| //===-- 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 will multi-block loops only if they contain no non-unrolled |
| // subloops. The process of unrolling can produce extraneous basic blocks |
| // linked with unconditional branches. This will be corrected in the future. |
| // |
| //===----------------------------------------------------------------------===// |
| |
| #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/ConstantFolding.h" |
| #include "llvm/Analysis/LoopInfo.h" |
| #include "llvm/Analysis/LoopPass.h" |
| #include "llvm/Transforms/Utils/Cloning.h" |
| #include "llvm/Transforms/Utils/Local.h" |
| #include "llvm/Support/CFG.h" |
| #include "llvm/Support/Compiler.h" |
| #include "llvm/Support/CommandLine.h" |
| #include "llvm/Support/Debug.h" |
| #include "llvm/ADT/Statistic.h" |
| #include "llvm/ADT/STLExtras.h" |
| #include "llvm/ADT/SmallPtrSet.h" |
| #include "llvm/IntrinsicInst.h" |
| #include <cstdio> |
| #include <algorithm> |
| using namespace llvm; |
| |
| STATISTIC(NumUnrolled, "Number of loops completely unrolled"); |
| |
| namespace { |
| cl::opt<unsigned> |
| UnrollThreshold("unroll-threshold", cl::init(100), cl::Hidden, |
| cl::desc("The cut-off point for loop unrolling")); |
| |
| class VISIBILITY_HIDDEN LoopUnroll : public LoopPass { |
| LoopInfo *LI; // The current loop information |
| public: |
| bool runOnLoop(Loop *L, LPPassManager &LPM); |
| BasicBlock* FoldBlockIntoPredecessor(BasicBlock* BB); |
| |
| /// 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.addRequiredID(LCSSAID); |
| AU.addRequired<LoopInfo>(); |
| AU.addPreservedID(LCSSAID); |
| AU.addPreserved<LoopInfo>(); |
| } |
| }; |
| RegisterPass<LoopUnroll> X("loop-unroll", "Unroll loops"); |
| } |
| |
| LoopPass *llvm::createLoopUnrollPass() { return new LoopUnroll(); } |
| |
| /// 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 (isa<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, |
| DenseMap<const Value *, Value*> &ValueMap) { |
| for (unsigned op = 0, E = I->getNumOperands(); op != E; ++op) { |
| Value *Op = I->getOperand(op); |
| DenseMap<const Value *, Value*>::iterator It = ValueMap.find(Op); |
| if (It != ValueMap.end()) Op = It->second; |
| I->setOperand(op, Op); |
| } |
| } |
| |
| // FoldBlockIntoPredecessor - Folds a basic block into its predecessor if it |
| // only has one predecessor, and that predecessor only has one successor. |
| // Returns the new combined block. |
| BasicBlock* LoopUnroll::FoldBlockIntoPredecessor(BasicBlock* BB) { |
| // Merge basic blocks into their predecessor if there is only one distinct |
| // pred, and if there is only one distinct successor of the predecessor, and |
| // if there are no PHI nodes. |
| // |
| BasicBlock *OnlyPred = BB->getSinglePredecessor(); |
| if (!OnlyPred) return 0; |
| |
| if (OnlyPred->getTerminator()->getNumSuccessors() != 1) |
| return 0; |
| |
| DOUT << "Merging: " << *BB << "into: " << *OnlyPred; |
| |
| // Resolve any PHI nodes at the start of the block. They are all |
| // guaranteed to have exactly one entry if they exist, unless there are |
| // multiple duplicate (but guaranteed to be equal) entries for the |
| // incoming edges. This occurs when there are multiple edges from |
| // OnlyPred to OnlySucc. |
| // |
| while (PHINode *PN = dyn_cast<PHINode>(&BB->front())) { |
| PN->replaceAllUsesWith(PN->getIncomingValue(0)); |
| BB->getInstList().pop_front(); // Delete the phi node... |
| } |
| |
| // Delete the unconditional branch from the predecessor... |
| OnlyPred->getInstList().pop_back(); |
| |
| // Move all definitions in the successor to the predecessor... |
| OnlyPred->getInstList().splice(OnlyPred->end(), BB->getInstList()); |
| |
| // Make all PHI nodes that referred to BB now refer to Pred as their |
| // source... |
| BB->replaceAllUsesWith(OnlyPred); |
| |
| std::string OldName = BB->getName(); |
| |
| // Erase basic block from the function... |
| LI->removeBlock(BB); |
| BB->eraseFromParent(); |
| |
| // Inherit predecessors name if it exists... |
| if (!OldName.empty() && !OnlyPred->hasName()) |
| OnlyPred->setName(OldName); |
| |
| return OnlyPred; |
| } |
| |
| bool LoopUnroll::runOnLoop(Loop *L, LPPassManager &LPM) { |
| bool Changed = false; |
| LI = &getAnalysis<LoopInfo>(); |
| |
| BasicBlock* Header = L->getHeader(); |
| BasicBlock* LatchBlock = L->getLoopLatch(); |
| |
| BranchInst *BI = dyn_cast<BranchInst>(LatchBlock->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! |
| |
| // Guard against huge trip counts. This also guards against assertions in |
| // APInt from the use of getZExtValue, below. |
| if (TripCountC->getValue().getActiveBits() > 32) |
| return Changed; // More than 2^32 iterations??? |
| |
| uint64_t TripCountFull = TripCountC->getZExtValue(); |
| if (TripCountFull == 0) |
| return Changed; // Zero iteraitons? |
| |
| unsigned LoopSize = ApproximateLoopSize(L); |
| DOUT << "Loop Unroll: F[" << Header->getParent()->getName() |
| << "] Loop %" << Header->getName() << " Loop Size = " |
| << LoopSize << " Trip Count = " << TripCountFull << " - "; |
| uint64_t Size = (uint64_t)LoopSize*TripCountFull; |
| if (Size > UnrollThreshold) { |
| DOUT << "TOO LARGE: " << Size << ">" << UnrollThreshold << "\n"; |
| return Changed; |
| } |
| DOUT << "UNROLLING!\n"; |
| |
| std::vector<BasicBlock*> LoopBlocks = L->getBlocks(); |
| |
| unsigned TripCount = (unsigned)TripCountFull; |
| |
| BasicBlock *LoopExit = BI->getSuccessor(L->contains(BI->getSuccessor(0))); |
| |
| // For the first iteration of the loop, we should use the precloned values for |
| // PHI nodes. Insert associations now. |
| DenseMap<const Value*, Value*> LastValueMap; |
| std::vector<PHINode*> OrigPHINode; |
| for (BasicBlock::iterator I = Header->begin(); isa<PHINode>(I); ++I) { |
| PHINode *PN = cast<PHINode>(I); |
| OrigPHINode.push_back(PN); |
| if (Instruction *I = |
| dyn_cast<Instruction>(PN->getIncomingValueForBlock(LatchBlock))) |
| if (L->contains(I->getParent())) |
| LastValueMap[I] = I; |
| } |
| |
| // Remove the exit branch from the loop |
| LatchBlock->getInstList().erase(BI); |
| |
| std::vector<BasicBlock*> Headers; |
| std::vector<BasicBlock*> Latches; |
| Headers.push_back(Header); |
| Latches.push_back(LatchBlock); |
| |
| assert(TripCount != 0 && "Trip count of 0 is impossible!"); |
| for (unsigned It = 1; It != TripCount; ++It) { |
| char SuffixBuffer[100]; |
| sprintf(SuffixBuffer, ".%d", It); |
| |
| std::vector<BasicBlock*> NewBlocks; |
| |
| for (std::vector<BasicBlock*>::iterator BB = LoopBlocks.begin(), |
| E = LoopBlocks.end(); BB != E; ++BB) { |
| DenseMap<const Value*, Value*> ValueMap; |
| BasicBlock *New = CloneBasicBlock(*BB, ValueMap, SuffixBuffer); |
| Header->getParent()->getBasicBlockList().push_back(New); |
| |
| // Loop over all of the PHI nodes in the block, changing them to use the |
| // incoming values from the previous block. |
| if (*BB == Header) |
| for (unsigned i = 0, e = OrigPHINode.size(); i != e; ++i) { |
| PHINode *NewPHI = cast<PHINode>(ValueMap[OrigPHINode[i]]); |
| Value *InVal = NewPHI->getIncomingValueForBlock(LatchBlock); |
| if (Instruction *InValI = dyn_cast<Instruction>(InVal)) |
| if (It > 1 && L->contains(InValI->getParent())) |
| InVal = LastValueMap[InValI]; |
| ValueMap[OrigPHINode[i]] = InVal; |
| New->getInstList().erase(NewPHI); |
| } |
| |
| // Update our running map of newest clones |
| LastValueMap[*BB] = New; |
| for (DenseMap<const Value*, Value*>::iterator VI = ValueMap.begin(), |
| VE = ValueMap.end(); VI != VE; ++VI) |
| LastValueMap[VI->first] = VI->second; |
| |
| L->addBasicBlockToLoop(New, *LI); |
| |
| // Add phi entries for newly created values to all exit blocks except |
| // the successor of the latch block. The successor of the exit block will |
| // be updated specially after unrolling all the way. |
| if (*BB != LatchBlock) |
| for (Value::use_iterator UI = (*BB)->use_begin(), UE = (*BB)->use_end(); |
| UI != UE; ++UI) { |
| Instruction* UseInst = cast<Instruction>(*UI); |
| if (isa<PHINode>(UseInst) && !L->contains(UseInst->getParent())) { |
| PHINode* phi = cast<PHINode>(UseInst); |
| Value* Incoming = phi->getIncomingValueForBlock(*BB); |
| if (isa<Instruction>(Incoming)) |
| Incoming = LastValueMap[Incoming]; |
| |
| phi->addIncoming(Incoming, New); |
| } |
| } |
| |
| // Keep track of new headers and latches as we create them, so that |
| // we can insert the proper branches later. |
| if (*BB == Header) |
| Headers.push_back(New); |
| if (*BB == LatchBlock) |
| Latches.push_back(New); |
| |
| NewBlocks.push_back(New); |
| } |
| |
| // Remap all instructions in the most recent iteration |
| for (unsigned i = 0; i < NewBlocks.size(); ++i) |
| for (BasicBlock::iterator I = NewBlocks[i]->begin(), |
| E = NewBlocks[i]->end(); I != E; ++I) |
| RemapInstruction(I, LastValueMap); |
| } |
| |
| |
| |
| // Update PHI nodes that reference the final latch block |
| if (TripCount > 1) { |
| SmallPtrSet<PHINode*, 8> Users; |
| for (Value::use_iterator UI = LatchBlock->use_begin(), |
| UE = LatchBlock->use_end(); UI != UE; ++UI) |
| if (PHINode* phi = dyn_cast<PHINode>(*UI)) |
| Users.insert(phi); |
| |
| for (SmallPtrSet<PHINode*,8>::iterator SI = Users.begin(), SE = Users.end(); |
| SI != SE; ++SI) { |
| Value* InVal = (*SI)->getIncomingValueForBlock(LatchBlock); |
| if (isa<Instruction>(InVal)) |
| InVal = LastValueMap[InVal]; |
| (*SI)->removeIncomingValue(LatchBlock, false); |
| if (InVal) |
| (*SI)->addIncoming(InVal, cast<BasicBlock>(LastValueMap[LatchBlock])); |
| } |
| } |
| |
| // 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)); |
| Header->getInstList().erase(PN); |
| } |
| |
| // Insert the branches that link the different iterations together |
| for (unsigned i = 0; i < Latches.size()-1; ++i) { |
| new BranchInst(Headers[i+1], Latches[i]); |
| if(BasicBlock* Fold = FoldBlockIntoPredecessor(Headers[i+1])) { |
| std::replace(Latches.begin(), Latches.end(), Headers[i+1], Fold); |
| std::replace(Headers.begin(), Headers.end(), Headers[i+1], Fold); |
| } |
| } |
| |
| // Finally, add an unconditional branch to the block to continue into the exit |
| // block. |
| new BranchInst(LoopExit, Latches[Latches.size()-1]); |
| FoldBlockIntoPredecessor(LoopExit); |
| |
| // 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. |
| const std::vector<BasicBlock*> &NewLoopBlocks = L->getBlocks(); |
| for (std::vector<BasicBlock*>::const_iterator BB = NewLoopBlocks.begin(), |
| BBE = NewLoopBlocks.end(); BB != BBE; ++BB) |
| 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. |
| // Remove the loop from the parent. |
| LPM.deleteLoopFromQueue(L); |
| |
| ++NumUnrolled; |
| return true; |
| } |