402004-01-15 18:34:11 +00001889where we are going:</p>
1890
1891</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +00001892
1893<!-- _______________________________________________________________________ -->
Chris Lattner89256272004-03-17 21:09:55 +00001894<div class="doc_subsubsection">
Misha Brukmanc5402402004-01-15 18:34:11 +00001895 <a name="SMP">Multithreaded LLVM</a>
1896</div>
Chris Lattnerc6bb8242002-08-08 20:11:18 +00001897
Misha Brukmanc5402402004-01-15 18:34:11 +00001898<div class="doc_text">
1899
1900<p>Multiple CPU machines are becoming more common and compilation can never be
Chris Lattnerc6bb8242002-08-08 20:11:18 +00001901fast enough: obviously we should allow for a multithreaded compiler. Because of
1902the semantics defined for passes above (specifically they cannot maintain state
1903across invocations of their <tt>run*</tt> methods), a nice clean way to
1904implement a multithreaded compiler would be for the <tt>PassManager</tt> class
Misha Brukmanbc0e9982003-07-14 17:20:40 +00001905to create multiple instances of each pass object, and allow the separate
Misha Brukmanc5402402004-01-15 18:34:11 +00001906instances to be hacking on different parts of the program at the same time.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +00001907
Misha Brukmanc5402402004-01-15 18:34:11 +00001908<p>This implementation would prevent each of the passes from having to implement
Chris Lattnerc6bb8242002-08-08 20:11:18 +00001909multithreaded constructs, requiring only the LLVM core to have locking in a few
1910places (for global resources). Although this is a simple extension, we simply
1911haven't had time (or multiprocessor machines, thus a reason) to implement this.
Misha Brukmanc5402402004-01-15 18:34:11 +00001912Despite that, we have kept the LLVM passes SMP ready, and you should too.</p>
Chris Lattnerc6bb8242002-08-08 20:11:18 +00001913
Chris Lattnerb5c87f62007-05-18 05:36:14 +00001914</div>
1915
Chris Lattnerc6bb8242002-08-08 20:11:18 +00001916<!-- *********************************************************************** -->
Misha Brukmanc5402402004-01-15 18:34:11 +00001917<hr>
1918<address>
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Misha Brukmanc5402402004-01-15 18:34:11 +00001924 <a href="mailto:sabre@nondot.org">Chris Lattner</a><br>
Reid Spencer05fe4b02006-03-14 05:39:39 +00001925 <a href="http://llvm.org">The LLVM Compiler Infrastructure</a><br>
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