diff --git a/lib/Transforms/Scalar/LoopUnroll.cpp b/lib/Transforms/Scalar/LoopUnroll.cpp new file mode 100644 index 00000000000..d337a431321 --- /dev/null +++ b/lib/Transforms/Scalar/LoopUnroll.cpp @@ -0,0 +1,247 @@ +//===-- LoopUnroll.cpp - Loop unroller pass -------------------------------===// +// +// The LLVM Compiler Infrastructure +// +// This file was developed by the LLVM research group and is distributed under +// the University of Illinois Open Source License. See LICENSE.TXT for details. +// +//===----------------------------------------------------------------------===// +// +// This pass implements a simple loop unroller. It works best when loops have +// been canonicalized by the -indvars pass, allowing it to determine the trip +// counts of loops easily. +// +// This pass is currently extremely limited. It only currently only unrolls +// single basic block loops that execute a constant number of times. +// +//===----------------------------------------------------------------------===// + +#define DEBUG_TYPE "loop-unroll" +#include "llvm/Transforms/Scalar.h" +#include "llvm/Constants.h" +#include "llvm/Function.h" +#include "llvm/Instructions.h" +#include "llvm/Analysis/LoopInfo.h" +#include "llvm/Transforms/Utils/Cloning.h" +#include "llvm/Transforms/Utils/Local.h" +#include "Support/CommandLine.h" +#include "Support/Debug.h" +#include "Support/Statistic.h" +#include +using namespace llvm; + +namespace { + Statistic<> NumUnrolled("loop-unroll", "Number of loops completely unrolled"); + + cl::opt + UnrollThreshold("unroll-threshold", cl::init(100), cl::Hidden, + cl::desc("The cut-off point for loop unrolling")); + + class LoopUnroll : public FunctionPass { + LoopInfo *LI; // The current loop information + public: + virtual bool runOnFunction(Function &F); + bool visitLoop(Loop *L); + + /// This transformation requires natural loop information & requires that + /// loop preheaders be inserted into the CFG... + /// + virtual void getAnalysisUsage(AnalysisUsage &AU) const { + AU.setPreservesCFG(); + AU.addRequiredID(LoopSimplifyID); + AU.addRequired(); + } + }; + RegisterOpt X("loop-unroll", "Unroll loops"); +} + +FunctionPass *llvm::createLoopUnrollPass() { return new LoopUnroll(); } + +bool LoopUnroll::runOnFunction(Function &F) { + bool Changed = false; + LI = &getAnalysis(); + + for (LoopInfo::iterator I = LI->begin(), E = LI->end(); I != E; ++I) + Changed |= visitLoop(*I); + + return Changed; +} + +/// ApproximateLoopSize - Approximate the size of the loop after it has been +/// unrolled. +static unsigned ApproximateLoopSize(const Loop *L) { + unsigned Size = 0; + for (unsigned i = 0, e = L->getBlocks().size(); i != e; ++i) { + BasicBlock *BB = L->getBlocks()[i]; + Instruction *Term = BB->getTerminator(); + for (BasicBlock::iterator I = BB->begin(), E = BB->end(); I != E; ++I) { + if (isa(I) && BB == L->getHeader()) { + // Ignore PHI nodes in the header. + } else if (I->hasOneUse() && I->use_back() == Term) { + // Ignore instructions only used by the loop terminator. + } else { + ++Size; + } + + // TODO: Ignore expressions derived from PHI and constants if inval of phi + // is a constant, or if operation is associative. This will get induction + // variables. + } + } + + return Size; +} + +// RemapInstruction - Convert the instruction operands from referencing the +// current values into those specified by ValueMap. +// +static inline void RemapInstruction(Instruction *I, + std::map &ValueMap) { + for (unsigned op = 0, E = I->getNumOperands(); op != E; ++op) { + Value *Op = I->getOperand(op); + std::map::iterator It = ValueMap.find(Op); + if (It != ValueMap.end()) Op = It->second; + I->setOperand(op, Op); + } +} + + +bool LoopUnroll::visitLoop(Loop *L) { + bool Changed = false; + + // Recurse through all subloops before we process this loop. Copy the loop + // list so that the child can update the loop tree if it needs to delete the + // loop. + std::vector SubLoops(L->begin(), L->end()); + for (unsigned i = 0, e = SubLoops.size(); i != e; ++i) + Changed |= visitLoop(SubLoops[i]); + + // We only handle single basic block loops right now. + if (L->getBlocks().size() != 1) + return Changed; + + BasicBlock *BB = L->getHeader(); + BranchInst *BI = dyn_cast(BB->getTerminator()); + if (BI == 0) return Changed; // Must end in a conditional branch + + ConstantInt *TripCountC = dyn_cast_or_null(L->getTripCount()); + if (!TripCountC) return Changed; // Must have constant trip count! + + unsigned TripCount = TripCountC->getRawValue(); + if (TripCount != TripCountC->getRawValue()) + return Changed; // More than 2^32 iterations??? + + unsigned LoopSize = ApproximateLoopSize(L); + DEBUG(std::cerr << "Loop Unroll: F[" << BB->getParent()->getName() + << "] Loop %" << BB->getName() << " Loop Size = " << LoopSize + << " Trip Count = " << TripCount << " - "); + if (LoopSize*TripCount > UnrollThreshold) { + DEBUG(std::cerr << "TOO LARGE: " << LoopSize*TripCount << ">" + << UnrollThreshold << "\n"); + return Changed; + } + DEBUG(std::cerr << "UNROLLING!\n"); + + assert(L->getExitBlocks().size() == 1 && "Must have exactly one exit block!"); + BasicBlock *LoopExit = L->getExitBlocks()[0]; + + // Create a new basic block to temporarily hold all of the cloned code. + BasicBlock *NewBlock = new BasicBlock(); + + // For the first iteration of the loop, we should use the precloned values for + // PHI nodes. Insert associations now. + std::map LastValueMap; + std::vector OrigPHINode; + for (BasicBlock::iterator I = BB->begin(); + PHINode *PN = dyn_cast(I); ++I) { + OrigPHINode.push_back(PN); + if (Instruction *I =dyn_cast(PN->getIncomingValueForBlock(BB))) + if (I->getParent() == BB) + LastValueMap[I] = I; + } + + // Remove the exit branch from the loop + BB->getInstList().erase(BI); + + assert(TripCount != 0 && "Trip count of 0 is impossible!"); + for (unsigned It = 1; It != TripCount; ++It) { + char SuffixBuffer[100]; + sprintf(SuffixBuffer, ".%d", It); + std::map ValueMap; + BasicBlock *New = CloneBasicBlock(BB, ValueMap, SuffixBuffer); + + // Loop over all of the PHI nodes in the block, changing them to use the + // incoming values from the previous block. + for (unsigned i = 0, e = OrigPHINode.size(); i != e; ++i) { + PHINode *NewPHI = cast(ValueMap[OrigPHINode[i]]); + Value *InVal = NewPHI->getIncomingValueForBlock(BB); + if (Instruction *InValI = dyn_cast(InVal)) + if (InValI->getParent() == BB) + InVal = LastValueMap[InValI]; + ValueMap[OrigPHINode[i]] = InVal; + New->getInstList().erase(NewPHI); + } + + for (BasicBlock::iterator I = New->begin(), E = New->end(); I != E; ++I) + RemapInstruction(I, ValueMap); + + // Now that all of the instructions are remapped, splice them into the end + // of the NewBlock. + NewBlock->getInstList().splice(NewBlock->end(), New->getInstList()); + delete New; + + // LastValue map now contains values from this iteration. + std::swap(LastValueMap, ValueMap); + } + + // If there was more than one iteration, replace any uses of values computed + // in the loop with values computed during last iteration of the loop. + if (TripCount != 1) + for (BasicBlock::iterator I = BB->begin(), E = BB->end(); I != E; ++I) { + std::vector Users(I->use_begin(), I->use_end()); + for (unsigned i = 0, e = Users.size(); i != e; ++i) { + Instruction *UI = cast(Users[i]); + if (UI->getParent() != BB && UI->getParent() != NewBlock) + UI->replaceUsesOfWith(I, LastValueMap[I]); + } + } + + // Now that we cloned the block as many times as we needed, stitch the new + // code into the original block and delete the temporary block. + BB->getInstList().splice(BB->end(), NewBlock->getInstList()); + delete NewBlock; + + // Now loop over the PHI nodes in the original block, setting them to their + // incoming values. + BasicBlock *Preheader = L->getLoopPreheader(); + for (unsigned i = 0, e = OrigPHINode.size(); i != e; ++i) { + PHINode *PN = OrigPHINode[i]; + PN->replaceAllUsesWith(PN->getIncomingValueForBlock(Preheader)); + BB->getInstList().erase(PN); + } + + // Finally, add an unconditional branch to the block to continue into the exit + // block. + new BranchInst(LoopExit, BB); + + // At this point, the code is well formed. We now do a quick sweep over the + // inserted code, doing constant propagation and dead code elimination as we + // go. + for (BasicBlock::iterator I = BB->begin(), E = BB->end(); I != E; ) { + Instruction *Inst = I++; + + if (isInstructionTriviallyDead(Inst)) + BB->getInstList().erase(Inst); + else if (Constant *C = ConstantFoldInstruction(Inst)) { + Inst->replaceAllUsesWith(C); + BB->getInstList().erase(Inst); + } + } + + // FIXME: Should update analyses + + // FIXME: Should fold into preheader and exit block + + ++NumUnrolled; + return true; +}