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<title>Writing an LLVM Pass</title>
- <link rel="stylesheet" href="llvm.css" type="text/css">
+ <link rel="stylesheet" href="_static/llvm.css" type="text/css">
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OPTIONS:
Optimizations available:
...
- -funcresolve - Resolve Functions
- -gcse - Global Common Subexpression Elimination
- -globaldce - Dead Global Elimination
- <b>-hello - Hello World Pass</b>
- -indvars - Canonicalize Induction Variables
- -inline - Function Integration/Inlining
- -instcombine - Combine redundant instructions
+ -globalopt - Global Variable Optimizer
+ -globalsmodref-aa - Simple mod/ref analysis for globals
+ -gvn - Global Value Numbering
+ <b>-hello - Hello World Pass</b>
+ -indvars - Induction Variable Simplification
+ -inline - Function Integration/Inlining
+ -insert-edge-profiling - Insert instrumentation for edge profiling
...
</pre></div>
-<p>The pass name get added as the information string for your pass, giving some
+<p>The pass name gets added as the information string for your pass, giving some
documentation to users of <tt>opt</tt>. Now that you have a working pass, you
would go ahead and make it do the cool transformations you want. Once you get
it all working and tested, it may become useful to find out how fast your pass
<div>
<div class="doc_code"><pre>
- <b>virtual bool</b> runOnModule(Module &M) = 0;
+<b>virtual bool</b> runOnModule(Module &M) = 0;
</pre></div>
<p>The <tt>runOnModule</tt> method performs the interesting work of the pass.
<div>
<div class="doc_code"><pre>
- <b>virtual bool</b> doInitialization(CallGraph &CG);
+<b>virtual bool</b> doInitialization(CallGraph &CG);
</pre></div>
<p>The <tt>doIninitialize</tt> method is allowed to do most of the things that
<div>
<div class="doc_code"><pre>
- <b>virtual bool</b> runOnSCC(CallGraphSCC &SCC) = 0;
+<b>virtual bool</b> runOnSCC(CallGraphSCC &SCC) = 0;
</pre></div>
<p>The <tt>runOnSCC</tt> method performs the interesting work of the pass, and
<div>
<div class="doc_code"><pre>
- <b>virtual bool</b> doFinalization(CallGraph &CG);
+<b>virtual bool</b> doFinalization(CallGraph &CG);
</pre></div>
<p>The <tt>doFinalization</tt> method is an infrequently used method that is
<div>
<div class="doc_code"><pre>
- <b>virtual bool</b> doInitialization(Module &M);
+<b>virtual bool</b> doInitialization(Module &M);
</pre></div>
<p>The <tt>doIninitialize</tt> method is allowed to do most of the things that
<div>
<div class="doc_code"><pre>
- <b>virtual bool</b> runOnFunction(Function &F) = 0;
+<b>virtual bool</b> runOnFunction(Function &F) = 0;
</pre></div><p>
<p>The <tt>runOnFunction</tt> method must be implemented by your subclass to do
<div>
<div class="doc_code"><pre>
- <b>virtual bool</b> doFinalization(Module &M);
+<b>virtual bool</b> doFinalization(Module &M);
</pre></div>
<p>The <tt>doFinalization</tt> method is an infrequently used method that is
<div>
<div class="doc_code"><pre>
- <b>virtual bool</b> doInitialization(Loop *, LPPassManager &LPM);
+<b>virtual bool</b> doInitialization(Loop *, LPPassManager &LPM);
</pre></div>
<p>The <tt>doInitialization</tt> method is designed to do simple initialization
<div>
<div class="doc_code"><pre>
- <b>virtual bool</b> runOnLoop(Loop *, LPPassManager &LPM) = 0;
+<b>virtual bool</b> runOnLoop(Loop *, LPPassManager &LPM) = 0;
</pre></div><p>
<p>The <tt>runOnLoop</tt> method must be implemented by your subclass to do
<div>
<div class="doc_code"><pre>
- <b>virtual bool</b> doFinalization();
+<b>virtual bool</b> doFinalization();
</pre></div>
<p>The <tt>doFinalization</tt> method is an infrequently used method that is
<div>
<div class="doc_code"><pre>
- <b>virtual bool</b> doInitialization(Region *, RGPassManager &RGM);
+<b>virtual bool</b> doInitialization(Region *, RGPassManager &RGM);
</pre></div>
<p>The <tt>doInitialization</tt> method is designed to do simple initialization
<div>
<div class="doc_code"><pre>
- <b>virtual bool</b> runOnRegion(Region *, RGPassManager &RGM) = 0;
+<b>virtual bool</b> runOnRegion(Region *, RGPassManager &RGM) = 0;
</pre></div><p>
<p>The <tt>runOnRegion</tt> method must be implemented by your subclass to do
<div>
<div class="doc_code"><pre>
- <b>virtual bool</b> doFinalization();
+<b>virtual bool</b> doFinalization();
</pre></div>
<p>The <tt>doFinalization</tt> method is an infrequently used method that is
<div>
<div class="doc_code"><pre>
- <b>virtual bool</b> doInitialization(Function &F);
+<b>virtual bool</b> doInitialization(Function &F);
</pre></div>
<p>The <tt>doIninitialize</tt> method is allowed to do most of the things that
<div>
<div class="doc_code"><pre>
- <b>virtual bool</b> runOnBasicBlock(BasicBlock &BB) = 0;
+<b>virtual bool</b> runOnBasicBlock(BasicBlock &BB) = 0;
</pre></div>
<p>Override this function to do the work of the <tt>BasicBlockPass</tt>. This
<div>
<div class="doc_code"><pre>
- <b>virtual bool</b> doFinalization(Function &F);
+<b>virtual bool</b> doFinalization(Function &F);
</pre></div>
<p>The <tt>doFinalization</tt> method is an infrequently used method that is
<div>
<div class="doc_code"><pre>
- <b>virtual bool</b> runOnMachineFunction(MachineFunction &MF) = 0;
+<b>virtual bool</b> runOnMachineFunction(MachineFunction &MF) = 0;
</pre></div>
<p><tt>runOnMachineFunction</tt> can be considered the main entry point of a
<div>
<div class="doc_code"><pre>
- <b>virtual void</b> print(std::ostream &O, <b>const</b> Module *M) <b>const</b>;
+<b>virtual void</b> print(std::ostream &O, <b>const</b> Module *M) <b>const</b>;
</pre></div>
<p>The <tt>print</tt> method must be implemented by "analyses" in order to print
<div>
<div class="doc_code"><pre>
- <b>virtual void</b> getAnalysisUsage(AnalysisUsage &Info) <b>const</b>;
+<b>virtual void</b> getAnalysisUsage(AnalysisUsage &Info) <b>const</b>;
</pre></div>
<p>By implementing the <tt>getAnalysisUsage</tt> method, the required and
<div>
<div class="doc_code"><pre>
- <i>// This example modifies the program, but does not modify the CFG</i>
-
<b>void</b> <a href="http://llvm.org/doxygen/structLICM.html">LICM</a>::getAnalysisUsage(AnalysisUsage &AU) <b>const</b> {
- AU.setPreservesCFG();
-
AU.addRequired<<a href="http://llvm.org/doxygen/classllvm_1_1LoopInfo.html">LoopInfo</a>>();
- }
+<i>// This example modifies the program, but does not modify the CFG</i>
+<b>void</b> <a href="http://llvm.org/doxygen/structLICM.html">LICM</a>::getAnalysisUsage(AnalysisUsage &AU) <b>const</b> {
+ AU.setPreservesCFG();
+ AU.addRequired<<a href="http://llvm.org/doxygen/classllvm_1_1LoopInfo.html">LoopInfo</a>>();
+}
</pre></div>
</div>
want, and returns a reference to that pass. For example:</p>
<div class="doc_code"><pre>
- bool LICM::runOnFunction(Function &F) {
- LoopInfo &LI = getAnalysis<LoopInfo>();
- ...
- }
+bool LICM::runOnFunction(Function &F) {
+ LoopInfo &LI = getAnalysis<LoopInfo>();
+ ...
+}
</pre></div>
<p>This method call returns a reference to the pass desired. You may get a
For example:</p>
<div class="doc_code"><pre>
- bool ModuleLevelPass::runOnModule(Module &M) {
- ...
- DominatorTree &DT = getAnalysis<DominatorTree>(Func);
- ...
- }
+bool ModuleLevelPass::runOnModule(Module &M) {
+ ...
+ DominatorTree &DT = getAnalysis<DominatorTree>(Func);
+ ...
+}
</pre></div>
<p>In above example, runOnFunction for DominatorTree is called by pass manager
if it is active. For example:</p>
<div class="doc_code"><pre>
- ...
- if (DominatorSet *DS = getAnalysisIfAvailable<DominatorSet>()) {
- <i>// A DominatorSet is active. This code will update it.</i>
- }
- ...
+...
+if (DominatorSet *DS = getAnalysisIfAvailable<DominatorSet>()) {
+ <i>// A DominatorSet is active. This code will update it.</i>
+}
+...
</pre></div>
</div>
for the Analysis Group Interface itself, because it is "abstract":</p>
<div class="doc_code"><pre>
-
<b>static</b> RegisterAnalysisGroup<<a href="http://llvm.org/doxygen/classllvm_1_1AliasAnalysis.html">AliasAnalysis</a>> A("<i>Alias Analysis</i>");
+<b>static</b> RegisterAnalysisGroup<<a href="http://llvm.org/doxygen/classllvm_1_1AliasAnalysis.html">AliasAnalysis</a>> A("<i>Alias Analysis</i>");
</pre></div>
<p>Once the analysis is registered, passes can declare that they are valid
//<i> Declare that we implement the AliasAnalysis interface</i>
INITIALIZE_AG_PASS(FancyAA, <a href="http://llvm.org/doxygen/classllvm_1_1AliasAnalysis.html">AliasAnalysis</a>, "<i>somefancyaa</i>",
"<i>A more complex alias analysis implementation</i>",
- false, // <i>Is CFG Only?</i>
- true, // <i>Is Analysis?</i>
- false, // <i>Is default Analysis Group implementation?</i>
- );
+ false, // <i>Is CFG Only?</i>
+ true, // <i>Is Analysis?</i>
+ false); // <i>Is default Analysis Group implementation?</i>
}
</pre></div>
"<i>Basic Alias Analysis (default AA impl)</i>",
false, // <i>Is CFG Only?</i>
true, // <i>Is Analysis?</i>
- true, // <i>Is default Analysis Group implementation?</i>
- );
+ true); // <i>Is default Analysis Group implementation?</i>
}
</pre></div>
href="#getAnalysisUsage"><tt>getAnalysisUsage</tt></a> method to our pass:</p>
<div class="doc_code"><pre>
- <i>// We don't modify the program, so we preserve all analyses</i>
- <b>virtual void</b> getAnalysisUsage(AnalysisUsage &AU) <b>const</b> {
- AU.setPreservesAll();
- }
+<i>// We don't modify the program, so we preserve all analyses</i>
+<b>virtual void</b> getAnalysisUsage(AnalysisUsage &AU) <b>const</b> {
+ AU.setPreservesAll();
+}
</pre></div>
<p>Now when we run our pass, we get this output:</p>
allocator machine pass.</p>
<p>Implement your register allocator machine pass. In your register allocator
-.cpp file add the following include;</p>
+<tt>.cpp</tt> file add the following include;</p>
<div class="doc_code"><pre>
- #include "llvm/CodeGen/RegAllocRegistry.h"
+#include "llvm/CodeGen/RegAllocRegistry.h"
</pre></div>
<p>Also in your register allocator .cpp file, define a creator function in the
form; </p>
<div class="doc_code"><pre>
- FunctionPass *createMyRegisterAllocator() {
- return new MyRegisterAllocator();
- }
+FunctionPass *createMyRegisterAllocator() {
+ return new MyRegisterAllocator();
+}
</pre></div>
<p>Note that the signature of this function should match the type of
"installing" declaration, in the form;</p>
<div class="doc_code"><pre>
- static RegisterRegAlloc myRegAlloc("myregalloc",
- " my register allocator help string",
- createMyRegisterAllocator);
+static RegisterRegAlloc myRegAlloc("myregalloc",
+ "my register allocator help string",
+ createMyRegisterAllocator);
</pre></div>
<p>Note the two spaces prior to the help string produces a tidy result on the
<p>And finally, declare the command line option for your passes. Example:</p>
<div class="doc_code"><pre>
- cl::opt<RegisterMyPasses::FunctionPassCtor, false,
- RegisterPassParser<RegisterMyPasses> >
- MyPassOpt("mypass",
- cl::init(&createDefaultMyPass),
- cl::desc("my pass option help"));
+cl::opt<RegisterMyPasses::FunctionPassCtor, false,
+ RegisterPassParser<RegisterMyPasses> >
+MyPassOpt("mypass",
+ cl::init(&createDefaultMyPass),
+ cl::desc("my pass option help"));
</pre></div>
<p>Here the command option is "mypass", with createDefaultMyPass as the default
projects / oota-llvm.git / blobdiff