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LoopExtractor.cpp

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00001 //===- LoopExtractor.cpp - Extract each loop into a new function ----------===//
00002 // 
00003 //                     The LLVM Compiler Infrastructure
00004 //
00005 // This file was developed by the LLVM research group and is distributed under
00006 // the University of Illinois Open Source License. See LICENSE.TXT for details.
00007 // 
00008 //===----------------------------------------------------------------------===//
00009 //
00010 // A pass wrapper around the ExtractLoop() scalar transformation to extract each
00011 // top-level loop into its own new function. If the loop is the ONLY loop in a
00012 // given function, it is not touched. This is a pass most useful for debugging
00013 // via bugpoint.
00014 //
00015 //===----------------------------------------------------------------------===//
00016 
00017 #include "llvm/Transforms/IPO.h"
00018 #include "llvm/Instructions.h"
00019 #include "llvm/Module.h"
00020 #include "llvm/Pass.h"
00021 #include "llvm/Analysis/Dominators.h"
00022 #include "llvm/Analysis/LoopInfo.h"
00023 #include "llvm/Transforms/Scalar.h"
00024 #include "llvm/Transforms/Utils/FunctionUtils.h"
00025 #include "llvm/ADT/Statistic.h"
00026 using namespace llvm;
00027 
00028 namespace {
00029   Statistic<> NumExtracted("loop-extract", "Number of loops extracted");
00030   
00031   // FIXME: This is not a function pass, but the PassManager doesn't allow
00032   // Module passes to require FunctionPasses, so we can't get loop info if we're
00033   // not a function pass.
00034   struct LoopExtractor : public FunctionPass {
00035     unsigned NumLoops;
00036 
00037     LoopExtractor(unsigned numLoops = ~0) : NumLoops(numLoops) {}
00038 
00039     virtual bool runOnFunction(Function &F);
00040     
00041     virtual void getAnalysisUsage(AnalysisUsage &AU) const {
00042       AU.addRequiredID(BreakCriticalEdgesID);
00043       AU.addRequiredID(LoopSimplifyID);
00044       AU.addRequired<DominatorSet>();
00045       AU.addRequired<LoopInfo>();
00046     }
00047   };
00048 
00049   RegisterOpt<LoopExtractor> 
00050   X("loop-extract", "Extract loops into new functions");
00051 
00052   /// SingleLoopExtractor - For bugpoint.
00053   struct SingleLoopExtractor : public LoopExtractor {
00054     SingleLoopExtractor() : LoopExtractor(1) {}
00055   };
00056 
00057   RegisterOpt<SingleLoopExtractor> 
00058   Y("loop-extract-single", "Extract at most one loop into a new function");
00059 } // End anonymous namespace 
00060 
00061 bool LoopExtractor::runOnFunction(Function &F) {
00062   LoopInfo &LI = getAnalysis<LoopInfo>();
00063 
00064   // If this function has no loops, there is nothing to do.
00065   if (LI.begin() == LI.end())
00066     return false;
00067 
00068   DominatorSet &DS = getAnalysis<DominatorSet>();
00069 
00070   // If there is more than one top-level loop in this function, extract all of
00071   // the loops.
00072   bool Changed = false;
00073   if (LI.end()-LI.begin() > 1) {
00074     for (LoopInfo::iterator i = LI.begin(), e = LI.end(); i != e; ++i) {
00075       if (NumLoops == 0) return Changed;
00076       --NumLoops;
00077       Changed |= ExtractLoop(DS, *i) != 0;
00078       ++NumExtracted;
00079     }
00080   } else {
00081     // Otherwise there is exactly one top-level loop.  If this function is more
00082     // than a minimal wrapper around the loop, extract the loop.
00083     Loop *TLL = *LI.begin();
00084     bool ShouldExtractLoop = false;
00085     
00086     // Extract the loop if the entry block doesn't branch to the loop header.
00087     TerminatorInst *EntryTI = F.getEntryBlock().getTerminator();
00088     if (!isa<BranchInst>(EntryTI) ||
00089         !cast<BranchInst>(EntryTI)->isUnconditional() || 
00090         EntryTI->getSuccessor(0) != TLL->getHeader())
00091       ShouldExtractLoop = true;
00092     else {
00093       // Check to see if any exits from the loop are more than just return
00094       // blocks.
00095       std::vector<BasicBlock*> ExitBlocks;
00096       TLL->getExitBlocks(ExitBlocks);
00097       for (unsigned i = 0, e = ExitBlocks.size(); i != e; ++i)
00098         if (!isa<ReturnInst>(ExitBlocks[i]->getTerminator())) {
00099           ShouldExtractLoop = true;
00100           break;
00101         }
00102     }
00103     
00104     if (ShouldExtractLoop) {
00105       if (NumLoops == 0) return Changed;
00106       --NumLoops;
00107       Changed |= ExtractLoop(DS, TLL) != 0;
00108       ++NumExtracted;
00109     } else {
00110       // Okay, this function is a minimal container around the specified loop.
00111       // If we extract the loop, we will continue to just keep extracting it
00112       // infinitely... so don't extract it.  However, if the loop contains any
00113       // subloops, extract them.
00114       for (Loop::iterator i = TLL->begin(), e = TLL->end(); i != e; ++i) {
00115         if (NumLoops == 0) return Changed;
00116         --NumLoops;
00117         Changed |= ExtractLoop(DS, *i) != 0;
00118         ++NumExtracted;
00119       }
00120     }
00121   }
00122 
00123   return Changed;
00124 }
00125 
00126 // createSingleLoopExtractorPass - This pass extracts one natural loop from the
00127 // program into a function if it can.  This is used by bugpoint.
00128 //
00129 ModulePass *llvm::createSingleLoopExtractorPass() {
00130   return new SingleLoopExtractor();
00131 }
00132 
00133 
00134 namespace {
00135   /// BlockExtractorPass - This pass is used by bugpoint to extract all blocks
00136   /// from the module into their own functions except for those specified by the
00137   /// BlocksToNotExtract list.
00138   class BlockExtractorPass : public ModulePass {
00139     std::vector<BasicBlock*> BlocksToNotExtract;
00140   public:
00141     BlockExtractorPass(std::vector<BasicBlock*> &B) : BlocksToNotExtract(B) {}
00142     BlockExtractorPass() {}
00143 
00144     bool runOnModule(Module &M);
00145   };
00146   RegisterOpt<BlockExtractorPass>
00147   XX("extract-blocks", "Extract Basic Blocks From Module (for bugpoint use)");
00148 }
00149 
00150 // createBlockExtractorPass - This pass extracts all blocks (except those
00151 // specified in the argument list) from the functions in the module.
00152 //
00153 ModulePass *llvm::createBlockExtractorPass(std::vector<BasicBlock*> &BTNE) {
00154   return new BlockExtractorPass(BTNE);
00155 }
00156 
00157 bool BlockExtractorPass::runOnModule(Module &M) {
00158   std::set<BasicBlock*> TranslatedBlocksToNotExtract;
00159   for (unsigned i = 0, e = BlocksToNotExtract.size(); i != e; ++i) {
00160     BasicBlock *BB = BlocksToNotExtract[i];
00161     Function *F = BB->getParent();
00162 
00163     // Map the corresponding function in this module.
00164     Function *MF = M.getFunction(F->getName(), F->getFunctionType());
00165 
00166     // Figure out which index the basic block is in its function.
00167     Function::iterator BBI = MF->begin();
00168     std::advance(BBI, std::distance(F->begin(), Function::iterator(BB)));
00169     TranslatedBlocksToNotExtract.insert(BBI);
00170   }
00171 
00172   // Now that we know which blocks to not extract, figure out which ones we WANT
00173   // to extract.
00174   std::vector<BasicBlock*> BlocksToExtract;
00175   for (Module::iterator F = M.begin(), E = M.end(); F != E; ++F)
00176     for (Function::iterator BB = F->begin(), E = F->end(); BB != E; ++BB)
00177       if (!TranslatedBlocksToNotExtract.count(BB))
00178         BlocksToExtract.push_back(BB);
00179 
00180   for (unsigned i = 0, e = BlocksToExtract.size(); i != e; ++i)
00181     ExtractBasicBlock(BlocksToExtract[i]);
00182   
00183   return !BlocksToExtract.empty();
00184 }