| //===-- 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 "llvm/Support/CommandLine.h" |
| #include "llvm/Support/Debug.h" |
| #include "llvm/ADT/Statistic.h" |
| #include "llvm/ADT/STLExtras.h" |
| #include "llvm/IntrinsicInst.h" |
| #include <cstdio> |
| #include <set> |
| #include <algorithm> |
| #include <iostream> |
| using namespace llvm; |
| |
| namespace { |
| Statistic<> NumUnrolled("loop-unroll", "Number of loops completely unrolled"); |
| |
| cl::opt<unsigned> |
| 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.addRequiredID(LoopSimplifyID); |
| AU.addRequired<LoopInfo>(); |
| AU.addPreserved<LoopInfo>(); |
| } |
| }; |
| RegisterOpt<LoopUnroll> X("loop-unroll", "Unroll loops"); |
| } |
| |
| FunctionPass *llvm::createLoopUnrollPass() { return new LoopUnroll(); } |
| |
| bool LoopUnroll::runOnFunction(Function &F) { |
| bool Changed = false; |
| LI = &getAnalysis<LoopInfo>(); |
| |
| // Transform all the top-level loops. Copy the loop list so that the child |
| // can update the loop tree if it needs to delete the loop. |
| std::vector<Loop*> SubLoops(LI->begin(), LI->end()); |
| for (unsigned i = 0, e = SubLoops.size(); i != e; ++i) |
| Changed |= visitLoop(SubLoops[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<PHINode>(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 if (DbgInfoIntrinsic *DbgI = dyn_cast<DbgInfoIntrinsic>(I)) { |
| // Ignore debug instructions |
| } 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<const Value *, Value*> &ValueMap) { |
| for (unsigned op = 0, E = I->getNumOperands(); op != E; ++op) { |
| Value *Op = I->getOperand(op); |
| std::map<const Value *, Value*>::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<Loop*> 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<BranchInst>(BB->getTerminator()); |
| if (BI == 0) return Changed; // Must end in a conditional branch |
| |
| ConstantInt *TripCountC = dyn_cast_or_null<ConstantInt>(L->getTripCount()); |
| if (!TripCountC) return Changed; // Must have constant trip count! |
| |
| uint64_t TripCountFull = TripCountC->getRawValue(); |
| if (TripCountFull != TripCountC->getRawValue() || TripCountFull == 0) |
| 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 = " << TripCountFull << " - "); |
| uint64_t Size = (uint64_t)LoopSize*TripCountFull; |
| if (Size > UnrollThreshold) { |
| DEBUG(std::cerr << "TOO LARGE: " << Size << ">" << UnrollThreshold << "\n"); |
| return Changed; |
| } |
| DEBUG(std::cerr << "UNROLLING!\n"); |
| |
| unsigned TripCount = (unsigned)TripCountFull; |
| |
| BasicBlock *LoopExit = BI->getSuccessor(L->contains(BI->getSuccessor(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<const Value*, Value*> LastValueMap; |
| std::vector<PHINode*> OrigPHINode; |
| for (BasicBlock::iterator I = BB->begin(); isa<PHINode>(I); ++I) { |
| PHINode *PN = cast<PHINode>(I); |
| OrigPHINode.push_back(PN); |
| if (Instruction *I =dyn_cast<Instruction>(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<const Value*, Value*> 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<PHINode>(ValueMap[OrigPHINode[i]]); |
| Value *InVal = NewPHI->getIncomingValueForBlock(BB); |
| if (Instruction *InValI = dyn_cast<Instruction>(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 the last iteration of the loop. |
| if (TripCount != 1) { |
| std::set<User*> Users; |
| for (BasicBlock::iterator I = BB->begin(), E = BB->end(); I != E; ++I) |
| Users.insert(I->use_begin(), I->use_end()); |
| |
| // We don't want to reprocess entries with PHI nodes in them. For this |
| // reason, we look at each operand of each user exactly once, performing the |
| // stubstitution exactly once. |
| for (std::set<User*>::iterator UI = Users.begin(), E = Users.end(); UI != E; |
| ++UI) { |
| Instruction *I = cast<Instruction>(*UI); |
| if (I->getParent() != BB && I->getParent() != NewBlock) |
| RemapInstruction(I, LastValueMap); |
| } |
| } |
| |
| // 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); |
| } |
| } |
| |
| // Update the loop information for this loop. |
| Loop *Parent = L->getParentLoop(); |
| |
| // Move all of the basic blocks in the loop into the parent loop. |
| LI->changeLoopFor(BB, Parent); |
| |
| // Remove the loop from the parent. |
| if (Parent) |
| delete Parent->removeChildLoop(std::find(Parent->begin(), Parent->end(),L)); |
| else |
| delete LI->removeLoop(std::find(LI->begin(), LI->end(), L)); |
| |
| |
| // FIXME: Should update dominator analyses |
| |
| |
| // Now that everything is up-to-date that will be, we fold the loop block into |
| // the preheader and exit block, updating our analyses as we go. |
| LoopExit->getInstList().splice(LoopExit->begin(), BB->getInstList(), |
| BB->getInstList().begin(), |
| prior(BB->getInstList().end())); |
| LoopExit->getInstList().splice(LoopExit->begin(), Preheader->getInstList(), |
| Preheader->getInstList().begin(), |
| prior(Preheader->getInstList().end())); |
| |
| // Make all other blocks in the program branch to LoopExit now instead of |
| // Preheader. |
| Preheader->replaceAllUsesWith(LoopExit); |
| |
| Function *F = LoopExit->getParent(); |
| if (Parent) { |
| // Otherwise, if this is a sub-loop, and the preheader was the loop header |
| // of the parent loop, move the exit block to be the new parent loop header. |
| if (Parent->getHeader() == Preheader) { |
| assert(Parent->contains(LoopExit) && |
| "Exit block isn't contained in parent?"); |
| Parent->moveToHeader(LoopExit); |
| } |
| } else { |
| // If the preheader was the entry block of this function, move the exit |
| // block to be the new entry of the function. |
| if (Preheader == &F->front()) |
| F->getBasicBlockList().splice(F->begin(), |
| F->getBasicBlockList(), LoopExit); |
| } |
| |
| // Remove BB and LoopExit from our analyses. |
| LI->removeBlock(Preheader); |
| LI->removeBlock(BB); |
| |
| // Actually delete the blocks now. |
| F->getBasicBlockList().erase(Preheader); |
| F->getBasicBlockList().erase(BB); |
| |
| ++NumUnrolled; |
| return true; |
| } |